microstructure of high temperature 73 c siliceous sinter deposited around hot springs and geysers yellowstone national park the role of biological and abiological processes in sedimentation slightly alkaline hot springs and geysers in yellowstone national park exhibit distinctive assemblages of high temperature 73 c siliceous sinter reflecting local hydrodynamic conditions the main depositional zones include subaqueous pool and channel bottoms and intermittently wetted subaerial splash surge and overflow areas subaqueous deposits include particulate siliceous sediment and dendritic and microbial silica framework silica framework forms thin porous microbe rich films coating subaqueous surces spicules with intervening narrow crevices dominate in splash zones surge and overflow deposits include pool and channel rims columns and knobs in thin section subaerial sinter is composed of i dark brown nearly opaque laminated sinter deposited on surfaces that evaporate to dryness ii clear translucent silica deposited subaqueously through precipitation driven by supersaturation iii heterogeneous silica representing silica encrusted microbial filaments and detritus and iv sinter debris brownish laminations form the framework of most sinter deposited in surge and overflow zones pits and cavities are common architectural features of subaerial sinter and show concave upward pseudo cross laminations and micro unconformities developed through migration marked birefringence of silica deposited on surfaces that evaporate to dryness is probably a strain effect repeated wetting and evaporation often to dryness and capillary effects control the deposition morphology and microstructure of most high temperature sinter outside of the fully subaqueous zone microbial filaments are abundant on and within high temperature sinter but do not provide the main controls on morphology or structuring except in biofilms developed on subaqueous surfaces millimetre scale lamination cyclicity in much high temperature sinter represents annual layering and regular seasonal fluctuations in silica sedimentation

evidence of a shallow water submarine hydrothermal field off zannone island from morphological and geochemical characterization implications for tyrrhenian sea quaternary volcanism discoveries from multibeam bathymetry and geochemical surveys performed off zannone island western pontine archipelago tyrrhenian sea provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water 250 m that host pockmarks mounds small cones and active fluid vents and which are interpreted as complex fluid escape features developed both through vigorous explosive events and steady seepage their spatial distribution suggests that the ne sw trending faults bounding the ponza zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids moreover we performed a detailed geochemical study to investigate the source of the hydrothermal fluids the geochemical signature of the collected fluids provides information of active co2 dominated degassing with a significant contribution of mantle volatiles with measured 3he 4he values 3 0 ra that are similar to those recorded at stromboli and panarea volcanoes the hydrothermal system produces volatiles that may originate from residual magma batches similar to the pleistocene trachytes cropping out in the se sector of ponza island that were probably intruded in the shallow crustal levels and never erupted the discovery of the zannone hydrothermal field updates the record of active hydrothermal areas of the mediterranean sea moreover the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the mediterranean sea

seasonal changes in silica deposition in hot spring systems abstract monthly monitoring of water chemistry at octopus spring yellowstone national park reveals no changes in the chemical composition over this eight month study differences in silica deposition are attributed to flow dynamics and seasonal air temperatures colder air temperatures in winter promote visible accumulation of siliceous sinter probably as a result of decreased solubility periodic drying promotes accumulation and subsequent dehydration of the silica this combination of intermittent supply and periodic dehydration may account for the laminated siliceous deposits observed in the geological record the processes described herein are important in the siliceous preservation of microbial fossils but the following observations underscore the difficulty in preserving microbial fabrics in the geological record pools populated by cyanobacteria are bounded by margins built of silicified microbial mats silicification of the pool margins occurs through an evaporative process called wicking silica rich water is transported upward through the microbial mats by capillary action depositing silica at the surface of the mat as water evaporates the upper surface of such wicking deposits is extremely resistant to brecciation but the underlying support is highly friable and would be difficult to preserve intact in winter months temporary isolation of some pools from active flow causes fragile silica deposition around biological and other debris film coated gas bubbles on the surfaces of microbial mats are observed during all seasons and probably are filled with oxygen released during photosynthesis although this has not been confirmed they become coated with silica during winter months presumably because of increased cooling possibly forming thin discontinuous silica sheets as observed in the geological record

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

evolution of a dynamic paleo hydrothermal system at mangatete taupo volcanic zone new zealand abstract recent quarrying and active faulting at mangatete taupo volcanic zone tvz new zealand illuminate a rare spatial and temporal window on a dynamic late quaternary geothermal system detailed geological mapping stratigraphic logging ams 14 c dating and textural and mineralogical analyses were used to construct a complex history of hydrothermal volcanological and tectonic activity from 36 to 2 ka extinct surface hydrothermal manifestations occur over a 2 km 2 area and include in situ siliceous sinters distributed on normal fault terraces an inferred hydrothermal eruption breccia heb containing acid etched sinter blocks another probable heb that was bathed in silicifying thermal fluids and sinter clasts that were entrained in a debris flow associated with a volcanic ash event preserved sinter textures typical of near neutral ph alkali chloride spring discharge channels aprons terraces and affiliated marshes comprise plant rich palisade tufted bubble mat and domal stromatolitic fabrics in addition a packed fragmental sinter facies is shown herein to constitute silicified microbial mats that were broken transported and deposited as point bar deposits in thermal spring fed streams moreover four unusual siliceous sinter fabrics vuggy globular spongy scalloped and arcuate wavy layered are interpreted to have formed from local acid sulfate chloride thermal springs possibly associated with paleo fumaroles the reconstructed history of paleo hydrothermal activity indicates that the oldest sinters 36 ka at mangatete developed in alkali chloride hot springs but then underwent post depositional alterion overprinting by acid sulfate steam condensate and were dismembered possibly by a hydrothermal eruption low ph hot spring discharges forming the unusual inferred acid sinter fabrics were localized in the same area a shift in paleo hydrology is evidenced by unaltered alkali chloride sinters dated between 22 and 3 ka a cluster of sinter dates between 22 7 and 20 7 ka denote thermal fluid emissions around the time of the okareka eruption 22 1 ka an 11 kyr gap in sinter ages followed which overlaps with a time of relative quiescence in local fault movement in between the rotorua and rotoma eruptions as determined from previous paleo seismicity studies on the whirinaki fault in the mangatete area at 9 4 ka hot spring activity in thermally fed streams slightly post dated the rotoma eruption 9 5 ka the locations and ages of the youngest post 9 4 ka alkali chloride sinters and silicified paleosols in relation to whirinaki fault movements indicate an overall westward migration of siliceous spring discharge dated charcoal 1 8 kyr in ash at the base of a locally extensive volcaniclastic debris flow containing sinter blocks of a range of ages and mineralogical maturity suggests its affiliation with the taupo eruption mangatete sinters occur along sw ne striking faults parallel to the regional trend of the tvz which dissect the topography into stepped terraces inferred basement cross faults in the study area i e structural lineaments orthogonal to this trend may have served as fluid pathways at depth initiating and maintaining hydrothermal activity at mangatete for more than 30 kyr within the larger ngakuru graben 150 km 2 the ages and distributions of sinters and hydrothermal eruption breccias including those at mangatete show that significant hydrothermal activity occurred for more than 60 kyr in an area lacking such activity today thus mangatete retains a rare stratigraphic record within the tvz sinter archive of changing geothermal fluids resulting from shifts in paleo phreatic water levels moreover although limited the presented age data imply a relationship among seismic activity volcanic ash fall events and the occurrence of permeable pathways for upward migration of thermal fluids finally whereas currently active tvz geothermal fields appear to be stable over tens of thousands of years or more the fossil hydrothermal systems in the wider mangatete area demonstrate the possibility of much greater temporal variability in the lateral expression of local surface manifestations of thermal fluid discharge through time

