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1.
AN ECOSYSTEM MODEL ANALYSIS OF THE EFFECT OF MINE TAILINGS ON THE EUPHOTIC ZONE OF A PELAGIC ECOSYSTEM 总被引：1，自引：0，他引：1
A computer analysis was performed on experimental results obtained when mine tailings were added to seawater. The Mixed Upper-Layer Ecotrophie Simulation (MULES) model was tested by changing the extinction coefficient and the abundance of heterotrophic zooflagellates. Increasing the extinction coefficient resulted in a delay of phytoplankton growth, an increase in zooplankton standing stock and better growth of autotrophic flagellates compared with diatoms. Zooflagellates in the ecosystem influence the growth of zooplankton; secondary production by zooplankton was markedly depressed at low levels of zooflagellates. These results are believed to be of general significance for the diagnosis of suspended sediment effects on planktonic ecosystems. 相似文献
2.
The Klokken Gabbro--Syenite Complex, South Greenland: Cryptic Variation and Origin of Inversely Graded Layering 总被引：2，自引：0，他引：2
The Klokken stock has an outer sheath of vertically banded alkaligabbro which passes through syenogabbros into unlaminated syenitessurrounding a central layered syenite core. The layered seriescomprises sheets of granular syenite interleaved with drusylaminated syenite which shows repeated inversely graded minerallayering in which normal leucosyenite becomes progressivelymore hedenbergite-rich upwards. Tops to layers are nearly feldspar-free,fayalite—magnetite horizons. Model cumulate textures areexhibited, and cross-bedding and normally graded channel structuresare encountered. Granular layers often rest on ultramafic layersand load structures occur at the junctions. The series is cutby a sheet of biotite-syenodiorite and finally by quartzsyeniteaplites. Plagioclase (An57 in gabbros) is progressively mantled by ternaryalkali feldspar and is absent only in the layered series inwhich alkali feldspars cluster around Ab65 Or35. Pyroxene showsunbroken evolution with respect to Fe/Fe + Mg, from augite toferrohedenbergite and sodie hedenbergite, with acmite in aplites,but Al and Ti decrease suddenly between syenogabbro and unlaminatedsyenite stages. Olivines show parallel evolution but there isa jump in Fe: Mg between gabbros and unlaminated syenites fromFo52 to Fo34, with subsequent steady evolution to Fo3Te5Fa92in laminated syenites. Biotites show steady increase in Fe/Fe+ Mg throughout the syenites, approaching pure annite, but thegabbro-syenogabbro series show a reversal, interpreted as indicatingcrystallization under conditions of increasing fo2. Ilmenomagnetitesshow systematically varying minor element ratios, with a suddendrop in MgAl2O4 content between gabbros and syenites. Amphiboles(ferroedenites and sodic hastingsites) appear only in the mostfractionated syenites in the layered series. The Klokken chamber was lined by gabbro with only limited insitu fractionation to syenogabbro. The termination of gabbrocrystallization was marked by ingress of water into the conduit,perhaps causing the liquid to embark on its fractionation trendtowards oversaturated residua. The mineralogical breaks areconsistent with a drop in temperature, and increase in aSIO2at this point. The chamber was subsequently filled by a drytrachytic liquid which fractionated in situ, initially by congelationagainst the walls as unlaminated syenite. The layered seriesdeveloped within this chamber. The granular syenites show invertedcryptic and phase-layering (downward appearance of amphibole),and downward increase in grain size. They are sheets stopedoff the roof of the intrusion, representing chilled equivsalentsof the fractionating trachytic liquid of which the laminatedsyenites are the bottom accumulated products. In the inverselygraded layers the cumulus phases have slightly more advancedcompositions than the same phases in either normal rock or whenpresent as an intercumulus phase in adjacent parts of layers.The layering is attributed to crystallization at varying degreesof undercooling in a magma in which all phases exhibit a narrowcrystallization interval and which was subject to rhythmic P-build-upand sudden release. Crystal accumulation took place under nearstagnant to rhythmie P-build-up and sudden release. Crystalaccumulation took place under near stagnant conditions in athin chamber immediately beneath the roof of the intrusion. 相似文献
3.
