chemistry of hydrothermal fluids from the 17 s active site on the north fiji basin ridge sw pacific abstract in june 1989 a diving cruise of the french submersible nautile was made along the north fiji basin spreading ridge the objective was the geological and geochemical study of the active spreading axis and of the hydrothermal processes discovered during the kaiyo cruise in 1988 active anhydrite chimneys associated with underlaying sulfide deposits were studied in the central spreading ridge the transparent venting fluid showed significant salinity depletion the extrapolated concentrations of all the chemical species in the pure end member showed a signature similar to that of the cl depleted hydrothermal fluid from the ashes vent site in the juan de fuca ridge these features suggest that the present hydrothermal end member resulted from subcritical phase separation which generated a low salinity vapor phase followed by condensation and mixing with normal seawater in the last part of the plumbing system of the vents

sedimentologic and stratigraphic properties of early cretaceous neo tethys shelf margin of arabia the qamchuqa formation of the zagros folded zone kurdistan region of iraq abstract the qamchuqa formation is well exposed in the high folded zone hfz of northeast iraq the formation is highly dolomitized and contains thick reservoir units in the subsurface region south of the hfz deposition of the formation took place at the shelf margin of early cretaceous neo tethys ocean it merges south and southeastward to the shallow marine shelf of arabia and to deep basin accumulations farther north in the study area the formation is divided into three members lower member 250m thick of interbedded bioclastic calcimudstone wackestone mw bioclastic packstone bp bioclastic floatstone bf and medium to coarse crystalline dolorudstone dolograinstone cd these strata accumulated in low to medium energy subtidal fore shoal setting the middle member consists of thick succession 325m of massively bedded cd lithofacies interpreted as high energy shoal facies which represents barremian aptian main shelf margin succession the upper member 155m thick consists of three lithofacies of mw cd and fine crystalline dolomudstone fd in ascending order it is interpreted as lagoon mw through subtidal carbonate sand shoal cd to supratidal penecontemporaneous dolomudstone fd the lower two members represent a long term barremian to aptian shallowing upward megacycle capped by late aptian unconformity incurred by relative sea level drop this temporal gap is coeval with an erosional vacuity recognized throughout the arabian peninsula sea level rise in early albian heralded deposition of the upper member which also represents a shallowing upward cycle surmounted by regionally extensive subaerial unconformity recognized in the arabian peninsula correlation and stratigraphic position of the formation under regional context has been discussed

reappraisal of the beekmantown group sedimentology and stratigraphy montreal area southwestern quebec implications for understanding the depositional evolution of the lower middle ordovician laurentian passive margin of eastern canada detailed lithostratigraphic mapping of the beekmantown group of southwestern quebec has refined the field application of the previously proposed tripartite division of the group i e theresa beauharnois and carillon formations the group is a peritidal dominated succession that accumulated on the epicontinental laurentian passive margin biostratigraphic data based on conodonts from this group indicate an early to early middle ordovician age and are partially time correlative with the wallace creek to naylor ledge strata of the philipsburg group southern quebec this conodont biostratigraphy sheds new light on the temporal evolution and depositional framework of the beekmantown platform the platform evolved as a distally steepened ramp during deposition of the theresa formation and the ogdensburg member of the beauharnois formation early to middle ibexian correlative strata of the philipsburg group include the wallace creek and morgan corner formations which represent outer platform sediments the coarse grained sandstone of the theresa formation accumulated in the innermost platform whereas coarse grained carbonates of the ogdensburg member indicate open marine subtidal to intertidal carbonate sand shoals by late ibexian the platform developed a pronounced margin where thrombolites flourished under high energy conditions these are represented by the thrombolite rich hasting creek and naylor ledge formations of the philipsburg group consequently a broad lagoon formed on the lee side of the platform margin where low energy conditions prevailed and accumulation of burrow mottled dolostones of the huntingdon member of the upper beauharnois formation took place the lagoon became more restricted during the latest stages of the basin fill whiterockian and high intertidal to supratidal sediments of the carillon formation were deposited

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

petrology of the axial ridge of the mariana trough backarc spreading center abstract the axial ridge of the mariana trough backarc basin between 17 40 n and 18 30 n rises as much as 1 km above the floor of a 10 15 km wide rift valley physiographic segmentation with minor ridge offsets and overlaps coincides with a petrologic segmentation seen in trace element and isotope chemistry analyses of 239 glass and 40 aphyric basalt samples collected with alvin and by dredging show that the axial ridge is formed largely of olivine hypersthene normative tholeiitic basalt about half of these are enriched in both lil elements and volatiles but are depleted in hfs elements like other rocks found throughout much of the mariana trough the lil enrichments distinguish these rocks from n morb even though nd and sr isotope ratios indicate that much of the crust formed from a source similar to that for n morb in addition to lil enriched basalt there is lil depleted basalts even more closely resembling n morb in major and trace elements as well as sr nd and pb isotopes both basalt varieties have higher al and lower total fe than morb at equivalent mg level mg ranges from relatively primitive e g mg 65 70 to more highly fractionated e g mg 45 50 highest parts of the axial ridge are capped by pinnacles with elongated pillows of basaltic andesite e g 52 56 sio 2 these are due to extreme fractional crystallization of basalts forming the axial ridge active hydrothermal vents with chimneys and mats of opaline silica barite sphalerite and lesser amounts of pyrite chalcopyrite and galena formed near these silicic rocks the vents are surrounded by distinctive vent animals polychaete worms crabs and barnacles isotope data indicate that the mariana trough crust was derived from a heterogeneous source including mantle resembling the morb source and an arc source component the latter was depleted in hfs elements in previous melting events and later modified by addition of h 2 o and lil elements

depositional environment reservoir units evolution and hydrocarbon habitat of shuaiba formation lower cretaceous abu dhabi united arab emirates the shuaiba formation aptian is a thick porous shelf carbonate present in the subsurface over much of the arabian gulf it is the uppermost formation of the thamama group lower cretaceous and is overlain by the nahr umr formation albian and overlies the kharaib formation barremian the formation is divided into nine reservoir units a to i from the base upward reservoir units a b and c represent calcareous algal platform sediments showing some open marine influence they are dominated by chalky lime mudstones to wackestones with abundant codiacian green algae bacinella irregularis and lithocodium aggregatum and stylolite seams reservoir units d and f are deeper open marine shelf facies dominated by dense argillaceous lime mudstones to wackestones whic are burrowed and bioturbated reservoir units g and i represent lagoonal facies dominated by dense argillaceous wackestones to packstones which are sparsely fossiliferous and commonly stylolitic reservoir unit h represents a shallow water coarser grained shelf limestone containing abundant rudists algae orbitolinids and other foraminifers reservoir unit ho represents a shoal facies characterized by wackestone to packstone sediment with abundant orbitolina and scattered rudist debris and other foraminifers in northeast and southeast dhabi the basinal shuaiba equivalent bab member was deposited under slightly deeper quieter marine conditions and is dominated in parts of the section by dense argillaceous lime mudstones and shaly wackestone and calcareous shale i tervals the major reefal shuaiba buildup in abu dhabi trends northwest southeast it is in this trend that the major oil fields shah bu hasa and zurarah shaybah were discovered and from which some wells produce in western abu dhabi e g ruwais 2 hydrocarbons also occur outside of the rudist trend in the shuaiba formation in the asab jarn yaphour and sahil onshore oil fields and the zakum and mandous offshore oil fields local reefal anomalies are also encountered in parts of the deep marine basin of eastern abu dhabi these are formed by an unusual pre reefal growth of orbitolinids rudists and algae an isolated buildup patch reef consisting of coralgal boundstones encountered in jarn yaphour and zabbara fields may represent organic growth over either a rising salt structure or an uplifted zone formed by deep seated faults geochemical studies reveal that the main source for the thamama oils are the upper jurassic dukhan formation onshore abu dhabi or diyab formation offshore abu dhabi however some shuaiba source rocks may have existed in intrashelf basinal areas in the upper thamama zone the nahr umr shale acts as a seal for the shuaiba reservoir in this area

