Fayalitic olivine in matrix of the Krymka LL3.1 chondrite: Vapor-solid growth in the solar nebula     

MICHAEL K. WEISBERG  MICHAEL E. ZOLENSKY  MARTIN PRINZ 《Meteoritics & planetary science》1997,32(6):791-801

Abstract— Fayalitic olivine (Fa_54–94) is a ubiquitous component in the matrix of Krymka (LL3.1) as well as in other highly unequilibrated chondrites (ordinary and carbonaceous). In Krymka, the fayalitic olivine has an unusual anisotropic platy morphology that occurs in at least five types of textural settings that can be characterized as: (1) isolated platelets, (2) clusters of platelets, (3) euhedral to subhedral crystals, (4) overgrowths of platelets on forsteritic olivine, and (5) fluffy (porous) aggregates. From transmission electron microscope (TEM) investigation, the direction of elongation of the platy olivine overgrowths on forsteritic olivine substrates is along the c axis and in most cases it corresponds with the c axis of the substrate olivine, which suggests that the fayalitic olivine grew in this unusual morphology and is not a replacement product of preexisting material. The fayalitic olivine in the matrix of Krymka is compositionally similar to olivine with platy morphology in the matrix of some CV3 chondrites and both have similar Fe/Mn ratios, but important morphological differences indicate that their relationship needs to be explored further. Textural and compositional data indicate that the fayalitic olivine in the matrix of Krymka, as well as in some other unequilibrated ordinary chondrites, formed prior to final lithification of the meteorite and probably prior to parent body accretion. We find that formation of the fayalitic olivine by vapor-solid growth provides the best explanation for our observations and data and is the only feasible mechanism for the formation of fayalitic olivine in the matrix of Krymka. We propose that the fayalitic olivine formed by vaporization and recondensation of olivine rich-dust, during a period of enhanced dust/gas ratio in the nebula.  相似文献   

Future changes of the atmospheric composition and the impact of climate change     

VOLKER GREWE  MARTIN DAMERIS  RALF HEIN  ROBERT SAUSEN  BENEDIKT STEIL 《Tellus. Series B, Chemical and physical meteorology》2001,53(2):103-121

The development of the future atmospheric chemical composition is investigated with respect to NO _y and O₃ by means of the off‐line coupled dynamic‐chemical general circulation model ECHAM3/CHEM. Two time slice experiments have been performed for the years 1992 and 2015, which include changes in sea surface temperatures, greenhouse gas concentrations, emissions of CFCs, NO _x and other species, i.e., the 2015 simulation accounts for changes in chemically relevant emissions and for a climate change and its impact on air chemistry. The 2015 simulation clearly shows a global increase in ozone except for large areas of the lower stratosphere, where no significant changes or even decreases in the ozone concentration are found. For a better understanding of the importance of (A) emissions like NO _x and CFCs, (B) future changes of air temperature and water vapour concentration, and (C) other dynamical parameters, like precipitation and changes in the circulation, diabatic circulation, stratosphere‐troposphere‐exchange, the simulation of the future atmosphere has been performed stepwise. This method requires a climate‐chemistry model without interactive coupling of chemical species. Model results show that the direct effect of emissions (A) plays a major rôle for the composition of the future atmosphere, but they also clearly show that climate change (B and C) has a significant impact and strongly reduces the NO _y and ozone concentration in the lower stratosphere.  相似文献   

Evidence from Muriah, Indonesia, for the Interplay of Supra-Subduction Zone and Intraplate Processes in the Genesis of Potassic Alkaline Magmas   总被引：11，自引：5，他引：6  

EDWARDS  CAROLINE; MENZIES  MARTIN; THIRLWALL  MATTHEW 《Journal of Petrology》1991,32(3):555-592

The high-K alkaline volcano Muriah is situated in central Javaand has erupted two lava series, a younger highly potassic series(HK) and an older potassic series (K). The HK series has higherK2O contents for a given MgO content; greater silica undersaturation;and higher concentrations of LILE (Rb, Sr, Ba, and K), LREE(La and Ce), and HFSE (Nb, Zr, Ti, and P), than the K series.The HK series lavas have incompatible trace element patternssimilar in many respects to ocean island basalts. The K serieshas slightly higher ⁸⁷Sr/⁸⁶Sr (O70453 [GenBank] -O70498) and ¹⁸O (+6?2to + 8?4%o) and lower ¹⁴³Nd/¹⁴⁴Nd (0?512530–0?5126588)than the HK series (for which 87Sr/86Sr = 0?70426–0?70451,<518O = +6?52 to +7–0%o, and 1*3Nd/1*4Nd= 0?512623–0?512679),and higher LILE/HFSE and LREE/ HFSE ratios. A7/4 and A8/4 arehigh and do not show any systematic change from the K to theHK series. The proposed model for the Muriah lavas involvesthree source components: (1) the astheno-sphere of the mantlewedge of the Sunda arc, which has Indian Ocean MORB characteristics;(2) a metasomatic layer situated at the base of the lithosphere,which has characteristics similar to enriched mantle (i.e.,EMU); (3) subducted pelagic sediments from the Indian Ocean. Trace element and isotope data indicate that the characteristicsof the K series are produced by mixing of two endmember magmas:an undersaturated magma derived wholly from within-plate sourcesand a calc-alkaline magma derived from the subduction-modifiedasthenospheric mantle. The calc-alkaline magma is believed tobe contaminated by the arc crust before mixing. Low-pressurefractionation took place in the K series after mixing. Initiallithospheric extension in the Bawean trough (in which Muriahis located), may be responsible for decompressive melting ofthe metasomatic layer and thus the production of the HK serieslavas. The magmas erupted from Muriah show a transition fromintraplate to subduction zone processes in their genesis.  相似文献   

