Driving subsidence mechanisms during the formation of the intracratonic General Levalle Basin, Central Argentina

Abstract

The Cretaceous-Cenozoic General Levalle rift basin (GLB) in Central Argentina, near 900 km east from the modern Chile-Peru trench, is an exploratory hydrocarbon frontier located within an intracratonic setting. The basin is 4.5 km deep and can be divided into three major evolutionary stages, synrift, intermediate and postrift. To date, the basin subsidence has not been yet addressed. We particularly made emphasis on the postrift sequence given that records of thousands of metres of Cretaceous and Cenozoic Strata and tectonic and thermal events are not known to account for these large accumulations. In this work we performed a backstripping analysis, in combinationwith a stretching-thermal model, which were then compared to different dynamic topography studies. From our backstripping models we found a typical rift basin curve, with the largest subsidence at the synrift stage followed by a decrease in values during the postrift. Assuming the synrift stage was driven by tectonic extension, we correlated the tectonic subsidence curve, obtained from backstripping studies, with a stretching-thermal subsidence model. The best fit among subsidence curves was obtained with a stretching factor = 1.285. However, we observed a mismatch along the postrift part of both curves, resulting in a residual subsidence of ∼323 m.When this anomalous tectonic subsidence was compared to the latest six dynamic topography models, we found a good correlation with one of them. For the models that did not match and using simple isostatic computations, we estimated a lithospheric mantle thickening of 35.4 km to account for the residual subsidence and dynamic topography models. From our analysis it turns out that, in addition to stretching and thermal subsidence, mantle thickening in the lithosphere and in the asthenosphere, controlled the total subsidence in the General Levalle basin. The subduction history of Nazca Plate could have affected the postrift stage in this basin.