low temperature silica rich gold mineralization in mafic vms systems evidence from the troodos ophiolite cyprus the troodos ophiolite cyprus hosts the on land analogue for actively forming mafic cu rich or cyprus type vms deposits in addition to high temperature 350 c sulfide mound related mineralization other fossil seafloor mineralizing systems are known to operate including those characterized by an enrichment in au and abundant silicification in this study the mineralogy and geochemistry of four au and silica rich localities in troodos are considered and these include kokkinovounaros mathiatis south touronjia and alpen rose we present whole rock geochemical and mineralogical data characterizing the distribution of au in the hydrothermal systems of troodos samples from silica rich localities have two distinct sample mineralogies supergene samples that contain predominantly goethite hematite and jarosite and hypogene samples that contain quartz amorphous silica and minor hematite hypogene samples from mathiatis south and kokkinovounaros are enriched in au with a median concentration of 1 5 ppm relative to supergene samples that contain 0 1 ppm n 107 this indicates that au enrichment occurred on the seafloor and is not solely related to supergene weathering of silica rich mineralization we suggest that silica rich au mineralization in troodos formed during the migration of newly formed crust off axis or as white smokers proximal to known vms deposits in silica rich mineralization that is located distally from known massive sulfide deposits au was probably remobilized from shallow crustal reservoirs during the low temperature fluid flow 100 300 c in the lower extrusive sequence as the crust cooled and migrated off axis based on modern seafloor analogues we propose a revised model for the troodos hydrothermal system that explains the distribution of au in silica rich mineralization that formed off axis and postdates vms formation and in zones proximal to vms deposits that formed simultaneously as white smoker type vents we suggest that silica rich mineralized zones formed an intermediary between high temperature 350 c on axis vms deposits and the low temperature silicification of umbers 100 c

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

southern kermadec submarine caldera arc volcanoes sw pacific caldera formation by effusive and pyroclastic eruption abstract three newly identified submarine caldera volcanoes brothers healy and rumble ii west of the southern kermadec arc within water depths 80 and low density 0 3 0 5 g cm 3 erupted pumiceous clasts these observations are interpreted as evidence of subaqueously quenched pyroclastic eruption s sheathed by ambient water flashing to steam discharging some 5 km3 of pyroclastic material from healy volcano caldera collapse is inferred to be penecontemporeous with the pyroclastic eruption s although it is possible formation as an explosive crater occurred but we consider the latter unlikely given the volume of erupted material and water depth extrapolation of these observations to other submarine arcs indicates pyroclastic eruption of silicic magmas and syn eruptive caldera collapse is possible within water depths of 500 1000 m

mechanisms of the 1997 1998 el nino la nina as inferred from space based observations 1 the intensity of the 1997 el nino and the 8 c sudden drop in sea surface temperature sst around 0 130 w during the turn into la nina in 1998 were a surprise to the scientific community this succession of warm and cold events was observed from start to finish with a comprehensive set of remotely sensed and in situ observations in this study we employ space based observations to demonstrate for the first time their maturity in capturing the preconditioning onset evolution and decay of the 1997 el nino and its transition into the 1998 la nina an accumulation of warm water in the west and equatorial wave reflection on the western ocean boundary appeared favorable for the development of el nino however the action of a series of westerly wind bursts from december 1996 to june 1997 notably in march 1997 was instrumental in setting up this huge el nino the westerly wind bursts excited equatorial downwelling kelvin waves and advected the eastern edge of the warm pool eastward which triggered a distinct warming over the central and eastern parts of the equatorial basin once these warmed regions joined the coupling between the sst and surface winds was fully effective and el nino reached its mature phase by that time much of the warm waters of the western equatorial pacific was transferred toward the east by surface eastward currents the demise of el nino and its turn into la nina in spring 1998 were due to the arrival in the east of various interrelated phenomena upwelling was brought from the west by favorable off equatorial wind stress curl and equatorial kelvin waves generated by easterly winds and wave reflection on the western ocean boundary additional upwelling was brought from the east by equatorial rossby waves generated by westerly winds these various upwelling signals were added to the general uplifting of the thermocline because of the slow discharge of the upper layer of the equatorial basin by diverging surface currents a series of equatorial kelvin and rossby waves characterized by upwelling and opposite surface currents led to the breakup of the warm waters the surfacing of the thermocline and the drastic drop in sst in may 1998 around 0 130 w with the arrival of cold water in the east the easterly winds expanded from the west and la nina turned into a growing mode this view of the 1997 1998 el nino la nina afforded from space enables the testing of various el nino theories

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

degassing of rhyolitic magma during ascent and emplacement the degassing history of a rhyolitic igneous system was documented from analyses of drill core samples through the extrusive and intrusive portions of obsidian dome and of surface samples of associated tephra the initial volatile composition of the inyo magma was estimated to be 4 0 wt h2o 500 ppm f 800 ppm cl and 80 ppm s retained volatile contents of glassy and crystalline samples reflect the effects of decompression and second boiling decompression is rapid and involves loss of water rich fluid until a close approach to lithostatic equilibrium is achieved second boiling is a slower process and produces a chlorine rich fluid some of which can be trapped during development of extremely fine crystallization textures nearly complete dewatering during decompression of surface extruded magma strongly undercools the system t 175 c suppressing crystallization and yielding glassy rhyolitic lava partial degassing of shallowly intruded magma permits pervasive crystallization even at high cooling rates the subvolcanic intrusive regime is the zone of maximum volatile release because second boiling is incomplete in extrusives and volatile bearing crystalline phases are stable in magma crystallized at greater depth

submarine venting of magmatic volatiles in the eastern manus basin papua new guinea abstract the susu knolls and desmos hydrothermal fields are located in the back arc extensional transform zone of the eastern manus basin in 2006 highly acidic and so4 rich vent fluids were collected at both sites and analyzed for the chemical and isotopic composition of major and trace species fluids exiting the seafloor have measured temperatures from 48 to 215 c and are milky white in appearance due to precipitation of elemental s0 vent fluid concentrations of na k and mg are depleted by as much as 30 relative to seawater but have the same relative abundance in contrast the fluids are highly enriched in dissolved co2 cl sio2 aq fe and al relative to seawater measured ph 25 c ranged from 0 95 to 1 87 and aqueous so4 ranged from 35 to 135 mmol kg the chemical and isotopic composition points to formation via subsurface mixing of seawater with a na k mg and ca free volatile rich magmatic fluid exsolved from subsurface magma bodies during a process analogous to subaerial fumarole discharge estimates of the magmatic end member composition indicate a fluid phase where h2o so2 co2 cl f the hydrogen and oxygen isotopic composition of h2o and carbon isotopic composition of co2 in the vent fluids strongly suggest a contribution of slab derived h2o and co2 to melts generated in the mantle beneath the eastern manus volcanic zone abundant magmatically derived so2 undergoes disproportionation during cooling in upflow zones and contributes abundant acidity so42 and s0 to the venting fluids interaction of these highly acidic fluids with highly altered mineral assemblages in the upflow zone are responsible for extensive aqueous mobilization of sio2 aq fe and al temporal variability in the speciation and abundance of aqueous s species between 1995 and 2006 at the desmos vent field suggests an increase in the relative abundance of so2 in the magmatic end member that has mixed with seawater in the subsurface results of this study constrain processes responsible for the formation of hot spring fluids in magmatically active back arc environments and the resulting chemical exchange between the lithosphere and water column

