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

incorporating full attenuation mechanisms of poroelastic media for realistic subsurface sensing porous materials are ubiquitous in the subsurface formations of the earth where acoustic and seismic waves are used for remote sensing however it is not well understood how the dissipation and the dispersion of poroelastic waves are caused by the viscoelastic and viscous properties of the constituents such as solid grains and pore fluid and by the viscoelastic dissipation of the solid frame as well as the viscodynamic coupling of the pore fluid to the solid frame due to its global and local flows relative to the solid grains such attenuation mechanisms have seldom been incorporated in subsurface sensing simulations although they can be very important to applications in this paper we propose a complete attenuation model including both full stiffness and viscodynamic dissipation for poroelastic media in seismic wave simulations completely based on a generalized zener model the effects associated with physical dissipation and frequency dependent dispersion are accurately simulated by a finite difference time domain algorithm verifications with analytical solutions show the accuracy efficiency and flexibility of our method numerical results demonstrate that the attenuation of biot s model in the sediment of the seafloor has significant effects on acoustic wave scattering from complex geologic structures

primary magmatic calcite reveals origin from crustal carbonate abstract we have investigated lava flows representative of the whole eruptive history of the colli albani ultrapotassic volcanic district central italy one of the most intriguing features concerning some of these lava flows is the occurrence of primary magmatic calcite in the groundmass the primary magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i interstitially associated with clinopyroxene nepheline and phlogopite ii in spherical ocelli associated with nepheline fluorite and tangentially arranged clinopyroxene and iii in corona like reaction zones around k feldspar xenocrysts these microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass implying that the temperature of the system was above the solidus of the hosted lava flow 850 c geochemical features of calcite crystals i e stable isotope values and trace element patterns corroborate their primary nature and give insights into the origin of the parental carbonate melt the trace element patterns testify to a high temperature crystallization process not hydrothermal involving a carbonate melt coexisting with a silicate melt the high 18o around 27 smow and wide 13c 18 to 5 pdb values measured in the calcites preclude a mantle origin but are consistent with an origin in the crust in this framework the crystallization of calcite can be linked to the interaction between magmas and carbonate bearing wall rocks and in particular to the entrapment of solid and or molten carbonate in the silicate magma the stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn eruptive time scales

mafic magma intraplating anatexis and hybridization in arc crust bindal batholith norway distinct with nd and o in the migmatites from 7 6 to 9 6 the dioritic velfjord plutons 448 ma were emplaced into and from 10 9 to 13 5 and in the contact granites regional migmatitic metapelitic and metacarbonate rocks at midfrom 5 2 to 7 5 and from 9 6 to 12 3 respectively crustal levels corresponding to pressures of 700 mpa exthus the contact granites could have a source that is isotopically humation to 400 mpa began while the migmatites were in a distinct from but mineralogically similar to the diatexites or they partly molten state with increasing proximity to the plutons could result from mixing of magma similar to the high k leucosomes regional stromatic migmatites change to diatexite and diatexitic with dioritic magmas mass balance calculations are consistent dikes are common within 500 m of the contacts we interpret these with the latter interpretation with proportions of granitic to dioritic relationships to indicate that heat from the plutons resulted in contact magmas from 7 1 to 7 3 emplacement and solidification of the migmatization in a zone up to 1 km wide typical residual dioritic plutons provided zones of structural anisotropy along which mineralogy in the diatexites is plagioclase quartz biotite high k leucosome magmas and contact granite magmas collected garnet sillimanite k feldspar consistent with biotite these magmas were injected by additional dioritic magma and dehydration melting podand dike like leucosomes consist of two further hybridized because the solidi of the plutons were several types earlier high k granitic ones with mineral assemblages hundred degrees higher than that of the granitic magmas the pluton identical to the migmatites and later low k tonalitic ones in which walls acted as long lived hot rigid surfaces along which magmas sillimanite is sparse and garnet absent the high k leucosome collected and migrated magmas can be explained by biotite dehydration melting at 700 mpa within the aureole mafic magmas were locally injected into and hybridized with the diatexites and the high k leucosome

