amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

igneous microstructures in migmatites clear differences between the microstructures of leucosomes and mesosomes occur in some nebulitic migmatites in the proterozoic arunta block central australia the leucosomes show crystal faces of k feldspar microcline microperthite cordierite andalusite and plagio clase against quartz indicating crystallization of a melt in contrast the mesosomes show predominantly polygonal grain shapes modified by 001 crystal faces of biotite and rare crystal faces in some porphyroblasts of garnet cordierite and orthopyroxene indicating re crystallization in the solid state the occurrence of abundant crystal faces in minerals such as feldspar cordierite and andalusite which typically grow crystal faces in magmas but generally not in metamorphic rocks is evidence of former melt therefore igneous microstructures can be preserved in leucosomes that have not undergone penetrative subsolidus deformation and recrystallization the cores of many of the crystals of cordierite and k feldspar have small locally oriented inclusions similar to those in the same minerals in the mesosomes these indicate that the cores remained solid during crystallization of the leucosome which produced inclusion free euhedral rims these crystals provide criteria for recognizing possible restite in granitoid magmas

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

geophysical signatures for low porosity can mimic natural gas hydrate an example from alaminos canyon gulf of mexico natural gas hydrate in sand sediments can increase both the measured compressional velocity and resistivity the same geophysical signatures occur however in low porosity sand we investigate the possible occurrence of natural gas hydrate in a sand interval in alaminos canyon block 21 ac 21 in the gulf of mexico drilled by the u s gas hydrate joint industry project the sand interval has an increase in resistivity 2 2 m and a strong peak and trough at the top and bottom of the sand on exploration seismic which has been interpreted as natural gas hydrate we reexamine the logging data and construct a new reservoir model that matches the measured resistivity the high density sublayers in the sand and the surface seismic trace our model shows that the sand interval in ac 21 is most likely water saturated and the slight increase in resistivity higher measured density and the seismic amplitudes are caused by a reduction in porosity to 30 in the sand interval relative to a porosity of 42 in the surrounding marine muds more broadly we show that the average depth where the porosity of marine muds becomes lower than sand sediment is 900 mbsf though it could be as shallow as 600 mbsf for high porosity sands in any case the similar geophysical signatures for water saturated sand and low saturations of natural gas hydrate in sand probably occur throughout the gas hydrate stability zone at most sites worldwide

the canadian ice island drift deterioration and detection ci2d3 database this project was undertaken with the financial support of the government of canada through environment and climate change canada and through the polar knowledge canada project safe passage funding from the canadian foundation for innovation and the ontario research fund supported the purchase of computer equipment radarsat 1 and 2 data were supplied by the canadian ice service through a joint project agreement

chemical characteristics of migmatites accessory phase distribution and evidence for fast melt segregation rates equilibration between melt and solid is inhibited by rapid melt extraction and by restricted equilibration armouring slow dissolution when segregation occurs by channelised migration along high porosity pathways melt migration is more rapid than trace element diffusion rates in silicates and faster than accessory phase dissolution rates evidence for channelised flow and deformation enhanced melt segregation into boudin necks fractures and micro shears at low melt fractions is present in the moine kirtomy migmatitie suite kms in sutherland scotland melt migration distances are on a metre to tens of metres scale concordant leucosomes in stromatic migmatities in the kms have low zr contents low lree light rare earth element and h heavy ree contents and positive eu anomalies ree patterns of this type can be produced by removal of leucosome before complete equilibration with source due to the inhibited dissolution of lree and hree bearing accessory phases in water undersaturated melts melting in the kms however occurred at or near the wet granite solidus leaving biotite as a residual phase detailed back scattered electron imaging shows that ree bearing accessory phases remained as residual phases and were concentrated in the melanosome and at the melanosome leucosome boundary irregularly shaped patches of diatexite contain a small proportion of excess zr consistent with entrainment of melanosome schlieren enriched in zircon these data indicate that deformation enhanced melt extraction led to the rapid migration of small melt fractions from the melting site on a time scale less than that required to saturate the melt in zr leucosomes were thus prevented from equilibrating with accessory phases before extraction

hornblende garnet plagioclase thermobarometry a natural assemblage calibration of the thermodynamics of hornblende calibrations are presented for an independent set of four equilibria between end members of garnet hornblende plagioclase and quartz thermodynamic data from a large internally consistent thermodynamic dataset are used to determine the g of the equilibria then with the known mixing properties of garnet and plagioclase the non ideal mixing in amphibole is derived from a set of 74 natural garnet amphibole plagioclase quartz assemblages crystallised in the range 4 13 kbar and 500 800 c the advantage of using known thermodynamic data to calculate g is that correlated variations of composition with temperature and pressure are not manifested in fictive derived entropies and volumes but are accounted for with non ideal mixing terms the amphibole is modelled using a set of ten independent end members whose mixing parameters are in good agreement with the small amount of data available in the literature the equilibria used to calibrate the amphibole non ideal mixing reproduce pressures and temperatures with average absolute deviations of 1 1 kbar and 35 c using an average pressure temperature approach and 0 8 kbar with an average pressure approach the mixing data provide not only a basis for thermobarometry involving additional phases but also for calculation of phase diagrams in complex amphibole bearing systems

modified effective medium model for gas hydrate bearing clay dominated sediments in the krishna godavari basin abstract during nghp expedition 01 well logs were obtained for gas hydrate exploration in krishna godavari kg offshore basin these logs coupled with a suitable rock physics model can be used to understand the interaction between the sediment grains of unconsolidated marine sediments as well as with hydrate in this paper we study the friction dependent effective medium model emm to understand these grain interactions the compressional p and shear s wave velocities of fluid saturated sediments are estimated using different friction parameters at site nghp 01 03 which represent the background fluid saturated marine sediment and are compared with the observed velocities derived from sonic logs our analysis shows that the shear velocity is overestimated for the hertz mindlin contact theory no slip across the grain contact but can be accurately estimated for the walton s smooth contact model zero friction across the grain contact it suggests that the background shear wave velocity need to be modeled without friction at the grain contact for unconsolidated marine sediments further the friction dependent emm theory is tested at site nghp 01 07 which represents the load bearing gas hydrate deposits in kg basin the comparison between the gas hydrate saturations estimated from sonic and resistivity logs shows that saturations estimated from p wave velocity match well with those estimated from resistivity and chloride anomaly and is largely independent of the frictional parameter however gas hydrate saturations estimated from shear wave velocity is overestimated in the absence of friction but agrees with the other estimates if an arbitrary small friction is included in the emm we further extended the friction dependent emm for multi grain contact clay quartz hydrate in which the effective modulus of sediment matrix is estimated by accounting for all possible contact combinations among the grains like quartz quartz qq clay clay cc clay quartz qc quartz hydrate qh clay hydrate ch and hydrate hydrate hh the gas hydrate saturations estimated from shear velocity assuming the same non zero friction term are underestimated as compared to those estimated from p wave velocity interestingly the saturations estimated assuming zero friction from both p and s wave velocities are comparable to each other and show a good match with those estimated from resistivity logs and chloride anomalies the proposed emm with zero friction and mixed grain contact is able to predict the velocities of fluid saturated sediments as well as gas hydrate bearing sediments in kg offshore basin

pervasive granitoid magma transfer through the lower middle crust during non coaxial compressional deformation granitic magmas migrated through early proterozoic middle lower crust at mt hay central australia via a diverse network of narrow structurally controlled channelways during a period of progressive w sw directed thrusting d1a d1d they utilized existing folds boudins and shear zones or created new channels by magmatic fracture either parallel to layering or rarely in irregular arrays the magmas rose obliquely parallel to the plunging 50 60 regional elongation direction which was defined by coaxial folds boudin necks and a strong mineral elongation lineation megacrystic charnockitic magmas migrated through metre scale conduits during d1a d1b but leucosomes were generally restricted to smaller centimetre scale structures that existed throughout the entire deformation history thus d1a d1b leucosomes were potential feeders of in situ partial melts to the adjacent larger conduits of charnockite magma thereby providing a pervasive interconnected network that allowed efficient migration of all magma types during the early stages of thrusting the upper middle crust of the anmatjira reynolds range area contains abundant megacrystic granitoid sheets that are of similar age and geochemistry to those at mt hay they are considered to have formed as syntectonic intrusions emplaced during w sw directed thrusting as at mt hay suggesting that granitic magmas formed near the base of the continental crust passed through the mid lower crustal level 25 30 km exposed at mt hay and accumulated in batholithic proportions at shallower crustal levels 12 20 km such as the anmatjira reynolds range area the observations imply that granitoid magmas in the deep crust are capable of pervasive migration through the crust during major compressive noncoaxial shear deformation localization of magmas by sequentially developed narrow compressive structures suggests that dilatancy followed successive foliation forming events a situation that can occur during steady state deformation if the effective confining pressures are low which would be a result of high and possibly variable rates of magma influx the inferred rapid melt segregation and migration during deformation suggest that large chambers do not form until magma reaches neutral buoyancy in the middle to upper continental crust

p and s wave velocity models of shallow dry sand formations from surface wave multimodal inversion abstractsurficial formations composed of loose dry granular materials constitute a challenging target for seismic characterization they exhibit a peculiar seismic behavior characterized by a nonlinear seismic velocity gradient with depth that follows a power law relationship which is a function of the effective stress the p and s wave velocity profiles are then characterized by a power law trend and they can be defined by two power law exponents p s and two power law coefficients p s in case of depth independent poisson s ratio the p wave velocity profile can be defined using the vs power law parameters and poisson s ratio because body wave investigation techniques e g p wave tomography may perform ineffectively on such materials because of high attenuation we addressed the potential of surface wave method for a reliable seismic characterization of shallow formations of dry uncompacted granular materials we took into account the dependence of seismic wave velocity on effective pressure

soil density elasticity and the soil water characteristic curve inverted from field based seismic p and s wave velocity in shallow nearly saturated layered soils abstractsoil density porosity elastic moduli and the soil water characteristic curve swcc are important properties for soil characterization however geotechnical and laboratory tests for soil properties are costly and limited to point sampling sites seismic surveys can provide laterally continuous seismic soil property values that may complement geotechnical borehole tests with less cost we have developed a workflow to invert for soil properties and the swcc from seismic p and s wave velocity versus depth profiles interpreted from shallow 99 the inversion is performed by using the covariance matrix adaptation evolution strategy to search automatically for optimal input soil property values by minimizing the misfit between field based velocity profiles and predicted velocity profiles based on the hertz mindlin and biot gassmann theories the results from seismic soil property inversion are validated by comparis

