differentiation and crystallization conditions of basalts from the kerguelen large igneous province an experimental study phase relations of basalts from the kerguelen large igneous province have been investigated experimentally to understand the effect of temperature fo2 and fugacity of volatiles e g h2o and co2 on the differentiation path of lip basalts the starting rock samples were a tholeiitic basalt from the northern kerguelen plateau odp leg 183 site 1140 and mildly alkalic basalt evolved from the kerguelen archipelago mt crozier on the courbet peninsula representing different differentiation stages of basalts related to the kerguelen mantle plume the influence of temperature water and oxygen fugacity on phase stability and composition was investigated at 500 mpa and all experiments were fluid saturated crystallization experiments were performed at temperatures between 900 and 1 160 c under oxidizing log fo2 qfm 4 and reducing conditions log fo2 qfm in an internally heated gas pressure vessel equipped with a rapid quench device and a pt membrane for monitoring the fh2 in all experiments a significant influence of the fo2 on the composition and stability of the mg fe bearing mineral phases could be observed under reducing conditions the residual melts follow a tholeiitic differentiation trend in contrast melts have high mg mg2 mg2 fe2 and follow a calk alkalic differentiation trend at oxidizing conditions the comparison of the natural phenocryst assemblages with the experimental products allows us to constrain the differentiation and pre eruptive conditions of these magmas the pre eruptive temperature of the alkalic basalt was about 950 1 050 c the water content of the melt was below 2 5 wt h2o and strongly oxidizing conditions log fo2 qfm 2 were prevailing in the magma chamber prior to eruption the temperature of the tholeiitic melt was above 1 060 c with a water content below 2 wt h2o and a log fo2 qfm 1 early fractionation of clinopyroxene is a crucial step resulting in the generation of silica poor and alkali rich residual melts e g alkali basalt the enrichment of alkalis in residual melts is enhanced at high fo2 and low ah2o

experimental and thermodynamic constraints on mineral equilibrium inpantelleritic magmas abstract crystallization experiments on two pantellerites from pantelleria italy provide new evidence for the relationships between mineral phases in pantelleritic rocks as well as the influence of temperature and redox conditions on mineral assemblages experiments were performed at 1 kbar with temperature ranging between 750 900 c and fluid saturation conditions with xh2o h2o h2o co2 between 0 and 1 redox conditions were fixed at or slightly below the fmq buffer results show that at temperature of 900 c pantelleritic magmas are well above the liquidus regardless their water content we also observed a decrease in liquidus temperature 800 c with increasingly reducing conditions mineral assemblages of the natural rocks have been successfully reproduced particularly the relationship between fayalite and aenigmatite which appear to be strongly controlled by melt peralkalinity temperature and redox conditions this is the first time that fayalitic olivine have been synthetized in experimental studies on pantellerites which was found to be stable only for temperatures 750 c while amphibole can be stable at temperatures as high as 800 c at high ff2 experimental results have been compared with the composition of mineral phases as well as with the results obtained from mineral equilibrium geothermometry and oxygen barometry studies on pantelleritic lava and tuffs from pantelleria italy eburru kenya and menengai kenya petrological characteristics appear similar at different locations worldwide with typical assemblages of anorthoclase and sodian clinopyroxene with variable fayalite aenigmatite fe ti oxides and amphibole

influence of oxygen fugacity on mineral compositions in peralkaline melts the katzenbuckel volcano southwest germany the igneous rocks of the katzenbuckel southwest germany represent a unique and unusual alkaline to peralkaline association within the european volcanic province the magmatic activity can be subdivided into two main phases phase i comprises the main rock bodies of phonolite and nepheline syenite which were later intruded by different peralkaline dyke rocks tinguaites and alkali feldspar syenite dykes of phase ii the dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late stage pneumatolytic activity causing autometasomatic alterations as is typical for alkaline to peralkaline igneous rocks early mafic minerals of phase i rocks comprise olivine augite and fe ti oxides which are substituted in the course of fractionation by na amphibole and na pyroxene for the early magmatic stage calculated temperatures range between 880 and 780 8c with low silica activities 0 4 to 0 6 but high relative oxygen fugacities between 0 5 and 1 9 log units above the fmq buffer even higher oxygen fugacities above the hm buffer are indicated for the autometasomatic alteration which occurred at temperatures between 585 and 780 8c and resulted in the formation of pseudobrookite and hematite the unusually high oxygen fugacities even during the early magmatic stage are recorded by the major element compositions of the mafic minerals forsterite content in olivine between 68 and 78 mol up to 6 2 wt zro2 and 8 5 wt tio2 in clinopyroxene the unusual mineral assemblages pseudobrookite freudenbergite and by the enrichment of fe 3 in the felsic

