柴北缘绿梁山地区早古生代弧后盆地型蛇绿岩的年代学、地球化学及大地构造意义  

Geochronology,geochemistry and significance of the Early Paleozoic back-arc type ophiolite in Lvliangshan area,North Qaidam

作　　者：朱小辉[1,2] 陈丹玲[2] 刘良[2] 赵姣[2] 张乐[2,3] 

机构地区：[1]国土资源部岩浆作用成矿与找矿重点实验室,中国地质调查局西安地质调查中心,西安710054 [2]西北大学大陆动力学国家重点实验室,西北大学地质学系,西安710069 [3]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州510640

出　　处：《岩石学报》2014年第3期822-834,共13页Acta Petrologica Sinica

基　　金：国家基础研究规划"973"项目(2009CB825003);国家自然科学基金项目(41072051);中国地质调查局工作项目(1212011121137)联合资助

摘　　要：岩石学、地球化学、年代学及Lu-Hf同位素综合研究表明在柴北缘西段绿梁山大平沟地区出露一套弧后盆地型蛇绿岩,岩石类型主要包括变质橄榄岩、变火山岩、变辉长岩及斜长花岗岩。其中变火山岩具有LREE亏损,类似N-MORB的稀土配分模式,同时又具有富集大离子亲石元素,亏损Nb、Ta等高场强元素的岛弧火山岩的地球化学特征,应形成在弧后盆地环境。斜长花岗岩为低钾准铝质花岗岩,具有LREE略微富集,HREE平坦的稀土配分型式,显示强烈Eu正异常,其εHf(t)值介于13.7～15.3之间,为变辉长岩部分熔融的产物,熔融温压条件可能为P=0.8～0.9GPa和T=～800℃。年代学研究结果表明变辉长岩的形成时代为535±2Ma,斜长花岗岩的形成时代为493±3Ma,指示本地区弧后盆地拉张时限至少介于493～535Ma之间,而柴北缘地区古大洋俯冲消减作用应早于535Ma。Petrological, geochemical, geochronological and Lu-Hf isotopic studies indicate there is an ophiolite m61ange in the Lvliangshan area, west segment of the North Qaidam of China. This ophiolite melange mainly consists of metaperidotite, metavolcanie, metagabbro and plagiogranite. The geochemical characteristics of metavolcanic show LREE depletion, similar to N-MORB, and its spider diagram shows the enrichment of the LILE and depletion of HFSE which formed in a back-arc basin setting. The plagiogranite is low-potassium metaluminous granite with the characteristics of relative enrichment of LREE and positive Eu anomaly. Zircons from plagiogranite have sHf （t） = 13. 7 - 15. 3, indicating the plagiogranite could have originated by partial melting of metagabbro under the conditions of P = 0. 8 - 0.9GPa and T = -800℃. Zircon U-Pb geochronological studies suggest that the formation ages of metagabbro and plagiogranite are 535 ± 2Ma and 493 ±3Ma, respectively. In this study, we proposed the existence of back-arc basin in Lvliangshan area between 493 -535Ma, and the oceanic slab subduction occurred before 535Ma in the North Qaidam.

关 键 词：地球化学 锆石U-Pb年龄和Hf同位素特征 弧后盆地型蛇绿岩 柴达木盆地北缘 

分 类 号：P588.1[天文地球—岩石学] P597.3[天文地球—地质学]