the closing of tethys and the tectonics of the himalaya recent geological and geophysical data from southern tibet allow refinement of models for the closing of southern neo tethys and formation of the himalaya shelf sediments of the indian passive continental margin which pass northward into deep sea tethyan sediments of the indus tsangpo suture zone were deposited in the late cretaceous an andean type margin with a 2 500 km long trans himalayan kohistan ladakh gangdese granitoid batholith formed parallel to the southern margin of the lhasa block together with extensive andesites rhyolites and ignimbrites lingzizong formation the southern part of the lhasa block was uplifted deformed and eroded between the cenomanian and the eocene in the western himalaya the kohistan island arc became accreted to the northern plate at this time the northern part of the lhasa block was affected by jurassic metamorphism and plutonism associated with the mid jurassic closure of the bangong nujiang suture zone to the north the timing of collision between the two continental plates ca 50 40 ma marking the closing of tethys is shown by 1 the change from marine flysch like to continental molasse like sedimentation in the indus tsangpo suture zone 2 the end of gangdese i type granitoid injection 3 eocene s type anatectic granites and migmatites in the lhasa block and 4 the start of compressional tectonics in the tibetan tethys and indus tsangpo suture zone south facing folds south directed thrusts after the eocene closure of tethys deformation spread southward across the tibetan tethys zone to the high himalaya deep crustal thrusting barrovian metamorphism migmatization and generation of oligocene miocene leucogranites were accompanied by south verging recumbent nappes inverting metamorphic isograds and by south directed intracontinental shear zones associated with the main central thrust continued convergence in the late tertiary resulted in large scale north directed backthrusting along the indus tsangpo suture zone more than 500 km shortening is recorded in the foreland thrust zones of the indian plate south of the suture and 150 km shortening is recorded across the indian shelf zanskar range and the indus suture in ladakh there was also large scale shortening of the karakoram and tibetan microplates north of the suture as much as 1 000 km shortening occurred in tibet the more recent deformation however involved the spreading of this thickened crust and the lateral motion of the tibetan block along major approximately east west trending strike slip fault zones

geology and geochemistry of middle eocene maden complex ferromanganese deposits from the elazig malatya region eastern turkey abstract in the study region the puturge precambrian permian metamorphic rocks the upper jurassic lower cretaceous guleman ophiolites the upper cretaceous lower eocene hazar unit the campanian lower maastrichtian aged elazig magmatics and the middle eocene maden complex crop out extensively the maden complex containing ferromanganese mineralization unconformably overlies the puturge metamorphic rocks the guleman ophiolites and the hazar unit and is unconformably overlain by plio quaternary sediments the ferromanganese mn fe ores in the elazig malatya region eastern turkey are hosted in the mudstone member of the volcano sedimentary part of the middle eocene maden complex as lenses or interbedded layers in the elazig malatya region mn fe ores occur at eight localities namely beyhan palu sarikamis kockale germili hazar alihan and kom mn fe ores are found in the kockale and palu deposits as a single bed but in the hazar and kom deposits as two beds and in the sarikamis germili and alihan deposits in three levels the thickness of these mineralized levels ranges from 0 3 m to 10 m all the investigated mineralizations are conformable with the foot wall mudstones braunite bixbyite jacobsite pyrolusite manganite and psilomelane are the main manganese oxide minerals hematite barite and pyrite are also found in variable amounts in the ferromanganese ores the trace element content of all studied ferromanganese deposits is generally in low concentrations and tends to enrichment in the assemblage of ba sr v cu pb zn and as with a geochemical characteristic similar to hydrothermal deposits rare earth element ree patterns of the maden complex mn fe deposits support a hydrothermal origin with a slight enrichment in the middle ree 4 04 29 91 ppm average 16 49 and a slightly high concentration of total ree 92 40 738 23 ppm average 517 85 in all the investigated deposits ree patterns displayed negative ce 0 08 to 0 72 average 0 15 and eu 0 55 to 0 82 average 0 72 anomalies this shows that low temperature hydrothermal fluids played an important role in the formation of mineralization the ore deposition is similar to that of sedimentary exhalative mineralization deposited within the maden marginal basin

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

breccia hydrothermal alteration and structural geology of the huangtun porphyry au cu deposit in the middle lower yangtze metallogenic belt eastern china abstract luzong basin is an important part of the middle lower yangtze metallogenic belt in eastern china in which the dominant types of deposits are iron oxide apatite and skarn iron deposits however a new porphyry gold copper deposit huangtun deposit has recently been discovered in the north eastern margin of the basin detailed studies of geological characteristics and metallogenic processes of huangtun gold copper deposit are needed to supplement the mineralisation type of the luzong basin based on drill core logging and petrology observations of thin sections and polished sections a north striking sinistrial strike slip major fault and a series of secondary ne striking sinistrial strike slip faults have been identified in the mining area a mineralised breccia pipe at the intersection of the two groups of faults is the main host of the au ore body the alteration types in the mining area from deep to shallow include an albite alteration zone a biotite albite alteration zone a chlorite alteration zone and a sericite pyrite alteration zone a detailed mapping of the breccia pipe has been provided in the mining area seven different breccias facies have been divided according to the internal structure composition morphology matrix content and alteration assemblages genesis of the different breccia facies have been identified based on crosscutting relationships and clast in clast textures which revealed that there are two different faulting and brecciation stages during the first stage matrix supported breccia formed near the fracture zone gold copper mineralisation then occurred along the intersection of the two groups of fracture zones which formed k na silicate to sericite altered magmatic hydrothermal breccia from deep to shallow in addition these different facies of breccia correspond to four stages of fluid evolution the albite stage biotite albite stage chlorite stage and sericite pyrite stage hydrothermal breccia with a high matrix cement ratio then formed when mineralizing fluid permeated the fracture zone during the second stage the ore bodies were faulted to form tectonic breccia containing some massive carbonate quartz pyrite clusters as clasts based on the current study we conclude that the locations of the intersection of fault zones in the northern part of the luzong basin and the northern part of the mining area have potential for further gold mineralisation

the waziristan ophiolite pakistan general geology and chemistry of chromite and associated phases the waziristan complex covering over 500 km 2 was tectonically emplaced during the paleocene to early eocene it consists of ultramafic rocks gabbros sheeted dikes pillow lavas and pelagic sediments a typical ophiolite suite however a complete sequence does not occur in any single locality due to tectonic dismemberment the podiform chromitites consist of aluminochromite cr 2 o 3 49 61 with subordinate chromian chlorite and or chromian serpentine magnetite in cr al fe super 3 ti space the chromites plot in the area of alpine chromites but on other diagrams they overlap the fields of chromites from alpine and stratiform complexes many chromites are zoned with ferrit chromit margins richer in cr cr al and poorer in mg mg fe super 2 than the unaltered cores the chlorites are generally rich in sio 2 and mgo and poor in al 2 o 3 it appears that during greenschist facies metamorphism or alteration diffusion of mg al and some cr from the chromite margins toward the silicate matrix resulted in the development of ferrit chromit and chlorite

conditions for long lasting gas eruptions the 2013 event at fiumicino international airport rome italy abstract a hazardous gas eruption from two very close shallow boreholes occurred near the fiumicino international airport of roma italy from august to december 2013 the erupted gas was mostly co 2 of deep origin and gas output was high and sustained over time reaching values of nearly 20 t day 1 after 3 months the gas flux was still above 5 t day 1 and was only stopped in december 2013 by long and expensive works of closure of the boreholes the gas eruption was uncommon as being associated with the building of two mud volcanoes this style of sustained deep co 2 eruptions contrasts with the more common short lived eruptions of shallow biogenic methane dominated gas pockets in this work we present the chronology of the event the results of geological geochemical and geophysical monitoring and a numerical modeling we propose that the august december 2013 sustained and prolonged event does not relate to the simple degassing of a shallow isolated pocket of gas on the contrary it reflects very specific conditions in a shallow reservoir hosted in a 10 m thick gravel layer at 40 m within the tiber river delta deposits related to the interplay between the total pressure and the fraction of free co 2 initially present across very narrow value ranges around 0 59 mpa and 0 18 respectively the coexistence of short lived and long lived eruptions from the same reservoir suggest that these conditions are not achieved everywhere in the gas reservoir despite its homogeneous properties this consideration implies either a pressure compartmentalization of the reservoir or the occurrence of a transient possibly associated with an impulsive release of gas from greater depths the involvement of deeper and larger gas reservoirs connected along faults is evidenced by geophysical investigations this conceptual model bears significant implications for gas hazard studies

collision tectonics in the nw himalayas west himalayan tectonics involve the collision of microplates between the indian and asian plates the kohistan complex consists largely of tightly folded basic volcanics and sediments generated as late jurassic to late cretaceous island arcs these were intruded by post folding mid cretaceous eocene plutonics produced from continued subduction of the indian plate after closure of a suture between kohistan and the karakorum the himalayan structures show major thrust sheets and the kohistan arc is essentially a crustal pop up with southward upright and northward verging structures developed above a thick ductile decoupling zone the indus suture which can be traced for 100 km beneath kohistan on large reentrants this pop up formed by a two stage process closure of the northern suture followed by closure of the southern indus suture granitic rocks of the kohis tan ladakh batholith dated at 100 40 ma post date most of the structures related to the northern suture but were deformed and carried southwards on shear structures related to the indus suture postcollisional deformation carried this kohistan complex on deep decoupling zones over the indian plate on a series of imbricated gneiss sheets the thrusts climbing up section in the movement direction so that in the far s some override their own molasse debris folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms i e the nanga parbat and hazara syntaxes the nanga parbat syntaxis probably formed due to a shear couple near a branch line where one of the main himalayan thrusts joined the indus suture beneath kohistan crustal delamination to produce the imbricated gneiss sheets could not account for all the displacement of india into asia suggested by palaeomagnetic data there must also have been lateral displacement as demonstrated by the large oblique slip shear zone in the hunza valley n of kohistan

