petrogenesis of the tertiary anorogenic volcanic series of southern queensland australia in the light of trace element geochemistry and o sr and pb isotopes the magmas of the tertiary volcanic province of s queensland are chemically bimodal and occur in numerous volcanic centres at least three representing original shield volcanoes the mafic lavas are dominantly hawaiites and tholeiitic andesites whereas the silicic magmas comprise mainly trachytes rhyolites and comendites the silicic rocks exhibit variable trace element abundance patterns there is a progressive depletion of sr ba v mg ni cr mn and p through the trachytes to the rhyolites and comendites while the behaviour of zr nb lree y and zn is very variable rb th and to a lesser extent pb exhibit a more regular behaviour becoming most generally concentrated in the comendites and rhyolites these trace element patterns are modelled by application of the rayleigh distillation model using partition coefficients based on analysed phenocrysts from the s queensland silicic lavas trace mineral phases namely zircon chevkinite and allanite are shown to be important in the probable control of lree zr and th abundances while nb and zn are probably controlled during fractionation by magnetite trace element data for the hawaiites and tholeiitic andesites also indicate extensive although variable levels of fractional crystallization of these magmas the sr and o isotopic compositions of the mafic lavas trachytes comendites and rhyolites are as follows initial 87sr 86sr ratios 0 70357 0 70456 0 70432 0 70589 0 70495 0 70917 and 0 70708 0 70863 respectively 18o range between 5 6 7 0 mafic lavas 4 9 8 7 trachytes 5 0 7 6 comendites and 8 1 10 4 per mil rhyolites pb isotopic compositions are variable showing a variation of 6 7 per cent for 206pb 204pb ratios through the range of volcanic compositions the rhyolites exhibit a much greater divergence in their o sr and pb isotopic compositions compared with those of associated mafic lavas than is found in the trachytes and comendites within the silicic volcanics positive correlations exist between 18o and initial sr ratios and between pb isotopic compositions and initial sr ratios with one group of trachytes providing a noteworthy exception these correlations are not so clearly defined for the mafic lavas although these do exhibit positive correlations between differentiation index 18o and initial sr isotope ratios the development of the silicic magmas excepting two groups is interpreted in terms of a model in which assimilation and fractional crystallization occur concurrently involving a basalt or hawaiite magma component and a crustal component modelled on the analysed carboniferous basement greywackes outeropping in the region the data indicate however that differentiation continued in isotopically closed systems i e isolated from the wallrocks the highly depleted sr and ba abundances of the rhyolites and comendites suggest that contamination did not occur after differentiation had ceased the rhyolites have the highest isotopic input of the crustal components and are interpreted as crustal anatectic melts produced locally within the crust in response to basalt hawaiite magma intrusion whereas most of the trachytes and comendites are interpreted as primarily the differentiated products from original mafic parental magmas with variable assimilation of crustal wallrock components the isotopic data suggest that only the minerva hills trachytic lavas and a glass house comendite have not been significantly modified by wallrock assimilation processes the erpted mafic magmas were also evidently modified by isotopic crustal wallrock interactions which independent petrological data suggest has occurred at intermediate to lower crustal depths

the geochemical evolution of clinopyroxene in the roman province a window on decarbonation from wall rocks to magma abstract we present results from magma carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the roman province central italy atmospheric pressure experiments were performed at 1140 1160 and 1180 c under nno mh and air oxygen buffering conditions the starting materials were a shoshonite and a phonotephrite doped with different amounts of cao and cao mgo whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite respectively the results show that clinopyroxenes spinels and residual glasses are ubiquitous phases in all run products calcite doped runs crystallize more clinopyroxene than dolomite doped runs at the same conditions this leads to the formation of strong desilicated cao rich melts showing compositions comparable to those of magmatic skarns during magma carbonate interaction the content of fe3 in clinopyroxene increases with increasing fo2 promoting the substitution of al for si in tetrahedral site local charge imbalances are also compensated by the incorporation of highly charged cations such as ti into the crystal lattice according to this cation substitution al ca fe3 ti rich clinopyroxenes of the skarn environment testify to continuous co2 fluxes produced by the thermal decomposition of carbonate wall rocks nevertheless the oxidative capacity of co2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of si fe2 mg rich clinopyroxenes

