Plume-Lithosphere Interactions in the Generation of the Basalts of the Kenya Rift, East Africa   总被引：22，自引：0，他引：22  

MACDONALD  R.; ROGERS  N. W.; FITTON  J. G.; BLACK  S.; SMITH  M. 《Journal of Petrology》2001,42(5):877-900

Major and trace element and Sr–Nd–Pb isotopic datafor mafic volcanic rocks are used to assess the number of mantleplumes contributing to the Tertiary–Holocene magmatismof the Kenya Rift Valley, current estimates of which vary fromnone to three. Rocks ranging in composition from nepheliniteto hypersthene-normative basalt have been sampled from threelithospheric zones: the Tanzanian craton, the craton marginreworked during the late Proterozoic, and the Mozambique mobilebelt. The magmas are interpreted as the products of variabledegrees of partial melting within the spinel–garnet peridotitetransition zone. Trace element and isotopic compositions fromall three zones are broadly similar to those of oceanic islandbasalts, but there is considerable compositional variation,which is related to a strong overprint from the lithosphereon plume-derived melts. Sr and Nd isotopic ratios provide theonly clear distinction between magmatic rocks from the threelithospheric domains. Within each setting, mafic magmatism hastended to become less silica undersaturated with time, and atany one locality magmatism has migrated towards the centre ofthe rift. Magmas may have formed as a result of the infiltrationof plume-derived melts into the base of the lithosphere. Theextent of interaction of inferred plume melts with the lithospherehas not varied systematically in time or space. The plume componentappears to be similar to the source of oceanic island basalts. KEY WORDS: Kenya Rift Valley; mantle plumes; geochemistry; metasomatism  相似文献   

A Tale of Two Cities: The Experience of Housing Problems in Auckland and Christchurch     

CHRISTOPHER J. SMITH  ROBIN A. KEARNS  MAX W. ABBOTT 《New Zealand geographer》1992,48(1):2-10

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Assessing costs and benefits of geographical information systems: methodological and implementation issues     

DOUGLAS A. SMITH  ROGER F. TOMLINSON 《International journal of geographical information science》2013,27(3):247-256

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Probabilistic noise reduction     

JAMES A. HANSEN  LEONARD A. SMITH 《地球，A辑:动力气象学与海洋学》2001,53(5):585-598

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The thermal structure of an air-water interface at low wind speeds     

HANDLER R. A.  SMITH G. B.  LEIGHTON R. I.     《地球，A辑:动力气象学与海洋学》2004,56(2):176-176

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NWA 1152 and Sahara 00182: New primitive carbonaceous chondrites with affinities to the CR and CV groups     

Caroline L. SMITH  Sara S. RUSSELL  Matthieu GOUNELLE  Richard C. GREENWOOD  Ian A. FRANCHI 《Meteoritics & planetary science》2004,39(12):2009-2032

Abstract— We have investigated the mineralogy, petrography, bulk chemistry, and light element isotope composition of the ungrouped chondrites North West Africa (NWA) 1152 and Sahara 00182. NWA 1152 contains predominantly type 1 porphyritic olivine (PO) and porphyritic olivinepyroxene (POP) chondrules. Chondrule silicates are magnesium‐rich (Fo_{98.8 ± 1.2}, n = 36; Fs_{2.3 ± 2.1} Wo_{1.2 ± 0.3}, n = 23). Matrix comprises ?40 vol% of the sample and is composed of a micron sized silicate groundmass with larger silicate, sulfide, magnetite, and Fe‐Ni metal (Ni ?50 wt%) grains. Phyllosilicates were not observed in the matrix. Refractory inclusions are rare (0.3 vol%) and are spinel pyroxene aggregates or amoeboid olivine aggregates; melilite is absent from the refractory inclusions. Sahara 00182 contains predominantly type 1 PO chondrules, POP chondrules are less common. Most chondrules contain blebs of, and are often rimmed with, Fe‐Ni metal and sulfide. Chondrule phenocrysts are magnesium‐rich (Fo_{92.2 ± 0.6}, n = 129; Fs_{4.4 ± 1.8} Wo_{1.3 ± 1.1}, n = 16). Matrix comprises ?30 vol% of the meteorite and is predominantly sub‐micron silicates, with rare larger silicate gains. Matrix Fe‐Ni metal (mean Ni = 5.8 wt%) and sulfide grains are up to mm scale. No phyllosilicates were observed in the matrix. Refractory inclusions are rare (1.1 vol%) and melilite is absent. The oxygen isotope composition of NWA 1152 falls within the range of the CV chondrites with δ¹⁷O = ?3.43%0 δ¹⁸O = 0.70%0 and is similar to Sahara 00182, δ¹⁷O = ?3.89%0, δ¹⁸O = ?0.19%0 (Grossman and Zipfel 2001). Based on mineralogical and petrographic characteristics, we suggest NWA 1152 and Sahara 00182 show many similarities with the CR chondrites, however, oxygen isotopes suggest affinity with the CVs. Thus, neither sample can be assigned to any of the currently known carbonaceous chondrite groups based on traditionally recognized characteristics. Both samples demonstrate the complexity of inter‐ and intra‐group relationships of the carbonaceous chondrites. Whatever their classification, N WA 1152 and Sahara 00182 represent a source of relatively pristine solar system material.  相似文献   

