东天山三岔口地区早、晚古生代岩体成因及其对康古尔缝合带演化的意义  

Petrogenesis of Early and Late Paleozoic Plutons in Sanchakou Area of East Tianshan and Their Implications for Evolution of Kangur Suture Zone

作　　者：王超[1,2] 陈斌[3] 马星华[4] 鄢雪龙[5] 

机构地区：[1]北京大学地球与空间科学学院,北京100871 [2]北京大学造山带与地壳演化教育部重点实验室,北京100871 [3]合肥工业大学资源与环境工程学院,安徽合肥230009 [4]中国地质科学院矿产资源研究所,国土资源部成矿作用与资源评价重点实验室,北京100037 [5]万宝矿产有限公司,北京100053

出　　处：《地球科学与环境学报》2015年第5期52-70,共19页Journal of Earth Sciences and Environment

基　　金：国家305项目(2011BAB06B04-2);国家自然科学基金项目(41202033)

摘　　要：对东天山地区三岔口矿岩体和三岔口东岩体的成因及构造背景进行探讨。三岔口矿岩体为一套花岗闪长岩一闪长岩体，形成于443Ma，为晚奥陶世岩浆作用产物。三岔口矿岩体具有轻稀土元素及大离子亲石元素富集、高场强元素亏损的特征，表明其形成于岛弧环境，高放射成因Nd（εNd（t）=6．6～7．5）和低初始N（87Sr）／N（86Sr）值（0．70369～0．70389）表明岩浆混合中的基性端元很可能起源于俯冲带亏损的岩石圈地幔，幔源岩浆底侵导致下地壳部分熔融，并与生成的花岗质熔体混合形成中酸性岩浆。三岔口东岩体为一套花岗岩一花岗闪长岩一闪长岩体，侵位时代约为322Ma，属于中亚造山带碰撞后岩浆作用的产物。三岔口东岩体同样具有岛弧岩浆特征，富集轻稀土元素及大离子亲石元素，亏损高场强元素，但其岛弧特征继承自其下地壳源区的性质，东天山地区下地壳主要是早古生代形成的深埋弧岩浆岩拼贴而成的。三岔口东岩体同样由壳幔岩浆混合作用形成，其基性端元可由区内同期基性一超基性岩体模拟。三岔口矿火山弧岩浆组合的确立可将康古尔地区俯冲作用的时间追溯至奥陶纪。晚石炭世早期，康古尔缝合带区域构造由挤压向拉伸转换，三岔口东岩体对应区域的后碰撞构造演化阶段。The petrogenesis and tectonic setting of Sanchakou deposit pluton and East Sanchakou pluton in East Tianshan area were discussed. Sanchakou deposit pluton consists mainly of granodiorite-diorite, and LA-ICP-MS zircon U-Pb dating results indicate that Sanchakou deposit pluton forms at 443 Ma and is the product of Late Ordovician magmatism. This pluton exhibits island arc setting with the characteristics of enrichment in light rare earth element （LREE） and large ion lithophile element （LILE）, and depletion in high field strength element （HFSE）. High εNd（t） （6. 6-7. 5） and low initial N（87Sr）/N（86Sr） （0. 703 69-0. 703 89） suggest that the mafic end-member during magma mixing could have been originated from a young lithospheric mantle source, which is previously metasomatized by subduction zone melts/fluids in Early Paleozoic. Underplating of mantle-derived basaltic magma leads to partial melting of lower crust. Mixing of basaltic magma and the resultant crustal granitic melt forms the intermediate and acid magma. East Sanchakou pluton is mainly made up of granite-granodiorite-diorite, and LA-ICP-MS zircon U-Pb dating results suggest that this pluton is emplaced at about 322 Ma and is the product of post collisional magmatism of Central Asian orogenic belt. This pluton also exhibits island arc setting with the characteristics of enrichment in LREE and LILE, and depletion in HFSE, but the island arc setting characteristics are probably inherited from the lower crust source, which is dominated by Early Paleozoic deep island arc magmatite. This pluton is also formed by the mixing of crustal-mantle magma, and its marie end- member can be simulated by the homochronous mafic-ultramafic pluton in East Tianshan area. The establishment of volcanic arc magmatic assemblage of Sanchakou deposit pluton shows that the subduction time in Kangur area can date back to Ordovician. Region tectonic transforms extrusion into extension at the early Late Carboniferous, East Sanchakou pluton is corresponding

关 键 词：花岗岩 壳幔岩浆混合 古生代 岛弧 康古尔缝合带 构造演化 东天山 新疆 

分 类 号：P581[天文地球—岩石学]