Abstact Cherts have been considered to be formed mainly through processes involving biosilicification, riverine inputs and hydrothermal activities. In the Permian, massive cherts are widely distributed in South China, bearing significant implications for the reconstruction of paleogeography and paleoceanography of the eastern Paleo-Tethys Ocean. The origin of the Permian cherts in South China, however, remains inconclusive due to a lack of systematic petrographic and geochemical study. In this article, we analyze the petrologic and geochemical characteristics of the cherts collected from five outcrops in the northwestern Sichuan Basin, South China. These cherts are found from the Upper Guadalupian Maokou Formation (ca. 268–259 Ma) and Upper Lopingian Dalong Formation (ca. 254–252 Ma). Field and microscopic observations suggest that cherts from the Maokou Formation occur mainly in nodular forms, and consist of microcrystalline quartz, silicified bioclasts and siliceous fossil debris. Both petrographic observation and geochemical analysis suggest that the Maokou cherts are mainly of hydrothermal origin near deep faults in the southwest and of biogenetic origin with less hydrothermal influence in the northeast of the studied area. The Dalong cherts occur in both nodular and bedded forms, with more abundant siliceous fossil debris than the Maokou cherts. Major, trace and rare earth element data support that the Dalong cherts are influenced by both biosilicification and hydrothermal activities. The spatial heterogeneity of the cherts origin in South China is largely controlled by tectonic activities associated with the Emeishan large igneous province (ELIP) event and the closure of the Paleo-Tethys Ocean. The troughs formed by the extensional tectonic activity linked to the ELIP could provide accommodation space and activate deep faults allowing the rise of silicon-rich hydrothermal fluids from the deep and nutrient-rich water from volcanogenic upwellings. Subsequent cooling may have facilitated the precipitation of large amounts of silica and the formation of cherts in the study region. This work demonstrates that the origin of the Guadalupian-Lopingian cherts in South China is predominantly controlled by tectonic and biological activities, which sheds light on the global “Permian Chert Event”.

中文翻译：

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四川盆地西北部瓜达鲁普阶-洛平阶硅质岩的构造控制

抽象硅质岩被认为主要是通过涉及生物硅化、河流输入和热液活动的过程形成的。在二叠纪，大量硅质岩广泛分布于华南地区，对东古特提斯洋古地理和古海洋学的重建具有重要意义。然而，由于缺乏系统的岩石学和地球化学研究，华南二叠纪燧岩的起源仍然没有定论。在本文中，我们分析了从华南四川盆地西北部五个露头采集的燧石的岩石学和地球化学特征。这些硅质岩发现于上瓜达鲁皮阶茅口组（约 268-259 Ma）和上洛平阶大龙组（约 254-252 Ma）。野外和显微镜观察表明，茅口组燧石主要以结节形式存在，由微晶石英、硅化生物碎屑和硅质化石碎片组成。岩石学观察和地球化学分析表明，茅口硅质岩主要为西南深断裂附近的热液成因，研究区东北部为生物成因，热液影响较小。大龙燧石以结节状和层状两种形式出现，硅质化石碎片比茅口燧石更丰富。主要、微量和稀土元素数据支持大龙燧石受生物硅化和热液活动的影响。华南燧石成因的空间异质性主要受峨眉山大火成岩省（ELIP）事件和古特提斯洋闭合的构造活动控制。由与 ELIP 相关的伸展构造活动形成的海槽可以提供容纳空间并激活深部断层，从而使富含硅的热液从深部和富含营养物质的火山上升流中上升。随后的冷却可能促进了研究区域内大量二氧化硅的沉淀和燧石的形成。这项工作表明华南瓜达鲁普阶-洛平阶燧石的起源主要受构造和生物活动控制，为全球“二叠纪燧石事件”提供了线索。