HR: 17:30h
AN: T32F-07    [PDF]
TI: Two-stage exhumation history of Miocene high-pressure, low-temperature rocks from the footwall of the Cretan detachment fault, Crete, Greece
AU: * Rahl, J M
EM: jeffrey.rahl@yale.edu
AF: Yale University, Dept. of Geology and Geophysics P.O. Box 208109, New Haven, CT 06520-8109 United States
AU: Brandon, M T
EM: mark.brandon@yale.edu
AF: Yale University, Dept. of Geology and Geophysics P.O. Box 208109, New Haven, CT 06520-8109 United States
AU: Reiners, P W
EM: peter.reiners@yale.edu
AF: Yale University, Dept. of Geology and Geophysics P.O. Box 208109, New Haven, CT 06520-8109 United States
AB: The island of Crete represents an emergent fore-arc high in the modern Hellenic subduction zone. The island exposes high-pressure, low-temperature metamorphic rocks (maximum P-T conditions estimated at 1 GPa, $>$250 C) juxtaposed against unmetamorphosed rocks by the Cretan detachment fault, a major structure that excises at least 20 km of structural section. We present new zircon (U-Th)/He data to constrain the cooling and exhumation history of the high-pressure metamorphic rocks. Additionally, we combine new stratigraphic and microstructural observations with a review of previously published thermochronologic data to create a revised interpretation of the P-T-t evolution of the lower plate. Stratigraphic constraints require that the metasediments of the lower plate were deeply subducted sometime after 36 to 32 Ma. White mica Ar-Ar ages, interpreted here as sub-closure crystallization ages, suggest peak metamorphic conditions were reached between 24 and 20 Ma. Previously published zircon He ages reveal cooling through 240 C at about 18 Ma. Our new zircon He ages show that the lower plate rocks cooled below 210 C around 10 Ma. Finally, conglomeratic deposits indicate exposure of the HP rocks at the surface at about 8.5 Ma. Exhumation rates are estimated using a one-dimensional thermal model to account for advection of isotherms and the Dodson relationship to account for the effect of cooling rate on effective closure temperature. This analysis indicates an exhumation rate of 0.7 km/m.y. during 18 to 10 Ma, followed by faster exhumation, at about 2 km/m.y., between 10 and 8.5 Ma. These rates are much smaller than previous estimates by Thomson et al. (1998) of sustained rates of 4 km/m.y. We use these results to constrain the rate of slip on the Cretan detachment, which is widely considered to have formed as a low-angle normal fault. Previous workers have argued that, given its low dip, slip on the Cretan detachment must have been 20 to 30 km/m.y., which is approaching the modern convergence rates estimated for the Hellenic subduction zone that underlies Crete (40 km/m.y.). This conclusion is in contrast to fault slip rates determined from studies of the metamorphic core complexes of the Basin and Range province, which typically are 3 to 8 km/m.y. and generally no more than 10 km/m.y. Our results indicate much slower slip rates for the Cretan detachment. Assuming that exhumation is entirely due to slip on a low angle detachment, we estimate that the slip rate was about 1.5 km/m.y. from 18 to 10 Ma, and about 4 km/m.y. after 10 Ma.
DE: 8010 Fractures and faults
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting