东天山星星峡缝合带早古生代强过铝质花岗岩的研究及其地质意义

铅炉子过铝质花岗岩带发育于中天山岛弧带南缘的星星峡缝合带内,为一长条形的二云母花岗岩。岩体地球化学特征是高Si、Al和K,低Mg、Fe的组份,全碱含量中等,σ=1.74～1.9,K_2ONa_2O,A/CNK1.1,属于高钾钙碱性过铝质花岗岩类(SP)。岩体的CaO/Na_2O和Al_2O_3/TiO_2比值都相对较低,分别为(0.06～0.07)和(48.9～55.3);REE、Nb、Y含量和Rb/Sr、Rb/Ba比值相对较高;Rb、Th和LREE相对富集,Ba、Si、Eu、Ti、P和HREE相对亏损;ε_(HF)(t)=-2.3～+1.6表明岩体还具有较高的锆石同位素特征,T_(2DM)变化范围为1573～1329 Ma。这些地质学和地球化学研究表明铅炉子二云母花岗岩形成于后碰撞的伸展环境中,是在高温、中低压条件下发生重熔形成的,其源岩为古老的地壳物质和年轻的增生物质通过物理风化作用形成泥质岩。本文通过测年获得二云母花岗岩锆石LA-ICPMS年龄为444.5±2.2 Ma,表明铅炉子过铝质花岗岩形成于晚奥陶世,是中天山岛弧带和公婆泉岛弧带的碰撞时间的上限,它也是中天山岛弧带与公婆泉岛弧带碰撞造山作用的产物,是中亚增生造山带的增生方式之一。

The study of Early-Paleozoic peraluminous granite(SP) and its tectonic significance in the Xingxingxia suture zone,eastern Tianshan Mountains,Xinjiang,northwest China

The Qianluzi granite intruded along the Xingxingxia fault at the south margin of the central Tianshan Mountains.The granite is characterized by high absolute Si,Al and K,whereas low Mg,Fe contents,K_2O＞Na_2O,A/CNK＞1.1,is high K calc-alkaline peraluminous granite(SP).The rocks also are characterized by relatively low CaO/Na_2O(0.06～0.07)and Al_2O_3/TiO_2(48.9～55.3)ratios;high REE,Nb and Y abundance,enriched LREE and LILE(Rb,U,Th,K);strongly depleted Ba,Sr P,Ti,Eu and HREE;relatively high zircon Hf isotopic(ε_(Hf)(t)=-2.3～+1.6).These characters indicate the Qianluzi granite is the post-collision granite;the source rocks are mud-rocks which are the mixtures matters that origin from the whethering of the growth crust and the old crust;is recycle of the accretionary crust.In the post-collision strike-extension setting,the mantle raised along the fault and lead partial-melting of the mud rocks.The Zircon U-Pb dating by LA-ICPMS shows that its crystallization age is 444.5±2.2 Ma,in the late Ordovician,limits the collision time of the central Tianshan tarrane and the Gongpoquan arc.Summary,the Qianluzi peraluminous granite(SP)is the result of the collision between the central Tianshan terrane and the Gongpoquan Tarrane,and is the one of the results of the crustal growth in the Central Asian Orogeny Belt.