low temperature hydrothermal maturation of organic matter in sediments from the atlantis ii deep red sea abstract hydrocarbons and bulk organic matter of two sediment cores no 84 and 126 chain 61 cruise located within the atlantis ii deep have been analyzed although the brines overlying the coring areas were reported to be sterile microbial inputs and minor terrestrial sources represent the major sedimentary organic material this input is derived from the upper water column above the brines both steroid and triterpenoid hydrocarbons show that extensive acid catalyzed reactions are occurring in the sediments in comparison with other hydrothermal guaymas basin or intrusive systems cape verde rise the atlantis ii deep exhibits a lower degree of thermal maturation this is easily deduced from the elemental composition of the kerogens and the absence of polynuclear aromatic hydrocarbons of a pyrolytic origin in the bitumen the lack of carbon number preference among the n alkanes suggests especially in the case of the long chain homologs that the organic matter of atlantis ii deep sediments has undergone some degree of catagenesis however the yields of hydrocarbons are much lower than those observed in other hydrothermal areas the effect of lower temperature and poor source rock characteristics appear to be responsible for the differences

geochemistry of interstitial gases in quaternary sediments of the gulf of california abstract interstitial gases from the deep sea drilling project dsdp ipod leg 64 sites 474 477 479 and 481 in the gulf of california have been analyzed by gas chromatography and stable isotope mass spectrometry in order to evaluate their compositions in terms of biogenic and thermogenic sources the hydrocarbon gas c 1 c 5 concentrations were comparable to the shipboard data and no olefins could be detected the 13 c data for the ch 4 confirmed the effects of the thermal stress on the sedimentary organic matter in that the values were typically biogenic near the surface and become more depleted in 12 c vs depth at sites 474 478 and 481 the ch 4 at site 477 was the heaviest in 13 c and at site 479 it did not show a predominant high termperature component the co 2 at depth from most sites was of a primarily thermogenic origin from carbonate decomposition

anomalous high frequency wave propagation from the tonga kermadec seismic zone to new zealand summary bulletins of the international seismological centre isc show very large residuals up to 15 s early for arrivals from events in the tongakermadec subduction zone to the new zealand network of seismometers the very early arrivals are confined to events south of about 22 s and shallower than about 350 km the waveforms show two distinct phases an early emergent first phase with energy in the high frequency band 2 10 hz and a distinct second phase containing lower frequency energy arriving at about the time predicted by jb tables the residuals are attributed to propagation through the cold subducted lithosphere which has a seismic velocity 5 per cent faster on average than normal ray tracing shows that the ray paths lie very close to the slab for events south of 22 s but pass well beneath the slab for events further north corresponding to the change in residual pattern this characteristic of the ray paths is due to the curved shape of the seismic zone and in particular to the bend in the zone where the louisville ridge intersects the trench at 25 s the residuals can only be explained if the high velocity anomaly extends to a depth of 450 km in the region of the gap in deep seismicity from 32 to 36 s the very high frequency character of the first phase requires the path from the bottom of the slab to the stations to be of high q and to transmit 2 10 hz energy with little attenuation the absence of low frequency energy in the first phase is due to the narrowness of the high velocity slab which transmits only short wavelength waves the second phase which contains low frequencies is identified as a p wave travelling beneath the subducted slab in normal mantle there is no need to invoke any special structures such as low velocity waveguides or reflectors to explain any of the observations the s wave arrivals show similar effects

hydrothermal effects on organic matter high vs low temperature components abstract hydrothermal activity and sea bed mounds have been explored in guaymas basin central gulf of california by the deep sea drilling project piston coring dredging and diving with the d s r v alvin the deep seated magmatic heat flow causes extensive thermal alteration of both organic and mineral matter especially in the case of the south rift of guaymas basin this results in hydrothermal circulation with concomitant migration of organic pyrolysate to the seabed the bitumen at depth of dsdp sites 477 and 481 contained thermogenic components such as primary olefins thermodynamically stabilized molecular markers 17 h hopanes and elemental sulfur with traces of polynuclear aromatic hydrocarbons pah the major components were n alkanes with no carbon number predominance and unresolvable complex branched and cyclic hydrocarbons hump which are typical of mature petroleum and were generated by the heat from the intrusives and magma dredge samples recovered from a mound in guaymas basin contained petroleum of a thermogenic origin as confirmed by the presence of gasoline range hydrocarbons a broad distribution of n alkanes c13 c33 no carbon number predominance hump pristane and phytane olefins and pah and large amounts of aromatic naphthenic and asphaltic material similar petroleums subsequently recovered from other active mounds in the southern rift by the d s r v alvin had analogous compositions ranging from volatile to heavy oils in pyrrhotite chimneys the extractable organic matter consisted of mainly higher molecular weight pah these petroleums are derived from the immature primarily marine organic matter at depth by thermal alteration rapid quenching by hydrothermal removal and migration followed by condensation at the sea bed results in the manifestations of oil as part of the sulfide formations exterior exposed oil samples are degraded and leached whereas interior samples are essentially unaltered the pah are high temperature resynthesis aromatization products that condense in the hottest parts of the vent systems

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

dispersion of p waves in subducted lithosphere evidence for an eclogite layer cold subducted lithosphere has relatively fast seismic velocity which leads to early arrivals for some event station paths the effect is very large for events in the tonga kermadec deep seismic zone recorded at certain new zealand stations these particular arrivals are very high frequency 3 hz or greater and sometimes resemble two distinct phases the later arrival appearing at about the time predicted by jeffreys bullen tables data from the digital station snzo in wellington confirm the travel time results of the analog stations and furthermore show frequencies above 5 hz much higher than can be seen on analog records and up to 4 dispersion in the range 1 8 hz energy in the second phase which is often absent at snzo is mainly 1 2 hz the digital data support the idea proposed earlier that the effect is caused by propagation through a thin slab which passes only short wavelength waves the essential features of the wave propagation are modeled by acoustic waves in a one dimensional high velocity slab the waveforms produced by the model are discussed in terms of the leaky modes of the system and calculated by a reflectivity method a very thin 15 km uniform slab provides the required dispersion but the waves are heavily attenuated and would never be observed at teleseismic distances a thicker slab allows the energy through but does not give enough dispersion altering the variation of velocity across the slab provides the required dispersion if a thick high velocity layer with wave speed increasing gradually with height is overlain by a thin lid of even higher velocity for the models considered the lid thickness must lie in the range 6 15 km and be continuous from a depth of about 50 km to the bottom of the earthquake zone the thick layer could arise from the thermal anomaly in the subducted lithosphere the thin lid may be the gabbroic part of the subducted crust that has transformed to eclogite

composition and origin of hydrothermal petroleum and associated lipids in the sulfide deposits of the rainbow field mid atlantic ridge at 36 n the lipid components in hydrothermal sulfide deposits from the rainbow vent field mid atlantic ridge at 36 n were studied by gas chromatography mass spectrometry the rainbow vent field is one of two known active hydrothermal systems related to abyssal circulation where high temperature fluids are formed during serpentinization of ultrabasic crustal rocks the major amount of the extractable organic matter from the sulfides consists of normal and branched alkanes ucm pahs terpenoids and fatty acids the branched alkanes are comprised of unique gem diethylalkane series possibly from sulfide oxidizing bacteria and biphytanes from archaea the characteristic lipid and biomarker compounds found in the hydrothermal samples support a predominantly biological origin of the bitumens from the thermal transformation of the biomass of microorganisms bacteria and archea and minor macrofauna of this vent field a search for molecular evidence for abiogenic thermocatalytic synthesis of organic compounds was negative however methane in the hydrothermal fluids and possibly a minor amount of the alkanes in the sulfides may be of an abiogenic origin in the rainbow vent field

