High-relief glacial valleys shape the modern topography of the Southern Patagonian Andes, but their formation remains poorly understood. Two Miocene plutonic complexes in the Andean retroarc, the Fitz Roy (49°S) and Torres del Paine (51°S) massifs, were emplaced between 16.9–16.4 Ma and 12.6–12.4 Ma, respectively. Subduction of oceanic ridge segments initiated ca. 16 Ma at 54°S, leading to northward opening of a slab window with associated mantle upwelling. The onset of major glaciations caused drastic topographic changes since ca. 7 Ma. To constrain the respective contributions of tectonic-mantle dynamics and fluvio-glacial erosion to rock exhumation and landscape evolution, we perform inverse thermal modeling of a new dataset of zircon and apatite (U-Th)/He from the two massifs, complemented by apatite 4He/3He data for Torres del Paine. Our results show rapid rock exhumation recorded only in the Fitz Roy massif between 10 and 8 Ma, which we ascribe to local mantle upwelling forcing surface uplift and intensified erosion around 49°S. Both massifs record a pulse of rock exhumation between 7 and 4 Ma, which we interpret as enhanced erosion during the beginning of Patagonian glaciations. After a period of erosional and tectonic quiescence in the Pliocene, increased rock exhumation since 3-2 Ma is interpreted as the result of alpine glacial valley carving promoted by reinforced glacial-interglacial cycles. This study highlights that glacial erosion was the main driver to rock exhumation in the Patagonian retroarc since 7 Ma, but that mantle upwelling might be a driving force to rock exhumation as well.

The combination of different thermochronologic techniques on the same samples or even the same grains has become in a useful tool, to establish a complete history of the geological process that has controlled a rock, and for gaining information on sediment provenance and the exhumation of sediment source areas. Determination of crystallization and cooling ages of detrital zircon from modern river sediments is a powerful method for tracing sediment provenance and exhumation of orogenic mountain belts. In this work we explain with new examples of modern river samples from the Colombian Andes how zircon fission-track (ZFT) and U-Pb dating can be used in provenance studies to better understand the temporal association between source and depositional site and how the evolution of orogenic mountain belts from such data in a setting where large amounts of sediment are recycled from sedimentary source rocks and volcanic input may complicate the exhumational signal. Whereas the ZFT data provide information about the most recent thermal history and exhumation of the source rocks, they are complementary to U-Pb data which reflect the original zircon crystallization age and its ultimate provenance. The study contains data of detrital zircon U-Pb and zircon fission-track dating from modern river sediments of the Guatiquia and Guayuriba rivers in the eastern foothills of the EC, and the Magdalena River at Girardot on the western flank of the EC. Each individual dating technique offers unique information with respect to provenance and exhumation. We use our data to highlight certain advantages and limitations of using zircon U-Pb and FT dating in provenance studies, including the identification of original source areas, sediment recycling and the difficulty of detecting amagmatic orogens in the detrital zircon record. The data obtained in this study allows us to better understand the association between exhumation of sources and their detrital zircon signatures in modern rivers that drain a part of the EC The results obtained allowing us to make first-order observations about the provenance signal in modern rivers on the east flank of the Eastern Cordillera, our data clearly show that the zircon U-Pb age spectra of the Paleozoic through Mesozoic sedimentary section being eroded is related to sources in the Amazon Craton, the magmatic Paleozoic basement of the same EC, and exhumation of proximal Precambrian basement blocks. On the other hand, the Magdalena River sample indicates the presence of these same EC sources plus the addition of younger Permo-Triassic and Jurassic zircons derived from reworking of Upper Magdalena Valley sedimentary units and/or the crystalline basement of the CC. The ZFT data presented here complements the existing record of recent exhumation for the EC and the Magdalena River at Girardot on the western flank of the EC. Each individual dating technique offers unique information with respect to provenance and exhumation.

Located at the northern tip of the Altiplano, the Abancay Deflection marks abruptly the latitudinal segmentation of the Central Andes spreading over the Altiplano to the south and the Eastern Cordillera northward. The striking contrast in terms of morphology between the low-relief Altiplano and the high-jagged Eastern Cordillera makes this area a privileged place to determine spatio-temporal variations in surface and/or rock uplift and discuss the latest phase of the formation of the Central Andes. Here, we aim to quantify exhumation and uplift patterns in the Abancay Deflection since 40 Ma, and present new apatite (U-Th)/He and fission-track data from five altitudinal profiles and additional individual samples. Age-Elevation relationships and thermal modeling both evidence that the Abancay Deflection experienced a moderate, spatially-uniform and steady exhumation at 0.2±0.1 km/m.y. between 40 Ma and ~5 Ma implying common large-scale exhumation mechanisms. From ~5 Ma, while the northern part of the Eastern Cordillera and the Altiplano registered similar ongoing slow exhumation, the southern part of the Eastern Cordillera experienced one order-of-magnitude of exhumation acceleration (1.2±0.4 km/m.y). This differential exhumation since ~5 Ma implies active tectonics, river capture and incision affecting the southern Eastern Cordillera. 3D thermo-kinematic modeling favors a tectonic decoupling between the Altiplano and the Eastern Cordillera through backthrusting activity of the Apurimac fault. We speculate that the Abancay Deflection, with its “bulls-eye” structure and significant exhumation rate since 5 Ma, may represent an Andean proto-syntaxis, similar to the syntaxes described in the Himalaya or Alaska.