Exhumation of old rocks during the Zagros collision in the northwestern part of the Zagros Mountains, Iran

Arabia-Eurasia convergence is accommodated in the Zagros Mountains of southwestern Iran and in the seismic belts of the central Caspian, Alborz, and Kopeh Dagh of northern Iran. The Zagros is a NW-trending fold-and-thrust belt made up of a 6-15-km-thick sedimentary pile, which overlies the Precambrian metamorphic basement. During the Zagros orogeny, some of the Precambrian basement and Lower Paleozoic strata were exhumed from depth and are now exposed in the Golpayegan region in the northwestern part of the Zagros Mountains. The tectonic evolution of the Golpayegan region and the exhumation of the old rocks are interpreted as the product of three major sequential geotectonic events. (1) Major thrusts formed during shortening and exposure of the basement rocks in the Aligudarz block. The rock units are strongly imbricated and sheared, which suggest a high amount of cumulative shortening in the northern Zagros. (2) NE-SW-trending extensional faults (e.g., Eastern Mute, Western Mute, and Mahallat faults) formed during lateral extensional movement after middle Miocene time. In this event, a set of NE-SW-trending horsts and grabens was formed. In the horsts (e.g., Hassan-Robat, Mute, and Mahallat horsts), the Precambrian basement rocks and Lower Paleozoic strata are exposed. (3) Strike-slip movements began that remain active today. Strike-slip motions are well documented for the late Pliocene-Quaternary period. In the Golpayegan region, the Shazand and Dehagh faults cut through the NE-trending normal faults and through Quaternary deposits. Drainages are displaced by approximately 4 km of dextral movement along the Shazand fault and near the city of Golpayegan.