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

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

evidence for 1 8 ga extension of the eastern block of the north china craton from shrimp u pb dating of mafic dyke swarms in shandong province abstract a large mafic dyke from the nnw trending dyke swarms in the eastern block of the north china craton was dated by shrimp u pb age analysis this dyke occurs near mt taishan in shandong province it cuts neoarchean tonalite adamellite and diorite plutons two types of zircons were found in the dyke type 1 zircons were inherited from the host rocks and gave a shrimp u pb age of 2544 24 ma with a weighted mean 207pb 206pb age of 2523 18 ma type 2 zircons were crystallized from the dyke magma and yielded a concordant shrimp u pb age of 1830 17 ma with a weighted mean 207pb 206pb age of 1837 18 ma indicating that the large dyke at taishan was emplaced at 1830 ma the mafic dyke swarm provides evidence of a phase of extension in the eastern block of the north china craton at 1 8 ga this dyke has a similar age to dyke swarms in the western block and in the central orogen belt of the north china craton this lithospheric extension led to the opening of the yanliao and zhongtiao aulacogens the similar ages and orientations of 1 8 ga dyke swarms throughout the north china craton demonstrate that at that time the eastern and western blocks were united and that the amalgamated craton experienced widespread extension

influence of gas hydrate morphology on the seismic velocities of sands this paper reports the results of a series of resonant column tests on specimens where gas hydrate has been formed in sands using an excess water technique in these specimens the amount of hydrate formed is restricted by the amount of gas in the specimen and with an excess of water being present in the pore space results of resonant column tests carried out to determine compressional and shear wave velocities suggest that gas hydrate formed in this way are frame supporting in contrast the behavior observed in sands where the hydrate is formed from finite water where the remaining pore space is saturated with methane gas termed in this paper the excess gas method exhibits a cementing behavior while tetrahydrofuran hydrate sands or where the hydrate is formed from dissolved methane within the pore water exhibit a pore filling behavior for hydrate saturations less than 40 for sands where the hydrate is formed using the excess water method much larger volumes of hydrate are required before a significant increase in shear wave velocity occurs although increases in compressional wave velocity are seen at lower hydrate contents these results suggest that hydrate interaction with the sediment is strongly dependent on morphology and that natural hydrate may exhibit contrasting seismic signatures depending upon the geological environment in which it forms

effects of stress reduction on geomechanical and acoustic relationship of overconsolidated sands abstract relationship between different geomechanical and acoustic properties measured from seven laboratory tested unconsolidated natural sands with different mineralogical compositions and textures were presented the samples were compacted in the uniaxial strain configuration from 0 5 to 30 mpa effective stress each sand sample was subjected to three loading unloading cycles to study the influence of stress reduction geomechanical elastic and acoustic parameters are different between normal compaction and overconsolidation unloaded and reloaded stress path k0 data differ between normal consolidated and overconsolidated sediments the k0 value of approximately 0 5 is founded for most of the normal consolidated sands but varies during unloading depending on mineral compositions and textural differences the k0 and overconsolidation ratio relation can be further simplified and can be influenced by the material compositions k0 can be used to estimate horizontal stress for drilling applications the relationship between acoustic velocity and geomechanical is also found to be different between loading and unloading conditions the static moduli of the overconsolidated sands are much higher than normal consolidated sands as the deformation is small small strain the correlation between dynamic and static elastic moduli is stronger for an overconsolidation stage than for a normal consolidation stage the results of this study can contribute to geomechanical and acoustic dataset which can be applied for many seismic geomechanics applications in shallow sands where mechanical compaction is the dominant mechanism

grain scale melt distribution in two contact aureole rocks implications for controls on melt localization and deformation the grain scale spatial arrangement of melt in layer parallel leucosomes in two anatectic rocks from two different contact aureoles located in central maine usa is documented and used to constrain the controls on grain scale melt localization the spatial distribution of grain scale melt is inferred from microstructural criteria for recognition of mineral pseudomorphs after melt and mineral grains of the solid matrix that hosted the melt in both rocks feldspar mimics the grain scale distribution of melt and quartz is the major constituent of the solid matrix the feldspar pockets consist of individual feldspar grains or aggregates of feldspar grains that show cuspate outlines they have low average width length ratios 0 54 and 0 55 respectively and are interstitial between more rounded and equant width length ratios 0 65 for both samples quartz grains in two dimensions the feldspar pockets extend over distances equivalent to multiple quartz grain diameters possibly forming a connected three dimensional intergranular network both samples show similar mesoscopic structural elements and in both samples the feldspar pockets have a shape preferred orientation in one sample feldspar inferred to replace melt is aligned subparallel to the shape preferred orientation of quartz indicating that pre or syn anatectic strain controlled the grain scale distribution of melt in the other sample the preferred orientation of feldspar inferred to replace melt is different from the orientations of all other mesoscopic or microscopic structures in the rock indicating that differential stress controlled grain scale melt localization this is probably facilitated by conditions of higher differential stress which may have promoted microfracturing grain scale melt distribution and inferred melt localization controls give insight into possible grain scale deformation mechanisms in melt bearing rocks application of these results to the interpretation of deep crustal anatectic rocks suggests that grain scale melt distribution should be controlled primarily by pre or syn anatectic deformation feedback relations between melt localization and deformation are to be expected with important implications for deformation and tectonic evolution of melt bearing rocks

constraining depth to basement for mineral exploration using microtremor a demonstration study from remote inland australia abstractwe constrain the depth and seismic structure of stiff sediment cover overlying a prospective basement terrane using a passive seismic technique which uses surface wave energy from microtremor also known as ambient seismic energy or seismic noise this may be applied to mineral exploration under cover to decrease the inherent ambiguity in modeling potential field data for exploration targeting we use data from arrays of portable broadband seismometers processed using both the multimode spatially averaged coherency mmspac method and the horizontal to vertical spectral ratio hvsr method to produce profiles of seismic velocity structure along a 12 km transect we have developed field protocols to ensure consistent acquisition of high quality data in near mine and remote locations and a variety of ground conditions a wavefield approaching the theoretical ideal for mmspac processing is created by combining the energy content of an off road vehicle driven around the seismometer array and ambi

seismic ground roll absorption and reemission by sand dunes this work was performed at schlumberger cambridge research where m i arran was a case student intern and e muyzert is a senior research scientist

using melt inclusions to determine parent magma compositions of layered intrusions application to the greenhills complex new zealand a platinum group minerals bearing island arc intrusion the permian greenhills complex of southland new zealand is a small ultramafic to mafic layered intrusion that hosts primary magmatic platinum group minerals pgms as inclusions in cumulus chromian spinel grains we have determined the major and trace element chemistry of the parent magmas of the complex using the composition of rehomogenized melt inclusions trapped in cumulus spinel grains from dunite these melt inclusions have compositions similar to those of primitive ankaramite dikes that cut the complex verifying that our data are representative of the parent melt chemistry these magmas have high mgo and cao and are enriched in pb sr and large ion lithophile elements compared to high field strength and rare earth elements we suggest that the parent magmas to the complex were primitive low k island arc tholeiite basalts that formed by high degrees of melting of a spinel peridotite source the platinum group element contents of such magmas are expected to be very high therefore the primary pgms at greenhills are suggested to have precipitated directly from the melt following differentiation and cooling in a shallow magma chamber

origin of k poor leucosomes in a metasedimentary migmatite complex by ultrametamorphism syn metamorphic magmatism and subsolidus processes two types of stromatic leucosomes are identified in metasedimentary rocks from the skagit migmatite complex north cascades washington state u s a both types are trondhjemitic and appear similar in outcrop but although both contain low abundances of ree one type consists of leucosomes that are relatively ree enriched compared to the other and contains 1 small 700 c water rich fluid present inferences about the origin of the above listed mineralogical and fluid inclusion features and modeling of leucosome trace element abundances the second type of leucosome is interpreted to have formed entirely by subsolidus processes e g metamorphic differentiation because these leucosomes lack features consistent with an origin by partial melting k poor tonalitic trondhjemitic leucosomes associated with metasedimentary biotite bearing source rocks may form by water saturated partial melting or by subsolidus processes both general leucosome forming mechanisms may operate at different times during upper amphibolite facies regional metamorphism partial melting may be initiated by syn metamorphic magmatic activity if crystallizing plutons serve as external sources of the water rich fluid necessary for ultrametamorphism in the middle crust during orogenesis large scale migmatite complexes such as the skagit migmatites may form at least in part in response to contact effects of plutonism associated with high grade metamorphism so although migmatite complexes are a volumetrically substantial part of many orogenic belts they may not themselves represent a significant original source of magma for larger scale igneous bodies

experimental mechanical compaction of reconstituted shale and mudstone aggregates investigation of petrophysical and acoustic properties of sw barents sea cap rock sequences abstract this study investigates petrophysical and acoustic properties of experimentally compacted reconstituted samples of seal sequences from the southwestern barents sea the aggregates were collected from drill cuttings of mudstone and shale formations of two exploration wells 7220 10 1 salina discovery and 7122 7 3 goliat field the washed and freeze dried samples were characterized for grain size distributions geochemical analyses and mineralogical compositions a total of 25 compaction tests 12 dry and 13 brine saturated were performed with a maximum effective vertical stress of 50 mpa the laboratory measurements demonstrated that petrophysical and acoustic properties of argillaceous sediments can change within a sedimentary basin and even within a given formation the results show that the collected aggregates from goliat field are compacted more compared to salina discovery the maximum and minimum compaction are measured in samples collected from snadd and fuglen formations respectively the final porosity of brine saturated specimens varies between 5 and 22 the ultrasonic velocity measurements depict that samples with the same porosity values can have a broad range of velocity values the resulting compaction trends in this study were compared to published compaction curves for synthetic mixtures of quartz and clay all compaction trends show higher porosity reduction than the silt fraction with 100 quartz comparison of experimental compaction result of each mudstone and shale aggregate with its corresponding acquired well log data helps to delineate the burial history and exhumation in the study area a net exhumation of 950 m and 800 m is estimated at salina and goliat wells respectively the outcomes of this study can provide insights for hydrocarbon prospect discovery in a pre mature sedimentary basin in terms of exploration and production and also for geological co2 storage sites the experimental results may provide information for well log and seismic interpretation basin modeling and seal integrity of investigated horizons

archean crustal evolution in china the taishan complex and evidence for juvenile crustal addition from long term depleted mantle abstract the main framework for crustal evolution of the late archean taishan complex in the shandong province of china is constructed using data from field investigation petrographic examination geochemical analysis and isotopic age determination the history of the complex began with emplacement of basic and tonalitic magmas about 2 7 2 75 ga ago which were metamorphosed designated as metamorphism i to amphibolites and grey gneisses shortly after their emplacement these rocks constitute a metamorphic basement termed the wangfushan gneisses the basement gneisses were later intruded by a plutonic association including 1 alkali and light rare earth element lree enriched dioritic rocks and their differentiates 2 6 ga ago 2 granites and trondhjemites collectively termed the hushan granites also 2 6 ga ago and 3 the aolaishan type granites sensu stricto 2 4 2 5 ga ago the plutonic association in conjunction with the older basement gneisses was later subjected to a second period of deformation and metamorphism metamorphism ii 2 ga ago as inferred from published k ar biotite dates the chronological order of all the above events has been determined by a multichronometric approach and the age results in ma with 2 uncertainties are summarized as follows the relatively low i sr initial 87 sr 86 sr ratio and high positive nd t values for the wangfushan gneisses and the diorite group provides strong evidence for continental growth by addition of juvenile material ultimately separated from long term depleted mantle sources by contrast the sr and nd isotopic data for the aolaishan type granites coherently suggest that they are likely to be derived by anatexis of the basement gneisses at shallow depths crustal evolution of the taishan complex offers an additional example supporting the concept of a continental accretion differentiation superevent that during such a worldwide tectonothermal episode particularly in the archean important differentiation of the upper mantle has contributed to the growth of the continental crust by addition of juvenile material

