intraseasonal modulation of the north pacific storm track by tropical convection in boreal winter abstract the modulation of the north pacific storm track by tropical convection on intraseasonal time scales 30 90 days in boreal winter december march is investigated using the ncep ncar reanalysis and noaa satellite outgoing longwave radiation olr data multivariate empirical orthogonal function meof analysis and case compositing based upon the principal components pcs of the eofs reveal substantial changes in the structure and intensity of the pacific storm track quantified by vertically 925 200 mb averaged synoptic eddy kinetic energy seke during the course of a typical madden julian oscillation mjo event the storm track response is characterized by an amplitude varying dipole propagating northeastward as the center of the anomalous tropical convection moves eastward across the eastern indian ocean and the western central pacific a diagnosis of the seke budget indicates that the storm track anomaly is induced primarily by changes in the convergence of energy flux baroclinic conversi

2 3 day convective variability in the tropical western pacific abstract this paper is an examination of 2 3 day convective variability in the tropical pacific region the initial focus of the paper is on the western tropical pacific during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare intensive observation period iop high spatial and temporal resolution outgoing longwave radiation olr data and sea surface temperatures are filtered to eliminate diurnal and lower frequency variability the propagation of the 2 3 day convective variability is also studied westward propagation appears to be favored in some regions indicative of the events being influenced by westward propagating inertio gravity waves however many regions have 2 3 day events that divide fairly equally into eastward and westward propagations indicating that both eastward and westward propagating inertio gravity waves are influencing the oscillation the sst data during the 4 month iop dataset show evidence of a 2 3 day variability during those con

controls on the siting and style of volcanogenic massive sulphide deposits abstract volcanogenic massive sulphide vms deposits form in subaqueous environments from circulating hydrothermal fluids heated by volcanic activity these deposits form as sulphide mounds stratiform exhalative and or replacive bodies and commonly have stockwork vein mineralization in their immediate footwall these various styles are essentially facies of mineralization each one being the product of a particular set of conditions that control the ore forming processes and the consequent geometry and architecture style of the deposits these controls include the physical and or chemical nature of the host rocks the temperature and composition of the hydrothermal fluids and the redox state of the depositional environment the style of exhalative deposits is controlled by the salinity of the vented fluids and the redox state at the seafloor hydrothermal fluids with salinities less than twice that of seawater that vented into open oxic oceanic environments typically formed small mound and chimney complexes unless they were rapidly covered by sediments or volcanic rocks the massive sulphides were rapidly oxidized and partly dissolved by seawater in contrast stratiform sheet like deposits are typically formed in anoxic bottom waters anoxic marine conditions were periodically of global extent particularly prior to 2 4 ga or of a regional nature local anoxic conditions can also be self induced by the exhalation of saline and reducing hydrothermal fluids that ponded in bathymetric depressions such as second or third order basins to form a brine pool these exhalative systems may have been initiated as chimney vent complexes and subsequently overlain by stratiform sulphides formed under the self induced anoxic conditions deposits formed in anoxic environments can be significantly larger than those in oxic settings and this is attributed to several factors that include longer lived hydrothermal circulation more efficient sulphide precipitation and reduced or inhibited oxidation thereof replacement of volcanic and sedimentary strata by sulphide typically occurs within the feeder zones beneath the exhalative mineralization however successions with abundant porous permeable and or reactive rocks such as glassy and or pumiceous volcaniclastic rocks and in some cases limestone favoured the development of large replacive deposits that may have had little surficial expression on the sea floor vms deposits at spreading centres within oceanic crust formed almost exclusively as mounds most of them have not been preserved likely due to oxidation of the sulphides in the prevailing oxic environment and or destruction of oceanic crust during subsequent subduction intra continental rifts arc rifts and back arc rifts commonly have more complexity in their structure and facies architecture and environments and can host all styles of vms mineralization in these settings early extension favoured the formation of restricted basins with ideal conditions for the onset of hydrothermal activity and development of anoxic bottom waters whereas in mature rifts the conditions were less conducive for the formation of regionally extensive anoxic environments formation of replacive deposits was permissible in all settings with porous or reactive subsea floor strata replacive mineralization is the most likely to be preserved in the geological record due to the sulphides being physically shielded from oxidative weathering and mechanical erosion at the seafloor the various styles of vms mineralization can rarely be distinguished using a single criterion in most cases multiple criteria are required mound style mineralization is distinguished by a mound or lens shaped morphology b presence of chimney fragments c presence of abundant sedimented sulphide breccias d location on a stratigraphic boundary ore horizon and e association with a thin horizon or thicker stratigraphic interval of fine grained clastic rocks e g shale mudstone that accumulated at slow sedimentation rates stratiform exhalative mineralization is distinguished by a sheet like morphology prior to deformation b presence of fine grained clastic host rocks that accumulated at relatively slow rates e g mudstone c presence of local or extensive planar stratification replacive mineralization is characterized by a irregular geometry and distribution of sulphide bodies b gradation from massive sulphides to semi massive sulphides and disseminated mineralization with relict textures of the host rock and c originally pumiceous glassy or reactive host rocks emplaced at high depositional rates mass flow deposits lavas carbonate altered mass flow deposits or limestone one deposit or district may comprise two or more of these main styles of mineralization in many cases the main styles of vms mineralization present in a particular region can be predicted from examination of the facies architecture and depositional environments of the host succession recognition of the style s of mineralization that occur in a particular basin or mineral belt enables exploration models to be improved and should influence the strategy of exploration for vms deposits

apparent welding textures in altered pumice rich rocks fiamme and eutaxitic texture are common in ancient non welded pumice breccias the fiamme are phyllosilicate rich lenses that define a bedding parallel foliation resembling eutaxitic texture in welded ignimbrites pumice breccias in the cambrian mount read volcanics australia are composed of tube pumice clasts bubble wall shards plagioclase crystal fragments and volcanic lithic clasts and contain dark green fiamme and stylolites these sericite or chlorite sericite fiamme are aligned roughly parallel to regional bedding and are enclosed in pale pink feldspar quartz altered domains of uncompacted randomly oriented tube pumice clasts and bubble wall shards similarly pumice breccias in the miocene green tuff belt in the hokuroku basin japan comprise tube pumice clasts fiamme bubble wall shards crystal fragments and non vesicular volcanic clasts the dark green wispy smectite or chlorite fiamme are aligned parallel to bedding and are enclosed in domains of variably clay zeolite and sericite altered uncompacted pumice clasts and shards the fiamme in these examples vary in length 0 5 mm to 1 m length to height ratio 3 1 to 40 1 shape e g flame like feathery branching bow tie wedge and internal texture porphyritic massive vesicular or stylolitic the fiamme define an anastomosing bedding parallel pre tectonic eutaxitic texture delicate feathery terminations and locally preserved vesicles indicate that the fiamme are altered compacted pumice clasts the presence of bedding parallel stylolites and solution seams undeformed shards and pumice clasts adjacent to the fiamme and the overprinting of fiamme by the regional cleavage suggest that the fiamme formed during diagenesis prior to tectonic deformation and that compaction did not involve welding fiamme and eutaxitic texture in these examples resulted from the alteration dissolution and mechanical compaction of cold tube pumice clasts during diagenesis and lithification

diagenesis of sandstones in the back arc basins of the western pacific ocean sandstones occur in back arc basins of the western pacific at dsdp sites 299 sea of japan 297 northern shikoku basin 445 and 446 daito ridge and basin province 453 mariana trough 286 new hebrides basin and 285 south fiji basin these sandstones are dominantly volcaniclastic arenites derived from andesitic island arcs the degree of sandstone diagenesis is dependent on original composition burial rate heat flow history of the basin and timing of sandstone deposition with respect to rifting processes and associated high heat flow sandstones containing a larger proportion of volcaniclastic components showed more diagenetic effects than sandstones containing a significant volume of other rock fragments and mineral components sandstones deposited during early stages of rifting sites 445 446 with a slow burial rate and high crustal heat flow showed the greatest degree of downhole diagenetic change these diagenetic changes include early pore space reduction and rim cementation by clay minerals followed later by calcite and subsequent pore fill cementation by clinoptilolite heulandite analcite and later calcite replacement of recognizable volcanic rock fragments by chert calcite and zeolites was observed in the deepest part of the hole sandstones deposited after rifting under conditions of associated lower heat flow showed considerably less diagenetic changes particularly if burial was rapid the high heat flow associated with earliest rifting associated fluid circulation driven by thermal convection and slow burial rate controlled the diagenetic history of these sandstones thus timing of sandstone deposition with rifting stage and associated burial rates were key factors in controlling sandstone diagenesis in back arc basins

large scale rhyolite peperites jurassic southern chile development of a jurassic volcano tectonic rift basin in the southern andes created a setting in which thick rhyolitic volcaniclastic sequences accumulated in submarine environments and were penetrated by hypabyssal intrusions during or shortly after deposition in the ultima esperanza district of southern chile extensive masses of peperite were produced when rhyolite magma underwent quenching disruption and commingling with wet unconsolidated sediments during intrusion at shallow levels beneath the sea floor the peperite forms discordant intrusive masses with volumes of up to several cubic kilometers in which large widely spaced coherent rhyolite feeder pods are surrounded by and grade into closely packed and dispersed peperite closely packed peperite consists of tightly fitting clasts separated by sediment filled fractures in dispersed peperite the sediment forms a matrix surrounding large masses of fractured rhyolite and smaller more widely separated rhyolite clasts evidence of in situ quench fragmentation is well preserved on both outcrop and thin section scales thin sections show that clast margins and in some cases entire small clasts underwent cooling contraction granulation releasing shards of quenched rhyolite and fragments of phenocrysts into the adjacent sediment interaction between magma and wet sediment was non explosive and involved fluidization of the host sediments creating space for the intruding magma and causing pervasive injection of highly mobile sediment along thermal contraction cracks in quench fragmented rhyolite the ability of the magma to undergo complex intermixing with large volumes of sediment with widespread preservation of in situ fragmentation textures is interpreted to reflect a relatively low magma viscosity presumably caused by retention of volatiles in the magma at the ambient pressures involved beds of redeposited peperite within the rift basin fill indicate that some of the intrusive peperite masses reached the sea floor undergoing slumping and mass flow the peperites were thus an important local source of coarse grained debris during the evolution of the basin

