The Mesoarchaean Akia terrane, West Greenland, revisited : new insights based on spatial integration of geophysics, field observation, geochemistry and geochronology

NJG thanks Australian Research Council grant FL160100168 for financial support.The northern part of the North Atlantic Craton (NAC) in southern West Greenland comprises a large tract of exposed Meso-Neoarchaean continental crust, divided into the ca 3300–2900 Ma Akia and ca 2900–2500 Ma Tuno terranes. We combine aeromagnetic, stream sediment geochemical, new litho-chemical and zircon geochronological data with previously published data to re-evaluate the crustal architecture and evolution of the Akia terrane and its boundary towards the Tuno terrane. The previously recognised, but overlooked, Alanngua complex, situated between the Akia and Tuno terranes is bounded by aeromagnetic lineaments interpreted as Neoarchaean shear zones and has a distinct spectrum of Neoarchaean magmatic and metamorphic zircon ages that are rare in the Akia terrane. The Alanngua complex comprises components derived from both the Akia and Tuno terranes and is interpreted as a tectonic melange created during the Neoarchaean assembly of the NAC. Within the Akia terrane, the chemistry of orthogneiss samples indicate that a large percentage is too mafic to classify as TTG s.s., implying that not only partial melting of mafic crust, but also some yet unaddressed mantle involvement is necessary in their formation. Previous models for the generation of the ca. 3015–2990 Ma quartz-dioritic Finnefjeld and Taserssuaq complexes conflict with their geochemical variation. The complexes are spatially associated with strong aeromagnetic responses that are interpreted to reflect a large gabbro-diorite intrusion, and we propose that the protoliths of the Finnefjeld and Taserssuaq complexes are genetically linked to such intrusion. Formed at same time are carbonatite, high-Mg gabbro and tonalite-trondhjemite, and we propose that this wide spectrum of rocks could have formed by lithospheric and crustal melting in response to asthenospheric upwelling possibly in an extensional setting. Periods of extensive magmatism in the Akia terrane were previously recognised at ca. 3220-3180 Ma and 3070-2970 Ma. We now subdivide the latter period into three episodes: juvenile basaltic-andesitic volcanism at 3070–3050 Ma; tonalitic and dioritic plutonism at 3050–3020 Ma, and gabbroic-dioritic plus tonalitic-trondhjemitic plutonism at 3020–2985 Ma. This last episode was immediately followed by crustal reworking during collision at 2980–2950 Ma.Publisher PDFPeer reviewe

Cell transformation assays for prediction of carcinogenic potential: State of the science and future research needs

Copyright @ 2011 The Authors. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Cell transformation assays (CTAs) have long been proposed as in vitro methods for the identification of potential chemical carcinogens. Despite showing good correlation with rodent bioassay data, concerns over the subjective nature of using morphological criteria for identifying transformed cells and a lack of understanding of the mechanistic basis of the assays has limited their acceptance for regulatory purposes. However, recent drivers to find alternative carcinogenicity assessment methodologies, such as the Seventh Amendment to the EU Cosmetics Directive, have fuelled renewed interest in CTAs. Research is currently ongoing to improve the objectivity of the assays, reveal the underlying molecular changes leading to transformation and explore the use of novel cell types. The UK NC3Rs held an international workshop in November 2010 to review the current state of the art in this field and provide directions for future research. This paper outlines the key points highlighted at this meeting

Differentiating between inherited and autocrystic zircon in granitoids

The Maniitsoq map project is supported by the Ministry of Mineral Resources, Government of Greenland. The LA-ICP-MS instruments in the JdLC were funded via an Australian Geophysical Observing System grant provided to AuScope Pty Ltd. by the AQ44 Australian Education Investment Fund program.Inherited zircon, crystals that did not form in situ from their host magma but were incorporated from either the source region or assimilated from the wall-rock, is common but can be difficult to identify. Age, chemical and/or textural dissimilarity to the youngest zircon fraction are the primary mechanisms of distinguishing such grains. However, in Zr-undersaturated magmas, the entire zircon population may be inherited and, if not identifiable via textural constraints, can lead to erroneous interpretation of magmatic crystallization age and magma source. Here, we present detailed field mapping of cross-cutting relationships, whole-rock geochemistry and zircon textural, U-Pb and trace element data of trondhjemite, granodiorite and granite from two localities in a complex Archean gneiss terrane in southwest Greenland, which reveal cryptic zircon inheritance. Zircon textural, U–Pb and trace element data demonstrate that, in both localities, trondhjemite is the oldest rock (3011 ± 5 Ma, 2σ), which is intruded by granodiorite (2978 ± 4 Ma, 2σ). However, granite intrusions, constrained by cross-cutting relationships as the youngest component, only contain inherited zircon derived from trondhjemite and granodiorite based on ages and trace element concentrations. Without age constraints on the older two lithologies, it would be tempting to consider the youngest zircon fraction as recording crystallization of the granite but this would be erroneous. Furthermore, whole-rock geochemistry indicates that the granite contains only 6 µg g-1 Zr, extremely low for a granitoid with ∼77 wt. % SiO2. Such low Zr concentration explains the lack of autocrystic zircon in the granite. We expand on a differentiation tool that uses Th/U ratios in zircon versus that in the whole rock to aid in the identification of inherited zircon. This work emphasizes the need for field observations, geochemistry, grain characterization, and precise geochronology to accurately determine igneous crystallization ages and differentiate between inherited and autocrystic zircon.PostprintPeer reviewe

