TIMING OF THRUST ACTIVITY IN THE HIGH ZAGROS FOLD-THRUST BELT, IRAN, FROM (U-TH)/HE THERMOCHRONOMETRY

Apatite and zircon (U-Th)/He cooling ages are used to quantify the timing of exhumation associated with thrust faulting in the High Zagros fold-thrust belt. Single-grain cooling age data were collected from (1) Cambrian sandstone in various thrust sheets, (2) sandstone and basement clasts derived from structurally-controlled salt plugs or fault-bounded slices, and (3) syntectonic Neogene siliciclastics strata. In the northwestern (Kuhrang) and central (Kuh-e Lajin) High Zagros, apatite (U-Th)/He (AHe) ages range from ~26.7 to ~0.38 Ma. Most cooling and exhumation occurred in the early to middle Miocene, constrained by AHe ages ~19-15 Ma from the High Zagros thrust sheet, localized faults, and reset cooling ages from Bakhtiyari deposits. In the southeastern High Zagros (Kuh-e Dinar), cooling occurred later with AHe ages ranging from ~16.5 to ~0.79 Ma. Here most cooling and exhumation occurred in the late Miocene, constrained by AHe ages ~11-8 Ma from the High Zagros fault, and exhumed Paleozoic clasts in synorogenic strata. Zircon (U-Th)/He (ZHe) ages from bedrock samples across the High Zagros are reflective of the pre-collisional thermal history of the Zagros and Neotethyan continental margin. The preservation of pre-collisional ZHe ages limits the pre-Miocene maximum burial temperature of the exhumed strata to <180°C, and indicate <7-9 km of maximum exhumation in the central Zagros. This study shows that thrust activity in the High Zagros and continental suturing along the Zagros suture was underway by at least 19 Ma, and initiated no later than latest Oligocene to early Miocene time (~23 Ma).