the impact of oxic alteration on plume derived transition metals in ridge flank sediments from the east pacific rise we describe transition metal behaviour during early diagenesis in sediments collected along a transect across the eastern flank of the east pacific rise epr at 14 s overlying crust with magnetic ages of 0 36 ma to 4 6 ma the sediments are lithologically simple and consist of biogenic carbonate hydrothermal plume precipitates and minor basaltic debris sedimentation rates range from 1 cm ka in the near axis region 0 36 ma to 0 1 0 2 cm ka across the young ridge flank by 1 9 ma or within 142 km from axis redox indicators porewater mn ii aq and solid phase mo mn ratios indicate fully oxic conditions in near axis sediments changing to mildly suboxic conditions across the ridge flank sequential extraction analysis of sediments from the 0 36 ma site indicates that oxic alteration of fe oxyhydroxides is dominated by transformation of ferrihydrite to goethite implying that alteration occurs via dissolution followed by nucleation and precipitation the extent of alteration amorphous fe total plume derived fe ranges from 0 3 to 0 8 and the time to half conversion is on the order of 100 ka v associated with plume derived ferrihydrite is strongly discriminated against during alteration to goethite and the distribution coefficient dv v fe goethite v fe dissolved is in the range 0 45 0 59 cu zn and ni are delivered to the sediment in association with both fe oxyhydroxides and mn oxides where 70 of cu and zn and 10 of ni are associated with fe oxyhydroxides the fe adsorbed cu and zn are incorporated quantitatively into the lattice structure of goethite during alteration the fe associated ni most likely represents ni co precipitated as ni fe ferrihydrite and incorporated into goethite during alteration co is associated only with mn oxides the oxic alteration of hydrothermal fe oxyhydroxides therefore represents a relatively permanent sink where goethite dissolution is a prerequisite for metal release for a maximum of 70 of plume derived cu and zn 50 of v 10 of ni and 0 of co in oxic sediments the remaining plume derived metals are retained in association with amorphous fe oxyhydroxides and mn oxides although this fraction is highly susceptible to diagenetic remobilization under suboxic conditions

tungsten accumulation in pacific ferromanganese deposits tungsten has often been reported in marine ferromanganese deposits and the question arises as to how the large oxyanionic species wo42 enters the appropriate phases very low w concentrations in seawater less than 0 0002 g kg suggest that it is not directly related to precipitation processes of all the comparable marine samples manganese micronodules have the highest w contents in the range 1 4 to 3 6 times 3 higher than in the associated macronodules a depositional record for more than 60 million years obtained for a thick manganese crust shows that the tungsten distribution with depth correlates best with as and to a lesser extent with fe the mechanism favoured for enrichment of w is precipitation onto fine hydrothermal manganese rich particles supplied by ridge volcanic activity such particle plumes are usually released in cycles stay for comparatively long periods in the water column and are then transported from the hydrothermal centres to the deep basins where they settle and probably contribute to the growth of ferromanganese oxide phases on the ocean floor which is mainly by diagenetic and hydrogenetic processes

the physical basis of mb ms and variable frequency magnitude methods for earthquake explosion discrimination we use recent results from deterministic numerical modeling of earthquakes and explosions to develop an improved physical basis for earthquake explosion discrimination we use six three dimensional finite difference simulations of earthquakes for the earthquake source models and four empirical and four numerical models for explosions in different materials four factors contribute to the success of the mb ms discriminant source spectra focal mechanism near source elastic properties and interference of p spectral differences contribute about 0 5 magnitude unit to the separation between earthquake and explosion populations for large events but this difference vanishes for events with mb 4 0 using a frequency band of 0 5 3 0 hz for small events the vfm discriminant is complementary to mb ms in several ways vfm is improved by p interference while mb ms is degraded vfm is more effective for hard rock explosions while mb ms will preferentially discriminate explosions in low velocity materials and vfm is insensitive to fault orientation vfm is more sensitive to noise and regional attenuation differences than mb ms simultaneous use of both methods should allow improved discrimination of small events

hydrothermal activity at the trans atlantic geotraverse hydrothermal field mid atlantic ridge crest at 26 n the first submersible observations of the only known active submarine hydrothermal field on a slow spreading oceanic ridge are incorporated with results of 10 prior years of investigation to derive an understanding of periodicity duration and varying intensity of hydrothermal activity at the trans atlantic geotraverse tag hydrothermal field on the mid atlantic ridge crest near latitude 26 n hydrothermal activity has persisted at this location for at least 1 106 years based on the distribution of hydrothermal and hydrogenous mineralization with respect to crustal age the hydrothermal activity has been cyclic multistage and episodic prior high temperature hydrothermal venting stages with a periodicity of the order of 1 104 years and duration of the order of 101 years are deduced from the estimated ages of discrete sedimentary layers anomalously enriched in cu fe and zn and correspond with the independently determined periodicity of volcanic eruptive cycles on the mid atlantic ridge the most recent episode of high temperature venting is inferred to have ceased in the recent past based on metal enrichment cu fe zn in the surficial sediment layer low temperature hydrothermal venting stages with a duration of the order of 1 104 years intervene between the short high temperature stages and produce stratiform deposits of layered and earthy manganese oxide iron oxide hydroxide and silicate bivalve like forms with the characteristics of vent clams in various stages of dissolution are identified on bottom photographs the fresh appearance of intact tubules composed of iron hydroxide that acted as vents on relict deposits conductive heat flow anomalies in the sediment column and the record of temperature anomalies and excess 3he in the near bottom water column suggest that the low temperature hydrothermal discharge is intermittent at individual vents on a time scale of years

discriminating hydrothermal and terrigenous clays in the okinawa trough east china sea evidences from mineralogy and geochemistry abstract the okinawa trough ot in the east asian continental margin is characterized by thick terrigenous sediment and ubiquitous volcanic hydrothermal activities in this study the clays collected during iodp expedition 331 to the middle ot iheya north knoll were analyzed for mineralogical and geochemical compositions by comparing with the clays from the east china sea shelf and surrounding rivers we examine different clay origins the hydrothermal field in the mid ot is dominated by mg rich chlorite while the recharge zone has clay mineral assemblages similar to the shelf and rivers showing high content of illite subordinate chlorite and kaolinite and scarce smectite compared to the terrigenous clays the hydrothermal clays in the ot have high concentrations of mg mn and zr but low fe na k ca ba sr p sc and ti while the hydrothermal clays in the mid ocean ridge are relatively enriched in fe and v and depleted in al mg zr sc and ti different fractionation patterns of rare earth elements also register in the terrigenous and hydrothermal clays diagnostic of variable clay origins we infer that the ot hydrothermal clay was primarily formed by the chemical alteration of detrital sediments subject to the hydrothermal fluids the remarkably different compositions of hydrothermal clays between the sediment rich back arc basin like ot and the sediment starved ocean ridge suggest different physical and chemical processes of hydrothermal fluids and fluid rock sediment reactions under various geologic settings

actinide series disequilibrium as a tool to establish the chronology of deep sea hydrothermal activity this paper describes the different radiochronological methods used to date geologically recent i e 400 000 years deep sea hydrothermal deposits as well as the basic conditions necessary to obtain reliable dates the limitations of the different techniques also are described using measurements of 210pbpb 228th228ra 230th234u 231pa235u and 228ra226ra the authors have undertaken an exhaustive chronological study of the hydrothermal deposits along the east pacific rise the mid atlantic ridge and in some back arc basins the objectives of this study were to obtain regional chronologies and to establish a general synthesis on the evolution of the hydrothermal processes at the scale of the mid oceanic ridge system some results obtained by other authors are included in this synthesis the dependence of the general trends of temporal development of the hydrothermal chimneys edifices and fields on their tectonic settings is discussed this study demonstrates that hydrothermal activity does not represent a regular input of matter to the ocean and that its pulsed character must be taken into account in all modeling attempts chemical biological and tectonic affected by hydrothermal processes in areas of rapid spreading like the east pacific rise recent and fossil deposits are spatially separated by contrast at the slow spreading mid atlantic ridge fossil and present activity are found in the same location

constraints on the energy and chemical balances of the modern tag and ancient cyprus seafloor sulfide deposits the size chemical composition energy flux and fluid composition of the tag hydrothermal sulfide deposit at the mid atlantic ridge and the size chemical composition and reaction zone characteristics of the skouriotissa volcanogenic massive sulfide deposit of the troodos ophiolite in cyprus are used to examine the energy requirements and chemical balances associated with the generation of a large volcanogenic massive sulfide deposit we conclude that formation of large sulfide deposits from oceanic hydrothermal systems is a geologically rapid process and occurs on timescales of hundreds of years with episodes of activity as short as a few tens of years separated by thousands of years of inactivity about 2 1019 j of energy supplied at high temperature is required to form a deposit the size of the tag mound metals up to 4 times the mass of any element present in the sulfide deposit are leached out of relatively small reaction zones most likely at the base of the sheeted dikes chemical balance can be struck for all elements except sulfur with a reaction zone 1 2 km3 in volume from which a small proportion of iron and large proportions of copper zinc and manganese are removed a sulfur balance requires that a significant fraction of sulfur be derived from reduction of seawater sulfate as suggested by stable isotope analyses we argue that the principal source of energy that drives hydrothermal circulation is latent heat of crystallization of magma close to the top of the plutonic section furthermore we speculate that activity of the tag hydrothermal system is related to periods of more rapid magma supply from the mantle at magma supply rates similar to those observed in volcanoes in hawaii and iceland

