Exhumation of the west-central Alborz Mountains, Iran, Caspian subsidence,and collision-related tectonics

Crystallization and thermal histories of two plutons in the west-central Al borz (also Elburz, Elburs) Mountains, northern Iran, are combined with cros scutting relations and kinematic data from nearby faults to determine the C enozoic tectonic evolution of this segment of the youthful Euro-Arabian col lision zone. U/Pb, Ar-40/Ar-39, and (U-Th)/He data were obtained from zirco n, biotite, K-feldspar, and apatite, The Akapol pluton intruded at 56 +/- 2 Ma, cooled to similar to 150 degreesC by ca, 40 Ma, and stayed near that t emperature until at least 25 Ma. The nearby Alam Kuh granite intruded at 6. 8 +/- 0.1 Ma and cooled rapidly to similar to 70 degreesC by ca. 6 Ma. Thes e results imply tectonic stability of the west-central Alborz from late Eoc ene to late Miocene time, consistent with Miocene sedimentation patterns in central Iran. Elevation-correlated (U-Th)/He ages from the Akapol suite in dicate 0.7 km/m.y. exhumation between 6 and 4 Ma, and imply similar to 10 k m of Alborz uplift that was nearly synchronous with rapid south Caspian sub sidence, suggesting a causal relation, Uplift, south Caspian subsidence and subsequent folding, reversal of Alborz strike-slip (from dextral to sinist ral) and(?) eastward extrusion of central Iran, coarse Zagros molasse depos ition, Dead Sea transform reorganization, Red Sea oceanic spreading, and(?) North and East Anatolian fault slip all apparently began ca. 5 +/- 2 Ma, s uggesting a widespread tectonic event that we infer was a response to buoya nt Arabian lithosphere choking the Neo-Tethyan subduction zone.