calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

regional tilt of the mount stuart batholith washington determined using aluminum in hornblende barometry implications for northward translation of baja british columbia we have developed a new quantitative method to estimate paleohorizontal in granitic plutons using the aluminum in hornblende ah barometer the method is used to correct previously published paleomagnetic data from the 93 96 ma mount stuart batholith of the cascades mountains washington state for the effects of postemplacement tilting ah barometry was done on 46 samples from the batholith using the compositions of hornblende rims coexisting with the full mineral assemblage required for pressureestimation high contrastback scatteredelectronimagingwas usedtoensurethattheanalyzedhornblendeswerenotsignificantly affected by subsolidus alteration the success of the ah barometry is indicated by two observations first increases in the al content of the hornblendes are governed almost entirely by a pressure sensitive tschermak type substitution second amphibole plagioclase thermometry indicates that assemblage equilibration occurred at or very near magmatic conditions 650 c and that temperature has a negligible effect on our pressure estimates ah barometry results indicate that the depth of crystallization across the batholith decreases systematically from 0 3 gpa in the northwest to 0 15 gpa in the southeast consistentwithindependentbarometryforthecontactaureole ofthebatholithandregionalstructuralandstratigraphicrelations using a best fit planar tilt model and bootstrap analysis of uncertainties we estimate that the paleohorizontal plane has a strike of 43 630 4 and dip of 7 62 0 southeast 695 confidence our estimated paleohorizontal allows us to restore the paleomagnetic data of beck et al 1981 and to estimate the original paleolatitude of the mount stuart batholith beck et al found that the southern part of the batholith yielded a number of sites with a well defined high coercivity remanence the carrier of this remanence was not resolved but the following four lines of evidence stronglysuggestthatthepublisheddirectionswereacquiredshortly after emplacement of the batholith 1 the stable sites all came from the shallowest and most rapidly cooled portions of the batholith as indicated by our ah results and concordant k ar ages for hornblende biotite pairs 2 the high coercivity component was always normal in polarity which is consistent with emplacement of the mount stuart batholith at the end of the cretaceous long normal 3 sites from the batholith and the contact aureole gave similar directions 4 the directions show no indication of tilt related smearing after restoration the paleomagnetic data indicate 42 6 11 clockwise rotation and 3100 6 600 km of northward offset

n body simulations of oligarchic growth of mars implications for hf w chronology dauphas and pourmand 2011 hf w th evidence for rapid growth of mars and its status as a planetary embryo nature 473 489 492 estimated the accretion timescale of mars to be 1 8 1 0 0 9myr from the w isotopes of martian meteorites this timescale was derived assuming perfect metal silicate equilibration between the impactor and the target s mantle however in the case of a small impactor most likely only a fraction of the target s mantle is involved in the equilibration while only a small part of the impactor s core equilibrates in the case of a giant impact we examined the effects of imperfect equilibration using results of high resolution n body simulations for the oligarchic growth stage these effects were found to be small as long as a planetary embryo has a deep liquid magma ocean during its accretion the effect due to partial involvement of the target s mantle in equilibration is small due to the low metal silicate partition coefficient for w suggested from the low hf w ratio of the martian mantle the effect due to partial involvement of the impactor s core is also small because a large fraction of the embryo mass is delivered from small planetesimals which are likely to fully equilibrate in the deep magma ocean on the embryo the accretion timescale of mars estimated by the hf w chronology is shorter than that expected for the minimum mass solar nebula model as long as more than 10 of each impactor s core re equilibrates with the martian mantle and the final stages of accretion are prolonged this probably indicates that accretion of mars rapidly proceeded due to solid and gas surface densities significantly larger than those for the minimum mass solar nebula or due to accretion of small fragments or pebbles

a re evaluation of metal diapir breakup and equilibration in terrestrial magma oceans abstract due to mechanisms such as impact heating early atmospheric thermal blanketing and radioactive heating the presence of at least one global magma ocean stage in the early histories of terrestrial planets seems unavoidable in such a context a key question to constrain the early thermo chemical evolution of the earth is how much iron diapirs provided by differentiated impactors emulsified during their sinking towards the bottom of an early magma ocean in the past years several workers have focused on this question using however various approaches and making different assumptions while most studies favor rapid breakup and equilibration of iron bodies during their sinking through the magma ocean recent work suggests that iron bodies of size comparable or greater than a few tens of kilometers may preserve most of their initial volume as they reach the bottom of a magma ocean therefore leading to metal silicate disequilibrium to clarify the discrepancies and the differences among studies i have conducted a series of numerical simulations and theoretical calculations to derive the conditions and the timing for the breakup of metal diapirs of any size sinking through a silicate magma ocean with a large range of plausible viscosity values the obtained breakup criterion is used to derive stable diapir sizes and their ability to equilibrate with the surrounding silicates i show that for plausible magma ocean viscosities diapirs with initial radii smaller than the thickness of a magma ocean rapidly break up into stable diapir sizes smaller than 0 2 m at which metal silicate equilibration is rapidly achieved

magmatic conditions and magma ascent as indicated by hornblende phase equilibria and reactions in the 1995 2002 soufriere hills magma a study of amphiboles and associated minerals in samples of soufri ere hills andesite erupted from 1995 to 2002 shows significant compositional variations within hornblende phenocrysts a separate set of small pargasitic crystals in the groundmass and two types of reaction rims on the phenocrysts the composition of the amphiboles and coexisting phases defines the thermal history of the erupting magma as many as seven zones 5200 mm wide in the hornblende phenocrysts begin with a sharp increase in mg and si and then change gradually to a more feand al rich hornblende a transition that is consistent with a temperature rise analyses of the hornblende phenocrysts and associated fe ti oxides verify previous conclusions that the pre eruption magma was at 130mpa and 830 10 c but was variably heated before eruption the heating occurred within 30 days of eruption for all magmas erupted based on the width of ti rich rims on titanomagnetite phenocrysts experimental phase equilibria for the andesite confirm that the natural hornblende phenocrysts would be stable between 825 and 855 c at a ph2o of 130mpa and would be even more al rich if crystallized at higher pressure pargasite is not stable in the andesite and its presence along with high an plagioclase microphenocrysts requires mafic magma mingling and hybridization with pre existing andesite experimental melts of the andesite at 130mpa and 830 and 860 c compare well with melt inclusions in quartz and plagioclase respectively reaction rims on a few hornblende crystals in each andesite sample are rich in high ca pyroxene and are produced experimentally by heating the andesite above the stability limit for hornblende decompression induced breakdown rims occur in some samples and the rate of this reaction has been experimentally calibrated for isothermal andesite magma ascent at 830 860 c the average ascent rate of magma during much of the 1995 2002 eruption has been40 02 m s the rate that allows hornblende to erupt free of decompression induced reaction rims

construction of a pluton evidence from an exposed cross section of the searchlight pluton eldorado mountains nevada a top to bottom cross section of the searchlight pluton is exposed in a large tilt block in the colorado river extensional corridor of southern nevada hornblende barometry and geologic relations indicate that the pluton was about 10 km thick extending from approximately 3 to 13 km depth the pluton is stratified with about 2 km of fine grained quartz monzonite below the roof 2 km of granite in the center and 6 km of coarser more mafic quartz monzonite at the bottom the lower unit has a pronounced magmatic foliation that was subhorizontal prior to tilting contacts between the units are gradational over a few centimeters to about 20 m geometry field relations and elemental and isotopic data suggest that the three units mark the terminal stages of evolution of magma that filled a very thick magma chamber the upper unit formed as a solidification front that migrated downward from the roof and the middle unit granite and the lower unit represent complementary segregated melt and crystal rich cumulate thus the dominant part of the pluton appears to have solidified in monotonic fashion from more or less uniform magma that was compositionally similar to the upper unit the basal quartz monzonite and the lower part of the granite enclose widely scattered synplutonic hornblende gabbro and diorite pods that range from centimeter to kilometer scale these rocks are commonly fine grained and formed as quenched mafic melts they are isotopically distinct from the main sequence and represent discrete injections into the magma chamber the mafic magmas were contaminated by but did not strongly affect the main sequence magma the nd and sr isotopic compositions of the main sequence magma are intermediate between those of regional crust and enriched mantle derived basalts like those represented by the mafic pods this suggests that the principal magma was a hybrid with about 60 mantle component and thus the pluton represents both addition to and internal reorganization of the crust

the origin of brown hornblende in the artfjallet gabbro and dolerites brown hornblende occurs in minor amounts in the artfjallet gabbro and dolerites except in quartz dolerites where a pale green hornblende occurs in the gabbro brown hornblende is mostly ti bearing pargasite or kaersutite it occurs along veins of orthopyroxene as rims around and blebs in pyroxenes with orthopyroxene in coronas between olivine and plagioclase and in coronas between ilmenite and plagioclase in the olivine dolerites and orthopyroxene dolerites brown hornblende is ferroan titanian pargasite or ferroan kaersutite the pale green hornblende in the quartz dolerites is a magnesio hornblende the hornblendes in the dolerites are interstitial or granular in some dolerites occurring as coarse oikocrysts it is proposed that under certain conditions the ti content of hornblende can be used as a thermometer derived from experimental data of helz 1973 microstructures compositions and formation temperatures 1 040 c show that the brown hornblende in the gabbro is not magmatic but of subsolidus origin probably it formed as a result of the introduction of water into the gabbro during a deformation event that occurred early in the cooling history of the gabbro least squares modelling of hornblende formation indicates that all magmatic minerals must have participated in the reaction and that the reaction probably was not isochemical microstructures compositions and formation temperatures 1 030 965 c of brown hornblende in the dolerites are consistent with late stage crystallization from the magma for the pale green hornblende in the quartz dolerites a magmatic origin is likely but cannot be proven

