--> Deformation and Stratigraphic Models of the Bolivian and Argentinean Sub-Andean System: Evolution of Knowledge, Current Trends and the importance of dating

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Deformation and Stratigraphic Models of the Bolivian and Argentinean Sub-Andean System: Evolution of Knowledge, Current Trends and the importance of dating


The many structural cross-sections constructed since 1960, with the aim of modeling and understanding the mechanisms involved in the sub-Andean deformation and the resulting structural styles, have allowed the increase of knowledge regarding the variables involved, shortening values, and the associated rates and timing for the different structures. The cross-sections constructed across the southern sub-Andean of Bolivia and northern Argentina system show a thin-skinned deformation with different structural styles, which can be grouped into four geometries: fault bend/propagation, passive roof duplex, active roof duplex, and composite roof duplex. In this workshop, the structural framework presented describes a lithological column involved in the deformation, divided into four rheological levels modeled by trishear (RLs 1 and 3) or parallel folding with parallel shear (RLs 2 and 4). In particular, trishear modeling allows the Devonian reservoir rocks (the Huamampampa Formation, RL 2) to reach a high structural position as it has been demonstrated by well data (e.g., Caigua x-1002D) without the necessity of stacking duplex structures. The deformation mechanisms presented here are consistent with a general west to east in sequence timing for the formation of the structures in the sub-Andean fold-and-thrust belt. The slip transfer mainly occurs through the basal detachment level, while the slip transfer using the upper detachment level would represent a minor component allowing the structure to balance itself. Under these premises, the structure width can work as an exploration proxy to understand the structural position of rocks of the Huamampampa Formation reservoir. This idea, although it does not modify the established exploration paradigms, does open an interesting and different perspective for analysis when a map view widening is observed within a particular structure. If this broad structure situation (generated by the interference with oblique deep structures) were combined with those zones with greater shortening values (in general, the central areas), the result would be a structurally higher Huamampampa Formation. The current state of knowledge about the sub-Andean system in general, and its southern part in Bolivia and northwestern Argentina in particular, requires solid surface and subsurface data through the acquisition of timelines based on absolute dating techniques, palynology data, and paleomagnetic determinations, with the aim of defining the stratigraphic age of the sedimentary infilling involving source, seal and reservoir rocks. On the other hand, it is indispensable to precisely define the timing of structural growth of the structures (trap generation) to be drilled through thermochronological analysis (fission-track and (U-Th-Sm)/He in apatites and zircons) based on the definition of time-temperature paths applicable to petroleum system modeling. These definitions are especially important for dating the slip entering a particular structure, for estimating the magnitude of structural uplift in relation to a passive roof wedge through the upper detachment level, for quantifying the slip value transferred to an adjacent structure to the east, and lastly, for determining the simultaneous growth of adjoining anticline structures.