藏南桑单林地区晚白垩世—始新世砂岩物源区分析  

Provenance Analysis of Late Cretaceous-Early Eocene Sandstones in the Sangdanlin Area, Southern Tibet

作　　者：王建刚[1] 胡修棉[1] 黄志诚[1] 

机构地区：[1]南京大学地球科学系,南京210093

出　　处：《地质学报》2008年第1期92-103,共12页Acta Geologica Sinica

基　　金：国家重点基础研究发展规划项目(编号2006CB701402);国家自然科学基金项目(编号4077207040302017);新世纪优秀人才支持计划资助的成果

摘　　要：西藏南部桑单林地区出露一套晚白垩世—始新世深水沉积的地层,下部为晚白垩世以石英砂岩和粉砂质页岩为主的桑单林组,上部为始新世含长石岩屑砂岩、硅质岩和硅质页岩的者雅组,由于断层错断,二者之间的古新世地层缺失。砂岩的岩石学分析表明,桑单林组石英砂岩的成分成熟度和结构成熟度均较高,杂基含量少,为硅质胶结;者雅组长石岩屑砂岩中,不稳定组分明显增加,杂基含量高,主要为泥质胶结。运用重矿物组合以及全岩主量元素、微量元素和稀土元素组成对砂岩的物源区分析表明,桑单林组砂岩形成于稳定的被动大陆边缘,碎屑物质来源于印度克拉通内部,而者雅组砂岩中存在明显的火成岩物质的输入,这些火山物质只可能来自于沉积盆地北部。桑单林组和者雅组砂岩的物源区的明显变化,反映了古新世末期—早始新世的一次碰撞事件:印度大陆与亚洲大陆的碰撞或者印度大陆与洋内岛弧的碰撞。The Yarlung Tsangpo suture zone in Tibet marks the tectonic boundary between Eurasian and Indian plates and the sedimentary rocks can provide valuable records for the evolution of Neo-Tethys Ocean. During our field work in the summer of 2005 and 2006, we examined the Sangdanlin section, which lies in sedimentary melange of Yarlung Tsangpo suture zone in Gyirong, southern Tibet. The Sangdanlin section consists of the Sangdanlin Formation （Late Cretaceous） and the overlying Zheya Formation （Early Eocene）. The Sangdanlin Formation consists mainly of quartzitic sandstone, silty shale and siliceous rocks, sandstones which are comprised of monocrystalline quartz grains with good maturity in both composition and structure, and no volcanic lithoclast was observed. In contrast, the Zheya Formation makes up of sandstone, siliceous shale, clay shale and siliceous rocks. Sandstones are feldspathic litharenite, in which the presence of chromian spinel and volcanic lithoclast indicates ophiolite and volcanic arc detritus input. Heavy mineral assemblages and major and trace elements, and rare earth element concentrations in sandstones indicate that the source of sandstones in the Sangdanlin Formation was probably from the India continent, whereas sandstones in the Zheya Formation were mainly derived from ophiolite and volcanic arc north of the Sanganlin section. We suggest that the provenance change recorded a collision event, either India Eurasia collision or India oceanic arc collision.

关 键 词：藏南 始新世 砂岩 物源区分析 碰撞事件 

分 类 号：P534.53[天文地球—古生物学与地层学]