intra oceanic subduction related hydrothermal venting kermadec volcanic arc new zealand intra oceanic volcanic arcs mark the boundaries between converging lithospheric plates where subduction produces volcanic and tectonic activity that ensures a steady supply of magmatic heat and hydrothermal fluids to the seafloor here we report on the first broad and systematic survey of hydrothermal emissions generated along a submarine arc front more than half seven of 13 of the volcanoes surveyed along 260 km of the southern kermadec arc ne of new zealand are hydrothermally active our results indicate that volcanic arcs represent a previously unheeded but potentially extensive source of shallow 2 km water depth vent fields expelling fluids of a unique and heterogeneous composition into the oceans

regional metamorphism in transform zones during supercontinent breakup late proterozoic events of the scottish highlands a new model for regional metamorphism within major strike slip zones is presented that may be applicable to the generation of many small metamorphic terranes long lived transform zones developed during continental break up are prone to alternating local compression and extension periodic closure of pull apart basins formed within such zones causes internal thickening of the sediment pile and formation of small low or medium grade metamorphic terranes with well defined frequently reactivated margins the late proterozoic dalradian and moine blocks of the scottish highlands are examples of such regional metamorphic terranes generated during the prolonged breakup of the rodinia supercontinent

tonian cryogenian boundary sections of argyll scotland abstract the tonian cryogenian system boundary is to be defined at a gssp global boundary stratigraphic section and point beneath the first evidence of widespread glaciation a candidate lies within the dalradian supergroup of scotland and ireland which is least deformed and metamorphosed in argyll western scotland we present new stratigraphic profiles and interpretations from the isle of islay and the garvellach islands update the chemostratigraphy of the appin group tonian carbonates underlying the thick ca 1 km glacigenic port askaig formation paf and demonstrate an environmental transition at the contact the appin group forms a regionally extensive 4 km thick succession of limestones shales and sandstones deposited on a marine shelf on islay the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure oolite stromatolitic dolomite and intraclastic microbial mounds significantly deeper erosion at the unconformity at the base of the overlying paf is demonstrated in the southern section carbonate facies show a gradual decline in 13 c vpdb from 5 to 2 upwards in ne garbh eileach garvellach islands a continuously exposed section of appin group carbonates 70 m thick here designated the garbh eileach formation gef lies conformably beneath the paf the gef and the gef paf boundary relationships are re described with new sedimentological logs petrological and stable isotope data interstratified limestone and dolomicrosparite with 13 c of 4 to 7 a feature named the garvellach anomaly replacing the term islay anomaly are overlain by dolomite in which the isotope signature becomes weakly positive up to 1 upwards shallow subtidal conditions become peritidal upwards with evidence of wave and storm activity gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the gef the basal diamictite d1 of the paf is rich in carbonate clasts similar to slightly deeper water parts of the underlying succession d1 is typically several metres thick with interstratified sandstone and conglomerate but dies out laterally scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft sediment deformation is interbedded with carbonate below and above d1 dolomite beds with derived intraclasts and gypsum pseudomorphs are found above d1 or equivalent position where d1 is absent published and new sr isotope studies including successive leach data demonstrate primary tonian 87 sr 86 sr values of 0 7066 0 7069 on islay decreasing to 0 7064 0 7066 in the younger gef limestones on the garvellachs with 1700 2700 ppm sr other typically tonian characteristics of the carbonates are the sr rich nature of limestones molar tooth structure and dolomitized peritidal facies with evidence of aridity seabed surveys suggesting uniformly dipping strata and shallow borehole core material illustrate the potential for extending the tonian record offshore of the garvellachs a candidate tonian cryogenian gssp is proposed on garbh eileach within the smooth 13 c profile at the cross over to positive 13 c signatures 4 m below the first occurrence of ice rafted sediment and 9 m below the first diamictite although lacking radiometric constraints or stratigraphically significant biotas or biomarkers the scottish succession has a thick and relatively complete sedimentary record of glaciation coherent carbon and strontium chemostratigraphy lateral continuity of outcrops and 100 exposure at the proposed boundary interval

a review and synthesis of glendonites pseudomorphs after ikaite with new data assessing applicability as recorders of ancient coldwater conditions abstract calcite pseudomorphs after ikaite glendonite are associated with coldwater depositional systems including glaciomarine and deepwater settings as dictated by the limited stability field of ikaite ikaite precipitation is favored by elevated alkalinity and dissolved phosphate conditions encountered commonly in association with organic rich marine sediments where methane oxidation is occurring the rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss producing a highly porous crystal mesh preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures during later burial diagenesis remaining pore space may be filled with deeper burial calcite cement glendonites from the permian of the sydney basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater carbon signatures are usually strongly negative relative to normal marine carbonate consistent with derivation of carbonate from methane oxidation review of published data suggests that while holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of primary depositional conditions bulk glendonite samples from the permian sydney basin australia have a broad range of 18 o and 13c 18opdb 5 to 15 13c 8 to 16 in contrast to the narrow range for brachiopod carbonate 18opdb 1 to 5 13c 5 to 7 from the same strata handpicked separates of primary glendonite and secondary calcite also have a wide range of stable isotope values the data from sydney basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of primary ikaite replacement calcite at the scale of micosampling done in this study

submarine hydrothermal activity along the mid kermadec arc new zealand large scale effects on venting 1 the 2 500 km kermadec tonga arc is the longest submarine arc on the planet here we report on the second of a series of cruises designed to investigate large scale controls on active hydrothermal venting on this arc the 2002 nzaplume ii cruise surveyed 12 submarine volcanic centers along 580 km of the middle kermadec arc mka extending a 1999 cruise that surveyed 260 km of the southern kermadec arc ska average spacing between volcanic centers increases northward from 30 km on backarc crust along the ska to 45 km on backarc crust along the southern mka to 58 km where the mka joins the kermadec ridge volcanic cones dominate in the backarc and calderas dominate the kermadec ridge the incidence of venting is higher along the mka 83 10 of 12 volcanic centers than the ska 67 8 of 12 but the relative intensity of venting as given by plume thickness areal extent and concentration of dissolved gases and ionic species is generally weaker in the mka this pattern may reflect subduction of the 17 km thick oceanic hikurangi plateau beneath the ska subduction of this basaltic mass should greatly increase fluid loss from the downgoing slab initiating extensive melting in the upper mantle wedge and invigorating the hydrothermal systems of the ska conversely volcanic centers in the southern mka are starved of magma replenishment and so their hydrothermal systems are waning farther north where the mka centers merge with the kermadec ridge fewer but larger magma bodies accumulate in the thicker older crust ensuring more widely separated caldera dominated volcanic centers

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

ikaite pseudomorphs in neoproterozoic dalradian slates record earth s coldest metamorphism calcite pseudomorphs have replaced euhedral ikaite caco 3 6h 2 o porphyroblasts in dalradian calcareous slates and metadolostones of western scotland with a volume decrease of at least 47 porphyroblast fabric relationships indicate that the initial growth of ikaite post dates a penetrative tectonic fabric developed during upright folding this is the first reported occurrence of metamorphic ikaite porphyroblasts and points towards growth within the slates during an ultra low temperature metamorphism with an exceptionally low geothermal gradient this event is associated with the penetration of long lived and extreme permafrost deep into subaerially exposed bedrock during neoproterozoic glaciation the presence of the well preserved pseudomorphs within the easdale slates of the argyll group implies that a neoproterozoic orogenic unconformity exists above the stratigraphic position of these rocks

