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Recent studies on shallow-level arcuate intrusions have identified numerous examples of horizontal mineral fabrics. These are commonly interpreted as reflecting considerable lateral flow during magma emplacement, thus querying established ‘semi-vertical’ ring-dyke models. We question the recent lateral emplacement model proposed for the Palaeocene Slieve Gullion Ring-complex, NE Ireland, where the absence of steep fabrics in parts of the ring-complex has been used to support a shallow, semi-horizontal sheet intrusion mechanism. We argue that such simple flow models cannot be applied to explosive ring-fissure eruptions and that fabric data alone do not warrant rejection of the ring-dyke model. Moreover, the apparent ‘absence of steep intrusive contacts’ along the intrusion’s perimeter is readdressed and we present numerous examples of outcrops (27) with steep-sided geometries. The Camlough Breccias are reinterpreted as the product of gas-driven tuffisites injected along the active ring-fault (rather than of purely tectonic origin). Crucially, the porphyritic microgranite and porphyritic rhyolite ring-dyke rocks exhibit geochemical and petrographic signatures of contamination by the geographically restricted Palaeozoic Newry granodiorite and are best explained through crustal interaction vertically beneath the ring-complex. Subsequently, these silicic magmas rose into ignimbrite feeders along a caldera ring-fault system that was emplaced into near-surface vent-filling breccias.

The Western Irish Namurian Basin (WINB) preserves classic examples of basin floor sequences through to slope deposits and deltaic cyclothems. Despite over 50 years of research into the WINB, its sediment provenance remains highly contested. Sedimentological arguments, including palaeocurrent vectors and palaeoslope indicators have been invoked to propose a sediment source from the NW or the west (i.e. from within Laurentia). These same indicators have been subsequently reinterpreted to reflect a southern provenance. It is not clear from sedimentological arguments alone which interpretation more accurately reflects the infilling of the WINB. Regional-scale constraints on WINB provenance may be obtained with detrital zircon U–Pb geochronology. U–Pb LA-ICP-MS detrital zircon analysis was undertaken on samples from three sandstone units at different stratigraphic levels within the WINB siliciclastic sedimentary fill (Ross Formation, Tullig Sandstone, Doonlicky Sandstone). The samples are dominated by 500–700 Ma zircons, which can be correlated with Cadomian–Avalonian orogenic activity within terranes to the south of the WINB (Avalonia/Ganderia, Armorica and Iberia). In contrast, Eastern Laurentia, to the north of the WINB, was devoid of orogenic activity at this time. WINB samples also yield age populations younger than 500 Ma, and older than 700 Ma. These are not diagnostic of a particular source terrane and thus could be derived from terranes north and/or south of the WINB. WINB detrital zircon age spectra can be reconciled by an Avalonian or combined Avalonian–Laurentian provenance for WINB sedimentary strata. Further research is required in order to distinguish between these two possibilities. Copyright © 2011 John Wiley & Sons, Ltd.

The British–Irish Palaeogene Igneous Province (BIPIP) is part of the larger North Atlantic Igneous Province and includes the lava fields of Antrim, Mull, and Skye. The Tardree Rhyolite Complex (TRC) in Northern Ireland forms an important stratigraphic unit between the Lower and Upper Basalt Formations of the Antrim Lava Group (ALG). Previous zircon age determinations obtained from the TRC have been used as a standard in zircon fission track studies, but contradict several 40Ar/39Ar sanidine and U–Pb zircon results. We provide new 40Ar/39Ar sanidine and U–Pb CA-TIMS zircon ages which resolve this discrepancy. Two sanidine samples from the Sandy Braes vent and the columnar-jointed dome-forming rhyolites of Tardree Forest yield a weighted mean 40Ar/39Ar age of 61.13 ± 0.42 Ma (2σ, internal error). Ten U–Pb CA-TIMS zircon analyses were undertaken, eight of which employed the CA-TIMS approach on both multi-grain fractions and single grains. Six of the CA-TIMS data yield a disequilibrium-corrected weighted mean 206Pb–238U age of 61.32 ± 0.09 Ma (2σ). The consistency of the 40Ar/39Ar ages with the CA-TIMS U–Pb zircon age, points to a closed system of both K and Ar since eruption. We propose that the crystallization age of the TRC be taken as 61.32 ± 0.09 Ma and that the currently used age of the zircon fission track standard (58.4 ± 0.7 Ma) be changed accordingly. This also places the eruption of the TRC in magnetochron C26r, which is consistent with the reversed polarity magnetic remanence observed in the ALG, and supports the conclusion of Ganerod et al. (2010) that the Lower Basalt Formation is older than the Vaigat Formation in Western Greenland. No resolvable zircon inheritance has been detected by the TIMS analyses, consistent with the fact that the temporal and geographic extent of rhyolitic magmatism within this sector of the BIPIP was very limited, and hence was unlikely to provide inherited magmatic zircons from slightly older magmas (antecrysts). Potentially older zircon xenocrysts would be derived from the underlying Caledonian basement (> 400 Ma) or yet older rocks. These should be easily detectable if the Tardree zircon was to be employed as a U–Pb zircon standard. The paired 40Ar/39Ar and 206Pb–238U results from this study indicate an age of 28.393 ± 0.194 Ma for the widely used Fish Canyon sanidine standard and gives further support to the recent calibrations of Kuiper et al. (2008) and Renne et al. (2010).

New Re–Os geochronology for the Ballachulish Slate Formation of the Dalradian Supergroup, Scotland yields a depositional age of 659.6 ± 9.6 Ma. This age represents the first successful application of the Re–Os system to rocks that have extremely low Re and Os abundances (

Zoned eruption deposits commonly show a lower felsic and an upper mafic member, thought to reflect eruption from large, stratified magma chambers. In contrast, the Montana Reventada composite flow (Tenerife) consists of a lower basanite and a much thicker upper phonolite. A sharp interface separates basanite and phonolite, and chilled margins at this contact indicate the basanite was still hot upon emplacement of the phonolite, i.e. the two magmas erupted in quick succession. Four types of mafic to intermediate inclusions are found in the phonolite. Inclusion textures comprise foamy quenched ones, others with chilled margins and yet others that are physically mingled, reflecting progressive mixing with a decreasing temperature contrast between the end-members. Analysis of basanite, phonolite and inclusions for majors, traces and Sr, Nd and Pb isotopes show the inclusions to be derived from binary mixing of basanite and phonolite end-members in ratios of 2:1 to 4:1. Although, basanite and phonolite magmas were in direct contact, contrasting 206Pb/204Pb ratios show that they are genetically distinct (19.7193(21)–19.7418(31) vs. 19.7671(18)–19.7807(23), respectively). We argue that the Montana Reventada basanite and phonolite first met just prior to eruption and had limited interaction time only. Montana Reventada erupted from the transition zone between two plumbing systems, the phonolitic Teide-Pico Viejo complex and the basanitic Northwest rift zone. A rift zone basanite dyke most likely intersected the previously emplaced phonolite magma chamber. This led to eruption of geochemically and texturally unaffected basanite, with the inclusion-rich phonolite subsequently following into the established conduit.

