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Goeppertella has been postulated as a monophyletic group, whose precise position within the Gleichenoid families Dipteriaceae and Matoniaceae, remains poorly understood. Previously described Goeppertella specimens are based on frond fragments and its fertile morphology is represented by a few, poorly preserved specimens. We describe a new species based on the largest collection of fertile specimens known to date and discuss the evolutionary history of the genus based on the additional reproductive characters provided by the fossils described. Plant impressions were collected in Early Jurassic sediments of Patagonia, Argentina. The specimens were described, and silicone rubber casts were developed to examine in detail vegetative and reproductive features. The new species was compared with other Goeppertella species. Finally, a backbone analysis was performed in the context of a previously published combined matrix of Dipteridaceae, using the maximum parsimony criterion. The new species is described based on a combination of features that have not been previously reported. The vegetative morphology shows affinities with most fossil and extant Dipteriaceae, contrasting with the reproductive morphology which is more comparable with the scarce number of fossil dipteridaceous forms and it is more spread in the sister family, Matoniaceae. The backbone analysis indicates that the position of the new species vary among different positions among Dipteridaceae and Matoniaceae. Additional analyses, discriminating the signal of reproductive and vegetative character, are provided to discuss the base of this uncertainty. We consider Goeppertella as a member of the family Dipteridaceae since we interpret most shared features with Matoniaceae as plesiomorphic conditions for the family. In contrast, most shared features with Dipteridaceae represent apomorphies for the group. Thus, Goeppertella would represent an early diverging genus in Dipteridaceae, considering the venation characters as the most important in order to define the family. [ABSTRACT FROM AUTHOR]

Osteological knowledge of the sauropod dinosaur Ligabuesaurus leanzai is increased by the description of new postcranial elements assigned to the holotype MCF-PVPH-233. Furthermore, a newly referred specimen, MCF-PVPH-228, is recognized after a detailed revision of the abundant sauropod material collected from the Lohan Cura Formation outcrops in the Cerro de los Leones locality (southern Neuquén Basin, Patagonia, Argentina). Recent laboratory preparation and fieldwork allowed us to recognize several new morphological features of the pectoral and pelvic girdles and the cervical and caudal anatomy. Thus, a new diagnosis of Ligabuesaurus is proposed that includes new autapomorphies and a unique combination of features. A phylogenetic analysis based on this new material recovers Ligabuesaurus as a non-titanosaurian somphospondylan, more derived than Sauroposeidon. Therefore, we discuss the palaeobiogeographical implications for the diversification and distribution of South American somphospondylans, especially in the Neuquén Basin, which are closely related to the early stages of evolution of Titanosauria. In this context, Ligabuesaurus represents one of the more complete Early Cretaceous Titanosauriformes and the earliest non-titanosaurian somphospondylan of South America. Finally, the new information on Ligabuesaurus contributes not only to reconstruction of the sauropod faunal composition of south-western Gondwana, but also sheds light on the early stages and emergence of titanosaurians. [ABSTRACT FROM AUTHOR]

We present a systematic review of the extinct species included in the family Caenolestidae, one of the few South American metatherian groups that has survived to the present. We perform a cladistic analysis based on a data matrix consisting of all extant and extinct species that have been referred to this family, 100 morphological characters and two sets of molecular data (cytochrome b and cytochrome c oxidase I). Morphological and molecular data were analysed separately and in combination, under maximum parsimony and maximum likelihood methods. As a result, caenolestids are recovered as a monophyletic group within which we formally recognize three new taxa: Caenolestoides miocaenicus gen. & sp. nov. Gaimanlestes pascuali gen. & sp. nov. and Stilotherium parvum sp. nov. from the Early Miocene of Patagonia, Argentina. Stilotherium is the earliest diverging lineage of caenolestids followed by Gaimanlestes , while C. miocaenicus was recovered as the extinct species most closely related to extant caenolestids. [ABSTRACT FROM AUTHOR]

