塔中地区上奥陶统热液流体与热化学硫酸盐还原作用  

Hydrothermal fluid activity and thermochemical sulfate reduction in the Upper Ordovician,Tazhong area

作　　者：李开开[1] 蔡春芳[1] 蔡镠璐[1] 张春明[2] 

机构地区：[1]中国科学院矿产资源研究重点实验室 [2]长江大学地球化学系,湖北荆州434023

出　　处：《石油与天然气地质》2008年第2期217-222,共6页Oil & Gas Geology

基　　金：国家重点基础研究发展规划(973)项目(2006CB202304);国家自然科学基金项目(40573034)

摘　　要：对塔中地区奥陶系裂缝充填矿物（方解石、萤石、重晶石等）进行稀土元素、^87Sr/^86Sr值以及流体包裹体测定。结果显示。所有裂缝充填矿物的^87Sr/^86Sr值（0.70889-0.71036）和地层水的^87Sr/^86Sr值都高于碳酸盐岩全岩及同期海水，裂缝充填物流体包裹体的均一化温度较上奥陶统所经历的最高温度高约20％，反映该区存在热液流体，且具有富^87Sr的特征。高^87Sr/^86Sr值的热液流体可能来源于寒武系或前寒武碎屑岩地层；而且该热液流体中Eu^2＋与Sr^2＋具有相似的成因，导致沉淀矿物具有正铕异常，且铕与锶呈良好的线性关系。该热液促使发生热化学硫酸盐还原作用（TSR），导致H2S气体和黄铁矿的产生。另一方面，富^87Sr、相对低温低盐度裂缝充填萤石矿物的存在，反映了本区除受热液流体影响外还受到大气淡水或低温盆地流体的影响。Measurements of rare earth elements, value of ^87Sr/^86Sr and fluid inclusion, had been carried out on facture-filling minerals （such as calcite, fluorite and barite） in Tazhong area. Results show that the ^87Sr/^86Sr values of all the filling minerals （0.70889 -0.71036） and formation water are higher than that of the whole-rock samples of fracture-carbonate rock and sea water in the same period, and the homogenization temperature of fluid inclusion is about 20℃ higher than that of the highest temperature ever experienced by the Upper Ordovician, signaling the presence of hydrothermal fluid and a high concentration of ^87Sr. The hydrothermal fluid with high ^87Sr/^86Sr value is most likely derived from the Cambrian or pre-Cambrian clastic rocks. Its Eu^2＋ and Sr^2＋ are of similar origin, resulting in a positive Eu anomaly and a good linear relationship between Eu and Sr in the fracture fillings. It induced TSR and generated HSS and pyrite. Consequently, the process led to the replacement of barite by calcite. The presence of fracture-filling ^87Sr-rich fluorite with relatively low temperature and low salinity as indicates that beside the influence of hydrothermal fluid, the area might also be affected by fresh water and basin fluid of low temperature.

关 键 词：稀土元素 铕异常 热液流体 热化学硫酸盐还原作用 塔中地区 

分 类 号：P632[天文地球—地质矿产勘探]