granite ascent and emplacement during contractional deformation in convergent orogens based on a case study in the central maine belt of west central maine u s a it is proposed that crustal scale shear zone systems provide an eaective focussing mechanism for transfer of granite melt through the crust in convergent orogens during contractional deformation flow of melt in crustal materials at depths below the brittle plastic transition is coupled with plastic deformation of these materials the flow is driven by pressure gradients generated by buoyancy forces and tectonic stresses within the oblique reverse central maine belt shear zone system stromatic migmatite and concordant to weakly discordant irregular granite sheets occur in zones of higher strain which suggests percolative flow of melt to form the migmatite leuco somes and viscous flow of melt channelized in sheet like bodies possibly along fractures cyclic fluctuations of melt pressure may cause instantaneous changes in the eaective permeability of the flow network if self propa gating melt filled tensile and or dilatant shear fractures are produced due to melt enhanced embrittlement in homogeneous migmatite and schlieric granite occur in zones of lower strain which suggests migration of partially molten material through these zones en masse by granular flow and channelized flow of melt carrying entrained residue founded on the central maine belt case study we develop a model of melt extraction and ascent using the driving forces stress conditions and crustal rheologies in convergent especially transpressive orogens ascent of melt becomes inhibited with decreasing depth as the solidus is approached for intermedi ate a h2o muscovite dehydration melting the water saturated solidus occurs between 400 and 200 mpa near the brittle plastic transition during high t low p metamorphism where the balance of forces favors sub horizontal fracture propagation emplacement of melt may be accommodated by ductile flow and or stoping of wall rock and inflation may be accommodated by lifting of the roof at shallower crustal levels and or sink ing of the pluton floor the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduits although these plutons may have locally discordant relations with country rock structures when viewed at the crustal scale granite ascent and emplacement in convergent orogens are syn tec tonic processes 1998 elsevier science ltd all rights reserved

on the spatial and temporal relationship between auroral intensification and flow enhancement in a pseudosubstorm event 1 we present a joint study of substorm growth phase flow enhancements observed by super dual auroral radar network hf radars and auroral optical intensifications observed by canadian auroral network for the open program unified study meridian scanning photometers msps during the event time 0426 0500 ut on 26 december 1998 a flow enhancement structure was observed by hf radar from just equatorward of the polar cap boundary whose location is estimated from the msp observation of the poleward edge of 630 nm emissions down to 68 5 0 4 magnetic latitude which is the boundary between the boundary plasma sheet and the central plasma sheet cps inferred from the analysis of radar doppler spectral widths we suggest that the flow enhancements were associated with the tail reconnection process in response to the solar wind activation the auroral optical intensifications were located inside the cps a zonal flow shear region characteristic of the harang discontinuity was also inferred from the radar observation and was found to be closely associated with the auroral intensification structure the flow enhancement and auroral intensifications were well correlated and occurred almost simultaneously we found that existing models associating the tail reconnection process and near geosynchronous onset of substorms do not explain this temporal relationship very well and thus we propose a new model

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

hydrothermal activity on near arc sections of back arc ridges results from the mariana trough and lau basin 1 the spatial density of hydrothermal venting is strongly correlated with spreading rate on mid ocean ridges with the interesting exception of hot spot affected ridges evidently because spreading rate is a reliable proxy for the magma budget this correlation remains untested on spreading ridges in back arc basins where the magma budget may be complicated by subduction induced variations of the melt supply to address this uncertainty we conducted hydrothermal plume surveys along slow spreading 40 60 mm yr and arc proximal 10 60 km distant sections of the southern mariana trough and the valu fa ridge lau basin on both sections we found multiple plumes overlying 15 20 of the total length of each section a coverage comparable to mid ocean ridges spreading at similar rates these conditions contrast with earlier reported results from the two nearest arc segments of a faster spreading 60 70 mm yr back arc ridge the east scotia ridge which approaches no closer than 100 km to its arc there hydrothermal venting is relatively scarce 5 plume coverage and the ridge characteristics are distinctly slow spreading small central volcanic highs bookended by deep median valleys and axial melt lenses restricted to the volcanic highs two factors may contribute to an unexpectedly low hydrothermal budget on these east scotia ridge segments they may lie too far from the adjacent arc to benefit from near arc sources of melt supply and subduction aided migration of mantle from the bouvet hot spot may reduce hydrothermal circulation by local crustal warming and thickening analogous to the reykjanes ridge thus the pattern among these three ridge sections appears to mirror the larger global pattern defined by mid ocean ridges a well defined trend of spreading rate versus hydrothermal activity on most ridge sections plus a subset of ridge sections where unusual melt delivery conditions diminish the expected hydrothermal activity

water column hydrothermal plumes on the juan de fuca ridge hydrographic surveys on the juan de fuca ridge jdfr carried out from 1980 to 1987 show a complex pattern of sup 3 he and mn rich water column plumes produced by venting from several submarine hot spring areas in the vicinity of axial volcano at latitude 46 degree n distinct plumes were detected in 1980 1982 and 1983 with sup 3 he signatures up to delta sup 3 he 64 at approximately 1 500 m depth at distances of approximately 10 km from the seamount summit however the same plumes had no detectable thermal signature a paradox which is attributed to the high sup 3 he heat ratios and low salinities of the fluids venting within the caldera of axial volcano profiles directly over the seamount show hydrothermal sup 3 he in the water column up to 300 m above the caldera floor with the sup 3 he signal increasing with depth to very high and uniform ratios of delta sup 3 he 108 150 below the approximately 1 500 m caldera sill depth another apparent locus of hydrothermal input is helium basin a depression on the northeast flank of axial volcano which had delta sup 3 he 51 when first sampled in 1980 however subsequent hydrocasts into helium basin in 1982 and 1983 yielded lowermore helium enrichments suggesting either a decrease in hydrothermal input or flushing of the basin via a mixing event to the south of axial volcano high delta sup 3 he values of approximately 40 observed over the ridge axis at 45 degree 18 prime n and 45 degree 39 prime n indicate venting on this previously unexplored section of the ridge the water column plumes over the us geological survey vent site at approximately 44 degree 40 prime n on the southern jdfr have very high mn sup 3 he ratios of 4 600 mol cm sup 3 an apparently unique characteristic which can be used to distinguish these plumes from those originating at other jdfr vent fields less

ammonium partitioning and nitrogen isotope fractionation among coexisting micas during high temperature fluid rock interactions examples from the new england appalachians abstract despite recent advances in the field of n isotope geochemistry our understanding of the behavior of this element in the solid earth remains limited by a lack of fundamental information regarding the partitioning of ammonium and isotopic fractionation of n among coexisting mineral and fluid phases study of n behavior in regionally metamorphosed rocks provides the opportunity to assess intermineral nh 4 partitioning and n isotope fractionation among coexisting micas during metamorphism and affords an application of the n system as a tracer of high t fluid rock interactions analyzed mica samples range in 15 n air from 3 3 to 11 9 and contain 9 to 1820 ppm n the outcrop at townshend dam vermont allows examination of n behavior across strike on a relatively small scale and samples from western maine demonstrate the effect of varying metamorphic conditions on n behavior in metapelites 15 n bt w mica 15 n biotite 15 n white mica ranges from 0 9 to 2 7 for all samples from both suites mean 0 36 with 1 0 79 with samples containing a separate paragonite white mica phase showing the greatest range 0 12 to 1 02 mean 0 58 1 1 03 thirteen samples containing only na poor muscovite six from townshend dam seven from western maine have mean 15 n bt w mica of 0 07 1 0 41 in both suites biotite nearly always contains more n than coexisting white mica but n w mica n bt also shows some significant scatter mean n w mica n bt 0 46 with 1 0 34 the thirteen samples containing only a na poor muscovitic white mica phase have mean n w mica n bt 0 39 with 1 0 26 similar to that reported by others for other metamorphic suites containing only muscovite as the white mica phase there is no obvious suggestion of equilibrium n isotopic fractionation among coexisting micas at epidote amphibolite to amphibolite facies metamorphic conditions although nh 4 appears to partition systematically among coexisting biotite and white mica significant scatter in both 15 n bt w mica and nh 4 partitioning conceivably the result of differential closure to exchange during cooling or of retrograde replacements could however obscure observation of small equilibrium intermica fractionations related to the characteristics of the interlayer sites in which nh 4 resides samples most unlike the mean in both 15 n bt w mica and n w mica n bt contain abundant chlorite some of which is likely retrograde based on petrographic observations chl chl bt 0 3 thus retrograde replacement of biotite by chlorite may have been accompanied by fluid mineral n isotope exchange perhaps involving the production of fine grained retrograde n bearing white mica observed petrographically for some samples it is also possible that sampling at scales greater than those of n isotope equilibrium domains e g across fine interlayers results in some scatter because of varying relative modal proportions of the two micas in adjacent fine interlayers although further investigation of the extent of retrograde reequilibration of mica n systematics is warranted the observed lack of systematic n isotope fractionation among coexisting micas and the reasonably systematic nh 4 partitioning data for these phases provide important preliminary constraints for attempts to model n isotope behavior in fluid rock systems these results and other attempts to calibrate n isotope fractionation through field studies point to the conspicuous lack of experimentally determined mica fluid n isotope fractionation factors

chemical and physical responses to deformation in micaceous quartzites from the tauern window eastern alps micaceous quartzites from a subvertical shear zone in the tauern window contain abundant quartz clasts derived from dismembered quartz tourmaline veins bulk plane strain deformation affected these rocks at amphibolite facies conditions shape changes suggest net shortening of the clasts by 11 64 with a mean value of 35 quartz within the clasts accommodated this strain largely via dislocation creep processes on the high stress flanks of the clasts however quartz was removed via solution mass transfer pressure solution processes the resulting change in bulk composition allowed growth of porphyro blastic staurolite chlorite kyanite on the clast flanks matrix sio2 contents decrease from c 83 wt away from the clasts to 49 58 in the selvages on the clast flanks the chemical changes are consistent with c 70 volume loss in the high stress zones calculated shortening values within the clast flanks are similar to the volume loss estimates and are greatly in excess of the shortening values calculated from the clasts themselves flow laws for dislocation creep versus pressure solution imply large strain rate gradients and or differential stress gradients between the matrix and the clast selvages in a rock containing a large proportion of semirigid clasts weakening within the clast flanks could dominate rock rheology in our samples however weakening within the selvages was self limiting 1 growth of strong staurolite porphyroblasts in the selvages protected remaining quartz from dissolution and 2 overall flattening of the quartz clasts probably decreased the resolved shear stress on the flanks to values near those of the matrix which would have reduced the driving force for solution transfer creep extreme chemical changes nonetheless occurred over short distances the necessity of maintaining strain compatibility may lead to significant localized dissolution in rocks containing rheologic heterogeneities and overall weakening of the rocks may result solution transfer creep may be a major process whereby weakening and strain localization occur during deep crustal metamorphism of polymineralic rocks

