新疆温泉县别珍套山新元古代花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其成因

LA-ICP-MS zircon U-Pb age,geochemistry and genesis of Neoproterozoic granitoids in the Biezhentao Mountain of Wenquan County,Xinjiang

对新疆温泉县别珍套山新元古代花岗岩开展了相关研究。获得了3个片麻状-眼球状花岗岩4件锆石样品年龄,其中206Pb/238U年龄值一致,大多集中在910~950 Ma之间。极少量继承锆石的年龄大于1000 Ma。这些花岗岩以特有的粗粒、巨大的眼球状片麻结构为特征。岩体具有高硅(≥70%)、富碱(K2O+Na2O,6.5%~8.9%)且K2O>Na2O的特征,表现出从钙碱性到钾玄岩演化的变化趋势。稀土元素特征表明其与碱性花岗岩相似。样品的微量元素蛛网图几乎完全相同,均明显亏损Ba、Nb、Ta、Sr、P、Ti,富集Rb、Th、U、K等元素,显示活动大陆边缘岩石特征。全岩Sr-Nd同位素特征表明具典型壳源花岗岩(S型花岗岩)的特征。Lu-Hf同位素特征表明单阶段Hf模式年龄(tDM1)为883~1351 Ma,平均为1133 Ma;二阶段Hf模式年龄(tDM2)为891~1588 Ma,平均为1250 Ma,与锆石形成年龄较接近。新元古代早期(约9 Ga)片麻状花岗岩可能是与Rodinia超大陆会聚有关的格林维尔期造山作用、地壳增厚导致地壳物质部分熔融的产物。

The Neoproterozoic granites of the Biezhentao Mountain in Wenquan County of Xinjang were studied in this paper.Four LA-ICP-MS zircon U-Pb ages of 910~950 Ma were obtained for granitic gneisses in the Biezhentao Mountain of Wenquan County of Xinjiang.These new zircon LA-ICP MS U-Pb ages,together with previously published data,indicate that the granites were emplaced during 910~950 Ma.A few inherited old zircons U-Pb ages of>1000 Ma were found in all dated samples;they may have derived from the source rocks.These granitoids are characterized by a very coarse grained and huge augen gneiss texture.Major element data indicate that they belong to peraluminous monzogranite,with SiO 2(≥70%),K2O+Na2O(6.5%~8.9%),and K2O>Na2O,thus defined as calcalkaline to shoshonitic rocks.These rocks show nearly parallel REE patterns with different abundances and distinct negative Eu anomalies.All the granitoids display similar spider diagrams with obvious negative anomalies of Ba,Nb,Ta,Sr,P and Ti,and obvious enrichment of Rb,Th,U,K.Sr-Nd data suggest that the protoliths of Neoproterozoic granitoids belong to peraluminous S-type granites.ZirconεHf(t)values range from+1.7 to+5.7,with model ages(tDM1)of 883~1351 Ma and model ages(tDM2)of 891~1588 Ma.Furthermore,with the age information on the ancient terranes of Tarim basin,the authors hold that the Tianshan ancient block probably formed a part of Rodina supercontinent during Early Neoproterozoic period and these granitoid rocks were linked to lithospheric thickening.