epithermal gold mineralization in a fossil hot spring system red butte oregon the red butte gold prospect is a well preserved sediment hosted fossil hot spring system located within the lake owyhee volcanic field of eastern oregon 10 km west of the owyhee reservoir its features include siliceous hot spring sinter a blanket of intense argillic alteration produced by surficial steam heated waters and a 50 m wide hydrothermal eruption crater filled with bedded breccia deposits mineralization is hosted by north and northwest striking faults in volcaniclastic sediments of the miocene deer butte formation red butte is capped by 10 m of syngenetic fluvial sedimentary rocks consisting of a basal silicified mudstone overlain by arkosic sandstones and conglomerates interbedded with siliceous hot spring sinter the sediments at this paleosurface horizon have been cemented by hydrothermal quartz and adularia and form the resistant cap of the butte a blanketlike zone of pervasive argillic alteration occurs at the base of the fluvial sediments numerous hydrothermal veins and breccias located within the lacustrine sedimentary rocks beneath the argillic blanket contain a telescoped mineral assemblage related spatially to the paleosurface quartz and adularia are the most abundant hydrothermal minerals in this zone along with minor pyrite marcasite electrum bladed calcite stellerite ca 4 al 8 si 28 o 72 28h 2 o illite smectite and smectite clays the veins and argillic blanket are cut by a 50 m wide hydrothermal eruption crater filled with bedded breccia deposits the delta 18 o smow values for hydrothermal quartz and adularia range from 5 3 to 8 3 and 0 1 to 2 4 per mil respectively the delta 18 o smow and delta 13 c pdb values for calcite range from 3 6 to 8 9 and 8 9 to 5 2 per mil respectively these values are consistent with those of minerals from meteoric hydrothermal systems a plot of delta 18 o versus delta 13 c values for calcite shows that hco super 3 was the dominant aqueous carbon species inaa analyses of altered sedimentary rocks and hydrothermal vein and breccia samples reveal the presence of anomalous concentrations of au ag as sb hg and mo q mode factor analysis indicates that much of the variation in the geochemical data set can be explained in terms of five end member components factors which reflect the composition and evolution of the hydrothermal fluid and the initial composition of the host rock elemental associations for these factors are 1 au k 2 o ag feo hg 2 cao mo hg as 3 feo na 2 o hg sb 4 k 2 o zn na 2 o as and 5 as mo sb ag the abundance of adularia and stability of stellerite at red butte suggests that fluids reaching the surface had experienced a high degree of vapor separation due to boiling au mineralization occurred at the peak of hydrothermal activity in response both to boiling and mixing of the boiling hydrothermal fluid with surficial steam heated waters

propagation mechanisms for the madden julian oscillation the madden julian oscillation mjo is examined using 20 years of outgoing long wave radiation and national centers for environmental prediction national center for atmospheric research re analysis data two mechanisms for the eastward propagation and regeneration of the convective anomalies are suggested the first is a local mechanism operating over the warm pool region at the phase of the mjo with a dipole structure to the convection anomalies there is enhanced tropical convection over the eastern indian ocean and reduced convection over the western pacific over the equatorial western indian ocean the equatorial rossby wave response to the west of the enhanced convection includes a region of anomalous surface divergence associated with the anomalous surface westerlies and pressure ridge this lends to suppress ascent in the boundary layer and shuts off the deep convection eventually leading to a convective anomaly of the opposite sign over the indonesian sector the equatorial kelvin wave response to the east of the enhanced convection includes a region of anomalous surface convergence into the anomalous equatorial surface easterlies and pressure trough which will tend to favour convection in this region the indonesian sector is also influenced by an equatorial rossby wave response of opposite sign to the west of die reduced convection over the western pacific which also has a region of anomalous surface convergence associated with its anomalous equatorial surface easterlies and pressure trough hence convective anomalies of either sign tend to erode themselves from the west and initiate a convective anomaly of opposite sign via their equatorial rossby wave response and expand to the east via their equatorial kelvin wave response the second mechanism is global involving an anomaly completing a circuit of the equator enhanced convection over the tropical western pacific excites a negative mean sea level pressure m s l p anomaly which radiates rapidly eastward as a dry equatorial kelvin wave at approximately 35 m s 1 over the eastern pacific it is blocked by the orographic barrier of the andes and central america for several days before propagating through the gap at panama after rapidly propagating as a dry equatorial kelvin wave over the atlantic the m s l p anomaly is delayed further by the east african highlands before it reaches the indian ocean and coincides with the development of enhanced convection at the start of the next mjo cycle

jurassic hot spring activity in a fluvial setting at la marciana patagonia argentina silicified rocks at la marciana farm deseado massif argentinean patagonia represent an ancient hot spring discharging into an active fluvial setting their fortuitous burial erosion history and minimal post depositional structural modification provide an unparalleled view of a complete exhumed late jurassic geothermal landscape and thus an opportunity to illuminate hot spring geological context and palaeoenvironmental gradients geological mapping stratigraphy and petrography revealed hydrothermal eruption events the spring vent source structural relationships dimensions of the discharge apron and hot spring facies distributions remarkable similarities to quaternary analogues from the taupo volcanic zone new zealand and yellowstone national park usa are apparent with respect to scale spatial distribution of facies and types of microbial and other palaeoenvironmentally significant fabrics

the diurnal cycle of precipitation over the maritime continent in a high resolution atmospheric model climate models can exhibit systematic errors in their mean precipitation over the maritime continent of the indonesian archipelago at the heart of the tropical warm pool these can often be traced back to an erroneous simulation of the diurnal cycle and can lead to errors in global climate through planetary wave propagation here we examine the simulation of the diurnal cycle over the maritime continent in a series of high resolution integrations of the uk met office atmospheric model with horizontal resolutions of 40 and 12 km where the convection is parametrised and 4 km where the convection is explicitly resolved as part of the cascade project in these models the vertical heating profile over the islands changes from a convective profile with a mid tropospheric maximum in the early afternoon to a more stratiform profile with upper tropospheric heating and mid tropospheric cooling later the convective heating profile forces a first internal mode gravity wave that propagates rapidly offshore the deep warm anomalies behind its downwelling wavefront suppress convection offshore during early afternoon the stratiform heating profile forces a gravity wave with a higher order vertical mode that propagates slowly offshore later in the afternoon this mode has a negative destabilising temperature anomaly in the mid troposphere together with the convergence zone between the wave fronts of the two modes favourable conditions are created for offshore convection in the 4 km explicit convection model the offshore convection responds strongly to this gravity wave forcing in agreement with observations supporting a gravity wave convection paradigm for the diurnal cycle over the maritime continent however the convective response in the lower resolution models is much less coherent leading to errors in the diurnal cycle and mean precipitation hence to improve climate model simulations sensitivity to gravity wave forcing should be a factor in future convective parametrisation schemes copyright c 2011 royal meteorological society

origin of the mclaughlin mine sheeted vein complex metal zoning fluid inclusion and isotopic evidence the mclaughlin deposit is a large hot spring type gold deposit located in the northern coast ranges of california at the faulted lithologic contact between the coast range ophiolite and the great valley sequence the mclaughlin deposit is centered around the sheeted vein complex a large multistage vein swarm localized in a dilation zone formed by rheologic contrasts in the footwall polymictic melange the surface expression of the sheeted vein complex is a subaerial sinter terrace which merges into the sheeted vein complex metal zoning in the sheeted vein complex is highly telescoped the sinter is enriched in mercury whereas gold and silver are restricted to the upper 350 m with the proportion of gold to silver decreasing with depth gold is typically present as electrum and is associated with silver and base metal bearing sulfosalts below 350 m mineralization is dominated by small quartz veins with base metal sulfides fluid inclusion studies indicate that nacl is the main dissolved salt in concentrations averaging 2 4 wt percent nacl equiv the bulk of the salinity data can be explained by variable amounts of adiabatic boiling and mixing with steam heated ground water fluid inclusion homogenization data ranges from 121 degrees to 263 degrees c with the deepest portion of the system examined having the highest temperatures and the shallowest samples having the lowest temperatures fluid inclusion gas concentrations vary with depth below the sinter co 2 and to a lesser extent ch 4 shows a systematic increase with depth fluid pressures calculated from fluid inclusion homogenization temperatures and gas analysis are in excess of the hydrostatic pressure and approach or exceed lithostatic pressure self sealing of the system and tectonic dilation most likely resulted in catastrophic phase separation and hydrothermal eruption breccias geothermometry results based on fluid inclusion gas ratios show a reasonable correspondence with the highest fluid inclusion homogenization temperatures there is a strong trend for decreasing delta 18 o quartz values with depth due to the effect of temperature the calculated delta 18 o sub h 2 values are fairly constant at about 9 to 10 per mil oxygen and hydrogen isotope values as well as geologic relationships are consistent with those of hydrothermal fluids originating as meteoric water these evolved to increasingly high ones by interaction with great valley sequence sedimentary rocks lead isotope compositions of sulfides and potential source rocks indicate that lead and by inference other metals was derived from a crustal source the lead source may have been detritus from the sierra nevada batholith that comprises the great valley sequence or alternatively it may have been derived from a thorough mixture of radiogenic lead and nonradiogenic lead that occurred prior to mineralization

