the origin of jadeitite forming subduction zone fluids cl guided sims oxygen isotope and trace element evidence jadeitite a rare high p t rock is associated spatially with blueschist and or eclogite terranes scanning electron microscope sem and cathodoluminescence cl petrography of jadeitite samples from several major occurrences in burma myanmar guatemala japan kazakhstan and the u s a show that grains were deposited from s uids jadeite grain compositions indicate these s uid compositions changed with time cl imagery guided the acquisition of oxygen isotope and trace element analyses with the ion microprobe jadeite grains in each rock grew in cycles that began with red and or blue luminescent and ended with green luminescent zones the cl images were used to order the data into crystallization sequences these data and electron microprobe major element analyses document the association of green cl with increases in ca mg and cr 1 toward grain exteriors 2 in ne grained matrix around porphyroblasts 3 in shear zones that cut grains 4 in former open spaces now lled with jadeite or 5 in veins abundances of many trace elements are greater in green cl jadeitite compared with the red or blue cl zones some of these elements in particular li rb sr ti hf zr y and ree are unlikely to have been derived from serpentinite although crystal chemical effects may explain some of the trace element systematics e g preferential incorporation of ree into ca richer jadeite some kinetic control is suggested by sector zoned rhythmically zoned grains the oxygen isotope data suggest that jadeitite depositing s uids either had multiple sources or evolved in composition along their s ow paths or both

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

ferroan alkalic volcanism associated with calymmian rifting in the paramirim aulacogen sao francisco craton brazil new insights from lithofacies analysis and evidence of mantle derived alkaline h2o rich metasomatic fluids affecting ancient crustal materials abstract rift related volcanism is widely used in models of supercontinent reconstruction while the associated metasomatic fluids provide information about the mantle crust process during intracrustal melting events the paleoproterozoic mesoproterozoic paramirim aulacogen corresponds to multiple intracratonic rift cycles that register many basin developing events intense volcanic activity is recorded in some rift events but the volcanic lithofacies and their petrogenesis are poorly constrained herein we present lithofaciological characterization whole rock and mineral chemistry and u pb and lu hf isotope data from the 1 58 ga volcanic rocks trachytic and trachy andesitic lava flows and primary to secondary volcaniclastic lithotypes characterize this volcanism the primary volcaniclastic rocks resulted from direct volcanic activity and can be divided into pyroclastic and hydroclastic lithofacies associations the pyroclastic lithotypes correspond to air fall density currents and block and ash flow deposits formed in explosive eruptions hydroclastic lithotypes are represented by hyaloclastites and peperites reflecting effusive eruptions and interactions between magma water and sediments the secondary volcaniclastic lithotypes resulted from late stage reworking processes and consist of debris flows ephemeral streams associated with high energy and gravitational flow deposits the lava flows show well preserved primary volcanic features such as magma flow textures and euhedral phenocrysts based on petrographic and chemical characteristics associated with negative hf t values we infer that high melt rate of an ancient crust previously metasomatized by h2o rich alkaline mantle derived fluids generated the alkalic ferroan lavas these fluids promoted potassic and sodic metasomatism that affected all the volcanic rocks modifying the chemistry of the feldspars to pure orthoclase or96 98 and albite ab98 100 in some lavas a higher concentration of na rich fluids synthesized aegirine at a minimum temperature of 200 c and promoted its peralkaline character the potassic sodic metasomatism influenced the volcano sedimentary sequence of the pajeu group and the oldest rocks of the basement but did not affect the overlying sedimentary sequences indicating that fluids ceased with the end of volcanism we suggest that the h2o rich alkaline fluids arose by focused degassing in response to a rising asthenospheric mantle during the calymmian rift of the paramirim aulacogen

the role of hydrothermal processes in the granite hosted zr y ree deposit at strange lake quebec labrador evidence from fluid inclusions abstract the strange lake zr y ree nb and be deposit is hosted by a small high level late proterozoic peralkaline granite stock that intruded into high grade metamorphic gneisses on the quebec labrador border the stock is extensively altered early alteration is manifested by the replacement of arfvedsonite with aegirine later alteration involved ca na exchange zr ti y rees nb and be are concentrated in ca bearing minerals that together with quartz commonly pseudomorph na bearing minerals fluid inclusions in pseudomorphs comprise several distinct types high salinity 13 to 24 wt nacl eq ca rich aqueous inclusions that homogenize to liquid between 135 and 195 c mixed aqueousmethane inclusions methane inclusions and solid bearing inclusions aqueous methane inclusions represent heterogeneous entrapment of immiscible high salinity aqueous liquid and methane bastnasite tentatively identified by sem analysis occurs as a daughter mineral other daughter or trapped minerals include a y hree bearing mineral possibly gagarinite and hematite galena sphalerite fluorite pyrochlore kutnahorite and griceite the first three inclusion types also occur in quartz in pegmatites and veins together with lower temperature lower salinity na dominated aqueous inclusions the entrapment temperature inferred for the aqueous inclusions from microthermometry and the na k ca geothermometer range from 155 to 195 c for the higher salinity inclusions and 100 to 165 c for the low salinity inclusions a model is proposed in which the intrusion of a peralkaline granite to high crustal levels initiated a ground formational water dominated hydrothermal system in adjacent gabbroic calc silicate and graphitic gneisses reaction of the high salinity ca rich liquid with the graphitic gneisses led to the production of an immiscible methane gas subsequent interaction of this liquid with the granite led to extensive replacement of sodic minerals by calcium analogues at temperatures of less than 200 c some time after the onset of ca metasomatism the high salinity liquid mixed with a ca poor low salinity low temperature liquid that had leached f and rare metals from the granite yttrium and ree mineral deposition occurred as a result of the decreased ligand concentration that accompanied fluorite deposition during mixing of the ca rich and ca poor aqueous liquids

bitumen biomarkers in the mid proterozoic ilimaussaq intrusion southwest greenland a challenge to the mantle gas theory abstract gc and gc ms ms analysis on rock extracts has shown that the bitumen in the peralkaline ilimaussaq intrusion previously assumed to be abiogenic is biotic in origin a biotic origin is in accordance with previously published stable carbon isotopic data on bituminous matter in the rocks the biomarker distribution in the bitumen including the less common bicadinanes resembles that of oil seeps on the central west greenland coast 2200 km farther north whose source rocks and migration history are relatively well established we use a recent re construction of the subsidence and later exhumation of the west greenland coastal region during the mesozoic cenozoic japsen et al 2006a b to anticipate that hydrocarbons migrated from deeper parts of the basin offshore west of greenland the rocks of ilimaussaq were probably more deeply invaded than the surrounding granites due to their higher proportion of corroded minerals which may explain why bitumen has not been observed elsewhere in the area hydrocarbon gases c1 c5 present in fluid inclusions were also analysed after having been released by treatment with hydrochloric acid that resulted in an almost complete disintegration of the ilimaussaq intrusion rocks the acid extraction method proved generally more efficient than the crushing procedure applied by others but gave similar results for the chemical composition of the gas ch4 88 97 and isotopic ratios 13 c ch 4 1 6 to 5 0 13 c c 2 h 6 9 2 to 12 5 with the exception of hydrocarbons hosted in quartz which showed significantly lower isotopic values for methane graser et al 2008 previous researchers have suggested an abiotic origin for these hydrocarbon gases but we suggest a biotic origin for the majority of them not just those in quartz assuming that the isotopic ratio of the constituents have changed due to loss of gas by diffusion the assumption of gas loss via diffusion is supported by published studies on micro fissures in minerals typical of the ilimaussaq and field investigations showing diffusive loss of gas from the peralkaline khibina and lovozero massifs on the kola peninsula russia which are in many respects of mineralogy and hydrocarbon content similar to the ilimaussaq intrusion both the hydrocarbon gases and bitumen in the khibina and lovozero massifs have been cited as prime examples of a deep mantle source although the carbon isotopic ratio of the bitumen clearly pointed to an organic origin the trends in carbon isotopic ratio of methane released with time from freshly exposed rocks also supports our hypothesis of 13c enrichment of the methane remaining within the rock thus there is good evidence that the hydrocarbons in the kola alkaline massifs are mostly biotic in origin in which case the probability of finding economic hydrocarbon accumulations from a deep mantle source seems exceedingly small

