Crustal and upper mantle investigations of the Caribbean-South American plate boundary

The evolution of the Caribbean --- South America plate boundary has been a matter of vigorous debate for decades and many questions remain unresolved. In this work, and in the framework of the BOLIVAR project, we shed light on some aspects of the present state and the tectonic history of the margin by using different types of geophysical data sets and techniques. An analysis of controlled-source traveltime data collected along a boundary-normal profile at ∼65°W was used to build a 2D P-wave velocity model. The model shows that the Caribbean Large Igenous Province is present offshore eastern Venezuela and confirms the uniformity of the velocity structure along the Leeward Antilles volcanic belt. In contrast with neighboring profiles, at this longitude we see no change in velocity structure or crustal thickness across the San Sebastian - El Pilar fault system. A 2D gravity modeling methodology that uses seismically derived initial density models was developed as part of this research. The application of this new method to four of the BOLIVAR boundary-normal profiles suggests that the uppermost mantle is denser under the South American continental crust and the island arc terranes than under the Caribbean oceanic crust. Crustal rocks of the island arc and extended island arc terranes of the Leeward Antilles have a relatively low density, given their P-wave velocity. This may be caused by low iron content, relative to average magmatic arc rocks. Finally, an analysis of teleseismic traveltimes with frequency-dependent kernels produced a 3D P-wave velocity perturbation model. The model shows the structure of the mantle lithosphere under the study area and clearly images the subduction of the Atlantic slab and associated partial removal of the lower lithosphere under northern South America. We also image the subduction of a section of the Caribbean plate under South America with an east-southeast direction. Both the Atlantic and Caribbean subducting slabs penetrate the mantle transition zone, affecting the topography of the 410-km and 660-km discontinuities

Cartografía de cobertura del suelo mediante datos de teledetección en la planicie de desborde del río Apure (Venezuela)

La cobertura del suelo es un indicador fundamental para identificar los factores que actúan en el desarrollo de la geomorfología de una planicie aluvial. Esta cobertura se caracteriza por el control que ejerce la vegetación en los procesos hidromorfológicos, así como el mantenimiento y estabilidad de los canales. Se presenta un registro sobre la distribución de cobertura del suelo en el curso medio del sistema anastomosado del río Apure. Se analiza la distribución de los ambientes geomorfológicos en un área de 65 km2 a partir de una combinación de datos de imágenes Landsat-8 y Sentinel-2, integrados en un Sistema de Información Geográfica (SIG). Se estableció una clasificación supervisada mediante los algoritmos Máquinas de Soporte de Vectores y Máxima Verosimilitud. La imagen Landsat fue procesadas a través de una corrección atmosférica, para posteriormente calcular las firmas espectrales. Se encontró seis coberturas: a) sabana arbolada, b) bosque, c) sabana abierta, d) cultivos, e) cuerpos de agua, y f) matorral. No existen diferencias sustanciales en la fiabilidad lograda con los algoritmos de clasificación Máquinas de Soporte de Vectores y Máxima Verosimilitud. Se mostró que la cobertura de sabana arbolada es la de mayor representatividad en el área de estudio con una extensión total de 5.717,26 ha (39%), de las 14.658,77 ha. La clasificación desarrollada presentó una exactitud temática global de 98,08% e índice de Kappa de 0,98. Como resultado se generó una cartografía de cobertura del suelo a partir del mejor clasificador, basándose en el índice Kappa. Estos hallazgos sirven como un referente para aumentar los registros de caracterización de cobertura del suelo, y pueden ser útiles en estudios sobre gestión y uso del territorio, para identificar lugares más susceptibles a la degradación y proponer medidas para el manejo y conservación de los recursos hídricos, que puede ser potencialmente aplicable en ambientes fluviales similares de otras latitudes.

