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| 2-D Magnetotellurics At The Geothermal Site At Soultz-Sous-Forets- Resistivity Distribution To About 3000 M Depth + | With the aim of investigating the possibilities of magnetotelluric methods for the exploration of potential Enhanced Geothermal System (EGS) sites in the Upper Rhine valley, a 2-D magnetotelluric (MT) survey has been carried out on a 13 km long profile across the thermal anomaly in the area of the geothermal power plant of Soultz-sous-Forets in the winter 2007/08. Despite strong artificial noise, processing using remote referencing and Sutarno phase consistent smoothing revealed significant results from 10 out of 16 sites. Indication for 1-D structures was found in the shortest periods, 2-D effects in the periods up to 40 s, and 3-D effects in the long period range. Since 3-D effects were found in the longer periods, 2-D inversion was carried out for periods smaller than 40 s. The results of the inversion are consistent with the geology of the geothermal site and distinguish well the sediments from the granitic basement including the structures given by the faults. A conductive anomaly with a resistivity of about 3 Ωm has been found at a depth down to 2000 m in the area of the Soultz and Kutzenhausen faults, which is attributed to geothermal processes. |
| 2.8-Ma Ash-Flow Caldera At Chegem River In The Northern Caucasus Mountains (Russia), Contemporaneous Granites, And Associated Ore Deposits + | Diverse latest Pliocene volcanic and plutonic rocks in the north-central Caucasus Mountains of southern Russia are newly interpreted as components of a large caldera system that erupted a compositionally zoned rhyolite-dacite ash-flow sheet at 2.83 ± 0.02 Ma (sanidine and biotite 40Ar/39Ar). Despite its location within a cratonic collision zone, the Chegem system is structurally and petrologically similar to typical calderas of continental-margin volcanic arcs. Erosional remnants of the outflow Chegem Tuff sheet extend at least 50 km north from the source caldera in the upper Chegem River. These outflow remnants were previously interpreted by others as erupted from several local vents, but petrologic similarities indicate a common origin and correlation with thick intracaldera Chegem Tuff. The 11 _ 15 km caldera and associated intrusions are superbly exposed over a vertical range of 2,300 m in deep canyons above treeline (elev. to 3,800 m). Densely welded intracaldera Chegem Tuff, previously described by others as a rhyolite lava plateau, forms a single cooling unit, is > 2 km thick, and contains large slide blocks from the caldera walls. Caldera subsidence was accommodated along several concentric ring fractures. No prevolcanic floor is exposed within the central core of the caldera. The caldera-filling tuff is overlain by andesitic lavas and cut by a 2.84 ± 0.03-Ma porphyritic granodiorite intrusion that has a cooling age analytically indistinguishable from that of the tuffs. The Eldjurta Granite, a pluton exposed low in the next large canyon (Baksan River) 10 km to the northwest of the caldera, yields variable K-feldspar and biotite ages (2.8 to 1.0 Ma) through a 5-km vertical range in surface and drill-hole samples. These variable dates appear to record a prolonged complex cooling history within upper parts of another caldera-related pluton. Major W-Mo ore deposits at the Tirniauz mine are hosted in skarns and hornfels along the roof of the Eldjurta Granite, and associated aplitic phases have textural features of Climax-type molybdenite porphyries in the western USA. Similar 40Ar/39Ar ages, mineral chemistry, and bulk-rock compositions indicate that the Chegem Tuff, intracaldera intrusion, and Eldjurta Granite are all parts of a large magmatic system that broadly resembles the middle Tertiary Questa caldera system and associated Mo deposits in northern New Mexico, USA. Because of their young age and superb three-dimensional exposures, rocks of the Chegem-Tirniauz region offer exceptional opportunities for detailed study of caldera structures, compositional gradients in volcanic rocks relative to cogenetic granites, and the thermal and fluid-flow history of a large young upper-crustal magmatic system. |
| 2010 Carbon Sequestration Atlas of the United States and Canada: Third Edition + | This atlas updates the carbon dioxide (CO2) sequestration potential for the United States and Canada, and it provides updated information on field activities of the regional carbon sequestration partnerships (RCSPs). In addition, the atlas outlines the U.S. Department of Energy's (DOE) Carbon Sequestration Research Program, DOE’s international carbon capture and sequestration (CCS) collaborations, worldwide CCS projects, and CCS regulatory issues. It presents updated information on the location of stationary sources of CO2 emissions as well as the locations and sequestration potential of various geologic storage sites. Finally, the atlas provides information about the commercialization opportunities for CCS technologies from each RCSP. Access to individual sections of the resource is available on the [http://www.netl.doe.gov/technologies/carbon_seq/refshelf/atlasIII/ website for the atlas]. |
| 2010 Solar Market Transformation Analysis and Tools + | This document describes the DOE-funded solar market transformation analysis and tools under developm |
| 2010 Vehicle Technologies Market Report + | This report details the major trends in the United States transportation sector in 2010, as well as the underlying trends that caused them. The report opens with a summary of the economic sector, including sector-wide energy consumption trends. The second section includes a discussion on light-duty vehicles, and the third section discusses heavy-duty vehicles. The fourth section discusses the policies that shape the transportation sector, and the fifth section makes projections about what will happen in the highway sector in the next five years. A section on the freight rail industry completes the report. |
| 238U Decay Series Systematics Of Young Lavas From Batur Volcano, Sunda Arc + | Activities of 238U decay series radioisotopes have been determined for both postcaldera basalts erupted between 1849 and 1974 and genetically related young precaldera dacites from Batur volcano, Bali, Sunda arc. All rocks possess (230Th/238U) = 1 within 2 sigma error indicating that little, if any, fractionation between Th and U occurred during their genesis, or in their source regions, within approximately the last 350 ka. Both the basaltic and the dacitic rocks possess (230Th/232U) ~ 0.71, consistent with both having a common mantle source with an unusually high Th/U weight ratio of 4.4 and with the dacitic magma having formed by closed-system convective fractionation of the same basaltic magma from which the postcaldera lavas were derived. The historical basalts possess (226Ra/230Th) > 1, indicating a significant Ra enrichment relative to Th and U within approximately the last 8 ka. The highest degree of 226Ra enrichment occurs in the most mafic basaltic lavas, which form a cycle of mafic volcanism between 1888 and 1926. If Ra enrichments were produced during mantle-melting as a result of its greater incompatibility relative to Th then variations in (236Ra/230Th) may reflect the presence at Batur of a periodically replenished, but poorly mixed, open-system magma chamber. In addition, this result implies that the primitive Batur basaltic magmas take considerably less than about 8 ka to travel from their mantle source through the Batur magma chamber to the surface. Whole rock (210Pb/226Ra) > 1 in the youngest historical basalts indicates that Pb has been enriched relative to Ra within about 100 years of their eruption. Because Pb is expected to be less incompatible then Ra during mantle melting, the enrichments are probably due to late stage processes, such as accumulation of 210Pb-rich plagioclase phenocrysts or post-eruptive condensation of volatile Pb salts in vesicles. |
| 2D Joint Inversion Of Dc And Scalar Audio-Magnetotelluric Data In The Evaluation Of Low Enthalpy Geothermal Fields + | Audio-magnetotelluric (AMT) and resistivity (dc) surveys are often used in environmental, hydrological and geothermal evaluation. The separate interpretation of those geophysical data sets assuming two-dimensional models frequently produces ambiguous results. The joint inversion of AMT and dc data is advocated by several authors as an efficient method for reducing the ambiguity inherent to each of those methods. This paper presents results obtained from the two-dimensional joint inversion of dipole-dipole and scalar AMT data acquired in a low enthalpy geothermal field situated in a graben. The joint inverted models show a better definition of shallow and deep structures. The results show that the extension of the benefits using joint inversion depends on the number and spacing of the AMT sites. The models obtained from experimental data display a low resistivity zone (< 20 Omega m) in the central part of the graben that was correlated with the geothermal reservoir. The resistivity distribution models were used to estimate the distribution of the porosity in the geothermal reservoir applying two different approaches and considering the clay minerals effect. The results suggest that the maximum porosity of the reservoir is not uniform and might be in the range of 12% to 24%. |
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| 3-D Density Model Of Mt Etna Volcano (Southern Italy) + | A detailed density model of Mt. Etna and its surrounding areas has been evaluated using a 3-D inversion of the gravimetric data acquired in the 1980's. Several high-density and low-density bodies are found, penetrating from shallow depths as far down as 12 km bsl. A positive correlation (in terms of location, extent, density, and velocity) is established between several anomalies of the density model and features identified in previously published seismic tomographies. A prominent high-density body extending down to 7 km bsl is recognized in the southern part of the Valle del Bove, and interpreted as a solidified magmatic intrusion. On the western boundary of this anomaly, a low-density body is interpreted as a bubble and liquid magma mixture. Outside the central area, three other high-density anomalies are imaged and attributed to the earliest phases of volcanic activity in the area. Several interesting low-density anomalies are also identified and correlated with known fault lines and other structural features of the region. |
| 3-D Interpretation Of Magnetotelluric Data At The Bajawa Geothermal Field, Indonesia + | Three-dimensional (3-D) interpretation was carried out for the magnetotelluric (MT) data obtained in a geothermal area in Indonesia. The inversion scheme was based on the linearized leastsquares method with smoothness regularization. In addition to the subsurface resistivity structure, static shifts were also included as unknown parameters in the inversion. Forward modeling was by the finite difference scheme. The sensitivity matrix was computed once for a homogeneous half space and used at all iterations to save the computation time. The 3-D interpretation of the Indonesian data has revealed that the method can be applied practically I O O S and efficiently to magnetotelluric data and that a more reliable model was obtained for evaluation on geothermal reservoir |
| 3-D Inversion Of Borehole-To-Surface Electrical Data Using A Back-Propagation Neural Network + | The "fluid-flow tomography", an advanced technique for geoelectrical survey based on the conventional mise-a-la-masse measurement, has been developed by Exploration Geophysics Laboratory at the Kyushu University. This technique is proposed to monitor fluid-flow behavior during water injection and production in a geothermal field. However data processing of this technique is very costly. In this light, this paper will discuss the solution to cost reduction by applying a neural network in the data processing. A case study in the Takigami geothermal field in Japan will be used to illustrate this. The achieved neural network in this case study is three-layered and feed-forward. The most successful learning algorithm in this network is the Resilient Propagation (RPROP). Consequently, the study advances the pragmatism of the "fluid-flow tomography" technique which can be widely used for geothermal fields. Accuracy of the solution is then verified by using root mean square (RMS) misfit error as an indicator. |
| 3-D Seismic Methods For Geothermal Reservoir Exploration And Assessment-Summary + | A wide variety of seismic methods covering the spectrum from DC to kilohertz have been employed at one time or the other in geothermal environments. The reasons have varied from exploration for a heat source to attempting to find individual fractures producing hot fluids. For the purposes here we will assume that overall objective of seismic imaging is for siting wells for successful location of permeable pathways (often fracture permeability) that are controlling flow and transport in naturally fractured reservoirs. The application could be for exploration of new resources or for in-fill/step-out drilling in existing fields. In most geothermal environments the challenge has been to separate the ''background'' natural complexity and heterogeneity of the matrix from the fracture/fault heterogeneity controlling the fluid flow. Ideally one not only wants to find the fractures, but the fractures that are controlling the flow of the fluids. Evaluated in this work is current state-of-the-art surface (seismic reflection) and borehole seismic methods (Vertical Seismic Profiling (VSP), Crosswell and Single Well) to locate and quantify geothermal reservoir characteristics. The focus is on active methods; the assumption being that accuracy is needed for successful well siting. Passive methods are useful for exploration and detailed monitoring for in-fill drilling, but in general the passive methods lack the precision and accuracy for well siting in new or step out areas. In addition, MEQ activity is usually associated with production, after the field has been taken to