Origin and geochemical reaction paths of sabkha brines: Sabkha Jayb Uwayyid, eastern Saudi Arabia
Origin and geochemical reaction paths of sabkha brines: Sabkha Jayb Uwayyid, eastern Saudi Arabia
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sabkha 卤水的起源和地球化学反应路径：沙特阿拉伯东部 Sabkha Jayb Uwayyid
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发表时间：
2008
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通讯作者：
Nasser A. Alsaaran
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作者：
Nasser A. Alsaaran
Sabkhas是沙特阿拉伯东部普遍存在的地貌特征。七个盐水样本取自沙特阿拉伯东部的Sabkha Jayb Uwayyid。研究了卤水化学、碳酸盐和蒸发矿物的饱和状态以及蒸发驱动的地球化学反应路径，以描绘卤水的起源以及卤水化学和sabkha矿物学的演化。sabkha盐水中溶解固体的平均总量为243克/升。阳离子优势顺序为Na+ >> Mg2+ >> Ca2+>K+，阴离子优势顺序为Cl−>> SO42−>> HCO3−。根据化学分划原理和观测到的离子比，得出结论：sabkha盐水来自深层地下水，而不是来自直接降雨、周围径流或浅层地下水的流入。水相形态模拟结果表明：(1)7种盐水中方解石、白云石和菱镁矿均为过饱和，卤石为欠饱和；(2)三种卤水中石膏和硬石膏均为欠饱和，三种卤水中石膏和硬石膏均为过饱和；(3)硬石膏在四种卤水中是比石膏更稳定的固相。使卤水到达岩盐相边界所需的蒸发系数为1.016 ~ 4.53。当二氧化碳被脱气，白云石从盐水中析出时，所有到岩盐相边界的反应路径都遵循中性路径。平均而言，含1 kg H2O的sabkha卤水沿反应路径析出7.6 g矿物，其中硬石膏占52%，石膏占35.3%，白云石占12.7%。碳酸氢盐是白云石沉淀的限制因素，硫酸盐是sabkha盐水中石膏和硬石膏沉淀的限制因素。
Sabkhas are ubiquitous geomorphic features in eastern Saudi Arabia. Seven brine samples were taken from Sabkha Jayb Uwayyid in eastern Saudi Arabia. Brine chemistry, saturation state with respect to carbonate and evaporate minerals, and evaporation-driven geochemical reaction paths were investigated to delineate the origin of brines and the evolution of both brine chemistry and sabkha mineralogy. The average total dissolved solids in the sabkha brines is 243 g/l. The order of cation dominance is Na+ >> Mg2+ >> Ca2+>K+, while anion dominance is Cl− >> SO42− >> HCO3−. Based on the chemical divide principle and observed ion ratios, it was concluded that sabkha brines have evolved from deep groundwater rather than from direct rainfall, runoff from the surroundings, or inflow of shallow groundwater. Aqueous speciation simulations show that: (1) all seven brines are supersaturated with respect to calcite, dolomite, and magnesite and undersaturated with respect to halite; (2) three brines are undersaturated with respect to both gypsum and anhydrite, while three brines are supersaturated with respect to both minerals; (3) anhydrite is a more stable solid phase than gypsum in four brines. Evaporation factors required to bring the brines to the halite phase boundary ranged from 1.016 to 4.53. All reaction paths to the halite phase boundary follow the neutral path as CO2 is degassed and dolomite precipitates from the brines. On average, a sabkha brine containing 1 kg of H2O precipitates 7.6 g of minerals along the reaction path to the halite phase boundary, of which 52% is anhydrite, 35.3% is gypsum, and 12.7% is dolomite. Bicarbonate is the limiting factor of dolomite precipitation, and sulfate is the limiting factor of gypsum and anhydrite precipitation from sabkha brines.