SHRIMP U-Pb zircon age of the granulite from the Qingshuiquan area, Central Eastern Kunlun Suture Zone
SHRIMP U-Pb zircon age of the granulite from the Qingshuiquan area, Central Eastern Kunlun Suture Zone
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作者：
Li Huai-kun
东昆仑缝合带中段清水泉地区发育石榴石-斜长石-斜长石麻粒岩、石榴石-斜长石-石榴石麻粒岩、石榴石-斜长石-斜长石麻粒岩、石榴石-单斜长石麻粒岩等一组基性麻粒岩。这些麻粒岩与一系列高品位变质岩一起，包括混合云母-石榴石麻粒岩、黑云母-辉石麻粒岩、石墨大理岩、含透辉石-透闪石大理岩、透辉石大理岩、黑云角闪岩和片麻岩，以及纯橄榄岩、方辉橄榄岩、斜方沸石、辉长岩、辉绿岩和玄武岩等岩浆岩，定义了蛇绿岩构造混杂岩。清水泉麻粒岩的变质作用发生在温度T=760~880℃、压力p=8.3~12 kbar的高温、中高压条件下，发生深度为40~45 km。石榴石二辉石斜长石麻粒岩麻粒岩相变质SHRIMP U-Pb锆石年龄为507.7±8.3 Ma(2σ)。清水泉地区保存的蛇绿岩起源于~520 Ma，俯冲至40~45 km深度范围~508 Ma，经历高温、中高压麻粒岩相变质作用，后受构造抬升并折返至现地表。研究表明，清水泉地区的高品位变质岩和镁铁质-超镁铁质岩浆岩勾画出早至中寒武世构造混杂岩，是古生代早期重要的板块组合边界。
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.