hydrothermal input into sediments of the mid atlantic ridge abstract the analysis of geochemical profiles in metalliferous sediment cores obtained from the mid atlantic ridge rift valley at the tag mark and 15 n hydrothermal vent fields and near 27 10 n allowed a study of the history of hydrothermal processes of the three hydrothermal zones of the tag field the north hydrothermal zone reached its maximum activity between 6000 and 25 000 years ago the mir mound 10 000 years ago and the active mound 15 000 years ago evidence of intensive hydrothermal sedimentation is not seen near the mark field the mark sulphide mounds were probably formed in the course of a single hydrothermal episode that began 4000 years ago most of the sulphides of the newly found hydrothermal field near 15 n were formed in the course of an event traced by a fe enriched layer 70 90 cm below the seafloor at present this field is only slightly hydrothermally active three fe enriched layers correspond to the possible stages of ore formation at a site of presumed hydrothermal activity near 27 10 n their relative intensity is decreasing with time

hydrothermal manganese plumes in the mid atlantic ridge rift valley the concentration of dissolved manganese in sea water can be used as a chemical tracer of hydrothermal activity on the underlying sea floor here we present vertical profiles of seawater manganese concentrations above the rift valley of the mid atlantic ridge mar the values obtained indicate the presence of plumes that are presently active generated by hydrothermal vents in the rift valley these plumes are confined to the rift valley and do not spill over into the adjacent deep ocean basins differences between them suggest that there are at least five hydrothermal sources along this 1 700 km long section of mid ocean ridge

backazimuth estimation reliability using surface wave polarization 1 backazimuth estimates derived from surface wave polarization can be used to test association of an observed surface wave with a seismic event however commonly used techniques for estimating the backazimuth are subject to a number of errors and are often inaccurate we evaluate the performance of a new algorithm for determining rayleigh wave propagation direction from the cross correlation of the horizontal and hilbert transformed vertical seismograms this proves to be more accurate and much less error prone than current automatic processing procedures and the cross correlation value provides a good measure of the reliability of the backazimuth estimate consequently the new algorithm will permit more reliable event association at a lower magnitude threshold

relict hydrothermal zones in the tag hydrothermal field mid atlantic ridge 26 n 45 w two relict hydrothermal zones were delineated between water depths of 3400 and 3500 m at the lower part of the east wall of the rift valley of the mid atlantic ridge in the tag hydrothermal field using a deep towed side scan sonar tow and a camera temperature tow along the northern 3 km of the wall and a submersible transect named the north and mir relict zones they are located about 4 km and 2 km northeast respectively of the known active high temperature sulfide mound between water depths of 3625 and 3670 m on the rift valley floor near the base of the east wall the north zone extends about 2 km along the northern end of the lower east wall the zone includes two moundlike features up to 30 m high by 200 m in diameter imaged by side scan sonar within a 2 km long line of discontinuous hydrothermal deposits comprising inactive toppled and standing chimneys layered material and patchy dark stains on sediment photographed by the camera temperature tow several other moundlike features were imaged with the side scan sonar outside of the photographic coverage the mir relict hydrothermal zone 2 km south of the north zone named after the mir submersible used to investigate it consists of three subzones 1 a 200 m wide area of diverse types of hydrothermal materials exposed by normal faulting at its western margin 2 a 400 m wide by 700 m long central area of discrete groups of toppled and standing inactive sulfide chimneys up to 25 m high on a substrate of red metalliferous sediment and carbonate lutite spires sampled on the highest chimneys are composed of coarse grained recrystallized sulfides dominated by pyrite and chalcopyrite which contain the first primary free gold grains 2 3 m diameter found at a hydrothermal site on a mid ocean ridge and 3 a 150 m wide hummocky area of layered hydrothermal material with the appearance of low temperature precipitates and carbonate lutite with patchy dark stains at its eastern margin the active sulfide mound the north zone and the mir zone are each located on the fractured western margins of gentle dome shaped areas of pillow flows typically 500 m in diameter interpreted as summits of volcanic centers that may have supplied heat to drive adjacent hydrothermal activity the distribution and size of the active and inactive hydrothermal zones of the tag field the chronology and the characteristics of relict samples recovered indicate a history of at least 100 103 years of high temperature hydrothermal episodes with multiple overprinting stages of mineralization accompanied by alteration

an automated rayleigh wave detection algorithm abstract the desire to operate denser networks in order to monitor seismic activity at lower thresholds leads to greater emphasis on automated data processing an algorithm for detecting and characterizing long period rayleigh wave arrivals has been developed and tested the routine continuously monitors all directions of approach to a station in a manner similar to beamforming the detector is based on cro ss powers between the hilbert transformed vertical and rotated horizontal signals so it is sensitive to both the power and polarization properties of the three component wavefield elliptically polarized rayleigh arrivals are enhanced while linearly polarized love waves and body phases are suppressed a test using one month of data from station anmo demonstrated that this technique can with high reliability detect rayleigh arrivals which would be visible to an analyst the measured arrival times and azimuths are accurate enough to permit automated association of the detections to events in a bulletin

hydrothermal sulfide and oxide deposits on seamounts near 21 n east pacific rise hydrothermal deposits were sampled by submersible from the calderas and summit benches of two seamounts 20 and 30 km west of the east pacific rise at 21 n the deposits document a wide variety of off axis hydrothermal activity including samples from the interiors of seafloor sulfide deposits in contrast to most mid ocean ridge deposits sulfide deposits on green seamount are rich in si fe and cu are poor in zn and contain abundant quartz sulfide chimneys grew by quenching of hydrothermal fluids and deposition of walls of colloform pyrite marcasite zn sulfide and minor galena whereas coarse grained pyrite and chalcopyrite were deposited at higher temperatures 250 c in chimney interiors as chimney walls grew outward into sea water increased temperatures in the inner walls resulted in recrystallization to pyrite and deposition of pyrite and chalcopyrite in pore space cooling in the outer portions of chimneys caused deposition of opal at temperatures of about 80 170 c as chimneys coalesced and opal rich material was heated in the interiors of sulfide edifices opal was recrystallized to chalcedony and quartz faulting has exposed the interiors of sulfide deposits where further recrystallization and deposition of chalcopyrite and quartz occurred at temperatures of 230 320 c clogging of chimneys changes in flow paths and cooling of the deposits led to the deposition of late mixed layer illite smectite iron sulfides fe poor sphalerite opal and barite the sulfide deposits formed over a time span of at least 140 000 to 70 000 yr ago probably coincident with caldera and pit crater formation the ages of the sulfide deposits provide constraints on the last volcanic and tectonic activity and they also suggest that it took a maximum of 260 000 yr for the seamount to reach its present height red seamount is presently hydrothermally active and deposits consisting predominantly of amorphous fe oxyhydroxide are forming on small pillow cones in the caldera at temperatures of 10 15 c hydrothermal nontronite deposits capped by mn oxide crusts cover much of the southern summit bench of red seamount and formed at temperatures of around 30 c iron rich talc and sulfide grains in nontronite provide evidence of former high temperature activity and suggest that a sulfide deposit is present nearby

evidence for episodic hydrothermal activity in the red sea from the composition and formation of hydrothermal sediments thetis deep abstract sediments obtained from the ne thetis deep during the sonne cruise so 29 consist of a manganite facies and various types of fe facies hematite magnetite goethite and lepidocrocite facies the sediments have a chemical and mineralogical composition similar to some of the lithological units previously described from the atlantis ii deep 160 km to the southeast in contrast to the atlantis ii deep no stable brine pool recently exists in the ne thetis deep however based on the fe mn fractionation in the fe facies types an intermittent brine filling of the ne thetis deep has probably existed we propose that the formation of the brine pools correlate to the volume of discharging fluids the chronology of hydrothermal deposition in the ne thetis deep seems to correlate with similar events in the atlantis ii deep suggesting that major tectonic events in the red sea may have caused large scale pulses of hydrothermal activity

low temperature fluid flow through sulfidic sediments from tag modification of fluid chemistry and alteration of mineral deposits low temperature fluid flow has been identified as an important component of the heat mass and chemical flux at sites of active venting one way to study the movement of water through hydrothermal deposits is to analyse the pore fluids extracted from sulfidic sediments the composition of diffuse flow fluids in one sediment core from the south of the active tag mound reflects the dilution of high temperature black smoker fluids with modification inside the mound during ongoing circulation fluid modification includes conductive cooling removal of si from solution and entrainment and removal of u from seawater which can represent significant sinks of these elements precipitation of clay minerals and fe oxides is currently occurring within this sediment core generating ochreous type material subsurface extensive low temperature alteration of basaltic material at the core top is apparent in conjunction with supergene enrichment of cu and mn

the role of prokaryotes in subsurface weathering of hydrothermal sediments a combined geochemical and microbiological investigation a detailed geochemical and microbiological study of a 2 m sediment core from the inactive alvin mounds within the tag hydrothermal field was conducted to examine for the first time the role of prokaryotes in subsurface weathering of hydrothermal sediments results show that there has been substantial post depositional remobilisation of metal species and diagenetic overprinting of the original high temperature hydrothermal minerals and aspects have involved prokaryotic processes prokaryotic enumeration demonstrates the presence of a population smaller than the average for deep sea sediments probably due to the low organic carbon content but not inhibited by and hence adapted to the metal rich environment there was a small but significant increase in population size associated with the active redox boundary in an upper metal sulphide layer 50 70 cm around which active metal remobilisation was concentrated cu au cd ag u zn and zn hence subsurface prokaryotes were potentially obtaining energy from metal metabolism in this near surface zone close association of numbers of culturable mn and fe reducing prokaryotes with subsurface fe2 and mn2 pore water profiles suggested active prokaryotic metal reduction at depth in core cd102 43 to 175 cm in addition a prokaryotic mechanism which is associated with bacterial sulphate reduction is invoked to explain the u enrichment on pyrite surfaces and zn and pb remobilisation in the upper sediment although prokaryotic populations are present throughout this metalliferous sediment thermodynamic calculations indicated that the inferred low ph of pore waters and the suboxic anoxic conditions limits the potential energy available from fe ii oxidation which may restrict prokaryotic chemolithotrophic biomass this suggests that intense prokaryotic fe oxidation and weathering of seafloor massive sulphide deposits may be restricted to the upper portion of the deposit that is influenced by near neutral ph and oxic seawater unless there is significant subsurface fluid flow