The Chiquerio Formation (Fm.) is a thick glaciogenic succession deposited unconformably on gneisses of the Arequipa massif in southern Peru. It has undergone greenschist facies metamorphism during Early Palaeozoic orogenesis. The Chiquerio Fm. consists of nearly 400 m of diamictite, sandstone, mudstone and carbonate, with a thin (11 m) cap dolostone at the top of the formation. It is overlain by the San Juan Fm., a 2-km-thick carbonate succession. The thick glacially influenced succession was deposited in deep marine conditions and consists mainly of massive diamictites (representing either ice-rafted debris or submarine debris flows) interbedded with turbiditic sandstones. Where internal lamination is present (e.g. bedding in the turbiditic packages), abundant dropstones can be recognized. There is no evidence of shallow marine reworking of the succession. No absolute age constraints on the depositional timing of the Chiquerio Fm. exist, because no volcanic tuffs have yet been identified. U–Pb dating of detrital zircons (U–Th–Pb SIMS) from the Chiquerio Fm. and the overlying San Juan Fm. suggest it is autochthonous with respect to Amazonia, as the detrital zircon age spectra suggest derivation from the Amazonian craton. Detrital grains as young as c. 700 Ma have been documented in the post-glacial San Juan Fm. The sparse (chemo)stratigraphic data available for the Chiquerio Fm. exhibit patterns similar to those observed generally in Neoproterozoic post-glacial carbonate sequences. Palaeogeographic models for the deposition of the Chiquerio Fm. are critically dependent on the timing of the docking of the basement of the Arequipa massif with the South American craton (Amazonia). Presently there are no palaeomagnetic constraints. More research on the chronological and palaeogeographical constraints of this succession is required. Supplementary material: Data are available at http://www.geolsoc.org.uk/SUP18479.

Apatite is a common U- and Th-bearing accessory mineral in igneous and metamorphic rocks, and a minor but widespread detrital component in clastic sedimentary rocks. U–Pb and Th–Pb dating of apatite has potential application in sedimentary provenance studies, as it likely represents first cycle detritus compared to the polycyclic behavior of zircon. However, low U, Th and radiogenic Pb concentrations, elevated common Pb and the lack of a U–Th–Pb apatite standard remain significant challenges in dating apatite by LA-ICPMS, and consequently in developing the chronometer as a provenance tool. This study has determined U–Pb and Th–Pb ages for seven well known apatite occurrences (Durango, Emerald Lake, Kovdor, Mineville, Mud Tank, Otter Lake and Slyudyanka) by LA-ICPMS. Analytical procedures involved rastering a 10 μm spot over a 40 × 40 μm square to a depth of 10 μm using a Geolas 193 nm ArF excimer laser coupled to a Thermo ElementXR single-collector ICPMS. These raster conditions minimized laser-induced inter-element fractionation, which was corrected for using the back-calculated intercept of the time-resolved signal. A Tl–U–Bi–Np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias. External standards (Plesovice and 91500 zircon, NIST SRM 610 and 612 silicate glasses and STDP5 phosphate glass) along with Kovdor apatite were analyzed to monitor U–Pb, Th–Pb, U–Th and Pb–Pb ratios Common Pb correction employed the 207Pb method, and also a 208Pb correction method for samples with low Th/U. The 207Pb and 208Pb corrections employed either the initial Pb isotopic composition or the Stacey and Kramers model and propagated conservative uncertainties in the initial Pb isotopic composition. Common Pb correction using the Stacey and Kramers (1975) model employed an initial Pb isotopic composition calculated from either the estimated U–Pb age of the sample or an iterative approach. The age difference between these two methods is typically less than 2%, suggesting that the iterative approach works well for samples where there are no constraints on the initial Pb composition, such as a detrital sample. No 204Pb correction was undertaken because of low 204Pb counts on single collector instruments and 204Pb interference by 204Hg in the argon gas supply. Age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common Pb-corrected ages, a Tera–Wasserburg Concordia intercept age and a Tera–Wasserburg Concordia intercept age anchored through common Pb. The samples in general yield ages consistent (at the 2σ level) with independent estimates of the U–Pb apatite age, which demonstrates the suitability of the analytical protocol employed. Weighted mean age uncertainties are as low as 1–2% for U- and/or Th-rich Palaeozoic–Neoproterozoic samples; the uncertainty on the youngest sample, the Cenozoic (31.44 Ma) Durango apatite, ranges from 3.7–7.6% according to the common Pb correction method employed. The accurate and relatively precise common Pb-corrected ages demonstrate the U–Pb and Th–Pb apatite chronometers are suitable as sedimentary provenance tools. The Kovdor carbonatite apatite is recommended as a potential U–Pb and Th–Pb apatite standard as it yields precise and reproducible 207Pb-corrected, 232Th–208Pb, and common Pb-anchored Tera–Wasserburg Concordia intercept ages.

Samples in this paper have been assigned formations based on the Geological Survey of Ireland shapefile released prior to the commencement of the study. However, the authors were not aware that, since obtaining the samples, an updated shapefile had been released. This update affects three of the four apatite samples assigned to the Lower Devonian Ballymore Formation. The location of samples Mb-1, Mb-4 and Mb-5 now places them well within the undifferentiated, Upper Devonian Slieve Mish Group. As outlined in our paper, the apatite ages were originally produced concurrently with apatite fission track analysis and were later used in our study to provide additional provenance information in support of the detrital zircon geochronological data. In the second paragraph of the discussion section we say the following: "Williams et al. (1999) obtained an age of 411 Ma for the Cooscrawn Tuff Bed in the Ballymore Formation, which is older than 22 of the 70 detrital apatites analysed in this formation". The reassignment of the three samples to the Upper Devonian Slieve Mish Group nullifies the above statement. However, our interpretation that the depositional age of the Ballymore Formation is younger than the 411 Ma age given by Williams et al. (1999) is predominantly based upon the evidence given by the six youngest detrital zircons from the formation which underlies the Ballymore Formation (i.e. the Slea Head Formation). These zircons give a concordia age of 405 ± 4 Ma. This suggests that the Ballymore Formation was more than likely deposited after 409 Ma. We do not believe that the reassignment of the three samples has any major impact on our provenance interpretations. The ∼420 Ma age of the majority of the apatites in samples Mb-1, Mb-4 and Mb-5 actually fits with the range of Palaeozoic detrital zircons in sample AK-17 which was taken from the Slieve Mish Group, thereby supporting minor input of rocks affected by end-Scandian metamorphism.

Plate tectonic reconstructions of the late Mesoproterozoic–Neoproterozoic supercontinent of Rodinia juxtapose the western margin of Amazonia against eastern Laurentia based on palaeomagnetic, isotopic, and geological evidence. Mesoproterozoic (‘Grenvillian’) orogenic belts are of crucial importance to these reconstructions as they act as key tectonic tracers for Amazonia–Laurentia interactions. They include orogenic belts sited on Amazonia (such as the Sunsas Orogen), paraautochthonous elements such as the Mesoproterozoic metamorphic basement inliers within the Andean Belt (e.g. in the Colombian Andes), exotic terranes accreted to Amazonia during Rodinia assembly (such as the Arequipa Massif), and orphaned fragments of Amazonian basement in Central and North America. A review of the timing of Sunsas orogenesis demonstrates that it occurred from about 1.2–1 Ga in eastern Bolivia and the western Amazon region of Brazil. This is significantly older than the timing of metamorphism in Mesoproterozoic basement inliers of the Colombian Andes, which record a late metamorphic event between 0.9 and 1.0 Ga. Orphaned fragments of Amazonian basement in Laurentia (such as the Blue Ridge/Mars Hill terrane) suggest collision between southeastern Laurentia and Amazonia at ca. 1.15 Ga. The Arequipa Massif (and Antofalla Basement) most likely represents an exotic basement terrane that was caught up in the collision of southeastern Laurentia with western Amazonia. Recent palaeomagnetic data suggest that Amazonia moved northeastwards along the eastern Laurentian margin during Grenvillian collision. Amazonia evidently collided with southern Laurentia at ca. 1200 Ma and, as a result of progressive dextral transcurrent movement, it encountered the Labrador–Greenland sector of eastern Laurentia (and possibly Baltica) by 980 Ma. The timing of the Rodinia break-up in western Amazonia is poorly constrained. Evidence exists supporting a Neoproterozoic western Amazonian active margin, which would imply its at least partial separation from the conjugate rift margin of eastern Laurentia (i.e. formation of a proto-Iapetus Ocean) prior to ca. 650 Ma. This rifting event may be linked to A-type magmatism at ca. 770–690 Ma which is documented in both southeast Laurentia and western Amazonia. Final separation must have been completed by Early Cambrian times based on the unequivocal evidence for drift-related sedimentation on the Laurentian margin of the Iapetus Ocean.

