PMC

(1) The cratonic mantle is disrupted by rifting and/or a mantle plume and is fragmented into the asthenosphere, after which it is transported to a mid-ocean ridge. (2) The recycled cratonic mantle is incorporated into the oceanic lithospheric mantle at a mid-ocean ridge during ultraslow seafloor spreading where it can be exposed and sampled. (3) Ultimately, subduction returns the fragments of transported Archean cratonic mantle back to the convective mantle from which it was originally extracted. The artwork was designed by Shen-Wen Wang@Institute of Planets Inc.

a Narrow rifting with simultaneous rupture of crust (orange) and mantle lithosphere (green), followed by accretion of normal oceanic crust (black). b Wide rifting with distributed deformation in the crust (orange) and narrow rupture of the mantle lithosphere. Note the differential motion between the crust and mantle lithosphere in wide rifting. Preferential removal of the mantle lithosphere leads to accumulation of magmatic addition (black) to the extending continental crust above. Note both narrow and wide rift scenarios have the same (normal) mantle potential temperature. Shown are melt window (grey region), new lithosphere (yellow), directions of extension (arrows) and flow path of passive mantle upwelling (dashed lines).

A. Mantle around the exhalant siphon. B. Mantle around the inhalant siphon. C, D. Ventral mantle margin. The periostracum can be seen emerging behind the middle mantle fold in C, whereas it is absent in D, thus leaving the internal surface of the outer mantle fold and the periostracal groove exposed. IMF, inner mantle fold; MMF, middle mantle fold; OMF, outer mantle fold; PG, periostracal groove; Po, periostracum; Tl, tentacle.

A cartoon model for the possible spatial distribution of the Indian MORB mantle beneath the Lau basin. (A) Pacific asthenosphere mantle is mixed with DUPAL-like Indian MORB mantle showing its longitudinal distribution beneath the back-arc spreading center. Profile A-B is at the depth of this mixed asthenosphere underlying the lithosphere. (B) The possible spatial distribution of asthenosphere mantle at the depth of Profile A-B. The pacific asthenosphere mantle components beneath the NWLSC, CLSC, ELSC, Valu Fa ridge and Tofua volcanic arc have been replaced by the DUPAL-like Indian MORB mantle, whereas Lau ridge and Tonga ridge are still maintaining the properties of pacific mantle asthenosphere. The asthenosphere mantle contaminated by Samoa plume is shown at the northeast of Lau basin. The colour gradient from red to yellow represents the influence strength of the Indian MORB mantle.