Are ‘hot spots’ hot spots?

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractThe term 'hot spot' emerged in the 1960's from speculations that Hawaii might have its origins in an unusually hot source region in the mantle. It subsequently become widely used to refer to volcanic regions considered to be anomalous in the then-new plate tectonic paradigm. It carried with it the implication that volcanism a) is emplaced by a single, spatially restricted, mongenetic melt-delivery system, assumed to be a mantle plume, and b) that the source is unusually hot. This model has tended to be assumed a priori to be correct. Nevertheless, there are many geological ways of testing it, and a great deal of work has recently been done to do so. Two fundamental problems challenge this work. First is the difficulty of deciding a 'normal' mantle temperature against which to compare estimates. This is usually taken to be the source temperature of midocean ridge basalts (MORB). However, Earth's surface conduction layer is ~ 200 km thick, and such a norm is not appropriate if the lavas under investigation formed deeper than the 40-50 km source depth of MORB. Second, methods for estimating temperature suffer from ambiguity of interpretation with composition and partial melt, controversy regarding how they should be applied, lack of repeatability between studies using the same data, and insufficient precision to detect the 200-300˚C temperature variations postulated. Available methods include multiple seismological and petrological approaches, modelling bathymetry and topography, and measuring heat flow. Investigations have been carried out in many areas postulated to represent either (hot) plume heads or (hotter) tails. These include sections of the mid-ocean spreading ridge postulated to include ridge-centred plumes, the North Atlantic Igneous Province, Iceland, Hawaii, oceanic plateaus, and high-standing continental areas such as the Hoggar swell. Most volcanic regions that may reasonably be considered anomalous in the simple plate-tectonic paradigm have been built by volcanism distributed throughout hundreds, even thousand of kilometres, and as yet no unequivocal evidence has been produced that any of them have high temperature anomalies compared with average mantle temperature for the same (usually unknown) depth elsewhere. Critical investigation of the genesis processes of 'anomalous' volcanic regions would be encouraged if use of the term 'hot spot' were discontinued in favor of one that does not assume a postulated origin, but is a description of unequivocal, observed char...

Why Is Crustal Underplating Beneath Many Hot Spot Islands Anisotropic?

“…An outstanding paradox of the plume model is that heat flow does not correlate with bathymetric features according to simple thermal models (e.g., Crough, ). The lack of heat‐flow variation across hot spot swells (DeLaughter et al, ; Von Herzen et al, ) is inconsistent with thermal erosion at the base of the lithosphere, leaving the hot spot swell to be supported by buoyancy flux or compositional variations (Foulger, ; Stein & Stein, ). Similar conclusions can be drawn from correlations between residual topography and gravity in global‐ocean bathymetry (Crosby & McKenzie, ; Tondi et al, ).…”

Thermal evolution of the North Atlantic lithosphere: New constraints from magnetic anomaly inversion with a fractal magnetization model

“…To the north of the Charlie Gibbs Fracture Zone, high thermal anomalies do appear around Iceland, but neither Iceland itself nor the proximal Jan Mayen microcontinent and the Iceland transverse ridge (including the Greenland‐Iceland and Iceland‐Faeroe ridges, abbreviated as GIR and IFR, respectively) are anomalously hot, especially on the Z b map estimated from EMAG2. This may explain why Iceland shows no evidence for significantly higher temperatures associated with a mantle plume [ Stein and Stein , ] and leaves further speculations on whether the Icelandic lithosphere is rather colder than hotter [ Menke and Levin , ; Menke et al ., ; Foulger et al ., ], and whether Iceland is associated with a geochemical or a thermal anomaly [ Anderson , ; Foulger , ]. There are also other uncertainties and difficulties in interpreting estimated bottom of magnetic sources beneath Iceland, arising from a deep Moho serving likely as a local magnetic boundary, and from possible changes in the fractal parameter, in the Curie temperature due to a geochemical anomaly, and/or in the magnetic data specifications.…”

“…In this case, often only idealized geometries are taken. Surface‐heat‐flow measurements suffer from being only available at sparse and irregular locations and are relatively insensitive to deep temperature variations due to a long delay between a change in asthenosphere temperature and a measurable effect arriving at the surface [ Korenaga , ; Foulger , ]. Therefore, surface heat flow alone is not sufficient in inferring deep lithospheric temperature.…”

Destruction of the North China Craton: a perspective based on receiver function analysis

“…Elevated temperature is predicted to deepen the 410 km discontinuity from its global average value by ∼8 km/100 °C. For a plume with a 200–300 °C temperature anomaly, a downward deflection of ∼15–25 km is expected (Foulger, ). Our results indicate a significant deepening of both the 410 and 660 km discontinuities by around 15 km.…”