high precision isotopic characterization of usgs reference materials by tims and mc icp ms the pacific centre for isotopic and geochemical research pcigr at the university of british columbia has undertaken a systematic analysis of the isotopic sr nd and pb compositions and concentrations of a broad compositional range of u s geological survey usgs reference materials including basalt bcr 1 2 bhvo 1 2 andesite agv 1 2 rhyolite rgm 1 2 syenite stm 1 2 granodiorite gsp 2 and granite g 2 3 usgs rock reference materials are geochemically well characterized but there is neither a systematic methodology nor a database for radiogenic isotopic compositions even for the widely used bcr 1 this investigation represents the first comprehensive systematic analysis of the isotopic composition and concentration of usgs reference materials and provides an important database for the isotopic community in addition the range of equipment at the pcigr including a nu instruments plasma mc icp ms a thermo finnigan triton tims and a thermo finnigan element2 hr icp ms permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the tims and mc icp ms methods e g nd isotopic compositions for each of the reference materials 5 to 10 complete replicate analyses provide coherent isotopic results all with external precision below 30 ppm 2 sd for sr and nd isotopic compositions 27 and 24 ppm for tims and mc icp ms respectively our results also show that the first and second generation usgs reference materials have homogeneous sr and nd isotopic compositions nd isotopic compositions by mc icp ms and tims agree to within 15 ppm for all reference materials interlaboratory mc icp ms comparisons show excellent agreement for pb isotopic compositions however the reproducibility is not as good as for sr and nd a careful sequential leaching experiment of three first and second generation reference materials bcr bhvo agv indicates that the heterogeneity in pb isotopic compositions and concentrations could be directly related to contamination by the steel mortar pestle used to process the materials contamination also accounts for the high concentrations of certain other trace elements e g li mo cd sn sb w in various usgs reference materials

growth history of a diffusely venting sulfide structure from the juan de fuca ridge a petrological and geochemical study centimeter scale mineralogical and chemical analyses of a diffusely venting 280 c sulfide structure called roane from the mothra hydrothermal field on the juan de fuca ridge reveal a complex growth history these analyses document four well defined zones which from the exterior to the interior of the structure include a barite silica zone fossil worm tube zone a silica sulfide zone silica zone a sulfide silica zone outer sulfide zone and a sulfide gordaite silica zone inner sulfide zone these features are a product of a myriad of processes that include extensive mineral replacement ingress of seawater fracturing and breakout of hot hydrothermal fluids significant conductive cooling and the sustained broad scale outflow of warm fluids from the walls through a porous and permeable matrix roane lacks an open throughgoing chalcopyrite lined central conduit instead it hosts an anastomosing discontinuous network of tortuous channels within the interior of a sponge like matrix of amorphous silica sulfide sulfate and clay minerals megafaunal communities at the summit and sides of this mature diffusely venting chimney provide a constructional framework for new growth isolation of hydrothermal fluid from seawater during progressive fossilization of megafauna and the early formation of barite silica assemblages promote flow of higher temperature fluids within the interior continued isolation of interior higher temperature fluids through increased mineral precipitation and expansion of the structure leads to a zn sulfide pyrite dominated permeable matrix and a network of tortuous channels that form a central porous conduit this conduit is shielded by a weakly silicified metal sulfide inner wall and a strongly silicified outer wall the most outer portions of the walls are highly porous and sites of significant advection and mixing between hydrothermal fluids and seawater the mineralogy and chemistry of roane are strongly affected by ammonia ammonium buffering of the ph during cooling of the hydrothermal fluids the two major results of the buffering are 1 precipitation of zn sulfide at higher temperatures than are typical for bare rock systems leading to the correlation of cu zn cd and se and 2 increased deposition of amorphous silica and clay minerals

dissolved and particulate fe in a hydrothermal plume at 9 45 n east pacific rise slow fe ii oxidation kinetics in pacific plumes production of fe iii particles in hydrothermal plumes is of fundamental importance to the long term effect of hydrothermal circulation on seawater composition to elucidate the fundamental controls on fe redox kinetics and solution particle partitioning in neutrally buoyant plumes we sampled near field 3 km plume particles at 9 45 n on the east pacific rise in 1996 returning in 1997 to sample both particulate and dissolved phases 0 40 m filter concentrations of dissolved fe varied from 320 to 20 nm in proximal 0 3 km from vent site to distal samples 1 3 km downfield constituting 85 50 of total fe respectively based on vent fluid dilution factors calculated from dissolved mn a mass balance for vent fluid fe at this site indicates that 65 of fe is lost to particulate sulfide settling in the buoyant plume and that particulate fe in distal 1 3 km samples is twice as concentrated as predicted from dilution of particles in proximal plume water these observations are consistent with a calculated fe ii oxidation half time of 3 3 h long enough that fe iii colloid production and aggregation occurs primarily in the neutrally buoyant plume at relatively high dilutions preventing generation of high particulate fe concentrations 11 56 nm observed a general investigation of fe ii oxidation rates in plumes worldwide gives fe ii oxidation half lives as short as 17 min at some atlantic sites and as long as 6 h at some pacific sites the calculations indicate that the distribution of fe particles in plumes depends chiefly on inter basin differences in ambient deep water chemistry primarily ph and dissolved o2 and on local currents driving plume dilution and to a much lesser extent on variations in primary vent fluid composition long term changes in thermohaline circulation or ocean biogeochemistry may therefore alter fe dynamics and minor element fluxes associated with global hydrothermal activity independent of variations in crustal production rates

magnetite melt hfse partitioning abstract results from doped hydrous experiments on natural mafic to intermediate composition lavas at 2 5 kbar pressure were combined with existing 1 atm data to evaluate the effects of composition and temperature on the partitioning behavior of the high field strength elements hfse zr nb ta and hf between magnetite and natural silicate melts magnetite composition was found to be the strongest controlling factor on partitioning behavior the partition coefficients d for zr nb hf and ta correlate with d ti ti and al content of the magnetite temperature and pressure the partition coefficients for the hfse are similar to one another for any given magnetite melt pair but range from 2 in titanomagnetite in addition the relationship between ti and the hfse changes as a function of pressure and temperature with the hfse becoming more incompatible relative to ti at lower temperatures and or higher pressures this change in the relationship between d ti and d hfse with temperature and pressure means that the expressions presented in nielsen et al 1994 nielsen r l forsythe l m gallaghan w e fisk m r 1994 major and trace element magnetite melt partitioning chem geol 117 167 191 are not valid for hydrous aluminous systems expressions were derived to describe the relationship between d hfse and temperature pressure fe 2 mg exchange ti al ratio of the magnetite and d ti these expressions reproduce the input data within 35 50 1 over a range extending from highly incompatible to compatible

petrology and geochemistry of mafic rocks in the acasta gneiss complex implications for the oldest mafic rocks and their origin abstract the acasta gneiss complex located in the western part of the slave province canada is widely recognized as the oldest eoarchean terrane in addition to felsic gneisses with the ages of 3 6 4 0 ga minor mafic rocks occur as rounded to elliptical enclaves and inclusions within the felsic gneisses despite serving as potential sources of geochemical information on the hadean mantle the mafic rocks have received less attention in previous studies thus we conducted a comprehensive geological petrological and geochemical investigation on the acasta mafic rocks to constrain their petrogenesis and geodynamic setting the mafic rocks comprise massive to weakly foliated amphibolite garnet amphibolite and hornblendite with variable abundances of hornblende plagioclase chlorite and quartz and subordinate clinopyroxene garnet and cummingtonite they commonly underwent high grade metamorphic recrystallization under amphibolite to upper amphibolite facies conditions the observed variations in mineral assemblages abundances and compositions reflect large differences in whole rock compositions likely caused by crustal anatexis during the eoarchean thermal events responsible for the generation of the surrounding felsic gneisses infiltration or extraction of felsic melts formed due to partial melting of precursor rocks can account for an overall negative correlation between al 2 o 3 and mgo contents and variable enrichments in the incompatible elements despite the widespread influence of anatexis on the geochemistry of acasta mafic rocks we identified the precursor compositions of the least modified amphibolites as basaltic magmas they are characterized by intermediate al 2 o 3 and mgo contents on the observed array and by near chondritic patterns for incompatible trace elements except for slightly negative nb and ta anomalies we considered two scenarios to explain the origin of eoarchean basaltic rocks with nb ta anomalies 1 generation of nb ta deficient basaltic magma in a suprasubduction setting analogous to modern arcs derived magmas and 2 generation of nb ta deficient basaltic magma from the melting of a nb ta deficient primitive mantle possible if the core contains significant proportions of the earth s nb and ta budget although the operation of plate tectonics and the presence of subduction zones at the end of hadean may be an attractive explanation for the observed nb ta depletions the chondritic relative proportions of other immobile trace elements for acasta mafic rocks leave open the possibility of their formation from an nb ta deficient primitive mantle

age and petrology of alkalic postshield and rejuvenated stage lava from kauai hawaii at the top of the waimea canyon basalt on the island of kauai rare flows of alkalic postshield stage hawaiite and mugearite overlie tholeiitic flows of the shield stage these postshield stage flows are 3 92 ma and provide a younger limit for the age of the tholeiitic shield stage the younger koloa volcanics consist of widespread alkalic rejuvenated stage flows and vents of alkalic basalt basanite nephelinite and nepheline melilitite that erupted between 3 65 and 0 52 ma all the flows older than 1 7 ma occur in the west northwestern half of the island and all the flows younger than 1 5 ma occur in the east southeastern half the lithologies have no spatial or chronological pattern the flows of the koloa volcanics are near primary magmas generated by variable small degrees of partial melting of a compositionally heterogeneous garnet bearing source that has about two thirds the concentration of p2o5 rare earth elements and sr of the source of the honolulu volcanics on the island of oahu the same lithology in the koloa and honolulu volcanics is generated by similar degrees of partial melting of distinct source compositions the lavas of the koloa volcanics can be generated by as little as 3 percent to as much as 17 percent partial melting for nepheline melilitite through alkalic basalt respectively phases that remain in the residue of the honolulu volcanics such as rutile and phlogopite are exhausted during formation of the koloa volcanics at all but the smallest degrees of partial melting the mantle source for kauai lava becomes systematically more depleted in 87sr 86sr as the volcano evolves from the tholeiitic shield stage to the alkalic postshield stage to the alkalic rejuvenated stage at the same time the lavas become systematically more enriched in incompatible trace elements on a shorter timescale the lavas of the koloa volcanics display the same compositional trends but at a lower rate of change the source characteristics of the koloa volcanics considered along with those of the honolulu volcanics support a mixing model in which the source of rejuvenated stage lava represents large percent melts of a plume source mixed with small amounts of small percent melts of a heterogeneous mid ocean ridge source

a model for the deposition of hydrothermal manganese near ridge crests a two stage scavenging model is used to describe the transport of hydrothermal mn to the sediments adjacent to ridge crests dissolved mn is hypothesized to be scavenged by slowly settling metal depositing capsuled bacteria which in turn are incorporated into rapidly settling macroaggregates upon reaching the seafloor the mn is subject to resuspension in particulate form and to remobilization within the sediment column and release back into the water column as dissolved mn measured mn distributions in the vicinity of the southern juan de fuca ridge and estimated values of process rate constants are used to limit the range of possible model outcomes the results present a picture of water column distributions and fluxes of dissolved fine particulate and large particle associated mn in a plume advecting off axis the model and best available parameter values suggest that more than 80 of the hydrothermal mn is deposited within several hundred kilometers of the ridge crest though dissolved mn concentrations beyond that distance exceed background levels by many times the residence time of hydrothermal mn in the water column is of the order of several years an off axis component of advection of the order of 0 1 0 3 cm s is needed to make similar the model and measured distributions of mn depositing in the sediments

