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How and why did the Alpine Rhodope
collapse
during the ore‐rich Oligocene times?
Jean‐Pierre BURG, ETH‐Zurich
Perth, June 06, 2012
A pre‐Hellenistic (Thracian) mining region
From Tonkova M. In: Geoarchaeology and Archaeomineralogy. Proceedings of the International Conference, 29‐30 October 2008 Sofia, Publishing House “St. Ivan Rilski”, 266‐270.
A pre‐Hellenistic (Thracian) mining region
Silver mine ‐ Thorikos
Mine workshop ‐ Lavrion
A still (+/‐) active mining region
Ore deposits in European Mountains
Heinrich & Neubauer 2002 Mineralium Deposita 37, 533–540
Archean “Zwischengebirge”
Rhodope Massif: simplified map
Early Paleozoic protoliths
590‐420 Ma
Mesozoic protoliths
170‐120 Ma
Paleozoic protoliths
335‐270 Ma
Jurassic rocks
160‐150 Ma
UHP and HP rocks: subduction
Metamorphic conditions
1.5‐2 GPa; 700‐800°C
Ages
from 170 to 120 Ma
Mylonitic gneiss and sense of shear
Mylonitic gneiss and sense of shear
Structural constraints: sense of shear
Late deformation pegmatites
Liati et al. 2002 Chemical Geology 184: 281‐299
Rhodope Massif: simplified map
Oldest unconformity
Maastrichtian
70‐65 Ma
Cretaceous Rhodope
Paleocene‐Eocene Rhodope
Marine (Gilbert Delta) Lutetian
(48‐40 Ma)
Geochronological constraints (as per 2012)
Protolith ages excluded
Ar‐Ar & K‐Ar
Zr rims
(eclogites?)
Ar‐Ar
Zr rims
pegmatites
HP rocks
Granites
Migmatitic domes T = 560‐680°C; P = 3‐6 kbar
Migmatitic domes T = 560‐680°C; P = 3‐6 kbar
Liati & Gebauer 1999 Contributions to Mineralogy and Petrology 135: 340‐354 This image cannot currently be display ed.
Migmatite domes: Cooling
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Extensional detachments and faulting
General cross section
Moho after Geiss 1987 Annales Geophysicae 5B(6): 623‐630
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Extension and magmatism
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Schefer et al. 2011
Int.J.Earth.Sci. 100:
1181–1206
Hydrothermal ore formation
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Hydrothermal replacement front of marble by PbS+ZnS ore
Marble
Ca‐Mn‐silicate
(“skarn")
Qz + galena + sphalerite
10 cm
(Madan, Bulgaria)
Ore precipitation and deformation
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Sphalerite‐rich vein with later calcite
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~ 20 cm
Vein sequence:
~ 20 cm
Early barren / py‐rich breccia with chl‐seric alteration, then main qtz‐ base metal sulfide veins
finally late carbonates
Ore deposits and extension
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Ore (gold) deposits and extension
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Why extension so late after orogeny?
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Van Hinsbergen et al. 2008 Earth and Planetary Science Letters 273(3‐4) 345‐358
Why a thermal flare some Ma after orogeny?
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Geological setting
Experimental migmatitic domes
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Modelling extensional core complexes
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Two extension modes
Asthenosphere‐triggered doming
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Tomography: no slab breakoff
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van Hinsbergen et al. 2005 Geology 33(4) 325‐328
Model of syn‐collision delamination
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Delamination after stagnation
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Delamination from Rhodope to Aegean
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Eocene‐Oligocene Rhodope
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In summary
• The Rhodope records Cretaceous collision.
• Only one slab preceded, participated to and
followed collision.
• The Rhodope records a southwestward migration of
mass transport, thermal events (magmatism,
metamorphic cooling, hydrothermalism) and
extension.
• The tectono‐metamorphic and magmatic history of
the Rhodope is best explained with syn‐ to post‐
collision mantle delamination (peeling off the
mantle).
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Thanks for your attention
Galena‐Chalcopyrite‐Quartz
Mine 9 of September
Madan (Bulgaria)