Volatile elements released from the subducting slab play a fundamental role during the formation of arc magmas in the mantle wedge. Advances of melt inclusion studies enlarged the data on volatile abundance in arc magmas, and it is now possible to characterize some volatile contents in arc primary magmas, in particular F and Cl. A recent study of Mt Shasta melt inclusions (LeVoyer et al., 2010) shows that fractionation of F and Cl potentially contains information about arc magma genesis. In order to trace the source of arc magmas, fluorine and chlorine partitioning was investigated. Here, I present new experimental determinations of Cl and F partition coefficients between dry and hydrous silicate melts and mantle minerals: olivine, orthopyroxene, clinopyroxene, plagioclase, garnet and also pargasite and phlogopite. The values were compiled from more than 300 measurements in 24 melting experiments, conducted between 8 and 25 kbars and between 1180 and 1430˚C. The low abundance F, Cl measurements in minerals were done by Cameca IMF 1280 at WHOI using the negative secondary ion mode. The results show that DOpx/meltF ranges from 0.123 to 0.021 and DCpx/meltF ranges from 0.153 to 0.083, while Cl partition coefficient varies from DOpx/meltCl from 0.002 to 0.069 and DCpx/meltCfrom 0.008 to 0.015, as well. Furthermore, DOl/meltF ranges from 0.116 to 0.005 and DOl/meltCl from 0.001 to 0.004; DGrt/meltF ranges from 0.012 to 0.166 and DGrt/meltCl from 0.003 to 0.087 with the increasing water amount and decreasing temperature. I also show that F is compatible in phlogopite DPhl/meltF > 1.2) while DAmp/meltF is incompatible in pargasite DAmp/meltF from 0.36 to 0.63). On the contrary, Cl is more incompatible in phlogopite (DPhl/meltCl > 1.2 on average 0.09 ± 0.02), than in pargasite (DPhl/meltCl from 0.12 to 0.38). This study demonstrates that F and Cl are substituted in specific oxygen site in minerals that lead then to be more sensitive than trace elements to crystal chemistry and water amount variations thus melting conditions. Using those new partition coefficients, I modelled melting of potential sub-arc lithologies with variable quantity aqueous-fluid. This model is able to decipher 1) amount of aqueous-fluid involved in melting, 2) melting induced by fluid or melting of an hydrous mineral-bearing source and 3) melting of either pargasite-bearing lithology or phlogopite-bearing lithology and shows that sources of some primitive melts, for instance from Italy, bear pargasite and phlogopite, while some primitve melts seem to be the results of fluid-induced melts.

Les éléments volatils libérés de la plaque plongeante lors de la subduction jouent un rôle fondamental durant la formation des magmas d'arc dans le coin mantellique. Depuis quelques années, les développements des techniques d'analyse par sonde ionique ont permis l'analyse de ces éléments, en particulier F et Cl, dans les magmas d'arc, et notamment dans les magmas d'arc primaires grâce aux avancées des études sur les inclusions magmatiques. Une récente étude des inclusions magmatiques du Mont Shasta (E. U.) (Le Voyer et al., 2010) a montré que le fractionnement du F et du Cl apportait des informations sur la genèse des magmas d'arc. Afin de caractériser la source de ces magmas, j'ai étudié les coefficients de partage du fluor et du chlore. Dans cette étude, je présente les premiers coefficients de partage du F et du Cl, entre des liquides de fusions silicatés anhydres et hydratés et des minéraux mantelliques tels que olivine, orthopyroxène, clinopyroxène, plagioclase, grenat ainsi que pargasite et phlogopite. Les valeurs sont issues de 300 mesures dans 24 expériences de fusion, réalisées entre 8 et 25 kbars et, 1180 et 1430˚C. Les faibles concentrations en F et Cl dans les minéraux ont été analysées par la sonde ionique Cameca IMF 1280 de WHOI en utilisant le mode d'ions secondaires négatifs. Les résultats montrent que DOpx/meltF varient de 0.123 à 0.021 et DCpx/meltF de 0.153 à 0.083, tandis que