INDIMEDEA Project Overview

INDIMEDEA is an ERC Starting Grant funded for 5 years to determine the depths and growth mechanisms of diamond formation by characterising the mineral inclusions in diamonds.


Inclusions of other minerals within diamonds are the only direct and unaltered samples that we have of the Earth’s mantle below the crust. Because the inclusions are encapsulated and protected by the chemically inert diamond, the characterization of diamond inclusions not only gives us a real and unique picture of “what is there” and “what happens” at depths from 150 to about 700 km but also provides a signature of this deep region practically uncorrupted over the extremely wide range of geological time over which diamonds have been formed.

Using the chemistry and mineralogy of the inclusions to deduce the detailed chemistry and mineralogy of the Earth at a given depth therefore clearly depends on two key issues:

 

 

Diamond with a single crystal inclusion of olivine
Uncut diamond from Udachnaya (Russia) with a single
crystal inclusion of olivine (photo by Matteo Chinellato)


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 geothermobarometry.

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

Duration: 60 months

Total ERC-funding: 1.423.000 €

The project is hosted by the Department of Geosciences, University of Padova (Italy).