depositional features and stratigraphic sections in granitic plutons implications for the emplacement and crystallization of granitic magma abstract many granitic plutons contain sheet like masses of dioritic to gabbroic rocks or swarms of mafic to intermediate enclaves which represent the input of higher temperature more mafic magma during crystallization of the granitic plutons small scale structures associated with these bodies e g load cast and compaction features silicic pipes extending from granitic layers into adjacent gabbroic sheets indicate that the sheets and enclave swarms were deposited on a floor of the magma chamber on granitic crystal mush and beneath crystal poor magma while the mafic magma was incompletely crystallized these structures indicate way up typically toward the interior of the intrusions and appear to indicate that packages of mafic sheets and enclave concentrations in these plutons are a record of sequential deposition hence these plutons preserve a stratigraphic history of events involved in the construction filling replenishment and crystallization of the magma chamber the distinctive features of these depositional portions of plutons allow them to be distinguished from sheeted intrusions which usually preserve mutual intrusive contacts and dike sill relations of different magma types the considerable thickness of material that can be interpreted as depositional and the evidence for replenishment suggest that magma chamber volumes at any one time were probably much less than the final size of the pluton thus magma chambers may be constructed much more slowly than presently envisaged the present steep attitudes of these structures in many plutons may have developed gradually as the floor of the chamber along with the underlying solidified granite and country rock sank during continuing episodes of magma chamber replenishment these internal magmatic structures support recent suggestions that the room problem for granites could be largely accommodated by downward movement of country rock beneath the magma chamber

calcic amphibole growth and compositions in calc alkaline magmas evidence from the motru dike swarm southern carpathians romania a late pan african calc alkaline dike swarm basalt andesite dacite rhyolite has been investigated in a region of over 2000 km 2 in the alpine danubian window south carpathians romania amphibole phenocrysts and microphenocrysts have been investigated by wavelength dispersive microprobe analysis and bse imaging the ca amphibole population represented in all the lithologies displays a large compositional range interpreted as the result of two processes 1 magmatic evolution kaersutite ti pargasite pargasite ti magnesiohastingsite magnesiohastingsite edenite tschermakite magnesiohornblende linked to magmatic differentiation from andesitic basalt to rhyolite and 2 deuteritic alteration of the primary amphibole related to late emplacement hydrothermal activity yielding numerous varieties comprising those cited above in all rock types amphibole phenocrysts equilibrated at a nearly constant pressure of about 0 6 0 1 gpa but their temperatures of crystallization ranged from 1000 900 c for basaltic andesites to 700 600 c for dacites in rhyolites edenite to magnesiohornblende crystals res ect a continuous range of p t conditions from 700 c 0 6 gpa to 600 c 0 1 gpa in agreement with their change of habit from euhedral to subhedral complex zonations in pargasite magnesiohastingsite including resorption are interpreted in term of self organization of

magma ocean formation due to giant impacts current understanding of the last stages of planetary accretion suggests that mass and energy accumulation are dominated by a few large impacts an important thermal consequence of such impacts is melting and formation of a large melt pond if the planet s isostatic adjustment time scale is short compared to the magma pond s cooling time scale the melt may be extruded onto the surface and form a magma ocean of approximately uniform depth although a giant impact striking at 10 15 km s 1 deposits enough energy to melt the entire planet the distribution of that energy is important in determining the thermal outcome of the collision we examine the thermal effects of giant impacts by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths additionally we examine the effects of the planet s initial temperature on the generated melt volume the hugoniot curve plotted in pressure entropy space is used to determine the shock pressure required to completely melt the material for room temperature dunite this pressure is about 150 gpa and the partial melt region is narrow for dunite initially at the solidus temperature this pressure is about 115 gpa the partial melt region extends throughout the planet once the melting pressure is known an impact melting model based on the second hugoniot equation the linear shock particle velocity relationship and the empirical particle velocity distance relationship is used to estimate the radial distance melting occurred from the impact site once the distance is found the melt region s geometry determines the associated melt volume partial melt volume is also estimated the melt fraction that is not excavated during crater formation is estimated and magma ocean depths resulting from both excavated and retained melt are calculated the model is also used to estimate the fraction of a planet melted by the initial shock wave nominal conditions of the moon forming giant impact projectile planet mass 0 14 impact speed 15 km s 1 generate melting of 30 65 of the planet depending on its initial temperature whole planet melting requires projectile planet mass ratios of 0 4 for a 15 km s 1 impact if the planet was near its solidus before the impact isostatic relaxation may generate a significant volume of additional melting

