A trace-gas climatology above Zotino, central Siberia   总被引：1，自引：1，他引：1  

JON LLOYD  RAY L. LANGENFELDS  ROGER J. FRANCEY  MANUEL GLOOR  NADEJDA M. TCHEBAKOVA  DANIIL ZOLOTUOKHINE  WILLI A. BRAND  ROLAND A. WERNER  ARMIN JORDAN  COLIN A. ALLISON  VITALY ZRAZHEWSKE  OLGA SHIBISTOVA  E.-D. SCHULZE 《Tellus. Series B, Chemical and physical meteorology》2002,54(5):749-767

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Resolving Sediment Subduction and Crustal Contamination in the Lesser Antilles Island Arc: a Combined He-O-Sr Isotope Approach   总被引：2，自引：0，他引：2  

VAN SOEST  MATTHIJS C.; HILTON  DAVID R.; MACPHERSON  COLIN G.; MATTEY  DAVID P. 《Journal of Petrology》2002,43(1):143-170

We report an extensive helium isotope survey of basaltic toandesitic lavas from the Lesser Antilles island arc—anarc system with well-documented evidence of crustal contamination.Given the sensitivity of helium isotopes as a tracer of theeffects of crustal additions, our aim is to evaluate the relationshipof ³He/⁴He ratios to other indices of contamination processessuch as oxygen and strontium isotopes. To this end, we havecarried out 53 ³He/⁴He analyses on separated minerals (olivinesand pyroxenes) from throughout the arc, which we compare withwhole-rock strontium and phenocryst oxygen isotope measurements.We show that the three isotopic tracers show coherent patternsthroughout the Lesser Antilles, indicating a regional controlon crustal contamination. The southern section of the arc (Grenadato Martinique) shows clear evidence for major crustal contaminationin all three isotopic systems with results for our samples inthe range ³He/⁴He_(olivine) 3·6–7·6R_A,  相似文献   

A nitrogen and argon stable isotope study of Allan Hills 84001: Implications for the evolution of the Martian atmosphere     

MONICA M. GRADY  IAN P. WRIGHT  COLIN T. PILLINGER 《Meteoritics & planetary science》1998,33(4):795-802

Abstract— The abundances and isotopic compositions of N and Ar have been measured by stepped combustion of the Allan Hills 84001 (ALH 84001) Martian orthopyroxenite. Material described as shocked is N-poor ([N] ～ 0.34 ppm; δ¹⁵N ～ +23%); although during stepped combustion, ¹⁵N-enriched N (δ¹⁵N ～ +143%) is released in a narrow temperature interval between 700 °C and 800 °C (along with ¹³C-enriched C (δ¹³C ～ +19%) and ⁴⁰Ar). Cosmogenic species are found to be negligible at this temperature; thus, the iso-topically heavy component is identified, in part, as Martian atmospheric gas trapped relatively recently in the history of ALH 84001. The N and Ar data show that ALH 84001 contains species from the Martian lithosphere, a component interpreted as ancient trapped atmosphere (in addition to the modern atmospheric species), and excess ⁴⁰Ar from K decay. Deconvolution of radiogenic ⁴⁰Ar from other Ar components, on the basis of end-member ³⁶Ar/¹⁴N and ⁴⁰Ar/³⁶Ar ratios, has enabled calculation of a K-Ar age for ALH 84001 as 3.5–4.6 Ga, depending on assumed K abundance. If the component believed to be Martian palaeoatmos-phere was introduced to ALH 84001 at the time the K-Ar age was set, then the composition of the atmosphere at this time is constrained to: δ¹⁵N ≥ +200%, ⁴⁰Ar/³⁶Ar ≤ 300 and ³⁶Ar/¹⁴N ≥ 17 × 10^?5. In terms of the petrogenetic history of the meteorite, ALH 84001 crystallised soon after differentiation of the planet, may have been shocked and thermally metamorphosed in an early period of bombardment, and then subjected to a second event. This later process did not reset the K-Ar system but perhaps was responsible for introducing (recent) atmospheric gases into ALH 84001; and it might mark the time at which ALH 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages.  相似文献   

Nunataks of the last ice sheet in northwest Scotland   总被引：1，自引：0，他引：1  

DANNY McCARROLL  COLIN K. BALLANTYNE  ATLE NESJE  SVEIN-OLAF DAHL 《Boreas: An International Journal of Quaternary Research》1995,24(4):305-323

