Search USGS⌕ Search

Geology topics

E. H. Christiansen

Publications and source records attributed to E. H. Christiansen.

10 recordsLinked to original sources
USGS2012

Hotspot: the Snake River Geothermal Drilling Project--initial report

The Snake River volcanic province (SRP) overlies a thermal anomaly that extends deep into the mantle; it represents one of the highest heat flow provinces in North America. The primary goal of this project is to evaluate geothermal potential in three distinct settings: (1) Kimama site: inferred high sub-aquifer geothermal gradient associated with the intrusion of mafic magmas, (2) Kimberly site: a valley-margin setting where surface heat flow may be driven by the up-flow of hot fluids along buried caldera ringfault complexes, and (3) Mountain Home site: a more traditional fault-bounded basin with thick sedimentary cover. The Kimama hole, on the axial volcanic zone, penetrated 1912 m of basalt with minor intercalated sediment; no rhyolite basement was encountered. Temperatures are isothermal through the aquifer (to 960 m), then rise steeply on a super-conductive gradient to an estimated bottom hole temperature of ~98°C. The Kimberly hole is on the inferred margin of a buried rhyolite eruptive center, penetrated rhyolite with intercalated basalt and sediment to a TD of 1958 m. Temperatures are isothermal at 55-60°C below 400 m, suggesting an immense passive geothermal resource. The Mountain Home hole is located above the margin of a buried gravity high in the western SRP. It penetrates a thick section of basalt and lacustrine sediment overlying altered basalt flows, hyaloclastites, and volcanic sediments, with a TD of 1821 m. Artesian flow of geothermal water from 1745 m depth documents a power-grade resource that is now being explored in more detail. In-depth studies continue at all three sites, complemented by high-resolution gravity, magnetic, and seismic surveys, and by downhole geophysical logging.

Snake River↗
USGS2002

The oligocene Lund Tuff, Great Basin, USA: A very large volume monotonous intermediate

Unusual monotonous intermediate ignimbrites consist of phenocryst-rich dacite that occurs as very large volume (> 1000 km3) deposits that lack systematic compositional zonation, comagmatic rhyolite precursors, and underlying plinian beds. They are distinct from countless, usually smaller volume, zoned rhyolite-dacite-andesite deposits that are conventionally believed to have erupted from magma chambers in which thermal and compositional gradients were established because of sidewall crystallization and associated convective fractionation. Despite their great volume, or because of it, monotonous intermediates have received little attention. Documentation of the stratigraphy, composition, and geologic setting of the Lund Tuff - one of four monotonous intermediate tuffs in the middle-Tertiary Great Basin ignimbrite province - provides insight into its unusual origin and, by implication, the origin of other similar monotonous intermediates. The Lund Tuff is a single cooling unit with normal magnetic polarity whose volume likely exceeded 3000 km3. It was emplaced 29.02 ?? 0.04 Ma in and around the coeval White Rock caldera which has an unextended north-south diameter of about 50 km. The tuff is monotonous in that its phenocryst assemblage is virtually uniform throughout the deposit: plagioclase > quartz ??? hornblende > biotite > Fe-Ti oxides ??? sanidine > titanite, zircon, and apatite. However, ratios of phenocrysts vary by as much as an order of magnitude in a manner consistent with progressive crystallization in the pre-eruption chamber. A significant range in whole-rock chemical composition (e.g., 63-71 wt% SiO2) is poorly correlated with phenocryst abundance. These compositional attributes cannot have been caused wholly by winnowing of glass from phenocrysts during eruption, as has been suggested for the monotonous intermediate Fish Canyon Tuff. Pumice fragments are also crystal-rich, and chemically and mineralogically indistinguishable from bulk tuff. We postulate that convective mixing in a sill-like magma chamber precluded development of a zoned chamber with a rhyolitic top or of a zoned pyroclastic deposit. Chemical variations in the Lund Tuff are consistent with equilibrium crystallization of a parental dacitic magma followed by eruptive mixing of compositionally diverse crystals and high-silica rhyolite vitroclasts during evacuation and emplacement. This model contrasts with the more systematic withdrawal from a bottle-shaped chamber in which sidewall crystallization creates a marked vertical compositional gradient and a substantial volume of capping-evolved rhyolite magma. Eruption at exceptionally high discharge rates precluded development of an underlying plinian deposit. The generation of the monotonous intermediate Lund magma and others like it in the middle Tertiary of the western USA reflects an unusually high flux of mantle-derived mafic magma into unusually thick and warm crust above a subducting slab of oceanic lithosphere. ?? 2002 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗
USGS1993