elemental evidence for crustal contamination of mantle derived caledonian syenite by metasediment anatexis and magma mixing abstract this paper presents elemental evidence that the mafic unit of the caledonian glen dessarry syenite northern scotland u k has been variably contaminated with material derived from the surrounding moine metasediments uncontaminated portions are shown to have trace element abundances and ratios similar to those of the central leucosyenite and island arc high k or shoshonitic magmas from present day oceanic settings by comparison contaminated samples display grossly disturbed trace element patterns including higher u th zr hf nb ta and heavy rare earths lower ba and sr and negative eu anomalies these features are matched in the elemental systematics of the moinian envelope but bulk incorporation of excessive amounts of metasediment would be required to reproduce the observed perturbations in especially the high field strength elements xenoliths within the contaminated mela syenites and parts of the adjacent country rock show petrographic evidence of melting since the source composition moine metasediment and residual mineralogy xenoliths are known simple geochemical models of melting and subsequent mixing with uncontaminated melasyenite melt have been computed the results provide close approximations to the observed geochemistry of the contaminated melasyenites particularly for the ree s moreover the residues of this hypothetical process have similar ree patterns to several samples of metasediment from immediately adjacent to the syenite contact nevertheless contemporaneous crystal liquid separation is required to explain the full range of elemental data contamination by this mechanism of melting followed by magma mixing is not immediately apparent in the major element relationships of the two melasyenite groups this seems to be the result of the approximate colinearity of the established melasyenite crystal fractionation path and the proposed granitic contaminant and may be a more general problem in the recognition of in situ contamination with metasedimentary melts in plutons whose fractionation itself proceeds towards a broadly granitic terminus

volcanic edifice weakening via decarbonation a self limiting process 1 the inherent instability of volcanic edifices and their resultant propensity for catastrophic collapse is a constant source of volcanic risk structural instability of volcanic edifices may be amplified by the presence of carbonate rocks in the sub volcanic strata due to the debilitating response of carbonates to thermally induced alteration nonetheless decarbonation reactions the primary weakening mechanism may stall when the system becomes buffered by rising levels of a reaction product carbon dioxide such thermodynamic stalling might be inferred to serve to circumvent the weakness of volcanic structures however the present study shows that even when decarbonation is halted rock physical properties continue to degrade due to thermal microcracking furthermore as a result the pathways for the escape of carbon dioxide are numerous within a volcanic edifice therefore in the case of an edifice with a sub volcanic sedimentary basement the generation of carbon dioxide via decarbonation is unlikely to hinder its impact on instability and thus potentially devastating flank collapse

early magmatic phase in the oslo rift and its related stress regime abstract the earliest magmatic rocks in the oslo graben consist of a complex of sills and dykes intermediate to felsic syenites termed maenaites and basic camptonites intruded into cambrian and lower ordovician pre rift sediments no volcanism appears to be associated with this intrusive phase the sill intrusions are regional in extent and can be found in all parts of the oslo graben except in the north samples from six maenaite sill occurrences dated by the rb sr method yielded late carboniferous ages ranging from 304 to 294 ma these ages place the sill intrusions in the same evolution phase as the proto rift asker group sediments interpreting the sill complex as a paleostress indicator and applying the tectonic model for the sill forming mechanism the deviatoric stress in the crust at the time of intrusion is found to be compressive at the level of the sills and shallower in contrast the succeeding evolution of the oslo graben was dominated by tensile deviatoric stress the timing of the incipient magmatic event in the oslo graben and its state of deviatoric compressive stress support the concept that the oslo rift developed initially in response to the build up foreland compressional stresses in conjunction with the hercynian orogeny there is no evidence for an early pre rift crustal doming stage

monte carlo simulation of stress associated scattering attenuation from laboratory ultrasonic measurements abstract seismic coda waves scattered by small scale heterogeneities contain information on stress changes of the medium because of changes in the physical state of materials based on the ultrasonic measurements under different stresses for a cylindrical sandstone sample we investigate the influence of stress changes on ultrasonic s coda attenuation and aim to characterize its stress frequency dependent pattern considering the complexity of ultrasonic coda waveforms measured from finite size rock samples in laboratory experiments the monte carlo simulation is employed to synthesize ultrasonic envelopes which act by incorporating the effect of multiple scatterings and boundary reflections on coda waves the optimal simulation parameters estimated by minimizing the residual between the observed and synthesized envelopes indicate that the rock sample under study presents moderate heterogeneities the relationship between attenuation and stress is similar for direct and coda s waves and remains stable in the range of high effective stresses around 30 60 mpa with less stress sensitivity enhanced attenuation for both types of waves occurs at lower effective stresses but with coda attenuation much faster and stronger presenting a quite different nonlinear behavior with respect to stress coda attenuation increases drastically at extremely low effective stresses below 15 mpa because of the increase in rock compliance showing much greater sensitivity to high pore pressure than intrinsic attenuation this study improves our understanding of the mechanism of ultrasonic coda attenuation and its scaling dependence on stress and frequency

