mica liquid trace elements partitioning and the granite pegmatite connection the st sylvestre complex western french massif central abstract we constrain the genetic relation between granite and pegmatite parental melts from the variscan saint sylvestre leucogranite complex and associated pegmatite bodies massif central france through compositions of micas using mica trace element concentrations and available partition coefficients for li rb ba cs and f we calculated the trace element contents of granitic and pegmatitic melts at equilibrium with micas biotite in leucogranites and pegmatites ranges mostly from fe biotite to siderophyllite more evolved facies contain protolithionite and zinnwaldite and lepidolite occurs in the most fractionated pegmatite white micas have homogeneous compositions from muscovite to li phengite in granites biotite and muscovite trace element distributions are clustered in pegmatites mica trace element contents globally follow differentiation from the least to the most evolved body the reconstructed pegmatitic and granitic melts present strong compositional similarities such as enrichments in li rb cs and depletion in ba that suggest a similar origin however micas are shown to have selectively equilibrated with the last melt or fluid in contact and so trace element concentrations of early magmatic liquids are rarely preserved inversion of the mica data constrains the composition of parental melts and the trace element evolutions during crystallization leucogranite and pegmatite melts show mutual incompatible element evolutions inconsistent with a parent daughter genetic relation the data and the modelling suggest that they represent non cogenetic melts generated by discrete episodes of partial melting differentiation is thus inherited from source processes rather than being the consequence of fractional crystallization of a common parental melt magma we suggest that both the leucogranites and the pegmatites originate from partial melting of a heterogeneous source rather than pegmatites being the product of granite crystallization

fluid inclusion characteristics and geological significance of the xi ao copper tin polymetallic deposit in gejiu yunnan province abstract the newly discovered xi ao cu sn polymetallic deposit is located in the inner alteration zone of the laochang kafang granite edge in gejiu yunnan province the mineralization process of this deposit can be divided into four stages cassiterite and chalcopyrite mainly formed at stages ii and iii respectively fluid inclusions at different stages were studied by petrography microthermometry and laser raman spectrometry five fluid inclusion types are observed microthermometry results revealed that the ore forming fluid evolved from high temperature with low to intermediate salinity to low temperature with low salinity at stage i the fluid was under near critical conditions and then separated into coexisting liquid and vapor phases at stage ii finally the fluid was boiling and immiscible at stage iii a meteoric fluid mixing process was also observed at this stage laser raman spectra identified ch4 at the skarn and mineralization stages combined with other geological features the deposit was concluded to have formed under a relatively reduced environment the co2 component abruptly increased at stage iii and probably originated from the exterior fluorine may play an important role in mineralization cassiterite and chalcopyrite were mainly deposited at 340 440 and 300 400 c under pressures of 18 50 and 12 36 mpa respectively boiling and immiscibility are probably the main reason for mineral deposition the deposit of cassiterite and chalcopyrite showed similar salinities but higher temperatures than other mineralization types of deposits in the gejiu area this finding indicated that the study deposit probably represents the high temperature part of the gejiu mineralization system thereby benefiting mineral explorations in the gejiu area

from magmatic to hydrothermal sn li nb ta w mineralization the argemela area central portugal abstract the argemela mineralized area ama central portugal exhibits a nearly continuous magmatic to hydrothermal ore forming sequence typical of variscan granite related rare metal deposits disseminated and vein type mineralization are distributed in two systems the argemela mine am and the cabeco da argemela ca disseminated mineralization includes montebrasite cassiterite and columbite tantalite dispersed in rare metal granites vein type mineralization occurs both in granites and country rocks the ca system exposes three generations of intragranitic veins with montebrasite in the two earliest and montebrasite wolframite cassiterite and columbite tantalite in the latest country rock veins include a swarm of cassiterite and montebrasite veins am and rare isolated wolframite veins ca disseminated cassiterites are enriched in ta2o5 and nb2o5 compared to vein cassiterites disseminated columbite tantalites evolve toward mn and ta rich chemistries that contrast with the more fe and nb rich compositions in intragranitic veins in the ca system both intragranitic and country rock veins crystallize early mn rich wolframites followed by late more fe rich compositions associated with nb ta poor cassiterite the later replaced by stannite field relations structural mineralogical and geochemical data suggest that the disseminated and vein type mineralization are expressions of a continuous metallogenic evolution initiated at the magmatic stage pursued during the magmatic hydrothermal transition and ended with hydrothermal circulations in country rock the two mineralized systems share similarities but they also show major differences structural analysis demonstrates that the intragranitic veins in the ca and the country rock veins in the am were emplaced under the same tectonic regime therefore the two systems are variants of the same local metallogenic evolution sn and w show markedly contrasted behaviors both have a magmatic source but only sn reaches concentrations leading to saturation of the melt with cassiterite w is deposited later and preferentially to sn in intragranitic veins at the hydrothermal stage cassiterite and wolframite deposition are disconnected and overall wolframite occurs only in minor amounts the metallogenic model proposed for the ama emphasizes magmatic rare metal concentration processes exsolution of magmatic fluids and selective deposition of metals during the magmatic hydrothermal and later hydrothermal stages the sn li nb ta dominated and w poor signature of the ama makes it similar to lct pegmatites of the central iberian zone but is distinctive from the world class w sn cu panasqueira deposit nearby

petrogenesis and magmatic hydrothermal evolution time limitation of kelumute no 112 pegmatite in altay northwestern china evidence from zircon upb and hf isotopes abstract granitic pegmatites and associated rare metal deposits unique features in the altay orogen are located in a key tectonic position of the southern central asian orogenic belt caob and document the tectonic evolution of the paleo asian ocean the kelumute no 112 pegmatite which intruded into the jideke two mica granites hosts abundant rare metal e g li be nb ta ore deposits and ranks only second to the koktokay no 3 pegmatite in both size and reserves to explore the evolution time limitation of magmatic magmatic hydrothermal and hydrothermal stages in the pegmatite magma system the tectonic setting and the genetic relationship between pegmatites and granites this study presents zircon u pb and hf isotopic compositions of the kelumute no 112 pegmatite and the wall rocks two mica granite and biotite granite as determined by la icpms and la mc icpms the weighted mean 206 pb 238 u ages of the internal textural zones of the pegmatite including zones i ii iii v and vi are 238 3 2 0 ma 233 5 3 7 ma 188 3 1 7 ma 218 8 1 9 ma and 210 7 1 6 ma respectively wall rocks of two mica granite and biotite granite are dated at 445 6 4 3 ma and 455 6 5 4 ma respectively zircons from the kelumute no 112 pegmatite have lower positive e hf t values 0 03 to 2 35 with t dm model ages of 1112 1225 ma wall rocks show similar zircon e hf t values 1 41 to 4 13 and t dm model ages 1172 to 1515 ma however three xenocrystic zircons from the granites are characterized by larger negative ehf t values 5 85 to 9 83 and older t dm model ages 1839 to 2090 ma thus the following conclusions can be drawn 1 the kelumute no 112 pegmatite and its wall rocks jideke two mica granite and biotite granite have no genetic relationship as indicated by the large gaps between their formation ages however they did originate from a common source composed of ancient crust and mantle derived materials under two different tectonic settings 2 the magmatic magmatic hydrothermal transition and hydrothermal stages of the no 112 pegmatite magma lasted for 5 ma 23 ma and 22 ma respectively and 3 the no 112 pegmatite magma was most likely formed in a post collision tectonic setting indicating that block amalgamation and collisional orogeny of the caob continued into the triassic

s rich apatite hosted glass inclusions in xenoliths from la palma constraints on the volatile partitioning in evolved alkaline magmas the composition of s rich apatite of volatile rich glass inclusions in apatite and of interstitial glasses in alkaline xenoliths from the 1949 basanite eruption in la palma has been investigated to constrain the partitioning of volatiles between apatite and alkali rich melts the xenoliths are interpreted as cumulates from alkaline la palma magmas apatite contains up to 0 89 wt so3 3560 ppm s 0 31 wt cl and 0 66 wt ce2o3 sulfur is incorporated in apatite via several independent exchange reactions involving p5 ca2 vs s6 si4 na and ce3 the concentration of halogens in phonolitic to trachytic glasses ranges from 0 15 to 0 44 wt for cl and from 0 2 wt so3 dsapatite glass is only slightly dependent on the melt composition and can be expressed as so3 apatite wt 0 157 ln so3 glass wt 0 9834 the phonolitic compositions of glass inclusions in amphibole and hauyne are very similar to evolved melts erupted on la palma the lower sulfur content and the higher cl content in the phonolitic melt compared to basaltic magmas erupted in la palma suggest that during magma evolution the crystallization of hauyne and pyrrhotite probably buffered the sulfur content of the melt whereas the evolution of cl concentration reflects an incompatible behavior trachytic compositions similar to those of the water rich glass inclusions analyzed in apatite and clinopyroxene are not found as erupted products these compositions are interpreted to be formed by the reaction between water rich phonolitic melt and peridotite wall rock

