Diffusion of 40Ar in hornblende   总被引：8，自引：0，他引：8  

T. Mark Harrison 《Contributions to Mineralogy and Petrology》1982,78(3):324-331

Measured radiogenic ⁴⁰Ar loss from two compositionally contrasting hornblendes following isothermal-hydrothermal treatment have provided model diffusion coefficients in the temperature range of 750° C to 900° C. Eight experiments using a hornblende (77–600) with a Mg/(Mg +Fe) ratio of 0.72 yield a linear array on an Arrhenius plot with a slope corresponding to an activation energy of 66.1 kcal-mol^–1 and a frequency factor of 0.061 cm²-sec^–1, assuming spherical geometry for the mineral aggregate. Five experiments undertaken on a hornblende (M Mhb-1) with a Mg/(Mg+Fe) ratio of 0.36 show similar behavior to the Mgrich sample, suggesting that the diffusivity of Ar in hornblendes is not sensitive to the Mg/Fe ratio.These data are consistent with kinetic information obtained from a geological experiment using the thermal effect of a granitoid intrusion. Together these data yield an activation energy of 64.1±1.7 kcal-mol^–1 and a frequency factor of 0.024± _0.011 ^0.053 cm²-sec^–1. For a hornblende with an effective diffusion radius of 80 m, these diffusion parameters predict closure temperatures between 578° C and 490° C for cooling rates in the range 500 to 5° C-Ma^–1.  相似文献   

Excess⁴⁰Ar in metamorphic rocks from Broken Hill,New South Wales: implications for⁴⁰Ar/³⁹Ar age spectra and the thermal history of the region     

T. Mark Harrison  Ian McDougall 《Earth and Planetary Science Letters》1981,55(1):123-149

⁴⁰Ar/³⁹Ar age spectrum analyses of samples from Broken Hill, New South Wales, indicate that the region has experienced a complex thermal history following high-grade metamorphism, 1660 Ma ago. The terrain cooled slowly (～3°C Ma^?1) until about 1570 Ma ago, when the temperature fell below about 500°C. Following granitoid emplacement ～1500 Ma ago, the region remained relatively cold until affected by a thermal pulse 520±40Ma ago, causing temperatures to rise to～350°C in some places. During this event, accumulated⁴⁰Ar was released from minerals causing a significant Ar partial pressure to develop. Laboratory Ar solubility data combined with the⁴⁰Ar/³⁹Ar age spectra gives a local estimate of this partial pressure of ～10^?4atm. The region finally cooled below 100°C about 280 Ma ago.⁴⁰Ar/³⁹Ar age spectrum analyses of hornblende, plagioclase and clinopyroxene containing excess⁴⁰Ar are characterized by saddle-shaped age spectra. Detailed analysis of plagioclase samples reveals a complex diffusion behaviour, which is controlled by exsolution structures. This effect, in conjunction with the presumed different lattice occupancy of excess⁴⁰Ar with respect to radiogenic⁴⁰Ar, appears to be responsible for the saddle-shaped age spectra.  相似文献   

Towards Adaptive Grids for Atmospheric Boundary-Layer Simulations   总被引：1，自引：0，他引：1  

J. Antoon van Hooft  Stéphane Popinet  Chiel C. van Heerwaarden  Steven J. A. van der Linden  Stephan R. de Roode  Bas J. H. van de Wiel 《Boundary-Layer Meteorology》2018,167(3):421-443

We present a proof-of-concept for the adaptive mesh refinement method applied to atmospheric boundary-layer simulations. Such a method may form an attractive alternative to static grids for studies on atmospheric flows that have a high degree of scale separation in space and/or time. Examples include the diurnal cycle and a convective boundary layer capped by a strong inversion. For such cases, large-eddy simulations using regular grids often have to rely on a subgrid-scale closure for the most challenging regions in the spatial and/or temporal domain. Here we analyze a flow configuration that describes the growth and subsequent decay of a convective boundary layer using direct numerical simulation (DNS). We validate the obtained results and benchmark the performance of the adaptive solver against two runs using fixed regular grids. It appears that the adaptive-mesh algorithm is able to coarsen and refine the grid dynamically whilst maintaining an accurate solution. In particular, during the initial growth of the convective boundary layer a high resolution is required compared to the subsequent stage of decaying turbulence. More specifically, the number of grid cells varies by two orders of magnitude over the course of the simulation. For this specific DNS case, the adaptive solver was not yet more efficient than the more traditional solver that is dedicated to these types of flows. However, the overall analysis shows that the method has a clear potential for numerical investigations of the most challenging atmospheric cases.  相似文献   

