U-Th-Pb and Lu-Hf isotopic constraints on the evolution of sub-continental lithospheric mantle, French Massif Central     

Nadine Wittig  Joel A. Baker  Hilary Downes 《Geochimica et cosmochimica acta》2007,71(5):1290-1311

We have carried out a Pb double-spike and Lu-Hf isotope study of clinopyroxenes from spinel-facies mantle xenoliths entrained in Cenozoic intraplate continental volcanism of the French Massif Central (FMC). U-Th-Pb and Lu-Hf isotope systematics verify the existence of different lithospheric domains beneath the northern and southern FMC. Northern FMC clinopyroxenes have extreme Lu/Hf ratios and ultra-radiogenic Hf (ε_Hf = +39.6 to +2586) that reflect ∼15-25% partial melting in Variscan times (depleted mantle model ages ∼360 Ma). Zr, Hf and Th abundances in these clinopyroxenes are low and unaffected by hydrous/carbonatitic metasomatism that overprinted LILE and light REE abundances and caused decoupling of Lu/Hf-Sm/Nd ratios and Nd-Hf isotopes (ε_Nd = +2.1 to +91.2). Pb isotopes of northern FMC clinopyroxenes are radiogenic (²⁰⁶Pb/²⁰⁴Pb > 19), and typically more so than the host intraplate volcanic rocks. ²³⁸U/²⁰⁴Pb ratios range from 17 to 68, and most samples have distinctively low ²³²Th/²³⁸U (<1) and ²³²Th/²⁰⁴Pb (3-22). Clinopyroxenes from southern FMC lherzolites are generally marked by overall incompatible trace element enrichment including Zr, Hf and Th abundances, and have Pb isotopes that are similar to or less radiogenic than the host volcanic rocks. Hf isotope ratios are less radiogenic (ε_Hf = +5.4 to +41.5) than northern FMC mantle and have been overprinted by silicate-melt-dominated metasomatism that affected this part of FMC mantle. Major element and Lu concentrations of clinopyroxenes from southern FMC harzburgites are broadly similar to northern FMC clinopyroxenes and suggest they experienced similar degrees of melt extraction as northern FMC mantle. ²³⁸U/²⁰⁴Pb (53-111) and ²³²Th/²⁰⁴Pb ratios (157-355) of enriched clinopyroxenes from the southern FMC are extreme and significantly higher than the intraplate volcanic rocks. In summary, mantle peridotites from different parts of the FMC record depletion at ∼360 Ma during Variscan subduction, followed by differing styles of enrichment. Northern FMC mantle was overprinted by a fluid/carbonatitic metasomatic agent that carried elements like U, Pb, Sr and light REE. In contrast, much of the southern FMC mantle was metasomatised by a small-degree partial silicate melt resulting in enrichment of all incompatible trace elements. The extreme mantle ²³⁸U/²⁰⁴Pb (northern and southern FMC), ²³²Th/²³⁸U (northern FMC) and ²³²Th/²⁰⁴Pb ratios (southern FMC), coupled with unremarkable present-day Pb isotope ratios, constrain the timing of enrichment. Mantle metasomatism is a young feature related to melting of the upwelling mantle responsible for Cenozoic FMC volcanism, rather than subduction-related metasomatism intimately associated with mantle depletion during the Variscan orogeny. The varying metasomatic styles relate to pre-existing variations in the thickness of the continental lithospheric lid, which controlled the extent to which upwelling mantle could ascend and melt. In the northern FMC, a thicker and more refractory lithospheric lid (?80 km) only allowed incipient degrees of melting resulting in fluid/carbonatitic metasomatism of the overlying sub-continental lithospheric mantle. The thinner lithospheric lid of the southern FMC (?70 km) allowed larger degrees of melting and resulted in silicate-melt-dominated metasomatism, and also focused the location of the volcanic fields of the FMC above this region.  相似文献   

The late-glacial and early-Holocene palaeoecology of cladoceran microfossil assemblages at Kråkenes, western Norway, with a quantitative reconstruction of temperature changes   总被引：2，自引：0，他引：2  

