Cenozoic Surface Uplift and Basin Formation in the Peruvian Central Andes


Surface uplift and basin subsidence are central to the debate regarding geodynamic processes involved in the development and maintenance of high topography in the central Andes, yet these issues remain largely unaddressed in the high-elevation hinterland of southern Peru. This dissertation presents a combination of stratigraphy, sediment provenance, and stable isotopic geochemistry which bear on the geodynamic controls of orogen evolution in southern Peru. Basin analysis and modeling of the Altiplano region provides updated characterization, chronology, and quantitative provenance information. Results show that the Western Cordillera was a progressively more proximal source for the Altiplano basin sediments and that sediment accumulation rates increased from ~36 m/Myr to >150 m/Myr between 58 and 23 Ma, consistent with deposition in a northeastward-migrating flexural foreland basin system. Transition to hinterland basin deposition in the northernmost Altiplano is marked by a 23–9 Ma angular unconformity, after which localized sedimentation began again with increased accumulation rates >800 m/Myr, likely due to strike-slip subsidence. Late Oligocene to modern surface uplift patterns were determined from regional stable isotopic trends of water preserved in hydrated volcanic glasses benchmarked against isotopic signatures of modern waters. Results show the northern cordilleras of southern Peru were at modern elevation by ~22Ma. To the south, elevation increased rapidly by ~2.5 km between 22 and 17 Ma in the Western Cordillera, and between 17 and 12 Ma in the Altiplano, pointing to isostatic uplift interpreted to be from foundering of mantle lithosphere via Rayleigh-Taylor instability. The Eastern Cordillera was uplifted much slower, with ~2 km of elevation gain between 25 and 10 Ma, consistent with crustal shortening in the absence of significant lithospheric thickening. Collectively, results highlight along- and across-strike variability in geodynamic processes consistent with models of orogenic cyclicity. Cenozoic foreland basin variability along orogenic strike between southern Peru and northwest Argentina was controlled by Paleozoic–Mesozoic stratigraphic and structural fabric that resulted in thicker deposits, earlier onset of rapid sediment accumulation, and earlier higher-frequency high-flux magmatism in the north. New U-Pb data visualization/reduction and mixture modeling software packages (UPbToolbox and DZmix) were developed for, and provided with this work.



Stratigraphy, Geodynamics, Altiplano