chemical processes in buoyant hydrothermal plumes on the east pacific rise near 21 n hydrothermal plume water containing suspended particles of precipitated black smoke has been sampled from three hydrothermal vent fields on the east pacific rise near 21 n the samples were taken within the lower 22 m of the buoyant plumes directly above 273 350 c black smoker vents using go flo bottles mounted on the submersible alvin based on li as a conservative tracer of the high temperature endmember solution mixing ratios of 102 to 104 g seawater g vent water are achieved within the lower 22 m of the plumes the particle concentrations sampled in the lower 13 m of the plumes are much larger than predicted for these mixing ratios suggesting that the particles are settling within the lower part of the plume the major minerals in the smoke are pyrrhotite fe rich sphalerite pyrite unidentified fe s si and fe si s phases chalcopyrite amorphous silica sulfur fe oxyhydroxides including goethite and anhydrite present in trace quantities are barite isocubanite wurtzite covellite marcasite and unidentified silicates and alsilicates organic matter is common the composition of the plume solutions indicates that 35 25 of the hydrothermally injected fe remains in dissolved form i e 0 45 m within the lower 22 m of the plume in spite of a 3 to 9 fold excess of h2s in the vent solutions nearly all of the mn and si and most of the ba also remain in solution h2s by contrast has been largely 70 100 removed by precipitation as sulfides and sulfur but mainly by oxidation to dissolved species with intermediate oxidation states its early removal implies that 50 30 of the injected fe will eventually precipitate as primary oxides rather than as sulfides and that fe can be fractionated from the other chalcophile metals during sulfide precipitation compared with the vent water the particles are enriched in cu co ag cd al zn pb and ni by factors of 4 to 20 relative to fe and depleted in ba s si and mn scavenging from seawater may play a role in co and cu enrichment at the ngs field and for ag cd and ni at all three fields but is negligible for pb and zn these results indicate that two distinct metalliferous components are delivered to the distal regions of a plume as a result of reactions in the lower part of the buoyant plume 1 1 a dissolved component that includes about half the fe and all of the mn and will eventually precipitate as oxides and 2 2 a particulate component consisting of fine grained sulfide minerals that are enriched in ore metals by factors of 4 to 20

near vent chemical processes in a hydrothermal plume insights from an integrated study of the endeavour segment support from onc for sample collection is gratefully acknowledge as is the analytical expertise of jody spence bruno keiffer and maureen soon who helped generate the data set reported here funding for sample analysis came from an nserc discovery grant to l a c ocean networks canada is supported through the canadian foundation for innovation all data are provided in the supporting information or through onc at http dmas uvic ca datasearch

isotopic evolution of lavas from haleakala crater hawaii pb and sr isotopic ratios have been determined for tholeiitic shield building alkalic cap and post erosional stage lavas from haleakala crater pb isotopic compositions of the tholeiites overlap those of the alkalic cap lavas although87sr 86sr ratios of these two suites are distinct alkalic cap and post erosional lavas appear to be indistinguishable on the basis of sr and pb isotopic composition sr and pb isotopic ratios of haleakala post shield building lavas are positively correlated such a trend is previously undocumented for any suite of hawaiian lavas and contrasts with the general negative correlation observed for data from hawaiian tholeiites these relations are consistent with a three component petrogenetic mixing model specifically it is proposed that magma batches at individual hawaiian volcanoes formed by 1 mixing of melts generated from mantle plumes containing two isotopically distinct mantle components primitive vs enriched and 2 subsequent variable degrees of interaction between these plume melts and a third morb signature mantle reservoir prior to their emplacement in a crustal magma chamber these observations and inferences provide new constraints on physical models of hawaiian magmatism based on observed temporal isotopic variations of haleakala lavas it is suggested that the ratio of enriched primitive mantle components in the hawaiian plume source decreases during the waning stages of alkalic volcanism over the same time interval both decreasing melt production and protracted residence of ascending melts within the upper mantle contribute to a systematic increase in the ratio of depleted vs plume component

hydrothermal cooling of midocean ridge axes do measured and modeled heat fluxes agree abstract accurate estimates of near axis hydrothermal cooling are keys to understanding many geological chemical and biological processes at midocean ridges at present however field observations h heat flux vent field are few and imprecise and model results h m heat flux km of axis vary widely depending on assumptions about crustal formation crustal composition and the cooling efficiency and spatial and temporal extent of hydrothermal circulation in this paper i compare all published vent field scale measurements of h to a range of published h m for slow 40 mm yr and fast 40 mm yr ridges to assess the present state of knowledge about the magnitude of near axis hydrothermal cooling h has been evaluated 28 times either by point measurements using inventories of individual sources 362 552 mw n 12 measurements or by integrated measurements using water column observations 876 1011 mw n 16 comparable estimates of mean vent field expected h at any spreading rate can be derived by merging h m from various models with the predicted global inventory of active vent sites these estimates range from 1 1 5 gw field and are approximately constant for all spreading rates this range agrees with the best constrained results of h from slow ridge vent fields 1669 1354 mw but is considerably higher than those from fast ridges 245 170 mw inferences about the spatial and temporal variability of h can be gained by defining the parameter l h h m equivalent to the axis length needed to continuously power a hydrothermal field the resultant large l values 13 333 km for slow ridges 1 32 km for fast demand punctuated cooling where for short periods h h m the percentage of time that a given vent field might be active can be speculatively estimated by dividing l by the length of axis the field cools examples of this percentage range from a low of 50 for some fast ridge fields

petrology and geochronology of basalt breccia from the 1996 earthquake swarm of loihi seamount hawaii magmatic history of its 1996 eruption samples of basalt were collected during the rapid response cruise to loihi seamount from a brec cia that was probably created by the july to august 1996 loihi earthquake swarm the largest swarm ever recorded from a hawaiian volcano 210 po 210 pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996 making this the first documented historical eruption of loihi sonobuoys deployed during the august 1996 cruise re corded popping noises north of the breccia site indicat ing that the eruption may have been continuing during the swarm all of the breccia lava fragments are tho leiitic like the vast majority of loihi s most recent lav as reverse zoning at the rim of clinopyroxene pheno crysts and the presence of two chemically distinct oliv ine phenocryst populations indicate that the magma for the lavas was mixed just prior to eruption the trace element geochemistry of these lavas indicates there has been a reversal in loihi s temporal geochemical trend although the new loihi lavas are similar isotopically and geochemically to recent kilauea lavas and the man tle conduits for these two volcanoes appear to converge at depth distinct trace element ratios for their recent lavas preclude common parental magmas for these two active volcanoes the mineralogy of loihi s recent tho leiitic lavas signify that they crystallized at moderate depths f8 9 km within the volcano which is approx imately 1 km below the hypocenters for earthquakes from the 1996 swarm taken together the petrological and seismic evidence indicates that loihi s current magma chamber is considerably deeper than the shal low magma chamber f3 4 km in the adjoining active shield volcanoes

measuring fluid flow and heat output in seafloor hydrothermal environments we have designed built calibrated and tested new anemometer and turbine flow meter devices to measure fluid velocity at high and low temperature focused and diffuse discharge sites at oceanic spreading centers the devices perform at ocean floor depths and black smoker temperatures and can be used to measure flow rates ranging over two orders of magnitude flow velocity is determined from the rotation rate of the rotor blades or paddle assembly these devices have an open bearing design that eliminates clogging by particles or chemical precipitates as the fluid passes by the rotors the devices are compact and lightweight enough for deployment from either an occupied or remotely operated submersible the measured flow rates can be used in conjunction with vent temperature or geochemical measurements to obtain heat outputs or geochemical fluxes from both vent chimneys and diffuse flow regions the devices have been tested on 30 alvin dives on the juan de fuca ridge and 3 jason dives on the east pacific rise epr we report 102 new measurements over a wide range of discharge temperatures 5 363 c velocities 2 199 cm s and depths 1517 2511 m these include the first advective heat output measurements at the high rise vent field and the first direct fluid flow measurement at middle valley our data suggest that black smoker heat output at the main endeavor vent field may have declined since 1994 and that after the 2005 2006 eruption the high temperature advective flow at the epr 9 50 n field may have become more channelized predominately discharging through the bio 9 structure we also report first direct advective measurements in the lau basin and at the epr 9 39 5 n with flow meters that predated devices described in this work and were used in the process of their development we discuss potential error sources and how they may affect the accuracy of measurements by our and other devices in particular we use the turbulent plume theory to evaluate the effect of entrainment of ambient seawater

geochemical evolution of kohala volcano hawaii kohala volcano the oldest of five shield volcanoes comprising the island of hawaii consists of a basalt shield dominated by tholeiitic basalt pololu volcanics overlain by alkalic lavas hawi volcanics in the upper pololu volcanics the lavas become more enriched in incompatible elements and there is a transition from tholeiitic to alkalic basalt in contrast the hawi volcanics consist of hawaiites mugearites and trachytes 87sr 86sr ratios of 14 pololu basalts and 5 hawi lavas range from 0 70366 to 0 70392 and 0 70350 to 0 70355 respectively this small but distinct difference in sr isotopic composition of different lava types especially the lower 87sr 86sr in the younger lavas with higher rb sr has been found at other hawaiian volcanoes our data do not confirm previous data indicating sr isotopic homogeneity among lavas from kohala volcano also some abundance trends such as mgo p2o5 are not consistent with a simple genetic relationship between pololu and hawi lavas we conclude that all kohala lavas were not produced by equilibrium partial melting of a compositionally homogeneous source

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

distribution and sources of pre anthropogenic lead isotopes in deep ocean water from fe mn crusts abstract the lead isotope composition of ocean water is not well constrained due to contamination by anthropogenic lead here the global distribution of lead isotopes in deep ocean water is presented as derived from dated ca 100 ka surface layers of hydrogenetic fe mn crusts the results indicate that the radiogenic lead in north atlantic deep water is probably supplied from the continents by river particulates and that lead in pacific deep water is similar to that characteristic of island and continental volcanic arcs despite a short residence time in deep water 80 100 a the isotopes of lead appear to be exceedingly well mixed in the pacific basin there is no evidence for the import of north atlantic deep water derived lead into the pacific ocean nor into the north indian ocean this implies that the short residence time of lead in deep water prohibits advection over such long distances consequently any climate induced changes in deep water flow are not expected to result in major changes in the seawater pb isotope record of the pacific ocean

engineering behaviour of phyllites abstract the physico mechanical behaviour of intrinsically anisotropic rocks cannot be assessed through common engineering experiences due to a number of governing intrinsic factors e g variation of mineral assemblage fabric and physical and mechanical properties the study of such rocks under the stress conditions existing within the drilling reach of the earth s crust has not been given due attention not even in laboratory simulated conditions therefore it seemed worthwhile to undertake a comprehensive study using three varieties of intrinsically anisotropic phyllites obtained from the vicinity of the chamera hydroelectric project site in the himalayan region attention has been paid to their petrographic and petrofabric analyses through thin sections x ray diffraction and scanning electron microscopy and the physical and geotechnical properties with special reference to their anisotropyp compression tests were run from unconfined to a maximum confining pressure 3 of 70 mpa for the three phyllites at specified orientation angles angle between the plane of weakness and the direction of the major principal stress 1 of 0 15 30 45 60 75 and 90 thus the physico mechanical response of the phyllites as a function of confining pressure and the orientation angle has been determined and the degree of anisotropy could be quantified in terms of physically measureable parameters

pb isotopes in sulfides from mid ocean ridge hydrothermal sites the authors report pb isotope ratios of sulfides deposited at seven recently active mid ocean ridge mor hydrothermal vents sulfides from three sediment starved sites on the juan de fuca ridge contain pb with isotope ratios identical to their local basaltic sources lead in two deposits from the sediment covered escanaba trough gorda ridge is derived from the sediments and does not appear to contain any basaltic component there is a range of isotope ratios in a guaymas basin deposit consistent with a mixture of sediment and mor basalt pb lead in a galapagos deposit differs slightly from known galapagos basalt pb isotope values the faithful record of pb isotope signatures of local sources in mor sulfides indicates that isotope ratios from ancient analogues ca be used as accurate reflections of ancient oceanic crustal values in ophiolite hosted deposits and continental crustal averages in sediment hosted deposits the preservation of primary ophiolitic or continental crustal pb isotope signatures in ancient mor sulfides provides a powerful tool for investigation of crustal evolution and for fingerprinting ancient terranes

effect of planar structures on the anisotropy of ranyah sandstone saudi arabia the anisotropy of metamorphic and sedimentary rocks is mainly due to the presence of a single set of discontinuity surfaces such as cleavage foliation schistosity joints microfissuring or bedding the uniaxial compressive strength anisotropy curve is usually u shaped however the presence of more than one discontinuity modifies the shape of the anisotropy curve therefore ranyah sandstone having two sets of mutually perpendicular discontinuities was selected and tested the investigation includes the geological and engineering geological descriptions as well as the classification of the rock mass it also includes the determination of the physical mechanical and dynamic properties of the rock material the most sensitive engineering property to the anisotropic behaviour for ranyah sandstone was found to be the compressive strength a w shaped anisotropy curve was obtained this shape is due the superimposed effects of the two directions of bedding and microfissures acting almost at right angles to each other and is in line with hoek and brown s hoek e brown e t 1980 underground excavations in rock the institution of mining and metallurgy london p 165 hypothesis for two mutually perpendicular discontinuities a comparison of the anisotropic behaviour of the ranyah sandstone with same foreign sandstones of different origin was also made

relict hydrothermal events along the super slow southwest indian spreading ridge near 63 56 e mineralogy chemistry and chronology of sulfide samples abstract during the indoyo cruise in 1998 with shinkai 6500 a massive sulfide field was located in a water depth of about 2940 m near 27 51 s 63 56 e east of the melville fracture zone the newly discovered hydrothermal field is situated at the summit of an axial volcanic ridge informally called mount jourdanne within the field inactive chimneys as well as hydrothermal mounds were observed on the ocean floor but no indications such as shimmering water chemical anomalies in the water column or faunal relicts which might point to an active vent site were observed our discovery proves for the first time that high temperature massive sulfide chimneys can also develop at a super slow spreading ridge such as the southwest indian ridge this discovery of massive sulfides will possibly open new aspects in the understanding of hydrothermal processes along super slow spreading ridges since the sulfide samples from mt jourdanne show interesting differences in their mineralogical as well as chemical compositions when compared to sulfide samples from faster opening ridge environments to reconstruct the history of the evolution of this field age dating studies were carried out on the recovered sulfide samples these indicate activity between 70 000 and 13 000 years ago

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

an assessment of the effect of chemical scavenging within submarine hydrothermal plumes upon ocean geochemistry profiles of 210pb over the endeavour and north cleft segments of the juan de fuca ridge are used to model a time scale for the scavenging by hydrothermal plumes of reactive elements in seawater the hydrothermal plumes above these ridge segments are sites of intense scavenging removal of 210pb at endeavour the total 210pb activities within the plume are as low as 8 dpm 100 l and dissolved activities are as low as 3 dpm 100 l at the north cleft which is characterized by higher particulate fe concentrations the total 210pb activities are 4 5 dpm 100 l the dissolved activities are 1 2 dpm 100 l and the 210pb activities are deficient with respect to the activity of the 210po daughter these are perhaps the lowest 210pb activities ever measured in the deep sea the large gradient of 210pb between the plume and surrounding deep water suggests that scavenging is focused into the plumes through horizontal transport the implication therefore is that this process might impact the ocean on a scale larger than that local to the ridge crest by coupling published measurements of particle flux from endeavour with 210pb activities on particles trapped at that site the total volume of seawater stripped of 210pb per year for that site was calculated to be 7 4 1012 l y globally the extrapolated volume flux of seawater stripped of reactive constituents is 5 7 1015 l y such that the entire ocean is processed in this manner in 2 4 105 y the geochemical cycle of elements with ocean residence times much shorter than this e g pb and th will not be greatly affected by hydrothermal scavenging on the other hand this process holds significance for the geochemistry of other elements scavenged by hydrothermal plumes such as p and v whose ocean residence times are 104 y

linkages between mineralogy fluid chemistry and microbial communities within hydrothermal chimneys from the endeavour segment juan de fuca ridge rock and fluid samples were collected from three hydrothermal chimneys at the endeavour segment juan de fuca ridge to evaluate linkages among mineralogy fluid chemistry and microbial community composition within the chimneys mossbauer midinfrared thermal emission and visible near infrared spectroscopies were utilized for the first time to characterize vent mineralogy in addition to thin section petrography x ray diffraction and elemental analyses a 282 c venting chimney from the bastille edifice was composed primarily of sulfide minerals such as chalcopyrite marcasite and sphalerite in contrast samples from a 300 c venting chimney from the dante edifice and a 321 c venting chimney from the hot harold edifice contained a high abundance of the sulfate mineral anhydrite geochemical modeling of mixed vent fluids suggested the oxic anoxic transition zone was above 100 c at all three vents and that the thermodynamic energy available for autotrophic microbial redox reactions favored aerobic sulfide and methane oxidation as predicted microbes within the dante and hot harold chimneys were most closely related to mesophilic and thermophilic aerobes of the betaproteobacteria and gammaproteobacteria and sulfide oxidizing autotrophic epsilonproteobacteria however most of the microbes within the bastille chimney were most closely related to mesophilic and thermophilic anaerobes of the deltaproteobacteria especially sulfate reducers and anaerobic hyperthermophilic archaea the predominance of anaerobes in the bastille chimney indicated that other environmental factors promote anoxic conditions possibilities include the maturity or fluid flow characteristics of the chimney abiotic fe2 and s2 oxidation in the vent fluids or o2 depletion by aerobic respiration on the chimney outer wall

composition and dissolution of black smoker particulates from active vents on the juan de fuca ridge during two atlantis ii alvin cruises to the juan de fuca ridge in 1984 active high temperature 140 284 c vents were sampled for black smoker particulates using the grassle pump individual mineral phases were identified using standard x ray diffraction and petrographic procedures in addition elemental compositions and particle morphologies were determined by x ray energy spectrometry and scanning electron microscope x ray energy spectrometry techniques the vent particulates from the southern juan de fuca ridge vent sites were highly enriched in s si fe zn and cu and were primarily composed of sphalerite wurtzite pyrite pyrrhotite barite chalcopyrite cubanite hydrous iron oxides and elemental sulfur two additional unidentified phases which were prevalent in the samples included an fe si phase and a ca si phase the grain sizes of the individual particle phases ranged from 100 m for the fe si particles grain size and current meter data were used in a deposition model of individual phase dispersal for many of the larger sulfide and sulfate particles the model predicts dispersal to occur over length scales of only several hundreds of meters the high temperature black smokers from the more northerly endeavour segment vents were highly enriched in fe s ca cu and zn and were primarily composed of anhydrite chalcopyrite sphalerite barite sulfur pyrite and other less abundant metal sulfide minerals the grain sizes of the individual particles ranged from 10 m to slightly larger than 500 m the composition and size distributions of the mineral phases are highly suggestive of high temperature mixing between vent fluids and seawater a series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals the dissolution rates ranged over more than 3 orders of magnitude from 3 2 10 8 cm s 1 for anhydrite to 1 2 10 12 cm s 1 for chalcopyrite the results indicate that for some minerals particularly anhydrite and marcasite total dissolution occurs within a few hours to a few weeks of their formation for other more stable minerals including pyrite sphalerite and chalcopyrite the time required for total dissolution is much longer and consequently individual crystals may be expected to persist in the sediments for considerable periods of time after deposition

shear fractures in anisotropic ductile materials an experimental approach abstract analogue models have been used to investigate the influence of planar mechanical anisotropy on the orientation of shear fractures in an elastoviscous brittle material multilayered models consisting of a mixture of plasticine vaseline and preferentially oriented paper flakes have been coaxially deformed for this purpose the evolution of the orientation length and connectivity of fracture sets has been systematically analysed with progressive coaxial deformation the experimental results show that the orientation of fractures with respect to the deformation axes depends on the orientation of transverse anisotropy two symmetrical sets of shear fractures are formed in models with layering parallel to the extension axis x while the fracture network is asymmetrical with respect to the deformation axes for cases with oblique anisotropy the average dihedral angles between fracture sets are higher than 100 with the obtuse bisector between the two sets oriented perpendicular to layers the stress fields calculated from fracture data differ from the boundary conditions applied by the deformation apparatus this misorientation is related to the degree of anisotropy in models with high oblique anisotropy both fracture arrays rotate in a dextral sense together with layers towards the x axis indicating that the presence of a strong anisotropy controls their evolution with progressive deformation

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

constrained circulation at endeavour ridge facilitates colonization by vent larvae understanding how larvae from extant hydrothermal vent fields colonize neighbouring regions of the mid ocean ridge system remains a major challenge in oceanic research1 2 among the factors considered important in the recruitment of deep sea larvae are metabolic lifespan the connectivity of the seafloor topography and the characteristics of the currents3 here we use current velocity measurements from endeavour ridge to examine the role of topographically constrained circulation on larval transport along ridge we show that the dominant tidal and wind generated currents in the region are strongly attenuated within the rift valley that splits the ridge crest and that hydrothermal plumes rising from vent fields in the valley drive a steady near bottom inflow within the valley extrapolation of these findings suggests that the suppression of oscillatory currents within rift valleys of mid ocean ridges shields larvae from cross axis dispersal into the inhospitable deep ocean this effect augmented by plume driven circulation within rift valleys having active hydrothermal venting helps retain larvae near their source larvae are then exported preferentially down ridge during regional flow events that intermittently over ride the currents within the valley

geochemistry and morphology of metalliferous sediments and oxyhydroxides from the endeavour segment juan de fuca ridge abstract we present first data on the geochemistry mineralogy and morphology of near vent sediments 35 and 200 m from active vent and ridge flank sediments approximately 3 km from the vent field as well as oxyhydroxide deposits from the endeavour segment juan de fuca ridge the purpose of the study was to understand better the origin and characteristic features of metalliferous sediments associated with base and precious metal massive sulfides in volcanic terrains hydrothermal components in sediments are fe si s rich and mn fe si rich phases sulfides and barite which were exclusively derived from plume fallout sulfides are only a minor constituent of near vent sediments 2 4 wt and were not detected in ridge flank sediments the study suggests that the distribution of hydrothermal phases and associated elements in near vent and ridge flank sediments is affected mainly by processes of agglomeration dissolution absorption and settling that take place within a plume and to a lesser extent post depositional processes rapid deposition of sulfides in the vicinity of the vents is reflected in a sharp drop of the cu concentrations in sediments with increasing distance from the vents besides sulfides important carriers of pb cu zn and co in near vent sediments are fe mn oxyhydroxides that occur together with silica as aggregates of gel like material and flaky particles and as coatings on filaments away from the vents trace metals are mostly in fe mn oxyhydroxides and authigenic fe rich montmorillonite oxyhydroxides at the main endeavour field are interpreted to have originated from oxidation of mound sulfides accompanied by precipitation of primary fe oxyhydroxide silica from low temperature fluids at the mothra field seafloor deposits and chimney crusts composed of fe oxyhydroxide mn silica are considered to be direct precipitates from hydrothermal fluids that have been less diluted with seawater oxyhydroxide deposits exhibit unique microtextures that resemble mineralized microorganisms and may indicate existence of diverse microbial communities

large massive sulfide deposits in a newly discovered active hydrothermal system the high rise field endeavour segment juan de fuca ridge submersible observations and side scan sonar imagery delineate ten large venting sulfide sulfate silica structures located on an uplifted block of the axial valley floor on the central portion of the endeavour segment juan de fuca ridge this newly discovered vent field lies 1 8 km north of the main endeavour vent field the axial valley a horst and faults controlling sulfide deposition trend parallel to the ridge axis the horst rises 10 to 15 m above the valley floor and offsets a lava lake which extended 500 m in width across the valley the largest sulfide structures are perched along the major horst bounding faults one structure is the tallest single edifice 45 m reported in the pacific ocean smaller less active and inactive sulfide edifices are associated with faulted remnants of the lava lake surface fissured pressure ridges and at the edge of collapse pits based on the relationship between faults and sulfide structures the morphology of sulfide edifices and their venting characteristics we infer that sulfide structures grow vertically by chimney accumulation and laterally by flange development late stage deposition of amorphous silica toughens the large deposits and may be responsible for the unusual size and aspect ratio of endeavour edifices

east molokai and other kea trend volcanoes magmatic processes and sources as they migrate away from the hawaiian hot spot 1 there are geochemical differences between shield lavas from the two parallel trends kea and loa defined by young hawaiian volcanoes the shield of east molokai volcano at greater than 1 5 ma is the oldest volcano on the kea trend sequences of older tholeiitic to younger alkalic basalt that erupted as this volcano evolved from the shield to postshield stage of volcanism are well exposed much younger 0 34 0 57 ma alkalic basalt and basanite erupted during rejuvenated stage volcanism like rejuvenated stage lavas erupted at other hawaiian volcanoes rejuvenated stage east molokai lavas have relatively low 87sr 86sr and high 143nd 144nd such ratios reflect a source component with a long term depletion in abundance of incompatible elements on the basis of positive correlations of 87sr 86sr versus 206pb 204pb and negative correlations of these isotopic ratios with nb zr a smaller proportion of this depleted component also contributed to the late shield postshield lavas erupted at east molokai and the other kea trend volcanoes haleakala and mauna kea at each of these kea trend volcanoes as the volcano moved away from the hot spot the extent of melting and magma supply from the mantle decreased the depth of melt segregation increased and there was an increasing role for a component with long term relative depletion in incompatible elements this depleted component has kea trend pb isotopic characteristics and relatively low 208pb 204pb at a given 206pb 204pb and it is probably not related to oceanic lithosphere or the source of mid ocean ridge basalt the overlap in sr nd and pb isotope ratios of recent kilauea shield lavas and 550 ka mauna kea shield lavas has been used to argue that kea trend shield volcanism samples a vertically continuous geochemically distinct stripe which persisted in the hot spot source for 550 kyr eisele et al 2003 abouchami et al 2005 as kea trend volcanoes migrate away from the hot spot and evolve from the shield to postshield stage there are systematic changes in sr nd and pb isotope ratios however the overlap of sr nd and pb isotope ratios in late shield postshield lavas from mauna kea 350 ka and east molokai 1 5 ma show that the periphery of the hot spot sampled by kea trend postshield lavas also had long term geochemical homogeneity

