the skaergaard layered series part vi excluded trace elements in contrast to the smooth trends of major elements and mineral principal minerals of the skaergaard layered series my purpose here is to examine the corresponding excluded compositions the excluded trace elements in the skaergaard layered series have an irregular distribution that does not conform to the elements and their relations to progressive differentiation of the skaergaard magma the principal conclusion that normal trends of rayleigh type fractionation their concentrations are about constant or even decline through the lower and middle will emerge is that the trends of enrichment of these elements differ markedly from those of the major elezones before increasing sharply to reach maximum concentrations 100 200 m above the sandwich horizon as in the case of ments possibly because their distribution was affected by a build up and eventual exsolution of volatile comincluded elements the relative concentrations of excluded elements in coexisting phases deviate widely from those predicted by exponents in the magma it will also be shown that the observed partition coefficients differ widely from those perimentally determined partition coefficients under presumed magmatic conditions this is seen most clearly in the immiscible predicted from experimental studies several earlier studies addressed various aspects of the melanogranophyres and conjugate ferrogabbros although the major elements conform to the experimentally determined relations for skaergaard trace elements haskin and his co workers haskin haskin 1968 paster et al 1974 were the first immiscible liquids the trace elements do not they follow a totally independent trend the abrupt increase in the concentrations of to attempt to reconcile the distribution of excluded trace elements with earlier interpretations of trace element excluded elements in the upper part of the intrusion could plausibly be attributed to an addition of new magma or to a density inversion behavior during crystallization and differentiation of the layered series other previous work has been sumthat resulted in upward migration of a late liquid or fluid but these possibilities are inconsistent with the compositional and spatial marized by wager brown 1968 and more recently by mcbirney 1996 1998a relations of the upper parts of the intrusion although a late residual liquid certainly migrated upward the most likely explanation for the structural form of the intrusion and its principal units illustrated in simplified form in fig 1 have already the observed distribution of excluded elements is that the partition coefficients were altered by volatile components which gradually been described at length mcbirney 1989 1995 1996 boudreau mcbirney 1997 mcbirney nicolas 1997 increased during the early stages of crystallization then began to exsolve near the top of the middle zone sonnenthal mcbirney 1998 and need not be repeated apart from minor differences noted in the appendix the distribution and selection of samples as well as the methods by which they have been analyzed are essentially the same as those described in part v of this

static and dynamic moduli of malm carbonate a poroelastic correlation the static and poroelastic moduli of a porous rock e g the drained bulk modulus can be derived from stress strain curves in rock mechanical tests and the dynamic moduli e g dynamic poisson s ratio can be determined by acoustic velocity and bulk density measurements as static and dynamic elastic moduli are different a correlation is often required to populate geomechanical models a novel poroelastic approach is introduced to correlate static and dynamic bulk moduli of outcrop analogues samples representative of upper malm reservoir rock in the molasse basin southwestern germany drained and unjacketed poroelastic experiments were performed at two different temperature levels 30 and 60 circ c for correlating the static and dynamic elastic moduli a drained acoustic velocity ratio is introduced corresponding to the drained poisson s ratio in poroelasticity the strength of poroelastic coupling i e the product of biot and skempton coefficients here was the key parameter the value of this parameter decreased with increasing effective pressure by about 56 from 0 51 at 3 mpa to 0 22 at 73 mpa in contrast the maximum change in p and s wave velocities was only 3 in this pressure range this correlation approach can be used in characterizing underground reservoirs and can be employed to relate seismicity and geomechanics seismo mechanics

the low δ18o late stage ferrodiorite magmas in the skaergaard intrusion result of liquid immiscibility thermal metamorphism or meteoric water incorporation into magma abstractwe report new laser fluorination oxygen isotope analyses of selected samples throughout the skaergaard intrusion in east greenland particularly relying on 1 mg separates of the refractory alteration resistant minerals zircon sphene olivine and ferroamphibole we also reexamine published oxygen isotope data on bulk mineral separates of plagioclase and clinopyroxene our results show that the latest stage strongly differentiated magmas represented by 3 to 6 km3 of ferrodiorites around the sandwich horizon sh where the upper and lower solidification fronts met became depleted in 18o by about 1 5 2 relative to the original skaergaard magma and the normal mantle derived mid ocean ridge basalt earlier studies did not recognize these low 18o ferrodiorite magmas 18o 3 4 because after the intrusion solidified much of the intrusion and its overlying roof rocks were heavily overprinted by low 18o meteoric hydrothermal fluids we consider three possible ways of producing these low

a note on induced stress changes in hydrocarbon and geothermal reservoirs abstract earthquakes have been induced by oil and gas production where pore pressures have decreased in some cases by several tens of mpa it has previously been suggested that such earthquakes are caused by poroelastic stressing of crust surrounding the reservoir induced earthquakes are also common in geothermal fields such as the geysers where strong correlations between both steam production and condensate injection and earthquake activity have been observed over the last several decades stress measurements within hydrocarbon reservoirs show that the least horizontal stress decreases with declining reservoir pressure as predicted by poroelasticity for circular disk shaped reservoirs isothermal reduction in pore pressure induces a relative horizontal tension within the reservoir production induced stressing may promote frictional sliding on pre existing faults within the reservoir itself normal faulting is promoted if the regional stress is extensional and the biot coefficient is sufficiently large 0 85 for reasonable coefficients of friction on the other hand dilatant fracturing and normal faulting are always promoted in extensional environments near the edge of the reservoir or in regions of high pore pressure gradient it is suggested that such fracturing could enhance fracture permeability in tight rocks adjacent to portions of the reservoir that experience large reductions in pore pressure due to production in regional compressional environments production modestly favors reverse faulting above and below the reservoir the ratio of thermal to poroelastic stress can be quite large in geothermal reservoirs such as the geysers reservoir wide energy balance considerations suggest that the average temperature has declined at the geysers by 6 c during the past 20 years reservoir average stress changes are thus on the order of 2 mpa and are certainly much larger near injection wells and steam producing fractures

