Artículos científicos

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Subduction-zone structure and magmatic processes beneath Costa Rica constrained by local earthquake tomography and petrological modelling
(Royal Astronomical Society, 2003-10-01) Husen, S.; Quintero, R.; Kissling, E.; Hacker, B.
A high-quality data set of 3790 earthquakes were simultaneously inverted for hypocentre locations and 3-D P-wave velocities in Costa Rica. Tests with synthetic data and resolution estimates derived from the resolution matrix indicate that the velocity model is well constrained in central Costa Rica to a depth of 70 km; northwestern and southeastern Costa Rica are less well resolved owing to a lack of seismic stations and seismicity. Maximum H2O content and seismic wave speeds of mid-ocean ridge basalt and harzburgite were calculated for metamorphic phase transformations relevant to subduction. Both the 3-D P-wave velocity structure and petrological modelling indicate the existence of low-velocity hydrous oceanic crust in the subducting Cocos Plate beneath central Costa Rica. Intermediate-depth seismicity correlates well with the predicted locations of hydrous metamorphic rocks, suggesting that dehydration plays a key role in generating intermediate-depth earthquakes beneath Costa Rica. Wadati– Benioff zone seismicity beneath central Costa Rica shows a remarkable decrease in maximum depth toward southeastern Costa Rica. The presence of asthenosphere beneath southeastern Costa Rica, which entered through a proposed slab window, may explain the shallowing of seismicity due to increased temperatures and associated shallowing of dehydration of the slab. Tomographic images further constrain the existence of deeply subducted seamounts beneath central Costa Rica. Large, low P-wave velocity areas within the lower crust are imaged beneath the southeasternmost volcanoes in central Costa Rica. These low velocities may represent anomalously hot material or even melt associated with active volcanism in central Costa Rica. Tomographic images and petrological modelling indicate the existence of a shallow, possibly hydrated mantle wedge beneath central Costa Rica.
The synchronous occurrence of shallow tremor and very low frequency earthquakes offshore of the Nicoya Peninsula, Costa Rica
(American Geophysical Union, 2013-03-05) Walter, Jacob I.; Schwartz, Susan Y.; Protti, Marino; Gonzalez, Victor
The occurrence of transient, shallow slow slip at seismogenic zones has important implications for earthquake and tsunami hazards. Here we provide evidence that a tremor and slow slip event occurred at shallow depth offshore of the Nicoya Peninsula, Costa Rica, in August 2008. The temporal coincidence of offshore tremor, very low frequency earthquakes (VLFEs), motions consistent with slow slip on the plate interface on western coastal GPS stations, and a pressure transient in an IODP borehole all indicate slow slip occurring at shallow depths. Large ocean loading stresses on the shallow plate interface modulate tremor activity, with the peak Coulomb stress forced by semi-diurnal ocean tides correlating with tremor productivity. Based on beamforming data, we constrain that the VLFE activity occurs in the same region as the tremor and slow slip. The presence of slow slip at shallow depth has important implications for the up-dip extent of earthquake rupture. The proximity of the 5 September 2012, Mw 7.6 megathrust earthquake to slow slip, tremor, and VLFE activity in the 2008 event suggests abrupt frictional transitions from locked to conditionally stable behavior on the plate interface offshore of the Nicoya Peninsula.
Effect of subducting sea-floor roughness on fore-arc kinematics, Pacific coast, Costa Rica
(Geological Society of America, 1998-05-01) Fisher, Donald M.; Gardner, Thomas W.; Marshall, Jeffrey S.; Sak, Peter B.; Protti, Marino
Fault kinematics and uplift in the Costa Rican fore arc of the Middle America convergent margin are controlled to a large extent by roughness on the subducting Cocos plate. Along the northwest flank of the incoming Cocos Ridge, seafloor is characterized by short wavelength roughness related to northeast-trending seamount chains. Onland projection of the rough subducting crust coincides with a system of active faults oriented at high angles to the margin that segment the fore-arc thrust belt and separate blocks with contrasting uplift rates. Trunk segments of Pacific slope fluvial systems typically follow these margin-perpendicular faults. Regionally developed marine and fluvial terraces are correlated between drainages and acrossfaults along the Costa Rican Pacific coast. Terrace separations across block-bounding faults reveal a pattern of fore-arc uplift that coincides roughly with the distribution of incoming seamounts. Magnitude and distribution of Quaternary uplift along the Costa Rican Pacific coast suggests that, despite a thin incoming sediment pile, the inner fore arc shows an accumulation of mass—a characteristic that may be due to underplating of seamounts beneath the fore-arc high.