hydrothermal sulfide accumulation along the endeavour segment juan de fuca ridge highlights high resolution auv bathymetry is used to identify hydrothermal sulfides on the seafloor 1 2 mt of massive sulfide is identified along 24 km of mid ocean ridge length massive sulfide accumulated at a rate of 400 t yr efficiency of sulfide deposition is 5 of total mobilized metals and reduced sulfur current global seafloor sulfide estimates likely underestimate amount present by about a factor of four abstract hydrothermal sulfide deposits that form on the seafloor are often located by the detection of hydrothermal plumes in the water column followed by exploration with deep towed cameras side scan sonar imaging and finally by visual surveys using remotely operated vehicle or occupied submersible hydrothermal plume detection however is ineffective for finding hydrothermally inactive sulfide deposits which may represent a significant amount of the total sulfide accumulation on the seafloor even in hydrothermally active settings here we present results from recent high resolution autonomous underwater vehicle based mapping of the hydrothermally active endeavour segment of the juan de fuca ridge in the northeast pacific ocean analysis of the ridge bathymetry resulted in the location of 581 individual sulfide deposits along 24 km of ridge length hydrothermal deposits were distinguished from volcanic and tectonic features based on the characteristics of their surface morphology such as shape and slope angles volume calculations for each deposit results in a total volume of 372 500 m3 of hydrothermal sulfide sulfate silica material for an equivalent mass of 1 2 mt of hydrothermal material on the seafloor within the ridge s axial valley assuming a density of 3 1 g cm3 much of this total volume is from previously undocumented inactive deposits outside the main active vent fields based on minimum ages of sulfide deposition the deposits accumulated at a maximum rate of 400 t yr with a depositional efficiency proportion of hydrothermal material that accumulates on the seafloor to the total amount hydrothermally mobilized and transported to the seafloor of 5 the calculated sulfide tonnage represents a four fold increase over previous sulfide estimates for the endeavour segment that were based largely on accumulations from within the active fields these results suggest that recent global seafloor sulfide resource estimates which were based mostly on the sizes and distribution of hydrothermally active deposits may be similarly underestimating the amount of sulfide along the global submarine neovolcanic zones

environmental controls on mid ocean ridge hydrothermal fluxes abstract high temperature hydrothermal fluxes at mid ocean ridges are thought to be an important component of oceanic biogeochemical cycles however little consideration has been given to how these fluxes vary as a consequence of changing environmental conditions over earth history here we consider how changes in sea level and ocean chemistry are likely to have impacted on axis high temperature hydrothermal fluxes focusing on phanerozoic conditions changes in sea level lead to changes in hydrostatic pressure near the base of hydrothermal systems where both peak fluid rock reaction temperatures and phase separation occur in general higher global sea level will lead to higher peak temperatures of fluid rock reaction additionally phase separation at higher pressure tends to lead to formation of a more cl rich vapor that constitutes a larger mass fraction of the system these combined factors may serve to significantly modify hydrothermal fluxes even for sea level changes on the scale of 100 m changes in ocean chemistry can also affect axial hydrothermal fluxes in several ways seawater sulfate contents control the amount of anhydrite that forms which has both physical porosity filling and chemical effects the most important aspect of ocean chemistry in controlling the composition of high temperature vent fluids may be ocean salinity if evaporite formation and dissolution has changed ocean salinity substantially over the phanerozoic hydrothermal fluxes could have been greatly modified ocean chemistry also plays a large role in controlling processes operating in hydrothermal plumes and hence the net flux of elements into and out of the ocean associated with hydrothermal systems we conclude that there is a need for substantial further work to quantify the effects of sea level and ocean chemistry on high temperature hydrothermal fluxes including the development of more robust models that integrate field laboratory and theoretical observations

plume dispersed hydrothermal particles a time series record of settling flux from the endeavour ridge using moored sensors abstract settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast pacific ocean provide information about the deep sea distribution of hydrothermal material results of an 8 day near field single trap experiment and a 340 day multi instrument 5 trap deployment two kilometers from the endeavour ridge vent field show variability in the quantity and composition of the plume to sediment particle flux over time with depth and with distance from the vent field hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment a factor of three variation in fe s among these periods reflects temporal changes in phase composition changes in flux with depth for example a 200 fold increase in cu and zn between above and below plume traps are evidence of hydrothermal input comparison of fluxes determined in the near and far field experiments reveals the spatial influence of vent effluent near field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in fe cu and organic carbon but depleted in mn calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field interpretation of elemental mineralogical and grain size analyses suggest that chemical precipitation kinetics other physical and biological particle forming processes changes in vent output and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations our findings suggest that these rate interdependent processes be included in realistic models of hydrothermal particle flux

engineering properties of quartz mica schist quartz mica schist which is a highly anisotropic metamorphic rock usually presents a geotechnical challenge in construction projects to ensure a safe and economical design a comprehensive in situ and laboratory investigation scheme is necessary for projects to be built in quartz mica schist in this study such a comprehensive laboratory study of the engineering behavior of quartz mica schist has been carried out the p wave velocity tests tensile and uniaxial compressive strength tests and creep deformation tests conducted on specimens with differently oriented schistose planes all reveal the strong anisotropic characters of the rock the relevant crack initiation stress and crack damage stress analysis in uniaxial compression test which has not been previously applied to studying schistose rock has been performed in the present study when loading is parallel to schistose planes crack initiation stress and crack damage stress are lower than those in other loading directions as the compressive loading is applied parallel to schistose planes local tensile stresses are preferentially induced normal to the relatively weak schistose planes cracks are thus easier to develop than in any other loading directions since schistose plane orientation is one of the key factors to control the formation of macro cracks and hence failures of unloading test specimens these engineering geological characters should be taken into consideration in engineering design

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

hydrothermal circulation within the endeavour segment juan de fuca ridge areas of the seafloor at mid ocean ridges where hydrothermal vents discharge are easily recognized by the dramatic biological physical and chemical processes that characterize such sites locations where seawater flows into the seafloor to recharge hydrothermal cells within the crustal reservoir are by contrast almost invisible but can be indirectly identified by a systematic grid of conductive heat flow measurements an array of conductive heat flow stations in the endeavour axial valley of the juan de fuca ridge has identified recharge zones that appear to represent a nested system of fluid circulation paths at the scale of an axial rift valley conductive heat flow data indicate a general cross valley fluid flow where seawater enters the shallow subsurface crustal reservoir at the eastern wall of the endeavour axial valley and undergoes a kilometer of horizontal transit beneath the valley floor finally exiting as warm hydrothermal fluid discharge on the western valley bounding wall recharge zones also have been identified as located within an annular ring of very cold seafloor around the large main endeavour hydrothermal field with seawater inflow occurring within faults that surround the fluid discharge sites these conductive heat flow data are consistent with previous models where high temperature fluid circulation cells beneath large hydrothermal vent fields may be composed of narrow vertical cylinders subsurface fluid circulation on the endeavour segment occurs at various crustal depths in three distinct modes 1 general east to west flow across the entire valley floor 2 in narrow cylinders that penetrate deeply to high temperature heat sources and 3 supplying low temperature diffuse vents where seawater is entrained into the shallow uppermost crust by the adjacent high temperature cylindrical systems the systematic array of conductive heat flow measurements over the axial valley floor averaged 150 mw m2 suggesting that only about 3 of the total energy flux of ocean crustal formation is removed by conductive heat transfer with the remainder being dissipated to overlying seawater by fluid advection

a seismic swarm and regional hydrothermal and hydrologic perturbations the northern endeavour segment february 2005 the february 2005 swarm at the overlapping spreading center osc on the northern end of the endeavour segment is the first swarm on the juan de fuca ridge recorded on a local seafloor seismic network the swarm included several larger earthquakes and caused triggered seismicity and a hydrothermal response in the endeavour vent fields as well as regional scale hydrologic pressure perturbations the spatial and temporal pattern of over 6000 earthquakes recorded during this seismic sequence is complex small magnitude events dominate and seismicity rates wax and wane indicating a magmatic process the main swarm initiates at the northern end of the endeavour ridge however most of the moment release including six strike slip events occurs in the southwest endeavour valley where the swarm epicenters generally migrate south the main swarm is contemporaneous with a hydrologic pressure response at four sealed seafloor boreholes 25 105 km away we infer that the seismic sequence is driven by a largely aseismic magma intrusion at the northern endeavour axis resulting stress changes trigger slip on tectonic faults and possibly dike propagation at the opposing limb of the endeavour osc in the southwest endeavour valley consistent with the eventual decapitation of the endeavour by the west valley segment furthermore 2 5 days after the start of the main swarm seismicity is triggered beneath the endeavour vent fields and temperature increases at a diffuse vent in the mothra field we infer that this delayed response is due to a hydrologic pressure pulse that diffuses away from the main magma intrusion

overlapping volcanoes the origin of hilo ridge hawaii the submarine hilo ridge has been interpreted as a part of mauna kea volcano but is crossed at 1100 m depth by a submerged shoreline terrace composed of basalts that are isotopically distinct from those of mauna kea and similar to those of kohala volcano this terrace evidently is a product of kohala instead of mauna kea almost all of hilo ridge below the terrace therefore must predate the principal growth of mauna kea which has superficially isolated the ridge from its kohala source by overlapping its proximal segment the mauna kea section penetrated by the hawaii scientific drilling project is predicted to be thinner than expected previously owing to the overlap similar overlaps are suspected among other volcanoes and may cause significant changes in the understanding of hawaiian volcanism

exploring the mineralogical heterogeneities of the louisville seamount trail diopside phenocrysts of the louisville seamount trail show an increase in ti al and na with decreasing mg mg fe as is typical for clinopyroxene in alkalic basalts chondrite normalized ree patterns of calculated liquids from la icpms analyses are comparable to whole rock and glass values exceptions are clinopyroxene crystals from the rigil seamount the second oldest seamount drilled at the northern end of the chain some crystals from this site are strongly zoned with distinct compositional boundaries between cores and mantles the cores have high mg mg fe and low al and ti concentrations compared to the mantles and phenocrysts major element clinopyroxene discrimination diagrams indicate that the clinopyroxene mantles and phenocrysts crystallized from alkalic basalts in contrast the mg rich cores have tholeiitic affinities the ree abundances of the cores are similar to that of clinopyroxene from transitional tholeiites of the kerguelen archipelago calculated liquid la yb values for the cores have ratios that are similar to transitional tholeiites in hawaii whereas the mantles have higher la yb values similar to hawaiian alkalic basalts the major and trace element compositions of clinopyroxene cores from the rigil seamount suggest that a transitional tholeiitic magma was present but no evidence for hawaiian shield type tholeiites was found plagioclase crystals from the rigil seamount have 86sr 86sr from 0 70306 to 0 70363 within the range of fozo the transitional tholeiitic signature of the mg rich clinopyroxene cores probably did not have a distinct source compared to other louisville magmas but more likely indicates a higher degree of partial melting 2 5 of that fozo source

magnitude and variance of near bottom horizontal heat flux at the main endeavour hydrothermal vent field 1 we characterize hydrothermal plumes and hydrography within the axial valley of the endeavour segment juan de fuca ridge northeast pacific using data from an autonomous underwater vehicle a lowered ctd and two current meter moorings our survey of the main endeavour hydrothermal vent field mef shows hydrographic variability on scales as short as 20 m and 10 min within the 100 m deep axial valley the mean flow is 1 5 cm s to the north and tidal oscillations have 5 cm s amplitude combining the mean flow with an estimate of the difference in average temperature observed north and south of mef we find that the net along axis horizontal heat flux has a mean magnitude of 8 42 mw an advection diffusion model forced by local current records explains the observed temporal hydrographic variability and shows that mean horizontal flux variance is correspondingly high standard deviation 63 mw a steady state mef heat budget constrained by the observed horizontal flux and measurements of vertical fluxes from other studies has two implications the mef heat flux is partitioned about equally between diffuse and focused vents and about 85 of the flux from diffuse plumes is entrained by focused plumes

