西藏罗布真矿区林子宗群火山岩锆石U-Pb年龄、地球化学特征及其地质意义
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摘要
罗布真铅锌多金属矿床位于冈底斯火山-岩浆活动带的中南部,矿区内广泛发育林子宗群火山岩,岩性为英安岩和流纹质晶屑凝灰岩。LA-ICP-MS锆石U-Pb定年结果显示,罗布真矿区内林子宗群英安岩的成岩年龄为(49. 14±0. 86) Ma,应属于帕那组火山岩地层,并非前人所认为的典中组。岩石具有高K、低Ti的特征,属于高钾钙碱系列;相对富集Rb、Th、U、K、Zr、Hf等元素,亏损Nb、Ta、P、Ti、Sr等元素,且轻重稀土分馏明显,具有明显的负铕(δEu=0. 50～0. 65)异常。在印度-亚洲大陆汇聚的过程中,新特提斯洋向欧亚大陆俯冲,约50 Ma发生了大规模的火山、岩浆作用,同时岩浆-热液成矿作用也进入高峰期,林子宗群火山岩的形成时代与该时代一致,形成于陆陆碰撞形成的板内环境。罗布真矿区林子宗群火山岩年龄的厘定,揭示了冈底斯带林子宗群帕那组火山岩具有赋矿潜力,对认识该地区林子宗群火山岩与热液脉型铅锌多金属矿化的关系具有指导意义。
The Luobuzhen Pb-Zn polymetallic deposit is located in the middle-southern part of the Gangdese magmatic belt. The Linzizong Group( Gp.) volcanic rocks are widely distributed in the mining area,and contain mainly dacite and rhyolitic crystal tuff. LA-ICP-MS zircon U-Pb dating reveals that the dacite was formed at( 49. 14 ± 0. 86) Ma,which was coeval with the Pana Formation volcanic sequence but not the Dianzhong Formation. The rocks are characterized by high K but low Ti contents and are high-K calc-alkaline. The elementsof Rb,Th,U,K,Zr,Hf and LREEs are enriched,while Nb,Ta,P,Ti,Sr and HREEs are depleted,and clear LREE/HREE fractionation is present. The volcanic rocks also have negative Eu-anomalies( δEu = 0. 50 to0. 65). The Neo-Tethys oceanic slab likely subducted beneath Eurasia during the incipient India-Asia collision.Extensive volcanism-plutonism occurred and mineralization reached a peak at ～ 50 Ma. The dacite volcanism was coeval with the regional magmatism,which suggests that the dacite was formed in an intraplate tectonic environment. This work re-determined the age of the Linzizong Gp. volcanic rocks and implied that the Pana Formation volcanic rocks in the Gangdese belt are potentially ore-bearing. Our finding also provides significant implication and prospecting guidance to understand the relationship between the Linzizong Gp. magmatism and the hydrothermal vein-type Pb-Zn polymetallic mineralization.
The Luobuzhen Pb-Zn polymetallic deposit is located in the middle-southern part of the Gangdese magmatic belt. The Linzizong Group( Gp.) volcanic rocks are widely distributed in the mining area,and contain mainly dacite and rhyolitic crystal tuff. LA-ICP-MS zircon U-Pb dating reveals that the dacite was formed at( 49. 14 ± 0. 86) Ma,which was coeval with the Pana Formation volcanic sequence but not the Dianzhong Formation. The rocks are characterized by high K but low Ti contents and are high-K calc-alkaline. The elementsof Rb,Th,U,K,Zr,Hf and LREEs are enriched,while Nb,Ta,P,Ti,Sr and HREEs are depleted,and clear LREE/HREE fractionation is present. The volcanic rocks also have negative Eu-anomalies( δEu = 0. 50 to0. 65). The Neo-Tethys oceanic slab likely subducted beneath Eurasia during the incipient India-Asia collision.Extensive volcanism-plutonism occurred and mineralization reached a peak at ～ 50 Ma. The dacite volcanism was coeval with the regional magmatism,which suggests that the dacite was formed in an intraplate tectonic environment. This work re-determined the age of the Linzizong Gp. volcanic rocks and implied that the Pana Formation volcanic rocks in the Gangdese belt are potentially ore-bearing. Our finding also provides significant implication and prospecting guidance to understand the relationship between the Linzizong Gp. magmatism and the hydrothermal vein-type Pb-Zn polymetallic mineralization.
引文
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(1)尼采,扎西,达瓦,等.西藏自治区昂仁县巴热拉矿区铅多金属矿普查报告[R].西藏自治区地质矿产勘查开发局区域地质调查大队,2012:1-70.
(2)张洪铭,余槐,陈小平,等.西藏日喀则昂仁县罗布真铅锌多金属矿详查年度工作总结[R].拉萨:西藏丰恩矿业有限公司,2016:1-89.
[2] MO X X,NIU Y L,DONG G C,et al. Contribution of syncollisional felsic magmatism to continental crust growth:a case study of the Paleogene Linzizong volcanic succession in southern Tibet[J]. Chemical Geology,2008,250:49-67.
[3]付刚燕.西藏拉萨地块南部新特提斯洋俯冲成岩成矿作用[D].北京:中国地质科学院,2017:1-171.
