Lateral thinking: 2-D interpretation of thermochronology in convergent orogenic settings   总被引：1，自引：0，他引：1  

Geoffrey E. Batt  Mark T. Brandon 《Tectonophysics》2002,349(1-4)

Lateral motion of material relative to the regional thermal and kinematic frameworks is important in the interpretation of thermochronology in convergent orogens. Although cooling ages in denuded settings are commonly linked to exhumation, such data are not related to instantaneous behavior but rather to an integration of the exhumation rates experienced between the thermochronological ‘closure’ at depth and subsequent exposure at the surface. The short spatial wavelength variation of thermal structure and denudation rate typical of orogenic regions thus renders thermochronometers sensitive to lateral motion during exhumation. The significance of this lateral motion varies in proportion with closure temperature, which controls the depth at which isotopic closure occurs, and hence, the range of time and length scales over which such data integrate sample histories. Different chronometers thus vary in the fundamental aspects of the orogenic character to which they are sensitive. Isotopic systems with high closure temperature are more sensitive to exhumation paths and the variation in denudation and thermal structure across a region, while those of lower closure temperature constrain shorter-term behaviour and more local conditions.Discounting lateral motion through an orogenic region and interpreting cooling ages purely in terms of vertical exhumation can produce ambiguous results because variation in the cooling rate can result from either change in kinematics over time or the translation of samples through spatially varying conditions. Resolving this ambiguity requires explicit consideration of the physical and thermal framework experienced by samples during their exhumation. This can be best achieved through numerical simulations coupling kinematic deformation to thermal evolution. Such an approach allows the thermochronological implications of different kinematic scenarios to be tested, and thus provides an important means of assessing the contribution of lateral motion to orogenic evolution.  相似文献   

Ore textures within the U lens of the Navan Zn-Pb deposit, Ireland     

Wendy M. Peace  Malcom W. Wallace  Mark P. Holdstock  John H. Ashton 《Mineralium Deposita》2002,38(5):568-584

Recent exploration in the vicinity of the giant (>90 Mt) Navan orebody has resulted in the discovery of ore-grade mineralisation to the southwest of the deposit, much of which occurs within the Upper Pale Beds, a horizon that is only weakly mineralised above the main orebody. Within this new U lens, mineralisation preferentially occurs within bioclastic carbonate grainstones and calcareous quartz sandstones, and is dominated by sulphide replacement of the carbonate component of the host sequence. Much of the replacive mineralisation is spatially associated with hydrothermal cavities, which are filled by a variable mixture of brecciated replacement sulphide minerals, space-filling sulphide and gangue cements, and internal sediments. Mineralisation also occurs within veins and dissolution seams, and as disseminated sulphide minerals. Massive mineralisation is typically a complex, chaotic, combination of replacement, cavity, and fracture-filling sulphides. Fluid inclusion analyses of ore-stage saddle dolomite indicate temperatures at the time of sulphide precipitation of ~90–150 °C, with a maximum of 175 °C. These temperatures are lower than those typically proposed for Irish-type deposits.  相似文献   

Excavating Lefebvre: The right to the city and its urban politics of the inhabitant   总被引：4，自引：0，他引：4  

Mark Purcell 《GeoJournal》2002,58(2-3):99-108

Much current activism and scholarship has raised concern that the various processes of neoliberal restructuring are threatening democracy. More specifically, researchers in geography and other social sciences have stressed that political and economic restructuring in cities is negatively affecting the enfranchisement of urban residents. Much recent research and writing has explored progressive responses to this perceived disenfranchisement in cities. One popular trend has been a fascination with the idea of the `right to the city' as a way to respond to neoliberal urbanism and better empower urban dwellers. I argue that the right to the city holds promise, but that in the literature the idea remains both theoretically and politically underdeveloped. It remains unclear (1) what the right to the city entails or (2) how it might address current problems of disenfranchisement. This paper examines the right to the city in greater depth. It does so by offering a close reading and analysis of the intellectual roots of the idea: the writings of Henri Lefebvre. I suggest that Lefebvre's right to the city is more radical, more problematic, and more indeterminate than the current literature makes it seem. The paper concludes by suggesting that the right to the city does offer distinct potential for resisting current threats to urban enfranchisement. However, the right to the city is not a panacea. It must be seen not as a completed solution to current problems, but as an opening to a new urban politics, what I call an urban politics of the inhabitant.  相似文献   

