Harvey M.C.,University of Auckland |
Rowland J.V.,University of Auckland |
Chiodini G.,Italian National Institute of Geophysics and Volcanology |
Rissmann C.F.,Institute of Geological & Nuclear Sciences |
And 3 more authors.
Geochimica et Cosmochimica Acta | Year: 2017
A new geothermometer (TCO2 Flux) is proposed based on soil diffuse CO2 flux and shallow temperature measurements made on areas of steam heated, thermally altered ground above active geothermal systems. This CO2 flux geothermometer is based on a previously reported CO2 geothermometer that was designed for use with fumarole analysis. The new geothermometer provides a valuable additional exploration tool for estimating subsurface temperatures in high-temperature geothermal systems. Mean TCO2 Flux estimates fall within the range of deep drill hole temperatures at Wairakei (New Zealand), Tauhara (New Zealand), Rotokawa (New Zealand), Ohaaki (New Zealand), Reykjanes (Iceland) and Copahue (Argentina). The spatial distribution of geothermometry estimates is consistent with the location of major upflow zones previously reported at the Wairakei and Rotokawa geothermal systems. TCO2 Flux was also evaluated at White Island (New Zealand) and Reporoa (New Zealand), where limited sub-surface data exists. Mode TCO2 Flux at White Island is high (320 °C), the highest of the systems considered in this study. However, the geothermometer relies on mineral–water equilibrium in neutral pH reservoir fluids, and would not be reliable in such an active and acidic environment. Mean TCO2 Flux at Reporoa (310 °C) is high, which indicates Reporoa has a separate upflow from the nearby Waiotapu geothermal system; an outflow from Waiotapu would not be expected to have such high temperature. © 2017 Elsevier Ltd
Alfredsson H.A.,University of Iceland |
Alfredsson H.A.,University Paul Sabatier |
Oelkers E.H.,University of Iceland |
Oelkers E.H.,University Paul Sabatier |
And 4 more authors.
International Journal of Greenhouse Gas Control | Year: 2013
The subsurface rocks at the Hellisheidi carbon injection site are primarily olivine tholeiite basalts consisting of lava flows and hyaloclastite formations. The hyaloclastites are low permeability glassy rocks formed under ice and melt water during glaciations that serve as the cap rock at the injection site; the boundaries between hyaloclastites and lava flows and those between individual lava flows boundaries are preferential fluid flow pathways. Some alteration is observed in the hyaloclastite cap rock situated at 100-300. m depth consisting primarily of smectite, calcite, Ca-rich zeolites, and poorly crystalline iron-hydroxides. Alteration increases with depth. These alteration phases lower the porosity and permeability of these rocks. Carbon dioxide injection will be targeted at a lava flow sequence at 400-800. m depth with the main aquifer located at 530. m depth. Loss on ignition suggests that over 80% of the primary rocks in the target zone are currently unaltered. The target zone rocks are rich in the divalent cations capable of forming carbonates; on average 6 moles of divalent cations are present per 1. kg of rock.The water in the target zone ranges in temperature from 15 to 35°C; the in situ pH ranges from 8.4 to 9.8. The partial pressure of CO2 and O2 suggest that the water in this system is isolated from the atmosphere. The concentration of Ca and Mg in these waters are limited by secondary mineral precipitation. All the waters are supersaturated with Ca-zeolite, analcime, Ca-Mg-Fe smectite, calcite, and aragonite, and some are supersaturated with respect to dolomite and Fe-Mg carbonates.Pure commercial CO2 and a 75%-24.2%-0.8% mixture of CO2-H2S-H2 gases will be dissolved into water prior to its injection into this system. The injected water will have a temperature of ~25°C and be equilibrated with ~25bar pressure of the CO2 gas, and ~14bar pressure of the CO2-H2S-H2 mixture. The injected gas will have total CO2 concentrations of ~0.8-0.42mole/kg H2O and a pH of 3.7-4.0, depending on the H2S concentration of the injected gas. All host rock minerals and glass will be strongly undersaturated with respect to the gas charged injection waters. The water will therefore create porosity in the near vicinity of the injection by dissolving primary and secondary minerals. Further from the injection, secondary minerals will precipitate, potentially clogging the system. Reaction path modeling shows that 1-2 moles of basaltic glass are needed to lower the injected CO2 concentration down to natural pre-injection concentrations, but less than 1 mole is needed for the sequestered H2S. Major carbonates formed were Ca-Mg-Fe-carbonate and dolomite at pH <5, whereas ankerite and calcite formed later at higher pH. Associated minerals at lower pH were chalcedony, kaolinite and iron hydroxide, followed by smectite and zeolites at higher pH. Modeling result suggest that the first sulfur bearing phase to precipitate is elemental sulfur, followed by greigite and mackinowite upon further basalt dissolution. © 2012 Elsevier Ltd.
