Resumo

GIMENEZ, Mario Ernesto et al. Isostatic subcompensation of the Rioja Valley (Argentina) indicated by the geoid undulations. Rev. mex. cienc. geol [online]. 2009, vol.26, n.2, pp.289-300. ISSN 2007-2902.

In the present contribution is shown that the free, online available geoid undulations are an efficient indicator of the isostatic condition of significant geologic structures. This is the case of the sedimentary basin known as the La Rioja valley, where a filtered maximum local undulation of -2 meters was found by applying the Eigen 03 model. Searching for a higher definition, the geoid undulations of this basin were calculated with: a) the planar Stokes' method, and b) the equivalent sources method. Both provide a maximum undulation of -1.8 meters, which coincides in approximately 90% with the undulation obtained with the Eigen 03 method. Comparing the values of -1.8 meters obtained from a) and b) with the undulation value found for a perfectly compensated Airy isostatic model, a negative residuum of -60 cm was determined, which clearly indicates the absence of an antiroot. This result agrees with the negative excess shown by the Bouguer anomalies, thus opening an expeditious new way for evaluating the isostatic balance.

Palavras-chave : isostasy; geoid; sedimentary basin; La Rioja Valley; Argentina.

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