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

evidence of sub vent biosphere enzymatic activities in 308 c deep sea hydrothermal systems at suiyo seamount izu bonin arc western pacific ocean abstract a high temperature deep sea hydrothermal system related to dacitic arc volcanism was drilled using a tethered submarine rock drill system as a part of the archaean park project the benthic multi coring system bms employed allowed for direct sampling of microorganisms rocks and fluids beneath hydrothermal vents the samples examined in this study were from sites apsk 05 and apsk 07 on the suiyo seamount of the izu bonin arc in the pacific ocean based on the vertical distribution of samples derived from this vigorous sub vent environment a model of deep sea subterranean chemistry and biology was determined detailing optimal microbial activities deep sea hydrothermal sub vent core samples of dacitic arc volcanism obtained at the suiyo seamount izu bonin arc western pacific ocean were analyzed for acid and alkaline phosphatase enzymatic activities useful biomarkers of acid phosphatase acp and alkaline phosphatase alp enzymatic activities were positively correlated against each other and was greatest at the partial middle core sequences acp and alp activities determined were as high as 5 10 and 6 80 nmol min g rock respectively biochemical indicators of acp and alp were consistent with the origin of biogenic amino acids occupied in the sub vent region and microbial cell number in the fluid the significant enzymatic activities demonstrated in this study provides crucial evidence that sub vent regions represent part of the previously unknown extreme environment biosphere extending the known subterranean habitable spaces of for example extremophilic microbes this boring trial was first example of discharging high temperature hydrothermal activities at the frontal arc volcanoes

collapse and reconstruction of monowai submarine volcano kermadec arc 1998 2004 monowai submarine volcano is one of the three most historically active volcanoes of the kermadec arc repeat multibeam surveys of monowai cone from september 1998 and september 2004 and t wave data recorded by the reseau sismique polynesien network for the same period document the collapse and subsequent regrowth of the cone within this 6 a period grid differencing of the two bathymetric data sets acquired 6 a apart reveals that a landslide 2230 m long occurred between the surveys within which a postcollapse cone and talus ridge 0 023 km3 in volume subsequently formed the volume of this collapse minus postcollapse construction is 0 085 km3 we interpret an unusual strong amplitude t wave event on 24 may 2002 as recording hot landsliding where the 100 to 160 m thick collapse has unroofed the uppermost parts of the vent conduit with the subsequent explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater this interpretation is consistent with the lack of emergent events sharp onset and large amplitude of the 24 may 2002 t waves the subsequent 2500 t wave events between november 2002 and september 2004 occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures which are interpreted as recording the regrowth of an 90 m high cone back to a near 1998 elevation at an average rate of 47 m a 1 this study provides 1 a lower bound for frequency magnitude relationships of landsliding for submarine arc volcanoes and 2 estimates of 0 013 km3 a 1 of submarine cone growth during eruptive cycles

a kuroko type polymetallic sulfide deposit in a submarine silicic caldera manned submersible studies have delineated a large and actively growing kuroko type volcanogenic massive sulfide deposit 400 kilometers south of tokyo in myojin knoll submarine caldera the sulfide body is located on the caldera floor at a depth of 1210 to 1360 meters has an area of 400 by 400 by 30 meters and is notably rich in gold and silver the discovery of a large kuroko type polymetallic sulfide deposit in this arc front caldera raises the possibility that the numerous unexplored submarine silicic calderas elsewhere might have similar deposits

transformation kinetics of polycrystalline aragonite to calcite new experimental data modelling and implications experimental data are used to model the transformation rate of polycrystalline aragonite grain diameter 80 m to calcite optimized values for nucleation and growth rates were obtained by numerically fitting the overall transformation rates from 280 to 380 c and 0 10 mpa to an expression for a grain boundary nucleated and interface controlled transformation the nucleation rate is 4 5 orders of magnitude faster than for calcite nucleated within aragonite grains and the growing in rate is slower below 300 c than for calcite growing in aragonite single crystals the activation enthalpy for growth in polycrystalline aggregate is 247kj mol compared to 163 kj mol for growth in single crystals permanent deformation of the phases limits the elastic strain energy due to the 7 volume change and reduces the coherency of the calcite aragonite interace theoretical expressions are used to extrapolate the data for nucleation and growth to other temperatures and data from 0 10 to 400 mpa are used to evaluate the effect of pressure on the grain boundary nucleation rate because of permanent deformation of the phases the effective strain energy for nucleation is 0 55 kj mol which is less than a quarter of the value for purely elastic deformation these data are used to predict the percent transformation for various p t t paths without heating during uplift partial preservation of aragonite in dry blueschist facies rocks can occur if the calcite stability field is entered at 235 c and the kinetic data are also consistent with published p t t paths which include heating during uplift the predicted percent transformation is relatively insensitive to variations in the initial grain size of the aragonite but strongly dependent on the effective strain energy

chemical and textural equilibration of garnet during amphibolite facies metamorphism the influence of coupled dissolution reprecipitation metamorphic equilibration requires chemical communication between minerals and may be inhibited through sluggish volume diffusion and or slow rates of dissolution in a fluid phase relatively slow diffusion and the perceived robust nature of chemical growth zoning may preclude garnet porphyroblasts from readily participating in low temperature amphibolite facies metamorphic reactions garnet is widely assumed to be a reactant in staurolite isograd reactions and the evidence for this has been assessed in the late proterozoic dalradian pelitic schists of the scottish highlands the 3d imaging of garnet porphyroblasts in staurolite bearing schists reveals a good crystal shape and little evidence of marginal dissolution however there is also lack of evidence for the involvement of either chlorite or chloritoid in the reaction staurolite forms directly adjacent to the garnet and its nucleation is strongly associated with deformation of the muscovite rich fabrics around the porphyroblasts cloudy fluid inclusion rich garnet forms in both marginal and internal parts of the garnet porphyroblast and is linked both to the production of staurolite and to the introduction of abundant quartz inclusions within the garnet such cloudy garnet typically has a mg rich mn poor composition and is interpreted to have formed during a coupled dissolution reprecipitation process triggered by a local influx of fluid all garnet in the muscovite bearing schists present in this area is potentially reactive irrespective of the garnet composition but very few of the schists contain staurolite the staurolite producing reaction appears to be substantially overstepped during the relatively high pressure barrovian regional metamorphism reflecting the limited permeability of the schists in peak metamorphic conditions fluid influx and hence reaction progress appear to be strongly controlled by subtle differences in deformation history the remaining garnet fails to achieve chemical equilibrium during the reaction creating distinctive patchy compositional zoning such zoning in metamorphic garnet created during coupled dissolution reprecipitation reactions may be difficult to recognize in higher grade pelites due to subsequent diffusive re equilibration fundamental assumptions about metamorphic processes are questioned by the lack of chemical equilibrium during this reaction and the restricted permeability of the regional metamorphic pelitic schists in addition the partial loss of prograde chemical and textural information from the garnet porphyroblasts cautions against their routine use as a reliable monitor of metamorphic history however the partial re equilibration of the porphyroblasts during coupled dissolution reprecipitation opens possibilities of mapping reaction progress in garnet as a means of assessing fluid access during peak metamorphic conditions

new evidence that the lower cambrian leny limestone at callander perthshire belongs to the dalradian supergroup and a reassessment of the exotic status of the highland border complex

metallogenesis and mineralization of intraoceanic arcs i kermadec arc introduction the kermadec intraoceanic arc marks the southernmost section of the pacific ring of fire in the western pacific region a chain of mostly underwater volcanoes that stretches from north of japan southward to new zealand the kermadec arc striking for 1 200 km from monowai volcano to the north island of new zealand represents the southern portion of the contiguous 2 500 km kermadec tonga arc fig 1 de ronde et al 2003 the kermadec arc is populated by almost 30 volcanic centers comprising single large caldera or cone volcanoes or less commonly groups of relatively smaller cones de ronde et al 2001 2007 graham et al 2008 all of these volcanic centers lie to the west of the kermadec ridge in the southern and mid parts of the arc by up to 70 km in the case of rumble ii west then merge with the kermadec ridge near the kermadec islands around 30 s the volcanoes then diverge away westward from the kermadec ridge in the northern reaches of the arc fig 1 fig 1 location map for the kermadec arc and the various volcanoes referred to in the papers of this special volume the kermadec arc havre trough system is made up from east to west of a number of tectonic elements including the kermadec trench the kermadec ridge the havre trough or kermadec back arc and the colville ridge the volcanoes of the active arc front lie immediately west of the kermadec ridge in the southern and mid parts of the arc then merge with the kermadec ridge to the north the underlying bathymetry in shaded relief is derived from the satellite altimetry grid of smith and sandwell 1997 with more up to date bathymetry over top especially in the southern

