0000000000724993
AUTHOR
Matías C. Ghiglione
Tectonic evolution of the northern Austral-Magallanes basin in the Southern Patagonian Andes from provenance analysis
We studied the northern tip of the Austral-Magallanes basin in the Southern Patagonian Andes, between the Buenos Aires Lake and the Mayer River at 46°35′ SL and 48°35′ SL, respectively. Proposed objectives were: i) to differentiate Mesozoic-Cenozoic tectonostratigraphic units and, ii) to characterize the different deformational events that took place in the area linked to a variable regional geodynamic context. Sandstones provenance analysis was performed on the Aptian - Albian compressive retroarc deposits and Cenozoic foreland deposits. Studied samples were classified using tectonic discrimination diagrams which show: i) for Cretaceous rocks a dominant sediment source from a recycled orog…
Seismotectonic implications of the south chile ridge subduction beneath the patagonian andes
International audience; The South Chile ridge (SCR) intersects the Patagonian trench around 46° 09’S, forming the triple junction among the Antarctic, Nazca, and South America plates. Subduction of the SCR since ~18 Ma produced the opening of a slab window beneath Patagonia and a noticeable magmatic gap in the cordillera, profuse volcanism, and topographic uplift in the retroarc. To study seismicity distribution and present‐day stress resulting from this particular framework, we analyze databases of seismic events and earthquake focal mechanisms. Our study finds that clusters of intraplate crustal seismic events are disrupted by a ~450‐470 km seismicity gap above the slab window. Calculated…
Trench-parallel spreading ridge subduction and its consequences for the geological evolution of the overriding plate: Insights from analogue models and comparison with the Neogene subduction beneath Patagonia
A series of 3-D asthenospheric-scale analogue models have been conducted in the laboratory in order to simulate the arrival of a spreading ridge at the trench and understand its effect on plate kinematics, slab geometry, and on the deformation of the overriding plate. These models are made of a two-layered linearly viscous system simulating the lithosphere and asthenosphere. We reproduce the progressive decrease in thickness of the oceanic lithosphere at the trench. We measure plate kinematics, slab geometry and upper plate deformation. Our experiments reveal that the subduction of a thinning plate beneath a freely moving overriding continent favors a decrease of the subduction velocity and…
The metamorphic rocks of the Nunatak Viedma in the Southern Patagonian Andes: Provenance sources and implications for the early Mesozoic Patagonia-Antarctic Peninsula connection
The Nunatak Viedma within the Southern Patagonian Icefield has been considered as a volcanic center based on its geomorphologic features, despite the fact that field explorations by Eric Shipton determined its metamorphic nature 70 years ago. We carried out fieldwork to characterize this isolated outcrop and performed the first U-Pb dating in detrital zircons from the basement rocks located inside the Southern Patagonian Icefield. We recognized very-low grade metamorphic rocks, corresponding principally to metapelites and metapsammites, and scarce metabasites. Detrital zircons in three metapsammitic samples (composite group of 240 grains) yielded prominent age population peaks at ∼1090, ∼96…
Late Cenozoic brittle deformation in the Southern Patagonian Andes: Record of plate coupling/decoupling during variable subduction?
The Andes of southern Patagonia experienced a Miocene shift towards faster and higher angle subduction followed by the approach and collision of the Chile oceanic ridge. We present a kinematic study characterizing palaeostress fields computed from brittle tectonics to better constrain upper crustal deformation during this complex scenario. Although previous studies already suggested variable kinematics, it is striking that in a long-lasting subduction environment, the computed palaeostress tensors are mostly strike-slip (55%), while 35% are extensional, and only 10% compressive which are concentrated along a main frontal thrust. Cross-cutting relationships and synsedimentary deformation ind…