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 Program for the Micro-­‐DICE European Science Foundation networking Programme on the Mico-­‐Dynamics of Ice Final conference Microstructural evolution during HT deformation: advances in the
characterization techniques and consequences to physical properties
Montpellier, France
30 March – 1 April 2015: Conference
2-3 April 2015: 2-day MTEX open source & free texture analysis training
workshop
Organised by David Mainprice, Andrea Tommasi and Maurine Montagnat
The conference is held at the CNRS Amphitheatre at the délégation
regionale de Languedoc Roussillon, 1919 route de Mende,
34293 Montpellier Cedex 05
France
The MTEX training workshop is held at the Université de Montpellier,
Faculté des Sciences, Place Eugène Bataillon
34095 Montpellier Cedex 05
France
Program for the Micro-­‐DICE European Science Foundation networking Programme on the Mico-­‐Dynamics of Ice Final conference A. 3-­‐day Meeting scientific program B. Abstracts for Oral presentations C. Abstracts for Poster presentations March 30th Day 1 Microstructure, Texture and Evolution 8h30-­‐9h30: Welcome & pick-­‐up of the Registration Package with coffee Session 1: Evolution of microstructures and textures during deformation and recrystallization 9h30: Welcome speech: David Mainprice 9h40-­‐10h40: Keynote 1: Evolution of microstructures and textures during deformation and recrystallization Martyn Drury (Utrecht University, NL) 10h40 – 11h10: Coffee break 11h10-­‐12h30: 4 short talks (20') 11h10-­‐11h30: Ductile strain localization assisted by fluids in the shallow subcontinental lithospheric mantle (Ronda massif, Betic Cordillera, South Spain) -­‐ Károly Hidas (Montpellier,F) 11h30-­‐11h50: Quantifying strain distribution in shear zones using crystal preferred orientations -­‐ David Wallis (Oxford,UK) 11h50-­‐12h20: Fabric variability and seismic velocities in the ocean crust from EBSD mapping of gabbroic rocks -­‐ Benoit Ildefonse (Montpellier,F) 12h10-­‐12h30: Modelling the effect of dynamic recrystallization on olivine texture evolution in simple shear -­‐ Andrea Tommasi (Montpellier,F) Lunch break 12h30-­‐14h00 14h-­‐15h: Keynote 2: Micro-­‐macro tracking of the deformation field: Application to halite rock. Michel Bornert (Université Paris-­‐Est, F) 15h00-­‐15h40 : 2 short talks (20') 15h00-­‐15h20: Strain field evolution during creep on ice. Impact of dynamic recrystallization mechanisms -­‐ Thomas Chauve (Grenoble,F) 15h20-­‐15h40: Modelling the influence of air on the deformation and recrystallization mechanisms in polar firn and ice -­‐ Steinbach Florian (Tuebingen,D) Coffee break 15h40-­‐16h10 16h10-­‐17h10: Keynote 3: Modelling Evolving Microstructures. Albert Griera (Barcelona,E) 17h10-­‐17h30 Full-­‐field modelling of strain heterogeneities during transient creep of polycrystalline ice using a FFT method. -­‐ Maurine Montagnat (Grenoble, F) 17h30-­‐18h30: Discussion (Animators: Maurine Montagnat, Martyn Drury, Michel Bornert, Albert Griera) 19h30 Conference Ice-­‐breaker Dinner at Trinquefougass March 31st Day 2 – High-­‐resolution study of microstructures 9h-­‐10h: Keynote 4: Local strain analysis by High Angular Resolution Electron BackScatter Diffraction. Claire Maurice (Saint-­‐Etienne, F) 10h00 – 10h30: Coffee break 10h30 -­‐ 11h50: 4 short talks (20') 10h30-­‐10h50: Intra-­‐grain orientation spreads in hot-­‐deformed aluminium: Properties and relation to crystal plasticity – Romain Quey (Saint-­‐Etienne, F) 10h50-­‐11h10: Quartz exsolution topotaxy in clinopyroxene from ultrahigh pressure eclogite: An EBSD study and its implications -­‐ Haijun Xu (Wuhan,China) 11h10-­‐11h30: Analysis of grain boundaries and subgrain structures in ice using optical characterization techniques -­‐ Binder Tobias (Bremerhaven ,D) 11h30-­‐11h50: Dislocation and disclination density fields from EBSD orientation mapping -­‐ Claude Fressengeas (Metz, F) 11h50-­‐12h30: Short poster presentations -­‐ 3 min. for each poster Lunch break 13h00-­‐14h30 14h00-­‐16h00: Poster session with coffee break at 15h30 16h00-­‐17h00: Keynote 5: Characterization of the dislocation content of EBSD maps. John Wheeler (Liverpool, UK) 17h00-­‐17h30 Discussion (Animators: David Mainprice, Claude Fressengeas, John Wheeler) April 1st Day 3 – Rheology: consequences of microstructure and texture evolution to large-­‐scale flow 9h-­‐10h: Keynote 6: Transients in strength and structure. Brian Evans, (MIT, USA) 10h00 – 10h30 Coffee break 10h30-­‐12h30: 6 short talks (20’) 10h30-­‐10h50: Intermediate and Deep Earthquakes: from the Lab to the Field -­‐ Thomas Ferrand (Paris,F) 10h50-­‐11h10: Rheology of phase A at high pressure-­‐high temperature -­‐ Nadège Hillairet (Lille,F) 11h10-­‐11h30: Investigating rheology in mantle minerals at very high pressure and temperature -­‐ Misha Bystricky (Toulouse,F) 11h30-­‐11h50: Intracontinental deformation and strain-­‐partitioning pattern in the oblique continental collision zone -­‐ Bo Zhang (Bejing,China) 11h50-­‐12h10: Microstructures And Deformation Mechanisms In High-­‐Temperature Mylonites From The Ribeira Belt, SE Brazil -­‐ Carolina Cavalcante (São Paulo, Brazil) 12h10-­‐12h30: Anisotropic viscosity of olivine aggregates: A laboratory, field, and numerical approach -­‐ Lars Hansen (Oxford,UK) Lunch break 12h30-­‐14h00 14h-­‐15h: Keynote 7: Impact of texture-­‐induced anisotropy on glacier flow. Fabien Gillet-­‐
Chaulet, (LGGE ,Grenoble, F) 15h00 – 15h30 Coffee break 15h30 -­‐ 16h00 Physical properties of polycystalline materials : from the atomic to the planetary scale -­‐ David Mainprice (Montpellier,F) 16h00-­‐16h30: Discussion (Animators: Lars Hansen, Brian Evans, Fabien Gillet-­‐Chaulet) 16h30: Final remarks & Logistics for the MTEX training workshop -­‐ David Mainprice (Montpellier,F) ABSTRACTS
Abstracts of all oral presentations including Keynotes in the order
they appear in the program above.
Abstract of posters and the 3 minute oral presentation by
alphabetical order.
Keynote 1: Evolution of microstructures and textures during deformation and recrystallization
Martyn Drury and Gill Pennock
Department of Earth Sciences, Utrecht University, PO bus 80.021, 3508TA Utrecht, The Netherlands
At elevated temperatures crystalline solids deform and recrystallize by a variety of mechanisms
involving the basic processes of dislocation motion, grain boundary migration/sliding and progressive
subgrain rotation. At high strains a stable microstructure (size, shape and internal structure of grains
and grain boundaries) and texture (crystallographic preferred orientations of grains, interfaces and
misorientations) is developed that depends on the mechanisms and deformation conditions.
Our EBSD studies on rocksalt (polycrystalline NaCl) will be reviewed to illustrate the evolution of
microstructures and crystallographic textures during modest to large strain deformation. NaCl is a
very interesting geological and analog material, like metals it is cubic with many potential slip
systems. The strength of the slip systems in NaCl is very different so the material has high plastic
anisotropy, similar to most minerals and ice. NaCl is also a type material for “subgrain rotation”
“grain boundary migration”recrystallization (Guillope and Porier 1979). Another useful feature of
NaCl for experimental studies is that grain boundary migration can be “turned on” by adding small
amounts of water (Urai et al. 1986). Thus, NaCl is a prefect material to study the microstructure and
textures produced by different recrystallization mechanisms. In most minerals and ice the effect of
deformation and recrystallization cannot be separated easily.
In dry salt deformed at 0.4 Tm, grain boundary migration is very slow, and slip on the [110](110)
system is a factor 10 weaker than slip on (100) and (111). Single crystals deformed at these
conditions undergo, rotation recrystallization, however work on polycrystals shows (Pennock et al.
2005) that subgrain misorientation builds up slowly with strain. The bulk textures developed in
compression and shear, can be predicted by Taylor/VPSC type models. Despite claims that there is no
simple relationship between texture maxima and kinematics, simple shear experiments show an
alignment of the [110] directions parallel to the shear direction and an alignment of the harder (100)
planes parallel to the shear plane.
In wet salt, fast grain boundary migration occurs resulting in the development and growth of strain
free grains after some 10-20% shortening. These new grains have a different texture with [100]
parallel to the compression axis. The high strain recrystallization texture corresponds to nucleation
and growth in the soft grains (Trimby et al. 2000). In contrast at lower strains, where deformation
occurs by dislocation creep and pressure solution, a modest micro-texture is formed by slow growth of
hard grains (Pennock et al. 2006).
In summary, in NaCl the different microstructure and texture regimes can be explained by the
operation of different recrystallization and deformation mechanisms. The relevance of the NaCl
behavior to materials with more (metals) or fewer slip systems (like olivine and ice) will be discussed.
Do these different classes of materials recrystallize by different mechanisms, or are the same
processes described by different terminology in different scientific fields?
Ductile strain localization assisted by fluids in the shallow subcontinental
lithospheric mantle (Ronda massif, Betic Cordillera, South Spain)
Károly Hidas1,*, Andréa Tommasi1, Carlos J. Garrido2, José Alberto Padrón-Navarta1, David
Mainprice1, Alain Vauchez1, Fabrice Barou1, Claudio Marchesi2
(1) Géosciences Montpellier, CNRS & Université Montpellier-2, Place E. Bataillon, 34095
Montpellier cedex 5, France
(2) Instituto Andaluz de Ciencias de la Tierra, CSIC & Universidad de Granada, Av. de las Palmeras
4, 18100 Armilla (Granada), Spain
* [email protected]
The Ronda massif (S-Spain) is the largest (ca. 300km2) of several orogenic peridotite massifs
exposed in the Betic and Rif (northern Morocco) mountain belts in the westernmost part of the Alpine
orogen that was tectonically emplaced during early Miocene times.
Here we report a microstructural study of strain localization in a mylonitic peridotite shear zone that
have been formed during the latest ductile history of the massif. Strain localization is associated with a
sudden decrease of grain size and the redistribution of orthopyroxene in the finest grained
microstructural domains (ultramylonites). Olivine crystallographic preferred orientation (CPO) shows
[100]-axes subparallel to the lineation and [001] at the pole of the foliation, whereas orthopyroxene
mimics the CPO of that of olivine. Although low-angle misorientations in neighboring pixels are
frequent in both phases, olivine and orthopyroxene CPO cannot be explained by coeval deformation
via dislocation creep mechanisms. Based on microstructural and major element geochemical data, we
propose strain localization at low temperature assisted by interstitial fluids that has led to the
dissolution of orthopyroxene porphyroclast and the precipitation of this mineral phase along the
ultramylonite bands.
Quantifying strain distribution in shear zones using crystal preferred orientations
David Wallis1, Richard J. Phillips2, Geoffrey E. Lloyd2 and Luiz F. Morales3
1
Department of Earth Sciences, University of Oxford, Oxford, UK, OX1
[email protected].
2
School of Earth and Environment, University of Leeds, Leeds, UK, LS2 9JT.
3
GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
3AN,
Determination of quantitative strain distributions within orogen-scale ductile shear zones is of
fundamental importance for understanding strain localisation processes and the macroscopic
architecture of fault zones. However, most crustal-scale shear zones lack sufficient strain markers. We
show that in such circumstances a suitable strain proxy can be provided by the strength of crystal
preferred orientations (CPO) using an eigenvalue-based intensity (I) parameter. This method is widely
applicable and can provide strain profiles at the resolution of sampling density. As a first order
attempt to calibrate CPO intensity for finite strain, we present visco-plastic self-consistent (VPSC)
simulations of CPO development which constrain minimum shear strains required to produce
observed CPO.