impact melting of lunar meteorite dhofar 458 evidence from polycrystalline texture and decomposition of zircon abstract dhofar 458 is a lunar meteorite consisting mainly of olivine plagioclase intergrowths pyroxene plagioclase intergrowths and plagioclase fragments pyroxene plagioclase globules are also common in this study we report the discovery of a polycrystalline zircon in this lunar meteorite the polycrystalline zircon contains small vesicles and rounded baddeleyite grains at its margin the polycrystalline and porous texture of the zircon indicates high pressure shock induced melting and degassing baddeleyite grains are derived from decomposition of zircon under high postshock temperature the shock features in zircon indicates that the shock pressure in dhofar 458 was greater than approximately 60 gpa and the postshock temperature greater than approximately 1700 c the polycrystalline and degassing texture and decomposition zircon also strongly indicates that dhofar 458 is a clast rich impact melt rock during this shock event most components were melted and grains of mafic minerals are interstitial to lath like plagioclase grains large fragments of olivine and chromite also formed polycrystalline texture at margins and chemically reequilibrated with surrounding melts we suggest that pyroxene plagioclase globules could be remains of melted target clasts whereas vesicles may form during shock induced degassing of the rock the u pb isotopic data plot on a well defined discordant line yielding the age of the zircon of 3434 15 ma 2 this age is interpreted as the time of the impact event that melted dhofar 458 and caused decomposition and recrystallization of this zircon in dhofar 458 which reset this zircon s u pb age

methods for amplitude calibration and orientation discrepancy measurement comparing co located sensors of different types in the southern california seismic network modern seismic networks commonly equip a station with multiple sensors to extend the frequency band and the dynamic range of data recorded at the station in addition in our recent study we showed that comparison of data from co located seismometers and accelerometers is useful for detecting instrument malfunctions and monitoring data quality in this study we extend comparison of data from different co located sensors to two other applications 1 amplitude calibration for data from vertical short period sensors with strong motion sensors as baseline and 2 measurement of orientation discrepancy between strong motion and broadband sensors we perform systematic analyses of data recorded by the california institute of technology u s geological survey southern california seismic network in the first application we compare the amplitude of data from vertical short period sensors to that of data from co located strong motion sensors and measure the amplitude calibration factors for 93 short period sensors among them 49 stations are measured at 1 0 42 measured at 0 6 as well as two outlying stations gff at 0 3 and chi at 1 3 these values are found to be related to the sensors sensitivity values in the second application we measure orientation discrepancy between 222 co located broadband and strong motion sensors all the vertical orientation differences are found to be within 5 however the horizontal orientation differences of 22 stations are greater than 6 among which four stations have reverse rotation or 180 from the expected orientation these measurements have been communicated to network operators and fixes are being applied this study together with our previously developed data monitoring framework demonstrates that comparison of different co located sensors is a simple and effective tool for a broad range of seismic data assessment and instrument calibration

the role of prokaryotes in supergene alteration of submarine hydrothermal sulfides we combine mineralogical stable isotope and organic biomarker data to understand the role of prokaryote activity in supergene reactions within submarine hydrothermal sulfidic sediments data are presented for two adjacent cores from the periphery of the inactive alvin hydrothermal mound the limit of oxygenated seawater penetration into the sulfidic sediments is expressed as a sharp peak in solid phase cu atacamite and secondary cu sulfides associated with supergene alteration of the sulfide pile total prokaryote numbers are low throughout the upper few metres of sediment relative to published data for deep sea sites however there is a statistically significant enrichment of prokaryote numbers at the redox front that coincides with abundant fe oxide filaments and a unique distribution of microbial biomarkers the dominance of quaternary branched alkanes in the oxidized transition zone immediately above the redox front and their absence below suggests a significant role of the source organisms in iron or sulfide oxidation under the more circumneutral conditions associated with the redox transition zone the morphology of the fe oxide filaments preserved within late stage silica and gypsum mineralization is consistent with a biogenic origin of the filaments gypsum sulfur isotopes are in equilibrium with fluids that are derived from quantitative sulfide oxidation and gypsum nucleation is inferred to be biologically induced these new data suggest that supergene alteration of sulfidic sediments generates sharp redox and ph gradients that stimulate prokaryotic activity in particular iron and sulfide oxidisers which in turn govern the distribution of secondary mineral phases and the abundance of redox sensitive trace metals

sims u pb study of zircon from apollo 14 and 17 breccias implications for the evolution of lunar kreep abstract we report the results of a sims u pb study of 112 zircons from breccia samples from the apollo 14 and 17 landing sites zircon occurs in the breccia matrices as rounded irregular shaped broken and rarely euhedral grains and as constituent minerals in a variety of lithic clasts ranging in composition from ultra mafic and mafic rocks to highly evolved granophyres crystallisation of zircon in magmatic rocks is governed by the zirconium saturation in the melt as a consequence the presence of zircon in mafic rocks on the moon implies enrichment of their parent melts in the kreep component our sims results show that the ages of zircons from mafic to ultramafic clasts range from ca 4 35 ga to ca 4 00 ga demonstrating multiple generations of kreepy mafic and ultramafic magmas over this time period individual zircon clasts in breccia matrices have a similar age range to zircons in igneous clasts and all represent zircons that have been incorporated into the breccia from older parents the age distributions of zircons from breccias from both the apollo 14 and apollo 17 landing sites are essentially identical in the range 4 35 4 20 ga however whereas apollo 14 zircons additionally show ages from 4 20 to 3 90 ga no zircons from apollo 17 samples have primary ages less than ca 4 20 ga also in contrast to previous suggestions that the magmatism in the lunar crust is continuous our results show that the zircon age distribution is uneven with distinct peaks of magmatic activity at ca 4 35 ga ca 4 20 ga in apollo 14 and 17 and a possible third peak in zircons from apollo 14 at ca 4 00 ga to explain the differences in the zircon age distributions between the apollo 14 and 17 landing sites we propose that episodes of kreep magmatism were generated from a primary reservoir and that this reservoir contracted over time towards the centre of procellarum kreep terrane we attribute the peaks in kreep magmatism to impact induced emplacement of kreep magma from a primary mantle source or to a progressive thermal build up in the mantle source until the temperature exceeds the threshold for generation of kreep magma which is transported into the crust by an unspecified possibly plume like process

origin of fe mn si layers associated with the permian volcanic hosted massive sulphide deposits in the tasik chini district peninsular malaysia abstract the volcanic hosted massive sulphide vhms deposits in the tasik chini district peninsular malaysia are hosted in permian volcano sedimentary rocks and are composed of fe mn si layers which occur stratigraphically above the ore bodies the oxide layers are 1 cm to 2 m thick and occur discontinuously throughout the bukit botol deposit whereas layer of oxides up to 10 m thick occurs continuously over a strike length of over 50 m at the bukit ketaya deposit their mineralogy is dominated by hematite quartz barite magnetite pyrite clastic components and commonly exhibit massive iron silica banding to microbreccia like textures the fe mn si layers from the bukit botol and bukit ketaya deposits generally have high si fe mn and base metals contents various proportions of al zr and ti and high levels of ba as u and v such mineralogical and geochemical concentrations and other geological suggest that the associated fe mn si layers were deposited by the mixing of mainly chemical components and to a smaller degree detrital components in a local submarine environment due to hydrothermal activity on the seafloor

fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge abstract a geochemical investigation has been conducted of a suite of four sediment cores collected from directly beneath the hydrothermal plume at distances of 2 to 25 km from the rainbow hydrothermal field as well as a large biogenic component 80 caco3 these sediments record clear enrichments of the elements fe cu mn v p and as from hydrothermal plume fallout but only minor detrital background material systematic variations in the abundances of hydrothermal elements are observed at increasing distance from the vent site consistent with chemical evolution of the dispersing plume further pronounced ni and cr enrichments at specific levels within each of the two cores collected from closest to the vent site are indicative of discrete episodes of additional input of ultrabasic material at these two near field locations radiocarbon dating reveals mean holocene accumulation rates for all four cores of 2 7 to 3 7 cm kyr 1 with surface mixed layers 7 to 10 cm thick from which a history of deposition from the rainbow hydrothermal plume can be deduced deposition from the plume supplies elements to the underlying sediments that are either directly hydrothermally sourced e g fe mn cu or scavenged from seawater via the hydrothermal plume e g v p as holocene fluxes into to the cores surface mixed layers are presented which typically are an order of magnitude greater than background authigenic fluxes from the open north atlantic one core collected closest to the vent site indicates that both the concentration and flux of hydrothermally derived material increased significantly at some point between 8 and 12 14c kyr ago the preferred explanation is that this variation reflects the initiation intensification of hydrothermal venting at the rainbow hydrothermal field at this time perhaps linked to some specific tectonic event in this fault controlled hydrothermal setting

hydrothermal scavenging at the mid atlantic ridge radionuclide distributions we have carried out a study of u series radionuclide distributions in the neutrally buoyant plume overlying the tag hydrothermal vent field at 26 n mid atlantic ridge limited uptake of u accompanies the formation of fe oxyhydroxide particulate material within the hydrothermal plume the particulate u concentrations are too small for measurable dissolved u anomalies to be produced within the water column at plume height however such uptake followed by deposition in the underlying sediments could account for 10 of the u enrichment that has been reported previously for metalliferous ridge crest sediments particulate 234th 230th and 228th activities in the tag hydrothermal plume represent 65 of total th activities typical of the deep ocean low dissolved th activities coincide with the high particulate th activities indicating that hydrothermal scavenging strongly affects th isotope distributions in the water column close to hydrothermal vents much of the scavenging occurs during the initial formation of fe rich hydrothermal precipitates but some further scavenging continues as the material is dispersed away from its source distributions of particulate 210pb and 231pa activities in the neutrally buoyant plume are also extremely high 7 12 dpm 102 l and 30 160 dpm 106 l respectively like th 210pb and231pa show evidence for scavenging within the hydrothermal plume total th activities at plume height are 50 higher than background this focusing of th into the plume is consistent with the entrainment and re emplacement at plume height of particulate material recycled from beneath the neutrally buoyant plume

