Abstract:
The Canary Island primitive basaltic magmas are thought to be derived from an HIMU-type upwelling mantle containing isotopically depleted (NMORB)-type component having interacted with an enriched (EM)-type component, the origin of which is still a subject of debate. We studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6-90.0 mol.% Fo, 1,722-3,915 ppm Ni, 1,085-1,552 ppm Mn, 1,222-3,002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine basaltic) lavas with their bulk rock Sr-Nd-Pb isotope compositions ( (super 87) Sr/ (super 86) Sr = 0.70315-0.70331, (super 143) Nd/ (super 144) Nd = 0.51288-0.51292, (super 206) Pb/ (super 204) Pb = 19.55-19.93, (super 207) Pb/ (super 204) Pb = 15.60-15.63, (super 208) Pb/ (super 204) Pb = 39.31-39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source. Using the model (Sobolev et al. in: Science 316:412-417, 2007) in which the reaction of Si-rich melts originated during partial melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free reaction pyroxenite, we obtain an end member composition for peridotite with (super 87) Sr/ (super 86) Sr = 0.70337, (super 143) Nd/ (super 144) Nd = 0.51291, (super 206) Pb/ (super 204) Pb = 19.36, (super 207) Pb/ (super 204) Pb = 15.61 and (super 208) Pb/ (super 204) Pb = 39.07 (EM-type end member), and pyroxenite with (super 87) Sr/ (super 86) Sr = 0.70309, (super 143) Nd/ (super 144) Nd = 0.51289, (super 206) Pb/ (super 204) Pb = 20.03, (super 207) Pb/ (super 204) Pb = 15.62 and (super 208) Pb/ (super 204) Pb = 39.84 (HIMU-type end member). Mixing of melts from these end members in proportions ranging from 70% peridotite and 30% pyroxenite to 28% peridotite and 72% pyroxenite derived melt fractions can generate the compositions of the most primitive Gran Canaria shield stage lavas. Combining our results with those from the low-silica rocks from the western Canary Islands (Gurenko et al. EPSL 277:514-524, 2009), at least four distinct components are required. We propose that they are (1) HIMU-type pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component from the asthenosphere or lithosphere above the plume center. Copyright 2009 Springer-Verlag