1. science
2. geology
3. seismology
4. earthquakes

Digital Comprehensive Summaries of Uppsala Dissertations
from the Faculty of Science and Technology 1223
Superimposition of Contractional
Structures in Models and Nature
HONGLING DENG
ACTA
UNIVERSITATIS
UPSALIENSIS
UPPSALA
2015
ISSN 1651-6214
ISBN 978-91-554-9160-4
urn:nbn:se:uu:diva-243235
Dissertation presented at Uppsala University to be publicly examined in Hambergsalen,
Geocentrum, Villavägen 16, Uppsala, Friday, 27 March 2015 at 10:00 for the degree of
Doctor of Philosophy. The examination will be conducted in English. Faculty examiner:
Professor Sudipta Sengupta (Department of Geological Science, Jadavpur University).
Abstract
Deng, H. 2015. Superimposition of Contractional Structures in Models and Nature. Digital
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and
Technology 1223. 45 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9160-4.
Superimposition of contractional structures is widely observed in different scales in the world.
Superimposed structures form due to different processes: change in strain accommodation from
one type of structure to another during a single progressive shortening; successive coaxial
shortening phases separated by an unconformity; superimposition of different non-coaxial
shortening phases. Using results of a series of systematic analogue models and detailed field
structural mapping, this thesis focuses on the geometry and kinematics of such superimposed
structures that are formed by these three processes. During a single progressive folding, thrusts
develop within a fold to accommodate stain variations in different regime of the fold. Limited
displacement along these thrusts does not significantly modify the geometry of the fold.
However, during multiple shortening phases (coaxial or non-coaxial), early formed structures
are modified by the later phase ones. The later thrusts can cut and displace the pre-existing
structures. The early folds are tightened or interfered by the later folding phase. Pre-existing
thrusts may be reactivated either in dip direction and/or along strike during the later shortening.
The pre-existing structures in turn influence development of the later structures, which results
in change in structure spacing. An angular unconformity between two shortening phases clearly
truncates the early phase structures and separates structures of different levels. Unlike in
the post-erosional layers, in the layers below the unconformity, complicated superimposed
structures are visible. This thesis shows that geometry and sequence of structures formed during
one progressive shortening or multiple shortening phases strongly depend on the mode of the
superimposition (coaxial, orthogonal or oblique) and the orientation of pre-existing structures.
Keywords: superimposition, progressive deformation, multiple phases, coaxial, non-coaxial,
analogue modelling, fold-and-thrust belts
Hongling Deng, Department of Earth Sciences, Solid Earth Geology, Villav. 16, Uppsala
University, SE-75236 Uppsala, Sweden.
© Hongling Deng 2015
ISSN 1651-6214
ISBN 978-91-554-9160-4
urn:nbn:se:uu:diva-243235 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-243235)
To my parents
献给我最亲爱的父母
邓家文，黄红群
Home is behind, the world ahead,
And there are many paths to tread.
Through shadows to the edge of night,
Until the stars are all alight.
Then world behind and home ahead,
We’ll wander back to home and bed.
Mist and twilight, cloud and shade,
Away shall fade! Away shall fade!
Fire and lamp, and meat and bread,
And then to bed! And then to bed!
J.R.R. Tolkien
List of Papers
This thesis is based on the following papers, which are referred to in the text
by their Roman numerals. Reprints were made with permission from the
respective publisher, Journal of Structural Geology, Elsevier.
I.
II.
III.
IV.
Deng H., Zhang C. and Koyi H.A., 2013. Identifying the characteristic signatures of fold-accommodation faults. Journal of Structural
Geology, 56, 1-19.
Deng H., Koyi H.A. and Froitzheim N., 2014. Modelling two sequential coaxial phases of shortening in a foreland thrust belt. Journal of Structural Geology, 66, 400-415.
Deng H. and Koyi H.A., 2014. Mega arrowhead interference pattern
in the Central part of the Yanshan Orogenic Belt, North China. Journal of Structural Geology, under review.
Deng H., Koyi H.A. and Nilfouroushan. F., 2015. Superimposed
folding and thrusting by two phases of non-coaxial shortening in
analogue models. Journal of Structural Geology, under review.
For paper I, the initial concept and design, field study and partly analyses,
were supervised by Prof. Zhang from China University of Geosciences (Beijing), China. Prof. Koyi, in addition to contributing to the text, reinterpreted
some of the examples and helped me to add displacement plots. My contribution is 65%.
The idea of paper II was initiated with Prof. Koyi who helped me to construct the initial models, which I continued with. We analysed model results
and I wrote a first draft which was modified and improved by my supervisor.
Prof. Froitzheim from University of Bonn, Germany wrote the field description of one of the natural examples. My contribution is 65%.
Paper III was the result of detailed field mapping and data collection by myself and partly my supervisor. Field data were analysed in Uppsala and I
wrote a first draft of the manuscript, which was modified and revised 3-4
times by my supervisor. My contribution is 65%.
The idea of paper IV was initiated during our field trip to the YOB where
two non-coaxial folding phases has occurred. We designed a series of systematic models, which I ran. We analysed the results and I wrote the first
draft which was modified and revised 3-4 times by my supervisor. Dr. Nilfouroushan contributed to this work by helping with the physical experiments and commenting on the final version of the manuscript. My contribution is 65%.
In addition, I have contributed to the following papers, which were published
during my PhD study time but not included in this thesis.
Zhang, C., Li, C., Deng, H., Liu, Y., Liu, L., Wei, B., Li, H. and Liu, Z.,
2011. Mesozoic contraction deformation in the Yanshan and northern Taihang mountains and its implications to the destruction of the North China
Craton. Sci China Earth Sci 54, 798-822.
Zhang, C., Deng, H., Li, C. Liu, Z., Deng H. and Teng, F., 2012. An out-ofsyncline thrust model for the ‘Chengde Thrust Sheet’ in central intraplate
Yanshan Orogenic Belt, northern North China Craton (in Chinese with English abs.). Earth Science Frontiers. 19(5), 27-40.
Deng H., Zhang C., Deng H. and Ouyang, J., 2012. Deformation mechanism
for the development of fold-accommodation faults: Examples of outcropscale structures from central intraplate Yanshan Orogenic Belt, North China
(in Chinese with English abs.). Earth Science Frontiers, 19(5), 61-75.
Contents
1.
Introduction ........................................................................................... 9
1.1 Superimposition of contractional structures ......................................... 9
1.2 Effect of erosion and sedimentation ................................................... 11
1.3 Thesis objectives ................................................................................ 12
2.
Methodology ........................................................................................ 14
2.1 Physical experiments .......................................................................... 14
2.2 Field mapping ..................................................................................... 18
3.
Summary of papers .............................................................................. 21
3.1 Identifying the characteristic signatures of fold-accommodation
faults ......................................................................................................... 21
3.2 Modelling two sequential coaxial phases of shortening in a
foreland thrust belt ................................................................................... 24
3.3 Mega arrowhead interference patterns in the Central part of the
Yanshan Orogenic Belt, North China....................................................... 28
3.4 Superimposed folding and thrusting by two phases of non-coaxial
shortening in analogue models ................................................................. 31
4.
Conclusions ......................................................................................... 35
5.
