欢迎访问现代地质!

现代地质 ›› 2023, Vol. 37 ›› Issue (03): 547-561.DOI: 10.19657/j.geoscience.1000-8527.2023.011

• 岩石学与岩石地球化学 • 上一篇    下一篇

西藏冈底斯南木林地区晚三叠世中酸性岩浆作用及构造意义

韩飞1(), 宋元宝1, 张伟1, 李道凌2, 黄永高1,3, 李应栩4, 贾小川1, 杨学俊1, 杨青松3, 宋旭波5, 卢柳5   

  1. 1.四川省地质调查院稀有稀土战略资源评价与利用四川省重点实验室,四川 成都 610081
    2.四川省阿坝州自然资源局,四川 马尔康 624000
    3.桂林理工大学广西隐伏金属矿产勘查重点实验室,广西 桂林 541004
    4.中国地质调查局成都地质调查中心,四川 成都 610081
    5.四川省煤炭设计研究院,四川 成都 610091
  • 收稿日期:2022-05-12 修回日期:2023-04-10 出版日期:2023-06-10 发布日期:2023-07-20
  • 作者简介:韩 飞,男,工程师,1988年出生,矿物学、岩石学、矿床学专业,主要从事区域地质调查和矿床成因研究。Email:cdhanfei7@163.com
  • 基金资助:
    国家自然科学基金项目“西藏喜马拉雅带错那洞铍稀有金属矿巨量富集机制研究”(91955208);“西藏康雄岩金矿形成背景与矿体暴露程度研究”(41702086);中国地质调查局项目“西藏山南地区铍锡多金属矿调查评价”(DD20190147);中国地质调查局项目“中国矿产地质志·四川卷”(12120114058201)

Petrogenesis and Tectonic Significance of the Late Triassic Nanmulin Intermediate-felsic Magmatic Rocks in the Gangdese Batholith, Southern Tibet

HAN Fei1(), SONG Yuanbao1, ZHANG Wei1, LI Daoling2, HUANG Yonggao1,3, LI Yingxu4, JIA Xiaochuan1, YANG Xuejun1, YANG Qingsong3, SONG Xubo5, LU Liu5   

  1. 1. Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province Sichuan Geological Survey, Chengdu, Sichuan 610081, China
    2. Sichuan Aba Prefecture Natural Resources Bureau, Maerkang, Sichuan 624000, China
    3. Key Laboratory of Hidden Metallic Ore Exploration & Guilin University of Technology, Guilin, Guangxi 541004, China
    4. Chengdu Center, China Geological Survey, Chengdu, Sichuan 610081, China
    5. Sichuan Provincial Coal Design & Research Institute, Chengdu, Sichuan 610091, China
  • Received:2022-05-12 Revised:2023-04-10 Online:2023-06-10 Published:2023-07-20

摘要:

拉萨地块新特提斯初期演化过程是构建特提斯时空格架的重要环节,受制于研究对象的匮乏,其认识尚待深入。为此,本研究选取中拉萨地块南木林甲措乡地区花岗闪长岩和石英闪长岩,进行锆石LA-ICP-MS U-Pb年代学和岩石地球化学分析,探讨岩石成因和源区,为新特提斯初期演化提供新的制约。分析结果表明,花岗闪长岩和石英闪长岩的锆石U-Pb年龄分别为(214.3±1.1) Ma和(206.1±1.3) Ma,代表晚三叠世两期次岩浆事件。岩浆岩里特曼指数(σ)介于1.79~4.71,具有钙碱性-碱性特征,Al2O3含量为15.01%~17.57%,A/CNK=0.76~1.12,显示出准铝质-过铝质的特征,此外花岗闪长岩具有高硅(SiO2含量61.87%~73.72%,平均65.76%)、高钾(最高达4.25%)、较低的Mg#(31~46,均值为41)特征。二者微量元素均表现为强烈富集Rb、U、K、Pb等大离子亲石元素(LILE)以及La、Ce等轻稀土元素,而亏损Nb、Ta、Ti等高场强元素(HFSE),表现出弧型岩浆岩的地球化学属性;Rb/Sr值(0.05~5.50,均值为2.54)指示壳源特征。(La/Yb)N值较高,平均12.05,反映了轻重稀土元素分馏显著的特征,Eu负异常不明显(δEu=0.57~1.01,平均0.73)。综合研究表明,南木林地区中酸性岩体为壳幔混合成因的I型花岗岩,其形成过程可能为:新特提斯洋北向俯冲导致地幔楔发生部分熔融,岩浆底侵形成新生下地壳,随后幔源岩浆热烘烤导致新生下地壳重熔,岩浆上升侵位形成甲措乡中酸性岩体。本研究指示新特提斯洋北向俯冲作用在晚三叠世(≈214 Ma)之前已经发生,早于新近发现的晚三叠世Be-Rb±(Nb-Ta)稀有金属矿化时限。

关键词: 拉萨地块, 南木林, 晚三叠世, 锆石U-Pb, 岩石成因

Abstract:

The initial Neo-Tethyan evolution in the Lhasa block is an important part for the reconstruction of the Tethys space-time framework. Due to the lack of research objective, its understanding needs to be deepened. The Nanmulin granodiorite and quartz diorite are located in the central Lhasa block. We conducted systematic zircon LA-ICP-MS U-Pb dating and whole-rock geochemical analyses for determining the petrogenesis and source region of these rocks. The results provide new constraints for the early Neo-Tethyan evolution. Zircon U-Pb dating shows that both lithologies were formed in the Late Triassic, with the granodiorite emplaced at (214.3±1.1) Ma and the quartz diorite at (206.1±1.3) Ma. Geochemically, these rocks have Rittmann index (σ) of 1.79-4.71 and are calc-alkaline. They are peraluminous with Al2O3 varying from 15.01% to 17.57%,and A/CNK=0.76-1.12. Moreover, the granodiorite has high SiO2(61.87%-73.72%, average 65.76%) and high K (up to 4.25%) and low Mg#(31-46, average 41). Rb, U, K, Pb and LREEs are enriched and Nb, Ta, Ti and HREEs are depleted, suggesting arc-related or crust-like geochemical affinities. Rb/Sr (0.05-5.50, average 2.54) values suggest that their parental magmas were crustal sourced. The granodiorite and quartz diorite have high (La/Yb)N values (average 12.05), with no clearly negative Eu anomalies (δEu=0.57-1.01, average 0.73). In summary, these data indicate that the Nanmulin intermediate-felsic rocks are I-type formed by the partial melting of juvenile crust. We propose that the northward subduction of the Neo-Tethyan was initiated before Late Triassic, which was before the formation of the newly-discovered Late Triassic Be-RB±(Nb-Ta) rare metal mineralization.

Key words: Lhasa block, Nanmulin, Late Triassic, zircon U-Pb geochronology, petrogenesis

中图分类号: