Documenting Mantle and Crustal Contributions to Flood Basalt Magmatism via Computational Modeling of the Steens Basalt, Southeast Oregon

Sylvana Bendaña
May 2014

Purpose and Introduction

Flood basalts are large terrestrial, volcanic events that occur within a geologically short period of time (a few million years) and profoundly affect climate, topography, and flora and fauna (Hofmann et al. 1997; Self et al. 2006). Due to the large extrusive and intrusive magmatic volumes, an important question emerges: what is the mass balance between crustal (assimilation) and mantle (mixing/magma recharge) input and does this change systematically with time? At the Steens Mountain in SE Oregon, a major basin-range fault scarp provides almost 2000m of relief over the Alvord Desert, exposing one of the world’s thickest single exposure of Tertiary basalt (Johnson et al., 1998). Two distinct sets of Steens Basalt, collectively comprised of over 200 fresh lava flows, have been identified: Lower Steens is composed of more primitive flows that contrast with more compositionally evolved Upper Steens flows higher in the stratigraphic column. These compositional distinctions lead to the hypothesis that the Lower Steens magmatic system was dominated by magma recharge whereas Upper Steens was dominated by crustal assimilation. I propose to test this hypothesis via collection of whole rock elemental and isotopic data, and computational modeling using Energy-Constrained Recharge Assimilation-Fractional Crystallization (EC-RAFC; Bohrson & Spera, 2001).

Full Thesis Proposal (PDF format)