摘要
新发现的西藏南木林地区达那古火山机构为探讨陆相火山机构岩相组成及其大地构造意义提供了窗口。本项研究对达那古火山机构开展了地质剖面测量、岩相学研究,并对期后侵入的斑状二长花岗岩进行了锆石U-Pb年代学和全岩地球化学分析。结果表明,斑状二长花岗岩锆石U-Pb年龄为54.0±1.4 Ma,具有高硅(SiO_(2)=71.03%~75.88%)、高钾低钠(K_(2)O/Na_(2)O=1.45~1.79)、富碱(ALK=8.97%~9.67%)、低钛(TiO_(2)=0.17%~0.37%)等特征,铝饱和指数(A/CNK)介于0.95~1.00之间,里特曼指数(σ)介于2.45~3.38之间,属于准铝质、钙碱性岩石系列;轻稀土元素富集而重稀土元素相对亏损(LREE/HREE=7.60~9.78),且分异特征明显,(La/Sm)_(N)=2.85~4.21;Rb、Th、U等大离子亲石元素(LILE)和不相容元素相对富集,Nb、Ta、P、Ti等高场强元素(HFSE)相对亏损,表现出具有典型的俯冲带弧型或者壳源岩浆岩的地球化学属性。综合上述地质信息表明,达那古火山机构形成于54 Ma之前,斑状二长花岗岩形成于印度-欧亚大陆碰撞期的活动大陆边缘构造背景,在幔源岩浆底侵作用下,中下地壳发生熔融,之后岩浆分异上升侵位于火山通道结晶而成。
The newly discovered Dana ancient volcanic edifice in the Nanmulin area of Xizang provides a window for exploring the lithofacies composition of continental volcanic edifice and its tectonic significance.This study conducts geological profile measurements and petrographic studies on the Dana ancient volcanic edifice,and conducts zircon LA-ICP-MS U-Pb dating and the whole-rock geochemical analysis for the porphyric monzonitic granite which intrusived into volcanic channel laterly.The results show that the zircon U-Pb age of the porphyric monzonitic granite is 54.0±1.4 Ma,with high silicon(SiO_(2)=71.03%~75.88%),high potassium and low sodium(K_(2)O/Na_(2)O=1.45~1.79),rich alkali(ALK=8.97%~9.67%),and low titanium(TiO_(2)=0.17%~0.37%)characteristics.The A/CNK value ranges from 0.95 to 1.00,and the Rittman index(σ)ranges from 2.45 to 3.38,belonging to the quasi-aluminous and calc-alkaline rock series.Enrichment of light rare earth elements and relative depletion of heavy rare earth elements(LREE/HREE=7.60~9.78),with obvious differentiation characteristics,(La/Sm)_(N)=2.85~4.21;Large ion lithophilic elements such as Rb,Th,U(LILE)and incompatible elements are relatively enriched,while high field strength elements such as Nb,Ta,P,Ti(HFSE)are relatively depleted,exhibiting typical geochemical properties of subduction arc or crustal magmatic rocks.Based on the above geological information,it is indicated that the Dana ancient volcanic edifice was formed before 54 Ma,and the porphyric monzonitic granite was formed in the tectonic background of the active continental margin during the India-Eurasia collision.Under the action of mantle-derived magma intrusion,the middle and lower crust melted,and then the magma differentiated and ascended to infiltrate and crystallize in the volcanic channel.
作者
韩飞
宋元宝
李峥
黄永高
代克刚
张伟
李应栩
贾小川
杨学俊
HAN Fei;SONG Yuan-bao;LI Zheng;HUANG Yong-gao;DAI Ke-gang;ZHANG Wei;LI Ying-xu;JIA Xiao-chuan;YANG Xue-jun(Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory,Sichuan Institute of Comprehensive Geological Survey,Chengdu 610081,China;The Fifth Geological Brigade,Tibet Bureau of Geology and Mineral Exploration and Development,Lhasa 850000,China;Chengdu Center,China Geological Survey,Chengdu 610081,China)
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2024年第4期803-820,共18页
Acta Petrologica et Mineralogica
基金
国家重点研发计划项目(2021YFC2901903)
第二次青藏高原综合科学考察项目(2019QZKK0806)
中国地质调查局项目(DD20230031,DD20240070-1,12120114058201)。
关键词
达那
古火山机构
二长花岗岩
地球化学
构造背景
西藏
Dana
ancient volcanic edifice
monzonitic granite
geochemistry
tectonic setting
Xizang