oxyanions in metalliferous sediments tracers for paleoseawater metal concentrations abstract the concentration of carbon fe mn s p v cr as mo cd u and re were determined in sediment core y 71 7 53p near an active hydrothermal location on the southern east pacific rise crest 10 s the goal was to determine the usefulness of hydrothermal iron oxides as carriers of elemental tracers of seawater concentrations the sediments are 70 carbonate and about 1 3 detrital material with the remainder having a hydrothermal origin rhenium concentrations are at detrital levels suggesting little anaerobic diagenesis beyond manganese remobilization however u cd and mo concentrations all indicate alteration after deposition oxyanion fe ratios of p v and as in surface sediments are lower than the ratios in plume particles and covary with fe content downcore the probable explanation for these variations is variable efficiency of incorporation of these metals during iron oxide formation or early diagenetic processes after deposition the p fe ratio in the core sediment is about half that in the plume particles among the oxyanion ratios only the v as ratio in the sediments is relatively constant at the present plume particle ratio during the past 60 70 kyr changes in sediments older than this could reflect variability in the incorporation efficiency or changes in v as ratio in seawater this study demonstrates the difficulties of using hydrothermal sediment element enrichments as tracers of past seawater chemistry changes in this core it appears that all oxyanion ratios change for reasons other than seawater metal concentration changes with the possible exception of the v as ratio

a 6 year time series of hydrothermal plumes over the cleft segment of the juan de fuca ridge the causal links between magmatic tectonic processes and hydrothermal venting along the mid ocean ridge axis will be difficult to discern without broadband observations of the temporal variability of hydrothermal activity i report here on temporal variability in the intensity and distribution of chronic and event plumes generated by continuous and episodic hydrothermal discharge at two vent fields on the cleft segment of the juan de fuca ridge hydrothermal temperature and light attenuation c anomalies were comprehensively mapped between 1 and 4 times per year during nine cruises from 1986 to 1991 intensity of and c in the chronic plume overlying the north cleft vent field showed more variability between years than within a given year both and c were exceptionally high in 1986 fell to moderate levels during 1988 to 1990 and declined to minimum values in 1991 the chronic plume over the south cleft vent field varied similarly superimposed on the chronic plumes were brief and intense releases of hydrothermal fluid that created event plumes distinguishable by their symmetry and exceptional rise height event plumes at the north cleft field ranged from the 1986 megaplume with a rise height exceeding 1000 m to smaller events in 1987 and 1989 with rise heights of 400 m chronic hydrothermal heat 660 277 1 mw and mass 204 86 1 g s 1 fluxes from the north cleft field were determined by assuming these fluxes were equivalent to the long term net advection of a mean cross section of the vertically integrated and c in the plume this 6 year history of hydrothermal plumes indicates that episodic discharge has been an important component of the recent hydrothermal flux and that the aggregate heat and mass fluxes declined significantly though not consistently between 1986 and 1991

hydrothermal iron rich deposits from the teahitia mehitia and macdonald hot spot areas southwest pacific abstract during cruise so 47 of r v sonne iron oxyhydroxide crusts of restricted extent were recovered from teahitia and moua pihaa seamounts in the teahitia mehetia hot spot area and from macdonald seamount in the macdonald hot spot area the crusts show complex layering and incorporate volcanic ash layers they consist of goethite feldspar and pyroxene and display low contents of transition elements apart from fe it is believed that the crusts were deposited from relatively low temperature hydrothermal fluids these low temperatures preclude the formation of sulphide deposits the type of hydrothermal mineral recovered may be a function of the thermal regime of the system and the elevation which controls the pressure of the venting fluids the shallower depths of these seamounts compared to the axes of mid ocean ridges may therefore be responsible for the style of mineralization initially magmatic vapours migrating upwards through the hot spot volcano are thought to be absorbed into seawater at comparatively shallow levels to deposit sulphide minerals within the volcanic pile the fe oxyhydroxide deposits are the residual low temperature deposits formed when the spent hydrothermal fluid reached the crest of the seamount these deposits therefore differ fundamentally from those found at the crest of mid ocean ridges where sulphide mounds are deposited directly upon interaction of the boiling hydrothermal fluid with seawater the discovery of hydrothermal iron oxyhydroxide crusts in these two hot spot areas is only the second such finding after loihi seamount southeast of hawaii

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

geochemical and thermal fluxes high temperature venting and diffuse flow from mid ocean ridge hydrothermal systems the tag hydrothermal field mid atlantic ridge 26 n

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

the relationship between p fe and v fe ratios in hydrothermal precipitates and dissolved phosphate in seawater a strong positive relationship between the molar p fe ratio in fresh hydrothermal fe ferrihydrite precipitates and seawater dissolved phosphate has been demonstrated using samples from the atlantic and pacific oceans we ascribe this relationship to scavenging of dissolved phosphate from seawater during the formation of hydrothermal fe rich particles above hydrothermal vents in contrast molar v fe ratios in hydrothermal particles are inversely correlated with dissolved phosphate these results indicate that inter ocean variations in dissolved phosphate control the p fe and v fe ratios in hydrothermal fe precipitates one of the precursors of metalliferous sediment

episodic preservation of pteropod oozes in the deep northeast atlantic ocean climatic change and hydrothermal activity an up to 13 cm thick pteropod ooze covers the ocean floor of the northeast atlantic ocean at five stations between 44 n and 48 30 n at around 25 w at water depths of between 2800 and 3200 m subsurface pteropod horizons occur at least at two different stratigraphic levels pteropod shells both from the surface layers and from the subsurface horizons are fe mn stained with an intensity of staining that increases with age ams 14c ages of single pteropods are between 1700 yrs b p and the present for the surface layer and between 7600 and 3300 yrs b p for the upper horizon in the sediment the mn fe ratios of the pteropod coatings are between 0 24 and 0 40 indicating a hydrothermal source apparently episodic pteropod preservations record pulses of hydrothermally derived elevated mn and fe concentrations we conclude that pteropod preservation is the combined result of episodic climatically induced non dissolution and subsequent hydrothermally induced protective fe mn coating

the origin of clay minerals in active and relict hydrothermal deposits samples of fe oxide rich hydrothermal sediments were collected from active and inactive portions of the transatlantic geotraverse tag hydrothermal field on the mid atlantic ridge clays separated from tag metalliferous sediments in this study all consist of al poor nontronite oxygen isotope thermometry of the clays yields formation temperatures of 54 67 c for samples from the inactive alvin mound compared with 81 96 c for samples from the active tag site the latter are the highest recorded temperatures for authigenic hydrothermal clays sr isotope analysis of the clays from the active mound suggests that they precipitated from seawater dominated fluids containing less than 15 hydrothermal end member fluid in contrast nontronite from the inactive alvin mound has 87sr 86sr values that closely resemble that of detrital north atlantic clays suggesting a dominantly continental source for the sr rare earth element data are consistent with a significant detrital input to the inactive site but also demonstrate the extent of hydrothermal input to the low temperature fluid crystallographic fractionation of the trivalent ree is apparent in the heavy ree enrichments for all nontronite samples the inferred formation mechanism for nontronite rich fe oxyhydroxide deposits at the surface of the active mound is by direct precipitation from low temperature fluids at the inactive alvin site in contrast the deposits form during alteration of pelagic sediments by diffuse fluids and replacement of biogenic carbonate with nontronite and fe oxyhydroxide these two modes of formation are both important in seafloor hydrothermal settings where clay minerals are a significant component of the hydrothermal deposit

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

the changing vision of marine minerals abstract non fuel marine minerals are reviewed from the perspective of resources and their value as active analogs that can advance understanding of types of ancient ore deposits that formed in marine settings the theory of plate tectonics is the largest influence in expanding our vision of marine minerals and in developing our understanding of geologic controls of mineralization in space and time prior to the advent of plate tectonics we viewed the ocean basins as passive sinks that served as containers for particulate and dissolved material eroded from land this view adequately explained marine placer deposits heavy minerals and gems aggregates sand and gravel and precipitates phosphorites and manganese nodules although numerous sites of placer mineral deposits are known on continental shelves worldwide current activity pertains to diamond mining off southwestern africa tin mining off southeastern asia and intermittent gold mining off northwestern north america which are all surpassed economically by worldwide recovery of marine sand and gravel in turn dwarfed by offshore oil and gas with the advent of plate tectonics plate boundaries in ocean basins are recognized as active sources of mineralization in the form of hydrothermal massive sulfide deposits and proximal lower temperature deposits hosted in oceanic crust mafic at ocean ridges and felsic at volcanic island arcs and of magmatic ni cu sulfide chromite and pge deposits inferred to be present in the oceanic upper mantle lower crust based on their occurrence in ophiolites some 300 sites of hydrothermal active and relict mineralization most of them minor are known at this early stage of seafloor exploration on ocean ridges in fore arc volcanoes at back arc spreading axes and in arc rifts deposits formed at spreading axes and transported off axis by spreading are present in oceanic lithosphere but are virtually unknown the tag trans atlantic geotraverse hydrothermal field in the axial valley of the mid atlantic ridge latitude 26 n is considered to exemplify a major volcanogenic massive sulfide vms deposit forming at a spreading axis the most prospective of these occurrences lie within the 200 nautical mile 370 km wide exclusive economic zone eez of the nations of the volcanic island arcs of the western pacific where metal content of massive sulfides ag au ba cu pb sb zn exceeds that at ocean ridges plate tectonics early provided a framework for mineralization on the scale of global plate boundaries and is providing guidance to gradually converge on sites of mineralization through regional scales of plate reorganization with the potential to elucidate the occurrence of individual deposits e g eocene carlin type gold deposits investigation of the spectrum of marine minerals as active analogs of types of ancient mineral deposits is contributing to this convergence consideration of questions posed by brian skinner 1997 of what we do and do not know about ancient hydrothermal mineral deposits demonstrates the ongoing advances in understanding driven by investigation of marine minerals