high resolution insights into episodes of crystallization hydrothermal alteration and remelting in the skaergaard intrusive complex this paper presents a new high precision zircon u pb geochronological view on the crystallization and assembly process of one of the most important and intensely studied intrusive bodies on earth the skaergaard intrusion in east greenland with analytical uncertainties of a few tens of thousands of years we were able to resolve several important events during cooling of this intrusion initial cooling of the shallowly intruded 300 km3 of tholeiitic basaltic magma from liquidus to zircon saturation at 1000 c is recorded by a precise zircon crystallization age of 55 960 0 018 ma of an intercumulus gabbroic pegmatite in the lower portion of the intrusion based on this zircon crystallization age and a published cooling model we estimate the true age of emplacement to be 56 02 ma the last portions of skaergaard appear to crystallize completely 100 ka after emplacement as recorded by abundant 55 91 55 93 ma zircons in the sandwich horizon sh where lower and upper solidification fronts met intrusion of an isotopically distinct new magma batch the 600 m thick basistoppen sill into the solidified upper portion of skaergaard happened at 55 895 0 018 ma suggesting close timing between crystallization of evolved rocks around the sh and intrusion of the basistoppen sill the novel result of this work is the demonstration that zircons in the sh 100 m below the basistoppen contact have a bimodal age distribution with the youngest population of 55 838 0 019 ma postdating intrusion of the basistoppen sill by 57 37 ka oxygen isotope analyses reveal that sh zircons are low and heterogeneous with respect to 18o these results support the proposed conclusion that the sh crystallized twice it was fully crystalline then hydrothermally altered by low 18o surface waters and subsequently partially remelted triggered by heat of the basistoppen sill the low degree partial melt generated during remelting partially migrated upward by intergranular compaction driven flow explaining the existence of the most incompatible trace element rich horizon 100 m above sh as the skaergaard intrusion is also the most classic example of a shallow meteoric hydrothermal system this work documents the alternating processes in a life of an intrusion with periods of hydrothermal cooling heating by new intrusions and related remelting events which cause the generation of low 18o magmas our precise temporal framework for intrusion crystallization also provides constraints for the timing of coeval flood basalt volcanism and its synchronicity with the paleocene eocene thermal maximum

liquid immiscibility and the evolution of basaltic magma this experimental study examines relationships between alternative evolution paths of basaltic liquids the so called bowen and fenner trends and silicate liquid immiscibility synthetic analogues of natural immiscible systems exhibited in volcanic glasses and melt inclusions were used as starting mixtures conventional quench experiments in 1atm gas mixing furnaces proved unable to reproduce unmixing of ferrobasaltic melts yielding instead either turbid opalescent glasses or crystallization of tridymite and pyroxenes in contrast experiments involving in situ high temperature centrifugation at 1000g g 1 4 9 8 m s did yield macroscopic unmixing and phase separation centrifugation for 3 4 h was insufficient to complete phase segregation and resulted in sub micron immiscible emulsions in quenched glasses for a model liquid composition of the middle zone of the skaergaard intrusion at super liquidus temperatures of 1110 11208c centrifugation produced a thin silicic layer 64 5 wt sio2 and 7 4 wt feo at the top of the main fe rich glass 46 wt sio2 and 21 wt feo the divergent compositions at the top and bottom were shown in a series of static runs to crystallize very similar crystal assemblages of plagioclase pyroxene olivine and fe ti oxides we infer from these results that unmixing of complex aluminosilicate liquids may be seriously kinetically hampered presumably by a nucleation barrier and thus conventional static experiments may not correctly reproduce it in the light of our centrifuge experiments immiscibility in the skaergaard intrusion could have started already at the transition from the lower to the middle zone thus magma unmixing might be an important factor in the development of the fe enrichment trend documented in the cumulates of the skaergaard layered series

disequilibrium partial melting and rheomorphic layer formation in the contact aureole of the basistoppen sill east greenland the tholeiitic basistoppen sill was intruded into the upper part of the skaergaard complex shortly after the skaergaard magma had solidified heat from the cooling basistoppen magma caused disequilibrium partial melting in the adjacent skaergaard ferrogabbros olivine ferrobustamite and magnetite were selectively melted and removed from the rock as an iron rich melagabbro magma plagioclase acted as a refractory phase during partial melting and was left behind as an anorthositic gabbro restite modal and grain size layering formed rheomorphically in the previously solidified host rocks as a result of partial melting and recrystallization the rheomorphic layers are distinct from those found elsewhere in the intrusion

differentiation of tholeiitic basalt to a type granite in the sept iles layered intrusion canada the undeformed 564 ma sept iles layered intrusion quebec canada is a large igneous body of c 20 000km3 from the base to the top it consists of a layered series dominated by troctolite and gabbro an anorthositic upper border series and a dominantly granitic upper series the parent magma of the layered series is inferred to be an iron rich tholeiitic basalt 48 wt sio2 15wt feot whole rock compositions from the chilled margin dykes cross cutting the layered series and silicic rocks from the upper series display continuous major and trace element geochemical trends ranging from basalts to ferroan metaluminous a type granites 77 wt sio2 initial 143nd 144nd 0 51201 0 51207 and 87sr 86sr 0 70353 0 70548 indicate a juvenile mantle source and minimal contamination by old crust 1 2 during crystallization geochemical modeling using the melts thermodynamic calculator combined with equations predicting mineral melt equilibria from experiments on tholeiitic basalts indicate that basaltic to monzonitic melt compositions are in equilibrium with the troctolites and gabbros of the layered series fe ti oxides saturate early in the layered series after 14 fractionation of plagioclase olivine cumulates further fractionation of fe ti oxide bearing gabbros drives the residual liquids toward silica enrichment and iron depletion major and trace element modeling indicates that the a type granites from the upper series were produced by protracted fractional crystallization of an iron rich basaltic parent magma at a fraction of residual liquid of only 8 the observed relative volumes of mafic cumulates and silicic rocks in the intrusion are in agreement with the calculations most of the intermediate compositions correspond to magmatic mafic enclave bearing granitoids and display geochemical evidence of hybridization intermediate compositions produced by fractional crystallization are scarce and a daly gap occurs from 57 to 67 wt sio2 this gap could result either from the fractional crystallization process or from silicate liquid immiscibility during that compositional interval

compressibility of porous rocks four compressibilities are defined for porous rock relating changes in the bulk and pore volumes to changes in the pore and confining pressures using a micromechanical theory based on classical linear elasticity three relations are found between these compressibilities two of these relations are verified experimentally for berea and bandera sandstone bounds are derived for these compressibilities involving only the porosity and the elastic moduli of the rock forming minerals for the strains to be unique functions of the stresses the compressibilities must be functions only of the difference between the confining and pore pressures this dependence is verified for berea bandera and boise sandstone while the strains cannot be expressed as functions of an effective stress regardless of how it is defined the elastic volumetric behavior of porous rocks can be studied through tests conducted at zero pore pressure

a discussion of hunter and sparks contrib mineral petrol 95 451 461 silica poor iron rich liquids like those estimated for skaergaard by wager and brown are preserved in labrador as chilled pillows iron rich rocks in the kiglapait intrusion have likewise been produced by liquids poor in silica there is no reason to expect such liquids in volcanoes so their absence as lavas means nothing about their possible plutonic occurrence successful tests of the siliceous liquid hypothesis would include showing that the proposed rhyolitic liquids can produce the observed olivines in the range fo 10 40 they would require showing that the observed low f o 2 oxide mineral assemblages can occur at the high silica contents proposed and that the silicate mineral assemblages and compositions can represent high silica liquids i doubt very much that these critical tests can be met

silicate perovskite analogue scalo3 temperature dependence of elastic moduli abstract the elastic moduli of scalo 3 perovskite a very close structural analogue for mgsio 3 perovskite have been measured between 300 and 600 k using high precision ultrasonic interferometry in an internally heated gas charged pressure vessel this new capability for high temperature measurement of elastic wave speeds has been demonstrated on polycrystalline alumina the temperature derivatives of elastic moduli of al 2 o 3 measured in this study agree within 15 with expectations based on published single crystal data for scalo 3 perovskite the value of k s t p is 0 033 gpa k 1 and g t p is 0 015 gpa k 1 the relative magnitudes of these derivatives agree with the observation in duffy and anderson duffy t s anderson d l 1989 seismic velocities in mantle minerals and the mineralogy of the upper mantle j geophys res 94 1895 1912 that k s t p is typically about twice g t p the value of k s t p for scalo 3 is intermediate between those inferred less directly from v p t studies of fe free and fe and al bearing mgsio 3 perovskites wang y weidner d j liebermann r c zhao y 1994 p v t equation of state of mg fe sio 3 perovskite constraints on composition of the lower mantle phys earth planet inter 83 13 40 mao h k hemley r j shu j chen l jephcoat a p wu y bassett w a 1991 effect of pressure temperature and composition on the lattice parameters and density of mg fe sio 3 perovskite to 30 gpa j geophys res 91 8069 8079 zhang weidner d 1999 thermal equation of state of aluminum enriched silicate perovskite science 284 782 784 the value of g t p for scalo 3 is similar to those of most other mantle silicate phases but lower than the recent determination for mgsio 3 perovskite sinelnikov y chen g neuville d r vaughan m t liebermann r c 1998 ultrasonic shear wave velocities of mgsio 3 perovskite at 8 gpa and 800k and lower mantle composition science 281 677 679 combining the results from the previous studies and current measurements on scalo 3 perovskite we extracted the parameters q and 0 needed to fully specify its mie gruneisen debye equation of state in this study we have demonstrated that acoustic measurements of k s t unlike v p t data tightly constrain the value of q it is concluded that scalo 3 has normal 0 1 3 and high q 3 6 the high value of q indicates that scalo 3 has very strong intrinsic temperature dependence of the bulk modulus similar behaviour has been observed in measurements on fe and al bearing silicate perovskites mao et al 1991 zhang and weidner 1999

the skaergaard layered series part vii sr and nd isotopes the initial isotopic ratios of strontium and neodymium in the skaergaard layered series vary both vertically and laterally on every scale from the intrusion as a whole down to coexisting minerals in a single rock the magma that filled the skaergaard chamber was contaminated to various degrees with the metamorphic rocks through which it rose and was never completely homogenized after being intruded the contamination was most pronounced in contact zones and aureoles around rare xenoliths the greater concentrations of lithophile trace elements in the upper border series was previously attributed to assimilation of buoyant fragments of gneiss that collected under the roof but most of the rocks of the upper border series are isotopically indistinguishablefromthoseofthelayeredseries itisdoubtful therefore that this part of the intrusion assimilated much more of the metamorphic basement than did the rest of the magma similarly the marked increase in the concentrations of excluded elements in the upper part of the layered series is not matched by a change in the isotopic character of the rocks and cannot be attributed to a later influx of new magma analyses of minerals separated from rocks with exceptionally mafic or felsic modal compositions revealed marked inhomogeneities in the isotopic compositions of their constituent minerals for example coexisting plagioclase and pyroxene from closely associated anorthosites and pyroxenites have very different initial isotopic ratios of both strontium and neodymium the same is true of mafic and felsic layers in modally graded gabbros these differences are unrelated to the low temperature alteration shown by oxygenisotopes they must have been introduced when the original gabbro was largely crystallized and underwent local metasomatic replacement by nearly mono mineralic mafic and felsic assemblages

