airglow observations and modeling of f region depletion zonal velocities over christmas island 1 we report image measurements of plasma depletions in the equatorial f region ionosphere over christmas island 2 1 n 157 4 w dip latitude 2 8 n in the central pacific ocean the observations were made during the equinox period september october 1995 using a utah state university ccd imaging system filtered to observe thermospheric o i 630 0 nm airglow emissions centered at 280 km altitude well defined magnetic field aligned depletions were observed on 18 nights during the campaign including strong postmidnight fossilized structures enabling detailed measurements of their morphology and dynamics the number of depletions was influenced by their initial onset times and their persistence the separations between adjacent depletions ranged from 150 to 250 km in good agreement with prior observations from other sites however measurements of their eastward zonal drift speeds indicated normal behavior peaking around 90 100 m s prior to local midnight with exceptionally high velocities 80 m s during the postmidnight period that persisted until dawn these results differ markedly from optical measurements at similar equatorial latitudes but at different longitude sectors suggesting that the zonal drift velocities can have a significant longitudinal dependence model drift velocities calculated using a simple electric field model with winds defined by the horizontal wind model hwm 07 produced an eastward drift throughout the night but their postmidnight magnitudes were much smaller than observed using a modified hwm 07 wind field a basic nighttime trend similar to the christmas island trend was successfully obtained

exploration for gas hydrates in the deepwater northern gulf of mexico part i a seismic approach based on geologic model inversion and rock physics principles this article presents the results of applying a five step process for using high quality seismic data to locate marine gas hydrates the process involved 1 reprocessing of seismic data for higher resolution 2 detailed stratigraphic evaluation and interpretation to locate possible hydrate bearing zones 3 seismic attribute analysis to further delineate these zones 4 seismic inversion to obtain appropriate elastic parameters of these zones in 3d and 5 quantitative estimation of gas hydrate saturation from seismic data using inversion and rock physics principles we used seismic data from keathley canyon 151 and atwater valley 14 in the northern gulf of mexico although careful analysis did indicate the presence of a bottom simulating reflector bsr our study mainly relied on a host of other seismic attributes e g gas chimneys seismically transparent zones other features associated with the petroleum system to characterize the occurrence of gas hydrates in these areas we tested and verified a viable rock model for hydrate bearing sediments using data from the mallik mckenzie delta canada and blake ridge odp leg 164 southeast u s atlantic margin wells and modified it for application in the current area we then used this model to estimate gas hydrate saturation in the host sediments of the northern gulf of mexico focus areas using estimates of p wave and s wave velocities from inversion of reflection seismic data in this paper we present the gas hydrate saturations predicted from the seismic processing methodology prior to 2005 drilling in the focus areas in frontier areas where no well data are available and lithologic heterogeneities are poorly understood implementing a seismic based technique like the one described here to identify potential gas hydrates can provide valuable pre drill information for site selection and for planning future characterization studies of gas hydrate bearing sediments

characteristics of equatorial plasma bubble zonal drift velocity and tilt based on hong kong gps cors network from 2001 to 2012 hong kong 22 3 n 114 2 e dip 30 5 n geomagnetic 15 7 n 173 4 w declination 2 7 w is a low latitude area and the hong kong continuously operating reference station cors network has been developed and maintained by lands department of hong kong government since 2001 based on the collected gps observations of a whole solar cycle from 2001 to 2012 a method is proposed to estimate the zonal drift velocity as well as the tilt of the observed plasma bubbles and the estimated results are statistically analyzed it is found that although the plasma bubbles are basically vertical within the equatorial plane the tilt can be as big as more than 60 eastward or westward sometimes and the tilt and the zonal drift velocity are correlated when the velocity is large the tilt is also large generally another finding is that large velocity and tilt generally occur in spring and autumn and in solar active years

archaeal lipid biomarkers and isotopic evidence of anaerobic methane oxidation associated with gas hydrates in the gulf of mexico abstract anaerobic oxidation of methane aom occurs in the gulf of mexico gas hydrate systems here we show lipid biomarker and isotopic evidence that archaea are involved in aom the estimated abundance of total archaeal lipids ranges from 44 8 to 60 4 g g dry sediment in hydrate bearing samples but is below detection limit in the hydrate free sample the 13c values of archaeal lipids range from 69 to 99 in hydrate bearing samples these results suggest that biomass of archaea is significantly enhanced through aom at the gas hydrate deposits these data also support a currently acknowledged mechanism of aom mediated by a consortium of sulfate reducing bacteria and archaea observed in a variety of methane rich marine settings anaerobic oxidation of oil hydrocarbons also occurs in the gulf of mexico gas hydrate systems as shown by degradation of n alkanes c15 in the anoxic sediments these processes convert hydrocarbons to carbon dioxide and increase pore water alkalinity which promote the precipitation of enormous volumes of authigenic carbonate rock depleted in 13c this long term geologic sequestration of carbon may affect models of global climate change

nature and distribution of deep crustal reservoirs in the southwestern part of the baltic shield evidence from nd sr and pb isotope data on late sveconorwegian granites late sveconorwegian postorogenic granites c 1 0 0 93 ga make up a voluminous and widespread suite of intrusions across south norway from radiogenic isotope data three groups of late sveconorwegian granites can be distinguished 1 granite with more than 150 ppm sr 87 rb 86 sr 87 sr 86 sr 0 93 ga nd 87 rb 86 sr 5 87 sr 86 sr 0 93 ga 0 710 and e nd 87 sr 86 sr 0 93 ga nd 0 granite plutons belonging to group 1 normal sr concentration granite occur all over south norway and include the largest batholiths ostfold fla herefoss granite plutons of group 2 low sr concentration granites are restricted to north central telemark rjukan rift and are associated with c 1 5 ga rjukan group rhyolite group 3 is represented by one intrusion only but still suggests input of mantle derived magma or the presence of young mantle derived rocks in the deep crust in the region at c 0 93 ga the group 1 granites are similar in sr and nd characteristics to some of the older 1 05 ga sveconorwegian granitic intrusions augen gneisses in the region in terms of radiogenic isotope systematics but pb isotopes suggest that the magmas did not form by simple remelting of augen gneiss the nd sr and pb isotopic systematics of the late sveconorwegian granites indicate mixing between a depleted mantle derived component and two or more major components with an extended crustal history one of the crustal end members is present throughout south norway and has an isotopic signature similar to older granitic rocks of the trans scandinavian igneous belt tib the other crustal end member is indistinguishable from rjukan group rhyolites and slightly younger intrusions associated with these and is restricted to areas within the mid proterozoic rjukan rift the available data suggest that the deep continental crust of south norway both east and west of the permian oslo rift is an integral part of the baltic shield with a common history back to 1 7 1 9 ga that is to the end of the svecofennian orogeny and the tib magmatism

low latitude zonal and vertical ion drifts seen by de 2 horizontal and vertical ion drift data from the de 2 spacecraft have been used to determine average zonal and vertical plasma flow electric field characteristics in the plus minus 26 degree dip latitude region during a time of high solar activity the data base consists of over 800 equatorial passes horizontal ion drift data were projected along magnetic field lines to the magnetic equator using a dipole model to yield their apex height dependence the average data local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time slt with a maximum westward velocity of 80 m s in the early afternoon there is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m s a secondary nighttime maximum exists a 0430 slt preceeding the reversal to westward flow this profile is in good agreement with jicamarca radar measurements made under similar solar maximum conditions harmonic analysis indicates a net superrotation which is strongest at lower apex altitudes the diurnal term is dominant but higher order terms through th quatradiurnal are significant vertical ion data taken at low plus minus 5 degree dip latitudes while possessing greatermore scatter generally agree wtih jicamarca values copyright american geophysical union 1989 less

influence of the carbon isotopic composition of methane and the proportion of methane derived bicarbonate on the 13c 12c ratio of dissolved inorganic carbon at the sulfate methane transition in the joetsu basin area eastern margin of the sea of japan abstract the geochemistry of interstitial waters associated with active marine hydrocarbon seepage provides insight into the source and ongoing dynamics of such systems in this investigation of interstitial waters obtained from sediments in a gas hydrate region of the sea of japan we compare carbon isotopic composition 13c of dissolved inorganic carbon dic at the sulfate methane transition smt with 13c of deeply sourced methane as inferred from the deepest samples obtained beneath the smt based on this comparison we distinguish two causes for lower values of 13cdic at the smt in group a 17 piston cores 13cdic values at the smt 30 0 to 9 7 vpdb correlate positively with 13c of deep methane 90 7 to 61 4 vpdb lowering of these 13cdic values was independent of methane flux which controls the generation rate of methane derived bicarbonate by anaerobic oxidation of methane owing to the influence of a high alkalinity flux from depth in the group b core samples 13cdic at the smt 41 6 to 14 2 vpdb relative to 13c of deep methane 68 2 to 40 5 vpdb is lower than that of group a implying a greater contribution of methane derived hco 3 with only two exceptions the group b core sites were located at areas of active gas seepage the admixture of methane from migrating methane bubbles with deep methane in the interstitial waters of sediments has the potential to significantly increase the overall methane flux at gas seep sites although the admixture may reflect higher 13c values of deep methane the increase in methane flux results in a higher proportion of methane derived hco 3 and lower 13cdic at the smt recovery of two group b cores adjacent a dormant pockmark suggests that the depression with seismic blanking beneath it similar to that of the gas seep sites is a previous gas seepage site

images of transequatorial f region bubbles in 630 and 777 nm emissions compared with satellite measurements images of transequatorial f region bubbles were obtained from magnetic field aligned airglow observations from haleakala hawaii for 9 nights in august 1988 bubbles of scale size 10 100 km were recorded with an intensified ccd detector attached to a filter wheel imager and sequential images were made in the plasma recombination emissions at 630 nm and 777 nm and in the background emissions the observations also yield information on the large scale structure of the ionosphere in the northern appleton anomaly region particularly on the latitude variations of plasma concentration and layer height measurements from the dmsp f8 and f9 satellites extend this to include the southern anomaly region the dmsp satellites were near 830 km in altitude and in near polar orbits at about 1800 and 2120 hours local time a comparison of the bubble images and the dmsp results with plasma concentration and drift velocities obtained from the san marco satellite allows us to put the measurements along the san marco track into the larger ionospheric context one to one correspondence is found between the presence of the optical bubbles and the presence of plasma depletions measured from the san marco satellite allowing identification on consecutive orbits of the same depletions this extends for up to 5 hours of the satellite measured information for individual depletions that is their vertical and horizontal drift velocities and the plasma concentration variations the images show the shapes of the depletions in apex height and longitude and their evolution horizontal drift velocities of the bubbles were determined by a correlation analysis bubble occurrence is compared with day to day changes in the equatorial fountain electric fields and transequatorial asymmetries caused by neutral winds and with measurements of radar backscatter from centimeter scale irregularities associated with bubbles in the kwajalein sector the development of 10 100 km scale size bubbles at a given time and location is clearly a consequence of the presence of even larger wavelike corrugations in the f layer provided there is also at least a moderately strong equatorial fountain

preliminary assessment of resources and economic potential of individual gas hydrate accumulations in the gulf of mexico continental slope abstract some global estimates suggest that gas hydrates represent the largest reservoir of fossil fuel however only a few studies of the resource and economic potential of individual gas hydrate accumulations exist here we estimate the volume of hydrate bound gas at gc green canyon blocks 184 185 gc 234 235 gb garden banks 388 mc mississippi canyon 798 842 gc 204 mc 852 853 and at atwater valley 425 426 sites in the gulf of mexico at water depths 500 2000 m the structural accumulations may contain from 4 7 10 8 to 1 3 10 11 m 3 of gas at standard temperature and pressure the resources in individual gas hydrate accumulations are comparable by volume with the reserves in very small to major conventional gas fields various geologic technologic and economic factors affect the economic potential of studied accumulations the mc 852 853 appears to be characterized by the most favorable combination of these factors and thus is suggested to have the highest economic potential the economic potential of gas hydrate accumulations at gc 204 gb 388 and at 425 426 sites is ranked as average gas hydrate accumulations at gc 234 235 gc 184 185 and mc 798 842 sites contain only small volumes of hydrate bound gas and likely have no economic potential future gas hydrate research should focus on the detailed study of large structural gas hydrate accumulations from which gas may be profitably recovered e g the mc 852 853 site

