Western Snake River Plain Research Articles

Thermal and tectonic implications of heat flow in the Eastern Snake River Plain, Idaho

Geothermal data from 248 wells and drill holes, a thermal model for the effects of the Snake Plain aquifer on observed heat flow, an estimate of the regional heat flow in the eastern Snake River Plain, a detailed moving source, regional thermal model, and a discussion of the origin and the relationship of the eastern and western halves of the Snake River Plain are included in this paper. In order to determine the thermal structure of the eastern Snake River Plain, an extensive geothermal gradient and heat flow survey was carried out. Data from 248 holes show high heat flow values along the margins but low values along the center because of effects of the extensive Snake Plain aquifer. Based on a thermal model of the aquifer, a heat budget was derived from which a mean heat flow for the eastern Snake River Plain of 190 m W m−2 was calculated. This value can be compared to observed values along the margins of 120 mW m−2 and two values in deep holes along the northeastern margin of 110 and 109 mW m−2. The areas of highest expected values, in the Island Park caldera region, have not been sampled by heat flow measurements, however. Based on the heat flow results from the eastern and the western Snake River Plain and other geophysical and geological data, a finite‐width moving‐source‐plane thermal model is developed for the Snake River Plain. Even though the geological and geophysical characteristics of the eastern and western Snake River Plain are somewhat different, they are attributed to the same moving heat source, and the spatial geological and geophysical differences are explained by different stages in a time‐related sequence of thermally driven geological and tectonic events. The Snake River Plain is due to a strong thermal source interacting with the crust with the resulting complete chemical reorganization of the crust. The major immediate driving mechanism is a thick mafic intrusive emplaced in the midlevels of the crust. Associated with this thermal event are regional uplift of a kilometer or so as the heating occurs, associated melting of the upper crust, and subsequent rapid subsidence of approximately 1/2 to 1 km because of the change in density of the crust and upper mantle section associated with the emplacement of the basic intrusive and the disruption of the granitic upper crust. After the heat source moves eastward, continued subsidence occurs due to cooling of the lithospheric section (similar to that seen for oceanic regions). Along with the subsidence and soon after completion of the extensive silicic volcanism, basalts began to be extruded. Thermal contraction also generates faulting on the sides and perhaps in the center of the hot spot track. The subsidence causes reversal of the dips of the silicic ash flows from their initial away‐from‐the‐source configuration, to the toward‐the‐source configuration observed in the Snake River Plain. Continued subsidence and cooling cause the formation of the basin which is then filled by sediments, causing additional subsidence due to isostatic adjustment (the western Snake River basin). Thus all aspects of the Snake River Plain‐Yellowstone region are consequences of a single thermal event, and all stages in the future history of the Yellowstone region and the past history of the western Snake River basin are represented by westward or eastward traverses (respectively) along the Snake River Plain.

Geothermal Research and Exploration in New Mexico: ABSTRACT

A Department of Energy (DOE)-sponsored evaluation of the hydrologic characteristics of New Mexico's low-temperature geothermal sites is being conducted. Over 40 areas have been designated for possible low-temperature geothermal application. There are nine areas with estimated temperatures of between 100 and 105°C, and three areas with estimated temperatures >= 150°C. Eight prospective high-temperature geothermal resource areas, where public knowledge of successful drilling is lacking, were designated for DOE by New Mexico researchers. Drilling on state and private lands is concentrated in the Lightning Dock and Radium Springs KGRA vicinities, west of Socorro, east of Las Cruces, east of the Jemez River, and in the Baca Loc. 1 KGRA. Drilling on federal land is concentrated in the Baca Loc. 1, Kilbourne Hole, Radium Springs, and Socorro Peak KGRAs. Geothermal research at Sandia Laboratories includes: (1) successful testing of a high-temperature borehole temperature-logging instrument, (2) development of an efficient continuous chain bit, and (3) continuation of the Magma Energy Research Project, which was recently involved in drilling into the Kilauea Iki lava lake. NMIMT has mapped a large, deep magma body and several shallow magma bodies in the crust of the Rio Grande rift near Socorro. The LASL Hot Dry Rock Geothermal Energy Project has yielded promising technical results; researchers are studying two out-of-state areas for possible hot dry rock demonstration sites: Stumpy Point-Wallops Island in Maryland, and the western Snake River Plain in Idaho. End_of_Article - Last_Page 761------------