the partial equilibration of garnet porphyroblasts in pelitic schists and its control on prograde metamorphism glen roy scotland garnet porphyroblasts in sillimanite bearing pelitic schists contain complex textural and compositional zoning with considerable variation both within and between adjacent samples the sillimanite bearing schists locally occur in regional barrovian garnet zone assemblages and are indicative of a persistent lack of equilibrium during prograde metamorphism garnet in these dalradian rocks from the scottish highlands preserves evidence of a range of metamorphic responses including initial growth and patchy coupled dissolution reprecipitation followed by partial dissolution individual porphyroblasts each have a unique and variable response to prograde metamorphism and garnet with mainly flat compositional profiles co exists with those containing largely unmodified characteristic bell shaped mn profiles this highlights the need for caution in applying traditional interpretations of effective volume diffusion eliminating compositional variation cloudy garnet with abundant fluid inclusions is produced during incomplete modification of the initial porphyroblasts and these porous garnet are then particularly prone to partial replacement in sillimanite producing reactions the modification of garnet via a dissolution reprecipitation process releases ca into the effective whole rock composition displacing the pressure temperature positions of subsequent isograd reactions this represents the first report of internal metasomatism controlling reaction pathways the behaviour of garnet highlights the importance of kinetic factors especially deformation and fluids in controlling reaction progress and how the resulting variability influences subsequent prograde history the lack of a consistent metamorphic response within and between adjacent schists suggests that on both local and regional scales these rocks have largely not equilibrated at peak metamorphic conditions

eruption fed particle plumes and volcaniclastic deposits at a submarine volcano nw rota 1 mariana arc 1 nw rota 1 is an active submarine volcano in the mariana arc with a summit depth of 517 m and an explosively erupting volcanic vent southwest of the summit at a depth of 530 560 m during a period of ongoing explosive eruptions particle plumes surrounded the volcano and at least 3 3 107 m3 of volcaniclastic material was deposited on the southern flank particle plumes over the summit were magmatic hydrothermal in origin characterized by 3he enrichment hydrothermal precipitates and low ph values plumes at multiple depths below the summit surrounded the volcano and were composed overwhelmingly of fresh glassy shards of basalt rare anhydrite particles were present but there was a complete absence of other hydrothermal components in the deep plume samples these short lived anhydrite particles indicate the source of the deep plumes is from within or very near the eruptive vent and the mechanism for transport down the flanks of the volcano must be far faster than settling of individual particles the deep plumes most likely originated from sediment gravity flows generated by explosive eruptions or slope failure and landslides of unstable materials that had accumulated near the eruptive vent suspended sediments detach from the volcano slopes at multiple depths and are transported laterally up to tens of kilometers where they contribute to fall out deposits in distal sediments these observations link mechanisms for the transport of volcanic ash in the submarine environment to the types of deposits common in volcaniclastic aprons and fine ash layers in distal sediments

physical volcanology of the submarine mariana and volcano arcs narrow beam maps selected dredge samplings and surveys of the mariana and volcano arcs identify 42 submarine volcanos observed activity and sample characteristics indicate 22 of these to be active or dormant edifices in the volcano arc are larger than most of the mariana arc edifices more irregularly shaped with numerous subsidiary cones and regularly spaced at 50 70 km volcanos in the mariana arc tend to be simple cones sets of individual cones and volcanic ridges are elongate parallel to the trend of the arc or at 110 counterclockwise from that trend suggesting a strong fault control on the distribution of arc magmas volcanos in the mariana arc are generally developed west of the frontal arc ridge on rifted frontal arc crust or new back arc basin crust volcanos in the central mariana arc are usually subaerial large 500 km3 and spaced about 50 70 km apart those in the northern and southern marianas are largely submarine closer together and generally less than 500 km3 in volume there is a shoaling of the arc basement around iwo jima accompanied by the appearance of incompatible element enriched lavas with alkalic affinities the larger volcanic edifices must reflect either a higher magma supply rate or a greater age for the larger volcanos if the magma supply estimated at 10 20 km3 km of arc per million years at 18 n has been relatively constant along the mariana arc we can infer a possible evolutionary sequence for arc volcanos from small irregularly spaced edifices to large over 1000 km3 edifices spaced at 50 70 km the volcano distribution and basal depths are consistent with the hypothesis of back arc propagation into the volcano arc

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

geothermal evidence of very low glacial temperatures on a rim of the fennoscandian ice sheet 1 the mean ground temperature as low as 10 c and the existence of more than 500 m thick permafrost during the last glacial are apparent from the analysis of deep borehole temperature profiles in north eastern poland the largest thickness of the permafrost and its survival deep into the holocene was restricted to a region known for its low terrestrial heat flow where the negative temperature gradient is observed in the uppermost 400 m we have shown that the profiles are consistent with warming from the glacial mean of 10 c to the holocene mean of 7 c 14 ka ago and to 8 c in the last 150 years

multiple hydrothermal sources along the south tonga arc and valu fa ridge 1 quantifying hydrothermal venting at the boundaries of tectonic plates is an outstanding geoscience problem considerable progress has been made by detailed surveys along mid ocean ridges mors but until recently little was known about fluid venting along volcanic arcs we present the first systematic survey for hydrothermal venting along the 425 km long south tonga arc and new chemistry data for particle and thermal plumes previously reported along an adjacent 88 km long section of the back arc valu fa ridge vfr eleven hydrothermal plumes recognized by their anomalous light backscattering eh temperature ph dissolved he 3 ch4 and total dissolvable fe and mn were identified arising from seven volcanic centers along the arc five plumes on the vfr were characterized chemically vent field density for the south tonga arc was 2 6 sites 100 km of arc front comparable to that found by surveys of the kermadec arc 1 9 to 3 8 sites 100 km and to mors in the eastern pacific average value for 2280 km of surveyed ridgecrest 3 2 sites 100 km a vent gap occurs along a 190 km section of the arc closest to the vfr and a site density twice the average for mors on the eastern edge of the pacific plate was found on this part of the vfr 6 6 sites 100 km we suggest magmas ascending under the adjacent south tonga arc have been captured by the vfr while chemical enrichments of plumes on the south tonga arc were in general slightly less than those on the kermadec arc several instances of excessive anomalies in ph suggest a similar presence of fluids enriched in magmatic volatiles co2 so2 h2s locally venting on the vfr has contributed to accumulations of 3 he fe and mn within the southern lau basin on a broader scale our results provide considerable support for the notion that venting from intraoceanic arcs on the convergent margin of the pacific plate adds significantly to the total hydrothermal input into the pacific ocean

