cretaceous accretionary collision complexes in central indonesia abstract the geology of cretaceous accretionary collision complexes in central indonesia is reviewed in this paper the author and his colleagues have investigated the cretaceous accretionary collision complexes by means of radiolarian biostratigraphy and metamorphic petrology as well as by geological mapping the results of their work has revealed aspects of the tectonic development of the sundaland margin in cretaceous time the cretaceous accretionary collision complexes are composed of various tectonic units formed by accretionary or collision processes forearc sedimentation arc volcanism and back arc spreading the tectonic units consist of chert limestone basalt siliceous shale sandstone shale volcanic breccia conglomerate high p t and ultra high p metamorphic rocks and ultramafic rocks dismembered ophiolite all these components were accreted along the cretaceous convergent margin of the sundaland craton in the cretaceous the southeastern margin of sundaland was surrounded by a marginal sea an immature volcanic arc was developed peripherally to this marginal sea an oceanic plate was being subducted beneath the volcanic arc from the south the oceanic plate carried microcontinents which were detached fragments of gondwanaland oceanic plate subduction caused arc volcanism and formed an accretionary wedge the accretionary wedge included fragments of oceanic crust such as chert siliceous shale limestone and pillow basalt a jurassic shallow marine allochthonous formation was emplaced by the collision of continental blocks this collision also exhumed very high and ultra high pressure metamorphic rocks from the deeper part of the pre existing accretionary wedge cretaceous tectonic units were rearranged by thrusting and lateral faulting in the cenozoic era when successive collision of continental blocks and rotation of continental blocks occurred in the indonesian region

hydrothermal alteration and gold mineralization of the awak mas metasedimentary rock hosted gold deposit sulawesi indonesia abstract the awak mas gold deposit is hosted by phyllites and schists indicated and infered resource are around 38 4 mt at 1 41 g t au equaling to total resource of 1 74 moz gold hydrothermal alteration zones proximal to the gold bearing veins are characterized by the mineral assemblage albite ankerite pyrite and marked by elevated na al ratios and depleted 3 k al ratios these changes are manifested by the replacement of muscovite by albite carbonate alteration with ankerite and siderite occured simultaneous to albitization proximal to the veins distal alteration zones are characterized by chlorite albite in phyllites and albite quartz in schists there are two types of au mineralizing veins in the deposit namely quartz albite ankerite veins and quartz ankerite siderite veins gold occurs in pyrite as sub microscopic inclusions and as fracture fillings with a gold fineness of 925 935 and au ag ratios between 12 1 and 14 1 the aqueous ore fluid was co2 poor and of low salinity with homogenization temperatures between 275 and 325 c fluid inclusion leachates have br cl ratios between 1 0 and 2 0 10 3 and i cl ratios of 5 6 to 18 3 10 5 suggesting that the ore fluids were derived from metamorphic dewatering of organic rich marine sedimentary rocks on the other hand br cl ratios between 1 6 and 3 0 10 3 and i cl ratios from 5 1 to 10 6 10 5 in the non mineralized veins indicate an input of magmatic hydrothermal fluids the results of this study show that the awak mas deposit is an epigenetic orogenic gold deposit which developed at the transition between the epizone and the mesozone

holocene storage of siliciclastic sediment around islands on the middle shelf of the great barrier reef platform north east australia thick sequences of sediment surround the whitsunday islands on the middle shelf of the great barrier reef gbr platform much of this sediment is siliciclastic material deposited since the sea level highstand at around 6 5 ka this raises a mass balance dilemma because modern terrigenous discharge to the gbr platform is restricted to the inner shelf shallow seismic profiles and sediment samples were collected over 450 km2 around the whitsunday islands to quantify the mass of siliciclastic sediment for a dynamic model of the shelf the sea floor and pre holocene surfaces were mapped using 4584 stations along the seismic profiles and a graphical computer program the total volume of sediment between these two surfaces is 3 67 0 45 109 m3 this volume is composed of buried reefs 0 13 0 01 109 m3 medium 0 70 0 30 109 m3 and fine grained shoals 2 84 0 35 109 m3 the volume estimates combined with measurements of carbonate concentration density and porosity indicate that 1850 380 mt of holocene siliciclastic sediment surround the whitsunday islands in medium 510 225 mt and fine grained shoals 1340 155 mt the total mass of siliciclastic material is 1 7 2 6 times that stored in cleveland bay a similar sized repository on the inner shelf a simple numerical model has been constructed to explain this large quantity of holocene siliciclastic sediment the model results in the appropriate siliciclastic mass next to the whitsunday islands by integrating regional shelf processes over time unlike the present day rivers discharged sediment to the middle shelf during the early holocene this material was subsequently focused by northward transport into the vicinity of the islands a geomorphologically complex region that serves as a sediment trap although direct riverine inputs to the middle shelf have stopped during the present sea level highstand previously deposited siliciclastic sediment is continually being winnowed from the middle shelf and redeposited next to the whitsunday islands the transport and distribution of siliciclastic sediment on the gbr platform is thus influenced significantly by storage around islands on the middle shelf