variable morphologic expression of volcanic tectonic and hydrothermal processes at six hydrothermal vent fields in the lau back arc basin ultrahigh resolution bathymetric maps 25 cm grid are used to quantify the physical dimensions of and spatial relationships between tectonic volcanic and hydrothermal features at six hydrothermal vent fields in the lau back arc basin supplemented with near bottom photos and nested within regional dsl 120a side scan sonar data these maps provide insight into the nature of hydrothermal systems along the eastern lau spreading center elsc and valu fa ridge vfr along axis transitions evident in localized volcanic morphology and tectonic characteristics include a change from broad low relief volcanic domes hundreds of meters wide 10 m tall that are dominated by pillow and lobate lava morphologies and are cut by faults and fissures to higher aspect ratio volcanic domes tens of meters wide tens of meters tall dominated by aa type lava morphologies with finger like flows and few tectonic structures these along axis differences in localized seafloor morphology suggest differences in hydrothermal circulation pathways within the shallow crust and correlate with regional transitions in a variety of ridge properties including the large scale morphology of the ridge axis shallow axial valley to axial high seafloor lava compositions and seismic properties of the upper crust differences in morphologic characteristics of individual flows and lava types were also quantified providing an important first step toward the remote characterization of complex terrains associated with hydrothermal vent fields

cyclicity and paleoenvironmental dynamics rocknest platform northwest canada the superbly exposed rocknest formation northwest territories canada contains 140 to 160 shallowing upward cycles 1 to 15 m thick that contain distinctive marker beds and can be correlated for 200 km parallel to strike and 120 km perpendicular to strike cycles are grouped according to cycle base lithology which reflects paleogeographic position on the platform shale based cycles of the distal inner shelf pass westward into dolosiltite based cycles then into tufa based cycles of the shoal complex and then into grainstone based cycles of the outer shelf cycles are bounded by erosional surfaces that become less pronounced away from the shoal complex cycles formed in response to small asymmetric rapid rise slow fall eustatic oscillations in sea level 10 m during sea level rise rapid transgression and submergence of tidal flats occurred along the eastern margin of the shoal complex followed by eastward expansion of the shoal complex and slow progradation of tidal flats over lagoonal facies during sea level fall a glacio eustatic model for cyclicity accounts for the data favoring asymmetric eustatic sea level oscillations subaerial exposure and vadose diagenesis of platform during sea level falls arrested progradation and incomplete shoaling of many cycles and cycle periods of 20 000 to 100 000 yr 18 000 to 30 000 yr for rocknest inner shelf slopes ranged from 8 cm km average at high sea level stand to 2 cm km average at low sea level stand tidal flat progradation rates were 7 to 9 km 1 000 yr interaction of inner shelf slope sea level fall rate and sedimentation rate generates complete condensed or expanded cycle profiles one dimensional computer modeling reveals that sedimentation rates of shoal complex facies were 250 cm 1 000 yr that lag times in sedimentation following transgression may have ranged from zero on the shoal complex to 2 000 yr on the distal inner shelf and that subtidal sedimentation rates may have ranged from 80 cm 1 000 yr for the proximal inner shelf to 20 cm 1 000 yr for the distal inner shelf

tectonic evolution of the oman mountains an introduction it is now more than 20 years since the geologicalsociety published the geology and tectonics ofthe oman region robertson et al 1990 as oneof its early special publications that volume the blue book as it became fondly known to multiplegenerations of undergraduates has been a majorreference on the geology of oman for many whowork in the region this present volume moremodest in its size compared to its illustrious prede cessor is the fruit of a conference on the geologyof the arabian plate and the oman mountainsheld in january 2012 at sultan qaboos universityin muscat organized by professor sobhi nasirwith colleagues from sultan qaboos university the oman government and the geological societyof oman since the rst comprehensive study ofthe geology of the oman mountains during thelate 1960s and early 1970s by ken glennie and histeam from shell the oman mountains have beenknown to contain some of the most spectacularand best exposed geology not only in the middleeast but across the world a summary of the geo logy and the lithostratigraphy is given in figure 1 the publications of glennie et al 1973 1974 building on many earlier shell geologists internalreports notably d m morton r h tschopp h h wilson b m reinhardt and m w hughes clarke set out the major stratigraphic frameworkfor the whole area de ned the major structuresand critically interpreted the semail ophiolite as athrust sheet of oceanic crust and upper mantleemplaced onto the previously passive continentalmargin of arabia since the glennie et al 1974 memoir was published oil companies have carriedout increasingly more intensive work comparingwell sections in the interior with the permian mesozoic shelf carbonates so beautifully exposedalong numerous wadis cutting through the jebelal akhdar and saih hatat massifs during the late 1970s and 1980s two majorresearchteamsfromtheusgs ledbybobcolemanand cliff hopson and the open university uk led by ian gass john smewing and steve lip pard conducted detailed geological surveys acrossthe ophiolite in the muscat ibra transect usgs and northern ophiolite ou respectively theirresults were published in a special issue of thejournal of geophysical research volume 86 editors coleman hopson 1981 and the geologi cal society of london memoir no 11 lippard etal 1986 major systematic mapping of the omanmountains as well as the interior batain coast anddhofar region has been carried out by the bureaude recherches ge ologiques et minieres brgm france the geological survey of japan and theuniversity of berne switzerland see for examplepeters et al 1991 and the whole uae part of thenorthern oman mountains was recently mapped bythe british geological survey uae ministry ofenergy petroleum mineral resources 2012 during the last 20 years major research groupsfrom france japan usa and the uk have con ducted research projects in the country detailed eld studies of the oman ophiolite have beencombined with geochemical and isotopic studiesto determine the tectonic setting and evolution ofthe late cretaceous oceanic crust and upper mantle boudier juteau 2000 field based studies havealso been linked to ocean drilling sites in particularthe east paci c rise to compare the ophiolite toregions of active fast spreading key to the obduc tion emplacement story are the amphibolite andgreenschist facies rocks in the metamorphic solethat record an inverted metamorphic eld gradientalong the base of the ophiolite the ophiolite hasbeen the source of recent detailed studies involvingthe possible sequestration of co

