Sunday, January 2, 2011

Further confirmation of hotspot trace overprinting: the end of the "super swell"?

Jackson et al. (2010, p. 17) write 
When backtracked through time using the plate motion model of Wessel and Kroenke [2008], the Rurutu hot spot passed through the WESAM province in the region of Bayonnaise seamount, then its trajectory bent to the northwest with the production of the Gilbert chain (Figure 7). The Macdonald hot spot [Hémond et al., 1994] back-tracks through the ESAM, and the hot spot reconstruction model has the chain turning northeast through the Tokelau chain [see also Koppers and Staudigel, 2005]. The reconstructed path of the Rarotonga hot spot passes along the southern fringes of the Samoan hot spot and trends through the Enriched Mantle 1 (EM1) seamounts in the Western Pacific Seamount Province (WSPC [Koppers et al., 2003]). Lending credence to the plate reconstructions, each lineament exhibits isotopic affinities with its respective active hot spot [Konter et al., 2008]. In summary, evidence from plate motion models supports the hypothesis of a “hot spot highway”: Older volcanism left over from three earlier hot spots could be present in the Samoan region.
Their interpretation is in accord, almost fully, with my previous observations:

Long-lived melting anomalies" (Plate-Frames) "...three melting anomalies in the South Pacific are not only responsible for 20 Ma and younger island/seamounts, but also much older seamounts from the Tokelau, Gilbert, and Magellan seamounts to the northwest. Add in the Foundation and Austral seamounts as another melting anomaly trace -- that makes four semi-aligned "hotspots" in the region: Foundation --Foundation and Austral seamounts; Macdonald - part of Cook Islands and Tokelau seamounts; Cook - part of Cook Islands and Gilbert seamounts; Samoa - Samoan islands and Magellan seamounts."
Discussion of "Break-up spots..." (EPSL): "Available isotopic age dates from the Foundation, Austral, Cook, Tokelau, and Gilbert island-seamount chains, combined with kinematic plate-hotspot modelling, indicate that the five chains originated from three distinct melting anomalies (or “hotspots”) well before the onset of postulated intraplate oblique extension. The kinematic pattern produces the observed range of dates due to overlap of the resulting traces. The oblique extension mechanism may have enhanced volcanism, but it cannot be the sole explanation."
Discussion: “Non-hotspot volcano chains..."  (Plate-Frames): "The present alignment of the Cook and Austral chains is an apparent coincidence, in that the Gilbert and Tokelau chains can be explained as originating from the same melting anomaly responsible for the Cook and Austral chains. The older chains (Gilbert and Tokelau) parallel each other, but are nowhere near co-linear; they predate the observed alignment for dates since 50 Ma."
Four hotspot traces overprint in the South Pacific: Foundation-Austral, Macdonald-Austral, Cook, and Samoa. Their distinctions are apparent from older continuations, especially the first three and, possibly, the last. The overprint is a recent coincidence, but may have been repeated in the oldest most continuations of the traces, in, for example, the Magellans.
Could it be that the so-called "South Pacific super swell" is a fiction? Nevertheless, there could be a common origin for all four melting anomalies, back in the Early Cretaceous or before. But what?

Jackson, M. G., Hart, S. R., Konter, J. G., Koppers, A. A. P., Staudigel, H., Kurz, M. D., Blusztajn, J., & Sinton, J. M., 2010, Samoan hot spot track on a “hot spot highway”: Implications for mantle plumes and a deep Samoan mantle source, Geochemistry, Geophysics, Geosystems (G3), 11, Q12009, 24 PP., doi:10.1029/2010GC003232.

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