the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

sedimentary recycling in arc magmas geochemical and u pb hf o constraints on the mesoproterozoic suldal arc sw norway the hardangervidda rogaland block within southwest norway is host to 1 52 to 1 48 ga continental building and variable reworking during the 1 1 to 0 9 ga sveconorwegian orogeny due to the lack of geochronological and geochemical data the timing and tectonic setting of early mesoproterozoic magmatism has long been ambiguous this paper presents zircon u pb hf o isotope data combined with whole rock geochemistry to address the age and petrogenesis of basement units within the suldal region located in the centre of the hardangervidda rogaland block the basement comprises variably deformed grey gneisses and granitoids that petrologically and geochemically resemble mature volcanic arc lithologies u pb ages confirm that magmatism occurred from 1 521 to 1 485 ma and conspicuously lack any xenocrystic inheritance of distinctly older crust hafnium isotope data range from ehf initial 1 to 11 suggesting a rather juvenile magmatic source but with possible involvement of late palaeoproterozoic crust oxygen isotope data range from mantle like 18o 5 to elevated 10 suggesting involvement of low temperature altered material e g supracrustal rocks in the magma source the hf o isotope array is compatible with mixing between mantle derived material with young low temperature altered material oceanic crust sediments and older low temperature altered material continent derived sediments this combined with a lack of xenoliths and xenocrysts exposed older crust afc trends and s type geochemistry all point to mixing within a deep crustal magma generation zone a proposed model comprises accretion of altered oceanic crust and the overlying sediments to a pre existing continental margin underthrusting to the magma generation zone and remobilisation during arc magmatism the geodynamic setting for this arc magmatism is comparable with that seen in the phanerozoic e g the sierra nevada and coast range batholiths with compositions in the suldal sector reaching those of average upper continental crust as within these younger examples factors that drive magmatism towards the composition of the average continental crust include the addition of sedimentary material to magma source regions and delamination of cumulate material underthrusting of sedimentary materials and their subsequent involvement in arc magmatism is perhaps a more widespread mechanism involved in continental growth than is currently recognised finally the suldal arc magmatism represents a significant juvenile crustal addition to sw fennoscandia

pore water geochemistry in shallow sediments from the northeastern continental slope of the south china sea abstract the northeastern continental slope of the south china sea is one of the promising areas for gas hydrates which is characterized by its variable topography and complex tectonics in this paper two gravity piston cores were sampled from the shallow sediments in the vicinity of the region where various morphologies of gas hydrate was recovered during the second gas hydrate expedition of guangzhou marine geological survey conventionally the identification of gas hydrate was primarily dependent on the bottom simulating reflector bsr apart from bsr the anomalies in pore water geochemistry which are highly related to various microbially mediated processes and features of fluid from deep hydrocarbon reservoir are also helpful for the gas hydrate exploration in this study upward methane flux may be responsible for distinct characteristics of pore waters observed at the two sample sites a reactive transport model was accordingly established to compare contrastive fluid features and to estimate the upward methane flux since fluid migration is typically associated with complex tectonic settings of the study area it is proposed that heterogeneous distribution of gas hydrates along the continental margin should be well considered

high resolution oi 630 nm image measurements of f region depletion drifts during the guara campaign a high performance all sky imaging system has provided data on the evolution and drift motions of f region depletions above the magnetic dip equator at alc ntara brazil 2 3 s 44 5 w monochromatic images of depletions in the oi 630 nm nightglow were recorded on eight nights during 1 16 october 1994 as part of the guara campaign the drift motions of the depletions were typically 80 100 m s eastward prior to local midnight and reduced to a minimum of 30 50 m s in the morning hours in accord with previous observations however on october 2 3 and 12 13 the depletions were observed to reverse direction for 60 90 min achieving westward speeds of 30 m s before the motion reverted to eastward around 0100 lt and accelerated to 35 45 m s near dawn magnetic activity and other evidence suggests that these reversals in the motion of the airglow depletions probably result from reversals in the f region dynamo rather than from shifts in the altitude of the shear in the nighttime f region plasma drift

lu hf and u pb isotope systematics of zircons from the storgangen intrusion rogaland intrusive complex sw norway implications for the composition and evolution of precambrian lower crust in the baltic shield abstract the storgangen orebody is a concordantly layered sill like body of ilmenite rich norite intruding anorthosites of the rogaland intrusive complex ric sw norway 17 zircon grains were separated from ca 5 kg of sand size flotation waste collected from the on site repository from ilmenite mining these zircons were analysed for major and trace elements by electron microprobe and for u pb and lu hf isotopes by laser ablation microprobe plasma source mass spectrometry eight of the zircons define a well constrained mswd 0 37 concordant population with an age of 949 7 ma which is significantly older than the 920 930 ma ages previously reported for zircon inclusions in orthopyroxene megacrysts from the ric the remaining zircons interpreted as inherited grains show a range of 207pb 206pb ages up to 1407 14 ma with an upper intercept age at ca 1520 ma the concordant zircons have similar trace element patterns and a mean initial hf isotope composition of 176hf 177hf949 ma 0 28223 5 ehf 2 2 this is similar to the hf isotope composition of zircons in a range of post tectonic sveconorwegian granites from south norway and slightly more radiogenic than expected for mid proterozoic juvenile crust the older inherited zircons show lu hf crustal residence ages in the range 1 85 2 04 ga one undated zircon plots well within the field of hf isotope evolution of paleoproterozoic rocks of the baltic shield these findings indicate the presence of paleoproterozoic components in the deep crust of the rogaland area but do not demonstrate that such rocks or a sveconorwegian mantle derived component contributed significantly to the petrogenesis of the ric if the parent magma was derived from a homogeneous lower crustal mafic granulite source the lower crustal protolith must be at least 1 5 ga old and it must have an elevated rb sr ratio this component would be indistinguishable in sr nd and hf isotopes from some intermediate mixtures between sveconorwegian mantle and paleoprotoerzoic felsic crust but it cannot account for the initial 143nd 144nd of the most primitive late sveconorwegian granite in the region without the addition of mantle derived material

pore water anomalies of submarine gas hydrate zones as tool to assess hydrate abundance and distribution in the subsurface what have we learned in the past decade abstract the most significant new contributions to the study of natural gas hydrates in the past decade have come from findings of the ocean drilling program odp notably legs 112 141 146 and 164 and to a lesser extent legs 131 160 170 and 186 leg 164 in particular was dedicated to gas hydrate drilling in the blake ridge gas hydrate field in the west atlantic in an unprecedented multidisciplinary research effort paull et al 1996 proc ocean drill program initial rep 164 623 pp paull c k matsumoto r wallace p j dillon w p eds 2000a proc ocean drill program sci results 164 ocean drilling program college station tx 459 pp most important for the progress of hydrochemical studies related to gas hydrates has been the growing awareness of the significance of diffusion modulated advective processes shaping the chemical and isotopic pore water profiles in hydrate zones this started with qualitative evidence for advective flow from drilling the hydrate bearing peru and hydrate free barbados active margins continued with the nankai trough accretionary prism the japan trench slope and the cascadia and costa rica active margins and culminated in the quantitative advection diffusion model of egeberg and dickens chem geol 153 1999 53 for the passive margin setting of the blake ridge advective flow regimes are different at active and passive margins as there is a tendency for the flow at active margins to be focussed along landward dipping thrust planes and faults in the wedge of imbricated thrust sheets that finds expression in a step pattern of the pore water profiles for passive margins but also for some active margin sites advection is from sources below the drilled section either through subvertical faults passive margins or from the decollement zone active margins we have learned that the well known coupled pore water anomalies that are ascribed to hydrate dissociation downward chlorinity decrease combined with 18 o increase hesse and harrison 1981 earth planet sci lett 55 1981 453 need not occur together in the presence of hydrates because the isotope effect may be overprinted by the effects of other reactions such as volcanic ash alteration or by the advection of low 18 o fluids however if the anomalies show up hydrates are present almost invariably with the exception of advected low cl high 18 o waters coming to terms with the effects of advection and diffusion has allowed successful modeling of the simpler hydrate affected pore water profiles at passive margins instrumental for modeling are chlorine isotopes which provide an effective tool to assess advection rates the egeberg and dickens model allows estimation of hydrate concentration and distribution in the subsurface because it separates the effects of advection diffusion and hydrate dissociation but critically depends on samples taken under in situ pressure and temperature conditions modeling the more complex pore water profiles of active margins is a challenge for the future compared to geophysical methods to estimate hydrate concentration the geochemical method gives minimum amounts

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

zircon u pb o and hf isotopic constraints on mesozoic magmatism in the cyclades aegean sea greece compared to the well documented cenozoic magmatic and metamorphic rocks of the cyclades aegean sea greece the geodynamic context of older meta igneous rocks occurring in the marble schist sequences and melanges of the cycladic blueschist unit is as yet not fully understood here we report o hf isotopic compositions of zircons ranging in age from ca 320 ma to ca 80 ma from metamorphic rocks exposed on the islands of andros ios sifnos and syros with special emphasis on triassic source rocks ion microprobe shrimp ii single spot oxygen isotope analysis of pre cretaceous zircons from various felsic gneisses and meta gabbros representing both the marble schist sequences and the melanges of the study area yielded a large range in 18o values varying from 2 7 to 10 1 vsmow with one outlier at 0 4 initial ehf values 12 5 to 15 7 suggest diverse sources for melts formed between late carboniferous to late cretaceous time that record derivation from mantle and reworked older continental crust in particular variable 18o and ehf t values for triassic igneous zircons suggest that magmatism of this age is more likely rift than subduction related the significant crustal component in 160 ma meta gabbros from andros implies that some jurassic gabbroic rocks of the hellenides are not part of ssz type supra subduction zone ophiolites that are common elsewhere along the margin of the pelagonian zone

anaerobic oxidation of methane and sulfate reduction along the chilean continental margin anaerobic oxidation of methane aom and sulfate reduction sr were investigated in sediments of the chilean upwelling region at three stations between 800 and 3000 m water depth major goals of this study were to quantify and evaluate rates of aom and sr in a coastal marine upwelling system with high organic input to analyze the impact of aom on the methane budget and to determine the contribution of aom to sr within the sulfate methane transition zone smt furthermore we investigated the formation of authigenic carbonates correlated with aom we determined the vertical distribution of aom and sr activity methane sulfate sulfide ph total chlorins and a variety of other geochemical parameters depth integrated rates of aom within the smt were between 7 and 1124 mmol m 2 a 1 effectively removing methane below the sediment water interface single measurements revealed aom peaks of 2 to 51 nmol cm 3 d 1 with highest rates at the shallowest station 800 m the methane turnover was higher than in other diffusive systems of similar ocean depth this higher turnover was most likely due to elevated organic matter input in this upwelling region offering significant amounts of substrates for methanogenesis sr within the smt was mostly fuelled by methane aom led to the formation of isotopically light dic 13c 24 6 vpdb and of distinct layers of authigenic carbonates 13c 14 6 vpdb

zircon in amphibolites from naxos aegean sea greece origin significance and tectonic setting we report u pb zircon ages of c 700 550 ma 262 220 ma 47 38 ma and 15 14 ma from amphibolites on naxos island in the aegean extensional province of greece the zircon has complex internal structures based on cathodoluminescence response zoning and crosscutting relationships a minimum of four zircon growth stages are identified inherited core magmatic core inner metamorphic rim and an outer metamorphic rim trace element compositions of the amphibolites suggest igneous differentiation and crustal assimilation zircon solubility as a function of saturation temperatures zr content and melt composition indicates that the zircon did not originally crystallize in the mafic bodies but was inherited from felsic precursor rocks and subsequently assimilated into the mafic intrusives during emplacement zircon inheritance is corroborated by the complex xenocrystic nature of the zircon in one sample ages of c 700 550 ma and 262 220 ma are assigned to inherited zircon available geochemical data suggest that the 15 14 ma metamorphic rims grew in situ in the amphibolites corresponding to a high grade metamorphic event at this time however the geochemical data cannot conclusively establish if the c 40 ma zircon rims also grew in situ or whether they were inherited along with the xenocrystic cores two scenarios for emplacement of the mafic intrusives are discussed i intrusion during late triassic to jurassic ocean basin development of the aegean realm in which case the 40 ma zircon rims would have grown in situ and ii emplacement in the miocene as a result mafic underplating during large scale extension in this case only the 15 14 ma metamorphic outer rims would have formed in situ in the amphibolitic host rocks

equatorial spread f related airglow depletions at arecibo and conjugate observations 1 we present evidence of the incursion into the caribbean region of airglow depletions associated with the equatorial rayleigh taylor instability data from the boston university all sky imager located at arecibo puerto rico 18 3 n 66 7 w 28 n magnetic latitude have been used to identify several nights with 630 0 nm airglow patterns that are typical signatures of equatorial spread f and distinctly different from the more common airglow bands frequently observed there two case studies 2 november 2002 and 26 february 2003 show the occurrence of simultaneous airglow depletions observed with another all sky imager located at el leoncito argentina 31 8 s 69 3 w 18 s magnetic latitude relatively close to the arecibo conjugate point supporting information is obtained from defense meteorological satellite program rocsat 1 and gps data all of them showing the presence of strong ionospheric irregularities collocated with the airglow depletions mapping the circular field of view from arecibo into the southern hemisphere reveals a distorted pattern due to the differences in the magnetic field characteristics in both hemispheres this adds an interesting spatial complexity to the formulation of conjugate point observing programs in the latin american longitude sector

