Examinando por Autor "Poblete, F."

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    Late Cretaceous–early Eocene counterclockwise rotation of the Fueguian Andes and evolution of the Patagonia–Antarctic Peninsula system
    (Elsevier B.V., 2016-02) Poblete, F.; Roperch, P.; Arriagada, C.; Ruffet, G.; Ramírez de Arellano, C.; Hervé, F.; Poujol, M.
    The southernmost Andes of Patagonia and Tierra del Fuego present a prominent arc-shaped structure: the Patagonian Bend. Whether the bending is a primary curvature or an orocline is still matter of controversy. New pa leomagnetic data have been obtained south of the Beagle Channel in 39 out of 61 sites. They have been drilled in Late Jurassic and Early Cretaceous sediments and interbedded volcanics and in mid-Cretaceous to Eocene intrusives of the Fuegian Batholith. The anisotropy of magnetic susceptibility was measured at each site and the influence of mag netic fabric on the characteristic remanent magnetizations (ChRM) in plutonic rocks was corrected using inverse tensors of anisotropy of remanent magnetizations. Normal polarity secondary magnetizations with west-directed declination were obtained in the sediments and they did not pass the fold test. These characteristic directions are similar to those recorded by mid Cretaceous intrusives suggesting a remagnetization event during the normal Cre taceous superchron and describe a large (N90°) counterclockwise rotation. Late Cretaceous to Eocene rocks of the Fueguian Batholith, record decreasing counterclockwise rotations of 45° to 30°. These paleomagnetic results are interpreted as evidence of a large counterclockwise rotation of the Fueguian Andes related to the closure of the Rocas Verdes Basin and the formation of the Darwin Cordillera during the Late Cretaceous and Paleocene. The tectonic evolution of the Patagonian Bend can thus be described as the formation of a progressive arc from an oroclinal stage during the closure of the Rocas Verdes basin to a mainly primary arc during the final stages of deformation of the Magallanes fold and thrust belt. Plate reconstructions show that the Antarctic Peninsula would have formed a continuous margin with Patagonia between the Early Cretaceous and the Eocene, and acted as a non-rotational rigid block facilitating the development of the Patagonian Bend. © 2015 Elsevier B.V. All rights reserved.
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    Re-evaluating the link between the Ellsworth Mountains and East Antarctica in the Neoproterozoic: Implications for the breakup of Rodinia and the existence of Pannotia
    (Elsevier, 2024-04) Castillo, P.; Poblete, F.; Fernández, R.; Bastías-Silva, J.; Fanning, M.
    Our current understanding of the Ellsworth Mountains stratigraphy suggests the oldest sedimentary sequence (Heritage Group) was deposited in a Cambrian rift setting. This early Paleozoic age is then used as a key piercing point to help define Cambrian paleogeography for the southern paleo-Pacific margin of Gondwana, which places the Ellsworth Mountains between southern Africa and East Antarctica as part of West Gondwana. However, U-Pb zircon dating of a micro-diorite from the Heritage Group reveals a crystallization age of 682 ± 10 Ma, challenging chronostratigraphic and tectonic interpretations. Positive εHft and mantle-like δ18O values for these Cryogenian zircons suggest that the rifting, affecting Mesoproterozoic crust, occurred during the Cryogenian rather than in the Cambrian. This finding strongly supports a connection between the Ellsworth-Whitmore Mountain crustal block and the Transantarctic Mountains in East Antarctica prior to the amalgamation of Gondwana. It also facilitates its contextualization during the breakup of Rodinia, likely positioned close to the Shackleton Range as a continuation of the Australia-Antarctic plate, which separated from Laurentia to form the proto-Pacific Ocean in the late Neoproterozoic. This connection is supported by the U-Pb, Hf, and O data in detrital zircon grains from the lowermost units of the Heritage Group, which indicate local, East Antarctic Shield, and probable Laurentian sources. A second magmatic event in the Cambrian (516 ± 7 Ma) is recorded through zircons from a basaltic andesite within the Liberty Hills Formation, which provides an absolute depositional age for this unit. This magmatism is linked to an extensional setting, albeit distinct from that of the Cryogenian micro-diorite. The Cambrian zircons yield elevated δ18O values, indicating a strong sedimentary influence on the magma source and crustal recycling. We interpret this Cambrian extensional magmatism as a result of a tectonic escape following the collision between the East Antarctic Shield and West Gondwana/Indo-Antarctic plates, leading to the formation of Gondwana. This interpretation argues against the hypothetical Pannotia supercontinent and the proposed Cambrian rift between this sector of the paleo-Pacific margin of Gondwana and southern Laurentia.
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    The curved Magallanes fold and thrust belt: tectonic insights from a paleomagnetic and anisotropy of magnetic susceptibility study
    (Blackwell Publishing Ltd, 2014-12) Poblete, F.; Roperch, P.; Hervé, F.; Diraison, M.; Espinoza, M.; Arriagada, C.
    The Magallanes fold and thrust belt (FTB) presents a large-scale curvature from N-S oriented structures north of 52°S to nearly E-W in Tierra del Fuego Island. We present a paleomagnetic and anisotropy of magnetic susceptibility (AMS) study from 85 sites sampled in Cretaceous to Miocene marine sediments. Magnetic susceptibility is lower than 0.0005 SI for 76 sites and mainly controlled by paramagnetic minerals. AMS results indicate that the sedimentary fabric is preserved in the undeformed areas of Tierra del Fuego and the more external thrust sheets units, where an incipient lineation due to layer parallel shortening is recorded. Prolate AMS ellipsoids, indicating a significant tectonic imprint in the AMS fabric, are observed in the internal units of the belt. AMS results show a good correlation between the orientation of the magnetic lineation and the fold axes. However, in Península Brunswick, the AMS lineations are at ~20° counterclockwise to the strike of the fold axes. Pretectonic stable characteristic remanent magnetizations (ChRM) were determined in seven sites. A counterclockwise rotation (21.2° ± 9.2°) is documented by ChRM data from four sites near the hinge of the belt in Península Brunswick and near Canal Whiteside while there is no evidence of rotation near the nearly E-W oriented Vicuña thrust within Tierra del Fuego. The curved shape of the Cenozoic Magallanes FTB is not related to vertical axis rotation, and thus, the Magallanes FTB can be considered as a primary arc.