HR: 1330h
AN: T22B-0516    [PDF]
TI: Slip rate estimation by low temperature thermochronology for major extensional detachments in Cycladic islands.
AU: * BRICHAU, S
EM: brichau@mail.uni-mainz.de
AF: Institut fuer Geowissenschaften, Johannes Gutenberg-Universitaet, FB22, Becherweg 21, MAINZ, 55099 Germany
AU: Ring, U
EM: ring@uni-mainz.de
AF: Institut fuer Geowissenschaften, Johannes Gutenberg-Universitaet, FB22, Becherweg 21, MAINZ, 55099 Germany
AU: Carter, A
EM: a.carter@ucl.ac.uk
AF: Department of Earth Sciences, University College, Gower Street, LONDON, WC1E6B United Kingdom
AU: BRUNEL, M
EM: brunel@dstu.univ-montp2.fr
AF: UMR. D.L., Universite Montpellier-II, Place E. Bataillon, cc 060, MONTPELLIER, 34095 France
AB: Rates of tectonic processes are of fundamental importance for understanding deformation of the lithosphere. Rates of extensional faulting in the magmatic arc of the Miocene Hellenic subduction zone in the Aegean, is one of the world's best examples of a retreating subduction zone. As subduction retreated with time to the south, accreted high-pressure rocks shifted from a fore-arc position via an intra-arc into a back-arc position. The Cycladic islands in the central Aegean became part of the magmatic arc in the Late Miocene and are now in a back-arc position. The Cyclades are famous for their blueschists and spectacular extensional detachments. The blueschists formed in the Early Tertiary at depths of 50-60 km, and it is widely assumed that subsequent exhumation of the blueschist unit was chiefly accomplished by detachment faulting. However, most of this detachment faulting operated in arc as indicated by intrusion of arc-related granites into the footwalls of detachments at a time when the blueschist were largely exhumed. Detachment faulting in fact accomplished less than 10 km of blueschist exhumation. Using apatite and zircon fission-track and apatite (U-Th)/He ages from a horizontal profile parallel to the tectonic transport direction of major extensional detachments on the Cycladic islands of Tinos, Mykonos and Naxos, we estimate slip rates for these detachments. For Tinos, zircon and apatite fission-track (FT) ages range respectively from 12.2 $\pm$ 0.6 to 14.4 $\pm$ 0.8 Ma and 11.9 $\pm$ 1.3 to 12.8 $\pm$ 1.2 Ma whereas (U-Th)/He apatite ages range from 10.0 $\pm$ 1.0 to 11.9 $\pm$ 1 Ma. For Mykonos, zircon FT ages range from 10.7 $\pm$ 0.6 to 13.0 $\pm$ 0.6 Ma and apatite FT ages from 10.5 $\pm$ 0.9 to 12.5 $\pm$ 1.2 Ma; (U-Th)/He apatite ages are from 8.9 $\pm$ 0.7 to 11.1 $\pm$ 0.9 Ma. Using the same methods on Naxos, we obtain 9.7 $\pm$ 0.5 to 11.8 $\pm$ 0.6 Ma (zircon FT method), 8.2 $\pm$ 0.6 to 11.2 $\pm$ 0.9 Ma (apatite FT) and 8.9 $\pm$ 0.9 to 10.7 $\pm$ 0.9 Ma (apatite (U-Th)/He). These three methods yielded consistent results and indicate that the ages decrease in the hanging-wall slip direction. The results permit to calculate slip rates for the detachment faults of $\sim$ 3 km Myr $^{-1}$ for Tinos, $\sim$ 6.5 km Myr $^{-1}$ for Mykonos and $\sim$ 5.5 km Myr $^{-1}$ for Naxos. Our slip rate for Naxos is in agreement with the only previously known estimate of $\sim$ 5.8 km Myr $^{-1}$ (John and Howard 1995) as deduced from K-Ar and Ar/Ar ages on biotite, white mica and hornblende. Furthermore, these ages suggest that all three detachments operated synchronously. They indicate rapid cooling of the footwalls as confirmed by long mean confined track lengths ($>$ 14 $\mu$m) for fission tracks in apatite. We propose that the development of the detachments in the thermally softened magmatic arc aided fast displacement. The higher slip rates on Naxos and Mykonos as compared to the slip rate on Tinos may be due to the fact that the Tinos granite intruded pretectonically to the Tinos detachments whereas the granites on Naxos and Mykonos intruded synkinematically to both detachments.
DE: 7221 Paleoseismology
DE: 8010 Fractures and faults
DE: 8020 Mechanics
DE: 8107 Continental neotectonics
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting