experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

a thermodynamic model for the plagioclase liquid hygrometer thermometer a new thermodynamic model for the plagioclase liquid exchange reaction between the albite naalsi 3 o 8 and anorthite caal 2 si 2 o 8 components is presented which can be used as a plagioclaseliquid hygrometer or thermometer the model incorporates calorimetric and volumetric data for the pure liquid and crystalline components which permits the effect of temperature and pressure on the exchange reaction to be calculated independently from the effect of composition this allows a more accurate assessment of the effect of melt composition including dissolved water concentration on the exchange reaction from plagioclase liquid equilibrium experiments activity composition relations for the plagioclase solid solution are taken from holland and powell 1992 the new hygrometer is calibrated on 71 plagioclase liquid experiments of which 45 are hydrous and 26 are anhydrous three filters were applied to the phase equilibrium data 1 crystallanities 30 2 pure h 2 o fluidsaturated and 3 compositional totals including h 2 o component of 97 101 for hydrous quenched glasses the final data set spans a wide range of liquid compositions 46 74 wt sio 2 plagioclase compositions an 93 an 37 temperatures 825 1230 c pressures 0 300 mpa and dissolved melt water concentrations 0 7 wt h 2 o the standard error of estimate see for the model is 0 32 wt h 2 o and all liquid compositions are fitted equally well when the model is used as a thermometer all measured temperatures are recovered equally well within 14 c on average the model is only recommended for applications that fall within the compositional bounds of the calibration data set i e metaluminous basalts through rhyolites in equilibrium with an 95 an 35 it is not yet calibrated for rhyolites crystallizing plagioclase more sodic than an 30 owing to an absence of phase equilibrium experiments on rhyolites that pass the required filters the new plagioclase liquid hygrometer thermometer is available as a visual basic program that runs on excel 2004

variations of natural gas carbon isotope type curves and their interpretation a case study natural gas is dominated by low molecular weight gaseous hydrocarbons c1 c5 whose genetic and diagenetic information is mainly obtained from stable carbon isotope compositions ordos basin is one of the largest natural gas provinces in china by means of examining the carbon isotope compositions of the ordos basin gases altered patterns of the isotopetype curves due to secondary cracking thermochemical sulphate reduction tsr and mixing of gases generated from different sources are recognized and discussed a typical carbon isotope type curve is nearly linear on the natural gas plot chung h m gormly j r squires r m 1988 origin of gaseous hydrocarbons in subsurface environments theoretical considerations of carbon isotope distribution chemical geology 71 97 103 our results show that the isotope type curve pattern of tsr and gas secondary cracking in coal is convex due to catalysis while the isotope type curve of gas secondary cracking in reservoirs is concave the natural gas of yulin suligemiao and wushenqi gas fields is coal derived gas both coal derived gas and mixed gas from oil and gas prone sources exist in the ordovician reservoirs of the jingbian gas field depending on the borehole locations in the ordovician carbonate reservoirs tsr is recorded but uncommon whereas secondary cracking in reservoirs is often observed 2007 elsevier ltd all rights reserved

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

dissolution kinetics of plagioclase in the melt of the system diopside albite anorthite and origin of dusty plagioclase in andesites the textures and kinetics of reaction between plagioclase and melts have been investigated experimentally and origin of dusty plagioclase in andesites has been discussed in the experiments plagioclase of different compositions an96 an61 an54 an23 and an22 surrounded by glasses of six different compositions in the system diopside albite anorthite was heated at temperatures ranging from 1 200 to 1 410 c for 30 min to 88 h textures were closely related to temperature and chemical compositions a crystal became smaller and rounded above the plagioclase liquidus temperature of the starting melt glass and remained its original euhedral shape below the liquidus whatever the temperature the crystal melt interface became rough and often more complicated sieve like texture composed of plagioclase melt mixture in the scale of a few m was developed from the surface of the crystal inward formation of mantled plagioclase if the crystal is less calcic than the plagioclase in equilibrium with the surrounding melt and the interface remained smooth if the crystal is more calcic than the equilibrium plagioclase from these results the following two types of dissolution have been recognized 1 a crystal simply dissolves in the melt which is undersaturated with respect to the phase simple dissolution and a crystal is partially dissolved to form mantled plagioclase by reaction between sodic plagioclase and calcic melt partial dissolution the amount of a crystal dissolved and reacted increased proportional to the square root of time this suggests that these processes are controlled by diffusion probably in the crystal mantled plagioclase produced in the experiments were very similar both texturally and chemically to some of the so called resorbed plagioclase in igneous rocks chemical compositions and textures of plagioclase phenocrysts in island arc andesites of magma mixing origin have been examined cores of clear and dusty plagioclase were clacic about an90 and sodic about an50 respectively this result indicates that dusty plagioclases were formed by the partial melting due to reaction between sodic plagioclase already precipitated in a dacitic magma and a melt of intermediate composition in a mixed magma during the magma mixing

magma storage and mixing conditions for the 1953 1974 eruptions of southwest trident volcano katmai national park alaska between 1953 and 1974 approximately 0 5 km3 of andesite and dacite erupted from a new vent on the southwest flank of trident volcano in katmai national park alaska forming an edifice now known as southwest or new trident field analytical and experimental evidence shows that the eruption commenced soon after mixing of dacite and andesite magmas at shallow crustal levels four lava flows 58 3 65 5 wt sio2 are the dominant products of the eruption these contain discrete andesitic enclaves 55 8 58 9 wt sio2 as well as micro and macro scale compositional banding tephra from the eruption spans the same compositional range as lava flows however andesite scoria 56 58 1 wt sio2 is more abundant relative to dacite tephra and is the explosively erupted counterpart to andesite enclaves fe ti oxide pairs from andesite scoria show a limited temperature range clustered around 1000 c temperatures from grains found in dacite lavas possess a wider range however cores from large 100 m magnetite and coexisting ilmenite give temperatures of 890 c taken to represent a pre mixing temperature for the dacite water contents from dacite phenocryst melt inclusions and phase equilibria experiments on the andesite imply that the two magmas last resided at a water pressure of 90 mpa and contained 3 5 wt h2o equivalent to 3 km depth if saturated unzoned pyroxene and sodic plagioclase in the dacite suggest that it likely underwent significant crystallization at this depth highly resorbed anorthitic plagioclase from the andesite suggests that it originated at greater depths and underwent relatively rapid ascent until it reached 3 km mixed with dacite and erupted diffusion profiles in phenocrysts suggest that mixing preceded eruption of earliest lava by approximately one month the lack of a compositional gap in the erupted rock suite indicates that thorough mixing of the andesite and dacite occurred quickly via disaggregation of enclaves phenocryst transfer from one magma to another and direct mixing of compositionally distinct melt phases

laser ablation icpms study of trace element partitioning between plagioclase and basaltic melts an experimental approach plagioclase melt partition coefficients d for 34 trace elements at natural concentration levels were determined experimentally in a natural morb composition at atmospheric pressure using thin pt wire loops experiments were carried out at three tempera tures 1 220 1 200 and 1 180 c and at three different oxygen fugacities fo2 iw qfm air in order to assess the effect of fo2 on the partitioning of elements with multiple valence fe eu cr run products were analyzed by laser ablation icp ms most trace element ds increase slightly as temperature decreases except for dzr dfe deu and dcr that vary systematically with fo2 applying the lattice strain model to our data suggests the presence of fe 2 entirely in the octahedral

basalt inherited microlites in silicic magmas evidence from mount pelee martinique french west indies during magma ascent in the volcanic conduit the decompression of a silicic melt may result in the crystallization of morphologically and compositionally specific crystals designated microlites hence microlites have been considered as probes of mechanisms and time scales of magma ascent some microlites however appear to be in strong thermodynamic disequilibrium with their surrounding melt we present here an experimental data set revealing that these microlites actually grew prior to ascent during mafic recharge of the magma chamber therefore these microlites have no genetic relation to decompression induced crystallization processes their presence may affect the rheological properties of the melt as well as crystal growth mechanisms and kinetics during magma ascent

dewatering induced subsidence during excavation in a shanghai soft deposit foundation dewatering has become a major cause of land subsidence in shanghai the burial depth of foundations in relation to geotechnical construction works is less than 75 m and the corresponding groundwater includes phreatic low pressure artesian and the first confined aquifers based on the geological and hydrogeological conditions beneath shanghai methods of dewatering may be divided into three modes and further five patterns according to the insertion depth of the dewatering retaining system the most common dewatering mode aims to reduce the water pressure in the confined aquifer by setting the dewatering wells inside the pit whilst the retaining walls are buried in the confined aquifer and partially cut off the confined aquifer layer to predict the settlement due to foundation dewatering numerical models are generally adopted which are similar to those used to predict land subsidence induced by regional groundwater withdrawal however since foundation dewatering is conducted along with the setting of retaining walls and foundation pit excavation which differs from regional groundwater withdrawal interactions between the retaining wall dewatering well the dewatering excavation and dewatering recharge are important factors affecting the analytical model since the grading of the shallow soil layers is different stratified settlement characteristics of the shallow soil strata and seepage erosion which results in additional deformation need to be given particular consideration

investigation of land subsidence with the combination of distributed fiber optic sensing techniques and microstructure analysis of soils abstract land subsidence is a global phenomenon caused by a variety of factors and there are still many challenges in land subsidence monitoring the results of an investigation of land subsidence using the combination of distributed fiber optic sensing dfos techniques and microstructure analysis of soil are here presented two dfos techniques brillouin optical time domain reflectometry botdr and fiber bragg grating fbg were developed in two boreholes namely gm03 and sz01 in su xi chang area china to monitor movement of strata crossed by the borehole and pore pressure in some specific strata scanning electron microscope sem and mercury intrusion porosimetry mip were employed to quantify and characterize the microstructures of undisturbed soils from the boreholes based on the botdr monitoring results the annual levels of land subsidence in gm03 and sz01 are 1 2 mm and 2 9 mm respectively and the movement history of strata were clearly tracked for both boreholes the main contributors to subsidence are two aquitards ad2 and ad3 that exist adjacent to the second aquifer af2 the results obtained by fbg based sensors indicate good agreement with botdr and it confirms that the deformation of aquifer is significantly controlled by pore pressure sem images were analyzed with pore particle and crack analysis system pcas three statistical parameters including average form factor ffavg fractal dimension df and area probability distribution index b were used to describe the geometric characteristics of pores it is found that larger average form factor larger fractal dimension and higher proportion of large pores in soil microstructures favors land subsidence mip results confirm that area probability distribution index can be used for the estimation of strata compression potential in land subsidence investigations

degassing of rhyolitic magma during ascent and emplacement the degassing history of a rhyolitic igneous system was documented from analyses of drill core samples through the extrusive and intrusive portions of obsidian dome and of surface samples of associated tephra the initial volatile composition of the inyo magma was estimated to be 4 0 wt h2o 500 ppm f 800 ppm cl and 80 ppm s retained volatile contents of glassy and crystalline samples reflect the effects of decompression and second boiling decompression is rapid and involves loss of water rich fluid until a close approach to lithostatic equilibrium is achieved second boiling is a slower process and produces a chlorine rich fluid some of which can be trapped during development of extremely fine crystallization textures nearly complete dewatering during decompression of surface extruded magma strongly undercools the system t 175 c suppressing crystallization and yielding glassy rhyolitic lava partial degassing of shallowly intruded magma permits pervasive crystallization even at high cooling rates the subvolcanic intrusive regime is the zone of maximum volatile release because second boiling is incomplete in extrusives and volatile bearing crystalline phases are stable in magma crystallized at greater depth

shale gas shale oil potential of upper visean black shales in the dniepr donets basin ukraine abstract upper visean rudov beds v 23 are considered as one of the main source rocks within the northwestern dniepr donets basin ddb average toc values within the srebnen bay northwestern ddb exceed 4 thickness up to 100 m average toc contents north and northwest of the srebnen bay up to 60 m are significantly lower 2 4 but still sufficient for unconventional hydrocarbon production whereas wells along the northeastern basin margin do not hold a shale oil gas potential 5 5 km although hydrogen index hi values of the most immature samples are 300 mghc gtoc basinal rudov beds host a potential to generate paraffinic naphthenic aromatic p n a low wax oil according to pyrolysis experiments a basinward maturity trend is visible but the maturity cut offs for shale oil gas production 0 8 rr 1 2 rr are reached at great depths 4 5 km 5 5 km only furthermore results of kinetic experiments do not argue for presence of type iis kerogen potentially triggering earlier hydrocarbon generation the mineralogy of rudov beds varies strongly in lateral and vertical directions limiting the predictability of mechanical behaviour samples from the siliceous basinal facies partly contain more than 60 of brittle minerals quartz feldspar carbonates etc suggesting a good fraccability this value is rarely reached by samples from the transitional and lagoonal calcareous and clayey facies the clay mineral fraction within many investigated rudov samples is dominated by kaolinite which is suggested to diminish the fraccability of shales apart from that expandable clay minerals ecm are present in samples from more than 5 km depth a result of low mesozoic heat flow

pre eruptive magmatic conditions at augustine volcano alaska 2006 evidence from amphibole geochemistry and textures variations in the geochemistry and texture of amphibole phenocrysts erupted from augustine volcano in 2006 provide new insights into preand syn eruptive magma storage and mixing amphiboles are rare but present in all magma compositions lowto high silica andesites from the 3 month long eruption unzoned magnesiohornblende in the highand low silica andesites exhibit limited compositional variability relatively high sio2 up to 49 7 wt and relatively lowal2o3 511 1wt intermediate silica andesites and quenched mafic enclaves contain amphiboles that vary in composition e g sio2 40 8 48 9 wt al2o3 6 52 15 2 wt and classification magnesiohornblende magnesiohastingsite tschermakite compositional variation in amphibole is primarily controlled by temperature dependent substitutions both highand low silica andesites represent remnant magmas that were stored in the shallow crust at 4 8 km depth remaining distinct owing to a complex subsurface plumbing system intermediate silica andesites and quenched mafic inclusions represent pre eruptive hybrids of resident highand low silica andesite magmas and an intruding basalt amphiboles in explosive phase high silica andesites are largely euhedral and unreacted consistent with the high magma flux rates from depth during this phase up to 13 800 m s phenocrysts from the other lithologies have reaction rims that range from 1 to41000 m in thickness reaction rim microlite sizes correlate with reaction rim thicknesses reaction rims550 m thick contain microlites 1 10 m in length whereas reaction rims480 m thick contain microlites 10 100 m in length differentiating between heatingand decompression induced amphibole reaction rim formation is problematic because of a lack of experimental constraints we attempt a new approach to assessing reaction rim formation based on a kinetic theory of crystal nucleation and growth in which the differences in reaction rim textures represent different degrees of amphibole disequilibrium large crystals and low number densities suggest relatively lower levels of disequilibrium resulting in growth dominated crystallization smaller crystals and larger number densities are indicative of higher nucleation rates and a high driving force

the petrologic history of the sanganguey volcanic field nayarit mexico comparisons in a suite of crystal rich and crystal poor lavas abstract to evaluate if intermediate magmas erupting from volcan sanganguey mexico and the surrounding volcanic field are formed by mixing of basalts and rhyolites or if they initially exist as intermediate liquids a detailed petrological study is presented for eight andesite and dacite magmas six of the samples erupted from the central edifice four andesites and two dacites are crystal rich 50 vol whereas the remaining two samples one andesite and one dacite erupted from monogenetic vents in the peripheral volcanic field and are crystal poor 5 vol despite the variation in crystallinity all samples are multiply saturated in five to seven mineral phases plagioclase orthopyroxene titanomagnetite ilmenite apatite clinopyroxene hornblende in all samples plagioclase spans a 30 40 mol an range in composition and orthopyroxene spans a range in mg of 5 10 pre eruptive temperatures and oxygen fugacites relative to the nno buffer range from 853 24 to 1085 16 c and 0 1 0 1 to 0 9 0 1 nno on the basis of fe ti two oxide thermometry application of the plagioclase liquid hygrometer to the samples reveals maximum h 2 o contents that range from 1 7 6 2 wt comparison with phase equilibrium experiments demonstrates that all plagioclase and orthopyroxene compositions in the crystal poor samples could have grown from their respective whole rock compositions comparison of crystal rich samples with phase equilibrium experiments reveals the presence of sodic xenocrysts which reflect resorption textures and an estimated excess plagioclase crystal cargo of 6 vol the excess plagioclase crystal cargo is not distinguishable from phenocrystic plagioclase based on composition or texture suggesting that they were also grown in intermediate melts and are therefore described as antecrystic no calcic plagioclase xenocrysts an 79 typical of hydrous arc basalts are observed thus it is likely that the excess plagioclase in the crystal rich samples were originally formed in intermediate magmas for the crystal poor samples we propose that the mechanism producing the complex phenocryst assemblages is degassing cooling as it may shift equilibrium plagioclase compositions kinetically inhibit crystal growth and increase melt viscosity leading to complex textures notably the hypothesis of degassing cooling induced crystallization requires that the intermediate melts initially exist as liquids prior to crystallization supporting the hypothesis that intermediate melts are generated in the deep crust and arrive in the upper crust as liquids for the crystal rich samples degassing cooling may also be the mechanism generating a portion of the compositional and textural variation in the mineral assemblages and some incorporation of antecrysts or xenocrysts must occur as evidenced by an excess plagioclase crystal cargo however we find no definitive evidence supporting the incorporation of crystals initially grown in basalts or rhyolites given the similarities in phase assemblage mineral compositions mineral textures and intensive variables between the crystal poor and rich samples we conclude that the melts arriving into the upper crust beneath volcan sanganguey and the surrounding peripheral volcanic field are intermediate in composition and are initially formed as liquids in the deep crust

pressure temperature and time indicators in mafic schist their application to reconstructing the polymetamorphic history of vermont mineral chemistry and overgrowth relationships in mafic schist from vermont are shown to be sensitive indicators of pressure temperature and relative time and to be good chronicles of the paleozoic history of this polymetamorphic terrane within the common assemblage amphibole chlorite epidote plagioclase quartz ti phase carbonate k mica fe 3 oxide electron microprobe analyses show that increasing metamorphic grade as defined by intercalated pelitic schist is recorded by an increase in the edenite glaucophane and tschermakite contents of amphibole in the anorthite content of plagioclase and in the substitution of al vi f 2 ti al iv for fe 2 mg mn si in biotite chlorite and muscovite with increasing pressure the glaucophane component of amphibole increases for medium pressure metamorphism the albite oligoclase gap is in the garnet zone where amphibole has between 1 2 and 1 8 formula proportion al iv and al vi fe 3 ti cr this gap is below the garnet isograd in low pressure mafic schist where al iv and al vi fe 3 ti cr in the amphibole are both less than 0 6 mineral growth periods observed are characterized by metamorphic grade and facies series and are assigned to two ordovician taconic and two devonian acadian events silurian devonian mafic schist in northeastern vermont records two periods of low pressure devonian metamorphism these events are expressed by medium pressure and low pressure metamorphism in the cambrian and ordovician rocks to the west and south in the pre silurian rocks high pressure and medium pressure metamorphism is assigned to the ordovician the observed high pressure metamorphism is confined to a 110 by 40 km area along the green mountain anticlinorium axis in north central vermont

aleutian tholeiitic and calc alkaline magma series i the mafic phenocrysts diagnostic mafic silicate assemblages in a continuous spectrum of aleutian volcanic rocks provide evidence for contrasts in magmatic processes in the aleutian arc crust tectonic segmentation of the arc exerts a primary control on the variable mixing fractional crystallization and possible assimilation undergone by the magmas end members of the continuum are termed calc alkaline ca and tholeiitic th ca volcanic rocks e g buldir and moffett volcanoes have low feo mgo ratios and contain compositionally diverse phenocryst populations indicating magma mixing their ni and cr rich magnesian olivine and clinopyroxene come from mantle derived mafic olivine basalts that have mixed with more fractionated magmas at mid to lower crustal levels immediately preceding eruption high al amphibole is associated with the mafic end member in contrast th lavas e g okmok and westdahl volcanoes have high feo mgo ratios and contain little evidence for mixing evolved lavas represent advanced stages of low pressure crystallization from a basaltic magma these lavas contain groundmass olivine fo 40 50 and lack ca poor pyroxene aleutian volcanic rocks with intermediate feo mgo ratios are termed transitional tholeiitic tth and calc alkaline tca tca magmas are common e g moffett adagdak great sitkin and kasatochi volcanoes and have resulted from mixing of high al basalt with more evolved magmas they contain amphibole high and low al or orthopyroxene or both and are similar to the japanese hypersthene series tth magmas e g okmok and westdahl contain orthopyroxene or pigeonite or both and show some indication of upper crustal mixing they are mineralogically similar to the japanese pigeonite series high al basalt lacks mg rich mafic phases and is a derivative magma produced by high pressure fractionation of an olivine tholeiite the low pressure mineral assemblage of high al basalt results from crystallization at higher crustal levels