Wild boar (Sus scrofa) is one of the most damaging invasive species in the world and can have a profound impact on the distribution of native species. Nevertheless, there still are limitations on the species' current fine-scale spatial information, which is needed to develop effective management measures. Here, we used Species Distribution Models (SDMs) and niche overlap analysis to estimate potential conflict areas between the wild boar and the native southern pudu (Pudu puda), which is a bioindicator of the forest conservation status within the Nahuel Huapi National Park (NHNP), Argentina. The two species' environmental niche overlaps by 40%, which results in a wide geographical overlap between wild boar and pudu distributions. The distribution model predicted that the wild boar potential distribution occupies 22% of the national park and overlaps up to 67% with the pudu distribution, which in turn occupies 20% of the park. Based on our models, we classified 12% of the park as extreme management priority areas, because both species are present. High priority areas, where wild boars have the potential to invade but will not overlap with pudu populations, represent 10% of the park. Medium priority areas, where wild boars do not threaten pudu populations, and low priority areas, with no potential presence of either species, are 8% and 68%, respectively. The results of this study show how SDMs developed at local scales can support the management and monitoring of native and invasive species and help guide the allocation of efforts and resources for management actions focused on protected areas. [ABSTRACT FROM AUTHOR]

This paper discusses the general atmospheric circulation over Patagonia on the basis of the principal palaeoclimate forcings: continental drift, orography, variations in the greenhouse gases in the Earth's atmosphere, evolution of the atmosphere and the oceans, changes in the orbit of the Earth, albedo feedbacks, and the land surface. These processes affect climate on time scales of millions to hundreds of thousands of years. Additionally, orbital forcing has had a major influence on climate during the Quaternary. The palaeo-atmospheric circulation of Patagonia is analyzed for the Early to Late Jurassic, the Cretaceous, the Late Palaeocene-Eocene Thermal Maximum, the Tortonian-Oligocene cooling, the Pliocene, the Quaternary including the Last Glacial Maximum, the Holocene Optimum, and the last millennium changes. Alternative palaeo-atmospheric circulations from climatic modelling scenarios through the ages are reviewed and compared with proxy data. Detailed and updated reference information on the topics analyzed is also provided. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, , 229-249. Este trabajo discute la circulación general de la atmósfera en la Patagonia. Se han explicado los principales forzantes del palaeoclima: deriva continental, orografía, variaciones en los gases de invernadero de la atmósfera terrestre, evolución de la atmósfera y los océanos, cambios orbitales, retroalimentación debida al albedo y las condiciones generales de la superficie terrestre. Estos parámetros afectan el clima en escalas temporales de millones a cientos de miles de años, así como los forzantes orbitales dominaron los cambios climáticos durante el Cuaternario. Las palaeo-circulaciones de la atmósfera sobre Patagonia son analizadas para el Jurásico Temprano y Tardío, el Cretácico, el Máximo Termal del Palaeoceno Tardío- Eoceno, el enfriamiento del Tortoniano- Oligoceno, el Plioceno, y el Cuaternario incluyendo el Último Máximo Glacial (UMG), el Óptimo del Holoceno y los cambios del último milenio. Las palaeo-circulaciones atmosféricas alternativas a través del tiempo a partir de escenarios de modelos climáticos son revisadas y comparadas con proxy datos. Una extensiva lista de referencias provee información detallada y actualizada (Noviembre del 2010) sobre los tópicos analizados en esta publicación. [ABSTRACT FROM AUTHOR]

We performed an integrated phylogeographical and palaeoclimatic study of an early-diverging member of Asteraceae, Duseniella patagonica , endemic to Argentina. Chloroplast and nuclear markers were sequenced from 106 individuals belonging to 20 populations throughout the species range. We analysed genetic spatial distribution, diversity and structure, tested for range expansion, estimated divergence times, reconstructed ancestral areas and modelled present and past species distributions based on climatic data. Duseniella diverged from its sister genera during the Late/Middle Miocene. Its ancestral area included southern Monte plus eastern and central Patagonia. A vicariant event separated Monte and Patagonian clades during the Plio-Pleistocene. This would have involved unfavourable climate, soil, elevation, volcanism and/or other geomorphological processes between 40 and 43.5°S, in the sourroundings of the Somuncura plateau. Each clade possesses its own haplotypes and nucleotypes. Two populations, one in southern Monte and the other in eastern Patagonia, contain the highest diversity and exclusive haplotypes, representing hypothetical ancestral refugia. Northern Monte and southern Patagonian populations show low to null genetic diversity, being the most recently colonized areas. Climatic models indicate that winter temperature influenced the distribution of Duseniella , with an increase in probability of occurrence during colder periods, thus enabling diversification during glacial episodes. [ABSTRACT FROM AUTHOR]

