Structural Evolution of the Northern Agrio Fold and Trust Belt (∼37°30′S), Neuquén Basin, Argentina, Derived From Low-Temperature Multi-Thermochronometry

Abstract

The Agrio Fold and Thrust Belt (FTB), situated in the Southern Central Andes at 37–39°S, underwent two phases of contractional deformation: Late Cretaceous-Eocene and middle-late Miocene. Despite advances in understanding its tectonic history, many questions persist regarding the timing and activity of specific structures during these deformation phases. By combining low-temperature multi-thermochronometry, inverse thermal models and field structural data, we present a new thermal-structural history for the northern Agrio FTB. Our findings unveil an initial cooling event between approximately 85–75 Ma and 55–50 Ma, involving cooling rates of 1.1–2°C/Ma and vertical displacement rates from 0.07 to 0.12 km/Ma. This slow event, confined to the inner zone, is associated with the growth of the basement-cored Manzano anticline. Additionally, still in the inner zone of the Agrio FTB, a second and faster cooling event from ∼15–10 Ma to 0 Ma, marked by a cooling rate of 7°C/Ma and a vertical displacement rate ranging from 0.11 to 0.17 km/Ma, results from in-sequence thick-skinned thrusting at depth. In the outer zone of the FTB, only the younger cooling event from 15–10 Ma to 0 Ma is evident, with a cooling rate of 8.8°C/Ma and a vertical displacement rate ranging from ∼0.14 to 0.26 km/Ma, attributed to displacement along the basement-involved Las Yeseras thrust. Furthermore, Apatite Fission Track (AFT) ages of detrital grains in the Tralalhué conglomerates support the maximum depositional age for these synorogenic strata to be between 14.1 and 9.2 Ma.