a tin mineralized topaz rhyolite dike with coeval topaz granite enclaves at qiguling in the qitianling tin district southern china abstract the qiguling topaz rhyolite is present as a dike within the qitianling biotite granite batholith of the nanling range of southern china here the rhyolitic dike 4 5 m wide and 500 m long contains enclaves of topaz granite these rhyolites contain up to 72 wt sio 2 have alumina saturation index asi 1 1 and have groundmasses with estimated fluorine contents of approximately 1 5 wt textural relationships provide evidence of a quenched silicate melt that contains quartz k feldspar albite and zinnwaldite phenocrysts in a groundmass containing abundant topaz the rhyolites in the study area are also strongly enriched in tin 90 2700 ppm and generally have a close association between cassiterite and zinnwaldite although cassiterite is also present as sponge textured fills between rock forming minerals granite enclaves and their hosted rhyolite have similar major geochemical compositions and mineralogies to each other zircon u pb dating indicates that the topaz rhyolite 147 150 ma and topaz granite enclaves 154 ma were formed contemporaneously with ages that overlap within analytical uncertainty in addition the major and trace element compositions of the rhyolite and their granite enclaves are dissimilar to those of the hosting qitianling biotite granite this discovery of granite enclaves within rhyolite dikes suggests the presence of a topaz bearing granite body at depth that may host tin mineralization the expected hidden tin granite may be of great interest in the further exploration

a 2d mechanical thermalfluid dynamical model for geothermal systems at calderas an application to campi flegrei italy abstract a finite difference method has been developed to simulate water flow in a 2d porous medium with boundary conditions specified in terms of pressure and temperature the method computes steady state solutions for temperature pressure and fluid velocities with an appropriate choice for boundary conditions it is possible to simulate the behaviour of a geothermal system with an incremental pressure and or temperature applied to a finite part of the base pressure and temperature changes produce a change in the fluid flow regime leading to different final temperatures pressures and fluid velocities steady state the method is particularly suitable for simulating the coupled mechanical and thermalfluid dynamical effects at calderas when increases in pressure and heat flow from a magma chamber perturb the conditions of the uppermost aquifer system several tests performed with realistic values for the parameters of the porous medium show that increases of pressure at the base are efficiently propagated in the upper medium by water flow so that the effective centre of overpressure is shifted to considerably shallower levels this effect can strongly modify the shape of ground deformations at calderas and strongly amplify the peak values the proposed method has been applied to the explanation of the very peculiar ground deformation observed at campi flegrei during 1982 1984 which showed very high uplifts 1 8 m and a strong concentration in a small area 3 3 km 2 an integrated mechanical thermalfluid dynamical model for this caldera is proposed which could be generalised to other areas

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

experimental evidence for a protracted enrichment of tungsten in evolving granitic melts implications for scheelite mineralization the solubility of scheelite in evolved granitic magmas qz ab or an system with minor feototal tio2 and cao added was studied experimentally at 200 mpa 750 850 c and relatively oxidizing condition logfo2 nno 2 3 where nno is ni nio oxygen buffer water saturated granitic melts have been equilibrated with seeds of scheelite crystals the resulted wo3 contents in the melts vary only slightly from 0 21 to 0 32 wt wo3 over the investigated temperature and compositional range 0 7 to 1 4 wt cao but tends to increase with increasing temperature and decreasing cao concentration one important message conveyed from the study is that wo3 concentrations at scheelite saturation are more dependent on temperature in evolved ca poor melts than in ca rich melts natural granitic rocks associated with scheelite mineralization and associated melt inclusions hosted in quartz have much lower w contents than the experimental melts equilibrated with scheelite this implies that enrichment of tungsten w at magmatic stages is not sufficient to produce significant scheelite mineralization and confirms the important role of w mobilization by magmatic hydrothermal fluids in the formation of scheelite deposits

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

thermodynamics of water permeated unwelded pyroclasts 1 equilibrium properties abstract we report here the results of an investigation of thermodynamic equilibrium properties of systems constituted by phlegraean unwelded pyroclasts dry or saturated with water we have experimentally measured the porosity of samples of phlegraean rocks and determined the values of the heat capacity and of thermal expansion of dry and water perfused tuffs having different texture structures also the energetics of the process of adsorption of water on the large internal surface of these porous materials has been investigated the amount of heat exchanged during the reversible formation of an adsorbed layer has been determined in dependence of its thickness and as a function of temperature the coherent picture emerging from the ensemble of all these measurements is that of a direct connection between the processes of adsorption desorption and the stress of the porous rock in very unsaturated soils these processes may constitute a much more efficient mechanism of transformation of thermal energy into soil deformation compared with that of thermal expansion of the solid matrix

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

differentiation of strongly peraluminous perphosphorus granites the pedrobernardo pluton central spain the pedrobernardo pluton 295 2 ma initial 87sr 86sr 0 7122 is a layered sheet like granite body with distinct vertical zoning biotite muscovite bearing granites in the lower zone muscovite biotite leucogranites in the middle zone and muscovite bearing aplites and pegmatites in the upper zone the magma was anatectically generated intruded almost free of restite and evolved as a closed system by crystallization in situ geochemical modelling indicates that the lower and middle zones followed an equilibrium crystallization path with no separation between solids and melt and the upper zone followed a fractional crystallization path magmatic fractionation produced leucocratic differentiates with high p concentrations and a p ca ratio higher than in apatite the excess p is located in plagioclase and k feldspar monazite apatite fractionation in the lower and middle zones produced extreme depletions in th u y and the rees and chondrite normalized ree patterns with low lrees hrees and a slight discontinuity between nd and sm about 90 of the th u y and rees reside in accessory minerals especially in monazite biotite and muscovite have very low ree contents with small positive or no eu anomalies k feldspar and plagioclase in both the lower and upper zones have moderate ree contents with positive eu anomalies feldspars from the upper zone in contrast have negative eu anomalies and have very low ree contents compared to available data from literature dsr ba th u y reesbio mineral are lower by one to three orders of magnitude and dreesplag kfsp are also lower by one order of magnitude these huge discrepancies are attributed not only to contamination with ree rich inclusions in mineral concentrates used in previous studies but to real differences in geochemical behavior of trace elements in peraluminous systems with respect to subaluminous systems biotite melt and probably k feldspar melt distribution coefficients for th u y and the rees in peraluminous magmas must be much lower than previously considered

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

geochemical specialization of the tin bearing granitoid massifs of nw bohemia the geochemistry of hercynian tin bearing granitoid massifs of the krusne hory mts erzgebirge slavkovsk les forest kaiserwald and smrciny eastern fichtelgebirge is compared by statistical processing of 270 analyses including a wide spectrum of major and trace elements seven different types of granites are distinguished out of these five types represent the successive differentiation of the largest massif of nw bohemia the karlovy vary karlsbad massif this comprises strongly differentiated peraluminous granites evolving towards extreme li rb cs f and sn enrichment in the youngest members which are albite topaz zinwaldite lithium granites the sixth and seventh types are different from the former by their location in the eastern krusne hory and tectonic setting and they display geochemical features of anorogenic granites they are metaluminous albite zinwaldite granites with marked enrichment of nb y and hree in addition to li rb cs f and sn indicating contamination by sub crustal material sn w mineralizations including flat peri contact greisen bodies steep greisen veins and tourmalinized phyllites are all intimately associated with the most strongly differentiated granites the li granite and the cinovec granite respectively