Regional zircon U-Pb geochronology for the Maniitsoq region, southwest Greenland

The Ministry of Mineral Resources, Government of Greenland, funded this project. Analyses in the JdLC GeoHistory Facility were enabled by instrumentation supported by AuScope (auscope.org.au) and the Australian Government via the National Collaborative Research Infrastructure Strategy. The Tescan Mira3 FEG-SEM was funded through the Australian Research Council LIEF program.Zircon U-Pb geochronology places high-temperature geological events into temporal context. Here, we present a comprehensive zircon U-Pb geochronology dataset for the Meso- to Neoarchean Maniitsoq region in southwest Greenland, which includes the Akia Terrane, Tuno Terrane, and the intervening Alanngua Complex. The magmatic and metamorphic processes recorded in these terranes straddle a key change-point in early Earth geodynamics. This dataset comprises zircon U-Pb ages for 121 samples, including 46 that are newly dated. A principal crystallization peak occurs across all three terranes at ca. 3000 Ma, with subordinate crystallization age peaks at 3200 Ma (Akia Terrane and Alanngua Complex only), 2720 Ma and 2540 Ma. Metamorphic age peaks occur at 2990 Ma, 2820-2700 Ma, 2670-2600 Ma and 2540 Ma. Except for one sample, all dated metamorphic zircon growth after the Neoarchean occurred in the Alanngua Complex or within 20 km of its boundaries. This U-Pb dataset provides an important resource for addressing Earth Science topics as diverse as crustal evolution, fluid-rock interaction and mineral deposit genesis.Publisher PDFPeer reviewe

Building Mesoarchaean crust upon Eoarchaean roots : the Akia Terrane, West Greenland

The Maniitsoq project is supported by the Ministry of Mineral Resources and Labour, Government of Greenland. NJG thanks Curtin University and Australian Research Council grant FL160100168 for financial support.Constraining the source, genesis, and evolution of Archaean felsic crust is key to understanding the growth and stabilization of cratons. The Akia Terrane, part of the North Atlantic Craton, West Greenland, is comprised of Meso-to-Neoarchaean orthogneiss, with associated supracrustal rocks. We report zircon U–Pb and Lu–Hf isotope data, and whole-rock geochemistry, from samples of gneiss and supracrustals from the northern Akia Terrane, including from the Finnefjeld Orthogneiss Complex, which has recently been interpreted as an impact structure. Isotope data record two major episodes of continental crust production at ca. 3.2 and 3.0 Ga. Minor ca. 2.7 and 2.5 Ga magmatic events have more evolved εHf, interpreted as reworking of existing crust perhaps linked to terrane assembly. Felsic rocks from the Finnefjeld Orthogneiss Complex were derived from the same source at the same time as the surrounding tonalites, but from shallower melting, requiring any bolide-driven melting event to have occurred almost simultaneously alongside the production of the surrounding crust. A simpler alternative has the Finnefjeld Complex and surrounding tonalite representing the coeval genesis of evolved crust over a substantial lithospheric depth. Hafnium isotope data from the two major Mesoarchaean crust-forming episodes record a contribution from older mafic Eoarchaean crust. Invoking the involvement of an Eoarchaean root in the growth of younger Mesoarchaean crust puts important constraints on geodynamic models of the formation of the discrete terranes that ultimately assembled to form Earth’s cratons.Publisher PDFPeer reviewe

The first three dimensional fossils of Cretaceous sclerorhynchid sawfish Asflapristis cristadentis gen et sp nov and implications for the phylogenetic position of the Sclerorhynchoidei (Chondrichthyes)