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

tectono stratigraphic development of the qamar basin eastern yemen abstract the qamar basin is a polyphase rift basin located in eastern yemen adjacent to the indian ocean it probably originated as part of an extensive rift system which developed during the late jurassic to early cretaceous and led to the break up of gondwanaland rift reactivation during the mid cretaceous affected limited areas including the qamar basin a third episode of rifting occurred during the oligo miocene prior to sea floor spreading in the gulf of aden since spreading in the gulf began in the middle miocene the offshore qamar basin has been thermally subsiding in contrast the onshore part of the basin has been elevated by over 1 km the nature of the pre mid cretaceous basin fill is unknown during santonian to early campanian times thick fluvio deltaic clastics accumulated in a rapidly subsiding depocentre marked deepening during the early campanian led to deposition of deep water limestones during the late campanian prograding deep marine clastics infilled the basin minor transgression during the maastrichtian caused a resumption of marine carbonate deposition sedimentation was interrupted during the early palaeocene following which shallow marine carbonates were deposited over a large area of the arabian peninsula after a hiatus spanning the late eocene to late oligocene carbonate sedimentation resumed offshore in an active rift basin deep water carbonates and carbonate turbidites accumulated in lows whilst reefs developed on footwall highs from the late miocene onwards the reefs have been gradually drowned by rapidly accumulating clastics onshore the tertiary rift episode was associated with major uplift and only a thin veneer of recent wadi deposits overlies the rift topography the superposition of jurassic cretaceous and tertiary rifts which has not been described elsewhere in the region is tentatively related to the evolution of the indian ocean

tide influenced acidic hydrothermal system offshore ne taiwan elemental sulfur and hydrogen sulfide emitted offshore of northeastern taiwan known to local fishermen for generations but never studied until recently are found to have originated from a cluster of shallow 92 with small amounts of h2s helium isotopic ratios 7 5 times that of air indicate that these gases originate from the mantle high temperature hydrothermal fluids have measured temperatures of 78 116 degrees c and ph 25 degrees c values as low as 1 52 likely the lowest to be found in world records low temperature vents 30 65 degrees c have higher ph values continuous temperature records from one vent show a close correlation with diumal tides suggesting rapid circulation of the hydrothermal fluids c 2005 elsevier b v all rights reserved

thermogenic hydrocarbons from the offshore calypso hydrothermal field bay of plenty new zealand hydrothermal gases from shallow seafloor vents in the bay of plenty new zealand contain co2 ch4 and the higher gaseous hydrocarbons up to i n c4h10 the gases are similar to those discharged at fumaroles on the nearby white island carbon isotope compositions for co2 fall between 3 4 and 5 5 pdb and reflect a shallow magmatic carbon source the 13c values of ch4 range from 24 6 to 28 9 pdb and the d values vary between 122 and 135 smow the ch4 isotope values and the presence of the higher hydrocarbon compounds such as c2h6 and c3h8 with 13c values near 20 pdb suggest hydrocarbon production by high temperature maturation of sedimentary organic matter and mixing 1 1 of the thermogenic ch4 with abiogenic ch4 long chained hydrocarbons occur in dredged samples close to the active vents their n alkane distribution has a high to moderate odd even predominance and an extensive hopane series indicative of higher land plant waxes and prokaryotic membranes in the source substantial amounts of unsubstituted polynuclear aromatic hydrocarbons pah mark the transition from aliphatic to aromatic dominated bitumens consistent with extensive source maturation resulting from thermal stress the bitumens are interpreted as pyrolysates derived from buried near coastal vegetation and terrestrial detritus under various thermal regimes mixed with immature seafloor organic matter

elemental mercury at submarine hydrothermal vents in the bay of plenty taupo volcanic zone new zealand hot springs in active geothermal areas such as yellowstone national park the geysers geothermal field in california and the taupo volcanic zone in new zealand are notably enriched in the trace metals au ag as sb and hg such near surface hot springs have formed many of the world s important deposits of gold and silver and some of the largest deposits of mercury the majority of these are associated with continental geothermal systems in subaerial environments here we report the discovery of active mercury depositing hot springs in a submarine setting at nearly 200 m water depth within the offshore extension of the taupo volcanic zone of new zealand these vents contain the first documented occurrence of elemental mercury on the sea floor and provide an important link between offshore hydrothermal activity and mercury depositing geothermal systems on land the discovery has implications for mercury transport in sea floor hydrothermal systems and underscores the importance of submarine volcanic and geothermal activity as a source of mercury in the oceans

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

blackriveran lower mohawkian upper ordovician lithostratigraphy rhythmicity and paleogeography ottawa embayment eastern ontario canada the ottawa embayment contains erosional remnants of a shallow water carbonate platform st lawrence platform of late ordovician caradocian age stratigraphy of three blackriveran formations in ascending order pamelia lowville and chaumont documents regional changes in continuity and types of depositional facies the pamelia formation contains two members each containing basin wide basal siliciclastic units overlain by interbedded limestone dolostone and shale an alternate division recognizes six shallowing upward units regionally extensive intertidal to supratidal dolomitic sandstone and or sandy dolostone define their tops sedimentary structures and isotope c o geochemistry support a syngenetic origin of this stratigraphic bedded dolomite the lowville formation contains two facies associations subtidal to lower intertidal bioclastic and oolitic packstone grainstone followed by lagoonal to intertidal mudflat facies lateral facies continuity is reduced compared to the pamelia formation the chaumont formation contains thick beds of burrowed bioclastic peloidal mudstone to packstone and minor shale no rhythmic pattern is recognized in these subtidal facies upsection decrease of rhythmic sedimentation with a decrease in lateral facies continuity of the studied strata reflects a progressive increase in net accommodation space related to taconic transgression higher order rhythmicity of dolostone and sandstones of the pamelia formation can be traced into adjacent regions new york and kingston ont dolomitic units may identify basin wide chronostratigraphic markers potentially useful for future sequence analysis regional correlation reveals a good oceanographic linkage between the ottawa embayment and the appalachian basin during pamelia time and a restricted access across a paleohigh in the montreal region by the time of lowville deposition taconic transgression had breached this restriction

sedimentology rhythmicity and basin fill architecture of a carbonate ramp depositional system with intermittent terrigenous influx the albian kharfot formation of the jeza qamar basin dhofar southern oman abstract the albian kharfot formation is preserved in the eastern margin of the jeza qamar basin which straddles across the oman yemen border this study addresses the sedimentological attributes of the formation and deduces its depositional setting cyclicity and relative sea level changes in local within the basin and regional arabian contexts the interaction among siliciclastic influxes in situ carbonate production and tectono climatic controls on the stacking nature of the various lithofacies that build up the formation is discussed in the study area the formation lies unconformably over barremian aptian qishn formation and conformably under late albian turonian dhalqut formation the kharfot formation thickens from 140 m in the eastern side of the study area to 300 m at the oman yemen border it consists of eight lithofacies orbitolina rich marls peloidal bioclastic packstone bioclastic mudstone to wackestone argillaceous bioclastic floatstone to rudstone bioclastic rudstone sandy peloidal bioclastic mudstone to packstone peloidal bioclastic grainstone and dolostone the vertical arrangement of these lithofacies defines recurring meter to decameter scale shallowing upward units deposited on a westward deepening inner to outer ramp setting tectonic rejuvenation of the siliciclastic source area was accompanied by warm humid climatic conditions as suggested by high kaolinitic marls of the kharfot fm and coeval quartz rich sandstone units harshiyat fm the shallowing upward rhythmic sedimentation of the formation has close resemblance with cycles of the nahr umr formation in northern oman and partially comparable with the global sea level changes the kharfot basin was an intrashelf depression that was part of the much larger arabian epeiric platform the latter is defined by a rimmed margin in northern oman where al hassanat formation represents platform margin deposits and nahr umr formation representing back rim intrashelf depression which received fine grained siliciclastic influx from the land westward in southern oman where kharfot formation accumulated the platform was unrimmed ramp type basin with high fine clastic influx along with elevated carbonate production

