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New geochemical and isotopic insights to evaluate the geothermal resource of the hydrothermal system of Rosario de la Frontera (Salta, northern Argentina)
Abstract
In this study, the chemical and isotopic composition of thermo-mineral springs from the Rosario de la Frontera hydrothermal system was used to construct a conceptual model describing the source regions the thermal fluids and the chemical-physical processes controlling the chemistry of waters and dissolved gases during their underground circulation. The main hydrothermal reservoir, hosted within the Cretaceous Pirgua Subgroup deposits, is fed by meteoric water and shows a Na-HCO3 composition produced by water-rock interactions involving sedimentary formations mostly consisting of conglomerates and sandstones, which are interbedded with alkaline volcanic rocks and shales and limestone deposits. This aquifer also receives significant contributions of crustal CO2 and He from mantle degassing, the latter being likely favored by the regional tectonic assessment that is characterized by a deep detachment (at about 10 km depth) in the basement of the Santa Bárbara thick-skinned thrust system and a thinned lithosphere. The uprising thermal fluids mix with a relatively high salinity Na-Cl dominated aquifer produced by the interaction of meteoric water with the Tertiary Anta Formation evaporite. The temperatures of the hydrothermal reservoir, estimated with water geothermometers, are up to 130 °C, which are consistent with the thickness of the hydrothermal circuit (2,700-3,000 m) and the relatively high local geothermal gradient (~ 40 °C/km). These results suggest that the heat stored in the fluid phase of RFHS is up to ~ 1 × 1018 J, a value significantly higher (20%) than that previously estimated assuming an average reservoir temperature of 90 °C.
... Due to the renewable and clean nature of geothermal resources, the demand for exploring geothermal resources is increasing year by year. At present, the development methods of geothermal resources such as [1,2] still rely on geological exploration, expert evaluation, on-site inspections, and other means, which require high costs. Exploring geothermal anomalies in ground areas through satellite remote sensing images is an extremely efficient means. ...
... In the comparative experiment of network depth, we adopted three U-Net network depths: [1,2,4], [1,2,4,8], [1,2,4,8,16]. The comparative experimental indices are shown in Table 4. ...
... In the comparative experiment of network depth, we adopted three U-Net network depths: [1,2,4], [1,2,4,8], [1,2,4,8,16]. The comparative experimental indices are shown in Table 4. ...
Geothermal resources are efficient, clean, and renewable energy sources. Using high-resolution images captured by remote sensing satellites for temperature retrieval and searching for geothermal anomaly areas is an efficient method. However, obtaining land surface temperature retrieval images requires multiple steps of calculation, which can result in a great loss of image information and resolution. Therefore, the super-resolution reconstruction of LST retrieval images is currently a challenge in geothermal resource exploration. Although the current super-resolution methods for LST retrieval images can appropriately restore image quality, the overall restoration of the surface temperature information in the region is still not ideal. We propose a cross-scale reference image super-resolution model based on a diffusion model using deep learning technology. First, we propose the Pre-Super-Resolution Network (PreNet), which can improve both indices and the visual effect of images. Second, to reduce the white noise in the super-resolution images, we propose the Cross-Scale Reference Image Attention Mechanism (CSRIAM). The introduction of this mechanism greatly reduces noise in the images and improves the overall image quality. Compared to previous methods, we improved both experimental indices such as Peak Signal-to-Noise Ratio (PSNR), Structural Similarity (SSIM), etc., and vision quality, and optimized the recovery of geothermal anomalies. Through our experimental results, we found that the CS-Diffusion model has a very strong ability to restore the image quality of the LST retrieval. After restoring its image quality, we can make a positive contribution to subsequent geothermal resource exploration.
... Several prior studies have characterized He-C isotope systematics in volcanic and geothermal systems in the Andes (Figure 1; e.g., Hilton et al., 1993;Hoke et al., 1994;Varekamp et al., 2006;Sepúlveda et al., 2007;Aguilera, 2008;Ray et al., 2009;Tassi et al., 2009;Tassi et al., 2010;Capaccioni et al., 2011;Tassi et al., 2011;Aguilera et al., 2012;Agusto et al., 2013;Benavente et al., 2013;Chiodi et al., 2015;Aguilera et al., 2016;Benavente et al., 2016;Roulleau et al., 2016;Tardani et al., 2016;Tassi et al., 2016;Arnold et al., 2017;Tassi et al., 2017;Lopez et al., 2018;Chiodi et al., 2019;Arnold et al., 2020;Inostroza et al., 2020;Robidoux et al., 2020;Lages et al., 2021;Tardani et al., 2021;Filipovich et al., 2022) to understand the source of the volcanic fluid and gas emissions. These studies demonstrate the cooccurrence of mantle ( 3 He/ 4 He up to~8 R A ) and crustal ( 3 He/ 4 He~0.05 ...
... Helium ( Figure 2) and carbon isotopic and relative abundance ratios ( Figure 3) are reported in Table 1. For comparison, we also compile data from a number of previous studies (Hilton et al., 1993;Hoke et al., 1994;Varekamp et al., 2006;Sepúlveda et al., 2007;Aguilera, 2008;Ray et al., 2009;Tassi et al., 2009;Tassi et al., 2010;Tassi et al., 2011;Capaccioni et al., 2011;Aguilera et al., 2012;Agusto et al., 2013;Benavente et al., 2013;Chiodi et al., 2015;Aguilera et al., 2016;Benavente et al., 2016;Roulleau et al., 2016;Tardani et al., 2016;Tassi et al., 2016;Tassi et al., 2017;Arnold et al., 2017;Lopez et al., 2018;Chiodi et al., 2019;Arnold et al., 2020;Inostroza et al., 2020;Robidoux et al., 2020;Tardani et al., 2021;Lages et al., 2021;Filipovich et al., 2022; Supplementary Table S1). We also compute and report estimates of subduction and mantle derived inputs, after Sano and Marty (1995) ( Table 2). ...
... ;Ray et al., 2009;Tassi et al., 2009;Tassi et al., 2010;Capaccioni et al., 2011;Tassi et al., 2011;Aguilera et al., 2012;Agusto et al., 2013;Benavente et al., 2013;Chiodi et al., 2015;Aguilera et al., 2016;Benavente et al., 2016;Roulleau et al., 2016;Tardani et al., 2016;Tassi et al., 2016;Arnold et al., 2017;Tassi et al., 2017;Lopez et al., 2018;Chiodi et al., 2019;Arnold et al., 2020;Inostroza et al., 2020;Robidoux et al., 2020;Lages et al., 2021;Tardani et al., 2021;Filipovich et al., 2022) and samples from this study(n = 14) ...
Subduction zones represent the interface between Earth’s interior (crust and mantle) and exterior (atmosphere and oceans), where carbon and other volatile elements are actively cycled between Earth reservoirs by plate tectonics. Helium is a sensitive tracer of volatile sources and can be used to deconvolute mantle and crustal sources in arcs; however it is not thought to be recycled into the mantle by subduction processes. In contrast, carbon is readily recycled, mostly in the form of carbon-rich sediments, and can thus be used to understand volatile delivery via subduction. Further, carbon is chemically-reactive and isotope fractionation can be used to determine the main processes controlling volatile movements within arc systems. Here, we report helium isotope and abundance data for 42 deeply-sourced fluid and gas samples from the Central Volcanic Zone (CVZ) and Southern Volcanic Zone (SVZ) of the Andean Convergent Margin (ACM). Data are used to assess the influence of subduction parameters (e.g., crustal thickness, subduction inputs, and convergence rate) on the composition of volatiles in surface volcanic fluid and gas emissions. He isotopes from the CVZ backarc range from 0.1 to 2.6 RA (n = 23), with the highest values in the Puna and the lowest in the Sub-Andean foreland fold-and-thrust belt. Atmosphere-corrected He isotopes from the SVZ range from 0.7 to 5.0 RA (n = 19). Taken together, these data reveal a clear southeastward increase in ³He/⁴He, with the highest values (in the SVZ) falling below the nominal range associated with pure upper mantle helium (8 ± 1 RA), approaching the mean He isotope value for arc gases of (5.4 ± 1.9 RA). Notably, the lowest values are found in the CVZ, suggesting more significant crustal inputs (i.e., assimilation of ⁴He) to the helium budget. The crustal thickness in the CVZ (up to 70 km) is significantly larger than in the SVZ, where it is just ∼40 km. We suggest that crustal thickness exerts a primary control on the extent of fluid-crust interaction, as helium and other volatiles rise through the upper plate in the ACM. We also report carbon isotopes from (n = 11) sites in the CVZ, where δ¹³C varies between −15.3‰ and −1.2‰ [vs. Vienna Pee Dee Belemnite (VPDB)] and CO2/³He values that vary by over two orders of magnitude (6.9 × 10⁸–1.7 × 10¹¹). In the SVZ, carbon isotope ratios are also reported from (n = 13) sites and vary between −17.2‰ and −4.1‰. CO2/³He values vary by over four orders of magnitude (4.7 × 10⁷–1.7 × 10¹²). Low δ¹³C and CO2/³He values are consistent with CO2 removal (e.g., calcite precipitation and gas dissolution) in shallow hydrothermal systems. Carbon isotope fractionation modeling suggests that calcite precipitation occurs at temperatures coincident with the upper temperature limit for life (122°C), suggesting that biology may play a role in C-He systematics of arc-related volcanic fluid and gas emissions.