Quartz c-axis CPO intensity transects across the Karakoram fault zone, NW India, provide rare
quantitative assessments of strain distribution across a large-scale shear zone. CPO intensity is
developed within multiple km-scale subparallel shear zones (I < 1.6) which cross-cut c. 16 Ma
granitoids and separate less deformed lenses (I < 0.2). Quartz c-axis Y-maxima CPO indicate
deformation dominated by prism-a (i.e. {10-10}<1-210>) slip and, along with deformation
microstructures, suggest deformation temperatures of c. 500°C. VPSC simulations of prism-a slip,
starting from a natural undeformed specimen CPO, suggest that minimum shear strains (γ) varying
between γ = 0.7 and γ = 5.5 are required to produce CPO observed in the shear zone strands. Al-inhornblende geobarometry on a cross-cut 17 Ma monzogranite gives 449 ± 72 MPa, corresponding to
an emplacement depth of c. 16.6 ± 3.7 km, thus providing a maximum depth constraint for the
formation of the strain profiles. These strain profiles provide an important insight into the distribution
of deformation in the region between localised brittle deformation in the seismogenic upper crust and
broadly distributed deformation of the mid-crust.
Fabric variability and seismic velocities in the ocean crust from EBSD mapping of
gabbroic rocks
Benoit Ildefonse
Géosciences Montpellier, CNRS & Université Montpellier, France
Crystallographic preferred orientations (CPO) of gabbroic rocks mineral phases are a key component
of our understanding of the dynamics and physical properties of the oceanic crust. In pre-EBSD times,
CPO in gabbros were rarely studied, because of the difficulty of measuring low-symmetry plagioclase
crystal (plagioclase, clinopyroxene) orientations using the universal stage. A compilation of ~170
plagioclase CPO measured over 15 years (Satsukawa et al., 213, doi:10.5194/se-4-511-2013) show
that all plagioclase CPO range between oblate fabrics (axial-B) defines by a strong point
concentration of (010) and girdle distributions of [100] and (001), and prolate fabrics (axial-A)
defined by a strong point concentration of [100] with parallel girdle distributions of (010) and (001).
Axial-A CPOs are less common; they represent ~20% of the samples deformed by crystal-plastic flow.
Magmatic microstructures have high (010) pole figures J indices, which increase linearly with ODF J
index, whereas the high [100] pole figures J indices of plastically deformed samples vary in a more
scattered manner with the ODF J index. The multistage nature of plastic deformation superposed on a
magmatic structure, and the large number of possible slip-systems in plagioclase probably account for
these differences.
Calculated anisotropies of the seismic velocities of plagioclase aggregates increase as a function of the
ODF J index. In foliated gabbroic rocks (i.e., plagioclase, olivine and clinopyroxene aggregates), the
effect of plagioclase (i.e., fast direction normal to foliation) is opposite to that of olivine and
clinopyroxene (i.e., fast direction parallel to foliation). This is illustrated with examples of Hess Deep
troctolites. The resulting Vp anisotropy is weak, with a fast-propagation direction that depends on the
intensity of the CPO and the modal composition of the rock. Plagioclase and olivine have similar
counteracting effects on S-wave anisotropy.
In the ocean crust, the characteristics and variability of magmatic fabrics (intensity and shape) is best
defined by plagioclase. End-member accretion models for the lower ocean crust predict distinct
vertical trends of fabric intensities over the ~4km thick gabbroic lower crust. The ODF J indexes
obtained from 48 samples in a single gabbro section in the Oman ophiolite show a general increase of
the plagioclase CPO intensity from the base of the sheeted dike complex to the mantle, with variations
at smaller scales, pointing to a model of accretion that combines aspects of the two end-member
models (known as "gabbro glacier" and "sheeted sills" models).
Modeling the effect of subgrain rotation recrystallization on the evolution of
olivine crystal preferred orientations in simple shear
Javier Signorellia and Andréa Tommasib
a
Instituto de Física Rosario, CONICET - Universidad Nacional de Rosario, Bv. 27 de Febrero 210
bis - Rosario – Argentina. http://www.ifir-conicet.gov.ar
b
Géosciences Montpellier – CNRS & Université de Montpellier 2, Place Eugene Bataillon,
Montpellier, France. http://www.gm.univ-montp2.fr
Homogenization models are widely used to predict the evolution of crystal preferred orientations
(CPO or texture) and resulting anisotropy of physical properties in metals, rocks, and ice. They fail
however in predicting two main characteristics of CPO evolution in simple shear (the dominant
deformation regime on Earth) for highly anisotropic crystals, like olivine or ice: (1) the fast rotation of
the CPO towards a stable position characterized by parallelism of the dominant slip system and the
macroscopic shear and (2) its asymptotical evolution towards a constant intensity. We have modified a
viscoplastic self-consistent code to simulate the effects of subgrain rotation recrystallization on the
CPO evolution. To each parent crystal is associated a finite number of fragments. Formation of a
subgrain corresponds to a transfer of weight from the parent to a fragment, introduction of
disorientation between them, and resetting of the fragment internal energy and shape. The probability
of formation of a subgrain is controlled by comparison between the local internal energy and the
average value in the polycrystal. A two-level mechanical interaction scheme is applied for simulating
the intracrystalline strain heterogeneity allowed by the formation of low-angle grain boundaries.
Within a crystal, interactions between subgrains follow a lower bound (constant stress) scheme. The
interactions between grains are simulated by a tangent viscoplastic self-consistent approach. This twolevel approach successfully reproduces simple shear CPOs for olivine. It also predicts lower strengths
for the polycrystal than tangent or second order viscoplastic self-consistent approaches, consistently
with experimental data.
Keynote 2: Micro-macro tracking of the deformation field.
Application to halite rock
M. Bornert1, A. Gaye1,
A. Dimanov2, M. Bourcier2, J. Raphanel2, E. Héripré2,
W. Ludwig3, A. King4
1
Laboratoire Navier, Université Paris-Est, ENPC, Marne-la-Vallée,
2
Laboratoire de Mécanique des Solides, Université Paris-Saclay,
Ecole polytechnique, Palaiseau,
3
ESRF, Grenoble, 4 Synchtrotron Soleil, Saint Aubain
Predictive micromechanical models of the constitutive relation of materials require appropriate
experimental data, in order to provide the right physically based inputs and to validate the models at
both global- and micro-scale. Many 2D and 3D imaging techniques are currently available to
characterise materials at some local scale of their microstructure. They provide a snapshot of the
latter at a given step of the evolution of the latter. When combined with in- or ex-situ mechanical
testing and adapted comparative image processing routines, such as Digital Image Correlation
techniques, tiny evolutions can be tracked, and allow one to highlight the active micromechanisms
and their complex interactions within a heterogeneous, possibly representative, volume element.
After a short overview of the various components of this experimental methodology (optical,
electron or X-rays imaging, testing devices, image processing, mechanical post-processing), the talk
will focus on the application on halite submitted to uniaxial compression. While this natural rock is
used as host rock for various underground storage application, it is also a nice model material to
understand the micromechanics of a larger class of polycrystalline materials, either natural or
manufactured.
Surface investigations on synthetic samples with controlled grain size, over a wide range of
scales (from centimeter to sub-micrometer) show that halite exhibits complex local strain fields, as the
consequence of its polycrystalline structure and the presence of several crystallographic slip systems
with contrasted properties. In addition, grain boundary sliding (GBS) is clearly observed. A more
detailed and quantitative analysis of the recorded images establishes that GBS is present from the
beginning of plasticity and is a necessary mechanism to develop irreversible deformation under the
considered experimental conditions. The comparison between quantitative results at room temperature
and at 350°C provides a possible explanation of the different overall hardening behaviour of the rock
at these temperatures.
These surface investigations are complemented by full volumetric analyses based on
synchrotron X-rays computed tomography. Full 3D strain fields are obtained on 4x4x6mm samples
with a spatial resolution close to 70µm, and exhibit a two-scale organisation, which qualitatively
confirms the surface observations. Grain boundary deformation mechanisms are also observed in the
bulk consistently with surface observations. Preliminary results of a comparison between XRCT
volume strain mapping and high-resolution SEM surface strain mapping on the same sample will also
be presented.
Strain field evolution during creep on ice. Impact of dynamic recrystallization
mechanisms.
T. Chauve1, M. Montagnat1, P. Vacher2
, Laboratoire de Glaciologie et Geophysique de l'Environnement, CNRS – Univ. Grenoble Alpes,
France
2
, Laboratoire SYMME, Univ. de Savoie, France
1
Email : [email protected]
Discontinuous Dynamic Recrystallization (DDRX) occurs in minerals, metals, ice and impacts on
texture and microstructure evolution during deformation. It therefore impacts on large scale
mechanisms as seismic anisotropy, mechanical properties inside the Earth mantle, material forming
and anisotropic flow in polar ice sheet, for instance. In this frame, ice can be considered as a model
material due to a strong viscoplastic anisotropy inducing strong deformation heterogeneities, that
are precursors of recrystallization.
During creep deformation at high temperature in the laboratory, DDRX occurs from 1% strain and
involves grain nucleation and grain boundary migration. As DDRX induces an evolution of
microstructure and texture, it strongly affects the mechanical behavior (1,2), and it is expected to
modify the strain field at the grain and/or the sample scale.
Compressive creep test (σ=0.5 MPa) were performed at high temperature (T/Tf 0,98) on columnar
polycrystalline ice S2 (microstructure 2D ½, grain size ~ 10 mm) up to 3 % strain. Columnar ice
provides interesting feature as it contains only one grain through the thickness and the columns can
be nearly parallel. Pre- and post-deformation analyses with an Automatic Ice Texture Analyzer
(AITA) (figure 1) are used to analyze the microstructure evolution and to discriminate without
ambiguity nucleus obtained during recrystallization.
During the experiment, local strain field is measured on the surface of the sample by Digital Image
Correlation (DIC) (3) with a spatial resolution between 0.2 and 0.5 mm, and a strain resolution
around 0.2% (figure 2). Grain size being large, we obtain a relatively good intra-granular resolution
of the strain field. Thanks to the 2D configuration of the columnar ice samples, we can superimpose
the initial microstructure to the strain field measured by DIC.
We will present an overview of the impact of DDRX on texture, microstructure and strain field
evolution, over entire 2D-1/2 samples down to a close focus on a triple junction.
We will provide original observations of strain-field evolution associated with the nucleation of new
grains and subboundaries close to a triple junction (Figure 1 and 2). Associated with postdeformation analyses by AITA, these observations enable to follow the strain field redistribution
due to nucleation.
Figure 1 : Orientation represented only azimuth angle for clarity obtained by AITA. Left : Azimuth
map (step size 20µm) before creep test. Rectangular box show the DIC surface analysis for strain
field measurement. Right : Azimuth map (step size 20µm) of DIC area after 3% strain showing
nucleus (arrows 1 and 2) and tilt sub-grains boundary (arrow 3).
Figure2 : Equivalent strain field evolution during uni-axial creep test. Each strain field map show
the integration of 0.1% macroscopic strain along compression axis y between the two picture taken
at the strain written below the map. Arrow
1 show the strain field concentration at the triple junction before grains nucleation which can be
follow with arrows 2 and 2'. Finally arrow 3 and 4 show the strain field during the nucleation of the
tilt sub-grain boundary.
Reference
1. T. Jacka, M. Maccagnan, Ice crystallographic and strain rate changes with strain in compression
and extension, Cold Regions Science and Technology 8 (1984) 269–286.
2. M. Peternell, M. Dierckx, C. J. Wilson, S. Piazolo, Quantification of the microstructural
evolution of polycrystalline fabrics using FAME: Application to in situ deformation of ice, Journal
of Structural Geology 61 (2014) 109–122.
3. F. Grennerat, M. Montagnat, O. Castelnau, P. Vacher, H. Moulinec, P. Suquet, P. Duval,
Experimental characterization of the intragranular strain field in columnar ice during transient
creep, Acta Materialia 60 (2012) 3655–3666.
Modelling the influence of air on the deformation
recrystallisation mechanisms in polar firn and ice
and
F. Steinbach (1), I. Weikusat (1,2), P.D. Bons (1), A. Griera (3), M.G. Llorens (1), Roessiger (1) (1)
Department of Geosciences, Eberhard Karls University of Tübingen, Germany,
(2) Alfred-Wegener-Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
(3) Departament de Geologia, Universitat Autònoma de Barcelona, Spain.
([email protected] / Phone: +49-7071-2973150)
Ice sheets on Earth contain a significant amount of air within their upper,
approximately thousand meters and air hydrates below. In the permeable firn, this air is
still exchanging with the atmosphere and is under atmospheric pressure, whereas the
air bubbles are entrapped at the firn-ice transition 60
– 120 m depth. As recent research showed, the presence of air bubbles can
significantly influence microdynamical processes such as grain growth and grain
boundary migration (Azuma et al., 2012, Roessiger et al., 2014). Understanding the
dominant deformation mechanisms has essential implications for paleo-atmosphere
research and allows more realistic modelling of ice sheet dynamics. Therefore,
numerical models were set up and performed focussing on the implications of the
presence of bubbles on recrystallisation and mechanical properties.