Persistent tremor within the northern Costa Rica seismogenic zone
(American Geophysical Union Advancing Earth and Space Sciences, 2011-01-13) Walter, Jacob I.; Schwartz, Susan Y.; Protti, Marino; Gonzalez, Victor
We identify tremor using a spectral detection method and characterize its occurrence over a period of four years (2006–2009) in the vicinity of the Nicoya Peninsula, Costa Rica. Although a few major tremor events accompanied by geodetic slow slip occur, much of the tremor record consists of minor episodes with short duration and no detectable geodetic slip. Its persistent occurrence suggests that some portion of the interface is experiencing slow slip nearly continuously driving small patches to fail in accelerated slip. Locations indicate that much of the tremor occurs at shallow depth, in freely slipping regions of the seismogenic zone. This result is significant in that locations of slow slip and tremor at other subduction zones are largely limited to the downdip frictional transition. Tremor locations may help to refine the heterogeneous distribution of locked and freely slipping patches within the Costa Rica seismogenic zone.
Quantifying recent pyroclastic and lava flows at Arenal Volcano, Costa Rica, using medium-footprint lidar
(American Geophysical Union Advancing Earth and Space Sciences, 2006-11-03) Hofton, M. A.; Malavassi, E.; Blair, J. B.
Arenal volcano is a small, active stratovolcano in Costa Rica. In 1998 and 2005, NASA’s Laser Vegetation Imaging Sensor (LVIS) was used to collect wide-swath 3- dimensional topographic images of the volcano. The LVIS is a full-waveform, scanning, medium-sized footprint, airborne laser altimeter system. By digitally recording the shape of the returning laser pulse (waveform), the LVIS provides a precise and accurate view of both the sub-canopy and canopy-top topographies as well as the vertical and horizontal structure of vegetation at 15– 25 m horizontal resolution. By comparing georeferenced waveform data collected in 1998 and 2005, we mapped lava and pyroclastic flows deposited during this period. The active crater grew by 3.82 m yr 1. A flow volume estimate of 2.19 107 m3 (Dense Rock Equivalent of 1.89 107 m3 or 0.085 m3s 1) Nwas obtained for the period 1998 to 2005. Precise elevation and elevation change data such as those provided by the LVIS are essential to calculate eruption volume and to study magma-supply dynamics, as well as assess the danger posed by the volcano to the local population from hazards such as pyroclastic flows.
Magma plumbing processes for persistent activity at Poás volcano, Costa Rica
(American Geophysical Union Advancing Earth, 2005-04-21) Rymer, Hazel; Locke, Corinne A.; Brenes, jorge; Williams-Jones, Glyn
New microgravity data from the active crater of Poás volcano, Costa Rica, collected in 2002 – 2004 extends the existing dataset to provide a unique 20-year time series. These data show that gravity has decreased monotonically in the north and east of the crater over the last 5 years, whilst it has increased to the west and remained approximately constant in the south. These changes are interpreted in terms of convective recharge within dendritic intrusions beneath the crater, with overall down-welling in the north and up-welling in the west. The data reveal a 5 –10 year periodicity in sub-crater mass movement, but overall, the upper part of the conduit system appears to have maintained a state of mass equilibrium.
High-resolution gravity survey: Investigation of subsurface structures at Poás volcano, Costa Rica
(Universidad Nacional, Costa Rica, 2003-08-03) Fournier, Nicolas; Rymer, Hazel; Williams-Jones, Glyn; Brenes, Jorge
Bouguer gravity surveys have long been used to investigate sub-surface density contrasts. The main sources of error in previous surveys have been the determination of relative elevations of stations and the effect of topography (removed via the terrain correction). The availability of high precision Kinematic GPS data now facilitates generation of high-resolution Digital Elevation Models that can help to improve the accuracy of relative elevation determination and the terrain correction. Here we describe a highresolution gravity survey at Poás volcano, Costa Rica. Our gravity modelling identifies small pockets of magma at shallow depths which relate to successive magma intrusion through time and shows that the persistent degassing in the eastern part of the crater is related to local deformation at the top of the volcano and changes in the fracture network, rather than to the presence of a shallow magma intrusion.