Sammanfattning på svenska ................................................................ 37
Acknowledgements ....................................................................................... 39
References ..................................................................................................... 41
1. Introduction
1.1 Superimposition of contractional structures
Superimposition of contractional structures that is formed during a single
progressive deformation or by multiple shortening phases (coaxial and noncoaxial) is widely reported from different parts of the world (e.g. Suppe,
1983; Mitra, 1990; Wrede, 2005; Ramon and Rosero, 2006; Misra and
Gupta, 2014). Superimposition related to a single progressive deformation
induces a close relationship between folding and thrusting. During development of a fault, the hanging wall layers may fold when they ride over the
fault bend (fault-bend fold), or slip is consumed by folding in the fault tip
(fault-propagation fold), or the relatively competent layers are folded in response to slip on a décollement (detachment fold) (Suppe, 1983; Jamison,
1987; Mitra, 1990; Suppe and Medwedeff, 1990; Erslev, 1991; Homza and
Wallace, 1995; Allmendinger and Shaw, 2000; Cristallini, 2002; Johnson
and Johnson, 2002; Cardozo et al., 2003; Mitra, 2003; Suppe, 2011). In contrast, during progressive folding, faults may develop to accommodate strain
variations related to structural and stratigraphic position within a fold. Such
faults are called fold-generated faults, fold-accommodation faults, and foldrelated faults (Johnson, 1980; Morley, 1994; Mitra, 2002; Wu et al., 2007).
When superimposition occurs where later deformation phases overprint preexisting structures (coaxial and non-coaxial), the early formed structures are
modified by a later phase shortening (i.e. they are cut by the later phase
faulting or folded by later phase folding) (Steiger, 1964; Roy, 1995; Saha,
2002; Weinberger et al., 2009; Dario et al., 2010; Cashman et al., 2011; Derryberry, 2011; Li et al., 2012; Shah et al., 2012; Sen and Pfander, 2013). In
some cases, the early phase structures may be reactivated during the later
shortening (Jayangondaperumal and Dubey, 2001; Corredor, 2003; Ramon
and Rosero, 2006; Soto et al., 2007; Cashman et al., 2011; Lim and Cho
2012).
Many researchers have been studying the superimposition related to a
single progressive deformation focusing on fault-related folds using analytical and experimental investigations, and natural example studies (Suppe,
1983; Jamison, 1987; Mitra, 1990; Suppe and Medwedeff, 1990; Erslev,
1991; Homza and Wallace, 1995; Storti et al, 1997; Bonini, 2003; Bernard et
al., 2007), Their works indicated that in fault-related folds formation of fold
is geometrically and kinematically controlled by slip along a fault surface.
9
Furthermore, some other investigations also documented that during development of fault-related folds, parameters such as variable mechanical stratigraphy, initial fault dip, inter-layer detachments, multi-ramps and friction
along fault ramp may affect the way faults propagate and thus fold geometry
(Medwedeff and Suppe, 1997; Maillot and Koyi, 2006; Albertz and Lingrey,
2012; Albertz and Sanz, 2012). In contrast, studies on fold-related faults or
fold-accommodation faults are relatively few. Mitra (2002) firstly provided a
systematic investigation to such structures, where he defined foldaccommodation faults and summarized the common types for these structures. The concept of fold-accommodation faults has been later applied to
interpret the tectonic evolution of some regions (Wrede, 2005; Mukhopadhyay, 2008). A primary question is though how to recognize foldaccommodation faults in nature. Some researchers have attempted to address
this question by providing identifying characteristics for foldaccommodation faults (Mitra, 2002; Wrede, 2005; Wu et al., 2007; Deng et
al., 2009). However, based on these published studies, fold-accommodation
faults could still not be distinguished from the general reverse faults and
thrusts in fault-related folds in an applicable and efficient way.
In the case of superimposition by multiple phases of shortening, reactivation of pre-existing thrusts during the later shortening phases has been reported from some areas, either during coaxial superimposition (Ramon and
Rosero, 2006), or non-coaxial shortening phases (Jayangondaperumal and
Dubey, 2001; Corredor, 2003; Lim and Cho, 2012). Superimposed folding
and thrusting have been widely reported in nature, where pre-existing thrusts
may be reactivated; fold-interference patterns develop; and pre-existing
structures are displaced by later phase thrusting (Corredor, 2003; Abu Sharib
and Bell, 2011; Lim and Cho, 2012; Shah et al., 2012; Crespo-Blanc, 2013).
During non-coaxial superimposition, when the later shortening direction is
oblique to the trends of pre-existing structures, reactivation may result in
both dip- and strike-slip along the pre-existing thrusts (Soto et al., 2007; Lim
and Cho, 2012). Superimposition of folding could result in tightening of the
pre-existing fold during coaxial shortening (Corredor, 2003; Derryberry,
2011) and formation of fold interference patterns during non-coaxial shortening (Aller and Gallastegui, 1995; Simon, 2004; Abu Sharib and Bell,
2011; Lim and Cho, 2012; Crespo-Blanc, 2013; Tian et al., 2013). Foldinterference patterns are also investigated analytically and experimentally
(Ramsay, 1962, 1967; Ghosh and Ramberg, 1968; Skjernaa, 1975; Thiessen
et al., 1980; Watkinson, 1981; Ramsay and Hube, 1987; Ghosh et al., 1992,
1993, 1995, 1996; Grujic, 1993; Grujic et al., 2002; Grasemann et al., 2004;
Sengupta et al., 2005). In such studies, geometry and kinematics of superimposed folds are well illustrated. However, the published analytical and experimental studies related to fold interference patterns have not considered
the effect of thrusting. Such common features, i.e. superimposition of thrustrelated folding need more analytical and experimental investigations, where
10
the interaction between folding and thrusting during superimposition could
be studied.
Published investigations on superimposed buckle folding indicate that
orientation and geometry of the early phase folds have significant influences
on the later phase folds and the final geometry of the fold-interference pattern (Ghosh and Ramberg, 1968; Skjernaa, 1975; Watkinson, 1981; Odonne
and Vialon, 1987; Ghosh et al., 1992, 1993; Grujic, 1993; Sengupta et al.,
2005). However, how the pre-formed structures and fault reactivation affect
the geometry, spacing and propagation of the later phase structures during
multiple phases of shortening (coaxial and non-coaxial) remains poorly understood.
1.2 Effect of erosion and sedimentation
Erosion and sedimentation commonly occur either synkinematically (i.e.
during development of structures) under one progressive shortening phase
(Hessami et al., 2001; Barrier et al., 2002; Bonnet et al., 2007; Malavieille,
2010; Sieniawska et al., 2010), or in an interval between two deformation
phases to form an unconformity (Corredor, 2003; Cashman et al., 2011).
Many published experiments have focused on syn-tectonic surface processes
during one progressive shortening (e.g. Storti and McClay, 1995; Mugnier et
al., 1997; Koyi et al., 2000; Persson and Sokoutis, 2002; Saura et al., 2004;
Konstantinovskaya et al., 2007; Cruz et al., 2010; Konstantinovskaya and
Malavieille, 2011). These studies illustrated that syn-tectonic erosion and
sedimentation could affect the number, geometry, activation and reactivation
of thrusts, and the propagation sequence of thrust wedges. However, few
studies have investigated the effect of an angular unconformity on the development of the newly formed structures and the reactivation of a set of preexisting thrusts during multiple shortening (both coaxial and non-coaxial).