Evaluating models for lithospheric loss and intraplate volcanism beneath the Central Appalachian Mountains

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Long, M. D., Wagner, L. S., King, S. D., Evans, R. L., Mazza, S. E., Byrnes, J. S., Johnson, E. A., Kirby, E., Bezada, M. J., Gazel, E., Miller, S. R., Aragon, J. C., & Liu, S. Evaluating models for lithospheric loss and intraplate volcanism beneath the Central Appalachian Mountains. Journal of Geophysical Research: Solid Earth, 126(10), (2021): e2021JB022571, https://doi.org/10.1029/2021JB022571.The eastern margin of North America has been shaped by a series of tectonic events including the Paleozoic Appalachian Orogeny and the breakup of Pangea during the Mesozoic. For the past ∼200 Ma, eastern North America has been a passive continental margin; however, there is evidence in the Central Appalachian Mountains for post-rifting modification of lithospheric structure. This evidence includes two co-located pulses of magmatism that post-date the rifting event (at 152 and 47 Ma) along with low seismic velocities, high seismic attenuation, and high electrical conductivity in the upper mantle. Here, we synthesize and evaluate constraints on the lithospheric evolution of the Central Appalachian Mountains. These include tomographic imaging of seismic velocities, seismic and electrical conductivity imaging along the Mid-Atlantic Geophysical Integrative Collaboration array, gravity and heat flow measurements, geochemical and petrological examination of Jurassic and Eocene magmatic rocks, and estimates of erosion rates from geomorphological data. We discuss and evaluate a set of possible mechanisms for lithospheric loss and intraplate volcanism beneath the region. Taken together, recent observations provide compelling evidence for lithospheric loss beneath the Central Appalachians; while they cannot uniquely identify the processes associated with this loss, they narrow the range of plausible models, with important implications for our understanding of intraplate volcanism and the evolution of continental lithosphere. Our preferred models invoke a combination of (perhaps episodic) lithospheric loss via Rayleigh-Taylor instabilities and subsequent small-scale mantle flow in combination with shear-driven upwelling that maintains the region of thin lithosphere and causes partial melting in the asthenosphere.The authors acknowledge support from the U.S. National Science Foundation EarthScope and GeoPRISMS programs via grants EAR-1460257 (R. L. Evans), EAR-1249412 (E. Gazel), EAR-1249438 (E. A. Johnson), EAR-1250988 (S. D. King), EAR-1251538 (E. Kirby), and EAR-1251515 (M. D. Long). The collection and dissemination of most of the geophysical data and models discussed in this study were facilitated by the Incorporated Research Institutions for Seismology (IRIS). The facilities of the IRIS Consortium are supported by the United States National Science Foundation under Cooperative Agreement EAR-1261681

Editorial

The purpose of this paper is to present some results obtained from the study of El Tamunangue, as a dramatic representation that narrates in a past and present time, a story that combines religiosity with secularity. This celebration is typical of the state of Lara, in Venezuela and revolves around the devotion to San Antonio. Together with Yolanda Salas, we analyzed the results obtained by Turner (1967 and 1969) when studying aspects of the Ndembu ritual in Zambia. Following his research, we organized the study of traditional festivals in three levels. During my fieldwork research, carried out between 1980 and 1990, I recorded a series of data related to El Tamunangue, which I processed and studied according to these three levels. Thus, I was able to depict what is said about this festivity; its execution as a devotion and as a religious tribute, in order to understand the symbolism of the festivity.El propósito de este trabajo es presentar algunos resultados obtenidos del estudio de El Tamunangue, como una representación dramática que narra en un tiempo pasado y presente, una historia que conjuga lo religioso con lo secular. Esta celebración es propia del estado Lara, en Venezuela y gira en torno a la devoción a San Antonio. Junto con Yolanda Salas analizamos los resultados que obtuvo Turner (1967 y 1969) al estudiar los aspectos del ritual ndembu, en Zambia. Siguiendo su investigación, ordenamos en tres niveles el estudio de las fiestas tradicionales. Durante mi trabajo de campo, realizado entre 1980 y 1990, registré una serie de datos relativos a El Tamunangue, los cuales procesé y estudié de acuerdo a estos tres niveles. Así pude exponer lo que se dice de esta fiesta, su ejecución como devoción y como pago de promesas, para llegar a comprender lo simbólico de la festividad