Search by property

From Open Energy Information

This page provides a simple browsing interface for finding entities described by a property and a named value. Other available search interfaces include the page property search, and the ask query builder.

Search by property

A list of values that have the property "Abstract" assigned.

Showing below up to 50 results starting with #51.

View (previous 50 | next 50) (20 | 50 | 100 | 250 | 500)


    

List of results

  • 40 C.F.R. § 124.12, current through August 14, 2014.  +
  • 40 C.F.R. § 124.3, current through August 14, 2014.  +
  • 40 C.F.R. § 124.6, current through August 14, 2014.  +
  • 40 C.F.R. § 124.7, current through August 14, 2014.  +
  • 40 C.F.R. § 280 (2015): These regulations outline requirements for Underground Storage Tank (UST) systems).  +
  • 40 CFR § 261, current through August 7, 2014.  +
  • 40Ar/39Ar ages for rocks from the Valles c
    40Ar/39Ar ages for rocks from the Valles caldera of New Mexico imply that resurgent uplift of the caldera floor occurred within 27 &plusmin; 27 k.y. of caldera collapse. Redondo Peak, part of the resurgent dome of the Valles caldera, was uplifted at least 1000 m above the surrounding caldera floor during resurgence. The lower time constraint on resurgence is the eruption of the upper Bandelier Tuff, which occurred concurrently with collapse of the Valles caldera. The upper time constraint is the emplacement of the oldest post-collapse ring fracture dome complex, Cerro del Medio, which displays no apparent faulting or deformation due to resurgence. 40Ar/39Ar dating places these time constraints at 1.256 &plusmin; 0.010 Ma (2�) for the upper Bandelier Tuff and 1.229 &plusmin; 0.017 Ma for Cerro del Medio. Therefore, resurgent uplift of the Valles caldera resurgent dome occurred at an average rate of ~3.7 cm/yr and probably not less than 1.9 cm/yr.The Deer Canyon and Redondo Creek Members of the Valles Rhyolite formation erupted prior to and during resurgence; both units stratigraphically overlie the upper Bandelier Tuff and are intricately interbedded with caldera fill sediments. Sanidine phenocrysts from the Deer Canyon Member yield 40Ar/39Ar single crystal laser fusion ages ranging from 1.229 &plusmin; 0.013 Ma to 1.283 &plusmin; 0.017 Ma (n=7). 40Ar/39Ar ages for the Redondo Creek Member range from 1.208 &plusmin; 0.017 Ma to 1.239 &plusmin; 0.017 Ma (n=2). With one exception from the Deer Canyon Member and one from the Redondo Creek Member, all ages obtained for these units are indistinguishable from the upper Bandelier Tuff at the 2� confidence interval, indicating that eruption of these post-collapse rhyolites probably commenced very soon after caldera formation. The possibility of excess argon in melt inclusions in post-collapse units was investigated. Although 40Ar/39Ar analysis of melt inclusion bearing quartz phenocrysts from the Deer Canyon Member demonstrates that some amount of excess argon resides in melt inclusions, there is no measurable effect on sanidine phenocrysts.Whole rock analyses of the Deer Canyon and Redondo Creek Members show that they are rhyolitic in composition and could have been part of the zoned upper Bandelier Tuff magma chamber. One possible scenario for their origin is one in which residual, zoned magma was left in the chamber after the eruption of the upper Bandelier Tuff and subsequently tapped after caldera collapse. This residual magma included the Deer Canyon rhyolites in the mid to upper parts of the felsic portion of the chamber and the Redondo Creek rhyolitic magma near the base. This model is supported by high Ba, Sr, and Ti content in the Redondo Creek Member, which is similar to enrichments observed in the least evolved upper Bandelier Tuff. In addition, magnetite/ilmenite pairs from the Redondo Creek Member yield eruption temperatures of 810 &plusmin; 6°C, which correspond to published temperatures for the latest erupted upper Bandelier Tuff.Megabreccia blocks are found surrounded by intracaldera upper Bandelier Tuff in the Valles caldera and provide insights into the events that were occurring during collapse. The distribution and sources of intracaldera megabreccia blocks are highly variable. 40Ar/39Ar ages of selected megabreccia blocks indicate that they are composed of older pre-caldera units that include the lower Bandelier Tuff (1.68 &plusmin; 0.03 Ma), and a dacitic tuff dated at 8.205 &plusmin; 0.083 Ma. The ages of these blocks and their field relationships suggest that they were emplaced due to catastrophic sliding of oversteepened caldera walls during and immediately after collapse.
    lls during and immediately after collapse.  +
  • 55,246 bottom hole temperature (BHT) value
    55,246 bottom hole temperature (BHT) values from petroleum exploration well logs of 28,260 wells have been used to estimate geothermal gradients in Alberta. A general decrease in geothermal gradient towards the east is apparent. High gradient areas occur in the Hinton - Edson area of west central Alberta, in the Fort McMurray area of northeast Alberta, in the Steen River area of northwest Alberta, and at the northwest corner of the province. Comparison with gravity, aeromagnetic and relief maps indicates close correspondence between topographic features and geothermal gradients. It is suggested that subsurface temperature distribution in Alberta is strongly influenced by groundwater motion.
    strongly influenced by groundwater motion.  +
  • A "retail electric utility" is any person
    A "retail electric utility" is any person or agency that operates, maintains, or controls a facility to provide a retail electric utility service. An electric utility must acquire a Certificate of Convenience and Necessity from the Public Utility Commission of Texas before providing an electric utility service.
    ore providing an electric utility service.  +
  • A 'nested graben' structural model, in whi
    A 'nested graben' structural model, in which multiple faults successively displace rocks downward to the deepest part of the basin, is supported by recent field geologic analysis and correlation of results to geophysical data for Dixie Valley. Aerial photographic analysis and detailed field mapping provide strong evidence for a deep graben separated from the ranges to the east and west by multiple normal faults that affect the Tertiary/Quaternary basin-fill sediments. Correlation with seismic reflection and gravity surveys shows that some faults recognized by minor displacements at the surface produce significant stratigraphic offsets at depth in basin-fill sediments and help to explain gravity gradients displaced basin- ward from the range-front. The concept of a complex series of faults (both synthetic and antithetic) separating the Stillwater Range from Dixie Valley allows for the possibility that the geothermal circulation encompasses multiple faults both inboard and outboard of the range-front fault. This geometry increases the exploration potential of the area by providing additional possibilities for fault-controlled permeability and larger volumes of permeable rocks.
    ity and larger volumes of permeable rocks.  +
  • A 16-station seismographic network, approx
    A 16-station seismographic network, approximately 40 km north-south by 30 km east-west, was installed in the Coso Range, California, in September 1975 as part of a geological and geophysical assessment of the geothermal resource potential of range. During the first 2 years of network operations, 4216 local earthquakes (0.5< or =m< or =3.9) defined zones of seismicity that strike radially outward from a Pleistocene rhyolite field located near the center of the Coso Range. Most earthquakes were located in zones showing a general northwest trend across the range. Six earthquake swarms occurred within the area that includes the rhyolite field. Fault plane solutions show regional north-south compression: earthquakes located in northwest striking zones generally had right lateral strike slip focal mechanisms, those in northeast striking zones left lateral strike slip focal mechanisms, and those in north-south striking zones both normal and strike slip focal mechanisms. Earthquake depths showed little variation across the Coso Range; the depth distribution is similar to that of several carefully studied segments of the central San Andreas fault. The b value calculated for the entire range is 0.99 +- 0.08. The rhyolite field has a significantly higher b value of 1.26 +- 0.16; if only the shallow events (depth <5 km) are used in the calculation, the b value for this area becomes even higher, 1.34 +- 0.24. The higher b values were interpreted as reflecting the existence of short average fault lengths (<5 km) within the rhyolite field. The seismic data and other data suggest that the fault system lying between the rhyolite field and the adjacent Coso Basin is an important tectonic boundary. Present information is insufficient to determine the geothermal production capability of this fault system, but is does suggest that the system is a good target for further exploration.