the skaergaard layered series part iv reaction transport simulations of foundered blocks during the middle stages of crystallization of the skaergaard layered series large numbers of blocks became detached from the upper border series and settled into the mush of crystals on the floor it has been recognized for some time that these blocks now have compositions and textures that differ markedly from those of the units from which they came they tend to be more plagioclase rich and seem to have lost mafic components to the surrounding gabbro numerical simulations coupling crystallization melting and heat and mass transfer for a multicomponent system show how the blocks reacted with the mush in which they were emplaced enhanced cooling and crystallization of a compositionally stratified mush adjacent to the blocks resulted in patterns of melt compositions similar to those of layering around the blocks volume changes during crystallization and melting induced convection of the interstitial melt leading to changes in the bulk compositions of the blocks and the surrounding mush inhomogeneities such as inclusions are likely to facilitate the onset of compositional convection in a chemically stratified solidification zone

provenance of marble sculptures from the national museum of carthage tunisia the results of a combined minero petrographic and isotopic study carried out on representative marble sculptures from the museum of carthage are presented pentelikon source has been identified for nine of the analyzed items carrara and prokonnesos sources have been also identified for three and one items respectively confirming in some cases previously made hypothesis local chemtou and djebel ichkeul stones present very different petrographic fabrics compared with the most recurrent marbles the undertaken approach adds value to the descriptions of the studied artifacts and could be extended to other art pieces of this and other museums

re os isotope geochemistry of tertiary picritic and basaltic magmatism of east greenland constraints on plume lithosphere interactions and the genesis of the platinova reef skaergaard intrusion abstract re os abundance and isotopic studies on a small number of samples from the lowermost part of the east greenland lava pile and the nearby skaergaard intrusion show that picrite and ankaramite lavas tend to have high os abundances and low re os ratios with most rocks having near chondritic values for initial 187 os 188 os one olivine basaltic sample with very high 187 os 188 os has most likely been affected by upper crustal contamination there is no clear evidence for recycled crustal material in the ancestral iceland plume source or for a significant degree of interaction of the picrites with ancient subcontinental lithospheric mantle of the north atlantic craton the platinova reef the precious metal enriched zone in the skaergaard intrusion has very high au and pd contents but very low pt and os contents compared to platiniferous horizons in other layered intrusions these characteristics are almost certainly due to the very late stage in the evolution of the skaergaard magma chamber at which the platinova reef formed the platinova reef yields a re os tchur model age that is younger than the age of the intrusion which was most likely produced by some form of post depositional disturbance to the re os isotopic system the high pge contents of the east greenland volcanic rocks indicate that they were formed from magmas that had the potential to form major accumulations of ni cu pge sulphide deposits had similar magmas undergone significant interaction with continental crust elsewhere in east greenland they may have formed massive magmatic sulphide deposits thus the potential for the discovery of large magmatic sulphide deposits of the noril sk talnakh type in east greenland must be considered excellent

permeability of triaxially compressed sandstone influence of deformation and strain rate on permeability the influence of differential stress on the permeability of a lower permian sandstone was investigated rock cylinders of 50 mm in diameter and 100 mm length of a fine grained mean grain size 0 2 mm low porosity 6 9 sandstone were used to study the relation between differential stress rock deformation rock failure and hydraulic properties with a focus on the changes of hydraulic properties in the pre failure and failure region of triaxial rock deformation the experiments were conducted at confining pressures up to 20 mpa and axial force was controlled by lateral strain with a rate ranging from 10 6 to 10 7 sec 1 while deforming the samples permeability was determined by steady state technique with a pressure gradient of 1 mpa over the specimen length and a fluid pressure level between 40 and 90 of the confining pressure the results show that permeability of low porosity sandstones under increasing triaxial stress firstly decreases due to compaction and starts to increase after the onset of dilatancy this kind of permeability evolution is similar to that of crystalline rocks a significant dependence of permeability evolution on strain rate was found comparison of permeability to volumetric strain demonstrates that the permeability increase after the onset of dilatancy is not sufficient to regain the initial permeability up to failure of the specimen the initial permeability which was determined in advance of the experiments usually was regained in the post failure region after the onset of dilatancy the permeability increase displays a linear dependence on volumetric strain

empirical calibration of oxygen isotope fractionation in zircon new empirical calibrations for the fractionation of oxygen isotopes among zircon almandine rich garnet titanite and quartz are combined with experimental values for quartz grossular the resulting a coefficients k2 are zrc alm grs ttn qtz 2 64 2 71 3 03 3 66 zrc 0 07 0 39 1 02 alm 0 32 0 95 grs 0 63 full size table table options view in workspace download as csv for the relation 1000 ln y x ay x 106 t2 the fractionation of oxygen isotopes between zircon and coexisting minerals can provide otherwise unavailable evidence of magmatic processes including crystallization remelting and assimilation fractional crystallization

thermoporoelastic properties of flechtinger sandstone abstract this research addresses the thermomechanical response of a saturated sandstone in a geothermal reservoir several experiments were performed using a triaxial testing system to investigate thermal effects on poroelastic parameters of flechtinger sandstone an outcropping equivalent of the rotliegend reservoir rock in drained experiments confining pressure was cycled pore pressure was maintained constant and temperature was increased step wise the temperature dependence of the drained bulk modulus differed at low and high effective pressures the unloading drained bulk modulus increased from 10 25 gpa to 11 74 gpa with increasing temperature from 30 c to 120 c at high stresses and decreased from 3 39 to 3 05 gpa at low stresses the biot coefficient decreased with increasing effective pressure and temperature the inelastic behavior of the rock the interrelation between thermal expansion coefficient and bulk modulus and the path dependence of heat transfer processes govern the temperature effect on granular rock and changes in pore geometry