systematic variations of trace element and sulfur isotope compositions in pyrite with stratigraphic depth in the skouriotissa volcanic hosted massive sulfide deposit troodos ophiolite cyprus the troodos ophiolite represents one of the best preserved fossil analogs of modern oceanic crust and includes numerous volcanic hosted massive sulfide deposits the skouriotissa deposit can be separated into a stockwork ore zone and an overlying massive sulfide lens that is covered by metalliferous sediments representing the former sulfide seawater interface pyrite is the dominant sulfide mineral within these ores the trace element composition of pyrite varies systematically with stratigraphic depth down to 150 mbsf probably reflecting fluid temperature variations and effects of phase separation co ni se te bi and cu metal remobilization due to hydrothermal zone refining zn sb and pb and fluid seawater mixing at the seafloor mo represent further important processes controlling the pyrite chemistry massive sulfide hosted sphalerite and euhedral pyrite probably formed from hot fluids 400 c while the occurrence of colloform pyrite indicates lower precipitation temperatures 400 c similar 18o quartz fluid equilibration temperatures 400 c in the stockwork zone suggest that the skouriotissa fluids did not cool significantly during the final 150 m of fluid ascent to the seafloor the 34s composition of deep stockwork pyrite 1 4 suggests that an isotopically light magmatic volatile phase 0 was added to the hydrothermal system of skouriotissa during further fluid ascent about 38 of cretaceous seawater 34s 18 19 was added leading to the precipitation of stockwork pyrite with positive 34s values 6 1 in addition the chemical and textural similarities between skouriotissa and modern seafloor vent systems and massive sulfide deposits suggest that the skouriotissa hydrothermal system has a modern analog

volcanic and hydrothermal processes in submarine calderas the kulo lasi example sw pacific abstract the study area is located at the transition between the northern end of the tonga trench and the north fiji fracture zone where tectonic movements are reputed to be the fastest in the world to the southeast of futuna island a broad area of volcanism occurs within a region characterized by a change in the tectonic fabric between a ne sw oriented volcanic graben and the n s oriented alofi ridge in 2010 the active volcano kulo lasi which represents the most recent volcanic episode in the futuna area was discovered in the center of this extensive volcanic zone kulo lasi is a 20 km diameter shield volcano that rises 400 m above the seafloor it is composed of basaltic to trachy andesitic lava with no obvious geochemical affinity with the tonga subduction that occurs 500 km to the east the central caldera is 5 km in diameter and 300 m deep and is located at a water depth of 1500 m diving operations with the submersible nautile and high resolution auv mapping have revealed the presence of numerous active and inactive hydrothermal fields on the floor and the walls of the caldera four tectono volcanic stages can be distinguished at kulo lasi caldera in stage 1 the shield volcano is built annular reverse faults develop at the summit and control circulation of water rock dominated hydrothermal fluids and high temperature alteration of rocks along the nascent normal faults mixing of hydrothermal fluids with seawater is favored along normal superficial faults leading to the formation of low temperature fe mn mineralization at the summit of the volcano during stage 2 the caldera collapse gradually revealing outcrops of the altered and mineralized zones formed during stage 1 as the magma chamber cools and collapses less heat is available as a result medium to low temperature

hydrothermal fluids associated with seafloor mineralization at two southern kermadec arc volcanoes offshore new zealand massive sulfide samples have been recovered from brothers and rumble ii west volcanoes of the southern kermadec frontal arc northeast of new zealand both are caldera forming volcanoes with brothers largely dacitic and rumble ii west basaltic to basaltic andesite in composition the sulfide samples are considered to be pieces of chimneys from near the base of the caldera walls and are dominated by cu fe ba pb chalcopyrite pyrite barite galena and to a lesser extent zn fe ba pb sphalerite pyrite barite galena mineralization gold is present in the samples up to 6 1 ppm paragenetic relationships suggest that the two hydrothermal systems have heated up and later cooled down oxidation of the sulfides is common and suggests that parts of the deposits are relatively old fluid inclusion microthermometric data show salinities fall predominantly in the range 3 0 to 3 4 wt nacl equivalent similar to seawater values 3 2 wt about 15 of the brothers salinity data range to both lower 2 2 wt and higher 3 9 wt than seawater values homogenization temperatures for type i inclusions in barite range between 175 and 322 c for the brothers samples and between 205 and 268 c for one rumble ii west sample a dramatic decrease in temperature and or change in the oxidation state of the hydrothermal fluid are considered the main mechanisms responsible for gold deposition at the kermadec vent sites this was achieved by mixing the hydrothermal fluid with ambient seawater within what are inferred to have been 300 c white smoker chimneys consistent with s isotope results fluid inclusion volatiles are dominated by h2o 99 81 99 98 mol followed by co2 0 03 0 17 and lesser amounts of n2 0 004 0 023 ch4 0 002 0 026 and trace cos and c2 c3 hydrocarbons fluid inclusions hosted by barite contain noticeably lesser amounts of gas than those within sulfides consistent with mixing the source of the relatively high concentrations of ch4 is enigmatic although may be related to the thermal degradation of organic rich sediments intercalated within the volcanic pile addition of a pressure correction and the effect of dissolved gases show that the hydrothermal fluids did not boil at the chimney depths however the range of measured salinities in the brothers field combined with slightly positive trends in fluid inclusion co2 ch4 versus co2 n2 plots suggest sub seafloor phase separation may have occurred in the hydrothermal system prior to venting

timing of glaciation during the last glacial cycle evaluating the concept of a global last glacial maximum lgm abstract it has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle often well before the global last glacial maximum lgm c 23 19 ka which is formally defined by peaks in global sea level and marine oxygen isotope records however there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global lgm but also some regions of the large continental glaciers the barents kara ice sheet in northern eurasia together with a majority of ice masses throughout asia and australasia reached their maximum early in the last glacial cycle a few thousand years before the global lgm period the east antarctic ice sheet also reached its maximum extent several millennia before the global lgm in numerous mountainous regions at high mid and low latitudes across the world glaciers reached their maximum extent before marine isotope stage mis 2 in mis 5 4 and 3 this is in contrast to most sectors of the laurentide ice sheet the cordilleran ice sheet the se sector of the fennoscandinavian ice sheet and the alpine ice sheet in central europe which appear to have reached their maximum close to the global lgm in mis 2 the diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle means that the term and acronym last glacial maximum lgm has limited chronostratigraphical meaning when correlating glacial deposits and landforms

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

a long late quaternary record from lake poukawa hawke s bay new zealand abstract the lake poukawa basin is a large co seismic depression located at 20 m above mean sea level in hawke s bay in eastern north island new zealand we present a detailed environmental history of the basin for the last c 60 ka based on analyses of the top 105 m of a 200 m core record dating control is provided by radiocarbon optically stimulated luminescence osl and u th disequilibrium ages the chronology is supported by nine tephras of inferred age including marker tephras kawakawa 22 590 230 yr bp at 18 25 m core datum tahuna c 35 43 ka at 33 1 m core datum and rotoehu 45 50 ka at 39 1 m core datum disagreements between some of the older tephra ages and the numerical ages from the osl and u th dating mean that more than one age model can be applied three major lithostratigraphic units are identified a basal calcareous silt with lignitic peats between 105 28 and 98 58 m of marine oxygen isotope stage mis 3 age an extended sequence of detrital shelly sands and silts between 98 58 and 8 m of mis 3 and 2 age and a holocene peat unit mis 1 from 8 to 0 m alternatively but less likely the basal unit may represent stage mis 5a and the detrital shelly sands would then contain an amalgam of mis 4 3 and 2 deposits we propose a notably moist phase represented by the peat which our numerical dating model places near the start of isotope stage 3 this suggests the existence of mild conditions during an interstadial in central new zealand at c 55 50 ka when a podocarp beech broadleaf forest of near interglacial affinity surrounded the basin the interstadial is marked by both lake and peat formation in the basin after 50 ka a thermal decline set in though the climate remained moist initially under these conditions the poukawa basin was rapidly infilled by alluvial fan deposits from the surrounding hills the floor of the basin was occupied by grasses and sedges responding to both the highly disturbed environment and swampy conditions in the basin after the deposition of the rotoehu ash effective precipitation declined markedly and woody shrubs expanded across the previously swampy basin floor the data suggest an apparent thermal decline of c 6 7 c for much of mis 2 and the latter half of mis 3 the holocene was marked by the establishment of fen and lake environments on the basin floor prior to human disturbance podocarp broadleaf forest surrounded the basin

