the transition from peraluminous to peralkaline granitic melts evidence from melt inclusions and accessory minerals fractional crystallization of peraluminous f and h2o rich granite magmas progressively enriches the remaining melt with volatiles we show that at saturation the melt may separate into two immiscible conjugate melt fractions one of the fractions shows increasing peraluminosity and the other increasing peralkalinity these melt fractions also fractionate the incompatible elements to significantly different degrees coexisting melt fractions have differing chemical and physical properties and due to their high density and viscosity contrasts they will tend to separate readily from each other once separated each melt fraction evolves independently in response to changing t p x conditions and further immiscibility events may occur each generating its own conjugate pair of melt fractions the strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained consequently the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions we demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore forming and accessory minerals and are visible on scales from a few micrometers to hundreds of meters

the solubility of nb ta zr hf w in granitic melts with li and li f constraints for mineralization in rare metal granites and pegmatites tantalum mineralization is associated with granites and pegmatites that invariably are rich in lithium this in part is due to the extreme fractionation that is necessary for melts to reach saturation in either a ta or an li phase however there may also be chemical interactions in melts that explain this association experiments therefore were conducted to determine the effect of lithium on the solubility of tantalite mnta 2 o 6 in water saturated granitic melts other important elements in rare metal granites include nb zr hf and w consequently the effect of li on the solubilities of columbite mnnb 2 o 6 zircon zrsio 4 hafnon hfsio 4 and hbnerite mnwo 4 in granitic melts was also investigated the haplogranitic melt compositions used in these experiments have constant mole percent si and al and the al li na k ratio was 1 0 for all experiments i e the lithium content was the only compositional variable columbite and tantalite solubilities in the granitic liquids increase by a factor of approximately 2 to 3 with the addition of 2 wt percent li 2 o to haplogranite at 750 degrees to 1 035 degrees c 2 kbars and water saturated conditions the solubility data were extrapolated to a lower temperature more reasonable for columbite tantalite crystallization then compared to compositions representative of evolved liquids from which rare metal granites and pegmatites crystallize it is estimated that at 600 degrees c these melt compositions could be saturated in columbite but not tantalite however tantalite saturation is predicted if the melts contained less li and f therefore the genesis of tantalum mineralization may be explained by ta being retained in the melt because of high li f concentrations tantalite crystallization is delayed until an li or f or p mineral crystallizes which lowers tantalite solubility and results in a general association of ta with li in mineralized granitic rocks in contrast to columbite and tantalite the solubility of wolframite is not affected by the lithium content of the melt with up to 3 8 wt li 2 o in starting glasses and the solubilities of zircon and hafnon decrease with increasing li content of the melt one possible interpretation of the hbnerite solubility data is that the melt contains dominantly w super 6 which behaves as a network former the decrease in zircon hafnon solubility with li may reflect the lower field strength of zr super 4 and hf super 4 compared to nb super 5 and ta super 5 i e zr and hf are less able to compete with li for nonbridging oxygens whereas nb and ta are more able to compete it is also significant that the solubility of hafnon is greater than that of zircon similar to the higher solubility of tantalite compared to columbite this can explain why zr hf and nb ta ratios both decrease with fractionation

observations of volcanic clouds in their first few days of atmospheric residence the 1992 eruptions of crater peak mount spurr volcano alaska abstract satellite so2 and ash measurements of mount spurr s three 1992 volcanic clouds are compared with ground based observations to develop an understanding of the physical and chemical evolution of volcanic clouds each of the three eruptions with ratings of volcanic explosivity index three reached the lower stratosphere 14 km asl but the clouds were mainly dispersed at the tropopause by moderate to strong 20 40 m s tropospheric winds three stages of cloud evolution were identified first heavy fallout of large 500 m pyroclasts occurred close to the volcano 25 km from the vent during and immediately after the eruptions and the cloud resembled an advected gravity current second a much larger highly elongated region marked by a secondary mass maximum occurred 150 350 km downwind in at least two of the three events this was the result of aggregate fallout of a bimodal size distribution including fine 25 m ash that quickly depleted the solid fraction of the volcanic cloud for the f

samples from the crystallising boundary layer of a zoned magma chamber the spatial and chemical relationships between the melt occupying the reservoir and the mineral assemblages crystallising at the margins are reconstructed for the magma chamber which produced the 11000 yr b p tephra deposit of laacher see volcano the melt showed vertical chemical zonation immediately prior to eruption and throughout most of the magma volume only a small fraction of crystals were present the eruption also ejected crystal rich nodules ranging from mafic to felsic in composition which are samples of the materials crystallising at the boundaries of the chamber new data on nodule petrography and chemical compositions of whole rocks minerals and interstitial glasses are presented volume fraction of interstitial glass is not systematically related to mineral assemblage and varies typically between 1 and 20 vol i e the crystals interlock one exception is a group of mafic nodules with glass volume fractions between 25 and 40 vol bulk compositions of mafic nodules show strong enrichments or depletions in all major elements relative to the mafic phonolite interstitial melt felsic nodules show much less pronounced differences with their interstitial melt felsic nodules contain interstitial glasses with a range of compositions similar to that in the zoned bulk of the chamber and were probably derived from different heights on the walls mafic nodules have glass compositions similar to those at the base of the zoned liquid column and were probably derived from the floor modal mineralogy glass composition and mineral composition are systematically related in the nodules whereas in individual pumices samples derived from the main body of the chamber a broader range of mineral compositions are often found mineral assemblages were especially diverse in the upper part of the chamber it is deduced that the whole of the essentially liquid part of the chamber was emptied by the eruption that strongly contrasting mineral assemblages were forming simultaneously on the walls and floor that the gradient in crystal content in the crystallisation boundary layer was more gradual at the floor than at the walls and that the pumice mineralogy is not a simple phenocryst assemblage but is a mixture of crystals which grew from melts separated in space and or time

influence of fluorine on the solubility of manganotantalite mnta2o6 and manganocolumbite mnnb2o6 in granitic melts an experimental study abstract solubility experiments of manganotantalite mnta 2 o 6 and manganocolumbite mnnb 2 o 6 were conducted under nearly fluid saturated conditions in synthetic haplogranitic hpg and natural granitic ng melts containing different amounts of fluorine at 800 to 1000 c and 200 mpa the experiments were carried out in cold seal pressure vessels at 800 c with water or ar as a pressure medium and in internally heated pressure vessels 1000 c with ar as a pressure medium the f contents vary from 0 to 11 43 wt in experiments using hpg melts and from 0 61 to 3 78 wt in experiments using ng melts additionally the ng melt contains minor amounts of p 2 o 5 0 44 to 0 64 wt in hpg melts alumina saturation index including mn asi mn 0 88 to 0 99 the solubility product values at 800 c yield log k sp ta and log k sp nb ranging from 3 36 0 10 to 2 92 0 10 mol kg and from 3 01 0 11 to 2 87 0 06 mol kg respectively in ng melts the log k sp ta and log k sp nb vary from 3 00 0 04 to 2 35 0 13 mol kg and from 2 83 0 06 to 2 67 0 18 mol kg at 800 c respectively the solubility products of both mnta 2 o 6 k sp ta and mnnb 2 o 6 k sp nb are not significantly affected by the f content for a given melt composition data are virtually identical within error the variation of the solubility products observed in this study is rather attributed to the changes in melt structure e g polymerization and in particular to the alumina saturation index by contrast there is no evidence for the formation of complexes associating f and nb and or ta our results also indicate that the structural changes caused by the incorporation of f in natural water rich silicate melts are not expected to significantly influence the maximum concentrations of nb and ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite

fumarole emissions at mount st helens volcano june 1980 to october 1981 degassing of a magma hydrothermal system abstract this study is an investigation of the chemical changes in the mount st helens fumarole gases up to october 1981 the sources of the fumarole gases and the stability of gas species in the shallow magma system these problems are investigated by calculations of element compositions thermodynamic equilibria and magmatic volatile hydrothermal steam mixing models the fumarole gases are treated as mixtures of magmatic volatiles and hydrothermal steam formed by magma degassing and boiling of local waters in a dryout zone near conduit and dome magma the magmatic volatile fraction is significant in fumaroles with temperatures in excess of the magma cracking temperature 700 c i e the temperature below which cracking is induced by thermal stresses during cooling and solidification linear composition changes of the fumarole gases over time appear to be the result of a steady decline in the magmatic volatile mixing fraction which may be due to the tapping of progressively volatile depleted magma the maximum proportion of hydrothermal steam in the fumaroles rose from about 25 35 in september 1980 to around 50 70 by october 1981 fractional degassing of magmatic co 2 and sulfur also contributed to the chemical changes in the fumarole gases the steady chemical changes indicate that replenishment of the magma system with undegassed magma was not significant between september 1980 and september 1981 extrapolations of chemical trends suggest that fumarole gases emitted at the time of formation of the first dome in mid june 1980 were more enriched in a magmatic volatile fraction and contained a minimum of 9 co 2 calculations show h 2 s is the predominant sulfur species in mount st helens magma below depths of 200 m rapid release of gases from magma below this depth is a plausible mechanism for producing the high h 2 s so 2 observed in mount st helens plumes during explosive eruptions this study suggests that dacite andesite volcanos may emit gases richer in co 2 during the earlier episodes of an eruptive cycle and burden the atmosphere with much more h 2 s than so 2 during explosive eruptions

geological setting of the early devonian rhynie cherts aberdeenshire scotland an early terrestrial hot spring system abstract the drilling of nine cored boreholes including a deep hole 233 m to a gabbroic basement in the vicinity of the rhynie chert locality has resulted in a major revision of the structure and stratigraphy of the area the main new structural element recognized is a low angle extensional fault system which defines the western edge of a half graben containing the early devonian succession the fault system was the main conduit for the fluids that fed the hot springs and a heat source to the southeast of rhynie is indicated rapid and unexpected lateral and vertical variations in lithology together with new lithological units have been identified the latter include a thick unit of intensely altered lapilli tuffs which are unique to the rhynie basin and to other devonian basins in ne scotland analysis of these lithologies in conjunction with the new structural model allows the succession at rhynie to be correlated with the succession in the rest of the basin and a model of basin evolution and hot spring development to be constructed siliceous sinters were deposited by multiple episodes of hot spring activity and are variably interbedded with shales sandstones and minor tuffs in a unit about 35 m thick sinter deposition was ultimately controlled by repeated subsidence along the basin margin geothermal activity was probably widespread in northern britain in the early devonian but the surface deposits are unlikely to be preserved the rhynie deposit has survived due to a fortuitous combination of circumstances

global lithium resources relative importance of pegmatite brine and other deposits abstract previous studies of the availability of lithium for use in batteries to power electric vehicles evs have reached the generally encouraging conclusion that resources are sufficient to meet growing demand for the remainder of the 21st century however these surveys have not looked past estimates of lithium resource to the geological constraints on deposit size and composition that will allow the resources to be converted to reserves from which lithium can be produced economically in this survey we review the relevant geological features of the best characterized pegmatite brine and other types of lithium deposits and compare their potential for large scale long term production the comparison shows that the average brine deposit 1 45 mt li is more than an order of magnitude larger than the average pegmatite deposit 0 11 mt li and that brine deposits especially the large atacama chile and uyuni bolivia deposits have a much larger total lithium resource 21 6 mt li brine deposits clearly have a much greater capacity for large scale long term production than do pegmatite deposits however individual brine deposits differ considerably and successful production from one deposit does not necessarily assure success at others conversion of brine resources to reserves will depend on the degree of compartmentalization of brine reservoirs the extent to which brine can be recovered without dilution from recharge waters and degradation of salt bearing reservoir rock and whether other constituents of the brines including potassium magnesium bromine and boron restrict processing or the capacity of production to respond to changes in demand for lithium despite their smaller size and total estimated resource 3 9 mt pegmatites will remain of interest because of their wider geographic distribution and consequently lesser susceptibility to supply disruptions and their more lithium dominant compositions which might allow more flexible response to market changes some deposits will be amenable to large scale mining but significant production might also come from selective underground mining of small deposits in areas with low labor costs even the largest pegmatite deposits such as those at greenbushes australia and manono kitolo democratic republic of congo have estimated resources that are similar to only an average brine deposit for this reason continuous long term production from pegmatites will require extensive exploration and discovery of new pegmatite deposits and districts two other types of lithium deposits unusual rocks and unusual fluids have also received attention deposits consisting of rocks and minerals that are enriched in lithium by interaction with brines and hydrothermal solutions including the large jadar serbia and king valley usa deposits have estimated resources of about 3 4 mt li unusual brines in oilfields and the salton sea geothermal field usa contain an estimated 2 mt li both of these deposit types will require new processing methods but are likely to become important because of their lithium dominant compositions and relatively large size the total lithium resource in these deposits 31 1 mt li far exceeds estimated lithium demand of up to 20 mt li including consideration for recycling in all markets through 2100 the difference between these two estimates should be vied largely as a challenge rather than a comfort evaluation of the economic extractability of these resources will require large investments and result in only partial success if prices provide sufficient encouragement and exploration is sustained however lithium resources should be available for the next century

evolution and environmental impacts of the eruption of laacher see volcano germany 12 900 a bp abstract laacher see volcano lsv 40 km south of bonn explosively erupted ca 6 3 km 3 of chemically strongly zoned phonolite magma probably during spring 12 900 years ago the resulting eruption column having reached at least 20 km in height the bulk of the laacher see tephra lst was deposited east of the volcano within the neuwied basin lst ashes form the most important stratigraphic marker in lateglacial deposits over much of central europe a minimum of 2 mt total s was calculated to have been released during the eruption by comparing pre and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses because a separate s bearing vapor phase was probably present in the magma prior to eruption as indicated by the high melt h 2 o contents close to saturation level the actual amount of s released during the eruption could have significantly exceeded 2 mt the sulfuric acid aerosol layer resulting from the massive stratospheric s input probably resided in the stratosphere for years and most likely had a significant impact on climate and thus the environment increased precipitation in central europe and or impairment of the vegetation cover for several years is suggested by several proxies especially increased sediment supply into lakes proximal to the eruptive center major environmental impacts include an initial blast that felled trees up to 4 km away from vent fast deposition of huge tephra volumes led to the complete disruption of rhine river within the lower neuwied basin and the damming up of a lake ca 140 km 2 in areal extent sudden collapse of the temporary tephra dam caused a catastrophic flood wave downstream whose deposits are recognized as far north as bonn reworking of unconsolidated tephra deposits over several 100 km 2 was widespread and extensive generating abundant lahars and flood plain deposits a braided river system established in neuwied basin probably persisted up to several years recent reports for a second eruption of lsv are not confirmed

injection of gases into the stratosphere by explosive volcanic eruptions 1 explosive eruptions can inject large amounts of volcanic gases into the stratosphere these gases may be scavenged by hydrometeors within the eruption column and high uncertainties remain regarding the proportion of volcanic gases which eventually reach the stratosphere these are caused by the difficulties of directly sampling explosive volcanic eruption columns and by the lack of laboratory studies in the extreme parameter regime characterizing them using the nonhydrostatic nonsteady state plume model active tracer high resolution atmospheric model atham we simulated an explosive volcanic eruption we examined the scavenging efficiency for the climatically relevant gases within the eruption column the low concentration of water in the plume results in the formation of relatively dry aggregates more than 99 of these are frozen because of their fast ascent to low temperature regions consideration of the salinity effect increases the amount of liquid water by one order of magnitude but the ice phase is still highly dominant consequently the scavenging efficiency for hcl is very low and only 1 is dissolved in liquid water however scavenging by ice particles via direct gas incorporation during diffusional growth is a significant process the salinity effect increases the total scavenging efficiency for hcl from about 50 to about 90 the sulfur containing gases so2 and h2s are only slightly soluble in liquid water however these gases are incorporated into ice particles with an efficiency of 10 to 30 despite scavenging more than 25 of the hcl and 80 of the sulfur gases reach the stratosphere because most of the particles containing these species are lifted there sedimentation of the particles would remove the volcanic gases from the stratosphere hence the final quantity of volcanic gases injected in a particular eruption depends on the fate of the particles containing them which is in turn dependent on the volcanic and environmental conditions

