Northwestern Corner Of South America Research Articles

Radial and azimuthal seismic anisotropy in NW South America: Insights into crustal deformation and mantle flow using ambient noise and surface wave tomography

We illuminate the crustal and upper mantle structure of the northwestern corner of South America by mapping radial and azimuthal seismic anisotropy. Radial anisotropy is inferred from the discrepancy between VSV and VSH polarized S-velocities in horizontally propagating Rayleigh and Love waves, respectively. First, short-period (7–35 s) phase and group velocities are estimated from ambient noise cross-correlations, and long-period (40–170 s) group velocities are determined from fundamental-mode, surface-wave trains from earthquake sources at regional and teleseismic epicentral distances. Dispersion velocities are then tomographically inverted to develop maps of group velocity variation for periods between 7 and 170 s including azimuthal velocity dependence. We observe that positive anisotropy in the upper crust is related to thick Quaternary sequences in sedimentary basins, while negative anisotropy is found beneath active volcanoes and igneous-metamorphic terrains. Negative anisotropy features observed in the lower crust beneath the Eastern Cordillera suggest the existence of sill-like intrusions that penetrate the lower crust, thus supporting underplating mechanisms. Our study reveals SW-NE oriented fast axes of azimuthal anisotropy beneath the Eastern Cordillera, which strongly suggest the presence of shear zones within the fold and thrust belt system. Notably, the fast axes align parallel to the regional faults in the area, indicating a significant role in controlling faulting processes. Finally, we observe a wide trench-parallel zone of azimuthal anisotropy beneath the Nazca Plate, the Panama Block, and the Caribbean, which we associate with subslab mantle flow.

Lithospheric and Slab Configurations From Receiver Function Imaging in Northwestern South America, Colombia

AbstractThe northwestern corner of South America presents a highly complex geodynamical setting including the convergence between South America, Nazca, and Caribbean plates; which also entails heterogeneity and complexity in the lithospheric structure. Here, we present depth‐migrated common‐conversion point (CCP) teleseismic receiver function profiles carried out using seismological data between 2011 and 2020 from the Colombian Geological Service, combined with some stations of observatories and international networks. These profiles provide better constraints on the lateral interpretation of the main lithospheric discontinuities in this region. We provide an updated crustal thickness map displaying some differences from previous studies, especially in the northernmost part of the cordilleran system. Our results also show some intracrustal features such as the regional detachment surface beneath the Eastern Cordillera and the presence of deep melt reservoirs under the Central Cordillera and the Paipa‐Iza complex in the Eastern Cordillera. We also discuss the lithospheric thickness and the potential existence of a highly hydrated and serpentinized mantle wedge under the forearc over the slab segment south of the Caldas tear. Furthermore, the CCP profiles further support the subduction system segmentation under northwestern South America, with at least five slab segments, two of them overlapping between ∼5.5 and ∼8°N, three belonging to the Nazca plate, and two having a Caribbean origin. The Bucaramanga nest appears to be linked to the interaction between the two northmost slab segments, while the Cauca cluster might be related to a slab dehydration process of a highly fractured zone.

Evolution of the Atlantic Intertropical Convergence Zone, and the South American and African Monsoons Over the Past 95‐Myr and Their Impact on the Tropical Rainforests

AbstractThe widening of the South Atlantic Basin led to the reorganization of regional atmospheric and oceanic circulations. However, the response of the Atlantic Intertropical Convergence Zone (ITCZ), and South American and African monsoons across paleoclimate states, especially under constant paleogeographic and climatic changes, has not been well understood. Here we report on paleoclimate simulations of the Cenomanian (∼95 Ma), early Eocene (∼55 Ma), and middle Miocene (∼14 Ma) using the Community Earth System Model version 1.2 to understand how the migration of the South American and African continents to their modern‐day positions, uplift of the Andes and East African Rift Zone, and the decline of atmospheric CO2 changed the Atlantic ITCZ, and the South American and African monsoons and rainforests. Our work demonstrates that the South Atlantic widening developed the Atlantic ITCZ. The South Atlantic widening and Andean orogeny led to a stronger South American monsoon. We find the orogeny of the East African Rift Zone is the primary mechanism that strengthened the East African monsoon, whereas the West African monsoon became weaker through time as West Africa migrated toward the subtropics and CO2 levels fell below 500 ppm. We utilize the Köppen‐Geiger Climate Classification as an indicator for maximum rainforest extent. We find that during the Cenomanian and early Eocene, a Pan‐African rainforest existed, while the Amazon rainforest was restricted toward the northwestern corner of South America. During the middle Miocene, the Pan‐African rainforest was reduced to near its modern‐day size, while the Amazon rainforest expanded eastward.

