西藏尕尔穷-嘎拉勒铜金矿集区两套火山岩浆源区及其地质意义——来自Hf同位素特征的指示
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摘要
尕尔穷-嘠拉勒铜金矿集区位于班公湖-怒江缝合带西段,区内发育有早白垩世及晚白垩世两套中酸性火山角砾岩。通过锆石Hf同位素测定,识别出矿集区两套火山岩浆源区。早白垩世朗久组英安质火山角砾岩ε_(Hf)(t)值变化于-13.93~-4.93之间,地壳模式年龄(t_(DM))变化于1 006Ma~1 354Ma之间,负的ε_(Hf)(t)值及老的模式年龄表明其岩浆源区起源于古老的成熟地壳,形成于古拉萨地体陆缘弧环境,与班公湖-怒江特提斯洋向南俯冲有关。晚白垩世多爱组安山质火山角砾岩ε_(Hf)(t)值变化于5.19~8.86之间,地壳t_(DM)模式年龄变化于404Ma~546Ma之间,其正的ε_(Hf)(t)值及相对较年轻的地壳模式年龄表明其形成于新生下地壳的部分熔融,与班公湖-怒江特提斯洋消亡后,南羌塘陆块与北冈底斯陆块碰撞闭合有关。通过对比南冈底斯及班公湖-怒江成矿带北缘典型矿床成矿岩体Hf同位素组成及相应的成矿作用,表明班公湖-怒江缝合带西段可能是区域上最具潜力的Cu,Au成矿地带,同时缝合带南缘具有寻找斑岩型铜金矿的巨大潜力。
Two series of early-late Cretaceous intermediate-acid volcanic breccias occur in the Ga′erqiong-Galale Cu-Au ore concentrated area in the western segment of the Bangonghu-Nujiang suture zone.Study of magma origin of these volcanic rocks is carried out by means of the Hf isotope determination.It shows that the zirconε_(Hf)(t) values of the Early Cretaceous dacitic volcanic breccias of Langjiu Formation range from-13.93 to-4.93,and the (t_(DM)) model ages range from 1 006 Ma to 1 354 Ma,indicating that the volcanic breccias are derived from the old and mature crust and formed in the continental margin arc environment related to the southward subduction of the Bangonghu-Nujiang Tethy Sea.The Late Cretaceous volcanic breccias of Duoai Formation show a narrow range of zircon ε_(Hf)(t) values from 5.19 to 8.86 with the (t_(DM)) model ages from 404 Ma to 546 Ma,indicating that the magma origin of volcanic breccias of Duoai Formation are the newly formed crust related to the collision of the Qiangtang block and the Gangdese block.A comparative study of the Hf isotope of the magmatic rock in the typical deposits in the southern Gangdese and the northern Bangonghu-Nujiang suture zone shows that the western Bangonghu-Nujiang suture zone has the potential to the Cu-Au mineralization,and the southern Bangonghu-Nujiang suture zone possesses the greatest potential to the prospecting of porphyry Cu-Au deposit.
Two series of early-late Cretaceous intermediate-acid volcanic breccias occur in the Ga′erqiong-Galale Cu-Au ore concentrated area in the western segment of the Bangonghu-Nujiang suture zone.Study of magma origin of these volcanic rocks is carried out by means of the Hf isotope determination.It shows that the zirconε_(Hf)(t) values of the Early Cretaceous dacitic volcanic breccias of Langjiu Formation range from-13.93 to-4.93,and the (t_(DM)) model ages range from 1 006 Ma to 1 354 Ma,indicating that the volcanic breccias are derived from the old and mature crust and formed in the continental margin arc environment related to the southward subduction of the Bangonghu-Nujiang Tethy Sea.The Late Cretaceous volcanic breccias of Duoai Formation show a narrow range of zircon ε_(Hf)(t) values from 5.19 to 8.86 with the (t_(DM)) model ages from 404 Ma to 546 Ma,indicating that the magma origin of volcanic breccias of Duoai Formation are the newly formed crust related to the collision of the Qiangtang block and the Gangdese block.A comparative study of the Hf isotope of the magmatic rock in the typical deposits in the southern Gangdese and the northern Bangonghu-Nujiang suture zone shows that the western Bangonghu-Nujiang suture zone has the potential to the Cu-Au mineralization,and the southern Bangonghu-Nujiang suture zone possesses the greatest potential to the prospecting of porphyry Cu-Au deposit.
引文
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[27]张立雪,王青,朱弟成,等.拉萨地体锆石Hf同位素填图:对地壳性质和成矿潜力的约束[J].岩石学报,2013,29(11):3 681-3 688.
[2]唐菊兴,孙兴国,丁帅,等.西藏多龙矿集区发现浅成低温热液型铜(金银)矿床[J].地球学报,2014,35(1):6-10.
[3]Wei S G,Tang J X,Song Y,et al.Early Cretaceous bimodal volcanism in the Duolong Cu mining district,western Tibet:Record of slab breakoff that triggered ca.108Ma~113Ma magmatism in the western Qiangtang terrane[J].Journal of Asian Earth Sciences,2017,138:588-607.