clay mineral assemblages from late quaternary deposits on vancouver island southwestern british columbia canada resume dans le secteur de l ile de vancouver les formations de dashwood drift cowichan head quadra sand et vashon drift se sont deposees au cours des periodes glaciaires et non glaciaires du pleistocene terminal elles presentent des variations importantes du cortege argileux dont certaines sont relatives aux fluctuations climatiques les periodes glaciaires sont caracterisees par des chlorites riches en fer des illites toutes deux bien cristallisees et des smectites avec une morphologie rappelant celle de smectites developpees a partir de roches volcaniques la mineralogie des argiles des depots non glaciaires est plus complexe elle est marquee en outre par la presence de vermiculite kaolinite halloysite et de mineraux interstratifies irreguliers ces assemblages sont mediocrement preserves et montrent une degre d alteration pedologique plus eleve par rapport aux assemblages glaciaires les variations importantes enregistrees dans les depots nonglaciaires sont egalement dues a des facteurs secondaires tels la sedimentation differentielle les sources sedimentaires variantes et des possibles modification diagenetiques toutefois ces facteurs ne semblent pas obliterer de maniere significative les empreintes climatiques des mineraux argileux cette etude permet egalement de differencier des sediments remanies sous regime glaciaire de determiner les relations entre les unites lithologiques d une meme coupe et d etablir l origine des mineraux argileux rencontres

mixing of metamorphic and surficial fluids during the uplift of the hercynian upper crust consequences for gold deposition a detailed geochemical study of fluids from representative quartz sealed faults hosting late hercynian gold concentrations shows that fluids percolating the mineralised faults had two main distinct reservoirs one was a quite shallow and the other rather deep seated both fluids have lost a great part of their original geochemical signature through interactions with host metamorphic formations early fluids present during the primary sealing of the faults by quartz are considered to have effectively equilibrated with the metamorphic pile and then predominantly flowed upwards along the faults they are characterised by ch4 co2 h2o ratios rather typical of fluids equilibrated with graphite and moderate to medium chlorinities with a high br cl ratio the striking feature of the gold bearing quartz is that gold is not synchronous within any quartz deposition and appears located in late microfractures and associated with pb bi sb sulphosalts and sulphides these late stages are characterised by fluids whose salinities decrease to very low values indicating their progressive dilution by waters of more surficial origin in the fault system the long lived activity of the fault favoured the connection between two distinct fluid reservoirs at a critical time during the basement uplift the fluids evolved through two main driving mechanisms which were responsible for the au deposition i decrease in temperature accompanying decompression from supra lithostatic to hydrostatic conditions which yielded in some instances volatile unmixing in the faulted systems ii mixing of the resulting fluids with waters entering the hydrological systems from shallower reservoirs in addition to dilution and fluid mixing which are favourable factors for decreasing the gold solubility the presence of microfractured sulphides could have enhanced gold precipitation through electrochemical processes d 2002 elsevier science b v all rights reserved

tornillos at vulcano clues to the dynamics of the hydrothermal system abstract the number of tornillo events has recently increased at the vulcano island italy while only 15 tornillos were recorded during 2004 2006 584 events occurred in 2007 2008 they were located just below la fossa crater at depths ranging between 0 1 and 1 km b s l during two intervals in 2007 2008 increases in the number of tornillos took place at the same time as temperature and geochemical anomalies were observed the spectral content of the tornillos generally characterized by one two dominant spectral peaks near 6 and 10 hz varied over time with changes also noted in the quality factors the simplest source mechanism proposed for tornillos is the free eigenvibration of a fluid volume within a crack or a conduit based on this model we propose a causal relationship between the temperature and geochemical anomalies and the increases in numbers of tornillos as the amount of hydrothermal fluids increases during the anomalies the upward flux of fluids grows the consequent changes in the pressure temperature and dynamics of the system of cracks and conduits result in the generation of tornillos based on the fluid filled crack conduit model the shallow depths of the sources and the values of the quality factors the fluid within the resonant crack conduit was inferred to be an ash gas or water droplet gas mixture moreover the observed variations in the wavefield can be caused by small changes in the location of the source in the source mechanism or in the medium in between the source and the seismic station finally another peculiar feature of tornillos is the amplitude modulation that can be explained as a result of a beating phenomenon