mantle and slab contributions in arc magmas destructive plate margins are major sites of terrestrial magmatism that have long had a key role in models for the generation of continental crust and the development of chemical heterogeneities in the upper mantle in these models it is important to evaluate the nature and size of contributions from preexisting crust in the generation of magmas above subduction zones and to constrain the size of the fluxes of different elements from the subducted crust and the overlying mantle wedge in arc magmas kay 1 980 hawkesworth ellam 1 989 hawkesworth et al 1 99 1 a mcculloch gamble 1 99 1 the more mobile components of the subducted oceanic crust are the products of element fractionation processes in the upper continental crust the ocean basins and hydrothermal systems on the ocean floor they therefore have distinctive isotope and even trace element ratios that in principle should be readily distinguished from those in peridotite in the mantle wedge prior to subduction in practice however element ratios are almost certainly fractionated during shallow level dehydration of sub ducted material and at greater depths where material from the slab appears to contribute in the generation of arc magmas moreover the isotope signal of slab derived material may be heavily diluted by exchange with

shrimp u pb ages of detrital zircons in metasedimentary rocks of the central ogcheon fold thrust belt korea evidence for tectonic assembly of paleozoic sedimentary protoliths abstract we analyzed detrital zircons in four metasandstones and two metadiamictites of the central ogcheon metamorphic belt omb in order to provide geochronologic constraints on the time of deposition and protolith age distributions shrimp u pb ages of the newly analyzed zircons range from archean to early paleozoic and their age patterns permit the definition of four lithotectonic slices upper and lower pibanryeong units consisting primarily of quartzite and metasandstone an upper poeun unit of black slate containing early permian plant fossils and a lower poeun unit made up of metasandstone and metadiamictite a quartzite of the upper pibanryeong unit yielded two major zircon age populations at 965 11 ma and 447 5 ma whereas two lower pibanryeong metasandstones show major age concentrations at 2 5 ga 1 0 0 9 ga and 545 535 ma the youngest components of these units suggest maximum ages of sedimentation as late ordovician and early cambrian respectively these upper and lower pibanryeong zircon age distribution patterns are consistent with those of ordovician and devonian sedimentary strata respectively from the south china craton scc on the other hand three samples of the lower poeun unit yielded two distinct age populations at 1 87 ga and 755 7 ma in addition a metadiamictite contains abundant mesoproterozoic zircons with two broad peaks centered at 1 3 and 1 6 ga protolith ages and distribution patterns are profoundly different between the pibanryeong and poeun lithotectonic packages suggesting the presence of a major thrust fault juxtaposing allochthons that are also characterized by large p t contrasts our detrital zircon results for the pibanryeong unit are compatible with derivation from the scc in apparent contrast with the poeun occurrence of early permian plant fossils most likely correlative with the north china craton ncc taken together the suturing of paleozoic metasedimentary terranes in the omb is a product of permo triassic orogeny reflecting collision of the north and south china cratons

vp vs ratio versus differential stress and rock consolidation a comparison between rock models and time lapse avo data the compressional to shear wave velocity ratio vp vs is an important parameter in seismic amplitude versus offset avo analysis and this parameter plays a key role especially for lithology and fluid prediction methods the p wave velocity is a key parameter in traditional pressure prediction methods because overpressure often results in a velocity reduction however for avo based pore pressure prediction methods one expects that the vp vs ratio also is a key parameter the hertz mindlin geomechanical model predicts a constant vp vs ratio as the differential stress changes in a dry package of identical spheres ultrasonic core measurements show increased vp vs ratios as the differential stress decreases especially for unconsolidated wet sands thus one is likely to assume that the vp vs ratio is dependent on rock consolidation by combining the hertz mindlin model with the gassmann model we show how to obtain a sim ple rock physics framework including both the differential stress and

anisotropic surface wave characterization of granular media abstractin unconsolidated granular media the state of stress has a major effect on the elastic properties and wave velocities effective media modeling of granular packs shows that a vertically oriented uniaxial state of stress induces vertical transverse isotropy vti characterized by five independent elastic parameters the rayleigh wave velocity is sensitive to four of these five vti parameters we have developed an anisotropic rayleigh wave inversion that solves for four of the five independent vti elastic parameters using anisotropic thomson haskell matrix equations that can be used to determine the degree of anisotropy and the state of stress in granular media the proposed method incorporates an initial model search guided by rock physics models and dispersion curve inversion that uses a gradient based solver we carried out the inversion on a synthetic example and a real data set in which we inverted for in situ elastic moduli of unconsolidated sands at very low effective stress the synthetic

tectonometamorphic evolution of the chuncheon amphibolite central gyeonggi massif south korea the chuncheon amphibolite part of the gubongsan group which overlies the yongduri gneiss complex is interlayered with calc silicate rock marble quartzite biotite schist and quartzofeldspathic gneiss in the central gyeonggi massif south korea metamorphic pressures and temperatures estimated from the amphibolite are 5 5 10 6 kbar and 615 714 c these p t conditions are close to those defined by the reaction curve between kyanite and sillimanite and suggest medium pressure type metamorphism of the chuncheon amphibolite for two metapelites intercalated with the amphibolite temperatures are estimated to be 607 699 c consistent with those obtained from the amphibolite on the other hand pressures estimated from these metapelites are significantly different 4 6 kbar and 9 13 kbar when rim and core compositions of garnet are respectively used these p t estimates obtained from the amphibolite and metapelite suggest a nearly isothermal decompression of 3 7 kbar during denudation rapid decompression is likely on the basis of the results of mineral chemistry phase equilibria and geothermobarometer moreover in conjunction with the occurrence of kyanite in the adjacent gyeonggi gneiss complex p t estimates of the chuncheon amphibolite and metapelite suggest a clockwise p t t path this evolutionary path may be related to the amalgamation of continents during the late proterozoic event which corresponds to the jinningian orogeny in the qinling belt of china

temporal and compositional differences between subsolidus and anatectic migmatite leucosomes from the quetico metasedimentary belt canada migmatites in the quetico metasedi mentary belt contain two types of leucosome 1 layer parallel leucosomes that grew during deformation and prograde metamorphism these are enriched in si02 sr and eu but depleted in ti02 fe203 mgo cs rb ree sc th zr and hf relative to the quetico metasediments 2 discordant leucosomes that formed after the regional folding events when metamorphic temperatures were at their peak these are enriched in rb ba sr and eu but display a wide range of lree th zr and hf contents relative to the quetico metasediments layer parallel leucosomes formed by a sub solidus process termed tectonic segregation this stress induced mass transfer pfocess began when the quetico sediments were deformed during burial and continued whilst the rocks were both stressed and heterogeneous sub solidus leucosome compositions are consistent with the mobilization of quartz and feldspar from the host rocks by pressure solution the discordant leucosomes formed by partial melt ing of the quetico metasediments possibly dur ing uplift of the belt the range of composition displayed by the anatectic leucosomes arises from crystal fractionation during leucosome emplacement some anatectic leucosomes pre serve primary melt compositions and have smooth ree patterns but those with negative eu anomalies represent fractionated melts and others with positive eu anomalies represent accumulations of feldspar plus trapped melt

the seismic sand curve revisited a sand curve described 25 years ago has been in continuous use by saudi aramco for seismic data processing in dune areas of the rub al khali refraction field methods behind this sand curve have many potential uncertainties recent laboratory data on dry sand similar to that in saudi arabia allows the calculation of a new sand curve for comparison the result is a remarkable level of agreement based on two very different kinds of measurement giving added confidence and refinement to the venerable sand curve

modeling of stress dependent static and dynamic moduli of weak sandstones 1 static and dynamic moduli of a sandstone may be different and stress sensitive knowledge about this is important for the interpretation of seismic data and sonic logs we use a numerical model which is based on the discrete element method dem to study the static and the dynamic mechanical behavior of weak sandstones we developed a constitutive contact law and implemented it into the dem model in order to properly simulate the deformation of weak sandstones the contact law includes the effect of nonlinear elasticity and plasticity at grain contacts the dem model can also capture the effect of the closing of pre existing cracks the formation of new cracks and slip at uncemented grain contacts due to stress alteration using such a model we simulated sandstone specimens under laboratory experimental conditions we calculated the static and the dynamic moduli of the dem model at different stress states the modeling results qualitatively agree with some published laboratory observations by applying different stress paths and stress histories we studied how the moduli were influenced by the stress state stress path and stress history in particular the simulations show the growing difference between the static and the dynamic moduli as failure is approached the simulations thus support the assumption that theoretical insight in the grain scale deformation mechanisms helps to understand and explain the difference between static and dynamic moduli as well as for the failure process

petrology of an intrusion related high grade migmatite implications for partial melting of metasedimentary rocks and leucosome forming processes intrusion related migmatites comprise a substantial part of the high grade part of the southern damara orogen namibia which is dominated by al rich metasedimentary rocks and various granites migmatites consist of melanosomes with biotite sillimanite garnet cordierite hercynite and leucosomes are garnet and cordierite bearing metamorphic grade throughout the area is in the upper amphibolite to lower granulite facies 5 6 kbar at 730 750 c field evidence petrographic observations chemical data and mass balance calculations suggest that intrusion of granitic magmas and concomitant partial melting of metasedimentary units were the main processes for the generation of the migmatites the intruding melts were significantly modified by magma mixing with in situ partial melts accumulation of mainly feldspar and contamination with garnet from the wall rocks however it is suggested that these melts originally represented disequilibrium melts from a metasedimentary protolith the occurrence of lile hfse and lree enriched and depleted residues within the leucosomes implies that both quartzo feldspathic and pelitic rocks were subjected to partial melting isotope ratios of the leucosomes are rather constant 143nd 144nd 500 ma 0 511718 0 511754 e nd 500 ma 3 54 to 5 11 and sr 87sr 86sr 500 ma 0 714119 0 714686 the metasedimentary units have rather constant nd isotope ratios 143nd 144nd 500 ma 0 511622 0 511789 e nd 500 ma 3 70 to 6 93 but variable sr isotope ratios sr 87sr 86sr 500 ma 0 713527 0 722268 the most restitic melanosome mel 4 has a sr isotopic composition of 87sr 86sr 500 ma 0 729380 oxygen isotopes do not mirror the proposed contamination process due to the equally high 18o contents of metasediments and crustal melts however the most lile depleted residue mel 4 shows the lowest 18o value 10 mass balance calculations suggest high degrees of partial melting 20 40 it is concluded that partial melting was promoted by heat transfer and release of a fluid phase from the intruding granites high degrees of partial melting can be reached as long as the available h2o derived from the crystallization of the intruding granites is efficiently recycled within the rock volume due to the limited amounts of in situ melting it seems likely that such regional migmatite terranes are not the sources for large intrusive granite bodies the high geothermal gradient inferred from the metamorphic conditions was probably caused by exhumation of deep crustal rocks and contemporaneous intrusion of huge masses of granitoid magmas the davetsaub area represents an example of migmatites formed at moderate pressures and high temperatures and illustrates some of the reactions that may modify leucosome compositions the area provides constraints on melting processes operating in high grade metasedimentary rocks

