Stretched Thin

Author(s): T. A. Ducharme, D. A. Schneider, B. Grasemann, I. Klonowska
Abstract: We present field-based structural, geochronological, and petrological evidence for a major new Oligocene extensional shear zone, the Evia Shear Zone (ESZ), on the island of Evia in the NW Aegean Sea. Strain related to this structure occurs in a diffuse zone structurally underlying the nappe contact between the Cycladic Blueschist Unit and Basal Unit, within rock previously attributed to the Tsakei Unit or Basal Unit metaflysch. Structures within the ESZ record stretching in both the X and Y directions under ductile and brittle-ductile conditions, indicative of a component of oblate coaxial strain during overall top-to-E general shear. New white mica 40Ar/39Ar geochronology from the ESZ shows that the structure was accommodating ductile deformation in the late Oligocene. Thermodynamic modeling shows that rock within the ESZ records greenschist facies retrogressive conditions of 310 ± 15°C and 7 ± 1 kbar. Zircon (U-Th)/He thermochronology demonstrates that both the CBU and Basal Unit had exhumed into the brittle crust by the middle Miocene, slightly earlier than indicated by low-temperature thermochronology for the HP-LT units throughout the Aegean. We interpret these data as evidence that the Basal Unit underwent rapid exhumation via syn-orogenic processes persisting until at least the early Miocene, facilitated in part by normal-sense displacement along the ESZ. The occurrence of structures representative of coaxial deformation in the shear zone alludes to a major role for ductile thinning in controlling exhumation of HP rocks in the Cyclades, perhaps influencing the relative rates of exhumation observed across the region.
Organisation(s): Department of Geology
External organisation(s): University of Ottawa, AGH University of Science and Technology, Uppsala University
Journal: Tectonics
Volume: 41
No. of pages: 28
ISSN: 0278-7407
DOI: https://doi.org/10.1029/2022TC007561
Publication date: 12-2022
Peer reviewed: Yes
Austrian Fields of Science 2012: 105124 Tectonics
Keywords
ASJC Scopus subject areas: Geophysics, Geochemistry and Petrology
Portal url: https://ucris.univie.ac.at/portal/en/publications/stretched-thin(a522ec5a-ec2b-442c-9cdc-55df755d1775).html

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