Scientific Reports

Dolomite problem, Mg isotope, Temperature estimation, Tarim basin, Ediacaran to ordovician

The "dolomite problem" has long been a signifcant challenge in sedimentology, particularly regardingthe determination of dolomite formation temperatures, a subject that remains highly debated.Magnesium (Mg) isotopes, due to their stability in dolomite during diagenesis and the strongrelationship between isotopic equilibrium fractionation and temperature, present a promising toolfor estimating the formation temperatures of dolomite. In this study, we analyzed the Mg isotopecomposition (826Mg) of various dolomite samples from the Ediacaran to Ordovician in the Tarim BasinChina, to assess the potential of Mg isotopes as a thermometer for dolomite formation.The 826Mgvalues of micro-fne crystaline dolomites (D1)ranged from -1.98 to -1.69%, fne-medium crystallinedolomites (D2)from -1.68 to -1.33%, and medium-coarse crystalline dolomites (D3) from -2.35to_1.99%.. Based on the Mg isotope temperature equilibrium fractionation equations, A26Mgdo-fuid=_0.1554(+0.0096)x106/T2 or A26Mg ol-ca=0.1453(+0.0106)x106/T2,the calculated formationtemperatures for Dl ranged from 45.0 to 65.4 'c, for D2 from 53.1 to 73.9 °c, and for D3 from 142.4 to173.9 °C or 156.4 to 189.0 °c, These temperature estimates align closely with those derived from fluidinclusions and clumped isotopes in previous literature studies of the same formations, supporting thereliability of Mg isotopes as a method for determining dolomite formation temperatures. This studyintroduces an innovative approach for assessing dolomite formation temperatures using Mg isotopesoffering crucial insights into the resolution of the "dolomite problem."

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2045-2322

SCI