Advances in multi-elementary analysis of fluid or solid micro-crystalline inclusions (12

Claire Ramboz (1) , David Strivay (1, 2) , T. Sauvage (3) , Olivier Rouer (1) , J.P. Gallien (4) , Sophie Gama (1, 5)

1 ISTO - Institut des Sciences de la Terre d'Orléans
2 Institut de Physique Nucléaire
3 CEMHTI - Conditions Extrêmes et Matériaux : Haute Température et Irradiation
4 LPS - Laboratoire Pierre Süe
5 SGR - Saint-Gobain Recherche

X-Ray-based analytical methods can be applied in an absolute fashion, provided that matrix effects are calculated and that parameters related to instrumental factors are controlled (Newbury, 1986). When EPMA (Electron Probe Micro Analysis) was conceived at the end of the 60's, this potentiality was abandoned, as the instrument works in a relative fashion, by comparison with standards. At the end of the 70's and in the 80's, PIXE (Proton Induced X-Ray Emission) by contrast was applied in a way that preserved the possibility of an absolute application: the computer programs developed to interpret PIXE spectra calculate matrix effects and also integrate instrumental factors (e.g., Maxwell et al., 1989). In spite of this advantage, and also despite the fact that PIXE application extends to trace element analysis, the development of PIXE in the scientific community was sluggish, in deep contrast with the widespread applications of EPMA. In the field of Earth Sciences particularly, EPMA was recognized by the Mineralogical Society of America to have had 'a revolutionary, profound impact on mineralogy and petrology'. In the same time, PIXE applications remained mainly restricted to trace element analysis, and the potential accuracy of the method was never clearly realized. A first aim of this presentation is to show that, using a simple standardization procedure, the multi-elementary absolute capability of PIXE can be revealed. This in turn changes PIXE into a tool of quantitative mineralogy and trace element geochemistry. We then show that, by coupling PIXE to PIGE (Proton Induced Gamma Ray Emission) and RBS (Rutherford Back Scattering) spectrometries, the Nuclear Microprobe becomes a tool for quantitative mineralogy s.l. and geochemistry, i.e., an instrument to analyze all major to trace elements from Li to U in minerals and their inclusions. In the second part of the presentation, we illustrate the capability of µ-PIXE to analyze in situ individual fluid inclusions that have been carefully localized in space and time. The Hercynian French Massif Central and its sedimentary eastern margin are part of a large European Carbonic Province, which hosts numerous deep CO2 reservoirs and carbonic springs (Blavoux, Dazy, 1990). Carbonic fluids are present at all stages of the long-lived evolution of this crustal segment, from deep metamorphic fluids involved in a thrusting event at 340 M.a to mantle-derived volcanic CO2 related to Neogene volcanism. In order to characterize the main aquo-carbonic fluid reservoirs through time in this crustal segment, we present preliminary data on the trace element content of aquo-carbonic inclusions trapped in the schists at peak and retrograde metamorphic conditions, and compare them to contemporaneous granite-related fluid inclusions

Domaines: Minéralogie

Claire Ramboz, David Strivay, T. Sauvage, Olivier Rouer, J.P. Gallien, et al.. Advances in multi-elementary analysis of fluid or solid micro-crystalline inclusions (12. XIII All-Russian conference on thermobarogeochemistry in conjunction with IV APIFIS symposium, Sep 2008, Moscou, Russia. ⟨insu-00331670⟩