circulation anomalies associated with tropical convection during northern winter abstract lagged cross correlations between outgoing longwave radiation olr and national meteorological center global analyses are utilized to isolate the preferred upper level and surface circulation anomalies associated with tropical convection during northern winter three intraseasonal time scales are studied 30 70 14 30 and 6 14 days in the 30 70 day band the upper level circulation signals are zonally elongated with zonal wavenumbers 0 2 dominant higher frequency signals are dominated by zonal wavenumbers 5 and 6 in the 14 30 day band convection over the eastern hemisphere is associated with upper level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains the strongest signals are for convection over africa australia and the eastern indian ocean only weak signals are seen for convection over indonesia in these regions of upper level easterlies olr anomalies peak prior to the maximum anomalies in wind suggesting forcing of the circulation b

extratropical extended range precursors near the tropopause preceding persistent strong precipitation in south china a climatology the pre summer rainy season psrs april june is the period of most frequent strong precipitation in south china sc persistent strong precipitation events pspes can cause greater loss of life and property than short lived strong precipitation this paper investigates extended range signals near the tropopause preceding two persistent positive climatological intraseasonal oscillations ppcisos in precipitation corresponding to two climatological pspes in sc during the psrs using the ciso analysis of isentropic potential vorticity ipv it is found that precursor signals can be better seen in ipv cisos than in unfiltered ipv the first rainfall ppciso is caused by an eastward propagation of high ipv cisos along the dynamical tropopause originating from the arctic region and west of the tibetan plateau the second is the most persistent 13 days its high ipv cisos originate over the arctic region and the tropical monsoon region respectively 20 or more days prior to the rainfall ciso peak the west of the tibetan plateau and the northern region of the east asian westerly jet near the tropopause are two transit points where extratropical high ipv cisos strengthen and then change their propagation direction the southward high ipv cisos and the northward positive ipv ciso caused by the monsoon begin to interact about 10 days prior to rainfall peak since then the interaction leads a narrow meridional positive pv channel on the inclined 345 k isentropic surface a specific ciso pattern characterized by an elongated high ipv ciso isolated by three negative ipv cisos the south asian the okhotsk and the western pacific subtropical highs is responsible for the long duration of the second rainfall ppciso

characteristics of 3 4 and 6 8 day period disturbances observed over the tropical indian ocean abstract a field observational campaign i e the mirai indian ocean cruise for the study of the mjo convection onset mismo was conducted over the central equatorial indian ocean in october december 2006 during mismo large scale organized convection associated with a weak madden julian oscillation mjo broke out and some other notable variations were observed water vapor and precipitation data show a prominent 3 4 day period cycle associated with meridional wind variations filtered anomalies at midlevels in reanalysis data i e the japan meteorological agency jma climate data assimilation system jcdas show westward phase velocities and the structure is consistent with mixed rossby gravity waves estimated equivalent depths are a few tens of meters typical of convectively coupled waves in the more rainy part of mismo 16 26 november the 3 4 day waves were coherent through the lower and midtroposphere while in the less active early november period midlevel fluctuations appear le

assessing hydrothermal alteration intensity in volcanic hosted massive sulfide systems using portable x ray fluorescence analysis of drill core an example from myra falls canada current portable x ray fluorescence pxrf technology can rapidly and inexpensively yield concentrations of geologically significant elements typically with instrument detection limits below several tens of parts per million based on conventional xrf whole rock geochemical data both the ishikawa alteration index and the chlorite carbonate pyrite index increase with proximity to sulfide mineralization at myra falls however available pxrf technology is typically unable to detect all the elements required to calculate these alteration indices as a result there is a need to utilize the elements that are readily detectable using pxrf and apply these to hydrothermal alteration assessment we propose that rb sr ratios provide a robust proxy for the ishikawa alteration index and demonstrate that conventional whole rock xrf analytical results for rb and sr can be reproduced using pxrf analysis from drill core surfaces at myra falls the rb sr ratios vary from 2 0 for intensely altered rocks downhole profiles of alteration intensity generated from systematic pxrf analysis of drill core surfaces can be used to inform drilling and targeting decisions the application of the rb sr ratio as a proxy for alteration intensity extends beyond this case study and can be applied to other hydrothermal systems that produce phyllosilicate minerals as alteration products of feldspar

the continuum of north pacific sea level pressure patterns intraseasonal interannual and interdecadal variability this study combines k means cluster analysis with linear unidimensional scaling to illustrate the spatial and temporal variability of the wintertime north pacific sea level pressure slp field daily wintertime slp data derived from the ncep ncar reanalysis are used to produce 16 slp anomaly patterns that represent a discretized approximation of the continuum of north pacific slp patterns this study adopts the continuum perspective for teleconnection patterns which provides a much simpler framework for understanding north pacific variability than the more commonly used discrete modal approach the primary focus of this research is to show that variability in the north pacific on intraseasonal interannual and interdecadal time scales can be understood in terms of changes in the frequency distribution of the cluster patterns that compose the continuum each of which has a time scale of about 10 days this analysis reveals 5 6 pacific north american like pna like patterns for each phase as well as dipoles and wave trains a self organizing map som analysis of coupled slp and outgoing longwave radiation data shows that many of these patterns are associated with convection in the tropical indo pacific region on intraseasonal time scales the frequency distribution of these patterns in particular the pna like patterns is

fiamme textures in volcanic successions flaming issues of definition and interpretation abstract fiamme are aligned flame like lenses found in welded ignimbrite fiamme also occur in welded pyroclastic fall deposits secondary welded pumice rich facies diagenetically altered and compacted non welded pumiceous volcaniclastic facies and lavas fiamme can be formed in a variety of ways the common genetic use of the term fiamme for pumice clasts that have undergone welding compaction is too narrow fiamme is best used as a descriptive term for elongate lenses or domains of the same mineralogy texture and composition which define a pre tectonic foliation and are separated by domains of different mineralogy texture or composition this descriptive term can be used regardless of the origin of the texture and remains appropriate for flattened pumice clasts in welded ignimbrite

isotopic insights into the degassing and secondary hydration of volcanic glass from the 1980 eruptions of mount st helens abstract the magmatic degassing history of newly erupted volcanic glass is recorded in its remaining volatile content however this history is subsequently overprinted by post depositional secondary hydration the rates and origins of which are not yet adequately constrained here we present the results of a natural experiment using products of the 1980 eruptions of mount st helens we measured water concentration dglass and 18obsg 18o of the bulk silicate glass of samples collected during the dry summer months of 1980 and compared them with material resampled in 2015 from the same deposits samples collected from the subsurface near gas escape pipes show elevated water concentrations near 2 0 wt and these are associated with lower dglass 110 to 130 and 18obsg 6 0 to 6 6 values than the 1980 glass 70 to 100 and 6 8 to 6 9 respectively samples collected in 2015 from the surface to 10 cm subsurface of the 1980 summer deposits have a small increase in average water contents of 0 1 0 2 wt but similar 18obsg 6 8 6 9 values compared to the 1980 glass values these samples however show 15 higher dglass values exchange with meteoric water is expected to yield lower dglass values we attribute higher dglass values in the upper portion of the 1980 deposits collected in 2015 to rehydration by higher d waters that were degassed for several months to a year from the hot underlying deposits which hydrated the overlying deposits with relatively high d gases our data also contribute to magmatic degassing of crystal rich volcanoes using the 1980 samples our reconstructed d h2o trends for the dacitic mount st helens deposits with rhyolitic groundmass yield a trend that overlaps with the degassing trend for crystal poor rhyolitic eruptions studied previously elsewhere suggesting similar behavior of volatiles upon exsolution from magma furthermore our data support previous studies proposing that exsolved volatiles were trapped within a rapidly rising magma and started degassing only at shallow depths during the 1980 eruptions

volcanic influences on hydrothermal and diagenetic alteration evidence from highway reward mount windsor subprovince australia synvolcanic sills and cryptodomes hosting the highway reward volcanic hosted massive sulfide deposit invaded wet poorly consolidated silt sand and pumice breccia margins of the porphyriric units display perlitic and quench fractures suggesting that they were formerly glassy interiors of the rhyolites rhyodacites and dacites were originally glassy partly glassy or comprised crystalline domains exhibiting spherulitic lithophysae and micropoikilitic textures no glass is preserved and the sills and cryptodomes are now completely crystalline primary devitrification structures crystallized early above the glass transition temperature and before the formarion of perlite or quench fractures crystallization of residual glass proceeded by diagenetic alteration volcanic associated hydrothermal alteration and ore associated hydrothermal alteration massive sulfide ore is enclosed in a discordant alteration envelope that extends at least 60 m above ore and is known to a depth of 150 m in the footwall in general there is a progression from central quartz sericite pyrite zones giving way to zones of chlorite n anhydrite n gypsum chlorite sericite quartz and finally chloritesericite distal to ore the outermost alteration grades into ithofacies that have altered to various background assemblages of feldspar hematite sericite chlorite quartz epidote and carbonate compared to least altered lithofacies the quartz sericite pyrite zones are enriched in sion k20 fe o3 s and ba and depleted in n o cao mgo and sr elevated concentrations of mgo fe203 and s coupled with low na o cao and k o values characterize chlorirized zones the pattern of low n o cao and mgo values and high k o values passing outward through the chlorite sericite n quartz zones is more erratic the ishikawa alteration index ai value and the chlorite carbonate pyrite index ccpi value become progressively larger passing from background altered facies ai 60 ccpi 20 55 into the footwall and hanging wall alteration zones ai 89 97 ccpi 41 99 at ai values greater than 90 cu bi and mo are elevated the s n o ratio increases toward ore whereas sr ba ratios are lowest at ai values above 90 the geochemical halo patterns reflect the composite response of lithofacies to mineralogical and textural chan es accompanying diagenetic alteration volcanic associated hydrothermal alteration and ore associated hydromermal alteration most alteration zones around ore display two or more overprinting alteration mineral assemblages within single alteration zones the distribution of alteration minerals and assemblages varies spatially in response to contrasring lithofacies character formerly glassy coherent and volcaniclastic facies display mineralogical and textural changes that reflect the influence of fracture perlitic quench and or matrix permeability and porosity on fluid migration crystalline domains of volcanic facies generally preserve their original texture although recrystallization has partly destroyed primary devitrification microstructures alteration minerals are localized along cooling joints hydraulic fractures and veins or form mottled patchy or wispy domains in contrast siltstone that separates intrusions and forms the matrix in peperite is relatively unaltered or was baked during magma sediment mixing in zones of intense quartz sericite n pyrite chlorite n anhydrite gypsum and sericite alteration high water rock ratios an extended history of fluid flow and elevated temperatures promoted large scale mobilization of elements in all facies relics of the early alteration mineral assemblages are locally preserved in these zones and imply a progression from initial volcanic determined

