the behavior of thallium during alteration of the k alkaline rocks from the roccamonfina volcano campania southern italy tl behavior in the alteration of leucite and related k alkaline rocks from the quaternary roccamonfina volcano has been outlined the dominant weathering product is analcite that shows a moderate loss of tl relative to the coexisting leucite r 0 74 0 21 weathering of leucite to halloysite is subordinate and characterized by a very strong depletion in tl r 0 14 0 15 the geochemical coherence between tl and k observed in the roccamonfina igneous rocks breaks down when leucite weathers to analcite as unlike tl k is almost totally lost in contrast in the alteration of leucite to halloysite both elements still behave coherently being almost totally mobilized to groundwater thermodynamic calculations show that tl in the roccamonfina groundwater occurs mostly as tl oh 3 aq thus as tl occurs in the igneous rocks as tl i it is apparent that it oxidizes to tl iii after introduction to the hydrosphere in spite of the significant amount of tl made available by weathering of tl rich country rocks groundwaters from the study area are not tl enriched their contents matching the average for natural waters on the other hand at roccamonfina widespread sedimentary fe rich mn bearing occurrences are richer in tl than any other rock these findings lead one to infer that tl mobility as well as its concentration level in groundwater are strongly attenuated due to the scavenging properties of such fe and mn bearing sediments

tectonic and metasomatic mixing in a high t subduction zone melange insights into the geochemical evolution of the slab mantle interface abstract the catalina schist california contains an amphibolite grade 0 8 1 1 gpa 640 750 c melange unit consisting of mafic and ultramafic blocks in high mg schistose melange matrix with varying modal proportions of talc chlorite anthophyllite calcic amphibole enstatite and minor phases including zircon rutile apatite spinel and fe ni sulfides this melange unit is interpreted as a kilometer scale zone of tectonic and metasomatic mixing formed within a juvenile subduction zone the study of which may yield insight into chemical mixing processes at greater depths in subduction zones relationships among the major and trace element compositions of the mafic and ultramafic blocks in the melange the rinds developed at the margins of these blocks and the surrounding melange matrix are compatible with the evolution of the melange matrix through a complex combination of infiltrative and diffusional metasomatism and a process resembling mechanical mixing simple linear mixing models are compatible with the development of the melange matrix primarily through simple mixture of the ultramafic and mafic rocks with cr al ratios serving as indicators of the approximate proportions of the two lithologies this conclusion regarding mafic ultramafic mixing is consistent with the field observations and chemical trends indicating strong resemblance of large parts of the melange matrix with rinds developed at the margins of mafic and ultramafic blocks the overall process involved development of metasomatic assemblages through complex fluid mediated mixing of the blocks and matrix concurrent with deformation of these relatively weak rind materials which are rich in layer silicates and amphibole this deformation was sufficiently intense to transpose fabrics progressively disaggregate more rigid block derived materials in weaker chorite and talc rich melange and in some particularly weak lithologies e g chlorite talc and amphibole rich materials intimately juxtapose adjacent lithologies at the sub cm scale approaching grain scale sampled by the whole rock geochemical analyses chemical systematics of various elements in the melange matrix can be delineated based on the cr al based mixing model simple mixing relationships exhibited by al cr mg ni fe and zr provide a geochemical reference frame for considerations of mass and volume loss and gain within the melange matrix the compositional patterns of many other elements are explained by either redistribution local stripping or enrichment at varying scales within the melange ca na k ba and sr or massive addition from external sources si and h2o the latter probably in infiltrating h2o rich fluids that produced the dramatic o and h isotopic shifts in the melange melange formation resulting in the production of high variance ultramafic assemblages with high volatile contents may aid retention of volatiles in this case h2o to greater depths in subduction zones than in original subducted mafic and sedimentary materials the presence of such assemblages i e containing minerals such as talc chlorite and mg rich amphiboles would impact the rheology of the slab mantle interface and perhaps contribute to the low velocity seismic structure observed at near the slab mantle interface in some subduction zones if operative along the slab mantle interface complex mixing processes such as these involving the interplay between fluid mediated metasomatism and deformation also could impact slab incompatible trace element and isotopic signatures ultimately observed in arc magmas producing fluids with geochemical signatures inherited from interactions with hybridized rock compositions

accessory minerals and subduction zone metasomatism a geochemical comparison of two melanges washington and california u s a abstract the ability of a subducted slab or subducted sediment to contribute many incompatible trace elements to arc source regions may depend on the stabilities of accessory minerals within these rocks which can only be studied indirectly in contrast the role of accessory minerals in lower t and p metasomatic processes within paleo subduction zones can be studied directly in subduction zone metamorphic terranes the gee point iron mountain locality of the shuksan metamorphic suite north cascades washington state is a high t melange of metamafic blocks in a matrix of meta ultramafic rocks this melange is similar in geologic setting and petrology to the upper part of an unnamed amphibolite unit of the catalina schist santa catalina island southern california both are interpreted as shear zones between mantle and slab rocks that formed during the early stages of subduction some garnet amphibolite blocks from the gee point iron mountain locality display trace element enrichments similar to those in counterparts from the catalina schist some catalina blocks are highly enriched in th rare earth elements ree the high field strength elements ti nb ta zr and hf hfse u and sr compared to mid ocean ridge basalt morb and to other garnet amphibolite blocks in the same unit textural and geochemical data indicate that accessory minerals of metamorphic origin control the enrichment of th ree and hfse in blocks from both areas the mg rich rinds around blocks and the meta ultramafic matrix from both melanges are highly enriched in a large number of trace elements compared to harzburgites dunites and serpentinites evidence for recrystallization or formation of accessory minerals in the former rocks suggests that these minerals control some of the trace element enrichments data from the gee point and catalina melanges suggest that the accessory minerals titanite rutile apatite zircon and ree rich epidote play a significant role in the enrichment of trace elements in both mafic and ultramafic rocks during subduction related fluid rock interaction mobilization of incompatible elements and deposition of such elements in the accessory minerals of mafic and ultramafic rocks may be fairly common in fluid rich metamorphic environments in subduction zones

geochemistry of champagne hot springs shallow hydrothermal vent field and associated sediments dominica lesser antilles the champagne hot springs chs shallow submarine hydrothermal system is located along the submerged flank of the plat pays volcanic system on the southwest section of the island of dominica lesser antilles we have conducted a detailed geochemical study of the hydrothermal system with the objectives to investigate the source of the hydrothermal fluids and gases their effect on sediment and precipitate chemistry as well as comparing the submarine vent chemistry with nearby on land hydrothermal vents finally we compare our findings to previous preliminary data from chs and compare sediment chemistry to that of average caribbean sediments we also report on a newly discovered area of submarine hydrothermal venting located approximately 40 m to the north of chs this area consists of hydrothermally altered areas of sand that contain abundant coatings of hydrous ferric oxides hfo on sediment grains geochemical and mineralogical analyses of vent waters pore waters gases sediments and precipitates reveal that the vent fluids consist of a mixture of entrained seawater and meteorically derived hydrothermal fluid in varying proportions vent fluids are depleted in br s o4 c l n a k and sr 2 relative to ambient seawater these species are all positively correlated with mg 2 which is also depleted relative to seawater boron fe as sb mn si and li are all enriched relative to ambient seawater pore waters in the hydrothermally altered sand patches have essentially the same chemistry mixing between fe 2 rich vent fluids and seawater causes rapid oxidation of fe 2 to insoluble fe 3 and leads to precipitation of hfo at the vent site and subsequent formation of hydrothermally altered sand patches the elevated concentrations of as and sb in the precipitates and sediments relative to average caribbean seafloor sediments reflect adsorption by hfo gas samples from the vent site are typical arc type gases and have both meteoric and magmatic signatures d 2005 elsevier b v all rights reserved

abundance and behavior of thallium in the k alkaline rocks from the roccamonfina volcano campania southern italy abstract the tl content in whole rocks matrix and mineral separates leucite sanidine biotite phlogopite from 58 igneous rocks of the k alkaline suites of the roccamonfina volcano has been measured by polarographic technique the tl content increases with magmatic differentiation indicating that tl is a magmaphile element in these magma suites the tl content does not distinguish mafic rocks of the high k series relative to those of the k series indicating that in this respect tl is not similar to k and other lil elements among minerals leucite x 6417 ppb is enriched in tl relative to sanidine x 2345 ppb and biotite x 2417 ppb average d leuc matrix tl d san matrix tl and d biot matrix tl are 3 67 0 65 and 1 86 respectively the roccamonfina primitive rocks display tl contents x 582 ppb similar to those of basalts of continental settings and close to the value of the average crust x 491 ppb both crustal contamination and mixing between a normal mantle and a lil enriched mantle material can account for such high tl contents in the roccamonfina primitive rocks

enrichment of trace elements in garnet amphibolites from a paleo subduction zone catalina schist southern california the abundance p t stability solubility and element partitioning behavior of minerals such as rutile garnet sphene apatite zircon zoisite and allanite are critical variables in models for mass transfer from the slab to the mantle wedge in deep regions of subduction zones the influence of these minerals on the composition of subduction related magmas has been inferred and disputed from inverse modelling of the geochemistry of island arc basalt or by experiment although direct samples of the dehydration partial melting region of a mature subduction zone have not been reported from subduction complexes garnet amphibolites from melanges of circumpacific and caribbean blueschist terranes reflect high t 600 c conditions in shallower regions such rocks record geochemical processes that affected deep seated high t portions of paleo subduction zones in the catalina schist a subduction zone metamorphic terrane of southern california metasomatized and migmatitic garnet amphibolites occur as blocks in a matrix of meta ultramafic rocks this mafic and ultramafic complex may represent either slab derived material accreted to the mantle wedge of a nascent subduction zone or a portion of a shear zone closely related to the slab mantle wedge contact or both the trace element geochemistry of the complex and the distribution of trace elements among the minerals of garnet amphibolites were studied by inaa xrf electron microprobe and sem in order of increasing alteration from a probable metabasalt protolith three common types of garnet amphibolite blocks in the catalina schist are 1 non migmatitic clinopyroxene bearing blocks which are compositionally similar to morb that has lost an albite component 2 garnet amphibolite blocks which have rinds that reflect local interaction between metabasite metaperidotite and fluid and 3 migmatites that are extremely enriched in th hfse lree and other trace elements these trace element enrichments are mineralogically controlled by rutile garnet sphene apatite zircon zoisite and allanite alkali and alkaline earth elements are much less enriched in the solid assemblage and thus appear to be decoupled from the other elements in the inferred metasomatic process es the compositions of migmatitic garnet amphibolite blocks seem to complement that of average island arc tholeiite trace element metasomatism reflects fluid solid rather than melt solid interaction the metasomatic effects indicate that h2o rich fluid perhaps with a significant component of na al silicate and alkalis carried th u sr ree and hfse fractionations of lree in migmatites resemble those of migmatitic metasedimentary rocks underlying the mafic and ultramafic complex exotic lree deposited in allanite in migmatites could have been derived from fluids in equilibrium with subducted sediment if the paleo subduction zone represented by the mafic and ultramafic complex of the catalina schist had continued its thermal and fluid evolution a selvage of similarly enriched rocks might have been generated along the slab mantle wedge contact between 30 and 85 km depth rocks affected by subduction zone metasomatism although rarely recognized at the surface could be volumetrically significant products of the initiation of subduction and may prove to be geochemical probes of convergent margins that approach the significance of xenoliths in the study of other magmatic environments

