The Institut des Sciences de la Terre d’Orléans invites for application for an ERC funded three-years PhD thesis in Geodynamics – Tectonics

The Institut des Sciences de la Terre d’Orléans invites for application for an ERC funded three-years PhD thesis in Geodynamics – Tectonics

Strain localisation in shear zones and the behaviour of the 40Ar-39Ar system

Key words: rheology, shear zone, field work, 40Ar-39Ar, strain localisation, radiometric dating, numerical modelling

Project description: Dating deformation processes is a first-order prerequisite to constrain the history of strain localisation and mountain building processes such as crustal thickening, high-pressure rocks exhumation or large-scale extension in the continental crust. The 40Ar-39Ar method is extensively used for such a purpose by virtue of the widespread availability of high-K fabric-forming mineral (micas) and network-supporting phases (K-feldspars) composing most crustal materials (felsic intrusives, gneisses and metapelites), including high Ar retentive minerals (amphibole) found in more mafic lithologies. Large variations in Ar retention properties among these minerals endow the 40Ar-39Ar techniques with a range of closure T-t pairs from about 550 °C to as low as 200 °C, thus permitting recovery of a substantial portion of the tectono-thermal history of the crust.
Moreover, it has been shown that micas may preserve cristallization ages, especially at low temperatures, thus opening the possibility to record the progressive localisation of strain within shear zones.
The goal of this PhD project is to explore the possibilities offered by the 40Ar-39Ar technique to constrain the rate of strain localisation in different tectonic settings (extension, strike-slip motion, etc.) and P-T conditions.
A limited number of shear zones (Alps, Norwegian Caledonides, Cyclades, Basin and Range), developed at different scales and P-T regimes (from HT-LP to HP-LT) will be selected and precisely quantified in terms of geometry, kinematics and P-T conditions. Dense 40Ar-39Ar sampling will be performed across the shear zones using the dedicated multi-instrument platform developed in the context of this project at ISTO. This will allow focussing on first order parameters (deformation, diffusion, grain size distribution, etc.) controlling age
variations across the shear zones by using high-resolution step-heating and spatially-resolved in-situ techniques to get rid of (or correct for) local effects/artefacts. Systematic exploration of the different P-T contexts will allow better characterization of the driving parameters operating under widely differing P-T-strain conditions. In addition, integration of the field and lab-based data with numerical thermo-mechanical models will be performed to rationalize the 40Ar-39Ar isotopic record in terms of these first-order processes from the individual shear zone up to the entire orogen.

The host institution and the laboratory: The University of Orléans (UO) is a medium-size campus with 13000 students in differents fields of research from Mathematics, Physics, Law, Economy, Biology to Earth and Space Sciences. The laboratory (Institut des Sciences de la Terre d’Orléans, ISTO) is part of the Observatoire des Sciences de l’Univers en Région centre (OSUC), an internal school of the UO devoted to research and teaching in geosciences, environmental sciences, atmospheric and space sciences. ISTO has developed research facilities in geodynamics and experimental petrology that are internationally recognized as proven by one ERC Advanced Research Grant RHEOLITH and two ERC Starting Research Grants. The OSUC has also been recently elected as a centre of excellence via two nationally-funded projects (Labex VOLTAIRE dedicated to the
study of fluids from the deep Earth to the atmosphere, and Equipex PLANEX dedicated to analyses and experiments in extreme environments) showing the steadily growing role played by ISTO at the national level. RHEOLITH will involve ~6 academic staffs, 7 PhD students, 3 engineers and 3 post-docs thus providing a strongly integrated and interactive academic-research environment for the PhD project .

Eligibility: We are seeking for a creative individual with a diploma or M.Sc. degree in geology. A solid background in geodynamics and petrology is an advantage.
Funding context: the research and the scholarship will be funded by the RHEOLITH ERC Advanced Research Grant (P.I. L. Jolivet, co-PI E. Burov)

Application: Requests and applications including a motivation letter, CV, as well as the names and email addresses of two potential referees should be submitted as a single pdf file by email to Laurent Jolivet (Laurent.jolivet@univ-orleans.fr), Stéphane Scaillet (stephane.scaille@cnrs-orleans.fr) and Romain Augier (romain.augier@univ-orleans.fr).

Deadline for application is June 30, 2013.

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