South Pacific superswell
South Pacific superswell | |
|---|---|
| Coordinates: 10°S 142°W / 10°S 142°W | |
| Age | |
The South Pacific superswell is a region of anomalously high seafloor topography several thousand kilometers in extent,[3] resulting in a shallow ocean region as a byproduct. There are many volcanoes associated with it,[3] often as chains of midplate volcanoes and seamounts.[4] It is believed to be related to a superplume which is a large upwelling of mantle material from the core–mantle boundary.[5][6]
Geography
The seafloor area of the superswell extends in northern and southern branches under French Polynesia between latitudes 10°N and 30°S and longitudes 130°W and 160°W and the seafloor change has a maximum height of 680 m (2,230 ft).[7]
Geology
The term superswell was first used to describe this area of several geophysical abnormalities in 1987.[8] These are:[4]
- Volcanoes
- The rate of volcanism is 3–4 times greater than other comparable oceanic crust.
- Active volcanoes include the Mehetiʻa island stratovolcano, the Adams, Arago, Macdonald, and Teahitiʻa seamounts.
- The age progression in the volcanic chains is often short with orientations not systematically related to the motion of the Pacific plate.
- In the area the mantle has slow seismic velocities.
- A positive ocean depth anomaly for the age of the crust has been characterised.[9]
- A negative geoid anomaly.[6]
Tectonics
The current best fit model for the dynamics of the South Pacific superplume requires a low viscosity asthenosphere, and a lower mantle a hundred times more viscous than the upper mantle.[6] Individual mantle plumes have been characterised above the superplume which extends from the bottom of the mantle to a depth of 1,000 km (620 mi).[10]
From seismic P wave data the superplume has been modelled in 3 dimensions, and its relationship in terms of the smaller and nearer to the surface mantle plumes that give rise to the current Arago, Macdonald, Marquesas, Rarotonga, Pitcairn, and Society hotspots has been explored. The Society, Arago, Macdonald, and Pitcairn hotspots are linked to the top of the superplume at 400–500 km (250–310 mi) depth and the Rarotonga hotspot at 1,000 km (620 mi), however there is no anomaly underneath the Marquesas hot spot in the upper mantle and the mantle transition zone.[10]
References
- ↑ Adam & Bonneville 2005, Figure 8.
- ↑ Adam & Bonneville 2005, Figure 3.
- 1 2 Clouard, Bonneville & Gillot 2003, p. 119.
- 1 2 Adam & Bonneville 2005, 2.1. Geophysical Characteristics.
- ↑ McNutt, M. K. (1998). "Superswells". Reviews of Geophysics. 36 (2): 211–244. Bibcode:1998RvGeo..36..211M. doi:10.1029/98RG00255.
- 1 2 3 Adam, C.; Yoshida, M.; Suetsugu, D.; Fukao, Y.; Cadio, C. (2014). "Geodynamic modeling of the South Pacific superswell". Physics of the Earth and Planetary Interiors. 229: 24–39. Bibcode:2014PEPI..229...24A. doi:10.1016/j.pepi.2013.12.014.
- ↑ Adam & Bonneville 2005, Abstract.
- ↑ Mcnutt, M.K.; Fischer, K.M. (1987). "The South Pacific superswell". In Keating, B.H. (ed.). Seamounts, islands, and atolls - Geophysical Monograph Series. Vol. 43. Washington D.C.: American Geophysical Union. pp. 25–34. ISBN 0875900682.
- ↑ Adam & Bonneville 2005, 2.2. Depth Anomaly.
- 1 2 Obayashi, M.; Yoshimitsu, J.; Sugioka, H.; Ito, A.; Isse, T.; Shiobara, H.; Reymond, D.; Suetsugu, D. (2016). "Mantle plumes beneath the South Pacific superswell revealed by finite frequency P tomography using regional seafloor and island data". Geophysical Research Letters. 43 (22): 11628–11634. Bibcode:2016GeoRL..4311628O. doi:10.1002/2016GL070793.
Sources
- Clouard, Valérie; Bonneville, Alain; Gillot, Pierre-Yves (2003). "The Tarava Seamounts: a newly characterized hotspot chain on the South Pacific Superswell". Earth and Planetary Science Letters. 207 (1–4): 117–130. Bibcode:2003E&PSL.207..117C. doi:10.1016/s0012-821x(02)01143-3.
- Adam, C.; Bonneville, A. (September 2005). "Extent of the South Pacific Superswell". Journal of Geophysical Research: Solid Earth. 110 (B9) B09408. Bibcode:2005JGRB..110.9408A. doi:10.1029/2004JB003465.