a comparison of phase inversion and traveltime tomography for processing near surface refraction traveltimes with phase inversion one can estimate subsurface velocities using the phases of first arriving waves which are the frequency domain equivalents of the traveltimes phase inversion is modified to make it suitable for processing traveltimes from near surface refraction surveys the modifications include parameterizing the model correcting the observed phases and selecting the complex frequency this modified phase inversion is compared to traveltime tomography for two comparisons using computer simulated traveltimes the difference between the estimated and correct models the residual mean and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography for a comparison using field data from an s wave refraction survey both methods estimate models that are consistent with the known geology nonetheless the phase inversion model includes small scale features in the bedrock that are geologically plausible the residual mean and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography

genesis of the kapuskasing ontario migmatitic mafic granulites by dehydration melting of amphibolite the importance of quartz to reaction progress migmatitic granulite grade mafic gneisses make up a significant part of the kapuskasing structural zone ksz ontario although they contain a common mineral assemblage hornblende hbl plagioclase pl diopside di garnet grt quartz qtz titanite ttn the mafic gneisses show wide variations in modal mineralogy from hornblende rich to diopside garnet rich varieties and all gradations between up to 25 vol segregated plagioclase quartz rich trondhjemitic leucosome tdh is intimately associated with the mafic gneiss occurring in a continuum of patches veins and transecting dykes at scales ranging from decimetres to micrometres the texture and composition of the leucosome combined with p t estimates for the host rocks above the solidus suggest it represents crystallized trondhjemitic melt quartz is mainly restricted to the segregated leucosomes but more rarely occurs in a variety of interstitial textures in the mafic gneiss suggesting that it crystallized from a melt phase rather than having been present as a solid phase at peak metamorphic conditions modal and textural data indicate a reaction relationship of the form hbl pl qtz grt di ttn leucosome tdh implying that the granulite forming process involved dehydration melting of an amphibolite protolith pressure temperature estimates from grt di pl qtz geothermobarometry are 9 kbar and 685 735 c however based on experimental studies of dehydration melting of amphibolite we estimate that peak conditions were closer to 11 kbar 850 c mass balance analysis using the technique of singular value decomposition and reaction space analysis were used to quantify the reaction and to determine the controls on reaction progress the following mass balance provides a model for the natural reaction 1 00 hbl 0 92 pl 3 76 qtz 1 14 grt 1 54 di 0 21 ttn 1 49 tdh 0 14 pg 0 39 fe 1mg 0 33 nasica 1al 1where pg is a pargasite like exchange in all model mass balances tested quartz is a reactant with a large coefficient we argue that the abundance of quartz in the amphibolite protolith was the primary control on the differing extents of reaction observed mineral compositional variation exerted a secondary control on reaction progress with fe richer layers containing an richer plagioclase and more actinolitic amphibole reacting earliest i e at lowest temperatures comparison of the calculated amount of melt produced in the gneisses with that now observed implies expulsion of 5 30 of the melt these volumes are similar to those predicted from ree modelling of archaean tonalities and trondhjemites from a garnet amphibolite source suggesting that the ksz mafic gneisses may be representative of partially depleted source rocks for trondhjemite tonalite generation

an experimentally based model for the origin of tonalitic and trondhjemitic melts abstract the results of melting experiments have been used to establish equations relating melt composition to temperature t pressure p and water content of the source y h2o for tonalitic and trondhjemitic melts produced by partial melting of average archean tholeiite aat a normative classification diagram for these rocks has been translated into a t p y h2o diagram showing the required conditions of partial melting tonalites form at high temperatures low pressures and high water contents while trondhjemites form at lower temperatures higher pressures and lower water contents as pressure increases the k content increases but the melts never achieve the composition of a granodiorite or granite a method for estimating the conditions for the formation of natural tonalites and trondhjemites is proposed the method has been successfully tested against other experimental studies and natural rocks where the temperature pressure conditions have been constrained by traditional geochemical methods

large scale melt depletion in granulite terranes an example from the archean ashuanipi subprovince of quebec this study uses field petrographic and geochemical methods to estimate how much granitic melt was formed and extracted from a granulite facies terrane and to determine what the grain and outcrop scale melt flow paths were during the melt segregation process the ashuanipi subprovince located in the north eastern superior province of quebec is a large 90 000 km2 metasedimentary terrane in which 85 of the metasediments are of metagreywacke composition that was metamorphosed at mid crustal conditions 820 900 c and 6 7 kbar in a late archean dextral transpressive orogen decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase together with preserved former melt textures indicate that anatexis was by the biotite dehydration reaction biotite quartz plagioclase melt orthopyroxene oxides using melt orthopyroxene ratios for this reaction derived from experimental studies the modal orthopyroxene contents indicate that the metagreywacke rocks underwent an average of 31 vol partial melting the metagreywackes are enriched in mgo cao and feot and depleted in sio2 k2o rb cs and u have lower rb sr higher rb cs and th u ratios and positive eu anomalies compared to their likely protolith these compositions are modelled by the extraction of between 20 and 40 wt granitic melt from typical archean low grade metagreywackes a simple mass balance indicates that about 640 000 km3 of granitic melt was extracted from the depleted granulites the distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary porous flow from the site of melting across the layers and into bedding planes between adjacent layers in other rocks pervasive grain boundary flow of melt occurred along the layers for a few to tens of centimetres followed by channelled flow of melt in a network of short interconnected and structurally controlled conduits visible as the net like array of leucosomes in some outcrops the leucosomes contain very little residual material 5 biotite orthopyroxene indicating that the melt fraction was well separated from the residuum left in situ as melt depleted granulite only 1 3 vol percentage melt remained in the melt depleted granulites hence the extraction of melt generated by biotite dehydration melting in these granulites was virtually complete under conditions of natural melting and strain rates in a contractional orogen

attenuation mechanisms in sands laboratory versus theoretical biot data the velocity and attenuation of compressional q 1p vp respectively and shear waves q 1s vs respectively determined with the pulse transmission technique at a frequency of about 100 khz are compared with the grain size shape porosity density and static frame compressibility of dry and water saturated sands except for vs all the quantities vp q 1p and q 1s are dependent on grain size and are higher in coarser grains than in finer grains q 1s decreases significantly with increasing differential pressure in coarse grained sediments but the same sediments show an anomalous increase with differential pressure in q 1p at low pressures we have also modeled the vp vs q 1p and q 1s of these samples to understand the mechanisms governing the observed changes the contact radius model with surface force effects predicts both vp and vs to be dependent on grain size frictional losses in unconsolidated coarse grained sands must also be considered at small strains 10 7 velocity and losses measured

melt segregation in the continental crust distribution and movement of melt in anatectic rocks the grain and outcrop scale distribution of melt has been mapped in anatectic rocks from regional and contact metamorphic environments and used to infer melt movement paths at the grain scale anatectic melt is pervasively distributed in the grain boundaries and in small pools consequently most melt is located parallel to the principal fabric in the rock typically a foliation short branched arrays of linked melt bearing grain boundaries connect melt depleted parts of the matrix to diffuse zones of melt accumulation protoleucosomes where magmatic flow and alignment of euhedral crystals grown from the melt developed the distribution of melt leucosome and residual rocks normally melanocratic in outcrop provides different but complementary information the residual rocks show where the melt came from and the leucosomes preserve some of the channels through which the melt moved or sites where it pooled different stages of the melt segregation process are recorded in the leucosome melanosome arrays regions where melting and segregation had just begun when crystallization occurred are characterized by short arrays of thin branching leucosomes with little melanosome a more advanced stage of melting and segregation is marked by the development of residual rocks around extensive branched leucosome arrays generally oriented along the foliation or melting layer places where melting had stopped or slowed down before crystallization began are marked by a high ratio of melanosome to leucosome because most of the melt has drained away very few leucosomes remain to mark the melt escape path this is common in melt depleted granulite terranes many migmatites contain abundant leucosomes oriented parallel to the foliation mostly these represent places where foliation planes dilated and melt drained from the matrix via the branched grain boundary and larger branched melt channel leucosome arrays collected melt collected in the foliation planes was partially or fully expelled later when discordant leucosomes formed leucosomes or veins oriented at high angles to the foliation layering formed last and commonly lack melanocratic borders hence they were not involved in draining the matrix of the melting layer discordant leucosomes represent the channels through which melt flowed out of the melting layer

small scale physical modeling of seismic wave propagation using unconsolidated granular media laboratory physical modeling and laser based experiments are frequently proposed to tackle theoretical and methodological issues related to seismic prospecting e g when experimental validations of processing or inversion techniques are required lasers are mainly used to simulate typical field acquisition setups on homogeneous and consolidated materials assembled into laboratory scale physical models pms of various earth structures we suggested the use of granular materials to study seismic wave propagation in unconsolidated and porous media and target near surface exploration and hydrogeologic applications we designed and tested the reproducibility of an experimental procedure to build and probe pms consisting of micrometric glass beads gbs a mechanical source and a laser doppler vibrometer were used to record small scale seismic lines at the surface of three gbs models when guided surface acoustic mode theory should prevail in such unconsolidated granular packed structure under gravity we only considered elastic wave propagation in stratified media to interpret recorded data thanks to basic seismic processing and inversion methods first arrivals and dispersion analyses we were able to correctly retrieve the gradients of pressure and shear wave velocities in our models a 3d elastic finite difference simulation of the experiment offered despite significant differences in terms of amplitudes a supplementary validation of our approximation as far as elastic properties of the medium were concerned

experimental mechanical compaction of sands and sand clay mixtures a study to investigate evolution of rock properties with full control on mineralogy and rock texture development of rock physical properties in well sorted and poorly sorted unconsolidated mono quartz sands and sand clay mixtures as a function of effective stress in both dry and brine saturated conditions is assessed in this study the tested samples were prepared with full control on their mineralogy grain size grain shape sorting and fabric the experiments were performed in a high stress uniaxial oedometer up to a maximum of 30 mpa vertical effective stress sand clay samples were a mixture of sand grains and clay particles kaolinite or smectite in different proportions the maximum clay volume fraction used in the experiments was at most 30 the initial bulk density of the tested sand dominated samples was adjusted to be close to the maximum index density expected for natural sediments sand clay mixtures during deposition in pure sand samples finer grained sand show higher initial porosity than relatively coarser grained sands moreover sand clay mixtures have lower initial porosity than pure sands porosity decreases as a function of increasing clay content the poorlysorted sand samples are less compaction prone than the well sorted sand samples among well sorted sand samples coarser grained sands are more compressible than finer grained sands at a given effective stress level sand clay mixtures are more compaction prone compared with their sand component alone pure sands and claypoor sand clay mixtures either sand kaolinite or sand smectite show almost the same degree of compaction when tested in both dry and brine saturated conditions in contrast clay rich sand kaolinite and sand smectitemixtures clay volume 20 are significantly more compact in brine saturated condition the vp values of brinesaturated sand kaolinite mixtures shows a positive correlation with the kaolinite content whereas vp starts to decrease substantially when the volume fraction of smectite exceeds 10 of the whole sand smectite samples saturated bulk moduli estimated by gassmann s fluid substitution agree with measurements for brine saturated clay poor sand samples however the model does not yield proper predictions for sand clay samples containing 20 clay volume and above particularly when the clay is mainly smectite the acoustic and physical properties derived from experimental compaction of pure sands and sand clay mixtures show a good agreement with rock properties derived from well logs of mechanically compacted pure sands and shaly sands in progressively subsided basins such as viking graben in the north sea thus the outcome of this study can provide reliable constraints for rock physical properties of sands and shaly sands within the mechanical compaction domain and contribute to improved basin modelling and identification of hydrocarbon presence overconsolidation and or undercompaction