structural setting and magmatic evolution of montefiascone volcanic complex vulsini district central italy abstract a comparative study concerning volcanological petrographic and geochemical aspects of montefiascone volcanic complex has been carried out this complex together with those of paleo bolsena bolsena and latera forms the vulsini volcanic district located in the northernmost part of roman comagmatic province four groups of lavas belonging to montefiascone volcanic complex have been recognized on petrographic and geochemical grounds tephritic leucitites tel leucite bearing basanites lbsn evolved tephritic leucitites etel and leucititic tephrites lt lavas clearly show ti and nb anomalies further supporting the genesis of these magmas from a subduction related metasomatized mantle source the majority of the lava erupted comparable in volume with the pyroclastic products appears to be of leucititic affinity having suffered only a slight amount of differentiation major and trace element compositions very similar to those of etel and lt have been obtained from tel and lbsn by means of simple mass balance and rayleigh fractional crystallization model according to petrographic observations main liquidus phases are clinopyroxene leucite olivine and magnetite and magmatic differentiation acts essentially by fractional crystallization eruptive activity is spread over a large area and the volcanic centres are aligned following nnw sse wnw ese and e w directions explosive activity on the other hand was mainly located at montefiascone caldera the great abundance of nearly primary magmas in the area leads us to think that the structural setting was not suitable for developing a great unique magma reservoir but rather a series of small elongated bodies

hydromechanical behavior of a deformable rock fracture subject to normal stress lbl 12297 preprint to be published in the journal of geophysical research hydromechanical behavior of a deformable rock fracture subject to normal stress y w tsang and p a witherspoon january 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info diu is ion ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

swarm satellite and eiscat radar observations of a plasma flow channel in the auroral oval near magnetic midnight we present swarm satellite and eiscat radar observations of electrodynamical parameters in the midnight sector at high latitudes the most striking feature is a plasma flow channel located equatorw

two component auroral electrojet importance for substorm studies this paper attempts to synthesize the diverse number of observations of electric fields and currents in the high latitude ionosphere during substorms by demonstrating that there are often spatial shifts among regions of high ionospheric conductivity large electric fields and intense currents in the auroral electrojet it is shown that substorm time variations of the current patterns over the entire polar region consist of two basic components the first is related to the two cell convection pattern and the second to the westward electrojet in the dark sector which is in turn related to the three dimensional wedge current system these two components result from the relative strength of electric fields and conductivities in the intensification of the auroral electrojet and are identified as the signatures for directly driven and the unloading components in solar wind magnetosphere interactions we contend that disturbed intervals do not necessitate the presence of substorm expansion phase activity and that the vast number of earlier complex results concerning the auroral electrojet can be ascertained from the high degree of variability of the two components depending on substorm events substorm phases and their own spatial temporal scale sizes it is demonstrated that several major issues that have remained controversial are now accounted for reasonably well in terms of this two component electrojet model we also predict specific features of the substorm auroral electrojet that have not yet been observed

the geochemistry of potassic lavas from vulsini central italy and implications for mantle enrichment processes beneath the roman region major and trace element and 143nd 144nd 0 51209 0 51216 and 87sr 86sr 0 70879 0 71105 isotope analyses are presented on a representative group of lavas from the vulsini district of the roman magmatic province three distinct series are identified the high k and low k series are similar to those described from other italian volcanoes while the third is represented by a group of relative ly undifferentiated leucite basanites which are thought to be near primary mantle melts major and trace element variations within the high k series are consistent with fractional crystallisation from a parental magma similar to the most magnesian leucitites crustal contamination resulted in an increase in 87sr 86sr with increasing fractionation but it was superimposed on magmas which had already inherited a range of incompatible element and isotope ratios from enrichment processes in the sub continental mantle these are reviewed using the available results from vulsini roccamonfina and ernici transition element abundances and ta yb ratios indicate that the pre enrichment mantle was similar to that of e type morb and that these elements were not mobilised by the enrichment process mixing calculations suggest that three components were involved in the enrichment process mantle comparable with the source of morb and two other components rich in trace elements one the low k component had high sr nd th ta and ba nb and no europium anomaly while the second had lower sr nd a negative europium anomaly and very high th ta it was also characterised by low nb ba and high rb ba ratios similar to those reported from phlogopite rich peridotite xenoliths the trace element enrichment processes are therefore thought to have occurred in the mantle wedge above a subduction zone with the trace element characteristics of the high k end member reflecting the subduction of sediments and the stabilisation of mantle phlogopite