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

mass balance control on the interaction of axial and transverse channel systems we present a geometric sediment mass balance model for the interaction of axial and transverse alluvial systems in a subsiding basin by comparing the model result with a flume experiment that employed a simplified half graben tectonic geometry with axial and transverse sediment sources we quantify rates of axial transverse erosional sediment mixing in the experiment the lateral migration rate of the axial transverse boundaries due to the sediment mixing scales with sediment supplies delivered by transverse drainages but not with water or sediment discharge from the axial channel or with tectonic tilting rate using an empirical lateral erosion rate the model shows how sediment supply partitioning among the axial hanging wall and footwall drainages controls the width and the location of the axial channel belt comparing the modeling results with field cases demonstrates that transverse sediment fluxes could slow the axial channel migration or even reverse the movement against the tectonic forcing

abiogenic hydrocarbon isotopic signatures in granitic rocks identifying pathways of formation abstract the stability and isotopic composition of hydrocarbons formed in the mantle are controversial subjects knowing the range in isotopic compositions of abiogenically derived hydrocarbons is important for recognising biological signatures in ancient and extra terrestrial materials in an effort to enhance this database stable isotope results are reported here for hydrocarbon bearing fluid inclusions hosted in two peralkaline igneous complexes from lovozero russia and strange lake canada based on the distribution of isotopic compositions we propose three pathways for abiogenically generated hydrocarbons type 1 13cch4 13cco2 and 13cc2 represents mantle derived hydrocarbons generated in equilibrium with hyperagpaitic magmas in the upper mantle and suggests that mantle ch4 and c2h6 13c and 2h could have values of 5 3 and 112 and 10 8 and 162 respectively type 2 13cco2 13cch4 13cc2 represents fischer tropsch type hydrocarbon generation in quartz bearing peralkaline rocks with co2 as the initial magmatic gas phase for type 2 13cco2 values are 2 whereas 13cch4 and 2hch4 values range from 32 to 20 and 170 and 160 respectively the 13cc2h6 values are slightly lower than associated 13cch4 values type 3 13cco2 13cch4

methane derived hydrocarbons produced under upper mantle conditions there is widespread evidence that petroleum originates from biological processes 1 3 whether hydrocarbons can also be produced from abiogenic precursor molecules under the high pressure high tem

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

the effect of oxygen fugacity on the rheological evolution of crystallizing basaltic melts abstract storage and transport of silicate melts in the earth s crust and their emplacement on the planet s surface occur almost exclusively at sub liquidus temperatures at these conditions the melts undergo crystallization under a wide range of cooling rates deformation rates and oxygen fugacities f o 2 oxygen fugacity is known to influence the thermodynamics and kinetics of crystallization in magmas and lavas yet its influence on sub liquidus rheology remains largely uncharted we present the first rheological characterization of crystallizing lavas along natural cooling paths and deformation rates and at varying f o 2 specifically we report on apparent viscosity measurements for two crystallizing magmatic suspensions 1 at log f o 2 of 9 15 quartz fayalite magnetite buffer qfm 2 1 and 2 in air these fugacities span a range of reduced to oxidized conditions pertinent to magma migration and lava emplacement we find that 1 crystallization at constant cooling rates results in a quasi exponential increase in the apparent viscosity of the magmatic suspensions until they achieve their rheological cut off temperature t cutoff where the melt effectively solidifies 2 the rheological departure and t cutoff increase with increasing f o 2 and 3 increasing f o 2 results in decreased crystallization rates based on the experimental results and by comparison with previous rheological isothermal studies we propose a generalisation of the effect of f o 2 on the dynamic rheological evolution of natural magmatic and volcanic suspensions we further discuss the implications for magmatic transport in plumbing and storage systems e g conduits dikes and magma chambers and during lava flow emplacement

subducting oceanic crust the source of deep diamonds inclusions of majoritic garnet in diamonds from the jagersfontein kimberlite formed at unusually great depths of 250 to 500 km in the asthenosphere and transition zone the original host rocks were derived from a much shallower basaltic eclogitic source the presence of negative eu anomalies in all majoritic garnets requires a crustal origin thereby linking these very deep diamond sources to subducting oceanic crust the carbon isotope values 13c of the host diamonds fall within a narrow range at 20 which is fundamentally different from the broad range 24 to 2 and bimodal distribution of carbon isotopes of jagersfontein diamonds that formed in the shallower lithosphere this indicates that majoritic garnet bearing diamonds at jagersfontein inherited their light carbon isotopic composition directly from organic matter contained in a subducting slab these diamonds were likely formed by direct conversion from graphite well within the diamond stability field

a review of the occurrence form and origin of c bearing species in the khibiny alkaline igneous complex kola peninsula nw russia abstract the khibiny complex hosts a wide variety of carbon bearing species that include both oxidized and reduced varieties oxidised varieties include carbonate minerals especially in the carbonatite complex at the eastern end of the pluton and na carbonate phases reduced varieties include abiogenic hydrocarbon gases particularly methane and ethane dispersed bitumens solid organic substances and graphite the majority of the carbon in the khibiny complex is hosted in either the carbonatite complex or within the so called central arch the central arch is a ring shaped structure which separates khibinites coarse grained eudialite bearing nepheline syenites in the outer part of the complex from lyavochorrites medium grained nepheline syenites and foyaites in the inner part the central arch is petrologically diverse and hosts the major ree enriched apatite nepheline deposits for which the complex is best known it also hosts zones with elevated hydrocarbon dominantly methane gas content and zones of hydrothermally deposited na carbonate mineralisation the hydrocarbon gases are most likely the product of a series of post magmatic abiogenic reactions it is likely that the concentration of apatite nepheline deposits hydrocarbon gases and na carbonate mineralisation is a function of long lived fluid percolation through the central arch fluid migration was facilitated by stress release during cooling and uplift of the khibiny complex as a result carbon with a mantle signature was concentrated into a narrow ring shaped zone

petrology and geochemistry of late stage intrusions of the a type mid proterozoic pikes peak batholith central colorado usa implications for petrogenetic models abstract the 1 08 ga anorogenic a type pikes peak batholith front range central colorado is dominated by coarse grained biotite amphibole syenogranites and minor monzogranites collectively referred to as pikes peak granite ppg the batholith is also host to numerous small late stage plutons that have been subdivided into two groups e g wobus 1976 studies in colorado field geology colorado school of mines professional contributions colorado 1 a sodic series sio 2 44 78 wt k na 0 32 1 36 composed of gabbro diabase syenite quartz syenite and fayalite and sodic amphibole granite and 2 a potassic series sio 2 70 77 wt k na 0 95 2 05 composed of biotite granite and minor quartz monzonite differences in major and trace element and nd isotopic characteristics for the two series indicate different petrogenetic histories potassic granites of the late stage intrusions appear to represent crustal anatectic melts derived from tonalite sources based on comparison of their major element compositions with experimental melt products in addition nd isotopic characteristics of the potassic granites e nd 1 08 ga 0 2 to 2 7 overlap with those for tonalites granodiorites ca 1 7 ga boulder creek intrusions e nd 1 08 ga 2 4 to 3 6 exposed in the region some of the partial melts evolved by fractionation dominated by feldspar the late stage potassic granites share geochemical characteristics with most of the ppg which is also interpreted to have an anatectic origin involving tonalitic crust the origin of monzogranites associated with the ppg remains unclear but mixing between granitic and mafic or intermediate magmas is a possibility syenites and granites of the sodic series cannot be explained as crustal melts but are interpreted as fractionation products of mantle derived mafic magmas with minor crustal input high temperature and low oxygen fugacity estimates e g frost et al 1988 american mineralogist 73 727 740 support a basalt fractionation origin as do e nd values for sodic granitoids e nd 1 08 ga 2 2 to 0 7 which are higher than e nd values for colorado crust at 1 08 ga ca 1 0 to 4 0 enrichments in incompatible elements e g rare earth elements rb y and depletions in compatible elements e g cr sr ba in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation accessory mineral fractionation release of fluorine rich volatiles and or removal of pegmatitic fluids could have modified abundances of ce nb zr and y in some sodic granitoid magmas gabbros and mafic dikes associated with the sodic granitoids have e nd 1 08 ga of 3 0 to 3 5 which are lower than depleted mantle at 1 08 ga and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction related processes however it is difficult to characterize the mantle component in these magmas because assimilation of crust during magma ascent could also result in their observed geochemical features the pikes peak batholith is composed of at least two petrogenetically different granite types both of which exhibit geochemical characteristics typical of a type granites models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central colorado at 1 1 ga