Gislason S.R.,University of Iceland |
Wolff-Boenisch D.,University of Iceland |
Stefansson A.,University of Iceland |
Oelkers E.H.,University Paul Sabatier |
And 8 more authors.
International Journal of Greenhouse Gas Control | Year: 2010
In this paper we describe the thermodynamic and kinetic basis for mineral storage of carbon dioxide in basaltic rock, and how this storage can be optimized. Mineral storage is facilitated by the dissolution of CO2 into the aqueous phase. The amount of water required for this dissolution decreases with decreased temperature, decreased salinity, and increased pressure. Experimental and field evidence suggest that the factor limiting the rate of mineral fixation of carbon in silicate rocks is the release rate of divalent cations from silicate minerals and glasses. Ultramafic rocks and basalts, in glassy state, are the most promising rock types for the mineral sequestration of CO2 because of their relatively fast dissolution rate, high concentration of divalent cations, and abundance at the Earth's surface. Admixture of flue gases, such as SO2 and HF, will enhance the dissolution rates of silicate minerals and glasses. Elevated temperature increases dissolution rates but porosity of reactive rock formations decreases rapidly with increasing temperature. Reduced conditions enhance mineral carbonation as reduced iron can precipitate in carbonate minerals. Elevated CO2 partial pressure increases the relative amount of carbonate minerals over other secondary minerals formed. The feasibility to fix CO2 by carbonation in basaltic rocks will be tested in the CarbFix project by: (1) injection of CO2 charged waters into basaltic rocks in SW Iceland, (2) laboratory experiments, (3) studies of natural analogues, and (4) geochemical modelling. © 2009 Elsevier Ltd. All rights reserved.
Rosenkjaer G.K.,University of British Columbia |
Gasperikova E.,Lawrence Berkeley National Laboratory |
Newman G.A.,Lawrence Berkeley National Laboratory |
Arnason K.,Iceland Geosurvey |
Lindsey N.J.,Lawrence Berkeley National Laboratory
Geothermics | Year: 2015
The magnetotelluric (MT) method is important for exploration of geothermal systems. The information on the Earth's resistivity obtained with MT methods has been valuable in imaging the hydrothermal alteration of such systems. Given its ability to recover complex resistivity models for the Earth, three-dimensional (3D) MT inversion has become a common practice in geothermal exploration. However, 3D inversion is a time-consuming and complicated procedure that relies on computer algorithms to search for a model that can explain the measured data to a sufficient level. Furthermore, many elements of inversion require input from the practitioner, which can easily bias the results. Consequently, final 3D MT results depend on various factors, including the inversion code, the model mesh used to represent the Earth, data quality and processing, and constraints imposed during the inversion procedure.In this paper, to explore how this variability in 3D MT modeling impacts the final model, we invert MT data sets from the Krafla and Hengill geothermal areas in Iceland, using three different inversion codes. In each case, the modelers had the freedom to select a subset of the data and implement the inversion for the respective code in an optimized way. We compare the results from all the inversion codes, as well as consider the setup and assumptions made during the inversion process, all of which helps enhance the robustness and quality of the results. The comparison is done in multiple ways, using visual comparison of the recovered resistivity models, as well as comparing the structural similarities of the models by employing a structural correlation metric based on cross-gradients and other types of metrics for structural correlation. This approach highlights structures that are common in all three models, and implies that these structures are independent of the inversion code and necessary to fit the data.All modeling results from both Krafla and Hengill are consistent to first order, recovering a conductive layer on top of a resistive core typical of high temperature geothermal systems. For Hengill, the models show strong structural agreement, with all inversions recovering a moderately layered resistivity model but adding detail to previous work done in the area. Major differences are found in areas with coarse data coverage and hence questionable model resolution. Where the recovered structures in different models coincide, our confidence that these structures are well-constrained by the data is elevated, in spite of the different setup and assumptions in the codes these structures are required; so they can be interpreted in terms of geology with more certainty. Results from Krafla are not as consistent as results for Hengill, related in part to the Krafla data being nosier than the Hengill data. The models from Krafla have coinciding larger structures, but small-scale structures there are less coherent. One of the consistent structures in all the models is a conductive zone reaching from a depth of 5. km to shallower depths in the northern part of the area. © 2015 Elsevier Ltd.
Rice M.S.,California Institute of Technology |
Cloutis E.A.,University of Winnipeg |
Bell J.F.,Arizona State University |
Bish D.L.,Indiana University |
And 6 more authors.
