摘要
华南板块西南缘中三叠统底部普遍发育凝灰岩夹层,但对火山灰的来源存在不同认识。位于华南板块西南缘的右江盆地在早—中三叠世为连续海相沉积,较为完整的火山沉积记录为探讨火山灰的来源提供了基础。本文以右江盆地者堡敢南一带早、中三叠世之交凝灰岩为研究对象,在剖面测制基础上,对含凝灰岩层段灰岩进行生物地层分析,划分为4个牙形石带,分别为Neospathodus pakistanensis间隔带;Neospathodus waageni—N.abruptus组合带;Neospathodus homeri—N.triangularis组合带以及Chiosella timorensis间隔带,由此确定第17层凝灰岩为中三叠统底界凝灰岩。凝灰岩岩石学、地球化学分析结果显示为流纹质玻屑凝灰岩,属于亚碱性系列。稀土配分曲线显示为右倾轻稀土富集,明显的负Eu异常。大离子亲石元素(LILE)(Rb、U、Th和Ba等)富集和高场强元素(HFSE)(Nb、Ta、P和Ti等)亏损,整体表现出与弧相关的地球化学特征。在生物地层、同位素年代学对凝灰岩形成时代进行精确限定的基础上,通过华南板块西南缘中三叠统底界凝灰岩的区域分布、矿物组成、地球化学特征,结合右江盆地中—下三叠统火山岩层序特征进行详细对比分析,结果显示广西凭祥—十万大山一带火山岩是其主要来源。
Objectives: The tuff interlayer is widespread in the bottom of Middle Triassic,southwestern margin of the South China plate,and there exist different viewpoints about the provenance of the volcanic ash. The Youjiang basin is located in the southwest margin of the South China plate,deposited a suit of marine sedimentation during Early-Middle Triassic stage,which provides basis material for exploring the provenance of the volcanic ash.Methods: This article focused on the Early Triassic and Middle Triassic tuff in Gannan region,Zhebao,Youjiang basin,based on the section measurement,biostratigraphic analysis results divided the limestone into 4 conodont zones, the Neospathodus pakistanensis zone, the Neospathodus waageni-N. abruptus zone, the Neospathodus homeri-N. triangularis and the Chiosella timorensis zone,respectively,which determined the 17 th bed tuff as the bottom of Middle Triassic.Results: The petrology analysis result shows that the tuff is subdivided into rhyolitic vitric tuff,belong to the alkali series,all samples are characterized by relative enrichment in light rare earth elements( LREE),obvious negative Eu anomaly,and displayed LILE( Rb,U,Th and Ba) enrichment and HFSE depletion( Nb,Ta,Ti and P),analogues to those of typical subduction-related geochemical. Based on the age of the tuff determined by the biostratigraphic and the isotope chronology,detailed comparative analysis through the regional distribution,the mineral composition and the geochemical characteristics of Middle Triassic boundary tuff in southwestern margin of the Yangtze plate,and the Lower-Middle Triassic volcanic rocks sequence features in Youjiang basin.Conclusions: Based on the age determine of the tuff by the biostratigraphic and the isotope chronology,combining with the regional distribution,the mineral composition and the geochemical characteristics of the Middle Triassic boundary tuff in southwestern margin of the South China plate,and the Early-Middle Triassic volcanic rock sequence features in Youjiang basin,detailed comparative analysis between the Middle Triassic tuff and the volcanic rocks in southwestern margin of the Yangtze plate and its adjacent region,and result show the Middle Triassic Pingxiang-Shiwandashan volcanic belt is the provenance of the lower Middle Triassic volcanic ash,Youjiang basin.
作者
向坤鹏
安亚运
贺永忠
赵磊
易成兴
刘奎勇
张厚松
黄勇
盘应娟
邓小杰
XIANG Kunpeng;AN Yayun;HE Yongzhong;ZHAO Lei;YI Chengxing;LIU Kuiyong;ZHANG Housong;HUANG Yong;PAN Yingjuan;DENG Xiaojie(Guizhou Geological Survey, Guiyang, 550005)
出处
《地质论评》
CAS
CSCD
北大核心
2019年第2期319-334,共16页
Geological Review
基金
中国地质调查局项目(编号:DD20160020)
贵州省地质矿产勘查开发局科研项目(编号:QDKKH[2017]28)的成果~~
关键词
凝灰岩
牙形石
中三叠统
地球化学特征
来源
敢南地区
tuff
conodont
middle Triassic
geochemical characteristics
provenance
Gannan region