... El calentamiento de las aguas termales se produciría entonces por la interacción de aguas de origen meteórico con rocas permeables a profundidades importantes. Este modelo hidrotermal fue propuesto para las termas de La Quinta y El Palmar (Claros, 2020), El Sauce (Chiodi et al. 2016) y Rosario de la Frontera (Seggiaro et al. 2015, Chiodi et al. 2015. No obstante, en el caso de Rosario de la Frontera se comprobó además la contribución de gases de origen mantélico (helio), vinculados a fracturas profundas que probablemente conecten el manto con el reservorio (Chiodi, 2015). ...
... Este modelo hidrotermal fue propuesto para las termas de La Quinta y El Palmar (Claros, 2020), El Sauce (Chiodi et al. 2016) y Rosario de la Frontera (Seggiaro et al. 2015, Chiodi et al. 2015. No obstante, en el caso de Rosario de la Frontera se comprobó además la contribución de gases de origen mantélico (helio), vinculados a fracturas profundas que probablemente conecten el manto con el reservorio (Chiodi, 2015). En lo referente al sector sur del Área 2, las evidencias sobre las fuentes de calor se determinaron a diferentes escalas. ...
... Zona Norte (Sistema conductivo). El sistema de Santa Bárbara está caracterizado por gradientes geotérmicos aproximadamente normales con existencia de reservorios geotérmicos profundos conectados por fallas de alto ángulo (Seggiaro et al. 2015, Chiodi et al. 2015. Las fallas juegan un rol preponderante como conductos o barreras que compartimentan el sistema en bloques. ...
This report show the Geothermal Play Fairway (GPF) methodology applied to vast
area (71 thousands square kilometers) of Northwestern Argentina, comprising the
morphostructural regions of Subandean Ranges, Eastern Cordillera, Santa Barbara System
and Chaco-Pampean Plain (Salta, Jujuy; Tucuman, Santiago del Estero and Catamarca
provinces).
Following the GPF methodology, in which varied, direct and indirect geological data
is integrated and modeled, Evidence maps of Permeability, Fluid and Heat subsystems were generated. These maps altogether form the resultant Geothermal Potential map, Area II. The three subsystems were analyzed, being the Permeability subsystem the highest ranked. This subsystem counts all mapped and subsurface-interpreted structures (faults, lineaments) or sets of structures that give the space for the geothermal fluids to reach the surface. These features were weighted by typology, age, interacting structures, and associated earthquake depth. Heat subsystem is the second in importance. Here, a deep source of heat was determined by geochemical evidence (geothermometry calculations on thermal waters). Well data and geophysical surveys have confirmed anomalous geothermal gradients. The lesser weight was assigned to the Fluid Subsystem, in which geochemical analysis of hydrothermal water springs concluded the involvement of high enthalpy geothermal fluids.Evidence map combination and their weightings led to a final geothermal favorability map in Area II, in which proven geothermal zones were located. These are:
Northern Zone: Located in the Santa Barbara System and classified as a Conductive
system. Characterized by normal geothermal gradients and deep geothermal reservoirs related to high-angle faults. These structures play the role of fluid conducts or barriers.
Southern Zone: Covers the Tucuman-Santiago plains and it is classified as a
Convective-Conductive system. Anomalous geothermal gradients are scattered all over the
area. Signs of a mantle-origin, ascending heat through basement and in association with deep structures, are interpreted.
Other zones with high probability of blind (not outcropping) geothermal systems
occurrence were highlighted.
... The widespread recent volcanic activity defines a variable-width Andean geothermal belt of anomalous heat flux (>150 mW/m 2 ) that are inferred to host vast high-temperature geothermal resources [3]. In addition, to the east, numerous thermal springs are located along the frontal structures of the Andean retro-wedge (Figure 1), although related to normal to slightly anomalous geothermal gradient, e.g., [3][4][5]. Despite these favourable geological conditions and its high potential, the Andes still represent the largest undeveloped geothermal region in the world due to financial and technical barriers as well as geoscientific aspects [6]. ...
... This is due mostly to the lack of detailed surficial geological information in several geothermal areas limiting the development of accurate conceptual models and interpretation of the available geophysical and geochemical data. In this sense, in recent years several research groups and private companies have revealed the existence of numerous sites of interest for geothermal exploitation in north-west Argentina, e.g., [4,5,[8][9][10][11][12][13]. One of the most promising geothermal prospects in north-western Argentina is the Tocomar Geothermal Field (TGF) [8,14], alongside with other systems in the Puna region [13] and in the Subandean fold-and thrust belt [4,5,10,11]. ...
... In this sense, in recent years several research groups and private companies have revealed the existence of numerous sites of interest for geothermal exploitation in north-west Argentina, e.g., [4,5,[8][9][10][11][12][13]. One of the most promising geothermal prospects in north-western Argentina is the Tocomar Geothermal Field (TGF) [8,14], alongside with other systems in the Puna region [13] and in the Subandean fold-and thrust belt [4,5,10,11]. The TGF is located in the Puna plateau across the NW-SE-trending Calama-Olacapato-El Toro (COT) lineament [15][16][17][18], one of the major active tectonic lineament in the Central Andes (Figures 1 and 2). ...
This paper presents a detailed geological map at the 1:20,000 scale of the Tocomar basin in the Central Puna (north-western Argentina), which extends over an area of about 80 km 2 and displays the spatial distribution of the Quaternary deposits and the structures that cover the Ordovician basement and the Tertiary sedimentary and volcanic units. The new dataset includes litho-facies descriptions, stratigraphic and structural data and new 234 U/ 230 Th ages for travertine rocks. The new reconstructed stratigraphic framework, along with the structural analysis, has revealed the complex evolution of a small extensional basin including a period of prolonged volcanic activity with different eruptive centres and styles. The geological map improves the knowledge of the geology of the Tocomar basin and the local interplay between orogen-parallel thrusts and orogen-oblique fault systems. This contribution represents a fundamental support for in depth research and also for encouraging geothermal exploration and exploitation in the Puna Plateau region.
... Encouraged by this pulse, geochemical investigations were recently carried out to describe the chemical and isotopic features of Tuzgle-Tocomar and Cerro Blanco hydrothermal fluids (Puna plateau) and Rosario de la Frontera, providing evidence for relatively high (≥200°C and 130°C, respectively) estimated reservoir https://doi.org/10.1016/j.jsames.2020.102627 Received 6 February 2020; Received in revised form 24 April 2020; Accepted 27 April 2020 temperatures Chiodi et al., 2015Chiodi et al., , 2019. Recently, Peralta Arnold et al. (2017) investigated the chemistry of thermal fluids from five zones in the northern Puna (Granada, Vilama, Pairique, Coranzuli and Olaroz; Jujuy Province) estimating reservoir temperatures of 150-200°C. ...
... Symbols as in Fig. 1. reservoir feeding EP and LQ springs, in this area locate at a depth > 2000 m. Hence, the relatively high estimated temperatures for these waters suggest the occurrence of an anomalous geothermal gradient in this province, as suggested for other hydrothermal systems in similar geotectonic contexts (Invernizzi et al., 2014;Chiodi et al., 2015;Maffucci et al., 2016). Actually, during the drilling of SA well, upwelling water from~1000 m depth yielded temperatures higher than 70°C (Palanca, 1991;Pesce and Miranda, 2003), i.e. almost the double of the expected temperature at that depth under a normal geothermal gradient. ...
... Notwithstanding, hydrothermal waters hosted at great depth (> 2000 m) within the geological units of the Salta Group in the SB domain, display a relatively high estimated temperature (~200°C). These results indicate the occurrence of an anomalous thermal gradient, in agreement with previous studies that investigated different hydrothermal systems in this province (Invernizzi et al., 2014;Chiodi et al., 2015;Maffucci et al., 2016). This work is an additional contribution to the knowledge of the NW Argentine geothermal resource, whose promising results encourage further geological and geophysical surveys in this area, mainly aiming to estimate the effective dimensions and the effective potential of this promising geothermal resource. ...
Fluid primary source(s) and chemical-physical processes controlling water and gas chemistry of thermal springs
from Eastern Cordillera, sub-Andean Ranges and Santa Bárbara (Jujuy Province, northern Argentina) were investigated
to provide information for a preliminary evaluation of the geothermal potential in these areas.
Thermal manifestations in Eastern Cordillera (Reyes) and part of those in the western sector of sub-Andean
Range (Aguas Calientes) are fed by shallow aquifers, interacting with Quaternary- Neogene rocks and the upper
portion of Pliocene-Miocene formations (Orán Group), whereas the meteoric water recharge area is located
at>2500 m a.s.l., corresponding to Chañi hill. Differently, El Jordán thermal spring in the sub-Andean Range is
fed by a hydrothermal aquifer hosted within highly porous and fractured formations of the Salta Group
(Yacoraite Formation) and recharged by meteoric water from Sierra de Calilegua (∼1500m a.s.l.). The latter is
the recharge area of the La Quinta geothermal waters as well, but these have been fed at higher altitudes
(> 2500 m a.s.l.) in the range. The hydrothermal reservoir feeding the other thermal springs from the Santa
Barbara system (Caimancito, El Palmar, and Siete Aguas) is recharged by meteoric water from Zapla Ranges and
Santa Barbara Hill at<2500m a.s.l. The high-TDS (> 16,000 mg/L) Na+-Cl- La Quinta thermal springs are
produced by interaction with the evaporite deposits of Salta Group, including halite, whereas the chemistry of El
Palmar, El Jordán and Caimancito thermal springs, showing a Na+-SO4
2-(Cl−) composition, depends on mixing
with shallower SO4
2--rich waters interacting with gypsum deposits of Anta Formation. Dissolved and bubbling
gases from all the investigated provinces are related to CO2- and CH4-rich crustal fluids produced by both
thermogenic processes occurring within the hydrothermal systems and microbial activity at relatively low depth,
with low to negligible mantle contribution, as indicated by the 3He/4He values ≤ 0.21 Ra. The fluid reservoir
feeding the Quinta thermal springs shows the highest estimated temperatures (> 200 °C), which, considering the
depth of Salta Group in the Santa Barbara system (~2000 m), support the idea, suggested by previous authors, of
an anomalous geothermal gradient for this area, a promising pre-requisite for future exploitation of the geothermal
resource.
... In this paper, we discuss the relationship between fracturing and thermal alteration of the cap rock of the Rosario de La Frontera geothermal system in the outer zone of the Andean retrowedge (NW Argentina). This active geothermal system is characterized by several hot springs mainly occurring at the northern edge of the Sierra de La Candelaria anticline, close to the town of Rosario de La Frontera (Moreno Espelta et al., 1975;Seggiaro et al., 1995;Pesce and Miranda, 2003;Invernizzi et al., 2014;Chiodi et al., 2015). At depths, reservoir rocks are fractured sandstones of the Cretaceous syn-rift deposits (Pirgua Subgroup) and cap rocks are low permeability post-rift and syn-orogenic deposits (Balbuena and Santa Bárbara Subgroups, and Metán Subgroup respectively; Moreno Espelta et al., 1975;Seggiaro et al., 1995Seggiaro et al., , 2015Invernizzi et al., 2014;Chiodi et al., 2015;Maffucci et al., 2015). ...
... This active geothermal system is characterized by several hot springs mainly occurring at the northern edge of the Sierra de La Candelaria anticline, close to the town of Rosario de La Frontera (Moreno Espelta et al., 1975;Seggiaro et al., 1995;Pesce and Miranda, 2003;Invernizzi et al., 2014;Chiodi et al., 2015). At depths, reservoir rocks are fractured sandstones of the Cretaceous syn-rift deposits (Pirgua Subgroup) and cap rocks are low permeability post-rift and syn-orogenic deposits (Balbuena and Santa Bárbara Subgroups, and Metán Subgroup respectively; Moreno Espelta et al., 1975;Seggiaro et al., 1995Seggiaro et al., , 2015Invernizzi et al., 2014;Chiodi et al., 2015;Maffucci et al., 2015). ...
... Furthermore, E-W normal faults, dissecting the anticline in its central portion, formed in the final stage of folding to accommodate fold culmination . The conceptual model of fluid circulation consists of two aquifers developed at different depths and detected on the basis of geochemical, hydrogeological (Invernizzi et al., 2014;Chiodi et al., 2015) and audiomagnetotelluric (Barcelona et al., 2013) investigations. The deepest hydrothermal reservoir, hosted within the Cretaceous Pirgua Subgroup deposits, is mainly recharged by meteoric water (Invernizzi et al., 2014;Chiodi et al., 2015;Seggiaro et al., 2015) and shows a Na-HCO 3 composition with significant contributions of crustal CO 2 and He from mantle degassing . ...
Cap rock characterization of geothermal systems is often neglected despite fracturing may reduce its efficiency and favours fluid migration. We investigated the siliciclastic cap rock of Rosario de La Frontera geothermal system (NW Argentina) in order to assess its quality as a function of fracture patterns and related thermal alteration. Paleothermal investigations (XRD on fine-grained fraction of sediments, organic matter optical analysis and fluid inclusions on veins) and 1D thermal modelling allowed us to distinguish the thermal fingerprint associated to sedimentary burial from that related to fluid migration. The geothermal system is hosted in a Neogene N-S anticline dissected by high angle NNW- and ENE-striking faults. Its cap rock can be grouped into two quality categories: • rocks acting as good insulators, deformed by NNW–SSE and E–W shear fractures, NNE-SSW gypsum- and N-S-striking calcite-filled veins that developed during the initial stage of anticline growth. Maximum paleo-temperatures (< 60 °C) were experienced during deposition to folding phases.• rocks acting as bad insulators, deformed by NNW-SSE fault planes and NNW- and WNW-striking sets of fractures associated to late transpressive kinematics. Maximum paleo-temperatures higher than about 115 °C are linked to fluid migration from the reservoir to surface (with a reservoir top at maximum depths of 2.5 km) along fault damage zones.This multi-method approach turned out to be particularly useful to trace the main pathways of hot fluids and can be applied in blind geothermal systems where either subsurface data are scarce or surface thermal anomalies are lacking.
... Geothermal systems consist of a region with system of faults and fractures, filled with geothermal fluids, which can have high concentrations of dissolved salts (e.g. Mazza and Capelli, 2010;Di Salvo et al., 2013;Chiodi et al., 2015), thus resulting in conducting electrolytes in a rock matrix (Pellerin et al., 1996;Muñoz, 2014). In general, bulk conductivity of earth materials varies with porosity, pore fluid content, saturation, salinity, temperature, and clay content , Muñoz, 2014. ...
The Tocomar Geothermal System is located in the Puna Plateau (NW Argentina), within the Central Puna Energy Hub, and is considered one of the most promising places to harness potential alternative of power and heat sources in the Central Andean Volcanic Zone (16-28 °S). It is related to the Calama-Olacapato-Toro lineament and to the Quaternary Tocomar volcanic centre. Moreover, it is surrounded by active and fossil geothermal manifestations, like hot-springs, travertines and siliceous sinter deposits. Despite some geological studies in the area, no geophysical investigations have targeted the geothermal fields along the Central Puna.
In this work we present a 3-D inversion of audio-magnetotelluric data around the Tocomar Geothermal System. These data was obtained in the frequency range of 1000-0.1 Hz to map the main elements of the geothermal system (clay cap and potential reservoir) at depths of approximately 1000 m. To achieve this goal, previous geoelectrical studies, the local geology and the trend of the main structures were also considered. For the 3-D inversion process the ModEM code was used.
The model shows a low-resistivity layer (less than 10 Ωm) at least 300 m thick, at a depth of about 200–500 m, aligned with both the strike of the Calama-Olacapato-Toro lineament and the local superficial geothermal manifestations (hot-springs and hydrothermally altered rocks). This low-resistivity layer is linked with the clay cap at the shallow depth of the geothermal reservoir. At depths greater than 800 m, a gradual increase in resistivity is observed related to a potential reservoir within the fractured Ordovician basement. The final 3-D resistivity model highly correlates with the conceptual models of high-temperature volcanic geothermal systems.
... • Geochemistry including natural CO2 emissions (Chiodi et al., 2015;Vannoli et al. 2021), ...
Favourability mapping to empower scalability of the geothermal proposition - mapping geothermal resource potential across a region in conjunction with mapping of infrastructure, market, competing resources, ESG factors and decarbonisation potential.
... For a detailed explanation of these methods the reader is directed to Vieira & Hamza (2019). Data include locations for Argentina (Henry & Pollack 1988;Miranda & Johanis 2000;Pesce & Miranda 2000Sylwan et al. 2008;Vergani et al. 2008;MACDSC 2014;Sylwan 2014;Chiodi et al. 2015Chiodi et al. , 2016Chiodi et al. , 2019Chiodi et al. , 2020Bona & Coviello 2016;Giordano et al. 2016;Ávila & Dávila 2018;Collo et al. 2018;Christiansen et al. 2021b), Bolivia (Henry & Pollack 1988;Springer 1999;Hamza et al. 2005), Brazil (Vitorello et al. 1978;Hurter & Pollack 1996;Hamza et al. 2005), Chile (Uyeda & Watanabe 1970;Cande et al. 1987;Muñoz & Hamza 1993;Murdie et al. 1998;Springer & Förster 1998;Springer 1999;Collo et al. 2018;Pickler et al. 2018;Stefani 2018), Paraguay , Perú (Springer 1999) and Uruguay (Morales et al. 2020). ...
The surface heat flow of southern South America was examined based on an updated database containing 1113 locations. Accordingly, this study presents the most accurate heat flow map of the southern portion of the continent (south of 16° 30'S latitude), covering areas that previously presented limited information. The main anomalies show a strong spatial correlation with geothermal zones and with the most up-to-date lithospheric thickness maps. The blanketing effect produced by the sedimentary basins was demonstrated to reduce the surface heat flow up to 27 mW/m2 over the thickest basins. The study region was separated into 4 large areas and their connection to tectonic processes analyzed. The Central Andes present high heat flow zones related to a thick radiogenic crust, volcanic activity, and a hot asthenospheric wedge. In the Pampean flat-slab region, the low heat flow coincides mostly with the horizontal projection of the Juan Fernández aseismic ridge and not with a wide region as previously thought. Furthermore, a close relationship between the subduction of the ridges at different angles and a cold upper-plate lithosphere is suggested. Besides active regions of arc magmatism and a thin lithosphere, we propose that a hot upper-plate upwelling beneath the Patagonian Platform is also contributing to the high heat flow in the area. The foreland region exhibits a low heat flow coinciding with a thick cratonic lithosphere, and local high heat flow values in suture zones possibly triggered by ancient delamination beneath these regions.
... The hydrochemical differentiation of the chloride-rich waters, related to the processes in the geothermal reservoir, can be noticed based on specific molecular ratios; these are more like other springs of the Chivay group, where waters are far from the Na/Cl stoichiometric line (Fig. 9A, Table S2). The Na/Cl molar ratio in waters of the Chivay group is >1, which is not related to halite dissolution and can be the result of Na-silicates leaching (e.g., of feldspars or their alteration products) (Chiodi et al., 2015) (Fig. 9A, Table S2). In contrast, thermal waters in Paclla display Na/Cl ratio equal to 1. On the other hand, the Ca/SO 4 ratio in waters in the Chivay geothermal area is close to 1 (Fig. 9B, Table S2), which most probably may result from the secondary dissolution of gypsum in the aquifer. ...
Thermal waters and vapor discharges (hot springs, geysers, solfataras, and fumaroles) are common phenomena in volcanic regions at active plate boundaries, and the Central Andes are no exception. The Colca River basin in S Peru is a highly diversified and complex thermal region with unresolved questions on the origin of thermal fluids, reservoir temperature, and connections with tectonic and/or volcanic activity. To answer these, we used hydrogeochemical analysis of 35 water samples from springs and geysers, together with isotopic (δ¹⁸O and δD) analysis, chemical and mineral studies of precipitates collected in the field around these outflows, and field observations. We aimed (1) to recognize the geochemistry of thermal waters and precipitates in the central part of the Colca River basin, (2) to identify fluid sources and their origin, (3) to estimate the temperature of a potential geothermal reservoir, and (4) to discuss the regional active tectonic and volcanic framework of this geothermal region and mutual relationships.
Our results corroborate a heterogeneous and complex geothermal system in the central part of the Colca River basin, with contrasting hydrogeochemical and physical properties, variable isotope composition, different reservoir temperatures, and associated precipitates around thermal springs. Processes controlling water chemistry are closely related to the Ampato-Sabancaya magmatic chamber's activity and tectonic structures that allow complex interactions of meteoric waters with magmatic fluids and gases. With a considerable gradient of pressure owing to local relief and deep incision in the Colca Canyon, these processes led to the differentiation of the thermal waters into three main groups. (1) Chloride-rich, mainly sodium chloride, thermal waters are of meteoric origin but mature within the geothermal reservoir possibly fed by magma degassing. These waters' chemical and isotopic composition results from water-rock interaction and mixing with magmatic waters within the reservoir. These waters discharge at the bottom of the Colca Canyon and Valley, presenting a broad hydrogeochemical spectrum and highly variable mineral phases precipitating at the outflows. The reservoir temperature estimated for these waters ranges from 180 to 200 °C. The group of hottest springs and geysers at the bottom of the Colca Canyon waters are fully equilibrated, with the reservoir temperature ~ 240 °C. (2) Sulfate-rich waters are shallow meteoric waters heated by ascending gases that form an independent group referring to the local water circulation, often controlled by tectonic barriers. (3) Bicarbonate-rich waters are the intermediate meteoric waters, divided into two hydrochemical groups: waters partially equilibrated with reservoir rocks and more similar to chloride-rich waters or additionally enriched with SO4 and more similar to sulfate-rich waters.
Studied thermal springs show a clear spatial correlation with active and seismogenic crustal W- to NW-tracing normal and strike-slip faults. These act as barriers to infiltrating meteoric waters, provide pathways to hydrothermal solutions and gases assisting in meteoric water heating, and yield passages for pressured by lithostatic load and heated waters to ascend to the surface.
... • Geochemistry including natural CO2 emissions (Chiodi et al., 2015;Vannoli et al. 2021), ...
Keywords
geothermal energy; prospectivity; workflow; favourability mapping; geospatial; commercial; market; gravity; magnetic; scalability; complexity; investment decision; repeatability; machine learning; heat; power; faults; permeability; volume; ranking.
... Recent research (e.g. Barcelona et al., 2013Barcelona et al., , 2014Invernizzi et al., 2014;Chiodi et al., 2015Chiodi et al., , 2016Maffucci et al., 2015Maffucci et al., , 2016Seggiaro et al., 2015) reveals the significant potential of the geothermal resources in this region. ...
