ALBERT

Description: We studied the petrogenesis of mafic igneous rocks in the Famatinian arc in the western Sierra Famatina (NW Argentina), an Early Ordovician middle-crustal section in the proto-Andean margin of Gondwana. Mafic rock types consist of amphibolite, metagabbro, and gabbro, as well as pod- and dike-like bodies of gabbro to diorite composition. Field relations together with geochemical and isotopic data for the mafic rocks of the western Sierra de Famatina (at 29°S) define two contrasting suites, which can be correlated with similar assemblages noted in other parts of the orogen. Amphibolite, metagabbro, and gabbro bodies are mostly the oldest intrusive rocks (older than 480 Ma), with the host tonalite and post-tonalite mafic dikes being slightly younger. The older mafic suite is tholeiitic to calc-alkaline and isotopically evolved, except for most of the amphibolite samples. The younger suite is calc-alkaline, typically displaying subduction-related geochemical signatures, and it is isotopically more juvenile. Whole-rock chemical composition and isotopic analyses are compatible with a progressive mixing of different isotopic reservoirs. Pyroxenite (±garnet) was likely the dominant source of the older gabbroic magmas, whereas peridotite dominated in the source of the younger suite, implying that the mafic magma experienced a progressive shift toward more juvenile compositions though time (over 20 m.y.). Pyroxenite-derived melts could have been generated by lithospheric foundering followed by upwelling of primitive melts by adiabatic decompression of mantle wedge peridotite.

Description: Supposed or potential Devonian igneous rocks in the accretionary complex of southern Chile were investigated using sensitive high-resolution ion microprobe U–Pb dating of zircon, with Hf- and O-isotope analyses of selected grains. Ages of 384 ± 3 and 382 ± 2 Ma are confirmed for two igneous bodies (another having been previously dated at 397 ± 1 Ma). Detrital zircon ages in the host rocks, some associated with Devonian marine fossils, indicate maximum possible sedimentation ages of c . 330 – 385 Ma. Devonian ages of 391 ± 10 and 374 ± 3 Ma for plutonic rocks at the western edge of the North Patagonian Massif are somewhat older than those of orthogneisses in the western flank of the Andes near Chaitén (361 ± 7 and 364 ± 2 Ma). O and Hf isotopes indicate that the Devonian intrusions in the accretionary complex crystallized from mantle-derived magmas, whereas those in the North Patagonian Massif show a strong crustal influence, corresponding to oceanic and continental margin subduction environments of magma genesis, respectively. Devonian zircon provenance in the accretionary complex was from the North Patagonian Massif and not from the mantle-derived intrusions, suggesting that the accretionary complex formed an integral part of the Gondwana margin during Devonian–Carboniferous times. Supplementary material: Description of analytical methods and tables of isotope analytical data are available at http://doi.org/10.6084/m9.figshare.c.2336728 .

Description: : The Early Palaeozoic stratigraphy and tectonic history of the Eastern Sierras Pampeanas of central Argentina are complicated by metamorphism and deformation resulting from the Pampean (545–510 Ma) and Famatinian (490–440 Ma) orogenies. We report U–Pb sensitive high-resolution ion microprobe dating of detrital zircons in two metasedimentary successions exposed at Quebrada de La Cébila ( c . 28°45'S, 66°25'W): the Ambato and the La Cébila metamorphic complexes. The Ambato zircons record age peaks corresponding to Pampean (530 ± 10 Ma), Brasiliano ( c . 570 and c . 640 Ma), Grenville ( c . 950 to c . 1025 Ma) and minor Neoarchaean ages. Similar peaks are also apparent in the La Cébila sample but it additionally contains Palaeoproterozoic zircons ( c . 2.1 Ga) corresponding to the age of the Rio de la Plata craton, from which they are considered to have been sourced. Our interpretation is that the protolith of the Ambato complex was deposited prior to juxtaposition with the craton and is older than the Early Ordovician La Cébila metamorphic complex. We infer that the craton reached its current relative position in the Mid- to Late Cambrian, after the main Pampean tectonothermal event (530–520 Ma) and before deposition of the La Cébila protolith and the Achavil Formation (Sierra de Famatina), which contain comparable detrital zircon populations.

Description: A multidisciplinary study (U–Pb sensitive high-resolution ion microprobe geochronology, Hf and O isotopes in zircon, Sr and Nd isotopes in whole-rocks, as well as major and trace element geochemistry) has been carried out on granitoid samples from the area west of Valcheta, North Patagonian Massif, Argentina. These confirm the Cambrian age of the Tardugno Granodiorite (528 ± 4 Ma) and the Late Permian age of granites in the central part of the Yaminué complex (250 Ma). Together with petrological and structural information for the area, we consider a previously suggested idea that the Cambrian and Ordovician granites of northeastern Patagonia represent continuation of the Pampean and Famatinian orogenic belts of the Sierras Pampeanas, respectively. Our interpretation does not support the hypothesis that Patagonia was accreted in Late Palaeozoic times as a far-travelled terrane, originating in the Central Transantarctic Mountains, and the arguments for and against this idea are reviewed. A parautochthonous origin is preferred with no major ocean closure between the North Patagonian Massif and the Sierra de la Ventana fold belt. Supplementary material: U–Pb SHRIMP analytical data, geochemical analyses and sample global positioning system locations are available at www.geolsoc.org.uk/SUP18722 .

