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

dynamical fault rupture processes in heterogeneous media abstract the fault rupture processes in a horizontally layered medium and also in a three dimensionally heterogeneous structure are investigated on three dimensional spontaneous dynamic shear crack models the wave equations for three dimensional space are solved numerically by a finite difference scheme under the appropriate boundary conditions and the finite stress fracture criterion the heterogeneous properties of the elastic medium particularly the existence of low velocity zones give remarkable effects on the rupture process yielding appreciably decelerated rupture velocities and large fault displacements in and around the zones and strong motions in the near field the large fault displacements are enhanced when the rupture breaks the ground surface the static seismic moment in the case with a low velocity zone is essentially the same as in a homogeneous half space an attempt is made to simulate the rupture process of a moderate size earthquake by applying the above shear crack model in a heterogeneous medium with depth dependent and laterally heterogeneous stress drop the model appears to explain the observed features to a satisfactory degree

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

evidence for pre seismic crustal movement in china and japan some recent chinese observations on precursory crustal movements detected by geodetic measurements such as short range levelling or base line survey across the active fault corroborate the three gamma phases model of fujita and fujii gamma 1 phase is pre slip along the imminent faulting gamma 2 is coseismic slip and gamma 3 is post slip along the main or subsidiary faulting after an earthquake typical of these are the results of short range levelling across the earthquake fault that ruptured during the 1976 tangshan earthquake ms 7 8 associated with the occurrence of the tangshan earthquake or the subsequent ninghe earthquake ms 6 9 remarkable gamma 2 phases were observed at this same location abnormal gamma 1 or gamma 3 phases were detected from the lulong 1982 earthquake ms 6 2 that originated from the north end of the tangshan fault and was one of the aftershocks of the tangshan earthquake these phases are interpreted by analogy with the recent experimental results of stick slip motion of the frictional sliding of rock

the role of fluorine in the concentration and transport of lithophile trace elements in felsic magmas insights from the gawler range volcanics south australia rhyolites of the mesoproterozoic gawler range volcanics grv of south australia are characterised by high concentrations of some trace elements ree y hfse rb and f in particular whole rock geochemical data suggest that these elements were incompatible during magma crystallisation accessory minerals fluorite zircon ree f carbonate ti oxide apatite and titanite can account for most of the trace element content of the rocks these minerals occur in vesicles micromiaroles lithophysal vugs and in interstices between major mineral phases quartz and feldspar as both phenocrysts and groundmass such textural evidence indicates that accessory minerals crystallised late in the history of the magma and that they were deposited from a volatile rich fluid phase these features are explained by the following sequence of events 1 f dissolved in the magma lowered the crystallisation temperature of accessory minerals causing trace elements ree y and hfse to behave as incompatible elements 2 protracted crystallisation of major mineral phases quartz feldspar and oxides formed a volatile and trace element enriched residual liquid 3 a volatile element h2o f and co2 rich phase late stage magmatic fluid evolved from the magma high concentration of fluorine and other complexing agents in this phase allowed trace elements to be transported in solution 4 accessory minerals crystallised from such a phase in vesicles micromiaroles and interstices between the major mineral phases

a possible rupture process of slow earthquakes on a frictional fault summary a possible mechanism for the occurrence of slow earthquakes is investigated by calculating numerical solutions for the dynamical rupture process on a quasi three dimensional fault with heterogeneous frictional strengths experimental friction laws for the dependence of sliding frictional stress on slip velocity which are based on the cohesive properties of fault asperities are taken into considerations it is found that the applied stress does not drop very rapidly with time and the rupture velocity remarkably decreases as the dependence on slip velocity becomes smaller these deceleration effects for the rupture propagation are greatly enhanced with increasing heterogeneities in the distribution of frictional strength and as the initial shear stress has lower levels with respect to the average strength for these cases the growth of rupture is extremely slow in a nucleus region with the dimension as large as 10 times the initial rupture length and gains a terminal velocity dependent on the above factors the displacement time function becomes noticeably extended in these cases and indicates a stick slip like phenomena in the extended time interval for a strongly heterogeneous fault it seems that these results could explain the characteristic features of slow earthquakes

on the net cyclonic circulation in large stratified lakes schwab et al have investigated a possible cause of long term cyclonic circulation often observed in stratified lakes they conclude that the adiabatic boundary condition applied to the bottom boundary leads to cyclonic circulation in this note the authors emphasize that it is the combination of vertical mixing of density the associated bottom and surface boundary conditions and variable bottom topography that is important the authors demonstrate the mechanism using a numerical model results also demonstrate the important role of the cross shore flow driven by vertical mixing of momentum in setting the maximum azimuthal flow speed and the cross shore structure of the azimuthal flow