petrological and geochemical relationships between pyroxene megacrysts and associated alkali basalts from massif central france major trace element and ree analyses as well as sr isotopic ratios have been obtained on twelve clinopyene megacrysts and phenocrysts and their alkali basalt hosts from the french massif central equilibrium between crystals and host was examined based on petrographic and geochemical data two types of pyroxenes are recognized the acmite bearing clinopyroxenes rich in incompatible elements and the salitic clinopyroxenes poor in incompatible elements 87sr 86sr isotopic data reveal no significant difference between clinopyroxenes and host lavas they are in apparent isotopic equilibrium the sr isotopic ratios of the two types of pyroxenes are also quite similar however pyroxene crystals from the first group are not in equilibrium with their host they have crystallized at high pressure from differentiated alkali lavas and have been incorporated in a more primitive magma pyroxene crystals from the second group are in apparent equilibrium with their host lava they have crystallized at various pressures for the latter distribution coefficients are proposed for compatible elements trace elements and ree

shock induced wave propagation over porous and fractured borehole zones theory and experiments borehole waves are strongly affected by adjacent porous zones or by fractures intersecting the borehole a theoretical description for both porous and fracture zones is possible based on the introduction of an effective borehole fluid bulk modulus characterizing the wave attenuation via borehole wall impedance this impedance can be calculated for both porous and fracture zones adjacent to the borehole thus predicting borehole wave attenuation transmission and reflection over such zones a shock tube setup generates borehole tube waves that are used for porous and fracture zone characterization a pvc sample is used to introduce and vary fractures in a cylindrical sample shock wave experiments show that attenuation in boreholes adjacent to porous zones can be predicted by theory the transmittivities of a borehole tube wave over 1 and 5 mm fractures are correctly predicted thus showing the potential of borehole wave experiments for fracture detection and characterization

sediment subduction and the source of potassium in orogenic leucitites leucitites from the italian volcanic province show a marked enrichment of the large ion lithophile elements lile over the high field strength elements hfse indicative of a subduction related origin despite sr and nd isotope ratios similar to those in lamproites trace element variations do not suggest the latter as a source for the k enrichment instead potassium and the other lile and rare earth elements ree are derived from subducted sediments in a multicomponent mixing process that involves both dehydration and partial melting of the subducted material the slightly elevated 18 o and high 87 sr 86 sr values of the primitive italian lavas are shown to be consistent with a three component mixing model which can also explain other unusual geochemical features of the italian lavas stabilization of phlogopite in hybridized mantle above the subduction zone is regarded as an essential aspect of the petrogenesis of the orogenic leucitites

a reassessment of models for hydrocarbon generation in the khibiny nepheline syenite complex kola peninsula russia although hydrocarbon bearing fluids have been known from the alkaline igneous rocks of the khibiny intrusion for many years their origin remains enigmatic a recently proposed model of post magmatic hc generation through fischer tropsch type reactions suggests a primary co2 fluid this hypothesis is based upon textural data gas bulk and isotopic composition and low entrapment temperature of fluid inclusions that indicate an abiogenic origin for the hc gases however new petrographic microthermometric laser raman bulk gas and isotope data are presented and discussed in the context of previously published work in order to reassess models of hc generation the gas phase is dominated by ch4 with only minor proportions of higher hydrocarbons no remnants of the proposed primary co2 rich fluid are found anywhere in the complex primary and secondary fluid inclusions show similar compositions and entrapment conditions the majority of the fluid inclusions are of secondary nature and trapped in healed microfractures this indicates a high fluid flux after magma crystallisation entrapment condtions for primary fluid inclusions are 450 550 c at 2 8 4 5 kbar these temperatures are too high for hc gas generation through the ft reaction chemical analyses of rims of fe rich phases suggest that they are not the result of alteration but instead represent changes in magma composition during crystallisation furthermore there is no clear relationship between the presence of fe rich minerals and fluid inclusion abundance as reported elsewhere fluid inclusion planes generally start and terminate at mineral boundaries 13c values for methane range from 22 4 to 5 4 confirming also an abiogenic origin for the gas these data support an abiogenic hc origin but are not consistent with a post magmatic ft type reaction the presence of primary ch4 dominated fluid and melt inclusions which contain a methane rich gas phase indicate that a magmatic origin is more likely an increase in methane content together with a decrease in 13c isotope values towards the intrusion margin suggest that magmatically derived abiogenic hydrocarbons may have mixed with biogenic hydrocarbons derived from the surrounding country rocks

free hydrogen hydrocarbon gases from the lovozero loparite deposit kola peninsula nw russia abstract the lovozero nepheline syenite massif in the north eastern fennoscandian shield well known to mineralogists and petrologists is also interesting with its high contents of hydrogen hydrocarbon gases in different forms of presence which is untypical of magmatic rocks the article systematizes and generalizes little known and unpublished data on the composition location character and scale intensity of the free gases fg emission within a major loparite deposit confined to the massif 4 and 2 are dominant in the fg composition the molecular weight distribution of hydrocarbon gas components corresponds to the classic anderson schulz flory distribution with a steep gradient carbon and hydrogen of the gases are characterized by rather heavy isotope compositions becoming lighter from the transition of methane to ethane the fg volume has been estimated as 0 2 1 6 m 3 of gas per 1 m 3 of undisturbed rock the gas recovery of walls in underground workings has been up to 0 2 ml min m 2 for 4 and 0 5 ml min m 2 for 2 in several years after their heading the discharge of some shot holes that characterizes the gas emission intensity 1 8 2 m deep and 40 mm in diameter is up to 300 ml min but its 1 2 orders lesser values dominate the discharge time in some sections varies from several days to 20 years the overpressure of gases towards the air mainly does not increase 100 hpa sometimes reaching 120 kpa it has been defined that fg distribute irregularly at the distance of centimeters to hundreds of meters and their composition and particularly emission intensity perform different temporal fluctuations the abiogenic origin of fg has been proposed with fg appearing as a mixture of gases in various proportions a gases remaining in microfissures at the massif s consolidation after the capture by fluid inclusions and those lost during degassing and b gases occurred in mechanic chemical reactions partial emission and concentration of occluded and diffusely scattered gases under the unstable stress strain mode of the rock mass combustible and explosive hydrogen hydrocarbon fg can accumulate in the air of underground workings and cause accidents disrupting the workflow the background for using characteristics of spatial temporal variations of the fg emission as precursors of dangerous geodynamic phenomena has been indicated

mineralogy and petrogenesis of a ba ti zr rich peralkaline dyke from sebkovice czech republic recognition of the most lamproitic variscan intrusion abstract a peralkaline ultrapotassic dyke found at sebkovice t ebic district western moravia is a mineralogically extreme member of a dyke swarm occurring along the south eastern border of the moldanubian region of the bohemian massif the dyke shows a simple zoning with a very fine grained marginal zone grading into a medium grained central zone it has a primary mineral assemblage of microcline and potassic amphiboles with accessory apatite and altered phlogopite the microcline exhibits an unusual red luminescence colour and pronounced substitution of fe3 for al with measured contents of fe2o3 up to 8 5 wt 0 31 apfu fe3 amphiboles have very high k up to 0 99 apfu and si contents their compositions follow an alkaline fractionation trend from potassic richterite to potassic magnesio arfvedsonite characterized by an increase of na k and a decrease of ca mg fe2 and ti via heterovalent substitutions b ca c mg fe2 b na c fe3 and ti mg 2fe3 the most evolved apatite is significantly enriched in sro up to 9 7 wt 0 49 apfu sr the core of the dyke and late veinlets contain unique late to post magmatic ba ti zr bearing mineral assemblages of baotite henrymeyerite titanite rutile benitoite and bazirite anhedral baotite fills interstices distributed inhomogeneously in the dyke centre it is locally replaced by a ba bearing titanite henrymeyerite rutile quartz assemblage henrymeyerite the second record in a lamproite shows variable fe ti ratios and represents a solid solution of the hepta and hexatitanate components euhedral crystals of benitoite and bazirite are enclosed in the late stage quartz titanite apatite veinlets in the fine grained margin of the intrusion in terms of a mineralogical genetic classification the sebkovice dyke can be considered as a new high silica 57 wt sio2 variety of lamproite variety sebkovice and represents a unique expression of post collisional potassic magmatism on the south eastern border of the bohemian massif the peralkaline dykes from this area show mineralogical and geochemical features similar to those of silica rich orogenic lamproites emplaced at destructive plate margins in terms of the modern classification of lamproites the sebkovice dyke is the first lamproite recognised in the variscan orogenic belt

