earthquake locations using single station deep borehole recordings implications for microseismicity on the san andreas fault in southern california we have located and estimated source parameters of 109 earthquakes 0 to 5 m using seismograms recorded at 2 5 km depth in the cajon pass borehole southern california the borehole is about 4 km from the san andreas fault at the boundary between the locked almost aseismic mojave and san bernardino segments where the san jacinto fault approaches the san andreas this area is of interest both on account of its tectonic complexity and its high potential seismic hazard the clear relatively unattenuated downhole recordings are rotated to determine the incoming azimuth of the p wave and the delay time between the p and s arrivals is used to estimate the hypocentral distance the difference between the hypocenters located this way and the southern california seismic network scsn locations of the same earthquakes increases with hypocentral distance from the borehole of the earthquakes within 20 km of the borehole 95 are within 1 2 km of the scsn epicenters and all are within 5 km of the scsn depths all but three of the 58 earthquakes located here which the scsn did not record were within 20 km of the borehole and so the location errors are similar to those of scsn a and b quality events most of the small earthquakes occurred within the relatively active san jacinto fault zone but at least eight are located close to or within the san andreas fault zone the stress drops for these events range from 0 1 to 18 mpa these earthquakes appear similar to the other events in this study suggesting that the san andreas fault is similar to other faults at the scale of these small earthquakes the variation in stress drop and slip orientation of these small earthquakes suggests that larger scale heterogeneity continues to these small scales also the location of these small earthquakes in major established fault zones implies that earthquake source dimensions are not geometrically controlled by fault zone width

gas geochemistry of the mount elbert gas hydrate stratigraphic test well alaska north slope implications for gas hydrate exploration in the arctic abstract gases were analyzed from well cuttings core gas hydrate and formation tests at the bpxa doe usgs mount elbert gas hydrate stratigraphic test well drilled within the milne point unit alaska north slope the well penetrated a portion of the eileen gas hydrate deposit which overlies the more deeply buried prudhoe bay milne point west sak and kuparuk river oil fields gas sources in the upper 200 m are predominantly from microbial sources c1 isotopic compositions ranging from 86 4 to 80 6 the c1 isotopic composition becomes progressively enriched from 200 m to the top of the gas hydrate bearing sands at 600 m the tested gas hydrates occur in two primary intervals units d and c between 614 0 m and 664 7 m containing a total of 29 3 m of gas hydrate bearing sands the hydrocarbon gases in cuttings and core samples from 604 to 914 m are composed of methane with very little ethane the isotopic composition of the methane carbon ranges from 50 1 to 43 9 with several outliers generally decreasing with depth gas samples collected by the modular formation dynamics testing mdt tool in the hydrate bearing units were similarly composed mainly of methane with up to 284 ppm ethane the methane isotopic composition ranged from 48 2 to 48 0 in the c sand and from 48 4 to 46 6 in the d sand methane hydrogen isotopic composition ranged from 238 to 230 with slightly more depleted values in the deeper c sand these results are consistent with the concept that the eileen gas hydrates contain a mixture of deep sourced microbially biodegraded thermogenic gas with lesser amounts of thermogenic oil associated gas and coal gas thermal gases are likely sourced from existing oil and gas accumulations that have migrated up dip and or up fault and formed gas hydrate in response to climate cooling with permafrost formation

behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma a series of three experiments was made at 125 c and 10 kbar in which a 1 gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6 5 mm diameter cylinder of partially molten fine grained granite detailed microprobe analysis 450 spots total of the quenched samples revealed progressive basalt granite interaction as run duration increased from 0 75 to 8 to 24 hours interdiffusion of melt components is limited for structure controlling species such as si 4 and al 3 and for divalent cations which all mix over a zone less than 0 5 mm wide in 24 hours at run conditions in contrast k and na are extremely mobile resulting in considerable uptake of k by the basalt melt and eventual loss of na from the basalt to the granite by uphill diffusion the chemical diffusivity of k in the basalt can be accurately estimated at 3 times 10 18 cm 2 sec for the specific experimental conditions used although this value is somewhat lower than previous estimates k o

local observations of the onset of a large earthquake 28 june 1992 landers california the landers earthquake mw 7 3 of 28 june 1992 had a very emergent onset the first large amplitude arrivals are delayed by about 3 sec with respect to the origin time and are preceded by smaller scale slip other large earthquakes have been observed to have similar emergent onsets but the landers event is one of the first to be well recorded on nearby stations we used these recordings to investigate the spatial relationship between the hypocenter and the onset of the large energy release and to determine the slip function of the 3 sec nucleation process relative location of the onset of the large energy release with respect to the initial hypocenter indicates its source was between 1 and 4 km north of the hypocenter and delayed by approximately 2 5 sec three station array analysis of the p wave shows that the large amplitude onset arrives with a faster apparent velocity compared to the first arrivals indicating that the large amplitude source was several kilometers deeper than the initial onset an ml 2 8 foreshock located close to the hypocenter was used as an empirical green s function to correct for path and site effects from the first 3 sec of the mainshock seismogram the resultant deconvolution produced a slip function that showed two subevents preceding the main energy release an mw 4 4 followed by an mw 5 6 these subevents do not appear anomalous in comparison to simple moderate sized earthquakes suggesting that they were normal events which just triggered or grew into a much larger earthquake if small and moderate sized earthquakes commonly detonate much larger events this implies that the dynamic stresses during earthquake rupture are at least as important as long term static stresses in causing earthquakes and the prospects of reliable earthquake prediction from premonitory phenomena are not improved

high frequency site effects at two parkfield downhole and surface stations abstract using stacked ratios of microearthquake source spectra recorded at the surface and 200 m downhole we have established the p and s wave site effect at two locations in parkfield california the frequency responses of both sites are bimodal being completely dominated by multiples and amplification below 10 hz and by attenuation above 30 hz the low frequency amplification factors show roughly three to five times more uphole motion compared to that downhole the multiples produce peaks with a maximum of nearly 10 times more uphole motion above 50 hz the downhole motion is always larger approaching a factor of 5 at the high frequency limits of our study when fit with a linear attenuation model the high frequency ratios yield compressional and shear q values between 6 and 19 the data were divided into subsets based on event location and time of year statistical comparison of these subsets shows no systematic variation with azimuth or season the results of our study accounts for the lack of high frequency surface reflections in the parkfield downhole data but not for the lack of source scaling of parkfield microearthquakes

a model for the simulation of combined major and trace element liquid lines of descent abstract variations of major and trace element partition coefficients as functions of temperature and composition have severely limited the range of composition for quantitative modeling of the differentiation of natural magmatic systems application of a two lattice melt model greatly reduces compositional dependence for trace elements this allows the temperature dependence of isobaric trace element partitioning to be evaluated independently thus making it possible to model an expanded range of conditions and compositions the first goal of this investigation was to construct a model to simulate major and trace element systematics of natural differentiation processes by combining trace element partitioning with a major element phase equilibrium model nielsen 1985b the second goal was the application of this model to the simulation of magma chamber recharge assimilation eruption and fractional crystallization these simulations indicate that the proportions of minerals fractionating from an open system are not necessarily the same as those in a closed system recharge or assimilation will drive a magma composition off the cotectic along which it is evolving however fractionation will drive the liquid back towards the cotectic in a recharged magma chamber as the recharge flux increases the fractionating mineral proportions will be increasingly biased towards those phases which appear first from the primitive magma the bulk partition coefficient for an open system can be considerably different 5 10 or more for some elements compared to a closed system paired assimilation and fractional crystallization are often cited as the mechanisms responsible for the origin of high al basalts and andesites however the addition of an al rich assimilant into a fractionating basaltic magma will increase the proportion of plagioclase to the extent that al in the derived liquids will be effectively buffered or even decrease the assimilation of forsteritic olivine by reaction keleman and ghiorso 1986 increases the proportions of pyroxene and olivine thus reducing the fe enrichment and al depletion characteristic of low pressure basalt fractionation

experimental interaction of granitic and basaltic magmas and implications for mafic enclaves we have performed time series experiments for periods ranging from 3 min to 44 h on the interaction of granite melt and partially molten basalt at 920 c and 10 kbar in the presence of 5 wt water with time the assemblage of the basalt domain changes from predominantly amphibole plagioclase to clinopyroxene garnet the melt fraction increases from 2 5 to 40 and between the two domains the melt compositions progressively equilibrate initially in each run melts of the basalt domain have uniform plateau concentrations for sio 2 al 2o 3 cao mgo and feo because the activities of these components are regulated by the mineral assemblage but at advanced stages of reaction no such control is evident we have derived analytical expressions to describe and simulate the diffusion profiles the concentration profiles for sio 2 al 2o 3 cao and na 2o in the granite emanating from the basalt granite interface have been used to estimate effective diffusivities the values from the shorter runs are compared with those of the experiment of longest duration for which we assumed finite couples in our calculations in the diffusion calculations for k2o the difference in melt fraction between the two domains is accounted for the resulting values in cm 2 s are d na 2o 6 10 7 d k 2o 3 10 7 d mgo 9 10 8 d cao 4 6 10 8 and d sio 2 and d al 2o 3 3 0 6 10 8 they are in reasonable agreement with values from other studies on the basis of our experiments we calculate that mafic enclaves of magmatic origin should equilibrate to a large degree with their host magma in slowly cooling non convecting granitic plutons enclaves approaching complete re equilibration retain distinctly higher modal amounts of mafic minerals they do not compositionally resemble binary magma mixtures but are more like host magma with accumulated crystals we show that the modal differences between enclave and host are indicative of the temperature of homogenization and that in principle this temperature can be deduced from equilibrium phase diagrams