oil of the volcano uzon caldera kamchatka there are reported gas chromatography gas chromatography mass spectrometry and carbon isotopic data on the oils sampled in caldera of the uzon volcano east kamchatka the uzon volcano is located in the west of the eastern kamchatka basin which is made up of thick paleogene neogene sedimentary rocks its caldera is made up of lacustrine volcanogenic sedimentary formations of pleistocene age 38 70 thousand years lying on dense basalts two samples studied were heavy oils 0 915 g ml and contained 2 sulfur 2 5 paraffin 9 3 waxes 1 4 wt olefinic hydrocarbons their gas chromatograms show a mono modal distribution for n alkanes with a maximum at c18 pristane phytane concentration ratios were measured to be 0 48 0 52 olefinic hydrocarbons were interpreted to be of hydrothermal origin sterane and triterpane biomarkers indicated a low maturation degree and a lacustrine orgin of the initial organic matter the uzon oil was found to be isotopically heavy with a 13c value of 21 14c isotope was detected which indicates that recent plant organic matter was significantly involved in oil generation process

high resolution nitrogen stable isotope sclerochronology of bivalve shell carbonate bound organics nitrogen stable isotope ratios 15n of organic material have successfully been used to track food web dynamics nitrogen baselines pollution and nitrogen cycling extending the 15n record back in time has not been straightforward due to a lack of suitable substrates in which 15n records are faithfully preserved thus sparking interest in utilizing skeletal carbonate bound organic matter cbom in mollusks corals and foraminifera here we test if calcite pecten maximus shells from the bay of brest and the french continental shelf can be used as an archive of 15n values over a large environmental gradient and at a high temporal resolution approximately weekly bulk cbom 15n values from the growing tip of shells collected over a large nitrogen isotope gradient were strongly correlated with adductor muscle tissue 15n values r2 0 99 n 6 p 0 0001 we were able to achieve weekly resolution on average over the growing season from sclerochronological profiles of three shells which showed large seasonal variations up to 3 4 however there were also large inter specimen differences up to 2 5 between shells growing at the same time and location generally high resolution shell 15n data follow soft tissue 15n values but soft tissues integrate more time hence soft tissue data are more time averaged and smoothed museum archived shells from the 1950s 1965 and 1970s do not show a large difference in 15n values through time despite expected increasing n loading to the bay over this time which could be due to anthropogenic n sources with contrasting values compiling shell cbom 15n data from several studies suggests that the offset between soft tissue and shell 15n values tissue shell differs between calcite and aragonite shells we hypothesize that this difference is caused by differences in amino acids used in constructing the different minerals which should be specific to the caco3 polymorph being constructed future work should use compound specific isotope analyses csia to test this hypothesis and to determine whether certain amino acids could specifically track n sources or possibly identify amino acids that are more resistant to diagenesis in fossil shells in conclusion bivalve shell cbom 15n values can be used in a similar manner to soft tissue 15n values and can track various biogeochemical events at a very high resolution

petroleum characteristics of the oil in a guaymas basin hydrothermal chimney abstract extensive petroleum shows have been sampled from the seabed of guaymas basin these petroleums were generated at depth by hydrothermal activity from immature sedimentary organic matter and migrated to the sea floor there the heavy ends solodify due to the temperature drop and the volatiles are emitted as plumes thus it is of interest to determine the petroleum characteristics of such oils for comparison with normal reservoir petroleums an oil saturated sample of a chimney alvin dive 1630 emitting water at 200 c was studied in contained 21 7 solvent extractable oil and 19 2 s moisture the oil has an api gravity of 27 6 a specific gravity at 20 c of 0 8891 and contains 0 99 s the astm distillation yields vol are gasoline 3 0 ibp 149 c ibp 300 f intermediates 149 315 c 300 660 f 61 0 gas oil 315 538 c 660 1000 f 21 0 and residue 538 c 1000 f 15 0 gas chromatography and ft infrared spectrometry indicate that this oil is similar to typical reservoir petroleum but with the low ends and aromatics depleted due to water washing mild thermal conditions are indicated by the absence of cracking products

upper mantle p wave velocities in the southeast north island new zealand abstract reversed pn velocities have been determined from regional earthquake sources for the wairarapa region in the southeast north island new zealand values were 8 64 0 13 km s in the easternmost part of the region and 8 90 0 13 km s in the central wairarapa which are consistent with subducted pacific plate lying at shallow depth under the region a value of 8 22 km s between wellington and the wairarapa region is interpreted as a possible difference in the velocity structure above the refractor between the two localities

liquid hydrocarbon bearing inclusions in modern hydrothermal chimmeys and mounds from the southern trough of guaymas basin gulf of california abstract liquid hydrocarbon bearing inclusions of variable shape e g spherical bowling pin rod and highly irregular occur in hydothermal minerals of chimneys and mounds in the southern trough of guaymas basin central gulf of california the inclusions are preferentially trapped in amorphous silica which occurs as spherules and 0 01 mm thick encrustations on sulfides sulfates and carbonates the inclusions are primary and pseudosecondary and were trapped during not after mineral growth the inclusions are both two phase liquid hydrocarbon and vapor gas and three phase liquid hydrocarbon aqueous fluid and vapor and range from 2 to 50 m in diameter the large range in liquid hydrocarbon and acqueous fluid contents indicates that the hydrothermall fluid and liquid hydrocarbon were never a homogeneous solution but that hydrocarbons were transported as immiscible and possibly solvated forms the liquid hydrocarbon varies in color from deep to pale orange brown and fluoresces a yellow color during excitation by u v light indicating a condesate mainly c 1 to c 10 hydrocarbons composition measurable quantities of hydrocarbons from the inclusions could not be isolated by mineral dissolution by pyrolsis and decrepitation analyses suggest that the more volatile components predominate two phase hydrocarbon inclusions homogenized with the liquid at temperatures ranging from 75 to 190 c excluding one high measurement to obtain true trapping temperatures an unknown pressure correction is required however the trapping temperature of these hydrocarbon inclusions was estimated by measuring trapping temperatures for adjacent aqueous inclusions which range from 116 to 226 c geochemical modelling using these trapping temperatures indicates that the amorphous silica precipitated from the hydrothermal fluid due to conductive cooling in addition to mixing with ambient sea water the temperatures required for the formation of petroleum and its transport to the seafloor in the guaymas basin coincide with those necessary for the precipitation of amorphous silica in the guaymas basin hydrothermal system