venting of a separate co2 rich gas phase from submarine arc volcanoes examples from the mariana and tonga kermadec arcs submersible dives on 22 active submarine volcanoes on the mariana and tonga kermadec arcs have discovered systems on six of these volcanoes that in addition to discharging hot vent fluid are also venting a separate co2 rich phase either in the form of gas bubbles or liquid co2 droplets one of the most impressive is the champagne vent site on nw eifuku in the northern mariana arc which is discharging cold droplets of liquid co2 at an estimated rate of 23 mol co2 s about 0 1 of the global mid ocean ridge mor carbon flux three other mariana arc submarine volcanoes nw rota 1 nikko and daikoku and two volcanoes on the tonga kermadec arc giggenbach and volcano 1 also have vent fields discharging co2 rich gas bubbles the vent fluids at these volcanoes have very high co2 concentrations and elevated c 3he and 13c co2 ratios compared to mor systems indicating a contribution to the carbon flux from subducted marine carbonates and organic material analysis of the co2 concentrations shows that most of the fluids are undersaturated with co2 this deviation from equilibrium would not be expected for pressure release degassing of an ascending fluid saturated with co2 mechanisms to produce a separate co2 rich gas phase at the seafloor require direct injection of magmatic co2 rich gas the ascending co2 rich gas could then partially dissolve into seawater circulating within the volcano edifice without reaching equilibrium alternatively an ascending high temperature co2 rich aqueous fluid could boil to produce a co2 rich gas phase and a co2 depleted liquid these findings indicate that carbon fluxes from submarine arcs may be higher than previously estimated and that experiments to estimate carbon fluxes at submarine arc volcanoes are merited hydrothermal sites such as these with a separate gas phase are valuable natural laboratories for studying the effects of high co2 concentrations on marine ecosystems

diffuse flow hydrothermal manganese mineralization along the active mariana and southern izu bonin arc system western pacific 1 abundant ferromanganese oxides were collected along 1200 km of the active izu bonin mariana arc system chemical compositions and mineralogy show that samples were collected from two deposit types fe mn crusts of mixed hydrogenetic hydrothermal origin and hydrothermal mn oxide deposits this paper addresses only the second type mn oxides cement volcaniclastic and biogenic sandstone and breccia layers mn sandstone and form discrete dense stratabound layers along bedding planes and within beds stratabound mn the mn oxide was deposited within coarse grained sediments from diffuse flow systems where precipitation occurred below the seafloor deposits were exposed at the seabed by faulting mass wasting and erosion scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 a and 7 a manganate minerals the fundamental chemical difference being high water contents in the amorphous mn oxides alternation of amorphous and crystalline laminae occurs in many samples which likely resulted from initial rapid precipitation of amorphous mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages the chemical composition is characteristic of a hydrothermal origin including strong fractionation between fe mean 0 9 wt and mn mean 48 wt for the stratabound mn generally low trace metal contents and very low rare earth element and platinum group element contents however mo cd zn cu ni and co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits for the mn sandstones fe mean 8 4 and mn 12 4 are not significantly fractionated because of high fe contents in the volcaniclastic material however the proportion of hydrothermal fe nondetrital fe to total fe is remarkably constant 49 58 for all the sample groups regardless of the degree of mn mineralization factor analyses indicate various mixtures of two dominant components hydrothermal mn oxide for the stratabound mn and detrital aluminosilicate for the mn cemented sandstone and two minor components hydrothermal fe oxyhydroxide and biocarbonate biosilica our conceptual model shows that mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along the flanks and within calderas the main source of hydrothermal fluid was seawater that penetrated through fractures faults and permeable volcanic edifices the fluids were heated by magma enriched in metals by leaching of basement rocks and sediments and mixed with magmatic fluids and gases dikes and sills may have been another source of heat that drove small scale circulation within sedimentary prisms

evidence for a major neoproterozoic orogenic unconformity within the dalradian supergroup of nw ireland an intriguing and contradictory scenario has recently developed in the caledonides of the british isles concerning the ages of deposition and deformation of the neoproterozoic dalradian supergroup isotopic evidence although limited suggests that the lower parts of the sequence may have been deposited and undergone precambrian deformation i e pre 600 ma prior to deposition of the upper parts of the sequence i e post 600 ma given these existing constraints it is clear that a major break or breaks would be required in the intervening sequence to maintain a coherent tectonostratigraphy we present evidence for such an unconformity preserved at the base of the easdale subgroup in nw ireland reworked clasts that contain a pre existing tectonometamophic history are identified within a conglomerate that lies along this regionally recognized boundary the underlying sequence also exhibits pre existing deformational fabrics that display erosional truncation at the base of the conglomerates these relationships together with significant erosion and excision of the footwall sequence and extensive thickness and facies variations in the hanging wall units imply that a major tectonic unconformity exists within this succession as the conglomerate lies stratigraphically below precambrian c 600 ma lavas the structural fabrics contained within the clasts and the underlying sequence must also be of precambrian age and totally unrelated to the well established early palaeozoic caledonian orogenic deformation observed in the younger parts of the sequence the dalradian supergroup as defined may actually comprise at least two distinct tectonostratigraphic sequences

calcium carbonate hexahydrate from organic rich sediments of the antarctic shelf precursors of glendonites large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the bransfield strait antarctic peninsula at a water depth of 1950 meters and sub zero bottom water temperatures the chemistry mineralogy and stable isotope composition of this hydrated calcium carbonate phase its environment of formation and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation

mineralized microbes from giggenbach submarine volcano 1 the giggenbach submarine volcano which forms part of the kermadec active arc front is located 780 km nne of the north island of new zealand samples collected from chimneys associated with seafloor hydrothermal vents on this volcano at a depth of 160 180 m contain silicified microbes and microbes entombed in reticular fe rich precipitates the mineralized biota includes filamentous rod shaped and rare coccoid microbes in the absence of organic carbon for rdna analysis or preserved cells the taxonomic affinity of these microbes in terms of extant taxa remains questionable because of their architectural simplicity and the paucity of taxonomically significant features the three dimensional preservation of the microbes indicates rapid mineralization with a steady supply of supersaturated fluids to the nucleation sites present on the surfaces of the microbes the mineralization styles evident in the microbes from the giggenbach submarine volcano are similar to those associated with mineralized microbes found in terrestrial hot spring deposits in new zealand iceland yellowstone and kenya these similarities exist even though the microbes are probably different and the fluids become supersaturated with respect to opal a by different mechanisms for ancient rocks it means that interpretations of the depositional settings cannot be based solely on the silicified microbes or their style of silicification

structure and petrology of newly discovered volcanic centers in the northern kermadec southern tofua arc south pacific ocean 1 the nzaplume iii expedition of september october 2004 to the northern kermadec southern tofua nkst arc between 28 52 s and 25 07 s resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known monowai seamount the volcanic centers form a sublinear chain that coincides with the kermadec ridge crest in the south hinetapeka and diverges 45 km westward of the ridge crest in the north v just to the south of where the louisville ridge intersects with the arc all of the centers contain calderas or caldera like structures as well as multiple cones domes fissure ridges and vent fields all show signs of recent eruptive and current hydrothermal activity there are strong structural controls on edifice location with cones and fissure ridges typically associated with faulting parallel to the regional 12 strike of the arc front several of the calderas are ellipsoidal orientated northwest southeast in the general direction of least compressive stress sampled volcanic rocks representing the most recently erupted lavas are all low k tholeiites two of the centers gamble and rakahore yielded only high silica dacite to rhyolite 69 74 wt silica whereas two others monowai and v yielded only basalt to andesite 48 63 wt silica mineral assemblages are plagioclase pyroxene dominated with accessory fe ti oxides apatite olivine and quartz tridymite cristobalite typical of dry volcanic arc systems hornblende occurs only in a felsitic rhyolite from hinepuia volcanic center and zircon is absent glass contents range to 57 in basalts andesites mean 20 and 97 in andesites rhyolites mean 59 and other quench textures including swallow tailed plumose or dendritic crystal forms and crystallites are common most lavas are highly vesicular 63 mean 28 and have low volatile contents mostly 2 wt which together with the occurrence of tridymite or cristobalite indicates explosive eruption and rapid cooling exceptions are rocks from u volcanic center which have low vesicularity and low glass contents across a wide compositional range indicating effusive eruption disequilibrium mineral textures the frequent occurrence of xenoliths and xenocrysts and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids having resided only a short time in upper crustal reservoirs prior to eruption silicic magmas are major components of nkst arc volcanism and caldera formation is the dominant eruptive style the scale of silicic magmatism is in marked contrast to the dominant basaltic andesitic magmatism in the southern kermadec arc with evidence from other arcs silicic magmatism is now recognized as a major feature of intraoceanic arcs globally