the structure of methane gas hydrate bearing sediments from the krishna godavari basin as seen from micro ct scanning abstract the indian national gas hydrate program nghp expedition 1 of 2006 cored through several methane gas hydrate deposits on the continental shelf around the coast of india the pressure coring techniques utilized during the expedition hyacinth and pcs enabled recovery of gas hydrate bearing fine grained sediment cores to the surface after initial characterization core sections were rapidly depressurized and submerged in liquid nitrogen preserving the structure and form of the hydrate within the host sediment once on shore high resolution x ray ct scanning was employed to obtain detailed three dimensional images of the internal structure of the gas hydrate using a resolution of 80 m the detailed structure of the hydrate veins present in each core could be observed and allowed for an in depth analysis of orientation width and persistence of each vein hydrate saturation estimates could also be made and saturations of 20 30 were found to be the average across the core section with some portions showing highs of almost 60 saturation the majority of hydrate veins in each core section were found to be orientated between 50 and 80 to the horizontal analysis of the strikes of the veins suggested a slight preferential orientation in individual sample sections although correlation between individual sections was not possible due to the initial orientation of the sections being lost during the sampling stage the preferred vein orientation within sample sections coupled with several geometric features identified in individual veins suggest that hydraulic fracturing by upward advecting pore fluids is the main formation mechanism for the veined hydrate deposits in the k g basin

magnetic fabric of the barrington passage pluton meguma terrane nova scotia a two stage fabric history of syntectonic emplacement abstract structural analysis and the anisotropy of magnetic susceptibility ams are used to document the internal magmatic to high temperature subsolidus fabrics of the tonalitic late devonian barrington passage pluton the ams fabric orientations compare favorably with mesoscopic scale fabrics in general the k1 k2 principal plane of the ams is close to the observed mineral foliation defined by biotite and plagioclase and the k1 axis is aligned parallel to a mineral lineation defined by the same minerals and to a locally developed weak extension lineation defined by quartz measurement of the anisotropy of anhysteretic remanence aar and image analysis of biotite preferred orientations confirm that the orientation of the ams is principally controlled by biotite locally anomalous ams orientations are attributed to the influence of fine grained magnetite crystals the presence of which is revealed by measurements of hysteresis and coercivity properties a two stage fabric history is revealed first horizontal fabrics were formed foliation compositional banding during emplacement of a laccolith like pluton the second stage involved synmagmatic folding of the horizontal foliation and banding in response to regional contraction associated with the acadian orogeny with development of a lineation that records stretching parallel to the fold axis the results demonstrate that the barrington passage pluton was emplaced during the main phase of the acadian orogeny a model is proposed that depicts the barrington passage pluton as the folded base of a larger syntectonic pluton that is now largely eroded off

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected

mount elbert gas hydrate stratigraphic test well alaska north slope coring operations core sedimentology and lithostratigraphy abstract in february 2007 bp exploration alaska the u s department of energy and the u s geological survey completed the bpxa doe usgs mount elbert gas hydrate stratigraphic test well mount elbert well in the milne point unit on the alaska north slope the program achieved its primary goals of validating the pre drill estimates of gas hydrate occurrence and thickness based on 3 d seismic interpretations and wireline log correlations and collecting a comprehensive suite of logging coring and pressure testing data the upper section of the mount elbert well was drilled through the base of ice bearing permafrost to a casing point of 594 m 1950 ft approximately 15 m 50 ft above the top of the targeted reservoir interval the lower portion of the well was continuously cored from 606 m 1987 ft to 760 m 2494 ft and drilled to a total depth of 914 m ice bearing permafrost extends to a depth of roughly 536 m and the base of gas hydrate stability is interpreted to extend to a depth of 870 m coring through the targeted gas hydrate bearing reservoirs was completed using a wireline retrievable system the coring program achieved 85 recovery of 7 6 cm 3 in diameter core through 154 m 504 ft of the hole an onsite team processed the cores collecting and preserving approximately 250 sub samples for analyses of pore water geochemistry microbiology gas chemistry petrophysical analysis and thermal and physical properties eleven samples were immediately transferred to either methane charged pressure vessels or liquid nitrogen for future study of the preserved gas hydrate additional offsite sampling analyses and detailed description of the cores were also conducted based on this work one lithostratigraphic unit with eight subunits was identified across the cored interval subunits ii and va comprise the majority of the reservoir facies and are dominantly very fine to fine moderately sorted quartz feldspar and lithic fragment bearing to rich sands lithostratigraphic and palynologic data indicate that this section is most likely early eocene to late paleocene in age the examined units contain evidence for both marine and non marine lithofacies and indications that the depositional environment for the reservoir facies may have been shallower marine than originally interpreted based on pre drill wireline log interpretations there is also evidence of reduced salinity marine conditions during deposition that may be related to the paleo climate and depositional conditions during the early eocene

mineralogy and geochemistry of microgranular enclaves in palaeoproterozoic malanjkhand granitoids central india evidence of magma mixing mingling and chemical equilibration palaeoproterozoic ca 2 480 ma felsic magmatism of malanjkhand region of central indian precambrian shield referred to as malanjkhand granitoids mg contain xenoliths of country rocks and mesocratic to melanocratic fine grained porphyritic microgranular enclaves me the shape of me is spheroidal ellipsoidal discoidal elongated and lenticular varying in size from a few centimeters to about 2 m across the contact of me with the host mg is commonly sharp crenulate and occasionally diffuse which we attribute to the undercooling and disaggregation of me globules within the cooler host mg the me as well as mg show hypidiomorphic texture with common mineral hbl bt kfs pl qtz assemblage but differ in modal proportions the variation in minerals composition presence of apatite needles elongated biotites resorbed plagiclase ocellar quartz and other mafic felsic xenocrysts strongly oppose the restite and cognate origins of me compositions of plagioclases an3 an29 amphiboles mg mg fe2 0 55 0 69 and biotites mg mg fe2 0 46 0 60 of me are slightly distinct or similar to those of mg which suggest partial to complete equilibration during mafic felsic magma interactions al in amphibole estimates the mg pluton emplacement at ca 3 4 0 5 kbar and therefore magma mixing and mingling must have occurred at or below this level the hbox fe rightleftharpoons hbox mg substitution in biotites of me and mg largely suggests subduction related calc alkaline metaluminous i type nature of felsic melts most major and trace elements against sio2 produce near linear variation trends for me and mg probably generated by the mixing of mafic and felsic magmas in various proportions trace including rare earth elements patterns of me mg pairs however show partial to complete equilibration most likely governed by different degrees of elemental diffusion the available evidence supports the model of me origin that coeval mafic enclave and felsic mg magmas produced a hybrid me magma layer which injected into cooler partly crystalline mg and dispersed mingled and undercooled as me globules in a convectively dynamic magma chamber

evidence for two stage mixing in magmatic inclusions and rhyolitic lava domes on niijima island japan abstract fine grained inclusions are found in the achiyama and the mukaiyama rhyolitic lava domes on niijima island japan the existence of fine grained rims in the inclusions indicates that these inclusions are a quenched mafic magma incorporated into their rhyolite host the chemical composition and the phenocryst assemblage of the inclusions in the achiyama dome are identical with those of the effusive basaltic lava on niijima island wakago basalt the inclusions of the mukaiyama dome are dacitic and have a disequilibrium phenocryst assemblage olivine clinopyroxene orthopyroxene hornblende biotite plagioclase quartz and opaque minerals whole rock compositions lie on a mixing line between the host rhyolite and wakago basalt the dacitic magma is therefore a product of mixing of the basaltic and rhyolitic magmas the occurrence of two different inclusions basaltic and dacitic in two different domes can be explained by a two stage magma mixing model the dacite is formed in the first stage by mixing in a vertically stratified magma chamber caused by an interfacial instability between rhyolitic and basaltic layers a small amount of rhyolitic magma is entrained into the lower basaltic magma layer and two magmas can mix essentially in a liquid state the mixed dacitic magma is formed in the lower layer the second stage is mixing caused by forced convection during the ascent through a conduit just before eruption the stably stratified silicic and mafic magmas in a magma chamber can turn over and efficiently mix because of the formation of an unstable flow in a conduit under this condition the system reaches thermal equilibrium immediately after the mafic magma is disaggregated and dispersed in the silicic host the mafic magma solidifies when the silicic endmember is predominant in the mixture hence the equilibrium temperature is below the solidus of the mafic magma mafic inclusions are formed at this stage whether the inclusions are basaltic or dacitic depends on whether the final ascent through a conduit eruption occurred before or after the formation of the layer of a mixed dacitic magma in a magma chamber

crystallization and hybridism in microgranitoid enclave magmas microstructural evidence microstructural evidence indicates that many microgranitoid enclaves mafic inclusions in granitoids crystallize from globules of magma that have undergone previous magma mixing hybridism the evidence includes 1 rounded xenocrysts ocelli of quartz rimmed with fine grained aggregates of early formed minerals especially mafic minerals 2 k feldspar megacrysts commonly rimmed with plagioclase rapakivi structure and 3 corroded cores dendritic overgrowths and calcic spikes in plagioclase initial quenching of a magma globule in felsic magma involves rapid temperature equilibration which causes a high rate of nucleation of minerals precipitating from the enclave magma at the time followed by a period of slow cooling during which the nucleation and growth rates of later crystallizing minerals are similar to the much slower rates prevailing in the granitic melt this may result in markedly poikilitic microstructures involving inclusion of the earlier formed finer grained minerals in quartz and or k feldspar which are common in microgranitoid enclaves

gas hydrate characterization and grain scale imaging of recovered cores from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract using cryogenic scanning electron microscopy csem powder x ray diffraction and gas chromatography methods we investigated the physical states grain characteristics gas composition and methane isotopic composition of two gas hydrate bearing sections of core recovered from the bpxa doe usgs mount elbert gas hydrate stratigraphic test well situated on the alaska north slope the well was continuously cored from 606 5 m to 760 1 m depth and sections investigated here were retrieved from 619 9 m and 661 0 m depth x ray analysis and imaging of the sediment phase in both sections shows it consists of a predominantly fine grained and well sorted quartz sand with lesser amounts of feldspar muscovite and minor clays cryogenic sem shows the gas hydrate phase forming primarily as a pore filling material between the sediment grains at approximately 70 75 saturation and more sporadically as thin veins typically several tens of microns in diameter pore throat diameters vary but commonly range 20 120 microns gas chromatography analyses of the hydrate forming gas show that it is comprised of mainly methane 99 9 indicating that the gas hydrate is structure i here we report on the distribution and articulation of the gas hydrate phase within the cores the grain morphology of the hydrate the composition of the sediment host and the composition of the hydrate forming gas

