1- The tracing of cosmic dust and impact events in sediments
Cosmic dust, composed of sub-millimetric particles, is continuously accreting onto Earth (about 40,000 tons/yr) and is trapped into sediments during their formation. It has been suggested that the variation of the cosmic dust flux falling onto Earth could be related to the climate cycles of Earth. Noble gases, such as helium and neon have distinct isotopic signatures in the extraterrestrial material compared to that at the Earth's surface. Thus, the cosmic dust flux can be studied by analysing noble gases in sediments (see illustrations below). Another ongoing work is to use noble gases to trace meteorite impact events.
2- Volcanic degassing
Volcanic eruptions release large amounts of volatile elements in the state of gases, such as CO2, which can affect the Earth's climate at geological timescales. It is thus important to understand the mechanisms and fluxes of volatile degassing during volcanic eruptions as well as their concentrations in the mantle source. The process of volcanic degassing can be assessed by using the vesicularity (=amount of bubbles) in mid-ocean ridge basalts coupled to geochemical and geophysical characterization of the samples (Chavrit et al. 2012, 2014). It allows to constrain :
- The CO2 deep cycle: degassing fluxes and mantle carbon content
- Degassing systematics and kinetics
3- Volatile recycling at subduction zones
Noble gases compositions of the mantle give constraints on the origin and evolution of the Earth. However, their primitive composition could have been overprinted with time by seawater-derived noble gases subducted into the deep mantle. It is thus important to assess whether they are recycled in the mantle through subduction zone. Halogens (Cl, Br, I) are good tracers of marine environment involvement and can be also used. To determine a mass balance of noble gases and halogens that can be recycled back into the mantle, samples coming in front of and behind the subduction zones can be studied:
- Assimilation of seawater-derived noble gases and halogens in the oceanic crust (Chavrit et al. 2016 GCA)
- Halogens in back-arc basin basalts
- Halogens in exhumed mafic and ultramafic rocks