Constraining Andean Propagation of Exhumation at the Limit of the Eastern Cordillera, NW Argentina, Using Low-Temperature Thermochronology in a Structural Context

Abstract

Within the Central Andes of NW Argentina, the spatiotemporal distribution and style of deformation is strongly influenced by pre-Cenozoic heterogeneities, mostly related to the Salta rift extension in the Cretaceous. At the enigmatic junction of the thin-skinned Subandean belt and the thick-skinned Santa Barbara System, the Tilcara Range and adjacent San Lucas block, located within the Eastern Cordillera, show thermochronological and field evidence of multiple exhumation events. Mesozoic (140-115 Ma), pre-Andean exhumation of basement highs is constrained by unconformities between basement and syn-rift strata, as well as zircon (U-Th-Sm)/He cooling ages. Cenozoic Andean exhumation is quantified by apatite (U-Th-Sm)/He and fission track cooling ages, which were reset between the Late Cretaceous and Miocene. These data show that the westernmost Tilcara Range began exhuming in the late Oligocene-early Miocene (26-16 Ma), after which exhumation propagated to the border of the Eastern Cordillera in the middle Miocene (22-10 Ma). The onset of rapid exhumation in the San Lucas block, which is located east of the Tilcara Range, occurred in the late Miocene (10-8 Ma) in its western part, and in the late Miocene-early Pliocene (6-4 Ma) in its eastern part. Internal deformation of the San Lucas block, disturbing zircon (U-Th-Sm)/He and apatite fission track age patterns, predates propagation of rapid exhumation. The here presented low-temperature thermochronology data set thus quantifies the multi-phase exhumation history of the Eastern Cordillera of NW Argentina and constrains the timing of Andean propagation of exhumation within the Eastern Cordillera and the adjacent structural transition zone.