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

magma mixing in the subvolcanic environment petrology of the gerena interaction zone near seville spain the mechanisms by which felsic and mafic magmas interact and approach a uniform hybrid composition through the processes of mingling and mixing have been studied in a high level subvolcanic setting in the spanish hercynian at gerena near seville the compositions involved are calc alkaline and the situation is one of tonalite quartz diorite synplutonic dykes injected into a granitic magma chamber the resulting hybrids include dykes pillows and globules of tonalite with chilled margins which are variously disrupted and homogenised with the host granite the present investigation is based on field and petrographic observations of hybridization textures the identification of different stages in the crystallisation history of the tonalite through mineral textures and the characterization of mineral compositions at these various stages proportions of the end member magmas involved were obtained by major oxide mixing models and tested satisfactorily with trace elements a mechanistic model is presented to account for these observations which involves the early quenching of the tonalite when it was emplaced into the granite magma chamber after high temperature crystallization had occurred the two magmas attained thermal equilibrium and disruption of the tonalite in the high energy regime of this subvolcanic complex resulted in dispersion of fragments and crystals through the granite giving rise to hybrid granodiorite compositions it is argued that such high energy flow conditions are a necessary requirement for effective hybridization in this environment in contrast to most large scale magma chamber settings where mixing is driven by thermal and buoyancy contrasts

interaction among upper crustal lower crustal and mantle materials in the port mouton pluton meguma lithotectonic zone southwest nova scotia the port mouton pluton is unique among the late devonian peraluminous granitoid bodies in the meguma lithotectonic zone of southwestern nova scotia in its lithological heterogeneity extensive physical and chemical interac tion with the country rocks clear evidence for mingling and mixing with mafic magmas and highly abundant pegmatites new u pb age determinations on monazite establish an intrusion age of 373 1 ma similar to the ages of other meguma lithotectonic zone granitoid plutons and mafic intrusions field relations petrology and geochemistry define three stages of intrusion of the port mouton pluton i early stage discontinuously exposed around the outer margin of the pluton dominated by coarse grained tonalite granodiorite and with rb sr 0 40 and gdn lun 0 55 eu eu 2 and iii late stage consisting of abundant minor sheets throughout the pluton dominated by fine grained tonalite granodiorite and leucogranite that are similar to rocks of the early and middle stages the port mouton pluton shows a wider range of 87 sr 86 sri 0 7036 0 7154 and a wider range and generally higher endi 3 72 to 2 12 than other granitoid rocks in the meguma lithotectonic zone potentially reflecting a com plex partially equilibrated interaction among mantle lower crust and upper crust field petrological and chemical evi dence for the involvement of mantle derived magmas and melting of upper crust permit modelling of the port mouton pluton granitoid compositions by three simultaneous mixing equations these mixing model results suggest that the early stage granitoid rocks can form from simple three component mixing relationships when the bulk distribution coefficients between residuum and melt for sr and nd range from 1 05 to 1 18 or two component mixing combined with fraction ation of material like the known felsic lower crust the middle stage granitoid rocks only yield solutions involving two component mixing and fractionation of material unlike the known felsic lower crust we conclude that the late devonian mafic magmas played a major role in the formation of granitoid magmas in the meguma lithotectonic zone by supplying heat and material to cause partial fusion of the avalon lower crust

downhole well log and core montages from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract the bpxa doe usgs mount elbert gas hydrate stratigraphic test well was an integral part of an ongoing project to determine the future energy resource potential of gas hydrates on the alaska north slope as part of this effort the mount elbert well included an advanced downhole geophysical logging program because gas hydrate is unstable at ground surface pressure and temperature conditions a major emphasis was placed on the downhole logging program to determine the occurrence of gas hydrates and the in situ physical properties of the sediments in support of this effort well log and core data montages have been compiled which include downhole log and core data obtained from the gas hydrate bearing sedimentary section in the mount elbert well also shown are numerous reservoir parameters including gas hydrate saturation and sediment porosity log traces calculated from available downhole well log and core data

geologic setting and lithologic column of the cajon pass deep drillhole the cajon pass deep drillhole penetrates a late tertiary basin developed on crystalline basement in the sw mojave desert 4 km from the san andreas fault cores continuous cuttings and geophysical logs from phase i show great diversity in rock types structure and alteration the hole encountered cajon formation arkoses granodiorite tonalite unusual megacrystic granite and augen gneiss granitic and pelitic gneisses with quartzite quartzofeldspathic orthogneiss cut by sheets of hornblende gabbro and interlayered mafic and quartzofeldspathic orthogneisses with rare calcsilicate intervals foliation and compositional layering have low dips throughout the column and layered gneisses contain 10 cm scale recumbent folds faults and alteration zones bound several rock units with low apparent dips basement cores are typically cut by steep fractures 1 mm wide that contain zeolites calcite or chlorite epidote fractures and faults decrease in abundance with depth

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

the magmatic hydrothermal transition evidence from quartz phenocryst textures and endoskarn abundance in cu zn skarns at the empire mine idaho usa information about the magmatic to hydrothermal transition is preserved in late stage features of quartz phenocrysts and endoskarn alteration in some cu zn skarn deposits such as the empire mine in idaho important features include 1 quartz phenocrysts with strong resorption textures such as vermicular zones of igneous groundmass cutting primary quartz cathodoluminescence banding 2 anomalous amounts of endoskarn more than 50 of mineralized rock 3 high f activities as evidenced by fluorite as an accessory mineral in igneous rocks in alteration assemblages and in fluid inclusions and by high f in hydroxyl sites in igneous biotite and amphibole and 4 direct association of zn which normally is deposited distally at low temperature with cu in proximal locations and in endoskarn these features are explained by the following model 1 f lowers the solidus temperature of the magma thus changing the timing temperature and duration of hydrothermal fluid exsolution 2 upon magmatic vapor saturation the f rich hydrothermal fluids form bubbles that adhere to quartz phenocrysts and chemically corrode tunnel into the quartz forming vermicular resorption textures 3 f rich hydrothermal fluids also promote the formation of endoskarn silicic rocks are attacked by f rich fluids in the same sense that carbonate wall rocks are dissolved by weakly to moderately acidic hydrothermal fluids 4 low fluid exsolution temperature facilitated by high f activity promotes high zn cu ratios in proximal locations due to the solubility of zn relative to cu at lower temperatures this model may be applicable at other localities such as the world class cu zn skarn antamina mine as well as some tin and rapakivi granites

x ray computed tomography examination and comparison of gas hydrate dissociation in nghp 01 expedition india and mount elbert alaska sediment cores experimental observations and numerical modeling abstract natural gas from methane hydrate could provide a desireable resource as part of a long term investigation of producing gas from methane hydrate lab scale gas production tests have been performed using natural cores from india s natural gas hydrate program 01 expedition nghp 01 and from the mount elbert stratigraphic well on the north slope of alaska prior to performing the gas production tests a number of cores from the nghp 01 were scanned using x ray computed tomography ct to examine the gas hydrate bearing sediment structure which guided the selection of the core for the gas production test disseminated gas hydrate gas hydrate in veins and gas hydrate in nodules were observed or inferred from the ct data data from numerous core segments are presented here and in the supplemental information in our gas production test the gas hydrate in the nghp 01 core was dissociated by warming the core to above the stability point and then depressurizing the sample a preserved sample of gas hydrate bearing sandstone from the mount elbert test well was dissociated by depressurization in both tests the internal temperature of the sample was monitored in two locations and the density changes at high spatial resolution were measured using x ray ct scanning although there were indications of dissociation in the nghp 01 core no gas was produced the mount elbert sample contained two distinct regions having different porosity and grain size distributions the gas hydrate dissociation occurred initially throughout the sample as a result of lowering the pressure below methane hydrate stability conditions this initial depressurization stage in the experiment reduced the temperature to the methane hydrate equilibrium point and the pressure was controlled so that the temperature remained above the ice point after that dissociation occurred from the outside into the core sample as a result of heat transfer from the controlled temperature bath surrounding the pressure vessel numerical modeling of the laboratory test results using tough hydrate yielded a gas production curve that closely matches the experimentally measured curve

application of la icp ms analysis of arsenopyrite to gold metallogeny of the meguma terrane nova scotia canada abstract investigation of gold metallogeny in the paleozoic meguma terrane canada is conducted through la icp ms analysis of arsenopyrite collected from eight slate belt style vein gold deposits using a novel approach integrating elemental distribution maps and their derived elemental paragenesis with multi element binary plots the data reveal two distinct gold events 1 an early event characterized by a co ni mo sb se elemental association related to initial growth of arsenopyrite that reflects the presence of invisible gold 10 ppm and 2 a second event spatially associated with late fracture sets that is characterized by an al ti v mn element association and reflects either remobilization or upgrading of primary invisible gold and is manifest as visible gold the results of this study indicate a complex and protracted history of gold mineralization which has important ramifications for the meguma gold deposits as well as other orogenic gold districts globally in the case of the meguma terrane it involves an initial gold event that is followed by element mobilization and in the case of precious metals au ag an upgrading through a zone refining process in addition the variable coupling and decoupling of elements is only revealed using in situ derived la icp ms data