the stratigraphy timing and climatic implications of glaciolacustrine deposits in the middle rakaia valley south island new zealand abstract stratigraphic interpretations and infrared stimulated luminescence irsl ages document the glacial history of the middle rakaia gorge section of the rakaia valley canterbury new zealand during the last two glacial cycles sheets of glaciolacustrine sediments several tens of metres in thickness can be traced at least 10 km upstream of the rakaia gorge the stratigraphic package is capped by outwash gravels associated with the last glacial maximum lgm advances the dominant inferred sedimentary environments in the sequence are 1 pro glacial and paraglacial lake beds 2 sub aqueous ice contact fans 3 sub aqueous mass flow deposits 4 supraglacial dump material and 5 outwash gravels syndepositional deformation associated with glacitectonic deformation is common the stratigraphy records glacier margin oscillations including six significant advances these occurred in early mis 6 mid mis 6 mis 5b c100 90 ka mis 5a 4 c 80 ka mid mis 3 c 48 ka and late mis 3 c 40ka all the post mis 6 advances can be corroborated from other sites in new zealand and the timings appear to coincide with both southern hemisphere insolation minima and maxima suggesting variable combinations of climatic forcing in new zealand glaciation

fluid fluid interactions in magmatic hydrothermal ore formation hydrothermal ore deposits have provided some of the first geological evidence for the interaction of multiple fluids in the earth s interior including fluid mixing as well as fluid phase separation physical evidence comes from veins and breccias documenting the impact of fluids in breaking rocks and creating fracture permeability for ore formation as a result of the fluid expansion that is commonly associated with phase separation between melts and multiple fluids chemical evidence of fluid fluid interaction includes the precipitation of minerals in veins as a result of fluid boiling or mixing between chemically contrasting fluids fluid inclusions record interactions of multiple fluids especially in magmatic hydrothermal ore deposits and associated igneous rocks fig 1 in recent years fluid inclusions have contributed to a more quantitative understanding of the role of fluid fluid interactions since new microanalytical techniques allow determination of element concentrations in all types of fluids from low density vapor through aqueous and hypersaline liquids to hydrous salt melts roedder 1984 samson et al 2003 figure 1 geological evidence for fluid phase separation in ore forming magmatic hydrothermal systems a bonanza grade gold 1 wt that was precipitated together with fine grained pyrite in a fluidized breccia resulting from instantaneous boiling and expansion of magmatic fluids ascending from an underlying andesite porphyry intrusion the breccia consists of adularia sericite altered clasts of sedimentary wall rock s and nodules of originally colloidal pyrite with bright specks of gold p g both cemented by roscoelite r vanadium rich muscovite and late calcite c zone vii ore body porgera papua new guinea ronacher et al 2004 b bladed manganocalcite the characteristic habit of calcite precipitated from aqueous epithermal fluids as a result of the ph change following loss of co2 to a separating vapor phase madan bulgaria kostova et al 2004 c growth band in a euhedral quartz

the trident pacific model part 1 simulating surface ocean currents with a linear model during the 1993 1998 topex poseidon period zonal advection by long equatorial waves has been shown to be an important process in the evolution of sea surface temperature in the central pacific on enso time scales the present study aims at investigating how well an oceanic model whose dynamics are based on long equatorial waves can simulate the large scale surface zonal current variability thus an ocean linear model which can be run with two or three layers is validated against several sets of observations in the pacific ocean topex poseidon sea level tao zonal currents surface current climatology the surface layer mixed layer has a constant depth therefore the layer model is equivalent to considering a shear layer solution and either one or two baroclinic modes it allows evaluation of the impact of adding a second baroclinic mode on the simulation of surface currents this evaluation is done for different friction parametrizations a weak linear rayleigh friction 24 months 1 a strong linear rayleigh friction 6 months 1 and a new parametrization using quadratic friction in the momentum equation only it is shown in all simulations using various rayleigh friction parametrizations that the addition of a second baroclinic mode always improves the simulation of both the sea level and the surface currents especially in the central western pacific in that region there is a reduction of the propagating long rossby waves whose amplitude is much too large when only one baroclinic mode is used despite this reduction the use of a weak friction 24 months 1 always yields results which compare only poorly to observations confirming results from previous studies the use of strong friction 6 months 1 improves the model simulation but surface current variability still remains too large finally the use of quadratic friction as proposed in the present study considerably improves the simulation of zonal currents and its comparison to all data sets this result gives more confidence in the choice of such a simple model to further explore the role of zonal advection by long equatorial waves on enso time scales

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

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

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

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

complex subsurface hydrothermal fluid mixing at a submarine arc volcano supports distinct and highly diverse microbial communities hydrothermally active submarine volcanoes are mineral rich biological oases contributing significantly to chemical fluxes in the deep sea yet little is known about the microbial communities inhabiting these systems here we investigate the diversity of microbial life in hydrothermal deposits and their metagenomics inferred physiology in light of the geological history and resulting hydrothermal fluid paths in the subsurface of brothers submarine volcano north of new zealand on the southern kermadec arc from metagenome assembled genomes we identified over 90 putative bacterial and archaeal genomic families and nearly 300 previously unknown genera many potentially endemic to this submarine volcanic environment while magmatically influenced hydrothermal systems on the volcanic resurgent cones of brothers volcano harbor communities of thermoacidophiles and diverse members of the superphylum dpann two distinct communities are associated with the caldera wall likely shaped by two different types of hydrothermal circulation the communities whose phylogenetic diversity primarily aligns with that of the cone sites and magmatically influenced hydrothermal systems elsewhere are characterized predominately by anaerobic metabolisms these populations are probably maintained by fluids with greater magmatic inputs that have interacted with different deeper previously altered mineral assemblages however proximal a few meters distant communities with gene inferred aerobic microaerophilic and anaerobic metabolisms are likely supported by shallower seawater dominated circulation furthermore mixing of fluids from these two distinct hydrothermal circulation systems may have an underlying imprint on the high microbial phylogenomic diversity collectively our results highlight the importance of considering geologic evolution and history of subsurface processes in studying microbial colonization and community dynamics in volcanic environments

helium isotope studies of geothermal fields in the taupo volcanic zone new zealand abstract we report new measurements of 3he 4he and ne on 69 samples of gas from geothermal fields in the central section of the ne sw trending taupo volcanic zone tvz we find 3 he 4 he ratios in the range 5 9 7 3 times the atmospheric ratio 5 9 7 3ra typical of subduction zone systems in some areas near the boundaries of the volcanic zone the ratio is much lower 2 4ra the values in the wairakei field are extremely uniform and vary by only a few per cent from 7 2 ra in contrast the wells in the ohaaki broadlands field show a striking factor of two variation with the west bank section characterised by values near 6 ra while the east bank section has values as low as 3 0 ra this suggests that mixing of two types of geothermal source fluids may be occurring at ohaaki broadlands an inverse relationship has been found between the 3 he 4 he ratio of the gases and the b cl ratios in the associated fluids thus the helium isotope ratios appear to be affected both by the flux of mantle helium associated with mantle subduction and also by the presence of sedimentary rocks beneath the geothermal field leaching by the hot ascending fluid of radiogenic 4he together with boron from the underlying high boron low chloride mesozoic greywacke basement is thought to be the cause of this inverse relationship the co 2 3 he ratio in the tvz exceeds the morb ratio by a factor of up to 100 with higher values corresponding to higher b cl fluid ratios suggesting that the greywacke may also be the major source of the co2 we have also measured argon concentrations and isotopes on 19 samples in the ohaaki broadlands area in order to further elucidate the nature of the striking helium isotope variations the argon isotope ratios are relatively close to atmospheric indicating that the majority of the argon comes from recirculated groundwater the simplified boiling model of mazor et al 1990 has been used to calculate the 3 he heat ratio in the ohaaki broadlands and wairakei fields the values obtained fall within the range previously reported for mid ocean ridge systems this model has been extended and has led us to the conclusion that compared to the 3 he 4 he ratio the 3 he 36 ar asw ratio is a much better indicator of the potential geothermal heat the 4 he 40 ar na where na non atmospheric ratio of both the high mantle derived and low crustal derived 3 he 4 he end members of the analyses reported here is about 3 6 but for samples with low 3 he 36 ar ratio this ratio falls to values below 0 5 the value of 3 6 is in the range which is expected for the radiogenic component and although considerably lower than that often found in subduction type mantle gases it is still within the accepted range of values

