extensive felsic lavas and rheoignimbrites in the keweenawan midcontinent rift plateau volcanics minnesota petrographic and field recognition the 8 km thick sequence of plateau lavas north shore volcanic group in northeastern minnesota that was erupted during the formation of the 1 1 ga midcontinent rift system includes an unusually large proportion 10 25 of felsic flows rhyolites and icelandites individual flows are now recognized with estimated volumes up to 600 km3 and lateral extents up to 40 km some were probably originally much broader many are anomalously large compared to most silicic lava flows primary structures and textures of these essentially unmetamorphosed rocks indicate eruptive style for most of these large flows in particular the features of the basal meter or so and uppermost several meters show that some flows were emplaced as fluid lavas and others as strongly rheomorphic tuffs it may be essential in interpreting the origin of felsic flows elsewhere to examine petrographically the lowermost few decimeters and the top where the only evidence poorly to strongly welded shards may exist of the pyroclastic origin of a large otherwise lava like flow interior textures of these crystalline flows provide evidence of high temperature eruption especially in the form of abundant paramorphs of magmatic tridymite in the groundmass commonly arranged in a pilotaxitic flow structure based on structures textures field relations and geochemistry we conclude that a all the icelandites and some rhyolites were emplaced as large moderately to very fluid lava flows that spread widely while crystallizing tridymite and that b some large rhyolites which are only sparsely phyric were emplaced as pyroclastic flows subsequently remobilized as rheoignimbrites the mode of emplacement of one of the largest aphyric flows remains enigmatic vent areas or characteristics are unknown the low apparent viscosity of the erupted magmas is probably attributable to compositional factors f content high fe2 as well as to high temperatures and eruption rates estimated temperatures of about 1000 1100 c are associated with the low water content and perhaps great depth of origin of the magmas at the time of massive influx of hot matic melts from the mantle during continental rifting

on the specific polarizability of sands and sand clay mixtures abstractthe concept of specific polarizability cp being the ratio between imaginary conductivity and specific surface area can be used to represent the polarization of the mineral fluid interface per unit pore volume normalized surface area spor and to account for the control of the fluid chemistry and or mineralogy on induced polarization ip measurements we used a database of ip measurements on sands and sand clay mixtures to investigate the variation in cp as a function of clay content and or mineralogy we found an apparent variation in cp between sands and sand clay mixtures when spor was calculated using the nitrogen adsorption brunauer emmett teller bet method with clays having an apparently higher cp than sands however this variation was considerably reduced when spor was calculated using a wet state methylene blue mb method that also sensed the surface area associated with internal layers of clay minerals inaccessible with the dry state bet method furthermore the imaginary conducti

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

diffusion of ca and f in haplogranitic melt from dissolving fluorite crystals at 900 1000 c and 100 mpa 1 the diffusion rates of ca and f into haplogranitic melt were determined by concentration profiles in glasses produced by dissolving fluorite crystals into haplogranitic melt at 900 1000 c and 75 100 mpa starting products were synthesized from oxides of haplogranitic composition at two aluminosities na2o k2o al2o3 1 05 and 1 68 fluorite crystals or crystal powders were coupled with powders or solid cylinders of haplogranitic glass water was added to the runs resulting in two runs at h2o 1 20 and 1 40 wt and three runs thought to be water saturated the materials were then subjected to the conditions of interest in either a stellite cold seal apparatus or an internally heated pressure vessel electron microprobe traverses of the quenched glasses produced in these experiments revealed negative concentration gradients in ca and f away from the fluorite glass boundary these gradients are comparable to an error function solution in the first approximation for specific ca and f diffusivities dca and df respectively the ca diffusion coefficient increased from 3 36 0 19 10 9 to 2 16 0 28 10 8 cm2 s and f diffusivity increased from 1 16 0 09 10 8 to 6 59 0 62 10 8 cm2 s as temperature increased from 900 to 1000 c these diffusivities are comparable to other published melt diffusion data for the dissolution of multicomponent minerals where the diffusants move independently calcium and fluorine diffusivities increase from 2 77 0 09 10 9 to 2 16 0 28 10 8 cm2 s and from 2 27 0 10 10 8 to 6 59 0 62 10 8 cm2 s respectively with increasing water content at 1000 c likely due to melt depolimerization the large difference in the concentrations of ca c0ca and f c0f at the fluorite glass interface suggests that these two elements diffuse independently in the melt in contrast the concentration gradient for na parallels that of f suggesting complexing between these two elements

shear parallel moist convection over the tropical ocean a case study from 18 february 1993 toga coare abstract this paper describes a newly observed form of shear parallel rainbands that were observed on 18 february 1993 in tropical ocean global atmosphere coupled ocean atmosphere response experiment using the ncar eldora airborne doppler radar interesting features of these rainbands included their rapidly changing and highly cellular nature their complicated and layered kinematic structure and the effects of the rainbands on the tropical environment in their lower levels the rainbands consisted of east west elongated clusters of small convective cells aligned with the z 0 5 km shear vector strong low level convergence inflow from the north and enhanced westerly winds extended from the surface up to 5 km much of this air was vented out of the storm at midlevels exiting to the north in the 0 c stable layer at z 5 7 km this midlevel outflow fed an area of widespread stratiform precipitation lying to the north of the rainband the cold pool outflow emanating from this area of precipitation t

trapped liquid from a nepheline syenite a re evaluation of na zr f rich interstitial glass in a xenolith from tenerife canary islands abstract interstitial glass and pyroxene in a nepheline syenite described by wolff 1987 have been more precisely and accurately re analysed using a cryogenic microprobe technique the glass compositions with na2o 13 4 17 0 wt and na k al 1 81 2 26 at sio2 53 56 5 wt on a 100 normalised basis are more extreme than any known erupted magma zro2 contents of the glasses are 1 4 1 8 by weight while f ranges between 1 and 1 4 the high zr content is due to the failure of a zr silicate phase to precipitate despite predicted zircon saturation of the liquids above their probable quench temperatures partitioning of zr between pyroxene and liquid is highly variable and apparently controlled by sector zoning zr is preferentially incorporated into aegirine 001 growth sectors the glasses demonstrate the extent to which peralkaline phonolitic liquids can be fractionated in closed magma systems

on the relationship between induced polarization and surface area in metal sand and clay sand mixtures induced polarization ip measurements were conducted on saturated kaolinite iron and magnetitesand mixtures as a function of varying percentage weight of a mineral constituent 0 100 for iron and magnetite and 0 32 for kaolinite we determined the specific surface area for each mineral using nitrogen gas adsorption where the porosity of each mixture was calculated from weight loss after drying we fit a colecole model cole and cole 1941 to the electrical data obtained for the magnetite and iron mixtures in contrast the kaolinite mixtures showed a power law dependence of phase on frequency the global polarization magnitude we obtained from the cole cole modeling of the iron and magnetite mixtures displays a single nearlinear dependence on the ratio of surface area to pore volume sp calculated for the mixtures a similar relationship is found using a local measure of polarization imaginary conductivity at 1 hz for the clay sand mixtures the sp appears to be a critical parameter for determining ip in both metallic and clay containing soils this result is not easily reconciled with traditional models of induced polarization

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

badrinath gangotri plutons garhwal india petrological and geochemical evidence for fractionation processes in a high himalayan leucogranite the gangotri leucogranite is the western end of the badrinath granite one of the largest bodies of the high himalayan leucogranite belt hhl it is a typical fine grained tourmaline muscovite biotite leucogranite the petrography shows a lack of restitic phases the inferred crystallization sequence is characterized by the early appearance of plagioclase quartz and biotite and by the late crystallization of the k feldspar this suggests that in spite of being of near minimum melt composition the granite probably had long crystallization or melting interval in agreement with previous experimental studies tourmaline and muscovite have a mainly magmatic origin even though the major element composition is homogeneous there are several geochemical trends when cao decreases there is an increase in na2o rb sn u b f and a decrease in k2o fe2o3 tio2 sr ba zr ree th which are best explained by a fractionation process with early crystallizing phases experimental solubility models for zircon and monazite in felsic melt support a magmatic origin for these two accessory phases as well rb sr isotope data show this granite to have like other hhl heterogeneous isotopic values for sr initial 87sr 86sr ratios calculated at 20 ma range between 0 765 and 0 785 therefore no mixing i e no convection occurred between the different batches of magma in contrast 18o data show little variation 13 04 0 25 implying a source with homogeneous 18o values differences in timing between fluid infiltration and the onset of melting related to differences in temperature of the source could explain why source homogenization occurred for the gangotri and not for the manaslu granite the use of experimental results for solubility and the position of the accessory minerals during melting predict a low viscosity for the melt during its extraction this in turn explains the lack of restitic phases major and accessory in the granite as well as some field features lensoid shape pronounced magmatic layering based on the petrographic and isotopic studies it is suggested that the mechanism of ascent was not diapiric but rather that the melt ascended along several fractures and the level of emplacement was partialy controlled by the density contrast between the melt and host rocks

