北大别山仙桥中生代酸性火山岩地球化学特征、锆石U-Pb年龄及其成矿构造背景  

Geochemical characteristics,zircon U-Pb age and metallogenic tectonic background of the Mesozoic acidic volcanic rocks from Xianqiao area in North Dabie Mountain

作　　者：骆亚南[1] 许栋 余少华 莘丰培 冼源宏 罗帅[1] LUO Ya’nan;XU Dong;YU Shaohua;XIN Fengpei;XIAN Yuanhong;LUO Shuai(No.3 Institute of Geological and Mineral Resources Survey,Henan Bureau of Geoexploration and Mineral Development,Xinyang 464000,He’nan,China;No.1 Institute of Geological and Mineral Resources Survey,Henan Bureau of Geoexploration and Mineral Development,Luoyang 471023,He’nan,China;Haikou Marine Geological Survey Center,China Geological Survey,Haikou 571127,Hainan,China)

机构地区：[1]河南省地质矿产勘查开发局第三地质矿产调查院,河南信阳464000 [2]河南省地质矿产勘查开发局第一地质矿产调查院,河南洛阳471023 [3]中国地质调查局海口海洋地质调查中心,海南海口571127

出　　处：《地质通报》2023年第5期802-812,共11页Geological Bulletin of China

基　　金：河南省两权价款地质科研项目《大别山铜钼金银铅锌成矿系统与成矿预测研究》(编号:豫国土资函[2015]258号11)。

摘　　要：东秦岭-北大别山构造-岩浆演化是热点研究问题,关于该带火山岩喷发时限存在较大的争议,其岩石成因和成岩构造环境尚不清楚。对北大别山西段仙桥膨润土矿床英安岩进行锆石U-Pb同位素测年和岩石地球化学研究,结果表明,仙桥酸性火山岩具有高钾(3.96%~5.01%)、富碱(K_(2)O+Na_(2)O介于7.97%~8.96%之间)、弱过铝质(A/CNK为1.0~1.15)等特点,属高钾钙碱性-钾玄岩系列火山岩。岩石轻稀土元素富集,重稀土元素亏损明显,负Eu异常不明显,Nb、Ta亏损明显,且具有高Nb/Ta、(La/Yb)N、Sr/Y值,表现为典型的埃达克质岩石地球化学特征。LA-ICP-MS锆石U-Pb同位素定年测得,仙桥成矿岩石英安岩喷发年龄为133±1 Ma,与邻区双桥膨润土、皇城山银矿床陈棚组火山岩的年龄一致。研究认为,仙桥火山岩具有埃达克岩的特征,由增厚下地壳物质部分熔融形成,产生于中生代后碰撞构造环境,在133 Ma左右,北大别山仙桥地区还未发生大规模的拆沉减薄的岩浆活动。The structural-magmatic evolution of East Qinling-North Dabie Mountains is a popular issue.The eruption time of the volcanic rocks in the belt still has a greater dispute for a long time,which is still unclear during rock formation and diagenetic tectonic environment.Based on the studies of geochemistry,zircon LA-ICP-MS U-Pb dating of dacite in Xianqiao bentonite deposit in the western segment of North Dabie Mountains,it is shown that acidic volcanic rocks from Xianqiao area display high contents of K_(2)O(3.96%~5.01%),are enriched in K_(2)O+Na_(2)O(7.97%~8.96%)and weak peraluminous,with A/CNK values of 1.0~1.15.The volcanic rocks should belong to high-K calc-alkaline to shoshonite series.The rocks are enriched LREE and depleted HREE,with weak negative Eu anomaly,strongly depleted in the high field strength elements Nb and Ta and high Nb/Ta ratio,and has high(La/Yb)N(25.68~28.25)and Sr/Y(34.92~41.42)ratios,which has obvious geochemical characteristics of adakite.Zircon LA-ICP-MS U-Pb dating result shows that the Xianqiao ore-forming rocks(dacite)was erupted at 133±1 Ma,consistent with the age of volcanic rocks of Chenpeng Formation in Shuangqiao bentonite deposit and Huangchengshan silver deposit.This research reveals that the Mesozoic acidic volcanic rocks from Xianqiao area with the characteristics of adakitic rocks were formed by partial melting of the thickened lower crust,which were formed at post-collisional tectonic setting in Mesozoic.The large-scale magma activity resulting from lower crust delamination and thinning of the lithosphere has not yet occurred in the Xianqiao area of North Dabie Mountains at about 133 Ma.

关 键 词：酸性火山岩 锆石U-PB年龄 岩石成因 北大别山 

分 类 号：P534.5[天文地球—古生物学与地层学] P588.14[天文地球—地质学] P597.3