detailed morphology and structure of an active submarine arc caldera brothers volcano kermadec arc a survey of the brothers caldera volcano kermadec arc with the autonomous underwater vehicle abe has revealed new details of the morphology and structure of this submarine frontal arc caldera and the geologic setting of its hydrothermal activity brothers volcano has formed between major sw netrending faults within the extensional field of the havre trough brothers may be unique among known submarine calderas in that it has four active hydrothermal systems two high temperature sulfide depositing sites associated with faulting on the northwestern and western walls i e the nw caldera and w caldera hydrothermal sites respectively and gas rich sites on the summits of the constructional cones that fill most of the southern part of the caldera i e the upper and lower cone sites the 3 0 3 4 km caldera is well defined by a topographic rim encompassing 320 of its circumference and which lies between the bounds of two outer half grabenshaped faults in the northwest and southeast sectors there is not a morphologically well defined continuous ring fault at the map resolution although near vertical scarps are present discontinuously at the base of sections of the wall the width of the wall varies from 200 m at its southwest portion to 750 m on its northern section the widest part of the wall is its northwest sector which also has the largest documented area of hydrothermal alteration and where sea floor magnetization is lowest in addition to primary northwest southeast elongation and southwest northeast structures caused by faulting within the regional back arc strain field there are also less well developed west southwestnorth northeast regional structures intersecting the volcano that is appar ent on the abe bathymetry and at outcrop scale from submersible observations asymmetrical trap doorstyle caldera collapse is considered a possible mechanism for the formation of the brothers caldera

chemical composition of hydrothermal fluids in the central and southern mariana trough backarc basin abstract we present a geochemical data set from hydrothermal fluids collected from the central and southern mariana trough during dive programs conducted in the 1990s the fluid samples were collected from two hydrothermal fields 1 the alice springs field 18 13 n 144 42 e water depth 3600 m on the axial ridge crest of the central marana trough and 2 the forecast field 13 24 n 143 55 e water depth 1470 m on peak b seamount one of a cluster of small volcanic seamounts which represents a unique tectonic setting in the southern mariana trough gas geochemistry of the alice springs fluid showed he and c isotope ratios in the range of morb whereas that of the forecast fluid showed a higher co 2 3 he ratio and 13 c enriched isotope ratio both of which are commonly recognized in hydrothermal fluids from intraoceanic arc volcanoes the major and minor element composition of the alice springs fluid is characterized by enrichment in mobile alkali elements such as k rb and cs this geochemical signature is in accordance with the well known characteristics of basaltic lava collected from the same area which show substantial enrichment in incompatible elements as interpreted in previous petrological studies this signature is considered to be an arc geochemical signal reflecting contribution from the subduction component the b concentration of the alice springs fluid is also high and is another arc geochemical signal the forecast fluid by contrast did not show enrichment in the mobile alkali elements although its b concentration is high the forecast fluid is characterized instead by enrichment in ca and sr coupled with depletion in na and li as discussed in previous studies this signature is attributed to hydrothermal reactions at rather low temperature due to the shallow water depth we recognize two different arc geochemical signals in these two hydrothermal fluids mobile alkali elements in the alice spring fluid and gaseous species in the forecast fluid this difference could reflect different behaviors of these species during magmatic processes in the mantle wedge beneath the mariana trough backarc spreading center

hydrothermal activity and volcano distribution along the mariana arc 1 submarine volcanic arcs extend for fully a third of the length of the mid ocean ridge system but systematic investigation of hydrothermal venting on those arcs is sparse here we report on the distribution of hydrothermal activity along the intraoceanic mariana arc we identify 76 volcanic edifices along 1370 km of arc grouped into 60 volcanic centers of which at least 26 20 submarine are hydrothermally or volcanically active the overall volcanic center density is 4 4 100 km of arc and that of active centers is 1 9 100 km an equal length of the tonga kermadec arc holds fewer centers 2 9 100 km but a similar density of active centers 1 8 100 km the lower percentage of active centers on the mariana arc results from its having both fewer caldera volcanoes since on both arcs calderas are twice as likely as cones to be active and a lower percentage of active calderas and cones active centers are found from 80 to 230 km above the subducting pacific slab and a quarter lie behind the arc front the frequency distribution of center spacing along the arc front peaks between 20 and 30 km and shows the asymmetric long tail shape typical for many other arcs especially those with volcano populations 20 there is no evidence for a regular spacing of volcanic centers using the new mariana data and recent data from the tonga kermadec arc we estimate that all intraoceanic arcs combined may contribute hydrothermal emissions equal to 10 of that from the global mid ocean ridge

fast tectonometamorphism and exhumation in the type area of the barrovian and buchan zones the beginning of the grampian episode of tectonometamorphism in scotland is dated by collision and obduction of the ballantrae ophiolite complex at 478 8 ma for the first time we have used zircon and garnet to radiometrically date the peak of the caledonian buchan and barrovian tectonometamorphism in their type areas as contemporaneous at 467 2 5 ma detrital garnet from the neighboring southern uplands flysch terrane has the same radiometric age and occurs in 465 2 5 ma molasse in the midland valley we show that the entire grampian episode lasted 15 2 5 m y and that it took fewer than 7 6 m y to expose high grade rocks following the peak of metamorphism those who study precambrian orogeny should note the brevity of this scottish tectonometamorphic episode and the speed of exhumation

unusual geochemistry of hydrothermal vents on submarine arc volcanoes kasuga seamounts northern mariana arc abstract dsrv alvin dives in the northern mariana island arc recovered warm hydrothermal fluids from the summit areas of seamounts kasuga 2 and kasuga 3 as well as hydrothermal deposits of elemental sulfur fe and mn oxides and nontronite the composition of a gas rich 39 c vent fluid sampled from kasuga 2 seamount is unusual compared to other submarine hydrothermal fluids in that it is enriched by 27 in mg 2 and 17 in so 4 2 and depleted by 64 in ca 2 relative to ambient seawater the elevated concentrations of dissolved co 2 calculated from ph and a t hco 3 and so 4 2 and near absence of h 2 s suggest that the unusual composition of this sample may result from the sub seafloor addition of volcanic co 2 and so 2 to a seawater derived hydrothermal fluid resulting in 1 chemical weathering reactions whereby igneous minerals or alteration phases are attacked by co 2 adding mg 2 and other cations si and hco 3 into solution and 2 hydrolysis of so 2 to so 4 2 and s 0 adding excess so 4 2 with a light 34 s signature to the fluid and causing deposition of elemental sulfur at the seafloor vents saturation state calculations suggest that the concentrations of si and ca 2 in the fluid may be controlled at saturation with amorphous silica and dolomite respectively the origin of the 9 3 c fluid collected from kasuga 3 is difficult to determine because it is compositionally close to ambient seawater and shows possible evidence of both high and low temperature seawater rock reaction banded and interlayered deposits of nontronite and fe and mn oxides were recovered from the kasuga 3 summit with oxygen isotope geothermometry suggesting a formation temperature of 22 c for the nontronite

a high precision u pb age for the ben vuirich granite implications for the evolution of the scottish dalradian supergroup high precision high accuracy u pb analyses of zircons from the ben vuirich granite in the scottish dalradian succession were performed on carefully picked high integrity abraded fractions of specific morphologies zircon needles which grew during crystallization give an age of 590 2 ma stubby prisms show inheritance with an upper concordia intercept of 1448 7 ma the age of intrusion at 590 ma contrasts strongly with a previous u pb zircon age of 514 6 7 ma determined on bulk fraction unabraded grains which it is argued must have suffered significant pb loss as the ben vuirich granite was emplaced between the regional d2 and d3 deformation events in the dalradian block the new data imply that all dalradian sedimentation was precambrian supposed lower cambrian fauna1 links between the dalradian succession and laurentia are thus discounted and the possibility that the dalradian supergroup has non laurentian affinities must be considered the early d1 d2 nappe forming grampian structures are also precambrian and may be associated with terrane docking along a tectonically active ocean margin later d3 structures and associated peak barrovian metamorphism suggest a subsequent thickening event possibly c 520 ma ago

