内蒙古阿拉善地区沙拉扎山花岗岩体TIMS锆石U-Pb年龄

内蒙古阿拉善地区的沙拉扎山处于华北板块、塔里木板块和天山-兴蒙造山带接触部位,恩格尔乌苏蛇绿岩带与查干础鲁蛇绿岩带之间。沙拉扎山内出露一套巨大花岗质岩基,为了认识其岩浆活动期次,对沙拉扎山岩体不同部位花岗质岩石样品进行了TIMS锆石U-Pb测年。结果表明,沙拉套尔汗花岗闪长岩年龄为233.1±5.8Ma,乌力吉花岗岩2个样品年龄分别为228.1±0.4Ma和207.7±0.8Ma。对比分析前人对该区岩体年龄的研究成果,认为沙拉扎山出露的花岗岩由早二叠世晚期(273~274Ma)、早三叠世(248~252Ma)、晚三叠世早期(228~236Ma)和晚三叠世末期(207Ma)4期岩浆活动叠加而成,同时发育在沙拉扎山的4期岩浆活动在巴音—诺尔公地区也有相应的岩浆记录。

TIMS zircon U-Pb isotopic dating of Salazha Mountain granites from the North Margin of Alxa, Inner Mongolia, and its tectonic implications

The Salazha Mountain on the north margin of Alxa Block is situated at the conjunction of North China Block and Tarim Block, or between Enger Us ophiolites belt and Quaganqulu ophiolites belt. To determine its magmatic issues, the authors collected samples from distinct positions of Salazha Mountain so as to conduct TIMS zircon U-Pb isotopic dating. The result shows that the granities were formed during Indosinian period. The ages of the three sampling spots are 233.1±5.8Ma, 228.1±0.4Ma, and 207.7±0.8Ma, representing the formation age of Salatoerhan granodiorite, Wuliji granite and granodiorite, respectively. A comparative analy-sis of the previous geochronologic results indicates that the Salazha granitic batholiths resulted from the superimposition of the follow-ing four magmatic stages, namely late Early Permian(273~274Ma), Early Triassic(248~252Ma), early Late Triassic(228~236Ma)and Late Triassic(207Ma). Theses magmatic activities are also seen in the Bayin-Nuoergong area, which has been taken as the margin of North China Block.