ESR dating of quartz phenocrysts in the El Cajete and Battleship Rock Members of Valles Rhyolite, Valles Caldera, New Mexico     

Shin Toyoda  Fraser Goff  Sumiko Ikeda  Motoji Ikeya 《Journal of Volcanology and Geothermal Research》1995,67(1-3)

The electron spin resonance (ESR) dating method was employed on quartz phenocrysts separated from pumice of the El Cajete and Battleship Rock Members of the Valles Rhyolite in the Valles caldera, New Mexico. The results of heating experiments indicate that Ti impurity centers have two components; a thermally stable one and a less stable, temperature sensitive one. ESR dates using the stable Ti center yield eruption ages of 59 ± 6 ka for the Battleship Rock Member and 53 ± 6 ka for the El Cajete Member while recent ¹⁴C dates (S. Reneau and J. Gardner, unpub. data) from carbonized logs in the El Cajete pumice indicate that its age is older than 50 ka. Our results indicate that volcanism in the Valles caldera is much younger than previously thought (≥ 130 ka) and that recent revisions to the post-0.5 Ma stratigraphy of Valles caldera are probably in error. The results suggest that ESR dating of quartz may be a useful method for obtaining ages of units in other Quaternary volcanic areas.  相似文献   

极隙区纬度Pc 5脉动的传播和起源          下载免费PDF全文

刘勇华  刘瑞源  杨少峰  贺龙松  B.J.Fraser 《地球物理学报》2001,44(Z1):8-15

南极中山站和戴维斯站均位于极隙区纬度附近,均安装了完全相同的感应式磁力计.选择两站的数据,1997年3月和1996年6、9、12月,运用信号互谱技术进行统计分析,结果得到:在中山站-戴维斯站,Pc5脉动出现时间范围较广,但以地方时中午/磁中午及磁午夜附近出现频次多,其振幅、传播及发生率季节变化不大.振幅白天变化小,中午有小峰,夜间有时有大值.传播方向白天以磁中午为界,晨侧向西传播,直至磁凌晨;昏侧向东传播,约在5:00MLT处转向.夜间约以20:00 MLT为界,之前向西传播,之后向东传播,磁黄昏附近,Pc5脉动传播方向变化较多,显得不规则.这些特征,反映了Pc5脉动在不同地方时段有不同的起源.  相似文献   

The petrogenesis of group 2 ultrapotassic kimberlites from Finsch Mine, South Africa     

K. J. Fraser  C. J. Hawkesworth   《Lithos》1992,28(3-6):327-345

Major, trace element and radiogenic isotope results are presented for a suite of hypabyssal kimberlites from a single pipe, at the Finsch Mine, South Africa. These are Group 2 kimberlites characterised by abundant phlogopite ± serpentine ± diopside; they are ultrabasic (SiO₂ < 42 wt.%%) and ultrapotassic (K₂O/Na₂O > 6.9) igneous rocks, they exhibit a wide range in major element chemistry with SiO₂ = 27.6−41.9 wt. % and MgO = 10.4−33.4 wt. %. (⁸⁷Sr/⁸⁶Sr)_i=0.7089 to 0.7106, ε_{Nd is} −6.2 to −9.7 and they have unradiogenic (²⁰⁷Pb/²⁰⁴Pb)_i contents which ensure that they plot below the Pb-ore growth curve. They have high incompatible and compatible element contents, a striking positive array between Y and Nb which indicates that garnet was not involved in the within suite differentiation processes, and a negative trend between K/Nb and Nb contents which suggests that phlogopite was involved. In addition, some elements exhibit an unexpected order of relative incompatibility for different trace elements which suggests that the intra-kimberlite variations are not primarily due to variations in the degree of partial melting. The effects of fractional crystallization are difficult to establish because for the most part they have been masked by the entrainment of 50–60% mantle peridotite. Thus, the Finsch kimberlites are interpreted as mixtures of a melt component and entrained garnet peridotite, with no evidence for significant contamination with crustal material. The melt component was characterised by high incompatible element contents, which require both very small degrees of partial melting, and source regions with higher incompatible element contents than depleted or primitive mantle. Since the melt component was the principal source of incompatible elements in the kimberlite magma, the enriched Nd, Sr and Pb isotope ratios of the kimberlite are characteristic of the melt source region. The melt fractions were therefore derived from ancient, trace elements enriched portions of the upper mantle, most probably situated within the sub-continental mantle lithosphere, and different from the low ⁸⁷Sr/⁸⁶Sr garnet peridotite xenoliths found at Finsch. Within the sub-continental mantle lithosphere old, incompatible element enriched source regions for the kimberlite melt fraction are inferred to have been overlain by depleted mantle material which became entrained in the kimberlite magma.  相似文献   

