Temporal patterns of detachment faulting along Cycladic extensional metamorphic domes, Aegean region
The Aegean region together with the surrounding mainland areas are known for Miocene to Recent active, notably extensional tectonics that are the result of the retreating Hellenic slab, gravitational collapse of the region and, since the Late Miocene to Early Pliocene, the westward escape of Anatolia relative to Eurasia. Project ACCEL (Aegean Core Complexes along an Extended Lithosphere) has collected an extensive modern structural dataset for the islands of Kea, Kithnos, and Serifos of the western Cyclades. On all three islands, crustal-scale, low-angle frictional-viscous shear zones have been identified and record strikingly consistent SSW-directed extensional kinematics together with a WNE-ESE shortening component. The geology of Kea is dominated by highly-strained, greenschist-facies schists, calc-silicates and marbles; a major, 100's m thick ultramylonite zone defines this northern island as a structural dome. White mica Ar-Ar thermochronometry performed on variably deformed units from different structural levels yield consistent Early Miocene (15-19 Ma) cooling ages across the entire island. Other pervasively deformed shallow crustal regions of the Cyclades (Tinos and Andros; b-type domes of Jolivet et al. 2004) also record similar Early Miocene cooling. Comparable geology and structure is exposed on Serifos although locally deformed under amphibolite-facies conditions and intruded in the south by a Late Miocene granodiorite. A major high strain zone that is present on the island is localized along an earlier (Late Eocene) granitic pluton. White micas from mylonites and gneisses along this shear zone and from rocks in the southern portion of the island yield Late Miocene (8-9 Ma) cooling ages, whereas greenschist-facies units in northern Serifos that are dominated by a different structural record of several phases of folding yield Oligocene (30-34 Ma) mica Ar-Ar cooling ages. Oligocene ages are similarly reported from Evvia and Sifnos, which are noted for their occurrences of the Cycladic Blueschist Unit. We interpret the Late Miocene cooling ages to represent the timing of extension and exhumation during metamorphic core complex genesis, which is coeval with the timing of exhumation the other Cycladic a-type metamorphic domes (Naxos and Paros) that represent deeper parts of the Hellenic accretionary complex. Since Late Miocene extension in the Aegean region has been generally considered to be N-directed, our results suggest a new domain in the Western Cyclades that has been exhumed by S-directed extension.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1140 Thermochronology;
- 8038 Regional crustal structure;
- 8109 Continental tectonics: extensional (0905)