Testing geodynamic models for surface uplift of the central Andean plateau through volcanic glass paleoaltimetry and basin analysis in southern Peru
Abstract:Differentiating between geodynamic models describing the formation mechanism(s) of the central Andean plateau (CAP) requires information concerning the timing and location of basin formation, crustal deformation, and surface uplift. All models involve the removal of lithospheric mantle, and typically fall into one of two end-members: 1) slow, continuous uplift (km over 10s of Myr) involving protracted removal of mantle lithosphere through ablative subduction or thermal weakening that is predicted to be coincident with crustal shortening, or 2) punctuated uplift (km over Myr) driven by rapid wholesale or piecemeal foundering of a dense lithospheric root, likely post-dating major crustal shortening. However, these models are not mutually exclusive, nor must any one geodynamic mechanism describe the entire history of the formation of the CAP, an area spanning ~1800 km N-S by up to 500 km E-W, comprised of multiple physiographic regions of differing compositional and geophysical characteristics resulting from protracted orogenesis.
We present new stratigraphic, stable isotopic, and geochronologic data for temporally overlapping yet spatially separate Cenozoic intermontane basins in the northern CAP to evaluate the contribution of these end-member scenarios to the formation of the CAP. Data span multiple physiographic regions of the CAP, including basins near Puquio (Western Cordillera), the Huacochullo basin (western Altiplano margin), and the Macusani and Crucero basins of the Cordillera de Carabaya (Eastern Cordillera). The magnitude of paleoelevation changes is reconstructed from δD values of volcanic glass, while timing is constrained by zircon U-Pb geochronology. Initial results indicate early, rapid, high-magnitude surface uplift from initially low elevations in the Western Cordillera but a later, lower-magnitude pulse of uplift from initially moderate elevations in the Eastern Cordillera. This diachronous uplift history, together with published reports of crustal deformation, suggests contrasting uplift mechanisms potentially explained by early Miocene foundering of a dense lithospheric root in the Western Cordillera, and a combination of continued Cenozoic crustal shortening and late Miocene lithospheric removal in the Eastern Cordillera.