Experimental Constraints on the Role of Garnet Pyroxenite in the Genesis of High-Fe Mantle Plume Derived Melts

摘要: The anhydrous phase relations of an uncontaminated (primitive), ferropicrite lava from the base Early Cretaceous Parana´- Etendeka continental flood basalt province have been determined between 1 atm and 7GPa. sample has high contents MgO (� 14� 9 wt %), FeO* (14� %) Ni (660ppm). Olivine phenocrysts maximum Fo 85 are in equilibrium with bulk rock, assuming a K Olliquid DFeMg 0� 32. A comparison our results previous experimental studies high-Mg rocks shows that FeO content causes expan- sion liquidus crystallization field garnet clinopyroxene relative to olivine; orthopyroxene was not observed any experiments. also decreases solidus temper- atures. Phase indicate melt last equili- brated either at � 2� 2GPa olivine-clinopyroxene residue, or 5GPa garnet-clinopyroxene residue. low bulk-rock Al2O3 (9 (Gd/Yb)n ratio (3� 1) consistent presence residual source favour high-pressure melting pyroxenite source. may represent subducted oceanic litho- sphereentrainedbytheupwellingTristanstartingmantleplumehead. During adiabatic decompression, intersection would occur mantle potential temperature 1550 C yield primary magma. Subsequent surrounding peridotite 4� be restricted by thickness overlying sub-continental lithosphere, such dilution component signific- antly less than intra-oceanic plate settings (where lithosphere is thinner). This model explain limited occurrence ferropicrites sequences their apparent absence ocean-island successions.