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SULFATE HYDROTHERMAL SYSTEMS IN COSTA RICA AND ICELAND. Brian M. Hynek1-2, J. Wang1, N. Dragone3, G. Avard4, G. E. Alvarado5 and L. McHenry6 1Lab. for Atmospheric and Space Physics, University of Colorado Boulder, USA, 2Dept. of... more
SULFATE HYDROTHERMAL SYSTEMS IN COSTA RICA AND ICELAND. Brian M. Hynek1-2, J. Wang1, N. Dragone3, G. Avard4, G. E. Alvarado5 and L. McHenry6 1Lab. for Atmospheric and Space Physics, University of Colorado Boulder, USA, 2Dept. of Geological Sciences, University of Colorado Boulder, 3Dept. Of Environmental and Evolutionary Biology, University of Colorado Boulder, 4OVSICORI, National University of Costa Rica, 5Centro de Investigaciones Ciencias Geológicas, Universidad de Costa Rica, 6Dept. of Geosciences, Univ. WisconsinMilwaukee. hynek@lasp.colorado.edu
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Costa Rica hosts ten volcanic complexes and is highly tectonically active due to its location at the interaction between the Cocos, Nazca, and Caribbean plates and the Panama microplate. Three of the five historically active volcanoes had... more
Costa Rica hosts ten volcanic complexes and is highly tectonically active due to its location at the interaction between the Cocos, Nazca, and Caribbean plates and the Panama microplate. Three of the five historically active volcanoes had frequent eruptions in 2019. The institutions in charge of monitoring the volcanoes of Costa Rica are the Observatorio Vulcanológico y Sismológico de Costa Rica from Universidad Nacional (OVSICORI-UNA) and the Red Sismológica Nacional (RSN: UCR-ICE that groups the Escuela Centroamericana de Geología from the Universidad de Costa Rica, and the Observatorio Sismológico y Vulcanológico de Arenal y Miravalles from the Instituto Costarricense de Electricidad; acronyms ECG, UCR, OSIVAM, and ICE). These institutions are focused on the most dangerous volcanoes, i.e. those closest to the Great Metropolitan Area (2.2 million inhabitants), which includes San José (the capital), and those near hydroelectrical and geothermal plants. In 2020, those institutions o...
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The fossil vertebrates of Guatemala are almost exclusively fossils of mammals and are of late Miocene (Hemphillian) and late Pleistocene (Rancholabrean) age. The only lower vertebrates are the crocodile fossil Crocodilus moreletti... more
The fossil vertebrates of Guatemala are almost exclusively fossils of mammals and are of late Miocene (Hemphillian) and late Pleistocene (Rancholabrean) age. The only lower vertebrates are the crocodile fossil Crocodilus moreletti collected in the Río La Pasión area, a turtle from El Trifinio and fishes from Río Carboneras. The late Miocene mammals are the proboscidean Gomphotherium, an aceratheriine rhinoceros and the horse Neohipparion from the Río Carboneras in Izabal; the holotype of “Serridentinus guatemalensis” (nomen dubium) from Chinautla in the Department of Guatemala is also a specimen of Gomphotherium of likely late Miocene age. Late Pleistocene vertebrates are known from at least 36 localities in Guatemala, but only six of these yield at least four documented genera of mammals—Chivacabé, Ciudad Real. El Rosario, Estanzuela, Río La Pasión and San Rafaelito. The combined list of Guatemalan late Pleistocene mammal genera is Canis, Cuvieronius, Dicotyles, Equus, Eremotherium...
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For the first time, a more accurate location and modern geoarcheological context to the Retes Site (C-378 Re) is assigned. Located at an altitude of 2660 m.s.n.m. and associated with the Cartago phase (800-1500 d.C.) of the Valle Central... more
For the first time, a more accurate location and modern geoarcheological context to the Retes Site (C-378 Re) is assigned. Located at an altitude of 2660 m.s.n.m. and associated with the Cartago phase (800-1500 d.C.) of the Valle Central cultural sequence, in which, the only radiocarbon result available so far comes from a wooden object with a calibrated age of 991-1183 (1δ) d. C. The lithic artifacts stand out for their predominance, made from volcanic rocks, as well as the unique and extraordinary objects made of wood and cotton. Here, some of their particularities are described and the possible sources of raw material are explored. In the case of lithic artifacts, they apparently come from volcanic rocks near Tierra Blanca and the Alto Grande hill, at a distance of 850 m and 10 km, respectively, from the Retes site. While one of the woods modified to make the artifacts, such as cocobolo (Dalbergia retusa), would have come from the low to moderate altitude floors (0-1000 m a.s.l, ...