Catherine A. Duigan  Hilary H. Birks 《Journal of Paleolimnology》2000,23(1):67-76

Cladoceran microfossil remains were analysed from a sediment core taken from a lake basin at Kråkenes, western Norway. The sequence included immediate post-glacial conditions (ca. 12,300 ¹⁴C BP), the Allerod, Younger Dryas, and early Holocene to approximately 8,500 ¹⁴C BP. The interpretation of changes in the cladoceran assemblages is based on the known ecology of the taxa, the documented environmental history of the study sequence, the variations in the organic content of the sediment, the radiocarbon dates, and the results of analyses of other biotic groups, including diatoms, macrophytes, and chironomids. In addition, a quantitative reconstruction of changes in air temperature is presented for the study period. This reconstruction is based on transfer functions developed from a separate Swiss surface-sediment cladoceran data set.The cladoceran assemblages throughout the sequence are dominated by littoral chydorid taxa. Bosmina, Daphnia, and Simocephalus represent the open-water component of the zooplankton. Chydorus piger and Daphnia were the only immediate post-glacial pioneer taxa. A rapid proliferation of the open-water and littoral cladoceran taxa began with the onset of the Allerod and persisted for approximately 1,000 yrs. At the start of the Younger Dryas a local glacier formed and drained into the lake, causing a sudden decline in chydorid diversity, with only Chydorus sphaericus and Acroperus harpae persisting throughout this period. Chydorid diversity started to recover in the upper Younger Dryas and continued in the early Holocene. Progressive acidification and oligotrophication are also discernible from the cladoceran assemblages present in the Holocene.The reconstructed mean summer air temperature was from 8-21 °C, with prediction errors of 1.8-2.5 °C. The Allerod was only slightly warmer than the Younger Dryas period, but a progressive increase in temperature is apparent during the early Holocene. In conclusion, the results of this study provide a further demonstration of the value of cladocera as indicators of a variety of palaeoenvironmental parameters, including temperature.  相似文献   

Geodigest     

Hilary Davies 《Geology Today》2019,35(5):162-173

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Trends in Extreme Precipitation Events in the Indus River Basin and Flooding in Pakistan     

Heike Hartmann  Hilary Buchanan 《大气与海洋》2014,52(1):77-91

In the absence of a sufficiently dense network of climate stations covering all topographic regions of the Indus River basin and delivering high quality data over the last 30 years or more, daily precipitation data were obtained from the National Centers for Environmental Prediction-Department of the Enviornment (NCEP-DOE) Reanalysis 2 dataset for the period 1979 to 2011. The daily precipitation data were transformed into time series of frequency of extreme precipitation events of 1-day and 10-day durations defined in terms of 90th and 99th percentile threshold exceedances. The non-parametric Mann-Kendall trend test was applied to determine whether statistically significant changes in precipitation extremes occurred over time, in due consideration of autocorrelation in the data.

Extreme precipitation showed a high spatial variability, with the highest daily and 10-day precipitation totals, and thus highest 90th and 99th percentiles, in the southeastern lowlands at the foot of the Himalayas and the lowest in the Karakorum. Significantly decreasing trends in extreme precipitation were observed in the western part of the Indus River basin; significantly increasing trends were mainly detected in the very high mountainous regions in the east (Transhimalaya and Himalayas) and in the north (Hindu Kush and Karakorum) of the Indus basin. High precipitation rates are not common in the arid climate of these high mountainous regions. Future flood management plans need to consider the increasing trends in extreme precipitation events in these areas.  相似文献   

A 500 yr speleothem-derived reconstruction of late autumn–winter precipitation, northeast Turkey     

Catherine N. Jex  Andy Baker  Jonathan M. Eden  Warren J. Eastwood  Ian J. Fairchild  Melanie J. Leng  Louise Thomas  Hilary J. Sloane 《Quaternary Research》2011,75(3):399-405

A verified instrumental calibration of annually resolved δ¹⁸O for a stalagmite from Gümü?hane in northeast Turkey is presented and cross-validated using a ‘leave-one-out’ technique. The amount of late autumn to winter precipitation is negatively correlated with stalagmite δ¹⁸O between AD 1938 and 2004. The observed relationship is extrapolated back to ~ AD 1500 leading to the first long winter precipitation reconstruction for this region. Modern day October to January precipitation is linked to pressure fields in Western Russia. Anomalously lower reconstructed rainfall is recorded in AD 1540–1560 at which time higher pressure over the Caspian Sea region is inferred.  相似文献   

Developing a long-term outlook for the Great Barrier Reef,Australia: A framework for adaptive management reporting underpinning an ecosystem-based management approach     

Kirstin Dobbs  Jon Day  Hilary Skeat  John Baldwin  Fergus Molloy  Laurence McCook  Margaret Johnson  Bruce Elliot  Andrew Skeat  Karen Vohland  David Wachenfeld  Richard Kenchington 《Marine Policy》2011

