Geology Department Colloquium, March 5th

Speaker: Anita Grunder, Oregon State University

Title: “Cause and effect of High Lava Plains volcanism, Oregon: Modification of the crust in an enigmatic tectonic setting”

Please join us: Tuesday, March 5th @ 11AM in Edmunds 130

Abstract:  The High Lava Plains of Oregon are an enigmatic volcanic province spanning from Miocene to Recent. Rhyolites of this bimodal province are successively younger to the west and so make a mirror image to the volcanic track of the Yellowstone hotspot. The High Lava Plains lie at the northwestern boundary of the Basin and Range extensional province and in the back arc of the Cascades, further complicating the tectonic setting. Although located in a continental setting, basalts of the High Lava Plains have affinity with oceanic rift  basalts. 

Exploration of the compositional variation of basalts and rhyolites in and around the High Lava Plains reveals evidence for creation of an increasingly mafic continental crust. Rising basalts modify the overlying crust by intrusion and by leaving mafic residua of differentiation as inferred from petrologic modeling. Protracted mafic intrusion also leads to crustal melting and more mafic crust yields more iron-rich rhyolites.  The basaltic magmatism is driven by shallow melting of the mantle welling up in the wake of the Juan de Fuca Plate as it rolls back and steepens beneath Cascadia.