Following the approach by Griera et al. (2013), the 2D numerical
microstructural modelling platform Elle was coupled to the full-field crystal plasticity
code of Lebensohn (2001), which uses a Fast Fourier Transform (FFT). Taking the
mechanical anisotropy of ice into account, FFT calculates the viscoplastic response of
polycrystalline and polyphase materials that deform by dislocation glide, predicts
lattice re-orientation and dislocation densities using the local gradient of the strain- rate
field. FFT was used for the simulation of dynamic recrystallization of pure ice by
Montagnat et al. (2014).
Polyphase grain boundary migration driven by surface energy and internal strain
energy reduction was incorporated in the code and now also enables us to model
deformation of ice with air bubbles. The approach is based on the methodology of
Becker et al. (2008) and Roessiger et al. (2014). Spherical to elliptical bubble shapes
are maintained during deformation only when surface energy based recrystallisation
is activated, whereas they quickly collapse at low strains in the absence of
recrystallisation. The presence of bubbles leads to increased localization of
stress, strain and dislocation densities and a reduction of the bulk strength.
Furthermore, it is confirmed that strain- induced grain boundary migration already
occurs in the uppermost levels of ice sheets (Kipfstuhl et al. 2009, Weikusat et al.
2009).
References
Azuma, N., et al. (2012) J. Struct. Geol., 42, 184-193
Becker, J.K., et al. (2008) Computers & Geosciences, 34, 201-212
Griera, A., et al. (2013) Tectonophysics, 587, 4-29
Kipfstuhl, S., et al. (2009) J. Geophys. Res., 114, B05204
Lebensohn, R.A. (2001) Acta Mater., 49, 2723-2737
Montagnat, M., et al. (2014) J. Struct. Geol., 61, 78-108
Roessiger, J., et al. (2014) J. Struct. Geol., 61, 123-132
Weikusat, I., et al. (2009) J. Glac., 55, 461-472
Keynote 3: Modelling Evolving Microstructures
Albert Griera
Departament de Geologia, Universitat Autònoma de Barcelona, Spain.
Abstract
Microstructure plays a fundamental role in controlling the mechanical properties in
rocks. As microstructures in natural rocks only show the final stage, its interpretation is a
challenging problem because its evolution is the result of the interaction of multiple
physical and chemical processes. Additionally, the role of deformation in modifying
structures has important features at multiple scales, particularly spatial and temporal
scales. The long time scales associated with some geologic processes (ductile
deformation, digenesis, metamorphism, etc) provide other challenges to predict
microstructure evolution: (1) the long timescales permit all available processes to be
activated during rock evolution, and (2) they limit direct experiments and force to
interpolation of results, with an increase of a riskier extrapolation. Numerical modeling
provides an alternative approach to follow the change of microstructure with time,
unconstrained by experimental limitations.
In this contribution, I will give my perspective on the currently available techniques for
numerical simulation on the deformation and recrystallization of polycrystalline
aggregates at high homologous temperatures. A particular emphasis will be done on the
potentials of the numerical platform “Elle”, a collaborative open-source code
specifically designed to simulate the evolution of microstructure during competition
between simultaneously operating processes. I will focus my contribution in two main
examples, (1) the simulation of olivine during plastic deformation and its influence on
the mechanical and geophysical properties and (2) the evolution of ice during dynamic
recrystallization and its potential application to interpret the microstructures observed
in ice cores.
Keynote 4: Local strain analysis by High Angular Resolution Electron
BackScatter Diffraction
Claire MAURICE
Ecole des Mines de Saint-Etienne – Laboratoire Georges Friedel (UMR CNRS 5307)
158 cours Fauriel, 42023 Saint-Etienne Cedex 2
Over the last two decades, Electron BackScatter Diffraction (EBSD) in the Scanning
Electron Microscope (SEM) has developed to become a standard microstructure
characterization tool allowing measurements of crystalline phase, orientation and lattice
perfection from probed volume of a few tens of nanometers in size. An EBSD pattern is
nothing more than the gnomonic projection of the crystal lattice cell geometry (recalling
that it projects a sphere onto a tangent plane, here the phosphor screen). As such, any
elastic distortion of the probed material will be mapped onto the EBSP. Following
pioneering work by Troost et al. [1] and Wilkinson et al. [2], this diffraction technique is
being pushed forward into the exciting field of strain mapping at a submicron spatial
resolution. The ability to measure intragranular strain heterogeneities opens up new
possibilities in micromechanics modelling of polycrystals undergoing elastic or
moderately severe plastic deformation.
This presentation aims at first describing standard EBSD measurements as performed on
a daily basis in many Material Science or geology laboratories. We then focus on the
effect of strain on EBSD patterns and how this can be measured and interpreted to
retrieve the strain/stress of the probed material.
High Angular Resolution EBSD is based on the comparison between a “reference” and
the “current” diffraction Kikuchi pattern. Digital Image Correlation techniques are
applied to the diffraction patterns to obtain the distortion field of the measure EBSP,
from which the transformation gradient tensor of the probed volume can be identified [3].
The current technique delivers the transformation gradient tensor with a sensitivity of
~1x10-4 and a lateral resolution of the order of 30 nm; this works well for small rotation
measurements and for determination of the strain tensor as long as the strain state of the
reference pattern is known. The method therefore has difficulties when examining
strained polycrystals with no obvious region that could be used to record the reference
pattern with known strain. Recent work carried out at EMSE aims at solving these
difficulties and will be reported:
• The current method fails when lattice rotations exceed a few degrees. A novel,
more general DIC technique has been developed to cope with this problem.
• Secondly, an image processing route for the absolute determination of orientation
and strain from one single EBSP is currently being explored.
• Finally, some examples of experimental applications will be shown to
demonstrate the potential of this emerging technique.
1. Troost, K.Z., Vandersluis P., and Gravesteijn D.J., (1993) Microscale Elastic-Strain Determination by
Backscatter Kikuchi Diffraction in the Scanning Electron-Microscope. Applied Physics Letters, 62(10) 11101112.
2. Wilkinson, A.J., Meaden, G., and Dingley, D.J. (2006) High-resolution elastic strain measurement from
electron backscatter diffraction patterns: New levels of sensitivity. Ultramicroscopy, 106(4-5), 307-313.
3. Villert, S., Maurice, C., Wyon, C., and Fortunier, R., (2009) Accuracy assessment of elastic strain measurement
by EBSD. Journal of Microscopy-Oxford, 233(2), 290-301.
Intra-grain orientation spreads in hot-deformed aluminium:
Properties and relation to crystal plasticity
R. Quey1, J.H. Driver1 and P.R. Dawson2
1
2
Ecole des Mines de Saint-Etienne, CNRS UMR 5307, FRANCE
Sibley School of Mechanical and Aerospace Engineering, Cornell University,
USA
The development of in-grain orientation spreads is analysed for 92 individual
grains of an aluminium polycrystal deformed in plane strain compression at
400 °C to a strain of 1.2. By a “microtexture tracking” experiment combining the
use of a split sample and EBSD measurements, the grain orientations were
characterized at successive strains of 0, 0.19, 0.42, 0.77 and 1.2, with more
than 1000 orientation measurements for each grain. A high-resolution finite
element simulation (1000 elements per grain in average) was conducted on a
polycrystal whose grains were assigned the experimental orientations. The
experimental and simulation orientation spreads were analysed in terms of
average disorientation angle and anisotropy properties, in particular preferential
disorientation axis. For both experiment and simulation, the average
disorientation angles were found to increase up to a strain of 0.5 and then to
saturate. It is shown that the preferential disorientation axes are distributed
about TD up to a strain of 0.5 and then migrate at large strains to directions
between RD and ND. Detailed crystal plasticity analyses show that the
distribution of preferential disorientation axes is related to two mechanisms: (i)
the development of an anisotropic orientation spread due to the association of
a particular slip geometry and stress heterogeneities, and (ii) the transformation
of the orientation spread associated to the reorientation velocity gradient.
Quartz exsolution topotaxy in clinopyroxene from ultrahigh pressure
eclogite: An EBSD study and its implications
Haijun Xu*, Junfeng Zhang, Keqing Zong
School of Earth Sciences, China University of Geosciences, Wuhan 430074, China. [email protected]
Abundant oriented silica precipitates of α-quartz (4.0 ± 1.0 vol.%), in part coexisting with calcic
amphiboles (<0.2 vol.%), have been identified in clinopyroxenes of eclogites from the Weihai area, Sulu
ultrahigh pressure terrane, eastern China. Electron backscatter diffraction (EBSD) analyses demonstrate
that the majority (97%) of quartz precipitates have topotactic relationships with their host clinopyroxenes.
Three types of crystallographic topotactic relationship have been identified between quartz and host
clinopyroxene: (1) 52% quartz precipitates share the same orientation for the c-axes with [0001]qz//[001]cpx;
＿
(2) 34% quartz precipitates share the same orientation for the a-axes with [112 0]qz//[001]cpx; (3) 11%
＿
quartz precipitates share the same orientation for the s-planes with (1121)qz//(100)cpx. Other quartz axes and
planes disperse in large or small girdles around the shared axes or planes. Many quartz rods/needles are
＿
elongated parallel to the [001]cpx with the long axes of quartz being either [0001]qz or [112 0]qz. Amphibole
precipitates have also a strong crystallographic relationship with host clinopyroxene, i.e., (100)amp//(100)cpx,
[010]amp//[010]cpx, and [001]amp//[001]cpx. These results provide quantitative microstructural evidence
supporting an exsolution origin for oriented quartz needles/rods in clinopyroxene and demonstrate that the
exsolution of quartz from clinopyroxene occurred within the stability field of α-quartz rather than coesite.
The oriented precipitates of α-quartz, in part coexisting with calcic amphiboles, in host clinopyroxene are
probably promoted by supercritical fluid or partial melting during the early exhumation of eclogites. Our
results suggest that oriented quartz precipitates in clinopyroxene cannot be used as an indisputable UHPindicator.
Analysis of grain boundaries and subgrain structures in ice using optical
characterization techniques
1,2
1,3
2
1
Tobias Binder , Ilka Weikusat , Christoph Garbe , Sepp Kipfstuhl
1
Alfred-Wegener-Institut Helmholtz-Zentrum für Polar und Meeresforschung,
Bremerhaven, Germany
2
University of Heidelberg, Interdisciplinary Center for Scientific Computing (IWR),
Heidelberg, Germany
3
Eberhard Karls Universität Tübingen, Geosciences, Tübingen, Germany
Optical characterization techniques play an important role in the analysis of ice samples
as these snapshots of microstructure evolution can be investigated to a greater extent
(and thus at higher time resolution) than feasible by high-resolution techniques. Modern
optical techniques are not limited to mean orientations of the optical axis (c-axis) per
grain or grain sizes, but also opens up the opportunity to analyze grain boundaries and
subgrain structures. The transition from subgrain boundaries to grain boundaries in ice
occurs at very small threshold angles (3-5°) with respect to other materials (metals: 1015°, minerals 5-10°). This steep evolution of the boundary energy with increasing
misorientation angles at low values (3-5°) causes different behavior of the boundary,
such as the thermal etching during sublimation leading to varying grooving along the
boundaries (gray values in images). Sublimation etch grooves reveal different types of
subgrain boundaries regarding their arrangements with respect to the crystal's
orientation: normal or perpendicular arrangement with the basal plane. The potential of
fast optical characterization techniques has been improved by automatic image
processing routines and systematic combination between different optical techniques. In
addition to the extraction of grain boundary grooves at high resolution, it allows deriving
reliable and statistically representative frequencies of the arrangements of subgrain
boundaries. This can be used to determine slip system activities in combination with
diffraction methods (e.g. EBSD or x-ray Laue): not only slip systems with dislocations
on the basal plane contribute to subgrain boundary formation, but also those on non-basal
planes significantly.
Dislocation and disclination density fields from EBSD orientation
mapping
Benoit Beausir and Claude Fressengeas
Laboratoire d'Etude des Microstructures et de Mécanique des Matériaux
Université de Lorraine/CNRS, Ile du Saulcy, 57045 Metz Cedex, France
Disclinations and dislocations are crystal defects simultaneously introduced by Volterra
[1]. Dislocations arise from translational incompatibility of the crystal lattice, whereas
disclinations originate in rotational incompatibility. By reflecting elastic rotation
discontinuities, disclinations are a priori well suited for the description of imperfect
lattice structures such as grain boundaries, where a single-valued elastic rotation field
does not exist. We indeed show widespread experimental evidence of the presence of
disclinations in polycrystalline aggregates of metals, ice and rocks. Using orientation
maps obtained from electron backscattered diffraction or transmission electron
microscopy, a method for the recovery of components of the dislocation and disclination
density tensor fields is presented and applied to various polycrystalline materials.