a mature state, thus in most cases it is assumed that there is not enough MEQ activity in unproduced areas to accurately find the permeable pathways. The premise of this review is that there may new developments in theory and modeling, as well as in data acquisition and processing, which could make it possible to image the subsurface in much more detail than 15 years ago. New understanding of the effect of fractures on seismic wave propagation are now being applied to image fractures in gas and oil environments. It now may be appropriate to apply these methods, with modifications, to geothermal applications. It is assumed that to implement the appropriate methods an industry coupled program tightly linked to actual field cases, iterating between development and application will be pursued. The goal of this work is to evaluate the most promising methods and approaches that may be used for improved geothermal exploration and reservoir assessment. It is not a comprehensive review of all seismic methods used to date in geothermal environments. This work was motivated by a need to assess current and developing seismic technology that if applied in geothermal cases may greatly improve the chances for locating new geothermal resources and/or improve assessment of current |
| 36Cl/Cl ratios in geothermal systems- preliminary measurements from the Coso Field + | The {sub 36}Cl/Cl isotopic composition of chlorine in geothermal systems can be a useful diagnostic tool in characterizing hydrologic structure, in determining the origins and age of waters within the systems, and in differentiating the sources of chlorine (and other solutes) in the thermal waters. The {sub 36}Cl/Cl values for several geothermal water samples and reservoir host rock samples from the Coso, California geothermal field have been measured for these purposes. The results indicate that most of the chlorine is not derived from the dominant granitoid that host the geothermal system. If the chlorine was originally input into the Coso subsurface through meteoric recharge, that input occurred at least 1-1.25 million years ago. The results suggest that the thermal waters could be connate waters derived from sedimentary formations, presumably underlying and adjacent top the granitic rocks, which have recently migrated into the host rocks. Alternatively, most of the chlorine but not the water, may have recently input into the system from magmatic sources. In either case, the results indicate that most of the chlorine in the thermal waters has existed within the granitoid host rocks for no more than about 100,00-200,00 years. this residence time for the chlorine is similar to residence times suggested by other researchers for chlorine in deep groundwaters of the Mono Basin north of the Coso field. |
| 3D Geological Modelling In Bavaria - State-Of-The-Art At A State Geological Survey + | Many Geological Survey Organisations (GSOs) are using 3D modelling software technology for a vast variety of applications. Initially many 3D tools were designed for the exploitation of digital seismic mass data existing in hydrocarbon exploration industry. Accordingly, GSOs have to adapt available software and to modify it to their special requirements, defining their own best practice. The Geological Survey of the Bavarian Environment Agency has developed procedures and workflows for a variety of 3D modelling applications. With limited staffing and resources effective software tools and workflows have been developed to create functional 3D geological models. The article's intention is to encourage smaller organisations to participate in this fast evolving community of 3D modelling by stating the obstacles and showing ways to overcome these hurdles. |
| 3D MAGNETOTELLURIC CHARACTERIZATION OF THE COSO GEOTHERMAL FIELD + | Knowledge of the subsurface electrical resistivity/conductivity can contribute to a better understanding of complex hydrothermal systems, typified by Coso geothermal field, through mapping the geometry (bounds and controlling structures) over existing production. Three-dimensional magnetotelluric (MT) inversion is now an emerging technology for characterizing the resistivity structures of complex geothermal systems. The method appears to hold great promise, but histories exploiting truly 3D inversion that demonstrate the advantages that can be gained by acquiring and analyzing MT data in three dimensions are still few in number. This project will address said issue, by applying 3D MT forward modeling and inversion to a MT data set acquired over the Coso geothermal field. The goal of the project is to provide the capability to image large geothermal reservoirs in a single self-consistent model. Initial analysis of the Coso