some aspects of the effect of surface friction on flows over mountains the effect of surface friction on flow over mountains in stratified fluids is investigated using a two dimensional version of the naval research laboratory s non hydrostatic coupled ocean atmosphere mesoscale prediction system coamps without surface friction flow over a mountain attains a maximum speed at the surface on the lee slope with surface friction the flow speed vanishes at the surface and reaches a maximum near the top of the boundary layer bl corresponding to this wind distribution is a shallow layer of very large vertical wind shear beneath the jet maximum and a weaker but deeper sheared layer elsewhere this strong shear generates maximum turbulent kinetic energy tke at the jet maximum region meanwhile the buoyancy effect associated with the mountain gravity wave inhibits the production of the tke above the jet maximum region the combined effects of shear and buoyancy lead to a very shallow bl on the lee slope in general surface friction reduces the amplitude of mountain gravity waves comparison of the flow fields with the outline of the bl height indicates that flow characteristics correspond closely to the distribution of the bl height it is hypothesized that the reduction in mountain wave amplitude in the presence of surface friction is due to the reduction in the slope of the bl height as compared to the terrain height for narrower and or higher mountains the bl height exhibits a secondary peak on the lee side that further modifies the wave simulations using the bl height as a solid mountain without surface friction confirm that characteristics of flow over the mountain are associated with the distribution of bl height rather than the terrain height field as the non dimensional mountain height increases the magnitude of the effect of surface friction decreases due to decreasing bl depth on the lee side with the result that the bl height profile becomes closer to the terrain height field the effect of surface friction on asymmetric mountains is also investigated without surface friction the pressure drag shows distinctive reduction with a secondary peak on the downstream side but the effect is less when the secondary peak is on the upstream side with surface friction all three mountains have similar pressure drag corresponding to their similar bl height profiles copyright 2003 royal meteorological society

vertical structures of precipitation in cyclones crossing the oregon cascades abstract the vertical structure of radar echoes in extratropical cyclones moving over the oregon cascade mountains from the pacific ocean indicates characteristic precipitation processes in three basic storm sectors in the early sector of a cyclone a leading edge echo lee appears aloft and descends toward the surface updraft cells inferred from the vertically pointing doppler radial velocity are often absent or weak in the middle sector the radar echo consists of a thick vertically continuous layer extending from the mountainside up to a height of approximately 5 6 km that lasts for several hours when the middle sector passes over the windward slope of the cascades the vertical structure of the precipitation exhibits a double maximum echo dme one maximum is associated with the radar reflectivity bright band the second reflectivity maximum is located approximately 1 2 5 km above the bright band the secondary reflectivity maximum aloft does not appear until the middle sector passes over the wi

the response of glaciers to intrinsic climate variability observations and models of late holocene variations in the pacific northwest discriminating between glacier variations due to natural climate variability and those due to true climate change is crucial for the interpretation and attribution of past glacier changes and for the expectations of future changes we explore this issue for the well documented glaciers of mount baker in the cascades mountains of washington state usa using glacier histories glacier modeling weather data and numerical weather model output we find that natural variability alone is capable of producing kilometer scale excursions in glacier length on multi decadal and centennial timescales such changes are similar in magnitude to those attributed to a global little ice age the null hypothesis that no climate change is required to explain the glacier fluctuations in this setting cannot be rejected these results for mount baker glaciers are also consistent with an earlier study analyzing individual glaciers in scandinavia and the alps the principle that long timescale fluctuations of glacier length can be driven by short timescale fluctuations in climate reflects a robust and fundamental property of stochastically forced physical systems with memory it is very likely that this principle also applies to other alpine glaciers and that it therefore complicates interpretations of the relationship between glacier and climate history however the amplitude and timescale of the length fluctuations depends on the details of the particular glacier geometry and climatic setting and this remains largely unevaluated for most glaciers

diffusion in magmas at depth in the earth the effects of pressure and dissolved h2o abstract experimental data on cation diffusion in silicate melts and glasses at atmospheric pressure cannot be quantitatively applied to diffusion in magmas at depth because pressure and dissolved h2o have significant effects diffusivities of ca and cs in soda lime aluminosilicate melt are reduced by roughly an order of magnitude as pressure increases from 1 to 30 kbar at 1100 c in the case of calcium the pressure effect is smaller at higher temperatures the influence of dissolved h2o is opposite to and for some ions far more important than that of pressure at 700 c cs diffusion in granitic obsidian is enhanced by four orders of magnitude by the addition of 6 wt h2o and ca diffusivity increases by 2 5 orders of magnitude sodium diffusion on the other hand is relatively immune to changes in h2o content the retarding effect of pressure on diffusion in deep seated magmas is largely compensated by higher magmatic temperatures such that overall depth effects on diffusion are of secondary importance diffusion rates in mantle melts are probably well approximated by 1 atm near liquidus values diffusion rates in crustal magmas however are extremely sensitive to h2o content so that models of rate controlled processes in hydrous magmas may be grossly in error if 1 atm diffusivity values are used

two dimensional idealized simulations of the impact of multiple windward ridges on orographic precipitation abstract this paper presents two dimensional 2d idealized simulations at 1 km grid spacing using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in order to illustrate how a series of ridges along a broad windward slope can impact the precipitation distribution and simulated microphysics the number of windward ridges for a 2000 m mountain of 50 km half width is varied from 0 to 16 over a 150 km distance using different stratifications freezing levels uniform ambient flows and ridge amplitudes a few 200 400 m windward ridges can enhance the precipitation locally over each ridge crest by a factor of 2 3 meanwhile a series of 8 16 ridges that are 200 400 m in height can increase the net precipitation averaged over the windward slope by 10 35 this average precipitation enhancement is maximized when the ridge spacing is relatively small 20 km since there is less time for subsidence drying within the valleys and the m

assessing the impact of the tropopause on mountain waves and orographic precipitation using linear theory and numerical simulations abstractthe partial reflection of mountain waves at the tropopause has been studied extensively for its contribution to downslope windstorms but its impact on orographic precipitation has not been addressed here linear theory and numerical simulations are used to investigate how the tropopause affects the vertical structure of mountain waves and in turn orographic precipitation relative to the no tropopause case wave induced ascent above the windward slope of a two dimensional ridge is found to be enhanced or diminished depending on the ratio of the tropopause height to the vertical wavelength of the mountain waves defined here as the nondimensional tropopause height in idealized simulations of flow over both two dimensional and three dimensional ridges variations in are found to modulate the precipitation rate by roughly a factor of 2 under typical atmospheric conditions the sensitivity of precipitation to is related primarily to the depth of windward ascent but also to the location and stren

experimental study of titanite fluorite equilibria in the a type mount scott granite implications for assessing f contents of felsic magma titanite and fluorite stability in melt were experimentally evaluated at 850 c 200 mpa f o 2 nno nickel nickel oxide oxygen buffer as functions of total f and h 2 o content experiments employed the metaluminous mount scott granite of the wichita igneous province oklahoma over a large range of added h 2 o 1 7 wt melts containing 1 wt f precipitated fluorite without titanite in addition at high f 1 2 wt plagioclase and hornblende reacted to form biotite thus an increase in f during crystallization may explain the observed higher modal abundance of plagioclase and hornblende in titanite dominant samples vs higher modal biotite in fluorite dominant samples within the mount scott granite pluton coexistence of magmatic titanite and fluorite in the mount scott granite pluton implies f m of 1 wt at the point in its crystallization history where these minerals coprecipitated we suggest that the presence of primary fluorite within high temperature shallowly emplaced moderate f o 2 subaluminous felsic rocks indicates high magmatic fluorine whereas titanite without fluorite in such rocks indicates low initial fluorine

solubility of fluorite in haplogranitic melt of variable alkalis and alumina content at 800 1000 c and 100 mpa 1 to study the behavior of fluorite in sio2 al2o3 na2o k2o h2o melts we conducted both crystallization and dissolution experiments in the first case fluorite crystallized from melts enriched in ca relative to f in the second case ground fluorite 10 m was partially dissolved into melts of initially f free or f doped glass experiments were conducted at 800 1000 c and 100 mpa for 7 to 240 hours using a series of finely ground subaluminous and peralkaline haplogranitic glasses electron microprobe emp analysis of the run products glass crystals documented increasing fluorite solubility with melt alkalinity these molar relationships can be described by cf 2 1 3 asi 2 3 at 900 c and cf 2 cca 2 1 asi 3 8 at 1000 c where asi is the aluminum saturation index measured in experimental glasses as al na k 2ca cf 2 is one half the molar concentration of f and cca is the mol of ca in the glass fluorite solubility may be defined as either cf 2 cca or both solubilities at 800 900 and 1000 c for the melts with asi between 0 58 and 0 59 approach log linear with 104 t k slope 0 45 the joint effect of f and temperature on fluorite solubility is significant solubility rises from 0 28 mol at 800 c 4 96 mol doped f to 0 99 mol at 900 c 2 17 mol doped f solubilities at 800 850 and 900 c for the melts with the same initial f contents 4 96 mol approach log linear with 104 t k slope 0 33

an observational and modeling study of the interaction of low level southwesterly flow with the olympic mountains during coast iop 4 abstract this paper presents an observational and modeling study of the three dimensional flow and precipitation around the olympic mountains of northwest washington state for a case of relatively steady south southwesterly flow this study utilized data from coast iop 4 the fourth intensive observing period during the coastal observation and simulation with topography field experiment that took place during 9 10 december 1993 one of the most important data sources was the noaa p 3 aircraft which provided flight level data reflectivity and doppler winds as it flew around the olympics features that were mapped successfully with the noaa p 3 included flow splitting around the windward pressure ridge strong southeasterlies to approximately 25 m s 1 northeast of the olympics caused by downgradient acceleration into the lee trough the rapid transition from strong southeasterlies to lighter easterlies 5 10 m s 1 in the strait of juan de fuca strong downslope flow and a hydraulic jump like transiti

