Central Costa Rica Research Articles

Lead isotope composition of Central American volcanoes: Influence of the Galapagos plume

Lead isotopic analyses of lavas from Central America, both along and behind the volcanic arc, help to clarify source components in the mantle wedge. Analysis of previous Pb isotopic data had implied that little or no marine sediment lead was added to the Central American source region, as all samples fell within the MORB field, in contrast to other information (e.g., Ba/La, 10Be, 87Sr/86Sr) that indicated a high subduction component. The data presented here include several analyses of local marine sediment, showing it to be exceptionally unradiogenic in Pb and thus permitting high sediment contributions to the mantle source region without significant changes in Pb isotopes. Combined Pb‐Nd and Pb‐Sr isotopic diagrams clearly illustrate the influence of crustal contamination for samples from Guatemala and Honduras, and of subducted sediment for all lavas of the volcanic front. Samples collected behind the volcanic front are derived from mixing between enriched and depleted mantle sources, and in central Costa Rica (extending to the back arc) overlap Pb, Sr and Nd isotope values for both Cocos Island and some components of the Galapagos hot spot. The restricted geographical occurrence of the enriched mantle signature in Central America, coupled with the persistence of the signal well into the back arc region, imply that these lavas are sampling Galapagos plume‐influenced mantle. The presence of this plume component beneath southern Central America and extending to the northeast beneath the Caribbean confirms a Galapagos hot spot origin for this part of Caribbean Plate.

The Bee Genus Andinaugochlora in Central America (Hymenoptera: Halictidae)

Abstract A new species of the neotropical bee genus Andinaugochlora (Halictinae: Augochlorini) is described and figured. Andinaugochlora centralpina, new species, is the first species of the genus discovered outside of northern South America. The new species was discovered at altitudes ranging from 1250–1510 m in central Costa Rica.

Parallopharynxs pp. (Trematoda: Digenea: Plagiorchioidea) in iguanian lizards from the Area de Conservación Guanacaste, Guanacaste, Costa Rica, including Parallopharynx matternae n. sp. in Chaetodon basiliscus (Squamata: Iguania: Corytophanidae).

We report 3 species of the digenean genus Parallopharynx, 1 previously undescribed, from the Area de Conservación Guanacaste (ACG) in northwestern Costa Rica. Parallopharynx gonzalezi, which was originally described in Basiliscus sp. and Ctenosoura similis from central Costa Rica, inhabits C. quinquecarinata; P. jonesi, originally described in Anolis lionotus (syn. Norops oxylophus) from Nicaragua, inhabits N. oxylophus, N. biporcatus, and Basiliscus basiliscus; and the new species, which inhabits B. basiliscus. Parallopharynx matternae n. sp. differs from all other members of the genus by having a metraterm extending posteriad from the genital pore to the posterior margin of the ventral sucker, whereas in P. arctus and P. gonzalezi, the metraterm never surpasses the midlevel of the ventral sucker and in P. jonesi it never passes the anterior margin of the ventral sucker, and by having an oral sucker that does not exceed 150 microm in diameter with a subsequent greater oral-ventral sucker width ratio ranging from 1:0.88-1.12 (averaging 1:1), whereas values range from 1:0.71-0.83 for P. gonzalezi and P. arctus, and from 1:0.59-0.68 for P. jonesi. Parallopharynx spp. possesses Y-shaped excretory vesicles with a long central stem and short arms bifurcating immediately posterior to the ovary; similar to those found in members of the Telorchiidae. Additional similarities in the relative positions of the gonads and the structure of the cirrus sac and metraterm indicate a close relationship between Parallopharynx and members of the Telorchiidae.

Cryocolaspis, a New Genus and Species of Eumolpinae (Chrysomelidae) from Costa Rica

Cryocolaspis crinita n. gen., n. sp. is described from the mountains of central Costa Rica. The genus is a member of the tribe Adoxini and can be distinguished from other setose Neotropical Eumolpinae genera Sphaeropis, Brevicolaspis, Trichospinthera, and Xanthonia by its long erect setae and the combination of bidentate margins and depressions on the disc of its pronotum.