    is a good target for further exploration.  +
  • A 1:1,000,000 scale geothermal favorabilit
    A 1:1,000,000 scale geothermal favorability map of the Great Basin is currently being published through the Nevada Bureau of Mines and Geology (NBMG) and is now available at the web site (http://www.unr.edu/geothermal/geothermal_gis2. htm) of the Great Basin Center for Geothermal Energy (GBCGE). This map allows for separate assessment of the potential for magmatically heated and extensional-type geothermal systems. Added to the map are temperature gradient wells from the Southern Methodist Laboratory (SMU) and United States Geological Survey (USGS) databases, thermal springs and wells from the Geo-Heat Center-compiled geochemical database, and Quaternary faults from the USGS Quaternary Fault and Fold Database. A background 200-meter-resolution shaded digital topographic map provides reference for location. Logistic regression was used to calculate a scaled favorability index on the map for extensional-type geothermal systems based on data input from maps of 1) horizontal gravity gradient, 2) horizontal topographic gradient, 3) crustal dilation as measured by GPS stations, 4) crustal extension calculated from slip rates along Quaternary faults, 5) temperature gradient in the upper crust, and 6) the number, magnitude, and distance to historic earthquakes. These input 'evidence' maps were chosen in part for their ability to model geothermal potential independently of groundwater characteristics and lithologic permeabilities that influence the ability of hot springs or fumaroles to form. Coefficients for the favorability index were calculated outside of known regional aquifers and then used to predict favorability in the aquifer areas to assess the extent to which regional aquifers may be concealing geothermal activity. The results indicate that known geothermal systems ≤ 150°C are underrepresented in areas underlain by regional aquifers, in essence confirming that these regions are either concealing geothermal systems or are under-explored relative to their non-aquifer counterparts. The factors controlling the location of extensional geothermal systems appear to change somewhat across the Great Basin. In the westernmost Great Basin (Walker Lane), geothermal systems are associated with higher earthquakes frequencies than in regions to the east, where steep gravity and topographic gradients are more diagnostic. These differences likely reflect a change in the character of active crustal tectonics across the basin, from relatively strike-slip dominant in the west, where pull-apart basins exist, to more purely extensional in the central and eastern portions in the basin
    central and eastern portions in the basin  +
  • A 23-m.y.-old, fossil meteoric-hydrotherma
    A 23-m.y.-old, fossil meteoric-hydrothermal system in the Lake City caldera (11 _ 14 km) has been mapped out by measuring Δ 18O values of 300 rock and mineral samples. Δ 18O varies systematically throughout the caldera, reaching values as low as -2. Great topographic relief, regional tilting, and variable degrees of erosion within the caldera all combine to give us a very complete section through the hydrothermal system, from the surface down to a depth of more than 2000 m. The initial Δ 18O value of the caldera-fill Sunshine Peak Tuff was very uniform (+7.2 ± 0.1), making it easy to determine the exact amount of 18O depletion experienced by each sample during hydrothermal alteration. Also, we have excellent stratigraphic control on depths beneath the mid-Tertiary surface, quantitative information on mineralogical alteration products, and accurate data on the shape of the central resurgent intrusion, which was the principal 'heat engine' that drove the hydrothermal circulation. Major conclusions are: (1) Although pristine mid-Tertiary meteoric waters in this area had Δ 18O = -14, these fluids were 18O-shifted upward to about Δ18O = -8 to -5 prior to entering the shallow convective system associated with the resurgent intrusive rocks. Although there was undoubtedly radial inflow toward the caldera from all directions, the highly fractured Eureka Graben, southwest of the caldera, was probably the principal source of recharge groundwater for the Lake City system. (2) Fluid flow within the caldera was dominated by three major categories of permeable zones: the porous megabreccia units (which dip outward from the resurgent dome), vertical fractures and faults related to resurgence, and the caldera ring fault itself. All of these zones exhibit marked 18O depletions, and they are also typically intensely mineralogically altered. (3) The resurgent intrusive stock and its contact metamorphic aureole of hornfels both experienced water/rock ratios lower than the permeable zones; however, they have similarly low Δ 18O values because they were altered at higher temperatures. (4) Throughout the caldera, the Δ 18O of Sunshine Peak Tuff decreases with increasing depth (about 6 per mil/km), indicative of a shallow thermal gradient, typical of a convective hydrothermal system. The near-surface portion of this gradient was controlled by the temperature drop associated with boiling in the uprising fluid. (5) Deeply circulating meteoric water rose along permeable ring fractures 3 to 5 km beneath the mid-Tertiary surface. These fluids were drawn into the shallow convective system through the lower, porous, megabreccia units. Near the resurgent intrusions, fluid flow was again directed upward where resurgence-related, near-vertical fractures intersect the megabreccia units.
    fractures intersect the megabreccia units.  +
  • A 2D reactive transport model of the Dixie
    A 2D reactive transport model of the Dixie Valley,Nevada, geothermal area was developed to assessfluid flow pathways and fluid rock interactionprocesses. Setting up the model includedspecification of the mineralogy of the different rockunits, the formulation of the corresponding mineraldissolution and precipitation reactions, the explicitdefinition of two major normal faults and thespecification of a dual continuum domain along theuppermost 1 km of one of these normal faults.The model was run using a range of permeabilitiesfor the dual continuum fault, whereas bulk rock fluidflow and thermal parameters were defined accordingto a previous flow simulation study performed byothers. Model results were tested against availablefield data such as chemical analysis of thermalsprings, isotherms inferred from geothermal wells,and results of the previous modeling study.Moreover, simulated chemical compositions for thegeothermal spring were combined with multicomponentgeothermometry to assess whether the modelreflects the observation that geothermal springs oftenare out of chemical equilibrium. Simulation resultsreveal that a minimum permeability of 10-12 m2 forthe spring-feeding fracture is needed to preserve thegeochemical signature of the reservoir. Thesimulations also suggest that the presence of suchsmall-scale spring-feeding fractures having anelevated permeability can significantly alter theshallow fluid flow regime of geothermal systems.