Ideal shocks in 2‐layer flow Part I: Under a rigid lid     

QINGFANG JIANG  RONALD B. SMITH 《地球，A辑:动力气象学与海洋学》2001,53(2):129-145

Previous work on the classical problem of shocks in a 2‐layer density‐stratified fluid used either a parameterized momentum exchange or an assumed Bernoulli loss. We propose a new theory based on a set of viscous model equations. We define an idealized shock in two‐layer density stratified flow under a rigid lid as a jump or drop of the interface in which (1) the force balance remains nearly hydrostatic in the shock, (2) there is no exchange of momentum between the two layers except by pressure forces on the sloping interface, and (3) dissipative processes can be treated with a constant viscosity. We proceed in two steps. First, we derive a necessary condition for shock existence based on a requirement for wave steepening. Second, we formulate and solve a set of viscous model equations. Some results are the following: Shocks require strong layer asymmetry; one layer must be much faster and/or shallower than the other layer. The linearized equations describing the shock tails provide boundary conditions and a proof of shock uniqueness. It is possible to derive an analytical solution for weak shocks if the steepening condition is met. The weak shock solutions provide closed form expressions for the Bernoulli loss in each layer. Bernoulli losses are strongly concentrated in the expanding layer as the relative layer depth change is much larger in that layer. Bernoulli losses are independent of layer viscosity. A sudden cessation of shock existence is found for strong shocks when the possible end state migrates into the supercritical regime. Surprisingly, the new ideal shock theory compares well with a 2‐D, time‐dependent shallow water model (SWM) with a flux formulation, but with no viscous formulation. Both the Bernoulli drop and shock cessation condition agree quantitatively.  相似文献   

Simulated climate conditions in Europe during the Marine Isotope Stage 3 stadial     

ERIK KJELLSTRÖM  JENNY BRANDEFELT  JENS‐OVE NÄSLUND  BEN SMITH  GUSTAV STRANDBERG  ANTJE H. L. VOELKER  BARBARA WOHLFARTH 《Boreas: An International Journal of Quaternary Research》2010,39(2):436-456

Kjellström, E., Brandefelt, J., Näslund, J.‐O., Smith, B., Strandberg, G., Voelker, A. H. L. & Wohlfarth, B. 2010: Simulated climate conditions in Europe during the Marine Isotope Stage 3 stadial. Boreas, 10.1111/j.1502‐3885.2010.00143.x. ISSN 0300‐9483. State‐of‐the‐art climate models were used to simulate climate conditions in Europe during Greenland Stadial (GS) 12 at 44 ka BP. The models employed for these simulations were: (i) a fully coupled atmosphere–ocean global climate model (AOGCM), and (ii) a regional atmospheric climate model (RCM) to dynamically downscale results from the global model for a more detailed investigation of European climate conditions. The vegetation was simulated off‐line by a dynamic vegetation model forced by the climate from the RCM. The resulting vegetation was then compared with the a priori vegetation used in the first simulation. In a subsequent step, the RCM was rerun to yield a new climate more consistent with the simulated vegetation. Forcing conditions included orbital forcing, land–sea distribution, ice‐sheet configuration, and atmospheric greenhouse gas concentrations representative for 44 ka BP. The results show a cold climate on the global scale, with global annual mean surface temperatures 5 °C colder than the modern climate. This is still significantly warmer than temperatures derived from the same model system for the Last Glacial Maximum (LGM). Regional, northern European climate is much colder than today, but still significantly warmer than during the LGM. Comparisons between the simulated climate and proxy‐based sea‐surface temperature reconstructions show that the results are in broad agreement, albeit with a possible cold bias in parts of the North Atlantic in summer. Given a prescribed restricted Marine Isotope Stage 3 ice‐sheet configuration, with large ice‐free regions in Sweden and Finland, the AOGCM and RCM model simulations produce a cold and dry climate in line with the restricted ice‐sheet configuration during GS 12. The simulated temperature climate, with prescribed ice‐free conditions in south‐central Fennoscandia, is favourable for the development of permafrost, but does not allow local ice‐sheet formation as all snow melts during summer.  相似文献   

Priority sites and conservation gaps of wintering waterbirds in the Yangtze River floodplain     

XIA Shaoxia  YU Xiubo  LEI Jinyu  HEARN Richard  SMITH Bena  LEI Gang  XIE Ping 《地理学报(英文版)》2020,30(10):1617-1632

The Yangtze River floodplain is critical for migratory waterbirds along the East Asian-Australasian Flyway(EAAF). Greater awareness of its global importance is urgently needed to ensure waterbird populations remain in favourable conservation status, as well as the enhancement of wider wetland biodiversity within this region. The designation of protected wetland areas and building a green ecological corridor in the Yangtze floodplain is now becoming a critical issue of interest to the Chinese government. Priority sites in this area were identified based on the criteria used to identify sites that qualify as Wetlands of International Importance(Ramsar Sites) and Important Bird and Biodiversity Areas(IBAs) by using multi-source data. The results show that 140 of the sites surveyed are priority sites. The Importance Index(I) for the whole floodplain decreased slightly from 2001–2005 and an unbalanced distribution pattern is evident with Jiangxi and Hunan provinces significantly higher than the other provinces in the floodplain. Although more than 60% of the priority sites are currently located outside protected areas, the average Conservation Effectiveness Index(C) of the whole floodplain is 75.6%, which suggests the coverage of protected areas for most wintering waterbird population is reasonable. Conservation of the Yangtze River floodplain needs to be further strengthened due to declining waterbird abundances and the mismatch between the distribution of protected areas and their importance for wintering waterbirds. A comprehensive system for priority site identification and protection and scientific review is needed. Multi-sourced data from regular, systematic and coordinated monitoring of waterbird distribution and abundance across the EAAF, as well as national scale citizen science programmes are also critically important.  相似文献   

Soil carbon storage in plantation forests and pastures: land-use change implications   总被引：14，自引：0，他引：14  

NEAL A. SCOTT  KEVIN R. TATE  JUSTIN FORD-ROBERTSON  DAVID J. GILTRAP  C. TATTERSALL SMITH 《Tellus. Series B, Chemical and physical meteorology》1999,51(2):326-335

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