the interaction of acid mine drainage with a carbonate terrane evidence from the obey river north central tennessee abstract the production of acidic drainage from active or abandoned coal mines is controlled by a complex series of reactions triggered by the oxidation of sulphide minerals limestone is frequently used as a neutralizing agent neutralization occurs both through dissolution of the limestone and exsolution of carbon dioxide from the water demonstration of these processes in a natural system is provided by the east fork of the obey river where acidic mine waters travel through conduits in limestone bedrock for several kilometers application of discharge concentration relationships allows tracking of the evolution of these waters within the karst aquifer several trends are evident virtually all of the iron in the acid mine drainage is precipitated along the flow path within the limestone the h released during this reaction together with the h generated by pyrite oxidation is largely neutralized by both exsolution of co 2 and dissolution of calcite dolomite in the carbonate bedrock releasing calcium and magnesium nevertheless the ph is still sufficiently low that all bicarbonate is converted to carbonic acid leaching of clay minerals by the acid waters releases small amounts of al and si the species cl f and no 3 are more or less inert the sulphate concentration substantially increases during evolution of the acid drainage this seems to be related to an input of sulphate enriched waters that have dissolved gypsum anhydrite as they follow deep flow paths within the limestone calculations of the relative proportions of h removed by reaction with calcite dolomite and co 2 degassing show that the latter is important in acidic waters that have reacted significantly with limestone and can readily lose co 2 to the atmosphere these results indicate that acid neutralization through carbonic acid dissociation in addition to neutralization through dissolution of carbonates is a useful method for the commercial a batement of acid mine drainage

the mineralogical diversity of alkaline igneous rocks critical factors for the transition from miaskitic to agpaitic phase assemblages geochemically the large family of alkaline plutonic rocks both qtz undersaturated and oversaturated compositions can be subdivided into metaluminous na 2 o k 2 o al 2 o 3 types in this paper we discuss two important aspects of the mineralogical evolution of such rocks with respect to their fe mg phases a major mineralogical transition observed is the precipitation of arfvedsonite or aegirine instead of fayalite or magnetite ilmenite the relative stability of these phases is controlled by oxygen fugacity and na activity in the crystallizing melts if na activity in the melt is high enough arfvedsonite aegirine form a common assemblage in peralkaline rocks under both reduced and oxidized conditions major mineralogical differences within this rock group exist with respect to their high field strength element hfse rich minerals most syenitic rocks known as miaskites contain zircon titanite or ilmenite as hfse rich minerals whereas in agpaites complex na k ca ti zr silicates incorporate the hfse similarly only a small group of peralkaline granites are found to lack zircon titanite or ilmenite but instead contain na k ca ti zr silicates here we present a detailed phase petrological analysis of the chemical parameters na 2 o cao k 2 o that influence the transition from miaskitic to agpaitic rocks based on the occurrence of ti and zr minerals several transitional mineral assemblages are identified and two major evolution trends for agpaites are distinguished a high ca trend which is exemplified by the alkaline rocks of the kola province russia and a ca depletion trend which is displayed by the alkaline rocks of the gardar province south greenland both trends show significant na enrichment during magmatic evolution high ca agpaites evolve from nephelinitic parental melts that did not crystallize large amounts of plagioclase in contrast agpaites showing ca depletion originate by extensive fractionation of plagioclase from basaltic parental melts in some peralkaline granites evolutionary trends are observed that culminate in agpaite like hfse mineral associations in the most evolved rocks

an experimental investigation of the influence of water and oxygen fugacity on differentiation of morb at 200 mpa crystallization experiments were performed at 200mpa in the temperature range 1150 950 c at oxygen fugacities corresponding to the quartz fayalite magnetite qfm and mno mn3o4 buffers to assess the role of water and fo2 on phase relations and differentiation trends in mid ocean ridge basalt morb systems starting from a primitive mgo 9 8 wt and an evolved morb mgo 6 49 wt crystallization paths with four different water contents 0 35 4 7 wt h2o have been investigated in primitive morb olivine is the liquidus phase followed by plagioclase clinopyroxene amphibole is present only at water saturated conditions below 1000 c but not all fluid saturated runs contain amphibole magnetite and orthopyroxene are not stable at low fo2 qfm buffer residual liquids obtained at low fo2 show a tholeiitic differentiation trend the crystallization of magnetite at high fo2 mno mn3o4 buffer results in a decrease of melt feo mgo ratio causing a calc alkaline differentiation trend because the magnetite crystallization temperature is nearly independent of the h2o content in contrast to silicate minerals the calc alkaline differentiation trend is more pronounced at high water contents residual melts at 950 c in a primitive morb system have compositions approaching those of oceanic plagiogranites in terms of sio2 and k2o but have ca na ratios and feo contents that are too high compared with the natural rocks implying that fractionation processes are necessary to reach typical compositions of natural oceanic plagiogranites

volatiles in a peralkaline system abiogenic hydrocarbons and f cl br systematics in the naujaite of the ilimaussaq intrusion south greenland agpaitic rocks comprise most of the exposed part of the 1 16 ga old 8 17 km large and about 1700 m thick ilimaussaq intrusion in south greenland within these more than 600 m thick sequence of sodalite rich naujaites mainly sodalite arfvedsonite alkali feldspar nepheline eudialyte aenigmatite are interpreted as a sodalite flotation cumulate sodalites show two to three different zones in cathodoluminescence cl and at least two zones in thin sections the cl zones can be related to chemical differences detectable by electron microprobe whereas relations with optical zonations are less obvious compositional trends in sodalite reflect trends in the evolution of volatile contents in the melt the sodalite at ilimaussaq is almost free of ca and closely corresponds to the pure na cl sodalite endmember with about 7 wt of cl s contents reach up to 0 9 wt cl br ratios range from 500 to 1700 raman spectroscopy shows that s is present as so4 2 in sodalite although sphalerite zns is a stable phase in naujaites peralkalinity and fo2 conditions allow s2 and so4 2 to be present contemporaneously the whole naujaite sequence is divided into two parts an upper part with low homogeneous s contents and cl br ratios in the sodalite cores and a lower part with strongly variable and higher s contents and with cl br ratios which are decreasing downwards the details of the s content and the cl br ratio evolution show that sodalite strongly influences the halogen contents of the melt by scavenging cl and br the naujaites were formed from a highly reduced halogen rich magma in equilibrium with magmatic methane at about 800 c which upon ascent cooling and fractionation exsolved an aqueous fluid phase both fluids were trapped in separate inclusions indicating their immiscibility micrometer sized aegirine crystals and primary hydrocarbon bearing inclusions are abundant in the crystal cores the inclusions were trapped at pressures up to 4 kbar although the emplacement pressure of the intrusion is about 1 kbar this indicates growth of the sodalite during melt ascent and a very effective mechanism of trace element scavenging during sodalite growth sodalite rims are devoid of aegirine or primary hydrocarbon inclusions and probably reflect the emplacement stage

geochemical modeling of coal mine drainage summit county ohio geochemical modeling was used to investigate downstream changes in coal mine drainage at silver creek metro park summit county ohio a simple mixing model identified the components that are undergoing conservative transport cl po43 ca2 k mg2 and na and those undergoing reactive transport do hco3 so42 fe2 mn2 and si fe2 is removed by precipitation of amorphous iron hydroxide mn2 are removed along with fe2 by adsorption onto surfaces of iron hydroxides do increases downstream due to absorption from the atmosphere the hco3 concentration increases downstream as a result of oxidation of organic material the rate of fe2 removal from the mine drainage was estimated from the linear relationship between fe 2 concentration and downstream distance to be 0 126 mg s results of this study can be used to improve the design of aerobic wetlands used to treat acid mine drainage

an experimental study of the influence of oxygen fugacity on fe ti oxide stability phase relations and mineral melt equilibria in ferro basaltic systems

phase equilibrium constraints on pre eruptive conditions of recent felsic explosive volcanism at pantelleria island italy we present experimental phase equilibria carried out on a pantelleritic bulk rock composition with a peralkalinity index pi molar na2o k2o al2o3 1 4 which is representative of the most energetic pumice fall eruption of the resurgent post caldera volcanism on pantelleria island for the explored conditions p 25 150 mpa t 680 800 c h2omelt up to 6 wt fo2 nno where nno is nickel nickel oxide buffer clinopyroxene is the liquidus phase followed by alkali feldspar and then quartz the crystallization of amphibole is limited to temperatures below 700 c aenigmatite crystallizes near the liquidus for p 100 mpa when clinopyroxene is the sole liquidus phase the coexisting melt is characterized by a decrease in peralkalinity index to 1 2 if compared with the starting material approaching comendite composition in contrast when alkali feldspar joins the liquidus phase assemblage residual melts become extremely peralkaline pi 3 2 with feo contents in excess of 14 wt comparison of our experiments with natural phase abundances and compositions constrains the depth of the fastuca pantellerite reservoir to be around 5 1 km or p 120 20 mpa at t 730 10 c with h2omelt around 4 wt and fo2 1 5 log unit below nno such conditions correspond to the dominant phase assemblage of feldspar clinopyroxene and aenigmatite amphibole occurrence requires both higher melt water contents and lower temperatures up to 6 5 wt at 680 c and may reflect provenance from a deeper and wetter portion of the tapped reservoir in contrast quartz is more probably related to crystallization during magma ascent which explains the lower melt water content of its melt inclusions overall the results confirm that pantellerites may be both water rich and reduced magmas these characteristics imply that any coexisting fluid phase in the reservoir will be dominated by water and hydrogen species the latter amounting to a few mole per cent magma unrest at pantelleria may thus be heralded by emissions of hydrous and reduced gases i e co2 poor and h2 rich if the present day reservoir is felsic in composition

arsenic copper and zinc occurrence at the wangaloa coal mine southeast otago new zealand abstract waste piles created from open cast coal mining activities at the abandoned wangaloa mine in se otago have exposed pyrite fes2 to atmospheric conditions this has led to the acidification of the surface tailings and nearby drainage waters acid mine drainage amd mobilisation of trace metals arsenic as copper cu and zinc zn has occurred partly as a result of the low ph levels ca ph 2 4 leading to elevated concentrations of these metals in receiving waters authigenic pyrite deposited in a marginal marine coal forming environment is enriched in as with levels reaching up to 100 ppm copper and zn in solid solution are not elevated above background levels in either coal measures or associated pyrite water discharges sediments waste rock and background samples were sampled and analysed during the driest summer and wettest winter seasons of 1998 and 1999 during the winter season water discharging from the waste piles contained up to 0 7 ppm mg kg as as measured in 1998 during the 1999 wettest season no such levels of as were observed with the highest level attaining 0 07 ppm as copper and zn were locally elevated in waters with zn concentrations reaching 1 ppm during the summer season of 1999 only one sampling site recorded elevated metal concentrations adverse effects from the remnant waste piles appear to be highly localised due to downstream natural remediation processes occurring in a wetland area the absence of strongly elevated metal concentrations during the drier season is a result of strongly depressed water levels within the waste piles flushing of acid and metals occurs when the water levels increase with the onset of the winter season during the summer season pyrite within the waste piles has been readily decomposing from the increased availability and transport of atmospheric oxygen

