Northern Andes Of Colombia Research Articles

Neogene variations in slab geometry drive topographic change and drainage reorganization in the Northern Andes of Colombia

The tropical Northern Andes of Colombia are one the world's most biodiverse places, offering an ideal location for unraveling the linkages between the geodynamic forces that build topography and the evolution of the biota that inhabit it. In this study, we utilize geomorphic analysis to characterize the topography of the Western and Central Cordilleras of the Northern Andes to identify what drives landscape evolution in the region. We supplement our topographic analysis with erosion rate estimates based on gauged suspended sediment loads and river incision rates from volcanic sequences. In the northern Central Cordillera, an elevated low-relief surface (2500 m in elevation, ~40 × 110 km in size) with quasi-uniform lithology and surrounded by knickpoints, indicates a recent increase in rock and surface uplift rate. Whereas the southern segment of the Central Cordillera shows substantially higher local relief and mostly well graded river profiles consistent with longer term uplift-rate stability. We also identify several areas of major drainage reorganization, including captures and divide migrations. These changes in the topography coincide with the proposed location of a slab tear and flat slab subduction under the northern Central Cordillera, as well as with a major transition in the channel slope of the Cauca River. We identify slab flattening as the most likely cause of strong and recent uplift in the Northern Andes leading to ~2 km of surface uplift since 8–4 Ma. Large scale drainage reorganization of major rivers is likely driven by changes in upper plate deformation in relation to development of the flat slab subduction geometry; however, south of the slab tear other factors, such as emplacement of volcanic rocks, also play an important role. Several biologic observations above the area of slab flattening suggest that surface uplift isolated former lowland species on the high elevation plateaus, and drainage reorganization may have influenced the distribution of aquatic species.

A pregnant Common Lancehead, Bothrops atrox (Viperidae), from the Northern Andes of Colombia

A pregnant Common Lancehead, Bothrops atrox (Viperidae), from the Northern Andes of Colombia

Environmental sound as a mirror of landscape ecological integrity in monitoring programs

Soundscape research has acquired a paramount role in biodiversity conservation as it may provide timely and reliable information about the ecological integrity. The relationship between soundscape complexity and ecological integrity in highly biodiverse environments, as well as the factors affecting this relationship require a thorough understanding. We determined how the soundscape relates to the landscape ecological integrity at different spatial and temporal scales in a montane forest in the northern Andes of Colombia. Between May–July 2018 we obtained acoustic recordings from 31 sampling sites in the protected area of a hydropower plant, and estimated nine acoustic indices and an ecological integrity index (EII) derived from fragmentation, connectivity, and habitat quality. Five of the acoustic indices, linked to the evenness of the acoustic signals and levels of the biophonic signals, were associated with changes in the EII and indicated the presence of more even, saturated, and acoustically rich soundscapes in sites with higher integrity. Relationships between acoustic indices and the EII were stronger at a smaller spatial scale (100 m) and responded to daily variation of the soundscape, with the strongest associations occurring mainly from sunrise to noon. We show that acoustic indices measuring the evenness of the acoustic activity distribution and the number of frequency peaks reliably reflect the changes in the ecological integrity, and can be integrated with remote sensing as a tool for landscape management. Our results highlight the soundscape analysis as a feasible approach for the monitoring and conservation planning of acoustically unknown and threatened Andean landscapes.

Late Jurassic syn-extensional sedimentary deposition and Cenozoic basin inversion as recorded in The Girón Formation, northern Andes of Colombia

The Yariguíes Anticlinorium, a regional structure located at the western flank of the Eastern Cordillera of Colombia, includes the thickest record of continental sedimentary rocks accumulated near to the Jurassic-Cretaceous boundary. The sedimentary rocks are lithoarenites and feldspathic arenites, grouped in the Girón Formation, and deposited in a Late Jurassic extensional basin interpreted in this work as a rift basin. We analysed the sedimentologic and compositional characteristics of two sections that accumulated in a complex rift system. We identified important thickness variations, from 3,350 m in the type section to at least 525 m in a reference section in the Zapatoca area, as well as petrographic and lithofacies changes. This led us to confirm that the Girón Formation encompasses all the continental facies, whose source rock correspond mainly to the exhumed blocks of the Santander Massif during the Late Jurassic. The synrift successions were segmented by transverse structures and regional longitudinal faults of the rift-shoulder, as the Suárez Fault. The tectonic frame of the study area shows the relevance of the W-E compressional regimes, explaining the local kinematics as a heritage of the former configuration and tectonic inversion of the basins. However, clockwise rotation of the stress field was detected from the stress tensor analysis. The latest orientation of the stress tensors and shear joints are related to the effect of the transpressional Bucaramanga and Lebrija faults along the study area.

How Much Did the Colombian Andes Rise by the Collision of the Caribbean Oceanic Plateau?

AbstractThe quantification of topographic growth at convergent margins is of primary importance to assessing the linkages between tectonic processes and landscape evolution. Traditionally, this task has relied on the applicability of conventional paleobotanical and isotopic methods to estimate paleoelevations, which is not always straightforward. Here, we use recent calibrations based on trace elements of arc‐related magmatic rocks to estimate crustal thickening and surface uplift of the northern Colombian Andes during the early Andean orogeny at ca. 70‐60 Ma. Increased Sr/Y and (La/Yb)N ratios of arc‐related intrusives suggest a ∼20 km crustal thickening that was probably accompanied by an isostatically compensated topographic uplift of up to ∼2 km along the proto‐Central Cordillera and the Santa Marta Range. This kilometer‐scale uplift was coeval with a regional shift from marine to continental deposition in foreland basins and was triggered by the collision of the Caribbean oceanic plateau.

A case study on causation of the landslide on 26 October 2016 in the northern Colombian Andes

This paper presents the results of a technical investigation on the causation of the landslide that occurred in Las Nieves quarry on October 26, 2016 in the municipality of Copacabana, located in the northern part of the Colombian Andes. This landslide caused the highest number of fatalities in Colombia in 2016, totalling 16 deaths. The study included field visits, soil sampling, study of the geology and geomorphology, as well as analysis of rainfall and groundwater flows presented in the area. The information collected in this study is consistent with the hypothesis that the regional groundwater flow which comes from recharge zones, generated an increase in water levels in the landslide zone thus triggering the landslide. Finally, a stability analysis (statistical analysis and sensitivity analysis) was performed using the limit equilibrium method, where the effect of the rise in the ground water table was modelled as the trigger. The results of the stability analysis showed a low safety factor for the slope, even when low water levels were considered.

Andesitic (SiO2: ~60 wt%) monogenetic volcanism in the northern Colombian Andes: Crystallisation history of three Quaternary volcanoes

The Quaternary Villamaría-Termales Monogenetic Volcanic Field (VTMVF) is one of the monogenetic fields located within the subduction related, volcanic chain in the northern Colombian Andes. The dominantly andesitic composition of the products from this field provides an opportunity to study the crystallisation history of monogenetic volcanic products, associated with long term crustal stagnation before eruption. This work focuses on the Victoria, Gallinazo and Tesorito monogenetic effusive volcanoes, using a combination of petrography, mineral chemistry and whole-rock chemical analysis, in addition to geothermobarometers, to estimate the crystallisation conditions of the main mineral phases and infer the depths at which such phases crystallised. We also present two K/Ar radiometric ages for Victoria and Gallinazo volcanoes in order to add to the known age (1.2 Ma) of the Tesorito volcano. This helps us to timeframe this volcanism within the ~140 km volcanic chain where it is located. The rocks are porphyritic with a glassy and microcrystalline groundmass, and display glomeroporphyritic and disequilibrium textures such as textures sieve in plagioclase and reaction rims in pyroxene. The main mineral phases forming the rocks are plagioclase (An22–67), orthopyroxene (Wo02 En65–80 Fs18–33), clinopyroxene (Wo39–45 En39–49 Fs07–17), amphibole (magnesiohastingsite, magnesihornblende, edenite and tschermakite), and Fe-Ti oxides Usp37–23 Mag63–77 and Ilm79–62 Hem21–39. Olivine (Fo71–87) only appears in the Victoria volcano. The volcanoes are subalkaline andesites with calc-alkaline affinity. Estimation of the crystallisation conditions (i.e. temperature and pressure) for in-equilibrium mineral phases, indicate the depths at which they crystallised. Olivine crystallised at 1198–1191 °C and ~1.4 GPa, orthopyroxene-clinopyroxene coexisted at 963–880 °C and 0.78–0.47 GPa, plagioclase formed at 928–908 °C and 0.76–0.17 GPa, amphibole crystallised at 998–877 °C and 0.79–0.16 GPa, and Fe-Ti oxides crystallised at 937–904 °C. This suggests that crystallisation starts at depths of ~53 km and it continues until the surface. The obtained radiometric ages for the Gallinazo (1.92 ± 0.06 Ma) and Victoria (1.97 ± 0.06 Ma) volcanoes indicate that they are ~0.7 Ma older than the nearby Tesorito volcano.

