R Jamali Ashtiani; Hassanzadeh J; M Rahgoshay; A Sharifi
Abstract
The Sanandaj-Sirjan zone is a NW-SE trending orogenic belt immediately north of the Zagros suture, which represents the former position of the Neotethys Ocean. This zone includes a Pan-African basement similar to the various terranes to the north in Central Iran. The crystalline basement is nonconformably ...
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The Sanandaj-Sirjan zone is a NW-SE trending orogenic belt immediately north of the Zagros suture, which represents the former position of the Neotethys Ocean. This zone includes a Pan-African basement similar to the various terranes to the north in Central Iran. The crystalline basement is nonconformably overlain by the Paleozoic-Triassic platform sediments, which in turn are unconformably covered by sedimentary and volcanic strata of the Jurassic arc. The Cretaceous carbonates overlie the older rocks with a regional angular unconformity. The Chadegan high-P metamorphic complex exposed along the upper Zayanderoud and consists of quartz schists, amphibolites, gneisses, marbles and eclogites, and is nonconformably underlain by the fossiliferous Permian carbonates, suggesting a Pre-Permian age. In this paper we present new data including whole rock major and trace element compositions, mineral chemistry and radiogenic isotope data for the selected metabasites. The high field strength element (HFSE) abundances and Sr-Nd-Hf ratios suggest tholeiitic compositions with distinct within plate affinity rather than MORB. We also present new 206Pb/238U zircon age of 568.0 ± 5.3 Ma for a crosscutting orthogneiss reconfirming the Late Neoproterozoic age for the granitic protolith. We conclude that previously presented Ar-Ar ages for white-micas in eclogites and gneisses are indicative of metamorphic crystallization due to the regional plutonic arc activity. A comparison is made with the well-investigated Menderes Massif in Turkey where an orthogneiss-metabsite association with similar age and chemistry makes extensive exposures. We also conclude that this rock complex is extended from Zayanderoud to Khoy and beyond to the Menderes Massif and discuss the connection with the final amalgamation tectonics of the Gondwana near the beginning of the Cambrian Period.
