a global review of sediment source fingerprinting research incorporating fallout radiocesium 137cs abstract information on the main sources supplying deleterious sediment loads to river systems is needed to improve our understanding of soil erosion processes to better target erosion control measures in particular it is important to quantify the respective contributions of surface and subsurface sources to material degrading waterbodies radiocesium 137cs emitted during thermonuclear bomb testing 1950 1980 and nuclear accidents provides significant discrimination between surface material exposed to atmospheric fallout and subsurface material sheltered from it a systematic worldwide review of research articles n 123 that used 137cs to trace sediment sources showed that the united kingdom n 24 australia n 23 and the united states n 20 had the highest number of publications utilizing 137cs in a sediment tracing framework in contrast few studies were published for catchments in africa n 9 or south america n 2 in the northern hemisphere positive relationships were evident between 137cs activities in surface and subsurface sources and the proportion of thermonuclear bomb fallout however given the low proportions of fallout received in regions between 0 and 20 n and 0 20 s the potential application of 137cs tracing techniques may be limited in this area of the world as well as in agricultural regions with severe soil erosion i e chinese loess plateau and south africa in total 94 of the studies researching surface and subsurface sources that analysed 137cs as a potential tracing property included this parameter in end member mixing models the main challenges for the future of this technique are related to the access to ultra low background gamma spectrometry facilities and the development of surrogate tracers future research should ensure that basic catchment information and details on the sampling design are properly documented to ensure studies are reproducible moreover researchers should provide raw measurement data to help improve our global understanding of 137cs dynamics in soil erosion research

interaction of magmatic fluids and silicate melt residues with saline groundwater in the footwall of the sudbury igneous complex ontario canada new evidence from bulk rock geochemistry fluid inclusions and stable isotopes abstract along the northern margin of the 1 85 ga sudbury igneous complex sic canada a volumetrically minor rock type known as the footwall granophyre fwgp preserves evidence of the interaction of magmatic fluid and groundwater the fwgp comprises veins dikes and irregular bodies of a quartz alkali feldspar plagioclase intergrowth that are most abundant near footwall style cu ni platinum group element mineralization textures and cross cutting relations show that the emplacement of the fwgp created favourable sites for the later deposition of sulfides geochemical and physical evidence show that the fwgp did not form by in situ partial melting of the archean country rocks in the footwall beneath the sic it represents a mobilized injected silicate residue from either the contact between partially melted country rocks and the sic or from the crystallizing sic itself its bulk composition can be modeled as the product of fractional crystallization of a liquid with an initial composition equivalent to granophyric matrix trapped liquid in the lowermost units of the sic norite and sublayer primary fluid saline h 2 o poor and melt silicate h 2 o rich inclusions hosted in quartz from the fwgp have bulk and trace element compositions consistent with those hosted in quartz from the granophyric matrix of the lower units of the sic norite sublayer fluid inclusions contain mixtures of a high salinity 44 70 wt nacl equivalent n 39 na fe rich aqueous magmatic fluid and a lower salinity ca and sr rich groundwater the magmatic end member is thought to be an sic derived volatile phase estimates of the mixing proportions show that primary and secondary inclusions in the fwgp contain 60 100 and 30 80 of the magmatic end member by mass respectively fluids responsible for the remobilization of ore metals represent mixtures containing a much higher proportion of the groundwater end member not less than 70 by mass compared to the fluids trapped in the fwgp at considerable distance 400 m from the sic the chlorine isotope composition of biotite in the fwgp is enriched in 37 cl 37 cl 0 98 to 1 61 scapolite from the high temperature veins and the interstices of rock types in the main mass of the sic shows similar enrichment in 37 cl up to 1 34 whereas biotite from the archean country rocks 37 cl 0 88 to 0 53 and associated groundwater are 37 cl depleted the results of this study lead to two important conclusions concerning genetic and exploration models for the footwall ore zones first magmatic end member fluid introduced into the footwall with the melt from which the fwgp crystallized contained very little cu rarely 100 ppm the main ore metal in the footwall ores this result questions hydrothermal models for footwall ore formation that hypothesize that cu and other ore metals were remobilized from sulfide deposits along the sic contact by magmatic hydrothermal fluids and redeposited in the footwall it is more likely that ore metals were only locally remobilized in the footwall ore zones when metal poor hybrid fluids interacted with pre existing sulfide veins of magmatic origin second inclusions containing the hybrid fluid occur in the fwgp rock type throughout the footwall in both mineralized and unmineralized areas therefore although the fwgp preserves stable cl isotope and fluid inclusion evidence that magmatic fluid was introduced into the footwall detection of this magmatic component alone will not serve as a useful exploration method in contrast mapping the distribution and abundance of fwgp may be ore predictive since fwgp emplacement and its higher abundance in mineralized areas appears to have been a structural and textural prerequisite for footwall ore emplacement

automated mapping of k feldspar by electron backscatter diffraction and application to 40ar 39ar dating abstract the ability to quantify feldspar microstructure using the electron backscatter diffraction ebsd method has direct application in the study of rock deformation and strain kinematics however automated ebsd analysis of low symmetry phases such as feldspar has previously proven difficult here we successfully apply the ebsd method to a number of granitic feldspars and develop automated phase and orientation mapping to discriminate k feldspar and plagioclase and quantify orientation variations within individual k feldspar grains these results represent the first automated quantitative mapping of orientation microstructure in k feldspar we use the method to evaluate the relationship between microstructure and 40 ar 39 ar age a controversial problem in thermochronology in a granitic k feldspar from central australia the range of observed orientation domains matches the small to intermediate and largest domain sizes predicted from multiple diffusion domain modeling in situ ultra violet laser microprobe analyses show that the youngest ages from the 40 ar 39 ar age spectra are recorded by grain mosaic k feldspars with diameter around 10 50 m these k feldspars are the smallest coherent microstructural features observed on scales of 1 m large 250 1000 m diameter microstructurally simple grains record the oldest ages observed in the age spectrum these results suggest a first order relationship between k feldspar microstructure and 40 ar 39 ar age and demonstrate a microstructural control on multidomain diffusion

the microstructures of perthitic alkali feldspars revealed by hydrofluoric acid etching etching of alkali feldspar cleavage fragments with hydrofluoric acid vapor followed by study of the surfaces by scanning electron microscopy sem is a simple and rapid technique for characterizing the microtextures of crypto and microperthites this technique has a number of advantages over conventional transmission electron microscopy tem including ease of sample preparation and the large areas of crystals which can be imaged alkali feldspars studied by the method can yield important information on the cooling history of igneous and metamorphic rocks fluid feldspar interactions and the morphology and microstructures of albite exsolution lamellae some of these applications are illustrated by examples of etched crypto and micro perthites from the klokken layered syenite south greenland and the shap granite north west england

volatile emission during the eruption of baitoushan volcano china north korea ca 969 ad magma volume dre 24 5 km3 the main phase ca 95 vol is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites the eruption column is estimated to have reached ca 25 km and thus entered the stratosphere a late phase 5 vol is represented by trachyte emplaced chiefly as moderately welded ignimbrites the comendites contain 3 and the trachytes 10 20 vol phenocrysts mainly anorthoclase hedenbergite and fayalite primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra whereas those in phenocrysts in the trachytes are devitrified the comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra the mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method the average h2o concentration of the comenditic matrix glass is 1 5 wt probably largely secondary and of the corresponding melt inclusions 5 2 wt melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm the comenditic matrix glasses are represented by a fluorine rich 3992 ppm f and fluorine poor group 2431 ppm f averaging 3853 ppm for chlorine only 20 of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of 250 ppm s the difference between pre and post eruptive concentration of h2o is at least 3 7 0 6 wt h2o taking into consideration re hydration of the matrix glass and possible leakage of melt inclusions the difference between pre and post eruptive concentrations of the halogens amounts to 909 90 ppm cl and 1863 280 ppm and 302 40 ppm f the difference for s was estimated based on the average of the maximum s concentrations in the melt inclusions 455 ppm s and the detection limit resulting in 205 40 ppm s the calculated mass of volatiles injected into the atmosphere based on the erupted magma volume and volatile data is 1796 453 megatons for h2o 45 10 megatons for chlorine 42 11 megatons for fluorine and 2 0 6 megatons for sulfur the 969 20 ad eruption of baitoushan volcano one of the largest eruptions of the past 2000 years is thought to have had a substantial but possibly short lived effect on climate

a novel method for determining residence times of river and lake sediments based on disequilibrium in the thorium decay series sediment fluxes in rivers have proved difficult to measure or model at timescales relevant to land and water resource management decisions determining transport rates and residence times is complicated by the intermittent movement and temporary storage of sediments in natural streams this paper presents a new tool for estimating the residence times of river borne sediments based on the observed disequilibria between the naturally occurring radionuclides 228ra and 232th in the thorium decay series disequilibrium between concentrations of 228ra half life 5 75 years and its long lived parent 232th has been observed in marine environments and in terrestrial freshwaters but has not been previously reported in fluvial sediments or soils here we report 228ra excesses in sandy stream and silty lake sediments from southeastern australia the excess is developed in hillslope soils in the catchment headwaters and begins to decay back to secular equilibrium once the sediment is finally removed from contact with the soil water the short half life of 228ra enables this process to be used to investigate fluvial sediment transfers and alluvial and lacustrine sediment storages over the past 30 years when combined with indicators of sediment source such as 226ra 232th and 230th 232th ratios observation of this excess should provide a useful new tool for examining the residence and transit times of bed load and suspended load sediments in streams and lakes

volatile contents of primitive bubble bearing melt inclusions from klyuchevskoy volcano kamchatka comparison of volatile contents determined by mass balance versus experimental homogenization primitive olivine hosted melt inclusions provide information concerning the pre eruptive volatile contents of silicate melts but compositional changes associated with post entrapment processes pep sometimes complicate their interpretation in particular crystallization of the host phase along the wall of the melt inclusion and diffusion of h through the host promote co2 and potentially s or other volatiles to exsolve from the melt into a separate fluid phase experimental rehomogenization and analysis of mi or a combination of raman spectroscopy numerical modeling and mass balance calculations are potentially effective methods to account for pep and restore the original volatile contents of melt inclusions in order to compare these different approaches we studied melt inclusions from a suite of samples from klyuchevskoy volcano kamchatka arc for which volatile compositions have been determined using experimental rehydration raman spectroscopy and numerical modeling the maximum co2 contents of melt inclusions are in agreement 3600 4000 ppm regardless of the method used to correct for co2 in the bubble but significantly more uncertainty is observed using mass balance calculations this uncertainty is largely due to the lack of precision associated with the petrographic method of determining bubble volumes and may also be related to the presence of daughter minerals at the glass bubble interface