magmatic metasomatism and formation of the merensky reef bushveld complex the rare earth element ree contents of pyroxenes and other minerals from the merensky reef and stratigraphically adjacent rocks of the atok section bushveld complex have been determined with the ion microprobe merensky reef clinopyroxene and orthopyroxene contain much higher and more variable concentrations of the ree than their cumulus counterparts in rocks several meters below the reef chondrite normalized merensky clinopyroxene ce contents vary from 10 to 90 for ce and from 4 to 17 for yb they also possess deep negative eu anomalies the eu anomalics being deeper for crystals having high ree contents and relatively shallow for pyroxenes with low ree contents similar compositional characteristics are displayed by cl rich apatite which is an accessory phase in the rocks interstitial pyroxene in cumulates above and below the reef also tends to have elevated ree contents and in general is not in equilibrium with coexisting cumulus minerals the melt from which the cumulus minerals crystallized falls within the compositional range of continental basalts that from which merensky and postcumulus pyroxenes crystallized is inferred to be much more highly enriched in ree than any normal tholeiitic or alkalic basalt despite their highly evolved nature in terms of the ree the merensky reef pyroxenes are not evolved in terms of major elements the decoupling of incompatible trace and major elements is best explained by a metasomatic process it is speculated that metasomatism involved upward percolation of hydrated silicate melt through and its reaction with the crystalline cumulate pile the fact that the rocks enriched in the platinum group elements are also those that show evidence for metasomatism suggests that these elements were also metasomatically redistributed

pyrite trace element geochemistry of mafic granulite xenoliths from xikeer implications for the source of cu in the sediment hosted mineralization in the northwestern tarim basin northwest china the xikeer mafic granulite xenoliths are hosted by a cenozoic basanite sill 20 ma in the northwest tarim basin northwest china sulfides identified in these xenoliths consist mainly of pyrite two groups of pyrite types a and b can be distinguished based on petrography and trace element geochemistry as determined by laser ablation icp ms analysis type a pyrite is subhedral and in general has lower trace element abundance than type b pyrite type b pyrite is fractured with ragged anhedral morphology and has extremely high cu tl ni and co abundance the low co and ni contents combined with a positive correlation between cu cr and pb all indicate that the type a pyrite may have formed from a high temperature magmatic hydrothermal fluid in contrast the cu tl ni and co rich type b pyrite was probably formed in a relatively low temperature basinal environment the cu mineralization at xikeer can be explained when cu tl ni and co were leached from the intruded basanites and subsequently enriched in circulating basin brines such enrichment of cu in basin brines could provide an important cu source for the cu mineralization in the xikeer district and other cenozoic sub basins in the tarim basin

the mineralogy of arsenic in uranium mine tailings at the rabbit lake in pit facility northern saskatchewan canada a detailed investigation of the mineralogy of as in the tailings of the rabbit lake uranium ore processing facility was conducted the milling ore extraction process was sampled at three different locations to obtain information about when where and under what condition secondary as phases form these samples were compared with four samples of varying as content from the rabbit lake in pit tailings management facility tmf up to 20 as in the tailings are present in primary minerals that reach the tailings directly because they are not dissolved during the uranium extraction the remaining 80 constitute as that was dissolved during ore extraction and then re precipitated before being discharged into the tailings pond it was not possible to conclusively identify any individual re precipitated secondary as minerals in the rabbit lake tmf indirect evidence from sequential extraction analyses suggests the presence of an amorphous ca as phase and a possible but unlikely minor amount of an amorphous fe as phase however the close association between hydrous ferric oxide hfo and as could be clearly demonstrated hfo was identified to be 2 line ferrihydrite and its xrd pattern geometry indicates a substantial amount of adsorbed as this is in good agreement with sem tem and sequential extraction analyses that all showed the close association of hfo and as

distribution and behavior of lithium in the k alkaline rocks from the roccamonfina volcano campania southern italy abstract the li content in whole rocks matrix and mineral separates biotite sanidine leucite phlogopite from 58 igneous rocks of the k alkaline suites of the roccamonfina volcano has been measured by atomic absorption among the minerals sanidine contains as much li as biotite x 41 8 ppm and x 40 2 ppm respectively while phlogopite and leucite have a much smaller amount x 6 0 ppm and x 2 6 ppm respectively average li distribution coefficients between minerals and groundmass are d biot matrix li 0 50 d san matrix li 0 84 and d leuc matrix li 0 06 respectively the li content increases with magmatic differentiation in the rocks of the k series showing an enrichment factor of 3 6 in the salic relative to the mafic rocks in the high k series the li content increases from primitive to intermediate rocks but shows a levelling off in the more salic rocks li acts incompatibly except in the most salic rocks whose li content was probably mainly controlled by diffusion processes through the magmas the li content in the roccamonfina primitive rocks x 20 ppm does not discriminate between the k and high k series and is higher than that of the average basalt x 10 ppm however it is similar to that of basalts from continental settings this relatively high li content in the roccamonfina primitive rocks can be accounted for by either crustal contamination or the existence of an enriched mantle region beneath the volcano but in both hypotheses there is a suggestion of some involvement of the lower crust in the generation of the roccamonfina parental magmas

precipitation of fe iii oxyhydroxide deposits from shallow water hydrothermal fluids in tutum bay ambitle island papua new guinea abstract previous research on sea floor fe iii oxyhydroxide deposits has focused primarily on deep sea hydrothermal systems found along volcanically active portions of the mid ocean ridges and on hydrogenetic deposits formed in deep basins and along continental shelves there is however not much known about their formation in shallow water settings associated with volcanic islands the hydrothermal system at ambitle island papua new guinea provides an excellent opportunity to study the formation of fe iii oxyhydroxides in a shallow water setting precipitation from the hydrothermal solution is caused by mixing with seawater based on a 87 sr 86 sr mixing model the calculated minimum and maximum seawater fractions are approximately 11 and 57 respectively thus precipitation of tutum bay fe iii oxyhydroxides takes place at a temperature range between approximately 60 and 93 c the chemical composition shows low mn contents fe mn 600 and elements that are usually enriched in fe iii oxyhydroxides such as co and v are below crustal abundance and well below their concentrations in island arc volcanics arsenic concentrations on the other hand are by two orders of magnitude higher than those in other marine deposits rare earth element ree concentrations reflect their concentration in the hydrothermal fluids rather than seawater the crystallinity of the deposits increases with age as protoferrihydrite is apparently altered to fe smectite and hematite and as bearing minerals are formed contact with seawater and therefore oxidizing conditions seems to be the factor increasing the crystallinity

hydrothermalism in the mediterranean sea abstract hydrothermalism in the mediterranean sea results from the collision of the african and european plates with the subduction of the oceanic part of the african plate below europe high heat flows in the resulting volcanic arcs and back arc extensional areas have set up hydrothermal convection systems most of the known hydrothermal sites are in shallow coastal waters

the primitive lavas of roccamonfina volcano roman region italy new constraints on melting processes and source mineralogy within a large collection of lavas from the roccamonfina volcano are rocks which represent the most mafic samples yet recorded from roccamonfina and which are amongst the least differentiated lavas found in the roman co magmatic region as a whole these rocks extend both high k and low k series to more primitive values however petrographic and geochemical considerations rule out a primary origin and even these mafic samples appear to record the effects of repeated episodes of fractional crystallization and hybridization relatively potassic samples from the low k series are apparently transitional between low k and high k series as previously delineated however these intermediate k samples are not transitional in their sr isotopic composition suggesting that there is no continuum between low k and high k magma source regions rather the compositional range within the low k series appears predominantly to reflect variation in the degree of melting of a common mantle source analysis of the low k series data using an inverse method suggests a source containing amphibole and garnet and indicates that these phases were consumed during the melting processes responsible for the low k series magmas the role of amphibole is further indicated by the association of low k2o with elevated rb concentration and for example higher ce yb such variations are taken to reflect the consumption of high k rb amphibole during the initial phase of partial melting

correlation of clayey gouge in a surface exposure of serpentinite in the san andreas fault with gouge from the san andreas fault observatory at depth safod abstract magnesium rich clayey gouge similar to that comprising the two actively creeping strands of the san andreas fault in drill core from the san andreas fault observatory at depth safod has been identified in a nearby outcrop of serpentinite within the fault zone at nelson creek each occurrence of the gouge consists of porphyroclasts of serpentinite and sedimentary rocks dispersed in a fine grained foliated matrix of mg rich smectitic clays the clay minerals in all three gouges are interpreted to be the product of fluid assisted shear enhanced reactions between quartzofeldspathic wall rocks and serpentinite that was tectonically entrained in the fault from a source in the coast range ophiolite we infer that the gouge at nelson creek connects to one or both of the gouge zones in the safod core and that similar gouge may occur at depths in between the special significance of the outcrop is that it preserves the early stages of mineral reactions that are greatly advanced at depth and it confirms the involvement of serpentinite and the mg rich phyllosilicate minerals that replace it in promoting creep along the central san andreas fault

relationships between chamber margin accumulates and pore liquids evidence from arrested in situ processes in ejecta latera caldera italy biotite and clinopyroxene rich mafic nodules occur together with syenite ejecta in ca 235 to 155 ka tuffs surrounding the latera caldera clinopyroxenites and leucite monzosyenites crystallized along the lower margins of a crustal magma system and record complex crystallization histories of potassic magmas that were parental to a range of lava and tuff compositions the mafic nodules have the mineral assemblage clinopyroxene biotite anorthite orthoclase leucite hauyne titanite apatite amphibole olivine phlogopite and comprise mesocumulate and orthocumulate layers that commonly alternate on the scale of several centimeters despite the apparently ultramafic nature of the early cumulate assemblage the common occurrence of intercumulate orthoclase leucite hauyne salitic clinopyroxene and vesicular glass indicates that interstitial liquids underwent late stage differentiation at relatively shallow depths but under highly variable conditions of volatile saturation many of the mafic nodules exhibit pronounced variations in the type and abundance of mineral reaction textures these range from unreacted assemblages to nodules in which cumulate megacrysts are surrounded by well developed symplectite halos the textural variability indicates strongly localized disequilibrium between cumulate frameworks and vapor saturated pore fluids and is attributed to convective fractionation of liquids through permeable crystal mush lithologic discontinuities exhibited by the xenolith suite and host magmas are best explained by variable communication between a compositionally stratified magma reservoir and its partly crystallized lower chamber margins periodic replenishment of this system by less evolved magmas subsequently promoted mixing and hybridization that are characteristic features of many latera lavas and tephra

life on the edge microbial biomineralization in an arsenic and lead rich deep sea hydrothermal vent abstract unravelling complex microbial activity in modern hydrothermal vents can provide crucial insights into the evolution of ancient life on earth it is well established that microorganisms in hydrothermal vents have a significant impact on the cycling of metals and mineral formation however the detailed roles played by microorganisms in driving sulfide deposition and cycling of toxic metals like arsenic as and lead pb in high temperature deep sea hydrothermal vents remain unknown the understanding of these mechanisms in extreme environments is of particular importance as as has been postulated as a driver of microbial activities on the early earth here we present the first geologic evidence of pb as rich microbial filamentous clusters observed in a modern high temperature black smoker from the manus back arc basin papua new guinea the clusters occur as net like structures on the surface of barite and sulfides and are composed of multiple filaments and fine grained pb as sulfosalt each of the filaments includes an as pb rich sulfosalt core and organic rich shell structure with elevated carbon nitrogen and phosphorus further synchrotron x ray absorption near edge structure analysis shows that the clusters contain a mixture of as ii and as iii additionally those filaments show a close association with realgar as4s4 by penetrating and dissolving this as sulfide mineral we interpret the filaments to be a result of as related microbial activity in as and pb enriched hydrothermal environments the findings show possible processes through which extremophiles live in pb and as rich environments during chimney growth in addition as hydrothermal vents are regarded as modern analogs of ancient volcanogenic massive sulfide deposits the observed biominerals present the potential to be used as proxies to trace the signatures of early life in ancient geological systems

