Seismic Imaging of the Transition From Normal to Flat Subduction in Southern Peru by Full Waveform Inversion of Teleseismic Waves

Abstract The high topography of the central Andes (15–28°S) is supported by thick crustal roots. The recent uplift of the Altiplano is often explained by crustal shortening and subsequent delamination of the lower crust, though its deep structure and plateau formation processes remain debated. The mechanism of flat subduction is also controversial in geodynamics. The well‐documented transition from normal to flat subduction beneath southern Peru provides an ideal setting to investigate these processes. In this study, we present a new multi‐parameter tomographic model of density, , , and beneath southern Peru. The model was obtained by inverting teleseismic P and SH waveforms recorded by temporary and permanent stations across 78°W–66°W and 10°S–19°S. Time and amplitude issues in the PeruSE data set were identified and corrected before inversion. The final model shows a normally dipping oceanic lithosphere in the south, with a continuous transition to flat subduction beneath central Peru, without a slab tear. The flat subducting lithosphere appears anomalously thin and hot, likely reflecting thermal erosion associated with the formation of the Nazca Ridge. This suggests that the buoyancy of the flat slab is not due to crustal thickening and delayed eclogitization reactions, as previously hypothesized, but rather to a thermally eroded and thinned oceanic lithosphere. We also detect a thin forearc crust (14°S–19°S) overlying a thick, cold mantle wedge. The Altiplano thickening may result from squeezing the crust between this strong forearc block and the Amazonian craton. Finally, the mantle lithosphere beneath the Altiplano is abnormally thin or absent, suggesting partial removal or delamination, which could explain the regional uplift over the past 10 Ma.