1. Whether the mineral inclusions grew at the same time as the diamond (syngenetic), as most often assumed, or whether the diamonds enclosed pre-existing mineral grains (protogenetic) (KEY ISSUE 1 of INDIMEDEA).
If the inclusions are syngenetic, they provide a direct and clean sample of the Earth at the time and depth of formation of the diamond. If the inclusions are syngenetic, then one can use their geochemical and isotopic compositions to determine the geochemical and physical environment and timing of the diamond forming processes. Indeed, what we
"know" about diamond genesis and distribution in the Earth's mantle often relies on the assumption that most inclusions are syngenetic.
If most inclusions were found to be protogenetic, several age determinations and thermobarometric evaluations might have to be reconsidered. A protogenetic nature of the inclusions would be consistent with models of diamond formation involving fluxes of C-bearing fluids through pre-existing mantle rocks.
2. What pressure and temperature (and thus depth) were the inclusion minerals trapped in the diamond? (KEY ISSUE 2 of INDIMEDEA).
If the inclusions are syngenetic, their composition could be used to estimate the physical conditions of diamond forming processes. If instead the inclusions are protogenetic, they might record conditions that existed long before the diamond formed and were thus unrelated to diamond formation. Barometric methods based on
the evaluation of residual pressure at the inclusions and thermoelastic properties of minerals do not suffer from this ambiguity; moreover, they allow evaluation of the pressure of entrapment (i.e., the pressure of diamond formation) for inclusions of minerals which are not amenable to conventional
The determination of the temporal growth relationships between inclusions and diamonds and the conditions of their formation are the goals of the INDIMEDEA project. The project will (a) establish definitive criteria to determine whether inclusions are syngenetic or protogenetic with respect to their diamond hosts (KEY ISSUE 1), and (b) determine the pressure of formation of diamond-inclusion pairs with unprecedented accuracy and precision (KEY ISSUE 2). The results will provide invaluable constraints on the mineralogy, geochemistry and geophysics of the interior of our planet.
Project starting date: January 1st 2013
ERC-funding: 1.423.000 €
project is hosted by the Department of Geosciences, University of Padova