the shape of triton from limb profiles abstract limb profiles from voyager 2 images of triton show it to be an ellipsoid of axes 1354 6 1352 8 and 1352 4 km 0 9 km topography on the limbs suggests no large provinces such as continents with relief over a kilometer the shape solution is not accurate enough to constrain triton s moments of inertia the apparently relaxed shape is consistent with the youthful geologic features and supports interpretations that atmospheric distortion suggested by occultation data is due to atmospheric phenomena rather than physical body distortions

origin of rhythmic layering in the calamity peak satellite pluton of the harney peak granite south dakota the role of boron abstract the calamity peak satellite granite pluton on the flanks of the harney peak granite south dakota displays prominent mineral and textural layering the latter defined by alternating fine grained and pegmatitic granite superimposed on the fine grained granite layers is a fine scale 0 1 5 cm rhythmic layering defined by modal differences in tourmaline microcline albite and muscovite there is very little variation in the major element mineral compositions in the whole complex analyses by prompt gamma neutron activation gave a b2o3 content of 0 07 in the light layers albite quartz and muscovite and 0 65 in the dark layers tourmaline microcline quartz and albite these contents are essentially proportional to tourmaline abundance in each layer the textural and mineralogic layering is the result of the interplay of tourmaline crystallization and shifts in phase equilibria due to changes in b concentration in the melt initial cotectic crystallization of albite quartz and muscovite increased the activity of fe and mg in the adjacent melt to levels sufficient for tourmaline to form tourmaline crystallization depleted b and decreased the solubility of h2o in the melt causing exsolution of h2o from the melt and further removal of b due to high fluid melt partition coefficient this process also resulted in the precipitation of k feldspar partly at the expense of muscovite and partly due to a slight increase in the solidus temperature once the crystallization front moved to an fe and mg poor region of the melt tourmaline precipitation ceased and the equilibrium shifted back toward quartz muscovite and albite the pegmatitic layers some of which cut across previously formed rhythmic layers and commonly have tourmaline along their borders appear to have crystallized from melt enriched in the exsolved fluid phase

fluorine in aluminosilicate systems phase relations in the system naalsi3o8 caal2si2o8 f2o 1 abstract the liquidus phase equilibria of 0 9 naalsi3o8 0 1caal2si2o8 f2o 1 was determined to 10 kbar for a composition with molar f f o 0 095 the temperature of the liquidus is depressed by 200 c at 1 bar 2 kbar and 10 kbar relative to the volatile free liquidus additional experiments were carried out at 2 kbar to examine the effects of increasing f content on phase equilibria increasing molar f f o to 0 156 at fixed pressure decreases the temperature of the liquidus 350 c from the temperature of the volatile free liquidus at constant f f o 0 095 xan of the plagioclase coexisting with the liquid decreased from an30 at 1 atm to an22 at 2 kbar and to an17 at 10 kbar increasing fluorine content of the liquid at 2 kbar decreased the an content of the feldspar to a value of an13 in equilibrium with the liquid with f f o 0 156 thermodynamic calculations demonstrate that the activity of naalsi3o8 in the liquid decreases with increasing fluorine content and concomitant decreasing temperature but to a lesser extent than would be expected by the magnitude of the decrease in temperature in contrast the activity of caal2si2o8 decreases to a greater extent than is attributable solely to the effect of temperature the effect of fluorine is in marked contrast to that of h2o which has little effect on the composition of the plagioclase in equilibrium with a melt of given anhydrous composition because of this the degree of plagioclase fractionation in a fluorine bearing anhydrous system would be in considerable excess of estimates based solely on the fluorine free anhydrous albite anorthite system or the h2o saturated albite anorthite h2o system rigorous application of these results to fractionation in late stage felsic systems will require additional experiments on the combined effects of h2o and f in ca bearing granitic systems

phase equilibria of a fluorine rich leucogranite from the st austell pluton cornwall highly evolved leucogranitic rocks in the st austell pluton cornwall of hercynian age contain accessory muscovite topaz and fluorite the authors have studied the h sub 2 o saturated melting behavior of one representative sample its solidus and liquidus pass through the points 663 and 725 sup 0 c respectively at 1 kbar 640 and 665 sup 0 c at 2 kbar 610 and 717 sup 0 c at 4 kbar and 608 and 700 sup 0 c at 8 kbar plagioclase is on the liquidus at low pressure and topaz is on the liquidus at 4 kbar the fluorite is consumed in the formation of the first formed liquid calcium can partition into an evolved granitic melt if complexed by fluorine the fluorite appears to be largely primary in fresh fluorite granite at st austell and not to reflect the albitization of oligoclase in the surrounding biotite granite such fluorine rich leucogranites can be expected to be of subsolvus character

prerequisites for explosive cryovolcanism on dwarf planet class kuiper belt objects explosive extrusion of cold material from the interior of icy bodies or cryovolcanism has been observed on enceladus and perhaps europa triton and ceres it may explain the observed evidence for a young surface on charon pluto s surface is masked by frosts here we evaluate prerequisites for cryovolcanism on dwarf planet class kuiper belt objects kbos we first review the likely spatial and temporal extent of subsurface liquid proposed mechanisms to overcome the negative buoyancy of liquid water in ice and the volatile inventory of kbos we then present a new geochemical equilibrium model for volatile exsolution and its ability to drive upward crack propagation this novel approach bridges geophysics and geochemistry and extends geochemical modeling to the seldom explored realm of liquid water at subzero temperatures we show that carbon monoxide co is a key volatile for gas driven fluid ascent whereas co 2 and sulfur gases only play a minor role n 2 ch 4 and h 2 exsolution may also drive explosive cryovolcanism if hydrothermal activity produces these species in large amounts a few percent with respect to water another important control on crack propagation is the internal structure a hydrated core makes explosive cryovolcanism easier but an undifferentiated crust does not we briefly discuss other controls on ascent such as fluid freezing on crack walls and outline theoretical advances necessary to better understand cryovolcanic processes finally we make testable predictions for the 2015 new horizons flyby of the pluto charon system

