渣尔泰山群及宝音图群大理岩古沉积环境研究

内蒙古霍各乞位于华北地台北缘西段,区内出露的渣尔泰山群和宝音图群对于揭示中—新元古代时期华北地台北缘的古沉积环境具有重要的科学意义,且这两个岩群均含有大理岩为其研究提供了可能。在对该地区渣尔泰山群和宝音图群大理岩进行详细的野外地质工作的基础上,进一步选取有代表性的大理岩样品做C、O同位素分析。结果显示,内蒙古霍各乞渣尔泰山群大理岩δ13C_V-PDB值为-2.4‰~4.3‰,δ18O_V-PDB值为-39.0‰~-15.3‰,δ18O_V-SMOW值为-8.2‰~15.2‰,宝音图群大理岩δ13C_V-PDB值为-1.1‰~5.9‰,δ18O_V-PDB值为-18.5‰~-7.8‰,δ18O_V-SMOW值为12.0‰~22.7‰,两者的C同位素均具有显著的正漂移特征,O同位素均发生了强烈的亏损。结合地质、地球化学特征综合分析认为:1）霍各乞渣尔泰山群大理岩原岩的古沉积环境为缺氧的浅海相环境,沉积期接受了丰富的陆源碎屑物质的混染,沉积期后发生了明显的碳酸盐溶解作用,大理岩C同位素正漂移与华北克拉通北缘裂解作用关系密切。2）霍各乞宝音图群大理岩原岩形成于相对闭塞的浅海相环境,沉积期受陆源碎屑物质的混染程度相对较小,沉积期后发生了明显的碳酸盐溶解作用,大理岩C同位素正漂移可能与沉积盆地的闭塞性有一定的关系。3）霍各乞渣尔泰山群和宝音图群大理岩原岩具有类似的古沉积环境。

Research on the Paleosedimentary Environments of Marble in the Zhaertai and Buyant Groups: A case study of Huogeqi area,Inner Mongolia

Huogeqi, Inner Mongolia, is located in the western region of the northern margin of the North China Platform. The marble content of both the Zhaertai Group and the Buyant Group in this area is significant for revealing the paleosedimentary environment of the northern margin of the North China Platform in the Meso- to Neoproterozoic. Following detailed geological fieldwork, representative samples of marble from both groups were selected for C and O isotopic analysis. Zhaertai Group marble samples contained δ13C_V-PDB values between -2.4‰ and 4.3‰； δ18O_V-PDB values between -39.0‰ and -15.3‰； and δ18O_V-SMOW values between -8.2‰ and 15.2‰. Buyant Group marble samples contained δ13C_V-PDB values from -1.1‰ to 5.9‰； δ18O_V-PDB values from -18.5‰ to -7.8‰； and δ18O_V-SMOW values from 12.0‰ to 22.7‰. The C isotopes in both groups display an apparent positive drift, and their O isotopes are strongly depleted. A comprehensive analysis of geological and geochemical characteristics indicated that: （1） The protolith of Zhaertai Group marble was formed in a shallow anoxic marine environment. It was contaminated by abundant terrigenous clastic materials during the depositional stage, and obvious carbonate dissolution occurred after deposition. The positive drift of the C isotope is closely related to the break-up of the northern margin of the North China Platform. （2） The protolith of Buyant Group marble was formed in a relatively closed shallow marine environment, and underwent somewhat less contamination by terrigenous clastic materials during deposition. After the deposition stage, obvious carbonate dissolution occurred. The positive drift of C isotopes may be related to occlusion of the sedimentary basin. （3） The protoliths of the marble in the Zhaertai Group and Buyant Group experienced similar paleosedimentary environments.