Deformation and erosion of the central Andean fold-thrust belt and Plateau.

摘要

Quantifying the timing, magnitude, and rates of deformation and erosion across the central Andean fold-thrust belt is a prerequisite for understanding the history of Andean Plateau (AP) evolution. This work integrates new low-temperature thermochronology data with structural, topographic, and sedimentologic observations to constrain the Tertiary exhumation and deformation history along the eastern AP flank in Bolivia. Results demonstrate: (1) Eo-Oligocene (∼40-20 Ma) exhumation in the Eastern Cordillera, (2) early-to-mid Miocene to recent (∼22-15 Ma to present) Interandean zone exhumation, (3) a second pulse of mid-Miocene to recent (∼15-0 Ma) exhumation in the Eastern Cordillera, (4) initial Miocene to recent (∼20-8 Ma to present) exhumation in the Subandes, (5) magnitudes of exhumation generally decrease eastward from maximums of 11-7 km in the Eastern Cordillera, to ∼6-4 km in the Interandean zone and ∼4-3 km in the Subandes, and (6) variable erosion rates of ∼1.0-0.1 mm/yr throughout the eastern AP flank in southern Bolivia since the PlioQuaternary (∼3-0 Ma). A review of constraints on the structure and history of the entire AP from southern Peru to northern Argentina shows deformation began as early as the Paleocene (∼60-40 Ma) and has generally migrated eastward. Data constraining the associated uplift history quantify a ∼1.5 km elevation gain since ∼10 Ma, but are equally consistent with a linear, slow and steady rise since ≥25 Ma as a rapid, recent rise of ∼2.7 km ∼10-6 Ma within error. Widespread, substantial incision (2.5-1 km) is observed along the western Altiplano flank since ∼11-8 Ma and is associated with surface uplift or climate change. Geophysical and geodynamic investigations identify an isostatically-compensated thick crust (∼80-65 km), elevated heat flow, zones of low and high velocity and attenuation in the crust and mantle, and stress the additional importance of weakened lithosphere, partial melt, and crustal flow or delamination to AP development. In conclusion, significant upper-plate deformation is an essential process in AP growth and that the history of shortening: (a) has taken significantly longer and (b) was more uniform over an along-strike distance of ∼1500 km than previously thought.