Paleozoic to Cenozoic History of Basin Subsidence in the Sub-Andean Zone of Bolivia and Argentina (21-22°S)

Abstract

The Sub-Andean basin is composed of a stratigraphic record of former tectonic events that is currently involved and influences the Central Andean orogenic wedge. In this dissertation I explore a diverse dataset to constrain a long history of basin evolution and to propose implications of presented interpretations on questions that improve the knowledge of the basin. By analysis of subsurface data (well logs and seismic reflection profiles) coupled to field geology and geochronology/thermochronology I provide models of basin subsidence for the Silurian-Devonian, Carboniferous-Permian and the transition from Mesozoic-Cenozoic to the Andean foreland basin setting. In the second chapter, I describe the Silurian-Devonian from outcrops in the Inter-Andean zone, was interpreted in terms of key stratigraphic surfaces and extended into the subsurface beneath the Chaco plain. I found that basin subsidence changed between Silurian and Devonian periods, and that the Devonian defines an intra-cratonic basin setting with a depocenter farther northeast. In addition, northward variation of thickness and lithofacies oblique to the Sub-Andean ranges modifies the mechanical stratigraphy and the style of Andean deformation along strike. In the third chapter, I briefly discuss the Carboniferous-Permian record and provide novel geochronological constraints that help to clarify the widely argued depositional age and timing of the transition from a glacial to post-glacial setting, in addition to recycling of sediments among subsequent units. Another novel geochronological result is provided in the fourth chapter to support the interpreted position of a major regional unconformity below the Tacuru Group, coeval with formation of uplifted archs surrounding the region (Izozog, Michicola and proto-Eastern Cordillera) and denoted by incursion of exotic zircon ages in the basin that contrast with the prevailing Paleozoic record. These arches were the core for later formation of the system of Mesozoic rifts. In the fourth chapter I also interpret the arrival of foreland subsidence by Andean tectonics, refined by new geochronological results and along-strike correlations of seismic and stratigraphic events. I discuss the known events of foreland basin advance with the growth and style of structures along the Sub-Andean foothills. These events are extended across the Sub-Andean ranges to constrain thickness control points that were restored from their deformed locations to exhibit the shape of the stepwise flexural profiles. These profiles were then inverted by flexural modeling to present a profile of elastic thicknesses that best represents the region. The results point toward a required bimodal lithosphere rigidity with elastic thickness of ~20 km beneath the western Sub-Andean ranges and above ~50 km eastward toward the craton. Finally in the firth chapter, based on new low-temperature thermochronological data (apatite fission track and apatite (U-Th)/He) and compared with previously published data and remodeled previous results, I propose a regional thermal history for the easter Eastern Cordillera and the Sub-Andean zone. This reconstruction takes into account both palinspastically restored structural cross-sections and the results of sequential flexural modeling to produce a regional history of cooling and inferred exhumation for the Central Andean orogenic wedge at 21-22°S.