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Introducción: El estudio interdisciplinario de los patrones de ocupación y desarrollo de la sociedad humana en tiempos prehispánicos es tenue en la zona del volcán Orosí. El contexto ambiental es usualmente descrito para ilustrar... more
Introducción: El estudio interdisciplinario de los patrones de ocupación y desarrollo de la sociedad humana en tiempos prehispánicos es tenue en la zona del volcán Orosí. El contexto ambiental es usualmente descrito para ilustrar patrones de subsistencia, sin mayor propósito de establecer formas de relación con los cambios que se vislumbran en la composición sociopolítica de los pobladores. Objetivo: En este trabajo, se explora la posibilidad de ilustrar instancias de relación entre los cambios que detecta el registro arqueológico, con potenciales factores naturales y culturales, según se destacan en los aportes de otras disciplinas científicas. Métodos: Una muestra de 111 componentes culturales identificados en sitios arqueológicos fue examinada en cuanto a su localización geográfica en diversos ecosistemas y su posición cronológica, respecto de los períodos culturales definidos en la región de Guanacaste. Resultados: Los componentes arqueológicos se confrontan con diversos factor...
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espanolEn este trabajo se revisa la informacion mineralogica-petrologica-geologica disponible sobre jade social (rocas “verdes”) utilizado en Costa Rica en epoca precolombina. Aproximadamente el 55 % o mas del jade social precolombino... more
espanolEn este trabajo se revisa la informacion mineralogica-petrologica-geologica disponible sobre jade social (rocas “verdes”) utilizado en Costa Rica en epoca precolombina. Aproximadamente el 55 % o mas del jade social precolombino costarricense pudo elaborarse con fuentes locales (lutitas y areniscas verdosas, serpentinita, jaspes y otros pedernales y cuarzos), pero el restante al parecer tiene por fuente rocas y minerales foraneos (i.e., jadeitita, onfacitita, cloromelanita, marmol, dolomia, talco) que no se encuentran en Costa Rica del todo, donde las condiciones geologicas en el pasado no favorecieron la formacion de jadeitita ni de las otras rocas y minerales citados. Por lo tanto, los jades sociales de rocas y minerales no presentes en Costa Rica deben de provenir de regiones metamorficas presentes desde el norte de Nicaragua hasta Mexico. La jadeita con toda probabilidad proviene de Guatemala, aunque Siuna (Nicaragua) es un posible candidato adicional por explorar. Las fue...
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ABSTRACT CONCLUSIONS The structural geology of Central America is best explained in its regional setting at the western end of the Caribbean. It is controlled by strain generated during Triassic– Jurassic rifting (reactivating older... more
ABSTRACT CONCLUSIONS The structural geology of Central America is best explained in its regional setting at the western end of the Caribbean. It is controlled by strain generated during Triassic– Jurassic rifting (reactivating older lineaments) and Jurassic–Cretaceous drifting of North America from South America. The structures have been reactivated through subsequent history, often in a reverse sense (inversion, change of strike-slip direction). They retain a regional integrity that harmonizes movement and deformation. If continental crust exists beneath Chorotega and Chocó, as argued in this chapter, distinction between Nuclear Central America (Maya and Chortis) and the “Isthmian Link” is inappropriate. The boundaries between Maya and Chortis and Chortis and Chorotega are broad zones of E–W strike-slip faulting. The boundary between the Panama arc and South America is probably a NE trending fault crossing the isthmus and running north of the Gulf of Urubá. The Chorotega-Chocó boundary is marked by the Panama fault zone. The Panama area (northern Chocó) is being shunted northwards over the southwestern-most part of the Caribbean plate, driving before it the North Panamanian fold belt sedimentary prism. The latter does not mark the northern boundary of Chocó or of Chorotega. Chorotega is fixed on the western margin of the Caribbean plate. The southern extension of Chocó is accreted to South America. Separation of stratigraphy premised upon perceived (modeled) “terranes” rather than its use to correlate between adjacent blocks should be reconsidered. Maya and Chortis share common geology. They are joined, not by a suture where pre-existing oceanic crust was consumed, but along a zone of sinistral shear. The only terranes in Central America may be small, accreted oceanic areas of western Costa Rica (Nicoya, Azuero), though reported paleomagnetic rotations/migrations could reflect local effects of strike-slip faulting. Chortis, Chorotega and Chocó have always been at the western end of the Caribbean area. Migration of the Caribbean plate from the Pacific was not possible. Future investigations could seek structures that conform (or not) to the suggested regional pattern. This indicates a systematic grid of “Guayape” trend faults throughout Central America, accompanied by oroclinal bending, folds and thrusts. Systematic sinistral/dextral fault interactions and related extension might control the spacing of volcanoes along Central America. Knowledge of the regional structural pattern could help understand earthquake and volcanic activity. The suggestion that Chorotega and Chocó are underpinned by continental crust should be investigated.