a comparison of the age and composition of the shelburne dyke nova scotia and the messejana dyke spain new 40ar 39ar age determinations on biotite from the shelburne dyke of nova scotia and from the messejana dyke of spain are identical at 203 2 ma in addition both dykes have similar chemical compositions and probably represent similar magma sources petrogenetic processes and tectonic settings related to an early phase of opening of the north atlantic ocean

hydrate morphology physical properties of sands with patchy hydrate saturation 1 the physical properties of gas hydrate bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase the host sediment grain size and the state of effective stress determine the hydrate morphology in sediments this information can be used to significantly constrain estimates of the physical properties of hydrate bearing sediments including the coarse grained sands subjected to high effective stress that are of interest as potential energy resources reported data and physical analyses suggest hydrate bearing sands contain a heterogeneous patchy hydrate distribution whereby zones with 100 pore space hydrate saturation are embedded in hydrate free sand accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate bearing sands and captures observed physical property dependencies on hydrate saturation for example numerical modeling results of sands with patchy saturation agree with experimental observation showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations the hydrate patch size itself impacts the physical properties of hydrate bearing sediments for example at constant hydrate saturation we find that conductivity electrical hydraulic and thermal increases as the number of hydrate saturated patches increases this increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross section of the specimen

progressive hybridisation between late devonian mafic intermediate and felsic magmas in the meguma zone of nova scotia canada two felsic plutons of late devonian 385 370 ma age in the meguma zone of southwestern nova scotia contain three circa 376 ma synplutonic mafic intermediate intrusions that collectively record progressive stages of in situ hybridisation a 5 m wide spessartite dyke in the port mouton pluton probably underwent rapid cooling and crystallisation immediately after intrusion which heated and coarsened the adjacent tonalite an 85 m long sheet of pillowed kersantite also in tonalite of the port mouton pluton presumably contained residual magma after quenching and obtained k p ba rb more radiogenic sr zr nb and light ree from the tonalite during magma mingling the third synplutonic body a 100 m wide diorite sheet intrudes granodiorite of the adjacent shelburne pluton and has a circa 45 m wide gradational contact of metaluminous hornblende tonalite this tonalite dominantly records magma mixing by the transfer of ti mg fe ca and v in hornblende biotite plagioclase and at least in part apatite xenocrysts derived from dioritic pillows that were originally disaggregated in the granodiorite probably in response to convection scattered data points unusual concave down variation trends for al2o3 p2o5 and sr and non hyperbolic sr nd isotopic characteristics in the tonalite apparently reflect syn or post mixing fractionation and accumulation of xenocrysts from residual magma phosphorus may have assisted diffusion of sr zr nb and light ree and caused premature quenching of the hybrids at mcleods cove and birchtown during magma mingling and mixing

chemical and structural characteristics of gas hydrates from the haima cold seeps in the qiongdongnan basin of the south china sea abstract crystalline structure cage occupancy and gas composition are important gas hydrate characteristics which can be used to calculate the gas hydrate s stability and to estimate the energy potential in may and october of 2015 a guangzhou marine geological survey team investigated two sites in the haima cold seeps in the qiongdongnan basin northern south china sea they recovered massive gas hydrate samples by conventional gravity coring after the shenhu sea area and dongsha sea area the qiongdongnan basin became a new area on the northern slope of the south china sea where gas hydrates have been found in order to reveal the structural and geochemical characteristics of the natural gas hydrates samples were analyzed by micro raman spectroscopy and x ray diffraction under ambient pressure and low temperature conditions the results indicate that the gas hydrate samples from the haima cold seeps are typical structure i hydrates with a hydration number of 6 12 6 19 in addition trace amounts of h2s trapped in the hydrate were identified based on its characteristic vibrational signature the gas composition and 13c ch4 of the hydrate bound gas samples were analyzed for gas source correlation all of the gas samples are dominated by methane with small amounts of ethane and propane and had relatively light 13c ch4 indicating that all of the hydrate bound gases are mixtures of biogenic and thermogenic gas the thermogenic gas is inferred to be mainly derived from the coal layers of the late miocene pliocene yacheng formation in the northern lingshui sag

pre and post drill comparison of the mount elbert gas hydrate prospect alaska north slope abstract in 2006 the united states geological survey usgs completed a detailed analysis and interpretation of available 2 d and 3 d seismic data along with seismic modeling and correlation with specially processed downhole well log data for identifying potential gas hydrate accumulations on the north slope of alaska a methodology was developed for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area the study revealed a total of 14 gas hydrate prospects in this area in order to validate the gas hydrate prospecting protocol of the usgs and to acquire critical reservoir data needed to develop a longer term production testing program a stratigraphic test well was drilled at the mount elbert prospect in the milne point area in early 2007 the drilling confirmed the presence of two prominent gas hydrate bearing units in the mount elbert prospect and high quality well logs and core data were acquired the post drill results indicate pre drill predictions of the reservoir thickness and the gas hydrate saturations based on seismic and existing well data were 90 accurate for the upper unit hydrate unit d and 70 accurate for the lower unit hydrate unit c confirming the validity of the usgs approach to gas hydrate prospecting the mount elbert prospect is the first gas hydrate accumulation on the north slope of alaska identified primarily on the basis of seismic attribute analysis and specially processed downhole log data post drill well log data enabled a better constraint of the elastic model and the development of an improved approach to the gas hydrate prospecting using seismic attributes

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

derivation of the early carboniferous wedgeport pluton by crystal fractionation of a mafic parental magma a rare case of an a type granite within the meguma terrane nova scotia canada the cambrian ordovician metasedimentary rocks of the meguma terrane canadian appalachians were extensively intruded by silicic plutons during middle devonian to early carboniferous times syn plutonic but volumetrically minor mafic ultramafic intrusions were also emplaced in most localities the silicic plutons and mafic ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources the attwoods brook gabbronorite of sw nova scotia yielded an in situ zircon weighted mean 206pb 238u age of 357 9 3 3 ma that is within the uncertainty of the age of the neighbouring wedgeport pluton 357 1 ma the wedgeport pluton is a rare example of a mantle derived peraluminous a type granite within the meguma terrane the similar ages and nd isotopes of the attwoods brook gabbronorite end t 1 1 to 4 0 and wedgeport pluton end t 2 1 to 3 3 suggest the two intrusions are petrogenetically related fractional crystallization modelling demonstrates that a parental magma similar to the attwoods brook gabbronorite can produce residual silicic liquids that resemble the granites of the wedgeport pluton indicating that they could be members of the same intrusive complex the emplacement of the gabbronorite and wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the maritimes basin that produced the fountain lake continental flood basalts and a type granites of the cobequid highlands within the avalon terrane it is possible that the early carboniferous rocks of sw nova scotia are related to the rifted related magmatism within the maritimes basin

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

interaction between basic and acid magmas during the latest stages of the post collisional variscan evolution clues from the gabbro granite association of ota corsica sardinia batholith abstract the intrusive association of ota post variscan corsica sardinia batholith consists of mafic rocks and granites displaying mingling relations the mafic rocks are olivine gabbros to quartz diorites and the granites are subsolvus and characterised by biotite as the only mafic phase minor amounts of amphibole bearing granodiorites to granites develop along the contacts between mafic rocks and granites the rather high initial e nd 4 5 of the most primitive mafic sample indicates that parental basic melts had an extensive contribution from a depleted mantle source in the mafic rocks the decrease of initial e nd to 2 1 is associated with an increase of th and u concentrations in clinopyroxene thus indicating that the ota basic melts underwent a process of crustal contamination associated biotite granites have low initial e nd 0 4 and high th and u concentrations the chemical evolution of ota basic melts most likely occurred through fractional crystallisation and concomitant contamination with the acid magma that gave rise to associated biotite granites the incompatible element signature of late stage anhedral amphibole from variably evolved mafic rocks is similar thus suggesting that the whole ota mafic sequence recorded the contamination process possibly by percolation within the gabbroic crystal mush of a melt contaminated by the acid magma hybridisation between basic and acid magmas is also documented by contact amphibole bearing granitoids in particular major and trace element zoning of amphibole from granodiorites reveals that such a hybridisation was associated with reactions between crystals from the basic magma amphibole and clinopyroxene and the acid melt the occurrence of chemically homogeneous amphiboles in associated granites suggests that contact hybridisation comprised also a process of gradient induced chemical diffusion

origin of sierra nevadan granite evidence from small scale composite dikes composite dikes at hell hole meadow in the central sierra nevada contain hybrids created by small scale mixing of andesitic and rhyolitic magmas early rhyolitic injections had partially solidified when subsequent andesitic magmas arrived and mixed with small increments of remnant rhyolitic magma in major element chemistry the hybrid rocks define linear mgo variation diagrams that closely resemble those for the half dome mt givens and eagle peak granodiorites the patterns suggest that mixing of mafic and felsic magmas has been important in the evolution of these plutons