shifting surface currents in the northern north atlantic ocean 1 analysis of surface drifter tracks in the north atlantic ocean from the time period 1990 to 2007 provides evidence that warm subtropical waters have recently increased their penetration toward the nordic seas prior to 2000 the warm water branches of the north atlantic current fed by the gulf stream turned southeastward in the eastern north atlantic since 2001 these paths have shifted toward the rockall trough through which the most saline north atlantic waters pass to the nordic seas these surface drifters are able to overcome the ekman drift which would force them southward under the westerly winds dominating the subpolar atlantic yet the changes in path cannot be accounted for by changes in ekman drift eddy kinetic energy from satellite altimetry shows increased energy along the shifted drifter pathways across the mid atlantic ridge since 2001 these near surface changes have occurred during continual weakening of the north atlantic subpolar gyre as seen by altimetry they are also consistent with the observed increase in temperature and salinity of the waters flowing northward into the nordic seas these findings suggest the changes in the vertical structure of the northern north atlantic ocean its dynamics and exchanges with the higher latitudes wind stress and its curl changes are discussed as a possible forcing of the changes in the pathways of the subtropical waters

contrasting evolution of fluorine and boron rich tin systems individual sn provinces or regions within provinces are sometimes enriched in fluorine or boron giving rise to fluorine rich and boron rich environments the structural styles of mineralisation within these environments are similar except that hydrothermal intrusive breccia pipes are more common in boron rich environments and apogranite massive greisen systems are more common in fluorine rich environments the increased solubility of h2o in b bearing magmas compared to f bearing magmas may play a role in the structural evolution of the mineralising systems the greater mechanical energy produced during crystallisation of b rich magmas provides a mechanism for breccia pipe and stockwork formation while the more passive crystallisation of f rich magmas often results in the formation of disseminated mineralisation the partitioning of boron toward the aqueous fluid phase and the enhanced solubility of silica in the fluid phase frequently results in tourmalinisation and silicification of the wall rocks in b rich environments in contrast feldspathic and sericitic alterations usually predominate in f rich environments

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

late cretaceous granitic magmatism and mineralization in the yingwuling w sn deposit south china constraints from zircon and cassiterite u pb geochronology and whole rock geochemistry abstract numerous late cretaceous w sn deposits associated with granitic rocks were developed in the southern part of south china however the relationship among granitic magma mineralization and tectonic setting remains disputed the yingwuling w sn deposit is spatially associated with k feldspar granite and biotite granite in the southwestern part of guangdong province south china la icp ms zircon u pb dating of k feldspar granite biotite granite and weathered ore bearing granites yielded ages of 79 ma which agree well with la icp ms cassiterite u pb age of 79 6 0 9 ma indicating a close genetic link between the yingwuling pluton and w sn mineralization geochemically both k feldspar granite and biotite granite show high sio 2 na 2 o k 2 o and low cao p 2 o 5 contents and they belong to shoshonitic series and high k calc alkaline series respectively high rb sr ratios and low nb ta and zr hf ratios of the yingwuling pluton indicate strong magmatic differentiation compared with k feldspar granite biotite granite experienced a higher degree of fractional crystallization as indicated by lower fe 2 o 3 tio 2 lree sr eu ba and zr contents and higher sio 2 hree rb cs and y contents their sr and nd isotope compositions initial 87 sr 86 sr 0 7027 and 0 7097 e nd t 5 6 and 5 7 are less radiogenic than that of the south china basement thus it is likely that some juvenile materials were involved in the formation of these granitic intrusions this is also favored by the wide range of zircon hf isotope values e hf t 6 6 to 0 8 which indicates mixing processes a type granite affinity of the yingwuling pluton shows that it was possibly formed in an extensional setting late cretaceous w sn deposits constitute an ew trending belt from guangdong to yunnan provinces which was compatible with the northward subduction of the neo tethys plate rather than the northwestward subduction of the pacific plate during late cretaceous combined with previous studies on magmatic rocks and tectonic activities during late cretaceous in south china this study suggests that the subduction of the neo tethys plate was most possibly responsible for the late cretaceous yingwuling granitic intrusion and associated w sn mineralization

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

viscoelastic stress relaxation on deep fault sections as a possible source of very long period elastic waves observations of very long period elastic waves are attributed to silent earthquakes events which are presumed to occur at depth in a nonbrittle regime the fault at depth is modeled as a thin viscoelastic gouge layer embedded in an elastic medium the source of silent earthquakes is envisaged as a prolonged slow slippage of the fault faces which yields a radiation spectrum strongly depleted in the high frequency components and dominated by the near field term the results of the model are compared with the dominant frequencies mean duration and amplitude of a long period perturbation recorded at trieste in the years preceding the 1976 friuli italy earthquake the role that silent earthquakes may play in the overall earthquake mechanism in particular as precursory phenomena is discussed

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

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

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

primary lithological variation in the kaolinized st austell granite cornwall england geological mapping of existing and redundant kaolin workings within the st austell granite has identified a suite of granitic rocks which show evidence of complex late stage magmatic and hydrothermal processes coarse porphyritic biotite granites like those which predominate in southwest england occur much more widely than previously acknowledged and are intruded by an apparently cogenetic suite of lithium mica granites and tourmaline granites the tourmaline granites characteristically exhibit very variable textures with coarse quartz grains set within a fine grained tourmaline rich matrix a highly evolved fine grained tourmaline granite represents the most evolved of this suite topaz granites intrude the earlier granite varieties and all are intruded by rhyolite porphyry dykes elvans major and trace element chemical data suggest that the biotite granite lithium mica granite tourmaline granite suite represents the product of crystallization of a granitic magma within which b but not f became progressively enriched until water saturation was achieved water exsolution effectively quenched any remaining granitic melt resulting in the very variable textures shown by the tourmaline granites the topaz granites are chemically distinct from their predecessors showing marked enrichment in f li and p 2 o 5 but not b instead of being products of differentiation of biotite granite magma the topaz granite melts may have been derived separately in a later episode of partial melting of the same source kaolinization is widespread throughout the western part of the st austell granite and deposits worked at present tend to be located in granite varieties other than biotite granite the geochemical parameters used to distinguish the primary granite types particularly nb v zr and ga nb zr plots are sufficiently robust to permit the parent granitic rock type to be identified for heavily kaolinized material

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

the role of wave current interaction in lake erie s seasonal and episodic dynamics although the significance of surface gravity waves has been consistently emphasized in previous limnetic studies the roles of wave current interactions in lake dynamics are not sufficiently understood due to the lack of high resolution wave information with a two way coupled hydrodynamic and wave model system this study investigated how the lake erie dynamics are impacted by the wave induced surface and radiation stresses on the seasonal mean and episodic scales the results showed that the surface radiation stress was the same as or an order of magnitude larger than the wave induced surface stress in the nearshore area 5 km offshore while the latter prevailed in the offshore areas by enhancing air lake momentum and heat transfers the wave enhanced surface stress improved the model s skill in simulating hydrodynamics in the central and eastern basins and it was of greater importance at least an order of magnitude larger in modifying surges offshore currents and thermal structures compared to those of the radiation stress nevertheless the radiation stress played key roles in wave induced nearshore currents especially in the shallow western basin their significances reached o 0 01 to 0 1 m s on the seasonal and episodic scales respectively and could have similar importance in other shallow water environments

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

summer thermal structure and anticyclonic circulation of lake erie 1 in most thermally stratified lakes the summer thermocline has the shape of a dome with a shallower depth offshore than nearshore this configuration is accompanied by a lake wide cyclonic circulation lake wide observations of subsurface temperature in central lake erie revealed an atypical depressed or bowl shaped thermocline in late summer with a deeper thermocline in the middle of the lake and a shallower thermocline nearshore currents measured in the central basin when the bowl shaped thermocline was observed were anticyclonic forming a single basin wide gyre it is suggested that the unusual bowl shaped thermocline is the result of ekman pumping driven by anticyclonic vorticity in surface winds the bowl shaped thermocline can lead to greater hypoxia in bottom waters and negative effects on biota by reducing the hypolimnetic volume