phlogopite clinopyroxenite nodules from high k magmas roccamonfina volcano italy evidence for a low pressure metasomatic origin dense nodules containing phlogopite mg number 80 clinopyroxene and vesicular glass with subordinate olivine and cr spinel are found at roccamonfina volcano in pyroclastic deposits of widely varying ages and compositions significantly phlogopite has never been observed as a phenocryst in any volcanic rock at roccamonfina in the nodules phlogopite shows a variety of reaction textures in relation to both clinopyroxene and olivine each of the major minerals and glass is compositionally homogeneous within a single nodule and the suite as a whole shows systematic correlations of mg number among these phases clinopyroxene en40 47 and olivine fo81 87 compositions closely match phenocryst compositions from basic lavas at roccamonfina but cr spinel compositions strongly diverge from those in roccamonfina volcanic rocks sr and nd isotopic compositions of whole rock nodules and constituent minerals fall within the field for high k series hks volcanic rocks although minor isotopic disequilibrium is noted among minerals of individual nodules euhedral crystals are enclosed by interstitial glass indicating that the glasses represent residual melts and are not products of in situ partial melting of analyzed glasses from five nodules three are ne normative and compositionally similar to hks tephrite magma compositions one is hy normative and similar to low k series lks trachyandesites and the other has larnite in the norm and is unlike any known volcanic rock in addition to other more basic host rock types phlogopite pyroxenites are found within voluminous pyroclastics ranging from leucite tephrites to highly evolved phonolites and trachytes these rocks have strong depletions in sr ba and eu consistent with extensive fractionation in low pressure magma chambers consequently the phlogopite pyroxenites are also constrained to have formed at low pressures this interpretation conflicts with several previous hypotheses for the origin of similar phlogopite pyroxenites at other potassic volcanic centers including metasomatism of mantle protoliths and origins as high pressure plutonic assemblages textures in the roccamonfina nodules indicate that both clinopyroxene and olivine were consumed by reactions producing phlogopite we envision formation of these nodules in sub volcanic magma chambers through open system reaction of hks clinopyroxene olivine cumulates with a rising potassic hks melt or vapor phase

geo genic arsenic contamination in the kerman cenozoic magmatic arc kerman iran implications for the source identification and regional analysis kerman cenozoic magmatic arc kcma is located in the southeastern part of the central iranian volcano plutonic copper belt arsenic contamination from geo genic source is one of the most important environmental concerns in this area the main objective of this study was to determine the role of geothermal related activities in the arsenic contamination for this purpose the old and active geological indicators of the geothermal activities were investigated through the quaternary travertine deposits and the present hydrothermal warm springs respectively results showed that arsenic is highly concentrated ranged mainly from 12 400 to 90 500 mg kg in the reddish brown deposits of the travertine rocks arsenic showed geochemical association with co cu mo sb tl se fe and mn in these samples yukonite ca7fe3 12 aso4 10 oh 2015h2o a rare ca ferric arsenate hydrous mineral was the only as bearing mineral identified in the reddish brown deposits of the travertine rocks arsenic concentration in the hydrothermal warm springs 38 c ranged from 15 900 to 30 500 g l the dominant form was as h3aso30 hydrothermal contaminated waters also were characterized by na cl type and high values of ec 11 400 s cm tds 8300 mg l b 42 700 g l li 3000 g l fe 900 g l sb 82 8 g l and si 47 000 g l and natural anomalies of cs mn mo rb se and tl the obtained hydro geochemical results are similar to those reported in the literature for worldwide hydrothermal waters although natural attenuation processes such as adsorption co precipitation or mixing dilution reduce most of the arsenic contamination from hydrothermal source but some urban and rural communities are still depending on the arsenic contaminated waters with arsenic concentrations higher than recommended values for drinking or irrigation a subject that increases the risk of arsenic related diseases in some areas of the kerman province

frictional properties of saponite rich gouge from a serpentinite bearing fault zone along the gokasho arashima tectonic line central japan abstract we studied a serpentinite bearing fault zone in gokasho arashima tectonic line mie prefecture central japan characterizing its internal structures mineral assemblage permeability and frictional properties the fault core situated between the serpentinite breccia and the adjacent sedimentary rocks is characterized by a zone locally altered to saponite the clayey gouge layer separates fault rocks of serpentinite origin containing talc and tremolite from fault rocks of sedimentary origin containing chlorite but no quartz the minerals that formed within the fault are the products of metasomatic reaction between the serpentinite and the siliceous rocks permeability measurements show that serpentinite breccia and fault gouge have permeability of 10 14 10 17 m 2 and 10 15 10 18 m 2 respectively at 5 120 mpa confining pressure frictional coefficient of the saponite rich clayey fault gouge ranged between 0 20 and 0 35 under room dry condition but was reduced to 0 06 0 12 when saturated with water the velocity dependence of friction was strongly positive mostly ranging between 0 005 and 0 006 in terms of a b values the governing friction law is not constrained yet but we find that the saponite rich gouge possesses an evolutional behavior in the opposite direction to that suggested by the rate and state friction law in addition to its direct velocity dependence

origin of the calderas and evolution of roccamonfina volcano roman region italy abstract the roccamonfina volcano consists of a volcanic fluvial succession dated 549 ka bp paleoauruncus overlain by a 546 ka bp stratacone main cone formed by leucite bearing lava and tephra the main cone was dissected by four nested calderas a ring fracture concentric with and outside of the central caldera is also present detailed mapping of the volcano inspection of landsat satellite images and radiometric dating establish that the gli stagli and northern calderas subsided between respectively 546 474 and 403 374 ka bp and that the summit part collapsed between 546 and 446 ka bp to form the central caldera a chronologically intermediate state dated in the range 376 323 ka bp was identified between the 549 374 ka bp leucite bearing high k series hks stage i and the 317 96 ka bp leucite free low k series lks stage ii this stage is made up of concurrent hks lks rocks stage ics the central gli stagli and northern calderas are older than blt and wtt as supported by the strong discrepancies between calculated volumes of these pyroclastic rocks and the volume of the caldera also caldera collapses due to sector sliding are improbable as tested by the absence of rock slide avalanche deposits the collapses occurred incrementally through repetitive draining of the magma chamber s resulting from a succession of moderate sized volcanic events gli stagli caldera was infilled by a lake early after collapse so that sediments alternated with leucite tephrite lava flows and tephra within the lake the sequence was overlain by a thick succession of young pyroclastic rocks downfaulting downsagging cut the flat lying gli stagli filling sequence resulting in the old valle caldera successive pyroclastic and debris flows derived by updoming of the central caldera deposits infilled the last structure and downfaulted part of the valle fill producing the young valle caldera

distribution and behavior of lead in the k alkaline rocks from the roccamonfina volcano southern italy abstract the pb content in whole rocks matrix and mineral separates sanidine leucite biotite and phlogopite from 53 igneous rocks of the k alkaline suites of the roccamonfina volcano has been measured by means of the polarographic technique an increase of the pb content is observed with magmatic differentiation indicating that pb behaves as a magmatophile element in these magma suites moreover pb is enriched by a factor of 1 7 in the primitive rocks of the high k series compared with the primitive rocks of the k series and in this respect pb is similar to k and other lil elements sanidine x 44 7 16 9 ppm is 10 times enriched in pb relative to both leucite x 3 6 1 9 ppm and biotite x 5 3 3 1 ppm and this is in good agreement with the different coordination numbers of k in the structures of these minerals average d san matrix pb d leuc matrix pb d biot matrix pb are 0 48 0 05 0 14 respectively primitive rocks of both the k series and the leucite basalt series have a much higher pb content alkali olivine basalts and olivine trachybasalts x 16 3 ppm leucite basalts x 9 7 ppm than the average alkali basalt x 4 3 ppm and close to the average crust x 12 ppm primitive rocks of the high k series display a pb content as high x 28 4 ppm as those of several granitic rocks plots of pb vs other incompatible elements ratio vs ratio suggest that the hks and ks parental magmas could be derived by mixing between a normal mantle material and a lil enriched mantle material

simulation of natural acid sulfate weathering in an alpine watershed streams with acidic sulfate compositions ph less than 3 5 are naturally generated in the alpine geneva creek basin of the southern rocky mountains an area underlain by proterozoic metamorphic and igneous rocks that are intruded by tertiary felsic stocks with associated pyritic alteration these naturally acidic waters are similar in composition to more familiar man made acid mine waters or to surface waters acidified by sulfate precipitation detailed study of the stream compositions has revealed the principal reactions driving the weathering process and was used to estimate the relative effects of snowpack ionic input versus the solute contribution from acid attack in soil zones and groundwater in the geneva creek basin atmospheric sources of solute represent a minor component to the stream water composition except for chloride which can be used to determine the fraction of contribution the weathering process is a balance between oxidation of sulfides dissolution of silicates formation of the clay minerals vermiculite kaolinite and smectite carbonate neutralization and precipitation of ferric and aluminum oxyhydroxides and aluminum sulfate the chemical analyses of snow samples multiple samples of water from geneva creek and its tributaries and the composition of primary and secondary minerals identified in the basin serve as input to a mass balance geochemical model which facilitates the interpretation of the principal geochemical processes

fluid flow and alkali transport within a metamorphic terrane western north carolina abstract this paper presents preliminary results from study of a metasedimentary terrane near the great smoky mountains of north carolina grade of metamorphism ranges from garnet to staurolite kyanite zone the stratigraphic section is dominated by metasandstone but contains thick pelitic horizons over the central portion anakeesta formation of the studied interval metasandstone beds contain numerous isolated calcite concretions these react to form leucocratic calc silicate rock at variable grade of metamorphism metasandstones themselves are unreactive study of calc silicate reaction permits the following statements regarding fluid flow and alkali transport within the studied terrane within unreacted concretions the typical mineral assemblage is quartz oligoclase muscovite biotite calcite reaction between micas and calcite proceeded through several stages forming as prograde minerals andesine bytownite clinozoisite zoisite garnet hornblende and chlorite reaction occurred in the presence of a fluid phase containing a h2o co2 ratio of 9 and resulted in massive expulsion of na2o k2o and co2 since postulated reactions would have produced on average a fluid phase whose h2o co2 ratio is only one flow of water rich fluid through the concretions accompanied reaction rough estimate suggests a volumetric ratio of external fluid to rock of at least 1 1 the metamorphic grade at which concretions undergo reaction is controlled by stratigraphic position of the host metasandstone relative to metashale within the anakeesta formation and overlying strata extensive reaction occurs near the pelitic staurolite and kyanite isograds within massive metasandstones of the underlying strata reaction is delayed to the middle staurolite kyanite zone 5 km upgrade some reaction occurs within the upper garnet zone but this is restricted to certain thin metasandstone beds interlayered with metashale study of dehydration reactions within metashale demonstrates that calc silicate reaction was coupled to production of h2o rich fluids within pelitic strata transport of h2o rich fluids beyond outcrop scale was by advection diffusion was limited to outcrop distance on most outcrops all isolated concretions show the same degree of reaction but at larger scale separate metasandstone packets bounded by metashale show differing degrees of reaction also all rocks underwent some degree of penetrative deformation during time of reaction the suggestion is made that advective flow was in fact channelized into fractures within metasandstone and that diffusion between fractures promoted reaction within outcrop size volumes of rock overall direction of fluid transport was in part upsection and in part channelized within metasandstone strata downsection flow was limited for the most part alkalis liberated by calc silicate reaction appear to have left the terrane metasandstones do not appear to constitute a sink for alkalis and no sink of any sort was found for sodium potassium metasomatism of pelitic rock did occur and is marked by conversion of chlorite to biotite but such k deposition is limited to sections within which metashale and calc silicate rock are within outcrop distance no sink is evident for most liberated potassium it is within conjecture that the liberated elements caused alkali metasomatism elsewhere within the metamorphic belt but such an event has yet to be demonstrated