geochemical observations within the water column at the co2 rich hydrothermal systems hatoma knoll and yonaguni knoll iv in the southern okinawa trough the okinawa trough is one of three known hydrothermal sites worldwide where liquid carbon dioxide is emitted from the seafloor into the water column in march 2008 investigations were performed at two active areas yonaguni knoll iv and hatoma knoll in order to identify impacts of hydrothermal venting on the water column chemistry vertical profiles of ph and redox potential eh were recorded and discrete water samples were taken for the analysis of total carbon dioxide ct and helium 3he 4he anomalies with respect to reference stations ct ph and 3he with respect to saturation with the atmosphere 3heexcess were used to characterize the impact of hydrothermal vents these data indicate that the flux of co2 into the water column is dominated by hot hydrothermal co2 rich vents located in close proximity to the liquid co2 emission sites bubbles and droplets sampled at the cold gas outlets at hatoma knoll differed considerably from the water column regarding co2 3he ratios and thus provide additional evidence that cold liquid phase co2 is of minor importance for the total co2 flux at both hydrothermal systems although hydrothermal vents at back arc basins are known to emit large amounts of acids other than co2 the correlation between ph and ct at both research areas clearly suggests that the observed ph reduction is mainly caused by the addition of co2 deviating ct 3he and ct ph ratios and the prevailing water currents indicate a yet undiscovered vent site at the flank of a seamount in the northeast

hydrothermal exploration of the fonualei rift and spreading center and the northeast lau spreading center we report evidence for active hydrothermal venting along two back arc spreading centers of the ne lau basin the fonualei rift and spreading center frsc and the northeast lau spreading center nelsc the ridge segments investigated here are of particular interest as the potential source of a mid water hydrothermal plume 1500 2000 m depth which extends more than 2000 km across the sw pacific ocean dispersing away from an apparent origin close to the most northeastern limits of the lau basin our results indicate the presence of at least four new hydrothermal plume sources three along the frsc and one on the nelsc the latter situated within 150 km of the maximum for the previously identified sw pacific regional scale plume however tdfe and tdmn concentrations in the southernmost frsc plume that we have identified only reach values of 19 and 13 nmol l and dissolved 3he anomalies in the same plume are also small both in relation to the sw pacific plume and to local background which shows evidence for extensive 3he enrichment throughout the entire lau basin water column our results reveal no evidence for a single major point hydrothermal source anywhere in the ne lau basin instead we conclude that the regional scale sw pacific hydrothermal plume most probably results from the cumulative hydrothermal output of the entire topographically restricted lau basin discharging via its ne most corner

the mechanism of ascent and emplacement of granite magma during transpression a syntectonic granite paradigm we propose a model for syntectonic ascent and emplacement of granite magma based on structural relations in part of the northern appalachians in the study area in western maine strain was distributed heterogeneously during devonian acadian transpression metasedimentary rocks migmatites at high grades record two contrasting types of finite strain in zones that alternate across strike rocks in both types of zones have a penetrative moderately to steeply ne plunging mineral elongation lineation defined by bladed muscovite fibrolite sillimanite at high grades in straight belts of enhanced deformation rocks have s l fabrics that record apparent flattening to plane strain apparent flattening zones afzs but rocks between these belts have l s fabrics that record apparent constriction apparent constriction zones aczs at metamorphic grades above the contemporary solidus rocks in afzs developed stromatic structure in migmatite which suggests that percolative flow of melt occurred along the evolving flattening fabric stromatic migmatites are intruded by concordant to weakly discordant m scale composite sheet like bodies of granite to suggest magma transport in planar conduits through the afz rocks inhomogeneous migmatite is found in the intervening aczs which suggests migration of partially molten material through these zones en masse probably by melt assisted granular flow inhomogeneous migmatites are intruded by irregular m scale bodies of granite that vary from elongate to sub circular in plan view and seem cylindrical in three dimensions these bodies apparently plunge to the northeast parallel to the regional mineral elongation lineation to suggest magma transport in pipe like conduits through the acz rocks we postulate that the form of magma ascent conduits was deformation controlled and was governed by the contemporaneous strain partitioning magma ascent in planar and pipe like conduits through migmatites is possible because oblique translation during contraction displaces isotherms upward in the orogenic crust to form a thermal antiform within this hot corridor it is the difference in temperature between melt producing reactions in the anatectic zone and the wet solidus for granite melt that enables magma to migrate pervasively up through the orogenic crust without congealing heat advected with the migrating melt promotes amplification of the thermal antiform in a feedback relation that extends the zone of plastic deformation and pervasive melt migration to shallower levels in the crust at the wet solidus we suggest melt flows obliquely toward axial culminations in the thermal antiform which are sites of melt accumulation and perturbations from which magma may escape to form plutons batches of melt that escape from these perturbations may be trapped by tectonic structures higher in the crust or ascent may become inhibited with decreasing depth by thermal arrest and solidification if the rate of arrival of subsequent melt batches exceeds the rate of crystallization at the site of pluton construction melt pressure ultimately may lead to sub horizontal magma fracture or viscous flow of wall rocks may allow lateral spreading the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduit as the thermal antiform decays the height of sub solidus crust that separates the deepest part of the pluton from the anatectic zone increases consequently pluton inflation declines and solidification leads to infilling of the magma feeder channel to form a root zone that passes downward into migmatite which may explain the difficulty of determining precisely the floor to these deeper segments of large plutons using gravimetry

using geochemistry to map mantle flow beneath the lau basin geochemical tracers can be used to map mantle flow beneath the lau basin tonga region over the past 6 m y and constrain the extent and means by which different components contribute to the magmas erupted there helium isotope data track the samoan plume to show that it infiltrated into the northwestern part of the lau basin at 40 mm yr 1 through an opening tear in the pacific plate in contrast to other recent studies our analysis indicates that this plume does not contribute to the arc lavas a louisville plume component is present in the northern tonga arc lavas but this was added from volcaniclastic sediments transported into the arc on the subducting slab and does not require the presence of plume material within the mantle wedge the louisville tracer has been used to infer that the mantle wedge beneath the island arc is downwelling at the rate of 20 40 mm yr 1 owing to viscous drag against the downgoing pacific plate a third geochemical tracer provided by the distinction between indian and pacific mantle indicates that indian mantle has migrated eastward at rates of 45 65 mm yr 1 the inferred rates of migration indicate that the translation of geochemical signatures occurs by mantle flow rather than by the order of magnitude faster movement of partial melts except for the flow in the mantle wedge the directions of mantle flow in this region are unrelated to the overlying plate motions

oblique diapirism the criffel granodiorite granite zoned pluton southwest scotland abstract strain trajectories strain gradients and quartz c fabrics have been used to propose an emplacement history of the criffel zoned pluton strain has been estimated from the microdioritic xenoliths included in the outer granodiorite textural criteria have been used to complete the pattern of strain variations throughout the pluton strain gradients are found to be related to the granodiorite granite boundary zone with highest strain towards the northeast side of the pluton giving an asymmetric horseshoe pattern quartz c fabrics allow two strain histories to be distinguished within the pluton an early coaxial flattening in the granodiorite followed by a non coaxial deformation in the granite and the adjacent granodiorite these features are interpreted as the result of an oblique diapiric intrusion of the inner granite into the partially emplaced and crystallized granodiorite

four large scale field aligned current systems in the dayside high latitude region a system of four current sheets of large scale field aligned currents facs was discovered in the data set of simultaneous viking and dmsp f7 crossings of the dayside high latitude region this paper reports four examples of this system that were observed in the prenoon sector the flow polarities of facs are upward downward upward and downward from equatorward to poleward the lowest latitude upward current is flowing mostly in the cps precipitation region often overlapping with the bps at its poleward edge and is interpreted as a region 2 current the pair of downward and upward facs in the middle of the structure are collocated with structured electron precipitation the precipitation of high energy 1 kev electrons is more intense in the lower latitude downward current sheet the highest latitude downward flowing current sheet is located in a weak low energy particle precipitation region suggesting that this current is flowing on open field lines simultaneous observations in the postnoon local time sector reveal the standard three sheet structure of facs sometimes described as region 2 region 1 and mantle referred to the midday region 0 currents a high correlation was found between the occurrence of the four fac sheet structure and negative interplanetary magnetic field imf by we discuss the fac structure in terms of three types of convection cells the merging viscous and lobe cells during strongly negative imf by two convection reversals exist in the prenoon sector one is inside the viscous cell and the other is between the viscous cell and the lobe cell this structure of convection flow is supported by the viking electric field and auroral uv image data based on the convection pattern the four fac sheet structure is interpreted as the latitudinal overlap of midday and morning fac systems we suggest that the four current sheet structure is common in a certain prenoon local time sector during strongly negative imf by

where are the undiscovered hydrothermal vents on oceanic spreading ridges abstract in nearly four decades since the discovery of deep sea vents one third of the length of global oceanic spreading ridges has been surveyed for hydrothermal activity active submarine vent fields are now known along the boundaries of 46 out of 52 recognized tectonic plates hydrothermal survey efforts over the most recent decade were sparked by national and commercial interests in the mineral resource potential of seafloor hydrothermal deposits as well as by academic research here we incorporate recent data for back arc spreading centers and ultraslow and slow spreading mid ocean ridges mors to revise a linear equation relating the frequency of vent fields along oceanic spreading ridges to spreading rate we apply this equation globally to predict a total number of vent fields on spreading ridges which suggests that 900 vent fields remain to be discovered almost half of these undiscovered vent fields comparable to the total of all vent fields discovered during 35 years of research are likely to occur at mors with full spreading rates less than 60 mm yr we then apply the equation regionally to predict where these hydrothermal vents may be discovered with respect to plate boundaries and national jurisdiction with the majority expected to occur outside of states exclusive economic zones we hope that these predictions will prove useful to the community in the future in helping to shape continuing ridge crest exploration

geochemical characterization of highly diverse hydrothermal fluids from volcanic vent systems of the kermadec intraoceanic arc abstract during the r v sonne cruise so253 in 2016 2017 hydrothermal vent sites along the kermadec intraoceanic arc were sampled for hydrothermal fluids at four active volcanoes macauley haungaroa brothers and rumble iii respectively water depths ranged between 290 m and 1700 m a new vent field was discovered at haungaroa the samples were taken from diffuse flow sites as well as from white and black smokers rich in metals and gases with discharge temperatures as high as 311 c their fluid composition is very variable but basically divides into two types one that indicates distinct magmatic input and another that shows evidence for intense water rock interaction under hot acidic conditions fluid samples from macauley the shallowest sampling site 300 m had fe concentrations as high as 1 7 mm al concentrations up to 122 m and h2s up to 10 mm at a ph of only 1 2 at brothers the deepest sampling site down to 1600 m we identified two different fluid types 1 a magmatically influenced type at the upper and lower cone with highest temperatures of 115 c up to 95 6 mm mg the highest mg concentration measured in fluids from intraoceanic arc systems so far elevated so42 76 9 mm high h2s 5 0 mm but fe concentrations of only 15 m and 2 a fluid with low mg 5 4 mm low h2s 1 1 mm temperatures reaching 311 c and high fe contents 12 4 mm at the upper caldera and nw caldera wall typical of a black smoker fluid chloride concentrations in all fluids were similar or highly enriched when compared to seawater e g up to 787 mm brine fluids with also one low chlorinity vapor phase fluid sample recovered indicating that phase separation is occurring at brothers unusual highly elevated mg concentrations in fluids from the brothers lower cone 95 6 mm compared to 53 2 mm in ambient seawater combined with highly elevated concentrations of so42 76 9 mm compared to 29 0 mm in ambient seawater indicate dissolution of mg and so42 bearing minerals in the subsurface such as caminite our data show how highly diverse and variable island arc systems can be with respect to their fluid chemistry both spatially and temporally it adds to the still limited data set of arc systems compared to mid ocean ridges and supplies an important contribution towards a better understanding of geochemical processes along arc volcanoes the higher range in fluid chemistry together with shallower water depth implies that the fluids from intraoceanic arcs may contribute a significant fraction of dissolved metals not only to the global oceanic biogeochemical cycle but also into the photic zone the area of highest bioproductivity

