📰 The Alps, an ideal natural kitchen to study the geochemistry of sulfur

The Gips Nappe is a salt formation from 228 to 216 million years old and present throughout the Alpine chain. Due to its special physico-chemical nature and its rheology, this unit plays an important role in the localization of deformation in the Alps. Despite its importance, the nature and geochemistry of the gypsum napkin have been very little studied. A team of French scientists set out for the first time to unravel the nature of the geological fluids generated during this formation’s history.


The reaction at work in the Gypsum Nappe: anhydrite in White (White is the color of a body heated to about 5000°C (see…) responded with methane (Methane is a hydrocarbon with the chemical formula CH4. It is the simplest compound of the…) formshydrogen (Hydrogen is a chemical element with symbol H and atomic number 1.) sulfur (H2S), carbonates from CO2 (grey) and sulfur (Sulphur is a chemical element of the chalcogen family, symbol S and…) native (yellow).
© Geosources

Thanks to the analysis of the minerals that accompany them, this team was able to show that salts were buried up to 60 km deep between 55 and 40 million years ago, between 55 and 40 million years ago. subduction (Subduction is the process by which one tectonic plate lies beneath another plate of…) continental part of the European plate. Thus, the formation was heated to 430°C and underwent Busy (Pressure is a fundamental physical concept. You can think of it as a reported force…) more than 16,000 times the air pressure (Atmospheric pressure is the air pressure at any point in an atmosphere.)† This exceptional situation made it possible to: walk (Walking (the pleonasm walking is also often used) is a…) a chemistry (Chemistry is a natural science subdivided into different specialties, to…) sulfur all (The whole understood as the whole of what exists is often interpreted as the world or…) quite special. the cast (Gypsum is a mineral composed of hydrated calcium sulfate from…) (sulfate of calcium (Calcium is a chemical element, symbol Ca and atomic number 20.) hydrated) that make up the gypsum nappe is dehydrated to anhydrite, releasing large amountswater (Water is a ubiquitous chemical compound on Earth, essential for everyone…)† In the presence of methane, these pressure-temperature conditions have: is on his way (An activated (or snap roll) is an aerobatic figure.) the Sulphate Thermo-Reduction reaction (TSR) which converts part of the sulfates into hydrogen sulfide.

Scientists were able to determine the conditions of this reaction by observing liquid inclusions. For example, for the first time in nature, they demonstrated the presence of new sulfur species such as:ion (An ion is an electrically charged chemical species. The term comes from English,…) S3 or polysulfides. Although these species had previously only been observed in the laboratory, this research has allowed to validate their importance in the natural sulfur cycle.

Scientists also wanted to know how to monitor this process and these specific sulfur species in other geological contexts. To do this, they analyzed the sulfur isotopes of the minerals formed using TSR (particularly pyrite and elemental sulfur). This way they could show that every kind (In the life sciences, the species (from the Latin species, “type”…) had a certain isotopic signature that allows to accurately trace the origin of the sulfur and the fate of the various products of the reaction. This study to big scale (The big ladder, also called air ladder or car ladder, is a…) has thus made it possible to better understand the role in the sulfur cycle of this important process, the TSR, as it makes it possible to explain the formation of metallic deposits or highly sulfur-rich oil deposits around the world.

Affected laboratories:

GeoRessources Laboratory (Nancy) in collaboration with seeker (A researcher (fem. researcher) refers to a person whose job it is to do research…).es of theInstitute (An institution is a permanent organization established for a particular purpose. It is…) science of Soil (Earth is the third planet in the solar system in order of distance…) (ISTerre/Grenoble), the Institute for physical (Physics (from the Greek φυσις, nature) is etymologically the…) of the globe Paris (Paris is a French city, capital of France and capital of the region…) (IPGP) and the Geosciences Le Mans laboratory.

References:

BARRÉ G., TRUCHE L., BAZARKINA EF, MICHELS R., DUBUSSY J. (2017) First evidence of the trisulfur radical ion S3 and other sulfur polymers in naturally (Natural is a semi-compiled programming language, published by the company…) liquid inclusions. Chemical Geology, 462, 1-14.

BARRÉ G., STRZERZYNSKI P., MICHELS R., GUILLOT S., CARTIGNY P., THOMASSOT E., LORGEOUX C., ASSAYAG N. TRUCHE L. (2020). Tectono-metamorphic evolution of an evaporative detachment as captured by mineral and liquid geochemistry: the “Nappe des Gypses” (Western Alps) case study. Lithograph 358-359,

BARRÉ G., THOMASSOT E., MICHELS R., CARTIGNY P., STRZERZYNSKI P., TRUCHE L. (2021). Multiple Sulfur Isotope Signature of Thermochemical Sulfate Reduction (TSR): Insights from Alpine Triassic Evaporites. EPSL 576, 117231.

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