塔北地区寒武系下丘里塔格群白云石化模式

针对塔北上寒武统下丘里塔格群复杂的白云石化作用，通过岩石学和地球化学分析认为下丘里塔格群埋藏后主要经历3期白云石化流体作用：早期浅埋藏环境下高浓度卤水在台缘带的迁移促进了渗透回流白云石化作用发生，形成残余颗粒幻影结构的粉晶白云岩，具有碳氧同位素负偏和微量元素Fe、Mn、Sr、Ba元素质量分数较低的特征；第二期流体主要为地层孔隙残余高盐度海水，在埋藏压实作用下白云岩发生重结晶作用，晶粒结构广泛发育，具有同位素碳正氧负和微量元素呈现富Mn贫Fe及低Sr高Ba的特征，该时期是晶间孔和晶间溶孔发育的主要时期；第三期流体主要为沿基底断裂上涌的高温富镁热液流体，发育构造-热液白云石化作用形成大量鞍状白云石，具有富Mn贫Fe和氧同位素负偏明显等特征。

Dolomitization Model of Lower Qiulitage Group in Tabei Area

This study is aim to clarify the complex dolomitization of dolostone in the Lower Qiulitage Group. Through analysis, the authors believe that the seepage reflux dolomitization was promoted by the migration of high concentration brine in marginal zone during the early shallow burial environment, which formed the residual particle dolomite with phantom structure with the characteristics of negative carbon and oxygen isotopic values, lower content of trace element iron, manganese, strontium and barium. The second stage fluid was mainly residual high salinity formation water in pore, which enhanced the dolomite recrystallization under the burial compaction, and caused the crystalline structure widely developed with the characteristics of positive oxygen isotopic and negative carbon isotopic values, high content of manganese and lower content of iron, lower content of strontium and higher content of barium. The inter-granular pores and dissolved pores were developed in this period. The third stage fluid was mainly hot magnesium-rich hydrothermal fluid along the basement faults, which formed a large number of saddle dolomite by tectonic and hydrothermal dolomitization with high content of manganese, lower content of iron, and negative oxygen isotopic values.