In situ Determination of the Partitioning of trace Elements between Hydrous Melts and Aqueous Fluids at High Pressure and Temperature
H. Bureau, B. Ménez, V. Malavergne, A. Somogyi, M. Munoz, A. Simionovici, D. Massare, M. Burchard, S. Kubsky, C. Shaw logo_tutelle logo_tutelle 

In situ SXRF mapping, at 25°C of a diamond anvil cell experiments performed with Pb-bearing haplogranite as the starting glass composition and a standard aqueous solution containing Sr, Rb, NaCl. Size is 80 µm x 70 µm, step 2 x 2 µm2, 10 sec/point. After the quench, Rb and Sr are enriched in the glassy globules whereas Pb is present in both phases: quench melt as a glass, and aqueous solution.

Subduction zones are the locations where the oceanic crust, which experienced intense interaction with seawater, is buried back into the Earth’s mantle. These environments play a critical role in the global geochemical cycle of Earth, being the location at which chemical components are both recycled into the mantle and returned to the atmosphere through volcanism. It is now generally admitted that magma genesis at subduction zones is mainly induced by the presence and movement of fluids (aqueous fluids and/or silicate melts) released continuously in large amounts due to dehydration reactions in the subducted slab. It is also believed that these fluids may be responsible of the atypical trace-element signature of the Island Arc Basalts (IAB), which are enriched in Large Ion Lithophile Element (LILE= Sr, Rb, Ba, Pb) and depleted in High-Field Strength Element (HFSE= Zr, Ti, Hf, Nb, Ta) compared to Mid-Ocean Ridge Basalts (MORB). This program combine diamond anvil cells experiments with the high-brillance third-generation synchrotron light source of the European Synchrotron Radiation Facility (ESRF µFID beam line, Grenoble, France,), to study in situ the partitioning of key elements (Pb, Rb, Sr) between aqueous fluids (pure water, NaCl aqueous solutions) and silicate melts, under subduction zones pressure and temperature conditions. We try to evaluate the effect of chlorine on the partition coefficients of elements such as Pb, Ba, Sr, Rb, Zr… as function of pressure and temperature. Related publication: EOS Trans. AGU 2004, 85(47), Fall Meet. Suppl., Abstract V11C-05.  

Maj : 25/03/2005 (367)

 

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