liquidus equilibria in the system k2o na2o al2o3 sio2 f2o 1 h2o to 100 mpa ii differentiation paths of fluorosilicic magmas in hydrous systems we investigated phase equilibria in the six component system na2o k2o al2o3 sio2 f2o 1 h2o at 100mpa to characterize differentiation paths of natural fluorine bearing granitic and rhyolitic magmas topaz and cryolite are stable saturating solid phases in calcium poor systems at 100mpa the maximum solidus depression and fluorine solubility in evolving silicic melts are controlled by the eutectics haplogranite cryolite h2o at 6408c and 4 wt f and haplogranite topaz h2o at 6408c and 2 wt f topaz and cryolite form a binary peralkaline eutectic at 6608c 100mpa and fluid saturation the low temperature nature of this invariant point causes displacement of multiphase eutectics with quartz and alkali feldspar towards the topaz cryolite join and enables the silicate liquidus and cotectic surfaces to extend to very high fluorine concentrations more than 30 wt f for weakly peraluminous and subaluminous compositions the differentiation of fluorine bearing magmas follows two distinct paths of fluorine behavior depending on whether additional minerals buffer the alkali alumina ratio in the melt in systems with micas or aluminosilicates that buffer the activity of alumina magmatic crystallization will reach either topaz or cryolite saturation and the system solidifies at low fluorine concentration in leucogranitic suites precipitating quartz and feldspar only the liquid line of descent will reach topaz or cryolite but fluorine will continue to increase until the quaternary eutectic with two fluorine bearing solid phases is reached at 5408c 100mpa and aqueous fluid saturation the maximum water solubility in the haplogranitic melts increases with the fluorine content and reaches 12 5 0 5 wt h2oat the quartz cryolite topaz eutectic composition a continuous transition between hydrous fluorosilicate melts and solute rich aqueous fluids is not documented by this study our experimental results are applicable to leucocratic fluorosilicic magmas in multicomponent systems however the presence of calcium may severely limit enrichment of fluorine by crystallization of fluorite

global color and albedo variations on triton global multispectral mosaics of triton have been produced from voyager approach images six spectral units are defined and mapped the margin of the south polar cap spc is scalloped and ranges in latitude from 10 deg to 30 deg a bright fringe is closely associated with the cap s margin form it diffuse bright rays extend north northeast for hundreds of kilometers thus the rays may consist of fringe materials that were redistributed by northward going coriolis deflected winds from 1977 to 1989 triton s full disk spectrum changed from markedly red and uv dark to nearly neutral white and uv bright this spectral change can be explained by new deposition of nitrogen frost over both the northern hemisphere and parts of a formerly redder spc frost deposition in the southern hemisphere during southern summer is possible over relatively high albedo areas of the cap stansberry et al 1990 which helps to explain the apparent stability of the unexpectedly large spc and the presence of the bright fringe

transport and concentration of molybdenum in granite molybdenite systems effects of fluorine and sulfur to investigate the effects of f and s on the transport and concentration of mo in granite molybdenite deposits we prepared four synthetic granite compositions with mo s and f each composition was run at 1000 c and 100 mpa with 6 wt h 2 o to stabilize the phase assemblage liquid aqueous vapor in all compositions mo is partitioned into the vapor phase and deposited on the capsule walls in vapor bubbles in the quenched glasses or in silica rich spherules f and s do not affect the partitioning of mo however s plays a critical role in the deposition of mo from the vapor phase thus the initial water content of the magma which controls the timing of vapor phase evolution and the presence of s are primary controls on mo ore deposition in these deposits

phosphorus and the rare earth elements in felsic magmas an assessment of the role of apatite abstract the solubility of fluorapatite in 17 silica rich melts in the system na 2 o k 2 o al 2 o 3 sio 2 with and without cao or caf 2 was determined at 1 kbar water pressure and 750 900 c apatite saturation occurs at levels of dissolved p 2 o 5 ranging between 0 04 0 02 and 0 28 0 13 wt with only 4 values outside the 0 09 0 20 wt range the results demonstrate not only that apatite is a common liquidus phase in felsic melts but also that under most circumstances it remains in the residue during episodes of partial fusion of the crust given a solubility limit of 0 14 wt dissolved p 2 o 5 the mean of the experimental values a source containing as little as 0 05 p 2 o 5 must be 35 melted before apatite is lost from the residue and no longer buffers the melt p 2 o 5 concentration at the saturation value higher abundances of p 2 o 5 in the source postpone the loss of residual apatite to still higher degrees of melting and if the source p 2 o 5 content exceeds 0 14 wt apatite must be residual for all degrees of melting increasing in abundance as melting proceeds the generally secondary influence of apatite on the rare earth element ree patterns of melt and residue is most apparent when garnet and or amphibole is minor or lacking in the residue fractional crystallization of intermediate e g andesitic magmas toward felsic compositions invariably results in saturation in apatite and some consequent depletion of ree in the melt

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

the probable occurrence of interstitial al in hydrous f bearing and f free aluminosilicate melts experiments carried out on the system sio2 naalsi3o8 kalsi3o8 qz ab or at 1 kbar in the presence of h2o and f show that the quartz alkali feldspar field boundary is progressively displaced towards the feldspar join as f contents increase from 0 to 4 wt f increasing p h 2 o in the absence of f has already been shown to have a similar effect tuttle and bowen 1958 luth jahns and tuttle 1964 the increased size of the quartz field in the f bearing system compared to the hydrous system is believed to be caused by progressive removal of al from the tetrahedral network of the melt by complexing with f the residual network in the melt is thus enriched in si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions the common presence of quench cryolite na3alf6 in certain experiments carried out with 4 wt f supports this interpretation and indicates that some al in the melt may be present in six fold coordination with f the effect of h2o in the absence of f may be similar with al being progressively removed from four fold coordination as more h2o is dissolved in the melt although a proportion of al in hydrous melts may occur in six fold coordination dry melts predominantly contain al in four fold coordination this major difference in al complexing may be one of the main causes for differences in the high pressure phase relations of wet and dry albearing silicate systems

neodymium and strontium isotope study of the blue tier batholith ne tasmania and its bearing on the origin of tin bearing alkali feldspar granites the middle to late devonian plutons of the blue tier and eddystone batholiths of ne tasmania intrude quartz wacke and mudstone of the ordovician devonian mathinna beds four granitoid types are recognized hornblende biotite granodiorite biotite granite biotite cordierite garnet granite and alkali feldspar granite afg minor diorite bodies and dolerite dykes are also present tin w mineralisation is genetically associated with the afg major granitoid types other than afg of the blue tier and eddystone batholiths all have similar 143nd 144nd initial ratios nd 5 0 to 6 5 at ma more fractionated felsic samples within individual plutons have lower nd values suggesting progressive involvement up to about 5 of the sedimentary country rocks which have nd of about 11 at 370 ma the source rock model age for all granitoids except afg based on a depleted mantle evolution model tdm is about 1 6 ga on the basis of geochemical data 87sr 86sr initial ratios 0 707 0 713 oxygen isotope ratios 180 9 to 12 and rb sr and k ar isotopic age dates 368 to 388 ma the major plutons were interpreted to have been generated independently from heterogeneous crustal sources geochemical variation within each major granitoid type with the possible exception of the afg is due to fractional crystallisation accompanied by some country rock assimilation integrated nd sr and o isotopic systematics of the blue tier batholith of the bassian terrain are different from granite batholiths in the mainland of the lachlan fold belt similarity of isotopic systematics of the blue tier batholith to those of devonian granites in central victoria reinforces the geological correlation between western tasmania and south australia in the early paleozoic two competing hypotheses for the generation of sn w mineralized afg have been proposed on the basis of geological relationships chemical and mineralogical trends and stable and radiogenic isotopes the first hypothesis groves et al 1977 higgins et al 1985 higgins 1990 links the afg with the country rock more mafic poimena granite through processes of fractional crystallisation and subsequent metasomatic modification the second hypothesis suggests that these afg are unrelated to the poimena granite they are specialised granites derived from a different parent with distinctive chemical isotopic systematics sun et al 1986 mackenzie 1986 mackenzie et al 1988 1990 according to the first hypothesis the afg exhibit a range in nd initial values from 5 9 to 2 2 however there is no known isotopic mechanism which can produce this range within the geological time frame of intrusion and solidification at this time the authors favour the second hypothesis because of chemical and isotopic correlations on the basis of a distinct discontinuity between poimena and afg on a y versus ga al plot there is also a clear grouping of initial nd for the poimena granite around 6 and the afg 2 4 it is argued that those few afg having much lower nd than 2 4 are either samples of altered poimena granite two samples with nd 6 8 and 9 1 or a result of extensive metasomatic modification one sample nd 5 9 involving circulation of fluids in equilibrium with the country rocks poimena granite initial nd 6 and mathinna beds 11 hydrothermal minerals from the anchor tin deposit show a range in initial nd and 87sr 86sr correlated with paragenesis apatite formed during albitisation of the lottah granite has nd and sr isotopic compositions intermediate between those of the lottah and poimena granites greisen fluorites have initial nd between 4 0 and 4 6 closer to the lottah average composition while initial 87sr 86sr approaches that of the metasedimentary country rock 0 729 fluorites formed during sericitic alteration have lower nd compositions 0 721 these data support an origin of tin mineralisation through mixing of an afg derived magmatic fluid with a externally derived meteoric groundwater dominated fluid