Mapping the disclination densities reveals their extensive presence at intra-granular lowangle boundaries, low and high-angle grain boundaries and triple junctions, irrespective
of the material symmetry and grain size. A significant amount of rotational
incompatibility, with dipolar distribution of the disclinations, is detected in all cases
investigated [2,3]. Since high-angle rotational incompatibility cannot be accounted for
consistently by dislocation-based models, the present results support considering
disclinations in addition to dislocations in the interpretation of grain boundaries and
triple junctions in crystalline materials [4].
References
[1] V. Volterra, Sur l'équilibre des corps élastiques multiplement connexes, Ann. Sci.
Ecol. Norm. Sup. III 24, 401-517 (1907).
[2] B. Beausir, C. Fressengeas, Disclination densities from EBSD orientation mapping,
Int. J. Solids & Structures 50, 137-146 (2013).
[3] P. Cordier, S. Demouchy, B. Beausir, V. Taupin, F. Barou and C. Fressengeas,
Disclinations provide the missing mechanism for deforming olivine-rich rocks in the
mantle, Nature 507, 51-56 (2014).
[4] C. Fressengeas, V. Taupin, L. Capolungo, Continuous modeling of the structure of
symmetric tilt boundaries, Int. J. Solids & Structures 51, 1434-1441 (2014).
Keynote 5: Characterization of the dislocation content of EBSD
J. Wheeler1, E. Mariani1, D.J. Prior2
… and a host of co-authors I will acknowledge in the particular case studies
1
2
Dept. Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 3GP, UK
Dept. Geology, University of Otago, Dunedin, Otago 9054, New Zealand
At high temperatures in crystalline materials dislocations may be produced: they
move under the influence of stress and/or to reduce energy during recovery. The density
of dislocations (a scalar) gives some insight into the strain energy a lattice contains
(which may then drive recrystallisation). A more complete description of dislocation
density is a second rank tensor (the Nye tensor), which contains directional information
related to dislocation lines and Burgers vectors. This then can give insight into the types
of dislocation present and hence slip systems.
There is an obsession with pursuing the scalar measure of dislocation density, but I
suggest that even if it can be obtained it does not directly tie to plastic strain energy
because of all the different types of dislocation that can conceivably contribute. All of
these might have different energies and in any case the stress fields of dislocations
overlap and the energy is not necessarily the sum of the individual energies.
The Nye tensor is related mathematically to lattice curvature. Basically, if one
neglects elastic strain, a lattice can be curved only if it contains dislocations. These are
referred to as geometrically necessary dislocations. So, in principle, measurement of
lattice curvature allows calculation of the Nye tensor but we need curvature in three
dimensions which cannot be obtained from a 2D EBSD map. Various techniques have
been devised to calculate the Nye tensor using additional assumptions but I am sceptical
of those assumptions. Alternatively we can calculate some of the components of the Nye
tensor without additional assumptions. Of the 9 components we can calculate 3 which
together we term the “Weighted Burgers Vector”. This is the total Burgers vector content
of dislocations which thread through the map (Wheeler et al. 2009). It has been used to
for instance in Mg metal. This is particularly useful for lower symmetry phases: for
example in hexagonal Mg it gives insight into whether Burgers vectors lie in the basal
plane or have at least a component parallel to c, highlighting non-basal slip. The power
of the WBV lies in its simplicity, the lack of potentially compromising assumptions in its
calculation, and the fact it can be used in “differential” (local) and “integral” (finite
region) calculations, the latter reducing errors.
The Matlab code “CrystalScape” is used for these calculations. This is not as
comprehensive as MTEX – but it has been in use for years, has a menu driven interface
and can be used for WBV and other calculations, which MTEX cannot currently
perform.
Wheeler, J., Mariani, E., Piazolo, S., Prior, D. J., Trimby, P. & Drury, M. R. 2009. The
Weighted Burgers Vector: a new quantity for constraining dislocation densities
and types using Electron Backscatter Diffraction on 2D sections through
crystalline materials. Journal of Microscopy 233(3), 482-494.
Keynote 6: Transients in strength and structure
Brian Evans, Dept. of Earth, Atmos., & Planet. Sci., Mass. Inst. Tech., Cambridge, MA, 02139, USA Steady state flow laws, developed with considerable effort, care, and insight, provide
constraints on dynamic processes; insights into appropriate deformation mechanisms;
and bounds, or at least, guides to rock strength during natural deformation. However,
transient mechanical behavior must also exist and is probably important in the production
of structural features including shear zones, faults, and deformation bands, which may
involve strain localization and mechanical instability. To develop quantitative
mechanical descriptions of the evolution of strength requires the identification of an
appropriate set of state variables, understanding their relative interactions and their
contribution to overall inelastic strain rate. The task is made more difficult by the
necessity of extrapolation to a broad range of strain rates, time durations, and conditions,
many of which are difficult to duplicate in the laboratory. Theoretical formulations are
guided by general thermodynamic principles, but specific choices for the details of
micromechanics, are required for the formulation of a transient creep law. Often, the rate
equations for the evolution of such state variables are under constrained. Additionally,
the inelastic strain may result from a combination of deformation mechanisms, perhaps
including micro cracking, twinning, dislocation generation and slip, and grain-boundary
production and migration. Bounds on inelastic strain rate are often made by assuming
control by a single rate-limiting mechanism, or by the simple addition of a small number
of them. Recent observations of damage mechanisms suggest that this view might be
overly simplified. Further progress begs several questions: What level of complexity is
needed for a more accurate formulation? How many state variables are needed and how
do their evolution rates change with changing conditions? And, finally, how does one
account for changing interactions between them? Answers will not be provided by a
single viewpoint, but will require intense interactions amongst workers using field
structural observations, theoretical considerations of deformation mechanisms, and
laboratory experiments.
ANR DELF
Intermediate and Deep Earthquakes: from the Lab to the Field
1,2
1,2
3,2
4,8,2
Thomas Ferrand , Alexandre Schubnel , Nadège Hilairet , Loïc Labrousse
,
1,2
5
6
7
1,2
Christian Chopin , Joerg Renner , Yanbin Wang , Wilson Crichton , Sarah Incel ,
7
1
2
5
Jérémy Guignard , Damien Deldicque , Yves Pinquier , Frank Bettenstedt
1: ENS Paris; 2: CNRS; 3: UMET Lille; 4: ISTeP-UPMC; 5: Ruhr Uni. Bochum;
6: ANL, Uni. of Chicago; 7: ESRF, Grenoble; 8: Ulaval Québec
Experimental constraints of the rheology of serpentinized peridotites at
high pressure and implications for the lower Wadati-Benioff plane of
seismicity
In light of field observations in two different mantle ophiolites in Balmuccia and Voltri,
northern Italy, the rheology of serpentinite and serpentinized peridotite need to be better
understood, especially during dehydration experiments. HP-HT experiments have been
performed in ESRF and APS Synchrotrons, where X-ray diffraction is used to estimate stressstrain relationship in sintered peridotite during D-DIA experiments. At the APS acoustic
emissions are recorded in order to trigger micro-earthquakes.
Additional experiments have been performed in Griggs-type apparatus, permitting nonhydrostatic conditions, high pressure (1-4GPa) and high temperature (500-1000°C) conditions at
the Ruhr Universität in Bochum. The same apparatus is being installed at the ENS and equipped
with acoustics.
Up to now, the results seem consistent. Mechanical instability may originate in
serpentinite dehydration for part of the intermediate-depth earthquakes. According to our
experiments, slightly serpentinized mantle, about 5%, have a seismogenic potential, contrary to
largely serpentinized mantle, in which the connection of the serpentine network prevents stress
to rise enough. These abductions need further experiments and may explain the seismicity of the
lower Wadati-Benioff plane.
Rheology of phase A at high pressure and high temperature
N. Hilairet1, E. Amiguet2, Nathalie Bolfan-Casanova3, Y. Wang4
1 - Unité Matériaux et Transformation, CNRS – ENSCL - Université Lille 1, Villeneuve
d'Ascq, France
2 - Earth and Planetary Science Laboratory, Ecole Polytechnique Fédérale de Lausanne,
Lausanne, Switzerland
3 – Laboratoire Magmas et volcans, CNRS - Université Blaise Plascal - OPGC,
Clermont-Ferrand, France
4 – CARS, The University of Chicago, Chicago, IL, USA
Subduction zones are locations where a tectonic plate slides and bends under another one.
Materials there undergo large and heterogeneous deformations and stresses which are released
through seismicity, occasionally. Thus plasticity of minerals filling faults and shear zones is a
critical parameter for understanding the stress balance of whole subduction zones. We present
a deformation study on a hexagonal hydrous phase that can exist in shear zones within
subducting slabs, phase A, after dehydration of serpentine into pyroxene phase A. Pure phase A
samples were synthesized at 11 GPa and ca. 1100K. Three samples were deformed at 11 GPa
confining pressure, and 400C or 580C, using a D-DIA apparatus [1] at 13B-MD at GSE-CARS,
APS, in uniaxial shortening up to -0.24 strain and at 5.10-5 s-1. Lattice strains (a proxy for
macro-stress), texture and strain were measured in-situ, using synchrotron radiation. Results
from lattice strain and texture analysis show a decrease in flow stress and a change in
deformation mechanisms with temperature, coherent with the findings in transmission electron
microscopy on samples recovered in relaxation experiments from [2]. The slip systems involved
during deformation were further analyzed using Visco-Plastic Self-Consistent (VPSC)
simulations [3]. The model inputs were known slip systems for hexagonal materials, including
the ones observed by [2], with tunable strengths, the strain rate, final strain, and either a random
texture or the starting experimental texture. The final experimental textures could be reproduced.
The slip systems that had to be activated for matching the experimental texture confirm the
observations by [2]: at 400C, the most active slip systems are prismatic and pyramidal, with the
requirement of a smaller activity on the basal system, and at 580C the basal system is the main
slip system activated.
Within subduction zones, the strong yield strength, intrinsic weak elastic anisotropy, together
with weak deformation textures, all indicate that phase A will homogenise deformation and
seismic anisotropy. [1] Wang et al, Review for Scientific Instruments, 74(6), 3002-3011, 2003 [2]
Mussi et al, European Journal of Mineralogy, 24, 429-238, 2012 [3] Lebensohn and Tome, Acta
Materialia, 41, 2611, 1993
Investigating the rheology of mantle minerals at very high pressures
and temperatures using synchrotron radiation
Misha BYSTRICKY, Frédéric BÉJINA, Arnaud PROIETTI, Julien BATICLE
Institut de Recherche en Astrophysique et Planétologie (IRAP), OMP, CNRS &
Université Paul Sabatier Toulouse III, FRANCE
While numerous experimental studies have focused on the rheology of mineral
aggregates at high temperatures, the effect of pressure on ductile flow of most minerals is
still poorly constrained. The pressure dependence of the viscosity of a material is
typically described through the activation volume in the creep flow law. Since each
deformation mechanism has its own activation volume, the deformation mechanism
controlling creep may change with pressure. In addition, pressure may enhance the
activation of some slip systems relative to others in the dislocation creep field, leading to
different crystallographic preferred orientations at large strains. When this is the case, it
is quite possible that several parameters in the flow law vary with pressure. Recent
technical developments now give the opportunity to investigate the rheology of rocks and
minerals at extreme pressure conditions using synchrotron radiation. We will present
some of these techniques and illustrate them with our results on the deformation of
olivine and pyroxene aggregates at upper mantle pressure and temperature conditions.
Intracontinental deformation and strain-partitioning pattern in the
oblique continental collision zone
Zhang Bo
The Key Laboratory of Orogenic Belts and Crustal Evolution, China
School of Earth and Space Sciences, Peking University, Beijing 100871, China
The large high–strain zones are common structures in continental deformation
localization, such as the active India–Eurasia collision zone, which accommodate
amounts of total shortening, or major and long–lasting structures that play a long–
standing role in the lateral extrusion of crustal or lithospheric–material. Around the
Eastern Himalayan Syntaxis (EHS) and the area to the southeast, the strike–slip–
dominated deformation fabrics were documented along these zones curve from
trending WNW–ESE at the eastern extremities of Tibet to trending NW–SE in
northwestern Yunnan, China, and the rocks are strongly metamorphosed and deformed
(Figure 1). The widespread deformation is represented by N–S, NW–SE, and NE–SW
trending ductile shear zones such as the Jiali, Ailao Shan–Red River, Chongshan,
Gaoligong, Mae Ping, Three Pagodas, and Sagaing fault zones.