acidic and sulfate rich hydrothermal fluids from the manus back arc basin papua new guinea hot 88 120 c and acidic ph 2 1 hydrothermal fluids rich in sulfate were discovered venting in the desmos caldera depth 1926 m eastern manus back arc basin bismarck sea surrounded by papua new guinea the abundant sulfate 32 8 m m higher than the seawater value of 28 m m with elemental sulfur deposition around the vents and remarkably low d h 2 o and 34 s h 2 s values 8 1 and 5 6 respectively are suggestive of the incorporation of a magmatic fluid and the disproportionation of the exsolved so 2 from a magma body the desmos fluid may be similar in origin to the acidic sulfate chloride hot springs associated with subaerial volcanic activity in contrast to the typical hydrothermal end member mg concentration of 0 the desmos fluids are rich in mg 46 52 m m probably because of mg dissolution by acid attack upon magnesium silicate minerals

hydrothermal alteration and volatile element halos for the rosebery k lens volcanic hosted massive sulfide deposit western tasmania a detailed study of alteration mineralogy mineral chemistry and lithogeochemistry in the host rocks surrounding the a b and k lenses at the north end of the rosebery mine has revealed a series of overlapping alteration halos with characteristic mineralogy and geochemistry the study involved logging and sampling from nine drill holes spaced at varying distances from the a b and k lenses the stratiform zn pb cu ore lenses have a sheetlike morphology and are hosted by a mixed sequence of rhyolitic to dacitic massive mediumgrained quartz porphyritic pumice breccia black mudstone and crystal rich volcaniclastic sandstone overlying a thick homogeneous sequence of rhyolitic pumice breccia the major alteration minerals at rosebery are arranged in a complex series of zones passing away from the deposit quartz sericite zone mn carbonate zone chlorite zone and outer sericite zone the chlorite zone is best developed in the immediate footwall below the copper pyrite rich ore lenses whereas the strongest mn carbonate alteration occurs in the immediate hanging wall volcanics or lateral to the ore lenses the outermost visible sericitic alteration extends about 60 to 100 m into the footwall 10 to 20 m into the hanging wall and over 500 m along the upper contact of the footwall pumice breccias thallium and antimony form the most extensive trace element halos related to the mineralization thallium forms a halo that extends 200 to 300 m into the overlying volcanics and 60 to 100 m into the footwall anomalously high thallium also occurs over 500 m along strike marking the contact between the footwall pumice breccias and the overlying volcaniclastic sandstones proximal to the ore lenses tl and sb values range from 10 to 100 ppm compared to the halo zone where they vary from around 1 to 10 ppm studies of alteration mineral chemistry at rosebery have revealed some important relationships that may assist exploration the mn content of alteration carbonate increases toward ore both along strike and across strike close to ore alteration carbonates contain 20 mole percent mnco3 kutnahorite rhodochrosite mn siderite and mn ankerite whereas at distances of 40 to 60 m across strike the mole percent mnco3 in carbonate drops to below 10 percent at greater than 80 m the carbonates are mn poor calcites and are commonly located in synmetamorphic structures white mica composition changes with stratigraphy and alteration assemblages and may be related to the mineralizing event although this has not been convincingly demonstrated proximal white mica contains minor ba substituting for octahedral al however except for their ba content these phengetic white micas are similar to those found in nonmineralized areas of the mount read volcanics sodic white mica with up to 0 35 na na k and a low phengite content 0 5 fe mg cations occurs in a zone of volcanic sandstones and black slates overlying the ore deposit this research has lead to the development of a series of proximal medial and distal vectors useful for both regional and mine scale exploration the most useful vectors listed from proximal to distal include zn ba content of white mica na2o k2o ishikawa alteration index ai s na2o ba sr mn content of carbonate tl and sb

crustal magnetization of brothers volcano new zealand measured by autonomous underwater vehicles geophysical expression of a submarine hydrothermal system near bottom magnetic anomaly data have been acquired using autonomous underwater vehicles at brothers volcano southern kermadec arc new zealand crustal magnetization for the study area was obtained by inverting the magnetic data and shows a strong correlation between areas of low magnetization and four hydrothermal fields one of which was unknown prior to our surveys the magnetization pattern is consistent with a model of discrete individual zones of fluid upflow focused along caldera ring faults that provide preferred pathways for the ascent of the hydrothermal fluids differences in the amplitude of the magnetization over the vent fields appear to correlate with age and temperature variations of the hydrothermal fields

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

role of high and low frequency winds and wave reflection in the onset growth and termination of the 1997 1998 el nino the present study aims at studying the role played by high frequency wind variability wave reflection and easterly wind anomalies in the western pacific in the onset growth and termination phases of the 1997 1998 el nino using the trident intermediate coupled model and observations while the anomalous strength of the trade winds in 1996 favored the initiation of a warm event in 1997 via western pacific boundary rossby wave reflection the actual timing of the onset and the amplitude of the event resulted from the large march 1997 wind event once initiated high frequency westerly winds strongly contributed to the rapid growth of the warm event and to the displacement of the eastern edge of the warm pool moreover both easterly and westerly high frequency wind variability in 1997 1998 contributed to the amplitude of the event set the evolution of the warm event and potentially influenced the equatorial pacific conditions at least one year after the el nino event in addition eastern boundary reflection also significantly contributed to the amplitude and duration of the warm event whereas its termination was a combination of various factors reflection of upwelling rossby waves at the western boundary and large easterly wind anomalies observed in the western pacific from november 1997 to early 1998 these factors were sufficient to terminate the event and to switch temperature anomalies from warm to cold to conclude understanding the coupling between the high and low frequency wind variability i e studying enso as a multi scale phenomenon will certainly lead to a better comprehension of the diversity of its behavior and potentially to an improvement of its predictability

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

high resolution hydrothermal mapping of brothers caldera kermadec arc submarine edifices with caldera summits are common along volcanic arcs and much more likely than simple cones to host hydrothermal venting compared with cones however locating all vent field locations on a caldera s complex bathymetry is a daunting logistical challenge here we describe the first use of an autonomous underwater vehicle abe to fully map the distribution of near bottom hydrothermal tracers over the caldera walls and cone complex of brothers volcano the most active hydrothermal source on the southern kermadec arc sensors on abe simultaneously measured hydrothermal plume anomalies in temperature light backscattering particle concentration and oxidation reduction potential dissolved reduced species every 2 to 3 m along track local maxima in these tracers confirmed known sites on the northwestern wall and the cone summits and more precisely mapped their extents we discovered evidence for new sites throughout the entire northwestern half of the caldera wall at the base of the southeastern wall and on the flanks of both cones systematic variations in the backscattering temperature ratio identified different types of fluid discharge plumes from high temperature metal rich sources dominated the caldera wall while on top of the caldera wall and on the cones we found only plumes from low temperature diffuse flow including occasional s rich plumes source distribution on the walls appears fault controlled but we detected no sources along the deepest fault defining the rim of the downdropped caldera floor advanced deep sea survey techniques using autonomous vehicles is an indispensible and cost effective tool for acquiring a comprehensive understanding of the relationship between hydrothermal discharge and geology on individual volcanoes

