青藏高原北羌塘地区晚三叠世地层展布和沉积型式
Distribution and sedimentary model of the Late Triassic strata in northern Qiangtang on the Qinghai-Xizang Plateau
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摘要: 北羌塘盆地地处拉竹龙-金沙江缝合带和双湖构造混杂岩带之间,自北向南可划分出5个沉积相带/岩石地层单位:以砂泥质复理石-洋岛、岛弧型火山岩-大理岩岩石组合沉积为特征的若拉岗日群,以深水复理石盆地相沉积为特征的藏夏河组,以深水暗色细碎屑岩盆地相沉积为特征的结扎群,以开阔台地相/缓坡相碳酸盐岩沉积为特征的菊花山组,以三角洲相含煤碎屑岩系沉积为特征的土门格拉群。晚三叠世北羌塘盆地显示为南缓北陡的箕状沉积格局,盆地内充填物为南薄北厚的楔形沉积体,且双物源、沉降中心和沉积中心不一致,表明其具有前陆盆地的一系列沉积特征。Abstract: The North Qiangtang Basin lies between the Lazhuglung-Jinshajiang suture zone and Shaunghu tectonic mélange zone.Five sedimentary facies belts/lithostratigraphic units have been distinguished for the Basin from north to south:Rola Kangri Group composed of sandy-muddy flysch-oceanic island and island arc volcanic rock-marble associations;Zangxiahe Formation dominated by grey deep-water flysch basin facies;Gyiza Group built up of dark deep-water fine-grained clastic basin facies; Juhuashan Formation consisting of open platform/ramp carbonate rocks,and Tumaingela Group filled by the deltaic coal-bearing clastic rock series. The North Qiangtang Basin once displayed the half-graben sedimentary framework of being gentle in the south and steeper in the north during the Late Triassic.The sediments in the basin pinch out southwards.The basin has double origins:the Rola Kangri thrust zone in the north and the Shuanghu mélange belt in the south. During the Late Triassic,the depocentre was located in the middle part of the basin,while the subsidence centre in the northern part of the basin,suggesting the sedimentary features of the basin as a foreland basin.