Implications of a two-component marble-cake mantle

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

“…We assume the mantle is composed everywhere of fusible veins or blobs [e.g., Sleep, 1984;Allégre and Turcotte, 1986] of material that is enriched in incompatible elements and radiogenic Pb (i.e., "enriched" material, EC), as well as a more refractory matrix that is depleted in incompatible elements and radiogenic Pb (i.e., depleted material, DC). The scale of the EC veins or blobs is assumed to be fine enough for the EC-DC mixture to be uniform at the scale of the control volume of the mantle continuum, but large enough so that the melting behavior of the two materials are chemically uncoupled.…”

“…Evidence for material with extreme compositions have been found at the Samoa hotspot [Jackson et al, 2007] but has yet to be discovered in the Galápagos area. The implication is that the Galápagos plume is composed of materials that have evolved very differently over geologic time to produce their strongly distinct isotope characteristics, but have since been mixed together so the heterogeneity is now present as small-scale blobs or veins [Sleep, 1984;Allégre and Turcotte, 1986].…”

Noble gases in diamonds: Occurrences of solarlike helium and neon

“…For example, Allegre and Turcotte [1986] have discussed a "marble cake" model for the mantle in which two distinctly different regions are convectively fltirred into it and deformed by elongation (thinning) so as to produce global mixing but striking local inhomogeneities, the older layers being all the thinner. The marbling is comprised of oceanic crust, partially depleted by subduction zone volcanism, and a complementary, highly depleted upper mantle.…”

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

“…However, based on geochemical arguments, a few pyroxenite occurrences have been interpreted to represent remnants of subducted mafic oceanic crust, streaked out during recycling through the convecting asthenosphere, until re-incorporated into the lithosphere (e.g., Allègre and Turcotte 1986;Kornprobst et al 1990). However, the majority of pyroxenites are well explained by mantle melts propagating along hydraulically opened cracks and crystallising cumulates/segregates (the actual pyroxenites), which may evolve later into parallel layers by plastic (sub-solidus) deformation (Bodinier and Godard 2003;Downes 2007, and references therein).…”