Application of radium isotopes to determine crustal residence times of hydrothermal fluids from two sites on the Reykjanes Peninsula, Iceland

Kadko, David; Butterfield, D. A.

doi:10.1016/j.gca.2007.09.018

Cited by 38 publications

(11 citation statements)

References 43 publications

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“…Thus, seawater dominated geothermal systems in Iceland, such as Reykjanes and Svartsengi, serve as valuable analogues for hydrothermal vent systems on the seafloor, in terms of authigenic mineralization, geothermal solutions and primary lithologies (Hannington et al, 2005;Hardardóttir et al, 2009;Hardardóttir et al, 2013;Kadko et al, 2007;Kleine et al, 2020;Kleine et al, 2018;Marks et al, 2011;Marks et al, 2015;Michard et al, 1984;Mottl and Holland, 1978). Surtsey volcano is located in the southern offshore extension of the Icelandic eastern rift zone (Einarsson, 2008;Jakobsson et al, 2009;Thorarinsson et al, 1964) (Fig.…”

Section: Introductionmentioning

confidence: 99%

The Surtsey volcano geothermal system: An analogue for seawater-oceanic crust interaction with implications for the elemental budget of the oceanic crust

et al. 2020

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Surtsey is a young volcanic island in the offshore extension of Iceland's southeast rift zone that grew from the seafloor during explosive and effusive eruptions in 1963-1967. In 1979, a cored borehole (SE-1) was drilled to 181 m depth and in 2017 three cored boreholes (SE-2a, SE-2b and SE-3) were drilled to successively greater depths. The basaltic deposits host a low-temperature (40-141 °C) seawater-dominated geothermal system. Surtsey provides an ideal environment to study water-rock interaction processes in a young seawater geothermal system. Elemental concentrations (SiO2, B, Na, Ca, Mg, F, dissolved inorganic carbon, SO4, Cl) and isotope contents (δD, δ 18 O) in borehole fluids indicate that associated geothermal waters in submarine deposits originated from seawater modified by reactions with the surrounding basalt. These processes produce authigenic minerals in the basaltic lapilli tuff and a corresponding depletion of certain elements in the residual waters. Coupling of measured and modeled concentrations investigates the effect of temperature and associated abundance of authigenic minerals on chemical fluxes from and to the igneous oceanic crust during lowtemperature alteration. The annual chemical fluxes calculated at 50-150 °C range from-0.01 to +0.1×10 12 mol yr-1 for SiO2, +0.2 to +129×10 12 mol yr-1 for Ca,-129 to-0.8×10 12 mol yr-1 for Mg and-21 to +0.4×10 12 mol yr-1 for SO4 where negative values indicate chemical fluxes from the ocean into the oceanic crust and positive values indicate fluxes from the oceanic crust to the oceans. These flux calculations reveal that water-rock interaction at varying water-rock ratios and temperatures produces authigenic minerals that serve as important sinks of seawaterderived SiO2, Mg and SO4. In contrast, water-rock interaction accompanied by dissolution of 2 basaltic glass and primary crystal fragments, provides a significant source of Ca. Such lowtemperature alteration could effectively influence the elemental budget of the oceanic igneous crust and ocean waters. The modelling provides insights into water chemistries and chemical fluxes in low-temperature MOR recharge zones. Surtsey also provides a valuable young analogue for assessing the chemical evolution of fluid discharge over the life cycles of seamounts in ridge flank systems.

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Section: Introductionmentioning

confidence: 99%

The Surtsey volcano geothermal system: An analogue for seawater-oceanic crust interaction with implications for the elemental budget of the oceanic crust

et al. 2020

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“…The reason for this complexity is the strikingly dynamic system (e.g. residence time of water in a hydrothermal system in Reykjanes, SW Iceland, is 5–6 yr; Kadko et al . 2007) under which the hydrothermal alteration process takes place over a long time period.…”

Section: Introductionmentioning

confidence: 99%

Modification of the magnetic mineralogy in basalts due to fluid-rock interactions in a high-temperature geothermal system (Krafla, Iceland)

