WP 1- Fluids in shear zones, magmas, hydrothermal systems, and sedimentary basins

We aim at performing experiments on (i) the role and behavior of volatiles during the deformation of rocks and magmas and in particular the rheology of multiphase systems undergoing phase transformations; (ii) the behaviour of metals and volatiles during magma cooling and degassing, either intrusive or extrusive; (iii) the fluid transport within porous media and associated reactive feedbacks.

Efforts will concentrate on the chemical characterisation of fluids, including their dating. These activities will be essentially laboratory based, implementing unique experimental and analytical devices, encompassing P-T conditions from the upper mantle to the shallow crust. The laboratory data will serve to feed numerical simulations aimed at predicting the long term evolution of systems. They are tightly connected with the production of a variety of ressources, risk management and geohazards and environmental issues.

The priority targets of WP1 are listed below

– 1 The interactions between deformation and deep fluid transfers. The experiments will address how fluid is transported in brittle to plastic crust which bears therefore on the connection of the aquifers through the whole crust; this will shed new light on the elemental transport in deforming rocks, that ultimately leads to the formation of orogenic shear zones and associated ressources. More specifically, deformation experiments will be carried out on crust- and mantle-like lithologies (ie smectite, quartz or olivine bearing) to fully characterise how deforming rocks can store and even pump fluids. We will also explore how deformation intervenes on diffusional processes, in particular on our understanding of Ar-Ar ages on metamorphic rocks, and conversely on the action of deformation to enhance fluid transfers at depth. Following the same objective, Ar and other noble gases may act as tracers of halogen transfers; the use of LA-ICPMS will allow us to obtain the halogen signatures of populations of fluid inclusions and to investigate the source of the fluid and the extent of their circulation.

       2 The building and functioning of magma reservoirs, including their degassing,and their role on ressources will be studied via: (i) the acquisition of constraints on metal transport in fluids escaping magmas via the systematic determination of fluid/silicate melt metal partitioning under relevant P-T-redox conditions of reference objects (Li, rare metals related to granites). Emphasis will be placed on the role of so-called minor volatiles (sulphur, halogens) which are instrumental in ore deposition processes. Experimental devices allowing in-situ analyses (PLANEX platform) will be privileged: (ii) the simulation of degassing, using the novel experimental devices developed within PLANEX, which allow first and second boiling of magmas to be studied in-situ, providing unique constraints on fluid compositions released either towards the encasing rocks or to the atmosphere; (iii) the systematic dating of geological reference objects (plutons, volcanic systems) using the Ar and LA-ICPMS platforms (minerals dating to define crystallisation and cooling ages). These data will be integrated into 3D numerical models taking into account P-T-fluid conditions as defined by experimental petrology. The aim here is to simulate long term magma cooling and associated fluid transfer and ore concentration. We will also investigate the physical properties of rocks and magmas at HP, to provide improved constraints on the thermal evolution of cooling magma bodies. Issues at stake are metal deposits and geothermal activity, precursor signals of eruptions, and the climate impact of volcanic degassing (in tandem with WP3)

3 Simulation of reactive transfer of fluid through solid media at various spatial scales (pore to m, large PTX range from capillary pressures to sub and super-critical fluids) will be a key assist to the development of integrated (coupled hydro-chemo-mechanical) numerical models of fluid transport in the deep to shallow crust (ie hot to cold environments). Emphasis will be on establishing the link between the petrophysical structures and fractured rocks and the properties of hosted, compositionally complex, solutions exibiting phase changes. Priority targets will be the functioning of hydrothermal systems, such as the study of H2 production in seafloor, or the behaviour of Li in geothermal fluids. Beyond those precise targets, the group aims at developing new concepts about the coupling between transport properties, water-rock reactivity, poromechanical balance integrating the role of the multiphase interfacial processes. The Integrating the thermal flux is also at stake, especially for the consideration of the thermal features of phase transitions (enthalpic component) which is a vital asset for rigorous quantitative predictive modelling. Considering the ability for the group to address biphasic fluids systems, the theoretical developments made will be common to WP2 as well.

Economic Impacts: energy transition and mineral resources
One of the main results obtained from different researches carried out in the VOLTAIRE 1 has been to prove that energy transition will move the anthropic pressure on subsoil resources from the extraction of fossils fuels to that of mineral resources, which are necessary to the production of renewable energy (Solar and Wind). This massive rise in the national and international demand for metals could have potential negative environmental consequences, and be potentially unsustainable. The consensus that arises from this interdisciplinary cooperation is that solutions exist, which combine technical evolution towards more environment friendly technologies, recycling practices and reduction in energy demand. But they need regulatory and economic incentives, which could be implemented by well-designed policies. Another important stake in this field is linked to the economic sustainability of mineral resources exploitation, from the double point of view of their economic impact in developing and emerging countries and their feasibility and acceptability in advanced countries. How to enable the exploitation of these resources to benefit to the local population, without crowding out other economic activities (the “resources curse”) in developing countries? In particular, how the discovery, production and trade of resources impact the aggregate welfare and the macroeconomic stability in these countries? In VOLTAIRE 1, a case-study in Burkina-Faso proved that artisanal mines development had helped to reduce poverty, but this result has to be confirmed on other cases. Another study performed at a macroeconomic level, showed in VoltaireVOLTAIRE 1 that this paradox holds only under specific conditions related to countries resources abundance and dependance. More work has to be done in order to provide more detailed results. Within this framework, a question that emerges is linked to the abilitity of advanced countries to produce at home the most sensible/critical metals in the cleanest way. First results have been obtained on the assessment of the Lithium-hard rock European resources, which will be extended to its economic aspects during VOLTAIRE 2.