hydrothermalism in the mediterranean sea abstract hydrothermalism in the mediterranean sea results from the collision of the african and european plates with the subduction of the oceanic part of the african plate below europe high heat flows in the resulting volcanic arcs and back arc extensional areas have set up hydrothermal convection systems most of the known hydrothermal sites are in shallow coastal waters

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

hydrothermal alteration and veins at the epithermal au ag deposits and prospects of the waitekauri area hauraki goldfield new zealand the waitekauri area of the hauraki goldfield new zealand contains several adularia sericite epithermal au ag deposits and prospects from west to east the area contains the sovereign jubilee scimitar scotia teutonic and jasper creek deposits and prospects which are hosted by andesitic and dacitic flows breccias and localized pyroclastic and air fall deposits drill core reveals spatial and temporal zonation of alteration and vein minerals along a 3 km long composite cross section through the area most host rocks are intensely altered with 100 percent of the igneous minerals replaced by hydrothermal minerals although the alteration intensity becomes more variable and weaker toward the east alteration minerals include quartz adularia albite chlorite pyrite illite interstratified illite smectite smectite calcite hematite and minor epidote many of these minerals have zoned distributions adularia is widespread at sovereign but is restricted to shallow levels at both scotia and jasper creek albite occurs in a discrete zone below adularia at scotia and minor epidote is restricted to sovereign and jubilee illite occurs throughout sovereign and jubilee and at the western margin of scotia and scimitar where it grades eastward into interstratified illite smectite and smectite at teutonic and jasper creek veins are typically less than 10 cm wide but have diverse mineralogy with zoned distributions quartz veins dominate at sovereign and jubilee whereas calcite veins are more abundant at scotia scimitar and jasper creek laumontite occurs at scotia and locally at scimitar whereas veins of clinoptilolite and mordenite calcite occur at jasper creek and stilbite veins occur at teutonic fluid inclusions in quartz and calcite homogenized between 132 and 310 c and trapped a dilute solution with an apparent salinity of less than 2 6 wt percent nacl equiv homogenization temperatures are highest at sovereign avg 241 c jubilee avg 239 c and scimitar avg 236 c lower at scotia avg 204 c and lowest at teutonic avg 168 c and jasper creek avg 162 c estimated positions of the paleowater table above sovereign jubilee scimitar scotia jasper creekg and teutonic relative to present elevations was at least 690 750 575 450 225 and 150 m above sea level respectively the deposits and prospects therefore span a 600 m vertical interval individual deposits and prospects have undergoen at least 35 to more than 455 m of erosion with the greatest erosion to the west alteration intensity alteration and vein mineral distributions and fluid inclusion microthermometry are interpreted to indicate that sovereign and jubilee formed at relatively high temperatures whereas teutonic and jasper creek formed at relatively cooler temperatures several hydrologic reconstructions are possible including 1 a single hydrothermal system with an inclined water table and significant lateral outflow to the east or 2 a single low relief hydrothermal system with a flat lying water table that has subsequently been displaced by postmineral faults or tilted approximately 10 to the east regardless of the preferred reconstruction the sovereign and jubilee deposits appear to have formed in the main zone of fluid upflow whereas the teutonic and jasper creek prospects appear to have formed toward the margin moreover the greatest erosion has occurred at the jubilee and sovereign deposits 300 400 m and these may represent the roots of a more extensive vein network that has largely been eroded

the kohuamuri siliceous sinter as a vector for epithermal mineralisation coromandel volcanic zone new zealand the kohuamuri siliceous sinter is the largest known fossil hot spring system in the hauraki goldfield a 200 40 km volcanic terrain with at least 50 adularia illite epithermal deposits formed 16 3 5 6 ma within the coromandel volcanic zone new zealand the sinter is associated with rhyolite and ignimbrite of the whitianga caldera miocene pliocene and consists of two deposits the kohuamuri deposit itself a large in situ outcrop 47 000 m2 and its associated sinter boulder field 4500 m2 and the kaitoke deposit 900 m to the southwest comprising boulders in a landslide situated on a normal fault the well preserved macroscopic and microscopic textures at kohuamuri are similar to actively forming and ancient hot spring deposits elsewhere derived from deep circulating magmatically heated near neutral ph alkali chloride fluids oversaturated in amorphous silica and that discharge at the earth s surface at 100 c lithofacies petrography mineralogy as well as trace element concentrations of the kohuamuri kaitoke deposits were used to locate likely palaeo thermal conduits from the deep reservoir and to reconstruct the palaeoenvironmental setting of the siliceous sinter as an aid to assessing the economic potential of the ancient geothermal system both deposits contain the high temperature 75 c geyserite lithofacies with the kohuamuri deposit also exhibiting textures affiliated with cooler middle and distal sinter apron areas as well as geothermally influenced marsh facies trace element analysis of sinter lithofacies revealed concentrations and zonations of au ag base metals pb cu zn and pathfinder elements as sb associated with epithermal deposits elevated in the proximal vent area and providing evidence of possible au and ag ore mineralisation at depth the methodology used in this study could be utilised globally to identify and assess as yet unidentified epithermal deposits

the role of topographically induced vortices in tropical cyclone formation over the indian ocean abstractthe role of sumatra and adjacent topographic features in tropical cyclone tc formation over the indian ocean io is investigated sumatra as well as the malay peninsula and java have mountainous terrain that partially blocks low level flow under typical environmental stratification for easterly low level flow these terrain features often produce lee vortices some of which subsequently shed and move westward from the northern and southern tips of sumatra and thence downstream over the io since sumatra straddles the equator extending in a northwest southeast direction from approximately 6 n to 6 s the lee vortices while counter rotating are both cyclonic hence they can serve as initial disturbances that eventually contribute to tc formation over the io in addition low level equatorial westerly flow impinging on sumatra is also typically blocked and diverges at times contributing to cyclonic circulations over the io primarily near the southern end of the island data from two recen

seasonality in the madden julian oscillation abstract this study using observational data and global reanalysis products synthesizes existing knowledge on the seasonality in the madden julian oscillation mjo and discusses its possible dependence on the mean background state the seasonality in the mjo is documented in terms of its components in low level zonal wind and precipitation a single peak season boreal winter exists near the equator in the indian and western pacific oceans for the broad tropical region however the seasonality in the mjo is featured by a latitudinal migration across the equator between two peak seasons the primary peak season is in boreal winter december march during which mjo signals are mainly confined to the indian and western pacific ocean and reach their maxima in the south pacific convergence zone the secondary peak season is boreal summer june september during which the strongest mjo occurs north of the equator from the bay of bengal to the south china sea and another separated region of strong mjo

