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敦煌地块南缘多坝沟花岗岩锆石U-Pb定年、地球化学特征及其地质意义 预览

Zircon U-Pb dating,geochemistry and geological significance of the Duobagou granite pluton on the southern margin of the Dunhuang landmass
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摘要 多坝沟黑云二长花岗岩体出露于敦煌地块南缘,呈近东西向带状分布,侵位于太古宙—古元古代敦煌岩群。LA-ICPMS锆石U-Pb年龄显示,该岩体形成于晚二叠世,206Pb/238U年龄加权平均值为252.1±2.3Ma。该岩体具高SiO2含量(68.32%~72.82%)和全碱含量(7.76%~8.00%);A/CNK值为0.97~1.02,均小于1.1,为高钾钙碱性准铝质花岗岩。岩石具有明显的轻、重稀土元素分异和弱的负Eu异常,具高Sr/Yb和(La/Yb)N值富集大离子亲石元素(K、Rb、Ba、Cs),显著亏损Nb、Ta、P和Ti,表明源岩具有经典岛弧岩石地球化学特征;(87Sr/86Sr)i值为0.707083,εNd(t)为-2.22,Nd模式年龄TDM2=1102Ma。元素和同位素地球化学特征显示,多坝沟花岗岩形成于加厚下地壳中岛弧玄武岩的部分熔融。结合岩体地质特征、年代学和区域地质背景,初步认为敦煌地块在晚古生代晚期依然受古亚洲洋汇聚碰撞相关的造山活动的影响,可能是中亚造山带的最南缘组成部分。 The Duobagou biotite monzonitic granitic pluton,distributed as a nearly EW-trending belt,intruded into Archean – Paleoproterozoic Dunhuang complexes in southern Dunhuang landmass.Zircon LA ICP-MS U-Pb data revealed the crystallization age of 252.1 ± 2.3Ma,suggesting that Duobagou pluton was formed in Late Permian.Geochemical characteristics of monzonitic granite are similar to those of typical arc rocks.For example,the granites have high content of SiO2(68.32%~ 72.82%)and total alkali(7.76%~ 8.00%),and their A/CNK ratios are 0.97 to 1.02,which are less than 1.1,indicating that Duobagou granites are high potassium calcium alkaline aluminium.They have obvious differentiation of REEs and weak Eu negative anomaly,and are characterized by strong enrichment of K,Rb,Ba and Cs and depletion of Nb,Ta,P,and Ti,with high ratios of Sr/Yb and(La/Yb)N.The sample PM04-1 shows high initial Sr isotopic ratio(0.707083),relatively low εNd(t)(-2.22)and Nd model ages(TDM2=1102Ma).The authors thus hold that the Duobagou biotite monzonitic granites may be the product of partial melting of island arc basalt in thickened low crust,and the Dunhuang landmass was likely to be involved into a series of orogenic events by the closing of the Palaeo-Asian Ocean at the end of Late Paleozoic,and possibly became the southernmost part of central Asian orogenic belt.
作者 王玉玺 董雅清 余超 张丹青 王金荣 张鑫 朱永新 WANG Yuxi;DONG Yaqing;YU Chao;ZHANG Danqing;WANG Jinrong;ZHANG Xin;ZHU Yongxin(Geological Survey of Gansu Province,Lanzhou 730000,Gansu,China;School of Earth Sciences,Lanzhou University/Key Laboratory of Mineral Resources in Western China,Lanzhou 730000,Gansu,China;Gansu Provincial Bureau of Geology and Mineral Exploration & Development,Lanzhou 730000,Gansu,China)
出处 《地质通报》 CAS CSCD 北大核心 2019年第2期242-253,共12页 Geologcal Bulletin OF China
基金 中国地质调查局项目《中国矿产地质与成矿规律综合集成和服务(矿产地质志)》(编号:DD20160346) 甘肃省地质勘查基金项目《甘肃省阿克塞县多坝沟金多金属矿普查》(编号:2017D18) 甘肃省基础地质调查项目《甘肃省多坝沟地区1∶5万矿产远景调查》(编号:20151616).
关键词 花岗岩 LA-ICP-MS锆石U-PB年龄 二叠纪 敦煌地块 中亚造山带 granites LA-ICP-MS zircon U-Pb age Permian Dunhuang landmass Central Asian orogenic belt
作者简介 王玉玺(1985-),男,博士,高级工程师,从事地质矿产勘查和矿床学研究。E-mail:wangyx15@lzu.edu.cn.
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