The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia     

NIGEL J. GRIFFEY  PETER WORSLEY 《Boreas: An International Journal of Quaternary Research》1978,7(1):1-17

BOREAS Griffey, N. J. & Worsley, P. 1978 03 01: The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia (Okstindan Research Project Report 26). Boreas, Vol. 7, pp. 1–17. Oslo. ISSN 0300–9483.
Historical, lichenometrical and stratigraphical evidence is combined to establish a provisional history of Neoglacial glacier variation in a mountainous environment approx. 66^oN. Attention is focussed on end moraine chronology. At five sites, derived organic materials have been located within end moraines and at two others in situ palaeosols occur buried beneath distal slopes. Organic rich samples from all the sites have been radiocarbon dated and the results permit the recognition of three major glacier expansion episodes, each of which contributes to the diachronous nature of the Okstindan outer Neoglacial limit. A widespread 'Little Ice Age' event with a maximum extent of probable eighteenth century age is confirmed. Limited areas of older moraine ridges peripheral to the 'Little Ice Age' maximal limit appear to date from about 3000-2500 ¹⁴C years B.P. and a younger period tentatively dated as about 1250-1000 ¹⁴C years B. P. which agrees with recent data from Engabreen in northwest Svartisen. No evidence for any extensive glacial activity after the inlandice wastage approx. 9000 ¹⁴C years B. P. and prior to 3000 ¹⁴C years B.P. was forthcoming.  相似文献   

Near-Ultrahigh Pressure Processing of Continental Crust: Miocene Crustal Xenoliths from the Pamir   总被引：8，自引：0，他引：8  

HACKER  BRADLEY; LUFFI  PETER; LUTKOV  VALERY; MINAEV  VLADISLAV; RATSCHBACHER  LOTHAR; PLANK  TERRY; DUCEA  MIHAI; PATINO-DOUCE  ALBERTO; McWILLIAMS  MICHAEL; METCALF  JIM 《Journal of Petrology》2005,46(8):1661-1687

Xenoliths of subducted crustal origin hosted by Miocene ultrapotassicigneous rocks in the southern Pamir provide important new informationregarding the geological processes accompanying tectonism duringthe Indo-Eurasian collision. Four types have been studied: sanidineeclogites (omphacite, garnet, sanidine, quartz, biotite, kyanite),felsic granulites (garnet, quartz, sanidine and kyanite), basalticeclogites (omphacite and garnet), and a glimmerite (biotite,clinopyroxene and sanidine). Apatite, rutile and carbonate arethe most abundant minor phases. Hydrous phases (biotite andphengite in felsic granulites and basaltic eclogites, amphibolesin mafic and sanidine eclogites) and plagioclase form minorinclusions in garnet or kyanite. Solid-phase thermobarometryreveals recrystallization at mainly ultrahigh temperatures of1000–1100°C and near-ultrahigh pressures of 2·5–2·8GPa. Textures, parageneses and mineral compositions suggestderivation of the xenoliths from subducted basaltic, tonaliticand pelitic crust that experienced high-pressure dehydrationmelting, K-rich metasomatism, and solid-state re-equilibration.The timing of these processes is constrained by zircon agesfrom the xenoliths and ⁴⁰Ar/³⁹Ar ages of the host volcanic rocksto 57–11 Ma. These xenoliths reveal that deeply subductedcrust may undergo extensive dehydration-driven partial melting,density-driven differentiation and disaggregation, and sequestrationwithin the mantle. These processes may also contribute to thealkaline volcanism observed in continent-collision zones. KEY WORDS: xenolith; high-pressure; subduction; Pamir; Tibet  相似文献   

Cotectic Proportions of Olivine and Spinel in Olivine-Tholeiitic Basalt and Evaluation of Pre-Eruptive Processes   总被引：1，自引：1，他引：1  

ROEDER  PETER; GOFTON  EMMA; THORNBER  CARL 《Journal of Petrology》2006,47(5):883-900

The volume %, distribution, texture and composition of coexistingolivine, Cr-spinel and glass has been determined in quenchedlava samples from Hawaii, Iceland and mid-oceanic ridges. Thevolume ratio of olivine to spinel varies from 60 to 2800 andsamples with >0·02% spinel have a volume ratio ofolivine to spinel of approximately 100. A plot of wt % MgO vsppm Cr for natural and experimental basaltic glasses suggeststhat the general trend of the glasses can be explained by thecrystallization of a cotectic ratio of olivine to spinel ofabout 100. One group of samples has an olivine to spinel ratioof approximately 100, with skeletal olivine phenocrysts andsmall (<50 µm) spinel crystals that tend to be spatiallyassociated with the olivine phenocrysts. The large number ofspinel crystals included within olivine phenocrysts is thoughtto be due to skeletal olivine phenocrysts coming into physicalcontact with spinel by synneusis during the chaotic conditionsof ascent and extrusion. A second group of samples tend to havelarge olivine phenocrysts relatively free of included spinel,a few large (>100 µm) spinel crystals that show evidenceof two stages of growth, and a volume ratio of olivine to spinelof 100 to well over 1000. The olivine and spinel in this grouphave crystallized more slowly with little physical interaction,and show evidence that they have accumulated in a magma chamber. KEY WORDS: olivine; spinel; basalt glass; volume %; cotectic  相似文献   

