Integration of stable isotopes, radiometric dating and microthermometry of saddle dolomite and host dolostones (Cretaceous carbonates, Kurdistan, Iraq): New insights into hydrothermal dolomitization.

This paper integrates Mg-, C-, O-, Sr-isotopes, fluid-inclusions microthermometry, and radiometric dating of dolostones and vug-filling saddle dolomite and calcite of the Upper Cretaceous Bekhme Formation, the Kurdistan Region of Iraq, provide new insights into the origin, timing and geochemical evolution of hydrothermal dolomitizing fluids. Similar isotopic compositions and fluid-inclusion microthermometry of the dolostones and saddle dolomite suggest formation by similar fluids. The U–Pb ages of dolostones and saddle dolomite suggest that dolomitization (74.8 Ma) was accomplished in 300 Ka at near Earth's surface by flow of hydrothermal fluids followed by dolostone dissolution and precipitation of vug-filling saddle dolomite (73.8 Ma). Mg isotopic compositions of the dolomites (26Mg DSM3= −0.81‰ to −0.76‰) are interpreted to indicate derivation of Mg from marine connate waters entrapped in overpressured basinal mudstones. Relatively high Sr-isotope ratios of the dolomites precludes the role of ophiolites as an important source of Mg in the basin. • Similar ranges of isotopes and microthermometry values of the dolostones and saddle dolomite suggest formation by similar fluids. • Dolomitization was accomplished in 300 Ka at near earth's surface by flow of hydrothermal fluids. • The source of Mg is interpreted to be basinal marine connate waters. [ABSTRACT FROM AUTHOR]