a diagnostic study of the evolution of the mjo from indian ocean to maritime continent wave dynamics versus advective moistening processes abstractthe evolution processes for propagating madden julian oscillations with strong magnitude over the indian ocean io and maritime continent mc are investigated through a diagnosis of ecmwf reanalysis data for november april 1982 2011 a scale separated lower tropospheric 1000 700 hpa moisture budget is analyzed for four stages of composite life cycle suppressed cloud developing convective and decaying overall the budgets in the io and mc are dominated by wave induced boundary layer convergence in the anomalous easterlies wc and advection starting from the suppressed stage in the central io moistening by wc and advection by easterly anomalies contributes to an initiation of the mjo convection in the western io while surface evaporation and or shallow convection moistens the central io in the following cloud developing and convective stage in the central io moistening by wc and advection by the downstream kelvin rossby wave east of central io lead to eastward propagation of deep conve

global association of the madden julian oscillation with monsoon lows and depressions previous research has revealed that monsoon lows and depressions are modulated on intraseasonal time scales in a few regions including india australia and the east pacific this study examines whether such modulation occurs on a global scale and in particular how the madden julian oscillation mjo is associated with changes in synoptic scale vortices across all monsoon regions the spatial climatology of monsoon disturbances is largely insensitive to mjo amplitude however monsoon disturbance frequency mdf varies substantially with mjo phase with regional perturbations of 25 to 90 percent of the seasonal mean value across the tropics in off equatorial locations mdf maxima occur in locations where the mjo enhances low level cyclonic vorticity typically near the western edge of mid level moisture perturbations in contrast equatorial mdf perturbations are in phase with mjo moisture and rainfall anomalies with maxima in regions with strong low level zonal wind convergence

epithermal au ag and related deposits of the hauraki goldfield coromandel volcanic zone new zealand epithermal au ag vein deposits of the hauraki goldfield in the coromandel volcanic zone new zealand produced 320 000 kg au and 1 5 million kg ag between 1862 and 2006 from a total land area of approximately 2 900 km2 approximately 69 percent of the production was from the world class martha deposit at waihi some 97 percent of total past gold production was from deposits hosted in miocene andesite and dacite of the coromandel group although this unit represents only 61 percent of the rocks exposed in the goldfield the deposits consist of quartz calcite vein systems 0 5 to 4 5 km long within alteration zones up to 20 km2 in size they were mined over vertical intervals of 170 to 330 m but up to 575 m at martha and 700 m at karangahake electrum and acanthite are the main ore minerals although pyrite sphalerite galena chalcopyrite sulfosalt minerals and te and se bearing minerals are present in some deposits stibnite and cinnabar occur locally as late minerals and some deposits are overprinted by late massive calcite fluid inclusion ice melting temperature tm measurements indicate that fluids associated with base metal and precious metal deposition had apparent salinities of between 0 5 and 2 wt percent nacl equiv with a maximum of 6 1 wt percent nacl equiv when fitted to hydrostatic boiling point with depth curves the homogenization temperature th data define paleodepths spanning a vertical interval from near the water table to a depth of approximately 1 300 m the presence of vapor rich fluid inclusions and occurrences of lattice textures and vein adularia indicate that periods of boiling coincided with deposition of some epithermal ores sulfur and carbon isotope values of vein minerals are consistent with a magmatic origin for sulfur and carbon oxygen isotope values of vein quartz and calcite are consistent with derivation from evolved meteoric water with possibly a small magmatic water component in some samples the epithermal deposits can be broadly subdivided into northern southern and eastern groups based on their host rocks age variability of vein strike au ag ratios occurrence or relative abundance of key minerals such as adularia calcite and arsenopyrite the grain size of vein quartz and differences in vein textures early ca 14 10 ma steeply dipping planar veins occur in the oldest andesite and dacite in the northern portion of the goldfield but some of these are bonanza grade veins that contained significant gold resources larger veins typically with well developed crustiform textures formed in andesite and dacite in the southern gold field at 7 to 6 ma and these contributed most of the au and ag that has been recovered from the goldfield in contrast rhyolite in the eastern goldfield hosts smaller less well developed veins plus stockworks that have produced the least amount of au and ag epithermal mineral deposits in the hauraki goldfield evolved through time reflecting changes in volcanic activity and more speculatively tectonic and structural history and setting

diurnal patterns of rainfall in northwestern south america part i observations and context one of the rainiest areas on earth the panama bight and pacific western littoral of colombia is the focal point for a regional modeling study utilizing the fifth generation pennsylvania state university ncar mesoscale model mm5 with nested grids in this first of three parts the observed climatology of the region is presented the seasonal march of rainfall has a northwest southeast axis with western colombia near the center receiving rain throughout the year this study focuses on the august september season the diurnal cycle of rainfall over land exhibits an afternoon maximum over most of south and central america typically composed of relatively small convective cloud systems over some large valleys in the andes and over lake maracaibo a nocturnal maximum of rainfall is observed a strong night morning maximum of rainfall prevails over the coastal ocean propagating offshore and westward with time this offshore convection often takes the form of mesoscale convective systems with sizes comparable to the region s coastal concavities and other geographical features the 10 day period of these model studies 28 august 7 september 1998 is shown to be a period of unusually active weather but with a time mean rainfall pattern similar to longer term climatology it is concluded that the rain producing processes during this time period are likely to be typical of those that shape the seasonal climatology

propagation of the madden julian oscillation through the maritime continent and scale interaction with the diurnal cycle of precipitation the convectively active part of the madden julian oscillation mjo propagates eastward through the warm pool from the indian ocean through the maritime continent the indonesian archipelago to the western pacific the maritime continent s complex topography means the exact nature of the mjo propagation through this region is unclear model simulations of the mjo are often poor over the region leading to local errors in latent heat release and global errors in medium range weather prediction and climate simulation using 14 northern winters of trmm satellite data it is shown that where the mean diurnal cycle of precipitation is strong 80 of the mjo precipitation signal in the maritime continent is accounted for by changes in the amplitude of the diurnal cycle additionally the relationship between outgoing long wave radiation olr and precipitation is weakened here such that olr is no longer a reliable proxy for precipitation the canonical view of the mjo as the smooth eastward propagation of a large scale precipitation envelope also breaks down over the islands of the maritime continent instead a vanguard of precipitation anomalies of 2 5 mm day 1 over 10 6 km 2 jumps ahead of the main body by approximately 6 days or 2000 km hence there can be enhanced precipitation over sumatra borneo or new guinea when the large scale mjo envelope over the surrounding ocean is one of suppressed precipitation this behaviour can be accommodated into existing mjo theories frictional and topographic moisture convergence and relatively clear skies ahead of the main convective envelope combine with the low thermal inertia of the islands to allow a rapid response in the diurnal cycle which rectifies onto the lower frequency mjo hence accurate representations of the diurnal cycle and its scale interaction appear to be necessary for models to simulate the mjo successfully

a large and complete jurassic geothermal field at claudia deseado massif santa cruz argentina abstract late jurassic geothermal deposits at claudia argentinean patagonia are among the largest 40 km 2 and most varied in the deseado massif a 60 000 km 2 volcanic province hosting precious metals au ag mineralization generated during diffuse back arc spreading and opening of the south atlantic ocean both siliceous sinter and travertine occur in the same stratigraphic sequence deposits range from those interpreted as fluvially reworked hydrothermal silica gels to extensive apron terraces to a clustering of high temperature subaerial vent mounds paleoenvironmentally diagnostic textures of sinters include wavy laminated bubble mat and nodular fabrics and for travertines comprise fossil terracette rims wavy laminated bubble mat spherulitic oncoidal and peloidal fabrics of special note is the presence of relatively large to 25 cm high inferred subaqueous conophyton structures in travertines which serve as analogs for some precambrian stromatolites and imply the presence of relatively deep pools maintained by voluminous spring discharges the claudia geothermal field is geographically and geologically linked to the cerro vanguardia epithermal project total resource of 7 8 million ounces au equivalent via proximity similar veins and structural linkages making it an especially large and relevant prospect for the region the combined claudia cerro vanguardia hydrothermal system likely represents a fortuitous alignment of focused fluid flow and structure conducive to forming a giant epithermal ore deposit with respect to size ore concentration and potentially duration in the late jurassic of patagonia

