The Dunedin Mayoral Election     

STEPHEN HORTON 《New Zealand geographer》1997,53(1):30-40

In an electoral upset in 1995 Dunedin elected its first woman and first Sikh mayor. This paper argues that the symbolic discourse of the mayoral election confronted the Dunedin electorate with the question of ‘fairness’ or equity in the city. Turner's victory signalled the symbolic rejection by a plurality of voters of the ruling neo-liberal political economy of Dunedin. In the same election the incumbent council, in a political reproduction of the ruling order, was returned. The paper explores this contradiction. It concludes that Dunedin's struggle for a new ruling political alliance necessary to combat a stagnant city economy has just begun.  相似文献   

A statistical assessment of tropical cyclone activity in atmospheric general circulation models   总被引：1，自引：0，他引：1  

SUZANA J. CAMARGO  ANTHONY G. BARNSTON  STEPHEN E. ZEBIAK 《地球，A辑:动力气象学与海洋学》2005,57(4):589-604

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Alkali Amphiboles from the Blueschists of Cazadero, California     

COLEMAN  R. G.; PAPIKE  J. J. 《Journal of Petrology》1968,9(1):105-122

Alkali amphiboles from Type III and Type IV metamorphic zonesin blueschist facies rocks of Cazadero, California, and fromcomparable New Caledonian rocks have been characterized by X-raycrystallographic, optical, and chemical methods. The compositionof any particular alkali amphibole is strongly controlled bythe bulk composition of the host rock. Within the blueschistfacies, metamorphic zones are not characterized by changes inamphibole composition. All the alkali amphiboles studied hereinbelong to the C2/m space group and complete miscibility betweenglaucophane and riebeckite has been demonstrated for the conditionsprevailing during metamorphism in the Cazadero and New Caledonianblueschists. Linear relationships are found between unit-celldimensions and variations in composition between glaucophaneand riebeckite. The alkali amphiboles of glaucophane compositionsbelong to the high pressure-low temperature series, glaucophaneII-riebeckite. Limited miscibility of actinolite in glaucophanemay be characteristic of blueschist facies metamorphism.  相似文献   

Komatiites I: Eruption and Flow   总被引：2，自引：1，他引：2  

HUPPERT  HERBERT E.; SPARKS  R. STEPHEN J. 《Journal of Petrology》1985,26(3):694-725

Because of their high eruption temperatures and ultrabasic composition,komatiite lavas had low viscosities, which typically rangedfrom 0-1 to 10 Pa s. A major consequence of this low viscosityis that most lavas erupted as turbulent flows. An analysis oftheir ascent through the lithosphere suggests ascent velocitiesin the range of 1 to over 10ms^–1 and Reynolds numbersmuch greater than the critical value of 2000. The lavas wouldhave remained turbulent for most or all of their subsequentflow and emplacement. Typical horizontal flow rates are estimatedto range from 0?5 to 100 m² s^–1 per unit width of flow.Such turbulent lava flows would have lost their heat by convectionto the surroundings, at rates which are orders of magnitudegreater than the rates for laminar flows, which cool by conduction.A quantitative analysis of the cooling of komatiites indicatescooling rates from over 1000 ?C hr^–1 to a few ?C hr^–1,while the flows remained turbulent. These rates are in an appropriaterange to cause phenomena such as high nucleation rates, strongsupersaturation of the lava, delayed nucleation of olivine,and skeletal or dendritic crystal morphologies. Komatiites often flowed over ground composed of rocks with lowermelting temperatures. It is proposed that the turbulent lavasmelted the ground to form deep thermal erosion channels. Meltingrates at the lava source are calculated at several metres perday, and deep troughs with depths of several metres to hundredsof metres and lengths of several kilometres probably formed.Laboratory experiments performed to simulate thermal erosionshow qualitative agreement with the theory with channel depthdecreasing downstream. The experiments also revealed that thechannel margins become undercut during thermal erosion to formoverhanging sides of the channel. Some sinuous rilles observedin the mare regions of the Moon are thought to have formed bythermal erosion (Hulme, 1973). They provide analogues of thechannels postulated to form in komatiite eruptions, where conditionswere in fact more favourable for thermal erosion. An assessmentof the role of olivine crystals, precipitated in the cooling,turbulent flows, indicates that they will remain in suspensionuntil the lava has come to rest. Contamination of komatiite lava by underlying rock can be asmuch as 10 per cent. Some illustrative calculations show howthe major element and trace element compositions of residualmelts can be significantly modified by combined assimilationand fractional crystallization in a moving flow. Assimilationof tholeiitic basalt into a komatiite can cause incompatibletrace element ratios, such as Ti/Zr and Y/Zr, and the rare earthpatterns of derivative lavas, to vary substantially. Some ofthe variations in such geochemical parameters, which are oftenascribed to mantle heterogeneity, also could have resulted fromassimilation of the ground. Assimilation could have modifiedthe isotope geochemistry of lava suites and led to apparentages which differ from the true eruption age. The thermal erosionmodel also provides an explanation of the formation of somenickel sulphide ores found at the bottom of thick komatiiteflows. It is proposed that ores can form by assimilation ofsulphur-rich sediment, which combines with Ni from the komatiiteto form an immiscible liquid.  相似文献   

