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As Sus scrofa is an invasive species in South America, it may have a significant impact on biodiversity. Evaluating this threat requires reliable data, and population density can serve as a critical measure. However, such data is currently lacking for the southern Andes region. To address this gap, we monitored wild boar density in the Villarrica National Park, located in the Andes of south-central Chile. This study area is notable not only for its challenging climatic conditions but also for its endangered Araucaria araucana forest, which provides abundant food resources during autumn seed fall. The density calculated for the entire study period was 1.4 individuals/km 2 , with no significant variation between cold and warm seasons. The encounter rate showed strongly monthly variations. Given that this represents the first density estimate for wild boar in this region, our findings emphasize the need for continued monitoring, particularly due to the potential threat to the ecosystem and the already endangered Araucaria forest., Competing Interests: The authors declare there are no competing interests., (©2025 Skewes et al.)

Abstract: The southern Patagonian Andes constitute the narrow, high-latitude end of the Andean orogen belt in South America, where inherited basin paleogeography, subduction processes, retroarc crustal thickening, and late Cenozoic glaciation have collectively influenced their unusual tectonic and physiographic evolution. New zircon and apatite (U–Th)/He thermochronology from the Patagonian Andes between 50°30′ and 51°30′S suggest concentrated exhumation across the retroarc (leeward) side of the orogen since early Miocene time. Zircon (U–Th)/He (ZHe) ages range from 44 to 10 Ma; oldest ages are recorded in the Patagonian batholith and along the far eastern frontal foreland monocline. Regionally-uniform ZHe ages between 22 and 18Ma, located across a ∼75km wide-zone of the Patagonian retroarc thrust-belt indicate widespread early Miocene cooling through the ZHe partial retention zone. Mesozoic sedimentary and volcanic rocks in this region have been exhumed from at least 5 to 6km depths. Early Miocene denudation of the thrust-belt, deformation, and increased foreland sedimentation rates coincided with opening of the Scotia Sea, suggesting a causal response of the foreland to changes in plate dynamics. The apatite (U–Th)/He (AHe) ages from a similar region range from 11 to 3Ma; the youngest ages (6–3Ma) are spatially clustered within the more deeply-exhumed central thrust domain. We interpret these AHe ages to record >1–2km of erosional denudation associated with late Cenozoic glaciation and fluvioglacial processes in Patagonia beginning ca. 7Ma. Zircon results indicate that since ca. 22Ma, long-term exhumation rates have been highest across the western and central thrust domains (0.22–0.37mmyr−1), and significantly lower along the eastern thrust front (0.10–0.17mmyr−1). Since ∼7Ma, apatite results from these same regions suggest comparable and slightly higher denudation rates (0.14–0.46mmyr−1), particularly within the eastern thrust domain, consistent with efficient erosional processes acting in the retroarc region. These results from the Patagonian retroarc region, particularly the predominance of <7–4Ma AHe ages, provide a new understanding for regional orogenic erosion models that are largely based on existing data from the windward regions. We suggest that retroarc denudation was enhanced by widespread Miocene structural uplift and unroofing of the fine-grained siliciclastic rocks of the marine Cretaceous Magallanes/Austral foreland basin. Furthermore, its location at the southern tip of the orogen, may have allowed additional moisture to reach the leeward side, leading to sustained late Cenozoic erosional denudation. [Copyright &y& Elsevier]

Abstract: Granitic and mafic magma pulses were sequentially accreted in the spectacularly exposed shallow crustal Torres del Paine laccolith, in southern Patagonia. This 12.5Ma pluton forms a composite intrusion with a subvertical feeding system in the west and a laccolith in the east. A key unknown in the formation of sill complexes is how individual magma pulses are assembled over time and the geometry and localization of their feeding system. High resolution zircon CA-ID-TIMS U–Pb dating shows that the laccolith grew first by under-accretion of granitic sills over 90±30ka, linked to a ‘sheet-like’ feeding system, followed by underplating of mafic sills after ~20ka of quiescence. In the mafic sills complex, individual sills were injected by over-accretion during 41±11ka. Our data show that successive granitic and mafic magmas emplacement generated a volume of ~88km3 in 162±11ka. [Copyright &y& Elsevier]