Dentro de un escenario de calentamiento global en busca de la transición energética de combustibles fósiles a fuentes de energías libres de emisiones de CO2, así como la mejora en la eficiencia y la diversificación energética, la energía geotérmica se posiciona como una fuente de energía promisoria. En este trabajo se presentan nuevos datos geoquímicos e isotópicos de los fluidos relacionados al sistema geotermal El Galpón con el objetivo de investigar las condiciones fisicoquímicas de los fluidos dentro del reservorio geotermal, presentar un modelo conceptual del sistema geotermal y realizar una evaluación del potencial geotérmico del área. La caracterización geoquímica se realizó mediante el muestreo directo de aguas y el posterior análisis de su composición química e isotópica, mientras que el modelado geológico 3D se realizó utilizando el software LeapfrogGeo. El reservorio geotermal profundo, con temperaturas ~111 °C y composición bicarbonatada sódica, se encontraría alojado en los sedimentos del Subgrupo Pirgua, mientras que los depósitos del Subgrupo Balbuena constituirían el sello del sistema. El agua de origen meteórica podría alcanzar profundidades de hasta 6 Km, adquiriendo las temperaturas estimadas por geotermómetros en un área de gradiente geotérmico normal. En su ascenso a la superficie, favorecido por las estructuras, el agua geotermal sufre procesos de mezcla con acuíferos más superficiales, de composición clorurada sulfatada sódica, alojados en el Grupo Orán. El potencial geotérmico del área modelada, expresado como calor almacenado tanto en la roca como en los fluidos, sería de 4.33 * 1017 J.
T he foothills of the central Andes of northwestern Argentina hinder the interpretation of the complex structural rift system developed during late Mesozoic extension. Andean compressive deformation inverted the Salta rift system, resulting in a series of complex structures with trends oblique to the main Andes. The Lomas de Olmedo basin, a failed branch of the rift system located east of the Andean orogenic front, was selected to undertake deep reprocessing of the available industrial seismic lines. A 150-km-long seismic section of the basin, recorded with Vibroseis and dynamite sources, was reprocessed. Extended correlation applied to the Vibroseis seismic data yielded reliable results down to 9 sec two-way travel time. Acoustic horizons identified within this interval include the deepest synrift deposits in the axial part of the basin and a deep oblique discontinuity in the crust. On this basis, a complete cross section of the basin was made. This study documents the asymmetry of the rift, with a prominent zone of thermal uplift in the northern edge. Truncation of the Paleozoic beds and identification of a deep oblique discontinuity at 7–8 sec (18–21 km deep) suggest that a northward-dipping detachment controlled the asymmetry of the system. The rift structure is mildly modified by folding related to Cenozoic tectonic inversion in the southern sector of the basin. This inversion was controlled mainly by strike-slip displacements along the previous normal faults. Resumen E l pie de monte de los Andes Centrales del noroeste de Argentina esconde la interpretación de un complejo sistema estructural desarrollado durante la extensión mesozoica tardía. La deformación compresiva ándica invirtió el sistema del rift Salta, produciendo una serie de estructuras complejas con arrum-bamientos oblícuos a los Andes. La cuenca de Lomas de Olmedo, una rama abortada del sistema de rift local-izado al este del frente orogénico ándico, fue seleccionada para realizar un reprocesamiento profundo de lineas sísmicas disponibles de la industria. En particular fue seleccionada una línea sísmica de la cuenca de 150 km de longitud, registrada en su mayor parte con Vibroseis y complementada con dinamita. Un algoritmo de correlación extendida se aplicó a los datos sísmicos de Vibroseis alcanzándose resultados confiables hasta profundidades correspondientes a 9 segundos de tiempo de travesía doble. Los horizontes acústicos identifi-cados dentro de este intervalo de tiempo incluyeron tanto los depósitos más profundos de sinrift en la parte axial de la cuenca, como una profunda discontinuidad oblícua en la corteza. Sobre esta base fue confeccionada una sección completa de la cuenca. Los resultados de este estudio documentaron la asimetría del rift, con una zona prominente de levantamiento térmico a lo largo del borde norte. El truncamiento de los estratos paleo-zoicos, así como la identificación de una profunda discontinuidad oblícua a los 7–8 segundos de doble tiempo de travesía (aproximadamente 18–21 km), sugieren que un nivel de despegue inclinado hacia el norte controló la asimetría del sistema. La estructura de rift fue suavemente modificada por el plegamiento relacionado a la inversión tectónica cenozoica en el sector sur de la cuenca. Esta inversión fue en parte acomodada preferente-mente por desplazamientos de rumbo a lo largo de las fallas normales previas.
The present work summarizes the geologic history of the Salta Group basin. The information available for carrying out the work is based on personal information which, with the data provided by the bibliography, adds up to some three hundred surface sections of the outcropping of the basin, in addition to the subsurface data published. The nature of the pre-Cretaceous basement is first analyzed, together with the structural frame in which sedimentation commenced. The sedimentary history of the Salta Group, the eruptive episodes and the structural processes which took place during and after the Salta Group deposition are then summarized, in the following order: a) The synrift accumulations of the Pirgua Subgroup redbeds during Kimmeridgian?- Early Cretaceous to Campanian times, which filled and levelled the rift troughs throughout the whole basin. b) The postrift accumulations, in the shape of the Balbuena Subgroup ingression and the final fill provided by the Santa Bárbara Subgroup, which occurred between Maastrichtian and Mid- Eocene times. c) Facies evolution and the flooding processes interbedded in the red bed sequences of the Salta Group. d) The eruptive processes which occurred in the basin, expressed in three magmatic cycles. e) The tectonic episodes which took place after the Salta Group deposition and the basin inversion during Late Tertiary time.
Discrete fracture network (DFN) models are three-dimensional stochastic or combined stochastic/deterministic representations of fractures network that characterizes natural fracture systems. They represent an important tool to investigate pathways for fluid flow in geothermal reservoirs in order to predict their behavior in prospect evaluation and reservoir management.
In this project a DFN model is applied to the geothermal system of Rosario de La Frontera, in the Salta province, with the aim to assess the effective permeability of its reservoir and to obtain input parameters for dynamic reservoir modeling. This active geothermal system is marked by several hot springs, with surface temperatures ranging between 50°C and 99°C, in the surroundings of the town of Rosario de la Frontera, to the north of La Candelaria Ridge. Fractured sandstones strata belonging to the syn-rift deposits of the Salta Group (Pirgua subgroup) provide the reservoir rocks of this geothermal fluids (Moreno Espelta et alii, 1975).
With the aid of dedicated software, a 3-D geological model of the La Candelaria anticline was built in order to extract a 3-D geocellular volume of the deep reservoir to constrain the fracture network model.
Stuctural study on outcrops of the reservoir rocks allowed us to elaborate a deterministic fracture network model and to calculate the input parameters for the generation of the DFN. Field work was dedicated both to a quantitative and qualitative analysis of the fractures and faults defining diagnostic parameters such as orientation, dimension, spatial distributions, surface texture, and to calculate their density distribution within the regional fold. The acquisition of these parameters was performed along scan-lines and on scan-areas of the outcropping reservoir rocks.
According to orientation, the observed discontinuities were classified as longitudinal, transverse and oblique with respect to the fold axis trend (e.g. Stearns, 1968; Hancock, 1985; Cooper, 1992), and in turn grouped into six sets. They show different frequency values across the anticline. In particular NNW-SSE and NE-SW trending fractures are predominant along the eastern and western limbs of the anticline, respectively.
In conclusion, DFN models were generated for each fractures set in order to evaluate their influence on the distribution of the permeability in different portions of the studied anticline.
PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations.
