Evidence of dehydration in peridotites from Eifel Volcanic Field and estimates of the rate of magma ascent

摘要: Abstract We report major element compositions and water contents in upper mantle minerals from peridotites transported by silica undersaturated, mafic alkaline lavas three volcanoes Rockeskyllerkopf, Dreiser Weiher, Meerfelder Maar of the Eifel Volcanic Field (West Germany). The hydrogen concentrations (expressed ppm wt. H2O) obtained unpolarized polarized Fourier transform infrared (FTIR) spectroscopy give for olivine, enstatite diopside ~ 6 ppm wt. H2O, ~ 200 ppm wt. H2O ~ 285 ppm wt. H2O, respectively. concentration individual olivine grains is strongly heterogeneous whereas that pyroxenes homogeneous. Profiles measured across crystallographically oriented single-crystals using radiation reveal depleted rims are interpreted to be due partial dehydration ionic diffusion during ascent xenolith surface. Using experimentally coefficients at high temperature pressure, we estimate duration spinel-bearing xenoliths limited a few hours yielding rates magma 3 ms− 1 12 ms− 1. Our study suggests based solely on measurements mantle-derived when not homogeneous, underestimate true content equilibrated uppermost better proxy constrain contents.