horizontal and vertical structure of observed tropospheric equatorial rossby waves equatorial rossby er waves are identified in an 8 year data set of national meteorological center operational analyses the westward moving waves have symmetric circulations about the equator and eastward energy dispersion with maximum zonal wind perturbations along the equator and meridional wind maxima roughly 10 15 off the equator they have maximum amplitude in the lower troposphere and are associated with convective signals at roughly the mean latitude of the tropical convergence zones the circulations thus possess many of the features of the equatorially trapped n 1 rossby modes derived by matsuno 1966 they are generally around zonal planetary wavenumber 6 scale and have a deep nearly equivalent barotropic structure up to 100 mbar this is in contrast with the madden julian oscillation and mixed rossby gravity waves which generally have a first baroclinic mode vertical structure during the intensive observing period iop of the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare and in other years westward propagating er disturbances along the equator are observed by using 6 to 30 day filtered circulation data at 850 mbar zonal wind anomalies at 850 mbar are preferentially associated with like signed anomalies in a deep layer at this frequency as was observed during coare the er waves are most common during northern winter in the central pacific although they can be detected sporadically over the other ocean basins and in other seasons as well one source for the equatorial rossby waves appears to be upper level extratropical rossby wave activity propagating into the eastern pacific although the equatorial waves are sometimes present during the northern summer when the extratropical source is absent we cite evidence that propagation of er wave activity from the central into the western pacific is related to occurrences of westerly wind bursts

tropical convection on 7 21 day timescales over the western pacific abstract evidence is presented to demonstrate that the oscillations of convection on 7 21 day timescales are an important component of the intraseasonal variability over the region spanning the equatorial western pacific to the subtropical south pacific in that area of the world these oscillations are largely confined to regions with high sea surface temperatures ssts or sst gradients consequently the patterns of 7 21 day variability of convection undergo significant changes as the el nin o southern oscillation reconfigures the distributions of sst a test is developed that detects episodes in which the 7 21 day oscillation of outgoing longwave radiation olr is particularly well defined for several cycles applying this test 29 episodes of high 7 21 day variability were defined based on this information the annual and longitudinal distribution of 7 21 day variability is discussed the 7 21 day oscillations of convection found at subtropical southern latitudes tend to have stronger wind shear i

na k ion exchange reaction between rhyolitic glass and na k c1 aqueous solution under hydrothermal conditions abstract hydrothermal experiments on ion exchange reactions were carried out using synthetic and natural rhyolitic glasses and na k cl aqueous solution at 200 300 c and 1000 bars the rhyolitic glass did not crystallize during the reaction even under hydrothermal conditions and it behaved as a na k ion exchanger the na k ion exchange properties of the glass were strongly influenced by its thermal history quenched glass preferentially fixed k rather than na and glass obtained by slow cooling showed the opposite trend the present experimental results show clearly that glass as well as minerals can control the composition of the coexisting aqueous solution in hydrothermal systems the present results also suggest that the chemical composition of coastal thermal waters in japan is controlled by the two stage episode of reaction between acidic volcanic rocks and seawater

origin of zn pb sb au mineralization adjacent to the paleoproterozoic boliden au rich vms deposit sweden evidence from petrographic and oxygen isotope characteristics adjacent to the world class boliden deposit fine to coarse grained zn pb sb au rich sulfide sulfosalt bearing horizons occur within the base of a metasedimentary succession that has previously been regarded to stratigraphically overlie the skellefte volcanics and boliden deposit the metasedimentary succession comprises interbedded mudstone and normal graded crystal rich volcanic sandstone siltstone units interpreted to be low density turbidity currents in a subaqueous environment below wave base the sharp contact between the mineralized intervals and volcanic sandstone is concordant to the bedding planes and compaction foliation above and below the mineralization the wall rocks contain well preserved plagioclase crystals partly enclosed by a weak alteration composed of bedding parallel metamorphic biotite sericite minerals these observations are consistent with burial or tectonic compaction and diagenetic alteration that was overprinted by metamorphic biotite the occurrence of biotite in the wall rocks and homogenization recrystallization of the sulfide sulfosalt assemblage in the mineralized intervals are consistent with peak metamorphic conditions 350 450 c 4 kbars in the boliden area however preservation of plagioclase and water rock interaction under rock dominant conditions suggest that high 18o values 10 7 to 13 5 acquired during diagenesis were unchanged by the metamorphic overprint the 18o values yield low temperatures 150 c which indicate pre metamorphic conditions these data suggest that the zn pb sb au rich intervals formed as pre metamorphic distal syn volcanic exhalative mineralization during sedimentation of the vargfors group metasedimentary rocks this implies that massive sulfide formation continued even during vargfors group time and therefore there is still potential for discovery of gold rich base metal ores in this part of the skellefte field stratigraphy

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

time constraints on magmatism mineralisation and metamorphism at the falun base metal sulphide deposit sweden using u pb geochronology on zircon and monazite abstract u th pb zircon and monazite ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the palaeoproterozoic falun base metal sulphide deposit in the bergslagen lithotectonic unit fennoscandian shield sweden and thereby the timing of mineralisation hydrothermal alteration and mineralisation at falun are constrained to a short interval of several million years between a 207pb 206pb weighted average age of 1894 3 ma for a rhyolitic sub volcanic rock in the felsic volcanic to sub volcanic host rock suite and a 207pb 206pb weighted average age of 1891 3 ma for a post sulphide porphyritic dacite dyke magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 3 1894 2 ma and 1893 3 ma the felsic sub volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity and burial of the supracrustal rocks two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the falun deposit yield 207pb 206pb weighted average ages of 1831 8 ma and 1822 5 ma respectively these ages fall well within the temporal range of a younger 1 84 1 81 ga m2 metamorphic episode during the 2 0 1 8 ga svecokarelian orogeny with the older episode m1 inside the bergslagen lithotectonic unit at around 1 86 ga this shows the major influence of the m2 event in the north western part of this unit leading to a complete resetting of the u th pb isotope system in monazite

further analysis of the relationship between circulation anomaly patterns and tropical convection tropical extratropical connections are investigated for 250 mbar stream function fluctuations in both intraseasonal and interannual bands the principal modes of anomalous 250 mbar stream function are computed and related to anomalous outgoing longwave radiation olr which is used as a proxy for deep tropical convection the leading mode for both boreal winter and summer displays a large zonally symmetric component which appears in both the intraseasonal is and interannual ia bands in the is band the dominant mode is an oscillation with a period of 48 days correlations between the principal component of this mode and olr anomalies indicate that this pattern is directly related to convection in the tropical pacific the second mode for the boreal winter consists of a wave train from the pacific ocean east northeastward to western north america and then east southeastward to the subtropical atlantic ocean this mode also exists in both ia and is bands simultaneous and lagged correlations between the amplitude time series of this mode and olr anomalies indicate that extreme amplitudes of this wave train are preceded by extremes in the olr anomalies cloud band activity in the subtropical north pacific enhanced cloud band activity in the vicinity of hawaii associated with an anomalousmore cyclonic 250 mbar circulation in the same region precedes the maximum development of a 250 mbar ridge south of the aleutian islands trough over western north america and another ridge along the east coast of the united states the second mode for boreal summer june august is associated with variations of the asian monsoon 36 refs 11 figs 1 tab less

false pyroclastic textures in altered silicic lavas with implications for volcanic associated mineralization there is strong emphasis in recent literature that zn cu pb massive sulfide deposits associated with felsic volcanism the kuroko type deposits are directly related to submarine calderas formed by large submarine pyroclastic eruptions altered silicic volcanic rocks with the appearance of welded and nonwelded pyroclastic flow deposits volcaniclastic debris flows and massive to thin bedded tuffaceous rocks form a major component of a silurian succession that hosts zn cu pb massive sulfide deposits at benambra southeastern australia however critical evaluation of rock textures indicates that these silicic volcanic rocks are mainly lavas and associated autoclastic facies with remarkably deceptive false pyroclastic and volcaniclastic textures including apparent pumice fiamme and glass shards intercalated sediments indicate that most of the silicic volcanics were emplaced in subaqueous settings ranging from relatively shallow water to deep marine the false textures were produced mainly in originally glassy lava by the combined effects of devitrification perlitic fracture and pervasive hydrothermal alteration these processes are related to the emplacement and cooling history of individual lavas and to a regional essentially synvolcanic hydrothermal system tectonic foliation of the more altered and mechanically weakened rocks has led to partial dismembering of phenocrysts and groundmass fabrics thereby further enhancing clastic appearance subsequent to recognition of widespread false pyroclastic textures at benambra similar features have been identified in three other australian massive sulfide districts these results suggest that a reinvestigation of host rocks is warranted at other deposits where submarine pyroclastics are documented noncaldera settings combining subsidence in an extensional volcano tectonic basin passive submarine lava effusion within the basin and ambient sedimentation derived from basin margins including resedimented pyroclastic debris may be more relevant models in a number of massive sulfide districts

an experimental investigation of high temperature interactions between seawater and rhyolite andesite basalt and peridotite natural seawater was allowed to react with rhyolite andesite basalt and peridotite at 200 500 c and 1 000 bars at water rock mass ratios of 5 and 50 in order to investigate the effects of rock type water rock ratio and temperature on solution chemistry and alteration mineralogy the results indicate that interactions of seawater with various igneous rocks are similar in the production of a hydrous mg silicate and anhydrite as major alteration products fluids involved in the interactions lose mg to alteration phases while leaching fe mn and si from the rocks the ph of the solutions is primarily controlled by mg oh silicate formation and therefore varies with mg and si concentration of the system other reactions which involve mg such as mg ca exchange or which produce free h cause major differences in fluid chemistry between different seawater rock systems high water rock ratio systems 50 1 are generally more acidic and more efficient in leaching than low ratio systems 5 1 due to relatively more seawater mg available for mgsilicate production the experiments show that large scale seawater rock interaction could exert considerable control on the chemistry of seawater as well as producing large bodies of altered rock with associated ore deposits

a composite study of the quasi periodic subtropical wind maxima over the south pacific during november 1984 april 1985 abstract a composite of 10 cases of zonal wind maxima at 200 hpa over the subtropical region stretching from australia to the central pacific is examined for the six month period november 1984 april 1985 this region is unique in that distinct westerly jets frequently form and propagate eastward at latitudes between 20 and 35 s in the summer season some statistical tests were applied and suggest that the flow patterns are quasi periodic consisting of a tendency for new jet streaks to develop over the eastern australian region approximately every one to two weeks these jets then take about 10 days to propagate across the western pacific before dissipating or perhaps moving toward higher latitudes their average propagation speed is approximately 4 m s 1 an examination of the case to case variability of the jets provides additional evidence that they are significant features a diagnosis of the trough ridge systems at 200 and 850 hpa together with calculations of the vertically integrated mean and