compositional variability of terrestrial mantle apatites thermodynamic modeling of apatite volatile contents and the halogen and water budgets of planetary mantles abstract apatites in ultramafic xenoliths from hawaii kamchatka nunivak island lunar crater volcanic field and the navajo volcanic field have variable volatile f cl oh compositions that correlate with their petrogenesis apatites in metasomatized lherzolite harzburgite xenoliths are relatively cl rich whereas apatites in igneous pyroxenite and amphibolite xenoliths are relatively f rich our results support the generalization of o reilly and griffin 2000 that metasomatic apatites tend to be cl rich and magmatic apatites tend to be f rich mantle metasomatism may largely be the consequence of devolatilization of cl rich fluids from subducted lithosphere however the occurrence of metasomatic xenoliths far removed from subduction zones e g bullenmerri as well as the geochemistry of cl in some plume basalts and diamonds indicates that not all metasomatism is subduction triggered thermodynamic modeling of the influence on apatite compositions of variable f cl h2o and p abundances as well as temperature is consistent with the idea that terrestrial mantle fluids are h2o rich and that halogen enrichment in terrestrial apatites need not represent large absolute halogen abundances in the fluids the models indicate that the occurrence of volatile poor calcium phosphate merrillite whitlockite in the martian and terrestrial mantles is facilitated by halogen and phosphorus rich and water poor environments the rarity of this assemblage in the terrestrial mantle compared to mars is consistent with the relatively wet and halogen and phosphorus poor nature of the terrestrial mantle compared to that of mars

modeling summer circulation and thermal structure of lake erie athree dimensionalprimitiveequationnumericalmodelwasappliedtolakeerieona2kmgridtostudyitssummercirculation andthermalstructure modelresultswerecomparedtolong termobservationsofcurrentsandtemperaturemadein2005at severallocations mostlyinitscentralbasin intheshallowandmostlyunstrati edwesternbasincirculationisdrivenbydetroitriverin ow modi edtosomeextentbywind andisfromwesttoeast inthecentralbasin which isofintermediate depthandhasarelatively atbottom themodeledcirculationisanticyclonic clockwise drivenbyanticyclonicvorticityinthesurfacewind andthethermocline isbowl shaped inlinewithobservations inthedeeppartoftheeastern basin the thermoclineisdome shapedandcirculationiscyclonic counter clockwise duetodensitygradients acon gurationtypicalforotherlargedeeplakes whileshallower areasareoccupiedbyanticyclonic circulationdrivenbyanticyclonic windvorticity inthe centralbasin modeledtemperatureandcirculationpatternsare quitesensitivetothespeci cationofthe wind eld anticyclonicwindvorticityleadstothinningofthehypolimnion inthecentralbasinandearlierdestrati cationinthefall

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

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

diagnostic study on the vertical circulation and the maintenance mechanisms of the cyclonic gyre in lake biwa lake biwa in japan has a stable cyclonic gyre during seasons of thermal stratification a vertical circulation consisting of downwelling in the central area and upwelling near the rim of the gyre is calculated by the diagnostic model the energetics in the model indicate that this vertical circulation corresponds to the decay process of the gyre tracking of drifters in summer supports the presence of a vertical circulation though its magnitude is about 50 less than that estimated by the diagnostic model this is explained from the ratio of kinetic energy and available potential energy of the gyre the realistic value of the vertical eddy viscosity is estimated to be 0 8 2 1 cm2 s 1 in summer monthly variations of the horizontal and vertical circulations are calculated by the diagnostic model using the monthly mean density fields the gyre and the vertical circulation are maximal in september the characteristic decay time scale of the gyre is estimated to be about 10 days the effect of topographic differential heating is considered to be one of the maintenance mechanisms of the gyre in early summer and the wind stress curl to be the important maintenance force for the gyre from late summer to late fall

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

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

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

numerical modelling of space and time variations of seismic activity before major earthquakes summary the spatial and temporal variations of seismic activity before large earthquakes including precursory swarm earthquakes clustering pre seismic quiescence in the epicentral area doughnut patterns and foreshocks are numerically modelled by quasi static and dynamical rupture processes on three dimensional heterogeneous faults with various types of non uniform strength distributions the main physical parameters that could yield these precursory changes of seismicity patterns are the form of distributions of static and sliding frictional strengths and their spatial variations over the fault and also the rate of increase of tectonic stress for weakly heterogeneous faults a large scale main shock rupturing the entire fault surface occurs without any precursory indications if the fault has moderately to heavily non uniform strengths on a small scale gradually increasing activity tends to occur over a long period prior to a main event with no swarms or quiescence for extremely heterogeneous faults including a number of small to moderate size asperities with medium to high strengths a typical sequence appears with swarms quiescence foreshocks and a main shock event the temporal behaviour of these events seems to depend primarily on the form of distribution of the strengths if the fault includes a large size asperity with medium to high strengths in its central part a doughnut pattern of seismicity repeatedly appears with high activity and quiescence in the surrounding and central asperity regions if a belt like barrier region with extremely high strengths lies in the central part of the fault dividing the entire region into two sections large scale shocks take place successively in the adjacent unruptured regions at slightly different times and a main shock event rupturing the entire fault occurs after a long period of quiescence these results from numerical simulations could provide possible explanations of observed seismicity patterns prior to major earthquakes

