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.

摘要

伊朗晚古生代岩石组合，特别是 A 型火成岩很少出露，但它们是重建特提斯洋演化史的关键。来自伊朗西北部 Pir-Eshagh 的代表性流纹岩样品的锆石 U-Pb 测年得出早石炭世（维森）结晶年龄为 340 ± 2.7 Ma。喷出流纹岩具有A ₁A型岩浆的亚型，为伸展盆地内的岩浆活动提供了证据。岩石的成分是金属铝质至微铝质和富含钾的，具有与 OIB 相似的微量元素特征。低 Y/Nb 和 Ce/Nb 比率与源富集和地壳污染的组合一致，最终研究的流纹岩是由富集地幔衍生的基性母岩浆分步结晶形成的，具有地壳相互作用。特提斯洋及其边界的古地理重建表明，原始特提斯洋并未在伊朗板块扩散，尽管以蛇绿岩单元形式存在的古特提斯和新特提斯的证据保存完好。