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东天山土墩岩体侵位于上石炭统梧桐窝子组中,与围岩呈热接触变质关系,该岩体由纯橄岩、方辉橄榄岩、堆晶二辉橄榄岩、辉长岩及角闪辉长岩组成。岩石以拉斑系列为主,少量钙碱性系列,镁铁质岩m/f比值均大于0.5,属铁质基性岩。球粒陨石标准化稀土元素配分曲线为平坦型,原始地幔标准化微量元素特征表现为相对富集大离子亲石元素(K、Sr、Ba、U),相对亏损高场强元素(Nb、Ta、P、Ti)及Th,适度亏损Zr、Hf。过渡元素蛛网图显示为“W”形的分配型式(Ti正异常、Cr、Ni负异常),为地幔岩派生的岩浆结晶分异所形成。对土墩角闪辉长岩进行锆石LA-ICP-MS法测年,结果为(298.37±0.94)Ma(MSWD=0.038)。结合黄山地区花岗岩特征及东天山北部A型花岗岩形成时代,显示岩体形成于碰撞后伸展的构造环境,为岩石圈伸展减薄期软流圈物质上涌且减压熔融的产物。
The East Tianshan mound intrusive is located in Wutongwozi Formation, Upper Carboniferous, and is in thermal contact metamorphism with the surrounding rock. The pluton is composed of dunite, hectorite, hematite, gabbro and Corner flash gabbro composition. The rocks are dominated by plaque series. A small amount of calc-alkaline series and mafic rocks have m / f ratios greater than 0.5, which are of iron basic rocks. The normalized REE distribution curve of chondrite is flat. The normalized trace elements in the original mantle are characterized by relative enrichment of large ion lithophile elements (K, Sr, Ba, U) and relatively depleted high field strength elements (Nb, Ta, P , Ti) and Th, a moderate loss of Zr, Hf. The transition elemental cobras showed “W” -shaped distribution patterns (positive Ti anomaly, negative Cr and Ni anomalies) formed by the differentiation of magmatic rocks derived from mantle rocks. The zircon quartz LA-ICP-MS method was used to measure the mound hornblented gibbsite. The result was (298.37 ± 0.94) Ma (MSWD = 0.038). Combined with the granite features of Huangshan area and the age of A-type granites in the northern part of East Tianshan Mountains, it is shown that the rock mass formed after the collision and extended tectonic environment, which is the product of asthenospheric material upwelling and depressurization and melting during lithospheric extension and thinning.