Tectonic implications of the heat flow of the western Snake River Plain, Idaho

Heat-flow values within the western Snake River Plain average about 1.7 ..mu..cal/cm/sup 2/ sec, but even higher values are measured in granitic rocks along the margins of the Snake River Plain (2.5 ..mu..cal/cm/sup 2/ sec or higher). The heat-flow distribution is related to the combined effects of crustal thermal refraction and a large, transient crustal heat source. A regional model consistent with the heat-flow pattern and other geophysical and geological data is described which assumes the emplacement of a large heat source (mafic intrusion) under the western Snake River Plain about 10 to 15 m.y. ago. An anomaly of about 0.3 ..mu..cal/cm/sup 2/ sec is predicted over the center of the heat source at the present time. The timing of the emplacement of the heat source corresponds with the age of voluminous silicic volcanism in the western Snake River Plain. A time-progressive thermal model is presented for the Snake River Plain which is consistent with the time progression of silicic volcanism. Based on the model, higher regional heat-flow values are predicted for the eastern Snake River Plain. Confirmation of the high regional heat-flow values is not possible in the boreholes available (200 +- m deep) because of regional circulation ofmore » cold groundwater in the Snake Plain Aquifer. However, a close correlation between integrated crustal and upper mantle temperature and observed elevation changes along the axis of the Snake River Plain is strong support for the heat-flow model. The possibility of high heat flow in the eastern part of the Snake River Plain implies that the area may have significant geothermal potential in spite of the low surface heat flow. The regional aseismic warping observed in the eastern Snake River Plain can be interpreted as a thermal contraction phenomenon involving the crust and upper mantle.« less

Columbia/Snake River—Yellowstone magmatism in the context of Western U.S.A. Cenozoic geodynamics

An attempt is made to calculate the total volume of Middle Cenozoic to Recent igneous rocks in the Columbia—Snake River—Yellowstone region by adding geophysically-derived estimates of the amounts of mafic intrusion to published data on the volumes of volcanic rocks. Recently published radiometric ages allow comparison of rates of basaltic magmatism in these ensialic provinces with those along equivalent lengths of mid-oceanic ridge. The rates of total magmatic activity (extrusive and intrusive) during the genesis of the Columbia River Plateau, Western Snake River Plain and Eastern Snake River Plain—Yellowstone sub-provinces were equivalent to those of mid-oceanic ridges with spreading half-rates of 10, 3 and 0.3 cm per year, respectively. It is shown that the hypothesis that magmatism in this region is the product of a deep-mantle convective plume, situated at present beneath Yellowstone, does not explain adequately several features of the Snake River Plain and becomes untenable when applied to the province as a whole. It is proposed instead that all major post-Eocene tectonic and magmatic features of the western U.S.A., east of the Sierra Nevada and Cascades, are products of comparatively shallow-rooted diapiric upwelling in the mantle; triggered at about 40 m.y. by extraction of mafic silicate melt and volatiles from the Farallon lithospheric plate, subducted at a comparatively low angle beneath the North American plate. During the Oligocene the diapirism appears to have become concentrated beneath the present sites of the Great Basin and Columbia River Plateau. Subsequent annihilation of the Farallon plate by the northward-propagating San Andreas transform fault released the compressive stress field across the Great Basin diapir, so that its heat content could disperse largely through attenuation and melting of the sialic crust, rather than mantle partial fusion and basaltic magmatism. Conversely, constriction of the Columbia River Plateau diapir by the subduction zone to its west led to “run away” mantle fusion and massive production of basic magmas. At 10–13 m.y. the E-W zone of offset at 42–44°N between these diapirs was the sub-sialic analogue of a transform fault. Lateral shearing of uppermantle peridotite within this zone caused the partial fusion which was the source of Western Snake River Plain magmatism. Once established, this upper-mantle thermal disturbance became self-perpetuating and, as the North American plate drifted westward over it, generated the Eastern Snake River Plain—Yellowstone “hot spot track”. The constant position of this hot spot in the mantle, relative to that beneath Hawaii, during the last 10 m.y. or so may indicate that its roots now penetrate down into the mesosphere.

Interpretation of a gravity profile across the western Snake River Plain, Idaho

The gravity and magnetic anomalies over the western Snake River Plain suggest that the plain is underlain by a layer of dense magnetic rock that may be the Miocene Columbia River Basalt Group and by a thin upper crust. The western Snake River Plain may have formed as a rift in Miocene time in response to northeast lateral spreading with the accumulation of more than a kilometre of basalt in the rift. The plain apparently is now in approximate isostatic balance with adjoining highlands.

