Using Geochemical Data

Rollinson, Hugh

doi:10.4324/9781315845548

Cited by 228 publications

(179 citation statements)

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“…This range of variation is typical of mantle-derived carbon dioxide (Rollinson, 1993;Deines, 2002) and is in agreement with what was suggested by the helium isotopic values from this study and other reports from many other areas along the Ethiopian Rift (Lee et al, 2016).…”

Section: Diagrams (See Text)supporting

confidence: 81%

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Minissale

Corti

Tassi

et al. 2017

Journal of Volcanology and Geothermal Research

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In this study, the occurrence, chemical composition, origin and geothermal significance of thermal springs and fumaroles naturally discharging in the area located north of the Lake Abaya (western margin of the Main Ethiopian Rift, East Africa) are reviewed in relation with recent tectonics. All thermal springs showed a dominantly Na-HCO 3 composition, consistent with observations dating from at least 1972, and most of them displayed a narrow range of δD and δ 18 O isotopic compositions for water similar to regional meteoric origins. These observations suggest that water-rock interaction processes occur in all aquifers and dominate the contributions of water that actively circulate within thermal fluids, and also suggest a similar elevation of groundwater recharge throughout the study area. Most of the thermal springs are dominated by a CO 2 -rich gas phase and discharge along the active faults bordering the western edge of the Main Ethiopian Rift valley. The δ 13 C values of CO 2 and the 3 He/ 4 He isotopic ratios are consistent with the presence of mantle-derived fluids similar to what is observed in many other areas along the kinematically active African Rift, especially within Ethiopia. The application of geothermometric techniques in the liquid and the gas phases suggests the presence of a deep reservoir in which the fluids equilibrated at a maximum temperature of approximately 180°C. Additionally, the presence of fumaroles at boiling temperatures and water/mud boiling pools in several places suggests that the geothermal reservoir is positioned at a relatively shallow depth and likely located in the western side of the study area. The analysis of data collected throughout time reveals that the waters of Lake Abaya have experienced an increase in salinity of 20% paralleled contemporaneously with a decrease in pH and δ 18 O and δD of water in the last 40 years; these changes do not appear to be related to climate changeinduced increases in temperature or evaporation at the global scale.

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Section: Diagrams (See Text)supporting

confidence: 81%

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Minissale

Corti

Tassi

et al. 2017

Journal of Volcanology and Geothermal Research

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“…Secondary interactions with evaporitic deposits added salinity (high TDS) and related solutes to the springs emerging in correspondence of salares. The carbon isotopic signature of CO 2 in the bubbling gases associated with most Na + -Cl − waters (Table 4) was in the range of gases from mantle degassing (from − 9‰ to − 2‰ vs. V-PDB; Barnes et al, 1978;Javoy et al, 1982;Rollinson, 1993;Ohmoto and Goldhaber, 1997;Hoefs, 2009). However, their high CO 2 / 3 He ratios (up to 2.9 × 10 12 ; Table 4), up to three orders of magnitude higher than the mantle value (~1.2 × 10 9 ; Marty and Jambon, 1987), allow to exclude a significant contribution of mantle CO 2 , notwithstanding the occurrence of up to 16% of mantle He, as indicated by the Rc/Ra values (Poreda and Craig, 1989;Hilton et al, 2002).…”

Section: Origin Of Gasesmentioning

confidence: 99%

Fluid geochemistry of a deep-seated geothermal resource in the Puna plateau (Jujuy Province, Argentina)

