The ICDP drilling in the Snake River Plain (SRP) volcanic province (western United States) was aimed at understanding the interaction of a hotspot with the continental lithosphere. This understanding requires information on the evolution of chemistry, sources, differentiation and storage conditions of both the rhyolitic and basaltic magmas that have been produced over the last 17 Ma years.The major objective of this project is to construct a model of magma plumbing system for the Snake River Plain (SRP) mafic to intermediate magmas. Using the information provided by the crystal cargoes in basaltic volcanic rocks from the Kimama ICDP bore hole (~ 1800 meters of more than 500 basaltic lava flows) the storage conditions of magma reservoirs, magma ascent pathways and transcrustal magmatic processes will be described. We will achieve this by coupling two types of investigations: 1) by linking textural and compositional information from zoned crystals and 2) by the analysis of the composition of re-homogenized melt inclusions in the mineral phases. The originality of the approach is the combination of the detailed analysis of different types of mineral phases (olivine, plagioclase, clinopyroxene and spinel) together with the analysis of melt inclusions in those minerals. Thermobarometric constraints and the origin of compositional zoning (e.g., textures related to different magmatic processes such as decompression melting, magma replenishment or convective processes) will be used to identify different populations of crystals and different magmatic environments. When present, diffusion profiles will be used to constrain time scales of magmatic processes (e.g., time that a crystal spent in a specific reservoir or environment).Since all basalts have a partially or fully crystallized groundmass, the composition of melts coexisting with the crystal cargo will be determined from re-homogenized glass inclusions. Re-homogenization will be performed at realistic temperatures (~ 1100 -1200 °C) in high pressure vessels (up to 500 MPa) which is necessary to avoid diffusive transfer of volatiles (mainly water) out of the inclusions (at least for olivine). The analysis of re-homogenized inclusions will provide the possibility to reconstruct the composition of melts (major elements, trace elements, amount of volatiles), to trace the melt compositions in the different environments, and to discuss the differentiation processes (as a complement to mineral compositions, see above). Using solubility models of H2O and CO2 in silicate melts, the estimations of volatile contents (H2O and CO2) will provide an additional tool to constrain the pressure of entrapment and will complement the thermobarometric information. Since primitive undifferentiated basaltic samples are not represented in the SRP, the major and trace element analysis of glass inclusions in olivine may also be useful to characterize the geochemical signature of the source region.