rainwater and ash leachate analysis as proxies for plume chemistry at soufriere hills volcano montserrat chloride and sulphate concentrations in rainwater and water soluble leachates from volcanic ash samples track the compositions of gas emissions at the soufriere hills volcano montserrat from 1996 to 2001 there are both systematic spatial and temporal variations in the chloride sulphate ratio expressed as the equivalent hcl so2 mass ratio in rainwater and ash leachates temporal variations reflect changes in eruption rate and eruptive style mass ratios of hcl so2 in ash leachates correspond closely with those obtained by open path fourier transform infrared op ftir spectroscopy and reflect changes in volatile emissions throughout the eruption both leachate and op ftir spectroscopic analyses show mass ratios of hcl so2 1 during dome growth and hcl so2 1 during non eruptive periods the hcl so2 mass ratios in rainwater samples from 1996 and 1997 show temporal variations that correlate with changes in extrusion rate the hcl so2 ratios in plume affected rainwater and ash leachates from june and july 2001 correlate positively with increasing rockfall energy and with increasing eruption rate prior to a dome collapse event the hcl so2 mass ratios in water soluble ash leachates and rainwater samples collected at the same time and from the same sites are linearly correlated with rainwater hcl so2 ratios systematically two to three times higher than ash leachate ratios spatial patterns of rainwater ph and hcl so2 in rainwater and ash leachates are principally influenced by the proximity of the sampling sites to the active dome and to the typical pattern of dispersion of the plume by tropospheric winds these results demonstrate that rainwater chemistry and ash leachate analysis provides a useful indicator of volcanic activity and represents a valuable supplement to volcano surveillance efforts

surface area porosity and water adsorption properties of fine volcanic ash particles our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary despite the importance of these reactions in influencing the chemistry and dynamics of a plume in this study six samples of fine ash 500 a all the specimens had similar pore size distributions with a small peak centered around 50 a these findings suggest that fine ash particles have relatively undifferentiated surface textures irrespective of the chemical composition and eruption type adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a s values enhanced reactivity of the ash surface towards water may result from i hydration of bulk ash constituents ii hydration of surface compounds and or iii hydroxylation of the surface of the ash the later mechanism may lead to irreversible retention of water based on these experiments we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions in addition capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume the total mass of water vapour retained by 1 g of fine ash at 0 95 relative water vapour pressure is calculated to be 10 2 g some volcanic implications of this study are discussed

tungsten solubility in evolved granitic melts an evaluation of magmatic wolframite abstract a variety of parameters that potentially control the solubilities of synthetic hubnerite mnwo4 and ferberite fewo4 in haplogranitic melts rich in fluxing compounds have been determined at 200 mpa in order to test the hypothesis that wolframite can occur as a magmatic mineral the melts considered representative of highly evolved pegmatites contain 1 1 1 7 and 2 02 wt of li2o p2o5 and b2o3 respectively although the molar al na k ratio is one if li is considered to be an alkali element the molar al na k li asili of the melt is 0 88 and the melt is peralkaline hubnerite and ferberite solubilities at 800 c are strongly controlled by melt composition they are much lower in subaluminous melt asili 1 05 than in peralkaline melt by contrast hubnerite and ferberite solubilities are nearly independent of the fluorine content of the melt for up to 8 wt f hubnerite and ferberite solubilities at 800 c are also nearly independent of oxygen fugacity over a log f o 2 range of approximately ni nio 3 to ni nio 2 which implies that the predominant oxidation state of tungsten in the melts is 6 even at moderately reduced conditions a series of experiments on haplogranitic melt rich in fluxing compounds with 0 and 6 wt f at 850 650 c shows that temperature strongly influences hubnerite solubility e g the solubility product of hubnerite k sp hub in the melts with 6 wt f decreases from 71 0 7 9 10 4 mol2 kg2 at 850 c to 4 4 2 3 10 4 mol2 kg2 at 650 c our experimental results show that ferberite solubilities are much higher than those of hubnerite with the same composition of melt but the mn fe and w concentrations in natural melt inclusions indicate that these melts were undersaturated with wolframite at 800 c however flux rich melts crystallize at lower temperatures in nature and the occurrence of natural magmatic wolframite was evaluated by comparing experimental solubility product values extrapolated to 500 c with wolframite activities at these temperatures magmatic wolframite is unlikely in flux rich peralkaline melts but by contrast flux rich subaluminous to peraluminous melt inclusions appear to have been saturated with wolframite at approximately 500 c because of the strong temperature dependence of wolframite solubility the dominant effect of fluxing compounds is to lower the solidus temperature of the melt

phosphorus distribution between potassic alkali feldspar and metaluminous haplogranitic liquid at 200 mpa h 2 o the effect of undercooling on crystal liquid systematics to evaluate the applicability of p2o5 concentration in potassic alkali feldspar as a monitor of p2o5 in melt for undercooled systems crystal melt partitioning for p was evaluated via feldspar growth experiments in p bearing 3 wt p2o5 water saturated haplogranitic liquids at 200 mpa with liquidus undercoolings t of 25 50 100 200 and 300 c increasing undercooling in the range t 25 200 c shows an evolution of crystal morphologies from euhedral and well filled individuals at t 25 50 c to radial clusters with increasingly skeletal habit at greater undercooling experiments at t 100 200 c also document the development of p up to 9 wt p2o5 and si enriched more alkaline boundary layers adjacent to crystals experiments at t 300 c show an additional change in crystallization fabric in which spherulites of skeletal crystals form in open vapor space created by the dissolution of bulk silicate and compositional boundary layers are not observed we interpret the changes in reaction products at t 300 c to indicate conditions below a glass transition hence partition coefficients were not determined for this undercooling values of k d p kfs melt from experiments at t 25 200 c calculated from pairs of crystal and immediately adjacent liquid compositions including boundary layers at higher undercooling are mostly in the range of 0 25 0 55 and show no effective change with increased undercooling essentially no change in k d p kfs melt with undercooling apparently stems from an interplay between boundary layer composition and a change in the substitution mechanism for p in feldspar from alpsi 2 common in peraluminous to metaluminous liquids near equilibrium to increasing proportions of p m si 1 with increased undercooling bulk glass and liquid beyond boundary layers in experiments with significant percentages of crystallization are homogeneous and show pronounced fractionation primarily due to the removal of an orthoclase component because crystallization was still in progress in experiments with t 200 c compositional homogeneity in the bulk liquid requires extremely rapid diffusion of most haplogranite components na k and al apparently resulting from chemical potential gradients stemming from the removal of components from the liquid by crystal growth similar homogeneity and bulk fractionation in experiments with t 300 c requires rapid diffusive equilibration for the alkalis even at temperatures below an apparent glass transition unlike the haplogranite components p is only concentrated in liquid boundary layers t 200 c or low density aqueous vapor t 300 c adjacent to crystals hence the p2o5 contents of melt inclusions likely are not representative of bulk melt concentrations in significantly undercooled systems t 50 100 c

late collisional granites in the variscan erzgebirge germany the late collisional erzgebirge granites 325 318 ma were introduction emplaced at shallow crustal levels in the variscan metamorphic the erzgebirge is a ne sw trending antiformal structure basement shortly after large scale extension caused by orogenic exposing variscan crystalline basement rocks at the northcollapse these granites comprise mildly peraluminous transitional ern margin of the bohemian massif the region is famous i s types and strongly peraluminous s type rocks which can be among economic geologists for its extensive and highly subdivided into three major groups low f biotite granites low f variable metallic ore deposits which have been mined two mica granites and high f high p2o5 li mica granites the since the middle ages e g stemprok seltmann 1994 highest degree of differentiation is reached in the li mica granites tischendorf forster 1994 and for the classic studies which exhibit strongly elevated concentrations of p f li rb cs in the fields of economic geology mining and metallurgy ta sn w and u but very low ti mg co ni sr ba y zr chemistry and mineralogy e g werner 1791 breithaupt hf th and rare earth elements crystal melt fractionation is the 1849 agricola 1974 dominant process controlling the bulk composition of all groups of as in many of the other variscan provinces in central granites however metasomatic processes involving late stage residual europe granitic rocks make up a large proportion of the melts and high t orthomagmatic fluids became increasingly more exposed rocks in the erzgebirge and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur fig 1 knowof mobile elements p f li rb cs ba sr in the li mica ledge of the processes involved in the generation and granites particularly isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the variscan precursor magma their discrete compositions are source related orogeny and also for the formation of metallic ore and are attributed to melting of quartzo feldspathic and pelitic deposits several lines of evidence indicate that early crustal lithologies in different proportions granites are common in high temperature sn w deposits are associated with the the central european variscides but the erzgebirge is unusual for emplacement of highly evolved volatile rich granitic the predominance of evolved li mica granites associated with melts tischendorf 1986 forster tischendorf 1992 economically important sn w and u deposits the abundance of stemprok 1993 the role of the granites in formation of li mica granites is attributed to a combination of favourable factors later permian u pb zn and younger ore mineralization 1 low degrees of anatectic melting of crustal protoliths 2 wide f ba is controversial but good evidence exists that the distribution of fertile lithologies rich in large ion lithophile elements vein type u deposits owe their uranium to leaching from and ore elements 3 extended magmatic differentiation by crystal the uraninite rich granites e g tischendorf forster melt fractionation and subsequent autometasomatism 1994

liquid immiscibility and its role at the magmatic hydrothermal transition a summary of experimental studies several types of fluid immiscibility may affect the evolution of volatile rich magmatic systems at the magmatic hydrothermal transition the topology of silicate salt h2o systems implies that three fluid immiscibility silicate melt hydrosaline melt vapour should be stable in a broad range of compositions and p t conditions the most important factor controlling the immiscibility appears to be the coulombic properties electric charges z and ionic radii r of the main network modifying cations and the capacity for immiscibility appears to decrease in the following sequence mg ca sr ba li na k liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as f cl co32 and bo33 in volatile rich magmatic systems the h2o is likely to react with the chloride fluoride borate and carbonate species and the chemical effects of high temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and li f rare metal granites

the effect of water on the viscosity of a haplogranitic melt under p t x conditions relevant to silicic volcanism the viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040 c have been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques the micropenetration viscometry has been performed in the viscosity range of 109 pa s to 1012 pa s the samples ranged in water content from 0 4 to 3 5 wt for samples with up to 2 5 wt h2o the water contents have been determined using infrared spectroscopy obtained before and after each viscometry experiment to be constant over the duration of the measurements above this water content a measurable loss of water occurs during the viscometry the viscosity data illustrate an extremely nonlinear decrease in viscosity with added water the viscosity drops drastically with the addition of 0 5 wt of water and then shallows out at water contents of 2 wt an additional viscosity datum point obtained from the analysis of fluid inclusions in a water saturated hpg8 confirms a near invariance of the viscosity with the addition of water between 2 and 6 wt these measurements may be compared directly with the data of hess et al 1995 in press for the effects of excess alkali and alkaline earth oxides on the viscosity of hpg8 also obtained at 1 bar the viscosity of the melts compared on an equivalent molar basis increases in the order h2o li2o na2o k2o rb2o cs2o bao sro cao mgo beo the extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation scheme of shaw 1972 for the range of water contents investigated here the speciation of water in the quenched glasses can be used to quantify the dependence of the viscosity on hydroxyl content considering only the hydroxyl groups as active fluidizers in the hydrous melts the nonlinearity of the viscosity decrease and the difference with the effects of the alkali oxides becomes larger consequences for degassing calcalkaline rhyolite are discussed

solubility and stability of beryl in granitic melts beryllium contents of granitic melts at saturation in beryl or chrysoberyl phenakite or quartz have been determined by forward and reverse direction experiments at 650 850 degrees c and 200 mpa using natural beryl or the compositionally equivalent mixture of phenakite alumina quartz added to metaluminous haplogranite peraluminous haplogranite and macusanite a peraluminous li b f and p enriched rhyolite obsidian from macusani peru chrysoberyl coexists with beryl or quartz in moderately to strongly peraluminous systems asi approximately or 1 05 the assemblage phenakite beryl chrysoberyl is stable in silica undersaturated bulk composition the beo content of the melts which ranged between 0 03 0 40 wt varies principally with temperature the solubility of beryl falls with decreasing t and with the activity product of beryl alpha beo 3 alpha al2o3 alpha sio2 6 beryllia contents are lowest in strongly peraluminous and quartz saturated haplogranite melts however the highest beo content measured in glass products occurs for the strongly peraluminous macusanite at 850 degrees c 4016 ppm we infer that the greater solubility of beryl in macusanite melt results from melt speciation reactions involving li f b and p for all bulk compositions studied the beo content of melt projects to a narrow range of similar values at low t near the solidus of haplogranite thus metaluminous to peraluminous granitic magmas with and without common volatile and fluxing components will if cooled to subsolidus temperatures have similarly low beo requirements for beryl saturation the small beo content of melt near the solidus of haplogranite results in a minor 10 degrees c depression of the freezing point compared to be free haplogranite melt the mean melt composition at the beryl saturated granite minimum shifts slightly toward quartz beryl is common in peraluminous granitic rocks in part because lower beo contents are required to saturate these melts in beryl and possibly because these melts acquire higher beo contents by mica melting reactions at their sources beryl is also a common constituent of border facies assemblages in granitic pegmatite dikes regardless of their asi values this early crystallization of beryl results from the low beo content required to saturate any granitic melt in beryl at the low t environments in which pegmatite dikes solidify

cooling rates and crystallization dynamics of shallow level pegmatite aplite dikes san diego county california pegmatites of the pala and mesa grande pegmatite districts san diego county california are typically thin sheet like composite pegmatite aplite dikes aplitic portions of many dikes display pronounced mineralogical layering referred to as line rock characterized by fine grained garnet rich bands alternating with albite and quartz rich bands thermal modeling was performed for four dikes in san diego county including the 1 m thick himalaya dike the 2 m thick mission dike the 8 m thick george ashley dike and the 25 m thick stewart dike calculations were based on conductive cooling equations accounting for latent heat of crystallization a melt emplacement temperature of 650 c into 150 c fractured gabbroic country rock at a depth of 5 km and an estimated 3 wt initial h 2o content in the melt cooling to 550 c at the center of each dike occurred in 9 years for the stewart dike 340 days for the george ashley dike 22 days for the mission dike and 5 days for the himalaya dike based on these calculations growth rates for large pegmatitic minerals such as the 10 cm long himalaya hanging wall tourmaline crystals may have been on the order of 10 5 cm s crystal size distribution csd studies of garnet from layered aplites suggest growth rates of about 10 6 cm s these results indicate that the dikes cooled and crystallized rapidly with variable nucleation rates but high overall crystal growth rates initial high nucleation rates coincident with emplacement and strong undercooling can account for the millimeter size aplite grains lower nucleation rates coupled with high growth rates can explain the decimeter size minerals in the hanging walls cores and miarolitic cavities of the pegmatites the presence of tourmaline and or lepidolite throughout these dikes suggests that although the melts were initially h 2o undersaturated high melt concentrations of incompatible or fluxing components such as b f and li h 2o aided in the development of large pegmatitic crystals that grew rapidly in the short times suggested by the conductive cooling models

fracture controls on valley persistence the cairngorm granite pluton scotland valleys are remarkably persistent features in many different tectonic settings but the reasons for this persistence are rarely explored here we examine the structural controls on valleys in the cairngorms mountains scotland part of the passive margin of the eastern north atlantic we consider valleys at three scales straths glens and headwater valleys the structural controls on valleys in and around the cairngorm granite pluton were examined on satellite and aerial photographs and by field survey topographic lineaments including valleys show no consistent orientation with joint sets or with sheets of microgranite and pegmatitic granite in this granite landscape jointing is not a first order control on valley development instead glens and headwater valleys align closely to quartz veins and linear alteration zones lazs lazs are zones of weakness in the granite pluton in which late stage hydrothermal alteration and hydro fracturing have greatly reduced rock mass strength and increased permeability lazs which can be kilometres long and 700 m deep are the dominant controls on the orientation of valleys in the cairngorms lazs formed in the roof zone of the granite intrusion although the cairngorm pluton was unroofed soon after emplacement the presence of old red sandstone ors outliers in the terrain to the north and east indicates that the lower relief of the sub ors basement surface has been lowered by 1 km of vertical erosion and for 400 myr this valley persistence is a combined product of regionally low rates of basement exhumation and of the existence of lazs in the cairngorm pluton and sub parallel caledonide fractures in the surrounding terrain with depths that exceed 1 km

