Genesis of flood basalts and Basin and Range volcanic rocks from Steens Mountain to the Malheur River Gorge, Oregon

Abstract

The middle and south forks of the Malheur River provide a unique mapping corridor connecting two flood-basalt successions-Steens basalt to the south and the basalt of Malheur Gorge to the north. Each contains chemically defined subtypes, which merge stratigraphically across the north-south length of the map area. The lowermost flows of Steens basalt are stratigraphically equivalent to the lowermost flows of the basalt of Malheur Gorge. The uppermost flows of Steens basalt pinch out in the map area, but are partly interbedded with the middle and uppermost flows of the basalt of Malheur Gorge, which continue to thicken northward. The upper part of the tholeiitic succession is interbedded with a group of previously unrecognized lavasthe Venator Ranch basalt flows. Tholeiitic volcanism ceased at ca. 15.3 Ma; the last tholeiitic unit erupted is the Hunter Creek basalt, which also thickens northward. Subsequent (younger than 15.3 Ma), more localized eruptions were dominated by calc-alkaline to mildly alkaline lavas associated with Basin and Range extension. Local uplift generated deep canyons, which were filled by andesitic lavas of the Keeney sequence (ca. 13-10 Ma). The final eruptive products include the Devine Canyon tuff (ca. 9.7 Ma), the Drinkwater basalt (ca. 6.9 Ma), and the Voltage flow (older than 32,000 yr B.P.). Major and trace element analyses demonstrate that (1) crystal fractionation was a universal process in the derivation of the

Bimodal volcanism of the High Lava Plains and Northwestern Basin and Range of Oregon: Distribution and tectonic implications of age‐progressive rhyolites

“…Basalts of a broadly similar age are associated with the $10.5 Ma emplacement of the Duck Butte Eruptive Center [Johnson and Grunder, 2000], Malheur caves area [Jordan et al, 2004], and the 12-9 Ma ''Southern Harney Basin Group'' [Brown et al, 1980] which is south of the proposed source location of the DCT (Figure 3d). In addition to these basalts, the more widely distributed $12.5-10 Ma Keeney Sequence flows crop out <45 km east of the source of the DCT [Hooper et al, 2002;Camp et al, 2003]. Only one basalt of this age crops out in the NWBR [Scarberry et al, 2010].…”

Field Mapping Investigation and Geochemical Analysis of Volcanic Units within the Dinner Creek Tuff Eruptive Center, Malheur County, Eastern Oregon

“…Vents and calderas for both the Clarno and John Day Formations occur to the north and west of the study area (McClaughery et al 2009a;McClaughery et al 2009b Camp et al 2003). Radiometric ages for the outcrops at Steens Mountain are ~24 -17 Ma (Langer, 1991).…”

A molecular phylogeny of aquatic gastropods provides a new perspective on biogeographic history of the Snake River Region

“…1) periodically spilled through the Malheur Gap to the Snake River Basin until becoming blocked by the Voltage basalt flow ca. 32 Ka (Camp et al, 2003;Gehr and Newman, 1978) and also subsequently overflowed its sill during several Holocene high stands (Dugas, 1998). This prior zone of aquatic continuity would have provided ample opportunities for inter-basinal dispersal of these snail species, both of which currently straddle the local divide between these areas (Fig.…”