the tholeiite to alkalic basalt transition at haleakala volcano maui hawaii previous studies of alkalic lavas erupted during the waning growth stages 0 9 ma to present of haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios these geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components we studied lavas from a 250 m thick stratigraphic sequence in honomanu gulch that includes the oldest 1 1 ma subaerial basalts exposed at haleakaka the lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic sr nd pb and incompatible element abundance ratios e g nb la la ce la sr hf sm ti eu these lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous clinopyroxene rich garnet lherzolite source the intercalated tholeiitic and alkalic honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume and we infer that the tholeiitic lavas reflect a melting range of 10 to 15 while the intercalated alkalic lavas reflect a range of 6 5 to 8 melting however within the uppermost 50 m of section 87sr 86sr decreases from 0 70371 to 0 70328 as eruption age decreased from 0 97 ma to 0 78 ma we infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at 0 93 ma the mixing proportions of source components changed with a morb related mantle component becoming increasingly important as eruption age decreased

melting in the hawaiian plume at 1 2 ma as recorded at maui nui the role of eclogite peridotite and source mixing 1 the volcanoes of maui nui west moloka i east moloka i lana i west maui haleakala and kaho olawe record hawaiian magmatism at 1 2 ma lavas from these volcanoes nearly span the compositional range erupted from all the hawaiian volcanoes over the past 5 myr and represent both the kea and ko olau compositional end members of hawaiian lavas many aspects of major and trace element and isotope compositions of hawaiian shield stage lavas are consistent with ancient recycled oceanic lithosphere in the plume sources of kea and ko olau type magmas lassiter and hauri 1998 blichert toft et al 1999 hypotheses that describe the compositional range of hawaiian lavas as originating from ancient oceanic lithosphere in the hawaiian plume implicitly or explicitly infer lithologic heterogeneity in the plume we present trace element models for the origin of these end members that explicitly address the petrologic complexities of melting eclogite derived from ancient oceanic lithosphere in the plume trace element la nb sm yb sm hf and sm nb major element and isotope compositions of lana i which erupts dominantly ko olau type lavas are consistent with the origin of these lavas in large degree 60 70 melts of ancient upper oceanic crust basalt sediment that mix with plume derived haleakala type melts trace element sm yb hf zr and hf nb and isotope compositions of west maui and east moloka i which erupt dominantly kea type magmas are consistent with an origin in ancient depleted oceanic lithosphere that has been refertilized with moderate degree melts 10 30 of associated crustal gabbro the physical mechanisms melt melt versus melt solid mixing through which the oceanic crustal components melt and mix within the plume lead to the generation of isotopically homogeneous kea type lavas and isotopically heterogeneous ko olau type lavas the volcanoes of maui nui record the exhaustion of the ko olau component and the initiation of the kea component as dominant compositional end members in the hawaiian plume

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

chronology chemistry and origin of trachytes from hualalai volcano hawaii 1 hualalai volcano is unique among hawaiian volcanoes in that it possesses a relatively high proportion of evolved trachytic lavas that were erupted at the beginning of the alkalic postshield phase of volcanism these evolved lavas yield insights into magma sources magma supply rates and the evolution of the subvolcanic magmatic plumbing system at this time trachyte lavas are exposed at the puu waawaa pumice dome and puu anahulu flow as blocks in maars on the south flank of the volcano and as flows in water wells drilled on the west flank of hualalai new 40ar 39ar dates show that the puu waawaa and puu anahulu complex is 114 ka a block from the waha pele maar is 103 ka and water well trachytes range from 107 to 92 ka in age indicating a range for trachyte volcanism of 20 ka nd and pb isotopic compositions overlap with younger alkalic basalts from hualalai but are distinct from hualalai tholeiitic basalts and pacific mid ocean ridge basalts linking the trachytes to alkalic parental magmas that underwent extensive crystallization to yield trachytic residual magmas both sr and o isotopic ratios are higher in the trachytes than in hualalai alkalic lavas which is best explained by reaction with or assimilation of altered hualalai shield basalts at shallow depth major trace element and isotopic variations between trachytes are consistent with their evolution by fractional crystallization from a puu anahulu parent the short time gap between the end of tholeiitic volcanism 133 ka and the onset of trachytic alkalic volcanism and the lack of deep origin xenoliths place the magma reservoir within which the trachytes evolved rapidly at shallow 7 km depth whereas mauna kea and kohala volcanoes produced small volumes of highly evolved lavas as magma supply rates dwindled through the postshield stage postshield magma intrusion rates at hualalai were lowest during trachyte formation and increased through a more recent period of alkalic basalt eruptions subtle rare earth element and radiogenic isotopic distinctions between trachytes from the three localities indicate that the roof of the shallow magma reservoir may have been irregular allowing some trachytes to evolve independently from others

nd sr pb isotope constraints on the sources of west maui volcano hawaii the origin of the emperor hawaiian volcanic chain is attributed to the northwesterly movement of the pacific plate over a stationary mantle plume hotspot 1 there has been considerable controversy as to the nature and number of sources of hawaiian hotspot volcanism thus far most geochemical models have been based on rock suites that are not representative of fully developed volcanoes nd and sr isotope ratios and trace element concentrations of volcanics from haleakala maui where all three volcanic stages are developed have been interpreted as reflecting a mixing process of two isotopically distinct sources2 3 in an attempt to test our earlier multiple source model4 we have analysed pb sr and nd isotope ratios in volcanics from west maui the only other volcano with a complete volcanic record our results presented here indicate at least three isotopically distinct sources one of which is heterogeneous with respect to pb furthermore the inferred depleted source for post erosional volcanics has a pb and sr isotope composition intermediate between those of depleted and enriched mid ocean ridge basalts morb n type and p type suggesting that this source is also heterogeneous

uptake and fractionation of rare earth elements on hydrothermal plume particles at 9 45 n east pacific rise abstract particulate samples 0 45 m from a neutrally buoyant hydrothermal plume at 9 45 n on the northern east pacific rise were collected using large volume in situ filtration and analyzed for fe al mn ni and fourteen rare earth elements ree the sm fe ratio a proxy for overall ree fe and nd er light heavy ree fractionation increased moderately with decreasing particulate fe chemically the sense of these relationships matched that documented previously in the tag plume on the mid atlantic ridge german et al 1990 although particulate fe was about 10 fold lower at 9 45 n spatial trends relative to the vent source however were opposite of expectation because slow fe ii oxidation and fe iii colloid aggregation over this interval led to increased particulate fe 10 26 nm with distance from source field and sherrell submitted after subtraction of non plume background particle composition plume particles at 9 45 n and tag had indistinguishable ranges of light ree enriched fractionation relative to ambient seawater and had very similar sm fe therefore kd for fe oxyhydroxides demonstrating that plume particles in both oceans reflect to a first degree the local seawater ree composition within plume ree variations at 9 45 n were investigated using a simple mixing model which accounts for the bulk fe al mn variations in the plume using two endmembers fresh hydrothermal oxyhydroxide precipitates and ridge crest background particles composed largely of locally resuspended sediment sm fe and nd er plot linearly with mixing ratio r 0 96 implying that the observed ree trends result from mixing of these two endmembers extrapolation to the composition of pure hydrothermal precipitates suggests that nd er is fractionated relative to seawater by a factor of 1 8 during adsorption onto fresh fe oxyhydroxide particles the ridge crest background particles are 5 fold higher in sm fe and nd er is 2 49 relative to seawater partly a result of enriched terrigenous component in the resuspended matter a reinterpretation of ree at tag reveals that positive curvature in ree vs fe plots argued previously to reflect continuous ree uptake i e increasing kd german et al 1990 may result from local depletion of the dissolved ree pool by partitioning onto fe particles at fe 100 nm similar drawdown effects could contribute to the variable degrees of curvature observed for all seawater source particle reactive species in plumes that are sampled at high particulate fe concentration in sum ree behavior in hydrothermal plumes is more consistent with equilibrium adsorption and mixing of distinct particle types than with kinetic uptake control precise measurements of rees in modern ridge crest metalliferous sediments could be compared to the endmember composition calculated from the plume data to evaluate long term changes in ree of the hydrothermal component

quantification of strength anisotropy of metamorphic rocks of the hamedan province iran as determined from cylindrical punch point load and brazilian tests abstract in this research different experimental techniques have been used to determine the strength of five types of anisotropic foliated rocks selected from different parts of the hamedan province west of iran for this purpose after sample preparation and assessment of mineralogical and physical properties selected samples were subjected to cylindrical punch point load and brazilian tests and their strengths were evaluated with respect to different angles beta i e 0 15 30 45 60 75 and 90 between anisotropy planes and the major loading directions data analyses show that the types and amounts of minerals have an influence on the physical and mechanical properties of the tested anisotropic rocks porosity and water absorption also have a dominant control on the mechanical indices such as cylindrical punch index cpi point load index is 50 and brazilian tensile strength bts on the basis of the test result two empirical equations eqs 3 and 5 are proposed for calculating cpi and is 50 other empirical equations relating studied indices are also presented

228th 228ra ages of a barite rich chimney from the endeavour segment of the juan de fuca ridge ages in the range 1 15 yr for chimneys deposited from hydrothermal vents from the endeavour segment of the juan de fuca ridge are estimated based on the ingrowth of228th from228ra cleaning samples by digestion in an acid bath confirms that the mineral barite is the phase being dated a detailed examination of sample alv 2463 r7 collected from the clam bed site yielded a vertical growth rate of 5 8 cm yr and a radial growth rate of 2 6 cm yr this investigation revealed that this chimney did not grow in a regular layer by layer accretion therefore an average of ages obtained from several barite crystals a few centimeters apart 10 cm was used to define the age of each segment ages obtained from the sulfide rich main field site sample alv 2466 r5 suggest that the barite in this sample is from late stage precipitation in contrast to the clam bed sample where barite formed the primary matrix these samples conform to different models of barite incorporation into hydrothermal chimneys

the proximal part of the giant submarine wailau landslide molokai hawaii abstract the main break in slope on the northern submarine flank of molokai at 1500 to 1250 m is a shoreline feature that has been only modestly modified by the wailau landslide submarine canyons above the break in slope including one meandering stream were subaerially carved where such canyons cross the break in slope plunge pools may form by erosion from bedload sediment carried down the canyons west molokai volcano continued infrequent volcanic activity that formed a series of small coastal sea cliffs now submerged as the island subsided lavas exposed at the break in slope are subaerially erupted and emplaced tholeiitic shield lavas submarine rejuvenated stage volcanic cones formed after the landslide took place and following at least 400 500 m of subsidence after the main break in slope had formed the sea cliff on east molokai is not the headwall of the landslide nor did it form entirely by erosion it may mark the location of a listric fault similar to the hilina faults on present day kilauea volcano the wailau landslide occurred about 1 5 ma and the kalaupapa peninsula most likely formed 330 5 ka molokai is presently stable relative to sea level and has subsided no more than 30 m in the last 330 ka at their peak west and east molokai stood 1 6 and 3 km above sea level high rainfall causes high surface runoff and formation of canyons and increases groundwater pressure that during dike intrusions may lead to flank failure active shield or postshield volcanism with dikes injected along rift zones and high rainfall appear to be two components needed to trigger the deep seated giant hawaiian landslides

anisotropic strength and deformational behavior of himalayan schists abstract anisotropy which is characteristic of metamorphic rocks such as schists is due to a process of metamorphic differentiation preferred orientation of minerals like mica and chlorite in response to tectonic stresses makes schistose rocks foliated as a result their engineering properties vary with the direction of loading the influence of transverse anisotropy on strength and deformational responses of four schistose rocks obtained from the foundation of two underground powerhouse sites in the himalayas has been critically examined specimens at different orientation of the foliations varying from 0 to 90 with respect to the axial stress 1 in the unconfined state and also in the confined states up to 100 mpa of confining pressure were tested to evaluate the applicability of the non linear strength criterion for the prediction of triaxial compressive strength and modulus based on the analysis of large experimental results it has been possible to predict strength and modulus with minimum pre evaluation experimental data i e only with three uniaxial compressive strength tests at 0 30 and 90 and two triaxial compression tests conducted at convenient confining pressures at 90 orientation predicted non linear stress strain curves using predicted values of strength and modulus have been found to match well with the experimental stress strain curves even at higher confining pressures