crystallographic control on lithium isotope fractionation in archean to cenozoic lithium cesium tantalum pegmatites the age distribution of lct pegmatites largely overlaps with major phases of collisional orogenic events and assembly of super continents some of the largest known lct pegmatite deposits formed in very short intervals 2 7 2 5 and 1 9 1 8 billion years ago ga corresponding to two major pulses of continental crust growth however the exact process of generation and segregation of large volumes of li bearing pegmatite liquids perhaps involving disequilibrium fractional crystallization and leaving residual melts enriched in fluxing elements such as b f h2o li and p remains largely obscure the new data on li contents and isotope compositions in major mineral phases from temporally and geographically separated pegmatite bodies document extreme variations in d7li values among individual large lct pegmatites in particular archean occurrences the observed 10 variations in d7li values for the same mineral phases from different localities i e beryl petalite spodumene lepidolite amblygonite muscovite contrast with globally homogeneous li isotope systematics of major mineral phases from unmodified mantle rocks consistent li isotope offsets between coexisting mineral phases are best explained by li isotope fractionation as a function of the bond length between li and neighboring ions o oh f we suggest that spatially distinct li isotope patterns act as fingerprints for different pegmatites and can be explained by the pre existing li isotope differences of their crustal sources at the time of pegmatite formation owing to differences in crustal age and evolution this would imply secular evolution of the continental crust over earth history toward present day globally broadly uniform crustal 7li 6li ratios d7li 0 the differences among archean occurrences could reflect possible archean paleogeography and perhaps be linked with different thermal regimes of individual cratons as a consequence of variations in crustal thickness

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

volatile composition of the phonolitic laacher see magma 12 900 yr bp implications for syn eruptive degassing of s f cl and h 2 o a volatile rich and chemically zoned phonolitic magma reservoir was tapped successively during the eruption of laacher see volcano ca 12 900 years bp and produced a tephra sequence consisting of phenocryst poor highly evolved phonolite at the base and phenocryst rich more mafic phonolite at the top the stratospheric volatile loading was estimated by comparing pre and post eruptive s f cl and h2o contents of undegassed glass inclusions and partially degassed matrix glasses glass inclusions 150 1490 ppm s and host matrix glasses 150 820 ppm s both document a strong s decrease during progressive magmatic differentiation which is interpreted to be partially caused by crystallization of hauyne the s6 stotal ratio of the pre eruptive melt increased with differentiation from 8 to 71 as indicated by s k wavelength shift measurements in glass inclusions sulfate rich highly evolved phonolitic magma was erupted during plinian and sulfide rich more mafic phonolitic magma during late phreatomagmatic phases f and cl became enriched during late stages of differentiation glass inclusions 690 4060 ppm f 1770 4400 ppm cl matrix glasses 680 3660 ppm f 2130 4330 ppm cl the most differentiated melts maximum 13 wt na2o occur only as matrix glass and are extremely f enriched 5080 8780 ppm but cl depleted 460 2820 ppm suggesting that f was retained in the melt whereas some cl was lost during pre and or syn eruptive degassing the h2o contents of glass inclusions increase irregularly with differentiation 2 5 5 7 wt matrix glasses are h2o depleted 0 2 2 8 wt compared to most glass inclusions showing that most h2o was released to the atmosphere by explosive degassing a mass balance calculation yields a syn eruptive volatile release of 1 9 tg stotal 6 6 tg cl and 403 tg h2o from the melt this is a minimum estimate since s and cl could have accumulated in a separate fluid phase as indicated by fluid inclusions in hauyne and pre eruption h2o contents close to saturation level at the likely pressure temperature conditions in the laacher see magma reservoir we estimate that at least ca 20 tg so2 were injected into the stratosphere causing a significant negative climate forcing as reflected by several paleoclimate proxies and as shown by recent modeling

volcanic degassing of bromine and iodine experimental fluid melt partitioning data and applications to stratospheric chemistry abstract in order to understand the degassing behavior of heavy halogens in volcanic processes we experimentally studied the distribution of cl br and i between albite melt and hydrous fluids containing 0 01 2 wt of nacl nabr or nai respectively all experiments were carried out at 2 kbar and 900 c in rapid quench cold seal autoclaves with a run duration of 7 days the major element compositions and cl contents of the glassy run products were measured by electron microprobe bromine and iodine were measured by proton induced x ray emission fluid compositions were obtained by mass balance all halogens investigated were found to partition strongly into the fluid phase over the range of concentrations studied the halogen contents in the melt are proportional to the concentrations in the fluid the fluid melt partition coefficients df m are 8 1 0 2 for cl 17 5 0 6 for br and 104 7 for i the logarithm of df m is linearly correlated with the ionic radius of the halogenide ion on the basis of our experimental data we estimate the amount of bromine injected into the stratosphere by major volcanic explosions for the 1991 mount pinatubo eruption we obtain br yields of 11 25 kt as minimum estimates these numbers are comparable to the total annual influx of bromine into the stratosphere from all other natural and anthropogenic sources about 100 kt year since bromine is much more efficient in destroying stratospheric ozone than chlorine it could at least be partially responsible for the massive ozone depletion observed after the 1991 mount pinatubo eruption

melt inclusions in quartz from an evolved peraluminous pegmatite geochemical evidence for strong tin enrichment in fluorine rich and phosphorus rich residual liquids abstract we have investigated the magmatic evolution of a late stage f and p rich pegmatite forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally crystallized melt inclusions in quartz and analyzing the quenched glass by epma and sims the quartz phenocrysts were sampled from a pegmatite that occurs in a variscan granite genetically associated with cassiterite and wolframite mineralized greisen veins at the ehrenfriedersdorf sn w deposit central erzgebirge se germany the melt inclusion compositions imply that the pegmatite forming liquid achieved extreme levels of chemical differentiation it contained high abundances of sn f p li rb cs nb ta and be and abnormally low concentrations of ca y sr and ree for a granite and it was strongly peraluminous the molar al 2 o 3 cao na 2 o k 2 o ranged from 1 3 to 2 0 fractions of the pegmatite forming liquid were extremely enriched in p 2 o 5 f al 2 o 3 and the molar abundances of f p in the glasses correlate strongly with moles of network modifying al ions implying that the bulk liquid included f p and al bearing complexes formation of these complexes reduced the activities of f p and al in bulk liquid suppressed the crystallization of magmatic topaz and p rich minerals and allowed the liquid to become enriched in these constituents some fractions of the ehrenfriedersdorf aluminosilicate liquid contained 1000 2000 ppm sn these levels of sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineralized metaluminous and peraluminous igneous materials and are consistent with some experimentally derived sn solubilities in cassiterite saturated granitic liquids at geologically relevant pressures and temperatures this concordance implies that cassiterite could have crystallized directly from this highly evolved p and f rich peraluminous granitic liquid without the involvement of hydrothermal fluids

changes in mid and far field human landscape use following the laacher see eruption c 13 000 bp abstract around 13 000 years ago the laacher see volcano east eifel volcanic field rhenish shield erupted cataclysmically the thick tephra blanket in the eruption s near field covered and thereby preserved a large number of archaeological sites ranging from very small to some of the largest and richest sites known from the late glacial in this proximal region there is a striking contrast in the number of sites prior to the eruption and the almost complete lack of sites dating to the period after the event i e to greenland interstadial 1a the preservative function of the tephra cover itself may explain this near field pattern but it is shown here that similar stratigraphic observations can also be made in the laacher see eruption s mid field towards the west and in particular to the north east the aim of this paper is to review the stratigraphic relations of known archaeological sites outside the near field of the laacher see event with a particular focus on the german federal state of hesse and adjacent areas of lower saxony and the thuringian basin here a number of archaeological sites are known where strata of laacher see tephra cap human occupation most often these sites are not reoccupied until much later in prehistory suggesting that the eruption may have led either to a complete or a near complete abandonment of the affected regions or at the very least to a major reorganisation of landscape use

the 12 900 years bp laacher see eruption estimation of volatile yields and simulation of their fate in the plume we estimated the volatile emissions of the 12 900 years bp eruption of laacher see volcano germany using a modified petrological method glass inclusions in phenocrysts and matrix glasses sampled over the laacher see tephra profile were analysed by synchrotron x ray fluorescence microprobe and electron microprobe to obtain the emitted masses of halogens sulphur and water these data were used to initialize the numerical plume model atham in order to investigate the fate of volcanic gases in the plume and to estimate volatile masses injected into the stratosphere the scavenging efficiency of each volatile component depends on its interactions with both liquid water and ice we found a scavenging efficiency of c 5 for the sulphur species and of only c 30 for hydrogen halides despite their high water solubility our simulations showed that the greatest fraction of hydrometeors freeze to ice due to the fast plume rise and great height of the eruption column for the dry atmospheric conditions of the laacher see eruption the amount of liquid water was not sufficient to completely scavenge hcl and hbr so that a large proportion could reach the stratosphere