relationship between rank and composition of aromatic hydrocarbons for coals of different origins distributions of di and tricyclic aromatics were determined for upper carboniferous to oligocene coals of various origins in addition to upper carboniferous ruhr coals wealden lower creataceous coals from north west germany lower cretaceous coals from western canada and tertiary coals from japan and colombia were studied the coals ranged from sub bituminous to anthracite in rank and showed vitrinite reflectance from 0 4 to 4 9 rm the previously established relationship between the rank of coal in terms of vitrinite reflectance and the distribution patterns of individual aromatic hydrocarbon isomers has been verified and refined it is demonstrated how the above relationships can be used to calculate vitrinite reflectance from the methylphenanthrene index mpi 1 the chemical rank levels of coals can now be defined in terms of the calculated vitrinite reflectance rc

a tale of two plutons petrographic and mineralogic constraints on the petrogenesis of the red lake and eagle peak plutons central sierra nevada california the red lake and eagle peak plutons are similar in age k ar 87 89 m y and range in composition from granodiorite to granite the red lake pluton is equigranular has a locally greisened marginal zone and shows only minor mineralogical and chemical zoning whereas the eagle peak pluton is mineralogically compositionally and texturally zoned with an equigranular margin and a porphyritic core modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar the formation of the prominent alkali feldspar megacrysts in the eagle peak core was promoted by plagioclase separation h 2 o undersaturation and a slower cooling rate relative to the red lake magma early loss of volatiles and a resulting increase in magma melt crystals viscosity inhibited crystal segregation within the red lake pluton and prevented the development of zoning late stage aplites associated with both plutons f

unraveling the presence of multiple plagioclase populations and identification of representative two dimensional sections using a statistical and numerical approach many plagioclase phenocrysts from volcanic and plutonic rocks display quite complex chemical and textural zoning patterns understanding the zoning patterns and variety of crystal populations holds clues to the processes and timescales that lead to the formation of the igneous rocks however in addition to a true natural complexity of the crystal population the large variety of plagioclase types can be partly artifacts of the use of two dimensional 2d petrographic thin sections and random cuts of three dimensional 3d plagioclase crystals thus the identification of the true number of plagioclase populations and the decision of which are representative crystal sections to be used for detailed trace element and isotope analysis is not obvious and tends to be subjective here we approach this problem with a series of numerical simulations and statistical analyses of a variety of plagioclase crystals zoned in 3d we analyze the effect of increasing complexity of zoning based on 2d chemical maps e g backscattered electron images bse we first analyze the random sections of single crystals and then study the effect of mixing of different crystal populations in the samples by quantifying the similarity of the compositional histogram of about a hundred 2d plagioclase sections it is possible to identify the so called reference and ideal sections that are representative of the real 3d crystal populations these section types allow filtering out the random cut effects and explain more than 90 of the plagioclase compositional data of a given sample our method allows the identification of the main crystal populations and representative crystals that can then be used for a more robust interpretation of magmatic processes and timescales

style and timing of salt tectonics in the dniepr donets basin ukraine implications for triggering and driving mechanisms of salt movement in sedimentary basins abstract the ukrainian dniepr donets basin ddb is a late palaeozoic intracratonic rift basin with sedimentary thicknesses up to 19 km displaying the effects of salt tectonics during its entire history of formation from late devonian rifting to the tertiary hundreds of concordant and discordant salt structures formed during this time it is demonstrated in this paper that the variety of styles of salt structure formation in the ddb provide important constraints on understanding the triggering and driving mechanisms of salt kinematics in sedimentary basins in general salt movement in the ddb began during the devonian syn rift phase of basin development and exerted controls on the later distribution of salt structures though the geometry of basement faults is not directly responsible for the regular spacing of salt structures post rift salt movements in the ddb occurred episodically episodes of salt movement were triggered by tectonic events specifically two extensional events during the carboniferous an extensional reactivation at the end of carboniferous earliest permian and a compressional event at the end of the cretaceous extensional events that induced salt movement were thick skinned i e basement involved in deformation rather than thin skinned most overburden deformation related to salt movements is ductile regardless of sedimentary bulk lithology and degree of diagenesis while the deformation of sedimentary cover in areas where salt is absent is mainly brittle this implies that the presence of salt changes the predominant mode of deformation of overlying sedimentary rocks episodes of salt movement lasted longer than the periods of active tectonics that initiated them buoyancy erosion and differential loading all played a role in driving halokinesis once tectonic forces had pushed the salt overburden system into disequilibrium among these factors erosion of overburden above growing salt structures acted as a key self renewing force for development of salt diapirs very high sedimentation rates related to high post rift tectonic subsidence rates particularly during the carboniferous were able to bury diapirs and to load salt bodies such that buoyancy erosion and differential loading forces eventually became insufficient to continue driving diapirism until the system was perturbed by an ensuing tectonic event in contrast some salt anticlines and diapirs developed continuously during the entire mesozoic because of much reduced tectonic subsidence rates and sedimentation supply during this time however a lower permian salt series and overhangs of buried diapirs played an important role in preventing overburden piercing and fracturing during the mesozoic and specifically during the late cretaceous salt diapirism phase

the influence of viscous and latent heating on crystal rich magma flow in a conduit the flow dynamics of crystal rich high viscosity magma is likely to be strongly influenced by viscous and latent heat release viscous heating is observed to play an important role in the dynamics of fluids with temperature dependent viscosities the growth of microlite crystals and the accompanying release of latent heat should play a similar role in raising fluid temperatures earlier models of viscous heating in magmas have shown the potential for unstable thermal runaway flow as described by a gruntfest number using an arrhenius temperature dependence for the viscosity but have not considered crystal growth or latent heating we present a theoretical model for magma flow in an axisymmetric conduit and consider both heating effects using finite element method techniques we consider a constant mass flux in a 1 d infinitesimal conduit segment with isothermal and adiabatic boundary conditions and newtonian and non newtonian magma flow properties we find that the growth of crystals acts to stabilize the flow field and make the magma less likely to experience a thermal runaway the additional heating influences crystal growth and can counteract supercooling from degassing induced crystallization and drive the residual melt composition back towards the liquidus temperature we illustrate the models with results generated using parameters appropriate for the andesite lava dome forming eruption at soufriere hills volcano montserrat these results emphasize the radial variability of the magma both viscous and latent heating effects are shown to be capable of playing a significant role in the eruption dynamics of soufriere hills volcano latent heating is a factor in the top two kilometres of the conduit and may be responsible for relatively short term days transients viscous heating is less restricted spatially but because thermal runaway requires periods of hundreds of days to be achieved the process is likely to be interrupted our models show that thermal evolution of the conduit walls could lead to an increase in the effective diameter of flow and an increase in flux at constant magma pressure

strontium and oxygen isotopic variations in mesozoic and tertiary plutons of central idaho regional variations in initial 87sr 86sr ratios r i of mesozoic plutons in central idaho locate the edge of precambrian continental crust at the boundary between the late paleozoic mesozoic accreted terranes and precambrian sialic crust in western idaho the r i values increase abruptly but continuously from less than 0 704 in the accreted terranes to greater than 0 708 across a narrow 5 to 15 km zone characterized by elongate lens shaped highly deformed plutons and schistose metasedimentary and metavolcanic units the chemical and petrologic character of the plutons changes concomitantly from ocean arc type diorite tonalite trondhjemite units to a weakly peraluminous calcic to calcalkalic tonalite granodiorite granite suite the idaho batholith plutons in both suites yield late cretaceous ages but permian through early cretaceous bodies are confined to the accreted terranes and early tertiary intrusions are restricted to areas underlain by precambrian crust the two major terranes were juxtaposed between 75 and 130 m y ago probably between 80 and 95 m y oxygen and strontium isotopic ratios and rb and sr concentrations of the plutonic rocks document a significant upper crustal contribution to the magmas that intrude precambrian crust magmas intruding the arc terranes were derived from the upper mantle subducted oceanic lithosphere and may have been modified by anatexis of earlier island arc volcanic and sedimentary units plutons near the edge of precambrian sialic crust represent simple mixtures of the precambrian wall rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0 7035 rb sr varies linearly with r i producing pseudoisochrons with apparent ages close to the age of the wall rocks measured 18o values of the wall rocks are less than those required for the assimilated end member by sr o covariation in the plutons however indicating that wall rock 18o was reduced significantly by exchange with circulating fluids metasedimentary rocks of the belt supergroup are similarly affected near the batholith documenting a systematic depletion in 18o as much as 50 km from the margin of the batholith plutons of the bitterroot lobe of the idaho batholith are remote from the accreted terranes and represent mixtures of precambrian wall rocks with melts dominated by continental lower crust r i 0 708 rather than mantle pseudoisochrons resulting from these data are actually mixing lines that yield apparent ages less than the true age of the wall rocks and meaningless ri assimilation fractional crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region

experimental constraints on magma ascent rate for the crater flat volcanic zone hawaiite phase equilibria and isothermal constant rate decompression experiments conducted on a hawaiite from the crater flat volcanic zone near yucca mountain nevada provide insight into the dynamics of magma transport for this magmatic province h 2 o contents up to 4 6 wt in melt inclusions the lack of plagioclase phenocrysts and the presence of amphibole all suggest that phenocrysts and melt in the crater flat volcanic zone were equilibrated at near water saturated conditions during ascent comparison of decompression induced crystallization of plagioclase microlites in experiments with natural tephra implies that magma ascent rates for the region are 0 04 m s if the magmas are water saturated estimates of minimum ascent rates increase if the magmas are water undersaturated a two stage process is needed to generate reaction rims found on natural amphibole suggesting that small batches of magma were briefly stored 3 5 days at depths as shallow as 800 m prior to eruption

