东天山白山斑岩钼矿床深部斑岩体锆石SIMS U-Pb定年、Hf同位素组成及其地质意义

白山钼矿位于东天山康古尔-黄山韧性剪切带三岔口-白山斑岩铜钼矿带中，为典型的斑岩型钼矿。本文以白山钼矿床深部花岗斑岩体为研究对象，对其进行了精确的锆石SIMS U-Pb定年以及锆石原位Hf同位素分析，旨在确定白山钼矿床深部斑岩体的形成时代以及岩石成因，进而分析其形成时的动力学背景。本文获得的白山钼矿床深部斑岩体锆石SIMS U-Pb年龄为(229.7±3.2) Ma，这一结果与前人获得的辉钼矿Re-Os等时线年龄225～229 Ma基本一致，因此可以代表成矿岩体的形成年龄为晚三叠世。锆石原位Hf同位素组成特征显示，εHf(t)均显示正值，为+8.3～+12，地壳模式年龄(TCDM)为556～758 Ma。结合前人研究成果及区域地质演化历史，可以确定白山钼矿床深部斑岩体形成于晚三叠世陆内伸展环境，由新生下地壳部分熔融形成。

SIMS U-Pb dating and Hf isotope of zircons from the deep granite porphyry in Baishan Mo deposit,eastern Tianshan,Northwest China,and their geological significance

The Baishan porphyry Mo deposit is located in the Sanchakou Baishan porphyry copper molybednum belt, which is hosted in the eastern part of Kangguer Huangshan ductile shear zone in eastern Tianshan, NW China. In this paper, SIMS U-Pb dating and in situ Hf isotope of zircons from the deep granite porphyry in Baishan deposit were systematically determined, so that we can constrain the petrogenesis and formation age of the granite porphyry emplaced in Baishan, and can reveal the geodynamical setting of the rock forming process of Baishan porphyry Mo deposit. Zircon SIMS U-Pb dating indicates that the magmatic activities in Baishan occurred at 229.7±3.2 Ma. Combined with the molybdenite Re Os isochron age (225229 Ma) reported by previous researchers, it is concluded that mineralization of the Baishan porphyry Mo deposit occurred in Triassic which is the same period as that of the rock formation. In situ Hf isotopic analyses of zircons that had previously been dated by SIMS yielded positive εHf(t) values ranging from +8.3 to +12 and the crustal model age ranging from 556 Ma to 758 Ma. Combined with the regional geological evolutionary history and isotopic data in this paper, we propose that the deep granite porphyry in Baishan deposit was formed in an intracontinental extension setting in the Late Triassic and the magma might be originated by partial melting of a juvenile lower crust.