mid proterozoic lamprophyre commingled with late stage granitic dikes of the anorogenic san isabel batholith wet mountains colorado more than a dozen composite mafic granitic dikes crop out along the northern margin of the san isabel batholith wet mountains colorado the dikes crosscut and contain xenoliths of 1441 ma granitic dikes and are in turn intruded by but probably are coeval with late stage granitic dikes of the 1360 ma san isabel batholith only two other mafic representatives of the mid proterozoic anorogenic suite are known from colorado in the field the dikes contain up to one third granitic material by volume textures range from a swirling lacy mortarlike granite within basalt to subovoid pillows of basalt in granite many of the pillows contain small ovoids of the granite the mutual inclusions and rounded to cuspate liquidlike contacts with minor mechanical mixing strongly indicate that these dikes formed through commingling of mafic and granitic liquids the mafic dikes have the mineralogy and chemistry of lamprophyres containing andesine amphibole biotite sphene and magnetite with minor quartz and epidote and rare k feldspar chemically they average average 52 sio2 and they are enriched in incompatible elements including the light rare earth elements they are tholeiitic compositionally similar to within plate basalts with rift affinity they partially mixed with the granite to produce intermediate composition rock with 56 sio2 the granite is a monzogranite with biotite hornblende and sphene its mineralogy and chemistry are characteristic of the san isabel batholith the lamprophyres may be related to mantle derived mafic liquids that were hypothesized to have melted lower crust to produce the san isabel batholith the lamprophyres may have migrated up around the margin of the batholith and mixed with late stage granite to form these composite dikes

effects of magma mingling in the granites of mount desert island maine textures and compositional relationships associated with dark colored fine grained enclaves in the cadillac mountain and somesville granites mount desert island maine preserve abundant evidence for contamination of host granitic magmas by enclave liquids fine grained enclaves which apparently represent chilled magmatic droplets have affected the composition and texture of the host granites by three possible mechanisms 1 crystallization of feldspar quartz hornblende pegmatite pods from fluids of enclave origin in the granite surrounding enclaves and the disaggregation of the pods and dispersion of crystals into the granite 2 ionic exchange between enclaves and granitic magmas 3 the generation around enclaves of rinds consisting of an inner alkali feldspar quartz zone and an outer zone of hornblende enriched granite coarse grained pegmatite pods that occur outside of enclaves may result from migration of a hydrous residual fluid evolved during enclave crystallization out of the enclave

crystallographic and geochemical properties of natural gas hydrates accumulated in the national gas hydrate program expedition 02 drilling sites in the krishna godavari basin off india abstract this study presents the crystallographic and geochemical properties of different types of pore space natural gas hydrate recovered by pressure core operations during the national gas hydrate program nghp expedition 02 at three study areas in the krishna godavari basin off eastern india the gas hydrate is structure i with hydration number n 6 1 6 2 formed predominantly from microbial methane and small amounts of heavier hydrocarbons up to c3 hydrate crystal lattice constants are nearly uniform regardless of sediment pore space size ethane concentration varies with clay content and to some extent depth and its measurement helps resolve the contributions of gases dissolved in pore water to hydrate formation we also assess the disturbance of the core through drilling using diffraction techniques and visual observation of hydrate bearing sediments

icp ms a powerful tool for high precision trace element analysis in earth sciences evidence from analysis of selected u s g s reference samples abstract inductively coupled plasma mass spectrometry icp ms is a powerful analytical technique with considerable application to geochemistry in this paper we demonstrate the power of icp ms as a tool in petrogenetic studies data for 28 elements in seven u s g s basalt and andesite reference samples agv 1 bcr 1 bhvo 1 bir 1 dnc 1 w 1 and w 2 are presented accuracy and precision standard deviation for 26 of these elements is either excellent a detailed description of the icp ms technique we have developed is given a simple hf hno 3 dissolution in screwtop teflon bombs was used for sample preparation icp ms instrumental sensitivity was measured by external solutions with surrogate calibration for 4 elements matrix correction was made by use of standard addition naturally occurring internal standards rb y ce and pb were used to correct for instrumental drift between sample and spiked sample measurements we report data for the elements li cs rb sr ba zr hf nb ta y sc u th pb and all 14 of the ree in addition the procedure acquired data for be mo w tl and bi many elements in this array are crucial for the evaluation of petrogenetic models and source tracing herein lies the real power of icp ms one technique one dissolution small sample size good limits of detection good to excellent accuracy and good precision for many geochemically important elements

characterization of natural gas hydrate recovered from pearl river mouth basin in south china sea abstract china carried out a drilling campaign in the eastern part of the pearl river mouth prm basin and successfully obtained natural gas hydrate samples in 2013 laboratory based studies for the characteristics of gas hydrate were carried out on one of the hydrate bearing sediment sample the gas hydrate sample shows nodular occurrence with host matrix predominantly composed of silty sand and clay on the basis of the raman spectroscopic and x ray diffraction results the gas hydrate demonstrates a typical structure i si with cage occupancy of methane is more than 99 5 in large cage and 91 4 in small cage respectively corresponding to a hydration numbers of 5 90 by thermodynamic calculation the molecular compositions of hydrate bound gas suggest that the guest molecules are predominantly methane 99 9 with trace amount of ethane 0 04 and propane 0 01 the isotopic analysis indicates that the methane of hydrate bound gas of the studied drilling well in prm basin is a typical microbial origin

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

seismic attenuation above 10 hz in southern california from coda waves recorded in the cajon pass borehole we estimate the attenuation around cajon pass southern california for frequencies above 10 hz and we find total q to exhibit only weak frequency dependence ranging from 800 at 10 hz to 1500 at 100 hz the intrinsic attenuation is approximately twice the level of the scattering attenuation measurements are made using earthquake seismograms recorded at 0 3 km depth using the multiple lapse time window method the results are not dependent on receiver depth and are consistent with previous estimates of q made from direct waves recorded at 2 5 km depth our q values are therefore thought to be representative of the seismogenic crust and the technique used is uncontaminated by the highly attenuating near surface at least above 10 hz we also calculate q from surface data between 1 and 10 hz and find a clear change in the frequency dependence of both intrinsic and scattering attenuation at 10 hz q exhibits strong frequency dependence below 10 hz 1 8 consistent with previous studies in active tectonic regions and only weak frequency dependence at higher frequencies 0 34 this change in behavior renders it unwise to extrapolate q measurements outside the frequency range from which they were derived for example in earthquake source studies possible factors responsible for the apparent change in frequency dependence of q are considered further work is required however to resolve the causes of this change

source parameters of small earthquakes recorded at 2 5 km depth cajon pass southern california implications for earthquake scaling a 2 5 km deep triaxial seismometer at cajon pass in southern california has recorded several hundred earthquakes ml4 0 occurring within the san andreas fault system at 2 5 km seismic background noise is below amplifier sensitivity and the 2 250 hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs compared with downhole recorded motion seismic amplitudes at the surface are amplified below 10 hz and severely attenuated above 30 hz we estimate that qs is at least 1000 for wave motion at 2 5 km and below and qp is over 2000 the range of source dimensions in the downhole recorded catalog is 10 m to 70 m ml 2 0 mo 108 nm to ml 2 7 mo 1013 nm the plot of log source radius vs log moment has a straight line trend compatible with earthquake scaling at constant stress drop inferred stress drops are scattered between 1 and 500 bars there is no evidence in the catalog for the proposed minimum source dimension at 100 m when the cajon pass borehole catalog containing some of the smallest recorded natural earthquakes is combined with 800 larger events from previous studies the moment radius trend suggests that natural earthquakes are self similar over a magnitude range m 2 to 8 we suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust

mount elbert gas hydrate stratigraphic test well alaska north slope overview of scientific and technical program abstract the mount elbert gas hydrate stratigraphic test well was drilled within the alaska north slope ans milne point unit mpu from february 3 to 19 2007 the well was conducted as part of a cooperative research agreement cra project co sponsored since 2001 by bp exploration alaska inc bpxa and the u s department of energy doe in collaboration with the u s geological survey usgs to help determine whether ans gas hydrate can become a technically and commercially viable gas resource early in the effort regional reservoir characterization and reservoir simulation modeling studies indicated that up to 0 34 trillion cubic meters tcm 12 trillion cubic feet tcf gas may be technically recoverable from 0 92 tcm 33 tcf gas in place within the eileen gas hydrate accumulation near industry infrastructure within ans mpu prudhoe bay unit pbu and kuparuk river unit kru areas to further constrain these estimates and to enable the selection of a test site for further data acquisition the usgs reprocessed and interpreted mpu 3d seismic data provided by bpxa to delineate 14 prospects containing significant highly saturated gas hydrate bearing sand reservoirs the mount elbert site was selected to drill a stratigraphic test well to acquire a full suite of wireline log core and formation pressure test data drilling results and data interpretation confirmed pre drill predictions and thus increased confidence in both the prospect interpretation methods and in the wider ans gas hydrate resource estimates the interpreted data from the mount elbert well provide insight into and reduce uncertainty of key gas hydrate bearing reservoir properties enable further refinement and validation of the numerical simulation of the production potential of both mpu and broader ans gas hydrate resources and help determine viability of potential field sites for future extended term production testing drilling and data acquisition operations demonstrated that gas hydrate scientific research programs can be safely effectively and efficiently conducted within ans infrastructure the program success resulted in a technical team recommendation to project management to drill and complete a long term production test within the area of existing ans infrastructure if approved by stakeholders this long term test would build on prior arctic research efforts to better constrain the potential gas rates and volumes that could be produced from gas hydrate bearing sand reservoirs

