Petrogenesis of peralkaline granite dykes of the Straumsvola complex,western Dronning Maud Land,Antarctica     

Chris?HarrisEmail authorView author&#;s OrcID profile  Tanya?Dreyer  Petrus?le?Roux 《Contributions to Mineralogy and Petrology》2018,173(1):8

Peralkaline syenite and granite dykes cut the Straumsvola nepheline syenite pluton in Western Dronning Maud Land, Antarctica. The average peralkalinity index (PI?=?molecular Al/[Na?+?K]) of the dykes is 1.20 (n?=?29) and manifests itself in the presence of the Zr silicates eudialyte, dalyite and vlasovite, and the Na–Ti silicate, narsarsukite. The dykes appear to have intruded during slow cooling of the nepheline syenite pluton, and the petrogenetic relationship of the dykes and the pluton cannot be related to closed-system processes at low pressure, given the thermal divide that exists between silica-undersaturated and oversaturated magmas. Major and trace element variations in the dykes are consistent with a combination of fractional crystallization of parental peralkaline magma of quartz trachyte composition, and internal mineral segregation prior to final solidification. The distribution of accessory minerals is consistent with late-stage crystallization of isolated melt pockets. The dykes give an Rb–Sr isochron age of 171?±?4.4 Ma, with variable initial ⁸⁷Sr/⁸⁶Sr ratio (0.7075?±?0.0032), and have an average ε _Nd of ? 12.0. Quartz phenocrysts have δ¹⁸O values of 8.4–9.2‰, which are generally in O-isotope equilibrium with bulk rock. Differences in the δ¹⁸O values of quartz and aegirine (average Δ_{quartz?aegirine} = 3.5‰) suggest aegirine formation temperatures around 500 °C, lower than expected for a felsic magma, but consistent with poikilitic aegirine that indicates subsolidus growth. The negative ε _Nd (< ? 10) and magma δ¹⁸O values averaging 8.6‰ (assuming Δ_quartz?magma = 0.6‰) are inconsistent with a magma produced by closed-system fractional crystallization of a mantle-derived magma. By contrast, the nepheline syenite magma had mantle-like δ¹⁸O values and much less negative ε _Nd (average ??3.1, n?=?3). The country rock has similar δ¹⁸O values to the granite dykes (average 8.0‰, n?=?108); this means that models for the petrogenesis of the granites by assimilation are unfeasible, unless an unexposed high-δ¹⁸O contaminant is invoked. Instead, it is proposed that the peralkaline syenite and granite dykes formed by partial melting of alkali-metasomatised gneiss that surrounds the nepheline syenite, followed by fractional crystallization.  相似文献   

The Ediacaran fossils of Charnwood Forest: Shining new light on a major biological revolution     

Charlotte G. Kenchington  Simon J. Harris  Philip B. Vixseboxse  Chris Pickup  Philip R. Wilby 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(3):264-277

Charnwood Forest (UK) hosts some of the oldest and best-preserved macrofossils known from the Ediacaran. It is the counterpoint to the more widely studied fossil sites of south-eastern Newfoundland (Canada), which include the recently-designated UNESCO World Heritage Site of Mistaken Point. Discoveries made in Charnwood Forest since 2008 have the potential to revolutionise our understanding of the evolution of complex macroscopic life and the subsequent development of ‘modern’ (i.e. Phanerozoic) ecosystems. The sites in Charnwood include the holotypes for several iconic Ediacaran taxa, and potentially both the oldest and youngest representatives of the deep-water Avalon Assemblage. These communities provide a unique opportunity to test models of community ecology, biological endemism and environmental sensitivity and adaptability in the Ediacaran. Here, we review the geology of Charnwood Forest and the palaeobiology of its biotas, and we summarise recent scientific advances in the context of our developing understanding of early macroscopic life. We review the application of Reflectance Transformation Imaging to these ancient communities, and signpost exciting new directions for research in Charnwood Forest, almost 170 years after the fossils were first brought to light.  相似文献   

Considering the potential effect of faulting on regional-scale groundwater flow: an illustrative example from Australia’s Great Artesian Basin   总被引：1，自引：1，他引：0  

Brian D. Smerdon  Chris Turnadge 《Hydrogeology Journal》2015,23(5):949-960

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Real-time earthquake warning for astronomical observatories     

Michael Coughlin  Christopher Stubbs  Sergio Barrientos  Chuck Claver  Jan Harms  R. Chris Smith  Michael Warner 《Experimental Astronomy》2015,39(2):387-404

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How well do integrated assessment models represent non-CO2 radiative forcing?     