K-Ar dating, Quaternary and Neogene volcanic rocks of the Snake River Plain, Idaho

Ninety-eight K-Ar dates for lavas of the Snake River Plain (SRP) and vicinity provide calibration for the stratigraphic framework discussed by Malde and Powers (1962). The Idavada Volcanics, predominantly silicic volcanic rocks, are 9 to 13 m.y. old in the western SRP. Rocks of similar type and comparable stratigraphic position are 8 to 10 m.y. old in the central SRP and as young as 4 to 5 m.y. old in the eastern SRP. This time-transgressive silicic volcanic assemblage merges in the east with the silicic volcanic units erupted during the last 2 m.y. from Island Park, Yellowstone, and related volcanic centers. The Idaho Group, consisting of intercalated basalt flows and sedimentary deposits in the western half of the SRP, ranges in age from about 0.6 to 11.5 m.y. (71 refs.)

Seismic-Refraction Study of Crustal Structure between the Nevada Test Site and Boise, Idaho

In 1962 a series of reversed seismic-refraction profiles was established over a line 454 km long between Eureka, Nevada, and Boise, Idaho; and additional recordings of nuclear events at the Nevada Test Site were made along the profile to southern Idaho. Shot points for the reversed profiles were located near Eureka, Elko, and Mountain City, Nevada, and near Bruneau and Boise, Idaho. Interpretation of the refracted and reflected P events indicates: (1) The crust in the northern Basin and Range province consists of a 6.0-km/sec layer 19–24 km thick above a 6.7-km/sec layer 10–12 km thick. (2) Both the crust as a whole and the 6.7-km/ sec layer thicken abruptly at the boundary between the northern Basin and Range province and the western Snake River Plain. The 6.0-km/sec layer thins across this boundary and may be absent under the Snake River Plain. (3) The crust in the western Snake River Plain consists of a 5.2-km/sec layer 8–10 km thick over a 6.7-km/sec layer 33–38 km thick. (4) The upper mantle under both the northern Basin and Range province and the western Snake River Plain has a P velocity of about 7.9 km/ sec. Amplitudes of P n decrease with the inverse third power of distance and indicate that the upper mantle consists of highly absorptive material or contains a low-velocity layer immediately below the M discontinuity.

Patterned Ground in the Western Snake River Plain, Idaho, and Its Possible Cold-Climate Origin

A distinctive sorted pattern of soil mounds and stone pavement, which resembles patterned ground of cold regions, is widely distributed in southern Idaho on gravel fans, basaltic lava flows, and marginal rocky colluvium, as well as on some outcrops of lake beds and welded tuff. Soil mounds in flat areas are closely packed, monotonously uniform circular heaps 50–60 feet across and 3 feet high, but on slopes they are elliptical and lie in rows along paths of soil that trend downhill. Each mound is composed of a lens-shaped cap of silt about 18 inches thick, abruptly underlain by 1–2 feet of brown clay that rests on siliceous hardpan. Stone pavement that surrounds mounds in rocky places consists of a shallow layer of well-sorted stones derived from underlying parent rocks. It is marked by vertical sorting (large stones on smaller ones), by tabular stones turned on edge (commonly parallel to the pavement border), and by numerous broken stones—all encrusted with lichens. The pattern varies with local slope. A net pattern, consisting of pavement woven between equally spaced mounds on flat terrain, gradually lengthens into a striped pattern, consisting of alternate rows of soil and pavement on hillsides. Striped patterns are first perceptible on grades of 3 per cent, dominant on grades of 10 per cent, and still recognizable on grades of 50 per cent. The patterned ground could have formed under a periglacial climate during the late Pleistocene when mass-wasting was presumably favored by freeze and thaw of saturated soil, but this origin is based only on analogy with patterns in cold regions, and the evidence of age is inconclusive. If this opinion is correct, the cold aspect of the Pleistocene extended several hundred miles farther south than has been generally assumed.

Gravity and crustal structure in the western Snake River Plain, Idaho

A gravity survey was made over the western Snake River Plain, Idaho, during the summers of 1959 and 1960. The data were reduced to sea level and expressed as simple Bouguer gravity anomalies for an assumed density of 2.67 g/cm3. Three elongated, northwest-trending, en echelon gravity highs were defined by the survey. The largest high is about 150 km long and 40 km wide; its maximum amplitude is 70 mgal. Application of limiting-depth methods implies that the tops of the disturbing bodies can be no deeper than 5 km below sea level. Two-dimensional analyses, based on a density contrast of 0.3 g/cm3, indicate that the anomaly-causing bodies extend from near sea level to at least 6 km below sea level and possibly to as much as 18 km below sea level. The total mass excess of the disturbing bodies is estimated to be 1×1019 g, and the corresponding volume for material 0.3 g/cm3 more dense than the surrounding material is approximately 33,000 km3. If the highlands on either side of the plain are regionally compensated, the crust under the plain is probably undercompensated by an amount proportional to the local anomalous bodies.

