Search

Lithospheric foundering is hypothesized to contribute to the formation of Earth's largest continental plateaus, but the predicted effects remain poorly constrained, especially considering variations in crustal strength. Here we propose that lithospheric foundering involving a hot, weak crust can explain aspects of topography and crustal deformation in mountain belts. We explore this hypothesis using numerical models of orogenesis and foundering in the Southern Puna Plateau in the Central Andes. Contrary to previous models of foundering involving a strong crust, which are characterized by subsidence and shortening, a weak crust results in surface uplift and upper‐crustal horizontal extension, which is accommodated by horizontal shortening in peripheral regions. Our model explains data such as the timing and location of exhumation and basin sedimentation as a response to foundering. The model also shows that foundering is capable of converting a high‐relief, broken‐foreland region into a high‐elevation, low‐relief plateau in a convergent tectonic setting. Plain Language Summary: Thickened crust can gravitationally unstable and founder into the mantle. This process could contribute to the formation of large plateaus such as Tibet and the Central Andes, which are composed of hot, felsic, and therefore weak crust. However, existing models have not thoroughly considered the implications of lithospheric foundering beneath a weak crust. We present numerical modeling experiments that show that a lithospheric drip can cause crustal flow and spreading, even when it takes place within a convergent tectonic setting, such as a major mountain belt. By comparing our models to geologic data from the Central Andes, we suggest that this scenario can explain many intriguing geological puzzles within the Puna Plateau, such as the timing and distribution of horizontal extension, the thickening of the crust, and the uplift history of the plateau. Future studies should consider the possibility of a weak, flowing crust during a lithospheric foundering event. Key Points: Lithospheric foundering under a hot, weak crust causes syn‐convergent, upper‐crustal extensionOur models successfully explain the Cenozoic uplift and deformation of the Puna Plateau as a result of this processThis style of foundering has been overlooked but may apply to other large orogens [ABSTRACT FROM AUTHOR]

New fieldwork and tectonic analysis has been carried out along the Andean morphotectonic frontline between 46°30' and 47°30′S. The right lateral transtensional Marques–Zeballos Pass fault system (MZPRS) controlled the 800–1200 m uplift of the Andes at 16.1–18.1 Ma. Our data and analysis indicate that there was no lower Miocene contractile event along the Andean morphotectonic frontline. The Main Andean Thrust (MAT), which is deeply rooted in the upper crust is a retroarc thrust dipping 10–15° westward, and provides evidence for major crustal shortening at ~120 Ma. At that time the arc volcanic strata of the Ibañez Fm (148–178 Ma) was transported eastward above the rift volcanic Quemado Fm (144179 Ma), which lies unconformably on the Deseado basement massif. The geologic records from the fieldwork together with the available data allow us to identify the processes controlling the dynamic evolution of the two main topographic features of the studied Andean segment. (1) Upward convection originating from the subducted South Chile Ridge −1 segment (SCR −1) is dynamically sustaining the high topography of the North Patagonian Icefield (4070 m at the Mt. San Valentin, ~2 km higher than the Southern South Volcanic Zone). This, together with the locus of maximum moisture being at 47°S during glacial events has resulted in producing the two largest glacial lobes of Patagonia. (2) The 180 km long, E –W trending antiformal arch structure of the Mt. Zeballos Ridge (MZR, a hinge zone trending N–S along the MZPRS) straddling the Andes and the Foreland is proposed to be the morphological "twin" of the South American Plate Moho Plateau (SAM MOHO P). The SAM MOHO P controls the location of both the MZPRS and the MZR boundaries location through time. The Patagonia Slab Window and SAM asthenospheric dynamics (upward and corner flows, respectively) and their in–depth interaction appear to control the morphotectonic evolution of the whole studied segment through a powerful feedback loop between tectonics, morphology, and climate, at least for the past 3–4 Myr. [ABSTRACT FROM AUTHOR]