|
Original Article |
1 1Institut für Geowissenschaften, Johannes Gutenberg-Universität, 55099 Mainz, Germany (e-mail: kumerics@mail.uni-maint.de)
2 2Present address: Department of Geology, University of Kansas, Lawrence, KS 66045, USA
3 3GeoForschungsZentrum Potsdam, 14473 Potsdam, Germany
4 4UMR 5573, Université Montpellier II, 34095 Montpellier Cedex 05, France
5 5Present address: Department of Geological Sciences, Canterbury Univeristy, Christchurch, New Zealand
Structural, thermochronological and metamorphic data are used to elucidate the tectonic nature and evolution of the ductile extensional Messaria shear zone and the associated brittle Messaria and Fanari detachment faults, which exhumed their footwall from mid-crustal depths on the island of Ikaria in the Aegean. Thermobarometric data indicate that the Messaria shear zone formed at 350–>400 °C and 3–4 kbar (i.e. at a depth of c. 15 km). Normal faulting was accompanied by the intrusion of two granites, which together with the thermobarometric data indicate a relatively high thermal field gradient of 25–35 °C km–1. Zircon and apatite fission-track and apatite (U–Th)/He ages demonstrate rapid cooling in the footwall of the Messaria detachment from c. 400 °C to c. 40 °C between 11 and 3 Ma. Age–distance relationships of the data suggest that the Messaria shear zone and the Messaria detachment slipped at apparent rates of c. 6–9 km Ma–1. Kinematic indicators show a consistent top-to-the-NNE shear sense for the extensional faults. However, at the southern part of the Messaria detachment some late-stage shear-sense indicators are top-to-the-SSW and are assumed to be associated with updoming of the footwall. Numerous deformed pegmatite veins in the Messaria shear zone allow the reconstruction of deformation and flow parameters. The mean kinematic vorticity number ranges from 0.13 to 0.80, indicating that shearing deviated significantly from simple shear; that is, extensional shearing was associated with vertical ductile thinning, which contributed to tectonic exhumation. Finite strain shows oblate geometries and axial ratios of the finite-strain ellipse in sections parallel to tectonic transport and normal to the mylonitic foliation range from 1.8 to 19.9. We calculate, using a 1D numerical model, that vertical ductile thinning contributed c. 20% to exhumation during extensional shearing. Normal faulting was the major agent exhuming the footwall from c. 15 km depth.
Key Words: Aegean Sea • Greece • exhumation • extension • ductile flow
This article has been cited by other articles:
 |
|
 |
|
  U. RING and C. KUMERICS Vertical ductile thinning and its contribution to the exhumation of high-pressure rocks: the Cycladic blueschist unit in the Aegean Journal of the Geological Society, 2008; 165: 1019 - 1030. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Brichau, U. Ring, A. Carter, R. Bolhar, P. Monie, D. Stockli, and M. Brunel Timing, slip rate, displacement and cooling history of the Mykonos detachment footwall, Cyclades, Greece, and implications for the opening of the Aegean Sea basin Journal of the Geological Society, 2008; 165: 263 - 277. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. SKARPELIS, B. TSIKOURAS, and G. PE-PIPER The Miocene igneous rocks in the Basal Unit of Lavrion (SE Attica, Greece): petrology and geodynamic implications Geological Magazine, 2008; 145: 1 - 15. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Verdel, B. P. Wernicke, J. Ramezani, J. Hassanzadeh, P. R. Renne, and T. L. Spell Geology and thermochronology of Tertiary Cordilleran-style metamorphic core complexes in the Saghand region of central Iran GSA Bulletin, 2007; 119: 961 - 977. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
U. Ring, J. Glodny, T. Will, and S. Thomson An Oligocene extrusion wedge of blueschist-facies nappes on Evia, Aegean Sea, Greece: implications for the early exhumation of high-pressure rocks Journal of the Geological Society, 2007; 164: 637 - 652. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. GLODNY and R. HETZEL Precise U-Pb ages of syn-extensional Miocene intrusions in the central Menderes Massif, western Turkey Geological Magazine, 2007; 144: 235 - 246. [Abstract] [Full Text] [PDF]
|
|