a dynamic model for fluid flow in open borehole fractures the attenuation of stoneley waves by an open borehole fracture is closely related to fluid flow in the fracture we consider the dynamic response of a viscous fluid in a borehole fracture to the oscillating pressure excitation of stoneley waves at the fracture opening a dynamic model has been developed to describe the fluid motion in the fracture this model relates both viscous shear effects at the fracture surface and the acoustic wave propagation in the fracture fluid the dynamic conductivity is derived to characterize the fluid conduction through the fracture this model is applied to study stoneley wave attenuation across a horizontal and along a vertical borehole fracture in the horizontal fracture case the theory is found to agree with laboratory fracture modeling data after minimizing scattering effects due to the fracture in the vertical fracture case where the scattering effects are minimal the theory is in excellent agreement with the laboratory data

geology and genesis of the toongi rare metal zr hf nb ta y and ree deposit nsw australia and implications for rare metal mineralization in peralkaline igneous rocks the toongi deposit located in central nsw australia hosts significant resources of zr hf nb ta y and ree within a small ca 0 3 km2 rapidly cooled trachyte laccolith toongi is part of regional late triassic to jurassic alkaline magmatic field but is distinguished from the other igneous bodies by its peralkaline composition and economically significant rare metal content that is homogenously distributed throughout the trachyte body the primary ore minerals are evenly dispersed throughout the rock and include lueshite natroniobite and complex na fe zr nb y ree silicate minerals dominated by a eudialyte group mineral egm the egm occurs in a unique textural setting in the rock commonly forming spheroidal or irregular shaped globules herein called snowballs within the rock matrix the snowballs are often protruded by aegirine and feldspar phenocrysts and contain swarms of fine aegirine and feldspar grains that often form spiral or swirling patterns within the snowball secondary ore minerals include ree carbonates y milarite catapleiite and gaidonnayite that fill fractures and vesicles in the rock based on bulk rock geochemical and nd isotope data and thermodynamic modelling of magma fractionation the alkaline rocks of the region are interpreted to represent extrusive to hyperbyssal products of mantle derived magma that ponded at mid crustal levels ca 0 3 gpa and underwent extensive fractionation under low oxygen fugacity conditions the high na2o peralkaline nature of the toongi deposit trachyte developed via extensive fractionation of an alkali olivine basalt parental magma initially in the mid crust and subsequently at shallow levels ca 0 1 gpa this extended fractionation under low fo2 and relatively low h2o activity conditions limited volatile release and allowed build up of rare metal contents to ore grades we speculate that the ore minerals may have originally formed from rare metal rich sodic silicate melt that formed immiscible globules subsequently crystallized to egm in the magma shortly before emplacement and rapid cooling subsequent hydrothermal alteration caused relatively limited and localized remobilization of some ore metals into fractures and vesicles in the rock

fracture evaluation using reflected stoneley wave arrivals we use the low frequency reflected stoneley wave mode to locate permeable fractures intersecting a borehole and to estimate their effective apertures assuming a model in which the average aperture of the fracture is roughly constant theoretical work relates the magnitude of the stoneley wave reflectivity to an effective fracture width we treat both the case of a horizontal fracture and the case of a fracture crossing the borehole at an angle laboratory experiments verify the analytic solution for the case of a horizontal fracture full waveform array sonic data were also acquired in a wellbore with a long recording time 25 5 ms in order to capture the late stoneley wave arrivals the data processing involves computation of the stoneley wave reflectivity response using the measured direct and reflected stoneley wave arrivals a least squares fit to the arrival time of the reflected wave arrivals is used to estimate the locations of permeable fractures and the effective width of the fractures is esti

minette lavas and associated leucitites from the western front of the mexican volcanic belt petrology chemistry and origin during the late pliocene k rich minette and leucitite lavas erupted in the western mexican volcanic belt near the town of los volcanes a region which is located much closer to the middle america trench than the main line of currently active andesite stratovolcanoes during this period the tectonic regime in western mexico was highly complex due to the simultaneous occurrence of active subduction of the young rivera plate and rifting caused by crustal extension most of these basic lavas contain phenocrysts of phlogopite augite and apatite along with microphenocrysts of leucite and fe ti oxide olivine is absent from all but two of the flows one an olivine leucitite and the other a felsic minette the phlogopite phenocrysts and high whole rock fe2o3 feo ratios which are characteristic of this suite record evidence of high magmatic water contents and oxygen fugacities all of these rock types are highly enriched in the large ion lithophile and light rare earth elements with sr 5100 ppm ba 4800 ppm and ce 330 ppm they are also mildly enriched in the high field strength elements e g zr 260 700 ppm and display the strong relative enrichment of the lile over the hfse that is characteristic of magmas erupted in convergent margins consideration of high pressure phase equilibria in the mg2sio4 camgsi2o6 kalsio4 sio2 system shows that the minettes from this region are not related through fractional crystallization to the more mgo rich olivinebearing minettes which have erupted in other parts of the western mexican volcanic belt during the quaternary this conclusion is consistent with both the trace element geochemistry of these lavas and with the results of fractional crystallization models instead the data suggests that these high k magmas were derived from a source region which consists predominantly of phlogopite clinopyroxene and apatite and which has formed through hydrous enrichment of the subarc mantle in response to subduction

magmatic co 2 and saline melts from the sybille monzosyenite laramie anorthosite complex wyoming there are three populations of fluid inclusions in quartz from the sybille monzosyenite early co2 secondary co2 and rare secondary brines the oldest consist of low density co2 0 70 inclusions that appear to be co magmatic the densities of these inclusions are consistent with the inferred crystallization conditions of the sybille monzosyenite namely 3 kilobars and 950 1000 c the other types of inclusions are secondary they contain co2 0 50 and secondary brine inclusions that form trains radiating out from a decrepitated inclusion the sites of these decrepitated inclusions are now marked by irregularly shaped fluid inclusions and solid inclusions of salt and carbonate rather than fluid inclusions feldspar contain abundant solid inclusions these consist of magmatic minerals hedenbergite hornblende ilmenite apatite and graphite intimately associated with k na chlorides we interpret these relations as follows the sybille monzosyenite formed from a magma that contained immiscible droplets of a halide rich melt along with a co2 vapor phase the salt was trapped along with the other obvious magmatic minerals during growth of the feldspars co2 may have also been included in the feldspars but it probably leaked later during exsolution of the feldspars and was not preserved both the saline melt and the co2 vapor were trapped in the quartz the melt inclusions in the quartz later decrepitated perhaps due to progressive exsolution of fluids to produce the secondary h2o and co2 inclusions these observations indicate that the sybille monzosyenite which is a markedly anhydrous rock was actually vapor saturated rather than being h2o however the vapor was co2 rich and possibly related to an immiscible chloride rich melt

