experimental study of subsolidus phase relations and mixing properties of pyroxene in the system cao al2o3 sio2 abstract subsolidus phase relations in the system cao al2o3 sio2 cas were experimentally determined with tight reversals of several univariant curves and with 14 equilibration experiments containing the assemblage pyroxene anorthite where pyroxene is a binary solid solution of ca tschermak cats caal2sio6 and ca eskola caes ca0 5alsi2o6 endmembers reversals were obtained on the following reactions bar c 3an gr 2ky q p 22t 700 3an cor gr 3ky p 21 8t 950 3cats gr 2cor p 55t 53900 and 6cats 1 x caesx 2 1 2x gr 4 1 2x cor 9xan observed slopes indicate 9 8 j mol k of al si disorder in ca tschermak pyroxene and 5 3 j mol k of al si disorder in anorthite at 1300 c it is suggested that al si disorder in anorthite increases by 1 9 j mol k from 700 c to 1300 c compositions of cats caes pyroxene in equilibrium with anorthite and pbo rich liquid were experimentally determined at 1400 1430 c and 22 7 30 8 kbar microprobe measurements gave compositions which are consistent with an ideal pyroxene solution and the following parameters for the reaction 3an 2cats 2caes j bar k 2rtln xcats xcaes 60200 86 4t 5 06 13 10 7p p 0 resulting in h0j 39 8 kj mol and s0 461 8 j mol k for the ca eskola endmember at 1300 c the obtained properties of the ca eskola component are necessary for thermobarometry based on pyroxene bearing assemblages containing plagioclase quartz or kyanite

geothermobarometry of high grade metapelites simultaneously operating reactions s u m m a r y experimental data on equilibria involving rock forming minerals in highgrade metapelites garnet orthopyroxene cordierite and plagioclase have been used to derive an internally consistent system of mineralogical thermometers and barometers based on component reactions and excess mixing properties of solid solutions application of these data to a granulite facies metapelite sample reveals that compositional inhomogeneity of minerals on a thin section scale is likely to be a result of several reactions opening simultaneously at the retrograde stage of metamorphic evolution the widely accepted practice of estimating pressure and temperature from separate reactions may thus lead to errors and misinterpretation of p t paths

geomechanics of hydraulic fracturing microseismicity part 1 shear hybrid and tensile events we investigate the geomechanical behavior of hydraulic fracturing induced microseismicity microseismic events are commonly used to discern stimulation patterns and hydraulic fracture evolution however techniques beyond fracture mapping are required to explain the mechanisms of microseismicity in this series we present an approach to combine seismological and geomechanical techniques to investigate how microseismicity relates to propagating hydrofractures as well as existing natural fractures and faults part 1 describes the first analysis step which is to characterize the microseismic events by their source parameters focal mechanisms and fault plane orientations these parameters are used to determine the mechanical conditions responsible for activation of discrete populations or subpopulations of microseismic events that then can be interpreted in their geological and operational context first we compare microseismic fault plane populations from a mississippian barnett shale texas data set that are determined using a traditional double couple model shear only with a tensile source model hybrid events which may be more suitable for hydraulic fracturing conditions second we employ a new method to distinguish fault planes from auxiliary planes using iterative stress inversion and critical stress instability selection criteria the result is an enhanced microseismic characterization that includes geomechanical parameters such as slip tendency and local activation stress state during the operation using this approach on the barnett shale data two microseismic fault sets are resolved an inclined northeast southwest set with dominant shear and a vertical north south set with more hybrid behavior the results are used in part 2 to further investigate the heterogeneity of the stimulations and to compare models for microseismic activation

the compositions of coexisting pyroxenes and garnet in the system cao mgo al2o3 sio2 at 900 1 100 c and high pressures the compositions of coexisting orthopyroxene clinopyroxene and garnet in the cao mgo al2o3 sio2 system are fixed at any givenp andt reversed hydrothermal experiments over thep t range 15 40 kb 900 l 100 c indicate that the garnet composition is nearly constant at py86gr14 the alcontent and ca ca mg values of the pyroxenes vary significantly however t p wt al2o3 frac ca ca mg times 100 c kbar in opx in cpx in opx in cpx 900 15 3 55 2 92 0 72 47 05 900 30 1 62 0 92 0 81 47 30 1 100 20 1 11 0 92 1 22 45 20 1 100 40 1 26 0 88 0 81 45 64 the significant variation of a12o3 content with pressure supports its use as a geobarometer the ca ca mg values of coexisting orthoand clino pyroxene have been used as a geothermometer however the present results show that the presence of a12o3 in the pyroxenes decreases significantly the mutual solubility of the pyroxenes which may cause errors of up to 200 c if the a12o3 effect is ignored

rutile solubility in albite h2o and na2si3o7 h2o at high temperatures and pressures by in situ synchrotron radiation micro xrf abstract rutile is an important mineral host for high field strength elements so its solubility in geologic fluids at high pressure and temperature plays an important role in the crustal and mantle processes that control the terrestrial cycling of these elements however experimental measurements of rutile solubility are in conflict by a factor of more than 100 at most studied conditions we performed new measurements of rutile solubility in h 2 o albite and h 2 o na 2 si 3 o 7 ns3 fluids by in situ synchrotron radiation x ray fluorescence spectroscopy using modified bassett type hydrothermal diamond anvil cells minimum detection limits were 1 9 and 2 3 ppm ti by weight for the two cells three albite h 2 o experiments at starting bulk compositions of 2 7 6 7 and 10 3 wt albite involved spectral acquisition at rutile saturation in the presence of albite crystals melt or a single homogeneous fluid phase after accounting for the additional phases corrected fluid compositions were 0 6 to 7 5 wt dissolved silicate over the run conditions at 2 7 wt albite rutile dissolution rate was slow and steady state was not achieved at 600 800 c however at higher dissolved albite contents constant solubility with time was observed rutile solubilities in the presence of a single fluid phase at 700 c 0 79 gpa 5 4 wt albite and at 800 c 1 10 gpa 6 7 wt albite were 37 2 and 156 6 ppm respectively these data agree with results acquired using hydrothermal piston cylinder methods with long run times and suppression of new crystal growth but not with data derived from visual observation in hydrothermal diamond anvil cells this discrepancy is likely due to lack of equilibrium in the latter approach two experiments in 10 and 30 wt ns3 at 660 800 c 0 5 0 1 gpa show extreme concentration dependent enhancement of rutile solubility to 4500 ppm the data indicate a strong positive correlation between rutile solubility and na al because na k al is likely to be greater than unity in aqueous fluids at high pressure and temperature due to incongruent dissolution of albite and micas the increase in rutile solubility along the albite ns3 join points to the possibility of significant ti transport by silicate bearing aqueous fluids in the lower crust and upper mantle

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

a survey of earthquakes and injection well locations in the barnett shale texas in august 2012 the proceedings of the national academy of sciences published my article surveying two years of seismicity in the barnett shale of texas the data showed that virtually all well located epicenters were situated within 3 km of high volume injection wells this article summarizes the results of that publication recently there has been concern about earthquakes possibly caused by the disposal of hydrofracture flowback fluids in injection wells most investigations of earthquakes caused by human activity take place only after an earthquake occurs that is severe enough to be felt by nearby residents and receive media attention such events usually have magnitudes m3 or greater and occur in populated areas limiting research only to these events does not help us understand why some injection wells trigger seismic activity and others do not

pressures and temperatures of metamorphism in the eastern dalradian pressures and temperatures have been determined from locations in the eastern dalradian using a number of different geothermometers and geobarometers temperatures range from 550 c in the low kyanite zone to about 800 c in the sillimanite k feldspar zone pressures range from about 5 5 kbar in glen esk to 9 10 kbar in the central highlands the barometric calibrations employed are consistent with the kyanite sillimanite equilibrium evidence from mineral zoning suggests that rocks outside the buchan area in the duchray hill gneiss glens clova and avon and in the schichallion area underwent a pressure decrease synchronous with the metamorphic peak regional temperature variations define a thermal high centred on the cromar glen muick duchray hill gneiss area to the w of this high temperatures decrease rapidly a sharp thermal break occurs between high grade sillimanite k feldspar gneisses in glen muick and kyanite staurolite schists to the w this thermal contrast is attributed to a structural break which may be analogous to a number of other thermal features in the dalradian

