ORCID Profile
0000-0003-1891-6474
Current Organisation
Università degli Studi di Milano-Bicocca
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Publisher: Elsevier BV
Date: 07-2023
Publisher: Authorea, Inc.
Date: 05-05-2023
DOI: 10.22541/ESSOAR.168332179.93378898/V1
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.
Publisher: Copernicus GmbH
Date: 25-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-226
Abstract: & & Late Miocene calc-alkaline intrusions in the back-arc of Southern Patagonia mark an eastward migration of the arc due to accelerated subduction velocity of the Nazca plate or slab flattening preceding active ridge subduction. Amongst these intrusions are the emblematic Torres del Paine (51& #176 S) and Fitz Roy (49& #176 S) plutonic complexes, crystalised at ca. 12.5 and ca. 16.5 Ma, respectively (Leuthold et al., 2012 Ram& #237 rez de Arellano et al., 2012). Both intrusions are located at the eastern boundary of the Southern Patagonian Icefield and form prominent peaks with steep slopes that are ~3 km higher in elevation than the surrounding low-relief foreland. Their exhumation has been proposed as a response to glacial erosion and associated glacial rebound since ca. 7 Ma (Fosdick et al., 2013), and/or by regional dynamic uplift between 14 and 6 Ma due to the northward migration of subducting spreading ridges (Guillaume et al., 2009). Here we present a new data set of apatite and zircon (U-Th)/He from both plutonic complexes, numerically modelled to unravel their late-Neogene to Quaternary thermal histories. Our results show three rapid cooling periods for the Fitz Roy intrusion: at ca. 9.5 Ma, at ca. 7.5 Ma, and since ca. 1 Ma. For Torres del Paine, inverse thermal modelling reveals short and rapid cooling at ca. 6.5 Ma followed by late-Quaternary final cooling. The 10 Ma cooling signal only evidenced in the northern plutonic complex (Fitz Roy) may represent an exhumation response to the northward migrating subduction of spreading ridge segments, causing localized dynamic uplift. Thus, the absence of exhumation signal before 6.5 Ma in the southern part (Torres del Paine) suggest that the spreading ridge subduction must have occurred before its 12.5 Ma emplacement. On the other hand, rapid cooling by similar magnitude in both plutonic complexes between ca. 7.5& #8211 .5 Ma, likely reflects the onset of late-Cenozoic glaciations in Southern Patagonia. Finally, the late-stage Quaternary cooling signals differ between Torres del Paine and Fitz Roy, likely highlighting different exhumation responses (& em& i.e. & /em& relief development vs. uniform exhumation) to mid-Pleistocene climate cooling. We thus identify and distinguish the causes of rapid exhumation periods in the Southern Patagonian Andes, and propose a first Late Miocene exhumation pulse due to subduction of spreading ridge dynamics, and two Late Cenozoic exhumation episodes due to regional climate changes that have shaped alpine landscapes in this region.& & & & References:& & & & Leuthold J., et al. 2012. Time resolved construction of a bimodal laccolith (Torres del Paine, Patagonia). EPSL.& & & & Ram& #237 rez de Arellano C., et al. 2012. High precision U/Pb zircon dating of the Chalt& #233 n Plutonic Complex (Cerro Fitz Roy, Patagonia) and its relationship to arc migration in the southernmost Andes. Tectonics.& & & & Fosdick J. C., et al. 2013. Retroarc deformation and exhumation near the end of the Andes, southern Patagonia. EPSL.& & & & Guillaume B. 2009. Neogene uplift of central eastern Patagonia: Dynamic response to active spreading ridge subduction? Tectonics.& &
Publisher: Copernicus GmbH
Date: 30-08-2022
DOI: 10.5194/EGUSPHERE-ALPSHOP2022-4
Abstract: & & Alpine landscapes form in mountain belts that likely experienced tectonic uplift during plate& #8217 s convergence, and efficient erosion dominated by glacial carving and circle retreat. In southern Patagonia N-S oriented late Miocene plutonic complexes are exposed in deep incised valleys with summits topographically above the glacial equilibrium line altitude. Two of the most emblematic ones are the Fitz Roy (Chalt& #233 n, latitude 49& #176 S) and the Torres del Paine (latitude 51& #176 S) plutonic complexes, ~2 km higher than the mostly flat bottom valley that is partially covered by the Southern Patagonian Icefield. This continental region is located above an asthenospheric window that opens and migrates from the latitude 54 & #176 S towards the latitude 46 & #176 S since ~16 Ma, and experienced dynamic uplift during episodes of spreading ridge collision with the continental margin. Here we present a new dataset of combined low-temperature thermochronometers from the Chalt& #233 n and Torres del Paine plutonic complexes, and their thermal history inversion numerical modeling, to identify the geodynamic processes forcing on the exhumation of the mountain belt. These complexes are separated by 200 km along the strike of the belt, and share a pulse of rapid exhumation at ca. 6 Ma, likely showing that glaciation was regionally starting at this moment. After a period of quiescence, in Torres del Paine the exhumation rate is accelerated from ~2 Ma to the present, interpreted as a signal of the Pleistocene climatic transition creating incise valleys. Only in the Fitz Roy a pulse of rapid exhumation is present at ca. 10 Ma, approximately coincident with the time range in which the ridge was subducting beneath the continent at that latitude. This allows us to separate the climatic from the tectonic/mantle forcing to the exhumation in southern Patagonia, and represents the first in-situ observation of the passage of the asthenospheric window in the low-temperature thermochronometric record of the region.& &
Location: United States of America
Location: United States of America
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Pietro Sternai.