contrast of metamorphic and structural histories across the work channel lineament coast plutonic complex british columbia a prominent topographic lineament along the western margin of the coast plutonic complex of southeast alaska and adjacent parts of british columbia separates terranes of contrasting metamorphic histories where it enters british columbia near prince rupert as the work channel lineament the western terrane preserves a regional medium high pressure metamorphic facies series increasing from chlorite grade in the west to kyanite muscovite migmatite near the lineament the metamorphic structural and age relations of the western terrane are consistent with a model of crustal thickening accompanied by westward transport of higher over lower grade metamorphic units during the jurassic this terrane was uplifted and cooled by cretaceous time 85 ma east of work channel lineament high temperature relatively low pressure assemblages are overprinted onto high pressure assemblages the low pressure metamorphic assemblages developed in the eocene during rapid uplift 2 mm yr of rocks which initially may have been metamorphosed at the same time and along the same pt gradient as those of the western terrane structures along the work channel lineament suggest vertical motion during uplift of the eastern terrane and after metamorphism of the western terrane because the metamorphic discontinuity across the lineament is 3 5 kbar at about 700 the lineament in the prince rupert area marks a major crustal break

basin evolution and coal geology of the donets basin ukraine russia an overview abstract the donets basin is a major coal mining district in eastern ukraine and adjacent portions of russia it comprises the donbas foldbelt which is the uplifted and compressionally deformed part of the pripyat dniepr donets pdd basin and the significantly less deformed western donbas region the pdd basin is a late devonian rift structure located within the east european craton thick coal measures formed during the post rift stage of the basin in serpukhovian to moscovian times when about 130 seams each with a thickness over 0 45 m have been deposited early serpukhovian coal accumulated in a relatively narrow shore zone it is rich in inertinite and liptinite and very low in ash bashkirian and moscovian coal have a significantly wider lateral extension and are generally rich in vitrinite bashkirian and moscovian coal seams usually have high ash yields 12 18 and high sulfur contents 2 5 3 5 but these data vary significantly depending on peat facies coal rank ranges from subbituminous to anthracite and is mainly controlled by the depth of the seams and the heat flow during maximum permian burial permo triassic thermal events locally overprinted the resulting coalification pattern coked coal occurs at the contact to presumed permian sills and dikes southwest of donetsk deep permian burial was followed by major permian and mesozoic uplift events the donets basin hosts proven reserves in the order of 60 gt at the exploitable depth the thickness of coal seams currently mined is in the range of 0 6 to 2 5 m production during 2009 was 68 7 mt in the ukrainian and 4 9 mt in the russian part of the basin coal mines in the donets basin are among the gassiest in the world the average methane content of coal is 14 7 m t but numerous seams have significantly higher gas content the high methane content presents a severe mine safety problem on the other hand it represents also a high potential for coal mine bed methane projects emissions of coal gas released by mining and related structurally induced underground hazards coal and gas outbursts are a major problem for safe and efficient coal exploitation in the basin

the microscopic characteristics of shanghai soft clay and its effect on soil body deformation and land subsidence compaction of the 40 m thick upper shanghai soft clay contributes to land subsidence in the shanghai region the upper clay a marine deposit continuously subsides at rate of 3mm years despite mitigation strategies designed to control land subsidence these strategies include the artificial injection of water into the subsurface data describing the particle size distribution pore size distribution microstructure mineralogical composition pore solution composition and cation exchange capacity indicate that the clay is semidispersed substable and susceptible to compaction an evaluation of soil body deformation caused by artificial injection of dilute water into a marine clay suggests that depression of the electrostatic double 1ayer in the marine clays may be responsible for the observed compaction and resulting subsidence a decrease in the swelling pressure of the marine clays might result from a reduction in the concentration of dissolved sodium in pore fluids when calcium bicarbonate water is injected thus ironically the strategy designed to mitigate land subsidence could be contributing to it increasing the concentration of dissolved salts in the injection water may prevent the collapse of the clay structure and halt or reverse the subsidence process the analysis results indicate the deformation of soft clay by consolidation is subject to its microscopic physical and chemical features rather than the fluctuation of groundwater level this continuous compression contributes as a major part to the land subsidence in shanghai

magma evolution and open system processes at shiveluch volcano insights from phenocryst zoning phenocryst zoning patterns are used to identify open system magmatic processes in the products of the 2001 eruption of shiveluch volcano kamchatka the lavas and pumices studied are hornblende plagioclase andesites with average pre eruptive temperatures of 840c and fo2 of 1 5 2 1 log units above nickel nickel oxide nno plagioclase zoning includes oscillatory and patchy zonation and sieve textures hornblendes are commonly unzoned but some show simple multiple or patchy zoning apatite microphenocrysts display normal and reverse zoning of sulphur the textural similarity of patchy hornblende and plagioclase together with ba sr systematics in patchy plagioclase indicate that the cores of these crystals were derived from cumulate material plagioclase liquid equilibria suggest that the patchy texture develops by resorption during h2o undersaturated decompression when h2o saturated crystallization recommences at lower pressure reduced ph2o results in lower xan in plagioclase causing more al rich hornblende to crystallize plagioclase cores with diffuse oscillatory zoning and unzoned hornblende crystals probably represent a population of crystals resident in the magma chamber for long periods of time in contrast oscillatory zoning in the rims of plagioclase phenocrysts may reflect eruption dynamics during decompression crystallization increasing fe al in oscillatory zoned rims suggests oxidation as a result of degassing of h2o during decompression a general lack of textural overlap between phenocryst types suggests that different phenocryst populations were spatially or temporally isolated during crystallization we present evidence that the host andesite has mixed with both more felsic and more mafic magmas olivine and orthopyroxene xenocrysts with reaction or overgrowth rims and strong normal zoning indicate mixing with basalt sieve textured plagioclase resulted from mixing of a more felsic magma with the host andesite the mineralogy and mineral compositions of a mafic andesite enclave are identical to those of the host magma which implies efficient thermal quenching and thus small volumes of intruding magma mixing of this magma with the host andesite results in phenocryst zoning because of differences in dissolved volatile contents we suggest that small magma pulses differentiated at depth and ascended intermittently into the growing magma chamber producing incremental variations in whole rock compositions

oil gas source rock correlations in the dniepr donets basin ukraine new insights into the petroleum system abstract the dniepr donets basin ddb hosts a multi source petroleum system with more than 200 oil and gas fields mainly in carboniferous clastic rocks main aim of the present study was to correlate accumulated hydrocarbons with the most important source rocks and to verify their potential to generate oil and gas therefore molecular and isotopic composition as well as biomarker data obtained from 12 oil and condensate samples and 48 source rock extracts was used together with usgs data for a geological interpretation of hydrocarbon charging history within the central ddb results point to a significant contribution from upper visean black shales highly oil prone as well as mixed oil and gas prone serpukhovian rocks and minor contribution from an additional tournaisian source devonian rocks an important hydrocarbon source within the pripyat trough have not been identified as a major source within the central ddb additional input from bashkirian to moscovian shebelinka field as well as tournaisian to lower visean rocks e g dovgal field with higher contents of terrestrial organic matter is indicated in the se and nw part respectively whereas oil source correlation contradicts major hydrocarbon migration in many cases for tournaisian to middle carboniferous reservoir horizons accumulations within upper carboniferous to permian reservoirs require vertical migration up to 4000 m along faults related to devonian salt domes 1 d thermal models indicate hydrocarbon generation during permo carboniferous time however generation in coal bearing middle carboniferous horizons in the se part of the basin may have occurred during the mesozoic

a process based model of pre eruption seismicity patterns and its use for eruption forecasting at dormant stratovolcanoes abstract using long term data sets the eruptive size timing and style can typically be successfully forecast for dormant volcanoes using current monitoring data and knowledge of precursory eruptive patterns the usaid usgs volcano disaster assistance program vdap utilizes seismic data over multiple eruption cycles and across volcano types to successfully forecast eruption size style and onset times as well as changes within ongoing eruptions from millions of seismic event observations we show that seismic data a proxy for rate dependent strain changes in the magmatic system combined with a process based conceptual geologic model enables eruption forecasting especially for stratovolcanoes dormant 20 years we show that this model often works for some open systems ones that sufficiently reseal to plug the conduit and also where a deep intrusion occurs after phreatic or phreatomagmatic explosions have begun this model is divided into four seismicity and geologic stages we describe each of the four stages of seismicity in detail and how they relate to the ongoing geologic process of that stage stage 1 deep intrusion and seismicity occurring at 10 to 40 km depth below the volcanic edifice stage 2 distal vt seismicity induced at distances from 2 to 30 km laterally from the summit by magma intruding into and inflating the upper crustal magma storage region stage 3 vent clearing seismicity associated with the initial vent creation and clearing phase of eruptive activity stage 4 repetitive event seismicity associated with the final ascent of magma from 2 km to the surface we present 36 examples of this seismic progression from 26 volcanoes we believe that this progression generally correlates with the magma flux and the eventual explosivity and is invaluable for forecasting eruptions

exsolution enthalpy of water from silicate liquids abstract because water dissolves in silicate melts as at least two species h2o molecules and oh groups the exsolution evaporation enthalpy of the h2o component from a silicate melt depends on species proportions which in turn depends on h2o pressure in this short communication a formal analysis of the exsolution enthalpy of water from a silicate melt is presented taking into account of the role of speciation the exsolution enthalpy from a rhyolitic melt at 850 c is found to increase with pressure at 100 bar and this increase is mostly caused by the speciation reaction sahagian and proussevitch sahagian d l proussevitch a a 1996 thermal effects of magma degassing j volcanol geotherm res 74 19 38 also found an increase of the exsolution enthalpy with pressure up to 20 bar for an albitic melt however the rate of increase determined from this work is an order of magnitude less than that determined by sahagian and proussevitch it is concluded that the strong pressure dependence of the exsolution enthalpy at low pressures they inferred is probably an artifact of their treatment the method presented here is general and can be applied to other multi species components