multiscale mountain waves influencing a major orographic precipitation event abstract this study combines high resolution mesoscale model simulations and comprehensive airborne doppler radar observations to identify kinematic structures influencing the production and mesoscale distribution of precipitation and microphysical processes during a period of heavy prefrontal orographic rainfall over the cascade mountains of oregon on 13 14 december 2001 during the second phase of the improvement of microphysical parameterization through observational verification experiment improve 2 field program airborne based radar detection of precipitation from well upstream of the cascades to the lee allows a depiction of terrain induced wave motions in unprecedented detail two distinct scales of mesoscale wave like air motions are identified 1 a vertically propagating mountain wave anchored to the cascade crest associated with strong midlevel zonal i e cross barrier flow and 2 smaller scale 20 km horizontal wavelength undulations over the windward foothills triggered by interaction

an intercomparison of model predicted wave breaking for the 11 january 1972 boulder windstorm abstract two dimensional simulations of the 11 january 1972 boulder colorado windstorm obtained from 11 diverse nonhydrostatic models are intercompared with special emphasis on the turbulent breakdown of topographically forced gravity waves as part of the preparation for the mesoscale alpine programme field phase the sounding used to initialize the models is more representative of the actual lower stratosphere than those applied in previous simulations upper level breaking is predicted by all models in comparable horizontal locations and vertical layers which suggests that gravity wave breaking may be quite predictable in some circumstances characteristics of the breaking include the following pronounced turbulence in the 13 16 km and 18 20 km layers positioned beneath a critical level near 21 km a well defined upstream tilt with height and enhancement of upper level breaking superpositioned above the low level hydraulic jump sensitivity experiments indicate that the structure of the wave bre

the equivalence of enthalpy and shear stress relaxation in rhyolitic obsidians and quantification of the liquid glass transition in volcanic processes abstract the relaxation of enthalpy and shear stress has been investigated for six silicic volcanic obsidians calc alkaline rhyolitic obsidians from ben lomond dome new zealand erevan dry fountain armenia and little glass butte usa peralkaline obsidians from mayor island new zealand and eburru kenya and a macusanite obsidian from se peru the temperature dependences of enthalpy and shear stress relaxation are obtained from the dependence of the calorimetric heat capacity peak temperature on heating rate and the dependence of shear viscosity on temperature respectively both processes enthalpy relaxation and shear stress relaxation can be approximated to be arrhenian in the investigated temperature ranges relevant to volcanological processes activation energies derived for enthalpy and shear stress relaxation for each sample are equal this equality permits the calculation of viscosity at the glass transition as a function of cooling rate of a volcanic melt the relationship between viscosity at the glass transition and the cooling rate is given by log10 s at tg k log10 q where s the shear viscosity at the glass transition q is the cooling rate in c s 1 and k is a constant the six melt compositions investigated here exhibit a value of k 10 49 0 31 for the modeling of volcanic processes this equation allows the prediction of the viscosity at the glass transition temperature for a given value of cooling rate taken together with the maxwell relation an effective relaxation time can be obtained for the cooling rate prediction of the glass transition temperature permits the allotment of temperature ranges for the liquid and glassy segments of the cooling history of the volcanic melt and thus for the correct assignment of glassy and liquid values of the derivative thermodynamic properties such as expansivity and heat capacity in thermodynamic modeling of late stage volcanic processes

acidity salinity diagrams application to greisen and porphyry deposits to a first approximation alteration minerals in greisen and related fluorine rich porphyry deposits lie in the system k 2 o al 2 o 3 sio 2 h 2 o f 2 o sub 1 equilibria in this model system can be depicted on quartz and fluid saturated chemical potential diagrams whose axes are mu hf acidity where mu hf mu hcl mu sub fcl sub 1 and mu kf salinity where mu kf mu nacl mu sub kna sub 1 mu sub fcl sub 1 advantages of this approach are that it reflects the fact that the anion f unlike cl is incorporated in greisen minerals mainly topaz fluorite and micas and that mineral stabilities can be correlated with possible ore forming processes the most important of these processes is probably vapor phase separation from an aqueous brine or magma first or second boiling fluid inclusion studies have shown that boiling occurs in all porphyry and many but not all greisen deposits vapor phase separation from a magma pneumatolysis must similarly be responsible for the formation of greisenlike mineral assemblages in miarolitic topaz rhyolite lava flows and is presumably also responsible for the formation of gem pockets in more deeply seated pegmatites and granites the result of boiling is an increase in mu hf and a decrease in mu kf in the vapor phase and the opposite in the residual brine or magma in deep greisen veins the muscovite stability field is encountered between the k feldspar and topaz fields whereas in f rich relatively shallow porphyry deposits such as henderson colorado boiling causes aqueous fluids to pass directly from the k feldspar ore zone to the overlying topaz magnetite zone muscovite or f bearing mn fe garnet is only encountered farther out as the fluids are condensed neutralized and diluted by cooler meteoric waters when ca fe mn be w o 2 s 2 and co 2 are added to the greisen model system scheelite is shown to transform to wolframite with increasing mu hf and beryl to phenakite with increasing mu hf or mu kf biotite transforms to magnetite hematite siderite pyrite chlorite or fayalite beyond the k feldspar field its stability is enhanced by high mu hf and chlorite cordierite or mn fe garnet transform to an mn fe carbonate oxide or sulfide or biotite beyond the al silicate field the ca content of plagioclase coexisting with fluorite decreases with an increase in either mu hf or mu kf and thus provides an indicator of total fluorine in both acid and neutral species

turbulence as a mechanism for orographic precipitation enhancement this study examines the dynamical and microphysical mechanisms that enhance precipitation during the passage of winter midlatitude systems over mountain ranges the study uses data obtained over the oregon cascade mountains during the improvement of microphysical parameterization through observational verification experiment 2 improve 2 november december 2001 and over the alps in the mesoscale alpine program map september november 1999 polarimetric scanning and vertically pointing s band doppler radar data suggest that turbulence contributed to the orographic enhancement of the precipitation associated with fronts passing over the mountain barriers cells of strong upward air motion 2ms 1 occurred in a layer just above the melting layer while the frontal precipitation systems passed over the mountain ranges upstream flow appeared to be generally stable except for some weak conditional instability at low levels in the two improve 2 cases the cells occurred in a layer of strong shear at the top of a low level layer of apparently retarded or blocked flow shown by doppler radial velocity data the shear apparently provided a favorable environment for the turbulent cells to develop the updraft cells appeared at the times and locations where the shear was strongest 10 m s 1 km 1 the richardson number was slightly less than 0 25 at the level where the cells were observed suggesting shear generated turbulence could have been the origin of the updraft cells another possibility is that the rough mountainous lower boundary could have triggered buoyancy oscillations within the stable sheared flow the existence of turbulent cells made possible a precipitation growth mechanism that would not have been present in a laminar upslope flow the turbulent cells appeared to facilitate the rapid growth and fallout of condensate generated over the lower windward slopes of the mountains in a laminar flow over terrain upward motions would be unlikely to produce liquid water contents adequate to increase the density and hence the fall speed of precipitating ice particles by riming the turbulent updraft cells apparently create pockets of higher values of liquid water content embedded in the widespread frontal cloud system and snow particles falling from the parent cloud systems can then rapidly rime within the cells and fall out observations by polarimetric radar and direct aircraft sampling indicate the occurrence of rimed aggregate snowflakes and or graupel in the turbulent layer inasmuch as the shear layer is the consequence of retardation or blocking of the low level crossbarrier flow and the turbulence is a response to the shear the shear induced cellularity is an indirect response of the flow to the topography the turbulence embodied in this orographically induced cellularity allows a quick response of the precipitation fallout to the orography since aggregation and riming of ice particles in the turbulent layer produce heavier more rapidly falling precipitation particles without the turbulent cells condensate would more likely be advected farther up and perhaps even over the mountain range small scale cellularity has traditionally been associated with the release of buoyant instability by the upslope flow our results suggest that cellularity may be achieved even if buoyant instability is weak or nonexistent so that even a stable flow has the capacity to form cells that will enhance the precipitation fallout over the windward slopes

partitioning of cl and f between fluid and hydrous phonolitic melt of mt vesuvius at 850 1000 c and 200 mpa abstract the solubilities of cl and or f bearing fluids in phonolitic melts of vesuvius volcano have been determined experimentally at temperatures of 845 865 c and 1000 c and pressure of 200 mpa at 845 865 c the maximum cl concentration in the melt m cl coexisting with cl rich 35 5 wt fl cl and f free fluid is about 0 5 wt an addition of f to the system increases the cl content of the melt up to 0 7 wt at 39 wt cl and 13 wt f in the fluid s the relationship between m cl and fl cl indicates that low density vapor and dense brine phases might have coexisted in some experiments the relationship between m cl and fl cl at 1000 c is similar to that determined at 845 865 c implying that variations of temperature in the range 850 1000 c have no significant effect on the partitioning of cl between fluid and phonolitic melt the concentration of f in phonolitic melt coexisting with f rich fluid s reaches at least 0 9 wt at 845 865 c and 1 3 wt at 1000 c the comparison of data from experiments conducted in au and pt capsules indicates that f may react with au which influences the quality of the experimental results the partition coefficients of f between bulk fluid and melt fl m d f are higher than 1 in all experiments indicating that fluorine is preferentially incorporated into the fluid phase in phonolitic systems in contrast to fl m d f values determined in rhyolitic systems the influence of cl on fl m d f is not detectable at the conditions of our experiments the experimental data imply that mt somma vesuvius phonolitic magmas from the eruptions between a d 79 and a d 1944 may have coexisted with cl rich and f rich fluid phase s prior to eruption