monitoring the crystallization of water saturated granitic melts in real time using the hydrothermal diamond anvil cell critical aspects of the crystallization dynamics of h2o saturated melts of a typical granitic composition as well as granitic melts enriched in lithium 8800 ppm were investigated in real time experiments using the hydrothermal diamond anvil cell at 480 700 c and 220 960 mpa complete crystallization of the charges was achieved within 5 118 h with average crystal growth rates ranging from 3 to 41 cm year for quartz and from 18 to 58 cm year for alkali feldspars demonstrating that crystals formed from a silicate melt in the presence of a coexisting aqueous phase crystallize rapidly the combination of substantial nucleation delays low nucleation densities and rapid growth rates for quartz and alkali feldspars led to the formation of euhedral megacrysts of these minerals in the vicinity of clusters comprised of much smaller muscovite or spodumene crystals subsolidus replacement processes initiated during crystal fluid interactions after the silicate melt was consumed were directly observed in the experiments the experimental results underscore the important role of water as a medium for the transport of essential elements such as si al na and k from the silicate melt to the newly formed crystals and provide important insights into the crystallization of miarolitic pegmatites

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

exploring the effect of lithium on pegmatitic textures an experimental study the effect of lithium li on the development of pegmatitic textures was evaluated experimentally at h 2 o saturated and h 2 o undersaturated conditions at 500 mpa pressure and temperatures ranging from 400 to 800 c the addition of 3700 ppm li to a starting material of common granitic composition lake county obsidian reduces the crystallization and melting temperatures by approximately 50 70 and 200 c respectively and promotes the formation of quartz feldspar graphic and granophyric intergrowths the presence of li in the hydrous granitic system lowers significantly the degree of undercooling needed for the development of graphic and granophyric intergrowths to 85 110 c in comparison with the li free systems where approximately 200 c of undercooling is necessary the feldspar crystals developed in li bearing samples can incorporate from 150 to 250 ppm li assume skeletal and spherulitic morphologies and exhibit one order of magnitude faster growth rates than crystals in li free samples the results of this study attest to the effectiveness of li as a fluxing agent and highlight the crucial role it plays in the development of pegmatitic textures leading to important implications for the conditions of formation of li bearing granitic pegmatites

volcanic particle aggregation in explosive eruption columns part ii numerical experiments abstract the goal of this paper is to determine the parameters that control the aggregation efficiency and the growth rate of volcanic particles within the eruption column numerical experiments are performed with the plume model atham active tracer high resolution atmospheric model in this study we employ the parameterizations described in a companion paper this issue the presence of hydrometeors promotes the aggregation of ash particles which strongly increases their fall velocities and thus their environmental impact the tephra mass is about two orders of magnitude greater than that of hydrometeors during typical plinian eruptions without interaction of external water ice is highly dominant in comparison to liquid water 99 by mass this is caused by the fast column rise 100 m s 1 on average to very cold altitudes most particles occur in the form of frozen aggregates with low ice content the collection efficiency is governed by the availability of hydrometeors acting as adhesives at the particles surface in our study and wet ash particles have a higher sticking capacity than icy ones therefore aggregation is fastest during the eruption within the column when limited regions of liquid water exist and when particle concentrations are very high of the order of 10 5 cm 3 increased humidity in the background atmosphere generally leads to enhanced ice formation but shows only a weak influence on the aggregation process first sensitivity studies showed however a significant increase of the liquid water fraction when considering salinity effects the availability of water or ice at the particles surfaces is also governed by the surface properties the porosity and permeability of ash which are not well established to date particle growth is significantly enhanced for greater differences in the sizes and fall velocities among particles as gravitational capture becomes more efficient our experiments indicate a major influence of the erupted particle size distribution first sensitivity studies show that electrostatic forces result in a significant enhancement of aggregated particles the present exploratory study provides new insights into the sensitivity of the ash aggregation process to a number of key parameters our results indicate the need of further constraining particle composition size porosity permeability and surface properties at low temperatures by in situ observations in the laboratory and in the field in addition further research on electrostatic aggregation would be desirable

lithium and nd isotopic constraints on the origin of li poor pegmatite with implications for li mineralization abstract although volumetrically minor in the upper continental crust pegmatites host lots of rare metal mineralization e g li be pegmatites and associated mineralization were generally thought to originate from extreme differentiation of a parent granite system we propose an alternative model to interpret the genesis of pegmatite and factors controlling li mineralization based on combined nd and li isotopic studies on the li poor pegmatites barren from the qinghe pegmatite field of the altai orogen nw china the qinghe pegmatites show significantly varied nd isotopic compositions end t 4 3 1 7 which overlap the surrounding schists 6 5 1 5 but lower than the granites 2 2 9 of the orogen these data together with the low ree 3 3 41 ppm and absence of biotite in the pegmatites suggest they were not derived from extreme differentiation of a parent granite as traditionally thought but from low degrees of partial melting of the schists involving muscovite dehydration melting under amphibolite facies conditions the pegmatites are characterized by heavy li 7li 4 1 14 5 and low li abundance 3 6 50 ppm which contrast to that of local schist 7li 0 9 3 0 li 24 123 ppm and granite 7li 0 9 3 0 li 24 70 ppm and also to that of global li rich pegmatites 7li 1 0 10 li 500 ppm modeling study indicates that li poor pegmatites always have heavy li signature compared with li rich pegmatites due to the abundance of biotite in the source the formation of li rich pegmatite with li mineralization is attributable to the distinct source characteristics with abundant fluxing components like li na co32 and hco3 and sufficient alumina rich clay phases and the fluxing components probably originated from evaporate interlayers in the source

evidence for lithium aluminosilicate supersaturation of pegmatite forming melts new experimental data on the solubility of lithium li at spodumene lialsi2o6 and petalite lialsi4o10 saturation at 500 mpa and 550 750 c reveal evidence for lithium supersaturation of pegmatite forming melts before the formation of li aluminosilicates the degree of li enrichment in granitic melts can reach 11 000 ppm above the saturation value before the crystallization of li aluminosilicate minerals at lower temperatures comparison of the experimental results with the spodumene rich moblan pegmatite quebec is consistent with extreme li enrichment of the pegmatite forming melt prior to emplacement which cannot be explained with equilibrium crystallization of li aluminosilicates from a common granitic melt the results of this study support the model of disequilibrium fractional crystallization through liquidus undercooling as the most plausible mechanism for the generation of such li rich ore resources

temperatures and duration of crystallization within gem bearing cavities of granitic pegmatites abstract crystallization within miarolitic cavities in granitic pegmatites begins with the primary igneous minerals feldspars quartz micas and lesser others along the margins of pockets and ends with the formation of zeolites carbonates and finally dense clay the euhedral and gem quality crystals for which many pegmatites are mined form within this interval and they are commonly suspended in the dense clay with no points of attachment to a substrate the sequence of mineral assemblages reflects a history of crystallization with cooling that continues well after and to temperatures below the initial magmatic stage low temperature assemblages of zeolites and clays are normally restricted to the miarolitic cavities themselves in otherwise fresh and unaltered pegmatite of igneous origin this study utilizes feldspar solvus thermometry to delineate the temperature interval over which the euhedral and gem quality crystals form additional data include a survey of al si order in k feldspar and the mineralogy of the clay size fraction from miarolitic cavities as further constraints on the conditions of crystallization the primary feldspars at pocket margins record an average crystallization temperature of 431 c 1 68 c approximately the same temperature at which crystallization takes place across the massive portions of thin miarolitic pegmatite dikes the average calculated temperature of closure of perthite exsolution occurred at 338 c 1 60 c pairings of glassy non perthitic rims on k feldspar with radial albite of cleavelandite habit on the k feldspar surfaces record the final stage of crystallization of the primary silicates in pockets at an average temperature of 359 1 64 c the glassy rims are not perthitic because they form close enough to the closure temperature of perthite that exsolution does not occur the zeolites which include stilbite ca laumontite and heulandite are restricted in their stability to less than 300 c and they follow the precipitation of the gem minerals in all known cases thus the gem forming stage likely falls between 435 355 c based on the feldspar solvus temperatures cookeite kaolinite montmorillonite and illite enclose zeolites and formed after them in a thermal model a dike 1 meter thick emplaced as hydrous granitic liquid at 700 c at a depth of 7 km ambient temperature of 160 c cools to 435 c at its center in 12 days and from 435 c to 355 c the interval over which the primary silicates crystallize in pockets in another 14 days increasing the host rock temperature to 300 c only extends the crystallization interval of the principal pocket silicates by another 5 2 months the dike center reaches 275 c at which temperature laumontite could crystallize approximately 55 days after emplacement clay minerals likely form and perhaps reform below 200 c the upper thermal stability limit of stilbite ca as the devitrified products of a remnant and flux depleted hydrosilicate glass that partially fills the miarolitic cavities the pegmatite achieves thermal equilibrium with the host rocks at 160 c more than 200 000 years later

