Figure 5: Models illustrating the geochemical evolution of the Tristan-Gough and Hawaiian hotspots.
From: How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot
(a) For the Tristan-Gough hotspot, the plume head is derived from the inner margin of the African low shear-wave velocity province (LLSVP) with enriched Gough composition. (b) The early plume stem continues to tap only LLSVP, but the margin of the LLSVP is continually drawn closer to the plume stem and/or the plume stem migrates towards the LLSVP boundary. (c) At ∼70 Ma, the LLSVP material on the northeastern side of the plume conduit is exhausted or the base of the plume may have migrated to the LLSVP boundary, so that depleted Tristan material from outside the LLSVP is also drawn into the plume conduit resulting in a zoned plume. (d) There is no geological evidence for the initiation of the Hawaiian plume. The oldest volcanic rocks associated with the hotspot are from ∼100 Myr old seamounts accreted to the forearc in Kamchatka17. The Hawaiian plume originally only taps the ambient depleted lower mantle (Kea component) between ∼100–47 Ma. (e) At some time between 45 and 5 Ma (most likely between ⩾15 and 7 Ma when there was a peak in volcanic flux from the Hawaiian plume), enriched Loa material is drawn into the Hawaiian plume from the Pacific LLSVP (which has a distinct composition from the African LLSVP) and the plume becomes zoned. (f) After ⩾15–5 Ma the Hawaiian Plume has remained zoned. S. Am., South American; Afr. Pl., African plate; CMB, core-mantle boundary. Profiles are not to scale. No distinction has been made between the thickness of oceanic and continental lithosphere.