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

olivine spinel transitions experimental and thermodynamic constraints and implications for the nature of the 400 km seismic discontinuity the sequence of high pressure phase transitions in olivine is traditionally used as a model for seismic velocity variations in the 200 to 650 km depth interval in a mantle of peridotitic bulk composition it has been proposed that the observed seismic velocity increase at 400 km depth is too sharp and of too small a magnitude to be attributable to the phase change and that the upper mantle must thus be chemically stratified with the 400 km discontinuity being due either to a combination of phase changes in a layer of pyroxene garnet rich piclogite composition or to a chemical boundary between such a piclogite layer and an overlying peridotitic layer using available calorimetric thermoelastic and synthesis data and their associated experimental uncertainties we have derived internally consistent high pressure phase relations for the mg2sio4 fe2sio4 join we find that the divariant transition which is generally regarded as occurring over a broad depth interval for mantle olivine compositions is in fact extremely sharp the seismic discontinuity corresponding to the transition in mg0 9fe0 1 2sio4 should occur over a depth interval isothermal of about 6 km at a depth of approximately 400 km the sharpness of this transition is quite insensitive to uncertainties in the constraining calorimetric thermoelastic and synthesis data in addition we have computed seismic velocity profiles for a model mantle consisting of pure olivine of mg0 9fe0 1 2sio4 composition comparison of these computed profiles to those derived from recent seismic studies indicates that the magnitude of the observed velocity increase at 400 km depth is consistent with a mantle transition zone composed of about 60 70 olivine we conclude that there is no need to infer the existence of pyroxene garnet rich compositions such as eclogite or piclogite in the transition zone since an upper mantle of homogeneous olivine rich peridotitic composition is consistent with the available seismic velocity data

long period long duration seismic events during hydraulic stimulation of shale and tight gas reservoirs part 2 location and mechanisms abstractlong period long duration lpld seismic events that have been observed during hydraulic stimulation of shale gas and tight gas reservoirs appear to represent slow shear slip on relatively large faults within the limitations of the recording geometry we determine the areas in the reservoirs where the events are located in two case studies in the barnett shale in one data set lpld events appear to occur in the region where the density of natural fractures as well as the fluid pressure during pumping were highest in the other data set the lpld events are observed to occur between two wells and seem to establish a hydraulic connection between them in both data sets the lpld events occur in areas with very few located microearthquakes a combination of factors such as high fluid pressure and or high clay content is potentially responsible for the slowly slipping faults the lpld events appear to be occurring only on faults large enough to produce a sequence of slow slip events we suggest that

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

archean upper crust transition from mafic to felsic marks the onset of plate tectonics the archean eon witnessed the production of early continental crust the emergence of life and fundamental changes to the atmosphere the nature of the first continental crust which was the interface between the surface and deep earth has been obscured by the weathering erosion and tectonism that followed its formation we used ni co and cr zn ratios in archean terrigenous sedimentary rocks and archean igneous metaigneous rocks to track the bulk mgo composition of the archean upper continental crust this crust evolved from a highly mafic bulk composition before 3 0 billion years ago to a felsic bulk composition by 2 5 billion years ago this compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks suggesting the onset of global plate tectonics at 3 0 billion years ago

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

experimental and modeled chlorine solubilities in aluminosilicate melts at 1 to 7000 bars and 700 to 1250 c applications to magmas of augustine volcano alaska hydrothermal experiments were conducted at ca 1 to 7000 bars and 700 to 1250 c in 121 rhyolitic to basaltic systems to determine cl solubility in silicate melts i e the maximum cl concentration in melts that are saturated in a hydrosaline liquid with or without an aqueous or aqueous carbonic vapor the cl concentration of melts increases with the cl contents of the fluid unless the melt coexists with vapor plus hydrosaline liquid at fixed pressure and temperature this phase assemblage buffers the cl content of each phase with increasing cl in the system the cl content of fluid s saturated melts is independent of the co 2 concentration of the saline liquid vapor with up to 21 wt co 2 in the fluid s the experiments show that cl dissolution in aluminosilicate melts increases with temperature and pressure chlorine solubility is also a function of melt composition it increases with the molar al 1 2 ca 1 2 mg 1 2 na si of the melt these experimental data have been integrated with results involving 41 other experiments webster and de vivo 2002 to develop a broadly expanded model that supports calculation of cl solubility in 163 aluminosilicate melts this empirical model applies to cl dissolution in melts of most silicate magmas at depths as great as 25 km it determines the exsolution of hydrosaline liquid with or without a coexisting vapor as magmas ascend from depth cool crystallize and differentiate from mafic to felsic compositions in combination with h 2 o solubility models our model supports determination of h 2 o cl solubility relations for most aluminosilicate magmas and is useful for barometric estimations based on silicate melt inclusions containing low co 2 and moderate to high cl concentrations the model is applied to the phase relations of fluids in volatile enriched magmas of augustine volcano alaska the cl and h 2 o concentrations of melt inclusions from 14 basaltic to dacitic eruptive units are compared with modeled solubilities of cl and h 2 o in augustine melts the majority of these eruptions involved magmas that first exsolved aqueous to aqueous carbonic vapors when the melts were dacitic in composition i e before the residual melts in these magmas had evolved to felsic compositions and well prior to the eruptions hydrosaline liquid with or without a vapor phase exsolved from other more felsic fractions of augustine melts at low near surface pressures of several tens of bars

the stability of mg rich garnet in the system cao mgo al 2 o 3 sio 2 at 1000 1300 degrees c and high pressure buffering assemblages are stable in separate divariant p t fields separated by three univariant reactions garnet quartz orthopyroxene anorthite sillimanite garnet quartz clinopyroxene orthopyroxene anorthite clinopyroxene sillimanite garnet quartz anorthite the sequence of mineral assemblages is consistent with natural parageneses modified journal abstract

geomechanics of hydraulic fracturing microseismicity part 2 stress state determination we investigate the hydraulic fracturing process by analysis of the associated microseismicity in part 1 we recognized double couple and hybrid microseismic events and their fault plane orientations critical stress instability and stress inversion techniques were used to assess fracture activation conditions in part 2 we apply results from the tensile source model to investigate how activated faults relate to the stress state and geologic setting we assess potential mechanisms for induced microseismicity including leakoff and diffuse pressurized fracture network flow stress shadowing adjacent to large parent hydraulic fractures and crack tip stress perturbations data are from the mississippian barnett shale texas and include microseismic events from sequential pumping stages in two adjacent horizontal wells that were recorded in two downhole monitor wells as well as operations wellbore derived stress and natural fracture data results point to activation of inclined faults whose orientation is dominantly northeast southwest and vertical north south faults the activation stress states for a range of modeling scenarios show stress rotation decreased mean stress and increased deviatoric stress this stress state cannot be explained by sidewall leakoff in the stress shadow region adjacent to hydrofractures but is consistent with hybrid and shear activation obliquely ahead of pressurized fractures information about hydrofracture evolution and operationally related dynamic stress change is obscured by geomechanical heterogeneity that is likely geologic in nature the most compelling observation is that the most highly misoriented microseismic faults occur in the same vicinity as a carbonate dominated submarine fan feature that was previously expected to act as a minor fracture barrier

increasing seismicity in the u s midcontinent implications for earthquake hazard abstract earthquake activity in parts of the central united states has increased dramatically in recent years the space time distribution of the increased seismicity as well as numerous published case studies indicates that the increase is of anthropogenic origin principally driven by injection of wastewater coproduced with oil and gas from tight formations enhanced oil recovery and long term production also contribute to seismicity at a few locations preliminary hazard models indicate that areas experiencing the highest rate of earthquakes in 2014 have a short term one year hazard comparable to or higher than the hazard in the source region of tectonic earthquakes in the new madrid and charleston seismic zones

the eclogite to garnetite transition experimental and thermodynamic constraints we have found that the forms of the experimentally determined phase diagrams for pyroxene garnet transformations require the volume changes for these reactions to be much smaller at 130 kbar 400 km than at 1 atm using these volume data we calculated the width of the eclogite garnetite transition in natural quartz tholeiite and alkali olivine basalt compo sitions taking account of mixing in multicom ponent pyroxene and garnet phases we find that the eclogite garnetite transition does not exhi bit any discontinuity in bulk sound velocity in the pressure range 110 to 230 kbar in addition this velocity when plotted as a function of pressure possesses a curvature which is in the opposite sense to that given by the preliminary reference earth model prem this phase transi tion therefore does not appear to be a satis factory model for the 400 km seismic discon tinuity

long period long duration seismic events during hydraulic fracturing implications for tensile fracture development long period long duration lpld seismic events are observed from a microseismic data set acquired by surface receivers in the eagle ford shale these events are characterized by low frequencies of 10 60 hz and long durations of 30 60 s the seismograms are dominated with p waves and the frequency spectra have peaks at several isolated frequencies similar to volcanic tremors the lpld events are located close to the horizontal hydraulic treatment well and migrate away from the well with time these observations suggest that the lpld events are related to hydraulic fracturing and are possibly caused by the jerky opening and resonance of fluid filled cracks imaging this type of lpld events can potentially map fluid flow and tensile fracture development during hydraulic fracturing

how feasible was subduction in the archean as the asthenospheric mantle rises at oceanic spreading centres it undergoes partial melting producing oceanic crust and depleted mantle both of which have lower intrinsic density than the asthenospheric mantle from which they were derived with a warmer asthenosphere in the archean these effects are enhanced leading to the possibility that subduction was no longer feasible i investigate the density of the oceanic crust and underlying mantle for a mantle with temperatures 200 c higher than today using models of the chemistry of melting and the mineralogy of the ensuing rocks for the melting model used crustal thicknesses are 21 km and the depth to which the mantle is partially melted is 114 km compared with 7 and 54 km for a comparable model of modern earth two thermal evolution models for archean oceanic lithosphere are examined one assumes twice the heat flow into the base of the plates which severely restricts the depths to which the plates can cool with age a second assumes the plates c