We have addressed the origins of methane in fumarolic, thermal and cold emissions discharging from a diversity of geological settings spread all over the Italian Peninsula and at Panarea and Pantelleria islands. Fluid discharges from the main geothermal systems of the peri-Tyrrhenian area (including Mt. Amiata, Larderello, Latera and Manziana) show δ13C-CH4 and δD-CH4 values >−28‰ V-PDB and >−160‰ V-SMOW, respectively, and C1/C2 + concentration ratios > 1000. These patterns suggest that CH4 discharged from these systems is primarily generated by abiogenic reduction of CO2 and/or CO. Methane seems to have, at least partially, a different origin than the higher hydrocarbons that might be entirely related to the thermal decomposition of organic matter or, alternatively, to methane polymerization. Fumaroles from the volcanic systems of Solfatara, Vesuvio, Panarea and Pantelleria have C1/C2 + concentration ratios in a wide range (from 17 to 4300), but δ13C-CH4 and δD-CH4 values >−21‰ V-PDB and >−120‰ V-SMOW, respectively. Such isotopic values are very similar to those reported for CH4 discharging from ultramafic hydrothermal systems. In agreement with recent evidence provided for Solfatara and Pantelleria we, therefore, infer that the CH4 in the volcanic fumaroles is mainly abiogenic, too. The δ13C-CH4 (from − 21.6 to − 36.9‰ V-PDB) and δD-CH4 (from − 113 to − 164‰ V-SMOW) values, as well as the C1/C2 + concentration ratios (from 19 to 2240), in the CO2-rich fluid discharges located between the geothermal-volcanic systems and the Apennine sedimentary chain tend to decrease eastwards as the temperatures of the fluid reservoirs progressively diminish, suggesting that the CH4 production is mainly related to thermogenic processes. According to this general trend, the CH4-dominated fluids from mud volcanoes located eastwards of the CO2-rich emissions are fed by an almost pure thermogenic source. The easternmost fluid discharges from the Po valley and the Adriatic coast, where organic matter evolves at relatively shallow depths in the presence of a low geothermal gradient, record the lowest δ13C-CH4 and δD-CH4 values, i.e. as low as − 69‰ V-PDB and <−190‰ V-SMOW, respectively, and C1/C2 + concentration ratios up to 5500, suggesting that the CH4 production is mainly from microbially driven processes.
In order to address the correct reporting and therefore comparison of isotopic measurements across different instrument types and instrumental techniques a prepared set of synthetic standards was sent to 28 laboratories for boron (B) isotopic analyses. Standards were prepared from enriched and purified isotopic salts to avoid any sample preparationfractionation. The range in uncertainties of the analyses between different instrumental analytical techniques is as large as the differences within an instrumental analytical technique obscuring any systematic offset. We conclude that uncertainties in the measurement of δ11B values were often underestimated and a procedure is suggested to allow a better comparison of the different techniques. Two new standards (JABA and JABB) have been quantified and these are available to all laboratories for testing their analyses. The δ11B values of these new standards are 10.0‰ and −23.7‰. The results from this exercise impact on the way all isotope measurements are performed and reported. Guidelines are defined to aid the comparison of measurements between different laboratories.
The El Tatio geothermal field is located at an height of 4200-4300 m on the Cordillera de los Andes (Altiplano). Geysers, hot pools and mudpots in the geothermal field and local meteoric waters were sampled in April 2002 and analyzed for major and trace elements, δ2H, δ18O and 3H of water, δ34S and δ18O of dissolved sulfate, δ13C of dissolved total carbonate, and 87Sr/86Sr ratio of aqueous strontium. There are two different types of thermal springs throughout the field, that are chloride-rich water and sulfate-rich water. The chemical composition of chloride springs is controlled by magma degassing and by water-rock interaction processes. Sulfate springs are fed by shallow meteoric water heated by ascending gases. In keeping with the geodynamic setting and nature of the reservoir rocks, chloride water is rich in As, B, Cs, Li; on the other hand, sulfate water is enriched only in B relative to local meteoric water. Alternatively to a merely meteoric model, chloride waters can be interpreted as admixtures of meteoric and magmatic (circa andesitic) water, which moderately exchanges oxygen isotopes with rocks at a chemical Na/K temperature of about 270°C in the main reservoir, and then undergoes loss of vapor (and eventually mixing with shallow water) and related isotopic effects during ascent to the surface. These chloride waters do not present tritium and can be classified as sub-modern (pre-1952). A chloride content of 5,400 mg/l is estimated in the main reservoir, for which δ2H and δ18O values, respectively of -78‰ and -6.9‰, are calculated applying the multistage-steam separation isotopic effects between liquid and vapor. From these data, the meteoric recharge (Cl≈0 mg/l) of the main reservoir should approach a composition of -107‰ in δ2H and -14.6‰ in δ18O, when a magmatic water of δ2H = -20‰, δ18O = +10‰ and Cl = 17,500 mg/l is assumed. The 87Sr/86Sr ratios of the hot springs are quite uniform (0.70876 to 0.70896), with values within the range observed for dacites of the Andean central volcanic zone. A water δ18O-87Sr/86 Sr model was developed for the main geothermal reservoir, by which a meteoric-magmatic composition of the fluids is not excluded. The uniform δ34S(SO42-) values of +1.4 to +2.6‰ in the chloride waters agree with a major deep-seated source for sulfur, possibly via hydrolysis in the geothermal reservoir of sulfur dioxide provided by magma degassing, followed by isotopic exchange between sulfate and sulfide in the main reservoir. This interpretation is supported by the largely negative δ34S(SO42-) value in steam-heated water sulfate (-9.8‰) and mass-balance calculation, which exclude leaching at depth of igneous iron-sulfides with δ34S near zero per mill. All the δ13C values of total carbonate in the chloride waters are negative, with variable values from -9.2 to -20.1‰, pointing to an important proportion of biogenic carbon in the fluids. The interpretation of these data is problematic, and a number of alternative explanations are reported in the text.
Volatiles are lost from the Earth’s mantle to the atmosphere, hydrosphere and crust through a combination of subaerial and submarine volcanic and magmatic activity. These volatiles can be primordial in origin, trapped in the mantle since planetary accretion, produced in situ, or they may be recycled—re-injected into the mantle via material originally at the surface through the subduction process. Quantifying the absolute and relative contributions of these various volatile sources bears fundamental information on a number of issues in the Earth Sciences ranging from the evolution of the atmosphere and hydrosphere to the nature and scale of chemical heterogeneity in the Earth’s mantle.
Noble gases have a pivotal role to play in addressing the volatile mass balance between the Earth’s interior and exterior reservoirs. The primordial isotope 3He provides an unambiguous measure of the juvenile volatile flux from the mantle (Craig et al. 1975). As such, it provides a means to calibrate other volatiles of geological and geochemical interest. A prime example is the CO2 flux at mid-ocean ridges (MOR): by combining estimates of the 3He flux at MOR with measurements of the CO2/3He ratio in oceanic basalts, Marty and Jambon (1987) derived an estimate of the CO2 flux from the (upper) mantle.
The approach of using ratios (involving noble gas isotopes) has also been extended to island arcs. Marty et al. (1989) found significantly higher CO2/3He ratios in arc-related geothermal fluids than observed at mid-ocean ridges, consistent with addition of slab-derived CO2 to the mantle wedge. Sano and Williams (1996) scaled the CO2 flux to 3He, showing that the output of CO2 at subduction zones was comparable in magnitude to that at spreading ridges. Therefore, for CO2 at least, subduction zones also …
Seismological and geological data show that tectonic segmentation of the Andes coincides with segmentation of the subducted Nazca plate, which has nearly horizontal segments and 30o E-dipping segments. Characterisitcs of Andean tectonics. Early Cenozoic tectonics of W N. America were quite similar to the Neogene Andes. However, duration of segmentation was longer and the width of deformation was greater in the W US. Patterns of crustal seismicity are systematically related to Plio-Quaternary structural provinces, implying that current deformational processes have persisted since at least the Pliocene. Strain patterns in the forearc region are complex and perhaps extensional and a broad region of the Altiplano-Puna and Eastern Cordillera appears to be aseismic.