    w fluid flow regime of geothermal systems.  +
  • A 3-D surface seismic reflection survey, c
    A 3-D surface seismic reflection survey, covering an area of over 3 square miles, was conducted at the Rye Patch geothermal reservoir (Nevada) to explore the structural features that may control geothermal production in the area. In addition to the surface sources and receivers, a high-temperature three-component seismometer was deployed in a borehole at a depth of 3900 ft within the basement below the reservoir, which recorded the waves generated by all surface sources. A total of 1959 first-arrival travel times were determined out of 2134 possible traces. Two-dimensional ray tracing was performed to simulate wave propagation from the surface sources to the receiver at depth. Travel time differences between observed and calculated times were mapped to topographic changes in the elevation of the interface between the carbonate basement and the sedimentary and volcanic unit above. Results indicate the presence of two dominant geologic features. The first confirms the regional trend of the geologic units in the Basin and Range province with a north-south strike and dip to the west, as expected for normal faulting encountered in an extensional regime. The second is a local disturbance of this regional pattern in form of an elevation of the interface between the carbonate basement and the overlying sedimentary sequence, striking east-west. The geometry of the structure is corroborated by results from a seismic-reflection survey, and by results of tomographic studies conducted as part of the seismic survey. Seismic waves, generated from far-offset shots during the 3-D surface survey, exhibit a sudden decrease in amplitudes while propagating across the boundaries of the elevation high. This apparent boundary correlates spatially with the location of the Rye Patch fault as interpreted from the 3-D seismic reflection data. Finite-difference modeling of elastic wave propagation is performed to estimate the structural parameters of the fault. Questions to be answered are fault width, strike, dip, and strength, to make inferences about the nature of the fault and the geologic process that could have formed
    he geologic process that could have formed  +
  • A 3-D surface seismic reflection survey, c
    A 3-D surface seismic reflection survey, covering an area of over 7.7 km2, was conducted at the Rye Patch geothermal reservoir (Nevada, USA) to explore the structural features that may control geothermal production in the area. In addition to the surface sources and receivers, a high-temperature three-component seismometer was deployed in a borehole at a depth of 1250 m within the basement below the reservoir, which recorded the waves generated by all surface sources. The objective of this study was to determine the subsurface structure of the reservoir based on this surface-to-borehole dataset. A total of 1959 first-arrival travel times were determined out of 2134 possible traces. Two-dimensional ray tracing was performed to simulate wave propagation from the surface sources to the receiver at depth. The ray tracing was based on a 2-D laterally homogeneous velocity model derived from results of a vertical-seismic-profile (VSP) experiment recorded in the same well. The method is an approximation where it is assumed that differences in travel time between the observed and modeled data are caused by structural deviations from a homogeneously layered model as estimated by the VSP profile, and thus are mapped into topographic changes at depth. The results indicate, to first order, the presence of two dominant geologic features. The first observation is consistent with the regional trend of the geologic units in the Basin and Range province with a north-south strike and dip to the west, as expected for this area west of the Humboldt Thrust Range. The second is a local feature in the form of an east-west ridge. The geometry of the structure is corroborated by results from a seismic-reflection survey, and by results of a gravity survey conducted in the area above the reservoir.
    conducted in the area above the reservoir.  +
  • A 3-D surface seismic survey was conducted
    A 3-D surface seismic survey was conducted to explore the structure of the Rye Patch geothermal reservoir (Nevada), to determine if modern seismic techniques could be successfully applied in geothermal environments. Furthermore, it was intended to map the structural features which may control geothermal production in the reservoir. The seismic survey covered an area of 3.03 square miles and was designed with 12 north-south receiver lines and 25 east-west source lines. The receiver group interval was 100 feet and the receiver line spacing was 800 feet. The source interval was 100 feet while the source line spacing was 400 feet. The sources were comprised of 4 vibrator trucks arranged in a box array. Seismic processing involved, among other steps, the picking of over 700,000 of the possible one million traces to determine first arrival travel times, normal moveout correction, 3-D stack, deconvolution, time migration, and depth conversion. The final data set represents a 3-D cube of the subsurface structure in the reservoir. Additionally, the travel times were used to perform tomographic inversions for velocity estimates to support the findings of the surface seismic imaging. The results suggest the presence of at least one dominant fault responsible for the migration of fluids in the reservoir. Furthermore, it is suggested that this feature might be part of a fault system that includes a graben
    t of a fault system that includes a graben  +
  • A 30-day closed-loop circulation test of t
    A 30-day closed-loop circulation test of the Phase II Hot Dry Rock reservoir at Fenton Hill, New Mexico, was conducted to determine the thermal, hydraulic, chemical, and seismic characteristics of the reservoir in preparation for a long-term energy-extraction test. The Phase II heat-extraction loop was successfully tested with the injection of 37,000 m/sup 3/ of cold water and production of 23,300 m/sup 3/ of hot water. Up to 10 MW/sub t/ was extracted when the production flow rate reached 0.0139 m/sup 3//s at 192/degree/C. By the end of the test, the water-loss rate had decreased to 26% and a significant portion of the injected water was recovered; 66% during the test and an additional 20% during subsequent venting. Analysis of thermal, hydraulic, geochemical, tracer, and seismic data suggests the fractured volume of the reservoir was growing throughout the test. 19 refs., 64 figs., 19 tabs.
    out the test. 19 refs., 64 figs., 19 tabs.  +
  • A 3D magnetic inversion method using a con
    A 3D magnetic inversion method using a conjugate gradient method (CG method) was developed for constructing 3D magnetization models of a volcanic edifice and applied to aeromagnetic anomalies of Izu-Oshima Volcano surveyed in 1986 and in 1997. The calculated results of the 1986 data show that the volcanic edifice of Izu-Oshima Volcano has a mean magnetization intensity ranging from 10.4 to 12.1 A/m. The derived 3D magnetic structure shows low magnetization zones beneath the west-northwest of the western caldera rim, beneath the west-southwest of Mt. Mihara and beneath Mt. Shiroishi. These features may be related with demagnetizations, reflecting a high thermal state due to magma activities in the 1986 eruption. The comparison between 3D magnetization models in 1986 and in 1997, indicates meaningful changes beneath the C-craters erupted in 1986, suggesting a recovery process of demagnetizations and a considerable decrease of magnetization intensities in the foot of Mt. Futago, indicative of demagnetizations. A derived magnetization model including Izu-Oshima Volcano and its surrounding sea areas clarifies the submerged volcanic edifices around Izu-Oshima Island, and suggests that the old volcanic edifices of Fudeshima, Gyojyanoiwaya, and Okata Volcanoes have been affected by eastward migrations due to massive intrusions of a dike-like structure inferred at the base of Izu-Oshima Volcano.
    nferred at the base of Izu-Oshima Volcano.  +
  • A 3D modeling of the residual aeromagnetic
    A 3D modeling of the residual aeromagnetic anomalies of the area including the Phlegraean Volcanic District (PVD; Campi Flegrei caldera (CFc), and Ischia and Procida-Vivara islands) and two volcanic islands of the Ponza archipelago (Ventotene and S. Stefano) has been carried out. The observed residual anomalies have been reproduced with several large magnetized bodies located at 2-10 km depth in the crust. A volcanological interpretation has been made possible only for those bodies that have been constrained by geological, geothermal and other geophysical data. The magnetized structures associated with CFc and Ischia, Procida-Vivara, Ventotene and Santo Stefano islands, have been interpreted as igneous bodies that may be solidified intrusions or magma reservoirs. On the basis of magnetic data, volcanological and magmatological history and geothermal heat flux distribution, the existence of a partially solidified magma chamber is suggested at Ischia. A speculation shows that the magnetization intensity assumed for the magnetic bodies located at Procida and south-west of Ventotene matches quite well with the calculated composition of a cooled residual magma resulting from crystallization processes within a chamber.