constraints on the mobilization of zr in magmatic hydrothermal processes in subduction zones from in situ fluid melt partitioning experiments the partitioning of zr between high p t aqueous fluids and melts has been investigated in situ in the haplogranite h2o and haplogranite f h2o systems to assess the mobilization of high field strength elements hfse in magmatic hydrothermal processes in subduction zones the partition coefficients d f mzr were determined from zr concentrations measured in situ by synchrotron x ray fluorescence sxrf in both aqueous fluids and f free or f bearing hydrous haplogranite melts equilibrated in diamond anvil cells at 575 to 800 c and 0 3 to 2 4 gpa this experimental approach eliminates the need for internal or external calibrations of the sxrf signal and or post mortem analysis of the melt phase hence decreasing the total uncertainties on d f mzr below 16 above 0 6 gpa zr partitions favorably into the hydrous silicate melt in both f free and f bearing systems with d f mzr that range between 0 19 0 02 and 0 38 0 03 however the relatively high d f mzr values indicate that alkali silica rich aqueous fluids generated by metamorphic devolatilization may contribute significantly to the recycling of hfse in subduction zones the efficient uptake of zr and likely other hfse by subduction zone fluids regardless of their nature aqueous fluid hydrous melt or supercritical fluid supports the idea that the typical hfse depletion recorded in arc magmas does not result from their incompatibility in water rich slab derived fluids but most probably originates from complex fluid melt rock interactions occurring at the slab interface and within the mantle wedge at shallow crustal pressure conditions 800 c and 0 3 gpa zr partitions reversely into the aqueous fluid in the presence of fluorine d f mzr 1 40 0 10 as observed for nb at similar conditions by webster et al 1989 the enrichment of the aqueous phase in hfse zr nb at shallow crustal conditions is likely related to the enhanced peralkalinity of low pressure f bearing aqueous fluid with temperature that provides the favorable conditions for their mobilization via the formation of hfse o si na clusters this mechanism may control the enrichment in hfse and plausibly other rare metals such as ree in early magmatic fluids exsolved from granitic melts leading to the formation of hfse enriched aggregates in shallow magmatic hydrothermal environments e g strange lake and thor lake nechalacho deposit canada galineiro complex spain

free energy minimization by simulated annealing with applications to lithospheric slabs and mantle plumes an optimization algorithm based upon the method of simulated annealing is of utility in calculating equilibrium phase assemblages as functions of pressure temperature and chemical composition operating by analogy to the statistical mechanics of the chemical system it is applicable both to problems of strict chemical equilibrium and to problems involving metastability the method reproduces known phase diagrams and illustrates the expected thermal deflection of phase transitions in thermal models of subducting lithospheric slabs and buoyant mantle plumes it reveals temperature induced changes in phase transition sharpness and the stability of fe rich phase within an field in cold slab thermal models and it suggests that transitions such as the possible breakdown of silicate perovskite to mixed oxides can amplify velocity anomalies

constraining the composition and thermal state of the mantle beneath europe from inversion of long period electromagnetic sounding data 1 we reexamine the problem of inverting c responses covering periods between 1 month and 1 year collected from 42 european observatories to constrain the internal structure of the earth earlier studies used the c responses which connect the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic variations to obtain the conductivity profile of the earth s mantle here we go beyond this approach by inverting directly for chemical composition and thermal state of the earth rather than subsurface electrical conductivity structure the primary inversion parameters are the composition of the earth s mantle within the system cao feo mgo al2o3 sio2 and geotherm given these parameters we calculate mineral modes at the prevailing physical conditions and combine these with laboratory based models for the conductivity of individual minerals to estimate the bulk earth electrical conductivity structure from which c responses are calculated to further constrain the radial density profile we also invert for mass and moment of inertia the results agree with earlier geophysically derived conductivity and seismic velocity models and confirm that inversion of geophysical data for compositional parameters planetary composition and thermal state is feasible the inversion indicates most probable lower mantle geothermal gradients of 0 58 k km core mantle boundary temperatures of 2900 c bulk earth molar mg si ratios of 1 1 intermediate between the chondrite and pyrolite models and no significant change in mantle composition across the 670 km seismic discontinuity

continuous reactions with amphibole garnet and plagioclase end member continuous and degenerate reactions are derived for the multisystem with the six components na2o cao mg fe o al2o3 sio2 h2o among the phases plagioclasess garnetss amphiboless cpx opx olivine spinel quartz and an aqueous fluid the chemography of this system is degenerate due to the co linearity 2opx ol qtz this co linearity has its implications both on reaction space and phase equilibria from a total of 28 reaction systems reaction space is derived for nine subsystems phases in parentheses are absent case a1 cpx ol cpx opx and cpx qtz case a2 spl ol spl opx and spl qtz case b ol opx ol qtz and opx qtz in the absence of either cpx or spl case a three reactions form an invariant point either cpx or spl where the co linear phases olivine opx and quartz coexist on the transformation line 2opx ol qtz changing mineral compositions force invariant points to move along the line with the different reaction curves changing their relative position according to schreinemakers rules zero contours i e the location where a phase s disappear s in reaction space correspond to singular points in phase diagrams two types are distinguished singular points of indispensable and of substitutable phases in the first case the phase disappears from the entire bundle while in the second it disappears from a single reaction in the specific case where the substitutable phases are also the co linear ones two of the three co linear phases disappear simultaneously two of the three reaction curves coincide in the system including cpx and spl case b three reactions ol opx ol qtz and opx qtz oppose three invariant points ol opx and qtz invariant points no longer move along the line 2opx ol qtz the coincidence of the zero contours of all three co linear phases in reaction space the result of the chemographic degeneracy causes the respective singular points to coincide in the phase diagrams this is the location where curves must be rearranged in a bundle to conform schreinemakers rules the reaction grs1prp2 2 ol an is fourth order degenerate and part of all nine subsystems cases a and b it can be used to relate the different phase diagrams to one another

uncertainty of mantle geophysical properties computed from phase equilibrium models phase equilibrium models are used routinely to predict geophysically relevant mantle properties a limitation of this approach is that nonlinearity of the phase equilibrium problem precludes direct assessment of the resultant uncertainties to overcome this obstacle we stochastically assess uncertainties along self consistent mantle adiabats for pyrolitic and basaltic bulk compositions to 2000 km depth the dominant components of the uncertainty are the identity composition and elastic properties of the minerals for p wave speed and density the latter components vary little whereas the first is confined to the upper mantle consequently p wave speeds densities and adiabatic temperatures and pressures predicted by phase equilibrium models are more uncertain in the upper mantle than in the lower mantle in contrast uncertainties in s wave speeds are dominated by the uncertainty in shear moduli and are approximately constant throughout the model depth range

garnet orthopyroxene plagioclase quartz barometry refinement and application to the english river subprovince and the minnesota river valley recent experimental theoretical and thermodynamic studies permit better calibration of two reactions for geobarometry grossular pyrope quartz anorthite enstatite grossular almandine quartz anorthite ferrosilite if both reactions are applied using the same thermodynamic data and activity models they should yield the same pressure for a given garnet pyroxene plagioclase quartz assemblage application to a variety of high grade terrains generally yielded excellent results however poor results have been obtained for high fe rocks which can be traced to errors in activity models for garnet and or pyroxene either a two site ideal mixing model for orthopyroxene cf wood and banno 1973 underestimates enstatite activity for high fe orthopyroxenes or the ganguly and saxena 1984 model overestimates pyrope activity in low mg garnets

very low solubility of rutile in h2o at high pressure and temperature and its implications for ti mobility in subduction zones the solubility of rutile in h2o has been measured at 1000 1100 c 1 2 gpa the data indicate that solubility is very low over the investigated range with a maximum of 4 7 millimol kg h2o at 1100 c 2 gpa the data were fit with the equation log m ti 4 892 10470 t 0 1923 p where m ti is ti molality t is in kelvins and p in gpa when compared to previous results the new data indicate substantially lower solubility opposite pressure dependence and thermodynamic properties of the reaction rutile tio2 aq that are now consistent with other oxide hydrolysis reactions calculations of ti transport during mantle metasomatism by h2o in subduction zone environments predict much lower ti mobility at all conditions these results offer strong support for models of ti retention in eclogites during slab devolatilization and require that examples of significant ti mass transfer be explained by complexing agents in solution most likely aluminosilicate complexes

