Geochronology and tectonic significance of A-type granite from Misho, NW Iran: Implications for the detachment of Cimmeria from Gondwana and the opening of Neo-Tethys

Abstract

The Cimmerian Terrane, part of which forms the Central Iranian Plateau, is one of several continental fragments produced during the early- to mid-Palaeozoic breakup of the northern margin of Gondwana. Magmatic evidence for the final separation of the Terrane from Gondwana and formation of the intervening Neo-Tethys Ocean is preserved in the Misho Mountains SW of Marand, NW Iran. A small ((similar to)30 km(2)) body of subalkaline granite intruding Precambrian sedimentary rocks of the Kahar Formation has numerous chemical features that identify it as an A-type granite, including high Ga/Al, K2O + Na2O, FeOt/(FeOt + MgO) and incompatible elements (LILE and HFSE), and low CaO and P2O5. Such features are consistent with the asthenospheric upwelling above a rising mantle plume. Zircon ages of 350.8 +/- 3.0, 345.4 +/- 3.2, and 343.6 +/- 4.0 Ma measured on three samples of the Misho A-type granite along with the same granites exposed in the western domain (Herris area, (similar to)306 Ma) reveal that the crystallization process occurred sequentially in different stages. The obtained ages record detachment of the Cimmerian Terrane from Gondwana and the initiation of Neo-Tethys at least in the Early Carboniferous, significantly earlier than previous researchers have proposed.