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En la cordillera de Talamanca los productos del magmatismo se encuentran ampliamente distribuidos, y corresponden con episodios intrusivos y extrusivos del Neógeno y del Cuaternario. En general es posible reconocer tres fases magmáticas:... more
En la cordillera de Talamanca los productos del magmatismo se encuentran ampliamente distribuidos, y corresponden con episodios intrusivos y extrusivos del Neógeno y del Cuaternario. En general es posible reconocer tres fases magmáticas: 1) Vulcanismo anterior al Mioceno Superior, de unos 17 a 11 millones de años atrás; 2) Plutonismo durante el Mioceno Medio-Superior, entre 12,5 y 7,5 millones de años, conocido como Grupo Intrusivo de Talamanca o Granito-Gabro de Talamanca; 3) Pulsos magmáticos post-intrusivos del Neógeno al Cuaternario, cuyo rango temporal se extiende entre 5 y 2 millones de años. Por primera vez se propone una diferenciación del magmatismo post-intrusivo en tres unidades, separables por aspectos petrográficos: a) Unidad Kámuk, constituida por andesitas con plagioclasa de tipo labradorita y ocasionalmente con ortopiroxeno; b) Unidad Dúrika, definida por plagioclasa de tipo andesina y biotita como fenocristal ferromagnesiano predominante; c) Unidad Río Lori, cuyos p...
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En la falda sureste del volcán Barva se encuentra el cono piroclástico compuesto Monte de la Cruz, a partir del cual fue emitida la colada de lava Ángeles (7,3 km, área 12,8 km2). Por medio de estudios geomorfológicos, petrográficos y... more
En la falda sureste del volcán Barva se encuentra el cono piroclástico compuesto Monte de la Cruz, a partir del cual fue emitida la colada de lava Ángeles (7,3 km, área 12,8 km2). Por medio de estudios geomorfológicos, petrográficos y trabajo de campo se dividió en dos unidades, Ángeles Inferior y Superior. Petrográficamente, Ángeles Inferior corresponde con una lava andesítico basáltica vesicular de textura hipocristalina porfirítica a levemente glomeroporfirítica, con fenocristales de plagioclasa, clinopiroxenos, ortopiroxenos, olivinos y opacos. Ángeles Superior, por su parte, es andesítica vesicular a andesítica con textura hipocristalina, glomeroporfirítica a glomeroporfirítica seriada, con fenocristales de plagioclasa, clinopiroxenos, ortopiroxenos, olivinos y opacos. Morfológicamente, fueron observadas kipukas y lévees. Regionalmente, se observa que el cono Monte de la Cruz, junto con otros conos satélites menores, están alineados N19°W a lo largo de 8,5 km, evidenciando un o...
