a reinterpretation of the delta d h 2 o of inclusion fluids in contemporaneous quartz and sphalerite creede mining district colorado a generic problem for shallow orebodies water extracted from fluid inclusions in quartz from shallow epithermal ore deposits often has a hydrogen isotope composition delta d different from that of water extracted from inclusions in associated minerals this difference is usually attributed to the involvement of primary fluids from multiple sources isotopic and homogenization and freezing temperature determinations on fluid inclusions from contemporaneous quartz and sphalerite from the epithermal silver and base metal orebodies of the oh vein creede district colorado suggest an alternative explanation in near surface deposits differences between delta d sub h 2 o of inclusion fluids in ore minerals and quartz may result instead from contamination during extraction of the fluids contained in primary inclusions by shallow ground water trapped in pseudosecondary inclusions in quartz quartz from the oh vein contains two principal petrographically distinct populations of fluid inclusions primary and pseudosecondary the primary inclusions have salinities ranging from 5 to 10 equiv wt percent nacl and the salinities of pseudosecondary inclusions cluster between 0 and 1 percent primary inclusions in quartz from one locality have a measured delta d sub h 2 o value of 69 per mil while pseudosecondary inclusions at the same locality have a delta d sub h 2 o value of 102 per mil both salinity and isotopic values for primary inclusions in quartz are similar to those for primary inclusions in contemporaneous sphalerite homogenization temperatures for primary and pseudosecondary inclusions in quartz range from 191 degrees to 280 degrees c and from 199 degrees to 278 degrees c respectively the delta d sub h 2 o value measured on fluid inclusions from bulk crystals ranges between 97 and 85 per mil and represents a mixture of fluids from both primary and pseudosecondary inclusions we interpret the data to indicate that one or more episodes of abrupt incursion of cooler overlying ground water into the ore zone caused thermal cracking of the quartz crystals during the time interval of mineralization subsequent healing of the fractures trapped heated low salinity ground water in pseudosecondary inclusions the abrupt incursions of overlying ground water are speculated to have resulted from either collapse of a transient vapor dominated region of the ore zone or catastrophic venting of the system through hydrothermal eruption s the unusually high contrast between the salinities of the ore depositing fluids and the ground water overlying the ore zone allowed recognition of this phenomenon at creede it is likely however that creede is not unique similar phenomena may be common in shallow ore zones where rapid fluctuation of an interface between a deep high temperature thermal plume and an overlying cooler ground water may be expected to occur careful study of the origins of fluid inclusions particularly in quartz is essential to characterize the primary ore fluids and to assess the role of ground water in the hydrology of shallow ore deposits

a low seismic wavespeed anomaly beneath northwestern india a seismic signature of the deccan plume abstract seismic tomography of the indian region using p wave arrival times reveals an approximately cylindrical region of lowered seismic velocities in the upper mantle to the north of the gulf of cambay and the present exposure of the deccan flood basalts this anomaly with low velocities interrupts the characteristically high seismic velocities in the lithosphere beneath peninsular india and extends from shallow depth down to a more extensive low velocity zone beneath 200 km the centre of the low velocity anomaly lies just below the earliest alkaline magmatism which has been directly associated with the deccan plume in the northern portion of the cambay graben these magmatic events precede the main deccan flood eruptions by at least 3 myr the lowered seismic wavespeeds link into the ancient narmada lineament and to some extent to the south but here unfortunately the tomographic image runs out of resolution synthetic tests indicate that such a zone of lowered wavespeeds can be recovered with some loss of amplitude towards the south the association of the current seismic anomaly with the deccan traps is intriguing since the cambay graben remains a place of raised heat flow one explanation would be that the seismic anomaly represents the signature of the initial conduit through which plume material forced its way through the lithosphere beneath the cambay rift the zone of lowered seismic velocities beneath the indian lithosphere might then represent the remains of the initial plume head which would need to have moved with india over the 65 myr since the deccan eruptions

seismic imaging of the aftershock zone of the 2001 mw 7 7 bhuj earthquake india 1 detailed seismic tomography reveals that the 2001 mw 7 7 bhuj earthquake was associated with a 10 14 increase in vp and vs and a 10 decrease in vp vs in the 10 to 35 km depth range covering a 2750 km2 area beneath the aftershock zone this anomaly could be attributed to the existence of a lithological heterogeneity or a pluton of mafic composition that might have intruded during the rifting in early jurassic 160 ma the banni basin and the wagad uplift are found to be associated with high velocity intrusive bodies extending from 5 to 35 km depth a few patches of low vp and vs and high vp vs between 10 to 30 km depth have also been detected on the causative 45 south dipping north wagad fault nwf for the 2001 mainshock which may be attributed to a fluid filled fractured rock matrix

the geochemistry of trace elements in geothermal fluids iceland abstract trace element geochemistry was studied in geothermal fluids in iceland the major and trace element compositions of hot springs sub boiling and two phase liquid and vapor wells from 10 geothermal areas were used to reconstruct the fluid composition in the aquifers at depth aquifer fluid temperatures ranged from 4 to 300 c ph values between 4 5 and 9 3 and fluids typically contained total dissolved solids

the chemistry of geothermal waters in iceland ii mineral equilibria and independent variables controlling water compositions abstract the major element chemistry of icelandic geothermal waters is predictable provided two parameters are known this follows from an attainment of or a close approach to an overall chemical equilibrium in the geothermal systems at temperatures as low as 50 c it is considered that the geothermal system composition temperature and kinetic factors determine which alteration minerals form the system composition is not so much fixed by rock composition as by the rate of leaching of the various constituents from the fresh rock and the composition of inflowing water the water chemistry is determined by the system composition and the external variables acting on the system they include temperature and the mobility of chloride pressure which theoretically should be regarded as an external variable has insignificant effect on water compositions in the range 1 200 bars occurring in the geothermal systems

the sao vicente earthquake of 2008 april and seismicity in the continental shelf off se brazil further evidence for flexural stresses summary the continental margin and shelf of most stable intraplate regions tend to be relatively more seismically active than the continental interior in the southeast continental margin of brazil a seismiczoneextendsfromriograndedosultoespeismicactivityoccurring mainly along the continental slope and suggesting a close relationship with flexural stresses caused by the weight of the sediments in this region earthquakes with magnitudes larger than 5m b occurevery20 25yr onaverage thefocalmechanismsolutionsofpreviousearthquakes in this zone indicated reverse faulting on planes dipping approximately 45 with horizontal p axes the recent 5 2m b earthquake of 2008 april 23 occurred 125 km south of s ao vicente and was well recorded by many stations in se brazil as well as at teleseismic distances in north america and africa its focal depth was 17 km locating the hypocentre in the lower crust a well determined focal mechanism solution shows one vertical nodal plane and one subhorizontal nodal plane thep a ndt axes exhibit large dips which were confirmed by ar egional moment tensor inversion this unusual orientation of the fault mechanism can be attributed to a rotation of the principal stress directions in the lower crust caused by flexural effects due to the load of recent sedimentation

a three dimensional numerical model of the waiotapu waikite and reporoa geothermal areas new zealand abstract a large scale three dimensional numerical model of the waiotapu waikite and reporoa geothermal fields new zealand is presented the model covers an area of 450 km 2 and extends to a depth of about 3 6 km it is based on geological geophysical and geochemical data and related interpretations available in the literature the model has been calibrated by varying its permeability structure and the fluid and heat input at its base so that the temperature distribution in the model associated with the convective and advective fluid flow matches the natural state conditions in the three fields good agreement has been obtained between model results and measured downhole temperature data as well as reproducing the location and magnitude of the surface heat discharge for each field in the best fit model 665 kg s of deep thermal fluid is transferred to the surface and to concealed shallow aquifers the subsurface extent of the geothermal reservoirs can be assessed from model blocks at temperatures greater than 220 c the waiotapu reservoir covers about 30 km 2 at a depth of 1 km below sea level whereas the hot zone in the reporoa caldera associated with the reporoa reservoir extends over about 13 km 2 a separate deep thermal upflow is required in the model in order to get a satisfactory match to temperatures in the reporoa field the modelling study shows that the waikite field is an outflow from the waiotapu field and the high temperature region beneath the waikite field only appears at shallow depths 500 mrl and above the model therefore well defines the waiotapu reporoa geothermal system which hosts the three geothermal fields at waiotapu waikite and reporoa

tectonics and crustal structures related to bhuj earthquake of january 26 2001 based on gravity and magnetic surveys constrained from seismic and seismological studies abstract gravity and magnetic data of the kachchh basin and surrounding regions have delineated major e w and nw se oriented lineaments and faults which are even extending up to plate boundaries in the north arabian sea and western boundary of the indian plate respectively the epicentral zone of bhuj earthquake and its aftershocks is located over the junction of rann of kachchh and median uplifts viz kachchh mainland and wagad uplifts which are separated by thrust faults gravity data with constraints from the results of the seismic studies along a profile suggest that the basement is uplifted towards the north along thrust faults dipping 40 60 south similarly gravity and magnetic modeling along a profile across wagad uplift suggest south dipping 50 60 basement contacts separating rocks of high susceptibility and density towards the north one of these contacts coincides with the fault plane of the bhuj earthquake as inferred from seismological studies and its projection on the surface coincides with the e w oriented north wagad thrust fault a circular gravity high in contact with the fault in northern part of the wagad uplift along with high amplitude magnetic anomaly suggests plug type mafic intrusive in this region several such gravity anomalies are observed over the island belt in the rann of kachchh indicating their association with mafic intrusions the contact of these intrusives with the country rock demarcates shallow crustal inhomogeneities which provides excellent sites for the accumulation of regional stress a regional gravity anomaly map based on the concept of isostasy presents two centers of gravity lows of 11 to 13 mgal 10 5 m s2 representing mass deficiency in the epicentral region their best fit model constrained from the receiver function analysis and seismic refraction studies suggest crustal root of 7 8 km deep crustal inhomogeneity under them for a standard density contrast of 400 kg m3 it is therefore suggested that significant amount of stress get concentrated in this region due to a buoyant crustal root b regional stress due to plate tectonic forces and c mafic intrusives as stress concentrators and the same might be responsible for the frequent and large magnitude earthquakes in this region including the bhuj earthquake of january 26 2001

boiling colloid nucleation and aggregation and the genesis of bonanza au ag ores of the sleeper deposit nevada a deep parent composition for bonanza oreforming fluids at the sleeper deposit was calculated by the computer program solveq using fluid inclusion microthermometric and gas data and by assuming equilibrium with the following minerals present in vein samples below the bonanza zones gold chalcedony adularia pyrite chalcopyrite and acanthite the calculated dissolved gold content of 295 ppb is approximately 2 orders of magnitude higher than that assumed for typical geothermal systems thus a gold enriched fluid appears to have been a principal factor in the genesis of bonanza au ag ores at the sleeper deposit geochemical modelling of possible ore forming processes using the computer program chiller with the reconstructed ore forming solution as a starting composition indicates that boiling most closely reproduces observed minerals and their relative abundances in bonanza ores the constraint imposed by the association of amorphous silica with gold precludes all of the mixing scenarios modelled such as mixing with cold and steam heated groundwaters acid sulfate co2 rich modelling indicates that boiling of a gold rich deep solution leads to rapid gold precipitation and that the amount of gold precipitated initially is large relative to other minerals these factors apparently led to nucleation of colloidal gold particles instead of in situ gold deposition or coprecipitation with other phases gold colloids apparently were entrained in the upward flowing hydrothermal solutions and grew as they travelled upon reaching a critical size 10 100 nm they were deposited due to orthokinetic aggregation at an elevation and temperature at which amorphous silica was nucleating and aggregating

variations of seismic velocities in the kachchh rift zone gujarat india during 2001 2013 abstract we herein study variations of seismic velocities in the main rupture zone mrz of the mw 7 7 2001 bhuj earthquake for the time periods 2001 05 2006 08 2009 10 and 2011 13 by constructing dvp dvs and d vp vs tomograms using high quality arrival times of 28 902 p and 28 696 s waves from 4644 precise jhd joint hypocentral determination relocations of local events differential tomograms for 2001 05 reveal a marked decrease in seismic velocities low dvp low dvs and high d vp vs in the mrz at 5 35 km depths during 2001 10 which is attributed to an increase in crack fracture density higher pore fluid pressure resulted from the intense fracturing that occurred during the mainshock and post seismic periods while we observe a slight recovery or increase in seismic velocities 2011 13 this could be related to the healing process lower pore fluid pressure due to sealing of cracks of the causative fault zone of the 2001 bhuj mainshock the temporal reduction in seismic velocities is observed to be higher at deeper levels more fluid enrichment under near lithostatic pressure than that at shallower levels fluid source for low velocity zone lvz at 0 10 km depths with high d vp vs could be attributed to the presence of meteoric water or soft alluvium sediments with higher water content while fluid source for lvz at 10 35 km depths could be due to the presence of brine fluids released from the metamorphic dewatering and volatile co2 emanating from the crystallization of carbonatite melts in the asthenosphere in fractures and pores we also imaged two prominent lvzs associated with the katrol hill fault zone and island belt fault zone extending from shallow upper crust to sub crustal depth which might be facilitating the deeper circulation of metamorphic fluids volatile co2 thereby the generation of lower crustal earthquakes occurring in the kachchh rift zone