the effect of water and fo2 on the ferric ferrous ratio of silicic melts new experiments on the effect of dissolved water on the ferric ferrous ratio of silicic melts have been performed at 200 mpa between 800 c and 1000 c and for fo2 between nno 1 35 and nno 6 6 water saturated conditions were investigated compositions studied include six metaluminous synthetic melts with feotot progressively increasing from 0 47 to 4 25 wt two natural obsidian glasses one peraluminous and the other peralkaline and a synthetic rhyolitic glass having the composition of the matrix glass of the june 15 1991 pinatubo dacite ferrous iron was analyzed by titration and feotot by electron microprobe variation of quench rate was found to have no detectable effect on the ferric ferrous ratio of the hydrous silicic melts investigated at nno no dependence of the ferric ferrous ratio with temperature is observed at fo2 nno 1 the experimental ferric ferrous ratios are equal or lower than calculated the peralkaline samples show the same type of behaviour a non linear relationship between xfe2o3 xfeo and fo2 implies that a term for dissolved water must be added to the kc equation if it is to be applied to the calculation of ferric ferrous ratios of hydrous silicic melts above nno 1 the ferric ferrous ratio is essentially controlled by the anhydrous melt composition and fo2 however differences exist between measured and calculated ferric ferrous ratios of silicic melts that are not all attributable to the effect of dissolved water additional work is needed to describe more precisely the dependence of the ferric ferrous ratio on anhydrous melt composition the oxidizing effect of water is restricted to relatively reduced magmatic liquids in oxidized calk alkaline magma series the presence of dissolved water will not largely influence melt ferric ferrous ratios

the amphiboles of the ree rich a type peralkaline strange lake pluton fingerprints of magma evolution abstract major and trace element compositions of amphibole in igneous environments commonly reflect evolving magma compositions in this study we use the amphibole group minerals from the strange lake ree enriched peralkaline granitic pluton to gain insights into the evolution of the magma this 1240 ma old pluton consists of two main intrusive facies an early hypersolvus granite which occurs as separate northern and southern intrusions and a more evolved transsolvus granite in the hypersolvus granite the amphibole is a late interstitial phase whereas in the transsolvus granite it is present as phenocrysts the amphibole compositions vary from calcic sodic ferro ferri katophorite in the southern hypersolvus granite to sodic arfvedsonite ferro ferri leakeite in the other more evolved granitic units high na si li and low al and ca concentrations in the amphibole phenocrysts of the transsolvus granite indicate formation from a more evolved magma compared to the hypersolvus granite despite the fact that these crystals formed early we interpret the increasing fe 3 fe 2 ratios in the amphibole of the hypersolvus granite to reflect crystal chemical effects na ca ratio and increasingly oxidizing conditions in the magma whereas in the phenocrysts of the transsolvus granite the increasing ratio was the product of increasing proportions of f and oh in the melt the amphiboles of all the granite units have elevated nb zr hf and ree concentrations compared to the bulk rock suggesting that these elements are compatible in amphibole by contrast the much lower ti concentration was due to saturation of the magma in sodium titanosilicates the amphibole ree concentrations vary greatly among the granite units amphibole of the southern and northern hypersolvus granite contains 0 16 and 0 07 wt ree y on average respectively and in the transsolvus granite the average ree content is only 0 01 wt despite the more evolved nature of its host transsolvus granite we intrepret this compositional difference to be due to the fact that the latter represents phenocrysts which crystallized early whereas the hypersolvus arfvedsonite is a late interstitial phase chondrite normalized ree profiles emphasise the wide range in lree and the narrow range in hree concentrations of the amphiboles the variations in the lree profiles reflect the variable crystallization of primary lree bearing phases including monazite ce pyrochlore group minerals and gagarinite ce prior to or contemporaneous with the amphibole as well as the exsolution of a lree rich fluoride melt the lree are incompatible in the amphibole structure apparent d d 1 owing to their small ionic radius and their compatibility with the amphibole structure hree concentrations were more controlled by partitioning crystal chemical effects than by the concentrations in the corresponding magma large proportions of the bulk hree content up to 70 reside in the amphibole and their later release through hydrothermal replacement helps to explain the extreme and unusual hree enrichment of the strange lake pluton

experimental constraints on pre eruption conditions of pantelleritic magmas evidence from the eburru complex kenya rift the phase relationships and compositions of a pantellerite from the eburru complex in the kenya rift valley have been determined at 150 mpa and under reducing conditions 2 log units below the ni nio solid buffer the effects of temperature and melt water content on phase relationships have been explored alkali feldspar and quartz crystallise alone at temperatures above 700 c irrespective of melt water content below 700 c sodic amphibole and clinopyroxene also crystallise the amphibole being the liquidus phase under water rich conditions the coexistence of amphibole phenocrysts with alkali feldspar and quartz in a crystal poor pantellerite implies temperatures below 700 c and melt water contents higher than 4 wt possibly up to 5 6 wt pantellerites have lower liquidus temperatures than associated comendites which supports a parent daughter relationship between the two magma types the melts produced in the experiments extend the compositional trend displayed by the natural rock series and reproduce some extreme compositions occasionally observed in alkaline volcanic series with feo contents above 12 wt and na2o contents approaching 10 wt pantellerites are therefore the true near minimum melt compositions of alkaline oversaturated magma series

