The provenance and tectonic setting of the Lower–Middle Triassic clastic sediments from the Napo basin, South China, have been examined here using detrital modes, whole-rock geochemistry and detrital zircon U–Pb ages. Field investigations indicate that these sediments consist of fan delta, slope and turbidity fan facies with dominantly southward palaeocurrent directions. Detrital modes and geochemical characteristics of the clastic rocks indicate that they were derived from mixed magmatic arc and Palaeozoic successions in a continental island arc setting, with no significant sediment recycling. The U–Pb age spectra of sandstone detrital zircons from different stratigraphic positions are similar, with one major group (300–230 Ma), two subordinate groups (400–320 Ma and 480–420 Ma, respectively) and two scattered groups (1200–800 Ma and 2000–1700 Ma, respectively). Thus, we consider that the north late Permian – Middle Triassic volcanic rocks and the uplifted Palaeozoic sedimentary/volcanic sequences constituted the predominant sources. The detritus derived from the late Permian Emeishan mafic rocks is subordinate and limited. The pre-Devonian zircons are likely sedimentary-recycled or magmatic-captured instead of directly derived from the early Palaeozoic orogen (e.g. Yunkai massif) and Neoproterozoic Jiangnan orogen because of the topographic barrier of a magmatic arc and carbonate platform. Considering the spatial and temporal distribution characteristics of the volcanic arc and ophiolite, we suggest that the Triassic Napo basin was a fore-arc basin within a continental island arc setting, which developed in response to the northward subduction of the Babu–Cao Bang branch ocean beneath the South China Block.

中文翻译：

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华南那坡盆地三叠系碎屑岩成因及构造背景：来自岩相学、全岩地球化学和碎屑锆石U-Pb年代学的证据

使用碎屑模式、全岩地球化学和碎屑锆石 U-Pb 年龄研究了华南那坡盆地下-中三叠统碎屑沉积物的物源和构造背景。实地调查表明，这些沉积物由扇三角洲相、斜坡相和浊度扇相组成，古洋流方向以南向为主。碎屑岩的碎屑模式和地球化学特征表明，它们来源于大陆岛弧环境中的混合岩浆弧和古生代演替，没有明显的沉积物循环。不同地层位置砂岩碎屑锆石的 U-Pb 年龄谱相似，有一个主群（300~230 Ma）、两个从属群（分别为 400~320 Ma 和 480~420 Ma）和两个散在的群（1200 Ma）。 –800 毫安和 2000–1700 毫安，分别）。因此，我们认为北部晚二叠世—中三叠世火山岩和隆起的古生代沉积/火山层序构成了主要的物源。来自晚二叠世峨眉山基性岩的碎屑是次要的、有限的。由于岩浆弧和碳酸盐台地的地形屏障，前泥盆纪锆石很可能是沉积循环或岩浆捕获的，而不是直接来源于早古生代造山带（如云开地块）和新元古代江南造山带。考虑到火山弧和蛇绿岩的时空分布特征，我们认为三叠纪那坡盆地是大陆岛弧背景下的弧前盆地，