This study addresses the timing and pressure-temperature (P-T) conditions of ophiolite obduction, one of the proposed causes of the ca. 470 Ma Grampian orogeny of Scotland and Ireland. This event gave rise to the main structural and metamorphic characteristics of the Grampian terrane-the type area for Barrovian metamorphism, the cause of which remains enigmatic despite a century of research. Zircons from the Highland Border ophiolite, Scotland, define a 499 +/- 8 Ma U-Pb concordia age, which is interpreted as dating magmatism. Its metamorphism is dated by a 490 +/- 4 Ma Ar-40-Ar-39 hornblende age, and a 488 +/- 1 Ma Ar-40-Ar-39 muscovite age from a metasedimentary xenolith within it, from which P-T estimates of 5.3 kbar and 580 degrees C relate to ophiolite obduction. Metamorphism of the Deerpark complex ophiolitic melange (Irish correlative of the Highland Border ophiolite) is constrained by a 514 +/- 3 Ma Ar-40-Ar-39 hornblende age, while mica schist slivers within it yield detrital zircon U-Pb ages consistent with Laurentian provenance and Rb-Sr and Ar-40-Ar-39 muscovite ages of ca. 482 Ma. P-T values of 3.3 kbar and 580 degrees C for the mica schist constrain the conditions of ophiolite obduction. Metamorphic mineral ages from the Grampian terrane (Dalradian Supergroup) are substantially younger (ca. 475-465 Ma) than those from the ophiolites. If conductive heating in overthickened crust was the cause of Barrovian metamorphism, then collisional thickening must have started soon after ophiolite obduction at ca. 490 Ma in order to generate the ca. 470 Ma metamorphic peak in the Grampian terrane. (Less)

Grenvillian crust is encountered in several basement inliers in the northern Andes of Colombia, Ecuador and Peru and is also represented as a major detrital or inherited component within Neoproterozoic to Paleozoic sedimentary and magmatic rocks. This review of the tectonic and geochronological record of the Grenvillian belt in the northern Andes suggests that these crustal segments probably formed on an active continental margin in which associated arc and back-arc magmatism evolved from ca. 1.25 to 1.16 Ga, possibly extending to as young as 1.08 Ga. The lithostratigraphic and tectonic history of the Grenvillian belt in the northern Andes differs from that of the Sunsas belt on the southwest Amazonian Craton and from the Grenvillian belt of Eastern Laurentia. It is considered that this belt, along with similar terranes of Grenvillian age in Middle America and Mexico define a separate composite orogen which formed on the northwestern margin of the Amazonian Craton. Microcontinent accretion and interaction with the Sveconorwegian province on Baltica is a feasible tectonic scenario, in line with recent paleogeographic reconstructions of the Rodinian supercontinent. Although Phanerozoic tectonics may have redistributed some of these terranes, they are still viewed as para-autocthonous domains that remained in proximity to the margin of Amazonia. Paleogeographic data derived from Phanerozoic rocks suggest that some of the Colombian Grenvillian fragments were connected to northernmost Peru and Ecuador until the Mesozoic, whereas the Mexican terranes where attached to the Colombian margin until Pangea fragmentation in Late Triassic times.

The Dalradian Supergroup contains three distinct glacigenic units, formerly termed ‘Boulder Beds’, which are correlated with widespread Neoproterozoic glaciations. The oldest and thickest unit, the Port Askaig Formation, marks the Appin–Argyll group boundary of the Dalradian Supergroup and has been correlated with the Middle Cryogenian (Sturtian) glaciation. The Auchnahyle Formation, a diamictite-bearing sequence near Tomintoul in NE Scotland, exhibits strong lithological similarities to the Port Askaig Formation. Both these glacigenic ‘Boulder Bed’ units contain abundant dolomite clasts in their lower parts and more granitic material at higher levels. Both metadiamictite units are overlain by thick shallow-marine quartzite units. C isotope data from Appin Group carbonate strata below the Auchnahyle Formation support this correlation. U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) detrital zircon data from the Auchnahyle Formation metadiamictite differ slightly from the Port Askaig Formation, but are similar to detrital zircon spectra obtained from the Macduff Formation, a diamictite unit in the younger Southern Highland Group of the Dalradian Supergroup; both apparently reflect derivation from local basement rocks. No detritus younger than 0·9 Ga is observed, so the data do not constrain significantly the depositional age of the glacial strata. A thin tholeiitic pillow basalt unit in the lower part of the Auchnahyle Formation is geochemically distinct from pre-tectonic metadolerite sills and from basic metavolcanic rocks up-section. A Sturtian (c. 720–700 Ma) age for the Auchnahyle Formation metadiamictite would imply that this basaltic volcanism represents the oldest recorded volcanic activity in the Dalradian Supergroup and is inferred to represent an early, local phase of proto-Iapetan rifting within the Rodinian supercontinent.

The composite intrusions of Drumadoon and An Cumhann crop out on the SE coast of the Isle of Arran, Scotland and form part of the larger British and Irish Palaeogene Igneous Province, a subset of the North Atlantic Igneous Province. The intrusions (shallow-level dykes and sills) comprise a central quartz–feldspar-phyric rhyolite flanked by xenocryst-bearing basaltic andesite, with an intermediate zone of dark quartz–feldspar-phyric dacite. New geochemical data provide information on the evolution of the component magmas and their relationships with each other, as well as their interaction with the crust through which they travelled. During shallow-crustal emplacement, the end-member magmas mixed. Isotopic evidence shows that both magmas were contaminated by the crust prior to mixing; the basaltic andesite magma preserves some evidence of contamination within the lower crust, whereas the rhyolite mainly records upper-crustal contamination. The Highland Boundary Fault divides Arran into two distinct terranes, the Neoproterozoic to Early Palaeozoic Grampian Terrane to the north and the Palaeozoic Midland Valley Terrane to the south. The Drumadoon Complex lies within the Midland Valley Terrane but its isotopic signatures indicate almost exclusive involvement of Grampian Terrane crust. Therefore, although the magmas originated at depth on the northern side of the Highland Boundary Fault, they have crossed this boundary during their evolution, probably just prior to emplacement.