ore genesis constraints on the idaho cobalt belt from fluid inclusion gas noble gas isotope and ion ratio analyses a reply the idaho cobalt belt is a 60 km long alignment of deposits composed of cobaltite co pyrite chalcopyrite and gold with anomalous nb y be and rare earth elements rees in a quartz biotite tourmaline gangue hosted in mesoproterozoic metasedimentary rocks of the lemhi group it is the largest cobalt resource in the united states with historic production from the blackbird mine all of the deposits were deformed and metamorphosed to upper greenschist lower amphibolite grade in the cretaceous they occur near a 1377 ma anorogenic bimodal plutonic complex the enhanced solubility of fe co cu and au as chloride complexes together with gangue biotite rich in fe and cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved the isotopes of b in gangue tourmaline are suggestive of a marine source whereas those of pb in ore suggest a u th enriched source the ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post ore minerals and metamorphic minerals such components can potentially be identified and distinguished by their relative abundances in contrasting samples therefore we obtained samples of co and cu sulfides gangue quartz biotite and tourmaline and post ore quartz veins as well as cretaceous metamorphic garnet and determined the gas noble gas isotope and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography the most abundant gases present in extracts from each sample type are biased toward the gas rich population of inclusions trapped during maximum burial and metamorphism all have co 2 ch 4 and n 2 ar ratios of evolved crustal fluids and many yield a range of h 2 ch 4 co 2 h 2 s equilibration temperatures consistent with the metamorphic grade cretaceous garnet and post ore minerals have high r h and r s values suggestive of reduced sulfidic conditions most extracts have anomalous 4 he produced by decay of u and th and 38 ar produced by nucleogenic production from 41 k in contrast some ore and gangue minerals yield significant so 2 and have low r h and r s values of a more oxidized fluid three extracts from gangue quartz have high helium r r a values indicative of a mantle source and neon isotope compositions that require nucleogenic production of 22 ne in fluorite from u th decay two extracts from gangue quartz have estimated 40 k 40 ar that permit a precambrian age extracts from gangue quartz in three different ore zones are biased toward the hypersaline population of inclusions and have a tight range of ion ratios na k nh 4 cl br f suggestive of a single fluid their na cl br ratios suggest this fluid was a mixture of magmatic and basinal brine na k ca temperatures 279 347 c are similar to homogenization temperatures of hypersaline inclusions the high k na of the brine may be due to albitization of k silicate minerals in country rocks influx of k rich brines is consistent with the k metasomatism necessary to form gangue biotite with high cl an extract from a post ore quartz vein is distinct and has na cl br ratios that resemble metamorphic fluids in cretaceous silver veins of the coeur d alene district in the belt basin the results show that in some samples for certain components it is possible to see through the cretaceous metamorphic overprint of great import for genetic models the volatiles trapped in gangue quartz have 3 he derived from a mantle source and 22 ne derived from fluorite both of which may be attributed to nearby 1377 ma basalt rhyolite magmatism the brine trapped in gangue quartz is a mixture of magmatic fluid and evaporated seawater the former requires a granitic intrusion that is present in the bimodal intrusive complex and the latter equatorial paleolatitudes that existed in the mesoproterozoic the results permit genetic models involving heat and fluids from the neighboring bimodal plutonic complex and convection of basinal brine in the lemhi group while the inferred fluid sources in the idaho cobalt belt are similar in many respects to those in iron oxide copper gold deposits the fluids were more reduced such that iron was fixed in biotite and tourmaline instead of iron oxides

the shallow porosity structure of the eel shelf northern california results of a towed electromagnetic survey a towed electromagnetic survey mapping the electrical resistivity of the seafloor was conducted over an area of the eel shelf off humboldt bay california continuous resistivity profiles to 20 m below the seafloor were measured along 120 km of track line from water depths of 100 m to around 30 m the shallow structure along the shelf is highly variable and we identify three distinct environments based on the recorded resistivities and the porosities inferred from them the first region is a mid shelf depocenter characterized by a thin 2 m moderately high porosity 45 60 surface layer which overlies a less porous 35 45 and homogeneous substrate uniform both laterally and vertically this region is found to the northwest of the humboldt bay entrance from water depths of about 65 m to at least 100 m and is roughly coincident with recent flood deposits the second region is located closer to shore and contains extremely high resistivities for a shallow sedimentary environment it reveals a high degree of spatial variability on length scales of several hundred meters several possibilities exist to explain such high resistivities and these include upwelling fresh water channeled to the seafloor through local fault and anticline systems a significant volume of natural gas within the sediments or a continuous process of carbonate precipitation through oxidation of methane near the seafloor which over time builds a substantial thickness of lithified material none of the above explanations are mutually exclusive and all could act in concert to increase resistivities the third region roughly coincides with the eel river delta and features a buried layer of moderately low porosity 30 35 at a depth of about 5 m and with a thickness of between 5 and 10 m this layer extends from near the entrance to humboldt bay in a southwesterly direction across the shelf 1999 elsevier science b v all rights reserved

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

source mechanism of volcanic tremor low frequency 10 hz volcanic earthquakes originate at a wide range of depths and occur before during and after magmatic eruptions the characteristics of these earthquakes suggest that they are not typical tectonic events physically analogous processes occur in hydraulic fracturing of rock formations low frequency icequakes in temperate glaciers and autoresonance in hydroelectric power stations we propose that unsteady fluid flow in volcanic conduits is the common source mechanism of low frequency volcanic earthquakes tremor the fluid dynamic source mechanism explains low frequency earthquakes of arbitrary duration magnitude and depth of origin as unsteady flow is independent of physical properties of the fluid and conduit fluid transients occur in both low viscosity gases and high viscosity liquids a fluid transient analysis can be formulated as generally as is warranted by knowledge of the composition and physical properties of the fluid material properties geometry and roughness of the conduit and boundary conditions to demonstrate the analytical potential of the fluid dynamic theory we consider a single phase fluid a melt of mount hood andesite at 1250 c in which significant pressure and velocity variations occur only in the longitudinal direction further simplification of the conservation of mass and momentum equations presents an eigenvalue problem that is solved to determine the natural frequencies and associated damping of flow and pressure oscillations for a simple constant pressure reservoir conduit orifice fluid system a change in orifice size can cause the source signal duration due to a single disturbance to change from several seconds to in excess of an hour fluid kinematic viscosity 0 412 m2 s is both included and neglected in the analysis to illustrate its effect upon system damping tremor magnitude is related to the magnitude of the conduit wall motion occurring in response to oscillating fluid pressures the entire volcanic fluid system does not generally experience a transient flow condition at a given time closed end and constant pressure fluid system boundaries reflect pressure waves and isolate components of the fluid system total fluid movement may not be accurately monitored by tremor data alone since steady state and slowly changing flows are aseismic

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

continuous gas monitoring at galeras volcano colombia first evidence abstract this paper describes a system of instruments for continuously monitoring fumarolic gases which is installed at galeras volcano colombia several parameters such as the concentration of co2 and rn in the fumarolic emissions as well as the temperature of the gases and their pressure are measured every 6 s we report variations in these parameters which were observed during a short flurry of seismic activity at the volcano at this stage it is uncertain whether the changes in the parameters are directly associated with volcanic processes from the data presented here we can conclude that ambient air can enter the fumarolic vent system in consequence the fumarole may be influenced by the direction and strength of the wind

period doubling and other nonlinear phenomena in volcanic earthquakes and tremor abstract evidence of subharmonic period doubling cascades has recently been recognized in seismograms of volcanic tremor from several volcanoes this phenomenon occurs only in nonlinear systems and is the commonest route by which such systems change from periodic to chaotic behavior it is predicted to occur in a model of volcanic tremor excitation by flow induced vibration and it might well also occur in other volcano seismic source process if the possibility of period doubling is not taken into account in interpreting spectra of tremor and long period earthquakes then low frequency sub harmonic oscillations may be mis identified as normal modes of a linear acoustic resonator leading to errors of an order of magnitude or more in inferred magma body dimensions this example illustrates the importance of nonlinear phenomena in attempts to understand volcano seismic phenomena physically linear systems are fundamentally incapable of causing earthquakes or exciting tremor so nonlinearity is essential to any theory of volcano seismic phenomena nonlinear processes are in many respects qualitatively different from linear ones a few of their characteristics that might be relevant in volcanoes include the possibility 1 that damping might increase rather than decrease oscillation frequencies and 2 that these frequencies might be functions of the amplitude of oscillation so that temporal variations in spectral peak frequencies might not be manifestations of changes of conditions within the magmatic system

stratigraphy and tectonic setting of the cretaceous and paleogene volcanic sedimentary successions in northwest sulawesi indonesia implications for the cenozoic evolution of western and northern sulawesi abstract new field and laboratory data from nw sulawesi indonesia integrated with existing information provide a tectonostratigraphic framework for the cretaceous and paleogene of this region the study area straddles two distinct provinces referred to as western and northern sulawesi western sulawesi forms the rifted continental margin of eastern sundaland it consists of a metamorphic basement partly of australian origin overlain by late cretaceous turbidites that were deposited in a fore arc setting latimojong formation these are in turn covered by volcanic sedimentary successions that were deposited during the early middle eocene to earliest miocene they represent a transgressive cycle from syn rift siliciclastics through nummulitic limestone and associated shelf sediments to deeper marine mudstones and turbidites budungbudung and tinombo formations during the same period northern sulawesi developed as an oceanic island arc characterized by bimodal volcanism papayato volcanics founded on back arc oceanic crust the cretaceous and paleogene volcanic and sedimentary suites show lithological and geochemical characteristics that reflect the contrasting tectonic setting of the two provinces the tectonic relationship between the two domains is not clear they probably formed a more or less continuous belt throughout the cenozoic but were definitely connected not later than the early miocene strong deformation in the paleogene formations in the northern part of nw sulawesi and their unconformable relationship with the overlying formations may be the result of the collision of the north arm of sulawesi with a continental fragment of australian derivation during the early miocene or it may be related to the formation of a metamorphic core complex in a mid miocene extensional tectonic setting a second major tectonic event which commenced in the pliocene and is still ongoing affected the entire region

preliminary analysis of volcanoseismic signals recorded at the tatun volcano group northern taiwan 1 the tatun volcano group lies at the northern tip of taiwan only 15 km north of the capital taipei a seismic array consisting of 5 stations equipped with both broadband and short period sensors was installed in 2003 in order to monitor the seismic activity of the area it recorded a variety of events including common volcano tectonic earthquakes and volcanoseismic signals like tornillos short duration monochromatic events 10 15 s and long duration spasmodic bursts 15 min an analysis of the complex frequencies of the tornillo monochromatic signals shows that q values are of the order of several hundreds based on the model of a fluid filled crack such q values can result from the oscillations of a crack containing a misty or dusty gas these observations put into doubt the long standing suggestion that the tatun volcanoes are extinct and prompt for a thorough assessment of the volcanic hazard for this area

