Self-accelerating volumetric dolomite-for-calcite replacement: A possible mechanism for high-temperature dolomitization?

• David W. Morrow ^[1]
  1. [1] Geological Survey of Canada (Calgary)
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 35, Nº. 2, 2020
• Idioma: inglés
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• Resumen

  • Quantitative calculations with the geochemical program PHREEQC© for the replacement of calcite by dolomite in brine solutions were performed under the condition that total mineral rock volume is conserved. These simulations, using brine solutions derived from the evaporation of two “end member” compositions for Phanerozoic seawater, indicate that calcium (Ca2+) molalities in solution do not increase exponentially, but instead exhibit monotonically decreasing rates of increase. Simulated rates for calcite dolomitization also decrease monotonically. This indicates that replacement of dolomite by calcite under a stricture of rock volume conservation does not cause a rapidly increasing rate of dolomitization in a self-accelerating manner, but rather is self-limiting. Preservation of sedimentary microfabrics in dolomitized limestones, although consistent with the recently proposed mechanism of dolomite-growth-driven pressure solution mechanism for volumetric dolomitization, is not definitive, as near-surface meteoric diagenesis of Pleistocene limestones causes similar preservation of microfabrics where aragonitic paleofauna and sediments have been replaced by calcite and dolomite in open fluid-rock systems.