角閃石中のアルミニウム圧力計を使って決定された ワシントン州 stuart山バソリスの広域的傾動 バハ ブリティシュコロンビアの北方への転移に関する意味

cannibalization of an amphibole rich andesitic progenitor induced by caldera collapse during the matahina eruption evidence from amphibole compositions the diverse range of calcic amphibole compositions in eruptive products from the ca 330 ka matahina eruption ca 160 km3 rhyolitic magma of the okataina volcanic complex taupo volcanic zone including crystal rich basalt dacite pumice from post collapse deposits reveals several pre and syn eruption magmatic processes 1 amphibole phenocrysts in the basaltic andesite and andesite crystallized at the highest pressures and temperatures p to 0 6 0 06 gpa and t to 950 c equivalent to mid crustal depths 13 22 km inter and intra crystalline compositions range from ti magnesiohastingsite ti tschermakite tschermakite magnesiohornblende and some display gradual decreases in t from core to rim both consistent with magma differentiation by cooling at depth 2 the largest amphibole crystals from the basaltic andesite to andesite display several core to rim increases in t to 70 c indicating that new hotter magma periodically fluxed the crystal mush 3 the dominant population of rhyolite amphibole is small and bladed magnesiohornblende and crystallized at low p t conditions p 0 3 gpa t 765 c equivalent to the eruptive p t conditions dacitic and low silica rhyolitic amphibole tschermakite magnesiohornblende form two distinct populations which nucleated at two different t high 820 c and low 750 c these compositional variations governed primarily by differences in t conditions during crystal growth record the mixing of two distinct amphibole populations that approached a thermal equilibrium at the eruptive temperature therefore the diversity in amphibole compositions can be reconciled as an exchange of crystals liquid between the basaltic andesite to dacite from the mid crust and rhyolite from the upper crust which quenched against one another modifying the dacite to low silica rhyolite compositions as the eruption progressed

energy release in subvolcanic environments implications for breccia formation mechanical pdelta v energy is released from hydrous magmas in subvolcanic environments by the two generally sequential processes of second boiling and subsequent decompression the second boiling process h 2 o saturated melt crystals h 2 o vapor releases sufficient pdelta v energy in the model system previously established by burnham 1979 and burnham and ohmoto 1980 to cause fracture failure of even the strongest wall rocks tensile strength approximately 3 77 x 10 10 ergs kg super 1 to depths of 4 or 5 km following fracture failure moreover expansion of already exsolved h 2 o and exsolution of additional h 2 o upon decompression into the model fracture system releases additional pdelta v energy 9 7 x 10 10 ergs kg super 1 of magma sufficient to lift an equivalent mass of rock nearly 1 km in the absence of frictional resistance this latter energy although a conservative value is model dependent to the extent that it is affected by changing any one of the following six independent model parameters 1 bulk composition of the magma hornblende biotite granodiorite in the model 2 depth of emplacement of the magma body approximately 2 3 km p t 0 6 kb 3 mass fraction of h 2 o in the initial melt f o w 0 027 2 7 wt h 2 o 4 mass fraction of melt in the magma at the time of emplacement f o m 1 0 100 liquid 5 tensile strength of the wall rocks 3 77 x 10 10 ergs kg super 1 and 6 depth to the top of the fracture once formed approximately 2 3 km p f 0 3 kb although all of these parameters except the first are of major importance in the formation of hydrothermal breccias generally the mass fraction of h 2 o in the initial melt f o w is regarded as the single most important factor in the formation of breccia bodies in typical porphyry type systems f o w not only determines primarily whether or not the second boiling reaction releases enough pdelta v energy to produce fractures it also determines the magnitude of the decompressional energy released into the fractures if formed magmas in which f o w 0 02 to 0 04 at liquidus temperatures generally release sufficient pdelta v energy not only to produce extensive porphyry type fracture systems but also to produce the breccia bodies these systems commonly contain magmas in which f o w 0 02 on the other hand generally do not release sufficient energy for extensive breccia formation except in structurally weak wall rocks at depths shallower than approximately 2 km magmas in which f o w raquo 0 04 at near liquidus temperatures are incapable of emplacement in the subvolcanic environment