Two New Species of Lepanthes (Orchidaceae: Pleurothallidinae) from Costa Rica

Despite the monumental work by C. A. Luer, which disclosed the high diversity of Lepanthes Sw. in Costa Rica (Luer 1987, 1995, 2003), novelties in this species-rich genus of the Orchidaceae are continuously arising from botanical exploration in the country (Pupulin 2001, 2003; Blanco 2003). This may sound obvious for less known areas, relatively difficult to access, but it is also true for well-explored regions such as Monteverde. More than 3000 species of vascular plants were recorded there by Haber (2000), 400 of which are orchids according to Atwood (2000). The area of El Empalme, along the PanAmerican Highway is similar; botanists have made important collections here for at least the last 50 years. This paper describes two new species of Lepanthes from the continental divide of the Cordillera de Tilarin and the Talamanca range in central Costa Rica. All cited specimens have been seen by the authors. Descriptive terminology follows Luer (1996).

Seismogenic zone structure of the southern Middle America Trench, Costa Rica

The shallow seismogenic portion of subduction zones generates damaging large and great earthquakes. This study provides structural constraints on the seismogenic zone of the Middle America Trench offshore central Costa Rica and insights into the physical and mechanical characteristics controlling seismogenesis. We have located ∼300 events that occurred following the MW 6.9, 20 August 1999, Quepos, Costa Rica, underthrusting earthquake using a three‐dimensional velocity model and arrival time data recorded by a temporary local network of land and ocean bottom seismometers. We use aftershock locations to define the geometry and characteristics of the seismogenic zone in this region. These events define a plane dipping at 19° that marks the interface between the Cocos Plate and the Panama Block. The majority of aftershocks occur below 10 km and above 30 km depth below sea level, corresponding to 30–35 km and 95 km from the trench axis, respectively. Relative event relocation produces a seismicity pattern similar to that obtained using absolute locations, increasing confidence in the geometry of the seismogenic zone. The aftershock locations spatially correlate with the downdip extension of the oceanic Quepos Plateau and reflect the structure of the main shock rupture asperity. This strengthens an earlier argument that the 1999 Quepos earthquake ruptured specific bathymetric highs on the downgoing plate. We believe that subduction of this highly disrupted seafloor has established a set of conditions which presently limit the seismogenic zone to be between 10 and 35 km below sea level.

Subduction-zone structure and magmatic processes beneath Costa Rica constrained by local earthquake tomography and petrological modelling

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.

Ixodes (Ixodes) dicei, a new tick species (Acari: Ixodida: Ixodidae) from a lagomorph in a restricted high-altitude habitat in talamanca, Costa Rica

Ixodes (I.) dicei n. sp. (Acari: Ixodidae) is described and illustrated from males and females collected from a cottontail rabbit. This species of cottontail is poorly known and is found only in a restricted high mountain range of central Costa Rica and western Panama.

Improved classification of Landsat Thematic Mapper data using modified prior probabilities in large and complex landscapes

The use of modified prior probabilities to exploit ancillary data and increase classification accuracy has been proposed before. However, this method has not been widely applied because it has heavy computing requirements and because obtaining prior probability estimates has presented practical problems. This article presents a procedure that generates large sets of prior probability estimates from class frequencies modelled with ancillary data and a Mahalanobis Distance selection of previously classified pixels. The method produces a pixel sample size that is large enough to estimate class frequencies in numerous strata, which is particularly desirable for the study of large and complex landscapes. A case study is presented in which the procedure made it possible to estimate 537 sets of prior probabilities for an entire Landsat Thematic Mapper (TM) scene of central Costa Rica. After modifying the class prior probabilities, the overall classification consistency of the training sites improved from 74.6% to 91.9%, while the overall classification accuracy of sites controlled in the field by independent studies improved from 68.7% to 89.0%. The classification accuracy was most improved for spectrally similar classes. The method improves classification accuracy in large and complex landscapes with spectrally mixed land-cover categories.

Landscape evolution within a retreating volcanic arc, Costa Rica, Central America

Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and landscape evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls landscape evolution in the volcanic arc. Field mapping, stratigraphic correlation, and 4 0 Ar/ 3 9 Ar geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo-Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic ash flows that buried the Valle Central and descended the Tarcoles gorge to the Orotina debris fan at the coast. Growth of the modern Cordillera Central accentuated relief along the new divide, establishing the Valle Central as a Pacific slope drainage basin. Arc migration, relocation of the Pacific-Caribbean drainage divide, and formation of the Valle Central basin resulted from slab shallowing as irregular, hotspot-thickened crust entered the subduction zone. The geomorphic evolution of volcanic arc landscapes is thus highly sensitive to changes in subducting plate character.