mueilha rare metals granite eastern desert of egypt an example of a magmatic hydrothermal system in the arabian nubian shield abstract the mueilha granite pluton is one of the rare metals bearing peraluminous granitic plutons in the arabian nubian shield it represents the apical part of a highly evolved magma chamber emplaced at a shallow level subsequent to the post pan african orogeny the pluton can be seen as a highly leucocratic medium grained albite oligoclase framework infilled with quartz k feldspar and muscovite that are variably overgrown by k feldspar muscovite quartz and topaz megacrysts the increasing number and size of the k feldspar megacrysts at the expense of the whitened albite oligoclase framework imparts variably red color to the mueilha granite contacts between the milky white and red granites are usually gradational but may be locally sharp or may form narrow transition zones resulting from abrupt variations in texture and lithology textural relations indicate an initial stage of hydrothermal albitization of magmatic plagioclase and crystallization of topaz megacrysts resulting from infiltration of na rich fluorine bearing fluids a subsequent stage of metasomatic enrichment is characterized by extensive growth of large k feldspar quartz and muscovite megacrysts at the expense of the albite oligoclase crystals as a result of infiltration of k si rich hydrous fluids post magmatic infiltration of hydrous fluids along the fault planes is shown by the intense replacement of alkali feldspar megacrysts by quartz development of myrmekitic intergrowth pockets along the k feldspar megacrysts and sealing of the micro fractures by cryptocrystalline mixtures of clay minerals iron oxides sericite and chlorite compositionally the red granitic rocks have higher sio 2 fe 2 o 3total k 2 o na 2 o ree y th u zr and zn and lower al 2 o 3 ga ta nb and mo compared to the milky white granites lile and sn do not show clear variation trends throughout the mueilha granite pluton suggesting their immobility during hydrothermal alteration microthermometric measurements indicate that the interactions with the hydrothermal fluids started at a minimum temperature 400 c most likely during the late stage crystallization of the mueilha granite and continued after their complete solidification i e subsolidus conditions at a temperature as low as 120 c the high fertility of mueilha granite is most plausibly the result of partial melting within the undepleted juvenile crust of the arabian nubian shield that has formed during the pan african orogeny

internal differentiation of rare element pegmatites effects of boron phosphorus and fluorine lithium rich rare element pegmatites are characterized by high concentrations of b p and f the interactions of these components with h2o and rare alkalis lower liquidas and solidus temperatures enhance silicate liquid h2o miscibility and control partitioning and concentration of group i elements and higher field strength cations boron f and perhaps p may form peralkaline na and li species that promote early saturation in mica quartz activities of f p and especially b are largely unbuffered throughout crystallization concentration of these components through fractional crystallization involving muscovite generates a peralkaline na aluminosilicate rich melt or vapor from which albitites rich in tourmaline phosphates f rich micas beryl zircon and nb ta sn oxides crystallize phase equilibrium experiments with peraluminous b p f rich rhyolite obsidian macusanite simulate many features of rare element pegmatites especially at h2o undersaturated conditions

petrogenesis of the ear mountain tin granite seward peninsula alaska ear mountain is part of a belt of cretaceous tin granites on the seward peninsula of western alaska porphyritic and seriate biotite quartz monzonite and quartz syenite represent early pluton units these were followed by equigranular and fine grained two mica tourmaline bearing granite late units are enriched in b f and na k and are depleted in ti a greisen alteration assemblage of tourmaline quartz cassiterite white mica or magnetite or pyrite or pyrrhotite or rutile or arsenopyrite is found in the granite and skarns surrounding the pluton granite compositions approximate the minimum in the synthetic granite system at a pressure of 0 5 kb compositions of fine grained granite are shifted toward the f enriched minimum in the synthetic system temperature estimates based on feldspar geothermometry range from 624 degrees to 501 degrees c and are close to the solidus temperature in the f and b enriched systems coexisting fe ti oxide mineral data give temperature estimates of 625 degrees to 675 degrees c and indicate cooling along a buffered path intermediate between the quartz fayalite magnetite and nickel nickel oxide curves biotite compositions fe fe mg 0 69 0 99 combined with the feldspar geothermometry also indicate that crystallization of the pluton followed a buffer near the nickel nickel oxide curve the tin contents of ear mountain granites largely correlate with degree of greisen alteration unaltered granites contain less than 80 ppm sn whereas thoroughly altered granites contain over 950 ppm sn tin concentrations in unaltered granitic rocks increase progressively from porphyritic to seriate to some equigranular rocks indicating a progressive concentration of sn with fractional crystallization most unaltered fine grained granites contain low sn values interpreted as results from sn lost to the evolved vapor phase the moderately reducing weakly peraluminous and low calcium conditions during crystallization of the ear mountain pluton allowed for concentration of sn into the melt high b and f contents in the melt promoted prolonged fractionation of the system and increased concentration of sn evolution of a vapor phase removed sn from the granitic melt and reaction of this vapor with the granite and the skarn produced the sn enriched greisen alteration there is no evidence that sn was remobilized from sn enriched biotites into greisen greisen development is not extensive at present levels of erosion abundant cassiterite in placers surrounding the pluton suggest much of the greisen zone has been removed by erosion the apical parts of other tin granites on the seward peninsula such as lost river and kougarok have well developed greisen zones ear mountain probably resembled these systems prior to erosion