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

age of the dahongliutan rare metal pegmatite deposit west kunlun xinjiang nw china constraints from la icp ms u pb dating of columbite fe and cassiterite abstract dahongliutan is a medium size li be ta nb rare metal pegmatite deposit in the tianshuihai terrane west kunlun orogenic belt nw china in this paper la icp ms u pb ages of columbite fe and cassiterite are reported to constrain the metallogenic age columbite fe with high u and low th yielded a late triassic weighted mean 206 pb 238 u age of 211 9 2 4 ma whilst cassiterite yielded a 206 pb 238 u 207 pb 235 u concordia lower intercept age of 218 12 ma and a tera wasserburg lower intercept age of 218 12 ma which is identical to the columbite fe u pb age and thus represents the emplacement age of the pegmatite dikes the ore hosting pegmatite dikes are intimately time space related to the dahongliutan s type granite ca 220 217 ma indicating that they may have been cogenetic integrating new and published geological data we suggest that the dahongliutan pegmatites may have evolved from the granitic magma represented by the dahongliutan s type pluton in a post collisional tectonic setting regionally the tianshuihai terrane is the western extension of the songpan ganzi block and thus the kunlun li mineralization belt may have been connected to the songpan ganzi li mineralization belt which contains eleven lithium deposits with about 9 8 of li 2 o reserves in china implying that the dahongliutan pegmatite deposit may also have favorable ore forming conditions the similar columbite fe and cassiterite ages demonstrate that these minerals can be precisely dated and could provide useful alternatives to accurately constrain the timing and evolution of rare metal mineralization

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 geochemistry of phosphorus in granite rocks and the effect of aluminium phosphorus has been shown to have a profound influence on the evolution of silicate melt systems it also controls the geochemical behavior of rare earths uranium thorium strontium and other elements through the relationships between melt and accessory phosphates based on experimental data harrison and watson 1984 proposed a model of saturation behavior of apatite in crustal melts as a function of temperature and silica content subaluminous granites fit in well with such a model but departures are evident in the case of peraluminous granites a systematic study of the distribution of p2o5 in granitoids from all over the world shows that there are two modes to describe phosphorus enrichment in peraluminous granitic rocks 1 the hoyos type trend which is parallel to the one in harrison and watson s hw model but with higher p2o5 concentrations at the same silica contents and 2 the pedrobernardo type trend implying an increase in phosphorus in the most sio2 rich differentiates of strongly peraluminous low ca granites pedrobernardo type leucogranites are characterized by the presence of rare phosphates or p rich feld spars since they have excess p2o5 over cao to form normative apatite we here propose the term perphosphorous granites high phosphorus contents appear to be due to elevated apatite solubility in peraluminous granitic melts rather than to high amounts of restitic apatite both the hoyos and pedrobernardo type departures from the hw model can be corrected by using the expression p2o5corrected p2o5hw efactor where p2o5hw is the prediction according to the hw model and factor is asi 1 6429t asi being the al2o3 cao na2o k2o molar ratio we suggest that such departures could be caused by a decrease in the ca activity in the melt as a result of increased peraluminousity the pedrobernardo type trend is a limiting case in which ca activity in the melt is nearly zero and calcium instead of phosphorus becomes the essential structural constituent esc of the apatite when this happens phosphorus starts behaving as an incompatible element that is concentrated in late fluids high p2o5 contents are more characteristic of s than other granite types no significant departures from the hw model have been found for i a or m type granites in central iberia granites associated with u sn and w mineralizations usually have high phosphorus contents values of p2o50 5 wt at sio270 wt are good indicators of economic mineralization

the thermal regime of the campi flegrei magmatic system reconstructed through 3d numerical simulations abstract we illustrate a quantitative conductive convective thermal model incorporating a wide range of geophysical petrological geological geochemical and isotopical observations that constrain the thermal evolution and present state of the campi flegrei caldera cfc magmatic system the proposed model has been computed on the basis of the current knowledge of 1 the volcanic and magmatic history of the volcano over the last 44 ka 2 its underlying crustal structure and 3 the physical properties of the erupted magmas 3d numerical simulations of heat conduction and convection within heterogeneous rock magma materials with evolving heat sources and boundary conditions that simulate magma rise from a deep 8 km depth to shallow 2 6 km reservoirs magma chamber formation magma extrusion caldera collapse and intra caldera hydrothermal convection have been carried out the evolution of the cfc magmatic system through time has been simulated through different steps related to its changes in terms of depth location and size of magma reservoirs and their replenishment the thermal modeling results show that both heat conduction and convection have played an important role in the cfc thermal evolution although with different timing the simulated present heat distribution is in agreement with the measured geothermal profiles agip 1987 reproduces the thermal gradient peaks at the cfc margins in correspondence to the anomalies in surface gradients corrado et al 1998 and suggests temperatures of 700 c at depth of 4 km in the central portion of the caldera in agreement with the estimated temperature for the brittle ductile transition hill 1992

regional reconstruction of subglacial hydrology and glaciodynamic behaviour along the southern margin of the cordilleran ice sheet in british columbia canada and northern washington state usa abstract subglacial landsystems in and around okanagan valley british columbia canada are investigated in order to evaluate landscape development subglacial hydrology and cordilleran ice sheet dynamics along its southern margin major landscape elements include drumlin swarms and tunnel valleys drumlins are composed of bedrock diamicton and glaciofluvial sediments their form truncates the substrate tunnel valleys of various scales km to 100s km length incised into bedrock and sediment exhibit convex longitudinal profiles and truncate drumlin swarms okanagan valley is the largest tunnel valley in the area and is eroded 300 m below sea level over 600 m of late wisconsin age sediments consisting of a fining up sequence of cobble gravel sand and silt fill okanagan valley landform substrate relationships landform associations and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds they are best explained by meltwater erosion and deposition during ice sheet underbursts during the late wisconsin glaciation okanagan valley functioned as part of a subglacial lake spanning multiple connected valleys few 100s km of southern british columbia subglacial lake development started either as glaciers advanced over a pre existing sub aerial lake catch lake or by incremental production and storage of basal meltwater high geothermal heat flux geothermal springs and or subglacial volcanic eruptions contributed to ice melt and may have triggered along with priming from supraglacial lakes subglacial lake drainage during the underburst s sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys progressive flow channelization focused flows toward major bedrock valleys in okanagan valley most of the pre glacial and early glacial sediment fill was removed a fining up sequence of boulder gravel and sand was deposited during waning stages of the underburst s and bedrock drumlins in okanagan valley were enhanced or wholly formed by this underburst s subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes the prevailing conceptual model for growth and decay of the cis suggests significantly thicker ice in valleys compared to plateaus subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner due to melting and enhanced sliding with significant transfer of ice toward the ice sheet margin subglacial lake drainage may have hastened deglaciation by melting ice lowering ice surface elevations and causing lid fracture this paper highlights the importance of ice sheet hydrology its control on ice flow dynamics distribution and volume in continental ice masses

revisiting complete miscibility between silicate melts and hydrous fluids and the extreme enrichment of some elements in the supercritical state consequences for the formation of pegmatites and ore deposits abstract using water and major and trace element data obtained from melt inclusions primarily in pegmatite quartz we have shown in this and previous papers that melt melt fluid immiscibility is widespread and an important process during the generation of granitic pegmatites furthermore we have shown that the formation of pegmatites actually begins in the supercritical melt fluid stage in this study we extend previous work and in particular explore the behavior of 10 different elements be f p s cl as rb sn cs and ta in the supercritical range from preliminary studies we suggest that other elements such as b na k zn nb and sb will behave similarly near the solvus crest of a generalized pseudo binary melt water system this provides important evidence that pegmatite forming processes have already begun at high temperatures in the range of 850 750 c and that may require a re think on the partitioning behavior of metals in late stage residual melts exsolved from granitic magmas the existence of this parental supercritical silicate melt fluid although derived from granitic magmas imposes significant constraints of its own so drawing conclusions about pegmatite forming processes from data gained from slightly modified granite compositions becomes highly problematic we propose that the extremely high concentration of some elements over a small but well defined water concentration range symmetrically distributed around the critical point of the pseudo binary solvus must be derived from the unusual properties of the near critical or supercritical phases these unusual properties include extremely low density viscosity and surface tension and high diffusivity reactivity and mobility these are exactly the qualities that make such supercritical fluids an excellent medium for the formations of pegmatites by reactions with the existing matrix melt crystal mush and for the extreme enrichment of some ore forming elements highly soluble in alkali and water rich supercritical fluids a very important point in mineral crystallization is the non uniform local enrichment of rare and economically significant elements at specific locations in pegmatites granites and other rocks given the properties of the supercritical phase identified from melt inclusions the process of ostwald ripening can operate very effectively the driving force for ostwald ripening arises because the concentration of solute in the vicinity of small crystals or clusters is greater than and in the vicinity of larger crystals or clusters less than the average supersaturation the solute in the supercritical fluid therefore flows from the small crystals to the larger crystals and permits the growth of very large crystals at the expense of smaller ones this is favored by the extraordinary properties of supercritical fluids given the low surface tension the supercritical fluid can move also through grain boundaries and small channels or dislocation pipes aiding incompatible element transport additionally their consequences for the formation of some important granite related ore deposits are briefly outlined