Mathijs J. H. M. Harmsen  Detlef P van Vuuren  Maarten van den Berg  Andries F Hof  Chris Hope  Volker Krey  Jean-Francois Lamarque  Adriana Marcucci  Drew T Shindell  Michiel Schaeffer 《Climatic change》2015,133(4):565-582

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Coupled atmosphere–ocean data assimilation experiments with a low-order model and CMIP5 model data     

Tardif  Robert  Hakim  Gregory J.  Snyder  Chris 《Climate Dynamics》2015,45(5-6):1415-1427

Climate Dynamics - Coupled atmosphere–ocean data assimilation (DA) experiments are performed for estimating the Atlantic meridional overturning circulation (AMOC). Recovery of the AMOC with...  相似文献   

Chironomid‐inferred late‐glacial summer air temperatures from Lough Nadourcan,Co. Donegal,Ireland     

Jenny E. Watson  Stephen J. Brooks  Nicki J. Whitehouse  Paula J. Reimer  H. John B. Birks  Chris Turney 《第四纪科学杂志》2010,25(8):1200-1210

Western Ireland, located adjacent to the North Atlantic, and with a strongly oceanic climate, is potentially sensitive to rapid and extreme climate change. We present the first high‐resolution chironomid‐inferred mean July temperature reconstruction for Ireland, spanning the late‐glacial and early Holocene (LGIT, 15–10 ka BP). The reconstruction suggests an initial rapid warming followed by a short cool phase early in the interstadial. During the interstadial there are oscillations in the inferred temperatures which may relate to Greenland Interstadial events GI‐1a–e. The temperature decrease into the stadial occurs in two stages. This two‐stage drop can also be seen in other late‐glacial chironomid‐inferred temperature records from the British Isles. A stepped rise in temperatures into the Holocene, consistent with present‐day temperatures in Donegal, is inferred. The results show strong similarities with previously published LGIT chironomid‐inferred temperature reconstructions, and with the NGRIP oxygen‐isotope curve, which indicates that the oscillations observed in the NGRIP record are of hemispherical significance. The results also highlight the influence of the North Atlantic on the Irish climate throughout the LGIT. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The 2dF Galaxy Redshift Survey: stochastic relative biasing between galaxy populations     

Vivienne Wild  John A. Peacock  Ofer Lahav  Edward Conway  Steve Maddox  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ian Lewis  Stuart Lumsden  Darren Madgwick  Peder Norberg  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2005,356(1):247-269

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Landscape influences on aluminium and dissolved organic carbon in streams draining the Hubbard Brook valley,New Hampshire,USA     

Sheila M. Palmer  Brian I. Wellington  Chris E. Johnson  Charles T. Driscoll 《水文研究》2005,19(9):1751-1769

Concentrations of both aluminium (Al) and dissolved organic carbon (DOC) in stream waters are likely to be regulated by factors that influence water flowpaths and residence times, and by the nature of the soil horizons through which waters flow. In order to investigate landscape‐scale spatial patterns in streamwater Al and DOC, we sampled seven streams draining the Hubbard Brook valley in central New Hampshire. We observed considerable variation in stream chemistry both within and between headwater watersheds. Across the valley, concentrations of total monomeric aluminium (Al_m) ranged from below detection limits (<0·7 µmol l⁻¹) to 22·3 µmol l⁻¹. In general, concentrations of Al_m decreased as pH increased downslope. There was a strong relationship between organic monomeric aluminium (Al_o) and DOC concentrations (R² = 0·92). We observed the highest Al_m concentrations in: (i) a watershed characterized by a steep narrow drainage basin and shallow soils and (ii) a watershed characterized by exceptionally deep forest floor soils and high concentrations of DOC. Forest floor depth and drainage area together explained much of the variation in ln Al_m (R² = 0·79; N = 45) and ln DOC (R² = 0·87; N = 45). Linear regression models were moderately successful in predicting ln Al_m and ln DOC in streams that were not included in model building. However, when back‐transformed, predicted DOC concentrations were as much as 72% adrift from observed DOC concentrations and Al_m concentrations were up to 51% off. This geographic approach to modelling Al and DOC is useful for general prediction, but for more detailed predictions, process‐level biogeochemical models are required. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Recent TIMS dating results from British Late Pleistocene vertebrate faunal localities: context and interpretation     

Mabs Gilmour  Andy Currant  Roger Jacobi  Chris Stringer 《第四纪科学杂志》2007,22(8):793-800

New TIMS dates from British sites underpin and extend the growing model of mammalian faunal history during the Late Pleistocene. The sequence of British faunas during the three successive warm phases of MIS 5 presents a challenging model in which the mammal faunas of the first two temperate phases, 5e and 5c is dominated by species of a classically interglacial character, while that of the final phase, sub‐stage 5a, is dominated by bison and reindeer. This we see as the ‘cold fauna’ appearing in Britain during the cool isotope sub‐stage 5b and subsequently isolated by the rising sea level of isotope sub‐stage 5a. All these three faunas are true island faunas. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献