experimental study on effects of geometric distortion upon suspended sediments in bending channels abstract different geometries of bending channels are set up without distortion and with distortion ratios of 2 4 6 8 and 10 in order to study its influence on bed deformation induced by suspended sediment transport in these channels experiment results show that the kinematics of suspended sediment is inversely proportional to the distortion ratio of the physical model but proportional to the width depth ratio and curvature ratio the similar bed deformation to that of the non distorted model is only observed in the distorted models with distortion ratios of not more than 4 and width depth ratios of not less than 6 3 it is recommended that the geometric distortion ratio be less than 4 in order to meet the similarity requirements of river bed deformation in bending channels with the same distortion ratio deviation of bed deformation was observed more in the bending reaches than in the straight ones and more with a fixed convex bank than with a mobile convex bank the geometric distortion affects the river bed deformation in the model i e the amount of deposition and erosion and the profiles of river bed deformation in longitude and transverse directions

petrogenesis of tourmaline granites and topaz granites the contribution of experimental data abstract fluorine and boron are generally only minor components of granitic rocks but may be found highly concentrated in certain tourmaline granites and topaz granites up to 1 wt b2o3 and 3 2 wt f respectively studies of various examples of these granite types which occur as small bodies emplaced at shallow levels p lithostatic textural and petrographic data indicate that the tourmaline and topaz granite magmas crystallized at low to moderate temperatures below 700 c and that a fluid phase may have been present during the crystallization interval both granites varieties are peraluminous co up to 5 characterized by the presence of white micas lithium micas or muscovite aluminium silicates and other al rich minerals garnet cordierite boron and fluorine are hosted by tourmaline schorl rich member of the schorl dravite series topaz and mica respectively these granites have low ca fe mg and ti contents each the crystallization of tourmaline granite and topaz granite magmas is discussed using experimental data derived from studies of granitic systems with added boron and fluorine both elements act as a flux enabling boron and fluorine enriched melts to persist to temperatures as low as 650 c at 1 kbar in addition the effect of increasing fluorine content displaces the minimum in q ab or at ph2o 1 kbar toward the albite apex plots of fluorine rich topaz granites coincide with this trend suggesting that the role of fluorine in magmatic processes may have affected the rock composition as well as crystallization temperatures boron rich granites plot near the low ph2o minima in qz ab or suggesting that boron has less of an influence on minimum melt compositions the low temperatures of crystallization permits phases such as muscovite or andalusite topaz and two alkali feldspars to crystallize directly from f and b enriched melts at low pressures in addition the limited available experimental data are used to compare the effects of fluorine and boron on major and trace element distribution during melt vapour interaction

dynamics of triton s atmosphere the recent voyager encounter established certain facts about triton s atmosphere the surface pressure is in the range 1 5 1 9 pa 15 19 bar the surface temperature is 38 3k ref 2 molecular nitrogen is the dominant atmospheric constituent hazes and clouds are visible not only on the limb but also against the surface the wind in the southern hemisphere is to the northeast at low altitudes as shown by streaks on the surface and to the west at high altitudes as shown by geyser like plume tails triton rotates with a period of 5 877 days in a right hand sense about the south pole where the season now is late spring4 here we argue that these features can be explained if triton like mars has a global well structured atmosphere in equilibrium with surface frosts the subliming frost cap produces a polar anticyclone at low altitudes with northeastward winds of 5 m s 1 within the ekman boundary layer the temperature contrast between the cold frost covered pole and the warm unfrosted equator produces westward winds at high altitudes

the system na 2 si 2 o 5 k 2 si 2 o 5 mos 2 h 2 o with implications for molybdenum transport in silicate melts the behavior of molybdenite in the system na 2 si 2 o 5 k 2 si 2 o 5 mos 2 h 2 o has been investigated from 340 bars to 1 36 kb in the temperature range 450 degrees to 850 degrees c phase relations in the system show enhanced molybdenite solubility in the alkali silicate liquids and coexisting vapors mos 2 solubility is up to 10 wt percent in vapor saturated na 2 si 2 o 5 melt and 12 5 wt percent in vapor saturated k 2 si 2 o 5 melt at 680 bars and 650 degrees c there is a positive pressure dependence of solubility but retrograde solubility is indicated as a function of temperature above about 650 degrees c at the pressures investigated the experimental data combined with published data on structure of silicate melts mysen and virgo 1980 suggest that mo silicate and or mo hydroxylated silicate complexes such as mosi 2 o super 2 5 mosi 2 o 6 and mosi 2 o 4 oh super 3 may account for the observed molybdenite solubility if these results can be extrapolated to nature it seems likely that geologically significant quantities of molybdenum may be transported in hydrous alkalic silicic melts as mo silicate complexes for eventual fractionation into the vapor phase during vapor generation such a transport mechanism would be consistent with the commonly observed association of mo with silica rich rocks

nd and sr isotope study of hydrothermally altered granite at san manuel arizona implications for element migration paths during the formation of porphyry copper ore deposits a study of the nd and sr isotope composition of the late cretaceous monzogranite stock at san manuel arizona and its mineralized alteration halo was undertaken in order to assess the transport of nd and sr that accompanied the hydrothermal alteration sampling was along a 1 km transect perpendicular to the alteration zones extending from the potassically altered core to the propylitically altered fringe of the system large isotopic differences between the stock and the enclosing 1 4 b y old granitic wall rock coupled with the original homogeneity of the latter provide optimal conditions for detecting evidence of chemical transport the mineralizing porphyry stock has a lower 87 sr 86 sr ratios 0 708 and a higher epsilon nd 6 than the precambrian granite wall rock 0 782 11 the 87 sr 86 sr ratios of the altered wall rock decrease regularly from 0 782 to 0 715 from the propylitic alteration zone to the stock contact indicating that material flow was primarily from the stock into the wall rock consistent with an orthomagmatic model for porphyry copper ore genesis the sr in the ore zone is 75 percent stock derived and evidence of stock derived sr is found up to 700 m into the wall rock the sr and rb concentration variations are mainly controlled by the alteration mineralogy and do not correlate with the isotopic variations the epsilon nd values and the sm and nd concentrations of the altered wall rock show subtle changes that are mostly confined to the potassically altered zone only one wall rock sample located 0 5 m from the stock contact is strongly disturbed the results suggest that sr isotopes may provide a useful tool for studying or locating fossil hydrothermal systems whereas the relatively immobile nd isotopes are reliable indicators of the magmatic provenance of altered intrusions

