塔里木东南缘安南坝地区约2.5Ga花岗闪长质片麻岩的发现及岩石成因  

Ca. 2.5Ga granodioritic gneiss in Annanba area of southeastern Tarim and its petrogenesis

作　　者：辜平阳[1] 徐学义[2] 何世平[1] 赵惠博 庄玉军 陈锐明[1] 查方勇[3] 郭亚鹏[1] GU Pingyang;XU Xueyi;HE Shiping;ZHAO Huibo;ZHUANG Yujun;CHEN Runming;ZHA Fangyong;GUO Yapeng(Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,MNR,Xi'an Geological Survey Center,CGS,Xi’an 710054,Shaanxi,China;China Geological Survey,Beijing 100037,China;Key Laboratory of Western China's Mineral Resources and Geological Engineering,Ministry of Education,Earth Science & Resources College of Chang'an University,Xi'an 710054,Shaanxi,China)

机构地区：[1]中国地质调查局西安地质调查中心/自然资源部岩浆作用成矿与找矿重点实验室,陕西西安710054 [2]中国地质调查局,北京100037 [3]长安大学地球科学与资源学院/西部矿产资源与地质工程教育部重点实验室,陕西西安710054

出　　处：《地质通报》2019年第5期834-844,共11页Geological Bulletin of China

基　　金：陕西自然科学基金项目《青海阿尔金东段新太古代米兰岩群中麻粒岩成因及变质作用过程研究》(编号:2017JM4001)、《新疆克拉玛依岩浆混合岩体中长石矿物微区精细结构特征研究》(编号:2017JM4031);国家自然科学基金项目《青藏高原羌塘地区地壳早期物质探索研究》(批准号:41002063);中国地质调查局项目《青海阿尔金1:5万打柴沟等6幅区调》(编号:1212011121193),《新疆1:5万喀伊车山口等3幅高山峡谷区填图试点》(编号:12120114042701)、《商丹—大柴旦地区区域地质调查》(编号:DD20190069)

摘　　要：塔里木东南缘安南坝地区新发现的花岗闪长质片麻岩主要由斜长石、碱性长石、石英、角闪石、黑云母等组成。岩石SiO2(>70%)、Al2O( 3 >15%)、Na2O(3.56%~4.15%)含量较高;MgO(0.39%~0.59%)、Fe2O( 3 0.23%~0.36%)、FeO(0.76%~1.11%)含量、K2O/Na2O值(0.64~0.81)及Mg^#值(19~27)均较低。花岗闪长质片麻岩稀土元素总量低(∑ REE=28.81×10^-6~68.51×10^-6),(La/Yb)N=(46.27~98.27),轻、重稀土元素分异明显,球粒陨石标准化稀土元素配分曲线表现为右倾型,Eu(δEu=1.57~2.00)呈明显的正异常。岩石Rb、Ba、Sr等大离子亲石元素含量较高,Nb、Ta等高场强元素及Cr、Ni等相容元素含量较低。地球化学特征显示,该花岗闪长质片麻岩具有高铝型TTG和低重稀土元素系列TTG的地球化学特征。研究表明,阿克塞县安南坝地区花岗闪长质片麻岩可能是在榴辉岩相压力条件下,由加厚的玄武质下地壳部分熔融形成,源区残留相主要为石榴子石、金红石(少量)及角闪石。LA-ICP-MS锆石U-Pb上交点年龄为2555±11Ma,代表了花岗闪长质片麻岩的成岩时代,说明新太古代晚期是塔里木东南缘重要的陆壳增生期。此外,岩石中还获得了约2.44Ga、约1.96Ga的变质年龄,表明塔里木东南缘基底岩石在古元古代经历了2期构造-热事件的叠加改造。The newly- discovered granodioritic gneiss is mainly composed of plagioclase,alkali feldspar,quartz,amphibolite and biotite in Ananab area,southeastern Tarim, characterized by high SiO2(>70%), Al2O3(>15%)and Na2O(3.56%~4.15%), and low MgO(0.39%~0.59%), Fe2O3(0.23%~0.36%), FeO(0.76%~1.11%), K2O/Na2O(0.64~0.81)and Mg^#(19~27). Meanwhile,the granodioritic gneiss has lower content of Σ REE,with strong fractionation of LREE/HREE((La/Yb)N=46.27~98.27);the chondrite-normalized REE patterns show right-inclined patterns with obvious positive Eu(δEu=1.57~2.00)anomalies. The rocks are enriched in LILE(such as Rb, Ba and Sr)and depleted in HFSE(such as Nb and Ta);in addition, the values of compatible elements(Cr, Ni)are relatively low. On the basis of the above data, the geochemical analyses indicate that granodioritic gneiss is characteristic of high-Al TTG series and low-HREE TTG. It is therefore held that the rocks might have been formed by partial melting of thickened mafic lower crust under the pressure condition of eclogite facies, with garnet, rutile and amphibole left in the residual magmas. LA-ICP-MS zircon U-Pb dating of granodioritic gneiss from Annanba area of Aksai yielded the formation time of 2555±11Ma, basically consistent with the age of magmatism of southeastern Tarim(2.5~2.6Ga), showing the significant continental crust accretion in late Neoarchean. In addition, the metamorphic ages of ca.2.44Ga and ca.1.96Ga were obtained for granodioritic gneiss, which implies that the basement rocks from southeastern Tarim were superimposed upon and reconstructed by two episodes of tectonic thermal events in Palaeoproterozoic.

关 键 词：太古宙 花岗闪长质片麻岩 地球化学 LA-ICP-MS锆石U-PB测年 安南坝地区 

分 类 号：P534.2[天文地球—古生物学与地层学] P588.12[天文地球—地质学]