云南会泽石炭系摆佐组白云岩地球化学特征及其成因分析

为了解云南会泽石炭系摆佐组中、粗晶白云岩的地球化学特征及其成因，对白云岩进行岩石学、岩石地球化学和同位素等分析、研究。研究区位于华南陆块群扬子微陆块滇中（昆明）中生代隆起带，白云岩岩石类型主要为灰-灰白色、肉红色、米黄色中、粗晶白云岩，白云岩在岩石学特征上具有半自形-自形结构，MgO-CaO分析显示白云石是交代或重结晶成因而非沉积成因的；微量元素分析显示白云岩中Sr含量较低，反映了白云岩可能是后期埋藏成岩作用过程中形成的，且白云化时间较晚，Sr已经大量流失，同时Sr/Ba比值较高，表明白云岩在深埋过程中所形成时水介质盐度较高；稀土元素配分模式显示Ce、Eu呈现负异常，Ce弱负异常由于Ce3+ 将不断被氧化成相对易溶的Ce4+ 离子被迁移而贫化，Eu弱负异常可能为Eu在化学风化过程中被优先带出而造成的；碳、氧同位素分析研究表明该区白云岩具有较高的成岩温度（52.40℃～69.44℃）和盐度指数Ｚ值（121～125），表明其形成环境为超咸浓缩海水环境并具较高的成岩温度，推测该地区白云岩为中深埋藏环境，根据区域地层资料、区域构造演化史推测其白云岩化时间可能发生于二叠纪，属后生白云岩。综合分析认为本区白云岩成因为埋藏成因，并且在后期可能受到了构造作用和地壳抬升作用的影响，使白云岩产生化学风化作用，造成Eu的负异常，这可能与滇东北地区印支-海西阶段所形成的拉张和垂直升降运动有关。

Geochemical Characteristics and Genetic Analysis of Carboniferous Dolomite in Huize Basin,Yunnan

The dolomite of Carboniferous in Baizuo Formation in Huize, Yunnan was studied by several methods such as petrological analysis, geochemistry analysis and isotope, in order to understand its geochemical characteristics and genesis. The study area is located in central Yunnan (Kunming) Mesozoic uplift zone, which belongs to the Yangtze micro-continent of the South China block group. The dolomite rock is mainly characterized by colors in gray-white gray, flesh red, beige, and coarse-grained dolomite, and  it has the subhedral-euhedral structure. The analysis based on MgO-CaO indicates that the formation of the dolomite is due to the accountable or recrystallization, and is not due to the sedimentation. The trace elements analysis shows that the content of Sr in the dolomite rock is low. It indicates  that  the dolomite may be formed in post-burial genesis and the time of dolomitization is late,Therefore, Sr had been an  abundant  loss, consequently, the Sr/Ba ratio is relatively high.The result indicates that the medium of water is high in salinity when the dolomite is  under  diagenesis in deep burial. The distribution pattern of rare earth elements shows a negative anomaly of Ce and Eu. Ce3+ ions is negative anomaly because Ce3+  was oxidized to the soluble Ce4+ ions. Eu is negative anomaly because it was brought out in priority in the chemical weathering process. According to the carbon and oxygen isotope, a relatively higher salinity index(121～125) and diagenetic temperature (52.40℃～69.44℃) were observed. It indicates that the illumincited dolostones were formed under the high concentrated salinity and high temperature. We inferred that the dolomite in the region was in deep burial environment. According to the report of the regional stratigraphy investigation and regional tectonic evolution, We speculated that the time of the dolomitization may occur in the Permian, and it should belong to the epigenetic dolomite. We concluded that the dolomite in Huizhe was formed under deep burial conditions. Due to the structure function and the influence of the earth's crust uplift, the Baizuo Formation was raised to the earth surface and the dolomite in this formation experienced the chemical weathering,then created the negative anomalies of Eu. This may be related to the tensile and vertical lifting movements of Indo-China-Hercynian stage in the Northeast Yunnan.