Periodic Reporting for period 1 - HAMA (New insights on Earth’s formation and differentiation processes from in situ analyses of halogens (F, Cl, Br and I) in meteorites and mantle samples)
Período documentado: 2019-09-01 hasta 2022-08-31
The transport of volatiles, in particular sulfur and halogens (F, Cl, Br and I), from surface reservoirs to the inner Earth and back in volcanic emissions is suggested by geochemical studies of magmas and volatile measurements on volcanoes. Furthermore, the widespread presence of sulfur-rich liquid phases has been proposed in the inner Earth by geophysical methods. However, the physicochemical properties of these liquids are poorly understood. In particular, the coupling between volatiles and metals, which controls geochemical transport processes from the inner Earth to the surface through porous and focused liquid migration, and then volcanic processes is not well known.
Understanding the behaviour of halogens and sulfur through magmatic processes is key for our society since volcanic emissions of these elements can locally or globally trigger environmental issues. This can happen, for instance, through climatic cooling by sulfur-bearing aerosols or metal pollution of agricultural areas, since these chemical compounds are produced during explosive volcanic eruptions triggered by magma degassing processes.
However, highly precious metals also occur among those which can be concentrated by halogens and sulfur in magmas. These chemical elements include ‘base’ metals (e.g. Cu) and ‘noble’ metals, the latter of which encompass Au, Re and platinum group elements (PGE’s) (Os, Ir, Ru, Rh, Pt, Pd). PGE’s are extremely rare in the earth's crust (<10-9 g.g-1 on average) and their use covers a wide field of applications in medicine, electronics and chemistry. These elements also play a key role in sustainable development, whether it involves reducing emissions of atmospheric pollutants or producing and managing clean and/or renewable energy. Due to the ever-increasing demands of our society, PGE’s are notably classified as critical and strategic resources by the European Union.
The overall objectives of the project HAMA were to investigate the behaviours of halogens and sulfur, together with precious metals, in natural samples from intra-oceanic subduction zones. For this to be achieved, several analytical and methodological developments needed to be undertaken. In parallel, a geochemical model (e.g. involving solubility and mineral/liquid partitioning properties) needed to be developed. The aim of this model is to simulate and predict the couplings between volatile compounds and metals in the mantle and the crust of the Earth.
Combining data from natural samples with the results of numerical simulations during the project HAMA aimed at providing new insights into two fundamental processes involved in the coupled mobilizations of volatiles and precious metals in the inner Earth: (i) partial melting in the deep Earth’s mantle to produce magmas; and (ii), physicochemical evolution of magmas during their emplacement in the upper part of the Earth’s mantle and in the Earth’s crust.
Understanding the behaviour of halogens and sulfur through magmatic processes is key for our society since volcanic emissions of these elements can locally or globally trigger environmental issues. This can happen, for instance, through climatic cooling by sulfur-bearing aerosols or metal pollution of agricultural areas, since these chemical compounds are produced during explosive volcanic eruptions triggered by magma degassing processes.
However, highly precious metals also occur among those which can be concentrated by halogens and sulfur in magmas. These chemical elements include ‘base’ metals (e.g. Cu) and ‘noble’ metals, the latter of which encompass Au, Re and platinum group elements (PGE’s) (Os, Ir, Ru, Rh, Pt, Pd). PGE’s are extremely rare in the earth's crust (<10-9 g.g-1 on average) and their use covers a wide field of applications in medicine, electronics and chemistry. These elements also play a key role in sustainable development, whether it involves reducing emissions of atmospheric pollutants or producing and managing clean and/or renewable energy. Due to the ever-increasing demands of our society, PGE’s are notably classified as critical and strategic resources by the European Union.
The overall objectives of the project HAMA were to investigate the behaviours of halogens and sulfur, together with precious metals, in natural samples from intra-oceanic subduction zones. For this to be achieved, several analytical and methodological developments needed to be undertaken. In parallel, a geochemical model (e.g. involving solubility and mineral/liquid partitioning properties) needed to be developed. The aim of this model is to simulate and predict the couplings between volatile compounds and metals in the mantle and the crust of the Earth.
Combining data from natural samples with the results of numerical simulations during the project HAMA aimed at providing new insights into two fundamental processes involved in the coupled mobilizations of volatiles and precious metals in the inner Earth: (i) partial melting in the deep Earth’s mantle to produce magmas; and (ii), physicochemical evolution of magmas during their emplacement in the upper part of the Earth’s mantle and in the Earth’s crust.
The main work performed during the project HAMA involved new analytical and methodological developments for the geochemical analyses of halogens and PGE’s.
This notably included the characterization of new mineral standards for halogen analysis by various techniques (e.g. electron probe microanalysis, laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectrometry).
Further analytical work notably included the acquisition of a large dataset for the abundances of noble metals in a variety of geological matrices, acquired using different sample pre-treatment procedures (e.g. wet chemistry versus NiS fire assay) and analytical conditions (e.g. isotopic dilution using either sector field or quadrupole mass spectrometers). These results for whole rocks were systematically supplemented with in situ data using electron microscopy and microanalysis, together with micro-spectroscopy. Both rocks representing erupted magmas and the residues of their formation in the Earth’s mantle were investigated using these various techniques.
A comprehensive numerical model was developed and applied to the generation of magmas and residues in the Earth’s mantle during the HAMA project.
