Discovery and Genetic Mechanism of Basic Granulite in the Altay Orogenic Belt, Xinjiang, NW China

Abstract

Abstract Altay granulite (AG), which represents the product of high‐grade metamorphism in the lower crust, was newly found in the Wuqiagou area, Fuyun County in the Altay orogenic belt, Northwest China. It is composed mainly of hypersthene, augite, basic plagioclase, amphibole and brown biotite. Its mineral compositions of amphibole and biotite are rich in Mg/(Mg+Fe2+) and Ti. Geochemically, the AG is enriched in Mg/(Mg+Fe2+) and Al2O3, and poor in CaO, with depletion of U, Th, K and Rb contents. Furthermore, geochemical data reflect that the protolith of the AG is igneous‐genetic calc‐alkaline basalt formed under an island arc environment. The AG has ΣREE of 92.38–96.58 ppm and enriched LREE model with weak positive Eu anomaly of 1.09–1.15. In the MORB normalized spider diagram, the AG shows tri‐doming pattern with a strong negative Nb anomaly and medium negative P and Ti anomalies, reflecting that the AG has tectonic relation with subduction or subduction‐related materials. The P‐T conditions of peak metamorphism of the AG are 750–780°C and >0.6–0.7 GPa. Retrograde metamorphism implies that the protolith of the Altay granulite might undergo a metamorphic process along a clockwise P‐T trajectory. Therefore, the formation and evolution of the AG may have a genetic association with continental collision/orogeny and the AG was taken into the Late Paleozoic meta‐strata by way of tectonic emplacement.