neoproterozoic chemostratigraphy and correlation of the port askaig glaciation dalradian supergroup of scotland the 13 c of preglacial carbonates beneath the glaciogenic port askaig formation falls from 5 to negative values while least altered 87 sr 86 sr values are close to 0 7067 postglacial cap carbonates of the bonahaven formation begin with negative 13 c carb values jumping sharply to 11 7 near the top which we correlate with excursions above the elbobreen wilsonbreen glaciations of svalbard and putative sturtian not varanger glaciations elsewhere dated at c 720 ma much of the succeeding terminal neoproterozoic is missing in ne svalbard and east greenland raising doubts about their use for global sr and c isotope curves in the neoproterozoic

submarine volcanoes and high temperature hydrothermal venting on the tonga arc southwest pacific submarine hydrothermal vents and associated seafloor mineralization on the tonga arc have been found for the first time in the summit calderas of two shallow water volcanoes greatly extending the known areas and diversity of seafloor hydrothermal activity in the western pacific region the highest temperature vents 245 265 c occur at water depths of 385 540 m near the summit of one volcano at 24 s the vents are spatially related to basaltic dike swarms exposed at a summit cone and in the caldera walls clusters of large to 10 m high barite anhydrite and sulfide chimneys on the summit cone are vigorously discharging clear hydrothermal fluids with temperatures on the seawater boiling curve there is abundant evidence of phase separation which can be seen as flame like jets of steam h2o vapor at the chimney orifices pyrite marcasite sphalerite and chalcopyrite line the interiors of the highest temperature vents similar to black smoker chimneys on the mid ocean ridges

intergranular diffusion rates from the analysis of garnet surfaces implications for metamorphic equilibration novel approaches to garnet analysis have been used to assess rates of intergranular diffusion between different matrix phases and garnet porphyroblasts in a regionally metamorphosed staurolite mica schist from the barrovian type area in scotland x ray maps and chemical traverses of planar porphyroblast surfaces reveal chemical heterogeneity of the garnet grain boundary linked to the nature of the adjacent matrix phase the garnet preserves evidence of low temperature retrograde exchange with matrix minerals and diffusion profiles documenting cation movement along the garnet boundaries garnet quartz and garnet plagioclase boundaries preserve evidence of sluggish mg mn and fe diffusion at comparable rates to volume diffusion in garnet whereas diffusion along garnet biotite interfaces is much more effective evidence of particularly slow al transport probably coupled to fe3 exchange is locally preserved on garnet surfaces adjacent to fe oxide phases the ca distribution on the garnet surface shows the most complex behaviour with long wavelength heterogeneities apparently unrelated to the matrix grain boundaries this implies that the ca content of garnet is controlled by local availability and is thought likely to reflect disequilibrium established during garnet growth geochemical anomalies on the garnet surfaces are also linked to the location of triple junctions between the porphyroblasts and the matrix phases and imply enhanced transport along these channels the slow rates of intergranular diffusion and the characteristics of different boundary types may explain many features associated with the prograde growth of garnet porphyroblasts thus minerals such as quartz fe oxides and plagioclase whose boundaries with garnet are characterized by slow intergranular diffusion rates appear to be preferentially trapped as inclusions within porphyroblasts as such grain boundary diffusion rates may be a significant kinetic impediment to metamorphic equilibrium and garnet may struggle to maintain chemical and textural equilibrium during growth in pelites

zoning and recrystallization of phengitic micas implications for metamorphic equilibration white micas phengites in the metasediments of the scottish dalradian display a large range of compositions within single samples the variations in the composition of these phengites are strongly controlled by their structural age with early fabrics containing a paragonite poor celadonite rich phengite whereas in later fabrics the micas are generally paragonite rich and celadonite poor retrograde phengite growth identified using back scattered electron imaging occurs as celadonite rich rims on micas within all existing fabrics and appears to be preferentially developed along existing white mica plagioclase grain boundaries the presence of these chemically distinct phengite populations within single samples implies that chemical exchange between the individual micas was inefficient it is proposed that diffusion controlled exchange reactions in phengites have relatively high closure temperatures below which major element exchange is effectively impossible this closed system behaviour of micas questions the ease with which phengites may equilibrate with other phases during prograde greenschist and lower amphibolite facies metamorphism many of the chemical variations preserved in phengites from such metamorphic rocks may reflect deformation recrystallization controlled equilibria

new multibeam mapping and geochemistry of the 30 35 s sector and overview of southern kermadec arc volcanism new multibeam mapping and whole rock geochemistry establish the first order definition of the modem submarine kermadec arc between 30 degrees and 35 degrees s twenty two volcanoes with basal diameters 5 km are newly discovered or fully mapped for the first time giggenbacb macauley havre haungaroa kuiwai ngatoroirangi sonne kibblewhite and yokosuka for each large volcano edifice morphology and structure surficial deposits lava fields distribution of sector collapses and lava compositions are determined macauley and havre are large silicic intra oceanic caldera complexes for both concentric ridges on the outer flanks are interpreted as recording mega bedforms associated with pyroclastic density flows and edifice foundering other stratovolcanoes reveal complex histories with repeated cycles of tectonically controlled construction and sector collapse extensive basaltic flow fields and the development of summit craters and or small nested calderas combined with existing data for the southernmost arc segment we provide an overview of the spatial distribution and magmatic heterogeneity along similar to 780 km of the kermadec arc at 30 degrees 36 degrees 30 s coincident changes in arc elevation and lava composition define three volcano tectonic segments a central deeper segment at 32 degrees 20 34 degrees 10 s has basement elevations of 3200 m water depth and relatively simple stratovolcanoes dominated by low k series basalt basaltic andesite in contrast the adjoining arc segments have higher basement elevations typically 3 km coincide with the shallower arc segments the dominant mode of large caldera formation is interpreted as mass discharge pyroclastic eruption with syn eruptive collapse hence the shallower arc segments are characterized by both the generation of volatile enriched magmas from crustal melting and a reduced hydrostatic load allowing magma vesiculation and fragmentation to initiate and sustain pyroclastic eruptions proposed initiation parameters for submarine pyroclastic eruptions are water depths 70 wt sio2 and a high discharge rate c 2005 elsevier b v all rights reserved

first results of study of sulphur rich hydrothermal activity from an island arc environment esmeralda bank in the mariana arc during cruise so 69 of r v sonne active hydrothermal exhalation and deposition along the northern caldera rim of esmeralda bank was observed and sampled esmeralda bank is one of the active submarine volcanoes in the southern seamount province of the mariana island are hydrothermal porous mounds and volcaniclastic breccias cover an area of at least 0 2 km2 on the caldera seafloor and exude vent waters with a minimum temperature of 78 5 c the hydrothermal mounds consist of layers of pyrite marcasite and pure sulphur that are at least 0 8 m thick bottom videos show turbulent gas rich plumes characterized by high methane concentrations of 2 9 104 nl l which are comparable to those found at the hydrothermal site of macdonald seamount in the southwest pacific the deposition of large amount of sulphides is probably related to rock water interaction and degassing from a shallow summit magma chamber in an island arc environment

