The Palaeoproterozoic Kangerluluk gold–copper mineralization (southeast Greenland): Pb and Nd isotopic constraints on its timing and genesis     

Henrik Stendal  Robert Frei  Mike A. Hamilton  Wulf U. Mueller 《Mineralium Deposita》2001,36(2):177-188

The Ketilidian Mobile Belt (KMB) in South Greenland is dominated by the Palaeoproterozoic Julianehåb Batholith (1,850–1,770?Ma) and is bordered by supracrustal sequences. The batholith is composed of granite, granodiorite, tonalite, diorite and subordinate gabbro and appinite and formed in a juvenile magmatic arc. The supracrustal rocks consist of psammites, pelites and subordinate, interstratified mafic volcanic rocks. A Rapakivi granite suite (1,755–1,735?Ma) intrudes them. Gold is an important metal in the KMB and occurs in various settings and element associations. Here, emphasis is placed on the Kangerluluk Cu–Au mineralization in the eastern part of the mobile belt. It is hosted within a remnant supracrustal succession dominated by redundant pillowed basalts. Structurally, a syn-volcanic association with gold can be distinguished from one that is clearly related to crosscutting quartz veins. In between, calc-silicate formation in the volcanic rocks occurred contemporaneously with a pervasive sericitization (bleaching) of leucocratic granitoids that are intrusive into the volcanic sequence. Bulk rock and mineral (sulfide) Pb isotope data are comparable in the Pb isotope space. The data define two groups of mineralization where one group is characterized by relatively higher ²⁰⁷Pb/²⁰⁴Pb at given ²⁰⁶Pb/²⁰⁴Pb ratios than the other. Pb stepwise leaching (PbSL) dating experiments performed on garnet and epidote associated with both groups of mineralization confirm the offset in the Pb isotope data. With the geochronological information from PbSL, the results indicate: (1) the initial gold mineralization was genetically related to metalliferous fluids associated with the emplacement of late intrusive stages of the Julianehåb Batholith (1,800–1,770?Ma); and (2) local remobilization of the initial mineralization (1,700–1,750) involved a Pb isotopically evolved fluid, which tentatively can be correlated with the intrusion of the Rapakivi granites in the area. Radiogenic Pb was not only found in altered host rocks but also in various sulfides, suggesting that fluids may have percolated through and/or originated from uranium-bearing graphitic schists which are abundant in the sedimentary package of the KMB. Lead isotopic results suggest that the Rapakivi granites may have supplied heat for renewed circulation of fluids within the supracrustal rock pile.  相似文献   

Dialogue, metaphors of dialogue and understandings of geography   总被引：2，自引：0，他引：2  

David Demeritt  & Sarah Dyer 《Area》2002,34(3):229-241

Increasingly, human and physical geographers alike describe their research practices as involving dialogue of some kind. However, the widespread popularity of the term belies some very different understandings of its meaning and methodological implications. In this paper we reflect on these different conceptions of 'dialogical' geography as a way, first, of illustrating the broad range of understandings of research methodology now current in the discipline and, second, of identifying their implications for three long–standing controversies in the discipline: relativism and the truth of geographical knowledge, the associated dualisms between subject/object, nature/society, and realism/constructionism, and the potential for unity between human and physical geography. We argue that, while dialogue is a potentially fruitful way of understanding and practising geography, that the defence of it, like the attacks on it, is often misconceived.  相似文献   

The Uranian satellites and hyperion: New spectrophotometry and compositional implications     