native metals and intermetallic compounds in subduction related ultramafic rocks from the stanovoy mobile belt russian far east implications for redox heterogeneity in subduction zones abstract plutonic associations in orogenic belts are potent indicators of multi stage fractionation of primitive arc magmas and growth of island arc crust under evolving redox conditions in ancient subduction zones ildeus lucha ultramafic mafic complex ilc was emplaced at 232 233 ma within the mesozoic stanovoy convergent margin and subsequently underwent multi stage hydrothermal alteration and greenschist to amphibolite facies metamorphism 140 ma followed by adakite and k lamprophyre magmatism 114 117 ma dunite wehrlite pyroxenite and gabbro in the ilc are composed of olivine clinopyroxene orthopyroxene plagioclase and late magmatic amphibole mineral compositions in the ilc are typical of island arc plutonic complexes characterized by early crystallization of orthopyroxene plagioclase intercumulus and presence of magmatic amphibole ultramafic mafic rocks display high field strength hfs element depletions coupled with large ion lithophile lil element enrichments indicating formation via crystal fractionation of mafic primary magma derived from a subduction related mantle source some ultramafic rocks from the ilc contain native metals w pt au ag zn bi and intermetallic compounds cu au ag pt rh pd cu sn zn etc included in silicate minerals or observed as discrete phases in the finer grained silicate oxide sulfide matrix textural evidence and association with either primary magmatic or secondary metasomatic or metamorphic mineral phases suggest either magmatic high temperature or metasomatic low temperature origin of metals and metallic compounds the following models of their formation can be proposed on the basis of the presented data a crystallization w and possibly pt from metal rich arc magmas under unusually reduced conditions in subduction related lithosphere b formation from magmatic sulfides during pervasive serpentinization and release of abiogenic hydrocarbons and c precipitation from chlorine rich saline aqueous fluids associated with collision related metasomatism of the stanovoy island arc crust

fluids and trace element transport in subduction zones melt inclusion data from primitive arc basalts from mexico and kamchatka show clear positive correlations of fluid mobile element h 2 o ratios with the cl h 2 o ratio suggesting that the trace element content of subduction zone fluids is strongly enhanced by complexing with chloride this effect is observed for large ion lithophile lile elements e g rb and sr but also for the light rare earth elements ree e g la and ce as well as for u the correlations of these elements with cl h 2 o cannot be explained by the addition of sediment melts or slab melts to the mantle source since cl has no effect on the solubility or partitioning of these elements in silicate melt systems on the other hand the observed relationship of trace element abundance with cl is consistent with a large body of experimental data showing greatly enhanced partitioning into aqueous fluid upon addition of chloride accordingly it appears that a dilute cl bearing aqueous fluid is the main carrier of lile light ree and u from the slab to the source of melting in arcs moreover elevated ce h 2 o ratios clearly correlate with fluid salinity and therefore are not suitable as a slab geothermometer from a synopsis of experimental and melt inclusion data it is suggested that the importance of sediment or slab melting in the generation of arc magmas is likely overestimated while the effects of trace element scavenging from the mantle wedge may be underestimated moreover establishing reliable data sets for the fluid mineral partition coefficients of trace elements as a function of pressure temperature and salinity requires additional efforts since most of the commonly used experimental strategies have severe drawbacks and potential pitfalls

the transition from pyroxene granulite facies to garnet clinopyroxene granulite facies experiments in the system cao mgo al2o3 sio2 the pressure temperature curve for the equilibrium anorthite 2enstatite pyrope diopside quartz has been determined in the system cao mgo al2o2 sio2 to be between 13 4 and 14 0 kbars at 900 c the slope up to 1 240 c is 8 5 bar k the entropy change at 1 200 k is 20 kj these data combined with data from the literature lead to a geobarometer equation which when applied to rocks from the agto area west greenland gives pressure estimates of 6 10 kbars at 800 c the results are consistent for rocks of differing fe mg ratios and are consistent with independent pressure estimates

u series isotope data on lau basin glasses the role of subduction related fluids during melt generation in back arc basins new thermal ionization mass spectrometry u series disequilibrium data are presented for 24 basaltic to dacitic glasses from active spreading centres in the back arc lau basin sw pacific together with additional inductively coupled plasma mass spectrometry trace element analyses and sr nd pb isotope data valu fa ridge samples adjacent to the arc front have high u th and 230th 238u 1 implying a recent 350 ka addition of a u rich slab derived fluid the valu fa data can be combined with existing 230th 238u data for the central tonga arc to infer a fluid addition event at 50 ka the similar sources and time scales for fluid transfer beneath the valu fa ridge and beneath the arc itself suggest that the valu fa ridge is propagating into the arc front region central lau basin samples further behind the arc have lower u th and 230th 238u 1 similar to typical mid ocean ridge basalts morb within the central lau basin a water rich subduction component is seen only in samples closest to the arc and this fluid does not have the high u th composition of the fluid at valu fa melt generation in the central lau basin appears to be dominated by normal ridge type processes but the relatively low 230th 238u for these shallow ridges compared with global morb could be a consequence of increased melt productivity as a result of the elevated water contents the transition from 238u to 230th excesses within the back arc basin is not a smooth function of decreasing addition of a u rich fluid moving away from the arc front but also reflects the complex dynamics between two major mantle domains within the mantle wedge pacific beneath valu fa ridge indian beneath the central lau basin

cell parameters of thermally treated anorthite al si configurations in the average structures of the high temperature calcic plagioclases thermal treatments of anorthite carried out at up to 1 547 c show that the unit cell parameter changes as a function of the treatment temperature the best fit curve found by non linear least squares analysis is 91 419 0 327 10 6 t2 0 199 10 12 t4 0 391 10 t6 the results obtained support significant al si disorder al 0 10 where al t1 0 1 3 t1 m t2 0 t2 m ribbe 1975 in anorthite equilibrated near the melting point and confirm a high temperature series differentiated from the low temperature series for calcic plagioclases in the an85 an100 range also in the plot vs an content the high and low temperature curves intersect at an85 composition and progressively diverge in the an85 an100 range the trends of the high and low temperature curves in this range are interpretable on the basis of the degree of al si order in the average structures of calcic plagioclases

a thermodynamic model for subsolidus equilibria in the system caomgoal2o3sio2 this study integrates phase equilibrium and calorimetric data for the following phases in the cao mgo al2o3 sio2 system clinopyroxene orthopyroxene garnet fomente anorthite spinel kyanite sillimanite corundum and quartz the internally consistent data set includes mixing properties for clinopyroxene orthopyroxene and garnet solid solutions and enables calculation of any equilibrium involving the components of the above 10 phases under any desired p t conditions major conclusions of the study apart from the data set are 1 1 spinel appears to have an enthalpy of mg al exchange on the order of 20 kcal or more substantially above the calorimetrically measured value 2 2 caal2sio6 pyroxene has virtually complete al si disorder 3 3 enstatite has an enthalpy of formation from oxides at 1000 k of about 16840 cal mole substantially greater than the calorimetric value of 17620 340 cal 4 4 anorthite has about 0 6 cal k entropy of al si disorder 5 5 cmas garnets of between pyrope100 and pyrope80grossular20 composition have almost zero excess entropy 6 6 nonstoichiometry in clinopyroxene has a moderate but predictable influence on reaction boundaries in sio2 saturated compositions

efforts to monitor and characterize the recent increasing seismicity in central oklahoma abstract the sharp increase in seismicity over a broad region of central oklahoma has raised concerns regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure efforts to monitor and characterize the earthquake sequences in central oklahoma are reviewed since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma to record the evolving seismicity a multiple event relocation method is applied to produce a catalog of central oklahoma earthquakes from late 2009 into early 2015 regional moment tensor rmt source parameters were determined for the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled determination of the length depth and style of faulting occurring on reactivated subsurface fault systems it was found that the majority of earthquakes occur on near vertical optimally oriented northeast southwest and northwest southeast strike slip fault

the al 2 o 3 contents of enstatite in equilibrium with garnet in the system mgo al 2 o 3 sio 2 at 15 40 kbar and 900 1 600 c forty six reversed determinations of the al2o3content of enstatite in equilibrium with garnet were made in the p t range 15 40 kbar 900 1 600 c in the mgo al2o3 sio2 system starting materials were mixtures of synthetic pyrope al free enstatite and pyrope enstatite 5 12 al2o3 al2o3 contents in reversal run pairs closely approached common values from both the high and low al sides most experiments were done in a piston cylinder device using a nacl medium some runs at very high temperatures were made in pyrex nacl or pyrex talc assemblies the measured enstatite compositions expressed as mole fractions of mg2 mgal alsi3 o12 x opy en were fitted by a monte carlo method to the equilibrium condition begin gathered delta h 970 0 970 delta s 970 0 hfill mathop smallint limits 1 p delta v 970 0 dp mathop smallint limits 970 t delta s t 0 dt rt ln x opy en 0 hfill end gathered where the best fit parameters of h s and v 1 bar 970 k for the reaction pyrope opy are 2 040 cal mol 2 12 eu and 9 55 cc mol in addition to the determination of al2o3 contents of enstatite the univariant reaction pyrope forsterite enstatite spinel was reversibly located in the range 1 100 1 400 c a best fit line passes through 22 22 5 and 25 kbar at 1 040 1 255 and 1 415 c respectively our results for the univariant reaction are in agreement with previous studies of macgregor 1974 and haselton 1979 however comparison of the experimentally determined curve with thermochemical calculations suggests that there may be a small error in the tabulated h f 970 1 0 value for enstatite a value of 8 32 rather than 8 81 kcal mole charlu et al 1975 is consistent with the present data application of garnet enstatite spinel forsterite equilibria to natural materials is fraught with difficulties the effects of nonternary components are poorly understood and the low solubilities of al2o3 in enstatite under most geologically reasonable conditions make barometric or thermometric calculations highly sensitive more detailed studies including reversed determinations in low friction assemblies are sorely needed before the effects of important diluents such as fe ca and cr can be fully understood

fluid generation and evolution during exhumation of deeply subducted uhp continental crust petrogenesis of composite granite quartz veins in the sulu belt china