tourmaline in a low grade clastic metasedimentary rock an example of the petrogenetic potential of tourmaline detrital tourmaline grains and their associated tourmaline overgrowths provide a means to unravel the provenance and petrogenetic history of low grade clastic metasedimentary rocks evidence derives from tourmaline grains found in a lithic wacke metamorphosed to chlorite zone conditions the detrital tourmaline cores are diagnostic indicators of the source rocks of the sediment whereas the overgrowths record both diagenetic and metamorphic reactions in the rock tourmaline grains consist of a detrital core surrounded by asymmetric overgrowths comprised of inner and outer rims abrupt chemical discontinuities between each of these zones implies that volume diffusion within tourmaline was minor under the conditions of formation compositions of the detrital cores vary widely yet can be correlated with source rock types that are consistent with lithic fragments recognizable in the metawacke at either the analogous or antilogous pole inner rim compositions proximal to the detrital cores converge despite the substrate tourmaline composition indicating an approach to chemical equilibrium however significant dufferences in al and x site vacancies at the expense of mg na and ti between the analogous and antilogous poles of the inner rims demonstrate the presence of significant amounts of compositional polarity outer rim compositions at either pole also converge but compositional polarity between the analogous and antilogous poles persists the presence of the inner and outer rims separated by a compositional discontinuity suggests punctuated evolution of the overgrowth this implies that boron was sporadically available during diagenesis and metamorphism based on boron contents of minerals this may correspond to a mechanism such as boron release due to polytypic change of illite or consumption of illite and or muscovite as such tourmaline growth stages may serve as a monitor of chemical reactions in low grade metamorphic rocks

the ti saturation surface for low to medium pressure metapelitic biotites implications for geothermometry and ti substitution mechanisms the ti content of biotite can serve as a geothermometer for graphitic peraluminous metapelites that contain ilmenite or rutile and have equilibrated at roughly 4 6 kbar the relationship between ti content temperature and mg mg fe value was calibrated empirically using an extensive natural biotite data set 529 samples from western maine and south central massachusetts in combination with the petrogenetic grid of spear et al 1999 the calculated ti saturation surface is curved such that for a given mg mg fe value ti concentration increases as a function of temperature in a nonlinear fashion and for a given temperature ti concentrations decrease with an increase in mg mg fe the fit to the ti saturation surface can be reformulated as the geothermometric expression t ln ti a c x mg 3 b 0 333 in which t is temperature in degrees celsius ti is the number of atoms per formula unit apfu normalized on the basis of 22 o atoms x mg is mg mg fe a 2 3594 b 4 6482 10 9 and c 1 7283 the calibration range for this expression is x mg 0 275 1 000 ti 0 04 0 60 apfu and t 480 800 c precision of the ti in biotite geothermometer is estimated to be 24 c at the lower temperature range and improves to 12 c at higher temperatures application of the ti in biotite geothermometer to ilmenite or rutile bearing graphitic peraluminous metapelites equilibrated at 3 6 kbar is generally consistent with independent temperature determinations but with some deviations that represent local reequilibration consequently the ti systematics in biotite can also serve as the basis of a very sensitive indicator of chemical equilibrium or lack thereof application of the geothermometer to metapelites not containing the requisite mineral assemblages can lead to minor to significant errors in estimated temperatures biotite ti substitution mechanisms are controlled by several factors based on the biotite calibration data set magnesian biotites x mg 0 65 incorporate ti in accordance with the exchange vector tial2r 1si 2 where r is the sum of the divalent cations mg fe mn this substitution mechanism is primarily a response to misfit of the octahedral and tetrahedral layers in magnesian biotites intermediate biotites x mg 0 65 particularly at higher temperatures exhibit enhanced ti concentrations most consistent with the ti deprotonation tio2r 1 oh 2 exchange vector dominance of ti deprotonation substitution is largely a function of reduction of h2o activity at higher metamorphic grades supplementary biotite data from metaluminous amphibolites and mafic granulites metamorphosed isothermally with variable h2o activities reveal that low al biotite incorporates significantly higher concentrations of ti relative to peraluminous biotite as a result of a combination of the exchange vectors tio2r 1 oh 2 and rsial 2 substituting in roughly an 8 1 ratio

a new methodology for the development of high latitude ionospheric climatologies and empirical models many empirical models and climatologies of high latitude ionospheric processes such as convection have been developed over the last 40 years one common feature in the development of these models is that measurements from different times are combined and averaged on fixed coordinate grids this methodology ignores the reality that high latitude ionospheric features are organized relative to the location of the ionospheric footprint of the boundary between open and closed geomagnetic field lines ocb this boundary is in continual motion and the polar cap that it encloses is continually expanding and contracting in response to changes in the rates of magnetic reconnection at the earth s magnetopause and in the magnetotail as a consequence models that are developed by combining and averaging data in fixed coordinate grids heavily smooth the variations that occur near the boundary location here we propose that the development of future models should consider the location of the ocb in order to more accurately model the variations in this region we present a methodology which involves identifying the ocb from spacecraft auroral images and then organizing measurements in a grid where the bins are placed relative to the ocb location we demonstrate the plausibility of this methodology using ionospheric vorticity measurements made by the super dual auroral radar network radars and ocb measurements from the image spacecraft fuv auroral imagers this demonstration shows that this new methodology results in sharpening and clarifying features of climatological maps near the ocb location we discuss the potential impact of this methodology on space weather applications

spatial distribution of average vorticity in the high latitude ionosphere and its variation with interplanetary magnetic field direction and season 1 we present a technique to measure the magnetic field aligned vorticity of mesoscale plasma flows in the f region ionosphere using line of sight velocity measurements made by the super dual auroral radar network superdarn vorticity is often used as a proxy for magnetic field aligned current fac intensity in the ionosphere but also provides information about turbulent processes in the ionosphere and magnetosphere using 6 years 2000 2005 inclusive of vorticity measurements made by six superdarn radars in the northern hemisphere we have compiled for the first time maps of average vorticity across the northern polar ionosphere these maps have been subdivided according to different seasonal and interplanetary magnetic field imf conditions the variations in the morphology of the vorticity maps with imf direction match very closely those seen in maps of average fac intensity determined using different methods and instrumentation suggesting that vorticity is a good proxy for fac in an averaged sense the variations in the morphology of the vorticity maps with season show differences from those seen in the fac maps illustrating that ionospheric conductance plays a major role in determining the differences between measurements of vorticity and fac

hydrothermal activity in the northwest lau backarc basin evidence from water column measurements 1 the northwest lau backarc basin consisting of the northwest lau spreading center nwlsc and the rochambeau rifts rr is unique in having elevated 3he 4he ratios up to 28 ra in the erupted lavas clearly indicating a hot spot or ocean island basalt oib type signature this oib type helium signature does not appear in any other part of the lau basin water column plume surveys conducted in 2008 and 2010 identified several sites of active hydrothermal discharge along the nwlsc rr and showed that the incidence of hydrothermal activity is high consistent with the high spreading rate of 100 mm year hydrocasts into the central caldera and southern caldera of the nwlsc detected elevated3he 4he 3he 55 and 100 respectively trace metals tmn tfe and suspended particles indicating localized hydrothermal venting at these two sites hydrocasts along the northern rift zone of the nwlsc also had excess 3he tmn and suspended particles suggesting additional sites of hydrothermal activity the rr are dominated by lobster caldera a large volcano with four radiating rift zones hydrocasts into lobster caldera in 2008 detected high 3he up to 239 and suspended particle and tmn signals indicating active venting within the caldera a repeat survey of lobster in 2010 confirmed the site was still active two years later plumes at lobster caldera and central caldera have end member3he 4he ratios of 19 ra and 11 ra respectively confirming that hot spot type helium is also present in the hydrothermal fluids

coupled deformation and metamorphism in the roof of a tabular midcrustal igneous complex the 370 377 ma mooselookmeguntic igneous complex was emplaced at 14 km depth into steeply dipping metaturbidites that were folded and metamorphosed ca 400 405 ma during the acadian orog eny gravity and drill hole data isograd geometry thermal modeling and struc tural measurements all indicate that the eastern aureole of the complex represents an areally extensive roof above the gently east dipping tabular shaped intrusion this roof preserves a classic example of low pressure high temperature metamorphism caused by the underlying intrusion ther mal modeling indicates that the roof is no more than 1000 m thick over an area exceed ing 100 km2 unlike other roofs described in the literature the mooselookmeguntic igneous complex roof preserves a thick 600 m emplacement related strain gradi ent with a deformational fabric that evolved through all stages of crenulation cleavage to become an intense nondifferentiated folia tion approximately parallel to the intrusive contact and perpendicular to the steeply dip ping regional acadian age foliation fabric evolution through all stages of crenulation cleavage requires the vertical growth of the tabular intrusion to have been largely accommodated by dissolution precipitation creep which is a linear viscous deformation mechanism that can occur at lower differ ential stress than for example dislocation creep as the crenulation cleavage evolves a stage is reached where further deformation requires a change in deformation mecha nism which may lead to hardening of the rock development of crenulation cleavage requires a mica rich foliation at an initially high angle to the emplacement related fl at tening plane and this confi guration may be the primary reason why the strain aureole in the mooselookmeguntic igneous complex roof is so well developed compared to other published examples of midcrustal roofs

extensive young silicic volcanism produces large deep submarine lava flows in the ne lau basin new field observations reveal that extensive up to 402 km2 aphyric glassy dacite lavas were erupted at multiple sites in the recent past in the ne lau basin located about 200 km southwest of samoa this discovery of volumetrically significant and widespread submarine dacite lava flows extends the domain for siliceous effusive volcanism into the deep seafloor although several lava flow fields were discovered on the flank of a large silicic seamount niuatahi two of the largest lava fields and several smaller ones northern lava flow fields were found well north of the seamount the most distal portion of the northernmost of these fields is 60 km north of the center of niuatahi caldera we estimate that lava flow lengths from probable eruptive vents to the distal ends of flows range from a few km to more than 10 km camera tows on the shallower near vent areas show complex lava morphology that includes anastomosing tube like pillow flows and ropey surfaces endogenous domes and or ridges some with crease like extrusion ridges and inflated lobes with extrusion structures a 2 1 5 km 30 m deep depression could be an eruption center for one of the lava flow fields the lau lava flow fields appear to have erupted at presumptive high effusion rates and possibly reduced viscosity induced by presumptive high magmatic water content and or a high eruption temperature consistent with both erupted composition 66 sio2 and glassy low crystallinity groundmass textures the large areal extent 236 km2 and relatively small range of compositional variation 0 60 for wt si02 within the northern lava flow fields imply the existence of large eruptible batches of differentiated melt in the upper mantle or lower crust of the ne lau basin at this site the volcanism could be controlled by deep crustal fractures caused by the long term extension in this rear arc region submarine dacite flows exhibiting similar morphology have been described in ancient sequences from the archaean through the miocene and in small batches on present day seafloor spreading centers this study shows that extensive siliceous lavas can erupt on the modern seafloor under the right conditions