Origin of silicic volcanic rocks in Central Costa Rica: a study of a chemically variable ash-flow sheet in the Tiribí Tuff

Chemical heterogeneities of pumice clasts in an ash-flow sheet can be used to determine processes that occur in the magma chamber because they represent samples of magma that were erupted at the same time. The dominant ash-flow sheet in the Tiribi Tuff contains pumice clasts that range in composition from 55.1 to 69.2 wt% SiO2. It covers about 820 km2 and has a volume of about 25 km3 dense-rock equivalent (DRE). Based on pumice clast compositions, the sheet can be divided into three distinct chemical groupings: a low-silica group (55.1–65.6 wt% SiO2), a silicic group (66.2–69.2 wt% SiO2), and a mingled group (58.6–67.7 wt% SiO2; all compositions calculated 100% anhydrous). Major and trace element modeling indicates that the low-silica magma represents a mantle melt that has undergone fractional crystallization, creating a continuous range of silica content from 55.1–65.6 wt% SiO2. Eu/Eu*, MREE, and HREE differences between the two groups are not consistent with crystal fractionation of the low-silica magma to produce the silicic magma. The low-silica group and the silicic group represent two distinct magmas, which did not evolve in the same magma chamber. We suggest that the silicic melts resulted from partial melting of relatively hot, evolved calc-alkaline rocks that were previously emplaced and ponded at the base of an over-thickened basaltic crust. The mingled group represents mingling of the two magmas shortly before eruption. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00445-001-0188-8.

Slab control over HFSE depletions in central Nicaragua

Mafic lavas from the central Nicaraguan portion of the Central American volcanic front exhibit considerable variability in the magnitude of high-field-strength element (HFSE) depletions. This variability cannot be attributed to variable magmatic differentiation, or more significantly, to variable depletion originating in the mantle wedge. Instead the HFSE depletions are thought to be the product of variable contributions from the subducting Cocos plate. Both subducted hemipelagic sediment and subducted oceanic crust are identifiable contributors to the overall signal. The latter could exert important control over HFSE depletions, but only if the dehydrating crust is rutile-saturated. Slab control over HFSE depletions is possible throughout the Central American subduction zone, even where slab contributions to magma generation are thought to be minimal, as in central Costa Rica. In some other subduction zones, slab control over HFSE depletions is apparent, but in others, such as the Marianas and the Aleutians, HFSE depletions are probably wedge-based.

Hijas, novias y esposas: Familia, matrimonio y violencia doméstica en el Valle Central de Costa Rica (1750–1850)

Hijas, novias y esposas: Familia, matrimonio y violencia doméstica en el Valle Central de Costa Rica (1750–1850)

Central Costa Rica deformed belt: Kinematics of diffuse faulting across the western Panama block

Fault kinematics, seismicity, and geodetic data across central Costa Rica reveal a diffuse fault zone, here named the Central Costa Rica Deformed Belt (CCRDB). The CCRDB defines the western margin of the Panama block and links the North Panama Deformed Belt (NPDB) along the Caribbean coast with the Middle America Trench (MAT) along the Pacific coast. The junction of the CCRDB and the MAT coincides with an abrupt transition from smooth to rough crust on the subducting Cocos plate (rough‐smooth boundary). Shallow subduction of rough, thickened oceanic crust associated with the Cocos Ridge shifts active shortening into the volcanic arc along faults of the CCRDB. Variable fault kinematics along this zone may reflect three combined deformation mechanisms: horizontal shortening and shear from oceanic ridge indentation, basal traction from shallow subduction, and localized block uplift from subducting seamount roughness. Within the forearc (domain 1), mesoscale faults express transtension where steep NE striking regional‐scale faults intersect the Pacific coast. Across the volcanic arc (domain 2), mesoscale faults exhibit mostly sinistral and dextral slip on NE and NW striking conjugate faults, respectively. Approaching the NPDB in the back arc (domain 3), transcurrent faulting is modified by transpression and crustal thickening. Fault kinematics are consistent with earthquake focal mechanisms and Global Positioning System (GPS) measurements. Radiometric age constraints confirm that faulting postdates the late Neogene onset of shallow subduction. The ensuing deformation front has propagated northward into the volcanic arc to its present position along the seismically active CCRDB. Within the forearc, the effect of shallow subduction is overprinted by local uplift related to underthrusting seamounts.