venting of acid sulfate fluids in a high sulfidation setting at nw rota 1 submarine volcano on the mariana arc a comprehensive survey of hydrothermal plumes and their geochemistry revealed 16 hydrothermally active volcanoes along 1 200 km of the mariana arc from 13 5 n to 22 5 n of these 16 one volcano nw rota 1 is discharging sulfuric acid rich fluids producing some of the largest chemical anomalies ever observed in non buoyant hydrothermal plumes two types of venting were observed one of focused flow rich in al s si co2 fe mn and 3he and a second of diffuse flow rich in fe mn co2 and 3he but without al s and si the plume waters from the acid rich focused flow showed decreases in ph up to 0 73 ph units compared to ambient seawater and an estimated 80 percent of this change was brought about by volcanic and or hydrothermal so2 and possibly hcl with the remaining 20 percent by co2 conservative estimates suggest that the ph of the venting fluids was 1 0 the chemistry of this plume was also greatly different from that observed in any other hydrothermal setting an acid sulfate or high sulfidation fluid source was indicated from plume water samples rich in sulfuric acid native s al sulfate phosphate minerals and weathered silicate and amorphous silica phases the alunite group minerals and acidic fluids indicate that the most important hydrothermal reactions taking place within the hydrothermal system were resulting in advanced argillic alteration of the host volcanic rocks gas chemistry of the fluids revealed an he isotope signature with r ra 8 35 and 3he co2 3 25 109 these values are similar to those found along the global midocean ridge mor suggesting that the source of the 3he and co2 found here is predominantly from the upper mantle consistent with the position of nw rota 1 closest to the back arc in a chain of cross arc volcanoes the chemical signatures of the plumes arising from the diffuse flow remain greatly enriched in fe mn 3he and co2 but compared to the focused flow are low in mineral acidity h al and s the source of this diffuse flow is likely a fluid similar to that producing the acid rich plume but with a lower water to rock ratio and a longer reaction time resulting in the consumption of the mineral acidity this results in an increase in ph and the deposition of the alunite phosphate sulfate and other minerals close to the seafloor by comparison it is likely that the low ph focused flow ejects the vast majority of its mineral load into the water column which is not conducive to the formation of a mineral deposit at the sea floor and potentially would produce a barren prospect

the focus thermal study around the spreading center of southwestern okinawa trough abstract voluminous hydrothermal systems are corresponding to the heat flow anomaly discovered from previous geophysical surveys in the southern okinawa trough sot which is an area with a high sedimentation rate supplied by the east china sea shelf and the island of taiwan our latest fifteen field measurements around the geolin mound glm 24 36 6 n 122 53 e are located at a sedimentary basin west of the yonaguni rift which is nearby the southwestern tip of a ne sw trending volcano trail in the sot the heat flow results illustrate a concentric decrease from 31 477 to 180 mw m2 in a 1 km radius around the glm evidently proving the focus fluid migration along the major fluid conduit the ultrahigh temperature observations revealed the existence of magmatic components in shallow sediments combining the subsurface profiles with the temperature fields around the glm a 0 16 km2 acoustic blanking area of the g1 fluid conduit was recognized from the chirp sonar image and numerous interpreted igneous reflections with fluids related features from seismic profiles as a result we proposed a conceptual model which simultaneously illustrates the hydrothermal circulation pattern from the previous general surveys and the enormous thermal anomaly from current detailed measurements the sill to sill feeding sedimentary basin of the glm is capable of demonstrating the enormous thermal anomaly around the spreading center of the sot and appropriately represents the potential hydrothermal discharge and recharge by heat flow distribution around the glm

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

hydrothermal helium plumes in the pacific ocean hydrothermal activity along the global mid ocean ridge system and at active seamounts introduces a 3 he rich signal into the deep ocean basins which can be used to trace patterns of ocean circulation and mixing this hydrothermal helium signal is especially strong in the pacific ocean where the spreading rate of the ridges is the greatest in several areas of the pacific the hydrothermal activity is of sufficient strength to produce intense helium plumes which clearly define the regional circulation among these are 1 a pair of helium plumes at 2500 m depth which extend westward from the east pacific rise at 10 n and 15 s into the interior of the pacific basin 2 a helium plume at 2000 m depth extending southwest from sources on the juan de fuca ridge in the northeast pacific and 3 a plume at 1100 m depth emanating from loihi seamount at 20 n which extends eastward from hawaii to the coast of mexico the flow field implied by the helium distribution appears to be in reasonable agreement with reid s 1997 steric height analysis for the pacific

shallow submarine epithermal pb zn cu au ag te mineralization on western milos island aegean volcanic arc greece mineralogical geological and geochemical constraints abstract milos island contains several epithermal deposits e g profitis ilias chondro vouno pb zn ag au te cu triades galana agathia kondaros pb zn ag bi w mo cu au and katsimoutis kondaros vani pb zn ag mn of late pliocene to early pleistocene age these deposits are hosted in calc alkaline volcanic rocks emplaced as a result of three successive magma pulses in an emergent volcanic edifice submarine rhyolitic to rhyodacitic cryptodomes at ca 2 7 ma profitis ilias chondro vouno submarine to subaerial andesite to dacite domes at ca 2 2 to 1 5 ma triades galana kondaros katsimouti vani hydrothermal alteration of the volcanic rocks includes advanced argillic both hypogene and steam heated argillic phyllic adularia sericite and propylitic types in the northern sector triades galana agathia kondaros initial magma degassing derived from andesitic dacitic intrusives along ne sw to e w trending faults resulted in the development of pre ore hypogene advanced argillic alteration dickite alunite diaspore pyrophyllite halite and pyrite in a submarine environment mineralogical data indicate common features among the profitis ilias chondro vouno kondaros katsimoutis vani and triades galana mineralized centers all of which are characterized by the presence of galena fe poor sphalerite and chalcopyrite as well as abundant barite adularia sericite and to a lesser extent calcite which are typical of intermediate sulfidation epithermal type deposits locally at triades galana and kondaros agathia high sulfidation conditions prevailed as suggested by the presence of coexisting enargite and covellite the high silver and gold content of the western milos deposits is derived from ag bearing sulfosalts polybasite pearceite pyrargyrite freibergite and tellurides gold at profitis ilias both as native gold and silver gold tellurides is present in base metal precipitates within multicomponent blebs which recrystallized to form hessite petzite altaite coloradoite and native gold mineralogical evidence e g microchimney structures copper sulfides widespread occurrence of barite aragonite suggests that precious metal mineralization in western milos mineralization formed in a submarine setting we present information on the surface distribution of au ag cu pb zn as sb hg mo bi w and cd at western milos gold is enriched at profitis ilias chondro vouno deposits and to a lesser extent at triades galana arsenic is absent from the southern sector but shows elevated concentrations together with molybdenum bismuth and tungsten at the northern sector triades galana vani deposits the differences in precious and base metal abundances may be related to the depths at which the deposits are exposed and or different sources of magma the metal signatures of the triades galana and agathia kondaros katsimouti vani mo bi w as hg ag au occurrences compared to profitis ilias te au ag reflect different sources of magma dacite rhyodacite for profitis ilias andesite dacite for triades galana and dacite for kondaros katsimoutis the enrichment of te mo w and bi in the deposits is a strong indication of a direct magmatic contribution of these metals at western milos precious and base metal vein mineralization was deposited during episodic injection of magmatic volatiles and dilution of the hydrothermal fluids by seawater the mineralization represents seafloor sub seafloor precipitation of sulfides that formed in stockwork zones base and precious metal mineralization formed from intermediate to high sulfidation state fluids and mostly under boiling conditions as indicated by the widespread occurrence of adularia associated with metallic mineralization we speculate that the widespread occurrence of boiling and the shallow depth of the precious and base metal emplacement prevented the formation of seafloor massive sulfides

on the impact of local feedbacks in the central pacific on the enso cycle abstract while sea surface temperature sst anomalies in the eastern equatorial pacific are dominated by the thermocline feedback in the central equatorial pacific local wind effects such as zonal advection are important as well el nino southern oscillation enso simulations with a linear model improve markedly if these effects are included as a local wind stress feedback on sst an atmosphere model that reacts both to eastern and central pacific sst anomalies is needed for producing a realistic enso cycle first simulations are studied of a linear 1 5 layer reduced gravity ocean model and a linear sst anomaly equation forced by observed monthly wind stress if only the thermocline feedback is present in the sst equation sst can be simulated well in the eastern pacific but contrary to observations central pacific sst is out of phase with the eastern pacific if a wind stress feedback is added in the sst equation as a term proportional to the zonal wind stress correlations between observed an