sedimentary facies and mineralogy of the late pleistocene umukuri silica sinter taupo volcanic zone new zealand abstract the umukuri silica sinter is a large late pleistocene hot spring deposit exposed along the eastern upthrown block of the umukuri fault one kilometer southwest of the active orakei korako geothermal area taupo volcanic zone new zealand uplift along the fault has frozen sinter maturation to produce a characteristic silica phase stratigraphy revealed by x ray diffraction paracrystalline opal ct dominates upper layers opal c occurs throughout middle and lower horizons and recrystallized fabrics of microcrystalline quartz constitute lowermost exposed layers original and secondary matrix fabrics in the sinter include fine grained porous friable dense vitreous and massive mottled diffusely layered original fabrics combine with silicified plant matter peloids pisoids sinter fragments detrital grains diatoms ostracodes and filamentous to tufted microbial remains to form nine depositional microfacies thinly laminated plant rich and palisade types dominate sinter breccia and wavy laminated varieties also are common whereas curved laminae with lenticular voids bubble mats clotted peloidal and pisolitic microfacies are minor umukuri microfacies represent silicification in mid to low temperature waters on sinter apron terrace and slope areas and in distal marshy settings closely spaced lateral and vertical intercalation of various microfacies in outcrop implies changing local flow and temperature conditions no facies typical of high temperature proximal vent areas have been identified comparison with modern thermal spring analogs suggests that original umukuri sinter fabrics recorded varying degrees of polymerization vs monomerization of juvenile opal a mineralogical and textural modification of matrix fabrics reflects a microscale incremental continuum following granular or fibrous habits along solution precipitation pathways late stage quartz rims and infills pores throughout the sinter

nature of the hydrothermal alteration of the miocene sigri petrified forest and host pyroclastic rocks western lesbos greece abstract the early miocene sigri pyroclastic formation in western lesbos island hosts the famous petrified forest of silicified tree fossils protected as a unesco geopark the formation consists primarily of flow tuffs mud flow deposits and stream conglomerate hydrothermal veins rich in silica iron and manganese are preferentially developed in major fault zones and along paleosols the purpose of this study is to understand the nature of the hydrothermal system and its relationship to the preservation of tree fossils samples were collected from fresh and altered pyroclastic rocks hydrothermal veins and petrified wood rock mineralogy and chemistry were investigated using a petrographic microscope scanning electron microscope electron microprobe laser raman spectroscopy and x ray powder diffraction early devitrification of volcanic glass in tuffs formed opaline silica and locally resulted in smectite at the same time fossil trees were partly replaced by amorphous silica epithermal alteration and hydrothermal veins include 1 adularia silica kaolinite 2 jarosite hematite amorphous silica and 3 fe oxide and or mn oxide amorphous silica the mnsi mixture and mn oxides comprise structurally amorphous romanechite with some more crystalline grains of todorokite ramsdellite and or nsutite the mixtures of fe oxides and silica are also largely amorphous and include cristobalite such mixtures replace parts of the petrified wood including cell walls the various colors observed from the petrified wood are principally related to the abundance of iron and organic matter faulting and complex hydrothermal alteration was related to the emplacement of laccoliths and dykes around 18 ma 1 3 ma after deposition of the sigri pyroclastic formation the observed types of low temperature epithermal alteration are compared with that produced by different circulating waters in the modern taupo volcanic zone of new zealand hydrothermal deposition of fe oxides and silica played an important role in the preservation of the petrified forest

deep sea and shallow water hydrothermal vent communities two different phenomena hydrothermal vent communities from 76 areas lying at depths from 0 to 4100 m were split into two groups bdeepq and bshallow waterq based on the occurrence of vent obligate restricted to hydrothermal vents taxa of a high rank genus and family the two groups were then compared based on a large set of environmental faunistic and community parameters the degree of obligacy of fauna sharply changes at the depth of approximately 200 m in 21 shallow water areas located at depths b200 m vent obligate taxa are absent or their taxonomic rank does not exceed a species the total number of vent obligate species in shallow water is 8 and their obligacy is uncertain data from 55 areas lying at depths from 200 to 4100 m indicate there are ca 400 obligate species in 47 of these areas obligate vent taxa of the genus or the family rank are present obligate taxa of the genus rank appear at 200 m depth and of the family rank at 386 m the depth ca 200 m corresponds well with differences in community structure and composition and environmental parameters deep sea n200 m hydrothermal communities differ from shallow water ones b200 m in a much higher ratio of vent obligate taxa deep sea vent communities are also distinguished by the lack of diatom and algae bacterial mats phytoplankton lower species richness the development of large sulphide structures higher role of active vents in structuring communities in space replication of a set of dominant taxa in communities within large regions reproduced through the succession at newly formed vent fields more pronounced concentric and vertical zonality higher biomass of macrofauna the important role of symbiotrophic forms dominating the biomass the ratio of species with a bpointq species range endemic to small areas is higher in the deep sea there are no significant differences between the vent and non vent biogeography both in shallow waters and the deep ocean modern deep sea hydrothermal vent communities have a longer evolutionary history than their shallow water counterparts to explain major differences between deep and shallow water hot vent communities evolutionary processes need to be analysed over long geological periods and within global vertical zones it is suggested that the proportion of organic matter derived from chemosynthesis and photosynthesis plays a crucial role in evolution when calculated for global zones this proportion increases with depth to a certain critical level that separates deep and shallow water hot vent communities and fauna vertical zonation in the distribution of obligate taxa in hydrothermal vent communities indicates that this level is reached at approximately 200 m depth

why precipitation is mostly concentrated over islands in the maritime continent abstract high resolution observations and regional climate model simulations reveal that precipitation over the maritime continent is mostly concentrated over islands analysis of the diurnal cycles of precipitation and winds indicates that this is predominantly caused by sea breeze convergence over islands reinforced by mountain valley winds and further amplified by the cumulus merger processes comparison of a regional climate model control simulation to a flat island run and an all ocean run demonstrates that the underrepresentation of islands and terrain in the maritime continent weakens the atmospheric disturbance associated with the diurnal cycle and hence underestimates precipitation the implication of these regional modeling results is that systematic errors in coarse resolution global circulation models probably result from insufficient representation of land sea breezes associated with the complex topography in the maritime continent it is found that precipitation in the maritime continent

progressive dolomitization of florida limestone recorded by alkaline earth element concentrations in saline geothermal submarine springs 1 studies in the late 1970s revealed that the effluents of saline geothermal submarine springs on the west florida shelf have compositions nearly identical to seawater except for distinct ca enrichments and mg depletions probably resulting from dolomitization during annual visits between 1996 and 2003 we collected high purity effluents from four submarine springs and from warm mineral springs wms which is located on land filtered effluents were analyzed for major ions and for sr and ba these analyses confirm the seawater like composition of the effluents as well as the ca enrichment and mg depletion the alkaline earth elements sr and ba like ca and ra are significantly enriched in the effluents compared to ambient seawater by average factors of 1 6 and 3 8 respectively about 9 and 12 for wms the mg depletion and the sr and ba enrichments while invariant over the 7 year sampling period increase gradually from south to north consistent with progressive dolomitization of limestone along the purported convective flow path of the warm seawater the ca enrichment shows no obvious trend because besides dolomitization gypsum dissolution is an independent source of ca a simple mass balance indicates that the ca excess is fully accounted for by these two processes in all four submarine springs this is not the case for wms where a residual ca excess points to a third source of ca presumably limestone dissolution that occurs upon mixing of the modified seawater with fresh groundwater from the floridan aquifer system