volatiles associated with alkaline igneous rift activity fluid inclusions in the ilimaussaq intrusion and the gardar granitic complexes south greenland abstract fluid inclusions in minerals from si oversaturated and si undersaturated alkalic igneous complexes belonging to the precambrian gardar rift province in south greenland contain distinctly different carbon bearing gases granites and quartz syenites are characterized by co2 and only minor ch4 whereas agpaitic nepheline syenites are dominated by hydrocarbons essentially ch4 and contain only insignificant amounts of co2 and or co in the alkaline ilimaussaq intrusion the hydrocarbon rich gases may well reflect equilibration with graphite at magmatic temperatures and at oxygen fugacities approaching those defined by the synthetic mw buffer reaction in general formation of hydrocarbon gases in agpaitic nepheline syenites is considered to reflect the fulfillment of three basic conditions 1 low oxygen fugacities 2 a wide temperature range of crystallization and a low temperature solidus and 3 retention of volatiles during crystallization the characteristic carbon bearing vapour associated with continental alkaline igneous activity is however considered to be co2

partial melting fractional crystallisation liquid immiscibility and hydrothermal mobilisation a recipe for the formation of economic a type granite hosted hfse deposits abstract a number of a type granites host resources of the high field strength elements hfse including the rare earth elements ree that have been considered for economic exploitation the best known of them is the strange lake pluton canada with a resource of 20 mt grading 1 44 wt ree2o3 of which 50 are heavy rare earth oxides in this paper we examine the various processes that are likely to be responsible for the hyper enrichment of the hfse starting with the generation of a parental magma through a very low degree of partial melting of a mantle plume or a metasomatically enriched mantle in both cases below a continental crust continental rift we trace the evolution of this magma olivine nephelinite through fractional crystallisation of olivine and clinopyroxene followed by plagioclase k rich alkali feldspar and arfvedsonite to the final residues of hyper enriched hfse granitic pegmatites in so doing we show that at least two additional steps are essential to the process of hfse enrichment the first of these is the abrupt termination of plagioclase crystallisation prior to the final consumption of ca or assimilation of a ca source and the resulting exsolution of an immiscible ca fluoride melt that sequesters the lree and y the second of these steps is prolonged crystallisation of arfvedsonite which delays saturation of the magma with an aqueous phase and ensures the development of an agpaitic assemblage of na bearing hfse minerals e g na zirconosilicates and na titanosilicates finally we show that saturation of the magma with an aqueous carbonic fluid which evolves to a very acidic composition is an essential ingredient in the recipe for the formation of an economic a type granite hosted hfse deposit

emplacement and geochemical evolution of highly evolved syenites investigated by a combined structural and geochemical field study the lujavrites of the ilimaussaq complex sw greenland abstract structural mapping and the combined study of magmatic to solid state deformation textures and mineral compositions in highly evolved nepheline syenites lujavrites of the alkaline to peralkaline ilimaussaq complex south greenland reveal detailed insight into the emplacement and geochemical evolution of the melts they crystallized from based on magmatic to solid state flow textures such as foliations and lineations we propose that the investigated rock sequence forms a sill like structure with a steep feeder zone that flattens out over a short distance and intrudes into less evolved overlying units as sub horizontal sheets by roof uplift systematic compositional variation of early magmatic eudialyte group minerals egm in the investigated rock sequence monitors the geochemical evolution of the lujavrite forming melt s the chlorine contents of egm decrease successively upwards within the rock sequence which probably indicates a successive increase of water activity during differentiation consistent with a change from sodic pyroxene aegirine to sodic amphibole arfvedsonite in the mineral assemblage both ree contents and fe mn ratios of egm are promising differentiation indicators which increase and decrease respectively upwards within the sequence due to fractional crystallization this closed system evolution is interrupted by a shift towards less evolved melt compositions in one lujavrite unit for which we assume magma recharge our study demonstrates the strength of a combined structural and petrological approach to understand the petrogenesis of an igneous body in more detail and highlights their close connection

sodium rich metasomatism in the upper mantle implications of experiments on the pyrolite na2o rich fluid system at 950 c 20 kbar abstract sodium rich metasomatism in the upper levels of the mantle has been modelled by reacting pyrolite with alkali bearing h2o fluids containing minor co2 and concentrations of na2o and na2o k2o k k na 0 1 up to 4 0 g alkalies 10 g h2o at 20 kbar and 950 c with increasing alkali concentration the amounts of amphibole pargasite edenite and olivine increase as orthopyroxene and clinopyroxene decrease amphiboles show progressive increases in na and k and si concentrations and decreases in al and ca concentrations suggesting the dominant substitution mechanism is na k sial ca these results and least squares mass balance calculations suggest the reaction of clinopyroxene orthopyroxene spinel produces amphibole olivine in nature upper mantle spinel lherzolite is commonly veined by a variety of rock types which may contain ti pargasite as a magmatic crystallization product pargasite edenite occurs interstitially in spinel iherzolite often spatially related to ti pargasite and may be produced by hydrous fluids evolved during late stage crystallization of the veined rocks this is supported by the close compositional correlation between the natural pargasite edenite amphiboles and those produced in this study the present study suggests that up to 43 wt amphibole may be accommodated in pyrolite in the presence of na2o rich h2o co2 fluids this represents 0 8 wt h2o and 1 7 wt na2o in the hydrated pyrolite composition and indicates the importance of sodium in determining the extent of metasomatism sodium also lowers the solidus temperature of pyrolite by more than 50 c over the h2o saturated pyrolite system at 20 kbar

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

wadeite k2zrsi3o9 an alkali zirconosilicate from the saima agpaitic rocks in northeastern china its origin and response to multi stage activities of alkaline fluids abstract the triassic saima alkaline complex in the liaodong peninsula of northeastern china covers an area of about 20 km 2 and is dominated by nepheline syenite with phonolite at its center and a concealed body of eudialyte bearing nepheline syenite in the northwest of the complex the phonolite has similar features to miaskite while the nepheline syenites are classified in the agpaitic group according to their mineral assemblage and the alkalinity and aluminum saturation indexes zircon is the dominant zr bearing mineral in the phonolite whereas wadeite occurs as the only primary zr bearing mineral in the nepheline syenites the transitional crystallization from zircon to wadeite reveals an increase in alkalis and a high k na ratio as the magmas evolved from the volcanic to the intrusive stage the primary wadeite grains underwent varying degrees of hydrothermal alteration overall the areas of weak medium and strong alteration are characterized by the following respective associations 1 wadeite secondary catapleiite gaidonnayite 2 wadeite secondary catapleiite gaidonnayite zircon and 3 pseudomorphs after wadeite the pseudomorphs are widespread and mainly consist of residual wadeite secondary zircon catapleiite gaidonnayite k feldspar calcite and some zr bearing titanite and vesuvianite all of the secondary zircon grains in the three associations are typically enriched in ca and al compared with the primary ca free zircons of the phonolite the progressive alteration of wadeite suggests that the saima complex underwent multiple episodes of fluid activity during a hydrothermal stage including an initial na metasomatism via alkaline fluids then stages most likely involving progressively co 2 rich fluids and an intensive episode involving a mixture of these fluids with externally derived ca rich fluids

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

petrogenesis of coexisting high silica aluminous and peralkaline rhyolites from yunshan yongtai southeastern china abstract the late cretaceous bimodal yunshan yongtai volcanics in fujian province contain peralkaline rhyolites the only presence of such rhyolites in southeastern china whole rock and mineral chemical compositions are analyzed for the coexisting aluminous metaluminous to weakly peraluminous peralkaline high silica rhyolites from the yunshan volcanics they are sparsely porphyritic and contain k feldspar ferromagnesian minerals quartz magnetite and titanomagnetite phenocrysts as well as accessory minerals such as fayalite chevkinite apatite and zircon the mineral assemblage indicates an oxidizing pre eruption condition these rhyolites exhibit diagnostic geochemical features of a type granites such as elevated 10 4 ga al mostly greater than 2 6 and feo t feo t mgo ratios enrichment in high field strength elements hfse such as zr 400 ppm and nb and strong depletion in al 2 o 3 2 o poor meta granitic igneous rocks in the deep crust and cannot be fractionated from the coeval yunshan mafic magmas geochemical variations of major and trace elements indicate the possible fractionation of k feldspar calcium rich pyroxene fe ti oxides and minor chevkinite during the magma evolution in peralkaline rhyolites we found that the pre existing fe ti oxide and hedenbergite phenocrysts had been transformed into aegirine oxide and aegirine oxide fluorite assemblages respectively these mineral assemblages are the products of the subsolidus reaction of pre existing phenocrysts and extraneous na f rich fluids such na f rich fluids may be derived from the degassing of the subvolcanic rocks the reactions indicate that the yunshan peralkaline rhyolites could be generated through the reaction of highly fractionated aluminous silica magmas and na f rich fluids

