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1.
ABSTRACT. Recent attempts by U.S. politicians to reform the nation'sschools have shifted the goal of education to school accountability as assessed in standardized testing. Such an emphasis undermines geographical education in schools because of geography'ssuperficial representation in tests and in the social studies curriculum. Fieldwork done in the classroom can point to means of circumventing this dilemma. Collaborative fieldwork between college faculty members and public‐school teachers has the potential for adding geography to the social studies curriculum in a substantive way. Work conducted jointly by Hartwick College and the Oneonta (New York) Middle School exemplifies such a partnership. 相似文献
2.
Temperatures of Granulite-facies Metamorphism: Constraints from Experimental Phase Equilibria and Thermobarometry Corrected for Retrograde Exchange 总被引:17,自引:7,他引:17
PATTISON DAVID R. M.; CHACKO THOMAS; FARQUHAR JAMES; MCFARLANE CHRISTOPHER R. M. 《Journal of Petrology》2003,44(5):867-900
This study assesses temperatures of formation of common granulitesby combining experimental constraints on the PT stabilityof granulite-facies mineral associations with a garnetorthopyroxene(GrtOpx) thermobarometry scheme based on Al-solubilityin Opx, corrected for late FeMg exchange. We appliedthis scheme to 414 granulites of mafic, intermediate and aluminousbulk compositions. Our findings suggest that granulites aremuch hotter than traditionally assumed and that the PTconditions of the amphibolitegranulite transition portrayedin current petrology textbooks are significant underestimatesby over 100°C. For aluminous and intermediate granulites,mean corrected temperatures based on our method are 890 ±17 and 841 ± 11°C, respectively (uncertainties reportedas 95% confidence limits on the mean), consistent with minimumtemperatures for orthopyroxene production by fluid-absent partialmelting in these bulk compositions. In contrast, mean temperaturesbased on GrtOpx FeMg exchange equilibria, usingthe same thermodynamic data, are 732 ± 22 and 723 ±11°C, respectively, well below the minimum temperaturesfor Opx stability. For mafic granulites, the mean correctedtemperature using our method is 816 ± 12°C, similarto the mean temperature of 793 ± 13°C from FeMgexchange. Reasons for the differences between the mafic granulitesand aluminousintermediate granulites are unclear butmay be due to the lower Al concentrations in Opx in the maficrocks and possible deficiencies in the thermodynamic modellingof these low concentrations. We discuss a number of well-knowngranulite terrains in the context of our findings, includingthe Adirondacks, the Acadian granulites of New England, theincipient charnockites of southern India and Sri Lanka, andthe Kerala Khondalite Belt. Our findings carry implicationsfor thermotectonic models of granulite formation. A computerprogram to perform our thermobarometry calculations, RCLC, isavailable from the Journal of Petrology website at http://www.petrology.oupjournals.orgor from the authors at http://www.geo.ucalgary.ca/~pattison/drm_pattison-rclc.htm. KEY WORDS: granulite-facies metamorphism; thermobarometry; garnet; orthopyroxene 相似文献
3.
The Palghat Gap region is located near the centre of the large southern Indian granulite terrane. at the northern edge of the Kodaikanal charnockite massif. The dominant rock types in the region are hornblende-biotite ± orthopyroxene gneisses and charnockites along with minor amounts of intercalated mafic granulite, metapelite and calc-silicate. The P-T estimates from garnetiferous mafic granulites and metapelite samples are generally in the range 9-10 kbar and 800-900 C using both conventional thermobarometric methods and the TWEEQU thermobarometry program. These P-T estimates, which should be taken as minimum values, are among the highest yet reported for South Indian and Sri Lankan granulites. The occurrence of orthopyroxene + plagioclase symplectites around embayed garnet grains in the mafic granulites and cordierite rims around garnet grains in metapelite suggest an isothermal decompression-type path. Similarly, a core-rim P-T trajectory indicates c. 3 and 7 kbar decompression at high temperature in the mafic granulites and metapelite, respectively. In both rock types, the key to the determination of the retrograde P-T path was the recognition of small amounts of second generation plagioclase with a more anorthitic composition than the matrix plagioclase. The preservation of high garnet-pyroxene temperatures in the mafic granulites (despite small garnet grain size) suggests rapid cooling of the terrane. Calculated minimum cooling rates range from 8 to 80 C Ma-1 . Such cooling rates are more rapid than those associated with normal isostatic processes and suggest that the terrane was tectonically exhumed at high temperature. 相似文献
4.