Emerging and vector-borne diseases: Role of high spatial resolution and hyperspectral images in analyses and forecasts     

Mark L. Wilson 《Journal of Geographical Systems》2002,4(1):31-42

 Many infectious diseases that are emerging or transmitted by arthropod vectors have a strong link to landscape features. Depending on the source of infection or ecology of the transmitting vector, micro-habitat characteristics at the spatial scale of square meters or less may be important. Recently, satellite images have been used to classify habitats in an attempt to understand associations with infectious diseases. Whether high spatial resolution and hyperspectral (HSRH) images can be useful in studies of such infectious diseases is addressed. The nature of questions that such studies address and the desired accuracy and precision of answers will determine the utility of HSRH data. Need for such data should be based on the goals of the effort. Examples of kinds of questions and applications are discussed. The research implications and public health applications may depend on available analytic tools as well as epidemiological observations. Received: 30 July 2001 / Accepted: 14 October 2001  相似文献   

Interactive Analysis Using Voronoi Diagrams: Algorithms to Support Dynamic Update from a Generic Triangle-based Data Structure     

Ickjai Lee  & Mark Gahegan 《Transactions in GIS》2002,6(2):89-114

This paper describes a series of dynamic update methods that can be applied to a family of Voronoi diagram types, so that changes can be updated incrementally, without the usual recourse to complete reconstruction of their underlying data structure. More efficient incremental update methods are described for the ordinary Voronoi diagram, the farthest-point Voronoi diagram, the order- k Voronoi diagram and the ordered order- k Voronoi diagram. A discussion is also given of one case where incremental update is not practical, that of the multiplicatively weighted Voronoi diagram. Update methods rely on a previously reported generic, triangle-based data structure (Gahegan and Lee 2000) from which local topology can be dynamically reconstructed following changes to the underlying pointset. An application, which implements these ideas, is available for download via the Internet as proof of concept. Results show that the algorithmic complexity of dynamic update methods vary considerably according to the Voronoi type, but offer in all cases (except the multiplicatively weighted Voronoi diagram) a substantial increase in performance, enabling Voronoi methods to address larger pointsets and more complex modelling problems without incurring too great a computational burden.  相似文献   

Datation UPb sur zircons des dolérites tholéiitiques pyrénéennes (ophites) à la limite Trias–Jurassique et relations avec les tufs volcaniques dits « infra-liasiques » nord-pyrénéens     

Philippe Rossi  Alain Cocherie  C.Mark Fanning  Yves Ternet 《Comptes Rendus Geoscience》2003,335(15):1071-1080

The tholeiitic doleritic magmatism (ophites) in the Aspe valley of the Pyrenees has been dated on the Triassic–Jurassic boundary (199±2 Ma) by the UPb method on zircon (SHRIMP). Emplacement of the ophites was probably synchronous with that of the earliest ‘Infraliassic’ Ségalas tuffs. The ophites are thus related to the Central Atlantic Magmatic Province (CAMP) whose emplacement linked with the fracturing of Pangea, preceded the opening of the Atlantic Ocean. To cite this article: P. Rossi et al., C. R. Geoscience 335 (2003).  相似文献   

Reflections on current developments in contemporary urban geography     

Susan Moore  James Faulconbridge  Clare Blake  David Westhead  Tom Slater  Gavin Brown  Mark Davidson  Margo Huxley  Eddie Huijbens 《Area》2003,35(2):217-219