reactive bulk assimilation a model for crust mantle mixing in silicic magmas bulk assimilation of small millimeters to 1 km fragments of crust driven and ultimately masked by reactions during xenolith melting and magma crystallization is an important mechanism for crust mantle mixing xenoliths containing mica or amphibole undergo dehydration melting when incorporated into a host magma yielding mainly plagioclase pyroxene fe ti oxides and hydrous melt the xenolith is physically compromised by partial melting and begins to disintegrate xenolithic melt and crystals are mixed into the host magma xenocrystic zircon is liberated at this stage the cryptic character of assimilation is greatly enhanced in any hydrous magma by hydration crystallization reactions the reverse of dehydration melting all pyroxenes and oxides phenocrysts xenocrysts or crystals having a hybrid signature will be subject to these reactions producing feldspars amphiboles and micas that incorporate material from several sources a particularly effective mixing mechanism implicit in the model is a reduced energy penalty for bulk assimilation much of the assimilant remains in solid form compared to melt assimilation models a large role for bulk assimilation supports stoping as a credible mechanism for the ascent of magmas while the assimilation of low density crust and concomitant fractionation provide the isostatic impetus for ascent the wholesale incorporation and processing of crustal rocks in the magma chamber helps create the room for ascent

petrogenesis of the massive chromitite layer from the jacurici complex brazil evidence from inclusions in chromite the jacurici complex hosts the largest chromite deposit in brazil in an up to 8 m thick chromitite layer within a tectonically segmented 300 m thick intrusion the ore has been interpreted as the result of crustal contamination driven crystallization in a magma conduit this study addresses the stratigraphy mineralogical and textural relationships and mineral chemistry of the monte alegre sul segment focusing on chromite hosted inclusions from the main chromitite layer to understand the role of volatiles in the genesis of the massive chromitite silicate inclusions enstatite phlogopite magnesiohornblende diopside and olivine are commonly monomineralic and sub to euhedral and crystallized prior to or coeval with the chromite crystallization carbonate inclusions dolomite and magnesite are irregular or have negative crystal shapes suggesting entrapment as melt droplets sulfides pentlandite millerite heazlewoodite polydymite pyrite and chalcopyrite are often polymineralic irregular or hexagonal shaped indicating entrapment as sulfide melt and as monosulfide solid solution the inclusions indicate an h2o and s saturated resident magma with immiscible droplets of carbonate melt during chromite crystallization inclusion rich and inclusion free chromites that occur together have similar compositions and are considered to have formed from the same magma in response to variations in the degree of cr saturation hot primitive magma might have heated and mobilized co2 and probably water from devolatized and assimilated carbonate rich wall rocks increasing fo2 and triggering chromite crystallization we propose that the formation of the chromitite layer started as in situ crystallization with additional material added by slumping of locally remobilized chromite slurries facilitated by the presence of volatiles

the squirt flow mechanism macroscopic description we introduce a poroelasticity model that incorporates the two most important mechanisms of solid fluid interaction in rocks the biot mechanism and the squirt flow mechanism this combined biot squirt bisq model relates compressional velocity and attenuation to the elastic constants of the drained skeleton and of the solid phase porosity permeability saturation fluid viscosity and compressibility and the characteristic squirt flow length squirt flow length is a fundamental rock property that does not depend on frequency fluid viscosity or compressibility and is determined experimentally we find that the viscoelastic response of many sandstones is dominated by the squirt flow component of the bisq mechanism and that the viscoelastic properties of these rocks can be expressed through a single dimensionless parameter omega r 2 kappa where omega is angular frequency r is the characteristic squirt flow length and kappa is hydraulic diffusivity the biot mechanism alone does not give an adequate explanation of the observed velocity dispersion and attenuation and the viscoelastic behavior of many sandstones