The overall frame included thermodynamic predictions of phase equilibrium, corrections applied through experimental melting reactions, and parameterizations of the individual geochemical behaviours of some minor and trace elements.
Within this overall frame, a sub-type of the numerical model was then adapted to the specific case of coupling the geochemical behaviours of volatiles and PGE's. New thermodynamic parameterizations of chemical reactions involving PGE’s in sulfide and silicate liquids were notably involved in these kinds of calculations.
Results of the HAMA project were either presented at scientific meetings or published in the peer-reviewed, scientific literature. This notably included three talks in international conferences, as well as five articles published, two articles currently under review, and several other manuscripts in preparation.
This notably included the characterization of new mineral standards for halogen analysis by various techniques (e.g. electron probe microanalysis, laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectrometry).
Further analytical work notably included the acquisition of a large dataset for the abundances of noble metals in a variety of geological matrices, acquired using different sample pre-treatment procedures (e.g. wet chemistry versus NiS fire assay) and analytical conditions (e.g. isotopic dilution using either sector field or quadrupole mass spectrometers). These results for whole rocks were systematically supplemented with in situ data using electron microscopy and microanalysis, together with micro-spectroscopy. Both rocks representing erupted magmas and the residues of their formation in the Earth’s mantle were investigated using these various techniques.
A comprehensive numerical model was developed and applied to the generation of magmas and residues in the Earth’s mantle during the HAMA project.
The overall frame included thermodynamic predictions of phase equilibrium, corrections applied through experimental melting reactions, and parameterizations of the individual geochemical behaviours of some minor and trace elements.
Within this overall frame, a sub-type of the numerical model was then adapted to the specific case of coupling the geochemical behaviours of volatiles and PGE's. New thermodynamic parameterizations of chemical reactions involving PGE’s in sulfide and silicate liquids were notably involved in these kinds of calculations.
Results of the HAMA project were either presented at scientific meetings or published in the peer-reviewed, scientific literature. This notably included three talks in international conferences, as well as five articles published, two articles currently under review, and several other manuscripts in preparation.
A first major output of the project HAMA included quantifying the relative effects of key physicochemical parameters involved in the mobilization of sulfur and PGE’s during magma generation in the Earth’s mantle (e.g. temperature and oxidation state). Notably, data acquired during the project allowed supporting a model of magma generation at intra-oceanic subduction zones under oxidized conditions, owing to the presence of sulfur-bearing compounds recycled from the subducted plate. This conclusion was reached, for the first time, using a combination of high-precision analyses of noble metals in samples from the Earth’s mantle and calculations using the numerical model developed during the project.
These results have far-reaching implications, notably for the deep recycling of surface-derived sulfur at subduction zones, and the global evolution of the ‘redox budget’ within portions of the Earth’s mantle and the Earth’s crust. The first point has notably been the subject of controversy in the recent scientific literature. These results further provided new evidence for the primary physicochemical state of magmatic sulfur, which is ultimately outgassed to the atmosphere through volcanic emissions at intra-oceanic subduction zones.
A second major output of the project HAMA included novel insights into the effects of the evolution of magmas during their final emplacement on the coupled behaviours of volatiles and PGE's, in particular enrichment processes of the latter. The physicochemical evolution of halogens, sulfur and PGE's was determined in detail in several types of magmas emplaced at the (sub-)surface. Some of the major conclusions in relation to this part of the project included determining the relative effects of magma cooling, redox exchange, and hydrothermal fluid formation on the concentration of PGE's in magmatic products. Some of the fundamental properties of volatiles, such as how they are distributed between different phases during magma evolution, were also derived.
Future perspectives include gaining new insights into how PGE's behave when magmas are stored in intermediate reservoirs in the crust. As such, the results acquired during the project HAMA will provide novel constraints on the origins of PGE's in exploitable abundances in magmatic systems. This work will also help to understand the behaviour of PGE's under more various conditions, experienced during their life cycle in the context of the circular economy.
These results have far-reaching implications, notably for the deep recycling of surface-derived sulfur at subduction zones, and the global evolution of the ‘redox budget’ within portions of the Earth’s mantle and the Earth’s crust. The first point has notably been the subject of controversy in the recent scientific literature. These results further provided new evidence for the primary physicochemical state of magmatic sulfur, which is ultimately outgassed to the atmosphere through volcanic emissions at intra-oceanic subduction zones.
A second major output of the project HAMA included novel insights into the effects of the evolution of magmas during their final emplacement on the coupled behaviours of volatiles and PGE's, in particular enrichment processes of the latter. The physicochemical evolution of halogens, sulfur and PGE's was determined in detail in several types of magmas emplaced at the (sub-)surface. Some of the major conclusions in relation to this part of the project included determining the relative effects of magma cooling, redox exchange, and hydrothermal fluid formation on the concentration of PGE's in magmatic products. Some of the fundamental properties of volatiles, such as how they are distributed between different phases during magma evolution, were also derived.
Future perspectives include gaining new insights into how PGE's behave when magmas are stored in intermediate reservoirs in the crust. As such, the results acquired during the project HAMA will provide novel constraints on the origins of PGE's in exploitable abundances in magmatic systems. This work will also help to understand the behaviour of PGE's under more various conditions, experienced during their life cycle in the context of the circular economy.