Geology Reports⌕ Search

Geology topics

George Walton Walker

Publications and source records attributed to George Walton Walker.

At least 19 recordsLinked to original sources
USGS1975

Geothermal significance of eastward increase in age of upper Cenozoic rhyolitic domes in southeastern Oregon

Rhyolitic domes, flows, and ash-flow tuffs of Miocene to Holocene age form an important part of the thick sequence of Cenozoic volcanic rocks that cover southeastern Oregon east of the Cascade Range. Rhyolitic domes 11-17 m.y. old are widespread, particularly in the easternmost part of the state and in adjacent parts of Idaho and Nevada. Domes younger than 11 m.y. occur principally in two 250-km-long belts that trend N. 75° W. On the basis of 47 K/Ar radiometric dates, the rhyolitic domes in and between these belts show a remarkably well defined monotonic age progression from less than 1 m.y. old in the west to about 10 m.y. old on the east. The progression in age of the domes is sufficiently well defined that the ages of the domes can be smoothly contoured and the age of most undated domes can be estimated to within 1 m.y. The age contours are oblique to the trend of the two belts; domes younger than 4 m.y. occur only in and near the northern belt. The rate of progression is about 1 cm/yr for domes younger than about 5 m.y. and 3 cm/yr for domes 5-10 m.y. old. The change in rate of progression about 5 m.y. ago is accompanied by a change in orientation of the age contours and in area of outcrop. Inferred vents for dated rhyolitic ash-flow tuffs younger than 10 m.y. are located in areas where domes are approximately the same age as the tuffs and thus also fit the age progression. Most electric-power-producing geothermal fields in the world occur in or proximal to areas of young silicic volcanic rocks. On the basis of the well-defined age progression of rhyolitic domes in southeastern Oregon, silicic intrusive bodies sufficiently young to be heat sources for geothermal systems are likely only in the vicinity of Newberry Volcano at the west end of the northern belt of domes.

Oregon↗
USGS1974

Some implications of late Cenozoic volcanism to geothermal potential in the High Lava Plains of south-central Oregon

Stratigraphic and volcanologic data obtained during reconnaissance mapping along the Brothers fault zone in the High Lava Plains of south-central Oregon (Walker and others, 1967; Greene and others, 1972) suggest a progressive decrease in age of eruption of silicic magmas from the Harney Basin westward to Newberry volcano and possibly beyond into the Cascade Range. South of the Brothers fault zone a separate, less well defined, parallel zone of silicic domes and flows extends westward from Beatys Butte; this zone also appears to show a decrease in age westward, although the time span apparently is shorter and the age decrease not as well documented. The apparent age progression and the obvious very young age and character of some of the silicic volcanic rocks at the western end of the zone is important in geologic evaluations of the geothermal potential of eastern Oregon. It suggests that igneous heat sources sufficiently young to have retained significant magmatic heat are most likely to occur at the western end of the zone. Geothermal energy associated with silicic volcanism is being explored or developed in several other parts of the world (White, 1965; Muffler and White, 1972; Grose, 1972). In areas of known geothermal potential, such as in New Zealand, Italy, Japan, and in North America at Yellowstone, the Jemez Mountains (N. Mex.), and probably the Geysers area of California, the age of silicic volcanism is very young, mostly less than a million years and commonly only a few tens or hundreds of thousands of years old, and the volume of silicic volcanism generally is large, in many places measured in terms of many cubic kilometers of magma. Because some domal masses at the west end of the Brothers fault zone are very young and some of the silicic volcanism along the zone was volumetrically large, the potential for magmatitic heat sources seems promising. To test the concept of an age progression in and along the Brothers fault zone, as determined from field geologic evidence, and to establish the absolute ages of some of the silicic volcanic rocks in and near this zone, several potassium argon ages have been determined on crystalline phases from rhyolitic, rhyodacitic, and dacitic domes and associated flows, on rhyolitic obsidian from chilled selvages on several domes and flows, and on crystals and glass from basal vitrophyre of small and large volume ash-flow tuffs erupted from centers spatially and probably genetically related to the Brothers fault zone.

Oregon↗
USGS1967

Mineral appraisal of the Harney Lake and Malheur Lake candidate areas of the Malheur National Wildlife Refuge, north-central Harney County, Oregon

The Harney Lake and Malheur Lake candidate areas are in the Malheur National Wildlife Refuge, north-central Harney County, Oreg. The two areas occupy the shallow center of the Harney Basin, a broad structural and physiographic depression filled by several varieties of silicic to mafic volcanic rocks, sedimentary rocks, and unconsolidated surficial deposits. Although some of the rocks in the Harney Basin are of Miocene age, all the rock in the two candidate areas are of Pliocene or younger age. Northwest-trending normal faults form prominent scarps in and near the two areas.

Oregon↗