    rystallization processes within a chamber.  +
  • A Certificate of Compliance is required for the development of utility facilities within the state.  +
  • A Miocene basanite dyke at Stanley, northw
    A Miocene basanite dyke at Stanley, northwestern Tasmania, Australia, displays well preserved peperite texture. The dyke is 2 m wide and has intruded basaltic breccia ("host sediment"). One contact of the dyke is fluidally shaped, and amoeboid apophyses 10-25 cm long extend into the host sediment, whereas the other contact is characterized by blocky peperite texture comprising tabular to wedge-shaped clasts up to 30 cm across separated by host sediment. The clasts have internal spherical fractures and some show splinter texture. Vesicles are common in the clasts, and those intersected by clast margins have been filled with sediment. The interior of the dyke comprises close-packed blocky peperite consisting of tabular, wedge-shaped and polyhedral clasts tens of centimetres across separated by host sediment. These clasts show well developed jigsaw-fit texture. The textures and structures in the basanite dyke are inferred to have formed in two stages: an earlier, hotter, apophysis-forming stage and a later, cooler, angular clast-forming stage, both of which occurred during the intrusion of magma into wet, poorly consolidated sediment in a shallow marine environment. During the apophysis-forming stage, the magma had relatively low viscosity and progressively displaced wet sediment. The wet sediment around the dyke was partly fluidized by vaporization of pore water. The angular clast-forming stage reflects a change in the rheological behaviour of the magma from ductile to brittle, most likely in response to decreasing temperature. The chilled parts of the dyke were subject to stress arising from cooling contraction and also from continued, pulsatory movement of hotter, still ductile magma in the interior of the dyke, resulting in brittle fragmentation. Brittle fragmentation was accompanied by movement of host sediment into the newly created open spaces, forming blocky peperite. Spherical fractures, splinter texture and sediment-filled vesicles formed during the angular clast-forming stage. Because the host sediment is texturally identical either side of the dyke, increasing magma viscosity as temperature decreased, combined with pulsatory intrusion, were evidently important in the production of the blocky peperite.
    in the production of the blocky peperite.  +
  • A Miocene submarine lava dome at Tate-iwa,
    A Miocene submarine lava dome at Tate-iwa, Atsumi, Yamagata, Japan, displays well-preserved primary morphological features. The dome currently rises above a wave-cut coastal platform and is 55 m high and 90-180 m across. It comprises a massive core and a lava lobe-hyaloclastite rim, both of which are composed of compositionally uniform, feldspar-phyric dacite (SiO2=64 wt.%). The boundary between these two zones is distinct but gradational. The massive core consists of homogeneous, coherent dacite and is characterized by flow banding along the margin and by columnar joints radiating from the centre to the margin. The lava lobe-hyaloclastite rim encircles the massive core and consists of a complex of 80-90% dacitic lava lobes and 10-20% hyaloclastite. The lava lobes are 1-6 m thick, 3-12 m wide and more than 5 m long. Each lobe consists of a radially columnar-jointed core and a glassy rim 10-30 cm thick. The hyaloclastite comprises polyhedral dacite clasts 5-100 cm across in a matrix of dacite fragments up to 5 mm across. The lava lobes and hyaloclastite have gradational contacts in places. Paleobathymetric studies based on foraminifera in sediment beneath the dome, and the K-Ar age of the dome, suggest that it was extruded in a middle-bathyal environment (1500-2000 m below sea level) at 12.9±0.6 Ma. The internal structures of the dome suggest that it formed by a combination of exogenous growth involving extrusions of small dacite lobes, and endogenous growth involving a continuous magma supply and simple expansion from the interior. The presence of small lava lobes along the rim suggests that the magma had relatively low viscosity at the time of extrusion, in spite of its high silica content. Magma temperatures calculated by two-pyroxene and Fe-Ti oxide geothermometers were 999-1042 and 957-1005°C, respectively. The inferred low viscosity may be attributed to the high temperature of the magma and/or a high confining pressure resulting from the deep-sea environment.
    e resulting from the deep-sea environment.  +
  • A Review focusing on the Least Developed Countries and Sub-Saharan Africa  +
  • A article that discusses Vermont's groundwater regulation.  +
  • A barometric pressure sensor produced for use in hot climates and designed for Aanderaa Automatic Weather Stations and Display Units.  +
  • A bathymetric survey of Kawah Ijen crater
    A bathymetric survey of Kawah Ijen crater lake was conducted by acoustic sounding in 1996 to compare the lake morphology with those measured in 1922, 1925 and 1938, and to calculate the present lake volume. Even though the lake experienced several hydrothermal eruptions, the maximum depth became shallower (182 m) than before (200 m), resulting in a reduced lake volume (3.0_107 m3). Fifty-two major and minor constituents including rare earth elements and polythionates (PT) of the lake waters at various depths were determined by ICP-AES, ICP-MS and HPLC, respectively. These ions except for several volatile elements are taken up by lake fringe through congruent dissolution of pyroclastics of Kawah Ijen volcano. Most ions are homogeneously distributed throughout the lake, although PT showed a considerable vertical variation. Rare earth elements (REE) in the Kawah Ijen water as well as those from other hyper-acidic crater lakes show distribution patterns likely due to the three rock dissolution (preferential, congruent and residual) types, and their logarithmic concentrations linearly depend upon the pH values of the lake waters. Using the PT degradation kinetics data, production rates of PT, injection rates of SO2 and H2S into the lake were estimated to be 114, 86 and 30 tons/day, respectively. Also travel time of the spring water at the Banyupahit Riverhead from Kawah Ijen was estimated to be 600-1000 days through the consideration of decreasing rates of PT. Molten sulfur stocks containing Sn, Cu, Bi sulfides and Pb-barite exposed on the inner crater slope were presumed to be extinct molten sulfur pools at the former lake bottom. This was strongly supported by the barite precipitation temperature estimated through the consideration of the temperature dependence of Pb-chlorocomplex formation.
    dependence of Pb-chlorocomplex formation.  +
  • A belt of moderate-temperature geothermal
    A belt of moderate-temperature geothermal activityruns east-west across central Alaska. Chena HotSprings (CHS) is one of several Interior Alaskan hotsprings in or near 55 Ma granites within Paleozoicmetamorphic rocks. CHS is located within the CHSpluton, a composite body of quartz diorite, tonalite,granodiorite, and granite of both mid-Cretaceous andEarly Tertiary ages. 40Ar/39Ar step heat analyses ofbiotite from the CHS pluton shows flat Tertiary agespectra (supporting previous studies that reported aTertiary age for the body); however, hornblendespectra show evidence for partial resets and suggest amagmatic age of about 90 Ma. The majority of theexposed CHS pluton displays features common toCretaceous (subduction-related) plutons elsewhere ininterior Alaska. The pluton is medium to coarsegrained,commonly hornblende and allanite-bearing,with intermediate to felsic compositions and low Rb-Y-Nb-U-Th concentrations. Small bodies ofmineralogically and texturally distinct syenograniteand alkali feldspar granite occur near the margins ofthe composite body. These rocks contain up to 8times as much U and 4 times as much Th and Rb asthe typical rocks of the CHS pluton, as is true of earlyTertiary (extension-related) granites elsewhere inInterior Alaska. DIGHEM airborne gamma raysurveys indicate that high U-Th anomalies spatiallycorrelate with outcrops of these chemically distinctgranites. Thus, we propose that most of the exposedCHS pluton is Cretaceous and is underlain by anU,Th-enriched Tertiary pluton with limited surfaceextent. This hypothetical body reset the argonisotopic systematics of biotite and partially reset thehornblende. We further propose that radioactivedecay of K, U and Th within the concealed Tertiarypluton is causing an anomalously high regionalgeothermal gradient, thereby providing the heat atCHS. The hydrothermal upwelling zone may occur ata fault zone junction and/or at the hypotheticalcontact between Cretaceous and Tertiary plutons.
