Variations in Subducted Plate Crustal Thickness Along the Perú–Chile Margin and Implications for Slab Dip

We use receiver function analysis to calculate the first regional-scale estimate of subducted oceanic plate crustal thickness along the Perú-Chile Subduction Zone (PCSZ). Previous studies have shown that the thickness of the subducting crust varies significantly along the margin and influences the evolution of the overriding plate and slab dip. In the PCSZ, offshore variations in crustal thickness are mainly associated with the presence of aseismic ridges. While offshore geophysical experiments measured oceanic crustal thickness prior to subduction, data from the subducted portion of the plate remain scarce. We calculate receiver functions between latitudes 10°S and 40°S to measure latitudinal and depth variations in the Nazca plate crustal thickness at depths up to ∼100 km (near eclogitization depths). Our results show that the downgoing plate crust varies in thickness from 6 to 22 km. The thickest oceanic crust is observed near subducting ridges, particularly in south Perú, where the Nazca Ridge subducts. We observe that crustal thickness patterns in the data outboard of the trench continue to greater depths in the subducting plate. The exception is at flat-slab segments, where we observe a broad thickening of the crust in a wider zone than implied by the ridges' expression offshore. Comparing our results with numerical model predictions suggests that the combined effect of age and crustal thickness on buoyancy is an important control on slab dip in our study area. However, our results indicate that a wide area (>400 km) of thickening might also be key to supporting flat-slab subduction and its lateral extent.