High-level weathering limits separating ice-scoured topography from an upper zone of frost-weathered detritus were identified on 17 mountains in NW Scotland at altitudes of <600 m to< 900 m, and a further 6 peaks were found to support evidence of ice scouring to summit level. Weathering limits are most clearly defined on Torridon Sandstone, which is resistant to frost shattering, but can also be mapped on Cambrian Quartzite, Lewisian Gneiss and Moine Schist. Contrasts in degree of rock surface weathering above and below the weathering limits were evaluated using measurements of joint depth and rock surface hardness, and through X-ray diffraction analyses of clay mineral assemblages. The results indicate significantly more advanced rock and soil weathering above the weathering limits. Widespread persistence of gibbsite above the weathering limits suggests that they represent the upper limit of Late Devensian glacial erosion, and the regularity of the decline in weathering limit altitude along former flowlines eliminates the possibility that it represents a former thermal boundary between protective cold-based and erosive warm-based ice. The weathering limits are therefore interpreted as periglacial trimlines defining the maximum surface altitude of the last ice sheet around former nunataks. Calculated basal shear stresses of 50–78 kPa are consistent with this interpretation. The altitude of the trimlines implies that the former ice shed lay at 900–930 m in the Fannich Mountains and descended gently northwards, and that the ice surface descended NW from the ice shed to >500 m over the extreme NW tip of Scotland and to 700–730 m at the head of Little Loch Broom.  相似文献   

Glacial activity in New Zealand near the Pleistocene-Holocene boundary in the light of new radiocarbon dates     

COLIN J. BURROWS  TREVOR CHINN  MICHAEL KELLY 《Boreas: An International Journal of Quaternary Research》1976,5(2):57-60

Burrows, C. J., Chinn, T. & Kelly, M. 1976 08 01: Glacial activity in New Zealand near the Pleistocene-Holocene boundary in the light of new radiocarbon dates.
Although glaciers in New Zealand were diminishing from the late Pleistocene onwards, there remained an extensive ice cover, greater than at present, well into early Holocene. The Birch Hill advances are dated to just before the Pleistocene-Holocene boundary at 10,000 B.P., and at least two lesser advances are recognised, at 9000 B.P. and 8000 B.P. A general parallel with northern hemisphere glacial activity is drawn.  相似文献   

Contradictory socio-economic consequences of structural adjustment in Kingston, Jamaica     

COLIN CLARKE  DAVID HOWARD† 《The Geographical journal》2006,172(2):106-129

Since the early 1980s, the introduction of International Monetary Fund-directed structural adjustment packages to stabilize the Jamaican economy has reduced the scope of the government, cut back its capacity to intervene in the housing market, opened the economy to foreign goods (but limited capital), and re-produced the colonial version of a non-dynamic, labour-surplus urban economy in Kingston. This paper traces the impact of structural adjustment on unemployment and class formation in Kingston, and the relationship of these issues to housing problems. Rented, poor-quality housing, underpinned by low socio-economic status and historically high rates of unemployment, has created an overt spatial concentration of poverty, located in West and East Kingston. Nevertheless, overall unemployment is currently lower than at independence in 1962, and virtually all housing indicators have recorded improvements over the same time period. These improvements have been due to a deceleration in the growth of Kingston's population since the mid-1960s; government commitment, despite structural adjustment, to improve the quality of collective consumption; and the determination of Kingston's citizens to build better homes for themselves, often aided by loans from local building societies and remittances from family members resident overseas. However, at least a quarter of Kingston's population remains both unemployed and concentrated into areas of poor quality housing. These circumstances in Kingston are compared with those in adjacent Latin American cites under structural adjustment.  相似文献   

Musical Words, Musical Worlds     

COLIN R. McLEAY 《New Zealand geographer》1995,51(2):1-6

The recent ‘cultural turn’ in human geography has neglected music and its impact in the construction and understanding of landscape and the politics of place. Using the songs of the rockgroup U2 to show how geographic imagery is used for political purposes, this paper attempts to ‘breakthe silence’ of contemporary cultural geography.  相似文献   