petrology and geochemistry of ultrapotassic rocks from the montefiascone volcanic complex central italy magmatic evolution and petrogenesis abstract the montefiascone volcanic complex belongs to the roman magmatic province of central italy the volcanic activity took place in an extensional post collisional setting during late pleistocene giving rise to lava flows and pyroclastic deposits the extrusive products consist of moderately to strongly undersaturated k rich lavas ranging in composition from trachybasalts through leucite basanites and leucititic tephrites to tephritic leucitites they show the typical geochemical and isotopic characters of the roman potassic magmas i e low tio2 low k2o al2o3 strong enrichment in lile high lile hfse ratios highly radiogenic 87 sr 86 sr ratios 0 71005 0 71112 and unradiogenic 143 nd 144 nd 0 51209 0 51229 corresponding to end 10 7 to 6 8 large chemical variations have been recognized within the montefiascone volcanics resulting both from the occurrence of different primary magmas and shallow level fractionation processes the differentiation mainly took place by means of closed system fractional crystallisation with local influence of crustal assimilation the leucite basanites represent primary mantle magmas which did not yield derivative products whereas the leucititic tephrites tephritic leucitites and trachybasalts comprise highly differentiated rocks strongly depleted in compatible elements and enriched in lile fractional crystallisation dominated respectively by clinopyroxene leucite and clinopyroxene plagioclase yielded the most evolved tephritic leucitites and trachybasalts in contrast assimilation of metamorphic basement rocks characterized by highly radiogenic 87 sr 86 sr is needed to explain the moderate increase of the 87 sr 86 sr ratio within the leucititic tephrites the geochemical and isotopic signatures shown by the montefiascone primary magmas require a clinopyroxene and phlogopite rich mantle source in particular partial melting of a veined lithospheric mantle can account for the occurrence of different primary magmas characterized by relatively constant sr and nd isotopic compositions depleted mantle nd model ages 1 1 1 5 ga suggest that the mantle enrichment may be a very old event unrelated to the subduction that preceded the roman magmatism this hypothesis is further supported by the strong similarity in age and isotopic composition between the montefiascone volcanics and the kamafugitic and carbonatitic rocks of the adjoining ultra alkaline umbria latium district

evidence for mantle metasomatism an oxygen and strontium isotope study of the vulsinian district central italy this paper presents new o and sr isotope data for lavas from the northern part of the roman perpotassic province the samples comprise the tephritic leucititic to leucite phonolitic lavas and the saturated lavas from the vulsinian district the olivine leucite melilitite of san venanzo and the kalsilite diopside melilitite of cupaello previous oxygen isotope work on the lavas of the vulsinian district suggested crustal contamination of normal mantle derived magmas the new data cover the ranges previously found o and sr isotope ratios of evolved lavas of the undersaturated suite indicate assimilation in variable amounts of up to ca 10 of continental crustal material the saturated lavas probably assimilated large amounts up to ca 50 of crust lavas chemically identified as corresponding to little modified mantle derived liquids are high in both87sr 86sr and 18o 0 7103 0 7107 7 8 to 9 4 vulsini 0 7104 12 3 san venanzo and 0 7112 14 4 cupaello these high values are interpreted to have been inherited from a metasomatized parental mantle hydrous fluids enriched in large ion lithophile elements and high in 18o and87sr 86sr are thought to have mixed with mantle of normal 18o and87sr 86sr the fluids probably origi dehydration of continent derived sediments which were subducted beneath a mantle wedge in the continent continent collision of the corsica sardinia block and the adriatic italian plate this hypothesis is supported by pb and nd isotopic evidence and is probably valid for the entire roman province

