Deep incised glacial valleys surrounded by high peaks form the modern topography of the Southern Patagonian Andes. Two Miocene plutonic complexes in the Andean retroarc, the cores of the Fitz Roy (49°S) and Torres del Paine (51°S) massifs, were emplaced at 16.7±0.3 Ma and 12.5±0.1 Ma, respectively. Subduction of ocean ridge segments initiated at 54°S, generating northward opening of an asthenospheric window with associated mantle upwelling and orogenic shortening since 16 Ma. Subsequently, the onset of major glaciations at 7 Ma caused drastic changes in the regional topographic evolution. To constrain the respective contributions of tectonic convergence, mantle upwelling and fluvio-glacial erosion to rock exhumation, we present 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 in the Fitz Roy massif between 10.5 and 9 Ma, which we ascribe to mantle upwelling and/or crustal shortening due to ridge subduction at 49°S. Both massifs record a pulse of rock exhumation between 6.5 and 4.5 Ma, which we interpret as the result of the onset of Patagonian glaciations. After a period of erosional quiescence during the Miocene/Pliocene transition, increased rock exhumation since 3-2 Ma to present day is interpreted as the result of alpine glacial valley carving promoted by reinforced glacial-interglacial cycles. This study demonstrates that along-strike thermochronological studies provide us with the means to assess the spatio-temporal variations in tectonic, mantle, and surface processes forcing on rock exhumation.

The timing of transition between the contractional and extensional regimes along the Pyrenean range remains debated. Compared to its central and western parts, the eastern part of the chain was significantly affected by extensional tectonics mostly related to the opening of the Gulf of Lion. The Têt normal fault is the best example of this tectonic activity, with topographic reliefs above 2,000 m in its footwall. In this study, we synthetized previous thermochronological data and performed new (U-Th)/He and fission-track dating in the Eastern Pyrenean massifs. Output apparent exhumation rate and thermal modeling in the hanging-wall of the Têt fault highlight a rapid exhumation (0.48 km/Ma) and cooling (~30°C/Ma) phase between 38 and 35 Ma, followed by slower exhumation/cooling afterwards. In the footwall, cooling subsequently propagated westward along the fault during Priabonian (35-32 Ma), upper Oligocene and lower Miocene (26-19 Ma), and Serravalian-Tortonian times (12-9 Ma). These data and modeling outcomes suggest that the exhumation of the Têt fault hanging-wall related to southward thrusting ended at 35 Ma, and was followed by different extensional stages, with a propagation of the deformation towards the West during the upper Miocene. We propose that the onset of extension in the Eastern Pyrenees occurred during the late Priabonian period, contemporaneously with the large-scale rifting episode recorded in Western Europe. After this event, the Têt fault activity and the westward propagation of the deformation appear mainly controlled by the opening of the Gulf of Lion.

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.