formation and evolution of granite magmas during crustal reworking the significance of diatexites taylor mclennan 1985 the physical processes ina continuous section through reworked archaean crust records the volved particularly how granite magma is formed remain generation of granitic magma and its subsequent development in the controversial miller et al 1988 white chappell opatica subprovince in the canadian shield there the transition 1990 a partially melted source can form a granitic from palaeosome to granite was a closed system process through magma only if large volumes of melt are separated from intermediate stages of patch migmatite and diatexite the average most of their residuum understanding this process is degree of partial melting was less than 30 but the melt crucial to determining how crustal recycling and differfraction was redistributed within individual diatexite layers during entiation occurs for example melt residuum separation deformation regions that lost melt became residual diatexites could be a nearly perfect single stage process at the enriched in tio2 feot mgo cao sc cr co sr rare earth site of partial melting as described for leucosomes in elements ree and high field strength elements hsfe melt metatexite migmatites wickham 1987a sawyer 1991 accumulated to create diatexite magmas enriched in large ion 1994 brown et al 1995 alternatively the separation lithophile elements lile but contaminated with residuum macould be an imperfect multi stage process that yields a terial such diatexite magmas are parental to granites found at magma with a large residual component as is observed higher crustal levels in the terrane flow of the diatexite magma in in diatexite migmatites bea 1991 greenfield et al response to deformation separated some of its residuum into schlieren 1996 sawyer 1996 the metatexite model necessarily parautochthonous plutons were created where ascending granitic produces leucocratic residuum free granites such as magma locally ponded below impermeable layers and structures those described by le fort 1981 and montel et al magma left the anatectic region in dykes and lost its remaining residuum as it crystallized consequently the allochthonous granite 1991 and maximizes the geochemical signature of magmas that rose through 20 km of crust to feed the highest level crustal differentiation in contrast the diatexite model plutons in this region are highly fractionated and essentially free of can produce residuum rich granites and so reduce the residuum geochemical effect of crustal differentiation as chappell 1996 noted how anatectic magmas formed in the deeper crust evolve to the granitic magmas emplaced in the upper crust is also poorly known because few crustal sections

p wave seismic attenuation by slow wave diffusion effects of inhomogeneous rock properties recent research has established that the dominant p wave attenuation mechanism in reservoir rocks at seismic frequencies is because of wave induced fluid flow mesoscopic loss the p wave induces a fluid pressure difference at mesoscopic scale inhomogeneities larger than the pore size but smaller than the wavelength typically tens of centimeters and generates fluid flow and slow diffusion biot waves continuity of pore pressure is achieved by energy conversion to slow p waves which diffuse away from the interfaces in this context we consider a periodically stratified medium and investigate the amount of attenuation and velocity dispersion caused by different types of heterogeneities in the rock properties namely porosity grain and frame moduli permeability and fluid properties the most effective loss mechanisms result from porosity variations and partial saturation where one of the fluids is very stiff and the other is very compliant such as a highly permeable sandstone at shallow depths saturated with small amounts of gas around 10 saturation and water grain and frame moduli variations are the next cause of attenuation the relaxation peak moves towards low frequencies as the background permeability decreases and the viscosity and thickness of the layers increase the analysis indicates in which cases the seismic band is in the relaxed regime and therefore when the gassmann equation can yield a good approximation to the wave velocity

numerical simulation of the biot slow wave in water saturated nivelsteiner sandstone the development of rock acoustic models is important for interpreting seismic data these models should relate seismic properties such as wave velocity and attenuation to the production and lithological properties of reservoir rocks such as porosity permeability fluid type and fluid saturation

relationships between ultrapotassic and carbonate rich volcanic rocks in central italy petrogenetic and geodynamic implications the pleistocene intra apennine volcanic iav centres occurring east of the potassium rich roman comagmatic province show variable petrological and geochemical composition some rocks have a strongly undersaturated ultrapotassic kamafugitic affinity with k2o na2o 8 20 whereas the rocks from the southern center of mt vulture are still strongly undersaturated in silica but are enriched in both na2o and k2o with k na around unity carbonate rich pyroclastic rocks believed to represent carbonatitic magmas are found in the iav centers kamafugites have high abundances of lile and high lile hfse ratios and their incompatible element patterns resemble closely those of ultrapotassic rocks from the adjoining roman province the vulture volcanics also display high contents of lile but their lile hfse ratios are intermediate between intraplate alkaline rocks and kamafugites the carbonate rich rocks exhibit an exotic mineralogy and high enrichments in lile which speaks for a carbonatitic affinity however they have similar incompatible element patterns but consistently lower abundances of almost all the elements than the associated silicate volcanics these data favour the hypothesis that the iav carbonate rocks may represent mixtures of silicate magmas and geochemically depleted carbonate material the sedimentary carbonates that crop out extensively along the apennine chain may be the source of barren carbonate material overall geochemical data of iav centres and of the rocks from the roman province display strong geochemical and isotopic evidence of being generated in an upper mantle that was modified by addition of upper crustal material brought down by subduction processes a possible exception is represented by mt vulture which however occurs east of the main axis of the apennines on the western margin of the foreland adria plate the occurrence of strongly undersaturated alkaline rocks requires magma generation at high pressures and xco2 this is in agreement with the hypothesis that subduction processes under the apennines occurred by consumption of poorly hydrated thinned or delaminated continental crust