native gold and gold rich sulfide deposits in a submarine basaltic caldera higashi aogashima hydrothermal field izu ogasawara frontal arc japan sulfide deposits with extremely high au concentrations up to 275 ppm avg 102 ppm n 15 high au ag ratios 0 24 n 15 and low cu cu zn ratios 0 03 n 15 were discovered in 2015 in active hydrothermal fields at a water depth of 760 m in a basalt dominated submarine caldera in the izu ogasawara frontal arc japan native gold grains occur in massive sulfide fragments concretions and metalliferous sediments from a sulfide mound 40 m across and 20 m high with up to 30 m high black smoker chimneys tiny native gold grains up to 14 m in diameter are mainly present in sulfide fallouts from chimney orifices and plumes larger native gold grains up to 150 m long occur mostly as discrete particles and or with amorphous silica and sulfides the larger gold grains are interpreted to represent direct precipitation from au bearing hydrothermal fluids circulating in and or beneath the unconsolidated sulfide mound deposits sulfur isotope compositions from a limited number of sulfide separates n 4 range from 4 3 to 5 8 34s similar to the quaternary volcanic rocks of the arc barite separates have values of 22 2 and 23 1 close to modern seawater values and indicate probable seawater sulfate origin the cu zn and pb concentrations in bulk samples of sulfide rich rocks are similar to those of volcanogenic massive sulfides formed in continental crustal environments the gold is interpreted to have formed by low temperature hydrothermal activity perhaps genetically different from systems with documented magmatic contributions or from seafloor hydrothermal systems in other island arc settings its presence suggests that basalt dominated submarine calderas situated on relatively thick continental crust in an intraoceanic arc setting such as the higashi aogashima knoll caldera may be perspective for gold mineralization

near bottom magnetic signatures of submarine hydrothermal systems at marsili and palinuro volcanoes southern tyrrhenian sea italy near bottom magnetic field data were collected using a towed magnetometer over selected parts of palinuro and marsili submarine volcanoes in the southern tyrrhenian sea italy we obtained equivalent magnetizations maps at these sites by inverting the corresponding magnetic anomalies highlighting the seafloor expression of hydrothermal alteration zones of reduced magnetization are interpreted as evidence for alteration related to hydrothermal processes they are associated with water column and seafloor observations of hydrothermal activity and altered host rocks at marsili volcano a large elliptical area of reduced magnetization is located south of the summit cone and perpendicular to the trend of marsili volcano itself this confirms the presence of a large hydrothermal system centered over the more recent eastern volcanic ridge and its associated magma chamber similarly areas of reduced magnetization over palinuro caldera are consistent with hydrothermal venting occurring along the caldera walls consistent with permeability structures related to caldera ring faults providing preferred pathways for the upflow of hydrothermal fluids

boiling vapour type fluids from the nifonea vent field new hebrides back arc vanuatu sw pacific geochemistry of an early stage post eruptive hydrothermal system in 2013 high temperature vent fluids were sampled in the nifonea vent field this field is located within the caldera of a large shield type volcano of the vate trough a young extensional rift in the new hebrides back arc hydrothermal venting occurs as clear and black smoker fluids with temperatures up to 368 c the hottest temperatures measured so far in the western pacific the physico chemical conditions place the fluids within the two phase field of nacl h2o and venting is dominated by vapour phase fluids with cl concentrations as low as 25 mm the fluid composition which differs between the individual vent sites is interpreted to reflect the specific geochemical fluid signature of a hydrothermal system in its initial post eruptive stage the strong cl depletion is accompanied by low alkali cl ratios compared to more evolved hydrothermal systems and very high fe cl ratios the concentrations of rey 180 nm and as 21 m in the most cl depleted fluid are among the highest reported so far for submarine hydrothermal fluids whereas the inter element rey fractionation is only minor the fluid signature which has been described here for the first time in a back arc setting is controlled by fast fluid passage through basaltic volcanic rocks with extremely high water rock ratios and only limited water rock exchange phase separation and segregation and at least two component fluid mixing metals and metalloids are unexpectedly mobile in the vapour phase fluids and the strong enrichments of fe rey and as highlight the metal transport capacity of low salinity low density vapours at the specific physico chemical conditions at nifonea one possible scenario is that the fluids boiled before the separated vapour phase continued to react with fresh glassy lavas the mobilization of metals is likely to occur by leaching from fresh glass and grain boundaries and is supported by the high water rock ratios the enrichment of b and as is further controlled by their high volatility whereas the strong enrichment of rey is also a consequence of the elevated concentrations in the host rocks however a direct contribution of metals such as as from magmatic degassing cannot be ruled out the different fluid end member composition of individual vent sites could be explained by mixing of vapour phase fluids with another fluid phase of different water rock interaction history

re assessment of the mid to late quaternary glacial and environmental history of the boco plain western tasmania the glacial geomorphology and drill core based stratigraphy of the boco plain western tasmania reveal a complex sequence of quaternary glacial and non glacial episodes the upper part of the southern boco plain stratigraphy was previously dated by 14c and u series on interbedded organics of mis 1 to mis 5 affinity u series dating of ferricretes associated with glacial diamictons from boco plain cores suggested that there were glacial advances broadly correlative with mis 6 8 and 10 however terrestrial cosmogenic nuclide 10be and 26al exposure ages for the moraine sequence preserved on the wider boco plain area indicate that moraines previously attributed to mis 6 and 8 advances were deposited during mis 10 or earlier cold stages there is no evidence for mis 2 4 or 6 affinity glacial advances onto the boco plain with ice of this age restricted to the west coast range new palynological records from the boco plain core 6690 confirmed the late quaternary ages of the upper part of the sequence whilst extinct palynomorphs indicate a pre quaternary age for the glacial diamictons at the base of core boco 4 and 10 consequently the mid pleistocene glacial sequence preserved in the boco plain is significantly older than previously envisaged with the post mis 10 to 12 geomorphology of the plain dominated by fluvial deltaic swamp peat and lacustrine environments

silica and germanium in pacific ocean hydrothermal vents and plumes dissolved silica si and inorganic germanium ge concentrations were measured in hydrothermal fluids from black smoker vents on the east pacific rise 21 n epr and the southern juan de fuca ridge 45 n sjdfr north and south cleft sites axial volcano these typically display end member concentrations ranging from 16 to 23 mm si and 150 to 280 nm ge and end member ge si ratios clustering between 8 and 14 10 6 more than 10 fold greater than the ratio entering the ocean via rivers 0 54 10 6 and being recycled in seawater 0 7 10 6 excess concentrations of dissolved si and ge above oceanic background are observed in mid water hydrothermal plumes over mid ocean ridge mor spreading centers on the southern epr sepr 10 20 s and the sjdfr the largest si and ge concentration anomalies occur over the north cleft segment of the sjdfr these are a factor of three greater than anomalies over the sepr 10 20 s excess ge correlates with excess3he in plumes at a ge 3he molar ratio of about 1 104 approximately the same ratio as in black smokers these observations combined with low abundances of ge in femn rich metalliferous sediments suggest that ge and si behave conservatively in mid ocean ridge hydrothermal plumes a simple ocean si and ge balance constrained by the global river silica flux and ge si ratios in hydrothermal vents rivers and biogenic silica suggests that the global hydrothermal silica flux is about 1 4 1011 mole yr 1 much lower than that estimated from3he either 1 70 80 of the ge flux to the ocean is removed in as yet undiscovered sinks not opal or 2 only 10 of the mantle to ocean3he and heat fluxes is associated with mor hydrothermal convection through the 350 c isotherm 90 is off ridge or 3 the oceanic ge si 3he and87sr86sr balances today are far from steady state

advances in quaternary studies in tasmania the last 35 years have seen rapid advances in our knowledge of climate change during the quaternary period in tasmania extensive mapping and new dating studies particularly since the advent of exposure dating have revealed that maximum ice advance occurred 1 ma ago and later advances were less extensive ice advances occurred several times during the last 100 ka not only during the last glacial maximum deglaciation was rapid after 18 ka and complete by 14 ka ice strongly affected limestone and produced extensive glaciokarst with deranged surface drainage glacial sediment plugged conduits to underground passages partially filled with glaciofluvial gravels periglacial erosion and human impact since late oxygen isotope stage ois 3 enhanced sediment influxes new pollen records particularly from lake selina provide a 125 ka vegetation and climate record representative of the southern hemisphere finally stable isotope studies of speleothem growth have revealed wide swings in climate the climate was warm and moist during ois 5e and early in ois 1 climate was cold and dry during ois 5d and 4 and prevented speleothem growth during ois 3 and ois 2

