Tectonic analysis of northwestern South America from integrated satellite, airborne and surface potential field anomalies.

摘要

Northwestern South America is one of the most populated regions of the Americas with more than 80 million people concentrated along the Andes Mountains. This region includes a complex and dangerous mosaic of tectonic plates that have produced devastating earthquakes, tsunamis, volcanic eruptions and landslides in the last decades. The region's economic development has also seriously suffered because the region is poorly explored for natural resources. To more effectively assess the tectonic hazards and mineral and energy resources of this region, we must improve our understanding of the tectonic setting that produced them.; This research develops improved tectonic models for northwestern South America from available satellite, airborne and surface gravity and magnetic data integrated with global digital topography, seismic, and GPS plate velocity data. Reliable crustal thickness estimates that help constrain tectonic stress/strain conditions were obtained by inverse modeling of the magnetic anomalies and terrain compensated gravity anomalies. Correlated positive Terrain Gravity Effects (TGE) and Free Air Gravity Anomalies (FAGA) suggest that the crust - mantle interface under the northwestern Andes is closer to the surface than expected, indicating that these mountains are not iso-statically compensated. Correlated negative FAGA anomalies observed along western South America and the Greater and Lesser Antilles islands are associated with iso-statically disturbed mantle displaced by subducting oceanic plates. Subtracting TGE from the terrain-correlated FAGA (TCFAGA) yield compensated terrain gravity effect (CTGE) anomalies that characterize the Andes Mountains with deep roots of low density crust displacing denser underlying mantle and thickening the local crust.; FAGA and TGE correlate at all levels of compensation, but the correlations are especially strong where the compensation is less than 100%. Correlated first vertical derivative FAGA (FVD(FAGA)) and differentially reduced-to-pole total field (DRTP) magnetic anomalies show crustal thickness variations and states of magneto-isostatic compensation. Continental crustal thickness estimates for the North Andes are in the range from roughly 34 km to 55 km, conforming well to and extending regional seismic constraints. The analysis highlights crustal deformation from plate collision and subduction in Northwestern South America.; Inversely correlated FVDFAGA and DRTP magnetic anomalies suggest thickness variations in the lower crust and thermal effects in terms of the Curie isotherm. Directly correlated FVDFAGA and DRTP magnetic anomalies indicate thickness variations of the upper crust due to the formation of recent topography.