evolution and emplacement of high fluorine rhyolites in the mesoproterozoic gawler silicic large igneous province south australia the gawler range volcanics grv and the hiltaba suite hs of south australia form a silicic dominated large igneous province the gawler slip emplaced in an intracontinental setting during the mesoproterozoic emplacement of the grv lasted for a short period of time 2 ma and can be separated into two main phases the first phase lower grv is composed of thick 3 km sequences erupted from distinct centres and includes small to moderate volume up to 150 km3 felsic lavas ignimbrites and minor mafic and intermediate lavas the upper grv include extensive felsic lavas that are up to 1000 of km3 in volume and 200 km across using well preserved quartz hosted melt inclusions we investigated the composition of the lower grv including major trace and volatile elements the results indicate high concentrations of k2o 7 8 wt rare earth and high field strength elements and low concentrations of ca mg ni cr sr and ba in comparison with felsic continental crust overall melt inclusion compositions match whole rock geochemical characteristics we demonstrate that the grv magma was f rich 1 3 wt and had high temperature for a silicic magma high f concentrations and high temperature would have resulted in lower than usual polymerisation of the melt and relatively low viscosity these characteristics help explain how very voluminous felsic magma was erupted effusively and emplaced as lavas other intracontinental slip contain extensive felsic lavas and ignimbrites which appear to share similar geochemical characteristics we also show that selective alteration caused depletion of whole rock compositions in some trace elements namely pb u and sn

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

layering in peralkaline magmas ilimaussaq complex s greenland abstract the peralkaline to agpaitic ilimaussaq complex s greenland displays spectacular macrorhythmic 5 m layering via the kakortokite agpaitic nepheline syenite which outcrops as the lowest exposed rocks in the complex this study applies crystal size distribution csd analyses and eudialyte group mineral chemical compositions to study the marker horizon unit 0 and the contact to the underlying unit 1 unit 0 is the best developed unit in the kakortokites and as such is ideal for gaining insight into processes of crystal formation and growth within the layered kakortokite the findings are consistent with a model whereby the bulk of the black and red layers developed through in situ crystallisation at the crystal mush magma interface whereas the white layer developed through a range of processes operating throughout the magma chamber including density segregation gravitational settling and flotation primary textures were modified through late stage textural coarsening via grain overgrowth an open system model is proposed where varying concentrations of halogens in combination with undercooling controlled crystal nucleation and growth to form unit 0 our observations suggest that the model is applicable more widely to the layering throughout the kakortokite series and potentially other layered peralkaline agpaitic rocks around the world

modeling the 1998 2003 summer circulation and thermal structure in lake michigan 1 a three dimensional primitive equation numerical model was applied to lake michigan on a 2 km grid for 6 consecutive years to study interannual variability of summer circulation and thermal structure in 1998 2003 the model results were compared to long term observations of currents and temperature at seven moorings and two noaa buoys the accuracy of modeled currents improved considerably relative to previous summer circulation modeling done on a 5 km grid while the accuracy of temperature simulations remained the same particle trajectory model results were also compared with satellite tracked surface drifter observations large scale circulation patterns tend to be more cyclonic counterclockwise toward the end of summer as the thermocline deepens and density effects become more important circulation in southern lake michigan appears to be more variable than circulation in northern lake michigan an important new feature not previously seen in observations was found in southern lake michigan an anticyclonic gyre extending northward from the southern shore of lake michigan sometimes occupying the entire southern basin

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

petrogenesis of u and mo bearing a2 type granite of the gattar batholith in the arabian nubian shield northeastern desert egypt evidence for the favorability of host rocks for the origin of associated ore deposits abstract hydrothermal ore deposits associated with granitic rocks are the result of combinations and series of successive processes events and conditions in a magma system and at post magmatic stage the metal content of a granitic magma as well as fractional crystallization metal ligand complexation emplacement mechanisms and tectonic processes influence the metal precipitation and content of a hydrothermal ore deposit the present study of the gattar batholith evaluates how these processes contribute to the generation of an ore deposit gattar batholith in the north eastern desert of egypt as part of the northern region of the arabian nubian shield ans is geographically mineralogically and geochemically divided into two distinctive areas the southern part mainly consists of syenogranite while the northern part is dominated by highly evolved alkali feldspar granite uranium and mo mineralization occurring here is mostly limited to the margin of the highly evolved alkali feldspar granites new u pb zircon geochronology within this study indicates an age of 620 600 ma although high common pb and discordant age data of many zircon grains reflect alteration by f rich fluids some zircons with distinct older u pb ages were considered to be inherited from the wall rocks representing juvenile crust of the ans the two different granitic rocks are comagmatic in origin and have a type characteristics generated by partial melting of lower juvenile crust of the ans geochemical data are in good agreement with a magmatic origin of the alkali feldspar granites suggesting fractional crystallization of a syenogranitic source as the most favorable process of their formation petrography geochemistry and geochronology studies of the gattar granites along with field observations provide evidence for multiple intrusions as a result of successive magma pulses with different chemical composition this led to the formation of reverse zoning within the intrusive complex this kind of magma emplacement promotes the escape of exsolved metal bearing volatile rich fluids into the boundary of the hammamat sedimentary rocks hsr and gattar granite at the northern part of the batholith build up of volatiles is a common phenomenon in granitic rocks and typically results in enhanced contents of f alkalis and ore metals released at subsolidus stage