a geothermally influenced wetland containing unconsolidated geochemical sediments hot spring waters flowing from porkchop geyser norris geyser basin yellowstone national park usa enter a shallow wetland basin and precipitate opal a silica particulate particulate formation by chemical rather than biochemical and colloidal mechanisms is suggested by floc and shard like particle morphologies comprising opal a silica nanospheres and microspheres of colloidal dimensions and precipitation from waters with opaque milky blue colouration indicative of aqueous silica sol conditions sediment accumulates in the wetland at a rate of ca 20 25 mm year is unconsolidated and massive to diffusely bedded to laminated post depositional features include soft sediment deformation and scouring and in drying conditions relatively deep desiccation establishment of geochemically dominated wetland sedimentation is favoured where alkali chloride hot spring fluids of circum neutral to basic ph and high silica concentration discharge to and cool to ca 35 c within topographic depressions that receive only small volumes of non hot spring water local wetland vegetation which is composed of hydrophytes halophytes and alkali tolerant species more typical of coastal wetlands colonizes the soft wetland substrate and may be relatively quickly buried by rapid sediment accumulation prior to the evolution of the diatom silica sink geothermal wetlands containing geochemically precipitated silica sediments may have been much more common and widespread rhizoliths chert nodules with organic cores scour fabrics soft sediment deformation desiccation cracks and massive to diffuse bedding preserved in palaeozoic geothermal environments may all be evidence of ancient unconsolidated geochemical sediments and geothermal wetland conditions

relationship between spring and geyser activity and the deposition and morphology of high temperature 73 c siliceous sinter yellowstone national park wyoming u s a abstract six classes of alkaline hot springs and geysers are here distinguished in yellowstone national park based on activity and eruptive style 1 non surging non boiling springs 2 gently surging non boiling springs 3 non surging to gently surging boiling springs 4 strongly surging springs 5 fountain geysers and 6 cone geysers each displays morphologically distinctive siliceous sinter deposits in the high temperature 73 c parts of the vent and outflow systems non surging and gently surging non boiling springs that do not overflow their rims develop thin digitate to lilypad like sinter rims that grow horizontally over the pool surfaces similar springs with rim overflow have rims that accrete vertically boiling springs often have nearly circular steep sided pools and rims dominated by splash and rim overflow and composed mainly of spicular and columnar sinter fountain geysers characterized by broad fountain like eruption bursts have a central vent surrounded by a zone of spicular sinter beyond which is a broad flat bottomed moat but lack steep sinter cones cone geysers have narrow vents jet like discharges that cool rapidly and fall close to the vent and steep sided spicule dominated sinter cones sinter deposition takes place within three main zones 1 fully subaqueous sides and bottoms of vent pools outflow basins and outflow channels 2 periodically wetted splash zones surrounding hot springs and geysers and 3 largely subaerial parts of the rim and outflow areas wetted mainly by overflow and surging and that dry quickly fully subaqueous surfaces are covered by fine earthy particulate siliceous sediment pss composed largely of amorphous silica spherules and spherule aggregates that appear to have precipitated around heterogeneous nuclei including microbes splash zones of hot springs and geysers are characterized by spicular sinter largely subaerial zones wetted mainly by rim overflow and surging with little or no splash show complex varieties of terraced columnar and knobby sinter the highest silica deposition rates occur where surfaces are wetted frequently and evaporate to dryness such as the tops of spicules columns and knobs associated lower areas and crevices that remain wet or moist show slow accumulation of pss most continuously wet surfaces in high temperature 73 c hot spring and geyser vent and outflow systems are probably covered by microbial biofilms although microbes may locally influence rates of silica deposition and sinter microstructure the results of this study suggest that the depositional sites morphology and macrostructuring of high temperature sinter are controlled largely by the processes of surface wetting evaporation and drying

a devonian auriferous hot spring system rhynie scotland the early devonian rhynie hot spring system is the oldest known and is of the low sulphidation type it extends for at least 1 5 km along a major fault zone defining the western margin of an outlier of fluvial and lacustrine sediments plant bearing sinters and andesitic lavas the age of sedimentation and hydrothermal activity has been determined by palynological pragian and radio metric 396 12 ma techniques the outlier is a half graben with a complex stepped western margin the devonian rocks show intense hydrothermal alteration along the fault zone the main alteration minerals are quartz k feldspar calcite hematite and illitic and chloritic clays multiple chert veining and brecciation are widely developed and geyserite and vent material are also present pyrite occurs in veins and all alteration facies sinters and altered rocks contain high concentrations of au as sb hg w and mo gold occurs in arsenian pyrite and as sub micron particles in oxidized rocks the fluid s responsible for most hydrothermal alteration were near neutral with low sulphur and oxygen activities and dominated by meteoric water however incursions of high temperature 300 440 c magmatic fluids occurred with d 65 and 18 o around 8 5 34 s pyrite and initial 87 sr 86 sr ratios vein calcite lie mainly within the ranges 3 4 to 8 5 and 0 71138 to 0 71402 respectively these data indicate that late proterozoic dalradian metasediments are a likely source for s and sr but other sources are possible 13 c values for caliche and vein calcite imply derivation of carbon from non organic sources the rhynie cherts were deposited from a low salinity fluid of probable meteoric origin 18 o chert 13 1 to 16 5 which had interacted with the basement rocks and sediments high xe ar br cl and i cl ratios plant bearing chert yielded an 40 ar 39 ar ratio 292 1 0 6 significantly less than that of modem air and may be the first valid determination of a sample of ancient atmosphere

the behaviour of antimony released from surface geothermal features in new zealand abstract antimony rich geothermal features in the taupo volcanic zone tvz of new zealand s north island drain directly into surface aquatic environments the discharge from champagne pool a mixed alkali chloride sulfate hot spring at wai o tapu geothermal field contains up to 194 g l sb the discharge from frying pan lake a chloride sulfate hot spring at waimangu geothermal field contains up to 21 5 g l sb at champagne pool downstream concentrations of sb show distinct diurnal variations particularly in winter when concentrations in the early morning were less than half those measured mid afternoon changes in sulfide sulfate equilibria and direct stibnite oxidation may explain this phenomenon in the discharge from frying pan lake sb exhibits little diurnal variation most 80 of the dissolved sb released from champagne pool is removed from solution at alum lake an acid sulfate hot pool containing elevated levels of dissolved sulfide therefore relatively little sb is discharged into the freshwater drainage in the area however in the absence of a sulfide rich feature at waimangu most of the sb discharged from frying pan lake remains dissolved and is transported into the freshwater drainage system of lake rotomahana the contrast in sb behaviour between these two sites confirms the importance of dissolved sulfide and low

factors controlling rain on small tropical islands diurnal cycle large scale wind speed and topography abstracta set of idealized cloud permitting simulations is performed to explore the influence of small islands on precipitating convection as a function of large scale wind speed the islands are situated in a long narrow ocean domain that is in radiative convective equilibrium rce as a whole constraining the domain average precipitation the island occupies a small part of the domain so that significant precipitation variations over the island can occur compensated by smaller variations over the larger surrounding oceanic area while the prevailing wind speeds vary over flat islands three distinct flow regimes occur rainfall is greatly enhanced and a local symmetric circulation is formed in the time mean around the island when the prevailing large scale wind speed is small the rainfall enhancement over the island is much reduced when the wind speed is increased to a moderate value this difference is characterized by a change in the mechanisms by which convection is forced a thermally forced se

barrier effect of the indo pacific maritime continent on the mjo perspectives from tracking mjo precipitation abstractexplanations for the barrier effect of the indo pacific maritime continent mc on the mjo should satisfy two criteria first they should include specific features of the mc namely its intricate land sea distributions and elevated terrains second they should include mechanisms for both the barrier effect and its overcoming by some mjo events guided by these two criteria a precipitation tracking method is applied to identify mjo events that propagate across the mc mjo c and those that are blocked by the mc mjo b about a half of mjo events that form over the indian ocean propagate through the mc most of them 75 become weakened over the mc the barrier effect cannot be explained in terms of the strength horizontal scale or spatial distribution of mjo convection when it approaches the mc from the west a distinction between mjo b and mjo c is their precipitation over the sea versus land in the mc region mjo c events rain much more over the sea than over land whereas rainfall over

