Lead isotope systematics of ore systems of the Macquarie Arc — Implications for arc substrate     

David B. Forster  Graham R. Carr  Peter M. Downes 《Gondwana Research》2011,19(3):686-705

The Macquarie Arc of New South Wales hosts several major Au and Cu deposits. We present new Pb isotope results for Cadia, the Copper Hill, Little Copper Hill and Cowal deposits, along with data from the CSIRO database. The results generally plot close to established mantle growth curves and are similar to oceanic basalts. Data for individual deposits mostly have Pb model ages consistent with independent age constraints on mineralization. Intrusions associated with the Early Silurian mineralization at Cadia and Goonumbla have narrow and distinct Pb isotope signatures that we interpret to be the result of partial melting of already LILE-enriched mantle-like sources. The data suggest that deposits of the Macquarie Arc derived Pb from one or more long-lived mantle-like Pb isotope reservoirs without significant contributions of crustal Pb prior to the Benambran Orogeny.Data for the Copper Hill deposits includes unradiogenic, possibly old Pb and supports previous workers who suggested that old MORB-like basalts may occur at depth in the area. The Peak Hill deposit has the most unradiogenic signature and has the lowest ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb. These signatures closely match Cambrian MORB-like basalts in the Koonenberry Belt and are unlike Cambrian mafic rocks in Victoria. Similar rocks could form part of the substrate to other parts of the Macquarie Arc.  相似文献   

The communication of physical science uncertainty in European National Adaptation Strategies   总被引：1，自引：0，他引：1  

S. Lorenz  S. Dessai  J. Paavola  P. M. Forster 《Climatic change》2015,132(1):143-155

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Shatter cones and planar deformation features confirm Santa Marta in Piauí State,Brazil, as an impact structure     

Grace Juliana Gonçalves de Oliveira  Marcos Alberto Rodrigues Vasconcelos  Alvaro Penteado Crósta  Wolf Uwe Reimold  Ana Maria Góes  Astrid Kowitz 《Meteoritics & planetary science》2014,49(10):1915-1928

A total of 184 confirmed impact structures are known on Earth to date, as registered by the Earth Impact Database . The discovery of new impact structures has progressed in recent years at a rather low rate of about two structures per year. Here, we introduce the discovery of the approximately 10 km diameter Santa Marta impact structure in Piauí State in northeastern Brazil. Santa Marta is a moderately sized complex crater structure, with a raised rim and an off‐center, approximately 3.2 km wide central elevated area interpreted to coincide with the central uplift of the impact structure. The Santa Marta structure was first recognized in remote sensing imagery and, later, by distinct gravity and magnetic anomalies. Here, we provide results obtained during the first detailed ground survey. The Bouguer anomaly map shows a transition from a positive to a negative anomaly within the structure along a NE–SW trend, which may be associated with the basement signature and in parts with the signature developed after the crater was formed. Macroscopic evidence for impact in the form of shatter cones has been found in situ at the base around the central elevated plateau, and also in the interior of fractured conglomerate boulders occurring on the floor of the surrounding annular basin. Planar deformation features (PDFs) are abundant in sandstones of the central elevated plateau and at scattered locations in the inner part of the ring syncline. Together, shatter cones and PDFs provide definitive shock evidence that confirms the impact origin of Santa Marta. Crystallographic orientations of PDFs occurring in multiple sets in quartz grains are indicative of peak shock pressures of 20–25 GPa in the rocks exposed at present in the interior of the crater. In contrast to recent studies that have used additional, and sometimes highly controversial, alleged shock recognition features, Santa Marta was identified based on well‐understood, traditional shock evidence.  相似文献   

A Radiative Pumping Scheme for OH and H<Subscript>2</Subscript>O Masers in Massive Star Forming Regions     

Hanping Liu  J. R. Forster  Yingping Liu  Jin Sun 《Astrophysics and Space Science》2007,307(4):357-363