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

lithium isotope behaviour during partial melting of metapelites from the jiangnan orogen south china implications for the origin of ree tetrad effect of f rich granite and associated rare metal mineralization abstract we carried out combined nd and li isotopic studies on the neoproterozoic biotite granites late mesozoic evolved two mica muscovite granites and associated the shuangqiaoshan group metapelites from the jiangnan orogen south china which along with petrological and geochemical data were used to constrain the lithium isotopic behavior during partial melting of metapelites the origin of the ree tetrad effect in evolved granites and implications for related rare metal mineralization the neoproterozoic biotite granites show features typical of s types e g high a cnk ratios and have end 6 9 to 10 and 7li 2 2 4 comparable to the shuangqiaoshan group metapelites with end 6 to 11 and 7li 2 3 7 respectively suggesting that the biotite granites were derived from melting of the metapelites and the li isotopic fractionation during the melting process appears negligible the two late mesozoic shimensi and zengjialong granites occur as small stocks showing high silica peraluminous low cao and sr contents variably enrichment in volatiles f b and are accompanied by w cu and sn mineralization the shimensi granites have end t values of 7 0 8 6 and 7li 2 7 3 9 similar to the shuangqiaoshan group metapelites whereas the zengjialong granites have relatively high end t values 5 1 7 3 and heavy li isotopic features mostly 7li 0 18 1 53 and particularly ree tetrad effect is seen in the latter we argue that the late mesozoic evolved granites formed as a result of re melting of the granulitic residues left in the lower crust after extraction of the neoproterozoic biotite granites from the metapelites such re melting of the residues was triggered by underplating of basaltic magma with more mantle input and f b as well in the source of the zengjialong granites the elevated 7li values of the zengjialong granites were probably caused by intense interaction between melt and external fluids during magma emplacement which in turn resulted in the formation of the ree tetrad effect in the granites isotopic modeling suggests that fluid exsolution from evolved granites is minor and is less likely to have been responsible for the extensive rare metal mineralization as traditionally thought

resolution of the slow earthquake high apparent stress paradox for oceanic transform fault earthquakes 1 oceanic transform fault earthquakes exhibit some interesting and apparently contradictory properties a number of earthquakes on oceanic transforms have been identified as slow on the basis of their weak seismic radiation at high frequencies on the other hand transform fault events as a population have been found to have high apparent stress indicating strong high frequency radiation since the seismic energy is concentrated at and above the corner frequency in an attempt to reconcile these observations we analyze seventy 5 8 mw 8 3 strike slip earthquakes from around the world four of these earthquakes have both exceptionally low apparent stress and large centroid time shifts for their seismic moment all four of them are located on oceanic transform faults if we include these events in the population we find that continental and oceanic strike slip earthquakes are not significantly different in their mean apparent stress but that there is greater variation for oceanic events we also find that in contrast to the low correlation between centroid time shift and apparent stress for continental earthquakes the oceanic ridge transform earthquakes have a high correlation between these two parameters we also observe cases of both ordinary and slow earthquakes on adjacent sections of the same transform these characteristics suggest significant differences in the faulting process between oceanic transforms and continental faults

a model of interseismic fault slip in the presence of asperities summary a 2 d model which represents a slipping fault with non uniform coulomb friction is studied the fault plane is subject to a uniform ambient shear stress slowly increasing with time aseismic fault creep is assumed to start in a weak zone when the ambient stress reaches a strength threshold the solution for the resulting dislocation is worked out analytically using a technique based on chebyshev polynomials it is found that the dislocation partially propagates into the adjacent asperities concentrating stress onto them and preparing the conditions which will produce the asperity failure and the accompanying earthquake propagation is not self similar and occurs at increasing velocity a non linear slip hardening effect is reproduced the nearness to earthquake instability is measured by a dimensionless parameter which depends on coulomb friction and ambient shear stress and decreases to zero with time an upper boundary to the critical value of this parameter at which instability may occur is estimated and is found to depend on the ratio between the sizes of the asperity and the weak zone