Morphometrical analysis of torrential flows-prone catchments in tropical and mountainous terrain of the Colombian Andes by machine learning techniques

Assessment of susceptibility to torrential flows at the catchment scale is a necessary step for prioritising zones that can be identified by hazard and risk maps. In the Andean region of Colombia, where these phenomena are common and highly destructive, few studies have been carried out on the subject. Considering that the effects of torrential flows will likely increase in the future due to extreme weather events and urbanisation of low prone areas, effective land management plans should include the assessment of susceptibility to this type of event. In this study, machine learning techniques were applied with morphometric parameters of mountainous catchments in the northern Colombian Andes to analyse torrential susceptibility in tropical environments. Several feature selection methods were implemented using statistics to evaluate the relationship between morphometric parameters and torrential susceptibility. The parameters that showed the strongest relationship with torrential catchments were selected for application of machine learning techniques, along with evaluation of performance and prediction ability. The analysis was carried out on morphometric parameters regarding the catchment’s drainage network, basin geometry, drainage texture, and relief characteristics. According to the results, the catchments characteristics related to relief and drainage texture are the most important for the study of torrential susceptibility. Within these groups of predictor parameters, relief ratio and constant of channel maintenance are the highest ranked variables. Although the Melton index shows a good prediction capacity, thresholds proposed in the literature are not valid in the Colombian Andes.

Thermochronological, petrographic and geochemical characteristics of the Combia Formation, Amagá basin, Colombia

The Amagá basin between the Western and Central Cordilleras of the Northern Andes of Colombia hosts the Neogene volcanic and volcaniclastic Combia Formation. Deposition of the Combia Formation in relation to Nazca plate subduction and arc volcanism is still a matter of debate. Therefore, the timing, petrography and geochemical characteristics of Combia Formation rocks were studied in the western and eastern parts of the Amagá basin, in order to gain more information on the type of magma generation and volcanic activity that led to the deposition of the Combia Formation.Apatite and zircon fission-track dating largely confirm a 12-6 Ma age for the deposition of the Combia Formation. Petrographic and major element analyses show that mainly trachy-andesite ignimbrites with a calc-alkaline composition were deposited in the western Amagá basin, whereas the volcanic rocks of the eastern Amagá basin are lavas flow and fall-out deposits of basaltic andesites of tholeiitic affinity. Trace element and isotopic analyses show that slab dehydration and sediment melting/decarbonation were important in primary magma generation in the mantle wedge, but the primary magma was mixed with lower continental crustal melts (e.g. High-Pb radiogenic), resulting in characteristic isotope signatures in the western and eastern Amagá basin. Then, the hot-zone developed a high Pb-radiogenic, garnet-bearing lower continental crustal (LCC) level as a consequence of the quantity of dehydration of the subducting slab and of changes in the tectonic regime. An extensional pull-apart event (12- 9 Ma), likely facilitated rapid magma ascend to the uppermost crust along a subvertical magma plumbing system throughout the Romeral Fault zone in the eastern Amagá basin, and calc-alkaline magmas with adakite-like signature, which may indicate contractile tectonics that allow the formation of middle-to upper-crustal magma chambers with a garnet fractionation at depth and the evolution of silicate melts into the hot zone mainly related to the amount of water (>4 wt %) present.

