Diamond and Associated Fluids in Subduction Zones

When a continent collides with another continent or an island arc, continental crust may be deeply subducted and exposed to extreme pressures. This process leads to the formation of ultra-high pressure (UHP) rocks such as eclogite.

However, eclogites constitute only a small portion within a volume of educted continental crust that is typically composed of gneisses devoid of UHP assemblages.

These observations led to the concept of a shallow, post-subduction juxtaposition of eclogites and host gneisses or that UHP metamorphism results from localized overpressure.

The basis for these models has been called in question by recent discoveries of UHP mineral indicators such as diamond and coesite, which have been made mainly in the gneisses.

Here it is proposed to investigate gneisses in UHP terranes in the Scandinavian Caledonides and Alps and search for various UHP indicators.

We will provide an isotopic characterization of diamonds and a structure of C-based phases inside fluids to find a C source in these UHP rocks. The methods for quartz and coesite include elastic barometry, trace element thermometry, and geospeedometry. These will allow evaluation of the depth reached by the gneisses and the exhumation rate back to mid-crustal levels.

Diamond Anvil Cell experiments will be carried out to simulate diamond growth.

The project will provide significant input into the ongoing global debate about the deep burial of continental crust in the collisional regime and deep Carbon cycle.