determining the orientations of ocean bottom seismometers using ambient noise correlation 1 the cross correlation of multicomponent ambient seismic noise can reveal both the velocity and polarization of surface waves propagating between pairs of stations we explore this property to develop a novel method for determining the horizontal orientation of ocean bottom seismometers obs by analyzing the polarization of rayleigh waves retrieved from ambient noise cross correlation we demonstrate that the sensor orientations can be estimated through maximizing the correlation between the radial vertical component and the phase shifted vertical vertical component of the empirical green s tensor we apply this new method to the elsc eastern lau spreading center obs experiment data set and illustrate its robustness by comparing the obtained orientations with results from a conventional method utilizing teleseismic p and rayleigh wave polarizations when applied to a large obs array the ambient noise method provides a larger number of orientation estimates and better azimuthal coverage than typically is possible with traditional methods

geochemistry of sediments from the tag hydrothermal field m a r at latitude 26 n abstract sediments from the tag hydrothermal field show evidence of hydrothermal inputs in the form of fe cu zn and mn enrichments the fe cu and zn are thought to have been introduced as finely divided sulphides precipitated from suspension after dispersion away from now inactive hydrothermal vents and have since been oxidised by contrast the manganese is believed to be in the form of primary oxide precipitate the processes of metal enrichment have been variably active during discrete intervals in the past geochemical partition analysis has demonstrated that the elements determined can be distributed differently between various phases in the different types of sediments studied and that diagenetic transfer of elements from one phase to another occurs on burial the general lack of metal enrichments in the sediments of the intensity sometimes found on the east pacific rise is thought to be largely the result of major metal precipitation subsurface

rare earth element geochemistry of hydrothermal deposits from the active tag mound 26 n mid atlantic ridge the rare earth element ree geochemistry of various phases from the active tag hydrothermal mound has been examined and related to their mineralogy and fluid chemistry the mound deposits range from black and white smoker chimneys massive anhydrite sulphide mixtures oxides and ochres all phases except black smoker chimney anhydrite demonstrate a positive eu anomaly when normalised to chondrite ree values ree substitution into sulphide and sulphate phases appears to be strongly influenced by crystallographic control for all ree other than eu precipitation of anhydrite within the tag mound is the major mechanism for removal of ree during mound circulation and 0 15 0 35 g anhydrite is inferred to precipitate from every kg of fluid venting from the white smoker chimneys oxides from the mound fall into three different categories with distinct ree patterns oxide rims on sulphides atacamite bearing oxides and silica rich fe oxides and ochres the oxide rim phases contain sulphide and seawater derived rees whereas the atacamite bearing oxides and the ochreous material exhibit no seawater signature which suggests precipitation from or alteration by a modified hydrothermal fluid

geochemistry of surface sediments from the mid oceanic kolbeinsey ridge north of iceland in order to assess recent submarine volcanic contributions to the sediments from the active kolbeinsey ridge surface samples were analyzed chemically the contribution of major and trace elements studied differ within the study area a statistical analysis of the geochemical variables using factor analysis and cluster method allows to distinguish possible sample groups cluster method identifies three distinct sediment groups located in different areas of sedimentation group 1 is characterized by highest contents of fe2o3 v co ni cu and zn demonstrating the input of volcaniclastic material group 2 comprises high values of caco3 cao and sr representing biogenic carbonate group 3 is characterized by the elements k rb cs la and pb indicating the terrigenous component the absolute percentage of the volcanic biogenic and terrigenous components in the bulk sediments was calculated by using a normative sediment method the highest volcanic component 60 on a carbonate free basis is found on the ridge crest the biogenic component is highest 10 30 in the eastern part of the spar fracture zone influenced by the east iceland current samples from the western and southeastern region of the study area contain more than 90 of terrigenous component which appears to be mainly controlled by input of ice rafted debris

geochemistry petrology and ages of the lunar meteorites kalahari 008 and 009 new constraints on early lunar evolution abstract kalahari 008 and 009 are two lunar meteorites that were found close to each other in botswana kalahari 008 is a typical lunar anorthositic breccia kalahari 009 a monomict breccia with basaltic composition and mineralogy based on minor and trace elements kalahari 009 is classified as vlt very low ti mare basalt with extremely low contents of incompatible elements including the ree the lu hf data define an age of 4286 95 ma indicating that kalahari 009 is one of the oldest known basalt samples from the moon it provides evidence for lunar basalt volcanism prior to 4 1 ga pre nectarian and may represent the first sample from a cryptomare the very radiogenic initial 176hf 177hf ehf 12 9 4 6 the low ree th and ti concentrations indicate that kalahari 009 formed from re melting of mantle material that had undergone strong incompatible trace element depletion early in lunar history this unusually depleted composition points toward a hitherto unsampled basalt source region for the lunar interior that may represent a new depleted endmember source for low ti mare basalt volcanism apparently the moon became chemically very heterogeneous at an early stage in its history and different cumulate sources are responsible for the diverse mare basalt types evidence that kalahari 008 and 009 may be paired includes the similar fayalite content of their olivine the identical initial hf isotope composition the exceptionally low exposure ages of both rocks and the fact that they were found close to each other since cryptomaria are covered by highland ejecta it is possible that these rocks are from the boundary area where basalt deposits are covered by highland ejecta the concentrations of cosmogenic radionuclides and trapped noble gases are unusually low in both rocks although kalahari 008 contains slightly higher concentrations a likely reason for this difference is that kalahari 008 is a polymict breccia containing a briefly exposed regolith while kalahari 009 is a monomict brecciated rock that may never have been at the surface of the moon altogether the compositions of kalahari 008 and 009 permit new insight into early lunar evolution as both meteorites sample lunar reservoirs hitherto unsampled by spacecraft missions the very low th and ree content of kalahari 009 as well as the depletion in sm and the lack of a kreep like signature in kalahari 008 point to a possible source far from the influence of the procellarum kreep terrane possibly the lunar farside

uranium enrichment in metalliferous sediments from the mid atlantic ridge abstract previous studies of metal rich sediments at mid ocean ridge spreading centres have suggested that u fe ratios are relatively constant from site to site a suite of cores from the mid atlantic ridge has been analysed for u and fe content and most samples exhibit constant u fe ratios sulphide bearing parts of one core however contain excess u compared with that observed in other metalliferous sediments but apparently only during oxidative alteration of pyrite phases fission track registration has demonstrated that this excess u is intimately associated with sulphide grains in the sediment scanning electron microscope examination indicates that this u enrichment is limited to very small areas within the oxidation layer and is associated with an enhanced p concentration ion probe analyses allow semi quantitative analyses of various elements through a u rich grain the observed distribution of u coupled with its specific enrichment suggests that microbial mediation might be controlling this enrichment u fe ratios in fully oxidised tag sediments are constant and approximately an order of magnitude higher than in young plume particulates this discrepancy is attributed to a second type of post depositional u enrichment producing an homogeneous distribution of u throughout the sediment

39ar 40ar dating of two lunar granites the age of copernicus previous investigations have suggested that kreep glass found in 12033 and other apollo 12 soils was ejected from the crater copernicus and deposited in a ray across this site soil fragment 12033 507 has been described as having a core of felsite granitic composition with a kreep glass shell 39ar 40ar dating of a sample of this granite material shows almost complete resetting 800 15 ma ago we interpret this age as giving the most precise determination to date for the formation time of copernicus cosmic ray exposure ages of the granite and associated kreep glass in soil 12033 about 250 ma are much less than the k ar age and suggest a complex postejection burial history the 39ar 40ar age of another granite fragment 14303 204 is determined to be in the range 3 80 3 85 ga this age is in agreement with 39ar 40ar ages determined for a few other lunar granites and is interpreted to represent resetting by a large basin forming impact probably imbrium

highly silicic compositions on the moon using data from the diviner lunar radiometer experiment we show that four regions of the moon previously described as red spots exhibit mid infrared spectra best explained by quartz silica rich glass or alkali feldspar these lithologies are consistent with evolved rocks similar to lunar granites in the apollo samples the spectral character of these spots is distinct from surrounding mare and highlands material and from regions composed of pure plagioclase feldspar the variety of landforms associated with the silicic spectral character suggests that both extrusive and intrusive silicic magmatism occurred on the moon basaltic underplating is the preferred mechanism for silicic magma generation leading to the formation of extrusive landforms this mechanism or silicate liquid immiscibility could lead to the formation of intrusive bodies

geochemical evidence for the hydrothermal origin of sulphur base metals and gold in proterozoic metamorphosed black shales kainuu and outokumpu areas finland metamorphosed black shale formations 120 150 m thick with median concentrations of 7 non carbonate carbon and 6 8 sulphur are abundantly met in drill cores in the kainuu and outokumpu areas carbon isotope 3c values are comparable to the average isotopic composition of non carbonate carbon in sedimentary rocks the rare earth element patterns show cerium depletion indicating a marine origin base metal concentrations in black shales are high in the talvivaara mineralization ore estimate 300 mt with 0 26 ni 0 14 cu and 0 53 zn and in the vicinity of ophiolite complexes in the kainuu schist belt the median value for gold is 35 ppb max 170 ppb in the western part and 16 ppb max 180 ppb in the east highest platinum and palladium concentrations encountered are 60 70 ppb it is shown that in the kainuu black shales concentrations of sulphur base metals and precious metals have been increased by hydrothermal processes as indicated by positive europium anomalies elevated mercury concentrations max 7 5 ppm high sulphur isotope 34s values and the enrichment of sulphur and base metals relative to carbon the processes operative during the deposition of these shales find an analogy in recent processes in ocean ridge spreading axes

