期刊
GEOCHIMICA ET COSMOCHIMICA ACTA
卷 358, 期 -, 页码 134-147出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2023.08.013
关键词
Aragonite; Stable Sr isotopes; First-principles calculations; Equilibrium fractionation
Experimental and first-principles simulations were used to determine strontium partitioning and isotope fractionation between aragonite and fluid. The results show variations in strontium distribution coefficient and isotope fractionation in aragonite with changes in aragonite growth rate.
Strontium partitioning and isotope fractionation between aragonite and fluid have been determined experimentally at low values of the fluid saturation state (& omega;) with respect to this mineral (1.1 & LE; & omega;aragonite & LE; 2.2), and the measured isotope fractionation has been compared with the results of first-principles simulations. For the latter, Density Functional Theory (DFT) was used for estimation of the equilibrium Sr isotope fractionation between aragonite and Sr2+(aq). The obtained results suggest that, for values of & omega;aragonite close to unity, the apparent distribution coefficient of Sr in aragonite (DSr ,aragonite= XSrCO3 XCaCO3 ([Ca][Sr])fluid) exhibits values higher than one that rapidly decrease at increasing aragonite growth rate. Under equilibrium conditions (i.e. & omega;aragonite=1) a DSr, aragoinite value of 2.7 can be extrapolated. Additionally, for aragonite growth rates rp & LE; 10 8.0 & PLUSMN;0.2 (mol/m2/s) the Sr isotope fractionation between aragonite and the fluid (i.e. & UDelta;88/86Sraragonite-fluid) shows a constant value of 0.1 & PLUSMN;0.05%o, whereas it decreases to 0.40%o when the growth rate increases to 10 7.7(mol/m2/s). The surface reaction kinetic model (SRKM) developed by DePaolo (2011) has been used to describe the dependence of DSr, aragonite and & UDelta;88/86Sraragonite-fluid on mineral growth rate. In this model the best fit for DSr,aragonite and & UDelta;88/86Srar-agonite-fluid were 4 and 0.01%o, respectively, whereas the kinetic isotope fractionation factor for & UDelta;88/86Sraragonite-fluid was 0.6%o. The results of first-principles calculations yield an equilibrium Sr isotope fractionation factor of 0.04%o which is in excellent agreement with the experimental value of the present study. These results are the first experimental measurements of Sr isotope fractionation during inorganic aragonite precipitation as a function of growth rate and the first DFT calculations of Sr equilibrium fractionation in the aragonite-fluid system. The results of this study provide new insight into the mechanisms controlling stable Sr isotope composition in aragonite, which has implications for using Sr isotopes for paleo-reconstructions of natural archives, particularly those of abiogenic origin.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据