准噶尔盆地西北缘二叠系云质碎屑岩地球化学特征及成因机理研究

通过岩石学、碳氧同位素和元素地球化学等方法对准噶尔盆地西北缘二叠系云质碎屑岩特征进行了研究，分析了白云岩化机理并建立了白云岩化作用成因模式。结果表明，研究区岩石类型为白云质泥岩、白云质粉砂岩、白云化凝灰质粉砂岩和白云化凝灰质泥岩等，白云石化以交代湖相灰泥质和硅质（凝灰质）组分形成的自形或半自形的粉晶-细晶白云石为主，常见残余方解石和晚期方解石胶结物充填。岩石中 V/ Ni比（1.2～4.8）、Sr含量（95.5～782.2 μg/g）、Mg/Ca比（0.5～3.0）、有序度（0.36~0.98）、δ18O_PDB（-14.8‰～3.2‰）和δ13C_PDB（-1‰～5.2‰）的变化范围都较大。研究区云质岩类形成于水动力条件较弱、水体较深、相对安静的半闭塞陆相微咸-咸水湖湾环境，具多期次成因；二叠系时期构造运动复杂，断裂发育，火山活动频繁，不仅提供了白云石化过程中Mg2+的来源，且为富镁流体的快速流动和渗透提供了通道。综合研究认为本区的云质岩有准同生白云岩化、埋藏白云岩化和热液白云岩化三种成因类型。

Geochemical Characteristics and Genetic Mechanism of Permian Dolomitic Clastic Rocks in Northwestern Junggar Basin

The types and lithology characters of Permian dolomitic clastic rocks in northwestern Junggar Basin are investigated by means of petrologic analysis, X ray indentification, carbon and oxygen isotope geochemistry and element geochemistry analysis, also analyzed Dolomization mechanism, Established dolomitization model. dolomitic clastic rocks in study areas include dolomitic mudstone, dolomitic siltstone, dolomitic tuffaceous siltstone, dolomitic tuffaceous shale,ect. And dolostones which are formed through dolomitization by replacing lacutrine plaster and siliceous (tuffaceous) components mainly consist of powder fine dolomites with automorphic or hypidiomorphic crystals, while residual calcite and late filled calcite cement commonly exist. The ratio of V/ Ni(1.2～4.8)content of Sr(95.5～782.2 μg/g)Mg/Ca(0.5～3.0),the degree of order(0.36~0.98)δ18O_PDB(14.8‰～3.2‰)and δ13C_PDB(1‰～5.2‰)all have larger variation range. The dolomitic rocks in this area mainly formed in a relatively weak hydrodynamic conditions, deep, peaceful, salt and low salt semi closed terrestrial bay environment, have a characteristic of several stages and various causes. During Permian periods, in the researching zone the tectonics is complex, fault development, subtropical hot climate and frequent volcanic which provide favourable source of Mg2+ and permeability channel for the rich magnesium fluid fast flow. Comprehensive research show that these dolomitic rocks have three kinds of genetic types: Penecontemporaneous dolomitization, buried dolomitization, hydrothermal dolomitization.