Studies of natural examples of fault reactivation and different structures
shown in the layers above and below an unconformity are usually conducted
based on the structures deciphered from seismic profiles (Corredor, 2003;
Cashman et al., 2011). Structures shown in the layers below an unconformity
may not be well displayed due to the presence of younger sediments above
the unconformity, and parts of structures may be missing due to later erosion. As such, experimental studies on multiple shortening phases separated
by an unconformity are needed. In such experiments, the entire geometry of
structures shown in the layers both above and below the unconformity can
be observed in either vertical or horizontal sections. In addition, reactivation
of the pre-existing structures can also be monitored during experiments.
11
1.3 Thesis objectives
The general objective of this thesis is to investigate superimposition of structures formed during either progressive deformation, or multiple phases of
shortening (coaxial and non-coaxial). The structures were studied in analogue modelling and in nature. Through this thesis, the following problems
are discussed and better understood: superimposition of faulting to the progressive folding phase (i.e. formation of fold-accommodation faults), reactivation of early phase structures by a later coaxial and non-coaxial shortening
phase, effect of pre-existing structures on development of later phase structures (e.g. spacing of the later phase structures), fold interference pattern
observed in natural examples and produced by experiments, interaction between folding and thrusting during multiple shortening, impact of erosion
and sedimentation between two shortening phases on development of new
structures, and reactivation of the pre-existing structures.
The detailed aims of the thesis are described as followed:
1) Study the geometric and kinematic relationship between foldaccommodation faults and their associated folds by detailed analyses of
structural and spatial distribution of faults within a fold, displacement distribution along the faults, and the change of cut-off angle between the faults
and folded layers in different fold regimes. (Paper I)
2) Summarize the characteristic signatures of fold-accommodation faults
in order to identify them from the general reverse faults and thrusts in faultrelated folds. (Paper I)
3) Study the geometric features of structures formed by two phases of
shortening (coaxial and non-coaxial), shown in vertical and horizontal sections. The focus has been on the following elements: feature of folds, thrusts,
fold interference patterns, and the relationship between folds and thrusts.
(Paper II and IV)
4) Study the development of structures during a later shortening phase by
monitoring structure spacing. To evaluate the effects of the pre-existing early
phase structures on the spacing of later phase structures. (Paper II and IV)
5) Investigate the reactivation of early phase structures (thrusts) during a
later shortening phase, by monitoring strike- and dip-slip along these thrusts
in profile and map-view. (Paper II and IV)
6) Study the effect of an angular unconformity on reactivation of preexisting structures, by changing the depth of erosion and the thickness of
post-erosional deposit above the unconformity, and addition of a weak layer
on the unconformity surface. (Paper II)
7) Study “large-scale” fold interference patterns formed during two
phases of non-coaxial shortening (orthogonal and oblique) where folds and
thrusts are superimposed, and comparing them with “pure” fold superimposition without the effect of thrusting. (Paper IV)
12
8) Study fold interference patterns from two kilometer-scale examples
exposed in the central part of the Yanshan Orogenic Belt, North China from
their map-view geometry and overprinting sequence of the two folding
phases and detailed field structural mapping. (Paper III)
9) Investigate the structural relationship between superimposed folds and
their bounded thrusts. The aim here has been to understand the time sequence of multiple shortening phases and the main shortening directions in
the study area, the central part of the Yanshan Orogenic Belt, North China.
(Paper III)
13
2. Methodology
2.1 Physical experiments
Scaled physical modelling (i.e. sandbox and centrifuge modelling) has been
widely used for simulating the progressive evolution of thrust and fold systems (Koyi, 1997; McClay, 2004). Some researchers have used sandbox
models to investigate development of thrusts that are influenced by syntectonic erosion and sedimentation during one continuous shortening process
(e.g. Storti and McClay, 1995; Koyi et al., 2000; Persson and Sokoutis,
2002; Konstantinovskaya and Malavieille, 2005, 2011; Bonnet et al., 2007;
Malavieille, 2010; Sieniawska et al., 2010). These studies have shown that
erosion and sedimentation can promote activity of internal structures, reactivate inactive thrusts, and result in out-of-sequence propagation in a fold-andthrust belt. Reactivation of faults during two separate deformation phases has
been studied by Soto et al. (2007) who experimented that a series of Riedel
faults formed by an initial pure strike-slip phase were reactivated as oblique
thrusts during later shortening. Fold interference patterns that are formed by
two phases of orthogonal shortening have also been studied using viscous
materials such as plasticine, modelling clay, silicone putty, and paraffin
waxes (e.g. Ghosh and Ramberg, 1968; Skjernaa, 1975; Ghosh et al., 1992,
1993; Grujic et al., 2002). Superimposed buckling in single or multilayers
was achieved in these studies, where fold interference patterns such as
dome-and-basin, mushroom- or arrowhead-shaped interference patterns were
displayed.
In this thesis, in order to investigate development and reactivation of
structures that have formed by multiple shortening phases, two types of
sandbox modelling were carried out, where the two shortening phases were
coaxial or non-coaxial. Two different granular materials were used in the
experiments. Quartz sand with grain size of 80-120 µm, density of 1.53
g/cm3, and internal friction angle of 30-33° (Maillot and Koyi, 2006) was
used to simulate the brittle upper crustal rocks. Another material, micro glass
beads, with the grain size of 50-100 µm, density of 1.46 g/cm3, and internal
friction angle of 19-23° (Maillot and Koyi, 2006) was used to simulate
weaker sedimentary rocks (shale and marl). The relatively weak glass beads
were used as a potential décollement horizon in the coaxial modelling.
In experiments with two phases of coaxial shortening, models were set up
in a rectangular sandbox (length 60 cm, width 39 cm). The initial thickness
14
of sand layers differs from model to model. All models were shortened from
one side to form a wedge (Figure 2.1). In some models, part of the wedge
was eroded and new sand layer were placed on the top of the erosional surface. A second deformation phase was then carried out by further shortening
the models in the same direction. A 0.5 cm thick glass beads layer was
placed on the top of the erosional surface in some models.
Figure 2.1 Simplified sketches of the different model setups.
In the experiments with two phases of non-coaxial shortening, all the sandbox models were built up with a uniform dimension (length 52 cm, width 48
cm, and sand thickness 1.5 cm). Basically, the models were shortened initially from one direction during the first deformation phase. During the second phase, some models were shortened from another direction that was
perpendicular to the first shortening phase and orthogonal superimposition
was achieved. Some other models were shortened in an oblique way, i.e. the
second shortening direction was oblique to the trend of the first phase structures. In order to carry out oblique superimposition, either a triangle backstop was used in the first shortening phase (Figure 2.2), or during the second
phase the model was shortened with a backstop that made an acute angle
with the first phase shortening direction.
15
Figure 2.2 a) Photography of the model setup for an oblique superimposition experiment. b) Schematic drawing of the model setup. The inbuilt triangular backstop
can induce structures striking parallel to the oblique boundary.
Two centrifuge models were carried out to investigate fold interference patterns excluding the effect of thrusting that developed in the sandbox models.