using csem techniques to map the shallow section of seafloor from the coastline to the edges of the continental slope many important processes occur within the shallow section of the seafloor on the continental shelf and slope yet conventional geophysical constraints on the physical properties within this critical boundary layer are limited some of the key constraints involve quantification of fluids within the seafloor which can be provided by electrical methods this paper reviews the application of a towed em system to map the uppermost 20 m of seafloor in a variety of settings ranging from nearshore regions in water depths of approximately 10 m on the continental shelf out to water depths of 1300 m the system is a mapping tool that provides areal maps of seafloor resistivity and has been used for a variety of purposes including sedimentary characterization and facies mapping evaluation of groundwater discharge and mapping seafloor mounds in the gulf of mexico thought to contain massive deposits of gas hydrate

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

electromagnetic surveying of seafloor mounds in the northern gulf of mexico seafloor controlled source electromagnetic data probing the uppermost 30 m of seafloor sediments have been collected with a towed magnetic dipole dipole system across two seafloor mounds at approximately 1300 m water depth in the northern gulf of mexico one of these mounds was the focus of a recent gas hydrate research drilling program rather than the highly resistive response expected of massive gas hydrate within the confines of the mounds the em data are dominated by the effects of raised temperatures and pore fluid salinities that result in an electrically conductive seafloor this structure suggests that fluid advection towards the seafloor is taking place beneath both mounds similar responses are seen at discrete locations away from the mounds in areas that might be associated with faults further suggesting substantial shallow fluid circulation raised temperatures and salinities may inhibit gas hydrate formation at depth as has been suggested at other similar locations in the gulf of mexico

design and application of a new free fall in situ resistivity probe for marine deep water sediments abstract we have developed a new type of sediment penetrating in situ probe which logs electrical resistivity in marine and limnic sediments in the uppermost 3 5 m as the instrument is fitted to a lister type heat flow instrument combined thermal and electrical conductivity measurements are possible the probe incorporates no moving mechanical parts is built to operate in water depths up to 4000 m and is relatively easy to deploy two separate electrode arrays provide for an instant repeatability test and rapid data quality assessment the probe was extensively tested in the laboratory field tests in lake konstanz and in the north sea produced consistent results this paper gives a description of the design of the probe and the test results a theoretical derivation of the probe s configuration factor is presented and theoretical results are verified in laboratory tests

delaciation of the prince rupert kitimat area british columbia late wisconsinan sediments in the prince rupert kitimat area of west central british columbia were deposited in an isostatically depressed marine environment affected by grounded tidewater glaciers the most common sediments are 1 massive bedded and laminated muds and 2 stratified sand and gravel the former are accumulations of clay and silt size detritus transported in suspension from the mouths of meltwater streams and possibly in turbidity flows generated by submarine slope failures the muds locally contain scattered ice rafted stones fossil marine molluscs and foraminifera the main sand and gravel deposits are elevated deltas including both small incised fan shaped forms at the margins of the main valleys and enormous ice contact delta sandur complexes on the floor of kitsumkalum kitimat trough the largest valley in the study area delaciation occurred by downwasting and complex frontal retreat between about 13 000 and 10 000 bp the open outer coast became ice free first in response