Robert Hamilton Brown 《Icarus》1983,56(3):414-425

New reflectance spectra at 3.5% resolution have been obtained for Ariel, Titania, Oberon, and Hyperion in the 0.8- to 1.6-μm spectral region. The new spectra show no absoptions other than the 1.5-μm water-ice feature (within the precision of the data), and demonstrate extension into the 0.8- to 1.6-μm region of the 1.5- to 2.5-μm spectral similarity of Ariel to Hyperion (R. H. Brown and D. P. Cruikshank (1983). Icarus55,93-92). The new data confirm the presence of dark, spectrally bland component on/in the water-ice surfaces of the Uranian satellites, which, with some reservations, has spectral similarities to the dark substance on the leading side of Iapetus and the dark material on/in the surface of Hyperion, as well as other dark, spectrally neutral substances such as charcoal. Attempts were made to match the spectra of Ariel, Titania, and Oberon with additive reflectance mixes (areal coverage) of fine-grained water frost and various dark components such as charcoal, lampblack, and charcoal-water-ice mixtures. The results were broad limits on the amounts of possible areal coverage of a charcoal-like spectral component on the surfaces of the Uranian satellites, but the data are not of sufficient precision to conclusively determine whether the dominant mode of contaminant dispersal is areal or voluminal. The effect of highly variegated albedos on the diameters derived by R. H. Brown, D. P. Cruikshank, and D. Morrison (1982a) (Nature300, 423–425) is found to be small.  相似文献   

Applied and theoretical considerations for constructing spatially explicit individual-based models of marine larval fish that include multiple trophic levels   总被引：3，自引：2，他引：3  

Hermann  Albert J.; Hinckley  Sarah; Megrey  Bernard A.; Napp  Jeffrey M. 《ICES Journal of Marine Science》2001,58(5):1030-1041

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Subsistence in coastal fisheries policy: What's in a word?   总被引：1，自引：2，他引：1  

Sarah Schumann  Seth Macinko   《Marine Policy》2007,31(6):706-718

Consideration of subsistence fishing activities seems particularly relevant to coastal fisheries policy, yet formal recognition of subsistence fishing is often absent from associated policy frameworks. A critical problem is the very meaning of the term “subsistence.” A review of the literature on subsistence, dominated until recently by North American research, reveals a schism between interpretations emphasizing material aspects of subsistence and interpretations highlighting cultural aspects. The North American literature on the subject is heavily influenced by a focus on Arctic indigenous populations emphasizing cultural survival. Ultimately, subsistence can be a matter of survival in the belly, the soul, or both. International case studies suggest that different interpretations of subsistence are appropriate in different circumstances, and that appropriate policy can be fashioned only after the local context of subsistence is understood.  相似文献   

A small-scale spatial analysis system for maritime Australia     

Neil T. M. Hamilton  K. D. Cocks 《Ocean & Coastal Management》1995,27(3)

Within the field of resource and environmental management, the paramount value of a spatial analysis system is as a tool for regionalising a case-area in diverse directed ways, each being useful for (i) increasing scientific understanding of that area (intellectualisation) or (ii) for allocating operational categories (for example, funding categories, regulatory categories) differentially between parts of the case-area (called operations support or policy support). Success in serving these scientific and administrative values depends in turn upon two primary attributes of the spatial analysis system and a larger number of secondary attributes. These primary attributes are (i) the range and quality of geocoded data sets held in store or able to be accessed and (ii) the range of spatial analysis techniques which can be called upon for operating on stored data sets. Secondary attributes influencing a spatial analysis system's value include its accessibility to potential users, its ease of use, the judgment and experience of its users and the quality of its cartographic and other outputs. The present paper is a status report on the Australian Coastal And Marine Resources Information System, CAMRIS, a spatial analysis system developed as a demonstration for Australia. CAMRIS contains or can access raw and value-added data sets which comprehensively cover both terrestrial and marine components of the Australian maritime estate. Onshore, for the immediate coastal strip, data held or accessible include geocoded data on vegetation, geology, landform, wetland and coastline type, land use, climate and population. For coastal drainage basins, data sets include river networks, river flows, wetland attributes, soils, geology, elevation, vegetation, mineral deposits, beach attributes, population and bird distributions. Nearshore data include geocoded data on estuary attributes, island attributes, seagrass beds and marine protected areas. Offshore (oceanic) geocoded data held or accessible include bathymetry, sea surface temperature and salinity/dissolved oxygen profiles, together with a variety of geophysical records including gravity, magnetics, seismic track lines, substrates, waves, winds, storms, tides and cyclones. While raw data are stored as such whenever available, many of these data sets are in value-added form, held perhaps as a surface or choropleth or as a function of primary data items. A range of spatial analysis techniques is routinely available for application to CAMRIS data sets including those within the SPANS, Arc Info, and Idrisi geographic information systems, the S Plus exploratory data analysis package, and specialist in-house packages such as PATN for multivariate positive classification and LUPIS for resource allocation and normative classification. CAMRIS demonstration studies in various stages of completion address: (1) selection of coastal and marine protected areas; (2) identification of priority areas for the management of land-based marine pollution; (3) planning for coastal population growth; and (4) synoptic impacts of climatic change in the coastal zone. Further candidate studies being considered include mariculture prospects and proactive management of oil spills and leaks. An important indicator of success for the CAMRIS project would be for it to be seen as a prototype for a properly-funded multi-agency national maritime (coastal and marine) spatial analysis system. Australia, with one of the worlds largest and most diverse maritime estates and with a small population imposing increasing pressures on that estate, needs powerful policy and operations support tools.  相似文献   