[4]侯增谦,赵志丹,高永丰,等.印度大陆板片前缘撕裂与分段俯冲:来自冈底斯新生代火山-岩浆作用的证据[J].岩石学报,2006,22(4):761-774.
[5]周肃,方念乔,董国臣,等.西藏林子宗火山岩氩-氩年代学研究[J].矿物岩石地球化学通报,2001,20(4):317-319.
[6]周肃,莫宣学,董国臣,等.西藏林周盆地火山岩40Ar/39Ar年代格架[J].科学通报,2004,49(20):2095-2103.
[7]董国臣,莫宣学,赵志丹,等.拉萨北部林周盆地林子宗火山岩层序新议[J].地质通报,2005,24(6):549-557.
[8]黄眏聪,杨德明,郑常青,等.西藏林周县扎雪地区林子宗群帕那组火山岩的地球化学特征及其地质意义[J].吉林大学学报(地球科学版),2005,35(5):576-581.
[9]李皓杨,钟孙霖,王彦斌,等.藏南林周盆地林子宗火山岩的时代、成因及其地质意义:锆石U-Pb年龄和Hf同位素证据[J].岩石学报,2007,23(2):493-500.
[10] HE S D,KAPP P,DECELES P G,et al. Cretaceous-Tertiary geology of the Gangdese Arc in the Linzhou Area,southern Tibet[J]. Tectonophysics,2007,433(1/4):15-37.
[11] LEE H Y,CHUNG S L,LO C H. Eocene Neo-Tethyan slab break off in southern Tibet inferred from the Linzizong volcanic record[J]. Tectonophysics,2009,477:20-37.
[12]王乔林.冈底斯西段林子宗起群火山岩的地球化学特征及锆石年代学研究[D].北京:中国地质大学(北京),2011:1-81.
[13]岳相元.西藏错勤地区典中组火山岩地球化学特征及其地质意义[D].成都:成都理工大学,2012:1-63.
[14]张小强.西藏则学林子宗火山岩岩石成因及其与成矿关系的研究[D].武汉:中国地质大学(武汉),2013:1-118.
[15]谢冰晶,周肃,谢国刚,等.西藏冈底斯中段孔隆至丁仁勒地区林子宗群火山岩锆石SHRIMP年龄和地球化学特征的区域对比[J].岩石学报,2013,29(11):3803-3814.
[16]谢克家,曾令森,刘静,等.藏南昂仁县桑桑地区林子宗群火山岩的形成时代和地球化学特征[J].地质通报,2011,30(9):1339-1352.
[17]付文春,康志强,潘会彬.西藏冈底斯带西段狮泉河地区林子宗群火山岩地球化学特征、锆石U-Pb年龄及地质意义[J].地质通报,2014,33(6):850-859.
[18]于枫,李志国,赵志丹,等.西藏冈底斯带中西部措麦地区林子宗火山岩地球化学特征及意义[J].岩石学报,2010,26(7):2217-2225.
[19]梁银平,朱杰,次邛,等.青藏高原冈底斯带中部朱诺地区林子宗群火山岩锆石U-Pb年龄和地球化学特征[J].地球科学,2010,35(2):211-224.
[20] DONALDSON D G,WEBB A A G,MENOLD C A. Petrochronology of Himalayan ultrahigh-pressure eclogite[J]. Geology,2013,41(8):835-838.
[21]刘安琳,朱弟成,王青,等.藏南米拉山地区林子宗火山岩LA-ICP-MS锆石U-Pb年龄和起源[J].地质通报,2015,34(5):826-834.
[22] ZHU D C,WANG Q,ZHAO Z D. Magmatic record of India-Asia collision[J]. Scientific Reports,2015,5:14289.
[23]西藏自治区地质调查院二分院.西藏朱诺地区矿产远景调查报告[R].北京:中国地质调查局,2010:36-98.
[24]欧阳海涛,孙祥,郑有业,等.西藏冈底斯罗布真铅锌矿床成矿流体特征[J].地质与勘探,2015,51(5):816-828
[25]高顺宝.西藏冈底斯西段铜铁多金属成矿作用与找矿方向[D].北京:中国地质大学(北京),2015:1-212.
[26]潘桂堂,莫宣学,侯增谦,等.冈底斯造山带的时空结构及演化[J].岩石学报,2006,22(3):521-533.
[27]朱弟成,潘桂裳,莫宣学,等.冈底斯中北部晚侏罗世—早白垩世地球动力学环境:火山岩约束[J].岩石学报,2006,22(3):534-546.
[28]吴松,张能军,孙祥,等.西藏朱诺整装勘查区专项填图与技术应用示范子项目成果报告[R].拉萨:西藏自治区地质矿产勘查开发局第二地质大队;北京:中国地质大学(北京),2016:1-302.
[29]付刚燕,胡古月,唐菊兴,等.西藏斯弄多低硫化型浅成低温热液Ag-Pb-Zn矿床:Si-H-O同位素示踪应用[J].地质学报,2017,91(4):836-848.
[30]姜军胜,郑有业,高顺宝,等.西藏查藏错铜铅锌矿床成因:C-H-O-S-Pb同位素制约[J].地球科学,2015,40(6):1006-1017.
[31]姜军胜.冈底斯西段林子宗群火山岩区多金属矿床成因及找矿潜力[D].北京:中国地质大学(北京),2018:1-229.
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