TECTONIC EVOLUTION OF THE NEYRIZ OPHIOLITE, IRAN: AN ACCRETIONARY PRISM MODEL

Abbed Babaei, Hassan A. Babaie, Mohsen Arvin

Abstract


The Neyriz ophiolite complex in south central Iran is an assemblage of Upper Cretaceous crustal and mantle ophiolite sequences and related pelite, thinbedded limestone, chert, and mélange with Permian-Cretaceous mega-clasts. The complex is thrust on shallow marine limestone of the Sarvak Formation to the southwest, and it is overthrust by arc-related volcanic and volcaniclastic rocks and forearc basin sediments from the northeast. The tectonic history of the ophiolite complex involved (i) rifting of the Afro-Arabian plate due to a late Carboniferous-early Permian uplift, which led to block-faulting along Precambrian basement faults and opening of the narrow Neo-Tethyan oceanic basin, (ii) sea-floor spreading, starting probably from Triassic, that produced an oceanic crust, and (iii) SW-NE directed contraction and arc-related volcanism, in the Late Cretaceous, through which slivers of the Neo-Tethyan oceanic lithosphere and overlying sediments were accreted into an accretionary prism, and then thrust onto the passive, block-faulted northeastern margin of the Afro-Arabian plate, along a northeast-dipping subduction zone. The close correspondence between the cooling ages of the ophiolitic gabbro and plagiogranite, deposition of thin limestone interbedded with radiolarian chert, and metamorphism of mylonitic amphibolite along the sole detachment of the ophiolitic complex, suggests that the emplacement of the complex occurred in a relatively short period of time during which a segment of young rocks of a subducting mid-ocean ridge was thrust under accreted contemporaneous and older sedimentary cover. Continued contraction led to offscraping and/or underplating of pelagic, abyssal, and slope facies, deposited along the leading, passive margin of Afro-Arabian plate, under the crustal and mantle ophiolite sequences, forming an accretionary prism. Tholeiitic, arc-related basalt and volcaniclastic rocks covered the prism in the forearc region. The prism grew by incorporating slivers of Permian-Upper Cretaceous limestone, which capped normal- faulted blocks of the passive margin, and radiolarian chert and pelite which were deposited between the blocks, forming the Hajiabad mélange. The final collision of the Eurasian and Arabian plates during the Miocene, which started when the Arabian plate separated from Africa, led to internal thrusting of the complex and the development of the cataclastic Zagros Crush zone immediately to the northeast of the ophiolite belt.

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DOI: https://doi.org/10.4454/ofioliti.v30i2.241