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Se presenta un mapa geológico, escala 1:50 000 del cuadrante Tapantí, el cual se encuentra en la región central de Costa Rica y forma parte del Cinturón Deformado del Centro de Costa Rica (CDCCR), producto de la interacción de la... more
Se presenta un mapa geológico, escala 1:50 000 del cuadrante Tapantí, el cual se encuentra en la región central de Costa Rica y forma parte del Cinturón Deformado del Centro de Costa Rica (CDCCR), producto de la interacción de la cordillera de Coco y la región W de la microplaca Panamá. Las rocas más antiguas cartografiadas son miocenas y están representadas por las formaciones sedimentarias Pacacua, Peña Negra, San Miguel y Coris, que forman el borde oriental de la cuenca Candelaria. Se distinguieron 3 eventos magmáticos; el arco volcánico Mioceno, representando por la Formación La Cruz y clastos volcánicos de la Formación Pacacua; un nuevo periodo de actividad ígnea entre 6 Ma y 4,2 Ma, representado por las Formaciones Grifo Alto, Doán y el Intrusivo de Tapantí y, finalmente, se desarrolla el arco volcánico actual, representado por las formaciones Paraíso y Cervantes, con un rango de edad entre los 0,6 Ma y 0,02 Ma. Desde el punto de vista geoquímico, se observa un fuerte cambio e...
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El presente trabajo documenta restos fósiles de peces cíclidos de Costa Rica, constituyendo el primer registro fósil de cíclidos en América Central. Estos fósiles provienen de rocas sedimentarias marinas de ambiente poco profundo,... more
El presente trabajo documenta restos fósiles de peces cíclidos de Costa Rica, constituyendo el primer registro fósil de cíclidos en América Central. Estos fósiles provienen de rocas sedimentarias marinas de ambiente poco profundo, posiblemente del Mioceno Superior, hallados en el Proyecto Hidroeléctrico Reventazón, así como de depósitos lacustres continentales del Pleistoceno Medio en San Miguel de Turrúcares. La ocurrencia de cíclidos miocénicos en sedimentos marinos en Costa Rica indica una posible dispersión marina de los cíclidos desde América del Sur a América Central y se ajusta a la idea de que migraron en el Mioceno y cruzaron las aguas marinas poco profundas para lograr su distribución actual. Los fósiles de cíclidos de Pleistoceno Medio de agua dulce de San Miguel de Turrúcares indican que, al menos para el Pleistoceno Medio, los cíclidos colonizaban hábitats de agua dulce, como ahora lo hacen en gran parte de América Central.
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A new period of eruptive activity started at Turrialba volcano, Costa Rica, in 2010 after almost 150 years of quiescence. This activity has been characterized by sporadic explosions whose frequency clearly increased since October 2014.... more
A new period of eruptive activity started at Turrialba volcano, Costa Rica, in 2010 after almost 150 years of quiescence. This activity has been characterized by sporadic explosions whose frequency clearly increased since October 2014. This study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years. We integrate 3He/4He data available on fumarole gases collected in the summit area of Turrialba between 1999 and 2011 with new measurements made on samples collected between September 2014 and February 2016. The results of a petrological investigation of the products that erupted between October 2014 and May 2015 are also presented. We infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of Turrialba by a new batch of magma. This is supported by the increase in 3He/4He values observed since 2005 at the crater fumaroles and by ...
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El presente trabajo muestra una serie de reflexiones autocríticas de la realidad de la volcanología latinoamericana, a partir de un análisis de sus debilidades, amenazas, fortalezas y oportunidades (DAFO) llevada a cabo en febrero del... more
El presente trabajo muestra una serie de reflexiones autocríticas de la realidad de la volcanología latinoamericana, a partir de un análisis de sus debilidades, amenazas, fortalezas y oportunidades (DAFO) llevada a cabo en febrero del 2008 en Antigua, Guatemala. Antes de llegar a este análisis, se hace una relatoría de los esfuerzos que se realizaron para unir a la comunidad volcanológica latinoamericana, hasta su culminación en la constitución de una asociación (Asociación Latinoamericana de Volcanología, ALVO) que permita fortalecer y promover los lazos de colaboración entre vulcanólogos de América Latina y sus instituciones para beneficio de la sociedad, particularmente en la atención de crisis eruptivas en los numerosos volcanes activos de la región latinoamericana
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ABSTRACT A new evaluation of seismic hazard in Central America has been carried out as part of the cooperation project named RESIS II under the auspices of the Norway Cooperation Agency (NORAD). Several seismic-hazard experts from Costa... more
ABSTRACT A new evaluation of seismic hazard in Central America has been carried out as part of the cooperation project named RESIS II under the auspices of the Norway Cooperation Agency (NORAD). Several seismic-hazard experts from Costa Rica, Guatemala, Honduras, Nicaragua, El Salvador, Panamá, Norway, and Spain participated in the study, which was aimed at obtaining results suitable for seismic design purposes. The analysis started with a thorough revision of the national seismic catalogs from which a catalog for Central America has been compiled and homogenized to moment magnitude, Mw. Seismotectonic models proposed for the region were revised, and a new regional zonation was proposed, taking into account seismotectonic data, seismicity, focal mechanisms, and GPS observations. Besides, ground-motion prediction equations (GMPEs) for subduction, volcanic, and crustal zones were revised, and the most suitable ones were calibrated with Central American strongmotion data. Subsequently, a seismic-hazard analysis was developed in terms of peak ground acceleration (PGA) and spectral accelerations SA (T) for periods of 0.1, 0.2, 0.5, 1, and 2 s, by means of the probabilistic seismic-hazard assessment (PSHA) approach. As a result, different hazard maps were obtained for the quoted parameters, together with uniform hazard spectra (UHS) for six of the capital cities of Central America. Disaggregation was also carried out in these capitals for the target motion given by the PGA and SA (1 s) and obtained for return periods of 500 years and 2500 years. Therefore, the control earthquakes for motions of short and long periods were derived. This is the first study developed in Central America at a regional scale after 10 years.
