anomalously low sodium morb magmas evidence for depleted morb or analytical artifact abstract one common characteristic of quenched natural basaltic glass is the presence of microcrystalline halos surrounding many microphenocrysts spherulites from our investigations of the composition of basaltic grasses in both quenched lavas and in plagioclase hosted melt inclusions we have discovered that quench halo portions of spherulites are over 100 times as susceptible to na loss during microprobe analysis than normal basaltic glass this implies that there may be a significant negative bias in published morb glass na contents this in turn would result in potential systematic errors in existing models of morb petrogenesis that are dependent on those data

noise based monitoring and imaging of aseismic transient deformation induced by the 2006 basel reservoir stimulation abstractwe have analyzed the time dependent properties of the ambient seismic wavefield between 0 1 and 8 hz to detect resolve monitor and image the deformation induced by the water injection associated with the stimulation of the 2006 deep heat mining project in the city of basel switzerland the application of passive methods allowed the detection of an aseismic transient of approximately 35 days duration that began with the onset of the reservoir stimulation peak deformation was reached some 15 days after the bleed off and after the induced seismicity ceased we resolved a significant increase in seismic velocities and a simultaneous decorrelation of the noise correlation coda waveforms the wavefield properties implied that the material response was monitored mainly in the sedimentary layer 2 5 km above the stimulated volume that was approximately 4 5 km deep we inverted the velocity change and decorrelation data to estimate the spatial distribution of the medium changes the resulting imag

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

seismicity triggered by fluid injection induced aseismic slip anthropogenic fluid injections are known to induce earthquakes the mechanisms involved are poorly understood and our ability to assess the seismic hazard associated with geothermal energy or unconventional hydrocarbon production remains limited we directly measure fault slip and seismicity induced by fluid injection into a natural fault we observe highly dilatant and slow 4 micrometers per second m s aseismic slip associated with a 20 fold increase of permeability which transitions to faster slip 10 m s associated with reduced dilatancy and micro earthquakes most aseismic slip occurs within the fluid pressurized zone and obeys a rate strengthening friction law 0 67 0 045ln v v with v 0 1 m s fluid injection primarily triggers aseismic slip in this experiment with micro earthquakes being an indirect effect mediated by aseismic creep

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

a numerical model for fluid injection induced seismicity at soultz sous forets abstract during fluid injection experiments at the geothermal site of soultz sous forets france more than 114 000 induced seismic events with magnitudes between 2 0 and 2 9 were detected by a local downhole monitoring network of these 35 039 events are sufficiently constrained to be located hypocenters align along a sub vertical planar structure with the apparent width being dominated by data scattering indicating that seismic activity predominantly occurs along a pre existing larger scale fault structure for this scenario we present a numerical model to simulate hydraulic overpressures and induced seismicity during hydraulic injection the numerical model is based on the physical processes of fluid pressure and stress diffusion with triggering of the induced seismicity being controlled by coulomb friction even in its simplest form of a fault zone without any structural heterogeneity the numerical model reproduces typical observations at soultz sous forets such as number and magnitude of induced events hypocenter locations including the kaiser effect occurrence of post injection seismicity and the largest magnitude event occurring several days after shut in

high definition analysis of fluid induced seismicity related to the mesoscale hydromechanical properties of a fault zone interactions between pore pressure strain and seismicity were analyzed in a 30 m thick shallow fault zone that was subjected to a small overpressure of 80 kpa to produce small changes in effective stress simultaneous pressure strain and seismic measurements taken in the fractured damage zone during the pressurization indicated that seismicity is triggered along low permeable highly rigid low dip angle mesoscale inherited fractures where deformation is controlled by the hydromechanical behavior of the surrounding high permeability not so rigid aseismic sub vertical fault related fractures using a three dimensional distinct element representation of the fractures network we show that the seismicity observed is mainly due to shear slip along inherited planes in response to the mechanical loading induced by the opening by a few microns of the surrounding subfaults

metamorphic amphiboles composition and coexistence amphiboles have long been key players in metamorphic petrology the concept of facies was developed for rocks of basaltic composition eskola 1920 1939 fyfe et al 1958 and within this concept amphiboles had a leading role the first appearance of amphiboles the presence of amphiboles of certain compositions or last appearance of amphiboles that are replaced by pyroxene bearing assemblages mark a number of major facies boundaries the transition from greenschist to amphibolite facies is marked in part by hornblende replacing actinolite and the granulite facies is defined by the breakdown of hornblende to orthopyroxene bearing assemblages the blueschist facies is defined by the appearance of glaucophane while the transition from blueschist facies to eclogite facies conditions is indicated by the breakdown of glaucophane to omphacitic pyroxene bearing assemblages references to amphibole names actinolite glaucophane or rocks characterized by certain amphiboles amphibolite hornblende figure prominently in six facies names turner 1981 liou et al 1985 oh et al 1988 evans 1990 peacock 1993 a large part of the literature that is devoted to metamorphic petrology of amphiboles concerns reactions which produce amphiboles from more hydrated mafic igneous rocks or lead to the destruction of amphiboles as they break down to form anhydrous or nearly anhydrous mineral assemblages consequently amphiboles can be thought of as occupying the wide intermediate portion of p t xfluid space in which metamorphic rocks are found the number of citations of the published amphibole nomenclature serves as a yardstick meterstick of the interest in amphiboles and a minimum estimate of the amount of literature devoted to this mineral two versions of the nomenclature of amphiboles have appeared 1978 and 1997 leake 1978 leake et al 1997 and they have been cited a over 2300 times in the past 28 years this works out to a minimum

magnitudes of induced earthquakes and geometric scales of fluid stimulated rock volumes sometimes rock stimulations by fluid injections into geothermal boreholes are able to trigger perceptible or even potentially damaging earthquakes this does not seem to be the case for hydraulic fracturing of hydrocarbon reservoirs reasons for such a difference and factors defining magnitudes of induced earthquakes triggered tectonicly as well as induced artificially remain unclear we analyzed microseismic data obtained by fluid stimulations at different geothermal and hydrocarbon sites this analysis indicates that a rupture corresponding to a fluid induced earthquake seems to be only probable along a surface located mainly inside a stimulated rock volume we approximated the stimulated volume by an ellipsoid and compared the statistics of induced events with the statistics of randomly distributed thin flat disks modeling rupture surfaces we found that one of the main factors limiting the probability to induce a large magnitude event is the minimum principal axis of a fluid stimulated rock volume

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

nucleation and arrest of dynamic slip on a pressurized fault 1 elevated pore pressure can lead to reactivation of slip on pre existing fractures and faults when the static coulomb failure is reached locally as the pressurized region spreads diffusively slip can accumulate quasi statically paced by the pore fluid diffusion or dynamically in this work we consider a prestressed fault with a locally peaked diffusively spreading pore pressure field to study 1 conditions leading to the escalation of slip and nucleation of dynamic rupture and 2 rupture run out distance before it is arrested nucleation appears in this model when the fault friction decreases from its peak value with slip while arrest of dynamic propagation is imminent on aseismic faults i e such that prestress b is less than the residual fault strength rat ambient conditions when fluid overpressure is a small to moderate fraction of the ambient value of normal effective stress and prestress is large enough for fault slip to be activated by overpressure dynamic rupture always nucleates and the nucleation length increases with decreasing prestress practically independently of the overpressure value transition from the ultimately unstable b r to the ultimately stable b r fault loading is marked by a strong increase of the nucleation length 1 b r 2 as b approaches r from above for aseismic faults b r no dynamic rupture is nucleated at large fluid overpressures for all but the smallest values of prestress the largest run out distances of dynamic slip on aseismic faults correspond to overpressure prestress just sufficient for slip activation in such cases the dynamically accumulated slip can lead to enhanced dynamic fault weakening resulting in a sustained dynamic rupture and generating a large earthquake this is consistent with field observations when the largest injection induced seismicity occurred after fluid injection ended

chemical and physical indicators of compromised melt inclusions abstract the utility of the geochemistry of basaltic suites as probes of mantle processes is encumbered by the processing those magmas undergo during transport from the field of melting to the ocean floor melt inclusions provide us with an opportunity to obtain information on intermediate stages in the evolution of a magma system such data can be an extra constraint for our modeling of petrologic processes however melt inclusions have generally undergone some degree of post entrapment crystallization therefore to quantify the details of geochemical trends represented by melt inclusion suites we must construct a set of criteria to evaluate the degree to which any inclusion or set of inclusions represents the original trapped liquid composition the problems encountered in evaluating the degree to which inclusion compositions depart from that standard fall into three categories 1 errors caused by the selection of the temperature or time of heating 2 loss or gain of volatiles caused by inclusion rupture 3 contamination from alteration products such as manganese oxides or salts in the host crystal the criteria that may be used to evaluate the veracity of rehomogenized inclusion compositions include examination of the relationship of the inclusion composition to the host lava suite the morphology of the inclusion the fe and s content relative to the host suite and the mno content relative to the inclusion suite and the host lavas