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

Emplacement of the Triassic Pueblito Pluton, NW Colombia: Implications for the Evolution of the Western Margin of Pangea

We present the first structural geology focused study of a Triassic pluton in the Northern Andes, which provides new insights into the understanding of the tectonically complex northwestern corner of South America. Based on a combination of field structural data (377 stations) and a detailed magnetic susceptibility survey, 159 sites, we studied the structure of the Pueblito Pluton (PP), an original suprasubduction mafic cumulate structure emplaced in the northern part of the Arquia Terrane (western margin of Central Cordillera of Colombia). Even though the PP has resided along an active margin for over 230 million years ago, geochronology suggests no postcrystallization Ar-loss and, probably, no major reset of the original emplacement fabric. The PP magnetic fabric is dominatly parallel to the measured field foliation and formed under submagmatic to high-temperature conditions, at the final stages of cooling. The pluton internal contacts, mylonitic structures along the western margin, shape of the pluton, scalar parameters of the magnetic fabric, the directional field/magnetic data, and the geochronological data are compatible with a sinistral transpressional tectonic regime of emplacement by ca 233 Ma. This regime was regionally extended in the Arquia and Tahami Terranes (western margin of Pangea).

Depth to the bottom of magnetic layer in South America and its relationship to Curie isotherm, Moho depth and seismicity behavior

We have estimated the DBML (depth to the bottom of the magnetic layer) in South America from the inversion of magnetic anomaly data extracted from the EMAG2 grid. The results show that the DBML values, interpreted as the Curie isotherm, vary between ∼10 and ∼60 km. The deepest values (>∼45) are mainly observed forming two anomalous zones in the central part of the Andes Cordillera. To the east of the Andes, in most of the stable cratonic area of South America, intermediate values (between ∼25 and ∼45 km) are predominant. The shallowest values (<∼25 km) are present in northwestern corner of South America, southern Patagonia, and in a few sectors to the east of the Andes Cordillera. Based on these results, we estimated the heat flow variations along the study area and found a very good correlation with the DBML. Also striking is the observation that the thermal anomalies of low heat flow are closely related to segments of flat subduction, where the presence of a cold and thick subducting oceanic slab beneath the continent, with a virtual absence of hot mantle wedge, leads to a decrease in the heat transfer from the deeper parts of the system.After comparing our results with the Moho depths reported by other authors, we have found that the Curie isotherm is deeper than Moho in most of the South American Platform (northward to ∼20°S), which is located in the stable cratonic area at the east of the Andes. This is evidence that the lithospheric mantle here is magnetic and contributes to the long wavelength magnetic signal. Also, our results support the hypothesis that the Curie isotherm may be acting as a boundary above which most of the crustal seismicity is concentrated. Below this boundary the occurrence of seismic events decreases dramatically.

A new species of the catfish genus Cordylancistrus (Siluriformes, Loricariidae) from the Sierra Nevada de Santa Marta, Colombia.