pollution of osheepcheon creek by abandoned coal mine drainage in dogyae area eastern part of samcheok coal field kangwon do korea osheepcheon creek running through the dogyae area is being polluted by the influx of the abandoned coal mine drainage generally the more polluted water has lower ph and eh and higher conductivity values the concentrations of mg ca fe so4 and some trace elements such as cd co cr mo ni pb rb sr u and zn are tens to hundreds of times more concentrated in the abandoned coal mine drainage than in the unpolluted streamwater however most immobile toxic pollutants from the mine drainage are quickly removed from the streamwater by the precipitation of amorphous fe hydroxide and sorption on the precipitated fe hydroxide the fast removal of the pollutants from the streamwater maintains the water quality of the creek as acceptable at most places along the stream path except where the abandoned coal mine drainage flows in however the creek has the potential of deteriorating quickly if the mine drainage is allowed to be continuously combined with the streams a function of ph eh and conductivity has been developed with discriminant function analysis for the purpose of easy fast and inexpensive measurement of the degrees of pollution of the streams the estimated pollution of the streams with the discriminant function are consistent with what the chemical compositions of the water samples indicate the pollution map of the study area was constructed from the calculated scores with the discriminant function the pollution map suggests that the pollutants mainly come from the west side of osheepcheon creek thus the abandoned coal mine drainage from the west side has to be appropriately treated as soon as possible to prevent osheepcheon creek from being further polluted considering the topography climate and the amount of the mine drainage an active treatment method is recommended

modification of a rare earth element deposit by low temperature partial melting during metamorphic overprinting norra karr alkaline complex southern sweden abstract rare earth elements play a crucial role in modern technologies and are necessary for a transition to a green economy potentially economic deposits of these elements are typically hosted in minerals such as monazite bastnasite and eudialyte a complex na ca fe zr silicate mineral with cl making these prime targets for geological research globally rare earth mineral deposits commonly show evidence of polyphase development and mineralisation processes which need to be better understood to improve exploration strategies the norra karr alkaline complex sweden contains a globally significant deposit of rare earth elements hosted in the mineral eudialyte in this study we focussed on eudialyte crystals in undeformed cross cutting pegmatoid veins from norra karr in order to determine their age we refined an established micromilling method to enable sampling of minerals rich in rare earth elements for precise analysis of major and trace elements nd isotope ratios and sm nd geochronology down to a scale of

on the controls of oxygen fugacity in the generation and crystallization of peralkaline melts the formation of peralkaline melts is generally recognized to be related to enrichment of the mantle in sodium or potassium during a metasomatic event that predated magma generation the wide range in mineral assemblages mineral compositions and fluid compositions in peralkaline melts are to a large extent a function of the sodium potassium content of these mantle metasomatizing fluids which also governs redox conditions we propose that sodic fluids will reduce the mantle assemblage by depleting ferric iron from garnet to form the aegirine component in pyroxene in contrast potassic fluids would oxidize the mantle assemblage by extracting al2o3 from the garnet to make phlogopite we suggest that during differentiation of peralkaline melts once fe ti oxides have been depleted from the assemblage simple crystallization reactions of common solid phases such as aegirine or arfvedsonite control the oxygen fugacity by equilibria such as

phase relations and liquid lines of descent of an iron rich peralkaline phonolitic melt an experimental study we experimentally investigated the phase relations of a peralkaline phonolitic dyke rock associated with the ilimaussaq plutonic complex south greenland the extremely evolved and iron rich composition magnesium number 2 alkalinity index 1 44 feo 12 wt may represent the parental magma of the ilimaussaq complex this dyke rock is therefore perfectly suited for performing phase equilibrium experiments since in contrast to the plutonic rocks of the complex no major cumulate formation processes complicate defining a reasonable starting composition experiments were carried out in hydrothermal rapid quench cold seal pressure vessels at p 100 mpa and t 950 750 c h2o contents ranging from anhydrous to h2o saturated 5 wt h2o and varying fo2 logfmq 3 to 1 where fmq represents the fayalite magnetite quartz oxygen buffer were applied reduced and dry conditions lead to substantial crystallization of alkali feldspar nepheline hedenbergite rich clinopyroxene fayalite rich olivine and minor amounts of ulvospinel rich magnetite which represent the phenocryst assemblage of the natural dyke rock oxidized and h2o rich conditions however suppress the crystallization of olivine in favor of magnetite and clinopyroxene with less or no alkali feldspar and nepheline formation accordingly combined low fo2 and ah2o force the evolution of the residual melt toward decreasing sio2 increasing feo and alkalinity index up to 3 55 on the contrary high fo2 and ah2o produce residual melts with relatively low feo high sio2 and a relatively constant alkalinity index we show that variations of ah2o and fo2 lead to contrasting trends regarding the liquid lines of descent of iron rich silica undersaturated peralkaline compositions moreover the increase in feo and alkalinity index reduced and dry conditions in the residual melt is an important prerequisite to stabilize late magmatic minerals of the dyke rock for example aenigmatite na2fe5tisi6o20 coexisting with the most evolved melts at 750 c contrary to what might be expected experiments with high ah2o and interlinked high fo2 exhibit higher liquidus t s compared with experiments performed at low ah2o and fo2 for experiments where magnetite is liquidus phase this is because ulvospinel poor magnetite crystallizes at higher fo2 and has a higher melting point than ulvospinel rich magnetite which is favored at lower fo2