understanding the seismic velocity structure of campi flegrei caldera italy from the laboratory to the field scale we report laboratory measurements of p and s wave velocities on samples of tuff from campi flegrei italy and a new tomographic velocity map of the campi flegrei caldera laboratory measurements were made in a hydrostatic pressure vessel during both increasing and decreasing effective pressure cycles selected samples were also thermally stressed at temperatures up to 600 c to induce thermal crack damage acoustic emission output was recorded throughout each thermal stressing experiment and velocities were measured after thermal stressing laboratory p and s wave velocities are initially low for the tuff which has an initial porosity of 45 but both increase by between 25 and 50 over the effective pressure range of 5 to 80 mpa corresponding to a decrease of porosity of 70 marked velocity hysteresis due to inelastic damage processes is also observed in samples subjected to a pressurization depressurization cycle tomographic seismic velocity distributions obtained from field recordings are in general agreement with the laboratory measurements integration of the laboratory ultrasonic and seismic tomography data indicates that the tuffs of the campi flegrei caldera can be water or gas saturated and shows that inelastic pore collapse and cracking produced by mechanical and thermal stress can significantly change the velocity properties of campi flegrei tuffs at depth these changes need to be taken into account in accurately interpreting the crustal structure from tomographic data

crystallization of accessory phases in magmas by local saturation adjacent to phenocrysts abstract accessory minerals commonly occur attached to or included in the major crystalline phases of felsic and some intermediate igneous rocks apatite is particularly common as inclusions but fe ti oxides pyrrhotite zircon monazite chevkinite and xenotime are also known from silicic rocks accessories may nucleate near the host crystal liquid interface as a result of local saturation owing to formation of a differentiated chemical boundary layer in which accessory mineral solubility would be lower than in the surrounding liquid differentiation of this boundary layer would be greatest adjacent to ferromagnesian phenocrysts especially fe ti oxides it is with oxides that accessories are most commonly associated in rocks a boundary layer may develop if the crystal grows more rapidly than diffusion can transport incorporated and rejected elements to and from the phenocryst diffusion must dominate over convection as a mode of mass transfer near the advancing crystal liquid interface in order for a boundary layer to exist accumulation of essential structural constituent elements of accessory minerals owing to their slow diffusion in evolved silicate melt also may force local saturation but this is not a process that applies to all cases local saturation is an attractive mechanism for enhancing fractionation during crystallization differentiation if accessory minerals attached to or included in phenocrysts formed because of local saturation their host phenocrysts must have grown rapidly when accessories nucleated in comparison to lifetimes of magma reservoirs some inconsistencies remain in a local saturation origin for accessory phases that cannot be evaluated without additional information

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

subglacial jokulhlaup deposition jotunheimen norway abstract the aim of this paper is to discuss the origin of a linear boulder deposit near the mjolkedalsbreen jotunheimen norway subglacial fluvial deposition is suggested by palaeoflow indicators showing flow directions uphill along the axis of a ridge like deposit and the close association of this deposit with an ice contact boulder delta peak discharges of repeated jokulhlaups from the former ice dammed ovre mjolkedalsvatn were estimated at 1188 m3 s 1 using evidence derived from the proglacial jokulhlaup routeway former ice tunnel dimensions and flow conditions associated with the ridge like deposit were derived from a simple pipe flow equation flow velocities of 9 8 11 6 m s 1 and shear stresses of 1440 2018 n m2 were reconstructed for a tunnel less than 3 m in average height and 45 m wide such flows would have been capable of transporting boulders of greater than 3 m in diameter as traction load and material of gravel cobble size in suspension material of this size has been deposited downflow as an ice contact delta linear ridges of boulder gravel with up slope gradients found in association with ice contact deposits in other formerly glaciated areas may similarly be of jokulhlaup origin

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

microthermometric study of silicate melt inclusions in variscan granites from se germany volatile contents and entrapment conditions melt inclusions in granitic rocks are generally crystalline and must oberpfalz regions along the northern margin of the be homogenized to glass before analysis we employ a simple kinetic bohemian massif some of these granites particularly in technique with microthermometry to estimate total volatile contents the german erzgebirge are highly evolved geochemically and p t conditions of trapping of the melts from their hoand famous for the tin and uranium mineralization mogenization behaviour this information complements chemical associated with them several publications have condata from microprobe or ion probe analysis and can be obtained centrated on the geology geochemistry and ore from inclusions too small for direct analysis we present here values associations of the granites forster tischendorf 1994 for volatile contents as equivalent wt h2o trapping temperatures seltmann 1994 tischendorf forster 1994 hecht et and trapping pressures derived from studies of melt inclusions in some al 1997 siebel et al 1997 but their magmatic volatile variscan granites of the erzgebirge fichtelgebirge and oberpfalz contents and emplacement level are difficult to determine germany the volatile concentrations range from 3 to 10 equiv wt and have not often been addressed the granites from h2o microprobe analysis shows that the most volatile rich these regions contain abundant melt inclusions and these inclusions contain up to 8 wt f estimates of trapping offer the potential of constraining melt water contents pressures and temperatures suggest that crystallization began at an and conditions of trapping emplacement level of 3 6 5 km near 700 c with normal biotite all three regions contain composite plutons or plutonic and two mica granites and ended with topaz albite granite complexes which range in composition from un 650 c and pegmatitic phases down to 520 c this wide differentiated biotite granites to more highly evolved tworange of trapping temperatures and volatile contents is a general mica granites and finally to extremely evolved granites feature of melt inclusions in granites many of the granites studied containing li micas and topaz in some cases this comare highly evolved geochemically but the extreme volatile enrichment positional range is covered by different units of a single typical for these also occurs locally in the unspecialized granites pluton e g falkenberg granite oberpfalz whereas in other places individual plutons are more restricted in composition the erzgebirge region is particularly rich

the geochemical differentiation of s type pegmatites constraints from major trace element and li b isotopic composition of muscovite and tourmaline pegmatites often exhibit regional as well as internal zonation in this study we use major and trace element and li b isotopic composition of muscovite and tourmaline from internally zoned and un zoned s type pegmatites and their host granites to characterize the geochemical and isotopic fractionation associated with their formation the internally zoned pegmatites comprise three distinct textural zones namely wall intermediate and core muscovite and tourmaline occur in all the zones of these pegmatites the trace element concentrations ratios of muscovite from the three zones form well defined differentiation trends marked by enrichment of incompatible elements such as rb cs sr b zn nb ta p and the depletion of ni co v sc ti ba from the wall zone through the intermediate zone to the core zone this is suggestive of a strong role of fractional crystallization in producing the compositional diversity in the internally zoned pegmatites alkali element ratios such k rb and k cs in muscovite exhibit near exponential decline from the wall to the core zone which is suggestive of rayleigh type fractional crystallization fractional crystallization modelling reveals that the formation of the wall zone requires 69 crystallization the intermediate zone 85 95 and the core zone ca 99 crystallization leading to extreme enrichment of rb and cs and other incompatible elements muscovites and tourmaline from the un zoned pegmatites display similar compositional trends as the internally zoned ones but with a significant compositional gap between the host granite and the pegmatite lithium isotopic composition of muscovites and b isotopic composition of tourmalines become progressively lighter from wall to core zone of the internally zoned pegmatite and from the granite to the pegmatite for the un zoned pegmatites this is suggestive of an important role of vapour exsolution in the formation of the pegmatites taken together the geochemical and isotopic trends in the pegmatites can be explained by rayleigh fractional crystallization operating in tandem with vapour exsolution

crystallization conditions and evolution of magmatic fluids in the harney peak granite and associated pegmatites black hills south dakota evidence from fluid inclusions abstract a microthermometric study of inclusions in granites and pegmatites in the proterozoic harney peak granite system identified four types of inclusions type 1 inclusions are mixtures of co2 and h2o and have low salinities on average 3 5 wt nacleq type 2 inclusions are aqueous solutions of variable salinities from 0 to 40 wt nacleq type 3 inclusions are carbonic dominated by co2 with no detectable water and type 4 inclusions consist of 20 to 100 solids with the remaining volume occupied by a co2 h2o fluid many inclusions have a secondary character however a primary character can be unambiguously established in several occurrences of the type 1 inclusions these inclusions were trapped above the solidus and represent the exsolved magmatic fluid the secondary populations of types 1 2 and 3 probably formed as a result of reequilibration and unmixing of the type 1 fluid that progressively changed composition and density with decreasing temperature and pressure and was finally trapped along healed microfractures under subsolidus conditions type 4 inclusions are primary and are interpreted to be trapped fluid bearing complex silicate melts that subsequently solidified or underwent other posttrapping changes it is demonstrated that primary type 1 fluid inclusions that coexist with crystallized melt inclusions in the complex li bearing tin mountain pegmatite were trapped along the two fluid phase boundary in the system co2 h2o nacleq consequently the temperature and pressure conditions of trapping are identical to the bulk homogenization conditions on average 340 c and 2 7 kbar these conditions indicate that this li cs rb p and b rich pegmatite crystallized at some of the lowest known temperatures for a silicate melt in the crust an internally consistent empirical solvus surface in p t xco2 coordinates was generated for the pseudobinary co2 h2o 4 3 wt nacleq pegmatite fluid system distribution coefficients for the major species co2 h2o nacl and ch4 between the immiscible co2 rich and h2o rich fluid phases as a function of pressure and temperature were extracted from data for the two cogenetic fluid inclusions types

rock jointing and abrasion forms on roches moutonnees sw finland the influence of bedrock structures especially joints on the formation of roches moutonnees and different glacial abrasion forms on roches moutonnees were studied in the southwest archipelago of finland the size and form of roches moutonnees are closely connected with the frequency and state of joints in the bedrock the fewer and smaller the joints are the larger are the roches moutonnees that can be formed vertical joints in the direction of the ice movement form the weakest zones and determine the width of the roches moutonnees joints dipping against glacial movement determine the dip of the eroded rock surface horizontal joints provide a suitable base for large and gently dipping roches moutonnees which are normally lower than others with less frequent horizontal joints striae friction cracks facets fracture lines and plucked surfaces and their positions on the surfaces of roches moutonnees were observed on the basis of these observations a stereographic model of the distribution of different abrasion features on the surfaces of roches moutonnees was produced

monitoring and modelling hydrothermal fluid emission at la solfatara phlegrean fields italy an interdisciplinary approach to the study of diffuse degassing discharge of hydrothermal fluids at la solfatara is one of the many pieces of evidence testifying to the level of activity and the potential danger characterizing the volcanic complex of the phlegrean fields recent measurements of diffuse degassing shed light on the unexpected magnitude of this process and prompted further research to improve our understanding of the hydrothermal system feeding the surface phenomenon at la solfatara in this work we first present new data on co2 diffuse degassing that were collected during a campaign in july 2000 and confirm previous measurements of the degassing rate these data together with other information on subsurface structures and conditions provided the necessary constraints to perform physical modelling of the hydrothermal fluid circulation at la solfatara numerical simulations describe the ascent and evolution of a hot multi phase and multi component fluid composed of water and carbon dioxide through a homogeneous porous medium when certain system properties and conditions are used this model reproduces some of the main features which characterize the natural system including the energy budget associated with the ascent and condensation of hot fluids and the development of a single phase gas region whose existence was inferred from independent chemical data further simulations investigated the effects associated with changes in rock properties and fluid injection rates results showed that an increase in the permeability at shallow depth may have an important influence on the system conditions and fluid discharge they imply that surface phenomena accompanied by very high temperatures at shallow depths may survive long after deep feeding has ceased

controls on back arc crustal accretion insights from the lau manus and mariana basins abstract together the lau manus and mariana basins encompass a broad range of conditions of back arc basin development marine surveys have determined the tectonic setting and reconnaissance scale geophysical and geochemical properties of the extension axes in these basins we review these data to examine crustal accretion characteristics in the back arc setting in each basin magmatism is enhanced in spreading centres near the arc volcanic front but decreases becoming deficient in axes further from the arc in the lau and manus basins the axes extend far behind the arc and develop typical mid ocean ridge mor like characteristics we propose that these variations are controlled by the subducting slab which shapes composition and flow within the mantle wedge water released from the slab lowers the mantle solidus and increases in concentration toward the volcanic arc spreading centres near the arc advect the hydrated mantle material enhancing melt production slab induced flow carries melt depleted mantle material back beneath the basin where it mixes with ambient mantle spreading centres further from the arc advect this mantle mixture and produce thinner than normal crust far from the arc spreading centres advect essentially mid ocean ridge basalt morb source mantle and their characteristics are mor like thus in addition to spreading rate effects on mantle melting that predominate at mors in back arc basins the subducting slab introduces additional systematic effects

the beauvoir topaz lepidolite albite granite massif central france the disseminated magmatic sn li ta nb be mineralization the beauvoir topaz lepidolite albite granite french massif central is the latest intrusion in a variscan peraluminous granitic complex composed of three units successively emplaced the concealed la bosse granite the colettes two mica granite and the beauvoir granite the 900 m deep drill hole of the geologie profonde de la france deep drilling program of the continental crust has provided a continuously cored section of the beauvoir granite the exposed section of the beauvoir granite is presently mined for kaolin in the upper 200 m it also represents a huge subeconomic disseminated li sn ta be deposit sharing many characteristics with rare metal bearing pegmatites compared to similar li f rich igneous bodies the beauvoir granite is strongly enriched in sn 200 1 400 ppm ta 20 400 ppm and be 20 300 ppm li is located in lepidolite and amblygonite ta and nb mainly in columbo tantalite and uranium rich microlite and sn in cassiterite be is located in lepidolite crystals and in unidentified mineral s the major element composition of the beauvoir granite is similar to that of macusani volcanic glasses of peru and ongonite subvolcanic rocks of mongolia the main structural textural mineralogical and geochemical characteristics of the beauvoir granite can be explained by extreme fractionation of f and li rich magmas and associated fluid phases most trace elements show a strong upward enrichment the high f sub o 2 low solidus temperature and high fluorine content of the beauvoir magma have considerably reduced sn and w fractionation in the expelled magmatic fluid despite its high chlorine content 25 30 wt nacl equiv however f and li enriched geochemical halos have developed in the enclosing mica schist in response to the boiling of the magmatic fluid the relatively deep emplacement of the granite 3 km has limited the development of hydraulic fracturing and subsequent hydrothermal circulation and mineralization thus despite the very high specialization of the beauvoir granite no significant vein type mineralization is directly related to it the la bosse quartz ferberite stockwork was developed before the emplacement of the colettes and beauvoir granites and is related to the earlier concealed la bosse granite

a physical appraisal of a new aspect of bradyseism the miniuplifts 1 the campi flegrei caldera is characterized by well known episodes of fast uplift called bradyseism the last of which produced 1 8 m of maximum vertical displacement in the period 1982 1984 less known is a particular aspect of campi flegrei unrests detected only in the last 20 years namely the occurrence of miniuplift episodes characterized by relatively small positive vertical displacements in the range 0 03 0 11 m miniuplift episodes occurred in 1989 1994 and 2000 and probably one or two times in the period 1972 1982 these small ground uplifts were also accompanied by moderate seismicity each of them was followed by a short phase of relatively quick subsidence after which the previous rate of subsidence of the period was resumed an order of magnitude analysis of the forces energy and power that can cause the onset and determine the evolution of these events is derived on the basis of a thermal fluid dynamical approach it allows the quantitative correlation of the power input from the energy source with the rate of energy dissipation in the geologic system during the miniuplifts in order to assess the likelihood of our fluid dynamical model for these episodes theoretical ground displacements have been computed these displacements result from the changes in pressure as a function of depth predicted by the fluid dynamical model for reasonable perturbations of the geothermal system described as changes of the peclet number theoretical results agree extremely well with the observed amounts of the miniuplifts