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

routine characterization and interpretation of complex alkali feldspar intergrowths almost all alkali feldspar crystals contain a rich inventory of exsolution twin and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions sometimes multiple microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering they are central to the retention or exchange of trace elements and of radiogenic and stable isotopes this review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process we suggest a systematic approach that employs methods available in most well founded laboratories the crystallographic relationships of complex feldspar intergrowths were established by the 1970s mainly using single crystal x ray diffraction but such methods give limited information on the spatial relationships of the different elements of the microtexture or of the mode and chronology of their formation which require the use of microscopy we suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections sections cut parallel to the perfect 001 and 010 cleavages are the easiest to locate and most informative techniques described are light microscopy scanning electron microscopy using both backscattered and secondary electrons including the use of surfaces etched in the laboratory electron probe microanalysis and analysis by energy dispersive spectrometry in a scanning electron microscope transmission electron microscopy we discuss the use of cathodoluminescence as an auxiliary technique but do not recommend electron backscattered diffraction for feldspar work we review recent publications that provide examples of the need for great care and attention to pre existing work in microtextural studies and suggest several topics for future work

peralkaline granitoid magmatism in the mongolian transbaikalian belt evolution petrogenesis and tectonic significance article i nfo the central asian orogenic belt caob is well known for its massive generation of juvenile crust in the phanerozoic in eastern caob voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanics were emplaced in three stages from early permian to late mesozoic 295 270 ma 230 190 ma and 150 120 ma they occur as huge granitoid belts in extensional tectonic settings and form a complex network of about 12 million km 2 in area among them the 2500 km long mongolian transbaikalian belt mtb is the most spectacular and it comprises more than 350 granite syenite plutons and stocks with numerous co genetic volcanic fields the three stages of granitoids have similar chemical compositions but show temporal variation in nd isotopic composition initial end t values range from 1t o 5 for the early permian 0 to 4 for the early mesozoic and 2t o 3 5 for the late mesozoic granitoids the negative end t values observed in the mtb are not typical of the caob granitoids which are generally characterized by positive values however several pieces of evidence suggest that the mtb peralkaline and alkali feldspar granitoids were produced from enriched mantle derived sources the evidence includes 1 felsic and mafic rocks formed in the same stage have similar initial nd sr isotopic ratios and sm nd model ages tdm 2 the granitoid belts extend over thousands of kilometers and intersect distinct crustal provinces but no correlation is found in chemical compositions between the granitoids and country rocks 3 the abundant syenites are considered to be cogenetic or in some cases parental to the granites experimental and isotope data argue for the derivation of syenites from an enriched mantle source thus the granites and comendites are regarded as mantle derived 4 a study of melt inclusions in quartz phenocrysts of comendite indicates a high liquidus temperature of 1000 1100 c for the magma generation this suggests that the silicic magma was generated in an unusually high temperature condition which is likely produced by basaltic magma that underplated the lower crust the generation of voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanic rocks represents an important addition of juvenile crustal mass to the earth s continental crust during a time span of about 150 ma from late paleozoic to late mesozoic

re equilibration of primary fluid inclusions in peritectic garnet from metapelitic enclaves el hoyazo spain abstract primary appearing fluid fi and melt fi inclusions occur in peritectic garnet from restitic enclaves from el hoyazo spain the inclusions were trapped under conditions of immiscibility during partial melting of the enclaves trapped fluids in bt grt sil and spl crd enclaves have been characterized by microthermometric raman spectroscopic electron microprobe emp and transmission electron microprobe tem analyses to better constrain melt and fluid products and pressure conditions of the partial melting event in bt grt sil enclaves fi are one phase and contain a co2 n2 mixture sometimes with graphite as trapped phase in spl crd enclaves fi are two phase and contain an h2o rich 90 mol with minor amounts of co2 n2 and traces of h2s and ch4 graphite often occurs as a trapped phase in the h2o rich fi and rare carbonates and other accessory minerals are also observed although decrepitation features are not recognized during examination with a petrographic microscope fi densities based on mass balance constraints are always lower than expected at the inferred pt conditions of entrapment 5 7 kbar and 800 900 c extremely low densities 0 1 g cm 1 of fi in bt grt sil enclaves suggest a pressure 500 bar at 800 900 c while densities up to 0 53 g cm 1 in spl crd enclaves indicate p 3 kbar at 800 900 c re equilibration is likely to have occurred via partial decrepitation as suggested by tem studies that show rare partially annealed sub m cracks containing small cavities which may have been the pathways for fluid movement out of the inclusions mi coexisting with fi have a rhyolitic peraluminous composition with higher h2o contents of mi in spl crd enclaves 9 wt compared to mi in bt grt sil enclaves 3 wt based on published data peritectic garnet in spl crd enclaves grew in the presence of a leucogranitic melt saturated in an h2o rich fluid in good agreement with the inferred garnet pt growth conditions the composition of the fluid phase coexisting with melt in bt grt sil enclaves cannot be evaluated owing to the almost complete decrepitation and fluid loss from fi and may only be inferred to have been more co2 rich based on the lower h2o content of the coexisting melt

the formation of the yichun ta nb deposit south china through fractional crystallization of magma indicated by fluid and silicate melt inclusions abstract the yichun ta nb deposit which is located in jiangxi province south china can be divided into four lithological zones from bottom upward two mica granite muscovite granite albite granite and lepidolite albite granite zones it remains controversial whether these distinct vertical zones were formed through late magmatic hydrothermal metasomatic alteration or fractional crystallization of magma to investigate the evolution mechanism of rock and ore forming fluid in this deposit we studied fluid and melt inclusions in quartz and lepidolite in these four granite zones these fluid inclusions are mainly composed of h2o nacl and have homogenization temperatures ranging from 160 c to 240 c with densities between 0 86 and 0 94 g cm3 and salinities between 0 5 and 6 5 wt nacl equivalent raman spectroscopic analyses showed that the daughter minerals contained in silicate melt inclusions are mainly quartz lepidolite albite muscovite microcline topaz and sassolite from the lower to upper granite zones the albite contents in silicate melt inclusions increase while the muscovite contents decrease gradually until muscovite is substituted by lepidolite in the lepidolite albite granite zone additionally the calculated densities of the silicate melt inclusions exhibit decreasing trends from bottom upward the total homogenization temperatures of silicate melt inclusions which were observed under external pressures created in the sample chamber of a hydrothermal diamond anvil cell decreased from 860 c in the lower lithological zone to 776 c in the upper lithological zone and the initial melting temperatures of solid phases were 570 710 c the calculated initial h2o contents of granitic magma showed an increasing trend from the lower 2 wt in the two mica granite zone to the upper granitic zones 3 wt in the albite granite zone all of these features illustrate that the vertical granite zones in the yichun ta nb deposit formed through the continuous fractional crystallization of the granitic magma additionally the low h2o contents and gradual enrichment of incompatible elements f b li ta nb etc in the residual granitic magma favored the formation of a granite type ta nb deposit

magmatic immiscibility and fluid phase evolution in the mount genis granite southeastern sardinia italy the mount genis granite is one of the post tectonic intrusives emplaced late in the magmatic history of the hercynian batholith in sardinia devitrified silicate melt inclusions are present in some magmatic rock forming and miarolitic quartz these magmatic remnants show initial melting at 680 720 c high temperature observations 700 800 c revealed the presence in some of the inclusions of mixed hydrosaline melt l1 and silicate melt l2 with extremely variable l1l2 ratios electron microprobe analyses indicate l1 to be k na dominated chlorides inclusions of mixed silicate and hydrosaline melts are interpreted to have been formed by heterogeneous trapping of two immiscible fluid phases silicate hydrosaline after second boiling most likely during the final crystallization stage magma derived brines 63 eq wt nacl circulated at subsolidus conditions from 600 c and were retained in the miarolitic cavities down to about 400 c fluid unmixing occurred locally in the miarolitic cavities from 550 to 412 c at temperatures of 400 to 100 c the microgranite was invaded by diluted waters 4 5 eq wt nacl a possible model for fluid evolution begins with a hydrosaline melt exsolving from the magma at the late magmatic stage the absence of boiling within the volatile hydrosaline system shows that brines can occur by direct magmatic immiscibility the comprehensive hydrothermal evolution suggests a nearly isobaric cooling path with local boiling episodes in the miaroles probably in coincidence with invasion of external waters

a petrologic assessment of internal zonation in granitic pegmatites abstract cameron et al 1949 devised the nomenclature and delineated the patterns of internal zonation within granitic pegmatites that are in use today zonation in pegmatites is manifested both in mineralogy and in fabric mineral habits and rock texture although internal zonation is a conspicuous and distinctive attribute of pegmatites there has been no thorough effort to explain that mineralogical and textural evolution in relation to the zoning sequence presented by cameron et al 1949 or in terms of the comprehensive petrogenesis of pegmatite bodies pressure temperature and whole rock composition this overview of internal zonation within granitic pegmatites consists of four principal parts 1 a historic review of the subject 2 a summary of the current understanding of the pegmatite forming environment 3 the processes that determine mineralogical and textural zonation in pegmatites and 4 the applications of those processes to each of the major zones of pegmatites based on the concepts presented in london 2008 the fundamental determinates of the internal evolution of pegmatite zones are 1 the bulk composition of melt 2 the magnitude of liquidus undercooling prior to the onset of crystallization 3 subsolidus isothermal fractional crystallization by which eutectic or minimum melts fractionate by sequential non eutectic crystallization 4 constitutional zone refining via the creation of a boundary layer liquid chemically distinct from but continuous with the bulk melt at the crystallization front and 5 far field chemical diffusion the long range and coordinated diffusion of ions particularly of alkalis and alkaline earths through melt

magnetite scavenging and the buoyancy of bubbles in magmas part 1 discovery of a pre eruptive bubble in bishop rhyolite little is known about the presence distribution and size of bubbles in rhyolitic magmas prior to eruption using x ray tomography to study pumice from early erupted bishop rhyolite we discovered a large vesicle with abundant magnetite crystals attached to its walls attachment of magnetite crystals to bubble walls under pre eruptive conditions can explain the cluster of magnetite crystals as a result of bubbles rising and collecting magnetite crystals alternatively bubbles may have nucleated on magnetite crystals and then coalesced to form one large bubble with multiple magnetite crystals attached to it we argue that the clusters of magnetite crystals could not have formed during or after eruptive decompression and conclude that this vesicle corresponds to a bubble present prior to eruptive decompression the inferred presence of pre eruptive bubbles in the bishop magma confirms the interpretation that the magma was volatile saturated prior to eruption the pre eruptive size of this bubble is estimated based on three independent approaches 1 the current size of the vesicle 2 the total cross sectional area of the magnetite crystals and 3 the bubble size required for the aggregate to be neutrally buoyant these approaches suggest a pre eruptive bubble 300 850 m in diameter with a preferred value of 600 750 m

formation of extremely f rich hydrous melt fractions and hydrothermal fluids during differentiation of highly evolved tin granite magmas a melt fluid inclusion study quartz crystals from topaz zinnwaldite albite granites from zinnwald erzgebirge germany contain in addition to primary and secondary fluid inclusions fis abundant crystalline silicate melt inclusions mis with diameters up to 200 m these mis represent various stages of evolution of a highly evolved melt system that finally gave rise to granite related sn w mineralization the combination of special experimental techniques with confocal laser raman microprobe spectroscopy and empa permits precise measurement of elevated contents of h2o f and b in re homogenized mis the contents of h2o and f were observed to increase from 3 to 30 and 1 9 to 6 4 wt respectively during magma differentiation however there is a second mi group very rich in h2o with values up to 55 wt h2o and an f concentration of approximately 3 wt ongoing enrichment of volatiles h2o f b and cl and of cs and rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus is suggested to reflect elemental abundances in natural magmas and not boundary layer melts partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements particularly sn the coexistence of two types of mis with primary fis indicates fluid saturation early in the history of magma crystallization connected with a continuous sequestration of sn f and b the results of this study provide additional evidence for the extraordinary importance of the interplay of h2o f and b in the enrichment of sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid

systematic variations of argon diffusion in feldspars and implications for thermochronometry abstract coupled information about the time dependent production and temperature dependent diffusion of radiogenic argon in feldspars can be used to constrain the thermal evolution attending a host of earth and planetary processes to better assess the accuracy of thermal models an understanding of the mechanisms and pathways by which argon diffuses in feldspars is desirable here we present step heating ar diffusion experiments conducted on feldspars with diverse compositions structural states and microstructural characteristics the experiments reveal systematic variations in diffusive behavior that appear closely related to these variables with apparent closure temperatures for 0 1 1 mm grains of 200 400 c assuming a 10 c ma cooling rate given such variability there is no broadly applicable set of diffusion parameters that can be utilized in feldspar thermal modeling sample specific data are required diffusion experiments conducted on oriented cleavage flakes do not reveal directionally dependent diffusive anisotropy to within the resolution limits of our approach approximately a factor of 2 additional experiments aimed at constraining the physical significance of the diffusion domain are presented and indicate that unaltered feldspar crystals with or without coherent exsolution lamellae diffuse at the grain scale whereas feldspars containing hydrothermal alteration and or incoherent sub grain intergrowths do not arrhenius plots for argon diffusion in plagioclase and alkali feldspars appear to reflect a confluence of intrinsic diffusion kinetics and structural transitions that occur during incremental heating experiments these structural transitions along with sub grain domain size variations cause deviations from linearity i e upward and downward curvature on arrhenius plots an atomistic model for arrhenius behavior is proposed that incorporates the variable lattice deformations of different feldspars in response to heating and compression the resulting implications for accurately extrapolating laboratory derived diffusion parameters to natural settings and over geologic time are discussed we find that considerable inaccuracies may exist in published thermal histories obtained using multiple diffusion domain mdd models fit to arrhenius plots for exsolved alkali feldspar where the inferred ar partial retention zones may be spuriously hot

dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling we have developed a model of diffusive and decompressive growth of a bubble in a finite region of melt which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between magmatic system parameters such as viscosity volatile concentration and diffusivity on the basis of our formulation we constructed a numerical model of bubble growth in volcanic systems we conducted a parametric study in which a saturated magma is instantaneously decompressed to one bar and the sensitivity of the system to variations in various parameters is examined variations of each of seven parameters over practical ranges of magmatic conditions can change bubble growth rates by 2 4 orders of magnitude our numerical formulation allows determination of the relative importance of each parameter controlling bubble growth for a given or evolving set of magmatic conditions an analysis of the modeling results reveals that the commonly invoked parabolic law for bubble growth dynamics r t1 2 is not applicable to magma degassing at low pressures or high water oversaturation but that a logarithmic relationship r log t is more appropriate during active bubble growth under certain conditions a second aspect of our study involved a constant decompression bubble growth model in which an initially saturated magma was subjected to a constant rate of decompression model results for degassing of initially water saturated rhyolitic magma with a constant decompression rate show that oversaturation at the vent depends on the initial depth of magma ascent on the basis of decompression history explosive eruptions of silicic magmas are expected for magmas rising from chambers deeper than 2 km for ascent rates 1 5 m s 1

fragmentation phenomena in populations of magmatic crystals fragmentation of crystals is an important mechanism and a component of particle dynamics in igneous and metamorphic rocks that has received surprisingly little attention recent advances in textural analysis extraction techniques digital imaging and computer assisted measurements enable rapid accumulation of 3d data on particle shapes and size distributions this paper reviews fragment size distributions fsd that result from fragmentation lognormal fractal loggamma and weibull discusses their genesis mechanisms and presents relevant examples of fragmentation from experimental physics next the paper considers fsds of feldspars on digitized images of thin sections and on published images and quartz extracted from vesicular pumice by acid from eight well known large volume eruptive units the acid solution of pumice enables examination of volume abundance 3d shapes proportions of fragmented crystals and measurements of their csds and fsds fsds were also measured in samples of welded tuff and a granite disaggregated by electric pulse products of syneruptive shock wave fragmentation and fragmentation by an electric pulse are found to be fractal with large breakage probabilities branching ratios and fractal dimensions of 2 to 3 in contrast most quartz fragments in pumice obey a lognormal distribution and fragmentation is driven by a melt inclusion decrepitation mechanism which results in low breakage probability and small number 2 3 of fragments per breakage cycle these results are consistent with one atmosphere heating experiments of quartz phenocrysts that led to melt inclusion decrepitation and caused quartz to break up into several smaller pieces collectively having lognormal fsd measured melt inclusion size distributions suggest decrepitation of outermost melt inclusions and low survival rate for large inclusions and inclusions with large radius crystal size ratio the modeling of periodic fragmentation of crystals with melt inclusions due to overheating and or decompression which may occur many times during the lifetime of a long lived magma body may explain concave down lognormal csds abundant in igneous rocks the genesis of lognormality can be explained by the fragmentation algorithm of kolmogorov 1941 other algorithms may generate lognormal like loggamma distributions fragmentation serves as an important size limiting factor a nucleation aid and it facilitates isotopic and trace elemental exchange

heterogeneous melt and hypersaline liquid inclusions in shallow porphyry type mineralization as markers of the magmatic hydrothermal transition cerro de pasco district peru recently identified occurrences of porphyry style mineralization evidence the link of the world s second largest known epithermal base metal cerro de pasco deposit peru to a porphyry system emplaced at depth they consist of i quartz monzonite dykes and ii the south western part of the large diatreme dome complex adjacent to the main ore bodies of cerro de pasco and iii stockwork of banded quartz magnetite chalcopyrite pyrite porphyry type veinlets crosscutting trachyte porphyritic intrusion cropping out at surface in the central part of the diatreme dome complex the latter porphyry type mineralization observed at the same erosion level as the main epithermal base metal carbonate replacement ore bodies is the subject of this work geological constraints indicate a shallow emplacement level depth 1 km p 270 bar implying rather unusual low pressure and high temperature environment for the formation of porphyry style mineralization the banded porphyry type veinlets record a multiphase history of formation with two successive high temperature n600 c stages followed by a lower temperature b350 c stage more than 90 of the quartz in veinlets precipitates during the first two high temperature stages stage 1 is characterized by the entrapment in hydrothermal quartz of inclusions containing variable proportions of both silicate melt and metal rich hypersaline n90 wt nacl eq liquid hereafter referred to as heterogeneous silicate melt inclusions hsmis the latter are rarely described in porphyry type mineralization we suggest that during stage 1 the inclusions result from heterogeneous entrapment of an evolved hydrous rhyolitic melt mixed with a hypersaline fluid phase at low pressure 270 bar and high temperature n600 c the stage 2 is marked by the entrapment of metaland sulfur rich hypersaline liquid inclusions with salinity around 70 wt nacl eq originated from the adiabatic ascent of magmatic hypersaline fluids transferred fromdeeper parts of the system the lower temperature stage 3 is characterized by an important temperature drop from n600 c to b350 c as revealed bymicrothermometry of aqueous two phase liquid vapor l v inclusions quartz textures revealed by sem cl imaging allowascribing the sulfide precipitation to the low temperaturemineralization stage 3 in situ sims 18o 16o isotope analyses of quartz across the veinlets are indicative of a magmatic signature of the fluids during the first two stages while quartz from stage 3 has oxygen isotopic compositions suggestive of minor contribution of meteoric waters to a predominantly magmatic aqueous fluid 10 vol of meteoric input which probably triggered cu fe sulfide precipitation in the stockwork high metal and sulfur contents of hsmis and hypersaline liquid inclusions determined by la icp ms are interpreted to represent the fluid composition prior to the main sulfide precipitation event the similar pb zn ratio of the bulk ore extracted from the epithermal ore bodies at cerro de pasco and the hsmis and hypersaline liquid inclusions suggest a common source of the fluids associated with the different mineralization styles at cerro de pasco

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

segregation of magmatic fluids and their potential in the mobilization of platinum group elements in the south kawishiwi intrusion duluth complex minnesota evidence from petrography apatite geochemistry and coexisting fluid and melt inclusions abstract pegmatitic and other felsic rock pockets and dike like intrusions are abundant in the south kawishiwi intrusion of the duluth complex including the basal cu ni pge mineralized units these occurrences are found as pockets pods or as veins and contain abundant accessory apatite and quartz quartz hosts primary fluid inclusions as well as silicate melt inclusions combined microthermometry and raman spectroscopy helped to determine the bulk composition of primary fluid inclusions that are co 2 rich 95 mol and contain small amounts of h 2 o 4 5 mol ch 4 0 4 mol and trace n 2 respectively this combined technique also made it possible to measure total homogenization temperatures of the inclusions th tot 225 10 c otherwise not detectable during microthermometry silicate melt inclusions have been quenched to produce homogeneous glasses corresponding to the original melt composition of the entrapped melt is granitoid peraluminous and is very poor in mafic components we interpret the melt as a product of partial melting of the footwall rocks due to the contact effect of the south kawishiwi intrusion the presence of co 2 in the vapor bubbles of the quenched melt inclusions and petrographic evidence suggest that the fluid and melt inclusion assemblages are coeval the composition of the fluid and melt phase implies that the fluid originates from the mafic magma of the south kawishiwi intrusion and the fluid and melt phases coexisted as a heterogeneous melt fluid system until entrapment of the inclusions coexistence of primary fluid and melt inclusions makes it possible to calculate a minimum entrapment pressure 1 7 kbar and thus estimate formation depth 5 8 km for the inclusions chlorine is suggested to behave compatibly in the silicate melt phase in the fluid melt system represented by the inclusions indicated by the high up to 0 3 cl concentrations of the silicate melt and co 2 rich nature of the fluid apatite halogen contents provide further details on the behavior of cl apatite in pegmatitic pockets often has elevated cl concentrations compared to troctolitic rocks suggesting enrichment of cl with progressive crystallization systematic trends of cl loss at some differentiated melt pockets suggest that in some places cl exsolved into a fluid phase and migrated away from its source the segregation of cl from the melt is probably inhibited by the presence of co 2 rich fluids until the last stages of crystallization increasing the potential for the development of late stage saline brines platinum group minerals are often present in microcracks in silicate minerals in late stage differentiated sulfide veinlets and in association with chlorapatite indicating the potential role of cl bearing fluids in the final distribution of pges

argon loss by alkali feldspars abstract ar loss is generally thought to preclude the use of alkali feldspars for dating old rocks by the k ar method and has been thought to occur via structural features such as the boundaries of perthite lamellae or twins we have done a 40 ar 39 ar step heating study of a suite of alkali feldspars from the klokken syenite intrusion u pb age 1166 4 ma which have been fully characterized by transmission electron microscopy all are low albite low microcline intergrowths but some are non turbid strain controlled cryptoperthites while others are turbid coarse microperthites geological and textural evidence suggests that the turbidity developed by fluid rock interactions during the initial cooling of the pluton in the stability field of low microcline 5 a after crystallization the finest cryptoperthites have numerous fully coherent perthite lamellar boundaries lamellar periodicity 40 nm and twin composition planes the have retained radiogenic 40 ar and yield total degassing ages as high as 1125 16 ma and maximum ages on the age spectra of 1162 16 ma the coarse turbid microperthites with patchy intergrowths and twins on the mm scale gave total degassing ages as low as 650 ma maximum age 750 ma argon leakage occurs least in feldspars with the most lamellar interfaces but in proportion to the degree of turbidity which is thought to be caused by large numbers of micropores strain controlled intergrowths in perthites allow the recognition of volumes of alkali feldspar crystals which have not interacted with deuteric fluids these retain argon and can give reliable k ar ages in old rocks saddle shaped age spectra appear to result from the preferential degassing at 1000 c of part of the feldspar structure which has lost more of its argon in nature the laboratory degassing does not occur in a manner analogous to that which has occurred naturally