hydrocarbon and ore bearing basinal fluids a possible link between gold mineralization and hydrocarbon accumulation in the youjiang basin south china the youjiang basin which flanks the southwest edge of the yangtze craton in south china contains many carlin type gold deposits and abundant paleo oil reservoirs the gold deposits and paleo oil reservoirs are restricted to the same tectonic units commonly at the basinal margins and within the intrabasinal isolated platforms and or bioherms the gold deposits are hosted by permian to triassic carbonate and siliciclastic rocks that typically contain high contents of organic carbon paragenetic relationships indicate that most of the deposits exhibit an early stage of barren quartz pyrite stage i a main stage of auriferous quartz arsenian pyrite arsenopyrite marcasite stage ii and a late stage of quartz calcite realgar orpiment native arsenic stibnite cinnabar dolomite stage iii bitumen in the gold deposits is commonly present as a migrated hydrocarbon product in mineralized host rocks particularly close to high grade ores but is absent in barren sedimentary rocks bitumen dispersed in the mineralized rocks is closely associated and or intergrown with the main stage jasperoidal quartz arsenian pyrite and arsenopyrite bitumen occurring in hydrothermal veins and veinlets is paragenetically associated with stages ii and iii mineral assemblages these observations suggest an intimate relationship between bitumen precipitation and gold mineralization in the paleo petroleum reservoirs that typically occur in permian reef limestones bitumen is most commonly observed in open spaces either alone or associated with calcite where bitumen occurs with calcite it is typically concentrated along pore vein centers as well as along the wall of pores and fractures indicating approximately coeval precipitation in the gold deposits aqueous fluid inclusions are dominant in the early stage barren quartz veins stage i with a homogenization temperature range typically of 230 c to 270 c and a salinity range of 2 6 to 7 2 wt nacl eq fluid inclusions in the main and late stage quartz and calcite are dominated by aqueous inclusions as well as hydrocarbon and co2 rich inclusions the presence of abundant hydrocarbon fluid inclusions in the gold deposits provides evidence that at least during main periods of the hydrothermal activity responsible for gold mineralization the ore fluids consisted of an aqueous solution and an immiscible hydrocarbon phase aqueous inclusions in the main stage quartz associated with gold mineralization stage ii typically have a homogenization temperature range of 200 230 c and a modal salinity around 5 3 wt nacl eq homogenization temperatures and salinities of aqueous inclusions in the late stage drusy quartz and calcite stage iii typically range from 120 c to 160 c and from 2 0 to 5 6 wt nacl eq respectively in the paleo oil reservoirs aqueous fluid inclusions with an average homogenization temperature of 80 c are dominant in early diagenetic calcite fluid inclusions in late diagenetic pore and fissure filling calcite associated with bitumen are dominated by liquid c2h6 vapor ch4 ch4 h2o and aqueous inclusions with a typical homogenization temperature range of 90 c to 180 c and a salinity range of 2 8 wt nacl eq it is suggested that the hydrocarbons may have been trapped at relatively low temperatures while the formation of gold deposits could have occurred under a wider and higher range of temperatures the timing of gold mineralization in the youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits among the limited isotopic data the rb sr date of 206 12 ma for au bearing hydrothermal sericite at jinya as well as the re os date of 193 13 ma on auriferous arsenian pyrite and 40ar 39ar date of 194 6 2 ma on vein filling sericite at lannigou may provide the most reliable age constraints on gold mineralization this age range is comparable with the estimated petroleum charging age range of 238 185 ma and the sm nd date of 182 21 ma for the pore and fissure filling calcite associated with bitumen at the shitouzhai paleo oil reservoir corresponding to the late indosinian to early yanshanian orogenies in south china the close association of carlin type gold deposits and paleo oil reservoirs the paragenetic coexistence of bitumens with ore stage minerals the presence of abundant hydrocarbons in the ore fluids and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated migrated and precipitated along with the hydrocarbons in an immiscible gold and hydrocarbon bearing basinal fluid system

geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock macraes gold mine otago schist new zealand abstract the macraes gold deposit in the otago schist new zealand formed during late metamorphic fluid flow through a lower greenschist facies shear zone mineralisation occurred near to the brittle ductile transition at about 300 c large volumes of host rock in a shear zone up to 120 m thick have been hydrothermally altered by this fluid activity most alteration is not structurally controlled apart from proximity to the shear zone ductile and brittle microshears traverse the most mineralised rocks and some structural control of fluid flow occurred as well fluid flow was slow similar to that in metamorphic rocks mm year and diffusion through interconnected fluid was a significant chemical process localised extensional hydrofractures m scale are filled with mineralised quartz most alteration of the host rocks was isochemical with respect to the lithophile elements and mineralised rocks have been variably enriched in as au sb w mo and bi but not co or cd addition of sulphur has occurred to both host rocks and mineralised rocks up to 1 wt above a background of 0 1 wt host rock sulphur is mainly pyritic and is not structurally controlled mineralised rocks have pyrite and arsenopyrite along microshears pyrite chalcopyrite sphalerite and galena have formed from sulphidation of silicates with no addition of metals graphite has been added to mineralised rocks along microshears up to 3 wt locally above a background of 0 1 wt noncarbonate carbon graphite deposition may have occurred as a result of mixing of two fluids water methane and water carbon dioxide graphitisation and sulphidation reactions released low d water which accumulated in the slow moving mineralising fluid distinction between this low d reaction water and meteoric water incursion is difficult

hydrothermal transport and depositional processes in archean lode gold systems a review abstract compelling evidence now exists for the formation of archean lode gold deposits over a substantial range in metamorphic conditions and crustal depth the commonality of ore fluid isotopic and geochemical characteristics the extreme fluid rock ratios within actual ore zones and the observed depth continuity within individual orebodies all suggest that these deposits formed within vertically extensive crustal scale hydrothermal systems calculations based on new thermodynamic data and estimated ore fluid conditions suggest that gold would have been transported as au hs 2 over most of this range gold transport in the ore fluids that formed some diopside and diopside k feldspar class deposits t 550 c would have been as aucl2 whereas the au hs complex may have been significant in some of the lower temperature 270 c less alkaline ore fluids the high solubility of gold in lode gold ore fluids at amphibolite facies conditions 10 s to 1000 s ppb suggests that fluids may have been undersaturated in gold within their source regions promoting the ore fluid s capacity to retain gold in solution over the large transport distances involved ore depositional mechanisms were also likely to vary between crustal levels fluid rock interactions and wallrock sulphidation in particular appear to be the most important type of precipitation mechanism however with decreasing depth of formation the scope of other depositional mechanisms notably phase separation and fluid mixing becomes greater

