东准噶尔卡拉麦里地区巴塔玛依内山组火山岩LA-ICP-MS锆石U-Pb年龄

巴塔玛依内山组是一套以火山岩为主的陆相火山-沉积地层,在东准噶尔地区广泛分布,规模巨大,且形成时代久存争议。通过对卡拉麦里地区巴塔玛依内山组层型剖面的重新实测,以及对该组中下部层位玄武岩进行LA-ICP-MS测年,获得锆石U-Pb年龄为(338.7±7.7) Ma(MSWD=0.24)。所测锆石的CL图像上可见明显的震荡环带结构,且锆石Th/U比值为0.11～0.95,均大于0.10,13颗锆石的Th/U平均值为0.56,Th/U呈正相关,说明属岩浆锆石,指示其代表了巴塔玛依内山组的形成时代。结合前人的年代学数据及化石资料,将巴塔玛依内山组时代确定为早石炭世中期—晚石炭世初期,认为其中下部层位时代不晚于338.7 Ma。该成果进一步约束了区内陆相火山地层的时代,并为研究东准噶尔构造带的火山岩浆作用及其构造演化提供了新的年代学依据。

Zircon LA-ICP-MS U-Pb Dating of Volcanics in Batamayineishan Formation of Kalamaili Area,Eastern Junggar

Batamayineishan Formation is a set of continental volcanic-sedimentary strata dominated by volcanic rocks. It is widely distributed in eastern Junggar,with a huge scale and a long-standing controversy about its age.The U-Pb zircon U-Pb age of Batamayineishan Formation in Kalamali area is(338.7±7.7) Ma(MSWD=0.24)by LA-ICP-MS dating of basalts in the middle and lower strata of the Formation.The CL images of the zircons show obvious oscillatory zonal structure,and the Th/U ratios of the zircons are between 0.11 and 0.95,all of which are greater than 0.10.The Th/U average of 13 zircons is 0.56.There is a positive correlation between the Th/U values,indicating that the zircons belong to magmatic zircons and represent the formation age of the Batamayineishan Formation.Based on previous chronological data and fossil data,the age of the Batamayineishan Formation is defined as the middle of the Early Carboniferous to the early stage of the Late Carboniferous.It is considered that the lower strata should be no later than 338.7 Ma.This result further constrains the age of continental volcanic strata and provides a new chronological basis for the study of volcanic magmatism and tectonic evolution in the eastern Junggar tectonic belt.