A new fossil batoid (ray) Asflapristis cristadentis gen. et sp. nov. is described from six exceptionally well-preserved, three-dimensional skeletal remains from the Turonian (Late Cretaceous) of Morocco. Mechanical and acid preparation and CT scanning of these specimens reveal details of much of the proximal skeleton, especially the skull, synarcual and pectoral skeleton, with only the more distal parts of the skeleton missing. These fossils represent a relatively large animal (62 cm preserved length, estimated total length to approximately 2 meters) possessing a robust rostrum that lacks enlarged rostral denticles. It has a narrow and small chondrocranium with jaws that are relatively large compared to the rest of the skull and robust with highly ornamented teeth that lack cusps. The branchial skeleton shows a large second hypobranchial without anterior process which was probably fused to the basibranchial as in other sclerorhynchoids. The synarcual is large and lacks centra through its entire length, and with no direct connection to the pectoral girdle was observed. Pectoral fins probably possessed enlarged proximal elements (propterygium, mesopterygium and metapterygium), the reduced articulation facet between the coracoid with the pectoral elements was reduced. A phylogenetic analysis using both parsimony and bayesian methods was performed incorporating this new taxon. Both analyses recovered a phylogenetic topology that places the sclerorhynchoids in a close relation to rajoids and clearly separated from the morphologically similar Pristidae within the Rhinopristiformes. In respect to the extant taxa, the phylogenies generated are similar to that obtained in molecular analysis of modern batoids. The palaeoecological implication of this discovery suggests that the Asfla assemblage was not from a ‘normal’ open carbonate shelf but rather a restricted environment favouring a low diversity chondrichthyan fauna

Full Genome Characterization of the Culicoides-Borne Marsupial Orbiviruses: Wallal Virus, Mudjinbarry Virus and Warrego Viruses

Viruses belonging to the species Wallal virus and Warrego virus of the genus Orbivirus were identified as causative agents of blindness in marsupials in Australia during 1994/5. Recent comparisons of nucleotide (nt) and amino acid (aa) sequences have provided a basis for the grouping and classification of orbivirus isolates. However, full-genome sequence data are not available for representatives of all Orbivirus species. We report full-genome sequence data for three additional orbiviruses: Wallal virus (WALV); Mudjinabarry virus (MUDV) and Warrego virus (WARV). Comparisons of conserved polymerase (Pol), sub-core-shell 'T2' and core-surface 'T13' proteins show that these viruses group with other Culicoides borne orbiviruses, clustering with Eubenangee virus (EUBV), another orbivirus infecting marsupials. WARV shares <70% aa identity in all three conserved proteins (Pol, T2 and T13) with other orbiviruses, consistent with its classification within a distinct Orbivirus species. Although WALV and MUDV share <72.86%/67.93% aa/nt identity with other orbiviruses in Pol, T2 and T13, they share >99%/90% aa/nt identities with each other (consistent with membership of the same virus species - Wallal virus). However, WALV and MUDV share <68% aa identity in their larger outer capsid protein VP2(OC1), consistent with membership of different serotypes within the species - WALV-1 and WALV-2 respectively

Cellular senescence in brain aging and cognitive decline

Cellular senescence is a biological aging hallmark that plays a key role in the development of neurodegenerative diseases. Clinical trials are currently underway to evaluate the effectiveness of senotherapies for these diseases. However, the impact of senescence on brain aging and cognitive decline in the absence of neurodegeneration remains uncertain. Moreover, patient populations like cancer survivors, traumatic brain injury survivors, obese individuals, obstructive sleep apnea patients, and chronic kidney disease patients can suffer age-related brain changes like cognitive decline prematurely, suggesting that they may suffer accelerated senescence in the brain. Understanding the role of senescence in neurocognitive deficits linked to these conditions is crucial, especially considering the rapidly evolving field of senotherapeutics. Such treatments could help alleviate early brain aging in these patients, significantly reducing patient morbidity and healthcare costs. This review provides a translational perspective on how cellular senescence plays a role in brain aging and age-related cognitive decline. We also discuss important caveats surrounding mainstream senotherapies like senolytics and senomorphics, and present emerging evidence of hyperbaric oxygen therapy and immune-directed therapies as viable modalities for reducing senescent cell burden

Race, colonial history and national identity: Resident Evil 5 as a Japanese game

Resident Evil 5 is a zombie game made by Capcom featuring a White American protagonist and set in Africa. This paper argues that approaching this as a Japanese game reveals aspects of a Japanese racial and colonial social imaginary that are missed if this context of production is ignored. In terms of race, the game presents hybrid racial subjectivities that can be related to Japanese perspectives of Blackness and Whiteness where these terms are two poles of difference and identity through which an essentialised Japanese identity is constructed in what Iwabuchi calls “strategic hybridism” (Iwabuchi, 2002). In terms of colonialism, the game echoes structures of Japanese colonialism through which Japanese colonialism is obliquely memorialised and a “normal” Japanese global subjectivity can be performed