The Early Ordovician Grampian Orogeny in the British Isles represents a classic example of collision between an oceanic island arc and a passive continental margin, starting around 480 Ma. The South Mayo Trough in western Ireland preserves a complete and well-dated sedimentary record of arc collision. We sampled sandstones and conglomerates from the Rosroe, Maumtrasna and Derryveeny Formations in order to assess erosion rates and patterns during and after arc collision. U–Pb dating of zircons reveals a provenance dominated by erosion from the upper levels of the Dalradian Supergroup (Southern Highland and Argyll Groups), with up to 20% influx from the colliding arc into the Rosroe Formation, but only 6% in the Maumtrasna Formation (~ 465 Ma). The dominant source regions lay to the northeast (e.g. in the vicinity of the Ox Mountains, 50 km distant, along strike). The older portions of the North Mayo Dalradian and its depositional basement (the Annagh Gneiss Complex) do not appear to have been important sources, while the Connemara Dalradian only plays a part after 460 Ma, when it supplies the Derryveeny Formation. By this time all erosion from the arc had effectively ceased and exhumation rates had slowed greatly. The Irish Grampian Orogeny parallels the modern Taiwan collision in showing little role for the colliding arc in the production of sediment. Negligible volumes of arc crust are lost because of erosion during accretion to the continental margin.

The Scandinavian Caleclonides have been viewed as resulting from either a single Silurian (i.e. Scandian) event or from polycyclic orogenies involving several collisions on the margin of Baltica. Early studies of the Kalak Nappe Complex (KNC) in Finnmark, Arctic Norway, led to the hypothesis of an Early Cambrian-Early Ordovician (520-480 Ma) Finnmarkian Crogeny, though the nature of this tectonic event remains enigmatic. In this contribution we have employed in situ UV laser ablation Ar-Ar dating of fine-grained phyllite and schist from the eastern Caledonides of Arctic Norway to investigate the presence of pre-Scandian tectonometamorphic events. U-Th-Pb detrital zircon and whole rock Sm-Nd analyses have been used to test the regional stratigraphic correlations of these metasedimentary rocks. These results indicate that the Berlevag Formation within the Tanafjord Nappe, previously assumed to be part of the KNC, was deposited after 1872 Ma and prior to a low temperature hydrothermal event at 555 +/- 15 Ma. It has a likely provenance on the Baltica continent, lacks any Grenville-Sveconorwegian detrital zircons, and thus cannot be part of the KNC which contains abundant detritus in this age range. Instead the Berlevag Formation is interpreted as part of the Laksefjord Nappe Complex, which structurally underlies the KNC. Laser-ablation argon-argon dating also shows that late Caledonian (i.e. Scandian) tectonometamorphism affected both the KNC and its immediate footwall at c. 425 +/- 15 Ma. This is corroborated by a step-heating argon-argon muscovite age of 424 +/- 3 Ma which is interpreted as dating cooling. However, within two samples from the KNC, an earlier (Middle-Late Cambrian) metamorphic event is also recorded. A biotite-grade schist yielded an Ar-Ar inverse isochron age of 506 +/- 17 Ma from whole rock surfaces, in which the mineral domains are too fine-grained to date individually. An early generation of muscovite from a coarser-grained amphibolite-facies sample yielded an inverse isochron of 498 +/- 13 Ma. Both isochron ages have atmospheric argon intercept values. Previous studies have documented similar Cambrian ages in the Caledonian nappes below the KNC. These results suggest correlative tectonometamorphic events in the eastern KNC and its footwall at c. 500 Ma. This Cambrian event may reflect the arrival of the Kalak Nappe Complex as a previously constructed exotic mobile belt onto the margin of Baltica. Combined with recent studies from the western Kalak Nappe Complex, the results do not support the traditional constraint on the Finnmarkian Orogeny sensu stricto. However they vindicate classic tectonic models involving a Cambrian accretion event. (c) 2008 Elsevier B.V. All rights reserved. (Less)

The Tyrone Central Inlier is a metamorphic terrane of uncertain affinity situated outboard of the main Dalradian outcrop (south of the Fair Head–Clew Bay Line) and could represent sub-arc basement to part of the enigmatic Midland Valley Terrane. Using a combination of isotopic, structural and petrographic evidence, the tectonothermal evolution of the Tyrone Central Inlier was investigated. Sillimanite-bearing metamorphic assemblages ( c . 670 °C, 6.8 kbar) and leucosomes in paragneisses are cut by granite pegmatites, which post-date two deformation fabrics. The leucosomes yield a weighted average 207 Pb/ 206 Pb zircon age of 467 ± 12 Ma whereas the main fabric yields a 40 Ar– 39 Ar biotite cooling age of 468 ± 1.4 Ma. The pegmatites yield 457 ± 7 Ma and 458 ± 7 Ma Rb–Sr muscovite–feldspar ages and 40 Ar– 39 Ar step-heating plateaux of 466 ± 1 Ma and 468 ± 1 Ma, respectively. The metasedimentary rocks yield Palaeoproterozoic Sm–Nd model ages and laser ablation inductively coupled plasma mass spectrometry detrital zircon U–Pb analyses from a psammitic gneiss yield age populations at 1.05–1.2, 1.5, 1.8, 2.7 and 3.1 Ga. Combined, these data permit correlation of the Tyrone Central Inlier with either the Argyll or the Southern Highland Group of the Dalradian Supergroup. The inlier was thus part of Laurentia onto which the Tyrone ophiolite was obducted.

The timing of peak Grampian metamorphism is well constrained from the detrital record of the adjacent fore-arc basin fill and geochronology of synorogenic intrusive rocks, but the onset of collision is less certain. Proximal Silurian conglomerates contain plagiogranite boulders unequivocally derived from the Lough Nafooey arc, two of which yield U–Pb secondary ionization mass spectrometry zircon ages of 489.9 ± 3.1 Ma and 487.8 ± 2.3 Ma. Nd isotopic evidence (ϵNd(490) c. 0) demonstrates that the plagiogranites assimilated significant amounts of old continental crust. This provides an absolute age constraint on a previously poorly constrained and inferred event, demonstrating that the arc had encountered subducting Laurentian margin sediments by 490 Ma.

In a clinical in vivo study, wound blood collected from an autologous reinfusion drain of patients undergoing elective total knee arthroplasty was examined to investigate if hydrogen peroxide bone surface preparation had an adverse effect on blood destined to be reinfused. The post-operative drain blood of thirty-eight patients was collected after pre-implantation bone preparation being performed either with or without the use of hydrogen peroxide. Filtered drain blood samples were analyzed and mean results for treatment / control groups respectfully were: haemoglobin (g/L) 98.6/100.9, p=0.7221; haemoglobin change from baseline (g/L) -39.1/-32.9, p=0.2117; MCV (fL) 94.6/93.1, p=0.2897; MCV change from baseline (fL) 2.0/2.5, p=0.6417; potassium (mmol/L) 4.5/4.6, p=0.8212; free haemoglobin (g/L) 1.2/1.3, p=0.4387; methaemoglobin (%) 0.2/0.2, p=0.8112; presence of echinocytes (%) 14/18, p=1.0000. These were all within safe limits for reinfusion. Under the study conditions, application of hydrogen peroxide followed by thorough lavage of the knee joint did not appear to result in any untoward degradation of the extravasated blood that might preclude its use for postoperative autologous drainage blood reinfusion.

Introduction Malorientation of the socket contributes to instability after hip arthroplasty but the optimal orientation of the cup in relation to the pelvis has not been unequivocally described. Large radiological studies are few and problems occur with film standardisation, measurement methodology used and alternative definitions of describing acetabular orientation. Methods A cohort of 1,578 patients from a single institution is studied where all patient data was collected prospectively. Risk factors for patients undergoing surgery are analysed. Radiological data was compared between a series of non-dislocating hips and dislocating cases matched 2:1 by operation type, age and diagnosis. Results The overall dislocation rate for all 1,578 cases was 3.23% but the rate varied according to the type of surgery performed. The rate in uncomplicated primary cases was 2.4% which increased to 9.3% for second stage implantation for a two stage procedure for infection. There was no significant difference in the variability of the dislocating and non-dislocating groups for either inclination (p = 0.393) or anteversion (p = 0.661). Conclusions A “safe zone” for socket orientation to avoid dislocation could not be defined. The cause of dislocation is multifactorial, re-establishing the anatomic centre of rotation, balancing soft tissues and avoidance of impingement around the hip are important considerations.

Apatite can provide geologists with an exceptionally wide range of ages and temperatures to investigate processes that operate from Earth's surface right down to the lower crust. Apatite is a widespread accessory mineral in igneous, metamorphic, and clastic sedimentary rocks and can be dated using four radioactive decay schemes, each with a different temperature window for isotopic closure: Lu–Hf (675–750 °C); U–Pb (350–550 °C); apatite fission track (60–110 °C); (U–Th)/He (40–80 °C). The fission-track and (U–Th)/He methods are popular for studying upper-crustal and near-surface processes, whereas the U–Pb and Lu–Hf systems are used to investigate the thermal, tectonic, and magmatic histories of the deeper crust.

Please click here to download the map associated with this article. In Ireland, a major NE-SW trending fault zone (the Fair Head—Clew Bay line) separates high-grade metamorphic rocks (the Dalradian Supergroup) that were originally deposited on an ancient continental margin from lower-grade rocks of oceanic affinity (the Clew Bay Complex). This fault zone continues towards the NE into Scotland, where it is known as the Highland Boundary Fault, and to the west into Newfoundland and the Appalachians, where it is termed the Baie Verte—Brompton line. As such, it is one of the longest fault zones in the Caledonian/Appalachian mountain belt. It has been active several times during this mountain-building episode, and has thus played an important role during the evolution of this orogenic belt. In Scotland and most of Ireland, this fault zone is generally very poorly exposed, and the relationships between the rock units on either side of this discontinuity have therefore proved controversial in the past. ...

Collision of the oceanic Lough Nafooey Island Arc with the passive margin of Laurentia after 480 Ma in western Ireland resulted in the deformation, magmatism and metamorphism of the Grampian Orogeny, analogous to the modern Taiwan and Miocene New Guinea Orogens. After f470 Ma, the metamorphosed Laurentian margin sediments (Dalradian Supergroup) now exposed in Connemara and North Mayo were cooled rapidly (>35 jC/m.y.) and exhumed to the surface. We propose that this exhumation occurred mainly as a result of an oceanward collapse of the colliding arc southwards, probably aided by subduction rollback, into the new trench formed after subduction polarity reversal following collision. The Achill Beg Fault, in particular, along the southern edge of the North Mayo Dalradian Terrane, separates very low-grade sedimentary rocks of the South Mayo Trough (Lough Nafooey forearc) and accreted sedimentary rocks of the Clew Bay Complex from high-grade Dalradian meta-sedimentary rocks, suggesting that this was a major detachment structure. In northern Connemara, the unconformity between the Dalradian and the Silurian cover probably represents an eroded major detachment surface, with the Renvyle–Bofin Slide as a related but subordinate structure. Blocks of sheared mafic and ultramafic rocks in the Dalradian immediately below this unconformity surface probably represent arc lower crustal and mantle rocks or fragments of a high level ophiolite sheet entrained along the detachment during exhumation. Orogenic collapse was accompanied in the South Mayo Trough by coarse clastic sedimentation derived mostly from the exhuming Dalradian to the north and, to a lesser extent, from the Lough Nafooey Arc to the south. Sediment flow in the South Mayo Trough was dominantly axial, deepening toward the west. Volcanism associated with orogenic collapse (Rosroe and

Rb–Sr and 40 Ar/ 39 Ar step-heating and in situ 40 Ar/ 39 Ar laserprobe dating of fabric-forming micas provide new constraints on the timing of Grampian orogenesis and the associated development of blueschist-facies metamorphism at the Laurentian margin in NW Ireland. Early (MP 1 ) blueschist-facies assemblages were developed in metabasites of the Dalradian Supergroup deposited near the edge of the incipient Laurentian margin, contemporaneous with Barrovian metamorphism in the Dalradian closer to the Laurentian foreland. The regional D 2 event is associated with the formation of orogen-scale fold nappes and is constrained in the Dalradian by S 2 muscovite ages of c . 460 Ma, which are probably recording crystallization. Importantly, the Clew Bay Complex, previously considered as an exotic terrane (correlated with the Highland Border Complex of Scotland) and the Dalradian are in structural continuity. Muscovite from the S 2 nappe fabric in the Clew Bay Complex also yields identical c . 460 Ma ages. During D 3 , dextral shearing tilted the recumbent D 2 nappes into a vertical, downward-facing orientation adjacent to the Laurentian margin. D 3 is constrained by S 3 muscovite ages of c . 448 Ma. Synchronous deformation of the Dalradian Supergroup and the Clew Bay Complex in the mid-Ordovician Grampian orogeny casts doubt on both the validity of Silurian microfossil dates obtained from the Clew Bay Complex and the exotic status of both this ‘terrane’ and the correlative Highland Border Complex of Scotland.

The relationship between the Dalradian Supergroup and the Highland Border Complex in Scotland has remained contentious for over a century. In western Ireland, the contact between the Dalradian Supergroup and the Clew Bay Complex (a correlative of the Highland Border Complex) is superbly exposed on the island of Achill Beg on the North Mayo coast. The unfossiliferous South Achill Beg succession has been traditionally assigned to the Clew Bay Complex, and this interpretation is supported by a combination of Sm–Nd model age data, heavy mineral analysis and lithostratigraphic correlation. TDM ages range from 1.99–2.66 Ga (mean=2.28 Ga, n=6). Detailed structural mapping shows that both the Dalradian and the Clew Bay Complex share the same structural history. A D1 high strain event is common to both units, and is associated with the development of tectonic slides. The D2 event is responsible for the formation of crustal-scale nappes. In both units, beds are consistently downward facing on the S2 foliation. Later dextral shearing (D3) resulted in the tilting of the originally recumbent, S-facing D2 nappes into this downward-facing orientation. Rb–Sr and 40Ar–39Ar radiometric dating of muscovite confirms that both units were deformed contemporaneously as the S2 nappe fabric in each is dated at c. 460 Ma. This Middle Ordovician age for deformation of the Clew Bay Complex is highly significant, not least because published microfossil data suggest a Silurian age.

We present here a low-temperature thermochronological study that combines the apatite fission-track and (U + Th)/He dating methods with a pseudo-vertical sampling approach to generate continuous and well-constrained temperature–time histories from the onshore Irish Atlantic margin. The apatite fission-track and (U + Th)/He ages range from the Late Jurassic to Early Cretaceous and the mean track lengths are relatively short. Thermal histories derived from inverse modelling show that following post-orogenic exhumation the sample profiles cooled to c . 75 °C. A rapid cooling event to surface temperatures occurred during the Late Jurassic to Early Cretaceous and was diachronous from north to south. It was most probably caused by c . 2.5 km of rift-shoulder related exhumation and can be temporally linked to the main stage of Mesozoic rifting in the offshore basins. A slow phase of reheating during the Late Cretaceous and Early Cenozoic is attributed to the deposition of a thick sedimentary sequence that resulted in c . 1.5 km of burial. Our data imply a final pulse of exhumation in Neogene times, probably related to compression of the margin. However, it is possible that an Early Cenozoic cooling event, compatible with our data but not seen in our inverse models, accounts for part of the Cenozoic exhumation. Supplementary material: Details on the apatite fission-track and (U + Th)/He methods are available at www.geolsoc.org.uk/SUP18765.