Present and historical climate variability in South West England     

A. Kosanic  S. Harrison  K. Anderson  I. Kavcic 《Climatic change》2014,124(1-2):221-237

West Cornwall is the most south westerly part of mainland United Kingdom with a strong maritime climate. This paper analyses the earliest archived instrumental meteorological records collected in West Cornwall (SW England). Observations were obtained from the Met Office archive (Camborne 1957–2010; Culdrose 1985–2011), Trengwainton Garden (1940–2010), and from the Royal Cornwall Polytechnic Society, (data for Falmouth (1880–1952) and Helston (1843–1888)). Homogeneity tests were used (Levene and Brown-Forsythe tests) to exclude any trends not related to climate variability. The data exhibit trends in annual mean and maximum temperatures over the timescales analysed, and show a general temperature increase in the 20th and 21st century. Annual and seasonal temperature change was found to vary locally with strongly positive trends in autumn, spring and summer seasons. Trends in precipitation are positive only for the 19th century and only for one station. Correlation with the North Atlantic Oscillation (NAO) index gives negative results for precipitation data. However correlation with the NAO index is positive with temperature, especially in the winter season. Return period analysis shows a decrease in intensity and frequency of extreme precipitation events in the post-1975 period (Camborne and Trengwainton Garden stations). Climate change in the 20th century and future continued warming is likely to have major implications on biodiversity in this region.  相似文献   

Exposed evaporite diapirs and minibasins above a canopy in central Sverdrup Basin,Axel Heiberg Island,Arctic Canada     

J. C. Harrison  M. P. A. Jackson 《Basin Research》2014,26(4):567-596

Axel Heiberg Island (Arctic Archipelago, northern Nunavut, Canada) contains the thickest Mesozoic section in Sverdrup Basin (11 km). The ca. 370‐km‐long island is second only to Iran in its concentration of exposed evaporite diapirs. Forty‐six diapirs of Carboniferous evaporites and associated minibasins are excellently exposed on the island. Regional anticlines, which formed during Paleogene Eurekan orogeny, trend roughly north on a regular ca. 20‐km wavelength and probably detach on autochthonous Carboniferous Otto Fiord Formation evaporites comprising halite overlain by thick anhydrite. In contrast, a 60‐km‐wide area, known as the wall‐and‐basin structure (WABS) province, has bimodal fold trends and irregular (<10 km) wavelengths. Here, crooked, narrow diapirs of superficially gypsified anhydrite crop out in tight anticline cores, which are separated by wider synclinal minibasins. We interpret the WABS province to detach on a shallow, partly exposed canopy of coalesced allochthonous evaporite sheets. Surrounding strata record a salt‐tectonic history spanning the Late Triassic (Norian) to the Paleogene. Stratigraphic thinning against diapirs and spectacular angular unconformities indicate mild regional shortening in which diapiric roof strata were bulged up and flanking strata steepened. This bulging culminated in the Hauterivian, when diapiric evaporites broke out and coalesced to form a canopy. As the inferred canopy was buried, it yielded second‐generation diapirs, which rose between minibasins subsiding into the canopy. Consistent high level emplacement suggests that all exposed diapirs inside the WABS area rose from the canopy. In contrast, diapirs along the WABS margins were sourced in autochthonous salt as first‐generation diapirs. Apart from the large diapir‐flanking unconformities, Jurassic‐Cretaceous depositional evidence of salt tectonics also includes submarine debris flows and boulder conglomerates shed from at least three emergent diapirs. Extreme local relief, tectonic slide blocks, steep talus fans and subaerial debris flows suggest that many WABS diapirs continue to rise today. The Axel Heiberg canopy is one of only three known exposed evaporite canopies, each inferred or known at a different structural level: above the canopy (Axel Heiberg), through the canopy (Great Kavir) and beneath a possible canopy (Sivas).  相似文献   

Exploring climate change vulnerability across sectors and scenarios using indicators of impacts and coping capacity     

R. Dunford  P. A. Harrison  J. Jäger  M. D. A. Rounsevell  R. Tinch 《Climatic change》2015,128(3-4):339-354

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Developing a reduced-form ensemble of climate change scenarios for Europe and its application to selected impact indicators     

Martin Dubrovsky  Miroslav Trnka  Ian P. Holman  Eva Svobodova  Paula A. Harrison 《Climatic change》2015,128(3-4):169-186

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Carbon capture and sequestration versus carbon capture utilisation and storage for enhanced oil recovery   总被引：1，自引：1，他引：0  

Bob Harrison  Gioia Falcone 《Acta Geotechnica》2014,9(1):29-38

There are 74 integrated carbon capture projects worldwide currently listed by the Global CCS Institute, including the few already running and those still at the identification, evaluation, definition or execution stage for operation by 2018. Significant funding programmes have recently been launched by the European Commission (NER300 in November 2011) and by the UK Department of Energy and Climate Change (CCS Commercialisation Programme in April 2012) for commercial demonstration projects leading to innovation across the CCS/CCUS technology chain to reduce energy system costs. In their calls for proposals, these programmes were open to both CCS and CCUS projects. However, there are significant technical and commercial differences between projects for enhanced oil recovery and those for permanent storage of carbon dioxide in saline aquifers or in depleted hydrocarbon reservoirs, the same way that there exist more complexities and limitations for offshore implementation. Such differences are accompanied by different levels of field verification of the various storage and utilisation concepts, with permanent sequestration having only a more recent history and smaller-scale implementation. In this scenario, the need for appropriate due diligence workflows and screening criteria to assess the technical viability and the deliverability of different CCS/CCUS projects remains crucial, vis-à-vis the high component costs, efficiency penalties, reservoir uncertainties and the many challenges related to full chain integration (from carbon dioxide capture to underground sequestration). Based on information in the public domain, this paper reviews the current status of offshore CCS/CCUS implementation worldwide and discusses screening criteria for use by governments, operators and investors alike.  相似文献