Sapphirine-bearing high pressure mafic granulite and its implications in the south Altyn Tagh

Abstract

Sapphirine-bearing high pressure mafic granulites are recognized in the Bashiwake area of the south Altyn Tagh. Mafic granulites and associated peridotites occur as lenses within kyanite-bearing high pressure felsic granulites. Sapphirine occurs as intergrowths with corundum, spinel and Ca-rich plagioclase in symplectite in between garnet and clinopyroxene. Reaction textures and mineral compositions indicate that sapphirine-bearing symplectites formed by reactions consuming kyanite, garnet and clinopyroxene. Therefore, both petrographic observations and the mineral compositions suggest that these quartz-free mafic granulites had an eclogite origin with an assemblage of garnet + clinopyroxene + kyanite, which is estimated to be stable atT = 1000 °C andP ⩾ 2.1 GPa. The sapphirine-bearing symplectites are resulted from isothermal decompression or decompression with slight cooling during exhumation of the host rock.