Chemical variation in biotite from the KJokken gabbro-syeniteintrusion in the Proterozoic Gardar province in South Greenlandhas been investigated by electron probe and, for F and Li, ionmicroprobe. Most mica occurs in small amounts as fringes onilmenomagnetite or fayalite, rarely as an intercumulus or poikiliticphase. The micas range continuously from Phlog70Ann30 in a gabbro,to Phlog4Ann96 in the most evolved (slightly persilicic andperalkaline) syenite. In the syenites Fe-Mg partitioning betweenbiotite and olivine can be described by a single distributioncoefficient, Kd = XF XBiotMs/XBiotFe 3, suggesting that thesereactant phases mix ideally at the reaction T. Experimentaldata for Fe-Mg exchange via aqueous chloride solutions (Schulien,1980) imply low T (32Q?C). F was absent in the experiments andmay significantly affect the exchange equilibrium. Kd in thegabbros is 1, consistent with equilibrium via a fluid depletedin F because of crystallization of large amounts of amphibole. Al, Mn, and Ti vary regularly throughout the series and canbe used as markers of cryptic variation in the layered syenites.(Al + Si): 22 O is always in the range 7.7–7.85. A1/(A1+ Si) decreases from 0.31 in gabbros to 0.25 in the most Fe-richmicas. Li is always < 260 ppm w. In the syenite series, Fshows a near-linear inverse relationship with Fe/(Fe + Mg) whichpasses close to OF at Ann100 with l.4 wt% F(0–7 F to 44positive charges) at Ann44. Biotites in the gabbro unit (whichforms an outer sheath to the intrusion) have relatively lessF, probably because it was consumed by coexisting amphibole.I8O is similar for both gabbros and syenites, and it is unlikelythat an envelope fluid was involved in the reactions. G reachesa maximum of 0.3 wt. % in biotite except for that in one syenitesample with 0–7 wt. %. Calculation of relative F-OH fugacitiesfrom the reaction OH-phlogopite + F-annite = F-phlogopite +OH-annite, as calibrated by Munoz (1984), appears to suggestthat each horizon in the layered series was in equilibrium witha slightly different fluid. In view of the intimate interleavingof these lithologies, this is improbable. The equilibrium constantof the exchange reaction, obtained from the experimental data,seems not to be appropriate to the Klokken assemblage, or toother examples of regular F-Fe avoidance. Explanations may includeshort-range Fe-Mg ordering in the natural examples or the effectof additional components in the fluid. F contents are high incomparison with biotites from calc-alkaline complexes; highmagmatic F may account for the igneous layering common in theGardar. Temperatures calculated from reactions involving fayaliteand magnetite show that most biotites grew subsolidus. The F-poorannites grew > 300 ?C subsolidus even when texturally intercumulus.Stable isotope data are consistent with the separation and retentionof a deuteric fluid during the final stage of magmatic crystallization.Klokken was not generally subject to the pervasive, long-range(in both distance and time) dydrothermal interactions demonstratedin calcalkaline and theleiitic intrusions, although more extensivefluid flow is indicated for the more permeable laminated syenites.The biotites preserve chemical variation indicating local equilibriumwith other mafic phases, and halogens provide a useful markerof subsolidus fluid flow. 相似文献
4.
5.
Trace and Minor Element Chemistry of Alkali Feldspars in the Klokken Layered Syenite Series 总被引：2，自引：1，他引：2
Trace and minor element concentrations in alkali feldspars fromthe layered syenite series in the Klokken gabbro-syenite complex,South Greenland have been measured using an ion microprobe.The technique has high precision, avoids problems of mineralseparation, and has allowed investigation of zoning and theeffects of deuteric alteration. Li, Be, B, Cs and Pb occur at< 1 p.p.m. levels, but Ba, Sr, Rb, Mg, Fe, Ti and P are presentin the 1–7000 p.p.m. range. Provided unaltered strain-controlledcrypto- or microperthitic feldspar is sampled and deutericallycoarsened material is avoided, all of the latter elements exceptMg show systematic variation. This confirms the evidence forin situ fractionation of a single syenitic magma-pulse affordedby major element variation in coexisting mafic minerals, particularlypyroxenes and olivines. The distinction between granular andlaminated syenites in the series is supported by the trace elements,which confirms the view that the granular syenites are a condensedroof-chill series with inverted cryptic variation, while thelaminated syenites are a bottom accumulated sequence. Using mainly experimentally determined partition coefficientsfrom the literature and a simple Rayleigh fractionation modelbased on the variation in Ba, Sr and Rb (elements whose concentrationin the melt is largely controlled by feldspar) we calculategeologically reasonable minimum thicknesses for the entire layeredseries of 1370–3260 m. Ti variation in the feldspars wascontrolled by Fe-Ti oxide fractionation, and Fe contents alsowere controlled by mafic phases. Controls of Mg, and particularlythe irregular P levels, are not clear. Behaviour of Ca, whichis present at < 6000 p.p.m. levels in the feldspars, is qualitativelyexplained in terms of the ternary feldspar phase diagram. 相似文献
6.
