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1.
Calcite dendrite crystals are important but poorly understood components of calcite travertine that forms around many hot springs. The Lýsuhóll hot-spring deposits, located in western Iceland, are formed primarily of siliceous sinters that were precipitated around numerous springs that are now inactive. Calcite travertine formed around the vent and on the discharge apron of one of the springs at the northern edge of the area. The travertine is formed largely of two types (I and II) of complex calcite dendrite crystals, up to 1 cm high, that grew through the gradual addition of trilete sub-crystals. The morphology of the dendrite crystals was controlled by flow direction and the competition for growth space with neighbouring crystals. Densely crowded dendrites with limited branching characterize the rimstone dams whereas widely spaced dendrites with open branching are found in the pools. Many dendrite bushes in the pools nucleated around plant stems. Growth of the dendrite crystals was seasonal and incremental. Calcite precipitation was driven by rapid CO2 degassing of CO2-rich spring waters during the spring and summer. During winter, when snow covered the ground and temperatures were low, opal-A precipitated on the exposed surfaces of the dendrites. Segmentation of dendrite branches by discontinuities coated with opal-A and overgrowth development around sub-crystals resulted from this seasonal growth cycle. The calcite dendrite crystals in the Lýsuhóll travertine differ in morphology from those at other hot springs, such as those at Lake Bogoria, Kenya, and Waikite in New Zealand. Comparison with the calcite dendrite crystals found at those sites shows that dendrite morphology is site-specific and probably controlled by carbonate saturation levels that, in turn, are controlled by the rate of CO2 degassing and location in the spring outflow system.  相似文献   
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The Perseverance ultramafic complex is a body of olivine-richkomatiitic rocks spatially associated with the Agnew nickeldeposit, in the Agnew-Wiluna greenstone belt of the ArchaeanYilgarn Block in Western Australia. The complex consists ofa central lenticular body, up to 700 m thick, of olivine adcumulates,flanked by laterally extensive sheet-like bodies of olivineorthocumulates and spinifextextured komatiite flows. Rocks progressivelyfurther away from the central lens have chemical compositionsreflecting higher original proportions of komatiite liquid tocumulus olivine. Parent liquids had MgO contents between 25and 32% MgO, approximately chondritic Al/Ti ratios and HREEpatterns, and moderate depletion in LREE. Olivines within the adcumulate lens show a progressive increasein forsterite content from Fo93 at the bottom to Fo94?5, atthe top. Calculated original olivine compositions in the flankingrocks are similar to those at the base of the central lens.Original olivine nickel contents show a symmetrical variationfrom maximum values of 3500 ppm at the top of the central lens,through minimum values of 1000 ppm at the base and margins ofthe central lens to intermediate values in the distal rocks.The complex as a whole shows evidence for nickel depletion relativeto other komatiite suites. These observations are explained in terms of prolonged eruptionand flow of komatiitic lava down a major flow channel or lavariver. Adcumulates crystallized on the floor and sides of thecentral channel, which was formed at an early stage by thermalerosion of floor rocks. Episodic overflow of the central channelproduced distal ‘flood plain’ rocks consisting ofolivine orthocumulates and layered flows. Lavas became moremagnesian and nickel-rich with time, giving rise to the observedspatial variation in primary olivine composition. Nickel depletionof the earliest lavas is attributed to pre-eruption segregationof large volumes of immiscible Fe-Ni-sulfide, which were concentratedto form the underlying Agnew nickel deposit.  相似文献   
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Deinstitutionalisation of psychiatric patients since the 1980s has introduced a new population and a new land use to New Zealand's urban areas. This paper reviews the geography of deinstitutionalisation, and investigates whether the North American phenomenon of a service-dependent ghetto can be identified in Dunedin.  相似文献   
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The nutrient status of soils surrounding ten snow petrel Pagodroma nivea nests was investigated by sampling along four transects (One up-slope and three down-slope) from each nest. The highest levels for total N and P.% C. nitrite and ammonia (but not nitrate) were associated with the nest itself. Elevated levels of all nutrients still occurred at I m from the nest but dropped to levels similar to those of non-bird influenced soils at 2 m or 5 m from the nest. Highest bacterial and algal numbers were also associated with the nest. An experiment to examine the breakdown of guano showed nitrification levels to be insignificant and nutrient release levels very slow.  相似文献   
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This paper reports on log transportation as a health-related issue in the Hokianga district of Northland at a time when forestry activity in the area is expanding and radical reforms to New Zealand's roading network have been proposed. Drawing on technical information and key informant interviews, the potential impacts of logging trucks on Hokianga roads are considered, the costs associated with forestry traffic are estimated, and the routes most likely to be affected are identified. Possible responses to the log transport problem are discussed, and it is concluded that rural communities such as Hokianga are vulnerable to both logging truck activity and changes in government policy.  相似文献   
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Abstract. .Series of experimental trawls repeated over the same area during both 12 and 24 h cycles coupled with an analysis of the stomach contents of the bib demonstrated quantitative and qualitative variations in the predator's diet. The population studied feeds continuously over 24 h, the coefficient of "fullness" is relatively constant, and freshly eaten prey can be observed both during the day and at night. The proportion of brown shrimp in the food increases after high tide, especially when this occurs at night, coinciding with the shrimp's period of maximum activity. However, the overall impact of the bib on the shrimp population depends more on the abundance of the former than on variations in their individual food intake.  相似文献   
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THE WRITING'S ON THE WALL   总被引:1,自引:0,他引:1  
Graffiti can be a marker of territory. Youthful grafffiti writers in Auckland have adopted ‘tagging’, a form of graffiti writing linked to the Americanisation of popular culture in New Zealand. Regularities in the presence of ‘tags’ are documented through field observation in suburban and central city locations and related to the daily activities of the taggers. Self-proclamation, not the marking out of turf appears to underlie the territorial dimensions of graffiti in Auckland's urban space.  相似文献   
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