seismic velocities of unconsolidated sands part 2 influence of sorting and compaction induced porosity variation unaccounted for porosity variation in unconsolidated sediments can cloud the interpretation of the sediment s seismic velocities for factors such as fluid content and pressure however an understanding of the effects of porosity variation on the velocities can permit the remote characterization of porosity with seismic methods we present the results of a series of measurements designed to isolate the effects of sorting and compaction induced porosity variation on the seismic velocities and their pressure dependences in clean unconsolidated sands we prepared a set of texturally similar sand and glass bead samples with controlled grain size distributions to cover an initial porosity range from 0 26 to 0 44 we measured the compressional and shear wave velocities and porosity of dry samples over a series of hydrostatic pressure cycles from 0 1 to 20 mpa over this rangeof porosities the velocities of the dry samples at a given pressure vary by 15 however the water saturated compressional wave ve

petrology and u pb geochronology of the telohat migmatites aleksod central hoggar algeria the aleksod region is composed of metasedimentary rocks and large areas of biotite and hornblende bearing migmatites anatexis associated with the main deformation stages occurred under high pressure and temperature conditions estimated at 13 2 kbar and 750 50 c the bulk mineralogical composition of the telohat migmatites shows that their protolith was granodioritic internal structures of zircons and u pb data suggest a polyphased evolution with a 2131 12 ma age for the protolith and a 609 17 ma age for the pan african tectono metamorphic evolution thus precluding any kibaran event in the aleksod area leucosomes are richer in sr and display lower rb zr nb y th u and ree contents than melanosomes wherein accessory phases are stored eu contents are also lower in the leucosomes but in lesser proportion than the other rare earth s leading to a significant positive anomaly petrogenetic modelling accounting for accessory mineral phases clearly shows that the trace element contents of leucosomes and melanosomes follow a distribution law consistent neither with equilibrium nor fractional melting their trace element patterns are best explained by the model of disequilibrium melting with mixing of a few residual phases the present results and previous sr isotopic data as well raise the question of disequilibrium melting in anatexis of crustal material

rock physics modeling of unconsolidated sands accounting for nonuniform contacts and heterogeneous stress fields in the effective media approximation with applications to hydrocarbon exploration by treating contact stiffness as a variable one can extend the effective medium approximation used to obtain elastic stiffness of a random pack of spherical grains more specifically we suggest calibrating effective media approximation based on contact mechanics by incorporating nonuniform contact models the simple extension of the theory provides a better fit for many laboratory and field experiments and can provide insight into the micromechanical bonds associated with unconsolidated sediments this approach is motivated by repeated observations of shear wave measurements in unconsolidated sands where observed shear wave velocities are lower than predicted by the hertz mindlin contact theory we present the calibration process for well log data from a north sea well penetrating a shallow gas discovery and a deepwater well in the gulf of mexico finally we demonstrate the benefit of using this model for amplitude variation with angle ava analysis of shallow sand targets in exploration and reservoir studies

migmatites formed by water fluxed partial melting of a leucogranodiorite protolith microstructures in the residual rocks and source of the fluid abstract the opatica subprovince in the canadian shield is a late archaean 2761 2702 ma plutonic arc formed above a north dipping subduction zone anatexis 2690 2677 ma of leucogranodiorite and leucotonalite orthogneisses in the opatica generated migmatites in an area of north vergent back thrusts visible at the surface and in l ithoprobe seismic profile 48 schollen diatexite migmatites occur in the thrusts and metatexite migmatites between them the modal mineralogy microstructure and whole rock major trace and oxygen isotope compositions of the protolith and migmatites were investigated to 1 determine the melting reaction 2 find microstructural criteria for identifying residual rocks in leucocratic systems where there is no melanosome and 3 to determine the source of the fluid involved in anatexis partial melting of the protolith did not change the mineral assemblage but the abundance of quartz and microcline both declined and plagioclase and biotite increased in the residual rocks quartz plagioclase and microcline show evidence for dissolution and biotite does not thus water fluxed melting of quartz plagioclase microcline occurred a mass balance indicates 25 30 partial melting the melting reaction consumed the microcline and created essentially monomineralic domains of plagioclase extraction of 80 90 of the melt left a thin film of melt on the grain boundaries and crystallization of these in the plagioclase domains created diagnostic microstructures microcline fills the last remaining pore space and forms high aspect ratio crystals between plagioclases or triangular crystals at grain junctions quartz shows a range of morphologies from high aspect ratio films through the string of beads to isolated rounded grains as the microstructure progressively equilibrated after crystallisation most accessory phases including zircon remained in the residuum however almost all the schollen migmatites have high contents of th u nb ta and ree relative to the protolith due to contamination by accessory phases derived from mafic rocks disaggregation of the mafic rocks may have been facilitated by the high strain in the back thrusts where the schollen diatexites formed average whole rock 18 o for the protolith and migmatites are similar ca 8 2 and the small difference between melt rich 8 6 and residuum rich rocks 8 0 is consistent with fractionation thus the fluid that caused melting was probably of metamorphic origin with 18 o similar to the protolith the seismic profile shows several reflectors extending to a present depth of 20 km ca 40 km in the late archaean under the migmatites these are the paths along which the metamorphic fluid migrated and generated the migmatites now at the surface a new type of neosome reported in this study may have formed along fractures that the fluids migrated along however these are peripheral pathways in the metatexites adjacent to the back thrusts and schollen diatexites

appraisal of waveform repeatability for crosshole and hole to tunnel seismic monitoring of radioactive waste repositories countries worldwide are seeking solutions for the permanent removal of high level radioactive waste from the environment surrounding the waste with multiple engineered barriers and emplacement in deep geological repositories is widely accepted as a safe means of isolating it from the biosphere for the necessary 105 106 years as a precautionary measure society demands that repositories be monitored for 100 300 years after they are backfilled and sealed effective monitoring that does not compromise the engineered and natural barriers is challenging to address this issue we investigate the viability of crosshole and hole to tunnel seismic methods for remotely monitoring high level radioactive waste repositories measurements are made at two underground rock laboratories in switzerland one within granitic rock and one within clay rich sediments numerical simulations demonstrate that temporal changes of the monitored features i e bentonite plug excavation damage zone sand filled microtunnel sh

using a pseudo steady state flow equation and 4d seismic traveltime shifts for estimation of pressure and saturation changes abstractpressure and saturation changes cause a change in seismic p wave velocity resulting in a shift in 4d traveltime a discrimination between both effects is important to enhance reservoir management decisions we explored the possibility of linking the fields of reservoir engineering and 4d seismic a simple inversion scheme based on a reservoir engineering flow equation for pore pressure predictions combined with the hertz mindlin and gassmann rock physics models to discriminate pressure and saturation effects from 4d time shifts was presented to account for no flow reservoir boundaries the pseudo steady state flow equation giving the pressure distribution was extended with a superpositioning method during the inversion three parameters were determined by a nonlinear least squares fitting method the thickness of the hydrocarbon column the pressure at the well position and its decay rate away from the well we successfully tested our approach on a synthetic and a field data case where the co

geochronology and geochemistry of leucosomes in the north dabie terrane east china implication for post uhpm crustal melting during exhumation migmatites are widespread in the north dabie ultrahigh pressure metamorphic terrane ndt of dabie orogen east china idiomorphic and poikilitic amphibole grains in both leucosome and melanosome contain inclusions of plagioclase quartz and biotite suggesting formation of leucosome by fluid present melting of biotite plagioclase quartz bearing protoliths at p 5 7 kbar t 700 800 c precise sims zircon u pb dating indicates that migmatization of dabie orogen initiated at 140 ma and lasted for 10 ma coeval with the formation of low mg adakitic intrusions in dabie orogen based on mineralogical petrographic and geochemical data leucosomes in ndt can be subdivided into three groups 1 high la yb n medium sr y group group i whose high dy yb n but medium sr y ratios are caused by amphibole and plagioclase residual during partial melting of dioritic to granodioritic gneisses 2 low la yb n low sr y group group ii whose flat hree patterns are produced by entrainment of peritectic amphiboles into melts derived from partial melting of dioritic gneiss 3 high la yb n high sr y and eu group group iii whose extremely high sr and eu but low other ree concentrations are caused by accumulation of plagioclase and quartz although group i and iii fall in the adakitic fields on la yb n yb n and sr y y diagrams they are chemically distinct from contemporary high pressure adakitic intrusions in dabie orogen in a series of geochemical indexes for example lower dy yb n and or sr y ratios at given la yb n ratio lower sr cao ratios lower rb concentration but higher k rb ratios therefore leucosomes are produced by anatexis of the exhumed ultrahigh pressure metamorphic rocks at middle crustal level instead of partial melting of thickened lower crust with garnet rich and plagioclase poor residual the coeval occurrence of migmatites and high pressure adakitic intrusions in dabie orogen indicates large scale partial melting of middle to thickened lower crustal column in the early cretaceous the required heat source may be the mantle heat conducting through the lithospheric mantle whose lower parts have been convectively removed

accessory phase controls on the geochemistry of crustal melts and restites produced during water undersaturated partial melting the profound geochemical conseqences of accessory phase behaviour during partial melting of highgrade metapelites are demonstrated with reference to two geochemically distinct crustal melts produced by biotite dehydration melting reactions under granulite facies kbar 860 cc conditions these two leucogneiss suites from the brattstrand bluffs coastline eastern antarctica have similar field relations transport distances 10 100 s of metres and major element chemistry type 1 leucogneisses have low zr th and lree positive eu anomalies and zr zr and lreet lreet values less than 1 0 i e less than required to saturate the melt mass balance constraints suggest that these melts have been extracted before equilibration with host melanosomes the dry peraluminous nature of vapour undersaturated melts inhibits monazite and zircon solubility and results in concentration of these phases in the residue melts are consequently depleted in lree and hree melanosomes show complementary enrichment in lree while hree patterns are dominated by residual garnet type 2 leucogneisses in contrast have strongly enriched zr th and lree abundances negative eu anomalies and zr zr and lreet lreet 1 resulting from accessory phase entrainment vapour absent partial melting under moderate 6 8 kbar pressure granulite facies conditions of a pelitic source containing monazite is likely to give disequilibrium melts depleted in lree and hree as monazite and garnet are concentrated in the residue if temperatures are high enough 850 870 c to permit relatively large degrees of partial melting then the feldspar component of the source will be removed almost completely giving melts with large positive eu anomalies melts formed under vapour present conditions are unlikely to show such extreme lree and hree depletion or positive eu anomalies even at high degrees of partial melting disequilibrium melting coupled with source entrainment could fortuitously produce ree and trace element signatures similar to those typical of s type granites and usually ascribed to equilibrium melting conditions

an effective medium model for p wave velocities of saturated unconsolidated saline permafrost abstractto better understand the relationship between p wave velocities and ice content in saturated unconsolidated saline permafrost we constructed an effective medium model based upon ultrasonic p wave data that were obtained from earlier laboratory studies the model uses a two end member mixing approach in which an ice filled fully frozen end member and a water filled fully unfrozen end member are mixed together to form the effective medium of partially frozen sediments this mixing approach has two key advantages 1 it does not require parameter tuning of the mixing ratios and 2 it inherently assumes mixed pore scale distributions of ice that consist of frame strengthening i e cementing and or load bearing ice and pore filling ice the model predicted p wave velocities agree well with our laboratory data demonstrating the effectiveness of the model for quantitatively inferring ice content from p wave velocities the modeling workflow is simple and is largely free of calibration paramete