complete miscibility between silicate melts and hydrous fluids in the upper mantle experimental evidence and geochemical implications the phase relationships between silicate melts and hydrous fluids were studied by direct visual observation in an externally heated diamond anvil cell complete miscibility of silicate melt and water was observed for a wide range of melt compositions including nepheline jadeite dacite haplogranite and ca bearing granite some evidence for complete miscibility was also observed in the system basalt h2o the critical temperatures in all systems decrease rapidly with pressure at 15 kbar the critical temperature for nepheline is around 550 c for jadeite around 800 c and for granitic compositions it is close to 900 c in general the critical temperatures appear to increase with silica content in the system our results suggest that there is complete miscibility between silicate melts and water in most of the upper mantle except at very shallow depths this means that a water saturated solidus cannot be defined any more in the deeper parts of the upper mantle very silica rich melt inclusions found in spinel lherzolites associated with fluid inclusion are probably the result of the unmixing of a supercritical fluid containing comparable amounts of water and silicate components the decomposition of amphibole in a subducted slab occurs at conditions where the miscibility gap between fluid and silicate melt is not yet closed while the decomposition of phengite and lawsonite occurs far beyond the critical curve accordingly the fluids released by the breakdown of these minerals should have very different properties highly mobile hydrous fluids containing little dissolved silicate should be produced by amphibole breakdown while the decomposition of lawsonite and phengite will lead to much more silicate rich and less mobile fluid phases

calibration of al si order variations in anorthite new single crystal diffraction data for natural and heat treated anorthite crystals angel et al 1990 allow the determination of their states of al si order in terms of a macroscopic order parameter qod for the transition numerical values ofqod obtained from estimates of site occupancies are shown to vary with the scalar spontaneous strain es as es qod2 and with the ratio of the sums of typeb superlattice reflections and typea sublattice reflections as ib ia qod2 an empirical calibration for pure anorthite is obtained giving q od 10 1 left 5 right sqrt varepsilon s varies between 0 92 and 0 87 in samples equilibrated at t 1300 c but then falls off relatively rapidly with increasing temperature reaching 0 7 near the melting point 1557 c the observed temperature dependence does not conform to the predictions of the simplest single order parameter models coupling ofqod withq of the transition is suspeeted

on the nature of long period long duration seismic events detected during hydraulic fracturing abstractlong period long duration lpld seismic events are low amplitude tremor like seismic signals that have been observed in some microseismic monitoring data sets acquired during hydraulic fracturing operations the lpld events have been interpreted to be associated with slow slip along preexisting fractures presumed to either have high clay content or be misaligned with respect to the current day principal stress directions however a recent study indicates that regional earthquakes when recorded on vertical downhole monitoring arrays have similar signal characteristics to lpld events and that care must be taken when analyzing and interpreting such signals using data from a hydraulic fracturing microseismic data set in which lpld events have previously been identified and well documented together with data from the earthscope transportable usarray we have investigated the hypothesis that the documented lpld events were regional earthquakes we have determined that the lpld events corresponded

electrical conductivity of nacl bearing aqueous fluids to 600 c and 1 gpa the electrical conductivity of aqueous fluids containing 0 01 0 1 and 1 m nacl was measured in an externally heated diamond cell to 600 c and 1 gpa these measurements therefore more than double the pressure range of previous data and extend it to higher nacl concentrations relevant for crustal and mantle fluids electrical conductivity was generally found to increase with pressure and fluid salinity the conductivity increase observed upon variation of nacl concentration from 0 1 to 1 m was smaller than from 0 01 to 0 1 m which reflects the reduced degree of dissociation at high nacl concentration measured conductivities can be reproduced r2 0 96 by a numerical model with log sigma 1 7060 93 78 t 0 8075 log c 3 0781 log rho log varlambda 0 t rho where sigma is the conductivity in s m 1 t is temperature in k c is nacl concentration in wt rho is the density of pure water in g cm3 at given pressure and temperature and varlambda 0 t rho is the molar conductivity of nacl in water at infinite dilution in s cm2 mol 1 varlambda 0 1573 1212 rho 537 062 t 208 122 721 t2 this model allows accurate predictions of the conductivity of saline fluids throughout most of the crust and upper mantle it should not be used at temperatures below 100 c in general the data show that already a very small fraction of nacl bearing aqueous fluid in the deep crust is sufficient to enhance bulk conductivities to values that would be expected for a high degree of partial melting accordingly aqueous fluids may be distinguished from hydrous melts by comparing magnetotelluric and seismic data h2o nacl fluids may enhance electrical conductivities in the deep crust with little disturbance of vp or vp vs ratios however at the high temperatures in the mantle wedge above subduction zones the conductivity of hydrous basaltic melts and saline aqueous fluids is rather similar so that distinguishing these two phases from conductivity data alone is difficult observed conductivities in forearc regions where temperatures are too low to allow melting may be accounted for by not more than 1 wt of an aqueous fluid with 5 wt nacl if this fluid forms a continuous film or fills interconnected tubes

long period long duration seismic events during hydraulic stimulation of shale and tight gas reservoirs part 1 waveform characteristics abstractlong period long duration lpld seismic events are relatively low amplitude signals that have been observed during hydraulic fracturing in several shale gas and tight gas reservoirs these events are similar in appearance to tectonic tremor sequences observed in subduction zones and transform fault boundaries lpld events are predominantly composed of s waves but weaker p waves have also been identified in some cases microearthquakes are observed during the events based on the similarity with tectonic tremors and our observations of several impulsive s wave arrivals within the lpld events we interpret the lpld events as resulting from the superposition of slow shear slip events on relatively large faults most large lpld waveforms appear to start as a relatively slower low amplitude precursor lacking clear impulsive arrivals we estimate the energy carried by the larger lpld events to be 1000 times greater than a mw 2 microseismic event that is typical of the events that occur during hyd

garnet pyroxene equilibria in the system cao mgo al 2 o 3 sio 2 cmas prospects for simplified t independent lherzolite barometry and an eclogite barometer new experimental data on compositions of garnets in two pyroxene garnet assemblages in the system cao mgo al2o3 sio2 cmas are presented for conditions between 1 100 and 1 570 c and 30 to 50 kb garnets in these assemblages become less calcic with increasing pressure garnet orthopyroxene barometry al solubility barometry pertinent to geobarometry for garnet lherzolites has been evaluated with a set of experimental data covering the range 900 to 1 570 c and 15 to 100 kb various formulations of this barometer work well to 75 kb phase equilibria are not sufficient to positively verify the thermodynamic validity of any of such models empirical garnet orthopyroxene barometry at least in the system cmas can be formulated to obtain a pressure estimate without previous temperature estimation p kb 34 4 19 175 1n x al m1 17 702 1n x ca m2 the potential application of an analogous garnetclinopyroxene equilibrium is limited because the amount of ca tschermaks in natural clinopyroxenes is usually quite small in garnet lherzolites and many eclogites the ca mg exchange between garnet and clinopyroxene appears however sufficiently sensitive to pressure to allow calibration of a cmas barometer the reaction 3camgsi2o6 mg3al2si3o12 3mg2si2o6 ca3al2si3o12 has a v o of 3 5 cm3 the total pressure dependency of this reaction is however closer to a theoretical v o of about 5 cm3 when excess volume properties of the phases involved are taken into account we have calibrated such a barometer mean error of estimate 2 8 kb for assemblages with pyrope rich py 80 garnets and orthopyroxenes this may provide the basis for a geobarometer for eclogites from kimberlites

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

theoretical prediction of phase relationships in planetary mantles calorimetric and phase equilibrium data have been used to establish an internally consistent thermodynamic data base for the silica undersaturated part of the system na2o feo cao mgo al2o3 sio2 this data base has been used to calculate the stability fields of assemblages involving the phases olivine ol orthopyroxene opx clinopyroxene cpx spinel sp plagioclase plag and garnet gt at high pressures and temperatures in the six component system all these phases are solid solutions their mixing properties were also obtained from phase equilibrium and calorimetric data in the model system cao mgo al2o3 sio2 cmas the stable assemblages are ol opx cpx plag at pressures less than 8 kb at 1300 c and less than 6 kb at 900 c above these pressures spinel replaces plagioclase until pressures of 16 kb at 1300 and 14 kb at 900 c are reached at higher pressures garnet lherzolite ol opx cpx gt is stable stable phase assemblages have also been calculated for sodium and iron bearing compositions postulated as possible martian mantles the mcgetchin smyth composition would not contain orthopyroxene and a low pressure assemblage of plag ol cpx sp would be replaced by gt ol cpx sp at pressures above 13 kb in contrast the morgan anders composition has stability fields of plagioclase iherzolite p 8 kb and a small field of spinel iherzolite at about 6 kb at temperatures below 900 c