hydrothermal geochemistry of sediments and pore waters in escanaba trough odp leg 169 geochemical studies of pore fluids and solid phases in two ocean drilling program odp drill sites sites 1037 and 1038 in the escanaba trough off northern california have provided further data on the hydrothermal processes associated with the spreading of the gorda ridge previous work in the area of odp site 1038 includes the discovery of a hydrothermal system and associated sulfide deposits centered around an uplifted sediment hill in this sedimented extensional environment this earlier work provided some insights into the present nature of venting however only deep drilling investigations can provide the means to fully understand the genesis and evolution of this system and associated hydrothermal deposits odp leg 169 is the third deep drilling operation to explore the magnitude genesis and evolution of hydrothermal systems on sedimented ridges previous studies centered on the guaymas basin in the gulf of california and the middle valley in the ne pacific ocean pore water studies in the reference odp site 1037 and in the hydrothermally active area of odp site 1038 have revealed the presence of a complex system of hydrothermally originated fluids whereas the data in the reference site indicate recent hydrothermal activity in the basal part of the drill site the evidence in site 1038 suggests that fluids of hydrothermal origin spread out at shallow depths around the central hill causing substantial sediment alteration as well as deposition of hydrothermal sulfides in the near surface zone of the sediments a second major discovery at site 1038 was the evidence for fluid phase separation at depth at temperatures possibly in excess of 400 c this conclusion is based on the presence of both low cl and high cl fluids the latter appear to be advected rapidly towards the surface presumably along cracks and faults the low cl fluids however appear to be transported laterally along sandy horizons in the sediments thus signifying two very different migration pathways for high cl and low cl hydrothermally phase separated fluids studies of the organic geochemistry of dissolved gases and matured organic matter corroborate these findings of extensive hydrothermal alteration of the sediments

late holocene radiocarbon and aspartic acid racemization dating of deep sea octocorals abstract primnoa resedaeformis is a deep sea gorgonian coral with a two part skeleton of calcite and gorgonin a fibrillar protein potentially containing long term records of valuable paleo environmental information for various reasons both radiocarbon and u th dating of these corals is problematic over the last few centuries this paper explores aspartic acid racemization dating of the gorgonin fraction in modern and fossil specimens collected from the nw atlantic ocean radiocarbon dating of the fossil specimen indicates a lifespan of 700 100 years the longest yet documented for any octocoral gorgonin amino acid compositions were identical in the fossil and modern specimens indicating resistance to organic diagenesis similar to bone collagen the fibrillar protein of gorgonin may impose conformational constraints on the racemization of asp at low temperatures the rate of racemization of aspartic acid d l asp was similar to previously published results from an 1800 year old anemone gerardia the age equation was age years bp 2000 ad d l 0 020 002 0011 0001 2 r2 0 97 p d l asp was marginally better than that for 14c dating over the most recent 50 200 years although the dating error may be improved by inclusion of more samples over a broader time range these results suggest that d l asp dating may be useful in augmenting 14c dating in cases where 14c calibrations yield two or more intercept ages or in screening samples for further 14c or u th dating

sources and hydrothermal alteration of organic matter in quaternary sediments a synthesis of studies from the central gulf of california abstract deep sea drilling in the central gulf of california a young and active spreading centre shows that the high heat flow typical of these regions causes extensive alteration of sediment organic matter especially near sills and above magma chambers where hydrothermal activity is concentrated even on the nearby passive margin where there are no sills heat flow is moderately high and hydrocarbon generation has begun in immature sequences migrating light hydrocarbons are detected especially where hydrothermal activity is concentrated thermogenic methane is more widespread though not in the passive margin bordering the spreading centre despite the incidence of hydrocarbon generation and migration the amounts of hydrocarbons involved are relatively small and apparently do not lead to commercially significant accumulations of petroleum the organic matter in these sediments is mostly marine because the gulf of california generally has low runoff from land and highly productive surface waters turbidites rich in terrigenous organic material are locally abundant in the mainly pelagic section in the guaymas basin the highest concentrations of organic matter are found in laminated diatomites deposited on the guaymas passive margin within the oxygen minimum zone

decadal change in the relationship between the oceanic entrainment temperature and thermocline depth in the far western tropical pacific n n the interaction between the thermocline and mixed layer is a key process important to the el nino southern oscillation enso in the tropical pacific climate system decadal changes in the relationships between the depth of 20 degrees c isotherm d 20c and the temperature of subsurface water entrained into the mixed layer t e are analyzed using observed temperature data during the periods 1955 2003 in association with the 1976 77 climate shift the thermocline in the western tropical pacific is anomalously deep before the shift but shallow after the shift it is found that the relationship has undergone decadal change in the far western tropical pacific west of 160 degrees e the effects of the decadal changes in the d 20c t e relationships on enso properties are further examined using an intermediate coupled model icm it is demonstrated that enso properties are sensitive to the decadal changes in the d 20c t e relationship in the far western tropical pacific

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

organic geochemistry of deep sea drilling project sediments from the gulf of calofornia hydrothermal effects on unconsolidated diatom ooze abstract the effects of intrusive thermal stress have been studied on a number of pleistocene sediment samples obtained from leg 64 of the dsdp ipod program in the gulf of california samples were selected from sites 477 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions for comparison purposes samples from sites 474 and 479 were selected as representative of unaltered material the gc and gc ms data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher plant detritus samples from sill proximities were found to contain thermally derived distillates and those adjacent to sills contained essentially no lipids curie point pyrolysis combined with gc and gc ms was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin pyrograms of the altered kerogens were much less complex than the unaltered samples reflecting the thermal effects the kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated wet sediments resulted in in situ pyrolysis of the organic matter examination of the kerogens by esr showed that spin density and line width pass through a maximum during the course of alteration but esr g values show no correlation with maturity stable carbon isotope 13 c values of kerogens decrease by 1 1 5 near the sills at sites 477 and 481 and the atomic n c decreases slightly with proximity to a smaller sill at site 478 differences in maturation behavior between site 477 and 481 and site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of guaymas basin protokerogen

the effect of the descending lithosphere beneath the tonga island arc on p wave travel time residuals at the warramunga seismic array abstract p wave travel time residuals at the warramunga seismic array wra in the northern territory australia have been studied from 49 earthquakes with epicenters south of 19 s in the fiji tonga region focal depths are between 42 and 679 km as determined from pp p using the jeffreys bullen and the herrin travel time tables the epicentral parameters have been redetermined by considering only normal seismic stations in the location procedure these are those stations where p wave travel times are probably not affected by lateral heterogeneities caused by the lithosphere descending beneath the tonga trench epicenters of deep earthquakes below 300 km have been relocated by using stations at 25 only epicenters from shallower depth earthquakes have been recalculated without using stations between 35

characteristics and source of inorganic and organic compounds in the sediments from two hydrothermal fields of the central indian and mid atlantic ridges a combined inorganic and organic geochemical study was carried out on sediments collected from the kairei hydrothermal field on the central indian ridge cir and the logatchev hydrothermal field on the mid atlantic ridge mar analysis of the major and trace elements as well as the minerals shows that the kairei hydrothermal sediments are formed by the mixing of silica rich hydrothermal fluids with mg rich seawaters but the logatchev sediments are associated with pelagic carbonate oozes containing some precipitates derived from hydrothermal plume fall out the rare earth element ree patterns of kairei sediments show a character of light ree lree enrichment and positive eu anomaly whereas two of the three logatchev sediment samples lack positive eu anomaly and have negative ce anomaly patterns of aliphatic hydrocarbon fractions in the sediments from both hydrothermal fields exhibit high relative concentrations of volatile resolved components smooth n alkane distributions and high concentrations of the isoprenoids pristane and phytane the composition of organic matter and c isotope composition of individual n alkanes indicate that they come from marine photosynthetic autotrophs and hydrothermal organisms as well as terrestrial inputs in the kairei and the logatchev hydrothermal fields several parameters of organic geochemistry used for assessing the maturity of bitumen are well correlated with one another in general these parameters indicate that the kairei sediments are more mature than the logatchev sediments the relationship between the inorganic parameters ree fe and eu eu and the organic parameter bitumen maturity might reflect changes of the hydrothermal influence on the sediments the results of this study provide an insight into the variation of inorganic and organic geochemistry in deep sea hydrothermal systems