New insights into the magmatic-hydrothermal system and volatile budget of Lastarria volcano, Chile: Integrated results from the 2014 IAVCEI CCVG 12th Volcanic Gas Workshop
(Geological Society of America, 2018-05-07) Lopez, Taryn; Aguilera, Felipe; Tassi, Franco; De Moor, J. Marteen; Bobrowski, Nicole; Aiuppa, Alessandro; Tamburello, Giancarlo; Rizzo, Andrea L.; Liuzzo, Marco; Viveiros, Fátima; Cardellini, Carlo; Silva, Catarina; Fischer, Tobias; Philippe, Jean-Baptiste; Kazayaha, Ryunosuke; Hidalgo, Silvana; Malowany, Kalina; Lucic, Gregor; Bagnato, Emanuela; Bergsson, Baldur; Reath, Kevin; Liotta, Marcello; Carn, Simon; Chiodini, Giovanni
Recent geophysical evidence for large-scale regional crustal inflation and localized crustal magma intrusion has made Lastarria volcano (northern Chile) the target of numerous geological, geophysical, and geochemical studies. The chemical composition of volcanic gases sampled during discrete campaigns from Lastarria volcano indicated a well-developed hydrothermal system from direct fumarole samples in A.D. 2006, 2008, and 2009, and shallow magma degassing using measurements from in situ plume sampling techniques in 2012. It is unclear if the differences in measured gas compositions and resulting interpretations were due to artifacts of the different sampling methods employed, short-term excursions from baseline due to localized changes in stress, or a systematic change in Lastarria’s magmatic-hydrothermal system between 2009 and 2012. Integrated results from a two-day volcanic gas sampling and measurement campaign during the 2014 International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Commission on the Chemistry of Volcanic Gases (CCVG) 12th Gas Workshop are used here to compare and evaluate current gas sampling and measurement techniques, refine the existing subsurface models for Lastarria volcano, and provide new constraints on its magmatic-hydrothermal system and total degassing budget. While compositional differences among sampling methods are present, distinct compositional changes are observed, which if representative of long-term trends, indicate a change in Lastarria’s overall magmatic-hydrothermal system. The composition of volcanic gases measured in 2014 contained high proportions of relatively magma- and water-soluble gases consistent with degassing of shallow magma, and in agreement with the 2012 gas composition. When compared with gas compositions measured in 2006–2009, higher relative H2O/CO2 ratios combined with lower relative CO2/St and H2O/St and stable HCl/St ratios (where St is total S [SO2 + H2S]) are observed in 2012 and 2014.
50 years of steady ground deformation in the Altiplano-Puna region of southern Bolivia
(Geological Society of America, 2017-12-20) Gottsmann, Joachim; Del Potro, Rodrigo; Muller, Cyril
The Altiplano-Puna Volcanic Complex of the Central Andes is host to an ~150-km-wide, quasi-circular ground deformation anomaly centered on Uturuncu volcano (Bolivia). The precise onset and duration of this deformation is unclear, but geomorphologic studies bracket its initiation at less than a few hundred years ago. Here we report on the deformation history over an ~50 yr period by deriving orthometric height changes from leveling and global navigation satellite system (GNSS) observations at 53 benchmarks along a regional leveling line that crosses the deformation anomaly. The comparison of interferometric synthetic aperture radar (InSAR) line-of-sight (LOS) displacements and LOS-projected orthometric ground velocities in a common reference frame reveal central uplift extending to ~35 km from Uturuncu at a maximum orthometric rate of 1.2 cm yr–1, and peripheral subsidence at a maximum rate of 0.3 cm yr–1 to ~60 km from Uturuncu. This pattern is consistent with the spatial extent and average rate of deformation observed by InSAR. Our interpretation of the data is that long-wavelength ground uplift at Uturuncu has likely occurred at a quasi-constant rate for at least half of a century. This study bridges the observational time spans between modern satellite geodetic observations (up to a few decades) and geomorphological observations (a few centuries and longer) of the recent deformation history of the continental crust in the Central Andes and adds to a select group of case studies of quantifiable long-term volcano deformation worldwide.
GPS measurements of crustal deformation associated with the 22 April 1991, Valle de la Estrella, Costa Rica Earthquake
(Universidad Nacional, Costa Rica, 1993-03-05) Lundgren, Paul R.; Kornreich Wolf, Susan; Protti, Marino; Hurst, Kenneth J.