[4]康志强,许继峰,王保弟,等.拉萨地块北部白垩纪多尼组火山岩的地球化学:形成的构造环境[J].地球科学-中国地质大学学报,2009,34(1):89-104.
[5]康志强,许继峰,王保第,等.拉萨地块北部去申拉组火山岩:班公湖-怒江特提斯洋南向俯冲的产物[J].岩石学报,2010,26(10):3 106-3 116.
[6]朱弟成,莫宣学,赵志丹,等.西藏冈底斯带措勤地区则弄群火山岩锆石U-Pb年代学格架及构造意义[J].岩石学报,24(3):401-412.
[7]张志,陈毓川,唐菊兴,等.西藏嘎拉勒铜金矿床地质特征及矽卡岩矿物学特征研究[J].矿床地质,2013,32(5):915-931.
[8]Zhang Z,Yao X F,Tang J X,et al.Lithogeochemical,Re-Os and U-Pb Geochronological,Hf-Lu and S-Pb Isotope Data of the Ga′erqiongGalale Cu-Au Ore-Concentrated Area:Evidence for the Late Cretaceous Magmatism and Metallogenic Event in the Bangong-Nujiang Suture Zone,Northwestern Tibet.China:Resource Geology,2015,65(2):76-102.
[9]张志,唐菊兴,李志军,等.西藏尕尔穷-嘎拉勒铜金矿集区侵入岩岩石地球化学特征及其地质意义[J].地质与勘探,2013,49(4):676-688.
[10]姚晓峰,唐菊兴,王友,等.西藏尕尔穷铜金矿金矿物特征研究[J].地质与勘探,2011,47(6):1 018-1 025.
[11]张志,唐菊兴,杨毅,等.西藏尕尔穷铜金矿元素空间分布规律及地球化学勘查模型[J].地球学报,2012,33(4):663-672.
[12]张志,陈毓川,唐菊兴,等.西藏尕尔穷-嘎拉勒铜金矿集区火山岩年代学及地球化学-对班公湖-怒江特提斯洋南向俯冲至碰撞的响应[J].地球科学-中国地质大学学报,2015,40(1):77-97.
[13]吕立娜,崔玉斌,宋亮,等.西藏嘎拉勒夕卡岩型金(铜)矿床地球化学特征与锆石的LA-ICP-MA定年及意义[J].地学前缘,2011,18(5).224-242.
[14]宋彪,张玉海,万渝生,等.锆石SHRIMP样品靶制作、年龄测定及有关现象讨论[J].地质论评,2002,48(增刊):26-30.
[15]Wu F Y,Yang Y H,Xie L W,et al.Hf isotope composition of the standard zircons and baddeleyites used in U-Pb geochronology[J].Chemical Geology,2006,234:105-126.
[16]Crofu F,Hanchar J M,Hoskin P W,et al.Atlas of zircon textures[J].Reviews Mineral Geochemistry,2003,53:469-495.
[17]潘桂棠,王立全,朱弟成.青藏高原区域地质调查中几个重大科学问题的思考[J].地质通报,2004,(1):12-19.
[18]Pearce J A,Deng Wanming.The ophiolites of the Tibet Geotraverses,Lhasa to Golmud(1985)and Lhasa to Kathmandu(1986)[J].Phil Trans Roy Soc Lond Math Phys Sci,1988,327(1594):215-238.
[19]秦克章,李光明,张旗,等.西藏浅成低温金-银矿的成矿条件与可能产出区分析-从斑岩-浅成低温铜金成矿系统的角度[A].见:陈毓川,毛景文,薛春纪(主编),第八届全国矿床会议论文集[C].北京:地质出版社,2006,666-670.
[20]Zhu D C,Zhao Z D,Niu Y L,et al.The Lhasa Terrane:Record of a microcontinent and its histories of drift and growth[J].Earth and Planetary Science Letters,2011,301(1-2):241-255.
[21]张志,宋俊龙,唐菊兴,等.西藏嘎拉勒铜金矿床的成岩成矿时代与岩石成因:锆石U-Pb年龄、Hf同位素组成及辉钼矿Re-Os定年[J].地球科学,2017,42(06):862-880.
[22]杨志明.西藏驱龙超大型斑岩铜矿床-岩浆作用与矿床成因(博士论文)[D].北京:中国地质科学院,2008,1-212.
[23]王立强.西藏邦铺式钼多金属矿床-简论冈底斯成矿带东段钼多金属矿床成矿规律(博士论文)[D].北京:中国地质科学院,2013,1-224.
[24]姚晓峰.西藏甲玛、驱龙矿床成矿作用对比研究(博士论文)[D].北京:中国地质大学,2013,1-198.
[25]黄勇.西藏谢通门县雄村斑岩铜金矿床地质特征及成因研究(博士论文)[D].成都:成都理工大学,2013,1-186.
[26]李金祥.班公湖带多不杂超大型富金斑岩铜矿床的成岩成矿年代学、岩石学及高氧化岩浆-流体-成矿作用(博士论文)[D].北京:中国科学院,2008,1-235.
[27]张立雪,王青,朱弟成,等.拉萨地体锆石Hf同位素填图:对地壳性质和成矿潜力的约束[J].岩石学报,2013,29(11):3 681-3 688.