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141.
Application of the QUILF thermobarometer to the peralkaline trachytes and pantellerites of the Eburru volcanic complex, East African Rift, Kenya 总被引:1,自引:0,他引:1
Minghua Ren Peter A. Omenda Elizabeth Y. Anthony John C. White Ray Macdonald D.K. Bailey 《Lithos》2006,91(1-4):109-124
The Quaternary Eburru volcanic complex in the south-central Kenya Rift consists of pantelleritic trachytes and pantellerites. The phenocryst assemblage in the trachytes is sanidine + fayalite + ferrohedenbergite + aenigmatite ± quartz ± ilmenite ± magnetite ± pyrrhotite ± pyrite. In the pantellerites, the assemblage is sanidine + quartz + ferrohedenbergite + fayalite + aenigmatite + ferrorichterite + pyrrhotite ± apatite, although fayalite, ferrohedenbergite and ilmenite are absent from more evolved rocks (e.g. with SiO2 > 71%). QUILF temperature calculations for the trachytes range from 709 to 793 °C and for the pantellerites 668–708 °C, the latter temperatures being among the lowest recorded for peralkaline silicic magmas. The QUILF thermobarometer demonstrates that the Eburru magmas crystallized at relatively low oxidation states (ΔFMQ + 0.5 to − 1.6) for both trachytes and pantellerites. The trachytes and pantellerites evolved along separate liquid lines of descent, the trachytes possibly deriving from a more mafic parent by fractional crystallization and the pantellerites from extreme fractionation of comenditic magmas. 相似文献
142.
143.
M. Catherine Eimers Andrew M. Paterson Peter J. Dillon Sherry L. Schiff Brian F. Cumming Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109
Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in
the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~
20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ 34S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment
were relatively low (1.9–5 mg S g−1 dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in
δ 34S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally
reciprocal depth pattern between total S concentration and δ 34S ratios. While initial shifts in total S and δ 34S were likely due to enhanced SO4 reduction of newly available anthropogenic SO4, both the magnitude and pattern of up-core S enrichment and shifts in δ 34S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and
δ 34S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake
characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S
deposition in this region, likely due to redox-related mobility of S in upper sediment. 相似文献
144.
145.
146.
Semi-Analytic Modelling of Subsidence 总被引:2,自引:0,他引:2
This paper presents a forward model for subsidence prediction caused by extraction of hydrocarbons. The model uses combinations
of analytic solutions to the visco-elastic equations, which approximate the boundary conditions. There are only a few unknown
parameters to be estimated, and, consequently, calculations are very fast. The semi-analytic model is applicable to a uniform
and layer-cake stratigraphy, with visco-elastic parameters changing per layer, and an arbitrary depletion pattern. By its
capabilities to handle a multi-layered visco-elastic subsurface, the semi-analytic model fills the gap between the analytic
single-layered elastic models available to date and the more elaborate numerical, e.g. finite element, models. 相似文献
147.
Geographic Information System (GIS) software is constrained, to a greater or lesser extent, by a static world view that is not well-suited to the representation of time (Goodchild 2000). Space Time Intelligence System (STIS) software holds the promise of relaxing some of the technological constraints of spatial only GIS, making possible visualization approaches and analysis methods that are appropriate for temporally dynamic geospatial data. This special issue of the Journal of Geographical Systems describes some recent advances in STIS technology and methods, with an emphasis on applications in public health and spatial epidemiology.The STIS expert workshops were funded in part by grants R01CA092669 and R01CA096002 from the National Cancer Institute, and by grants R43-ES010220 and R44-ES010220 from the National Institute of Environmental Health Sciences. Gillian AvRuskin provided cheerful editorial assistance. We thank the participants at the workshops for providing invaluable expertise and critical insights. 相似文献
148.
Heidi M. Cullen Alexey Kaplan Phillip A. Arkin Peter B. deMenocal 《Climatic change》2002,55(3):315-338
Interannual to decadal variations in Middle Eastern temperature, precipitationand streamflow reflect the far-field influence of the North Atlantic Oscillation (NAO), a dominant mode of Atlantic sector climate variability. Using a new sea surface temperature (SST) based index of the NAO and availablestreamflow data from five Middle Eastern rivers, we show that the first principal component of December through March streamflow variability reflects changes in the NAO. However, Middle East rivers have two primary flooding periods.The first is rainfall-driven runoff from December through March, regulated on interannual to decadal timescales by the NAO as reflected in local precipitation and temperature.The second period, from April through June, reflects spring snowmelt and contributes in excess of 50% of annual runoff.This period, known locally as the khamsin, displays no significantNAO connections and a less direct relationship with local climatic factors, suggesting that streamflow variability during this period reflects land-cover change, possibly related to agriculture and hydropower generation, and snowmelt. 相似文献
149.
Lake Teletskoye occupies a narrow graben located in the northwestern sector of the Altai fold belt in South Siberia. The lake basin is thought to have formed during the Pleistocene as a distant result of the Cenozoic collision of India and Eurasia that caused a tectonic reactivation of the Palaeozoic Gorny–Altai (GA) and West Sayan (WS) blocks.The present work reports of a pilot fission-track study performed on 13 apatite separates collected from rocks that were sampled along two profiles in close proximity of the lake. The age–length data and AFT thermochronological modelling reveal two important phases of cooling in the Altai Mountains, a first one during the Late Jurassic–Early Cretaceous and a second one that started in the Miocene–Pliocene and that persists until today. The first event is interpreted to result from uplift-induced denudation probably related to the closure of the Mongol–Okhotsk Ocean; the second event can be linked to the young Cenozoic movements that lie at the origin of the formation of the Lake Teletskoye basin. 相似文献
150.
Christoph Gaedicke Hans-Ulrich Schlüter Hans Albert Roeser Alexander Prexl Bernd Schreckenberger Heinrich Meyer Christian Reichert Peter Clift Shahid Amjad 《Tectonophysics》2002,355(1-4)
The nature and origin of the sediments and crust of the Murray Ridge System and northern Indus Fan are discussed. The uppermost unit consists of Middle Miocene to recent channel–levee complexes typical of submarine fans. This unit is underlain by a second unit composed of hemipelagic to pelagic sediments deposited during the drift phase after the break-up of India–Seychelles–Africa. A predrift sequence of assumed Mesozoic age occurring only as observed above basement ridges is composed of highly consolidated rocks. Different types of the acoustic basement were detected, which reflection seismic pattern, magnetic anomalies and gravity field modeling indicate to be of continental character. The continental crust is extremely thinned in the northern Indus Fan, lacking a typical block-faulted structure. The Indian continent–ocean transition is marked on single MCS profiles by sequences of seaward-dipping reflectors (SDR). In the northwestern Arabian Sea, the Indian plate margin is characterized by several phases of volcanism and deformation revealed from interpretation of multichannel seismic profiles and magnetic anomalies. From this study, thinned continental crust spreads between the northern Murray Ridge System and India underneath the northern Indus Fan. 相似文献