Interstellar H₂O and OH masers associated with massive star-forming regions can be classified into three morphological types: isolated H₂O masers; isolated OH masers; and spatially overlapping OH/H₂O maser groups. In a large sample of star-forming regions the total number of maser groups of each type is approximately equal. In order to account for these statistics we propose a pumping scheme based on a broadband radiative pump which produces inverted populations of both OH and H₂O masers by a process involving predissociation and dissociation of H₂O. This scheme overcomes some drawbacks of earlier radiative pumping models, and may account for the association of OH and H₂O masers in massive star forming regions.  相似文献   

Early and Middle Valdaian glaciations, ice-dammed lakes and periglacial interstadials in northwest Russia: new evidence from the Pyoza River area     

Michael Houmark-Nielsen  Igor Demidov  Svend Funder  Kari Grsfjeld  Kurt H. Kjr  Eiliv Larsen  Nadya Lavrova  Astrid Lys  Jan K. Nielsen 《Global and Planetary Change》2001,31(1-4)

The Pyoza River area in the Arkhangelsk district exposes sedimentary sequences suitable for study of the interaction between consecutive Valdaian ice sheets in Northern Russia. Lithostratigraphic investigations combined with luminescence dating have revealed new evidence on the Late Pleistocene history of the area. Overlying glacigenic deposits of the Moscowian (Saalian) glaciation marine deposits previously confined to three separate transgression phases have all been connected to the Mikulinian (Eemian) interglacial. Early Valdaian (E. Weichselian) proglacial, lacustrine and fluvial deposits indicate glaciation to the east or north and consequently glacier damming and meltwater run-off in the Pyoza area around 90–110 ka BP. Interstadial conditions with forest-steppe tundra vegetation and lacustrine and fluvial deposition prevailed at the end of the Early Valdaian around 75–95 ka BP. A terrestrial-based glaciation from easterly uplands reached the Pyoza area at the Early to Middle Valdaian transition around 65–75 ka BP and deposited glaciofluvial strata and subglacial till (Yolkino Till). During deglaciation, laterally extensive glaciolacustrine sediments were deposited in ice-dammed lakes in the early Middle Valdaian around 55–75 ka BP. The Barents–Kara Sea ice sheet deposited the Viryuga Till on the lower Pyoza from northerly directions. The ice sheet formed the Pyoza marginal moraines, which can be correlated with the Markhida moraines further east, and proglacial lacustrine deposition persisted in the area during the first part of the Middle Valdaian. Glacio-isostatic uplift caused erosion followed by pedogenesis and the formation of a deflation horizon in the Middle Valdaian. Widely dispersed periglacial river plains were formed during the Late Valdaian around 10–20 ka BP. Thus, the evidence of a terrestrial-based ice sheet from easterly uplands in the Pyoza area suggests that local piedmont glaciers situated in highlands such as the Timan Ridge or the Urals could have developed into larger, regionally confined ice sheets. Two phases of ice damming and development of proglacial lakes occurred during the Early and Middle Valdaian. The region did not experience glaciation during the Late Valdaian.  相似文献   

Development and propagation of severe thunderstorms in the Upper Danube catchment area: Towards an integrated nowcasting and forecasting system using real-time data and high-resolution simulations     

A. Tafferner  C. Forster  M. Hagen  C. Keil  T. Zinner  H. Volkert 《Meteorology and Atmospheric Physics》2008,101(3-4):211-227

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Exploring pathways for sustainable water management in river deltas in a changing environment   总被引：2，自引：1，他引：1  

Marjolijn Haasnoot  Hans Middelkoop  Astrid Offermans  Eelco van Beek  Willem P. A. van Deursen 《Climatic change》2012,115(3-4):795-819

Exploring adaptation pathways into an uncertain future can support decisionmaking in achieving sustainable water management in a changing environment. Our objective is to develop and test a method to identify such pathways by including dynamics from natural variability and the interaction between the water system and society. Present planning studies on long-term water management often use a few plausible futures for one or two projection years, ignoring the dynamic aspect of adaptation through the interaction between the water system and society. Our approach is to explore pathways using multiple realisations of transient scenarios with an Integrated Assessment Meta Model (IAMM). This paper presents the first application of the method using a hypothetical case study. The case study shows how to explore and evaluate adaptation pathways. With the pathways it is possible to identify opportunities, threats, timing and sequence of policy options, which can be used by policymakers to develop water management roadmaps into the future. By including the dynamics between the water system and society, the influence of uncertainties in both systems becomes clearer. The results show, among others, that climate variability rather than climate change appears to be important for taking decisions in water management.  相似文献   