the magnitude frequency distribution of earthquakes recorded with deep seismometers at cajon pass southern california abstract the cumulative b value the slope of the gutenberg richter relationship between earthquake occurrence rate and magnitude is commonly found to be constant 1 network catalogues however reveal a decrease at small magnitudes b value is not just an artifact of catalogue incompleteness but that small earthquakes are really not as numerous as a constant b value extrapolated from larger events would predict in the cajon pass area southern california the b value of seismicity recorded by the local network scsn appears to decrease below about m l 1 6 in order to investigate whether this decrease is real or simply represents the network detection threshold we use seismicity recorded by the deep 1 5 and 2 5 km seismometers deployed in the cajon pass scientific drillhole between april 1992 and october 1994 the maximum amplitudes recorded downhole are compared to scsn magnitudes for events recorded by the network to determine the relationship between amplitude and m l as a function of hypocentral distance from the borehole magnitudes are then calculated for 1300 earthquakes which occurred within 40 km of the borehole magnitude frequency curves are calculated for those events within 18 km of the borehole and a constant b value is observed to m l 0 5

chemical and isotopic composition of the lower crust beneath the meguma lithotectonic zone nova scotia evidence from granulite facies xenoliths granulite facies xenoliths from an upper devonian lamprophyre dyke near tangier nova scotia provide new information about the lower crust in the meguma zone two mineralogically and chemically distinet groups of xenoliths occur both groups contain quartz feldspar biotite fe ti oxides sulfides in addition group a contains garnet graphite aluminosilicates spinel sapphirine hight al2o3 subgroups a1 and a2 or clinopyroxene sphene apatite high cao sub group a3 group b has highly variable proportions of orthopyroxene b1 clinopyroxene b2 and amphibole b3 trace element contents of the highly aluminous xenoliths compare closely with average to upper crustal model compositions and are similar in many aspects to other undepleted granulite facies rocks lowp t sedimentary assemblages of quartz chlorite clay minerals calcite albite or paragonite can account for the compositions of group a xenoliths within group b a high mgo mgo 13 wt subgroup with high transition metal contents and low mgo mgo 9 wt sub groups with higher lil large ion lithophile element contents exist although the rare earth and high field strength elements indicate a tholeiitic or low k calc alkaline chemistry the lil elements are as high as those from high k calc alkaline volcanic are rocks isotopically group a ranges from endt 2 56 to 0 80 and87sr 86srt 0 7046 to 0 7182 fort 370 ma for group b these values are 1 45 to 5 33 and 0 7028 to 0 7048 respectively model ages tchur are correspondingly low and are tightly constrained 544 52 ma these young ages contrast with the middle proterozoic nd model ages of the overlying meguma zone low grade flysch this time inverted stratigraphy appears to be the product of a tectonic break between a younger autochthonous tangier lower crust avalon and an older allochthonous meguma group upper crust

the characteristics of gas hydrates recovered from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract systematic analyses have been carried out on two gas hydrate bearing sediment core samples hypv4 which was preserved by ch 4 gas pressurization and hyln7 which was preserved in liquid nitrogen recovered from the bpxa doe usgs mount elbert stratigraphic test well gas hydrate in the studied core samples was found by observation to have developed in sediment pores and the distribution of hydrate saturation in the cores imply that gas hydrate had experienced stepwise dissociation before it was stabilized by either liquid nitrogen or pressurizing gas the gas hydrates were determined to be structure type i hydrate with hydration numbers of approximately 6 1 by instrumentation methods such as powder x ray diffraction raman spectroscopy and solid state 13 c nmr the hydrate gas composition was predominantly methane and isotopic analysis showed that the methane was of thermogenic origin mean 13 c 48 6 and d 248 for sample hyln7 isotopic analysis of methane from sample hypv4 revealed secondary hydrate formation from the pressurizing methane gas during storage

evaluation of failure modes and undrained shear strength by cone penetrometer for natural gas hydrate bearing pressure core sediment samples recovered from the krishna godavari basin offshore india abstract compressional wave velocity measurements and cone penetration tests were carried out for pressure cores recovered from the krishna godavari basin off the eastern coast of india using an instrumented pressure testing chamber constructed by the japanese national institute of advanced industrial science and technology for pressure cores with high gas hydrate saturations sh and exhibited high compressional wave velocities also display a high loading force that resulted in tensile failure a pressure core sample with low compressional wave velocities and low gas hydrate saturations led to a low loading force which resulted in radial shear the cone factor connecting the cone resistance and the undrained shear strength nk was estimated using cone penetration testing and the uniaxial compressional results we estimated its value as nk 45 by using a uniaxial compression loading speed of 0 01 min and a cone insertion loading speed of 0 25 mm s undrained shear strengths estimated from cone penetration results using nk 45 were assumed to be equal to the tensile strengths between hydrate hydrate and hydrate particle interface when sh is less than 50 and increases when sh is more than 50 assuming that gas hydrate morphology was matrix supporting

physical properties of sediment from the mount elbert gas hydrate stratigraphic test well alaska north slope this study characterizes cored and logged sedimentary strata from the february 2007 bp exploration alaska department of energy u s geological survey bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope ans the physical properties program analyzed core samples recovered from the well and in conjunction with downhole geophysical logs produced an extensive dataset including grain size water content porosity grain density bulk density permeability x ray diffraction xrd mineralogy nuclear magnetic resonance nmr and petrography this study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate gas hydrate gh occurs in three unconsolidated coarse silt to fine sand intervals within the paleocene and eocene beds of the sagavanirktok formation unit d gh 614 4 m 627 9 m unit c gh1 649 8 m 660 8 m and unit c gh2 663 2 m 666 3 m these intervals are overlain by fine to coarse silt intervals with greater clay content a deeper interval unit b is similar lithologically to the gas hydrate bearing strata however it is water saturated and contains no hydrate in this system it appears that high sediment permeability k is critical to the formation of concentrated hydrate deposits intervals d gh and c gh1 have average plug intrinsic permeability to nitrogen values of 1700 md and 675 md respectively these values are in strong contrast with those of the overlying gas hydrate free sediments which have k values of 5 7 md and 49 md respectively and thus would have provided effective seals to trap free gas the relation between permeability and porosity critically influences the occurrence of gh for example an average increase of 4 in porosity increases permeability by an order of magnitude but the presence of a second fluid e g methane from dissociating gas hydrate in the reservoir reduces permeability by more than an order of magnitude published by elsevier ltd

the port mouton shear zone intersection of a regional fault with a crystallizing granitoid pluton abstract the peraluminous tonalite monzogranite port mouton pluton is a petrological geochemical structural and geochronological anomaly among the many late devonian granitoid intrusions of the meguma lithotectonic zone of southern nova scotia the most remarkable structural feature of this pluton is a 4 km wide zone of strongly foliated 040 subvertical monzogranites culminating in a narrow 10 30 m straight zone of compositionally banded rocks that extends for at least 3 km along strike the banded monzogranites consist of alternating melanocratic and leucocratic compositions that are complementary to the overall composition of that part of the pluton suggesting an origin by mineral melt and mineral mineral sorting biotite and feldspar are strongly foliated in the plane of the compositional bands these compositional variations and foliations originated by a process of segregation flow during shearing of the main magma with a crystallinity of 55 75 subsequent minor brittle fracturing of feldspars twinning of microcline development of blocky sub grains in quartz and kinking of micas demonstrate overprinting by a high temperature deformation straddling the monzogranite solidus small folds and late sigmoidal dykes indicate dextral movement on the shear zone this port mouton shear zone pmsz is approximately co linear with the only outcrops of late devonian mafic intrusions in the area two of which are syn plutonic with well developed mingling textures in the marginal tonalite of the port mouton pluton also closely co linear with the mafic intrusions are a granitoid dyke that extends well beyond the outer contact of the port mouton pluton a swarm of large aligned angular xenolithic slabs a zone of thin wispy schlieren banding a large be bearing pegmatite and a breccia pipe with abundant garnetiferous metapelitic xenoliths in various ways the shear zone may control all of these features the port mouton shear zone is parallel to many other ne trending faults and shear zones in the northern appalachians probably related to the docking of the meguma zone along the cobequid chedabucto fault system

enclaves from the a type granite of the megantic complex white mountain magma series clues to granite magmagenesis the subsolvus biotite hornblende granite at megantic contains mafic to leucocratic enclaves the groundmass of leucocratic enclaves is microgranitic that of mafic enclaves is meladioritic apatite is commonly acicular in the enclaves suggesting quenching of mafic magmas commingled with the granitic host mafic enclaves contain mafic clots hornblende cores biotite rims some with relic cores of vial cr rich diopsidic augite similar to phenocrysts in associated basaltic dykes the clots are interpreted to be pseudomorphs after mafic phenocrysts the enclaves also contain granitic microxenoliths xenocrysts of quartz with hornblende reaction rims partially resorbed oligoclase and perthite megacrysts and biotite xenocrysts the xenocrysts record hybridization between a mafic enclave magma and a granitic magma and or rock enclaves define mixing lines on many variation diagrams however rb sr ba zr nb y ree zn pb and f do not fit this pattern and appear to have been redistributed by residual granitic melts or exsolved volatiles the data suggest that the granite is anatectic heat being provided by crystallization of associated basalts mixing calculations suggest that as little as 5 hybridization with basalt or hawaiite can account for the sr isotopic heterogeneity of the granites

generation of porphyritic and equigranular mafic enclaves during magma recharge events at unzen volcano japan mafic to intermediate enclaves are evenly distributed throughout the dacitic 1991 1995 lava sequence of unzen volcano japan representing hundreds of mafic recharge events over the life of the volcano this study documents the morphological textural chemical and petrological characteristics of the enclaves and coexisting silicic host lavas the eruptive products described in this study appear to be general products of magma mingling as the same textural types are seen at many other volcanoes two types of magmatic enclaves referred to as porphyritic and equigranular are easily distinguished texturally porphyritic enclaves display a wide range in composition from basalt to andesite are glass rich spherical and porphyritic and contain large resorbed plagioclase phenocrysts in a matrix of acicular crystals and glass equigranular enclaves are andesitic non porphyritic and consist of tabular medium grained microphenocrysts in a matrix glass that is in equilibrium with the host dacite magma porphyritic enclaves are produced when intruding basaltic magma engulfs melt and phenocrysts of resident silicic magma at their mutual interface equigranular enclaves are a product of a more prolonged mixing and gradual crystallization at a slower cooling rate within the interior of the mafic intrusion