Pure plasticine (competent material) and mixture of plasticine with silicone
16
putty and barite powder (relatively less competent material) were used in
these centrifuge experiments (Figure 2.3). The pure plasticine has the density
of 1.64-1.65 g/cm3, and the viscosity is 2 to 6×108 Pa s, while the plasticineputty mixture had a density of 1.66-1.67 g/cm3 and the viscosity of 2×107 to
2×108 Pa s. The analogue materials were rolled out to 1 mm thick layers.
The two models were constructed of multiple layers with the dimensions of
15 ×15 ×1 cm and 18 ×16 ×1 cm, respectively. Two phases of folding was
achieved by two sequential orthogonal shortening phases during spinning in
the centrifuge at 700 G.
Figure 2.3 a) Oblique view of a centrifuge model before deformation showing the
plasticine and plasticine-putty layers. b) Pure-shear box used to shorten models in
the centrifuge. The back-stop is driven by a small motor attached to a worm screw.
In this image, model is shortened in one direction to 20%.
17
2.2 Field mapping
Model investigation has been combined with detailed structural mapping of
superimposed structures in the Yanshan Orogenc Belt (YOB). This belt is
generally trending E-W and NE-SW, and extends across the northern edge of
the North China crustal block (Figure 2.4). The characteristic basementinvolved thrusts, basement-cored anticlines and nappes were mainly formed
due to Mesozoic multiple phases of shortening (Davis et al., 2001; Cope et
al., 2007; Zhang et al., 2011). The Chengde-Pingquan area in the central part
of the YOB displays a number of thrusts, strike-slip faults, buckle folds that
are dominantly trending E-W, NE-SW and NW-SE. Two kilometer-scale
folds show fold interference patterns, which is resulted from two phases of
non-coaxial shortening, and hence suitable to compare with the superimposed structures shown in the models. Detailed field mapping was conducted
to decipher the geometry and kinematics of the two superimposed structures
that we called Daheishan and Pingquan folds in this thesis.
Based on the published geological map (HBG-SGSG, 1976), stratigarphic
and structural boundaries were checked by tracing their strikes and determining the lithologies and dips on either side of the boundaries. According to
our field data, several stratigarphic and structural boundaries have been
modified. Our mapping results are significant to better understand the geometry and kinematics of the Daheishan and Pingquan folds. The small-scale
structures related to folding such as cleavage, schistosity, crenulation, and
flexural-slip striations are poorly developed in these two superimposed structures. However, outcrop-scale folds and faults are abundantly observed
within the well-bedded strata. About 50 outcrop-scale folds were observed,
photographed, sketched and measured in the field. Measurements of bed dips
and fold axes were plotted using a Stereonet Program (version 9.1.0 by R.W.
Allmendinger). These stereonet plots of outcrop-scale folds were related to
the large-scale folds, and helped in interpreting the kinematics of regionalscale folding.
18
Figure 2.4 a) Simplified tectonic map of the central part of the Yanshan Orogenic Belt (YOB), North China, showing the trends of the major
structures (NC-North China; SC-South China). b) Modified and simplified geologic map of the Chengde-Pingquan area within the central part
of the YOB, with location of the studied examples outlined. CRF-Chengde County reverse fault; DSF-Dongshuiquan-Songzhangzi fault; GPFGubeikou-Pingquan fault; JF-Jiyuqing fault; SPF- Sangyuan-Pingquan fault; SF-Shuangmiao fault; XPF-Xiadian-Pingquan fault; CAChaoyangdong anticline; CDS-Chengde syncline; CDGS-Chaodaogou syncline; NS-Nandashan syncline; WS-Wulongji syncline (after HBGSGSG, 1976; Zhang et al, 2011; 2012).
3. Summary of papers
3.1 Identifying the characteristic signatures of foldaccommodation faults
In Paper I, we investigate hand-specimen and outcrop-scale examples of
folds to identify the characteristic signatures of fold-accommodation faults.
The geometric and kinematic relationship between thrusts and folds that they
reside in were described and analysed in detail.
The hand-specimen scale folds are formed in thin layers of limestone and
argillaceous limestone (Figure 3.1). They are generally open folds and have
round hinge zones. These hand-specimen scale folds are concentric where
individual layers display constant thickness throughout the fold. The outcrop-scale folds are seen in various lithologies. Some deformed layers are
composed of 5 to 15 cm thick siltstone and thin silty shale and/or shale interbeds (Figure 3.2). Other folds are formed in medium-thick beds of marble
or limestone. In most cases, the relatively competent layers have constant
thickness throughout the folds. These outcrop-scale folds have an angular,
chevron-like or round hinge zone. They are exposed in the scales varying
from several to dozens of meters. In these fold examples which are of different scales, geometries and lithologies, fold-accommodation faults are developed. Among them, out-of-syncline thrusts, into-anticline thrusts and wedge
thrusts are commonly observed.
Out-of-syncline and into-anticline thrusts are formed as the result of space
reduction in the core of a fold. In general, these thrusts originate in one limb
of the fold, and their tips are usually located at the hinge zone. In some
cases, the thrust can also cut through the hinge zone and tip in another limb
with a large cut-off angle. Displacement along out-of-syncline and intoanticline thrusts decrease toward the core of the fold, which is quantitatively
shown in a separation-distance plot. Wedge thrusts, which are another type
of fold accommodation faults, are commonly developed in interbedded strata
with competence contrast. Wedge thrusts usually display an flat-ramp geometry as they gradually cut through the competent layers up-section, and
slip parallel to bedding within the relatively incompetent layers. A wedge
thrust is commonly moving in the same direction as the sense of flexuralslip. A wedge thrust that forms in the hinge zone of a fold is called hinge
wedge thrust, while it also can develop in the limb of a fold, where it is
called limb wedge thrust. A series of hinge wedge thrusts can be developed
21
as imbricate thrusts with the same dip and moving sense, or as overlapping
wedges dipping and moving in opposite directions to each others. Formation
of overlapping wedges causes a significant thickening of the hinge zone in
comparison to the limbs of the fold. It is noticed that not all wedge thrusts
are fold-accommodation faults. Some thrusts may predate folding, and are
involved into a fold later. In this case, these thrusts are not necessarily moving in the same direction as the sense of the flexural-slip during folding.
Figure 3.1 Scanned images of the hand-specimen folds (left column) and their corresponding line drawings (right column). Out-of-syncline and into-anticline thrusts,
e.g. fault F5 (a) and fault F4 (b); Limb wedge thrust, e.g. faults F9 and F14 (c).
Based on observations from hand specimen, outcrop-scale structures, and
published literatures, several characteristic signatures that are summarized in
22
order to identify fold-accommodation faults from other types of thrusts.
Fold-accommodation faults extend both upwards and downwards within a
fold. Limited displacement along fold-accommodation faults renders the fold
relatively intact. Displacement along the out-of-syncline thrust decreases
from the limbs toward the hinge zone of the fold, and displays diagnostically
negative slope (separation value decreasing away from the upper fault tip) in
the separation-distance graph. Observations indicate that foldaccommodation faults usually have small cut-off angles in the limbs of the
fold, but in some cases the cut-off angle could be large when thrusts cut
through the hinge zone. Spatial distribution of fold-accommodation faults
displays a close relationship with the axial surface of the fold. Our analyses
also indicate that fold-accommodation faults display kinematic consistency
with flexural-slip folding.
