玉北地区下奥陶统白云岩岩石学、地球化学特征及成因

doi:10.11743/ogg20140314

摘要/Abstract

摘要：

通过岩心、薄片、扫描电镜、阴极发光、微量元素、同位素和包裹体测温等分析手段，对玉北地区下奥陶统白云岩岩石学特征、地球化学特征及成因进行研究。结果表明，该区白云岩主要由细晶、自形-半自形白云岩和细-粗晶、它形白云岩以及鞍形白云石充填物构成。白云岩的晶粒大小并不反映成因，反而是晶体结构特征（曲面-它形晶和平面-自形、半自形晶）与成因关系密切。细晶、自形-半自形白云岩具有高Sr、低Fe、Mn含量的特征以及与早奥陶世海水相似的O和C同位素组成，总体属于浅埋藏早期与海水有关的低温白云石化作用的产物。细-粗晶、它形白云岩的Sr含量较低而Fe和Mn含量相对较高，O同位素值明显偏负，包裹体测温结果显示部分样品具有较高的均一温度和盐度值，结合区域构造演化背景，认为该类白云岩以浅埋藏晚期到中埋藏阶段的高温白云石化为主，局部受热液改造，云化流体主要来自于地层中封存的海源卤水。鞍形白云石充填物有两期，一期与热液成因的基质白云岩形成时期相近，另一期则可能与二叠纪的岩浆期后热液有关。

关键词: 岩石学特征, 地球化学, 白云岩, 下奥陶统, 玉北地区, 塔里木盆地

Abstract:

The petrologic,geochemical characteristics and origin of the Lower Ordovician dolomite in Yubei area were investigated through the analysis of the cores,thin-sections,SEM,cathode luminescence,trace element,C-O isotope and microthermometry of fluid inclusions.The following results were obtained.Matrix dolomites are of two types:fine crystalline,euhedral-subhedral dolomite and fine to coarse crystalline,anhedral dolomite with saddle fillings.The origin of dolomite is closely related to crystal texture(nonplanar anhedral,planar euhedral/subhedral)instead of crystal size.The fine crystalline,euhedral-subhedral dolomite has high Sr and low Fe-Mn content,and C and O isotope composition similar to that of seawater in Early Ordovician.So this type of dolomite was overall the product of low-temperature dolomitization associated with the Ordovician seawater during the early stage of shallow burial.In contrast,the fine to coarse crystalline,anhedral dolomite has low Sr,relatively high Fe and Mn content and more negative O isotope value.And its fluid inclusion microthermometry result suggests that it has high homogenization temperature and salinity.Combined with the regional tectonic background,it is believed that this type of dolomite was primarily the product of high-temperature dolomitization during late stage of shallow burial to moderate burial,and was locally transformed by hydrothermal fluids from marine-sourced saline water in formation.Moreover,there are two stages of saddle dolomite fillings:one is coeval with the matrix dolomite of hydrothermal dolomitization origin and the other may be associated with the thermal fluid post-magmatic activity during the Permian.

Key words: petrologic characteristics, geochemistry, dolomite, Lower Ordovician, Yubei area, Tarim Basin

中图分类号:

TE121.3

黄擎宇,张哨楠,叶宁,等. 玉北地区下奥陶统白云岩岩石学、地球化学特征及成因[J]. 石油与天然气地质, 2014, 35(3): 391-400. doi: 10.11743/ogg20140314 Huang Qingyu,Zhang Shaonan,Ye Ning,et al. Petrologic,geochemical characteristics and origin of the Lower Ordovician dolomite in Yubei area[J]. Oil & Gas Geology, 2014, 35(3): 391-400. doi: 10.11743/ogg20140314

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