Filling the gaps in a highly diverse Neotropical lizard lineage: a new and endemic genus of Cercosaurinae (Squamata: Gymnophthalmidae) with the description of two new species from the Northern Andes of Colombia

In the last decade, understanding of the Neotropical lizards family Gymnophthalmidae has changed dramatically with the recognition of several new genera, resolution of non-monophyly, definition of previously unknown lineages and refined biogeographic hypotheses. Recent field explorations on the northern Cordillera Central in Colombia uncovered two undescribed species that cannot be assigned to any currently recognized gymnophthalmid genus. Based on a molecular phylogenetic analysis combined with morphological and genetic distances, we describe a new genus and two new species from the northern Andes of Colombia. Magdalenasaura gen. nov. is restricted to the Magdalena biogeographic province and is sister to the cis-Andean genus Gelanesaurus. The new genus can be readily distinguished from all other Cercosaurinae genera by a combination of genetic and morphological characters. The new genus contains Magdalenasaura leurosquama sp. nov. and M. adercum sp. nov., both found in forested habitats near streams at altitudes ranging from 1300 to 1850 m on the eastern flank of the northern Cordillera Central in Colombia. We differentiate the Cercosaurinae genera from Colombia based on general scutellation. Filling the gaps of the tremendous diversity of gymnophthalmid lizards will improve taxonomic and biogeographic hypotheses to better understand the evolution of endemic lineages from the north-western corner of South America. http://zoobank.org/urn:lsid:zoobank.org:pub:47E621FD-BEA9-4C65-87D8-D832C4EEC3A4

Editorial

Boletín Geológico number 46 (2020) publishes three articles on the disciplines of economic geology, hydrocarbon genesis, and basin evolution in several zones of Colombia. The following fragments have been taken from these articles respectively and introduce their contents.
 The Servicio Geológico Colombiano – SGC has carried out a large geophysical exploration campaign to acquire data and make it available to the academic community and mining industry. The SGC overflew the Andean and eastern part of Colombia and got more than 700,000 km of high resolution airborne geophysical (magnetometry and gamma spectrometry). Moyano et al. present an interpretation of isolated magnetic anomalies located in three different geologic environments in Colombia: San Lucas range, The Andes Cordillera, and the Amazonian craton.
 Rossello and Saavedra present a discussion about the structural aspects that contribute to the creation of the genetic and morphological characteristics of the bedding surfaces underlying the petrophysical potential of the Matachines field located in the Girardot subbasin, within the Upper Magdalena Valley basin (Valle Superior del Magdalena – VSM), Colombia. The authors focus on sectors where the primary permeability and porosity values are usually too low to meet economic expectations in hydrocarbon exploration or production activities.
 Rodríguez and Obando report new petrography, total rock chemistry and U-Pb zircon geochronology data of the La Quinta Formation, Serranía de Perijá, at the northern Andes of Colombia. This new information is correlated with other volcano-sedimentary sequences, specifies the distribution of arc volcanism and with the analysis of the inherited zircons in volcanic rocks improves the understanding of the basement distribution on which the arc is founded. 
 The editor acknowledges the efforts of the following reviewers whose comments and recommendations, on the eleven manuscripts submitted, contributed to the improvement of the three articles that were ultimately approved: Ana Ibis Despaigne, Andrés Cárdenas, Ariel Cadena, Barbara Martiny, Camilo Bustamante, César Mora, Germán Bayona, Gustavo Córdoba, Hermann Bermúdez, Hugo Murcia, Jhon Jairo Sánchez, José Luis Arce, Juan Carlos Molano, Juan Diego Colegial, Luis Castillo, Luis Enrique Cruz, Mario Moreno, Mauricio Bermúdez, Umberto Cordani, Natalia Pardo, Oswaldo Ordóñez, Thomas Cramer, and Yamirka Rojas. We recognize the final content of the articles does not necessarily reflect the thoughts of the reviewers and editors.