surface water influx in shallow level archean lode gold deposits in western australia archean shallow level lode gold deposits in western australia are located in rocks of prehnite pumpellyite to lower greenschist facies and are characterized by 1 predominantly brittle shear zones that formed well after volcanism and late in the structural history 2 breccia hosted lodes 3 low temperature ore and gangue minerals such as silver sulfosalts stibnite and precursor chalcedony and 4 vertical metal zonation of the orebodies ore fluid temperatures ranged from 150 to 325 c and a depth of em placement of 5 km is inferred isotopic analyses of alteration minerals such as quartz sericite and chlorite indicate higher dfluid 6 9 relative to smow 1 n 19 and lower 18ofluid 4 4 2 3 relative to smow 1 n 167 values compared to such values for hydrothermal fluids that deposited au in other archean lode gold deposits with similar structural timing the fluid inclusion and stable isotope data and the presence of chalcedony in this deposit style are best explained by the influx of surface water at shallow levels and interaction of that water with advecting metamorphic magmatic fluids

the multiparameter station at galeras volcano colombia concept and realization abstract volcanoes are complex systems in which the interaction of many different physical and chemical factors and processes contribute to changes in activity in the past 40 years our ability to observe and quantify short term changes in a volcano s activity has improved due to the installation of seismometers and tiltmeters and the continuous records they provide however due to instrumental limitations the observations have mainly been used phenomenologically to draw inferences about possible changes on the basis of previous experience since 1995 the bundesanstalt fur geowissenschaften und rohstoffe bgr and the instituto de investigacion e informacion geocientifica minero ambiental y nuclear ingeominas have been working to develop and deploy a multiparameter mp station on galeras volcano colombia this station is designed to concurrently measure various geophysical and geochemical parameters it includes three broadband seismometers at the crater rim as well as a more remotely located broadband seismic reference at other locations in the crater or on the rim electromagnetic probes an infrasound sensor and a weather station are operating the data from these sensors are digitized at each site with 24 bit digitizers and transmitted by spread spectrum radio via repeater when necessary to the observatorio vulcanologico y sismologico ovp in the city of pasto there they are received and displayed on a networked personal computer and recorded continuously the data flow into the routine analysis procedures of the ovp and the continuous data are archived on cd in addition to the other sensors a system of specially developed sensors continuously monitors the chemistry and physics of the gases at fumaroles on the active cone the data from this system are also transmitted in realtime to ovp and recorded the continuous recordings of the mp station are supplemented by regular thermographic measurements of the surface temperature in the crater using an infrared camera joint analysis and interpretation of the data streams from the many sensors of the mp station will improve our understanding of the physical processes occurring in galeras volcano

the polarization of volcanic seismic signals medium or source abstract with the proliferation of three component seismometers on volcanoes the temptation is great to use polarization analysis as we do in earthquake seismology to determine propagation direction and or wavetype in order to locate and characterize the wave s source in volcano seismology there are two impediments to such a procedure the complexity of the volcano s structure and the often long lasting volcanic seismic signals i develop a simple model of acoustic scattering and apply it to three simple theoretical source signals which represent the classes of signals encountered at volcanoes when the medium is strongly scattering the polarization at a receiver location for impulsive sinusoidal or square wave sources mimics the characteristics for volcanic shocks tornillos with a single frequency and multichromatic tremor or tornillos the polarization observed for the square wave source resembles that observed for multichromatic tremor at lascar volcano chile and multichromatic tornillos at galeras volcano colombia at low frequencies the particle motion is fairly linear and nearly constant but cannot necessarily be used directly to indicate the direction to the source at all frequencies the particle motion exhibits some characteristics of rayleigh waves namely ellipticity of varying degrees and an rz product that oscillates with twice the frequency of the mode if this model is correct the lack of change of fundamental wavefield parameters such as the polarization for low frequencies during any given tornillo and from one tornillo to the next implies that the location of the source is stable to within a resolution of about 200 m

late quaternary geology and geochronology of the central continental shelf of western canada piston cores and high resolution seismic profiles from queen charlotte sound have yielded new information on the late quaternary history of this part of the western canada continental shelf cores in three major troughs goose island mitchell s and moresby up to 130 km apart sample a similar sedimentary sequence this sequence comprises five units the lowest unit a which is up to 40 m thick is a laminated to massive mud containing coarse ice rafted debris deposited between pre 13 6 ka and 12 9 ka during deglaciation of queen charlotte sound this unit is overlain by a sequence of stratified sediments units b1 b3 up to 20 m thick deposited during the transition from the pleistocene to the holocene unit b1 directly overlies and is similar to unit a but lacks ice rafted detritus unit b2 is sandy mud locally gravelly deposited during a period of lagging and winnowing from about 12 9 to 10 2 ka when sea level in queen charlotte sound was lower relative to the land than it is today unit b3 is a laminated to massive mud similar to unit b1 deposited when water depths in queen charlotte sound rapidly increased at the end of the pleistocene due to the combined effect of eustatic sea level rise and forebulge collapse the sedimentary sequence is capped by up to 10 m of mud unit c which is more organic rich and contains more clay than any of the other units it was accumulating under present day conditions as early as 9 7 k y ago