The Puyehue-Cordón Caulle eruption of 4 June 2011 dispersed about 100 million tonnes of pyroclastic materials resulting in ash accumulations of 30 cm depth on the Patagonian steppe, an area occupied by several lizard species. Herein we analysed, by experimental trials, the effects of ash and slope on running performance of two endemic and vulnerable species, Phymaturus excelsus and Phymaturus sinervoi, restricted to volcanic rock outcrops in Patagonia. We also determined the effect of ash fall on body condition by comparing the same populations before and after the volcanic eruption. Locomotion of P. excelsus, adapted to rocky and steep outcrops, was more affected in a negative way by ash. In contrast, P. sinervoi, which lives in mixed habitats with flat rocks and sandy substrates, ran more slowly on the inclined surface but was unaffected by ash, suggesting the two species are well adapted to the habitats they occupy. In spite of impacts of ash deposition on locomotion and potentially the feeding, reproduction and dispersal activity of P. excelsus, lizards captured 18 months after ash deposition showed improved body condition. Our study site for P. sinervoi received less ash deposition and hence body condition was similar before and after ash fall. We hypothesize that negative effects of ash on lizards were counteracted by competitive release; ash deposition caused an acute and significant increase in mortality of herbivorous competitors such as hares and sheep that feed upon the same flowers and fruits included in the Phymaturus diet. [ABSTRACT FROM AUTHOR]

Understanding the influence of landscape features on population differentiation is fundamental to evolutionary biology studies. We examined spatial patterns of genetic and phenotypic variability among Galaxias maculatus populations in a complex of four postglacial lakes in northwestern Patagonia differing in size and connectivity among them. A hierarchical Bayesian analysis grouped the individuals collected from eleven localities into three genetic clusters, first defining the populations of the two large lakes and separating the two small lakes in subsequent analysis. Genetic structuring was restricted within large lakes. It is known that the larval stage of Galaxias maculatus migrate to the limnetic zone of Patagonian lakes, possibly exerting an homogenizing effect on gene flow within lakes. Gene flow asymmetry and divergences among lakes can be explained by a combination of landscape characteristics and the presence of predators in the short streams that connect them. Individuals from the small lakes are the most divergent morphologically and genetically. The population in the isolated Redonda Lake, exhibits meristic differences as well, suggesting strong drift and environmental effects. This population is likely to have been isolated following the decline in water level of a paleolake that existed in this region approximately 13.2 kya BP. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••-••. [ABSTRACT FROM AUTHOR]

Herein we describe a new rhynchocephalian taxon from the Middle Jurassic of Patagonia, Argentina, representing the first Jurassic record of the group in South America. The new taxon, consisting of a complete dentary, is ascribed to Sphenodontia based on the presence of a deep and wide Meckelian groove, long posterior process, well-developed coronoid process, and acrodont teeth showing dental regionalization including successional, alternate hatchling, and additional series. This allocation is reinforced by a phylogenetic analysis that places the new taxon in a basal position within a clade of sphenodontians that excludes Diphydontosaurus and Planocephalosaurus. Additionally, the new taxon clusters within a Gondwanan clade with the Indian Godavarisaurus from the Jurassic Kota Formation, sharing the presence of recurved and relatively large posterior successional teeth that are ribbed and bear a peculiar anterolingual groove. This sister-group relationship is intriguing from a palaeobiogeographical viewpoint, as it suggests some degree of endemism during the initial stages of the breakup of Pangaea. We also discuss the ontogenetic stage of the new taxon and provide insights on the evolution of successional dentition in rhynchocephalians. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 342-360. [ABSTRACT FROM AUTHOR]