    t between Cretaceous and Tertiary plutons.  +
  • A better understanding of active volcanic
    A better understanding of active volcanic areas in the United States through electromagnetic geophysical studies received foundation from the many surveys done for geothermal exploration in the 1970's. Investigations by governmental, industrial, and academic agencies include (but are not limited to) mapping of the Cascades. Long Valley/Mono area, the Jemez volcanic field, Yellowstone Park, and an area in Colorado. For one example - Mt. Konocti in the Mayacamas Mountains, California - gravity, magnetic, and seismic, as well as electromagnetic methods have all been used in an attempt to gain a better understanding of the subsurface structure. In each of these volcanic regions, anomalous zones were mapped. When conductive, these anomalies were interpreted to be correlated with hydrothermal activity and not to represent a magma chamber. Electrical and electromagnetic geophysical methods can offer valuable information in the understanding of volcanoes by being the method which is most sensitive to change in temperature and, therefore, can best map heat budget and hydrological character to aid in prediction of eruptions.
    aracter to aid in prediction of eruptions.  +
  • A borehole drilled at Fiumicino (Rome) dow
    A borehole drilled at Fiumicino (Rome) down to only 27 m depth in a zone where no gas emission at the surface was known, caused a gas blowout from a pressurized gas pocket confined beneath a clay cover. Gas slowly diffused from the borehole within superficial permeable sand. Seven persons living in three ground floor flats of a near building had to be hospitalized due to CO2 exposure. All the houses in the proximity were evacuated. At the request of the Fire Brigade two additional boreholes were drilled nearby, hoping that this could rapidly exhaust the gas stored underground. To the contrary the soil gas flux near houses increased and indoor CO2 air concentration rapidly rose to lethal values (15 to 30 vol.%). As a remediation we suggested to restore the continuity of the impervious gas cover by squeezing quick-setting cement into the formation through new boreholes to be drilled near the existing ones. Although the first cement squeeze reduced drastically the CO2 soil flux and indoor concentration, six additional squeezes had to be carried out in order to lower the gas emission below the gas hazard threshold. The gas was mostly made of CO2 (98 vol.%) with minor N2 and CH4. Its chemical and isotopic composition (Δ13CCO2 = - 1.55; 3He/4He = 0.314 Ra) is similar to that of the gas manifestations of Mts. Sabatini and Alban Hills volcanic areas. Though being somewhat contaminated by crustal and shallow organic volatiles, these gases likely have a component originated in the mantle, that beneath the volcanic Roman Comagmatic Province is probably deeply contaminated with crustal material. The Fiumicino gas blowout indicates that the area of Central Italy characterized by strong CO2 degassing extends westerly to include the Tyrrhenian coast.
    westerly to include the Tyrrhenian coast.  +
  • A borehole has been drilled to a depth of
    A borehole has been drilled to a depth of 1262 m (4141 ft) beneath the summit of Kilauea volcano, on the island of Hawaii. The purpose was to test predictions made from surface-based geophysical surveys and seek evidence of a hydrothermal system over a known magma body. Nearly all rocks penetrated by the borehole are olivine basalt, with minor amounts of olivine diabase, picrite diabase and olivine-poor basalt. While the rocks are petrographically uniform, their physical properties vary widely from flow to flow. Core samples have progressively more thermal and chemical alteration with increasing depth. The temperature distribution in the wellbore is strongly affected by fluid convection. The temperature distribution can be simulated by two-dimensional convection having half-cell dimensions of 700 by 700 m. However, the match is improved by assuming that heat transport takes place by conduction in the lower half, while convective heat transfer dominates the upper half.
    ve heat transfer dominates the upper half.  +
  • A boundary element model using Poly3D© has
    A boundary element model using Poly3D© has been developed to investigate the conditions in which the stress concentration below the floor of a borehole can cause tensile stress necessary to nucleate petal-centerline fractures. The remote stress state, borehole geometry, and traction boundary conditions on the borehole surface are taken from direct measurements in the 58A-10 borehole of the Coso Geothermal Field, CA in which the occurrence of petal-centerline fractures are confirmed by image logs. A sensitivity analysis revealed that outward directed traction boundary conditions on the borehole surface including weight on bit and excess drilling mud pressure suppress tensile stress below the borehole. Simulations of the potential for tension below the borehole floor due to remote stresses limited by the frictional strength of rock in the Earth's brittle crust reveal that petal-centerline fractures in vertical boreholes are favored in normal faulting environments. However, this behavior is highly sensitive to borehole deviation and deviation direction such that increased deviation towards SHmax increases tension by more than an order of magnitude over the vertical borehole in the stress state at the Coso Geothermal Field. These results demonstrate that the occurrence of petal-centerline fractures in cores or image logs of borehole walls constrain both the principal stress directions and to a lesser extent the magnitude of stresses in the shallow Crust.
    agnitude of stresses in the shallow Crust.  +
  • A boundary element model using Poly3D© has
    A boundary element model using Poly3D© has been developed to investigate the conditions in which the stress concentration below the floor of a borehole can cause tensile stress necessary to nucleate petal-centerline fractures. The remote stress state, borehole geometry, and traction boundary conditions on the borehole surface are taken from direct measurements in the 58A-10 borehole of the Coso Geothermal Field, CA in which the occurrence of petal-centerline fractures are confirmed by image logs. A sensitivity analysis revealed that outward directed traction boundary conditions on the borehole surface including weight on bit and excess drilling mud pressure suppress tensile stress below the borehole. Simulations of the potential for tension below the borehole floor due to remote stresses limited by the frictional strength of rock in the Earth’s brittle crust reveal that petal-centerline fractures in vertical boreholes are favored in normal faulting environments. However, this behavior is highly sensitive to borehole deviation and deviation direction such that increased deviation towards SHmax increases tension by more than an order of magnitude over the vertical borehole in the stress state at the Coso Geothermal Field. These results demonstrate that the occurrence of petal-centerline fractures in cores or image logs of borehole walls constrain both the principal stress directions and to a lesser extent the magnitude of stresses in the shallow Crust.
    agnitude of stresses in the shallow Crust.  +
  • A brief review of long run projections of demand for road transport suggests that problems related to road network congestion and greenhouse gas emissions are likely to become more pressing than they are now.  +
  • A broad outline of the habitat of hydrocar
    A broad outline of the habitat of hydrocarbons in the West Siberian basin is described. It comprises a number of hydrocarbon systems, each of which is characterised as having hydrocarbons in different phase states, and can be regarded as a standard for developing basic geological and geochemical indicators for the prediction of dry gas, wet gas, oil and gas condensate. It is considered that most of the hydrocarbons have been generated and accumulated very locally, and that lack of vertical migration has limited any significant distortion of the original vertical and regional genetic zones. From this zonation it is possible to demarcate the more prospective regions. It is shown that the large number of dry gas accumulations in the Albo-Cenomanian sands of northern West Siberia result from early biogenic transformation of in situ coaly material, which is now at the lignite to bituminous stage of maturation. Radiometric argon dating shows that structures were filled by Oligocene times, but modification of the geothermal regime during the Ice Age and by the continuing permafrost has caused reduction of gas volumes. Some of the gas accumulations have oil rims, and it is shown that both the oil and gas phases were of separate origin and emplacement. The condensates from the 'dry' gas of northern West Siberia are naphtenic. They are genetically related to the biogenic gases and not to the paraffinic wet gas and oil, with associated gas, of the Lower Cretaceous and Upper Jurassic of the central and southern provinces. A vertical and regional zonation of the hydrocarbon phases is established, which goes from shallow gas, through wet gas and oil with associated gas, to deeper gas condensate, and finally to dry gas. The exploration for gas condensates (with high condensate content) in the Lower Jurassic, Triassic and the Paleozoic series in the deeper parts of the West Siberian basin, is at an early stage.