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

first detection of the supersonic upward plasma flow structures in the early morning sector we present the first observations of the supersonic updrafting plasma drifts in the predawn sector two dmsp satellites quasi simultaneously detected two fast speed events one of 385 km spatial extension and with the maximum upward velocity of 1683 m s appeared at 3 lt and the other of 1500 km large with maximum speed of 1770 m s occurred at 5 lt both supersonic structures were observed above the eastern pacific region separated by 35 of longitude in space and by 45 min in time the events occurred at the recovery phase of the geomagnetic storm of 19 february 2014 during rapid oscillations of the interplanetary magnetic field b z and the interplanetary electric field e y components which increased the eastward electric field in the equatorial nighttime ionosphere and triggered the generation of plasma irregularities the storm time penetration electric fields seem to be the principal driver of the observed supersonic events

evolution of high ca high sr c series basalts from grenada lesser antilles the effects of intra crustal contamination basaltic lavas from grenada lesser antilles may be divided into two series on the basis of cao mgo relations the c series roughly corresponds to the ankaramites or high sr series of the earlier literature and may be distinguished from the m series basalts by higher cao at a given mgo and by their strongly augite phyric nature compositional variation within the c series is dominated by fractional crystallization of augite and plagioclase but this was accompanied by assimilation of sedimentary material from the island arc crust the assimilation fractional crystallization process is well illustrated by an increase in 206pb 204pb from 18 6 to 19 4 with fractionation and correlated increases in nd sr zr sm and rb ba the most primitive members of the c series can not be generated from erupted m series near primary basalts but instead show evidence for an origin by olivine fractionation from high mg basalts never seen at the surface these appear to have been derived from a source similar to that of morb but enriched in 87sr and other hydrophile elements by dehydration of subducted lithosphere and in ree and radiogenic pb by a small component of subducted sediment

super medium scale traveling ionospheric disturbance observed at midlatitude during the geomagnetic storm on 10 november 2004 1 medium scale traveling ionospheric disturbances mstids whose peak to peak amplitude was larger than 20 tecu 1016el m2 were observed at midlatitude during the geomagnetic storm on 10 november 2004 this amplitude was more than 10 times larger than that of the average mstid high resolution data of the gps earth observation network geonet clarified the characteristic of the total electron content tec disturbances over japan on 10 november 2004 the disturbances started around 1000 ut in the central part of japan the maximum of tec temporal change was 7 2 tecu in 30 s the disturbances had several wave fronts which extended from northwest to southeast and propagated from northeast to southwest tec data around japan revealed that the disturbances were mainly observed from 18 n s to 34 n s of the geomagnetic latitude in the both hemispheres since those characteristics were similar to those of mstids in spite of the unusual large amplitude the mstids are referred as super mstids in this paper tec variations of the super mstids were also observed at 460 km altitude by the grace satellite the ion density fluctuations of the super mstids were observed in situ by the champ and dmsp f15 satellites which flew at 360 km and 850 km respectively it is found that the plasma density variations of the super mstids occurred mainly above 360 km altitude the characteristics that distinguish the event from plasma bubbles are its successive wave fronts constant northwest southeast direction along which the wave fronts stretched and late local time of the occurrence it is found that the uplift of the ionosphere around sunset excited the super mstids at midlatitudes the uplift was attributed to the strong eastward electric field during the geomagnetic storm

petrogenesis of the kaikomagatake granitoid pluton in the izu collision zone central japan implications for transformation of juvenile oceanic arc into mature continental crust the miocene kaikomagatake pluton is one of the neogene granitoid plutons exposed in the izu collision zone which is where the juvenile izu bonin oceanic arc is colliding against the mature honshu arc the pluton intrudes into the cretaceous to paleogene shimanto accretionary complex of the honshu arc along the itoigawa shizuoka tectonic line which is the collisional boundary between the two arcs the pluton consists of hornblende biotite granodiorite and biotite monzogranite and has sio2 contents of 68 75 wt it has high k series compositions and its incompatible element abundances are comparable to the average upper continental crust major and trace element compositions of the pluton show well defined chemical trends the trends can be interpreted with a crystal fractionation model involving the removal of plagioclase biotite hornblende quartz apatite and zircon from a potential parent magma with a composition of 68 wt sio2 the sr isotopic compositions together with the partial melting modeling results suggest that the parent magma is derived by 53 melting of a hybrid lower crustal source comprising 30 shimanto metasedimentary rocks of the honshu arc and 70 k enriched basaltic rocks of the izu bonin rear arc region together with previous studies on the izu collision zone granitoid plutons the results of this study suggest that the chemical diversity within the parental magmas of the granitoid plutons reflects the chemical variation of basaltic sources i e across arc chemical variation in the izu bonin arc as well as a variable contribution of the metasedimentary component in the lower crustal source regions in addition the petrogenetic models of the izu collision zone granitoid plutons collectively suggest that the contribution of the metasedimentary component is required to produce granitoid magma with compositions comparable to the average upper continental crust the izu collision zone plutons provide an exceptional example of the transformation of a juvenile oceanic arc into mature continental crust

marine pore water sulfate profiles indicate in situ methane flux from underlying gas hydrate marine pore water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the carolina rise and blake ridge u s atlantic continental margin here sulfate gradients are linear implying that sulfate depletion is driven by methane flux from below rather than by the flux of sedimentary organic matter from above thus these linear sulfate gradients can be used to quantify and assess in situ methane flux which is a function of the methane inventory below

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

multiple sulfur isotope constraints on sulfate driven anaerobic oxidation of methane evidence from authigenic pyrite in seepage areas of the south china sea abstract multiple sulfur isotope signatures and secondary ion mass spectroscopy sims sulfur isotope compositions of pyrite from two seafloor sites dh cl11 and hd109 in seepage areas of the south china sea were measured in order to study isotope effects of sulfate driven anaerobic oxidation of methane so 4 aom the multiple sulfur isotopes of pyrite reveal variable ranges for both sites 34 s between 44 1 and 2 9 for dh cl11 and between 43 8 and 1 6 for hd109 33 s between 0 02 and 0 17 for dh cl11 and between 0 03 and 0 14 for hd109 sims analysis reveals an extreme variability of 34 s values between 50 3 and 2 7 in dh cl11 between 50 1 and 52 4 in hd109 for three types of pyrite 1 framboids 2 zoned aggregates with radial overgrowth surrounding a framboidal core and 3 euhedral pyrite crystals the synchronous changes of geochemical proxies sulfate and methane concentrations 34 s sulfate and 18 o sulfate 34 s pyrite and pyrite content at the sulfate methane transition zone smtz at site dh cl11 are interpreted to be induced by so 4 aom under steady state conditions in contrast pyrite content and 34 s value fluctuations throughout core hd109 suggest that the sediment at this site was affected by multiple pyritization events during diagenesis multiple sulfur isotope signatures of early diagenetic pyrite i e with low and high 34 s values the latter above 315 cmbsf in dh cl11 above 70 cmbsf in hd109 in the upper sediment column suggest that organoclastic sulfate reduction osr and sulfur disproportionation generated the observed isotopic signatures in contrast to the early diagenetic 34 s depleted framboids the higher sims 34 s values of overgrowth and euhedral crystals suggest a late diagenetic 34 s enriched pool of dissolved sulfide derived from so 4 aom at the current and paleo smtzs interestingly pyrite resulting from so 4 aom in the smtz at site dh cl11 reveals a distinct pattern with higher 33 s values different from pyrite resulting from osr and sulfur disproportionation therefore paired 34 s and 33 s values may allow to differentiate osr and so 4 aom although a full understanding of the isotope effects associated with so 4 aom is hampered by uncertainties on the actual electron transfer mechanism in the syntrophic so 4 aom consortium

comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over brazil 1 we present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble epb zonal drift velocities over northeastern brazil during the october to december months of 2009 and 2010 the epb zonal drift velocities are estimated utilizing images of the o i 630 0 nm emissions recorded by a wide angle imaging system at cajazeiras thermospheric neutral wind estimates are based upon common volume observations made by a bistatic fabry perot interferometer fpi experiment using fpis located at cajazeiras and cariri in brazil observing the doppler shift of the o i 630 0 nm emission the results illustrate a similar pattern of nighttime and night to night variations in the zonal neutral winds and epb zonal drift velocities in general the geomagnetic zonal neutral winds and the epb velocities show an excellent agreement illustrating that the f region dynamo is fully developed however in the early evening hours the epb zonal speed is slower than that of the background winds on several occasions we conclude that this indicates that during the bubble evolution period in the early evening the f region dynamo is not fully activated

do s type granites commonly sample infracrustal sources new results from an integrated o u pb and hf isotope study of zircon in contrast to i type granites which commonly comprise infracrustal and supracrustal sources s type granites typically incorporate predominantly supracrustal sources the initial aim of this study was to identify the sources of three scottish caledonian 460 ma s type granites kemnay cove and nigg bay by conducting oxygen u pb and hf isotope analyses in zircon in order to characterise one potential end member magma involved in the genesis of the voluminous late caledonian 430 400 ma i type granites field whole rock geochemical and isotopic data are consistent with the generation of the s type granites by melting their dalradian supergroup country rocks while hf isotope compositions of magmatic zircon u pb data of inherited zircons and high mean zircon 18o values of 9 0 2 7 2sd and 9 8 2 0 for the kemnay and cove granites support this model the nigg bay granite contains zircons with much lower 18o values 6 8 2 1 similar to those found in scottish i type granites this suggests that the nigg bay granite contains low 18o material representing either altered supracrustal material or more likely an infracrustal source component with mantle like 18o mixing trends in plots of 18o vs ehf for s type granite zircons indicate involvement of at least two sources in all three granites this pilot study of scottish caledonian s type granites demonstrates that while field and whole rock geochemical data are consistent with local melting of only supracrustal sources the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources

formation of authigenic carbonates at a methane seep site in the middle okinawa trough east china sea abstract the formation of authigenic carbonates at cold seep is closely related to underlying methane seepage and anaerobic oxidation of methane aom and these processes can be reflected in the geochemical characteristics of pore water in the sediments in terms of petrological mineralogical and geochemical analyses of research materials including authigenic carbonates and pore water samples from the middle okinawa trough east china sea these results show that authigenic carbonate minerals are mainly composed of high magnesium calcite low magnesium calcite dolomite and iron dolomite and exhibit extremely negative carbon isotopic compositions 13c 52 30 to 31 10 v pdb and positive oxygen isotopic compositions 18o 3 36 to 7 27 v pdb geochemical analyses of pore water suggest linear sulfate gradients and steep increase of methane and total alkalinity concentrations with depth which indicate sulfate induced aom activities based on the sulfate concentration reduction carbon isotope characteristics of dissolved inorganic carbon dic and increased methane concentration the sulfate methane interface smi is considered to be shallow these data combined with the variations in ion concentrations in pore water suggest that the leakage of biogenic methane and intense aom resulted in the formation of abundant authigenic carbonates which inherited light carbon 12c enriched isotopic signature of methane in the shallow sediments combined geochemical characteristics of pore water and authigenic carbonates intense methane seep activities and associated aom can be inferred both in present day and ancient geological records on the western slope of the middle okinawa trough

