中天山地块暗色岩墙LA-ICP-MS锆石U-Pb年龄和岩石地球化学特征

LA-ICP-MS zircon U-Pb age and geochemistry of the dark dykes in Central Tianshan Block

摘要: 中天山地块发育有大量的暗色岩墙，主要走向为北北西。对中天山暗色岩墙进行LA-ICP-MS锆石U-Pb测年，获得的年龄为304.8±1.5Ma，表明其形成于晚石炭世。这些暗色岩墙具有较高的SiO2，较低的Mg、Cr、Ni含量。它们富集大离子亲石元素（Rb、Ba、Th），亏损高场强元素（Nb、Ta、Ti），显示俯冲相关特征。上述特征暗示，中天山暗色岩墙可能是由俯冲板片流体交代的地幔楔部分熔融形成的。这一发现表明，准噶尔洋的闭合应该发生在晚石炭世之后。

Abstract: The NNW-trending dark dykes widely occur in Central Tianshan Mountains. The LA-ICP-MS zircon U-Pb dating of dark dyke yielded a weighted mean 206Pb/238U age of 304.8±1.5Ma, suggesting that they were generated in Late Carboniferous. The dark dykes are characterized by low Mg, Cr and Ni values. These samples are enriched in LILEs (e.g., Rb，Ba，Th) and depleted in HFSEs (e.g., Nb, Ta, Ti). The dark dykes were likely generated by interaction of mantle wedge with fluids derived from dehydration of the subducting slab. The closure of the Junggar Ocean probably terminated after Late Carboniferous.