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

Abstract

In the southern Oman Mountains, high-pressure metamorphic rocks of continental origin crop out beneath the Cretaceous Samail ophiolitic nappe. We collected 14 samples from 15 to 1200 m above sea level and at various structural 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 µm. Fission-track data optimization shows that the subophiolitic units cooled slowly below 60 °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. The subophiolitic basement was reheated to ∼70–80 °C at ca. 7–4 Ma, before final cooling. The reheating event is correlated with the late Miocene–Pliocene (Zagros) compressional phase. Post-Oligocene heating up to 80 °C is also documented by stable isotope study of the post-nappe 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.