experimental evidence for high noble gas solubilities in silicate melts under mantle pressures abstract the solubilities of ar and xe in fe free synthetic haplogranitic and tholeiitic melts were experimentally determined in the pressure range of 1 11 gpa and at temperatures between 1500 and 2000 c experiments were performed in a piston cylinder apparatus 1 3 gpa and in a multi anvil apparatus 2 11 gpa the noble gas concentrations in the quenched glasses were determined with electron microprobe as a function of pressure ar solubility increases linearly up to about 4 5 gpa where it reaches about 4 0 and 0 8 wt for the haplogranitic and tholeiitic melt respectively at higher pressure the amount of dissolved ar remains constant suggesting that some threshold concentration is reached the xe solubility in tholeiite melt exhibits a very similar pattern it increases linearly up to about 6 gpa where a threshold concentration of 0 8 wt is reached a further increase of pressure up to 11 gpa does not result in changes in xe solubility the leveling off in noble gas solubility at high pressures may imply that the interstitial sites in the melt structure suitable for the accommodation of noble gas atoms are fully occupied indeed the experimental data can be successfully reproduced with the langmuir isotherm implying a solubility model in which the gas atoms occupy a certain population of interstitial sites however the data can be equally well described by a model assuming mixing of the noble gas atoms with the oxygen atoms of the silicate melt from a thermodynamic point of view the constant noble gas solubility at high pressures simply implies that the partial molar volumes of the respective noble gas in the fluid and in the melt are equal our results differ from those of chamorro perez et al earth planet sci lett 145 1996 97 107 nature 393 1998 352 355 who reported an abrupt order of magnitude drop of ar solubility in silica and olivine melt at around 5 gpa suggesting that melt densification results in an abrupt decrease of the hole size distribution a geochemical consequence of our results is that noble gases remain incompatible elements at pressure conditions covering most of the upper mantle therefore partial melting remains an efficient process in extracting noble gases and other volatiles from the earth s mantle

shallow water polymetallic sulfide deposits in the aeolian island arc back arc basins represent the best known present day sites of ongoing massive sulfide deposition in subduction related tectonic settings here we present results obtained from shallow water sea floor sampling of barium rich zinc and lead sulfides genetically analogous to kuroko type black ore on an active island arc the samples come from a newly discovered hydrothermally active depression on the submerged volcanic edifice of panarea in the aeolian island arc tyrrhenian sea hydrothermal activity in the area is represented by extensive gas venting associated with white sea floor aprons of sulfate and iron oxide precipitates a series of barite rich sediment samples containing galena sphalerite and pyrite was recovered 40 cm below the sea bed at a water depth of 80 m the deposits represent a unique example of massive sulfide deposition in an active island arc not yet affected by strong extensional tectonics and reveal that in this environment the formation of kuroko type black ore sulfides can take place at shallow water depths

diffusive fractionation of noble gases and helium isotopes during mantle melting abstract the large differences in he and ar diffusivities in silicate minerals could result in fractionation of the he ar ratio during melting of the mantle producing he ar ratios in the primary mantle melts that are higher than those of the bulk mantle modeling noble gas diffusion out of the bulk mantle into fast diffusion pathways such as fractures or melt channels suggests that significant order of magnitude he ar fractionation will occur if the fast diffusion channels are spaced several meters apart and the noble gas residence in these diffusion channels is of the order days to weeks in addition the 15 difference in 3he and 4he diffusivities could also produce isotopic fractionation between the melt and its solid source modeling the behavior of he and ar during melting shows that small increases few in 3he 4he should be correlated with larger variations factor of 5 in 4he 40ar however in order to test this hypothesis the effects of subsequent he ar fractionation that occur during degassing have to be corrected i describe a scheme that can separate he ar variations in the primary melt from overprinted fractionation during magmatic degassing using the degassing corrected data there is a correlation between the primary melt s 4he 40ar and 3he 4he in mid ocean ridge basalts morbs the slope of the correlation is consistent with the models of preferential diffusion of 3he relative to 4he and of 4he relative to 40ar from the solid mantle into the melt diffusive fractionation of noble gases during melting of the mantle can also account for low 4he 40ar ratios commonly found in residual mantle xenoliths preferential diffusion of he relative to ar will produce some regions of the mantle with low 4he 40ar the complement of the high 4he 40ar ratios in basalts diffusive fractionation cannot however account for differences between the he and ne isotopic compositions of morbs compared with ocean island basalts oibs not only are the extremely high 3he 4he ratios of oibs up to 50 ra difficult to produce at reasonable mantle time and lengthscales but also the ne isotopic compositions of morbs and oibs do not lie on a single mass fractionation line therefore cannot result from diffusive fractionation of a single mantle ne source if preferential diffusion of he from the solid mantle into primary melts is a significant process during generation of morbs then it is difficult to constrain the he concentration of the mantle he concentrations in basalts and the he flux to the ocean essentially result from extraction of he from a larger and unknown volume of mantle than that that produced the basalts themselves the he concentration of the mantle cannot be constrained until more accurate estimates of the diffusion contribution are available

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

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

manetoe facies a gas bearing megacrystalline devonian dolomite yukon and northwest territories canada the manetoe facies is a broadly stratiform and regionally developed 38 000 km2 or 15 000 mi2 body of white sparry dolomite hosted in lower and middle devonian strata and is the northwestward continuation of the similar but better known presqu ile facies dolomite several large gas fields have been discovered within anomalously thick developments of the manetoe dolomite close to the northwest limit of the devonian elk point basin of alberta the external geometry of the manetoe facies indicates that it may have been a cavern or karst system excavated in the late middle devonian by a large vertically confined coastal aquifer the local regions of anomalously thick manetoe facies may have developed where the aquifer stoped upward into strata above the confining aquiclude of the headless formation shale dolomite cementation may have occurred during any of three possible episodes of large scale fluid movement fluid inclusion and strontium isotope data favor the hypothesis that manetoe dolomites precipitated from heated 150 210 c or 300 410 f hypersaline evaporitic brines that have interacted with the underlying precambrian crust probably in the late devonian lead isotope data support the general concept of pre mesozoic dolomite cementation and largely preclude a late early tertiary deep burial setting spectacular zones of detrital dolomite cement within the manetoe are most readily accommodated by a near surface very early middle devonian aquifer mixing model origin but the presence of these zones does not preclude the other possible origins carbon and xygen isotope data from the manetoe facies support the concept that the presqu ile and manetoe facies are physically continuous and had a common origin