The Squamata, a vertebrate group that includes 'lizards', amphisbaenians and snakes, have inhabited Patagonia since the Late Cretaceous. The Mesozoic record comprises an iguanian, a scleroglossan and a great diversity of snakes that include, among others, the most primitive terrestrial forms. Snakes were also well diversified in the Palaeogene, with fossils of madtsoiids and boids (including the oldest record of the extant Boa) found as far south as 46°S, following the then dominant subtropical conditions in the region. The Palaeogene record comprises small, medium-sized and large forms. The only boids that persisted at the beginning of the Neogene are all small forms, suggesting colder temperatures than during the Palaeogene. The oldest South American 'colubrids' made their first appearance at this time, reaching latitudes south of the current Patagonian distribution (50°S). The Neogene record also includes the first occurrence of extant iguanians ( Pristidactylus and Liolaemus) and teiids ( Tupinambis). The latter reached the southernmost distribution of its evolutionary history during the Miocene. The distribution of boids, 'colubrids' and tupinambine teiids at higher latitudes than at present indicates warmer conditions during the Miocene. The uplift of the Patagonian Andes, followed by a decrease in temperature and an increase in desertification, induced a strong contraction in the distribution of tupinambine teiids to northern regions of Patagonia and even forced the complete disappearance of boids from this region. In contrast, these changes appear to have favoured the diversification of iguanian genera on both sides of the Patagonian Andes. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, , 441-457. Los Squamata ('lagartos', anfisbenas y serpientes) habitan la Patagonia desde el Cretácico tardío. El registro Mesozoico comprende un iguanio, un esclerogloso, y una gran diversidad de serpientes que incluye las formas terrestres más primitivas. Las serpientes estaban bien diversificadas durante el Paleógeno, con madtsoideos y boidos (incluyendo el registro más antiguo de la actual Boa) que alcanzaron altas latitudes (46 °S) siguiendo las condiciones subtropicales dominantes en la región. En contraste con el Paleógeno, que incluye formas pequeñas, medianas y grandes, los únicos boidos que persisten a comienzos del Neógeno son todas formas pequeñas que sugieren temperaturas más bajas que durante el Paleógeno. Los más antiguos 'colúbridos' sudamericanos son del Neógeno, cuando alcanzan latitudes (50 °S) al sur de su actual distribución. El registro del Neógeno también incluye la aparición de géneros actuales de lagartos iguanios ( Pristidactylus y Liolaemus) y teidos ( Tupinambis). Tupinambis alcanza la distribución más austral durante el Mioceno. La presencia de boidos, 'colúbridos' y teidos tupinambinos a mayores latitudes que en el presente indica condiciones más cálidas durante el Neógeno. El levantamiento de los Andes Patagónicos, seguido por la disminución de la temperatura y el incremento de la aridez, produjo una fuerte contracción en la distribución de teidos tupinambinos hacia el norte y la desaparición total de boidos de Patagonia. En contraste, estos cambios parecen haber favorecido la diversificación de los géneros de iguanios a ambos lados de los Andes. [ABSTRACT FROM AUTHOR]

Amoroso, R. O., Parma, A. M., Orensanz, J. M., and Gagliardini, D. A. 2011. Zooming the macroscope: medium-resolution remote sensing as a framework for the assessment of a small-scale fishery. – ICES Journal of Marine Science, 68: 696–706. Management of small-scale fisheries targeting sedentary stocks requires integration of information about processes operating and observable at different spatial and temporal scales. An integrated approach was developed with a scallop (Aequipecten tehuelchus) fishery in a small, semi-enclosed Patagonian basin as a demonstration case. Medium-resolution (30 m2) satellite (Landsat) data, used to identify circulation patterns, were combined with information from fishery surveys and recruitment experiments to link oceanographic processes with population dynamics. A frontal system splits San José Gulf (northern Argentine Patagonia) into two oceanographic domains (East and West) with distinct hydrographic regimes. In the West Domain, where circulation is highly advective and governed by turbulent vorticial fluxes, larval settlement on artificial collectors was insignificant over five reproductive seasons and no important scallop grounds were ever found. In the East Domain, where the main fishing grounds are, spat abundance varied between sites and years, but was always significant. Growth rates displayed strong clinal variation within the East Domain, decreasing clockwise away from the entrance to the Gulf and reflecting inferred circulation and gradual nutrient extinction. A physical mechanism capable of dispersing larvae over long distances towards the north, into the adjacent San Matias Gulf, was identified from Landsat images. The large-scale patterns of variation in growth, distribution, and recruitment of the Tehuelche scallop stock could not have been interpreted without an integrative approach to data assemblage and analysis, including satellite remote sensing. [ABSTRACT FROM PUBLISHER]