charge contrast imaging of fine scale microstructure and compositional variation in garnet using the environmental scanning electron microscope gaseous secondary electron gse imaging of eclogite garnets under the environmental scanning electron microscope esem at low chamber gas pressures reveals detailed image contrast patterns charge contrast images cci that are not present in back scattered or secondary electron images image intensity is a function of the amount of surface charge accumulation successful acquisition of cci depends on frame size and beam scan rate at a given chamber gas pressure and beam current images are obtained in a few seconds and are stable and reproducible cci patterns do not correlate with cracks or grain boundaries but do correspond closely to variations in major element composition both in the form of concentric growth zoning and branching linear features interpreted as cracks that have been healed by new garnet growth causes of cci are not yet well understood but may be related to variations in lattice defect density and their influence on charge trapping and dissipation these in turn influence the rate of charge build up at or very close to the specimen surface one interesting possibility is that cci images detect vacancies related to non homovalent coupled substitutions involving for example ree and hydroxyl so the method offers a way of imaging the distribution of these trace species in garnets the cci images are rich in microstructural detail and offer the potential for rapid high resolution low noise reconnaissance mapping of intragranular microstructure and compositional variation in both natural and synthetic garnets

development of microporosity diffusion channels and deuteric coarsening in perthitic alkali feldspars turbidity is an almost universal feature of alkali feldspars in plutonic rocks and has been investigated by us in alkali feldspars from the klokken syenite using sem and tem it is caused by the presence of myriads of tubular micro inclusions either fluid filled micropores or sites of previous fluid inclusions and is associated with coarsening of microperthite and development of sub grains micropores are abundant in coarsened areas in which porosities may reach 4 5 but are almost absent from uncoarsened pristine braind microperthite areas the coarsening is patchy and involves a scale increase of up to 103 without change in the composition of the phases low albite and low microcline or in the bulk composition of the crystal it occurs abruptly along an irregular front within individual crystals which retain their original shapes the coherent braid microperthite gives way across the front to an irregular semi coherent film perthite over a few m and then to a highly coarsened irregular patch perthite containing numerous small sub grains on scales of a few hundred nm in both phases the coarsening and micropore formation occured at a t 400 450 c and it is inferred to have been driven by the release of coherent strain energy low angle grain boundary migration being favoured by a fluid the patchy nature of the coarsening and the absence of a relationship with initial grain boundaries suggest that the fluid was of local origin possibly arising in part through exsolution of water from the feldspar the sub grain texture and microporosity modify profoundly the permeability of the rock and greatly enhance the subsequent reactivity of the feldspars

the significance of various sediment magnetic mineral fractions for tracing sediment sources in killimicat creek abstract the mineral magnetic properties of sediment are increasingly being used to determine the sources of sediment and associated nutrients and contaminants in drainage basins this study was undertaken to measure the relative contributions of the magnetic mineral components in sediment i e components associated with surface bound fe the heavy mineral fraction and as inclusions in particles to determine the extent to which they represent the bulk of the sediment deposited channel sediment samples from the tributaries and downstream reach at the first major confluence in the headwaters of killimicat creek new south wales were sieved to separate 6 particle size fractions and the mineral magnetic properties measured to determine the relative contribution of sediment from the smaller tributary basin the finest sand component 63 125 m was then separated into light and heavy mineral fractions and magnetic measurements made on each fraction magnetic parameter data from the 63 125 m fraction measured before density separation show a dominance of sediment 70 12 derived from the smaller tributary basin measurements of the light sediment fraction give a similar result 73 13 the proportion of the heavy mineral fraction delivered from the smaller tributary is 78 38 the light mineral fraction of all of the samples were treated with hcl to remove surface bound fe and subsequent magnetic measurements show that 41 94 of the mass specific magnetic susceptibility is attributable to magnetic minerals associated with surface bound fe the heavy mineral component while 60 is associated with sediment particles rather than the discrete heavy mineral component

determining the origins and history of sedimentation in an underground river system using natural and fallout radionuclides abstract natural and anthropogenic radionuclides were used to characterize the source of sediment reaching the underground river in the karst system at jenolan new south wales australia it was found that the relationship between 226 ra and 232 th concentrations in both spatially averaged soil samples and transported sediments distinguished between two of the most likely source subcatchments sedimentary sequences collected from within the underground system showed that contemporary deposition was made up of an equal mixture of sediment from these two sources however at least three earlier deposition periods were also identifiable each with different relative contributions from the source catchments the first appearance of 137 cs in the sedimentary sequence and correlations with historical information provided a chronology for these changes and it is concluded that the contemporary phase was initiated in the early 1950s most probably by forestry activities this work demonstrates that natural radioactivity can be used as a tracer of the origins of sediment providing an important new approach to problems in sediment supply transport and deposition

multi year tracking of sediment sources in a small agricultural watershed using rare earth elements rare earth elements rees have been successfully used as a sediment tracer but the ree technique has never been used for studying sediment sources for a multi year period a nearly four year field experiment was conducted on a small agricultural watershed near coshocton oh usa to assess the applicability of the ree technique for a multi year period and to evaluate the relative contributions of sediment sources in the watershed tracer depletion and tracer enrichment ratio ratio of the tracer concentrations in sediment to the concentrations in the soil in the areas of application were evaluated to examine the applicability and accuracy of the technique a minimum of 91 per cent of the mass of the applied elements was still available on any individual morphological element at the end of the experimental period the tracer enrichment ratio varied from 0 4 to 2 3 and it was not significantly related to time the relative contributions of six morphological elements within the watershed were evaluated as proportions to total sediment yield the relative contribution of the lower channel was significantly increased as a function of the amount of sediment yield while that of the lower backslope was significantly decreased the relative contribution of the lower channel significantly decreased as a function of cumulative sediment yield while the contributions of the shoulder and the upper backslope significantly increased our results showed that the ree technique can be used to track sediment sources for a relatively long period with two limitations or potential sources of error associated with a selective depletion of tracers and a contamination of downslope areas with tagged sediments from upslope areas copyright 2006 john wiley sons ltd

microtextural controls of diagenetic alteration of detrital alkali feldspars a case study of the shap conglomerate lower carboniferous northwest england abstract the diagenetic alteration of detrital alkali feldspar grains in the lower carboniferous shap conglomerate which were derived from the nearby lower devonian shap granite was strongly influenced by their pre diagenetic microtextures alkali feldspars collected from a working quarry in the shap granite are perthites composed of two types of microtextures primary igneous and deuterically altered primary igneous microtextures which formed during early cooling of the pluton are composed of albite exsolution lamellae in tweed orthoclase small lamellae platelets form cryptoperthites whereas larger lamellae films form microperthites albite platelets have coherent interfaces with orthoclase i e the crystal structure is strained but continuous across the interface of the exsolution lamellae whereas larger films are semicoherent i e dislocations have formed to relieve strain at the exsolution interface deuteric alteration leads to the development of micropore rich veins composed of discrete subgrains of albite and microcline referred to as patch perthites which cut the cryptoperthites and microperthites these veins formed during fluid feldspar interaction within the granite in the later stages of igneous cooling subgrains within these veins are semicoherent or are incoherent i e there is no continuity in crystal structure across the subgrain boundary during diagenesis of shap granite derived alkali feldspars in the shap conglomerate the semicoherent and incoherent albite in microperthites and patch perthites was selectively dissolved or replaced by microcline whereas coherent albite platelets in cryptoperthites remained largely unaltered this diagenetic history reflects an interplay between two main determinants of alteration i the nature of the pore fluids which resulted in albite rich feldspar being more heavily altered than orthoclase rich feldspar and ii the coherency of interfaces which determined the specific albite rich feldspar microtextures that were affected fluid feldspar interaction was favored at semicoherent and incoherent interfaces owing to their high surface and strain energies release of energy stored at such interfaces is also the major intragranular driving force of deuteric alteration of alkali feldspars in cooling igneous rocks in general as a result petrographically and geochemically similar microtextures may result from both deuteric and diagenetic alteration and care must be taken to discriminate between them results of this study underscore the importance of understanding the nature of alkali feldspars in igneous and metamorphic rocks for an accurate interpretation of their subsequent diagenetic history

mobile sediment in an urbanizing karst aquifer implications for contaminant transport here we investigate geochemical characteristics of sediment in different compartments of a karst aquifer and demonstrate that mobile sediments in a karst aquifer can exhibit a wide range of properties affecting their contaminant transport potential sediment samples were collected from surface streams sinkholes caves wells and springs of a karst aquifer the barton springs portion of the edwards balcones fault zone aquifer central texas and their mineralogy grain size distribution organic carbon content and specific surface area analyzed statistical analysis of the sediments separated the sampling sites into three distinct groups 1 streambeds sinkholes and small springs 2 wells and 3 caves sediments from the primary discharge spring were a mix of these three groups high organic carbon content and high specific surface area gives some sediments an increased potential to transport contaminants the volume of these sediments is likely to increase with continued urbanization of the watershed

melt inclusion hosted excess 40ar in quartz crystals of the bishop and bandelier magma systems 40 ar 39 ar experiments on melt inclusion bearing quartz mibq from the bishop and bandelier tuff plinian deposits indicate high concentrations of excess 40 ar in melt inclusions two rhyolite glass melt inclusion populations are present in quartz exposed melt inclusions and trapped melt inclusions air abrasion mill grinding and hydrofluoric acid treatments progressively remove exposed melt inclusions while leaving trapped melt inclusions unaffected laser step heating of mibq yields increasing apparent ages as a function of exposed melt inclusion removal reflecting the higher nonatmospheric 40 ar concentrations hosted in trapped melt inclusions exposed melt inclusion free mibq from the bishop upper bandelier and lower bandelier tuffs yield total gas ages of 3 70 1 00 ma 11 54 0 87 ma and 14 60 1 50 ma respectively we interpret these old apparent ages as compelling evidence for the presence of excess 40 ar in mibq trapped melt inclusions in sanidine phenocrysts may contain excess 40 ar concentrations similar to those in mibq this excess 40 ar has the potential to increase single crystal laser fusion ages of sanidine by tens of thousands of years relative to the actual eruption age

alkali feldspar microtextures as provenance indicators in siliciclastic rocks and their role in feldspar dissolution during transport and diagenesis abstract alkali feldspars usually exhibit optical or sub optical intergrowths of albite and k feldspar known generically as perthite which have morphologies and crystallographic characteristics that are distinctive of the igneous or metamorphic environment in which they grew and cooled to surface temperatures we review the current terminology and understanding of how the microtextures form and discuss their role in feldspar dissolution during weathering transport and diagenesis we show how microtextures can be used as provenance indicators in arkosic siliciclastic rocks using examples from the fulmar formation a reservoir rock in the upper jurassic humber group in the central north sea in which feldspar dissolution is a major source of secondary porosity we describe the most effective techniques for routine characterization of which the most practical is back scattered electron imaging in a scanning electron microscope often coupled with cathodoluminescence we provide an atlas of the main types of perthitic intergrowth likely to be encountered in igneous and metamorphic rocks worldwide and show how many of the microtextures can be matched in clastic grains in the fulmar formation grains which are preferentially preserved have microtextures that make them relatively unreactive in aqueous fluids at low temperatures and we conclude that provenance has a major impact on reservoir quality detrital grains in the fulmar exhibit authigenic albitization k feldspar overgrowths and replacement and we discuss how diagenetic features can be distinguished from replacive features developed in the protolith

melt inclusion geochemistry and computer modeling of trachyte petrogenesis at ponza italy abstract the punta della guardia trachytic unit on the island of ponza italy is thought to represent the latest stage in the evolution of a parent basaltic melt in a shallow magma chamber undergoing fractional crystallization to test this hypothesis melt inclusions mi have been analyzed to constrain the crystallization history of the ponza trachyte the trachyte is a weakly porphyritic lava that contains phenocrysts of plagioclase k feldspar clinopyroxene and biotite melt inclusions were observed and measured in plagioclase clinopyroxene and k feldspar the crystallized devitrified melt inclusions were heated to dissolve melt the crystals quenched to a homogeneous glass and then analyzed for major elements by electron microprobe two different heating protocols one involving rapid heating in a one atmosphere furnace and the other involving slower heating in a microscope heating stage were used to homogenize the inclusions in order to investigate possible effects of heating rates on inclusion composition no detectable difference was found melt inclusion compositions suggest that the magma evolved from an early phase dominated by clinopyroxene plagioclase crystallization to a late stage in which melt composition was controlled by precipitation of two feldspars the potential basaltic parent magma does not crop out on ponza although more primitive and coeval basalts and trachybasalts are found on nearby ventotene island which is considered to be co magmatic with ponza using the program melts we have compared results obtained from melt inclusions in the ponza trachyte with melt compositions predicted for fractional crystallization of a magma having the composition of the ventotene trachybasalt crystallization trends predicted by melts are consistent with data from melt and host phases although differences in measured and predicted compositions are significant in some cases in spite of these differences the model results and measured compositions are consistent with the hypothesis of a genetic link between the magmatism of ponza and ventotene