distribution speciation and bioavailability of arsenic in a shallow water submarine hydrothermal system tutum bay ambitle island png shallow water hydrothermal vent systems can introduce large amounts of potentially toxic elements such as arsenic as into coastal marine environments the first step in understanding and describing the potential impact of these elements throughout hydrothermally influenced coastal ecosystems is to determine the element s distribution and speciation which in turn influences the availability of the toxin for biological uptake shallow submarine hot springs near ambitle island papua new guinea are discharging as much as 1 5 kg per day of arsenic directly into a coral reef ecosystem we have investigated the bioavailability of the as throughout tutum bay by studying vent fluid seawater pore water precipitates and sediments in addition to measuring as abundance as speciation as iii as v and the methylated species dma and mma was determined in various waters the as concentration for discrete mineral phases in vent precipitates and sediments was determined by sequentially extracting arsenic from the easily extractable carbonate fe oxyhydroxide or hydrous ferric oxide hfo and residual fractions each of which have a different bioavailability diffuse venting seems to play a critical role on the distribution of as throughout tutum bay surface sediments which have a mean as concentration of 527 ppm while excluding the vent precipitates range 1483 to 52 ppm up to 54 ppm as were extracted from the easily extractable fraction of surface sediments mean 19 7 ppm using a k2hpo4 kh2po4 buffer at ph 7 2 arsenic from this fraction is considered to be the most available for biological processes and therefore the most dangerous for biota however sequential extraction shows that 98 6 of the as in vent precipitates and a mean of 93 3 in surface sediments range 88 2 to 96 3 is coprecipitated with the hydrous ferric oxide hfo fraction thus the bulk of the as being discharged into tutum bay is scavenged by the hfo and should remain stable unless the physicochemical conditions surrounding the oxides change in surface seawaters of tutum bay we found as much as four times the average seawater concentration of as 8 4 ag l compared to 2 ag l the abundance of as in seawater just above the sediment water interface is near normal although as iii in both surface and bottom seawater throughout tutum bay is substantially enriched compared to average seawater hydrothermal venting therefore provides bioavailable as by two major pathways throughout tutum bay 1 easily exchangeable as from hydrothermally influenced sediments to as far away as 200 m from focused venting and 2 in surface seawaters which may allow for biological uptake by phytoplankton and transfer up the food web d 2005 elsevier b v all rights reserved

geochemistry of hydrothermal fluids from the ultramafic hosted logatchev hydrothermal field 15 n on the mid atlantic ridge temporal and spatial investigation abstract mantle derived ultramafic rocks commonly occur on the seafloor at slow spreading axes and are tectonically emplaced along shear zones since the early 1990s a growing number of hydrothermal systems have been detected in ultramafic settings but chemical data for fluid compositions in active systems are still limited besides the logatchev field at 15 n on the mid atlantic ridge mar the only other active high temperature 300 c hydrothermal field known to be strongly influenced by ultramafics is the rainbow field at 36 n on the mar the field at logatchev consists of six active vent sites at about 3000 m water depth situated along a nw se trending line with distances of 50 200 m between the individual sites the vent sites were mapped in detail and re sampled during two cruises in 2004 and 2005 using a rov the geochemical composition of the hydrothermal fluids is characterized by very high concentrations of dissolved methane and hydrogen up to 3 5 mm and 19 mm respectively related to serpentinization processes in the reaction zone together with moderate si concentrations of 9 mm a depletion in b compared to seawater and li concentrations lower than in basaltic systems this fluid composition has been identified as characteristic signature of high temperature hydrothermal fluids reacting with ultramafic rocks however additional alteration of gabbroic intrusions is likely the fluid composition is very similar at all vent sites indicating a common source in the reaction zone and little variation during upflow spatial differences in fluid composition were observed between smoking craters and the complex chimney system irina ii but are restricted to elements with strong temperature controlled solubility as cu and co these differences can be related to different exit temperatures up to 350 c and as it is known that more ultramafic hosted hydrothermal systems exist along slow spreading ridges this type of hydrothermal systems might have a significant influence on the elemental budget of the oceans detailed information about the fluid geochemistry and its spatial and temporal variations is an important prerequisite for an estimation of elemental fluxes in ultramafic hosted systems and their relative importance compared to basaltic hosted systems

metasomatism and the crystallization of zircon megacrysts in archaean peridotites from the lewisian complex nw scotland zircon megacrysts are locally abundant in 1 40 cm thick orthopyroxenite veins within peridotite host rocks in the archaean lewisian gneiss complex from nw scotland the veins formed by metasomatic interaction between the ultramafic host and si rich melts are derived from partial melting of the adjacent granulite facies orthogneisses the interaction produced abundant orthopyroxene and within the thicker veins phlogopite pargasite and feldspathic bearing assemblages two generations of zircon are present with up to 1 cm megacrystic zircon and a later smaller equant population located around the megacryst margins patterns of zoning rare earth element abundance and oxygen isotopic compositions indicate that the megacrysts crystallized from crustal melts whereas the equant zircon represents new neocryst growth and partial replacement of the megacryst zircon within the ultramafic host both zircon types have u pb ages of ca 2464 ma broadly contemporaneous with granulite facies events in the adjacent gneisses zircon megacrysts locally form 10 of the assemblage and may be associated to zones of localized nucleation or physically concentrated during movement of the siliceous melts their unusual size is linked to the suppression of zircon nucleation and increased zr solubility in the si undersaturated melts the metasomatism between crustal melts and peridotite may represent an analog for processes in the mantle wedge above subducting slabs as such the crystallization of abundant zircon in ultramafic host rocks has implications for geochemistry of melts generated in the mantle and the widely reported depletion of high field strength elements in arc magmas

inorganic and biogenic as sulfide precipitation at seafloor hydrothermal fields highlights as sulfides are minor minerals at volcanic arc and back arc hydrothermal settings there are two modes of as sulfide precipitation inorganic and biogenic the most stable as sulfide at low t seafloor hydrothermal conditions is orpiment biogenic type of orpiment represents completely mineralized fungal hyphae fungal orpiment precipitation is a mechanism of bio sequestration of hydrothermal as we investigated as sulfides orpiment as2s3 and realgar as4s4 from four seafloor hydrothermal fields three from back arc and one from mid ocean ridge settings our studies suggest two different modes of as sulfide precipitation at the seafloor hydrothermal sites inorganic and biogenic the eh ph modeling shows that the most stable as sulfide at low temperature t 100 c seafloor hydrothermal conditions is orpiment whereas realgar appears as a stable as sulfide phase at t 25 c and under a narrow range of eh ph values inorganically precipitated realgar forms euhedral crystals whereas the orpiment is mostly colloform the biogenic type of orpiment no realgar of this type was found represents completely mineralized fungal hyphae the proposed scenario of biogenic orpiment formation assumes that crack dwelling fungal filaments in the sub seafloor were killed by an as rich hydrothermal fluid moving along the same crack network the fungal organic matter served as a geochemical trap for hydrothermal as which reacted with s leached from the basement or reduced from seawater sulfate and mineralized the fungal hyphae as as2s3 this process of fungal orpiment precipitation is a mechanism of bio sequestration of hydrothermal as and another mode of soft tissue fossilization not described so far

stability and composition relations of calcic amphiboles in ultramafic rocks calcic amphiboles are observed in ultramafic rocks that have equilibrated under a broad span of geological conditions and might prove to be good indicators of metamorphic grade if their stabilities could be determined as a function of their compositions experiments were performed on the stability of tremolite plus forsterite in the system h2o cao mgo sio2 from 5 to 20 kbar a univariant curve was fitted to the experimental brackets using volume water fugacity and heat capacity data the results indicate that the maximum stability of tremolite in the presence of forsterite is about 825 c at 5 kbar addition of al2o3 to this system increases the stability of tremolitic amphibole by only 20 40 c and induces solubility of 5 7 wt al2o3 in the amphibole as determined from quantitative sem analyses of individual amphibole crystals thus substitution of the tschermakite component ca2 mg3al2 si6al2 o22 oh 2 alone cannot lead to the greatly enhanced al2o3 contents or thermal stability of natural calcic amphiboles

metamorphism of an ophiolitic tectonic melange northern california klamath mountains usa mineral assemblages in pelitic mafic calcareous and ultramafic rocks within a metamorphosed tectonic melange indicate that the marble mountain terrane and adjacent western hayfork subterrane northern california underwent regional low to medium pressure amphibolite facies metamorphism metamorphic conditions estimated by comparison of observed assemblages with experimentally determined reaction boundaries and by geothermometry constrain metamorphic temperatures between about 500 and 570 c the occurrence of andalusite in regionally metamorphosed pelites indicates pressures below about 370 mpa metabasite amphibole compositions also suggest low to intermediate metamorphic pressures metaserpentinites containing the upper amphibolite facies assemblage olivine enstatite anthophyllite are found locally within the study area and have been reported previously by other workers elsewhere in the marble mountain terrane these assemblages may reflect higher temperatures of recrystallization than assemblages in surrounding rocks and may represent vestiges of an earlier high temperature metamorphic event undergone by the ultramafic rocks prior to incorporation in the melange although the age of the low to intermediate pressure metamorphism is poorly constrained cross cutting plutons indicate that metamorphism must be older than about 162 ma therefore this regional metamorphic event which probably marks the accretion of these terranes to the north american continental margin is older than the currently accepted 151 147 ma age of the nevadan event in the klamath mountains the inferred low to intermediate pressures of metamorphism and the lithologies of the protoliths suggest a near arc tectonic setting and refute a subduction zone model for this event

carbonate compositions in cm and ci chondrites and implications for aqueous alteration abstract carbonate minerals in fourteen cm chondrites and two ci chondrites have been analyzed by electron microprobe to provide a better understanding of the aqueous processes that affected carbonaceous chondrite parent bodies calcites in cm chondrites and dolomites and magnesites in ci chondrites display the compositions expected of stable phases formed at low temperatures dolomites in cm chondrites identified here for the first time in five members of the group have small amounts of excess ca which may reflect metastable growth the distribution of fe between dolomite and coexisting serpentine differs in the two chondrite groups if the distributions reflect an approach to chemical equilibrium then the difference implies higher alteration temperatures for the ci group than the cm group in agreement with the results of previously published oxygen isotope thermometry and mineral solubility modeling of the alteration process dolomite fe contents are relatively uniform in the two chondrite groups dolomite mn contents by contrast vary widely the variations may reflect transport controlled coprecipitation of mn resulting from a heterogeneous distribution of the element in the anhydrous precursor material if this interpretation is correct then the altering fluids were essentially immobile while hydration reactions proceeded on the meteorite parent bodies the near closed system character of the alteration process long known from bulk chemical analyses of the meteorites is a direct consequence of the limited mobility of dissolved species