Figure 3.2 Photography and line drawing of one outcrop-scale fold asscoaited with
fold-accommodation faults. Faults F1, out-of-syncline thrust; F2, into-anticline
thrust; F3, limb wedge thrust.
23
3.2 Modelling two sequential coaxial phases of
shortening in a foreland thrust belt
Paper II presents the results of modelling the formation and reactivation of
structures during two sequential coaxial phases of shortening in a fold-andthrust belt. In these models, a sufficient hiatus between the two sequential
coaxial phases is considered. Erosion and sedimentation were conducted
after the first phase, which created an angular unconformity that was subsequently deformed during further coaxial shortening. Results of the analogue
models were compared with two examples of foreland thrust belt, one from
the northeastern Cordillera in Colombia and another from the Variscan frontal zone in Western Europe. In these two areas, an angular unconformity
separates at least two phases of shortening.
Two kinds of analogue materials were used in the experiments, dry and
loose quartz sand, and micro glass beads. A thin layer of glass beads was
placed on the erosion surface in some models to act as a potential décollement horizon, since glass beads has a relatively lower frication than quartz
sand. The initial thickness of shortened sand layers in the first phase and the
thickness of sediment on the erosion surface differed between models. After
sedimentation the total thickness of the shortened sand layers during the
second phase is 4 cm in some models and 4.5 cm in the others. In order to
discuss how thickness variation in the part of model above and below the
unconformity affects the second phase structures, a parameter of thickness
ratio [T2-T1]:T1 is introduced here, where T1 and T2 are the total thickness of
sand package after erosion and sedimentation, respectively. One standard
model was prepared, in which the 4 cm thick sand layers was shortened continuously without applying erosion or sedimentation. Structures formed during one continuous shortening in the standard model was compared with
structures formed by two sequential coaxial shortening phases separated by
an unconformity. All the models were shortened above the same basement
with a relatively low basal friction (µ = 0.23).
Vertical sections of the models show that the unconformity separates the
models into two parts (Figure 3.3). Above the unconformity, structures are
dominated by the reactivated first phase thrusts, second phase thrusts and
relatively broad second phase box-folds. Below the unconformity, superimposed coaxial shortening produces a complex structural style, where more
folds and thrusts are shown than above the unconformity. The first phase
folds are generally tighter, and their crests are truncated by the unconformity. Some of the first phase thrusts are inactive during the subsequent shortening, as they terminate at and do not displace the unconformity. Some others are reactivated and propagate up-section into the upper sediments displacing the unconformity. Along these reactivated thrusts, total displacement
abruptly increases downwards across the unconformity where these thrusts
accumulate two phases of displacement in the layers below the unconform24
ity. This feature could assist in distinguishing thrust reactivation in the field.
The second phase thrusts cut the layers below the unconformity. Some of
them just develop in the undeformed foreland of the first shortening phase.
Other second phase thrusts are formed in area containing the first phase
structures (hinterland), and hence cut across and displace the pre-existing
folds and thrusts.
Figure 3.3 Photograph and line drawing of one model which has experienced two
phases of coaxial shortening. a) A series of folds and thrusts formed after the first
shortening phase. b) After the second phase of shortening, newly thrusts formed
(e.g. T2 and T6); some early phase thrusts remained inactive (e.g. F3-5); whereas,
some early phase thrusts were reactivated (e.g. F12/T4).
Models results demonstrate that reactivation of pre-existing structures has
significant effect on structure spacing during the later shortening phase. In
the models which experienced two coaxial shortening phases, spacing of the
second phase structures is less than spacing of the structures of the standard
model, even though thickness of the shortened layers in both models is similar. Presence of a weak glass-beads layer at the unconformity level did not
actually act as an intermediate décollement. Reactivation of pre-existing
structures offsets the weak layer and hence, prevents it from acting as an
intermediate décollement. Model results also show that when the thickness
ratio is large, i.e. the proportion of post-erosional layers increases in the entire shortened package, relatively fewer first phase thrusts are reactivated
25
during the second shortening phase. Meanwhile, along the reactivated thrusts
less displacement occurs in models with a large thickness ratio.
Comparison between model results and the two regional examples display
good agreements. As in the models, both natural examples had relatively
tight folds below the unconformity. The crests of these folds were eroded
and incorporated into the later phase folding that folded both the unconformity boundary and the overlying upper sediments (Figure 3.4). In the Cordillera example, a series of imbricates was truncated by the unconformity and
remained inactive during the later phase of deformation. In the Variscan
frontal zone, a number of early phase thrusts were reactivated during the
later phase. They propagated through the unconformity, and had significantly larger displacement within the stratigraphy below the unconformity
than within those above it.
26
Figure 3.4 Seismic profile across the Los Deseos syncline in the Eastern Cordillera
fold belt, Colombia, and the corresponding line drawing (from figure 6 in Corredor,
2003).
27
3.3 Mega arrowhead interference patterns in the Central
part of the Yanshan Orogenic Belt, North China
In paper III, we investigated two kilometer-scale fold interference patterns
from the Central part of the Yanshan Orogenic Belt (YOB), the ChengdePingquan area, North China. We call these two examples Daheishan and
Pingquan folds here. Detailed geological mapping and measurements of
outcrop structures were conducted to decipher the geometry of the two superimposed structures. Age of the two folding phases that formed the Daheishan and Pingquan folds and their overprinting sequence were also discussed in this paper.
The E-W trending YOB has formed due to Mesozoic multiple shortening,
which has been suggested by other researchers (Zheng et al., 2000; Davis et
al., 2001; Deng et al., 2005; Cope et al., 2007; Zhang et al., 2007; Dong et
al., 2008). The Chengde-Pingquan area in the central part of the YOB is
characterized by a number of thrusts, strike-ship faults, buckle folds, where
some structures are trending E-W to NE-SW, and others are trending NWSE on the geological map (Figures 3.5 and 3.6). The Daheishan and
Pingquan folds which are exposed in this area display fold interference patterns (Figures 3.5 and 3.6). In general, two sets of fold axial traces can be
recognized in map-view, where one axial trace trends NE-SW to ENEWSW, and the other is roughly NW-SE. In the Daheishan and Pingquan
folds, small-scale structures, e.g. planar cleavage, schistosity, crenulation,
and flexural-slip striations are poorly developed. However, outcrop-scale
folds and faults are abundantly seen in the field. Stereonet plots of bedding
in these outcrop-scale folds are used to analyse kinematics and overprinting
relationship of the large Daheishan and Pingquan folds. Field mapping and
stereonet plots indicate that both the Daheishan and Pingquan folds show
arrowhead interference pattern in map-view (Figure 3.7). The NW-SE trending F1 folds were refolded by a later ENE-WSW F2 folding, and hence display the current crescent geometry. Bedding plots also show that the interlimb angles of the two phases folds are slightly larger than 90°, and the folds
have steeply inclined axial surfaces but no overturned limb.