experimental detection of a slow acoustic wave in sediment at shallow grazing angles following recent experimental results at sea n p chotiros proc oceans 89 that suggest the existence of a previously undetected type of acoustic wave in sandy sediments an experiment was designed to detect and measure the speed of acoustic waves in an isolated environment the experiment was conducted in a laboratory tank containing 1 m of unwashed river sediment under a 3 m water column observations were made of the travel time and attenuation of a pulse from an acoustic source located above the water sediment interface to a set of probes below the interface it was observed that at normal incidence the pulse traveled at about 1750 m s while at shallow grazing angles the pulse traveled through the sediment at close to 1200 m s an interesting possible explanation exists in the biot model m a biot j acoust soc am 28 168 191 1956 which predicts a slow acoustic wave in porous materials work funded by onr under noarl management

scale of pluton wall rock interaction near may lake yosemite national park ca usa interaction of magma with wall rock is an important process in igneous petrology but the mechanisms by which interactions occur are poorly known the western outer granodiorite of the cretaceous tuolumne intrusive suite of yosemite national park california intruded a variety of metasedimentary and igneous wall rocks at 93 1 ma the may lake metamorphic screen is a metasedimentary remnant whose contact zone exhibits a variety of interaction phenomena including xenolith incorporation disaggregation and partial melting the chemical contrast of these metasedimentary rocks with the invading pluton provides an excellent measure of pluton wall rock interactions wall rock xenoliths mostly pelitic quartzite are predominantly located in an elongate horizon surrounded by a hybridized fine grained granodiorite initial sr and nd isotopic ratios of the hybridized granodiorite indicate significant local incorporation of crustal material major and trace element geochemical data indicate that contamination of the granodiorite occurred via selective assimilation of both high k and low k high silica partial melts derived from pelitic quartzite although the hybridized granodiorite shows significant amounts of contamination adjacent to xenoliths the proportion of contamination is undetectable more than a meter away these results indicate that the chemical and isotopic variability of the tuolumne intrusive suite is not caused by magma contamination via in situ wall rock assimilation

finite difference modeling of wave propagation and diffusion in poroelastic media numerical modeling of seismic waves in heterogeneous porous reservoir rocks is an important tool for interpreting seismic surveys in reservoir engineering various theoretical studies derive effective elastic moduli and seismic attributes from complex rock properties involving patchy saturation and fractured media to confirm and further develop rock physics theories for reservoir rocks accurate numerical modeling tools are required our 2d velocity stress finite difference scheme simulates waves within poroelastic media as described by biot s theory the scheme is second order in time contains high order spatial derivative operators and is parallelized using the domain decomposition technique a series of numerical experiments that are compared to exact analytical solutions allow us to assess the stability conditions and dispersion relations of the explicit poroelastic finite differ ence method the focus of the experiments is to model wave induced flow accurately in the vicinity of mesoscopic hete