Zircon (ZrSiO4) is the most commonly used mineral in U-Pb geochronology. Although it has proven to be a robust chronometer, it can suffer from Pb-loss or elevated common Pb, both of which impede precision and accuracy of age determinations. Chemical abrasion of zircon involves thermal annealing followed by relatively low temperature partial dissolution in HF acid. It was specifically developed to minimize or eliminate the effects of Pb-loss prior to analysis using Thermal Ionization Mass Spectrometry (TIMS). Here we test the application of chemical abrasion to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) by analyzing zircons from both untreated and chemically abraded samples. Rates of ablation for high alpha-dose non-treated zircons are up to 25 faster than chemically abraded equivalents. Ablation of 91500 zircon reference material demonstrates a ca. 3 greater down-hole fractionation of206Pb/238U for non-treated zircons. These disparities necessitate using chemical abrasion for both primary reference material and unknowns to avoid applying an incorrect laser induced fractionation correction. All treated samples display a marked increase in the degree of concordance and/or lowering of common Pb, thereby illustrating the effectiveness of chemical abrasion to LA-ICP-MS U-Pb zircon geochronology. © 2014 by the authors; licensee MDPI, Basel, Switzerland.

This is a report of the first riot in Singapore since 1969 and the subsequent emergency response from the police force and emergency medical services. Lessons learned are discussed, and recommendations for future medical response in incidents of civil unrest are made.

Natural processes driven by heat flow can be understood using quantitative reconstruction of the thermal history of accessory and common minerals that were formed or modified in these processes. Thermochronology assumes that isotopes are lost from minerals by thermally-activated volume diffusion, and forms the basis of many studies of the thermal evolution of the crust. However, some studies challenge this assumption and suggest that the mechanisms controlling isotope transport in minerals over geological time-scales are dominated by aqueous fluid flow within mineral pathways. Here, we test these contrasting hypotheses by inverse modelling apatite uranium–lead (U–Pb) dates to produce theoretical t–T solutions assuming Pb was lost by volume diffusion. These solutions are compared with independent geological constraints and intra-grain apatite U–Pb dates, which demonstrate that volume diffusion governed the displacement of Pb. This confirmation, combined with an inverse-modeling procedure that permits reheating and cooling paths to be distinguished between ∼375 and 570 °C, provides geologists with a unique tool for investigating the high-temperature thermal evolution of accessory minerals using the U–Pb method.

The Caledonides of Britain and Ireland are one of the most intensively studied orogenic belts in the world. This review considers all the tectonic events associated with the development and closure of the Iapetus Ocean. It first summarizes the tectonic evolution of each segment involved in the Scottish–Irish sector of the Caledonides and then reviews the temporal evolution of the Caledonian Orogeny. Three main tectonic phases are recognized in the Scottish–Irish Caledonides: an Early–Middle Ordovician (475–465 Ma) phase termed the Grampian Orogeny; a phase of Silurian (435–425 Ma) tectonism restricted to the Northern Highland Terrane of Scotland termed the Scandian Orogeny; and an Early Devonian (395 Ma) phase termed the Acadian Orogeny. The Grampian Orogeny was caused by the collision of the Laurentian continental margin with an oceanic arc terrane and associated suprasubduction zone ophiolites during the latest Cambrian–Early Ordovician. Following the Grampian arc–continent collision event, there was a subduction polarity reversal. This facilitated continued subduction of Iapetan oceanic lithosphere and an Andean-type continental margin developed on and adjacent to the Laurentian margin in the Middle Ordovician along with a substantial thickness of accretionary prism sediments (the Southern Uplands–Longford Down Terrane). The Iapetus Ocean is believed to have disappeared by the Late Silurian based on the faunal record and a continent–continent collision ensued. The absence of significant regional deformation and metamorphism associated with the Late Silurian collision between Avalonia and the Scottish–Irish margin of Laurentia suggests that the continental collision in this sector of the Caledonian–Appalachian orogen was ‘soft’ or highly oblique. The exception is the Northern Highlands Terrane of Scotland that was believed to have been situated 500–700 km to the north along orogenic strike. This terrane records evidence for significant Silurian regional deformation and metamorphism attributed to the collision of the Laurentian margin of East Greenland with Baltica (the Scandian Orogeny). Current controversies in the Laurentian Caledonides of Scotland and Ireland are discussed at the end of this review.

This study presents apatite LA-ICP-MS U-Pb age and trace elements concentrations data from different granite types from the Tatra Mountains, Poland. Apatite from monazite and xenotime-bearing High Tatra granite was dated at 339 ± 5 Ma. The apatite LREE patterns reflect two types of magmas that contributed to this layered magma series. Apatite from a hybrid allanite-bearing diorite from the Goryczkowa Unit was dated at 340 ± 4 Ma with apatite LREE depletion reflecting the role of allanite and titanite during apatite crystallization. Apatite crystals from a hybrid cumulative rock from the Western Tatra Mountains were dated at 344 ± 3 Ma. Apatite is one of the main REE carriers in this sample and exhibit flat REE patterns. Taking into account the relatively low closure temperature of the U-Pb system in apatite (350–550°C), the c. 340 Ma apatite ages mark the end of high temperature tectonometamorphic activity in the Tatra Mountains.

coronary artery anomalies occur in approximately 1% to 2% of the population. In the majority of cases, they lack hemodynamic significance ([1][1]). A course of the left anterior descending or left main coronary artery between the aorta and pulmonary artery has been associated with ischemic events

Importance Because of the similarity in clinical outcomes after elective open and endovascular repair of abdominal aortic aneurysm (AAA), cost may be an important factor in choosing a procedure. Objective To compare total and AAA-related use of health care services, costs, and cost-effectiveness between groups randomized to open or endovascular repair. Design, Setting, and Participants This unblinded randomized clinical trial enrolled 881 patients undergoing planned elective repair of AAA who were candidates for open and endovascular repair procedures. Patients were randomized from October 15, 2002, to April 15, 2008, at 42 Veterans Affairs medical centers. Follow-up was completed on October 15, 2011, and data were analyzed from April 15, 2013, to April 15, 2016, based on intention to treat. Main Outcomes and Measures Mean total and AAA-related health care cost per life-year and per quality-adjusted life-year (QALY). Results A total of 881 patients (876 men [99.4%]; 5 women [0.6%]; mean [SD] age, 70 [7.8] years) were included in the analysis. After a mean of 5.2 years of follow-up, mean life-years were 4.89 in the endovascular group and 4.84 in the open repair group ( P = .68), and mean QALYs were 3.72 in the endovascular group and 3.70 in the open repair group ( P = .82). Total mean health care costs did not differ significantly between the 2 groups (endovascular group, $142 745; open repair group, $153 533; difference, −$10 788; 95% CI, −$29 796 to $5825; P = .25). Costs related to AAA, including the initial repair, constituted nearly 40% of total costs and did not differ significantly between the 2 groups (endovascular group, $57 501; open repair group, $57 893; difference, −$393; 95% CI, −$12 071 to $7928; P = .94). Lower costs due to shorter hospitalization for initial endovascular repair were offset by increased costs from AAA-related secondary procedures and imaging studies. The probability of endovascular repair being less costly and more effective was 56.8% when effectiveness was measured in life-years and 55.4% when effectiveness was measured in QALYs for total costs and 31.3% and 34.3%, respectively, for AAA-related costs. Conclusions and Relevance In this multicenter randomized clinical trial with follow-up to 9 years, survival, quality of life, costs, and cost-effectiveness did not differ between elective open and endovascular repair of AAA. Trial Registration clinicaltrials.gov Identifier:NCT00094575

Para-articular osteochondromas (PAOCs) are a rare benign subtype of chondroma that occur in the soft tissues around the joints. Initially hypothesized to be derived from cartilaginous metaplasia, its aetiology and pathogenesis are still not fully understood. This tumour often causes a diagnostic and management dilemma due to similar clinical and histopathological features compared with other pathology. We report the fourth case of PAOC arising from the suprapatella region of the knee joint and review the literature to update our understanding of this tumour. From the data analysed, a distinctive pattern of tumour formation within or adjacent to a fat pad structure was evident, while trauma appears to play a role in its pathogenesis. Histologically, the tumour consists of a cartilage cap, with varying degrees of trabecular bone and endochondral ossification. Importantly, there are no features of nuclear pleomorphism or increased mitotic activity suggestive of a malignant process. All tumours were surgically removed and behaved in a benign fashion without evidence of recurrence. PAOC may often be suspected for more malignant processes; thus, recognition of this entity is important as simple excision is curative.