geochemical and sr nd isotopic characterization of middle pleistocene sediments from the paleontological site of la polledrara di cecanibbio sabatini volcanic district central italy abstract six stratigraphically related samples of freshwater sediments from the middle pleistocene paleontological site of la polledrara di cecanibbio to nw of rome in the sabatini volcanic district svd have been characterized by their mineralogical geochemical and sr nd isotopic compositions these volcaniclastic sediments filled a valley incised by a former watercourse flowing through volcanic rocks the samples are composed of abundant analcite after leucite subordinate augite sanidine fluorite except for the stratigraphically deepest and most sio 2 poor sample and minor anorthite quartz is present only in the stratigraphically uppermost samples the mineralogical composition is consistent with the origin of the sediments from different source rocks of the svd major and trace elements allow for distinguishing among the samples in particular the four stratigraphically uppermost samples share close sio 2 intermediate between the contents of the other two samples although several chemical characteristics of the polledrara samples can be explained by impact of supergene processes on the sediments the overall composition supports an origin from different source rocks of the svd in particular the tufi stratificati varicolori di la storta tfvls and older pyroclastic rocks the 87 sr 86 sr ratios of the samples 0 710182 0 710433 support the distinction of the sediments based on chemistry and mineralogy and their sabatinian origin the isotopic range overlaps that in the lavas of phases iii iv of the svd and is slightly lower than the range in the tfvls likely because of advanced analcitization of the sediments the ammonium acetate extracts from the samples show a narrow isotopic range 0 709613 0 709735 which is lower than the range of the bulk sediments but close to the isotopic composition of fossil elephant remains in the polledrara sediments lastly except for the most sio2 rich sample exhibiting a higher value 0 512227 the 143 nd 144 nd ratios of the other samples show a narrow range 0 512147 0 512171 and cannot be distinguished from each other the isotopic range is similar to that of the tfvls but higher than that of sabatinian lavas supporting the origin of the sediments from the former rocks

distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix abstract to investigate the potential of mo and as as possible geogenic contaminants three sediment cores were examined to evaluate their mineralogical association distribution and mobility the cores were described and analyzed for total organic carbon toc ca mg si al p sr as mo fe and s content except in the uppermost segment limestone was the main lithology with the occasional presence of dolomite and clay that change in lithology was also observed in the bulk chemical composition where ca mg and sr concentrations increased with depth while si al and p concentrations decreased with depth minor minerals included pyrite fes 2 powellite camoo 4 and ferrihydrite the minimum maximum median and standard deviations for all analyzed elements including as and mo were comparable for all three cores molybdenum and as however varied significantly with depth and median as and mo values were above their respective crustal averages of approximately 1 1 mg kg and 1 5 mg kg the median values for as were 1 9 mg kg in core dep 1 3 3 mg kg in dep 2 and 1 mg kg in dep 5 the median values for mo were 2 3 mg kg in core dep 1 2 5 mg kg in dep 2 and 2 5 mg kg in dep 5 maximum concentrations for as were 101 9 mg kg 47 5 mg kg and 56 2 mg kg in cores dep 1 dep 2 and dep 5 respectively maximum concentrations for mo were 880 mg kg 123 mg kg and 225 mg kg in cores dep 1 dep 2 and dep 5 respectively electron microprobe analyses of individual minerals revealed variable concentrations of as ranging from approximately 300 to 9000 mg kg in pyrite and up to 17 600 mg kg in powellite camoo 4 the mo concentration in pyrite was consistently below the detection limit of approximately 100 mg kg in powellite the mo concentration was up to 42 wt a subset of 10 samples from different stratigraphic sections and with different as and mo concentrations was further investigated to assess as and mo mobility under changing physicochemical conditions leaching the aquifer matrix with a 1 m naoac solution at a ph of 8 1 removed more than 70 mo in 8 of the 10 samples the maximum value was 97 in contrast to mo as was mobilized to a lesser degree in 8 of the samples less than 30 were removed and the maximum was only 50 molybdenum which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix while as on the other hand should be much less mobile because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite thus it is advisable to include mo in the analytical program whenever elevated as concentrations are encountered in groundwater

arsenic in hot springs of bahia concepcion baja california peninsula mexico abstract high arsenic concentrations 0 15 to 0 78 mg l were measured in water discharged from hydrothermal vents at bahia concepcion baja california sur additionally concentrations above the average for the continental crust 1 8 mg kg were determined in rocks and marine sediments rock samples collected around intertidal and submarine hydrothermal discharges are encrusted by deposits of opaline silica barite calcite and mn oxides and in subordinate amounts of pyrite and ferrihydrite sequential extraction showed that arsenic is adsorbed mainly on amorphous and crystalline iron oxides and in lower concentrations to the easily extractable phase when hydrothermal fluids mix with oxidizing and alkaline seawater ph about 8 3 arsenic in h 3 aso 3 is oxidized to form h 2 aso 4 or possibly a deprotoned form such as haso 4 2 in addition reduced iron from the hydrothermal fluid is oxidized to ferric ion and forms non crystalline ferric hydroxide fe oh 3 which is able to adsorb arsenic x ray elemental maps of the surface of the rock samples located near the submarine discharges show evidence that arsenate is adsorbed onto calcite surface iron oxyhydroxides with adsorbed as could be present on the seafloor forming deposits of flocculent material which can be incorporated into the tissue of some marine organisms e g holothurians that feed in the vicinity of the hydrothermal manifestations oxidation and adsorption processes control transport and mobilization of arsenic in bahia concepcion hydrothermal fluids

hydrothermal plumes along the east pacific rise 8 40 to 11 50 n particle distribution and composition the discovery of a volcanic eruption at the 9 45 52 n site on the east pacific rise epr led us to investigate how the composition of suspended matter in hydrothermal plumes may be used to provide a better understanding of the relative age and vent fluid characteristics of a ridge crest system during surface ship surveys during the troughs tropical ridge observations of underwater geochemical hydrothermal signals expedition we collected hydrothermal plume particles along a 350 km section extending from approximately 8 40 n to 11 50 n of the epr north and south of the clipperton transform fault over the segment south of the clipperton transform fault the sfe ratio in the particles ranged from about 0 9 to 10 with the highest values immediately over the new vent field at the 9 45 52 n site these enrichments exactly coincide with the elevated 3he heat and ch4mn ratios in the plumes over the same vent field the s rich particles are primarily organic and may be related to the bacteria blizzard associated with the eruption in addition very high cufe and znfe ratios were observed in the hydrothermal plumes south of the clipperton transform fault these high ratios are indicative of the predominance of high temperature h2s rich vents between 9 35 n and 9 50 n in contrast the samples from the segment north of clipperton transform fault had sfe ratios which ranged from 0 04 to 0 82 typical of mature fe rich hydrothermal plumes these results suggest that the gas rich vent fluids at the 9 45 52 n site produced the sulfur enriched particles in the water column gas rich plumes and sulfur enriched plume particles were also observed underneath the 1986 megaplume on the juan de fuca ridge jdfr suggesting a similar mode of formation north of the clipperton transform fault the hydrothermal particles are dominated by fe rich oxyhydroxide particles characteristic of mature high temperature vent fields the plume maximum is centered at 11 08 n the fe oxyhydroxide particles scavenge ca si p v cr and as from seawater for p and v the mean element fe ratios in the epr hydrothermal particles are intermediate between jdfr and tag hydrothermal systems for as the mean element fe ratios of all three systems are about the same new evidence for si scavenging by hydrothermal fe oxyhydroxide particles indicates that this sink for dissolved si in the oceans is small

sequential deformation from serpentinite mylonite to metasomatic rocks along the sashu fault sw japan the deformation of serpentinites along the sashu fault saganoseki peninsula sw japan involved both mylonitization and brecciation the brecciation was accompanied by metasomatism and the metasomatized rocks record additional ductile deformation serpentinite mylonite is composed mainly of antigorite with minor magnetite and cr spinel foliation and lineation in this rock type are defined by the shape preferred orientation of antigorite and the alignment of fine grained magnetite and carbonate minerals the antigorite also shows a lattice preferred orientation lpo as measured with a universal stage with c axes oriented near perpendicular to the foliation and b axes oriented parallel to the lineation brecciation is concentrated in the reaction zone along the boundary between serpentinites and surrounding country rocks talc and chlorite schists developed in this zone as a result of associated metasomatism and deformation consequently they contain composite planar fabrics and drag folds the breccias themselves are composed of serpentinite fragments cut by veins of calcite and talc analyses of fluid inclusions in calcite from the breccia indicate that brecciation occurred at 200 300 c at depths of 3 8 11 8 km metasomatic reactions particularly the formation of talc contributed to weakening of this serpentinite bearing fault zone

coarse grained and porphyritic inclusions in phonolitic lavas roccamonfina volcano italy abstract the inclusions in the 446 213 ka phonolite lavas of the roccamonfina volcano italy can be classified as coarse grained and porphyritic types both are wide varying in composition the coarse grained inclusions belong to a cumulate clinopyroxenite gabbro monzonitic clinopyroxenite monzonitic gabbro series and contain some interstitial vesicular glass the porphyritic inclusions show non cumulate structures and a coarse grained crystalline vesicular matrix they correspond to tephrites phonolitic tephrites trachybasalts and basaltic trachyandesites the glass in the coarse grained inclusions is similar in composition to the porphyritic inclusions but in part it deviates compositionally from the latter these glasses are referred to respectively as trapped interstitial liquid from which the cumulates crystallized and as injected foreign non comagmatic melt the phonolites vary in composition from tephritic phonolites to phonolites and nepheline phonolites and do not show any traces of vesicularity despite the large eruptive time span and the broad differentiation they constitute a coherent magmatic group mineralogical and chemical similarities between both inclusion categories and compositional similarity of the trapped glass to the porphyritic types suggest that both groups of inclusions are cogenetic by contrast deviations of many elements of this glass and of the inclusions from the ideal mixing line inclusions host phonolites rule out any genetic correlation among these rocks least squares mass balance calculations reinforce this lack of correlation this conclusion is also supported by the fact that the phonolites are the most evolved derivatives of the basic and middle terms of the roccamonfina high k series whereas the inclusions appear to constitute a potassic suite compositionally intermediate between both the roccamonfina high k and low k series mineralogical and petrologic features suggest that the parental magma of the porphyritic types underwent prolonged fractionation in one or more crustal reservoirs at depths exceeding the stability conditions of plagioclase the magma then migrated upwards to shallower reservoirs fractionation and crystal accumulation formed one or more layered crystal mush es of coarse grained rock types whereas the residual magma migrated toward the surface being stored in one or more shallower reservoir s when the residual melts of both cumulate and porphyritic layers still incompletely consolidated disrupted into coherent fragments and crystals they were brought to the surface by pulses of phonolitic magma coming from below and acting during a long time span the residual melts of cumulate and porphyritic types vesiculated during ascent to the surface quenching during eruption of the host phonolitic bodies

