北阿尔金拉配泉米兰群片麻岩及其中两期基性岩墙群LA-ICP-MS锆石U-Pb年龄及地质意义

北阿尔金拉配泉北侧米兰群混合角闪斜长片麻岩被2期基性岩墙群(辉绿玢岩和棕闪煌斑岩)侵位。本次分别对三者进行了LA-ICP-MS锆石U-Pb同位素侧年。混合岩化角闪斜长片麻岩中锆石结晶年龄为2007Ma±25Ma,结合西北地区2.0Ga左右广泛的构造-热事件,可能与Columbia超大陆汇聚有关。辉绿玢岩和棕闪煌斑岩的年龄结构相似,锆石较老年龄组分分别为1962～2093Ma和1804～2038Ma,系在侵位时从围岩(混合角闪斜长片麻岩)中捕获的锆石的年龄;最年轻的年龄组分(79～94Ma)代表基性岩墙群的侵位时间,与阿尔金北缘断裂伸展活动有关;古生代年龄(288～504Ma)为岩墙群上侵过程中同化混染北阿尔金蛇绿混杂岩带部分岩石的年龄。

LA-ICP-MS zircon U-Pb dating of gneiss of Milan Group and mafic dyke swarms from Lapeiquan in northern Altun and its tectonic significance

Two stages of basic dykes(diabase-prophyrite and barkevite lamprophyre)were emplaced in Milan Group migmatic hornblende plagioclase gneiss on the northern side of Lapeiquan in northern Altun Mountains. This paper presents the zircon LA-ICP-MS U-Pb dating for these three types of rocks. The crystallizing age of migmatic hornblende plagioclase gneiss is 2007Ma±25Ma, which, together with structural thermal event of about 2.0Ga in northwest region, might suggest the probable relationship with the convergence of Columbia Supercontinent. There exists similar age structure between diabase-prophyrite and barkevite lamprophyre. These zircons of the old ages, which are respectively 1962-2093Ma and 1804-2038Ma, were captured from hornblende plagioclase gneiss; the youngest ages show that the emplacement of basic dykes occurred in 79-94Ma, suggesting a product of extension in the Late Cretaceous; and the Paleozoic ages(288-504Ma)imply that the rocks of northern Altun ophiolite belt were involved in the provenance for basic dykes.