the effect of nonlinear decompression history on h2o co2 vesiculation in rhyolitic magmas magma ascent rate is one of the key parameters that controls volcanic eruption style tephra dispersion and volcanic atmospheric impact many methods have been employed to investigate the magma ascent rate in volcanic eruptions and most rely on equilibrium thermodynamics combining the mixed h2o co2 solubility model liu et al 2005 with the diffusivities of both h2o and co2 for normal rhyolitic melt zhang et al 2007 behrens and zhang 2009 we model the kinetics of h2o and co2 in rhyolitic eruptions that involve non linear decompression rates our study focuses on the effects of the total magma ascent time the non linearity of decompression paths and the influence of different initial co2 h2o content on the post eruptive h2o and co2 concentration profiles around bubbles within the melt our results show that under most circumstances volatile diffusion profiles do not constrain a unique solution for the decompression rate of magmas during an eruption but instead provide a family of decompression paths with a well defined trade off between ascent time and non linearity an important consequence of our analysis is that the common assumption of a constant decompression rate averaged value tends to overestimate the actual magma ascent time

hematite in porous red clouded feldspars evidence of large scale crustal fluid rock interaction abstract transmission electron microscopy shows that red clouded alkali feldspars from granitic rocks contain numerous open pores up to several hundred nanometres in cross section and that almost every pore contains rosettes or needles of crystalline hematite in the samples described here the hematite forms at the reaction interfaces at which plagioclase feldspar is replaced by alkali feldspar these observations together with the fact that the origin of the porosity can be explained by the mechanism of sub solidus mineral fluid replacement processes indicate that hematite is a direct product of fluid rock interaction and is not a solid state exsolution product from the feldspar

water solubility and chlorine partitioning in cl rich granitic systems effects of melt composition at 2 kbar and 800 c abstract experiments have been conducted in the system na2o k2o al2o3 sio2 h2o cl2o 1 at 2 kbar and 800 c to determine the effects of melt composition on the solubility of water in haplogranite melt and on the distribution of cl between aqueous fluid and haplogranite melt the melts studied include peraluminous subaluminous and peralkaline haplogranites and quartz albite and quartz orthoclase compositions the solubility of water at 2 kbar and 800 c in water saturated haplogranite melts varies strongly as a function of melt composition water solubility in melt decreases in the order strongly peralkaline haplogranite quartz albite composition moderately peralkaline haplogranite peraluminous haplogranite subaluminous haplogranite quartz orthoclase composition d cl wt cl in fluid wt cl in melt is a strong function of system composition d cl increases as the concentration of cl in the system increases a comparison of the distribution of cl between haplogranite melts of subaluminous peraluminous and peralkaline compositions and aqueous fluids shows that with similar concentrations of cl in the system d cl is largest for subaluminous melts a nk 1 having relatively high k2o concentrations as the a nk of melt increases or decreases from 1 or as the n nk of the melt increases both d cl and the concentration of cl in the fluid decrease the experimental data imply that complexes involving cl and na in hydrous subaluminous granite melts are dominant furthermore the data imply that in hydrous peraluminous granite melts cl complexes with network modifying a13 and in hydrous peralkaline granite melts cl complexes with network modifying na k on a molar basis cl apparently complexes with network modifying a13 in peraluminous melts as strongly as it does with na and k in peralkaline melts experimental studies of cl partitioning in granitic systems suggest that the strongest enrichment of magmatic hydrothermal fluids in cl and ore metals complexed with cl will most likely occur in fluids exsolved from subaluminous granite magmas that are relatively enriched in k2o sio2 and cl and relatively depleted in f co2 and na2o

ar ar dating of authigenic k feldspar quantitative modelling of radiogenic argon loss through subgrain boundary networks we have analysed two distinct generations of authigenic k feldspar in fucoid bed sandstones from an t sron and skiag bridge nw highlands scotland which have experienced post growth heating to levels in excess of the predicted ar closure temperature authigenic k feldspars show microtextural similarities to patch perthites that is subgrains separated by dislocation rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon the two generations of authigenic k feldspar in the fucoid bed sandstones can be distinguished by different microtextural zones bulk mineral compositions fluid inclusion populations and inferred temperatures and chemistries of parent fluids ar ar age data obtained using high resolution ultraviolet laser ablation show that the first cementing generation is ordovician and the second cementing generation is silurian modelling of ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono thermal thrust model assuming transient heating of the fucoid beds is inconsistent with observed data removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed ar ar ages for both generations of cement alternatively ar diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the fucoid bed palaeothermal maxima and determined ar ar age ages for the two generations of k feldspar cement based on this alternate explanation we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic k feldspars explaining the apparent robustness of authigenic k feldspar with respect to ar retention

origin of broken phenocrysts in ash flow tuffs surprisingly little attention has been devoted to the textural nature of phenocrysts of feldspar and quartz in tuff although many geologists have briefly alluded to broken phenocrysts none have addressed their origin in any detail petrographic study of 117 cooling units in the middle tertiary ash flow province of the great basin united states provides a basis for characterization of the shapes and for interpretation of the origin of felsic phenocrysts in ash flow tuffs although not proven to be wholly ineffective breakage of phenocrysts by mutual impact in the erupting magma and pyroclastic flow is doubtful for at least four reasons first the statistical probability of mutual collision between phenocrysts diminishes exponentially as their proportion to vitroclasts diminishes e g only 1 probability for 10 phenocrysts collision is less likely if pyroclasts move by laminar rather than turbulent flow second the coating of glass and or melt on the phenocrysts provides a cushion that absorbs the impact force third plagioclases broken by impact in the laboratory have unusual shapes unlike those seen in great basin tuffs fourth euhedral phenocrysts of feldspar are commonplace in many great basin tuffs and in some they constitute a significant proportion of the phenocrysts indicating that mutual impact does not modify all intratelluric crystals during explosive eruption the two most populated categories of phenocryst shape in great basin tuffs probably correspond to what has been previously called broken phenocrysts somewhat less than half of the plagioclase and many sanidine phenocrysts are subhedral to anhedral these are similar in shape size and composition to grains in polycrystalline aggregates within the same thin section kindred aggregates and discrete phenocrysts could have been derived from holocrystalline to partly crystalline material in the magma chamber that was disaggregated to varying extents during explosive eruption more than half of the plagioclase and all of the quartz phenocrysts in great basin tuffs consist of irregularly shaped fragments with cuspate embayed outlines resembling pieces of a jigsaw puzzle which we call phenoclasts inclusions of glass are common and are especially evident in larger more or less whole crystals textural features of some phenocrysts in cognate pumice clasts in the tuffs reveal that they broke apart while still in the vesiculating but unfragmented magma as the erupting magma decompressed vesiculation of the melt that was entrapped at higher pressures as inclusions within the phenocrysts blew them apart forming the phenoclasts shapes of felsic phenocrysts in volcanic rocks provide insight into their mode of emplacement euhedral phenocrysts are common in ash flow tuffs as well as lava flows phenoclasts however are diagnostic of ash flow tuffs because they do not occur in plinian ash fall deposits and are rare in lava flows these textural contrasts are useful for interpretation of generally older but in any case altered and recrystallized volcanic rocks in such rocks critical groundmass features and field relations that could provide clues to their origin have been obscured but the shapes of relict phenocrysts are commonly well preserved

synthetic fluid inclusions xiv coexisting silicate melt and aqueous fluid inclusions in the haplogranite h2o nacl kcl system coeval silicate melt and aqueous synthetic fluid inclusions were introduction formed at 800 c and 2000 bars in the quartz saturated haploin recent years the study of silicate melt inclusions has granite h2o nacl kcl system the equilibrium assemblage congained considerable popularity as a method to charsisted of ab19 2or31 1qtz49 1 melt quartz and an aqueous solution acterize the ptx evolution of igneous processes andwith a composition of 7 4 wt nacl 5 9 wt kcl the erson 1974 roedder 1979 lowenstern 1995 of melt contained 0 18 wt cl and 5 5 wt h2o the special interest has been the study of melt inclusions calculated partition coefficient of chloride between the melt and trapped in an immiscible fluid melt system roedder aqueous fluid d m aq cl c m cl c aq cl is 0 021 the calculated dis1979 1984 1992 hansteen lustenhouwer 1990 tribution coefficient of na and k between the melt and the aqueous frezzotti 1992 naumov et al 1992 1996 yang phase d m aq na k c m na c m k c aq na c aq k is 0 40 homogenization bodnar 1994 student bodnar 1996 microtemperatures of synthetic silicate melt inclusions obtained by heating thermometric data from such inclusions can be used in 10 0 c day increments in a tube furnace agreed with known directly to determine formation temperatures and presformation temperatures with no size dependence when measured sures without the necessity of invoking difficult to prove in a high temperature heating stage a heating rate of 1 c min assumptions or requiring an independent geobarometer produced homogenization temperatures that were about 10 c lower or geothermometer roedder bodnar 1980 than those obtained from the same inclusions using a heating rate roedder 1992 described specific types of magmatic of 3 c min although both heating rates produced homogenization immiscibility immiscibility being defined as the existence temperatures above the formation temperature a positive correlation of two or more non crystalline multi component sobetween inclusion size and th was observed for both heating rates lutions which differ in properties and composition at results confirm that microthermometric data from coeval silicate equilibrium including silicate melt silicate melt silicate melt and aqueous fluid inclusions can be used to accurately predict melt sulfide melt and silicate melt aqueous fluid in this p t formation conditions if data from the smallest melt inclusions study we have investigated the behavior of synthetic fluid are used or if the melt inclusions are homogenized using a slow inclusions trapped under conditions of silicate melt heating rate 1 c min aqueous fluid immiscibility in the haplogranite

microtextures of authigenic or rich feldspar in the upper jurassic humber group uk north sea detrital alkali feldspars currently at burial depths of 3 2 3 5 km in the upper jurassic humber group of the fulmar oilfield uk north sea are overgrown and have been partially replaced by authigenic or rich feldspar intracrystal microtextures suggest several different provenances for the detrital grains the overgrowths are uniformly non cathodoluminescent and have occasional celsian rich zones transmission electron microscopy shows that they are composed of a microporous mosaic of sub m to m sized sub grains associated with barite illite and pyrite the subgrains are somewhat rounded but have an approximate 110 adularia habit and display a faint modulated microtexture on the nanometre scale they have triclinic symmetry but the lattice angles depart only slightly from monoclinic symmetry these features are characteristic of k feldspar precipitated relatively rapidly and at low temperature authigenic or rich feldspar has also partially replaced microcline and perthitic albite within the detrital grains often at a suboptical scale although like diagenetic albitization replacement by k feldspar is probably a very common diagenetic reaction it has rarely been reported owing to difficulties in imaging the diagnostic textures with the scanning electron microscopy techniques used by most workers the permeability of the subgrain microtexture may significantly hinder the use of feldspar overgrowths for k ar and 4 0 ar 3 9 ar dating of diagenesis and the existence of suboptical replacive authigenic k feldspar within detrital grains may significantly modify the apparent ar ages of detrital grains similar subgrain microtextures in optically featureless quartz overgrowths are also illustrated

