滇西北石鼓杂岩中花岗质片麻岩年代学、地球化学特征及地质意义  

Geochronology,geochemical features and geological significance of the granitic gneiss in the Shigu complex,northwest Yunnan,China

作　　者：罗改[1] 张彤[1] 贾小川[1] 杨学俊[1] 肖典 谭晓莲[3] LUO Gai;ZHANG Tong;JIA Xiaochuan;YANG Xuejun;XIAO Dian;TAN Xiaolian(Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province,Sichuan Geological Survey,Chengdu,Sichuan 610081,China;Faculty of Geosciences and Enrironmental Eng ineering,Southuest Jiaotong University,Chengdu,Sichuan 611756,China;Chengdu Geological Survey,Sichuan Bureau of Metallurgical Geological,Chengdu,Sichuan 610203,China)

机构地区：[1]稀有稀土战略资源评价与利用四川省重点实验室,四川省地质调查院,四川成都610081 [2]西南交通大学地球科学与环境工程学院,四川成都611756 [3]四川省冶金地质勘查局成都地质调查所,四川成都610203

出　　处：《地质学报》2021年第11期3335-3351,共17页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号DD20160345-01、DD20190053、DD20190370)联合资助的成果。

摘　　要：青藏高原东南缘滇西北前寒武纪石鼓变质杂岩中新识别出一套花岗质片麻岩。采用LA-ICP-MS方法进行锆石U-Pb年代学分析,获得^(206)Pb/^(238)U加权平均年龄分别为790±11 Ma(MSWD=2.1,n=10)和814±15 Ma(MSWD=5.7,n=9),显示其形成于新元古代早期。地球化学特征显示,岩石具有高硅(SiO;=66.05%~77.16%)、高K;O/Na;O(0.90~9.26,均值2.57)特征,MgO=0.35%~3.60%,TFeO=1.02%~4.86%,P;O;=0.03%~0.17%。铝饱和指数A/CNK为1.08~2.51,矿物组合中出现石榴子石和白云母等富铝矿物,CIPW标准矿物中刚玉分子平均含量为4.72%,显示为强过铝质花岗岩。球粒陨石标准化稀土配分显示轻稀土元素富集,(La/Yb)_(N)=1.79~12.34,具明显的Eu负异常(δEu=0.21~0.67)。原始地幔标准化蛛网图显示,岩石富集Rb、U,明显亏损Ba、Ta、Nb、Sr、P、Ti元素。综合分析认为,花岗质片麻岩原岩主要为低成熟度、黏土贫乏的砂质岩在高温条件下部分熔融的产物,形成于后碰撞构造环境,是Rodinia超大陆汇聚事件在滇西北石鼓地区的响应。A suite of granitic gneiss was identified new within the Precambrian Shigu metamorphic complex to thenorthwest of Yunnan,southeastern margin of the Tibet plateau.LA-ICP-MS Zircon U-Pb dating indicates that,the granitic gneiss was formed during early Neoproterozoic,and the weighted mean ages of^(206)Pb/^(238)U were 790±11 Ma(MSWD=2.1,n=10)and 814±15 Ma(MSWD=5.7,n=9).Geochemical characteristics show that,the rocks were characterized by high silicon(SiO;=66.05%~77.16%),high K;O/Na;O(0.90~9.26,mean of 2.57),MgO=0.35%~3.60%,TFeO=1.02%~4.86%,P;O;=0.03%~0.17%,and belong to strongly peraluminous granites,with A/CNK=1.08~2.51,aluminium-rich minerals(such as garnet and muscovite),and corundum molecules(av.4.72%).The chondrite normalized REE patterns of samples show enrichment of LREE((La/Yb)_(N)=1.79~12.34)and strong negative Eu anomalies(δEu=0.21~0.67).The primitive mantle normalized trace element diagrams show enrichment of Rb and U,and depletion of Ba,Ta,Nb,Sr,P and Ti.It is suggested that,the granitic gneiss protoliths resulted from partial melting of arenaceous rock with less mature and poor clay underhigh temperature conditions.They were formed in a post-collision tectonic setting,in response to the Rodinia supercontinent amalgamation in the Shigu area,northwest of Yunnan.

关 键 词：新元古代 花岗质片麻岩 强过铝质花岗岩 石鼓杂岩 RODINIA 

分 类 号：P588.3[天文地球—岩石学] P597.3[天文地球—地质学]