  相似文献   

Dispelling a myth? Second homes in rural Wales   总被引：1，自引：0，他引：1  

Nick Gallent  Alan Mace  Mark Tewdwr-Jones 《Area》2003,35(3):271-284

Second homes have been a source of considerable controversy in Wales for more than three decades. In this article we argue that they have, in reality, become less important in recent times, with the market contracting during the 1990s and other more fundamental demographic changes and housing pressures coming to the fore. Second homes are a highly localized issue, affecting a minority of communities – though, at times, quite severely. Retirement and other housing pressures, however, bring more significant socio-economic changes and these pressures are all too frequently amplified by a planning system used to restrict housing supply rather than manage growth. This paper has three parts, beginning with a general review of the second home debate followed by an examination of the changing geography of second homes, showing how the distribution of these properties altered during the 1990s and how the market contracted. It ends with a review of secondary data, revealing that second homes are a relatively small component of wider processes affecting rural communities, though extremely significant in some areas.  相似文献   

The CERES‐Rice Model‐Based Estimates of Potential Monsoon Season Rainfed Rice Productivity in Bangladesh*     

Rezaul Mahmood  Mark Meo  David R. Legates  Mark L. Morrissey 《The Professional geographer》2003,55(2):259-273

Agricultural practices in Bangladesh are largely dependent on the monsoonal rainfall. Historically, Bangladesh often experiences severe droughts and floods during the monsoon months, with significant crop losses during both extreme conditions. This article provides a quantitative assessment of potential monsoon‐season aman rice for four transplanting dates: 1 June, 1 July, 15 July, and 15 August. A crop‐growth simulation model, the CERES‐Rice, is applied to sixteen locations representing major rice‐growing regions of Bangladesh to determine baseline yield estimates for four transplanting dates. The applications were conducted for 1975 through 1987. Average potential yield in Bangladesh is 6,907, 5,039, 3,637, and 1,762 kg ha^?1 for the above transplanting dates, respectively. In other words, Bangladesh would obtain 27 percent, 48 percent, and 75 percent less yield for 1 July, 15 July, and 15 August transplanting, respectively, than for 1 June transplanting. Potential yield vulnerability is the least for 1 June transplanting (up to 5 percent) and the highest (up to 66 percent) for 15 July transplanting date. The model applications show that regional variations exist for potential yield and yield vulnerability for a particular transplanting date. In addition, response of yield and vulnerability for a region changes with transplanting dates.  相似文献   

Measurements Of Thermal Updraft Intensity Over Complex Terrain Using American White Pelicans And A Simple Boundary-Layer Forecast Model     

Harlan D. Shannon  George S. Young  Michael A. Yates  Mark R. Fuller  William S. Seegar 《Boundary-Layer Meteorology》2002,104(2):167-199

An examination of boundary-layer meteorological and avian aerodynamic theories suggests that soaring birds can be used to measure the magnitude of vertical air motions within the boundary layer. These theories are applied to obtain mixed-layer normalized thermal updraft intensity over both flat and complex terrain from the climb rates of soaring American white pelicans and from diagnostic boundary-layer model-produced estimates of the boundary-layer depth z_i and the convective velocity scale w_*. Comparison of the flatland data with the profiles of normalized updraft velocity obtained from previous studies reveals that the pelican-derived measurements of thermal updraft intensity are in close agreement with those obtained using traditional research aircraft and large eddy simulation (LES) in the height range of 0.2 to 0.8 z_i. Given the success of this method, the profiles of thermal vertical velocity over the flatland and the nearby mountains are compared. This comparison shows that these profiles are statistically indistinguishable over this height range, indicating that the profile for thermal updraft intensity varies little over this sample of complex terrain. These observations support the findings of a recent LES study that explored the turbulent structure of the boundary layer using a range of terrain specifications. For terrain similar in scale to that encountered in this study, results of the LES suggest that the terrain caused less than an 11% variation in the standard deviation of vertical velocity.  相似文献