a staurolite talc assemblage in tourmaline phlogopite chlorite schist from northern victoria land antarctica and its petrogenetic significance staurolite and corundum are found as inclusions in tourmaline in a talc phlogopite chlorite albite chist near mount bernstein 71 37 s 163 07 e northern victoria land antarctica these inclusions are interpreted as relics of a staurolite talc corundum chlorite assemblage that was stable during an early stage in the metamorphic cycle and subsequently armored by tourmaline probably during the middle stage pressures and temperatures during the middle stage are estimated to be 650 700 c and 5 5 6 4 kbar the transition from the early to the middle stage represents a roughly isothermal decrease in pressure of 2 3 kbar during a late retrograde stage t 300 370 c p 3 5 kbar staurolite was partly replaced by a muscovitic aggregate containing clinozoisite pumpellyite and margarite

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

frictional heterogeneities on carbonate bearing normal faults insights from the monte maggio fault italy observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and or spatial heterogeneity of fault frictional behavior such complex slip patterns have been observed for earthquakes on normal faults throughout central italy where many of the mw 6 to 7 earthquakes in the apennines nucleate at depths where the lithology is dominated by carbonate rocks to explore the relationship between fault structure and heterogeneous frictional properties we studied the exhumed monte maggio fault located in the northern apennines we collected intact specimens of the fault zone including the principal slip surface and hanging wall cataclasite and performed experiments at a normal stress of 10 mpa under saturated conditions experiments designed to reactivate slip between the cemented principal slip surface and cataclasite show a 3 mpa stress drop as the fault surface fails then velocity neutral frictional behavior and significant frictional healing overall our results suggest that 1 earthquakes may readily nucleate in areas of the fault where the slip surface separates massive limestone and are likely to propagate in areas where fault gouge is in contact with the slip surface 2 postseismic slip is more likely to occur in areas of the fault where gouge is present and 3 high rates of frictional healing and low creep relaxation observed between solid fault surfaces could lead to significant aftershocks in areas of low stress drop

on the relationship between fault permeability increases induced stress perturbation and the growth of aseismic slip during fluid injection author s cappa f guglielmi y nussbaum c birkholzer j abstract 2018 american geophysical union all rights reserved fluid injections into the deep subsurface can at times generate earthquakes but often they only produce aseismic deformations here we analyze the influence of fault hydromechanical properties on the growth of injection induced aseismic slip using hydromechanical modeling we show how permeability enhancement in addition to the background stress and frictional weakening has an important effect on the pressure diffusion and slip growth during injection we find that the more pronounced the fault permeability enhancement the stronger is the growth of the aseismic slip zone the effect of enhanced permeability is more pronounced when the fault is initially close to failure our results show that aseismic slip grows beyond the pressurized zone when the fault permeability increases while slip remains behind the pressurized zone when permeability does not vary from its initial preslip value thus fault permeability increases should be considered as complementary mechanism to current models of fluid induced aseismic slip

dehydration and partial melting of tremolitic amphibole coexisting with zoisite quartz anorthite diopside and water in the system h 2 o cao mgo al 2 o 3 sio 2 the greenschist to amphibolite transition as modeled by the reaction zoisite tremolite quartz anorthite diopside water has been experimentally investigated in the chemical system h2o cao mgo al2o3 sio2 over the range of 0 4 0 8 gpa this reaction is observed to lie within the stability fields of anorthite water and of zoisite quartz in accord with phase equilibrium principles and its position is in excellent agreement with the boundary calculated from current internally consistent data bases the small dp dt slope of 0 00216 gpa k 21 6 bars k observed for this reaction supports the pressure dependency of this transition in this chemical system experimental reversals of the al content in tremolitic amphibole coexisting with zoisite diopside quartz and water were obtained at 600 650 and 700 c and indicated al total cations atoms per formula unit apfu of only up to 0 5 0 08 at the highest temperature thermodynamic analysis of these and previous compositional reversal data for tremolitic amphibole indicated that of the activity composition relationships considered a two site coupled cation substitution model yielded the best fit to the data and a s0 1 bar 298 k of 575 4 1 6 j k mol for magnesio hornblende the calculated isopleths of constant al content in the amphibole are relatively temperature sensitive with al content increasing with increasing temperature and pressure finally several experiments in the range of 1 0 1 3 gpa were conducted to define the onset of melting and thus the upper thermal limit for this mineral assemblage which must involve an invariant point located at approximately 1 05 gpa and 770 c