Vulnerability of Rural Communities to Change in an Ecosystem Service Provision: Surface water supply. A Case Study in the Northern Andes, Colombia

The understanding of how socio-ecological systems respond to environmental change is an essential issue in land use planning processes. Vulnerability analyses in the context of socio-ecological systems are a useful tool to this end. The study of social vulnerability seeks to analyze how the characteristics of beneficiaries of ecosystem services and their relation to the ecosystems, determine their sensitivity and their capacity to adapt to changes in the provision of said services. In this paper, we evaluate the social vulnerability of rural communities in the face of changes in the levels of the provision of surface water in the Riogrande basin, which is located in the Northern Andes in Colombia. Social vulnerability is evaluated based on two components. First, the initial, inherent vulnerability, which depends on parameters such as current level and the change in the level of benefits, types of needs met by the ecosystem service analyzed, and the capacity for substitution. The second component is the final, inherent vulnerability that considers the beneficiary’s adaptive capacity determined by individual and institutional characteristics. The information was collected through semi-structured interviews and site-level surveys, as well as the use of available existing data for the area of study. The results show that beneficiaries of the ecosystem service which was analyzed have a low vulnerability to changes in the levels of water supply given their high substitution capacities and medium-high adaptive capacity.

Ecoacoustics in the rain: understanding acoustic indices under the most common geophonic source in tropical rainforests

AbstractRainfall is one of the most predominant geophonic sources in nature, and the major climatic phenomenon influencing species biology in tropical ecosystems. Although its effects on acoustic indices have been studied, rainfall is recognized as a nuisance factor affecting their estimation. Consequently, files with rainfall sounds are typically removed from ecoacoustic analyses. In tropical rainforests, where rainfall is a common and unpredictable event, its influence on acoustic indices needs to be explicitly examined before implementing acoustic passive monitoring. Using mixed‐effects models we assessed the effect of different rainfall conditions on the direction and magnitude of the values of eight commonly used acoustic indices. We obtained 18336 1‐min recordings from 28 sampling sites in a montane forest on the northern Andes of Colombia between May‐July 2018. We identified 2867 1‐min recordings containing light to heavy rainfall. We found that both rainfall occurrence and its variation in intensity were associated with increases in ACI, ADI, H, and M index values, and decreases in AEI, BI, NDSI, and NP values. The estimated indices exhibited differential sensitivity to rainfall, with M, NDSI, and NP showing higher differences associated with increasing frequency and intensity of rainfall. Regardless the direction of change in index values caused by rainfall, we found that the magnitude of variation depended on the index. For instance, ACI and BI indices showed low sensitivity and can be considered as reliable acoustic metrics, even during heavy intensity rainfall. In contrast, M, NDSI, and NP might lead to misleading inferences, if rainfall events are not considered during calculation. We stress the importance of careful interpretation of biological inferences based on these sensitive indices and encourage an explicit assessment of rainfall, particularly in short‐term acoustic surveys in highly pluvious regions where rainfall is a conspicuous component of the soundscape.

Present-day structural frame of the Santander Massif and Pamplona Wedge: The interaction of the Northern Andes

Based on regional geology and stress tensor analysis from fault slickensides, we propose a structural model to explain the present-day configuration of a crystalline core in the northern Andes of Colombia (the Santander Massif - SM). The SM has undergone transpressional tectonics in a domino-style, controlled by longitudinal sinistral strike-slip faults as the Bucaramanga Fault. The tectonic style also exhibits NE-SW trending transverse inner faults with dextral strike-slip kinematics. The transpressional regime of the SM differs from the compressive regime that characterizes nearby blocks (northern Perijá Range, southern Floresta Massif, and eastern Pamplona Wedge). Transpressional structures result from a regional W-E horizontal compression corresponding to the current stress field as determined here by cross-cutting relations, mainly observed in the Pamplona Wedge. Stress tensors also show maximum horizontal stress (SHmax) in radial pattern towards the wedge deformation front, whose influence spreads over the SM western border. The W-E regional compression also explains the tectonic syntaxes formed by the Pamplona Wedge to the north and the Sierra Nevada de Güicán or El Cocuy to the south. These two areas are characterized by the opposite outward vergence of their compressive deformation fronts.

<p><strong>A new species of <em>Meriania</em> of the Brachycera group (Melastomataceae: Merianieae) with dimorphic stamens</strong></p>

Meriania juan-canoi, a new species endemic to the northern Andes in Colombia is described and illustrated. This new species belongs to the Brachycera group and can be distinguished from the other species by its apically rounded calyptra, completely free ovary and dimorphic stamens. The description of this new species from a relatively well collected area near a major road in southeastern of Medellín, Colombia, confirms our lack of knowledge on the vegetation of several Neotropical regions. Due to the intense agricultural activity in the area where this species grows and the small area where it occurs, we recommend a conservation classification of Critical Risk (CR).