We present three new high-precision U–Pb zircon chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) dates from western European Carboniferous diagenetically altered volcanic ash layers (bentonites and tonsteins) that occur interbedded with cyclic siliciclastic sedimentary rocks. The dates constrain the average periodicity of western European late Carboniferous (Arnsbergian to early Langsettian) cyclic sedimentation to between 89 and 124 ka per cycle. This is consistent with the 100 ka ‘short’ eccentricity Milankovitch cycle and supports previous suggestions that the cycles are the product of glacio-eustasy. Cyclostratigraphic tuning of Namurian cycles to the 100 ka eccentricity cycle revises the timing of the global Mississippian–Pennsylvanian boundary to c . 323.9 Ma. CA-ID-TIMS dates also facilitate correlation between different facies belts where biostratigraphical correlations are difficult. Correlation between eastern and western European sequences confirms that the base of the Moscovian stage is located within the Duckmantian (Westphalian B) western European regional substage. Supplementary materials: Zircon separation and concentration procedures, U–Pb zircon CA-ID-TIMS methods and data table, average periodicity calculations for western and central European Namurian and Westphalian sedimentary cycles, and procedures for recalibrating legacy 40 Ar/ 39 Ar dates are available at www.geolsoc.org.uk/SUP18547.

The Tyrone Igneous Complex is one of the largest areas of ophiolitic and arc-related rocks exposed along the northern margin of Iapetus within the British and Irish Caledonides. New U–Pb zircon data and regional geochemistry suggest that the Tyrone Plutonic Group represents the uppermost portions of a c . 480 Ma suprasubduction-zone ophiolite accreted onto an outboard segment of Laurentia prior to 470.3 ± 1.9 Ma. The overlying Tyrone Volcanic Group formed as an island arc that collided with the Laurentian margin during the Grampian phase of the Caledonidan orogeny. Early magmatism is characterized by transitional to calc-alkaline, light REE (LREE)-enriched island-arc signatures, with an increasing component of continentally derived material up sequence. Tholeiitic rhyolites with flat to U-shaped REE profiles and LREE-depleted basalts, located stratigraphically below a c . 473 Ma rhyolite of the upper Tyrone Volcanic Group, suggest initiation of intra-arc rifting at c . 475 Ma. Metamorphic cooling ages from the Tyrone Central Inlier imply arc–continent collision before 468 ± 1.4 Ma, with the emplacement of the Tyrone Volcanic Group onto the margin. A suite of 470.3 ± 1.9 Ma to 464.3 ± 1.5 Ma calc-alkaline intrusions are associated with the continued closure of Iapetus. Supplementary material: Geochemical data and petrography are available at http://www.geolsoc.org.uk/SUP18467.

blocks along its southern margin. New U/Pb, 40 Ar/ 39 Ar, apatite fission track, and apatite (U‐Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during ∼90 to ∼87Ma and crops out onAruba. Subsequent structural displacements resulted in >80°C of cooling on Aruba during 70–60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85–80 Ma and 55–45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at ∼65 Ma and exhumed rapidly at 55–45 Ma. We attribute Maastrichtian‐Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene–early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ≤1 km. Late Miocene–recent transpression caused inversion and ≤1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block. Citation: van der Lelij, R., R. A. Spikings, A. C. Kerr, A. Kounov, M. Cosca, D. Chew, and D. Villagomez (2010), Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone, Tectonics, 29, TC6003, doi:10.1029/2009TC002654.

This study integrates U-Pb zircon geochronology (from LAM-ICP-MS, SHRIMP, and TIMS) with Nd isotopic data from orthogneisses and metasedimentary rocks of the pre-Mesozoic basement of the eastern Peruvian Andes to provide new information on the tectonic evolution and Neoproterozoic-Paleozoic paleogeography of this segment of the protoAndean margin. A high-grade orthogneiss unit yields U-Pb zircon protolith crystallization ages of ∼613 Ma. It was metamorphosed and intruded by an Early Ordovician granitoid. Subsequently, two different volcano-sedimentary sequences were laid down and metamorphosed, probably as a consequence of terrane accretion. The older sequence was deposited and metamorphosed between 450 and 420 Ma, and the younger one was deposited after 320 Ma and metamorphosed at 310 Ma. U-Pb detrital zircon age patterns from the two sequences are within the age intervals 315–480, 480–860, 960–1400, and 11400 Ma. These data strongly suggest geological and spatial links between the different units, implying the existence of active magmatism contemporaneous with the reworking of previously formed orogenic complexes. Mesoproterozoic and older ages suggest that the detrital sources are on the western margin of Gondwana, near the Amazonian Craton and/or other Grenvillian-type domains, such as those found within the Andean belt. Neoproterozoic to Ordovician zircons suggest that this crustal segment was formed on an active margin along the western side of the Amazonian Craton. Whole-rock Nd isotope data from metasedimentary rocks of the two younger units yield Nd (450 Ma, 310 Ma) values between 6.3 and 13.2 and Sm-Nd TDM model ages between 1.6 and 2.1 Ga. The comparison of the Nd isotope record with the U-Pb detrital zircon data suggests that recycling of older crust was an important factor in the growth of the central Peruvian segment of the proto-Andean margin during the Proterozoic and the Early Paleozoic. Different tectonic and paleogeographic models are discussed in light of the new data presented here.

The Rum Igneous Centre comprises two early marginal felsic complexes (the Northern Marginal Zone and the Southern Mountains Zone), along with the later central ultrabasic–basic layered intrusions. These marginal complexes represent the remnants of near-surface to eruptive felsic magmatism associated with caldera collapse, examples of which are rare in the North Atlantic Igneous Province. Rock units include intra-caldera collapse breccias, rhyolitic ignimbrite deposits and shallow-level felsic intrusions, as well the enigmatic ‘Am Màm intrusion breccia’. The latter comprises a dacitic matrix enclosing lobate basaltic inclusions (~1–15 cm) and a variety of clasts, ranging from millimetres to tens of metres in diameter. These clasts comprise Lewisian gneiss, Torridonian sandstone and coarse gabbro. Detailed re-mapping of the Am Màm intrusion breccia has shown its timing of emplacement as syn-caldera, rather than pre-caldera as previously thought. Textural analysis of entrained clasts and adjacent, uplifted country rocks has revealed their thermal metamorphism by early mafic intrusions at greater depth than their present structural position. These findings provide a window into the evolution of the early mafic magmas responsible for driving felsic magmatism on Rum. Our data help constrain some of the physical parameters of this early magma–crust interaction and place it within the geochemical evolution of the Rum Centre.

