湖南衡阳盆地东缘冷家溪群岩石地球化学特征:物源、古风化和构造背景

    Geochemical characteristics of the Lengjiaxi Group, eastern edge of the Hengyang Basin: provenance, paleoweathering, and tectonic setting

    • 摘要: 本文以湖南省衡阳盆地东缘冷家溪群黄浒洞组-小木坪组剖面为研究对象,采集17件碎屑沉积岩样品,通过测试其主量元素、微量元素和稀土元素等含量,结合相关分析方法与判别图解,对冷家溪群的物源组成、古风化强度、沉积环境及构造背景展开系统研究。研究结果表明:冷家溪群物源主要为长英质火山岩,可能含少量中基性火山岩物质,源区沉积母岩中碱性长石含量较低;源岩经历中等程度风化作用,从黄浒洞组到小木坪组,风化程度逐渐增强,且可能受后期钾质交代作用影响;其属于次深海-深海浊流沉积,黄浒洞组和小木坪组不同段分别对应浊积扇的中扇沉积环境或外扇沉积环境,沉积时期气候温暖湿润,处于弱氧化弱还原界面附近,形成于活动大陆边缘构造背景。本研究为区域地质演化提供了新的地球化学证据。

       

      Abstract: This paper focuses on the Huangxudong Formation-Xiaomuping Formation section of the Lengjiaxi Group in eastern edge of the Hengyang Basin, Hunan Province. Seventeen clastic sedimentary rock samples are collected, and their major elements, trace elements, and rare earth elements contents are tested. Combined with relevant analytical methods and discriminant diagrams, a systematic study is conducted on the provenance composition, paleoweathering intensity, sedimentary environment, and tectonic setting of the Lengjiaxi Group. The results show that the provenance of the Lengjiaxi Group is mainly felsic volcanic rocks, possibly containing a small amount of intermediate-basic volcanic rock materials, and the content of alkaline feldspar in the source area sedimentary parent rocks is low. The source rocks have undergone moderate weathering, and the weathering degree gradually increases from the Huangxudong Formation to the Xiaomuping Formation, which may be affected by later potassic metasomatism. It belongs to bathyal-abyssal turbidite deposits. Different segments of the Huangxudong Formation and the Xiaomuping Formation correspond to the middle fan or outer fan sedimentary environment of the turbidite fan respectively. During the sedimentary period, the climate is warm and humid, and the sedimentary site is near the weak oxidation-weak reduction interface. It is formed in the tectonic setting of an active continental margin. This study provides new geochemical evidence for regional geological evolution.

       

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