HEAMAN LARRY M.; CREASER ROBERT A.; COOKENBOO HARRISON O.; CHACKO TOM 《Journal of Petrology》2006,47(4):821-858
The Jericho kimberlites are part of a small Jurassic kimberlitecluster in the northern Slave craton, Canada. A variety of datingtechniques were applied to constrain the nature and age of twoJericho kimberlites, JD-1 (170·2 ± 4·3Ma RbSr phlogopite megacrysts, 172·8 ±0·7 Ma UPb eclogite rutile, 178 ± 5 MaUPb eclogite zircon lower intercept) and JD-3 (173 ±2 Ma RbSr phlogopite megacryst; 176·6 ±3·2 Ma UPb perovskite), and all yielded identicalresults within analytical uncertainty. As there is no discernibledifference in the radiometric ages obtained for these two pipes,the composite RbSr phlogopite megacryst date of 173·1± 1·3 Ma is interpreted as the best estimate forthe emplacement age of both Jericho pipes. The initial Sr isotopecomposition of 0·7053 ± 0·0003 derivedfrom phlogopite megacrysts overlaps the range (0·70430·7084)previously reported for Jericho whole-rocks. These strontiumisotope data, combined with the radiogenic initial 206Pb/204Pbratio of 18·99 ± 0·33 obtained in thisstudy, indicate that the Jericho kimberlites are isotopicallysimilar to Group 1 kimberlites as defined in southern Africa.The Jericho kimberlites are an important new source of mantlexenoliths that hold clues to the nature of the Slave cratonsubcontinental mantle. A high proportion (30%) of the Jerichomantle xenolith population consists of various eclogite typesincluding a small number (23%) of apatite-, diamond-,kyanite- and zircon-bearing eclogites. The most striking aspectof the Jericho zircon-bearing eclogite xenoliths is their peculiargeochemistry. Reconstructed whole-rock compositions indicatethat they were derived from protoliths with high FeO, Al2O3and Na2O contents, reflected in the high-FeO (22·627·5wt %) nature of garnet and the high-Na2O (8·479·44wt %) and high-Al2O3 (13·1214·33 wt %)character of the clinopyroxene. These eclogite whole-rock compositionsare highly enriched in high field strength elements (HFSE) suchas Nb (1331134 ppm), Ta (528 ppm), Zr (17794934ppm) and Hf (2364 ppm). This HFSE enrichment is linkedto growth of large (up to 2 mm) zircon and niobian rutile crystals(up to 3 modal %) near the time of eclogite metamorphism. Thediamond-bearing eclogites on the other hand are characterizedby high-MgO (19·621·3 wt %) garnet andultralow-Na2O (0·441·50 wt %) clinopyroxene.Paleotemperature estimates indicate that both the zircon- anddiamond-bearing eclogites have similar equilibration temperaturesof 9501020°C and 9901030°C, respectively,corresponding to mantle depths of 150180 km. Integrationof petrographic, whole-rock and mineral geochemistry, geochronologyand isotope tracer techniques indicates that the Jericho zircon-bearingeclogite xenoliths have had a complex history involving Paleoproterozoicmetamorphism, thermal perturbations, and two or more episodesof Precambrian mantle metasomatism. The oldest metasomatic event(Type 1) occurred near the time of Paleoproterozoic metamorphism(1·8 Ga) and is responsible for the extreme HFSE enrichmentand growth of zircon and high-niobian rutile. A second thermalperturbation and concomitant carbonatite metasomatism (Type2) is responsible for significant apatite growth in some xenolithsand profound light rare earth element enrichment. Type 2 metasomatismoccurred in the period 1·01·3 Ga and isrecorded by relatively consistent whole-rock eclogite modelNd ages and secondary UPb zircon upper intercept dates.These eclogite xenoliths were derived from a variety of protoliths,some of which could represent metasomatized pieces of oceaniccrust, possibly linked to east-dipping subduction beneath theSlave craton during construction of the 1·881·84Ga Great Bear continental arc. Others, including the diamond-bearingeclogites, could be cumulates from mafic or ultramafic sillcomplexes that intruded the Slave lithospheric mantle at depthsof about 150180 km. KEY WORDS: zircon- and diamond-bearing eclogites; Jericho kimberlite, geochronology; Precambrian metasomatism, northern Slave Craton 相似文献
5.
Fluid-absent Melting of High-grade Semi-pelites: P-T Constraints on Orthopyroxene Formation and Implications for Granulite Genesis 总被引:4,自引:0,他引:4
Rocks of semi-pelitic composition are common in high-grade terranes.The first appearance of orthopyroxene in these rocks marks thetransition from amphibolite- to granulite-facies conditions,and is commonly attributed to the process of fluid-absent partialmelting. We have conducted fluid-absent melting experimentson two natural semi-pelitic rocks (quartz, plagioclase, alkalifeldspar, biotite and garnet) with the specific objective ofdetermining the pressuretemperature conditions necessaryto produce orthopyroxene. In contrast to previous experimentalstudies, our starting materials were obtained from a transitionalamphibolitegranulite terrane. Importantly, the high TiO2(>5 wt %) and F (>1 wt %) contents of biotite in our experimentsare more representative of biotite found in rocks on the vergeof granulite-facies conditions than those used in earlier studies.Experiments were conducted in a piston-cylinder apparatus at8001050°C and 715 kbar. We reversed the firstappearance of orthopyroxene in two-stage experiments at 7 and10 kbar. Fluid-absent melting of biotite began at 相似文献
6.