a preliminary investigation of chlorine xanes in silicate glasses 1 chlorine speciation in silicate melts affects volatile exsolution rheology and thermodynamic properties of the melt but is poorly known x ray absorption near edge structure xanes spectra have been used to investigate cl speciation in 26 silicate glasses and to test the hypothesis that cl in silicate melts is hosted by species that combine cl and network modifying cations such as ca and mg results indicate that cl in cmas cao mgo al2o3 sio2 plus na2o k2o or mno silicate glasses exists as a combination of ca clx and mg clx species or possibly as mixed ca mgy clx species the geometry and stoichiometry of the proposed species is unknown but there are similarities between spectra from ca bearing melts and the spectra of hydrated cacl2 2h2o suggesting that the ca clx species could have a salt like atomic arrangement and ionic bonding further investigations using xanes alternative spectroscopic techniques and forward modeling approaches are required to distinguish between these possibilities

constraints on dacite magma degassing and regime of the june 15 1991 climactic eruption of mount pinatubo philippines new data on melt and crystal inclusions in quartz abstract to better constrain processes that operated prior to and during the dacite magma eruption of mount pinatubo on june 15 1991 primary inclusions found in quartz phenocrysts of white dacite pumice have been studied by combining micro analytical techniques with homogenisation experiments inclusion morphology and composition before and after homogenisation experiments performed in gas pressure vessels at 760 780 c and 185 200 mpa distinguish two stages of magma degassing during the first stage which occurred prior to eruption the host quartz trapped a fluid saturated rhyolitic melt with an average of 78 6 0 7 wt sio2 12 4 0 5 wt al2o3 and 7 0 3 wt h2o and a water rich fluid microanalyses on the quartz hosted multiphase and crystal inclusions indicate that the dacite magma crystallised at 750 5 c an oxygen fugacity of 1 5 1 7 log fo2 units above the nno nickel nickel oxide buffer and a total pressure of 190 50 mpa corresponding to depths from 4 to 7 km in the second stage which corresponds to the magma eruption and decompression to 12 23 mpa volatile exsolution provoked decrepitation of unstable melt inclusions and the loss of initially high h2o contents from all 80 m glassy and hourglass inclusions to 1 7 0 3 wt h2o the exsolution of 5 wt h2o from the dacite magma might have occurred at depths of 300 700 m due to vent blockage caused by the sudden collapse of the conduit walls these conditions of the climactic eruption in combination with an extreme mass eruption rate reaching 2 109 kg s 1 could create oscillations between convecting and collapsing columns which explains the alternation of pyroclastic flow deposits with plinian pumice fall deposits reported in previous studies

eruption mechanisms and short duration of large rhyolitic lava flows of yellowstone abstract large volume effusive rhyolite lava flows are a common but poorly understood occurrence from silicic volcanic centers we integrate characterization of lava flow topographic morphology and petrographic textures and zoning of crystals with physical models of viscous fluid flow in order to interpret the eruption durations and discharge rates for the most recent effusive volcanic eruptions from yellowstone these large volume 10 70 km3 crystal poor rhyolite lavas erupted within the yellowstone caldera as 100 200 m thick flows and have a cumulative erupted volume of 650 km3 that is similar to less frequent caldera forming events but occur as individual eruptions spread over 100 ka most of this work is focused on the axisymmetric 124 ka 50 km3 summit lake flow we examined crystallinity major and trace element concentrations oxygen and hydrogen isotopic values and quartz morphology and zoning in samples from the center to margin of this flow water contents down to 0 1 wt and d values of 110 are low and require closed system degassing until near surface lithostatic pressure while major elements are consistent with water undersaturated pre eruptive storage and crystallization at 4 8 km depth we found some evidence for subtle km scale zoning within the lavas but describe significant microscopic scale compositional diversity including sharp boundaries between high ti cores and 200 m thick rims on quartz phenocrysts embayed quartz external morphology and rim growth may be the result of undercooling during coalescence of magma bodies during shallow transport between dikes and sills modeling the emplacement of the lava flow as a simple viscous fluid suggests that emplacement of rhyolite lava at 800 c occurred over 2 to 5 yrs with high discharge rates 100 m3 s such high magma discharge rates are accommodated through 6 km long fissures that allow for slower magma ascent velocities of 10 yr flow durations and significant cooling of the flow front that should result in a more complex compound flow morphology than observed higher temperatures require unrealistically wide 50 m dike widths to accommodate large discharge rates petrographic and isotopic evidence from crystals suggests recharge and merger of individual magma batches occurs on a similar timescale to the eruption duration and may directly cause overpressure and emplacement of these rhyolite lava flows from a shallow ephemeral magma chamber large volume rhyolitic lavas are able to erupt effusively through elongate fissures that utilize preexisting zones of crustal weaknesses such as ring fractures less common explosive eruptions at yellowstone may result when ascending magmas are forced through narrower conduits or when recharge rates are especially high the results of this study provide a unique top down constraint on effusive eruption rates make new interpretations of common petrographic textures and presents a comprehensive model for eruption control

40 ar 39 ar thermochronology using alkali feldspars real thermal history or mathematical mirage of microtexture the multiple diffusion domain mdd theory of ar loss based on the 40ar 39ar method has been used to obtain thermal histories over tens of millions of years in the range 500 c to near surface temperatures of alkali feldspars from slowly cooled geological environments and recovered in situ from sedimentary basins and geothermal systems it assumes that ar diffuses in nature over geological time from the same domains and by the same processes that control its diffusion during laboratory step heating experiments mathematically the model has many stringent requirements the domains must form at t above those being modelled and must remain unchanged during geological time and during step heating must not interact must occur in discrete size ranges sharing one simple geometrical shape contain no compositional gradients in 40k and release ar into an infinite reservoir we describe the nature of possible diffusion domains and the fast pathways for diffusion between them known to exist in alkali feldspars from direct electron microscopic observations and explore their time temperature evolution based on established phase behaviour both over geological time and during step heating strain controlled microtextures whose morphology is controlled by the minimization of coherency strain energy do not provide fast pathways for ar loss and behave as crystallographically complex but single domains for ar subregular dislocations may form over a range of t in some strain controlled intergrowths but in nature the majority form closed loops and do not provide pathways to the crystal surface deuteric microtextures cut across strain controlled microtextures and are composed of microporous subgrain and grain mosaics with many pathways and a wide spectrum of possible domain sizes and shapes the deuterically altered zones provide pathways for ar diffusion out of the crystal although some ar is retained in fluid inclusions all microtextures likely to define diffusion domains form below 500 c over a range of t and in slowly cooled rocks of times the most important involve fluid feldspar reactions which can reset ar and continue to surface t feldspars in geothermal systems and young sedimentary basins are subject to ongoing chemical and microtextural changes because the microtextures are metastable during step heating experiments in the t range over which most ar is released domains and pathways for rapid diffusion of ar between domains will be significantly modified during step heating particularly above 750 c when departures from a simple arrhenius diffusion law are most marked pre melting is likely to be an important cause of complexity in ar loss behaviour few if any of the requirements of the mdd model are met and we conclude that thermal histories cannot be obtained from alkali feldspars using this method

the effects of deformation induced microstructures on intragrain 40ar 39ar ages in potassium feldspar a combination of forescattered scanning electron microscopy and both ultraviolet uv laser and cycle stepped heating 40 ar 39 ar dating techniques have been applied to a single deformed grain of potassium feldspar to investigate the relationship between microstructure and 40 ar 39 ar isotope systematics the form and distribution of deformation induced microstructures have been mapped by using intragrain variations in lattice orientation these variations are related to thin section and regional structural data to provide a well constrained deformation history for the feldspar grain thirty uv laser 40 ar 39 ar analyses show age variations that correlate with the internal microstructure stepped heating data provide further evidence of this relationship our approach allows the recognition of different ar reservoirs within the deformed feldspar and identifies microstructural controls on ar migration such a relationship has important implications for the understanding and interpretation of 40 ar 39 ar geochronological data and the subsequent use of such data to constrain the temperature vs time evolution of deformed rocks

significance of high temperature fluids and melts in the grasberg porphyry copper gold deposit abstract a study of quartz sulfide veins from the grasberg cu au deposit has shown that the quartz crystals initially grew from the walls of the veins into open fractures cathodoluminescence cl imaging shows concentric growth zones in the larger crystals and changes in the orientation of the growth zones with occasional truncation of the zoning towards the centre of veins the crystals become smaller and irregularly shaped but exhibit cl banding parallel to vein walls which is normally associated with crack seal processes the vein quartz contains silicate and sulfide rich melt inclusions virtually water free salt melt inclusions and coexisting hypersaline and vapour rich inclusions late stage secondary aqueous inclusions are also present in some veins most fluid inclusions homogenised at temperatures below 620 c however hypersaline b2 inclusions had a very complex behaviour and exhibited partial homogenisation to salt melt and clear immiscible fluid at temperatures ranging from 820 c to 1300 c these inclusions contain the highest cu concentrations up to 6 3 wt suggesting they play a role in metal transport the contemporaneous trapping of the k feldspar rich melt inclusions hypersaline and vapour rich inclusions suggests a common source for these fluids and a process involving heterogeneous entrapment of immiscible silicate melt hypersaline fluid and vapour as previously proposed for other porphyry copper deposits furthermore the grasberg deposit is estimated to have formed at pressures below 400 bar which may explain the presence of salt melt inclusions as the vapour halite field of the h2o nacl system is dominant below 800 c at these pressures the unrealistically high temperatures reported herein may have resulted from entrapment of either immiscible silicate melt hypersaline fluid and vapour or cumulates of an evolving silicate melt saturated in k spar brine and vapour although these temperatures may not be directly useful these inclusions give important clues to metal enrichment processes these melt and fluid inclusions record cycles of transitory high temperature 700 c hydrofracturing melt and fluid release and vein formation in a cooler 500 600 c background host rock thermal regime high sulfur and cu contents of sulfide melt and hypersaline b2 inclusions are interpreted to be the fluid composition before the main sulfide precipitation event and therefore may be used as tracers of the magmatic body from which they exsolved at depth

cryptic microtextures and geological histories of k rich alkali feldspars revealed by charge contrast imaging charge contrast imaging in the scanning electron microscope can provide new insights into the scale and composition of alkali feldspar microtextures and such information helps considerably with the interpretation of their geological histories and results of argon isotope thermochronological analyses the effectiveness of this technique has been illustrated using potassium rich alkali feldspars from the dartmoor granite uk these feldspars contain strain controlled lamellar crypto and microperthites that are cross cut by strain free deuteric microperthites the constituent albite and orthoclase rich phases of both microperthite generations can be readily distinguished by atomic number contrast imaging the charge contrast results additionally show that sub micrometre sized albite platelets are commonplace between coarser exsolution lamellae and occur together to make cryptoperthites furthermore charge contrast imaging reveals that the orthoclase rich feldspar is an intergrowth of two phases one that is featureless with uniform contrast and another that occurs as cross cutting veins and grains with the 110 adularia habit transmission electron microscopy shows that the featureless feldspar is tweed orthoclase whereas the veins and euhedral grains are composed of irregular microcline that has formed from orthoclase by unzipping during deuteric or hydrothermal alteration the charge contrast imaging results are especially important in demonstrating that deuteric perthites are far more abundant in alkali feldspars than would be concluded from investigations using conventional microscopy techniques the unexpected presence of such a high volume of replacement products has significant implications for understanding the origins and geological histories of crustal rocks and the use of alkali feldspars in geo and thermochronology whilst the precise properties of feldspars that generate contrast remain unclear the similarity between charge contrast images and corresponding cathodoluminescence images of deuteric microperthites indicates that trace element chemistry and possibly also elastic strain within the crystal play a major role