The Role Of Halocarbons In The Climate Change Of The Troposphere And Stratosphere     

Piers M. De F. Forster  Manoj Joshi 《Climatic change》2005,71(1-2):249-266

Releases of halocarbons into the atmosphere over the last 50 years are among the factors that have contributed to changes in the Earth’s climate since pre-industrial times. Their individual and collective potential to contribute directly to surface climate change is usually gauged through calculation of their radiative efficiency, radiative forcing, and/or Global Warming Potential (GWP). For those halocarbons that contain chlorine and bromine, indirect effects on temperature via ozone layer depletion represent another way in which these gases affect climate. Further, halocarbons can also affect the temperature in the stratosphere. In this paper, we use a narrow-band radiative transfer model together with a range of climate models to examine the role of these gases on atmospheric temperatures in the stratosphere and troposphere. We evaluate in detail the halocarbon contributions to temperature changes at the tropical tropopause, and find that they have contributed a significant warming of ~0.4 K over the last 50 years, dominating the effect of the other well-mixed greenhouse gases at these levels. The fact that observed tropical temperatures have not warmed strongly suggests that other mechanisms may be countering this effect. In a climate model this warming of the tropopause layer is found to lead to a 6% smaller climate sensitivity for halocarbons on a globally averaged basis, compared to that for carbon dioxide changes. Using recent observations together with scenarios we also assess their past and predicted future direct and indirect roles on the evolution of surface temperature. We find that the indirect effect of stratospheric ozone depletion could have offset up to approximately half of the predicted past increases in surface temperature that would otherwise have occurred as a result of the direct effect of halocarbons. However, as ozone will likely recover in the next few decades, a slightly faster rate of warming should be expected from the net effect of halocarbons, and we find that together halocarbons could bring forward next century’s expected warming by ~20 years if future emissions projections are realized. In both the troposphere and stratosphere CFC-12 contributes most to the past temperature changes and the emissions projection considered suggest that HFC-134a could contribute most of the warming over the coming century.  相似文献   

Response Surface Designs for Scenario Management and Uncertainty Quantification in Reservoir Production   总被引：1，自引：0，他引：1  

Astrid Jourdan  Isabelle Zabalza-Mezghani 《Mathematical Geology》2004,36(8):965-985

Response surface experimental designs provide a framework for evaluating sensitivities and assessing uncertainties in reservoir-production forecasts for continuous parameters (i.e. permeability, flow rate, etc.). In this paper, the method is extended in order to integrate both continuous and discrete parameters (i.e. fault status: open/close, injection scheme: SWAG/WAG, etc.). This paper presents an appropriate experimental designs approach, notably the regression models associated with, and the statistical interpretation (sensitivity study, Monte Carlo simulations, etc.). The method has been successfully applied to a reservoir oil-production simulation problem. The objective was to define the best production scheme by optimizing the well-completion level. This application has highlighted the advantages of this new approach, both in terms of decreasing simulation cost and improving the interpretation quality.  相似文献   

Estimation of SPOT P-mode point spread function and derivation of a deconvolution filter     

B.C. Forster  P. Best 《ISPRS Journal of Photogrammetry and Remote Sensing》1994,49(6)

The integrating effect of the point spread function of a satellite remote sensing system significantly affects the signature from a single cover class if the surrounding cover is dissimilar and also reduces the spatial resolution of the output data. Digital SPOT P-Mode data acquired over linear ground edge and impulse features were analysed to determined the SPOT system's line spread function. This was integrated to give the normalised point spread function, and then inverted to derive an equation to estimate the true ground response by deconvolution of the observed response. The paper describes the procedures used in determining the point spread function, and applies the result to a number of urban features. A significant improvement in the image quality resulted.  相似文献