Dear colleagues,
please see the attached file for a full-time 3-year PhD opportunity in
metamorphic petrology - geochronology at Rennes University, France.
Please don't hesitate to transfer it to the potentially interested
candidates.
All the best,
Pavel
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A critical study of age constraints on metamorphism in convergence
zones: from burial to exhumation
3-year PhD position at the University of Rennes (France)
Advisors: Pavel Pitra, Marc Poujol, Philippe Yamato
Dating metamorphic events is a major challenge for the understanding of
orogenic processes. It brings temporal constraints on the
pressure-temperature evolution (P-T path) of rocks during their burial
(e.g. in subduction zones) and subsequent exhumation. Coupling
metamorphic and geochronological data is therefore crucial for the
understanding of the dynamics of convergence zones and, consequently,
for proposing any geodynamic reconstructions. The robustness of this
link is therefore a first-order issue. As an example,
sub-contemporaneous ages obtained for both the high- and low-pressure
metamorphic stages in a same geological domain can lead to either (i)
propose extremely fast exhumation rates, the physical and/or tectonic
mechanisms of which remain unknown, or (ii) question the classic
interpretation of the pressure recorded by metamorphic rocks in terms of
burial depth, or (iii) reconsider the overall interpretation of the
acquired radiometric data in metamorphic rocks.
High-pressure rocks (e.g. eclogites) that have undergone significant
decompression (e.g. in the low-pressure granulite facies) are the most
interesting targets for addressing these issues. Classically, P-T paths
are linked to ages through the analysis of trace elements in the dated
minerals, which are supposed to reflect the moment of crystallization of
the mineral along the P-T path. However, our preliminary results from
several variscan eclogites show the limitations of this approach, as it
does not necessarily yield reliable results. This has a strong impact on
the geodynamic interpretation of the studied region.
This study will be focused on two specific eclogite-facies rock targets,
the Norwegian Caledonides and the Rhodope belt, where the ‘issue’ of
sub-contemporaneous ages attributed to the high- and low-pressure stages
of their respective metamorphic evolution is known. The advantage of
these two orogens is also that they cover a large time span to explore
(~400 Ma for the Caledonian belt and ~50 Ma for the Rhodope). The goal
of this PhD project is to combine state-of-the-art petrological,
geochemical and geochronological analyses on these eclogite-facies
rocks, using a large spectrum of methods:
- a detailed petrological analysis, including meticulous petrography and
phase equilibria modelling (Theriak-Domino, THERMOCALC)
- combination of several dating techniques (U-Th-Pb on zircon, monazite,
rutile, titanite, apatite,…, Sm-Nd and Lu-Hf on garnet)
- trace elements (REE) partitioning between the dated minerals and the
main metamorphic rock-forming phases
- using Raman spectroscopy to identify inclusions in the dated minerals
and to constrain their entrapment pressure (shift of spectral peaks)
- trace-element thermobarometry (Ti-in-zircon, Zr-in-rutile, Ti-in-quartz)
Requirements: The candidate must hold a Master diploma (MSc or
equivalent) in geology and have solid basic knowledge in metamorphic
petrology, geochronology and tectonics. Previous experience with one or
several of the methods used is a plus. Good communication skills are
expected.
Some more details can be found at
https://theses.u-bretagneloire.fr/egaal/theses-2018. The application
must also be done through this web page, but interested candidates are
invited to first contact the advisors (Pavel Pitra
<[log in to unmask]>, Marc Poujol
<[log in to unmask]>, Philippe Yamato
<[log in to unmask]>) and send a full CV, a statement of
interest, mark reports, details about previous internships etc., and the
names and emails of two references, *before mid-May*. The deadline for
online application is May 31, 2018.
--
Pavel PITRA
Géosciences Rennes [log in to unmask]
Université Rennes 1 tel: (++33) 2.23.23.65.06
Campus de Beaulieu - Bat. 15
F - 35 042 RENNES CEDEX
FRANCE http://www.geosciences.univ-rennes1.fr/
https://geosciences.univ-rennes1.fr/interlocuteurs/pavel-pitra
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