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11.
KIM E. LOWELL JOSEPH H. ASTROTH Jr 《International journal of geographical information science》2013,27(1):69-81
Abstract A geographical information system (GIS) approach was used successfully on a federal wilderness area in southwestern Missouri to examine vegetative succession relative to fire management in a glades ecosystem. Maps of vegetation were obtained by interpreting aerial photographs taken in 1938, 1958, 1966, 1975 and 1986. Maps of topography, streams, soils and the location of fires which burned during the period 1938 to 1986 were also procured from a variety of public agencies. All maps were digitized and incorporated into a raster-based GIS with 25 m pixels. It was concluded that (1) both glades and oak-hickory forest have an affinity for distinct physiographic areas and (2) fire can help decrease the rate of processes of natural succession which cause glades to convert to forest. The probable effects of controlled fire on three areas proposed by the Forest Service were evaluated and summarized. 相似文献
12.
JOSEPH WOOD 《International journal of geographical information science》2013,27(4):513-514
Geographic information systems (GIS) and spatial regression modeling techniques were used to evaluate the spatially prioritized relationships between grave density and various spatial parameters for a total of 5549 grave locations. Solar radiation was the most important predictor of grave density in the Feng‐Shui locations. Similarly, spatial clustering technology identified the fact that high concentrations of grave necessarily accompany the significantly increasing trends of solar radiation. The results of the regression analyses indicate that the grave density could be explained by the four landform parameters alone yielding R 2 values of 0.751. In contrast to the typical theory, slope and aspect were not a dominant determining factor upon the dependent variable of grave density. Also, the significantly increasing trends of grave density were not observed in line with a southern direction. A clear verification has been made for the hidden assumptions in Feng‐Shui's long history that its approach is found to be more appropriate in avoiding shadow conditions, rather than exploring the ideal landform location. 相似文献
13.
Residence, Resorption and Recycling of Zircons in Devils Kitchen Rhyolite, Coso Volcanic Field, California 总被引:14,自引:1,他引:14
Zircons from the Devils Kitchen rhyolite in the PleistoceneCoso Volcanic field, California have been analyzed by in situPb/U ion microprobe (SHRIMP-RG) and by detailed cathodoluminescenceimaging. The zircons yield common-Pb-corrected and disequilibrium-corrected206Pb/238U ages that predate a previously reported KArsanidine age by up to 200 kyr, and the range of ages exhibitedby the zircons is also approximately 200 kyr. Cathodoluminescenceimaging indicates that zircons formed in contrasting environments.Most zircons are euhedral, and a majority of the zircons areweakly zoned, but many also have anhedral, embayed cores, witheuhedral overgrowths and multiple internal surfaces that aretruncated by later crystal zones. Concentrations of U and Thvary by two orders of magnitude within the zircon population,and by 1020 times between zones within some zircon crystals,indicating that zircons were transferred between contrastingchemical environments. A zircon saturation temperature of 750°Coverlaps within error a previously reported phenocryst equilibrationtemperature of 740 ± 25°C. Textures in zircons indicativeof repeated dissolution and subsequent regrowth are probablycaused by punctuated heating by mafic magma input into rhyolite.The overall span of ages and large variation in U and Th concentrations,combined with calculated zircon saturation temperatures andresorption times, are most compatible with crystallization inmagma bodies that were emplaced piecemeal in the crust at Cosoover 200 kyr prior to eruption, and that were periodically rejuvenatedor melted by subsequent basaltic injections. KEY WORDS: zircon geochronology; residence time; rhyolite; ion microprobe; California 相似文献
14.
15.
