On the Direction and Magnitude of Oxygen Isotope Fractionation Between Calcite and Aragonite at Thermodynamic Equilibrium |
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Authors: | Gen-Tao Zhou Yong-Fei Zheng |
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Institution: | (1) CAS Kay Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China |
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Abstract: | Oxygen isotope fractionation factors between calcium carbonates and water have been applied to ancient marine geochemistry
principally for the purpose of geothermometry. The problem was encountered, however, with respect to the direction and magnitude
of oxygen isotope fractionation between calcite and aragonite at thermodynamic equilibrium. This basically involves sound
understanding of both thermodynamics and kinetics of oxygen isotope fractionation between inorganically precipitated carbonate
and water at low temperatures. Thus the crucial issues are to acknowledge the processes of chemical reaction and isotopic
exchange during precipitation of CaCO3 minerals in solution, the kinetic mechanism of isotope equilibrium or disequilibrium, the effect of polymorphic transition
from metastable aragonite to stable calcite under hydrous or anhydrous conditions, and the presence or absence of isotope
salt effect on oxygen isotope exchange between carbonate and water in response to the hydrous or anhydrous conditions at thermodynamic
equilibrium. Because good agreements exist in carbonate–water oxygen isotope fractionation factors between theoretical calculations
and experimental determinations, it is encouraging to applying the thermodynamic and kinetic data to isotopic paleothermometry
and geochemical tracing. |
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Keywords: | calcium carbonate experimental determination fractionation factor kinetic mechanism oxygen isotope theoretical calculation thermodynamic equilibrium |
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