Melt inclusions from the deep Slave lithosphere: implications for the origin and evolution of mantle-derived carbonatite and kimberlite   总被引：1，自引：0，他引：1  

Esm van Achterbergh  William L. Griffin  Chris G. Ryan  Suzanne Y. O'Reilly  Norman J. Pearson  Kevin Kivi  Buddy J. Doyle 《Lithos》2004,76(1-4):461-474

Melt inclusions in clinopyroxenes from lherzolitic xenoliths from the deep lithospheric mantle beneath the Slave Craton (Lac de Gras area, Canada) reveal multiple origins for carbonatitic melts. One type of inclusions consists of a series of silicate–carbonate–silicate concentric layers, interpreted to have unmixed under disequilibrium conditions during rapid ascent to the surface. Bulk major- and trace-element compositions are typical of Group 1 kimberlites and quantitative nuclear microprobe imaging of the globules reveals fractionation of related elements (e.g. F–Br, Nb–Ta) between the silicate and carbonate components. The globules probably formed by partial melting of carbonated peridotite, consistent with results of melting experiments and some models for the generation of kimberlite magmas. They provide evidence for a genetic relationship between some carbonate-rich magmas and ultramafic silicate magmas, and for the possibility of unmixing processes of these melts during their evolution.

The second inclusion type comprises carbonate-rich globules interpreted as samples of Mg-carbonatite melt that quenched on ascent to the surface. Bulk major- and trace-element compositions indicate that the melts were derived from a carbonate-rich source and oxygen, carbon, and strontium isotope data are consistent with the involvement of recycled crustal material and suggest that some mantle-derived carbonatites are unrelated to kimberlites.  相似文献   

Supply limited sediment transport in a high-discharge event of the tropical Burdekin River, North Queensland, Australia   总被引：1，自引：0，他引：1  

Kathryn J. Amos  Jan Alexander  Anthony Horn†  Geoff D. Pocock‡  Chris R. Fielding§ 《Sedimentology》2004,51(1):145-162

Interactions between catchment variables and sediment transport processes in rivers are complex, and sediment transport behaviour during high‐flow events is not well documented. This paper presents an investigation into sediment transport processes in a short‐duration, high‐discharge event in the Burdekin River, a large sand‐ and gravel‐bed river in the monsoon‐ and cyclone‐influenced, semi‐arid tropics of north Queensland. The Burdekin's discharge is highly variable and strongly seasonal, with a recorded maximum of 40 400 m³ s^?1. Sediment was sampled systematically across an 800 m wide, 12 m deep and straight reach using Helley‐Smith bedload and US P‐61 suspended sediment samplers over 16 days of a 29‐day discharge event in February and March 2000 (peak 11 155 m³ s^?1). About 3·7 × 10⁶ tonnes of suspended sediment and 3 × 10⁵ tonnes of bedload are estimated to have been transported past the sample site during the flow event. The sediment load was predominantly supply limited. Wash load included clay, silt and very fine sand. The concentration of suspended bed material (including very coarse sand) varied with bedload transport rate, discharge and height above the bed. Bedload transport rate and changes in channel shape were greatest several days after peak discharge. Comparison between these data and sparse published data from other events on this river shows that the control on sediment load varies between supply limited and hydraulically limited transport, and that antecedent weather is an important control on suspended sediment concentration. Neither the empirical relationships widely used to estimate suspended sediment concentrations and bedload (e.g. Ackers & White, 1973) nor observations of sediment transport characteristics in ephemeral streams (e.g. Reid & Frostick, 1987) are directly applicable to this river.  相似文献   

Lateglacial and Holocene talus slope development and rockwall retreat on Mynydd Du, UK   总被引：1，自引：0，他引：1  

Alastair M. Curry  Chris J. Morris 《Geomorphology》2004,58(1-4):85-106

Modification of Lateglacial and Holocene talus sheets by debris flows and gully incision on Mynydd Du, Wales, has resulted in a convergence of upper slope form characterised by an upper rectilinear slope gradient of 36°±3° and a range of concavities of c. 0.1–0.2. In most cases, gully incision and accumulation of debris cones have led to an increase in slope concavity. Evidence for talus erosion, reworking and redeposition on the upper slope emphasises secondary reworking processes, as well as primary talus accumulation on the upper slope, and permits construction of a model of talus development at Mynydd Du. On the basis of talus volume, calculation of the first rockwall retreat data set for southern Britain suggests that c. 7.1 m (84%) of overall rockwall retreat (8.5 m) took place during the Lateglacial, and only c. 1.4 m (16%) occurred during the Holocene. These figures imply that Lateglacial retreat rates ranged from 1.01 to 2.44 m ka⁻¹, with an overall mean rate of 1.23 m ka⁻¹. In contrast, Holocene rockwall retreat rates range from 0.10 to 0.17 m ka⁻¹, with a mean rate of 0.12 m ka⁻¹. Approximately 27% of cliff retreat is attributed to microgelivation. While similar to Holocene and present-day alpine environments, these Lateglacial retreat rates are one order of magnitude higher than most equivalent values for arctic sites. This reflects both ‘alpine-style’ diurnal freeze–thaw activity on Mynydd Du during the Younger Dryas and paraglacial rock-mass instability following deglaciation. Assuming an exponential decline in rockwall sediment release, it is estimated that approximately half the talus had accumulated within c. 1 ka of deglaciation. At one site, paraglacial talus accumulation appears to have contributed significantly to the glacial sediment transport system of a subsequent ice advance. Present-day rates of rockwall retreat and talus accumulation by rockfall are estimated to be 0.014 and 0.022 mm yr⁻¹ (m ka⁻¹), respectively, similar to values for other British sites and markedly lower than Holocene rates of cliff recession due to microgelivation. By implication, the geomorphic significance of microgelivation may have been greatly underestimated in studies of inland rock-slope evolution in temperate, mid-latitude environments.  相似文献   

Smoothing/filtering LiDAR digital surface models. Experiments with loess regression and discrete wavelets     

Nicholas J. Tate  Chris Brunsdon  Martin Charlton  A. Stewart Fotheringham  Claire H. Jarvis 《Journal of Geographical Systems》2005,7(3-4):273-290

This paper reports on the smoothing/filtering analysis of a digital surface model (DSM) derived from LiDAR altimetry for part of the River Coquet, Northumberland, UK using loess regression and the 2D discrete wavelet transform (DWT) implemented in the S-PLUS and R statistical packages. The chosen method of analysis employs a simple method to generate ‘noise’ which is then added to a smooth sample of LiDAR data; loess regression and wavelet methods are then used to smooth/filter this data and compare with the original ‘smooth’ sample in terms of RMSE. Various combinations of functions and parameters were chosen for both methods. Although wavelet analysis was effective in filtering the noise from the data, loess regression employing a quadratic parametric function produced the lowest RMSE and was the most effective.  相似文献   

The eruptive history of the Tequila volcanic field, western Mexico: ages, volumes, and relative proportions of lava types     

Catherine B. Lewis-Kenedi  Rebecca A. Lange  Chris M. Hall  Hugo Delgado-Granados 《Bulletin of Volcanology》2005,67(7):694-694

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LNAPL in fine-grained soils: Conceptualization of saturation, distribution, recovery, and their modeling     

Mark Adamski  Victor Kremesec  Ravi Kolhatkar  Chris Pearson  Beth Rowan 《Ground Water Monitoring & Remediation》2005,25(1):100-112

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Sediment resuspension events within the (microtidal) coastal waters of Thermaikos Gulf, northern Greece   总被引：2，自引：0，他引：2  

D. Paphitis  M.B. Collins   《Continental Shelf Research》2005,25(19-20):2350

High-frequency flow, pressure and suspended sediment concentration (SSC) measurements are presented from the Paralia-Katerinis coastal area, in Thermaikos Gulf. The data were collected along a cross-shore transect, between the 6 and 12 m water depth contours. The relative importance of wave- and tidally-induced resuspension is examined. Resuspension events are shown to be dominated by wind-generated waves, especially under storm conditions. Some evidence is provided for tidal resuspension, but the overall impact of this process is minimal, compared to wave resuspension. Such resuspension, under storm conditions, increased the SSC levels in the waters of the nearshore zone to 35 mg/l; this is a >15-fold increase over the ambient levels (1–2 mg/l) of turbidity.  相似文献   

Felsic lavas or rheomorphic ignimbrites: is there a chemical distinction?   总被引：3，自引：0，他引：3  

Linda A. Kirstein  Chris J. Hawkesworth  Frances G. Garland 《Contributions to Mineralogy and Petrology》2001,142(3):309-322

In the environment of felsic magma generation associated with continental flood basalt (CFB) provinces there is a close association between magma composition, phenocryst assemblage, temperature and eruption mechanism. In this paper we propose that by examining the chemical composition and, in particular the high field strength element (Zr and Nb) contents of the high silica rocks, we can identify those that contained halogen-rich volatiles and which degassed at different levels (deep versus shallow). The degassing depth has a direct influence on the type of eruption, with shallow degassing promoting explosive rather than effusive behaviour and consequentially the former is more likely to give rise to ignimbrites. Thus, we can infer likely eruption mechanisms, as high concentrations of F and Cl dramatically decrease magma viscosities and should favour deep degassing and hence promote lava effusion rather than explosive pyroclastic eruption. This hypothesis is tested by constraining the other possible variables which have an effect on the mode of eruption, and by examining the nature and composition of melt and fluid inclusions in quartz from CFB-associated felsic volcanic rocks.  相似文献   

A Ground-Water Tracer Test with Deuterated Compounds for Monitoring In Situ Biodegradation and Retardation of Aromatic Hydrocarbons   总被引：4，自引：0，他引：4  

Joseph Thierrin  Gregory B. Davis  Chris Barber 《Ground water》1995,33(3):469-475

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Book reviews     

Vernon F. Cormier  Gregory A. Houseman  David F. McTigue  Manfred Koch  William L. Power  Marek Lewandowski  Chris J. Marone  Carlo Denis  Brian F. Farrell  Timothy J. Fuller-Rowell 《Pure and Applied Geophysics》1993,140(4):729-754

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