experimental constraints on the storage conditions of phonolites from the kerguelen archipelago phase relations of a phonolite k1 and a tephri phonolite k2 from the upper miocene lavas in the southeast province of the kerguelen archipelago have been investigated in the p t range 100 500 mpa and 700 900 c at two fo2 conditions nno and nno 2 3 to clarify the differentiation and pre eruptive conditions of these magmas crystallization experiments were performed in cold seal pressure vessels cspv and internally heated pressure vessels ihpv at various xh2o under reducing log fo2 nno and oxidizing conditions log fo2 nno 2 3 under reducing conditions the resulting phase assemblage for k1 was titanomagnetite nepheline alkali feldspar clinopyroxene and biotite under oxidizing conditions the assemblage was magnetite plagioclase alkali feldspar nepheline titanite minerals given in the order of appearance with decreasing t at 200 mpa for 4 wt water in the melt it is emphasized that an effect of fo2 on the phase stability of feldspars and feldspathoides was observed comparison of the natural and experimental phase assemblages shows that the pre eruptive conditions for k1 must have been in the log fo2 range nno 1 nno 2 at pressures above 200 250 mpa assuming a temperature of 800 c the water content of the melt is constrained to be between 4 and 6 wt h2o the pre eruptive fo2 conditions for the less evolved sample k2 are more oxidizing with log fo2 close to nno 2 3 the experimental results show that the enrichment of alkalis in residual melts during differentiation of tephri phonolites is enhanced at high fo2

phase relations and liquid lines of descent in hydrous ferrobasalt implications for the skaergaard intrusion and columbia river flood basalts crystallization experiments using a hydrous ferrobasalt as starting material conducted at 200mpa 940 12008c at a wide range of water activities 0 1 1 and redox conditions qfm 3 to qfm 4 where qfm is the quartz fayalite magnetite oxygen buffer show that h2o influences significantly the differentiation history of ferrobasaltic magmas a combination of our data with published experiments on dry ferrobasalt at 1atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical fe rich tholeiitic system under both dry and hydrous conditions the addition of h2o decreases liquidus temperatures and changes significantly the proportions temperature range and sequence of crystallizing mineral phases the dry liquidus is at about 11708c whereas the liquidus for h2o saturated melts is at 10608c the main phases crystallizing from h2o bearing ferrobasalt at the investigated conditions are olivine ol clinopyroxene cpx plagioclase pl magnetite mt hematite hm ilmenite ilm and amphibole am the phase assemblage is similar to that of the dry system except for the presence of hm at extremely oxidizing conditions and am at low temperatures 59508c and h2o saturated conditions the important observation made in this study is that the stability of fe ti oxides and in particular mt as well as the simultaneous coprecipitation of mtand ilm are almost independent of the activity of h2o ah2o in the system whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing ah2o the stabilities of oxides are controlled mainly by the redox conditions prevailing in the system the most pronounced effect of ah2o on the liquidus temperatures of silicates is observed for pl which shows a considerable delay in crystallization with progressive magma differentiation early crystallization of fe ti oxides in h2o bearing ferrobasaltic compositions precludes any significant fe enrichment during differentiation as fe enrichment is a characteristic feature of the skaergaard intrusion it implies that the skaergaard parental magma did not contain considerable amounts of water on the other hand our experiments indicate that the differentiation of some ferrobasaltic series from the columbia river flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles 0 5 3 wt h2o

the redox state of pinatubo dacite and the ilmenite hematite solvus the oxidation state of the 1991 pinatubo dacite and many other oxidized silicic arc volcanic rocks has been overestimated we reproduce the compositions of magnetite and ferrian ilmenite found in pinatubo dacite by doing crystallization experiments at 780 degrees c 2 2 kbar and nno 1 7 or 0 2 log units the extra components in igneous ilmenite notably geikielite expand the solvus in a way that is not correctly accommodated in current formulations of the iron titanium oxide thermobarometer

experimental study of chlorine behavior in hydrous silicic melts chlorine solubility in silicate melts has been investigated at 830 850 plus minus 5c and at pressures ranging from 50 to 200 mpa using both natural pantellerite rhyolite phonolite and synthetic sio sub 2 al sub 2 o sub 3 k sub 2 o na sub 2 o compositions and a stated h sub 2 o nacl kcl fluid phase near 4 molal at 100 mpa cl contents in pantelleritic melts reach a solubility plateau at initial aqueous phase molality near 2 this plateau coincides with a large immiscibility gap between aqueous and chloride rich fluids with the coexisting cl saturated aqueous phase cl ranges from 2 720 plus minus 120 ppm in rhyolite to 8 960 plus minus 85 ppm in pantellerite and reaches 6 270 plus minus 170 ppm in phonolite at 100 mpa between 50 and 200 mpa the cl content in pantelleritic melt decreases from 9 640 plus minus 200 ppm to 5 040 plus minus 150 ppm although cl solubility increases with increasing feo sup in high sio sub 2 melts it is mainly controlled by the al si and na k al molar ratios of the melt with a minimum at na k al 1 in a series of synthetic rhyolitic to pantelleritic melts the experimental results suggest that chlorine occurs as alkali chloride complexes in high sio sub 2 more melts they also indicate that cl is concentrated in the aqueous fluids in equilibrium with sio sub 2 rich melts the exact value of d depending on melt composition and melt chlorine concentration volcanic degassing will create chlorine rich hydrothermal fluids and decrease chlorine melt content less