Probabilistic landslide susceptibility analysis in tropical mountainous terrain using the physically based r.slope.stability model

Abstract. Landslides triggered by rainfall are very common phenomena in complex tropical environments such as the Colombian Andes, one of the regions of South America most affected by landslides every year. Currently in Colombia, physically based methods for landslide hazard mapping are mandatory for land use planning in urban areas. In this work, we perform probabilistic analyses with r.slope.stability, a spatially distributed, physically based model for landslide susceptibility analysis, available as an open-source tool coupled to GRASS GIS. This model considers alternatively the infinite slope stability model or the 2.5-D geometry of shallow planar and deep-seated landslides with ellipsoidal or truncated failure surfaces. We test the model in the La Arenosa catchment, northern Colombian Andes. The results are compared to those yielded with the corresponding deterministic analyses and with other physically based models applied in the same catchment. Finally, the model results are evaluated against a landslide inventory using a confusion matrix and receiver operating characteristic (ROC) analysis. The model performs reasonably well, the infinite slope stability model showing a better performance. The outcomes are, however, rather conservative, pointing to possible challenges with regard to the geotechnical and geo-hydraulic parameterization. The results also highlight the importance to perform probabilistic instead of – or in addition to – deterministic slope stability analyses.

Sedimentary record of the Cretaceous–Paleocene arc–continent collision in the northwestern Colombian Andes: Insights from stratigraphic and provenance constraints

The collision of intra-oceanic arcs with continental margins is a primary factor controlling the evolution, modification, and growth of continental crust. Syn- to post-collisional basins are formed on both the oceanic and continental sides of an accretionary orogen as a consequence of tectonic activity, which preserve the associated erosional and exhumation record of the colliding element. During the late Cretaceous–Paleogene, the evolution of the northern Colombian Andes was shaped by an oceanic arc-continent collision as a result of the interaction between the Caribbean and South American plates. The timing and stratigraphic record of the collision have mostly been reconstructed from foreland and hinterland basins. In this contribution, we present the results of an integrated stratigraphic, paleontological, and provenance study of Upper Cretaceous sedimentary sequences accumulated on the oceanic side, to the west of the collisional event. Our results suggest that clastic rocks mainly accumulated in short depositional systems in deep marine settings. Two stratigraphic units can be distinguished: A volcanoclastic unit, composed of dark gray siliceous mudrocks interlayed with thick to medium volcanic-rich sandstone layers, accumulated in a turbidite system . A siliciclastic unit (Urrao Member) composed of dark gray mudrocks, and thin to thick, fine- to medium-grained feldspathic litharenites and lithic arkoses accumulated in the lobes and splays of submarine fans. Polymictic conglomerates and sandstones associated with submarine channels and levees are less common and can be used as stratigraphic markers. The Urrao Member was mostly sourced from igneous, sedimentary, and metamorphic Cretaceous and older rocks forming the continental paleo-margin that was being rapidly exhumed as suggested in previous works. Zircon crystal morphology and depositional ages suggest volcanism simultaneous with sedimentation. The maximum depositional UPb ages of zircons and poorly preserved macro- and microfossils (mollusks and calcareous microfossils) suggest a Coniacian and Campanian–Maastrichtian age for the volcanoclastic and siliciclastic units, respectively; nevertheless, regional paleontological and geochronological data indicate that marine siliciclastic sedimentation continued into the Paleocene. These new data suggest that the late Cretaceous–Paleocene interaction of the Caribbean and South American plates did not trigger considerable and long-lasting uplift/erosion of the colliding oceanic domain and that magmatism was active during collision.