Steronet plots for some outcrop-scale folds show that some of these outcrop-scale folds are roughly trending ENE-WSW, plunging sub-horizontally,
and have cynlindrical or sub-cynlindrical geometries. We interpret that these
outcrop-scale folds were formed during F1 folding phase. However, stereonet
plots for some other outcrop folds indicate that the trends of their axial traces
vary from SSW, WSW to NW, and their plunge is variable (10-30°). Additionally, these outcrop-scale folds are spatially located in the limbs and/or
close to the hinge zone of the large-scale F1 folds. We interpret that these
outcrop-scale folds were formed during F1 folding, and probably rotated with
the large-scale F1 folds and even refolded during the F2 folding. The Daheishan and Pingquan folds are cut by faults with different trends. Restoration
28
of the later faults displayed two mega arrow-head interfernce patterns indicating the superimposition of two phases of folding. These restored mapviews of the Daheishan and Pingquan folds show that an arrowhead interference pattern (here called modified type-2 pattern) also can form, when the
early F1 folds have an interlimb angle slightly larger than 90° but their axial
surfaces are inclined.
Figure 3.5 Geological map of the Daheishan folds and the related thrusts. CDFCaoniangou-Dajikou fault; SPF- Sangyuan-Pingquan fault; XPF-Xiadian-Pingquan
fault; XSF-Xiadianzi-Shangyuan fault; YSF-Yuzhangzi-Shangyuan fault (modified
after HBG-SGSG, 1976).
Figure 3.6 Geological map of the Pingquan folds and the related thrusts. DSFDongshuiquan-Songzhangzi fault; GPF-Gubeikou-Pingquan fault; LLF-Lijialiangzi
fault; WZF- Wanzhangzi fault (modified after HBG-SGSG, 1976).
29
Figure 3.7 Restored map view geometry of the Pingquan area. An arrowhead interference pattern is shown. Apparent displacement along later faults is removed.
Several kilometre-scale faults are shown in the Chengde-Pingquan area. The
strikes of these faults are generally NW-SE and NE-SW, sub-parallel to the
axial traces of F1 and F2 folds, respectively. The geological map and our
field observations show that these faults clearly cut the interference patterns
of the Daheishan and Pingquan folds. This structural relationship together
with the unconformable relationship implies that these faults postdate the
two folding phases that formed the interference pattern. Based on our analyses of field data and reinterpretation of the findings of previous studies, we
suggest five deformation phases in the Chengde-Pingquan area, the central
part of the YOB. Superimposition of the roughly NW-SE trending F1 folds
and the ENE-WSW trending F2 folds resulted in the formation of the arrowhead interference pattern during the first two shortening phases, which had
occurred earlier than Late Triassic. Proterozoic and Paleozoic units were
folded during the two folding phases, and later unconformably covered by
upper Triassic units. The NE-SW trending faults were formed during a third
deformation phase (thrust SPF in Figure 3.5, and thrust DSF in Figure 3.6),
from late Triassic to early Jurassic. These faults were later displaced by the
NW-SE trending faults of the fourth deformation phase in about Middle
Jurassic. The fifth deformation phase formed another set of faults that are
trending ENE-WSW to NE-SW and cut SPF and DSF, and YSF and LLF
structures of the third and fourth deformation phases.
30
3.4 Superimposed folding and thrusting by two phases
of non-coaxial shortening in analogue models
In paper IV, superimposition of folds and thrusts were studied using results
of a series of systematically designed analogue models. The models simulate
superimposed structures that were formed by the second phase folds and
thrusts overprinting the first phase ones, either orthogonally or obliquely.
The surface of the models was monitored by a high-resolution laser scanner.
Centrifuge models were also run to help better understanding fold interference patterns by excluding the effect of thrusting, since in sandbox models
folds and thrusts developed together. Pure quartz sand was used in the sandbox models, while in the centrifuge models two analogue materials were
used, pure plasticine and plasticine-silicone putty mixture. After experiments, horizontal sections were taken at different levels in each model, from
which the 3D geometry of the structures can be observed.
In the sandbox modelling, after the first shortening phase, a wedge
formed and thickened hinterland, whereas towards the foreland the sand
layers remained undeformed keeping their original thickness. During the
second shortening phase, the newly formed structures superimposed the
early phase wedge orthogonally or obliquely. As a result, in the area where
two phases of hinterlands superimposed, the highest topography was created
and deepest layers were exhumed. On the contrary, the lowest topography
was created in the part of the models where the forelands of the two shortening phases superimposed. During the second shortening phase, thrusts laterally propagated from the first phase thin foreland to the thickened hinterland.
As such, structure spacing is larger in the thickened hinterland areas and
smaller where such thickening is limited. However, the increase in structure
spacing in the thickened hinterland is not as large as expected in thick models where no earlier shortening has taken place. During oblique superimposition, the pre-existing first-phase thrusts were reactivated during the second
shortening phase, where dip- and/or strike-slip were observed along these
thrusts.
Model results seen in both topography and horizontal sections show that
the trends of structures that were formed during two orthogonal shortening
phases are approximately orthogonal to each other (Figure 3.8). In oblique
superimposition, the second phase structures are striking obliquely to the
first phase ones in the thin foreland areas, while the two structural trends
tend to be orthogonal to each other where the layers were thickened by the
first phase (hinterland) (Figure 3.9). Presence of an unconformity between
the two shortening phases causes formation of different structures at different structural levels. At shallow levels, if erosion removes part of the structures above the unconformity boundary, only the later phase structures can
be seen in the post-erosional layers. At deeper levels below the unconformity, the superimposed and the firsts phase structures are shown.
31
In the horizontal sections (map-view), dome-and-basin fold interference
pattern is commonly seen in the sandbox and centrifuge models. Arrowheadshape interference pattern is also seen in the centrifuge models. Where an
anticline overprints an anticline, a dome structure is formed and the deep
structural level is uplifted. Bedding is curved outwards in the dome, and bed
dip and fold plunge are outwards. A syncline overprints a syncline to form a
basin, where bedding is curved outwards in map-view, and bed dip and fold
plunge are inwards. A relatively shallow structural level is exposed in the
basin. In areas where an anticline overprints a syncline and/or a syncline
overprints an anticline, bedding is curved inwards, and anticlines plunge
inwards whereas synclines plunge outwards. In the arrowhead-shaped interference pattern developed in the centrifuge models, the overprinting sequence of two folding phases could be determined according to the mapview geometry. In the neck of the arrow, the early phase folds clearly show
the inwards curved bedding and outwards plunging closures for an early
syncline and inwards plunging for an early anticline.
Model results are compared with three natural examples from the Chungnam Basin, Korea, the Mount Isa Inlier, Australia, and the central part of the
Yanshan Orogenic Belt. All these tectonic areas have undergone multiple
phases of non-coaxial shortening. As shown in the models, dome-and-basin
and arrowhead-shaped fold interference patterns are displayed on an
orogeny-scale in these areas. The pre-existing early phase thrusts can be
reactivated by the later shortening phase. In each shortening phase deformation might not develop throughout everywhere. As such, superimposed structures can be seen in some areas, whereas, only one phase structure is shown
in other places. In the models, thrusts and folds are formed together in each
shortening phase. Therefore, development of thrusts does not modify the
fold interference patterns. However, in some natural examples the map- view
geometry of fold interference patterns are modified by the later phase thrusting.