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Pacific drill sites offshore Central America provide the unique opportunity to study the evolution of large explosive volcanism and the geotectonic evolution of the continental margin back into the Neogene. The temporal distribution of... more
Pacific drill sites offshore Central America provide the unique opportunity to study the evolution of large explosive volcanism and the geotectonic evolution of the continental margin back into the Neogene. The temporal distribution of tephra layers established by tephrochonostratigraphy in Part 1 indicates a nearly continuous highly explosive eruption record for the Costa Rican and the Nicaraguan volcanic arc within the last 8 Myr. The widely distributed marine tephra layers comprise the major fraction of the respective erupted tephra volumes and masses thus providing insights into regional and temporal variations of large‐magnitude explosive eruptions along the southern Central American Volcanic Arc (CAVA). We observe three pulses of enhanced explosive volcanism between 0 and 1 Ma at the Cordillera Central, between 1 and 2 Ma at the Guanacaste and at >3 Ma at the Western Nicaragua segments. Averaged over the long‐term the minimum erupted magma flux (per unit arc length) is ∼0.0...
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AB4STRACT Costa Rica is located at the boundary of four tectonic plates where the regularity of destructive earthquakes highlights the necessity of seismic hazard estimations. This study contains the most recent Probabilistic Seismic... more
AB4STRACT Costa Rica is located at the boundary of four tectonic plates where the regularity of destructive earthquakes highlights the necessity of seismic hazard estimations. This study contains the most recent Probabilistic Seismic Hazard Assessment (PSHA) for Costa Rica, calculated with the largest and the most updated earthquake database from both—the Earthquake Engineering Laboratory and the National Seismological Network of the University of Costa Rica. For the PSHA, we updated the seismicity parameters for the upper plate, subduction interplate, and intraslab tectonic domains, characterized the upper-plate zones by percentages of fault types, and used weighted ground-motion models for each of the tectonic domains. The resulted maps of peak ground acceleration (PGA) at return periods of 475 yr (PGA-475) and 2475 yr, as well as the spectral accelerations, show geographic trends that allow for the division of the country in four seismic hazard levels: (1) extremely high for the ...
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The Central American subduction zone is particularly interesting due to its pronounced lateral variability. To explore the deeper structure of the subduction zone, a transect of broadband seismometres across the Talamanca Range (Southern... more
The Central American subduction zone is particularly interesting due to its pronounced lateral variability. To explore the deeper structure of the subduction zone, a transect of broadband seismometres across the Talamanca Range (Southern Costa Rica) was operated from spring 2005 to spring 2007. This region is characterized by the subduction of the aseismic Cocos Ridge, which has been observed to dip at an angle of 18 deg down to depths of about 40 km. Based on this shallow angle, it was speculated that shallow underplating of the Cocos Ridge is responsible for the gap in active volcanism and strong uplift in this region.