motion and erosion of the nightside plasmapause region and of the associated subauroral electron temperature enhancement cosmos 900 observations ion densities n i and electron temperatures t e measured on board cosmos 900 satellite launched at march 30 1977 into near polar circular orbit i 83 h 500 km orbital period 94 min are used to study the behavior of the ionosphere during the prestorm initial and main phases of the magnetic storm of december 1 2 1977 the spatial resolution of the measurement was 0 3 latitude for t e and 0 1 latitude for n i during this period 27 orbits were recorded in the onboard large storage memory this enabled detailed study of the positions and latitude profiles of midlatitude ionospheric trough and subauroral electron temperature enhancement sete in the midnight local time sector simultaneous proton density data measured on the high altitude satellites prognoz 5 and prognoz 6 confirm that the poleward boundary of the t e peak corresponds to the ionospheric magnetic field projection of the high altitude plasmapause density knee during the main phase of a geomagnetic storm the polar edge of the sete becomes very steep it coincides with an equally steep poleward edge of the midlatitude ionospheric trough and with the position of the newly forming density gradient of the high altitude plasmapause the sequence of cosmos 900 observations clearly shows how the nighttime midlatitude ionospheric trough fills up as well as how the subauroral electron temperature enhancement and the outer layers of the plasmasphere are eroded during a geomagnetic storm these results shed new light on the formation of the plasmapause in the postmidnight sector and on the time dependent electric field distribution in the nightside sector before and during a geomagnetic storm

day night coupling by a localized flow channel visualized by polar cap patch propagation we present unique coordinated observations of the dayside auroral oval polar cap and nightside auroral oval by three all sky imagers two super dual auroral radar network superdarn radars and defense meteorological satellite program dmsp 17 this data set revealed that a dayside poleward moving auroral form pmaf evolved into a polar cap airglow patch that propagated across the polar cap and then nightside poleward boundary intensifications pbis superdarn observations detected fast antisunward flows associated with the pmaf and the dmsp satellite whose conjunction occurred within a few minutes after the pmaf initiation measured enhanced low latitude boundary layer precipitation and enhanced plasma density with a strong antisunward flow burst the polar cap patch was spatially and temporally coincident with a localized antisunward flow channel the propagation across the polar cap and the subsequent pbis suggests that the flow channel originated from dayside reconnection and then reached the nightside open closed boundary triggering localized nightside reconnection and flow bursts within the plasma sheet

high resolution observations of the small scale flow pattern associated with a poleward moving auroral form in the cusp 1 in this paper we present high resolution observations by the eiscat svalbard radar of the localized ionospheric flow response due to one single flux transfer event and the relative location of a poleward moving auroral form in a fast scan mode the radar was tracking a 50 60 km wide channel of westward flow in the cusp region this flow channel was surrounded by flow running in the opposite direction at the poleward edge of the narrow flow channel a poleward moving auroral form was situated consistent with the auroral form being the signature of an upward birkeland current filament our observations can be interpreted in terms of the southwood 1985 1987 flux transfer model and the fte twin cell flow pattern appears to be a ripple onto the larger scale background convection

a dynamical model of high latitude convection derived from superdarn plasma drift measurements 1 a discrete set of climatological patterns of high latitude ionospheric convection are derived using line of sight plasma drift data from the super dual auroral radar network superdarn the patterns are derived independently for the northern hemisphere and southern hemisphere and for varying solar wind interplanetary magnetic field imf and dipole tilt angle conditions by interpolating between discrete patterns a dynamical model of convection is obtained which can uniquely specify the high latitude electrostatic potential distribution for a wide range of solar wind imf and dipole tilt parameter values accounting for solar wind velocity dependencies in convection leads to better resolving the large scale convection pattern as compared to previous statistical models based on superdarn data it is shown that the mesoscale features of the climatological model compare favorably to the features seen in instantaneous patterns of convection observed with superdarn comparison of the model to other statistical or empirical models derived from ground and space based measurements shows good agreement with most models

altitude adjusted corrected geomagnetic coordinates definition and functional approximations analysis of the functional approximations used to transform between geo graphic and altitude adjusted corrected geomagnetic aacgm coordinates reveals that errors of 50 km can occur in the auroral and polar regions these errors are the result of efforts to better approximate aacgm coordinates near the magnetic equator and the south atlantic anomaly in these regions aacgm coordinates are not defined and alternate coordinates have been used this augmentation and emphasis on the so lution in regions near the equator result in spherical harmonic approximating functions that are less accurate than need be in the auroral and polar regions in response a new set of spherical harmonic coefficients have been derived that better represent aacgm coordinates in these regions these new aacgm coefficients are limited to below 2000 km in altitude in order to ensure accuracy for altitudes above 2000 km a magnetic field line tracing solution is recommended a software package developed to take advantage of the new aacgm coefficients provides the capability of tracing magnetic field lines at any altitude for improved accuracy in addition linear interpolation between 5 year epochs is used to produce coordinates that vary smoothly over the entire period from 1965 present the intent of this work is to provide a more accurate procedure for de termining aacgm coordinates in the auroral and polar regions for the study of mag netospheric and ionospheric processes