characteristics of djerfisherite from fluid rich metasomatized alkaline intrusive environments and anhydrous enstatite chondrites and achondrites djerfisherite is a k cl bearing sulfide that is present in both ultra reduced extraterrestrial enstatite meteorites enstatite chondrites or achondrites and reduced terrestrial alkaline intrusions kimberlites ore deposits and skarns major element chemistry of two terrestrial occurrences of djerfisherite from the ilimaussaq and khibina alkaline igneous suites and three extraterrestrial examples of djerfisherite have been determined and combined with petrographic characterization and element mapping to unravel three discrete modes of djerfisherite formation high fe cu is characteristic of extraterrestrial djerfisherite and low fe cu is typical of terrestrial djerfisherite ilimaussaq djerfisherite which has high fe contents 55 wt is the exception low ni contents are typical of terrestrial djerfisherite due to preferential incorporation of fe and or cu over ni but ni contents of up to 2 2 wt are measured in extraterrestrial djerfisherite extensive interchange between k and na is evident in extraterrestrial samples though na is limited

bulk and mush melt evolution in agpaitic intrusions insights from compositional zoning in eudialyte ilimaussaq complex south greenland

baogutu an example of reduced porphyry cu deposit in western junggar abstract classic oxidized porphyry copper deposits opcd are characterized by high tonnage and elevated f o 2 and contain highly oxidized minerals including primary anhydrite and hematite in contrast the baogutu deposit contains abundant hypogene pyrrhotite and methane rich fluid inclusions characteristic of lower tonnage reduced porphyry copper deposits rpcd mineral paragenesis and mineral chemistry studies reveal two mineralization periods magmatic and hydrothermal with the hydrothermal period further subdivided into three paragenetic stages including ca na alteration potassic alteration and propylitization locally overlapped by phyllic alteration several independent geothermometers indicate that the temperatures of the magma potassic and propylitization alteration are estimated to be 600 900 c 200 400 c and 200 300 c respectively multiple indicators including mineral assemblages apatite so 3 content whole rock fe 2 o 3 feo ratios and fluid compositions indicate the f o 2 of the magma and hydrothermal fluid to be nno and nno nno 2 respectively hydrothermal fluids associated with primary biotite yield log f h 2 o f hcl fluids values of 4 8 6 2 for diorite and 4 1 4 5 for granodiorite porphyry the log f s2 of the magmatic and potassic alteration are estimated to be 0 7 to 3 0 and 5 5 to 11 0 respectively based on pyrrhotite and sulfide assemblages mineral assemblage and hessite composition suggest the log f te2 of the potassic alteration is 8 5 to 14 5 the low tonnage baogutu deposit displays significantly lower f o 2 than opcds nno 2 and on this basis could be classified as a rpcd other physicochemical conditions including t f s2 log f h2o f hcl fluid do not show obvious differences to those of opcds we deduce that the low f o 2 of baogutu metallogenic granitoids and aqueous fluids likely produced the unusual pyrrhotite arsenopyrite mineral assemblage and the nacl h 2 o ch 4 co 2 ore forming fluids and small tonnage typical of rpcds previous obtained fluid inclusion h o isotope data and sulfide s pb isotope data suggest the methane rich ore forming fluids were derived from deep mantle source with little contamination from sedimentary components however detailed studies are needed to clarify the origin of the ch 4

zr and ree mineralization in sodic lujavrite from the saima alkaline complex northeastern china a mineralogical study and comparison with potassic rocks abstract the triassic saima alkaline complex on the liaodong peninsula northeastern china consists mainly of potassic phonolite nepheline syenite and sodic lujavrite the lujavrite shows significant zr ree mineralization which is present in the form of early magmatic zr ree enriched clinopyroxene 30 40 titanite 5 and loparite ce and late magmatic to hydrothermal wadeite widespread eudialyte group minerals 5 10 and catapleiite ultimately the fractionation of the alkaline magma leads to the crystallization of mosandrite and hezuolinite textural relations and compositional variation among the characteristic zr ree bearing minerals record that both zr and rees were strongly incompatible in the sodic melt but that zr mineralization preceded ree mineralization the main zr ree mineralization in the saima lujavrite resulted from the high peralkalinity na k ratio and hfse content low oxygen fugacity and the intensive activity of water and volatiles of its evolving magma the discontinuous and abrupt changes in melt composition and mineral assemblage from the potassic nepheline syenite of the complex to the sodic lujavrite suggest that their magma was derived from different episodes of magmatic activity with different physico chemical characteristics rather than from the continuous evolution of a single magmatic event

hydrocarbons in crystalline rocks commercial oil deposits in basement rocks are not geological accidents but are oil accumulations which obey all the rules of oil sourcing migration and entrapment therefore in areas of not too deep basement oil deposits within basement rocks should be explored with the same professional skill and zeal as ccumulations in the overlying sediments landes et al 1960 aapg bulletin given that most opec countries are currently at or within 5 production capacity there is a growing need to look for new oil and other hydrocarbons in non traditional sources while oil and gas fields in crystalline basement are still discovered mostly by accident as shown in this book such reservoirs can be very prolific especially if the basement rock is highly faulted or fractured the chapters in this volume cover a diverse range of topics related broadly to the theme of hydrocarbons in crystalline rocks and challenge explorationists definition of basement rock which needs to be less narrow and more responsive to new geological ideas

isotope major minor and trace element geochemistry of late magmatic fluids in the peralkaline ilimaussaq intrusion south greenland abstract the persodic 1 16 ga old ilimaussaq intrusion consists of alkali granites syenites and agpaitic nepheline syenites these rocks are cut by late magmatic veins and lenses consisting of albite aegirine ussingite na2alsi3o8 oh fluorite and occasionally quartz oxygen isotope compositions of quartz indicates both orthomagmatic 18oqtz 8 5 and country rock influenced 18oqtz 10 origin while albite and aegirine do not contain fluid inclusions suitable for investigations ussingite contains secondary hydrocarbon fluid inclusions fluorite contains brine inclusions of primary and secondary origin with up to 26 3 wt naclequiv and quartz contains predominantly secondary brine inclusions with up to 29 7 wt naclequiv or ch4 h2o nacl mixtures these fluids are interpreted to reflect fluids in equilibrium with late stage melts at ilimaussaq at 450 c the carbon and hydrogen isotope composition of ch4 in ussingite 13c 6 to 3 d 121 is indicative of a magmatic abiogenic origin however the isotopic composition of ch4 in fluid inclusions in quartz veins resembles the signature of thermogenic ch4 13c 43 to 23 d 176 to 121 but the higher hydrocarbons are mostly 13c depleted in relation to ch4 up to 7 3 which is typical of abiogenically derived hydrocarbons ion chromatography of fluid inclusion leachates from the late stage veins reveals cl br ratios of 100 as such values seem to be typical of peralkaline magmatic rocks at least in the gardar province of south greenland it is suggested that this ratio is typical of gardar magmatic fluids and may be characteristic of the cl br ratio of the lithospheric mantle from which these alkaline melts are derived