the spectrum of ore deposit types volcanic environments alteration halos and related exploration vectors in submarine volcanic successions some examples from australia variations in shape metal content alteration mineralogy and volcanic host rocks of the ore deposits in the two major volcanic hosted massive sulfide vhms districts of eastern australia the cambrian mount read volcanics and the cambro ordovician mount windsor subprovince strongly reflect their volcanic environment conditions of ore formation and hydrothermal alteration processes lens and sheet style polymetallic zinc rich deposits such as rosebery hellyer que river and thalanga are considered to have formed in moderate to relatively deep water environments 500 1 000 m these deposits probably formed either on the sea floor e g hellyer que river or by replacement of porous volcaniclastic units directly below the sea floor e g rosebery the footwall alteration associated with these polymetallic vhms deposits was controlled by host rock permeability and porosity which are in turn related to volcanic facies type degree of fracturing and synvolcanic structural architecture focusing of hydrothermal fluids along synvolcanic structures has resulted in well zoned chlorite sericite footwall alteration pipes within footwall lavas at hellyer on the other hand diffuse fluid flow through very thick pumice breccia at rosebery and hercules has resulted in strata bound sericite dominated footwall alteration zones parallel to the paleosea floor and the ore lenses massive and disseminated pyritic cu au deposits such as those in the mount lyell field and at highway reward formed by subsea floor replacement and are associated with only minor zinc lead massive sulfide ore these deposits formed from higher temperature fluids 300 degrees c in which copper transport is enhanced and are commonly located in felsic volcanic centers dominated by shallow porphyritic intrusions e g highway reward the cu au ore lenses may be strata bound e g mount lyell or crosscutting pipes e g highway reward depending on the structure and permeability characteristics of the felsic volcanic host rocks the presence of high sulfidation alteration minerals e g pyrophyllite zunyite in some of the cu au deposits e g mount lyell field indicates that fluids were relatively acidic and suggests the possibility of magmatic fluid input into the hydrothermal system alteration zonation associated with the cu au vhms deposits is more symmetrical than that of the zn rich deposits with sericite rich alteration extending into the hanging wall in keeping with the subsurface replacement origin of these deposits synvolcanic gold rich deposits with high gold base metal ratios are less common than the cu au and zn rich vhms ore types the gold rich ores e g henty south hercules are strata bound in nature have low sulfide contents and are associated with central zones of intense silicification surrounded by envelopes of sericite pyrite and carbonate alteration volcanological and geochemical studies at henty indicate the gold rich ore formed by the replacement of particular volcanic units deposited in a relatively shallow water environment dominated by volcaniclastic facies lavas and limestones this spectrum of cu au zn rich and au only deposits in the mount read volcanics and the mount windsor subprovince is interpreted to represent a continuum from classic sea floor vhms ores toward those with features more akin to porphyry cu au and epithermal au ag deposits this spectrum relates to the interplay between factors in the submarine volcanic environment and the character of the hydrothermal fluid as follows 1 proportions of volcaniclastic lava and subvolcanic intrusive facies 2 depth of seawater 3 permeability and porosity of volcanic host rocks 4 balance between magmatic components and seawater components in the ore fluid and 5 temperature and acidity of the ore fluid mineralogical lithogeochemical and isotopic studies have revealed a range of alteration vectors useful in exploration for both the zn rich and cu au vhms deposits carbonate and white mica compositional variations are highlighted as important mineralogical vectors thallium and antimony halos may be useful trace element vectors and oxygen and sulfur provide important isotope vectors toward the center of the hydrothermal system

large scale circulation patterns and related rainfall in the amazon basin a neuronal networks approach this study describes the main circulation patterns cp in the amazonian basin over the 1975 2002 period and their relationship with rainfall variability cps in the amazonian basin have been computed for each season from the era 40 daily 850 hpa winds using an approach combining artificial neural network self organizing maps and hierarchical ascendant classification a 6 to 8 cluster solutions depending on the season considered is shown to yield an integrated view of the complex regional circulation variability for austral fall winter and spring the temporal evolution between the different cps shows a clear tendency to describe a cycle with southern wind anomalies and their convergence with the trade winds progressing northward from the la plata basin to the amazon basin this sequence is strongly related to eastward moving extra tropical perturbations and their incursion toward low latitude that modulate the geopotential and winds over south america and its adjoining oceans during austral summer cps are less spatially and temporally organized compared to other seasons principally due to weaker extra tropical perturbations and more frequent shallow low situations each of these cps is shown to be associated with coherent northward moving regional rainfall patterns both in in situ data and era 40 reanalysis and convective activity however our results reveals that precipitation variability is better reproduced by era 40 in the southern part of the amazonian basin than in the northern part where rainfall variability is likely to be more constrained by local and subdaily processes e g squall lines that could be misrepresented in the reanalysis dataset this analysis clearly illustrates the existing connections between the southern and northern part of the amazonian basin in terms of regional circulation rainfall patterns the identification of these cps provide useful information to understand local rainfall variability and could hence be used to better understand the influence of these cps on the hydrological variability in the amazonian basin

tropical plumes over eastern north africa as a source of rain in the middle east tropical plumes tps reflect tropical extratropical interaction associated with the transport of moisture from the tropics to extratropical latitudes they are observed in satellite images as continuous narrow cloud bands ahead of upper level subtropical troughs at times when the subtropical jet is highly perturbed rainstorms usually develop in the exit regions of tps so their presence over northern africa has an impact on the precipitation regime in the southeastern mediterranean based on satellite images and rainfall measurements from israel 10 tps over eastern north africa between 1988 and 2005 in which considerable rain was recorded were selected using the ncep ncar reanalysis data the structure and evolution of these tps were characterized and their regional canonical features were identified a typical tp that occurred in march 1991 is described in detail the main canonical characteristics are as follows the tp development is preceded by an incubation period expressed either as a stationary upper level trough persisting 2 6 days or as two consecutive tp pulses the preferred location for tp origin is 5 15 n 5 w 15 e the tp is separated from the underlying dry saharan pbl the subtropical trough undergoes a phase locking with the lower tropical trough the cloudiness in the tp induced rainstorm is mostly stratified with continuous moderate rain originating from midlevel moisture and the tp tends to be followed by a midlatitude cyclogenesis over the eastern mediterranean this analysis proposes several explanations for the efficiency of the tps in transporting moisture over a 2000 km distance

a preliminary assessment of geodynamic controls on depositional systems and sandstone diagenesis in back arc basins western pacific ocean abstract nine depositional systems are recognized in cores recovered by the deep sea drilling project from the back arc basins of the western pacific these systems include submarine fan debris flow silty basinal turbidite biogenic pelagic carbonate resedimented carbonate biogenic pelagic silica pyroclastic hemipelagic and turbid layer clay and pelagic clay depositional systems the occurrence of these depositional systems in time and space is correlated with regional uplift and volcanism climatic change biological productivity and critical relations of sediment yield from potential sources which experience sufficient uplift and development of an extensive drainage and erosional regimen debris flows and submarine fan systems tend to accumulate after uplift of andesitic volcanic arc sources following development of a regional drainage network biogenic pelagic systems tend to be controlled by biological productivity and are indicators of back arc basin movement through such productivity zones by regional crustal shift hemipelagic and turbid layer clay systems are derived from terrigenous sources and their volume is dependent on climatically controlled sediment yield from such sources resedimented carbonate systems tend to occur during times of active basinal faulting volcaniclastic sandstones recovered in back arc basin dsdp cores show evidence of diagenetic alteration in response to burial depth temperature and thermally driven fluid circulation younger sandstones tend to show pore space reduction rim cementation by chlorite and mixed layer illite smectite and pore filling cementation by clinoptilolite downhole pores are filled with heulandite and analcite older sandstones show pore filling with sparry calcite and replacement of component minerals and rock fragments by calcite chert and zeolites the distinct age depth zonation of diagenetic changes suggests that thermally driven interstitial fluids combined with advection of ocean waters and basement waters accounts best for the mineralogical reactions observed

district scale alteration associated with massive sulfide deposits in the mount read volcanics western tasmania the distribution of secondary mineral assemblages in six mineralized areas of the mount read volcanics defines a district wide zonation which is subconformable with massive sulfide host horizons and the contacts of sill like granitoids where present the relationships between alteration patterns and elements of cambrian geology strongly suggest that the alteration is related to cambrian hydrothermal circulation responsible for massive sulfide mineralization there is a later greenschist facies metamorphic overprint the major components of the principal assemblages are quartz albite chlorite epidote quartz albite chlorite calcite quartz sericite chlorite and quartz k feldspar chlorite several complex assemblages involving the above minerals biotite magnetite pyrite and tourmaline are characteristic of granite contacts secondary biotite is also present sporadically in the rosebery area probably related to devonian granitoids at depth there is a districtwide zonation of sodic or calcic versus nonsodic noncalcic assemblages in felsic volcanic rocks in preore volcanics nonsodic noncalcic assemblages occur immediately beneath the host horizon and may persist several hundred meters before passing into a zone including granite contacts where calcium minerals and albite occur sporadically the nonsodic noncalcic assemblages are predominantly sericitic but assemblages with prominent k feldspar occur locally in postore volcanics sericitic non sodic noncalcic assemblages may persist up to 200 m above the ore horizon before passing into relatively fresh volcanics with common albite and calcic greenschist minerals preore assemblages probably largely reflect downward circulation upwelling zones are characterized by intense sericite chlorite or chlorite development with or without k feldspar lateral spreading of solutions immediately beneath the ore horizon is common chlorite compositions preserve local patterns due to cambrian hydrothermal processes but they do not vary systematically with alteration assemblages throughout the province chlorite mg to fe ratios appear to have been preserved through metamorphism a combination of structural and alteration data is useful to mapping in the mount read volcanics this approach indicates that most syngenetic deposits and sedimentary lenses in the rosebery hercules area may lie on a single host horizon and suggests a continuity of geology from mount farrell through red hills to mount sedgwick

