The isotopic systems of light noble gases, and in particular those of helium and neon (3He / 4He and 4He / 20Ne), vary by several orders of magnitude between atmospheric, crustal and mantle end-members reservoirs. As such, they are the most effective isotopic tracers for deconvolving mixing of these different reservoirs in magmas and crustal fluids that transport them to superficial environments. They have logically been used for several decades to trace the history and the mixtures of such crustal fluids, whether for (i) aquifer systems, or (ii) natural hydrothermal systems associated with volcanoes, seismogenic zones, and geothermal sites. They have also been used as potential tracers in the case of superficial transfers induced by anthropogenic exploitation of the subsoil, in particular for the pilot CO2 storage studies. These elements possess also the particularity of being conservative during transfers, thanks to the chemical properties of their last saturated electronic layer. Their diffusive or convective transport through the crust is therefore less sensitive to water-rock interactions (precipitation or dissolution processes) which can affect the balance of other geochemical tracers (i.e. major elements and isotopes of H, C, O, S). This potential coupling / decoupling between the signal of the light noble gases and that of the other geochemical tracers represents a very interesting tool for studying and highlighting some of the complex processes related to fluids transfer in the crust. Despite these potentialities, the use of such tracers has been up to now limited to a first-order description of natural systems, because precise isotope measurements can not be carried out on site and need to be performed in the laboratory with mass spectrometers. This particular aspect has represented in the last decades a certain limitation of geochemical measurements (in general) compared to geophysical measurements for fully describing natural systems and their dynamics, especially for the short-term variations when their equilibrium is disturbed by discrete hazards. Until now, the geochemical description of natural systems has generally been based on discrete sampling campaigns, with a more or less regular recurrence. In order to capture potential events on a scale of a few months or days, the accurate monitoring of a system requires significant human resources for sampling, which are often difficult to implement. This is currently changing, with the miniaturization of measurement techniques of elemental and even isotopic compositions (i.e. stable isotopes of C, O, H with infrared spectroscopic measurements), which can now been deployed on site to realize continuous record. Technological innovation is advancing very rapidly, and it is not unrealistic to imagine that all elemental and isotopic systems (including noble gases) will in the future be measured on devices that are compatible with in situ deployment. However, our current knowledge of how these crustal systems operate over short time scales remains highly incomplete and needs to be improved before any future approach of continuous monitoring. This is particularly true for processes that govern the perturbations of these steady state systems during natural (i.e. seismic and volcanic hazards) or anthropogenic (i.e. exploitation of the subsoil) Hazards.
In anticipation of future analytical improvements, approaches based on continuous sampling techniques can be developed to understand the transfer dynamics of crustal fluids with a resolution identical to that of geophysics. This project is based on such a view and proposes (i) to improve a technique of continuous sampling for crustal fluids, and (ii) to set it up in some selected sites to understand the processes that govern fluids transfer at short time scale, especially in the context of natural hazards (earthquakes, volcanic eruptions), as well as potential disturbances that could result from the exploitation of the subsoil by non-conventional methods.
The CRPG rare gas laboratory, has been active for many years in this field of crustal fluid geochemistry, and has recently initiated scientific projects for geochemical observation and monitoring of several of these natural systems in collaboration with the INGV (Palermo, Italy). The main goal is to track and highlight geochemical variations within fluids with a temporal resolution not yet reached, in order to be able to unravel processes acting before, during and after hazards. Because it is not possible to instrument sites with mass spectrometers that are still too voluminous, the approach will be to sample continuously using the SPARTAH autosampler system (Barry et al., 2009). Three of these systems have already been built at CRPG / INGV to be: (i) installed on specific natural areas; and (ii) to serve as laboratory test to improve the sampling, preservation, and extraction technique necessary for extensive measurements. The first experimental results in the laboratory are encouraging and demonstrate that the system can be used for 6-month deployment periods, without altering the continuous chemical message.
The thesis project will focus on the implementation of this approach: (i) from a methodological point of view, and (ii) from a conceptual point of view with validation on natural examples. Main scientific goals rely on understanding the exchange and transfer of fluids in sub-surface systems, at a short time scale. Such information is essential to refine our understanding of the natural processes involved in volcanic and seismogenic zones during main hazards and their potential predictions (i.e. control of fluids mixings and water/rock interactions by strain distribution and accumulation or detection of fresh magma input in magma chambers before potential eruptions). For this the project will be developed in direct collaboration with the team of the INGV in Palermo (Istituto Nazionale di Geofisica e Volcanologia - Universita di Palermo). This project is part of the "Impact project" "DeepSurf" of Lorraine University of Excellence (LUE), with the aim of developing a method capable of being applied to the monitoring of potential disturbances generated during the anthropogenic exploitation of the subsoil, and their transfer to the surface. Such an approach could be implemented in future pilot sites in the Lorraine region.
It will initially be necessary to complete the development of the continuous sampling method with a series of laboratory tests (diffusion and preservation of the geochemical signal, rapid measurement procedures, etc.). Methodological possibilities to cross the noble gas isotopic information with other elemental and isotopic geochemical tracers, which are commonly measured on instrumented pilot sites (as per example in the Apennines with the pilot site of the INGV), will be central. Several sites of interest will be instrumented on the volcanic and seismo-tectonic zones of Italy, Réunion Island and Iceland. These very active regions have the dual interest of (i) representing areas where improving the monitoring and forecasting of hazards is very important, and also of (ii) representing areas were potential significant geochemical changes are anticipated during hazards. This will represent an ideal configuration for testing the approach both methodologically and conceptually.
Skills of potential candidates:
Potential candidates for this PhD project must possess strong basis in geochemistry, and preferentially noble gas geochemistry. Candidates will have to develop and improves analytical apparatus either on site or in the laboratory, and will have to perform substantial amount of isotopic measurements on noble gas mass spectrometers. An affinity with such analytical activities is therefore fundamental in the candidate skills and motivations.
This project will be financed by Lorraine Université d'Excellence (LUE) for 3 years, with starting date on 1st October 2019.
This project is part of Deep-Surf (Impact project of LUE: http://lue.univ-lorraine.fr/fr/impact-deepsurf), and will be conducted on CRPG-Nancy (http://www.crpg.cnrs-nancy.fr/index.php) and INVG-Palermo (https://www.pa.ingv.it/) noble gas laboratories, in collaboration with GeoRessources for the Lorraine site instrumentation.
Advisors of the PhD candidate will be Raphaël Pik (DR-CNRS at CRPG-Nancy) and Antonio Caracausi (CR at INGV-Palermo).
Collaborations: Bernard Marty (CRPG, Pr. Univ. Lorraine) and Laurent Zimmermann (CRPG, IE - CNRS), Andrea di Muro (IPGP, Observatoire de la Réunuion), Alasdair Skelton (Pr. Stockholm Univ.), Jacques Pironon (Dr. CNRS, GeoRessources).
Raphaël Pik: email@example.comContinue reading
|Title||Continuous isotopic tracing of crustal fluids transfer to the surface, in the specific context of natural (seismic / volcanic) or anthropogenic hazards|
|Employer||Lorraine Université d'Excellence (LUE)|
|Job location||34 Cours Léopold, 54000 Nancy|
|Published||May 13, 2019|
|Job types||PhD  |
|Fields||Analytical Chemistry,   Geochemistry,   Volcanology,   Seismology  |