班公湖-怒江缝合带西段改则地区木嘎岗日群物源特征和形成环境  

The provenance characteristics and forming environment of the Mesozoic Mugagangri Group in the western segment of the Bangong-Nujiang suture zone

作　　者：刘升武 王自剑[1] 杨文光[1] 朱利东[1] 童馗 华天 李轲 李智武[1] LIU Shengwu;WANG Zijian;YANG Wenguang;ZHU Lidong;TONG Kui;HUA Tian;LI Ke;LI Zhiwu(Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]油气藏地质及开发工程国家重点实验室(成都理工大学),成都610059

出　　处：《成都理工大学学报（自然科学版）》2020年第3期274-289,共16页Journal of Chengdu University of Technology: Science & Technology Edition

基　　金：中国地质调查局项目(1212011086065)。

摘　　要：中生代木嘎岗日群作为班公湖-怒江缝合带的标志性构造-地层单元,其形成环境与班公湖-怒江中特提斯洋的消亡过程密切相关;但由于后期遭受强烈的构造剪切,对其原始沉积环境和构造属性的认识分歧较大。本文针对班公湖-怒江缝合带西段改则地区的木嘎岗日群,通过野外地质调查、砂岩薄片分析和碎屑组分统计,对其基本组成和碎屑物质来源进行分析,进而探讨其形成环境。木嘎岗日群主要由基质和岩块两部分构成,其中基质为一套深海复理石沉积,岩块主要为中基性火山岩岩块、大理岩化灰岩岩块以及由二者砾石构成的砾岩岩块。基质与岩块通常为构造接触,局部亦可见沉积接触关系。基质砂岩主要为岩屑石英砂岩类和岩屑长石砂岩类。岩屑石英砂岩类的碎屑组分以石英为主,磨圆度中等或中等偏差,分选性差,杂基的体积分数为2%~15%,表明其成分成熟度较高,结构成熟度较低;岩屑长石砂岩类的碎屑组分以长石和岩浆岩碎屑为主,分选性中等,磨圆度差,杂基的体积分数约10%,表明其成分成熟度中等,结构成熟度较低。碎屑组分Dickinson三角图解显示岩屑石英砂岩类在Qm-F-Lt图中主要落入再旋回造山带物源区,在Qp-Lv-Lsm图中主要落入碰撞缝合线及褶皱-逆冲带物源区,少量位于混合造山带物源区;岩屑长石砂岩类在Qm-F-Lt图中主要落入过渡弧物源区,在Qp-Lv-Lsm图中主要落入火山弧造山带物源区,少量位于混合造山带物源区。砂岩成分、结构和物源区构造背景判别一致表明,研究区木嘎岗日群基质砂岩的碎屑物质具有双物源供给的特点:岩屑石英砂岩类主要来自羌塘地体,岩屑长石砂岩类主要来自洋岛。综合前人研究结果,认为研究区木嘎岗日群是一套总体无序、局部有序且遭受强烈剪切变形的沉积混杂岩,形成于海沟外侧的大洋盆地。Mugagangri Group is a structural-stratigraphic unit in the Bangong-Nujiang suture zone and its formation environment is closely related to the demise of the Bangong-Nujiang Mid-Tethys Ocean.Based on the field geological investigation,analysis of rock thin sections and statistics of clastic components,the basic compositions and the source of clastic materials of the Mugagangri Group in the west section of Bangong-Nujiang suture zone are analyzed,and its forming environment is discussed.It shows that the Mugagangri Group in the study area is mainly composed of two parts,the matrix and the rock block.The former is a set of deep-sea flysch deposits,and the latter mainly consists of intermediate basic volcanic rock block,the marmarization limestone block and the conglomerate blocks which are composed of the volcanic rock block and limestone block.The matrix and the rock block are usually in structural contact,and the sedimentary contact can also be seen locally.Matrix sandstones consist of lithic quartz sandstones and lithic feldspar sandstones.The detrital components of the lithic quartz sandstones are mainly quartz,with medium to medium deviation in rounding and poor in sorting,and with about 2% ~15% of matrix,characteristic of high component maturity and low structural maturity.Detrital components of the lithic feldspar sandstones are mainly feldspar and magmatic rock debris,poor in rounding,medium deviation in sorting and with about 10% of matrix,characteristic of medium component maturity and low structural maturity.Plot of Dickinson trigonometric diagram for detrital components shows that the lithic quartz sandstones mainly fall into the source area of recycle orogenic belt in the Qm-F-Lt diagram,and mainly fall into the source area of collision suture belt and fold thrust belt in the Qp-Lv-Lsm diagram,with a small amount in the source area of mixed orogenic belt.The lithic feldspar sandstones mainly fall into the source area of the transition arc in the Qm-F-Lt diagram and mainly fall into the source area of vo

关 键 词：班公湖-怒江缝合带 木嘎岗日群 砂岩 碎屑组分 物源 沉积环境 大洋盆地 

分 类 号：P534.5[天文地球—古生物学与地层学]