were intercalated komatiites and dacites at the black swan nickel sulphide mine yilgarn craton western australia emplaced as extrusive lavas or intrusive bodies the significance of breccia textures and contact relationships intercalated archean komatiites and dacites sit above a thick footwall dacite unit in the host rock succession at the black swan nickel mine north of kalgoorlie in the yilgarn craton western australia both lithofacies occur in units that vary in scale from laterally extensive at the scale of the mine lease to localized thin irregular bodies from 100 m thick to only centimetres thick some dacites are only slightly altered and deformed and are interpreted to post date major deformation and alteration late porphyries however the majority of the dacites display evidence of deformation especially at contacts and metamorphism varying from silicification and chlorite alteration at contacts to pervasive low grade regional metamorphic alteration represented by common assemblages of chlorite sericite and albite texturally the dacites vary from entirely massive and coherent to partially brecciated to totally brecciated strangely some dacites are coherent at the margins and brecciated internally breccia textures vary from cryptically defined to blocky closely packed in situ jig saw fit textures with secondary minerals in fractures between clasts to more apparent matrix rich textures with round clast forms giving apparent conglomerate textures some clast zones have multi coloured clasts giving the impression of varied provenance strangely however all these textural variants have gradational relationships with each other and no bedding or depositional structures are present this indicates that all textures have an in situ origin the komatiites are generally altered and pervasively carbonate veined preservation of original textures is patchy and local but includes coarse adcumulate mesocumulate orthocumulate crescumulate harrisite and occasionally spinifex textures where original contacts between komatiites and dacites are preserved intact i e not sheared or overprinted by alteration the komatiites have chilled margins whereas the dacites do not the margins of the dacites are commonly silicified and inclusions of dacite occur in komatiite even at the top contacts of komatiite units but komatiite clasts do not occur in the dacites the komatiites therefore were emplaced as sills into the dacites and the intercalated relationships are interpreted as intrusive the brecciation and alteration in the dacites are interpreted as being largely due to hydraulic fracturing and alteration induced by contact metamorphic effects and hydrothermal alteration deriving from the intrusion of komatiites into the felsic pile the absence of autobreccia and hyaloclastite textures in the dacites suggest that they were emplaced as an earlier intrusive sill complex at a high level in the crust

a model for submarine rhyolite dome growth ponza island central italy abstract the late pliocene rhyolitic submarine volcanic rocks of ponza island italy can be interpreted as the subaqueous equivalent of subaerial dome complexes in terms of geometry and structure three coalescing domes of about 1 km radius and aligned along a ne trending regional fracture have been identified the main difference between subaqueous and subaerial lava domes is that in a subaqueous environment lava is likely to undergo pervasive hyaloclastic brecciation so that domes are mainly composed of variously brecciated in situ to clast rotated hyaloclastite rather than coherent lava we suggest that the shape and rheologic behaviour through time of submarine domes are closely controlled by the development and thickness of the particulate hyaloclastic carapace which assumes the role of the solid crust of domes in subaerial environment the thickness of the hyaloclastic carapace at ponza is greater than 150 m and emplaced during several different pulses or eruptions in the earliest pulses lava is directly extruded on the seafloor and produces hyaloclastite the degree of brecciation of which decreases inward to the coherent flow banded rhyolite lava of the feeder dike once the hyaloclastic carapace is formed further pulses of magma combined with increase in height of the dome result in a local stress pattern characterised by a vertical 1 2 3 producing concentric and radial fractures and normal faults the newly rising magma shielded by the hyaloclastic carapace can intrude along these fault and fracture systems and invade previously emplaced but still water saturated hyaloclastite this produces the characteristic pattern of dikes observed at ponza as a series of concentric dikes that are progressively less inclined outward with respect to the dome centre these late stage dikes in turn produce hyaloclastite at their margins but generally less fragmented than the embedding hyaloclastite probably because the ascending magma is better shielded from direct contact with sea water periodic gravity collapses of the dome maintain the equilibrium between height and radius of the dome as suggested at ponza by the presence of mass flow deposits and the development of small topographic basins on top of the domes probably related to debris removal some of these topographic depressions host subaqueous pyroclastic deposits suggesting that if due to vertical growth of the dome water depth above the dome becomes shallower hydromagmatic explosions may occur

magma flow within dykes in submarine hyaloclastite environments an ams study of the miocene cabo de gata volcanic units this research has been funded by projects cgl2005 03511 bte hi2006 0073 prin2009 prin 2009h37m59 and prin 2010 11 2010tt22sc and 2010tt22sc 003

paleozoic and mesozoic stratigraphy of the peshawar basin pakistan correlations and implications the most complete paleozoic sequence described from pakistan is exposed in bedrock inliers and in ranges fringing the eastern peshawar basin interbedded quartzite and argillite of the precambrian and cambrian tanawal formation is overlain unconformably by the cambrian ambar formation the misri banda quartzite unconformably overlies the ambar and contains ordovician cruziana ichnofossils new conodont discoveries restrict the ages of overlying formations as follows panjpir formation llandoverian to pridolian nowshera formation lochkovian to frasnian and jafar kandao formation kinderhookian to westphalian the karapa greenschist consisting of metamorphosed lava flows separates the jafar kandao from upper triassic carnian marbles of the kashala formation the upper triassic and jurassic nikanai ghar formation forms the top of the section correlatives to the peshawar basin stratigraphy are present locally in the sherwan synclinorium of hazara and in the khyber pass region the sequence contrasts markedly with the paleozoic and mesozoic section exposed south of the khairabad thrust in the attock cherat range this thrust and its northeastern continuation in hazara north of abbottabad thus form the boundary in pakistan between the lesser himalayan and tethyan himalayan sections a function performed by the main central thrust mct in the central himalaya of india and nepal the newly dated carboniferous to triassic horizons provide the first firm age constraints on the protoliths of the high grade swat metasediments the dating of the metasediments has in turn provided age constraints on pre himalayan tectonism and associated intrusions two major tectonic episodes during the late cambrian and carboniferous produced positive areas north of the peshawar basin that provided coarse detritus to the misri banda quartzite and jafar kandao formation

development and maintenance mechanism for the semiannual oscillation of the north pacific upper level circulation abstractthe north south semiannual oscillation sao of the north pacific jet stream part of the atmospheric sao in the northern hemisphere can be well depicted by the semiannual component of the monthly mean eddy streamfunction expressed by the semiannual eddy streamfunction budget the dynamic processes develop and maintain the sao including the adjustment between vorticity advection and convergence of vorticity flux of the monthly mean mode and the convergence of transient vorticity flux an empirical orthogonal function analysis of these dynamic processes shows an east west elongated cyclonic anticyclonic cell of the semiannual eddy streamfunction anomaly which appears in january and july october and april south of the siberia alaska landmass the maximum minimum adjustment processes by the monthly mean mode and the maximum minimum feedback impact of transient activity on the sao occur in december and june september and march a month ahead of the maximum minimum north south sao of th

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

submarine gold mineralization near lihir island new ireland fore arc papua new guinea gold rich siliceous veins with disseminated polymetallic sulfides and pyritic stockwork mineralization have been recovered from the top of conical seamount a shallow 1 050 m water depth submarine volcano located about 10 km south of lihir island papua new guinea grab samples from the summit of conical seamount contain the highest concentration of gold yet reported from the modern sea floor max 230 ppm au avg 26 ppm n 40 the gold occurs in sulfide rich veins of black amorphous silica hosted by intensely altered high k calc alkaline basalts sulfides in the veins consist of sphalerite galena pyrite chalcopyrite marcasite and a variety of cu pb as sb sulfosalts the gold occurs as native gold and electrum in the amorphous silica and as inclusions in the sulfides the highest gold concentrations are associated with high ag as sb and hg zoned alteration adjacent to the veins consists of illite smectite amorphous silica k feldspar secondary plagioclase minor chlorite and trace carbonate the association of gold with illite smectite amorphous silica and k feldspar indicates deposition from near neutral ph hydrothermal fluids however the auriferous polymetallic sulfide veins and the associated alteration are overprinted on stockwork pyrite mineralization that is associated with earlier acid alteration containing alunite aluminum phosphate sulfates kaolinite and other clay minerals the platy habit of the alunite in this assemblage the presence of alumium posphate sulfate minerals and the sulfur isotope ratios of the crystalline pyrite 8 6 to 0 2 34 s n 28 and alunite 7 5 and 6 4 34 s are consistent with a contribution of magmatic volatiles in the earliest stages of the hydrothermal system framboidal pyrite within and at the margins of the mineralized zone has 34 s values suggesting involvement of biogenic activity 11 6 to 13 9 34 s the gold rich veins at conical seamount are distinct from sea floor massive sulfide deposits and represent a new style of mineralization on the modern sea floor the mineralogy alteration geochemistry and texture of the veins resemble those of some subaerial epithermal gold deposits and indicate that features long considered to define a subaerial setting can also form in a submarine environment the proximity of conical seamount to the giant ladolam epithermal gold deposit on nearby lihir island also raises the possibility that both subaerial and submarine gold mineralization in the region may be related to the same district scale magmatic events

geochemistry of manganese bearing cherts associated with alpine ophiolites and the hawasina formations in oman abstract based on correlation coefficients and analogies with studies on recent mn enrichments the major and trace elements of mn occurrences associated with ophiolites that have been variously affected by regional alpine metamorphism were attributed to different origins mn zn v ce nd and la are hydrothermal al ti k zr rb ga sc and some fe and pb are detrital and si p u y nb and the remainder of the fe are biogenic preliminary studies of mn occurrences in the wahrah formation of oman reveal a very similar geochemistry as the extensive exposure of this formation does not display any evidence of hydrothermal systems only a hydrothermal supply of mn to seawater from a distant source is envisaged for these and other deposits

submarine gas burst at panarea island southern italy on 3 november 2002 a magmatic versus hydrothermal episode 1 on 3 november 2002 fishermen observed the sudden appearance at the sea surface of three large whitish plumes 3 km offshore of panarea island aeolian islands southern italy caused by the uprising from the seafloor of huge columns of gas bubbles mixed with sediments and colloidal sulfur the degassing event partly superimposed an already existing gentle degassing fumarolic field since 12 november 2002 a discontinuous geochemical monitoring program of these new discharging fluids have been carried out the submarine emissions collected on november 2002 were an emulsion made by a co2 dominated continuous gas phase with suspended sediments colloidal sulfur and water condensate microdroplets acidified by dissolution of compounds such as so2 hcl and hf in the gas phase light unsaturated hydrocarbons also occurred possibly related to relatively high temperature and oxidizing conditions due to local input of magmatic fluids at depth whose occurrence was also supported by the relative high values of 3he 4he isotopic ratio r rair 4 62 with respect to previously measured values r rair 4 2 the flux of the submarine emissions significantly decreased in a couple of months together with the almost complete disappearance of the magmatic chemical markers and the decrease of the helium isotopic ratio thus the most striking feature of the temporal and spatial evolution in the chemical and isotopic compositions of the submarine fumaroles was the relatively rapid restoration since january 2003 of the precrisis conditions i e typical of a stationary hydrothermal system

structural control on geothermal circulation in the cerro tuzgle tocomar geothermal volcanic area puna plateau argentina abstract the reconstruction of the stratigraphical structural framework and the hydrogeology of geothermal areas is fundamental for understanding the relationships between cap rocks reservoir and circulation of geothermal fluids and for planning the exploitation of the field the cerro tuzgle tocomar geothermal volcanic area puna plateau central andes nw argentina has a high geothermal potential it is crossed by the active nw se trans andean tectonic lineament known as the calama olacapato toro cot fault system which favours a high secondary permeability testified by the presence of numerous springs this study presents new stratigraphic and hydrogeological data on the geothermal field together with the analysis from remote sensed image analysis of morphostructural evidences associated with the structural framework and active tectonics our data suggest that the main geothermal reservoir is located within or below the pre palaeozoic ordovician basement units characterised by unevenly distributed secondary permeability the reservoir is recharged by infiltration in the ridges above 4500 m a s l where basement rocks are in outcrop below 4500 m a s l the reservoir is covered by the low permeable miocene quaternary units that allow a poor circulation of shallow groundwater geothermal fluids upwell in areas with more intense fracturing especially where main regional structures particularly nw se cot parallel lineaments intersect with secondary structures such as at the tocomar field away from the main tectonic features such as at the cerro tuzgle field the less developed network of faults and fractures allows only a moderate upwelling of geothermal fluids and a mixing between hot and shallow cold waters the integration of field based and remote sensing analyses at the cerro tuzgle tocomar area proved to be effective in approaching the prospection of remote geothermal fields and in defining the conceptual model for geothermal circulation

mineralogy geochemistry and genesis of the ferromanganese ores from hazara area nw himalayas northern pakistan abstract ferromanganese ores occur in hazara area near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate in pakistan the hazira formation of cambrian age is a relatively thin unit up to 150 m thick which consists of either thin ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite or thicker evenly bedded reddish brown siltstone it has a conformable lower contact with the abbottabad formation cambrian and an unconformable upper contact with the samana suk limestone jurassic the ferromanganese ores of the hazara area were studied in terms of their mineral and geochemical composition mineralogically a variety of mn and fe phases have been noticed in kakul galdanian and chura gali ferromanganese ores bixbyite is the principal mn phase while pyrolusite hollandite partridgeite and braunite occur in lesser amounts hematite however is the only fe phase in these ores gangue minerals include carbonates cryptocrystalline quartz iron clay and variable amounts of apatite plumbogummite and barite glauconite occurs in traces textural features suggest remobilization and subsequent precipitation of early diagenetic mn and fe phases along the fractures and interstices of the gangue minerals during later metamorphism chemical analyses show that the mn fe ratio in the ores is highly variable and ranges from 0 46 to 5 25 these ores exhibit a line of descent from lree to hree with a small positive ce anomaly their ree is higher than the hydrothermal mn deposits and lower than the hydrogenous crust the petrochemical characteristics suggest a mixed hydrothermal hydrogenetic source for the ferromanganese ores which have formed in shallow water or continental shelf environment due to the upwelling of anoxic deep seated water

compositional spatial zonation and 2005 2013 temporal evolution of the hydrothermal magmatic fluids from the submarine fumarolic field at panarea island aeolian archipelago southern italy abstract the november 2002 submarine gas blast at panarea island sicily southern italy was an unexpected reactivation event able to locally affect this hydrothermal magmatic system whose the youngest eruptive products were dated at 20 000 2000 years bp the presence of magmatic gases so 2 and hf in the fumarolic gas discharges after the violent exhalative event was indicative of a magmatic input that temporary displaced the hydrothermal system a few months later these acidic gases were indeed not detected in any of the studied fumaroles nevertheless new geochemical data obtained by periodical sampling up to june 2013 suggest that the chemical physical conditions of the hydrothermal magmatic system at panarea were not completely restored with respect to the geochemical data obtained in the early nineties thus the 2002 gas burst has unequivocally caused a permanent modification to the fluid circulation system feeding the submarine fumaroles in addition strong compositional differences were observed by the 46 gases collected in 2012 2013 from submarine fumaroles located in different sites of the studied area allowing to distinguish three different groups of fumaroles a h 2 and co rich gases which also show relatively low ar concentrations b h 2 s rich gases having variable co ch 4 ratios and c ar rich gases having relatively low h 2 concentrations gases from group a are distributed along nw and ne trending fault systems whereas those of groups b and c discharge at increasing distance from the intersection of the two fault systems indicating a spatial and compositional control by the local tectonic setting the h 2 co ratios of groups a and b gases are significantly lower than those measured prior to 2012 this would imply an increase of gas pressure at depth possibly caused by continuous addition of gas and energy from the magmatic source to the hydrothermal reservoir continuation of this process may lead to the occurrence of gas burst events in the next future a hypothesis that is supported by the strong ongoing degassing activity at the surface notwithstanding a decrease of temperatures at depth a geochemical seismological and ground deformation monitoring of the panarea submarine fumarolic field is highly recommended to obtain precursory signals of new strong degassing phenomena

geochemistry and origin of mn deposits in the waziristan ophiolite complex north waziristan pakistan the waziristan ophiolite complex is located along the western margin of the indian plate in northwestern pakistan the mn deposits in the saidgi and shuidar areas are part of this ophiolite complex these deposits both banded and massive in nature are hosted by metachert and are generally overlying metavolcanics braunite and cryptocrystalline quartz are the main constituents of the manganese ores in both areas hematite occurs in the shuidar deposits as a minor phase metacherts are microcrystalline aggregates of microcrystalline quartz chalcedony and lesser hematite chemically the studied mn deposits and associated metacherts are very similar to those formed by submarine hydrothermal effusive processes the deposits originated along sea floor spreading centers mid ocean ridges within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

hydrothermal brecciation due to fluid pressure fluctuations examples from the olary domain south australia abstract two breccias the doughboy and cathedral rock breccias hosted by the willyama supergroup in the olary domain northeastern south australia were mapped and described in this study mapping of the breccias has demonstrated that they are controlled by the regional deformational history of the area and they are intimately related to episodes of hydrothermal fluid flow and alteration the clast morphology particle size distribution dilation ratio structural position and contact relationships with the host rocks allow the degree of maturity and the nature of the fluid rock interactions for each breccia to be determined breccia clast size distribution and morphology were quantified using fractal analysis techniques textural analysis revealed significant differences in particle size distribution and clast morphology for the different breccias the results of the fractal analysis indicate that the doughboy breccia is the result of multiphase tectonic and fluid assisted failure on a fault plane whereas the cathedral rock breccia is the result of fluid assisted failure during fold related faulting due to the high fluid pressure constraints on reverse fault initiation large fluid pressure differentials are generated during the opening of dilatant sites it is the opening of these dilatant spaces which provides the room to accommodate and the mechanism for brecciation reverse faulting created dilatant spaces that due to the large pressure differential between the wall rock and the dilational space initiated failure of the wall rock whether this was a single event such as at cathedral rock or occurred during multiple events such as at doughboy can be deduced via the fractal characteristics collectively these observations shed light on the processes that occur during regional deformational events associated with multiple generations of hydrothermal activity the relationship between fluid pressure and brecciation may explain why they are the sites where the most intense effects of hydrothermal activity in the olary domain occur

alteration styles in the orion central volcanic complex fort a la corne kimberlite field saskatchewan and their effects on primary volcaniclastic textures implications for facies mapping and diamond exploration diamond grade distributions within individual kimberlite bodies are controlled by physical emplacement processes which are generally determined from volcaniclastic facies characteristics however the effects and distribution of secondary alteration styles which usually mask primary kimberlite facies have been given little attention at the fort a la corne kimberlite field saskatchewan complex overprinting alteration textures and mineral phases are recognized this study documents the characteristics overprinting relationships and spatial distribution of alteration styles within a crater filling volcaniclastic deposit body 219 of the orion central volcanic complex data were acquired from macroscopic drill core observations microscopic petrography sem imaging eds element mapping and xrd analyses olivine crystals display a mesh fracture pattern and have been replaced by multiple generations of serpentine and magnetite late stage serpentine has migrated into the interstitial medium bulk rock alteration textures include 1 fine grained crystal rich domains which are alteration pseudoclasts and or relict juvenile pyroclasts 2 a heterogeneous interstitial medium varying from early stage disseminated calcite rich serpentine to amorphous serpentine and crystalline calcite and 3 overprinting serpentine carbonate and magnetite veins and serpentine nodules alteration styles defined by unique alteration characteristics are spatially zoned through the body 219 volcaniclastic deposit and this is a result of multiple reaction fronts associated with the influx of fluids of varying composition over time and permeating different parts of the deposit recognition of alteration processes their paragenesis and spatial controls can assist in defining and constraining the distribution of primary kimberlite facies and by consequence the distribution of diamond grades