submarine hydrothermal mineralization in the okinawa trough sw of japan an overview abstract the okinawa trough is a heavily sedimented rifted back arc basin formed in an intracontinental rift zone submarine hydrothermal activity is located within the six back arc rifts located in the middle and southern okinawa trough and its distribution is controlled principally by tectonic factors subduction of the daito and gagua ridges beneath the ryukyu arc has resulted in fracturing of the brittle lithosphere beneath the okinawa trough hydrothermal activity is strongest in the volcanic arc rift migration phenomenon vamp area plus the jade site and southernmost part of the okinawa trough spot area which form the prolongation of these two ridges these areas are characterized by extremely high heat flow locally submarine hydrothermal fluids from the okinawa trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and nh 4 concentrations of the fluids the fluids also contain high concentrations of co 2 of magmatic origin submarine hydrothermal mineralization in the trough is diverse the clam site consists principally of carbonate chimneys interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site this is most probably a sediment hosted deposit in which sulphide minerals have deposited within the sediment column leaving spent ore fluids to emerge at the seafloor the jade site consists of active and inactive sulphide sulphate chimneys and mounds the zn pb rich sulphides at this site contain the highest concentrations of pb ag and au so far recorded in submarine hydrothermal sulphide deposits at minami ensei knoll and hatoma knoll active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor an intense black smoker has recently been discovered at yonaguni knoll in the spot area if it is confirmed that sulphide mineralization is dominant at this site this could be a highly prospective area the most prospective areas for economic grade minerals in the okinawa trough appear to be the jade site and the spot area

marine shallow water hydrothermal activity and mineralization at the wakamiko crater in kagoshima bay south kyushu japan abstract submarine hydrothermal fluid emanation from a small sediment mound associated with bubbling gas was observed in the wakamiko crater that is located 5 km offshore at 200 m depth in kagoshima bay southern kyushu japan in 2003 and 2005 surface sediments up to 30 cm from inside and outside of the hydrothermal mound were sampled using the submersible rov hyper dolphine jamstec chemistry of pore fluids inside the mound showed a clear difference from those collected from outside the mound which is explained by mixing of the ascending hydrothermal component and seawater estimated chemical composition of the hydrothermal end member suggests that the fluid experienced hydrothermal interaction at a temperature range of about 175 to 200 c this is consistent with the observed mound temperature of 137 c hydrothermal minerals such as barite stibnite and realgar were identified in the mound sediment suggesting their precipitation due to mixing of the ascending hydrothermal fluid with seawater isotopic composition of the hydrothermal endmember can be explained by mixing product of seawater magmatic water and meteoric water the marine shallow water hydrothermal system in the wakamiko crater is considered to be driven by a magmatic heat source beneath the crater which also contributes elements such as arsenic antimony mercury and magmatic water to the hydrothermal fluid

rare earth element abundances in hydrothermal fluids from the manus basin papua new guinea indicators of sub seafloor hydrothermal processes in back arc basins abstract rare earth element ree concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the manus back arc basin vienna woods pacmanus desmos and susu knolls vent areas sampled vent fluids show a wide range of absolute ree concentrations and chondrite normalized reen distribution patterns lan smn 0 6 11 lan ybn 0 6 71 eu n eu n 1 55 reen distribution patterns in different vent fluids range from light ree enriched to mid and heavy ree enriched to flat and have a range of positive eu anomalies this heterogeneity contrasts markedly with relatively uniform reen distribution patterns of mid ocean ridge hydrothermal fluids in manus basin fluids aqueous ree compositions do not inherit directly or show a clear relationship with the ree compositions of primary crustal rocks with which hydrothermal fluids interact these results suggest that the rees are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of rees in submarine hydrothermal fluids in contrast differences in aqueous ree compositions are consistently correlated with differences in fluid ph and ligand chloride fluoride and sulfate concentrations our results suggest that the rees can be used as an indicator of the type of magmatic acid volatile i e presence of hf so2 degassing in submarine hydrothermal systems additional fluid data suggest that near seafloor mixing between high temperature hydrothermal fluid and locally entrained seawater at many vent areas in the manus basin causes anhydrite precipitation anhydrite effectively incorporates ree and likely affects measured fluid ree concentrations but does not affect their relative distributions

geochemistry of hydrothermal fluids from the pacmanus northeast pual and vienna woods hydrothermal fields manus basin papua new guinea abstract processes controlling the composition of seafloor hydrothermal fluids in silicic back arc or near arc crustal settings remain poorly constrained despite growing evidence for extensive magmatic hydrothermal activity in such environments we conducted a survey of vent fluid compositions from two contrasting sites in the manus back arc basin papua new guinea to examine the influence of variations in host rock composition and magmatic inputs both a function of arc proximity on hydrothermal fluid chemistry fluid samples were collected from felsic hosted hydrothermal vent fields located on pual ridge pacmanus and northeast ne pual near the active new britain arc and a basalt hosted vent field vienna woods located farther from the arc on the manus spreading center vienna woods fluids were characterized by relatively uniform endmember temperatures 273 285 c and major element compositions low dissolved co 2 concentrations 4 4 mmol kg and high measured ph 4 2 4 9 at 25 c temperatures and compositions were highly variable at pacmanus ne pual and a large newly discovered vent area fenway was observed to be vigorously venting boiling 358 c fluid all pacmanus fluids are characterized by negative d h 2 o values in contrast to positive values at vienna woods suggesting substantial magmatic water input to circulating fluids at pual ridge low measured ph 25 c values 2 6 2 7 high endmember co 2 up to 274 mmol kg and negative 34 s h 2 s values down to 2 7 in some vent fluids are also consistent with degassing of acid volatile species from evolved magma dissolved co 2 at pacmanus is more enriched in 13 c 4 1 to 2 3 than vienna woods 5 2 to 5 7 suggesting a contribution of slab derived carbon the mobile elements e g li k rb cs and b are also greatly enriched in pacmanus fluids reflecting increased abundances in the crust there relative to the manus spreading center variations in alkali and dissolved gas abundances with cl at pacmanus and ne pual suggest that phase separation has affected fluid chemistry despite the low temperatures of many vents in further contrast to vienna woods substantial modification of pacmanus ne pual fluids has taken place as a result of seawater ingress into the upflow zone consistently high measured mg concentrations as well as trends of increasingly non conservative so 4 behavior decreasing endmember ca cl and sr cl ratios with increased mg indicate extensive subsurface anhydrite deposition is occurring as a result of subsurface seawater entrainment decreased ph and endmember fe mn ratios in higher mg fluids indicate that the associated mixing cooling gives rise to sulfide deposition and secondary acidity production several low temperature 80 c fluids at pacmanus ne pual also show evidence for anhydrite dissolution and water rock interaction fixation of b subsequent to seawater entrainment hence the evolution of fluid compositions at pual ridge reflects the cumulative effects of water rock interaction admixing and reaction of fluids exsolved from silicic magma phase separation segregation and seawater ingress into upflow zones