Arnold

Cabassi

Tassi

et al. 2017

Journal of Volcanology and Geothermal Research

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This study focused on the geochemical and isotopic features of thermal fluids discharged from five zones located in the high altitude Puna plateau (Jujuy Province between S 22°20′-23°20′ and W 66°-67°), i.e. Granada, Vilama, Pairique, Coranzulí and Olaroz. Partially mature waters with a Na + -Cl − composition were recognized in all the investigated zones, suggesting that a deep hydrothermal reservoir hosted within the Paleozoic crystalline basement represents the main hydrothermal fluid source. The hydrothermal reservoirs are mainly recharged by meteoric water, although based on the δ 18 O-H 2 O and δD-H 2 O values, some contribution of andesitic water cannot be completely ruled out. Regional S-oriented faulting systems, which generated a horst and graben tectonics, and NE-, NW-and WE-oriented transverse structures, likely act as preferentially uprising pathways for the deep-originated fluids, as also supported by the Rc/Ra values (up to 1.39) indicating the occurrence of significant amounts of mantle He (up to 16%). Carbon dioxide, the most abundant compound in the gas phase associated with the thermal waters, mostly originated from a crustal source, although the occurrence of CO 2 from a mantle source, contaminated by organic-rich material due to the subduction process, is also possible. Relatively small and cold Na + -HCO 3 − -type aquifers were produced by the interaction between meteoric water and Cretaceous, Palaeogene to Miocene sediments. Dissolution of evaporitic surficial deposits strongly affected the chemistry of the thermal springs in the peripheral zones of the study area. Geothermometry in the Na-K-Ca-Mg system suggested equilibrium temperatures up to 200°C for the deep aquifer, whereas lower temperatures (from 105 to 155°C) were inferred by applying the H 2 geothermometer, likely due to re-equilibrium processes during the thermal fluid uprising within relatively shallow Na-HCO 3 aquifers. The great depth of the geothermal resource (possibly N 5000 m b.g.l.) is likely preventing further studies aimed to evaluate possible exploitation, although the occurrence of Liand Ba-rich deposits associated may attract financial investments, giving a pulse for the development of this remote region.

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“…This hypothesis is confirmed by the δ 13 C-CO 2 values of the sampled waters, ranging from −27.6 to +2.3‰ vs. VPDB [19,39,40], which suggest that CO 2 has a two-fold origin: relatively negative δ 13 C-CO 2 values of the low pCO 2 waters imply dominant CO 2 contribution from soil respiration and aerobic decay of organic matter [44]; conversely, less negative δ 13 C-CO 2 values of the medium-to-high pCO 2 waters point to CO 2 production from thermo-metamorphic reactions involving carbonate formations (δ 13 C-CO 2 values from −2.0 to +2.3‰ vs. VPDB [45]) and minor contribution from mantle degassing (δ 13 C-CO 2 values from −7.0 to −3.0‰ vs. VPDB [46]). Consistent with this hypothesis, the different populations highlighted in the QQ plot (Figure 3) can be interpreted as representative of pCO 2 values fed by both biological and endogenous sources.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of the Theoretical Geothermal Potential of Inferred Geothermal Reservoirs within the Vicano–Cimino and the Sabatini Volcanic Districts (Central Italy) by the Application of the Volume Method

Cinti

Procesi

Poncia³

2018

Energies

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Abstract:The evaluation of the theoretical geothermal potential of identified unexploited hydrothermal reservoirs within the Vicano-Cimino and Sabatini volcanic districts (Latium region, Italy) has been made on the basis of a revised version of the classical volume method. This method is based on the distribution of the partial pressure of CO 2 (pCO 2 ) in shallow and deep aquifers to delimit areas of geothermal interest, according to the hypothesis that zones of high CO 2 flux, either from soil degassing and dissolved into aquifers, are spatially related to deep hydrothermal reservoirs. On the whole, 664 fluid discharges (cold waters, thermal waters, and bubbling pools) have been collected from shallow and deep aquifers in the Vicano-Cimino Volcanic District and the Sabatini Volcanic District for chemical and isotopic composition, in an area of approximately 2800 km 2 . From this large hydro-geochemical dataset the pCO 2 values have been computed and then processed to obtain a contour map of its spatial distribution by using geostatistical techniques (kriging). The map of pCO 2 has been used to draw up the boundaries of potentially exploitable geothermal systems within the two volcanic districts, corresponding to the areas where endogenous CO 2 raise up to the surface from the deep hydrothermal reservoirs. The overall estimated potential productivities and theoretical minimum and maximum thermal power of the two volcanic districts are of about 45 × 10 3 t/h and 3681-5594 MWt, respectively. This makes the Vicano-Cimino Volcanic District and the Sabatini Volcanic District very suitable for both direct and indirect exploitation of the geothermal resources, in view of the target to reduce electricity generation from conventional and poorly sustainable energy sources.

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Using Geochemical Data

Cited by 228 publications

References 0 publications

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Fluid geochemistry of a deep-seated geothermal resource in the Puna plateau (Jujuy Province, Argentina)

Evaluation of the Theoretical Geothermal Potential of Inferred Geothermal Reservoirs within the Vicano–Cimino and the Sabatini Volcanic Districts (Central Italy) by the Application of the Volume Method

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