Events

A special seminar cohosted by the University of Texas Institute for Geophysics and the Bureau of Economic Geology.

Speaker: Gene Humphreys, Professor, Department of Geological Sciences, University of Oregon

Host: Thorsten Becker

Title: The Columbia River flood basalts– plume-triggered delamination and lithospheric reconstruction

Abstract: The Columbia River flood basalts present the interesting case of Yellowstone plume interacting with both subducting slab and North American lithosphere. The flood basalt’s eruptive distribution and intensity were strongly controlled by a piece of plume-destabilized lithosphere. In particular, this lithosphere delaminated when Yellowstone melt separated it from North America, and the delaminating lithosphere drew Yellowstone plume (and uplift and volcanism) rapidly northward. The uplift and lithospheric weakening caused crustal extension (gravitational collapse), which in turn enabled abundant diking and intense volcanism.

The first stage of continental construction occurs with addition of basalt to the crust; subsequent melting can segregate the basalt into granitic rock and residuum, and the residuum can eventually sink back into the mantle. As it turns out, the delamination removed lithosphere from beneath an older (Cretaceous) granite-residuum pair, allowing the residuum to sink. This drove uplift of the granitic Wallowa batholith, and the evacuated lower crust drove crustal flow into the volume beneath the batholith.

Maybe the main lesson here is that plumes and lithospheres are each gravitationally unstable, and in an inherently complicated continental environment, many interactive gravitationally unstable processes are likely to occur and even accentuate each other.