Description: The genesis of Permian magmatism in southern South America is actively debated, particularly in relation to the origin of Patagonia. U–Pb zircon ages of c. 255 Ma for igneous rocks from the basement of Tierra del Fuego are the first evidence for southerly prolongation of this magmatism. Zircon in these rocks has Hf t values 〈–1 and 18 O 〉 7.4, indicating recycling of Cambrian rocks. Permian granites in the north of the North Patagonian Massif record mantle-like 18 O magmatic input at c. 280 and 255 Ma, but reworking of upper crust between these two events, paralleling the recognized deformational history. In northwestern Patagonia, Early Permian granitic rocks have zircon with Hf t values ranging from +0.1 to –7.2, and 18 O 〉 6.2, suggesting continuity of the Permian magmatic belt along the western margin of South America farther north. Comparison with a sample from the Sierra de la Ventana suggests melting of similar crust on both sides of the Patagonia–South American hypothetical suture. These features, together with other geological considerations, are consistent with an autochthonous or parautochthonous origin of northern Patagonia and connection between southern Patagonia and the Antarctic Peninsula in late Palaeozoic time. Supplementary material: U–Pb SHRIMP, O and Hf analytical data are available at https://doi.org/10.6084/m9.figshare.c.3768710

Description: The Ellsworth-Whitmore Mountain terrane of central Antarctica was part of the early Paleozoic amalgamation of Gondwana, including a 13,000 m section of Cambrian–Permian sediments in the Ellsworth Mountains deposited on Grenville-age crust. The Jurassic breakup of Gondwana involved a regional, bimodal magmatic event during which the Ellsworth-Whitmore terrane was intruded by intraplate granites before translation of the terrane to its present location in central Antarctica. Five widely separated granitic plutons in the Ellsworth-Whitmore terrane were analyzed for their whole-rock geochemistry (X-ray fluorescence), Sr, Nd, and Pb isotopic compositions, and U-Pb zircon ages to investigate the origins of the terrane magmas and their relationships to mafic magmatism of the 183 Ma Karoo-Ferrar large igneous province (LIP). We report high-precision (±0.1 m.y.) isotope dilution–thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon ages from granitic rocks from the Whitmore Mountains (208.0 Ma), Nash Hills (177.4–177.3 Ma), Linck Nunatak (175.3 Ma), Pagano Nunatak (174.8 Ma), and the Pirrit Hills (174.3–173.9 Ma), and U-Pb sensitive high-resolution ion microprobe (SHRIMP) ages from the Whitmore Mountains (200 ± 5 Ma), Linck Nunatak (180 ± 4 Ma), Pagano Nunatak (174 ± 4 Ma), and the Pirrit Hills (168 ± 4 Ma). We then compared these results with existing K-Ar ages and Nd model ages, and used initial Sr, Nd, and Pb isotope ratios, combined with xenocrystic zircon U-Pb inheritance, to infer characteristics of the source(s) of the parent magmas. We conclude that the Jurassic plutons were not derived exclusively from crustal melts, but rather they are hybridized magmas composed of convecting mantle, subcontinental lithospheric mantle, and lower continental crustal contributions. The mantle contributions to the granites share isotopic similarities to the sources of other Jurassic LIP mafic magmas, including radiogenic 87 Sr/ 86 Sr (0.706–0.708), unradiogenic 143 Nd/ 144 Nd ( Nd 〈 –5), and Pb isotopes consistent with a low-µ source (where μ = 238 U/ 204 Pb). Isotopes and zircon xenocrysts point toward a crustal end member of predominantly Proterozoic provenance (0.5–1.0 Ga; Grenville crust), extending the trends illustrated by Ferrar mafic intrusive rocks, but contrasting with the inferred Archean crustal and/or lithospheric mantle contributions to some basalts of the Karoo sector of the LIP. The Ellsworth-Whitmore terrane granites are the result of mafic rocks underplating the hydrous crust, causing crustal melting, hybridization, and fractionation to produce granitic magmas that were eventually emplaced as post-Ferrar, within-plate melts at higher crustal levels as the Ellsworth-Whitmore terrane rifted off Gondwana (47°S) before migrating to its current position (82°S) in central Antarctica.

Description: Early Jurassic silicic volcanic rocks of the Chon Aike Province (V1: 187 – 182 Ma) are recognized from many localities in the southern Antarctic Peninsula and NE Patagonia and are essentially coeval with the extensive Karoo (182 Ma) and Ferrar (183 Ma) large igneous provinces of pre-breakup Gondwana. Until recently, plutonic rocks of this age were considered either rare in or absent from the Antarctic Peninsula batholith, which was thought to have been mainly constructed during the Middle Jurassic and the mid-Cretaceous. New U–Pb zircon geochronology from the Antarctic Peninsula and recently published U–Pb ages from elsewhere in the Peninsula and Patagonia are used to demonstrate the more widespread nature of Early Jurassic plutonism. Eight samples are dated here from the central and southern Antarctic Peninsula. They are all moderately to strongly foliated granitoids (tonalite, granite, granodiorite) and locally represent the crystalline basement. They yield ages in the range 188 – 181 Ma, which overlap with published ages of 185 – 180 Ma from granitoids from elsewhere on the Antarctic Peninsula and from the Subcordilleran plutonic belt of Patagonia (185 – 181 Ma). Whereas Early Jurassic plutons of the Subcordilleran plutonic belt of Patagonia are directly related to subduction processes along the proto-Pacific margin of Gondwana, coeval volcanic rocks of the Chon Aike Province are interpreted to be directly associated with extension and plume activity during the initial stages of Gondwana breakup. This indicates that subduction was continuing when Chon Aike Province volcanism started. The Early Jurassic plutonism on the Antarctic Peninsula is transitional between subduction-related and breakup-related magmatism. Supplementary material : Cathodoluminescence images of analysed zircon grains from sites on the Antarctic Peninsula are available at https://doi.org/10.6084/m9.figshare.c.3521973

Description: Genomic epidemiology of global Klebsiella pneumoniae carbapenemase (KPC)-producing Escherichia coli Scientific Reports, Published online: 19 July 2017; doi:10.1038/s41598-017-06256-2