surface waves in the western taiwan coastal plain from an aftershock of the 1999 chi chi taiwan earthquake significant surface waves were recorded in the western coastal plain wcp of taiwan during the 1999 chi chi taiwan earthquake and its series of aftershocks we study in detail the surface waves produced by one aftershock 20 september 1999 18hr 03m 41 16sec m 6 2 in this paper we take the chelungpu chukou fault to be the eastern edge of the wcp because it marks a distinct lateral contrast in seismic wave velocities in the upper few kilometers of the surface for many records from stations within the wcp body waves and surface waves separate well in both the time domain and the period domain long period e g 2 sec ground motions in the plain are dominated by surface waves significant prograde rayleigh wave particle motions were observed in the wcp the observed peak ground velocities are about 3 5 times larger than standard predictions in the central and western part of the plain observed response spectra at 3 sec 4 sec and 5 sec at the center of the plain can be 15 times larger than standard predictions and 10 times larger than the predictions of joyner 2000 based on surface wave data from the los angeles basin the strong surface waves were probably generated at the boundary of the wcp and then propagated toward the west largely along radial directions relative to the epicenter the geometry of the boundary may have had a slight effect on propagation directions of surface waves group velocities of funda mental mode rayleigh and love waves are estimated using the multiple filter analysis mfa technique and are refined with phase matched filtering pmf group velocities of fundamental mode surface waves range from about 0 7 km sec to 1 5 km sec for the phases at periods from 3 sec to 10 sec one important observation from this study is that the strongest surface waves were recorded in the center of the plain the specific location of the strongest motions depends largely on the period of surface waves rather than on specific site conditions or plain structures accordingly we conjecture that surface waves could be generated in a wide area close to boundaries of low velocity sedimentary wave guides in the case studied in this article the area can be as wide as 30 km from the chelungpu fault to the center of the plain surface waves converted by p and s waves at different locations would overlap each other and add constructively along their propagation paths as a result the surface waves would get stronger and stronger beyond a certain distance to the boundary no more surface waves would be generated consequently no more local surface waves would be superimposed into the invasive surface waves and the surface waves would tend to decay in amplitude with distance

metalliferous sediments associated with presently forming volcanogenic massive sulfides the susu knolls hydrothermal field eastern manus basin papua new guinea short sediment cores were examined from the active susu knolls hydrothermal field in the eastern manus back arc basin papua new guinea in order to explain the origin of the currently accumulating metalliferous sediments the mineralogy and geochemistry of the sediments were studied by x ray diffraction scanning electron microscopy energy dispersive x ray fluorescence and instrumental neutron activation analysis sediments of the suzette site originated from the deposition of volcaniclastic material with the addition of a hydrothermal component from the mass wasting of old oxidized chimneys a strong mass wasting event was recognized at the base of the studied sedimentary succession from the occurrence of chalcopyrite pyrite and barite aggregates similar to those found in chimneys as well as the presence of atacamite the metalliferous component is characterized by high concentrations of cu up to 2 3 and au up to 3 5 ppm elevated concentrations of as ba zn and fe as well as a positive eu anomaly the material derived from eroded chimneys was deposited together with abundant glass fragments eroded from the volcanic edifice the mass wasting was succeeded by deposition of volcaniclastic sediment containing dacite fragments ca plagioclase pyroxene glass shards cristobalite si rich amorphous material alunite pyrite barite and magnetite the volcaniclastic sediment may have originated from hydrothermal eruptions at north su and south su the present day plume at suzette is a likely source of rare barite aggregates amorphous cu containing aggregates and cu fe sulfides creating geochemical anomalies of ba and cu in the uppermost sediments at suzette interbedded volcaniclastic and hemipelagic sediments were retrieved east and west of susu knolls the enrichment of mn in these sediments is considered to be a result of settling of mn oxides from a hydrothermal plume

particle recycling in the tag hydrothermal plume abstract analysis of th isotope distributions in the tag hydrothermal plume yields evidence for pronounced 234 th 230 th isotope fractionation this fractionation can be attributed to a combination of four processes 1 particle ageing 2 differential scavenging of 234 th and 230 th 3 differential focusing of 234 th and 230 th and 4 recycling of old particles we present arguments for the importance of the last of these processes particle recycling particles in the tag hydrothermal plume exhibit grain sizes which fall in the range 1 10 m applying the range of densities reported for amorphous iron oxyhydroxide and iron oxide mineral phases stokes law predicts that these particles should achieve terminal settling velocities ranging between 4 and 8 m d 1 for coarse grained 5 m radius particles and 0 2 0 3 m d 1 for fine grained particles 1 m radius these velocities have been used in a physical model of re entrainment and recycling in neutrally buoyant plumes our results indicate that particle recycling and re entrainment in hydrothermal plumes may be important over length scales of 1 10 km the model predicts that the proportion of particles re entrained is independent of particle size but increases with plume strength for plumes with volumetric fluxes greater than 10 3 m 3 s 1 the proportion of particles re entrained exceeds 50 in agreement with previous calculations based upon 230 th distributions sampling strategies in the past have typically concentrated upon processes operating within 1 km of active vent fields and will need to be revised accordingly in the future

the trans atlantic geotraverse hydrothermal field a hydrothermal system on an active detachment fault abstract over the last ten years geophysical studies have revealed that the trans atlantic geotraverse tag hydrothermal field 26 08 n on the mid atlantic ridge is located on the hanging wall of an active detachment fault this is particularly important in light of the recognition that detachment faulting accounts for crustal accretion extension along a significant portion of the mid atlantic ridge and that the majority of confirmed vent sites on this slow spreading ridge are hosted on detachment faults the tag hydrothermal field is one of the largest sites of high temperature hydrothermal activity and mineralization found to date on the seafloor and is comprised of active and relict deposits in different stages of evolution the episodic nature of hydrothermal activity over the last 140 ka provides strong evidence that the complex shape and geological structure of the active detachment fault system exerts first order but poorly understood influences on the hydrothermal circulation patterns fluid chemistry and mineral deposition while hydrothermal circulation extracts heat from a deep source region the location of the source region at tag is unknown hydrothermal upflow is likely focused along the relatively permeable detachment fault interface at depth and then the high temperature fluids leave the low angle portion of the detachment fault and rise vertically through the highly fissured hanging wall to the seafloor the presence of abundant anhydrite in the cone on the summit of the tag active mound and in veins in the crust beneath provides evidence for a fluid circulation system that entrains significant amounts of seawater into the shallow parts of the mound and stockwork given the importance of detachment faulting for crustal extension at slow spreading ridges the fundamental question that still needs to be addressed is how do detachment fault systems and the structure at depth associated with these systems e g presence of plutons and or high permeability zones influence the pattern of hydrothermal circulation mineral deposition and fluid chemistry both in space and time within slowly accreted ocean crust

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

tracing dust input to the mid atlantic ridge between 14 45 n and 36 14 n geochemical and sr isotope study abstract a geochemical and sr isotope study was carried out on sediment cores collected from the logatchev hydrothermal vent site 14 45 n on the mid atlantic ridge with the aim of identifying aeolian inputs into the overlying water column the logatchev vent site lies beneath the ne trade winds which transport large amounts of detrital material across the north atlantic sequential dissolution of the sediments has been used to discriminate the detrital fraction from other types of sediment ree patterns for the acetic acid fraction at the logatchev site record contributions from biogenic carbonate seawater like ree pattern and oxy hydroxides which exhibit positive eu and negative ce anomalies typical of hydrothermal origin the logatchev site leach fractions have similar major element compositions to terrigenous al fe mn oxides whose ree patterns show strong positive ce and negative eu anomalies that are comparable to those of preformed fe mn oxides of continental origin based on major element and ree data and 87sr 86sr ratios 0 7197 0 7236 the residue fractions at the logatchev site contain a significant contribution from aeolian sources whose chemical composition is virtually identical to oligotrophic settling particles in the equatorial atlantic ocean in comparison residues from the rainbow hydrothermal site 36 14 n have geochemical composition controlled by hydrothermal anhydrite chavagnac v german c r milton j a palmer m r 2005 sources of ree in sediment cores from the rainbow vent site 36 14 n mar chem geol 216 329 352 they are characterised by 87sr 86sr ratios of 0 7087 0 7093 which are significantly less radiogenic than those of the saharan dust hence the data suggest 1 a significant contribution of aeolian material to the sediments at 14 45 n that is not present at 36 14 n 2 that this material is most likely of north african origin and 3 that this source of aeolian material has remained relatively constant over the last 13 kyr

verifying single station seismic approaches using earth based data preparation for data return from the insight mission to mars abstract the planned insight mission will deliver a single seismic station containing 3 component broadband and short period sensors to the surface of mars in 2016 while much of the progress in understanding the earth and moon s interior has relied on the use of seismic networks for accurate location of sources single station approaches can be applied to data returned from mars in order to locate events and determine interior structure in preparation for the data return from insight we use a terrestrial dataset recorded at the global seismic network station bfo located at the black forest observatory in germany to verify an approach for event location and structure determination based on recordings of multiple orbit surface waves which will be more favorable to record on mars than earth due to smaller planetary radius and potentially lower background noise with this approach applied to events near the threshold of observability on earth we are able to determine epicentral distance within approximately 1 corresponding to 60 km on mars and origin time within 30 s with back azimuth determined from rayleigh wave polarization absolute locations are determined generally within an aperture of 10 allowing for localization within large tectonic regions on mars with these locations we are able to recover earth mantle structure within 5 the insight mission requirements for martian mantle structure using 1d travel time inversions of p and s travel times for datasets of only 7 events the location algorithm also allows for the measurement of great circle averaged group velocity dispersion which we measure between 40 and 200 s to scale the expected reliable frequency range of the insight data from earth to mars data using the terrestrial data we are able to resolve structure down to 200 km but synthetic tests demonstrate we should be able to resolve martian structure to 400 km with the same frequency content given the smaller planetary size