observations of very high p velocities in the subducted slab new zealand and their relation with the slab geometry summary a set of high quality aftershock data recorded on a closely spaced network of seismographs at wellington new zealand has enabled the determination of apparent wavefront speeds and azimuths controlled by the subducting pacific plate the former were very high 8 7 f 0 2 km s and the latter were shifted by as much as 10 eastward of the source receiver line which made an angle of about 12 downdip with the strike of the subducted slab beneath the north island the wavefront characteristics are modelled in terms of head wave propagation along a curved refractor with a cylindrical geometry using both a simple geometrical approach as well as a 3 d ray tracing program with this structure it is not possible to explain both the high apparent velocity as well as the large azimuthal anomaly without the presence of an unusually high p wave velocity of around 9 0 km s within the upper mantle of the subducted pacific plate such high velocities although reported previously in the north island are very hard to reconcile with known upper mantle rock velocities other alternatives were sought to explain the apparent slowness in particular modifications in the slab curvature along strike according to proposed models were found to contribute to the high wavefront speeds but very high intrinsic p velocities 8 8 km s l are still required from slowness vector data it is not possible to constrain the depth at which such velocities have to exist however traveltime considerations limit them to depths between the base of the subducted oceanic crust to about 12 km deeper

seismic anisotropy in the fore arc region of the hikurangi subduction zone new zealand abstract shear waves from local earthquakes recorded on an array of nine broad band seismograph stations have been used to investigate the anisotropic structure within the crust of the overlying australian plate and within and below the subducting slab underlying the southern north island new zealand earthquakes near the plate interface were used to image the crustal anisotropy whereas deeper down dip subduction zone events were used to sample the subducting slab and the mantle below apart from a small amount of variable near surface anisotropy top few kilometres of the crust the measured fast shear wave directions of both the crust of the overlying plate 51 18 and the mantle 41 15 are similar and are nearly parallel to the strike of the subduction zone and the dominant geological features of the region sks measurements which mainly sample the mantle beneath the subducting plate give a value of 28 11 and measurements made elsewhere in the new zealand region using sks and scs2 produce similar results the measurements of crustal anisotropy are similar to those found further south on the wellington peninsula and confirm the presence of near surface anisotropy the maximum delay times for crustal earthquakes indicate a pervasive shear wave velocity anisotropy of 4 in the crust of the overlying plate and the increase in the delay times with depth for the subduction zone earthquakes translates to a shear wave velocity anisotropy of 1 4 in the mantle below the subducting slab these results when combined with the sks measurements suggest trench parallel flow in the mantle below the subducted slab and a coherence of the deformation processes in the crust of the overlying plate and the mantle beneath the subducting slab

penetration of anthropogenic carbon into organic particles of the deep ocean 1 in the late 1980s bomb 14c was present in suspended particulate organic carbon poc from the north central pacific ncp and sargasso sea ss throughout most of the water column demonstrating that deep poc had exchanged with atmospheric co2 in the past 30 years upon reoccupation of these sites in 1999 and 2000 respectively we observed that the 13c values of suspended poc were lower than those measured a decade earlier this demonstrates that anthropogenic co2 from fossil fuel and biomass burning has penetrated a major organic matter pool in the deep ocean 14c measured in the suspended poc showed similar or higher values in the deep sargasso sea and decreased values in the deep ncp compared to those measured previously we use a box model to show that the differences in the radiocarbon results are likely due to the presence of resuspended sediment that is laterally advected from the continental margin to the deep sargasso sea

anisotropic models of the upper mantle long period rayleigh wave and love wave dispersion data particularly for oceanic areas have not been simultaneously satisfied by an isotropic structure in this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy anelastic dispersion sphericity and gravity we assume that the surface wave data represents an azimuthal average of actual velocities thus we can treat the mantle as transversely isotropic the resulting models for average earth average ocean and oceanic regions divided according to the age of the ocean floor are quite different from previous results which ignore the above effects the models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies the correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive for most of the earth sh sv in the vicinity of the low velocity zone neat the east pacific rise however sv sh at depth consistent with ascending flow anisotropy is as important as temperature in causing radial and lateral variations in velocity the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age this layer defines the lid or seismic lithosphere in the pacific the lid thickens with age to a maximum thickness of 50 km this thickness is comparable to the thickness of the elastic lithosphere the lid thickness is thinner than derived using isotropic or pseudo isotropic procedures a new model for average earth is obtained which includes a thin lid this model extends the fit of a prem type model to shorter period surface waves

geochemical study of hydrothermal core sediments and rocks from the guaymas basin gulf of california abstract a geochemical study of core sediments from the guaymas basin was undertaken by x ray analysis and showed minerals such as barite gypsum wurtzite chalcopyrite marcasite galena and calcite the random relation between metal concentration and core depth apparently reflects the chages in hydrothermal activity mineral grains with holes and cavities were observed by sem photomicrography these holes are probably due to degastification of the samples which can be related to the presence of the guaymas basin is due to active extensional tectonics the associated seismic activity in the southern rift valley and the high rate of sedimentation

hydrothermal petroleum generation in red sea sediments from the kebrit and shaban deeps abstract petroleum impregnated sediments and massive sulfides have been found in two deeps of the northerns red sea biological marker distributions in extracts and polar fraction degradation products were analyzed in order to elucidate the source of the petroliferous material two organic phases could be distinguished according to their source and maturity the amounts of n alkanes show a marked decrease with depth whereas the concentrations of various branched and cyclic hydrocarbons increase resulting in a humpof unresolvable compounds in a depth as shallow as 300 cm changes in concentrations and distributions of hopanoids in the kebrit deep sediments indicate a rapid increase of maturity with depth the deepest core section 300 cm and the masive sulfide reveal comparable maturation indices typical for mature oils by chemical degradation of the polar fractions a series of c 40 isoprenoids was obtained which reveals a considerable contribution from methanogenic and thermophilic archapbacteria to the immature organic matter the data suggest that petroliferous material ofthermogenic origin migrates through the younger sequences superimposes the autochthonous organic substances in the sediments and furthermore forms asphaltic impregnations in the massive sulfides

p wave travel times from the tonga subduction zone to stations on the oceanic side of the tonga kermadec trench p waves propagating from shallow earthquakes in the tonga kermadec seismic zone to regional stations in raratonga and niue are associated with large negative travel time residuals observed minus jeffreys bullen time of the order of 10 s for focal depths below 100 km the magnitude of residuals decreases sharply to about 2 5 s for depths near 200 km the pattern of residuals is explained by a model of oceanic lithosphere possessing an upper mantle p wave velocity of 8 3 km s and having its base at a depth near 100 km

