Garnet zoning and the identification of equilibrium mineral compositions in high-pressure–temperature granulites from the Moldanubian Zone, Austria     

Cooke  O'Brien  & Carswell 《Journal of Metamorphic Geology》2000,18(5):551-569

A detailed investigation of the compositional variation in garnet has been undertaken in a garnet–pyroxene‐bearing granulite from the high‐grade Gföhl Unit, Moldanubian Zone, Lower Austria. Textural observations, together with the interpretation of the preserved garnet chemistry, enables the recognition of both prograde core and peak metamorphic garnet mantle growth stages, an extremely rare feature in high‐P–T granulite facies rocks. Initial thermobarometric calculations undertaken across whole garnet zoning profiles show how correct interpretation of a zoning profile is essential if the maximum peak metamorphic P–T conditions are to be recovered. The effect of retrograde decompression‐ and cooling‐driven reactions on inclusion and host garnet compositions has also been assessed. The results indicate that caution should be exercised when utilizing inclusion and adjacent garnet compositions for the thermobarometric evaluation of peak metamorphic equilibration conditions. Peak P–T conditions were determined by the TWEEQU thermobarometric method, utilizing the core compositions of matrix phases combined with the interpreted high‐P–T garnet mantle composition, to give 15.6 kbar and 1090 °C, consistent with previously determined results for Moldanubian granulites. Similar high‐P–T estimates are also provided by a re‐evaluation of previously published results for a granulite sample from the same lithological unit, using a modified interpretation of garnet and plagioclase compositional data. The new estimates presented confirm the previously disputed idea that the Gföhl Unit underwent a high‐pressure granulite facies stage and is therefore distinctly different from the underlying tectonostratigraphic units. It is emphasized that any interpretation of the peak metamorphic conditions in high‐grade rocks must be based on detailed petrographic observations combined with a thorough understanding of the co‐existing equilibrium mineral compositions.  相似文献   

Transitional blueschist–epidote amphibolite facies metamorphism in the Frankenberg massif, Germany, and geotectonic implications     

RÖtzler  Carswell  Gerstenberger  & Haase 《Journal of Metamorphic Geology》1999,17(1):109-125

Bimodal metavolcanic rocks, granitic gneisses and metasediments are associated in the Frankenberg massif, Germany. These rocks are faulted against underlying very low-grade Palaeozoic sequences and adjacent metamorphic complexes of the Variscan basement. The granitic gneisses record an Rb–Sr whole-rock isochron age of 461±20  Ma that is taken as at least a minimum protolith age. The bimodal meta-igneous suites are interpreted to have formed during rifting of the Gondwana continental margin in the Cambro-Ordovician. The various metamorphic units have all experienced a common P–T  history. The peak-pressure stage is constrained to around 490–520  °C and 10–14  kbar (10–12  kbar being most realistic). The metamorphism proceeded along a clockwise P–T path towards conditions of around 580–610  °C and 7–8.5  kbar at the thermal peak followed by a final low-pressure overprint which spanned amphibolite facies to prehnite–actinolite facies temperatures. Owing to a secondary Rb–Sr whole-rock isochron age of 381±24  Ma, interpreted to date the retrograde stage, the whole metamorphic cycle in the Frankenberg massif is ascribed to the late Silurian–early Devonian high-pressure event widely recorded in the European Variscides. The antiformal complexes bordering the Frankenberg massif underwent a well-documented early Carboniferous metamorphism, suggesting that the Frankenberg massif constitutes a klippe which was overthrust towards the end of this second metamorphic cycle.  相似文献   

Exceptional fidelity of preservation in a reworked fossil,Chalk drift,South London,England     

Stephen K. Donovan  Fiona E. Fearnhead 《Geological Journal》2015,50(1):104-106

Reworking of fossils commonly leads to loss of morphological detail and inferior preservation; the main contributions of such specimens to geology are in sedimentology, regional geology and neoichnology. A reworked specimen of the Late Cretaceous (chalk) sponge boring Entobia cretacea Portlock is unusually well preserved. This specimen is from superficial deposits and is well enough preserved that delicate apertural and intercameral canals are apparent. Two factors are recognized as important in maintaining the fine features of this trace fossil: preservation in flint and, presumably, minimal fluvial transport. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Describing long-term trends in precipitation using generalized additive models     

Fiona M. Underwood 《Journal of Hydrology》2009,364(3-4):285-297

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Spatial fluctuations in the spectral shape of the ultraviolet background at 2 < z < 3 and the reionization of helium     

James S. Bolton  Martin G. Haehnelt  Matteo Viel  Robert F. Carswell 《Monthly notices of the Royal Astronomical Society》2006,366(4):1378-1390

The low-density hydrogen and helium in the intergalactic medium (IGM) probed by quasi-stellar object (QSO) absorption lines is sensitive to the amplitude and spectral shape of the metagalactic ultraviolet (UV) background. We use realistic H  i and He  ii Lyα forest spectra, constructed from state-of-the-art hydrodynamical simulations of a Λ cold dark matter (ΛCDM) universe to confirm the reliability of using line profile fitting techniques to infer the ratio of the metagalactic H  i and He  ii ionization rates. We further show that the large spatial variations and the anticorrelation with H  i absorber density observed in the ratio of the measured He  ii to H  i column densities can be explained in a model where the H  i ionization rate is dominated by the combined UV emission from young star-forming galaxies and QSOs and the He  ii ionization rate is dominated by emission from QSOs only. In such a model the large fluctuations in the column density ratio are due to the small number of QSOs expected to contribute at any given point to the He  ii ionization rate. A significant contribution to UV emission at the He  ii photoelectric edge from hot gas in galaxies and galaxy groups would decrease the expected fluctuations in the column density ratio. Consequently, this model appears difficult to reconcile with the large increase in He  ii opacity fluctuations towards higher redshift. Our results further strengthen previous suggestions that observed He  ii Lyα forest spectra at z ∼ 2–3.5 probe the tail end of the reionization of He  ii by QSOs.  相似文献   

Cosmological evolution of heavy-element and H₂ abundances     

S. J. Curran  J. K. Webb  M. T. Murphy  R. F. Carswell 《Monthly notices of the Royal Astronomical Society》2004,351(1):L24-L28

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Farmer-driven Innovation in New South Wales,Australia     

Fiona McKenzie 《The Australian geographer》2013,44(1):81-95

Knowledge generation and the interactions that allow for knowledge exchange are key processes of innovation. Yet these processes are not well understood at the farm level, nor are they well reflected in policy approaches for agricultural innovation. Farmers in New South Wales have used diverse ways to implement innovations in land management. They employ a range of strategies including observing signals from the landscape, independent testing and trialling, use of agronomists, participation in farmer groups and in farmer-driven research programmes. Steps to foster farmer-driven innovations and knowledge-intensive agricultural systems require greater subtlety to enable flexibility, the incorporation of contemporary scientific knowledge and support for sustainable initiatives. More research on innovation and on policy engagement is required to foster on-farm innovative capacity.  相似文献   

Adaptation of water resources systems to changing society and environment: a statement by the International Association of Hydrological Sciences     

Serena Ceola  Alberto Montanari  Tobias Krueger  Fiona Dyer  Heidi Kreibich  Ida Westerberg 《水文科学杂志》2013,58(16):2803-2817

ABSTRACT

We explore how to address the challenges of adaptation of water resources systems under changing conditions by supporting flexible, resilient and low-regret solutions, coupled with on-going monitoring and evaluation. This will require improved understanding of the linkages between biophysical and social aspects in order to better anticipate the possible future co-evolution of water systems and society. We also present a call to enhance the dialogue and foster the actions of governments, the international scientific community, research funding agencies and additional stakeholders in order to develop effective solutions to support water resources systems adaptation. Finally, we call the scientific community to a renewed and unified effort to deliver an innovative message to stakeholders. Water science is essential to resolve the water crisis, but the effectiveness of solutions depends, inter alia, on the capability of scientists to deliver a new, coherent and technical vision for the future development of water systems.