temporal and spatial history of the 1999 2000 endeavour segment seismic series juan de fuca ridge 1 two large clusters of earthquake activity in june of 1999 and january of 2000 have dominated recent seismicity along the endeavour segment of the juan de fuca ridge the impacts of the june 1999 sequence on the hydrologic system which include changes in vent temperature and chemistry within the main endeavour vent field have been well documented previously analysis of seismic and hydroacoustic data indicates that both sequences exhibit a swarm like behavior characterized by the absence of a dominant main shock event the epicentral locations of events within the two swarms overlap spatially with centroid positions near 47 49 and 47 46 n latitude during the june 1999 swarm the initial activity spans the along axis region where a shallow axial magma chamber reflector was later imaged the epicenters then migrate 12 km to the south at a rate of 0 3 m s consistent with lateral dike propagation a distinct subcluster of events also occurred in the vicinity of surveyor volcano on the overlapping portion of the cobb segment given its distance from the main swarm this activity may represent a triggered response to dynamic shaking the january 2000 swarm has a more limited along axis extent relative to the june 1999 swarm with no indication of lateral migration much of this activity is concentrated in a region predicted to have undergone extension due to dike propagation in 1999 although it contains fewer total events and is of shorter duration relative to the june 1999 swarm the january 2000 activity exhibits a higher peak rate of seismicity and greater mean event magnitude as in situ temperature monitoring was not in place during january 2000 and vent fluids were not sampled until june 2000 the impacts of this swarm on the hydrothermal system are unknown the southernmost tip of the endeavour segment also is found to be a region of repeating swarm activity although morphologic evidence indicates the cobb segment has been propagating northward recently this seismic activity suggests that the western limb of the endeavour cobb overlap zone remains active

chemical microenvironments within sulfide structures from the mothra hydrothermal field evidence from high resolution zoning of trace elements abstract massive portions of a 300 c black smoker finn and a diffusely venting intermediate temperature 200 c chimney roane recovered from the mothra hydrothermal field on the juan de fuca ridge have been analyzed in detail for bulk chemistry the size of the recovered pieces of chimney enabled physical segregation and analysis of distinct chemical zonation within the structures in particular large variations in the concentrations of minor and trace elements in the different mineralogical zones provide new insight into the processes involved in chimney growth that are not evident from the bulk mineralogy systematic zonation of trace and minor elements is strongly influenced by redox conditions multiple host phases single or dual fluid source and the mixing cooling history of the fluids even within an individual mineralogical zone distinct chemical microenvironments within the chimneys are recognized that provide a basis for detailed reconstruction of the changing conditions in the interiors of the chimneys during their growth in finn 14 discrete chemical microenvironments are recognized in 80 of 90 samples based on high resolution zoning of major and trace elements four of the microenvironments are cu rich three are zn rich one is fe rich with low cu two are ca rich three are sio2 rich and one is ba and sio2 rich in roane 24 discrete chemical microenvironments are recognized six of the microenvironments are sio2 poor

near field hydrothermal plume dynamics at brothers volcano kermadec arc a short lived radium isotope study abstract the naturally occurring radium ra isotope quartet was measured for the first time at an intraoceanic arc hydrothermal setting along the kermadec island arc sw pacific 224ra 3 7 d half life and 223ra 11 4 d half life are assumed to be tracers solely originating from hydrothermal discharge and have been used to resolve near field hydrothermal plume dynamics by applying both advection and eddy diffusion based dispersion models assuming dominant advective processes we identified different horizontal plume age structures at brothers volcano with a slow moving plume inside the caldera 0 060 cm s and a faster moving plume outside the caldera 0 323 cm s indicating a longer plume residence time within the caldera structure the decreasing trend in ra activity also allows the calculation of horizontal eddy diffusion coefficients inside and outside of the caldera with 0 164 m2 s and 3 545 m2 s for 224ra respectively these trends are in accordance with the radial horizontal eddy diffusion model our results reveal that net advection might not necessarily play a major role at brothers as radial horizontal eddy diffusion reproduces the observed ra activity distribution to the same degree additional model simulations based on a combination of advection and diffusion favor slow net advection to explain the ra activity distribution within the rising non buoyant plume ra isotopes suggested constant dilution along the first 170 m of the vertical water column and a vertical transport velocity on the order of 0 156 cm s for altitudes up to 150 m above the vent and around 0 004 cm s for altitudes above 150 m when a common source of diffuse and focused venting is assumed and only small amounts of ra are added to the ascending plume due to recoil originating from high water to rock ratios fluids from diffuse vents show a slower migration rate through the subsurface than fluids from focused vents our data imply that the fluids from diffuse vents needed approximately five days longer to percolate through the underlying subsurface to reach the water column plume compared to the fluids from direct vents which emanate through chimney structures this study demonstrates the potential of short lived ra isotopes as tracers of near field plume dynamics which will improve our understanding of hydrothermal vents as sources for various trace elements to the global ocean

numerical simulation of hydrothermal vent induced circulation at endeavour ridge hydrothermal venting at endeavour ridge is focused at five major vent fields spaced at 2 km intervals along a narrow 1 km wide north south trending rift valley a princeton ocean model with an axially symmetric rift valley centered within a rotating full depth 2400 m stratified ocean is used to simulate the circulation and associated temperature and salinity fields generated by vertical heat fluxes from the five vent fields steady seafloor heat fluxes are introduced instantaneously to a quiescent ocean using the model provision for boundary fluxes the model achieves a quasi steady state in about 80 days results are consistent with observation in particular buoyant plumes emanating from the larger vent fields rise to trapping depths as shallow as 1850 m 350 m above bottom and spread laterally with the vent induced circulation plume anomalies remain confined to within several kilometers of the ridge except to the west where anomalies extend more than 10 km off axis as with observations modeled currents within the valley consist of a strong 10 cm s 1 poleward inflow within roughly 75 m of the bottom and an equally strong equatorward counterflow above that depth weak 1 cm s 1 equatorward flow develops over the flank of the west ridge and weak poleward flow over the flank of the east ridge cyclonic relative vorticity dominates the model circulation within the valley while anticyclonic vorticity prevails above the depth of neutral plume buoyancy findings support the notion that turbulent entrainment by buoyant plumes forces a mean poleward flow within the confines of the endeavour ridge axial valley

surface sediment composition and distribution of hydrothermal derived elements at the duanqiao 1 hydrothermal field southwest indian ridge abstract the study of the hydrothermal component in oceanic sediments provides key data for locating active and inactive hydrothermal systems in this work we report the geochemistry of surface sediments collected in the newly discovered basaltic hosted duanqiao 1 hydrothermal field dhf on the southwest indian ridge swir the sediments are mainly composed of a pelagic fraction carbonate ooze with minor clay contents basaltic debris fe mn oxyhydroxides and hydrothermal components hydrothermal elements in the dhf exhibit a precipitation sequence of cu co zn pb fe mn ni as proximal sediments to the hydrothermal discharge area are characterized by high cu pb zn and co concentrations and higher cu fe and zn fe ratios decreasing abruptly within the first kilometer after this proximal area an evident increase of mn concentrations and mn fe ratios was observed denoting higher oxidizing conditions of the hydrothermal plume hydrothermal derived pb and co precipitated together with the sulfide phases whereas at the distal sediments pb co ni and as seem to be scavenged from seawater by oxyhydroxides this was corroborated by increased ree fe ratios with distance to the discharge zone the geochemistry of dhf sediments is consistent with an effective separation of metals during gradual cooling and concomitant eh and ph modifications of the hydrothermal plume when in contact with seawater this promotes the precipitation of cu sulfides first closest to the discharge area followed by cu zn and fe sulfides and fe mn oxyhydroxides in more distal areas a comparison of the dhf sediments with those from dragon horn another hydrothermal site at the swir suggests that the hydrothermal fluids responsible for mineral precipitation at dhf are less reduced favoring the formation of sulfides and oxyhydroxides at shorter distances from the discharge zone these findings are particularly valuable to the understanding of the variation in hydrothermal anomalies detected in sediments from proximal and distal areas of discharge zones contributing to the development of tools for the discovery of hydrothermal fields

discrete and diffuse heat transfer atashes vent field axial volcano juan de fuca ridge abstract heat fluxes of discrete and diffuse components of hydrothermal discharge are estimated from submersible measurement in the ashes vent field located in the caldera of axial volcano on the central juan de fuca ridge the discrete component comprises discharge from individual vents and the diffuse component comprises seepage from large areas of the seafloor the investigation centered on the high temperature portion of the field a 100 100 m area of fractured lobate and sheet lava flows encompassing discrete discharge 326 c from seven individual vents and diffuse flow from intervening areas a total of 4 4 2 10 6 w was estimated for the discrete heat flux based on measurements of effluent temperature flow rate and orifice diameter at all the known individual vents by d s v alvin in september 1987 a total of 15 75 10 6 w was calculated with a standard plume model for the diffuse flux based on a grid of temperature measurements at altitudes of 1 m and 20 m above the study area using a 1 m long vertical array of temperature sensors mounted at the front of alvin s instrument platform the study indicates that 1 the diffuse component rises separately from the discrete component of hydrothermal discharge and is laterally advected by a prevailing current below the discrete component and that 2 the diffuse component of convective heat flux is approximately an order of magnitude greater than the discrete component in the high temperature portion of the ashes vent field

in situ observations of dissolved iron and manganese in hydrothermal vent plumes juan de fuca ridge in situ measurements of dissolved manganese and total dissolved iron were conducted in hydrothermal plumes over the juan de fuca ridge using a submersible chemical analyzer scanner the scanner was deployed as part of a ctd transmissometer rosette instrument package on both tow yos and vertical casts during the vents leg i cruise in 1989 dissolved manganese and total dissolved iron concentrations along with temperature and light attenuation anomalies were determined over the ridge crest every 5 s discrete samples for laboratory analyses of dissolved iron ii total dissolved iron ii iii and manganese were also collected metal to heat ratios me q measured in situ were extremely variable in one steady state plume while an event plume had constant me q uniform values of mn q in the event plume demonstrate that mn behaves conservatively in the near field plume variability in the mn q ratios in a steady state plume indicated the presence of at least two hydrothermal sources with distinct me q values a simple mixing model shows that the contribution of mn from high me q sources with a composition characteristic of black smoker vents varies between 1 and 99 within the core of the steady state plume with an average value of 55 on average over 50 of the excess heat within the plume originates from low me q ratio sources with a composition characteristic of low temperature diffuse flow vent fluids less than 4 of the volume of hydrothermal fluids in the plume originates from black smokers the fe ii concentrations were used to provide an estimate of plume age on a transect across the ridge axis plume ages were about 2 5 days on axis and 12 days off axis these plume ages were modeled to provide estimates of plume transport and horizontal diffusion and show excellent agreement with ages determined using 222rn

sulfide geochronology along the endeavour segment of the juan de fuca ridge 1 forty nine hydrothermal sulfide sulfate rock samples from the endeavour segment of the juan de fuca ridge northeastern pacific ocean were dated by measuring the decay of 226ra half life of 1600 years in hydrothermal barite to provide a history of hydrothermal venting at the site over the past 6000 years this dating method is effective for samples ranging in age from 200 to 20 000 years old and effectively bridges an age gap between shorter and longer lived u series dating techniques for hydrothermal deposits results show that hydrothermal venting at the active high rise sasquatch and main endeavour fields began at least 850 1450 and 2300 years ago respectively barite ages of other inactive deposits on the axial valley floor are between 1200 and 2200 years old indicating past widespread hydrothermal venting outside of the currently active vent fields samples from the half graben on the eastern slope of the axial valley range in age from 1700 to 2925 years and a single sample from outside the axial valley near the westernmost valley fault scarp is 5850 205 years old the spatial relationship between hydrothermal venting and normal faulting suggests a temporal relationship with progressive younging of sulfide deposits from the edges of the axial valley toward the center of the rift these relationships are consistent with the inward migration of normal faulting toward the center of the valley over time and a minimum age of onset of hydrothermal activity in this region of 5850 years

