Geochemical and Isotope Characterisation of Thermo-Mineral Springs of Corsica Island: From Geological Complexity to Groundwater Singularity

Understanding hydrogeological processes at the origin of thermal and mineral groundwater are necessary to ensure their sustainable management. However, many processes are involved in their genesis and often only one or two processes are investigated at the same time. Here, we propose to use an innovative combination of geochemical, isotopic (34S, 14C, 18O, 2H) and geothermometry tools to identify, for the first time in a multi-composite geological context, all processes at the origin of diversified thermo-mineral waters. 19 springs covering a wide range of temperature and chemical composition emerging on a restricted area of Corsica Island (France) were selected. Geochemical results highlight five geochemical provinces, suggesting a common origin for some of them. Geothermometry tools show the unexpected involvement of a common deep groundwater reservoir within this non-active zone. Water stable isotopes highlight a contrasted altitude in recharge areas supplying lowland springs. This suggests that different flow patterns have to be involved to explain the wide geochemical diversity observed and to allow the design of a very first conceptual groundwater-flow model. This paper demonstrates the efficiency of the combination of the selected tools as tracers of water–rock interaction, independently of flow depth, intrinsic water properties, geological conditions and interaction time disparities.

Inherited geochemical diversity of 3.4 Ga organic films from the Buck Reef Chert, South Africa

Archean rocks contain crucial information about the earliest life forms on Earth, but documenting these early stages of biological evolution remains challenging. The main issue lies in the geochemical transformations experienced by Archean organic matter through its multi-billion-year geological history. Here we present spatially resolved chemical investigations conducted on 3.4 Ga organic films from the Buck Reef Chert, South Africa which indicate that they possess significantly different chemical compositions. Since these organic films all underwent the same post-depositional geological history, this geochemical diversity is most likely inherited, reflecting original chemical differences which were not completely obliterated by subsequent burial-induced degradation processes. These results demonstrate that early Archean organic films carry chemical information directly related to their original molecular compositions. This paves the way for the reconstruction of the initial chemical nature of organic microfossils found in ancient rocks, provided that the geologically-induced chemical transformations they underwent are properly constrained.

Experimental Access to Volcanic Processes

<p>Volcanism, and its underlying magmatic origins, are key elements of the Earth System. Their central role can be summed up in the convention that a planet without volcanism is classified as dead. The scientific investigation of the origins, nature and impact of volcanic eruptions is currently one of the most vibrant areas of the solid earth sciences. Observation and quantification of volcanism is greatly assisted by its very nature which includes solid earth processes at the planetary surface and whose dynamics occur on observable timescales. Thus time and location work in our favour. Working against us however is the generally highly energetic, often highly violent, explosive nature of volcanism which frequently precludes deep access to eruptive processes during their operation. Here, the investigation of eruptive processes, together with their causes and consequences, has been greatly assisted by experimental approaches.</p><p>Highlights of the experimental investigation of volcanism have included the following:</p><p>1) The geochemical diversity of magma, together with its highly variable phase state, yield a very wide range of magmatic properties which form the basis for much of the variety of volcanic expression.</p><p>2) The eruptive products of volcanism present a wide range of types of information on the nature of volcano dynamics that can be calibrated with experimental methods.</p><p>3) The fate and influence of volcanic materials in the Earth System, whose investigation is often accessible via highly novel experiments,  provide a rich palette of impacts that have likely made the presence of volcanism on Earth a defining element in the atmosphere, hydrosphere, biosphere and elsewhere.</p><p>Experimental volcanology has a rich future...  </p>