Structural and thermochronologic constraints on kinematics and timing of inversion of the Salta rift in the Tonco-Amblayo sector of the Andean retroarc fold-thrust belt, northwestern Argentina

Inherited architecture of the Cretaceous Salta rift is a primary influence on Andean deformation in northwestern Argentina. The Tonco-Amblayo thrust belt (TATB) of the Eastern Cordillera exhibits a complex interplay between thick-skinned and thin-skinned shortening styles, controlled by reactivated Salta rift normal faults. Geological mapping, cross-sections, and apatite (U-Th)/He dating document Miocene shortening and exhumation. Regional structures comprise basement-involved reverse faults and steep-overturned fault-propagation folds. Inversion of east-dipping normal faults results in a hindward verging back-thrust belt. Apatite (U-Th)/He data document eastward younging cooling ages from ~12Ma to ~6Ma, suggesting that deformation propagated forward. Kinematic models require structure at depth to accommodate changes in structural elevation and basement shortening. Basement wedging, by a single thrust sheet or passive-roof duplex, provides a kinematically viable model. Shortening in the Eastern Cordillera is ~36% (53km). Revised total shortening (~118km) falls short of solving shortening discrepancies suggested by crustal thickness.