thermal history of apollo 12 granite and kreep rich rock clues from pb pb ages of zircon in lunar breccia 12013 abstract with the mafic to ultramafic petrology of the moon the presence of granite appears anomalous however fragments of rocks with a definite granitic textures and mineralogy have been recovered from the maria where their ages point to an ultimate origin in the highlands apollo 12 mare breccia 12013 is one of these unique lunar rocks containing abundant granitic components it consists of a black portion composed mainly of fragments of plagioclase and noritic rock with minor fragments of granitic rock and a gray portion that is dominated by an overall granitic component zircon grains from this breccia were studied by combining cathodoluminescence cl imaging and micron scale ion microprobe dating techniques zircon grains from the black portion have a large age variation 4 0 4 3 ga a few of them exhibit complex age zoning within individual grains corresponding to cl zoning zircon grains from the gray portion show no cl zoning features but also have a large age variation between different grains 4 2 4 3 ga in this study we suggest that the large age variations of zircon in 12013 among different grains and within individual grains were caused by post crystallization impact events and most of them are not original crystallization ages the 4 3 ga zircon age probably represents the minimum crystallization age of the granitic component in 12013 similar to lunar granites from the apollo 14 and 17 landing sites this old crystallization age also implies that various ree patterns of lunar granites might not be entirely related to their crystallization ages based on comparison with the 207pb 206pb ages for zircon from the apollo 12 14 and 17 landing sites we suggest that there was at least one pre 3 9 ga major impact event on the moon at 4 2 ga

sediments of the active rift zone in the western woodlark basin and the development of hydrothermal and volcanic activity abstract in the western woodlark basin within the neovolcanic zone sediments form ponds in fissures and between individual pillows and tubes a continuous thin sediment cover appears only at the base of the neovolcanic zone its thickness increases with the distance from the zone data on the lithology mineralogy and chemistry of sediment cores from the spreading centre in the western woodlark basin and adjacent areas show that these calcareous sediments avg 44 1 caco 3 contain significant amounts of terrigenous arc volcanic hyaloclastic and hydrothermal material the latter constituting up to 15 of the non carbonate fraction two types of sedimentary sequences occur in the studied area those of the first type were formed by particle by particle sedimentation horizons of redeposited sediments occur in sequences of the second type redeposition of sediments is widespread and is tentatively correlated with cycles of volcanic activity at swells along the spreading centre these alternate with hydrothermal cycles which were determined by the presence of hydrothermal matter in sediments radiocarbon dating of sediments showed that both cycles are of similar duration of the order of 10 000 years they are not synchronous along the spreading axis each swell having a specific evolution based on these determinations we can say that within the studied spreading centre only the franklin seamount swell is prospective for contemporary hydrothermal activity

orienting ocean bottom seismometers from p wave and rayleigh wave polarizations we present two independent automated methods for estimating the horizontal misorientations of ocean bottom seismic sensors from their recorded data the techniques measure the three dimensional directions of particle motion of 1 p waves and 2 rayleigh waves of earthquake recordings for p waves we used a principal component analysis to determine the directions of particle motions polarisations in multiple frequency passbands since p wave polarisation may deviate from the direction of propagation due to seismic anisotropy and dipping discontinuities beneath stations we further corrected for these deviations using a simple fit equation which yields sensor orientations of significantly increased accuracy for rayleigh waves we evaluated the degree of elliptical polarisation in the vertical plane in the time and frequency domain we apply both methods to 57 three component broadband and wideband seismometers that were installed for 13 months on the ocean floor around la reunion hotspot as part of the rhum rum project http www rhum rum net for p wave polarisations we obtained misorientation estimates for 31 out of 44 functioning ocean bottom seismometers obs with an average uncertainty 95 confidence interval of 11 per station at 7 of these obs data coverage was sufficient to correct polarisation measurements for underlying seismic anisotropy and dipping discontinuities which improved the average orientation uncertainty to 6 per station for rayleigh wave polarisations we obtained misorientation estimates for 40 out of 44 functioning obs with an average uncertainty 95 confidence interval of 16 per station results obtained from the two methods are fully consistent within their respective error bars the orientation angles differ on average by 3 1 and 3 7 for circular mean and median statistics respectively the good agreement between the two methods also makes them useful for reliably detecting possible misorientations of terrestrial seismic stations

a probabilistic framework for single station location of seismicity on earth and mars abstract locating the source of seismic energy from a single three component seismic station is associated with large uncertainties originating from challenges in identifying seismic phases as well as inevitable pick and model uncertainties the challenge is even higher for planets such as mars where interior structure is a priori largely unknown in this study we address the single station location problem by developing a probabilistic framework that combines location estimates from multiple algorithms to estimate the probability density function pdf for epicentral distance back azimuth and origin time each algorithm uses independent and complementary information in the seismic signals together the algorithms allow locating seismicity ranging from local to teleseismic quakes distances and origin times of large regional and teleseismic events m 5 5 are estimated from observed and theoretical body and multi orbit surface wave travel times the latter are picked from the maxima in the waveform envelopes in various frequency bands for smaller events at local and regional distances only first arrival picks of body waves are used possibly in combination with fundamental rayleigh r1 waveform maxima where detectable depth phases such as pp or pmp help constrain source depth and improve distance estimates back azimuth is determined from the polarization of the rayleigh and or p wave phases when seismic signals are good enough for multiple approaches to be used estimates from the various methods are combined through the product of their pdfs resulting in an improved event location and reduced uncertainty range estimate compared to the results obtained from each algorithm independently to verify our approach we use both earthquake recordings from existing earth stations and synthetic martian seismograms the mars synthetics are generated with a full waveform scheme axisem using spherically symmetric seismic velocity density and attenuation models of mars that incorporate existing knowledge of mars internal structure and include expected ambient and instrumental noise while our probabilistic framework is developed mainly for application to mars in the context of the upcoming insight mission it is also relevant for locating seismic events on earth in regions with sparse instrumentation

black smokers massive sulphides and vent biota at the mid atlantic ridge the discovery of black smokers massive sulphides and vent biota in the rift valley of the mid atlantic ridge demonstrates that this assemblage of hydrothermal phenomena is not limited to intermediate to fast spreading oceanic ridges hydrothermal exchange processes may thus be important at the ridges which extend through the atlantic ocean and western indian ocean comprising more than half of the 55 000 km global length of seafloor spreading centres

geochronology of tag and snakepit hydrothermal fields mid atlantic ridge witness to a long and complex hydrothermal history geochronological studies of a large number of precipitates from the tag hydrothermal field and of few samples from snakepit hydrothermal field of the mid atlantic ridge show intermittent repeated hydrothermal events at both sites 210pb pb and 230th 234u measurements of sulfides iron and manganese oxides and 14c measurements of carbonates combined with observations of hydrothermal events recorded as discrete layers in sediment cores provide the basis for unravelling the temporal history of the fields the tag field shows intermittent activity over the past 120 000 years as evidenced by ages of low temperature mn oxides the presently active black smoker mound first formed about 40 000 50 000 years ago with precipitation of massive sulfides it has had intermittent pulsed high temperature activity every 5000 6000 years over the past 20 000 years which may reflect renewed magmatic activity at the ridge axis fluid flow is focussed at the mound site by structural and tectonic control suggested by the intersection of n s ridge parallel lystric normal faults and an e w transform fault periods of inactivity are marked by covering of the mound with pelagic carbonate ooze which is probably partially dissolved and reprecipitated as aragonite at the end of each high temperature event the snakepit field had an initial event about 4000 years ago probably shortly after the eruption of the volcanic ridge on which it sits a recent renewal still presently active was probably initiated by recent fissuring of the volcanic pile

history and geochemistry of a metalliferous sediment core from the mid atlantic ridge at 26 n fourteen thousand years of hydrothermal deposition are recorded in a metalliferous sediment core recovered from the trans atlantic geotraverse tag hydrothermal field on the mid atlantic ridge at 26 n an estimated 26 to 96 of the sediment at this core site is hydrothermally derived as determined from the caco3 al and fe data layers of essentially pure vent precipitates contain 3 caco3 and 0 5 al with high concentrations of fe 43 cu 4 1 zn 1 2 mn 1 1 v 480 ppm pb 175 ppm cd 32 ppm and hg 3 8 ppm sediment accumulation rates vary from 1 to 30 g cm2 1000 y throughout the core a function of the intensity of hydrothermal inputs distinct hydrothermal events are recorded at 6000 and 8500 y b p in layers containing 90 vent derived material vertical metal profiles and interelement relationships in the core result from variable deposition of oxides and sulfides oxidation and dissolution of sulfide phases and scavenging of metals from seawater

geochemistry of a hydrothermal sediment core from the obs vent field 21 n east pacific rise abstract we report a geochemical investigation of near vent hydrothermal sediment from the east pacific rise collected in a short 11 cm core by submersible from the obs vent site at 21 n the sediment has high concentrations of fe 23 25 cu 10 22 zn 4 13 and s 22 30 but low mn concentrations 108 279 ppm indicating a much fresher sulfidic input than in previously reported near vent sediments from the mid atlantic ridge further studies are required to fully characterise near field hydrothermal sediments but the data in this study allow the first comparisons with similar near vent material collected previously from the mid atlantic ridge as well as ridge flank data from the epr and juan de fuca ridge compared to ridge flank sediments the near field sediments exhibit high ratios of fe mn cu fe and zn fe unlike cu and zn pb is not so significantly enriched pb isotope compositions are indistinguishable from local morb indicating a dominant hydrothermal source for this element in these sediments this may not necessarily be the case for ridge flank sediments however where scavenging from seawater may also be important ree distributions throughout the core exhibit low concentrations and characteristics typical of vent fluids with lree enrichments and pronounced positive eu anomalies these patterns are similar to those of relatively fresh sulfides but there is also evidence for progressive oxidation downward into the core by ingressing seawater

complex magmatic and impact history prior to 4 1 ga recorded in zircon from apollo 17 south massif aphanitic breccia 73235 abstract sample 73235 is one of several aphanitic impact melt breccias collected by the apollo 17 mission at stations 2 and 3 on the slopes of the south massif this study presents a detailed investigation of internal structures and u pb ages of large zircon grains from this breccia sample new data combined with the results of previous studies of zircon grains from the same location indicate that most zircon clasts in breccias from stations 2 and 3 formed during multiple magmatic events between 4 37 and 4 31 ga although the oldest zircon crystallized at about 4 42 ga and the youngest at 4 21 ga in addition zircons from the aphanitic breccias record several impact events prior to the 3 9 ga late heavy bombardment the results indicate that the zircons probably crystallized at different locations within the procellarum kreeep terrane and were later excavated and modified by several impacts and delivered to the same locality within separate ejecta blankets this locality became a source of material that formed the aphanitic impact melt breccias of the south massif during a 3 9 ga impact however the zircons showing old impact features are not modified by this 3 9 ga impact event suggesting that i this common source area was located at the periphery of excavation cavity and ii the 3 9 ga ages recorded by the zircon grains could date large basin forming events as significant as major later 3 9 ga collisions such as imbrium and serenitatis

