塔里木柯坪地区下丘里塔格群白云岩成因

The Origin of Xiaqiulitaga Group Dolomite in Keping Area, Tarim Basin

根据白云岩的岩石学特征、化学元素分析和X衍射分析以及包裹体测温等多项资料,对塔里木盆地柯坪地区下丘里塔格群白云岩的成因进行了讨论。认为不同类型的白云岩形成于不同的沉积环境,其白云石化模式也不相同。潮坪—泻湖相的藻屑白云岩和泥晶白云岩,主要由泥晶白云石组成,白云石晶粒细小,晶形差,微量元索含量较高。元素Sr,Ba大于100ppm,B大于1ppm,白云石有序度较高(δ=0.84),为库龙白云石化的产物:浅滩相的颗粒白云岩、白云石晶粒变化较大,白云石有序度低(δ=0.56～0.76),为混合白云石化的产物;潮坪相结晶自云岩,由细—中晶白云石组成,有少量的粗晶白云石,白云石呈半自形、自形或他形,白云石有序度高(δ=0.88～0.95),为深埋藏白云石化的产物。

The origin of Xiaqiulitaga group dolomite in Keping area, Tarim Basin, Xinjiang is discussed in this paper according to the textures of dolomite, geochemical analysis of elements, x-ray diffraction and inclusion thermometry. It is concluded that different dolomites formed in different environments have different models of dolomitization. Algal dolomite and mud crystalline dolomite in tidal flat or lagoon, consisting for its greater part of mud crystalline dolomite and with a high ordering degree(equal to 0.84), contain a large amount of trace elements(Sr, Ba more than 100 ppm and B more than 1ppm). These facts show that Algal dolomite and mud crystalline dolomite were formed by Coorong dolomitization. Grain dolomite in shoal, consisting of mud crystalline and coarsely crystalline dolomite and with a poor ordering degree (about 0.56 to 0.76), was formed by meteoric-marine mixing dolomitization. Crystalline dolomite in tidal flat, consisting of different forms and sizes of dolomite and with the ordering degree as high as 0.88 to 0.95, was formed by deep burial dolomitization.