Upper Cenozoic Stratigraphy of Western Snake River Plain, Idaho

The Snake River Plain west of Twin Falls, Idaho, contains a section of upper Cenozoic volcanic and detrital rocks several thousand feet thick. The rocks are entirely continental but extend below sea level, thereby demonstrating regional subsidence. Based partly on terminology of earlier classifications, these rocks are divided in this paper into four broad units: an unnamed sequence of Miocene age, the Idavada Volcanics, the Idaho Group, and the Snake River Group. The Miocene rocks include thick lava flows of basalt and layers of rhyolite, interbedded with sandstone, shale, and water-laid silicic pyroclastic material generally altered to yellow, gray, and brown clay. The rhyolite contains conspicuous phenocrysts of quartz, sanidine, and oligoclase, and locally hornblende and biotite. Several thousand feet of this unit is exposed in highlands north and south of the central lowland, where it is cut by gold-bearing veins and considerably disarranged by north-trending faults and folds. The Idavada Volcanics, locally more than 3000 feet thick, unconformably overlie the Miocene rocks and consist dominantly of nonmineralized silicic flows of welded ash and beds of vitric tuff. They rarely contain quartz or sanidine and contain no hornblende or biotite. The Idavada Volcanics form large parts of the uplands and are broken by northwest-trending faults that define the central lowland. For the most part, this unit is of early Pliocene age in the western Snake River Plain but contains fossils of middle Pliocene age in the eastern Snake River Plain. The Idaho Group, at least 3000 feet thick, occupies the central lowland, where the successively younger rocks usually lie in troughs bounded in part by the next older rocks. The group is divided, in ascending order, into the Poison Creek Formation (lower Pliocene), the Banbury Basalt (middle Pliocene), the Chalk Hills Formation (middle Pliocene), the Glenns Ferry Formation (upper Pliocene and lower Pleistocene), the Tuana Gravel (lower Pleistocene), the Bruneau Formation (middle Pleistocene), and the Black Mesa Gravel (middle Pleistocene). The Snake River Group, which crops out mostly in the eastern Snake River Plain, was formed during entrenchment of the present Snake River canyon. The group is subdivided into formations of comparatively local extent, which are from oldest to youngest: the Madson Basalt, the Sugar Bowl Gravel, the Thousand Springs Basalt, the Crowsnest Gravel, the Sand Springs Basalt, the Bancroft Springs Basalt, the Melon Gravel, and Recent basaltic lava flows.

Fault Zone along Northern Boundary of Western Snake River Plain, Idaho

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.

An Old Erosion Surface in Idaho: Its Age and Value as a Datum Plane

Previous articleNext article FreeAn Old Erosion Surface in Idaho: Its Age and Value as a Datum PlaneJoseph B. UmplebyJoseph B. Umpleby Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 20, Number 2Feb. - Mar., 1912 Article DOIhttps://doi.org/10.1086/621941 Views: 33Total views on this site Citations: 4Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Kelsey F. Wetzel, Jessica R. Stanley Linking exhumation, paleo-relief, and rift formation to magmatic processes in the western Snake River Plain, Idaho, using apatite (U-Th)/He thermochronology, Geosphere 18, no.22 (Feb 2022): 885–909.https://doi.org/10.1130/GES02453.1Jeff E. Larimer, Brian J. Yanites, William Phillips, Eric Mittelstaedt Late Miocene rejuvenation of central Idaho landscape evolution: A case for surface processes driven by plume-lithosphere interaction, Lithosphere 11, no.11 (Dec 2018): 59–72.https://doi.org/10.1130/L746.1Randall L. Gresens Extension of the telluride erosion surface to Washington State, and its regional and tectonic significance, Tectonophysics 79, no.3-43-4 (Nov 1981): 145–164.https://doi.org/10.1016/0040-1951(81)90111-6J. P. Buwalda THE AGE OF THE PAYETTE FORMATION AND THE OLD EROSION SURFACE IN IDAHO, Science 60, no.15641564 (Dec 1924): 572–573.https://doi.org/10.1126/science.60.1564.572