clumped isotope thermometry of magnesium carbonates in ultramafic rocks abstract magnesium carbonate minerals produced by reaction of h 2 o co 2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes including 1 deposition of ore grade massive vein cryptocrystalline magnesite 2 formation of hydrous magnesium carbonates in weathering environments and 3 metamorphic carbonate alteration of ultramafic rocks however the application of traditional geochemical and isotopic methods to infer temperatures of mineralization the nature of mineralizing fluids and the mechanisms controlling the transformation of dissolved co 2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved clumped isotope compositions of magnesium carbonates provide a means to determine primary mineralization or re equilibration temperature which permits the reconstruction of geologic processes that govern magnesium carbonate formation we first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite along with natural metamorphic magnesite and low temperature hydromagnesite precipitated within a mine adit we show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error in addition we employ carbonate clumped isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings cryptocrystalline magnesite vein deposits from california red mountain magnesite mine austria kraubath locality turkey tutluca mine eskisehir district and iran derakht senjed deposit exhibit broadly uniform 47 compositions that yield apparent clumped isotope temperatures that average 23 7 5 0 c based on oxygen isotope thermometry these clumped isotope temperatures suggest mineralization at shallow crustal depths in the presence of meteoric water hydrous magnesium carbonates from a 400 km latitudinal transect along the serpentinized peridotite bodies of the california coast ranges record clumped isotope temperatures between 14 2 and 22 7 2 8 c in agreement with historical maximum temperatures during the rainy season for california talc carbonate alteration of ultramafic rocks in greenland isua supracrustal belt and vermont ludlow yields clumped isotope alteration temperatures of magnesite and dolomite between 326 and 490 c broadly consistent with paragenesis and thermodynamic analysis for co 2 metasomatism of ultramafic rocks these metamorphic carbonates extend the applicability of clumped isotope thermometry to high temperature magnesium carbonate systems and indicate equilibrium blocking temperatures for magnesite of 490 c our study demonstrates the applicability of the clumped isotope approach to provide information on the formation of magnesium carbonates as ore resources surface records of climate and metamorphic assemblages

trace element behavior during weathering of leucite in potassic rocks from the roccamonfina volcano campania southern italy and environmental implications abstract trace element contents in leucite and its alteration mineral phases from the quaternary potassic rocks of the roccamonfina volcano have been determined the dominant weathering phase of leucite is analcite in the early stages of the conversion process it concentrates mainly rb and sr with minor amounts of ba ni v zn la ce and zr at more advanced stages of the conversion process only rb and y persist while all other elements except cu and cr that are essentially immobile are lost particularly zn and to a lesser extent la ce and nd besides analcite leucite may also subordinately alter to halloysite this probably occurs by interaction of waters of low cation h ratio halloysite concentrates mainly sr and to a lower extent ba environmental implications are significant only for k as the release of this element to groundwaters increases greatly the fertility of soils

using the geologic setting of talc deposits as an indicator of amphibole asbestos content this study examined commercial talc deposits in the u s and their amphibole asbestos content the study found that the talc forming environment directly influenced the amphibole and amphibole asbestos content of the talc deposit large talc districts in the u s have mined hydrothermal talcs that replaced dolostone hydrothermal talcs created by siliceous fluids heated by magmas at depth consistently lack amphiboles as accessory minerals in contrast mineable talc deposits that formed by contact or regional metamorphism consistently contain amphiboles locally as asbestiform varieties examples of contact metamorphic deposits occur in death valley california these talc tremolite deposits contain accessory amphibole asbestos talc bodies formed by regional metamorphism always contain amphiboles which display a variety of compositions and habits including asbestiform some industrial mineral deposits are under scrutiny as potential sources of accessory asbestos minerals recognizing consistent relations between the talc forming environment and amphibole asbestos content may be used in prioritizing remediation or monitoring of abandoned and active talc mines

processes influencing extreme as enrichment in shallow sea hydrothermal fluids of milos island greece abstract arsenic as is naturally enriched in most terrestrial and marine hydrothermal systems its discharge from shallow sea hydrothermal vents into coastal marine environments can dramatically affect the surrounding ecosystems shallow sea hydrothermal venting of acidic ph 5 hot 40 116 c and highly sulfidic up to 3 1 mm h2s fluids occurs at palaeochori and spathi bays off the southeast coast of milos island greece two distinct types of fluids both extremely as enriched were collected from the submarine vents often within a few meters of each other 1 a high cl fluid enriched in cl by up to 47 relative to seawater depleted in mg and so4 and enriched in major na ca k b sr and br and minor trace elements si li rb ce as fe mn and ba and 2 a low cl fluid depleted in cl by up to 66 relative to seawater also depleted in na mg so4 and br the maximum concentration of as reached 39 m in the high cl fluids and up to 78 m in the low cl fluids this is approximately 3000 times the concentration of as in seawater and far exceeds the concentrations typically found in mid ocean ridge mor and back arc basin bab fluids which are typically we used a combination of elemental analyses and stable and radiogenic isotope data oxygen deuterium and strontium to understand the primary controls on as enrichment those parameters all indicated that the fluids were a mixture of seawater and a hydrothermal fluid originally derived from seawater but altered by water rock interaction subcritical phase separation boiling and vapor brine segregation since as was extremely enriched in both the high cl and the low cl thermal fluids we conclude that this element readily partitions into the vapor phase in the milos hydrothermal system the original source of as is most likely the leaching of the greenschist facies metamorphic basement rocks transpierced by an abundance of secondary quartz and calcite veins rich in pyrite it is possible that these veins were deposited from as rich magmatic fluids similar to some epithermal au deposits a poorly crystalline orpiment precipitates as hydrothermal fluids mix with overlying seawater and removes much of the dissolved as prior to discharge

chemical controls on fault behavior weakening of serpentinite sheared against quartz bearing rocks and its significance for fault creep in the san andreas system 1 the serpentinized ultramafic rocks found in many plate tectonic settings commonly are juxtaposed against crustal rocks along faults and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults to investigate this possibility we conducted triaxial experiments under hydrothermal conditions 200 350 c shearing serpentinite gouge between forcing blocks of granite or quartzite in an ultramafic chemical environment the coefficient of friction of lizardite and antigorite serpentinite is 0 5 0 6 and increases with increasing temperature over the tested range however when either lizardite or antigorite serpentinite is sheared against granite or quartzite strength is reduced to 0 3 with the greatest strength reductions at the highest temperatures temperature weakening and slowest shearing rates velocity strengthening the weakening is attributed to a solution transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks the operation of this process will promote aseismic slip creep along serpentinite bearing crustal faults at otherwise seismogenic depths during short term experiments serpentine minerals reprecipitate in low stress areas whereas in longer experiments new mg rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite crustal rock contact long term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages which may include extremely weak minerals such as saponite or talc to play an increasingly important role in the mechanical behavior of the fault our results may explain the distribution of creep on faults in the san andreas system

behaviour of tl relative to k rb sr and ba in mineralized and unmineralized metavolcanics from the dir area northern pakistan copper mineralization in the dir area of northern pakistan is confined to the quartz veins and associated with hydrothermally altered metavolcanics chalcopyrite is the main copper bearing phase with subordinate amounts of bornite chalcocite covellite malachite and azurite both mineralized quartz veins and associated unmineralized least altered and mineralized strongly altered metavolcanics have been analyzed for cu au ag tl k rb ba and sr an increase of cu au ag rb sr and tl sr and a decrease of sr and k rb is observed in both mineralized metavolcanics and mineralized quartz veins thallium shows lithophile behaviour in the dir metavolcanics and no chalcophile behaviour was observed the tl sr ratio might be an indirect guide for the exploration of volcanic hosted hydrothermal copper deposits

hydrogeochemistry of roccamonfina volcano southern italy this is the first hydro geochemical investigation carried out on the roccamonfina volcanic complex groundwaters the chemistry of roccamonfina waters is defined by water rock and water rock gas interactions in fact interactions between rocks of the first eruptive high k formations and circulating groundwaters are recognized by high k concentrations on the other hand inverse concentration of calcium versus alkali metals is related to two different rock interactions occurring in different areas of the volcano a within the caldera where groundwaters flow within latite and pyroclastic formations releasing calcium and b similarly at the base of the volcano where groundwaters flowing from surrounding carbonates got strongly enriched in ca these geochemical processes are also associated with k se of caldera and mg ca in sites located at the ne base of the volcano decrease completely different dynamics occurs at riardo groundwaters se here waters are the result of a mix between the roccamonfina deep aquifer and the carbonate aquifer of the riardo plain rich co2 emissions make these waters strongly mineralized minor elements show a similar geochemical behavior of major ions and are crucial defining interactions processes the evolution of roccamonfina groundwaters is also evident along the simultaneous enrichment of ba sr and ca ba increase is the result of deep local carbonate alteration enhanced by co2 emissions and the lower sr ca ratio from 10 to 2 ppb ppm is also due to the same process in the light of our results the roccamonfina aquifer can be schematically divided into two main reservoirs a a superficial aquifer which basically follows the volcanic structure morphology and tectonics and b a deeper reservoir originating within the oldest roccamonfina volcano ultra potassic lavas and then flowing into the carbonate aquifers of the neighboring plain eventually the chemistry of the roccamonfina aquifer does not show any specific and visible pollution contrary to what happens in the volcano surrounding plains in fact only 14 of the samples we collected 206 show a no3 content 30 mg l these sites are all located at the base of the volcano near the plain

enhanced geochemical gradients in a marine shallow water hydrothermal system unusual arsenic speciation in horizontal and vertical pore water profiles the shallow marine hydrothermal vents near ambitle island in eastern papua new guinea discharge hot slightly acidic as rich chemically reduced fluid into cool slightly alkaline oxygenated seawater gradients in temperature ph and total as as t among others are established as the two aqueous phases mix the hydrothermal fluid contained 900lg l as t almost exclusively present as the reduced as iii while local seawater measured between 1 2 and 2 4lg l as with approximately equal levels of as iii and as v of particular interest in this study was as speciation and abundance in pore waters as a function of sediment depth and as a function of distance from the area of focused venting with increasing distance as t concentration in the pore water decreased rapidly but remained elevated up to 300 m from the area of focused venting when compared to a non hydrothermal control site as a function of depth to 100 cm as t concentration in the pore water profiles was elevated and generally increased with depth surprisingly aqueous as v far exceeded aqueous as iii at almost all distances and depths investigated while at the control site the as iii concentration exceeded that of as v in the tutum bay hydrothermal system chemical disequilibria among as species provide potential metabolic energy for arsenite oxidizing microorganisms where hydrothermal fluid mixes with seawater near the vent orifice and for arsenate reducing microorganisms with increasing distance and depth from the hydrothermal point source 2007 elsevier ltd all rights reserved