alvin seabeam studies of the sumisu rift izu bonin arc abstract bimodal volcanism normal faulting rapid sedimentation and hydrothermal circulation characterize the rifting of the izu bonin arc at 31 n analysis of the zigzag pattern in plan view of the normal faults that bound sumisu rift indicates that the extension direction 080 10 is orthogonal to the regional trend of the volcanic front normal faults divide the rift into an inner rift on the arc side which is the locus for maximum subsidence and sedimentation and an outer rift further west transfer zones that link opposing master faults and or rift flank uplifts further subdivide the rift into three segments along strike volcanism is concentrated along the ene trending transfer zone which separates the northern and central rift segments the differential motion across the zone is accommodated by interdigitating north trending normal faults rather than by ene trending oblique slip faults volcanism in the outer rift has built 50 700 m high edifices without summit craters whereas in the inner rift it has formed two multi vent en echelon ridges the largest is 600 m high and 16 km long the volcanism is dominantly basaltic with compositions reflecting mantle sources little influenced by arc components an elongate rhyolite dome and low temperature hydrothermal deposits occur at the en echelon step in the larger ridge which is located at the intersection of the transfer zone with the inner rift the chimneys veins and crusts are composed of silica barite and iron oxide and are of similar composition to the ferruginous chert that mantles the kuroko deposits a 1 2 km transect of seven alvin heat flow measurements at 30 48 5 n showed that the inner rift bounding faults may serve as water recharge zones but that they are not necessarily areas of focussed hydrothermal outflow which instead occurs through the thick basin sediments the rift basin and arc margin sediments are probably dominated by permeable rhyolitic pumice and ash erupted from submarine arc calderas such as sumisu and south sumisu volcanoes

thermal constriction and slab tearing at the origin of a superinflated spreading ridge marsili volcano tyrrhenian sea 1 recently acquired swath bathymetry of the marsili basin has offered an unprecedented opportunity to study the processes of back arc ocean basin development in the tyrrhenian sea in particular the detailed morphology of marsili seamount a large strongly elongated volcano located in an axial position within the 2 ma ocean crust floored marsili basin is a key to understanding the mechanisms governing lithosphere formation in this young basin the basin is near circular in shape with diameter on the order of 120 km and is positioned in the southern tyrrhenian sea above the steeply dipping ionian oceanic slab of mesozoic age it is bounded southward by the aeolian volcanic arc and the calabrian accretionary wedge surface evidence of the northwesterly directed subduction the most outstanding feature of the basin is the elongated 3000 m high marsili volcano which reveals distinctive morphology strikingly akin to the high order segmentation and volcanic landforms described in mid ocean slow spreading ridges on the basis of its distinctive morphology and incremental growth relationship we propose that marsili volcano represents a superinflated spreading ridge resulting from a distinct thermal pulse of increased melt production occurring within the young and immature marsili basin surrounding cooler continental lithosphere thermally constricts ridge propagation and crust production in marsili basin to the finite scale of marsili volcano increased melt production to feed the superinflated marsili ridge is generated by deep lateral asthenospheric mantle flow produced at the edges of tears that bound the subducting ocean crust of the ionian plate slow spreading plate separation outpaced by the increase in magma generation results in vertical accretion to produce the superinflated ridge the existence of dip directed tears delimiting the narrow ionian slab is supported by the geological evolution of the surrounding foreland and apennine maghrebid mountain belt during early middle pleistocene i e the time of formation of the marsili volcano present day structure and volcanism furnish direct and indirect surface evidence of the presence and location of the slab tears

hydrothermal precipitates associated with bimodal volcanism in the central bransfield strait antarctica polymetallic sulfide sulfate mineralization enriched in pb ag as sb hg occurs in the bransfield strait a late tertiary quaternary marginal basin close to the antarctic peninsula the mineralization is associated with bimodal volcanism and pelagic and volcaniclastic sediment in rifted continental crust hydrothermal precipitates have been recovered from two shallow 1 050 1 000 m water depth submarine volcanoes hook ridge and three sisters in the central bransfield strait mineralization at hook ridge consists of polymetallic sulfides massive barite and pyrite and marcasite crusts in semilithified pelagic and volcaniclastic sediment native sulfur commonly infills void space and cements the volcaniclastic sediment the polymetallic sulfides are dominated by sphalerite with minor galena enargite tetrahedrite tennantite pyrite chalcopyrite and traces of orpiment cemented by barite and opal a the presence of enargite at hook ridge the abundance of native sulfur and the low fe content of sphalerite indicate a high sulfur activity of the hydrothermal fluids responsible for mineralization the sulfur isotopic composition of hook ridge precipitates documents the complexity of the sulfur sources in this hydrothermal system with variable influence of biological activity and possibly magmatic contributions homogenization temperatures and salinities of fluid inclusions in barite and opal a suggest that boiling may have affected the hydrothermal fluids during their ascent the discovery of massive barite silica precipitates at another shallow marine volcano three sisters volcano attests to the potential for hydrothermal mineralization at other volcanic edifices in the area the characteristics of the mineralization in the bransfield strait with rifting of continental crust the presence of bimodal volcanism including highly evolved felsic volcanic rocks the association with sediments and the pb ag as sb hg enrichment are similar to the setting of massive sulfide deposits in the okinawa trough and distinct from those of sediment dominated hydrothermal systems such as escanaba trough middle valley and guaymas basin the geological setting of the bransfield strait is also broadly similar to that of some of the largest volcanogenic massive sulfide deposits in the ancient record such as the iberian pyrite belt

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

tide influenced sedimentation in a rift basin cretaceous qishn formation masila block yemen a billion barrel oil field the lower cretaceous qishn clastics member in masila block 14 hadhramaut region republic of yemen has estimated reserves of 1 1 billion bbl recoverable oil and has produced 600 million bbl of oil sedimentation took place in an elongate paleogulf of the say un al masila basin with open marine carbonates to the east the qishn clastics member unconformably overlies mixed carbonates and clastics of the sa af member lower qishn onlap resulted in deposition of brackish and tidal likely macrotidal estuarine to open bay or gulf deposits the middle portion of the lower qishn clastics member shows evidence of arid nonmarine sedimentation including debris flow deposits red beds and shale clast conglomerates in turn overlain by interfingering coastal and nonmarine deposits the lower qishn clastics member is truncated by a sequence boundary overlain by an extensive sandstone deposited in a low accommodation braid plain close to the shoreline a flooding surface is present at the top of the sandstone over which progradational tide influenced deltaic strata were deposited delta progradation culminated in shallow water clastic dolomitic deposits on the coastal plain with subsequent transgression a rising water table caused a nonmarine flooding surface with lakes and lacustrine deltas overlain by tidal flat deposits ongoing transgression resulted in wave ravinement overlain by shallow shelf clastics and then deposition of slightly deeper shelf carbonates the uppermost unit comprises bioturbated clastic shelf deposits related to a drop in relative sea level throughout much of the qishn clastics interval accommodation was moderate except for low accommodation associated with regional sheet sandstone at the base of the upper qishn clastics member virtually all marine and brackish deposits show evidence of tidal sedimentation climate was arid and seasonally wet