helium isotopic composition of the tabar lihir tanga feni island arc papua new guinea helium abundances and isotopic ratios have been measured in samples of geothermal gases submarine ultramafic xenoliths and subaerial mafic phenocrysts and xenoliths from the tabar lihirtanga feni tltf arc in the bismarck archipelago of papua new guinea these unusual volcanoes are produced by adiabatic decompression melting of subduction modified upper mantle and apparently carry an exceptionally large slab derived component they therefore provide an ideal setting for studying the role of subducted helium in arc volcanoes helium isotopic ratios in the geothermal fluids submarine xenoliths and most helium rich subaerial samples indicate the mantle source regions beneath the tabar island group and lihir island have 3he 4he ratios of about 7 2 times the atmospheric ratio r a whereas the mantle source for ambitle island feni group in the more southern tltf arc has a lower ratio of about 6 6 r a these ratios are only slightly lower than typical depleted upper mantle values of about 8 5 r a indicating that even severely slab modified mantle wedge carries a relatively minor slab derived helium component the systematically lower 3he 4he ratios of the ambitle samples are interpreted to reflect a slightly greater slab derived helium component helium isotopic ratios as low as 2 r a which are correlated with low total helium abundances were observed in subaerial augitic clinopyroxene phenocrysts coexisting olivine and sodium rich acmitic clinopyroxene have higher helium abundances and isotopic ratios this isotopic disequilibrium between coexisting mineral phases is interpreted as crustal level addition of a low 3he 4he component to an actively outgassing magma from which different mineral phases trap helium sequentially

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

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

flux of volatiles and ore forming metals from the magmatic hydrothermal system of satsuma iwojima volcano the satsuma iwojima volcano southwest japan degasses 5 x 10 6 t yr h 2 o 9 x 10 4 t yr s and 6 x 10 4 t yr cl from high temperature 880 c fumaroles atop a now altered rhyolite dome that erupted 1200 yr ago acidic hot springs ph 1 1 1 8 discharge 20 x 10 6 t yr h 2 o to the sea this water is composed of 1 part magmatic vapor absorbed by 6 parts meteoric ground water the cl and so 4 in solution originate from the vapor whereas cation components are derived largely by dissolution of the rhyolite the flux of pb zn cu and mo in the vapor and acidic springs ranges from 0 1 to 10 t yr each whereas the au flux is 10 5 and 10 3 t yr respectively the low concentrations of nacl and metals in the vapor are due to the condensation of a hypersaline liquid from the vapor during ascent and depressurization meaning that the atmospheric pressure vapor does not reflect the composition of the fluid exsolving from the magma neither this low pressure vapor nor the acidic waters can account for high sulfidation cu au ore deposits deduced to have formed in this environment such mineralization requires the subsequent ascent of a metal rich fluid

dating the late cenozoic glacial sequence pieman river basin western tasmania australia abstract the pieman river basin western tasmania displays one of the most complete middle to early pleistocene glacial sequences from a southern hemisphere mid latitude site most of the glacial deposits exceed the 14 c limit although mapping of the depositional units using morphostratigraphic post depositional weathering criteria and magnetostratigraphy shows that the sediments of the boco and bobadil glaciation were deposited during the brunhes normal chron 275 kyr late last margaret glaciation advances in the pieman basin are much more restricted in extent and display evidence for multiple stillstand readvance phases during the decay of the system with most of the ice having disappeared by 14 kyr bp

variability in the microbial communities and hydrothermal fluid chemistry at the newly discovered mariner hydrothermal field southern lau basin 1 a newly discovered hydrothermal field called the mariner field on the valu fa ridge in the southern lau basin was explored and characterized with geochemical and microbiological analyses the hydrothermal fluid discharging from the most vigorous vent snow chimney maximum discharge temperature 365 c was boiling at the seafloor at a depth of 1908 m and two distinct end member hydrothermal fluids were identified the fluid chemistry of the typical cl enriched and cl depleted hydrothermal fluids was analyzed as was the mineralogy of the host chimney structures the variability in the fluid chemistry was potentially controlled by the subseafloor phase separation vapor loss process and the microbial community activities microbial community structures in three chimney structures were investigated using culture dependent and independent techniques the small subunit ssu rrna gene clone analysis revealed that both bacterial and archaeal rrna gene communities on the chimney surfaces differed among three chimneys cultivation analysis demonstrated significant variation in the culturability of various microbial components among the chimneys particularly of thermophilic h2 oxidizing and s oxidizing chemolithoautotrophs such as the genera aquifex and persephonella the physical and chemical environments of chimney surface habitats are still unresolved and do not directly extrapolate the environments of possible subseafloor habitats however the variability in microbial community found in the chimneys also provides an insight into the different biogeochemical interactions potentially affected by the phase separation of the hydrothermal fluids in the subseafloor hydrothermal habitats in addition comparison with other deep sea hydrothermal systems revealed that the mariner field microbial communities have unusual characteristics

rare earth elements as indicators of hydrothermal processes within the east scotia subduction zone system the east scotia subduction zone located in the atlantic sector of the southern ocean hosts a number of hydrothermal sites in both back arc and island arc settings high temperature 348 c black smoker vents have been sampled at three locations along segments e2 and e9 of the east scotia back arc spreading ridge as well as white smoker 212 c and diffuse 28 c hydrothermal fluids from within the caldera of the kemp submarine volcano the composition of the endmember fluids mg 0 mmol kg is markedly different with ph ranging from 1 to 3 4 cl from 90 to 536 mm h2s from 6 7 to 200 mm and f from 35 to 1000 m all of the vent sites are basalt to basaltic andesite hosted providing an ideal opportunity for investigating the geochemical controls on rare earth element ree behaviour endmember hydrothermal fluids from e2 and e9 have total ree concentrations ranging from 7 3 to 123 nmol kg and chondrite normalised distribution patterns are either light ree enriched lacn ybcn 12 8 30 0 with a positive europium anomaly eucn eu cn 3 45 59 5 or mid ree enriched lacn ndcn 0 61 with a negative eu anomaly eucn eu cn 0 59 by contrast fluids from the kemp caldera have almost flat ree patterns lacn ybcn 2 1 2 2 eucn eu cn 1 2 2 2 we demonstrate that the ree geochemistry of fluids from the east scotia back arc spreading ridge is variably influenced by ion exchange with host minerals phase separation competitive complexation with ligands and anhydrite deposition whereas fluids from the kemp submarine volcano are also affected by the injection of magmatic volatiles which enhances the solubility of all the rees we also show that the ree patterns of anhydrite deposits from kemp differ from those of the present day fluids potentially providing critical information about the nature of hydrothermal activity in the past where access to hydrothermal fluids is precluded

cosmogenic radionuclide chronology of pre last glacial cycle moraines in the western arthur range southwest tasmania cosmogenic 10be and 26al exposure ages of 12 boulders from two moraine complexes in the western arthur range of southwest tasmania which previously were considered to have been deposited during the last glacial maximum predate the last glacial cycle zero erosion minimum exposure ages range from 95 ka to 232 ka based on weighted mean 10be and 26al ages per boulder for a reasonable choice of erosion rates 10be boulder ages range from 105 to 326 ka respectively although a direct association of moraine construction to a specific marine isotope stage mis glaciation is not definitive erosion corrected exposure ages indicate glacial advances commensurate with mis 6 and 10 although the latter advance may be attributable to mis 8 if the erosion rate correction is an over estimate given the relatively close proximity of the dated moraines to their source cirques this new cosmogenic glacial chronology implies a very limited extent for any younger glacial advances that occurred in the western arthur range during the last glacial cycle post mis 5 including the global lgm