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

uranium lead ages for lunar zircons evidence for a prolonged period of granophyre formation from 4 32 to 3 88 ga the ages of a number of small fragments of lunar granophyre have been determined by the in situ u th pb isotopic analysis of zircon using a sensitive high mass resolution ion microprobe shrimp i the zircon from lunar granophyre is characterized by consistently high u and th contents most 200 500 ppm and 100 300 ppm respectively compared to zircon from mafic lunar rocks some fragments of lunar granophyre are found to be as old as 4 32 ga supporting other evidence that the original lunar magma ocean crystallized completely within 200 ma of the formation of the moon itself other fragments are as young as 3 88 ga which is much later than the time of formation of most of the lunar crust the older lunar granophyres have rare earth element ree patterns that are similar to lunar kreep whilst the younger granophyres have bow shaped ree patterns that feature a greater relative enrichment in the heavy ree the wide range of ages of numerous lunar zircons lunar granophyres and other rocks indicates that zircon forming magmatism in the lunar highlands was most active prior to 4 3 ga but continuous until at least 3 88 ga the u pb isotopic composition of much lunar zircon is near concordant but the effects of isotopic disturbance as late as 1 0 ga are observed in some zircon both within granophyre fragments recrystallized by reheating and within fragments in which the original delicate silica k feldspar granophyric intergrowth is well preserved it is therefore essential to make multiple analyses of individual zircon grains and preferably analyses of suites of zircons from lunar igneous rocks if they are to be dated reliably by the u pb method it is possible that some of the younger lunar granophyres are the product of large scale silicate liquid immiscibility within late stage differentiates but this remains unproven until remnants of demonstrably cogenetic fe rich immiscible liquid are positively identified

the comparative behavior of apatite zircon u pb systems in apollo 14 breccias implications for the thermal history of the fra mauro formation we report secondary ion mass spectrometry sims u pb analyses of zircon and apatite from four breccia samples from the apollo 14 landing site the zircon and apatite grains occur as cogenetic minerals in lithic clasts in two of the breccias and as unrelated mineral clasts in the matrices of the other two sims u pb analyses show that the ages of zircon grains range from 4023 24 ma to 4342 5 ma whereas all apatite grains define an isochron corresponding to an age of 3926 3 ma the disparity in the ages of cogenetic apatite and zircon demonstrates that the apatite u pb systems have been completely reset at 3926 3 ma whereas the u pb system of zircon has not been noticeably disturbed at this time the apatite u pb age is slightly older than the ages determined by other methods on apollo 14 materials highlighting need to reconcile decay constants used for the u pb ar ar and rb sr systems we interpret the apatite age as a time of formation of the fra mauro formation if the interpretation of this formation as an imbrium ejecta is correct apatite also determines the timing of imbrium impact the contrast in the pb loss behavior of apatite and zircon places constraints on the temperature history of the apollo 14 breccias and we estimate from the experimentally determined pb diffusion constants and an approximation of the original depth of the excavated samples in the fra mauro formation that the breccias experienced an initial temperature of about 1300 1100 c but cooled within the first five to ten years

anisotropy beneath a highly extended continental rift we have employed shear wave splitting techniques to image anisotropy beneath the d entrecasteaux islands in southeastern papua new guinea our results provide a detailed picture of the extending continent that lies immediately ahead of a propagating mid ocean ridge tip we image the transition from continental to oceanic extension a dense shear wave splitting data set from a 2010 to 2011 passive source seismic deployment is analyzed using single and multichannel methods splitting delay times of 1 1 5 s are observed and fast axes of anisotropy trending n s parallel to rifting direction predominate the results this trend is linked to lattice preferred orientation of olivine primarily in the shallow convecting mantle driven by up to 200 km of n s continental extension ahead of the westward propagating woodlark rift this pattern differs from several other continental rifts that evince rift strike parallel fast axes and is evident despite the complex recent tectonic history we contend that across most of this rift the unusually high rate and magnitude of extension has been sufficient to produce a regime change to a mid ocean ridge like mantle fabric stations in the south of our array show more complex splitting that might be related to melt or to complex inherited structure at the edge of the extended region

iron and copper enrichment of suspended particles in dispersed hydrothermal plumes along the mid atlantic ridge particulate fe and cu concentrations are used in conjunction with dissolved mn values to identify hydrothermal venting at several sites along the mid atlantic ridge mar in dispersed hydrothermal plumes as defined by dissolved mn anomalies suspended matter fe and cu values were as high as 15 8 and 1100 g g respectively relative to al at 1 7 suspended matter fe and cu values correlate well with dissolved mn concentrations tracing the intensity of dispersed plumes in contrast with fe and cu particulate mn values in vent plumes were low at 700 1200 g g calculated al fe mn al ratios for mar particles increase with increasing dissolved mn concentrations this ratio is used to estimate the percent hydrothermal component of the suspended matter these sensitive tracers identify a 2 20 hydrothermal contribution to the 10 2 g of total suspended matter 1 found along the rift valley

hydrothermal activity and sulphide formation in axial valleys of the east pacific rise crest between 18 and 22 s abstract deep grabens some 90 m in depth occur on the crest of the east pacific rise between 17 9 and 18 6 s and between 21 1 and 21 7 s and are found within the topographic highs in these regions along the rise axis these axial valleys mark areas of recent faulting and intensive hydrothermal activity which is associated with the formation of metalliferous sediments and of massive sulphides of iron copper and zinc most iron and manganese released from the ore fluids continues to be deposited outside the grabens preferentially on the western flank of the rise a tendency which can be recognised also in older sediments of this area

arrival angle anomalies across the usarray transportable array abstract we construct composite maps of surface wave arrival angle anomalies using clustered earthquakes and an array method for measuring wave front geometry this results in observations of arrival angles covering the entire footprint of the usarray transportable array during 2006 2010 bands of arrival angle deviations in the propagation direction indicate the presence of heterogeneous velocity structure both inside and outside of the array we compare the observed patterns to arrival angles predicted using two global tomographic models the mantle model s362ani and the surface wave dispersion model gdm52 we use both ray theory based prediction methods and measurements on synthetic data calculated using a spectral element method both models and all prediction methods produce similar mean arrival angles and long wavelength patterns of anomalies which are similar to the observations predicted short wavelength features generally do not agree with the observations the spectral element method produces some complexity that is not obtained using the ray theory based methods this predicted complexity is similar in character to the observed patterns but does not match them

analysis of rayleigh wave particle motion from active seismics abstract back azimuth analysis is a classical method used in seismological studies for the determination of the direction azimuth of an otherwise unknown seismic source this is accomplished through the analysis of three component 3c data according to a procedure based on the evaluation of rayleigh wave polarity and is typically accomplished by assuming a retrograde motion the same principles are here considered in the framework of the analyses performed while considering active data collected by a 3c geophone thus enabling us to easily and unambiguously compute the rayleigh wave particle motion rpm frequency curve that describes the motion of rayleigh waves as a function of the frequency the analyses performed for three test sites characterized by different stratigraphic conditions show that contrary to the common assumption in the considered frequency range about 2 40 hz prograde motion is actually quite common although for two of the three presented case studies we consider a single offset acquisition in order to evaluate the variations of the rpm frequency curve as a function of the offset we also considered two multi offset datasets one synthetic and one from a field acquisition results seem to indicate that although some dependency on the offset necessarily exists the overall trend is a characteristic of the site potential applications of the described approach are discussed in particular with respect to seismic hazard studies as well as in the light of the exploitation of the rpm frequency curve for better constraining the subsurface model electronic supplement animations of particle motion

native copper and α copper zinc in sediments from the tag hydrothermal field mid atlantic ridge 26 n nature and origin abstract native copper and copper zinc occur as strands and elongated grains up to 300 m in length within the sediments from the trans atlantic geotraverse tag hydrothermal field mid atlantic ridge 26 n they are remarkably similar in composition and crystal structure to copper and copper zinc occurrences found in other natural environments the results of mineralogical studies are discussed in terms of the possible mechanisms of native metal formation in the complex tag field with an asymmetric and highly fractured rift valley and mature active and relict sulfide mounds native copper and copper zinc grains disseminated in the tag sediments are either inherited from 1 primary magmatic or metamorphic crustal source 2 hydrothermal deposits and 3 the alteration of primary deposits or formed 1 authigenically or 2 biogenically within on the sediment cover native metallic particles could have been formed as accessory minerals disseminated in the ridge crest basic rocks and or massive sulfide mounds degradation of these rocks and mass wasting of the mounds have liberated the metallic grains which have in turn been deposited into adjacent sediments