investigation of injection induced seismicity using a coupled fluid flow and rate state friction model we describe a numerical investigation of seismicity induced by injection into a single isolated fracture injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems egs during which water is injected into fractured low permeability rock triggering slip on preexisting large scale fracture zones a model was developed and used that couples 1 fluid flow 2 rate and state friction and 3 mechanical stress interaction between fracture elements based on the results of this model we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation which we refer to as the sequential stimulation ss mechanism if the ss mechanism is realistic it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity we investigated the effect of injection pressure on induced seismicity for injection at constant pressure there was not a signifi

rupture propagation behavior and the largest possible earthquake induced by fluid injection into deep reservoirs earthquakes caused by fluid injection into deep underground reservoirs constitute an increasingly recognized risk to populations and infrastructure quantitative assessment of induced seismic hazard however requires estimating the maximum possible magnitude earthquake that may be induced during fluid injection here i seek constraints on an upper limit for the largest possible earthquake using source physics simulations that consider rate and state friction and hydro mechanical interaction along a straight homogeneous fault depending on the orientation of the pressurized fault in the ambient stress field different rupture behavior can occur 1 uncontrolled rupture front propagation beyond the pressure front or 2 rupture front propagation arresting at the pressure front in the first case fault properties determine the earthquake magnitude and the upper magnitude limit may be similar to natural earthquakes in the second case the maximum magnitude can be controlled by carefully designing and monitoring injection and thus restricting the pressurized fault area

petrological evolution of amphibolite shear zones cheyenne belt south eastern wyoming usa abstract metre scale amphibolite boudins in the cheyenne belt of south eastern wyoming are cut and deformed by shear zones which preserve a full strain transition across 7 cm from relatively undeformed amphibolite with a relict igneous texture to mylonitic amphibolite with an l s tectonic fabric the strain transition is marked by the progressive rotation of amphibole plagioclase aggregates into parallelism with the shear zone boundary an increase in strain magnitude is indicated by development of the tectonic fabric and progressive reduction of amphibole and plagioclase grain size as a result of cataclasis bulk chemistry of five samples across a single strain transition shows no significant or systematic variation in major element chemistry except for a minor loss of sio2 which indicates that the shear zone was a system essentially closed to non volatile components during metamorphism and deformation amphibolites throughout the shear zone consist of amphibole and plagioclase with only minor amounts of quartz chlorite epidote titanite and ilmenite within the relatively undeformed amphibolite amphibole and plagioclase have wide compositional ranges in single thin sections amphibole compositions vary from actinolitic hornblende to magnesio hornblende with increases in al fe na and k contents and decreases in si and mg that can be modelled as progress along tschermakite edenite and femg 1 exchange vectors from tremolite plagioclase ranges from an60 in cores to an30 within grain boundary domains with increasing strain magnitude local variation of amphibole composition decreases as amphibole becomes predominantly magnesio hornblende plagioclase composition range also decreases although grain boundary domains still have higher albite content these petrological data indicate that shear zone metamorphism was controlled by the magnitude of strain during synmetamorphic deformation sem and microprobe imaging indicate that chemical reactions occurred by a dissolution and reprecipitation process during or after cataclastic deformation this suggests that grain boundary formation was an important process in the petrological evolution of the shear zone possibly by providing zones for fluid ingress to facilitate metamorphic reactions these results highlight the necessity for conducting detailed microstructural evaluation of rocks in order to interpret petrological isotopic and geochronological data