super dual auroral radar network radar imaging of dayside high latitude convection under northward interplanetary magnetic field toward resolving the distorted two cell versus multicell controversy data from the kapuskasing and saskatoon radars of the evolving super dual auroral radar network superdarn hf radar network have been analyzed to study the two dimensional structure and dynamics of dayside high latitude ionospheric convection under northward interplanetary magnetic field imf conditions a period extending from 1600 to 2030 ut 0900 1330 mlt on january 10 1994 was examined during this interval magnetic field data were available from the imp 8 satellite and indicated moderately stable northward imf conditions for the first few hours of observation the by component of the imf was positive reasonably steady and approximately twice the magnitude of bz during this interval the high latitude convection images obtained with the superdarn radars were very similar to the distorted two cell convection maps for positive by as presented by heppner and maynard 1987 at 1840 ut a decrease in by in association with an increase in bz led to an extended period with by bz during this second interval the convection patterns were highly variable and even chaotic finally a sharp decrease in the by component at 1914 ut probably in association with a rotational discontinuity in the solar wind led to an extended period with by bz during this third interval the high latitude convection pattern was again stable and exhibited a single counterclockwise rotating vortex consistent with one of the polar cap merging cells proposed by dungey 1963 burke et al 1979 and reiff and heelis 1994 the transition to the counterclockwise rotating vortex occurred over a large spatial area within two radar scans 200 s and appeared to proceed via an equatorward incursion of the vortex into the previous convection configuration once this polar cap merging cell was formed it remained stable for the remainder of the period 40 min that by remained small sunward convection was also observed in the polar cap of the conjugate hemisphere at 1932 ut by the dmsp f11 satellite confirming that both magnetopause and internal reconnection sites were active at that time

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

superdarn observations of quasi stationary mesoscale convection vortices in the dayside high latitude ionosphere during the past few years of superdarn observations mesoscale 500 1000 km diameter clockwise sense convection vortices which do not show significant movement in any direction have been observed in the postnoon sector these convection vortices or small convection cells are herein named quasi stationary convection vortices qscvs in this paper a statistical study of 28 qscvs is presented using saskatoon kapuskasing radar data from the period october 1993 to march 1997 these qscvs occur in the magnetic latitude interval 72 81 between 1430 and 1630 magnetic local time mlt and are centered near the western end of the afternoon convection cell the qscvs occur mainly during southward interplanetary magnetic field imf but sometimes for northward imf they appear at lower latitudes as the imf bz becomes more negative they occur at higher latitudes and earlier local times for positive imf by and at lower latitudes and later local times for negative imf by all the qscvs appear to be associated with large amplitude fluctuations either in the imf or in the solar wind pressure or in both it is found that the time of the ionospheric convection change in response to the fluctuations in the imf and solar wind pressure at the magnetopause is about 6 9 min the observations have shown some evidence that the termination of the vortex is caused also by large changes in the imf and or solar wind pressure the lifetime of the qscvs is typically 10 20 min but it can be as long as 50 min the qscvs have clockwise rotational sense and are closely associated with the region 1 field aligned currents unlike traveling convection vortices the qscvs do not appear to be related to any instability at the magnetopause or low latitude boundary layer the large fluctuations in the solar wind pressure and imf seem to be likely initiating mechanisms for the qscvs

hydrothermal activity along the southwest indian ridge twenty years after the discovery of sea floor hot springs vast stretches of the global mid ocean ridge system remain unexplored for hydrothermal venting the southwest indian ridge is a particularly intriguing region as it is both the slowest spreading of the main ridges1 and the sole modern migration pathway between the diverse vent fauna of the atlantic and pacific oceans2 a recent model postulates that a linear relation exists between vent frequency and spreading rate3 and predicts vent fields to be scarcest along the slowest spreading ridge sections thus impeding migration and enhancing faunal diversity2 here however we report evidence of hydrothermal plumes at six locations within two 200 km long sections of the southwest indian ridge indicating a higher frequency of venting than expected these results suggest that fluxes of heat and chemicals from slow spreading ridges may be greater than previously thought and that faunal migration along the southwest indian ridge may serve as an important corridor for gene flow between pacific and atlantic hydrothermal fields

scales of equilibrium and disequilibrium during cleavage formation in chlorite and biotite grade phyllites se vermont detailed electron microprobe analyses of phyllosilicates in crenulated phyllites from south eastern vermont show that grain scale zoning is common and sympathetic zoning in adjacent minerals is nearly universal we interpret this to reflect a pressure solution mechanism for cleavage development where precipitation from a very small fluid reservoir fractionated that fluid multiple analyses along single muscovite biotite and chlorite grains 30 200 m in length show zoning patterns indicating tschermakitic substitutions in muscovite and both tschermakitic and di trioctahedral substitutions in biotite and chlorite using cross cutting relationships and mineral chemistry it is shown that these patterns persist in cleavages produced at metamorphic conditions of chlorite grade chlorite grade overprinted by biotite grade and biotite grade zoning patterns are comparable in all three settings requiring a similar cleavage forming mechanism independent of metamorphic grade moreover the use of 40ar 39ar geochronology demonstrates this is true regardless of age furthermore samples with chlorite grade cleavages overprinted by biotite porphyroblasts suggest the closure temperatures for the diffusion of al si mg and fe ions are greater than the temperature of the biotite isograd 400 c parallel and smoothly fanning tie lines produced by coexisting muscovite chlorite and muscovite biotite pairs on compositional diagrams demonstrate effectively instantaneous chemical equilibrium and probably indicate simultaneous crystallization these results do not support theories suggesting cleavages form in fluid dominated systems if crenulation cleavages formed in systems in which the chemical potentials of all major components are fixed by an external reservoir then the compositions of individual grains defining these cleavages would be uniform on the contrary the fine scale chemical zoning observed probably reflects a grain scale process consistent with a pressure solution mechanism in which the aqueous activities of major components are defined by local dissolution and precipitation thus the role of fluids was probably limited to one of catalysing pressure solution and fluids apparently did not drive cleavage development

emplacement kinematics of a granite diapir the chindamora batholith zimbabwe the geometric features of a large 50 40 km granitic batholith and its surrounding greenstone belt envelope are described the batholith is made up of several intrusive components and an intrusion sequence based on contact relations and xenoliths has been established the igneous rocks show a local foliation s fabric and preferred orientation of minerals the intensity of this fabric accords with the finite strain determined from xenolith shape analysis when the strain variations are analysed in detail it appears that the batholith was built up by a succession of magmatic pulses each of which led to a stretching of the previously consolidated igneous material so called balloon tectonics evidence is presented that xenolith deformation commences only when the surrounding igneous material has crystallized and a method is suggested whereby the position of the surface separating crystal supported phase plastic behaviour from melt supported phase liquid behaviour at different stages in the plutonic history can be determined ductile shear zones are present and their geometry accords well with the shape changes necessary to allow the outer parts of the pluton to stretch

understanding a submarine eruption through time series hydrothermal plume sampling of dissolved and particulate constituents west mata 2008 2012 four cruises between 2008 and 2012 monitored the continuing eruption of west mata volcano in the ne lau basin as it produced plumes of chemically altered water above its summit although large enrichments in 3he co2 fe and mn were observed in the plumes the most notable enrichment was that of h2 which reached concentrations as high as 14 843 nm strongly enriched h2 concentrations in the water column result from reactions between seawater or magmatic water and extremely hot rocks in 2008 the observation of elevated h2 concentrations in the water column above west mata pointed to vigorous ongoing eruptions at the volcano s summit the eruption was confirmed by visual observations made by the rov jason 2 in 2009 and demonstrated that h2 measurements are a vital instrument to detect ongoing volcanic eruptions at the seafloor elevated h2 in 2010 showed that the eruption was ongoing although at a reduced level given a maximum h2 concentration of 4410 nm in 2012 h2 levels in the water column declined significantly to a maximum of only 7 nm consistent with visual observations from the quest 4000 rov that found no evidence of an ongoing volcanic eruption methane behaved independently of other measured gases and its concentrations in the hydrothermal plume were very low we attribute its minimal enrichments to a mixture of mantle carbon reduced to ch4 and biological ch4 from diffuse flow sites this study demonstrates that ongoing submarine volcanic eruptions are characterized by high dissolved h2 concentrations present in the overlying water column

deep sea hydrothermal communities in southwestern pacific back arc basins the north fiji and lau basins composition microdistribution and food web abstract during the year 1989 two diving cruises of the french deep sea submersible nautile were devoted to the study of hydrothermal vent biology in spreading centers of two southwestern pacific back arc basins lau basin and north fiji basin in both cases two major active sites were visited white lady and mussel valley in the north fiji basin and hine hina and vai lili in lau basin the faunal associations clustered around active vents are dominated by two species of snails ifremeria nautilei and alviniconcha hessleri and one or two species of mytilids belonging to bathymodiolus these species are associated with chemoautolithotrophic bacteria in intracellular symbiosis as detected by the activity of the calvin benson cycle diagnostic enzyme rubpcase pedunculate and sessile barnacles dominated the outer rim of the site and are analogs of the fiter feeding serpulids living in the epr sites the hot extremes of the sites are poorly or not colonized by alvinellids or other taxa in the lau basin cold seep sites are found at the periphery of active hot or warm ventsand are dominated by vestimentiferans and pogonophorans no major differences were seen between associations of the two back arc basins at the generic level with the exeption of the abundance of synaptid holothurians associated with bathymodiolus in side the mussel valley site

temporal variability of the hydrothermal plume above the kairei vent field 25 s central indian ridge 1 continuous profiling of the nonbuoyant plume above a hydrothermal vent site can be used to determine the interaction between the plume formed by venting high temperature fluids and changing background temperature salinity and current fields over a tidal cycle we have conducted a 12 hour monitoring of the nonbuoyant plume above the kairei vent field 25 s central indian ridge the depth of the plume particle maximum varies significantly in the water column from 2150 m to 2350 m but remains strongly associated with the 2 36 987 potential density isopycnal we have used the interaction between two unrelated physical oceanographic phenomena to isolate the section of the time series record most suitable for determining the heat flux of the kairei source on the basis of the rise height of the plume to neutral buoyancy at the start of the time series internal waves are observed with a period similar to the calculated buoyancy period n 1 about 3 hours no consistent relationship is observed between the rise height of the plume and the calculated heat flux for the last 6 hours of the time series isopycnal surfaces are compressed above a strongly developed nonbuoyant plume such that the calculated buoyancy period is less than that of the internal waves a more constant heat flux can be calculated on the basis of the plume rise height from this part of the record