We carried out experiments to evaluate the effects of solar ultraviolet radiation (UVR; 280–400 nm) upon primary production of different natural phytoplankton assemblages (i.e. characteristic of a seasonal cycle) from Patagonia (Argentina) from January 2001 to January 2002. The short-term impact of UVR (i.e. measured as radiocarbon incorporation) was assessed by exposing samples to solar radiation under six radiation treatments: uncovered quartz tubes and tubes covered with different cut-off Schott filters (WG295, WG305, WG320, WG360), and Plexiglas UF-3 (cut-off at 400 nm), so that samples received radiation at five different intervals within the UVR in addition to photosynthetically active radiation (PAR), and only PAR, respectively. Phytoplankton composition and abundance allowed us to differentiate pre-bloom, bloom and post-bloom periods, with pre- and post-bloom samples characterized by small cells (e.g. flagellates <10 μm), whereas the bloom was dominated by large diatoms (∼50 μm). Absolute values of photosynthesis inhibition were lower during the bloom, but biological weighting functions (i.e. inhibition per unit energy) indicated that this assemblage was more sensitive to UVR (especially in the UV-B region, 280–320 nm) than those of the pre- and post-bloom periods. UV-A radiation (320–400 nm) accounted for most of the reduction in carbon incorporation (>60%), especially during the pre- and post-bloom periods. Most of the observed variability was inter-seasonal, although small intra-seasonal fluctuations were also observed. Our results indicate that the taxonomic composition and cellular size are especially important when addressing UVR effects upon these assemblages. However, other factors such as mixing can also contribute to the variability in responses to UVR. [ABSTRACT FROM AUTHOR]

Neogene plateau lavas in Patagonia, southern Argentina, east of the volcanic gap between the Southern and Austral Volcanic Zones at 46·5° and 49·5°S are linked with asthenospheric slab window processes associated with the collision of a Chile Ridge segment with the Chile Trench at 12 Ma. The strong ocean-island basalt (OIB)-like geochemical signatures (La/Ta <20; Ba/La <20; 87Sr/86Sr = 0·7035–0·7046; 143Nd/144Nd = 0·51290–0·51261; 206Pb/204Pb = 18·3–18·8; 207Pb/204Pb = 15·57–15·65; 208Pb/204Pb = 38·4–38·7) of these Patagonian slab window lavas contrast with the mid-ocean ridge basalt (MORB)-like, depleted mantle signatures of slab window lavas elsewhere in the Cordillera (e.g. Antarctic Peninsula; Baja California). The Patagonian lavas can be divided into a voluminous ∼12–5 Ma, tholeiitic main-plateau sequence (48–55% SiO2; 4–5% Na2O + K2O) and a less voluminous ∼7–2 Ma alkaline post-plateau sequence (43–49% SiO2; 5–8% Na2O + K2O). Moderately high FeOT (9–11%), and low heavy rare earth element (HREE), Y, and Sc concentrations in all lavas are consistent with melt generation just below the garnet–spinel transition at a depth of ∼70 km. The main-plateau lavas from the western back-arc can be modeled by ∼10–15% partial melting of an OIB-like asthenospheric mantle source with additions from slab fluid–melt components coupled with crustal contamination (AFC). A three-stage petrogenetic model is envisaged: (1) decompression melting and source region contamination of an OIB-like subslab asthenospheric source by slab melts of the trailing edge of the subducted Nazca Plate; (2) minor contamination of slab window melts with arc components ‘stored’ in the supraslab mantle wedge and/or basal continental lithosphere; (3) further modification by addition of crustal components during magma ascent. The main-plateau lavas from the eastern back-arc can be modeled by ∼7% partial melting of the same asthenospheric source as the influence of arc components diminishes and the intensity of mantle upwelling into the slab window decreases. All post-plateau lavas can be modeled as 1–4% partial melts of the pristine OIB-like asthenospheric source in the widening slab window. [ABSTRACT FROM PUBLISHER]