origin of petroliferous bitumen from the buyuk menderes gediz geothermal graben system denizli saraykoy western turkey abstract the kb 5 well is located at the intersection of the geothermally active menderes and gediz graben systems in western turkey significant volumes of petroleum like material plm with its associated thermal water 120 c erupted onto the surface during drilling from a depth of 120 132 m i e from the claystone and marl rich early to middle pliocene kolonkoya formation the purpose of this paper is 1 to characterize this plm 2 to assess the source characteristics from which the plm was likely generated and 3 to recognize the generation mechanism considering the geothermal gradual versus the hydrothermal rapid processes analytical organic geochemistry using thin layer chromatographic separation followed by gas chromatography mass spectrometry gc ms was carried out the plm is composed primarily of polar nso compounds asphaltenes 77 this feature is similar to hydrothermal petroleums e g calcite springs yellowstone national park wyoming the plm shows n alkanes ranging from n c 19 to n c 38 i e with a maximum at n c 30 but n alkanes are depleted in n c 19 an absence of acyclic isoprenoids pristane and phytane and considerably large ucm unresolved complex mixture indicate that the plm has been subjected to a moderate degree of alteration possibly by the accompanying hot geothermal waters the source specific biomarkers i e low c 29 nh c 30 h ratio presence of gammacerane and 18 h oleanane high c 35 c 34 homohopane ratio and c 29 sterane concentration n c 28 n c 27 n c 29 c 28 27 29 r steranes c 29 r c 27 r suggest that the plm is a petroleum and was most likely generated from a tertiary source rock with a carbonate clay rich lithology the source organic matter was predominantly terrestrial and bacterial detritus deposited in relatively saline anoxic environmental conditions maturity sensitive biomarker parameters i e t m t s c 29 sterane 20 s 20 s 20 r 0 35 c 32 hopane 22 s 22 s 22 r 0 57 low diasterane regular sterane ratio correspond to a maturity level of approximately 0 50 0 60 r o this level of maturation could not be reached by such a young upper miocene lower pliocene and shallow sedimentary column max 600 m in the absence of instantaneous hydrothermal activity pahs are not detectable but series of alkylbenzenes alkyltoluenes alk 1 enes and triaromatic steranes are present the lack of organic richness and maturity in the drilled section of the kb 5 well indicates that the petroleum was generated in the deeper sections of the formation the temperature profile of the well and composition of the hydrocarbons in the petroleum suggest that the temperature of the hydrothermal activity during hydrocarbon generation was

organic geothermometry of petroleum from escanaba trough offshore northern california abstract we have measured the extent of hopane and sterane isomerization and of monoaromatic steroid hydrocarbon aromatization in a sample of hydrothermally derived petroleum from the escanaba trough a sediment covered volcanically active ridge axis the results along with kinetic parameters predict the possible time temperature history of the petrolum forming process for this sample the extent of these reactions is consistent with petroleum formation by intense heating about 300 350 c if the time period of this heating was as short as about 100 yr such a time scale is reasonable for hydrothermal discharge events associated with ridge crest volcanism

the p velocity within the tonga benioff zone determined from traced rays and observations p waves with travel time residuals between 0 s and 12 s are observed at regional stations in samoa afi and raoul island rao for 39 earthquakes in tonga with focal depths between 70 km and 300 km these anomalously large residuals apparently are produced because seismic phases travel along the strike of the tonga benioff zone within the high velocity subducted lithosphere for up to 1200 km before arriving at afi and rao to eliminate erroneous residuals caused by poor event locations we selected 11 stations and reread the available p times at these stations for the 39 events these arrivals and pp p intervals were used to relocate the events using a variant of the joint hypocenter determination method then the pattern of residuals at afi and rao not used in the relocation was compared to the pattern of residuals expected for various models of the subducted lithosphere as determined by ray tracing the observed pattern of residuals at afi is consistent with the ray traced models if some of the first arrivals are produced by rays traveling directly along the strike of the subducting lithosphere and if others are produced by rays which reflect once off the upper surface of the subducting lithosphere before arriving at afi the observed residuals can be explained by a model where the p velocity in the subducted lithosphere is 8 higher than the velocity in the herrin model the residuals are fit even better by a layered slab model in which the seismic velocity is about 6 higher than the herrin velocity at the upper surface of the subducted lithosphere and about 9 higher at the bottom of the slab these velocity contrasts could be produced if the temperature in the slab was 700 c cooler than the surrounding mantle and if there were no partially melted material within the slab the existence of these anomalously large residuals suggests that the high velocity region in the upper 300 km of the mantle beneath tonga must be fairly continuous over distances of 1000 km and more

upper mantle anisotropy in the s w pacific from earthquake travel time analysis abstract the negative p residuals from readings at stations on niue rarotonga and the chatham islands of shallower events along the tonga kermadec trench and below the north island new zealand exhibit a scatter too large to be accounted for solely by observation and mislocation errors the corresponding wavepaths cover a range of propagation azimuths between n30 e and n180 e travel times from a large number of events reveal a variation of p velocity with azimuth which is consistent with large scale upper mantle anisotropy in this area the p velocity varies from a maximum of 8 4 km s 1 along n62 e to a minimum of 7 8 km s 1 along a perpendicular axis perhaps indicating a fossil spreading direction along n62 e there is also a very consistent but unexplained variation of p residuals with earthquake depths between 0 and 100 km an observation warranting further study

hydrothermal petroleum in the sediments of the andaman backarc basin indian ocean abstract recent sediments of the andaman backarc basin indian ocean between the andaman nicobar islands and the malay peninsula have been analyzed for biomarker lipids three cores were selected one each from the fault zone in a deep basin a graben between two fault systems another from a location adjacent to the fault and the third from the topographic high in the rift valley the molecular composition of the lipid classes n alkanes isoprenoids alkylbenzenes alkylcyclohexanes hopanoids polycyclic aromatic hydrocarbons steranes alcohols sterols and fatty acids was examined by gas chromatography gc and gc mass spectrometry to understand the nature and source of the hydrocarbons present and the processes of maturation of organic matter the data show that the hydrocarbons are of hydrothermal origin derived from thermal alteration of sedimentary organic matter consisting of a mixture predominantly of marine derived components with some terrestrial inputs normal alcohols and fatty acids also corroborate the distribution of n alkanes the distribution profiles and various parameters computed from the concentration of the target compounds suggest that oxidative reactions and microbial degradation in this environment are insignificant triterpane and pah compositions indicate that the thermal maturity of the bitumen in the samples is comparable to or lower than that found at other hydrothermal regions such as the northern juan de fuca ridge guaymas basin and escanaba trough

solution and laser ablation inductively coupled plasma mass spectrometry measurements of br i pb mn cd zn and b in the organic skeleton of soft corals and black corals proxy records can be derived from soft corals and black corals using minor and trace element measurements of the organic skeleton of these corals here concentrations of br i pb mn cd zn and b in the organic skeleton were determined using solution inductively coupled plasma mass spectrometry icp ms in one black coral from 5 m depth and two soft corals from 85 and 105 m depth collected from a reef offshore of palau in the western tropical pacific solution icp ms results indicate that concentrations of some elements vary as expected with depth cd and mn while others are taxa specific i or colony specific br pb zn and b the intensities of the same elements normalized to 13c were also measured at high resolution using laser ablation la icp ms along radial transects covering the lifespan of the colonies the results here indicate that high resolution la icp ms elemental records in black corals could be more fully developed for paleoceanographic reconstructions in contrast results of the laser transects from the two soft corals were not reproducible for any of the elements and no discernible patterns were detected that could be developed into reliable proxy records using the current la icp ms method

