西准噶尔北部比图岩体的地球化学特征及构造环境

选择西准噶尔北部晚志留世比图岩体进行系统的岩石学、地球化学特征研究,揭示其岩石成因及形成的大地构造环境。比图岩体岩性以钾长花岗岩为主,边部为碱性花岗岩、正长岩和闪长岩。钾长花岗岩和正长岩贫Mg O(0.3%~0.5%)、CaO(0.8%~1.1%),稀土含量高(105~204μg/g),Eu异常明显,属于碱性高分异I型花岗岩;碱性花岗岩富碱(6.8%)、贫Al_2O_3(9.9%),稀土含量较高(271μg/g),极度亏损Sr、Ba、Eu,属于典型的A型花岗岩。闪长岩富MgO(4.1%)和CaO(7.5%),稀土含量较高(93μg/g),属于高钾钙碱性系列,源自富水地幔的部分熔融。岩体地球化学特征表明比图钾长花岗岩、碱性花岗岩、正长岩均是新生地壳部分熔融之后不同程度结晶分异的产物;比图岩体的各种岩性普遍具有富碱、轻稀土和大离子亲石元素(Rb、K),弱亏损高场强元素(Nb、Ta)的地球化学特征,形成于后碰撞的伸展环境。

Geochemical characteristics and tectonic setting of Bitu complex in northern West Junggar

Systematic petrological and geochemical analysis were conducted Late Silurian Bitu complex in northern West Junggar, with the attempt to reveal its petrogenesis and tectonic setting. The Bitu complex mainly consists of syenogranite and subordinate alkaline granite, syenite and diorite. The syenogranite and syenite are highly-fractionated I-type granitoids, characterized by low contents of MgO (0.3%~0.5%), CaO (0.8%~1.1%), high REE (105~204 μg/g) and strong Eu anomalies. The alkaline granite shows low Al2O3 (9.9%), high total alkalis (6.8%) and REE (271 μg/g), strong depletion in Sr, Ba, Eu, with the affinity of A-type granite. The diorite exhibits high MgO (4.1%) and CaO (7.5%),and relatively high REE abundance (93 μg/g). It belongs to high-K calc-alkaline series and was formed by partial melting of H2O-rich mantle. Geochemical data suggest that granitic rocks of Bitu complex were originated from crystallization differentiation of partial melting juvenile crust. The Bitu complex is enriched in alkali, light rare earth elements and large ion igneous elements (such as Rb and K) and slightly depleted in Nb and Ta, indicating that it was generated in a post-collisional extensional setting.