藏东同普二叠纪高分异花岗岩的锆石U-Pb年龄和岩石成因

发布时间：2018-02-23 22:17

本文关键词： 藏东同普岩基高分异花岗岩锆石U-Pb年龄岩石成因　出处：《岩石学报》2017年08期 　论文类型：期刊论文

【摘要】：对具有富U或高U锆石的高硅花岗岩进行准确定年并进行成因讨论是花岗岩研究中的难题。本文以青藏高原东部江达-维西构造带北部同普岩基边缘相的高硅花岗岩为对象,开展了锆石U-Pb年代学、锆石Hf同位素和全岩元素地球化学研究。采用大激光束斑(100μm)先剥蚀2~3个脉冲的预剥蚀方法,获得了这套含富U或高U锆石高硅花岗岩的可靠锆石UPb年龄(260±1Ma)。这套高硅花岗岩具有高的Si O2含量(74.92%~76.46%)、高的全碱含量(Na2O+K2O;7.61%~8.55%)和高的分异指数(92~96),明显的Eu(Eu/Eu*=0.17~0.41)异常和显著亏损Ba、Nb、Sr、P和Ti等特征,属于典型的高分异花岗岩。本文数据,结合文献数据,指示同普高硅花岗岩为高分异I型花岗岩。富集的锆石Hf同位素组成(εHf(t)=-9.9~-5.8)指示它们来源于古老地壳物质的部分熔融。定量模拟表明它们可能由同期花岗闪长质母岩浆经历斜长石、磷灰石和富钛矿物的分离结晶作用形成。
[Abstract]:Accurate dating and genetic discussion of high-silica granites with rich U or high U zircon are difficult problems in the study of granites. In this paper, the high-silica granites in the north of the Jiangda-Wixi tectonic belt in the eastern part of the Qinghai-Xizang Plateau are taken as objects. Zircon U-Pb geochronology, zircon HF isotope and element geochemistry of the whole rock have been studied. The reliable zircon UPb age of high U rich or high U zircon high silicon granite is 260 卤1 Ma. This set of high silicon granite has the characteristics of high Sio 2 content (74.92), high total alkali content (Na 2O K _ 2O) 7.61 ~ 8.55) and high differentiation index (92 ~ 96), obvious EU ~ ((+)) EU / EU ~ (0.17) ~ (0.17) ~ 0.41) anomaly and significant depletion of Baan Nbn ~ (P) P and Ti, etc. Belong to the typical high grade isomorphic granite. The data of this paper, combined with the literature data, The enriched zircon HF isotopic composition (蔚 Hfftnl-9.9 ~ 5.8) indicates that they originated from the partial melting of ancient crustal materials. The quantitative simulation shows that they may have experienced plagioclase from the corresponding granodiorite mother magma. Separation and crystallization of apatite and titanium-rich minerals.
【作者单位】：地质过程与矿产资源国家重点实验室中国地质大学地球科学与资源学院;中国科学院青藏高原地球科学卓越研究中心;
【基金】：国家“973”项目(2015CB452604) 国家重点研发计划(2016YFC0600304)联合资助
【分类号】：P588.121;P597.3

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