Is the Greenland Ice Sheet in a state of collapse?     

Poul Christoffersen  Michael J. Hambrey 《Geology Today》2006,22(3):98-103

The Greenland Ice Sheet is thinning at an accelerating pace and the ice sheet's contribution to sea-level rise has doubled in less than a decade. New data show rapid and widespread changes in the behaviour of the ice sheet, particularly along the coastal margin. These changes coincide with a decade of sustained Arctic warming of up to 3 °C. Decay of the Greenland Ice Sheet in response to global warming will not only be governed by increased surface melting during longer and warmer summers but also by a speed-up of coastal glaciers that drain the interior ice sheet. A precise estimate of sea-level rise in the twenty-first century relies on improved theoretical treatment of these glaciers in computer models.  相似文献   

Influence of oxygen fugacity on mineral compositions in peralkaline melts: The Katzenbuckel volcano, Southwest Germany     

Ute Mann  Michael Marks  Gregor Markl   《Lithos》2006,91(1-4):262-285

The igneous rocks of the Katzenbuckel, Southwest Germany, represent a unique and unusual alkaline to peralkaline association within the European Volcanic Province. The magmatic activity can be subdivided into two main phases. Phase I comprises the main rock bodies of phonolite and nepheline syenite, which were later intruded by different peralkaline dyke rocks (tinguaites and alkali feldspar syenite dykes) of phase II. The dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late-stage pneumatolytic activity causing autometasomatic alterations.

As is typical for alkaline to peralkaline igneous rocks, early mafic minerals of phase I rocks comprise olivine, augite and Fe–Ti oxides, which are substituted in the course of fractionation by Na-amphibole and Na-pyroxene. For the early magmatic stage, calculated temperatures range between 880 and 780 °C with low silica activities (0.4 to 0.6) but high relative oxygen fugacities between 0.5 and 1.9 log units above the FMQ buffer. Even higher oxygen fugacities (above the HM buffer) are indicated for the autometasomatic alteration, which occurred at temperatures between 585 and 780 °C and resulted in the formation of pseudobrookite and hematite.

The unusually high oxygen fugacities (even during the early magmatic stage) are recorded by the major element compositions of the mafic minerals (forsterite content in olivine between 68 and 78 mol%, up to 6.2 wt.% ZrO₂ and 8.5 wt.% TiO₂ in clinopyroxene), the unusual mineral assemblages (pseudobrookite, freudenbergite) and by the enrichment of Fe³⁺ in the felsic minerals (up to 2.8 wt.% Fe₂O₃ in alkali feldspar and up to 2.6 wt.% Fe₂O₃ in nepheline). These observations point to a metasomatically enriched and highly oxidized lithospheric mantle as a major source for the Katzenbuckel melts.  相似文献   

U–Pb and Hf isotopic analysis of zircon in lower crustal xenoliths from the Navajo volcanic field: 1.4 Ga mafic magmatism and metamorphism beneath the Colorado Plateau     

James L. Crowley  Mark D. Schmitz  Samuel A. Bowring  Michael L. Williams  Karl E. Karlstrom 《Contributions to Mineralogy and Petrology》2006,151(3):313-330

Zircon from lower crustal xenoliths erupted in the Navajo volcanic field was analyzed for U–Pb and Lu–Hf isotopic compositions to characterize the lower crust beneath the Colorado Plateau and to determine whether it was affected by ∼1.4 Ga granitic magmatism and metamorphism that profoundly affected the exposed middle crust of southwestern Laurentia. Igneous zircon in felsic xenoliths crystallized at 1.73 and 1.65 Ga, and igneous zircon in mafic xenoliths crystallized at 1.43 Ga. Most igneous zircon has unradiogenic initial Hf isotopic compositions (ɛ_Hf=+4.1–+7.8) and 1.7–1.6 Ga depleted mantle model ages, consistent with 1.7–1.6 Ga felsic protoliths being derived from “juvenile” Proterozoic crust and 1.4 Ga mafic protoliths having interacted with older crust. Metamorphic zircon grew in four pulses between 1.42 and 1.36 Ga, at least one of which was at granulite facies. Significant variability within and between xenoliths in metamorphic zircon initial Hf isotopic compositions (ɛ_Hf=−0.7 to +13.6) indicates growth from different aged sources with diverse time-integrated Lu/Hf ratios. These results show a strong link between 1.4 Ga mafic magmatism and granulite facies metamorphism in the lower crust and granitic magmatism and metamorphism in the exposed middle crust.  相似文献   