We present analysis results for Global Positioning System (GPS) measurements made at sites in Costa Rica during two campaigns in February and July 1991. GPS solutions for 5 sites (Limon, Liberia, Bratsi, ETCG, and Vueltas) reveal significant horizontal and vertical displacements relative to their February positions. Horizontal displacements relative to Liberia, measured 244.7 ± 0.8, 89.2 ± 0.9, 12.4 ± 1.3, and 1.9 ± 0.9 cm at Limon, Bratsi, Vueltas, and ETCG respectively. Vertical displacements relative to Liberia measured 163 ± 2.1, 15.3 ± 3.0, −10.5 ± 4.4, and −0.6 ±2.1 cm at Limon, Bratsi, Vueltas, and ETCG respectively. We find differences in the GPS derived vertical and horizontal displacements compared to other types of geodetic measurements of uplift in the coastal region and their associated models. To address these differences we compute a dislocation model which fits the GPS measured displacements. A simple uniform planar slip model can not reconcile the differences between the coastal uplift data or the seismic moment, suggesting considerable complexity of the earthquake source.
Strain release at the trench during shallow slow slip: The example of Nicoya Peninsula, Costa Rica
(Universidad Nacional, Costa Rica, 2017-05-29) Jiang, Yan; Zhen, Liu; Davis, Earl E.; Schwartz, Susan Y.; Dixon, Timothy H.; Voss, Nick; Malservisi, Rocco; Protti, Marino
The near-trench behavior of subduction megathrust faults is critical for understanding earthquake hazard and tsunami generation. The shallow subduction interface is typically located in unconsolidated sediments that are considered too weak to accumulate elastic strain. However, the spectrum of shallow fault slip behavior is still elusive, due in large part to the lack of near-field observations. Here we combine measurements from seafloor pressure sensors near the trench and an onshore GPS network in a time-dependent inversion to image the initiation and migration of a well-documented slow slip event (SSE) in 2007 at the Nicoya Peninsula, Costa Rica. Our results show that the shallow SSE initiated on the shallow subduction interface at a depth of ~15 km, where pore fluid pressure is inferred to be high, and propagated all the way to the trench. The migrating event may have triggered a second subevent that occurred 1 month later. Our results document the release of elastic strain at the shallow part of the subduction megathrust and suggest prior accumulation of elastic strain. In conjunction with near-trench shallow slow slip recently reported for the Hikurangi subduction zone and trench breaching ruptures revealed in some large earthquakes, our results suggest that near-trench strain accumulation and release at the shallower portions of the subduction interface is more common than previously thought.
Slow slip events in Costa Rica detected by continuous GPS observations, 2002–2011
(American Geophysical Union, 2012-04-18) Jiang, Yan; Wdowinski, Shimon; Dixon, Timothy H.; Hackl, Matthias; Protti, Marino; Gonzalez, Victor
Una red de estaciones GPS de registro continuo ha operado en la Península de Nicoya en el norte de Costa Rica desde 2002. Procesamos todos los datos disponibles de esta red para el período 2002-2011 para investigar la ocurrencia de Eventos de Deslizamiento Lento (SSE) en la interfaz de subducción entre las placas de Cocos y Caribe. Con el fin de superar el enmascaramiento de la señal por los altos niveles de ruido troposférico, desarrollamos una nueva técnica que facilita la detección de eventos transitorios en presencia de ruido. Identificamos cinco SSE significativos durante el período 2002-2011, con tiempos medios de evento en 2003, 2005, 2007, 2009 y 2011, con un intervalo de recurrencia promedio de 216 meses. El análisis de series de tiempo muestra que la deformación transitoria imparte una firma similar a la caminata aleatoria. La eliminación de los SSE y los errores regionales de modo común de la serie de tiempo redujo la incertidumbre de la velocidad en casi un orden de magnitud. Los datos limitados disponibles para los eventos de 2003, 2005 y 2011 impiden la caracterización detallada de estos eventos. Sin embargo, una buena cobertura espaciotemporal de los eventos de 2007 y 2009 sugiere que ambos eventos tuvieron una duración y distribución irregulares. En el evento de 2007, el deslizamiento lento comenzó en el área costera del noroeste y migró hacia el sureste durante un período de 1 mes. El evento de 2009 tuvo una duración significativamente mayor y un mayor desplazamiento en la superficie. Las estaciones en el área noroeste observaron dos SSE separados en 2008.6 y 2009.4, correlacionándose bien con los episodios de temblores en alta mar, lo que indica un parche de deslizamiento SSE poco profundo con un intervalo de recurrencia más corto. Las diferencias significativas entre los eventos de 2009 y 2007 nos llevan a cuestionar el modelo simple de intervalo de recurrencia para el SSE en Nicoya.
