Insights into Moho depth beneath the northwestern Andean region from gravity data inversion

Abstract

SUMMARY The complex Moho topography beneath the northwestern Andes is the result of multiple geodynamic processes during the Cenozoic. To contribute to our understanding of the Moho depth distribution beneath this region, we inverted gravity data from two widely used satellite-derived data sets (EGM2008 and EIGEN-6C4) and one regional airborne Bouguer gravity anomaly map (ANH2010). Their inversion allowed choosing the ANH2010, based on lower residual gravity and a higher agreement with seismic estimations, as the most suitable data set to gain insights into the Moho depth beneath the northwestern Andes and its relationship with previously identified tectonic features. The inverted Moho argues for a 40–50 km depth beneath the Central and Eastern cordilleras, reaching depths beyond 50 km below the Eastern Cordillera, and shallower depths between 30 and 40 km mainly along the foreland region to the east, the Western Cordillera and the coastal plains. Three main thickened crust features of regional extent were identified: (1) a deep Moho expression with a crustal thickness greater than 40 km in the northwesternmost foreland region, which we consider a direct consequence of the adjacent thickened Eastern Cordillera involving the fold and thrust deformation migration from the range towards the foreland, and the flexural deformation proposed for the eastern foothills; (2) a regional deep Moho expression (50–60 km) along the axis of the Eastern Cordillera, related to its shortening history including multiple phases of Cenozoic thick-skinned deformation and magmatic underplating; and (3) a Moho deeper than 60 km in a southern latitude (1°S–1°N) beneath the modern magmatic arc, whose interpretation is more complex, likely a combined result of mafic addition to the base of the crust, foundering tectonics, and lateral displacement of the lower crust prompted by the subducting Carnegie ridge.