geological and geochemical constraints on the cheshmeh frezi volcanogenic stratiform manganese deposit southwest sabzevar basin iran abstract the cheshmeh frezi mn deposit belongs to the southwest sabzevar basin to the north of the central iranian microcontinent this basin which hosts abundant mineral deposits including mn exhalative and besshi type cu zn volcanogenic massive sulfide deposits followed an evolution closely related to the subduction of the neo tethys oceanic crust beneath the central iranian microcontinent two major sedimentary sequences are recorded within this basin i the lower late cretaceous volcano sedimentary sequence llcvss and ii the upper late cretaceous sedimentary dominated sequence ulcss the cheshmeh frezi mn deposit is hosted within red tuff with interbeds of green tuffaceous sandstone of the llcvss mineralization occurs as stratiform blanket like and tabular orebodies psilomelane pyrolusite and braunite are the main minerals of the ore which display a variety of textures such as layered laminated disseminated massive replacement or open space fillings the footwall and hanging wall volcanic rocks are predominantly andesite and trachyandesite rocks footwall and hangingwall volcanic rocks at cheshmeh frezi are enriched in light rare earth elements lrees compared to chondrite have steep ree patterns and generally show ta and nb depletions relative to chondrite which are characteristic of back arc environments the significant geochemical characteristics of ore such as high mn content 12 41 33 14 wt average 19 41 wt low concentration of fe 0 64 2 27 wt average 1 63 wt high ba 49 7 9901 ppm average 2728 67 ppm lree hree and negative ce and eu anomalies reveal a primary distal hydrothermal exhalative source for mineralization cheshmeh frezi deposit in comparison with different types of volcanogenic manganese deposits shows broad similarities with the cuban type mn deposits such as tectonic host and associated rock types geometry textures structures mineralogy and lithogeochemistry

analysis of meteorological precursors to ordinary and explosive cyclogenesis in the western north pacific abstract thirty five cases of cyclogenesis that occurred during the cold seasons from 1975 to 1995 in the western north pacific ocean are studied to determine common and disparate dynamic and thermodynamic structures in both the ordinary and rapid developments an analysis of 1000 hpa height and 1000 500 hpa thickness anomalies with respect to the 20 yr climatology reveals the following results though each sample of cyclogenesis is characterized by a favorable appearing thickness trough ridge structure important differences are found both the upstream surface anticyclone and the downstream precedent cyclone are preferentially stronger at the beginning of the most rapid cyclogenesis in the strong sample because of the consequently stronger equatorward flow the 1000 500 hpa thickness anomaly in the strong sample is colder by approximately 40 m 2 c in the region of incipient cyclogenesis and eastward by 1500 km a harmonic time series analysis of ncep gridded fields partitions the geopotential height

life history of mobile troughs in the upper westerlies abstract increasing evidence indicates that surface cyclogenesis is predominantly a response to the approach of a preexisting trough at upper levels a question then arises about the origin of the upper level predecessor as an initial approach to this question mobile troughs in the major band of westerlies were crudely tracked in daily northern hemispheric 500 mb analysis during nine recent cold seasons these troughs were identified only in the 552 dam height contour between 8 and 15 of them were present on a given day study of a particular cold season showed a median duration of 12 days and a mode of 5 days average zonal phase speed was 13 m s 1 locations or origin and termination of individual troughs were distributed over all longitudes but births greatly exceeded deaths over and east of the rocky mountains in north america and the highlands of central asia trough terminations dominated over the eastern portions of the oceans within the quasi steady planetary waves origins and terminations o

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

structure and tectonics of the himalaya constraints and implications of geophysical data the himalayan range is a product of continental collision between india and eurasia and for several reasons it is a logical place to examine the physical causes and mechanisms of mountain building the exceptionally high mountains and the great length of the range alone single the himalaya out as a major structural feature the convergence rate between india and eurasia of about 50 mm yr 1 minster jordan 1978 requires rapid rates of slip and the occurrence of four major earthquakes with magnitudes in excess of 8 4 in the last 100 years attests to a high level of seismicity and a rapid rate of active deformation e g richter 1958 seeber armbruster 1981 the exposures of high grade metamorphic rocks in the greater himalaya may suggest large vertical transport of lower crustal rocks e g valdiya 1980a b and the occurrences of young postcollision granites imply recent large perturbations of the temperature structure of the range e g lefort 1981 moreover as sediments derived from the himalaya fill the broad ganga basin south of the range the mountain belt simul taneously seems to override the basin e g g d johnson et al 1979 n m johnson et al 1982 as such the processes occurring now and since the collision began in the early tertiary as well as the present structure of the himalayan belt are probably similar to those at different stages of collision and mountain building in other older orogenic belts such as the appalachians the scottish and scandinavian caledonides the alps and

hydrothermal breccias and veins at the kelian gold mine kalimantan indonesia genesis of a large epithermal gold deposit mineralized hydrothermal breccias and veins formed during and after the waning stages of maar diatreme related volcanic activity at kelian kalimantan indonesia subsurface phreatic explosions occurred around the margins of the diatreme breccia complex focusing high temperature fluid flow and generating several large mineralized hydrothermal breccia bodies tectonic phreatomagmatic and hydraulic processes also contributed to hydrothermal brecciation explosive phreatic brecciation was followed by in situ hydraulic brecciation and then by minor veining as the system returned to steady state geothermal conditions brecciation and mineralization mostly occurred 400 to 700 m below the paleowater table the kelian deposit contained more than 240 t au prior to mining precious metals occur with sulfide minerals as disseminations in sheeted and conjugate veins and as breccia cement there is a progression from pyrite dominated stage 1 to base metal sulfide dominated stages 2 and 3 to sulfosalt dominated hydrothermal breccias and veins stage 4 in terms of gangue minerals the system evolved from illite quartz to adularia and or quartz and or illite dominated and then carbonate dominated boiling produced abundant bladed carbonate during stages 3 and 4 overall carbonate and base metal sulfide minerals are abundant whereas quartz is comparatively minor free gold is most abundant in stages 3 and 4 but also occurs in stages 1 and 2 native gold occurs principally as inclusions in pyrite sphalerite galena arsenopyrite quartz bladed carbonate and sulfosalts hydrothermal alteration assemblages are zoned about contacts faults breccias and veins and consist of secondary quartz illite pyrite chlorite and various carbonate minerals kelian preserves evidence of a magmatic component to the mineralizing fluids fluid inclusion analyses revealed the presence of saline fluid inclusions in particular from stage 3 isothermal mixing of low salinity 0 to 2 wt nacl equiv with moderate salinity fluids 10 to 25 wt nacl equiv rather than boiling resulted in the range of salinity and homogenization temperatures of fluid inclusions in sphalerite carbonate and quartz deposited during stage 3 salinities of 4 to 6 wt percent nacl equiv for inclusions in adularia and quartz from stages 2 and 4 and in rhodochrosite and proustite pyrargyrite from stage 4 may also reflect a component of mixing of low salinity water with a moderately saline fluid sulfur isotope values from kelian sulfides 34s 1 4 to 5 5 per mil are consistent with a magmatic sulfur source both boiling and fluid mixing contributed to high grade au mineralization at kelian rapid formation hundreds of years or less is inferred for the individual hydrothermal breccia bodies 2008 society of economic geologists inc

geochemistry and depositional environment of mn oxide deposits in the tokoro belt northeastern hokkaido japan numerous early cretaceous mn oxide and mn fe deposits are distributed in the tokoro belt northeastern hokkaido japan the mn oxide deposits usually occur in the southwestern part of the belt and within bedded cherts whereas the mn fe deposits are restricted to the northeastern part of the belt and occur between bedded cherts and underlying basaltic pillow lava the mn oxide ores are characterized by low fe mn ratios and the trace element concentrations and rare earth element ree patterns are similar to those of the submarine hydrothermal mn deposits distribution patterns of trace elements co ni cu and zn and ree in the mn oxide ores determine two types of deposits hydrogenous deposits which have relatively high concentrations and submarine hydrothermal deposits which have low concentrations these compositional trends and geologic evidences of the tokoro mn deposits suggest that the fe phases precipitated first closer to their source whereas the mn phases deposited later at a distance from their source some hydrogenous effects on the mn oxide deposits are due to the adsorption of trace elements from seawater trace element concentrations of tokoro mn oxide deposits show that they formed within 40 km from their source

facies architecture and origin of a submarine rhyolitic lava flow dome complex ponza italy the islands of ponza and gavi western pontine archipelago italy preserve parts of a subaqueously emplaced high silica 75 77 sio2 rhyolitic lava flow that overlies the margins of three older domes exposures of the lava alone cover 24 km2 and with a thickness of 150 m exposed in the cliffs the preserved volume of the lava flow is 3 6 km3 and the original volume is likely to have exceeded 7 km3 the lava flow consists of coherent obsidian and several hyaloclastite facies including in situ and clast rotated breccias and sandstones which all exhibit gradational relationships the coherent obsidian occurs as separate domains and is often flow banded although flow folds occur the banding is generally subhorizontal dipping gently to the nne the hyaloclastite representing 90 of the lava by volume has a diffuse layering varying from 0 5 to 2 m in thickness this layering also dips gently to the nne and is marked in places by alternation of some coherent horizons coarse and finely fragmented in situ hyaloclastite pumiceous hyaloclastite and clast rotated hyaloclastite the layering is laterally continuous and consistent in orientation over most of the 13 km length of ponza the subhorizontal orientation of the flow banding and presence of resedimented deposits in the upper parts of the sequence indicate that the unit is a lava flow the resedimented deposits comprise both proximal and distal deposits of debris flows and turbidity currents initiated by gravitational instability of the upper and marginal parts of the lava flow and include stratified monomictic obsidian breccias and bedded vitric siltstones and sandstones the lava flow has been intruded and crosscut by rhyolitic bodies of various ages including discordant coherent to internally fractured contemporaneous rhyolite bodies and late penecontemporaneous dikes with glassy margins and alteration haloes

hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication od ocean ridge activity adachi m yamamoto k and sugisaki r 1986 hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication of ocean ridge activity sediment geol 47 i25 148 analyses of 42 cretaceous rock samples from deep sea drilling project dsdp leg 32 in tile northern pacific show that chert and porcellanite are enriched in fe mn p cu ba mo ni and pb relative to both triassic biogenic cherts of central japan and cretaceous dsdp cherts of leg 62 the iron enrichment up to 6 68ve fe20 as total iron is most prominent in chert immediately overlying basal basah which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions chemical features characterized by a low ratio for a1 ai fe mn and ai z tio 2 and a high ratio for total fe2oj tio 2 mno tio 2 and mo tio 2 as well as petrological evidence indicatc that the cherts formed in an intense submarine hydrothermal environment on or near the cretaceous japanese spreading center which separated the kula plate from the pacific plate the spreading rate of the cretaceous japanese spreading center estimated from the chemical composition of the cherts was about 3 7 cm r i the rate is comparable to that inferred from the geomagnetic data

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

hydrothermal breccia textures and processes lisca bianca islet panarea volcano aeolian islands italy panarea is a largely submarine to partly subaerial quaternary lava dome complex stratovolcano with a long lived active shallow hydrothermal system located in the aeolian islands volcanic arc of southern italy the emergent top of the volcano forms a small archipelago made up of calc alkaline basaltic andesite to rhyolite lava domes ca 150 20 ka we document the facies outcropping on lisca bianca islet panarea archipelago based on grain size clast fabric and degree of hydrothermal alteration identifying coherent facies boulder breccia facies cobble breccia facies pebble breccia facies and pervasively altered andesite facies alunite marcasite sulfur the breccias all have ubiquitous jigsaw fit clast textures and are variably hydrothermally altered the breccias are interpreted as hydrothermal breccias and are distinguished from primary volcanic facies based on their distinguishing characteristics the breccias formed through a cyclical process involving the following stage 1 progressive build up of fluid pressure toward the level of the tensile strength of the host andesite stage 2 incipient fracturing of the andesite when fluid pressure approaches and then exceeds the tensile strength of the andesite under critical fracturing conditions stage 3 pervasive fracturing of the host andesite leading to an increase in permeability as a network of fractures develops stage 4 declining pressure with fluid flow rates that lead to infilling and sealing of fractures by natroalunite thereby reducing permeability leading to progressive build up of fluid pressure again and the beginning of a new cycle

the himalayan arc large scale continental subduction oroclinal bending and back arc spreading abstract palaeomagnetic results from the himalayan arc and southern tibet compared with simulated apparent polar wander paths for the indian plate show a consistent pattern of rotations of the himalayan arc relative to the indian shield varying gradually from 45 clockwise in the northwestern himalaya to slightly counterclockwise in the lhasa region this pattern is consistent with continental underthrusting of greater india beneath the tibetan plateau since the early miocene over at least 650 km at the longitude of western nepal and oroclinal bending since the latest miocene available palaeomagnetic observations support the steady state model for the formation of the himalayan arc with refinements as follows 1 collision between greater india s northern boundary and southern asia occurred at equatorial latitudes with progressive suturing from palaeocene in the northwestern himalaya until early eocene in the eastern himalaya 2 continuing convergence and indentation of greater india into southern asia over about 2000 km up to the early miocene resulted in southeastward extrusion of indochina and 3 neogene counterclockwise rotational underthrusting of greater india along the main central thrust with pliocene quaternary oroclinal bending of the himalayan arc

late diagenetic changes in manganese ores of the upper proterozoic penganga group india sedimentary manganese oxide ores occur interstratified with chert and minor calcareous shale and enclosed in limestone in the transgressive upper proterozoic marine sequence of the penganga group andhra pradesh india this sequence shows no evidence of volcanism or hydrothermal activity and is not metamorphosed the manganeseoxide ores show unusual coexistence of the primary sedimentary minerals todorokite and birnessite with their diagenetic conversion products manganite braunite and bixbyite the mineralogical characters and chemical compositions of the important phases as well as their texture are discussed braunite occurs in two generations one earlier or contemporaneous with bixbyite and the other later than bixbyite the different stages of conversion of todorokite and birnessite to braunite and todorokite to manganite are preserved the general observations suggest that bixbyite was also produced by conversion of todorokite birnessite pyrolusite and cryptomelane conventionally considered as diagenetic products of mn oxide hydroxide precursors deposited as primary sediments are here rarely present and then only as supergene derivatives this documentation of diagenetic transformation of primary todorokite and birnessite directly to braunite and bixbyite should be considered while extrapolating the progenitor mineralogy of the metamorphosed manganese oxide ores that abound in the precambrian

investigation on the role of microorganisms in manganese mineralization from abadeh tashk area fars province southwestern iran by using petrographic and geochemical data abstract hydrothermal manganese and ferromanganese deposits associated with neyriz ophiolite colored melange occurred as small ore deposits in the abadeh tashk area se of fars province sw iran the deposits are found in three types a banded syngenetic ores b massive boudin and lens shaped diagenetic ores and c vein and veinlet epigenetic ores microtextural geochemical and mineralogical data associated with petrographic raman ftir and sem studies indicated that the primary fe compounds formed series of microbially mediated biomats and mn compounds were precipitated as an amorphous oxide on an active oxide surface accompanying silica gels field relationships between ore and host rock high mn fe ratio 17 43 to 40 79 lree positive eu and negative ce anomalies in syngenetic ore types reveal that the ores were formed by hydrothermal fluid in an oceanic floor environment manganese was fractionated from iron due to physicochemical changes as well as microbial activities in the sedimentary environment microbial remains as filamentous beads with regular circular shapes vermiform structures series of fe rich biomats traces of embedded organic material besides trace metals and ree concentrations in mn ores emphasize the role of microorganisms in fe and mn precipitation syngenetic mineralization took place under suboxic neutrophilic conditions while diagenetic processes resulted in variably reduced fe and mn oxides via organic matter decomposition forming rhodochrosite as the end product braunite formation occurred most probably as a biogeochemically mediated early diagenetic product diagenetic and epigenetic mn ores were formed when primary mn deposits underwent subsequent diagenetic and remobilization redeposition events respectively

dome growth rates eruption frequency and assessment of volcanic hazard insights from new u th dating of the panarea and basiluzzo dome lavas and pyroclastics aeolian islands italy abstract new geochronological data are presented and discussed together with field data in order to reconstruct the geo volcanological evolution of panarea island attention is focused on the discrepancies between geochronological data compared with field evidence field data provide evidence that the panarea dome was continuously built up without a significant break in volcanic activity continuous extrusion of new magma allowed the dome to emerge subaerially subaerial effusive activity followed with the alternation of exogenous and endogenous phases of growth that led to the formation of radial and tangential lava lobes and plugs the younger volcanic products are represented by a thick succession of pyroclastic products discontinuously outcropping all over the island dated here for the first time samples were dated through the u th disequilibrium method which is also able to provide information on the geological processes at the origin of u th fractionation the chronology of the volcanic events at panarea suggests that the volcanic activity developed through two main phases effusive activity mainly characterized the first phase of the dome growth while during the second phase explosive activity prevailed the second phase occurred from 31 7 to 20 2 ka assessing the age of the first phase is more difficult the age of 155 12 ka which is in the same time span obtained from k ar or ar ar methods is not consistent with field evidence furthermore although the alignment of the points on the isochron is very good the initial value of the 230th 232th ratio is very low and does not have a clear meaning our data strongly suggest that the age of 155 12 ka is not realistic two alternative scenarios are proposed implying a revision of the geological and geochronological evolution of the island together with the significance of the marine terraces on panarea

north pacific cold season surface cyclone activity 1975 1983 abstract an eight year sample of cold season 1 october through 31 march extratropical cyclones in the pacific ocean basin is used to study central pressure changes and life cycle characteristics we find that over 90 of the cyclones passing through the area of the kuroshio current intensify in this region corresponding percentages in excess of 60 extend from the kuroshio south of 45 n eastward to 130 w mean 24 h central pressure falls of all cyclones exceed 9 mb through the entire basin west of 140 w in the latitude band 30 to 50 n a statistical analysis of 24 h central pressure changes is performed on all cyclones within our domain a frequency distribution of 1996 cases of 24 h maximum deepening reveals statistically significant departures from a gaussian distribution with the coefficient of skewness substantially negative we also find similarly significant departures from normal in a frequency distribution of all 24 h central pressure changes in spite of the fact that this distribution wo

genetic diversity of manganese deposition in the terrestrial geological record terrestrial manganese deposits formed by hydrothermal sedimentary and supergene processes ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction related settings and those deposited from terrestrial hot springs are discussed sedimentary mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea level changes mn carbonate deposits probably formed by diagenesis through mn oxyhydroxide reduction coupled with organic matter oxidation climatic variation and basin water stratification responsible for mn concentration were manifestations of atmospheric coz content prompted by tectonism supergene manganese enrichment in continental weathering profiles was mainly dictated by climate topography and drainage systems manganese deposits of diverse genetic types occur in the terrestrial geological record roy 1981 these were produced by direct hydro thermal activity sedimentary processes and continental weathering although the processes may be interrelated each involves distinct mechanisms that place the deposits into specific genetic types some of these processes are best understood in preset day depositional sites the ancient environments were determined by the intensity and style of tectonism volcanism and hydrothermal activity the composition of the atmosphere and the hydrosphere and the development of the biosphere which all varied with time it is my intention to unfold the total panorama of the environmental evolution during different time envelopes that produced a variety of manganese deposits in the past only major deposits and those providing distinctive evidence of their environment of deposition will be considered here

origin of manganese giants sea level change and anoxic oxic history inversely graded pisolites of manganese oxide in the mid cretaceous manganese giant at groote eylandt australia were deposited during a regional fall in sea level as indicated by their relationships to wave cut benches dissolved manganese was concentrated in relatively anoxic waters of the intracratonic basin during a marine transgression and precipitated as oxides and carbonates during a regression ore bodies ultimately formed by concentration of abundant particulate manganese by a tidal lag mechanism

