东昆仑中部缝合带清水泉麻粒岩锆石SHRIMP U-Pb年代学研究  

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

作　　者：李怀坤[1] 陆松年[1] 相振群[1] 周红英[1] 郭虎[1] 宋彪[2] 郑健康[3] 顾瑛[3] 

机构地区：[1]天津地质矿产研究所,天津300170 [2]北京离子探针中心,北京100037 [3]青海省地质调查院,青海西宁810012

出　　处：《地学前缘》2006年第6期311-321,共11页Earth Science Frontiers

基　　金：国家自然科学基金资助项目(40032010-C);国土资源大调查项目(200313000060;1212010560801-04)

摘　　要：东昆仑中部缝合带清水泉一带发育石榴斜长紫苏麻粒岩、紫苏辉石黑云母石榴子石麻粒岩、石榴二辉斜长麻粒岩和石榴单斜辉石麻粒岩，它们与混合岩化黑云母石榴子石变粒岩、黑云母辉石变粒岩、石墨大理岩、含透辉石透闪石大理岩、透辉石大理岩、黑云斜长角闪岩和片麻岩等高级变质岩系以及纯橄岩、辉橄岩、橄长岩、辉长岩、辉绿岩和玄武岩等共同构成蛇绿混杂岩。麻粒岩相变质作用的温压条件为丁=760-880℃，P=830～1200MPa，为高温中高压麻粒岩相变质作用，估算其形成深度为40～45km。麻粒岩相变质作用的SHRIMP锆石U-Pb年龄为（507．7±8．3）Ma。清水泉地区蛇绿岩形成于～520Ma，到～508Ma时俯冲至地下40-45km深处而发生中高压麻粒岩相变质作用，然后发生构造折返而剥露至地表。证实了清水泉高级变质岩和基性超基性岩片是形成于早中寒武世的蛇绿混杂岩，标志一个古生代早期的非常重要的板块汇聚边界，这对于进一步研究东昆仑造山带构造演化、乃至中国西部大地构造格局具有非常重要的意义。A suite of basic granulites including garnet-plagioclase-hypersthene granulite, hypersthene-biotitegarnet 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=7604880℃ and pressure p= 8. 34 12 kbar, the conditions of high temperature and medium to high pressure, occurring at a depth range of 40445 km. The SHRIMP U-Pb zircon age of granulite facies metamorphism of the garnet two-pyroxene-plagioclase granulite is 507.7±8. 3 Ma （2a）. Ophiolites preserved in the Qingshuiquan Area originated at 4520 Ma, and subducted to a depth range of 40445 km by 4508 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.

关 键 词：SHRIMP U-PB年龄 麻粒岩 构造混杂岩 东昆仑中部缝合带 

分 类 号：P597.3[天文地球—地球化学] P588.3[天文地球—地质学]