SHRIMP U-Pb zircon age of the granulite from the Qingshuiquan area, Central Eastern Kunlun Suture Zone

A suite of basic granulites including garnet-plagioclase-hypersthene granulite, hypersthene-biotite-garnet granulite, garnet two-pyroxene-plagioclase granulite and garnet-clinopyroxene granulite are present in the Qingshuiquan Area of the Central Eastern Kunlun Suture Zone, Northwest China. These granulites together with a series of high grade metamorphic rocks, including migmatitized biotite-garnet granulite, biotite-pyroxene granulite, graphite marble, diopside-tremolite-bearing marble, diopside marble, biotite amphibolite and gneisses, and magmatic rocks, such as dunite, harzburgite, troctolite, gabbro, diabase and basalt, define an ophiolitic tectonic melange. The metamorphism of the Qingshuiquan granulites took place under temperature T=760~880℃ and pressure p=8.3~12 kbar, the conditions of high temperature and medium to high pressure, occurring at a depth range of 40~45 km. The SHRIMP U-Pb zircon age of granulite facies metamorphism of the garnet two-pyroxene-plagioclase granulite is 507.7±8.3 Ma (2σ). Ophiolites preserved in the Qingshuiquan Area originated at ~520 Ma, and subducted to a depth range of 40~45 km by ~508 Ma and experienced high temperature and medium to high pressure granulite facies metamorphism, and then were tectonically uplifted and exhumed to the present surface. This study demonstrates that the high grade metamorphic rocks and the mafic-ultramafic magmatic rocks in the Qingshuiquan Area outline an Early to Middle Cambrian tectonic melange, marking a significant plate assembly boundary of the early stage of Paleozoic.