BASALT SOURCE EVOLUTION AT THE INTERSECTION OF THE SNAKE RIVER PLAIN-YELLOWSTONE AND HIGH LAVA PLAINS-NEWBERRY MAGMATIC PROVINCES

Variously described in the literature as part of the northern Basin & Range province, the southern Oregon Plateau, and the Owyhee Plateau, the Idaho-Oregon-Nevada border area (ION) serves as the geographic and chronologic initiation region for the mirror-image magmatic trends that extend northeast to Yellowstone and northwest to Newberry volcano, and is host to a continuous record of basalt production over the past 17 Ma. These basalts are not devoid of characteristics introduced via transport through and residence in heterogeneous crustal domains as evidenced by the fact that basaltic andesite compositions are present, albeit not dominant. Nevertheless, the basalt suite preserves evidence of first-order geochemical heterogeneities that reflect spatial and temporal variations in the mantle source reservoirs, variations that can only be adequately explained by considering the effects of lithosphere age, composition and architecture; pre- and post-mid Miocene plate interactions between the Pacific and North American systems; and a prolonged history of mantle depletion and enrichment events intimately linked to these geographic and physical complexities. Additional important “knowns” that impact on models of basalt genesis and evolution in the ION region are that it is a volcanic upland that has remained relatively undeformed over at least the past 16.5 Ma; is located within a region of transitional lithosphere; preserves a spectrum of basalt eruptive styles and processes from large volume flood basalt to small volume monogenetic basalt systems; preserves numerous alignments of basalt vents, often displaying within and between vent geochemical heterogeneities; preserves a basalt compositional suite unique to this portion of the western United States that includes voluminous high-Fe tholeiites, calc-alkaline basalts and basaltic andesites, LIL and HFS element depleted through enriched olivine tholeiites, and transitional to alkaline olivine basalts; and preserves basalt chemical and isotopic heterogeneities that vary as a function of age and that often are decoupled. Existing and new field, chronologic, major and trace element, and Sr, Nd, Pb, and Os isotope data will be discussed. This will serve as a basis for critical evaluation of current hypotheses and as a backdrop for new avenues of inquiry.