the petrogenesis of alkaline intrusives from arabia and northeast africa and their implications for within plate magmatism abstract trace element data from alkaline intrusions on both sides of the red sea indicate a within plate origin rb sr geochronology however demonstrates that alkaline magmatism in arabia was restricted to a post island arc emplacement of alkaline granite 650 500 ma whereas in northeast africa alkaline magmatism began with a similar phase but continued sporadically until the opening of the red sea at 30 ma with magmas becoming progressively undersaturated in silica with time isotope geochemistry of the earlier alkaline granites indicates a rb and lree depleted source region for the magmas and is consistent with a source in crustal rocks which had an age of less than 800 ma it is proposed that the time dependent undersaturation in silica resulted from the increasing role of asthenospheric volatiles and possibly magma in the petrogenesis of the younger alkaline magmas comparison between apparent polar wandering paths for africa inferred from recently published palaeomagnetic data and rb sr isochron ages from northeast africa and other alkaline provinces in africa active between 8 and 30 ma supports the theory that within plate magmatic emplacement is suppressed during periods of rapid lithospheric movement

estimates of p t ph2o and fo2 for lavas from patmos greece and implications for magmatic evolution abstract various geothermometers and geobarometers are used to estimate the conditions at which magmas erupted on patmos crystallized equilibrium phenocryst compositions are used as input data for the calculations and previously reported activity composition relationships for minerals and melts are used the results constitute an internally consistent set of estimates of t p p h 2 o and f o 2 but there are large auncertainties in values of p 2 kbar p h 2 o up to 0 7 kb and f o 2 up to 1 4 log units the ne trachybasalt hy trachybasalt hy trachyandesite q trachyte lavas of the main volcanic series mvs crystallized over a temperature interval of 1173 920 c at 2 4 kbar water contents calculated from p h 2 o ranged from 2 5 in the least evolved magmas to 5 6 in the q trachytes oxygen fugacity about 3 log units above values for the fmq buffer during crystallization of the ne trachybasalt was similar to values for alkaline lavas from arcs and from oceanic islands calculated oxygen fugacities for crystallization of the evolved mvs magmas are lower within about 1 log unit of the fmq buffer and this partly reflects uncertainties in calculation of the activity of annite the ne trachybasalts of the young volcanic series yvs crystallized at 1141 1121 c at values of f o 2 about 2 log units above those defined by the fmq buffer these magmas contained 2 2 3 8 h 2 o prior to eruption crystallization of the yvs magmas was polybaric and occurred over the pressure range 7 2 kbar the higher pressure indicates that magma evolution began in chambers sites at or near the base of the crust about 28 km the results place constraints on models for the evolution of the magmas erupted on patmos the data are consistent with eruption of the mvs magmas from a single chamber sited at a depth of 11 5 km or from several chambers sited over a depth interval of 8 5 to 14 5 km the f o 2 t data do not necessarily indicate that the trachyandesites and q trachytes are unrelated to the ne trachybasalts other factors such as assimilation and degassing prior to eruption can lead to a lowering of f o 2 during evolution polybaric crystallization of the yvs magmas as they traversed crust heated by previous magmatic activity is consistent with evolution via assimilation coupled with fractionation the preservation of xenocrysts of mantle olivine in the primitive mvs and yvs ne trachybasalts requires magma ascent times of less than about 78 days calculated from published diffusion data it is suggested that the yvs ne trachybasalts experienced fractional crystallization in the mantle prior to picking up the xenocrysts the phenocrysts in the mvs ne trachybasalt record low pressure 2 3 kbar crystallization indicating that either a these magmas represent hybrids formed by mixing of a primitive xenocryst bearing magma with a more evolved magma or b they evolved via fractional crystallization within the crust mixing is not consistent with mineralogical and geochemical data and the latter alternative is preferred crystallization occurred rapidly under supercooled conditions when magma ascent was temporarily arrested in low pressure chambers containing less dense evolved magmas hy trachybasalt to q trachyte fractionation probably reflects preferential nucleation and growth along the chamber margins it is apparent that xenocryst bearing magmas can evolve via fractional crystallization and an important implication is that xenolith xenocryst bearing magmas may also assimilate crustal material hence the trace element and isotopic signatures of such magmas do not necessarily reflect those of the upper mantle source region