the characteristics of gas hydrates recovered from shenhu area in the south china sea abstract for the first time gas hydrate samples were recovered in the south china sea during a drilling campaign implemented in shenhu area in june 2007 laboratory based studies for the characteristics of gas hydrate were carried out on two hydrate bearing sediment samples observations found that gas hydrates occurred in the pores of fine grained sediments the hydrates were structure i based on the raman spectroscopic results the guest gas molecules in hydrate cages were predominantly methane 99 3 and trace amount of ethane 0 4 and propane 0 04 as determined with the method of gas chromatography as estimated from the intensities of raman peaks the cage occupancy rates were more than 99 in large cage and 86 in small cage respectively corresponding to a hydration number of 5 9

the petrology and geochemistry of the handkerchief mesa mixed magma complex san juan mountains colorado the handkerchief mesa mixed magma complex is one of several late cenozoic volcanic complexes in the southeastern san juan mountains characterized by mingling and limited mixing of basalt and rhyodacite stratigraphy in the dissected vent complex at handkerchief mesa records three phases of volcanism the first and third displaying evidence for coeruption of mafic and silicic magmas phases 1 and 2 erupted silicic pyroclastics and basaltic lava flows respectively phase 3 eruptions were dominated by rhyodacite lava flows rhyodacite dikes and abundant mingled and mixed hybrid lavas pre and syneruptive basalt rhyodacite mixing of phase 3 eruptions is shown by 1 inclusions of quenched basalt in rhyodacite 2 partially disaggregated basalt inclusions in mixed hybrids and rhyodacites 3 interfingering lenses of mixed hybrid lavas and rhyodacite whole rock major and trace element analyses support a two component mixing model whereby intermediate hybrids are produced by mixing of basalt and rhyodacite up to 30 basalt 70 rhyodacite disequilibrium phenocryst textures and mineral compositions are consistent with multistage mixing culminating in an eruptive mixing event protracted mixing along a boundary zone at the base of a rhyodacite magma chamber may be responsible for stabilizing fe rich olivine phenocrysts in some hybrids basalt rhyodacite mixing is inhibited by rapid crystallization in the basalt shortly after inclusion within the lower temperature melt the degree to which mechanical dispersion and blending ensues is a critical function of the initial temperature contrast ti between the two magmas thermal models simulating the conductive cooling histories for basalt spheres in rhyodacite reservoirs suggest that at large ti s 200 rapid cooling of the inclusion leads to disequilibrium crystallization with concomitant depression of equilibrium solidi grain boundary wetting by residual liquids and limited disaggregation of the inclusion imposed by movement of the host for small ti s 100 temperatures within the inclusion can be maintained above the solidus for prolonged time periods enhancing the possibility of producing homogeneous mixed hybrids through mechanical blending and diffusion both mechanisms operated at handkerchief mesa and contributed to the range of observed textures and compositions

a summary of attenuation measurements from borehole recordings of earthquakes the 10 hz transition problem earthquake seismograms recorded by instruments in deep boreholes have low levels of background noise and wide signal bandwidth they have been used to extend our knowledge of crustal attenuation both in the near surface and at seismogenic depths site effects are of major importance to seismic hazard estimation and the comparison of surface shallow and deep recordings allows direct determination of the attenuation in the near surface all studies to date have found that q is very low in the near surface 10 in the upper 100 m and increases rapidly with depth unlike site amplification attenuation at shallow depths exhibits little dependence on rock type these observations are consistent with the opening of fractures under decreasing lithostatic pressure being the principal cause of the severe near surface attenuation seismograms recorded in deep boreholes are relatively unaffected by near surface effects and thus can be used to measure crustal attenuation to higher frequencies 100 hz than surface recordings studies using both direct and coda waves recorded at over 2 km depth find q to be high 1000 at seismogenic depths in california increasing only weakly with frequency between 10 and 100 hz intrinsic attenuation appears to be the dominant mechanism these observations contrast with those of the rapidly increasing q with frequency determined from surface studies in the frequency range 1 to 10 hz further work is necessary to constrain the factors responsible for this apparent change in the frequency dependence of q but it is clearly unwise to extrapolate q estimates made below about 10 hz to higher frequencies

silicic magma chambers as traps for basaltic magmas the cadillac mountain intrusive complex mount desert island maine the cadillac mountain intrusive complex located on mount desert island maine provides a superb record of episodic invasion of a floored silicic magma chamber by many pulses of basaltic magma the complex consists of three units the cadillac mountain granite cmg the somesville granite sg and gabbro diorite g d basaltic magmas were emplaced before during and after the emplacement and crystallization of the granitic plutons and the chambers of silicic magma acted as traps for basaltic magma basaltic magma emplaced into the surrounding country rocks crystallized as homogeneous diabase and gabbro while basaltic magma emplaced within the perimeter of the granite displays abundant evidence for commingling with silicic magma the g d unit about 1 5 km thick consists of interlayered gabbroic dioritic and granitic rocks although thin 1 m thick gabbroic layers in the g d unit are typically chilled on all margins thicker layers of gabbro commonly form the lower parts of macrorhythmic units

reliable and economical high temperature deep borehole seismic recording abstract recording earthquakes with borehole seismometers has become increasingly popular in recent years as the advantages in noise reduction and also the distorting effects of near surface rocks especially sediments have become well known borehole recording can be extremely complex involving active sensors special cables and downhole electronics such installations however are often not very reliable at the high temperatures reached in active tectonic areas at depths of 1 km and greater here we describe a simple and reliable system for 3 component recording of local earthquakes at single and multiple depths greater than 1 5 km and temperatures up to 120 c our system was designed and developed for experiments in the cajon pass scientific drillhole of southern california the borehole packages are made of titanium with spring loaded clamping allowing easy retrieval standard seven conductor oil well logging cables are used together with a specially designed cablehead the data recorded have been used for investigating earthquake source scaling attenuation in the mid crust and also near surface site effects

insights into magmatic evolution and recharge history in capraia volcano italy from chemical and isotopic zoning in plagioclase phenocrysts plagioclase phenocrysts in dacites from the high k calc alkaline capraia volcano were investigated for major trace element and sr isotope variations in order to gain better insight into the proposed open system behaviour of the volcano repeated dissolution zones in plagioclases from the early erupted monte castello mc and later monte rucitello mr dacitic units are associated with a sharp increase in an content and variation in isotopic compositions 87sr 86sr 0 70872 0 71004 which argue for repeated magma mixing in particular petrographic and mineralogical evidence suggest that recharge with hot basaltic magma occurred repeatedly during the lifetime of the capraia volcanic system we attempted to correlate shared crystallization and resorption histories using chemical mol an fe and sr isotopic zoning in plagioclase in this correlation framework the observed mismatch between chemical and isotopic data in some phenocrysts is interpreted to reflect either growth of phenocrysts in a separate magma chamber or compositional zoning within a single magma chamber a minor role of crustal contamination is inferred instead the intra crystal variations in isotopic composition in plagioclase reflect the existence of distinct components that may have thoroughly mixed at the end of the mc plagioclase growth history the dominant radiogenic component is similar to lamproites occurring in tuscany recharge with this component occurred throughout the genesis of the mr dacites but was restricted to the early growth history of the mc dacites the mr plagioclases are inferred to have crystallized from separate more differentiated batches of magma that were likely to have evolved at the top of a zoned magma reservoir decrease in the an content after most dissolution zones in all phenocrysts and low temperature estimates from zircon saturation thermometry 800 c also emphasize the importance of crystal fractionation during the evolution of the volcano in agreement with the occurrence of a significant amount of rhyolitic material thus it is inferred that a rather large magma chamber may have existed during the first cycle of eruptive activity

simultaneous inversion for q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock an inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite assuming a 2 source model the inversion fits the p wave spectra of microearthquake waveforms to determine individual values of corner frequency and low frequency spectral amplitude for each event and one average frequency independent q for all source receiver paths we also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra the waveforms analyzed were recorded by a borehole seismometer the p wave q was found to be 1070 for q values as low as 600 and as high as 3000 the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a q of 1070 average stress drop was 3 7 bars seismic moments obtained from spectra ranged from 1013 to 1018 dyne cm the low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock stress drops were found to be larger near the edges of the seismic zone in regions that had not been seismically active during previous injections the seismic moments determined from spectra were used to obtain a coda length to moment relation then moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal to noise ratio the constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions the slope is so high that the seismic energy release is dominated by the large number of small events in the absence of information about the number of events smaller than we studied we cannot estimate the total seismic energy released by the hydraulic injection

petrochemistry tectonic history and sr nd systematics of the liscomb complex meguma lithotectonic zone nova scotia the liscomb complex area ca 240 km2 located in the meguma lithotectonic zone of the canadian appalachians consists of three main lithological components high grade gneisses mafic plutons and peraluminous granitoid bodies field relations and 40ar 39ar dating 369 377 ma embracing all three lithological groups show that the complex is post acadian the gneisses occur as a domal uplift and represent a mixed volcano sedimentary package that is structurally metamorphically and chemically distinct from the surrounding low grade metawackes and metapelites of the meguma group the mafic intrusions quartz gabbro to quartz diorite have major and trace element compositions e g ti zr y nb zr y th yb ta yb rare earth elements typical of within plate or volcanic arc materials the peraluminous granitoid rocks range from two mica granodiorites to leucomonzogranites and are mineralogically and chemically very similar to granitic rocks elsewhere in the meguma zone neodymium and strontium isotopic

