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Do hotspots correlate with– asthenospheric shear (Conrad et al., King), extensional stress (Favela, Lithgow-Bertelloni), plate architecture & anisotropy (LLAMA), the lower mantle (Burke & Torsvik), absence of subduction (Anderson); distance from cratons, distance from active tectonic regions, near ridge-like passive upwellings…plate divergence associated with upper mantle downwellings (Husson & Conrad 2014)?
Yes. Does this mean that all of the above correlate with each other? Of course not.
Don L. Anderson
2 May 2011 (March 2014)
(note that all volcanoes are in extensional regions, including on Nazca plate (JF,SF), Cameroon, Afar, Easter, Reunion, Atlantic etc.; also all ridges)
Edges of slabs?
All active hotspots & all reconstructed positions of LIPs lie above regions that did not experience Jurassic-Eocene subduction. LVsLs in the lower mantle fall below these regions
HOTSPOTS (CIRCLES) are where slabs are not
Predicted locations of slab material; correlations best @ 800km
THE TRANSITION REGION
“…the key to a number of geophysical problems…”Francis Birch 1952
Degree 2 pattern in TZ is due to past subduction
Upper & lower mantle regions cooled by subduction
Long-lived slabs in the transition region cool off the top of the lower mantle. Stagnant long-lived blobs in lower mantle do the same to the upper mantle.
Apparent continuity of tilted oS2 feature does not imply whole-mantle convection
Only 5 out of 27 oceanic hotspots occur outside of of the 3 % slow contour associated with ridges
IT IS CLEAR FROM BACKTRACKING OF EASTERN HEMISPHERE LIPS THAT ALL OF THEM FORMED FROM MANTLE THAT WAS UNDER SUPERCONTINENTS FOR LONG PERIODS OF TIME AND OVER REGIONS OF THE MANTLE THAT THEN BECOME SITES OF HOTPOT MAGMATISM AND OF SPREADING RIDGES. PACIFIC LIPS AND HOTSPOTS ALL STARTED ON RIDGES & TJs. Essentially all backtracked LIPs end up over today’s ridges.
110 km. The slowest [hottest?] regions follow the midoceanic ridges and subduction zones (backarc basins). Fig. 2 (middle). Shear velocity at a depth of 110 km. Total range in velocity is +-4.5%. Note the sinuous LVA following the Atlantic and Indian ocean ridges. Continental shields are very fast. Fig. 3 (bottom). Shear velocity at a depth of 210 km. Total range is +-4%. Note the sinuous LVAs in the Atlantic and Indian oceans, which are offset from the current ridges.