using in situ trace element determinations to monitor partial melting processes in metabasites peak metamorphism 800 850 c 8 10 kbar in the harts range meta igneous complex harts range central australia was associated with localized partial melting by the reaction hornblende plagioclase quartz h2o1 4 garnet clinopyroxene titanite melt in situ trace element determinations of prograde peak and retrograde minerals in migmatitic metabasites and associated tonalitic melts using laser ablation icp ms has allowed monitoring of a range of partial melting processes melting melt segregation and back reaction between crystallizing melt and restitic minerals mass balance calculations indicate that titanite is a major carrier of trace elements such as ti nb ta sm u and th and therefore may be an important accessory phase to control the redistribution of these elements during the partial melting of amphibolites titanite preferentially incorporates ta over nb and hence residual titanite might assist in the formation of melts with high nb ta the fact that single minerals record different rare earth element ree patterns from prograde to peak to retrograde conditions demonstrates that ree diffusion is not significant up to 800 c therefore trace element analysis in minerals can be a powerful tool to investigate high grade metamorphic processes beyond the limits given by major elements

granite migmatite genetic link the example of the manaslu granite and tibetan slab migmatites in central nepal in central nepal the tibetan slab is made up of biotite gneisses metapelites and metagreywackes orthogneisses metagranites and migmatites melanosomes are generally biotite muscovite bearing but locally they may be tourmaline rich when associated with boron rich granitic material leucosomes occur as lenses conformable with the foliation veins patches or as fillings in shear zones and extensional structures field relationships and mineralogical and chemical data show that three processes may have contributed to the formation of the tibetan slab leucosomes metamorphic differentiation or disequilibrium partial melting low zr tonalitic leucosomes in situ equilibrium partial melting high zr leucosomes and some granitic leucosomes and injection of externally derived melts most granitic and some tonalitic leucosomes the manaslu pluton belongs to the high himalayan leucogranite belt and was emplaced at the top of the tibetan slab it corresponds to a muscovite biotite leucogranite that has been assumed to derive from melting of the tibetan slab gneisses formation i phase relationships a more magnesian chemistry of the ferromagnesian minerals from the tibetan slab migmatites as compared to the manaslu leucogranite the microtextures of accessory phases and trace element compositions lower u li f and higher sr eu y yb contents in the migmatite leucosomes show that the in situ himalayan migmatites at the crustal level presently exposed have not been produced under the same p t xh2o conditions as the manaslu leucogranite magma while the formation i was the probable source for the manaslu granite migmatites within the formation are not the remanants of a melting process from which the manaslu granite was derived both the tibetan slab migmatites and the manaslu leucogranite may be considered as evidence of dehydration and melting at deeper crustal levels and of percolation of melts and hydrothermal fluids through the crust

seismic monitoring of radioactive waste repositories abstractsafe isolation of high level radioactive waste hlw and spent nuclear fuel sf from the biosphere is an important concern for humanity many countries consider monitoring the evolving conditions of a hlw sf repository over a long period noninvasively in such a way as to not compromise the sealing of the repository remote active seismic methods are possible options we performed extensive seismic measurements at the mont terri rock laboratory located within a clay formation that is a potential host rock in the swiss hlw sf program a scaled down hlw sf repository was simulated as a 13 m long microtunnel of 1 m diameter the dry sand filled microtunnel was progressively water saturated and slightly overpressured the monitoring system consisted of a pressure seismic source and a hydrophone cable located in two boreholes drilled perpendicular to the microtunnel and eight geophones equally distributed around the periphery of the microtunnel nonlinear anisotropic tomography of crosshole traveltim

evolution of structurally contrasting anatectic migmatites in the 3 kbar ballachulish aureole scotland anatectic migmatites of contrasting structural style are found adjacent to the contacts of the ballachulish igneous complex argyllshire scotland on the east flank evidence for migmatization is largely restricted to the local development of millimetre centimetre scale kfs qtz rich leucocratic segregations which accompany fragmentation of brittle hornfels layers and ductile deformation of mm cm scale semipelitic layers large volumes of semipelitic rock rich in feldspar and quartz on the east flank show no migmatitic features and bedding is usually preserved undisturbed right up to the contact on the west flank in contrast similar semipelitic rocks show widespread migmatitic features and disruption of layering is substantial and widespread over a 400 m wide zone within the west flank migmatites 1 100 cm scale rigid bedding fragments schollen may be suspended and disoriented in a semipelitic matrix that underwent ductile deformation the p t conditions on both flanks are in the same range 3 kbar and 650 700 c the contrast in gross structural style is believed to result from differences in the volumes of melt produced and differences in the proportion of rock in which the critical melt fraction of the rocks was exceeded on the east flank only on a mm cm scale was enough melt locally accumulated to cause disruption of some layers and segregation of melt on the west flank melting proceeded substantially in a broad tract of semipelitic rocks resulting in larger scale contrasts in rheology that led to the present chaotic structures in this zone because migmatization occurred at a pressure too low for muscovite dehydration melting and at temperatures too low for substantial biotite dehydration melting the different amounts of melting on the east and west flanks most probably resulted from the introduction of differing amounts of externally derived water on the east flank and throughout most of the aureole the absence of melting even in quartzofeldspathic protoliths indicates that there was no substantial movement of fluid towards or away from the igneous complex during migmatization the contrasting situation on the west flank may have resulted from devolatilization of underlying quartz diorite magma 690 710 c which released heat and fluids into the overlying quartz and feldspar rich semipelites solidus temperature 650 680 c

internal differentiation of the archean continental crust fluid controlled partial melting of granulites and ttg amphibolite associations in central finland fault bound blocks of granulite and enderbite occur within upper amphibolite facies migmatitic tonalitic trondhjemitic granodioritic ttg gneisses of the iisalmi block of central finland these units record reworking and partial melting of different levels of the archean crust during a major tectonothermal event at 2 6 2 7 ga anhydrous mineral assemblages and tonalitic melts in the granulites formed as a result of hydrous phase breakdown melting reactions involving amphibole at peak metamorphic conditions of 8 11 kbar and 750 900 c a nominally fluid absent melting regime in the granulites is supported by the presence of carbonic fluid inclusions the geochemical signature of light rare earth element lree depleted mafic granulites can be modelled by 10 30 wt partial melting of an amphibolite source rock leaving a garnet bearing residue the degree of melting in intermediate granulites is inferred to be less than 10 wt and was restricted by the availability of quartz pressure temperature estimates for the ttg gneisses are significantly lower than for the granulites at 660 770 c and 5 6 kbar based on the p t conditions melting of the ttg gneisses is inferred to have occurred at the wet solidus in the presence of an h 2 o rich fluid a hydrous mineralogy abundant aqueous fluid inclusions and the absence of carbonic inclusions in the gneisses are in accordance with a water fluxed melting regime low ree contents and strong positive eu anomalies in most leucosomes irrespective of the host rock composition suggest that the leucosomes are not melt compositions but represent plagioclase quartz assemblages that crystallized early from felsic melts furthermore similar plagioclase compositions in leucosomes and adjacent mesosomes are not a migmatite paradox as both record equilibration with the same melt phase percolating along grain boundaries

amphibole plagioclase equilibria an empirical model for the relation albite tremolite edenite 4 quartz equilibria between plagioclase calcic amphibole and quartz can be described in part by the relation among mineral components naalsi3o8 ca2mg5si8o22 oh 2 naca2mg5alsi7o22 oh 2 4sio2 this relation governs the partitioning of na between plagioclase and the a site of coexisting amphibole data from natural amphibolites reveal that this partitioning is systematic and sensitive to metamorphic grade the ideal portion of the equilibrium constant kid xna a x a xab derived from natural samples is sensitive to bulk composition inasmuch as both plagioclase and amphibole are highly non ideal samples from a single outcrop have values ranging from 0 5 xab 0 74 to 4 1 xab 0 10 the continuous reaction naalsi3o8 ca2mg5si8o22 oh 2 naca2mg5alsi7o22 oh 2 4sio2 proceeds to the right with increasing grade of metamorphism and for a given bulk composition kid increases with increasing temperature two related discontinuous reactions actinolite albite hornblende oligoclase quartz and actinolite oligoclase hornblende anorthite quartz also proceed to the right with increasing metamorphic grade and result in changes in the topology of a phase diagram that describes the partitioning of na between plagioclase and amphibole a site a schreinemakers net is presented that is consistent with natural occurrences the results of this study should aid in the delineation of metamorphic facies within amphibolites

test of rock physics models for prediction of seismic velocities in shallow unconsolidated sands a well log data case this paper tests the ability of various rock physics models to predict seismic velocities in shallow unconsolidated sands by comparing the estimates to p and s sonic logs collected in a shallow sand layer and ultrasonic laboratory data of an unconsolidated sand sample the model fits are also evaluated with respect to the conventional model for unconsolidated sand our main approach is to use hertz mindlin and walton contact theories assuming different weight fractions of smooth and rough contact behaviours to predict the elastic properties of the high porosity point using either the hertz mindlin or walton theories with rough contact behaviour to define the high porosity endpoint gives an over prediction of the velocities the p velocity is overpredicted by a factor of 1 5 and the s velocity by a factor of 1 8 for highly porous gas sand the degree of misprediction decreases with increasing water saturation and porosity using the hertz mindlin theory with smooth contact behaviour or weighted walton models gives a better fit to the data although the data are best described using the walton smooth model to predict the properties at the lower porosities the choice of bounding model attached to the walton smooth model controls the degree of fit to the data where the reuss bound best captures the porosity variations of dry and wet sands in this case since they are caused by depositional differences the empirical models based on lab experiments on unconsolidated sand also fit the velocity data measured by sonic logs in situ which gives improved confidence in using lab derived results

melt segregation in migmatites anatectic stromatic migmatites have a symmetrical layered structure with a low ratio of thickness to length and a periodicity features that have not been explained satisfactorily but which are related to physical processes of melt segregation we evaluate the compaction model for segregation as it applies to migmatites and develop models for melt segregation based upon convection driven by volume change and upon advection down pressure gradients that result from applied differential stress acting on an anisotropic multilayer protolith compaction by gravity driven two phase flow results in asymmetric separation yields calculated segregation times that are slow or geologically unreasonable and yields relative volumes that are not consistent with the abundance of leucosome seen in natural migmatites although calculated segregation times for very wet granite might allow segregation by compaction some driving force in addition to gravity is needed to cause widespread melt segregation in the crust for segregation at low volume fraction of melt we develop a two dimensional two phase matrix and fluid viscous flow cell model length much greater than thickness with phase changes which predicts either expansion or contraction convection depending on whether volume change vr is positive or negative convection leads to melt segregation to form a stromatic structure in a geologically reasonable timescale at moderate volume fraction of melt segregation may occur by filter pressing in compositionally layered rocks in response to applied differential stress melt migration is by porous medium flow driven by differences in mean normal stress between the layers as a consequence of differences in rheology and shear enhanced matrix collapse calculated segregation rates are fast and the model yields adequate volume of leucosome the positive vr for volatile phase absent melting reactions under crustal pressures promotes melt escape unless extensional deformation facilitates melt accumulation if the rate of melt production exceeds the rate of melt escape then the increase in melt pressure may lead to melt enhanced embrittlement and fracture and melt may migrate out of the system in contrast water rich volatile phase present melt producing reactions have a negative vr which promotes melt retention after segregation unless deformation generates melt escape pathways evolution of stromatic structure through anatectic erosion of mesosome by increasing the melt fraction in situ may lead to breakdown of the solid matrix and will lead to instability due to buoyancy and magma may become mobile and entrain residual material restite