controls on chemical evolution and rare element enrichment in crystallising albite spodumene pegmatite and wallrocks constraints from mineral chemistry abstract internal differentiation and consequent geochemical evolution in pegmatites are significant processes in the development of economically viable deposits of metal bearing minerals albite spodumene pegmatites which represent important resources of li and ta worldwide challenge the general rules of pegmatite petrogenesis as these are nearly homogeneous bodies with little or no intrusion scale pegmatite zonation bulk intrusion concentrations of li are in the uppermost range obtained by magmatic enrichment experiments around 2 wt li2o and extensive volumes of saccharoidal or platy albite are present in leinster southeast ireland weakly zoned to homogeneous albitised spodumene pegmatites and their wallrocks were studied to compare mineral chemistry variations and understand the internal evolution of pegmatites characteristics linked to the poor development of zonation and links between internal evolution and pegmatite wallrock interactions leinster pegmatites present mineralogical textural and geochemical characteristics coherent with li saturation and possibly supersaturation prior to crystallisation weak border to centre zonation in the thickest bodies can be attributed to geochemically evolved initial melt likely leading to nearly contemporaneous crystallisation throughout the intrusion and resulting in limited internal geochemical fractionation increased abundance of minerals bearing highly incompatible elements e g columbite group minerals and cassiterite and network modifiers e g phosphates in albitite indicates it is a fractionation product from pegmatite crystallisation enrichment in incompatible elements b li rb cs and f in spodumene pegmatite exocontacts in different country rock types suggests unmixing of a hydrous fluid from the residual melt after the crystallisation of main pegmatitic assemblages and that the h2o rich component was mobilised into country rocks

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

piston cylinder calibration at 400 to 500 mpa a comparison of using water solubility in albite melt and nacl melting a crushable alumina pyrex nacl solid media assembly for the piston cylinder apparatus was calibrated by nacl melting at 500 mpa 920 c and used to assess a new calibration technique based upon the solubility of water in albite melt at 400 to 500 mpa 800 and 1200 c use of the difference from 100 technique to measure water solubility with the electron microprobe produces a calibration accuracy of 25 mpa both calibration techniques agree and demonstrate that the real pressure is 50 mpa greater than the nominal pressure the water solubility in albite calibration is advantageous because it can be used to demonstrate that pressure temperature and time have no effect on the pressure calibration additionally a single capsule containing albite water can act as an in situ pressure monitor in solid media assemblies containing other experiments these calibrations demonstrate that the piston cylinder apparatus can be used reliably at middle to upper crustal conditions for long duration experiments

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

early devonian geothermal systems in northeast scotland exploration targets for epithermal gold early devonian geothermal activity is recognized in northeast scotland by the remnants of silica sinter a hot spring manganese deposit an area of steam alteration and hydrothermal eruption breccias at least five systems were active at this time three of which are located on or near the intersection of major faults and lineaments two deposits can be dated as early devonian whereas others show a spatial relation to 408 ma caledonian granitoids the proposed heat sources for the geothermal systems fault zones active at this time provided channelways for fluids in the convecting systems the shallow sections of these systems have been preserved in the arndilly dalroy lecht and rhynie areas which is encouraging for gold prospecting six targets for epithermal gold exploration are identified the four areas named above and two areas at the intersection of major faults and lineaments

spodumene pegmatites from the pusila pluton in the higher himalaya south tibet lithium mineralization in a highly fractionated leucogranite batholith abstract the himalayan leucogranite belt is evaluated as a prospect for rare metal mineralization the pusila pluton is located 44 km northwest of mount everest and consists of two mica granite muscovite granite albite granite and pegmatites numerous pegmatite dikes have intruded the higher himalayan crystalline sequence and the granites oligocene pegmatites in the chomogu and cuore areas which we constrain to have formed at ca 25 23 ma were investigated in this study because they are strongly enriched in li up to 8460 ppm and contain abundant spodumene petalite lithium was progressively enriched from the two mica granite to the muscovite granite and finally li mineralization occurred in the highly fractionated pegmatites the chomogu no 1 pegmatite is a well zoned dike that hosts beryl columbite cassiterite and li minerals which are concentrated in the inner parts of the dike scanning electron microscopy and cathodoluminescence images reveal two stages of li mineralization primary spodumene spd 1 crystallized in the magmatic stage whereas secondary spodumene spd 2 and petalite formed later in the hydrothermal stage the pusila pluton is thus an important site of li mineralization in the himalayan leucogranite belt

moist convection and the injection of volcanic ash into the atmosphere if unsaturated water vapor is carried upward by a volcanic eruption column it may eventually become saturated owing to the decrease in temperature of the column as it expands through decompression and transfers heat to entrained air heat released as a result of the subsequent condensation of water vapor causes the air within the column to expand we show that this increases the buoyancy and therefore the total height of rise of the column the increase in height is significant in relatively small sub plinian and strombolian eruptions in which mass eruption rates lie in the range 103 to 106 kg s in such eruptions the latent heat released as the entrained water vapor condenses may provide the main source of heat which drives the ash and clasts upward the height of rise then becomes relatively insensitive to the mass flux erupted at the vent and depends primarily upon the vapor loading of the atmosphere in a moist atmosphere ash may rise several kilomtres higher than in an eruption of comparable strength in a dry environment moist convection leads to much wider ash dispersal particularly from very small eruptions subsequently rain flushing of ash from umbrella clouds may result from the water which forms through the condensation of entrained vapor the ash provides natural condensation nuclei for some of this entrained vapor whose mass may be much greater than that of the ash in small columns 107 kg s the latent heat released by condensation of vapor is relatively small in comparison with the thermal energy provided by the hot clasts and therefore moisture has no significant effect upon the eruption column dynamics furthermore the mass of water vapor originating from the erupted volatiles is usually comparable to or greater than that entrained from the ambient air our model also shows that if the erupting mixture becomes buoyant then the eruption columns associated with phreatomagmatic eruptions ascend nearly as high as plinian columns with the same mass eruption rate this is because the water which is vaporized by the hot ash at the source condenses higher in the column and thereby restores its latent heat to the ascending ash

the effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts abstract the solubilities of columbite tantalite wolframite rutile zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts all experiments were conducted at 1035 c and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt h 2 o accessory phase solubilities are not affected by the water content of the peralkaline melt by contrast solubilities are affected by the water content of the subaluminous melt where the solubilities of all the accessory phases examined increase with the water content of the melt up to 2 wt h 2 o at higher water contents solubilities are nearly constant it can be concluded that water is not an important control of accessory phase solubility although the water content will affect diffusivities of components in the melt thus whether or not accessory phases will be present as restite material the solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies which have observed differences in the coordination of high field strength elements in dry vs wet subaluminous granitic glasses but not for peralkaline granitic glasses lastly the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species