    West Siberian basin, is at an early stage.  +
  • A calibrated Engineered Geothermal System
    A calibrated Engineered Geothermal System (EGS) exploration methodology is being developed using the Dixie Valley Geothermal Wellfield (DVGW) and its surroundings in central Nevada as a laboratory test site. The DVGW was chosen because in the public domain, it is a highly characterized Basin and Range site with considerable geoscience and well data.This paper presents the qualitative and quantitative geoscience assessment used to develop a baseline geothermal system conceptual model based on existing available data. This assessment includes the integration of geophysical, geological, and geochemical data sets coupled with subject matter expertise (SME), and geostatistical exploratory data analysis (EDA). The baseline model is then used to generate paired EGS favorability and trust maps from the integrated evaluation of the following three principal EGS parameters of interest: temperature, rock type, and stress, at depths from +1km to -4km above sea level. Trust maps provide a data reliability indicator. When coupled, the two maps provide an EGS favorability determination, a SME evaluation of the reliability of the underlying data used in this determination, and an indication where additional data may be required. For example, an area could be mapped as being highly favorable but the underlying supporting data used in the favorability determination is of low reliability.Statistical relationships among select geoscience parameters are also described. In part, these relationships have provided insight into which geoscience parameters may be used as a predictor of subsurface temperature and rock type. Calibration of the exploration assessment methodology is based on the cross-correlation of the aforementioned findings with known well results.This paper builds upon the progress report provided in Iovenitti et al. (2011a, 2011b) and presents additional details of the geoscience assessment, EDA, and baseline EGS favorability/trust maps. Finally, much of the data and the approach presented herein are also applicable to the exploration/development of the hydrothermal component of the geothermal system.
    hermal component of the geothermal system.  +
  • A characteristic temperature versus depth
    A characteristic temperature versus depth (T-D) profile is observed in various geothermal environments. Particular features of the T-D profile can be explained in terms of a simple time-dependent two-dimensional (x, z) hydrothermal model. In this model a hot fluid is constrained to flow along a thin aquifer buried at a depth l from the surface with conductive heat transfer into the rocks both above and below the aquifer. In many geothermal systems transient changes in the flow patterns occur whose thermal effects can be described in terms of this model. The mathematical representation is that of a layer of thickness l over a half-space with specified temperature on the surface and variable temperature along the interface. An approximate analytical solution is derived using the Laplace transform solution technique and compared to a numerical Fourier transform solution. This approximate analytical solution is computationally simple and can be expressed in terms of key parameters of the fluid flow system. These key parameters are useful in understanding and exploring the sometimes complex hydrology of geothermal systems. Because of the simple computational form, the solution is easily implemented in an inverse solution scheme. Two T-D profiles, one from the Oregon Cascade Range and one from Arizona, are forward and inverse modeled, respectively. Fluid flow, velocity, time since initiation of flow, and background gradient are estimated parameters.
    kground gradient are estimated parameters.  +
  • A checklist of requirements for a(n) (applicant) developer seeking to submit a Physical Alteration Permit.  +
  • A clear and comprehensive purpose and need
    A clear and comprehensive purpose and need statement is a critical component of any energy project. The purpose and need identifies why the Federal agency is responding to the project being proposed, and provides the foundations of a defensible National Environmental Policy Act of 1969 (NEPA) analysis process. The purpose and need statement is intended to drive the organization and structure of the entire environmental analysis, and may be the first thing scrutinized if there is opposition that results in litigation. Similar statements may be required for other local and state permitting processes, and the guidance in this best practice may be used for any type of energy-related purpose and need statement.
    energy-related purpose and need statement.  +
  • A close spatial relationship exists betwee
    A close spatial relationship exists between Quaternary borate deposits and moderate to high temperature (>=150oC) geothermal systems in the western part of the Great Basin. Similarly, a strong correlation exists between high concentrations of boron in groundwater and geothermal activity in the Great Basin. These relationships hae special significance for geothermal exploraion becauase ina number of cases, Quaternary surface borates occur without associated springs, and thus the borates can, and are, serving as a guide to locating otherwise blind geothermal systems. Using borates as an exploation guide, and with key assistance from remote sensing techniques, three new geothermal targets have been identified in west-central Nevada at Rhodes, Teels, and Columbus Salt Marhas (playas). In each of these playas, geothermometry data from springs and wells suggest the possible presence of geothermal reservoirs at depth. Borate minerals are typically bright white in color and are difficult to distinguish visually from more common chloride and sulfate evaporites. For exploration for borates to be practical, it is essential to have an efficient means of identifying them in teh field. Kratt et al., (2006) have developed such means using field spectroradiometers and remote sensing methods.
    troradiometers and remote sensing methods.  +
  • A closed-loop circulation test was conduct
    A closed-loop circulation test was conducted from 10 May to 14 July 1995 on the Hot Dry Rock (HDR) reservoir at Fenton Hill, New Mexico after a hiatus of nearly two years. Changes in heat transfer and reservoir volume were investigated and compared to previous circulation tests. Chemical tracers can be used to measure the volume of flow paths in hydrologic systems. Usually, tracers are used in low temperature situations, but the application to high temperature systems has been established for certain tracer compounds. During the 1995 flow testing at Fenton Hill, both a conservative and a non conservative tracer were injected into the reservoir in each of two separate experiments. The purpose was to determine the volume of the most direct flow paths and to estimate the total volume of fractures in the system. The results indicate a relatively static reservoir volume between June and July, yet with an increase in flow dispersion. It can be assumed that channeling of flow did not occur in the main body of the reservoir due to continuous operation. However, a new flow path adjacent to the injection well did develop, and its affect on reservoir flow was investigated using tracer technology. The tracer data collected during that period shows that there is a minor contribution of flow from a previously under-developed region of the HDR reservoir.
    der-developed region of the HDR reservoir.  +
  • A cluster of hot springs in Bakreswar geot
    A cluster of hot springs in Bakreswar geothermal area, which belongs to the Chotanagpur Gneissic Complex in the eastern part of Peninsular India, is characterised by varying temperature and similar chemical composition. Vertical electrical sounding (VES) investigations in and around Bakreswar reveal the presence of two to four prominent lithologic layers under prevailing hydrodynamic conditions. The intermediate weathered zone and the fractured rocks constitute a single aquifer system of varied hydraulic conductivity under water table condition. Lithology and groundwater conditions, as inferred from the VES, as well as hydrological studies, an in agreement with the nearby bore hole lithologs. Water table contours accompanied by VES findings of the region indicate that the occurrence and movement of groundwater take place mostly within the weathered and fractured rocks under unconfined condition. 1D interpretation of VES results reveals few promising groundwater potential zones in the eastern part of the region. Wenner resistivity profiling, coupled with VES and geological studies, indicates the presence of a nearly N-S striking buried fault providing passage for hot water to emerge in the form of springs. (C) 2000 Elsevier Science B.V. All rights reserved.