experimental and thermodynamic constraints on the sulphur yield of peralkaline and metaluminous silicic flood eruptions many basaltic flood provinces are characterized by the existence of voluminous amounts of silicic magmas yet the role of the silicic component in sulphur emissions associated with trap activity remains poorly known we have performed experiments and theoretical calculations to address this issue the melt sulphur content and fluid melt partitioning at saturation with either sulphide or sulphate or both have been experimentally determined in three peralkaline rhyolites which are a major component of some flood provinces experiments were performed at 150mpa 800 900 c fo2 in the range nno 2 to nno 3 and under water rich conditions the sulphur content is strongly dependent on the peralkalinity of the melt in addition to fo2 and reaches 1000ppm at nno 1 in the most strongly peralkaline composition at 800 c at all values of fo2 peralkaline melts can carry 5 20 times more sulphur than their metaluminous equivalents mildly peralkaline compositions show little variation in fluid melt sulphur partitioning with changing fo2 ds 270 in the most peralkaline melt ds rises sharply at fo2 nno 1 to values of 500 the partition coefficient increases steadily for sbulk between 1 and 6wt but remains about constant for sbulk between 0 5 and 1wt at bulk sulphur contents lower than 4wt a temperature increase from 800 to 900 c decreases ds by 10 these results along with 1 thermodynamic calculations on the behaviour of sulphur during the crystallization of basalt and partial melting of the crust and 2 recent experimental constraints on sulphur solubility in metaluminous rhyolites show that basalt fractionation can produce rhyolitic magmas having much more sulphur than rhyolites derived from crustal anatexis in particular hot and dry metaluminous silicic magmas produced by melting of dehydrated lower crust are virtually devoid of sulphur in contrast peralkaline rhyolites formed by crystal fractionation of alkali basalt can concentrate up to 90 of the original sulphur content of the parental magmas especially when the basalt is co2 rich on this basis we estimate the amounts of sulphur potentially released to the atmosphere by the silicic component of flood eruptive sequences the peralkaline ethiopian and deccan rhyolites could have produced 10 17 and 10 18 g of s respectively which are comparable amounts to published estimates for the basaltic activity of each province in contrast despite similar erupted volumes the metaluminous parana etendeka silicic eruptives could have injected only 4 6 10 15 g of s in the atmosphere peralkaline flood sequences may thus have greater environmental effects than those of metaluminous affinity in agreement with evidence available from mass extinctions and oceanic anoxic events

ferric iron in catio3 perovskite as an oxygen barometer for kimberlite magmas ii applications we apply an oxygen barometer based on the fe content of catio3 perovskite to estimate the oxygen fugacity fo2 during the crystallization and emplacement of kimberlites in different eruptive phases of a single pipe or between different pipes clusters or provinces mineral chemical data for perovskite were compiled from the literature and obtained in our detailed study of perovskites from 11 kimberlites at somerset island and lac de gras canada perovskite compositions in kimberlites record a range in fo2 of many orders of magnitude from nno 5 to nno 6 where log fo2 is given relative to the nickel nickel oxide nno buffer the range of fo2 recorded by different parageneses of perovskite within a single pipe can vary up to three orders of magnitude with trends toward both oxidation and reduction during crystallization kimberlites record some of the greatest ranges and the highest known fo2 conditions for any terrestrial magma this is attributed to the presence of deep and oxidized source regions and the variable interplay of ferric ferrous vs carbon fluid equilibria during ascent of kimberlite magmas three kimberlite pipes from the lac de gras field show that higher fo2 values correlate with higher proportions of more resorbed diamonds suggesting that this variable has a measurable effect on the physical properties of diamonds in a pipe

agpaitic nepheline syenites a potential source of rare elements abstract the agpaitic nepheline syenites may with regard to their elevated contents of a number of rare elements be compared with the complex granite pegmatites both rock types form highly evolved magmas under closed system conditions which prevent volatiles from escaping agpaitic rocks are peralkaline nepheline syenites characterized by the presence of complex rare element minerals such as eudialyte and mosandrite instead of the simple minerals such as zircon and ilmenite uranium deposits have been found in agpaitic rocks in brazil pocos de caldas china saima and greenland ilimaussaq nb and apetite deposits in russia lovozero and khibina the type locality of agpaitic rocks the ilimaussaq complex in south greenland is characterized by elevated contents of elements such as zr ree y be li nb u th and f not only in pegmatites late veins and contact fenites but also in some of the rocks especially lujavrite and kakortokite the most important rare element containing minerals are eudialyte zr ree y nb steenstrupine u th ree rinkite nb ree y u pyrochlore and perovskite nb ta li mica li chkalovite be and villiaumite f occurrences of eudialyte rich kakortokite and lujavrite are presently being explored in the ilimaussaq complex as sources of zr ree y and nb

mafic potassic lavas of the quaternary west eifel volcanic field major and trace element analyses for 103 volcanoes of the quaternary west eifel volcanic field show the lavas to be dominantly primitive mgo 7 wt and potassic na2o k2o 1 the rocks are divided into 1 a foidite f suite volumetrically dominant and consisting of four types leucitites and nephelinites melilite bearing foidites olivine free foidites sodalite bearing melilite free foidites and 2 a younger olivine nephelinite and basanite onb suite concentrated in the southeastern part of the field dominantly cpx phyric f suite magmas differ from the dominantly ol phyric onb suite mainly in higher k2o na2o and cao al2o3 ratios higher rb cu h2o co2 and lree concentrations and slightly lower sr ni and y contents most magmas have fractionated small amounts of olivine clinopyroxene and minor phlogopite systematic compositional variations within volcanoes or volcano groups are rare five more differentiated volcanoes 2 tephrites 3 phonolites occur in the center of the field their magmas are interpreted to have formed by fractionation within crustal magma chambers

sr and pb isotopes u and th chemistry of the alkaline monteregian and white mountain igneous provinces eastern north america the monteregian hills and younger white mountain alkaline intrusions were emplaced into the cambro ordovician sediments of the st lawrence lowlands and the folded and thrusted lower paleozoic sequence of the appalachian orogen age relations indicate that there is a fine scale structure to the igneous activity with slightly undersaturated to critically saturated rocks emplaced between 141 and 128 ma and strongly undersaturated rocks emplaced between 121 and 117 ma sr and pb isotopic data for the mantle derived alkali picrite alkali olivine basalt and basanite magmas indicate derivation from a depleted mantle similar to that which produces present day oceanic island basalts for the most isotopically primitive samples decay corrected 87sr86sr 0 7030 0 7037 206pb204pb 19 05 19 72 207pb204pb 15 56 15 65 and 208pb204pb 38 64 39 26 on pb sr isotope correlation diagrams the data define trends similar to those for mor basalts implying mantle heterogeneity which requires the presence of a component enriched in radiogenic pb relative to sr the interaction of these isotopically primitive magmas with the crust can be defined in terms of a three component system depleted mantle grenville age crust lower paleozoic age crust the granitic magmas were apparently derived from the lower paleozoic crust of the appalachian orogen for the mantle derived magmas th u ratios vary from 2 5 estimated ratio for morb source to 5 1 with the mean value near that of the bulk earth the variations in th u suggest mantle heterogeneity on a local scale and the high th u of some samples suggests that the mantle was enriched in incompatible elements shortly before melting the magmas derived by partial melting of the crust have th u of 3 3 to 8 7 and the higher ratios are associated with rocks crystallized from magmas that originated by melting of lower paleozoic sediments the sr and pb isotopic data support the conclusion of bellet al 1982 that the subcontinental mantle under eastern canada underwent a precambrian depletion event this depleted mantle apparently extends under the white mountain province and is isotopically similar to the mantle which gives rise to oceanic island basalts in contrast pb isotopic ratios for the new england seamount chain taras and hart 1983 which apparently represents the oceanic extension of this magmatic activity are significantly more radiogenic it is possible that a mantle plume provided the heat energy and perhaps metasomatic fluids to trigger melting in the subcontinental mantle whereas in the case of the oceanic extension the plume directly contributed to the observed magmatism as reflected in the more radiogenic pb ratios

borehole stoneley wave propagation across permeable structures this study investigates the propagation of borehole stoneley waves across permeable structures by modeling the structure as a zone intersecting the borehole a simple 1d theory is formulated to treat the interaction of the stoneley wave with the structure this is possible because the stoneley wave is a guided wave with no geometric spreading as it propagates along the borehole the interaction occurs because the zone and the surrounding formation possess different stoneley wavenumbers given appropriate representations of the wavenumber the theory can be applied to treat a variety of structures including a fluid filled fracture of special interest are the cases of permeable porous zones and fracture zones the results show that while stoneley wave reflections are generated strong stoneley wave attenuation is produced across a very permeable zone this result is particularly important in explaining the observed strong stoneley wave attenuation at major fractures where it has been difficult to explain the attenuation in terms of the single planar fracture theory in addition by using a simple and sufficiently accurate theory to model the effects of the permeable zone a fast and efficient method is developed to characterize the fluid transport properties of a permeable fracture zone