Snow and cloud feedbacks modelled by an atmospheric general circulation model     

R A Colman  B J McAvaney  J R Fraser  L J Rikus  R R Dahni 《Climate Dynamics》1994,9(4-5):253-265

One of the most important parametrizations in general circulation models used for climate change experiments is that of the surface albedo. The results of an albedo feedback experiment carried out under the auspices of the US Department of Energy are presented. An analysis of long and short wave components of the model response shows that short wave response dominates changes in fixed to variable albedo experiments, but that long wave response dominates in clear to cloudy sky changes. Cloud distribution changes are also discussed and are related to changes in global sensitivity. At the surface, the heat balance change for perturbed sea surface temperatures is dominated by changes in latent heat flux and downward long wave radiation. If albedo is freed up however, the major contrast lies in the change in surface reflected short wave radiation, amplified by changes in downward short wave radiation caused by cloud amount changes.  相似文献   

Annual mean meridional energy transport modelled by a general circulation model for present and 2 × CO2 equilibrium climates     

R A Colman  B J McAvaney  J R Fraser  S B Power 《Climate Dynamics》1994,10(4-5):221-229

The meridional energy flux modelled by the Bureau of Meteorology Research Centre general circulation model is examined. It is divided into atmospheric and oceanic components, and the resolved atmospheric components in turn into mean and eddy circulations. Comparison with observations shows the modelled total planetary meridional energy transport to be low, but shows better agreement for the resolved atmospheric component alone. The overall patterns of the individual circulation and energy components of the model also agree well, although strengths and locations do show some discrepancies. The doubled CO₂ climate change is analyzed in terms of the changes in each of the circulation and energy components. It is found that the changes are the relatively small residual of larger, and generally opposing changes in sensible heat and potential energy fluxes. Despite the general decrease in poleward energy flux, the poleward latent heat flux is found to increase. The reduction in poleward transport is found to be dominated by changes in the mean meridional circulation at low southern latitudes, and changes in both mean circulations and eddy fluxes elsewhere.  相似文献   

Io's surface composition based on reflectance spectra of sulfur/salt mixtures and proton-irradiation experiments     

Douglas B. Nash  Fraser P. Fanale 《Icarus》1977,31(1):40-80

The available full-disk reflectance spectra of Io in the range 0.3 to 2.5 μm have been interpreted by comparison with new laboratory spectra of a wide variety of natural and synthetic mineral phases in order to determine a surface compositional model for Io that is consistent with Io's other known chemical and physical properties. Our results indicate that the dominant mineral phases are sulfates and free sulfur derived from them, which points toward a low temperature and initially water-rich surface assemblage. Our current preferred mineral phase mixture that best matches the Io data and is simultaneously most consistent with other constraints, consists of a fine-grained particulate mixture of free sulfur (55 vol%), dehydrated bloedite [Na₂Mg(SO₄)₂·xH₂O] (30 vol%) ferric sulfate [Fe₂(SO₄)₃·xH₂O] (15 vol%), and trace amounts of hematite [Fe₂O₃]. Other salts may be present, such as halite and sodium nitrate, as well as clay minerals. Such a model is consistent with a probable pre- and post-accretion thermal history of Io-forming material and Io's observed Na emission and other properties. These results further support the evaporite surface hypothesis of Fanale et al'; while not precluding the presence of certain silicate phases such as montmorillonite.The average surface of Io's leading hemisphere appears to contain less free sulfur and more salts and to be finer grained than that of the trailing hemisphere. Since Io is immersed in Jupiter's magnetosphere, irradiation damage effects from low-energy proton bombardment were studied. Irradiation damage of lattices is estimated to be a relatively minor but operative process on the surface of Io; irradiation darkening by sulfate reduction to free sulfur and by F-center production in salts may be partly responsible for the differences in albedo of leading and trailing hemispheres and equatorial and polar regions of Io, but slight regional differences in relative intrinsic phase concentration on the surface may likewise account for these global variations in albedo.Possible unusual surface properties predicted by this model include: posteclipse darkening in certain wavelenghts, limb brightening in certain wavelengths, and unusual surface electrical properties. Further refinement of Io's surface composition model and better understanding of surface irradiation effects will be possible when observational data in the range 0.20 to 0.30 μm are obtained and when improved spectra in the range 0.30 to 5.0 μm are obtained having increased spectral, spatial, and temporal resolution.  相似文献   