The Great Barrier Reef Outlook Report 2009 was the first produced in response to a newly legislated requirement for five-yearly reports on the status of and outlook for the Great Barrier Reef. It adopted an ecosystem approach, assessing all habitats and species, ecosystem processes and major uses. By then considering the factors affecting the ecosystem, coupled with an assessment of management effectiveness, it provided a risk-based forward-looking projection for the ecosystem. Rarely has such a comprehensive, ecosystem-based report been produced to guide government action. With no pre-determined path to follow for interpreting the legislative requirements, the Great Barrier Reef Marine Park Authority (GBRMPA) developed a repeatable structure and method for Great Barrier Reef Outlook Reports that impartially and consistently considers the evidence and clearly presents the findings. The GBRMPA worked closely with relevant Australian and Queensland Government agencies as well as researchers, industry representatives and the community while developing the report. That such a report must be produced every five years allows an overview of the effectiveness of management responses to be regularly assessed. It also provides a transparent means of highlighting and tracking emerging risks facing the Great Barrier Reef.  相似文献   

Japanese investment in the US fishing industry and its relation to the Two-Hundred-Mile Law     

Hilary K. Josephs 《Marine Policy》1978,2(4):255-267

After providing a statistical survey of Japanese direct investment in the US fishing industry, and a historical background of Japanese-US fishing relations, the author examines the statutory regulation of foreign direct investment (FDI) in the fishing industry. She then discusses international practice and restrictions on FDI, the recent response of Congress in view of the Two-Hundred-Mile Law, and the issue of protectionism and the competitive position of the US fishing industry.  相似文献   

Development of a Multimetric Index for Integrated Assessment of Salt Marsh Ecosystem Condition     

Jessica L. Nagel  Hilary A. Neckles  Glenn R. Guntenspergen  Erika N. Rocks  Donald R. SchoolmasterJr  James B. Grace  Dennis Skidds  Sara Stevens 《Estuaries and Coasts》2018,41(2):334-348

Tools for assessing and communicating salt marsh condition are essential to guide decisions aimed at maintaining or restoring ecosystem integrity and services. Multimetric indices (MMIs) are increasingly used to provide integrated assessments of ecosystem condition. We employed a theory-based approach that considers the multivariate relationship of metrics with human disturbance to construct a salt marsh MMI for five National Parks in the northeastern USA. We quantified the degree of human disturbance for each marsh using the first principal component score from a principal components analysis of physical, chemical, and land use stressors. We then applied a metric selection algorithm to different combinations of about 45 vegetation and nekton metrics (e.g., species abundance, species richness, and ecological and functional classifications) derived from multi-year monitoring data. While MMIs derived from nekton or vegetation metrics alone were strongly correlated with human disturbance (r values from ?0.80 to ?0.93), an MMI derived from both vegetation and nekton metrics yielded an exceptionally strong correlation with disturbance (r = ?0.96). Individual MMIs included from one to five metrics. The metric-assembly algorithm yielded parsimonious MMIs that exhibit the greatest possible correlations with disturbance in a way that is objective, efficient, and reproducible.  相似文献   

Globalisation and Border Dynamics: impacts on the urban development of Darwin,Australia     

Jiaping Wu  Hilary P.M. Winchester 《The Australian geographer》2015,46(2):255-270

National boundaries and border cities have been transformed globally. This is partly due to neoliberal globalisation, the continuous formation of a ‘borderless world’ and partly to the global ‘war on terror’. Darwin, the capital city of the Northern Territory (NT), is on the northern coast of Australia, bordering its overseas Asian neighbours. Far away from the main Australian population centres in the south, the city grows slowly, relying mainly on Australian government investments, infrastructure, and the incorporation of defence programs in the north. The rise of Asia, as well as Australia's increasing economic reliance on Asia, has created new opportunities for Darwin's growth. The development of Asian economies has resulted in growing global investment in resource extraction in NT. Asia, though, has been seen as a key threat in the modern history of Australia. This national sensitivity is underpinned by the global ‘war on terror’ in which Australia is deeply involved. Australia has tight border control regimes and a growing military presence on the northern border area. This paper examines how these co-existing but contradictory dynamics have reshaped the urban development of Darwin City. The consequential social and spatial patterns are identified and discussed.  相似文献   

Imagery Scale and Type for Natural Hazards Analysis: Classroom Examples Using Forest Fires and Snow Avalanches     

David R. Butler  Hilary J.M. Sandford 《国际地球制图》2013,28(1):73-78

Abstract

The type of remotely sensed imagery best suited for natural hazards analysis is largely dependent on the geographic size and discreteness of the hazard in question. Some forms of imagery that are appropriate for analyses of spatially fixed, relatively fine‐scale hazards are inappropriate for use with geographically widespread and transient hazards, and vice versa. In this paper we utilize one study area, Waterton‐Glacier International Peace Park (Canada and USA), and two natural hazard types (snow avalanches and forest fires), to illustrate how these remote sensing principles can be presented to students of natural hazards. We also address the issue of familiarity, or lack thereof, that students have with different images from a variety of platforms.  相似文献