The 6 September 1997 (Mw4.5) Coatzacoalcos-Minatitlán, Veracruz, Mexico earthquake: implications for tectonics and seismic hazard of the region
(Universidad Nacional Autónoma de México, 2015-06-30) Singh, Shri Krishna; Pacheco, Javier Francisco; Pérez-Campos, Xyoli; Ordaz, Mario; Reinoso, Eduardo
Analizamos el sismo del 6 de septiembre de 1997 (Mw4.5), que se produjo a unos 25 km al SE de Coatzacoalcos, Veracruz. El sismo fue registrado por la estación local TUIG de banda ancha de (tiempo S-P = 5 s). Las polaridades de la onda P a distancias regionales y telesísmicas, y el modelado de las formas de onda de desplazamiento en TUIG sugieren un mecanismo focal inverso (f = 150º; d = 70º; l = 90º). En la misma región ocurrió un sismo destructivo el 26 de agosto de 1959 (Mw6.4), a una profundidad similar y con un mecanismo similar. El análisis del sismo de 1997 refuerza la conclusión anterior de que la corteza inferior bajo la cuenca del Coatzacoalcos-Minatitlán, está en un régimen de esfuerzos de fallamiento inverso, en contraste con la parte superficial de la corteza que se caracteriza por un fallamiento normal; esto implica una permutación con la profundidad de los esfuerzos principales máximo y mínimo. Esto está de acuerdo con las observaciones, en otros sitios, que el estado de esfuerzos en las cuencas sedimentarias pueden ser diferentes del que se tiene a mayor profundidad. Mecanismos focales están disponibles para siete sismos en y cerca del Golfo de México. Todos estos eventos muestran en la región una corteza media y baja en un régimen de fallamiento inverso. La tendencia observada de los ejes P de estos sismos se puede explicar por una o más de las siguientes causas: acoplamiento fuerte a lo largo de la interfase de la placa en subducción fuera de la costa en Tehuantepec; el movimiento absoluto de la placa de América del Norte; y el hundimiento de la litosfera debido a la acumulación de la carga de los sedimentos. Usamos los registros del sismo de 1997 como función de Green empírica para simular los movimientos de tierra en la región epicentral de un sismo de Mw6.4 postulado en la cuenca Comalcalco. Bajo supuestos razonables, los valores esperados de aceleración, velocidad y desplazamiento picos son 120-260 gales, 12 a 28 cm/s, y 6 a 11 cm, respectivamente. La extensa licuefacción reportada en Coatzacoalcos durante el sismo de 1959, Mw6.4, sugiere que los sedimentos de la cuenca se comportan de manera no lineal bajo tal excitación.
Holocene forearc block rotation in response to seamount subduction, southeastern Península de Nicoya, Costa Rica
(Geological Society of America, 2001-02) Gardner, Thomas; Marshall, Jeffrey; Merritts, Dorothy; Bee, Bhavani; Burgette, Reed; Burton, Emily; Cooke, Jennifer; Kehrwald, Natalie; Protti, Marino; Fisher, Donald; Sak, Peter
The southeastern tip of the Penı´nsula de Nicoya, Costa Rica, on the Caribbean plate margin lies inboard of the rough bathymetric terrain on the subducting Cocos plate and along the landward projection of the convergence vector for the Fisher seamount group. The southern tip of the peninsula has nearly orthogonal coastlines and extensive, well-preserved, Holocene marine terraces,and is ideally situated to evaluate the spatial distribution of forearc deformation in response to seamount subduction. Two marine terraces that yielded 35 radiocarbon dates give information on the rates, style, and timing of deformation along 40 km of coastline. Ages range from 3.5 to 7.4 ka for a higher terrace and from 0.3 to 2.9 ka for a lower terrace. A maximum uplift rate is ;6.0 m/k.y. along the southeastern tip of the peninsula. Uplift rates decrease linearly to ,1.0 m/k.y. along both orthogonal coastlines and thus landward from the Middle America Trench and away from the line of subducting seamounts. The ;400km2 region along the tip of the peninsula can be approximated as a rotating block with an angular rotation rate of 0.028/k.y. about an axis with an azimuth of 808. Given the modern elevation and dip of the late Quaternary Cobano surface, this style of deformation is limited to a duration of 100–200 k.y. Deformation is occurring in response to seamount bypass or underplating onto the Caribbean plate margin.
