Petrogenetic processes of île de la Possession lavas (Crozet archipelago) and implications for lithological heterogeneities in hotspots sources

• Main Author: Segard, Mélanie
• Other Authors: Laboratoire de Planétologie et Géodynamique UMR 6112 (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Nantes, Eric HUMLER([e-mail]), IPEV, IUEM, IDES
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2013
• Subjects: hotspot; mantle heterogeneity; primary melt; geochemistry; petrology; fractional crystallization; partial melting; point chaud; Crozet; hétéogénéité mantellique; magma primaire; géochimie; pétrologie; cristallisation fractionnée; fusion partielle; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; Possession Island
• Online Access: https://tel.archives-ouvertes.fr/tel-01058681; https://tel.archives-ouvertes.fr/tel-01058681/document; https://tel.archives-ouvertes.fr/tel-01058681/file/TheseSEGARD_vf.pdf

We present a new and comprehensive data set of major and trace elements and Sr-Nd-Pb isotopes for Crozet hotspot lavas (Possession island). Major element variations and petrological characteristics define an alkali silica-saturated magmatic suite. I estimate two extreme compositions of primary melts on the basis of selected fractionation-corrected lava compositions unaffected by accumulation and magma mixing processes. The first estimation display a major element composition approaching those of experimental partial melts of a garnet-lherzolite, whereas the second is characterized by a composition resembling to experimental partial melts of a carbonated eclogite. These contrasted results reveal that the fractionation correction is a critical step to interpret major element contents in terms of lithological source heterogeneities in oceanic island lavas. The REE systematic appears to be less sensitive to uncertainties in fractionation corrections compared to major elements. The REE inversion of estimated primary melts reveals in both cases a peridotitic source enriched in incompatible elements relative to chondrites (LaN/SmN=3). The Sr-Nd-Pb isotopic compositions do not display any correlation with major elements nor REE contents or ratios and reveal a homogeneous source with moderate time-integrated enrichment relative to the chondritic reservoir ( Nd=+4,3). The Pb isotope systematic indicates the presence of 2 mantle components in the Crozet mantle source, one relatively unradiogenic compatible with an EM-1 or DUPAL signature, and the other one relatively radiogenic. The mixing of both components gives rise to an isotopic signature akin to EM-2 type. Cette étude présente le premier jeu de données complet en éléments majeurs, traces et en isotopes Sr-Nd-Pb sur les laves du point chaud de Crozet (île de la Possession). La pétrologie et les variations en éléments majeurs de ces laves révèlent une suite magmatique alcaline saturée en silice. Les compositions chimiques des magmas primaires sont estimées à partir ...