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

ta and sn concentration by muscovite fractionation and degassing in a lens like granite body the case study of the penouta rare metal albite granite nw spain abstract the penouta peraluminous low phosphorous granite is the most important low grade high tonnage sn ta nb bearing albite granite from the iberian massif a sheet or laccolith shape instead of a stock is inferred for the penouta granite maybe in relation with the low viscosity and high mobility of a fluorine bearing melt subhorizontal lateral extension of the magma is also inferred via vertical and horizontal geochemical variations the absence of compositional gaps in variation diagrams coupled with continuous evolutionary trends of compatible and incompatible elements with height discard a multi pulse intrusion and point to a single magma pulse mineral chemistry trace element and least squares mass balance modelling support a differentiation process from bottom to top in the emplacement place the absence of switch from incompatible to compatible behaviour bell shaped trends in sn nb and ta variation diagrams coupled to experimental constraints on tantalite and cassiterite saturation suggest that nb ta oxides and probably cassiterite were not fractionated mineral phases their crystallisation being related to concentration gradients within a trapped intercumulus melt major and trace element modelling support that the concentration upwards of ta and the ta nb ratio could be a consequence of mineral fractionation with a key role of muscovite mainly primary for the ta nb ratio as this mineral has a higher partition coefficient for nb than ta our results suggest that fluorine and peraluminosity had a limited effect in the ta nb ratio variations hence ta enrichment is mainly controlled by fractional crystallisation processes in most cases sn enrichment was also concomitant with ta indicating that crystal melt fractionation processes also played an important role in sn concentration nevertheless the strongest sn enrichment in the granite e g central part of the granite body does not correspond to a significant ta enrichment the high affinity of sn for fluids and the high partitioning of ta for melt could explain this decoupling nevertheless the magmatic signature of cassiterites in these strongly sn enriched zones central part of the granite body rules out a hydrothermal subsolidus origin for this fluid by analogy with models carried out in sill like bodies it seems likely that the sn enrichment in the central part of the granite body is related to fluid saturation degassing occurred in the lower margin as a consequence of cooling and crystallisation of mostly anhydrous minerals i e second boiling the vapour exsolved migrated into the hotter melt up to the central part where it probably was reabsorbed yielding cassiterite with a magmatic signature moreover we suggest that heat loss in the upper margin of the granite body might also contribute to the formation of a second fluid saturated zone as a result pegmo aplites and greisen were developed

wind driven surface transport in stratified closed basins direct versus residual circulations a numerical model has been used to investigate the wind driven circulation in a stratified basin of moderate size lake tahoe california nevada two types of circulation are identified direct circulations in which the current directions remain relatively constant and the mean circulation formed over several days resembles the instantaneous circulation and residual circulations in which the currents fluctuate continuously and the mean circulation is characterized by small net displacements of parcels after large oscillations previous studies of stratified closed basins have emphasized residual circulations caused by cyclonically propagating internal basin modes resulting in a single cyclonic mean gyre during light to moderate winds observations at lake tahoe have shown currents which are more constant in direction with a double gyre pattern of surface circulation dominated by an anticyclonic northern gyre model experiments of lake tahoe demonstrate that the curl of the wind stress must be included to obtain a direct double gyre circulation similar to the observations horizontally uniform winds cause a residual circulation similar to that reported at other lakes use of the model to calculate the vorticity budget clarifies the role of the wind stress curl in creating the direct double gyre

modeling circulation and thermal structure in lake michigan annual cycle and interannual variability a three dimensional primitive equation numerical model was applied to lake michigan for the periods 1982 1983 and 1994 1995 to study seasonal and interannual variability of lake wide circulation and thermal structure in the lake the model was able to reproduce all of the basic features of the thermal structure in lake michigan spring thermal bar full stratification deepening of the thermocline during the fall cooling and finally an overturn in the late fall large scale circulation patterns tend to be cyclonic counterclockwise with cyclonic circulation within each subbasin the largest currents and maximum cyclonic vorticity occur in the fall and winter when temperature gradients are low but wind stresses are strongest the smallest currents and minimum cyclonic vorticity occur in spring and summer when temperature gradients are strong but wind stresses are weakest all these facts are in agreement with observations the main shortcoming of the model was that it tended to predict a more diffuse thermocline than was indicated by observations and explained only up to half of the variance observed in horizontal currents at timescales shorter than a day