Impacto de las politicas estatales en la autonomía de los territorios indígenas en la Zona Sur de Costa Rica el caso del territorio de Salitre
(Geo UERJ, 2017-09-14) Vargas Rojas, Guido Alonso; Campos Durán, Daniela
Este artículo tiene como objetivo realizar un análisis, mediante revisión bibliográfica, de los conflictos que se han dado entre los indígenas y la población no indígena en la comunidad Bribri de Salitre. Donde se determinó que la principal problemática que enfrenta la población autóctona, son actos de violencia por parte de los no indígenas, a causa de la tenencia de la tierra, quienes han organizado grupos de carácter paramilitar con el objetivo de reprimir a los nativos. Ante esta situación la respuesta del estado ha sido débil y ambigua, ya que no ha planteado soluciones claras al conflicto, dejando abierta la posibilidad a los blancos de ocupar estos territorios, contraponiéndose así a las leyes de la República y convenios internacionales que los defienden, tales como el Convenio 169 “Convenio sobre Pueblos Indígenas y Tribales en Países Independientes” y la Ley N° 6172 “Ley Indígena” de la República de Costa Rica.
Detailed data available for recent Costa Rica earthquake.
(University of South Florida, 2013) Dixon, Timothy H.; Schwartz, Susan; Protti, Marino; Gonzalez, Victor; Newman, Andrew; Marshall, Jeff; Spotila, Jim
On 5 September 2012 a magnitude 7.6 earthquake occurred beneath the Nicoya Peninsula of northwestern Costa Rica, rupturing the subduction zone between the Cocos and Caribbean plates. In most subduction zones the locus of seismic slip lies far offshore, making it difficult to infer interface seismogenic processes from on-shore observations. In contrast, the Nicoya Peninsula lies close to the trench (within 70 kilometers), allowing observations directly over the earthquake rupture zone.
Microbial Survival in an Extreme Martian Analog Ecosystem: Poás Volcano, Costa Rica
(Frontiers, 2022-01-28) Wang, Justin L.; Dragone, Nicholas B.; Avard, Geoffroy; Hynek, Brian M.
Past acid-sulfate hydrothermal systems on Mars have promise in their ability to have hosted life for billions of years. One method for analyzing these systems is to study analog environments on Earth. To assess the astrobiological potential of Martian acid-sulfate hydrothermal systems, the crater lake of the active Poás Volcano, Laguna Caliente, was sampled in 2013 and 2017. Laguna Caliente presents an extremely dynamic terrestrial environment with near-ambient to boiling temperatures, pH fluctuations from −0.87 to 1.5, a wide range of chemistries and redox potential, and frequent phreatic-tophreatomagmatic eruptions. Samples of lake fluid, sulfur clumps, and lake bottom sediment underwent 16S rRNA gene sequencing and metagenomic “shotgun” sequencing, which revealed this lake hosts an extremely low biodiversity of microorganisms dominated by Acidiphilium spp. Shotgun metagenomics of the samples suggests this community has numerous genetic adaptations that confer survival, including functional pathways to reduce the effects of toxic metals and numerous metabolic pathways utilizing a variety of simple and complex sugar molecules. The identification of these various metabolic pathways suggests adaptations related to carbon limited environments, fulfillment of high energy requirements, and survival in a hostile volcanic setting. The perseverance of life in Laguna Caliente indicates life on Mars could have thrived in analogous environments, stressing the need for the search for life in relict Martian acid-sulfate hydrothermal systems.
The Helium and Carbon Isotope Characteristics of the Andean Convergent Margin
(Frontiers, 2022-06-13) Barry, P. H.; De Moor, J. M.; Chiodi, A.; Aguilera, F.; Hudak, M. R.; Bekaert, D.V.; Curtice, J.; Turner, S. J.; Seltzer, A. M.; Jessen, G. L; Osses, E.; Blamey, J. M.; Amenábar, M. J.; Selci, M.; Cascone, M.; Bastianoni, A.; Nakagawa, M.; Filipovich, R.; Bustos, E.; Schrenk, M. O.; Buongiorno, J.; Ramírez, J. C.; Rogers, T. J.; Lloyd, K. G.; Giovannelli, D.
