投稿时间：2011-07-09
修订日期：2013-05-20
中文摘要:扎日加花岗岩直接侵入到已发生褶皱的三叠纪地层中,岩石类型主要为花岗闪长岩和二长花岗岩,两者呈渐变过渡关系,岩石具粗粒结构或斑状结构。地球化学研究显示,北巴颜喀拉扎日加花岗岩具有高硅[w(SiO2)为66.29%~73.03%]、高碱(ALK=6.59~9.26)、过铝质(ASI=1.45~1.648)的特征;稀土元素球粒陨石标准化图解表现出轻稀土元素相对富集,重稀土元素相对亏损,具中等至弱Eu的负异常;原始地幔标准化蛛网图表现出相对富集Cs、Rb、Ba、U等大离子亲石元素及LREE,亏损Nb、Ta、Zr、Hf、HREE等高场强元素,指示其为壳源型高钾钙碱性系列的强过铝质S型花岗岩。在主量元素构造判别图解FeO*/(FeO*+MgO)-SiO2和R1-R2及微量元素构造判别图解Rb-(Y-Nb)、Rb-(Yb+Ta)、Ta-Yb、Nb-Y及Rb-Hf-Ta上,所有点均落于同碰撞或后碰撞花岗岩区,且都落于Sr-Yb图的低Sr、低Yb区,表明扎日加花岗岩形成于巴颜喀拉山造山带陆内碰撞造山阶段的同碰撞至后碰撞初期,为挤压向拉张构造体制转变的过渡时期,以挤压构造环境为主。LA-ICP-MS微区原位U-Pb定年获得该岩体的侵位时间为200 Ma左右,属晚三叠世—早侏罗纪,表明大场地区处于巴颜喀拉造山带陆内碰撞造山阶段的同碰撞向后碰撞初过渡时期,并且至少在(193±4) Ma时已进入伸展构造环境。对比已有的大场金矿成矿年龄,显示扎日加花岗岩与大场金矿的形成均为巴颜喀拉造山带陆内碰撞造山阶段的产物,成岩与成矿之间可能存在内在联系。
Abstract:Zharijia granitiods directly intruded folded Triassic strata. The granites composed of granodiorite and adamellite showing transitional relationship have porphyritoid or porphyritic texture and abundant aluminum and potassium. Geochemical researches indicate that Zharijia granitiods from Dachang area in the North Bayan Har Mountains have high silica [w(SiO2)=66.29%~73.03%], high alkali (ALK=6.59~9.26), and peraluminous (ASI=1.45~1.648) characteristics. The granite intrusions are enriched in LREE and depleted in HREE with weak to moderate negative anomalies, suggesting typical high-K calc-alkaline S-type granites characterized by enrichment of LILE (Rb, Ba, Cs and U) and depletion of HREE, Nb, Ta, Zr and Hf. As for major element and trace element tectonic discrimination of the granitoids, almost all the samples lie in syn-COLG-syn-collision and post-COLG areas in FeO*/(FeO*+MgO)-SiO2 and R1-R2 diagrams as well as Rb-(Y-Nb), Rb-(Yb+Ta), Ta-Yb, Nb-Y and Rb-Hf-Ta diagrams, and all points fall into area of low Sr and Yb type granites in Sr-Yb plot. These data show that Zharijia granitoids were formed in the period from syn-collision to the beginning of post-collision during the Bayan Har intracontinental orogenic activity. The granitiods were formed in the transitional period from compression to extension during the collisional orogeny, with the compressional action being dominant. Zircons from the granites assume euhedral and magmatic zones on the CL images. Zircon LA-ICP-MS in situ U-Pb dating yielded an age of 200 Ma, which should be the formation age of the granites, belonging to late Triassic-early Jurassic. It is thus held that the tectonic setting of Dachang area was the transition from the collision stage to the beginning of the post-collision stage during the Bayan Har intracontinental orogenic activity in Triassic-early Jurassic period, and that Dachang area was in an extensional environment at least at (193±4) Ma. Based on a comparison with the metallogenic age of the known Dachang gold ore bodies, the authors infer that the Dachang gold ore deposit and Zharijia granites were both produced during the Bayan Har intracontinental orogenic activity, and that the formation of the gold deposit had something to do with the formation of the granitiods.
keywords:geochemistry zircon LA-ICP-MS U-Pb dating geotectonic setting Zharijia granities Dachang gold deposit Bayan Har Mountains qinghai
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中图分类号：P618.51;P597
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基金项目:本文得到青海大场地区金矿整装勘查项目;西北大学大陆动力学国家重点实验室科技部专项经费;国家自然科学基金(批准号41173060)和陕西省"13115"重大科技专项(2008ZDKG-48)的联合资助
引用文本：
边飞,吴柏林,高永旺,张昆宏,李连松,王福德,马晔,吴伟,王海桐,魏安军.2013.青海扎日加花岗岩地球化学、锆石LA-ICP-MS U-Pb定年及地质意义[J].矿床地质,32(3):625~640BIAN Fei,WU BoLin,GAO YongWang,ZHANG KunHong,LI LianSong,WANG FuDe,MA Ye,WU Wei,WANG HaiTong,WEI AnJun.2013.Geochemistry, zircon LA-ICP-MS U-Pb dating and geological significance of Zharijia granitoids in Dachang area, Qinghai Province[J].Mineral Deposits32(3):625~640
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