2 7 ga plume associated vhms mineralization in the eastern goldfields superterrane yilgarn craton insights from the low temperature and shallow water ag zn au nimbus deposit economic volcanic hosted massive sulfide vhms deposits of the archaean yilgarn craton of western australia are restricted to zones of juvenile crust as revealed through regional nd pb and hf isotopic variations and the geochemistry of felsic volcanic rocks interpreted as archaean paleo rift zones one of these runs n s through the eastern goldfields superterrane broadly coincident with the kurnalpi terrane and is associated with the high grade ca 2690 ma teutonic bore jaguar and bentley deposits plus sub economic vhms mineralization further south to date only small historic cu occurrences e g anaconda and barren pyritic lenses have been recognized in the older 2 7 ga plume dominated lower stratigraphy of the eastern goldfields superterrane the nimbus ag zn au deposit 12 1 mt at 52 g t ag 0 9 zn and 0 2 g t au is located approximately 10 km east of kalgoorlie near the margin of the kurnalpi terrane its origin has been contentious for a number of years with previous models favouring seafloor sub seafloor vhms mineralization or a high sulfidation fault hosted system we present a detailed account of the deposit its host stratigraphy and associated hydrothermal alteration plus two new shrimp u pb zircon ages pb isotope galena and o isotope zircon constraints compared to other vhms occurrences in the yilgarn craton the nimbus deposit is unusual in terms of its tectono stratigraphic position the geochemistry of its host sequence i e fi affinity felsic volcanic rocks ocean plateau like low th basalts mineralogy e g abundance of ag sb pb as bearing sulfosalts high hg low cu and quartz carbonate sericite dominated alteration assemblages classification of nimbus as a shallow water and low temperature vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit is consistent with its position near the margin of the kurnalpi paleo rift zone and radiogenic 238u 204pb values the recognition that the nimbus deposit is associated with c 2705 ma plume magmatism opens new areas for vhms exploration in the eastern goldfields superterrane over a strike length exceeding 500 km

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

coeval strombolian and vulcanian type explosive eruptions at panarea aeolian islands southern italy in this paper we document the evolution of the emergent panarea dome in the aeolian islands southern italy placing particular emphasis on the reconstruction of the explosive events that occurred during the final stage of its evolution two main pyroclastic successions exposing fall deposits with different compositions have been studied into detail the andesitic palisi succession and the basaltic punta falcone succession the close in time deposition of the two successions the dispersal area and grain size distribution of the deposits account for their attribution to vents located in the western sector of the present island and erupting almost contemporaneously vents could have been aligned along nne trending regional fracture systems controlling the western flank of the dome and possibly its collapse laboratory analyses have been devoted to the characterization of the products of the two successions that have been ascribed to vulcanian and to strombolian type eruptions respectively the vulcanian eruption started with a vent clearing phase that occurred by sudden decompression of a pressurized magma producing ballistic bombs and a surge blast and the development of a vulcanian plume vulcanian activity was almost contemporaneous to strombolian type fall out eruptions the coeval occurrence of basaltic and andesitic eruptions from close vents and the presence of magmatic basaltic enclaves in the final dacitic lava lobe of the dome allow us to speculate that the intrusion of a basaltic dyke played a major role in triggering explosive eruptions the final explosive episodes may have been caused by extensional tectonics fracturing the roof of a zoned shallow magma chamber or by the intrusion of a new basaltic magma into a more acidic and shallow reservoir intrusion most likely occurred through the injection of dykes along the western cliff of the present panarea island inducing the collapse of the western sector of the dome

explosion craters associated with shallow submarine gas venting off panarea island italy explosions of hot water steam and gas are common periodic events of subaerial geothermal systems these highly destructive events may cause loss of life and substantial damage to infrastructure especially in densely populated areas and where geothermal systems are actively exploited for energy we report on the occurrence of a large number of explosion craters associated with the offshore venting of gas and thermal waters at the volcanic island of panarea italy demonstrating that violent explosions similar to those observed on land also are common in the shallow submarine environment with diameters ranging from 5 to over 100 m the observed circular seafloor depressions record a history of major gas explosions caused by frequent perturbation of the submarine geothermal system over the past 10 000 years estimates of the total gas flux indicate that the panarea geothermal system released over 70 mt of co2 over this period of time suggesting that co2 venting at submerged arc volcanoes contributes significantly to the global atmospheric budget of this greenhouse gas the findings at panarea highlight that shallow submarine gas explosions represent a previously unrecognized volcanic hazard around populated volcanic islands that needs to be taken into account in the development of risk management strategies

climatology of explosive cyclones off the east asian coast abstract the climatology of explosive cyclogenesis off the east asian coast was studied based on 30 years 1958 87 of surface analyses there were two favorable areas for explosive deepening one over the eastern sea of japan and the other over the northwestern pacific east and southeast of japan the latter was located close to the warm kuroshio current the frequency of explosive cyclogenesis reached a local minimum over japan the geographic distribution of explosive cyclone frequency suggests that the explosive cyclogenesis is influenced by the japanese islands in addition a positive correlation is found between explosive cyclogenesis frequency and the el nino episodes during 1958 87 the physical relationship between these two phenomena however is not well understood

evidence of a recent input of magmatic gases into the quiescent volcanic edifice of panarea aeolian islands italy istituto nazionale di geofisica e vulcanologia osservatorio vesuviano naples italy istituto nazionale di geofisica e vulcanologia sezione di palermo palermo italy dipartimento chimica e fisica della terra ed applicazioni palermo italy

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

braunite mineralogy and paragenesis from the kajlidongri mine madhya pradesh india the kajlidongri manganese deposit madhya pradesh india contains braunite belonging to at least two different parageneses i e a fine grained metamorphic type and a younger coarser grained hydrothermal type microanalyses of braunite from these paragenetic types indicate considerable variations in iron content from zero to 32 7 fe3o3 which the writers consider is due to varying proportions of braunite i and bixbyite modules in polysomatic braunite

the glaciovolcanic evolution of an andesitic edifice south crater tongariro volcano new zealand abstract unusual deposits mapped and logged in detail around the summit area of tongariro volcano tongariro volcanic centre new zealand indicate that the construction and evolution of a substantial portion of this andesitic stratovolcano was beneath a significant ice cap or summit glacier as the edifice was built under and through the overlying ice the style of volcanism evolved in a complex history of growth initially a 100 m thick widespread hyaloclastite deposit was emplaced within a subglacial eruption formed meltwater lake this was followed by several phases of effusive and explosive eruptions producing lava flows and primary volcaniclastic deposits emplaced along channels carved into the ice by heated meltwater the clastic deposits contain quenched bombs and structural features that indicate waterlain transport and emplacement and soft sediment deformation such accumulation of water on a steep sided edifice without evidence for a subaerial crater lake along with lava flow features indicating confinement suggest that a substantial summit glacier was responsible for the production and retention of water and the architecture of these deposits recent studies at nearby ruapehu volcano have provided good evidence for glaciovolcanic interactions during the last glacial period however until now little was known of the physical lava ice interactions in the centre during the last interglacial period and the earlier part of the last glacial period 110 64 ka these new data support a reinterpretation for the volcanic evolution of the older tongariro edifice and the emplacement mechanisms of primary volcaniclastic deposits they also help to constrain local ice thicknesses and extents at the times of eruption in addition this study contributes to a sparse global catalogue of glaciovolcanic deposits of andesitic composition particularly of primary volcaniclastics preserved at mid latitude stratovolcanoes the variety of deposit types indicates a volcano building and evolving with glaciation and is an outstanding example of the types of glaciovolcanic interaction that can occur at one volcano

sediment sea water interaction at 200 and 300 c 500 bars pressure the role of sediment composition in diagenesis and low grade metamorphism of marine clay experimental interaction of clay rich marine sediments with sea water at 200 and 300 c 500 bars and a water rock mass ratio of 5 resulted in the generation of relatively acid oxidizing conditions the development of acidity is attributed to the formation of smectite whereas the oxidation state of the fluids was dependent on the relative proportions of ferromanganese oxide phase ferrous rich silicate phases and organic carbon an experiment conducted with an oxidized sediment at 300 c thus produced higher aqueous concentrations of mn and associated base metals at a relatively high fo2 10 15 but an organic carbon rich sediment yielded fluids characterized by a lower fo2 10 20 lower concentrations of mn higher fe and exhibited substantial thermal alteration and dissolution of organic components silica concentrations in the experimental fluids ranged from cristobalite to amorphous silica saturation levels in response to the dissolution of amorphous silica comparison of fluid data and mineralogical assemblages from the gulf coast and salton sea regions with experimental results suggests that alteration processes in sedimentary basins can in large part be attributed to water rock interaction observed differences are apparently due to the higher degree of reaction in the geologic environment and to the increased stability of the illite chlorite assemblage at the lower silica activity characteristic of geologic fluids

