Confirmation of ultrahigh-temperature metapelitic granulite in the Altay orogen and its geological significance

Abstract

Through petrography, mineral compositions and P-T estimate results, an ultrahigh-temperature (UHT) metapelitic granulite has recently been identified from near Kalasu in the east of Altay city, with an assemblage gt-opx-sil-cd-sp-bt-pl-qtz. The orthopyroxene has a high-Al feature, and its Al2O3 content is as high as 8.7 wt%, indicating a UHT metamorphic condition. Its peak metamorphic condition is estimated as: P = ~0.80 GPa, T = ~960 °C. Metamorphic textural relations and P-T estimate results show a post-peak near-isobaric cooling anticlockwise P-T path. Zircon U-Pb age results (271 ± 5 Ma) support that the UHT metamorphic event in the region occurred in the Permian. The identification of the UHT metapelitic granulite from near Kalasu confirms the existence of the Permian UHT metamorphism in the Altay orogen, implying that the Permian extensional tectonic setting of a high-heat flow in the southern part of the Altay orogen may be closely associated with the Permian Tarim mantle plume activity.