wall rock alteration and metamorphism of a volcanogenic massive sulfide deposit at que river tasmania petrology and mineralogy the rocks in the alteration halo surrounding the polymetallic massive sulfide deposit at que river preserve primary hydrothermal mineral textures and assemblages despite the imprint of later prehnite pumpellyite facies regional metamorphism their textural preservation is attributed to the mechanical strength of many of the hydrothermal minerals such as pyrite carbonates except calcite and quartz the competency of some of the host rocks and the low strain that has affected many rocks at the margin of the halo assemblages include quartz white mica carbonates albitized plagioclase pyrite and chlorite closer to the ore as intensity of alteration increases albite disappears pyrite apatite rutile and anatase become more common white mica quartz carbonates and chlorite vary in abundance and are distributed irregularly these minerals also occur in hydrothermal veins throughout the stockwork zone several generations of veins are commonly developed with each generation having its own distinctive hydrothermal assemblage both hydrothermal and metamorphic phases are compositionally variable despite some overlap there appear to be systematic differences in composition x ray diffraction and microprobe analyses show that the hydrothermal white micas are variable in composition ranging from illites or muscovites to fuchsites their metamorphic counterparts contain less pyrophyllite and more celadonite the hydrothermal carbonates are most commonly ferroan dolomite magnesian siderite and ferroan magnesite the latter two are more abundant than dolomite where alteration is intense calcite and ferroan dolomite formed during metamorphism and the composition of the hydrothermal and metamorphic carbonates may be different in individual specimens both hydrothermal and metamorphic chlorites are ferro clinochlores and magnesio chamosites metamorphic chlorites outside the halo are more fe rich and more al vi deficient than those within the hydrothermal chlorites exhibit fe mg and al iv al vi si iv mg fe vi tschermakite substitutions and contain al iv contents suggesting temperatures of crystallization of 290 degrees to 320 degrees c similar to the temperature of 280 degrees c inferred from fluid inclusions the chemistry of the hydrothermal phases varies throughout the halo overall fe and mg do not show a systematic trend toward mineralization however fe enrichment of hydrothermal phases in the ore is apparent as is mg enrichment of locally developed chlorite carbonate rocks na and celadonite in white micas and ca in carbonates on the other hand decrease with increasing alteration mg only became an important component in the fluid when seawater infiltrated into the hydrothermal system the heterogeneous distribution of the hydrothermal phases is attributed to successive influxes of hydrothermal fluids of varying composition into the alteration pipe variable water rock ratios and seawater entrainment

the relationship between the north atlantic jet and tropical convection over the indian and western pacific oceans abstractboreal winter jet variability over the north atlantic is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data where the variability is defined by the first eof of the zonal wind on seven vertical levels the principal component time series of this eof is referred to as the jet index a pattern correlation analysis indicates that the jet index more accurately describes intraseasonal north atlantic zonal wind variability than does the north atlantic oscillation nao a series of composite calculations of the jet index based on events of intraseasonal convective precipitation over the tropical indian and western pacific oceans reveals the following statistically significant relationships 1 negative jet events lead enhanced indian ocean precipitation 2 positive jet events lag enhanced indian ocean precipitation 3 positive jet events lead enhanced western pacific ocean precipitation and 4 negative jet events lag enhanced western pacific ocean p

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

structure and characteristics of submonthly scale waves along the indian ocean itcz this study examines wave disturbances on submonthly 6 30 day timescales over the tropical indian ocean during southern hemisphere summer using japanese reanalysis jra25 jcdas products and national oceanic and atmospheric administration outgoing longwave radiation data the analysis period is december february for the 29 years from 1979 1980 through 2007 2008 an extended empirical orthogonal function eeof analysis of daily 850 hpa meridional wind anomalies reveals a well organized wave train pattern as a dominant mode of variability over the tropical indian ocean daily lagged composite analyses for various atmospheric variables based on the eeof result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the indian ocean intertropical convergence zone itcz the wave train is oriented in a northeast southwest direction from sumatra toward madagascar the waves have zonal wavelengths of about 3 000 5 000 km and exhibit westward and southwestward phase propagation individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of sumatra into madagascar meanwhile eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern indian ocean this could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern indian ocean along the mean monsoon westerly flow in addition the waves modulate the itcz convection correlation statistics show the average behavior of the wave disturbances over the tropical indian ocean these statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis the waves appear to be connected to the monsoon westerly flow the waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon westerly flow this suggests that the monsoon westerly flow provides favorable background conditions for the propagation and maintenance of the waves and acts as a waveguide over the tropical indian ocean the horizontal structure of the wave train may be interpreted as that of a mixture of equatorial rossby waves and mixed rossby gravity wavelike gyres

mineralization and alteration of a modern seafloor massive sulfide deposit hosted in mafic volcaniclastic rocks tinakula is the first seafloor massive sulfide deposit described in the jean charcot troughs and is the first such deposit described in the solomon islands on land or the seabed the deposit is hosted by mafic basaltic andesitic volcaniclastic rocks within a series of cinder cones along a single eruptive fissure extensive mapping and sampling by remotely operated vehicle together with shallow drilling provide insights into deposit geology and especially hydrothermal processes operating in the shallow subsurface on the seafloor mostly inactive chimneys and mounds cover an area of 77 000 m2 and are partially buried by volcaniclastic sand mineralization is characterized by abundant barite and sulfide rich chimneys that formed by low temperature 250 c venting over 5 600 years barite rich samples have high sio2 pb and hg contents the sulfide chimneys are dominated by low fe sphalerite and are high in cd ge sb and ag few high temperature chimneys including zoned chalcopyrite sphalerite samples and rare massive chalcopyrite are rich in as mo in and au up to 9 26 ppm locally as visible gold below the seafloor the mineralization includes buried intervals of sulfide rich talus with disseminated sulfides in volcaniclastic rocks consisting mainly of lapillistone with minor tuffaceous beds and autobreccias the volcaniclastic rocks are intensely altered and variably cemented by anhydrite with crosscutting sulfate minor sulfide veins fluid inclusions in anhydrite and sphalerite from the footwall to 19 3 m below seafloor m b s f have trapping temperatures of up to 298 c with salinities close to but slightly higher than that of seawater 2 8 4 5 wt nacl equiv these temperatures are 10 to 20 c lower than the minimum temperature of boiling at this depth 1 070 1 204 m below sea level m b s l suggesting that the highest temperature fluids boiled below the seafloor the alteration is distributed in broadly conformable zones expressed in order of increasing depth and temperature as 1 montmorillonite nontronite 2 nontronite corrensite 3 illite smectite pyrite 4 illite smectite chamosite and 5 chamosite corrensite zones of argillic alteration are distinguished from chloritic alteration by large positive mass changes in k2o enriched in illite smectite mgo enriched in chamosite and corrensite and fe2o3 enriched in pyrite associated with illite smectite alteration the 18o and d values of clay minerals confirm increasing temperature with depth from 124 to 256 c and interaction with seawater dominated hydrothermal fluids at high water rock ratios leaching of the volcanic host rocks and thermochemical reduction of seawater sulfate are the primary sources of sulfur with 34s values of sulfides from 0 8 to 3 4 and those of sulfate minerals close to seawater sulfate from 19 3 to 22 5

stratigraphic volcanic setting of massive sulfide deposits in the cambrian mount read volcanics tasmania the cambrian mount read volcanics of western tasmania host the volcanic hosted massive sulfide vhms deposits at hellyer que river rosebery hercules and mount lyell the volcanics were erupted along and partly onto the western margin of a precambrian basement terrane now represented by the tyennan region the volcanic belt is asymmetrical in section with a main eastern zone of relatively massive lava rich sequences accompanied by abundant intrusions and a broader western zone of volcano sedimentary sequences rich in volcaniclastic mass flow sandstone and breccia the rocks have been strongly deformed regionally metamorphosed to lower greenschist facies and hydrothermally altered in many areas stratigraphic and facies relationships within the highly complex volcanic belt are critically reviewed and reassessed the main volcanic zone is considered to comprise two interfingering lava rich associations the quartz feldspar porphyritic eastern sequence and the largely feldspar porphyritic central volcanic complex this lava rich zone interfingers with the western volcano sedimentary sequences herein referred to as the yolande river sequence the dundas group and the mount charter group new term recent volcanologic studies indicate that the lava rich sequences and indeed the bulk of the preserved mount read volcanics are submarine in character despite the presence of abundant ignimbritelike pumiceous deposits the early volcanism was predominantly rhyolitic dacitic in composition but was followed by a period of active andesitic basaltic volcanism during which the massive sulfide deposits at hellyer and que river and some of those at mount lyell were formed this widespread andesitic basaltic volcanism appears to coincide with a period of active extension and rifting along the belt focused to some extent on the henty fault system the rifting episode is evidenced by abundant tholeiitic dikes along the henty fault and throughout the northern central volcanic complex and by tholeiitic pillow lavas within the henty fault wedge the andesitic basaltic volcanism appears to have culminated in distinctive p 2 o 5 and light rare earth element lree enriched basalts at hellyer and similar rocks at lynch creek and howards plains near queenstown may be correlates the hellyer basalts were buried by black shale and the final volcanic phase was marked by a return to active felsic volcanism which produced widespread crystal and pumice rich mass flow deposits of the southwell subgroup and tyndall group

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

distribution and significance of crystalline perlitic and vesicular textures in the ordovician garth tuff wales diverse spherulitic and granular crystalline fabrics perlitic textures and fabrics related to the growth and migration of vesicles occur in the garth tuff a largely welded ordovician ignimbrite defining the distribution of such textures helps to constrain the ignimbrite s cooling and degassing history suites of spherulitic and perlitic textures closely reflect variation in cooling rates seven facies are defined based on the style and intensity of crystallisation 1 a medium to coarsely crystalline equigranular facies 2 an intensely spherulitic facies 3 a sparsely spherulitic facies 4 a pectinate facies 5 a microcrystalline to cryptocrystalline equigranular facies 6 a lithophysal facies and 7 a transitional perlite pectinate facies textural changes from facies 1 to 5 reflect progressively higher cooling rates facies 1 occurs in proximal settings in the ignimbrite s core facies 2 to 5 successively envelop facies 1 with facies 2 becoming the dominant fabric in the ignimbrite s core in medial settings facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite s welded margins crystallisation under hydrous conditions is reflected by second boiling textures in the sporadically developed lithophysal facies the seventh facies reflects a subtle interplay between cooling hydration and crystallisation which locally prevented perlitic fracturing the distribution of amygdales reflects patterns of volatile migration and entrapment in the lower levels of the ignimbrite amygdales occur in irregular concentrations or rare subvertical pipe like structures pipe like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state amygdales are widespread and evenly distributed in the upper levels of the ignimbrite however the top of the welding profile is characterised by a thin poorly vesiculated originally vitrophyric horizon that abruptly caps an intense concentration of amygdales ductile and brittle fabrics developed during the upward migration of gas microscopic drag folds occur around some amygdales jigsaw fit to clast rotated breccias originated through both late stage pneumatic fracturing and autobrecciation vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation secondary alteration has enhanced or modified some fabrics perlitic zones were susceptible to patchy chlorite sericite carbonate diagenetic alteration diagenesis and metamorphism have contributed to the infilling of vesicles