three dimensional seismic velocity imaging of the kachchh rift zone gujarat india implications toward the crustal mafic pluton induced intraplate seismicity abstract three dimensional tomographic images of seismic velocities have been constructed for the 2001 mw7 7 bhuj earthquake region using data from a dense 58 station seismograph network during 2001 16 two distinct prominent high velocity anomalies 10 14 increase in vp and vs and 10 11 decrease in vp vs have been mapped at 2 40 km depths below the banni and wagad uplift regions which could be attributed to mafic plutons we also image several high velocity zones intrusive mafic rocks and some low velocity patches meteoric water metamorphic fluids volatile co2 within the main rupture zone of the 2001 bhuj earthquake where maximum confinement of seismicity is noticed we propose that stresses induced by mafic plutons in response to the n s compression of the indian plate might have resulted in a stress regime near to critical for thesub parallel rift associated fault system within the main rupture zone thereby generating small to large earthquakes through small stress perturbations caused by crustal fluid flows and stress transfer

mineralization and hydrothermal history of the tiwi geothermal system philippines tiwi is one of several large geothermal fields in the philippines in 1992 the drilling of matalibong 25 provided nearly 1 650 m of continuous core from the geothermal reservoir a maximum temperature of 275 c at 1 829 m and intense hydrothermal alteration were encountered in this well six stages of alteration and vein mineralization have been documented in the cored portion of the well the earliest stage which reflects the initial development of the system is represented by the deposition of chalcedony and clays stage 1 the transition to a high temperature environment is marked by the appearance of sericite stage 2 deposited by steam heated waters stage 3 reflects episodic cycles of fluid upwelling and boiling followed by the incursion of cooler fluids veins deposited by boiling fluids are filled with quartz adularia epidote pyrite and base metal sulfides whereas heating of the recharging fluids led to the deposition of calcite and or anhydrite maximum temperatures of fluid inclusions trapped in two quartz crystals deposited by the upwelling fluids range from 325 to 332 c temperatures varied widely during the recharge phase of these cycles fluid inclusions trapped in calcite and anhydrite suggest that mineral deposition occurred at temperatures ranging from 333 c to less than 270 c fluid inclusion salinities indicate that seawater dominated below a depth of 1 600 m whereas fresh waters dominated at shallower depths gaseous species trapped in these inclusions were released by crushing or thermal decrepitation and analyzed with a quadrupole mass spectrometer co2 ch4 and n2 ar ratios indicate that the gaseous species trapped in calcite and anhydrite were derived primarily from meteoric and crustal sources in contrast gaseous species in quartz from matalibong 25 and advanced argillic assemblages from other tiwi wells have magmatic and crustal origins stage 4 represents a second major episode of sericite deposition subsequent mineralization consisted of wairakite epidote followed by actinolite and then calcite stage 5 the presence of actinolite implies that temperatures exceeded 300 c at the end of this stage thermochemical modeling indicates that the modern stage 6 fluids are again in equilibrium with sericite 40ar 39ar spectrum dating of stage 3 adularia from three depths has been combined with the mineral parageneses and fluid inclusion homogenization temperatures to constrain the thermal history of the geothermal system taken together these data record the deposition of adularia at 330 c between 314 and 279 ka minor cooling followed by reheating to produce stage 5 actinolite at 200 to 220 ka incursion of marginal waters and cooling to 235 c by 190 ka a long period of quiescence to 50 ka and finally development of the modern thermal regime at 10 to 50 ka in response to a recent subvolcanic intrusion

three dimensional ground motion modelling in the kachchh rift zone gujarat india abstract the strong motion dataset of the 6 april 2006 bhuj aftershock of mw5 5 from 16 three component accelerograph stations are used here to perform a detailed ground motion modelling in the kachchh rift basin first we estimate the 1 d velocity structure model down to the bedrock at 16 accelerograph sites through the genetic algorithm inversion of strong motion waveforms then a 3 d velocity structure model of the basin is constructed using the modelled 1 d velocity structure and constraints from earlier seismological vs30 estimation by ps logging and masw and seismic exploration studies in the region we modelled low frequency 0 1 1 hz ground motions excited by the 6 april 2006 event using the finite difference method fdm assuming a point source to access the robustness of the constructed velocity structure model at most of the stations the observed and simulated velocity waveforms are found to be in good agreement in terms of both amplitude and ground motion duration we also computed synthetic ground velocities at numerous locations within the basin for both the 2001 bhuj mainshock finite fault source and the 2006 aftershock point source cases using the 3 d velocity structure model for both the cases we notice significant amplifications of amplitudes and elongation of shaking at stations lying within the basin while smaller amplifications are noticed at stations away from the basin our fdm modelling for the 2001 bhuj mainshock at lower frequency

shear wave velocity structure in the northern basin and range province from the combined analysis of receiver functions and surface waves a new method based on the joint inversion of receiver functions and surface wave phase velocities results in well determined shear velocity structures that are consistent with the compressional wave structure gravity heat flow and elevation data in the northern basin and range this new inversion method takes advantage of average velocity information present in the surface wave method and differential velocity information contained in the receiver function method thus min imizing the nonuniqueness problem that results from the velocity depth trade off an unusually thick 38 kin and relatively faster crust and upper mantle are found in central and eastern nevada compared to the thin 28 to 34 km and slower crust and upper mantle of the western basin and range we interpret the regions of thicker and faster crust and upper mantle as zones that have undergone less cenozoic ex tension relative to the surrounding regions to the west and north the thick crust and consequently greater depth to the dense mantle material is consistent with the gravity low pattern in central and eastern nevada simple gravity modeling shows both local and regional isostatic compensation occur within 40 km of the surface indicating a near classical airy type of compensation in the province we analyze in detail the shear wave s wave velocity model derived from the receiver functions at station bmn and compressional wave p wave velocity models derived from the 1986 passcal experiment in northwestern nevada the most interesting feature of these models is the presence of negative velocity gradients in the s wave model with no corresponding velocity decrease in the p wave models between depths of 10 and 24 km this combined velocity model may be explained by high pore fluid pressures at these depths this model favors a layered fluid porosity model proposed in the literature to explain extensive middle to lower crust conti nental seismic reflections and high electrical conductivity an upper mantle grada tional low velocity zone is present between 32 and 38 km in the s wave model this upper mantle shear wave low velocity zone is consistent with partial melt which may be the source material for magmatic underplating in this region

bacterial s layer preservation and rare arsenic antimony sulphide bioimmobilization in siliceous sediments from champagne pool hot spring waiotapu new zealand siliceous sinter loose sediments and suspended flocs in champagne pool an anoxic hot 75 c spring at waiotapu new zealand are composed of opaline silica and metal rich sulphides that contain many well preserved mineralized microbes detailed analysis by transmission electron microscopy and energy dispersive spectrometry has shown that bacterial cell wall and capsular material is preserved by the immobilization of high levels of as sb and s in the organic matrix calculation of the probable metal species in the spring water suggests that arsenic and antimony are present in solution as negative and neutrally charged sulphide or hydroxide complexes such as has 2 s 4 h 3 aso 3 and hsb 2 s 4 the early adsorption of these complexes onto reactive groups on the bacterial surface may be paramount in the excellent preservation of cell morphology as biomineralization progresses biomineral composition commonly becomes dominated by the precipitation of a supersaturated al rich amorphous silica phase biomineralization commonly preserves s layers an ordered mosaic of proteins on the outer surface of the cell wall these are the finest ultrastructure details thus far found in microbes preserved by hydrothermal mineralization and can be used as an aid to identify microfossils the s layers preserved here probably belong to clostridium thermohydrosulfuricum or desulfotomaculum nigrifacans

