Advances in Earth Science
• Orginal Article •
), Xiangkun Zhu(
Aiguo Dong, Xiangkun Zhu. Mg Isotope Geochemical Cycle in Supergene Environment[J]. Advances in Earth Science, 2016, 31(1): 43-58.
Mg isotope fractionation in the supergene environment have been obtained many important advances in recent years, and these new knowledge supply the clues for further understanding Mg isotope geochemical cycle in the supergene environment. Mg isotope geochemical cycle in the supergene environment involves some important geological processes, such as weathering, river transportation, carbonate sedimentation and water-rock reaction. Mg isotope fractionates dramatically in weathering process. Silicate weathering products enrich in 26Mg (secondary clay minerals prefer to combine with 26Mg) and 24Mg prefer to be into the aqueous phase. Although there is not significant Mg isotope fractionation during river transportation, Mg isotope of river water could still be affected by the supplement of external sources. Most magnesium from river water are transported into the ocean, and then the carbonate precipitation prefers to remove 24Mg from ocean as carbonate minerals. Submarine low temperature waterrock reaction could transport less magnesium from ocean into the rocks during secondary mineral formation, which is associated with Mg isotope fractionation. However, most of magnesium (80%~87%) in seawater prefer to combine with the rock in high temperature waterrock reaction and recirculated hydrothermal fluid may be enriched in 24Mg. In brief, magnesium from upper crust (δ26Mg about -0.22‰) experiences weathering and transports by river water to ocean in the supergene environment. The magnesium in ocean could recycle into the rocks by the process of carbonate precipitation (δ26Mg is less than -1‰) or reacting with submarine basalt to form secondary mineral.