spatial variation in arsenic and fluoride concentrations of shallow groundwater from the town of shahai in the hetao basin inner mongolia abstract twenty nine wells were selected for groundwater sampling in the town of shahai in the hetao basin inner mongolia four multilevel samplers were installed for monitoring groundwater chemistry at depths of 2 5 20 m results show that groundwater as exhibits a large spatial variation ranging between 0 96 and 720 g l with 71 of samples exceeding the who drinking water guideline value 10 g l fluoride concentrations range between 0 30 and 2 57 mg l there is no significant correlation between as and f concentrations greater as concentrations were found with increasing well depth however f concentrations do not show a consistent trend with depth groundwater with relatively low eh has high as concentrations indicating that the reducing environment is the major factor controlling as mobilization low as concentrations 2 into the aquifers and lead to reducing conditions that favor as release sediment composition is an additional factor in determining dissolved as concentrations in aquifers composed of yellowish brown fine sands at depths around 10 m groundwater generally has low as concentrations which is attributed to the high as adsorption capacity of the yellow brown fe oxyhydroxide coatings fluoride concentration is positively correlated with ph and negatively correlated with ca 2 concentration all groundwater samples are over saturated with respect to calcite and under saturated with respect to fluorite dissolution and precipitation of ca minerals such as fluorite and calcite and f adsorption desorption are likely controlling the concentration of f in groundwater

the origin of pyrite mineralization implications for late cambrian geology of the holy cross mountains south central poland abstract this paper presents results of a petrographic mineralogical and geochemical study of ore gangue and rock forming minerals that occur within the upper cambrian furongian age siliciclastic rocks of the wi niowka massif western part of the main range holy cross mountains south central poland this area is characterized by the presence of ubiquitous pyrite that makes up two stratiform mineralization zones assigned to the early and middle late cambrian giving rise to acid mine drainage the oldest zone comprises additionally sedimentary breccias with intraclast supported pyrite cement the predominant microscopic colloform and partly framboidal pyrite typically shows high concentrations of as up to 8 23 wt and a distinct enrichment in the light sulfur isotope 34s from 41 4 to 23 6 the occurrences of large amounts of as rich pyrite showing strongly negative 34s values are rather uncommon in paleozoic sedimentary formations worldwide that exhibit distinctly smaller amounts of as and mostly enrichments in heavier sulfur isotope 34s up to 63 another specific feature of the wi niowka rock series is the presence of ree bearing aluminophosphate and phosphate minerals that occur primarily in clayey silty shales and bentonites based on the results obtained a sequence of hydrothermal index minerals was discriminated including pyrite whose grains are usually made of alternating arsenic rich and arsenic poor bands as well as paragenetic assemblages of dickite nacrite xenotime and the crandallite series of aluminum phosphate sulfate minerals both mineral composition and specific microtextures are indicative of multistage hydrothermal activity that took place in the wi niowka depositional basin during the late cambrian time this is in distinct contrast to the remaining part of the main range which is devoid of the hydrothermal pyrite imprint moreover the results of this study give insight into the complex sedimentary and early diagenetic history of the southwestern passive margin of the baltica craton this currently makes up a part of the ysogory block terrane that borders on the trans european suture zone separating the precambrian east european craton from the paleozoic platform of central europe this study is important because we still lack the full knowledge about the hydrothermal processes that took place in early paleozoic depositional basins

hydrothermal frictional strengths of rock and mineral samples relevant to the creeping section of the san andreas fault abstract we compare frictional strengths in the temperature range 25 250 c of fault gouge from safod cdz and sdz with quartzofeldspathic wall rocks typical of the central creeping section of the san andreas fault great valley sequence and franciscan complex the great valley and franciscan samples have coefficients of friction 0 35 at all experimental conditions strength is unchanged between 25 and 150 c but increases at higher temperatures exceeding 0 50 at 250 c both samples are velocity strengthening at room temperature but show velocity weakening behavior beginning at 150 c and stick slip motion at 250 c these rocks therefore have the potential for unstable seismic slip at depth the cdz gouge with a high saponite content is weak 0 09 0 17 and velocity strengthening in all experiments and decreases at temperatures above 150 c behavior of the sdz is intermediate between the cdz and wall rocks

extreme magnesium isotope fractionation at outcrop scale records the mechanism and rate at which reaction fronts advance isotopic fractionation of cationic species during diffusive transport provides a novel means of constraining the style and timing of metamorphic transformations here we document a major 1 decrease in the mg isotopic composition of the reaction front of an exhumed contact between rocks of subducted crust and serpentinite in the syros melange zone this isotopic perturbation extends over a notable length scale 1 m implicating diffusion of mg through an intergranular fluid network over a period of 100 kyr these novel observations confirm models of diffusion controlled growth of reaction zones formed between rocks of contrasting compositions such as found at the slab mantle interface in subduction zones the results also demonstrate that diffusive processes can result in exotic stable isotope compositions of major elements with implications for mantle xenoliths and complex intrusions

li pb and tl abundances in the k alkaline rocks from the middle latina valley volcanoes southern latium italy and their petrological significance li pb and tl contents of 15 primitive lava samples from the middle latina valley volcanoes southern latium italy are higher in the high k than in the k series rocks the enrichment factors roughly following the increase of the ionic size of the elements

stratigraphy chronology and sedimentology of ignimbrites from the white trachytic tuff roccamonfina volcano italy abstract we describe the stratigraphy chronology and grain size characteristics of the white trachytic tuff wtt of roccamonfina volcano italy the pyroclastic rock was emplaced between 317 and 230 ma bp during seven major eruptive events units a to g and three minor events units bc cd and de these units are separated by paleosol layers and compositionally well differentiated pyroclastic successions stratigraphic control is favored by the occurrence at the base of major units of marker layers four wtt units 1 to 4 occur within the central caldera these are not positively correlated with specific extracaldera units the source of most of the wtt units was the central caldera units b and c were controlled by the western wall of the caldera whereas units d and e were able to overcome this barrier spreading symmetrically along the flanks of mc the maximum pumice size mp of units increases with distance from the caldera whereas the maximum lithic size ml decreases mp and ml of the marker layer of unit d mkda mkdp do not show any systematic variations with respect to the central caldera in contrast the thickness of surge mkda decreases with distance from the source and mkdp accumulates to the north of mc probably controlled respectively by mobility transport power and by wind blowing northwards the grain size characteristics of the wtt deposits are used for classifying the units there is no systematic variation of the grain size as a function of stratigraphic height either among units or within single units large variation of components in subunit e1 with repetitive alternation of pyroclastic flow to surge through fallout vs surge deposits suggests that the process of eruption took place in a complex or piecemeal fashion pumice concentration zones pcz occur at all wtt levels on the volcano but they are much thicker and pumice clasts are much larger within the central caldera these were probably originated by the disruption of lava flow or dome to pumice fragments and fine ash due to sudden depressurization and interaction with lake waters of the molten lava local basal pcz are in some cases similar to the lapilli rich layer 1p that has been described elsewhere and may have been deposited from currents transitional between pyroclastic surge and flow other basal pcz formed in response to small undulations in the substrate or can be originated by fallout lenticular pcz within ignimbrite interiors and tops are interpreted to record marginal pumice levees and pumice rafts some of which were buried by subsequant pyroclastic flows lithic concentration zones lcz also occur at various stratigraphic height within the extracaldera ignimbrites whereas intracaldera lcz are absent probably due to the fact that ignimbrite currents are strongly energetic and erosive near vent lcz at the top of basal inversely graded layers are formed by mechanical sieving or dispersive pressure in response to variable velocity gradients and particle concentration gradients a segregation process coarse lcz and coarse lithic breccias lb that reside in the interior or tops of pyroclastic flows and that occur in medial to distal areas are interpreted to be the result of slugs of lithic rich debris introduced by vent collapse or rockslides into the moving pyroclastic flows along their flow paths these lcz become mixed to varying degrees due to differential densities and velocities relative to the pyroclastic flows desegregation processes

sidewall differentiation in an alkalic magma chamber evidence from syenite xenoliths in tuffs of the latera caldera italy feldspathoidal and quartz bearing syenite xenoliths in c 235 to 155 ka tuffs surrounding the latera caldera have textures and mineral assemblages that indicate an origin from the crystalline margins of a shallow magma chamber this lithic suite exhibits a diversity of plutonic fabrics unaltered glass bearing nodules with undeformed sanidine frameworks coexist with completely crystallized clasts many of which show evidence of subsolidus modification the syenites comprise eutectic mineral assemblages with high percentages of titanite apatite and melanite garnet as accessory minerals ubiquitous reaction textures in syenite accompany progressive changes in mineral assemblages and they show the decreasing influence of limestone contamination with distance from the contact of syenite and skarn wallrock diagnostic mineral assemblages include nepheline rich in calcite inclusions coexisting titanite and metamorphic perovskite zircon with baddeleyite inclusions fluorapatite mantled by a possible carbonate bearing apatite francolite melanite garnet intergrown with clinopyroxene and interstitial hauyne rich in pyrrhotite inclusions at latera pumice fragments in the same deposit can exhibit up to ten fold differences in vesicularity and crystal content from 50 vol phenocrysts these clasts in conjunction with glass bearing syenite and skarn xenoliths may represent a range of progressively crystallized magmas that were quenched at the instant of their eruptive entrainment the major element abundances of pumices and syenite reflect the fractionation of plagioclase and sanidine with lesser amounts of fassaitic diopside leucite biotite apatite and alkali amphibole trace element ratios e g rb sr nb ta zr hf lree hree on the other hand are highly variable for crystalline and pumiceous ejecta and some element variations e g li ta nb th cannot be entirely reconciled with simple crystal liquid fractionation the syenite clasts span a range of compositions from strongly fractionated assemblages rich in accessory minerals to compositions that more closely approximate quenched reservoir liquids these features reflect processes that range from pure fractional crystallization to in situ crystallization where fractionated liquid was trapped in the pores of sidewall cumulates along the chamber roof and walls

hydrothermal venting within a coral reef ecosystem ambitle island papua new guinea shallow water 5 10 m hydrothermal venting in a nearshore coral reef environment at ambitle island in the tabar feni island arc east of papua new guinea occurs as focused discharge of boiling fluid from discrete ports 10 15 cm in diameter and as dispersed discharge of diffuse bubble streams that issue through the sandy mixed carbonate volcaniclastic sea floor abiotic aragonite and microcrystalline ferroan low mg calcite interlaminated with fe oxyhydroxides are the prominent hydrothermal precipitates geochemical attributes of aragonite 18o 13c and fluid inclusions suggest that cements formed from a solution with salinities 5 at temperatures of 100 c with probable contribution of hydrothermal co2 sr isotope ratios in abiotic hydrothermal aragonite 0 704 15 are similar to those in island arc basalt and denote considerable subsurface water rock interaction of meteoric water derived from the adjacent volcanic island the sr isotope ratio of a coral sample 0 707 46 collected adjacent to a vent portal suggests coral growth within a mixed seawater hydrothermal environment

the origin of blue coloration in a fulgurite from marquette michigan abstract few rocks or minerals display a blue hue this is especially true for natural glasses as glasses are already uncommon compared to crystalline rocks due to their instability the rarity of blue glass makes a fulgurite found in marquette michigan worthy of further examination we study the morphology and the chemical and structural characteristics of the blue fulgurite using raman spectroscopy x ray fluorescence analysis election microprobe analysis and transmission election microscopy we use the experimental results to compare the fulgurite with another blue natural glass zhanmanshinite an impact glass named after an exposed impact crater in kazakhstan and to evaluate the support for several hypotheses of the origin of the blue color in the fulgurite