effect of oxygen fugacity and water on phase equilibria of a hydrous tholeiitic basalt the influence of oxygen fugacity and water on phase equilibria and the link between redox conditions and water activity were investigated experimentally using a primitive tholeiitic basalt composition relevant to the ocean crust the crystallization experiments were performed in internally heated pressure vessels at 200 mpa in the temperature range 940 1 220 c the oxygen fugacity was measured using the h2 membrane technique to study the effect of oxygen fugacity three sets of experiments with different hydrogen fugacities were performed showing systematic effects on the phase relations and compositions in each experimental series the water content of the system was varied from nominally dry to water saturated conditions causing a range of oxygen fugacities varying by 3 log units per series the range in oxygen fugacity investigated spans 7 log units systematic effects of oxygen fugacity on the stability and composition of the mafic silicate phases cr spinel and fe ti oxides under varying water contents were recorded the mg of the melt and therefore also the mg of olivine and clinopyroxene changed systematically as a function of oxygen fugacity an example of the link between oxygen fugacity and water activity under hydrogen buffered conditions is the change in the crystallization sequence olivine and cr spinel due to a change in the oxygen fugacity caused by an increase in the water activity the stability of magnetite is restricted to highly oxidizing conditions the absence of magnetite in most of the experiments allows the determination of differentiation trends as a function of oxygen fugacity and water content demonstrating that in an oxide free crystallization sequence water systematically affects the differentiation trend while oxygen fugacity seems to have a negligible effect

mineral stability in peralkaline silicic rocks information from trachytes of the menengai volcano kenya electron microprobe analyses are presented for phenocrysts and matrix glass in peralkaline silica oversaturated trachytes from the menengai volcano kenya rift valley the dominant phenocryst assemblage is alkali feldspar hedenbergite fayalite titanomagnetite apatite aenigmatite amphibole and quartz occur rarely in more peralkaline rocks quilf calculations indicate that the trachytic magmas crystallised at temperatures of 854 870 c at relatively low oxidation states fmq 1 6 to 1 7 and silica activity asio2 qtz of 0 60 0 66 the new analyses are used along with published data to outline the distribution of the main phases in the compositional spectrum of peralkaline quartz trachytes and rhyolites there is uncertainty about the nature or even existence of a low temperature zone in the alkali feldspar primary phase region the equivalent of the thermal valley in the haplogranite system quartz phenocrysts may appear early or late in the crystallisation sequence even in rocks of similar bulk composition its appearance perhaps being a function of the f content of the melts whereas hedenbergite and fayalite show fairly systematic compositional trends with increasing host rock peralkalinity amphibole compositions are variable for reasons not yet understood aenigmatite crystallisation is at least partly controlled by oxygen fugacity and silica activity with rare exceptions ilmenite and titanomagnetite are incompatible phases but the factors controlling their relative stabilities are not clear it appears that peralkaline trachyte rhyolite sequences evolve along many crystallisation paths the paths perhaps being strongly influenced by ph2o pf2 melt f cl ratios and perhaps total pressure

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

experimental constraints on pre eruptive conditions of phonolitic magma from the caldera forming el abrigo eruption tenerife canary islands abstract we have performed phase equilibrium experiments to determine the pre eruptive conditions of the largest caldera forming eruption 20 km 3 of dre that has occurred on tenerife canary islands the abrigo ignimbrite is phonolitic and was erupted during the last caldera forming episode ca 190 ka prior to the construction of the teide pico viejo active central complex the abrigo phonolite contains low amounts of phenocrysts ca 7 vol mainly sanidine biotite clinopyroxene and magnetite with minor amounts of titanite apatite and hauyne we have investigated pressures from 50 to 250 mpa temperatures of 700 900 c water contents in the melt from 1 5 to ca 10 wt and oxygen fugacity f o 2 from 1 log unit above the ni nio solid buffer to quartz magnetite fayalite comparison of the natural and experimental phase proportions and compositions indicates that the phonolite at the roof of the abrigo magma reservoir was at 130 50 mpa corresponding to ca 4 5 km below the surface 825 25 c with 3 1 wt dissolved h 2 o and f o 2 at the ni nio buffer 1 log unit this shows that the magma that produced the largest ignimbrite on tenerife was stored at relatively shallow depths but was water undersaturated and its eruption was probably triggered by input of fresh mafic magma comparison of the abrigo phase equilibrium results with those obtained in other phonolitic magmas e g eifel kerguelen somma vesuvius shows that the major element and probably fluid composition h 2 o cl and s may have a strong effect on the presence or absence of phases and their compositions extrapolating phase equilibria results obtained on a specific phonolite to constrain the pre eruptive conditions of other phonolites should be done with care

compositional variation of apatite from rift related alkaline igneous rocks of the gardar province south greenland textural and compositional variations of apatite from rift related gabbros syenogabbros syenites quartz syenites and nepheline syenites of the mid proterozoic gardar province south greenland are presented and compared to apatite compositions from other rock suites the observed zoning textures of apatite are interpreted to represent 1 primary growth zonation concentric and oscillatory that formed during magmatic differentiation and 2 secondary irregular overgrowths patchy zonation and resorption textures assigned to metasomatic overprinting due to interaction with fluids melts and intra crystalline diffusion compositional variation in the apatites is mainly due to coupled substitutions of ca and p by variable amounts of si na and ree which show increasing concentrations during magmatic differentiation furthermore f concentrations in apatites increase from gabbroic through syenogabbroic to syenitic rocks whereas cl concentrations show the opposite trend compared to apatite compositions from gabbroic dioritic and granitic rocks in general apatites from alkaline rock suites are characterized by exceptionally high contents of ree and si and in some alkaline rocks they attain sr contents comparable to those reported from carbonatites typical low mn and s contents are probably a result of low oxygen fugacity during crystallization at relatively high temperatures