constraints on water depth of massive sulfide formation evidence from modern seafloor hydrothermal systems in arc related settings the results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment the shallowest hydrothermal systems in subduction related settings are hosted by arc volcanoes these shallow vent sites have a number of features in common with subaerial epithermal systems massive sulfide occurrences in arc related rifts the most likely setting for many ancient analogs are generally restricted to water depths from 700 to 2 000 m with rifts developing within old arc crust at the deeper end of this range back arc spreading centers proximal to arcs host massive sulfide deposits at depths of 1 500 to 2 000 m the deepest hydrothermal systems occur along mature back arc spreading centers distal to volcanic arcs where water depths range from 2 000 to 3 700 m these deeper vent sites probably represent the best modern analogues of ophiolite hosted massive sulfide deposits boiling of the hydrothermal fluids is common at volcanic arcs and in arc related rifts in these environments elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss by contrast the high ambient pressures in deep marine hydrothermal systems along mature back arc spreading centers prevent fluids from boiling during their ascent to the seafloor boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and therefore influences the metal content of seafloor sulfide deposits copper rich massive sulfides typically occur at water depths exceeding 1 000 m whereas zn and pb rich occurrences may form at any water depth boiling can be an important control on ag and au grades but is not the only factor controlling precious metal enrichment in massive sulfides shallow marine hot spring deposits can be highly enriched in trace metals such as as hg and sb submarine volcanic arc and back arc settings are geologically complex and significant variations in water depth can occur over short distances paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth the relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic hosted massive sulfide deposits

mineralogy and geochemistry of volcanogenic sulfides from the myojinsho submarine caldera the shichito iwojima ridge izu ogasawara arc northwestern pacific abstract hydrothermal massive barite and sulfide samples and rocks with disseminated sulfides including quartz and sulfide veinlets were recovered from the myojinsho submarine caldera the shichito iwojima ridge izu ogasawara arc northwestern pacific these are the first extensive hydrothermal massive sulfide deposits in the front of a volcanic arc to be reported three stages of major sulfide mineralization took place in the caldera in the following sequence pyritization quartz and sulfide veinlet type mineralization which occurs in pyritized rocks and massive barite and sulfide minerals the microscopic texture pellet type colloform pyrite and rosette growth of sphalerite galena tennantite and barite and the mode of occurrence of the massive barite and sulfide samples suggest that the deposit is comparable with kuroko type deposits from the green tuff region of japan in addition the characteristics of the samples with respect to the zn maximum 43 wt pb maximum 10 2 wt cu maximum 2 4 wt au maximum 2700 ppb ag maximum 350 ppm au ag ratios 0 003 0 028 and sulfur isotopic composition of bulk sulfides 34s 2 1 2 8 in sample types c and b and barite 19 5 20 1 in sample types a and b appear to be consistent in part with those of the kuroko type deposits and the izena cauldron okinawa trough backarc basin lesser amounts of tellurobismuthite in pyrite and of greencokite with sphalerite also occur in quartz veinlets and vug fillings respectively the chemical and mineralogical characteristics may indicate a unique chemical composition of the basement rocks in the myojin reef region the hydrothermal deposit is characterized by zn pb cu ag au enrichment

a new view of the he ar co2 degassing at mid ocean ridges homogeneous composition of magmas from the upper mantle abstract deep sea exploration is rapidly improving our understanding of volatiles geochemistry in mid ocean ridge igneous products it is also placing greater constraints on degassing processes of the earth s mantle with the result that degassing models based on vapour melt equilibrium are no longer able to explain the increasing number of data in fact such models force to postulate an upper mantle strongly heterogeneous at any scale and cannot account for the widespread carbon supersaturation of the recovered igneous products here we review the global he ar co 2 dataset of fluid inclusions in mid ocean ridge glasses using the framework of advanced modelling of multicomponent bubble growth in magmas we display that non equilibrium fractionations among he ar and co 2 driven by their different diffusivities in silicate melts are common in most of the natural conditions of magma decompression and their signature strongly depends on pressure of degassing due to the comparable ar and co 2 diffusivity magma degassing at low pressure fractionates both the he ar and he co 2 ratio by a similar extent while the slower co 2 diffusion at high pressure causes early kinetic effects on ar co 2 ratio and dramatically changes the degassing path on this ground the very different geochemical signatures among suites of data coming from different ridge segments mainly depend on the depth of the magma chamber where the melt was stored besides the variations inside a single suite highlight variable ascent speed and cooling rate of the emplaced lava the large variations in both the he co 2 and ar co 2 ratios at almost constant he ar displayed in glasses coming from the mid atlantic ridge 24 30 n segment and the rodriguez triple junction are therefore interpreted as a high pressure signature in contrast the simultaneous increase in both he co 2 and he ar of the east pacific rise pito seamount and south east indian ridge data sets suggests the dominance of low pressure fractionation implying that the shallow magma chambers are at a lower depth than those of the mid atlantic ridge 24 30 n and rodriguez triple junction our conclusions support the presence of a relationship between spreading rate and depth of high temperature zones below ridges and are consistent with the depth of magma chambers as suggested from seismic studies non equilibrium degassing explains the volatile systematics of mid ocean ridge basalts by starting from a single mantle derived magma dispensing with the supposed need for heterogeneities in abundance ratios of volatiles in the mantle below oceanic ridges

shallow submarine hydrothermal activity with significant contribution of magmatic water producing talc chimneys in the wakamiko crater of kagoshima bay southern kyushu japan abstract active hydrothermal venting from shallow seafloor 200 m depth with talc chimneys has been discovered at the wakamiko crater floor in the aira caldera southern kyushu japan the major chemical composition of the fluids suggests that the fluids are supplied from a single reservoir the fluid is characterized by a low chloride concentration low d value and a high 18 o value suggesting that the endmember hydrothermal fluid is a mixture of seawater and andesitic water and possibly contribution of meteoric water and or phase separation such noticeable magmatic input may be supported by high helium isotopic ratio 6 77 r a of fumarolic gas discharging from the crater silica and alkaline geothermometers indicate that the fluid rock interaction in the reservoir occurs in the temperature range of 230 to 250 c the high alkalinity and high ammonium and dissolved organic matter concentrations in the fluid indicate interaction of the fluid with organic matter in sedimentary layers at least three hydrothermal vents have been observed in the crater two of these have similar cone shaped chimneys the chimneys have a unique mineralogy and consist dominantly of talc kerolite and hydrated talc with lesser amounts of carbonate dolomite and magnesite anhydrite amorphous silica and stibnite the precipitation temperature estimated from 18 o values of talc was almost consistent with the observed fluid temperature geochemical modeling calculations also support the formation of talc and carbonate upon mixing of the endmember hydrothermal fluid with seawater and suggest that the talc chimneys are currently growing from venting fluid

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

tectonic and magmatic controls on hydrothermal activity in the woodlark basin the woodlark basin is one of the rare places on earth where the transition from continental breakup to seafloor spreading can be observed the potential juxtaposition of continental rocks a large magmatic heat source crustal scale faulting and hydrothermal circulation has made the woodlark basin a prime target for seafloor mineral exploration however over the past 20 years only two locations of active hydrothermalism had been found in 2009 we surveyed 435 km of the spreading axis for the presence of hydrothermal plumes only one additional plume was found bringing the total number of plumes known over 520 km of ridge axis to only 3 much less than at ridges with similar spreading rates globally particularly the western half of the basin 280 km of axis is apparently devoid of high temperature plumes despite having thick crust and a presumably high magmatic budget this paucity of hydrothermal activity may be related to the peculiar tectonic setting at woodlark where repeated ridge jumps and a re location of the rotation pole both lead to axial magmatism being more widely distributed than at many other more mature and stable mid ocean ridges these factors could inhibit the development of both a stable magmatic heat source and the deeply penetrating faults needed to create long lived hydrothermal systems we conclude that large seafloor massive sulfide deposits potential targets for seafloor mineral exploration will probably not be present along the spreading axis of the woodlark basin especially in its younger western portion