Ultrahigh-Temperature Metamorphism and Multistage Evolution of Garnet-Orthopyroxene Granulites from the Proterozoic Epupa Complex, NW Namibia   总被引：2，自引：0，他引：2  

BRANDT  SONKE; KLEMD  REINER; OKRUSCH  MARTIN 《Journal of Petrology》2003,44(6):1121-1144

Migmatitic semipelitic granulites of the Proterozoic Epupa Complex,NW Namibia, underwent ultrahigh-temperature metamorphism asis indicated by the high alumina contents of orthopyroxene (8–11wt % Al₂O₃) coexisting with garnet. Peak P–T conditionsof  相似文献   

TransCom 3 CO₂ inversion intercomparison: 1. Annual mean control results and sensitivity to transport and prior flux information     

KEVIN ROBERT GURNEY  RACHEL M. LAW  A. SCOTT DENNING  PETER J. RAYNER  DAVID BAKER  PHILIPPE BOUSQUET  LORI BRUHWILER  YU-HAN CHEN  PHILIPPE CIAIS  SONGMIAO FAN  INEZ Y. FUNG  MANUEL GLOOR  MARTIN HEIMANN  KAZ HIGUCHI  JASMIN JOHN  EVA KOWALCZYK  TAKASHI MAKI  SHAMIL MAKSYUTOV  PHILIPPE PEYLIN  MICHAEL PRATHER  BERNARD C. PAK  JORGE SARMIENTO  SHOICHI TAGUCHI  TARO TAKAHASHI  CHIU-WAI YUEN 《Tellus. Series B, Chemical and physical meteorology》2003,55(2):555-579

  相似文献   

VARIATIONS OF SNOW DEPTH AND DURATION IN THE SWISS ALPS OVER THE LAST 50 YEARS: LINKS TO CHANGES IN LARGE-SCALE CLIMATIC FORCINGS   总被引：2，自引：1，他引：2  

MARTIN BENISTON 《Climatic change》1997,36(3-4):281-300

A study of snow statistics over the past 50 years at several climatological stations in the Swiss Alps has highlighted periods in which snow was either abundant or not. Periods with relative low snow amounts and duration are closely linked to the presence of persistent high surface pressure fields over the Alpine region during late Fall and in Winter. These high pressure episodes are accompanied by large positive temperature anomalies and low precipitation, both of which are unfavorable for snow accumulation during the Winter. The fluctuations of seasonal to annual pressure in the Alpine region is strongly correlated with anomalies of the North Atlantic Oscillation index, which is a measure of the strength of the westerly flow over the Atlantic. This implies that large-scale forcing, and not local or regional factors, plays a dominant role in controling the timing and amount of snow in the Alps, as evidenced by the abundance or dearth of snow over several consecutive years. Furthermore, since the mid-1980s, the length of the snow season and snow amount have substantially decreased, as a result of pressure fields over the Alps which have been far higher and more persistent than at any other time this century. A detailed analysis of a number of additional Alpine stations for the last 15 years shows that the sensitivity of the snow-pack to climatic fluctuations diminishes above 1750 m. In the current debate on anthropogenically-induced climatic change, this altitude is consistent with other studies and estimates of snow-pack sensitivity to past and projected future global warming.  相似文献   

Convergent flow of ice within the Astrolabe subglacial basin, Trre Adélie, East Antarctica: an hypothesis derived from nummerical modelling experiments     

MARTIN J. SIEGERT  NEIL F. GLASSER 《Polar research》1997,16(1):63-72

The existence of a large subglacial lake beneath the antarctic Ice Sheet at Terre Adélie indicates the presence of basal ice at its pressure-melting temperature. A numerical model of the ice-sheet thermal regime is employed using the balance velocity of the ice sheet as an initial model input in order to calculate ice-sheet basal temperatures. However, the results from this model show the Terre Adélie area to be characterised by basal freezing. Heat in addition to that accounted for in the model is thus required at the ice-sheet base in order for pressure melting temperatures to be attained. The sources for such heat are (1) an enhanced geothermal heat flux and (2) an increase in frictional heating caused by the flow of ice. In this paper the latter possibility is expanded by hypothesising that subglacial topography induces convergent ice flow around Terre Adélie, causing enhanced basal ice velocities. Model experiments indicate that an increase in ice velocity (from 7 to at least 42 m yr⁻¹) is required to raise the temperature of the basal ice to the pressure melting value. Increased ice velocity, and consequent frictional heat production due to convergent ice flow, may therefore be important in explaining the location of the subglacial lake in this region. These results allow the process of convergent ice flow within a contemporary ice sheet to be quantified. A verification (or otherwise) of the model results may be possible if ice surface velocity measurements from modem GPS methods are made.  相似文献   