the modulation of the subtropical and extratropical atmosphere in the pacific basin in response to the madden julian oscillation abstract the 40 yr ecmwf re analysis era 40 data are combined with a number of novel climatologies to conduct a comprehensive examination of the response of the subtropical and extratropical atmosphere over the pacific basin to an evolving madden julian oscillation mjo event the adopted approach constitutes a symbiosis of a climatological analysis during the northern hemisphere winter from 1979 to 2002 and a case study analysis of a distinct mjo event that occurred in january february 1993 the former is designed to obtain the general characteristics observed during a composite mjo life cycle while the latter is used to provide insight into the instantaneous mechanisms responsible for the observed composite evolution a primary component of the study involves the diagnosis of anomalous wave breaking activity in response to mjo forcing in the form of tropical convection and or upper level divergence wave breaking events are separated by their characteristic life cycles lc1 anticyclonic and lc2 c

archean subqueous high silica rhyolite coulees examples from the kidd munro assemblage in the abitibi subprovince abstract subaqueous high silica rhyolite in prosser township southern abitibi subprovince ontario consists of intercalated thin mass balance calculations and textural analysis demonstrate that the high silica aphyric rhyolites were originally glassy having been recrystallized to a pseudo spherulitic quartz albite mixture which was subsequently sericitized and chloritized the ree were moderately mobile 10 40 whereas the high field strength elements were less mobile the viscosity of the aphyric lava protolith was estimated to be 7 8 10 6 pa s based on an eruption temperature of 850 c calculated from measurements using the ti in zircon saturation thermometer this viscosity estimate is similar to the calculated viscosity 4 10 7 pa s of the subaerial namshraun rhyolite flow iceland the prosser and namshraun rhyolites have comparable dimensions and eruption temperature it is concluded that the low aspect ratio of the prosser township flows may have been controlled by a number of environmental factors including paleo slope magma rheology eruption rate and the insulative effects of the flow breccia

evidence for voluminous bimodal pyroclastic volcanism during rifting of a paleoproterozoic arc at snow lake manitoba the thrust bounded mcleod road birch lake mb sequence occurs within the paleoproterozoic snow lake arc sla assemblage of the flin flon belt stratigraphic correlation of volcanic strata of the mb sequence with strata of the thrust bounded chisel sequence indicates that distinctive submarine eruption fed pyroclastic flow deposits are more extensive and voluminous than previously recognized 10 km3 these voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the sla the felsic pyroclastic deposits define the remnants of a basin or of nested basins that formed during arc rifting and subsidence and their eruption immediately preceded formation of the chisel sequence volcanogenic massive sulfide vms deposits although the chisel sequence ore interval is recognized in the mb sequence the lack of vms related alteration indicates that vms hydrothermal activity was restricted to the chisel portion of the

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

a new 14 c age for the oruanui wairakei eruption new zealand the oruanui eruption was the largest known outburst of taupo volcano new zealand and is among the larger quaternary eruptions documented the eruption deposits are variously known as the oruanui wairakei kawakawa tephra or aokautere ash formations and represent a bulk volume probably exceeding 500 km 3 four new 14 c age determinations on carbonized vegetation in the non welded oruanui ignimbrite are combined to give a conventional age of 22590 230 yr b p compared with the previously accepted figure of 20000 yr b p this new age resolves the anomaly of apparently older 14 c ages being obtained from a demonstrably younger new zealand deposit and strengthens correlation of this eruption with an antarctic ice core acid anomaly the trace of this eruption has great potential as a time plane marker in the antarctic just prior to the last glacial maximum the close similarity in ages between the oruanui and a comparable sized eruption ito aira tn in japan suggests that this period of activity may represent the best chance of resolving any linkages between large scale explosive silicic volcanism and climate changes

mobility of trace elements and leaching rates of rhyolitic glass shards from some new zealand tephra deposits abstract it is shown that glass shards from volcanic eruptions of known age are useful in natural analogue studies connected with nuclear waste disposal they may be sequentially leached in bulk with hf and the hydration layer thickness determined if they have also been irradiated with neurons in a reactor some elemental profile information is available at the same time applying this to new zealand volcanic glass shards gave as many as 15 different fractions and information about the distribution of up to 16 trace elements those shards from a 22 ka eruption yielded hydration rates of 2 5 10 11 g cm 2 d while rates from a 340 ka eruption were 1 5 10 12 1 2 10 11 g cm 2 d the percentage of the total mass hydrated ranged between 5 and 35 as found in some other studies many elements accumulate on the surface of the shards particularly cr co and fe but it is shown here that they mostly originate in surrounding groundwater rather than the bulk glass rubidium and cs tend to be removed instead there was no obvious correlation between degree of hydration and the environment of deposition the use of glass shards from volcanic eruptions is recommended for such studies because they are ubiquitous and occurrence is less dependent on local geology than for some sample types

short wavelength infrared swir spectral analysis of hydrothermal alteration zones associated with base metal sulfide deposits at rosebery and western tharsis tasmania and highway reward queensland spectral analysis of rock samples by short wavelength infrared swir analysis using the portable infrared mineral analyzer pima spectrometer is a relatively new field method with applications in mineral exploration the technique allows rapid field based identification of hydrothermal alteration minerals and delineation of alteration zones variations in mineral composition crystallinity and relative abundance may also be determined phyllosilicates including white mica and chlorite are particularly amenable to short wavelength infrared analysis these are prominent alteration minerals in the felsic volcanic rocks in the mount read volcanics tasmania and the mount windsor subprovince north queensland they have regional distributions as diagenetic and metamorphic products and exist locally in alteration zones associated with volcanic hosted sulfide deposits a geochemical and spectral investigation of white micas in the least altered rocks in the mount read volcanics has shown considerable background compositional variations the white micas range from phengite to moderately sodic muscovite and swir spectral measurements provide reliable estimates of their compositions chlorites also have a broad compositional range in these rocks however swir spectral analysis has proven to be unreliable in determining chlorite composition in samples where chlorite exists in low proportions relative to white mica or in mixed assemblages with epidote white micas in footwall alteration zones of the rosebery stratiform zn pb deposit tasmania are variably phengitic similar to those in regional background volcanics a unit of relatively unaltered volcaniclastic sandstone in the rosebery hanging wall sequence contains anomalous sodic muscovite in proximity to ore lenses white micas associated with the disseminated to massive pyritic cu au deposits at western tharsis tasmania and highway reward north queensland range in composition from phengite to slightly sodic muscovite in these symmetrically zoned alteration systems white micas grade in composition from phengite in peripheral zones to slightly sodic muscovite in proximal zones near ore in all three cases the white mica compositional variation is a vector to ore that is effectively measured by swir spectrometry with particular application in prospect scale exploration chlorite compositions at rosebery are not strictly spatially related to ore but tend to be most magnesian in zones of high chlorite abundance in the outer alteration zone at western tharsis there is a faint proximal trend to iron rich chlorites however it does not represent a well defined vector to ore in either case attempts at quantitative estimation of the relative abundance of white mica and chlorite in mixed samples by spectral analysis have produced results that are imprecise in comparison to geochemically derived estimates the data scatter relates to the low proportions of chlorite in the majority of the samples analyzed resulting in weak chlorite absorptions better results may be obtainable in specific alteration or lithostratigraphic domains by use of customized spectral unmixing software this investigation has shown that pima based swir spectrometry is a potent field method of mapping compositional variations in white micas that represent empirical vectors to at least some types of volcanic hosted sulfide deposits it has also highlighted its effectiveness in field identification of megascopically difficult or indeterminate alteration minerals such as pyrophyllite zunyite and topaz which may have genetic implications and exploration significance

high precision u pb zircon chronostratigraphy of the mount read volcanic belt in western tasmania australia implications for vhms deposit formation the middle cambrian mount read volcanics of western tasmania australia host several world class volcanic hosted massive sulfide vhms deposits representing a wide range of deposit styles although the deposits and their host sequences are variably deformed and locally preserve spectacular examples of primary textures and structures rapid lateral and vertical facies changes and faults with uncertain sense and magnitude of displacement have made it impossible to correlate stratigraphy across the belt previous dating studies in the area have yielded relatively imprecise crystallization ages we have employed the chemical abrasion isotope dilution thermal ionization mass spectroscopy id tims u pb zircon method to obtain highly precise crystallization ages for a total of 18 samples of volcanic and intrusive rock units from throughout the mount read volcanics and underlying mafic ultramafic complexes the new data permit detailed resolution of age relationships within the belt the study establishes an age of 516 0 0 9 ma for the mcivor hill gabbro which is part of a mafic ultramafic complex interpreted to underlie the mount read volcanics magmatism in the central mount read volcanics lasted at least 12 7 m y from 506 8 1 0 ma for a massive dacite unit in the lower part of the central volcanic complex to 496 0 0 9 ma for a welded ignimbrite in the lower tyndall group together with previous age constraints results of the study provide a precise chronostratigraphic framework for magmatism and vhms deposit formation within the mount read volcanics the precise age data indicate that north of the henty fault magmatism occurred in three discrete pulses at least two of which were separated by periods of sedimentation we demonstrate that vhms deposits in the mount lyell roseberry hercules and que hellyer districts comprising the majority of the known significant vhms deposits in the belt formed within a narrow time interval at 500 1 ma at a relatively late stage in the evolution of the belt some of the larger intrusions in the belt e g the bonds range porphyry 500 4 0 8 ma were emplaced contemporaneously with vhms deposit formation however other bodies such as the murchison granite 497 3 0 9 ma are younger than the deposits and are unlikely to have been involved in their genesis as has previously been suggested these conclusions will aid explorers in targeting vhms mineralization in the mount read volcanics

interactions between enso transient circulation and tropical convection over the pacific abstract the interannual variability of transient waves and convection over the central and eastern pacific is examined using 30 northern winters of ncep ncar reanalyses 1968 69 1997 98 and satellite outgoing longwave radiation data starting in 1974 there is a clear signal associated with the el nino southern oscillation such that differences in the seasonal mean basic state lead to statistically significant changes in the behavior of the transients and convection with periods less than 30 days which then feed back onto the basic state during a warm event el nino phase the northern hemisphere subtropical jet is strengthened over the central pacific the region of upper tropospheric mean easterlies over the tropical western pacific expands eastward past the date line and the upper tropospheric mean westerly duct over the tropical eastern pacific is weakened the transients tend to propagate along the almost continuous waveguide of the subtropical jet equatorward propagation into the westerly

