西藏纳如松多铅锌矿床石英闪长岩成因:地球化学及Sr-Nd-Pb同位素证据  

Petrogenesis of quartz diorites of Narusongduo Pb-Zn deposit, Tibet:Constraints from geochemistry and Sr-Nd-Pb isotopes

作　　者：龚雪婧 杨竹森[2] 庄亮亮[3] 马旺[4] GONG XueJing;YANG ZhuSen;ZHUANG LiangLiang;MA Wang(China Deep Exploration Center-SinoProbe Center, Chinese Academy of Geological Sciences, Beijing 100037, China;MNR Key Laboratory and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;Institute of Geology,Chinese Academy of Geological Sciences, Beijing 100037, China)

机构地区：[1]中国地质科学院地球深部探测中心,北京100037 [2]自然资源部成矿规律与资源评价重点实验室中国地质科学院矿产资源研究所,北京100037 [3]中国地质大学地球科学与资源学院,北京100083 [4]中国地质科学院地质研究所,北京100037

出　　处：《矿床地质》2019年第1期48-60,共13页Mineral Deposits

基　　金：国家重点研发计划"深地资源勘查开采"重点专项(编号:2016YFC0600306);地质调查项目(编号:DD20179172)的联合资助

摘　　要：纳如松多矿区石英闪长岩具有低SiO_2、富MgO、CaO的特征,含10%～15%的角闪石,为准铝质、分异程度较低的高钾钙碱性-钾玄岩系列I型花岗岩。岩体发育较弱的Eu负异常,富集强不相容元素Rb、Th、U,而亏损Nb、Ta、Ti等高场强元素。同位素测试结果显示,纳如松多石英闪长岩具有相对较高的^(87)Sr/^(86)Sr初始比值(0.709 13～0.709 68)与负的ε_(Nd)(t)值(-5.8～-5.2),Pb同位素的^(206)Pb/^(204)Pb为18.6091～18.6438,^(207)Pb/^(204)Pb为15.6900～15.6986,^(208)Pb/^(204)Pb为39.2116～39.2225,指示岩浆可能为特提斯洋俯冲消减阶段产生的岛弧地幔楔部分熔融的产物。一种可能的成因模式为:晚白垩世,随着雅鲁藏布江板块向拉萨地块之下俯冲,俯冲板片流体交代上覆地幔楔,形成幔源基性岩浆,上侵到地壳后,诱发了岛弧基底物质的部分熔融,形成了中基性的纳如松多石英闪长岩,其形成可能是晚白垩世北向俯冲的新特提斯洋板块在回转初期的岩浆活动响应。The Late Cretaceous quartz diorite containing 10%~15% amphibole in Narusongduo Pb-Zn deposit with characteristics of low content of SiO2 and high content of MgO and CaO is aluminous I-type granite with low degree of differentiation, belongs to high potassium calc alkaline to shoshonite series. The rock is characterized by weakly developed Eu negative anomaly, enrichment of strong incompatible elements such as Rb, Th and U, and depletion of Nb, Ta, Ti and other high field strength elements. The isotope analyses show that the Narusongduo quartz diorite has a relatively high 87Sr/86Sr initial ratios (0.709 13~0.709 68) and negative εNd values (-5.8^-5.2), with the lead isotope ratio of 206Pb/204Pb being 18.6091~18.6438, 207Pb/204Pb being 15.6900~15.6986, and 208Pb/204Pb being 39.2116~39.2225. The geochemical and isotopic geochemical studies show that the magma might have originated from the partial melting of the island arc mantle wedge produced during the subduction of the Tethys Ocean. A possible genetic model is as follows: In the Late Cretaceous, along with the subduction of Yarluzangbo Plate beneath the Lhasa block, the subducting slab fluid metasomatized the overlying mantle wedge, forming the mantle-derived magma. The ascending emplacement of the mantle-derived magma induced partial melting of the island arc basement material and formed the Narusongduo quartz diorites. The formation was probably the magmatic response to the rolling-back of the northern subducting Neo-Tethys Oceanic Plate in Late Cretaceous.

关 键 词：地球化学 晚白垩世 石英闪长岩 纳如松多矿床 西藏 

分 类 号：P618.42[天文地球—矿床学] P618.43[天文地球—地质学]