新疆阿勒泰青河地区玛因鄂博二叠纪辉长岩年龄、地球化学特征及地质意义

Age,Geochemistry and Geodynamic Implications of the Permian Gabbroic Intrusions along the Erqis Belt in Qinghe County,Southern Altaid

新疆阿勒泰青河县玛因鄂博断裂带内,发育大量的辉长岩岩脉(株),辉长岩侵入到前寒武纪片麻岩和前二叠纪的不同类型花岗岩中,主要的岩石类型包括含长辉石岩、斑状细粒含长辉石岩、辉长岩以及少量的粗粒辉长岩.锆石SHRIMPU-Pb年龄表明这些辉长岩形成时代为272.5±2.4Ma.系统的元素地球化学及同位素地球化学研究表明,这些辉长岩具有高Mg-Fe、低Ti、低碱度特征,轻稀土及大离子亲石元素轻微富集,具有高的Nd初始值.上述特征表明,玛因鄂博辉长岩原始岩浆来自被交代的极度亏损的岩石圈地幔高度部分熔融所形成的拉斑质玄武岩浆.二叠纪辉长岩与阿勒泰南缘喀拉通克含Cu-Ni硫化物矿超镁铁—镁铁杂岩和大量的二叠纪花岗岩形成时代一致,是塔里木二叠纪大火成岩省在阿勒泰南缘的岩浆岩响应.

Gabbroic intrusions widely occur along the Erqis belt＇in Qinghe area, southern of Altaid. They intrude the Pre-Permian granites and Precambrian metamorphic rocks and main rock types include fine- grained plagioclase-bearing pyroxenite, gabbro and minor coarse-grained gabbro. Zircon SHRIMP U-Pb age indicates that these gabbros crystallized at ca.273 Ma. Geochemistry analyzes exhibit they enrich in Mg, A1, Fe and depleted in Ti and total alkali. Combing with their Sr-Nd istopic characteristics, we suggest that they derived from high-degree partial melting of a pre-metasomatized extremely depleted lithospheric mantle source. Integrating the voluminous Permian basaltic igneous activity in Tarim Block and the western part of the Central Asian Orogenic Belt, the Mayinebo gabbros are igneous product of the Permian Tarim mantle plume.