Carlos Izarra

Bio: Carlos Izarra is an academic researcher from Simón Bolívar University. The author has contributed to research in topics: Seismic refraction & Lithosphere. The author has an hindex of 6, co-authored 15 publications receiving 150 citations. Previous affiliations of Carlos Izarra include University of Liverpool.

Analyzing gravity anomalies over the caribbean and northern Venezuela tectonic plate boundary

Abstract: The tectonic border between northern South-American and Caribbean plates consists of compressive, extensional and strike-slip tectonic regimes and its location is under current debate (Fig. 1). Caribbean plate moves eastwards at a rate of about 2 cm/yr (Mann, el al., 1990, Perez el al ., 2001) with respect to SouthAmerican plate. Different theories show the Caribbean Plate as a large basaltic province migrating from west to east since Late Cretaceous-Early Cenozoic times (Pindell, 1994; Meschede and Frisch, 1998). The present eastern border of the Caribbean Plate is the Lesser Antilles subduction zone, where Atlantic oceanic lithosphere subducts at about 4 cm /yr (DeMets el al., 1994). The interaction between Caribbean and South-American plates has generated foredeeps and thrust folds on the continental deformation front observed along the coastline in Venezuela with the oldest located in the west and the recent on es in the east, close to the Orinoco Delta. Allocthonous material has been added and placed onto the Guyana Shield. During this time two important foreland basins has been formed: Barinas-Apure and Oriental Basins. Barinas-Apure is mainly a foreland basin generated by flexural response to the Merida-Andes Mountain load (Chac in el al ., 2005) . White the Oriental Basin can be considered as the result of many equally important processes (Jâcorne el al., 2003): (a) flexural loading of the Cordiliera de la Costa Range; (b) large and continuous deposition of continental material from the Guyana Shield ; and (c) the subduction dynamics in the east. The deformation zone due to interaction between these two plates goes parallel to Venezuelan coastline and is more than 300 km wide (Audernard , et al ., 1997) . In the last years different projects have been set up in order to collect geophysical, geologicaJ and geodesie data that may help to constraint the understanding of this boundary. At Simon Bolivar Univers ity (USB) , an investigation about the nature of gravity anomalies over this zone and its implications in terms of sedirnentary , crustal and lithopheric mantle bodies is undergoing. A new database has been produced at the USB that cons ists of more than 90000 gravity stations, comprising about 80000 observations on land and more than 10000 stations offshore (Fig. 2) . Gravity anomalies ranges from -250 to 200 mGal, with a prominent low observed in eastern Venezuela associated to the large amount of sediments deposited in the Eastern Basin (Fig. 3). Offshore the trench-type gravity anomaly is observed along the interpreted subduction zone. Different gravity patterns are observed from west to east on the continent, which suggests diverse sources along the same deformation zone in the Caribbean-South-American plate boundary. A final goal is to produce 3D gravity inversion models of the deformation zone constrained by deep wide-angle seismic refraction sections, which has been recently collectee and interpreted along four north-south regional transects located close to meridians 70W, 67W, MW, and 62W (Schmitz el al., 2005). Gravity inversion may be useful in examining different density models and its correlations with available surface geology and geodynamic information.

Upper mantle structure of South America from joint inversion of waveforms and fundamental mode group velocities of Rayleigh waves

Abstract: [1] A new tomographic S wave velocity model for the upper mantle beneath South America is presented. We developed and applied a new method of simultaneously inverting regional S and Rayleigh waveforms and fundamental mode Rayleigh wave group velocities, to better constrain upper mantle S velocity structure and Moho depth. We used � 5700 Rayleigh wave group velocity dispersion curves and 1537 regional wave trains with paths principally passing through the South American continent. The joint inversion of this data set provided a new three-dimensional (3-D) upper mantle S velocity model and a Moho depth model for South America, which fits both the group velocity and regional waveform data sets well. New features of the final three-dimensional (3-D) S velocity and Moho depth model correlate well with known geotectonic units on a regional scale. The Moho depth ranges from 30 km in the central Chaco basin to 42 km beneath the Amazonian craton and 45–70 km beneath the orogenic Andean belt. The imaged S velocity indicates an average lithosphere thickness of around 160 km for the Amazonian craton. High velocities are imaged beneath the Amazon and part of the Parana´ and Parnao´ba basins down to about 150 km. Low to very low velocities are imaged ! ! !

The assembly of montane biotas: linking Andean tectonics and climatic oscillations to independent regimes of diversification in Pionus parrots

Abstract: The mechanisms underlying the taxonomic assembly of montane biotas are still poorly understood. Most hypotheses have assumed that the diversification of montane biotas is loosely coupled to Earth history and have emphasized instead the importance of multiple long-distance dispersal events and biotic interactions, particularly competition, for structuring the taxonomic composition and distribution of montane biotic elements. Here we use phylogenetic and biogeographic analyses of species in the parrot genus Pionus to demonstrate that standing diversity within montane lineages is directly attributable to events of Earth history. Phylogenetic relationships confirm three independent biogeographic disjunctions between montane lineages, on one hand, and lowland dry-forest/wet-forest lineages on the other. Temporal estimates of lineage diversification are consistent with the interpretation that the three lineages were transported passively to high elevations by mountain building, and that subsequent diversification within the Andes was driven primarily by Pleistocene climatic oscillations and their large-scale effects on habitat change. These results support a mechanistic link between diversification and Earth history and have general implications for explaining high altitudinal disjuncts and the origin of montane biotas.

Models of Crustal Thickness for South America from Seismic Refraction, Receiver Functions and Surface Wave Tomography

Abstract: An extensive compilation of crustal thicknesses is used to develop crustal models in continental South America. We consider point crustal thicknesses from seismic refraction experiments, receiver function analyses, and surface-wave dispersion. Estimates of crustal thickness derived from gravity anomalies were only included along the continental shelf and in some areas of the Andes to fill large gaps in seismic coverage. Two crustal models were developed: A) by simple interpolation of the point estimates, and B) our preferred model, based on the same point estimates, interpolated with surface-wave tomography. Despite gaps in continental coverage, both models reveal interesting crustal thickness variations. In the Andean range, the crust reaches 75 km in Southern Peru and the Bolivian Altiplano, while crustal thicknesses seem to be close to the global continental average (~ 40 km) in Ecuador and southern Colombia (despite high elevations), and along the southern Andes of Chile–Argentina (elevation lower than 2000 m). In the stable continental platform the average thickness is 38 ± 5 km (1-st. deviation) and no systematic differences are observed among Archean–Paleoproterozoic cratons, NeoProterozoic fold belts, and low-altitude intracratonic sedimentary basins. An exception is the Borborema Province (NE Brazil) with crust ~ 30–35 km thick. Narrow belts surrounding the cratons are suggested in central Brazil, parallel to the eastern and southern border of the Amazon craton, and possibly along the TransBrasiliano Lineament continuing into the Chaco basin, where crust thinner than 35 km is observed. In the sub-Andean region, between the mid-plate cratons and the Andean cordillera, the crust tends to be thinner (~ 35 km) than the average crust in the stable platform, a feature possibly inherited from the old pre-Cambrian history of the continent. We expect that these crustal models will be useful for studies of isostasy, dynamic topography, and crustal evolution of the continent.