effect of the volume of the drainage system on the measurement of undrained thermo poro elastic parameters abstract for evaluation of the undrained thermo poro elastic properties of saturated porous materials in conventional triaxial cells it is important to take into account the effect of the dead volume of the drainage system the compressibility and the thermal expansion of the drainage system along with the dead volume of the fluid filling this system influence the measured pore pressure and volumetric strain during an undrained thermal or mechanical loading in a triaxial cell the correction methods previously presented by wissa pore pressure measurement in saturated stiff soils asce j soil mech found div 1969 95 sm 4 1063 73 bishop influence of system compressibility on observed pore pressure response to an undrained change in stress in saturated rock geotechnique 1976 26 2 371 5 and ghabezloo and sulem stress dependent thermal pressurization of a fluid saturated rock rock mech rock eng 2009 42 1 1 24 only permit one to correct the measured pore pressures during an undrained isotropic compression test or an undrained heating test an extension of these methods is presented in this paper to correct the measured volumetric strain and consequently the measured undrained bulk compressibility and undrained thermal expansion coefficients during these tests two examples of application of the proposed correction method are presented for an undrained isotropic compression test and an undrained heating test performed on a fluid saturated granular rock a parametric study has demonstrated that the porosity and the drained compressibility of the tested material and the ratio of the volume of the drainage system to the one of the tested sample are the key parameters that most influence the error induced by the drainage system

the differentiation of the skaergaard intrusion mcbirney and naslund have missed the two central points that we reiterate for clarity first the composition of the cotectic cumulate extract for the lzc best estimated from the average composition of adcumulate rocks had a substantially lower silica content than any conceivable basaltic liquid so silica enrichment is unavoidable this is true of all the dyke compositions reported by brooks and nielsen even the anomalous rock e with sio2 46 second it is the normal behaviour of tholeiite basaltic magma to produce increasingly iron rich cumulate extracts with little change in silica until feti oxide precipitation occurs when silica enrichment and compositional divergence begins such divergence between equivalent cumulate plutonic and fractionated volcanic rocks hads been widely documented skaergaard magmas do have some uncommon features however similar assemblages exist in volcanic rocks as in the andesitic to rhyolitic glasses of the loch ba ring dyke mull sparks 1988 it is also a basic principle that elements enriched in cumulate rocks often become depleted in the corresponding liquids iron enrichment in the skaergaard cumulates is complementary to iron depletion in liquids

a poroelastic description of permeability evolution pore pressure changes in a geothermal reservoir as a result of injection and or production of water result in changes of stress acting on the reservoir rock and consequently changes in the mechanical and transport properties of the rock bulk modulus and permeability were measured at different pressures and temperatures an outcropping equivalent of rotliegend reservoir rock in the north german basin flechtinger sandstone was used to perform hydrostatic tests and steady state fluid flow tests permeability measurements were conducted while cycling confining pressure the dependence of permeability on stress was determined at a constant downstream pressure of 1 mpa also temperature was increased stepwise from 30 to 140 c and crack porosity was calculated at different temperatures although changes in the volumes of cracks are not significant the cracks control fluid flow pathways and consequently the permeability of the rock a new model was derived which relates microstructure of porosity the stress strain curve and permeability porosity change was described by the first derivative of the stress strain curve permeability evolution was ascribed to crack closure and was related to the second derivative of the stress strain curve the porosity and permeability of flechtinger sandstone were reduced by increasing the effective pressure and decreased after each pressure cycle

40ar39ar dating of the skaergaard intrusion we report the first 40ar 39ar data for the skaergaard intrusion based on analyses of hornblende and biotite from a transgressive granophyre from upper zone a uza of the layered series hornblende separates heated in a resistance furnace and laser heated single crystals of biotite from the granophyre give plateau ages that are consistent with isochron ages of 55 48 0 30 and 55 40 0 14 ma respectively 2 internal uncertainty with initial 40ar39ar ratios of 292 4 19 0 and 291 1 7 2 if uncertainties in the ages of 40ar 39ar standard fluence monitors are considered external uncertainties 2 errors are 0 76 and 0 72 ma respectively resistance heating analysis of biotite separated from a gabbro from lower zone a lza of the skaergaard layered series indicates that the sample has been extensively contaminated by ar inherited from old crust and does not constrain the intrusion age apart from indicating that it is less than approximately 57 ma old the ar cooling ages are consistent within uncertainty with both pluton cooling models presented by norton and taylor 1 but the data agree best with their model s2 which assumes a smaller permeability 10 13 cm2 combination of the new ages and the norton and taylor cooling models constrains the emplacement and final crystallization of the skaergaard magma chamber to be at 55 75 0 30 ma and 55 65 0 30 ma respectively evidence for late crystallizing quartz and tridymite near the sandwich horizon sh combined with phase equilibria constraints on the near solidus crystallization temperature of the sh 975 25 c require the pressure of sh solidification to be 60 15 mpa this means that the tertiary basalts and sediments overlying the kangerdlugssuaq region were 3 2 0 8 km thick at 55 65 0 30 ma assuming that the 6 7 km thick tertiary section exposed further east along the east greenland coast is representative of that which accumulated above the skaergaard we infer that the skaergaard emplacement occurred during the main stage of the east greenland flood basalt event after approximately half of the tertiary section had erupted the onset of coastal flexure in the kangerdlugssuaq region was after 55 48 0 76 ma

the differentiation of the skaergaard intrusion we find no support for the claim that the skaergaard magma followed the trend of common tholeiitic volcanic magmas such as those of iceland and the scottish tertiary the end product of differentiation was not a large mass of rhyolite but an iron rich silica poor liquid not unlike that deduced by wager in 1960 the proposal that a large mass of rhyolitic liquid occupied the upper levels of the intrusion finds no support in the field the thick series of ferrogabbos which became richer in iron and poorer in silica until they reached a field of immiscibility cannot be reconciled with crystallization of a large mass of felsic magma mass balance calculations that indicate otherwise are invalid because they fail to take into account large volumes of rocks that differ in composition from those assumed in the calculations while ignoring the existence of major units of the intrusion hunter and sparks propose that lavas in scotland and iceland are more relevant to the liquid compositions than rocks that are intimately associated with the intrusion their argument that the skaergaard intrusion followed a trend of silica enrichment that is universal to tholeiitic magmas is based on an incomplete knowledge of the rocks and faulty calculations of mass balance relations we agree that much remains to be learned about the skaergaard intrusion and the basic mechanisms of magmatic differentiation in this case however we are ready to hang our case on well established field relations and a mass of laboratory data for what must be the most intensely studied body of rock on earth