palaeoproterozoic accretionary processes in fennoscandia abstract accretionary processes contributed to major continental growth in fennoscandia during the palaeoproterozoic mainly from 2 1 to 1 8 ga the composite svecofennian orogen covers c 1 10 6 km 2 and comprises the lapland savo fennia svecobaltic and nordic orogens it is a collage of 2 1 2 0 ga microcontinents and 2 02 1 82 ga island arcs attached to the archaean karelian craton between 1 92 and 1 79 ga andean type vertical magmatic additions especially at c 1 89 and c 1 8 ga were also important in the continental growth the palaeoproterozoic crust is the end product of accretionary growth continental collision and orogenic collapse preserved accretional sections are found in areas where docking of rigid blocks has prevented further shortening the pirkanmaa belt represents a composite accretionary prism and other preserved palaeosubduction zones are identified in the gulf of bothnia and the baltic sea areas in the southern segment of the lapland savo orogen collision between the archaean continent lower plate and the palaeoproterozoic arc microcontinent assembly upper plate produced a special type of lateral crustal growth the archaean continental edge decoupled from its mantle during initial collision and overrode the arc and its mantle during continued collision

gas and gas hydrate distribution around seafloor seeps in mississippi canyon northern gulf of mexico using multi resolution seismic imagery abstract to determine the impact of seeps and focused flow on the occurrence of shallow gas hydrates several seafloor mounds in the atwater valley lease area of the gulf of mexico were surveyed with a wide range of seismic frequencies seismic data were acquired with a deep towed helmholz resonator source 220 820 hz a high resolution generator injector air gun 30 300 hz and an industrial air gun array 10 130 hz each showed a significantly different response in this weakly reflective highly faulted area seismic modeling and observations of reversed polarity reflections and small scale diffractions are consistent with a model of methane transport dominated regionally by diffusion but punctuated by intense upward advection responsible for the bathymetric mounds as well as likely advection along pervasive filamentous fractures away from the mounds

mechanisms of contamination in lesser antilles island arc magmas from radiogenic and oxygen isotope relationships abstract oxygen sr and nd isotopic compositions for 29 volcanic samples from the lesser antilles are reported these span a considerable range in 18o from values similar to those of mantle derived lavas 18o 6 6 to 18o 14 0 although the highest 18o results are obtained from evolved andesites and dacites there is no clear correlation between 18o and sio2 an attempt is made to eliminate the effects of varying magma chemistry on 18o through differentiation by normalising to the chemical index of garlick 1 this enables the effects on 18o of processes other than magmatic fractionation to be more clearly assessed it is concluded that the range in 18o values measured cannot result from hydrothermal interaction or weathering alone although limited alteration of a few samples may be responsible for some scatter in the oxygen isotope data when 18o is plotted against radiogenic isotopic compositions well correlated trends are observed 18o increases with increasing87sr 86sr and decreasing143nd 144nd such behaviour is consistent with the contamination of mantle derived magmas by variable amounts of an ancient crustal component the shapes of mixing curves defining this process suggest that contamination occurs largely within the arc crust constraints from geochemical and geophysical data suggest that a terrigenous sediment intercalated within the arc crust is assimilated however subsequent fractional crystallisation at more shallow levels in the crust has obscured any chemical trends which might have resulted from combined assimilation fractional crystallisation furthermore it is suggested that the mantle derived magma has already undergone source contamination by the introduction of a slab derived fluid into the overlying mantle wedge

possible evidence of gravity wave coupling into the mid latitude f region ionosphere during the seek campaign on five of eight observation nights during the 1996 seek sporadic e experiment over kyushu campaign japan unusual wave like structures were imaged in the 630 nm thermospheric nightglow emis sion four of these events were observed to travel to wards the southwest providing new evidence in support of recent theories describing the coupling of medium scale gravity waves into the mid latitude f region iono sphere available ionosonde data and the visual charac teristics of the wave structures indicate no association

last glacial emplacement of methane derived authigenic carbonates in the sea of japan constrained by diatom assemblage carbon 14 and carbonate content abstract we studied diatom assemblages and caco 3 contents of methane derived authigenic carbonates from the eastern margin of the sea of japan and assessed the formation time of these samples radioactive 14 c date was determined in selected samples to obtain the maximum age of the time the results of our study suggest mass formation of carbonate nodules in a glacial period within 40 ky consistent with a published u th dating result of carbonate nodules in the study area diatom assemblages and contents in the carbonate nodules abundance of 10 6 g dominance of neritic littoral species warm cold water species ratio lower than 25 differ from the near seafloor sediments in the study area which have characteristics of holocene sediments in the sea of japan and suggest cementation of glacial sediments laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi enclosed ocean similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules glacial sediments with oceanic cold water species as low as holocene sediments restricts the sediment age to before 20 cal ky bp carbonate contents higher than 78 wt suggest the cementation of poorly compacted sediments near the seafloor and the date of carbonate cementation is therefore close to that of the cemented sediments most carbonate nodule samples in this study were formed in a glacial period and detection of 14 c restricts this period to within 40 ky

equatorial ionospheric plasma bubble irregularity occurrence and zonal velocities under quiet and disturbed conditions from polarimeter observations amplitude scintillation and faraday rotation angle fluctuations of satellite vhf beacons registered by electronic polarimeters operated at two stations spaced 110 km apart in the magnetic east west direction namely cachoeira paulista 22 41 s 45 w dip angle of 26 and sao jose dos campos 23 12 s 45 51 w dip angle of 26 in brazil are analyzed for equinoctial and summer months of 1982 1983 to determine the irregularity patch occurrence characteristics and their zonal velocities under varying levels of magnetic disturbances the scintillation patch occurrences and total electron content fluctuations representing plasma depletion structures decrease during premidnight hours and are enhanced in the postmidnight period the occurrences often extend to morning hours with increasing magnetic activity index while the night events are associated with eastward irregularity patch motion the morning events have westward velocities the reversal occurring around 0400 lt reflecting the morning velocity reversal in the f region bulk plasma motion reported earlier from jicamarca radar measurements the westward plasma bubble motions reported here represent the first observation of this kind another important finding from the present investigation is a clear tendency for the zonal plasma motion namely the equatorial meridional electric field to become enhanced mainly in the premidnight hours immediately following strong magnetic activity

equatorial ionospheric zonal drift by monitoring local gps reference networks 1 the propagation of electromagnetic waves through the turbulent ionosphere produces scintillations through diffraction and understanding the physical nature of scintillations is important for engineers and technologists as well as for scientists in recent years the establishment of the global positioning system gps provided a new technique that can be used to study ionospheric scintillations the usual way of doing that is the deployment of gps receivers closely spaced in east west magnetic direction and then estimating the zonal drift velocities based on the signal power observations one of the weaknesses of this method is that high rate sampling such as 20 hz is required for close spaced stations and generally no such data are available for studying ionospheric scintillation in the past years in this research work a scintillation monitoring method based on slant tec stec observations of local gps continuously operating reference station cors network is proposed first the past research works on the equatorial ionospheric drift velocities are summarized then by comparing the scintillation pattern of the signal power and stec observations of california local gps reference network we find that the stec is a good choice for estimating the ionospheric zonal drift velocity then it is illustrated how to calculate the ionospheric scintillation velocity based on stec finally the proposed method is applied to hong kong gps reference network and several cases of the calculated ionospheric zonal velocities are given

a hafnium isotopic record of magmatic arcs and continental growth in the iapetus ocean the contrasting evolution of ganderia and the peri laurentian margin abstract we test the sensitivity of combined u pb hf isotopic analyses of detrital and magmatic zircon to document complex processes in accretionary orogens using ganderia from the canadian appalachian orogen as an example ganderia hosted a long lived magmatic arc that began at least by 650 ma and continued until 450 ma during which time it drifted northward from the amazonian margin its isotopic record suggests arc activity began earlier possibly at 750 ma proto ganderia within an oceanic domain the u pb hf zircon isotopic array suggests that ganderia formed on a sliver of paleoproterozoic mesoproterozoic basement tdmc 2 2 1 1 ga a transition towards more evolved hf isotopic compositions between 650 and 600 ma is interpreted to coincide with its accretion to the amazonian margin of gondwana consistent with other geological evidence accretion was followed by increasing amounts of juvenile crustal inputs between 550 and 500 ma which is interpreted to reflect subduction roll back and the onset of drift from the gondwanan margin trench retreat culminated in the separation of the ganderia arc and formation of the exclusively oceanic 510 450 ma penobscot popelogan victoria arcs on ganderia accretion of ganderia to the active notre dame subzone along the laurentian margin occurred in the late ordovician and is marked by the abrupt termination of ganderian arc magmatism the notre dame arc evolved along the laurentian margin between 515 and 425 ma and was built on paleoproterozoic archean t dm c 2 9 2 5 ga crust supra subduction zone magmatism occurred at 490 460 ma during the closure of the taconic seaway and was dominated by the recycling of laurentian crust with progressive mixing of evolved and juvenile arc magmas over time the preservation of very evolved notre dame arc zircon in ganderian overstep sequences confirms the arrival of the leading edge of ganderia to laurentia by 450 ma the hafnium isotopic method is proven here to be a powerful tool when used in conjunction with geological constraints and is able to identify the changing nature of magmatism during the evolution of complex accretionary systems

focussed fluid flow on the hikurangi margin new zealand evidence from possible local upwarping of the base of gas hydrate stability the southern hikurangi subduction margin is characterized by significant accretion with predicted high rates of fluid expulsion bottom simulating reflections bsrs are widespread on this margin predominantly occurring beneath thrust ridges we present seismic data across the porangahau ridge on the outer accretionary wedge the data show high amplitude reflections above the regional bsr level based on polarity and reflection strength we interpret these reflections as being caused by free gas we propose that the presence of gas above the regional level of bsrs indicates local upwarping of the base of gas hydrate stability caused by advective heatflow from upward migrating fluids although we cannot entirely rule out alternative processes simplified modelling of the increase of the thermal gradient associated with fluid flow suggests that funnelling of upward migrating fluids beneath low permeability slope basins into the porangahau ridge would not lead to the pronounced thermal anomaly inferred from upwarping of the base of gas hydrate stability focussing of fluid flow is predicted to take place deep in the accretionary wedge and or the underthrust sediments above the high amplitude reflections sediment reflectivity is low a lack of lateral continuity of reflections suggests that reflectivity is lost because of a destruction of sediment layering from deformation rather than gas hydrate related amplitude blanking structural permeability from fracturing of sediments during deformation may facilitate fluid expulsion on the ridge a gap in the bsr in the southern part of the study area may be caused by a loss of gas during fluid expulsion we speculate that gaps in otherwise continuous bsrs that are observed beneath some thrusts on the hikurangi margin may be characteristic of other locations experiencing focussed fluid expulsion

