TSK 11 Göttingen 2006 Voit et al.
 Kinematics and deformation
 structures in a crustal-scale
 shear zone on Kea (W. Cy-
 clades, Greece) Poster
 Klaus Voit1 Bernhard Grasemann1
 Erich Draganits3 Michael A. Edwards1
 Monika Müller1 Christoph Iglseder1
 Konstantin Petrakakis2 Ulrike Exner1
 It is generally agreed upon that the ex-
 humation of metamorphic rocks in the
 Aegean is caused by post orogenic ex-
 tension in the late Oligocene to early
 Miocene. This extension is in princi-
 ple largely accommodated by low-angle
 crustal detachment faulting possibly re-
 sulting in the formation of metamorphic
 core complexes (MCC).
 Here, we present data from recent struc-
 tural investigations on the island of Kea
 in the W. Cyclades, Greece. Our work
 focussed in the north of the island. Of
 the ca. 270m total structural thickness
 that was mapped, the entire section
 of rocks are highly strained. Exhuma-
 tion during progressive deformation is
 recorded by the transition from ductile
 to brittle/ductile to brittle conditions.
 The regional characteristics and types
 of deformation structures vary depend-
 ing on the protolith and the intensity of
 strain.
 The lower portions comprise albite
 blast-bearing greenschist gneiss that be-
 comes intensely folded structurally up-
 wards and then changes through in-
 creasing strain and decreasing temper-
 atures into a fine-grained greenschist-
 1 Department of Geodynamics and Sedimen-
 tology, Structural Processes Group, University
 of Vienna, A-1090 Vienna, Austria 2 De-
 partment of Geodynamics and Sedimentol-
 ogy, University of Vienna, A-1090 Vienna,
 Austria 3 Institute for Engineering Geology,
 Vienna University of Technology, A-1040 Vi-
 enna, Austria
 bearing internal gneiss lamellae.
 This central unit of fine-grained green-
 schist comprises a series of interlayered
 cm- to m-scale marbles and composi-
 tionally varying schist layers. These
 host structural features such as macro-
 scopic S–C fabric, lensoidal to angular
 boudins. All sections are overprinted
 by polyphase brittle/ductile to brittle
 deformation. Also present are brit-
 tle fault zones that are concentrated
 on rheologically-distinct weak layers.
 These layers often contain serpentinite
 lenses and talc. Additionally, cata-
 clasites with slickensides and Riedel-
 fractures are present in these zones.
 A high density of syn-post mylonitic
 quartz veins are present as well as dis-
 tinctive ultramylonite (graphitic) shear
 zones testifying diffusive mass trans-
 fer and solution/precipitation mecha-
 nisms during deformation. Late stage
 fluid-related activity resulted in alter-
 ations and minaralizations including a
 conspicuous ankeritization of dolomitic
 megaboudins.
 The uppermost portion comprises a
 10’s m thick marble-ultramylonite with
 dolomite lenses at its base that forms
 very coherent km-long blocks. The com-
 petency contrast between the marble-
 ultramylonite layer and the underlying
 fine-grained greenschists is frequently
 marked by a metre-scale zone of very
 high strain as indicated by the pres-
 ence of sheath folds. Within the marble-
 ultramylonite, a-type flanking folds rep-
 resent the last stage of deformation.
 The lineations show a NNE–SSW-
 direction on mostly NE-dipping folia-
 tion planes (with an average dip of
 30°). All ductile (SC′ or SCC′, clasts
 with monoclinic symmetry, shear bands,
 SPO and LPO in quartz mylonites),
 brittle/ductile (rotated veins, flanking
 1
Voit et al. TSK 11 Göttingen 2006
 structures, asymmetric boudinage) and
 brittle (Riedl fractures, slickensides)
 shear sense indicators show a consis-
 tent top to SSW direction. Although
 the low-angle fault system in the north-
 ern part of Kea has the current orien-
 tation of a thrust, in analogy to other
 metamorphic core complexes (e.g. Seri-
 fos) we speculate that the fault zone is
 part of an up-warped extensional crustal
 scale detachment.
 The low-angle extensional faulting re-
 lated structures are overprinted by
 younger and possibly still active steeply
 dipping conjugate fault zones, which
 strike NNE–SSW and NW–SE respec-
 tively. A possible regional genetic
 link with the actively widening Gulf of
 Corinth is subject of further investiga-
 tions.
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