mineralogy fluid inclusions and s pb h o isotopes of the erdaokan ag pb zn deposit duobaoshan metallogenic belt ne china implications for ore genesis abstract the recently discovered erdaokan ag pb zn deposit is located in the duobaoshan gold copper metallogenic belt in the eastern part of the central asian orogenic belt the ore bodies occur mainly as veins hosted in the breccia three stages of mineralization including early magnetite quartz pyrite middle silver sulfide bitumen quartz and late carbonate stages were recognized here we report results from electron microprobe analysis epma s pb h o isotopes and fluid inclusions studies to gain insights into the salient characteristics of the ore mineralization and mechanism of silver precipitation the silver occurs mainly as argentite pyrargyrite and invisible silver in the tetrahedrite grains in which ag fe and as isomorphically substituted cu zn and sb respectively the homogenization temperatures of fluid inclusions in the early middle and late stage mineralisation range from 96 to 179 c 78 to 178 c and 98 to 191 c respectively the fluid salinities vary from 0 35 to 5 54 wt nacl equiv the 34s values of the pyrite and galena show a range from 0 97 to 9 31 206pb 204pb vary from 18 0125 to 18 1864 207pb 204pb from 15 561 to 15 081 and 208pb 204pb from 38 0445 to 37 6979 with a mean of 18 0298 15 5125 and 37 7281 respectively the d and 18owater values of the quartz from the ore body range from 119 1 to 109 7 and 4 64 to 1 98 respectively based on these results we argue that the ore forming fluids were derived from a magmatic source with fluid mixing as the dominant mechanism for silver precipitation involving hydrocarbon fluid interaction as inferred from the presence of bitumen in the ore

crustal and lithospheric thinning beneath the seismogenic kachchh rift zone gujarat india its implications toward the generation of the 2001 bhuj earthquake sequence a high resolution passive seismic experiment in the kachchh rift zone of the western india has produced an excellent dataset of several thousands teleseismic events from this network 500 good teleseismic events recorded at 14 mobile broadband sites are used to estimate receiver functions for the 30 310 back azimuth ranges which show a positive phase at 4 5 6 1 s delay time and a strong negative phase at 8 0 11 0 s these phases have been modeled by a velocity increase at moho i e 34 43 km and a velocity decrease at 62 92 km depth the estimation of crustal and lithospheric thicknesses using the inversion of stacked radial receiver functions led to the delineation of a marked thinning of 3 7 km in crustal thickness and 6 14 km in lithospheric thickness beneath the central rift zone relative to the surrounding un rifted parts of the kachchh rift zone on an average the kachchh region is characterized by a thin lithosphere of 75 9 5 9 km the marked velocity decrease associated with the lithosphere asthenoshere boundary lab observed over an area of 120 km 80 km and the isotropic study of xenoliths from kachchh provides evidence for local asthenospheric updoming with pockets of partial melts of co2 rich lherzolite beneath the kachchh seismic zone that might have caused by rifting episode at 88 ma and the associated deccan thermal plume interaction at 65 ma episodes thus the coincidence of the area of the major aftershock activity and the moho as well as asthenospheric upwarping beneath the central kachchh rift zone suggests that these pockets of co2 rich lherzolite partial melts could perhaps provide a high input of volatiles containing co2 into the lower crust which might contribute significantly in the seismo genesis of continued aftershock activity in the region it is also inferred that large stresses in the denser and stronger lower crust at 14 34 km depths induced by ongoing banni upliftment crustal intrusive marked lateral variation in crustal thickness and related sub crustal thermal anomaly play a key role in nucleating the lower crustal earthquakes beneath the kachchh seismic zone

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

quantifying mixing boiling degassing oxidation and reactivity of thermal waters at vonarskard iceland abstract the chemical composition of geothermal fluids may be altered upon ascent from the reservoir to surface by processes including boiling degassing mixing oxidation and water rock interaction in an attempt to quantify these processes a three step model was developed that includes 1 defining the composition of the end member fluid types present in the system 2 quantifying mixing between the end members using non reactive elemental concentrations and enthalpy and 3 quantifying the changes of reactive elements including degassing oxidation and water rock interaction the model was applied to geothermal water at vonarskard iceland for demonstration having temperatures of 3 98 c ph of 2 15 9 95 and tds of 323 2250 ppm and was thought to be produced from boiled reservoir water condensed steam and non thermal water most geothermal water represented mixture of non thermal water and condensed steam whereas the boiled reservoir water was insignificantly mixed co2 and h2s degassing was found to be quantitative in steam heated water with oxidation of h2s to so4 also occurred in contrast major rock forming elements are enriched in steam heated water relative to their mixing ratios suggesting water rock interaction in the surface zone boiled reservoir water observed in alkaline hot springs have however undergone less geochemical changes upon ascent to surface and within the surface zone

new field evidence bearing on the origin of the el laco magnetite deposit northern chile a reply the el laco magnetite deposit has been interpreted as lava flows and feeder dikes formed from iron oxide magma but more recently as a product of metasomatic replacement open pit exposure created at laco sur during the 1990s reveals that the massive magnetite contains magnetite veined blocks and smaller fragments of altered andesitic volcanic rock clearly supporting the replacement origin open space growth of magnetite and pyroxene along the walls of chimney structures and veins within magnetite indicates precipitation from aqueous fluid rather than from gas alone the native sulfur bearing cristobalite alunite alteration widespread at el laco and broadly contemporaneous with magnetite formation is recognized as part of a steam heated horizon generated in the vadose zone above a paleowater table consequently the magnetite replacement must have taken place beneath the paleowater table but probably 300 m beneath the paleosurface thus magnetite deposition at or immediately beneath the paleosurface is precluded the main outstanding question is how hot hypersaline brine the probable ore forming fluid at el laco attained such shallow crustal levels within a high volcanic edifice without undergoing the extensive groundwater dilution documented from most shallowly preserved hydrothermal systems

