Abstract: It has been shown in the accompanying paper that the Sub-Andean foreland can be subdivided longitudinally into a number of tectonostratigraphic domains. To test the hypothesis that changes in palaeo-depositional setting rely on the presence of a series of transverse zones of structural accommodation, data have been digitally compiled from across the South American continent. Spatial and temporal geological relationships have been analysed and evaluated as a means of identifying the position of tectonostratigraphic domain boundaries (structural accommodation zones), and patterns of subsidence and intraplate deformation. The results suggest that individually these structural accommodation zones represent a composite of deep crustal fractures which, on a regional scale, interlink to form a transcontinental belt or zone that can accommodate intraplate deformation during episodes of plate reorganization. Their strong spatial relationship with Mesozoic, intraplate, alkaline igneous activity suggests that they exerted an important control on lithospheric melt siting during Gondwana breakup. These localized zones of high heat flow have important implications for source rock maturity in the interior, Phanerozoic intracratonic basins of South America. On the South Atlantic margin, the majority of these crustal lineaments correlate with failed arms of triple-junction rifts and define the boundaries to tectonostratigraphic domains recognized along the South Atlantic Rift System.
Based on spatial and temporal changes in palaeo-depositional setting, the Sub-Andean region can be subdivided longitudinally into a number of tectonostratigraphic domains (Jacques 2003). The differential amount of subsidence between two adjacent tectonostratigraphic provinces or sub-provinces relies on the presence of a transverse zone of structural accommodation. Two predominant sets of basement lineaments arc recognized: ENE-WSW and NW-SE (Fig. 1). The relative dominance of one set of crustal lineaments over the other changes approximately halfway down the length of the Andes, across a broad transition zone structurally expressed by the Arica Deflection-Bolivian Orocline, with ENE-trending crustal lineaments dominating in the north and NW-trending crustal lineaments dominating in the south. Both sets of lineaments occur as major structural anisotropies throughout the basement rocks of South America, providing zones of weakness, which were repeatedly reactivated and, at least in part, controlled: (1) the geometry of inter- and intracratonic rifting; (2) rates of subsidence and uplift along the Andean depositional axis; (3) the position of basin-bounding and intra-basinal highs or arches; (4) the structural geometry of the Andean Deformation Zone, correlating with changes in deformational style and major deflections; (5) the location of magmatism.
Twelve transverse structural lineaments (accommodation zones) are recognized (see Fig. 2) and, from north to south, are referred to as: the ENE Tumbes-Guayaquil-Tacutu Tectonic Lineament; the ENE Solimoes-Amazonas Megashear (diffuse zone of deformation); the ENE Pisco-Abancay-Fitzcarrald Tectonic Lineament; the ENE Arica-Paraguai-Araguaia Tectonic Lineament; the ENE Michicola Tectonic Lineament; the ENE La Serena-Ribeira Tectonic Lineament; the NW Martin Garcia Tectonic Lineament; the NW Valle Fertil Tectonic Lineament; the NW San Rafael Tectonic Lineament; the NW Gastre-Agulhas Megashear; the NW South Malvinas Tectonic Lineament; the east-west North Scotia Tectonic Lineament.
Based on this relative dominance, together with the segmentation of the Andean Belt into tectonostratigraphic provinces and sub-provinces by these first-order, transverse crustal lineaments, it is suggested that the Sub-Andean Belt can be separated longitudinally into five tectonic domains (Fig. 1): Northern Tectonic Domain; Western Tectonic Domain; Central (Transitional) Tectonic Domain; Eastern Tectonic Domain; Southern Tectonic Domain. It has been also shown (Jacques 2004) that this regional tectonic framework has had a profound influence on source rock distribution and hydrocarbon occurrence, subdividing the Sub-Andean region into a number of petroleum provinces or megasystems characterized by marked contrasts in source rock age (Fig. 1). The structural, depositional and igneous characteristics of these tectonic domains and their boundaries have been discussed by Jacques (2003).
The aim of this paper is two-fold: to define the position and continuity of the tectonostratigraphic domain boundaries across the South American Plate, and to assess their role in accommodating intraplate deformation during the Mesozoic breakup of the Gondwana Supercontinent.
Analysing geospatial relationships across South America
All structural and geology maps were compiled digitally as point and geographical (arc) coverages using ESRI's ARC/VIEW(TM) and ARC/INFO(TM) GIS (Geographic Information System) formats at a basin scale of around 1:500 000 to 1:2 000 000 (see Jacques 2003 for an example 'clip-out' map from the main digital coverage). A complete structural and geological coverage for South America has been achieved. This not only includes the foreland-style basins of the Sub-Andean and Southern Caribbean regions, as reviewed by Jacques (2003), but also includes the large intracratonic, interior sag basins (e.g. Solimoes Basin) and the passive margin basins of the South Atlantic (Brazil, Uruguay and Argentina) and Equatorial, Central Atlantic (Guyana, Surinam, French Guiana and Brazil) regions (Fig. 3). Each basin has been interpreted in its evolving plate tectonic context using a process-based form of stratigraphic analysis. For each basin, the aim has been to synthesize the tectonic, structural and depositional history. Because these geological data have been captured digitally as point and geographical (arc) coverage GlS formats, this allows for individual digital datasets to be visualized separately at any scale or in combination. The superimposition of one dataset onto another allows for spatial relationships to be recognized and analysed. An attempt has been made to provide a simplified map from the coverage to highlight some geospatial relationships, particularly with reference to the position, orientation and continuity of transverse, deep crustal structures across South America (Fig. 3). This has ultimately provided the basic structural framework from which subsidence patterns across South America can be analysed.