Soutenance HDR - Erwan Martin

A 14h00 dans l'amphithéâtre Durand

Le magmatisme: de sa genèse à ses interactions avec les enveloppes externes de la terre

Based on geochemical approaches, my research aims to broaden the knowledge on magmatism from its sources to its interactions with the hydrosphere and atmosphere. In association with other petro-geochemicalapproaches, stable isotopes of light elements such as oxygen, sulfur and hydrogen, which are sensitive to fluidrockinteractions, are my main exploration tools. The three main research topics I aminterested in are:

1- Magma genesis: I focused on silicic magmatism in Iceland in order to explain their unusual abundance on such an oceanic plateau. I demonstrated that partial melting of the Icelandic basaltic crust is responsible for their high production, and I discussed the implications on the geodynamic evolution of Iceland as well as tackling whetherIceland could be an analogue to the formation of the earliest continental crust on Earth. I also proposed an oxygen isotope model of subduction zones, in which subduction fluids play the key role and can explain the variability of arc lava compositions

2- Origin of water in volcanic glass: It appears from my studies that the content, speciation and isotopic composition of water in volcanic glass can reveal its origin. If the study of water in volcanic glass can be a way to understand volcanic dynamics controlled by magma degassing during its ascent, volcanic glass secondary hydration seems to play a more prevalent role than previously expected. In the future, I will focus my research on trying to better understand the conditions of such a secondary hydration, as it can occur in the volcanic plume or in the volcanic deposits at high or low temperatures, with magmatic or meteoric water. This is primordial as the water composition in volcanic glass can thus, depending on its origin, be interpreted in terms of magma degassing processes or paleoclimatic reconstitutions.

3- “Volcanism-atmosphere” interactions: My research that lies in between volcanology and atmospheric chemistry seeks to demonstrate that oxygen and sulfur multi-isotope compositions of volcanic sulfate aerosols help to track the oxidation pathways of volcanic sulfur gases back into the atmosphere. These oxidation channels are dependent on atmospheric but also on volcanic conditions. In the coming years, I will focus this research on studying old volcanic deposits and black crusts on building walls in order to study the volcanic and anthropic sulfur oxidation pathways in the past atmosphere. This could reveal the evolution of the oxidation capacity of the atmosphere in the past, which is a key to understanding atmosphere chemistry and therefore climate evolution.