groundwater dilution and residence times and constraints on chloride source in the mokai geothermal system new zealand from chemical stable isotope tritium and 36cl data the mokai geothermal system new zealand is located within a volcanic collapse structure comprised of flat lying silicic rocks the deep chloride fluid rises in the south inside the caldera margin near the surface the fluid flows laterally more than 12 km to the north because of the hydraulic gradient caused by 300 m of relief the maximum measured temperature of the production wells is near 323 c at 2500 m depth whereas temperatures in two wells on the northern margin of the upflow are 200 c with thermal inversions at 350 and 1000 m indicating lateral flow these two marginal wells have about 50 of the chloride of the deep fluid indicating dilution by cold ground water chloride bearing springs discharge 6 km north of the zone of upflow and are even further diluted by cold groundwater than the wells on the margin of the system the tritium data in this hydrologically rather simple system indicate that there is a mean residence time of greater than 100 years for the groundwater diluent also older water is mixed with 25 of young thermonuclear post 1955 water before the mixture dilutes outflowing chloride fluid from the deep system the deep chloride fluid has a 36cl cl ratio of 2 6 10 15 and a 36cl concentration of 106 atoms per 10 6 kg this fluid has a lower ratio by a factor of 90 and a higher absolute concentration by a factor of 7 than present day stream water however the marginal wells have been diluted by groundwater with at least 500 36cl atoms per 10 6 kg 30 times richer in 36cl than present day stream waters this spike is most likely due to circulation of precipitation formed during thermonuclear testing to depths of 1000 m though the component with the 36cl spike only makes a moderate 25 contribution to the groundwater diluent most of the diluent is much older pre 1955 the amount of 36cl in the deep fluid at mokai is 5 10 times less than that predicted from a calculation of the neutron fluxes in the silicic reservoir and underlying greywacke basement rocks this indicates that the chloride was not derived from host rock leaching in the upper 3 km rather the fluids have interacted with more primitive rocks below the drilled depths of the taupo volcanic zone with the chloride possibly derived from a magmatic brine

the ad1315 tarawera and waiotapu eruptions new zealand contemporaneous rhyolite and hydrothermal eruptions driven by an arrested basalt dike system a series of large hydrothermal eruptions occurred across the waiotapu geothermal field at about the same prehistoric time as the ad1315 kaharoa rhyolite magmatic eruptions from tarawera volcano vents 10 20 km distant triggering of the waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent ngapouri fault the kaharoa rhyolite eruptions are now recognised as primed and triggered by multiple basalt intrusions beneath the tarawera volcano a 1000 t day pulse of co2 gas is recorded by alteration mineralogy and fluid inclusions in drill core samples from waiotapu geothermal wells this co2 pulse is most readily sourced from basalt intruded at depth and although not precisely dated it appears to be associated with the waiotapu hydrothermal eruptions we infer that the hydrothermal eruptions at waiotapu were primed by intrusion of the same arrested basalt dike system that drove the rhyolite eruptions at tarawera this dike system was likely similar at depth to the dike that generated basalt eruptions from a 17 km long fissure that formed across the tarawera region in ad1886 fault ruptures that occurred in the waiotapu area in association with both the ad1886 and ad1315 eruptions are considered to be a result rather than a cause of the dike intrusion processes

co2 discharge from the bottom of volcanic lake rotomahana new zealand 1 from april 2010 to february 2011 co2 flux surveys were performed on lake rotomahana new zealand the area has been hydrothermally active with fumaroles and sublacustrine hydrothermal activity before and since the eruption of mt tarawera in 1886 the total co2 emission from the lake calculated by sequential gaussian simulation is 549 72 t d 1 two different mechanisms of degassing diffusion through the water air interface and bubbling are distinguished using a graphical statistical approach the carbon dioxide budget calculated for the lake confirms that the main source of co2 to the atmosphere is by diffusion covering 94 5 of the lake area mean co2 flux 25 g m 2 d 1 and to a lesser extent bubbling mean co2 flux 1297 g m 2 d 1 mapping of the co2 flux over the entire lake including over lake floor vents detected during the survey correlates with eruption craters formed during the 1886 eruption these surveys also follow regional tectonic patterns present in the southeastern sector of lake rotomahana suggesting a deep magmatic source 10 km for co2 and different pathways for the gas to escape to the surface the values of 13cco2 2 88 and 2 39 confirm the magmatic origin of co2

sulfur redox chemistry governs diurnal antimony and arsenic cycles at champagne pool waiotapu new zealand abstract champagne pool a sulfidic hot spring in new zealand exhibits distinct diurnal variations in antimony sb and arsenic as concentrations with daytime high and night time low concentrations to identify the underlying mobilization mechanisms five sites along the drainage channel of champagne pool were sampled every 2 h during a 24 h period temporal variations in elemental concentrations and sb as and sulfur s speciation were monitored in the discharging fluid total trace element concentrations in filtered and unfiltered samples were analyzed using icp ms and sb as and s species were determined by ic icp ms sulfur speciation in the drainage channel was dominated by thiosulfate and sulfide at night while sulfate dominated during the day the distinct diurnal changes suggest that the transformations are caused by phototrophic sulfur oxidizing bacteria these bacteria metabolize thiosulfate and sulfide in daylight to form sulfate and as suggested by modeling with phreeqc elemental sulfur sulfide consumption during the day results in undersaturation of antimony sulfides which triggers the additional release of dissolved sb for as diurnal cycles were much more pronounced in speciation than in total concentrations with di and trithioarsenate forming at night due to excess sulfide and monothioarsenate forming from arsenite and elemental sulfur during the day sulfur speciation was thus found to control sb and as in terms of both solubility and speciation

evolution of high level magmatic hydrothermal systems new insights from ore paragenesis of the veladero high sulfidation epithermal au ag deposit el indio pascua belt argentina

sediment thicknesses and qs vs qp relations in the kachchh rift basin gujarat india using sp converted phases delineation of the top sedimentary structure and its qs vs qp relationship using the travel time difference of direct s and converted sp phase is key to understanding the seismic hazard of any sedimentary basin area we constructed filtered displacement waveforms from local etna episensor acceleration recordings as well as local velocity recordings of aftershocks of the 2001 bhuj earthquake recorded by the kachchh seismological network of the national geophysical research institute ngri hyderabad india during 2001 2004 stations are within 15 70km of epicenters and the resulting displacement waveforms are generally simple displaying prominent p sp and s wave pulses particle motion of p and s waves suggest near vertical raypaths consistent with preliminary depth estimates the direct s wave on the horizontal component is characterized by lower frequency content than the converted sp phase on the vertical component this difference in frequency content between s and sp phases can be explained in terms of different attenuation effects for p and s waves in the unconsolidated sediments the sp phase is generated by s to p phase conversion at the base of mesozoic sediments of the kachchh basin travel time inversion velest of 2565 p and 2380 s arrivals from 658 well located aftershocks recorded at 8 14 three component local seismic stations led to 1 d velocity models indicated very slow sediments in the upper 0 2 km depth range vp 2 92 km s and vs 0 90 km s and an increasing trend of velocities with depth at 2 40 km depth the estimated sediment thicknesses beneath 12 accelerograph and 6 seismograph sites from the estimated velocity model and the travel time difference between s and converted sp phases reaches a maximum of 1 534 0 117 km beneath bandri near the location of 2001 bhuj mainshock and attains a minimum sediment thickness of 0 858 0 104 km beneath ramvav and burudia the spectral ratios between sp and s from 159 three component accelerograms have been used to study seismic wave attenuation in the kachchh rift basin the estimated qs vs qp relations for 12 accelerograph sites vary from qs 0 184 qp at chobari to qs 0 505 qp at dudhai for stations chobari chopdwa jahawarnagar vondh and tapar the spectral ratio slopes and hence the calculated qs vs qp relations are effectively the same and the correlation coefficients are quite high 0 91 0 93 stations adhoi manfara new dudhai dudhai and sikara have similar qs vs qp relationships to each other and also have high correlation coefficients 0 78 0 87 the spectral ratios for stations anjar and ramvav are small and poorly constrained resulting in less reliable qs vs qp relations this could be due to noisy data fewer available waveforms or scattering due to velocity heterogeneities and or interface irregularities

