东昆仑中灶火地区中三叠世花岗岩LA-ICP-MS锆石U-Pb定年、岩石成因及构造意义

摘要

东昆仑中灶火地区的石英闪长岩—花岗闪长岩—二长花岗岩具有连续的成分变化.岩石具有中等到高的SiO2含量(58.15％ ～71.12％),适度的高铝和全碱含量,为中—高钾钙碱性的准铝质Ⅰ型花岗岩.岩石相对富集大离子亲石元素和轻稀土元素,并亏损高场强元素,显示出弧岩浆岩的—般地球化学特征.锆石地质年代学分析获得石英闪长岩和花岗闪长岩的锆石结晶年龄约为243 Ma,表明本文研究的花岗岩类为中三叠世岩浆岩.结合地质、地球化学研究,这套花岗岩形成于陆缘弧环境,是古特提斯洋俯冲晚期的岩浆记录.其成因为俯冲动力学背景下,幔源岩浆的底侵作用导致下地壳部分熔融,随后壳源熔体与幔源熔体发生不同程度的混合形成母岩浆,又经历了较高程度的结晶分异形成石英闪长岩—花岗闪长岩—二长花岗岩序列.%Objectives:Based on Petrology study and method of zircon LA-ICP-MS age dating and geochemistry,to explore the Middle Triassic Granites petrogenesis and tectonic implications in the Zhongzaohuo Area,East Kunlun.Methods:Calculate the age of granites by zircon U-Pb dating and their petrology characteristics by whole rock analysis.Results:Plutons in the Zhongzaohuo area consists of quartz-diorite,granodiorite and monzogranite were emplaced in Middle Triassic as demonstrated by the ca.243 Ma zircon crystallization age for both the quartz-diorite and monzogranite units.These rocks have varying SiO2 contents,moderate to high Al2O3 and total Alkaline.They are middle—high potassium series,meta-aluminous granotoids.The geochemical and petrographic features indicate those rock suits are Ⅰ-type granite.This rock assembly shows enrichment of LREE and highly incompatible elements but depleted in high field strength elements typical of continental arc.The consistent linear variation between silica and other major elements and the gradual transition rather than intrusive and sharp relationship of the suites indicate an important role of fractional crystallization for the composition variation of the granotoids.Parental magma was formed by partial melting of crustal materials that heated by underplating of basaltic magma represented by gabbro in the adjacent region.Conclusions:During the subduction of the Paleo-Tethys,mantle derived melt intruded into lower or middle crutal resulted in partial melting of crustal components.Different degree of crystallization differentiation of parental magma that generated by processes of mixing or mingling of crust—mantle derived melt has contributed to the genesis of the quartz-diorite,granodiorite and monzogranite suites.