The Santa Barbara System (SBS) of northern Argentina is a 400 km long segment of the Subandean foreland thrust belt. It is characterized by predominantly west verging, relatively high-angle thrust faults. Many of these faults are reactivated normal faults from one branch of a complex Cretaceous to Paleogene rift system. Heteroaxial folding in parts of the SBS is probably due to a slight component of range-parallel dextral strike-slip motion acting on preexisting faults striking north and NE during inversion. Regional balanced cross sections along two transects across the northern SBS indicate that the major faults flatten into a detachment in the basement at about 10 km depth. Neogene E-W contraction in the SBS is of the order of 21-26 km. Rift extension is not very well constrained but was probably less than 10 km. The structural style of the SBS differs from the thin-skinned Subandean thrust belt to the north and from the large-wavelength Sierras Pampeanas basement uplifts to the south. The changes between the different styles are sharp and coincide with the northern and southern boundaries of the rift in the foreland, suggesting that crustal or lithospheric heterogeneities exert an overriding control on foreland structural style.
The study of the crust beneath the eastern Andean foreland is analyzed. In the area, a pervasive change controls the tectonic features, which is interpreted as a consequence of the interaction between the Andean orogeny and preexistent Cretaceous rifting. This inversion tectonics did not only result in a particular suite of near to surface structures but also modified deeply the mass distribution within the crust. From a gravimetrical point of view, the Bouguer-anomaly of the area shows a strong overprint related with the Andean root. Some smaller changes in the field however indicate the existence of local sources, which were the target of the modelling. The effect of the inverted rift tectonics at the eastern edge of the basin was studied. These upthrusts correlate with a readily identifiable positive anomaly within the residual field. In addition, the foredeep related with the tectonic load of the Andean overthurst, was modelled. In the region, where Cretaceous rifting structures were not overprinted by the Andean orogeny an obvious asymmetry of the basin was defined, being the master detachment dipping to the northeast. The gravity field in this area shows the combined effects of the regional Andean gradient with the more local effects of the basement tectonics (inverted rifting) and the overthrusted foredeep. -from Author
Fluids play a critical role in the geochemical and geodynamical evolution of the crust, and fluid flow is the dominant process associated with mass and energy transport in the crust. In this Perspectives, we summarise the occurrence, properties and role that fluids play in crustal processes, as well as how geoscientists' understanding of these various aspects of fluids have evolved during the past century and how this evolution in thinking has influenced our own research careers. Despite the wide range of possible fluid sources in the crust, fluids in sedimentary, magmatic and metamorphic environments are all approximated by the system H2O - "gas" - "salt" and normally reflect equilibrium with rocks and melts at the relevant PT conditions. The "gas" component in many environments is dominated by CO2, but CH4, as well as various sulphur and nitrogen-rich gases, may also be important. The major "salt" components are usually NaCl and/or CaCl2, but salts of K, Mg and Fe can be major components in specific circumstances. While the activities of many fluid components can often be calculated assuming equilibrium with coexisting minerals, salinity is normally unbuffered and must be determined independently from observations of fluid inclusions. Solubilities of "gas" and "salt" in H2O generally rise with increasing temperature and/or pressure, but in many environments compositions are such that phase separation (immiscibility or boiling) leads to the development of salt-rich aqueous fluids coexisting with a volatile-rich phase. Chloride content, buffering assemblages, temperature and, to a lesser extent pressure, all play a role in determining the dissolved load of crustal fluids. In addition to equilibrium considerations, kinetic factors can play an important role in relatively shallow, low temperature environments. The most important distinction between relatively shallow basinal or geothermal fluids and deeper metamorphic or magmatic ones is the physical behaviour of the fluid(s). In regions where fluid pressure corresponds to hydrostatic pressure, extensive circulation of fluid is possible, driven by thermal or compositional gradients or gravity. In contrast, at greater depths where fluids are overpressured and may approach lithostatic pressure, fluid can only escape irreversibly and so fluxes are generally much more limited. Much of our understanding of crustal fluids has come from studies of ore-forming systems that are present in different crustal environments. Thus, studies of Mississippi Valley-Type deposits that form in sedimentary basins have shown that the fluids are dominantly high salinity (Na, Ca) brines that have significant metal-carrying capacity. Studies of active continental geothermal systems and their fossil equivalents, the epithermal precious metal deposits, document the importance of boiling or immiscibility as a depositional mechanism in this environment. Ore-forming fluids associated with orogenic gold deposits show many similarities to low salinity metamorphic fluids, consistent with their formation during metamorphism, but similar fluids are also found in some magmatic pegmatites, demonstrating the difficulty in distinguishing characteristics derived from the fluid source from those that simply reflect phase relationships in the H2O - "gas"- "salt" system. Magmatic fluids associated with silicic epizonal plutons are consistent with experimental and theoretical studies related to volatile solubilities in magmas, as well as the partitioning of volatiles and metals between the melt and exsolving magmatic fluid. Ore fluids are generally representative of crustal fluids in comparable settings, rather than unusual, metal-rich solutions. During progressive burial and heating of sediments and metamorphic rocks, there is continuous fluid release and loss and the rocks remain wet and weak. Fluid composition evolves continuously as a result of changing conditions. Once rocks begin to cool, fluid is consumed by retrograde reactions and in much of the crust the rocks are effectively dry with a notional water fugacity buffered by the coexisting high-T and retrograde phases. In this case rocks are strong and unreactive. Our understanding of crustal fluids has advanced by leaps and bounds during the past few decades, and we expect new and exciting results to continue to emerge as new analytical methods are developed that allow us to analyse smaller fluid inclusions in particular, and as theoretical models and experiments advance our understanding of how fluids interact with rocks and minerals in the crust, changing both chemical and physical characteristics.
Nuclear fusion is the main process which produces both stable helium isotopes in nature. The abundance of primordial He in stars is so high that the isotope ratio 3He/4He varies little from approx 10-4. The radioactive alpha -decay of heavy elements in planets and meteorites also yields He rich in 4He whereas the interaction between high-energy galaxy rays and matter produces He mostly enriched in the light isotope 3He. In this book the geochemistry of helium is reviewed, and the origin, history and contemporary distribution of the helium isotopes are described, including experimental data from the Soviet Union. A model is presented for the degassing and differentiation of the Earth, which shows a quantitative correspondence between the abundance of radioactive elements and primordial and radiogenic noble gases on the one hand and new data on the field of He isotope geochemistry on the other.-R.A.H.
Tertiary foreland basin evolution in northwestern Argentina is addressed in the light of new chronostratigraphic information. We interpret strata from the Lumbrera (II) Formation deposits (the top of the Santa Bárbara Subgroup, Salta Group) to the Angastaco Formation deposits (Payogastilla Group) and its temporal equivalent, the Metán Subgroup (base of Orán Group). Middle Ec̈ene foreland basin development began in response to intense tectonic activity in the west. The triangular-shaped region received ephemeral stream and dry mudflat deposits of the Lumbrera (II) Formation. During the Oligocene stage of tectonic quiescence a lens-shaped basin developed where ephemeral streams, dry mudflats and eolian strata were deposited in the Los Colorados Formation at the base of the Payogastilla Group. The second stage of tectonic activity started in the early to middle Miocene (to 12.5 Ma approximately). This established a foreland basin system in which characteristic wedge top, foredeep, forebulge and backbulge depozones are recognized. In the wedge top depozone (Valle Calchaqui) thick braided stream facies accumulated in the lower and middle section of the Angastaco Formation in the Payogastilla Group. In the foredeep depozone, proximal, medial and distal ephemeral stream and playa lake strata of the Rio Seco and the Anta formations (Metán Subgroup) were deposited. The middle Miocene was tectonically quiescent. Eastward progradation of proximal facies continued in the wedge top, foredeep, forebulge and backbulge depozones. These deposits constitute the upper portion of the Angastaco Formation and ephemeral systems of the Jesús Maria Formation (the top of Metán Subgroup).
Investigations on chemical composition and gaseous flow in volcanic areas consider preferentially high-T manifestations, which appear to be affected only to a minor extent by possible surface contamination. This situation is rare, however, and the possibility of obtaining useful information concerning the activity stage of volcanic systems depends on other types of surface evidence, such as low-T fumaroles, bubbling gases or thermal waters. Variations in the original character of deep fluids possibly produced in a shallow environment are considered. The relative concentrations of H and CH4 for low-T fumaroles, and of 041NH+4, B and Li for thermal waters, appear to be useful in determining the genetic processes involved. -J.M.H.