genesis and mobility of the h2o co2 fluid phase during regional greenschist and epidote amphibolite facies metamorphism a petrological and stable isotope study in the scottish dalradian during high pressure low temperature greenschist and epidote amphibolite facies metamorphism in dalradian rocks of the sw scottish highlands mineral assemblages in metabasites and calcareous metasediments were dominantly controlled by infiltration of hydrous fluids consequently mineral assemblages capable of buffering the fluid phase composition were rare equilibrium prograde h 2 o co 2 fluids usually contained less or much less than about 1 2 mol co 2 three fluid infiltration events are recognized during prograde greenschist facies metamorphism metabasic sills were infiltrated by large volumes of co 2 bearing hydrous fluid carbon isotope studies indicate that the co 2 was locally derived by widespread oxidation of graphite or other organic carbon in adjacent metasediments this may have occurred under approximately lower greenschist facies conditions as a result of mixing of fluids of varying f o 2 initiated by thermal expansion of water during heating decompression and consequent hydraulic fracturing in the epidote amphibole facies garnet zone dehydration reactions in metabasites generated large quantities of water which removed carbonate from metabasites on a regional scale and infiltrated calcareous metasediments to produce assemblages containing grossular diopside k feldspar amphibole clinozoisite and sphene a late retrograde infiltration of co 2 bearing hydrous fluid under lower greenschist facies conditions generated assemblages containing k feldspar chlorite rutile dolomite in calcareous rocks and albite prophyroblast schists in zones of intense secondary deformation large scale infiltration of fluid into greenschist facies metadolerite sills was intimately related to and possibly controlled by penetrative deformation and in the absence of a penetrative deformation grain boundary diffusion by itself was an ineffectual mechanism of fluid transport

extreme spatial and temporal variability of hydrothermal microbial mat communities along the mariana island arc and southern mariana back arc system 1 twenty five microbial communities were sampled from 18 different hydrothermal systems located at seven different sites along the mariana island arc and at a single site from the southern mariana spreading center over a 3 year period terminal restriction fragment length polymorphism t rflp analysis of the small subunit rrna gene revealed that the microbial community diversity is much greater along the mariana arc back arc than at either hot spot volcanoes or mid ocean ridges along the same spatial scale cluster analysis of t rflp fingerprints reveals the microbial communities formed three distinct clusters designated mariana clusters i ii and iii microbial communities in mariana cluster i are all associated with iron rich microbial mats and are dominated by members of the proteobacteria and by unique phylotypes clustering deeply in the proteobacteria and within the nitrospira division mariana cluster ii communities are all from shallow hydrothermal systems and mostly from colder sediments or microbial mats that are dominated by putative heterotrophic phylotypes usually associated with seawater and sediments not generally associated with hydrothermal fluid inputs mariana cluster iii is generally from much hotter vent sites and is dominated by sulfur oxidizing proteobacteria quantitative polymerase chain reaction q pcr of archaeal abundance reveal that all of the microbial communities are dominated by members of the bacterial domain sampling of microbial mats from iceberg vent at nw rota 1 in 2004 and again in 2006 reveal the community has shown a transition from caminibacter group proteobacteria phylotypes to a mixed population of caminibacter sulfurovum and sulfurimonas group proteobacteria

methane enrichment in low temperature hydrothermal fluids from the suiyo seamount in the izu bonin arc of the western pacific ocean 1 the gas geochemistries of high temperature and low temperature hydrothermal fluids hthfs and lthfs respectively were studied for the suiyo seamount hydrothermal system 140 39 e 28 33 n in the southern izu bonin ogasawara arc of the western pacific ocean hthfs 290 20 c were collected from four active vents using a gas tight fluid sampler which prevented the loss of volatile components through degassing during sample processing the end member ch4 concentrations were homogeneous across the vent fields lthfs were collected from four diffuse flow zones using a funnel which was deployed on the seafloor with replacement of the seawater inside the funnel by the lthf strong linear relationships were found among the concentrations of ch4 co2 and si of the obtained samples which ensured that the end member chemical composition of the lthfs could be accurately estimated while the co2 concentrations of the hthfs and lthfs were similar all four lthfs showed enrichment of ch4 as compared to the hthfs the carbon isotopic composition of ch4 also revealed a significant difference the lthfs 13c ch4 4 8 0 3 pdb showed 13c enrichment as compared to the hthfs 13c ch4 5 8 0 4 pdb the 13c enrichment can be explained by a combination of microbial ch4 production and oxidation after formation of the lthfs on the basis of the observed differences in ch4 concentrations and carbon isotopic compositions of the hthfs and lthfs microbial methane oxidation and production are estimated to have comparable impacts these results support the notion of a subseafloor microbial consortium of methanogens and methanotrophs

peculiar features of suiyo seamount hydrothermal fluids izu bonin arc differences from subaerial volcanism abstract this is the first report of the dissolved gas composition of a deep sea venting hydrothermal system originating from arc volcanism the origin of dissolved gases in hydrothermal fluids from the suiyo seamount in the southern izu bonin ogasawara arc is discussed on the basis of chemical and isotopic compositions twelve high temperature up to 310 c fluid samples were collected from three vents of the hydrothermal system using the submersible shinkai 2000 the average 3 he 4 he ratio of the dissolved he is 8 1 r r atm which is within the range of values reported for n morb the co 2 3 he ratio is 12 109 which is within the range of arc volcanic gas values the 13c values of co2 and ch4 are 1 and 8 5 respectively which is quite high compared with other subaerial arc volcanic gases and those from mid ocean ridges these results which do not accord with those from subaerial volcanism are unlikely to result from fractionation or addition of carbon sources during the fluid circulation but are regarded as characteristic of the magma source of suiyo seamount a simple mixing of 97 morb mantle with 3 subducting slab explains well the composition of the helium and carbon in the parent magma

prograde temperature time evolution in the barrovian type locality constrained by sm nd garnet ages from glen clova scotland abstract the timing of garnet growth during metamorphism associated with the grampian orogeny in the sillimanite zone of the barrovian type locality in glen clova scotland was determined by sm nd geochronology two high precision garnet whole rock ages were achieved by employing hf partial dissolution of garnet separates to optimize purity multiple garnet growth generations were identified on the basis of the geochronology and detailed textural and chemical data an early stage at 472 9 2 9 ma during d 2 deformation under garnet zone conditions c 500 550 c and a later stage at 464 8 2 7 ma during or slightly after d 3 deformation mostly under sillimanite zone conditions peak temperature of c 660 c but possibly including some growth during kyanite zone conditions when combined with recently published garnet ages from the kyanite and garnet zones the data suggest that peak metamorphic temperatures in at least these three of barrow9s zones were achieved roughly contemporaneously the difference between garnet zone and sillimanite zone peak temperature attainment is 2 8 3 7 ma the near contemporaneity of peak temperature attainment in different metamorphic zones requires an additional source of heat beyond thermal relaxation of a variably over thickened crust we suggest that local igneous intrusions with synmetamorphic ages provided that additional heat

foreland normal fault control on northwest himalayan thrust front development in the trans indus ranges along the western part of the northwest himalayan thrust front unconformities changes in paleocurrent directions and locally derived conglomerates in synorogenic foreland basin deposits provide evidence for major local deformation at 3 5 ma the tectonic history of the trans indus ranges has previously been described in terms of a single episode of major thrusting at 1 ma thus our work implies that there were two distinct phases of deformation in conjunction with published evidence in the salt range to the east for two phases of deformation 6 to 5 ma and 2 5 ma to present this study demonstrates that these two phases of deformation are regionally significant and probably correlative along the entire present day nw himalayan thrust front reconstruction of possible source areas for the locally derived conglomerates shows that the earlier deformation is probably related to normal faulting these results suggest that the tectonic evolution of the area along the present day thrust front is characterized by 1 latest miocene to early pliocene formation of north dipping normal fault zones total throw 600 m within the foreland basin related to syn orogenic flexure of the indian plate and 2 late pliocene to early pleistocene initiation of south directed thrusting along the present day thrust front related to outward growth of the nw himalayan thrust wedge the location of the present day thrust front appears to be controlled by north dipping normal faults and monoclines that formed during the earlier deformation and subsequently localized structural ramps during later thrusting