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

sand curve facelift empirical to polynomial model and the effect on the tomogram abstractan empirical thickness versus time relationship sand curve has been established in the rub al khali desert and verified by a theoretical curve from the direct measurements of sand the empirical sand curve has variable success in other areas of saudi arabia we established a theoretical sand curve model to determine the single way time in dry sand tomographic modeling of a higher resolution 3d seismic survey contributes more data to refine the relationship polynomial curves were used in the calculation of near surface static corrections to improve the solution for low relief structures

nd isotope disequilibrium during crustal anatexis a record from the goat ranch migmatite complex southern sierra nevada batholith california geological and geochemical studies of a pelitic migmatite complex within the isabella pendant of the southern sierra nevada batholith california suggest that the leucosomes represent the products of partial melting of the metapelite host driven by the emplacement of the adjacent goat ranch pluton ca 100 ma the leucosomes preserve a record of largemagnitude nd isotope disequilibrium with respect to their pelitic source the leucosomes have a wide range of nd 100 ma from 26 0 to 211 0 as compared to 28 7 to 211 3 for the source they can be subdivided into two groups based on their major elements and sr and nd isotope geochemistry group i leucosomes have higher p2o5 contents and nd 100 ma values than those of group ii the nd 100 ma values of group i leucosomes are significantly higher than those of metapelites and migmatites by two to four epsilon units suggesting that group i leucosomes are in nd isotope disequilibrium with their sources correlations among p2o5 contents nd 100 ma values and sm nd ratios in the leucosomes suggest that apatite or monazite has played a dominant role in fractionating sm from nd and generating nd isotope disequilibrium dissolution of apatite or monazite might play a critical role in regulating the behavior of the sm nd isotope systems and thus the nd isotope compositions of melts generated during crustal anatexis especially in metasedimentary protoliths

trace element partitioning in the granulite facies analyses of trace elements in the mineral phases of granulites provide important information about the trace element distribution in the lower crust since granulites are often considered residues of partial melting processes trace element characteristics of their mineral phases may record mineral melt equilibria thus giving an opportunity to understand the nature and composition of melts in the lower continental crust this study provides an extensive set of mineral trace element data obtained by la icp ms analyses of mafic and intermediate granulites from central finland mass balance calculations using the analytical data indicate a pronounced contribution of the accessory minerals apatite for the ree and ilmenite for the hfse coherent mineral mineral ratios between samples point to a close approach to equilibrium except for minerals intergrown with garnet porphyroblasts mineral trace element data were used for the formulation of a set of d mineral melt partition coefficients that is applicable for trace element modelling under lower crustal conditions d mineral melt were derived by the application of predictive models and using observed constant mineral mineral ratios the comparison of the calculated d mineral melt with experimental data as well as the relationship between mineral trace element contents and a leucosome with a composition close to an equilibrium melt provides additional constraints on mineral melt partitioning the d values derived in this study are broadly similar to magmatic partition coefficients for intermediate melt compositions they provide a first coherent set of d values for sc v cr and ni between clinopyroxene amphibole garnet orthopyroxene ilmenite and melt in addition they emphasize the strong impact that ilmenite exerts on the distribution of nb and ta

shear zone hosted migmatites eastern india the role of dynamic melting in the generation of ree depleted felsic melts and implications for disequilibrium melting in the ranmal migmatite complex non anatectic foliated granite protoliths can be traced to polyphase migmatites structural microtextural relations and thermobarometry indicate that syn deformational segregation crystallization of in situ stromatic and diatexite leucosomes occurred at 8008c and 8 kbar the protolith the neosome and the mesosome comprise quartz k feldspar plagioclase hornblende biotite sphene apatite zircon and ilmenite but the modal mineralogy differs widely the protolith composition is straddled by element abundances in the leucosome and the mesosome the leucosomes are characterized by lower cao feo mgo mg number tio2 p2o5 rb zr and total rare earth elements ree and higher sio2 k2o ba and sr than the protolith and the mesosome whereas na2o and al2o3 abundances are similar the protolith and the mesosome have negative eu anomalies but protolith normalized abundances of ree depleted leucosomes show positive eu anomalies the congruent melting reaction for leucosome production is inferred to be 0 325 quartz 0 288 k feldspar 0 32 plagioclase 0 05 biotite 0 014 hornblende 0 001 apatite 0 001 zircon 0 002 sphene1 4melt based on the reaction large ion lithophile element ree and zr abundances in model melts computed using dynamic melting approached the measured element abundances in leucosomes for40 5 mass fraction of unsegregated melts within the mesosome disequilibrium accommodated dynamic melting and equilibrium crystallization of melts led to uniform plagioclase composition in migmatites and ree depletion in leucosome

the s type ladybird leucogranite suite of southeastern british columbia geochemical and isotopic evidence for a genetic link with migmatite formation in the north american basement gneisses of the monashee complex abstract the 62 52 ma ladybird granite lbg suite is a peraluminous leucocratic s type quartz monzonitic to granitic suite which occurs as batholiths stocks dikes sills and pegmatite veins predominantly in the high grade rocks of the shuswap complex in southeastern british columbia the emplacement of the lbg was synchronous with the production of abundant migmatites within thor odin dome of the monashee complex an exposure of north american basement exhumed from depths of ca 26 33 km by eocene extensional faults the lbg and the leucosome in migmatites from thor odin dome have similar major and trace element patterns and are both characterized by zircons which have inherited precambrian cores whole rock nd isotope compositions show a range of values for the lbg with end 55 ma values from 5 0 to 17 2 the end 55 ma for the leucosome samples range from 9 5 to 23 6 overlapping with those of the granitic suite these data support the interpretation of a genetic link between formation of the lbg suite and melting of north american basement rocks such as those exposed in the core of thor odin dome the leucosome samples have lower high field strength element hfse concentrations and positive eu anomalies whereas the lbg samples have higher hfse concentrations and negative eu anomalies the similar trace element characteristics suggest that the leucosome from the migmatites and the lbg are related whereby most of the leucosome samples are cumulates and the lbg samples represent evolved or residual melts the initial 87sr 86sr isotope values for both the lbg and leucosome samples have a large range however the initial sr isotopic ratios for the lbg suite are lower than those of the leucosome samples with 87sr 86sr 55 ma ranging from 0 70603 to 0 73688 and 0 74256 to 0 76593 respectively this isotopic discrepancy suggests either a isotopic disequilibrium during partial melting in the mid to lower crust where the leucosome formed b the distribution of sr during partial melting was controlled by different melt producing reactions and or c isotopic heterogeneity in the source rocks at least part of the lbg suite likely formed via melting of north american basement rocks that were dominantly of sedimentary origin melting of the proterozoic supracrustal metasedimentary rocks overlying north american basement may also have contributed to the formation of the different phases of the suite found at the regional scale however the abundant leucosomes in the basement rocks of thor odin dome may mark the paths along which anatectic melt migrated in the structurally overlying ladybird granites of the south fosthall pluton

mechanical compaction and ultrasonic velocity of sands with different texture and mineralogical composition this study presents the results of experimental compaction while measuring ultrasonic velocities of sands with different grain size shape sorting and mineralogy uniaxial mechanical compaction tests up to a maximum of 50 mpa effective stress were performed on 29 dry sand aggregates derived from eight different sands to measure the rock properties a good agreement was found between the gassmann saturated bulk moduli of dry and brine saturated tests of selected sands sand samples with poor sorting showed low initial porosity while sands with high grain angularity had high initial porosity the sand compaction tests showed that at a given stress well sorted coarse grained sands were more compressible and had higher velocities vp and vs than fine grained sands when the mineralogy was similar this can be attributed to grain crushing where coarser grains lead to high compressibility and large grain to grain contact areas result in high velocities at medium to high stresses the angular coarse to medium grained sands both sorted sands and un sorted whole sands showed high compaction and velocities vp and vs the small grain to grain contact areas promote higher deformation at grain contacts more crushing and increased porosity loss resulting in high velocities compaction and velocities vp and vs increased with decreasing sorting in sands however at the same porosity the velocities in whole sands were slightly lower than in the well sorted sands indicating the presence of loose smaller grains in between the framework grains quartz poor sands containing less than 55 quartz showed higher velocities vp and vs compared to that of quartz rich sands this could be the result of sintering and enlargement of grain contacts of ductile mineral grains in the quartz poor sands increasing the effective bulk and shear stiffness tests both from wet measurements and gassmann brine substitution showed a decreasing vp vs ratio with increasing effective stress the quartz rich sands separated out towards the higher side of the vp vs range the gassmann brine substituted vp and vs plotted against effective stress provide a measure of the expected velocity range to be found in these and similar sands during mechanical compaction deviations of actual well log data from experimental data may indicate uplift the presence of hydrocarbon overpressure and or cementation data from this study may help to model velocity depth trends and to improve the characterization of reservoir sands from well log data in a low temperature 80 100o c zone where compaction of sands is mostly mechanical

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

rock physics modelling of 4d time shifts and time shift derivatives using well log data a north sea demonstration abstract rock physics models for fluid and stress dependency in reservoir rocks are essential for quantification and interpretation of 4d seismic signatures during reservoir depletion and injection for siliciclastic sandstone reservoirs the gassmann theory successfully predicts changes in seismic properties associated with fluid changes however our ability to predict the sensitivity to pressure from first principles is poor especially for cemented sandstones in this study we demonstrate how we can use a patchy cement rock physics model to quantify the combined effect of stress and fluid changes in terms of seismic time shifts and time shift derivatives during depletion or injection the time shifts are estimated directly from well log data without core calibration of stress sensitivity by assuming non uniform grain contacts where some grain contacts are cemented and others are loose we can combine the contact theory for cemented sandstones with the contact theory for loose sands in order to predict stress sensitivity in a patchy cemented sandstone reservoir time shift derivatives are also useful estimates as this parameter reveals which part of the reservoir is most stress sensitive and contributes most to the cumulative time shift we test out our new approach on well log data from troll east north sea and compare the predicted time shifts with observed 4d seismic time shifts we find that there are good agreements between predicted time shifts and observed time shifts furthermore we confirm that there are local geological trends controlling the fluid and stress sensitivity of the reservoir sands on troll east in particular we observe a lateral stiffening of the reservoir from west to east probably associated with the tectonic and burial history of the area the combined effect of a thinning gas cap and stiffening reservoir sands amplifies the eastward decrease in time shifts associated with reservoir depletion we manage to disentangle these two effects using rock physics analysis it is essential to identify and map the static rock stiffness spatial trends before interpreting time shifts and time shift derivatives in terms of dynamic i e 4d pressure and fluid changes