fluorine and boron geochemistry of an ensialic marginal basin volcano deception island bransfield strait antarctica abstract we present the initial results of a quantitative investigation of the volatile geochemistry of deception island an active volcano situated near the spreading axis of a quaternary ensialic marginal basin bransfield strait northern antarctic peninsula fluorine contents in deception island magmas 112 461 ppm are comparable with lavas from a range of tectonic environments but f k 2 o relationships most closely compare with continental flood basalts and lavas from island arcs and some marginal basins boron contents are high 4 3 16 3 ppm and the values overlap with those of arc lavas they provide strong support for the presence of a mantle source component derived from the slab subducted at the coeval trench by melting at the slab wedge interface and or during slab dehydration both f and b acted incompatibly in deception island magmas but there is significant variation in incompatible element ratios such as k f k b p f p b which strongly suggests that the magmatic system was open to some or all of these elements during differentation the variations in these ratios also provide evidence for the presence of at least two stages in the magmatic evolution of the volcano during pre caldera times mafic magma was emplaced into the upper crust where it evolved and may have reacted with the crustal envelope thus changing the contents of some or all of the elements f b k and p and their inter element ratios a later large influx of hot mafic magma into the chamber may have been responsible for a major eruption that ultimately led to the formation of the caldera k f k b etc ratios in the magma chamber were reset and subsequently continued to change possibly by further crustal interaction during melt evolution in post caldera times

acoustic identification of buried underwater unexploded ordnance using a numerically trained classifier l using a finite element based structural acoustics code simulations were carried out for the acoustic scattering from an unexploded ordnance rocket buried in the sediment under 3 m of water the simulation treated 90 rocket burial angles in steps of 2 the simulations were used to train a generative relevance vector machine rvm algorithm for identifying rockets buried at unknown angles in an actual water sediment environment the trained rvm algorithm was successfully tested on scattering measurements made in a sediment pool facility for six buried targets including the rocket at 90 120 and 150 a boulder a cinderblock and a cinderblock rolled 45 about its long axis

fluorine as a tool in the petrogenesis of quartz bearing magmatic associations applications of an improved f oh biotite apatite thermometer grid abstract fluorine contents of whole rock and biotites allow to discriminate quartz bearing magmatic associations through the nature of protoliths and petrogenetic processes f and rb are used to discriminate crustal and mantle derived melts with the exception of calcalkaline association in which mantle contribution may be significant the other quartz bearing associations are essentially derived from crustal melting by biotite and or amphibole vapor absent reactions based on experimental data and on an improved biotite apatite thermometer grid closure temperatures from near liquidus to near solidus conditions as well as fh2o fhf evolution during cooling are determined for the different magmatic associations it appears that the liquidus temperature and fh2o fhf decreases in the order high silica alkaline high k calcalkaline and calcalkaline associations while the solidus temperature follows an inverse order the fh2o fhf values for the peraluminous associations vary over a wide range and overlap the fh2o fhf values of the high k calcalkaline and calcalkaline associations

hydrogen and carbon isotope studies on the graphite bearing metapelites in the northern kiso district of central japan measurements were made of the hydrogen isotope ratios of hydrous silicates mica and amphibole and whole rocks and the carbon isotope ratios of graphite and carbonaceous matter in the metamorphic rocks from the northern kiso district in central japan d values of hydrous silicates in the graphite bearing metapelites are always higher than those in graphite free schists even though the sample localities of the two rock types are very close hydrogen isotopic equilibrium has been attained between the coexisting minerals d h ratios of water in the metamorphic fluids seem to depend strongly on the presence or absence of graphite and seem to be not constant throughout the district the district is divided into three areas of low metamorphic zones i ii medium zones iiia v and high 13cgr value zones via vii areas in the high 13cgr values area the carbon contents of the graphite bearing rocks decrease slightly from zones via to vii whereas the 13cgr values increase sharply from the upper part of zone via to vib the d values of biotite in these graphite bearing rocks are higher than those in the medium 13cgr area this suggests that methane enriched inh and12c is produced and liberated by the devolatilization reactions between muscovite graphite and water the fluid produced is composed of water methane and a subordinate amount of carbon dioxide and its logfo2 value is deduced to be about 1 2 lower than that defined by the fmq buffer in the medium 13cgr area the 13c values of graphite are nearly constant 20 8 while the fe2o3 fe2o3 feo ratio of the graphite bearing rocks apparently decreases with increasing metamorphic grade d differences in hydrous silicates between graphite bearing and graphite free rocks are observed these facts are interpreted to mean that methane was produced in addition to water and carbon dioxide and that its generation x text ch text 4 x text co text 2 ratio of the fluid was about 2 had practically no isotope effect on the graphite in the low 13cgr area the carbon contents of the rocks decrease clearly from zones i to iiia the d and 13cgr values of the non metamorphosed shales are much lower than those of the low grade graphite bearing metapelites this suggests that methane is produced and liberated from the rocks even at the incipient stage of metamorphism