geochemistry of submarine warm springs in the limestone cavern of grotta azzurra capo palinuro italy evidence for mixing zone dolomitisation abstract subtidal springs in and around the submarine limestone cavern of grotta azzurra at capo palinuro italy discharge fluids which are warm 10 excess si alkalinity ca2 sr2 and mn relative to seawater are likely derived from the groundwater component or dissolution hydrothermal alteration of the host rocks magnesium has been removed from the seawater component in exchange for ca2 due to dolomitisation of the limestone and or hydrothermal alteration reactions saturation state calculations suggest that the vented fluids are near saturation with respect to calcite and supersaturated with respect to dolomite this and the presence of dolomite in the host rocks and cave floor sediments suggest that mixing zone dolomitisation of the limestones is occurring perhaps kinetically assisted by elevated temperature and or bacterial mediation in the reducing subseafloor zone one possible end member condition is considered for the thermal fluid zero mg which suggests an end member temperature of 50 5 c and a fluid composition derived from 38 seawater and 62 groundwater the heat source for the circulating fluids is uncertain but may involve warm underlying igneous rocks or heating via the geothermal gradient a continuous in situ record of vent fluid temperature salinity ph and o2 concentration collected within the cavern is consistent with our interpretation of the fluid origin and suggests that tidal forcing affects circulation and venting of the warm fluids

the miocene atastra creek sinter bodie hills volcanic field california and nevada 4d evolution of a geomorphically intact siliceous hot spring deposit abstract the atastra creek siliceous hot spring deposit or sinter occurs in the paramount bald peak alteration zone due north of the bodie precious metals mining district in the miocene bodie hills volcanic field california and nevada u s a distinctive features include its geomorphically intact geyser vent mounds the presence of growth fault stepped sinter terraces that developed westward along a nnw trending fault and atypical hg sb and as concentrations high temperature 75 c subaerial proximal apron sinter occurs in two settings 1 radiating botryoidal geyserite in vent mounds and 2 bedded geyserite columnar nodular size sorted geyser eggs intercalated with mid to low temperature

modulation of hurricane activity in the gulf of mexico by the madden julian oscillation the madden julian oscillation mjo is a large scale episodic modulation of tropical winds and precipitation that travels eastward from asia to america with a characteristic repeat time of 30 to 60 days here it is shown that when mjo wind anomalies in the lower troposphere of the eastern pacific are westerly gulf of mexico and western caribbean hurricane genesis is four times more likely than when the mjo winds are easterly accurate predictions of the mjo may lead to improved long range forecasts of tropical cyclone activity

geyserite in hot spring siliceous sinter window on earth s hottest terrestrial paleo environment and its extreme life siliceous hot spring deposits or sinters typically form in active terrestrial on land volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the earth s surface as silica charged geothermal fluids geyserites are sinters affiliated with the highest temperature 75 100 c natural geothermal fluid emissions comprising localized lithologically distinctive hydrothermal silica precipitates that develop around geysers spouters and spring vents they demarcate the position of hot fluid upflow zones useful for geothermal energy and epithermal mineral prospecting near vent areas also are extreme environment settings for the growth of microbial biofilms at near boiling temperatures microbial biosignatures e g characteristic silicified microbial textures carbon isotopes genetic material lipid biomarkers may be extracted from modern geyserite however because of strong taphonomic filtering and subsequent diagenesis fossils in geyserite are very rare in the pre quaternary sinter record which in and of itself is patchy in time and space back to about 400 ma only a few old examples are known such as geyserite reported from the devonian drummond basin australia devonian rhynie cherts scotland and a new example described herein from the spectacularly well preserved late jurassic 150 ma yellowstone style geothermal landscapes of patagonia argentina there geyserite is associated with fossil vent mounds and silicified hydrothermal breccias of the claudia sinter which is geologically related to the world class cerro vanguardia gold silver deposit of the deseado massif a part of the chon aike siliceous large igneous province tubular filament like micro inclusions from claudia were studied using integrated petrographic and laser micro raman analysis the results of which suggest a biological origin the putative fossils are enclosed within nodular geyserite a texture typical of subaerial near vent conditions overall this worldwide review of geyserite confirms its significance as a mineralizing geological archive reflecting the nature of earth s highest temperature habitable terrestrial sedimentary environment hot spring depositional settings also may serve as analogs for early earth paleoenvironments because of their elevated temperature of formation rapid mineralization by silica and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures

jurassic hot spring deposits of the deseado massif patagonia argentina characteristics and controls on regional distribution abstract the deseado massif santa cruz province argentinean patagonia hosts numerous middle to late jurassic age geothermal and epithermal features represented by siliceous and calcareous chemical precipitates from hot springs sinters and travertines respectively hydrothermal breccias quartz veins and widespread hydrothermal silicification they indicate pauses in explosive volcanic activity marking the final stages in the evolution of an extensive jurassic ca 178 151 ma volcanic complex set in a diffuse extensional back arc setting heralding the opening of the atlantic ocean published paleo hot spring sites for the deseado massif plus additional sites identified during our recent field studies reveal a total of 23 locations five of which were studied in detail to determine their geologic and facies associations they show structural lithologic textural and biotic similarities with miocene to recent hot spring systems from the taupo and coromandel volcanic zones new zealand as well as with modern examples from yellowstone national park u s a these comparisons aid in the definition of facies assemblages for deseado massif deposits proximal middle apron and distal siliceous sinter and travertine terraces and mounds with preservation of many types of stromatolitic fabrics that likely were controlled by formation temperature ph hydrodynamics and fluid compositions locally the mapped hot spring deposits largely occur in association with reworked volcaniclastic lacustrine and or fluvial sediments silicic to intermediate lava domes and hydrothermal mineralization all of which are related to local and regional structural lineaments moreover the numerous geothermal and significant epithermal those with published minable resources deposits of the deseado massif geological province mostly occur in four regional nnw and wnw hydrothermal structural belts northwestern northern central and southern defined here by alignment of five or more hot spring deposits and confirmed as structurally controlled by aeromagnetic data the northern and northwestern belts in particular concentrate most of the geothermal and epithermal occurrences hence jurassic hydrothermal fluid flow was strongly influenced by the most dominant and long active geological boundaries in the region the outer limits of the deseado massif horst itself

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

mechanisms for the dipolar patterns of rainfall variability over large islands in the maritime continent associated with the madden julian oscillation abstractbefore the eastward propagating rainy envelope of a madden julian oscillation mjo arrives at the maritime continent mc some islands in the mc experience dipolar patterns of rainfall va

hot spring and geyser sinters the integrated product of precipitation replacement and deposition complex ornate sinter deposits are found in many hot spring and geysers systems throughout the world including those located in the taupo volcanic zone on the north island of new zealand those sinters are formed of opal a that replaced microbes opal a precipitated as cement accessory minerals e g kaolinite jarosite calcite biological detritus e g leaves wood pollen grains and lithic detritus the opal a is compositionally variable because of the amount of water oh and h2o and in some cases accessory elements e g au ag bound into its structure the composition and fabric of the siliceous sinter found at any locality reflect the relative balance among the processes of replacement precipitation and deposition the microbes that inhabit these systems are of critical importance because they are commonly replaced by and or encrusted with opal a in many settings copious amounts of opal a are precipitated as cement around the frameworks of silicified filaments the cementation pro