32
Figure 3.8 Horizontal section of a model showing orthogonal superimposed structures. Fold and thrust traces are separately shown in a)
and b). c) Enlarged part of the map-view geometry, showing the second phase thrust cuts through the first phase structures.
Figure 3.9 Horizontal section of one model showing oblique superimposed structures. Trends of the second phase structures are changing
when they propagate through the model.
4. Conclusions
In this thesis, superimposition of structures which are resulted from progressive deformation (fold-thrust relationship) or multiple shortening phases i.e.
coaxial and non-coaxial (orthogonal or oblique) are investigated in models
and nature. Analogue models are designed to simulate two phases of shortening, where the early phase structures are superimposed by a later coaxial
or non-coaxial phase. The main findings of this thesis are summarized below:
1) During progressive folding, thrusts can develop in either the hinge
zone or the limbs of the fold, which accommodates strain variations during
fold evolution. These thrusts, which are called fold-accommodation faults,
are secondary structures, and their superimposition does not significantly
modify the geometry of the fold. However, such thrusts can cut through the
fold axial plane or thicken its hinge zone. Displacement along the thrusts is
relatively limited, and usually decreases towards the hinge zone of the fold.
Our studies also suggest kinematic consistency between foldaccommodation faults and the flexural-slip folding, which has been reported
previously.
2) During coaxial superimposition, more folds and thrusts are seen in the
layers below the unconformity. The first phase folds are truncated by the
unconformity and are tightened during the later coaxial shortening phase.
Some early formed thrusts are inactive during the later shortening and also
truncated by the unconformity. Some of the pre-existing structures are cut
and displaced by the later thrusting. These features are clearly seen in natural
examples from the northeastern Cordillera (Colombia) and the Variscan
frontal zone in western Europe, where tightened and partly eroded early
phase folds and truncated early phase thrusts indicate two phases of coaxial
superimposition.
3) During non-coaxial superimposition, hinterland overprinting hinterland
creates the highest topography, where superimposed structures and deepest
units are shown in map-view after erosion. Formation of an unconformity
between two non-coaxial shortening phases separates different structures.
Below such an unconformity, superimposition is only seen in the deeper
layers. In contrast, layers above the unconformity show only the later phase
structures.
4) Dome-and-basin (type 1) and arrowhead-shaped (modified type 2 here)
interference patterns are formed by non-coaxial superimposition. Both in the
35
domes and the basins, bedding is curved outwards in map-view. In the dome,
layers are dipping and anticlines are plunging outwards, whereas, in the basin the dip of layers and the plunge of synclines are inwards. Where an anticline is superimposed by a syncline or a syncline is superimposed by an anticline, bedding is curved inwards, and the anticlines plunge inwards and the
synclines outwards. The latter feature could be used to determine the overprinting sequence for the arrowhead-shaped interference pattern. Such orogenic-scale dome-and-basin and arrowhead-shaped interference patterns are
shown in nature where two non-coaxial shortening phases have occurred, for
example the Chungnam Basin, Korea, and the central part of the Yanshan
Orogenic Belt, North China.
5) Reactivation of early phase thrusts during the later shortening phase is
commonly observed in coaxial and oblique non-coaxial superimposition. In
coaxial superimposition, displacement increases downwards across the unconformity along reactivated thrusts. This feature is also seen in the profile
of a reactivated thrust from the Variscan frontal zone in western Europe,
where significantly larger offset in the rocks below the unconformity is seen
than in those above the unconformity.
In models with oblique non-coaxial superimposition, pre-existing thrusts
are reactivated in both dip direction and along strike. Such reactivation is
seen in the Chungnam Basin, Korea, where some segments of the early
phase thrusts are reactivated in strike-slip during the later deformation phase.
6) Spacing of later phase structures is significantly affected by preexisting structures. Basically, structure spacing is much less in models with
pre-existing structures than in models where the layers have the same thickness but no earlier shortening has taken place. In the case of non-coaxial
superimposition, structure spacing is variable being larger in areas where a
hinterland overprints a hinterland, and smaller towards the area where a foreland overprints a foreland.
36
5. Sammanfattning på svenska
Överprägling av geologiska kompressionsstrukturer i olika skalor är vanligt
förekommande i naturen. Överpräglade strukturer bildas på grund av olika
processer: ändring i deformation-anpassning från en struktur till en annan
under enstaka progressiva hopskjutningar; successiva coaxiella hopskjutningsfaser separerade av en unconformitet; överprägling av olika ickecoaxiella, hopskjutande faser. Genom att använda serier av systematiska
analoga modeller kombinerat med detaljerad strukturell kartering i fält, fokuserar denna avhandling på geometrin och kinematiken hos överpräglade
strukturer som bildas av dessa tre processer. Under en progressiv veckning
bildas överskjutningar i ett veck för att anpassa variationer av deformation i
olika delar av vecket. Veckets geometri påverkas inte i någon större utsträckning av begränsade förskjutningar längs dessa överskjutningar. Under
multipla hopskjutningsfaser (coaxiella eller icke-coaxiella),kan däremot de
senare överskjutningarna skära av, förskjuta, eller trycka ihop de redan existerande strukturerna. Tidigare existerande överskjutnngar kan reaktiveras i
stupningsriktningen och/eller längs strykningen under senare hopskjutning.
Tidigare existerande strukturer influerar i sin tur utvecklingen av senare
strukturer, vilket resulterar i variation av strukturernas inbördes avstånd. En
vinkel-unconformitet mellan två hopskjutande faser skär tydligt tidigare
strukturer, och separerar strukturer på olika nivåer. Komplicerade överpräglade strukturer är synliga i lagren under unconformiteten, i motsats till i posterosionslagren . Denna avhandling visar att geometrin och struktursekvensen som bildas under en progressiv eller multipel hopskjutning är
starkt beroende på om överpräglingen är coaxiell, ortogonal eller i i vinkel,
samt av de tidigare strukturernas orienteringen.
Denna studie har kommit till följande slutsatser:
1) Under progressiv veckning kan överskjutningsförkastningar bildas, i
veckets omböjning eller veckben, vilket anpassas efter deformationsvariationer under förkortningen. Dessa överskjutningar, vilka kallas veckanpassade förkastningar, är sekundära strukturer, och deras överprägling modifierar inte veckets geometri i någon högre grad. Sådana överskjutningar kan
dock skära genom veckaxelplanet eller förtjocka veckomböjningen. Förskjutning längs överskjutningarna är relativt begränsad och avtar vanligtvis
mot veckets omböjning. Våra resultat är kongruenta med tidigare studier
som visar på en kinematisk koppling mellan veckanpassade förkastningar
och ”flextur-slip” veckning.
37
2) Under coaxiell öveprägling syns fler veck och förkastningar i lagren
under unconformiteten. Den första fasens veck skärs av unconformiteten och
blir tätare under den senare coaxiella hopskjutningfasen. En del tidigare bildade överskjutningar är inaktiva under den senare hopskjutningen och skärs
också av unconformiteten. Andra tidigare existerande strukturer skärs och
förskjuts av senare överskjutning. Dessa fenomen kan tydligt observeras i de
naturliga exemplen från den nordöstra Kordilleran i Colombia och från den
variskiska frontalzonen i Västeuropa, där förtätade och delvis eroderade
veck och avklippta förkastningar indikerar två faser av coaxiell överprägling.