MT data has been carried out using 2D MT imaging technology to construct an initial 3D resistivity model from a series of 2D resistivity images obtained using the inline electric field measurements (Zxy impedance elements) along different measurement transects. This model will be subsequently refined through a 3D inversion process. The initial 3D resistivity model clearly shows the controlling geological structures possibly influencing well production at Coso. The field data however, also show clear three dimensionality below 1 Hz, demonstrating the limitations of 2D resistivity imaging. The 3D MT predicted data arising from this starting model show good correspondence in dominant components of the impedance tensor (Zxy and Zyx) above 1Hz. Below 1 Hz there is significant differences between the field data and the 2D model data. |
| 3D Magnetotelluic characterization of the Coso Geothermal Field + | Electrical resistivity may contribute to progress in understanding geothermal systems by imaging the geometry, bounds and controlling structures in existing production, and thereby perhaps suggesting new areas for field expansion. To these ends, a dense grid of magnetotelluric (MT) stations plus a single line of contiguous bipole array profiling has been acquired over the east flank of the Coso geothermal system. Acquiring good quality MT data in producing geothermal systems is a challenge due to production related electromagnetic (EM) noise and, in the case of Coso, due to proximity of a regional DC intertie power transmission line. To achieve good results, a remote reference completely outside the influence of the dominant source of EM noise must be established. Experimental results so far indicate that emplacing a reference site in Amargosa Valley, NV, 65 miles from the DC intertie, is still insufficient for noise cancellation much of the time. Even though the DC line EM fields are planar at this distance, they remain coherent with the nonplanar fields in the Coso area hence remote referencing produces incorrect responses. We have successfully unwrapped and applied MT times series from the permanent observatory at Parkfield,CA, and these appear adequate to suppress the interference of the cultural EM noise. The efficacy of this observatory is confirmed by comparison to stations taken using an ultra-distant reference site east of Socorro, NM. Operation of the latter reference was successful by using fast ftp internet communication between Coso Junction and the New Mexico Institute of Mining and Technology, using the University of Utah site as intermediary, and allowed referencing within a few hours of data downloading at Coso. A grid of 102 MT stations was acquired over the Coso geothermal area in 2003 and an additional 23 stations were acquired to augment coverage in the southern flank of the first survey area in 2005.These data have been inverted to a fully three-dimensional conductivity model. Initial analysis of the Coso MT data was carried out using 2D MT imaging. An initial 3D conductivity model was constructed from a series of 2D resistivity images obtained using the inline electric field measurements (Zyx impedance elements) along several measurement transects. This model was then refined through a 3D inversion process.This model shows the controlling geological structures possibly influencing well production at Coso and correlations with mapped surface features such as faults and regional geoelectric strike. The 3D model also illustrates the refinement in positioning of conductivity contacts when compared to isolated 2D inversion transects. The conductivity model has also been correlated with microearthquake locations, well fluid production intervals and most importantly with an acoustic and shear velocity model derived by Wu and Lees (1999). This later correlation shows the near-vertical high conductivity structure on the eastern flankof the producing field is also a zone of increased acoustic velocity and increased Vp/Vs ratio bounded by mapped fault traces. South of the Devil's Kitchen is an area of high geothermal well density, where highly conductive near surface material is interpreted as a clay cap alteration zone manifested from the subsurface geothermal fluids and related geochemistry. Beneath the clay cap, however, the conductivity is nondescript, whereas the Vp/Vs ratio is enhanced over the production intervals. It is recommended that more MT data sites be acquired to the southwest of the Devil's Kitchen area to better refine the conductivity model in that area. |