an automated strategy for calculation of phase diagram sections and retrieval of rock properties as a function of physical conditions we formulate an algorithm for the calculation of stable phase relations of a system with constrained bulk composition as a function of its environmental variables the basis of this algorithm is the approximate representation of the free energy composition surfaces of solution phases by inscribed polyhedra this representation leads to discretization of high variance phase fields into a continuous mesh of smaller polygonal fields within which the composition and physical properties of the phases are uniquely determined the resulting phase diagram sections are useful for understanding the phase relations of complex metamorphic systems and for applications in which it is necessary to establish the variations in rock properties such as density seismic velocities and volatile content through a metamorphic cycle the algorithm has been implemented within a computer program that is general with respect to both the choice of variables and the number of components and phases possible in a system and is independent of the structure of the equations of state used to describe the phases of the system

a geophysical perspective on the bulk composition of mars we invert the martian tidal response and mean mass and moment of inertia for chemical composition thermal state and interior structure the inversion combines phase equilibrium computations with a laboratory based viscoelastic dissipation model the rheological model which is based on measurements of anhydrous and melt free olivine is both temperature and grain size sensitive and imposes strong constraints on interior structure the bottom of the lithosphere defined as the location where the conductive geotherm meets the mantle adiabat occurs deep within the upper mantle 250 500 km depth resulting in apparent upper mantle low velocity zones assuming an fe fes core our results indicate 1 a mantle with a mg molar mg mg fe of 0 75 in agreement with earlier geochemical estimates based on analysis of martian meteorites 2 absence of bridgmanite and ferropericlase dominated basal layer 3 core compositions 13 5 16 wt s core radii 1640 1740 km and core mantle boundary temperatures 1560 1660 c that together with the eutectic like core compositions suggest the core is liquid and 4 bulk martian compositions that are overall chondritic with a fe si wt ratio of 1 63 1 68 we show that the inversion results can be used in tandem with geodynamic simulations to identify plausible geodynamic scenarios and parameters specifically we find that the inversion results are reproduced by stagnant lid convection models for a range of initial viscosities 1019 1020 pa s and radioactive element partitioning between crust and mantle around 0 001 the geodynamic models predict a mean surface heat flow between 15 25 mw m2

mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab slab derived fluids play an important role in heat and material transfer in subduction zones dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow nevertheless direct observations of the fluid chemistry and pressure temperature conditions of fluids are few this report describes co2 bearing saline fluid inclusions in spinel harzburgite xenoliths collected from the 1991 pinatubo pumice deposits the fluid inclusions are filled with saline solutions with 5 1 1 0 wt nacl equivalent magnesite crystals co2 bearing vapor bubbles and a talc and or chrysotile layer on the walls the xenoliths contain tremolite amphibole which is stable in temperatures lower than 830 c at the uppermost mantle the pinatubo volcano is located at the volcanic front of the luzon arc associated with subduction of warm oceanic plate the present observation suggests hydration of forearc mantle and the uppermost mantle by slab derived co2 bearing saline fluids dehydration and decarbonation take place and seawater like saline fluids migrate from the subducting slab to the mantle wedge the presence of saline fluids is important because they can dissolve more metals than pure h2o and affect the chemical evolution of the mantle wedge

the 400 km seismic discontinuity and the proportion of olivine in the earth s upper mantle the 400 km seismic discontinuity has traditionally been ascribed to the isochemical transformation of olivine to the modified spinel structure in a mantle of peridotitic bulk composition1 6 it has recently been proposed7 8 that the observed seismic velocity increase at 400km depth is too abrupt and too small to result from a phase change in olivine but instead requires that the transition zone be chemically distinct in bulk composition from the uppermost mantle by requiring phase relations in the mg2sio4 fe2sio4 system to be internally consistent thermodynamically we find that the transition in olivine of mantle mg0 9fe0 1 2sio4 composition is extremely sharp occurring over a depth interval isothermal of 6 km the magnitude of the predicted velocity increase is in agreement with that observed seismically9 10 if the transition zone is composed of 60 70 olivine thus our results indicate that seismic velocities across the 400 km discontinuity are consistent with a transition zone of homogeneous peridotitic composition and do not require chemical stratification

crust mantle relationships in the french variscan chain the example of the southern monts du lyonnais unit eastern french massif central garnet lherzolite from the lyonnais area eastern french massif central occurs as several lenses elongated within the regional foliation of garnet biotite sillimanite gneisses within the peridotites a mylonitic foliation can be observed which clearly is oblique to the regional foliation of the surrounding gneisses petrological and thermobarometric studies emphasize a tectonometamorphic re equilibration for both crustal and mantle rocks characterized by a prograde metamorphic stage followed by retrograde evolution during the burial stage interpreted as lithospheric subduction the peridotites underwent their mylonitic deformation under high pressure conditions 23 30 kbar in contrast the paragneisses have suffered their deformation during the retromorphic evolution under mesozonal conditions 6 8 kbar 700 c our thermobarometric investigations allow us to interpret the granulitic ultramafic association from the monts du lyonnais area as a lithospheric section buried into a palaeozoic subduction zone laminated during continental collision and uplifted by erosion processes

long period long duration seismic events during hydraulic fracture stimulation of a shale gas reservoir we report here a series of long period and long duration lpld seismic events observed during hydraulic fracturing in a shale gas reservoir these unusual events 10 100 s in duration are observed most clearly in the frequency band of 10 80 hz and are remarkably similar in appearance to tectonic tremor sequences first observed in subduction zones these complex but coherent wave trains have finite moveouts obtained from cross correlation the moveout direction of the events confirms that they originate in the reservoir from the area where the fracturing is going on clear p and s wave arrivals cannot be resolved within the lpld episodes but in some cases small micro earthquakes occur in the sequences whether these micro earthquakes are causal or coincidental is not known it has also been observed that in three contiguous frac stages all lpld events appear to come from two distinct places along one of two hypothetical fracture planes interestingly the stages which have the largest number of lpld

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

the meta igneous granulite xenoliths from kerguelen archipelago evidence of a continent nucleation in an oceanic setting xenoliths of meta igneous origin occur as one of the two main types of ultramafic and mafic xenoliths entrained by alkaline lavas of the kerguelen islands these are designated type ii xenoliths and are subdivided into three mineralogical groups subtype iia and iic xenoliths are interpreted as crystallisation products of basaltic melts that were emplaced near the crust mantle boundary during the early tholeiitic transitional magmatic activity of the kerguelen islands younger magmatism became more alkaline and subtype iib xenoliths were formed as high pressure alkaline cumulates related to the last alkaline volcanic stage subsequently the plagioclase bearing type ii rocks have been re equilibrated under granulite facies conditions this addition of mafic material around the crust mantle boundary is consistent with seismic evidence for crustal thickening to 14 20 km calculated compressional seismic velocities vp for the basic granulites are consistent with the range of observed vp in the low velocity region underlying the oceanic crust such growth in the thickness of the oceanic crust may be caused by intrusion of basalts at different levels in the lithosphere and may provide the heat responsible for granulitic metamorphism in the oceanic setting this study suggests that basic granulites can account for the observed seismic characteristics of oceanic plateaux and can be important components of kerguelen oceanic lithosphere where there has been large scale magma production moreover we speculate that the kerguelen islands and perhaps the surrounding plateau represent a continental nucleation process

fault structure stress or pressure control of the seismicity in shale insights from a controlled experiment of fluid induced fault reactivation clay formations are present in reservoirs and earthquake faults but questions remain on their mechanical behavior as they can vary from ductile aseismic to brittle seismic an experiment at a scale of 10 m aims to reactivate a natural fault by fluid pressure in shale materials the injection area was surrounded by a dense monitoring network comprising pressure deformation and seismicity sensors in a well characterized geological setting thirty two microseismic events were recorded during several injection phases in five different locations within the fault zone their computed magnitude ranged between 4 3 and 3 7 their spatiotemporal distribution compared with the measured displacement at the injection points shows that most of the deformation induced by the injection is aseismic whether the seismicity is controlled by the fault architecture mineralogy of fracture filling fluid and or stress state is then discussed the fault damage zone architecture and mineralogy are of crucial importance as seismic slip mainly localizes on the sealed with calcite fractures which predominate in the fault damage zone as no seismicity is observed in the close vicinity of the injection areas the presence of fluid seems to prevent seismic slips the fault core acts as an impermeable hydraulic barrier that favors fluid confinement and pressurization therefore the seismic behavior seems to be strongly sensitive to the structural heterogeneity including permeability of the fault zone which leads to a heterogeneous stress response to the pressurized volume

the solubility of cepo4 monazite and ypo4 xenotime in kcl h2o fluids at 800 c and 1 0 gpa implications for ree transport in high grade crustal fluids

