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Geochemical Kinetics of Oxygen Isotope Exchange During Fluid-Rock Interactions:A Review

NI Huai-wei, ZHENG Yong-Fei, ZHA0 Zi-Fu   

  1. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
  • Received:2003-06-20 Revised:2003-06-20 Online:2003-06-20 Published:2003-06-20

Abstract: Oxygen isotope studies play an important role in tracing the time-integrated fluxes (or fluid/rock ratio),flow directions and sources of fluid during fluid-rock interactions.Based on the principle of mass balance,oxygen isotope exchange models ale built for“closed”systems and open systems The ”closed” systems ale classified into closed, batch volatilization and Rayleigh volatilization systems .Rayleigh volatilization results in more 18O depletion of rock than batch volatilization,but there is no significant difference between them in geological practice.Mechanisms of oxygen isotope transport in continuum mechanic models of open systems include diffusion/dispersion and advection.Peclet number,defined by the rates of fluid flow to diffusion/dispersion, determines relative contribution of the above two mechanisms to oxygen isotope transport on some scales .Fluid-rock exchange is controlled by surface kinetics.When exchange rate is faster than fluid flow,equilibrium in oxygen isotope fractionation between fluid and rock is achieved,otherwise the equilibrium will not be attained .Damkohler number,defined by the rates of fluid flow to fluid-rock exchange,determines the extent of reaction towards equilibrium .If more than one mineral is considered 88 a monitoring phase,the inner-mineral fractionations may distinguish these two models. This article reviews geochemical kinetics of oxygen isotope exchange during fluid-rock interactions,whose principles an d models can also be extended to studies on other elements.