Hydrothermal fluids associated with seafloor mineralization at two southern Kermadec arc volcanoes,offshore New Zealand   总被引：2，自引：0，他引：2  

Cornel E. de Ronde  Kevin Faure  Colin J. Bray  Debra A. Chappell  Ian C. Wright 《Mineralium Deposita》2003,38(2):217-233

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Eastern Laurentia in Rodinia: constraints from whole-rock Pb and U/Pb geochronology   总被引：1，自引：0，他引：1  

Staci L. Loewy  James N. Connelly  Ian W. D. Dalziel  Charles F. Gower 《Tectonophysics》2003,375(1-4):169

Whole-rock Pb isotopic signatures and U/Pb geochronology refute a Rodinian correlation of northeastern Laurentia and proto-Andean Amazonia. According to this previously proposed model, the Labrador–Scotland–Greenland Promontory (LSGP) of northeastern Laurentia collided with the proto-Andean margin of Amazonia, at the Arica Embayment, during the Grenville/Sunsás Orogeny (ca. 1.0 Ga). Links between the two margins were based upon the correlation of the LSGP with Arequipa-Antofalla Basement (AAB), a Proterozoic block along the proto-Andean margin of Amazonia adjacent to the Arica Embayment. Specifically, similarities in 1.8–1.0 Ga basement rocks in both regions suggested that the AAB was originally a piece of the LSGP. Furthermore, similarities in unique, post-collisional, but pre-rift, glacial sedimentary sequences also supported a link between the AAB and LSGP.Tests of these apparent similarities fail to support correlation of the AAB and the LSGP and, thus, eliminate a direct link between northeastern Laurentia and southwestern Amazonia in Rodinia. However, Pb isotopic compositions and U/Pb geochronology provide the basis for two new correlations, namely, (1) the ca. 1.3–1.0 Ga basement in the central and southern Appalachians may be an allochthonous block that was transferred to Laurentia from Amazonia at ca. 1.0 Ga, and (2) an allochthonous AAB may be a piece of the Kalahari Craton that was transferred to Amazonia at ca. 1.0 Ga. Based on these new correlations and a previously proposed Grenvillian connection between southern Laurentia (Llano) and Kalahari, we propose that Amazonia may have collided with a contiguous southeastern Laurentia/Kalahari margin at ca. 1.0 Ga.  相似文献   

G.S. Henderson and D.R. Baker (eds): Synchrotron Radiation: Earth,Environmental and Material Sciences Applications. (Short Course Series Volume 30)     

Ian M. Steele 《Mineralium Deposita》2003,38(4):516-516

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Atmospheric deposition of Be and Be in New Zealand rain (1996-98)     

Ian Graham  Robert Ditchburn 《Geochimica et cosmochimica acta》2003,67(3):361-373

Beryllium isotope concentrations were determined in monthly rainfall collections at three sites across New Zealand (36 to 45° S), from October 1996 to November 1998. At the northern sites of Leigh (near Auckland) and Gracefield (near Wellington), ⁷Be and ¹⁰Be concentrations are relatively constant at 1.2 to 1.4 × 10⁷ atoms kg⁻¹ rain and 2.1 to 2.6 × 10⁷ atoms kg⁻¹ rain, respectively. These concentrations correspond to annual flux rates of ∼15 and ∼27 × 10⁹ atoms m⁻² y⁻¹, respectively. At the southern site of Dunedin, concentrations are similar to those at the northern sites, but flux rates are significantly lower at ∼ 9 and ∼19 × 10⁹ atoms m⁻² y⁻¹, respectively, because of lower average rainfall east of the Southern Alps mountain range. These results are broadly similar to those reported by Brown et al. (1989) and Knies et al. (1994) for rain from midlatitude sites in the USA sampled from 1986 to 1994. Mean ⁷Be/¹⁰Be ratios for New Zealand (0.47 to 0.61) are, however, significantly lower than for the USA (0.69 to 0.78), due in part to the addition of ¹⁰Be from re-suspended dust. Subtraction of the dust component increases the New Zealand ⁷Be/¹⁰Be ratios to 0.70 (Leigh), 0.65 (Gracefield) and 0.50 (Dunedin). The adjusted results provide evidence for transfer of older stratospheric air to the troposphere in late-spring-summer, an effect which is strongest in the north. The overall reduction of ⁷Be/¹⁰Be from north to south implies an increase in residence time from ∼ 80 to ∼100 d for Be isotopes in the atmosphere above New Zealand.  相似文献   

UV Laser Ablation ICP-MS: Some Applications in the Earth Sciences   总被引：4，自引：0，他引：4  

Robert W. Nesbitt  Takafumi Hirata  Ian B. Butler  James A. Milton 《Geostandards and Geoanalytical Research》1997,21(2):231-243

This study reports a series of applications of UV laser ablation ICP-MS in the geological sciences. The advantages and disadvantages of the PQ "S" option and the use of nitrogen in the carrier gas are discussed. A general problem common to all ablation techniques is the calibration technique and experiments involving synthetic calibration samples are covered. Zircon geochemistry and geochronology by LA-ICP-MS are discussed and data are presented for REE, Hf and U for a standard zircon (91500) as well as a series of zircons from Zimbabwe. The potential of using Ce and Eu anomalies in petrologic studies is illustrated by zircons from a fractionated gabbroic-granite in the Urals. The potential of the LA-ICP-MS method to utilise standard X-ray fluorescence glass discs is demonstrated as a useful semi-quantitative tool in determining REE patterns. LA-ICP-MS is a powerful tool in the analysis of the platinum group elements (and Re) and some examples are given in the successful application of the technique to partitioning in iron meteorites.  相似文献   

Shear-wave anisotropy: spatial and temporal variations in time delays at Parkfield, Central California   总被引：4，自引：0，他引：4  

Yun Liu  Stuart Crampin  Ian Main 《Geophysical Journal International》1997,130(3):771-785

Shear-wave splitting is analysed on data recorded by the High Resolution Seismic Network (HRSN) at Parkfield on the San Andreas fault, Central California, during the three-year period 1988-1990. Shear-wave polarizations either side of the fault are generally aligned in directions consistent with the regional horizontal maximum compressive stress, at some 70° to the fault strike, whereas at station MM in the immediate fault zone, shear-wave polarizations are aligned approximately parallel to the fault. Normalized time delays at this station are found to be about twice as large as those in the rock mass either side. This suggests that fluid-filled cracks and fractures within the fault zone are elastically or seismically different from those in the surrounding rocks, and that the alignment of fault-parallel shear-wave polarizations are associated with some fault-specific phenomenon.
Temporal variations in time delays between the two split shear-waves before and after a M_L = 4 earthquake can be identified at two stations with sufficient data: MM within the fault zone and VC outside the immediate fault zone. Time delays between faster and slower split shear waves increase before the M_L = 4 earthquake and decrease near the time of the event. The temporal variations are statistically significant at 68 per cent confidence levels. Earthquake doublets and multiplets also show similar temporal variations, consistent with those predicted by anisotropic poroelasticity theory for stress modifications to the microcrack geometry pervading the rock mass. This study is broadly consistent with the behaviour observed before three other earthquakes, suggesting that the build-up of stress before earthquakes may be monitored and interpreted by the analysis of shear-wave splitting.  相似文献   

The Organization of Production in High Technology Industries: An Empirical Assessment*     

Audrey E. Clarke  Brian P. Holly 《The Professional geographer》1996,48(2):127-139

Recent attention given to the concept of vertical integration and disintegration of production processes has identified the existence of a continuum, with small, flexibly specialized producers at one end and large, mass production units at the other end. Firms along the continuum constantly strive for the optimum combination of economies of scale and scope. This paper attempts to identify the organizational characteristics of high technology firms in one industrial complex of the U.S. Manufacturing Belt. A principal components analysis is performed on a number of theoretically relevant variables for a sample of high technology establishments in Northeast Ohio. The results indicate that the region contains a variety of organizational forms ranging from isolated workshops to large, vertically integrated assembly plants. These findings conform to expectations derived from recent conceptualizations in the literature. Additional empirical research will further enhance understanding of the processes that shape the organization of production in territorial complexes.  相似文献   

Radiative Exchange in an Urban Street Canyon   总被引：1，自引：4，他引：1  

Ian N. Harman  Martin J. Best  Stephen E. Belcher 《Boundary-Layer Meteorology》2004,110(2):301-316

The influence of building geometry on the radiation terms ofthe surface energy balance is a principal reason for surfacetemperature differences between rural and urban areas.Methods exist to calculate the radiation balance in an urban area,but their validity across the range of urban geometries andmaterials has not been carefully considered.Here the exchange of diffuse radiation in an urban street canyon isinvestigated using a method incorporating all reflections of radiation.This exact solution is compared to two commonly used approximationsthat retain either no reflections, or just one reflection of radiation.The area-averaged net radiative flux density from the facets of the canyondecreases in magnitude monotonically as the canyon aspect ratio increases.The two approximate solutions possess unphysical differences from thismonotonic decrease for high canyon aspect ratios or low materialemissivities/high material albedos.The errors of the two approximate solutions are small for near blackbodymaterials and small canyon aspect ratios but can be an order ofmagnitude for intermediate material properties and deep street canyons.Urban street canyon models need to consider at least one reflectionof radiation and multiple reflections are desirable for full applicability.  相似文献   

International and National Aspects of a Legislative Framework to Manage Soil Carbon Sequestration   总被引：1，自引：0，他引：1  

Ian Hannam 《Climatic change》2004,65(3):365-387

This article discusses the international and national environmental law framework for the management of soil carbon sequestration. Aspects of the legislative framework important to this process include its ability to recognise carbon sinks, expand existing sinks, and the procedures available to return and store carbon in soil reservoirs. International law provides global standards and guidelines and national legislative systems provide the substantive and procedural legal mechanisms to manage soil carbon. The United Nations Framework Convention on Climate Change and the Kyoto Protocol are the primary international legislative instruments but other international instruments and strategies have a significant synergistic role. Various approaches are presented for framing new legislation or to reform existing legislative frameworks to improve the procedures to manage soil carbon.  相似文献   

Human exploration of the Moon and Mars: implications for Aurora   总被引：1，自引：0，他引：1  

Ian A Crawford 《Astronomy& Geophysics》2004,45(2):2.28-2.29

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