coordinated superdarn themis asi observations of mesoscale flow bursts associated with auroral streamers 1 nightside auroral zone localized flow channels typically associated with auroral poleward boundary intensifications and streamers are an important component of high latitude ionospheric plasma dynamics we investigate the structure of these flow channels using two dimensional line of sight flow observations from the super dual auroral radar network superdarn radars and auroral images from the time history of events and macroscale interactions during substorms themis ground based all sky imager asi array radar echoes captured 500 km horizontal distance from the radars were mainly used to detect small scale flow structures that would otherwise be missed or poorly resolved in long range radar echoes after identifying 135 auroral streamers in the asi images at close radar capture locations we examined the associated ionospheric flow data in the radar echoes flow bursts and streamers are invariably correlated in all events the flow bursts are often directed equatorward and appear simultaneously with the streamers equatorward flows are located just to the east of the streamers less frequently 10 of the time a poleward flow enhancement was detected even when a streamer propagated equatorward the poleward flow enhancement being located to the west of the auroral streamer or to the east of the equatorward flow enhancement consistently with the spatial relationship between flow shear and upward field aligned currents in plasma sheet flow bursts the azimuthal width of the flow channel is on average 75 km and the azimuthal offset of the equatorward flow channel relative to the auroral streamer is 57 km eastward this study demonstrates the capability of radar imager pairs for identifying the 2 d structure of localized flows associated with plasma sheet flow bursts

superdarn assimilative mapping 1 an assimilative mapping procedure is developed to optimally combine information from super dual auroral radar network superdarn plasma drift observations and a background statistical convection model to derive global distributions of electrostatic potential this procedure takes into account statistical properties of the background model errors obtained through the empirical orthogonal function analysis technique described in a companion paper the assimilative mapping procedure is evaluated quantitatively using cross validation and is found to reduce median prediction errors by up to 43 as compared to the existing linear regression based superdarn mapping procedure furthermore the mapped results from the assimilative procedure show a greater dynamic range in convection strength than do those of the regression based procedure i e the cross polar cap potential is smaller for weak driving conditions and larger for strong driving conditions the application of the assimilative procedure is demonstrated for a case study containing a geomagnetic storm it is shown that qualitatively the results of the assimilative procedure appear more smooth and consistent across both data dense and data sparse regions than do those of the regression based procedure

single fractures under normal stress the relation between fracture specific stiffness and fluid flow abstract fracture specific stiffness and fluid flow through a single fracture under normal stress are implicitly related through the geometry of the void space and contact area that comprise the fracture data from thirteen different rock samples each containing a single fracture show that relationships between fracture specific stiffness and fluid flow through a fracture fall into two general classes of behavior fractures either fall on a loosely defined universal curve relating fluid flow to fracture specific stiffness or else the flow is weakly dependent on fracture specific stiffness the second relationship shows that flow decreases slowly with increasing fracture specific stiffness the first relationship shows that flow decreases rapidly for increases in fracture specific stiffness to understand this behavior computer simulations on simulated single fractures were performed to calculate fluid flow fracture displacement and fracture specific stiffness as a function of normal stress simulated fractures with spatially correlated and uncorrelated aperture distributions were studied fractures with spatially uncorrelated aperture distributions tend to exhibit a weak dependence of fluid flow on fracture specific stiffness because these fractures tend to have multiple connected paths across the sample which can support flow with uniformly distributed contact area thus an increment in stress will increase the stiffness of the fracture without greatly reducing the amount of fluid flow on the other hand fractures with spatially correlated aperture distributions tend to belong to the universal relationship because correlated fractures tend to have only one or two dominant flow paths and the contact area is limited to a few regions resulting in a compliant fracture thus an increment in stress on a spatially correlated fracture will result in an increase in stiffness and rapid decrease in fluid flow these spatial correlations in fracture void geometry can be differentiated in the laboratory based on the observed fracture specific stiffness fluid flow relationship for a single fracture under normal loading