hydrothermal plumes above the east scotia ridge an isolated high latitude back arc spreading centre we have identified first evidence for the presence of submarine hydrothermal activity along the east scotia ridge an isolated back arc spreading centre located at 55 60 s in the atlantic sector of the southern ocean using a combination of in situ optical light scattering sensor data and total dissolvable mn concentrations we demonstrate the existence of hydrothermal plumes overlying two segments of this 500 km ridge crest both segments exhibit anomalous topography and at least one segment is also underlain by an axial magma chamber seismic reflector future investigation of the fauna that inhabit these remote hydrothermal environments may provide an important missing link between the distinct biogeographical provinces delimited from previous investigation of northern atlantic versus eastern pacific vent sites

controls on back arc crustal accretion insights from the lau manus and mariana basins abstract together the lau manus and mariana basins encompass a broad range of conditions of back arc basin development marine surveys have determined the tectonic setting and reconnaissance scale geophysical and geochemical properties of the extension axes in these basins we review these data to examine crustal accretion characteristics in the back arc setting in each basin magmatism is enhanced in spreading centres near the arc volcanic front but decreases becoming deficient in axes further from the arc in the lau and manus basins the axes extend far behind the arc and develop typical mid ocean ridge mor like characteristics we propose that these variations are controlled by the subducting slab which shapes composition and flow within the mantle wedge water released from the slab lowers the mantle solidus and increases in concentration toward the volcanic arc spreading centres near the arc advect the hydrated mantle material enhancing melt production slab induced flow carries melt depleted mantle material back beneath the basin where it mixes with ambient mantle spreading centres further from the arc advect this mantle mixture and produce thinner than normal crust far from the arc spreading centres advect essentially mid ocean ridge basalt morb source mantle and their characteristics are mor like thus in addition to spreading rate effects on mantle melting that predominate at mors in back arc basins the subducting slab introduces additional systematic effects

detection of hydrothermal plumes along the southeast indian ridge near the amsterdam st paul plateau a new self contained profiling instrument attached to 91 lowerings of waxcores and dredges along a 1600 km stretch of the southeast indian ridge found six sites having optical back scatter anomalies indicative of hydrothermal plumes from high temperature seafloor venting at five other sites back scatter anomalies were less distinct and at the remaining sites anomalies were absent these are the first documented hydrothermal sites along this intermediate rate spreading center and are among the very few yet discovered in the indian ocean basin some profiles exhibit complex back scatter anomalies suggestive of multiple sources of seafloor discharge at one site near bottom temperature anomalies of 0 1 c and the recovery of a vent specific barnacle provide the first precise seafloor location of active venting in the deep indian ocean although this study is only reconnaissance in nature venting along this portion of the seir appears to be significantly less than predicted by global correlations of plume incidence as a function of spreading rate nevertheless these sites may be important as biological connections between distinct faunal assemblages of atlantic and pacific vent fields

short term variations in the distribution of hydrothermal plumes along a superfast spreading center east pacific rise 27 30 32 20 s 1 a multidisciplinary expedition to the southern east pacific rise 27 30 32 20 s provided an opportunity to compare the efficiency and effectiveness of two methods for mapping hydrothermal plumes the standard conductivity temperature depth optical ctdo tow yo method and a towed fixed array of hydrographic and optical sensors miniature autonomous plume recorders maprs six second order segments were mapped twice once with ctdo tow yos and then again with a fixed array of maprs attached to the cable of a deep towed side scan sonar we found a high degree of overall agreement between the two methods in both the distribution and optical intensity of hydrothermal plumes between survey differences increased as time between surveys increased from 6 days presumably because of advection of the plumes by local currents plume locations changed by as much as 10 km implying a confidence limit in predicting vent site location using segment scale hydrothermal plume surveys towed mapr arrays proved an efficient and effective method for acquiring coregistered geological and hydrothermal plume data

structure and emplacement history of a multiple center cone sheet bearing ring complex the zarza intrusive complex baja california mexico the cretaceous zarza intrusive complex located in the peninsular ranges of baja california norte mexico is perhaps the bestpreserved multiple center cone sheet bearing ring complex documented in north america the 7 km 2 elliptical complex hosts three nested non concentric intrusive centers that are successively younger to the south the northern and central centers show the same evolutionary sequence of 1 intrusion of concentric gabbroic cone sheets 2 intrusion of massive core gabbros and 3 development of subvertical ductile ring faults ring fault kinematics indicate that both centers moved down relative to the surrounding country rocks suggesting collapse into an underlying magma chamber the southern center is composed of approximately equal proportions of gabbro and tonalite and lacks cone sheets aluminumin hornblende barometry on the tonalite indicates a maximum emplacement depth of 2 3 0 6 kbar the zarza intrusive complex is surrounded by a ductile deformation aureole and bedding is inward dipping and inward younging around the entire complex excellent preservation of the intrusive history allowed us to evaluate the origin of the aureole and the three most applicable models are 1 collapse of the complex into its underlying magma chamber 2 sinking of the complex and its chamber after solidification and 3 formation of the aureole prior to emplacement of the complex the preserved structural and intrusive relationships provide information on the dynamic evolution of subvolcanic magma chambers and suggest that the complex may have been overlain by a caldera

elemental distributions and neodymium isotopic compositions of silurian metasediments western maine usa redistribution of the rare earth elements abstract pelitic schists from the lower garnet to lower staurolite zones from the rangeley perry mountain and smalls falls formations of western maine were analyzed for major elements trace elements and neodymium isotopes these formations were derived from highlands created during the taconian orogeny deposited into a trough and metamorphosed during subsequent orogenic events most major and trace element abundances relative to al 2 o 3 were statistically identical between zones of the same formation as well as between formations although the average major element composition of these formations are the same there are systematic variations in some elements notably plots of sio 2 vs al 2 o 3 and k 2 o vs al 2 o 3 suggest that most of the variation could be produced by mixing of a fairly constant ratio of clay minerals and feldspar with varied amounts of quartz due to sorting in the sedimentary system different amounts of these minerals should not influence the shape of the ree patterns of the metapelites but higher amounts of quartz and feldspar may dilute the rees and most elemental abundances of the clay minerals and lead to lower elemental abundances the major difference between the samples within the perry mountain formation are different lree and mree abundances relative to al 2 o 3 which are not correlated to differences in major element or other trace element abundances relative to al 2 o 3 the samples in the perry mountain with higher lree and mree abundances have for example 42 3 8 3 ppm and those with low abundances have 5 6 3 6 ppm the samples with the high ree abundances of the perry mountain formation are similar in abundances and ree patterns to those of the rangeley and smalls falls formations typical of mudstones derived from granitoids another difference between the low and high ree abundance samples are the calculated t dm model ages the high ree abundance samples of the perry mountain formation show t dm similar to the samples of the rangeley formation with ages of about 1 7 1 8 ga the perry mountain samples with low ree abundances however give unrealistically old t dm s between 2 5 and 5 3 ga these unrealistically old t dm s are due to the relatively high sm nd ratios compared to crustal values which are characteristic of samples of the perry mountain formation with lower ree abundances we therefore suggest that these samples may be indicators for open system behavior of the neodymium isotopic system the timing of this disturbance of the neodymium isotope system is difficult to determine and cannot be tied to weathering or a definite postdepositional event the complexities of the data suggest more than one resetting event the most likely event that could have produced much of the movement of the lrees and mrees could have been due to small scale migration between anoxic hemipelagites and turbidite mudstones during diagenesis but some migration may have continued during metamorphism in order to reconcile the neodymium isotopic data

crustal structure of the niuafo ou microplate and fonualei rift and spreading center in the northeastern lau basin southwestern pacific the northeastern lau basin is one of the fastest opening and magmatically most active back arc regions on earth although the current pattern of plate boundaries and motions in this complex mosaic of microplates is reasonably understood the internal structure and evolution of the back arc crust are not we present new geophysical data from a 290 km long east west oriented transect crossing the niuafo ou microplate back arc the fonualei rift and spreading center frsc and the tofua volcanic arc at 17 20 s our p wave tomography model and density modeling suggest that past crustal accretion inside the southern frsc was accommodated by a combination of arc crustal extension and magmatic activity the absence of magnetic reversals inside the frsc supports this and suggests that focused seafloor spreading has until now not contributed to crustal accretion the back arc crust constituting the southern niuafo ou microplate reveals a heterogeneous structure comprising several crustal blocks some regions of the back arc show a crustal structure similar to typical oceanic crust suggesting they originate from seafloor spreading other crustal blocks resemble a structure that is similar to volcanic arc crust or a hydrous type of oceanic crust that has been created at a spreading center influenced by slab derived water at distances 50 km to the arc throughout the back arc region we observe a high velocity vp 7 2 7 5 km s 1 lower crust which is an indication for magmatic underplating which is likely sustained by elevated upper mantle temperatures in this region

a new radar auroral backscatter experiment in 1982 a new radar auroral backscatter system sabre sweden and britain radar experiment commenced operation in northern europe observations with this ground based system allow estimates to be made of the electric fields in the auroral e region as an electric field probe the coherent radar technique is unique in that measurements are made over a large area 200 000 km2 with good spatial resolution 20 20 km2 and with a temporal resolution of typically 20 s the system field of view covers an l value range 4 3 5 8 this region in the magnetosphere ionosphere system is now accessible for the first time for detailed electric field studies we present here observations of two pulsation events

unique event plumes from a 2008 eruption on the northeast lau spreading center the creation of ocean crust by lava eruptions is a fundamental earth process involving immediate and immense transfers of heat and chemicals from crust to ocean this transfer creates event plumes megaplumes massive ellipsoidal eddies with distinctive and consistent chemical signatures here we report the discovery of unique event plumes associated with a 2008 eruption on the northeast lau spreading center instead of a large plume hundreds of meters thick we detected at least eight individual plumes each 50 m thick and apparently only 1 3 km in diameter yet still rising 200 1000 m above the eruption site low and uniform 3he heat 0 041 10 17 mol j and dissolved mn heat 0 04 nmol j ratios in water samples were diagnostic of event plumes high h2 concentrations up to 9123 nm and basalt shards confirmed extensive interactions between molten lava and event plume source fluids remote vehicle observations in 2009 mapped a new small 1 5 5 8 106 m3 lava flow our results suggest that event plumes are more variable and thus perhaps more common than previously recognized small event plumes may be preferentially associated with small or sheet flow eruptions and massive event plumes with slowly extruding pillow mounds 25 75 m thick despite this correlation and high h2 concentrations existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes the creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation

a three plate kinematic model for lau basin opening 1 we present revised compilations of bathymetry magnetization acoustic imagery and seismicity data for the lau basin and surrounds we interpret these data to more precisely locate the plate boundaries in the region and to derive a three plate kinematic model for the opening of the lau basin during the brunhes chron our tectonic model includes the niuafo ou microplate which is separated from the australian plate along the peggy ridge lau extensional transform zone central lau spreading center and from the tongan plate along the newly discovered fonualei rift and spreading center our model shows that australia tonga plate motion between 15 5 s and 19 s is partitioned across the microplate and it resolves the former apparent conflict between geodetic versus seafloor spreading velocities regionally this implies that the angular rate of opening of the lau basin has been faster than that of the havre trough to the south and that the rapid current rates of pacific subduction at the tonga trench 240 mm yr at 16 s have been sustained for at least 0 78 m y