second boiling effects on the al content of hornblende rims from an exhumed cretaceous arc pluton stewart island new zealand high resolution transects across amphiboles from the layered mafic felsic halfmoon pluton suggest that amphibole compositions in the outermost 40 m of grains analyzed fluctuate in response to p t p h2o conditions during the final stages of pluton emplacement and crystallization detailed transects 10 15 m point spacing across 15 crystals from six representative rock types within the compositionally stratified halfmoon pluton revealed that in almost all crystals altot increased over at least the outer 40 m coupled with a decrease in temperature and ti content p t estimates for halfmoon pluton amphiboles using the al in hornblende geobarometer and the hornblende plagioclase geothermometer are consistent with upper crustal emplacement depths amphibole altot within the core and midsections is controlled by the temperature dependent edenite and ti tschermak exchanges and is interpreted to reflect the influence of repeated injections of hot mafic magma into the magma reservoir during crystallization increases in altot at all amphibole rims arise from a notable increase in vial and small increases in ival indicating that unlike the core and midsections that exhibit a strong temperature dependence rim altot is a function of the pressure dependent al tschermak exchange pressure estimates calculated for amphibole rims record a rim ward increase in p equivalent to between 0 2 and 1 9 kbar which corresponds to increases in depth of crystallization of 0 7 and 6 7 km respectively this observed increase in pressure at the rims of all amphibole grains analyzed is not consistent with increasing lithostatic pressure as a result of pluton burial but to an increase in p h2o in response to second boiling a common process during late stage crystallization of h2o rich intermediate silicic magmas the presence of water escape structures throughout the pluton and the predominance of biotite rich mafic enclaves that commonly contain amygdules toward the inferred top of the magmatic stratigraphy provide further evidence to support the process of second boiling these results indicate that caution is required in choosing suitable analytical sites when applying the al in hornblende geobarometer particularly within plutonic bodies where there is evidence for vesiculation and water escape structures as the outer rim compositions of amphiboles may not be a function of lithostatic pressure alone

field and geochemical constraints on mafic felsic interactions and processes in high level arc magma chambers an example from the halfmoon pluton new zealand the 140 ma halfmoon pluton of stewart island new zealand provides direct evidence for a number of physico chemical processes that operate at depth within active arc settings it is characterized by a sequence of mingled mafic sheets and enclaves that are preserved within intermediate felsic host rocks way up structures and textures are consistent with a younging direction to the south and allow a south dipping magma chamber stratigraphy to be constructed the similarity in modal mineralogy geochemistry and isotopic signature between the various components and their proximity in space and time indicates that the system can be considered as a single composite pluton with discrete portions active at different times interpretation of mingling structures and textures in the field combined with detailed geochemical and geochronological analyses has allowed the identification of several physical and chemical processes operating within the chamber including 1 multiple mafic magma pulses that were extensively mingled and sometimes physically mixed at the exposed level and at depth 2 the development of mineral fabrics e g aligned plagioclase and hornblende crystals and alignment of mafic enclaves caused by processes of crystal accumulation magmatic flow and compaction 3 shortening of the chamber during crystallization as a result of magmatic loading 4 fractional crystallization of the intermediate felsic host magma that was interrupted periodically by mafic magma intrusion 5 incremental assembly of the pluton from the base up 6 limited chemical transfer between the mingled mafic sheets and enclaves and the surrounding intermediate felsic host rocks variations in morphology chemistry and texture of the mingled mafic rocks relative to their position within the magmatic stratigraphy indicate that processes operating within the chamber varied in both space and time mineral assemblages chemical characteristics primitive isotopic signatures and a lack of zircon inheritance indicate that the amphibole rich calc alkaline halfmoon pluton was emplaced into a juvenile arc setting and experienced no contamination with ancient crustal materials a model of pluton construction and evolution is presented that shows that the halfmoon pluton consisted of at least two adjacent magma pods that grew incrementally by episodic replenishments of mafic magma into a magma chamber of evolving intermediate felsic composition data are consistent with a model whereby hydrous amphibole rich basaltic magmas ponded at the crust mantle interface and episodically rose injected and mingled

experiments on turbulent metal silicate mixing in a magma ocean we compare the results of laboratory fluid dynamics experiments with theoretical models of turbulent entrainment in two phase buoyant plumes and thermals to estimate the amount of mixing between the iron core of a planetesimal or planetary embryo and the molten silicates in a magma pool formed by its impact with a growing planet during accretion we demonstrate experimentally that turbulent plumes in immiscible fluids fragment into droplets and that the envelope of the droplet distribution is indistinguishable from the envelope of a turbulent plume in a single phase fluid under the same dynamical conditions implying that turbulent entrainment concepts are applicable to immiscible fluids mixing a series of experiments are made on the time evolution of a two phase turbulent thermal representing a planetesimal core falling under its own negative buoyancy in a spherical fluid representing an impact produced magma pool two stages of mixing are observed in these experiments the first corresponding to turbulent entrainment during free fall of the thermal the second corresponding to entrainment in turbulent gravity currents that form after the thermal reaches the base of the magma pool we demonstrate that the amount of mixing between metals and silicate liquids in a magma pool depends on the rouse number of the metal fragments and increases rapidly with the radius of the proto planet we derive a similarity model for metal silicate mixing in a spherical magma pool assuming a constant entrainment coefficient for the turbulent liquid metal phase this model supports our experimental finding that a small metal core of an impactor will become diluted i e mix within a deep magma pool but a large impacting core will not fully dilute before reaching the base of the magma pool

