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Research about Idaho, Oregon, Washington

Source-linked reports with geographic coverage including Idaho, Oregon, Washington.

60 records · Page 4Linked to original sources
USGS1985

Genetic interpretation of lead-isotopic data from the Columbia River basalt group, Oregon, Washington, and Idaho

Lead-isotopic signatures of basalts from the Columbia River Basalt Group of central Oregon, Washington, and western Idaho, and of the high-alumina olivine basalts from southeastern Oregon plot mostly in the field of Pb-isotopic data from volcanic rocks of the Cascade Range. In contrast to the mid-ocean ridge basalts (MORB), the Pb-isotopic data for several of the formations form small, tight clusters, and the Nd- and Sr-isotopic data show discrete variation between these basalt groups. Pseudoisochrons are not observed. A single model will account for the observed isotopic and trace-element data from samples from most of the Columbia River Basalt Group. This model calls for partial melting of the convecting oceanic-type mantle and mixing with, or contamination by, fluids derived from continental-derived sediments. It requires that crustal components are not only subducted along the trench, but that they are also transported in the low-velocity zone of the mantle at least 400 km behind the active volcanic arc into the back-arc environment represented by the Columbia Plateaus province. Lead isotopes in the Saddle Mountains Basalt, the youngest formation, suggest that these magmas were formed by partial melting of a 2.6-b.y.-old subcontinental lithosphere that extends as far west as south-central Washington near Ice Harbor Dam. The source material for these flows is characterized by high Th/U, Th/Pb, Rb/Sr, and Nd/Sm ratios and light REE enrichment. An additional component, presumably granitic crust, is necessary to explain the Pb-isotopic data of the Umatilla and perhaps the Pomona Members of the Saddle Mountains Basalt. This contamination model is supported by published δ 18 O data and petrological interpretation. Published studies of basalts from the Deccan Traps, the Tasmanian dolerites, the Snake River Group, and the volcanics of the Yellowstone Plateau province also suggest that melting of old subcontinental lithosphere beneath the continental crust may be an important process in basalt genesis on a global scale.

Idaho, Oregon, Washington↗
USGS1977

The Permian and Triassic Seven Devils Group, western Idaho and northeastern Oregon

Volcanogenic Permian and Triassic rocks in the Snake River Canyon of western Idaho and northeastern Oregon and in the adjacent Seven Devils Mountains of western Idaho are assigned to the Seven Devils Group. New rock-stratigraphic units are the Windy Ridge Formation of probable Early Permian age, the Hunsaker Creek Formation of Early Permian age, the Wild Sheep Creek Formation of Middle and Late Triassic age, and the Doyle Creek Formation of Late Triassic age. The Pittsburg Formation of former usage is abandoned, the rocks being renamed the Kurry Creek Member and assigned to the newly named Doyle Creek Formation. Overlying strata are the Martin Bridge Limestone of Late Triassic age, the Hurwal Formation of Late Triassic age, the Coon Hollow Formation of Middle(?) and Late Jurassic age, and the Columbia River Basalt Group of Miocene age. Underlying rocks are assemblages of metagabbro, metamorphosed quartz diorite, metabasalt, metadiabase, amphibolite, schist, mylonite, and phyllite that are exposed at The Oxbow of the Snake River near Oxbow, Oreg., along a 7-km segment of the Snake River south of Pittsburg Langing, and near the mouth of the Imnaha River. Gabbro, quartz diorite, and rare granodiorite plutons are concentrated in these assemblages, but some also cut the overlying strata. The Seven Devils Group is the result of volcanism, tectonism, and sedimentation that occurred within and near volcanic arcs at converging plate boundaries during the Permian and Triassic Periods. Large parts of these old arcs probably were consumed during later subduction, although direct evidence is lacking in the area considered here.

Idaho, Oregon, Washington↗
USGS1959

Fault zone along northern boundary of western Snake River Plain

Gravity, seismic, and geologic studies indicate that at least 9000 ft of aggregate throw along a zone of northwest-trending, high-angle faults has displaced the western Snake River Plain downward relative to highlands on the north. At least 5000 ft of movement occurred between the early and middle Pliocene. Progressively diminishing movement since then amounts to 4000 ft.

Idaho, Oregon, Washington↗