ALGEBRAIC PROCESSING TECHNIQUES FOR ESTIMATING SHEAR-WAVE SPLITTING IN NEAR-OFFSET VSP DATA: THEORY1     

XINWU ZENG  COLIN MACBETH 《Geophysical Prospecting》1993,41(8):1033-1066

A vector convolutional model for multicomponent data acquired in an anisotropic earth is used as a basis for developing algebraic solutions to interpret near-offset VSP data. This interpretation of the cumulative or interval medium response (Green's tensor) for shear waves, determines a polarization azimuth for the leading shear wave and the time-delay between the fast and slow split waves. The algebraic solutions effectively implement least-squares eigenanalysis or singular value decomposition. Although the methodology for shear-wave analysis is strictly relevant to a transmission response, it can be adapted to surface data for a uniform anisotropic overburden. The techniques perform well when calibrated and tested using synthetic seismograms from various anisotropic models. Noise tests demonstrate the sensitivity of the interval measurements to local interferences, particularly if the shear waves are generated by one source. Although the algorithms are faster than numerical search routines, this is not seen as their major advantage. The solutions may have potential in near real-time interpretation of shear-wave data in well logging, where they may be coded on a microchip to provide a direct stream of separated shear waves, or polarization and birefringence information. There may also be some benefit for large prestack multicomponent surface data sets, where the solutions provide a direct transformation to the split-shear-wave components, reducing the storage space for further processing.  相似文献   

DIFFERENTIAL ROCK WEATHERING IN THE 'VALLEY OF THE BOULDERS', KÄRKEVAGGE, SWEDISH LAPLAND   总被引：1，自引：1，他引：0  

ROBERT G. DARMODY  COLIN E. THORN  JOHN C. DIXON 《Geografiska Annaler: Series A, Physical Geography》2008,90(3):201-209

Kärkevagge is an alpine valley in the low arctic of Swedish Lapland. It is named after, and famous for, its large deposit of immense (c. 10–15 m) boulders that almost fill the lower valley. Above the boulder deposit, on the flanks of the valley, are more recent and generally much smaller (c. 1–3 m) individual boulders that have fallen from the valley-wall cliff face, presumably from post-glacial valley-side unloading. Some of these smaller boulders are seemingly fresh and unweathered while others have been reduced to no more than mounds in the tundra. These boulders must be younger than the larger, lower giant boulder deposit, but are not particularly recent rockfalls as they are partially buried in colluvium. Comparisons of mineralogy and chemistry indicate that the possibility exists that the incompetent, 'rotten' rocks, if not considerably older than their competent neighbors, are inherently self-destructive. They have evidence of increased sulfur content, which is a proxy for pyrite, a known weathering accelerant in Kärkevagge.  相似文献   

CHANNEL ADJUSTMENT OF AN UNSTABLE COARSE-GRAINED STREAM: OPPOSING TRENDS OF BOUNDARY AND CRITICAL SHEAR STRESS,AND THE APPLICABILITY OF EXTREMAL HYPOTHESES     

ANDREW SIMON  COLIN R. THORNE 《地球表面变化过程与地形》1996,21(2):155-180

Channel adjustments in the North Fork Toutle River and the Toutle River main stem were initiated by deposition of a 2.5 km³ debris avalanche and associated lahars that accompanied the catastrophic eruption of Mount St. Helens, Washington on 18 May 1980. Channel widening was the dominant process. In combination, adjustments caused average boundary shear stress to decrease non-linearly with time and critical shear stress to increase non-linearly with time. At the discharge that is equalled or exceeded 1 per cent of the time, these trends converged by 1991–1992 so that excess shear stress approached minimum values. Extremal hypotheses, such as minimization of unit stream power and minimization of the rate of energy dissipation (minimum stream power), are shown to be applicable to dynamic adjustments of the Toutle River system. Maximization of the Darcy–Weisbach friction factor did not occur, but increases in relative bed roughness, caused by the concomitant reduction in hydraulic depths and bed-material coarsening, were documented. Predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991–1992 geometries and bed-material characteristics measured in the field. It is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision, retreat of stream-side hummocks, and establishment of riparian vegetation to limit the destabilizing effects of large floods. Further, prediction of energy slope (and consequently stream power) by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained (sand and gravel) bank materials (relative to the coarsened channel bed) from bank retreat and from upstream terrace erosion.  相似文献