gas driven filter pressing in magmas most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less the buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization and this process of gas driven filter pressing assists the crystallization differentiation of magmas for gas driven filter pressing to be effective the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt these conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs gas driven filter pressing thereby adds fractionated melt to magma bodies gas driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons this process could also account for the production of voluminous crystal poor rhyolites

petrology and geochemistry of the late eocene harrison pass pluton ruby mountains core complex northeastern nevada which suggest a single mixing event before emplacement in the upper the late eocene harrison pass pluton was emplaced in the crust late stage activity consisted of three pulses of monzogranitic transition zone between the infrastructure and suprastructure of the magma plus sparse mafic dikes the largest and youngest of these ruby mountains core complex emplacement was at 3 kbar pulses the two mica monzogranite of green mountain creek is pressure and was in two stages early stage tonalitic to monzogranitic distinct from all other units in the presence of restitic enclaves low magmas followed by late stage monzogranites and mafic dikes nd and high initial sr sr pod like bodies of leucocratic biotite the early stage began with emplacement of biotite hornblende amphibole monzogranite and sheets and dikes of leucocratic granodiorite of toyn creek followed by the biotite monzogranite of two mica monzogranite make up the other late stage granites these corral creek quenched equivalents of these units are preserved as rocks display deep negative eu anomalies and show wide nonporphyritic dikes in the roof leucocratic monzogranite that forms systematic concentrations of high field strength elements however cupolas in the roof zone represents the product of fractional crystheir isotopic compositions are identical to those of the early stage tallization of the early magmas al in hornblende barometry and rocks they are thought to be small melt fractions of the lower to the presence of magmatic epidote suggest that early stage magmas middle crust their elemental compositions are thought to result resided at a pressure of 5 6 kbar before emplacement in the from the effects of residual plagioclase and accessory minerals the upper crust compositional variation in the toyn creek and corral variable and non systematic isotopic compositions of all granitic creek units is essentially linear and can be explained by mixing units in the pluton suggest a heterogeneous source region such as of a tonalitic end member with a monzogranitic end member such the proterozoic mojave province as evolved samples of the monzogranite of corral creek the tonalitic end member was itself a hybrid that formed by interaction

magma mixing in the genesis of hercynian calc alkaline granitoids an integrated petrographic and geochemical study of the sazava intrusion central bohemian pluton czech republic the devonian early carboniferous 354 1 3 5 ma conventional zircon u pb age sazava intrusion biotite amphibole quartz diorite tonalite and granodiorite of the central bohemian pluton cbp associated with bodies of olivine pyroxene amphibole gabbro gabbrodiorite quartz diorite and rare hornblendite gives an opportunity for a comparative study of a rather shallow calc alkaline magma mixing zone at two levels separated by a vertical difference of approximately 1 km the deeper section p ibram displays the direct evidence for the existence of a long lived periodically tapped and replenished floored magma chamber masli the contacts between the subhorizontal sheet like basic bodies and the surrounding commonly cumulus rich sazava granitoid are arcuate and cut by a series of veins and ascending pipes shallow dipping swarms of strongly elongated and flow aligned mafic microgranular enclaves mme concordant with the contacts of the basic bodies are commonplace the higher level teletin section shows relatively independent basic intrusions some of them distinctly hybrid in character and mainly of quartz dioritic composition surrounded by relatively homogeneous nearly cumulus free sazava tonalite rich in texturally variable mme larger quartz microdiorite bodies and the mme both interpreted as hybrids contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning particularly well shown by cathodoluminescence cl most often the megacrysts have cores of labradorite anorthite partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth also characteristic are long prisms of apatite oikocrysts of quartz and k feldspar and zoned amphibole the latter has brown pargasite and magnesiohastingsite cores resorbed and overgrown by magnesiohornblende compositionally similar to the amphibole in the sazava tonalite the brown cores are probably relics of a higher p t stage with temperature exceeding 900 c plots of major element analyses of the teletin quartz microdiorite and the mme fall close to the line joining the compositions of the evolved sazava granodiorite tonalite and the associated gabbros the estimated minimal proportions of the acidic end member range from ca 15 to 20 for the quartz microdiorite and ca 40 to 60 for the enclaves field relationships macroscopic and mineralogical features and whole rock geochemistry are consistent with a hybrid origin of the quartz microdiorite masses and enclaves unzoned calcic plagioclase cores are interpreted as having crystallized from a basic magma prior to its injection into a high level acidic magma chamber the sudden decrease in ca activity and introduction of water due to magma mixing with tonalitic melt led to their resorption and brecciation quartz ocelli that are abundant locally in some basic bodies are most likely xenocrysts introduced from the felsic magma in the basic melt they were resorbed and became a substrate for heterogeneous nucleation of the amphibole or pyroxene coronas strong undercooling of the basic magma resulted in the growth of long prismatic apatite together with dendritic boxy cellular plagioclase both types of plagioclase cores were subsequently overgrown by more sodic mantles at the same time small unzoned plagioclase crystals nucleated in the groundmass following thermal re adjustment crystallization of the hybrid magma ended with considerably slower growth of quartz and k feldspar oikocrysts