fischer tropsch synthesis of hydrocarbons during sub solidus alteration of the strange lake peralkaline granite quebec labrador canada abstract the composition of the carbonic phase s of fluid inclusions in pegmatite quartz from the strange lake peralkaline complex has been analysed by gas chromatography using online extraction of inclusion contents and a poraplot q capillary column the measured gas species are in order of abundance ch 4 h 2 c 2 h 6 co 2 n 2 ca n c 4 h 10 n c 5 h 12 c 2 h 2 i c 4 h 10 and c 2 h 4 minor amounts of i c 5 h 12 n c 6 h 14 i c 6 h 14 and neo c 6 h 14 were also detected but not quantified in some samples a suite of quartz samples from ca metasomatised pegmatites contains fluid inclusions with a similar distribution of hydrocarbons but much higher proportions of c0 2 the carbonic fluid coexisted immiscibly with a brine salvi and williams jones 1992 which on the basis of field and petrographic evidence was interpreted to have originated from the magma however thermodynamic calculations indicate that the above gas species specifically the hydrocarbons could not have coexisted at equilibrium in the proportions measured at any geologically reasonable conditions either prior to or post entrapment we propose instead that the gas compositions measured in the strange lake inclusions and in inclusions from other alkalic complexes resulted from the production of h 2 during the alteration of arfvedsonite to aegirine and the subsequent reaction of this h 2 with orthomagmatic c0 2 and co to form hydrocarbons in a magnetite catalysed fischer tropsch synthesis locally influx of an oxidised calcic brine derived externally from the pluton altered the original composition of the fluid by converting hydrocarbons to c0 2

a new type of silicate liquid immiscibility in peralkaline nepheline syenites lujavrites of the ilimaussaq complex south greenland the 1 15 ga old ilimaussaq intrusive complex in south greenland shows an extensive fractionation trend from alkaline augite syenite to various varieties of strongly peralkaline agpaitic nepheline syenites lujavrites the lujavrites are rocks with highly fluidal textures and are interpreted to have compositions close to melt compositions with the possible exception of significant loss of volatiles they crystallized between 800 and 450 c at 1 kbar and the different textural and mineralogical varieties exhibit variable but extreme enrichment in incompatible elements such as u th nb li be ree zr or rb dykes of one variety of these extreme agpaites exhibit spectacular features of macroscopically visible liquid immiscibility between an fe mn nb ree rich and a na al rich melt the latter forms light greyish pillow like structures of up to some centimetres size comparable to the ocelli known from lamprophyres in a dark fine grained matrix which is one of the most nb and ree rich melts known up to 1 2 wt nb2o5 and up to 6 6 wt reetot 2o3 unmixed between 500 and 600 c at 1 kbar both former melt phases crystallized assemblages involving arfvedsonite k feldspar steenstrupine and a variety of rare trace minerals presumably the na al rich melt additionally crystallized nepheline which was completely converted to analcime in an auto hydration process during cooling thisoccurrence offers the possibility to study the effect of compositional changes in melts and their bearing on immiscibility in great detail because the two immiscible melt phases are macroscopically visible can easily be separated from each other and a large part of the fractionation trend towards the solvus is recorded in the various lujavritic rock types of the ilimaussaq complex

proterozoic ferroan feldspathic magmatism abstract the proterozoic eon is characterized by an unusual abundance of ferroan feldspathic rocks that range in composition from granite to quartz syenites to feldspathoid bearing syenites three associations of ferroan rocks may be recognized on the basis of major element compositions 1 metaluminous alkalic to alkali calcic syenites and granites associated with anorthosites and iron rich basaltic rocks 2 alkaline intrusions in continental rifts and 3 calc alkalic metaluminous to peraluminous granitoid plutons that are less strongly ferroan than the other two groups the first two groups form by differentiation of tholeiitic to alkali basaltic parental magmas the third by partial melting of quartzo feldspathic crust although all three associations may form in intraplate settings only the alkaline intrusions which typically contain high incompatible trace element abundances plot entirely within the within plate granite fields on trace element discrimination diagrams processes of crustal melting and magma mixing have had a greater effect on the trace element compositions of ferroan granitoids from the other two associations causing some rocks to plot outside this field of these three associations the granitoids associated with anorthosites are the most voluminous and are essentially restricted to the proterozoic special conditions perhaps related to the presence of a long lived supercontinent under which widespread mantle upwelling took place appear required to explain the abundance of these rocks ferroan alkaline rocks although rarely preserved in archean crust are present in proterozoic and phanerozoic rifts the earliest alkaline intrusions thus may mark the establishment of rigid continents capable of rifting the formation of ferroan calc alkalic granites does not appear to be time dependent these granites have been generated throughout earth history in response to crustal melting

ore forming potential of alkaline magmas abstract geochemical models of the genesis of the largest rare metal deposits connected with agpaitic nepheline syenites are discussed in this paper thermodynamic calculations demonstrate that high alkalinity prevents the separation of volatile components into the gas phase the rare earth deposits have been formed at the magmatic stage during the process of crystal differentiation jointly with convection in the magmatic system the saturation of alkaline magma in respect of ore minerals at early stages of crystallization is considered to be the necessary condition for the formation of cumulative magmatic deposits these considerations are proved by data on micro inclusions

the magmatic and fluid evolution of the motzfeldt intrusion in south greenland insights into the formation of agpaitic and miaskitic rocks the 1 275 ga motzfeldt intrusive complex in the gardar failed rift province in south greenland formed from six successively intruding melt batches sm1 sm6 interpreted to be derived from a common magma source at depth five units sm1 sm5 crystallized an alkaline to peralkaline miaskitic mineral assemblage of amphibole clinopyroxene feldspar nepheline fe ti oxides zircon apatite fluorite and rarely olivine the last magmatic batch sm6 is characterized by an agpaitic mineral assemblage of aegirine nepheline alkali feldspar eudialyte and rare fluorite or sodalite coexisting mafic minerals constrain the crystallization conditions of the miaskitic rocks to about 850 6008c whereas solidus temperatures below 5008c are indicated by coexisting alkali feldspars in the agpaitic rocks oxygen fugacities during the orthomagmatic stage are below the fmq fayalite magnetite quartz buffer fmq 0 5t o 2 0 whereas late hematite provides evidence of a higher relative oxygen fugacity during late stage alteration the nd and oxygen isotope compositions of amphiboles and pyroxenes are homogeneous throughout the complex and suggest a common mantle derived magma source for all six units which is comparable with other gardar intrusions the hydrogen isotopic composition of amphiboles dd 99 to 132 indicates lowtemperature fluid rock interaction with low fluid rock ratios fluid inclusion studies indicate that h2o nacl fluids present during the magmatic stages in the miaskitic units had salinities of510 wt nacl eq calcite crystals in fluid inclusions within these rocks suggest that co2 or hco3 was an important component of the original fluid phase in contrast the agpaitic unit is characterized by a ch4 h2o naclfluid the c o h isotope compositionsofthefluid inclusions in all units are consistent with mixing between a small volume of magmatic fluid and a large volume of meteoric water the chemical evolution of the motzfeldt complex is a type example of the connection of the transition from miaskitic to agpaitic mineral assemblages with redox dependent fluid solid equilibria thetransitionfromarelatively oxidized to a relatively reduced fluid is correlated with a change from a more reduced fe 2 bearing miaskitic taramite arfvedsonite zircon sm1 sm5 to a more oxidized fe 3 bearing agpaitic assemblage aegirine eudialyte sm6 we suggest that coupled fluid solid redox equilibria involving fe 2 f e 3 c o2 and ch4 in this case were simply driven by temperature decrease and an overall increase in na k in the melt this observation sheds light on the heavily debated miaskite agpaite transition the combined temperature and compositional effect stabilized fe 3 c h 4 and enhanced the solubility of zr possibly as na zr si o complexes in the latest stage melt sm6 resulting in the crystallization ofan agpaitic mineral assemblage in terms of redox conditions during crystallization the motzfeldt rocks represent an intermediate case in the gardar province between more oxidized co2dominated intrusions such as the syenite carbonatite complex of