Ongoing Compression Across Intraplate South America: Observations and Some Implications for Petroleum Exploitation and Exploration

Abstract

Stress data compilations, intraplate stress field numerical models and space-based geodetic results show that the South American plate is now in horizontal compression and shortening. Plate wide deformation related to the Andean tectonics has been put in evidence by analyses of integrated visualizations of plate-scale information on tectonics, continental geology, topography/bathymetry, seismicity, stresses, active deformation, residual isostatic anomalies, fission track analyses, and seismically derived Moho depths and P and S wave velocity anomalies. Here, a few results of these analyses are presented and some implications of the ongoing compression for petroleum exploitation and exploration are discussed. A conceptual model for the plate-wide deformation is presented. The model states that in response to the compression, the lithosphere as a whole (or only the crust if thermal gradients are high enough) tends to buckle. The resulting antiforms are responsible for uplift along erosional borders of the basins, whereas the resulting synforms are sites of continental sedimentation, at basin centers. The denudation of sedimentary covers promotes the exhumation of increasingly deeper rocks and the adiabatic decompression, facilitating fusion and hence the observed Upper Cretaceous and Tertiary alkali-magmatism. The basement low topography adjacent to the retreating scarps is frequently associated with large Neogene basins (e.g. the Pantanal). The tendency to buckle is controlled by the previous lithospheric/crustal structure. The perception of ongoing compression opens up new perspectives for petroleum exploitation and exploration. The knowledge of the stress field is crucial for secondary recovery, hydraulic fracturing, fracture reservoir characterization and well design. About 82% of the total reserves are found along the actively deforming border between the South American and the Caribbean plates. The most important intraplate accumulations (about 5% of the total reserves) are found in the Southeastern Brazilian margin, which has been deformed the most with respect to other margins during the Cenozoic, and continues to be the most seismically active. These facts suggest that the actual role of the active tectonics on the petroleum accumulation patterns may have been underestimated.

A tectonostratigraphic synthesis of the Sub-Andean basins: inferences on the position of South American intraplate accommodation zones and their control on South Atlantic opening

“…This may provide support for and an explanation of the concept of Cenozoic intraplate shortening and the creation of deep-seated folds attributed to lithospheric buckling, controlled by preexisting crustal structure (e.g. Lima 2000), which has been used to explain the spatial distribution of several interior Neogene depocentres (e.g. Pantanal and Bananal Basins; Fig.…”

“…3a). This lineament, together with the NE-SWtrending Transbraziliano Fault Zone, spatially defines a transcontinental chain of isostatic positive anomalies associated with present-day seismicity crossing the plate from the central Andean foreland, across the Pantanal Basin (which is itself bounded by both megafractures), to the NE continental edge of the continent, the Potiguar Basin in NE Brazil (see Lima 2000, and references therein). Accommodating horizontal compression and shortening, this broad chain of seismicity defines the position of a major Neoproterozoic midplate boundary between the Transamazonico (c. 2000 Ma) and Braziliano (c. 700-450 Ma) domains (Brito Neves 1991).…”

Quaternary deformation around the Palo Negro area, Pampa Norte, Argentina

“…However, based on compilations of stress data, stress field numerical model (Meijer and Wortel, 1992;Coblentz and Richardson, 1996) and spatial geodesic information, it is proposed that the South American plate is presently under compressive horizontal regimen and shortening (Lima, 2000). Apart from regional components, other local sources of stress like cortical flexural strains due to sediment load over the platform or tectonic load by cortical thickening in shortening zones are very important and sometimes they can be larger than regional stress (Assumpçao, 1998).…”

“…Geological, geomorphological, and geophysical information has been applied in order to verify neotectonic activity in relatively stable regions in South America. Mainly Brazilian researchers, have advanced by establishing constrains to neotectonic character of the deformation and the stress fields, from seismological data such as focal mechanisms obtained from instrumental record (Assumpç-ao, 1992(Assumpç-ao, , 1998, breakouts in boreholes (Lima et al, 1997;Lima, 2000) and geological information (Riccomini et al, 1989;Bezerra and Vita-Finzi, 2000;Bezerra et al, 2001Bezerra et al, , 2006Saadi et al, 2002;Modenesi Gautieri et al, 2002;Salmuni et al, 2003). Furthermore, a number of groups have recently exploited the numerous available data regarding remote sensors products, both optical and radar satellite data (Assine and Soares, 2004;Grohmann, 2004;Grohmann et al, 2007).…”

Quaternary deformation and stress field in the Río de la Plata Craton (Southeastern South America)

“…The South American plate as a whole was thought to be subjected to horizontal compression and shortening (Lima, 2000). This statement is based on stress data compilations and numerical models (Meijer and Wortel, 1992;Coblentz and Richardson, 1996).…”