However, the curvature along these fault boundaries corresponds to variations in
strain patterns and kinematics along these strongly-deformed zones. The occurrence of
vertical movement in these high strain zones imply an oblique vector movement that
can be partitioned into two components, a simple shearing component (strike-slip
shearing) and a pure shearing component (responsible for the uplift) (Figure 2). In
earlier studies (e.g., Leloup et al., 1995; Wang and Burchfiel, 1997; Burchfiel et al.,
2003), the ductile fabrics within the Gaoligong, Ailao Shan-Red River gneissic domes
were interpreted to be solely related to the Eocene–Oligocene sinistral simple shearing.
However, our new data suggest that a compressional component during the shortening
was more important, similar to that in a contractional gneiss dome (Figure 2). The
presence of the antiformal domes along the high-strain zones in the linkage area
between the Tibetan Plateau and extruded southeastern Asia, implies a compressional
regime, and provides clear evidences of horizontal shearing and vertical extrusion in
the middle and/or lower crust. During oblique continental collision setting, strain can
be partitioned into shortening and lateral extrusion.
Figure 1. Topography and regional tectonic framework in southeastern Asia.
MICROSTRUCTURES AND DEFORMATION MECHANISMS IN HIGHTEMPERATURE MYLONITES FROM THE RIBEIRA BELT, SE BRAZIL
Geane Carolina G. Cavalcante1,2, Alain Raymond Vauchez2 and Marcos Egydio-Silva1
(1) USP University of São Paulo, São Paulo, Brazil, (2) University de Montpellier,
Montpellier Cedex 05, France
The Neoproterozoic Ribeira belt, formed by the collision between the São Francisco and
Congo cratons, comprises tectono-stratiphrafic domains of different nature and ages. Its
northern termination displays a transcurrent shear zone network, the ~250 km long Além
Paraíba-Pádua transpressional shear zone, which involves a variety of mylonites deformed
under granulite and amphibolite facies conditions and that display different fabric pattern,.
A detailed microstructural and crystallographic preferred orientation (CPO) study of the
rock-forming minerals was undertaken to infer constraints on the rheology of the lower
crust during the development of this shear zone. The CPO of quartz, feldspar, amphibole,
pyroxene and biotite.in the mylonites have been measured by Electron Backscatter
Diffraction (EBSD). Fine-grained mylonites are composed of alternating monomineralic
layers, usually continuous quartz ribbons and recrystallized feldspar. Some of the quartz
ribbons contain strongly elongated "platen-quartz", probably formed by grain boundary
migration along the ribbon during annealing. Coarse-grained mylonites have porphyroclasts
of K-feldspar and andesine up to 6 mm long, which often exhibit subgrains, undulose
extinction, deformation twins, myrmekite, and core-mantle structure. Quartz occurs as large
(up to 1 mm wide) discontinuous polycrystalline ribbons, but also as porphyroclast. The
quartz ribbons frequently wrap the K-feldspar porphyroclasts. The fabric of gneiss
mylonites is characterized by alternating domains of an anastomosing foliation, defined by
biotite and sillimanite grains, and isolated bands of quartz ribbons with strong shape
preferred orientation, oblique to the foliation, indicating both dextral and sinistral shear
sense. CPO of feldspar is often not well defined. However, few samples display
concentrations of [001] close to the lineation, [010] close to the pole of the foliation and
[100] close to the Y strain axis, suggesting the activation of the [001](010) slip system,
consistent with medium to high-grade metamorphic conditions. CPO of hornblende is well
defined, with (100) concentration close to the Z strain axis and [001] close to the lineation,
indicating the activation of the (100)[001] slip system, typical of high temperature
conditions. In the highest temperature mylonites some CPO of quartz are suggestive of
plastic deformation with the activation of prismatic [c] slip system, when others display a
dominant parallelism of the Rhomb planes with the foliation. This suggests that the CPO
was significantly modified during post-kinematic annealing, making these crystallographic
fabric difficult to interpret. Anisotropic viscosity of olivine aggregates: A laboratory, field, and
numerical approach
Lars N. Hansen1, Clinton P. Conrad2, Jessica M. Warren3, David Wallis1, David L. Kohlstedt4
1
Dept. Earth Sciences, University of Oxford, Oxford, OX1 3AN, UK
Dept. Geology & Geophysics, SOEST, Univ. Hawaii at Manoa, Honolulu, HI 96822, USA
3
Geological & Environmental Sciences, Stanford University, Stanford, CA 94305, USA
4
Dept. Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA
2
Shearing of mantle rocks within Earth’s lithosphere and asthenosphere causes mantle
minerals, particularly olivine, to develop crystallographic textures that can be detected
seismically. In laboratory studies, such crystallographic textures have also been associated
with dependence of the viscosity of a mineral on the orientation of an applied stress. This
anisotropic viscosity may affect tectonic plate motions and the stability of the lithospheric
base, but it is highly dependent on 1) the rate of fabric development and 2) the poorly
constrained viscosity tensor, which relates the stress applied to an olivine crystal of known
orientation to the resulting strain-rate.
Here we constrain the importance of viscous anisotropy in the upper mantle using
deformation experiments conducted in a gas-medium apparatus. Olivine aggregates were
deformed at a temperature of 1200°C and confining pressure of 300 MPa. One set of samples
was initially deformed in torsion and subsequently deformed in tension. A second set of
samples was initially deformed in tension and subsequently deformed in torsion. Torsion
experiments reached a maximum shear strain of ~20. This combination of strain paths
allowed us to quantify the effect of evolving crystallographic texture on multiple components
of the viscosity tensor.
We developed a micromechanical model that allows estimation of the complete viscosity
tensor based on a measured texture. The primary unknown is the single-crystal viscosity
tensor. We then invert for this latter tensor using the applied stresses, measured textures, and
measured strain rates from deformation experiments. We developed a second, independent
model of olivine textural development that takes into account the strength of individual slip
systems when tracking grain rotations, yet is stable to high strains. We calibrate this texture
model through comparison to the strengths and shapes of measured textures in experimental
samples. Together, these two calibrated models allow us to constrain the rate of texture
development in an arbitrary deformation geometry and also the resulting macroscopic
viscosity tensor.
Our results indicate that olivine textural development can yield viscosities that vary by over
an order of magnitude depending on the orientation of the applied stress relative to the
dominant crystallographic texture. We test our mechanical and textural evolution models
through comparison to natural peridotite shear zones exposed in the Josephine Peridotite.
We find that (1) the natural textural development is well approximated by our numerical
model and (2) a significant portion of the strain localization can be attributed to the
development of viscous anisotropy.
Keynote 7: Impact of texture-induced anisotropy on glaciers flow.
Fabien Gillet-Chaulet (LGGE, CNRS/Univ. Grenoble, France)
For conditions typical of polar ice sheets and glaciers, the ice behaves as a viscous material.
Due to the strong mechanical anisotropy of the ice single crystal, the bulk rheological
properties of ice strongly depend on the fabric or texture (crystal c-axis orientations). A
polycrystal of ice with most of its c-axes oriented in the same direction deforms at least ten
times faster than an isotropic polycrystal, when sheared parallel to the basal planes.
At the highest elevations snow accumulates and is turned into glacial ice resulting in nearly
random c-axis orientations and thus isotropic mechanical properties. Then, under the effect of
its own weight, the ice deforms slowly and flows. Depending on the flow conditions (stresses
and temperature), fabrics can develop and strongly influence the response of ice layers to
imposed stresses.
In polar ice sheets, fabrics basically develop as the result of lattice rotation by intracrystalline
slip. In the bottom layers, where temperatures are close to the melting point and where
stresses are the highest, or in temperate glaciers, fabrics are mainly governed by dynamic
recristallisation. This fabric development, in turn, affects the stress pattern in the ice sheets
and glaciers and thus their large scale flow.
Accurate modeling of ice flow under natural conditions is relevant for many scientific
objectives, such as the response of ice sheet to climate changes and especially their
contribution to sea-level rise, or the interpretation of climate signals extracted from ice cores.
In this presentation, we will review the observations of fabrics and their effects in polar ice
sheets and glaciers. We will discuss the challenge of representing this evolving anisotropy
in large scale ice flow models.
Physical properties of polycystalline materials:
from the atomic to the planetary scale
David Mainprice
Géosciences Montpellier, Université de Montpellier, Montpellier, France.
E-mail: [email protected]
http://www.gm.univ-montp2.fr/PERSO/mainprice/
Physical and mechanical properties have their origins at the atomic scale. The first and
second law of thermodynamics indicates that the most fundamental elastic strain of a crystal occurs
when either pressure or the temperature is changed, which leads to the equation of state between the
volume of the crystal, pressure and temperature. The elastic strain with temperature is called linear
thermal expansion and elastic strain with pressure is called linear compressibility, both these
properties vary with direction. These properties can be directly linked for simple structures to an
almost universal internal energy versus atom separation curve, which has a characteristic asymmetric
trough shape. The arrangement of atoms in repeated way in crystals results in symmetry, which affects
properties in a fundamental way so that certain bulk properties are present (e.g. piezoelectricity when
there is no center of symmetry) or not, other properties may be isotropic (e.g. thermal conductivity for
cubic symmetry) or anisotropic (e.g. thermal conductivity for hexagonal symmetry).
Atomic modeling of elastic properties has been applied to perfect crystals at conditions of
pressure and temperature often outside the range of experimental measurement. Consideration of
atomic arrangement can be extended to crystals containing defects, such as point defects (e.g.
vacancies) or line defects (e.g. dislocations), characteristics of these defects have been the subject of
atomic modeling in recent years. To transfer the scale of properties from the single crystal to the
polycrystal has been successfully applied using various simple volume averaging schemes.
Verification of these methods by experimental measurements has been done by many times. The
extrapolation to larger length scales requires coherent structure at the appropriated distance
(correlation length), which tends to be organized by convection in cooling terrestrial planetary
interiors. The link to larger scales can achieved by comparing observed seismic anisotropy from the
borehole scale (10m to 10 km), glacier scale (2 km), crustal scale (1 km to 30 km), lithosphere scale
(30 to 250 km), mantle scale (250 to 2800 km) etc to models based on field geology of exposed
lower crust (Greenland), crustal-mantle sections (North Italy), predicted mantle flow patterns and
CPO (Crystal Preferred Orientation) development. Model predicted ab initio dislocation properties
of deep mantle phases combined with predicted elastic properties and visco-plastic self-consistent
(VPSC) CPO flow patterns. Even the prediction of the Earth’s inner core (360 GPa, 6000 K) seismic
properties based on ab initio elasticity …
Tuesday 11h50-12h30: Short poster presentations
3 minutes for each poster
Abstract of posters and 3 minute presentation by
alphabetical order
El Messbahi Hicham
Fernández-Roig Merce
Ferrando Carlotta
Filippelli Ernesto F.
Goryaeva Alexandra
Hashim Leïla
Hidas Károly
Incel Sarah
Journaux Baptiste
Kourim Fatna
Proietti Arnaud
Viegas Gustavo
Violay Marie
Wallis David
Yin Congyuan
Peridotite xenoliths from the Tafraoute maar (Middle Atlas, Morocco):
microstructural evidence for melt-assisted deformation enhancing strain
localisation in lithospheric mantle.
Hicham El Messbahi1,2, Jean-Louis Bodinier2, Alain Vauchez2, Jean-Marie Dautria2, Houssa
Ouali1, and Carlos J. Garrido3
1.
Equipe Géomatériaux, Université Moulay Ismaïl, Faculté des Sciences, BP 11201, Zitoune, Meknès,
Morocco ([email protected]) ;
2.
Géosciences Montpellier, Université de Montpellier 2 and CNRS, Cc 60, Place Eugène Bataillon,
34095 Montpellier Cedex 05, France ;
3.
Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC and UGR, Avenida de las Palmeras 4, 18100
Armilla, Granada, Spain.
Abstract
The Middle Atlas is a region where xenolith-bearing volcanism roughly coincides with the maximum of
lithospheric thinning beneath continental Morocco. It is therefore a key area to study the mechanisms of
lithospheric thinning and constrain the component of mantle buoyancy that is required to explain the Moroccan
topography.
Tafraoute maar is situated about 45 km away, on the North Middle Atlas Fault that separates the ‘folded’
Middle Atlas, to the Southeast, from the ‘tabular’ Middle Atlas, to the Northwest. Xenoliths from Tafraoute have
been investigated for their mineralogy, microstructures, crystallographic preferred orientation, and whole-rock
and mineral compositions. These peridotites show a variety of microstructures: coarse-equant, porphyroclastic,
granular, mylonitic that record different stages of deformation, most probably associated with decompression
and lithospheric thinning. Porphyroclastic samples likely derive from coarse-equant peridotites through dynamic
recrystallization. The presence of close sub-boundaries with a frequent fan-like disposition in porphyroclasts of
partially recrystallized samples, in contrast with the spaced sub-boundaries observed in coarse-equant xenoliths,
suggests that they were deformed under relatively high stress conditions.