Integrating dynamic environmental models in GIS: The development of a Dynamic Modelling language   总被引：3，自引：0，他引：3  

CEES G WESSELUNG  DERC-JAN KARSSENBERG  PETER A BURROUGH  WILLEM P A VAN  DEURSEN 《Transactions in GIS》1996,1(1):40-48

  相似文献   

Acid Rain and Below-Cloud Scavenging in South-Western China   总被引：1，自引：0，他引：1  

PETER A. TANNER  HENG-CHI LEI  MEI-YUAN HUANG  ZHI-LAI SHEN 《Journal of Atmospheric Chemistry》1997,27(1):71-78

Major urban areas in south-western China exhibit unique air pollutionproblems due to increasing use of high sulphur-content fuels in an environmentof unfavourable topography and climate. Ambient levels of sulphur dioxideexceed the air quality objectives, and this gas is the major precursor of acidrain. Cloudwater chemistry studies are reported for urban, suburban andcountryside locations, during the period 1985–1989. Although cloudwateracidity was found to increase towards the cloud base, the acidity was muchgreater for rainwater samples collected simultaneously, and was morepronounced in urban rather than neighbouring suburban or countryside regions.The main contribution to the acidity arises from below-cloud scavenging of gasand aerosol and model calculations are able to simulate this behaviour.  相似文献   

One-dimensional models of groundwater flow, sediment thermal history and petroleum generation within continental rift basins   总被引：1，自引：0，他引：1  

MARK Person  DENAH Toupin†  PETER Eadington‡ 《Basin Research》1995,7(1):81-96

We investigate the effects of convective heat transfer on the thermal history of sediments and petroleum formation within continental rift basins using one-dimensional mathematical modelling. The transport equations used in this study to describe vertical groundwater flow and conductive/convective heat transfer are solved by the finite element method. Sediment thermal history is quantitatively represented using first-order rate kinetic expressions for kerogen degradation and an empirical fanning Arrhenius model for apatite fission track annealing. Petroleum generation is also represented in the model by a suite of first-order rate kinetic expressions. The analysis provides insights into how pore fluid circulation patterns are preserved in the rock record as anomalies in palaeogeothermometric data within continental rifts. Parameters varied in the numerical experiments include the ratio of conductive to convective heat transfer (thermal Peclet number; Pe) and the composition of the disseminated organic matter in the sediment (type II and III kerogen). Quantitative results indicate that vertical groundwater flow rates on the order of a mm/yr cause a change in computed vitrinite reflectance of the rocks and a shift in the depth to oil generation by as much as 3000 m. Differences in thermal gradients between recharge and discharge areas (Pe= 0.6) also change the width of the zone of oil generation by a factor of two. Even more dramatic, however, are the large changes in predicted apatite fission track length distributions and model ages between recharge and discharge areas. For example, a sediment package buried to a depth of 2400 m over 200 Myr within the groundwater recharge column had a fission track length distribution with a computed mean and standard deviation of 12.83 μm and 0.77 μm, respectively. The fission track model age for this sediment package was 209 Ma. The same sediment package in the discharge area has a distribution with a mean track length of 5.68 μm, a standard deviation of 3.37 μm, and a fission track model age of 2.6 Ma. Transient groundwater flow simulations, in which fluid circulation ceases after a period of time within the rift basin, are also presented to illustrate how disturbances in palaeogeothermometric parameters are preserved on geological time-scales. Vitrinite reflectance profiles require about 10 Myr to return to conductive conditions within groundwater recharge areas while the convective disturbances are preserved indefinitely along the discharge column, as long as further subsidence does not occur. Ancient groundwater flow systems are preserved as anomalies in computed apatite fission track model ages and distributions much longer after groundwater flow stops, relative to organic-based geothermometers. Significant differences exist in model ages between recharge (145 Ma) and discharge (90 Ma) areas 200 Myr after flow has ceased. However, calculated fission track histogram distributions are virtually identical in recharge and discharge areas after about 50 Myr. Our study suggests that ancient groundwater flow systems can be detected by comparing thermochronometric data between suspected recharge and discharge areas within continental rifts. Vitrinite reflectance profiles, observed offsets in the depth to the onset of petroleum generation, and apatite fission track annealing studies are all well suited for detecting groundwater flow systems which have been relatively long lived (10⁷ years). Apatite fission track age data are probably best suited for identifying ancient groundwater flow systems within rifts long (>200 Myr) after flow ceases.  相似文献   

Maintaining the Rural Landscape     

SHERRY OLSON  PETER HOLLAND 《New Zealand geographer》1995,51(2):16-24

Cultural landscapes require maintenance. The example of hedging in South Island, New Zealand, is used to explore the factors which generate perennial crises of maintenance, and ultimately affect the sustainability of a productive rural landscape. This logic of maintenance is applicable to other forms of landscape investment in drains, buildings, sown pastures and soils.  相似文献   

