Trace element chracteristics of the Columbia River Basalts
Primary author: John Wolff
Co-author(s): Arron Steiner
Primary college/unit: Agricultural, Human and Natural Resource Sciences
Investigations in the Peter Hooper GeoAnalytical Laboratory (School of the Environment) are leading to a new and radical model for the origin of the Miocene (~16 million years ago) Columbia River flood basalts of the inland PNW. The flood basalts erupted from fissures mostly located in eastern WA and northeatern OR, and flowed westwards from there to create the Columbia and Oregon plateaux. The fissures were fed by magma-filled dikes at depth. Traditionally, these dikes were thought to directly tap sources of magma deep within Earth’s mantle. Our observations and geochemical analyses, especially of trace elements in the basalt lavas, point instead to a new interpretation where the dikes are feeding magma northwards from a volcanic hyper-system located around Vale, OR. This system extended 8 km depth down to the base of the crust and fed lava super-eruptions continuously and copiously for about 700,000 years. Towards the end of that time, activity gradually shifted to even more deadly explosive rhyolitic super-eruptions such as produced the Mascall tephra, which we have identified as far away as New Mexico. After a further 1 million years, volcanism reverted to basaltic to produce the youngest Columbia River lavas. These later lavas have unusual trace element features that suggest the new magmas re-occupied the old hyper-system, melting and re-cycling it. Our poster presents the evidence for (1) a centralized source for basalt magma, (2) its depth range, (3) switching between basaltic and explosive rhyolitic volcanism, and (4) rejuvenation of the system.