petrology and geochemistry of the nyamuragira volcano zaire abstract nyamuragira volcano in the western rift of the east africa rift valley is characterized by violent volcanic eruptions the most recent of which occurred in 1967 1971 1976 1977 1980 and 1981 1982 its extrusives consist of a highly potassic suite of olivine basanite tephritic phonolites among which phonolitic tephrite is the commonest the petrographic features of the whole suite such as phenocryst and groundmass mineral assemblages and modal variations are rather simple major elements vary smoothly from olivine basanite to phonolitic interstitial glass without any abrupt change with increasing k 2 o in addition the typical incompatible trace elements ba ce f nb rb and sr increase continuously with the increase of k 2 o these suggest that chemical variations were controlled mainly by the effective fractionation of olivine and clinopyroxene associated with plagioclase and titanomagnetite furthermore in the k 2 o incompatible trace element diagrams trend lines extrapolated to zero converge on the coordinate axes of the vertical and horizontal lines this suggests that these incompatible elements were preferentially moved toward the primitive basaltic magma during the partial melting of metasomatized upper mantle peridotites furthermore these elements are concentrated almost completely in residual liquids during fractional crystallization

fluorine geochemistry of basaltic rocks from continental and oceanic regions and petrogenetic application fluorine contents in about 300 samples of various types of basalts and related rocks from continental southwestern u s a zaire deccan and south africa and oceanic regions hawaii and mid atlantic ridge between 23 n and 40 n were determined by a selective ion electrode method

biotite and apatite as tools for tracking pathways of oxidized fluids in the archean east repulse gold deposit australia fluid pathways in hydrothermal ore deposits can potentially be traced through alteration zoning patterns and the chemistry of mineral phases i e major trace elements and isotopic composition which provide insight into the physico chemical gradients within and adjacent to pathways world class neoarchean gold deposits of the eastern yilgarn can be zoned with respect to alteration assemblages but in many cases fluid pathways are poorly understood which makes it difficult to identify the nature and source of fluids this study conducted detailed core logging sem mineral mapping of alteration assemblages and microprobe analysis of biotite and apatite in order to identify chemical gradients across the east repulse gold deposit of the st ives gold camp eastern yilgarn western australia results show that the east repulse deposit is vertically zoned with relatively oxidized sulfate rich alteration in the footwall of the deposit anhydrite celestine and or barite sulfide rich alteration in the core of the deposit pyrite magnetite with minor barite and celestine and relatively reduced sulfide only assemblages pyrite pyrrhotite with minor pentlandite millerite and cobaltite in the hanging wall of the deposit gold was identified as inclusions in pyrite and associated biotite implying a link between biotite pyrite alteration and gold mineralization the abundance of f in biotite and apatite progressively decreases from the footwall of the deposit into the mineralized core this trend of decreasing f in biotite and apatite with decreasing depth is consistent with an hypothesis that oxidized f and k bearing fluids were focused along subvertical pathways beneath the deposit within or subjacent to granitoid dikes the biotite apatite geothermometer shows that these fluids were relatively hot 480 60 c at the time of alteration these relatively high temperature oxidized f and k bearing fluids may have been derived from a proximal magmatic source

fluid absent melting of f rich phlogopite rutile quartz fluid absent melting is believed to be an important process in the generation of melts m the lower crust and upper mantle breakdown of phlogopite makes h 0 available and thus controls the conditions at which fluid absent melting occurs both f2andti in biotite ha e been shown to affect strongly the thermal stability of biotite to model better the fluid absenti eltmg of a ssemblagescontaining phlogopite the reaction f phlogopite quartz rutile enstatite melt has been studied experimentally experiments were pe o med at 7 10 and 15 kbar using a natural f rich phlogopite with a starting com os tion off f oh 0 43 and mg mg fe in molar proportions 0 94 results mdlcate that the therma l stability of f rich phlogopite quartz rutile is extended by as much as 450 c relative to the kmash system and by 300 c relative to the ti free f kmash system approach to equilibrium in the experiments was assessed by convergence of results of melting and crystallization experiments phlogopite compositions from e penmental products show that although f rich phlogopite incorporates relatively little ti 3 wt i02 the combination of f and ti increases the stability of phlogopite to considerably higher temperatures 300 0c than that of either component alone melts formed by the fluid absent melting off rich phlogopite quartz rutile at temperatures 1000 care anitic and stro g1yperaluminous the compositions of these melts suggest that the formationofmetalummous to peralkaline a type granites by fluid absent melting of halogen enriched sources is unlikely

fluorine chlorine and lithium distribution in igneous rocks of lipari and vulcano aeolian islands italy fluorine and chlorine have been determined in samples of lavas and pyroclastic products from the islands of lipari and vulcano which form the southernmost portion of the aeolian arc because their present distribution may provide additional information for a better understanding of the differentiation and eruptive mechanisms affecting these volcanoes

chemical and isotopic compositions of volcanic gases from the east sunda and banda arcs indonesia the easternmost sunda arc and the banda arc represent a continent arc collision zone where magma genesis is influenced by subducted continent derived material chemical and isotopic studies of volcanic gas samples from this environment provide information on the sources of volatiles in arc magmas these volcanic gases some of which last equilibrated at magmatic temperatures are characterized by anomalous low sup 3 he sup 4 he values but by common arc values of c s approx 2 4 delta sup 13 c approx minus 3 per thousand and delta sup 34 s sub tot approx 5 per thousand abundant helium and high he ar ratios are consistent with the subduction of terrigenous components in local sediments or slivers of continental crust although individual concentration and isotope ratios of volatile components may be explicable by complex fractionation in the recycling process the combined data are in agreement with an important role of subducted sedimentary source components comparison of the authors results with volcanic gas data from other arcs indicates that the carbon and sulfur signals in arc gases are relatively insensitive to the amount and nature of sediment on the subsiding plate hence a contribution to arc volcanic gases from subducted altered oceanic crust cannot be excluded

heat sources and melting in subduction zones in order to understand the mechanism of melt generation and the origin of high heat flow in subduction zones a series of numerical models of the thermal and flow structures in the mantle have been tested in two dimensional boxes with an inclined subducting slab of constant velocity in contrast to previous models 1 large convecting cells are used without imposing a high temperature profile on the backarc boundary which enables us to discuss the global heat balance and to seek for the heat sources responsible for the melting and high heat flow observed in subduction zones and 2 various mechanical conditions e g coupling between the slab and overlying mantle wedge buoyancy associated with melting and heat sources e g heat flux from below internal heat generation viscous heating are tested in varying proportions in all the calculations steady state or near steady state with a small instability periodically occurring at the upper thermal boundary layer is achieved under these conditions the global heat balance can be described by a simple boundary layer argument the results show that in order to attain a high enough temperature for melting and a high heat flux a large amount of internal heating i e more than 2 5 10 7 w m3 is required if the convection is limited within the upper mantle the high internal heating required may be explained if the radioactive nuclides in fluids expelled from the subducting slab are added to the wedge and circulate in the convection cell for a sufficient time another possible explanation for melting and the high heat flux is that the hot material is supplied from the lower mantle based on the thermal and flow structures obtained melting regimes in subduction zones are discussed in which the following key processes take place 1 melting associated with pressure change of a rock packet with its movement especially compression melting in the downward flow of the mantle wedge along the slab and 2 melting due to compositional change of the rock packet associated with migration of h2o and melt to solve these problems in detail further studies on distribution and migration of the fluids will be required

an experimental study of partitioning of fluorine between k richterite apatite phlogopite and melt at 20 kbar phase relations have been determined at 20 kbar and primarily under suprasolidus conditions in the fe ti free f bearing k richterite phlogopite and k richterite apatite systems in order to assess the partitioning of f among phlogopite k richterite apatite and melt under upper mantle conditions both systems are pseudoternary because they contain forsterite enstatite and a diopside rich clinopyroxene from the breakdown of the mica and k richterite the f bearing k richterite systems have lower minimum melting temperatures than the f bearing phlogopite apatite system at the same pressure however in the systems studied f in phlogopite appears the most effective component in altering minimum liquid compositions whereas comparison between the present study and previous systems suggests that the presence of p2o5 during melting may result in more k enriched melts variations in the compositions of the f bearing phases are primarily controlled by the bulk compositions of the end member minerals and by temperature although buffering by non f bearing minerals e g clinopyroxene may be effective distribution coefficients as wt ratios between f bearing minerals and coexisting liquids have been determined as functions of bulk composition and temperature for products of experiments distribution coefficients between k richterite liquid apatite liquid and phlogopite liquid are 1 to slightly 1 for most bulk compositions indicating thatf is generally a compatible element this conclusion is in agreement with the sequence off distribution for similar phases in ultrapotassic rocks these results preclude f bearing mineral reservoirs in the mantle at depths corresponding to 20 kbar being capable of producing f enrichment in ultrapotassic magmas or being effective in redox melting processes