The application to analytical hydrogeochemistry of a spectrophotometric method for boron determination was studied. The method utilizes azomethine-H and is very simple and fast when compared with other current colorimetric methods for B determination. The sensitivity obtained was approx 0.03 ppm. The precision was assessed by ten replicate analyses of both artificially prepared and natural solutions. The coefficient of variation was <5%. The accuracy was tested by addition of known amounts of standard solutions to natural samples. The average of four determinations shows differences of <3% between the theoretical and determined B concentrations. Results obtained with azomethine- H were in close agreement with those obtained by the 1,1' dianthrimide method. Ions commonly occurring in natural waters do not interfere with the method.-J.M.H.
The kinetic and equilibrium fractionation effects for 13C during CO2 gas transfer (εk and εag−g) have been measured in acidified distilled water. The equilibrium fractionation effects between bicarbonate and carbonate and gaseous C02 (εHCO3−g and εCO3−g) have been measured in NaHC03 and NaHC03 + Na2C03 solutions, respectively, from 5° to 25°C. The measured fractionations, except εCO3−g, agreed with earlier work to within 0.2‰. εCO3−g was about 2‰ smaller than most values previously reported. The temperature dependence of the fractionation for 13C between bicarbonate and carbonate and gaseous CO2 was found to be εHCO3−g = −(0.141 ± 0.003)T(°C) + 0.05)‰ and εCO3−g = −(0.052 ± 0.03) T(°C)E+ (7.22 ± 0.46)‰ respectively. The fractionation during gas dissolution was εCO3−g = −0.03)T(°C) + (1.31 ± 0.06%. and the kinetic effect during gas transfer, εk, was −0.81 ± 0.16‰ at 21°C and −0.95 ± 0.20‰ at 5°C.
Relative Rb, Cs and contents of waters discharged from geothermal systems over t h e Taupo Volcanic Zone are very uniform. They are thought to reflect the composition of a common d e e p brine formed through absorption of magmatic vapors into d e e p ground water followed by rock dissolu-tion and double diffusive mixing with more s h a l l o w ground water. Relative B contents are uniform over the backarc basin, but increase rapidly towards the eastern boundary, the volcanic arc. These marked differences bet-ween a r c and backarc systems are reflected in t h e m u c h higher contributions from magmatic t o gas discharges along the SE boundary of the TVZ. The increased discharge of volatile species there is ascribed to recent injection of heat by intrusion of andesitic to dacitic magma. Associated sti-mulation of convective flow is likely t o be responsible f o r the establishment of a series of geothermal systems (Rotokawa, Ohaaki, Waiotapu, Kawerau) of which Ohaaki East is probably the youngest, t o o young to have produced major surface manifestations.
This work is part of a project aimed to the development and application of hydrogeological, hydrogeochemical and geological methodologies for the study of the geothermal system of Rosario de La Frontera (NW Argentina).
The surface thermal manifestations of this area, whose temperatures range from 22.6 to 92.6°C, are mainly located in the northern sector of Sierra de la Candelaria anticline. This regional structure crops out between the provinces of Salta and Tucuman (NW Argentina), at the foothills of the central Andean retro-wedge.
The present investigation focuses on hydrogeological and structural data, and isotopic compositions (18O, D and 3H) of thermal springs.
Preliminary results allowed to define: i) the meteoric origin of spring water and their long (more than 50 years) residence time at depth, ii) a positive water balance, ranging between 2 and 4 millions of m3/yr , and iii) a conservative geothermal reservoir volume of about 39 Km3, iv) a geothermal potential with Er = 5.6 *1018 J and Ef = 0.8 *1018 J
Despite its reduced penetration depth, audiomagnetotelluric (AMT)
studies can be used to determine a broad range of features related to
little studied geothermal fields. This technique requires a stepwise
interpretation of results taking into consideration diverse information
(e.g. topographic, hydrological, geological and/or structural data) to
constrain the characteristics of the study area. In this work, an AMT
study was performed at the hot springs in the northern segment of the La
Candelaria Range in order to characterize the area at depth. Geometric
aspects of the shallow subsurface were determined based on the
dimensional and distortion analysis of the impedance tensors. Also, the
correlation between structural features and regional strikes allowed us
to define two geoelectric domains, useful to determine the controls on
fluid circulation. The subsurface resistivity distribution was
determined through 1D and 2D models. The patterns of the 1D models were
compared with the morpho-structure of the range. Shallow and deep
conductive zones were defined and a possible shallow geothermal system
scheme proposed. A strong correlation was found between the AMT results
and the geological framework of the region, showing the relevance of
using AMT in geothermal areas during the early stages of subsurface
prospecting.
We have measured the boron isotope composition and boron and chloride concentrations of 27 Icelandic geothermal fluids from both high- and low-temperature systems. The 11 B values range from -6.7 in the Krafla system, to +25.0 in a warm spring from the Southern Lowlands. In addition, we have also determined the 11 B values of basaltic glass from Nesjavellir (-5.3 ± 1.4 ) and travertine from Snaefellsnes (-22 ± 0.5 ). The B isotope and Cl/B systematics of the high-temperature systems are dominated by the composition of the local basalts. The lower temperature systems show evidence for mixing with B and Cl of a marine origin, together with some uptake of B into secondary mineral phases. The data from the Snaefellsnes geothermal system indicate that the fluids have undergone interaction with basalts that have undergone significant low-temperature alteration by seawater.
Magnetostratigraphy, isotopic dating, and sandstone petrography establish age limits on the depositional history of ∼2100 m of foreland basin strata in the Neogene Metán Subgroup of northwest Argentina. The strata were deposited between ca. 15.1 and 9.7 Ma in the eastern Sistema de Santa Bárbara. The region is positioned above the Cretaceous Salta rift basin, in the Transition Zone between modern relatively steep and flat subducting segments of the Nazca plate. Formations within the subgroup are shown to be diachronous over a 60 km distance; the younger ages are in the east. Changes in paleocurrent flow directions and the lithic clast component of sandstones collected from the Arroyo González section suggest that basal fluvial strata were derived from the craton to the east beginning in middle Miocene time, just prior to 15.1 Ma. By ca. 14.5 Ma, the paleocurrent flowed from a source in the west and sediment accumulation rates increased dramatically. These changes correlate with contemporaneous tectonism in the west. A local increase in basin accommodation may be partly related to a zone of weakness near the eastern boundary of the Salta rift. Uplift in the western Cordillera Oriental apparently began by 13.7 Ma and thrusting rapidly migrated eastward. The eastern Cordillera Oriental ranges began to rise between 25° and 26°S ca. 10 Ma. As thrusting migrated eastward, low-energy depositional environments were overwhelmed ca. 13.7 Ma. Above an erosional unconformity that removed strata to an age of ca. 9.7 Ma, basal strata from the overlying Jujuy Subgroup were deposited beginning after 9 Ma. Sandstones from Río Yacones suggest that the Cordillera Oriental uplift continued for several million years longer between 24° and 25°S. Uplift of the Sistema de Santa Bárbara, in the distal portion of the foreland, did not begin until after ca. 9 Ma.
Five samples of hydrothermal fluids from two vent areas on the southern Juan de Fuca Ridge were analyzed for dissolved gases. Concentrations in the end-member hydrothermal fluid of H2 (270–527 μmol/kg), CH4 (82–118 μmol/kg), and CO2 (3920–4460 μmol/kg) are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems. The carbon isotopic ratios of the CH4 (δ13C = −17.8 to −20.8) and CO2 (δ13C = −3.6 to −4.7) suggest that at least some of the CH4 and CO2 in the fluids is basalt-derived. The range of δ13C values for the basalt-derived CO2 is −6.8 to −9.7, calculated by assuming conservation of recharge ΣCO2 during hydrothermal circulation. Apparent temperatures of equilibration between the CH4 and the basalt-derived CO2 range from 640°C to 750°C. Small amounts of ethane (C2H6/CH4 ≅ 0.9 × 10−3−2.2 × 10−3), propane, and butane detected in the samples may also have formed in the basalt. One sample of almost pure (95.5%) hydrothermal fluid contained a significant fraction, up to 63% and 74%, respectively, of the recharge Ar and N2. This suggests that the fluid has not undergone extensive vapor-liquid phase separation.