西秦岭江里沟复式岩体LA-ICP-MS锆石U-Pb年龄、地球化学和Hf同位素特征及其地质意义

发布时间：2018-05-17 13:39

  本文选题：锆石U-Pb定年 + 混合作用　； 参考：《岩石学报》2017年03期

【摘要】：古特提斯洋在三叠纪时期沿现今勉略缝合带的闭合,标志着华北板块(NCB)和扬子板块(YZB)的最终拼贴完成。秦岭造山带西段发育印支期花岗岩浆活动,为该地区的成矿作用提供了有利的条件。对这些岩浆岩的形成时代、地化属性、演化、来源等的研究将有助于了解该时期的构造背景及动力学环境。本文以西秦岭北亚带的江里沟复式岩体作为研究对象,通过LA-ICP-MS锆石U-Pb测年、锆石Hf同位素测试和主微量元素分析,对该岩体进行了系统的研究。结果显示:江里沟复式岩体的三种主要岩性为斑状黑云母二长花岗岩、花岗斑岩和细粒花岗岩,加权平均年龄分别为:229.1±1.8Ma(MSWD=0.82)、222.5±1.4Ma(MSWD=0.41)和217.1±1.8Ma(MSWD=1.4),指示该岩体形成于晚三叠世。其地球化学性质具有高硅(SiO_2=72.67%~77.84%),富碱(K_2O+Na_2O=7.67%~8.75%),弱过铝质(A/CNK=1.01~1.06),高度分异(岩体由早至晚DI及Rb/Sr均升高,DI=88.9~95.36,Rb/Sr=1.76~12.19),富集Rb、Th、U、Ta、Zr、Hf和HREE元素特点,亏损Ba、Sr、P、Ti等元素;三个侵入体均发育明显负Eu异常(δEu=0.54~0.62、0.26~0.47、0.20~0.60);P_2O_5含量与SiO_2呈明显的负相关关系,而Y的含量反之,综合判定认为,岩体属高分异I型花岗岩。岩石形成温度从早至晚明显降低(平均由786℃至755℃)。εHf(t)值少数0外,绝大多数介于0.1~4.8之间,相应tDM2=0.95~1.25Ga。综合推断认为,江里沟岩体的原始岩浆是由部分熔融的岩石圈地幔与中新元古代的地壳混合,形成的混合岩浆,后经强烈的结晶分异作用形成江里沟复式岩体。
[Abstract]:The closure of the PaleoTethys Ocean in the Triassic along the present Mian suture zone marks the completion of the final collage of the North China Plate (NCBB) and the Yangtze Plate (YZB). Indosinian granitic magma was developed in the western part of Qinling orogenic belt, which provides favorable conditions for mineralization in this area. The study of the age, geochemistry, evolution and source of these magmatic rocks will be helpful to understand the tectonic background and dynamic environment of the period. The Jiangligou complex rock mass in the northern subzone of the Qinling Mountains west of this paper was studied systematically by LA-ICP-MS zircon U-Pb dating zircon HF isotope test and principal trace element analysis. The results show that the three main lithologic types of the Jiangligou complex are porphyry biotite monzogranite, granitic porphyry and fine-grained granite, with weighted mean ages of 229.1 卤1.8 Mai MSWD 0.42 卤222.5 卤1.4 Ma-MSWDU 0.41 and 217.1 卤1.8 Ma-MSWD1.4T respectively, indicating that the rock was formed in the late Triassic. Its geochemical properties are high SiOS _ 2 / 72.67 / 77.84, alkali-rich K _ 2O Na _ 2O 7.67 and 8.75m, weak peraluminous / ACNK _ (1.01C) 1.01C ~ (1.06C), high differentiation (the rock mass increases from early to late, DI and Rb/Sr are higher than RbSrLi 1.7612.19), rich in elements such as RbThU, HREE, and so on. The negative EU anomaly (未 EU ~ (0.54) 0.62) 0.260.260.70 ~ (0.20) 0.20 ~ (0.60) P _ 2O _ 5 is negatively correlated with SiO_2 in all the three intrusions, whereas the Y content is the opposite. It is considered that the rock mass belongs to high-grade hetero-I-type granite. The formation temperature of the rocks decreased obviously from early to late (from 786 鈩，

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