Tsunamis and Tsunami Hazards in Central America

A tsunami catalogue for Central America is compiledcontaining 49 tsunamis for the period 1539–1996,thirty seven of them are in the Pacific and twelve inthe Caribbean. The number of known tsunamis increaseddramatically after the middle of the nineteenth century,since 43 events occurred between 1850 and 1996. This isprobably a consequence of the lack of populationliving near the coast in earlier times. The preliminary regionalization of the earthquakessources related to reported tsunamis shows that, inthe Pacific, most events were generated by theCocos-Caribbean Subduction Zone (CO-CA). At theCaribbean side, 5 events are related with the NorthAmerican-Caribbean Plate Boundary (NA-CA) and 7 withthe North Panama Deformed Belt (NPDB). There are ten local tsunamis with a specific damagereport, seven in the Pacific and the rest in theCaribbean. The total number of casualties due to localtsunamis is less than 455 but this number could behigher. The damages reported range from coastal andship damage to destruction of small towns, and theredoes not exist a quantification of them. A preliminary empirical estimation of tsunami hazardindicates that 43% of the large earthquakes (Ms ≥7.0) along the Pacific Coast of Central America and100% along the Caribbean, generate tsunamis. On thePacific, the Guatemala–Nicaragua coastal segment hasa 32% probability of generating tsunamis after largeearthquakes while the probability is 67% for theCosta Rica–Panama segment. Sixty population centers onthe Pacific Coast and 44 on the Caribbean are exposedto the impact of tsunamis. This estimation alsosuggests that areas with higher tsunami potential inthe Pacific are the coasts from Nicaragua to Guatemalaand Central Costa Rica; on the Caribbean side, Golfode Honduras Zone and the coasts of Panama and CostaRica have major hazard. Earthquakes of magnitudelarger than 7 with epicenters offshore or onshore(close to the coastline) could trigger tsunamis thatwould impact those zones.

Stress Field in Costa Rica, Central America

We have relocated 1658 earthquakes whichoccurred in Costa Rica, and its vicinity. Theserelocated earthquakes were then used to investigatethe stress and orientation of fault planes within thestudy area. The analysis was made using the polaritiesof first motion P-waves. We found that the subductionzone for Costa Rica is mainly characterized by thrustfaulting, with some areas also exhibiting a componentof strike-slip motion. The intraplate Caribbeanseismicity in central Costa Rica shows a predominantshallow left-lateral strike-slip faulting. In southernCosta Rica, the subduction of very young oceaniclithosphere beneath the Caribbean plate (i.e. PanamaBlock), enhanced by the collision and subduction ofthe Cocos Ridge, has produced a highly compressivestress regime. This highly compressive regime ischaracterized by strike-slip faults oriented in aNE-SW direction, extending all the way from thePacific margin into the back-arc, connecting with theNorth Panama Deformed Belt.

Chemical mixing model of streamflow generation at La Selva Biological Station, Costa Rica

La Selva Biological Station occupies an area of lowland tropical rainforest in central Costa Rica. Sodium and chloride data were used to quantify the mixing proportions of local runoff and geothermal groundwater at several sites throughout the stream channel system in late April, at the end of the dry season. The fraction of streamflow accounted for by geothermal groundwater varied spatially between 0 and 0.85, indicating a significant contribution to streamflow and to stream solute loads from geothermal groundwater at some sites. In general, higher inputs of geothermal groundwater were found at lower elevations. Over half the flow from one basin (the Salto) was due to geothermal groundwater, suggesting a minimum annual runoff of about 0.7 m of geothermal groundwater from this basin. A plot of Na Cl vs. fraction of geothermal groundwater revealed watershed-scale chemical differences between the two major drainage systems (the Sura and the Salto), differences that were not apparent from a traditional two-solute plot of Cl vs. Na concentration. A small (21 mm) storm produced relatively little change in mixing proportions, as most throughfall was apparently retained in the relatively dry soils.