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

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

hydrologic and geomorphic effects of temporary ice dammed lake formation during jokulhlaups glacial outburst oods jokulhlaups occur frequently in glaciated environments and the resultant ooding causes geomorphic change and in some instances damage to local infrastructure during some jokulhlaups oodwater is stored temporarily in ice marginal locations in july 1999 a linearly rising jokulhlaup burst from solheimajokull iceland during this remarkable event subglacial oodwater pooled transiently in two relict ice dammed lake basins before draining suddenly back into solheimajokull the signi cance of such rapid formation and attendant drainage of temporary ice dammed lakes during jokulhlaups has not been addressed consequently this paper i assesses the hydrologic and geomorphic effects of temporary ice dammed lake formation caused by lake basin retro lling and ii discusses the impact and signi cance of transient retro lling under jokulhlaup conditions pre and post ood eldwork at solheimajokull enabled the impact and signi cance of lake basin retro lling to be assessed field evidence demonstrates that the july 1999 jokulhlaup had an unusually rapid rise to peak discharge resulting in subglacial oodwater being purged to ice marginal locations the propensity for temporary retro lling was controlled by rapid expulsion of oodwater from solheimajokull coincident with locations suitable for oodwater storage floodwater inundated both ice marginal lake basins permitting signi cant volumes of sediment deposition coarse grained deltas prograding from the ice margin and boulders perched on scoured bedrock provide geomorphic records of sudden retro lling the depositional characteristics of lake basin deposits at solheimajokull are similar to jokulhlaup sediments documented in proglacial settings elsewhere however their depositional setting and association with ice marginal landforms is distinctive findings suggest that temporary ice dammed lake formation and drainage has the capacity to alter the shape of the ood hydrograph especially if drainage of a temporary lake is superimposed on the original jokulhlaup deposits associated with lake basin retro lling have a long term preservation potential that could help to identify temporary ice dammed lake formation in modern and ancient glacial environments copyright 2003 john wiley sons ltd

a new model for the granite pegmatite genetic relationships in the kaluan azubai qiongkuer pegmatite related ore fields the chinese altay pegmatites commonly form in the waning stage of magma evolution by fractional crystallization of volatile rich magmas and may be important host rocks of strategic metals e g li be cs ta and nb and high quality gem minerals this study reports new zircon u pb dating results and hf isotopic compositions of the kla803 pegmatite the azb 01 pegmatite the jmk 09 pegmatite abbreviated as the k a j pegmatites and the halong granite from the chinese altay to determine the potential petrogenetic relationships between them the geochronological data document that the k a j pegmatites were emplaced at 224 6 2 3 ma 191 6 2 0 ma and 192 0 2 3 ma respectively and they are characterized by negative to low positive epsilon hf t values from 1 0 to 63 and old model ages t dm with the t dm1 from 874 to 597 ma and t dm2 from 1298 to 833 ma in contrast the halong granite has an emplacement age of 398 3 2 4 ma and is characterized by higher positive epsilon hf t values from 9 9 to 15 2 and younger model ages t dm with the t dm1 from 626 to 414 ma and t dm2 from 760 to 423 ma they all have intruded into the kulumuti group stratum which has negative initial epsilon nd t values from 4 3 to 0 2 and old t dm model ages between 1 22 and 1 56 ga based on the calculated results of the mixing ratios f of the initial magmas and the prevailing paleozoic tectonic framework of the chinese altay we establish two petrogenetic models for the k a j pegmatites model 1 refers to that these pegmatites originated from a mixed magma that was composed of 72 91 wt depleted mantle components and 9 28 wt lower crust components and model 2 refers to that they were derived from the partial melting of 38 83 wt halong granite and 17 62 wt sedimentary rocks from the kulumuti group we also suggest that the initial magma of the halong granite was significantly contributed by juvenile materials with a slight involvement of crustal materials in model 1 because lct type pegmatites classified as li cs ta enriched pegmatites associated with s type granite that was produced by the partial melting of preexisting sedimentary rocks have close geochemical affinities with crustal materials the excessively high weight percentages 72 91 wt of the depleted mantle components in the initial magma of the k a j pegmatites indicate that this model is unrealistic therefore we consider that model 2 is more reasonable at present for interpreting the petrogenesis of the k a j pegmatites and it needs to be verified in other pegmatite fields of the chinese altay c 2016 elsevier ltd all rights reserved

textural features and chemical evolution in ta nb oxides implications for deuteric rare metal mineralization in the yichun granite marginal pegmatite southeastern china

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

the effect of collapse structures on ground deformations in calderas ground deformations related to unrest episodes in calderas are generally interpreted like in other volcanic environments in terms of increased pressure within a magma chamber embedded in a continuous elastic medium in this framework the depth of the pressure source is inferred from the size of the deformed area this scheme works quite well for individual volcanoes for instance hawaiian shields where a good correspondence between inflation events and eruptive episodes has been observed ground deformation in calderas however show unusual features that are difficult to interpret within such a scheme because considerable positive deformation in the order of several meters and microfracturing i e intense seismicity may occur without eruptions altough the estimated depth for the magma source is sometime very shallow less than 1 2 km it has been recently suggested that the contact zones at the border of collapsed calderas could act as stress strain discontinuity zones and thus bias modeling results obtained for continuous elastic media we use both observations and theoretical modeling based on 3 d finite element techniques to show that ground deformations in collapsed calderas are strongly influenced by the caldera structure giving a new perspective in related geological and geophysical observations in such areas

vertical surface displacements at yellowstone caldera wyoming 1976 1986 between first order leveling surveys in 1976 and 1986 the east central floor of yellowstone caldera rose 15 4 1 4 mm yr and the west central floor rose 17 0 2 0 mm yr with respect to points on the south caldera rim the same pattern has prevailed since an initial survey in 1923 except that the western caldera rose 30 faster during 1976 1986 than during 1923 1976 the 1976 1986 uplift extends beyond the northwest caldera rim near the adjacent hebgen lake fault zone site of a magnitude 7 3 earthquake in august 1959 marginally significant displacements in the eastern caldera suggest that uplift continued during 1983 1984 stopped during 1984 1985 and reversed to subsidence during 1985 1986 thus long term uplift may accumulate episodically historical uplift is especially noteworthy because regional crustal extension and thermal contraction during cooling would cause the caldera floor to subside if other processes were not acting to warp it upward the pattern and dimensions of the uplift indicate a source in the upper crust beneath yellowstone caldera probably a reservoir of rhyolite magma within a cooling granitic pluton a simple point source model would suggest a source 10 15 km deep but the reservoir is probably lens shaped and closer to the surface uplift may be caused by basaltic intrusions near the base of the reservoir or accumulation of magmatic fluids during cooling and crystallization within the reservoir subsidence might be a response to regional tectonic extension or release of trapped magmatic fluids magmatic inflation volatile accumulation and crustal extension may culminate eventually in renewed eruptive activity but there is no evidence of an imminent volcanic hazard

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

analysis of surface deformation data kilauea volcano hawaii october 1966 to september 1970 a least squares inversion technique has been applied to surface displacement measurements made at kilauea volcano hawaii in an attempt to locate centers of intrusive activity utilizing analytic expressions for the displacement field arising from dilatational sources in an elastic half space this technique allows for the simultaneous inversion of level tilt and horizontal distance measurements in terms of the location and volume of the intrusive body a variety of simple elastic model geometries representing possible shapes for intrusive bodies in the summit region of kilauea were examined none of the model geometries considered significantly improved the quality of the model fit to the available data over that obtained by a point source model calculations based on elastic models to consecutive level surveys were compared to available tilt data and horizontal distance measurements these comparisons indicate occasional departures from ideal elastic behavior the departure of measured tilt patterns from calculated tilt values may be the result of earthquake activity or episodic block movements superimposed on larger elastic displacements the departure of measured and calculated horizontal measurements reveals a gradual north south extensional strain across the summit caldera of kilauea in addition to the elastic uplift and subsidence patterns determined from level surveys a minimum estimate for the magma supply rate to kilauea is provided by the elastic models to the level data the average rate for the period from october 1966 to september 1970 was 0 07 km3 per year

enhanced vapor phase transport of tin in hydrothermal systems or experimental artifacts comments on the role of vapor in the transportation of tin in hydrothermal systems experimental and case study of the dachang deposit china by zhang et al j volcanol geotherm res 173 2008 313 324