The layered syenite series in the Klokken stock formed by continuousin situ fractionation of a trachytic magma in a chamber linedby gabbro with 3000 m of cover rocks. The following mineralsand reactions are assessed as geothermometers and barometers:two feldspars; hypersolvus ternary feldspars; ferrohedenbergite-ß-wollastonite;clinopyroxene-olivine Fe-Mg exchange; Fe-Ti oxides; sanidine-magnetite-annite;ferroedenite stability. Estimates of silica activity are obtainedfrom the silica-magnetite-fayalite assemblage. The gabbros ended magmatic crystallization at > 1000–1050°C.The less fractionated members of the syenite range probablycrystallized with PH2O < Ptotal, at T > 870°C and,PH2O 800 bars. In the more fractionated syenites PH2O = Ptotalduring intercumulus feldspar growth, and all magmatic phasescrystallized within the interval 940–830°C and PH2O< 1100 bars. Magmatic fO2 (bars) was 1 log unit below theQFM buffer. aSIO2 in gabbros was slightly above the albite-nephelinebuffer, but rose suddenly to just <1 in the syenites, a jumpmirrored by minor elements in pyroxenes and opaque oxides. Biotitegrew subsolidus in most rocks, at fO2 < QFM, except in intermediaterocks when fO2 > QFM and was defined by the sanidine-magnetite-biotiteassemblage. In these rocks PH2O of 450 bars at 760°C isobtained using existing experimental data, but application ofthis data to Fe-rich biotites in the layered series (where biotiteis an intercumulus phase) requires P > 10 kb at magmatictemperatures. High TiO2 or F: OH probably accounts for increasedT stability of natural annites at low P. The syenitic liquid fractionated down a low temperature zonein a multicomponent system precipitating alk fsp + ol + cpx+ mt and the more fractionated members of the layered serieshad a negligible crystallization interval, a prerequisite forthe development of the unique Klokken-type inversely gradedmineral layering. 相似文献
7.
Biotites as Indicators of Fluorine Fugacities in Late-Stage Magmatic Fluids: the Gardar Province of South Greenland 总被引：5，自引：0，他引：5
The major element chemistry and fluorine contents of biotitesfrom the Gardar alkaline province of South Greenland providean insight into the F contents of late-stage fluids associatedwith the magmatism. Biotites were taken from composite intrusionsranging from alkali gabbro to syenites, nepheline syenites andalkali granites. In each complex they show a large range ofFe/(Fe+Mg) (from 0•2 to 1) and exhibit strong Fe-F avoidance.There is considerable variation in F for any value of Fe/(Fe+Mg)but for each centre maximum F values plotted against Fe/(Fe+Mg)define a nearly straight line of characteristic slope towardslow or zero F at pure annite. Micas in the SiO2 undersaturatedcentres have higher F contents than those from oversaturatedcentres. Cl is low (0•69 wt%) except in the Kûngnâtintrusion, where it reaches 1•4 wt%. Phase equilibriumand textural considerations suggest that most or all biotitesgrew subsolidus in a pervasive deuteric fluid. 18O values suggestthat these fluids were largely magmatic in character and thatextensive reactions with envelope fluids did not occur. Metasomaticresetting of F in biotites in early intrusive units in the aureoleof later units can be demonstrated. Experimental data of Munoz (Mineralogical Society of America,Reviews in Mineralogy 13, 469–494, 1984) were used tocalculate families of curves showing variation in F with Fe/(Fe+Mg)for biotites in equilibrium with fluids of fixed fugacity ratio,f(HF)/f(H2O), at fixed P and T. The resulting curves cut sharplyacross the maximum fluorine lines observed in the natural examples.As it seems highly unlikely that changes in fluid compositionand T, acting together, could produce the observed linear relationship,we conclude that the partitioning of F between fluid and micain the plutonic environment is not well modelled by the experiments.Possible explanations are short-range order (SRO) of Fe andMg on octahedral sites in biotite (Mason, Canadian Mineralogist30, 343–354, 1992) or effects resulting from differentF speciation in alkaline fluids. If perfect Fe-F avoidance isassumed, Fe-Mg SRO can increase maximum F content. The F levelsseen in the silica-saturated centres are broadly consistentwith a cooling-rate related control. It is possible that thehigher F in biotites in the undersaturated centres reflectsdifferent speciation in the fluid rather than higher F contents,with strongly bound SiF4° complexes more common. KEY WORDS: biotites; Gardar; fluorine; alkaline rocks; fluids 相似文献
8.
