Geochemists’toolkit for tracing the global deep carbon cycle has recently been augmented by the analysis of magnesium isotopes.Light Mg-isotopic compositions normally occur uniquely in carbonates precipitated from seawater,either in the form of sedimentary limestones/dolomites or as sea-waterprecipitated alteration products impregnating the oceanic crust.But Chinese geochemists have found that large numbers of volcanic rocks from the eastern Geochemists’ toolkit for tracing the global deep carbon cycle has recently been augmented by the analysis of magnesium isotopes. Light Mg-isotopic compositions normally occur uniquely in carbonates precipitated from seawater, either in the form of sedimentary limestones / dolomites or as sea-waterprecipitated alterations products impregnating the oceanic crust.But Chinese geochemists have found that large numbers of volcanic rocks from the eastern