kelvin helmholtz waves in extratropical cyclones passing over mountain ranges kelvin helmholtz billows with horizontal scales of 3 4 km have been observed in midlatitude cyclones moving over the italian alps and the oregon cascades when the atmosphere was mostly statically stable with high amounts of shear and ri 0 25 in one case data from a mobile radar located within a windward facing valley documented a layer in which the shear between down valley flow below 1 2 km and strong upslope cross barrier flow above was large several episodes of kelvin helmholtz waves were observed within the shear layer the occurrence of the waves appears to be related to the strength of the shear when the shear attained large values an episode of billows occurred followed by a sharp decrease in the shear the occurrence of large values of shear and kelvin helmholtz billows over two different mountain ranges suggests that they may be important features occurring when extratropical cyclones with statically stable flow pass over mountain ranges

upstream orographic enhancement of a narrow cold frontal rainband approaching the andes abstractupstream orographic enhancement of the rainfall from an extratropical cyclone approaching the andes from the pacific is investigated using the weather research and forecasting wrf model and the tropical rainfall measuring mission trmm precipitation radar the main precipitation from the cyclone over central and coastal chile fell when a narrow cold frontal rainband ncfr interacted with a midlevel layer cloud deck formed from the orographically induced ascent of the prefrontal atmospheric river upstream of the andes model output indicates that low level convergence enhanced the ncfr where it met low level blocked flow near the mountains the ncfr had stronger updrafts with decreasing distance from the mountains and the ncfr produced larger rain accumulations over the land region upstream of the andes than over the open ocean a sensitivity simulation with a 50 reduction in the andes topography for comparison to various west coast mountain ranges of north america demonstrates that the e

rheological properties of basaltic lavas at sub liquidus temperatures laboratory and field measurements on lavas from mount etna models of many magmatic processes require accurate data on the rheological properties of lava at sub liquidus temperatures laboratory measurements of the rheological properties of basalts erupted on mount etna in 1983 were made at various crystal concentrations in a specially designed furnace using a haake rotovisco viscometer attached to a spindle designed to eliminate slippage at the melt spindle interface measurements were made at strain rates between 0 3 and 5 s 1 over the range of eruption temperatures on mount etna 1084 1125 c at temperatures above 1120 c the 1983 lava behaves as a newtonian fluid at lower temperatures the lava is a thixotropic pseudoplastic fluid with a maximum yield strength of 78 pa at a temperature of 1087 c in view of its low yield strength over this temperature range the theological behaviour of the lava approximates to that of a power law fluid apparent viscosities at unit shear strain rates increase from 150 pa s at 1125 c to 3000 pa s at 1084 c unit strain rate apparent viscosities measured in the field using a rotating vane viscometer range from 1385 pa s to 1630 pa s these values are in close agreement with those measured at the same temperature in the laboratory and with those calculated theoretically from the physico chemical properties of the lava

cross barrier flow during orographic precipitation events results from map and improve abstract ground based and airborne doppler radar data collected during passage of frontal rainstorms over the european alps and cascade mountains of oregon are found to exhibit characteristic cross barrier flow and precipitation patterns a stably stratified layer of blocked or partially blocked low momentum flow below mountain crest level is separated from strong cross barrier flow aloft by a concentrated layer of vertical wind shear this shear layer slopes upward toward the mountain crest and persists for several hours as the storm passes over the mountain range this pattern is remarkably similar from case to case and from one mountain range to the other the orographically enhanced precipitation in these cases exhibits stratiform structure marked by a radar bright band which often drops to a lower height indicating locally cooler conditions immediately adjacent to the windward mountain slopes a terrain induced gravity wave produces strong downslope flow and spillover of precipitation onto the

deep orographic storms over the sierra nevada part i thermodynamic and kinematic structure abstract two deep orographic storms were documented over the sierra nevada with an instrumented aircraft and with a single doppler radar in both storms the geographic winds were normal to the barrier with speeds of 15 to 30 m s 1 because of blocking the measured wind component normal to the barrier was substantially less than the geostrophic wind component especially below barrier crest height in the very stable case a barrier jet was present below 1 km agl and had peak winds of 28 m s 1 in the slightly stable case a barrier jet was present at 1 km agl and had peak winds of 21 m s 1 other than the speed and altitude of the barrier jet the other measured characteristics of the airflow and thermal fields were rather similar between these two storms the forced ascent of stable air plus the diabatic process of melting caused the isotherms to descend near the barrier the barrier jet can be expressed by the thermal wind relation and is therefore a quasi geostrophic phenomenon the derived vertical

experimental generation of volcanic pseudotachylytes constraining rheology volcanic systems are highly dynamic environments that comprise rocks and magmas which in the process of strain localisation e g in catastrophic flank collapse or dome building events are candidate materials for the occurrence of frictional melting and the formation of pseudotachylytes we evaluate the frictional behaviour of a plagioclase two pyroxene and glass bearing andesite and introduce an approach to constrain the rheology of frictional melts frictional slip at a rate of 1 3 m s under an axial stress of 1 5 mpa induces heating at a rate approximating 130 c per meter of slip and frictional melting of the andesite occurs at 1000 c which corresponds to a peak in shear stress with continuing displacement the shear stress decreases by 25 from the peak strength and stabilises while the temperature equilibrates to 1230 1290 c the shear stress for the system is congruent with a non arrhenian temperature dependent frictional melt rheology exhibiting a non newtonian viscosity evolving from approximately 104 2 to 103 4 pa s post experiment analysis show a gradation from 1 the host rock to 2 an extraordinary zone of unmelted yet viscously deformed material to 3 a thin outer region of chemically heterogeneous protomelts and to 4 an inner region of chemically homogeneous frictionally generated modified melt in the core of the slip zone we discuss the role and identification of frictional melting in volcanic systems and the implication of viscous remobilisation of magmatic plugs during frictional slip of glass bearing volcanic materials

the a type mount scott granite sheet importance of crystal magma traps the presence of rapakivi feldspar and of distinctive porphyritic texture of mount scott granite indicates a period of crystallization prior to final emplacement beneath an extensive penecontemporaneous rhyolite volcanic pile final crystallization conditions are interpreted to have been 50 mpa at depths 1 4 km based on stratigraphic constraints however geobarometry based on the al content of amphibole phenocrysts and comparison of granite compositions with phase relations in the sio2 naalsi3o8 kalsi3o8 ternary system both yield pressure estimates of 200 mpa these pressure estimates are interpreted as plumbing the depth of a temporary storage chamber at 7 8 km this depth coincides in this case both with the probable proterozoic basement cover contact and with the calculated brittle ductile transition at time of ascent of mount scott magma although rising magma that fed the preceeding voluminous carlton rhyolite apparently rose unimpeded past these horizontal anisotropies rising magma that formed mount scott granite temporarily paused at this depth based on magmastatic calculations we suggest that horizontal anisotropies e g brittle ductile transition become crustal magma traps where the magma driving pressure exceeds the lithostatic load when the anisotropy is encountered during rifting initial large influxes of magma may proceed passed crustal anisotropies but have the effect of increasing the relative magma driving pressure through reducing horizontal stress thus magma driving pressure may eventually exceed the lithostatic load at the depth of the brittle ductile transition thereby activating this crustal magma trap ponding of magma at the brittle ductile transition chokes the eruption such a pause in magma supply rate may permit a return to initial stress conditions and deactivate the crustal magma trap once again magma will rise to the surface initiating a new magmatic cycle

electrical properties and its correlation to the petrology of the upper yangtze organic shales abstractshale gas is a particularly important research target on chinese energy resources especially in the upper yangtze region complex topography and geologic conditions challenge seismic exploration of shale gas in this area and ground based electromagnetic em methods are used to aid recognition of the best reservoirs however the electrical properties of organic shale epos and its correlation to shale gas petrology remain poorly understood we studied epos and their correlation to shale petrology by measuring and analyzing the petrochemical features and complex impedance of rock samples from the silurian longmaxi and cambrian niutitang formations in the upper yangtze southwest china our study indicates that the organic shale in the upper yangtze features low resistivity and high polarizability in terms of a high negative phase but no obvious low resistivity is observed among shaly sandstone and shales with lower and higher total organic carbon pyrite and quartz contents in the organic shal

halogens in volcanic systems the transport degassing and atmospheric release of halogens from active volcanism on earth have been the focus of increasing interest over the last few decades and have recently been the subject of the 1st workshop on halogens in volcanic systems and their environmental impacts that was held in december of 2007 at yosemite lodge in yosemite national park california as an introduction to this chemical geology special issue collecting contributions from many of the participants at the workshop we review here recent advances in this field including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems we discuss previous research on several aspects of halogen geochemistry including halogen abundances in the mantle and magmas on earth the effects of halogens on phase equilibria and melt viscosities their partitioning between melt and fluid phase s upon decompression cooling and crystallisation of magmas in the earth s crust and their final atmospheric release as volcanic gases the role of halogens in the genesis of hydrothermal systems and in the transport of ore forming metals is also reviewed and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere and their consequent impacts in spite of these recent advancements our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary and the key questions that require answers from future research are summarised in our conclusions

orographic modification of convection and flow kinematics by the oregon coast range and cascades during improve 2 abstract this paper describes the kinematic and precipitation evolution accompanying the passage of a cold baroclinic trough over the central oregon coast range and cascades during 4 5 december 2001 of the second improvement of microphysical parameterization through observational verification experiment improve 2 field project in contrast to previously documented improve 2 cases the 4 5 december event featured weaker cross barrier winds 15 20 m s 1 weaker moist static stability nm 0 006 s 1 and convective cells that preferentially intensified over oregon s modest coastal mountain range these cells propagated eastward and became embedded within the larger orographic precipitation shield over the windward slopes of the cascades the weather research and forecasting model version 2 2 at 1 33 km grid spacing was able to accurately replicate the observed evolution of the precipitation across western oregon as a result of the convective cell development the precipitation enhancement over the co