the enrichment of heavy iron isotopes in authigenic pyrite as a possible indicator of sulfate driven anaerobic oxidation of methane insights from the south china sea abstract sulfate driven anaerobic oxidation of methane so4 aom and organiclastic sulfate reduction osr in marine sediments commonly lead to the precipitation of authigenic pyrite with characteristic sulfur isotopic compositions yet no reports on the iron isotopic composition of so4 aom generated pyrite exist to the best of our knowledge and the processes controlling the distribution of iron isotopes during this biogeochemical process are not understood to investigate the mechanisms involved in iron isotope fractionation during so4 aom we analyzed the isotopic composition of authigenic pyrite from two seafloor sites hs148 and hs217 in the shenhu gas hydrate area south china sea the 56fe values of pyrite were found to vary from 0 349 to 0 267 in core hs148 and from 0 793 to 0 178 in core hs217 relative to average igneous rock with distinct trends towards higher values with increasing burial depth in both cores the 56fe values correlate positively with the extent of pyritization fepy fehr derived from a sequential iron extraction procedure osr was found to drive early diagenetic pyrite formation at shallow depth resulting in relatively 56fe depleted pyrite peaks in the extent of pyritization of 0 45 and 0 47 at ca 6 and 7 m below the sediment surface respectively correlate with high 56fe and high 34s values and are interpreted to reflect periods of enhanced so4 aom in paleo sulfate methane transition zones smtzs the great variability in iron isotopic composition and the observed trends are best explained as a function of the availability of dissolved sulfide reflecting sulfide formation by osr and so4 aom the successive conversion of reactive iron to pyrite via sulfidization apparently resulted in the enrichment of 56fe in the iron reservoir upon the preferential consumption of isotopically light iron leading to the formation of successively 56fe enriched pyrite especially at or in close proximity to the smtz therefore we hypothesize that the combined enrichment of heavy iron isotopes and 34s in authigenic pyrite is a possible tracer of so4 aom in modern and ancient sedimentary sequences

hydrocarbon seepage and its sources at mud volcanoes of the kumano forearc basin nankai trough subduction zone twelve submarine mud volcanoes mv in the kumano forearc basin within the nankai trough subduction zone were investigated for hydrocarbon origins and fluid dynamics gas hydrates diagnostic for methane concentrations exceeding solubilities were recovered from mvs 2 4 5 and 10 molecular ratios c1 c2 40 v pdb indicate that hydrate bound hydrocarbons hcs at mvs 2 4 and 10 are derived from thermal cracking of organic matter considering thermal gradients at the nearby iodp sites c0009 and c0002 the likely formation depth of such hcs ranges between 2300 and 4300 m below seafloor mbsf with respect to basin sediment thickness and the minimum distance to the top of the plate boundary thrust we propose that the majority of hcs fueling the mvs is derived from sediments of the cretaceous to tertiary shimanto belt below pliocene pleistocene to recent basin sediments considering their sizes and appearances hydrates are suggested to be relicts of higher mv activity in the past although the sporadic presence of vesicomyid clams at mv 2 showed that fluid migration is sufficient to nourish chemosynthesis based organisms in places distributions of dissolved methane at mvs 3 4 5 and 8 pointed at fluid supply through one or few mv conduits and effective methane oxidation in the immediate subsurface the aged nature of the hydrates suggests that the major portion of methane immediately below the top of the methane containing sediment interval is fueled by current hydrate dissolution rather than active migration from greater depth

2 7 ga plume associated vhms mineralization in the eastern goldfields superterrane yilgarn craton insights from the low temperature and shallow water ag zn au nimbus deposit economic volcanic hosted massive sulfide vhms deposits of the archaean yilgarn craton of western australia are restricted to zones of juvenile crust as revealed through regional nd pb and hf isotopic variations and the geochemistry of felsic volcanic rocks interpreted as archaean paleo rift zones one of these runs n s through the eastern goldfields superterrane broadly coincident with the kurnalpi terrane and is associated with the high grade ca 2690 ma teutonic bore jaguar and bentley deposits plus sub economic vhms mineralization further south to date only small historic cu occurrences e g anaconda and barren pyritic lenses have been recognized in the older 2 7 ga plume dominated lower stratigraphy of the eastern goldfields superterrane the nimbus ag zn au deposit 12 1 mt at 52 g t ag 0 9 zn and 0 2 g t au is located approximately 10 km east of kalgoorlie near the margin of the kurnalpi terrane its origin has been contentious for a number of years with previous models favouring seafloor sub seafloor vhms mineralization or a high sulfidation fault hosted system we present a detailed account of the deposit its host stratigraphy and associated hydrothermal alteration plus two new shrimp u pb zircon ages pb isotope galena and o isotope zircon constraints compared to other vhms occurrences in the yilgarn craton the nimbus deposit is unusual in terms of its tectono stratigraphic position the geochemistry of its host sequence i e fi affinity felsic volcanic rocks ocean plateau like low th basalts mineralogy e g abundance of ag sb pb as bearing sulfosalts high hg low cu and quartz carbonate sericite dominated alteration assemblages classification of nimbus as a shallow water and low temperature vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit is consistent with its position near the margin of the kurnalpi paleo rift zone and radiogenic 238u 204pb values the recognition that the nimbus deposit is associated with c 2705 ma plume magmatism opens new areas for vhms exploration in the eastern goldfields superterrane over a strike length exceeding 500 km

first results of the limb imaging of 630 0 nm airglow using formosat 2 imager of sprites and upper atmospheric lightnings 1 this is the first report of the most comprehensive 630 0 nm airglow limb images taken using imager of sprites and upper atmospheric lightnings isual onboard formosat 2 the limb scans reveal two distinct airglow layers the upper one corresponds to the thermospheric o 1d emission and the lower one corresponds to the oh 9 3 emissions sequences of such observations are combined to generate altitude latitude maps of the emissions which reveal intensity enhancements of both the layers at certain locations where they often appear to be linked joined vertically a detailed analysis of the location and occurrence of the enhancements in the entire observations together with simulations of the emissions suiting the isual limb geometry are carried out to understand the causes and related processes

deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off namibia abstract porewater concentrations of sulfate methane and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off namibia which were recovered from the continental slope at water depths of 1300 and 2000 m at all four stations a distinct sulfate methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100 of deep sulfate reduction within the sulfate methane transition zone and consumes the total net diffusive sulfate flux a significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could therefore be excluded we state that porewater profiles of sulfate with constant gradients above the transition zones are indicative for anaerobic methane oxidation controlling sulfate reduction

a study of rare earth element ree sio 2 variations in felsic liquids generated by basalt fractionation and amphibolite melting a potential test for discriminating between the two different processes the origin of felsic magmas 63 sio2 in intra oceanic arc settings is still a matter of debate two very different processes are currently invoked to explain their origin these include fractional crystallization of basaltic magma and partial melting of lower crustal amphibolite because both fractionation and melting can lead to similar major element trace element and isotopic characteristics in felsic magmas such lines of evidence have been generally unsuccessful in discriminating between the two processes a commonly under appreciated aspect of rare earth element ree solid liquid partitioning behavior is that d ree for most common igneous minerals especially hornblende increase significantly with increasing liquid sio2 contents for some minerals e g hornblende and augite ree partitioning can change from incomptatible d 1 at high liquid sio2 when this behavior is incorporated into carefully constrained mass balance models for mafic basaltic amphibolite melting intermediate andesitic amphibolite melting lower or mid to upper crustal hornblende present basalt fractionation and mid to upper crustal hornblende absent basalt fractionation the following general predictions emerge for felsic magmas e g 63 to 76 sio2 partial melting of either mafic or intermediate amphibolite should regardless of the type of melting equilibrium fractional accumulated fractional yield ree abundances that remain essentially constant and then decrease or steadily decrease with increasing liquid sio2 content at high liquid sio2 contents lree abundances should be slightly enriched to slightly depleted i e c l c o 2 to 0 2 while hree abundances should be slightly depleted c l c o 1 to 0 2 lower crustal hornblende bearing basalt fractionation should yield roughly constant ree abundances with increasing liquid sio2 and exhibit only slight enrichment c l c o 1 2 mid to upper crustal hornblende bearing basalt fractionation should yield steadily increasing lree abundances but constant and then decreasing hree abundances at high liquid sio2 contents lree abundances may range from non enriched to highly enriched c l c o 1 to 5 while hree abundances are generally non enriched to only slightly enriched c l c o 1 to 2 hornblende absent basalt fractionation should yield steadily increasing ree abundances with increasing liquid sio2 contents at high sio2 contents both lree and hree are highly enriched c l c o 3 to 4 it is proposed that these model predictions constitute a viable test for determining a fractionation or amphibolite melting origin for felsic magmas in intra oceanic arc environments where continental crust is absent

preliminary interpretation of electromagnetic heat flow seismic and geochemical data for gas hydrate distribution across the porangahau ridge new zealand porangahau ridge located offshore the wairarapa on the hikurangi margin is an active ocean continent collision region in northeastern new zealand coastal waters bottom simulating reflections bsrs in seismic data indicate the potential for significant gas hydrate deposits across this part of the margin beneath porangahau ridge a prominent high amplitude reflection band has been observed to extend from a deep bsr towards the seafloor review of the seismic data suggest that this high amplitude band is caused by local shoaling of the base of gas hydrate stability due to advective heat flow and it may constitute the location of elevated gas hydrate concentrations during r v tangaroa cruise tan0607 in 2006 heat flow probing for measurements of vertical fluid migration sediment coring for methane concentrations and additional seismic profiles were obtained across the ridge in a subsequent 2007 expedition on r v sonne cruise so191 a controlled source electromagnetic csem experiment was conducted along the same seismic geochemical and heat flow transect to reveal the electrical resistivity distribution csem data highlight a remarkable coincidence of anomalously high resistivity along the western landward flank of the ridge which point to locally higher gas hydrate concentration above the high amplitude reflection band measured sediment temperature profiles also along the western flank consistently show non linear and concave geothermal gradients typical of advective heat flow geochemical data reveal elevated methane concentrations in surface sediments concomitant with a rapid decline in sulfate concentrations indicating elevated methane flux and oxidation of methane in conjunction with sulfate reduction at the landward ridge base together these data sets suggest that the western rim of porangahau ridge is a tectonically driven zone of rising fluids that transport methane and cause an upward inflection of the base of gas hydrate stability and the formation of locally enriched gas hydrate above the reflective zone

oxygen isotope systematics of the banda arc low delta o 18 despite involvement of subducted continental material in magma genesis abstract this study reports new laser fluorination oxygen isotope data for 60 volcanic rocks and 15 sediments distributed over the whole length of the banda arc eastern indonesia the melt oxygen isotope values 18omelt were calculated from phenocryst 18o data using theoretical and empirical mineral melt fractionation factors the 18omelt of individual volcanic centers within the arc varies between 5 57 and 6 54 except for serua 18omelt 6 13 7 48 and ambon 18omelt 8 12 8 38 these 18omelt values are up to 2 lower than new and previously published oxygen isotope data obtained on whole rock powders by conventional methods we attribute this discrepancy to post emplacement low temperature alteration and or to a systematic deviation of the bulk analysis sediment 18owr calculated from the 18o carbonate and silica fractions both measured conventionally range between 12 9 and 24 2 the low 18omelt values excluding serua and ambon overlap with the mantle range and are in agreement with simple two component source mixing models that predict 1 5 addition of subducted continental material to a depleted morb type source in the sub arc mantle this percentage is consistent with previous models based on sr nd pb th he hf isotope data however correlations between incompatible trace element ratios and oxygen isotope systematics requires involvement of partial melts derived from subducted continental material as the major slab component rather than bulk addition the contribution of hydrous fluids from both subducted altered oceanic crust and continental material is probably of minor importance magma mantle wedge interaction models could account for the observed low 18o signatures but predicted effects are difficult to distinguish from models without mantle wedge interaction assimilation of arc crust material is thought to be important for the high 18omelt values of serua and ambon afc modelling suggests up to 20 and 80 assimilation at serua and ambon respectively inclusions of meta sedimentary material and whole rock sr nd isotopes point to assimilation processes at nila but this probably had little effect on the 18o of phenocrysts which record original source values according to radiogenic isotope data magma sources in the banda arc are the most heavily influenced by fluxes of subducted continental material among currently active oceanic island arcs hence the results of this study suggest that high 18o 6 5 in arc lavas are difficult to reconcile with addition of subducted components to magma sources but must reflect assimilation of arc crustal material