As a part of an assessment of loricariid catfishes inhabiting the Andes of Colombia, specimens belonging to an interesting new species were identified. The new species is described herein, and it is tentatively included in the genus Cordylancistrus. The new species can be easily distinguished among its congeners by the presence of a unique diagnostic character: a fleshy keel or excrescence, black or dark brown, over the posterior tip of supraoccipital. Specimens of the new species were captured in rivers of the Sierra Nevada de Santa Marta and the Sierra de Perijá that drain to the Magdalena River Basin and Caribbean Sea. The occurrence of one species of Cordylancistrus in the Sierra Nevada de Santa Marta could have interesting biogeographic implications for hypotheses related to the geological history of northwestern corner of South America or to the dispersal or vicariance models used to explain biogeographical patterns of related species in Colombia.

Birds of Antioquia: Georeferenced database of specimens from the Colección de Ciencias Naturales del Museo Universitario de la Universidad de Antioquia (MUA).

The department of Antioquia, Colombia, lies in the northwestern corner of South America and provides a biogeographical link among divergent faunas, including Caribbean, Andean, Pacific and Amazonian. Information about the distribution of biodiversity in this area is of relevance for academic, practical and social purposes. This data paper describes the dataset containing all bird specimens deposited in the Colección de Ciencias Naturales del Museo Universitario de la Universidad de Antioquia (MUA). We curated all the information associated with the bird specimens, including the georeferences and taxonomy, and published the database through the Global Biodiversity Information Facility network. During this process we checked the species identification and existing georeferences and completed the information when possible. The collection holds 663 bird specimens collected between 1940 and 2011. Even though most specimens are from Antioquia (70%), the collection includes material from several other departments and one specimen from the United States. The collection holds specimens from three endemic and endangered species (Coeligena orina, Diglossa gloriossisima, and Hypopirrhus pyrohipogaster), and includes localities poorly represented in other collections. The information contained in the collection has been used for biodiversity modeling, conservation planning and management, and we expect to further facilitate these activities by making it publicly available.

The initial human settlement of Northwest South America during the Pleistocene/Holocene transition: Synthesis and perspectives

The northwestern corner of South America, represented by the current territory of Colombia, is a key region to assess some relevant issues linked with the initial human peopling of the area, including population dispersals, cultural diversity, and early adaptations to the changing environmental conditions experienced by lowland and highland north-Andean Neotropical ecosystems at the Pleistocene/Holocene transition. The aim of this paper is to present a synthesis of the archaeological research about early peopling carried out in Northwest South America during the last four decades. Specifically, it will focus on the adaptive strategies and the cultural diversity patterns exhibited by the early hunter-gatherer groups that entered the region since late Pleistocene times. The classic ideas about the time of arrival of the first settlers, the dispersal routes, the incidence of the climate change in on the rate of dispersal and colonization of different habitats, and the role of the megafauna in the subsistence will be reviewed, prior to the formulation of new hypotheses about the meaning of the apparent intraregional diversity of the archaeological record and the evolution of economic strategies over time.

Paleomagnetism in Mesozoic rocks of the Northern Andes and its Implications in Mesozoic Tectonics of Northwestern South America

AbstractNew paleomagnetic data isolated in Upper Triassic to Aptian rocks exposed in the Colombian Andes and west of the Guyana craton, in conjunction with paleomagnetic data from the Andes of Venezuela and the South American craton, permit the interpretation of along-margin northward translations of Andean Colombian terranes during the Early-Middle Jurassic. Field tests and comparison with reference paleopoles for South America indicate that characteristic components uncovered in red-siliciclastic and igneous rocks are primary, or near-depositional, and they are carried dominantly by hematite, magnetite and Ti-magnetite. Difference in declination values of characteristic components isolated in fault-bounded blocks document counter-clockwise rotations previous to syn-extensional deposition. The Jurassic tectonic scheme proposed here for the northwestern corner of South America shows an Early Jurassic, linear subduction-related magmatic arc evolving to Late Jurassic rift-related setting associated to the opening of the Proto-Caribbean Ocean and westward retreat of the subduction zone. A similar tectonic evolution for the Jurassic has been proposed for southwestern USA and the Nazas arc in Mexico.

