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引用本文:谭人文,王永,陈柏林,石永红,高允,申景辉. 西秦岭何家庄—老虎窑岩体U-Pb年龄和成因及其对板块俯冲时间的限定[J]. 中国地质, 2020, 47(4): 1155-1172.
TAN Renwen,WANG Yong,CHEN Bailin,SHI Yonghong,GAO Yun,SHEN Jinghui. U-Pb age and genesis of the Hejiazhuang-Laohuyao intrusion in West Qinling and limitation of plate subduction time[J]. Geology in China, 2020, 47(4): 1155-1172(in Chinese with English abstract).
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西秦岭何家庄—老虎窑岩体U-Pb年龄和成因及其对板块俯冲时间的限定
谭人文1,2, 王永2, 陈柏林2, 石永红1,2, 高允1,3, 申景辉1,2
1.中国地质科学院地质力学研究所, 古地磁与古构造重建重点实验室, 北京 100081;2.中国地质大学(北京), 北京 100083;3.中国地质大学(武汉), 湖北 武汉 430074
摘要:
何家庄—老虎窑岩体位于勉略缝合带以北,靠近秦岭微板块北部的商丹断裂带西段内部,两者的主体岩性为花岗闪长岩。本文对何家庄—老虎窑岩体进行了LA-ICP-MS锆石U-Pb同位素定年和地球化学特征以及Hf同位素特征研究。结果表明,西部何家庄附近花岗闪长岩侵位时间为235~240 Ma,东部老虎窑附近花岗岩侵位时间为239 Ma,两者均侵位于早三叠世。何家庄—老虎窑岩体花岗闪长岩均为高钾钙碱性系列,表现出强过铝质特征,属于I型花岗岩。两者岩浆锆石的εHft)值都是以负值为主,包含一到两个正值,地壳模式年龄为中元古代(1255~1754 Ma),指示它们的源岩有地幔物质的加入,可能是以中元古代古老地壳的部分熔融为主的壳源物质与地幔物质混合的岩浆。且表现出与埃达克质岩相似的地球化学特征,反映其岩浆可能起源于俯冲洋壳在高压环境下部分熔融产生的溶体与由于底侵作用被橄榄岩混染的下地壳部分熔融产生的高钾溶体的岩浆混合。两者的侵位年龄和成因证明了扬子板块与秦岭微板块在235~240 Ma的这个期间处于俯冲阶段。
关键词:  商丹断裂带  何家庄-老虎窑岩体  锆石U-Pb年龄  地球化学  Hf同位素  西秦岭造山带  地质调查工程
DOI:10.12029/gc20200416
分类号:P597.3
基金项目:中国地质调查局地质调查项目(DD20160053,DD20190161)、中国地质调查局中央级公益性科研院所基本科研业务费(JYYWF20183702和JYYWF20180602)联合资助。
U-Pb age and genesis of the Hejiazhuang-Laohuyao intrusion in West Qinling and limitation of plate subduction time
TAN Renwen1,2, WANG Yong2, CHEN Bailin2, SHI Yonghong1,2, GAO Yun1,3, SHEN Jinghui1,2
1.Key Laboratory of Paleomagnetism and Tectnoic Reconstruction, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;2.China University of Geoscience(Beijing), Beijing 100083, China;3.China University of Geoscience(Wuhan), Wuhan 430074, Hubei, China
Abstract:
The Hejiazhuang-Laohuyao intrusions are located in the north of the Mianlue suture zone, close to the west section of the Shangdan fault zone in the north of the Qinling microplate, and their main lithology is granodiorite. The authors studied the LA-ICP-MS zircon U-Pb ages, geochemical characteristics and Hf isotope characteristics of the Hejiazhuang-Laohuyao intrusions. The results show that the emplacement time of the Hejiazhuang intrusion is 235-240 Ma and that of the Laohuyao intrusions is 239 Ma, suggesting that their emplacement epochs were the early Triassic. The granodiorite in the Hejiazhuang and Laohuyao intrusions are both high-potassium calcareous and alkaline series, showing strong over-aluminum characteristics and belonging to type I granite. The εHf (t) values of both magmatic zircons are mostly negative and contain one or two positive values. The model age of the crust is Mesoproterozoic (1255-1754 Ma), indicating that their source rocks experienced the addition of mantle materials, which might have been magma mixed with mantle materials dominated by partial melting of Mesoproterozoic ancient crust, showing similar geochemical characteristics to adakianrocks and indicating that the magma might have originated from high potassium solution magma mixing produced by partial melting of subducted oceanic crust under high pressure and partial melting of lower crust contaminated by peridotite due to bottom transgression. The emplacement time and genesis of them indicate that the Yangtze plate and Qinling microplates were subducted during the period of 235-240 Ma.
Key words:  Shangdan fault zone  Hejiazhuang-Laohuyao intrusions  zircon U-Pb age  geochemistry  Hf isotope  West Qinling orogenic belt  geological survey engineering