LONG-TERM THERMAL AND EXHUMATION EVOLUTION OF THE CHARAGUA RANGE, REVEALED TO FISSION-TRACK DATASET, SOUTHERN SUBANDEAN REGION, BOLIVIA

RICARDO PEREYRA; BECCHIO, R.; GLASSMACHER, U.; HERNANDEZ. R; VERGANI, G; PEREYRA, M; DALENZ-FARJAT, A

Heildelberg

Simposio; LAK 2011. 22th International Colloquium on Latin American Earth Sciences; 2011

Universität Heidelberg

During the last years, the study of fold and thrust belts by the petroleum industry has been driven by the application of new and more precise analytical techniques. One of the most important goals is to know the exhumation histroy of the different mountain ranges during the evolution of the fold and thrust belt. The Charagua Range is part of the southern bolivian subandean area. It has been structured during the formation of the Central Andes. This range constitute of asymmetrical and symmetrical anticlines, with N-S trending direction. We present the first thermochronological data revealed by apatite fission-track technique on samples from a stratigraphical sequence of Middle Paleozoic, Mesozoic, Paleogene to Neogene age. Ten apatite fission-track analysis (AFT) have been made in these sequences. AFT data results, and AFT t-T modeling, combined with Charagua Range architecture and lithostratigraphy, helped to identify at least two burial–exhumation events that took place simultaneously with tectonic deformation in the Southern Subandean region of Bolivia. According to the samples studied, a thermal subsidence interval linked to the development of a passive margin related basins took place in Carboniferous to Devonian time. During the early break-up of the Atlantic Ocean, an oblique extensional tectonic setting developed inland, causing the opening of grabens and the differential exhumation of certain blocks giving place to the development of basins shoulders. Carboniferous and Devonian sequences analysed in Charagua would have been partially exhumed from about 280 Ma until Jurassic deposition, causing the erosion of the upper part of the sequence. This Paleogeographic evolution is verified in the stratigraphic column of Charagua Range, by a Permian to Triassic hiatus. During the Triassic, the Grupo Cuevo basin is filled, closed, and aborted. During the Jurassic, a widespread desert environment is developed. It is represented by fluvioeolian deposits of Grupo Tacuru. The following cycle corresponds to the filling and burial of sediments linked to the foreland basins system, during the Paleogene, since the Eocen. According to AFT data, a first exhumation stage occur in the Late Paleogene. At the same time the Andean peripheral bulge deformation started and continued with the migration of the orogenic front to the east. Thus, according to the thermocronological results and the AFT T-t modeling, two exhumation events occur in the Charagua Anticline. These events are important for the understanding of the life of the hydrocarbon system in the associated to fold and thrust belts in Central Andes.