U-Pb zircon geochronology of the Daraban leucogranite, Mawat ophiolite, Northeastern Iraq: A record of the subduction to collision history for the Arabia-Eurasia plates

摘要

The Mawat ophiolite is part of the Mesozoic Neo-Tethyan ophiolite belt of the Middle East and is located in the Zagros Imbricate Zone of Iraq. It represents fossil fragments of the Neo-Tethyan oceanic lithosphere within the Alpine collisional system between the Arabian and Eurasia Plates. The first U-Pb zircon dating of the Daraban leucogranite from the Mawat ophiolite provides a 207Pb-206Pb age of 96.8 +/- 6.0 Ma. The age is 59.0 +/- 6.0 m. y. older than the previously published age of the Daraban leucogranite obtained by 40Ar-39Ar muscovite dating method. The U-Pb dating of magmatic zircons collected from the Daraban leucogranite, which intrudes into the Mawat ophiolite, reveals that melting of the pelagic sediment beneath the hot Zagros proto-ophiolite in an intra-oceanic arc environment led to anatexis at the subduction front and the generation of granitic melts at 96.8 +/- 6.0 Ma, which were emplaced in the overlaying mantle wedge. This process was a response to the initial formation of the Neo-Tethys ophiolite above a northeast-dipping intra-oceanic subduction zone at 96.8 +/- 6.0 Ma. Published 40Ar-39Ar muscovite dating from the same leucogranite dike yields plateau ages of 37.7 +/- 0.3 Ma, reflecting that the age was reset during the Arabia-Eurasia continental collision. Therefore, the bimodal age populations from the granitic intrusion in the Mawat ophiolite preserve a record of the subduction to the collision cycle of the Zagros Orogenic Belt. The 59.0 +/- 6.0 m. y. age difference from the Daraban leucogranite represents the duration of the subduction-collision cycle of the Zagros Orogenic Belt in the Kurdistan region of Iraq and the time span for the closure of the Neo-Tethys Ocean along the northern margin of the Arabian plate.