fluorine geochemistry of quaternary volcanic rocks from southwestern british columbia some petrogenetic implications fluorine contents in 38 quaternary volcanic rocks representing calc alkaline andesite eruptive groups from the garibaldi lake area were determined by a selective ion electrode method a close relationship is evident between f abundance and the type of ferromagnesian phenocrysts present in the andesitic rocks hypersthene andesites have the lowest f contents 142 212 ppm whereas hornblende biotite andesites exhibit the highest f values 279 368 ppm hornblende andesites have intermediate f contents 238 292 ppm the hornblende free desolation valley basaltic andesite has a lower f content than the hornblende bearing sphinx moraine basaltic andesite 122 ppm versus 317 333 ppm

the role of apatite in mantle enrichment processes and in the petrogenesis of some alkali basalt suites analyses of sr and ree in apatites from a variety of mantle derived parageneses are used in conjunction with trace element data from the literature to investigate relationships between alkali basalts and apatite rich materials in upper mantle source regions despite difficulties in interpretation positive p anomalies in the hygromagmatophile element abundance patterns of some continental primary alkali basalts suggest either p enrichment of their source or assimilation of p rich material or both amphibole and apatite rich xenoliths occur in several alkali basalt provinces and by virtue of the p and lree enrichment represent a probable source of the p anomalies and part of the other trace element enrichments of these magmas incorporation of such apatite rich materials by later primary magmas would be enhanced by the high p2o5 concentrations required to achieve apatite saturation in basaltic liquids in the early stages of mantle diapirism an undersaturated magma produced by slight partial melting of garnet peridotite might fractionate as it rises to the range of amphibole stability hygromagmatophile element patterns of clinopyroxenite xenoliths indicate that clinopyroxene fractionation could produce p enriched liquids which might subsequently crystallize amphibole and apatite rich materials now represented by xenoliths during generation of later primary magma apatite rich materials might preferentially contaminate the liquids to yield positive p anomalies this model requires that magmas undergo prolonged fractionation at considerable depth 100 km a process which is apparently most probable in subcontinental environments an apatite and zircon bearing mica clinopyroxenite xenolith from matsoku provides a link between the s african marid suite and amphibole and apatite rich xenoliths from various alkali basalt provinces unusual ree patterns lan cen ndn cen yn 10 of apatites in this xenolith suggest a link between the marid suite xenoliths and postulated pre karroo mantle metasomatism

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

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

zonal structure of cenozoic basalts related to mantle upwelling in southwest japan cenozoic olivine bearing basaltic rocks in the central chugoku district form eight provinces each 20 to 30 km in diameter these provinces can be grouped into three zones almost parallel to the elongation of the sw japan arc based on geological and petrological characteristics the san yo zone the closest to the nankai trough is characterized by a small amount of alkaline basalt in the sekiryo zone intermediate zone transitional basalt is dominant the san in zone along the japan sea coast is characterized by subalkaline basalt and a large amount of andesitic rocks the eruption volume of these volcanics exponentially increases toward the back arc side less than 1 km3 to more than 100 km3 chemical compositions of relatively undifferentiated basalts show systematic across arc variations sio2 and al2o3increase and feo mgo and cao decrease toward the back arc side 44 to 54 13 to 18 11 to 6 13 to 7 and 12 to 8 wt at feo mgo 0 85 respectively melting experiments on the basalt h2o co2 systems show that the pressure and temperature of magma segregation decrease toward the back arc side 17 19 kbar and 1340 1320 c to 8 kbar and 1250 c and the coexisting phases change from a spinel lherzolite assemblage to a harzburgite assemblage these pt conditions define a trend which can be interpreted as a pt path for adiabatic upwelling of the mantle material consequently the observed volcanism and zonation may have been caused by upwelling of a plume from a deep part of the mantle

thermal and geochemical evolution of the mantle wedge in the northeast japan arc 1 contribution from experimental petrology melting phase relations at high pressures have been examined for four mg rich basalts from both the trench and the backarc sides of the miocene ne japan arc all these basalts crystallize olivine and orthopyroxene on the liquidus at pressures lower and higher than the point of multiple saturation with those two phases respectively the pressure of multiple saturation is rather constant for all samples 1 0 1 4 gpa suggesting that 1 there was no across arc variation in the depth of magma segregation in the miocene ne japan arc 2 the depth of magma segregation remains constant since 20 ma in the trench side of the volcanic arc whereas it has changed from 30 40 km to 60 km beneath the backarc side of the arc this temporal variation may be caused by increasing thickness of the lithosphere beneath the backarc region associated with cooling of the mantle wedge after the opening of the japan sea backarc basin in the early miocene