sulfur abundance and its speciation in oxidized alkaline melts abstract the sulfur concentrations and the relative proportions of s2 and s6 were measured by electron microprobe in a series of melt inclusions trapped in phenocrysts from different subduction related and within plate volcanoes the melt inclusions correspond to potassic and shoshonitic primary melts to tholeiitic and hawaiitic primitive melts in the tholeiitic and the transitional basaltic melt inclusions sulfur is mainly present as s2 s 6 s total 0 03 to 0 08 and varies from 0 13 to 0 18 wt the occurrence of immiscible sulfides attests to their saturation in shoshonitic and potassic primary melts sulfur s 0 12 to 0 32 wt is dissolved as both s2 and s6 s 6 s total 0 3 to 0 7 their oxygen fugacity estimated from the s 6 s total ratios ranges from ninio to ninio 1 log unit hawaiitic melts may also dissolve up to 0 3 wt sulfur possibly because of their oxidation state close to ninio as illustrated by samples from mt etna italy variations of sulfur at constant s 6 s total ratio and temperature in both the potassic and shoshonitic primary melts indicate that these melts are undersaturated with respect to a s rich condensed phase in agreement with their relatively high oxidation state it strongly suggests that sulfur behavior in relatively oxidized primary alkaline melts is controlled by the mantle source melting conditions

the geochemistry and petrogenesis of the lavas of the vulsinian district roman province central italy the vulsinian lavas are dominated by a suite of undersaturated leucite bearing basic to intermediate compositions the remaining lavas are mainly oversaturated and have shoshonitic affinities one hundred and thirty five samples have been analysed for major elements and most for 20 trace elements twenty seven lavas have been analysed for ree they are all perpotassic for the undersaturated lavas k2o na2o 2 8 and have very high lil element concentrations e g rb 400 800 ppm th 25 150 ppm ree reecho c 200 lree hree cho c 20 even in the most basic rocks

evidence for sub lacustrine volcanic activity in lake bolsena central italy revealed by high resolution seismic data sets abstract the bolsena caldera that formed between 0 6 and 0 2 ma has a well preserved structural rim which makes it an ideal site to study the tectonic and volcanic evolution of calderas however the main area is covered by a 150 m deep lake which makes it rather difficult to investigate the subsurface structure directly to overcome this problem new high resolution hydro acoustic surveys using a multichannel reflection seismic system and a sediment echo sounder system were conducted in september 2012 as space was limited we used a rowing boat towed by a rubber boat to handle a 36 m long and 24 channel streamer to receive seismic reflections produced using a mini gi gun 0 25 l the subsurface structure of lake bolsena was imaged up to a sediment depth of 190 m which is estimated to have filled over a period of 333 kyrs however massive pyroclastic flow deposits found in the deeper parts of the basin indicate an initial infill of volcanic deposits from two adjacent younger calderas the latera w and montefiascone se calderas our data suggest that the caldera has a long history of active volcanism because the lacustrine sediments show post sedimentary influences of geothermal fluids we mapped several mound structures at various stratigraphic depths two volcanic structures outcrop at the modern lake surface implying recent activity one of these structures is hardly covered by sediments and has a crater like feature in its summit the other structure shows a pockmark like depression on top another observable feature is a partially sediment filled crater located in the western part of the lake which further implies the existence of a magma chamber located beneath the bolsena caldera since the late pleistocene and holocene the sedimentation was mainly hemipelagic evidenced by a sediment drape of up to 10 m thick sediment drape on the uppermost sediments beneath the drape we found evidence for a distal tephra layer likely related to an explosive eruption from the campanian volcanic province occurring as the neapolitan yellow tuff our new geophysical data set is a valuable record with a potential to constrain the sedimentary and volcanic evolution of the vulsini volcanic district in areas that have not been assessed previously due to logistical challenges of conducting surveys in water filled settings

