THE MESO-CENOZOIC WILSON CYCLE OF IRAN

The Wilson Cycle describes the cyclical opening and closing of ocean basins. Along with its terrigeneous complement, the Supercontinent Cycle, it is a central implication of plate tectonics. In spite of the key role that it plays in our science, there is surprisingly no evidence until now for a Mesozoic or Cenozoic (<250 Ma) Wilson Cycle. Recent advances in understanding the geologic evolution of Iran and its western extension in Turkey indicates a ongoing Wilson Cycle. This began when Cadomian (~550 Ma) continental crust rifted and drifted away from northern Gondwana in the Late Paleozoic and collided with Eurasia ~250 Ma. Accretion was followed by Jurassic rifting along the southern Iran-Turkey margin. This continental rift is best preserved as the Sanandaj-Sirjan Zone (SaSZ), which also represents a volcanic rifted margin. Jurassic (~180-150 Ma) rifting was followed in Early Cretaceous time by subsidence to form a S-facing passive continental margin, with a break-up unconformity between the SaSZ and overlying thick transgressive sediments. These sedimentary rocks host abundant sediment-hosted Pb-Zn deposits, as expected for young passive margins. This passive margin collapsed ~95 Ma to form a new subduction zone, 2800 km long from Cyprus to Oman-Makran. Evidence of subduction initiation (SI) is preserved in ophiolites of this age in what became the forearc in Zagros. Mid-Cretaceous ophiolites, sedimentary basins, and core complexes are found well to the north of Zagros, indicating that what became the upper plate was strongly stretched during SI. This is the first compelling case of a <250 Ma SI at a passive margin and we are using 3D explore how it happened. Normal subduction began in the Late Cretaceous, forming a strongly extensional Andean-type margin and the Urumieh-Dohktar Magmatic Belt. Collision with Arabia began earlier (Eocene) in Turkey than in Iran (Miocene), so evidence of rifting and SI is best preserved in Iran. Porphyry copper mineralization in Iran is mostly hosted by Miocene and younger adakites, which formed by upper plate shortening and crust thickening following continental collision. Continuing collision with Arabia completes the cycle.