    Elsevier Science B.V. All rights reserved.  +
  • A collaborative effort among U. S. Departm
    A collaborative effort among U. S. Department of Energy sponsored remote sensing specialists and industry recently culminated in the acquisition of hyperspectral data over a new exploration target in Dixie Valley, Nevada, U. S. A. Related research at the Energy & Geoscience Institute is currently focused on mineralogy mapping at the outcrop level. This will be extended to piedmont and valley fill soils to detect soil mineral anomalies that may be related to buried structures and sinters. Spectral mineral end-members have been extracted and relative mineral abundance maps have been created. Papers and data from this project can be found at http://wwwS.egi.utah.edu under the geospatial data link.
    i.utah.edu under the geospatial data link.  +
  • A combination of available geological, geo
    A combination of available geological, geophysical and geochemical evidence indicates that significant parts, or components, of Archean Au-quartz vein, epithermal Au-Ag and Au skarn ore fluids were magnetically derived, and that Au. Ag and associated, enriched elements were also magnetically derived (e.g., Giggenbach, 1986; Henley and Hoffmann, 1987; Sillitoe, 1989; Sillitoe and Bonham, 1990; Spooner, 1991 a,b). There is a significant core of commonality in element occurrence in Archean Au-quartz vein, Archean Hemlo-type, epithermal Au-Ag and Au skarn systems which suggests a shared genetic process. For instance, 44% (n = 12) of 27 elements occur in more than seven of ten ore deposit subdivisions: Au, Ag, Fe, Cu, Pb, Zn, Hg, Mo, Sb, As, Te and S (nine metals; two metalloids; one non-metal). Addition of B and W gives 52% (n = 14) in more than five subdivisions. The frequency of occurrence of enriched chalcophile/siderophile elements is high at 85%; 23 out of 27. The converse is also high at 74% (23 of 31); all significant chalcophile/siderophile elements occur enriched in Archean Au-quartz vein, Archean Hemlo-type, epithermal Au-Ag and Au skarn deposits. However, if magma volatile saturation occurred after gravitational toss of magmatic sulphide melt/suspended solids, then Au, Ag and associated chalcophile elements would have been effectively removed from the magma because of known high sulphide-melt/silicate-magma partition coefficients of approximately 10(2)-10(4) (e.g., Au at approximately 3 X 10(4); Se at approximately 10(3)). Hence, it is proposed that Archean Au-quartz vein, Archean Hemlo-type, epithermal Au-Ag and Au skarn ore fluids derive their characteristic element enrichments by high-temperature fluid/vapour dissolution of magmatic sulphide-liquid droplets/solids (T < approximately 1010-1050-degrees-C) enriched in Au and associated elements (e.g.. 1-13 ppm Au in MORB sulphide globules; Mathez and Peach, 1989) in mafic/intermediate igneous compositions before sulphide loss. The key components of the mineralization enrichment process are sulphide melt/silicate magma partition, during which ore-grade Au concentrations can be produced from non-anomalous background Au abundances of approximately 1 ppb (enrichment factor = approximately 10(4)), high aqueous-phase sulphide solubilities at high temperatures (e.g.. Hemley et al., 1986; to 600-degrees-C), and selective Au precipitation. Support for this hypothesis is provided by: (a) the element association in Au skarns which shows 81% and 75% overlaps with associations in epithermal Au-Ag and Archean Au-quartz vein systems, respectively: (b) being able to explain enrichments of a variety of low-abundance elements simply because they are chalcophile (e.g.. Se, Tl; Sb, Hg, Bi, As, Te; Ni, Co, Cd, Pd, Pt; Mo, W as scheelite); and (c) being able to explain a tendency for certain large Au-Ag systems to occur associated with volatile-rich (e.g.. subduction zone magmas. 3-7 wt% H2O; sodic alkaline magmas, approximately 0.5-1 wt% H2O; C.f., approximately 0.1 wt% H2O in MORB). more mafic/intermediate magma compositions (e.g.. Au skarns, Meinert, 1989; Hollinger-McIntyre, approximately 995 tonnes Au; Ashanti, approximately 710 tonnes Au; Cripple Creek, approximately 590 tonnes. Au; Ladolam, approximately 570 tonnes Au; Porgera, approximately 4 10 tonnes Au; Kerr Addison-Chesterville, - 335 tonnes Au; Emperor, Fiji. approximately 120 tonnes Au). On the basis of well-defined igneous intrusive associations, the typical presence of H2O-CO2 low-salinity ore fluids. and particularly the presence of carbonate (delta C-13 = approximately 4.5 +/- 0.6 parts per thousand) and a chalcophile element association (Au-Ag-S-Fe-Cu-Pb-Zn-Mo-W-As-Sb-Bi-Te) which is very similar to those of Archean. Au-quartz vein. epithermal Au-Ag and Au skarn ore systems, a magmatic origin for Cordilleran Au-quartz vein ore systems may be assessed (e.g., Sierra Nevada Au province, California; approximately 3,150 tonnes Au; Clarke, 1970). This proposal can explain why Archean Au-quartz and, particularly. epithermal Au-Ag systems occur associated with several different magma series such as calc-alkaline, shoshonitic, sodic alkaline with and without Ti-Nb-Ta subduction depletions. and components of the Archean tonalite-trondhjemite-granodiorite (TTG) association. These series share a common property of being relatively volatile-rich, thus causing magnetic volatile saturation in more mafic compositions before loss of magmatic sulphide. This process is essentially unavoidable, and should have repeated in space and time. Implications for mineral exploration include a justification for-large-tonnage, low-grade. Au targets in, or related to, mafic/intermediate intrusions in Archean terrains (e.g., Moss Lake, N.W. Ontario; diorite hosted, > 65 mtonnes at approximately 1 g/tonne Au: > 65 tonnes Au) and a justification for evaluating mafic, sodic and potassic alkaline complexes.
    ic, sodic and potassic alkaline complexes.  +
  • A compact fully integrated sensor for meas
    A compact fully integrated sensor for measuring the wave and tide conditions. The 5218 sensor is designed to be mounted on the Aanderaa SeaGuard top-end plate or connected to SmartGuard using AiCaP CANbus or in other measurement systems using the RS-232 interface.