| 3D Magnetotelluric Characterization Of The Geothermal Anomaly In The Llucmajor Aquifer System (Majorca, Spain) + | In the Llucmajor aquifer system (Majorca Island, Spain) some geothermal evidences have appeared. This phenomenon is not isolated to Majorca and it is present in other areas, where it can be associated with structural conditions, especially to the extensional event suffered by the island after the Alpine Orogeny. However, the origin of this anomaly in Llucmajor is not well known, and there is no surface geological evidence of these structural conditions. With the aim of delineating the geoelectrical structure of the zone and identifying the geological structure that allows the presence of this anomaly, an audiomagnetotelluric (AMT) survey was carried out. The AMT data was processed using a Wavelet Transform-based scheme. Dimensionality analysis indicates that the geoelectrical structure is mainly 3D. The 3D model was obtained by trial and error forward modeling, taking accounting of the responses from the determinant of the impedance tensor. The model shows a vertical resistivity distribution with three horizons associated with different units: on the top, a shallow high resistive media related to an unconfined shallow aquifer; in the middle, a conductive layer related to the aquitard, and below it, another resistive media related to the confined deeper aquifer. The intermediate horizon shows a sudden thinning beneath the thermal anomalous zone that can be identified as a weakness zone (fault or fracture) connecting both aquifers. An exploratory well was drilled after the AMT survey and reached almost 700 m in depth. This allowed correlating the resistivity distribution of the 3D model with data logging and lithology obtained from the well, showing a proper agreement between them. |
| 3D Mt Resistivity Imaging For Geothermal Resource Assessment And Environmental Mitigation At The Glass Mountain Kgra, California + | MT and TDEM surveys acquired in 2005 were integrated with existing MT and TDEM data recovered from obsolete formats to characterize the geometry of the geothermal reservoir. An interpretation based on the correlation of the 3D MT resistivity with well properties indicated that most of the previous exploration wells had been tarted close to but not in the center of areas tha appeared most likely to be permeable. Such characterizations can be considered in teh context of both potential environmental impacts and reservoir engineering anlayses in assessing drilling target priorities. The details of this Glass Mountain MT project are elaborated in a report to the CEC, currently under review. |
| 3D Relationships Between Sills And Their Feeders- Evidence From The Golden Valley Sill Complex (Karoo Basin) And Experimental Modelling + | In this paper, we address sill emplacement mechanisms through the three-dimensional relationships between sills and their potential feeders (dykes or sills) in the well-exposed Golden Valley Sill Complex (GVSC), Karoo Basin, South Africa. New field observations combined with existing chemical analyses show that: 1) the contacts between sills in the GVSC are not sill-feeding-sill relationships, and 2) there are, however, close structural and geochemical relationships between one elliptical sill, the Golden Valley Sill (GVS), and a small dyke (d4). Such relationships suggest that GVS is fed by d4 and that the linear shape of d4 may have controlled the elliptical development of the GVS. To test this hypothesis, we present preliminary results of experimental modelling of sill emplacement, in which we vary the shape of the feeder. In the first experiment (E1) with a punctual feeder the sill develops a sub-circular geometry, whereas in the second experiment (E2) with a long linear feeder the sill develops an elliptical geometry. The geometrical relationships in E2 show that the elliptical shape of the sill is controlled by the linear shape and the length of the linear feeder. The experiment E2 presents strong similarities with the GVS-d4 relationships and thus supports the proposition that d4 is the feeder of the GVS. Our experimental results also indicate that the feeders of the other elliptical sills of the GVSC may be dykes. |
| 3D Tomographic Imaging Of The Southern Apennines (Italy)- A Statistical Approach To Estimate The Model Uncertainty And Resolution + | A new dataset of first P-wave arrival times is used to derive the 3D tomographic model of the Campania-Lucania region in the southern Apennines (Italy). We address the issue related to the non-uniqueness of the tomographic inversion solution through massive numerical experimentation based on the global exploration of the model parameter space starting from a large variety of physically plausible initial models. The average of all the realizations is adopted as the best-fit solution and the uncertainty of the model parameters is studied using a statistical approach based on a Monte Carlo-type analysis. How the uncertainty in the initial model, earthquake locations, and data influences the inversion result is studied by considering separately the individual effects. Checkerboard tests are performed to estimate the resolving power of the dataset. Re-located seismicity in a reliable new 3D tomographic model allows us to correlate the earthquake distribution with the main seismogenic structures present in the area. |