THE EFFECT OF MINE TAILINGS ON THE PRODUCTION OF PLANKTON 总被引：4，自引：0，他引：4
Mine tailings at levels of ca 30 and 300 ppm were added to two plankton communities contained in 60 ton Controlled Experimental Ecosystems (CEE); a third CEE was used as a control. The mine tailings caused (1) a delay in the primary productivity and chlorophyll a maxima; (2) a shift in the size spectrum of primary producers towards autotrophic flagellates compared with diatoms in the control; (3) a suppression of heterotrophic microflagellates; and (4) an increased production of zooplankton compared with the control. Zooplankton were observed to have consumed tailings but no changes were observed in the structure of the zooplankton community as a result of tailings additions. 相似文献
9.
The highly feldspathic syenites are divided on field evidenceinto three phases, S1, S2, and S3. S3 overlies S1 and S2, andencloses xenoliths and xenocrysts from the underlying and earliersyenites. The feldspars show a range of forms and coarseness of perthite,and show enrichment in potassium from Or20 to Or40, and increasein 2V, in successive syenites. X-ray diffractometer and single-crystalmethods show that SI has a dominantly monoclinic K-phase, S2a microcline with some monoclinic material, and S3 a highlyoblique microcline, exclusively. The earlier feldspars preservethese features even when enclosed by later S3 material. Thereis a suggestion of systematic regional distribution of obliquityvalues. The compositional range of the feldspars is related to the experimentallydetermined minimum in the Ab-Or-An system. The feldspars crystallizedas sodium-rich sanidines. Temperature-pressure limits are deduced,and the unmixing history of the perthites discussed. A mechanismfor the preservation of orthoclase in S1 and S2 is suggested. 相似文献
10.
RANSOME K. T. CORNEY† JEFFREY PEAKALL DANIEL R. PARSONS LIONEL ELLIOTT† KATHRYN J. AMOS JAMES L. BEST GARETH M. KEEVIL DEREK B. INGHAM† 《Sedimentology》2006,53(2):249-257
The planform patterns of meandering submarine channels and subaerial fluvial bends show many similarities that have given rise to strong analogies concerning the fluid dynamics of these channel types. Existing models of helical motion in open‐channel bends depict flow that is characterized by surface flow towards the outer bank, and basal flow towards the inner bank. This paper investigates and compares, through an analytical model and physical experiment, flows within fluvial meanders, and submarine channel bends that contain density‐driven gravity currents. The results indicate that the sense of helical motion can be reversed in submarine bends that contain density currents when compared with fluvial bends, and that the orientation of the helical flow is dependent on the vertical distribution of downstream velocity. Specifically, the sense of helical motion is reversed in bends when the maximum downstream velocity is near the bed, resulting in near‐bed flow towards the outer bank. These findings suggest that the dynamics of sediment transport and deposition in curved channels with such velocity profiles will be fundamentally different to those currently assumed from sinuous open‐channels. 相似文献