Abstract: The Canal de las Montañas Shear Zone (CMSZ), southern Patagonian Andes (51–52°S), is a low-grade mylonite belt generated from felsic ignimbritic, pelitic and basaltic protoliths of the Late Jurassic–Early Cretaceous Rocas Verdes basin. The different types of rock fabrics across the CMSZ are thought to be associated with relatively intermediate and high strain conditions, characterized by the development of a narrow western belt of S–C´-type mylonites and phyllonites interpreted as the metamorphic sole thrust of the Sarmiento Ophiolitic Complex. Highly strained rocks of the CMSZ display a reverse, continent-ward tectonic transport, with a minor dextral component of shearing. Transitional pumpellyite–actinolite and upper greenschist facies metamorphic conditions at ca. 5–6kbar and 230–260°C indicate that the primary shearing event occurred in a subduction zone setting. In-situ 40Ar/39Ar laserprobe chronology yielded ages of ca. 85Ma on syntectonic phengite which are interpreted as representing cooling synchronous with mica crystallization during the main compressive deformational event. The 78–81Ma U–Pb zircon crystallization ages of cross-cutting plutonic and hypabyssal rocks and 40Ar/39Ar amphibole age of ca.79Ma from lamprophyric dikes within the fold-thrust belt constrain an upper age limit of the ophiolite tectonic emplacement deformation. [Copyright &y& Elsevier]

Abstract: This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west–east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes. [Copyright &y& Elsevier]

The kinematic evolution of the enigmatic arc-shaped southernmost Andes of Patagonia and Tierra del Fuego has been a subject of debate for most of the past century. We compared the results from analog sandbox experiments with the tectonic evolution and actual configuration of the mountain chain in order to elucidate whether oroclinal bending took place during the Tertiary, or if the southernmost Andes have been a curved orogen since at least Late Cretaceous time. Experiments simulating oroclinal rotation produced strong along-strike variations in shortening and failed to account for structural data compiled from the Fuegian Andes. Results from experiments simulating an L-shaped, concave-to-foreland indenter were in agreement with the known Tertiary structural evolution of the southernmost Andes. The diachronicity of principal shortening events previously recognized in Patagonia and Tierra del Fuego could only be reproduced by moving the indenter in two successive orthogonal directions: first approximately northward to form the Fuegian fold-and-thrust belt, and then approximately eastward to propagate thrusting in the Patagonian Andes. This two-phase evolution is consistent with a recorded change in the convergence direction of the Farallon-Nazca plate that occurred at ca. 27 Ma. [ABSTRACT FROM AUTHOR]

This study examines the response of a forearc to the increase in sediment flux to the trench caused by the onset of glacial denudation in the Patagonian Andes. We investigated shelf-coastal basins in south-central Chile, which generally comprise Eocene-early Miocene nearshore facies overlain by late Miocene-early Pliocene deep-water siltstones and by late Pliocene-Quaternary nearshore deposits. Seismic profiles and coastal exposures reveal Eocene-early Pliocene extension followed by ongoing late Pliocene compression evidenced from growth strata adjacent to seismically active reverse faults. The onset of major global cooling ca. 6 Ma triggered glacial denudation in the uplifted high Andes. Exhumed material transported along the steep and humid Andean western slope increased trench sedimentation rates and caused continuous accretion and subduction of terrigenous material. We interpret forearc basin inversion as a response to a decrease in slope and basal friction of the wedge caused by frontal accretion and subduction of water-rich material, respectively, in order to reach a critical taper. This process lifted the shelf ∼1.5 km during the middle Pliocene. The Juan Fernández Ridge and Chile Rise confined >2 km trench fill between 45 and 34°S, limiting accretion and basin inversion. Glacial age trench fill and the steady decrease in plate convergence rate shifted this segment of the margin from erosive to accretionary during the Pliocene. [ABSTRACT FROM AUTHOR]