Voluminous rhyolitic volcanism along the palaeo-Pacific margin of Gondwana was marked by three principal episodes of magmatism. The first of these ( V1) is essentially coincident with the main episode of Karoo–Ferrar magmatism at ∼184 Ma. A younger ( V2) episode occurred at ∼168 Ma, and a third episode ( V3) occurred in the interval 157–153 Ma. We evaluate the origin of V1 and V2 rhyolites from the Antarctic Peninsula using major and trace element and isotopic (Sr, Nd, O) data. An isotopically uniform (87Sr/86Sri ∼0·707; εNdi ∼ −3) andesite–dacite magma was generated as a result of anatexis of ‘Grenvillian age’ hydrous mafic lower crust, linked to earlier, arc-related underplating. The lower-crustal partial melts would have mixed with fractionated components of the mafic underplate, followed by subsequent storage and homogenization. Early Jurassic ( V1) rocks of the southern Antarctic Peninsula are interpreted as melts of upper-crustal paragneiss, which have mixed with the isotopically uniform magma in upper-crustal magma chambers. The V2 rhyolites are the result of assimilation–fractional crystallization of the isotopically uniform magma. This occurred in upper-crustal magma chambers involving assimilants with similar isotopic composition to that of the magma. A continental margin setting was crucial in developing hydrous, readily fusible lower crust. Lower-crustal anatexis was in response to mafic underplating associated with the Discovery–Shona–Bouvet group of plumes, thought to be responsible for the Karoo magmatic province. The progression (old to young) of volcanism from NE to SW in Patagonia and south to north in the Antarctic Peninsula is consistent with migration away from the mantle plumes towards the proto-Pacific margin of Gondwana during rifting and break-up. [ABSTRACT FROM PUBLISHER]

The toxic dinoflagellate Alexandrium tamarense and other dinoflagellate species were studied, along with water temperature and nutrient concentrations, from September 1995 to December 1998 in the Golfo Nuevo, Chubut, Argentina. Nutrient concentrations were low, showing a peak of high concentration in winter and a phase of depletion in late spring and summer. Dinoflagellates tended to be abundant during spring and summer, when Prorocentrum micans was the most important species. Other dinoflagellates were Pyrophacus horologium and Dinophysis acuminata. Ceratium tripos, C. fusus and C. horridum were present during the autumn, and a C. tripos peak up to 5.9 × 103 cell l–1 was observed in May 1997. Alexandrium tamarense showed strong interannual variation, the highest concentration being found in spring (September–October) 1995, with densities up to 15 × 103 cells l–1. The second A.tamarense peak was observed during October–November 1998 with maximal densities up to 5 × 103 cells l–1. Moderately high A. tamarense cyst densities, up to 300 cysts cm–3 of sediment, were found in the deep zone of the Golfo Nuevo basin. Among meteorolog-ical variables, increased late winter rain and higher solar radiation during spring may have influenced A. tamarense blooms. [ABSTRACT FROM PUBLISHER]