variable regimes in magma systems documented in plagioclase zoning patterns el misti stratovolcano and andahua monogenetic cones abstract magmas may experience closed or open system evolution during their ascent and evolution in the upper crust chemically closed system processes can involve heat transfer from underplating mafic magmas or decompression due to magma ascent on the other hand newly injected magmas can mix with the residing magma and hybridize plagioclase zonation patterns and electron microprobe major and trace element analysis constrain these contrasting scenarios for andesites from the 80 km3 el misti stratovolcano 5822 m and a field of relatively small monogenetic andahua scoria cones both in southern peru in particular fe concentration in plagioclase reveals valuable information within a magmatic system to explore the dominance of closed vs open system processes large and correlated anorthite fe contrasts at resorption zones identify compositional mixing related to recharge subhorizontal an fe variations record thermal or water induced effects el misti volcano a large but still relatively youthful stratovolcano is dominated during most of its approx 120 ka history by closed system effects during its evolution recharge and mixing mostly occurred cryptically as it is not recorded in drastic compositional changes in magmas or their phenocrysts a small volume erupted at el misti however is affected by strong open system behaviour as reflected in strongly correlated variations in an and fe contents of plagioclase compositions its crystal population is texturally and chemically very similar to lavas of the monogenetic cinder cones of the andahua volcanic field for the el misti magma reservoir resorption events caused by thermal effects or magma ascent are more frequent in comparison to the actual eruption frequencies many cycles of closed system evolution heat transfer and decompression therefore occurred without resulting in an eruption plagioclase zonations from lavas of the monogenetic andahua field indicate that any mafic batch that intruded the much smaller reservoirs immediately triggered an eruption by contrast a large magma system that feeds el misti volcano can easily accommodate a new batch without causing eruption

the 1996 eruption of karymsky volcano kamchatka historical record of basaltic replenishment of an andesite reservoir the simultaneous eruption in 1996 of andesite from karymsky volcano and of basalt from the academy nauk vent 6km away appears to provide a case of mafic recharge of an andesite reservoir for which the time of recharge is exactly known and direct samples of the recharging magma are available the explosive phreato magmatic eruption of basalt was terminated in less than 24h whereas andesite erupted continuously during the following 4 years detailed petrological study of volcanic ash bombs and lavas of karymsky andesite erupted during the period 1996 1999 provides evidence for basaltic replenishment at the beginning of the eruptive cycle as well as a record of compositional variations within the karymsky magma reservoir induced by basaltic recharge shortly after the beginning of the eruption the composition of the matrix glass of the karymsky tephra became more mafic and then within 2 months gradually returned to its original state and remained almost constant for the following 3 years further evidence for basaltic replenishment is provided by the presence of xenocrysts of basaltic origin in the andesite of karymsky a conspicuous portion of the plagioclase phenocrysts in the karymsky andesite has calcic cores with compositions and textures resembling those of plagioclases in the academy nauk basalt similarly the earlier portion of the andesite of the eruption sequence contains rare olivines which occur as resorbed cores in pyroxenes the composition of the olivine matches that of olivines in the academy nauk basalt the sequence of events appears to be 1 injection of basaltic magma into the karymsky chamber with immediate compensating expulsion of pre existing chamber magma from the karymsky central vent 2 direct mixing of basaltic and andesitic magmas with dispersal of phenocrysts associated with the basalt throughout the andesite so that newly mixed magma appeared at the vent within 2 months 3 re establishment of thermal and chemical equilibrium within the reservoir involving crystallization in the new hybrid liquid which returned the melt composition to normal formed rims on inherited calcic plagioclase and caused the resorption of dispersed olivine xenocrysts taken together these findings indicate that the karymsky magma reservoir was recharged by basalt at the onset of the 1996 eruptive cycle the rapidity and thoroughness of mixing of the basalt with the preexisting andesite probably reflects the modest contrast in temperature viscosity and density between the two magmas

stratigraphic distribution of macerals and biomarkers in the donets basin implications for paleoecology paleoclimatology and eustacy abstract more than one hundred and thirty coal seams and coaly layers occur in the donets basin donbas twenty eight 52 samples of them ranging in age from serpukhovian late mississipian to gzhelian late pennsylvanian 33 clastics and three limestones were studied in terms of maceral composition sulphur contents and biomarker distribution diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp hopanes are a measure of bacterial activity in the peat and steranes indicate the relative input of wood and algae stratigraphic trends in these parameters are discussed in relation to paleoenvironment climatic changes and eustacy a tropical climate prevailed in the donbas from serpukhovian to kasimovian times nevertheless periods with drier and wetter conditions can be distinguished based on maceral and biomarker data relatively dry conditions are observed during serpukhovian and vereian times whereas wetter climates with a maximum of coal deposition occurred during the late bashkirian most of the moscovian and the earliest kasimovian no economic coal seams are hosted in upper kasimovian and gzhelian deposits a result of a change to an arid climate our data also suggest climatic changes during sequences of different order for the second order third order and fourth order sequences relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract an intermediate climate during the transgressive systems tract and the maximum flooding and a wet climate during the highstand systems tract the results for high frequency sequences support the cecil s paleoclimatic model an intermediate paleoclimate during lst sandstone and levee siltstone a wet climate during early tst coal and a dry climate during late tst limestone mfs claystone and hst deltaic siltstone coals deposited during maximum flooding periods are more enriched in c27 steranes derived from algae and contain lower proportions of c29 steranes derived from the wood of higher plants

decompression experiments as an insight into ascent rates of silicic magmas an experimental study of h2o exsolution bubble growth and microlite crystallisation during ascent decompression of silicic magmas in the volcanic conduit is presented isobaric and decompression experiments were performed on a rhyolitic melt at 860 c nno 1 h2o saturation and pressures between 15 and 170 mpa two sets of decompression experiments were performed with decompression rates varying between 0 001 and 960 mpa min 1 from 150 to 50 mpa high pressure decompression and 2 from 50 to 15 mpa low pressure decompression the experiments highlight incomplete h2o exsolution for decompression rates 100 mpa min incomplete bubble growth for decompression rates 0 1 mpa min crystal nucleation time lags and incomplete chemical re equilibration to final pressures the observed crystallisation process i e growth versus nucleation depends on the decompression range indeed decompression induced crystallisation during high pressure decompressions is dominated by growth of existing crystals whereas during low pressure decompressions crystal nucleation is the dominating process this study provides a means to infer magma ascent rates in eruptions of silicic magmas through a combined petrologic and experimental approach

eruption dynamics inferred from microlite crystallization experiments application to plinian and dome forming eruptions of mt pelee martinique lesser antilles decompression experiments have been conducted to simulate syn eruptive crystallization in volcanic conduits to infer magma ascent rates and conditions during dome forming and plinian eruptions of silicic arc volcanoes the experiments were carried out on starting material with the composition of mt pele e rhyolitic interstitial melt 76 wt sio2 and consisted of three consecutive steps hydration decompression and annealing hydration saturated and undersaturated was performed at 8508c and 200mpa and was followed by isothermal decompression either linearly or stepwise to a final pressure pf of 30 or 5 10mpa decompression rates range from 0 003 to 25mpamin 1 decompression durations of 15 min to 40 days two samples were cooled by 258c and 508c during a 3 day step at pf subsequent to decompression the samples were held for up to 15 days at pf the experiments generated three types of crystals as products of pre syn and post decompression crystallization the experiments basically differ from previous studies in that they are specifically designed to discriminate crystal nucleation from growth and to evaluate the influence of pre decompression crystals on the decompression induced crystallization the effects of pre decompression crystals decompression rate undercooling pf and terminal cooling have been determined on plagioclase nucleation growth morphology and composition the main results suggest a positive correlation between decompression rate and the number density of plagioclase crystals nucleated at pf and highlight the effect of pre decompression crystals in further decompression induced crystallization the relations between the decompression conditions and the plagioclase characteristics have been used to infer mt pele e eruption dynamics suggesting that 1 plinian magmas ascend from the reservoir within less than 1h 1 10 m s 2 dome and block and ash flow magmas ascend within more than 2 5 days giving time for syn decompression crystallization around pre existent microlites 3 dome magmas provide evidence for long stagnation and cooling at low pressure and 4 surge magmas ascend without significant crystallization within less than 4 days and massively nucleate plagioclase at very low pressure the extent and violence of dome destruction may depend on the size or age of the dome with large or old domes favouring mildly explosive block and ash flows whereas small or young protodomes may generate highly explosive surges

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

thermal effects of magma degassing abstract the thermodynamics of diffusive bubble growth is dominated by latent heat of water exsolution vaporization and the work of gas expansion p dv work a numerical assessment of the effects of these on cooling of bubbly magma water in albite indicates that a magma can exsolve volatiles at equilibrium or with varying degrees of oversaturation depending on decompression history and degassing kinetics heat of water exsolution vaporization from magmatic melts has not previously been experimentally or analytically determined and we have evaluated it from others thermodynamic functions known for the albite water system heat of exsolution is small for pressures over 100 mpa but can reach 20 kj mole at 1 2 mpa 10 20 bar oversaturation degassing at 10 20 bar can cause cooling of albite by 8 k wt of exsolved water the thermal effect of equilibrium degassing depends on the starting pressure of decompression because it follows the solubility curve for a saturated melt at 100 mpa 4 wt water it can cool a magma at least by 35 k before it disrupts into spray as gas volume fraction exceeds 0 8 although we do not specifically consider the dynamics of bubble interactions in this study our results suggest that the dynamic cooling rate could be significant at the vent of an erupting magma column and under extreme eruption conditions can lead to glass formation around fast growing bubbles of magmatic foam this could cause fragmentation into fine ash by brittle failure conversely bubble wall cooling even before glass formation can serve to reduce diffusive volatile flux into bubbles decreasing the overall cooling of the system and lead to solidification of oversaturated magmas as occasionally observed in eruption products

pre eruptive reheating during magma mixing at quizapu volcano and the implications for the explosiveness of silicic arc volcanoes effusive explosive transitions are observed in volcanoes erupting water rich magmas that lack mineralogical evidence of degassing suggesting that gas loss occurred rapidly and ascent was fast despite the high viscosity of rhyodacitic to rhyolitic melts here we show that pre eruptive heating of water rich silicic magma by mixing with hot recharge in subvolcanic chambers controls the effusive explosive transition volcan quizapu chile emitted a 5 km3 mingled dacite andesite lava flow in a d 1846 1847 that was 130 c hotter than the 5 km3 of the same dacite that lead to a plinian eruption in a d 1932 we explain the suppression of explosive fragmentation in the 1846 1847 lavas by enhanced syneruptive magma degassing as a consequence of late reheating following mixing with andesite recharge higher magma temperatures led to the transitioning into effusive eruptive behavior by significantly accelerating volatile diffusion and lowering melt viscosity which facilitated bubble nucleation growth and coalescence while also inhibiting brittle fragmentation thus recharge by mafic magmas in subvolcanic magma chambers may reduce the risk of explosive eruptions in cases where heat can be efficiently transferred to cold volatile rich silicic magmas