microbial diversity and potential for arsenic and iron biogeochemical cycling at an arsenic rich shallow sea hydrothermal vent tutum bay papua new guinea the shallow submarine hydrothermal systems of tutum bay papua new guinea are an ideal opportunity to study the influence of arsenic on a marine ecosystem previous reports have demonstrated that the hydrothermal vents in tutum bay release arsenic in reduced hydrothermal fluids into the marine environment at the rate of 1 5 kg of arsenic day aqueous arsenite is oxidized and adsorbed onto hydrous ferric oxides hfos surrounding the venting area we demonstrate here that microorganisms are key in both the oxidation of fe ii and as iii in the areas immediately surrounding the vent source surveys of community diversity in biofilms and in vent fluid indicate the presence of zeta proteobacteria alpha proteobacteria persephonella and close relatives of the archaeon nitrosocaldus the iron oxidizing zeta proteobacteria are among the first colonizers of solid substrates near the vents where they appear to be involved in the precipitation of the hydrous ferric oxides hfos further the biofilm communities possess the genetic capacity for the oxidation of arsenite the resulting arsenate is adsorbed onto the hfos potentially removing the arsenic from the immediate marine system no evidence was found for dissimilatory arsenate reduction but the arsenate may be remobilized by detoxification mechanisms this is the first demonstration of the genetic capacity for arsenic cycling in high temperature shallow sea vent communities supporting recent culture based findings in similar systems in greece handley et al 2010 these reports extend the deep sea habitat of the zeta proteobacteria to shallow submarine hydrothermal systems and together implicate biological oxidation of both iron and arsenite as primary biogeochemical processes in these systems providing a mechanism for the partial removal of aqueous arsenic from the marine environment surrounding the vents

arsenic antimony and bismuth in sediments and waters from the santorini hydrothermal field greece abstract chemical analyses for as and sb in santorini sediments and as in waters from the vicinity of active hydrothermal vents indicated hydrothermal enrichments of these elements in the santorini sediments relative to normal marine sediments and of as in the waters relative to normal seawater bi in the sediments falls within the range of its concentrations in normal clastic sediments as fe ratios in the sediments increase with increasing distance from the hydrothermal vents which coupled with a strong association between as and fe demonstrated by partition analysis suggests that hydrothermal as is scavenged into the sediments by freshly precipitating fe oxides and that the conditions for this become increasingly favourable away from the vents

an investigation of acidic head water streams in the judith mountains montana usa abstract acid rock drainage exists in three headwater streams armells creek collar gulch chicago gulch in the judith mountains central montana usa the streams drain opposing sides of a central pyrite rich hydrothermally altered granite porphyry intrusion although significant production of precious metals has occurred elsewhere in the judith mountains no present day mining is taking place and the drainages of interest have not been heavily impacted by historical mining activities all three streams are acidic ph

the precipitation of aragonite from shallow water hydrothermal fluids in a coral reef tutum bay ambitle island papua new guinea the fringing reef in tutum bay on the west side of ambitle island papua new guinea is the only presently known coral reef exposed to the extensive discharge of a hot mineralized hydrothermal fluid there aragonite and ferrihydrite a hydrous ferric oxide are the prominent hydrothermal precipitates aragonite forms two distinct crystal habits a euhedral pseudohexagonal crystals up to 2 cm long and b micro crystals similar in appearance to feather dendrite aragonite encrusts dead coral fragments volcaniclastic boulders and pebbles and fills secondary fracture and remaining primary intergranular porosity within volcaniclastic arenite the hydrothermal aragonite has a distinctively different isotopic composition when compared to normal shallow water marine inorganic and organic carbonate that precipitated from seawater this difference arises from precipitation at high temperature from a mixture of seawater and hydrothermal fluid that has lower 87 sr 86 sr and d 18 o values than seawater based on a 87 sr 86 sr mixing model aragonite precipitated from a hydrothermal fluid seawater mixture of approximately 9 1 precipitation from the hydrothermal solution is mainly caused by co2 degassing but mixing between hydrothermal fluid and seawater may have enhanced precipitation due to an increase in ph the d 13 c of tutum bay hydrothermal aragonite ranges from 1 9xto 2 2x vpdb this range of values is in good agreement with experimental data j phys chem 72 1968 800 geochim cosmochim acta 61 1997 3461 indicating that c 13 equilibirum has been reached during its formation values for d 18 o range from 14 2xto 14 7xand calculated isotopic equilibrium temperatures are approximately 20 jc lower than directly measured vent fluids and those temperatures obtained from fluid inclusion experiments and the 87 sr 86 sr mixing model this indicates that either oxygen isotope equilibrium was not attained or that the calcite water fractionation factor for oxygen isotopes is not applicable for the precipitation of tutum bay hydrothermal aragonite trace element concentrations except for the rees y and sr are low the ree patterns of aragonite are similar to those of tutum bay vent water indicating the hydrothermal origin of the aragonite rare earth element concentrations are higher in the coarse than in the fine grained aragonite which might be caused by a change in precipitation rate and seawater mixing d 2004 elsevier b v all rights reserved

petrogenesis of the merensky reef in the rustenburg section of the bushveld complex a petrogenetic model for the merensky reef in the rustenburg section of the bushveld complex has been developed based on detailed field and petrographic observations and electron microprobe data the model maintains that the reef formed by reaction of hydrous melt and a partially molten cumulate assemblage the model is devised to account for several key observations 1 although the dominant rock type in the rusterburg sections is pegmatoidal feldspathic pyroxenite there is a continous range of reef lithology from pyroxenite to pegmatoidal harzburgite and dunite and small amounts of olivine are present in nearly all pegmatoids 2 the pegmatoid is usually bounded above and below by chromitite seams and the basal chromitite separated from underlying norite by a centimeter thick layer of anorthosite the thicknesses of the two layers exhibit a well defined positive correlation 3 inclusion of pyroxenite identical to the hanging wall and of leuconorite identical to the footwall are present in the pegmatoid the leuconorite inclusions are surrounded by thin anorthosite and chromitite layers in the same sequence as that at the base of the reef 4 chromite in seams adjacent to plagioclase rich rocks is characterized by higher mg mg fe and al r3 and lower cr r3 than that in seams adjacent to pyroxene rich rocks similar variations in mineral compositions are observed across individual chromitite seams where the underlying and overlying rock types differ the chromite compositional variations cannot be rationalized in terms of either fractional crystallization or reequilibration with surrounding silicates it is proposed that the present reef was originally a melt rich horizon in norite immediately overlain by relatively crystallized pyroxenite magmatic vapor generated by crystallization of intercumulus melt migrated upward through fractures in the cumulate pile below the protoreef the melt rich protoreef became hydrated because fractures were unable to propagate through it and because the melt itself was water undersaturated hydration of the intercumulus melt was accompanied by melting and the hydration melting front migrated downward into the footwall and upward into the hanging wall in the footwall melting resulted first in the dissolution of orthopyroxene and then of plagioclase with continued hydration chromite was stabilized as melt alumina content increased the regular variations in chromite compositions reflect the original gradients in melt composition at the hydration front the stratigraphic sequence downward through the base of the reef or pegmatoid melt chromitite anorthosite norite represents the sequence of stable mineral assemblages across the hydration melting front the sequence is shown to be consistent with knowledge gained from experiments on melting of hydrous mafic systems at crustal pressures with cooling the hydrated mixture from partial melting of norite footwall and more mafic hanging wall crystallized in the sequence chromite olivine pyroxene plagioclase with peritectic loss of some olivine calculations of mass balance indicate that a significant proportion of the melt was lost from the melt rich horizon variations in the development of the pegmatoid and associated lithologies and amount of modal olivine in the pegmatoids along the strike of the merensky reef resulted because the processes of hydration melting and melt loss operated to varying extents

chemical processes and migration of elements during retrogression of a staurolite zone assemblage in western north carolina a detailed study of retrograde alteration of a staurolite porphyroblast and its surrounding matrix of mica schist has made use of petrographic modal and microprobe analysis retrogression was to the garnet zone of metamorphism and apparently occurred largely after a temperature decline of 70 100 c the event caused metasomatic removal of zn but may have been isochemical relative to other analyzed elements the best estimate of the overall reaction is 1 staurolite 3 018 biotite 3 550 quartz 0 629 albite 0 014 anorthite 0 678 nacl 14 004 h2o 3 274 na rich muscovite 3 561 chlorite 0 273 ilmenite 0 110 chloritoid 0 039 garnet 0 339 zncl2 non systematic variation in composition of analyzed minerals is revealed by statistical treatment of replicate analyses such variation involves monovalent and divalent cations within many minerals but is most pronounced within retrograde muscovite muscovite variation involves si and al as well as fm and alkalis and does not follow a phengite law of charge coupled substitution relative to the core of the retrograded staurolite crystal zoning is seen in averaged muscovite compositions and in development of incompatible mineral assemblages which include chloritoid well within retrograded staurolite but biotite within the matrix a local gradient in the chemical potential of an al bearing component was likely present during retrogression alteration of staurolite was probably accomplished by reaction and diffusion through the medium of an intergranular fluid phase relative to staurolite migration of elements involved immigration of considerable amounts of mg na k and h and expulsion of al fe zn and o it is inferred that concentration of al within the fluid phase was considerably lower than those of monovalent and divalent cations preservation of considerable staurolite and evidence for a local concentration gradient of al in the fluid phase suggest that limited amounts of h2o were available expulsion of zn suggests that much water was not consumed locally but exited the terrane an attempt at resolution of this dilemna involves fracture channelized infiltration of h2o into the rock a more regional petrographic study of retrogression suggests that h2o which entered the rock may have been liberated initially by prograde dehydration at a moderately greater depth of 2 3 km results of this study especially the non phengitic nature of crystal chemical substitution within muscovite indicate chemical reaction under conditions of disequilibrium apparently extent of retrogression was controlled by availability of h2o rather than by thermochemical equilibria

cumulate inclusions from k rich magmas roccamonfina volcano italy over 200 plutonic xenoliths have been collected from the pyroclastic deposits of roccamonfina volcano twenty nine representative specimens have been analyzed for major and trace elements and the main mineral phases probed in 20 of these the nodules belong to two cumulate fractionation series a pyroxenite gabbro anorthosite monzonite syenite foidal syenite series and an olivine pyroxenite phlogopite pyroxenite series the various nodule types are not simply related to the stratigraphic position of their host pyroclastics olivine clinopyroxene plagioclase mica biotite and phlogopite k feldspar magnetite apatite and sphene occurring in various proportions and textures represent the cumulus minerals amphibole appears as a secondary product pseudomorphing pyroxene and biotite intercumulus nepheline sodalite hauyne garnet and cancrinite appear in foidal syenites modal and chemical relations suggest that pyroxenites gabbros monzonites syenites and foidal syenites correspond to accumulative material from stage i high k series lavas with respective phenocryst associations cpx trace ol cpx pl trace ol cpx pl trace k spar k spar cpx pl and k spar cpx pl sod the olivine pyroxenites and a single phlogopite pyroxenite specimen appear to be related to stage ii k series ol cpx pl bearing quartz normative trachybasahs the inferred genetic connections however are only partially supported by comparison of phenocryst and cumulus mineral compositions the discrepancies may reflect 1 disequilibrium of nodule and individual lava mineral assemblages due to the contrary motion of different crystal species during fractionation 2 mixing in minor fractionation chambers of crystalline material nodule and magmatic fluids during the eruption of the main magmatic system 3 lower equilibration temperature and higher equilibration pressures of the nodules relative to cogenetic lavas and 4 nodule fractionation from separate episodes of magmas evolved independently from the parental magmas