The Findings of the Columbia River Study
Subduction occurs when one of the earth’s crustal plates is forced below another, causing it to be subsumed into the mantle. The Columbia River Province is located close to a subduction zone, in which the Pacific Plate is being forced below the North American continent. The study suggests that the eruption of the flood basalts was associated with the now-almost disappeared Farallon Plate, of which only fragments now remain.
Young, warm crust near the edge of the plate is relatively malleable and bends easily – creating a steep gradient. Dr Liu explained to Decoded Science how the colder, more rigid crust at the centre trapped molten rock beneath it, allowing pressure to build up. ‘The material below the central part of the slab … maintains a higher pressure. The final breakup of the slab is a competition of the pressure underneath the slab and the slab strength – pressure wins!’
The research doesn’t replace the theory of mantle plume formation for igneous provinces – Dr Liu noted, for example, that it could not be applied to the Deccan Traps because at the time of their formation they were located on a passive margin, where subduction did not occur.
Subduction Zones and Flood Basalts:Why is This New Theory Important?
The significance of the research lies in the fact that it’s the first time that the formation of a flood basalt has been linked to a subduction zone. While the findings may, in the future, be considered as an explanation for the formation of other large igneous provinces, it provides an additional explanation, rather than a replacement mechanism, for the development of flood basalts.
Liu, L. and Stegman, D. R. Origin of Columbia River flood basalt controlled by propagating rupture of the Farallon slab. (2012). Nature. Accessed February 19, 2012.
Hooper, P. R. et al. The Origin of the Columbia River Flood Basalt Province: Plume versus Nonplume Models. (2007). Geological Society of America. Accessed February 19, 2012.
United States Geological Survey. This Dynamic Earth. Accessed February 19, 2012.
Colling, A. et al. Earth and Life: The Dynamic Earth. (1997). The Open University.
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