observations and impacts of upstream blocking during a widespread orographic precipitation event a unique combination of airborne and ground based doppler radar observations stretching continuously from the alps south to the mediterranean sea is assembled to document profoundly blocked airflow and associated modification of precipitation processes upstream of the alps during intensive observing period 8 of the mesoscale alpine programme this diversion of incident southerly low level winds in advance of a deep baroclinic trough served to reduce markedly the transport of warm moist mediterranean air toward the steep alpine slopes heavy rains forecast in this flood prone region thus failed to materialize with lighter though protracted stratiform precipitation extending over the comparatively flat reaches of the adjacent po valley release of convective instability did occur but was displaced well south of the alps over the coastal apennine mountain chain and adjacent waters of the mediterranean sea influences on a variety of scales that evidently led to development of this blocked flow are examined and multiple expressions of upstream blocking are identified these range from pervasive down valley flows observed within multiple deep alpine river drainages to a larger scale cool easterly low level flow channelled alongside the curving south face of the alps which was ultimately extruded southward over the mediterranean observed thermodynamic profiles in these contrasting regimes are presented and related to the observed precipitation structure copyright 2003 royal meteorological society

chemical diffusion of fluorine in melts in the system na2oal2o3sio2 the volatilization of fluorine from three melts in the system na2oal2o3sio2 has been investigated at 1 atm pressure and 1200 1400 c the melts chosen have base compositions corresponding to albite jadeite and a peraluminous melt with 75 mole sio2 melt spheres were suspended from platinum loops in a vertical tube furnace in a flow of oxygen gas then quenched sectioned and analysed by electron microprobe the microprobe scans indicate that transport of fluorine to the melt vapor interface is by binary concentration independent interdiffusion of fluorine and oxygen fo interdiffusivity increases in the order albite peraluminous jadeite there is no simple reciprocal relationship between fo interdiffusivity and melt viscosity comparison with data on high pressure interdiffusivity of fluorine and oxygen in jadeite melt indicates that fo interdiffusivity increases with pressure from 0 001 to 10 kbar while the activation energy remains unchanged fluorine chemical diffusivity in albite melt is substantially lower than h2o chemical diffusivity in obsidian melts suggesting that different diffusive mechanisms are responsible for the transport of f and h2o in igneous melts fluorine diffuses in albite melt via an anionic exchange with oxygen whereas water probably diffuses in obsidian melt via an alkali exchange mechanism

boundary layer turbulence and orographic precipitation growth in cold clouds evidence from profiling airborne radar data abstractairborne vertically pointing doppler radar data collected in 10 winter storms over the medicine bow range in wyoming are used to examine the importance of boundary layer bl turbulence for orographic precipitation growth in all 10 cases the cloud base temperature was below 0 c and the bulk froude number was more than 1 0 implying little or no blocking of the flow by the mountain barrier seven of the 10 storms sampled were postfrontal with weak static stability and relatively shallow cloud tops doppler vertical velocity transects depict an approximately 1 km deep turbulent layer draped over the terrain sometimes clearly distinct from the stratified flow in the free troposphere aloft where vertical motion is largely controlled by gravity wave dynamics spectral analysis of near surface doppler vertical velocity data in terrain following coordinates reveals an inertial subrange with decreasing power with height toward the bl top the composite of radar data profiles from the 10 flights is ana

apatite dissolution into peraluminous haplogranitic melts an experimental study of solubilities and mechanisms apatite ap dissolution and solubility in the peraluminous haplogranite system were investigated in three sets of experiments at 750 c and 200 mpa ph2o as functions of ap grain size abundance melt ap ratio and melt asi alumina saturation index mol al2o3 na2o k2o cao between an asi of 1 1 1 metaluminous to mildly peraluminous the solubility of ap as measured by p2o5 in the melt is low 0 1 wt p2o5 which agrees with previous work in equilibrium runs with more strongly peraluminous compositions however ap solubility increases linearly with asi to p2o5 0 63 wt in melt at asi 1 3 and can be denned by a simple equation p2o5 3 4 3 1 asi r 0 833 which agrees within error with previous calculations reported in the literature in experiments where ap grains are sparce and widely separated i e simulating ap distribution in an ap bearing peraluminous protolith undergoing anatexis the dissolution of ap involves transient disequilibrium that promotes higher solubility of p2o5 up to nearly six times the equilibrium values adjacent to ap at a given bulk asi of melt and this increases the al si of melt in the ap dissolution aureole the approach to equilibrium between ap and melt is hastened by increasing the ap melt ratio within the local melt pool e g the capsule or by decreasing ap grain size for a similar melt ap ratio diffusivity calculations using inverse error function methods for the normal diffusion of p and ca yield dp 10 11 cm2 s and dca 10 10 cm2 s confirming prior results that diffusion of p away from ap surfaces is the rate limiting factor in ap dissolution these results combined with previous work at higher temperatures but on similar hydrous melts yield an activation energy e for p diffusion of 16 5 kcal mol and a frequency factor d0 of 1 4 10 3 cm2 s phosphorus diffusion through the melt is accompanied by uphill diffusion of al resulting in an increase of up to 2 wt al2o3 in melt near the ap within the ap dissolution aureole melt contains one additional al cation for every p cation i e al p 1 1 which is suggestive of an associated alpo4 complex the exchange reaction in melt is represented by alpsi 1 in which 2 to4 clusters are created in the place of 1 this exchange should be accompanied by discernable changes in melt properties e g density molar volume viscosity the results have applications to equilibrium and local disequilibrium effects during anatexis of apbearing metapelites and to the saturation limits of ap during crystallization of peraluminous magmas the dissolution of flux bearing minerals such as ap e g those containing p b or f may influence the stability and solubility of other trace element bearing minerals during anatexis of metapelites texture e g grain size and distribution and spacial relationship to other minerals plays an important role in reaction kinetics and at least temporarily in mineral solubilities the disequilibrium behavior of accessory minerals has critical consequences for ree modelling of granites

kinematic and thermodynamic structures of sierra barrier jets and overrunning atmospheric rivers during a landfalling winter storm in northern california abstractthis study characterizes kinematic and thermodynamic structures of sierra barrier jets sbjs atmospheric rivers ars and their interaction over the period 14 16 february 2011 when a winter storm made landfall in northern california a suite of scanning and profiling doppler radars rawinsondes and gps receivers is used to document these structures across the central valley and up the western sierra slope to the crest along an 200 km segment of the sierra the winter storm is grouped into two episodes each having an ar that made landfall low level winds in the sbj observed during episode 1 were southeasterly and embedded in a stably stratified air mass along barrier wind speeds u340 reached maximum values of 25 30 m s 1 as low as 0 2 km msl over the central valley and as high as 1 5 km msl over the western sierra slope southwesterly winds associated with the ar overlaid the sbj along an interface that sloped upward from southwest to northeast with a southwestern extent at the western

investigation of orographic precipitation over an isolated three dimensional complex topography with a dense gauge network radar observations and upslope model abstractthis study uses a dense rain gauge network radar observations and an upslope model to document the detailed aspects of precipitation over da tun mountain dt of northern taiwan under pre

mountain volume control on deep convective rain amount during episodes of weak synoptic forcing abstractthermally driven upslope flows in mountainous areas provide favorable conditions for diurnal deep moist convection especially during episodes of weak synoptic forcing the present study inv

fluorite stability in silicic magmas recent experimental evidence is used to assess the conditions under which fluorite forms an early crystallising phase in silicic magmas fluorite solubility primarily depends on the na k al balance in the coexisting silicic melt reaching a minimum in metaluminous melts it can display reaction relationships with topaz and titanite depending on changes in melt composition during crystallisation an empirical model of fluorite stability in ca poor peralkaline rhyolite melts is derived and applied to selected rocks text f text melt left text wt right left left text na text k text al right left 2 1110 3 text t left circ c right 1 5778 right right 2 789

halogen diffusion in magmatic systems our current state of knowledge diffusion of halogens has the potential to influence petrogenetic processes in magma chambers and conduit degassing processes this contribution reviews our current state of knowledge concerning halogen diffusion and the influence of halogens on the diffusion of major elements in silicate melts the addition of halogens to silicate melts at common natural concentration levels will have little effect on the diffusion of major elements however the differences between the diffusivity of water the diffusivities of halogens and the diffusivity of sulfur are significant enough that during melt inclusion entrapment or during rapid bubble or crystal growth diffusive fractionation between water and the halogens and between halogens and sulfur are expected to occur and can influence the compositions of melt inclusions crystals and volcanic gases

enclaves from the a type granite of the megantic complex white mountain magma series clues to granite magmagenesis the subsolvus biotite hornblende granite at megantic contains mafic to leucocratic enclaves the groundmass of leucocratic enclaves is microgranitic that of mafic enclaves is meladioritic apatite is commonly acicular in the enclaves suggesting quenching of mafic magmas commingled with the granitic host mafic enclaves contain mafic clots hornblende cores biotite rims some with relic cores of vial cr rich diopsidic augite similar to phenocrysts in associated basaltic dykes the clots are interpreted to be pseudomorphs after mafic phenocrysts the enclaves also contain granitic microxenoliths xenocrysts of quartz with hornblende reaction rims partially resorbed oligoclase and perthite megacrysts and biotite xenocrysts the xenocrysts record hybridization between a mafic enclave magma and a granitic magma and or rock enclaves define mixing lines on many variation diagrams however rb sr ba zr nb y ree zn pb and f do not fit this pattern and appear to have been redistributed by residual granitic melts or exsolved volatiles the data suggest that the granite is anatectic heat being provided by crystallization of associated basalts mixing calculations suggest that as little as 5 hybridization with basalt or hawaiite can account for the sr isotopic heterogeneity of the granites