petrogenesis of leucosome sheets in migmatitic uhp eclogites evolution from silicate rich supercritical fluid to hydrous melt abstract recent studies of eclogite in the ultrahigh pressure uhp zone of the central sulu belt in china have shown that phengite remained stable during exhumation from the metamorphic peak to hp eclogite facies conditions this observation requires that some other source of fluid was involved in the production of melts generated during exhumation from uhp metamorphic conditions here we investigate decimeter to meter thick leucosome sheets in retrogressed and migmatitic uhp eclogite in the central sulu belt the leucosomes have variable mineral modes and deformation fabrics some are composite with marginal and interior facies whereas others are not they range from granite to trondhjemite with high abundances of sio2 k2o na2o and al2o3 similar to hydrous melts and have major oxide and trace element variations consistent with modal changes in phengite and albite epidote sensu lato the leucosomes are enriched in large ion lithophile elements relative to high field strength elements and have rare earth element ree patterns enriched in light ree relative to heavy ree generally with small positive or negative eu anomalies newly crystallized zircon in the leucosomes records weighted mean ages of c 223 218 ma early formed leucosome has sr nd isotope compositions similar to those of nearby unretrogressed uhp eclogites whereas younger leucosome has sr nd isotope compositions intermediate between the eclogites and surrounding gneisses ti in zircon thermometry combined with si in phengite barometry indicates crystallization of the leucosomes between 850 and 770 c over a wide range of pressure p from 3 5 to 2 2 gpa which correlates with age from older higher p to younger lower p at the metamorphic peak which may have exceeded 5 5 gpa the source rocks were likely fluid deficient or fluid absent during exhumation from uhp conditions we posit that exsolution of water stored in nominally anhydrous minerals formed a silicate rich supercritical fluid in eclogite that evolved to a denser more viscous and more polymerized hydrous melt phengite barometry indicates that the early formed leucosomes crystallized at pressures close to the critical line for the basalt plus water system possibly by diffusive loss of water to the host eclogite infiltration of solute rich supercritical fluid from the surrounding gneisses blended with melt in the eclogites generating variable sr nd isotope composition intermediate between these end members as recorded by leucosomes that crystallized at lower pressures the youngest leucosomes crystallized at pressures near the critical line for the ca granite plus water system creating a low volume of aqueous fluid that precipitated quartz veins associated with the leucosome sheets particularly at their margins subsequently limited phengite breakdown melting in the leucosomes is recorded by aggregates of plagioclase biotite around phengite and thin films and cuspate veinlets and patches of k feldspar along grain boundaries phase equilibrium modelling indicates that this late stage melting occurred at p t conditions near the transition from hp eclogite to amphibolite facies with final subsolidus equilibration at 1 0 0 9 gpa and t

composition of barian mica in multiphase solid inclusions from orogenic garnet peridotites as evidence of mantle metasomatism in a subduction zone setting multiphase solid inclusions in minerals formed at ultra high pressure uhp provide evidence for the presence of fluids during deep subduction this study focuses on barian mica which is a common phase in multiphase solid inclusions enclosed in garnet from mantle derived uhp garnet peridotites in the saxothuringian basement of the northern bohemian massif the documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite kmg3 si3al o10 oh 2 kinoshitalite bamg3 al2si2 o10 oh 2 and ferrokinoshitalite bafe3 al2si2 o10 oh 2 in addition to ba 0 24 0 67 apfu mica is significantly enriched in mg xmg 0 85 to 0 95 cr 0 03 0 43 apfu and cl 0 04 0 34 apfu the substitution vector involving ba in the i site which describes the observed chemical variability can be expressed as bafeivalclk 1mg 1si 1 oh 1 a minor amount of cr and vial enters octahedral sites following a substitution vector vi cr al 2 vi mg fe 3 towards chromphyllite and muscovite as demonstrated by variable ba and cl contents positively correlating with fe barian mica composition is partly controlled by its crystal structure textural evidence shows that barian mica together with other minerals in multiphase solid inclusions crystallized from fluids trapped during garnet growth the unusual chemical composition of mica reflects the mixing of two distinct sources 1 an internal source i e the host peridotite and its garnet providing mg fe al cr and 2 an external source represented by crustal derived subduction zone fluids supplying ba k and cl at uhp uht conditions recorded by the associated diamond bearing metasediments c 1100 c and 4 5 gpa located above the second critical point in the pelitic system the produced subduction zone fluids transporting the elements into the overlying mantle wedge had a solute rich composition with properties of a hydrous melt the occurrence of barian mica with a specific chemistry in barium poor mantle rocks demonstrates the importance of its thorough chemical characterization

u th and ra disequilibria sr nd and pb isotope and trace element variations in sunda arc lavas predominance of a subducted sediment component the time scales of magma formation transfer and storage beneath island arc volcanoes are important because of the insights they provide into the physical processes of magma formation and evolution with possible links to the prediction of eruptive hazards here we present new mass spectrometric u th and ra and sr nd and pb isotope data along with major and trace element data from 19 lavas along the sunda arc indonesia the lavas range in sio2 from 49 to 75 and the combination of high sio2 and low 143nd 144nd indicates an important role for shallow level contamination by ancient crustal materials in sumatra diagrams of 143nd 144nd versus th ce and u th versus 87sr 86sr reveal negative trends which allow contributions from both subducted sediments and fluids to be identified the fluid component as expressed in elevated u th 238u 230th and 226ra 230th o ratios is ubiquitous in all of the lavas including near primary lavas from galunggung sr isotope data indicate that the fluids had variable composition and derived from altered oceanic crust and the u th and ra isotope data suggest that some fluid components must have been added less than 8 000 years ago tholeiitic lavas from flores have the lowest th contents in the arc and accordingly the highest 226ra 230th o and 238u 230th for these there is evidence that both u and ra addition probably occurred less than a few thousand years ago this suggests that the onset of melting was linked to fluid fluxing and cannot have been due to decompression alone in contrast the sediment component may have been added as a partial melt and sediment addition can account for the observed along arc variations in sr nd pb and th isotopes there is no requirement in our data for an oib component in the mantle wedge increases in sio2 in the galunggung lavas are accompanied by decreases in both 238u 230th and 226ra 230th o which are inferred to reflect mixing with melts of pre existing mafic lavas mixing and differentiation must have occurred faster than could be recorded by either the 238u 230th or 226ra 230th systems there is little evidence in our data for any effect of the australia indonesia collision on the composition of the lavas across arc trends in lava composition indicate an increasing relative contribution from subducted sediment a correspondingly weaker fluid signal and probable decreases in the degree of partial melting residual aluminous clinopyroxene or garnet may become important in controlling ree and u th fractionation in the far back arc

long period long duration seismicity observed during hydraulic fracturing of the marcellus shale in greene county pennsylvania abstract hydraulic fracturing is a well completion activity that enables the economic extraction of hydrocarbons from unconventional reservoirs such as shale which are of a naturally low permeability during hydraulic fracturing the movement of water into the reservoir from newly created hydraulic fractures reactivates preexisting faults and fractures initiating shear failure on a complex network of planar features although the energy released during hydraulic fracturing is small the seismic emissions arising from shear failure can be detected using surface and borehole seismometers and these emissions are an important diagnostic tool for evaluating the effectiveness of reservoir stimulation to investigate seismic activity during hydraulic fracturing of six horizontal marcellus shale wells in greene county pennsylvania we deployed a surface seismometer within the footprint of the horizontal wells we recorded 53 high amplitude impulsive events and 144 long period long duration lpld events lp

the effects of the spinel garnet phase transition on the formation of rifted sedimentary basins summary we have examined the effects of the spinel garnet phase transition on subsidence of extensional sedimentary basins for a constant positive clapeyron slope dp dt the phase boundary moves downwards in the syn rift and upwards in the post rift phase for a non linear clapeyron curve dp dt 0 above 900 c and dp dt 0 below 900 c theory predicts for the reaction of the spinel garnet phase transition the direction of phase boundary movement is dependent on the stretching factor the position of the clapeyron curve and the lithospheric thickness a smaller syn rift and larger post rift subsidence are predicted for a deeper phase boundary and a thicker lithosphere the model with a non linear clapeyron curve is applied to the subsidence histories of a young extensional basin gulf of lion and an old continental margin eastern canada the observed syn rift uplift and the larger post rift subsidence can be reasonably explained by this model where the optimum depth of the phase boundary for eastern canada 90 km is consistent with the estimate from seismic observations and is larger than that for the gulf of lion 50 km the depth of the spinel garnet phase boundary is sensitive to the composition of mantle rocks and increases with the extraction of basaltic components from the lithosphere compatible with our result that the phase boundary is deeper for an older and thicker lithosphere thus the surface movement associated with the rifting for these areas may reflect the chemical evolution of the continental lithosphere

solubility of cepo4 monazite and ypo4 xenotime in h2o and h2o nacl at 800 c and 1 gpa implications for ree and y transport during high grade metamorphism abstract monazite and xenotime are important accessory minerals in metasediments because they host ree and are useful for geochronology and geothermometry it is therefore essential to understand their behavior during metasomatic processes that attend metamorphism and subduction in order to constrain the solubility of monazite and ypo 4 xenotime at high pressure and temperature we carried out weight loss experiments on synthetic single crystals of cepo 4 monazite and ypo 4 xenotime using hydrothermal piston cylinder methods at 800 c and 1 gpa in h 2 o and h 2 o nacl fluids results indicate that cepo 4 and ypo 4 dissolved congruently and that their solubilities in pure h 2 o are very low 0 04 0 04 and 0 25 millimolal respectively the solubility of cepo 4 rises to an increasing extent with added nacl to 7 94 0 07 millimolal at 50 mol nacl in contrast the solubility of ypo 4 rises to a decreasing degree with increasing nacl to 4 36 0 08 millimolal at 50 mol nacl best fit equations for the solubilities of the two phases are m cepo 4 3 56 10 5 5 82 10 3 x nacl 1 97 10 2 x 2 nacl and m ypo 4 2 48 10 4 1 26 10 2 x nacl 8 89 10 3 x 2 nacl the solubility of ypo 4 is greater than that of cepo 4 at nacl mole fractions x nacl of 0 00 0 27 the solubility enhancement behavior implies that ce dissolves as anhydrous chloride complexes whereas y forms mixed cl oh solutes the results provide a simple mechanism for redistributing ree and y in deep crustal and upper mantle environments the h 2 o ce ratio inferred for subduction zone melts and silicate rich fluids can also be produced by a cepo 4 saturated fluid with x nacl 0 1 in addition neutral ph h 2 o nacl fluids can transport substantial ree and y obviating the need to invoke highly acid solutions in environments where they are unlikely

