新疆和硕县包尔图一带花岗岩LA-ICP-MS锆石U-Pb年龄及其地质意义

摘要

新疆和硕县包尔图一带地处中天山中段,花岗岩十分发育.包尔图北侧的乌苏通沟岩体属于北天山,为一套中酸性侵入岩,矿物组合显示其为典型的钙碱性火山弧花岗岩,地球化学特征显示富集大离子亲石元素而亏损高场强元素,是洋壳俯冲导致的下地壳物质部分熔融和上地壳同化混染的产物,LA-ICP-MS锆石U-Pb同位素测年结果为(358.9±3.5)Ma,说明乌苏通沟岩体形成于泥盆纪末一早石发世早期,是北天山洋向中天山陆块之下俯冲的产物,且是泥盆纪俯冲事件的最新地质记录.包尔图南侧的红山岩体属于南天山,是一套酸性侵入岩,矿物共生组合显示出钙碱性同碰撞花岗岩的特征,岩相学特征显示岩浆混合的典型特征,岩石地球化学特征显示Ta、Nb不同程度的贫化,说明该侵入体是陆壳增厚的产物,代表了一次重要的陆壳垂直生长事件,LA-ICP-MS锆石U-Pb同位素测年结果为(295.8±1.2 )Ma,说明红山岩体侵位于石炭纪末—早二叠世早期.包尔图一带花岗岩分别记录了南、北天山2次重要的地质事件,为研究天山地区的构造演化提供了重要的依据.%A lot of granitoids exist at Baoertu of Hoxud County in Xinjiang,lying in the middle segment of Middle Tianshan Mountains. Petrologic, mineralogical and gcochemical investigations indicate that Wusutonggou pluton, which occurs in northern Baoertu area and belongs to Northern Tianshan Mountains, is composed of a suite of intermediate-acid intrusive rocks showing features of typical calc-alkaline volcanic arc granitoids which are enriched in LILE and depleted in HFSE and have genetic relation with the melting of the lower crust and the assimilation-hybridization of the upper crust resulting from the subduction of the ocean crust. The U-Pb LA-ICP-MS isotope age shows that the Wusutonggou pluton intruded at 358.9±3.5 Ma, belonging to the last stage of Devonian to rnthe early stage of Lower Carboniferous. Wusutonggou granitoids resulted from the southward subduction of northern Tianshan Ocean beneath the middle Tianshan landmass, and could serve as the newest geological record of the subducting events in Devonian. Petrologic, mineralogical and geochemical investigations show that Hongshan pluton, which occurs in southern Baoertu area and belongs to Southern Tianshan Mountains, is a suite of acid intrusive rocks of typical calc-alkaline syn-collision granitoids, having typical characteristics of magma mixing and lower contents of Nb and Ta. Hongshan granitoids resulted from increasing thickness of continual crust and represented an important vertical development of the continual crust. LA-ICP-MS U-Pb isotope age shows that the Hongshan pluton intruded at 295.8±1.2 Ma, belonging to the last stage of Carboniferous to the early stage of Lower Permian. Studies show that granitoids in Baoertu area have recorded two important geological events and offered the important evidence for the tectonic evolution in Tianshan area.