Spinel-facies mantle xenoliths occur in a diatreme cutting through the Neogene Southern Patagonia Plateau at Gobernador Gregores (Santa Cruz Province, Argentina). This plateau is in a back-arc position with respect to the Chile trench. Xenoliths differ in their whole-rock composition from other South America occurrences, having higher CaO/Al2O3 ratios and, in some samples, TiO2 enrichment, whereas the Na2O/Al2O3 variation range is similar. Three assemblages can be distinguished. Assemblage 1, in anhydrous protogranular lherzolites and harzburgites, contains clinopyroxene with a depleted major and trace element composition, indicating pre-metasomatic depletion processes. This assemblage fully recrystallized to Assemblage 2 (amphibole ± phlogopite ± Cl-apatite-bearing) during a metasomatic episode. This causes clinopyroxene to acquire geochemical characteristics often attributed to carbonate-melt metasomatism. Noticeably, amphibole is markedly enriched in Nb (up to 298 ppm), especially when depleted in Ti. A further event, related to decompression during xenolith uplift to the surface, induces closed-system (perhaps with the exception of CO2 addition) disequilibrium melting of Assemblage 2, dominantly of amphibole. It is found in pockets (where amphibole is a residual phase) consisting of Na–Si-rich glass and carbonate (Mg-rich calcite) drops, and in veins originating from the pockets (Assemblage 3). Euhedral olivine, clinopyroxene and spinel crystallize only in the silicate glass. So do new, euhedral apatite crystals when glass is in contact with previous Assemblage 2 apatite. Textural evidence and comparison with experimental work suggest that silicate glass and carbonates are the result of unmixing of a former homogeneous melt. Because of the different flow rates of carbonate and silicate melt, the xenoliths become enriched in carbonate, which is found in the veins during their migration. Thus, the high CaO/Al2O3 ratio of whole rocks provides inconclusive evidence of carbonatite metasomatism. This factor, and other minor deviations from the expected results of carbonatite metasomatism, lead us to hypothesize an aqueous, Cl-rich fluid, possibly slab derived, as an alternative agent. Amphibole, resulting from reactive porous flow of this agent in the mantle, could fully explain the observed geochemical features, as indicated by estimates of its partition coefficients. [ABSTRACT FROM PUBLISHER]

New SHRIMP U–Pb zircon, Rb–Sr whole-rock, and 40Ar–39Ar data are presented for the Jurassic silicic volcanic rocks and related granitoids of Patagonia and the Antarctic Peninsula. U–Pb is the only reliable method for dating crystallization in these rocks; Rb–Sr is prone to hydrothermal resetting and Ar–Ar is additionally affected by initial excess 40Ar. Volcanism spanned more than 30 My, but three episodes are defined on the basis of peak activity: V1 (188–178 Ma), V2 (172–162 Ma) and V3 (157–153 Ma). The first essentially coincides with the Karoo–Ferrar mafic magmatism of South Africa, Antarctica and Tasmania. The silicic products of V1 are lower-crustal melts that have incorporated upper-crustal material. The geochemistry of V2 and V3 ignimbrites is more characteristic of destructive plate margins, but the presence of inherited zircon still points to a crustal source. The pattern of volcanism corresponds in space and in time to migration away from the Karoo mantle plume towards the proto-Pacific margin of Gondwana during rifting and break-up. The heat required to initiate bulk crustal fusion may have been supplied by the spreading plume-head, but thinning of the crust during continental dispersion would also have facilitated anatexis. [ABSTRACT FROM PUBLISHER]

Prahuaniyeu, located on the NW margin of the Somoncura Large Igneous Province in northern Patagonia, is one of two known localities in Argentina where mantle-derived garnet- and spinel-bearing peridotites occur associated with alkali basalts; the other locality is the Pali Aike volcanic field of southern Patagonia. Most of the Prahuaniyeu garnet-bearing peridotites are fertile in terms of their Al2O3 and CaO contents, whereas the spinel-bearing peridotites cover a wide range from fertile to depleted compositions. Whole-rock light rare earth element (LREE) enrichment in the garnet-bearing peridotites and partly in the spinel-peridotites is consistent with intergranular percolation of the host basalt melt, as hydrous phases are not present and the clinopyroxenes and garnets are not enriched in LREE. Lack of slab-derived component(s) in the metasomatic products rules out the participation of a subducted slab in the generation of these basalts. In situ clinopyroxene analyses suggest that a group of spinel-peridotites experienced cryptic metasomatism by carbonatitic melts. Non-metasomatized garnet- and spinel-peridotites have experienced fractional melting ranging from 1 to 3% and from 5 to 12%, respectively. The Prahuaniyeu xenoliths lie on an elevated geotherm (high temperatures at low pressure) implying convective heat transport. The two most fertile samples, which indicate apparent internal ‘ages’ between c. 10 and 30 Ma for the sub-Prahuaniyeu lithospheric mantle, suggest resetting of the Sm–Nd isotopic system under a high-temperature regime and most probably reflect closure of the system following this ‘high-T event’, which can be related to extensive magmatic activity within the Somoncura province, starting in the Eocene and finishing in the Miocene. [ABSTRACT FROM AUTHOR]