The choco block in the northwestern corner of South America: Structural, tectonostratigraphic, and paleogeographic implications

The Choco Block, located in the northwestern corner of South America, comprises the isthmus of Panama east of the Canal Zone and northwestern Colombia, including the westernmost flanks of the Cordillera Occidental above latitude 4°N. Three major structural and lithogenetic elements compose this terrain: the Dabeiba and Baudo Arches, the Atrato-Chucunaque Basins, and the Istmina Deformed Zone. The Dabeiba and Baudo Arches outline the external boundaries of the Choco Block and display similar characteristics: (a) mostly positive gravity anomalies and association of igneous bodies of oceanic origin with sedimentary suites, and (b) occurence of Upper Cretaceous to Miocene pelagic and hemipelagic and terrigenous strata in blocks of different ages and environments associated with mafic igneous rocks. The Dabeiba Arch exhibits a melange fabric, particularly at its eastern margin, in which disrupted strata and inclusions of Upper Cretaceous-Paleocene, Eocene-Oligocene, and Miocene exotic blocks are dispersed in a sheared pelitic matrix of middle Miocene age. The Atrato-Chucunaque Basins contain sedimentary fill exceeding 10 km in thickness. Two distinctive stratigraphic sequences comprise: (1) an outcropping and apparently continuous Oligocene to middle Miocene sequence composed mostly of pelagic and hemipelagic strata, overlain by hemipelagic and terrigenous strata of latest Middle Miocene to Pliocene age, and (2) an underlying middle Miocene and older sequence, composed mostly of turbidities, which has been recognized only in subsurface sections. An evaluation and synthesis of the structural and lithogenetic information of the Choco Block indicate the following conclusions. The Choco Block is an exotic terrane with no lithogenetic affinity with South America, accreted onto the northwestern flanks of the Cordillera Occidental during the middle Miocene. The occurence of exotic upper Paleocene planktic foraminiferal assemblages in the Dabeiba Arch suggests an origin for the Choco Block as distant as the northern latitudes of Guatemala and Mexico. The Uramita Fault Zone is the suture between the Choco Block and the Cordillera Occidental in NW South America. The young intermontane Atrato and Chucunaque Basins and the Istmina Deformed Zone were formed as a result of the accretion of the Choco Block to the northwestern flanks of the Cordillera Occidental during middle Miocene time.

Neotectonics of the Caribbean

A compilation of earthquake focal mechanism solutions together with the interpretation of inclined, intermediate‐depth seismic zones, Neogene strike‐slip faults, fault‐controlled basins, and volcanism is used to test three existing models for the neotectonic (i.e., Neogene or post‐Oligocene) development of the Caribbean. The current models, although based on different hypotheses using different data sets, are similar and suggest varying degrees of convergence between the Caribbean and either North or South American plates or convergence between the Caribbean plate and continental fragments of the northwestern corner of South America. Using model 1, previous workers have interpreted the disposition of fracture zones and magnetic anomalies in the central and South Atlantic as indicating that the Caribbean plate is being compressed by north‐south convergence between the Americas with the result that it is being driven eastward relative to the Americas along strike‐slip faults while producing east‐west trending subductionlike convergent zones along northern and southern plate margins. Using model 2, previous workers have interpreted the azimuths of active strike‐slip faults and focal mechanism solutions and closure of three‐plate velocity circuits as indicating that the South American plate converges in a west‐northwesterly direction on the southern margin of the Caribbean plate and has produced compressional features, while strike‐slip motion dominates along the northern boundary. Using model 3, previous workers have interpreted focal mechanism solutions and the pattern of strike faulting and basin development in northwestern South America to suggest right‐lateral displacement of the northwestern corner of South America relative to the craton with convergence and compression in the south central Caribbean. Our integration of geologic information on faults, basins, and volcanism considerably extends the limited record of plate interactions known from historical reports of the past few hundred years and recorded earthquakes and suggests that (1) relative motion between the North American and Caribbean plates is dominantly east‐west strike‐slip motion, although areas of complex internal deformation associated with restraining bend or compressional strike‐slip fault segments have been identified in Jamaica, Hispaniola and Central America (2) relative motion between the South American and Caribbean plates is dominantly east‐west strike‐slip motion, although an area of restraining bend deformation has been identified in the Araya Peninsula of Venezuela; (3) relative motion between a triangular continental fragment of northwestern South America (the “Maracaibo Block”) ranges from northwest to northeast along the south central margin of the Caribbean and appears to be driven mostly by the late Miocene‐Pliocene collision of the Panama arc, although additional driving forces may include the collision of the Carnegie Ridge and/or oblique subduction (to the northeast) in Ecuador; and (4) relative motion (internal deformation) may be occurring at a very slow rate between fault‐bounded blocks within the Caribbean plate as a result of the convergence of the Maracaibo Block and/or eastward motion of the Caribbean plate relative to a continental promontory of North America in northern Central America. Because the Caribbean margins are composed mainly of anisotropic, easily deformed continental and arc lithosphere, plate boundaries are zones of diffuse deformation, and it is difficult to assess the degree of convergence between the Americas, although data from the Caribbean itself suggest that it may be smaller than the amount inferred by some workers using model 1 (fracture zone and magnetic anomalies in the Atlantic). Some of the compressional features cited as evidence for the relative convergence of the Americas may be instead related to the convergence between the Maracaibo Block relative to the southern margin of the Caribbean. Many aspects of Caribbean neotectonics remain less than completely understood, but more integration of seismic and geologic studies (particularly exploratory fault trenching of onshore faults and seismic profiling of offshore faults) should lead to rapid advances.