a possible origin of intraplate earthquakes in the kachchh rift zone india since the 2001 mw7 7 bhuj earthquake abstract we herein use the joint inversion of p receiver functions and fundamental mode group velocity dispersion data 9 70 s of rayleigh and love waves to estimate crustal and lithospheric thicknesses at twenty three component mobile broadband stations in kachchh gujarat modeled moho depths range from 35 to 43 km while lithospheric thicknesses vary from 64 to 106 km the main result of our modelling is the delineation of a marked crustal 2 4 km as well as lithospheric 10 20 km thinning and a 2 6 drop in vs across the lithosphere asthenosphere boundary lab within the samkhiali graben associated with gravity high underlying the central kachchh rift zone krz where 95 of the continued aftershock activity took place since 2001 such a large drop in vs could be attributed to the presence of carbonatite melts in the upper mantle our modeling reveals a 4 km crustal thinning below the central krz and a 4 km crustal thickening below the surrounding riftless regions this kind of crustal structure is inferred to induce large flexural deviatoric stresses 50 100 mpa in the upper crust thereby these stresses in the presence of regional plate tectonic stresses can bring the samkhiali graben below the central krz near to the critical stress level while stress transfer meteoric water in the upper crust and metamorphic fluid as well volatile co2 flows in the lower crust provide the required triggering effect to the critically stressed graben structure down to 35 km depth for generating continued aftershock activity in the kachchh rift zone since 2001 we also propose that the deeper circulation of volatile co2 through the inferred conduit related to the 65 ma deccan plume activity extending from lower crust down to asthenosphere plays a key role in the generation of uninterrupted occurrence of earthquakes in the kachchh rift zone gujarat india

the evolution of the waiotapu geothermal system new zealand based on the chemical and isotopic composition of its fluids minerals and rocks abstract the waiotapu geothermal system is hosted by silicic rocks of the taupo volcanic zone new zealand exploration drilling in the late 1950s down to 1100 m provided physical information on the system measured temperatures show a boiling profile to 295 c with shallow inversions particularly in the north total discharge fluid samples were collected the geothermometry and measured temperatures show that fluids derive mainly from a shallow 400 m deep reservoir at about 225 c petrologic study of drillcore samples recovered from seven wells reveals an alteration assemblage of quartz and albite adularia with a variable distribution of chlorite pyrite calcite zeolites epidote pyrrhotite sphene leucoxene apatite and minor base metal sulfides white mica is a late overprint particularly well developed at shallow depths surficial alteration of kaolin cristobalite alunite and smectite clays reflect alteration by acid sulfate steam heated waters the activities of components in minerals determined from microprobe analyses and composition activity relations and fluids speciated to reservoir conditions indicate equilibrium now exists between the fluids and white mica the na k ratio of the fluid is being controlled by dissolution of albite and adularia while its h 2 h 2 s ratio is buffered by pyrite replacing pyrrhotite the fluids are now slightly undersaturated with respect to calcite the present deep fluids boil adiabatically from at least 300 c to 230 c at depths of 500 m this ascending chloride fluid is variably diluted by a steam heated water of zero chloride that lies over and occurs on the margin of the system like a discontinuous umbrella the steam heated water is relatively co2 rich 0 1 m the cooling at shallow levels by this mixing has shifted the alteration from albite adularia stability to white mica stability this shift is enhanced by the co2 rich nature of the diluent dilution of ascending chloride fluids by shallow waters is also supported by the oxygen and hydrogen isotopic composition of the mixture with the deep fluid being enriched in 18o and d from local meteoric by 7 and 10 respectively the patterns in whole rock 18o indicate that they were largely shifted in isotopic composition prior to incursion of steam heated waters possibly induced by a series of hydrothermal eruptions 900 years ago in contrast the 18o composition of late vug calcite indicates its formation is related to the initial incursion of steam heated groundwater and subsequent cooling this is supported by fluid inclusion evidence the d shift from local groundwater composition and the 13c composition of co2 determined from calcite 4 to 6 may be evidence for a magmatic input to the meteoric convection cell the shallow portion of the waiotapu geothermal system has recently evolved both chemically and physically by incursion of fluids from a steam heated carapace continued refluxing of these relatively cool hybrid fluids progressively deeper with their recycled co2 content will hasten hydrolytic leaching in contrast to a single pass of adiabatically cooling deep fluids this action accompanied by argillic alteration may eventually seal the deeper portions of the system hastening its demise there is evidence for similar events occurring in the fossil environment at epithermal depths

boiling and dilution in the shallow portion of the waiotapu geothermal system new zealand abstract the waiotapu geothermal system is the largest in terms of surface extent and heat flow 17 km2 and 600 mw respectively of the 20 major geothermal systems in the taupo volcanic zone new zealand two extinct dacite cones and a rhyolite dome rise about 500 m above the waiotapu valley the majority of thermal features occurs in the valley over a relief of only 100 m and lies within coincident apparent resistivity and 30 m depth thermal anomalies thermal features comprise near neutral ph chloride springs often boiling acid sulfate springs and mud pools and mixed waters the latter including both bicarbonate chloride and acid sulfate chloride springs the majority of the sulfate discharges to the surface in the northern higher altitude area while most chloride that reaches the surface does so in the southern portion of the system comparison of measured and calculated surface chloride flux the latter from measured heat flow and reservoir chloride concentrations indicates that at least half of the deep chloride does not discharge at the surface but flows laterally to the south at shallow depths mixing with groundwater the composition of well discharges indicates a shallow 400 m reservoir of chloride fluid about 1350 mg cl kg at 230 c is diluted by a co2 rich steam heated water nil chloride at about 160 c the latter located on the margins of the system this same dilution trend is apparent from the compositional variation and k na and k mg geothermometry of hot spring waters however there is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels and very near the surface steam heated acid sulfate waters mix with the upflow boiling of the deep chloride fluids prior to dilution results in the stabilization of k feldspar in contrast dilution at shallower depths by the steam heated waters both co2 rich and acid sulfate leads to the water compositions initially shifting to k mica and interstratified clay stability and to kaolinite stability with further dilution and temperature decrease the composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core although boiling occurs at deeper levels and up to the surface in the upflow zone at waiotapu mixing is also common and is the dominant process on the margin and in the near surface portion of the system boiling of deep chloride fluid is very common in the upper 1 2 km of the upflow zone of most geothermal systems though it may be quenched by mixing with marginal waters either cold groundwater in high relief terrane or steam heated waters in areas of lower relief co2 rich steam heated waters are common on the margins of systems and will generally underlie the near surface acid sulfate steam heated waters interaction with co2 rich waters will form k mica and interstratified clays while acid sulfate waters cause kaolinite and even alunite to form the former assemblage is commonly associated with typical low sulfidation epithermal gold mineralization as wallrock alteration where gold bearing veins comprise adularia and illite in contrast kaolinite is rare and alunite absent from a direct spatial and genetic association with gold mineralization in this environment this implies that mixing of the deep neutral ph chloride fluid with surficial acid sulfate waters does not commonly lead to ore grade gold deposition mixing with and cooling by co2 rich steam heated waters leads to clay stability accounting for the large halos of clay alteration and low grade metal anomalies which often surround veins of high gold grade in contrast mixing with surficial acid sulfate waters is unlikely to cause precious metal mineralization because the chloride fluids have already lost the majority of their gold through deeper boiling and dilution

