Patterns and timing of exhumation and deformation in the Eastern Cordillera of NW Argentina revealed by (U‐Th)/He thermochronology

Abstract

The Eastern Cordillera (EC) and related ranges of Bolivia and Argentina exhibit a wide variety of structural features, both thick and thin skinned, that make this region a prime area to study the evolution of these two contrasting styles. Using a combination of structural, geochronological, and thermochronological techniques, this study investigates how and in what order the various structures of the Argentinean EC from 25 to 26°S have developed during the Cenozoic. New mapping in the Angastaco area preserves one of the thickest Cenozoic stratigraphic sections and records a complex structural evolution during the Neogene, characterized by inversion of Cretaceous Salta Rift structures. Detrital zircon U‐Pb geochronology combined with stratigraphic and structural features typical of synsedimentary deformation constrains the age of orgenic growth in the area to ∼14 Ma. Detrital apatite (U‐Th)/He thermochronology on samples collected across the width of the southernmost EC at this latitude document an eastward younging of ages interpreted as the result of sequential eastward propagation of exhumation (and inferred deformation) from ∼14 to 3 Ma at a rate of ∼8.3 mm/a. Our data, when compared with existing data, show that the Puna Plateau of NW Argentina was exhuming and deforming at the same time as the EC and inter‐Andean regions of Bolivia, suggesting that the deformation front connects along strike despite of the differences in structural style. Whereas the deformation front reached the sub‐Andes of Bolivia by ∼10 Ma, deformation localized in the EC of NW Argentina until ∼4 Ma. Rates of propagation through the whole region seem to be quasi‐uniform regardless of different structural styles. This study investigates the timing of basin exhumation in NW Argentina The new data set shows coeval deformation and sedimentation in the Cenozoic The new data help resolve the evolution of the overall EC