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在有大规模钙华沉积的四川黄龙沟中,使用化学成分数据以及碳氧稳定同位素组成对其水文地球化学特征进行了分析研究。研究区钙华沉积的地表溪流水质基本上受到两种水混合的制约,即断层泉水和山区的融雪(冰)水。泉水中含有高浓度的经由断层提供的CO2,结果高浓度的溶解CO2使得其溶解的碳酸盐岩比普通的岩溶泉溶解的碳酸盐岩高得多,同时也导致硅酸盐岩的溶解。黄龙沟中上游的泉水相对于方解石接近于平衡。溶解无机碳(DIC)的浓度和它们的δ13C值是大约由c=0.02mol·L1δ13C=-3‰的CO2(aq)与含有δ13C=+3‰的碳酸盐岩在封闭系统条件下反应的结果。估计这些CO2中约有70%来自上地幔。所有泉水的水化学数据均落在高岭石稳定域内,但对Na长石和Ca长石具有侵蚀性。由于这些长石矿物的溶解速率太慢,所以水中的化学成分远离长石稳定域。地表溪流的DIC种类之间达到同位素平衡,在不同观测点发现的δ13CDIC变化主要是由于从水中释放出的CO2的程度不同引起的。水样的δ18O值与其采集点的海拔高度之间存在线性关系;研究区的地表溪流的氧同位素组成受到蒸发的制约。在流经钙华沉积物的地表溪流中白天和夜晚的水化学及pH的日变化表明生物作用促进了碳酸盐的沉积,尽管作用不显著。据估计研究区碳酸钙的日沉积速率是4778kg·km2,即约1mm·a1。
Hydrochemical characteristics of Huanglonggou, a large-scale travertine deposit, were analyzed using chemical composition data and stable oxygen and carbon isotope composition. The surface water quality of travertine sediments in the study area is basically restricted by the mixing of two kinds of water, namely, fault springs and snowmelt (ice) water in mountainous areas. The spring water contains a high concentration of CO2 provided through the fault, with the result that high concentrations of dissolved CO2 result in much higher dissolved carbonate rocks than normal karst volcanic carbonate rocks and also lead to the dissolution of silicate rocks . The spring water in the upper reaches of Huanglong Dao is close to equilibrium with respect to calcite. Concentrations of dissolved inorganic carbon (DIC) and their δ13C values are approximated by the reaction of CO2 with a δ13C = +3 ‰ carbonate (aq) at c = 0.02 mol·L1 δ13C = -3 ‰ under closed system conditions result. It is estimated that about 70% of these CO2 come from the upper mantle. All spring water chemistry data fall within the kaolinite stable zone, but are aggressive to Na feldspar and Ca feldspar. Because of the dissolution rate of these feldspar minerals, the chemical composition of the water is far away from the feldspar stable domain. The isotopic balance between DIC species in surface streams is reached. The δ13CDIC changes observed at different observation points are mainly due to the different degrees of CO2 released from the water. There is a linear relationship between the δ18O value of water samples and the altitude at the sampling point. The oxygen isotope composition of surface streams in the study area is restricted by evaporation. Diurnal and night water chemistry and pH diurnal variations in surface streams flowing through the travertine deposits indicate that biological effects promote the deposition of carbonates, albeit with insignificant effects. It is estimated that the daily deposition rate of calcium carbonate in the study area is 4778 kg · km2, that is, about 1 mm · a1.