西秦岭天水地区晚三叠世柴家庄二长花岗岩及其暗色包体地球化学--岩石成因及岩浆混合作用  

LATE TRIASSIC MONZOGRANITE AND ITS MAFIC ENCLAVES FROM THE CHAIJIAZHUANG PLUTON IN TIANSHUI AREA,WESTERN QINLING MOUNTAINS:Petrogenesis and Magmatic Mixing

作　　者：巨银娟[1] 王邢颖 张泽中[1] JU Yin-juan;WANG Xing-ying;ZHANG Ze-zhong;ZHANG Zhe(State Key Laljoratory for Continental Dynamics/Deportment of Geology,Northwest University,X i'an 710069,China)

机构地区：[1]西北大学大陆动力学国家重点实验室/地质学系,西安710069

出　　处：《地质与资源》2018年第1期41-47,59,共8页Geology and Resources

基　　金：国家自然科学基金项目“南北构造带中新生代构造演化”(编号41421002);陕西省青年科技新星项目“南秦岭五龙复式花岗岩体岩浆起源机制研究”(编号2014KJXX-60)

摘　　要：晚三叠世花岗岩类在秦岭-大别造山带西端广泛分布,其成因机制及地球动力学背景的研究对于反演华北、扬子两大板块沿秦岭-大别造山带在三叠纪时期的拼合历史具有重要意义.本文选择西秦岭天水地区柴家庄晚三叠世二长花岗岩及其中的暗色包体进行精细的岩石学和地球化学研究.暗色包体中普遍发育针状磷灰石及斜长石捕掳晶,暗示岩浆混合作用;暗色包体具有较低的Si O2(60.27%~60.38%)、高的Mg#(54~55)和Nb/Ta比值(14.8~16.6),表明其来源于富集岩石圈地幔的部分熔融作用;寄主二长花岗岩表现出典型埃达克岩的地球化学特征,其富集Sr、Ba,亏损Y和HREE,岩石的Sr/Y比值介于88~98之间,Y/Yb比值介于13~15之间,暗示源区有石榴石残余.结合前人的研究结果,提出柴家庄二长花岗岩可能为增厚的造山带下地壳在碰撞后伸展环境下发生部分熔融作用的产物,可能与晚三叠世时期秦岭造山带的板片断离作用有关.The Late Triassic granitoid is widely distributed in the western Qinling-Dabie orogenic belt.The paper chooses the Late Triassic monzogranite and mafic enclaves from Chaijiazhuang pluton of western Qinling Mountains for detailed petrological and geochemical study.Acicular apatite and plagioclase megacrysts are developed in the mafic enclaves,suggesting the magmatic mixing process.The mafic enclaves are characterized by low Si0 2(60.27%-60.38%),high Mg#(54-55)and Nb/Ta ratio(14.8-16.6),which indicates that they were derived from the partial melting of subcontinental lithospheric mantle.Geochemically,the host monzogranite shows adakitic affinity with enrichment of Sr and B a,depletion of Y and H R E E s,high Sr/Y ratio(88-98)and Y/Yb ratio(13-15),hinting at the residue of garnet in the source area.Combining with previous researches,it is suggested that the monzogranite in the study area is the product of partial melting of thickened lower crust under the post-collision extension background caused by the Late Triassic subducting slab break-off in Western Qinling orogenic belt.

关 键 词：晚三叠世 岩石成因 埃达克岩 暗色包体 岩浆混合作用 秦岭造山带 板片断离作用 

分 类 号：P588.12[天文地球—岩石学] P591[天文地球—地质学]