塔里木盆地西南缘铁克里克地区博查特塔格组的组成和时代：来自碎屑锆石U-Pb年龄的指示

博查特塔格组分布于塔里木地块西南缘的铁克里克地区,前人认为其主要由一套海相碳酸盐岩组成,底部为含砾粗砂岩,并将其时代划为蓟县纪。笔者对来自博查特塔格组中的条带状大理岩和含砾粗砂岩中的碎屑锆石样品进行了LA-ICP-MSU-Th-Pb同位素分析。分析结果显示,含砾粗砂岩中的碎屑锆石频谱图具有1953、2038、2163-2182、2225-2243、2281-2343Ma等多个年龄峰值,2281-2343Ma年龄值为主要峰值,其中最小谐和年龄1953Ma代表了该粗砂岩最早的沉积时代;条带状大理岩中的碎屑锆石年龄峰值主体介于772-856Ma之间,最小谐和年龄值为772Ma,代表了该大理岩最早的沉积时代。分析结果说明,原划为蓟县系的博查特塔格组由不同时代的物质组成,该地层单元需要解体。博查特塔格组的岩石组合应为中上部的碳酸盐岩夹细碎屑岩建造,该地层最早的沉积时代为772Ma,形成时代为南华纪。

Detrital zircon U-Pb dating from Tiekelike of southwestern Tarim Basin：Implications for the age and composition of Bochatetag Formation

The Bochatetag Formation outcrops at Tiekelike on the southwestern margin of the Tarim Craton.The sedimentary rocks of the formation contain conglomerate and shallow-marine carbonatite.Previous researchers assigned its formation age to Mesoproterozoic Jixian System.Detrital zircons in conglomerate on the base of the Bochatetag Formation yielded U-Pb ages ranging from 2.3 to 1.9 Ga,with the youngest detrital zircon concordant age being 1953 Ma.In contrast,the overlying marble in the middle-upper formation which contains significant Neoproterozoic detrital zircon grains has ages ranging from 0.77 to 0.85 Ga,with the youngest detrital zircon concordant age being 772 Ma.Therefore,the composition and age of the Bochatetag Formation should be redefined.The carbonatite constitutes the main composition of the formation and its formation age should be of the Nanhua system.The concordant age of 772 Ma represents the maximum deposition age.