oxygen isotope constraints on terrane boundaries and origin of 1 18 1 13 ga granitoids in the southern grenville province granitic rocks related to 1 18 to 1 13 ga anorthosite mangerite charnockitegranite plutonism stitch three terranes in the southwestern grenville province adirondack highlands morin terrane frontenac terrane elzevir terrane because of the refractory nature of zircon zrn analysis of oxygen isotope ratios of dated igneous zircon from these rocks allows calculation of 18 o values of original magmas even if the rocks were subjected to late magmatic assimilation postmagmatic alteration or metamorphism documented variability in 18 o zrn for these granitic rocks corresponds to their geographic location seven plutons from the central frontenac terrane ontario have a high average 18 o zrn 11 8 1 0 which corresponds to 18 o magma values of 12 4 14 3 in contrast twenty seven other plutons and dikes of this suite new york ontario and quebec average 18 o zrn 8 2 0 6 with a typical igneous range of 8 6 to 10 3 for 18 o magma values high 18 o values in the frontenac terrane are some of the highest magmatic oxygen isotope ratios recognized worldwide but these plutons are not unusual with respect to whole rock chemistry or radiogenic isotope compositions such high 18 o values can result from mixing between paragneiss 18 o 15 and hydrothermally altered basalts and or oceanic sediments 18 o 12 in the source region we propose that high 18 o hydrothermally altered basalts and sediments were subducted or underthrust to the base of the frontenac terrane during closure of an ocean basin between the frontenac terrane and the adirondack highlands at or prior to 1 2 ga

oxygen isotope and trace element geochemistry of zircons from porphyry copper system implications for late triassic metallogenesis within the yidun terrane southeastern tibetan plateau abstract it is intriguing to investigate the generation of the magmatic system and the geochemical signatures that distinguish the ore bearing ones from barren ones especially by examining the oxygen isotopic and trace element compositions of zircon the oxygen isotopic composition and trace element abundances of zircons from the mineralized pulang porphyries and the coeval disuga and lannitang andesites of the yidun terrane eastern tibetan plateau have been determined by secondary ion mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms in this study respectively analyzed zircons have relatively high but invariant 18 o values 5 8 6 9 that are indicative of derivation from homogeneous mantle or mantle derived magmas together with contribution of mature crustal materials we propose a model for the late triassic magmatism in the yidun terrane involving magmas derived from partial melting of subduction metasomatized mantle peridotites that subsequently experienced melting assimilation storage homogenization mash processes the low calculated ti in zircon temperatures 644 c 863 c generally between 640 c and 690 c for these zircons may be caused by the lower solidus temperature for zircon in hydrous magmas and partly controlled by the crystallization of amphibole zircon grains from porphyry copper system display small negative europium anomalies mostly eu eu 0 5 contrasting with pronounced negative eu anomalies in zircons mostly eu eu magmato hydrothermal quartz vein cu mo w deposit magmato hydrothermal quartz vein mo w deposit this study suggests that zircon trace element geochemistry probably bears significant implications for elucidating the origin of the arc magmatism and guiding exploration strategies for porphyry copper deposits

analysis of methane and sulfate flux in methane charged sediments from the mississippi canyon gulf of mexico abstract sediment porewater geochemical data so4 2 ch4 dic 13c dic and cl were obtained from piston cores collected in atwater valley gulf of mexico prior to 2005 drilling to study gas hydrates in the region the geochemical data were used for a study of shallow sediment ch4 cycling on a seafloor mound mound f where an apparent upward deflection of the bottom simulating reflector bsr suggested vertical fluid advection fifteen sediment cores ranging from 300 to 800 cm long were collected from locations on top of the mound and across a transect up to 3 5 km off the mound the sulfate methane transition smt was determined in each core from porewater so4 2 and ch4 concentration profiles and occurred at depths ranging from 0 to 410 cm below the seafloor cmbsf the shape of porewater so4 2 profiles plotted against depth also varied from linear to non linear along the transect diffusion rates estimated from linear so4 2 concentration gradients ranged from 20 4 to 249 1 mmol m 2 a 1 with the greatest rate measured in sediments on the mound the large variation in smt depth and so4 2 profiles along the transect indicates lateral differences in total vertical ch4 flux between locations results suggest steady state and non steady state ch4 fluxes both on the mound and transitioning off the mound and likely differences in the relative contribution of fluid advection to local shallow sediment ch4 cycling cores collected from on the mound had high porewater headspace ch4 concentrations up to 8 34 mm coupled with elevated cl concentrations up to 956 5 mm at shallow depths suggesting that salt diapirism in deep sediments may be inhibiting hydrate stability and increasing vertical ch4 flux

implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults abstract reservoirs associated with salt diapirs that are circular or elliptical in plan view can be segmented by radial faults concentric faults both or neither explanations for this variation are offered based on integration of fault kinematics published studies and seismic examples strata around diapirs can be divided into three structural domains with characteristic fault styles 1 roof zone between the present day depositional surface and crest of a buried inactive diapir this zone is characterised by doming radial faults and occasionally conic graben doming is usually caused by differential compaction and increases with depth 2 a steeply dipping sheath of strata surrounds the diapir out to a distance of less than one diapir radius recording near surface diapir growth in poorly lithified sediments these contain early gravity slumps and late concentric extensional faults regional layer bound polygonal fault systems form radial faults within approximately one diapir radius the only significant radial faulting mechanism below the roof zone 3 diapir root zone of strata whose structural architecture records the diapirs initiating mechanism typically rim synclines or graben that detach on the salt source layer concentric faults at radial distances of a kilometre or more have been found only in root zone rim synclines and sheared sheath strata these models and observations can assist seismic interpretation and structural model building in areas of poor geophysical imaging for instance below overhanging salt

crustal evolution of southern laurentia during the paleoproterozoic insights from zircon hf isotopic studies of ca 1 75 ga rocks in central colorado lu hf depleted mantle model tdm ages obtained by analysis of zircons previously dated by u pb methods demonstrate that ca 1 75 ga bimodal paleoproterozoic rocks in the gunnison salida region of central colorado and by extension in much of the southwestern u s were formed by partial melting of preexisting crustal rocks the ages of which mostly ages greater than 2 0 ga indicate that range from 1 83 to 1 87 ga some calculated lu hf tdm even older crust was probably involved consistent with the limited presence of ca 2 5 ga xenocrystic zircons in some rocks these results suggest that rocks related to the trans hudson and penokean orogens are cryptically present much farther to the south than previously believed coupled with the bimodality of the volcanic suite in central colorado and indeed in much of the southwestern u s these results indicate that in contrast to current juvenile arc accretion models melting of older crust related to extensional tectonics played an important role in the genesis of many magmatic rocks between 1 6 and 1 8 ga

ionospheric zonal velocities at conjugate points over brazil during the copex campaign experimental observations and theoretical validations 1 we analyze in detail the zonal velocities of large scale ionospheric plasma depletions over two conjugate stations inferred from oi 630 nm airglow all sky images obtained during the conjugate point equatorial experiment copex campaign carried out in brazil between october and november 2002 the conjugate stations were boa vista bv geogr 2 8n 60 7w dip angle 22 0 n and campo grande cg geogr 20 5s 54 7w dip angle 22 32 s over campo grande the zonal velocities were measured also by a system of spaced gps scintillation receivers the airglow zonal velocities at the conjugate sites were seen to agree very closely except for a slightly increased velocity over cg which we attribute to the presence of the geomagnetic anomaly the results show a high degree of alignment of the bubbles along the geomagnetic field lines during the bubble development phase and as the bubbles travel eastward thereby suggesting that the neutral zonal wind effect in the zonal plasma motion is an integrated effect along the flux tube the zonal velocities obtained from the gps technique were always larger than those calculated by the airglow technique which permitted observation of zonal plasma velocity shear between the altitudes of the airglow emitting layer and of the gps scintillation theoretical ambient plasma zonal velocities calculated using the formulations by haerendel et al 1992 and eccles 1998 are compared with the experimental results our results also reveal some degree of dependence of the zonal velocities on the solar flux f10 7 and magnetic kp indices during the copex period

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

gulf of mexico sediment sources and sediment transport trends from magnetic susceptibility measurements of surface samples abstract the magnetic properties from 200 trigger core top and van veen grab sediment samples recovered from throughout the gulf of mexico have been analyzed and used to characterize sediment source and flow pattern distributions magnetic parameters included are anhysteretic remanent magnetism arm and magnetic susceptibility ms measurements results from these measurements are compared to previously determined calcium carbonate percentages and clay and hematite influx trajectories into the gulf of mexico for the same samples reported by balsam and beeson balsam w l and beeson j p 2003 sea floor sediment distribution in the gulf of mexico deep sea res i 50 1421 1444 the arm results give an estimate of magnetic grain size distributions and by analogy grain size distributions in general whereas ms patterns show high detrital sediment accumulation zones within the gulf the dominant influx of modern high susceptibility sediment into the gulf of mexico appears to originate from the red river flow into atchafalaya river basin and out into the gulf from atchafalaya bay with significant additional contributions from the mississippi river through the southwest pass of the mississippi river delta this material then moves across the continental shelf and down through the mississippi canyon into the deep gulf where it is redistributed at depths 3600 m the eastern shelf margins in the gulf offshore from alabama and florida are accumulating calcite or quartz rich medium to fine grained sediment that has a very low or diamagnetic ms signature from the louisiana to texas gulf coast margins ms is moderate to high suggesting a river influx of magnetic constituents from the volcanic fields in new mexico and from igneous and metamorphic sources in the mississippi basin offshore from western mexico the ms is high to moderate but the yucatan shelf margin is characterized by low to diamagnetic ms values due to sediment dominated by calcite sands and oozes a trend that continues to the east onto the west florida shelf additional measurements of samples collected in association with sites characterized by hydrocarbon seepage exhibit anomalously low ms values the samples from the lower shelf and slope areas are typified by iron reduction by bacterial organisms in these samples these results produce anomalous localized lows in the ms trends observed

sulfate reduction and methane oxidation in continental margin sediments influenced by irrigation south east atlantic off namibia abstract sulfate reduction rates srr and concentrations of so 4 2 h 2 s pyrite sulfur total sulfur ch 4 and organic carbon were measured with high depth resolution through the entire length of the so 4 2 zone and well into the ch 4 zone at two continental slope stations in the eastern south atlantic benguela upwelling area the sediments were characterized by a high organic carbon content of approx 7 5 at geob 3703 and 3 7 at geob 3714 at geob 3703 so 4 2 concentrations decreased linearly with depth to about 40 m at the sulfate methane transition zone smt at 3 5 m while at geob 3714 so 4 2 remained at sea water concentration in the top 2 m of the sediment and then decreased linearly to about 70 m at the smt at 6 m direct rate measurements of srr 35 so 4 2 showed that the highest srr occurred within the surface 3 5 cm with peak rates of up to 20 and 7 nmol so 4 2 cm 3 day 1 at geob 3703 and geob 3714 respectively srr decreased quasi exponentially with depth at geob 3703 and the cumulative srr over the length of the so 4 2 zone resulted in an areal srr srr area of 1114 3493 mol m 2 day 1 median value 2221 mol m 2 day 1 at geob 3703 with more than 80 of the total sulfate reduction proceeding in the top 30 cm sediment at geob 3714 srr exhibited more scatter with a cumulative srr area of 398 1983 mol m 2 day 1 median value 1251 mol m 2 day 1 and with 60 of the total sulfate reduction occurring below a depth of 30 cm due partially to a deeply buried zone of sulfate reduction located between 3 and 5 m depths srr peaks were also observed in smt of both cores ostensibly associated with methane oxidation but with rates about 10 times lower than at the surface modeled srr balanced both methane oxidation rates and measured srr within the smt but severely underestimated by up to 89 the total srr area that were obtained from direct measurements modeled and measured srr were reconciled by including solute transport by irrigation described by a non local pore water exchange function which had values of up to 0 3 year 1 in the top sediment and decreased exponentially to zero i e no irrigation at 2 3 meters i e above smt these results suggested that co existing sulfate reduction processes and linear so 4 2 gradients can be maintained by a non local transport mechanism such as irrigation by which pore water in tubes or burrows is exchanged with bottom waters by activities of tube dwelling animals or some similar physical transport phenomenon i e bubble ebullition further support for an irrigation mechanism was found in the observations of open tubes of up to 8 mm id at depths down to 6 m which also contained fecal pellets indicating that these tubes were or had been inhabited

assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern gulf of mexico pore waters extracted from 18 piston cores obtained on and near a salt cored bathymetric high in keathley canyon lease block 151 in the northern gulf of mexico contain elevated concentrations of chloride up to 838 mm and have pore water chemical concentration profiles that exhibit extensive departures concavity from steady state linear diffusive equilibrium with depth minimumd 13 c dissolved inorganic carbon dic values of 55 9 to 64 8 at the sulfate methane transition smt strongly suggest active anaerobic oxidation of methane aom throughout the study region however the nonlinear pore water chemistrydepth profiles make it impossible to determine the vertical extent of active aom or the potential role of alternate sulfate reduction pathways here we utilize the conservative non reactive nature of dissolved chloride to differentiate the effects of biogeochemical activity e g aom and or organoclastic sulfate reduction relative to physical mixing in high salinity keathley canyon sediments in most cases the dic and sulfate concentrations in pore waters are consistent with a conservative mixing model that uses chloride concentrations at the seafloor and the smt as endmembers conservative mixing of pore water constituents implies that an undetermined physical process is primarily responsible for the nonlinearity of the pore water depth profiles in limited cases where the sulfate and dic concentrations deviated from conservative mixing between the seafloor and smt the d 13 c dic mixing diagrams suggest that the excess dic is produced from a 13 c depleted source that could only be accounted for by microbial methane the dominant form of methane identified during this study we conclude that aom is the most prevalent sink for sulfate

equatorial plasma bubble zonal velocity using 630 0 nm airglow observations and plasma drift modeling over ascension island 1 we present oi 630 0 nm airglow image data from ascension island geographic 7 9 s 14 4 w dip latitude 16 s in the southern atlantic ocean taken with the utah state university all sky ccd camera during 20 march to 7 april 1997 in order to study plasma bubbles occurring in the low latitude nighttime ionosphere the initial plasma bubble onset occurs in the early evening hours at 19 15 20 00 lst and is followed by eastward propagation with an average speed of 90 120 m s prior to local midnight rapidly decreasing around the midnight and postmidnight periods the ascension results are compared with similar observations from christmas island in order to examine the longitudinal variations of epb development and propagation the observed epb velocities from ascension island are also compared with the results of a plasma drift model in a case study during the night of 4 5 april the velocity reveals unusual latitudinal shear up to 0 12 m s km with a reversal to westward flow at low latitudes while eastward flow is maintained at higher latitudes consequently the bubble rotates counterclockwise and tilts eastward significantly away from alignment with the geomagnetic field lines the westward reversal of the drift motion near the geomagnetic equator is most likely the result of a reversal in the f region dynamo or from a large increase in the altitude of the shear node in the f region plasma drift at the geomagnetic equator

methane release from pingo like features across the south kara sea shelf an area of thawing offshore permafrost the holocene marine transgression starting at 19 ka flooded the arctic shelves driving extensive thawing of terrestrial permafrost it thereby promoted methanogenesis within sediments the dissociation of gas hydrates and the release of formerly trapped gas with the accumulation in pressure of released methane eventually triggering blowouts through weakened zones in the overlying and thinned permafrost here we present a range of geophysical and chemical scenarios for the formation of pingo like formations plfs leading to potential blowouts specifically we report on methane anomalies from the south kara sea shelf focusing on two plfs imaged from high resolution seismic records a variety of geochemical methods are applied to study concentrations and types of gas its character and genesis plf 1 demonstrates ubiquitously low methane concentrations 14 2 55 3 ppm that are likely due to partly unfrozen sediments with an ice saturated internal core reaching close to the seafloor in contrast plf 2 reveals anomalously high methane concentrations of 120 000 ppm where frozen sediments are completely absent the methane in all recovered samples is of microbial and not of thermogenic origin from deep hydrocarbon sources however the relatively low organic matter content 0 52 1 69 of seafloor sediments restricts extensive in situ methane production as a consequence we hypothesize that the high methane concentrations at plf 2 are due to microbial methane production and migration from a deeper source

geochronology of caledonian metamorphic allochthons in the otta heidal region south norway tectonostratigraphic and palaeogeographical implications the caledonian appalachian belt formed in the early paleozoic by the assembly and dispersal of continental and oceanic crustal fragments of diverse provenance the characterization of these terranes and information on their origins are essential in reconstructing the course of the orogeny the region of northern gudbrandsdalen in norway is important for elaborating these questions as it represents a geological transition in architectural style and composition of the caledonian nappes and the meeting point of tectonic elements with diverse geological histories of both baltic and exotic origins in the past century this complexity has generated conflicting interpretations which we have tested with new mapping and isotope dilution thermal ionization mass spectrometry u pb dating the new data show the following 1 a metagabbro low in the tectonostratigraphy has an age of 1497 5 ma correlating with the espedalen complex of telemarkian 1550 1480 ma affinity 2 the structurally higher crystalline rudihoe mukampen suite was metamorphosed at high grade during the sveconorwegian orogeny mainly between 980 and 900 ma with older components pointing to a gothian 1700 1600 ma affinity 3 these ages and mapping indicate that the rudihoe mukampen suite is a lateral equivalent of the upper jotun nappe 4 the overlying dominantly metasedimentary steinho complex was metamorphosed in the ordovician at about 473 3 ma 5 both the rudihoe mukampen suite and steinho complex were intruded by trondhjemite dykes at 430 427 ma these units are structurally overlain by the lowest elements of the trondheim nappe complex which includes serpentinite lenses and conglomerates the products of hyperextension locally with ordovician fossils the new results dispel some of the problematic interpretations proposed earlier and represent new firm elements that will anchor future tectonic reconstructions of the caledonides in this region

supracrustal input to magmas in the deep crust of sierra nevada batholith evidence from high δ 18 o zircon oxygen isotope ratios of zircon zc from intrusives exposed in the tehachapi mountains southern california reveal large inputs of high 18 o supracrustal contaminant into gabbroic and tonalitic magmas deep 30 km in the cretaceous sierra nevada batholith high 18 o zc values 7 8 0 7 predominate in the deep parts of the batholith but lower values 6 1 0 9 occur in shallower parts this indicates a larger gradient in 18 o with depth in the batholith than occurs from west to east across it oxygen sr and nd isotope data show that the supracrustal contaminant was likely young paleozoic or mesozoic hydrothermally altered upper oceanic crust or volcanic arc sediments such rocks were subducted or underthrust beneath the sierran arc during accretion of oceanic terranes onto north america this component yielded high 18 o magmas that were added to the base of the batholith on average gabbros in the southern sierra contain at least 18 of the subducted supracrustal component some tonalite and granodiorite magmas were additionally contaminated by kings sequence metasedimentary rocks as evidenced by 18 o zc and initial 87 sr 86 sr that trend toward values measured for the kings sequence besides high 18 o values in the southern sierra xenoliths in the central sierra also have elevated 18 o which confirms the widespread abundance of supracrustal material in the sub arc lithospheric mantle in contrast to 18 o zc whole rock 18 o values of many samples have undergone post magmatic alteration that obscures the magmatic contamination history of those rocks such alteration previously prevented confident determination of the mass of young hydrothermally altered mantle rocks that contributed to sierran granitoids

radiogenic isotope systematics of the herefoss granite south norway an indicator of sveconorwegian grenvillian crustal evolution in the baltic shield abstract a new pb pb mineral isochron dates the crystallization of the herefoss granite south norway to 926 8 ma confirming earlier rb sr evidence of a late sveconorwegian grenvillian age initial sr and nd isotopic compositions recalculated to esr 926 ma 40 end 926 ma 3 2 to 0 8 indicate that the magma has originated from a mixture of two distinct source components 1 a crustal component which has resided in a moderately lile enriched reservoir f rb 7 to 8 238 u 204 pb 17 22 since 1 6 1 9 ga this crustal component is clearly distinct from the extremely lile enriched metasedimentary country rocks of the granite f rb 21 238 u 204 pb 24 2 a mantle derived component e nd 4 6 to 5 9 e sr 12 to 9 238 u 204 pb 7 96 younger than 1 5 ga the ranges of initial sr nd and pb composition observed in the intrusion indicate that the magma was isotopically heterogeneous at the time of emplacement and that the crustal contribution amounted to 35 55 by the end of the sveconorwegian orogeny the southwestern part of the baltic shield had acquired a compositionally layered structure where an uppermost zone of the crust with extreme lile enrichment was underlain by a heterogeneous layer consisting of rocks with normal upper crustal degree of lile enrichment and mafic intrusions younger than 1 5 ga there is no evidence of involvement of lile depleted deep continental crust source material in the petrogenesis of the herefoss granite rejuvenation of the lower crust by injection of mantle derived magmas underplating has been an important process in the evolution of the southwestern part of the baltic shield the absence of a young mantle derived component from 1 12 ga charnockitic intrusions in the bamble sector and from the 989 ma grimstad granite suggests that this process may have been contemporaneous with late sveconorwegian mafic magmatism in the rogaland vest agder sector further to the west

subsurface methane sources and migration pathways within a gas hydrate mound system gulf of mexico 1 geochemical profiles were coupled with seismic information to examine subsurface hydrocarbon source migration and fate at a gulf of mexico carbonate gas hydrate mound woolsey mound three seafloor features were investigated in detail 1 major faults resulting from a rising salt body 2 an acoustic backscatter anomaly and 3 a pockmark associated with a major fault we analyzed sulfate chloride dissolved inorganic carbon and hydrocarbon concentrations and carbon isotopes in pore water extracted from 20 m piston cores to characterize gas source and calculate methane flux dissolved biogenic methane dominated the off fault sites while the contribution of thermogenic methane increased near a major fault where thermogenic gas hydrates were recovered within the pockmark methane concentrations were low and isotopes indicated a biogenic source since pockmarks are typically formed from expulsive fluid flow this suggests that either the pockmark is the legacy of a conduit that has become plugged or that the expulsed fluid is confined within the fault walls at the acoustic anomaly nonsteady state sulfate profiles suggested temporal variability in methane flux estimates from 75 gravity cores collected across woolsey mound since 2002 were mapped to display the spatial variability in methane flux relative to the faults methane flux to the seafloor was generally low but increased several fold near the faults suggesting that the faults may provide conduits for hydrocarbons to bypass the microbial biofilter and cross the sediment water interface

airglow characteristics of equatorial plasma depletions a new low light level all sky 6300 a airglow imaging system has been developed for ground based studies of the optical signatures of equatorial plasma depletions the system was designed for narrowband interference filters 6 a full width at half power with interchangeable all sky 180 and narrow field 60 lenses and records images photographically by using a standard 35 mm camera a field test of the apparatus was conducted on ascension island 8 0 s 14 4 w from january 24 to february 10 1981 the photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail the initial results to come from these observations show that airglow depletions occur most often during the 2030 2330 lt period often covering one fourth of the visible sky they extend from the magnetic equator to beyond the crest of the equatorial anomaly with east west cross sections of 100 km to several hundred kilometers they are usually not aligned with magnetic meridians showing a progressive skewness to the west at further distances from the equator several cases of apparently twisting overlapping and bifurcating depletions were observed the depletions drifted to the east with speeds that decreased from 190 m s at 2100 lt to 80 m s at 0100 lt the airglow intensities within depletions were typically 40 50 of the background levels and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls

how sulfate driven anaerobic oxidation of methane affects the sulfur isotopic composition of pyrite a sims study from the south china sea abstract sulfate driven anaerobic oxidation of methane so4 aom in marine sediments commonly leads to the precipitation of pyrite it is however frequently challenging to unequivocally unravel the entire history of pyritization because of the common coexistence of so4 aom derived pyrite with pyrite resulting from organiclastic sulfate reduction osr to better understand how so4 aom affects pyritization in methane bearing sediments and how this can be identified we applied secondary ion mass spectroscopy sims to analyze the sulfur isotope composition 34s of authigenic pyrite in addition to sulfur isotope measurements of bulk sulfide and hand picked pyrite aggregates from the two seafloor sites hs148 and hs217 in the shenhu seepage area south china sea authigenic mostly tubular pyrite aggregates from these sites consist of three types of pyrite framboids zoned aggregates with radial overgrowths surrounding a framboidal core and euhedral pyrite crystals framboids with low sims 34s values as low as 41 6 at hs148 and 38 8 at hs217 are dispersed throughout the cores but are especially abundant in the shallow part of the sedimentary column i e above 483 cmbsf in hs148 above 670 cmbsf in hs217 these patterns are interpreted to reflect the dominance of osr during early diagenetic processes in the shallow sediments with increasing depth both 34s values of bulk sulfide minerals and hand picked pyrite aggregates increase sharply at 483 cmbsf in core hs148 and at 700 cmbsf in core hs217 respectively radial pyrite overgrowths and euhedral crystals become abundant at depth typified by high 34s values for hand picked pyrite moreover sims analysis reveals an extreme variability of 34s values for the three pyrite types on a small scale in these zones besides some moderately 34s enriched framboids most of the overgrowths and euhedral crystals display extremely high sims 34s values as high as 114 8 at hs148 and 74 3 at hs217 representing the heaviest stable sulfur isotope composition of pyrite ever reported to the best of our knowledge such an abrupt and extreme increase in 34spyrite values with depth is best explained by an enrichment of 34s in the pool of dissolved sulfide caused by so4 aom in the sulfate methane transition zone smtz the increase in 34s values from framboidal cores to overgrowth layers and euhedral crystals indicates continuous and finally near to complete exhaustion of dissolved sulfate at the smtz following a rayleigh distillation process so4 aom allowed for subsequent growth of later stage pyrite over the initial framboids part of which formed earlier and at shallower depth by osr the combination of a detailed petrographic study of authigenic pyrite with sims analysis of stable sulfur isotopes in organic rich strata proves to be a powerful tool for reconstructing the dynamics of sulfur cycling in modern and potentially ancient sedimentary sequences

relating sulfate and methane dynamics to geology accretionary prism offshore sw taiwan geochemical data ch4 so42 i cl particulate organic carbon poc 13c ch4 and 13c co2 are presented from the upper 30 m of marine sediment on a tectonic submarine accretionary wedge offshore southwest taiwan the sampling stations covered three ridges tai nan yung an and good weather each characterized by bottom simulating reflectors acoustic turbidity and different types of faulting and anticlines sulfate and iodide concentrations varied little from seawater like values in the upper 1 3 m of sediment at all stations a feature that is consistent with irrigation of seawater by gas bubbles rising through the soft surface sediments below this depth sulfate was rapidly consumed within 5 10 m by anaerobic oxidation of methane aom at the sulfate methane transition carbon isotopic data imply a mainly biogenic methane source a numerical transport reaction model was used to identify the supply pathways of methane and estimate depth integrated turnover rates at the three ridges methane gas ascending from deep layers facilitated by thrusts and faults was by far the dominant term in the methane budget at all sites differences in the proximity of the sampling sites to the faults and anticlines mainly accounted for the variability in gas fluxes and depth integrated aom rates by comparison methane produced in situ by poc degradation within the modeled sediment column was unimportant this study demonstrates that the geochemical trends in the continental margins offshore sw taiwan are closely related to the different geological settings

a cryptic record of magma mixing in diorites revealed by high precision sims oxygen isotope analysis of zircons high precision in situ ion microprobe sims oxygen isotope analysis of zircons from two diorite intrusions associated with the late caledonian lochnagar pluton in scotland has revealed large differences in the degree of heterogeneity in zircon 18o between the diorites zircon crystals from the cul nan gad diorite cng show a unimodal distribution of oxygen isotope values 18o 6 0 0 6 2 and no or only minor grain scale variation those from the allt darrarie diorite ad1 show a large range in 18o and an apparent bimodal distribution with modes of 6 6 0 4 and 7 3 0 4 variations of up to 1 2 occur between and within grains both an increase and decrease in 18o with zircon growth has been observed the 18o composition of growing zircon can only change if open system processes affect the magma composition i e if material of contrasting 18o composition is added to the magma the variability in ad1 is interpreted to represent a cryptic record of magma mixing a deep crustal hot zone is a likely site for generation of the dioritic magmas which developed by mixing of residual melts and crustal partial melts or by melting of mafic lower crustal rocks the overall small number of zircons with mantle like 18o values 5 3 0 6 2 in the lochnagar diorites is largely the product of crustal differentiation rather than crustal growth the 18o of quartz from the cng and ad1 diorites shows only minor variation cng 10 9 0 5 2 ad1 11 7 0 6 2 within single populations with no evidence of mixing quartz zircon isotopic disequilibrium is consistent with later crystallisation of quartz from late magmatic fluids and in case of the ad1 diorite after the inferred magma mixing from a homogenised higher 18o melt high precision sims oxygen isotope analysis of zircon provides a new approach to identifying and resolving previously undetected early stage magma mixing and constraining the compositions and origins of the component magmas a combination of zircon quartz and whole rock data has proven to be a powerful tool in reconstructing the petrogenetic evolution of diorite from early crystallisation to late alteration

shear in the zonal drifts of 3 m irregularities inside spread f plumes observed over sanya incoherent scatter radars near magnetic equator regularly measured a vertical shear in zonal drifts of the evening background plasma with westward drifts below the equatorial f region peak and eastward drifts above we report here observations of a clear shear structure in the zonal drifts of 3 m irregularities inside spread f sf backscatter plumes measured with a 47 5 mhz coherent scatter radar operated at a low latitude site sanya 18 4 n 109 6 e dip latitude 12 8 n the radar interferometry analysis on the zonal drifts of the 3 m irregularities yields results consistent with that estimated from the irregularity echo doppler velocity measurements with multiple beams it is shown that the sf 3 m irregularities move westward at the lowest altitudes while at higher altitudes in the same sf plume structure the 3 m irregularities drift eastward one interesting point is that the vertical shear of zonal drifts was centered at 300 km altitude over sanya which maps to an apex altitude of 650 km at magnetic equator and is thus apparently higher than the apex altitudes 250 450 km where the zonal velocity shear has usually been observed analysis of the observations suggests that while the possibility of local generation of the shear flow of the irregularities can exist the possibility of a plasma vortex appearing at relative high altitudes causing the zonal drift shear of f region 3 m irregularities measured over sanya cannot be totally ruled out

western grenville province holds key to midcontinental granite rhyolite province enigma the mesoproterozoic granite rhyolite provinces in north america consist of a type granitic and rhyolitic rocks and their formation is commonly ascribed to continental extension or rifting the tectonic environment of the extension is however poorly understood new sm nd isotopic data from the central gneiss belt grenville province ontario suggest that rocks compositionally and temporally similar to those in the granite rhyolite provinces formed in and behind an active continental arc undergoing intra arc and back arc extension basaltic underplating accompanied extension providing heat and juvenile material source rocks vary from juvenile within the arc to more mature with increasing distance behind the arc recent investigations from sw baltica show that the rjukan group a proposed granite rhyolite province correlative also formed inboard of an active continental arc a tectonically and temporally similar and probably recurrent evolution along the vast laurentia baltica margin points to active continental margin processes as first order controls on back arc granite rhyolite magmatism

sources of methane inferred from pore water δ13c of dissolved inorganic carbon in pockmark g11 offshore mid norway abstract pockmark g11 is the most spectacular one among the pockmarks located at the southern border of voring plateau and 1 2 km away from the northern flank of the storegga slide mid norwegian continental margin for the first time detailed pore water geochemical studies were conducted to address methane hydrate occurrence methane seepage and associated geochemical processes and methane characteristics in the pockmark pore waters collected from five sediments cores inside and one sediment core outside the pockmark were analyzed for dissolved cl sulfate so42 total hydrogen sulfide h2s ca2 mg2 dissolved inorganic carbon dic 13cdic and 18o methane hydrates were recovered in all sediments below 0 75 m in a core inside pockmark g11 which is in good accordance with heavy oxygen isotope 1 9 to 2 3 smow and low cl concentrations 84 9 to 16 1 mm in pore waters pore water profiles indicate that upward migrating methane fluids are spatially variable in the pockmark with methane fluxes ranging from below detection in the center and outside to 0 30 0 54 mol m 2 a 1 inside in the cores with active methane fluxes maximum dic concentrations 19 4 to 21 5 mm and corresponding minimum 13cdic values 52 3 to 54 6 pdb occur within sulfate methane transition smt zones from 0 40 to 0 50 m below seafloor mbsf close to the seafloor simple mass balance modeling and 13cdic measurements within the smt zones suggest that methane in shallow sediments within pockmark g11 is microbial in origin pore water geochemistry and seabed observations suggest that methane fluxes inside pockmark g11 are episodic and derived mostly from the recycling of methane hydrate at depth during sediment burial

proterozoic onset of crustal reworking and collisional tectonics reappraisal of the zircon oxygen isotope record a global u pb and 18o zircon database shows temporal changes in the magmatic record related to changes in the degree of crustal reworking the 18o composition of bulk sediment remains relatively constant through geologic time with a mean value of 14 9 in contrast the 18o values in magmatic zircons vary from relatively low values averaging 6 in the archean to increasingly higher and scattered values defining a series of peaks and troughs in post archean data the degree of crustal reworking increases at times of supercontinent assembly therefore we attribute the pattern of post archean 18o values recorded by magmatic zircons to a significant increase in the incorporation of high 18o sediment in response to enhanced crustal thickening and reworking associated with the onset of collisional tectonics especially during formation of supercontinents

a photographic and acoustic transect across two deep water seafloor mounds mississippi canyon northern gulf of mexico in the northern gulf of mexico a series of seafloor mounds lie along the floor of the mississippi canyon in atwater valley lease blocks 13 and 14 the mounds one of which was drilled by the chevron joint industry project on methane hydrates in 2005 are interpreted to be vent related features that may contain significant accumulations of gas hydrate adjacent to gas and fluid migration pathways the mounds are located w150 km south of louisiana at w1300 m water depth new side scan sonar data multibeam bathymetry and near bottom photography along a 4 km northwest southeast transect crossing two of the mounds labeled d and f reveal the mounds detailed morphology and surficial characteristics mound d w250 m in diameter and 7 10 m in height has exposures of authigenic carbonates and appears to result from a seafloor vent of slow to moderate flux mound f which is w400 m in diameter and 10 15 m high is covered on its southwest flank by extruded mud flows a characteristic associated with moderate to rapid flux chemosynthetic communities visible on the bottom photographs are restricted to bacterial mats on both mounds and mussels at mound d no indications of surficial gas hydrates are evident on the bottom photographs published by elsevier ltd

isotopic evidence for rapid continental growth in an extensional accretionary orogen the tasmanides eastern australia the trace element signature of earth s continental crust resembles that of arc lavas but the continents may have formed during ancient igneous pulses that are hard to reconcile with supra subduction zone magmatism we explore the role of coupled arc back arc accretionary processes in crust generation by considering the tectonic context of whole rock nd isotope and zircon hf o isotope data from igneous rocks of the australian tasmanides 515 230 ma which is thought to have evolved by the repeated opening and closure of sediment filled back arc basins behind a long lived subduction zone the significance of this process for continental crust formation has yet to be evaluated from an isotopic perspective granitic rocks in this area define striking secular end ehf 18o trends that correlate with the pattern of deformational events and register changes in magma source during tectonic activity these trends reveal that juvenile magmatic input was enhanced during extensional back arc rifting episodes that immediately followed crustal thickening suggesting a relationship between slab rollback and continental growth interaction between juvenile magma and sedimentary units deposited during a preceding back arc rifting cycle was integral to the formation of stable continental material this highlights the importance of back arc environments for both the generation and differentiation of continental crust the juvenile component within the tasmanide igneous rocks increased from the cambrian to the triassic consistent with a diminished input from cratonderived metasedimentary material as the subduction zone migrated outboard of the gondwana margin subduction zone retreat formed large tracts of new crust in eastern australia at comparable rates to crust generation at modern island arcs providing a mechanism for rapid continental growth at convergent margins using isotopic tracers to link tectonic evolution and crust generation in modern and ancient orogens can lead to a better understanding of the geodynamic controls on planetary differentiation