DOpx/meltCl varient de 0.002 à 0.069 et DCpx/meltCl de 0.008 à 0.015. De plus, DOl/meltF de 0.116 à 0.005 et DOl/meltCl de 0.001 à 0.004 ; DGrt/meltF de 0.012 à 0.166 et DGrt/meltCl de 0.003 à 0.087 avec l'augmentation de la teneur en eau et la diminution de la température dans les expériences. Je montre aussi que le F est compatible dans la phlogopite (DPhl/meltF >1.2) alors qu'il est incompatible dans la pargasite (DAmp/meltF de 0.36 à 0.63). A l'inverse, Cl est plus incompatible dans la phlogopite (DPhl/meltCl en moyenne 0.09±0.02), que dans la pargasite (DAmp/meltCl de 0.12 à 0.38). Cette étude démontre que F et Cl sont substitués dans des sites spécifiques de l'oxygène, ce qui les rend plus sensibles que les éléments traces aux variations de chimie des cristaux et de la quantité d'eau, et donc aux conditions de fusion. En utilisant ces nouveaux coefficients de partage, j'ai modélisé la fusion de lithologies potentielles du manteau sub-arc permettant de 1) déterminer la quantité de fluide aqueux impliqué dans la fusion, 2) distinguer la fusion induite par apport de fluides de la fusion d'une source à minéraux hydratés et 3) la fusion d'une lithologie à pargasite de celle à phlogopite, et montre que la source de certains magmas primaires d'arc, par exemple d'Italie, contient de la pargasite et de la phlogopite, tandis d'autres magmas primaires d'arc résultent d'une fusion par apport de fluides. / Volatile elements released from the subducting slab play a fundamental role during the formation of arc magmas in the mantle wedge. Advances of melt inclusion studies enlarged the data on volatile abundance in arc magmas, and it is now possible to characterize some volatile contents in arc primary magmas, in particular F and Cl. A recent study of Mt Shasta melt inclusions (LeVoyer et al., 2010) shows that fractionation of F and Cl potentially contains information about arc magma genesis. In order to trace the source of arc magmas, fluorine and chlorine partitioning was investigated. Here, I present new experimental determinations of Cl and F partition coefficients between dry and hydrous silicate melts and mantle minerals: olivine, orthopyroxene, clinopyroxene, plagioclase, garnet and also pargasite and phlogopite. The values were compiled from more than 300 measurements in 24 melting experiments, conducted between 8 and 25 kbars and between 1180 and 1430˚C. The low abundance F, Cl measurements in minerals were done by Cameca IMF 1280 at WHOI using the negative secondary ion mode. The results show that DOpx/meltF ranges from 0.123 to 0.021 and DCpx/meltF ranges from 0.153 to 0.083, while Cl partition coefficient varies from DOpx/meltCl from 0.002 to 0.069 and DCpx/meltCfrom 0.008 to 0.015, as well. Furthermore, DOl/meltF ranges from 0.116 to 0.005 and DOl/meltCl from 0.001 to 0.004; DGrt/meltF ranges from 0.012 to 0.166 and DGrt/meltCl from 0.003 to 0.087 with the increasing water amount and decreasing temperature. I also show that F is compatible in phlogopite DPhl/meltF > 1.2) while DAmp/meltF is incompatible in pargasite DAmp/meltF from 0.36 to 0.63). On the contrary, Cl is more incompatible in phlogopite (DPhl/meltCl > 1.2 on average 0.09 ± 0.02), than in pargasite (DPhl/meltCl from 0.12 to 0.38). This study demonstrates that F and Cl are substituted in specific oxygen site in minerals that lead then to be more sensitive than trace elements to crystal chemistry and water amount variations thus melting conditions. Using those new partition coefficients, I modelled melting of potential sub-arc lithologies with variable quantity aqueous-fluid. This model is able to decipher 1) amount of aqueous-fluid involved in melting, 2) melting induced by fluid or melting of an hydrous mineral-bearing source and 3) melting of either pargasite-bearing lithology or phlogopite-bearing lithology and shows that sources of some primitive melts, for instance from Italy, bear pargasite and phlogopite, while some primitve melts seem to be the results of fluid-induced melts.