Abstract
We have analysed strain and flow kinematics in the footwall of the South Cyclades Shear Zone (SCSZ), an important tectonic boundary within the Attic-Cycladic Crystalline Complex exposed on Ios Island, Cyclades, Aegean Sea. Coarse-grained augen gneisses in the basement unit flooring the SCSZ and forming a metamorphic core complex are excellently suited to measure finite strain using the Fry method and estimate the vorticity number (W k) of flow with the “blocked-object” method. The results show that Oligo-Miocene exhumation of the basement unit during extension brought approximately 70 % N–S crustal stretching and up to 40 % subvertical shortening in a plane strain environment (k = 0.99). Linear down-section strain decrease constrains a zone of contact deformation of the SCSZ of about 1.5 km thick. Kinematic vorticity number estimates suggest little deviation from pure shear (W k = 0.26). Finite strain and W k are not correlated, indicating that the Ios basement and the overlying cover units were stretched compatibly. While the SCSZ is a localized zone of high strain, net displacement, however, may be restricted to about ten kilometres. This has important repercussions on large-scale tectonic models for extension in the Aegean.
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Acknowledgments
This work profited from intensive discussions with Gordon Lister and Erik Duesterhoeft that helped to sharpen our thinking. Constructive and detailed reviews by David Iacopini and Uwe Ring, as well as editorial advice by Paris Xypolias, helped to improve an earlier version of the manuscript. Kiriakos Batsalis is especially acknowledged for invaluable logistical support during our stays on Ios Island in the years 2013 and 2014.
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This is a contribution to Eastern Med. Tectnonics edited by Xypolias et al.
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Mizera, M., Behrmann, J.H. Strain and flow in the metamorphic core complex of Ios Island (Cyclades, Greece). Int J Earth Sci (Geol Rundsch) 105, 2097–2110 (2016). https://doi.org/10.1007/s00531-015-1259-y
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DOI: https://doi.org/10.1007/s00531-015-1259-y