vailulu u undersea volcano the new samoa 1 vailulu u seamount is identified as an active volcano marking the current location of the samoan hotspot this seamount is located 45 km east of ta u island samoa at 169 03 5 w 14 12 9 s vailulu u defines the easternmost edge of the samoan swell rising from the 5000 m ocean floor to a summit depth of 590 m and marked by a 400 m deep and 2 km wide summit crater its broad western rift and stellate morphology brand it as a juvenile progeny of ta u seven dredges ranging from the summit to the se rift zone at 4200 m recovered only alkali basalts and picrites isotopically the volcano is strongly em2 in character and clearly of samoan pedigree 87sr 86sr 0 7052 0 7067 143nd 144nd 0 51267 0 51277 206pb 204pb 19 19 19 40 the 210po 210pb data on two summit basalts indicate ages younger than 50 years all of the recovered rocks are extremely fresh and veneered with glass an earthquake swarm in early 1995 may attest to a recent eruption cycle a detailed nephelometry survey of the water column shows clear evidence for hydrothermal plume activity in the summit crater the water inside the crater is very turbid nephelometric turbidity unit ntu values up to 1 4 and a halo of smog several hundred meters thick encircles and extends away from the summit for at least 7 km the turbid waters are highly enriched in manganese up to 7 3 nmol kg providing further evidence of hydrothermal activity vailulu u is similar to loihi hawaii in being an active volcanic construct at the eastern end of a hotspot chain it differs importantly from the hawaiian model in its total lack of tholeiitic basalt compositions

modeling dislocation creep as a near field material transfer process during spherical pluton expansion implications for strain rates and their preservation in pluton aureoles abstract in this paper we model coupled spatial and temporal changes in stress and temperature to calculate dislocation creep strain rates in host rock associated with spherical magma chamber expansion with and without material removal by stoping and or assimilation given a constant magma chamber pressure of 100 mpa we show that stress and temperatures in the host rock range from 100 to 10 mpa and 800 to 300 c respectively using a flow law for dislocation creep of wet quartzite with recently calibrated parameters maximum dislocation creep strain rates on the order of ca 10 10 s 1 occur only close to the pluton margin despite the simple geometry relative to real plutons the models yield several thought provoking predictions if the outer portions of the pluton are allowed to cool a wide thermal and structural aureole forms maintaining the liquidus temperature in the entire pluton allows for rapid aureole deformation resulting in a narrow thermal and structural aureole because the deformation outpaces heat conduction dislocation creep strain rates in the inner portions of aureoles are extremely sensitive to pressure changes only potentially resulting in large transient variations in strain rate under isothermal conditions evidence for elevated strain rates in pluton aureoles may not be preserved in host rock aureoles if solidified pluton participates in the deformation or it may be completely removed

birkeland current system key parameters derived from iridium observations method and initial validation results 1 the iridium satellites in 780 km altitude circular polar orbits provide continuous global monitoring of the birkeland current system via engineering magnetometer data these data have been used to characterize basic features of the global field aligned currents facs with a time window of 45 min and a time step of 15 min the three sigma magnetometer data noise threshold is 93 nt on average the fraction of measurements above the noise is used to provide one measure of the location of the auroral facs measures are also presented for the mean latitude and equatorward poleward extent of the region 1 region 2 fac system the equatorward latitude of region 1 region 2 facs is anticorrelated with kp r 0 68 indices are presented for the net fac intensity in terms of the eastward westward magnetic perturbation in the northern southern hemisphere by analogy with the ae au and al indices the iridium system indices show high correlation with the quick look auroral electrojet indices both in individual cases and statistically r 0 73 between their logarithms results are presented for two storms 22 23 september 1999 dst minimum approximately 160 nt and 21 22 october 1999 dst minimum approximately 230 nt reflecting that intensification and equatorward expansion of the global facs occur in response to southward imf enhanced dynamic pressure promotes more rapid equatorial expansion 10 in 1 5 hours for the september storm for which the dynamic pressure was enhanced 15 20 npa at southward imf turning as opposed to the october case 13 over 8 hours for which the southward turning occurred during nominal dynamic pressure 5 npa in both storms the current intensity decreases to prestorm levels within an hour when the imf turns northward or nearly horizontal at the beginning of storm recovery the key parameters are a useful means of accessing the iridium system data for preliminary analyses and the initial results provide motivation for future analyses to quantify the accuracy and reliability of products derived from the iridium system data index terms 2708 magnetospheric physics current systems 2409 2736 magnetospheric physics magnetosphere ionosphere interactions 2407 ionosphere auroral ionosphere 2704 2794 magnetospheric physics instruments and techniques 2788 magnetospheric physics storms and substorms keywords iridium constellation birkeland field aligned currents

titanium in biotite from metapelitic rocks temperature effects crystal chemical controls and petrologic applications an extensive natural biotite data set from western maine constrains the temperature and crystal chemical controls on the saturation ti levels in biotites from metapelites the geologically and petrologically well characterized metamorphic terrain associated with the m3 metamorphism of the acadian orogeny of western maine is ideal for this approach in that metamorphism occurred at roughly isobaric conditions of 3 3 kbar and chemical equilibrium was closely approached the data set from these metapelites exhibits systematic variations in ti contents over a continuum of metamorphic grades garnet through sillimanite k feldspar zones mineral assemblages and bulk compositional ranges samples were selected so that competing substitutions are restricted to those in metapelites with quartz aluminous phases chlorite staurolite or sillimanite ti phases ilmenite or rutile and graphite due to crystal chemical factors in any given metamorphic zone an inverse linear relationship exists between ti and mg contents decreasing octahedral ti and increasing tetrahedral si in mg rich biotite helps alleviate size disparity between octahedral and tetrahedral sheets for a biotite with a given mg content ti most dramatically increases above staurolite zone conditions our constrained data set allows us to calculate a ti saturation surface for natural biotite as a function of temperature and mg content at 3 3 kbar the ti saturation surface can be used to establish several important metamorphic features in similar metamorphic settings these include a general approach to equilibrium local and or subtle departures from equilibrium due to minor alteration to chlorite and relative and absolute geothermometry based on ti in biotite inclusions in refractory minerals and in matrix biotite

regional estimation of electric fields and currents in the polar ionosphere a new technique is presented to estimate electric fields and currents in a localized region of the high latitude ionosphere by combining two magnetogram inversion algorithms this paper describes the concept and practical procedures of the method as well as the first results of our efforts in which this new scheme is applied to northern scandinavia computing the ionospheric parameters on a small scale examining latitudinal profiles of these parameters and precipitating particles it is found that the region of the most intense precipitation in the morning sector is located equatorward of the region of the strongest electric field to evaluate the relative importance of ionospheric and magnetospheric effects the field aligned current is divided into two components e and e these two components give often the opposite directions in the resultant field aligned currents the relative strength of the two components appears to vary considerably with latitude

hydrothermalism in the tyrrhenian sea inorganic and microbial sulfur cycling as revealed by geochemical and multiple sulfur isotope data abstract the palinuro volcanic complex and the panarea hydrothermal field both located in the tyrrhenian sea italy are associated with island arc magmatism and characterized by polymetallic sulfide mineralization dissolved sulfide concentrations ph and eh measured in porewaters at both sites reveal a variable hydrothermal influence on porewater chemistry multiple sulfur isotopic measurements for disseminated sulfides crs chromium reducible sulfur extracted from sediments at palinuro yielded a broad range in 34s range between 29 8 and 10 2 and 33s values between 0 015 and 0 134 in contrast sediments at panarea exhibit a much smaller range in 34scrs with less negative values between 11 3 and 1 8 the sulfur isotope signatures are interpreted to reflect a mixture between hydrothermal and biogenic sulfide with a more substantial biogenic contribution at panarea multiple sulfur isotope measurements were performed on sulfides and elemental sulfur from drill core material from the palinuro massive sulfide complex 34s and 33s values for pyrite between 32 8 and 1 1 and between 0 012 to 0 042 respectively as well as for elemental sulfur with 34s and 33s values between 26 7 and 2 1 and between 0 035 and 0 109 respectively point to a microbial origin for much of the sulfide and elemental sulfur studied moreover data suggest a coupling of bacterial sulfate reduction sulfide oxidation and sulfur disproportionation in addition 34s values for barite between 25 0 and 63 6 are also in agreement with high microbial turnover of sulfate at palinuro although a magmatic so2 contribution towards the formation of the palinuro massive sulfide complex is very likely the activity of different sulfur utilizing microorganisms played a fundamental role during its formation thus porewater and multiple sulfur isotope data reveal differences in the hydrothermal activity at palinuro and panarea drill sites and underline the importance of microbial communities for the origin of massive sulfide mineralizations in the hydrothermal subsurface

discovery of abundant hydrothermal venting on the ultraslow spreading gakkel ridge in the arctic ocean submarine hydrothermal venting along mid ocean ridges is an important contributor to ridge thermal structure and the global distribution of such vents has implications for heat and mass fluxes from the earth s crust and mantle and for the biogeography of vent endemic organisms previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow spreading ridges ridges with full spreading rates 2 cm yr 1 which make up 25 per cent of the global ridge length and that such vent systems would be hosted in ultramafic in addition to volcanic rocks here we present evidence for active hydrothermal venting on the gakkel ridge which is the slowest spreading 0 6 1 3 cm yr 1 and least explored mid ocean ridge on the basis of water column profiles of light scattering temperature and manganese concentration along 1 100 km of the rift valley we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites our discovery of such abundant venting and its apparent localization near volcanic centres requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow spreading ridges

opposing trends in crustal thickness and spreading rate along the back arc eastern lau spreading center implications for controls on ridge morphology faulting and hydrothermal activity abstract along back arc ridges located near the arc volcanic front crustal thickness is observed to vary systematically with arc proximity independent of spreading rate this effect is especially well expressed by the 400 km long eastern lau spreading center elsc where approaching the arc volcanic front from 100 to 40 km crustal thickness nearly doubles 5 5 9 km as spreading rates decrease by more than half 97 39 mm yr the crustal thickness variations at the elsc appear to result primarily from changes in mantle wedge composition caused by subduction we investigated the effects of these large and opposed crustal thickness and spreading rate variations on ridge morphology faulting and hydrothermal activity as part of the first phase of ridge2000 integrated studies in the lau back arc basin we used deep towed side scan sonar instruments dsl120a and imi30 to continuously map the near axis region within broader coverage ship multibeam bathymetry and acoustic imagery swaths an array of optical sensors maprs concurrently surveyed the near bottom water for hydrothermal plume anomalies hydrocasts made at identified plume sites confirmed their hydrothermal origin the data show that as spreading rates increase and crustal thicknesses decrease along the elsc 1 morphology transitions from shallow peaked volcanic highs to a deeper flat axis 2 faults become larger and more widely spaced 3 hydrothermal activity as measured by plume incidence increases and appears to reach levels higher than the global mid ocean ridge trend with spreading rate the observations indicate that crustal thickness magma supply has a greater control on ridge morphology and faulting than spreading rate even at fast rates where the thermal lithosphere should be thin however heat input from mantle advection proportional to spreading rate perhaps in combination with increased fault permeability appears to have a greater control on hydrothermal activity than crustal thickness and the magmatic robustness of the ridge although subduction effects give rise to the opposed trends in crustal thickness and spreading rate at the elsc the observed effects may have generic implications for controls of seafloor spreading characteristics at mid ocean ridges