SEISMIC INVERSION BY A RMS BORN APPROXIMATION IN THE SPACE-TIME DOMAIN1     

JAKOB T. FOKKEMA  PETER M. VAN DEN BERG 《Geophysical Prospecting》1989,37(1):53-72

A new approximate method to calculate the space-time acoustic wave motion generated by an impulsive point source in a horizontally layered configuration is presented. The configuration consists of a stack of fluid layers between two acoustic half-spaces where the source and the receiver are located in the upper half-space. A distorted-wave Born approximation is introduced; the important feature of the method is the assumption of a background medium with vertical varying root-mean-square acoustic wave speed. A closed-form expression for the scattered field in space and time as a function of the contrast parameters is deduced. The result agrees closely with rigorously calculated synthetic seismograms. In the inverse scheme the wave speed and mass density can be reconstructed within a single trace. Results of the inversion scheme applied to synthetic data are shown.  相似文献   

The Cr-minerals of Outokumpu--Their Chemistry and Significance   总被引：2，自引：0，他引：2  

TRELOAR  PETER J. 《Journal of Petrology》1987,28(5):867-886

The massive Cu–Co–Zn sulfide ores at Outokumpu inFinnish Karelia are unusual among Cyprus type deposits by virtueof the high Cr content exhibited by both the ores and the hostrocks. Throughout both the ore horizons and the metasedimentaryhost rock, bulk-rock Cr content averages 0.2 per cent Cr₂O₃.The high Cr contents result in an unusual degree of Cr substitutionin a number of silicate and oxide phases. Cr₂O₃ analyses presentedhere include values up to 3.74 per cent in tremolite, 3.65 percent in diopside, 26.90 per cent in uvarovitic garnet, 15.37per cent in epidote, 24.63 per cent in muscovite, 8.56 per centin biotite, 5.18 per cent in chlorite, 2.99 per cent in staurolite,and 72.65 per cent in chromite. Cr contents of these mineralscan be extremely variable even on the thin-section scale. Thehigh level of Cr in the metasediments, together with that ofNi, reflects their enhanced concentration in the original sedimentsdue to presumed derivation from a Cr-rich komatiite-bearingsubstrate. High levels of both elements in the stock works indicatethat they may have been partly re-distributed by the hydrothermalore-forming fluids. The variability of Cr content within individualsilicate grains suggests that they overgrew small-scale variationsin sedimentary Cr content sufficiently rapidly to preclude diffusivesmoothing of µ_Cr gradients. This suggests that while Crmay be mobile in hydrothermal systems, it is immobile undermetamorphic conditions.  相似文献   

The Effect of Postcumulus Reactions on Composition of Chrome-spinels from the Jimberlana Intrusion   总被引：2，自引：2，他引：2  

ROEDER  PETER L.; CAMPBELL  IAN H. 《Journal of Petrology》1985,26(3):763-786

Chromites in olivine adcumulates, mesocumulates and orthocumulatesfrom drill core of the Jimberlana intrusion have been analysedand related to the cumulate type and to the nature of the surroundingsilicate mineral. Chromites in adcumulates and mesocumulatesshow a restricted range of composition and are high in Mg, Aland Cr. The orthocumulate chromites vary in composition fromthat found in adcumulates to chromites which are much higherin Fe and Ti and with a higher Fe^3?: Fe^2? ratio. The chromitesin orthocumulates vary in composition depending upon the natureof the enclosing silicate mineral. This is believed to reflectthe ability of the enclosing mineral to protect the originalcumulus chromite from reaction with the intercumulus liquid.Thus chromite within early bronzite oikocrysts was protectedfrom reaction whereas that in plagioclase and phlogopite wasprotected at a much later stage and has a higher Fe and Ti contentChromite within olivine appears to have been able to equilibratewith intercumulus liquid until late in the magmatic historyexcept where the olivine enclosing chromite has itself beensurrounded by bronzite. It is suggested that chromite can exchangeelements with intercumulus liquid through the olivine. Thereare two possibilities; either elements such as Cr, Al, Ti andFe^{3 ?} were able to diffuse through the olivine structure orthe apparently enclosed chromite crystals were able to maintaindirect contact with the melt along fine fractures produced bythe differential thermal contraction of olivine and chromite. The average diameters of chromite crystals within orthocumulatebronzite and olivine are 28 and 20 microns respectively whereaschromites in plagioclase and phlogopite have average diametersof 48 and 56 microns. There is no obvious correlation betweenthe size of the chromite and their composition for grains foundwithin a particular silicate. Chromites of every size have beenable to equilibrate with the liquid unless they were protectedfrom reaction. Nucleation of reaction products played an important role indetermining the final composition of any particular chromitecrystal. The significance of reaction and nucleation on a localscale of millimetres is considered with respect to the majorsilicates and to the location of the last liquid. It is suggestedthat the last liquid tended to concentrate in pockets of reactantcrystals, where product crystals failed to nucleate until latein the magmatic history. It is estimated that in rocks withan orthocumulate texture, the intercumulus liquid crystallizedover a temperature range as large as 300 ?C and that it becamesignificantly more oxidizing near the solidus temperature.  相似文献