included blocks and blocks within blocks in the skaergaard intrusion geologic relations and the origins of rhythmic modally graded layers the early eocene skaergaard intrusion of greenland includes enormous numbers of rocks of both exotic and cognate origins the lower parts of the marginal border series contain abundant fragments of feldspathic peridotite that are possibly autoliths intermixed with occasional xenoliths of precambrian gneiss and metasomatized cretaceous paleocene sediments derived from adjoining country rocks the upper border series includes one exceptionally large block of gneiss several hundred meters across and numerous smaller fragments these originating from the intrusion9s footwalls plus a few pieces of peridotite the layered series contains countless autoliths of troctolite gabbroic anorthosite and oxide magnetite ilmenite gabbro broken from parts of the upper border series that have otherwise been lost to erosion at the upper midlevel of its western half it contains a few xenoliths of basalt derived probably from the now eroded eocene roof of the intrusion a distinctive postintrusion composite basaltic dike at one place contains 40 or more xenoliths of troctolite olivine gabbro and gabbroic anorthosite that may represent parts of the layered series still hidden at depth the layered series autoliths range from fragments a few centimeters on a side to blocks more than 400 m across and they typically are coarser grained than their host cumulates being in this respect more like upper border series rocks the autoliths are spread stratigraphically through the lower 70 of the exposed 2500 m thickness of the layered series and are generally concentrated in three broad stratigraphic zones their physical relationships to their host rocks particularly the way they indent older layers beneath and are covered by younger layers above provide abundant evidence that there was generally a sharp well defined interface between the top of the cumulate pile and the main body of magma in the intrusion while the layered series was forming the distribution of the autoliths between and through the well known rhythmic thin modally graded layers shows that these layers were spread by magmatic currents and their relations to the more extensive macrorhythmic layering suggest that it too was significantly shaped by currents many of the larger autoliths are crudely layered internally and in places it is evident that their stratification existed before they broke loose therefore it must have formed in the upper border series one particularly large block of oxide gabbro exhibits extraordinarily well developed modal and textural layering and includes small troctolitic autoliths of an earlier generation and it provides evidence that currents also spread crystalline materials across the top of the magma body many of the very small autoliths in the layered series are highly anorthositic in composition apparently because they were leached of mafic minerals and some of the larger blocks show local patchy internal replacement by anorthosite most large blocks show little sign of postaccumulation modification and some have thin fine grained augite rich rims or rinds demonstrating that even though they were out of thermal and chemical equilibrium with their host cumulates they still were effectively armored against extensive chemical change also documented is a large block that was cut by several early basaltic dikes before it broke free from the top of the intrusion these early dikes transgress small anorthositic replacement pipes in the block showing that the replacement process also occurred in the upper border environment two mechanisms are described whereby graded cumulate layers can be sorted and deposited by magmatic crystal liquid suspension currents one involving density surge currents has been advocated previously the other is a new concept based on boundary flow separation and reattachment vortex cells the two mechanisms are used in complementary ways to illustrate the formation of 1 some of the principal skaergaard structures involving blocks and layers 2 modally graded layers in the layered series that rhythmically alternate with uniform layers and 3 modally sorted layers in the upper border series featuring underside draping beneath small included blocks explanations are provided for 1 why plagioclase did not float away from the tops of graded layers even though it was less dense than the liquid and 2 how the liquid part of a current was fractionated away from the crystalline materials modal and grain size data from skaergaard intrusion graded layers are shown to be in excellent accord with characteristics predicted for layers sorted by currents a synthesis diagram is presented illustrating how all the above processes may have functioned in concert in the intrusion

assemblages with titanite catiosio4 ca mg fe olivine and pyroxenes fe mg ti oxides and quartz part ii application in the system cao mgo feo fe2o3 tio2 sio2 equilibria among titanite pyroxene s olivine spinel phase ilmenite and quartz constrain f o2 t a sio2 a tio2 a fe and the compositional variables tife2 fe 23 c a mg fe 1 and consequently mg fe 1 among the silicate and oxide phases these equilibria can provide the framework for a better understanding of relevant titanite bearing natural assemblages in addition such equilibria can constrain the variables that operate during crystallization of igneous and metamorphic rocks titanite bearing assemblages with pyroxene s fe mg ti ilmenite and spinel olivine and quartz are rare in metamorphic rocks but are common in igneous rocks where they are more commonly reported in plutonic than in volcanic rocks probably because at high temperatures titanite cannot coexist with the relative common in volcanic rocks sub assemblage augite orthopyroxene olivine spinel phase ilmenite moreover decreasing pressure and temperature conditions appear to favor titanite thus it is not surprising that titanite is commonly observed in slowly cooled rocks albeit most typically in association with amphibole we argue that the titanite amphibole association is favored by high a h2o and because a h2o typically increases during crystallization of a pluton titanite amphibole and consequently titanite is more common in plutonic than in volcanic rocks we have used a modified version of the program quilf that includes our thermodynamic data for titanite and appropriate titanite bearing assemblages to estimate the equilibrium crystallization conditions of samples from 1 a tonalite from the myoken zan granitic complex in japan 2 the sandwich horizon in the skaergaard intrusion in greenland 3 rhyodacites dacites and andesites from the sajama porquesa and parinacota volcanoes in the andes 4 the fish canyon tuff in colorado and 5 a quartz rich calc silicate gneiss adjacent to the horse creek anorthosite complex in wyoming the calculations suggest that 1 these titanite bearing assemblages crystallized at values of f o2 that ranged from slightly below fmq to more than 3 log f o2 units above fmq at 500 800 c and 2 the stability of titanite is controlled by t f o2 a sio2 and the compositions of the coexisting oxides and silicates

