Granulitic xenoliths from the Eocene and Oligocene volcanic rocks in NW of Central-East Iranian microcontinent: Evidence from petrology of deep crust
Abstract
Calc-alkaline to shoshonitic Eocene and alkaline Oligocene volcanic rocks are exposed in Godar-e-Siah and Toveiereh areas, respectively, northwest of the Central-East Iranian Microcontinent (CEIM). Granulitic xenoliths have been found in these volcanic rocks. The Godar-e-Siah xenoliths comprise the Ca-poor plagioclase (An33) + phlogopite + corundum + sillimanite + spinel ± garnet. This mineral assemblage corresponds to conditions characteristic of peak of granulite facies metamorphism. The Toveireh xenoliths consist of spinel and plagioclase as major minerals and corundum, rutile, ilmenite and magnetite as accessory ones. The presence of Al-rich minerals and the absence of quartz suggest the Al-saturated but Si-undersaturated nature for the xenoliths. Mineralogical characteristics, thermobarometry estimates and use of experimental petrogenetic grids indicate that the estimated P-T conditions for Toveireh (8 –10 kbar, 800 – 900 °C) and Godar-e-Siah (7.8 kbar, 780 °C) xenoliths are consistent with the granulite facies rocks near anatectic condition. The Toveireh xenoliths are Al-rich granulites (Al2O3 = 33 – 34 wt%) and have LREE-enriched patterns with large positive Eu anomalies (Eu/Eu* = 3 – 5). These patterns indicate that the plagioclase rich restites of the lower continental crust devel-oped as a result of the removal of Neoproterozoic-Cambrian S-type granitic magma. The Aeirakan S-type granites and the xenolith bearing rocks are located at the northwest of the CEIM along the Great Kavir Fault. The parental magma of the Aeirakan S-type granite which is located at northeast of the xenolith bearing sites (Toveireh and Godar-e-Siah) is formed by anatexis and dehydration melting of such Al-saturated Si-undersaturated crustal granulites during Pan-African orogeny. It is probable that some parts of these dehydrated materials are brought to the surface as granulitic xenoliths by Eocene and Oligocene volcanism in Godar-e-Siah and Toveireh areas, respectively. © 2024 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.