stable nitrogen and carbon isotope δ15n and δ13c variability in shallow tropical pacific soft coral and black coral taxa and implications for paleoceanographic reconstructions abstract soft corals and black corals are useful proxy tools for paleoceanographic reconstructions however most work has focused on deep water taxa and few studies have used these corals as proxy organisms in shallow water

biogeochemical characterization of particulate organic matter from a coastal hydrothermal vent zone in the aegean sea abstract three particle interceptor traps were moored from june to september 1996 along the se coast of milos island aegean sea in an area known for its extensive seabed geothermal activity the settling particles collected differed between sites not only in quantity but also in their geochemical composition in the area directly influenced by warm water vents the vertical flux of particulate material was almost one order of magnitude higher than that observed at the reference sites 6 5 km away from the vents with a higher contribution of biogenic material in the former the neutral lipid fractions exhibited a significant zooplankton biomarker signature e g cholesterol and wax esters followed by those of microalgal and terrigenous remains the biogeochemical cycle of sterols included the formation of steroidal ketones thiols and stanols the latter two particularly associated with the venting activity moreover the aliphatic and aromatic hydrocarbons in the particles from the venting area reflected a locally enhanced maturity of the organic matter although part of the material collected in the traps may have been exported in the vent waters the higher fluxes observed in the vicinity of the hydrothermal plumes are mainly the result of an assemblage of zooplankton which in turn may contribute significantly to the sedimentation through fast sinking faecal pellets of the petrogenic hydrocarbons possibly generated in the vents

organic geochemistry of core samples from an ultradeep hot well 300 c 7 km south texas cores of lower cretaceous rocks from a depth of 6400 8 to 7544 6 m at present day temperatures of 262 296 c have high concentrations of c15 hydrocarbons bitumen coefficients range from 105 to 367 mg g and c15 extractable bitumen ranges from 500 to 2200 ppm some generation potential remains associated with the kerogen of these rocks in addition to exhibiting the above organic geochemical properties characteristic of the zone of intense hydrocarbon generation these rocks also have organic geochemical properties attributed to the zone of hydrocarbon extinction or greenschist metamorphism these characteristics are high vitrinite reflectance r0 values 4 4 4 8 low h c ratios 0 30 0 58 high saturate aromatic hydrocarbon ratios 7 05 20 6 high hydrocarbon nso ratios 2 65 4 66 and high transformation index ratios s1 s1 s2 0 61 0 87 the data from this and other wells we have studied show that high concentrations of c15 hydrocarbons are thermally stable to high temperatures at least 300 c in abnormally pressured semi closed systems over geologic time concepts prevelant among petroleum organic geochemists concerning the thermal fate of hydrocarbons with subsequent graphite formation and greenschist metamorphism are in sharp contradiction to these data conventional concepts of the distribution of heavy hydrocarbons with increasing temperature and depth apparently require further review and revision

anisotropic structure under a back arc spreading region the taupo volcanic zone new zealand 1 we investigate anisotropy surrounding a continental back arc spreading region the central volcanic region cvr in the north island of new zealand and present a simple method for spatial averaging to examine heterogeneous anisotropy s phases from local earthquakes yield consistent trench parallel fast directions in the southern compressional region but varied directions in the northern extensional region in the forearc east of the cvr is nearly trench parallel suggesting shear in the mantle or trench parallel flow in the western cvr local phases from 50 to 80 km depth give parallel to extension 120 and phases from 150 to 220 km depth yield similar 150 these results suggest asthenospheric flow with olivine a axes oriented in the extension direction down to 100 150 km depth in the eastern cvr local phases show mixed suggesting that it is a transition between the western cvr and the forearc trench parallel for shallow local events within the cvr may be caused by fluid filled cracks trench parallel for deeper local events and for sks phases can be explained by standard olivine fabrics developed by lithospheric shearing by trench parallel flow and by fossil anisotropy in the subducting oceanic lithosphere alternatively in the cvr they could be caused in part by hydrous minerals at the slab mantle upper interface which could cause olivine a axes to orient parallel to the trench due to a maximum shear stress oriented perpendicular to the trench along the slab we suggest that trench perpendicular flow in the extensional region helps to drive fluids away from the slab while in the compressional region trench parallel flow fails to distribute the fluids explaining the location of changes in geophysical properties

three dimensional distribution of seismic anisotropy in the hikurangi subduction zone beneath the central north island new zealand 1 we use earthquake arrival time data in the central north island new zealand in inversion for 3 d vp azimuthal anisotropy it is parameterized with an isotropic component and two azimuthal anisotropy parameters for each node and local earthquake shear wave splitting observations define the initial anisotropy model our results suggest that mantle flow either within the mantle wedge or below the subducted slab is not the primary source of anisotropy in the hikurangi subduction zone the largest region of anisotropy that we image is within the subducted slab where anisotropy is consistently trench parallel and 5 9 magnitude from 32 to 185 km depth bending induced yielding in the slab offshore and as it passes through the trench provides an explanation for this slab anisotropy beneath the taupo volcanic zone tvz there is 1 4 trench normal anisotropy within 30 km of the surface of the slab within a region entrained with motion of the slab in contrast only very weak 0 2 anisotropy is imaged in the region of high temperature partial melt arising from active corner flow in the mantle wedge in the crust geologic structure is important with the largest crustal anisotropy 14 related to schist we image significant anisotropy aligned with the margins of the tvz related to extensive fracturing on the margins as the tvz actively extends within the heavily intruded and underplated tvz lower crust the orientation of anisotropy switches to align with the extension direction this orientation is consistent with other geophysical data suggesting the presence of connected melt in this region

the nature and origin of light hydrocarbon gases associated with mineralization in the northern pennines abstract earlier studies have shown the occurrence of anomalous amounts of methane in rocks associated with lead zinc mineralization in a number of deposits in the british isles and europe this has led to speculation that the gas may have originated either as a consequence of reactions involved in the mineralization process or as a result of maturation of the organic matter in the sediment or from a deep source new data are presented showing the distribution of light hydrocarbon gases from fluid inclusions in minerals from the north and south pennine orefields which differ from those observed in the host rocks possible sources for the gases in the host rocks and the minerals are examined based on the close correlation between the distribution of the gases in the carbonate rocks of northern england and the conodont colour alteration index map for the area it is suggested that the anomalous amounts of methane gas in the northern pennine host rocks are the result of maturation prior to mineralization the distribution of gases in the fluid inclusions in the minerals serves as a distinguishing feature and two assemblages are recognized from the south pennine orefield both of which are distinct from that of the northern pennines it is concluded that these gases trapped at the time of mineralization originate as a consequence of reactions which occurred during mineral deposition