Fossils explained 15: Palaeozoic crinoids     

STEPHEN K. DONOVAN 《Geology Today》1995,11(5):196-199

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Sun, sand and sea urchins     

STEPHEN K. DONOVAN 《Geology Today》1991,7(3):101-106

Jamaica, land of holiday dreams, is also fascinating to the geologist. In particular, the fossil record is diverse, the ancient fauna containing many rarities. The fossil ochinoid fauna is especially large and varied for such a small island, with about 130 nominal species ranging from the late Cretaceous to the Pleistocene.  相似文献   

Comments on "Chaos in Daisyworld" by X. Zeng et al.     

STEPHEN D. JASCOURT  WILLIAM H. RAYMOND 《Tellus. Series B, Chemical and physical meteorology》1992,44(3):243-246

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Is Archaeopteryx the only old,cracked fossil?     

STEPHEN MORETON 《Geology Today》1988,4(3):83-84

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REE and PGE Geochemical Constraints on the Formation of Dunites in the Luobusa Ophiolite, Southern Tibet   总被引：19，自引：0，他引：19  

ZHOU  MEI-FU; ROBINSON  PAUL T.; MALPAS  JOHN; EDWARDS  STEPHEN J.; QI  LIANG 《Journal of Petrology》2005,46(3):615-639

The Luobusa ophiolite, Southern Tibet, lies in the Indus–YarlungZangbo suture zone that separates Eurasia to the north fromthe Indian continent to the south. The ophiolite contains awell-preserved mantle sequence consisting of harzburgite, clinopyroxene(cpx)-bearing harzburgite and dunite. The harzburgite containsabundant pods of chromitite, most of which have dunite envelopes,and the cpx-bearing harzburgites host numerous dunite dykes.Dunite also exists as a massive unit similar to those of themantle–crust transition zones in other ophiolites. Allof the dunites in the ophiolite have a similar mineralogy, comprisingmainly olivine with minor orthopyroxene and chromite and tracesof clinopyroxene. They also display similar chemical compositions,including U-shaped chondrite-normalized REE patterns. Mantle-normalizedPGE patterns show variable negative Pt anomalies. Detailed analysisof a chromite-bearing dunite dyke, which grades into the hostcpx-bearing harzburgite, indicates that LREE and Ir decrease,whereas HREE, Pd and Pt increase away from the dunite. Thesefeatures are consistent with formation of the dunite dykes byinteraction of MORB peridotites with boninitic melts from whichthe chromitites were formed. Because the transition-zone dunitesare mineralogically and chemically identical to those formedby such melt–rock reaction, we infer that they are ofsimilar origin. The Luobusa ultramafic rocks originally formedas MORB-source upper mantle, which was subsequently trappedas part of a mantle wedge above a subduction zone. Hydrous meltsgenerated under the influence of the subducted slab at depthmigrated upward and reacted with the cpx-bearing harzburgitesto form the dunite dykes. The modified melts ponded in smallpockets higher in the section, where they produced podiformchromitites with dunite envelopes. At the top of the mantlesection, pervasive reaction between melts and harzburgite producedthe transition-zone dunites. KEY WORDS: melt–rock interaction; REE; PGE; hydrous melt; mantle; ophiolite; Tibet  相似文献   

Porosity–permeability relationships in Miocene carbonate platforms and slopes seaward of the Great Barrier Reef, Australia (ODP Leg 194, Marion Plateau)     

STEPHEN N. EHRENBERG  GREGOR P. EBERLI†  GREGOR BAECHLE† 《Sedimentology》2006,53(6):1289-1318

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