texture mineralogy and geochemistry of hydrothermally altered submarine volcanics recovered southeast of cheshire seamount western woodlark basin the western woodlark basin lies within a gold rich metallogenic province this area is characterized by detachment faults that record ongoing extension and act as major pathways for the circulation of hydrothermal fluids dredging from the flanks of a submarine ridge southeast of cheshire seamount western woodlark basin retrieved hydrothermally altered monomictic to polymictic crackle mosaic and chaotic breccias with at least 30 clasts n2 mmin diameter the precursor rocks are andesitic to rhyolitic in composition but have been intensely hydrothermally altered with about 90 of the volcanic glass replaced by secondaryminerals the breccias show five generations of quartz growth with the first being related to magmatic processes and the remaining four to alteration stages including silicification chloritization illitization sericitization albitization and sulfidation needle like crystals ofmordenite zeolite withmultiple growth centers growon the fourth generation of quartz notable textural variants in the breccias are vesicles perlitic cracks and zoned alteration halos that mantle the rims of clasts electron microprobe analyses on chlorite from breccia samples have identified clinochlore as the main chlorite type and indicate a formation temperature in the range of 210 304 c this and the elevated au as ag hg zn pb sb contents of a mineralized sample indicate hydrothermal alteration temperatures n200 c suggesting that these breccias may represent the upflow zone of a hydrothermal system and highlight the potential for seafloor massive sulfides in the area the breccias show elevated contents of immobile trace elements and lree as well as a depletion in ta and nb suggesting that the precursor rocks were formed in a rift related suprasubduction environment

a new look at the midlatitude mjo teleconnection in the northern hemisphere winter the midlatitude to madden julian mjo teleconnection in the northern hemisphere wintertime was investigated using twenty years of outgoing long wave radiation and national center for atmospheric research national centers for environmental prediction re analysis data it is revealed through empirical orthogonal functions and regression analyses that the tropical upper level divergence convergence associated with enhanced reduced tropical convection has a subtropical counterpart of upper level convergence divergence as the convective region of mjo moves eastward from the indian ocean to the western pacific the divergent circulation connecting the tropics and subtropics moves eastward from an analysis of vertical motion diagnosed by the generalized omega equation it was revealed that the position of the subtropical rossby gyres of the mjo with respect to the asian pacific jet was the most important factor affecting the existence of the localized divergence convergence and associated lower level vertical motion in the subtropics as the subtropical rossby gyres pass by the longitudinal position of the asian pacific jet vertical motion occurs to meet the balance required by quasi geostrophic theory since this anomalous vertical motion is large enough to cause convection at that region the diabatic heating process reinforces the vertical motion furthermore other dynamical processes neglected in quasi geostrophic theory are activated and contribute to the vertical motion balancing the diabatic heating as a result of the vertical motion near the jet entrance region in the subtropics the vorticity advection by vertical wind and the tilting of vorticity become important since these two terms are similar in shape and magnitude they reinforce each other during the development phase of the midlatitude mjo teleconnection combining these two terms we define the baroclinic jet source bjs in order to evaluate the bjs as a source for the midlatitude mjo teleconnection a numerical experiment is carried out the linear barotropic model is forced by only two terms yet the model captured clearly the main feature of the midlatitude mjo teleconnection copyright 2006 royal meteorological society

statistical properties of episodes of enhanced 2 3 day convection in the indian and pacific oceans abstract using 9 yr of ir brightness temperature values as a proxy for tropical convection the climatology and statistics of the 2 3 day convective oscillation signal are examined these higher frequency oscillations are shown to have a very different spatial distribution than the signal associated with the 25 70 day intraseasonal oscillation making it quite unlikely that these oscillations simply represent a form of noise in the time series the characteristics of the oscillations are shown to be strong functions of latitude season and strength of the oscillation itself only the strongest of the 2 3 day oscillations prove to be in good agreement with the properties shown in previous studies which were based on smaller spatial and temporal domains these strong oscillations manifest a strong association with the intraseasonal oscillation and westerly wind bursts particularly in the deep tropics weaker oscillations on the other hand are found to be more stochastic and less dependent on larger sca

geochemistry of the mount windsor volcanics implications for the tectonic setting of cambro ordovician volcanic hosted massive sulfide mineralization in northeastern australia the mount windsor subprovince is an important relic of upper cambrian to lower ordovician sedimentation and volcanism in the northern part of the tasman orogenic zone volcanic hosted massive sulfide mineralization occurs at several stratigraphic horizons within the volcano sedimentary package and one major mine is operational within the belt major and trace element data and nd isotope ratios are presented for the least altered coherent units from the three major volcanic bearing formations in the mount windsor subprovince the data are used to discriminate four major phases of volcanism and related intrusive activity derived from three isotopically discrete sources and to assess the geodynamic setting in which the volcanism occurred the earliest phase of mafic volcanism has minor and trace element characteristics suggesting an alkaline intraplate or rift association and it was probably produced by partial melting of attenuated subcontinental lithospheric mantle the overlying mount windsor formation silicic volcanics have nd isotope characteristics epsilon sub nd 480 ma 4 7 to 12 8 that suggest they were produced by partial melting of underlying precambrian crustal rocks mafic volcanics of the overlying trooper creek formation include a low tio 2 suite and a high tio 2 suite with a range of distinguishing chemical characteristics but similar nd isotope ratios epsilon sub nd 480 ma 3 8 2 3 which indicate derivation from relatively depleted asthenospheric mantle variably modified by subduction processes the high tio 2 suite is also represented by abundant intrusions within the underlying volcanic package the more silicic volcanics in the trooper creek formation appear to be cogenetic with their mafic associates but have varying nd isotope ratios which suggest progressive crustal interaction with increasing sio 2 content comparisons with modern volcanic compositions and ore depositional environments suggest that the volcanic and sedimentary units within the mount windsor subprovince were deposited in a back arc basin developed by extension of continental lithosphere along the eastern australian margin in the late cambrian and early ordovician mineralization and volcanic deposits of similar age farther north in the tasman orogenic zone suggest that this basin may have had a north south orientation although there is no clear evidence remaining of the original arc front deposits

volcanic reconstruction of the paleoproterozoic stroud breccia understanding the transition from a primitive to mature arc and its impact on vms ore formation snow lake manitoba canada abstract the stroud breccia is a 400 m thick package of dominantly felsic volcaniclastic rocks within the paleoproterozoic snow lake arc assemblage it stratigraphically overlies the ore interval for the anderson stall and rod volcanogenic massive sulfide vms deposits at snow lake manitoba canada and occupies the stratigraphic interval between the underlying primitive arc anderson sequence and the overlying mature arc chisel sequence the stroud breccia is interpreted to be a product of subaqueous pyroclastic and effusive dominantly rhyolitic volcanism and concomitant subsidence it consists of felsic tuff to lapilli tuff crystal rich felsic tuff felsic lapillistone felsic tuff breccia mafic tuff to lapilli tuff heterolithic tuff breccia to breccia and rhyolite the finer felsic volcaniclastic units are characterised by angular or broken quartz crystals angular lithic rhyolite lapilli and pumice fine ash broken crystals and pumice suggest they were deposited by eruption fed density currents associated with a phreatomagmatic eruption the coarser felsic volcaniclastic units are characterized by blocks of strongly quartz feldspar porphyritic rhyolite and pumice and are interpreted to have been deposited during the reworking of pyroclastic debris flow deposits on the seafloor during mass wasting events at fault scarps planar and cross laminations graded beds and bomb sag structures suggest the mafic tuff to lapilli tuff unit was deposited by a combination of subaqueous eruption fed density currents and eruption driven ballistically emplaced ejecta likely through subaqueous tephra jetting lithofacies analyses and geochemistry has allowed comparison between the felsic volcanic rocks of the stroud breccia and those that host the anderson stall and rod vms deposits detailed mapping has led to the identification of synvolcanic faults defining basins and volcanic vents that indicate that the process of incipient rifting of the anderson sequence primitive arc continued during emplacement of the stroud breccia these structures also define magma and fluid pathways critical in controlling the formation of the anderson vms deposits meaning they represent deep seated and long lived structures that can be used as vectors to mineralization at depth

tropical rainforest vegetation climate and sea level during the pleistocene in kerala india abstract the southwestern ghats region of the indian peninsula is unique for its extant endemic rainforest flora supported by high rainfall throughout the year the record of tropical rainforest corresponding to the dynamic series of pleistocene interglacial glacial cycles is poorly known from peninsular india this communication discusses the palynological study of organic matter om deposits 40 ka bp in two well sections chaganachery kerala from the indian peninsula west coast a rich archive of tropical rainforest pollen spores and marine dinoflagellate cysts indicates anoxic fluvio marine estuarine depositional environments during warmer climates with an intensified asian monsoon the geochemical fingerprinting of glass shards indicates the presence of youngest toba ash of 74 ka from northern sumatra and therefore establishes a time controlled stratigraphy thus the depositional time period of the om is related to the sea level highstand of marine isotopic stage 5 1 80 ka which was the host to the ytt shards the late quaternary pollen spores diversity suggests that the modern climatic conditions in the southwestern ghats have facilitated the conservation of moist evergreen rainforest and dry moist deciduous forest the pollen grains show its lineage with the extant flora and some of the fossil pollen recorded during the mesic tertiary period from the indian peninsula thus it appears that the tropical rainforest survived here as plant refugia in xeric glacial quaternary periods perhaps as riparian vegetation and was rejuvenated during the holocene as modern extant flora

a pole to pole west pacific atmospheric teleconnection during august 1 an observational analysis is presented that reveals an august teleconnection involving both the northern hemisphere nh and the southern hemisphere sh the teleconnection includes three primary anomalies in the monthly average surface pressure field 1 a high southern latitude component including wilkes land antarctica the nearby southern ocean and the ross sea 2 a sh midlatitude component near australia and new zealand and 3 a nh subtropical component over the extreme western pacific ocean surface pressure for the sh high latitude anomaly is negatively correlated to the other two primary anomalies the sh midlatitude and nh subtropical component are positively correlated furthermore the teleconnection is correlated to surface pressure near the aleutian islands the teleconnection anomalies result from tropical convection on intraseasonal timescales monsoon rainfall over east asia during august is correlated to the teleconnection furthermore august precipitation at several other locations in the nh and sh is modulated by the teleconnection two different sets of numerical experiments with the national center for atmospheric research ncar community climate model version 2 ccm2 show a similar appearing teleconnection during late boreal summer the modeled teleconnection however is forced from high southern latitudes