nd isotopes demonstrate the role of contamination in the formation of coexisting quartz and nepheline syenites at the abu khruq complex egypt the petrogenesis of abu khruq an 89 ma alkaline ring complex of eastern egypt which is composed of alkali gabbros and both silica over and undersaturated syenites has been investigated major and trace element relationships and nd and sr isotope data are consistent with formation of the gabbros from an alkaline mafic magma that experienced extensive fractionation and all syenites from a felsic derivative of this melt the parental magma had an 87sr 86sr of 0 7030 and an 143nd 144nd of 0 512750 nd 4 4 indicating derivation from a depeleted mantle source the initial 143nd 144nd ratios are 0 512721 to 0 512748 for the gabbros 0 512739 to 0 512750 for the alkali syenites and trachytes 0 512717 to 0 512755 for the nepheline syenites and 0 512706 to 0 512732 for the quartz syenites in contrast analyzed precambrian granites from eastern egypt have generally lower 143nd 144nd ratios ranging from 0 51247 to 0 51261 or nd 0 8 to 1 7 for 89ma their nd model ages range from 775 to 935 ma and suggest there was no significant input of pre pan african crust in their formation among abu khruq rocks 143nd 144nd ratios indicate that the quartz syenites formed by open system crustal contamination processes whereas the nepheline syenites experienced little or no contamination modeling shows that contamination occurred at various stages affecting both mafic and more evolved compositions with input of about 20 crustal nd for the most contaminated samples the degree of contamination is related to the silica saturation of the quartz syenites simplified modeling of magma evolution within petrogeny s residua system demonstrates the ability of afc processes to cause a critically undersaturated magma to evolve across the feldspar join and produce oversaturated rocks the oversaturated syenites at abu khruq were produced in this manner whereas the nepheline syenites formed by fractionation without similarly large degrees of contamination the results have broad implications for the formation of subvolcanic complexes in continental settings beyond the important production of silica oversaturated compositions from crustal interaction they underscore the importance of crustal interactions in the formation of the various lithologies such interactions occur at various stages in the evolution of the magmas and as such are not strictly coupled with fractional crystallization while previous study of abu khruq has demonstrated extensive hydrothermal alteration of o and sr isotopes the present work shows that the nd isotope ratios were not significantly affected and thus reflect magmatic signatures this feature combined with relatively small corrections for initial ratios emphasizes the utility of nd isotopes for petrogenetic studies

an equivalent medium model for wave simulation in fractured porous rocks seismic wave propagation in reservoir rocks is often strongly affected by fractures and micropores elastic properties of fractured reservoirs are studied using a fractured porous rock model in which fractures are considered to be embedded in a homogeneous porous background the paper presents an equivalent media model for fractured porous rocks fractures are described in a stress strain relationship in terms of fracture induced anisotropy the equations of poroelasticity are used to describe the background porous matrix and the contents of the fractures are inserted into a matrix based on the fractured equivalent medium theory and biot s equations of poroelasticity two sets of porosity are considered in a constitutive equation the porous matrix permeability and fracture permeability are analysed by using the continuum media seepage theory in equations of motion we then design a fractured porous equivalent medium and derive the modified effective constants for low frequency elastic constants due to the presence of fractures the expressions of elastic constants are concise and are directly related to the properties of the main porous matrix the inserted fractures and the pore fluid the phase velocity and attenuation of the fractured porous equivalent media are investigated based on this model numerical simulations are performed we show that the fractures and pores strongly influence wave propagation induce anisotropy and cause poroelastic behaviour in the wavefields we observe that the presence of fractures gives rise to changes in phase velocity and attenuation especially for the slow p wave in the direction parallel to the fracture plane

pervasive assimilation of carbonate and silicate rocks in the hortavaer igneous complex north central norway the intrusive complex at hortav r represents a magma transfer zone in which multiple pulses of gabbroic and dioritic magmas evolved along fe and alkali enrichment trends extreme alkali enrichment resulted in nepheline normative and sparse nepheline bearing monzodioritic and monzonitic rocks more evolved monzonitic and syenitic rocks are silica saturated and in some cases quartz bearing previous and current research recognized an abundance of clinopyroxene and other ca rich phases such as scapolite grossular rich garnet and igneous textured calcite among the mafic and intermediate rocks even the most pyroxene rich samples contain low sc concentrations which suggests early intense fractionation of clinopyroxene these features and the alkali enrichment are consistent with assimilation of carbonate rich host rocks carbon isotope ratios of the igneous textured calcite indicate an origin of the carbon from host rocks rich in calcite consistent with assimilation however low end values 3 4 to 10 2 and moderate initial 87 sr 86 sr values 0 7052 to 0 7099 indicate the need for assimilation of quartzofeldspathic rocks as well models of combined assimilation and fractional crystallization indicate that assimilation of simple end members either carbonate or silicate cannot explain the entire data set instead variable proportions of carbonate and silicate materials were assimilated with the most pronounced assimilation effects in the mafic rocks the reasons for variable degrees of assimilation are as yet uncertain it is possible that assimilation of calc silicate rocks with variable carbonate silicate proportions resulted in the range of observed compositions however the importance of carbonate assimilation in mafic rocks compared to felsic ones suggests that assimilation of carbonates was predominant at high temperature and or mafic magma compositions and assimilation of silicates was predominant at lower temperature and or felsic magma compositions we suggest that the ability of the mafic magma to dissolve higher proportions of carbonate contaminants is the result of the magma s ability to form clinopyroxene as a product of assimilation in any case extensive carbonate assimilation was possible because co2 escaped from the system d 2004 elsevier b v all rights reserved