partitioning of f between h2o and co2 fluids and topaz rhyolite melt implications for mineralizing magmatic hydrothermal fluids in f rich granitic systems fluid melt distribution coefficients for f have been determined in experiments conducted with peraluminous topaz rhyolite melts and fluids consisting of h2o and h2o co2 at pressures of 0 5 to 5 kbar temperatures of 775 1000 c and concentrations of f in the melt ranging from 0 5 to 6 9 wt the major element f and cl concentrations of the starting material and run product glasses were determined by electron microprobe and the concentration of f in the fluid was calculated by mass balance the h2o concentrations of some run product glasses were determined by ion microprobe sims the solubility of melt in the fluid phase increases with increasing f in the system the solubility of h2o in the melt is independent of the f concentration of the system with up to 6 3 wt f in the melt no evidence of immiscible silica and fluoriderich liquids was detected in the hydrous but water undersaturated starting material glasses 8 5 wt f in melt or in the water saturated run product glasses f concentrates in topaz rhyolite melts relative to coexisting fluids at most conditions studied however df wt f in fluid wt f in melt increases strongly with increasing f in the system maximum values of df in this study are significantly larger than those previously reported in the literature linear extrapolation of the data suggests that df is greater than one for water saturated peraluminous granitic melts containing 8 wt f at 800 c and 2 kbar df increases as temperature and as h2o h2o co2 of the fluid increase for topaz rhyolite melts containing 1 wt f and with h2o rich fluids df is independent of changes in pressure from 2 to 5 kbar at 800 c for melts containing 1 wt f and in equilibrium with co2 bearing fluids the concentrations of f in fluid increases with increasing pressure f and lithophile element enriched granites may evolve to compositions containing extreme concentrations of f during the final stages of crystallization if f in the melt exceeds 8 wt df is greater than one and the associated magmatic hydrothermal fluid contains 4 molal f such f enriched fluids may be important in the mass transport of ore constituents i e f mo w sn li be rb cs u th nb ta and b from the magma

microstructures and composition of melt inclusions in a crustal anatectic environment represented by metapelitic enclaves within el hoyazo dacites se spain abstract this article reports microstructures and compositions of melt inclusions in anatectic metapelites found as enclaves within el hoyazo dacites in the neogene volcanic province of southeastern spain the enclaves represent fragments of continental crust partially melted at 800 850 c and 5 7 kbar and brought to surface rapidly within the host volcanics while they still were in a molten state rapid cooling produced the solidification of silicate melt to glass in the rock matrix and in inclusions within minerals melt inclusions mi are present within nearly all mineral phases in the enclaves and their associated microstructures indicate a primary or pseudo secondary origin the entrapment mechanisms of mi within plagioclase were associated with 1 the presence of micron sized solids mostly graphite on the surface of growing crystals 2 partial resorption of crystals generation of embayments and later growth in the presence of melt and 3 entrapment of melt during crystal growth within crystallographic controlled planar structures e g on crystal faces melt inclusions in garnet are commonly associated with regularly oriented planar discontinuities filled with glass interpreted either as spaces left between adjacent mineral growth spirals or as crystallographic controlled cracks generated in between stages of mineral growth melt was trapped or percolated along these microstructures and later on necking down phenomena individualized inclusions with negative crystal shape melt inclusions in biotite are abundant show negative crystal shape and parallel cleavage planes melt inclusions in cordierite alkali feldspar and ilmenite are isolated sparse and sometimes rather large the composition of glass from all mi is leucogranitic and peraluminous with small differences among glasses in each mineral host there is some variation in glass composition within each textural location as well compositional heterogeneity can be partially explained by a combination of processes such as generation of boundary layers during mineral growth crystallization of daughter phases and hydrogen loss via diffusion through the host mean glass compositions in the several textural locations however can be tentatively interpreted as reflecting the evolution of melt chemistry during the prograde low to medium pressure anatexis of quartz poor metapelites

extreme halogen abundances in tin rich magma of the taylor creek rhyolite new mexico crystal bearing glass inclusions are hosted by quartz phenocrysts in eruptive units of the tin mineralized taylor creek rhyolite new mexico inclusions from four units were refused at 2 to 4 kbars and temperatures or 890 degrees c and analyzed for major and minor elements by electron microprobe and for h li be b rb st y nb mo sn cs ce th and u by ion microprobe average glass inclusion compositions are chemically representative of taylor creek melt and comparison of inclusion compositions with their whole rock equivalents suggests that li f cl ca and h 2 o degassed from cooling lava and or magma after inclusion entrapment taylor creek magma was strongly and variably enriched in f and cl prior to eruption average f concentrations of melt apparently ranged from 0 15 to 3 9 wt percent eruptive units containing the most f enriched glass inclusions are characterized by comparatively high average molar na 2 o na 2 o k 2 o ratios low li concentrations and relatively low phenocryst contents which are compatible with high preeruptive concentrations of f in magma average c1 concentrations were more uniform ranging from 0 23 to 0 37 wt percent high concentrations of f and cl are in accord with the style and extent of alteration in vapor phase altered parts of taylor creek rhyolite and are consistent with alkali chloride rich fluid inclusions in vapor phase minerals of altered rhyolites preeruptive enrichments in other volatiles were not as significant b in melt was 100 ppm and the apparent h 2 o content of melt was 2 wt percent geochemical studies of other tin topaz rhyolites and molybdenite bearing climax type porphyritic granites imply that their magmatic f concentrations were highly variable and that some fractions of magma were strongly enriched in halogens we suggest that such high levels of halogen enrichment may be generally representative of other highly evolved granitic magmas genetically associated with lithophile mineralization

magmatic hydrothermal transition of mo w mineralized granite pegmatite greisen system recorded by trace elements in quartz krupka district eastern krusne hory erzgebirge abstract magmatic hydrothermal transition of highly evolved granitic melts enriched in volatile and incompatible elements can involve disequilibrium intermediate products between aluminosilicate melt and hydrothermal fluid hydrosilicate liquids with high ore forming potential we investigate evolution from li f rich granites through pegmatites greisens and quartz veins in a composite stock at knottel in the krupka district eastern krusne hory erzgebirge mountain range by monitoring trace element variations in quartz interelemental correlations reveal si4 li al3 and likely si4 h al3 to be the most important substitution mechanisms variations in ti vs li be and al define distinct evolutionary trends i magmatic high li ti or al ti trend granites aplites k feldspar pegmatite ii transitional medium li ti trend quartz megacrysts and pegmatite lenses in granite quartz protolithionite pegmatite iii hydrothermal low li ti or al ti trend stockwork of coarse grained hydrothermal quartzites and quartz veins quartz replacement in greisens the medium li ti trend represents hydrosilicate liquid an h2o and sio2 rich medium with low density and effective viscosity that was probably formed during disequilibrium crystallization in front of rapidly propagating solidification front thermal evolution of the magmatic hydrothermal system was monitored by ti in quartz thermometry calculated rutile activity of the granites is very low 0 3 0 05 but it increases up to 1 that is saturation towards pegmatites and hydrothermal veins magmatic crystallization granites and aplites is constrained to 700 580 c pegmatite and bulk greisenization stage occurred at 600 500 c followed by a late hydrothermal stage associated with the formation of distal quartz veins at 500 390 c the granite pegmatite systems at knottel and in erzgebirge in general reach extremely high al li rb and ge and low ti concentrations in quartz in comparison with igneous rocks worldwide the knottel stock belongs to p poor a type granites in the erzgebirge and is linked with them by similar evolutionary trends in quartz trace elements furthermore the knottel system exhibits be enrichment in quartz probably related to high contents of f and this appears to be typical feature of mo w mineralized systems in general the hydrothermal phase with mo w mineralization at knottel is closely related to the magmatic phase of parental granite body which seems to be an important condition for mo w mineralization formation

phosphorus in s type magmas the p2o5 content of feldspars from peraluminous granites pegmatites and rhyolites

advances in lithium analysis in solids by means of laser induced breakdown spectroscopy an exploratory study lithium is an important geochemical tracer for fluids or solids however because the electron microprobe cannot detect li variations of li abundance at the micrometric scale are most often estimated from bulk analyses in this study the li intense emission line at 670 706 nm in optical emission spectroscopy was used to perfect the analysis of li at the micrometric scale by means of laser induced breakdown spectroscopy libs to estimate lithium content for different geological materials libs calibration of the emission line at 670 706 nm was achieved by use of synthetic glasses and natural minerals the detection limit for this method is 5 ppm li three applications to geological materials show the potential of libs for lithium determination namely for li bearing minerals melt inclusions quartz and associated fluid inclusions for spodumene and petalite from granite pegmatite dikes portugal the li2o concentrations are 7 6 1 6 wt and 6 3 1 3 wt respectively by use of libs these values agree with ion microprobe analyses bulk analyses or both for eucryptite crystals the li concentrations are scattered because grain size is smaller than the libs spatial resolution 6 to 8 m lithium concentrations of melt inclusions from the streltsovka u deposit siberia are in the range of 2 to 6 2 wt li2o for li rich daughter minerals lithium estimations on silicate glasses display values between 90 and 400 ppm lithium was also analyzed as a trace element in quartz transverse profiles were performed in hydrothermal barren quartz veins from the spanish central system sierra de guadarrama the highest li concentrations 250 to 370 ppm were found in specific growth bands in conjunction with the observed variation in optical cathodoluminescence intensity considering the fluid inclusion analysis the source of fluid responsible to the li enrichment in quartz is probably high salinity fluids derived from sedimentary basins