seismic velocities of unconsolidated sands part 1 pressure trends from 0 1 to 20 mpa knowledge of the pressure dependences of seismic velocities in unconsolidated sands is necessary for the remote prediction of effective pressures and for the projection of velocities to unsampled locations within shallow sand layers we have measured the compressional and shear wave velocities and bulk shear and pwave moduli at pressures from 0 1 to 20 mpa in a series of unconsolidated granular samples including dry and water saturated natural sands and dry synthetic sand and glass bead samples the shear wave velocities in these samples demonstrate an average pressure dependence approximately proportional to the fourth root of the effective pressure vsp 1 4 as commonly observed at lower pressures for the compressional wave velocities the exponent in the pressure dependence of individual dry samples is consistently less than the exponent for the shear wave velocity of the same sample averaging 0 23 for the dry sands and 0 20 for the glass bead samples these pressure dependences are generally consistent over the entire pressure range measured a comparison of the empirical results to theoretical predictions based on hertz mindlin effective medium models demonstrates that the theoretical models vastly overpredict the shear moduli of the dry granular frame unless the contacts are assumed to have no tangential stiffness the models also predict a lower pressure exponent for the moduli and velocitiesvp1 6 than is generally observed in the data we attribute this discrepancy in part to the inability of the models to account for decreases in the amount of slip or grain rotation occurring at grain to grain contacts with increasing pressure

generation of tonalitic and dioritic magmas by coupled partial melting of gabbroic and metasedimentary rocks within the deep crust of the famatinian magmatic arc argentina the source regions of dioritic and tonalitic magmas have been identified in a deep crustal section of the famatinian arc sierras pampeanas of western argentina the source zones of intermediate igneous rocks are located at the transition between a gabbro dominated mafic unit and a tonalite dominated intermediate unit in the upper levels of the mafic unit mafic magmas intruded into metasedimentary wall rocks crystallized mainly as amphibole gabbronorite and caused the partial melting of the surrounding metasediments in turn the leucogranitic melts sourced from the metasedimentary rocks intruded into the newly crystallized but still hot mafic layers and catalysed the process of partial melting of the gabbroic plutonic rocks the gabbroic rocks became mafic migmatites comprising amphibole rich pyroxene bearing mesosomes and leucotonalitic veins significantly most of the mafic migmatites have isotopic compositions sr sr t 50 7063 and end t 1 4 0 94 to 2 24 similar to those of the gabbroic rocks and distinct from those of their complementary leucotonalitic veins sr sr t 1 4 0 7075 0 7126 and end t 5 2 65 providing evidence for the idea that melting of the mafic rocks was triggered by the intrusion of leucogranitic anatectic melts sr sr t 1 4 0 715 and end t 1 4 6 21 mass balance calculations show that the model reaction plagioclase amphibole leucogranitic melt leucotonalitic melt clinopyroxene orthopyroxene can better explain the partial melting of the gabbroic rocks based on field observations we argue that the coalescence of leucotonalitic veins in the mafic migmatites led to breakdown of the solid matrix to form melt dominated leucotonalitic pools however the leucotonalitic veins that crystallized before leaving behind the mafic migmatitic rock are chemically elemental and isotopic more evolved than the dioritic and tonalitic rocks we envisage that once detached from their source region the leucotonalitic magmas were able to react commingle and mix with entrained fragments of both mafic and metasedimentary rocks this process gave rise to melts that became tonalitic and dioritic magmas this study concludes that the generation of intermediate magmas is a multistage process with three critical steps 1 influx and emplacement of hydrous mafic magmas into a deep crust containing metasedimentary country rocks 2 physically and chemically coupled melting of mafic and metasedimentary rocks leading to the formation of a leucotonalitic vein and dyke system that coalesces to form leucotonalitic or tonalitic magma bodies 3 retrogression of the leucotonalitic magmas by partially assimilating entrained fragments of their mafic and metasedimentary precursors the dimensions of the

a study of consolidation using mechanical and electromagnetic waves consolidation has been a central topic of research in geotechnical engineering most studies have been conducted in oedometric cells and have attempted to assess the influence of multiple material

crustal evolution of the gyeonggi massif south korea nd isotopic evidence and implications for continental growths of east asia abstract we investigated the sm nd isotopic characteristics of the gyeonggi massif korea in order to delineate its crustal growth history nd isotopic depleted mantle model ages t dm obtained from 32 new measurements of basement and supracrustal samples and from the literature suggest that the gyeonggi massif is as old as middle archean 3 0 ga and was primarily extracted from the mantle during the late archean 2 9 2 5 ga in addition minor crustal formation occurred during the early proterozoic ca 1 9 1 8 ga late archean early proterozoic crustal growth of the gyeonggi massif is comparable with that of the sino korean or yangtze craton the t dm distribution pattern alone is not sufficient to determine the crustal affinity of the gyeonggi massif with either of the chinese cratons however late proterozoic crustal evolution of the gyeonggi massif appears to favor its tectonic correlation with the yangtze craton

magma migration folding and disaggregation of migmatites in the karakoram shear zone ladakh nw india effi cient extraction of granitic magma from crustal sources requires the development of an extensive permeable network of melt bearing channels during deformation we investigate rocks that have undergone deformation and melting within the karakoram shear zone of ladakh nw india in which leucosome distribution is inferred to record the permeable network for magma extraction delicate structures preserved in these rocks record the development of this permeable magma network and its subsequent destruction to form a mobile mass of melt and solids resulting from the interplay between folding and magma migration during folding magma migrated from rock pores into layer parallel and axial planar sheets forming a stromatic migmatite or metatexite with two communicating sets of sheets intersecting parallel to the fold axis once the network was developed folding and stretching was eased by magma migration and slip along axial planar magma sheets folding and magma migration led to layer disaggregation transposition and the formation of a diatexite where rock coherency and banding were destroyed a number of structures developed during this process such as cuspate fold hinges disharmonic folds truncated layering shear along axial planar leucosomes and fl ow drag and disruption of melanosomes in this system magma migration was an integral part of deformation and assisted the folding and stretching of metatexites while folding gave rise to a magma sheet network now preserved as leucosomes as well as the pressure gradients that drove magma migration and the breakup of the metatexite thus metatexite folding increased melt interconnectivity while magma mobility increased strain rate and released differential stresses

estimation of porosity and water saturation in dual porosity pyroclastic deposits from joint analysis of compression shear and electromagnetic velocities in situ measurements of porosity and water saturation of pyroclastic deposits have the potential to improve interpretations of geology and hydrology in volcanic regions and provide more accurate estimates of dense rock equivalent for volcanic eruptions however rock property models must consider the dual porosity structure of pyroclastic deposits i e vesicles within pumices and intergranular pores vesicularity intergranular porosity and water saturation all affect the density elasticity and dielectric properties of pyroclastic materials which control seismic and electromagnetic velocities the data from active seismic and ground penetrating radar techniques may improve porosity and water saturation estimation if the responses of seismic and electromagnetic waves to porosity and water saturation variations are complementary in pyroclastic rocks we develop a dual porosity petrophysical model to calculate seismic and electromagnetic velocities of pumice with known intergranular porosity vesicul

the petrogenesis of some migmatites and granites central damara orogen namibia evidence for disequilibrium melting wall rock contamination and crystal fractionation

migmatite structures in the central gneiss complex boca de quadra alaska migmatite structures in the coast plutonic metamorphic complex are well exposed in the inlet of boca de quadra southeast alaska two types of anatectic migmatites are present patch migmatites formed by in situ melting and subsequent crystallization of melt diktyonitic migmatites comprise a discontinuous veined network of leucocratic material in which leucosomes enclose boudins of host rock the margins of these boudins show the development of both melanosomes and shear band fabrics strain analysis of diktyonitic melanosomes indicates that these regions have undergone volume decreases of 20 27 this volume decrease is attributed to melt extraction into the adjacent fracture filling leucosomes thus diktyonitic migmatites formed by shear induced segregation of partial melt whereas in patch migmatites the lack of shear stresses inhibited melt segregation the variable structural style of anatectic migmatites in boca de quadra is not related to host rock composition but may be due to differences in the amount of differential stress during migmatization these in turn may be controlled by host rock strength and or diachroneity of migmatization and deformation determination of volume changes during migmatization using strain analysis is potentially capable of discriminating intrusive and anatectic migmatites and consequently of documenting melt segregation and subsequent migration across crustal levels

fluid present disequilibrium melting in neoarchean arc related migmatites of daeijak island western gyeonggi massif korea the melting process of meta igneous rocks was investigated via field petrographic and geochemical analyses of the neoarchean 2 51 ga migmatite complex in daeijak island western gyeonggi massif this complex consists primarily of garnet free amphibolites and tonalitic migmatites both of which contain hornblende plagioclase and quartz as major constituents neosomes and leucosomes in the migmatite have dioritic tonalitic and tonalitic trondhjemitic compositions respectively compositions of hornblende xfe 0 39 0 42 and plagioclase an24 27 vary little between the neosomes and leucosomes the amphibolites show distinct depletions in nb ta zr and ti relative to large ion lithophile elements suggesting an arc related origin for their basaltic protolith leucosomes have lower contents of k2o mgo feo tio2 zr rb and rare earth elements ree than amphibolites and neosomes but are higher in sio2 na2o and sr contents leucosomes and neosomes have positive eu eu n 1 32 7 26 and negative 0 71 0 97 eu anomalies respectively which are attributed to the variable degree of plagioclase fractionation during the partial melting the p t condition for the migmatite formation was estimated to be 700 730 c and 4 7 5 5 kbar primarily based on the hornblende plagioclase thermobarometry and phase equilibria various lines of textural evidence such as the channel flow of melt along migmatitic layers and the segregation of melt into shear bands or boudin necks suggest a syn deformation crystallization of melt chemical disequilibrium in migmatites is documented not only by petrographic and geochemical data but also by the ree modeling between melt product and source rock disequilibrium process is most likely attributed to the rapidity of melt extraction or migration compared to chemical diffusion rate in summary the fluid present disequilibrium melting of dioritic tonalitic protoliths has produced tonalitic trondhjemitic leucosomes in a dynamic arc environment prevalent in the neoarchean crust of the korean peninsula as well as the shandong peninsula north china craton

melt segregation and far field melt transfer in the mid crust abstract migmatites in the damara belt in namibia preserve relationships between anatectic leucosomes and intrusive leucogranite sheets illustrating the consecutive stages of partial melting local melt segregation and far field mobilization of melts over hundreds of metres and out of the anatectic region initial melting and localized segregation of melts are controlled by gradients in fluid pressure created by pervasively developed shallowly dipping dilatant fractures subsequent melt transfer out of these initial sites of melting and melt storage occurs along subvertical disc shaped leucogranite sheets that intersect the leucosomes the leucogranite sheets propagate as isolated melt filled hydrofractures driven by the pressure differential along the subvertical fractures the collapse of wall rocks into former melt bearing fractures and the presence of residual peritectic phases of the melting reaction trapped in wall rocks testify to the efficient extraction of melt by the mobile hydrofractures during their ascent this process of melt drainage into and transport by hydrofractures leaves almost no trace of the ascent conduits this study also shows that melt transport and the stability of melt pathways in strongly layered mid crustal levels characterized by low deviatoric stresses are determined by the presence of pre existing anisotropies and the progressively evolving structure in deforming orogens