observation of the biot slow wave in water saturated nivelsteiner sandstone acoustic signals are used extensively in the oil industry to determine the physical properties of reservoir rock in the interpretation of these signals empirical laws play a major role to obtain a more fundamental interpretation of the recorded wavetrains the need for a comprehensive theory for acoustic wave propagation and damping in rocks is obvious in this respect biot s 1956a b theory is a straightforward and effective two phase theory in contrast to biot who derived the macroscopic equations for wave propagation in saturated poro elastic material by postulating definite positive energy density functions burridge and keller 1981 whitaker 1986a b c and pride et al 1992 applied rigorous averaging techniques to derive the poro elastic equations from a microscale de vries 1989 and geerits 1996 used the averaging techniques to derive macroscopic poro elastic equations for the nonviscous case the fundamental feature of all these theoretical descriptions is the existence of both a fa

imaging the mountainless root of the 1 8 ga cheyenne belt suture and clues to its tectonic stability receiver function analysis across the cheyenne belt an archean proterozoic suture images a 100 km wide zone of 50 60 km thick crust this thick crust is thought to be a remnant from the original 1 8 ga suturing event the thick and presumably buoyant crust is remarkable in that it is not associated with a large topographic or gravitational anomaly suggesting isostatic balance and a high density mass at depth to compensate the crustal root these features could account for the lithosphere s long term stability the presence of eclogite below the crustal root is a likely source for the high density mass as it would not produce a seismically unusual moho yet it would provide the required excess mass

zircon as a metamorphic timekeeper a case study from the caledonides of central norway abstract during metamorphism inherited or detrital zircon grains commonly serve as a template onto which new generations of metamorphic zircon precipitates charting successive episodes in the thermal history of rocks in addition chemical modification of pre metamorphic zircon can leave an imprint in the u pb systematics we present a case study from a sample of migmatitic amphibole biotite gneiss from central norway that contains zircon grains that chart much of the history of an entire orogenic episode not only through generation of new zircon but also resetting of the u pb system via radiogenic pb loss the investigated gneiss from the helgeland nappe complex within the uppermost allochthon of the scandinavian caledonides records a prolonged metamorphic evolution phase equilibria modelling implies peak metamorphic conditions of 7 5 8 0 kbar and 650 675 c consistent with low degree partial melting and the presence of small volumes of leucosome laser ablation split stream analysis that simultaneously measures u pb ree and lu hf in the same volume of zircon yields a range of analyses that spread along concordia a zircon population between 485 and 443 ma is characterized by faded and blurred oscillatory zoned domains that have gained nonformula elements these analyses are interpreted to indicate the presence of reactive solutions during this time period that led to leaching and mobility of pb another texturally distinct zircon component yields an age of 478 4 ma has typical igneous ree zircon profiles and records low apparent alpha doses interpreted to reflect new zircon growth during migmitization a further population of zircon rims and discrete grains yields an age of 453 2 ma interpreted as a later episode of zircon growth during high grade metamorphism a final set of zircon overgrowths yield an age of 439 3 ma also interpreted to reflect new metamorphic growth many zircon growth phases in this rock have similar ree patterns implying broadly isochemical metamorphism consistent with the evidence for only limited partial melting furthermore the hf isotopic signature in the analyzed zircon grains suggests that there was no release of radiogenic hf during metamorphism the metamorphic zircon in the studied rock records several episodes of growth and or alteration over a period of 40 ma that was related to protracted destruction of the iapetus ocean in the context of regional data the new results suggest that the helgeland nappe complex which is generally considered to be exotic to baltica underwent geographically widespread long lived ordovician high temperature metamorphism this record of metamorphism is distinct from that recorded by tectonostratigraphically lower units which are conventionally regarded to have been derived from baltica the results shed light on the assembly of the scandinavian caledonides and show that zircon from individual samples may be used to unravel complex orogenic histories

