DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Resultados da Pesquisa
Item Study of the erosion rates in the upper Maracujá Basin (Quadrilátero Ferrífero/MG, Brazil) by the in situ produced cosmogenic 10Be method.(2007) Salgado, André Augusto Rodrigues; Varajão, César Augusto Chicarino; Colin, Fabrice; Braucher, Régis; Varajão, Angélica Fortes Drummond Chicarino; Nalini Júnior, Hermínio AriasThe present work quantifies the erosive processes in the two main substrates (schists–phyllites and granites–gneisses) of the upper Maracujá Basin in the Quadrilátero Ferrífero/MG, Brazil, a region of semi-humid tropical climate. Two measuring methods of concentration were used: (i) in situ produced 10Be in quartz veins (surface erosion rates) and (ii) 10Be in fluvial sediments (basin erosion rates). The results confirm that (i) erosion tends to be more aggressive close to the headwaters than in the lower parts of the basin and (ii) the region is now affected by dissection.Item Denudation rates of the Southern Espinhaço Range, Minas Gerais, Brazil, determined by in situ-produced cosmogenic beryllium-10.(2013) Barreto, Helen Nébias; Varajão, César Augusto Chicarino; Braucher, Régis; Bourlès, Didier Lionel; Salgado, André Augusto Rodrigues; Varajão, Angélica Fortes Drummond ChicarinoTo investigate denudation rates in the southern part of the Espinhaço Range (central-eastern Brazil) and to understand how this important resistant and residual relief has evolved in the past 1.38 My, cosmogenic 10Be concentrations produced in situ were measured in alluvial sediments from the three main regional basins, whose substratum is composed primarily of quartzites. The long-term denudation rates (up to 1.38 My) estimated from these measurements were compared with those that affect the western (São Francisco River) and eastern (Doce and Jequitinhonha Rivers) basins, which face theWest San Francisco craton and the Atlantic, respectively. Denudation rates were measured in 27 samples collected in catchments of different sizes (6–970 km2) and were compared with geomorphic parameters. The mean denudation rates determined in the northern part are low and similar to those determined in the southern part, despite slightly different geomorphic parameter values (catchment relief and mean slope). For the southern catchments, the values are 4.91±1.01 mMy−1 and 3.65±1.26 mMy−1 for the Doce and São Francisco River basins, respectively; for the northern catchments, they are 4.40±1.06 mMy−1 and 3.96±0.91 mMy−1 for the Jequitinhonha and São Francisco River basins, respectively. These low values of denudation rates suggest no direct correlation if plotted against geomorphic parameters such as the catchment area, maximum elevation, catchment relief, average relief and mean slope gradients. These values show that the regional landscape evolves slowly and is strongly controlled by resistant lithology, with similar erosional rates in the three studied basins.Item Long-term evolution of denudational escarpments in southeastern Brazil.(2012) Cherem, Luís Felipe Soares; Varajão, César Augusto Chicarino; Braucher, Régis; Bourlès, Didier Lionel; Varajão, Angélica Fortes Drummond Chicarino; Salgado, André Augusto RodriguesTopographic relief in southeastern Brazil consists of a sequence of stepped surfaces that formed after the fragmentation of Gondwana during the Cretaceous, Tertiary and Quaternary tectonic pulses. This region is drained by four major rivers within four major river basins, with interfluves that contain denudational escarpments, fault escarpments and mountain ranges. This study presents an analysis of the long-term evolution of two denudational escarpments, the Cristiano Otoni and the São Geraldo steps, which divide the river basins of the São Francisco, Doce and Paraíba do Sul rivers in southeastern Brazil. Denudation rates were obtained through the measurement of mean concentrations of in situ produced cosmogenic 10Be in sand-sized fluvial quartz sediments collected fromgranitic terrains. The rates were calculated and comparedwith one another and correlated to the basin-scale mean relief, slope, area, and stream power. The mean denudation rates of the Cristiano Otoni and São Geraldo highlands are 8.77 (±2.78)m My−1 and 15.68 (±4.53)m My−1, respectively. The mean denudation rates of the Cristiano Otoni and São Geraldo escarpments are 17.50 (±2.71)m My−1 and 21.22 (±4.24)m My−1, respectively. The denudation rates of the catchments of highlands that drain toward the escarpments are similar to those of their respective highlands. The results demonstrate that relief and slope have similar positive control on the denudation rates for all of the samples despite their different geomorphic context and history of landscape evolution. The São Francisco River Basin is losing area to the Doce River Basin, which, in turn, is losing area to the Paraíba do Sul River Basin.