The Tafraoute suite records heterogeneous infiltration of smaller melt fractions that migrated
diffusively, by intergranular porous flow, most likely during extensional lithospheric thinning related to
Mesozoic rifting. In contrast, the lithospheric mantle beneath the Middle Atlas volcanic province, e.g., at Bou
Ibalghatène, was strongly modified by melt–rock interactions during the Cenozoic. The two xenolith suites
illustrate distinct mechanisms of lithospheric thinning: extensional thinning in Tafraoute, where hydrous
incongruent melting triggered by decompression likely played a key role in favouring strain localisation, vs.
thermal erosion in Bou Ibalghatene, favoured and guided by a dense network of melt conduits. Our results lend
support to the suggestion that lithospheric thinning beneath the Atlas Mountains results from the combination
of different mechanisms and occurred in a piecewise fashion at a short wavelength scale.
Microstructures and crystal preferred orientations in the subcontinental lithospheric mantle of (NE Spain): EBSD data on xenoliths from the Catalan Volcanic Zone M. Fernández-­‐Roig1, G. Galán 1, E. Mariani 2 1
Departament de Geologia, Universitat Autònoma de Barcelona, Edifici C (sur), Carrer dels Til·∙lers, 08193 Bellaterra, Barcelona, Spain 2
School of Environmental Sciences, University of Liverpool, 4 Brownlow Street, L60 3GP Liverpool, UK The Catalan Volcanic Zone (CVZ) is part of the Neogene-­‐Quaternary volcanism in the Iberian Peninsula. It comprises three sub-­‐zones: L'Empordà, La Selva and La Garrotxa, which are basins, limited by a NW-­‐SE and NE-­‐
SW fracture system, caused by the rift-­‐type extensional tectonic that affected the western Mediterranean since the Miocene. Anhydrous spinel lherzolites and harzburgites with minor olivine websterites form a suite of mantle xenoliths included in the alkaline basaltic rocks of the CVZ. The peridotites are considered residues of variable degrees of partial melting, later affected by metasomatism. The websterites are interpreted as cumulates from alkaline mafic silicate melts causing the metasomatism. Protogranular microstructure is dominant in all rock types, but lherzolites display a continuous variation from protogranular to prophyroclastic and equigranular microstructures. To understand the relationships between the deformation fabrics, processes and microstructures of the lithospheric mantle represented by these xenoliths, the crystal-­‐preferred orientations (CPOs) of olivine and pyroxenes were studied in eighteen new samples, using the EBSD-­‐SEM technique. Protogranular samples show well-­‐developed olivine CPO characterized by a strong point concentration of the [010] axis normal to the foliation and girdle distribution of [100] and [001] axes within the foliation plane, called [010]-­‐fiber type, which is the dominant one in this zone. In lherzolites, olivine CPO varies continuously from [010]-­‐fiber to orthorhombic and rare [100]-­‐fiber types. The orthorhombic patterns are characterized by scattered maxima of the three axes, which are normal between them. The [100]-­‐fiber type is characterized by a strong point concentration of [100] axis, whereas the other two form incomplete girdles normal to it. Pyroxene CPOs is weaker than those of olivine, but there is good correlation between the [100] olivine axis and the [001] pyroxene axis in most protogranular samples. However, the [001] axes of all olivine and pyroxenes are parallel in equigranular and some porphyroclastic lherzolites. The CPO strength of the three main silicates decreases with grain size reduction. These data of CPOs suggest a deformation by dislocation creep, with preferential activation of the [100](010) slip system in olivine and the [001](100) and [001](010) for in orthopyroxene. Furthermore, in porphyroclastic and equigranular lherzolites, there is subsidiary contribution of the [100]{0kl}, [001](100) and [100](001) slip systems for olivine. Temperature estimates with the two-­‐pyroxene thermometer indicate higher values for protogranular harzburgites, lherzolites and websterites than for porphyroclastic and equigranular lherzolites. The jadeite component of clinopyroxene also decreases in the same direction. These results suggest that the lithospheric mantle in the CVZ would have undergone different stages of deformation that would have taken place at decreasing temperature and pressure. Protogranular microstructures with olivine [010]-­‐fiber patterns would represent an earlier stage. This could be caused by axial shortening, transpression and subsequent recovery and annealing may be assisted by partial melting. Porphyroclastic and equigranular lherzolites, with orthorhombic and [100]-­‐fiber patterns for olivine, would represent later deformation stages, which would come most likely from an active shear zone at shallower upper mantle level, in relation with the opening of the Neogene rifting. Transient deformation patterns for olivine, grain size reduction along with weakening of the fabric strength could be due to dynamic recrystallization through grain boundary migration and subgrain rotation mechanisms, during the later deformation stages. Microstructural analysis of olivines in Erro-Tobbio troctolites
crystallographic preferred orientations and misorientation patterns.
:
Carlotta Ferrando and Benoit Ildefonse
Géosciences Montpellier, CNRS & Université Montpellier, France
Olivine-rich gabbroic rocks (troctolites) are often described in modern oceanic lithosphere at
fast- and slow-spreading ridges, and in ophiolite outcrops. Primitive troctolites are present in
the Erro-Tobbio mantle peridotites (Voltri Massif, Ligurian Alps, Italy) as distinct bodies that
range from homogeneous granular troctolites to heterogenous troctolites with granular and
harrisitic olivines. Melt-rock interactions processes are invoked as a major cause of the
variable textures and geochemical compositions of the Erro-Tobbio troctolites, with
compositions intermediate between those of mantle peridotites and primitive cumulates. A
detailed microstructural study was performed on the Erro-Tobbio troctolites in order to
further constrain the origin of olivine crystals. EBSD maps were processed with MTEX to
produce olivine Crystallographic Preferred Orientations (CPO), and to image misorientation
patterns within olivine single crystals. Olivine CPO are distinct in the two types of troctolites.
In homogeneous troctolites, they are much weaker than in heterogeneous troctolites, and are
characterized by uncommon [001] point concentrations. The latter was interpreted as resulting
from melt impregnation of mantle peridotites in a recent study of olivine-rich troctolites
sampled
by
drilling
at
the
Mid-Atlantic
Ridge
(Drouin
et
al.,
2010,
doi:10.1029/2009GC002995). Olivine grains in homogeneous granular troctolites show
substructures that reveal dislocation creep, consistent with activation of the main high-­‐
temperature slip systems, dominantly (010)[100]. On the other hand, olivines from texturally
heterogeneous troctolites contain less organized misorientation patterns, forming a random
mesh with low misorientation angles. These structures differ from the well-­‐developed
subgrains commonly described in olivines recording dislocation creep, and are mostly evident
in medium to highly serpentinezed harrisitic olivine. We interpret these unusual features as
low misorientation angles between fragments of single crystal olivines, resulting from the
local partial disruption of the olivine structure during the serpentinization process.
In situ characterization of dislocation boundaries in a plastically deformed Al polycrystal by three-­‐dimensional X-­‐Ray Diffraction
(a)
E. F. Filippelli , L. Renversade(a), R. Quey(a), A. Borbély(a) a
École des Mines de Saint-­‐Étienne, Laboratoire Georges Friedel, CNRS UMR 5307, 158 cours Fauriel 42023 Saint-­‐Étienne cedex 2 It is well known that macroscopic plastic deformation of most metals results from nucleation and gliding of dislocations. These defects often gather to form dislocation boundaries, which in turn lead to lattice orientation gradients within the grains. For this reason, they are often referred to as Geometrically Necessary Boundaries (GNBs). Dislocation boundaries play a very important role in the work hardening of metals, since they act as obstacles in front of dislocation movement. As a consequence, many studies have been carried out to characterize them in the last decades, in particular by Transmission Electron Microscopy (TEM) [1] and high resolution X-­‐Ray Diffraction [2]. In these works, GNBs were shown to form just after the onset of plastic deformation [2] and to align with particular crystallographic directions [1]. Unfortunately, due to its destructive nature TEM cannot describe the evolution of these boundaries, which might be important for theories describing their formation and dynamics. In the present work, we have applied three-­‐dimensional X-­‐Ray Diffraction (3DXRD) to characterize in situ dislocation boundaries formed in individual grains of an Al-­‐0.1%Mn polycrystal subjected to tensile deformation. It is well known that a reciprocal space map investigation of diffraction peaks gives information about the type of defects prevailing in the material. In particular, through the analysis of azimuthal broadening of diffraction spots it is possible to characterize the disorientation axis of GNBs [3]. We have detected dislocation boundaries formed already at the onset of macroscopic plastic deformation (0.2% strain), and we have found that their structure depends strongly on the initial crystallographic orientation of the parent grains. Grains with orientation close to the 111 and 110 corners of the inverse pole figure contain mainly tilt and twist type dislocation boundaries, respectively. For grains in the centre of the stereographic triangle, GNBs have a mixed tilt-­‐twist character. On the opposite, no boundaries were found for grains close to 001 pole, in agreement with previous results showing the presence of only dislocation cell blocks [4]. Furthermore, the evolution of spots' shape has been analysed to understand how GNBs structure changes with deformation. Finally, grain orientation path has been traced on a stereographic triangle and compared to the predictions of the Taylor model. Present results confirmed previous findings by Winther et al. [5]. [1] C. Hong, Phil. Magazine (2013) 93, 3118-­‐3141 [2] B. Jakobsen, et al. Science 312 , 889 (2006) [3] R. I. Barabash, J. of Appl. Cryst., (1999), 32, 1050-­‐1059 [4] G. Winther, Mat. Sc. and Eng. A, (2008), 40-­‐46 [5] G. Winther, Acta Mater. 52, (2004), 2863-­‐2872 Atomistic Modeling of Dislocations in MgSiO3 Post-Perovskite Alexandra Goryaeva, Philippe Carrez, Patrick Cordier
Unité Matériaux et Transformations, CNRS UMR 8207, Université des Sciences et Technologies de Lille 1,
59655 Villeneuve d'Ascq
[email protected]
The recently discovered MgSiO3 post-perovskite phase (Cmcm) is only stable at high pressure and temperature
conditions corresponding to the lowermost ~150 km of the mantle (the D'' layer) [1, 2]. The unusual, for a highpressure phase, layer-like structure of the post-perovskite may be responsible for the observed seismic
anisotropy of the D'' layer. However, information about mechanical properties, easier slip systems, dislocations
and their behaviour under stress are not well known still. This work represents a theoretical study of the postperovskite within the semi-empirical approach using the Buckingham interatomic potential parameters
previously derived by [3].
To describe the energy cost incurred as a result of a shear and to deduce the most favorable slip systems, the
GSF excess energies are calculated at 120 GPa. The lowest energy barrier as well as the smallest values of the
ideal shear stress (ISS), are related to the slip systems with the smallest [100] Burgers vector (b=2.521 Å) and to
the slip system [001](010) with the glide plane cutting only Mg-O bonds. Good agreement with the ab-initio
results [4] verifies the accuracy of the chosen inteatomic potential model [3].
The C-lattice of the post-perovskite results in four potential Burgers vectors: [100], [010], [001] and ½[011].
Taking into account the estimated GSF energies for different slip systems, we focus on mobility of screw and
edge dislocations with Burgers vectors [100], [010] and ½[110]. The evaluated values of lattice friction suggest
(010) slip plane parallel to the Si- and Mg-layers in the post-perovskite strucure to be the most probable .
References
[1] Murakami, M. et al., Geophys. Res. Lett. (2005), 32, L03304.
[2] Oganov, A. & Ono S., Nature (2004), 430, 44– 448.
[3] Oganov A. et al., Phys. Earth Planet. Int. (2000), 122, 277-288.
[4] Carrez Ph. et al., Philosoph. Mag. (2007), 87, 3229-3247.
MELT IN NATURAL OLIVINE AGGREGATES:
INTERCONNECTIVITY AND ITS INFLUENCE ON GRAIN GROWTH
Leïla Hashim1,2,3, David Sifré1,2,3, Jacques Précigout1,2,3, Emmanuel Gardés4, Luiz F. G.