drill core based facies reconstruction of a deep marine felsic volcano hosting an active hydrothermal system pual ridge papau new guinea odp leg 193 abstract pual ridge is a deep marine felsic volcanic edifice in the eastern manus back arc basin papua new guinea with an estimated volume of 6 to 9 km 3 it is 1 1 5 km wide 20 km long and rises 500 600 m above the surrounding ocean floor the active pacmanus hydrothermal field on the crest of pual ridge at 1640 1690 m below sea level was the target of ocean drilling program leg 193 variably altered dacite lavas have been recovered from the subsurface of a low t discharge site snowcap and a high t black smoker site roman ruins reaching a maximum depth of 380 m below seafloor mbsf volcanic facies interpretation of these cores is difficult due to incomplete recovery and widespread pseudoclastic textures generated by fracturing and multi phase incomplete fluid dacite interaction however distinction of genuine volcaniclastic facies and facies with alteration related clastic appearance is important in order to define paleo seafloor positions within the volcanic stratigraphy that may be prospective for massive sulfide mineralization this has been accomplished using remnant primary characteristics indicative of transportation such as polymictic composition grading or textural evidence for differential movement of individual clasts three phases of volcanic activity can be distinguished and a proximal facies association dominated by coherent facies of dacite lavas exists below snowcap at roman ruins a medial facies association consists of lava flows with about equal proportions of coherent and volcaniclastic facies endogenous growth was an important process during lava flow emplacement and groundmass textures such as perlite flow banding and spherulites indicate that cooling rates were variable locally allowing for high temperature devitrification a tube pumice breccia unit is interpreted as the resedimented facies of a quench fragmented highly vesicular dacite lava carapace sulfide accumulations in the subsurface are restricted to roman ruins suggesting that the abundance of volcaniclastic facies favored ascent of metal bearing fluids due to the inherent high permeability evidence for mineralization at paleo seafloor positions at 110 and 195 mbsf indicate a complex interrelationship between volcanic and hydrothermal activity a facies model has been developed which may help to locate subaqueous felsic lava dominated volcanic centers and associated sulfide deposits in ancient volcano sedimentary successions

origin of the fluorine rich highly differentiated granites from the qianlishan composite plutons south china and implications for polymetallic mineralization abstract many composite granite plutons occur in south china accompanied by large scale polymetallic mineralization each composite pluton is composed of main phase granite and late stage highly differentiated granite traditionally the highly differentiated granite is thought to be residual melt of the former via fractionation and ore forming materials and fluids are from granite magma itself we propose a different model for the origin of the granites and related mineralization based on petrological and geochemical studies on the qianlishan composite plutons that host the supergiant shizhuyuan w sn bi mo deposit the main phase granite shows features of normal granites while the highly differentiated granite is characterized by f rich water deficient low f o 2 alkalinity ree tetrad effect and modified behavior of some trace elements e g very high k ba and low k rb and zr hf ratios we suggest that the parent magma of the highly differentiated granite was derived from melting of dominantly lower crustal rocks triggered by underplating of a new pulse of basaltic magmas small amounts of basaltic magmas and volatiles such as fluorine were involved in the source of the granite addition of fluorine lowered the solidus temperature and viscosity of granite magma and thus prolonged the process of magma evolution this resulted in extreme fractional crystallization and intense interaction between melt and circulating waters from country rocks forming the unusual geochemical features of the granite the high temperature circulating waters along with metamorphic fluids released from deep crustal rocks subsequently extract ore forming metals from country rocks through forming f bearing complexation forming the polymetallic deposits

on the relationship between induced polarization and surface conductivity implications for petrophysical interpretation of electrical measurements abstractpetrophysical interpretation of resistivity measurements is often hindered by the dependence of resistivity on the interconnected pore fluids and the interconnected pore surfaces induced polarization ip measurements yield parameters that are only controlled by the interconnected pore surfaces thereby offering the opportunity to constrain interpretation of resistivity measurements using a database composed of 63 sandstone and unconsolidated sediment samples covering nine independent investigations we identified a strong linear relationship between the real part of surface conductivity surf determined from multisalinity w resistivity measurements and the imaginary conductivity measured with ip at a frequency of about 1 hz we found surf l 0 042 with a coefficient of determination r2 of 0 911 and a standard deviation of l of 0 022 we found a similar relation when the normalized chargeability from debye decomposition of the frequency dependence of the ip response is used in

the overamplification of gravity waves in numerical solutions to flow over topography abstract the tendency of high resolution numerical weather prediction nwp models to overpredict the strength of vertically propagating mountain waves is explored discrete analytic mountain wave solutions are presented for the classical problem of cross mountain flow in an atmosphere with constant wind speed and stability time dependent linear numerical solutions are also obtained for more realistic atmospheric structures on one hand using second order accurate finite differences on an arakawa c grid to model nonhydrostatic flow over what might be supposed to be an adequately resolved 8 x wide mountain can lead to an overamplification of the standing mountain wave by 30 40 on the other hand the same finite difference scheme underestimates the wave amplitude in hydrostatic flow over an 8 x wide mountain increasing the accuracy of the advection scheme to the fourth order significantly reduces the numerical errors associated with both the hydrostatic and nonhydrostatic discrete solutions the coupl

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

the kinematic structure of a wasatch mountain winter storm during ipex iop3 the influence of orographic circulations on the precipitation structure of a wasatch mountain winter storm is examined using observations collected during the third intensive observing period iop3 of the intermountain precipitation experiment ipex the event featured the passage of a midlevel 700 550 hpa trough followed 3 h later by a surface trough prior to and during the midlevel trough passage large scale southwesterly flow impinged on the wasatch mountains low level confluence was observed between this southwesterly flow and along barrier southerly flow within 20 40 km of the wasatch mountains this confluence zone which moved toward the wasatch mountains during and following the passage of the midlevel trough was accompanied by low level convergence and precipitation enhancement over the upstream lowlands dual doppler analysis revealed the presence of a shallow along barrier jet near the base of the wasatch mountains that was surmounted by southwesterly cross barrier flow at mid and uppermountain levels this cross barrier flow produced strong 1 2 m s 1 ascent as it interacted with the steep windward slopes of the wasatch mountains where precipitation was roughly double that observed in the lowlands upstream flow deflection and splitting were also observed near the highest terrain features a narrow region of strong subsidence which at times exceede d2ms 1 was found to the lee of the wasatch and based on radar imagery appeared to modulate hydrometeor spillover aloft processes contributing to the evolution of the near barrier flow field including topographic blocking diabatic effects and surface friction contrasts are discussed

interactions between topographic airflow and cloud precipitation development during the passage of a winter storm in arizona abstract a case study showing comparisons between observations and numerical simulations of the passage of a winter storm over complex terrain is presented the interactions between the mesoscale and cloud environments and the microphysical and dynamical processes are addressed using both observations and numerical simulations a three dimensional time dependent nested grid model was used to conduct numerical simulations of the three dimensional airflow and cloud evolution over the mogollon rim and adjacent terrain in arizona the modeling results indicated that the flow patterns and cloud liquid water clw were closely linked to the topography to a large extent gravity waves excited by the flow over the mountains determine the distribution of clouds and precipitation the waves extend through deep layers of the atmosphere with substantial updrafts and downdrafts at times exceeding 5 m s 1 the simulated vertical velocities and horizontal wavelengths of about 20 km were in good agreement with the air

structures within large volume rhyolite lava flows of the devonian comerong volcanics southeastern australia and the pleistocene ngongotaha lava dome new zealand abstract many rhyolitic units within the late devonian comerong volcanics erupted as lava flows and domes some up to 18 km long and 350 m thick the textural and structural characteristics that distinguish the flows and domes as lava rather than rheomorphic ignimbrite include unbroken phenocrysts zones of autobrecciation and finely developed flow layering with individual layers continuous for several metres the flow layering is typically contorted into isoclinal folds with forms suggesting fluidal deformation and is interlayered with and gradational into restricted zones of pumice rich lapilli tuff and zones of lenticulite breccia the lenticulite breccia comprises discontinuous lenticular rhyolite fragments the long axes of which define a foliation parallel to flow layering lenticles in the breccia vary from elongate layers up to 1 m long and several millimetres thick to short fragments less than 10 cm long and several centimetres wide similar zones of lenticulite breccia consisting of glassy lenticular clasts in a devitrified spherulitic matrix of cristobalite and albite exist within the late pleistocene ngongotaha dome near rotorua new zealand the lenticulite breccia is considered to form by aqueous diffusion and selective devitrification of the rhyolite along anastomosing fluid paths and to be modified by mechanical fracturing of the lava in a zone of high shear stress geochemically the rhyolites are high si and a type with high zr and y contents indicating that they formed from high temperature relatively anhydrous f rich melts a type granitoids crop out intermittently along the length of and adjacent to the volcanic complex and are comagmatic with the rhyolite the high temperature low bubble and phenocryst content and a high eruptive rate of the rhyolite likely resulted in a low effective viscosity and extensive flow units

comment on on the relationship between induced polarization and surface conductivity implications for petrophysical interpretation of electrical measurements a weller l slater and s nordsiek geophysics 78 no 5 d315 d325 weller et al 2013 have recently presented an attempt to connect the surface and quadrature conductivities of porous media using the polaris model developed by revil 2012 this is an important contribution because the development of such a model can be applied in hydrogeophysics and well logging to determine in a more accurate way textural properties including the pore size distribution the porosity and the permeability of sedimentary rocks in the last decade a growing number of researchers have oversold what can be accomplished by resistivity alone neglecting the effect of surface conductivity unfortunately the paper of weller et al 2013 contains inaccurate statements that are discussed below in more detail three points deserve a more careful discussion 1 weller et al 2013 argue that the value of the mobility ratio i e the ratio of the mobility of the counterions in the stern layer by the mobility of the counterions in the diffuse layer is the same for silicates and aluminosilicates at the opposite the polaris model revil 2012 2013a 2013b predicts two distinct values for this ratio one for silicates and one for aluminosilicates 2 the implications that the mobility ratio is not the same for silica sands and clayey materials may imply that the relationship between the surface conductivity and the quadrature conductivity is not universal the polaris model at the opposite of what is claimed by weller et al 2013 predicts the existence of two distinct trends one for silicates and one for aluminosilicates 3 the relationship between surface and quadrature conductivities both in the paper of weller et al 2013 and in the polaris model is also based on another key parameter the fraction of counterions in the stern layer f also known as the partition coefficient in polaris according to weller et al 2013 f should

