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引用本文:李康宁,刘伯崇,狄永军. 三叠纪西秦岭西北部洋俯冲的记录:来自镁安山岩/高镁安山岩的证据[J]. 中国地质, 2020, 47(3): 709-724.
LI Kangning,LIU Bochong,DI Yongjun. Triassic oceanic subduction in northwestern West Qinling Mountain: Evidence from Mg andesite and high-Mg andesite[J]. Geology in China, 2020, 47(3): 709-724(in Chinese with English abstract).
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三叠纪西秦岭西北部洋俯冲的记录:来自镁安山岩/高镁安山岩的证据
李康宁1,2, 刘伯崇1, 狄永军2
1.甘肃省地质矿产勘查开发局第三地质矿产勘查院, 甘肃 兰州 730050;2.中国地质大学 (北京) 地球科学与资源学院, 北京 100083
摘要:
三叠纪以来,西秦岭地区构造-岩浆活动极为强烈,中酸性侵入岩呈北西向弧状分布,前人做了大量卓有成效的工作,但对出露较少的火山岩鲜有研究。本次工作选取青海省同仁县麦秀和甘肃省夏河县甘加、德乌鲁3个地区的安山岩,从岩石学、岩石地球化学、年代学等进行分析。结果显示安山岩均属于钙碱性系列,具有富钾火山岩的特征。其中,麦秀安山岩中既有高镁安山岩,也有镁安山岩,而甘加与德乌鲁安山岩属于镁安山岩,为洋壳俯冲作用形成的两种典型火山岩类型。西秦岭地区安山岩形成时间东早西晚,由西向东安山岩基性程度降低,K2O、Na2O、∑REE等含量增高,MF、FL、DI、La/Sm等值变大,SI、Mg#等值降低,并且呈明显的线性特征,构成同仁—合作镁安山岩(镁闪长岩)岩浆弧组合,和北部隆务峡蛇绿岩带一起,组成岩性分布极性,从而判断出西秦岭西北部在三叠纪存在隆务峡蛇绿岩代表的洋壳板块向南俯冲作用。
关键词:  镁安山岩  高镁安山岩  俯冲  地质调查工程  西秦岭  青海
DOI:10.12029/gc20200311
分类号:P542.4;P588.14+4
基金项目:国家重点研发计划深地资源勘查开采专项“深部矿产资源三维找矿预测评价示范”课题(2017YFC0601506)下属“甘肃省玛曲—合作地区资源潜力评价与深部找矿预测示范”专题、中国地质调查局项目“甘肃省夏河—合作地区金矿整装勘查区矿产调查与找矿预测”(12120100000160901-60)及甘肃省基础地质调查研究项目“甘肃玛曲—合作整装勘查区深部找矿预测”联合资助。
Triassic oceanic subduction in northwestern West Qinling Mountain: Evidence from Mg andesite and high-Mg andesite
LI Kangning1,2, LIU Bochong1, DI Yongjun2
1.Third Institute of Geology and Mineral Exploration of Gansu Bureau of Geology and Mineral Resources, Lanzhou 730050, Gansu China;2.School of Earth Sciences and Resources, China University of Geosciences, Beijing 10083, China
Abstract:
Since the Triassic, tectono-magmatic activity in West Qinling Mountains has been very intense and the intermediate-acid intrusive rocks are distributed in a NW-trending arc. A lot of effective work has been done by previous researchers, but research on volcanic rocks with less exposure remain insufficient. Petrological, geochemical and chronologic analysis was used for andesite in Maixiu County and Tongren County of Qinghai Province and Ganjia and Dewulu areas in Xiahe County of Gansu Province. The results show that andesite belongs to calc-alkaline series and shows the characteristics of potassium-rich volcanic rocks. Maixiu andesite contains both high-magnesium andesite and magnesian andesite, while Ganga and Deuru andesite belongs to magnesian andesite, being two typical types of volcanic rocks formed by oceanic crust subduction. The formation of andesite in West Qinling area occurred early in the East and late in the west. From west to east, andesite in West Qinling Mountain presents the following characteristics:1) The values of SiO2 and alkali decrease; 2) The formation of andesite took place earlier; 3) The values of K2O, Na2O, ∑REE increase; 4) The values of MF, FL, DI, La/Sm is larger; 5) The values of SI, Mg# decrease, with significant linear features. The magmatic arc assemblage of Xiahe-cooperative magnesian andesite (mafic diorite) is composed of Tongren-Hezuo magnesian magmatic arc assemblage and Longwu gorge ophiolite belt in the north. Polarity indicates that the oceanic crust plate represented by Longwu gorge ophiolite subducted southward in the Triassic in the northwestern part of West Qinling Mountain.
Key words:  Mg andesite  high Mg andesite  subduction  geological survey engineering  West Qinling Mountain  Qinghai