flow through fractures flow through fractures is often idealized as flow between two parallel plates plane poiseuille flow the opening or aperture between parallel plates is unambiguous and its relation to flowrate is well known however fractures in rock have uneven walls and a variable aperture a model for flow in a fracture is proposed wherein the fracture is represented by a set of parallel plate openings with different apertures the model leads to a modified poiseuille equation for flow which includes an aperture frequency distribution for the fracture any arbitrary aperture distribution can be used in order to simplify computation and demonstrate the properties of the model a log normal form of distribution is assumed even when an analytical form of the distribution is assumed two parameters rather than a single value representing aperture size are required to determine flowrate models of aperture change for a fracture undergoing compression fracture walls deforming and extension fracture walls separating are developed which constrain the additional parameter and allow calculation of flowrate as a function of mean aperture the theoretical relationships developed between mean aperture and flowrate can be used to interpret published laboratory data for single fractures

petrogenesis and tectonic setting of the roman volcanic province italy abstract the volcanism in the roman province of italy can be modelled by the partial melting of heterogeneously enriched mantle sources the heterogeneity was created by materials derived from a subducted slab which can still be traced geophysically beneath the central apennines new petrographical and chemical data are presented for the high k calc alkaline and the shoshonitic volcanics of the campania region primary magmas are present only locally the existence of spatial zonation in the volcanism of campania is documented for the first time the shoshonitic leucite basanitic and leucititic volcanics of the phlegraean fields procida ischia and the somma vesuvius areas are at similar degrees of evolution about two times richer in nb and ba than those of northwestern campania and the latium part of the roman province accordingly distinct north western and south eastern subprovinces can be defined the evaluation of enrichment factors that is the abundance ratio between the average contents of each element in the relatively primitive lavas of the low k and the high k suites shows that the mantle sources prior to k metasomatism were different in the two sub provinces of the roman province in the north western one they resembled the sources of ocean island tholeiites and moderately enriched mor basalts in the south east they were similar to those of ocean island alkaline lavas and enriched morb s modelling based on k p ce sr rb ba th sm eu gd y nb and 87 sr 86 sr was carried out it indicates that the range of mantle sources of the volcanics in northwestern campania and latium can be modelled by the addition of 3 to 20 of materials derived by partial melting of carbonaceous pelites to a sr enriched mantle wedge comparable to the honolulu mantle source least enriched in nb the production of sr enriched mantle wedge requires either the action of fluids produced by dehydration of subducted oceanic crust or a small amount of metasomatism caused by the presence of carbonatite melts the near absence of ti ta nb yb and the highly fractionated ree in the metasomatizing component requires the presence of residual garnet and accessory ti rich minerals during the partial melting of the subducted sediments the writers propose that the mantle wedge overlying the subducted slab was hybridized by melts produced by partial fusion of subducted material derived from the continental crust probably sediments this process played a dominant role in the generation of the mantle sources from which the high k calc alkaline shoshonitic leucite basanitic and leucititic magmas of the roman province were derived

hydraulic mechanical properties of microfaults in granitic rock using the punch through shear test abstract fault zones are key features in crystalline geothermal reservoirs or in other subsurface environments due to the fact that they act as main fluid pathways an adequate experimental description of the evolution of permeability of a realistic microscopic fault zone under in situ reservoir and fracture parallel flow conditions is required to address this topic we demonstrate a novel experimental set up punch through shear test that is able to generate a realistic shear zone microfault under in situ reservoir conditions while simultaneously measuring permeability and dilation three samples of intact granite from the odenwald upper rhine graben were placed into a mts 815 tri axial compression cell where a self designed piston assembly punched down the inner cylinder of the sample creating the desired microfault geometry with a given offset permeability was measured and fracture dilation was inferred from an lvdt extensometer chain as well as the balance of fluid volume flowing in and out of the sample after fracture generation the shear displacement was increased to 1 2 mm and pore pressure changes of 5 or 10 mpa were applied cyclically to simulate injection and production scenarios formation of a microfault increased the permeability of the granite rock by 2 to almost 3 orders of magnitude further shear displacement led to a small increase in permeability by a factor of 1 1 to 4 0 but permeability was reduced by a factor of 2 5 to 4 within 16 h due to compaction and fault healing effective pressure cycling led to reversible permeability changes ct images showed that the fracture network is rather complex but depicts all features commonly observed in larger scale fault zones