Morales5, Emmanuel Le Trong1,2,3 and Fabrice Gaillard1,2,3
1,2,3
Université d'Orléans, ISTO, UMR 7327, 45071 Orléans, France; CNRS/INSU, ISTO, UMR 7327, 45071
Orléans, France; BRGM, ISTO, UMR 7327, BP 36009, 45060 Orléans, France
4
Commissariat à l'Énergie Atomique-CNRS-École nationale supérieure d'ingénieurs de Caen-Université de Caen
Basse Normandie, Centre de Recherche sur les Ions, les Matériaux et la Photonique, UMR 6252, BP 5133,
14070 Caen, France
5
Deutsches GeoForschungsZentrum (GFZ), Section 3.2 Telegrafenberg, 14473, Potsdam, Germany
Olivine is generally assumed to deform plastically by four deformation mechanisms
acting in parallel (diffusion creep, dislocation creep, Peierls mechanism and grain boundary
sliding), two of which are highly grain size-dependent (i.e. diffusion creep and grain
boundary sliding). During static or dynamic experiments, the average grain size of olivine
aggregates increases. Normal grain growth is characterized by the time evolution of the
average grain size, 𝑑, usually described by (Atkinson, 1988):
𝐸!
𝑑 ! − 𝑑!! = 𝑘𝑡 with 𝑘 = 𝑘! 𝑒𝑥𝑝 −
𝑅𝑇
where 𝑑! represents the average grain size at time t , n is the grain size exponent, t is the
elapsed time, k0 is a material-dependent constant, Ea the activation energy of grain growth, R
the gas constant and T the temperature.
In order to better define the melt effect on the rheological response of a partially molten
olivine aggregate, we have experimentally investigated the effect of melt on olivine grain
growth and the connectivity of this melt phase. Experiments were performed in 3/4” piston
cylinders (talc-Pyrex-graphite assemblages) at different temperatures (1200°C, 1250°C and
1350°C), four durations (1h, 12h, 72h and 15 days) and at two confining pressures (0.5 GPa
and 1.5 GPa). Starting material was composed of natural San Carlos olivine aggregates
initially containing different amounts of volatile-free basalt (0 wt%, 1 wt%, 2 wt% and 12
wt%).
Grain size analyses were performed by electron back-scattered diffraction mapping of
the end products. Preliminary results indicate that melt has no effect on grain growth rates. A
scanning electron microscope (SEM) was used for the textural characterization of the melt
distribution and indicates melt forming tubules in 3D (i.e. located at triple junctions in 2D
images), as commonly accepted, but that grain boundaries are also wetted by nanometricthick films, therefore forming a 3D interconnected melt network. Melt, through its influence
on grain growth and through its interconnectivity, could have significant impact on the
rheological properties of the mantle. The parameters constrained in this study could ultimately
help answering some of the key questions on the geodynamic aspects of our planet’s interior.
Reference
Atkinson, H., 1988. Overview no. 65: theories of normal grain growth in pure single phase
systems. Acta Metallurgica 36 (3), 469–491.
Strain analysis by EBSD during annealing of ice Ih
Károly Hidas1,*, Andréa Tommasi1, David Mainprice1, Thomas Chauve2, Fabrice Barou1,
Maurine Montagnat2
(1) Géosciences Montpellier, CNRS & Université Montpellier 2, Place E. Bataillon, 34095
cedex 5, France
(2) Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS & Université
Joseph Fourier Grenoble, 54 rue Molière, 38402 Saint-Martin d’Hères cedex, France
* [email protected]
Static recrystallization and grain growth take place during high-temperature annealing
following deformation at lower temperature, and they reorganize grain and subgrain
boundaries to produce entirely new, strain-free grains. These processes influence the
microstructure and mechanical behavior of the material by reducing the level of long-range
internal stress field. The non-linear flow law of ice Ih makes it an ideal analogue to model
rock deformation, thus analyses of recrystallized ice textures contribute to understanding
mechanisms which control the nucleation and grain growth deep in the Earth’s interior. Water
ice microstructures allow for the study of grain-scale processes including nucleation, grain
growth, recovery and recrystallization. On the other hand, these mechanisms directly
influence the behavior of terrestrial ice systems (e.g., glaciers and ice sheets) in response to
deformation. Therefore, their understanding may help us to improve climatic signal
interpretation and predictions, that are mostly based on ice dynamics. However, at present
there are no data by which recovery, and strain energy-driven grain boundary migration rates
in ice can be estimated.
Here we present the results of annealing experiments of pre-deformed polycrystalline water
ice together with microstructural analyses by means of Automatic Ice Texture Analyzer
(AITA) and high-resolution electron backscatter diffraction (EBSD) crystal orientation maps.
We performed constant load uniaxial compression creep experiments at -7°C on columnar
samples, composed of mm-sized polycrystals, to attain 4% deformation and we applied postdeformational heat treatment at -5°C. We carried out a series of AITA and EBSD maps in
representative time steps up to 25 hours of total annealing in order to study the
microstructural evolution. In this contribution, we evaluate the stored energy distribution and
the rate of grain boundary migration during post-dynamic and static recrystallization, that
control strain energy-driven grain boundary mobility of water ice.
Experimental constraints on rheology during eclogite facies metamorphic
reactions
Sarah Incel1, Nadège Hilairet2, Loïc Labrousse3 Joerg Renner4, Yanbin Wang5, Christian Chopin1, & Alexandre
Schubnel1,
1
Ecole Normale Supérieure, 24 Rue Lhomond, 75005 Paris, France
Université Lille 1, 59655 Villeneuve d'Ascq, France
3
Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris cedex 05, France
4
Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
5
GeoSoilEnviroCARS, University of Chicago, Argonne, IL 60439, USA.
2
Corresponding author: [email protected]
Natural glaucophane / lawsonite mixtures (approx. 30 microns grainsize, coming from alpine
Corsica) were sintered using a piston cylinder apparatus under 3 GPa confining pressure, and
respectively 550 °C, 650 °C and 750 °C. The 550°C assemblies exhibit no reaction, while
lawsonite and glaucophane dehydration products (omphacite and garnet) were found in
samples sintered at 650°C and 750°C respectively.
Deformation experiments were performed on similar mixtures, using a DDIA apparatus
mounted on a synchrotron beamline at the APS. Preliminary results demonstrate that
glaucophane, when deformed metastable under P-T conditions approx. 3 GPa, 500 °C, exhibit
stick-slip behavior. Each stress drop can be correlated with an acoustic emissions that was
captured during the experiment, and inferred to come from the sample assembly. The
underlying mineral reaction which took place during the experiment is glaucophane ↔ 2
jadeite + talc. This observation was confirmed on a pure tremolite (a calcic amphibole, from
Balmatt, NY) mineral assembly, which also exhibited stick-slip behaviour under 2-3 GPa.
The underlying mineral reactions which took place during this experiment is tremolite ↔ 2
diopside + talc. During a third experiment, performed at higher temperature where the
expected reactions are lawsonite and glaucophane dehydrations under eclogite facies
conditions, no stick-slip behaviour was observed, but acoustic emissions were nevertheless
detected at low temperature.
The fact that the high pressure amphibole breakdown reactions of tremolite and glaucophane
generated mechanical instabilities which lead to little earthquakes in the laboratory and the
dehydration reactions did not, suggest, that these mineral reactions could potentially play an
important role in the generation of intermediate earthquakes.
Additional experiments, both in Griggs and DDIA apparatus, will be performed in the near
future in order to confirm our preliminary results. Microstructural analysis using SEM,
Raman and EMPA is also planned.
Preliminary 3D In-situ measurements of the texture evolution of strained
H2O ice during annealing using neutron Laue diffractometry
Baptiste Journaux1, Maurine Montagnat1, Thomas Chauve1, Bachir Ouladdiaf2, John Allibon2
1
Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS, Univ. Grenoble Alpes, 38402 SaintMartin d’Heres, France
2
Institut Laue Langevin, 6 rue Jules Horowitz, BP156, 38042 Grenoble Cedex 9, France
Dynamic recrystallization (DRX) strongly affects the evolution of microstructure (grain size and shape) and
texture (crystal preferred orientation) in materials during deformation at high temperature. Since texturing leads
to anisotropic physical properties, predicting the effect of DRX is essential for industrial applications, for
interpreting geophysical data and modeling geodynamic flows, and predicting ice sheet flow and climate
evolution. A large amount of literature is available related to metallurgy, geology or glaciology, but there
remains overall fundamental questions about the relationship between nucleation, grain boundary migration and
texture development at the microscopic scale.
Previous measurements of DRX in ice were either conducted using 2D ex-situ techniques such as AITA [1,
2] or Electron Backscattering Diffraction (EBSD) [3], or using 3D statistical ex-situ [4] or in-situ [5] techniques.
Nevertheless, all these techniques failed to observe at the scale of nucleation processes during DRX in full 3D.
Here we present a new approach using neutron Laue diffraction, which enable to perform 3D measurements
of in-situ crystals orientation evolution. We tested it on strained polycrystalline H2O ice (ε > 2%) during
annealing at 268.5 K. Thanks the CYCLOPS instrument [6] (Institut Laue Langevin Grenoble, France) and the
intrinsic low background of this setup, preliminary observations enabled us to follow, in H2O ice, the evolution
of serrated grain boundaries, and kink-band during annealing. The long exposure (> 1h) required to obtain the
orientations of every crystallite in the sample is due to the incoherent scattering coming from the Hydrogen. It
still represents a limitation to obtain time resolved evolution of individual orientations through annealing or insitu deformation processes.
Nevertheless, our observations show a clear evolution of the texture and internal misorientation over the
course of few hours at an annealing temperature of 268.5 K. In the contrary, ice kink-band structures seem to be
very stable over time at near-melting temperatures. The same samples have been analyzed ex-situ using EBSD
for comparison.
These results represent a first step toward in-situ microscopic measurements of dynamic recrystallization
processes in ice during strain. This experiment has been conducted in the frame of the ANR-funded DREAM
project that focuses on the recrystallization processes in anisotropic materials.
References
[1] D. S. Russell-Head and C.J.L. Wilson., 2001, Journal of Glaciology, 24, 117-130.
[2] Wilson, C.J.L., Peternell, M., Piazolo, S., Luzin, V., 2014, Journal of Structural Geology, Microdynamics of Ice, 61, 50-77.
[3] M. Montagnat, T. Chauve, F. Barou, A. Tommasi, B. Beausir, C. Fressengeas., in prep.
[4] T. H. Jacka and J. Li., 2000, In T. Hondoh, editor, Physics of Ice Core Records, pages 83-102.
Hokkaido University Press, Sapporo.
[5] S. Piazolo, C. J. L. Wilson, V. Luzin, C. Brouzet, and M. Peternell., 2013, Geochemistry, Geophysics, Geosystems, 14, 4185-4194.
[6] B. Ouladdiaf et al., 2011, Journal of Applied Crystallography, 44, 392-397.
Nature and evolution of the lithospheric mantle beneath the Hoggar
swell (Algeria): a record from mantle xenoliths
Fatna Kourim1,2, Jean-Louis Bodinier1, Olivier
3
1
Abderrahmane Bendaoud , and Jean-Marie Dautria
Alard1,
Alain
Vauchez1,
1 : Geosciences Montpellier, Université de Montpellier 2 and CNRS, Cc 60, Place Eugène
Bataillon, 34095 Montpellier Cedex 05, France
2 : Laboratoire Magmas et Volcans, Université Jean Monnet, 23 rue du Dr. Paul Michelon,
42023 Saint Etienne, France ([email protected])
3 : Laboratoire de Géodynamique, Géologie de l’Ingénieur et Planétologie, FSTGAT, BP 32
USTHB, 16123 Bab-Ezzouar, Alger, Algérie
We present the results of an integrated petrological, geochemical and
petrophysical study of mantle xenoliths sampled by Cenozoic volcanism in the
Hoggar massif (Algeria). The samples were collected in two volcanic districts
(Tahalgha and Manzaz) located at the periphery and in the central part of the
Hoggar massif, respectively. The Tahalgha sampling also straddles a mega panAfrican shear zone (the 4°35 fault) between two major structural domains of the
Tuareg Shield basement: the Central Polycyclic Hoggar to the East (LATEA
terranes) and the Western Hoggar domain to the West (Iskel block). The studied
xenoliths provide information on the evolution of the lithospheric mantle from
the late Pan-African orogeny up to the Cenozoic events responsible for the
topographic upwelling and volcanism. The Pan-African heritage is preserved in
xenoliths from the peripheral Tahalgha district. These samples are distinguished
by low equilibrium T (750-900°C) and LREE-depleted clinopyroxene
compositions. They are considered to represent the sub-continental lithosphere
after the rejuvenation processes that occured during the late stages of the PanAfrican orogeny. They show well preserved deformation textures assigned to
these events and characterized by preferential crystallographic orientations
(CPOs) of olivine (axial- [010]) consistent with a transpressional regime. The
Cenozoic events are marked by partial annealing of these textures, particularly
pronounced in the Manzaz samples, as well as in the Tahalgha xenoliths
equilibrated at medium to high T (900-1150°C). The Cenozoic events were also
responsible for a change in olivine CPOs. However, the first-order lithosphere
modifications ascribed to the Cenozoic event are observed either at the scale of
the whole Hoggar swell, or at the small scale of magma conduits and their wall
rocks. Conversely, our data show little changes at intermediate scales on either
sides - or at different distances - from the 4°35. As regards the origin of the
Hoggar volcanic swell, this result favours relatively large-scale asthenospheric
upwelling related to upper mantle instabilities or local convections, rather
than a process involving merely the reactivation of pan-African lithospheric
faults.
