Late thermal evolution of the Oman Mountains subophiolitic windows: Apatite fission-track thermochronology

In the southern Oman Mountains, high-pressure metamorphic rocks of continen tal origin crop out beneath the Cretaceous Samail ophiolitic nappe. We coll ected 14 samples from 15 to 1200 m above sea level and at various structura l levels that show apatite fission track ages between 40 +/- 7 and 55 +/- 5 Ma, The mean confined track lengths vary from 13.08 to 13.70 um. Fission-t rack data optimization shows that the subophiolitic units cooled slowly bel ow 60 degrees C at ca. 53 Ma, then remained at low temperature until ca. 19 Ma, i.e., during the weak postorogenic subsidence of the obduction belt. T he subophiolitic basement was reheated to similar to 70-80 degrees C at ca. 7-4 Ma, before final cooling. The reheating event is correlated with the l ate Miocene-Pliocene (Zagros) compressional phase. Post-Oligocene heating u p to 80 degrees C is also documented by stable isotope study of the post-na ppe Eocene-Oligocene onlap. Both the Paleocene and the Pliocene-Quaternary denudation rates are close to 0.3 mm/yr, and compatible with isostatically assisted erosion processes.