新疆阿尔泰蒙库同造山斜长花岗岩年代学、地球化学及其地质意义

Geochronology,Geochemistry and Geological Implications of the Mengku Synorogenic Plagiogranite Pluton in Altay,Xinjiang

对新疆阿尔泰蒙库铁矿区斜长花岗岩体进行了锆石SHRIMP—U—Pb年龄测定，获得了400±6Ma（MSDW=1．3）的生成年龄，与1号矿体北部黑云母花岗岩年龄相似（锆石SHRIMP—U—Pb年龄404±8Ma），表明岩体侵位时代为早泥盆世早期。这些岩体侵入到康布铁堡组中，限定康布铁堡组时代大于404Ma。同时蒙库铁矿的形成与岩浆热液活动有关，也限定铁矿成矿时代略晚于404~400Ma。蒙库斜长花岗岩具有高硅，富钠，Th、La、Ce、Nd、LREE元素相对富集，贫钾，Nb、Ta、Sr、P、Ti具有明显负异常和中等负铕异常（δEu=0．38～0．50）的特点。Na2O／K2O=6．36～13．3，属低钾（拉斑玄武质）系列。铝过饱和指数为1．03～1．09，为微过铝质。Isc=0．70438-0．70986，εNd（t）=1．04～2．17，表明蒙库岩体物源以幔源物质为主，有少量壳源物质的混入。结合区域地质资料，认为蒙库岩体形成于活动大陆边缘的陆弧环境，处于拉张环境中。

SHRIMP-U-Pb zircon dating on the Mengku plagiogranite pluton in the Mengku iron deposit district Xinjiang shows that it was formed at 400±6 Ma （MSDW= 1.3）. This age is similar to that of biotite granite at the north part of the No. 1 orebody （SHRIMP-U-Pb dating is 404±8 Ma）, indicating that they were formed at the beginning of the Early Devonian. These plutons intrude into the Kangbutiebao Formation, showing that Kangbutiebao Formation could have been much earlier than 404 Ma. The Mengku iron deposit is related to magmatic hydrothermal activity, and the ages of the plutons shows that iron mineralization formed in slightly later than 404-400 Ma. Geochemically, the Mengku plagiogranite is enriched in silica, Na, Th, La, Ce, Nd and LREE, is depleted in K with negative anomaly in Nb, Ta, St, P, Ti and moderate Eu negative anomaly （δEu=0.38-0.50）. The Na2O/ K2O ratios are 6.36 to 13.3, indicating low-K series, and samples fall in the tholeiitic field in the SiO2-K2O diagram. The A/CNK ratios range from 1.03 to 1.09, indicating that the pluton is weakly peraluminous. The 87Sr/86 Sr initial ratios range from 0. 70438 to 0. 70986. The εNd（t） values of 1. 04 to 2. 17 indicate that the sources of the plagiogranite was mainly derived from mantle-derived components, with limited assimilation of old crustal material. In combination with previous studies, we concluded that the Mengku pluton was formed in a continental arc and under an active extensional continental margin setting.