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

light stable isotope systematics of granitic pegmatites from north america and norway abstract oxygen hydrogen and carbon isotope analysis of minerals whole rocks and fluid inclusions were performed on pegmatites and associated wall rocks from ten pegmatite districts and individual occurrences of precambrian late cretaceous age the pegmatites and pegmatite districts include the evje iveland area norway harding pegmatite new mexico u s a tanco pegmatite manitoba canada kiawa pegmatite new mexico u s a and the crestmore pegmatite california u s a the results of more than 350 isotopic analyses indicate no principal isotopic differences among pegmatites of widely different age the 18 o of quartz for analyzed pegmatites varies from 18 o 8 6 to 11 8 the 18 o of quartz from a sanidine bearing pegmatite in a sub volcanic environment is 7 10 late stage lower temperature quartz is typically the heaviest in any pegmatite the whole rock isotopic compositions of the pegmatites analyzed appear to largely reflect composition of the melt although some isotopic exchange with the wall rocks may have occurred oxygen isotope fractionations can be used to indicate a magmatic temperature range for crystallization 540 750 c compatible with experimental data on li bearing and simple granitic bulk compositions lower solidus temperatures for the li bearing pegmatites are reflected by larger isotopic fractionations continued subsolidus crystallization and replacement of many pegmatite minerals is compatible with both isotopic mineralogie and textural evidence the hydrogen isotope composition of muscovite and biotite varies for most samples from 45 to 70 depending to a large degree on the temperature of crystallization d of water from primary fluid inclusions from the same samples are enriched in d relative to the hydrous minerals the hydrogen isotope fractionations between inclusion fluid and muscovite or biotite indicate in most cases a range in crystallization temperature compatible with that suggested on the basis of oxygen isotope fractionations and experimental data interaction with meteoric water is not typical of pegmatite emplacement and crystallization the carbon isotope composition of c0 2 in most fluid inclusions is typically 6 1 to 7 1 several 13 c values heavier than 6 1 to 2 2 may record either contamination or isotopic effects due to separation of c02 from the melt

anastomosing river system along the subsiding middle yangtze river basin southern china the study focuses on the formation processes of the uprivermost jingjiang reach of three anastomosing river reaches along the middle yangtze river downstream of the three gorges dam site and 1700 km upriver from the seacoast at shanghai in southern china the jingjiang reach consists of large anastomosing channels the songzi hudu anxiang and ouchi rivers which depart from the yangtze trunk channel and flow southward and southeastward up to 200 km into the dongting basin and lake the lake rejoins the yangtze at chenglingji the 7000 km 2 anastomosing reach is characterized by multiple stable low gradient channels 0 00004 m m 4 cm km with low width depth ratios 40 low stream powers 7 w m 2 with very high sedimentation rates 33 5 123 3 mm year in some channels tectonic subsidence caused by the himalayan orogeny is thought to be the primary forcing mechanism in causing the anastomosing channel processes and deposition historical documents have shown that the jingjiang channels were caused by repetitive avulsions southward from the yangtze channel the earliest recorded avulsion occurred in a high flood period before 1644 and subsequent avulsions have continued to modify the topography three major avulsion channels have diverted 14 33 of the discharge and 17 47 of suspended sediment load from the yangtze channel these channels have remained laterally stable a characteristic of anastomosing rivers due to their low gradient silt clay banks densely vegetated natural levees and stable interchannel islands consisting of clayey silt that supports dense riparian vegetation data derived from hydrological gauging stations over the last 45 years demonstrate that total discharge and sediment load of anastomosing channels has decreased by two thirds largely due to sediment aggradation on channel beds reduced sediment load and discharge and human caused channel modification were more pronounced in the eastern channels with the completion of the 3 gorges dam in 2009 the anastomosing channels will cease to carry significant quantities of water and sediment to maintain fluvial vigor in the next 100 years the yangtze main channel may become the only active channel as the anastomosing channels slowly will be infilled c 2004 elsevier b v all rights reserved

triton s streaks as windblown dust the encounter of the voyager 2 spacecraft with neptune s satellite triton revealed many dark about 10 20 darker than the adjacent frost surface streaks in triton s southern hemisphere1 resembling the streaks that are due to windblown dust on mars2 it seems therefore that dust transport by winds in triton s tenuous atmosphere is required the main question being the mechanism for raising dust from the surface or sub surface the two obvious candidates are geyser like eruptions and direct lofting by surface winds1 here we show that despite triton s tenuous 16 3 bar atmosphere3 low cohesion grains with diameters of 5 m may be carried into suspension by aeolian surface shear stress given expected geostrophic wind speeds4 of l0ms 1 the wind velocities needed to lift grains as cohesive as those found on earth however are implausibly high for erupting plumes we show that dust settling timescales and expected wind velocities yield streak length scales in good agreement with those observed both candidate mechanisms therefore seem to be consistent with present observations of triton

tracing fluid saturation during pegmatite differentiation by studying the fluid inclusion evolution and multiphase cassiterite mineralisation of the gatumba pegmatite dyke system nw rwanda abstract aqueous fluid saturation during the internal evolution of phosphorus and boron rich pegmatites in nw rwanda has been investigated using petrography fluid inclusion microthermometry and microanalysis of minerals and fluid inclusions raman microspectroscopy and la icp ms the gatumba dyke system gds in rwanda has been selected for this study because it hosts a multiphase cassiterite mineralisation in wall core and internal replacement zones suggesting an advancing influence of magmatic hydrothermal conditions during dyke solidification as such multiphase cassiterite precipitation is applied as a tracer for magmatic to hydrothermal crystallisation processes in granitic pegmatites the gds consists of a group of six major lct lithium caesium tantalum family dykes which all belong to the most differentiated rare element pegmatites in the gatumba gitarama field petrography identified a well developed internal anatomy consisting of a border wall intermediate and a quartz core zone in addition replacement zones developed as cleavelandite after perthitic microcline units in the intermediate zone and as muscovite quartz pockets in the intermediate and wall zones the latter replacement zone display muscovitisation reactions with the formation of greisens texturally the greisen pockets replace the secondary cleavelandite units during internal differentiation multiphase cassiterite mineralisation formed in 1 large microcline crystals of the wall zone cst1 2 assemblage with quartz f poor montebrasite and carbonate and boron enriched mn fluorapatite in the core zone cst2 and 3 the greisen replacement units in the wall and intermediate zones cst3 fluid inclusion micro analyses demonstrate that a saline aqueous h2o nacl kcl co2 n2 l1 type fluid 20 wt nacl and 3 wt kcl was saturated during onset of crystallisation of the wall and intermediate zones and precipitation of the disseminated magmatic hydrothermal cst1 mineralisation in and around large perthitic k feldspars isochore reconstructions of this l1 fluid indicate crystallisation conditions of 535 560 c and 5 1 5 6 kbar for the gds extensive microcline fractionation and subsequent replacement reactions of cleavelandite after microcline in the intermediate zone were induced by a li enriched and more na depleted h2o nacl licl co2 n2 l2 type fluid which was present during solidification of the core zone and present during precipitation of cst2 phase mineralisation 6 12 wt nacl 1 10 wt licl late stage hydrothermal cst3 mineralisation in the greisen pockets precipitated from a cs enriched h2o nacl kcl co2 n2 l3 type fluid 15 wt nacl distinctly after the formation of the cleavelandite replacement units subsolidus cst3 precipitation is dominantly driven by metasomatic hydrolytic fluid rock reactions combining textural microthermometric and fluid compositional data with reported sn melt fluid partitioning and solubility data demonstrate that primary cassiterite i e cst1 and cst2 in the wall and core zone of the gds precipitated from the exsolved saline aqueous l1 and l2 fluid present at the interface of the highly fractionated melt phase fast disequilibrium growth of near anhydrous mineral assemblages likely caused the formation of flux rich and at least locally water saturated melt compositions at the crystallisation front of the large crystals this study emphasises the importance of local magmatic hydrothermal conditions and the presence of an immiscible aqueous fluid phase during the internal crystallisation and cassiterite mineralisation of rare element pegmatites