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

geochemical evidence for a multistage magmatic genesis of ta sn li mineralization in the granite at beauvoir french massif central the beauvoir rare metal granite at the southern edge of the echassieres granite massif french massif central is mineralized by disseminated ta sn and li the granite body formed from an independent melt which was emplaced soon after the main granite facies of the massif the geochemistry of the beauvoir granite relates it to the phosphorus rich type of ta bearing granites and geochemical and mineralogical data establish its similarity to pegmatite melts the beauvoir granite results built up from two distinct intrusions both intrusions are cogenetic and were emplaced within a short time interval a geochemical study of a deep drill hole bored down to 900 m under the surface to the floor of the granite sheet with selected key zones observed in greater detail has allowed the recreation step by step of a long process leading to the economic concentration of ta sn and li the comparison of major element trace element and isotopic geochemistry with the petrology makes it possible to unravel the numerous processes contributing to the ore formation local events need to be determined before main events can be identified constraints on the interpretation of the ore genesis are provided by a careful observation of data interpretations of these observations are strongly backed up by experimental data e g keppler 1993 the source rock was most likely enriched in sn and w at about 10 ppm precluding a slightly enriched granitic melt by partial melting it is not known whether the melt was already enriched in ta but this is not a prerequisite subsequently deep seated fractional crystallization produced granitic magma similar in composition ta nearly equal 9 m to the adjacent colettes granite and further fractionation processes led to a melt already strongly enriched in ta ca 40 ppm strongly peraluminous and enriched in the depolymerizing elements f and p the viscosity was therefore very low allowing easy ascent during transport small scale fluctuations in the viscosity were amplified by upward movement leading to an f and p rich melt preceding the magma batch this less viscous melt again underwent crystallization while moving through the upper

genesis and evolution of unrest episodes at campi flegrei caldera the role of thermal fluid dynamical processes in the geothermal system we develop a model for describing water flow in a porous medium under the effect of thermal and pressure gradients the model simulates geothermal systems in calderas given the boundary conditions and the fluid dynamical properties of the medium the model allows computation in fluid dynamical stationary states of parameters characterizing the flow such as flow velocity and temperature and pressure distributions at depth the model is applied to investigate the effects of the local geothermal system on the unrest episodes at campi flegrei caldera using experimentally determined fluid dynamical parameters for the caldera rocks we show that changes of water flow in shallow aquifers under the effect of pressure and or temperature variations within the geothermal system can be very important in the genesis and evolution of unrest crises in particular they can strongly amplify the effect of pressure increase in the magma chamber on ground uplift they can also explain the timescales of evolution of ground movements in terms of transit times of the water front and of the connected temperature fronts due to advective transport on such grounds an integrated mechanic thermal fluid dynamical model was built allowing us to give a semiquantitative global explanation to the genesis and evolution of unrest phenomena results obtained here can be generalized to other similar calderas

beryllium in silicic magmas and the origin of beryl bearing pegmatites this chapter addresses the portion of the geochemical cycle of beryllium that entails its transfer through the continental crust by the generation and migration of silicic magmas which will be referred to loosely as granitic but will include all of the textural variants of rocks derived from the granitic bulk compositions within the granite system we will examine the distribution of be between anatectic melts and residual crystals and we will track the accumulation of be in melt via crystal fractionation culminating in the saturation of pegmatite forming melts in the mineral beryl beryl is unquestionably the most common manifestation of be enrichment and the most abundant of the phases that contain essential beryllium see cern this volume to explain the presence of beryl in pegmatites we pose four questions 1 how much be does it take to saturate a granitic pegmatite forming melt in beryl 2 how much be is likely to be incorporated in silicic partial melts at their source 3 consequently how much fractionation of a typical granitic magma must occur to achieve beryl saturation in pegmatitic derivatives or is beryl saturation possible without extended magmatic fractionation 4 and should all granitic magmas be expected to achieve beryl saturation eventually or are there special attributes of the source material or crystalline phases in the magma that predetermine the likelihood of forming beryl in pegmatitic differentiates to address these questions we start with a review of beryl saturation in pegmatites we then examine the likely abundance of be derived by anatexis at the sources of granitic magmas with the two ends of the system bracketed we can then subject be fractionation to conventional modeling methods to ascertain how much fractionation must take place to bring granitic melts to beryl saturation as a review this chapter relies as much as possible on readily available publications

herderite from mogok myanmar and comparison with hydroxyl herderite from ehrenfriedersdorf germany the crystal structures of herderite cabepo 4 f 0 75 oh 0 25 a 9 7446 4 b 7 6769 3 c 4 7633 2 a 90 667 1 v 356 31 4 a 3 p 2 1 a and z 4 from the mogok stone tract myanmar and hydroxyl herderite cabepo 4 oh 0 52 f 0 48 a 9 7615 4 b 7 6680 3 c 4 7853 2 a 90 184 1 v 358 18 4 a 3 p 2 1 a and z 4 from the sauberg mine morgenrother zug ehrenfriedersdorf germany have been refined to r 1 indices of 1 7 in both cases using mo k single crystal x ray diffraction data herderite from mogok is associated with complex rare element beryl type granite pegmatite most herderite series minerals are the product of late stage processes in granite pegmatite evolution typically of an exsolved fluid upon crystallization and significant f enrichment in these fluids appears to result in the domination of herderite over hydroxyl herderite herderite is now documented from mogok myanmar yichung china brazil and probably erongo namibia the pegmatites at ehrenfriedersdorf germany have produced samples at the boundary between herderite and hydroxyl herderite if not possibly herderite as well

ground deformations in collapsed caldera structures abstract a method is presented to analyze the effect of stress strain discontinuities on the ground deformations generated by a pressure source this is meant to simulate the effects due to caldera structures likely to present fractured zones at the borders of the collapsed area a method originally developed by crouch 1976 to solve plane strain problems has been used to simulate deformation curves for several source and discontinuity geometries the main result is that the location of the discontinuities controls the extension of the deformed zone and always reduces it with respect to a continuous medium with respect to a homogeneous medium the presence of lateral discontinuities also acts towards lowering the overpressure required to produce a given amount of deformation these results indicate that when analyzing ground deformations in calderas the use of classical methods involving continuous media should be avoided or at least taken with caution these methods in fact assume that the extension of the deformed zone is only linked to the source depth some examples of ground deformations in active calderas have been analyzed in the framework of the results obtained from theoretical modeling four calderas recently affected by ground deformations have been considered rabaul new guinea campi flegrei italy long valley and yellowstone u s a the effects of collapsed structures on the deformation field are possibly evidenced for all the four calderas at rabaul and campi flegrei the fracture systems mainly affecting the ground deformations probably represent younger innermost collapses and are well evidenced by seismicity studies ground deformations are here concentrated in an area much smaller than the one enclosed by geologically visible caldera rims in particular at rabaul the effect of the innermost collapse can explain the high concentration of the uplift in the period 1971 1985 previously modeled by a very shallow source 1 3 km in terms of overpressure in the main magma chamber probably located at 4 5 km of depth

geochemistry of the rare metal bearing pegmatite no 3 vein and related granites in the keketuohai region altay mountains northwest china abstract the chemical composition of a barren biotite granite a two mica granite and a rare metal bearing pegmatite the no 3 vein in keketuohai altay mountains northwest china along with mineral separates of apatite and mica were analyzed and compared in the present work bulk chemistries of biotite granite two mica granite and pegmatite rim are consistent with fractional crystallization trend from granites toward pegmatite changes in pegmatite composition can be explained mainly by fractional crystallization of biotite rb sr isochrons yield 248 8 7 5 ma for the biotite granite 247 8 6 3 ma for the two mica granite and 218 4 5 8 ma for the pegmatite rim similar geochemical characteristics including initial e nd t values ranging from 0 76 to 3 04 for apatites similar initial e nd t values for whole rock samples of studied granites and pegmatite ranged from 1 40 to 3 21 and for biotites from granites ranged from 2 75 to 3 15 suggest that these rocks were derived from a common magma source old continental crust may have played a significant role in magma generation based on these data we interpret the evolution of the keketuohai granite pegmatite by magma differentiation from a common source biotite granite was the first to crystallize followed by two mica granites the residual melt was probably stored in a granitic batholith the pegmatite veins were injected 30 m y later during another episodic tectono magmatic event in the altay mountains