The role of subducted sediments in the formation of intermediate mantle-derived magmas from the Northern Colombian Andes

Unraveling the sources and processes that produce intermediate continental arc volcanoes is still a challenge for geoscientists. To address this problem, here we use comprehensive geochemical and isotopic data from Nevado del Santa Isabel and Cerro Machín volcanoes in the North Volcanic Province of Colombia, and from oceanic sediments sampled outboard the Colombian continental margin. Volcanoes along this province have been influenced by the subduction of a compositionally contrasting sedimentary column constituted by a carbonate-rich pelagic layer overlain by a clay-and-apatite-rich hemipelagic unit. The studied volcanoes exhibit the high Mg# (~60) and calc-alkaline affinities that are typical of continental arcs but display unusually high and contrasting Th(U)/La, Nb/Ta and Dy/Yb ratios and isotopic compositions. We argue that the geochemical variations within and among these volcanoes are not controlled by differentiation or crustal contamination of a parental basaltic magma but formed by melting of different kinds of subducted sedimentary materials detached from the slab as buoyantly rising diapirs at various depths. This model accounts for the reworking of refractory carbonates into arc magmatism and suggests that the geochemical diversity of the North Volcanic Province is mainly controlled by the nature of the subduction inputs and their exhumation pathways within the mantle wedge.

Getting better temporal and spatial ecology data for threatened species: using lightweight GPS devices for small primate monitoring in the northern Andes of Colombia.

The use of GPS telemetry has been a reliable research tool for the study of primate biology in recent years. Although in the past technological restrictions limited its use mainly to large primates, recent improvements in battery size make it possible to use this technology for small species. We used GPS devices for monitoring two adult white-footed tamarins (Saguinus leucopus) from a free-ranging group, and assessed its applicability for recording spatial and ecological data. GPS devices were operational for 66 and 85days, recording 221 positions (36.6% acquisition rate; 73% of which were highly accurate) and 3195 activity values for both individuals. Depending on the estimation method, we calculated the home range size for the group to be 19.4 and 22.9ha, which were within the range for the species in other localities. The animals were active each day for 11h, with high activity during the early morning. The monkeys showed a constant and alternate use of four sleeping sites with a limited reuse of the same site on consecutive nights. These daily activity and sleeping site use patterns are similar to those reported for other Saguinus species. Based on the kind and quality of the data recorded, we consider GPS telemetry to be an efficient and advantageous method for tracking and obtaining ecological information from S. leucopus. In comparison to other data collection methods, GPS telemetry required fewer personnel and less time commitment to record data without compromising the accuracy of the spatial and activity information we obtained.

The Paleogene arcs of the northern Andes of Colombia and Panama: Insights on plate kinematic implications from new and existing geochemical, geochronological and isotopic data

The northern Andes of Colombia comprise two non-cogenetic Paleogene arcs formed in contrasting geodynamic settings including continental and oceanic domains. New whole-rock geochemistry and isotopic constraints, together with a review of 332 geochemical, 76 isotopic and 204 geochronological data from Paleocene to Eocene volcanic and plutonic rocks exposed in central and western Colombia and Panama, are used to evaluate cause-effect relations between regional plate kinematics and the spatio-temporal distribution of the circum-Caribbean magmatic arcs. Short-lived, ~60–45 Ma arc-like magmatism in the Central Cordillera of Colombia was emplaced in a thickened continental crust due to the oblique subduction of the Caribbean oceanic plate underneath South America, as suggested by the high Sr/Y ratios. Conversely, the Panama Arc, and its poorly explored extension in the northwestern segment of the Western Cordillera of Colombia document a major phase of tholeiitic to calc-alkaline arc magmatism between ~71 Ma and ~34 Ma, mostly derived from a hydrated mantle wedge, and emplaced in an oceanic plateau crust. This arc record a major phase of magmatic activity between 40 Ma and 50 Ma that can be associated to changes in the convergence direction and subduction rates of the Farallon plate.Farther to the south, in the Pacific region of Colombia, Eocene arc-related rocks from the Timbiqui Complex show a geochemical signature that suggests a magmatic origin from melting of both a subduction-modified mantle and lower tectonically thickened crust. A possible interpretation for the Pacific and Western Colombia-Panama Arc systems, and its analogous in Ecuador, recall an Aleutian-type convergent margin in which the continental arc laterally switches to a purely oceanic system along the trailing edge of the Caribbean plate as consequence of eastward subduction of the Farallon plate.