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During the night of December 8th, 1994, along an unstable area at the northern fl ank of Irazu volcano, Costa Rica, a small volcanic debris avalanche and subsequent debris fl ows took place, followed by an “ashfall” that reached 30 km... more
During the night of December 8th, 1994, along an unstable area at the northern fl ank of Irazu volcano, Costa Rica, a small volcanic debris avalanche and subsequent debris fl ows took place, followed by an “ashfall” that reached 30 km southwest from the volcano. At that time, these processes were interpreted as the result of a phreatic explosion. However, a review of the descriptions given in the technical reports and other documents of the time, together with the analysis of the geomorphology obtained from aerial photographs taken on December 20, 1994, by the Costa Rica National Geographic Institute, lead to discuss the validity of this interpretation, which although not ruled out, it seems unlikely. This paper proposes, based on the facts and information available, a new hypothesis of the occurrence of a volcanic debris avalanche resulting from a major landslide near the northern summit area. Consequently, the following “ash” fall could be interpreted as generated by the dust prod...
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Se presenta una estimación en valor presente de las pérdidas económicas causadas por la actividad volcánica en Costa Rica en el período comprendido entre 1953 y 2016. Se brinda información detallada de los daños en agricultura, ganadería,... more
Se presenta una estimación en valor presente de las pérdidas económicas causadas por la actividad volcánica en Costa Rica en el período comprendido entre 1953 y 2016. Se brinda información detallada de los daños en agricultura, ganadería, infraestructura, entre otros, clasificada según el año en que ocurrió la actividad y el volcán que la generó. Durante este tiempo ocurrieron tres emergencias nacionales disparadas por erupciones volcánicas: Irazú en 1963 - 1965, Arenal en 1968 y Poás en 1990, cuyas pérdidas se estimaron (en dólares estadounidenses en valor presente al 2016) en US$117,3 millones, US$5,8 millones y entre US$1,1 y US$2,3 millones, respectivamente. Si se toman en consideración otros períodos de afectación volcánica, el total estimado de pérdidas económicas en Costa Rica por causa del vulcanismo es de entre US$174,1 y US$193,1 millones en valor presente. Este es un monto mínimo dado que muchas de las pérdidas económicas no fueron cuantificadas.
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Quaternary volcanism in the Central Cordillera of Costa Rica has created an orographic barrier that concentrates rainfall on its northern side. This humid climate produces weathered bedrock prone to landsliding. Ash fall from explosive... more
Quaternary volcanism in the Central Cordillera of Costa Rica has created an orographic barrier that concentrates rainfall on its northern side. This humid climate produces weathered bedrock prone to landsliding. Ash fall from explosive eruptions kills the vegetation cover and intensifies erosion processes. These eruptions, hydrothermal activity and associated earthquakes destabilize the slopes of river valleys, and even the volcanic edifices, producing landslides and large debris avalanches. All these processes mobilize an extra sediment input that is deposited in the piedmont lowlands forming the Santa Clara megafan. The megafans described in the literature mainly grow according to climatic fluctuations; however, sedimentation in the Santa Clara megafan is also controlled by endogenic processes with longer recurrence periods. Analysis of this megafan provides new insight into the origin and evolution of these landforms. In volcanic regions, active volcanism should be considered when investigating the formation of some megafans.
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Island arcs are proposed to be essential building blocks for the crustal growth of continents; however, island arcs and continents are fundamentally different in bulk composition: mafic and felsic, respectively. The substrate upon which... more
Island arcs are proposed to be essential building blocks for the crustal growth of continents; however, island arcs and continents are fundamentally different in bulk composition: mafic and felsic, respectively. The substrate upon which arcs are built (oceanic crust versus large igneous province) may have a strong influence on crustal genesis. We present results from an across‐arc wide‐angle seismic survey of the Costa Rican volcanic front which test the hypothesis that juvenile continental crust is actively forming at this location. Travel‐time tomography constrains velocities in the upper arc to a depth of ~15 km where average velocities are <6.5 km/s. The upper 5 km of crust is constrained by velocities between 4.0 and 5.5 km/s, which likely represent sediments, volcaniclastics, flows, and small intrusions. Between 5 and 15 km depth, velocities increase slowly from 5.5 to 6.5 km/s. Crustal thickness and lower crustal velocities are roughly constrained by reflections from an in...