the solubility and stabilization of ikaite caco3 6h2o from 0 to 25 c environmental and paleoclimatic implications for thinolite tufa we determined the solubility of ikaite from 0 to 25 c to model its saturation state in natural waters and test the hypothesis that it is the precursor of the calcite pseudomorphs in thinolite tufa of quaternary lake lahontan reversible solubility at buffered p co 2 yields the following expression for the dissolution constant of ikaite log k ikaite 0 15981 2011 1 t where t circ k and 0 circ c leq t leq 25 circ c derived standard state properties are delta g ikaite circ 2541 9 kjmol 1 pm 0 66 delta h ikaite circ 2973 4 kjmol 1 pm 1 02 s ikaite circ 306 6 jt 1 mol 1 pm 1 2 modeling shows that ikaite is undersaturated at all temperatures in seawater and in alkaline lakes but that it rapidly approaches saturation near 0 c its precipitation in near freezing marine sediments requires large additions of hco 3 to pore fluids from the diagenetic decomposition of organic matter its crystallization in tufas of alkaline lakes howeve

glacial trinity neoproterozoic earth history within the british irish caledonides two distinct neoproterozoic glacial episodes are known for the dalradian supergroup in the british irish caledonides the port askaig formation and the inishowen loch na cille ice rafted debris ird beds here we describe a third intermediate between those two the stralinchy reelan formations composed of diamictite and ird developed directly above these rocks is the cranford limestone which consists of a basal 1 6 m thick tan gray dolostone overlain by a variably developed but as much as 340 m thick sequence of thin bedded limestone and dolostone this unit exhibits a c isotopic trend that begins negative in the basal dolostone reaches a nadir of 7 and then rises to 0 2 these characteristics match strikingly those of marinoan style cap carbonates consequently we interpret the port askaig formation the stralinchy reelan units and the inishowan loch na cille beds as equivalents of the ca 700 ma sturtian the 635 ma marinoan and the ca 580 ma gaskiers glacials respectively two additional observations are noteworthy carbonate rocks below the port askaig formation record a 13c decline to 6 that implies that such downturns may occur in both pre sturtian and pre marinoan strata in addition the bonahaven dolomite is not a cap carbonate to the port askaig formation but exhibits a 13c rise to 12 which we correlate with the inferred global keele peak these data further document the utility of neoproterozoic glacial cap carbonate sequences in global correlations and denote the base of the cranford linestone as the cryogenian ediacaran boundary

observations of regional seismicity and local harmonic tremor at brothers volcano south kermadec arc using an ocean bottom hydrophone array 1 four ocean bottom hydrophones obhs were deployed for 7 months on the caldera floor of brothers volcano located within the southern kermadec intraoceanic arc roughly 350 km northeast of new zealand the volcanic edifice is 13 8 km at the seafloor with a 3 km wide caldera that has a floor depth of 1850 m and which is surrounded by 290 to 530 m high walls encompassing a 350 m high dacite cone three of the obhs recorded low frequency 0 5 110 hz acoustic t waves from regional and local earthquakes as well as harmonic tremor from within the brother volcano the fourth obh was not recovered intact the t wave derived locations for 964 regional earthquakes show that the majority of events cluster beneath the dacite cone in the southern quadrant of the caldera and the east flank of brothers volcano in addition regional seismicity was observed along a ne sw trending fault structure to the southeast and northwest of the volcano in a small basin in the kermadec back arc and along the kermadec arc and fore arc a total of 2470 discrete harmonic tremor events were recorded on all three obhs with a fundamental frequency of 3 0 5 hz the majority of tremor signals were detected on obh 2 implying that a greater number of hydrothermal fluid conduits chambers exist within the southern caldera quadrant in comparison with the eastern or western quadrants of the caldera

discovery of hydrothermal sulfide mineralization from southern kermadec arc volcanoes sw pacific abstract we report the discovery of hydrothermal sulfide mineralization within the summit caldera of two southern kermadec frontal arc volcanoes brothers and rumble ii west of the 1200 km long kermadec havre arc back arc system the brothers and rumble ii west calderas both with re surgent domes and comprising mostly dacite and basalt andesite host rocks respectively rise to water depths of 1500 m these calderas comprise mostly effusive lavas and volcaniclastic deposits including talus breccias along their inner caldera walls these two southern kermadec hydrothermal sites have similar geological settings and mineralogy to other arc front vent sites two principle ore assemblages are identified comprising i chalcopyrite pyrite barite and ii sphalerite marcasite barite pyrite the most prevalent ore texture consists of massive chalcopyrite pyrite sphalerite commonly overprinting barite early marcasite cores within large euhedral pyrites and trails of pyrite inclusions within chalcopyrite are indicative of recrystallization the ore mineralogy is consistent with postulated venting temperatures of 300 c sulfide geochemistry is consistent with the ore mineralogy with concentrations of cu fe and zn up to 15 3 19 1 and 18 8 wt respectively the sulfide geochemistry is distinct however from comparable western pacific vent sites and may reflect source heterogeneity due to proximity to continental new zealand and sediment recycling along the southern kermadec trench arc system the recovery of two partial caridean vent shrimps suggests that present day hydrothermal venting is occurring within the brothers caldera

the magmatic plumbing of the submarine hachijo nw volcanic chain hachijojima japan long distance magma transport 1 recent geophysical observations on basaltic composite volcanoes in izu bonin arc reveal the process of long distance lateral magma transport within arc crust to clarify a long distance magma transport system of the basaltic arc volcano from geological and petrological aspects we investigated 20 km long submarine volcanic chains hachijo nw chain and hachijo kojima chain and cones on the northeastern slope ne edifices as well as subaerial satellite cones nested hachijo nishiyama volcano in the northern izu arc front basalts from hachijo nw chain have more primitive composition than those from other edifices the composition of the hachijo nw chain basalts is controlled by fractional crystallization while plagioclase accumulation occurred in ne edifices and subaerial satellite cones trace element and isotopic characteristics indicate that the same basaltic primary magma is involved in all sections of the volcano this leads us to consider that magma was transported long distances between the nishiyama volcano and the hachijo nw chain primitive magma was laterally transported nnw for at least 20 km in the middle to lower crust 10 20 km deep from nishiyama volcano with only minimal crustal level modifications and formed hachijo nw chain on the other hand magmas experienced crystal fractionation and accumulation at shallow magma chamber beneath nishiyama volcano seems to have been transported in a short distance 5 km and formed ne trending edifices and subaerial satellite cones the long distance magma transport seems to be controlled by a regional extensional stress regime while short distance transport may be controlled by local stress regime affected by load of main volcanic edifice

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

glendonites in neoproterozoic low latitude interglacial sedimentary rocks northwest canada insights into the cryogenian ocean and precambrian cold water carbonates stellate crystals of ferroan dolomite in neritic siliciclastic and carbonate sedimentary rocks between sturtian and marinoan glaciations in the mackenzie mountains are interpreted as replaced glendonites these pseudomorphs after ikaite indicate that shallow seawater at that time was near freezing stromatolites verify that paleoenvironments were in the photic zone and physical sedimentary structures such as hummocky cross bedding confirm that the seafloor was repeatedly disturbed by storms glendonites within these low latitude continental shelf to coastal sedimentary deposits imply that global ocean water during much of cryogenian time was likely very cold such an ocean would easily have cooled to yield widespread sea ice and through positive feedback growth of low latitude continental glaciers in this situation gas hydrates could have formed in shallow water cold shelf sediment but would have been particularly sensitive to destabilization as a result of sea level change co occurrence of pisolites and glendonites in these rocks additionally implies that some ooids and pisoids might have been unlike phanerozoic equivalents characteristic of cold water sediments