Calcium and strontium isotopic fractionation at high temperature: Applications on the formation of the Earth and its evolution
IPGP - Îlot Cuvier
Soutenances de thèses
Cosmochimlie, Astrophysique et Géophysique expérimentale (CAGE)
The formation of the Solar System and its evolution remain poorly known despite the explosion of space exploration in the mid 20th century. Meteorites and terrestrial igneous rocks are particularly useful objects of study for gaining insights into the formation and evolution of the Earth: the former existed before the planets and the latter reflect the composition of the terrestrial mantle. For this thesis, we performed Ca, Sr and Rb isotopic analyses using MC-ICP-MS technique on a variety of terrestrial and extra-terrestrial rocks. The fractionation of Ca and Sr stable isotopes allows for tracing processes and source effects and Rb-Sr system enables us to date primordial events. Chondrules, a major component of chondrites, are analysed for Ca isotopic composition to test and confirm the pebble accretion model for the formation of the Earth. The timing of the heating event of thermally metamorphosed carbonaceous chondrites is estimated using Rb-Sr chronology and reveals the process of the event as impacts in the asteroid belt. From Earth, komatiites, OIBs and MORBs samples are analysed to estimate the Ca and Sr isotopic composition and evolution of the mantle. The stable isotopic composition of Sr in the mantle is homogenous through the evolution of the mantle while Ca isotopes reveal preservation of early heterogeneities. Carbonatites, rare igneous rocks containing 50 % of carbonate minerals, are studied for Ca isotopic composition in order to indicate their origin. We suggest that the enrichment in lighter Ca isotopes of the carbonatites compared to the bulk silicate Earth’s value derives from a contribution of recycled components through subduction in their mantle source. This thesis explores the wide applications of Ca and Sr isotopic fractionation in high temperature geochemistry.