Position: 3-year Ph.D. position in Institut des Sciences de la Terre, Orléans University, France (October 2018-October 2021)
Advisors: Romain Augier, Hugues Raimbourg, Mohammed Boussafir, Yan Chen (ISTO), Abdeltif Lahfid (BRGM) et Asuka Yamaguchi (University of Tokyo)
Carbonaceous material is a common component of metasediments in collision and accretion belts, mainly deriving from the diagenetic and then the metamorphic evolution of the organic matter initially present within the sediment. This progressive transformation through carbonization and graphitization corresponds at microscopic scale to the irreversible organization of the carbonaceous materials toward well-crystallized graphite, the last step in the evolution. Consequently, the degree of crystalline organization of the carbonaceous material has been considered as a reliable indicator of the metamorphic conditions at peak-conditions (e.g. Rietmeijer & Mackinnon, 1985; Wada et al., 1996). More recently, the quantification of the degree of crystalline organization of the carbonaceous material by Raman spectrometry has been proposed as a new geothermometer (RSCM geothermometer) for a wide range of temperature (200-650°C ; Beyssac et al., 2002 ; Rahl et al., 2006 ; Lahfid et al., 2010). This geothermometer is currently became a reliable tool in metamorphic petrology (e.g. Cottle et al., 2011 ; Scharf et al., 2013 ; Augier et al., 2015 ; Beaudoin et al., 2016). However, the fine understanding of the graphitization processes remains limited particularly concerning the loss of functional groups and the formation of a lattice of graphene. In addition, the effect of deformation is often proposed to explain locally anomalous temperatures in a first order temperature gradient. Nevertheless, this effect of the deformation on the organization of carbonaceous material remains poorly studied, except in the case of fast movements responsible for frictional heat release. Recent studies performed pseudotachylites (Ito et al., 2016 ; Yamaguchi et al, in prep) have indeed shown a moderate increase of the organization of carbonaceous material. In this case, it is not possible to make clearly the difference between the effect of temperature and the potential effect of deformation. Besides, numerous questions remain currently unexplored such as the effects of localized deformation that do not produce partial melting (brecciation) or the effect of ductile deformation (mylonitization).
This PhD project explores the effects of both temperature and deformation on the organization of the carbonaceous material in naturally and experimentally strained rocks. Crystalline structure evolution will be followed with Raman spectrum, along with other complementary methods (RockEval, InfraRed, reflection microscopy…). A dense sampling at different scales will be performed on the field, along strain gradients already recognized by the members of the supervising team (Japan, Spain ou Greece). Variations in the organization of carbonaceous material will be compared with estimates of the amount of strain. In parallel, experiments in a Paterson rig will be conducted with controlled temperature, duration and amount of simple shear deformation on natural shales whose carbonaceous content will be finely characterized from the textural, chemical and functional points of view. Maturation experiments (at fixed temperature) will also be performed in order to estimate the kinetics of the transformation when no deformation is involved.
Qualified individuals need to have a MSc-degree in Geosciences at the time of appointment. The appointment will be for a period of 3 years and is available from October 2018 onwards.
Further enquiries about the position should be addressed to Romain AUGIER (firstname.lastname@example.org), Hugues Raimbourg (email@example.com).
The deadline for the application is the 23rd of April 2018. The application, consisting in a CV, a statement of interest and two reference people to be potentially contacted, should be submitted electronically to Romain Augier. The advertisement can also be found on: https://www.isto-orleans.fr/recrutement/offre-de-these-geodynamique/