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An Andean tectonic cycle:From crustal thickening to extension in a thin crust(34°-37°SL)

Geoscience Frontiers 2014年第3期5卷 351-367页

作者： Victor A.Ramos Vanesa D.Litvak Andrés Folguera Mauro Spagnuolo laboratorio de tectonica andina del Instituto de Estudios Andinos Don Pablo GroeberCONICET-Universidad de Buenos AiresArgentina

Several orogenic cycles of mountain building and subsequent collapse associated with periods of shal- lowing and steepening of subduction zones have been recognized in recent years in the Andes. Most of them are characterized by widespread crustal delamination expressed by large calderas and rhyolitic flare-up produced by the injection of hot asthenosphere in the subduction wedge. These processes are related to the increase of the subduction angle during trench roll-back. The Payenia paleoflat-slab, in the southern Central Andes of Argentina and Chile （34° -37°S） recorded a complete cycle from crustal thickening and mountain uplift to extensional collapse and normal faulting, which are related to changes in the subduction geometry. The early stages are associated with magmatic expansion and migration, subsequent deformation and broken foreland. New ages and geochemical data show the middle to late Miocene expansion and migration of arc volcanism towards the foreland region was associated with important deformation in the Andean foothills. However, the main difference of this orogenic cycle with the previously described cycles is that the steepening of the oceanic subducted slab is linked to basaltic flooding of large areas in the retroarc under an extensional setting. Crustal delamination is concentrated only in a narrow central belt along the cordilleran axis. The striking differences between the two types of cycles are interpreted to be related to the crustal thickness when steepening the subducting slab, The crustal thickness of the Altiplano is over 60-80 km, whereas Payenia is less than 42 km in the axial part, and near 30 km in the retroarc foothills. The final extensional regime associated with the slab steepening favors the basaltic flooding of more than 8400 km3 in an area larger than 40,000 km2, through 800 central vents and large fissures. These characteristics are unique in the entire present-day Andes.

关键词： Andes Retroarc magmatism Basaltic floods Crustal delamination Flat-slab

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Introduction, Establishment, and Invasion of Digitonthophagus gazella (Fabricius, 1787) (Coleoptera: Scarabaeinae) in the Savannas of Venezuela and Colombia

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Natural Resources 2017年第5期8卷 370-381页

作者： Jorge Ari Noriega Oona delgado Joffre Isnar Blanco Jorge Gámez José Clavijo laboratorio de Zoología y Ecología Acuática—LAZOEA Universidad de Los Andes Bogotá Colombia department of Biogeography and Global Change National Museum of Natural Science (CSIC) Madrid Spain Museo del Instituto de Zoología Agrícola Francisco Fernández Yépez—MIZA Facultad de Agronomía Universidad Central de Venezuela Maracay Venezuela laboratorio de Entomología Universidad Nacional Experimental del Táchira San Cristóbal Venezuela Fundación Entomológica andina Mérida Venezuela

The invasion process involves overcoming certain barriers with negative effects on the biodiversity and ecosystem function. This is the case of the African dung beetle Digitonthophagus gazella, which was introduced in the United States and other countries in Central and South America to help in dung removal activity. The distribution of D. gazella has been documented in the Americas, but in Venezuela there is little information. Trying to understand the process of invasion of the Colombian-Venezuelan savannas and measure their potential impact, the information stored in collections and literature was collected. Five new state records were reported for Venezuela, as well as four scenarios of the process of introduction and establishment of this species in the region. Although the amount of records has increased, the number of individuals sampled is still incipient. The possible areas of invasion and the potential negative effects that the presence of this species exerts in these regions are also discussed. In addition, potential areas of invasion and negative effects of this species are discussed. Results emphasize the importance of generating models of the invasive process in order to design programs that monitor the effects incurred by the presence of D. gazella on native species and propose control and mitigation mechanisms.

关键词： Anthropic Introduction Biodiversity Dung Beetles Invasive Species Scarabaeidae

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