A large-scale domal relief due to intraplate neotectonic compression in central Amazonia

In intracratonic South America, the origin of neotectonic activity and its impact on large Amazonian rivers have been of continuous research interest. Despite the low relief of the land surface, which has generally been attributed to tectonic stability, there is increasing evidence of Neogene fault reactivation within central Amazonia. Recent research has also reported surface folding during the Quaternary, but this record was based only on morphological analysis of remote sensing data. This investigation focuses on a megascale (~60,000 km2) domal relief from central Amazonia (the Juruá dome). It firstly aims to verify the domal relief relationship to folding. It then explores the origin of the stress field from which it has developed within the context of Andean uplift and the westward movement of the South American plate. The approach consisted of analyzing river adjustments based on morphological and morphometric information from remote sensing imagery, integrated with subsurface data Bouguer gravity and magnetic anomaly maps, well logs, and seismic reflection sections. The results revealed that the Juruá dome coincides with the location of a basin depocenter. Subsurface evidence exists for the growth of a broad anticline producing thicker sedimentary units away from the dome core. NE- and NW-striking normal and reverse faults with flower structure geometries are abundant and suggest deformation from strike-slip tectonics. Gravity and magnetic data revealed that the fold and many of its associated faults are deep-rooted into basement rocks. Within the analyzed stratigraphic interval, faults are mostly developed into pre-Cretaceous units, but often propagate to the surface, where they define the edges of the dome and partly deform its overall shape. The fold and its related faults have modified the course of several rivers within the domal relief area, including the Juruá River, which is entrenched along NE-striking faults that are configured to release stress along the fold axis. The geomorphological and structural data are collectively compatible with a long-term NW-trending maximum horizontal compressive stress-field that is driving basin inversion. This neotectonic activity can be linked to far-field stresses from the pushes from the Andean orogeny and the movement of the South American plate against the North Andean and Nazca plates.