protolith carbon isotope ratios in cordierite from metamorphic and igneous rocks cordierite commonly contains h 2 o and co 2 in the channels formed by its ring structure in many studies cordierite has been shown to have volatile contents and carbon isotope ratios consistent with high temperature equilibrium suggesting preservation of protolith carbon isotope ratios and motivating this survey of carbon isotopes in cordierite co 2 cordierite co 2 from pelitic country rocks in the etive aureole have 13 c values of 20 70 1 27 n 10 that are unaffected by a ca 150 c thermal gradient and fluid saturated and undersaturated regimes these 13 c values are consistent with expected carbon isotope ratios of organic carbon in protolith sediments similar lithologies from the cooma and huntly aureoles show more variable behavior in a more limited data set with some rocks preserving organic carbon 13 c values and others that may have been affected by externally derived fluids in cordierite gedrite gneisses carbon isotopes of cordierite crd are distinct from those of cordierite in pelites when excluding one outlier new data plus those from the literature average 13 c crd 12 51 2 45 n 17 these isotope ratios are higher than those of cordierite in typical metasedimentary protoliths and are similar to published carbon isotope ratios of trace carbonate in altered submarine volcanic rocks which are likely analogs for protoliths of many cordierite gedrite rocks igneous cordierite from granitic plutons have 13 c 23 61 2 08 n 13 which is interpreted as reflecting a magmatic carbon budget dominated by organic carbon from sedimentary source rocks in contrast small pegmatites reported in the literature have 13 c crd 10 20 3 06 n 6 which may indicate derivation from orthogneiss source materials these new data show that carbon isotopes in cordierite can be used to help understand the protolith of even carbon poor metamorphic rocks and can also shed light on carbon in the sources of magmatic rocks this latter approach has the potential for helping constrain the source rocks of peraluminous granitoids which is controversial determining the extent to which organic carbon 13 c is preserved in granitoids is important for understanding the deep carbon cycle and could serve as an important constraint in the search for low 13 c graphite inclusions in hadean detrital zircons which have been reported as a potential biosignature for the early earth

thermal weakening of the carbonate basement under mt etna volcano italy implications for volcano instability abstract the physical integrity of a sub volcanic basement is crucial in controlling the stability of a volcanic edifice for many volcanoes this basement can comprise thick sequences of carbonates that are prone to significant thermally induced alteration these debilitating thermal reactions facilitated by heat from proximal magma storage volumes promote the weakening of the rock mass and likely therefore encourage edifice instability such instability can result in slow gravitational spreading and episodic to continuous slippage of unstable flanks and may also facilitate catastrophic flank collapse understanding the propensity of a particular sub volcanic basement to such instability requires a detailed understanding of the influence of high temperatures on the chemical physical and mechanical properties of the rocks involved the juxtaposition of a thick carbonate substratum and magmatic heat sources makes mt etna volcano an ideal candidate for our study we investigated experimentally the effect of temperature on two carbonate rocks that have been chosen to represent the deep heterogeneous sedimentary substratum under mt etna volcano this study has demonstrated that thermal stressing resulted in a progressive and significant change in the physical properties of the two rocks porosity wet i e water saturated dynamic poisson s ratio and wet vp vs ratio all increased whilst p and s wave velocities bulk sample density dynamic and static young s modulus dry vp vs ratio and dry dynamic poisson s ratio all decreased at temperatures of 800 c the carbonate in these rocks completely dissociated resulting in a total mass loss of about 45 and the release of about 44 wt of co 2 uniaxial deformation experiments showed that high in situ temperatures 500 c significantly reduced the strength of the carbonates and altered their deformation behaviour above 500 c the rocks deformed in a ductile manner and the output of acoustic emissions was greatly reduced we speculate that thermally induced weakening and the ductile behaviour of the carbonate substratum could be a key factor in explaining the large scale deformation observed at mt etna volcano our findings are consistent with several field observations at mt etna volcano and can quantitatively support the interpretation of 1 the irregularly low seismic velocity zones present within the sub volcanic sedimentary basement 2 the anomalously high co 2 degassing observed 3 the anomalously high vp vs ratios and the rapid migration of fluids and 4 the increasing instability of volcanic edifices in the lifespan of a magmatic system we speculate that carbonate sub volcanic basement may emerge as one of the decisive fundamentals in controlling volcanic stability