Three-dimensional velocity structure of the upper mantle beneath Costa Rica from a teleseismic tomography study

A tomographic study has been carried out in Costa Rica utilizing teleseismic events recorded by the national seismic network OVSICORI-UNA. The data consist of 130 earthquakes which occurred at epicentral distances of 23°–100° (P phases) and 110°–180° (PKP phases). 1378 IASP91 traveltime residuals were computed and inverted using an iterative linearized inversion procedure which incorporates 3-D minimum-traveltime ray tracing. The 3-D velocity structure of the upper mantle, as derived from teleseismic tomography, shows a northeastward-dipping high-velocity body beneath northern Costa Rica, interpreted as the subducting Cocos plate. Although less evident, a similar pattern of lateral heterogeneities characterizes the deep structure of central Costa Rica. There is no evidence for deep high-velocity bodies beneath southern Costa Rica. The 3-D reconstruction of the subducting Cocos Plate shows a steeply dipping slab (subvertical) beneath northern Costa Rica. Here the oceanic lithosphere is older and denser than in central Costa Rica, where the slab dips at about 60°. Southern Costa Rica does not show a dipping slab; this is in accordance with the subduction/collision of the thick and buoyant Cocos Ridge. The geometry of the slab, the maximum velocity anomalies and the sudden change in the local seismicity depth pattern suggest the existence of a tear in the subducted plate, located between the northern and central Costa Rican subduction zones. The strain field in the overriding plate indicates a strong structural control induced by the along-trench variations in subduction. Northern Costa Rica shows slight tensile deformation, while southern Costa Rica displays moderate to strong compressive deformation. The maximum horizontal gradient of the strain field is located in central Costa Rica where a sinistral transcurrent fault system crosses the country from the Pacific to the Atlantic coast. This system is likely to be generated by the along-trench variations in subduction.

Application of pattern recognition techniques to long-term earthquake prediction in central Costa Rica

The expert system GEO 2.5 has been applied to the analysis of geophysical and geological data from Costa Rica. Geophysical data consist of seismic tomography, Bouguer anomalies, seismic catalogue (RSN-ICE, 1984–1993) and seismic historical catalogue. Among the geological data, faults, lineaments, topography and a structural zonation of the region concerned have been used. Many other features have been obtained through the calculation of statistical functions of the original data such as nearness, density, length and b-value, other functions were secondary derivatives and modulus of horizontal gradient. A first analysis, mainly based on seismic tomography data and seismic catalogue, has led to the identification of a few seismogenic structures in the upper crust characterized by a high statistical correlation coefficient between seismic activity and positive velocity anomalies. Pattern recognition techniques have been applied to the long-term earthquake prediction by the definition, in the feature space, of non-linear regression functions between geophysical/geological data and a preliminary estimate of expected maximum magnitude. This preliminary estimate has been formulated on the basis of both the historical seismic catalogue and the structural zonation. This approach gives the empirical relationships among different geophysical and geological features, which are potentially related to the phenomenon of stress release. Due to the high non-uniqueness of such an approach, the results have to be physically understandable and each function has to be interpreted. The obtained multi-dimensional function has been applied to the calculation of a forecast maximum magnitude field for central Costa Rica. The results are to be considered preliminary. An improvement of such a forecast could be achieved by new data, such as heat flow, depth of Mohorovicic surface, active faults, vertical movement velocities, etc.

Contemporary Short Stories from Central America

This volume collects some of the best short fiction from the six Spanish-speaking countries of Central America-Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, and Panama. Selected from stories written between 1963 and 1988, it is a broad representation of active Central American writers. Many of the stories are quite sophisticated and utilize elements of the absurd or techniques of magical realism. Some stories deal with war-the unending struggle against dictators and military power that engrosses Central Americans. Others explore the realm of the writer's imagination. Some of the writers included are Augusto Monterroso (Guatemala), Carmen Naranjo and Samuel Rovinski (Costa Rica), Rosa Maria Britton and Jaime Garcia Saucedo (Panama), and Alfonso Quijada Urias (El Salvador).