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

upper mantle shear velocity structure below northwestern india based on group velocity dispersion abstract we derive a well resolved 1d model of shear wave velocity v s through both linear and nonlinear joint inversions of rayleigh and love wave group velocity dispersion data our best model from the deterministic approach suggests a two layered crust over a half space the upper crust is 13 8 km thick with a shear velocity of 3 22 km s for the lower crust they are 24 9 km and 3 62 km s respectively finally we use a global optimization method very fast simulated annealing to estimate shear wave velocity multiple models give acceptable fits to the observed data a common feature of these models is a low velocity zone lvz with its upper boundary at 60 70 km depth at this depth the temperature depth profile of kachchh cuts the wet peridotite geotherm resulting in increased water content due to partial melting and thus the decreased shear velocity this lvz extends down to a depth of 120 130 km where the temperature depth profile of kachchh cuts the dry peridotite geotherm that leads to a sharp decrease in water content thereby a sharp increase in shear velocity the maximum v s perturbation of 3 in the upper mantle can be explained by the presence of 100 150 k excess temperature beneath northwestern india at 70 120 km depth relative to the adjacent mantle along with the presence of 1 penny shaped melt inclusions probably co 2 rich carbonatite melts in the upper mantle this is likely related to the imprints of the initial deccan reunion plume head that might have moved with india since the deccan volcanism at 65 ma

occurrences of large magnitude earthquakes in the kachchh region gujarat western india tectonic implications abstract moderate to large damaging earthquakes in the peninsular part of the indian plate do not support the long standing belief of the seismic stability of this region the historical record shows that about 15 damaging earthquakes with magnitudes from 5 5 to 8 0 occurred in the indian peninsula most of these events were associated with the old rift systems our analysis of the 2001 bhuj earthquake and its 12 year aftershock sequence indicates a seismic zone bound by two linear trends nnw and nne that intersect an e w trending graben the bouguer gravity values near the epicentre of the bhuj earthquake are relatively low 2 mgal the gravity anomaly maps the distribution of earthquake epicentres and the crustal strain rate patterns indicate that the 2001 bhuj earthquake occurred along a fault within strain hardened mid crustal rocks the collision resistance between the indian plate and the eurasian plate along the himalayas and anticlockwise rotation of the indian plate provide the far field stresses that concentrate within a fault bounded block close to the western margin of the indian plate and is periodically released during earthquakes such as the 2001 m w 7 7 bhuj earthquake we propose that the moderate to large magnitude earthquakes in the deeper crust in this area occur along faults associated with old rift systems that are reactivated in a strain hardened environment

stress perturbation associated with the amazonas and other ancient continental rifts the state of stress in the vicinity of old continental rifts is examined to investigate the possibility that crustal structure associated with ancient rifts specifically a dense rift pillow in the lower crust may modify substantially the regional stress field both shallow 2 0 2 6 km depth breakout data and deep 20 45 km depth crustal earthquake focal mechanisms indicate a n to nne maximum horizontal compression in the vicinity of the paleozoic amazonas rift in central brazil this compressive stress direction is nearly perpendicular to the rift structure and represents a 75 rotation relative to a regional e w compressive stress direction in the south american plate elastic two dimensional finite element models of the density structure associated with the amazonas rift as inferred from independent gravity modeling indicate that elastic support of this dense feature would generate horizontal rift normal compressional stresses between 60 and 120 mpa with values of 80 100 mpa probably most representative of the overall structure the observed 75 stress rotation constrains the ratio of the regional horizontal stress difference to the rift normal compressive stress to be between 0 25 and 1 0 suggesting that this rift normal stress may be from 1 to 4 times larger than the regional horizontal stress difference a general expression for the modification of the normalized local horizontal shear stress relative to the regional horizontal shear stress shows that the same ratio of the rift normal compression relative to the regional horizontal stress difference which controls the amount of stress rotation also determines whether the superposed stress increases or decreases the local maximum horizontal shear stress the potential for fault reactivation of ancient continental rifts in general is analyzed considering both the local stress rotation and modification of horizontal shear stress for both thrust and strike slip stress regimes in the amazonas rift case because the observed stress rotation only weakly constrains the ratio of the regional horizontal stress difference to the rift normal compression to be between 0 25 and 1 0 our analysis is inconclusive because the resultant normalized horizontal shear stress may be reduced for ratios 0 5 or enhanced for ratios 0 5 additional information is needed on all three stress magnitudes to predict how a change in horizontal shear stress directly influences the likelihood of faulting in the thrust faulting stress regime in the vicinity of the amazonas rift a rift normal stress associated with the seismically active new madrid ancient rift may be sufficient to rotate the horizontal stress field consistent with strike slip faults parallel to the axis of the rift although this results in a 20 40 reduction in the local horizontal shear stress within the seismic zone sparse stress data in the vicinity of the seismically quiescent midcontinent rift of the central united states suggest a stress state similar to that of new madrid with the local horizontal shear stress potentially reduced by as much as 60 thus the markedly different levels of seismic activity associated with these two subparallel ancient rifts is probably due to other factors than stress perturbations due to dense rift pillows the modeling and analysis here demonstrate that rift normal compressive stresses are a significant source of stress acting on the lithosphere and that in some cases may be a contributing factor to the association of intraplate seismicity with old zones of continental extension

intra plate seismicity and flexural stresses in central brazil 1 explaining intra plate seismicity is a challenging task different models have been proposed combining weak zones and stress concentration mechanisms here we propose that flexural deformation is a major factor to explain seismicity in central brazil a sw ne oriented seismic zone between the amazon and the sao francisco cratons coincides with high gravity anomalies possibly due to a sw ne belt of thin crust the load from the high density shallow mantle rocks causes upper crustal compressional stresses up to 100 mpa in the 200 km wide seismic zone away from the central zone of horizontal compression extensional stresses in the peripheral bulge balance the regional compression explaining the aseismic areas three other seismic clusters in brazil also correlate with high gravity anomalies suggesting that flexural deformation contributes significantly to explain mid plate seismicity in brazil