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

phosphorus in s type magmas the p2o5 content of feldspars from peraluminous granites pegmatites and rhyolites

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

field evidence of magma mixing from microgranular enclaves hosted in palaeoproterozoic malanjkhand granitoids central india abstract the malanjkhand granitoids mg pluton about 1500 sq km occurs in the balaghat district of madhya pradesh the mg 2400 ma represent an episode of palaeoproterozoic felsic magmatism in central india and hosts potential cu mo au deposits the enclaves hosted in mg can be broadly classified into two categories microgranular enclaves dark coloured fine grained magmatic and xenoliths of country rocks the microgranular enclaves me may be rounded ellipsoidal discoid elongated lenticular or tabular and their size commonly reaches up to 2 metres across the me have sharp and in places diffuse contacts with their host granitoids the shape and size of me indicate contemporaneous flow and mingling of partly crystalline felsic mafic magmas some me exhibit dark crenulated margins giving them a pillow like form that has been attributed to undercooling of a me magma as globules intruded into a granitoid magma the presence of corroded felsic and mafic minerals xenocrysts in me is interpreted as the result of mechanical transfer during the mafic felsic magma interaction and mixing event mafic minerals biotite rim the quartz xenocrysts giving rise to ocellar texture which exhibit signatures of resorption under hybrid enclave magma conditions all these features suggest an origin for the calc alkaline intermediate granitoid magma in malanjkhand involving a magma mixing process

magmatic inclusions in rhyolites of the spor mountain formation western utah limitations on compositional inferences from inclusions in granitic rocks inclusions of quenched mafic magma occur in a 21 ma rhyolite lava and precursory non welded tuff that form the spor mountain formation in west central utah the mafic inclusions are not lithic inclusions no comparable volcanic unit was present at the surface when the spor mountain formation erupted mineral and bulk compositions preclude liquid immiscibility the mafic inclusions show clear morphologic and textural effects of magma mingling shortly before eruption of the rhyolite globular inclusions from both units are vesicular phenocryst poor plagioclase sanidine clinopyroxene orthopyroxene magnetite ilmenite latites and trachytes with quench temperatures of about 1000 c although overlapping in sio2 tio2 zr and hf concentrations inclusions from the underlying tuff lack negative eu anomalies and are enriched in p2o5 k2o al2o3 sr pb cr and ni whereas those hosted in the overlying lava have small negative eu anomalies and two fold enrichments in fe2o3 mno hree y ta th rb and cs the most reasonable explanation for the differences between the two sets of inclusions lies in selective chemical exchange between the rhyolite lava and the mafic inclusions after eruption limited mechanical mixing occurred after the inclusions solidified and became chemically modified the textures of the inclusions in the lavas and the elements selectively mobilized in the inclusions imply that vapor phase transport occurred in this low pressure volcanic environment if such substantial variations in inclusion compositions can arise during what must have been a short period of time before chemical reactions were halted by rapid cooling it seems unlikely that the compositions of mafic inclusions formed by magma mingling in slowly cooled granites preserve their original compositions mineralogies or information about their ultimate sources using the compositions of such chemically modified inclusions as end members for mixing calculations may lead to erroneous results regarding the significance of magma mixing in plutonic rocks

effects of volatiles on mixing in calc alkaline magma systems the intimate mixing between different magmas of disparate densities characteristic of some calc alkaline magma systems is explained by a new mechanism involving the emplacement of a layer of wet undersaturated mafic magma at the base of a magma chamber containing more differentiated magma turbulent transfer of heat between the mafic magma and the overlying magma leads to crystallization and exsolution of volatiles in the lower layer for an initial water content of a few per cent the bulk density of the mafic magma can become equal to that of the overlying magma causing overturning and intimate mixing of the magmas the mechanism is most probable in the low pressure environment of a high level magma chamber

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

petrogenesis of early silurian granitoids in the longshoushan area and their implications for the extensional environment of the north qilian orogenic belt china abstract analyses of the zircon u pb age mineralogical chemistry and whole rock geochemistry of the jiling pluton along the southern margin of the alxa block were conducted the results of these analyses will provide crucial information for investigations of paleozoic crust mantle interactions in the north qilian orogenic belt nqob and explorations of the transition age from a compressional to extensional environment during the collision between the alxa block and the qilian qaidam block the zircon dating results reveal that the jiling pluton is composed of early silurian granitoids 435 442 ma with contemporaneous mafic microgranular enclaves mmes most granitoids contain amphibole and titanite and have a cnk values

examination of core samples from the mount elbert gas hydrate stratigraphic test well alaska north slope effects of retrieval and preservation abstract collecting and preserving undamaged core samples containing gas hydrates from depth is difficult because of the pressure and temperature changes encountered upon retrieval hydrate bearing core samples were collected at the bpxa doe usgs mount elbert gas hydrate stratigraphic test well in february 2007 coring was performed while using a custom oil based drilling mud and the cores were retrieved by a wireline the samples were characterized and subsampled at the surface under ambient winter arctic conditions samples thought to be hydrate bearing were preserved either by immersion in liquid nitrogen ln or by storage under methane pressure at ambient arctic conditions and later depressurized and immersed in ln eleven core samples from hydrate bearing zones were scanned using x ray computed tomography to examine core structure and homogeneity features observed include radial fractures spalling type fractures and reduced density near the periphery these features were induced during sample collection handling and preservation isotopic analysis of the methane from hydrate in an initially ln preserved core and a pressure preserved core indicate that secondary hydrate formation occurred throughout the pressurized core whereas none occurred in the ln preserved core however no hydrate was found near the periphery of the ln preserved core to replicate some aspects of the preservation methods natural and laboratory made saturated porous media samples were frozen in a variety of ways with radial fractures observed in some ln frozen sands and needle like ice crystals forming in slowly frozen clay rich sediments suggestions for hydrate bearing core preservation are presented

instrumented pressure testing chamber for characterizing sediment cores recovered at in situ hydrostatic pressure marine sediments retrieved with pressure coring systems such as those used by the integrated ocean drilling program maintain samples at in situ hydrostatic pressure throughout recovery such pressure cores are particularly important for the study of gas hydrate bearing sediments which must be maintained within the gas hydrate stability field during shipboard core characterization until now there has been no device capable of directly measuring a suite of physical properties on sediments contained in pressure cores without first depressurizing them this study describes the design construction and deployment of the instrumented pressure testing chamber iptc which was first used to measure the physical properties of pressure cores recovered 1530 m below the sea surface during 2005 drilling in the gulf of mexico the iptc permits drilling through the plastic liner while the core is under pressure and the sequential measurement of p and s wave velocities undrained strength and electrical conductivity preliminary results indicate that the seismic velocities measured on a pressure core with the iptc are more representative of in situ seismic velocities at comparable depths than are velocities measured on conventional cores from these same depths the flexibility of the iptc design allows future modifications to account for restoration of effective not just hydrostatic stress the addition of new types of measurements sampling of pore fluids and sediments under pressure and use of the device as a laboratory reactor for gas hydrates studies

petrogenesis and regional tectonic significance of late devonian mafic intrusions in the meguma zone nova scotia late devonian 377 368 ma 40ar 39ar 376 ma u pb mafic intrusions in the meguma zone crop out as dykes plugs and synplutonic bodies of gabbro diorite or lamprophyre all of the intrusions have similar lithologie characteristics and hydrous ferromagnesian mineral assemblages and they appear to represent a genetically related series of mafic bodies with similar petrogenetic histories in the crust of the meguma zone the intrusions show wide chemical variation of sio2 45 7 65 7 wt al2o3 8 9 26 5 wt mgo 2 8 26 5 wt cao 1 2 11 2 wt and k2o 0 1 4 4 wt and they have calc alkaline high k calc alkaline and shoshonitic characteristics large ion lithophile elements lile are present at variable but high concentrations e g ba 62 1920 ppm sr 176 2567 ppm relative to most high field strength element hfse abundances e g y 10 37 ppm zr 8 421 ppm and light rare earth elements lree have much higher concentrations than heavy rare earth elements hree la lu 24 3

40ar 39ar dating of hydrothermal biotite from high grade gold ore tangier gold deposit nova scotia further evidence for 370 ma gold metallogeny in the meguma terrane a hydrothermal biotite carbonate alteration zone adjacent to a high grade multi ounce gold vein in the tangier gold deposit meguma terrane nova scotia has given an 40 ar 39 ar plateau age of 374 ma the alteration halo is part of a vein package in the hinge zone of the tangier anticline which contains abundant auriferous quartz veins formed during flexural slip folding during a late stage reactivation of the regional fold belt the 374 ma age is similar to 40 ar 39 ar ages determined for hydrothermal vein minerals at seven other meguma gold districts thereby suggesting a terrane wide metallogenic event a similar age of vein formation and by inference gold mineralization and granite emplacement across the meguma terrane suggest that the cospatial and cotemporal nature of the two geological events may be related an integrated model including anatexis and devolitization of the lower crust possibly as a consequence of overriding a mantle plume in concert with late stage reactivation of the fold belt owing to continued transpression along a terrane bounding fault is proposed

physical property changes in hydrate bearing sediment due to depressurization and subsequent repressurization physical property changes in hydrate bearing sediment due to depressurization and subsequent repressurization w f waite 1 t j kneafsey 2 w j winters 1 d h mason 1 u s geological survey 384 woods hole road woods hole ma 02543 usa lawrence berkeley national laboratory 1 cyclotron rd ms 90r1116 berkeley ca 94720 usa