LANDSCAPE PERMANENCE AND NUCLEAR WARNINGS     

MARTIN J. PASQUALETTI 《Geographical review》1997,87(1):73-91

ABSTRACT. From the perspective of a human lifetime, the hazards of some nuclear wastes are permanent, so the warnings we place at contaminated nuclear sites must be permanent too. I address questions of how best to provide one hundred centuries of public warning at the first facility for permanent disposal, the Waste Isolation Pilot Plant in New Mexico. Scenarios of intrusion developed to guide the design of warning markers predicted that most of the changes in the area will be social and cultural. Because blatant and permanent markers will increase, not reduce, the probability of inadvertent intrusion, the most appropriate warning is a “landscape of illusion.” Such a landscape needs not permanent surface markers but underground warning devices beneath a soft surface marker. No warning can guarantee deterrence for 10,000 years, however.  相似文献   

The Perseverance Ultramafic Complex, Western Australia: The Product of a Komatiite Lava River   总被引：3，自引：0，他引：3  

BARNES  STEPHEN J.; HILL  ROBIN E. T.; GOLE  MARTIN J. 《Journal of Petrology》1988,29(2):305-331

The Perseverance ultramafic complex is a body of olivine-richkomatiitic rocks spatially associated with the Agnew nickeldeposit, in the Agnew-Wiluna greenstone belt of the ArchaeanYilgarn Block in Western Australia. The complex consists ofa central lenticular body, up to 700 m thick, of olivine adcumulates,flanked by laterally extensive sheet-like bodies of olivineorthocumulates and spinifextextured komatiite flows. Rocks progressivelyfurther away from the central lens have chemical compositionsreflecting higher original proportions of komatiite liquid tocumulus olivine. Parent liquids had MgO contents between 25and 32% MgO, approximately chondritic Al/Ti ratios and HREEpatterns, and moderate depletion in LREE. Olivines within the adcumulate lens show a progressive increasein forsterite content from Fo₉₃ at the bottom to Fo_94?5, atthe top. Calculated original olivine compositions in the flankingrocks are similar to those at the base of the central lens.Original olivine nickel contents show a symmetrical variationfrom maximum values of 3500 ppm at the top of the central lens,through minimum values of 1000 ppm at the base and margins ofthe central lens to intermediate values in the distal rocks.The complex as a whole shows evidence for nickel depletion relativeto other komatiite suites. These observations are explained in terms of prolonged eruptionand flow of komatiitic lava down a major flow channel or lavariver. Adcumulates crystallized on the floor and sides of thecentral channel, which was formed at an early stage by thermalerosion of floor rocks. Episodic overflow of the central channelproduced distal ‘flood plain’ rocks consisting ofolivine orthocumulates and layered flows. Lavas became moremagnesian and nickel-rich with time, giving rise to the observedspatial variation in primary olivine composition. Nickel depletionof the earliest lavas is attributed to pre-eruption segregationof large volumes of immiscible Fe-Ni-sulfide, which were concentratedto form the underlying Agnew nickel deposit.  相似文献   

3D ELECTROMAGNETIC INVERSION USING INTEGRAL EQUATIONS1     

PERRY A. EATON 《Geophysical Prospecting》1989,37(4):407-426

Utilizing electromagnetic data in geophysical exploration work is difficult when measured responses are complicated by the effects of 3D structures. 1D and 2D models may not be capable of accurately simulating the physical processes that contribute to a measured response. 3D conductive-host modelling is difficult, costly and time-consuming. Using a 3D inverse procedure it is possible to automate the interpretation of controlled-source electromagnetic data. This procedure uses an inverse formulation based on frequency-domain, volume integral equations and a pulse-basis representation for the internal electrical field and anomalous conductivity. Beginning with an initial model composed of a 3D inhomogeneous region residing in a laterally homogeneous (layered-earth) geoelectrical section, iterative least-squares algorithms are used to refine the geometry and the conductivity of the inhomogeneity. This novel approach for 3D electromagnetic interpretation yields a reliable and stable inverse solution provided constraints on how much the variable can change at each iteration are incorporated. Integral-equation-based inverse formulations that do not correctly address the non-linearity of this inverse problem may have poor convergence properties, particularly when dealing with the high conductivity contrasts that are typical of many exploration problems. While problems associated with contamination of the data by random noise and non-uniqueness of solutions do not usually influence the inverse solution in an adverse manner, problems associated with model inadequacy and errors in an assumed background conductivity structure can produce undesirable effects.  相似文献