reply to n c higgins comment on origin of alkali feldspar granites an example from the poimena granite northeastern tasmania australia this paper acts as a rebuttal to comments made by other scientists regarding the origin of the poimena granite as discussed in an earlier paper by these authors the lottah granite and the enclosing poimena granite of northeastern tasmania represent one of the best documented and most intensely li f rich alkali feldspar granite and its much more voluminous biotite granite host the issue under debate is which of the two most generally supported models for the origin of li f sn granites magmatic or metasomatic hydrothermal best explains the data obtained from the lottah and poimena granites it is not the authors intent to imply that alkali feldspar granites cannot be generated from granites similar to the poimena granite by fractional crystallization the st austell granite is an excellent example of such a relationship nor do the authors intend to imply that metasomatic and hydrothermal processes have not operated at all in the lottah granite they seek rather to demonstrate that magmatic processes alone are capable of generating alkali feldspar granites enriched in sn li rb f etc and that such granites need not be genetically linked to spatially associated normal granites some of the arguments and data are subsequently presented in this paper

phase relations of tourmaline leucogranites and the significance of tourmaline in silicic magmas by means of melting and recrystallization tourmaline seeded experiments phase relations of two natural tourmaline bearing fe rich members of the schorl dravite series leucogranites have been determined between 1 and 3 kbar under h2o saturation with fo2 close to ni nio the presence of tourmaline slightly lowers the solidus temperatures of both samples from 5 to 20 c compared to the corresponding tourmaline free solidus quartz k feldspar and plagioclase phase relations are not significantly dependent on the presence of tourmaline tourmaline is the last major phase to disappear for both samples and a demonstrated liquidus phase exists for one in the recrystallization experiments the compositions of the tourmalines growing from the melt change from more mg rich at high temperatures to more fe rich at lower temperatures the tourmalines are always richer in mg than the melt is but fe and mg are not especially partitioned between crystallizing tourmaline and melt melt compositions do not depart

martian and terrestrial dust devils test of a scaling theory using pathfinder data the mars pathfinder meteorological station recorded wind pressure and temperature fluctuations that have been interpreted as dust devils warm core vortices that form at the bottom of connective plumes we apply a scaling theory renno et al 1998 developed to explain terrestrial dust devil observations to test the validity of this interpretation and to provide a simple physical interpretation of the general characteristics of martian dust devils the theory is based on the thermodynamics of heat engines and predicts the central pressure and the wind speed of the connective vortices our findings are as follows for the best documented candidate event sol 25 observed wind and pressure fluctuations are consistent with those predicted by the model and hence strengthen the interpretation of this case as a dust devil a number of other candidates less well documented however also are consistent with passage of a dust devil over or near the lander temperature fluctuations observed on other sols permit dust devils an order of magnitude larger than the ones measured by the meteorology package the strongest dust devils predicted by our theory have a central pressure deficit of about 50 pa and wind speed of about 60 m s 1 the strongest dust devils are capable of lofting dust and hence support the interpretation of selected pathfinder images as showing the passage of dust devils within sight of the lander

distorted froude scaled flume analysis of large woody debris this paper presents the results of a movable boundary distorted froude scaled hydraulic model based on abiaca creek a sand bedded channel in northern mississippi the model was used to examine the geomorphic and hydraulic impact of simplified large woody debris lwd elements the theory of physical scale models is discussed and the method used to construct the lwd test channel is developed the channel model had bed and banks moulded from 0 8 mm sand and flow conditions were just below the threshold of motion so that any sediment transport and channel adjustment were the result of the debris element dimensions and positions of lwd elements were determined using a debris jam classification model elements were attached to a dynamometer to measure element drag forces and channel adjustment was determined through detailed topographic surveys the fluid drag force on the elements decreased asymptotically over time as the channel boundary eroded around the elements due to locally increased boundary shear stress total time for geomorphic adjustment computed for the prototype channel at the q2 discharge discharge occurring once every two years on average was as short as 45 hours the size depth and position of scour holes bank erosion and bars created by flow acceleration past the elements were found to be related to element length and position within the channel cross section morphologies created by each debris element in the model channel were comparable with similar jams observed in the prototype channel published in 2001 john wiley sons ltd

apatite solubility in peraluminous liquids experimental data and an extension of the harrison watson model abstract new experimental data at 750 1000 c 2 5 kbar and for peraluminous melt compositions show a dramatic increase of apatite solubilities and phosphorus melt contents when compared to metaluminous or peralkaline compositions harrison and watson 1984 the formation of alumino phosphate units in peraluminous melts qualitatively explains our data a new apatite solubility model incorporating the data for the peraluminous region is presented application of this model to examples of peraluminous felsic suites is discussed

postorogenic alkali feldspar granite and associated pegmatites in west avalonia the petrology of the neoproterozoic georgeville pluton antigonish highlands nova scotia the 579 8 2 2 ma 40ar 39ar muscovite georgeville pluton in mainland nova scotia is an epizonal body consisting of alkali feldspar granite and related pegmatite the pluton intrudes the ca 619

comment on origin of alkali feldspar granites an example from the poimena granite northeastern tasmania australia in the last decade much research into the origin and evolution of tin granites and rare metal pegmatites has concentrated on understanding the processes of their emplacement crystallization chemical and fluid evolution and mineralization in this regard the granites of eastern australia and particularly the blue tier batholith btb of eastern tasmania have been important in contributing to our knowledge of these complex systems since highly differentiated tin granites and pegmatites are commonly the last phase of intrusion in complex batholiths the age difference between them and earlier phases is extremely important in assessing rival models for the evolution of the tin granites in the blue tier batholith and in general elsewhere if the lottah granite is 10 ma younger than the poimena granite then they must be separate unrelated melts if the data are inconclusive regarding an age difference then alternative explanations for the genesis of the afg cannot be discounted a re appraisal of the data of mackenzie et al 1988 does not lend support to their conclusion that there is an age difference and this combined with a balanced assessment of the chemical and mineralogical data suggests that an earlier model for the evolution of the lottah andmore other afg of the btb is more appropriate higgins et al 1985 less