argon solubility in silicate melts at very high pressures experimental set up and preliminary results for silica and anorthite melts a co2 laser heated diamond anvil cell was used for performing argon solubility experiments in silicate melts this technique allowed solubility experiments to be carried out at much higher pressures than in a piston cylinder type apparatus when the beam of the co2 laser is focused on the silicate sample argon acting as a pressure transmitting medium melts by conductive heating from the molten sample and can disserve into the melt preliminary results for argon solubility in silica and anorthite melts up to 10 gpa are presented in anorthite melt the ar content levels up at 0 5 wt above 5 gpa for silica melt ar contents increase up to nearly 5 wt at 5 gpa and decrease below 1 at higher pressures this behaviour is interpreted as resulting from a profound change in the structure of the melt above 5 gpa probably related to an increase in the proportion of 4 and 3 membered sio4 rings

the effect of compression on noble gas solubility in silicate melts and consequences for degassing at mid ocean ridges abstract the effect of compression on noble gas solubility in silicate melts is still badly understood due to a lack of theoretical guidance in the experimental literature noble gases dissolving in liquid silicates are found to concentrate almost linearly with increasing pressure up to several tens of kbar suggesting that henry s law could be valid up to very high pressures although this law stipulates that the gaseous phase in contact with the liquid must be ideal recently new experiments dealing with the dissolution of argon in synthetic and natural silicate melts have pointed out that the evolution of concentration with pressure exhibits a departure from linearity in the 50 100 kbar range leading either to a levelling off or to a sudden collapse of the argon concentration above 50 kbar here we investigate by means of liquid state physics how volatile species dissolve into silicate melts under pressure we use a hard sphere model the reference fluid in liquid state physics to describe silicate melts and gas at high pressures one of our main results is that when pressure increases the concurrent compaction of gas and melt explains the almost linear behaviour of the noble gas concentration up to several tens of kbars before melt compaction dominates and concentration either levels off or decreases gradually in the 50 100 kbar range in spite of the existence of a quasi linear regime over a large pressure range our work disqualifies the use of the henry law when dealing with high pressures the implication of these findings to provide an understanding of degassing at mid ocean ridges is next investigated applying our model to the scenario where co 2 vesicle generation occurs in the magma at mantle depths during its ascent from melting regions we evaluate magma vesicularity as well as noble gas concentrations in the basalt melt and in vesicles as a function of pressure at depth it is stressed that the variable and usually strong noble gas elemental fractionation observed in mid ocean ridge basalts can be explained by assuming a sequence of several vesiculation stages interrupted by vesicle loss during magma ascent

olivine flotation in mantle melt abstract molten komatiite and peridotite have been compressed in an octahedral multi anvil device up to 10 gpa densities of the melts were measured at pressure intervals in the range 7 to 10 gpa by observing sinking and floating san carlos olivines and synthetic forsterite marker spheres the multi anvil results for komatiite when combined with piston cylinder measurements done at 4 to 6 gpa and a calculated reference density at 105 pa yield a birch murnaghan isothermal bulk modulus of k1900c 26 gpa and pressure derivativek 4 25 the pressure of neutral buoyancy for olivine in komatiite is confirmed to be near 8 gpa as predicted in earlier work olivine flotation in the experimental komatiite commences at a pressure close to where the liquidus phase changes from olivine to denser garnet leading to the possibility of density driven crystal sorting during fractionation molten peridotite klb 1 shows an isothermal compression 2000 c of 0 065 g cm 3 gpa 1 in the interval 105 pa to 8 2 gpa the olivine liquid peridotite density crossover is predicted to lie between 9 and 11 gpa indicating that olivine flotation can operate at depths of 300 500 km in a molten peridotitic mantle

global comparisons of volcanic associated massive sulphide districts although volcanic associated massive sulphide vms deposits have been studied extensively the geodynamic processes that control their genesis location and timing remain poorly understood compar

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

orbitolina episodes in carbonate platform evolution the early aptian model from se spain abstract among the orbitolininae palorbitolina lenticularis blumenbach is a common facies marker in upper barremian lower aptian shallow water mesogean deposits and was hitherto ascribed to specific but contrasting paleoenvironments within the carbonate platform facies suites the albacete prebetic area se spain illustrates a model in which the palorbitolina facies spread over the whole platform system the development of the palorbitolina sediments coincided with a transgressive trend at the end of an important terrigenous period this model could also be applied to similar middle crotaceous orbitolina facies

back arc basin basalt systematics the mariana east scotia lau and manus back arc basins babs have spreading rates that vary from slow 100 mm yr and extension axes located from 10 to 400 km behind their island arcs axial lava compositions from these babs indicate melting of mid ocean ridge basalt morb like sources in proportion to the amount added of previously depleted water rich arc like components the arc like end members are characterized by low na ti and fe and by high h2o and ba la the morb like end members have the opposite traits comparisons between basins show that the least hydrous compositions follow global morb systematics and an inverse correlation between na8 and fe8 this is interpreted as a positive correlation between the average degree and pressure of mantle melting that reflects regional variations in mantle potential temperatures lau manus hotter than mariana scotia this interpretation accords with numerical model predictions that faster subduction induced advection will maintain a hotter mantle wedge the primary compositional trends within each bab a positive correlation between fe8 na8 and ti8 and their inverse correlation with h2o 8 and ba la are controlled by variations in water content melt extraction and enrichments imposed by slab and mantle wedge processes systematic axial depth as a proxy for crustal production variations with distance from the island arc indicate that compositional controls on melting dominate over spreading rate hydrous fluxing enhances decompression melting allowing depleted mantle sources just behind the island arc to melt extensively producing shallow spreading axes flow of enriched mantle components around the ends of slabs may augment this process in transform bounded back arcs such as the east scotia basin the re circulation by mantle wedge corner flow to the spreading axes of mantle previously depleted by both arc and spreading melt extraction can explain the greater depths and thinner crust of the east lau spreading center manus southern rifts and mariana trough and the very depleted lavas of east scotia segments e8 e9 the crust becomes mid ocean ridge mor like where the spreading axes further away from the island arc and subducted slab entrain dominantly fertile mantle

static compression and olivine flotation in ultrabasic silicate liquid piston cylinder techniques have been used to observe static compressions of ultrabasic silicate liquids to 6 gpa and 2000 c compressions are measured by bracketing sinking and floating of olivine crystals of known density at run conditions komatiite peridotite and their liquid mixtures with fe2sio4 all show constant density changes with pressure of 0 07 g cm3 gpa along their liquidi these results confirm shock wave studies and ultrasonic studies which show weak compositional effects on compressibility of basic to ultrabasic silicate liquid the techniques converge in supporting the conjecture of stolper et al 1981 that ultrabasic silicate liquids may be denser than their equilibrium coexisting olivines and pyroxenes at high compressions the pressure of this density inversion is 7 8 gpa for the compositions studied olivine flotation provides an important constraint upon earth evolution models that include extensive melting during early differentiation it also provides a mechanism for concentrating high mg si olivine in the upper mantle without unduly perturbing other geochemical parameters a full evaluation of the physical and geochemical consequences is required at an early date