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 3 He/4 He, 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 4 He) to the helium budget.
The Geothermal Resource in the Guanacaste Region (Costa Rica) New Hints From the Geochemistry of Naturally Discharging Fluids
(Frontiers, 2018-06-05) Tassi, Franco; Vaselli, Orlando; Bini, Giulio; Capecchiacci, Francesco; De Moor, J. Marteen; Pecoraino, Giovannella; Venturi, Stefania
The Guanacaste Geothermal Province (GGP) encompasses the three major volcanoes of northern Costa Rica, namely from NW to SE: Rincón de la Vieja, Miravalles, and Tenorio. The dominant occurrence of (i) SO4-rich acidic fluids at Rincón de la Vieja, (ii) Cl-rich mature fluids at Miravalles, and (iii) HCO−3-rich and low-temperature fluids at Tenorio was previously interpreted as due to a north-to-south general flow of thermal waters and a magmatic gas upwelling mostly centered at Rincón de la Vieja, whereas Miravalles volcano was regarded as fed by a typical geothermal reservoir consistingof a highly saline Na-Cl aquifer. The uniformity in chemical and isotopic (R/Ra andδ 34S) compositions of the neutral Cl-rich waters suggested to state that all the thermal discharges in the GGP are linked at depth to a single, regional geothermal system. In thisscenario, the thermal manifestations related to Tenorio volcano were regarded as a distal and diluted fluid outflow. In this study, a new gas geochemical dataset, including both chemical and isotopic (δ 13C-CO2 and R/Ra) parameters of fluid discharges from the three volcanoes, is presented and discussed. Particular attention was devoted to the Tenorio thermal manifestations, since they were poorly studied in the past because this area has been considered of low geothermal potential. The aim is to provide insights into the magmatic-hydrothermal fluid circulation and to verify the spatial distribution of the heat fluid source feeding the fluid manifestations. According to this new dataset, CO2, i.e., the most abundant dry gas in the fluid manifestations, is mostly produced by limestone, whereas the mantle CO2 contribution is ≤3.3%. Strongly acidic gas compounds from magma degassing were absent in the discharged fluids, being scrubbed by secondary processes related to prolonged fluid-rock interactions and mixing with shallow aquifers. Our results only partially confirm the previously depicted model, because the geochemical and isotopic features (e.g., relatively high concentrations of temperature-dependent gases and high R/Ra values) shown by fluids seeping out from the southern sector of Tenorio volcano are more representative of medium-to-high enthalpy volcanic systems than those typically occurring in distal areas. This implies that the geothermal potential in the south of the GGP is higher than previously thought.
Sampling across large-scale geological gradients to study geosphere–biosphere interactions
(Frontiers, 2022-10-31) Giovannelli, Donato; Barry, Peter H.; De Moor, J. Maarten; Jessen, Gerdhard L.; Schrenk, Matthew O.; Lloyd, Karen G.
Despite being one of the largest microbial ecosystems on Earth, many basic open questions remain about how life exists and thrives in the deep subsurface biosphere. Much of this ambiguity is due to the fact that it is exceedingly difficult and often prohibitively expensive to directly sample the deep subsurface, requiring elaborate drilling programs or access to deep mines. We propose a sampling approach which involves collection of a large suite of geological, geochemical, and biological data from numerous deeply-sourced seeps—including lower temperature sites—over large spatial scales. This enables research into interactions between the geosphere and the biosphere, expanding the classical local approach to regional or even planetary scales. Understanding the interplay between geology, geochemistry and biology on such scales is essential for building subsurface ecosystem models and extrapolating the ecological and biogeochemical roles of subsurface microbes beyond single site interpretations. This approach has been used successfully across the Central and South American Convergent Margins, and can be applied more broadly to other types of geological regions (i.e., rifting, intraplate volcanic, and hydrothermal settings). Working across geological spatial scales inherently encompasses broad temporal scales (e.g., millions of years of volatile cycling across a convergent margin), providing access to a framework for interpreting evolution and ecosystem functions through deep time and space. We propose that tectonic interactions are fundamental to maintaining planetary habitability through feedbacks that stabilize the ecosphere, and deep biosphere studies are fundamental to understanding geo-bio feedbacks on these processes on a global scale.

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