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“ Hotspot ” correlations have been proposed with:

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“ Hotspot ” correlations have been proposed with:

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  1. 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)

  2. “Hotspot” correlations have been proposed with: • Faults, FZs, edges • Plate Extension • Diverging flow lines • Lack of anisotropy • Absence of subduction, cratons, anisotropy • Asthenosphere shear • Low seismic velocity and average velocity • Gradients in one parameter or another • Transition zone thickness; depth of 650 • Lower mantle • Far from tectonically active regions • Median value of wavespeed at CMB

  3. continued • Previous supercontinent positions • Duration of magmatism • Middle of LVZs • Edges of LVZs • No anomaly bands • Strong anisotropy • Absence of anisotropy • Gradients of some parameter

  4. Strong non-correlations • Transition zone (TZ) parameters (depths of 410 & 650; thickness) • Magma temperatures & TZ parameters • Wavespeeds at any depth • Helium content • Presence of any one of Courtillot’s criteria • Heatflow

  5. Extensional regions (red) correlate with magmatism (note that all volcanoes are in extensional regions, including on Nazca plate (JF,SF), Cameroon, Afar, Easter, Reunion, Atlantic etc.; also all ridges)

  6. Ritsema & Allen Edges of slabs?

  7. 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

  8. The Degree 2 Paradox THE TRANSITION REGION Region B “…the key to a number of geophysical problems…”Francis Birch 1952 Center of LLAMA 350 km Degree 2 Degree 2 pattern in TZ is due to past subduction Region C Upper & lower mantle regions cooled by subduction Scale change

  9. 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. High velocity Apparent continuity of tilted oS2 feature does not imply whole-mantle convection

  10. Only 5 out of 27 oceanic hotspots occur outside of of the 3 % slow contour associated with ridges

  11. 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.

  12. 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. 310 km

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