Postdoctoral position in igneous petrology at CRPG-CNRS

A 2-year postdoctoral scholar position is available at the University de Lorraine (Nancy, France) in igneous petrology to study the kinetics of oceanic crust formation and evolution (starting date: ~September 2025). This postdoctoral position will be hosted in Dr Lydéric France group at CRPG in the frame of the collaborative MUSH-OCEAN ANR project. Applicants should submit by May 21st 2025, a cover letter, a CV, and (optional) up to 3 letters of recommendation (to: lyderic.france@univ-lorraine.fr ).Almost 2/3 of Earth’s surface is covered by oceanic crust formed at mid-ocean ridges where >70% of the total magma flux is concentrated. In the last decades it has been shown that the magmatic system, which has long been seen as a melt-dominated system, is rather mushy: magmatic but with a high crystal fraction. This modifies the expected thermal regime, the modes of melt migration, and the igneous processes that give rise to the crust by differentiation and magma emplacement. Despite tremendous progress made over the last decades by a multidisciplinary marine geoscience community, our understanding of the oceanic magma plumbing architecture and of the related igneous processes at both fast- and slow-spreading ridges still needs to be refined and quantified. More specifically, the modes of differentiation that have been considered during decades to be governed by fractional crystallization (operating in crystal-poor mediums) are now revisited, and a yet poorly constrained reactive porous flow process is now widely proposed. The objective of MUSH-OCEAN is to make a breakthrough in our understanding of oceanic magmatic systems. With MUSH-OCEAN we will provide brand new constraints on 1/ the temporal (e.g., lifespan), spatial, and thermal relations between magma (s.s.) bodies (with 40 % crystals, thus not mobilizable), 2/ the kinematics of melt collection and migration in mushy reservoirs, and 3/ the igneous processes that govern mush evolution, and thus the overall differentiation of oceanic igneous reservoirs (reactive porous flow).In the context of MUSH-OCEAN, this postdoctoral project will focus on quantifying the kinetics of cooling rates and the microtextural maturation of plutonic rocks related to slow cooling. The main tools will be those of diffusion chronometry (e.g. Ca in Ol1), and the use of dihedral angles in solidified plutonic rocks.A key objective will be to improve current approaches to quantify those cooling rates by providing 1/ a finite difference model to fit Ca profiles in olivine and calculate associated cooling rates, 2/ an analysis of uncertainty propagation for these models, and 3/ a global unified database of existing data that could be used together with the new numerical model to compare cooling rates in the various available sections of oceanic crust. These, together with new data from natural samples from selected areas, will be used to improve our understanding of the formation and evolution of oceanic crust. Samples from several drilled and dredged areas are available in the CRPG collection (EPR: Hess Deep, MAR: Atlantis Massif, SWIR: Atlantis Bank, Oman ophiolite, and several others). These new cooling rate results will be complemented by a detailed microstructural study focusing mainly on grain and grain boundary shapes (aspect ratio & dihedral angles) to unravel the unique message recorded in plutonic rock textures.The postdoctoral fellow will work with Dr Lydéric France at CRPG, and will collaborate with Jean-Marc Montel (CRPG), David Jousselin (CRPG), and Marian Holness (Cambridge, UK). We are looking for highly motivated candidates with demonstrated interest in numerical models and/or diffusion chronometry models. The project involves petrography (dihedral angle measurements), so candidates with an interest in this domain are expected, but no specific background is expected as learning this approach will be part of the project.ReferenceFaak & Gillis (2016) Slow cooling of the lowermost oceanic crust at the fast-spreading East Pacific Rise. Geology 44.2: 115-118. https://doi.org/10.1130/G37353.1 #J-18808-Ljbffr