pressure dependent fracture permeability of marine shales in the northeast yunnan area southern china abstract a series of pressure dependent permeability experiments were conducted on the lower silurian longmaxi organic rich shales in northeast yunnan area southern china to investigate the effects of sedimentary bedding fracture surface roughness fracture offset fracture aperture and effective pressure on shale permeability the results demonstrate that the sedimentary bedding of shale only has a slight influence on matrix permeability while the fractures can enhance shale permeability dramatically even at a maximum effective pressure of 48 mpa the permeabilities of aligned fractures without fracture offset can increase by about one order of magnitude over the permeabilities of the shale matrix a power law relation appears to better describe the pressure dependency of permeability for the tested shale samples than the exponential relationship the smoother the fracture surface is the higher the permeability of aligned fractures will be the fracture offset can improve fracture permeability distinctly however the increasing degree of offset fracture permeability is not proportional to the extent of fracture offset there is a lower pressure sensitivity for offset fracture than aligned fracture fracture aperture is the fundamental factor in controlling the fracture permeability which shows a positive relationship with the cube of fracture aperture the pressure dependence of aligned fractures in shale obeys the walsh permeability model but the pressure dependence of offset fractures in shale does not fit well with this model by combining the experimental results with the geological characteristics of different types of natural fractures we conclude that the denser vertical intra formational tension fractures connect with the bed parallel slip fractures are favorable for step like migration and enrichment of shale gas in structural highs the large scaled high angle shear fractures likely damage the preservation conditions of shale gas which is harmful to shale gas enrichment

coupling of dipolarization front flow bursts to substorm expansion phase phenomena within the magnetosphere and ionosphere 1 recent themis spacecraft observations have shown longitudinally narrow earthward moving plasma sheet flow channels with large abrupt magnetic field dipolarizations that have been referred to as dipolarization fronts we undertake a detailed study of the subset of these events that had good quality auroral imaging we find that many occurred during the substorm expansion phase after onset determined by auroral intensification and were related to auroral streamers both the fronts relation to streamers and their plasma sheet changes are similar to what has been previously shown for other plasma sheet flow channels and to other flow channels seen during the expansion phases of the events considered here surprisingly the dipolarization fronts examined made major contributions to substorm onset ground and space magnetic signatures these include substorm near earth dipolarization which indicates that the current wedge may develop via a series of well defined narrow post onset wedge like structures these also include the auroral zone ground magnetic field which showed only modest responses to the onsets but abrupt large responses to post onset dipolarization front related streamers and midlatitude positive bays which started near the time of streamer formation our observations suggest that traditional magnetic signatures of substorm onset such as near earth dipolarization auroral zone negative bays and midlatitude positive bays may misidentify the expansion phase onset determined by auroral intensification by up to 10s of minutes for some events it should be interesting in the future to determine the generality of the above relations between dipolarization front signatures and onset signatures

volcanological and petrological evolution of the eastern vulsini district central italy on the basis of recent field mapping data stratigraphic reconstruction and k ar datings a volcanological and petrological study of the bolsena and montefiascone volcanic zones eastern vulsini district has been carried out ten main eruptive phases with both effusive and explosive activity have been recognized these are characterized by a large range of magma compositions belonging to the leucitite basanite and shoshonite magmatic series within each series near primary magmas and slightly to strongly differentiated products are present although in different proportions the great majority of differentiated products mostly trachytic outcrops in the northern sectors of the eastern vulsini district bolsena volcanic zone where lavas or pyroclastics were erupted during moderate to large volume plinian type and ignimbrite forming explosive activity by contrast abundant rather undifferentiated magmas are more frequently found in the southern sectors of the eastern vulsini district montefiascone volcanic zone the structural setting of the sedimentary substratum as well as its lithological characteristics may have played an important role in producing this magma distribution the very shallow position a few hundred meters below the topographic surface of the top of the fracturated carbonate basement would have facilitated the uprising of abundant less evolved magmas in the montefiascone volcanic zone whereas relatively large magma bodies a few kilometer deep can only be inferred in the bolsena volcanic zone bolsena caldera where a front of overthrust sheets of the tuscan and umbrian sedimentology sequences is most probably present in this area source vents of explosive activity show a tendency to shift northeastward with time feeding systems were also differently oriented e w and wnw ese in the southern sectors and nw se and nnw sse in the northern sectors while a ns system was related to a late stage activity of the whole eastern vulsini district