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| 40 Years Of Dogger Aquifer Management In Ile-De-France, Paris Basin, France + | Geothermal energy has been supplying heat to district networks in the Paris Basin for more than 40 years. The most serious difficulties have been corrosion and scaling related problems that occurred in many geothermal loops in the mid-1980s. The main target of all exploration and exploitation projects has been the Dogger aquifer. Most of the operating facilities use the "doublet" technology which consists of a closed loop with one production well and one injection well. Injection of the cooled brines leads to the progressive exhaustion of the resource at the local doublet scale. Consequently, most of the research effort has been focused on quantifying the temporal evolution of the cooling, and to forecast the lifetimes of doublets and the occurrence of the "thermal breakthrough". At the turn of the 21st century, there was a revival of geothermal energy development in France and new projects are presently being considered. The 40 years of experience in geothermal exploitation of the Paris basin constitutes a firm basis upon which to devise a sustainable regional management approach for the geothermal resource. Several governmental policies seek to promote further geothermal development of the Dogger aquifer with structures in place to facilitate technical studies. |
| 40AR/39AR THERMAL HISTORY OF THE COSO GEOTHERMAL FIELD + | The age of the geothermal system and the granitic host rock at Coso geothermal system in California is poorly known. This is mainly due to a paucity of vein-type minerals (e.g. adularia, sericite) that can be directly dated. A downhole <sup>40</sup>Ar/<sup>39</sup>Ar thermochronology study of granitic host-rock Kfeldspar is presently being undertaken at the New Mexico Geochronology Research Laboratory at New Mexico Tech. The technique couples the measurement of argon loss from K-feldspar and knowledge of the diffusion parameters of transport in K-feldspar to estimate the longevity of the system at present day temperature and also to obtain an estimate of the host rock age. The study centers around a vertical distribution of samples obtained from Coso well 73-19 that reaches temperatures of 325°C at a depth of 1550m and thus represents one of the hottest producing wells in the Coso system. Four samples from Coso well 73-19, from depths 550m (downhole temperature 150°C), 700m (200°C), 1085m (275°C), and 1850m (325°C), were isolated from the granitic host rock chip samples. These samples were analyzed by the <sup>40</sup>Ar/<sup>39</sup>Ar age spectrum method where the data recorded significant and variable degrees of argon loss due to the range and magnitude of the present day temperatures sampled. The amount of argon loss from the samples analyzed increases as expected as depth and temperature increase downhole, yielding integrated ages that decrease with depth, but initial steps do not reach 0 apparent age. Lovera et al’s (1989) Multi Diffusion Domain method was used to compare thermal history models with measured data. The modeling supports a duration for the Coso geothermal system of definitely less than 100 ka, and possibly as short as 10 ka. This is much younger (< 100 ka vs. < 300 ka) than previous age estimates for the Coso geothermal system. Additional thermochronological sampling at Coso is planned to test the validity of these preliminary results. |
| 40Ar-39Ar Geochronology Of Magmatic Activity, Magma Flux And Hazards At Ruapehu Volcano, Taupo Volcanic Zone, New Zealand + | We have determined precise eruption ages for andesites from Ruapehu volcano in the Tongariro Volcanic Centre of the Taupo Volcanic Zone (TVZ) using 40Ar/39Ar furnace step-heating of separated groundmass concentrates. The plateau ages indicate several eruptive pulses near 200, 134, 45, 22 and <15 ka and, based on our and previous field mapping confirm the lavas of the Te Herenga Formation as the oldest exposed part of the volcanic edifice. The pulse at ~134 ka includes an entire >300-m section of lavas in Whangaehu gorge as well as some lavas in Ohinepango and Waihianoa catchments on eastern Ruapehu, and this suite of lavas belongs to the Waihianoa Formation. This pulse of activity is not represented on nearby Tongariro volcano, indicating that the two volcanoes have independent magmatic systems. A younger group of lavas yields dates between 50 and 20 ka and includes lava flows from the Turoa skifield and in the Ohinepango and Mangatoetoenui catchments and is consistent with two pulses of magmatism around the time of the last glacial maximum, relating it broadly to the Mangawhero Formation. Syn- and post-last glacial activity lavas, with ages <15 ka are assigned to the Whakapapa Formation, and include the voluminous flows of the Rangataua Member on southern Ruapehu. Magma flux, integrated over 1000-yr periods, averages 0.6 km3 ka-1 assuming a volcano lifespan of 250 ka. Fluxes for the Te Herenga, Waihianoa and Mangawhero Formations are consistent at 0.93, 0.9 and 0.88 km3 ka-1, respectively. These fluxes are broadly comparable with those measured at other modern andesite arc volcanoes (e.g. Ngauruhoe, 0.88; Merapi, 1.2 and Karymsky 1.2 km3 ka-1). The relatively low flux (0.17 km3 ka-1) calculated for the Whakapapa Formation may derive from underestimates of erupted volume arising from an increase in phreatomagmatic explosive eruptions in postglacial times. However, using volume estimates for the 1995-1996 eruptions and a recurrence interval of 25 yr has yielded an integrated 1000-yr flux of 0.8 km3 ka-1 in remarkable agreement to estimates for the prehistoric eruptions. Overall, Ruapehu shows consistency in magma flux, but at time scales of the order of one hundred to some thousands of years, field evidence suggests that short bursts of activity may produce fluxes up to twenty times greater. This is significant from the perspective of future activity and hazard prediction. |
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| 75Th Anniversary - The Historical Development Of The Magnetic Method In Exploration + | The magnetic method, perhaps the oldest of geophysical exploration techniques, blossomed after the advent of airborne surveys in World War II. With improvements in instrumentation, navigation, and platform compensation, it is now possible to map the entire crustal section at a variety of scales, from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale. Methods of data filtering, display, and interpretation have also advanced, especially with the availability of low-cost, high-performance personal computers and color raster graphics. The magnetic method is the primary exploration tool in the search for minerals. In other arenas, the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications, such as locating intrasedimentary faults, defining subtle lithologic contacts, mapping salt domes in weakly magnetic sediments, and better defining targets through 3D inversion. These new applications have increased the method's utility in all realms of exploration - in the search for minerals, oil and gas, geothermal resources, and groundwater, and for a variety of other purposes such as natural hazards assessment, mapping impact structures, and engineering and environmental studies. |
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| A 3D Magnetic Structure Of Izu-Oshima Volcano And Their Changes After The Eruption In 1986 As Estimated From Repeated Airborne Magnetic Surveys + | 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. |
| A Bme Solution Of The Stochastic Three-Dimensional Laplace Equation Representing A Geothermal Field Subject To Site-Specific Information + | This work develops a model of the geothermal field in the Nea Kessani region (Greece) by means of the Bayesian maximum entropy (BME) method, which describes the temperature variations across space in the underground geological formations. The geothermal field is formed by a thermal reservoir consisting of arcosic sandstones. The temperature distribution vs depth was first investigated by the Greek Institute of Geology and Mineral Exploration (IGME) using measurements in a set of vertical drill holes. These measurements showed that hot fluids rising from the deep enter the reservoir in a restricted area of the field and flow towards local thermal springs. The field modelling, which was based on the powerful BME concept, involves the solution of a stochastic partial differential equation that assimilates important site-specific information. The stochastic three-dimensional steady-state Laplace equation was considered as general knowledge and the drilling exploration data were used to construct the specificatory knowledge base in the BME terminology. The produced map is more informative and, in general, it gives higher temperature estimates compared to previous studies of the same region. This is also in agreement with the quartz geothermometry analysis carried out by IGME. |