Icarus | Year: 2013
Hydrated silica-rich materials have recently been discovered on the surface of Mars by the Mars Exploration Rover (MER) Spirit, the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), and the Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) in several locations. Having been interpreted as hydrothermal deposits and aqueous alteration products, these materials have important implications for the history of water on the martian surface. Spectral detections of these materials in visible to near infrared (Vis-NIR) wavelengths have been based on a H2O absorption feature in the 934-1009nm region seen with Spirit's Pancam instrument, and on SiOH absorption features in the 2.21-2.26μm range seen with CRISM. Our work aims to determine how the spectral reflectance properties of silica-rich materials in Vis-NIR wavelengths vary as a function of environmental conditions and formation. Here we present laboratory reflectance spectra of a diverse suite of silica-rich materials (chert, opal, quartz, natural sinters and synthetic silica) under a range of grain sizes and temperature, pressure, and humidity conditions. We find that the H2O content and form of H2O/OH present in silica-rich materials can have significant effects on their Vis-NIR spectra. Our main findings are that the position of the ~1.4μm OH feature and the symmetry of the ~1.9μm feature can be used to discern between various forms of silica-rich materials, and that the ratio of the ~2.2μm (SiOH) and ~1.9μm (H2O) band depths can aid in distinguishing between silica phases (opal-A vs. opal-CT) and formation conditions (low vs. high temperature). In a case study of hydrated silica outcrops in Valles Marineris, we show that careful application of a modified version of these spectral parameters to orbital near-infrared spectra (e.g., from CRISM and OMEGA) can aid in characterizing the compositional diversity of silica-bearing deposits on Mars. We also discuss how these results can aid in the interpretation of silica detections on Mars made by the MER Panoramic Camera (Pancam) and Mars Science Laboratory (MSL) Mast-mounted Camera (Mastcam) instruments. © 2012 Elsevier Inc.
Keshav S.,University of Bayreuth |
Keshav S.,Montpellier University |
Gudfinnsson G.H.,Iceland GeoSurvey |
Gudfinnsson G.H.,University of Iceland
American Mineralogist | Year: 2014
Pressure-temperature divariant melting phase relations of model carbonated peridotite in the system CaO-MgO-Al2O3-SiO 2-CO2 from 8 to 12 GPa are reported. From 8 to 12 GPa, melting temperatures on the studied pressure-temperature divariant surface rise quite rapidly. Liquids, in equilibrium with forsterite, orthopyroxene, clinopyroxene, and garnet, on the low-temperature side of the divariant surface are magnesiocarbonatitic in composition. With increasing temperature along an isobar on the pressuretemperature divariant surface, and with the same crystalline phase assemblage, liquids gradually become kimberlitic in their composition. Given the model system data reported here, Group IB kimberlites and perhaps some kimberlites from Greenland, Canada, and South Africa could be generated from direct melting of carbonated peridotite in the pressure range of approximately 6-8 GPa. Some kimberlites from Canada and Russia could have formed by partial melting of carbonated mantle peridotite at pressures of about 10-12 GPa. From 8 to 12 GPa, liquid compositions on the studied divariant surface show a limited compositional range, which implies that the divariant surface is essentially flat. The implied flatness of the divariant surface, and so long as the liquid is in equilibrium with the crystalline assemblage of forsterite + orthopyroxene + clinopyroxene + garnet on the divariant surface, indicate that kimberlites belonging to Group IA and those more magnesian than Group IA cannot have their origin in only being a melting product of carbonated mantle peridotite. The absence of topography of the studied pressure-temperature divariant surface in all likelihood limits the generation of kimberlites in the Earth's upper mantle only.
Gernigon L.,Geological Survey of Norway |
Blischke A.,Iceland GeoSurvey |
Nasuti A.,Geological Survey of Norway |
Sand M.,Norwegian Petroleum Directorate
Tectonics | Year: 2015
We have acquired and processed new aeromagnetic data that cover the entire oceanic Norway Basin located between the Møre volcanic rifted margin and the Jan Mayen microcontinent (JMMC). The new compilation allows us to revisit the structure of the conjugate volcanic (rifted) margins and the spreading evolution of the Norway Basin from the Early Eocene breakup time to the Late Oligocene when the Aegir Ridge became extinct. The volcanic margins (in a strict sense) that formed before the opening of the Norway Basin have been disconnected with the previous Jurassic-Mid-Cretaceous episode of crustal thinning. We also show evidence of relationships between the margin architecture, the breakup magmatism distribution along the continent-oceanic transition, and the subsequent oceanic segmentation. The Norway Basin shows a complex system of asymmetric oceanic segments locally affected by episodic ridge jumps. The new aeromagnetic compilation also confirms that a fan-shaped spreading evolution of the Norway Basin was clearly active before the cessation of seafloor spreading and extinction of the Aegir Ridge. An important Mid-Eocene kinematic event at around magnetic chron C21r can be recognized in the Norway Basin. This event coincides with the onset of diking and increasing rifting activity (and possible oceanic accretion?) between the proto-JMMC and the East Greenland margin. It led to a second phase of breakup and microcontinent formation in the Norwegian-Greenland Sea ~26 Myrs later in the Oligocene. Key Points 88.000 line km of new aeromagnetic data in the Norwegian-Greenland Sea Complete aeromagnetic coverage of the Norway Basin spreading system Prebreakup and postbreakup evolution of the rift/margin system/microcontinent ©2015. American Geophysical Union. All Rights Reserved.
