Examinando por Autor "Angiboust, Samuel"
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Ítem Field report: Sailing around the exhumed roots of the Mesozoic Patagonian paleo-accretionary wedge (Diego de Almagro Island, Chile)(Elsevier B.V., 2018-09) Angiboust, Samuel; Muñoz, JesusWe undertook a boat expedition to explore the geological framework of a very remote, lesser-known island, in the Chilean Patagonia: the Diego de Almagro Island (latitude S51°33′). This uninhabited, ca. 400 km2 Island is one of the very rare exposures of the Mesozoic accretionary subduction complex along the Chilean margin. Unstable weather, strong winds, steep topography, and very dense vegetation make an on-land mission difficult. Careful preparation based on high-resolution satellite images is advised to optimize shore access and minimize risks of injury. Despite a relatively important degree of regional re-equilibration of metamorphic assemblages due to sluggish exhumation through the forearc crust, our results have shown that the island is composed of a nappe stack of ocean-floor derived slivers of meta-sedimentary units that exhibit very different pressure-temperature-time paths during burial by subduction under the Chilean margin and subsequent exhumation. These rocks are witness to a complex thermal evolution of the subduction zone between Jurassic and Cretaceous times from granulite facies to blueschist facies conditions as well as multiple episodes of accretion at ca. 35–40 km in depth for almost 100 Ma over the Mesozoic era. © 2018 China University of Geosciences (Beijing) and Peking UniversityÍtem Hot subduction in the middle Jurassic and partial melting of oceanic crust in Chilean Patagonia(Elsevier Inc., 2017-02) Angiboust, Samuel; Hyppolito, Thais; Glodny, Johannes; Cambeses, Aitor; Garcia-Casco, Antonio; Calderón, Mauricio; Juliani, CaetanoRare remnants of a Mesozoic subduction high pressure (HP) accretionary complex are exposed on Diego de Almagro Island in Chilean Patagonia. We herein focus on the Lazaro unit, a coherent slice of oceanic crust exposed on this island that has been first affected by high temperature (HT) metamorphism followed by a lower temperature deformation event (LT). Its Pressure-Temperature-time (P-T-t) evolution is reconstructed using field and petrographic observations, phase relations, thermobarometry and geochronology. Remnants of a primary amphibolite to HP granulite-facies event in mafic rocks comprising garnet (with ilmenite exsolutions), diopside, trondhjemitic melt, pargasite, plagioclase ± epidote are reported for the first time in neosomes, indicating peak P-T conditions of 1.1–1.3 GPa and c. 750 °C. This peak T paragenesis has been thoroughly overprinted by a phengite-chlorite-actinolite assemblage during isobaric cooling down to c. 450 °C. U-Pb dating of zircon metamorphic rims from a metasedimentary rock yielded a homogeneous age population of 162 ± 2 Ma for the HT event. Sm-Nd dating of two peritectic garnet-bearing samples yield ages of 163 ± 2 Ma and 163 ± 18 Ma for the HT event. Multi-mineral Rb-Sr dating of a metasedimentary rock overprinted by LT deformation suggests retrograde shearing between 120 and 80 Ma. Our results show that the HT event in the Lazaro unit took place at around 160–165 Ma, shortly before the onset of Patagonian Batholith emplacement. Partial melting of subducted oceanic crust reported in the Lazaro unit is related to the early stages of hot subduction along the Gondwana western margin. The Lazaro unit remained at c. 40 km depth along the subduction interface for > 80 Ma, recording the deformation and long-term cooling of the subduction channel environment until the upper Cretaceous. © 2016 International Association for Gondwana Research