magmatism and the geodynamics of rifting of the pripyat dnieper donets rift east european platform abstract the distribution of volcanism in the late devonian pripyat dnieper donets rift within the east european platform based upon the results of deep drilling indicates that pre existing basement structures and the major rift bounding faults played an important role in channelling the magmas towards the surface major and trace element and sr nd isotopic studies of the most primitive basic and ultrabasic magmas combined with estimates of the amount of extension 1 1 to 1 3 strongly suggest that magmatism was triggered by the upwelling of a thermally and geochemically anomalous mantle plume from the deep mantle during the late frasnian the peak of the magmatism occurred in the famennian coincident with the maximum amount of lithospheric extension magmatism rifting and domal basement uplife were contemporaneous at several localities within the eep suggesting that the thermal and geodynamic evolution of the platform could have been influenced by a cluster of mantle plumes during the late devonian

the effects of artificial recharge of groundwater on controlling land subsidence and its influence on groundwater quality and aquifer energy storage in shanghai china long term groundwater overpumping in shanghai has caused serious land subsidence to restore the declined piezometric groundwater levels and to decrease the land subsidence rate artificial recharge ar of groundwater into confined aquifers through injected wells has been proposed as an important measurement since the beginning of the 1960s in the case of shanghai recharge source is tap water whose chemical constituents and temperature are different from groundwater consequently the issues of groundwater quality change and thermal energy are worthy of discussion in this paper we discussed the influences of ar for controlling land subsidence on 1 groundwater level and land subsidence rate 2 groundwater quality 3 aquifer thermal energy storage the results based on the collected long term historical data in the study area show that ar not only is beneficial to groundwater level rising and land rebound but also provides cheap energy sources for industrial production the groundwater quality presented the trend of desalination and a general increase in sulfate iron and manganese contents organic and nitrogenous compounds after the tap water injection however the ar s influence on groundwater quality was limited with the radius 100 m for single well recharge and 1000 m for well groups recharge to control the development of the land subsidence within a safe limit in the study area the injected confined aquifers and the distribution of the ar wells need to be further adjusted due to the limitation of current ar

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

recharge in volcanic systems evidence from isotope profiles of phenocrysts strontium isotope ratios measured from core to rim across plagioclase feldspar crystals can be used to monitor changes in the isotope composition of the magma from which they grew in samples from three magma systems from convergent margin volcanoes sudden changes in major element composition petrographic features and strontium isotope composition were found to correspond to discrete magmatic events most likely repeated recharge of more mafic magma with lower ratios of strontium 87 to strontium 86 into a crustally contaminated magma

degassing at the soufriere hills volcano montserrat recorded in matrix glass compositions compositions of matrix glasses from the current eruption of soufriere hills volcano indicate that decompression driven crystallization results in 20 70 wt groundmass crystallization during eruption and variable degassing variations in crystallinity and volatile contents water and chlorine of matrix glasses are attributed to variations in extrusion rates and residence times in the lava dome residual water contents in pumice clasts 0 2 0 6 wt indicate minimum pressures of 1 1 3 7 mpa in 1997 vulcanian explosions residual water contents of 1 6 wt in a ballistic block ejected in sub plinian explosive activity on 17 september 1996 imply larger pressure drops similar to20 mpa variable residual water contents in dome samples are consistent with pressure variations of up to 9 mpa in the lava dome interior large variation in chlorine contents between lava blocks compared with explosion pumice clasts indicates that shallow level processes dominate degassing low melt chlorine contents of dome samples cannot be explained by open or closed system degassing especially when crystallization is taken into account instead heterogeneous chlorine leaching by circulation of groundwater vapour in the dome is proposed variable and elevated matrix glass deltad values can also be attributed to interaction with isotopically heavy surface waters hcl emission during the current eruption can be accounted for by cl loss from the melt consistent with the melt being undersaturated in chlorine

hydrocarbon habitat of the dniepr donets depression abstract basin inversion depending on its intensity can enhance the trapping potential of a basin or causes destruction of major hydrocarbon resources post inversion subsidence depending on its magnitude and the amount of syn inversion erosion can induce a second phase of hydrocarbon generation and the charging of inversion structures however this mechanism which contributed for instance to the hydrocarbon habitat of inverted basins in the southern north sea was not effective in the dniepr donets basin the dniepr donets depression forms part of the pripyat dniepr donets donbass karpinsky aulacogen that evolved as a devonian rift the post rift subsidence of this basin was interrupted during the late early permian when its southeastern parts were partly inverted further inversion pulses straddle the jurassic cretaceous and the cretaceous tertiary boundaries the dniepr donets depression hosts the most important hydrocarbon province of the ukraine at the beginning of 1994 ultimate recoverable reserves in established accumulations past production and remaining reserves amounted to about 170 10 6 t of oil and gas condensate and 980 10 9 m 3 gas the bulk of oil and gas accumulations is contained in carboniferous to early permian postrift series source rocks occur in devonian syn rift and carboniferous post rift series these attained maturity prior to basin inversion hydrocarbon accumulations are characterized by multiple reservoir seal pairs the mature syn rift devonian and the immature post inversion series contain only minor hydrocarbon accumulations oil and gas accumulations are mainly trapped in syn rift salt induced and inversion related structures the latter received their hydrocarbon charge mainly due to inversion induced destruction of pre existing accumulations and ensuing re migration of hydrocarbons

pre eruptive magma mixing and crystal transfer revealed by phenocryst and microlite compositions in basaltic andesite from the 2008 eruption of kasatochi island volcano the august 7 8 2008 eruption of kasatochi island volcano located in the central aleutians islands alaska produced abundant compositionally heterogeneous basaltic andesite 52 55 wt sio2 that has been interpreted to result from pre eruptive magma mixing the basaltic andesite contains two populations of plagioclase phenocrysts the first volumetrically dominant population consists of oscillatory zoned phenocrysts with an overall normal zonation trend toward comparatively sodic rims an55 65 interrupted by dissolution features and spikes in calcium content up to an85 the second population consists of phenocrysts with highly calcic compositions an90 these phenocrysts contain sharp decreases in calcium content close to their rims reaching as low as an60 but are otherwise texturally and compositionally homogeneous groundmass plagioclase microlites are generally much more calcic than rims of the first phenocryst population with more than 50 of measured microlites containing an80 major minor and trace element concentrations of plagioclase microlites and phenocrysts indicate that oscillatory zoned phenocrysts derived from cooler 800 950 c more silicic mixing magma while unzoned calcic phenocrysts were associated with hotter 900 1050 c mafic magma the mixing of these magmas just prior to eruption followed by decompression during the eruption itself created high effective undercoolings in the mafic end member and lead to the nucleation of high an microlites mgo and feo concentrations of plagioclase microlites and high an phenocryst rims up to 0 4 and 1 3 wt respectively provide further evidence for high mixing and eruption induced effective undercoolings

numerical modelling of the thermal evolution of the northwestern dniepr donets basin ukraine abstract the dniepr donets basin ddb is a late devonian rift structure located within the east european craton numerical heat flow models for 13 wells calibrated with new maturity data were used to evaluate temporal and lateral heat flow variations in the northwestern part of the basin the numerical models suggest that heat flow was relatively high during late carboniferous and or permian times the relatively high heat flow is probably related to an early permian re activation of tectonic activity reconstructed early permian heat flow values along the axial zone of the rift are about 60 mw m2 and increase to 90 mw m2 along the northern basin margin these values are higher than those expected from tectonic models considering a single late devonian rifting phase the calibration data are not sensitive to variations in the devonian carboniferous heat flow therefore the models do not allow deciding whether heat flows remained high after the devonian rifting or whether the reconstructed permian heat flows represent a separate heating event analysis of the vitrinite reflectance data suggest that the northeastern dniepr donets basin is characterised by a low mesozoic heat flow 30 35 mw m2 whereas the present day heat flow is about 45 mw m2

hornblende dehydration reactions during magma ascent at soufriere hills volcano montserrat hornblende phenocrysts in recent andesites of the soufriere hills volcano display reaction rims of microcrystalline plagioclase pyroxene fe oxides and interstitial glass formed by decompression during magma ascent mass balance calculations give the following reactions with mineral proportions in agreement with modal abundances begin aligned 100 0 text hbl to 49 8 text cpx 27 6 text opx 18 2 text plag 4 5 text ti mag 100 0 text hbl to 53 9 text cpx 24 4 text opx 18 1 text plag 1 9 text ilm 1 7 text mag end aligned these reactions require an open chemical system with exchange of selected components with surrounding melt volatiles tio2 and alkalis are expelled and sio2 and feot are consumed matrix glasses fall into two compositional groups glasses in pumice are relatively rich in cao and poor in k2o and na2o compared to glasses in dome samples the former glasses formed by moderate amounts of groundmass crystallisation of plagioclase associated with rapid magma ascent in explosive eruptions the later glasses evolved in response to hornblende breakdown groundmass crystallisation and mixing of melts from different levels during slow magma ascent and extended residence time in the dome interstitial glass compositions in reaction rims reflect the compositions of the surrounding matrix glasses but show variable compositional differences mostly consistent with the proposed open system reactions