siderophile elements in martian meteorites and implications for core formation in mars noble metals mo w and 24 other elements were determined in six snc meteorites of presumably martian origin based on element correlations representative siderophile element concentrations for the silicate mantle of mars were inferred from a comparison with experimentally determined metal silicate partition coefficients of the moderately siderophile elements fe ni co w mo and ga it is concluded that equilibrium between core forming metal and silicates in mars has occurred at high temperatures around 2200 c and low pressures 1 gpa this suggests that metal segregation occurred concurrently with rapid accretion of mars which is consistent with the inference from excess 182w in martian meteorites lee and halliday 1997 concentrations of ir os ru pt and au in the analyzed martian meteorites except alh84001 are at a level of approximately 10 2 10 3 ci the comparatively high abundances of noble metals in martian meteorites require the addition of chondritic material after core formation the similarity in au la and pt ca ratios between alh84001 and the other martian meteorites suggests crystallization of alh84001 after complete accretion of mars

trace element indicators of crystal accumulation in silicic igneous rocks abstract if fractional crystallization coupled with some crustal assimilation afc is the dominant process for generating evolved magmas in the earth s crust large quantities of igneous cumulates must be present in the rock record however despite some reported occurrences intermediate to silicic rocks characterized by an unambiguous crystal accumulation signature have remained elusive the signature is expected to be subtle in viscous silicic magmas and sensitive criteria need to be developed to test whether these cumulates are truly rare or simply difficult to discern we propose models that use specific trace element concentrations and ratios zr ba eu eu and zr hf within a well constrained framework for the physical extraction of liquid from crystals mostly occurring between 50 and 70 vol crystals to identify silicic cumulates the results of these models indicate that crystal accumulation or melt extraction has occurred in multiple natural examples around the world both in plutonic and volcanic realms however these examples were selected because they represent conditions that are most favorable high amount of melt extraction well constrained initial liquid compositions for unambiguously identifying cumulate residue in many cases we show that the trace element signature for crystal accumulation will remain largely concealed in addition the different liquid lines of descent related to the various tectonic settings on earth dry reduced in hot spots divergent margins and wetter more oxidizing in arc environments will lead to different trace element evolution and each criterion must be applied on a case by case basis despite these limitations the undeniable but subtle presence of silicic cumulates in the mid to upper crust lends support to the idea that igneous differentiation is dominantly driven by melt extraction from partially crystalline reservoirs

direct numerical simulation of an iron rain in the magma ocean core formation in terrestrial planets is a complex process possibly involving several mechanisms this paper presents a direct numerical simulation of one of these the separation of an emulsion of metal in a magma ocean the model using a fully lagrangian approach called the moving particle semi implicit method solves the equations of fluid dynamics including a proper treatment of surface tension it allows investigation of the balances controlling the distribution of drop size and velocity in both two and three dimensional situations a scaling analysis where buoyancy is balanced by both surface tension and inertia correctly predicts the average values in these quantities the full calculation gives an average drop radius of 1 5 cm falling at a velocity of about 30 cm s 1 analysis of the full distribution remains interesting and shows that a significant part of the smallest droplets is entrained upward by the return flow in molten silicate and might be entrained by succeeding thermal convection in addition we investigate the conversion of gravitational energy into viscous heating and the thermal equilibration between both phases we find that viscous heating is essentially produced at the surface of iron drops and that thermal equilibration is dominated by advection scaling thermal diffusion to chemical diffusion leads to the estimation that the latter would happen in less than 100 m in the magma ocean

