Tethyan oceans reconstructions with emphasis on the Early Carboniferous Pir-Eshagh A-type rhyolite and the Late Palaeozoic magmatism in Iran
Susan Jamei, Mansour Ghorbani, Ian S. Williams, Mohsen Moayyed
Abstract
The Late Palaeozoic rock associations, in particular A-type igneous rocks, of Iran are rarely exposed, but they are key to reconstructing the evolutionary history of the Tethyan oceans. Zircon U–Pb dating of a representative rhyolite sample from Pir-Eshagh, NW Iran, yields an Early Carboniferous (Visean) crystallization age of 340 ± 2.7 Ma. The extrusive rhyolite has the chemical characteristics of the A1 subtype of A-type magmas, providing evidence for a magmatic activity within extensional basin. The composition of rocks is metaluminous to slightly peraluminous and K-rich, with trace element signatures similar to those of OIB. Low Y/Nb and Ce/Nb ratios are consistent with a combination of source enrichment and crustal contamination and ultimately that the studied rhyolites have formed by fractional crystallization from an enriched mantle-derived mafic parental magma, with crustal interactions. Palaeogeographic reconstructions of the Tethyan oceans and their borders imply that the Proto-Tethys Ocean has not spread in Iranian plate, although evidence for Paleo-Tethys and Neo-Tethys in the form of ophiolitic units is well-preserved. The Late Palaeozoic magmatic rocks of Iran define a trend parallel to the ridge separating Neo-Tethys the Iranian plate from Arabia and demonstrate that the separation of the Cimmerian terranes from northern Gondwana by the opening of the Neo-Tethys Ocean, and their drift northwards, began in the Late Devonian to Early Carboniferous.