bed topography and sediment sorting in channel bend with unsteady flow bed topography and transverse sediment sorting in an alluvial channel bend were investigated under unsteady flow conditions with nonuniform sediment five experiments each having the same initial sediment size gradation but a different inflow hydrograph were done in a 180 channel bend with a constant radius of curvature in addition bed elevations across various sections of the bend were measured and bed surface sediment were sampled at the peak and end of the hydrograph in each experiment experimental results indicated that the characteristics of the hydrograph have prominent influences on bed topography and transverse sediment sorting those cases with a higher ramping rate of the hydrograph have greater deposition heights near the inner bank and larger scour depths near the outer bank furthermore the sediment is finer near the inner bank and coarser near the outer bank in cases with a higher ramping rate the bed deformation and sediment size variation correlated well with the unsteady flow par

scaling and self similarity of one dimensional unsteady suspended sediment transport with emphasis on unscaled sediment material properties abstractcurrent methods utilized in scaling sediment transport in unsteady open channel flow result in a number of model and scale effects decreasing the accuracy and applicability of scale models identifying the conditions under which the governing equations of sediment transport are self similar and require no sediment diameter or density scaling can reduce scale effects and increase model applicability conditions for self similarity of one dimensional unsteady suspended sediment transport are identified by applying the one parameter lie group of point scaling transformations both for the general case and with unscaled sediment diameters under the scaling ratio relations found when holding sediment diameter to be unscaled sediment diameter density critical and total shear porosity kinematic viscosity and particle reynolds number are all unscaled it is shown that under lie group scaling the unsteady one dimensional suspended sediment transport process as an initial boundary value problem i

a 3d general circulation model for pluto and triton with fixed volatile abundance and simplified surface forcing abstract we present a 3d general circulation model of pluto and triton s atmospheres which uses radiative conductive convective forcing in both the pluto and triton models an easterly prograde jet is present at the equator with a maximum magnitude of 10 12 m s 1 and 4 m s 1 respectively neither atmosphere shows any significant overturning circulation in the meridional and vertical directions rather it is horizontal motions mean circulation and transient waves that transport heat meridionally at a magnitude of 1 and 3 107 w at pluto s autumn equinox and winter solstice respectively seasons referenced to the northern hemisphere the meridional and dayside nightside temperature contrast is small 5 k we find that the lack of vertical motion can be explained on pluto by the strong temperature inversion in the lower atmosphere the height of the voyager 2 plumes on triton can be explained by the dynamical properties of the lower atmosphere alone i e strong wind shear and does not require a thermally defined troposphere i e temperature decreasing with height at the surface underlying a region of temperature increasing with height the model results are compared with pluto stellar occultation light curve data from 1988 2002 2006 and 2007 and triton light curve data from 1997

sequence of mineral assemblages in differentiated granitic pegmatites revised sequence is 1 plagioclase quartz muscovite 2 plagioclase quartz 3 quartz perthite plagioclase 4 perthite quartz 5 quartz plagioclase perthite spodumene or petalite amblygonite 6 quartz spodumene or petalite 7 quartz microcline or perthite 8 quartz and 9 lepidolite or lithian mica plagioclase quartz microcline modified journal abstract

alkali feldspars as a main phosphorus reservoirs in rare metal granites three examples from the bohemian massif czech republic phosphorus rich alkali feldspars were found in three peraluminous highly differentiated albite topaz li mica granites in the w and s parts of the bohemian massif the average contents of p2o5 in k feldspars k i ovy kamen 0 57 wt homolka 0 77 wt and podlesi 0 83 wt are higher than the average contents of p2o5 in albites k i ovy kamen 0 23 wt homolka 0 23 wt and podlesi 0 39 wt the analyses of feldspars indicate that partition coefficient of phosphorus between k feldspar and albite range from 1 5 to 2 5 measured data in k feldspars suggest a statistically significant difference from the al3 p5 2 si4 substitution mechanism for higher phosphorus concentration the p content in k feldspars from the podlesi granite represent the highest p content in natural feldspar known to date up to 2 5 wt of p2o5 it is suggested that all studied granites retained nearly all phosphorus of granitic melts and that their alkali feldspars represent major reservoirs of phosphorus

phase equilibria of a be u and f enriched vitrophyre from spor mountain utah abstract the equilibrium melting relations of a vitrophyre representative of topaz rhyolites have been experimentally determined in order to constrain the pre eruption temperature and h2o content of topaz rhyolite magmas the vitrophyre sample is strongly enriched in f and incompatible elements and consists of approximately 70 unaltered volcanic glass and 30 crystals of biotite quartz sanidine plagioclase magmatic fluorite and a variety of accessory phases biotite stability is strongly dependent on temperature pressure and ah2o in the melt and is apparently independent of the variations in o2 over the range investigated in this study the thermal stability of biotite increases relative to that of quartz sanidine and plagioclase in water saturated melts as pressure increases from 1 2 to 2 kbar fluorite is stable to temperatures below but within 50 to 75 c of the biotite stability curve and topaz is present in the products of runs at and near the solidus for all fluid conditions investigated the 1 2 wt f in the vitrophyre results in very low solidus temperatures of 525 c for all fluid conditions studied comparison of the experimentally determined crystallization sequence of the vitrophyre with the observed crystallization sequence of the vitrophyre and of the overlying topaz rhyolites indicates that the phenocrysts in the vitrophyre and in the topaz rhyolites crystallized at a pressure 1 kb that the magma contained at least 4 wt water during initial crystallization of biotite and that the magma contained a pre eruption water content of 5 wt

a generalized exner equation for sediment mass balance 1 the advance of morphodynamics research into new areas has led to a proliferation of forms of sediment mass balance equation without a general equation it is often difficult to know what these problem specific versions of sediment mass balance leave out to address this we derive a general form of the standard exner equation for sediment mass balance that includes effects of tectonic uplift and subsidence soil formation and creep compaction and chemical precipitation and dissolution the complete equation 17 allows for independent evolution of two critical interfaces that between bedrock and sediment or soil and that between sediment and flow by eliminating terms from the general equation it is straightforward to derive mass balance equations applicable to a wide range of problems such as short term bed evolution basin evolution bedrock uplift and soil formation and carbonate precipitation and transport dropping terms makes explicit what is not being considered in a given problem and can be done by inspection or by a formal scaling analysis of the terms scaling analysis leads directly to dimensionless numbers that measure the relative importance of terms in the equation for example the relative influence of spatial versus temporal changes in sediment load on bed evolution combining scaling analysis with time averaging shows how the relative importance of terms in the equation can change with timescale for example the term representing bed evolution due to temporal change in sediment load tends to zero as timescale increases

evaluation of the micromodel an extremely small scale movable bed model the micromodel is an extremely small physical river model having a movable bed varying discharge and numerous innovations to achieve quick answers to river engineering problems in addition to its size being as small as 4 cm in channel width the vertical scale distortion up to 20 froude number exaggeration up to 3 7 and no correspondence of stage in model and prototype place the micromodel in a category by itself the writer was assigned to evaluate the micromodel s capabilities and limitations to ensure proper application a portion of this evaluation documents the deviation of the micromodel from similarity considerations used in previous movable bed models the primary basis for this evaluation is the comparison of the micromodel to the prototype the writer looked for comparisons that had 1 a reasonable calibration of the micromodel and 2 about the same river engineering structures constructed in the prototype that were tested in the micromodel and 3 a prediction by the micromodel of the a

high fluorine rhyolite an eruptive pegmatite magma at the honeycomb hills utah the honeycomb hills rhyolite dome in western utah displays chemical and mineralogical features characteristic of a rare element pegmatite magma the lavas show extreme enrichments in such trace elements as rb 1960 ppm cs 78 li 344 sn 33 be 270 and y 156 phenocrysts 10 50 by volume include sanidine or 66 70 plagioclase ab 83 92 quartz biotite approaching fluorsiderophyllite and fluortopaz as well as accessory phases common to highly differentiated granites and pegmatites including zircon thorite fluocerite columbite fergusonite and samarskite low temperatures 600 to 640 c coupled with high phenocryst and silica content might normally preclude eruption due to the extremely high viscosity of the melt however high concentrations of fluorine 2 3 could domal lavas significantly reduce viscosity and allow eruption of domal lavas even after dewatering of the mama during the initial pyroclastic phase of the eruptive cycle fractionation of phenocrysts and accessory phases for which partition coefficients have been measured is sufficient to account for most compositional gradients inferred in the preeruptive magma body although transport by a fluid phase formed a may have caused upward enrichments in li be and cs if the honeycomb hills magma had crystallized at depth it would have formed a rare element pegmatite

the origins of late stage rocks in the st austell granite a re interpretation the origin of the granite varieties present in the st austell granite body biotite granite megacrystic and non megacrystic lithium mica granite fluorite granite is discussed in the light of new petrographic chemical and experimental evidence there were essentially two stages of magmatic activity the first represented by the intrusion of several phases of biotite granite the second by a later intrusion of non megacrystic lithium mica granite which crystallized from a volatile rich residual differentiate of the biotite granite magma both intrusions suffered hydrothermal alteration which primarily involved at least two stages of exchange of components via a single aqueous fluid phase within the non megacrystic lithium mica granite topaz and lithium mica were among the first phases to break down releasing f and li to this aqueous phase f was locally fixed as fluorite removing ca derived from the host biotite granite from the fluid and giving rise to pockets of fluorite granite apart from losing ca from plagioclase the biotite granite gained li expressed as lithium rich mica resulting in an aureole of megacrystic lithium mica granite surrounding the second intrusion at least one pervasive hydrothermal system using joints and grain boundaries as fluid pathways may have been in existence water rock interaction during fluid circulation is believed to have modified considerably the composition of predominantly meteoric water to give rise to the hydrothermal fluid responsible for greisening and mineralization within its sphere of influence the alteration phenomena initiated by the proposed hydrothermal system may have culminated in the formation of the major kaolinite deposits currently worked in the area

experimental phase equilibria in the system lialsio4 sio2 h2o a petrogenetic grid for lithiumx rich pegmatites phase relations for the bulk composition lia1sis01z system lia1si04 sioz hzo have been investigated experimentally over the range 340 950 c and 0 5 6 0 kbar p hzo stability relations among eucryptite spodumene petalite b spodumene tetragonal and virgilite hexagonal have been determined for quartz saturated subsolidus conditions the result is a quantitative p t phase diagram that is applicable to quartz saturated lithium aluminosilicate assemblages in pegmatites and some volcanic rocks thermochemical data derived from these experimental results are internally consistent and in close agreement with values obtained from calorimetry under the quartz saturated conditions that prevail in pegmatites stability relations among the lithium aluminosilicates are a function of p and t and are largely independent of the nature and proportions of other phases in the chemically complex pegmatite system thus the lithium aluminosilicate phase diagram constitutes a petrogenetic grid from which p t conditions of emplacement and crystallization can be ascertained for many lithium alumino silicate bearing pegmatites

triton s plumes the dust devil hypothesis triton s plumes are narrow columns 10 kilometers in height with tails extending horizontally for distances over 100 kilometers this structure suggests that the plumes are an atmospheric rather than a surface phenomenon the closest terrestrial analogs may be dust devils which are atmospheric vortices originating in the unstable layer close to the ground since triton has such a low surface pressure extremely unstable layers could develop during the day patches of unfrosted ground near the subsolar point could act as sites for dust devil formation because they heat up relative to the surrounding nitrogen frost the resulting convection would warm the atmosphere to temperatures of 48 kelvin or higher as observed by the voyager radio science team assuming that velocity scales as the square root of temperature difference times the height of the mixed layer a velocity of 20 meters per second is derived for the strongest dust devils on triton winds of this speed could raise particles provided they are a factor of 103 to 104 less cohesive than those on earth

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

age and isotopic composition of late archean leucogranites implications for continental collision in the western superior province u pb and sm nd isotopic data are presented for leucogranites and pegmatites from the boundary zones of the english river winnipeg river and wabigoon subprovinces in the late archean superior prov

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

vapor undersaturated experiments with macusani glass h 2 o at 200 mpa and the internal differentiation of granitic pegmatites vapor undersaturated fractional crystallization experiments with macusani glass macusanite a peraluminous rhyolite obsidian at 200 mpa yield mineralogical fabrics and zonation and melt fractionation trends that closely resemble those found in zoned granitic pegmatites and other granitoids of comparable composition typically peraluminous li be ta rich deposits the zonation from the edge of charges inward is characterized by 1 fine grained sodic feldspar quartz border zones 2 a fringe of very coarse grained graphic quartz feldspar intergrowths that flair radially toward melt and terminate with nearly monophase k feldspar 3 cores of very coarse grained nearly monominerallic quartz or virgilite lialsi5o12 mica and 4 late stage fine grained albite mica intergrowths that are deposited from alkaline na rich interstitial melt at vapor saturation similar experimental products have been observed in compositionally simpler less evolved systems liquid lines of descent from initially h2o undersaturated runs are marked by a decrease in sio2 and increases in na k b p f h2o and a variety of trace lithophile cations these trends are believed to be governed by three factors 1 disequilibrium growth of feldspars quartz via metastable supersaturation 2 fractionation of melt toward sio2 depleted na rich compositions due to increases in b p and f and 3 changes in nucleation and growth rates mostly as a function of the h2o content of melt x w m in contrast experiments that are cooled below the liquidus from the field of melt aqueous vapor london et al 1988 fail to replicate pegmatitic characteristics in most respects on the basis of these and other experiments we suggest that the formation of pegmatite fabrics stems primarily from fractional crystallization in volatile rich melts and that enrichments in normally trace lithophile elements result from melt differentiation trends toward increasingly alkaline silica depleted compositions although vapor saturation at near solidus and subsolidus conditions may promote extensive recrystallization an aqueous vapor phase does not appear to be necessary for the generation of most of the salient characteristics of pegmatites