Diamonds – time capsules of volatiles and the key to dynamic Earth evolution

Noble gases analyses of Mid-Oceanic Ridge Basalts (MORB) and Ocean Island Basalts (OIB) have been used to determine the present-day structure of the Earth. Noble gas elemental and isotopic data of these samples seem to support a two-layer mantle model, with a slightly degassed lower mantle and highly degassed upper mantle. However, the extent and timing of mantle outgassing and the sources of volatiles are not well constrained. Quantifying these unknowns and uncertainties in the noble gas system are fundamental for developing a high resolution model of the structure of the Earth’s mantle and its evolution from an initial homogenous composition to a differentiated state.

Diamonds can contain high density fluid (HDF) inclusions that host volatiles. Previous research has shown that diamonds span a large formation age range up to 3.5 Ga. Therefore, noble gas studies of diamonds may provide the key to address the unknowns on the mantle noble gas composition through time. In this talk I will show noble gas data in combination with major and trace elements from fluid inclusions in diamonds. These provide new insights into the influence of subduction on the noble gas heterogeneity in the sub-continental lithospheric mantle. Subsequently I will show the new application of the U-Th/He system for dating diamonds and focus on the He isotopic composition over time in the sub-continental lithospheric mantle.