Oliva‐Urcia

Kontny²,

Vahle³

et al. 2011

Geophysical Journal International

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S U M M A R YActive high-temperature (>150 • C) geothermal areas like the Krafla caldera, NE-Iceland, often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity. The main alteration processes in such an environment are low-temperature oxidation (<350 • C, maghemitization) and fluid-rock interactions. We investigated the rock magnetic properties [natural remanent magnetization (NRM) magnetic susceptibility and their temperature and field variation] and the mineralogy, using X-ray diffraction, microscopic methods and electron microprobe analyses, of two drill cores (KH1 and KH3) from the rim of the Krafla caldera. The drill cores have distinctly lower NRM values (average <3 A m -1 ) compared to younger surface basalts (average 20 A m -1 ) along with a large variation in magnetic susceptibility (1.3 × 10 −7 -4.9 × 10 −5 m 3 kg -1 ). The secondary mineral assemblage (sulphides, sphene, rutile and chlorite) indicates an alteration within the chlorite-smectite zone for both cores without depth zoning. Optical miscroscopy in combination with the Bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite: (1) titanomaghemite with intermediate titanium concentration and probably high vacancy concentration, and (2) titanomaghemite with low titanium concentration and low vacancy concentration. The mineral assemblages, textures and magnetic properties deduced from the mentioned magnetic measurements indicate two-stage transformation mechanism:(1) Dissolution of titanium at low pH under oxidizing conditions. The ulvöspinel component of titanomagnetite and ilmenite forms rutile or sphene, and Fe 2 + migrates out of the spinel lattice forming titanomaghemite. (2) Formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions. The latter mechanism produces ghost textures (all titanomaghemite is transformed and only their former grain shapes are preserved), with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved. This mechanism could explain the significant magnetization loss, which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like Iceland or Hawaii. The production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of Krafla.

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“…The calculated saturation indices with respect to commonly observed secondary minerals revealed near-equilibrium between the fluids and quartz, whereas supersaturation occurs with respect to calcite, chlorite, feldspars, wollastonite, and zeolites ( Figure 5). Supersaturation may have resulted from high initial concentrations in the inlet experimental solutions relative to the equilibrium composition at 260°C and experimental durations of hours, compared to residence times of fluids in natural geothermal systems like at Krafla that are in the order of months to years [42,43]. We conclude that the chemical composition of geothermal fluids at subcritical temperatures is controlled by nearequilibrium with secondary minerals.…”

Section: Discussionmentioning

confidence: 83%

Supercritical Fluid Geochemistry in Geothermal Systems

2019

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Supercritical fluids exist in the roots of many active high-temperature geothermal systems. Utilization of such supercritical resources may multiply energy production from geothermal systems; yet, their occurrence, formation mechanism, and chemical properties are poorly constrained. Flow-through experiments at 260°C and 400-420°C were performed to study the chemical and mineralogical changes associated with supercritical fluid formation near shallow magmatic intrusions by conductive heating and boiling of conventional subcritical geothermal fluids. Supercritical fluids formed by isobaric heating of liquid geothermal water had similar volatile element concentrations (B, C, and S) as the subcritical water. In contrast, mineral-forming element concentrations (Si, Na, K, Ca, Mg, and Cl) in the supercritical fluid were much lower. The results are consistent with the observed mineral deposition of quartz, aluminum silicates, and minor amount of salts during boiling. Similar concentration patterns have been predicted from geochemical modeling and were observed at Krafla, Iceland, for the IDDP-1 supercritical fluid discharge. The experimental results confirm previous findings that supercritical fluids may originate from conductive heating of subcritical geothermal reservoir fluids characterized by similar or lower elemental concentrations with minor input of volcanic gas.

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Application of radium isotopes to determine crustal residence times of hydrothermal fluids from two sites on the Reykjanes Peninsula, Iceland

Cited by 38 publications

References 43 publications

The Surtsey volcano geothermal system: An analogue for seawater-oceanic crust interaction with implications for the elemental budget of the oceanic crust

The Surtsey volcano geothermal system: An analogue for seawater-oceanic crust interaction with implications for the elemental budget of the oceanic crust

Modification of the magnetic mineralogy in basalts due to fluid-rock interactions in a high-temperature geothermal system (Krafla, Iceland)

Supercritical Fluid Geochemistry in Geothermal Systems

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