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

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

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

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

wind generation of the costa rica dome upwelling in the costa rica dome is seasonal and the result of the localized cyclonic wind stress curl fluctuations in the wind stress curl in the fall release the upwelled region as a rossby wave similar low latitude domes are hypothesized to be ubiquitous to those oceans where a localized cyclonic wind stress curl is associated with an intertropical convergence zone

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

relative effects of wind stress curl topography and stratification on large scale circulation in lake michigan 1 this paper uses the results from two multiseason numerical model simulations of lake michigan hydrodynamics to examine the relative effects of wind stress curl topography and stratification on large scale circulation the multiseason simulations provide a period long enough to encompass the full range of atmospheric and thermal conditions that can occur in the lake the purpose of this paper is to diagnose the relative importance of various mechanisms responsible for the large scale circulation patterns by analyzing the vorticity balance in the lake on a monthly timescale five different model scenarios are used to isolate the predominant mechanisms 1 baroclinic lake spatially variable wind stress 2 barotropic lake spatially variable wind stress 3 baroclinic lake spatially uniform wind stress 4 barotropic lake spatially uniform wind stress and 5 barotropic lake linearized equations spatially uniform wind stress by comparing the results of these five model scenarios it is shown that the cyclonic wind stress curl in the winter and the effect of baroclinicity in the summer are primarily responsible for the predominantly cyclonic flow in the lake topographic effects are also important but are not as significant as wind stress curl and baroclinic effects nonlinear effects are much smaller

fault slip beyond a barrier on a transform plate boundary summary a strike slip plate boundary is considered with non uniform strength depth dependent slip on the fault surface is assumed to occur aseismically in the lower fault section in response to a basal shear stress and seismically in the brittle upper section the upper fault section acts as a barrier preventing aseismic slip from reaching shallower depths if however friction decreases in the proximity of the earth s surface brittle fracture may occur beyond the barrier it is found that when friction in the uppermost fault section exceeds the applied shear stress fault slip occurs there with a smaller amplitude than at larger depth this may explain the discrepancies which have been sometimes reported between fault offsets observed at the earth s surface and fault offsets inferred from seismograms by using simpler dislocation models

the formation of the late cretaceous xishan sn w deposit south china geochronological and geochemical perspectives abstract the xishan sn w deposit is spatially related to k feldspar granites in the yangchun basin western guangdong province south china la icp ms zircon u pb dating for the xishan pluton defines an emplacement age of 79 ma 78 1 0 9 ma 79 0 1 2 ma 79 3 0 8 ma consistent with the mineralization age of the xishan sn w deposit constrained by molybdenite re os isochron age 79 4 4 5 ma and la icp ms cassiterite u pb ages 78 1 0 9 ma and 79 0 1 2 ma for the cassiterite quartz vein these indicate a close genetic relationship between the granite and sn w mineralization the xishan k feldspar granites have geochemical characteristics of a type granites e g high total alkali na 2 o k 2 o 7 88 10 07 wt high ga al ratios 10000 ga al 2 6 and high zr nb ce y concentrations 350 ppm they are further classified as a 2 type granites the whole rock isotopic compositions of k feldspar granites initial 87 sr 86 sr 0 705256 0 706181 e nd t 5 4 to 4 8 and zircon e hf t values 7 8 to 2 0 suggest a mixed magma source the low zircon ce 4 ce 3 ratios 12 88 of k feldspar granites suggest low oxygen fugacities which is key for enrichment of tin in primary magmas the k feldspar granites have experienced strong differentiation as indicated by their high rb sr and k rb ratios and low nb ta and zr hf ratios which play an important role in ore forming element transportation and concentration a type granite characteristics of the xishan pluton show that it formed in an extensional environment the high f and low cl characteristics of the k feldspar granite are most probably attributed to slab rollback in the late cretaceous the xishan sn w deposit was located near the interaction of the circum pacific and the tethys tectonic realms late cretaceous sn w deposits including the xishan deposit form an ew trending belt from guangdong to yunnan province in south china this belt is in accordance with the direction of the neo tethys slab rollback in the late cretaceous in addition the ns trending extension has been recognized in the late cretaceous in south china we propose that the xishan sn w deposit should be attributed to the neo tethys slab rollback in the late cretaceous

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