sadanagaite and magnesio sadanagaite new silica poor members of calcic amphibole from japan sadanagaite k na ca2 fe2 mg ai fe3 ti 5 si a1 8022 oh 2j where fe2 mg al fe3 and si 5 5 and its mg rich analogue magnesio sadanagaite fe2 mg are extremely si02 poor new amphiboles which require the compositional extension of the edenite pargasite series and amending of the classification and nomenclature of amphiboles leake 1978 these are monoclinic c2 cm or c2 m a 9 922 10 b 18 03 2 c 5 352 9 a f3 105 30 10 z 2 for sadanagaite with si 5 0 and a 9 964 2 b 18 008 3 c 5 354 2 a f3 105 55 2 z 2 for magnesio sadanagaite with si 5 0 the strongest lines in the x ray powder pattern for magnesio sadanagaite are 8 48 80 iiq 3 39 40 131 3 28 100 240 3 15 70 310 2 951 50 221 2 823 30 330 2 766 45 331 2 707 60 151 2 594 35 061 2 162 55 261 1 654 30 461 these being similar to those of x ray powder patterns of si02 poor calcic amphiboles especially kaersutite both species have very similar physical properties and are dark brown to black with a vitreous luster streak very light brown cleavage 110 perfect h mohs 6 density calc 3 30 g cm3 for sadanagaite and 3 27 g cm3 for magnesio sadanagaite optically biaxial positive with 2v 80 90 meas 86 calc for sadanagaite and with 2v close to 90 meas 88 calc for magnesio sadanagaite refractive indices a 1 673 2 f3 1 684 2 y 1 697 2 c z 28 sadanagaite and a 1 674 2 f3 1 686 2 y 1 699 2 c z 26 magnesio sadanagaite pleochroism strong with x pale brown to z greenish brown sadanagaite and with x colorless to z brownish yellow magnesio sadanagaite the minerals are found in two separate localities yuge and myojin islands japan where they occur in ai tiand fe rich skarns in recrystallized limestone beds forming bands with vesuvianite spinel hercynite sphene ilmenite and apatite in the former locality and forming small lenses with titaniferous fassaite vesuvianite spinel hercynite sphene ilmenite magnetite apatite and perovskite in the latter among them the peculiar composition of titaniferous fassaite is discussed with special reference to its extremely si02 poor ah03and ti02 rich composition the names are for professor ryoichi sadanaga mineralogical institute university of tokyo in recognition of his outstanding contributions to the fields of mineralogy and crystallography 1 present address geological department geological survey of japan higashi 1 1 3 yatabe ibaraki 305 japan 0003 004x 84 0506 0465 02 00 465 466 shimazaki et al sadanagaite and magnesio sadanagaite

low sulfur content in submarine lavas an unreliable indicator of subaerial eruption low s content 250 ppm has been used to identify subaerially erupted hawaiian and icelandic lavas large differences in s content of submarine erupted lavas from different tectonic settings indicate that the behavior of s is complex variations is s abundance in undegassed submarine erupted lavas can result from different source compositions different percentages of partial melting and crystal fractionation low s concentrations in highly vesicular submarine lavas suggest that partial degassing can occur despite great hydrostatic pressure these processes need to be evaluated before using s content as an indicator of eruption depth

synthesis and characterization of amphiboles along the tremolite glaucophane join actinolite and glaucophane are the principal amphiboles in greenschist and blueschist facies metamafic rocks respectively and constitute an important mineral pair for deducing the conditions of medium and high pressure metamorphism here we present the crystal chemical properties of amphiboles synthesized along the tremolite glaucophane join as an important starting point for the more chemically complex samples occurring in nature amphiboles were synthesized in 10 mol increments at conditions ranging from 840 c and 0 6 gpa for tremolite rich to 750 c and 2 5 gpa for glaucophane rich amphiboles the amphibole yields were generally high 95 wt though minor quartz pyroxene and amorphous material either glass or quenched solute were often present electron microprobe analysis of the amphibole showed that deviations from the nominal or intended compositions occurred with the observed compositions showing solid solution primarily toward the katophorite component and reaching a maximum near the middle of the join unit cell dimensions showed a pronounced positive deviation from ideality even after linear correction for the non join components suggesting a strong tendency toward exsolution single crystal refinements of a couple of selected amphiboles confirmed the deviation from nominal composition and confirmed the presence of ana tal and cal the latter disordered between the m 2 and m 3 sites infrared spectra in the oh stretching region were measured on samples that were heated to 250 350 c to remove absorbed moisture the spectra consist of a main band centered in the 3675 3660 cm 1 region and two minor absorptions on both sides of the dominant central peak which are centered at 3720 and 3640 cm 1 and can be attributed to oh next to ana and cal respectively the main band is evidently composed of several overlapping components due to local arrangements of b cations typical of tremolite caca glaucophane nana and cummingtonite mgmg examination of several intermediate amphiboles by both single crystal xrd and by high resolution tem analysis could not identify evidence of reflections or ordered domains that would violate the c 2 m symmetry of the end member amphiboles comparing the compositions of the synthetic amphiboles from this study with winchite rich amphiboles in nature shows that deviations from the tremolite glaucophane join are common the inability to make pure winchite or even winchite rich amphiboles on the tremolite glaucophane join suggests that this structure is unstable