fossilised geothermal surface features of the whitianga volcanic centre miocene coromandel volcanic zone new zealand controls and characteristics abstract the late miocene whitianga volcanic centre of the coromandel volcanic zone north island new zealand is host to 18 known siliceous and intensely silicified deposits including silicified volcanics sediments of inferred lacustrine fluvial and mud pool origin siliceous hot spring deposits or sinters and silicic veins collectively these siliceous and silicified deposits indicate past geothermal activity that occurred at the earth s surface and in the shallow subsurface sinters in particular are of interest because they are derived from deep geothermal reservoirs and precipitate from discharged thermal fluids at the intersection of the water table with the land surface however some siliceous and silicified features in hydrothermal paleoenvironments have been misidentified as sinters by studying textural types distributions structural setting mineral paragenesis and trace elemental composition of the siliceous and silicified deposits in the whitianga volcanic centre it is possible to differentiate sinters and identify their spring vent source areas 100 70 c from more distal thermal spring discharge locations ag mineralisation may have occurred at depth this has important implications for the exploration of mineralised epithermal ore deposits at local to regional scales in particular for the hauraki goldfield of the coromandel volcanic zone

epithermal sinters of paleozoic age in north queensland australia silica sinters deposited from hot springs have been found associated with volcanic rocks of late devonian to late carboniferous age in north queensland australia these deposits have many features in common with modern hot spring sinters such as those of the taupo volcanic zone in new zealand they occur associated with subaerial volcanic rocks and are locally found with air fall tuffs and fluvial and lake deposits in which hydrothermal eruption breccias are common the associated rocks are extensively hydrothermally altered and are cut by silica veins showing characteristic epithermal vein textures the silica veins contain low salinity fluid inclusions trapped at epithermal temperatures and there is evidence of boiling textures preserved in the sinters are identical to those found in modern sinters they include columnar structures similar to bacterial stromatolites described from yellowstone national park as well as striated surfaces apparently resulting from silica deposition on filamentous algae plant fossils including oxroadia gracilis are abundant criteria applied to identify these ancient sinters may be applied to other possible sinter deposits and may provide evidence indicating the level of exposure of the former geothermal system which may be an important guide in exploration for epithermal precious metal deposits

geothermal springs of the west florida continental shelf evidence for dolomitization and radionuclide enrichment abstract on the sea bed of the west florida continental shelf about 45 km ssw of ft myers florida an 85 km 2 area has been discovered in which six thermal springs discharge warm chemically altered seawater from vents and seepage zones the spring water apparently originates in the subsurface ocean around the florida platform and penetrates the highly porous strata of the platform about 500 1000 meters below sea level it percolates toward the interior of the platform and is geothermally heated to about 40 c en route then it rises along more vertical flow channels and is discharged in warm submarine springs beneath the platform several chemical processes alter the percolating seawater one process seems to be a secondary dolomitization of the limestone of the platform because in the discharging seawater magnesium is lower by 2 7 mmole kg and calcium higher by 3 6 mmole kg than in normal seawater with the same chlorinity other reactions within the sediments of the platform enrich the spring effluents 1000 fold in 226 ra 10 000 fold in 222 rn and 90 fold in 228 ra compared to the seawater surrounding the platform thus the springs may be important sources of radionuclides for the gulf of mexico the percolating seawater also loses all of its oxygen and nitrate to reduction processes loses most of its phosphate and 40 of its 238 u and roughly quadruples its silica content coastal carbonate platforms are fairly common geological features thus processes like those beneath the west florida shelf may function on a world wide basis to play an important role in the diagenesis of carbonate sediments

jurassic geothermal landscapes and fossil ecosystems at san agustin patagonia argentina abstract an extensive well preserved late jurassic c 150 ma geothermal system at san agustin farm in the deseado massif patagonia argentina is described this deposit along with others previously known from the same region partially fills a considerable gap between cenozoic and scattered palaeozoic hot spring localities reported worldwide the san agustin deposit is novel because it represents a large 1 4 km 2 and nearly complete geothermal landscape siliceous hot spring facies both subaerial and subaqueous are exposed side by side in their original spatial and geological context set amongst intrusive rhyolite domes and fluviolacustrine sediments the jurassic hot springs have preserved an entire local ecosystem containing microbes arthropods gastropods and plants exhibiting lagerstatten style preservation plant preservation in particular ranges from decayed litter to seedling sprouts and to dense stands in life orientation with intact anatomy the san agustin deposit shares some ecological taphonomic and sedimentological characteristics with modern hot springs as it formed in a pre angiosperm world it is akin to the famous hot spring related devonian rhynie cherts of scotland it differs in having excellent exposure and thus will probably contribute to a better understanding of biosignal preservation in extreme environments in the geological record

mesoscale variation in diabatic heating around sumatra and its modulation with the madden julian oscillation abstractdiabatic heating in the maritime continent region is controlled by a unique blend of mesoscale variability associated with steep topography and complex coastlines and intraseasonal variabil

diurnal cycle of deep convection in super clusters embedded in the madden julian oscillation 1 the diurnal cycle of deep convection in the convectively active phase cap and convectively suppressed phase csp of the madden julian oscillation mjo was investigated using global infrared equivalent blackbody temperature tbb data from october 2000 to april 2005 we particularly focused on super clusters scs that occurred during the cap of the mjo to analyze the behavior of scs and the csp of the mjo statistically we created composites of tbb for each case four regions were examined 1 the indian ocean io 2 the ocean area of the maritime continent mco 3 the land area of the maritime continent mcl and 4 the western pacific wp the amplitude phase of the diurnal cycle of deeper convection in scs was larger than similar to that of the csp of the mjo this result is consistent with that found in a previous study however the diurnal cycle of deep convection in the csp of the mjo had a clear maximum peak especially over the mcl but that in scs had a broader maximum peak of deep convection especially in oceanic regions although the diurnal phase was similar between scs and the csp of the mjo this result statistically suggests that the organization of a convective system affects the diurnal cycle of its deep convection as described in a previous case study we also demonstrated that the difference in the diurnal cycle of deep convection in the io and wp regions arose from sea surface temperature differences in those regions

lithological and spatial controls on the distribution of quartz veins in andesite and rhyolite hosted epithermal au ag deposits of the hauraki goldfield new zealand vein distributions in line samples from four epithermal au ag deposits of the hauraki goldfield were logged and quantified by vein spacing vein density vein thickness and percentage of vein extension one deposit is hosted in andesite lavas martha hill one in andesite lavas and dacite porphyry dacitic tuffs and pyroclastic breccias golden cross and two in rhyolite lavas and rhyolitic tuffs with minor andesite lavas or andesite dikes ohui and wharekirauponga the vein systems in these deposits form fault controlled arrays of extensional veins vein spacing distributions are non fractal over two to three orders of magnitude 1 mm to 5 m and therefore fractal dimension statistics are not applicable the coefficient of variation cv of vein spacing was used as a measure of the degree of vein clustering rock type has a marked influence on vein spacing distributions with veining in rhyolite lava having lower average thickness and percentage extension but a generally higher degree of vein clustering compared with veining in andesite lava in the same deposit vein spacing distributions in well jointed lithologies mainly andesite lava have cv values 0 8 1 2 that are indicative of anticlustered to weakly clustered patterns particularly in the vein stockwork of the upper part of the golden cross deposit these cv values are consistent with field observations that joints are a major control on vein spacing in the poorly jointed dacitic and rhyolitic rocks the veins are weakly to strongly clustered as shown by higher cv values 1 2 2 4 and are commonly associated with normal faults overall andesite lava and dacite porphyry and pyroclastics host thicker and more persistent veins than rhyolite lava and tuff these larger veins contain significant volumes of high grade gold mineralisation the higher chemical reactivity to hydrothermal fluids of andesite and dacite compared with rhyolite may have aided propagation and thickening of the veins in andesite hosted deposits within an individual epithermal deposit location close to thick veins representing major fluid conduits commonly overrides the effect of different lithologies sites that are deeper and located within or adjacent to major vein structures have higher average vein thickness percentage extension and degree of vein clustering systematic collection and analysis of vein spacing thickness and density data can be used to define trends that are useful in the exploration of gold bearing epithermal vein deposits