New results on the resistivity structure of Merapi Volcano (Indonesia), derived from three-dimensional restricted inversion of long-offset transient electromagnetic data     

Michael Commer  Stefan L. Helwig  reas Hördt  Carsten Scholl  Bülent Tezkan 《Geophysical Journal International》2006,167(3):1172-1187

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The effects of hazard zone information on judgements about earthquake damage     

Michael Crozier  John McClure  Jessica Vercoe  Marc Wilson 《Area》2006,38(2):143-152

This study investigates the extent to which people's views on the causes and preventability of earthquake damage might be influenced by their degree of exposure to hazard as well as what information they have been given about the hazard. The results show that the provision of hazard zoning information influences judgements on preventability and causes of damage, but this effect depends on the degree of hazard faced by residents. In low hazard zones, information leads to the view that causes are manageable, whereas in high hazard zones information may induce a degree of fatalism. The use of public information in risk management needs to take into account the degree of risk faced by the recipients.  相似文献   

Basin-related effects on ground motion for earthquake scenarios in the Lower Rhine Embayment   总被引：1，自引：0，他引：1  

Michael Ewald  Heiner Igel  Klaus-Günter Hinzen  Frank Scherbaum 《Geophysical Journal International》2006,166(1):197-212

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A N–S receiver function profile across the Variscides and Caledonides in SW Ireland     

Michael Landes  J. R. R. Ritter  B. M. O'Reilly  P. W. Readman  V. C. Do 《Geophysical Journal International》2006,166(2):814-824

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Biological and Geochemical Record of Anthropogenic Impacts in Recent Sediments from Lake Pupuke, Auckland City, New Zealand     

Paul Augustinus  Michael Reid  Sofia Andersson  Yanbin Deng  Mark Horrocks 《Journal of Paleolimnology》2006,35(4):789-805

Frozen sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high resolution decadal to annual scale record of changing lake paleoenvironments and geochemistry that reflects changing landuse and hydrology in the catchment over the past c. 190 years. A reliable chronology is available from AMS ¹⁴C and ²¹⁰Pb dating of the sediments, with the timing of the older part of the record supported by the first appearance of pollen of introduced Pinus and Plantago lanceolata associated with European settlement of Auckland in the early 1840s. Diatom stratigraphy, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions commensurate with European development of the Lake Pupuke catchment, in particular enhanced algal productivity controlled by the influx of nutrients after c. 1920 AD. Attempts to prevent nuisance algal blooms in 1933, 1934 and 1939 using CuSO₄ addition produced Cu spikes in the sediment that allowed confirmation of the accuracy of the ²¹⁰Pb chronology. Hence, the elemental and isotopic composition of the Lake Pupuke sediments reflect the timing of significant anthropogenic activities, rather than climatic variations, that have occurred within the watershed over the past c. 190 years. The comparison of records of land use change in the catchment with the multi-proxy record of changes in the sediments usually allowed unambiguous identification of the signatures of change and their causes.  相似文献   

New Zealand historical geographies     

Eric Pawson  Michael RocheGuest Editors 《New Zealand geographer》2006,62(1):1-1

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Multicollinearity and correlation among local regression coefficients in geographically weighted regression   总被引：5，自引：3，他引：5  

David Wheeler  Michael Tiefelsdorf 《Journal of Geographical Systems》2005,7(2):161-187

Present methodological research on geographically weighted regression (GWR) focuses primarily on extensions of the basic GWR model, while ignoring well-established diagnostics tests commonly used in standard global regression analysis. This paper investigates multicollinearity issues surrounding the local GWR coefficients at a single location and the overall correlation between GWR coefficients associated with two different exogenous variables. Results indicate that the local regression coefficients are potentially collinear even if the underlying exogenous variables in the data generating process are uncorrelated. Based on these findings, applied GWR research should practice caution in substantively interpreting the spatial patterns of local GWR coefficients. An empirical disease-mapping example is used to motivate the GWR multicollinearity problem. Controlled experiments are performed to systematically explore coefficient dependency issues in GWR. These experiments specify global models that use eigenvectors from a spatial link matrix as exogenous variables.This study was supported by grant number 1 R1 CA95982-01, Geographic-Based Research in Cancer Control and Epidermiology, from the National Cancer Institute. The author thank the anonymous reviewers and the editor for their helpful comments.  相似文献