Possible secondary apatite fission track age standard from altered volcanic ash beds in the middle Jurassic Carmel Formation, Southwestern Utah

Secondary age standards are valuable in intra- and interlaboratory calibration. At present very few such standards are available for fission track dating that is older than Tertiary. Several altered volcanic ash beds occur in the Middle Jurassic Carmel Formation in southwestern Utah. The formation was deposited in a shallow marine/sabhka environment. Near Gunlock, Utah, eight ash beds have been identified. Sanidines from one of the ash beds (GUN-F) give a single-crystal laser-probe 40Ar/39Ar age of 166.3??0.8 Ma (2??). Apatite and zircon fission track ages range from 152-185 Ma with typically 15-20 Ma errors (2??). Track densities in zircons are high and most grains are not countable. Apatites are fairly common in most of the ash beds and have reasonable track densities ranging between 1.2-1.5 ?? 106 tracks/cm2. Track length distributions in apatites are unimodal, have standard deviations <1??m, and mean track lengths of about 14-14.5 ??m. High Cl apatites (F:Cl:OH ratio of 39:33:28) are particularly abundant and large in ash GUN-F, and are fairly easy to concentrate, but the concentrates contain some siderite, most of which can be removed by sieving. GUN-F shows evidence of some reworking and detriaal contamination based on older single grain 40Ar/39Ar analyses and some rounding of grains, but the apatite population appears to be largely uncontaminated. At present BJK has approximately 12 of apatite separate from GUN-F. ?? 1993.

Nuclear Tracks and Radiation Measurements↗
USGS1989

Oligocene caldera complex and calc-alkaline tuffs and lavas of the Indian Peak volcanic field, Nevada and Utah

The Indian Peak volcanic field is representative of the more than 50,000 km 3 of ash-flow tuff and tens of calderas in the Great Basin that formed during the Oligocene-early Miocene "ignimbrite flareup" in southwestern North America. The field formed about 32 to 27 Ma in the southeastern Great Basin and consists of the centrally positioned Indian Peak caldera complex and a surrounding blanket of related ash-flow sheets distributed over an area of about 55,000 km 2 . The field has a volume on the order of 10,000 km 3 . A cluster of two obscure source areas and four calderas comprise the ∼80 x 120 km caldera complex. Only minor volumes of rhyolite and two pyroxene andesite lavas were extruded episodically throughout the lifetime of the magma system that formed the field, chiefly during its youth and old age. Six ash-flow sequences alternate between rhyolite and dacite in a volume ratio of about 1:8, and a culminating seventh is trachytic. The first, fourth, and sixth tuff units are of rhyolite that contains sparse to modest amounts of phenocrysts, chiefly plagioclase and biotite, and abundant lithic and pumice lapilli; these deposits are confined within the caldera complex and form multiple and compound cooling units that are normally zoned with respect to bulk chemical composition and crystal type, content, and size. The second, third, and fifth tuff sequences are of crystal-rich dacite that forms extensive simple cooling-unit outflow sheets and partial caldera fillings of compound cooling units. Each dacite unit contains similar amounts of plagioclase, biotite, hornblende, quartz, two pyroxenes, and Fe-Ti oxides; trace amounts of sanidine and titanite also occur in the youngest. Cognate inclusions in the dacites show only slight intra- and inter-unit differences in bulk chemical composition. The seventh eruptive sequence consists of several cooling units of trachydacite tuff containing small to modest amounts of plagioclase and two pyroxenes. These dominantly high-K calc-alkaline rocks are a record of the birth, maturation, and death of a large, open, continental magma system that was probably initiated and sustained by influx of mafic magma derived from a southward-migrating locus of magma production in the mantle. The small volumes of chemically diverse andesitic rocks were derived from separately evolving magma bodies but are modified representatives of the mantle power supply. Recurrent production of very large batches (some greater than 3,000 km 3 ) of quite uniform dacite magmas appears to have required combination of andesite magma and crustal silicic material in vigorously convecting chambers. Compositional data indicate that rhyolites are polygenetic. As the main locus of mantle magma production shifted southward, trachydacite magma could have been produced by fractionation of andesitic magma within the crust.

