新疆可可托海3号伟晶岩脉成岩时代的限定:来自辉钼矿Re-Os定年的证据

New age constraints on Koktokay pegmatite No.3 Vein,Altay Mountains,Xinjiang: Evidence from molybdenite Re-Os dating

可可托海3号伟晶岩脉因其完美的岩浆结晶分异特征而闻名世界,但针对其年代学方面的认识仍存在较大分歧。本次工作采集到产于3号脉边部带中的6件辉钼矿样品。其产出地质特征显示属于3号伟晶岩脉边部带形成时与围岩的热液交代成因,形成时间应与边部带近于同时或稍晚。文章利用辉钼矿Re-Os测年技术进行的年代学研究结果表明,6件辉钼矿Re-Os等时线年龄为(208.8±2.4)Ma(MSWD=0.89)以及模式年龄为(209.9±1.3)Ma(MSWD=0.69),在误差范围内一致,可忽略辉钼矿Re-Os体系可能产生的失偶现象,代表了辉钼矿在流体中沉淀的时间。在研究前人年代学成果基础上,笔者认为3号伟晶岩脉的形成起始于209 Ma左右,即中三叠世晚期。

No. 3 pegmatite vein in Koktokay is famous for perfect magmatic differentiation. However, there have been still obviously different views about its chronology. The authors collected 6 molybdenite samples from the margin zone of No. 3 vein whose geological features indicate that there existed hydrothermal metasomatism and that molybdenite was formed simultaneously with or a bit later than the margin zone. The Re-Os dating results of 6 molybdenite samples indicate that the isochron age of （208.8 ± 2.4） Ma （MSWD = 0.89） is consistent with the model age of （209.9 ±1.3） Ma （MSWD= 0.69） within error limits, implying that decoupling of Re-Os within molybdenites can be neglected, and that the results obtained by the authors can represent the time of rnolybdenite detsitition from the fluid. Based on studying previous chronologic results, the authors hold that the formation ofNo. 3 vein began at 209 Ma, namely in the late middle-Triassic period.