Partial chemical analyses of the accessory iron oxide and iron-titaniumoxide minerals from more than one hundred samples of Adirondackigneous, metamorphic, and metasomatic rocks portray the degreeof oxidation of the minerals and afford a basis for a discussionof their relation to the accompanying silicate assemblage andpetrogeny. Among the granitic igneous rocks, the green pyroxenicfacies have the least oxidized iron-titanium oxide mineralsand a pink potassium-rich microperthitic microcline facies themost oxidized. Granites and syenites may crystallize with eitheran iron-rich variety of hornblende (or pyroxene) plus ilmenite,or with an iron-magnesium variety of hornblende (or of pyroxene)plus magnetite plus ilmenite, depending on the degree of oxidation.The granite facies of the orthogneisses of the Diana Complex(Precambrian) have a more oxidized mineral assemblage than thesyenitic and quartz syenitic facies. The anorthosites and gabbroanorthosites have relatively oxygen-rich oxide minerals. Orthogneissesin the granulite facies have a lower ratio of Fe2O3/FeO thansimilar gneisses in the amphibolite facies. At least part ofthis lower ratio is due to metamorphism at higher temperaturesand pressures. A regional belt of granitic orthogneiss metamorphosedin the amphibolite facies has a magnetite-sphene instead ofa magnetite-ilmenite assemblage. Metasomatism of biotite-quartz-plagioclasegneiss to sillimanitic quartz-microcline gneisses is accompaniedby decrease in mafic silicates and a series of changes of mineralsin intermediate stages such that, in general, biotite yieldswith increasing degrees of oxidation successively such assemblagesas (1) biotite, garnet, magnetite, hemo-ilmenite, and ilmeno-hematite;(2) pale brown mica, sillimanite, magnetite, and ilmeno-hematite;and (3) rutilo-hematite, rutile, and meagre silicates includingsillimanite, muscovite, and chlorite. Diabase altered to monzodioriteby potassium-bearing solutions has ilmeno-magnetite partly alteredto ilmeno-maghemite. 相似文献
16.
Rapid Temporal Changes in Ocean Island Basalt Composition: Evidence from an 800 m Deep Drill Hole in Eiao Shield (Marquesas) 总被引:1,自引:1,他引:1
CAROFF MARTIAL; MAURY RENE C.; VIDAL PHILIPPE; GUILLE GERARD; DUPUY CLAUDE; COTTEN JOSEPH; GUILLOU HERVE; GILLOT PIERRE-YVES 《Journal of Petrology》1995,36(5):1333-1365
The Dominique drill hole has penetrated the volcanic shieldof Eiao island (Marquesas) down to a depth of 800 m below thesurface and 6915 m below sea-level with a percentage ofrecovery close to 100%. All the lavas encountered were emplacedunder subaerial conditions. From the bottom to the top are distinguished:quartz and olivine tholeiites (800686 m), hawaiites,mugearites and trachyte (686415 m), picritic basalts,olivine tholeiites and alkali basalts (4150 m). The coredvolcanic pile was emplaced between 556007 Ma and522006 Ma. Important chemical changes occurred during this rather shorttime span (034 013 Ma). In particular, the lowerbasalts differ from the upper ones in their lower concentrationsof incompatible trace elements and their Sr, Nd and Pb isotopicsignature being closer to the HIMU end-member, whereas the upperbasalts are EM II enriched. The chemical differences betweenthe two basalt groups are consistent with a time-related decreasein the degree of partial melting of isotopically heterogeneoussources. It seems unlikely that these isotopic differences reflectchanges in plume dynamics occurring in such a short time span,and we tentatively suggest that they result from a decreasingdegree of partial melting of a heterogeneous EM IIHIMUmantle plume. Some of the intermediate magmas (the uppermost hawaiites andmugearites) are likely to be derived from parent magmas similarto the associated upper basalts through simple fractionationprocesses. Hawaiites, mugearites and a trachyte from the middlepart of the volcanic sequence have SrNd isotopic signaturessimilar to those of the lower basalts but they differ from themin their lower 206Pb/204Pb ratios, resulting in an increasedDMM signature. Some of the hawaiites-mugearites also displayspecific enrichments in P2O5, Sr and REE which are unlikelyto result from simple fractionation processes. The isotopicand incompatible element compositions of the intermediate rocksare consistent with the assimilation of MORB-derived wall rocksduring fractional crystallization. The likely contaminant correspondsto Pacific oceanic crust, locally containing apatite-rich veinsand hydrothermal sulphides. We conclude that a possible explanationfor the DMM signature in ocean island basalts is a chemicalcontribution from the underlying oceanic crust and that studiesof intermediate rocks may be important to document the originof the isotopic features of plume-derived magmas. KEY WORDS: alkali basalt; assimilation; mantle heterogeneity; Marquesas; tholeiile
*Corresponding author 相似文献
17.