The results of a coupled, in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb study on zircon and geochemical characterization of the Eastern Cordilleran intrusives of Peru reveal 1.15 Ga of intermittent magmatism along central Western Amazonia, the Earth's oldest active open continental margin. The eastern Peruvian batholiths are volumetrically dominated by plutonism related to the assembly and breakup of Pangea during the Paleozoic-Mesozoic transition. A Carboniferous-Permian (340-285 Ma) continental arc is identified along the regional orogenic strike from the Ecuadorian border (6 degrees S) to the inferred inboard extension of the Arequipa-Antofalla terrane in southern Peru (14 degrees S). Widespread crustal extension and thinning, which affected western Gondwana throughout the Permian and Triassic resulted in the intrusion of the late- to post-tectonic La Merced-San Ramon-type anatectites dated between 275 and 220 Ma, while the emplacement of the southern Cordillera de Carabaya peraluminous granitoids in the Late Triassic to Early Jurassic (220-190 Ma) represents, temporally and regionally, a separate tectonomagmatic event likely related to resuturing of the Arequipa-Antofalla block. Volcano-plutonic complexes and stocks associated with the onset of the present Andean cycle define a compositionally bimodal alkaline suite and cluster between 180 and 170 Ma. A volumetrically minor intrusive pulse of Oligocene age (ca. 30 Ma) is detected near the southwestern Cordilleran border with the Altiplano. Both post-Gondwanide (30-170 Ma), and Precambrian plutonism (691-1123 Ma) are restricted to isolated occurrences spatially comprising less than 15% of the Eastern Cordillera intrusives. Only one remnant of a Late Ordovician intrusive belt is recognized in the Cuzco batholith (446.5 +/- 9.7 Ma) indicating that the Famatinian arc system previously identified in Peru along the north-central Eastern Cordillera and the coastal Arequipa-Antofalla terrane also existed inboard of this parautochthonous crustal fragment. Hitherto unknown occurrences of late Mesoproterozoic and middle Neoproterozoic granitoids from the south-central cordilleran segment define magmatic events at 691 +/- 13 Ma, 751 +/- 8 Ma, 985 +/- 14 Ma, and 1071-1123 +/- 23 Ma that are broadly coeval with the Braziliano and Grenville-Sunsas orogenies, respectively. Our data suggest the existence of a continuous orogenic belt in excess of 3500 km along Western Amazonia during the formation of Rodinia, its "early" fragmentation prior to 690 Ma, and support a model of reaccretion of the Paracas-Arequipa-Antofalla terrane to western Gondwana in the Early Ordovician with subsequent detachment of the Paracas segment in form of the Mexican Oaxaquia microcontinent in Middle Ordovician. A tectonomagmatic model involving slab detachment, followed by underplating of cratonic margin by asthenospheric mantle is proposed for the genesis of the volumetrically dominant Late Paleozoic to early Mesozoic Peruvian Cordilleran batholiths

The presence of major crystalline basement provinces at depth in NW Ireland is inferred from in situ Hf isotope analysis of zircons from granitoid rocks that cut structurally overlying metasedimentary rocks. Granitoids in two of these units, the Slishwood Division and the Tyrone Central Inlier, contain complex zircons with core and rim structures. In both cases, cores have average ϵHf values that differ from the average ϵHf values of the rims at 470 Ma (the time of granitoid intrusion). The Hf data and similarity in U–Pb age between the inherited cores and detrital zircons from the host metasedimentary rocks suggests local contamination during intrusion rather than transport of the grains from the source region at depth. Rims from the Slishwood Division intrusions have average ϵHf470 values of −7.7, consistent with a derivation from juvenile Palaeoproterozoic crust, such as the Annagh Gneiss Complex or Rhinns Complex of NW Ireland, implying that the deep crust underlying the Slishwood Division is made of similar material. Rims from the Tyrone Central Inlier have extremely negative ϵHf470 values of approximately −39. This isotopic signature requires an Archaean source, suggesting rocks similar to the Lewisian Complex of Scotland, or sediment derived wholly from it, occurs at depth in NW Ireland.

We investigated the Neoproterozoic–early Paleozoic evolution of the Gondwanan margin of the north-central Andes by employing U-Pb zircon geochronology in the Eastern Cordilleras of Peru and Ecuador using a combination of laser-ablation–inductively coupled plasma–mass spectrometry detrital zircon analysis and dating of syn- and post-tectonic intrusive rocks by thermal ionization mass spectrometry and ion microprobe. The majority of detrital zircon samples exhibits prominent peaks in the ranges 0.45–0.65 Ga and 0.9–1.3 Ga, with minimal older detritus from the Amazonian craton. These data imply that the Famatinian-Pampean and Grenville (= Sunsas) orogenies were available to supply detritus to the Paleozoic sequences of the north-central Andes, and these orogenic belts are interpreted to be either buried underneath the present-day Andean chain or adjacent foreland sediments. There is evidence of a subduction-related magmatic belt (474–442 Ma) in the Eastern Cordillera of Peru and regional orogenic events that pre- and postdate this phase of magmatism. These are confirmed by ion-microprobe dating of zircon overgrowths from amphibolite-facies schists, which reveals metamorphic events at ca. 478 and ca. 312 Ma and refutes the previously assumed Neoproterozoic age for orogeny in the Peruvian Eastern Cordillera. The presence of an Ordovician magmatic and metamorphic belt in the north-central Andes demonstrates that Famatinian metamorphism and subduction-related magmatism were continuous from Patagonia through northern Argentina to Venezuela. The evolution of this extremely long Ordovician active margin on western Gondwana is very similar to the Taconic orogenic cycle of the eastern margin of Laurentia, and our findings support models that show these two active margins facing each other during the Ordovician.

Objective Prior analysis in the Open vs Endovascular Repair Veterans Affairs (VA) Cooperative Study (CSP #498) demonstrated that survival, quality of life, and total health care costs are not significantly different between the open and endovascular methods of repair of abdominal aortic aneurysm. The device is a major cost of this method of repair, and the objective of this study was to evaluate the costs of the device, abdominal aortic aneurysm repair, and total health care costs when different endograft systems are selected for the endovascular repair (EVR). Within each selected system, EVR costs are compared with open repair costs. Methods The study randomized 881 patients to open (n = 437) or EVR (n = 444). Device selection was recorded before randomization; therefore, open repair controls were matched to each device cohort. Data were excluded for two low-volume devices, implanted in only 13 individuals, leaving 423 control and 431 endovascular patients: 166 Zenith (Cook Medical, Bloomington, Ind), 177 Excluder (W. L. Gore & Associates, Flagstaff, Ariz), and 88 AneuRx (Medtronic, Minneapolis, Minn). Mean device, hospitalization, and total health care costs from randomization to 2 years were compared. Health care utilization data were obtained from patients and national VA and Medicare data sources. VA costs were determined using methods previously developed by the VA Health Economics Resource Center. Non-VA costs were obtained from Medicare claims data and billing data from the patient's health care providers. Results Implant costs were 38% of initial hospitalization costs. Mean device (range, $13,600-$14,400), initial hospitalization (range, $34,800-$38,900), and total health care costs at 2 years in the endovascular (range, $72,400-$78,200) and open repair groups (range, $75,600-$82,100) were not significantly different among device systems. Differences between endovascular and corresponding open repair cohorts showed lower mean costs for EVR (range, $3200-$8300), but these were not statistically different. Conclusions The implant costs of endovascular aneurysm repair are substantial. When evaluating total health care system expenditures, there is large individual variability in costs, and there is no significant difference at 2 years among systems or when an individual system is compared with open repair.