hydrothermal plumes along segments of contrasting magmatic influence 15 20 18 30 n east pacific rise influence of axial faulting 1 vertical profiles of light backscattering and temperature recorded on 133 rock cores and dredge hauls between the orozco and rivera transform faults on the east pacific rise epr 15 20 18 30 n provide an opportunity to compare the hydrothermal environment of three adjacent but distinctly different segments that span the maximum range of axial cross section at a relatively constant spreading rate contrary to predictions based on data from other pacific ridges hydrothermal plumes over the inflated 16 n segment were less extensive and weaker than along the narrower rifted 17 n segment remarkably the 17 n segment has a plume incidence equal to the mean of superfast spreading segments from the southern epr the data suggest that the local permeability environment in this region controls the expression of hydrothermal activity in the water column the 16 n segment which has little or no indication of faulting may have its hydrothermal activity presently suppressed by widespread volcanic flows that act as an impermeable cap over much of the segment activity on the 17 n segment may be tectonically enhanced with hydrothermal fluids circulating through deep faults to a cracking front within each segment intense hydrothermal plumes characteristic of focused discharge seem associated with clearly rifted areas while weaker water column signals characteristic of diffuse discharge are associated with unrifted portions of the ridge axis that appear dominated by magmatism previous studies at intermediate to superfast spreading ridges have emphasized a positive correlation between local magmatic budget and hydrothermal activity our data suggest however that even at fast rates local tectonics can control the extent and nature of hydrothermal activity as documented for several sites on the slow spreading mid atlantic ridge despite the segment scale incongruity between hydrothermal activity and magmatic budget the fraction of total ridge length between 15 20 and 18 30 n overlain by plumes 0 39 follows the existing global correlation between plume incidence and spreading rate

ammonium loss and nitrogen isotopic fractionation in biotite as a function of metamorphic grade in metapelites from western maine usa abstract ammonium fixed in micas of metamorphic rocks is a sensitive indicator both of organic inorganic interactions during diagenesis as well as of the devolatilization history and fluid rock interaction during metamorphism in this study a collection of geochemically well characterized biotite separates from a series of graphite bearing paleozoic greenschist to upper amphibolite facies metapelites western maine usa were analyzed for ammonium nitrogen nh 4 n contents and isotopic composition 15nnh4 using the hf digestion distillation technique followed by the ea irms technique biotite separates sampled from 9 individual metamorphic zones contain 3000 to 100 ppm nh 4 n with a wide range in 15n from 1 6 to 9 1 average nh 4 n contents in biotite show a distinct decrease from about 2750 ppm for the lowest metamorphic grade 500 c down to 218 ppm for the highest metamorphic grade 685 c decreasing abundances in nh 4 are inversely correlated in a linear fashion with increasing k in biotite as a function of metamorphic grade and are interpreted as a devolatilization effect despite expected increasing 15nnh4 values in biotite with nitrogen loss a significant decrease from the garnet zones to the staurolite zones was found followed by an increase to the sillimanite zones this pattern for 15nnh4 values in biotite inversely correlates with mg mg fe ratios in biotite and is discussed in the framework of isotopic fractionation due to different exchange processes between nh 4 nh 3 or nh 4 n 2 reflecting devolatilization history and redox conditions during metamorphism

vailulu u seamount samoa life and death on an active submarine volcano submersible exploration of the samoan hotspot revealed a new 300 m tall volcanic cone named nafanua in the summit crater of vailulu u seamount nafanua grew from the 1 000 m deep crater floor in 4 years and could reach the sea surface within decades vents fill vailulu u crater with a thick suspension of particulates and apparently toxic fluids that mix with seawater entering from the crater breaches low temperature vents form fe oxide chimneys in many locations and up to 1 m thick layers of hydrothermal fe floc on nafanua high temperature 81 c hydrothermal vents in the northern moat 945 m water depth produce acidic fluids ph 2 7 with rising droplets of probably liquid co2 the nafanua summit vent area is inhabited by a thriving population of eels dysommina rugosa that feed on midwater shrimp probably concentrated by anticyclonic currents at the volcano summit and rim the moat and crater floor around the new volcano are littered with dead metazoans that apparently died from exposure to hydrothermal emissions acid tolerant polychaetes polynoidae live in this environment apparently feeding on bacteria from decaying fish carcasses vailulu u is an unpredictable and very active underwater volcano presenting a potential long term volcanic hazard although eels thrive in hydrothermal vents at the summit of nafanua venting elsewhere in the crater causes mass mortality paradoxically the same anticyclonic currents that deliver food to the eels may also concentrate a wide variety of nektonic animals in a death trap of toxic hydrothermal fluids

preface petrologic mineralogy the study of minerals in context a memorial in honor of charles v guidotti this special issue of the american mineralogist honors the memory and life s work of our friend colleague mentor and consummate teacher of mineralogy and petrology charles v guidotti 1935 2005 these papers were largely derived from a special topical session held in his honor at the 2006 annual meetings of the geological society of america the session provided an opportunity for mineralogists and petrologists inspired by charlie s example and teaching to present their latest research topics presented both orally and in posters included the crystal chemistry of a variety of minerals chemical composition of metamorphic and igneous rocks origin of unusual metasedimentary rock bulk compositions and their relation to the minerals composing them responses of mineral assemblages and compositions to variations in intensive variables such as pressure temperature and activities of fluid components and behavior of minerals and rocks during deformation in this special issue we present 17 papers that reflect some of the breadth presented at that meeting but represent only a part of charlie s interests across the spectrum of field geology mineralogy and metamorphic petrology charlie was born in somerville massachusetts but spent his childhood

near field variability of the tag non buoyant plume 26 n mid atlantic ridge we report the initial results of a nine hour monitoring of the non buoyant plume above the tag hydrothermal vent field at 26 n on the mid atlantic ridge a ctd conductivity temperature and pressure and nephelometer particle sensor were continuously raised and lowered through the non buoyant plume for nine hours at a site situated 100 m south of the hydrothermal mound this method permits a detailed record of the variability of the non buoyant plume close to the vent field to be made our results show that the particulate maximum of the non buoyant plume appears 150 m lower in the water column at the start and end of the record compared with profiles recorded towards the middle of the record a corresponding structure also appears in the temperature and salinity records with the result that the plume particle maximum resides on the 27 8035 isopycnal throughout modelling of the rise height of an axisymmetric plume can only account for 95 m of the variability in the final level of neutral buoyancy plume bending due to currents is a likely explanation for the recorded temporal variability

hydrothermal activity along the slow spreading lucky strike ridge segment mid atlantic ridge distribution heatflux and geological controls we have reviewed available visual information from the seafloor and recently acquired microbathymetry for several traverses across the lucky strike segment to evaluate the distribution of hydrothermal activity we have identified a new on axis site with diffuse flow ewan and an active vent structure similar to 1 2 km from the axis capelinhos these sites are minor relative to the main field and our total heatflux estimate for all active sites 200 1200 mw is only slightly higher than previously published estimates we also identify fossil sites w of the main lucky strike field a circular feature similar to 200 m in diameter located on the flanks of a rifted off axis central volcano is likely a large and inactive hydrothermal edifice named grunnus we find no indicator of focused hydrothermal activity elsewhere along the segment suggesting that the enhanced melt supply and the associated melt lenses required to form central volcanoes also sustain hydrothermal circulation to form and maintain large and long lived hydrothermal fields hydrothermal discharge to the seafloor occurs along fault traces suggesting focusing of hydrothermal circulation in the shallow crust along permeable fault zones

abundant hydrothermal venting along melt rich and melt free ridge segments in the lau back arc basin 1 the relationship between the spatial density of hydrothermal venting ph and spreading rate us is undefined along back arc ridges here we report a continuous survey of hydrothermal plumes along the 400 km long eastern lau spreading center the mean ph us ratio for each of three tectonic segments followed the global midocean ridge trend with ph doubling as us increased northward from 39 to 96 mm yr however we found little correlation between ph and the previously imaged distribution of axial melt lenses which are near continuous along the southern two segments but wholly absent along the northernmost segment we infer that venting on the southern segments is melt driven whereas venting on the northern elsc is entirely powered with heat extracted by deep circulation through hot rock this segment may be a rare example of an entire fast spreading segment where hydrothermal convection cells are powered by downward migrating cracking fronts

evidence for an extensive hydrothermal plume in the tonga fiji region of the south pacific 1 several hydrographic stations in the vicinity of the samoa islands have 3he 4he above the regional background in the depth range of 1500 1800 m indicating injection of mantle helium from a local hydrothermal source the highest 3he 43 4 was detected at 1726 m depth at 15 0 s 173 1 w in the bathymetric gap between the samoa islands and the northern end of the tonga kermadec arc the 3he profile at this station decreases to 3he 26 at 2500 m depth the relatively shallow depth of the maximum hydrothermal signal suggests a source different from the conventional pacific basin helium plume centered at 2500 m that is carried westward from the east pacific rise stations to the west of this locality show a progressive decrease in the maximum 3he values in the depth range of 1480 1790 m out to 169 e stations east of the tonga fiji region show lower 3he values 26 at 1700 m and the profiles are dominated by a deeper maximum at 2500 m presumably the distal traces of hydrothermal input from east pacific rise this pattern in the 3he distribution suggests that the 1700 m deep helium plume is carried in a northwesterly direction some 2000 km from its source near the northern end of the tonga kermadec arc at this time very little is known about the source of this hydrothermal plume or the details of its areal extent numerous seamounts and rift zones in the region are possible hydrothermal sources for the plume the summit crater of vailulu u a young seamount at the eastern end of the samoa chain was recently discovered to be hydrothermally active at 600 m depth hart et al 2000 however this shallow hydrothermal field on vailulu u is an unlikely source for the deeper 1700 m signal the most likely source would appear to be the extensional zones of the northern lau basin system such as the mangatolo triple junction just as the helium plume emanating from lo ihi has helped our understanding of the circulation near the hawaiian islands lupton 1996 this helium plume in the tonga fiji region has great potential for delineating circulation in this area of the south pacific

iron ii distribution and oxidation kinetics in hydrothermal plumes at the kairei and edmond vent sites indian ocean deep sea hydrothermal activity cycles the entire volume of the global ocean through deep sea hydrothermal plumes at least every 4 8 103 a a rapid timescale that is comparable to global deep ocean mixing an important process within hydrothermal plumes is the oxidation of dissolved iron discharged with vent fluids leading to the co precipitation of many other vent sourced metals thus modifying gross hydrothermal fluxes to the deep ocean and acting as a net sink in the ocean chemical budgets of certain key tracers here we report direct measurements of dissolved fe ii oxidation rates from two recently discovered indian ocean vent sites that are intermediate between pacific and atlantic values thus demonstrating that the rate of iron oxidation and formation of scavenging fe iii solid phases in hydrothermal plumes varies systematically along the global deep ocean conveyor the average pseudo first order rate constant for the oxidation reaction is 0 303 h 1 and the corresponding half life 2 31 h the rate plots show some curvature however indicating additional processes possibly interactions with organic matter may also influence the net oxidation removal rate different rates of oxidation of iron in hydrothermal plumes in different ocean basins have important implications for the dispersion of produced oxide phases which in turn may impact on uptake of other metals from seawater and deposition into underlying ridge crest and ridge flank sediments

hydrothermal activity on the eastern swir 50 70 e evidence from core top geochemistry 1887 and 1998 evidence for hydrothermal activity on the eastern swir has been reported previously in the form of optical backscatter anomalies interpreted to indicate the presence of hydrothermal plumes here i report on a brief reconnaissance analysis of the geochemical composition of core top samples collected from sites both beneath and away from those previously reported plume signals to determine whether evidence for fall out of hydrothermal plume material is discernible samples used for this study were collected using the deep diving submersible shinkai 6500 in 1998 and from the tallow coatings applied to lead sounding lines 111 years earlier aboard hms egeria the data indicate hydrothermal input to all but one of eight shinkai 6500 cores along the length of the eastern swir rift valley including the site of strongest previously reported plume anomalies comparison with a recent mar study suggests that the cores analyzed here however may predominantly lie distant from any current or recently active source of venting