GEOGRAPHIC AND REPRODUCTIVE ISOLATION IN ATLANTIC AND PACIFIC POPULATIONS OF PANAMANIAN BATHYGOBIUS.

Thoughout most of the Tertiary the Atlantic and Pacific oceans were continuous and connected over much of the area that is now Central America and the northwestern corner of South America. Presumably populations of many marine species were also continuous in this range. The rise of the Isthmus of Panama 2-5 million years ago (Woodring, 1966) split this vast biota into two disjunct populations, the western Atlantic and the eastern Pacific. The land bridge has remained as a geographic barrier between the oceans and as such has provided a unique opportunity to study the evolution of many marine organisms. The Panama Canal has had little effect on the distribution of most groups because of the fresh water of Gatun Lake. Few marine species can survive a canal transit. (Concerning fishes see Hildebrand, 1939; R. W. Rubinoff and I. Rubinoff, 1968 and 1969). The species that were separated have continued to evolve independently and diverge from each other with time. Some groups are still morphologically identical on both coasts. Others have changed radically, probably in response to different selective pressures. These pairs of populations, with an obvious common origin, have been called geminate. It seems likely that some of the geminate populations have evolved potential reproductive isolating mechanisms. But since the presence of reproductive isolation is not necessarily correlated with morphological divergence, it would be difficult to predict which pairs are still conspecific. The Isthmus of of Panama is, both historically and logistically (the oceans are only 50 miles apart), ideally suited to an experimental laboratory study of isolating mechanisms. Most studies of isolating mechanisms have involved field work on species that are already sympatric. Some experimental studies on allopatric populations have been conducted with a limited number of terrestrial and fresh water animals (Littlejohn, 1969), but marine species have been largely ignored.

QUESTION OF CARDIAC HYPERTROPHY IN RESIDENTS OF HIGH ALTITUDES

The Republic of Colombia, located at the northwestern corner of South America, is a tropical country. For this reason there are no seasonal changes in the whole of its territory, as there are in the Temperate Zone. The temperature is uniform all through the year in all the cities, but it varies in accordance with the altitude above sea level at which they are located. It is therefore erron eous to believe, as some residents of the Temperate Zone do, that every tropical city enjoys a hot climate. This is true only of those that are located at sea level. As the altitude increases the temperature drops, and it is for this reason that the city of Bogota, the capital of Colombia, built on a plateau at 8,016 feet (2,440 meters) above sea level, has a normal temperature of 14.55 C. (58 F.); that is to say, a relatively cold