Shona hotspot

The Shona or Meteor hotspot is a volcanic hotspot located in the southern Atlantic Ocean. Its zig-zag-shaped hotspot track, a chain of seamounts and ridges, stretches from its current location at or near the southern end of the Mid-Atlantic Ridge to South Africa.

Hotspots
The Meteor hotspot is marked 27 on map.

Location

The present location of the hotspot is disputed. Hartnady & le Roex 1985 proposed a location below a small seamount, the "Shona Seamount" (54°30′S 6°00′W / 54.5°S 6.0°W), just west of the Mid-Atlantic Ridge.[1] This location was used by O'Connor & Duncan 1990. Morgan & Morgan 2007 however proposed 51°24′S 1°00′E / 51.4°S 1.0°E, the eastern end of the Shona Rise/Shona Ridge.[2] O'Connor et al. 2012 simply located the hotspot at 56°06′S 1°00′E / 56.1°S 1.0°E where its volcanic trail begin.[3]

Discovery

The hotspot was first proposed by Hartnady & le Roex 1985. They noted that the Meteor Rise and Cape Rise seamount chain (west of South Africa) could not be associated with the Bouvet hotspot and therefore predicted the existence of another hotspot near the southern end of the Mid-Atlantic Ridge. Hartnady and le Roex explained the peculiar zig-zag pattern of this seamount chain as the result of the hotspot crossing the Agulhas Falkland Fracture Zone (AFFZ, a system of ridges stretching across the South Atlantic; the Mid-Atlantic Ridge makes a 'jump' just south of the AFFZ).[4] The tracks of the Bouvet and Shona hotspots probably passed under the Agulhas Ridge (eastern part of the AFFZ) during the Mesozoic 80 to 69 Ma and supplied the ridge with excess material.[5]

Plume–Mid-ocean ridge interaction

Between 51°S and 52°S the mid-ocean ridge basalts (MORBs) of the Mid-Atlantic Ridge have a composition that is associated with hotspots.[2] Based on anomalously high Nb/Zr ratios in the southern end of the ridge, le Roex in 1987 suggested that the plume interacts with the ridge. Furthermore, inflated bathymetry and gravity coupled with increase in (La/Sm)n ratios (ratio of light rare-earth elements in MORBs) are indications that the plume is interacting with the ridge.[1] le Roex et al. 2010 analysed lavas dredged from the Shona Ridge System, the hotspot track formed by the Shona Rise, Meteor Rise, Agulhas Ridge, and Cape Rise, and concluded that those lavas are geochemically enriched compared to the MORBs, an indication that the Mid-Atlantic Ridge is interacting with a plume.[6]

References

Notes

  1. ^ a b Douglass, Schilling & Fontignie 1999, 3.3. Shona Region (49°-50°S), p. 2946
  2. ^ a b Morgan & Morgan 2007, pp. 17–18
  3. ^ O'Connor et al. 2012, Fig. 1, p. 1
  4. ^ Hartnady & Roex 1985, Abstract
  5. ^ Uenzelmann-Neben & Gohl 2004, Abstract; Influence of a hotspot, pp. 314-315
  6. ^ le Roex et al. 2010, Abstract

Sources

  • Douglass, J.; Schilling, J.-G.; Fontignie, D. (1999). "Plume-ridge interactions of the Discovery and Shona mantle plumes with the southern Mid-Atlantic Ridge (40°-55°S)". Journal of Geophysical Research. 104 (B2): 2941–2962. doi:10.1029/98JB02642.
  • Hartnady, C. J. H; le Roex, A.P., le (1985). "Southern Ocean hotspot tracks and the Cenozoic absolute motion of the African, Antarctic, and South American plates". Earth and Planetary Science Letters. 75 (2–3): 245–257. doi:10.1016/0012-821X(85)90106-2.
  • le Roex, A.; Class, C.; O’Connor, J.; Jokat, W. (2010). "Shona and Discovery Aseismic Ridge Systems, South Atlantic: Trace Element Evidence for Enriched Mantle Sources" (PDF). Journal of Petrology. 51 (10): 2089–2120. doi:10.1093/petrology/egq050. Retrieved May 2015. Check date values in: |accessdate= (help)
  • Morgan, W. J.; Morgan, J. P. (2007). "Plate velocities in hotspot reference frame: electronic supplement" (PDF). GSA Special Papers. 430. Retrieved May 2015. Check date values in: |accessdate= (help)
  • O'Connor, J. M.; Duncan, R. A. (1990). "Evolution of the Walvis Ridge‐Rio Grande Rise Hot Spot System: Implications for African and South American Plate motions over plumes" (PDF). Journal of Geophysical Research: Solid Earth. 95 (B11): 17475–17502. doi:10.1029/jb095ib11p17475. Archived from the original (PDF) on 2017-02-02. Retrieved May 2015. Check date values in: |accessdate= (help)
  • O'Connor, J. M.; Jokat, W.; le Roex, A. P.; Class, C.; Wijbrans, J. R.; Keßling, S.; Kuiper, K. F.; Nebel, O. N. (2012). "Hotspot trails in the South Atlantic controlled by plume and plate tectonic processes". Nature Geoscience. 5 (10): 735–738. doi:10.1038/ngeo1583. Retrieved May 2015. Check date values in: |accessdate= (help)
  • Uenzelmann-Neben, G.; Gohl, K. (2004). "The Agulhas Ridge, South Atlantic: the peculiar structure of a fracture zone" (PDF). Marine Geophysical Researches. 25 (3–4): 305–319. doi:10.1007/s11001-005-1338-8. Retrieved May 2015. Check date values in: |accessdate= (help)

Coordinates: 51°36′S 1°00′E / 51.6°S 1.0°E

Discovery Seamounts

Discovery Seamounts are a chain of seamounts in the Southern Atlantic Ocean, which include the Discovery Seamount. The seamounts lie 850 kilometres (530 mi) east of Gough Island and once rose above sea level. Various volcanic rocks as well as glacial dropstones and sediments have been dredged from the seamounts.

The Discovery Seamounts appear to be a volcanic seamount chain controlled by the Discovery hotspot, which had its starting point either in the ocean, Cretaceous kimberlite fields in southern Namibia or the Karoo-Ferrar large igneous province. The seamounts formed between 41 and 35 million years ago; presently the hotspot is thought to lie southwest of the seamounts, where there are geological anomalies in the Mid-Atlantic Ridge that may reflect the presence of a neighbouring hotspot.

Hotspot (geology)

In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.

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