青海石底泉地区宗务隆构造带花岗闪长岩LA-ICPMS锆石U-Pb年龄及其地质意义

    LA-ICP-MS zircon U-Pb ages and geological sig-nificance of granodiorite from Zongwulong tectonic belt in Delingha, Qinghai Province

    • 摘要: 对德令哈市石底泉地区宗务隆构造带内花岗闪长岩进行了锆石U-Pb测年和岩石地球化学分析。岩石地球化学分析结果显示,其具有岛弧或活动大陆边缘花岗岩的属性,原岩可能为新元古代早期(870.0±4.5Ma左右)硅铝地壳或地壳物质熔融的产物,它们的形成与板块的俯冲作用有关LA-ICP-MS锆石U-Pb测年显示2组年龄,分别为870.0±4.5Ma和443.3±2.3Ma。其中870.0±4.5Ma代表源区继承锆石的年龄,反映了新元古代时期的构造岩浆事件;443.3±2.3Ma代表花岗闪长岩岩浆锆石的结晶年龄,即花岗闪长岩侵位于晚奥陶世。综合分析可以确定,宗务隆构造带内花岗闪长岩与柴达木盆地北缘加里东期的板块汇聚碰撞造山作用有关,证实了宗务隆构造带内岩体形成时代并非全部是海西期一印支期。

       

      Abstract: Based on a study of zircon U-Pb dating and rock geochemical analysis of granodiorite from Zongwulong tectonic belt in Shidiquan area of Delingha, the authors revealed that the granodiorite has the characteristics of island arc or active continental margin granite. The original rock may be salic crust or the product of crustal melting formed in Early Neoproterozoic (870.0±4.5Ma). The granodiorite samples yielded ages of 870.0±4.5Ma and 443.3±2.3Ma respectively. The age of 870.0±4.5Ma represents provenance in-herited zircon age, which reflects the tectonic magmatic event during the Neoproterozoic, whereas the other age of 443.3±2.3Ma in-dicates the time of zircon crystallization of the granodiorite, which shows that the emplacement occurred in the Late Ordovician. Comprehensive analyses suggest that the granodiorite in the Zongwulong tectonic belt was related to plate convergent collisional orogeny of the Caledonian period on the northern margin of the Qaidam Basin, confirming that the formation of the rock in the Zongwulong tectonic belt did not wholly occurred in Hercynian-Indosinian period.

       

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