柴达木地块北缘全吉地块钾长石浅粒岩碎屑锆石LA-ICP-MSU-Pb定年——对达肯大坂岩群时代的约束  

Detrital zircon LA-ICP-MS U-Pb dating for K-feldspar leptite of Quanji massif in the north margin of Qaidam Block:constraint on the age of Dakendaban Group

作　　者：黄婉[1] 张璐[1,2] 巴金[1,2] 廖梵汐[1,2] 陈能松[1,3] 

机构地区：[1]中国地质大学(武汉)地球科学学院,湖北武汉430074 [2]中国地质大学研究生院,湖北武汉430074 [3]中国地质大学/地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《地质通报》2011年第9期1353-1359,共7页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:40772041);国家地质学理科基地人才培养基金项目(编号:J0830520)

摘　　要：为查明全吉地块基底中达肯大坂岩群的最大沉积年龄,用LA-ICP-MS技术测定了钾长石浅粒岩中的锆石U-Pb年龄。CL图像和Th/U比值指示这些锆石均为岩浆成因的锆石。36个测点207Pb/206Pb年龄变化范围为2094～2280Ma,其中年龄谐和度高于90%的30个测点的207Pb/206Pb年龄相对概率密度曲线呈单峰分布特征,峰值年龄为2190Ma左右。结合全吉地块最早一期变质事件的年龄,钾长石浅粒岩原岩碎屑和所在的达肯大坂岩群的沉积年龄范围被约束在1.95～2.19Ga之间。本研究表明,前人在侵入于达肯大坂岩群的伟晶岩脉中获得的约2.42Ga年龄的锆石应捕获于围岩,属于继承性岩浆碎屑成因,该类锆石年龄不能用来约束达肯大坂岩群原岩的最小沉积年龄。To determine the maximum deposition age of the Dakendaban Group,the authors measured detrital zircons from a K-feldspar leptite for U-Pb age using LA-ICP-MS technique.The CL images and the Th/U values show that the detrital zircons are of inherited magmatic origin.The 207Pb/206Pb age range of 36 measuring points is 2094-2280 Ma,the 207Pb/206Pb age relative probability density plot for 30 measuring points with concordant degree over 90% exhibits monomodal curve with peak age of ～2190 Ma.Combined with the age of the earliest metamorphic event,the deposition age span of the protolith sediments of the K-feldspar leptite and the Dakendaban Group is constrained to be 1.95-2.19 Ga.The previously reported ～2.42 Ga zircons from the pegmatite are of inherited magmatic origin and are considered to have been derived from the Dakendaban Group wall rock,so their age cannot be used to constrain the minimum deposition age of the protolith of the Dakendaban Group.

关 键 词：碎屑锆石 LA-ICP-MS锆石U-PB定年 达肯大坂岩群 全吉地块 

分 类 号：P588.346[天文地球—岩石学] P597.3[天文地球—地质学]