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

cyclic processes and factors leading to phreatic eruption events insights from the 25 september 2007 eruption through ruapehu crater lake new zealand abstract a dangerous block ash eruption occurred without warning from ruapehu crater lake on 25 september 2007 ending a 6 month period of temperature decline in the lake the northerly directed blast sent ballistics of up to 2 m diameter more than 2 km from the source the ejecta comprised a variety of volcano lacustrine lithologies many showing evidence of intense hydrothermal alteration petrographic studies of the ballistics reveal numerous examples of pores vesicles being filled with assemblages of elemental sulphur anhydrite pyrite and natroalunite and many ballistics exuded liquid sulphur from their pores during cooling at atmospheric pressure up to 5 of the ash was comprised of fine grained juvenile glass material confirming the presence of magma in the shallow vent environment a long recognised characteristic of this volcano is the thermal cycling behaviour of the crater lake behaviour which has remained effectively unchanged through two magmatic eruption events in 1945 and in 1995 96 airborne measurements of co2 and so2 flux from the volcano since 2003 show a strong positive correspondence with temperature cycling in the lake pointing to a definitive link between heat and mass discharge through the system low so2 emission rates and c s mole ratios 30 were typical of the period 2003 to early 2007 and appear to reflect vigorous scrubbing of s gases in the hydrothermal system during this time to better understand the chemical and physical processes operating in this very dynamic volcanic hydrothermal system and its propensity to develop potentially dangerous hydrothermal seals we have developed an integrated finite difference tough2 heat mass transport simulation of the hydrothermal environment the model which is constrained by observed heat and mass flux characteristics of the volcano demonstrates the transient nature of the heating cycles on the vent lake system of particular interest is the role of co2 as a relatively inert pressure transmitting medium in the hydrothermal environment seal formation was simulated using the reactive transport code x1t which showed that condensation of magmatic vapour into a highly porous medium of andesitic composition leads to rapid formation of an elemental sulphur anhydrite natroalunite mineral assemblage and a drastic reduction in permeability we suggest that since the 1995 96 vent clearing eruptions a shroud of elemental sulphur and other alteration phases formed along the margins of the 2 phase liquid vapour region enclosing the conduit this effectively seals the upper portion of the vent from the adjacent hydrostatically controlled environment and allows for development of pressurised vapour static gas columns beneath the northern and central vents

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

rapid rates of growth and collapse of monowai submarine volcano in the kermadec arc most of earth s volcanoes are under water as a result of their relative inaccessibility little is known of the structure and evolution of submarine volcanoes advances in navigation and sonar imaging techniques have made it possible to map submarine volcanoes in detail and repeat surveys allow the identification of regions where the depth of the sea floor is actively changing here we report the results of a bathymetric survey of monowai submarine volcano in the tonga kermadec arc which we mapped twice within 14 days we found marked differences in bathymetry between the two surveys including an increase in seafloor depth up to 18 8 m and a decrease in depth up to 71 9 m we attribute the depth increase to collapse of the volcano summit region and the decrease to growth of new lava cones and debris flows hydroacoustic t wave data reveal a 5 day long swarm of seismic events with unusually high amplitude between the surveys which directly link the depth changes to explosive activity at the volcano the collapse and growth rates implied by our data are extremely high compared with measured long term growth rates of the volcano demonstrating the pulsating nature of submarine volcanism and highlighting the dynamic nature of the sea floor

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

a special issue on archean magmatism volcanism and ore deposits part 2 volcanogenic massive sulfide deposits preface this is the second of a two part special issue of economic geology devoted to archean ore deposits the first part of the special issue vol 107 no 5 contains six papers that discuss craton to deposit scale controls on komatiite associated ni cu pge deposits barnes and fiorentini 2012 collins et al 2012 fiorentini et al 2012 heggie et al 2012a b taranovic et al 2012 and six papers that discuss the diversity and key aspects of greenstone hosted au deposits cote mantha et al 2012 garde et al 2012 leclerc et al 2012 mercier langevin et al 2012b schneider et al 2012 sherlock et al 2012 a general introduction to the special issue and an overview of some implications for exploration for greenstone hosted au and komatiite associated ni cu pge deposits in ancient belts is given in mercier langevin et al 2012a the ten papers in this second part of the special issue discuss specific aspects of archean volcanogenic massive sulfide vms deposits the archean which represents more than one third of earth s history was a prolific period for the formation of vms deposits franklin et al 2005 most of these deposits formed within a comparatively narrow time interval between 2740 and 2690 ma in the neoarchean approximately 8 of the global vms tonnage production reserves and geologic resources is contained within deposits of archean age fig 1a given the low degree of preservation of archean crust compared to phanerozoic crust e g veizer 1988 the abundance of archean vms deposits is remarkable proterozoic vms deposits account for approximately 20 of the global vms tonnage whereas the phanerozoic deposits contain 72 of the global tonnage the latter is due in large part to giant vms deposits of the iberian pyrite belt in spain and portugal the urals in russia the rudny

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

microearthquake patterns following the 1998 eruption of axial volcano juan de fuca ridge mechanical relaxation and thermal strain 1 ocean bottom seismic networks deployed following the 1998 eruption of axial seamount reveal an evolving pattern of microearthquake activity associated with subsurface magmatism and thermal strain seismicity rates decay steadily over 15 months of observation february 8 1998 to april 30 1999 consistent with a trend toward thermal and mechanical equilibrium in the shallow crust after the magmatic event immediately after the eruption seismicity rates were high for about 60 days in the southeast corner of the caldera where lava flows from the 1998 eruption were mapped a small burst of seismic activity was observed on the southeast shoulder of the volcano from 100 to 150 days after the eruption these events which are characterized by slip on nearly vertical faults in the shallow crust extend about 6 km from the southeast corner of the caldera and overlie a mid crustal low velocity zone after this episode seismicity rates remain low until the end of the observation period 455 days after the eruption shallow 0 7 km depth events consistent with thermal contraction and volume changes of 2 10 3 m3 in 5 m3 sources are observed in individual clusters beneath hydrothermal vents within the 1998 lava flow at the southeast edge of the caldera microearthquakes observed during the last 70 days of observation are distributed around the central caldera most likely representing small amounts of subsidence on caldera faults during the final stages of equilibration following melt withdrawal associated with the 1998 eruption

topographic and microclimatic impacts on glaciation of the denison range southwest tasmania abstract morphostratigraphic relationships between landforms and sediments comparative boulder weathering status and paired 10 be and 26 al exposure ages indicate the occurrence of at least three separate glaciations that are interpreted as dating from mis 2 6 and possibly 8 the rhona glacier remained at or close to its greatest lgm extent until 17 6 ka due to a very favourable micro climate that resulted from local topography that these factors were sufficient to over power relatively subtle zonal temperature shifts that caused significant changes in more exposed tasmanian glaciers implies a need for caution in correlating between glacier systems in markedly different topographic settings when environmental conditions are only marginally supportive of glaciation no evidence was detected for any greater ice extent during mis 3 or mis 4 than during mis 2 but much more extensive glaciations occurred during earlier glacial climatic cycles reduced local precipitation in parallel with increasing aridity of the australian continent may account for the progressively diminishing maximum extent of glaciers during the latter part of the pleistocene and it would have emphasized the importance of local topography and microclimate for the glaciers of southwest tasmania

magma storage beneath axial volcano on the juan de fuca mid ocean ridge axial volcano which is located near the intersection of the juan de fuca ridge and the cobb eickelberg seamount chain beneath the northeast pacific ocean is a locus of volcanic activity thought to be associated with the cobb hotspot1 the volcano rises 700 metres above the ridge has substantial rift zones extending about 50 kilometres to the north and south and has erupted as recently as 1998 ref 2 here we present seismological data that constrain the three dimensional velocity structure beneath the volcano we image a large low velocity zone in the crust consisting of a shallow magma chamber and a more diffuse reservoir in the lower crust and estimate the total magma volume in the system to be between 5 and 21 km3 this volume is two orders of magnitude larger than the amount of melt emplaced during the most recent eruption3 4 0 1 0 2 km3 we therefore infer that such volcanic events remove only a small portion of the reservoir that they tap which must accordingly be long lived compared to the eruption cycle on the basis of magma flux estimates we estimate the crustal residence time of melt in the volcanic system to be a few hundred to a few thousand years