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Resolving flow geometry in the mantle wedge is central to understanding the thermal and chemical structure of subduction zones, subducting plate dehydration, and melting that leads to arc volcanism, which can threaten large populations... more
Resolving flow geometry in the mantle wedge is central to understanding the thermal and chemical structure of subduction zones, subducting plate dehydration, and melting that leads to arc volcanism, which can threaten large populations and alter climate through gas and particle emission. Here we show that isotope geochemistry and seismic velocity anisotropy provide strong evidence for trench-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua. This finding contradicts classical models, which predict trench-normal flow owing to the overlying wedge mantle being dragged downwards by the subducting plate. The isotopic signature of central Costa Rican volcanic rocks is not consistent with its derivation from the mantle wedge (Feigenson et al., 2004, doi:10.1029/2003GC000621; Herrstom et al., 1995, doi:10.1130/0091-7613(1995)023<0617:VILCAW>2.3.CO;2; Abratis and Woerner, 2001) or eroded fore-arc complexes (Goss and Kay, 2006, doi:10.1029/2005GC001163) but instead from seamounts of the Galapagos hotspot track on the subducting Cocos plate. This isotopic signature decreases continuously from central Costa Rica to northwestern Nicaragua. As the age of the isotopic signature beneath Costa Rica can be constrained and its transport distance is known, minimum northwestward flow rates can be estimated (~63-190 mm/yr) and are comparable to the magnitude of subducting Cocos plate motion (approx85 mm/yr). Trench-parallel flow needs to be taken into account in models evaluating thermal and chemical structure and melt generation in subduction zones.
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This field-based and analytical laboratory study focuses on the genetic relationship between bimodal volcanic centres and fault types of an important tectonic transfer zone in the southern Central Andes, the NW–SE striking... more
This field-based and analytical laboratory study focuses on the genetic relationship between bimodal volcanic centres and fault types of an important tectonic transfer zone in the southern Central Andes, the NW–SE striking Calama–Olacapato–Toro (COT) volcanic belt. More specifically, tectono–magmatic relationships are examined for the 0.55 Ma Tocomar, the 0.78 Ma San Jerónimo and the 0.45 Ma Negro de Chorrillos volcanic
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On the flanks of the dormant Miravalles volcano, systematic fieldwork and radiocarbon dating of buried humus-rich soils (paleosols) and wood fragments, augmented by mineralogical and geochemical analysis, reveal extensive and previously... more
On the flanks of the dormant Miravalles volcano, systematic fieldwork and radiocarbon dating of buried humus-rich soils (paleosols) and wood fragments, augmented by mineralogical and geochemical analysis, reveal extensive and previously undocumented Holocene activity. Phase 1 consisted of 8.3 ka (~6300 BCE) volcanic debris avalanche and thick lapilli blast and fallout deposit that appear coeval. Hiatus 1 marks 2600 years of inactivity ensued followed by Phase 2 lapilli interbedded with ~5.5 ka lahars below a 5.3 ka basaltic lava flow (~3400 BCE). Hiatus 2 lasted 1800 years from 5.3 ka to 3.5 ka (3300-1500 BCE), after which a very active Phase 3 ensued (3.5 to 0.5 ka; 1600 BCE to 1500 CE) with > four lapilli eruptions, > 4 lahars, > 6 layers of ash and pumice, and small andesitic lava flows. The most recent evidence for eruption is an 880-year-old (0.9 ka; 1070 CE) lapilli overlain by gravels that may represent distal lahar sediments. Evidence indicates the occurrence of at ...
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ABSTRACT Explaining the occurrence of high-silica arc magmatism in the absence of continental crust remains a fundamental problem in igneous petrology. Recent work in the southern portion of the Central American volcanic arc has expanded... more
ABSTRACT Explaining the occurrence of high-silica arc magmatism in the absence of continental crust remains a fundamental problem in igneous petrology. Recent work in the southern portion of the Central American volcanic arc has expanded the database for the abundant high-silica ash-flow tuffs erupted on top of thick oceanic basement in Costa Rica and southern Nicaragua. Regional differences in geochemistry are observed in data from central and northern Costa Rica. In addition, local heterogeneities among units are demonstrated in plots of both major and trace elements. High-silica ash-flow tuffs in central Costa Rica include the Tiribi Tuff (~0.33 Ma) and Alto Palomo formation (~0.56 Ma). In northern Costa Rica, numerous large silicic ash-flow sheets are found in the Guanacaste province, ranging from late Miocene (