Cosmochemistry and Planetology

The goal of this theme for the next four years is to strengthen and continue the research carried out recently at CRPG in the field of cosmochemistry, broadly defined. To do this we will take advantage of new developments in analytical techniques: the ims 1270 ion microprobe, magnetic-sector ICP MS, and gas-source mass spectrometry coupled to micro-sample extraction lines. These developments will be applied to four main research projects:

• characterisation and dating of metal-silicate differentiation in meteorites (isotopic fractionation of Ge in iron meteorites and chondrites, extinct radioactivity of Tc: chronology of metal-silicate differentiation)
• study of different components implanted in lunar soils (isotopes of Li in lunar soils: record of solar activity, isotopes of N in lunar soils: record of cometary and meteoritic contributions to the moon and the Earth)
• experimental study of the chemical and isotopic dynamics of the protosolar nebula
• preparation for the study of martian and other extra-terrestrial samples of comets and planetesimals (evolution of the martian atmosphere, geologic history of martian oceans, surface alteration processes: geochemistry of Ge, martian chronology: ages of the minerals of martian soils)

In several of these projects the characterisation of natural objects will be combined with experimental simulations at high temperatures under controlled chemical and isotopic conditions of the solid and gas phases.

Analysis of a chondrite

Stromboli in eruption

Kinetics and mass balance of magmatic processes

This theme aims to quantify the role of magmatic processes in the evolution of the Earth and the planets. We combine a mass balance approach, essential in order to identify and quantify heat and mass transfers in magmatic systems, and a kinetic approach that is equally fundamental in that it takes time into account as a parameter. We concentrate on three principal fields of investigation:

• dynamics of magma chambers (evolution of the liquids and textures of minerals in basaltic chambers, structures and textures of solidification associated with the emplacement of plutons, mineralisation associated with magmatism)
• fractionation processes in meteorites (chemical diversity of achondrites and differentiation in a magmatic ocean , kinetics and chemical consequences of the metal-silicate differentiation following planetary accretion)
• crust-mantle-surface interactions (mantle melting and petrogenesis of MORBs, genesis of the lower crust, transfers associated with subduction)

These three subjects are linked by the common denominators of measuring elemental partion and diffusion coefficients, elucidating the mechanisms of crystal nucleation, growth, dissolution and the resulting (micro)textures, and coupling the petrographic and geochemical study of natural samples.

Space-time modelling of the lithosphere

We are interested in studying lithospheric processes in terms of (a) heat and mass transfer (solids and fluids) and (b) kinetic and kinematic coupling, by means of a specific approach integrating petrology, geochronology, the study of fluids, tectonics and geomathematics. Through this unusual combination of disciplines, exceptional for a research center, we focus on three main research priorities:

• the development, using the gOcad software, of 3-D modelling of geological objets
• the thermal, kinematic and geochronological modelling of orogens
• metallogeny and gems

This multidisciplinary approach is rooted in observation in the field, and associates field methods with laboratory methods such as geochronology, geometric modelling using gOcad, physical modelling and thermal modelling. These approaches facilitate the transfer of expertise among all the research groups of CRPG, especially for the geochronological and geochemical aspects of rocks and fluids.

Modelling with GOCAD

Grain of pollen

Environments and paleo-environments

Our objectives are to understand and quantify the processes that influence the past and present environment of the Earth, in particular the effects of certain anthropic activities. We seek to decipher, using chemical and isotopic tracers, information concerning environmental conditions provided by ancient rocks, microfossils and paleofluids, present-day hydrological systems, natural filters of atmospheric particles, and man-made materials.

• Hydro-geological tracers in the vicinity of the Bure subterranean laboratory (ANDRA)
• Watersheds and hydrological mass balance: Zone Atelier Moselle
• Stabilisation and dispersion of pollutant wastes
• Climatic- tectonic coupling using the example of Himalayan erosion
• Biomarkers and paleo-climates
• Tracer-based study of the sources of aerosols and atmospheric circulation
• Archean oceans and atmospheres: the record of cherts

These research projects lead us to develop new chemical and isotopic tracers specifically for (paleo)environmental conditions, for the dynamics of erosion, for physico-chemical alteration processes, and for the identification of sources in the transport process, notably in the case of pollution.