geothermal mineral equilibria the dominant reaction determining the chemistry of fluids in a geothermal system of the new zealand type consists of the conversion of primary plagioclase by co2 to calcite and clays with log pco2 15 26 7850 t 273 2 temperature t in c subsequent reactions involving secondary minerals control relative co2 h2s contents the distribution of mineral phases throughout a geothermal system reflects the stepwise conversion of thermodynamically unstable primary phases through a series of intermediate metastable phases to a thermodynamically stable secondary assemblage the relative stabilities of these phases was evaluated on the basis of their solubilities the least soluble aluminiumsilicate representing the thermodynamically most stable phase under a given set of conditions observed assemblages of secondary minerals in geothermal systems represent indicators allowing mineral fluidinteraction conditions to be evaluated on the basis of multi component mineral stability diagrams

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

the goshogake mud volcano field tohoku northern japan an acidic high temperature system related to magmatic volcanism abstract the high temperature 33 98 c highly acidic ph 2 44 2 94 goshogake mud volcano field in akita prefecture northern japan is a mud volcano system associated with the quaternary andesitic composite volcano akita yakeyama the mud volcano features observed in goshogake include salsa ponds gryphons and mud pots this is a rare example of mud volcano systems linked with magmatic volcanism with the full range of landforms observed primarily in low temperature mud volcanism in sedimentary settings the goshogake mud volcano field is probably not a simple hydrothermal system related to a magmatic volcano instead it appears to be a hybrid system sedimentary volcanism linked with deep mud sources and strongly influenced by its surrounding magmatic volcanism the identified mineral species in the sampled mud include quartz group hydrous silica muscovite kaolinite pyrite and sulfur the presence of high temperature silica polymorphs tridymite and cristobalite and or microcrystalline opals opal c opal ct and an amorphous form of silica opal a in the mineralogy indicates that the mud volcano system likely involves conditions and processes such as high temperature hydrothermal circulation dehydration reaction at certain depths underneath the goshogake mud volcano field although the source of the mud is not clearly determined possible options include 1 hydrothermal alteration products of host rocks and sediments 2 fine grained sedimentary layer s at depth or 3 a combination of 1 and 2 in situ measurement of emitted gases from vents detected methane which is possibly linked with the organic rich sedimentary layer s aside from being a product of thermodynamic equilibrium with co2 under the subsurface pressure temperature conditions the increases in d and 18o of water in goshogake mud volcanoes with respect to the values of current meteoric water indicates that the water was derived not only from meteoric water and deviation of the values may be explained by processes such as evaporation and mixing of other waters from deeper sources regarding the driving mechanisms at the goshogake mud volcanoes buoyancy of muddy sediment high fluid pressure under overpressured or under compacted conditions due to rapid sedimentation together with the presence of a gas phase in the sediment could be key factors although the goshogake mud volcano field currently maintains a low level activity resulting in only minor morphological changes of the mud volcano landforms enhanced activities have been documented in the last half century the historical records are inconclusive about the relationship between earthquakes and activity in the goshogake mud volcano field

artists before columbus a multi method characterization of the materials and practices of caribbean cave art abstract this study represents the first positive identification of plant gum binding media in pre columbian art and the first dates from indigenous cave art in the caribbean mona island reveals an extensive and well preserved pre columbian and early colonial subterranean cultural landscape with dense concentrations of newly discovered cave art in up to 30 caves a multi method approach to the research of pigments and binding media charcoal and cave sediments was used to elucidate the technologies chronologies and processes of indigenous art and artists analyses included on site use of a portable x ray fluorescence p xrf device to inform sample selection scanning electron microscopy with energy dispersive x ray spectroscopy sem edx on paint and charcoal samples polarized light microscopy plm for material characterizations and gas chromatography mass spectrometry gc ms and x ray diffraction xrd for detailed chemical analysis of paint structures and composition in addition direct dates of cave art using radiocarbon c14 and uranium thorium u th dating methods are discussed results demonstrate multiple centuries of cave use during indigenous occupation and multiple phases and techniques of mark making in dark zone locations within extensive cave systems visitors set out on pre meditated journeys underground making rock art using pigments from the cave floors which they mixed into complex paints with the addition of plant gums from outside this study is the first of its kind in the caribbean providing insight into native paint recipes material choices and mark making techniques the methods have scope for widespread application and advance the integration of cave art research in archaeology

actively growing siliceous oncoids in the waiotapu geothermal area north island new zealand oncoids that are actively growing in some of the shallow water pools around champagne pool waiotapu new zealand are formed of amorphous silica opal a with minor amounts of native sulphur the growth of these oncoids is being mediated by a high diversity microbial biota that achieves optimal growth in waters that have a temperature of 35 42 c and ph of 6 6 6 9 although this biota is dominated by coccoid bacilliform and filamentous cyanobacteria sulphur oxidizing bacteria are common in the cortical laminae of some oncoids in addition diatoms and silicified pollen grains are present in some cortical laminae the silicified microbes are superbly preserved with their three dimensional form and some of their internal structures being apparent including the sites of sulphur globules in the sulphur oxidizing bacteria the microbes probably acted as templates for silica precipitation and thereby mediated the growth of the oncoids some cortical laminae are formed entirely of silicified pollen grains that came from the pinus radiata that grow in the exotic pine plantations around champagne pool by using these laminae as a record of the annual pollination event typically in september november it can be shown that many of the oncoids are

passive source seismic imaging of the crust and upper mantle beneath the 2001 mw 7 7 bhuj earthquake region gujarat india abstract variations in crustal and lithospheric thicknesses below the kachchh rift kr zone have been investigated employing the joint inversion of p receiver functions rf and rayleigh wave and love wave group velocity dispersion 5 70 s on the broadband waveforms of teleseismic events estimated crustal and lithospheric thicknesses at 15 broadband sites led to the delineation of an updoming of 4 7 km in the moho and 6 12 km in the asthenosphere beneath the central kr relative to the surrounding unrifted regions the moho depths vary from 35 to 42 km and lithospheric thicknesses range from 62 to 78 km the observed marked shear velocity reduction 2 6 at the lithosphere asthenosphere boundary lab over an area of 120 km 80 km suggests the presence of patches of partial melt in the asthenosphere below the kr evidencing the possible presence of imprints of the deccan reunion mantle plume the coincidence of the area of updoming of the moho and asthenosphere and the confined aftershock activity below the central kr implies that these patches could provide a high input of volatile co 2 into the lower crust which might play a key role in generating the continued aftershock activity in the region since the occurrence of the 2001 m w 7 7 bhuj mainshock

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids