西准噶尔南部晚古生代侵入岩特征和构造背景

西准噶尔地区南部达拉布特断裂两侧广泛发育晚古生代花岗岩类，其锆石U-Pb年龄范围为337~276 Ma，属早石炭世-早二叠世.基于前人相关研究资料和成果，总结区内花岗岩类的岩石学、地球化学特征，认为：①岩石类型从早到晚由中性的闪长岩向酸性的花岗岩及碱长花岗岩转变.相应地，成因类型由埃达克岩质花岗岩→岛弧I型花岗岩→A型花岗岩.②岩石系列从早到晚由钙碱性向高钾钙碱性及后期钾玄岩系列转变.相应地，Na2O/K2O比值亦由大于1向小于1转变.③从早到晚区内花岗岩类的∑REE、δEu、L/H及Sr、Yb含量均呈规律性变化.并且相对富集LILE，亏损HFSE和不同程度亏损Nb、Ta.④均具有高正εNd（t）、低（87Sr/86Sr）i值和Nd模式年龄较小的特征.⑤在构造环境判别图解上，区内花岗岩从早到晚显示出由碰撞挤压向后碰撞伸展体制转换的趋势.上述几点说明区内花岗岩可能主要产出于后碰撞挤压-伸展转换和伸展拉张的构造背景，并且早阶段的岩浆活动可能与俯冲-碰撞背景下的俯冲板片断离密切相关.

CHARACTERISTICS AND TECTONIC SETTING OF LATE PALEOZOIC PLUTONS IN THE SOUTH OF WESTERN JUNGGAR

Abundant Late Paleozoic granitoid, which emplaced during Early Carboniferous Visean to Early Permian Artinskian with zircon U-Pb ages ranging from 337 to 276 Ma, is distributed along both sides of the Dalabute fault in the south of Western Junggar. Based on the previous published geological and geochemical data about the granitoid in this area, this paper concludes the changing tendency of the granitoid from early to late： 1 ） In corresponding to the rock type change from diorite to granite and alkali feldspar granite, the genetic types show the variation of adakitic granite - arc I-type granite - A-type granite. 2） The rock series present a regular variation of CA - HKCA - SH, with the ratios of Na20/K20 turning from Na20/K20 〉 1 to Na20/K20 〈 1, correspondingly. 3） The ∑ REE, 8Eu, L/H and contents of Sr and Yb of the granitoid vary regularly, with relatively enriched LILE but depleted HFSE, such as Nb, Ta, etc. 4） All the granitoid have high 6Nd （t） and low （S7Sr/S6Sr）i values, with young Nd-model ages. 5） On the discrimination diagram for tectonic setting, that of the granitoid turns from compressional setting associated with subduction-collisional to extensional setting of postcollision. All of these suggest that the granitoid should be resulted from the transition from compression to extension. The early magmatism is probably related to the breakup of the subducted slab.