《地球化学》第3章地表地球化学作用与元素迁移.ppt

Residence Time of Water ?Residence time of water in seawater average depth of the ocean ≈ 4000 m average rate of evaporation ≈ 0.01 m/year Residence time of water ≈ 4000/0.01 = 400,000 years (0.4 Ma) ? Residence time of major ions in seawater Residence time of Cl- = 68,000,000 years (68 Ma) Residence time of Na+ = 260,000,000 years (260 Ma) Residence time of water is 100X shorter than for ions ?Salinity controlled by evaporation and precipitation Residence Times of Some Elements Element Amount in Ocean (g) Residence Time (years) Na (sodium) 147 × 1020 260,000,000 K (potassium) 5.3 × 1020 8,000,000 Ca (calcium) 5.6 × 1020 2,000,000 Si (silicon) 5.2 × 1018 10,000 Mn (manganese) 1.4 × 1015 7000 Fe (iron) 1.4 × 1016 140 Al (aluminum) 1.4 × 1016 100 计算元素或离子在海水中的居留时间的方法 元素地球化学迁移概念 元素在水溶液中的迁移形式 定量计算元素迁移的方法 影响元素迁移的内部因素 影响元素迁移的外部因素 胶体作用和络合作用对元素迁移的意义 介质中pH值对元素发生沉淀与溶解的影响 介质中氧化还原反应对元素共生组合的影响 举例说明地表岩石风化过程的主要反应类型 硫化物矿床风化过程主要反应类型、典型剖面结构及可能发生次生富集的元素和矿石矿物? 河流入海口元素发生沉淀的原因 海洋中元素进入和带出海水的主要方式? 第三章复习思考题 1、湖南某热液充填型矿床产于花岗岩中，早阶段矿石由萤石、方铅矿、闪锌矿和黄铜矿组成，伴随有黄铁绢云岩化；晚阶段形成重晶石、方解石、方铅矿、闪锌矿组合，伴随有碳酸盐化蚀变。试分析两个矿化阶段氧化还原条件的酸碱度的特征。 2、河北某矽卡岩型铅-锌矿床中，存在两个世代的闪锌矿。早世代闪锌矿同镜铁矿（Fe2O3）共生，闪锌矿呈浅黄绿色，含铁低；晚世代闪锌矿同磁铁矿和穆磁铁矿（Fe3O4），由镜铁矿转变为磁铁矿而呈赤铁矿假象）共生，闪锌矿呈深褐色，且含铁高。说明两种闪锌矿形成时介质条件的差异，以及两种闪锌矿颜色深浅和含铁量不同的原因。（离子半径：RZn2+=0.83 ?; RFe2+=0.82 ?; RFe3+=0.67 ?） 课程作业 * * This world map shows how the salinity of the oceans changes slightly from around 32ppt (3.2%) to 40ppt (4.0%). Low salinity is found in cold seas, particularly during the summer season when ice melts. High salinity is found in the ocean deserts in a band coinciding with the continental deserts. Due to cool dry air descending and warming up, these desert zones have very little rainfall, and high evaporation. The Red Sea located in the desert region but almost completely closed, shows the highest salinity of all (40ppt) but the Mediterranean Sea follows as a close second (38ppt). Lowest salinity is found in the upper reaches of the Baltic Sea (0.5%)