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

geodynamics of the southeastern tibetan plateau from seismic anisotropy and geodesy ongoing plate convergence between india and eurasia provides a natural laboratory for studying the dynamics of continental collision a fi rst order process in the evolution of continents regional climate and natural hazards in southeastern tibet the fast directions of seismic anisotropy determined using shear wave splitting analysis correlate with the surfi cial geology including major sutures and shear zones and with the surface strain derived from the global positioning system velocity fi eld these observations are consistent with a clockwise rotation of material around the eastern himalayan syntaxis and suggest coherent distributed lithospheric deformation beneath much of southeastern tibet at the southeastern edge of the tibetan plateau we observe a sharp transition in mantle anisotropy with a change in fast directions to a consistent e w direction and a clockwise rotation of the surface velocity surface strain fi eld and fault network toward burma around the eastern himalayan syntaxis the coincidence between structural crustal features surface strain and mantle anisotropy suggests that the deformation in the lithosphere is mechanically coupled across the crust mantle interface and that the lower crust is suffi ciently strong to transmit stress at the southeastern margin of the plateau in yunnan province a change in orientation between mantle anisotropy and surface strain suggests a change in the relationship between crustal and mantle deformation lateral variations in boundary conditions and rheological properties of the lithosphere play an important role in the geodynamic evolution of the himalayan orogen and tibetan plateau and require the development of three dimensional models that incorporate lateral heterogeneity

isotopic and molecular composition of coal bed gas in the amasra region zonguldak basin western black sea previous studies on the coal bed methane potential of the zonguldak basin have indicated that the gases are thermogenic and sourced by the coal bearing carboniferous units in this earlier work the origin of coal bed gas was only defined according to the molecular composition of gases and to organic geochemical properties of the respective source rocks since data on isotopic composition of gases were not available furthermore in the western black sea region there also exist other source rocks which may have contributed to the coal bed gas accumulations the aim of this study is to determine the origin of coal bed gas and to try a gas source rock correlation for this purpose the molecular and isotopic compositions of 13 headspace gases from coals and adjacent sediments of two wells in the amasra region have been analyzed total organic carbon toc measurements and rock eval pyrolysis were performed in order to characterize the respective source rocks coals and sediments are bearing humic type organic matter which have hydrogen indices hi of up to 300 mghc gtoc indicating a certain content of liptinitic material the stable carbon isotope ratios 13 c of the kerogen vary from 23 1 to 27 7 o air free calculated gases contain hydrocarbons up to c 5 carbon dioxide 98 the stable carbon isotope ratios of methane ethane and propane are defined as 13 c 1 51 1 to 48 3 13 c 2 37 9 to 25 3 13 c 3 26 0 to 19 2 respectively the d 1 values of methane range from 190 to 178 according to its isotopic composition methane is a mixture partly generated bacterially partly thermogenic molecular and isotopic composition of the gases and organic geochemical properties of possible source rocks indicate that the thermogenic gas generation took place in coals and organic rich shales of the westphalian a kozlu formation the bacterial input can be related to a primary bacterial methane generation during carboniferous and or to a recent secondary bacterial methane generation however some peculiarities of respective isotope values of headspace gases can also be related to the desorption process which took place by sampling

triggering basaltic volcanic eruptions by bubble melt separation understanding the processes by which volcanic eruptions are triggered is crucial for volcanic hazard prediction and assessment in intermediate and silicic magmas where water is the dominant volatile phase1 2 second boiling provides an effective eruption trigger1 as the magma cools and crystallizes volatiles are increasingly concentrated in the residual melt where they eventually become saturated and are exsolved thereby raising the magma pressure to the point of eruption1 2 in contrast in basaltic magma chambers in which carbon dioxide is the dominant volatile phase the effect of second boiling is to decrease the chamber pressure but basaltic magmas are also relatively inviscid so volatile bubbles can separate from the turbulently convecting melt to produce a foam layer at the chamber roof3 4 decompression of the rising bubbles can increase the chamber pressure and so trigger an eruption5 6 here we model the complex competition between the processes of magma cooling and bubble ascent we find that in basalt of very low viscosity 1 10pas bubble separation dominates and can increase the reservoir pressure by as much as 10 mpa sufficient to trigger an eruption7 on timescales of 1 10 years comparable to the duration of eruptive episodes at kilauea volcano hawaii4 8

petrologic evidence for pre eruptive pressure temperature conditions and recent reheating of andesitic magma erupting at the soufriere hills volcano montserrat w i the recent eruption of the soufriere hills volcano in montserrat july 1995 to present september 1997 has produced an andesitic dome sio 2 59 61 wt the eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region p 130 mpa 5 km depth the composition of the andesite has remained essentially constant throughout the eruption but heating by the mafic magma increased the andesite temperature from 830 c to 880 c prior to being heated the stable mineral assemblage in the andesite was plagioclase amphibole orthopyroxene titanomagnetite ilmenite quartz the rise in temperature from 830 c to 880 c fo 2 1 log unit above nno has caused quartz to become unstable and has also caused changes in silicate and fe ti oxide mineral compositions the andesitic magma is likely saturated with an h 2 o rich vapor phase in the upper part of the magma storage region melt h 2 o content is 4 7 wt