The Plume Hypothesis

The fractures in the lithospheric mantle reduce the pressure which causes the rocks of the plume head and the adjacent lithosphere to melt by decompression. 

Faure and T.M. Mensing, The Transantarctic Mountains Rocks, Ice, Meteorites and Water, DOI 10.1007/978-90-481-9390-5 15, Springer Science+Business Media B.V. 2010 

Even the elevation of the West Antarctic ice sheet exceeds 2,000 m above sea level in the area of the Whitmore Mountains and in parts of Marie Byrd Land (Image from http //www.ngdc.noaa. gov/mgg/global/global.html The site is maintained by carla.j. moore noaa.gov ) 

The basalt magma that is thereby produced intrudes the fractures and rises toward the surface. If the magma reaches the surface, it is erupted to form large plateaus of tholeiite basalt (e.g., the Mesa Range in northern Victoria Land). Part of the magma may also intrude near-surface rocks in the form of sills and dikes (e.g., sills of Ferrar Dolerite), and it may form large tabular 

The basalt plateans that form by the extrusion of lava through deep fractures in the crust may be tom apart when the rifts widen into oceans (e.g., the Kirwan Volcanics of Queen Mand Land and the Karoo Basalt of Southern Africa). Other examples of paired basalt plateaus that are now separated by an ocean are the Edendeka Basalt of Namibia and the Parana Basalt of Brazil as well as the diabase dikes of Liberia in West Africa and the diabase and basalt along the east coast of North America. Additional, examples were described by Faure (2001). 

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In summary, the following lines of evidence are generally invoked in favour of the plume hypothesis ... 

One of the principal difficulties with the plume hypothesis is that it has been used by a very large number of geoscientists to explain... 

The geochemical arguments used in support of the plume hypothesis are ambiguous and do not require the deep and shallow sources proposed by plume theorists. 

If the receptor is within an area source, or if emission rates do not vary markedly from one area source to another over most of the simulation area, the narrow-plume hypothesis can be used to consider only the variation in emission rates from each area source in the alongwind direction. Calculations are made as if from a series of infinite crosswind line sources whose emission rate is assigned from the area source emission rate directly upwind of the receptor at the distance of the line source. The ATDL model (22) accomplishes this for ground-level area sources. The RAM model (8) does this for ground-level or elevated area sources. 

Finally, the Tyrrhenian Sea (i.e. the focus of the mantle plume ascent) has a considerable depth (3700 m) and magmatism is not particularly voluminous. These characteristics do not fit a plume hypothesis. The suggestion that lack of magmatism is related to the great depth of the plume head is reasonable. However, the idea that such a deep body would be able to induce basin opening of the order of several hundred km, and to generate a collisional chain, is difficult to accept and needs much further refinement to avoid scepticism. 

Portions of the material described here are derived from a comprehensive airshed modeling program in which the authors are participating (17). This chapter focuses on urban airshed models however novel models have been proposed for urban air pollution problems of a more restricted scale— particularly, the prediction of concentrations in the vicinity of major local sources, notably freeways, airports, power plants, and refineries. In discussing plume and puff models earlier we pointed out one such class of models. Other work is the model proposed by Eschenroeder (18) to predict concentrations of inert species in the vicinity of roadways and the modeling of chemically reacting plumes, based on the Lagrangian similarity hypothesis, as presented by Friedlander and Seinfeld (19). 

Phosphorus and vanadium, which are typically present in seawater as dissolved oxyanion species, have been shown to exhibit systematic plume-particle P Fe and V Fe variations which differ from one ocean basin to another (e.g., Trefry and Metz, 1989 Feely et al., 1990). This has led to the hypothesis (Feely et al., 1998) that (i) plume P Fe and V Fe ratios may be directly linked to local deep-ocean dissolved phosphate concentrations and (ii) ridge-flank metalliferous sediments, preserved under oxic diagenesis, might faithfully record temporal variations in plume-particle P Fe... 

Hartmaim WK (1984) Moon origin the impact-trigger hypothesis. In Hartmann WK, Philhps RJ, Taylor GJ (eds) Origin of the Moon. Lunar and Planetary Institute, Houston, p 579-608 Hauri EH, Whitehead JA, Hart SR (1994) Fluid dynamic and geochemical aspects of entraimnent in mantle plumes. J Geophys Res 99 24275-24300... 

The hypothesis of plate tectonics attempted to provide an explanation on the hoop movement of the continents on the Earth s spherical surface. But, it also encountered the difficulty of driving force. So, it introduced other mechanisms such as the presence of asthenosphere and/or mantle plumes. 

This chapter moves toward an alternate objective and dwells primarily on the macroscopic imprint of radionuclide plumes. Specifically, we proceed on the hypothesis that quantifying such macroscopic characteristics as plume dimensionality, length, and persistence might provide useful information about the primary soil processes that control the fate and transport of radioactive contaminants and the overall risk posed by radionuclide contaminant plumes. This approach is termed a historical case analysis. It builds on the molecular approach described in earlier chapters and provides some guidance to how standard fate and transport models might be modified to reflect better mechanistic process understanding. Specifically, a historical case analysis sets some bounds on what fate and transport models should predict. 

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