Extensive fieldwork carried out in the inner sectors of the Cordillera Patagónica has revealed evidence of alternate of periods of crustal extension and orogen formation since the Jurassic. The Patagonian lithosphere was extended during the Mesozoic and fractured and collapsed into numerous depocenters within the arc and retroarc. The last pulse of extension during this period occurred in the Early Cretaceous, related to a series of Pacific transgressions that formed the embayment of the Río Mayo basin, north of the Austral basin. The Río Mayo basin is part of a widespread Early Cretaceous synrift episode found throughout the Patagonian region between 155 and 140 Ma. The last part of this rifting episode, between 140 and 125 Ma, was spatially more limited, restricted to the arc and inner retroarc.The area of extension can be related to an early Paleozoic suture between the Somuncura Massif and the hanging wall of the Deseado Massif. The correct identification of this suture zone helps delimit distinctive volcanic provinces, as well as metallogenic ore districts.Thermal subsidence ceased as a consequence of a sudden tectonic inversion related to a major lithospheric reorganization at 120 Ma, during the breakup of southern Gondwana. The closure of the small Río Mayo intra-arc-retroarc basin occurred as a result of a fold-and-thrust belt, mainly by tectonic inversion of previous normal faults, and was partially related to thin-skinned deformation. The emplacement of the Eastern Patagonian batholith between 100 and 80 Ma destroyed the inner sectors of the fold-and-thrust belt. During this time, the collapse of the inner sectors allowed for the development of a second, more limited intra-arc basin. The orogenic wedge grew through the inversion of progressively deeper decollements and out-of-sequence thrusts and lasted until the Late Paleogene, with a period of probable quiescence during the highly oblique subduction of the Aluk (Phoenix) Plate in the early Paleogene. [Copyright &y& Elsevier]

Retroarc foreland basins are important archives of continental arc magmatism and upper plate deformational processes that control the evolution of continental lithosphere. However, resolving source areas in foreland basin infill dominated from mixed mafic and recycled sediment using conventional methods such as detrital zircon geochronology poses a challenge to thorough analysis due to lower zircon fertility and the higher susceptibility to weathering of mafic lithologies. Here, we integrate whole rock 40Ar/39Ar geochronology and major and trace element geochemistry data from volcanic clasts from the lower Miocene infill of the Magallanes-Austral Basin and local Sierra Baguales intrusive rocks to understand the distribution of mafic sources and Neogene changes in arc magmatism in between multiple ridge subduction events in the southern Patagonian Andes. Potential source areas for the coarse-grained mafic detritus include the Eocene plateau lavas, the Late Jurassic-Miocene Southern Patagonian batholith, and the Late Jurassic Sarmiento Ophiolitic Complex. Published detrital zircon U-Pb age spectra suggest that all three sources are viable contributors to the basin, though the paucity of Jurassic and Eocene zircons preclude these as major sources. Here, new 40Ar/39Ar dating of the volcanic clasts from the early Miocene Río Guillermo Formation reveals latest Oligocene to early Miocene eruptive ages (∼25-22 Ma), indicating syndepositional eruption with the ancestral Río Guillermo fluvial sedimentation. A single dated clast yields a Late Cretaceous age (∼102 Ma). The clasts are dominantly basaltic andesite with Ba/Ta ∼500-1000, La/Ta >20, and Ba/La >15, indicating an arc-derived melt source. We propose that the clasts record a Miocene mafic continental arc source area in the Patagonian Andes, which has since been removed by erosion and is thus sparsely represented in the batholith. Furthermore, we suggest that this early Miocene phase of arc volcanism, which postdates Eocene and Oligocene backarc magmatism and pre-dates middle Miocene to recent Chile Ridge backarc magmatism, reflects a return to normal arc volcanism along the Patagonian margin following a cessation due to ridge subduction and subsequent slab window migration. New geochemistry and 40Ar/39Ar data from a basaltic dike in the Sierra Baguales, which crosscuts the Cenozoic stratigraphic section, records plateau magmatism ∼16 Ma associated with incipient Chile Ridge slab window volcanism. [ABSTRACT FROM AUTHOR]