Mantle plume Did You Mean Mantle?

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A mantle plume is an upwelling of anomalously hot rock in the Earth's (or another planet's) mantle. Mantle plumes are thought to be the cause of volcanic centers known as hotspots and probably also have caused flood basalts.

In 1971, geophysicist, W. Jason Morgan proposed the theory of mantle plumes. In this theory, convection in the mantle slowly transports heat from the core to the Earth's surface. Plumes of hotter-than-average material rise through the mantle till it reaches the Earth's crust where it causes a hotspot. The plumes originate at a thermal boundary layer at the core-mantle boundary. The only such layer known to exist in the deep mantle is the coreantle boundary (D"), and thus Morgan-type plumes are generally assumed to rise from this layer. Due to the depth of such plumes, proving their existence is difficult and has led to some controversy over the theory.

Have to see

1 Evidence for the theory
2 Mantle plume locations
3 Clarification
4 Ore deposit association with mantle plume activity
5 References
6 External links

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Evidence for the theory

Density differences between a mantle plume and cooler material that surrounds it enable researchers to distinguish between the two. Seismic waves generated by large earthquakes are used to determine structure below the Earth’s surface. The waves slow down when they travel through low-density material.

By analyzing pressure pulses, or P-waves, a group of scientists at Princeton have identified 32 regions throughout the world where P-waves travel slower than average. They conclude that these areas are mantle plumes. The team used analysis of S-waves, another type of seismic wave generated by earthquakes, to determine that those plumes extend to the core-mantle boundary. (Montelli et al., 2004)

Computer modeling of the mantle plume theory shows that changes of temperature and chemical composition of rising plumes can lead to plumes of varying contours as opposed to the early conceptualization that plumes developed as a homogenous mushroom shape (Farnetani & Samuel, 2005).

Mantle plume locations

Two of the most well known locations that fit the mantle plume theory are Hawaii and Iceland as both have volcanic activity.

The P-wave and S-wave images show other locations that fit the mantle plume model. Ascension Island and St. Helena appear to originate from the same plume. Similarly, volcanic activity in the Azores and Canary Islands branch from a single trunk.

South of Java and in the Coral Sea, the images show possible formation of future plumes that currently extend only halfway to the surface.

Clarification

In a 2004 paper, Don L. Anderson and James H. Natland write:

"Unfortunately, the terms hotspot and plume have become confused. In recent literature the terms are used interchangeably. A plume is a hypothetical mantle feature. A hotspot is a region of magmatism or elevation that has been deemed to be anomalous in some respect because of its volume or location. In the plume hypothesis, a hotspot is the surface manifestation of a plume, but the concepts are different; one is the presumed effect, and the other is the cause."

Ore deposit association with mantle plume activity

Nickel deposits
Copper deposits
Diamond deposits
Sulfide deposits
Gold deposits (to a lesser extent)

References

Anderson, Don L. & Natland, James H. (June 23, 2004). A brief history of the plume hypothesis and its competitors: Concept and controversy. Retrieved Sep. 15, 2004.
Montelli R, Nolet G, Dahlen FA, Masters G, Engdahl ER, Hung SH (2004). Finite-frequency tomography reveals a variety of plumes in the mantle. Science 303 (5656): 338-43. PMID 14657505
Farnetani, C.G., and H. Samuel. 2005. Beyond the thermal plume paradigm. Geophysical Research Letters 32(April 16):L07311. Abstract.

External links

MantlePlumes.org

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