This paper reports on some individual constructions of ageing and how these relate to the mutual sustainability of lives and communities in the changing rurality of New Zealand in the 1990s. The Arena Society model is used to organise a discussion of the impact of technology on settlement systems, with reference to changes in the provision of banking services and their impact on the elderly. The views of older people living in the village of Tirau in the Waikato are used to ground the analysis in human experience. The concluding discussion focuses on the potential contribution of older rural residents to the ‘multiple agency’ that communities will need for survival in the ‘open society’. 相似文献
18.
JOSEPH J. HOBBS 《Geographical review》1998,88(1):64-85
ABSTRACT. Probably domesticated in Asia Minor, the opium poppy (Papaver somniferum) may have reached Egypt by 1500 b.c.e. Egyptian opium was important historically for medicinal uses, but increasing recreational use led to eradication efforts by the early twentieth century. With the closure of Lebanon's Bekáa Valley as a source of raw opium, poppy cultivation began in the Sinai Peninsula after 1990. Unemployment attracts bedouin men to this dangerous occupation. A heroin epidemic in Egypt is attributed to them, but their very modest opium production suggests wrongly so. A package of development activities with emphasis on backcountry tourism is proposed as an alternative to poppy farming. 相似文献
19.
High Field Strength Element Enrichment of Pliocene--Pleistocene Island Arc Basalts, Zamboanga Peninsula, Western Mindanao (Philippines) 总被引:37,自引:0,他引:37
SAJONA FERNANDO G.; MAURY REN C.; BELLON HERV; COTTEN JOSEPH; DEFANT MARC 《Journal of Petrology》1996,37(3):693-726
The PliocenePleistocene magmatic activity of the Zamboangaare is linked to the southward subduction of the OligoceneMio-ceneSulu Sea back-are basin along the Sulu Trench. The magmaticproducts include small amounts of adakites dated from 3.8 to0.7 Ma, abundant Nb-enriched basalts and basaltic andesites(NEB) dated from 2 to 1 Ma and a lone calc-alkaline potassicbasaltic andesite dated at 0.4 Ma. Three kinds of NEB are distinguished:nearly primitive Mg-rich (MG) basalts displaying positive orno Nb anomalies with respect to adjacent incompatible elementsand more evolved low-K (LK) and calc-alkaline (CA) lavas which,despite their Nb enrichment, display negative Nb anomalies.Although the role of OIB-type mantle components has been advocatedto explain the HFSE enrichment of NEB, the spatial and temporalassociation of these rocks with adakites suggests a petrogeneticlink between them. Trace element characteristics of the NEBimply that amphibole and ilmenite might be present in theirsource. We suggest that these minerals could be added metasomaticallyto the mantle through hybridization by percolating slab melts,during which Nb and Ti are preferentially extracted from theadakitic melts. In an early stage (43 Ma) of the subductionof the young and hot Sulu Sea basin crust beneath the Zamboangapeninsula, adakitic liquids formed at depths of 7585km. A few of them were emplaced at the surface but most wereconsumed through slab melt-mantle metasomatic reactions. Adakiteproduction and emplacement continued later (<2 Ma), whilethe Nb-enriched mantle was brought by convection to depths thatallowed its melting and the subsequent emplacement of NEB behindthe adakitic front of the Zamboanga are. KEY WORDS: adakite; metasomatism; Mindanao; Nb-enriched basalts; subduction
*Corresponding author. Present address: Mines and Geosciences Bureau, North Avenue, Diliman, 1100 Quezon City, Philippines 相似文献
20.
We demonstrate a methodology for executing ecosystem models on large regional data sets by organizing and reducing their size prior to executing the model. A knowledge-based (KB) classification method was constructed to aggregate large raster data layers into fewer biophysical landtypes as defined by a climate-soil-vegetation equilibrium. Statistical tests compared simulated seasonal water stress from raster data simulations to their KB landtype and verified that the KB classifications are ordered along a seasonal water stress gradient (p=0.95). The KB method produced a more distinct water stress classification than an alternative GIS overlay classification. Internal concepts modelled by the KB, such as snowpack persistence, were compared to simulated snowpack depletion dates for a range of sites. The KB exhibited the same sensitivity, in direction and magnitude of variation, as simulated snowpack depletion dates from the process model FOREST-BGC. The KB method was 1000 times faster than the optimized versions of the physically based models, justifying the use of a KB as an efficient preprocessor to reduce a large database prior to ecosystem simulations. 相似文献