Armannsson H.,Iceland GeoSurvey |
Hardardottir V.,Iceland GeoSurvey
Water-Rock Interaction - Proceedings of the 13th International Conference on Water-Rock Interaction, WRI-13 | Year: 2010
Studies of scales in the Asal, Djibouti and Reykjanes, Iceland geothermal systems are described and the results compared to those for the Milos, Greece and Salton Sea, California geothermal systems. At >16 bar a sulphides, such as galena, sphalerite, wurtzite, troilite, pyrite, chalcocite, chalcopyrite, and bornite, are the predominant deposits, but below that and down to amorphous silica saturation pressure iron silicates are most abundant after which amorphous silica predominates. The sulphides may be chemically inhibited and so can the iron silicates although their deposition can be prevented by keeping the wellhead pressure well above 16 bar a, and the amorphous silica deposition by keeping the separator pressure above the saturation pressure of amorphous silica. © 2010 Taylor & Francis Group, London.
Sveinbjornsson B.M.,Iceland GeoSurvey |
Thorhallsson S.,Iceland GeoSurvey
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013
Drilling performance of 77 production and reinjection wells in the Hengill Geothermal Area in Iceland is analyzed. The study compares workdays, and time spent on seven different drilling activities, in drilling holes with two casing diameter programs, both vertical and directional. The Monte Carlo method was applied to obtain a statistical estimate of the number of workdays and the cost of a 2235 m deep directional reference hole. On average this hole needed 45 workdays with a standard deviation of 7.2 days. The cost was inferred from time and usage data as the actual costs were not available for the study. The average cost for a large diameter reference well is 4.3 million USD or about 2000 USD/m. Drilling problems due to loss of circulation or collapsing geological formations led to higher drilling costs for 24 wells but the majority of holes were drilled according to the original schedule. The risk of drilling such holes in terms of cost and output is not as high as often alledged. To predict steam mass flow on the basis of the Injectivity Index, determined at the end of drilling, one must consider reservoir conditions and enthalpy of the expected inflow into wells. About 80% of the drilled wells are productive. The average generating capacity is ∼5.9 MWe per drilled well. Injection of waste water from the power plant resulted in thousands of earthquakes, of magnitude up to Ml 4. Copyright 2013 ARMA, American Rock Mechanics Association.
Keshav S.,University of Bayreuth |
Keshav S.,Montpellier University |
Gudfinnsson G.H.,Iceland GeoSurvey
Journal of Geophysical Research: Solid Earth | Year: 2013
Solidus phase relations of carbon dioxide-saturated (CO2 vapor) model peridotite in the system CaO-MgO-Al2O3-SiO 2-CO2 in the 1.1-2.1 GPa pressure range are reported. The solidus has a positive slope in pressure-temperature (PT) space from 1.1 to 2 GPa. Between 2 and 2.1 GPa, the melting curve changes to a negative slope. From 1.1 to 1.9 GPa, the liquid, best described as CO2-bearing silicate liquid, is in equilibrium with forsterite, orthopyroxene, clinopyroxene, spinel, and vapor. At 2 GPa, the same crystalline phase assemblage plus vapor is in equilibrium with two liquids, which are silicate and carbonatitic in composition, making the solidus at 2 GPa PT invariant. The presence of two liquids is interpreted as being due to liquid immiscibility. Melting reactions written over 1.1-1.9 GPa are peritectic, with forsterite being produced upon melting, and the liquid is silicate in composition. Upon melting at 2.1 GPa, orthopyroxene is produced, and the liquid is carbonatitic in composition. Hence, the invariance between 1.9 and 2.1 GPa is not only the reason for the dramatic change in the liquid composition over an interval of 0.2 GPa, but the carbonated peridotite solidus ledge itself most likely appears because of this PT invariance. It is suggested that because carbonatitic liquid is produced at the highest solidus temperature at 2 GPa in PT space in the system studied, such liquids, in principle, can erupt through liquid immiscibility, as near-primary magmas from depths of approximately 60 km. ©2013. American Geophysical Union. All Rights Reserved.