importance of iron rich tholeiitic magmas at divergent plate margins a reappraisal when a tholeiitic liquid differentiates it may give rise to either iron poor silica rich rhyolitic differentiates or to iron rich silica poor differentiates as found in the skaergaard intrusion iron rich differentiated liquids are rare among erupted rocks but are found in small quantities from several localities at divergent plate margins among the tertiary basalts and intrusions in east greenland normal erupted basalts may be mixtures of primitive liquid and differentiated iron rich liquid which exists at depth but normally does not reach the surface because of its high density the evolved liquids of the skaergaard intrusion were of this kind data from mid oceanic ridges confirm this view we believe that iron rich differentiated liquids despite their scarcity on the surface are much more voluminous at depth as picrites at the other side of the density minimum attained during liquid evolution are thought to be the trend toward iron enrichment develops when the tholeiitic magma differentiates in a closed system at a relatively low oxidation state whereas the trend toward silica enrichment and iron depletion occurs when the magma has interacted with the oxidized and hydrated surroundings in the crust

geology petrology and o and h isotope geochemistry of remarkably 18o depleted paleoproterozoic rocks of the belomorian belt karelia russia attributed to global glaciation 2 4 ga abstract this paper deals with strongly 18o depleted down to 27 3 vsmow 1 9ga paleoproterozoic mid grade metamorphic rocks found in the belomorian belt of karelia e baltic shield the protolith of these rocks is attributed to have been altered by glacial meltwaters during the world s first 2 4 2 3 ga paleoproterozoic slushball glaciation when karelia was located near equatorial latitudes we describe in detail three and report seven new localities with unusually depleted 18o signatures that now span 220 km across the belomorian belt hydrogen isotope ratios measured in amphibole biotite and staurolite also display remarkably low values of 212 to 235 isotope mapping in the three best exposed localities has allowed us to identify the world s most 18o depleted rock located at khitostrov with a 18o value 27 in khitostrov samples zircons have normal 18o detrital cores and low 18o metamorphic rims mapping demonstrates that zones of 18o depletion occur in a concentric pattern 100 400 m in dimension and each locality displays significant 18o and d heterogeneity on a meter to centimeter scale characteristic of meteoric hydrothermal systems worldwide the zone of maximum 18o depletions usually has the highest concentration of metamorphic corundum rutile and zircon and also display doubled concentrations of insoluble trace elements zr ti cr hree these results are explained by elemental enrichment upon mass loss during hydrothermal dissolution in ph neutral meteoric fluid remarkably low 18o and d values suggest that alteration could have only happened by glacial meltwaters in a subglacial rift zone many localities with 18o depletions occur inside metamorphozed 2 4 ga gabbro noritic intrusions or near their contact with belomorian gneisses implying that the intrusions were driving meteoric hydrothermal systems during the known 2 4 ga episode of belomorian rifting given that the isotopically depleted localities now spread over 200 km the extent of the karelian ice cap is estimated to be at least that large svecofennian 1 9 ga metamorphism is seen to cause metamorphic recrystallization of hydrothermally altered rocks into coarse grained assemblages and causing local metasomatism through devolatilization of the underlying hydrous low 18o protolith further depleting d via volatilization this process led to gem quality rubies and kyanites that preserve these remarkable 18o values in the geologic record

origin and evolution of silicic magmatism at yellowstone based on ion microprobe analysis of isotopically zoned zircons the origin of large volume yellowstone ignimbrites and smallervolume intra caldera lavas requires shallow remelting of enormous volumes of variably o depleted volcanic and sub volcanic rocks altered by hydrothermal activity zircons provide probes of these processes as they preserve older ages and inherited do values this study presents a high resolution oxygen isotope examination of volcanism at yellowstone using ion microprobe analysis with an average precision of 0 2o and a 10 mm spot size we report 357 analyses of cores and rims of zircons and isotope profiles of 142 single zircons in 11 units that represent majoryellowstone ignimbrites and post caldera lavas many zircons from these samples were previously dated in the same spots by sensitive high resolution ion microprobe shrimp and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination we additionally report oxygen isotope analyses of quartz crystals in three units the results of this work provide the following new observations 1 most zircons from post caldera low do lavas are zoned with higher do values and highly variable u pb ages in the cores that suggest inheritance from pre caldera rocks exposed on the surface 2 many of the higher do zircon cores in these lavas have u pb zircon crystallization ages that postdate caldera formation but pre date the eruption age by 10 20 kyr and represent inheritance of unexposed post caldera sub volcanic units that have do similar to the lava creek tuff 3 young and voluminous 0 25 0 1ma intra caldera lavas which represent the latest volcanic activity atyellowstone contain zircons with both high do and lowdo cores surrounded by an intermediate do rim this implies inheritance of a variety of rocks from high do pre caldera and low do post caldera units followed by residence in a common intermediate do melt prior to eruption 4 major ignimbrites of huckleberry ridge and to a lesser extent the lava creek and mesa falls tuffs contain zoned zircons with lower do zircon cores suggesting that melting and zircon inheritance from the lowdo hydrothermally altered carapace was an important process during formation of these large magma bodies prior to caldera collapse 5 the do zoning in the majority of zircon core rim interfaces is step like rather than smoothly inflected suggesting that processes of solution reprecipitation were more important than intracrystalline oxygen diffusion concave downward zircon crystal size distributions support dissolution of the smaller crystals and growth of rims on larger crystals this study suggests that silicic magmatism atyellowstone proceeded via rapid shallow level remelting of earlier erupted and hydrothermally alteredyellowstone source rocks and that pulses of basaltic magma provided the heat for melting each postcaldera yellowstone lava represents an independent homogenized magma batch that was generated rapidly by remelting of source rocks of various ages and do values the commonly held model of a single large volume super solidus mushy state magma chamber that is periodically reactivated and produces rhyolitic offspring is not supported by our data rather the source rocks for theyellowstone volcanism were cooled below the solidus hydrothermally altered by heated meteoric waters that caused low do values and then remelted in distinct pockets by intrusion of basic magmas each packet of new melt inherited zircons that retained older age and do values this interpretation may have significance for interpreting seismic data for crustal low velocity zones in which magma mush and solidified areas experiencing hydrothermal circulation occur side by side new basalt intrusions into this solidifying batholith are required to form the youngest volcanic rocks that erupted as independent rhyolitic magmas we also suggest that the lava creek tuff