monazite and xenotime solubility in granitic melts and the origin of the lanthanide tetrad effect the solubility of synthetic pure rare earth phosphates with monazite or xenotime structure lapo4 to lupo4 in hydrous haplogranitic melts was measured at 2 kbar and 800 1 100 c experiments were run for up to 2 months to attain equilibrium monazite and xenotime solubility decreases with increasing phosphorus concentration in the melt published equations for monazite solubility in felsic melts which do not explicitly include phosphorus concentration in the melt should therefore be treated with caution the effect of phosphorus can be quantitatively modeled if one assumes that monazite partially dissolves as ionic and molecular species in the melt ree3 and reepo4 equilibrium constants for the dissolution reactions as well as quantitative data on speciation were derived from the solubility data monazite and xenotime solubility strongly increases with the peralkalinity of the melt this effect is mostly due to an increase in the solubility of the ionic species which are probably stabilized by non bridging oxygen atoms in the melt in peraluminous melts the solubility of monazite and xenotime is nearly constant fluorine has no major effect on monazite and xenotime solubility in fact the solubility appears to slightly decrease with increasing fluorine content the solubility of rare earth phosphates is not a simple continuous function of atomic number or ionic radius rather the solubility shows a tetrad like pattern with several local maxima of solubility at individual rare earth elements the solubilities of neighboring rare earth elements sometimes differ by more than a factor of two these effects are far outside any analytical error the tetrad pattern is particularly clearly seen in some of the peralkaline melts and in the fluorine rich metaluminous melts some features however such as a solubility maximum at ytterbium are seen in virtually all melts the lanthanide tetrad effect in some highly evolved granites may therefore be a result of monazite and xenotime fractionation the solubility of monazite and xenotime in silicate melt probably shows the tetrad effect because of the very unusual coordination of the rare earth elements in these phosphate minerals which is different from the coordination of the melt and therefore causes different crystal field interactions with the partially filled f orbitals of the rare earths the tetrad effect in granites cannot be used as an indicator of fluid rock or fluid melt interaction since it can be experimentally reproduced in the absence of any fluids

mineral equilibrium in fractionated nebular systems we investigated the equilibrium mineral assemblages in chemically fractionated nebular systems using a computer routine that finds the set of minerals and gases which minimizes the gibbs free energy of a system with stipulated elemental abundances diagrams are presented showing the equilibrium mineralogy as a function of temperature 400 2300 k for unfractionated solar material and five fractionated systems the fractionated systems were defined by mixing in various proportions the following four volatility components that solar material can be divided into refractory dust carbonaceous matter ices and h2 gas dust enrichment is seen to increase temperatures of condensation evaporation and the fe2 content of mafic minerals and to permit existence of stable melt phases enrichment of dust and organic matter produces mineral assemblages that are similar in many ways to those of enstatite chondrites but with mafic minerals that are far more reduced fe2 poor than those in primitive enstatite chondrites enrichment of dust organics and ices leads to highly ferrous mineralogies even at the highest temperatures but does not predict the stability of hydrous phases above 450 k

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab mantle interface seismological studies of the interface between downgoing slabs of subducted lithosphere and the overriding mantle provide constraints against which models of mantle and slab temperature and bulk composition can be tested these studies employing waves reflected and converted at the slab mantle interface suggest that a velocity contrast of 5 10 occurs over a distance of 10 20 km to depths of at least 350 km the authors have investigated whether such sharp contrasts can result form thermal structure compositional differences phase changes or other effects such as preferred mineral orientation using a mantle and slab temperature model a petrologic model of mantle and slab mineralogy and a data base of elastic properties of mantle and slab phrases theoretical seismic velocities were calculated and compared with the observed velocity contrast and boundary thickness constraints at 9 6 gpa and 1000c conditions modeled at the slab mantle interface at approximately 280 km depth cooler temperatures in the slab interior produce at constant composition only approximately a 1 75 v sub p increase into the slab in any of the peridotitic and eclogitic mineralogies investigated variation in v sub p among the different bulk compositions is only approximately 0 5 these contrasts are substantially lower than those obtained from the seismological studies andmore indicate that temperature and bulk compositional differences between mantle and slab are inadequate to cause the observed velocity contrasts they propose that phase transformations in mantle and slab mineralogies notably elevation of the olivine spinel phase change normally occurring at 400 km depth are important factors in these sharp contrasts other contributing effects may include preferential mineral orientation near the slab surface and at shallower depths the presence of partial melt or hydrous fluid evolved from dehydration reactions along the interface less

determination of rupture duration and stress drop for earthquakes in southern california a simple technique is developed for determining the rupture duration and stress drop of earthquakes between magnitudes 3 5 and 4 0 using the time between the p wave onset and the first zero crossing 1 2 on seismograms from local seismic networks this method is applied to 10 main shocks in southern california to investigate regional variations in stress drop the initial pulse widths of 65 foreshocks or aftershocks of these events were measured values of 1 2 for small earthquakes below about magnitude 2 2 are generally observed to remain constant with decreasing magnitude in four sequences studied the relative pulse width of a particular main shock m 3 5 at a given station is found to be correlated with the relative pulse width of its aftershocks recorded at that station these observations are interpreted to signify that the waveforms of these small events m 2 2 are essentially the impulse response of the path between the source and receiver values of 1 2 determined from small foreshocks and aftershocks are therefore subtracted in effect deconvolved from those of each main shock to obtain an estimate of the rupture duration of the main shock which is corrected for path effects significant variations in rupture duration and stress drop are observed for the main shocks studied aftershock locations and azimuthal variations in 1 2 both indicate that the rupture zone of one earthquake expanded unilaterally a factor of 10 variation in stress drop is calculated for two adjacent events of similar seismic moments occurring 1 hr apart on the san jacinto fault system the first event in this pair had the highest stress drop of the events studied 860 bars and was followed within 8 months by a magnitude 5 5 earthquake 2 km away

earthquake hypocenters and focal mechanisms in central oklahoma reveal a complex system of reactivated subsurface strike slip faulting the sharp increase in seismicity over a broad region of central oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma in order to record the evolving seismicity in this study we apply a multiple event relocation method to produce a catalog of 3639 central oklahoma earthquakes from late 2009 through 2014 regional moment tensor rmt source parameters were determined for 195 of the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled us to determine the length depth and style of faulting occurring on reactivated subsurface fault systems results show that the majority of earthquakes occur on near vertical optimally oriented ne sw and nw se strike slip faults in the shallow crystalline basement these are necessary first order observations required to assess the potential hazards of individual faults in oklahoma

regional seismicity a potential pitfall for identification of long period long duration events long period long duration lpld events are tremorlike signals that have been observed during monitoring of hydraulic fracture treatment programs lpld events have been interpreted to reflect slow deformation processes on fractures or faults that are misoriented for reactivation with respect to the present day stress field regional earthquakes could easily be mistaken for lpld events because both are characterized by similar frequency content 100 hz and duration 1 min using data from a 10 5 month continuous downhole deployment of a 15 hz geophone array in a tight sand gas field in western canada we compared recordings of small earthquakes with previously published lpld events we determined that regional earthquakes can show similar waveform characteristics to lpld events underscoring the importance of distinguishing regional earthquake signals from lpld events to ensure robust interpretation of reservoir deformation processes

the stability of sapphirine clinopyroxene implications for phase relations in the cao mgo al2o3 sio2 system under deep crustal and upper mantle conditions reaction textures and chemographic relations in sapphirine bearing basic granulites at finero italy suggest that sapphirine and aluminous diopside were formed in mutual equilibrium from an inferred early spinel bearing assemblage finero appears to be the only known locality where this association has been found in situ although it is also known from kimberlite and breccia pipe nodules elsewhere the reactions deduced to have occurred in these rocks suggest the existence of stable invariant points involving the phases sapphirine spinel orthopyroxene clinopyroxene garnet anorthite and sapphirine two pyroxenes garnetanorthite kyanite or sillimanite in the cmas end member system p t estimates for the relevant rocks and the available experimental data suggest that these points lie at around 800 900 c 9 11 kbar a semi quantitative petrogenetic grid incorporating these invariant points with previously determined univariant reactions is proposed it is inferred that sapphirine diopside are stable relative to spinel bearing assemblages below 900 c the relatively low temperature explains why sapphirine has not to date been reported from experimental work on the cmas system it also suggests that sapphirine may be an important aluminous phase in mg rich metagabbros under conditions corresponding to the base of the continental crust despite the observed rarity of such rocks at the surface