Notes of a geological excursion in Switzerland     

T. McKenny Hughes  Horace W. Monckton  W. Fraser Hume 《Proceedings of the Geologists' Association. Geologists' Association》1895,14(2):40-58

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Hepatic mono-oxygenase induction in benthic flatfish sampled near coastal pulp mills in British Columbia     

R. F. Addison  T. F. Fraser 《Marine environmental research》1996,42(1-4)

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The crater lake and hydrothermal system of Mount Pinatubo,Philippines: evolution in the decade after eruption     

James?A.?StimacEmail author  Fraser?Goff  Dale?Counce  Adrienne?C.?L.?Larocque  David?R.?Hilton  Uwe?Morgenstern 《Bulletin of Volcanology》2004,66(2):149-167

The June 1991 eruption of Mount Pinatubo, Philippines breached a significant, pre-eruptive magmatic-hydrothermal system consisting of a hot (>300 °C) core at two-phase conditions and surrounding, cooler (<260 °C) liquid outflows to the N and S. The eruption created a large, closed crater that accumulated hydrothermal upwellings, near-surface aquifer and meteoric inflows. A shallow lake formed by early September 1991, and showed a long-term increase in level of ~1 m/month until an artificial drainage was created in September 2001. Comparison of the temporal trends in lake chemistry to pre- and post-eruptive springs distinguishes processes important in lake evolution. The lake was initially near-neutral pH and dominated by meteoric influx and Cl–SO₄ and Cl–HCO₃ hydrothermal waters, with peaks in SO₄ and Ca concentrations resulting from leaching of anhydrite and aerosol-laden tephra. Magmatic discharge, acidity (pH~2) and rock dissolution peaked in late 1992, during and immediately after eruption of a lava dome on the crater floor. Since cessation of dome growth, trends in lake pH (increase from 3 to 5.5), temperature (decline from 40 to 26 °C), and chemical and isotopic composition indicate that magmatic degassing and rock dissolution have declined significantly relative to the input of meteoric water and immature hydrothermal brine. Higher concentrations of Cl, Na, K, Li and B, and lower concentrations of Mg, Ca, Fe, SO₄ and F up to 1999 highlight the importance of a dilute hydrothermal contribution, as do stable-isotope and tritium compositions of the various fluids. However, samples taken since that time indicate further dilution and steeper trends of increasing pH and declining temperature. Present gas and brine compositions from crater fumaroles and hot springs indicate boiling of an immature Cl–SO₄ geothermal fluid of near-neutral pH at approximately 200 °C, rather than direct discharge from magma. It appears that remnants of the pre-eruptive hydrothermal system invaded the magma conduit shortly after the end of dome emplacement, blocking the direct degassing path. This, along with the large catchment area (~5 km²) and the high precipitation rate of the area, led to a rapid transition from a small and hot acid lake to a large lake with near-ambient temperature and pH. This behavior contrasts with that of peak-activity lakes that have more sustained volcanic gas influx (e.g., Kawah Ijen, Indonesia; Poas and Rincón de la Vieja, Costa Rica).Editorial responsibility: H. Shinohara  相似文献   

Regolith-atmosphere exchange of water and carbon dioxide on Mars: Effects on atmospheric history and climate change     

Fraser P. Fanale  Bruce M. Jakosky 《Planetary and Space Science》1982,30(8):819-831

Exchange of CO₂ and H₂O between the Mars regolith and the atmosphere-cap system plays an important role in governing the evolution of the martian atmosphere and the martian climate. Most of the exchangeable CO₂ (perhaps one or two orders of magnitude more than the atmospheric inventory) is currently adsorbed on the deep regolith, and can be “cryopumped” to a large quasipermanent CO₂ cap (not now present) during lowest Mars obliquity (θ). During the obliquity driven regolith-cap CO₂ exchange cycle, the atmospheric pressure varies harmonically between ~0.1 mb (lowest Θ) and ? 20 mb (highest Θ). The regolith buffer plays only a small or negligible role in the seasonal CO₂ pressure variations caused by atmosphere-cap exchange because adsorption greatly inhibits diffusion of the seasonal “pressure wave” into the regolith. In contrast, thermally driven H₂O seasonal exchange between the atmosphere and regolith appears to be in large part responsible for observed seasonal variations in the small atmospheric H₂O inventory. Long term exchange of H₂O may be dominated by transfer between the polar caps and ice in the regolith. Available and potential tests of regolith-atmospheric-cap volatile exchange models using ground-based and spacecraft-based techniques are discussed.  相似文献