pressure conditions for the solidification of the skaergaard intrusion eruption of east greenland flood basalts in less than 300 000 years abstract primary granophyres are differentiated from olivine tholeiitic magma and occur interstitially throughout the cumulus stratigraphy of the skaergaard intrusion east greenland samples from the lower zones a c lza c the middle zone mz and the sandwich horizon sh are included in the present study together with granophyric accumulations in gabbroic pegmatite from lza c fluid inclusions in quartz and the mineral assemblage in the granophyres record the pressure under which the skaergaard intrusion crystallised pegmatitic granophyre from lza c consists mainly of quartz plagioclase an 4 7 and alkali feldspar or 40 80 enclosing an earlier formed assemblage of ferrohastingsitic and ferroedenitic hornblende fayalite fo 4 5 titanite biotite and fluor apatite granophyric quartz albite and alkali feldspar crystallised from water saturated granitic melts near eutectic minimum conditions between 680 and 660 c the pressure of granophyre crystallisation was modelled by the intercept between fluid inclusion isochores and the minimum melt solidus for granitic compositions pressures recalculated to the roof pendant of the intrusion are 0 7 0 5 for lza 2 0 0 2 for lzb c 2 3 0 8 for mz the triple group level and 3 3 1 3 kb for sh amphibole geobarometry independently confirm the pressure estimates for pegmatitic granophyres in lza c the granophyres formed as the intrusion cooled through the minimum melt solidus in lza lzb lzc mz and sh respectively the pressure increase from lza to sh granophyres is explained by progressive burial during cooling of the intrusion and contemporaneous outpouring of 5 3 6 3 2 7 km of flood basalts during the initial opening of the northeast atlantic ocean accordingly the skaergaard intrusion evolved from a subvolcanic magma chamber at emplacement to a more deep seated igneous system during terminal crystallization when the majority of the intercumulus phases formed the present cooling history suggests the intrusion cooled through the temperature of granophyre formation in less than 300 000 years the increase in the pressure of granophyre formation therefore implies that 5 3 6 3 2 7 km of flood basalts were emplaced within this time window

mechanisms of differentiation in the skaergaard intrusion thanks to its magnificent exposures and extraordinary petrologic development the skaergaard intrusion provides an excellent test for three basic mechanisms of crystal liquid fractionation diffusive exchange compaction convective exchange 1 diffusive exchange at the solidification front does not seem to have played a major role for no obvious difference is seen in the behavior of components of widely differing diffusivities the effects of diffusion were probably masked by porous flow of the interstitial liquid 2 compaction and 9filter pressing9 of residual liquids can be tested by comparing concentrations of incompatible elements in parts of the intrusion that crystallized in different orientations with respect to gravity the contrast between the large concentrations of these elements in the upper border series and consistently smaller abundances in the layered series long thought to be due to contamination of the upper levels with crustal rocks is more likely a result of compaction that took place at the floor but not under the roof 3 convective exchange driven by differences in the compositional densities of the main magma and interstitial liquids seems to have been important at the steep walls and to a lesser degree under the roof it may also have been responsible for a large compositional anomaly near the centre of the layered series where an iron rich liquid percolated down through parts of lower and middle zones at later stages of crystallization when density relations were reversed a buoyant liquid rich in volatiles and incompatible elements rose from the layered series and permeated the upper part of the intrusion a liquid of this latter kind could have caused the pervasive metasomatic alteration seen in much of the layered series in both compaction and convective exchange re equilibration and reactions between migrating liquids and early formed crystals augmented permeabilities and brought about extensive compositional and textural changes although inhomogeneities in the initial magma could account for some of the compositional variations the main trend of differentiation can be ascribed to a combination of compaction and convective fractionation the convective flow was of two kinds one of descending iron rich liquids and another of more evolved rising liquids and fluids with low densities and large concentrations of incompatible elements in the early stages the proportions of iron rich liquids were much greater than those of the silica rich variety and until the crystallization fronts converged at the sandwich horizon the former made the greatest contribution to evolution of the main body of magma as crystallization advanced however light silica rich liquids became more important they permeated the upper border series and much of the upper part of the layered series this late stage liquid continued to differentiate after the crystallization fronts met a secondary sandwich horizon was formed where incompatible elements reach maximum concentrations in the lower part of the upper border series

laboratory measurements of a complete set of poroelastic moduli for berea sandstone and indiana limestone measurements have been completed for eight different poroelastic moduli of water saturated berea sandstone and indiana limestone as a function of confining pressure and pore pressure the poroelastic moduli for indiana limestone are generally consistent to 10 which was verified by a formal inversion procedure for independent moduli from the eight measurements for indiana limestone best fit values were drained bulk modulus 21 2 gpa the undrained bulk modulus 31 7 gpa drained poisson s ratio 0 26 undrained poisson s ratio 0 33 and pore pressure buildup coefficient 0 47 at 20 35 mpa effective stress the poroelastic moduli for berea sandstone are generally consistent to 20 the greater inconsistency is most likely caused by the nonlinear variation of the moduli at different strains for berea sandstone best fit values were drained bulk modulus 6 6 gpa undrained bulk modulus 15 8 gpa drained poisson s ratio 0 17 undrained poisson s ratio 0 34 and pore pressure buildup coefficient 0 75 at 10 mpa effective stress