NEOGENE TO QUATERNARY DEFORMATION AND INTERMONTANE BASIN EVOLUTION IN THE HUMAHUACA BASIN, EASTERN CORDILLERA OF THE CENTRAL ANDES, NW ARGENTINA (23.5°S)

The Humahuaca basin provides an excellent opportunity to explore both the controls on patterns of deformation within and at the margins of an intermontane basin in the Eastern Cordillera of NW Argentina and the relationships between this deformation and deposition in the basin. Thrust faults along the western margin of the northern Humahuaca basin expose a band of the Cretaceous-Paleogene Salta Group rocks in their hanging walls and include Neogene-Quaternary basin fill deposits in their footwalls. Inferred east-west-trending normal faults related to the Cretaceous Salta Rift result in segmentation of these north-south-trending thrust faults in the Humahuaca basin, with different styles of hanging-wall deformation along each of three segments. Multiple cross-cutting relationships with Neogene-Quaternary basin fill that contains numerous dated ash layers provides unusually tight constraints on the timing of displacement on individual faults and folds within the Humahuaca basin. Thrust faults in the basin were active from ~4.5 Ma until <1.6 Ma, coeval with the uplift of the bounding ranges to the east. Comparison with the timing of changes in sediment-accumulation rates and sedimentary facies in the basin suggests that faults in and on the western margin of the Humahuaca basin exerted a secondary control on deposition in the basin, which depended more strongly on the uplift of the bounding ranges to the east and the local climate changes associated with that uplift. The timing of deformation in the Humahuaca basin and bounding ranges is similar to the main phases of shortening and foreland fragmentation in the Eastern Cordillera and broken Salta foreland ~200 km to the south (~14 Ma, 10 Ma, ~5-4 Ma, and <2 Ma). Differences in the style and spatial distribution of deformation in these two regions may reflect differences in the position of each region relative to the Cretaceous Salta Rift and the orientation of rift-related normal faults.