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

testing the laacher see hypothesis a health hazard perspective it has recently been suggested that the laacher see volcanic eruption which occurred around 13 000 years ago initiated significant demographic fluctuations along the northern periphery of late glacial human settlement and that these led to a number of material culture transformations the origins of the southern scandinavian bromme culture and the northeastern european perstunian culture as well as the temporary abandonment of central european regions have been linked to this eruption however it remains unclear precisely which aspects of the eruption stimulated late glacial foragers to abandon their traditional ways of life paradoxically the culture historical impact of the eruption appears greater further away from the eruptive centre here we investigate one potential middle range link between the laacher see eruption and late glacial fauna and foragers tephra as a health hazard we use laser diffraction particle size analysis to quantitatively investigate tephra from one site with a secure late glacial archaeological deposit in addition we use values previously reported in the literature and a predictive model to calculate the hazard potential along a transect of two of the three major laacher see tephra fans our results show that the laacher see tephra may have posed a potential health hazard and that its hazard potential may have increased with distance from the vent to our knowledge this is the only study that attempts to quantify the changing grain size composition of tephra fall out longitudinally in this way at least with regard to a prehistoric eruption we close by discussing more speculatively other possible health pertinent effects of the laacher see eruption and suggest ways in which future work can further evaluate the impact of this eruption on late glacial populations

crustal melts below 400 c we propose that the internally zoned li bearing tin mountain pegmatite in the harney peak granite pegmatite system of the black hills south dakota crystallized from fluid rich compositionally complex melts at 400 350 c the low crystallization temperatures resulted from the combined fluxing effects of li b p h 2 o and carbonate anions the presence of hydrous silicate melts at temperatures of 350 c is revealed by microthermometric data on primary fluid inclusions cogenetic with crystallized melt inclusions mineral assemblages of the crystallized melt inclusions and chemistry of bulk fluid leachates indicate that the melts and fluids contained significant amounts of li and na as carbonates and or borates that acted as powerful fluxes the low temperatures give a new perspective on the stability of silicate melts in the crust

rapid crystallization of the animikie red ace pegmatite florence county northeastern wisconsin inclusion microthermometry and conductive cooling modeling we evaluated the crystallization regime of a zoned pegmatite dike and the degree of magma undercooling at the onset of crystallization by analyzing coeval fluid and melt inclusion assemblages the liquidus temperature of the pegmatite magma was 720 c based on re melting of crystallized melt inclusions in heating experiments the magma crystallized sequentially starting with a thin border zone which formed in less than one day at an average temperature of 480 c based on primary fluid inclusions meaning 240 c undercooling the primary inclusions from the outer zones were postdated by secondary inclusions trapped between 580 and 720 c representing fluid exsolved from hotter still crystallizing inner pegmatite units the huge temperature contrast between the pegmatite s inner and outer zones was simulated by conductive heat numerical modeling a 2 5 m wide dike emplaced in 220 c rocks cools entirely to 400 c in less than 50 days unidirectional and skeletal textures also indicate rapid disequilibrium crystallization

solubility of tin tungsten and molybdenum oxides in felsic magmas saturation versus undersaturation of granitic melts in tin tungsten and molybdenum oxides is discussed on the basis of experimental data results of dry and hydrothermal experiments are evaluated under the assumption of ideal solubility of sn w and mo oxides in granitic melts a conservative interpretation arrives at concentration levels of 1000 ppm sno2 wo3 and moo3 respectively considered as the maximum solubility of these components in granitic melts at 750 c 800 c such values are never reached in natural granites unaffected by hydrothermal alteration and therefore even highly evolved granites are expected to be undersaturated in these metals consequently cassiterite and scheelite are neither common liquidus minerals of ore bearing granites nor restite minerals from partial melting events

lithium isotope fractionation during fluid exsolution implications for li mineralization of the bailongshan pegmatites in the west kunlun nw tibet abstract granitic pegmatites are considered significant host rocks for the rare metal deposits however the enrichment mechanisms for the rare metal elements e g li be nb and ta remain debated here we report the whole rock and mineral e g muscovite and spodumene major trace elements and li isotopic compositions of the bailongshan granitic pegmatites in the west kunlun nw tibet to address this issue the bailongshan pegmatites hosting a super large li rb polymetallic deposit are composed of li poor and li rich pegmatites the li poor pegmatites display high 7li values in the whole rock 2 30 4 94 and muscovite 2 22 7 55 in contrast the li rich pegmatites show low 7li values in the whole rock 1 89 to 0 35 muscovite 3 39 to 4 49 and spodumene 2 83 to 1 87 these results together with the variations of the elements suggest that the li poor and li rich pegmatites were produced by the melt fluid separation during the late stage of granitic magma evolution this means that the li poor pegmatites were formed in a h2o poor silicate rich melt system while the li rich pegmatites were generated in a h2o rich silicate poor melt supercritical fluid system the melt fluid separation can lead to significant li isotope fractionation with 7li enriched in the strongly bonded residual silicate melt and 6li preferring to weaker hydrated bonds in the fluid alternatively the li rich pegmatites enriched in 6li could have been induced by preferential accumulation of the faster diffusing 6li in the supercritical or near critical fluid the li rich pegmatites experienced extensive crystal fluid interaction in a relatively closed magmatic hydrothermal system which resulted in the leaching and reprecipitation of ore forming elements but produced restricted li isotope fractionation the exsolved supercritical fluid is more enriched in alkali fluxing components li rb cs p and f by the continuous interaction with the residual silicate melt therefore the supercritical fluid exsolution plays an important role in the li isotope fractionation and rare metal mineralization

transport of atmospheric water vapor by volcanic eruption columns contrary to assumptions often made in the literature explosive volcanic eruptions are capable of transporting significant amounts of water into the stratosphere in addition to the magmatic water component atmospheric water vapor is entrained by the column at lower levels a theoretical model for the conservation of mass momentum and thermal energy of four separate components dry air water vapor liquid condensates and solid particles is used to determine the extent of atmospheric water redistribution we examine the effects of water vapor condensation on dynamical characteristics and ambient water vapor transport a simple technique is presented for deriving canonical forms for the complex system of ordinary differential equations governing the column components solutions of this model are presented that show the influence of different volcanic boundary conditions and a range of ambient water vapor distributions on transport of the buoyant column we show that the water component vapor liquid of small eruption columns rising through a wet atmosphere is dominated by entrained water whereas larger columns are dominated by the magmatic water this is due in part to the proportionately smaller entrainment surface area in relation to the control volume for the larger columns we also show that a maintained column with an initial mass flux of 2 7 108 kg s 1 erupted into a wet atmosphere would inject 96 mt of water vapor into the stratosphere over 24 hours comparable to the annual input from methane oxidation or 100 midlatitude thunderstorms this increase may accelerate the conversion of simultaneously erupted volcanic so2 into sulfuric acid

solubility of manganotantalite zircon and hafnon in highly fluxed peralkaline to peraluminous pegmatitic melts the behavior of tantalum and zirconium in pegmatitic systems has been investigated through the determination of ta and zr solubilities at manganotantalite and zircon saturation from dissolution and crystallization experiments in hydrous li f p and b bearing pegmatitic melts the pegmatitic melts are synthetic and enriched in flux elements 0 7 1 3 wt li2o 2 5 5 wt f 2 8 4 wt p2o5 and 0 2 8 wt b2o3 and their aluminum saturation index ranges from peralkaline to peraluminous asili al na k li 0 8 to 1 3 with various k na ratios dissolution and crystallization experiments were conducted at temperatures varying between 700 and 1 150 c at 200 mpa and nearly water saturated conditions for dissolution experiments pure synthetic end member manganotantalite and zircon were used in order to avoid problems with slow solid state kinetics but additional experiments using natural manganotantalite and zircon of relatively pure composition i e close to end member composition displayed similar solubility results zircon and manganotantalite solubilities considerably increase from peraluminous to peralkaline compositions and are more sensitive to changes in temperature or asi of the melt than to flux content a model relating the enthalpy of dissolution of manganotantalite to the asili of the melt is proposed hdiss kj mol 304 asili 176 in the peralkaline field and hdiss kj mol 111 asili 245 in the peraluminous field the solubility data reveal a small but detectable competitivity between zr and ta in the melt i e lower amounts of zr are incorporated in a ta bearing melt compared to a ta free melt under the same conditions a similar behavior is observed for hf and ta the competitivity between zr or hf and ta increases from peraluminous to peralkaline compositions and suggests that ta is preferentially bonded to non bridging oxygens nbos with al as first neighbors whereas zr is preferentially bonded to nbos formed by excess alkalies as a consequence zr ta ratios when buffered by zircon and manganotantalite simultaneously are higher in peralkaline melts than in peraluminous melts

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