矿床地质2013，Vol.32Issue(3)：625-640,16.
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
Geochemistry, zircon LA-ICP-MS U-Pb dating and geological significance of Zharijia granitoids in Dachang area, Qinghai Province
摘要
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 SrYb 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.关键词
地球化学/锆石LA-ICP-MS U-Pb定年/构造环境/扎日加花岗岩/大场金矿/巴颜喀拉/青海Key words
geochemistry/ zircon LA-ICP-MS U-Pb dating/ geotectonic setting/ Zharijia granities/Dachang gold deposit/ Bayan Har Mountains/ qinghai分类
天文与地球科学引用本文复制引用
边飞,吴柏林,高永旺,张昆宏,李连松,王福德,马晔,吴伟,王海桐..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,2013,32(3):625-640,16.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 （批准号41173060）