surface sediment geochemistry and hydrothermal activity indicators in the dragon horn area on the southwest indian ridge abstract the fluids found in sulfide producing hydrothermal vents are rich in ore forming elements these elements usually precipitate as solid particles that are dispersed by the plumes and deposited as sediments around the hydrothermal field to assess how the geochemical features of such sediments may be used in seafloor sulfide exploration this study analyzed the surface sediment geochemistry in the dragon horn area on the southwest indian ridge the results indicate that the sediments are mainly composed of pelagic material basalt and ultramafic debris mn fe oxyhydroxides and mn oxides hydrothermal components the debris content in this area is lower than that in sediments found at fast and medium spreading mid ocean ridges with relatively high amounts of ultramafic components indicating that ultramafic rock outcrops are present in the study area precipitated hydrothermal elements in the sediments exhibit zonation in the spatial distributions of zn cu fe and mn the sediments proximal to the hydrothermal field display high cu zn and fe contents and low mn contents hydrothermal cu and zn phases occurred within a limited range of the hydrothermal field and zn was found to precipitate earlier than cu during dispersal from the plume hydrothermal fe distributed similarly with cu spatially but with a larger dispersion distance hydrothermal mn was able to migrate beyond the ridge valley to precipitate in the ridge flank sediments two hydrothermal cu and zn anomalies were identified on the south ridge flanks which suggest the presence of undiscovered hydrothermal field the sediments in the study area are additionally characterized by relatively low mn contents and high fe mn molar ratios the relatively reducing environment of the plume may facilitate the migration of hydrothermal mn over large distances which probably accounts for the lower mn contents in the sediments the cu cu fe molar ratio model was proposed to identify mafic and ultramafic related hydrothermal field the low cu fe molar ratios and ree characteristics of the sediments suggest that ultramafic rocks are likely not the only source of the ore forming element for hydrothermal mineralization low temperature diffuse flow on the ridge flanks of the study area probably results from serpentinization of ultramafic rocks

experimental and theoretical study of the anisotropic properties of shale abstract the effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated with an emphasis on the shear parameters of the bedding planes this study is based on direct shear tests conducted on directional shale samples obtained from formations which exhibit well developed stratification the tested cylindrical specimens were prepared by coring at 30 intervals from the direction of the bedding planes the results indicate that the anisotropy of the shear strength of shale can be readily observed due to the anisotropic effects of bedding plane orientation and normal stress the shear parameters such as strength cohesion and internal friction angle reach their maximum and the minimum values at 60 and 0 respectively where is the angle between the bedding planes and the coring orientation which is also the direction of normal stress during the laboratory tests it is demonstrated that the bedding planes are weak not only with regards to cementing strength but also with regards to friction three different shear failure modes were built up depending on the shearing angle 1 sliding failure across the bedding planes 2 sliding failure along the bedding planes and 3 sliding failure across the bedding planes combined with tensile splitting along the bedding planes an expression of the shear stress concentration factor of the direct shear model is derived to evaluate the anisotropy of shear strength

mineral precipitation sequence and formation of the lacustrine hydrothermal sediments in the lower cretaceous tenggeer formation in the baiyinchagan sag china abstract cores from the lower cretaceous tenggeer formation in the baiyinchagan sag of the erlian basin present dolomitic mudstones and argillaceous dolostone with white grains and laminae thin section x ray diffraction xrd electron microprobe empa and scanning electron microscopy sem analyses show that in addition to terrigenous clastics dolomite analcime natrolite pyrite pistomesite fluorite talc barite etc are abundant compared with the conventional lacustrine sediments these rocks contain highly abundant exhalative textures and structures such as laminae and banded textures disseminated textures mesh vein structures breccia structures and contemporaneous deformations these types of mineral associations rock textures and structures are specific and uncommon previous works indicate that these rocks are of hydrothermal origin in this study we provide supplementary evidence and recognition to support the lacustrine hydrothermal sediment origin and further study the mineral precipitation sequence and formation conditions and processes with the use of 3d seismic data the magmatic intrusions hydrothermal ducts and hydrothermal vents are first identified on seismic sections the ni co zn and fe mn cu ni co 10 ternary diagrams confirm the hydrothermal origin of these sediments the sr ba ratio v v ni ratio oxygen and carbon isotope values of carbonate ph and eh values suggest anoxic reducing and alkaline sedimentary conditions based on the analysis of fluid inclusions rock textures and structures we find that the precipitation of minerals occurred in a specific sequence pyrite pistomesite analcime natrolite dolomite the nature of the magmatic intrusions the changes in environmental variables and fluid energy and the flow distance may be the controlling factors of this specific sequence a mode of lacustrine white smoker type hydrothermal sedimentation is presented in this study as the hydrothermal fluid sourced from the intermediate basic magmatic basement enriched in fe2 mg2 al3 si4 ca2 na and co32 rose and mixed with cool lake water ferromagnesian aluminosilicate and carbonate minerals formed successively from the ducts to the vicinity of the vents pulsing exhalation and overflow formed alternating deposits of hydrothermal sediments and lacustrine mudstones

geochemical constraints on the role of oceanic lithosphere in intra volcano heterogeneity at west maui hawaii 87 sr 86 sr 206 pb 204 pb variation in the stratigraphically lowest lavas is orthogonal to the all hawaii variation indicating that it is not the result of mixing between components normally sampled by hawaiian shield stage magmas we compare our west maui data with observed compositions of pacific oceanic basaltic and gabbroic crust and predicted compositions for 2ga basaltic and gabbroic oceanic crust the observed fine scale compositional variability in the stratigraphically lowest west maui lavas is consistent with 10 15 mixing of small degree 2 partial melts of the pacific gabbroic oceanic crust with plume derived kea type magmas mass balance considerations indicate that this geochemical signal can be present in no more than 5 of the total volume of lavas erupted at west maui

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

importance of atmospheric inputs and fe oxides in controlling soil uranium budgets and behavior along a hawaiian chronosequence abstract a long term budget of uranium calculated for a chronosequence of hawaiian soils demonstrates the importance of mineral aerosol deposition as a geochemical pathway a series of sequential extractions on the same soils shows a strong association between fe oxides and uranium especially the amorphous and poorly crystalline fe oxides present in intermediate age soils 20 and 150 ka despite intense leaching conditions soil u contents were found to increase between 20 fold and 60 fold with age along the chronosequence from 9 to 17 g cm 2 at 0 3 ka sites to 344 543 g cm 2 at the 4100 ka site an open system transport function comparing u to an index least mobile element nb was used to calculate u gains or losses from the soils relative to the input from parent material weathering results show small losses or small gains 25 of u occurred in soils 150 ka and younger while gains of up to 531 u occurred in soils older than 150 ka highlighting the importance of mineral aerosol dust deposition at the older sites in the 4100 ka soil the ratio of dust derived u inputs to parent material derived u inputs is approximately 6 sequential extractions show that between 0 1 and 1 2 of the total u in the soils was extracted with ammonium acetate indicating that very little u exists as exchangeable cations a second extraction employing citrate dithionate and hydroxylamine hydrochloride was performed to extract u associated with fe oxides average percent occurrences for u in the fe oxide extraction for each profile are 7 at 0 3 ka 53 at 20 ka 40 at 150 ka and 17 at 4100 ka illustrating an increase with age to 20 ka followed by a subsequent decline this parallels the trend observed in amorphous fe oxide content suggesting that adsorption on amorphous fe oxides is the dominant control on u in the intermediate age soils

shear behavior of inherently anisotropic rocks abstract the effect of schistosity plane orientations on failure mechanism and effective shear strength response of inherently anisotropic rocks are dealt with in this paper with an emphasis on shear parameters of the weak planes the study employed an oblique shear apparatus to apply shear and normal stress on specimens at three predetermined shear inclinations the concurrent application of confinement and shear loading was made to the apparatus both stresses were developed as a result of vertical loading confined stress conditions and hence their failure mechanisms the results indicate a transition state of shear strength values fluctuating from a minimum to a maximum based on angle due to the anisotropic effects of schistosity plane orientation coupled with confinement stress is the angle between strike of weak planes and the predetermined shear loading plane hence the anisotropic effect of weak planes orientation is a significant occurrence that must be noted in the analysis and failure mechanism studies it was also observed that different shearing failure modes were built up depending on the orientations of a family weak planes with respect to confinement stresses as 1 tensile fracture across the weak planes non sliding mode 2 tensile split along the weak planes non sliding mode and 3 sliding failure along the weak planes and or combination of these mechanisms the experimental results demonstrated that the failure modes were changed from non sliding into sliding along weak planes when dip of weak planes increases it was also noticed that due to the influence of confinement stresses failure occurred through rock material together with tensile splitting of weak planes this was more prominent for higher values of strike direction of weak planes investigations were extended to examine the influence of effective shear stresses on the failure mechanisms considering various dip and strike directions of weak planes

submarine hydrothermal activity and gold rich mineralization at brothers volcano kermadec arc new zealand brothers volcano of the kermadec intraoceanic arc is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world it has two distinct vent fields known as the nw caldera and cone sites whose geology permeability vent fluid compositions mineralogy and ore forming conditions are in stark contrast to each other the nw caldera site strikes for 600 m in a sw ne direction with chimneys occurring over a 145 m depth interval between 1 690 and 1 545 m at least 100 dead and active sulfide chimney spires occur in this field and are typically 2 3 m in height with some reaching 6 7 m their ages at time of sampling fall broadly into three groups 4 23 and 35 years old the chimneys typically occur near the base of individual fault controlled benches on the caldera wall striking in lines orthogonal to the slopes rarer are massive sulfide crusts 2 3 m thick two main types of chimney predominate cu rich up to 28 5 wt cu and more commonly zn rich up to 43 8 wt zn geochemical results show that mo bi co se sn and au up to 91 ppm are correlated with the cu mineralization whereas cd hg sb ag and as are associated with the dominant zn rich mineralization the cone site comprises the upper cone site atop the summit of the recent main dacite cone and the lower cone site that straddles the summit of an older smaller more degraded dacite cone on the ne flank of the main cone huge volumes of diffuse venting are seen at the lower cone site in contrast to venting at both the upper cone and nw caldera sites individual vents are marked by low relief 0 5 m mounds comprising predominately native sulfur with bacterial mats vent fluids of the nw caldera field are focused hot 300 c acidic ph 2 8 metal rich and gas poor calculated end member fluids from nw caldera vents indicate that phase separation has occurred with cl values ranging from 93 to 137 of seawater values by contrast vent fluids at the cone site are diffuse noticeably cooler 122 c more acidic ph 1 9 metal poor and gas rich higher than seawater values of so4 and mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water rock interactions iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from fe rich brines evidence for magmatic contributions to the hydrothermal system at brothers includes high concentrations of dissolved co2 e g 206 mm kg at the cone site high co2 3he negative d and 18oh2o for vent fluids negative 34s for sulfides to 4 6 sulfur to 10 2 and 15n2 to 3 5 vent fluid ph values to 1 9 and mineral assemblages common to high sulfidation systems changing physicochemical conditions at the brothers hydrothermal system and especially the cone site occur over periods of months to hundreds of years as shown by interlayered cu au and zn rich zones in chimneys variable fluid and isotopic compositions similar shifts in 3he 4he values for both cone and nw caldera sites and overprinting of magmatic mineral assemblages by water rock dominated assemblages metals especially cu and possibly au may be entering the hydrothermal system via the dissolution of metal rich glasses they are then transported rapidly up into the system via magmatic volatiles utilizing vertical 2 5 km long narrow 300 m diameter pipes consistent with evidence of vent fluids forming at relatively shallow depths the nw caldera and cone sites are considered to represent stages along a continuum between water rock and magmatic hydrothermal dominated end members

geochemistry of the hawi lavas kohala volcano hawaii hawi lavas form the late stage alkalic cap on kohala volcano and range in composition from hawaiite to trachyte new detailed field mapping of kohala and reinterpretation of previously published age data suggest that there was no significant eruption hiatus between the hawi and underlying pololu shield lavas as was previously suggested mineral and whole rock chemical data are consistent with a crystal fractionation origin for the hawaiite to trachyte compositional variation observed within the hawi lavas plagioclase clinopyroxene ti magnetite olivine and apatite fractionation are needed to explain this variation the clinopyroxene fractionation may have occurred at moderate pressure because it is virtually absent in these lavas and is not a near liquidus phase at pressures of less than 8 kb plagioclase would be buoyant in the hawi hawaiite magmas so a mechanism like dynamic flow crystallization is needed for its fractionation and to account for the virtual absence of phenocrysts in the lavas hawi lavas are distinct in sr and nd isotopic ratios and or incompatible element ratios from the pololu lavas thus they were derived from compositionally distinct sources compared to other suites of hawaiian alkalic cap lavas hawi lavas have anomalously high concentrations of phosphorus and rare earth elements these differences could be due to greater apatite content in the source for the hawi lavas