    rement systems using the RS-232 interface.  +
  • A comparative study concerning volcanologi
    A comparative study concerning volcanological, petrographic and geochemical aspects of Montefiascone Volcanic Complex has been carried out. This complex, together with those of Paleo-Bolsena, Bolsena and Latera, forms the Vulsini Volcanic District, located in the northernmost part of Roman Comagmatic Province. Four groups of lavas, belonging to Montefiascone Volcanic Complex, have been recognized on petrographic and geochemical grounds: Tephritic Leucitites (TEL), Leucite-Bearing Basanites (LBSN), Evolved Tephritic Leucitites (ETEL) and Leucititic Tephrites (LT). Lavas clearly show Ti and Nb anomalies, further supporting the genesis of these magmas from a subduction-related metasomatized mantle source. The majority of the lava erupted, comparable in volume with the pyroclastic products, appears to be of leucititic affinity, having suffered only a slight amount of differentiation. Major- and trace-element compositions very similar to those of ETEL and LT have been obtained from TEL and LBSN by means of simple mass balance and Rayleigh fractional crystallization model. According to petrographic observations, main liquidus phases are clinopyroxene, leucite, olivine and magnetite, and magmatic differentiation acts essentially by fractional crystallization. Eruptive activity is spread over a large area and the volcanic centres are aligned following NNW-SSE, WNW-ESE and E-W directions. Explosive activity, on the other hand, was mainly located at Montefiascone Caldera. The great abundance of nearly primary magmas in the area leads us to think that the structural setting was not suitable for developing a great, unique magma reservoir, but rather a series of small, elongated bodies.
    ather a series of small, elongated bodies.  +
  • A comparative work on the Vulsini calderas
    A comparative work on the Vulsini calderas has been carried out, fundamentally from volcanological field study, drilling and gravity anomalies data. On the basis of a detailed stratigraphy, four volcanic complexes have been recognized in the Vulsini Volcanic District from the oldest to the youngest: Paleo-Bolsena, Bolsena, Montefiascone and Latera, the latter two complexes having a contemporaneous evolution. In their activity, each complex gave rise to several little calderas caused by piecemeal collapses due to moderate-size explosive eruptions or coherent subsidence of a superficial piston-like block. Nevertheless, the extensional volcano-tectonic regime affecting this area could have accounted for as much of the total subsidence as the caldera-forming eruptions. Bolsena and Latera calderas, respectively 16 km and 8 km in average diameter, represent the main depressions of the Vulsini District and their topographic features are still well preserved. Several collapses forming the main poligenetic calderas of Bolsena and Latera are masked at present by the Bolsena Lake, the younger volcanic covering, the lacustrine deposits and erosion in a minor amount. Only the little Montefiascone and Vepe calderas, which represent the youngest collapses of the Vulsini area, have not been masked. Bolsena caldera could be considered a depression caused mostly by a subsidence hinged to the southwest, by down-sagging and by collapses which occurred after the most important explosive eruptions of the Paleo-Bolsena, Bolsena and Montefiascone volcanic complexes. Meanwhile, Latera caldera is mostly due to a piecemeal collapse linked to several moderate-size ignimbrite units which were emplaced throughout the explosive activity of the Latera complex. Therefore, the Vulsinian calderas did not form by catastrophic eruptions, because several and frequent moderate-size eruptions, downsagging and tectonic hinged subsidence concur, indicating an incremental growth.
    concur, indicating an incremental growth.  +
  • A comparison of the chemistry of olivine m
    A comparison of the chemistry of olivine melilitites (all possible primary magmas) from the Hawaiian Islands (Oahu), the Balcones Province (Texas), northern Hessen (Germany), Schwabische Alb (Germany) and Cape Province (South Africa) shows systematic changes between these provinces in the order listed. Al2O3/TiO2 and Na2O/K2O decrease, CaO/Na2O CaO/Al2O3 and CaO + MgO/SiO2 increase, CaO/MgO remains roughly constant. These chemical features constrain possible models of origin fairly tightly. Constant CaO/MgO indicates partial melting under P, T conditions where dolomite can be a solidus phase in a peridotite composition. Increasing CaO + MgO/SiO2 suggests increasing amounts of CO2 in the source region, decreasing degrees of partial melting (K2O and P2O5 increase) and increasing depth of origin. Conditions of origin were determined on an olivine melilitite (no. 2927) from Tasmania by Brey and Green (1977) who concluded that it can be derived as a 5% melt from a pyrolite composition at about 27 kbars and 1160°C with 7-8% H2O and 6-7% CO2 dissolved in the melt. More undersaturated olivine melilitites should be derived from greater depth and greater xCO2 in the source region. To test this model CaCO3 + MgCO3 was added to olivine melilitite 2927 in such amounts that the bulk composition matched the most undersaturated olivine melilitites from South Africa. The influence of varying xCO2 was tested at 30 and 35 kbars. Olivine + clinopyroxene are liquidus phases to higher xCO2 in the modified olivine melilitite than in 2927, but are separated at 30 kbars from garnet + orthopyroxene by a wide field with orthopyroxene alone. The stability of garnet increases rapidly to lower xCO2 with increasing pressure and a four phase saturation field (ol, opx, cpx, ga) is approached. Thus it is inferred that olivine melilitites like those from South Africa originate at about 35 kbars with higher CO2 contents in the source region than for the less undersaturated compositions. Kimberlites (from Russia and Lesotho) form a chemically continuous spectrum with olivine melilitites with similar CaO/Al2O3, lower Al2 O3/TiO2 and higher CaO + MgO/SiO2. However, the MgO/CaO ratio is 3-4 times higher than in olivine melilitites. It is suggested therefore, that kimberlite magmas are products of very low degrees of partial melting of a peridotitic source and originate at P, T conditions where magnesite is stable at the solidus of peridotite and where clinopyroxene is a more refractory phase than orthopyroxene because of carbonation reactions.
    pyroxene because of carbonation reactions.  +
  • A comprehensive database of temperature, h
    A comprehensive database of temperature, heat flow, thermal conductivity and geochemistry is the basis of geothermal modelling. The latest revision (1987) of the UK Geothermal Catalogue (UKGC) contains over 2600 temperatures at over 1150 sites and over 200 observations of heat flow. About 93% of the temperature data are from depths less than 2000 m and about 50% are Bottom Hole Temperatures (BHT). Heat-flow density distribution models can be expanded to include estimates of heat flow derived from BHT and thermal conductivity data contained in the UKGC. A simple quantitative assessment of the quality of individual heat-flow measurements has been devised, based on the type and frequency of temperature and conductivity measurements and the borehole depth. The dimensionless quality function (hfQ) has been defined so that for a heat-flow borehole with two equilibrium temperature measurements made across an interval with a mean depth of 1 km or greater, with complementary thermal conductivity determinations made at intervals of 1 m across this zone, the heat-flow quality function is 1.0. Over 50% of the UK heat-flow dataset has a hfQ function less than 0.10; the 4 highest quality observations have values above 1.0. The same function can be used to assess the quality of estimates of heat flow by assigning quality functions to various types of temperature and thermal conductivity observation schemes. Appraisal of the UK heat-flow dataset indicates that some of the observational data have a similar quality rating to estimates of heat flow derived from convolution of temperature and thermal conductivity data for deep boreholes within the catalogue. In eastern England, the heat-flow density pattern is significantly modified by incorporation of estimates of heat flow from deep boreholes which have hfQ values comparable with early heat-flow measurements made in this region.
    eat-flow measurements made in this region.  +
  • A comprehensive modeling study of the Kraf
    A comprehensive modeling study of the Krafla geothermal field in Iceland has been carried out. The study consists of four tasks: the analysis of well test data, modeling of the natural state of the field, the determination of the generating capability of the field, and modeling of well performance. The results of all four tasks are consistent with field observations.
    ks are consistent with field observations.  +