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PhD Light elements (Li, B) behaviour during magma degassing, Université Blaise Pascal, France
From: Olivier Roche <o.roche@xxxxxxxxxxxxxxxxxxxxxxx>
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*_Title of the thesis : _*
Light elements (Li, B) behaviour during magma degassing: experimental and geochemical approach
_Supervisor :_ Ivan Vlastélic and Estelle Rose-Koga__
_Laboratory : _Laboratoire Magmas et Volcans
_University : _Université Blaise Pascal
Replies should be sent to:
I.Vlastelic@xxxxxxxxxxxxxxxxxxxxxxx (33) 4 73 34 67 10
E.Koga@xxxxxxxxxxxxxxxxxxxxxxx (33) 4 73 34 67 61
*_Abstract :_*
There has been recently a growing interest in the behavior of light elements during late-stage magmatic processes. In particular, lithium properties (volatile and rapidly diffusing) were shown to be useful to track low-pressure degassing processes. Within the frame of this emerging approach, the aim of this thesis is to better understand the behavior of lithium and boron and their isotopes during magma degassing. One will consider the influence of parameters such as degassing rate, magma composition (acid vs basic) or system type (close vs open). Potential applications include for instance the identification of new geochemical precursor to volcanic activity.
An experimental and a geochemical (sensu stricto) approach are planned. In the first, the behavior of lithium and boron at pressure and temperature typical of degassing will be studied in the laboratory. Two types of experiment will be performed: a) at constant pressure, one will study Li and B partitioning between molten silicate and vapor. b) Experiment involving pressure release will be conducted in order to simulate magma ascent. This later experiment is intended to place constraints on how lithium and boron and their isotopes distribute between molten silicate and vapor as degassing operates. The second approach consists in analyzing the lithium and boron contents and the isotopic compositions in natural samples representative of volcanic gaz. The objective is to identify the chemical and isotopic fractionations that occur naturally between magmas and gaz, their variability and their link to volcanic context. Theses natural fractionations will be compared to those observed during laboratory experiments in order to understand how they occur. Both approaches will consider the two major types of volcanism, namely the andesitic explosive volcanism (e.g. Lascar, Chile) and the more progressively degassing basaltic volcanism (e.g. Piton de la Fournaise, Ile de la Réunion).
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