geochemistry of the cambrian volcanic hosted massive sulfide rich mount read volcanics tasmania and some tectonic implications the cambrian mount read volcanics belt in western tasmania hosts five major gold rich massive sulfide deposits and remains the focus of intense exploration activity and geologic research a geochemical study of least altered lavas and shallow intrusions with emphasis on basaltic to andesitic compositions was carried out to determine the primary magmatic affinities and tectonic setting of eruption of the mount read volcanics to aid in internal correlations within the belt and to provide starting material estimates for mineralization related alteration studies three calc alkaline suites one extending to shoshonitic compositions and two tholeitiic suites have been distinguished within the mount read belt suite i is voluminous and includes the eastern sequence central volcanic complex tyndall group the intrusive quartz feld spar porphyries and granitoids and the andesitic lavas of the que hellyer footwall sequence suite i andesites are transitional medium to high k calc alkaline rocks la yb n 5 12 avg 8 1 and are the least light ree enriched calc alkaline lavas in the mount read volcanics suite ii comprises intrusive and extrusive often hornblende porphyritic andesites and dacites mainly from the upper part of the southern central volcanic complex they are more p 2 o 5 and light ree enriched la yb n 10 26 avg 16 7 than suite i and have high k calc alkaline affinities suite iii includes basaltic and andesitic lavas from the que hellyer hanging wall sequence in the northern part of the belt the lynch creek basalts near queenstown and intrusive basalts in the howards plains area northwest of queenstown suite iii rocks show a striking compositional range from low tio 2 0 4 0 5 low p 2 o 5 0 1 basalts with la yb n values from 8 to 12 and almost flat heavy ree patterns to low tio 2 0 4 0 8 but strongly to exceptionally p 2 o 5 and light ree enriched basalts with up to 350 times chondritic la and la yb n values up to 34 the latter are regarded as shoshonites tholeiitic pillow basalts of the henty fault wedge and the closely related dikes of the henty dike swarm constitute suite iv these have tio 2 contents from 1 0 to 1 6 percent very low nb contents 3 ppm and only slightly light ree enriched ree patterns la yb n 1 4 3 4 they are considered to be most similar to suprasubduction zone basalts erupted during the early phase of arc splitting and back arc basin development and indicate a period of tension and rifting of the mount read belt in post central volcanic complex but pre tyndall group time suite v is constituted by the miners ridge basalts and includes low tio 2 0 7 basalts with strong light ree depletion la yb n 0 5 and higher tio 2 to 2 6 lavas with only slight light ree depletion la yb n 0 9 suite v basalts are tentatively correlated with rift tholeiite sequences associated with the crimson creek formation and therefore are regarded as part of the pre mount read volcanics basement the three calc alkaline suites occur in a general stratigraphic order with suites i and ii being more or less coeval near queenstown they indicate a magmatic evolution from transitional medium to high k rocks through high k rocks to strongly enriched shoshonitic rocks closest modern analogues are postcollisional volcanics in regions of arc continent collision e g east papua and the roman province the occurrence of boninite derived chromites probably derived from the allochthonous mafic ultramafic complexes outcropping just west of the mount read belt in two sedimentary units within the mount read volcanics sequence below suite iii basalts supports a postcollisional origin for at least the major part of the mount read volcanics other similar postcollisional sequences particularly if formed in a submarine setting must be considered highly prospective for vhms deposits

the boreal summer madden julian oscillation and moist convective morphology over the maritime continent abstractwhile the boreal summer madden julian oscillation mjo is commonly defined as a planetary scale disturbance the convective elements that constitute its cloud dipole exhibit pronounced var

isolating spatiotemporally local mixed rossby gravity waves using multi dimensional ensemble empirical mode decomposition tropical waves have relatively large amplitudes in and near convective systems attenuating as they propagate away from the area where they are generated due to the dissipative nature of the atmosphere traditionally nonlocal analysis methods such as those based on the fourier transform are applied to identify tropical waves however these methods have the potential to lead to the misidentification of local wavenumbers and spatial locations of local wave activities to address this problem we propose a new method for analyzing tropical waves with particular focus placed on equatorial mixed rossby gravity mrg waves the new tropical wave analysis method is based on the multi dimensional ensemble empirical mode decomposition and a novel spectral representation based on spatiotemporally local wavenumber frequency and amplitude of waves we first apply this new method to synthetic data to demonstrate the advantages of the method in revealing characteristics of mrg waves we further apply the method to reanalysis data 1 to identify and isolate the spatiotemporally heterogeneous mrg waves event by event and 2 to quantify the spatial inhomogeneity of these waves in a wavenumber frequency energy diagram in this way we reveal the climatology of spatiotemporal inhomogeneity of mrg waves and summarize it in wavenumber frequency domain the indian ocean is dominated by mrg waves in the period range of 8 12 days the western pacific ocean consists of almost equal energy distribution of mrg waves in the period ranges of 3 6 and 8 12 days respectively and the eastern tropical pacific ocean and the tropical atlantic ocean are dominated by mrg waves in the period range of 3 6 days the zonal wavenumbers mostly fall within the band of 4 15 with indian ocean has larger portion of higher wavenumber smaller wavelength components mrg waves

textural and mineralogical changes associated with the incipient hydrothermal alteration of glassy dacite at the submarine pacmanus hydrothermal system eastern manus basin variably altered dacite from the pacmanus vent field in the eastern manus back arc basin papua new guinea was studied to determine the textural and mineralogical characteristics of hydrothermal alteration taking place in the immediate subsurface of this modern seafloor hydrothermal system detailed textural investigations show that fluid flow through the glassy dacite has been strongly controlled by the primary volcanic textures quench fractures and networks of interconnected perlitic cracks linking vesicles provided pathways for hydrothermal fluids flowing up to the seafloor hydrothermal alteration along these pathways resulted in the formation of pseudoclastic textures textural evidence suggests that alteration of the glassy dacite has not been sustained the samples have been affected by incipient hydrothermal alteration that is typically not preserved in ancient volcanic rock hosted massive sulfide deposits interaction of the glassy dacite with hydrothermal fluids primarily resulted in the conversion of volcanic glass to dioctahedral smectite only minor amounts of trioctahedral smectite were formed destruction of the volcanic glass and the formation of smectite caused pronounced changes in the chemistry of the dacite samples in particular a decrease in the sio2 whole rock content and the na2o k2o ratio the two alkali elements behaved differently during hydrothermal alteration due to preferential incorporation of k into the interlayer position of the newly formed dioctahedral smectite smectite formation occurred under rock dominated conditions although the addition of mg was required to form trioctahedral smectite from the silicic volcanic glass primary plagioclase was resistant to hydrothermal alteration highlighting the fact that the destruction of volcanic glass and feldspar are not necessarily contemporaneous in massive sulfide forming hydrothermal systems incipient alteration of the glassy dacite close to the seafloor occurred at temperatures below 150 c in an environment that allowed the development of steep temperature gradients comparison of the new data to the findings of deep drilling during odp leg 193 suggests that the smectite rich alteration in the immediate subsurface of the pacmanus hydrothermal vent field represents the low temperature equivalent of illite and chlorite rich alteration associations forming in the upflow zones of the hydrothermal fluids in the deeper portion of the volcanic sequence

the influence of sea surface temperature on the tropical intraseasonal oscillation a numerical study abstract the development and movement of the tropical intraseasonal system tis exhibit remarkable annual variations it was hypothesized that spatial and temporal variation in sea surface temperature sst is one of the primary climatic factors that are responsible for the annual variation of tiss this paper examines possible influences of sst on the tis through numerical experiments with a 2 5 layer atmospheric model on an equatorial plane in which sst affects atmospheric heating via control of the horizontal distribution of moist static energy and the degree of convective instability the gradient of the antisymmetric with respect to the equator component of sst causes a southward propagation of the model tis toward northern australia in boreal winter and a northward propagation over the indian and western pacific oceans in boreal summer the phase speed of the meridional propagation increases with the magnitude of antisymmetric sst gradients the poleward propagation of the equatorial disturba

dynamics of an interhemispheric teleconnection across the critical latitude through a southerly duct during boreal winter abstractin this study an interhemispheric teleconnection pattern across the critical latitude from southern africa through south asia to the north pacific was revealed in boreal winter monthly averaged 250 hpa streamfunction fields obtained from both the 40 yr ecmwf re analysis era 40 and the ncep ncar reanalysis data from 1957 58 to 2001 02 classical rossby wave theory for zonally varying flow in which the effects of the basic state meridional wind are ignored predicts that stationary rossby waves cannot propagate across easterlies to elucidate the underlying mechanisms responsible for this interhemispheric teleconnection the theoretical basis for stationary wave propagation across the critical latitude is considered taking into account meridional ambient flow the theoretical results suggest that the southerly flow over east africa the western indian ocean and south asia creates a path for the northward propagation of stationary waves across the critical latitude stationary wavenumber and grou

textural and chemical characteristics of diagenetic and hydrothermal alteration in glassy volcanic rocks examples from the mount read volcanics tasmania the mount black and sterling valley volcanics comprise a complex cambrian succession of originally glassy felsic to mafic submarine volcanic facies in western tasmania the mount black and sterling valley volcanics have been modified by the combined effects of diagenesis hydrothermal alteration and regional metamorphism metamorphosed diagenetic and hydrothermal alteration facies have been distinguished using a combination of alteration mineralogy overprinting relationships texture distribution intensity and whole rock geochemistry alteration facies that are interpreted to be the regionally metamorphosed equivalents of diagenetic clays and zeolites are regionally extensive and overprinted by the regional cleavage although widespread their distribution is patchy and their intensities are highly variable reflecting the complexity of the original textures in glassy volcanic rocks thin films of sericite carbonate and chlorite sericite hematite replace clays that coated original glassy surfaces at the onset of diagenesis prior to compaction feldspar quartz sericite chlorite sericite and chlorite sericite hematite alteration facies replace zeolites and clays that filled pore space and altered glass prior to and synchronous with compaction the final diagenetic alteration facies chlorite epidote began after compaction and continued during metamorphism diagenetic alteration involved significant mineralogical and textural changes but only minor changes in chemistry the chemical changes associated with diagenetic alteration facies are consistent with the interaction of rhyolitic and basaltic glass with seawater during burial alteration facies that are interpreted to be hydrothermal are local in distribution crosscut stratigraphic boundaries and involve significant changes in texture mineralogy and composition early hydrothermal alteration facies quartz sericite and calcite quartz hematite predated compaction and were synchronous with diagenesis chlorite calcite magnetite and chlorite pyrite alteration facies were synchronous with regional deformation and are associated with tectonic breccias faults and shear zones chlorite quartz calcite alteration facies postdated regional deformation