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

quantifying the spatial variability of a snowstorm using differential airborne lidar author s brandt w tyler bormann kat j cannon forest deems jeffrey s painter thomas h steinhoff daniel f dozier jeff

fluoride silicate melt immiscibility and its role in ree ore formation evidence from the strange lake rare metal deposit quebec labrador canada pegmatites and adjacent subsolvus granites two alkali feldspars of the mid proterozoic strange lake pluton quebec labrador canada host potentially economic concentrations of high field strength elements hfse including the rare earth elements ree zirconium and niobium previous studies have proposed that these concentrations were the result of a com bination of extreme fractionation of a peralkaline granitic magma and later hydrothermal remobilization however the recent discovery of melt inclusions which after heating to 900 or 950 c quench to immiscible fluoride and silicate glasses suggests an additional mechanism of hfse concentration crystallized melt inclusions are common in quartz phenocrysts of the early hypersolvus and transsolvus granite after heating four types of inclusions were discerned type 1 inclusions quench to a single silicate glass containing a high concen tration of zr nb and ti quenching of type 2 inclusions produces a zr nb ti rich silicate glass containing a globule of calcium rich fluoride glass with a high concentration of the ree the third inclusion type is similar to type 2 except that the calcium rich fluoride glass contains a globule of ree fluoride glass up to 50 wt total ree type 4 inclusions contain calcium fluoride glass with multiple silicate globules we propose that during or soon after emplacement the early granitic magma exsolved a calcium fluoride melt into which rare earth elements ree partitioned preferentially the conjugate silicate melt was consequently depleted in ca and the ree and enriched in zr nb and ti crystallization of the fluoride melt occurred late in the crystallization history of the silicate magma allowing it to accumulate in the volatile rich residual magma that formed the pegmatites this played a major role in the extreme enrichment of the pegmatites in ca f and ree crystallization of the pegmatites proceeded inwards from an outer zone in which feldspars quartz arfvedsonite and zirconosilicate minerals dominate to a core where the immiscible fluoride liquid collected and crystallized fluorite and ree minerals fluid exsolved from the silicate melt reacted with the products of both the silicate and fluoride melts remobilizing most of the hfse including the ree this study reports a rare example of silicate fluoride melt immiscibility and the first in which such immiscibility played a role in concentrating the ree to potentially economic levels 2014 elsevier ltd all rights reserved

airborne doppler observations of a landfalling cold front upstream of steep coastal orography abstract this study uses airborne doppler radar observations to describe the mesoscale structure and evolution of a cold frontal system as it made landfall on the mountainous coast of oregon and northern california on 1 december 1995 during the coastal observations and simulations with topography experiment this section of coastline constitutes a steep approximately two dimensional north south oriented orographic barrier the front exhibited a northeast southwest orientation and thus intersected the axis of high terrain at an acute angle the along barrier pressure gradient and low level winds increased with time along the coastal zone and reached a maximum as the front made landfall stably stratified prefrontal flow was strongly blocked by the orography resulting in a confluent transition from pervasive southwesterly winds offshore to a narrow zone of accelerated south southwesterly flow near the coast where wind speeds approached 30 m s 1 at a height of 750 m above mean sea level postfrontal flow

surface microphysical observations within east coast winter storms on long island new york abstractsurface observations of ice habit and degree of riming were measured for 12 cyclone events over 3 winter seasons at stony brook new york on the northeast coast of the united states a total of 205 6 cm of snow accumulated during these storms with an average degree of riming of 1 25 out of 5 and snow to liquid ratio ranging from 3 1 to 17 1 there were consistent spatial patterns of habit and riming intensity relative to the cyclone structure cold type habits side planes and bullets commonly occurred within the outer comma head to the north and northeast of the cyclone center in the middle of the comma head moderately rimed dendrites plates and needles were observed close to the cyclone center heavy riming was observed with needles and graupel the western quadrant of the comma head had primarily plates and dendrites with little to no riming periods of light riming and high snow liquid ratios 13 1 are dominated by cold type habits dendrites and plates and have similar vertical m

structural environment around th4 in silicate glasses implications for the geochemistry of incompatible me4 elements the structural environment around th4 in several silicate glasses containing 1 3 wt th4 was investigated as a function of melt composition and polymerization using extended x ray absorption fine structure exafs spectroscopy one set of glasses had the bulk chemical composition of monticellite mo diopside di anorthite an albite al olivine basalt o bas tholeiitic basalt t bas calc alkaline dacite dac and calc alkaline rhyolite rhy a second set of th bearing glasses had the bulk al composition but also contained either 5 5 wt f or 2000 ppm cl in glasses containing 3 wt th th coordination varies from 8 d viiith o 2 41 0 02 a in mo and di to a mixture of 8 and 6 coordinations d vi viiith o 2 35 2 36 0 02 a in all other compositions the presence of viiith is related to the thorianite tho2 saturation in the glass in al glasses containing 1 wt th 6 fold coordinated th dominates d vith o 2 32 0 02 a no clear evidence for f or cl complexes around th is observed in any of the halogen containing glasses weak but significant interactions of th with tetrahedral si al network and or alkali elements are observed especially in highly polymerized compositions rhy in which th si ai na k contributions are detected between 3 25 and 3 50 0 05 a these results suggest that in this set of glasses th does not form complexes but rather acts as a weak network modifier the presence of vith in silicate glasses an unusual low coordination for th suggests that the ionic radius of th in magmatic systems is lower than previously reported rth 0 94 a the resulting high th o bond strength 0 7 vu unknown in minerals may explain the observed low crystal melt partition coefficients of th4 i e its incompatible character during magmatic differentiation increasing polymerization is predicted to favor higher coordination around th viii ix as a result of a shortage of nbo to which th preferentially bonds hence dramatic changes in the crystal chemistry of th are predicted i e the incorporation of th in minerals comparison with u4 suggests that vith is less abundant in similar glass melt systems compared with viu this may explain the u th fractionation often observed in zircon as well as the preferential incorporation of th in accessory minerals containing large sites in which th4 can be substituted e g the ca2 site in titanite apatite or zirkelite

the effect of fluorine on clinopyroxene melt trace element partitioning the impact of fluorine on phase relations and clinopyroxene melt element partitioning has been explored experimentally to better understand the effect of this halogen on the residual enrichment of the ree and hfse during crystallisation of alkaline and peralkaline magmas clinopyroxene was grown from three hbox h 2 hbox o saturated synthetic glasses of tephriphonolite to phonolite composition in a rapid quench internally heated pressure vessel at 650 800 circ c and 200 mpa with delta log f hbox o 2 fixed to ca fmq 1 the fluorine content in the charges was varied and produced quenched melts from fluorine free to 1 6 wt f the experiments yield an assemblage of melt fluid sodic clinopyroxene biotite magnetite k feldspar titanite fluorite and hiortdahlite a na ca ti f sorosilicate addition of fluorine markedly increases the mode of biotite without significantly affecting the mode of clinopyroxene relative to fluorine free compositions experiments with 1 6 wt fluorine in the melt show a strong decrease in clinopyroxene melt partition coefficients for the trivalent ree la dy and y with a lesser decrease for the d mathrm hree and d mathrm hfse 4 the diminished uptake of these metals by clinopyroxene may reflect changes to their speciation in the melt phase consistent with the formation of ree f complexes and with modifications to the medium range structural environment around hbox hfse 4 ions in the melt an increase in the fluorine content of the melt will thus make the ree and hbox hfse 4 progressively less compatible and therefore available for residual enrichment

