There are a number of hypotheses surrounding the source of the magmas in the Columbia River Basalt Group. The first division lies between those who support the mantle plume hypothesis, suggesting the asthenospheric mantle is the main source (e.g. ) and those who support back arc extension and point to the mantle lithosphere as the main source (e.g. McDougall, 1976). Alternate hypotheses include primitive mantle or MORB-type mantle as the main source. In more recent literature, more support for the asthenospheric mantle source can be found.
Whether authors support the asthenosphere or the mantle lithosphere as the main source of the basalts, almost everyone agrees that there has been some sort of mixing or contamination of the source. This leads to another debate over the source component. Hypotheses include enriched mantle lithosphere, ancient subcontinental mantle lithosphere, oceanic crust, overlying continental crust, or contamination by crustal sediments entrained in the downgoing slab. Various means have been used to find support for each hypothesis including non-radiogenic isotopes, radiogenic isotopes and trace element data.
Next, I will review the techniques and results of radiogenic isotope studies.
A good place to start is a radiogenic isotope review,
or to know more specifics about isotope systems you can learn about rubidium-strontium,
samarium-neodymium, or rhenium-osmium.
If you're up to par on all your geochemistry, you can go directly to the Columbia River Flood Basalt data pages.
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