Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

Twitter

Aller au compte twitter

  Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells

Type de publication:

Journal Article

Source:

Geochimica Et Cosmochimica Acta, Volume 74, Ticket 13, p.3839-3850 (2010)

ISBN:

0016-7037

Numéro d'accès:

ISI:000278510300011

URL:

http://www.sciencedirect.com/science/article/pii/S0016703710001754

Mots-clés:

UMR 7154 ; Minéralogie

Résumé:

The geochemical partitioning of bromine between hydrous haplogranitic melts, initially enriched with respect to Br and aqueous fluids, has been continuously monitored in situ during decompression. Experiments were carried out in diamond anvil cells from 890 degrees C to room temperature and from 1.7 GPa to room pressure, typically from high P. T conditions corresponding to total miscibility (presence of a supercritical fluid). Br contents were measured in aqueous fluids, hydrous melts and supercritical fluids. Partition coefficients of bromine were characterized at pressure and temperature between fluids, hydrous melts and/or glasses, as appropriate: D-fluid/melt(Br) = (Br)(fluid)/(Br)(melt), ranges from 2.18 to 9.2+/-0.5 for conditions within the ranges 0.66-1.7 GPa, 590-890 degrees C; and D-fluid/glass(Br) = (Br)(fluid)/(Br)(glass) ranges from 60 to 375 at room conditions. The results suggest that because high pressure melts and fluids are capable of accepting high concentrations of bromine, this element may be efficiently removed from the slab to the mantle source of arc magmas. We show that Br may be highly concentrated in subduction zone magmas and strongly enriched in subduction-related volcanic gases, because its mobility is strongly correlated with that of water during magma degassing. Furthermore, our experimental results suggest that a non negligible part of Br present in the subducted slab may remain in the down-going slab, being transported toward the transition zone. This indicates that the Br cycle in subduction zones is in fact divided in two related but independent parts: (I) a shallower one where recycled Br may leave the slab with a water and silica-bearing "fluid" leading to enriched arc magmas that return Br to the atmosphere. (2) A deeper cycle where Br may be recycled back to the mantle maybe to the transition zone, where it may be present in high pressure water-rich metasomatic fluids. (C) 2010 Elsevier Ltd. All rights reserved

Notes:

Bureau, Hélène Foy, Eddy Raepsaet, Caroline Somogyi, Andrea Munsch, Pascal Simon, Guilhem Kubsky, Stefan