anisotropy in the oceanic lithosphere theory and observations from the ngendei seismic refraction experiment in the south west pacific summary p wave travel time data from a seismic refraction experiment on the 1983 ngendei expedition to the south pacific indicate anisotropy at two levels in the oceanic lithosphere in the upper mantle p wave velocities vary between 8 0 and 8 5 km s 1 with the fast direction at n30 e crustal anisotropy within layer 2 is characterized by azimuthal p wave velocity differences of about 0 2 0 4 km s 1 with the fast direction at n120 e orthogonal to the upper mantle anisotropy the observed anisotropy is consistent with a model in which aligned olivine crystals cause anisotropy in the upper mantle and aligned cracks within layer 2 cause anisotropy in the crust we examine a model of p wave propagation from a point source in an isotropic layer above an anisotropic half space and show that under these conditions anisotropy can cause seismic ray paths to deviate from the vertical plane connecting source and receiver this deviation has a negligible effect on seismic travel times but must be taken into account in modelling p wave polarization anomalies p wave polarization anomalies within the anisotropic half space are the sum of the particle motion deviation from the ray path and ray path deviation from the source receiver azimuth and are typically range dependent p wave polarization anomalies will also occur in the overlying isotropic layer purely as a result of the ray path deviation with greater deviations at long ranges a simple model of upper mantle anisotropy 6kms 1 crust above 8 0 8 6 km s 1 anisotropic mantle produces surface polarization anomalies of 1 5 3 5 in practice p wave polarization anomalies are difficult to observe because they are small compared to observed scatter in polarization data and are sensitive to differences in horizontal seismometer gain levels we examine the implications of anisotropic ray path deviations on travel times and p wave polarizations for the ngendei data as well as some previous marine seismic refraction experiments

strong variations in seismic anisotropy across the hikurangi subduction zone north island new zealand abstract shear wave splitting measurements from sks skks s and scs phases reveal the anisotropic structure of north island new zealand waveforms were recorded on temporary and permanent broadband seismographs strong anisotropy varies rapidly across the hikurangi subduction zone these changes constrain the width of the deformation associated with the plate boundary and define three different regions of mantle flow stations in the fore arc region eastern central north island record fast polarisations subparallel to the trench and moderate delay times of around 2 5 s consistent with earlier studies of north island this is interpreted as caused by trench parallel mantle flow beneath the subducted slab with a possible contribution of trench parallel fossil anisotropy within the subducted slab delay times increase towards the extending central volcanic region cvr with values up to 4 5 s one of the largest delay times measured worldwide strong s wave anisotropy 7 5 through 80 km in the mantle wedge in addition to the sub slab anisotropy can explain the observed high delay times one mechanism to create such high anisotropy is melt segregation of partially molten rock a frequency dependence of this mechanism could also explain persisting discrepancies between local and teleseismic shear wave splitting measurements to the west delay times decrease systematically measurements in the far back arc region of western central north island show no apparent splitting this suggests that mantle wedge dynamics terminate beneath the western border of the cvr the apparent isotropy beneath the far back arc may be related to local small scale mantle convection or vertical mantle flow possibly caused by the detachment of lithosphere

hydrothermal petroleums from yellowstone national park wyoming u s a abstract in yellowstone national park oil is actively discharging with thermal waters at several widely separated thermal areas samples from two locations were studied petroleum from calcite springs occurs as vapor condensates in steam vents detailed geochemical analyses show a complex origin for the petroleum fluid deeply buried hydrothermally altered sedimentary rocks are believed to have contributed a high temperature pyrolysate consisting largely of polynuclear aromatic hydrocarbons and heterocyclic compounds shallow sedimentary rocks which are also hydrothermally altered have contributed large amounts of aromatic and polar compounds as well as minor amounts of hydrocarbons the permian phosphoria formation is suggested as a likely source rock for the bulk of the oils autochthonous pyrolysates and lipids from thermally altered surface and near surface bacterial and land plant debris have also been introduced to the vents the latter may have been introduced by downward percolating meteoric water the oil from rainbow springs is a highly paraffinic low s crude oil depleted in light hydrocarbons unlike the calcite springs samples the oil from rainbow springs is believed to have originated from a single sedimentary source rock with little or no hydrocarbon contributions from surface biota the oil contains a unique molecular marker assemblage that suggests both gymnosperm and angiosperm input and places the age of the source unit in the tertiary consideration of the local stratigraphy and water temperatures limits the probable source zone to the eocene aycross formation an intra volcanic lacustrine mudstone calculation of deep water temperatures indicates that this unit is exposed to thermal waters in an extensive near surface aquifer such conditions are consistent with the widespread surface manifestations and biomarker kinetic models consideration of the petroleum chemistry and regional hydrodynamics indicates that the yellowstone park oils did not migrate into the park from distant sources the chemical data are also inconsistent with the oils being generated and trapped prior to tertiary volcanism at both calcite springs and rainbow springs oil generation appears to be contemporaneous and is attributed to thermal alteration of relatively shallow sedimentary rocks by hydrothermal fluids

modelling shear wave splitting observations from wellington new zealand summary frequency dependent anisotropy was previously observed at the permanent broad band station snzo south karori wellington new zealand this has important implications for the interpretation of measurements in other subduction zones and hence for our understanding of mantle flow this motivated us to make further splitting measurements using events recorded since the previous study and to develop a new modelling technique thus in this study we have made 67 high quality shear wave splitting measurements using events recorded at the snzo station spanning a 10 yr period this station is the only one operating in new zealand for longer than 2 yr using a combination of teleseismic sks and s phases and regional scs phases provides good azimuthal coverage allowing us to undertake detailed modelling the splitting measurements indicate that in addition to the frequency dependence observed previously at this station there are also variations with propagation and initial polarization directions the fast polarization directions range between 2 and 103 and the delay times range between 0 75 s and 3 05 s these ranges are much larger than observed previously at snzo or elsewhere in new zealand because of the observed frequency dependence we measure the dominant frequency of the phase used to make the splitting measurement and take this into account in the modelling we fit the fast polarization directions fairly well with a two layer anisotropic model with horizontal axes of symmetry however such a model does not fit the delay times or explain the frequency dependence we have developed a new inversion method which allows for an inclined axis of symmetry in each of the two layers however applying this method to snzo does not significantly improve the fit over a two layer model with horizontal symmetry axes we are therefore unable to explain the frequency dependence or large variation in delay time values with multiple horizontal layers of anisotropy even allowing for dipping axes of symmetry for the upper layer of anisotropy the modelled fast polarization directions lie in the range 30 to 110 subparallel to the major geological features as well as the relative direction of plate motion we suggest that the upper layer of anisotropy consists of crust and subducting slab and that the lower layer consists of subslab mantle for the lower layer of anisotropy the modelled fast polarization directions lie in the range 50 to 30 which are intermediate

