Geodynamic and climatic forcing on late-Cenozoic exhumation of the
Southern Patagonian Andes (Fitz Roy and Torres del Paine massifs)
Abstract
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.