Rheology of olivine and orthopyroxene at upper mantle conditions
Arnaud PROIETTI 1, Misha BYSTRICKY 1, Frédéric BÉJINA1, Matthew L.
WHITAKER2, Haiyan CHEN 2
1 Institut de Recherche en Astrophysique et Planétologie (IRAP), OMP, CNRS & Université
Paul Sabatier Toulouse III, FRANCE
2 Mineral Physics Institute, Stony Brook University, Stony Brook & National Synchrotron
Light Source, Brookhaven National Laboratory, Brookhaven, N.Y., U.S.A.
Understanding the rheology of mantle rocks is fundamental to model the dynamics of
the interior of the Earth. Although many deformation studies have been performed on olivine,
the effect of pressure on its rheology remains poorly constrained. One of the main
experimental difficulties is to precisely control parameters such as pressure, temperature and
oxygen fugacity that affect the rheological properties of minerals. One must also note that
there are very few existing studies on orthopyroxene despite its importance as a major phase
of the upper mantle.
Recent developments in deformation apparatus allow compression experiments at high
pressures and temperatures. In this study, we deformed synthetic aggregates of olivine (Ol)
and pyroxene (Px) at upper mantle conditions. Synthetic samples were prepared by mixing
nano-size powder oxides of SiO2, MgO and Fe2O3 and reacting them in a one-atmosphere
furnace under controlled oxygen fugacity. Resulting Ol and Px powders were then sintered by
Spark Plasma Sintering (SPS) or in a vacuum furnace to obtain fully dense aggregates with
homogeneous microstructures and small grain sizes (below 1 µm). Finally, the aggregates
were deformed in a D-DIA apparatus coupled with synchrotron white X-ray beam installed at
the X17-B2 beamline of the National Synchrotron Light Source (Brookhaven National
Laboratory, NY, USA) at pressures between 3 and 6 GPa and temperatures from 1173 to
1473K. X-ray diffraction and radiography give us in situ information about stress and strain in
the samples, respectively. Data analysis indicates a viscosity contrast between olivine and
orthopyroxene which varies as a function of pressure and temperature conditions. After the
experiments, we observed the deformed microstructures with a SEM EBSD to determine the
active deformation mechanisms. These results and the effect of pressure on the rheology of
each phase will be discussed.
Quartz and feldspar rheology at mid-crustal conditions: the example of the
Pernambuco shear zone (NE Brazil)
G. Viegas1,2, L. Menegon1, C. Archanjo2, A. Vauchez3,
1School
of Geography, Earth and Environmental Sciences, Plymouth University,
Plymouth, UK. [email protected]
2Instituto de Geociências, Universidade de São Paulo, São Paulo, Brasil.
3Geosciences Montpellier, Universite Montpellier 2, Montpellier, France.
Rheological models that predict the strength of the middle- to upper continental crust are
mainly based on the behaviour of the two most common silicate minerals, feldspar and
quartz. At natural pressure-temperature conditions typical of the middle crust, quartz is
expected to be mechanically weaker than feldspars if deformation is accommodated by
crystal plasticity. Dislocation creep in quartz localizes in recrystallized layers while
feldspar forms stronger porphyroclasts. However, the presence of mineral reactions may
promote a drastic change in feldspar rheology, causing marked grain size reduction and
weakening due to activation of diffusion creep. Under such conditions, the feldsparderived reaction products represent the mechanically weak rheological phase that
accommodates most of the bulk strain while quartz deforms via dislocation creep. The
Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its
eastern segment, deforms granitoids at upper-greenschist/amphibolite facies conditions,
thus representing a preserved section of the middle continental crust. Initially coarse (> 50
µm) grained feldspar crystals are intensively fractured and reduced to an ultrafine-grained
mixture consisting of fractured albite and K-feldspar grains (~ 5-8 µm in size) localized in
C’ oriented shear bands. Detailed microstructural observations and EBSD analysis do not
show any evidence of intracrystalline plasticity in feldspars and/or fluid-enhanced reaction
weakening. Quartz occurs either as thick (~ 1mm) monomineralic bands or as thin ribbons
dispersed in the feldspathic mixture. The microstructure and recrystallized grain size (~ 20
µm) are similar in both the thick monomineralic band and in the thin ribbons. Elongated
quartz grains form [0001] axis maxima around Y in both the monomineralic band and in
the thin ribbons embedded in the feldspathic matrix. Fine-grained feldspar do not show
any clear crystallographic orientations and has the same composition as the fractured
porphyroclasts, suggesting that it deformed either by cataclastic flow/diffusion creep and
that no chemical changes were involved in feldspar deformation. Quartz ribbons
embedded in the fine-grained feldspathic matrix are not boudinaged or folded, suggesting
that quartz layers and feldspar aggregates were deformed at comparable viscosities. Overall,
our dataset indicates that feldspar underwent a brittle-viscous transition while quartz was
deforming via crystal plasticity. The resulting rock microstructure consists of a two-phase
rheological mixture (fine-grained feldspars and recrystallized quartz) without a clear
apparent viscosity contrast. The Pernambuco shear zone represents therefore a case in
which extensive grain-size reduction and weakening of feldspars is attained mainly via
fracturing without a prominent role of metamorphic hydration reactions.
BRITTLE VERSUS DUCTILE DEFORMATION AS THE MAIN
CONTROL OF THE DEEP FLUID CIRCULATION IN OCEANIC
CRUST.
Violay M.1, Gibert B2., Mainprice D2., Burg J.-P1.
1
2
ETH D-ERDW, Sonnegstrasse, 5 CH-8092, Zürich, Switzerland
Université de Montpellier - CC060, Place Eugène Bataillon, 34095 Montpellier cedex 5
The brittle to ductile transition may strongly influence hydraulic properties of rocks at the
depth and temperature ranges that hydrothermal fluids may circulate. To examine this
transition in the context of the oceanic crust, we conducted a series of deformation
experiments on a natural basalt sample at in-situ oceanic crust conditions. Dilatancy was
measured during deformation. The method consisted in monitoring the volume of pore fluid
that flows into or out of the sample at constant pore pressure. Mechanical and microstructural observations at experimental constant strain rate of 10− 5 s− 1 indicated that the
basalt was brittle and dilatant up to 850°C. At higher temperature, the deformation mode
became macroscopically ductile and samples compacted. These observations have important
implications on heat transfer, and fluid migration in oceanic crust.
Figure (A) Differential stress and (B) porosity variation versus strain curves for experiments
conducted at temperature between 600 and 1050°C and confining pressure of 130 MPa.
Pore fluid pressure (argon) was maintained at 30 MPa. The initial strain rate for all
experiments was 10-5 s-1. Correction for jacket contribution to mechanical strength is used for
copper jacket at 600 ºC and iron jacket at 800 ºC
Sensitivity testing of geometrically necessary dislocation density in olivine
from high resolution EBSD
1
David Wallis1, Lars N. Hansen1 and Angus J. Wilkinson2
Department of Earth Sciences, University of Oxford, Oxford, UK, OX1 3AN
2
Department of Materials, University of Oxford, Oxford, UK, OX1 3PH
Electron-backscatter diffraction (EBSD) is increasing in popularity as a tool for
characterising intragranular deformation in crystalline materials. Several recent studies have
developed and applied tools for analysing the defect content of deformed rocks using
(mis)orientation information derived from EBSD data (e.g., Wheeler et al., 2009; Cordier et
al., 2014), which allow the spatial distribution of different types of defects to be analysed and
related to thermomechanical conditions. However, EBSD techniques typically employed in
the Earth sciences utilise orientations determined by analysis of individual diffraction patterns,
which result in relatively large angular errors (~1°).
Recent developments in cross-correlation analysis of electron backscatter diffraction
patterns have provided a method to determine lattice misorientations at high spatial
(submicron) and angular (0.0025°) resolutions (HR-EBSD) (e.g., Wilkinson et al., 2006).
Such measurements allow high-precision measurements of lattice curvature for use in
estimates of geometrically necessary dislocation densities (GNDD) in the form of the Nye
tensor. Furthermore, these estimates can be used to invert for the densities of dislocations of
specific slip systems (Wilkinson and Randman, 2010). Indeed the inversion is often better
constrained for minerals than for metals due to the lower number of slip systems available.
Thus, HR-EBSD provides a powerful new tool for investigating dislocation processes in
crystalline materials. For instance, the relative densities of different types of dislocations can
be used to infer deformation conditions and test grain-scale models of crystal plasticity.
Additionally, average dislocation densities may be used to infer palaeostress from deformed
geological materials. These applications are especially attractive for minerals in which
imaging dislocations is notoriously difficult.
The use of HR-EBSD to investigate crystal plasticity in a quantitative manner requires
a sound understanding of the parameters that affect GNDD estimation. However, the impacts
of varying EBSD acquisition parameters (e.g. pattern binning, signal gain, step size, or map
area) on estimated distributions of GNDDs remain unconstrained for geological materials. We
use EBSD datasets collected on undeformed and experimentally deformed single crystals of
San Carlos olivine to test GNDD sensitivity under systematically varied acquisition settings.
In particular, we focus on lowering the GNDD noise floor in order to analyse low dislocation
densities that may result from low stress, high temperature deformation. We test the
sensitivity of measured GNDD to pattern binning, signal gain, step size, and total map area by
subsampling large, detailed EBSD datasets. Increasing step size lowers the GNDD noise floor
but clearly trades off with the spatial resolution of map data, and the lower fraction of the
total dislocation density that may be considered GNDD at the larger patch size. Initial results
from specimens deformed at 40–300 MPa and 1200–1400 °C indicate that appropriately
optimised HR-EBSD GNDD analysis can be used to derive piezometric relationships in
agreement with those determined using other methods of dislocation characterisation.
Cordier, P., Demouchy, S., Beausir, B., Taupin, V., Barou, F., & Fressengeas, C. (2014). Disclinations provide the missing
mechanism for deforming olivine-rich rocks in the mantle. Nature, 507(7490), 51-56.
Wheeler, J., Mariani, E., Piazolo, S., Prior, D. J., Trimby, P., & Drury, M. R. (2009). The weighted Burgers vector: a new
quantity for constraining dislocation densities and types using electron backscatter diffraction on 2D sections through
crystalline materials. Journal of microscopy, 233(3), 482-494.
Wilkinson, A. J., Meaden, G., & Dingley, D. J. (2006). High-resolution elastic strain measurement from electron backscatter
diffraction patterns: new levels of sensitivity. Ultramicroscopy, 106(4), 307-313.
Wilkinson, A. J., & Randman, D. (2010). Determination of elastic strain fields and geometrically necessary dislocation
distributions near nanoindents using electron back scatter diffraction. Philosophical Magazine, 90(9), 1159-1177.
Microstructural analysis of the Yingba detachment: Insights into extension
and exhumation of the Yingba Massif, Inner Mongolia
Congyuan Yin, Bo Zhang, Shiran Liu, Baofu Han, Yang Wang, Sheng Ai
The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space
Sciences, Peking University, Beijing 100871, China
The Yingba Massif is a northeast-southwest trending antiformal structure locating on the
middle of the boundary of China and Mongolia that is bound by the Yingba ductile
detachment zone on the northwest and southeast sides respectively. Structure, geometry,
kinematic and vorticity were analyzed, combined with temperature estimation on deformed
rocks from Yingba detachment zone. Four deformation stages were observed since late
Mesozoic and give evidence that the Yingba Massif is a metamorphic core complex.
Temperature of the shear zone was estimated from the fractal dimension, fabric of quartz and
two-feldspar geothermometry. Thermometry based on fractal dimension of the shear zone
give a temperature ranging from 530 to 670°C. The checked c-axis orientations are mostly
concentrated close to the Y-direction displaying prismatic <a> slip toward a coaxial
deformation. Such a situation represented a high temperature deformation under amphiboliteface metamorphic condition. The two-feldspar geothermometry of asymmetric strain-induced
myrmekite generate a temperature range between ~400 and 650 °C. Together with the
microstructural features of deformed quartz and feldspar, we conclude that the Yingba
detachment zone developed in the high temperature setting. Mean kinematic vorticity
estimates record that pure shear flow was dominant (48-62% pure shear) during the ductile
deformation. At last we summarize all the analysis and propose a model of evolution about
the Yingba Massif.
Kew words: Yingba Massif, Microstructures, Vorticity, Quartz fabrics, Deformation
temperature