spectral induced polarization of limestones time domain field data frequency domain laboratory data and physicochemical rock properties with advances in data acquisition and processing methods spectral inversion of time domain td induced polarization ip data is becoming more common geological interpretation of inverted spectral parameters for instance cole cole parameters often relies on results from systematic laboratory measurements these are most often carried out with frequency domain fd systems on sandstone samples however the two different methods of measuring the spectral ip response differ in both measurement technique and scale one of the main objectives of this study is thus to perform a direct comparison of inverted spectral parameters from td ip field data with fd ip spectra from laboratory measurements to achieve this field measurements were carried out before a 50 m long rock core was drilled down along one of the measurement lines solid parts of the core were vacuum sealed in plastic bags to preserve the natural groundwater in the samples after which the core samples were measured with fd spectral ip in laboratory the results showed that the inverted cole cole parameters closest to the borehole were comparable to the ip spectra measured at the core samples despite differences in measurement techniques and scale the field site chosen for the investigation was a limestone succession spanning over a well known lithological boundary the cretaceous palaeogene boundary little is known in previous research about varying spectral ip responses in limestones and an additional objective of this study was therefore to investigate possible sources of these variations in the laboratory the ip spectra were interpreted in light of measured lithological and physicochemical properties the carbonate texture differed strongly across the cretaceous palaeogene boundary from fine grained calcareous mudstone cretaceous to more well lithified and coarse grained wackestone and packstone palaeogene both laboratory and field spectral ip results showed that these differences cause a large shift in measured bulk conductivity across the boundary furthermore carbonate mound structures with limestone grains consisting mainly of cylindrical bryozoan fragments could be identified in the inverted cole cole parameters as anomalies with high relaxation times a general conclusion of this work is that limestones can give rise to a wide range of spectral responses the carbonate texture and the dominant shape of the fossil grains seem to have important control over the electrical properties of the material a main conclusion is that the inverted cole cole parameters from the field scale td ip tomography were comparable to the magnitude and shape of fd ip spectra at low frequencies this opens up large interpretational possibilities as the comprehensive knowledge about relationships between lithological properties and ip spectra from laboratory research can be used for field data interpretation less

mineralogy isotope geochemistry and ore genesis of the miocene cuonadong leucogranite related be w sn skarn deposit in southern tibet abstract the himalayan orogenic belt is characterized by widespread leucogranites which are mostly peraluminous with less than 5 mafic minerals previous studies mainly focused on the petrological characteristic genetic mechanism magmatic evolution and tectonic significance of these leucogranites however recently a skarn type be w sn polymetallic deposit which is spatially related to the cuonadong leucogranites of the himalayan leucogranites belt was discovered the orebodies occur in the inner and outer contact zones between the cuonadong leucogranites and their surrounding marble this study focuses on the the characteristics of the skarn mineral assemblages the deposit shows a typical skarn mineral zonation from inside to outside including dark pyroxene garnet skarn zone red garnet zone dark green amphibole specularite zone light green vesuvianite epidote ribbon and vesuvianite chlorite zone zircon u pb dating shows that the ore related leucogranite was emplaced at ca 18 ma geochemically the leucogranite has high sio2 al2o3 na2o k2o and low cao contents belonging to peraluminous granite the cuonadong leucogranite is characterized by right dipping chondrite normalized ree patterns with distinct negative eu anomalies importantly all samples show lanthanide tetrad effect on chondrite normalized ree patterns indicating significant melt fluid interaction has occurred due to strong fractional crystallization additionally the cuonadong leucogranite is enriched in large ion lithophile elements such as rb and relatively depleted in high field strength elements such as nb zr hf suggesting a crustal source region high f and b contents in the magma could have significantly increased the solubility of water in the magma while the magmatic hydrothermal solution enriched in f and b should have remarkably enhanced the metal carrying capacity and increased the permeability of surrounding rocks which in turn effectively facilitated water rock reaction

crystallization and melting experiments of a fluorine rich leucogranite from the xianghualing pluton south china at 150 mpa and h2o saturated conditions abstract crystallization and melting experiments were conducted with a fluorine rich granite from the xianghualing pluton south china in order to determine its crystallization sequence and melt fractionation trends at 150 mpa and h 2 o saturated conditions which are close to the crystallization conditions of this pluton the experimental results showed that quartz is the liquidus phase and is sequentially followed by k rich alkali feldspar zinnwaldite albite and topaz there are obvious evolutionary trends in the compositions of alkali feldspar and residual melt with decreasing temperature from liquidus to 600 c the or kalsi 3 o 8 content in alkali feldspar increases and the contents of ab naalsi 3 o 8 and an caal 2 si 2 o 8 decrease the most apparent fractionation trends in residual melt compositions are decreases in the sio 2 and k 2 o contents and si al ratio and increases in the contents of na 2 o f al 2 o 3 cao and the ratios of a nkc and na k these experimental results indicate that a low silica and sodic granitic melt could be derived from a relatively high silica and potassic f rich leucogranitic magma via fractional crystallization they also shed light on the fractional crystallization and vertical zoning of the xianghualing pluton and other similar high level f rich leucogranite plutons

interaction of an intense extratropical cyclone with coastal orography abstract observational analyses and numerical simulations are used to investigate the interaction of an intense extra tropical cyclone with the coastal orography of the pacific northwest known as the inauguration day cyclone the system made landfall upon the washington state coast on 20 january 1993 producing one of the most damaging wind storms in pacific northwest history the strongest winds accompanying the storm were associated with an intense low level pressure gradient that was concentrated along a bent back front mesoscale pressure perturbations produced by the time dependent interaction of the cyclone and bent back front with the coastal orography were isolated using numerical simulations the simulations showed that during the period of peak winds over puget sound there was only a minor enhancement of the local pressure gradient by troughing to the lee east of the olympic mountains gradual amplification of this olympic mountain lee trough over a period of 2 3 h extended the period of s

the climatology of small scale orographic precipitation over the olympic mountains patterns and processes the climatology of small scale patterns of mountain precipitation is poorly constrained yet important for applications ranging from natural hazard assessment to understanding the geologic evolution of mountain ranges synthesizing four rainy seasons of high resolution precipitation observations and mesoscale model output from the penn state ncar mm5 reveals a persistent small scale pattern of precipitation over the 10 km wide 800 m high ridges and valleys of the western olympic mountains washington state usa this pattern is characterized by a 50 70 excess accumulation over the ridge crests relative to the adjacent valleys in the annual mean while the model shows excellent skill in simulating these patterns at seasonal time scales major errors exist for individual storms investigation of a range of storm events has revealed the following mechanism for the climatological pattern regions of enhanced condensation of cloud water are produced by ascent in stable flow over the windward slopes of major ridges synoptically generated precipitation grows by collection within these clouds leading to enhanced precipitation which is advected by the prevailing winds instances of atypical patterns of precipitation suggest that under certain conditions during periods with a low freezing level or convective cells fundamental changes in small scale patterns may occur however case studies and composite analysis suggest that departures from the pattern of ridge top enhancement are rare the basic patterns and processes appear robust to changes in temperature winds and background rainfall rates copyright 2008 royal meteorological society

effect of the andes cordillera on precipitation from a midlatitude cold front the effects of the andes cordillera the major mountain range in south america on precipitation patterns of baroclinic systems approaching from the southeast pacific remain largely unstudied this study focuses on a case in late may 2008 when an upper level trough and surface cold front produced widespread precipitation in central chile the primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation weather research and forecasting wrf model simulations indicate that as an upper level trough approached central chile midtropospheric flow below 700 hpa was blocked by the high topography and deflected poleward in the form of a barrier jet this northerly jet had wind maxima in excess of 15 m s 21 was centered around 925 hpa and extended westward 200 km from the mountains it intersected the cold front which approached from the south near the coast thereby increasing convergence along the frontal surface slowing its equatorward progress and enhancing rainfall over central chile another separate region of heavy precipitation formed over the upwind slopes of the cordillera a trajectory analysis confirmed that the barrier jet moved low level parcels from their origin in the moist southeast pacific boundary layer to the coast when model topography was reduced to twenty percent of its original height the cold front advanced more rapidly to the northeast generated less precipitation in central chile between 338 and 368s and produced minimal orographic precipitation on the upwind andean slopes based on these findings the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley

small scale precipitation elements in midlatitude cyclones crossing the california sierra nevada abstractradar data in some frontal systems passing over the sierra nevada of california show large variance on scales of 10 km the most prominent features are a few kilometers in scale and are similar to small scale precipitation cells embedded in fronts seen over other mountain ranges other frontal systems crossing the sierras are characterized by more uniform air motions updrafts in large variance storms have characteristics of shear induced turbulence although buoyant instability may also contribute large variance storms occur under stronger upstream winds and vertically integrated cross and along barrier moisture fluxes rain gauges indicate that large variance storms have precipitation greater than smaller variance storms stronger horizontal moisture fluxes may provide greater mean upslope condensation rates however it is hypothesized that accelerated microphysical processes are needed to most efficiently convert the condensate into precipitation that falls out on the lower slopes before be

the effect of fluorine on viscosities in the system na2o al2o3 sio2 implications for phonolites trachytes and rhyolites the effect of fluorine on melt viscosities of five compositions in the system na2o al2o3 sio2h as been investigateda t one atmospherea nd 1000 1600 cb y concentric cylinder viscometry the compositions chosen were albite jadeite and nepheline on the join naalolsio2 and two others of the join at 75 mole percent sio2 one peralkaline and one peraluminous all melt viscosities were independent of shear rate over two orders of magnitude indicating newtonian behavior all viscosity temperature relationships were arrhenian within error fluorine reduces the viscosities and activation energies of all melts investigated the viscosity reducing power of fluorine increases with the sio2 content of melts on the join naalo2 sio2 and is a maximum at na al molar i for melts containing 75 mole percent sio2 fluorine and water have similar effects on aluminosilicate melt viscosities probably due to depolymerization of these melts by replacement of si o si al bridges with si oh and si f bonds respectively evidence from slag systems shows that fluorine also reduces the viscosity of depolymerized silicate melts the viscous flow of phonolites trachytes and rhyolites will be strongly afected by fluorine it appears that fluorine contents of igneous rocks may be combined with water in calculation schemes for determining the viscosity of natural melts