3) Under icke-coaxiell överprägling, bildas den högsta topografin då hinterland överpräglar hinterland, där överpräglande strukturer och de djupaste
enheterna kan ses i kartvy efter erosion. Bildning av en unconformitet mellan två icke-coaxiellt avkortande faser separerar olika strukturer. Under en
sådan unconformitet syns överprägling bara i djupare lager. I contrast till
detta syns bara de sena strukturer ovanför unconformiteten.
4) Dom-och-bassäng (typ 1) och pilspetsformade (modifierad typ 2) interferensmönster bildas av icke-coaxiell överprägling. Både i domerna och i
bassängerna är bäddningen kurvad utåt i kartvyn. I domen stupar lagren utåt,
liksom antiklinalerna, medan både lagren och synklinalerna stupar inåt i
bassängen. Där en antiklinal överpräglas av en synklinal eller en synklinal är
överpräglad av en antiklinal, kurvar bäddningen inåt, och antiklinalen stupar
inåt och synklinalen utåt. Det senare fenomenet kan användas för att bestämma överpräglingssekvensen för det pilspetsformade interferensmönstret.
I naturen kan man se sådana dom-och-bassäng samt pilspetsformade interferensmönster i orogen skala, där två icke-coaxiella förkortningsfaser har inträffat, till exempel Chungnambassängen i Korea, och den centrala delen av
Yanshan orogenesen i norra Kina.
5) Reaktivering av tidiga överskjutningar under den senare förkortningsfasen observeras ofta i coaxiella och vinklade, icke-coaxiella överpräglingar.
I coaxiella överpräglingar ökar förskjutningen nedåt över unconformiteten
längs reaktiverade överskjutningar. Detta fenomen kan också ses i profil i en
reaktiverad överskjutning från den variskiska frontalzonen i Västeuropa, där
signifikant större offset kan ses i bergarterna under unconformiteten än de
som ligger över den. I modeller med vinklad, icke-coaxiell, överprägling,
reaktiveras tidigare existerande överskjutningar, både i stupningsriktningen
och längs strykningen. Sådan reaktivering kan ses i Chungnambassängen
(Korea), där några segment av den tidigare fasens överskjutningar är reaktiverade i strike-slip under den senare deformationsfasen.
6) Skalan på sena strukturer är avsevärt påverkade av tidiga strukturer. I
grunden är skalan på strukturerna mycket mindre i modeller med redan existerande strukturer än i modeller där lagren har samma tjocklek utan att någon tidigare avkortning har skett. I fallet med icke-coaxiell överprägling, är
strukturskalan variabel, större i områden där hinterland överpräglade ett hinterland, och mindre i området där foreland överpräglade ett foreland.
38
Acknowledgements
For the past few years, I met many people; many things happened to me; a
lot of happy memories I keep in my heart; while a lot of sorrow inevitably
also accompanied. However, I have been given a lot during these four years
of my life. For all of these, I want to give my thanks, and I will never forget.
First and foremost, I sincerely thank my main supervisor Prof. Hemin
Koyi for all the help he has given to me. I am grateful for being given the
opportunity to come to Sweden and work with Hemin. Hemin is such a great
supervisor who always gave me his constant support, encouragement, advice
and guidance. I appreciate the way he expanded my mind when we did mapping in the field. I thank him for introducing me into the fantastic world of
analogue modelling. I will never forget the times when we discussed a structure in the field or modelling, revised each manuscript and debated the relevant scientific problems. Every piece of knowledge I learned from Hemin
helps me getting close to be a structural geologist.
I would like to thank my co-supervisors, Prof. Changhou Zhang from
China University of Geosciences (Beijing) and Dr. Faramarz Nilfouroushan.
Prof. Zhang who was my supervisor during my MSc study continued supporting the field surveys in China every summer. Without his arranging a
nice vehicle and the excellent divers, I couldn’t have worked in the field so
efficiently. I appreciate Prof. Zhang for his advice and support to my study
and life in Uppsala. I thank Faramarz for helping me a lot in the lab and being friendly to me all the time. I also want to thank my co-author Prof. Nikolaus Froitzheim from University of Bonn. Thanks to his contributions and
positive comments, so that we had a good publication.
Thanks to the MSc students Hongdan Deng, Jiasui Ouyang, Xiaolong Shi
and Yipeng Zhang from China University of Geosciences (Beijing) for assistance and friendly company in the field. Thanks also go to the Yong Zhang
and Zhangsheng Wang for their safe driving and help with practical things
during the field trips. I would like to thank the local people whom we met in
the field. They were all friendly to us even when we drove a jeep into their
villages and hammered rocks by the roadside.
Many thanks to the lovely colleagues at the department: Abigail Barker,
Steffi Burchardt, Michael Krumbholz, Frances Deegan, Lara Blythe, Peter
Dahlin, Ester M. Jolis, Kirsten Pedroza, Börje Dahren, Lukas Fuchs, David
Budd, Iwona Klonowska, Tobias Mattsson, Harri Geiger, Petar Lazor,
Håkan Sjöström, Karin Högdahl, Valentin Troll, Jochen Kamm. I thank all
39
of you who gave me the good times over the past years. I am particularly
grateful to Börje whom I had the pleasure to share the office with. Thanks
also to the technical and administration staff at Geocenter for their help and
support: Taher Mazloomian, Anna Callerholm, Tomas Nord, Ingegerd Ohlsson, Siv Petterson, Jeanette Flygare, Susanne Paul, Fatima Ryttare-Okorie,
Zara Witt-Strömer, Leif Nyberg. Many thanks go to Örjan Amcoff for translating the Swedish summary and Börje Dahren for correcting the translation.
Thanks to all my Chinese friends who have shared wonderful times and
exciting experiences with me: Zhina Liu, Ting Zhang, Yan Wang, Chunling
Shan, Zuo Xu, Fengjiao Zhang, Peng He, Peng Yi, Ping Yan, Shunguo
Wang, Lichuan Wu, Fei Huang, Na Xiu, Liang Tian, Haizhou Wang,
Zhibing Yang, Lebing Gong, Pianpian Wu, Zheya Sheng, Tianqing Zhu,
Long Zhou, Huiting Jia, Jie Song, Le Gao.
Speicial thanks go to the China Scholarship Council (CSC) for supporting
my PhD study in Sweden. My study was partly financially supported by the
Swedish Research Council (VR) through Hemin Koyi, and Department of
Earth Sciences at Uppsala University. I also want to thank Mr Wei Wang
from Chinese Embassy in Sweden and Fan Zhang from China University of
Geosciences (Beijing) who helped me a lot during the time I was on a sick
leave.
Last but not the least I would like to give me deepest gratitude to my parents for their endless love, support, understand and respect. No language in
the world is enough to express my love and gratitude to my parents. I appreciate every member in my big family in China for their concern, support, and
looking after my parents. Finally I thank my dearest friends in China and in
other countries for their precious friendship, which always encourages me to
keep moving on.
40
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45
Acta Universitatis Upsaliensis
Digital Comprehensive Summaries of Uppsala Dissertations
from the Faculty of Science and Technology 1223
Editor: The Dean of the Faculty of Science and Technology
A doctoral dissertation from the Faculty of Science and
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