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

glauconite formation as a factor in sedimentary manganese deposit genesis concentrations of manganese in the crust are dominated by a single ore type described as the orthoquartzite glauconite clay association or as manganese giants current research suggests that these large accumulations of manganese oxide and or carbonate are associated with relatively rapid marine transgressions and regressions across older basement rocks some of the larger deposits of this type such as nikopol and chiatura ussr and groote eylandt australia occur in petrologically simple terrigenous formations generally sandstones and shales interpreted as paleoshoreline sediments a major problem lies in the very high mn fe ratio of these deposits 30 50 as against that of ordinary sediments 0 02 research on the groote eylandt cenomanian age deposit suggests that the high mn fe of the primary ore 15 20 was associated with manganese enrichment in coastal waters which in part was related to glauconitization iron trapping reactions mineralogical evidence indicates a sequence from a well defined glauconite phase in deeper water off shore sediments with whole rock mn fe of 0 3 1 2 to a glauconite smectite in near shore estuaries and rivers as a minor component of pisolitic manganese oxides of mn fe ranging from 15 to 20 data on these glauconite minerals including x ray diffraction infrared spectroscopy microanalyzes textural occurrences and genesis are presented geologically glauconite is a product of a postoxic environment possibly related to fluctuating water depth during transgression regression seaward from the site of manganese oxide precipitation

manganese and ferromanganese ores from different tectonic settings in the nw himalayas pakistan abstract in pakistan manganese and ferromanganese ores have been reported from the hazara area of north west frontier province waziristan agencies in the federally administered tribal areas and the lasbela khuzdar regions of baluchistan this study is focused on comparison of mineralogy and geochemistry of the continental ferromanganese ores of hazara and the ophiolitic manganese ores of the waziristan area of pakistan in the hazara area ferromanganese ores occur at kakul galdanian and chura gali near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate the cambrian hazira formation is composed of reddish brown ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite in waziristan manganese ores occur at shuidar mohammad khel and saidgi within the waziristan ophiolite complex on the western margin of the indo pakistan plate in nw pakistan these banded and massive ores are hosted by metachert and overlie metavolcanics the ferromanganese ores of the hazara area contain variable amount of bixbyite partridgeite hollandite pyrolusite and braunite bixbyite and partridgeite are the dominant mn bearing phases hematite dominates in fe rich ores gangue minerals are iron rich clay alumino phosphate minerals apatite barite and glauconite are present in variable amounts in both fe rich and mn rich varieties the texture of the ore phases indicates greenschist facies metamorphism the waziristan ores are composed of braunite with minor pyrolusite and hollandite hematite occurs as an additional minor phase in the fe rich ores of the shuidar area the only silicate phase in these ores is cryptocrystalline quartz the chemical composition of the ferromanganese ores in hazara suggests that the mn fe was contributed by both hydrogenous and hydrothermal sources while the manganese ores of waziristan originated only from a hydrothermal source it is suggested that the fe mn ores of the hazara area originated from a mixed hydrothermal hydrogenetic source in shallow water in a ontinental shelf environment due to the transgression and regression of the sea while the mn ores of waziristan were formed at sea floor spreading centers within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

transient eddy forcing of the time mean flow as identified by geopotential tendencies abstract the forcing of the time mean flow by transient eddies is examined within the framework of a quasi geostrophic equation relating the geopotential tendency to the convergence of transient eddy transports of heat and vorticity the forcing functions of this equation are computed using observed circulation statistics for the wintertime northern hemisphere and solutions are sought for the three dimensional structure of geopotential and temperature tendencies associated with eddies of different time scales in general the geopotential tendencies associated with vorticity fluxes are of the same sign within a given atmospheric column whereas the polarity of the geopotential tendencies associated with heat fluxes in the lower troposphere is opposite to that in the upper troposphere the geostrophic wind tendencies associated with synoptic scale eddies with periods between 2 5 and 6 days are strongest in the vicinity of the oceanic storm tracks the enhanced poleward heat transports by active disturbanc

submarine volcanism eruption styles products and relevance to understanding the host rock successions to volcanic hosted massive sulfide deposits the increasing hydrostatic pressure of the water column with increasing water depth in subaqueous environments limits the ability of superheated volatiles to expand instantaneously against the ambient pressure explosive submarine eruptions are only likely in water depths less than 1 km and generally less than 500 m thus refuting models of highly explosive very deep water calderas popularly proposed as the host volcanic centers for the kuroko volcanic hosted massive sulfide vhms deposits of japan large volumes of blocky breccias can be produced by quench fragmentation during submarine lava eruptions and such deposits may have been mistaken for pyroclastic deposits in many cases in the past pyroclastic debris may occur in the host rock successions of some vhms deposits and may even be very voluminous however facies characteristics and theoretical constraints indicate that these are usually the products of mass flow deposition from shallow water or basin margin volcanic centers the maximum water depths for submarine explosive eruptions coincide approximately with the minimum pressures and water depths required to prevent boiling of mineralizing hydrothermal fluids in the stockwork before the fluids reach the sea floor the key elements in evaluating the prospectivity of ancient volcanic successions for vhms deposits appear to be deep water sediments and lavas or shallow intrusions in an extensional basin setting pyroclastic debris in many cases at least appears to be an accidental externally introduced component there is little evidence that explosive submarine calderas are essential as host volcanic centers to vhms deposits

the origin of hydrothermal metalliferous sediments associated with the early mesozoic othris and pindos ophiolites mainland greece abstract metalliferous sediments and sulphides are associated with the jurassic othris and pindos ophiolites central and northern greece these ophiolites formed at an early mesozoic spreading ridge within a small pindos ocean basin created by rifting of the northern margin of gondwanaland ubiquitous terrigenous silt was derived from adjacent continental margins mainly the pelagonian microcontinent to the east in the othris area disseminated massive and vein sulphides occur within and above morb type pillow lavas and volcaniclastic sediments sulphide was precipitated in quartz veins within fault controlled stockworks episode with local epidosite is locally very abundant in extrusives immediately underlying thick si fe rich hydrothermal sediments massive sulphides were precipitated as small fault controlled bodies that are directly overlain by fe rich mudstones and fe rich cherts strongly depleted in mn mudstones relatively enriched in hydrothermal fe mn cu zn pb ree and ba were ponded into small fault controlled hollows around the fringes of the sulphide precipitating field elsewhere e g northern othris manganese rich layers in ribbon radiolarites are strongly enriched in mn and trace elements metal enriched deposits are also found within slices of mid ocean ridge type lavas associated with melange avdella melange structurally underlying the pindos ophiolite nw greece sulphides there are restricted to tiny massive deposits overlying pillow lava and sulphide veins within ophiolitic extrusives pillow lavas are overlain by volcanic talus breccias shed from submarine fault scarps overlying metalliferous mudstones are enriched in fe and other hydrothermal constituents probably derived from nearby sulphide precipitating zones and mixed with lithogenous sediments the metalliferous deposits preserve a variety of hydrothermal deposits within an early mesozoic small ocean basin the pindos sediments reflect mixing of ferruginous hydrothermal constituents with terrigenous sediment possibly during the earlier stages of basin opening the othris sulphide and ferruginous oxide sediments record evidence of a small high temperature hydrothermal field formed near the spreading axis when the ocean neared its maximum width manganese rich cherts in the northern othris area reflect widespread accumulation of hydrothermal constituents on the abyssal plain derived from axial high temperature hydrothermal fields and or related to low temperature off axis discharge

alunite in the pascua lama high sulfidation deposit constraints on alteration and ore deposition using stable isotope geochemistry the pascua lama high sulfidation system located in the el indio pascua belt of chile and argentina contains over 16 million ounces moz au and 585 moz ag the deposit is hosted primarily in granite rocks of triassic age with mineralization occurring in several discrete miocene age phreatomagmatic breccias and related fracture networks the largest of these areas is brecha central which is dominated by a mineralizing assemblage of alunitepyrite enargite and precious metals several stages of hydrothermal alteration related to mineralization are recognized including all types of alunite bearing advanced argillic assemblages magmatic hydrothermal steam heated magmatic steam and supergene the occurrence of alunite throughout the paragenesis of this epithermal system is unusual and detailed radiometric mineralogical and stable isotope studies provide constraints on the timing and nature of alteration and mineralization of the alunite pyrite enargite assemblage in the deposit early preore alteration occurred prior to ca 9 ma and consists of intense silicic and advanced argillic assemblages with peripheral argillic and widespread propylitic zones alunite of this stage occurs as fine intergrowths of alunite quartz kaolinite dickite and pyrophyllite that selectively replaced feldspars in the host rock stable isotope systematics suggest a magmatic hydrothermal origin with a dominantly magmatic fluid source alunite is coeval with the main stage of au ag cu mineralization alunite pyrite enargite assemblage ore which has been dated at approximately 8 8 ma ore stage alunite has an isotopic signature similar to preore alunite and 34salun py data indicate depositional temperatures of 245 to 305 c the d and 18o data exclude significant involvement of meteoric water during mineralization and indicate that the assemblage formed from h2sdominated magmatic fluids thick steam heated alteration zones are preserved at the highest elevations in the deposit and probably formed from oxidation of h2s during boiling of the magmatic ore fluids coarsely crystalline magmatic steam alunite 8 4 ma is restricted to the near surface portion of brecha central postmineral alunite jarosite were previously interpreted to be supergene crosscutting veins and overgrowths although stable isotope data suggest a mixed magmatic meteoric origin for this late stage alteration only late jarosite veinlets 8 0 ma associated with fine grained pseudocubic alunite have a supergene isotopic signature the predominance of magmatic fluids recorded throughout the paragenesis of the pascua system is atypical for high sulfidation deposits which typically involve significant meteoric water in near surface and peripheral alteration and in some systems even ore deposition at pascua the strong magmatic signature of both alteration and main stage alunite pyrite enargite assemblage ore is attributed to limited availability of meteoric fluids this is in agreement with published data for the el indio pascua belt indicating an event of uplift and subsequent pediment incision as well as a transition from semiarid to arid climatic conditions during the formation of the deposit in the mid to late miocene

patterns of low frequency monthly sea level pressure variability 1899 1986 and associated wave cyclone frequencies abstract spatial patterns of low frequency sea level pressure slp variability are identified by performing rotated principal component analysis rpca on a long term 1899 1986 northern hemisphere gridded dataset the analysis is limited to the region 160 e eastward to 40 e due to missing data early in the century the objective is to identify a comprehensive set of highly recurrent slp teleconnection patterns to examine some aspects of their seasonality and to identify the associated mean winter pressure fields and cyclone frequencies occurring at times of opposite eigenvector polarity the results are further described in the context of the southern oscillation and known midtropospheric teleconnection patterns four low frequency variability patterns are identified over the atlantic european sector including i the north atlantic 0scillation nao and spatial patterns with slp variability centers over ii the eastern atlantic eatl iii southern europe and the northern mediterranean basin s

