Careful investigations presented in this paper showed that there are 17 olistostromes discretely distributed along the north margin of the Napo forearc basin in the China-Vietnam border area,and characterized by chaotic volcanic and carbonate olistoliths with interlayers of carbonate mass-and debris-flows and carbonate turbidites in distal.Volcanic olistoliths in the olistostromes are dominated by pillow lavas and completely similar to the volcanic rocks in the Jiajie arc in geochronologic and geochemical.Carbonate olistoliths are dominated by thin-bedded limestone sheets with soft-sediment deformation and tempestite interbed in thickness of ～30cm,which indicates that these carbonate olistoliths were originally deposited in the lagoon to tidal flat environment on the shelf of the volcanic arc.Compared with the forearc basins all over the world,such as Celica-Lancones (Ecuador),Savu (Indonesia),Sinop-Samsun (N.Turkey),south-central Alaska (USA) and Xigaze (Tibet,China) forearc basins,the olistostromes in the forearc basin are very common.They are the records of special event sediments in the tectonically active margins of the forearc basins,and can used to be the sedimentary indicator for discriminating the tectonic facies of forearc domain in the fossiled orogenic belts or subduction direction.Stereographic projection pole diagrams of bedding attribute of carbonate olistliths and axial surface attribute of the slump folds show a southwest (232° ～ 240°) towards slope of the Napo forearc basin or the flank of the volcanic arc,in accordance with the paleocurrent orientation determined by the ripple foresets in the calcareous turbidites,which indicates that the Paleotethys oceanic lithosphere subducted northward to the South China block in the early to middle Triassic.%本文详细调查揭示,位于中越边境地区的那坡弧前盆地北部边缘发育17处滑塌堆积,有些表现为火山岩-碳酸盐岩块混杂型滑塌堆积,即由火山岩滑塌块体和碳酸盐岩滑塌块体无序堆积而成;有些只是具软沉积变形特征的薄层碳酸盐岩滑塌块体;还有些是砂屑灰岩滑塌块体与碳酸盐岩(或钙质)浊积岩组合以及单一的碳酸盐岩浊积岩或碳酸盐岩碎屑流.碳酸盐岩质块体流和碎屑流一般夹于大型或巨型滑塌块体间,而碳酸盐岩(或钙质)浊积岩和块状砂岩等一般发育于滑塌堆积的远端,有的覆盖于滑塌块体之上.无论是时代还是地球化学组成,滑塌堆积中的具枕状构造的火山岩块与盆地北侧富宁县架街一带的早-中三叠世弧火山岩完全一致.具软沉积变形特征的薄层碳酸盐滑塌岩块中发育有厚30cm左右的风暴沉积层,暗示这些滑塌岩块是发育于火山弧边缘的或其上的局部的碳酸盐岩台地(主要为潮坪-渴湖相)沉积.与全球不同造山带弧前盆地对比表明,这些滑塌堆积是一种发育于构造活动强烈的弧前盆地边缘的特殊的事件沉积,可作为识别弧前域大地构造相单元的普适性沉积标志,也可用以分析断定俯冲增生造山极性.本文对碳酸盐岩滑塌块体的原始层理和软沉积变形的滑塌褶皱轴面方位测量统计揭示火山弧斜坡大体向南西方向(232°～240°)倾斜,滑塌堆积远端浊积岩古水流测量与校正结果揭示沉积物搬运方向为南或南西向,这表明华南地块与北越地决之间的古特提斯分支洋盆在早三叠世期间是向北俯冲消化减的.
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