Zhang Jixi
School of Geography and Environmental Science, Guizhou Normal University/State Engineering Technology Institute for Karst Desertification, Guiyang 550001, China.
School of Karst Science, Guizhou Normal University/State Engineering Technology Institute for Karst Desertification, Guiyang 550001, China.
Molecules. 2024 Feb 2;29(3):698. doi: 10.3390/molecules29030698.
The equilibrium oxygen isotope fractionation factor is widely used in geological thermometry. However, under most natural conditions, the oxygen isotope exchange is rare to reach equilibrium. Especially for the complex water-rock interaction process, the contribution of the HCO solution, CO solution, Ca(HCO) solution, and CaCO solution to the equilibrium oxygen isotope fractionation factor of this process is poorly understood. In view of this predicament, these key parameters are obtained by ab initio calculations. The results showed that the contributions of different carbonate minerals and different aqueous solutions to the equilibrium oxygen isotope fractionation factor were different. Among all nine carbonate minerals (dolomite, calcite, aragonite, magnesite, siderite, otavite, smithsonite, ankerite, and strontianite), the minerals with the highest and lowest reduced partition function ratios (RPFR) were siderite and strontianite, respectively. At the same time, the RPFR of nitratine, which has the same structure as carbonate, was studied. The RPFRs of the three most widely distributed carbonates in nature (dolomite, calcite, and aragonite) were dolomite > calcite > aragonite. Among the HCO solution, CO solution, Ca(HCO) solution, and CaCO solution, the HCO solution had the strongest ability to enrich O. In addition, the equilibrium oxygen isotope fractionation factors between aqueous solutions and gas phase species (CO(g), HO(g), and O(g), etc.) were calculated systematically. The results showed that the oxygen isotope fractionation factors between solutions and gas phases were often inconsistent with the temperature change direction and that the kinetic effects played a key role. These theoretical parameters obtained in this study will provide key equilibrium oxygen isotope constraints for water-rock interaction processes.
平衡氧同位素分馏系数在地质测温中被广泛应用。然而，在大多数自然条件下，氧同位素交换很少能达到平衡。特别是对于复杂的水岩相互作用过程，HCO溶液、CO溶液、Ca(HCO)溶液和CaCO溶液对该过程平衡氧同位素分馏系数的贡献尚不清楚。鉴于这一困境，通过从头计算获得了这些关键参数。结果表明，不同碳酸盐矿物和不同水溶液对平衡氧同位素分馏系数的贡献不同。在所有九种碳酸盐矿物（白云石、方解石、文石、菱镁矿、菱铁矿、菱锌矿、菱锰矿、铁白云石和天青石）中，约化配分函数比（RPFR）最高和最低的矿物分别是菱铁矿和天青石。同时，研究了与碳酸盐结构相同的钠硝石的RPFR。自然界中分布最广的三种碳酸盐（白云石、方解石和文石）的RPFR为白云石>方解石>文石。在HCO溶液、CO溶液、Ca(HCO)溶液和CaCO溶液中，HCO溶液富集O的能力最强。此外，系统计算了水溶液与气相物种（CO(g)、HO(g)和O(g)等）之间的平衡氧同位素分馏系数。结果表明，溶液与气相之间的氧同位素分馏系数往往与温度变化方向不一致，动力学效应起关键作用。本研究获得的这些理论参数将为水岩相互作用过程提供关键的平衡氧同位素约束。
