Program > Browse abstracts by speaker > Schettino Erwin

Mantle/melt partitioning of trace elements is governed by the mineral chemistry of peridotite-forming minerals (olivine, orthopyroxene, clinopyroxene and garnet/spinel), the latter being controlled by the pressure-temperature conditions at which they co-exist with the melt phase. Despite a large number of studies addressing mineral/melt partition coefficients in variable mantle lithologies and P-T conditions, none has constrained the partitioning behavior for a realistic carbonated silicate melt saturated with four phase peridotite along the mantle adiabat, conditions that are relevant for predicting the geochemical signatures of melts released by asthenosphere upwellings. To face this challenge, we performed “forced multiple saturation experiments” on a highly Si-undersaturated primitive ocean island basanite composition from Cape Verde. These experiments force this melt into equilibration with four-phase garnet lherzolites at adiabatic temperatures (1380-1420 oC) from 3 to 7 GPa. This experimental strategy allows to back-track the melt evolution through an asthenospheric melting column, down to its deepest root at the redox melting front at the base of the low-velocity zone (~200 km). In situ analyses by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were conducted to determine the mineral/melt partitioning of high field strength elements (HFSE: Nb, Ta, Zr, Hf), Ba, Sr REEs, Y, moderately siderophile elements (e.g., W, Mo), alkalis (K2O, Na2O) and other minor elements (TiO2, P2O5) at each pressure step. The experimental results, coupled with the stoichiometry of the with pressure evolving melting reaction, is then employed to model the geochemical signatures of these melts equilibrated, and compared with the trace element systematics of asthenosphere-derived primitive magmas sourced from different depths. These models are used to test whether the geochemical signature of magmas extruded at surface is controlled by the thickness of the lithospheric column they ascend through.