phase relations of a f enriched peraluminous granite an experimental study of the kymi topaz granite stock southern finland phase relations of f rich kymi equigranular topaz granite have been investigated experimentally at 100 500 mpa as a function of water activity and f content fluorite and topaz can crystallize as liquidus phases in f rich peraluminous systems but the f content of the melt should exceed 2 5 3 0 wt for the crystallization of topaz in peraluminous f bearing melts containing more than 1 wt f topaz and muscovite are expected to be the first f bearing phases to crystallize at high pressure whereas fluorite and topaz should crystallize first at low pressure following reaction models the saturation of fluorite and topaz caal2si2o8 plagioclase 2 alf3 melt caf2 fluorite 2al2sio4f2 topaz the obtained partition coefficient for f between biotite and glass d f bt glass ranges from 1 89 to 0 80 average value 1 29 and can be used as an empirical fluormeter to determine the f content of coexisting melts combined petrological and experimental studies of the kymi equigranular topaz granite indicate that plagioclase was the liquidus phase at nearly water saturated fluid saturated conditions and that the f content of the melt was at least 2 wt the mean f content of natural biotite 3 92 wt suggests that the late stage crystallization of biotite occurred in melts containing about 3 wt f the early crystallization of biotite and the presence of muscovite in our experiments at 200 mpa contrasts with the late stage crystallization of biotite and the absence of muscovite in the natural assemblage indicating that crystallization pressure may have been lower than 200 mpa for the granite

modelling the effect of chemical heterogeneity on acidification and solute leaching in overburden mine spoils abstract the generation of acid mine drainage from overburden spoil piles at open pit lignite mines is impacting the quality of groundwater and surface water bodies in large parts of the lusatian mining area in germany values of ph as low as 1 have been observed in the groundwater after decommissioning mine pits are generally converted to lakes which may also be acidic owing to the acidic groundwater discharge the acidic effluent is generated by sulphide oxidation in the unsaturated zone of the spoil pile which generally extends to large depths as a result of dewatering the long term evolution of the acidification is still largely unknown our research focuses on the effects of physical and chemical heterogeneity caused by mixing of soil materials that may have already been oxidized to different degrees during the deposition of the spoil pile processes considered include variably saturated groundwater flow oxygen diffusion in the soil gas kinetic pyrite oxidation and acidic effluent generation advective dispersive transport of the aqueous components equilibrium geochemical reactions between the chemical components and the soil minerals and possible buffering and acid neutralization several existing numerical codes were coupled to represent the complete set of processes simulations were carried out in one and two dimensions using representative characteristics of mine spoil piles with the two dimensional representation being based on spatially heterogeneous random fields of hydraulic conductivity and sulphide mineral fractions results show the long term evolution of the oxidation front the mass flux of oxidation products and the effects of system heterogeneity under conditions of constant flow the system is found to return to neutral conditions over a time period on the order of several decades further work including sensitivity analyses with respect to the controlling parameters and model calibration using site specific field data will be necessary to obtain a full understanding of the complex interacting mechanisms the simulation approach shows promise as a potentially useful tool for predicting the effects of sulphide oxidation on the water quality of pit lakes

the argentine neotropical loess an overview abstract the neotropical loess primary and reworked covers a large part of argentina north of 30 s it is different in some ways from the loess of the pampa which is generally considered the typical argentine loess the mineralogical chemical and physical composition of the neotropical loess has been analyzed and is here compared with both pampean and northern hemisphere european and north american loess the distribution of neotropical loess is established following the former teruggi scheme and the bio stratigraphical data indicating a late pleistocene age is described the great climatic variability of this period is documented through description of a loess paleosol sequence that mantles the pre andean valleys the influence of loess influx upon the genesis of the paleosols and the stadial interstadial environmental changes are considered in relation to the generalized truncation of paleoedaphic sequences the migration of the polar front and the weakness of the pacific high pressure system are also analyzed in relation to south american environmental evolution during the upper quaternary in that sense the genesis of pre andean fluvial valleys and mega fans extending outward into the andean piedmont plains having sources on the eastern dry side of the andes would have been influenced by such a paleoclimatic situation

distinguishing magmatic and metamorphic processes in peralkaline rocks of the norra karr complex southern sweden using textural and compositional variations of clinopyroxene and eudialyte group minerals

the potential formation of acid mine drainage in pyrite bearing hard coal tailings under water saturated conditions an experimental approach annually an amount of approximately 13 million cubic meters of hard coal tailings must be disposed of in the german ruhr valley besides the waste of land in a densily populated region the disposal of the pyrite bearing material under atmospheric conditions may lead to the formation of acid mine drainage amd therefore alternative disposal opportunities are of increasing importance one of which being the use of tailings under water saturated conditions such as in backfilling of abandoned gravel pits or in the construction of waterways in this case the oxidation of pyrite and hence the formation of amd is controlled by the amount of oxygen dissolved in the pore water of tailings deposited under water in case the advective percolation of water is suppressed by sufficient compaction of the tailings oxygen transport can be reduced to diffusive processes which are limited by the diffusive flux of dissolved oxygen in equilibrium with the atmospheric po2 calculations of the duration of pyrite oxidation based on laboratory experiments have shown that the reduction of oxygen is mainly controlled by the content of organic substance rather than the pyrite content a fact that is supported by results from oxidation experiments with nitrate a worst case study has lead to the result that the complete oxidation of a 1 5 m layer of hard coal tailings deposited under water saturated conditions would take as much as several hundred thousand years