anisotropic structure of the hikurangi subduction zone new zealand integrated interpretation of surface wave and body wave observations summary a model of subduction zone anisotropy for south and central north island new zealand is presented by integrating the observations of shear wave anisotropy from anomalous surface wave polarizations local s phases at a range of hypocentral depths and sks splitting analyses anomalous particle motions of the equivalent to fundamentalmode love waves have been measured for propagation paths approximately along the strike of the hikurangi subduction zone in eastern north island new zealand these observations are modelled in terms of an anisotropic crust and subducted pacific slab with a pseudo hexagonal symmetry axis plunging at 30 to the vertical and a fast axis parallel to the strike of the margin a shear wave anisotropy of 4 per cent is assumed shear wave splitting analyses of regional phases in central north island show no increase in fast slow delay time 0 21 0 03 s with increased hypocentral depth unlike previous observations in southern north island which display an increase in delay time of about 0 5 s over 250 km depth fast polarization directions are again approximately parallel to the strike of subduction observed sks splitting parameters on the other hand do not vary significantly between southern and central north island and over the mantle wedge in western north island a mean fast slow delay time of 1 5 0 3 s and a fast polarization direction of 25 7 subparallel to the strike of the subduction zone were determined for the sks observations both the surface wave polarization and local shear wave splitting observations were modelled by an anisotropic new zealand crust with a pseudo hexagonal symmetry axis plunging at 15 30 and a horizontal fast axis parallel to the strike of the subduction the variation of the splitting delay times with hypocentral depth between central and southern north island implies a horizontal symmetry axis in the subducted slab in the south but an axis plunging parallel to the plate interface in central north island in the mantle wedge above the slab in western north island and the mantle beneath the slab in central and southern north island a horizontal anisotropic symmetry axis fits the observations 4 per cent anisotropy was assumed throughout the models within the new zealand crust the plunge of the symmetry axis of the anisotropic structure is compatible with the structural trends of the regional geology and fault orientations the variation in the plunge of the anisotropic symmetry axis within the subducted pacific lithosphere from central to southern north island is interpreted to reflect the change in intraplate stress southwards towards south island where the india australian and pacific plates are locked the orientation of olivine due to trenchparallel flow would explain the observations in the mantle wedge and pacific mantle below the subducted plate

origin of the louisville ridge and its relationship to the eltanin fracture zone system we have combined shipboard and seasat altimeter derived data in an intergrated geological and geophysical study of the louisville ridge a 3500 km long seamount chain extending from the tonga trench to the eltanin fracture zone a break in the smooth trend of the ridge at latitude 37 5 s has been recognized in both bathymetric and altimetric data the 40ar 39ar dating of rocks dredged either side of the break suggest that it is analogous to the bend in the hawaiian emperor seamount chain although the general trend of the ridge can be fit by small circles about pacific absolute motion poles determined from other seamount chains the new bathymetric and age data allow us to refine pacific absolute motion poles the continuity in smooth trend of the ridge and the eltanin fracture zone suggests some relationship between them however a major offset developed on this transform between 60 and 80 ma prior to the oldest dated rocks from the ridge although magmatism was more or less continuous on the ridge during 28 60 ma it probably occurred on crust with little or no offset thus magmatism appears to have been little influenced by the developing fracture zone by 28 ma the distance between the magmatic source and the fracture zone had decreased sufficiently for a portion of the ridge to have been emplaced on crust with an offset after about 12 ma however volcanic activity on the louisville ridge apparently waned despite a possible influence on the magmatism of the fracture zone

proteinaceous corals as proxy archives of paleo environmental change abstract high resolution marine data are critical to evaluating anthropogenic impacts on our environment considering the spatial and temporal limitations of direct instrumental measurements proxy data extracted from marine environmental archives are necessary to separate anthropogenic changes from those that would occur naturally the majority of late holocene high resolution environmental reconstructions are derived from marine carbonates including tropical scleractinian corals bivalves crustose coralline algae and sclerosponges however these archives are restricted to the top hundreds of meters of the water column and only preserve environmental variability that is captured by calcium carbonate skeletons at a very few select locations marine sediments archive annual environmental variability in organic and inorganic materials recently additional types of corals are proving to yield information complimentary to these traditional marine archives including cold water scleractinian corals and proteinaceous corals a taxonomically diverse group the proteinaceous corals are broadly defined as those having a branching gross morphology with skeleton comprised at least partly of protein rich organic material they encode characteristics of their food and ambient environment into the chemical and physical composition of their skeleton this environmental encoding combined with their banded skeleton and significant longevity means that proteinaceous corals hold information in their skeleton that helps fill the spatial and temporal gaps in our knowledge of past and present ocean conditions here i review the environmental reconstructions derived from geochemical measurements of the proteinaceous coral skeletons this information is grouped into the mesopelagic environmental variability captured in the skeleton of bamboo corals surface processes captured in the organic skeletons of corals across all ocean depths and environmental variability documented by skeletal radiometric isotopes we include animals from two separate subclasses within the class anthozoa including the parasitic zoanthids that secrete a sclero proteic skeleton since the proteinaceous corals are taxonomically diverse we consider the unique features that define this group of corals including their distribution morphology nutrition and longevity we find that uncertainty surrounding biological parameters limits the precision of reconstructions derived from the calcitic skeleton in contrast analytical effort and cost constrain the number of reconstructions from the organic skeleton through this discussion we provide insights into the uses challenges and directions for future research for this important environmental archive

seismic determination of elastic anisotropy and mantle flow when deformed many rocks develop anisotropic elastic properties on many seismic records a long period 100 to 250 seconds quasi love wave with elliptical polarization arrives slightly after the love wave but before the rayleigh wave mantle anisotropy is sufficient to explain these observations qualitatively as long as the fast axis of symmetry is approximately horizontal quasi love observations for several propagation paths near pacific ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the pacific plate

nitrogen isotopic composition of organic matter from a 168 year old coral skeleton implications for coastal nutrient cycling in the great barrier reef lagoon abstract ongoing human activities are known to affect nitrogen cycling on coral reefs but the full history of anthropogenic impact is unclear due to a lack of continuous records we have used the nitrogen isotopic composition of skeleton bound organic matter cs 15 n in a coastal porites coral from magnetic island in the great barrier reef as a proxy for n cycle changes over a 168 yr period 1820 1987 ad the magnetic island inshore reef environment is considered to be relatively degraded by terrestrial runoff given prior cs 15 n studies from other regions there was an expectation of both secular change and oscillations in cs 15 n since european settlement of the mainland in the mid 1800s surprisingly cs 15 n varied by less than 1 5 despite significant land use change on the adjacent mainland over the 168 yr measurement period after 1930 cs 15 n may have responded to changes in local river runoff but the effect was weak we propose that natural buffering against riverine nitrogen load in this region between 1820 and 1987 is responsible for the observed stability in cs 15 n in addition to coral derived skeletal 15 n we also report for the first time 15 n measurements of non coral derived organic n occluded within the coral skeleton which appear to record significant changes in the nature of terrestrial n inputs in the context of previous cs 15 n records most of which yield cs 15 n changes of at least 5 the magnetic island coral suggests that the inherent down core variability of the cs 15 n proxy is less than 2 for porites

hunting for azimuthal anisotropy beneath the pacific ocean region lateral variations in azimuthal anisotropy cause significant waveform anomalies in long period surface waves 8 mhz suggesting lateral variations with wavelength twice the spacing of fracture zones in the north central pacific

hydrocarbons in surface sediments from a guaymas basin hydrothermal vent site petroleum like materials found at the guaymas basin hydothermal vent site gulf of california are derived from pyrolysis of organic matter two characteristics surface sediment cores differing in temperature profiles and other parameters were collected by dsv alvin sectioned and analyzed for hydrocarbons the quantitative and qualitative composition of alkanes steranes diasteranes and triterpanes differed between these cores as well as within sections of the same core these differences apparent for scales of tens of centimeters are related to interactive physical chemical and microbial processes as well as the influence of multiple sources for the petroleum