earthworms produce granules of intricately zoned calcite earthworms of the family lumbricidae which includes many common species produce and secrete up to millimeter sized calcite granules and the intricate fine scale zoning of their constituent crystals is unique for a biomineral granule calcite is produced by crystallization of amorphous calcium carbonate acc that initially precipitates within the earthworm calciferous glands then forms protogranules by accretion on quartz grain cores crystallization of acc is mediated by migrating fluid films and is largely complete within 24 h of acc production and before granules leave the earthworm variations in the density of defects formed as a byproduct of trace element incorporation during calcite crystal growth have generated zoning that can be resolved by cathodoluminescence imaging at ultraviolet to blue wavelengths and using the novel technique of scanning electron microscope charge contrast imaging mapping of calcite crystal orientations by electron backscatter diffraction reveals an approximate radial fabric to the granules that reflects crystal growth from internal nucleation sites toward their margins the survival within granules of acc inclusions for months after they enter soils indicates that they crystallize only within the earthworm and in the presence of fluids containing biochemical catalysts the earthworm probably promotes crystallization of acc in order to prevent remobilization of the calcium carbonate by dissolution calcite granules vividly illustrate the role of transient precursors in biomineralization but the underlying question of why earthworms produce granules in volumes sufficient to have a measurable impact on soil carbon cycling remains to be answered

melt pockets in phenocrysts and decompression rates of silicic magmas before fragmentation 1 a new method is presented to estimate the decompression rate of silicic magma prior to fragmentation and is applicable to rates of 1 100 kpa s this method uses the remaining concentrations of h2o and co2 in bubble free cylindrical melt now glass pockets in phenocrysts that are connected to the surrounding bubbly melt these melt pockets are common in volcanic rocks during magma ascent bubbles grow in the surrounding melt and the concentrations of dissolved h2o and co2 decrease establishing a boundary condition of low volatile concentration at the outlet of the melt pocket in turn volatiles diffuse from the melt pocket into the surrounding bubbly magma and form a gradient that is time dependent the volatile concentration at the inner limit of the melt pocket likewise diminishes with time knowing the diffusivity and solubility of h2o and co2 permits the remaining h2o and co2 contents to be estimated for different decompression rates using diffusion equations we apply this approach to the measured h2o and co2 contents in quartz hosted melt pockets in pumice from the phreatomagmatic 26 5 ka oruanui eruption taupo new zealand a decompression rate of 1 7 kpa s 5 35 cm s was obtained for oruanui magma

feldspar microtextures and multistage thermal history of syenites from the coldwell complex ontario optical and tem transmission electron microscopy observations of perthites from augite syenites in the coldwell complex ontario reveal a complex set of microtextures that outline a multistage thermal history regular microtextures linear or braid texture straincontrolled coherent intergrowths show a progressive evolution from the margin of the intrusion inwards with lamellar spacings in the range 40 100 nm the textures evolve in a manner similar to those for the klokken intrusion and reflect differences in cooling rates and bulk composition superimposed upon the regular microtexture are 10 m scale compositional fluctuations which we call ripples the boundary relationships and bulk composition of ripples which are themselves ab rich and or rich linear coherent cryptoperthites suggest that they formed by coarsening during a phase of high temperature 530 c fluid feldspar interaction this was followed by a return to coherent exsolution in which fluid was not involved coarse irregular patch microperthite cross cuts all other microtextures these final deuteric intergrowths are believed to result from a further low temperature 380 c fluid feldspar interaction and are associated with subgrain formation and the presence of micropores the outermost syenite sample against a gabbro ring structure has distinctive modified microtextures indicating that the gabbro is at least in part a later intrusion our findings show that tem work on alkali feldspar microtextures can identify discrete thermal events in the cooling history of igneous plutons and illustrates the potential of such microtextures for establishing the relative ages of intrusive rocks

the complex hydrothermal history of granitic rocks multiple feldspar replacement reactions under subsolidus conditions recurring subsolidus re equilibration of granitic feldspars induced by fluid infiltration events provides a record of fluid rock interactions that affect large volumes of the earth s continental crust this has a direct bearing on the interpretation of the present day granitic rock mineralogy and geochemistry we examine palaeoproterozoic grey and red stained granitoids from the simpevarp and laxemar areas in se sweden particularly focusing on consecutive feldspar replacement reactions to provide an in depth understanding of subsolidus re equilibration of granitic rocks with hydrothermal fluids the apparently most unaltered grey granitoids contain highly porous oligoclase grains that enclose crystallographically continuous microcline relicts this texture suggests that the oligoclase is already secondary and may be a replacement product of original microcline oligoclase is progressively replaced by albite an9 along polysynthetic twinning and intragranular fractures the features of this replacement are characteristic of a dissolution reprecipitation mechanism finegrained mica sericite is closely associated with the albite porosity within micron sized pores observable with scanning electron microscopy as well as in nanopores imaged with transmission electron microscopy the reddening phenomenon in the vicinity of fractures is contemporaneously related to the k feldspathization of sericite which is restricted to the altered oligoclase submicron size hematite precipitation within orthoclase pores at the replacement front results in the red coloration the complex associations between the fluid feldspar reactions indicate that the replacement reactions may be due to sequential fluid infiltration events and that the granitoids have undergone extensive subsolidus re equilibration changing the original magmatic mineralogy therefore the effects of large scale re equilibrations of granitic rocks through hydrothermal convection systems should be more closely considered

the application of fallout radionuclides to determine the dominant erosion process in water supply catchments of subtropical south east queensland australia previous studies using fallout radionuclides 137cs and 210pbex to determine the relative contributions of surface soil and channel erosion including gullies and channel banks to stream sediments have used a relatively small number of composite samples 25 to characterize the source end members and concentrations in each of the source end members have through the use of means and standard errors been assumed to be normally distributed here we examine 137cs activity concentrations to determine the erosion processes supplying sediment in seven water supply catchments in south east queensland first we test some of the underlying assumptions in the method using concentrations of 137cs and 210pbex in composite samples collected from 109 surface soil sites and 39 channel bank sites paired composite samples each consisting of 20 subsamples from five sites are used to demonstrate that this sampling approach was sufficient to average out any local variations in surface soil 210pbex and 137cs concentrations across the 300 m2 sampled we derive probability distributions for 137cs and 210pbex concentrations in the group of samples from each of the end members and show that only the distribution of 210pbex in samples from surface soils is normally distributed we use the probability distributions for 137cs which provides the greatest discrimination between sources to show that the 137cs concentrations on the river sediment samples are consistent with channel erosion being the dominant source conservation works aimed at reducing the supply of sediments in these catchments should therefore focus on rehabilitation of the channel network and decreasing the runoff to the channel network these findings are consistent with other similar studies on tropical australian rivers copyright 2012 john wiley sons ltd

sulphide melt and aqueous fluid saturation in the pge au mineralisation of the skaergaard intrusion evidence from melt inclusions the skaergaard intrusion in east greenland hosts mineralisation of platinum group elements and gold that is characterised by a remarkably low amount of sulphides about 0 02 wt sulphide and a very high metal sulphur ratio here we present the first quantitative analyses of sulphur s copper cu lithium li and other trace elements from melt inclusions in plagioclase to trace their evolution in the magma and to constrain the formation of the mineralisation the concentration of these elements in the melt inclusions varies considerably within each sample the s content in melt inclusions ranges from 165 to 320 ppm in the lower part of the intrusion but increases to 349 512 ppm immediately below the mineralisation interval in the same interval the li content increases from 22 43 to 40 69 ppm and cu ranges from 118 to 1586 ppm with no systematic variations across the mineralisation the li content drops an order of magnitude to 4 7 ppm and s drops to 250 326 ppm we explain these compositional changes as reflecting the magmatic evolution as the result of fractional crystallisation below and coinciding aqueous fluid exsolution and sulphide saturation across the mineralisation normally the s content of basaltic magmas is much higher at sulphide saturation we propose that sulphide saturation is possible nevertheless mostly due to the high cu content and high cu fe in the evolved ferrobasaltic melt resulting in a lowering of the s concentration required for sulphide saturation the relationship between exsolutions of aqueous fluids and sulphides remains unknown

titanium as a cathodoluminescence activator in alkali feldspars albite patches in coarsely mesoperthitic alkali feldspars from the klokken syenite have oscillatory zoning seen at blue wavelengths using cathodoluminescence using a five spectrometer high resolution elemental mapping technique in an electron probe we show a close correspondence between cl emission intensity and ti present at levels up to 200 ppm albite patches were analyzed for major and 16 trace elements by laser ablation inductively coupled plasma mass spectrometry sem elemental maps acquired simultaneously with the cl showed that a similar zoning pattern is exhibited by ca but there is no correlation between cl intensity and ca concentration none of the trace elements analyzed correlate with ti we conclude that tetrahedral ti is the most likely activator of blue luminescence in these albitic alkali feldspars possibly because of a defect associated with al o ti bridges

evidence for a copper bearing fluid in magma erupted at the valley of ten thousand smokes alaska several lines of evidence point to the existence of a pre eruptive fluid phase in the magmas erupted in 1912 at the valley of ten thousand smokes alaska the discovery of rare cu rich bubbles in some melt inclusions is best explained by the random entrapment of a low density fluid phase within growing phenocrysts the h2o s and cl concentrations of the high silica rhyolite are also consistent with fluid saturation in the rhyolite water contents as determined by infrared spectroscopy on doubly polished melt inclusions cluster between 3 5 and 4 5 wt h2o without any apparent differences between magmas vented explosively and effusively these concentrations would be sufficient for h2o saturation at a pressure of 100 mpa though the presence of other volatiles such as co2 and so2 could allow saturation with respect to a fluid phase at higher pressures the s cu and cl contents of the phenocryst assemblages as determined by xrf analyses are too low to account for the decrease in the concentrations of s and cu in the melt and only modest increase in cl with differentiation therefore the behavior of these volatile elements was controlled either by eryptic fractionation if phenocryst phasese or more likely by partitioning into a coexisting fluid phase the presence of this low density phase apparently provided metals such as cu with a volatile phase into which they could partition the concentration of cu in this fluid reached tens to hundreds of times that of the coexisting silicate melt and may have been as rich as 0 05 wt cu the distribution of cu in the magma was also controlled by sulfides such as intermediate solid solution and pyrrhotite which cyrstallized directly from the silicate melt

the role of discontinuous magma inputs in felsic magma and ore generation for a long time granites have been considered as passive bodies ascending under intrinsic negative density and viscosity contrasts with their host rocks chemical variations within a granitic body resulted from in situ differentiation and crystal fractionation since the mid 1980s this global view has been significantly modified by i shifting melting from water saturated conditions to fluid absent reactions ii increasing the role played by the mantle during granite generation iii reassessing the rheology of partially molten rocks iv demonstrating stepwise segregation and ascent of magmas by analogue and numerical models v combining structural geophysical and geochemical studies to reveal the internal structures in granitic plutons it results that a granitic body is built up by a discontinuous accumulation of successive magma intrusions the discontinuous nature of magma emplacement has also significant consequences for its ability to generate ore the processes that lead to ore deposits are examined with a brief review of the magmatic and fluid phases that concentrate ore forming elements examples are taken from crustal derived granites and porphyry type deposits those are considered as the two end members of magmatic and hydrothermal ore deposits the source characteristics of the magma the emplacement mechanisms and magma mixing processes are the frame that controls the potential to carry base metals with the magma the distribution of elements is controlled by diffusion partition between minerals and melt solubility and redox conditions variations of those parameters are examined by considering their activation energy which controls the exponential dependence with temperature a characteristic length depending on the activation energy temperature variation and time is estimated for a characteristic time lag of 30 ka the intrusion of a magma into a magma chamber of similar composition hence temperature has few effects on diffusion partition coefficient and redox conditions because of a too low temperature contrast the intrusion of a mafic magma into a felsic one induces a variation of 300 c in both magmas the characteristic length of diffusion may vary by up to two orders of magnitude whereas the variation of partition coefficients is only one order of magnitude the redox conditions are about 2 5 log unit in the mafic magma but they can vary by 7 log units in the felsic magma hence a strong decrease in d values is observed in porphyry type deposits the effect is a removal of the elements with higher activation energy w sn zr from the mafic to the felsic magma deformation during the late stages of emplacement also controls ore formation