petrology and sr nd and pb isotope geochemistry of mid ocean ridge basalt glasses from the 11 45 n to 15 00 n segment of the east pacific rise 1 basaltic glasses from the geophysically well studied section of the east pacific rise epr between 11 45 n to 15 00 n range from normal mid ocean ridge basalts morb to transitional morb and their major element variations correlate with isotopic and trace element indices of enrichment to first order basalts enriched in na8 0 incompatible elements 87sr 86sr and 206pb 204pb but low in fe8 0 and 143nd 144nd are more prevalent along the shallow portions of the ridge axis in detail the samples can be divided into two chemical and geographical groups the southern bathymetric dome extending from the 11 45 n overlapping spreading center to 14 10 n and the northern group extending from 14 10 n to the orozco transform the boundary between these two groups is apparent in a change in isotopic composition results indicate that there are three mantle source components that produce the compositional variability observed among samples from the 11 45 n to 15 00 n segment of the epr a depleted mantle component a seamount type enriched mantle component and an indian morb like mantle component south of 14 10 n the geochemical variability is dominated by binary mixing between a depleted mantle component and an enriched component similar to near ridge seamounts north of 14 10 n the low 206pb 204pb high 207pb 204pb indian morb like component exerts a major influence on the geochemical variability of the axial lavas regional averages of major element composition e g na8 0 and fe8 0 show relatively limited variability consistent with the restricted range in depth for this region and plot within the pacific field of the previously defined global trends major element variations among individual samples however parallel the global array and their correlation with indices of mantle enrichment supports the idea that the pacific type local trend results from small scale heterogeneities in the mantle beneath the epr our results also indicate that tectonic segmentation and magmatic boundaries are probably not causally related in this study area and that the sizes of the present magma chambers are not a dominant factor in determining the compositional variability of erupted lavas

eruptive and tectonic history of the endeavour segment juan de fuca ridge based on auv mapping data and lava flow ages high resolution bathymetric surveys from autonomous underwater vehicles abe and d allan b were merged to create a coregistered map of 71 7 km2 of the endeavour segment of the juan de fuca ridge radiocarbon dating of foraminifera in cores from three dives of remotely operated vehicle doc ricketts provide minimum eruption ages for 40 lava flows that are combined with the bathymetric data to outline the eruptive and tectonic history the ages range from modern to 10 700 marine calibrated years before present yr bp during a robust magmatic phase from 10 700 yr bp to 4300 yr bp flows erupted from an axial high and many flowed 5 km down the flanks some partly buried adjacent valleys axial magma chambers amcs may have been wider than today to supply dike intrusions over a 2 km wide axial zone summit seamount formed by 4770 yr bp and was subsequently dismembered during a period of extension with little volcanism starting 4300 yr bp this tectonic phase with only rare volcanic eruptions lasted until 2300 yr bp and may have resulted in near solidification of the amcs the axial graben formed by crustal extension during this period of low magmatic activity infrequent eruptions occurred on the flanks between 2620 1760 yr bp and within the axial graben since 1750 yr bp this most recent phase of limited volcanic and intense hydrothermal activity that began 2300 yr bp defines a hydrothermal phase of ridge development that coincides with the present day 1 km wide amcs and overlying hydrothermal vent fields

pore geometry as a control on rock strength the strength of rocks in the subsurface is critically important across the geosciences with implications for fluid flow mineralisation seismicity and the deep biosphere most studies of porous rock strength consider the scalar quantity of porosity in which strength shows a broadly inverse relationship with total porosity but pore shape is not explicitly defined here we use a combination of uniaxial compressive strength measurements of isotropic and anisotropic porous lava samples and numerical modelling to consider the influence of pore shape on rock strength micro computed tomography ct shows that pores range from sub spherical to elongate and flat ellipsoids samples that contain flat pores are weaker if compression is applied parallel to the short axis i e across the minimum curvature compared to compression applied parallel to the long axis i e across the maximum curvature numerical models for elliptical pores show that compression applied across the minimum curvature results in relatively broad amplification of stress compared to compression applied across the maximum curvature certain pore shapes may be relatively stable and remain open in the upper crust under a given remote stress field while others are inherently weak quantifying the shape orientations and statistical distributions of pores is therefore a critical step in strength testing of rocks

characteristics of hydrothermal plumes from two vent fields on the juan de fuca ridge northeast pacific ocean deep ctd transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally buoyant plumes emanating from each of two major vent fields on the southern symmetrical segment sss and endeavour segment es of the juan de fuca ridge at both vent fields emissions from point and diffuse hydrothermal sources coalesced into a single 200 m thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0 02 0 05 c and light attenuation anomalies of 0 01 0 08 m 1 10 80 g l above background temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped 10 15 km downcurrent light attenuation trends were non uniform and differed between plumes apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates vent fluids from the sss are metal dominated and mostly precipitate very fine grained hydrous fe oxides that remain suspended in the plume vent fluids from the es are sulfur dominated and precipitate a high proportion of coarser grained fe sulfides that rapidly settle from the plume the integrated flux of each vent field was estimated from measurements of the advective transport of each plume heat flux was 1700 1100 mw from the es and 580 351 mw from the sss particle flux varied from 546 312 g s to 204 116 g s at the es depending on distance from the vent field and was 92 48 g s from the sss

new k ar ages and the geologic evidence against rejuvenated stage volcanism at haleakalā east maui a postshield stage volcano of the hawaiian island chain the postshield and previously inferred rejuvenated stage history of haleakal volcano is reevaluated on the basis of 52 new k ar ages 42 from the postshield kula volcanics and 10 from the overlying h na volcanics postshield extrusion was robust from 0 93 to 0 76 ma a period of low extrusion rate or volcanic quiescence occurred between 0 76 and 0 65 ma well within kula time a chemical change to increasingly alkalic lava occurred at this time as the volcano changed from broadly hawaiitic to basanitic in its eruptive products and robust extrusion resumed a slightly longer period of low extrusion rate or quiescence occurred after ca 0 4 ma but only trifling change in geochemical character is observed geochemically the h na volcanics unit chiefly basanitic overlaps greatly with the upper part of the kula volcanics there is a weak tendency to slightly more alkaline character among the h na volcanics the age of the kula h na boundary is ca 0 15 0 12 ma thus volcanic quiescence of only 0 03 m y separates the two formations much shorter than the previously known limit of 0 25 0 30 m y the brevity of this hiatus coupled with coincident vent loci and broadly similar geochemical characteristics for the h na and the upper part of the kula volcanics indicates that the h na volcanics unit comprises deposits of postshield stage volcanism that has waned substantially since ca 0 4 0 3 ma haleakal has not yet begun a classically defined rejuvenated stage our findings support recent numerical modeling of plume lithosphere interactions that predict that haleakal is near the end of its postshield growth

evolution of alkalic lavas at haleakala volcano east maui hawaii the postshield and posterosional stages of haleakala volcano contain intercalated alkalic basalt and evolved alkalic lavas isotopic and incompatible element abundance ratios in the haleakala postshield basalts changed systematically with time providing evidence for significant temporal changes in the mantle components contributing to the magmatic sources specifically a depleted i e low87sr 86sr and high143nd 144nd mantle component is more abundant in younger lavas however as magma production rates decreased during the postshield and posterosional stages basaltic melts in magma reservoirs cooled and fractionated leading to evolved residual melts such as hawaiite because primary basalt compositions changed with time the evolved haleakala lavas formed from a range of parental compositions however basalts and evolved lavas of similar age and isotopic ratios sr and nd have major and trace element contents that are consistent with a crystal fractionation model although alkalic basalt and hawaiite are the dominant lavas of the postshield stages of both haleakala and mauna kea volcanoes there are important differences between their lavas for example compositional differences between the hawaiite suites at haleakala and mauna kea indicate that on average the evolved lavas at haleakala formed at lower pressures also at haleakala basalts are intercalated with hawaiites whereas at mauna kea basalts and hawaiites are separated by a sharp boundary these differences probably reflect a higher magma supply rate to the haleakala volcano

major and trace element variation in ilmenite in the skaergaard intrusion petrologic implications abstract ilmenite separates from the floor ls roof ubs and wall mbs sequences of the skaergaard intrusion were analyzed for major and trace elements using dcp aes and icp ms techniques in all three sequences feo progressively increases and mgo and al 2 o 3 progressively decrease with differentiation although trace element abundances are in general higher in ubs ilmenite than in mbs and ls ilmenite all three sequences have similar trends for trace element abundance vs crystallization ba cs rb sr th u y and the rees are excluded elements in ilmenite and remained at low abundances during differentiation cr ni sc and v are included elements in ilmenite and other mafic phases and decreased during differentiation v contents in ilmenite however do not decrease significantly until the upper part of the middle zone suggesting that magnetite did not begin to affect the magma differentiation trend until much later than when it first appears in the intrusion hf nb ta and zr which are strongly excluded elements in silicates are included elements in ilmenite the element ratios zr hf y ho nb ta and u th are relatively constant in skaergaard ilmenite from different parts of the intrusion suggesting that fluid transport did not significantly effect these elements during differentiation or post solidification cooling calculated partition coefficients for ilmenite in the skaergaard intrusion are similar to those reported from previous studies of lunar and terrestrial basalts and kimberlites and for most elements are significantly lower than those reported for ilmenite in rhyolitic magma similar d i s for zr hf nb and ta suggest that ilmenite crystallization did not significantly affect zr nb or hf ta in the skaergaard magma but the ratios of zr hf nb or ta to other high field strength elements such as th u y or the rees may have been altered by ilmenite fractionation

geochemistry of kauai volcanics and a mixing model for the origin of hawaiian alkali basalts a comprehensive model is developed to explain the major trace element and strontium and neodymium isotopic characteristics of alkali basalts from hawaii the model is similar to that of chen and frey 1983 in that it requires mixing of a small melt fraction of morb source material with another component to generate the alkalic suite of a particular hawaiian volcano it differs from the chen and frey model in that the other end member must be different from primitive mantle if it is to be consistent with both trace element and isotopic data alkali basalts and tholeiites from kauai analyzed in this study show a nearly complete transition in sr and nd isotopes there is a relatively well constrained array on a nd sr isotope correlation plot that can be explained by two component mixing of kauai tholeiite magma and a small amount of melt of east pacific rise source rock after corrections are made for fractional crystallization involving primarily clinopyroxene and olivine the sr and ba concentrations of kauai lavas plot along mixing curves defined by the above sources providing positive tests of the mixing hypothesis implications of this model are 1 the main source of hawaiian shield building tholeiites is a mixture of subducted crust primitive mantle and depleted asthenosphere that has been homogenized prior to melting 2 early alkalic volcanism as at loihi seamount will be characterized by greater isotopic heterogeneity than will late stage alkali basalt production and 3 there are two fundamentally distinct types of alkalic lavas erupted towards the end of magmatism at a given hawaiian volcano one represents smaller degrees of melting of the same source that generated shield building tholeiites kohala type the other derives from the mixed source discussed in this paper haleakala kauai type

tracking the dispersal of hydrothermal plumes from the juan de fuca ridge using suspended matter compositions in 1988 and 1989 particles from on and off axis neutrally buoyant plumes over the juan de fuca ridge were sampled to study their changing composition with distance from the ridge crest plume depth and particle composition in off axis hydrothermal plumes were used to identify plume sources and trajectories iron and phosphorus concentrations and in particular p fe molar ratios were found to be sensitive indicators of hydrothermal phases in the suspended matter phosphorus vanadium and arsenic are scavenged from solution where dissolved iron from hydrothermal vents oxidizes in seawater and forms submicrometer sized particles of fe oxyhydroxide the p fe molar ratio 0 23 is essentially the same for vent fields along cleft and endeavour segments indicating that the scavenging processes are the same for both regions high p fe ratios are observed over the south and north cleft segment vent fields and to the west along the vance seamount chain the seamounts evidently function as a barrier bathymetrically steering the hydrothermal plumes to the west away from the ridge crest since particles from the endeavour vent field are greatly enriched in copper relative to hydrothermal plumes from other vent fields along the juan de fuca ridge copper concentrations in the plumes can be used to distinguish plume sources based on water column depth and elemental composition hydrothermal plume particles from specific vent fields on the juan de fuca ridge may be tracked as much as several tens of kilometers from their source using particle compositions