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

direct determination of large scale magnetospheric field aligned currents with superdarn the superdarn super dual a uroral radar network radars measure large scale 2d images of the plasma convection velocity v in the high latitude f region from the 2d convection maps plasma flow vorticity can be directly calculated we show that the vorticity is a direct measure of jm p the magnetospheric component jm of the field aligned current fac per unit height integrated pedersen conductivity v the maps of jm p show clearly the region 0 1 and 2 currents uncontaminated by the ionospheric fac component ji caused by ionospheric pedersen and hall conductivity gradients which are important in the nightside substorm sector the generation of the large scale magnetospheric fac images of jm gp from the superdarn convection vorticity is explained and examples of dayside fac patterns for northward and southward imf conditions are presented for the superdarn radar pair in canada at saskatoon and kapus kasing by summer 1995 fac images will be available from three northern hemisphere superdarn radar pairs with a field of view extending over some 12 hours mlt from western canada to scandinavia and from one antarctic radar pair

pseudomorphs and associated microstructures of western maine usa abstract in metapelitic rocks of western maine a pluton related m3 metamorphic gradient ranging in grade from garnet to upper sillimanite zone was superposed on a fairly uniform m2 regional metamorphic terrain characterized by the assemblage andalusite staurolite biotite garnet as a result m2 assemblages re equilibrated to the p t and ah2o conditions of m3 and both prograde and retrograde pseudomorphism of m2 porphyroblasts occurred the type of pseudomorph and degree of development is directly related to the rock s position within the m3 metamorphic gradient a function of its proximity to the mooselookmeguntic pluton several hinge zones occur in which the m3 minerals that pseudomorphed a particular m2 phase change for example m2 garnet was replaced by m3 chlorite or biotite depending on its position within the m3 gradient similarly in a transition zone between m3 upper staurolite and lower sillimanite zones m2 staurolite was stable and shows m3 growth rims downgrade from this transition zone staurolite was pseudomorphed by chlorite and muscovite whereas upgrade the pseudomorphs contain muscovite and some biotite m3 pseudomorphs commonly retain crystal shapes of the original m2 porphyroblasts reflecting relatively low regional deviatoric stress during and after m3 although evidence for textural disequilibrium is common chemical equilibrium was closely approached during m3 this study demonstrates for m3 that 1 the pseudomorphic replacement was a constant volume process and 2 fabrics produced by tectonic events can be erased by subsequent deformation and or sufficiently intense subsequent recrystallization

exploring the ocean for hydrothermal venting new techniques new discoveries new insights abstract enumerating active hydrothermal fields on the seafloor has been a challenge since their discovery almost 40 years ago high temperature hydrothermal fields are readily discoverable primarily by detecting mineral laden plumes but low temperature particle poor vent fields resist discovery decades of exploration for vent fields have covered though often cursorily about one third of the global lengths of both oceanic spreading ridges osrs and volcanic arcs identifying some 630 active vent fields about 80 of these fields are on osrs and the spatial frequency of those fields is currently estimated as 0 5 5 100 km generally increasing with spreading rate over the last decade however a few detailed surveys have added sensors capable of detecting ephemeral chemical tracers oxidation reduction potential in addition to standard sensors that detect quasi conservative optical tracers such as light backscattering this approach has revealed a new view of the distribution of venting fields along fast spreading 55 mm yr osrs studies of four such ridge sections totaling 1470 km length suggest that the present inventory of vent fields may underestimate the true global population of vent fields on fast spreading osrs by a factor of 3 6 this increase implies that ridge axes are unexpectedly leaky reservoirs from which hydrothermal fluids escape at far more sites than presently assumed that the supply of dissolved hydrothermal iron which may be fertilizing the primary production of the southern ocean is higher than now calculated and that present estimates of recoverable sulfide tonnage from ridge axes may be too low along slow spreading ridges which account for 60 of the global osr length and 86 of known sulfide tonnage expansive axial valleys present special exploration challenges that will not be easily overcome

newly identified segments of the pacific australia plate boundary along the north fiji transform zone abstract the north fiji transform zone a 1500 km long and 200 km wide transform segment of the pacific australia plate boundary is one of the major transform fault systems of the earth new data collected during the alaufi cruise march 2000 on board the r v l atalante make it possible to define more accurately the geometry and kinematics of this transform plate boundary three spreading centers or extensional zones the north cikobia spreading center the futuna spreading center and the southeast futuna volcanic zone and a strike slip fault zone the futuna transform fault have been discovered over a distance of 500 km along the eastern north fiji transform zone from the north of the fiji platform to the east of the futuna archipelago the futuna transform fault oriented 100 has been mapped over a distance of 250 km it must be considered to be an important tectonic element of the transform plate boundary pure strike slip as well as transpression and transtension motions are responsible for the complex morphology of this feature the uplifted futuna alofi ridge represents a major compressional relay along the futuna transform fault the futuna spreading center trending 20 30 is composed of a series of en echelon left stepping spreading segments it represents a 200 km long extensional relay between the futuna transform fault and the western part of the north fiji transform zone the fiji transform fault which bounds the fiji platform to the north the opening rate at the futuna spreading center is estimated at 4 cm yr although the north cikobia spreading center and the southeast futuna volcanic zone have been only partly mapped bathymetric and reflectivity data clearly reveal that active extension also takes place along these two features a spreading rate of 2 cm yr is inferred at the north cikobia spreading center therefore the north fiji transform zone appears to be composed of two main overlapping transform segments relayed by parallel extensional zones the three active extensional zones have an ene wsw to nne ssw orientation while compressive features along the futuna transform fault are nw se to nnw sse oriented in accordance with the present day left lateral transform motion along this part of the pacific australia plate boundary

hydrothermal activity in the lau back arc basin sulfides and water chemistry the submersible nautile completed 22 dives during the nautilau cruise r v nadir april 17 may 10 1989 for a detailed investigation of the southern lau basin near tonga the objective of the scientific team from france germany and tonga was to understand the process of sea floor ore formation associated with hydrothermal circulation along the valu fa back arc ridge behind the tonga kermadec trench the four diving areas between lat 21 25 s and 22 40 s in water 2000 m deep were selected on the basis of results from cruises of the r v jeancharcot and r v sonne the nadir cruise provided proof of hydrothermal activity in all four areas over more than 100 km as indicated by the widespread occurrence of hydrothermal deposits and by heat flow conductivity and temperature measurements near the sea bottom the most spectacular findings were high temperature white and black smokers and associated fauna and ore deposits hydrothermal water chemistry and sulfide composition data presented here indicate that this hydrothermal field is very different from the hydrothermal fields in oceanic ridges this difference is seen in the water chemistry of the hydrothermal fluid ph 2 and high metal content and the chemical composition of sulfides enrichment in ba as and pb

a major helium 3 source at 15 s on the east pacific rise an extensive plume of water enriched with helium 3 has been discovered in the deep pacific ocean at latitude 15 s on the east pacific rise in the core of the plume at a depth of 2500 meters over the ridge crest the helium 3 helium 4 ratio is 50 percent higher than the ratio in atmospheric helium indicating a strong injection of mantle or primordial helium at the spreading center axis through local hydrothermal systems the helium 3 plume is completely absent east of the rise but it can be traced over 2000 kilometers to the west above a newly observed physical feature a density discontinuity here caled the ridge crest front the injected plume provides a unique deep sea tracer with an asymmetric distribution which shows that the deep circulation across the rise is from east to west the striking intensity and lateral extent of this helium 3 anomaly compared to observations at known oceanic hydrohrmal sites suggest that the largest hydrothermal fields in the ocean are yet to be discovered and that they will be found near 15 s on the east pacific rise

empirical high latitude electric field models electric field measurements from the dynamics explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn dusk ogo 6 measurements j p heppner 1977 the analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones paralleling the previous analysis the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the y component of the interplanetary magnetic field the objective which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns is met by deriving one pattern model bc for the northern hemisphere with a y interplanetary magnetic field imf and southern hemisphere with a y imf and two patterns models a and de for the northern hemisphere with a y imf and southern hemisphere with a y imf the most significant large scale revisions of the ogo 6 models are 1 on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the imf y component 2 on the nightside where a westward flow region poleward from the harang discontinuity appears under model bc conditions and 3 magnetic local time shifts in the positions of the convection cell foci the modeling above was followed by a detailed examination of cases where the imf z component was clearly positive northward neglecting the seasonally dependent cases where irregularities obscure pattern recognition the observations range from reasonable agreement with the new bc and de models to cases where different characteristics appeared primarily at dayside high latitudes the analysis of these differences for strong bz conditions using passes through different mlt zones led to finding that the deviations from both the bc and de models could be modeled by extending the evening cell foci toward and beyond noon with a deformation that roughly resembles a rotational twist of the extended evening cell the morning cell accommodation to the model bc deformation produces a narrow tongue of eastward convection near 75 invariant latitude on the dayside the model de deformation compresses the morning cell toward the night hours such that the sunward convection in the morning cell is diverted to polar latitudes in the 0400 to 0700 mlt sector in both cases the deformations of the two cell patterns lead to sunward convection in dayside polar regions while maintaining the integrity of the nightside convection pattern thus the nightside dilemmas that plague three and four cell models designed to explain sunward convection in polar regions under bz conditions do not appear

dayside ionospheric plasma convection electric fields and field aligned currents derived from the superdarn radar observations and predicted by the izmem model a recent deployment of the super dual auroral radar network superdarn hf radar network provides excellent opportunities to construct two dimensional maps of the ionospheric convection over large areas in both the northern and southern polar regions the institute of terrestrial magnetism ionosphere and radiowave propagation electrodynamic model izmem is a potentially useful tool for predicting also on a global scale the ionospheric plasma convection patterns electric fields magnetic disturbances ionospheric and field aligned currents comparisons of the izmem predictions with satellite and incoherent scatter radar data show that the model s performance is reasonably good but the model needs more extensive and accurate verifications in this paper several events under relatively stable imf conditions bz 0 are studied and discussed the superdarn izmem ion drift velocities are found to be in reasonable agreement in both magnitude and direction the average difference over the individual superdarn convection map between the predicted magnitude of the ion drift velocity and the measured magnitude is about 50 while the difference in the direction is typically less than 25 the izmem predictions of the location direction and magnitude of field aligned currents also agree well with the superdarn observations it is concluded that simultaneous use of superdarn data and izmem model can improve the specification of the polar ionospheric convection for space weather applications