科研之友
微信
新浪微博
Facebook
分享链接
摘要
New structural, petrologic, and thermochronologic data from Kea, West Cyclades, define a crustal-scale ductile shear zone and ductile/brittle low-angle normal fault (LANF) system. Both the greenschist-facies shear zone forming the footwall and the overlying LANF zone formed during constrictional strains, with a consistent top-to-SW-S shear sense, with increasing finite strains toward higher structural levels but decreasing temperatures from footwall to hanging wall. The tectonostratigraphy comprises a similar to 450 m thick footwall of shallowly dipping schists and calcite marbles representing the Intermediate Unit of the Attic-Cycladic Crystalline (ACC). Above the footwall is a similar to 60 m thick highly strained LANF zone, consisting of phyllonites, cataclastic schists, ultramylonitic calcite marbles, (proto) mylonitic calcite marbles, and cohesive cataclasites that arch over the whole island. These fault rocks exhibit multistage LANFs, evolving from ductile to brittle conditions. An up to similar to 50 m thick brecciated limestone and dolostone sequence forms the unmetamorphosed hanging wall which is most probably part of the Upper Unit of the ACC. Multiequilibrium P-T estimates on chlorite-white mica pairs in the footwall yield 7-5.5 kbar/36 degrees C-450 degrees C for inclusions in albite and epidote, 5.5-3 kbar/400 degrees C-350 degrees C for the main foliation, and 3-2 kbar/350 degrees C-280 degrees C in localized shear bands (C and C' foliations). The Ar-40/Ar-39 white mica footwall cooling ages demonstrate that greenschist-facies retrogression occurred between similar to 21 and 17 Ma. Localized, late decimeter thick shear zones were active and dynamically recrystallized before similar to 15 to 13 Ma. The LANF on Kea, together with similar structures in South Attica and the West Cyclades define the West Cycladic Detachment System, characterized by ductile to brittle top-SW-S shear sense.
- 出版日期2011-8-27