Structure of the Subtropical Front in the Tasman Sea   总被引：2，自引：0，他引：2  

L.J. Hamilton   《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(12):1989-2009

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Measurements of sediment transport on the sea bed southwest of England     

J. Hardisty  D. Hamilton 《Geo-Marine Letters》1984,4(1):19-23

Sand transport rates were measured via bedload traps that were inserted into the sediment surface on the continental shelf southwest of England. Analysis of the trapped mobile sediment shows this to be finer and better sorted than nearby Shipek grab samples. The transport rates are combined with simultaneous, near-bed flow measurements to assess a Bagnold type predictive equation,j = k ₁(u ² ₁₀₀ -u ² 100cr)u ₁₀₀. The measured transport rates vary between 0.41 × 10^–3 and 1.67 × 10^–3 gm/cm s. The data yield a mean calibration coefficient (k ₁) of 0.4 × 10^–6 which is slightly lower than values computed from flume and shallow water data.  相似文献   

Plio-Pleistocene microtephra in DSDP site 231, Gulf of Aden   总被引：1，自引：0，他引：1  

Sarah J. Feakins  Francis H. Brown  Peter B. deMenocal 《Journal of African Earth Sciences》2007,48(5):341-352

We reconstruct a Plio-Pleistocene microscopic tephrostratigraphy for DSDP Site 231 in the Gulf of Aden. Systematic microtephrostratigraphy increases the potential for identifying tephra horizons for regional stratigraphic correlation and age control, as well as providing information about eruptive histories. Microtephra reveal three main pulses of volcanism c. 4.0–3.2 Ma, 2.4 Ma and 1.7–1.3 Ma, corresponding to peaks in volcanic activity recorded in the East African Rift System. Previous studies of DSDP Site 231 have reported six visible tephra horizons (up to 25 cm thick) with geochemical compositions matching East African tuffs. We find 68 additional microtephra horizons through microscopic examination of 1050 samples (each integrating c. 3 ka) in over 200 m of marine sediments. We report the major and minor element geochemical compositions of individual glass shards in six of these microtephra horizons and establish a robust correlation at 168.73 m to the Lokochot Tuff (3.58 Ma), which together with previously identified tephra, provides a tightly constrained chronostratigraphy for the mid Pliocene.  相似文献   

Remote sensing for groundwater modelling in large semiarid areas: Lake Chad Basin,Africa     

Marc Leblanc  Guillaume Favreau  Sarah Tweed  Christian Leduc  Moumtaz Razack  Linus Mofor 《Hydrogeology Journal》2007,15(1):97-100

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