ELIZABETH K. TEATHER 《Geographical review》1999,89(3):409-430
ABSTRACT. A massive, voluntary shift to cremation has taken place in Hong Kong over the past forty years. The provision of facilities by the colonial government and private organizations began with niche walls in existing cemeteries. These were soon supplemented by sizable buildings known as columbaria. The largest and most recent columbarium, completed in 1996, provides 49,884 niches, each of which can hold at least two sets of ashes. Designing columbaria that are functional, sensitive, and culturally specific provides a fascinating challenge to architects. This article contrasts the conservative response of the public sector with the more expressive solutions of private providers. 相似文献
7.
Managing sustainable farmed landscape through 'alternative' food networks: a case study from Italy 总被引:1,自引:0,他引:1
LEWIS HOLLOWAY ROSIE COX† LAURA VENN‡ MOYA KNEAFSEY‡ ELIZABETH DOWLER§ HELENA TUOMAINEN§ 《The Geographical journal》2006,172(3):219-229
This paper focuses on a case study of an 'alternative' food network based in the Abruzzo National Park, Italy, to explore how ideas of sustainable farmland management can be expressed through broader understandings of developing networks of care concerned with local economies and societies, high-quality specialist food products, particular 'traditional' farming practices and livestock breeds, as well as the ecology of a farmed landscape. The scheme allows customers, internationally as well as in Italy, to 'adopt' a milking sheep on a large mountain farm. In return, adopters are sent food products from the farm. The adoption scheme is inter-twined with an agri-tourism project which provides accommodation, runs a restaurant and engages in educational activities. The scheme is the result of the individual initiative of its founder, and is associated with a strongly expressed ethical position concerning the value of sustaining valued local rural landscapes and lifestyles, and the importance of 'reconnecting' urban dwellers with rural areas, farming and 'quality' food production. Yet the localness of the scheme is sustained through wider national and international networks: volunteer and paid workers are drawn from several European countries, funding has been acquired from the EU LEADER programme, and internet and transport technologies are essential in connecting with and supplying an international customer base. The broader economy of care instanced in this case study draws attention to a need to develop strategies for sustainable farmland management constructed around wider programmes of social, economic and cultural, as well as environmental, concern. 相似文献
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9.
The sandy deposits produced by tsunamis and liquefaction share many sedimentary features, and distinctions between the two are important in seismically active coastal zones. Both types of deposits are present in the wetlands bordering Puget Sound, where one or more earthquakes about 1100 years ago caused both tsunami flooding and sediment venting. This co‐occurrence allows an examination of the resulting deposits and a comparison with tsunami and liquefaction features of modern events. Vented sediments occur at four of five wetland field localities and tsunami deposits at two. In comparison with tsunami deposits, vented sediments in this study and from other studies tend to be thicker (although they can be thin). Vented sediments also have more variable thickness at both outcrop and map scale, are associated with injected dykes and contain clasts derived from underlying deposits. Further, vented sediments tend to contain a greater variety of sedimentary structures, and these structures vary laterally over metres. Tsunami deposits compared with vented sediments are commonly thinner, fine and thin landward more consistently, have more uniform thickness on outcrop and map scales, and have the potential of containing coarser clasts, up to boulders. For both tsunami deposits and vented sediments, the availability and grain size of source material condition the characteristics of the deposit. In the cases presented in this paper, both foraminifera and diatom assemblages within tsunami deposits and vented sediments consisted of brackish and marine species, and no distinction between processes could be made based on microfossils. In summary, this study indicates a need for more careful analysis and mapping of coastal sediments associated with earthquakes to avoid misidentification of processes and misevaluation of hazards. 相似文献
10.
The Turiy Massif, Kola Peninsula, Russia: Isotopic and Geochemical Evidence for Multi-source Evolution 总被引:6,自引:1,他引:6
The Turiy Massif, lying within the Kandalaksha Graben, and onthe southern coast of the Kola Peninsula, contains carbonatites,phoscorites, melilitolites, ijolites and pyroxenites withinone central and four surrounding satellite complexes. SrNdisotopic data from the central complex phoscorites and carbonatites,and the nearby Terskii Coast kimberlites, combined with otherrecently published data on the Devonian Kola Alkaline Province,allow us to redefine the position of the Kola Carbonatite Line(KCL) of Kramm (European Journal of Mineralogy 5, 985989,1993). We propose that the revised-KCL mantle sources includea lower-mantle plume, and a second enriched source, which alsocontributed to the Terskii Coast and Archangelsk kimberlites.The Turiy Massif silicate rocks and northern complex carbonatiteshave more enriched isotopic signatures than the distinct, anddepleted signatures of the central complex phoscorites and carbonatites,particularly with respect to 相似文献