Nevada, Utah↗
USGS1983

The granite problem as exposed in the southern Snake Range, Nevada

A geochemically and mineralogically diverse group of granitoids is present within an area of 900 km2 in the southern Snake Range of eastern Nevada. The granitoids exposed range in age from Jurassic through Cretaceous to Oligocene and include two calcic intrusions, two different types of two-mica granites, and aplites. The younger intrusions appear to have been emplaced at progressively more shallow depths. All of these granitoid types are represented elsewhere in the eastern Great Basin, but the southern Snake Range is distinguished by the grouping of all these types within a relatively small area. The Jurassic calcic pluton of the Snake Creek-Williams Canyon area displays large and systematic chemical and mineralogical zonation over a horizontal distance of five km. Although major element variations in the pluton compare closely with Daly's average andesite-dacite-rhyolite over an SiO2 range of 63 to 76 percent, trace element (Rb, Sr, Ba) variations show that the zonation is the result of in situ fractional crystallization, with the formation of relatively mafic cumulates on at least one wall of the magma chamber. Models of trace element and isotopic data indicate that relatively little assimilation took place at the level of crystallization. Nonetheless, an initial 87Sr/86Sr value of 0.7071 and ??18O values of 10.2 to 12.2 permil suggest a lower crustal magma that was contaminated by upper crustal clastic sedimentary rocks before crystallization. The involvement of mantle-derived magmas in its genesis is difficult to rule out. Two other Jurassic plutons show isotopic and chemical similarities to the Snake Creek-Williams Canyon pluton. Cretaceous granites from eastern Nevada that contain phenocrystic muscovite are strongly peraluminous, and have high initial Sr-isotope ratios and other features characteristic of S-type granitoids. They were probably derived from Proterozoic metasediments and granite gneisses that comprise the middle crust of this region. Another group of granitoids (including the Tertiary aplites) show chemical, mineralogic, and isotopic characteristics intermediate between the first two groups and may have been derived by contamination of magmas from the lower crust by the midcrustal metasediments. ?? 1983 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1983

Preliminary assessment of the geochemistry and mineral favorability of the postorogenic granites of the southeastern Arabian Shield, Kingdom of Saudi Arabia

Chemical analyses of samples for 19 postorogenic plutons from the southeastern Arabian Shield show that these rocks have average potassium/rubidium ratios (162) and average rubidium/strontium ratios (11.8) characteristic of highly evolved granites. Most of the analyzed samples are peraluminous. Three plutons are physically similar in terms of shape and megascopic textural zonation to peralkaline complexes in the northeastern part of the Shield, but none of the samples from these plutons is peralkaline. However, these plutons do contain the least-evolved samples. Zinc, yttrium, uranium, thorium, and possibly copper, each occur in anomalously high concentrations in at least one pluton relative to contents typically cited for granite. The average regional concentrations of copper and zinc are anomalously high. These facts suggest at least a moderate potential for mineralization in the southeastern part of the Shield. Good correlations (r of 0.5 to 0.8) between uranium, thorium, yttrium, and rubidium and an excellent correlation (r=0.98) between uranium and radium-equivalent uranium suggest that secondary deposits of these elements are unlikely and that magmatic deposits, especially of a pegmatitic nature, are more likely. Concentrations of some major elements and several trace elements covary with sample location as measured by latitude and longitude. This fact is interpreted to reflect regional variations in the protolith that have been proposed on the basis of lead isotopic data. The chemical variations suggest a largely oceanic crustal component for granites in the southwestern part of the southeastern Shield and a largely continental crustal component to the northeast. Further quantitative analysis is recommended to verify and accurately delineate anomalous concentrations of trace elements. Trend surface analysis of all available data for postorogenic granites from the eastern Arabian Shield is suggested as a method for testing regional variations in the protolith that might control locations of highly favorable areas of ore deposition.

Open-File Report↗