argon diffusion domains in k feldspar i microstructures in mh 10 samples of mh 10 a k feldspar thought to contain discrete diffusion domains for argon have been examined by light and tem microsopy to search for domain boudaries we examined both unheated k feldspar separates and samples heated in vacuum between 750 and 1150 c in order to characterize the initial microstructure as well as any changes resulting from laboratory heating the mh 10 rock shows almost no evidence of plastic deformation and the k feldspar does not possess networks of dislocations which might define a subgrain structure derived from external stresses three classes of substructure are present in the k feldspar but only the third appears to have been affected by laboratory heating 1 cross hatched extinction in light microscope is common but variably developed tem reveals almost no albite pericline twinning but tweed microstructure is ubiquitous 2 turbid zones occur with about 5 volume abundance micropores 1 to 2 m in diameter characterize these regions which often also contain bleds of albite up to 40 m indiameter tem shows these turbid zones to be very complex with intricate twin and tweed structures at the sub micron scale and numerous dislocation and strain features 3 albitic exsolution lamellae 1 m thick 20 m long and separated by 1 m are rarely seen in the light microscope but tem shows that 0 01 m thick by 0 2 1 m long lamellae separated by 0 1 to 0 5 m occur in about 20 of the sample these lamellae are disk shaped have a semi coherent or coherent relationship to the host k feldspar and seem to disappear upon heating to 750 c extensive diffusion studies have been conducted on hm 10 and the results analyzed in terms of distribution of sizes of diffusion domains the preferred result of the analyses was a distribution consisting of three distinct sizes the largest domain size identified in this way is approximately 50 to 100 m and this corresponds to blocks of k feldspar defined by the network of fractured turbid zones the smallest domain size inferred from diffusion analysis is 0 1 m which corresponds to the spacing between albite exsolution lamellae that may represent fast diffusion pathways alternatively the modulated argon distribution accompanying the lamellar variation in feldspar composition may result in an overestimation of the initial diffusion coefficients even though a promising agreement exists between domain analyses based upon diffusional and microstructural analyses at least two questions remain unanswered firstly no clear candidate has been identified for a domain of intermediate size secondly the diffusion analysis has been formulated with independent gas release from all domains whereas the observed structures are likely to be nested i e small domains exist inside bigger domains with the network of semi coherent lamellar boundaries having connectivity and permeability which can provide only a modest increase in argon diffusivity over bulk values

microstructural evolution during experimental albitization of k rich alkali feldspar crystals of k feldspar c2 m in contact with highly concentrated aqueous nacl solutions at 500 c and 200 mpa are pseudomorphically replaced by high albite c bar 1 as a result of an interface coupled dissolution reprecipitation process the reaction occurs at an extremely sharp reaction front 10 nm and involves the complete breakdown of the initial framework structure this results in the release of tetrahedrally incorporated elements such as fe3 and ti4 and a significant increase in si al disorder across the reaction interface the evolving microstructure is controlled by crystallographic relations between the phases this leads to highly anisotropic sawtooth shaped intergrowths of albite and initial k feldspar resulting in the least structural misfit between the two framework structures as a result the newly formed interfaces appear to be semicoherent and cracks across the reaction fronts even indicate elastic strain the reaction produces 2 distinctive albite types albite 1 and albite 2 both are polycrystalline with albite 2 showing significantly larger subgrain sizes this indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product the reaction also produces a highly porous rim however the porosity is not evenly distributed resulting in a porous albite 1 and a non porous albite 2 that mostly surrounds large euhedral pores despite the substantial volume fraction of porosity in albite 1 no significant 3d interconnectivity could be detected making the presence of a pervasive porosity unlikely however the result of coarsening is the continuous modification of the 3d porosity distribution this could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved

fluid evolution in the nepheline syenites of the ditrău alkaline massif transylvania romania abstract the ditr u alkaline massif is an intrusion into the bucovina nappe system that is part of the mesozoic crystalline zone located in transylvania romania in the eastern carpathians nepheline syenites are the most abundant rocks in the central and eastern part of the massif and represent the last major intrusion of the complex fluid inclusions in nepheline aegirine and albite were trapped at magmatic conditions on or below the h 2 o saturated nepheline syenite solidus at about 400 600 c and 2 5 5 kbars early nepheline and to a lesser extent albite were altered by highly saline fluids to produce cancrinite sodalite and analcime during this process cancrinite also trapped fluid inclusions the fluids in most cases can be modeled by the h 2 o nacl system with varying salinity however inclusions with more complex fluid composition containing k ca co 3 etc in addition to nacl are common raman spectroscopic analyses of daughter minerals confirm the presence of alkali carbonate fluids in some of the earliest inclusions in nepheline aegirine and albite during crystallization the melts exsolved a high salinity carbonate rich magmatic fluid that evolved to lower salinity as crystallization progressed phases that occur early in the paragenesis contain high salinity inclusions while late phases contain low salinity inclusions the salinity trend is consistent with experimental data for the partitioning of chlorine between silicic melt and exsolved aqueous fluid at about 2 0 kbars the activity of water a h 2 o in the melt increases during crystallization resulting in the formation of hydrous phases during late stage crystallization of the nepheline syenites

rapid crystallization of the animikie red ace pegmatite florence county northeastern wisconsin inclusion microthermometry and conductive cooling modeling we evaluated the crystallization regime of a zoned pegmatite dike and the degree of magma undercooling at the onset of crystallization by analyzing coeval fluid and melt inclusion assemblages the liquidus temperature of the pegmatite magma was 720 c based on re melting of crystallized melt inclusions in heating experiments the magma crystallized sequentially starting with a thin border zone which formed in less than one day at an average temperature of 480 c based on primary fluid inclusions meaning 240 c undercooling the primary inclusions from the outer zones were postdated by secondary inclusions trapped between 580 and 720 c representing fluid exsolved from hotter still crystallizing inner pegmatite units the huge temperature contrast between the pegmatite s inner and outer zones was simulated by conductive heat numerical modeling a 2 5 m wide dike emplaced in 220 c rocks cools entirely to 400 c in less than 50 days unidirectional and skeletal textures also indicate rapid disequilibrium crystallization

petrogenesis of syenite granite suites from the bryansky complex transbaikalia russia implications for the origin of a type granitoid magmas abstract two syenite granite suites metaluminous and peralkaline that form the bryansky complex in transbaikalia russia have been studied with the aim to constrain the existing models of a type granitoid magma generation the bryansky complex is a large intrusive body of about 1600 km2 emplaced in the central part of the mongolian transbaikalian granitoid belt which extends for more than 2000 km and is 200 300 km wide the belt comprises about 350 a type granitoid plutons and numerous volcanic fields u pb and rb sr isotope dating revealed that all the intrusive rocks of the complex and closely associated comendites were emplaced within a narrow time span 279 285 ma the isotope characteristics are rather similar for all main rock types the metaluminous suite has a 87sr 86sr t value of 0 7050 0 001 end t from 1 9 to 3 0 and the peralkaline suite has 87sr 86sr t 0 7053 0 0008 end t 2 1 and 2 4 comendites and trachyandesites have similar end t values from 2 2 to 3 5 but a slightly higher 87sr 86sr t value of 0 7062 0 0002 the systematic change in chemical and mineralogical composition from syenitic to granitic rocks in both suites and the similar isotopic ratios suggest that the granites were formed by fractional crystallization of the syenite magmas several lines of evidence suggest that metaluminous syenite is the parental magma for the whole bryansky complex study of melt inclusions in quartz phenocrysts from the peralkaline granite and in pyroxene from the nordmarkite indicates that fractional crystallization has resulted in significant f enrichment in the granitic magma up to 1 5 1 7 wt the syenite magmas crystallized at rather high temperature 940 c whereas the near liquidus temperature of the peralkaline granite was lower 760 790 c very high homogenization temperatures of the melt inclusions in quartz phenocrysts from comendites 1000 1100 c suggest that the alkali rich silicic magma formed at a depth of 50 60 km far exceeding the normal crust thickness the sr nd isotope data advocate the main role of mantle derived material in the source region from which the alkali rich syenitic and granitic magmas were produced

fluid inclusion evidence for immiscibility in magmatic differentiation abstract after a brief review of recent work on melt inclusions in diamond and in normal magmatic environments the nature of the fluid inclusion evidence for various stages of magmatic immiscibility is summarized during magmatic differentiation by crystal fractionation from originally low volatile content silicate melts yielding normal plutonic rocks through hydrous silicate melts yielding pegmatites to late stage water rich fluids yielding quartz veins and ore deposits the composition of the residual liquid changes drastically in some geologic environments this change in composition of the residual liquid may be continuous with no phase change in the fluid part of the system under most natural conditions however it is far more likely to have one or more stages in the evolution during which globules of a separate new immiscible fluid phase exsolve the term immiscibility is used here in its more general sense to refer to the existence at equilibrium of two or more non crystalline polycomponent solutions fluids differing in properties and generally in composition i believe that the great bulk of the magmatic inclusions that are being studied today have come about through the intervention of one or more such stages of immiscible fluid separation i e magmatic differentiation by fluid immiscibility examples include silicate melt dense co2 fluid silicate melt sulfide melt silicate melt silicate melt silicate melt low density vapor i e vesiculation and as presented in more detail in this paper various stages of silicate melt hydrous saline melt aqueous fluid co2 fluid immiscibility generally only parts of these stages are recorded by the trapping of fluid inclusions and the interpretation of the inclusion record is commonly ambiguous and difficult particularly that stage between hydrous silicate melts and the hydrous saline melts and aqueous solutions responsible for many ore deposits the ambiguity results mainly from problems of inclusion origin and nonrepresentative trapping within any given individual inclusion thus the probability of trapping of only one vs various amounts of two immiscible fluids or of trapping solid phases along with the fluid present severe difficulties in addition there is the almost universal superposition of various stages of trapping of fluids within any given sample these problems can only be approached by very careful petrography and analysis of optimum material combined with field data and experimental p v t x studies of pertinent systems completely unequivocal statements of the course of evolution of the fluids in such natural systems may never be possible

compositional and microtextural zoning in alkali feldspars from the shap granite and its geochemical implications alkali feldspar phenocrysts in the lower devonian shap granite are compositionally and microtexturally zoned most of each phenocryst has exsolved to form microperthite with an approximate bulk composition of or 72 ab 28 an but sub millimetre wide zones within the phenocrysts with an approximate bulk composition or 69 ab 30 an 1 have exsolved to cryptoperthite the sub optical scale of exsolution microtextures in the narrow an rich zones is due to ca al coupling which slows rates of interdiffusion during exsolution relative to an poor volumes of feldspar this form of coupled compositional microtextural zoning has not been described previously from or rich alkali feldspars using electron microscopy but we have seen other examples and predict that it is common cryptoperthite zones are of particular importance because they will have trace element and isotopic compositions least altered subsequent to growth in the magma of any microtextures in alkali feldspars and so will be the most rewarding targets for chemical analysis

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization