Panafrican basement and Mesozoic gabbro in the Zagros orogenic belt in the Dorud-Azna region (NW Iran): Laser-ablation ICP-MS zircon ages and geochemistry

摘要

The Dorud-Azna region of the Sanandaj-Sirjan metamorphic zone (sswz) in NW Iran is part of the Zagros orogenic belt and exposes an amphibolite-grade metamorphic succession of mixed continental (e.g., the granitic Galeh-Doz orthogneiss) and oceanic or rift (e.g., various amphibolites) origin, which is intruded by the Darijune gabbro. Laser-ablation ICP-MS U-Pb zircon ages of 608 +/- 18 Ma and 588 +/- 41 Ma of the granitic Galeh-Doz orthogneiss indicate a Panafrican basement similar to that of the Yazd block of Central Iran. We therefore interpret this part of the SSMZ to represent a previously subducted part of the Panafrican basement of the Iranian microcontinent Based on geochemistry, amphibolites and metagabbros from the Amphibolite unit representially potentially the cover on the Panafrican Galeh-Doz orthogneiss are interpreted to have their origin in a likely Upper Paleozoic to Mesozoic rift or E-MORB ophiolite succession. One of the metagabbros, here termed Dare-Hedavand metagabbro yield a Pb-206/U-238 mean age of 314.6 +/- 3.7 Ma. Talc-bearing greenschists to epidote amphibolites of the Triassic June complex formed in a similar, but younger environment. Furthermore, the metamorphic complex is intruded by the Darijune gabbro, which yields a mean ICP-MS U-Pb zircon age of 170.2 +/- 3.1 Ma. The final stage of likely Jurassic greenschist facies-grade metamorphism postdates the gabbro intrusion. We interpret the Darijune gabbro to have resulted from the initial subduction of Neotethyan oceanic lithosphere in a continental arc setting. The new data combined with data from literature indicate that the SSMZ represents a tectonic element of a mixed continental and oceanic origin, likely accreted to Central Iran during a Jurassic tectonic process. The new data also constrains thick-skinned nappe stacking within the Sanandaj-Sirjan zone. (C) 2015 Elsevier B.V. All rights reserved.