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<jats:title>Abstract</jats:title><jats:p>The distribution of metamorphic rocks in the Antarctic Peninsula region, new quantitative peak pressure–temperature data along the Antarctic Peninsula, and a literature review on the current knowledge of metamorphic conditions in the Antarctic Peninsula region have been compiled into a single metamorphic map. The pressure–temperature data for the Antarctic Peninsula indicate (1) burial of supracrustal rocks to low to mid-crustal depth along the eastern and western side of the Antarctic Peninsula and on some islands adjacent to the western side of the peninsula; (2) uplift of lower- to mid-crustal metamorphic rocks along major shear and fault zones; and (3) a reversed succession of metamorphic grades for the western domain of the Antarctic Peninsula region compared to the eastern domain along the Eastern Palmer Land Shear Zone (EPLSZ) of the Antarctic Peninsula. The metamorphic data are consistent with oblique convergence between Alexander Island (the Western Domain), Palmer Land (Central Domain) and the Gondwana margin (the Eastern Domain), supporting a model of (1) exhumation and shearing of the higher pressure rocks from central western (up to 9.4 kbar) and from northeast (7 kbar to 9 kbar) Palmer Land, (2) the exhumation and shearing of low to medium pressure rocks in western Palmer Land and along the Eastern Palmer Land Shear Zone, and (3) shallow burial and subsequent exhumation of sediments of the Gondwana margin along the Eastern Palmer Land Shear Zone. Based on the high-amphibolite grade rocks exposed in central western Palmer Land, our data also support earlier suggestions that the Eastern Palmer Land Shear Zone is the surface expression of a northwest- to west-dipping, deep-level, high-temperature crustal shear zone extending below the western part of the Central Domain of the Antarctic Peninsula.</jats:p>

<jats:title>Abstract</jats:title><jats:p>This work characterizes Late Cretaceous calc-alkaline volcanic rocks in Gastre, Northern Patagonia, Argentina. These newly found porphyritic rocks bear an <jats:sup>40</jats:sup>Ar–<jats:sup>39</jats:sup>Ar amphibole age of ~ 74–76 Ma, a subduction-type geochemical signature and a deep, garnet-bearing source. Extruded in a stage of low magmatic activity in the Northern Patagonian Andes (~ 41–44° S), they could represent an eastward migration of the Late Cretaceous magmatic arc that was associated with a regional compressive deformational stage in the South American margin.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Metamorphic core complexes (MCCs) are interpreted as domal structures exposing ductile deformed high-grade metamorphic rocks in the core underlying a ductile-to-brittle high-strain detachment that experienced tens of kilometres of normal sense displacement in response to lithospheric extension. Extension is supposedly the driving force that has governed exhumation. However, numerous core complexes, notably Himalayan, Karakoram and Pamir domes, occur in wholly compressional environments and are not related to lithospheric extension. We suggest that many MCCs previously thought to form during extension are instead related to compressional tectonics. Pressures of kyanite-and sillimanite-grade rocks in the cores of many of these domes are <jats:italic>c.</jats:italic> 10–14 kbar, approximating to exhumation from depths of <jats:italic>c.</jats:italic> 35–45 km, too great to be accounted for solely by isostatic uplift. The evolution of high-grade metamorphic rocks is driven by crustal thickening, shortening, regional Barrovian metamorphism, isoclinal folding and ductile shear in a compressional tectonic setting prior to regional extension. Extensional fabrics commonly associated with all these core complexes result from reverse flow along an orogenic channel (channel flow) following peak metamorphism beneath a passive roof stretching fault. In Naxos, low-angle normal faults associated with regional Aegean extension cut earlier formed compressional folds and metamorphic fabrics related to crustal shortening and thickening. The fact that low-angle normal faults exist in both extensional and compressional tectonic settings, and can actively slip at low angles (&lt; 30°), suggests that a re-evaluation of the Andersonian mechanical theory that requires normal faults to form and slip only at high angles (<jats:italic>c.</jats:italic> 60°) is needed.</jats:p>

<jats:title>Abstract</jats:title><jats:p>During the Late Cretaceous Andean orogeny, the compressive deformation associated with the shallowing of the subducting slab caused the development of the arc-related igneous rocks known as the Naunauco Belt. This study presents petrographic, mineralogical and anisotropy of magnetic susceptibility data for the Varvarco Intrusives (the Varvarco Tonalite, Butalón Tonalite and Radales Aplite), which crop out in the Cordillera del Viento, Neuquén Province, Argentina. The assembly of plutons was formed by mafic magma episodic injection. Amphibole and biotite compositions suggest that the Varvarco Tonalite is related to calc-alkaline, I-type magmas, typical of subduction environments. Different geothermobarometers based on amphibole and plagioclase compositions for the Varvarco Tonalite suggest shallow emplacement conditions (∼2–3 kbar, equivalent to ∼12 km depth). Apatite fission-track analyses give exhumation ages of 67.5 ± 8 Ma for the Varvarco Tonalite and 50.3 ± 5.9 Ma for the Butalón Tonalite. A calculated continuous fast exhumation rate of at least 330 °C Ma<jats:sup>−1</jats:sup> is consistent with the shallow emplacement conditions, textural data and geobarometric estimations. In agreement with the thermal profile, the magmatic system was exhumed by ∼12 km within <jats:italic>c</jats:italic>. 2.1 Ma implying a geothermal gradient of ∼62.5 °C km<jats:sup>−1</jats:sup>. The last step of exhumation occurred between ∼65.3 and 56.9 Ma. The magmatic fabrics observed in the studied plutons reflect mostly magma chamber processes. The Varvarco Intrusives represent satellite calc-alkaline plutons of the North Patagonian Batholith which were emplaced syn- to post-tectonically with respect to a major deformation stage of the Southern Central Andes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We conducted a U–Pb–Hf isotope study on zircon crystals from ignimbrites of the Changhsingian to Olenekian (253–248 Ma) Los Menucos Basin in the North Patagonian Massif (NPM), Argentina, in order to evaluate the age and petrogenesis of the magmas. Additionally, a compilation of whole-rock geochemistry and U–Pb–Hf in zircon isotope data for the Permian to Middle Triassic rocks of the NPM, for comparison with our data, was made to assess whether Patagonia would have been an exotic terrane accreted to SW Gondwana during the late Palaeozoic. We interpret the available U–Pb–Hf data to suggest that northern Patagonia experienced eastward arc expansion from the early Permian, about 273 Ma ago. This ∼820 km arc expansion event involved crustal shortening and magmatism with high-silica adakitic affinity, resulting in Hf-isotopic pull-down. At 253 Ma, slab steepening became associated with the coeval emplacement of ignimbrites of the Los Menucos Basin, which involved post-orogenic to intraplate magmatism. During the Middle Triassic, a slab break-off triggered uplift and basaltic underplating, promoting the emplacement of dike swarms with C-type adakitic signature at 246–244 Ma. The Hf isotope data for SW Gondwana for the same period indicate distinct trends that are explained here by differential slab roll-back since the Guadalupian, in a slab-tearing setting. Therefore, Permian to Middle Triassic magmatism is interpreted as having been associated with an eastward-directed proto-Pacific subduction system, which ultimately supports an autochthonous origin for Patagonia.</jats:p>