a complex magma mixing origin for rocks erupted in 1915 lassen peak california the eruption of lassen peak in may 1915 produced four volcanic introduction rock types within 3 days and in the following order 1 hybrid magma mixing is an important process among interblack dacite lava containing 2 undercooled andesitic inclusions mediate magmas in volcanic arcs e g turner 3 compositionally banded pumice with dark andesite and light campbell 1986 philpotts 1990 and references therein dacite bands and 4 unbanded light dacite all types represent laboratory studies of synthetic analogs of silicate magma stages of a complex mixing process between basaltic andesite systems and mathematical modeling of mixing viscous and dacite that was interrupted by the eruption they contain liquids have suggested a range of possible mixing mechdisequilibrium phenocryst assemblages characterized by the coanisms e g cashman bergantz 1991 however use existence of magnesian olivine and quartz and by reacted and of these results to interpret magmatic systems is limited unreacted phenocrysts derived from the dacite the petrography and by the applicability of synthetic analogs to magmatic crystal chemistry of the phenocrysts and the variation in rock conditions and by the imprecise knowledge of the effective compositions indicate that basaltic andesite intruded dacite magma viscosity of silicate liquid crystal mixtures at magmatic and partially hybridized with it phenocrysts from the dacite magma temperatures and pressures if magmas mix incompletely were reacted cooling crystallization and vesiculation of the hybrid i e mingle features such as compositional banding or andesite magma converted it to a layer of mafic foam the decreased undercooled inclusions are usually apparent but if they density of the andesite magma destabilized and disrupted the foam mix completely mineralogical disequilibrium may be the blobs of foam rose into and were further cooled by the overlying dacite magma forming the andesitic inclusions disaggregation of only direct evidence for a mixing origin andesitic inclusions in the host dacite produced the black dacite and if the thermal and compositional contrasts between light dacite magmas formation of foam was a dynamic process two magmas are great and the ratio of silicic to mafic removal of foam propagated the foam layer downward into the magma is large there is little interaction between them hybrid andesite magma eventually the thermal and compositional and the mafic magma is undercooled e g bacon 1986 contrasts between the hybrid andesite and black dacite magmas were many undercooled inclusions contain reacted phereduced then they mixed directly forming the dark andesite magma nocrysts inherited from their host silicic magma heiken about 40 50 andesitic inclusions were disaggregated into the eichelberger 1980 and bacon 1986 pointed out host dacite to produce the hybrid black dacite thus disaggregation that undercooled inclusions are typically formed from of inclusions into small fragments and individual crystals can be hybrid magmas in general the formation of undercooled an efficient magma mixing process disaggregation of undercooled inclusions retards further mixing sakuyama 1984 inclusions carrying reacted host magma phenocrysts produces cothompson dungan 1985 sparks marshall 1986 existing reacted and unreacted phenocryst populations koyaguchi blake 1991 however fragmentation and or disaggregation of undercooled inclusions plays an important role in hybridization in some magma systems thompson dungan 1985 coulon et al 1986 clynne christiansen 1987 clynne 1989 linneman myers

natural and artificial maturation of biological markers in a toarcian shale from northern germany steroid and terpenoid biological marker evolution was studied in a maturity sequence of lias toarcian shales and adjacent strata from three shallow boreholes in the hils syncline northern germany excellent facies control within the study area ensures the comparability of the organic matter type among the stratigraphically equivalent samples of the natural maturation series in the early hydrocarbon generation stage 0 68 r0 a strong facies dependence of some sterane and hopane isomerisation values was found within the same borehole at only a few metres depth difference the extent of sterane isomerisation at c 14 and c 17 was close to 80 in the toarcian shale and between about 55 and 65 in the adjacent dogger and lias sediments similar differences were observed for the 17 h hopane moretane and 22 29 30 trisnor 18 h neohopane 22 29 30 trisnor 17 h hopane ratios whereas the 20s 20s 20r sterane isomerisation ratio did not show this difference the observed differences mostly disappear by the end of the main oil generation phase 0 88 ro where several reactions appear to have reached completion hydrous pyrolysis experiments by variations of time and temperature were used to simulate the natural evolution of the biological markers results for sterane isomerisation in the high temperature range were compared to those published by mackenzie and mckenzie geol mag 120 417 470 1983 for natural sediments kinetic data derived for this reaction from the hydrous pyrolysis results alone or from the combination of hydrous pyrolysis and natural data sets differ markedly from those determined by mackenzie and mckenzie 1983 the hydrous pyrolysis data alone yield an activation energy for sterane isomerisation at c 20 of 131 kj mol the combined data of 170 kj mol the frequency factors are in the 105 108 s 1 range the significance of the data is discussed in detail

land subsidence and pore structure of soils caused by the high rise building group through centrifuge model test abstract in the urban area of shanghai the dewatering of groundwater was controlled strictly and the engineering environment effect of the high rise building group became to be the main cause of land subsidence in shanghai based on the high rise building group in the soft soil area in shanghai the mechanism of land subsidence was studied in this paper by the centrifuge model test the central area of the building group has larger subsidence and the subsidence superimposition effect is obvious it can exceed the allowance and cause land subsidence hazard the land subsidence affected by the different building distances was also studied for smaller building distances the subsidence superimposition effect is more obvious the engineering characteristics of soils are controlled by the state of pore structure of soils to a great extent the parameter of specific subsidence was put forward as a tie to analyze the relationship between land subsidence and pore structure of soils the pore structure of each soil layer was studied by the mercury intrusion porosimetry test mip and the pore distribution of each soil layer was studied by the fractal theory there are mainly macropores in silty clay of layer no 4 clayey soil of layer no 8 silty sand of layer no 7 and layer no 9 in shanghai the ink bottle effect exists in the intrusion stage in the mip test there are four different fractal dimensions in silty clay of layer no 4 and clayey soil of layer no 8 and three different fractal dimensions in silty sand of layer no 7 and layer no 9

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

crustal growth in south eastern australia evidence from lower crustal eclogitic and granulitic xenoliths mafic and ultramafic xenoliths in a basaltic cone at the anakies in south eastern australia are geochemically equivalent to continental basaltic magmas and cumulates the xenolith microstructures range from recognizably meta igneous for intrusive rocks to granoblastic for garnet pyroxenites contact relationships between different rock types within some xenoliths suggest a complex petrogenesis of multiple intrusive metamorphic and metasomatic events at the crust mantle boundary during the evolution of south eastern australia unaltered spinel lher zolite typical of the uppermost eastern australian mantle is interleaved with or veined by the metamorphosed intrusive rocks of basaltic composition geothermobarometry calculations by a variety of methods show a concordance of equilibration temperatures ranging from 880 c to 980 c and pressures of 12 to 18 kbar 1200 1800 mpa these physical conditions span the gabbro to granulite to eclogite transition boundaries the water vapour pressure during equilibration is estimated to be about 0 5 of the load pressure using amphibole breakdown data large fluid inclusions of pure co2 are abundant in the mineral phases in the xenoliths and it is suggested that flux of co2 from the mantle has been an important heat source and fluid medium during metamorphism of the mafic and ultramafic protoliths at the lower crust upper mantle boundary the calculated pressures and temperatures suggest that the south eastern australian crust has sustained a high geothermal gradient in addition the nature of the mineral assemblages and the contact relationships of granulitic rock with spinel lherzolite characteristic of mantle material suggest that the moho is not a discrete feature in this region but is represented by a transition zone approximately 20 km thick these inferences are in agreement with geophysical data including seismic heat flow and electrical resistivity data determined for south eastern australia underplating at the crust mantle boundary by continental basaltic magmas may be an important alternative or additional mechanism to the conventional andesite model for crustal accretion

microlite transfer by disaggregation of mafic inclusions following magma mixing at soufriere hills volcano montserrat the soufriere hills volcano on montserrat has for the past 12 years been erupting andesite with basaltic to basaltic andesite inclusions the andesite contains a wide variety of phenocryst textures and strongly zoned microlites analysis of minor elements in both phenocrysts and microlites allows us to put detailed constraints on their origins compositions of clinopyroxene from overgrowth rims on quartz and orthopyroxene and coarse grained breakdown rims on hornblende are identical to those from the mafic inclusions indicating that these rims form during interaction with mafic magma in contrast resorbed quartz and reversely zoned orthopyroxenes form during heating microlites of plagioclase and orthopyroxene are chemically distinct from the phenocrysts being enriched in fe and mg and al and ca respectively however microlites of plagioclase orthopyroxene and clinopyroxene are indistinguishable from the compositions of these phases in the mafic inclusions we infer that the inclusions disaggregated under conditions of high shear stress during ascent in the conduit transferring mafic material into the andesite groundmass the mafic component of the system is therefore greater than previously thought the presence of mafic derived microlites in the andesite groundmass also means that care must be taken when using this as a starting material for phase equilibrium experiments

factors controlling shale microstructure and porosity a case study on upper visean rudov beds from the ukrainian dneiper donets basin the present contribution aims for a characterization of microstructure and pore space distribution of upper visean rudov beds considered the main source rock for conventional oil deposits in the ukrainian dneiper donets basin and a prospect for unconventional hydrocarbon production in recent years broad ion beam scanning electron microscopy sem mapping revealed a remarkably heterogeneous microstructure controlled by diagenetic precipitates fe mg carbonates albite formation of these precipitates is likely triggered by organic matter decomposition and represents an important influencing factor for overall porosity and permeability furthermore shale diagenesis also influences mechanical properties as suggested by nanoindentation tests the sem visible organic matter porosity is restricted to solid bitumen although pores less than 2 3 nm in vitrinites of overmature samples are indicated by focused ion beam sem results they cannot be resolved clearly by this method pore generation in solid bitumen that likely formed in situ in primary amorphous organic matter already starts at the early oil window in samples from the basinal oil prone organofacies whereas most porous solid bitumen at peak oil maturity was interpreted as relicts of primary oil migration representing an earlier oil phase that predominantly accumulated in quartz rich layers and became nanoporous during secondary cracking in the terrestrially dominated transitional to marginal organofacies pore generation in pyrobitumen resulting from gas generation occurs significantly later and is less intense formation of authigenic clay and carbonate minerals within pyrobitumen is likely related to organic acids formed during bitumen decomposition and implies the presence of an aqueous phase even in pores that are apparently filled exclusively with solid bitumen

the diversification of paleozoic fire systems and fluctuations in atmospheric oxygen concentration by comparing silurian through end permian 250 million years myr charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long term variations in fire occurrence and fire system diversification are related to fluctuations in late paleozoic atmospheric oxygen concentration charcoal a proxy for fire occurs in the fossil record from the late silurian 420 myr to the present its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13 to 35 the fire window herein we observe that as predicted atmospheric oxygen levels rise from 13 in the late devonian to 30 in the late permian so too fires progressively occur in an increasing diversity of ecosystems sequentially data of note include the occurrence of charcoal in the late silurian early devonian indicating the burning of a diminutive dominantly rhyniophytoid vegetation an apparent paucity of charcoal in the middle to late devonian that coincides with a predicted atmospheric oxygen low and the subsequent diversification of fire systems throughout the remainder of the late paleozoic first fires become widespread during the early mississippian they then become commonplace in mire systems in the middle mississippian in the pennsylvanian they are first recorded in upland settings and finally based on coal petrology become extremely important in many permian mire settings these trends conform well to changes in atmospheric oxygen concentration as predicted by modeling and indicate oxygen levels are a significant control on long term fire occurrence

partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity implications for archean and lunar anorthosites abstract experimental studies were undertaken to determine d for feot between plagioclase and melt as a function of oxygen fugacity for a basaltic composition that occurs as matrices for plagioclase megacrysts that are similar to those in calcic anorthosites at liquidus conditions the d for feot between calcic plagioclase and tholeiitic basalt changes very little from 0 030 to 0 044 between the very low o 2 of the iron wustite buffer and that of the quartz fayalite magnetite qfm buffer at fugacities above qfm the value for d increases rapidly to 0 14 at the magnetite hematite buffer and 0 36 in air the increase in d results from the fact that nearly all of the fe is in the fe2 state at o 2 below qfm and the fe 3 fe 2 ratio in the melt increases rapidly above qfm causing more fe to enter the plagioclase which accepts fe3 more readily than fe2 there is essentially no change in values of d over cooling rates that vary by two orders of magnitude the d for feot of 0 030 at iron wustite is in good agreement with earlier studies at low o2 terrestrial calcic plagioclase matrix pairs display ds of about 0 043 in excellent agreement with the experimental value of 0 044 at qfm which is the accepted fugacity for terrestrial tholeiitic basalts application of the ds for feot and other components to terrestrial calcic anorthosites indicates that the anorthosites were in equilibrium with nearby coeval tholeiitic basalts at qfm as was expected lunar anorthosites however have anomalously low contents of feot as well as mgo and would be in equilibrium with melts that are several times lower in these components than expected the low values of feot and mgo in the plagioclase of lunar anorthosites are a result of subsolidus reequilibration with pyroxene olivine and other fe mg bearing phases during high temperature metamorphism as is the case in terrestrial anorthosites that have undergone granulite grade metamorphism the ds for k2o mgo and tio2 were determined as 0 21 0 044 and 0 033 respectively and show no variation with o 2 the value for k2o is in good agreement with natural assemblages the values for mgo and tio2 however are lower in natural assemblages but the high degree of mobility of mg and the very low contents of tio2 in plagioclase makes the reliability of the natural values rather low also the d for tio2 may be affected by rate of cooling attempts to determine the d for cr2o3 as a function of o 2 were made difficult by the low levels of cr2o3 300 to 500 ppm in the melt when saturation with a cr spinel occurred because the cr concentrations in plagioclase are nearly 100 times less than those in the melt it was not possible to obtain reliable analyses for plagioclase these uncertainties constrain the d for cr to be less than 0 07 at the qfm buffer

magmatic interactions as recorded in plagioclase phenocrysts of chaos crags lassen volcanic center california the silicic lava domes of chaos crags in lassen volcanic national and mingling of this material into the silicic host these processes park contain a suite of variably quenched hybrid basaltic andesite are commonplace in some orogenic magma systems and may be magmatic inclusions the inclusions represent thorough mixing elucidated by isotopic microsampling and analysis of the plagioclases between rhyodacite and basalt recharge liquids accompanied by some crystallizing from them mechanical disaggregation of the inclusions resulting in crystals mixing into the rhyodacite host preserved by quenching on dome emplacement sr sr ratios 0 7037 0 7038 of the inclusions are distinctly lower than those of the host rhyodacite

mass balance and mass transfer in migmatites from the colorado front range metasomatic exchanges between the infiltrating fluids and wall rocks most likely initiated the formation of nine leucosomes in two large samples of the precambrian biotite quartz feldspar migmatites from the east central colorado front range the leucosomes 2 to 20 mm thick and enclosed in mafic salvages 1 to 10 mm thick are granitic to tonalitic in composition mass balance calculations suggest that each leucosome formed by local introduction of mass the net gains and losses calculated assuming that all such gains and losses were contained within the leucosome show that in general neither the gains nor the losses fit the composition of any silicate melt it is more likely that the components were transported in a fluid recalculated on constant al basis the most significant relative mass transfers were gain of k and losses of na and mg by the rocks the metasomatic reactions calculated are those for replacement of plagioclase by microcline and breakdown of biotite the reactions must have been the cause of incipient migmatization a mafic selvage formed from the paleosome by the loss of material whose composition is tonalitic to granodioritic varying systematically with the paleosome composition

effect of quaternary transgression and regression on the engineering properties of shanghai soft clays abstract the engineering properties of marine clays are closely related to its depositional environment however the correlation between the chemical properties and depositional environment and their effect on engineering properties of upper shanghai marine clay are still pending the sedimentary processes of upper shanghai marine clays from the quaternary transgression the correlation between the chemical properties and its depositional history are investigated in this study based on a series of laboratory experiments the distribution of chemical indicators e g ph value oxidation reduction potential and salt content with depth showed that the depositional environment directly affected the chemical properties of the soil layer the correlation of salt content with sensitivity liquid limit and liquidity index in upper shanghai layers represents a unique two stage distribution with the boundary at the bottom of the layer 4 clay the two stage distribution is caused by the quaternary transgression and regression which is confirmed to have different effects on the salt content sensitivity liquid limit and liquidity index the quantitative approaches used to evaluate the correlation between depositional environment chemical and mechanical properties can provide valuable references for investigating the engineering properties of soft clays

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

land subsidence in china land subsidence in china occurs in different regions it is primarily caused by excessive groundwater withdrawal other reasons for the subsidence include the oil warm groundwater withdrawal and the neotectonic movement the common characteristics of land subsidence in china are slow accumulative irreversible and other unique properties the range of subsidence still keeps extending and the accumulative subsidence increasing though some measures taken adjustment of the aquifer exploitation practice is a subsidiary way to control land subsidence but it cannot solve this problem completely in a specfic way of groundwater changing the contribution of a certain soil layer to the total subsidence depends on its compressibility and thickness besides the elasticity both cohesive soil layers aquitards and sand layers aquifers are observed to be plastic and creep when the groundwater level fluctuates in a specific way which often leads to subsidence delay

sedimentary cycles and paleogeography of the dnieper donets basin during the late visean serpukhovian based on multiscale analysis of well logs abstract an integrated approach combining the available geological geophysical information was employed to construct a series of paleogeographic maps of the northwestern part of the dnieper donets basin ddb during the late visean serpukhovian early carboniferous the major source of information consists of well log data the basin fill shows a pattern of stacked transgressive regressive units of different order correlations on the scale of the basin are based on biostratigraphy seismics cyclostratigraphic subdivisions and correlations of the successions throughout the basin the cyclicity has a multifold character short shallowing upward transgressive regressive t r cycles characterized by the presence of hydrocarbons productive horizons cover a time span of the order of 500 ka long cycles include 4 to 6 short t r cycles they seem to be correlatable to western europe and probably to north america the long cycles form part of higher order stacking patterns indicative of still longer cycles considering the variable thickness of the cycles throughout the basin tectonics must have influenced the character of the series in addition to glacio eustatic sea level fluctuations the paleogeographical development of the basin shows axial deposition during the late visean likely related to late stage rifting related subsidence of a central graben followed by basin wide subsidence related to thermal subsidence during the serpukhovian

crystallization kinetics in continuous decompression experiments implications for interpreting natural magma ascent processes decompression experiments were performed to study the kinetics of plagioclase crystallization during ascent of hydrous rhyodacite magma these experiments differ from previous studies in that they employ a continuous rather than stepwise pressure time trajectory four series of experiments were performed at rates of 0 5 10mpa h corresponding to ascent rates of 0 007 0 14 m s experiments quenched along each decompression path allow snapshot style monitoring of progressive crystallization as expected rates of plagioclase nucleation and growth depend strongly on decompression rate regardless of decompression rate approximately equal volumes of feldspar crystallize during a given decompression interval even when the observed crystallinity is lower than the equilibrium crystallinity apparently a constant degree of solidification is maintained by a crystallization mechanism striking a shifting balance between nuclei formation and growth of existing crystals other key results pertain to the efficacy with which experimental results allow interpretation of the decompression histories of natural rocks feldspar microlites do not maintain chemical equilibrium with melt they are more anorthite rich than equilibrium plagioclase suggesting that interpretations of magma ascent processes in nature require comparisons with dynamic rather than static phase equilibrium experiments although decompression rate is an important element controlling final textures in volcanic rocks no single compositional or textural parameter uniquely records this rate of the criteria examined microlite number density and morphology are the best indicators of magma decompression rate based on a small number of comparisons between continuous and multi step decompression style at the same time integrated decompression rate 1mpa h decompression path evidently influences crystal texture with stepwise decompression yielding textures correlative with faster decompression than indicated by the time integrated decompression rate thus consideration of magma ascent style in addition to rate will undoubtedly strengthen the interpretive power of experimental studies for constraining natural magma ascent processes

minor and trace element zoning in plagioclase implications for magma chamber processes at parinacota volcano northern chile textural and compositional zoning in plagioclase phenocrysts in a sample from parinacota volcano chile was investigated using backscattered electron images and electron microprobe analysis of major and trace elements large 2 mm oscillatory zoned crystals type i with resorption surfaces of moderate an discontinuities 10 an and decreasing trace element contents sr mg ti towards the rim reflect melt differentiation and turbulent convection in the main magma body early recharge with a low sr mafic magma is seen in the core small scale sr variations in the core indicate limited diffusion and thus residence and differentiation times of the magma shorter than a few thousand years smaller crystals type ii with low trace element an ratio reflect the influence of an h2o rich melt probably from a differentiated boundary layer closed system in situ crystallisation mafic magma recharge and the role of a water rich differentiated boundary layer can be distinguished from the an trace element relationships crystals apparently move relatively freely between different parts and regimes in the magma chamber evidence for convective crystal dispersion high sr type ii crystals indicate an earlier input of sr rich mafic magma recharge of two distinct mafic magma types is thus identified high sr and low sr which must have been present at increasing recharge rates with time in the plumbing system throughout the volcano s history

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods