Dolomitization

Dolomitized marble (Gouverneur Marble, New York (state)) - dolomitization by hydrothermal fluids

Dolomitization is a geological process by which the carbonate mineral dolomite is formed when magnesium ions replace calcium ions in another carbonate mineral, calcite. It is common for this mineral alteration into dolomite to take place due to evaporation of water in the sabkha area. Dolomitization involves substantial amount of recrystallization. This process is described by the stoichiometric equation:

2 CaCO_3(calcite) + Mg²⁺ ↔ CaMg(CO₃)_2(dolomite) + Ca²⁺

Dolomitization depends on specific conditions which include low Ca:Mg ratio in solution, reactant surface area, the mineralogy of the reactant, high temperatures which represents the thermodynamic stability of the system, and the presence of kinetic inhibitors such as sulfate.

If the kinetic inhibitors and high temperatures are compatible, then dolomitization can take place in saline environments above thermodynamic and kinetic saturation with respect to dolomite. This type of environment includes, freshwater and seawater mixing zones, normal saline to hypersaline subtidal environments, schizohaline environments (fluctuating salinity: fresh-water to hypersaline conditions) and hypersaline supratidal environments. When requirements are fulfilled, dolomitization can take place in alkaline environments which are those under the influence of bacterial reduction and fermentation processes, and areas with high input alkaline continental groundwaters. Environments with high temperatures (about 50 °C) such as subsurface and hydrothermal environments are conducive to dolomitization.

See also

• Diagenesis
• Dolomite (rock)

References

• Hardie, Lawrence A (1987), "Dolomitization; a critical view of some current views", Journal of Sedimentary Research, 57 (1): 166–183, Bibcode:1987JSedR..57..166H, doi:10.1306/212f8ad5-2b24-11d7-8648000102c1865d
• Machel, Hans-G.; Mountjoy, Eric W. (May 1986), "Chemistry and environments of dolomitization — A reappraisal", Earth-Science Reviews, 23 (3): 175–222, Bibcode:1986ESRv...23..175M, doi:10.1016/0012-8252(86)90017-6
• Whitaker, Fiona F.; Xiao, Yitian (June 2010), "Reactive transport modeling of early burial dolomitization of carbonate platforms by geothermal convection", AAPG Bulletin, 6, 94 (6): 889–917, doi:10.1306/12090909075, retrieved 2011-04-13
• Wilson, Edith Newton; Hardie, Lawrence A; Phillips, Owen M (1990), "Dolomitization front geometry, fluid flow patterns, and the origin of massive dolomite: the Triassic Latemar buildup, northern Italy", American Journal of Science, 290 (7): 741–796, Bibcode:1990AmJS..290..741W, doi:10.2475/ajs.290.7.741