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

a 15 year climatology of northern hemisphere 500 mb closed cyclone and anticyclone centers abstract a 15 year 1963 77 northern hemisphere 2 5 degree latitude longitude gridded dataset of 500 mb geopotential heights has been used to construct a climatology of 500 mb closed circulation centers these centers defined by at least one closed 30 m contour around a central minimum or maximum geopotential height value were identified objectively between 24 and 82 n from the twice daily analysis grids tracks for all closed circulation centers were computed to establish genesis and lysis distributions and to examine the monthly seasonal and interannual variability characteristics of the closed circulation center distributions for specified regions the occurrence of closed cyclone centers is maximized north of and within the main belt of westerlies extending from northeast asia to the gulf of alaska near 50 n and extending from eastern canada and the extreme northeast united states to southeast of greenland and west of the united kingdom their occurrence is also maximized south of the main be

associations between twice yearly oscillations of the north pacific cyclone track and upper tropospheric circulations over the eastern hemisphere abstract a reexamination is made of the seasonal course of extratropical cyclone activity over the north pacific based mainly on monthly cyclone statistics by whittaker and horn and upper tropospheric wind analyses by sadler with support by other investigations in the asiatic coastal region the prevailing cyclone track is south of japan from midwinter through spring shifting abruptly northward following a collapse of kuroshio cyclogenesis from june to july farther east over the central pacific this sequence gives way to a twice yearly oscillation tracks are farthest north in april and august and farthest south in january february and secondarily in june eastward from japan the oscillations of cyclone activity take place in unison with fluctuations in latitude of the monthly mean jet stream it is related to the intensifying and weakening phases of the subtropical jet during the winter monsoon regime and migrations of the mean jet between positions south and north of the tibetan plateau during mos

the 2002 2003 submarine gas eruption at panarea volcano aeolian islands italy volcanology of the seafloor and implications for the hazard scenario abstract a submarine gas eruption started in november 2002 offshore of panarea volcano aeolian islands italy the intensity of the gas emission and the considerable anomalies of the geochemical and geophysical parameters have alarmed the volcanological community and the italian civil protection agency on the possibility that this activity may represent a volcanic unrest at panarea volcano we used a high resolution marine digital terrain model mdtm with 0 5 m accuracy and detailed underwater surveys by scuba diving to study the exhalation centres and the geological morphological and structural features of the seafloor and to clarify the relationships between gas vents distribution submarine volcanological structures and the recent deformation of this area the underwater surveys revealed an exhalative field characterised by 21 main active gas vents and craters from metres to tens of metres in diameter and a pervasive exhalation from the seafloor hundreds of fossil craters associated with gas pipes and hydrothermal alteration are also present on the seafoor craters pipes and conduits are not associated with juvenile deposits and relate to a long standing history of gas exhalation and eruptions we present the first geological sketch map of the seafloor surrounding the exhalative area and establish the role of ne and nw trending fractures as the main pathways for the gas exhalation

a ground water mixing model for the origin of the imini manganese deposit cretaceous of morocco the imini deposit just south of the atlas mountains of morocco consists of three beds of manganese oxide ore in a slightly deformed dolomite unit about 10 m thick of cenomanian turonian late cretaceous age the dolomite host is sugary textured massive and permeable dolomite occurs as nearly euhedral rhombs each ore bed is about a meter thick and consists almost entirely of intergrowths of pyrolusite and hollandite family minerals bao up to 11 and pbo up to 28 with a flattened geode structure overlying the ore beds are solution collapse breccias with dolomite clasts janggunite mn fe oxide and dolomite matrix and pyrolusite hollandite calcite cement the ore solution collapse breccia and coarsely recrystallized pure dolomite are coextensive a zone only 400 to 1 000 m wide but 25 km long and elongate east northeast west southwest diagenetic features of the deposit are recrystallized texture of the dolomite flattened geode structure of the ore solution collapse breccia and associated draped laminae of the insoluble residues fossil replacement by mn oxides and zoned chert nodules with inclusions a mineralogic paragenesis shown independently in each of these features from older to younger is 1 precursor carbonates 2 dolomite janggunite and 3 hollandite pyrolusite chert calcite diagenesis probably occurred during the late cretaceous in a mixing zone of fresh and saline ground water as similar diagenetic sequences without manganese deposits are widely reported to have formed in such environments carbon and oxygen isotope compositions of carbonates and oxygen isotope compositions of chert show that an increasing component of fresh meteoric ground water was present as diagenesis proceeded falling sea level allowed the mixing zone to occupy various positions within the carbonate unit and convert the primary calcareous carbonate rocks to dolomite with chert nodules anoxic seawater is known both worldwide and from the local depositional basin atlas gulf in the cenomanian turonian this is believed to be the key to manganese deposition because anoxic conditions greatly enhance manganese solubility two specific versions of the mixing zone model are presented for manganese deposition one in which a primary sedimentary manganese precipitate formed along margins of the anoxic basin and was recrystallized during diagenesis in the mixing zone and the other in which anoxic saline ground water brought manganese into the mixing zone where it precipitated

environments and processes of manganese deposition concentration of manganese in solution and its deposition takes place by redox controlled processes in a variety of modern and ancient geologic and geochemical environments modern mn deposition occurs predominantly in deep sea areas rather than shallow water domains although deep sea sedimentary deposits dominate hydrothermal contribution of mn to the ocean system may be substantial mn deposition from hydrothermal solutions at or near sea floor spreading centers and less commonly in island arc areas is known in addition near and far field dispersion of mn from vent sites is also substantial such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of mn in seawater thus even in sedimentary deposit domains at least partial derivation of mn from a hydrothermal source is possible sedimentary fe mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid water column oxygen minimum zones thus the presence or absence of volcanic rocks is not a clear indication of whether sedimentary mn deposits particularly in the ancient geologic record are the result of a totally terrigenous or a totally volcanogenic source abyssal fe mn nodules are considered to form from a basin water hydrogenous and or pore water early diagenetic supply of metals but in most cases the extent of supply from either of the sources is unknown the metal incorporation mechanisms of free moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition therefore no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition the determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules biological participation directly or indirectly controls mn deposition the stratified black sea demonstrates the concentration of mn in solution in an anoxic zone its advection toward the redox interface and its precipitation in an oxygenated condition similar stratified basins are contemplated for ancient mn deposition in shallow water basin margin areas geologic and geochemical signatures indicate that during sea level highstands stratified basins formed in which mn was concentrated in solution in the anoxic part corresponding transgression led to the impingement of the redox interface on the continental shelf and precipitation of mn oxides could take place across the interface during transgression regression cycles offshore in anoxic or dysaerobic conditions mn carbonate could form by early diagenetic reaction of mn super 2 with co 2 or hco 3 super produced by organic carbon oxidation critical mn deposits occurring in transgressive glaciogenic and black shale bearing ancient sequences support this paleoenvironmental model for mn deposition

seasonal variations of the synoptic scale transient eddy activity and polar front jet over east asia abstract seasonal variations of the synoptic scale transient eddy activity stea and the jet streams over east asia are examined through analysis of the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data extracted from the 6 hourly upper level wind fields the distribution of the jet core numbers exhibits a distinct geographical border for the east asian subtropical jet easj and the east asian polar front jet eapj at the latitudes of the northern tibetan plateau tp in the cool seasons two branches of the stea and low level baroclinicity exist over the east asian landmass accompanied by the two jet state of the easj and eapj in the warm seasons a single jet pattern of the easj along the north flank of the tp is accompanied by the weakened stea over the mid to high latitudes of east asia further analysis shows two distinct features of the seasonal variations of the stea over east asia compared with that over the north pacific first during the transit

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

hydrothermal manganese deposits in island arcs and related to subduction processes a possible model for genesis abstract submarine hydrothermal manganese deposits have recently been recovered from a number of island arc settings such as the tonga kermadec ridge ogasawa arc trench bonin arc mariana arc and bismarck archipelago it has also been shown that large volumes of fluid are released during dewatering of subducting sediments the amount of water subducted globally 1 5 10 15 g yr 1 is about two orders of magnitude less than that advected at ocean spreading centres hydrothermal manganese deposits may be precipitated from these waters the distribution of terrestrial manganese deposits around the circum pacific belt and elsewhere suggests that some of these deposits may be of hydrothermal origin related to subduction processes at present most of these terrestrial deposits are inadequately described to permit the establishment of the precise tectonic setting at the time of deposition of the manganese deposits and therefore an unambiguous assessment of this hypothesis