measuring the shallow porosity structure of sediments on the continental shelf a comparison of an electromagnetic approach with cores and acoustic backscatter we validate estimates of shallow sedimentary porosities made on the continental shelf by electromagnetic methods through a comparison with those measured directly in cores specifically we show that an electromagnetic surveying system we have used to measure sediment resistivity in a number of seafloor locations returns porosity depth profiles that are related to those measured in cores and that our data have good sensitivity to the structure within the uppermost few tens of centimeters of seafloor we then consider inferences of sediment type made by observations of acoustic backscatter in the light of our porosity measurements our results suggest that electromagnetic methods provide complementary information that can be used to improve grain type estimates at and just below the seafloor especially when combined with acoustic backscatter data because the system is pulled along the seafloor data can be quickly collected from a large area of seafloor and can be used to interpolate facies conditions between core locations

geology and in situ sulfur and lead isotope analyses of the jinlongshan carlin type gold deposit in the southern qinling orogen china implications for metal sources and ore genesis abstract the jinlongshan gold deposit shaanxi province central china is a large deposit 150 t au in the southern qinling orogen gold mineralization is hosted in upper devonian to lower carboniferous carbonaceous clastic carbonate sequences four stages of pyrite and paragenetic sulfides have been identified based on morphology and paragenesis laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses were conducted to determine the chemical and s pb isotopic composition of the sulfides pre ore stage pyrites py1 and py2 contain relatively high concentrations of mn co ni cu zn sb and pb exhibiting a wide range of 34s values ranging from 29 9 to 48 4 these two pyrites were formed by bacterial and thermochemical sulfate reduction of upper devonian marine sulfate respectively main ore stage pyrite py3 and arsenopyrite apy contain high concentrations of au as cu sb hg and tl with restricted ranges of 34s values from 9 6 to 15 3 which is interpreted as resulting from the underlying low grade metamorphic paleozoic sedimentary rocks by the decomposition of pyrite and or inorganic reduction of sulfate late or post ore stage pyrite py4 is characterized by low concentrations of au ag sn hg and bi and exhibited variable 34s values ranging from 4 4 to 27 7 that may reflect the mixing of metamorphic fluids with meteoric water similarly the pb isotope composition of ore stage sulfides resembles those of underlying low grade metamorphic paleozoic sedimentary rocks whereas differs from precambrian metamorphic basement rocks and granitoids around the basin indicating that the metals of the jinlongshan gold deposit were sourced from the underlying paleozoic sedimentary rocks detailed fieldwork revealed that the deposit has mainly undergone four deformation events the ore bodies developed in ne trending dextral oblique slip reverse faults of d3 that crosscut wnw trending shear zones of d2 the timing and corresponding stress regimes of the d3 event suggest that it formed in a local extensional environment of yanshanian intracontinental orogeny of qinling orogenic belt gold metallogenesis of the jinlongshan gold deposit occurred during the transition of tectonic setting from compression to extension which reactivated the shear zones and migrated deep ore bearing fluids to ne trending brittle faults the geological and geochemical features of the jinlongshan gold deposit are more analogous to the carlin type deposits than other orogenic gold deposits worldwide therefore we propose it is a typical carlin type gold deposit in south qinling orogen

emplacement of the east sulawesi ophiolite evidence from subophiolite metamorphic rocks abstract a newly discovered high temperature metamorphic sole at the base of the extensive east sulawesi ophiolite in sulawesi indonesia yields new structural and petrological data with which to constrain the emplacement history the metamorphic sole is composed of a thin sequence of garnet and epidote amphibolite and basal greenschist metaclastics east dipping tectonite fabrics in the metamorphic sole amphibolite are coincident with those in subjacent basement mica schist and superjacent peridotite and indicate orthogonal east to west emplacement of the ophiolite in central sulawesi metabasite in the upper levels of the sole has morb geochemical characteristics was recrystallized at temperatures of about 700 c and yielded k ar radiometric ages of approximately 30 ma initial detachment of the ophiolite probably occurred at a ridge segment transform intersection in a back arc basin at the south east margin of sundaland detachment closely preceded nw directed overthrusting and orthogonal obduction on to the sundaland continental margin in the oligocene sinistral movement on a paleo transform boundary now the lawanopo fault may have facilitated obduction although the westernmost segments of ophiolite may represent younger more proximal slices of a marginal basin those further east probably represent successively older more distal slices of underthrust indian ocean back arc or forearc

electric dipole fields over an anisotropic seafloor theory and application to the structure of 40 ma pacific ocean lithosphere summary seismic anisotropy has been detected in the oceanic crust and upper mantle and likewise it is geologically reasonable to expect that a certain amount of lateral anisotropy exists in sea oor electrical properties anisotropy in earth properties can often lead to surprising eiects on geophysical responses that are not anticipated from simple isotropic theories here we investigate the eiects of lateral anisotropy on the frequency domain controlled source electromagnetic csem response of a uniaxially conducting non magnetic sea oor excited by a horizontal electric dipole whose moment is oriented obliquely with respect to the electrical strike direction a paradox of anisotropy is observed in which the sea oor electric eld strength is enhanced in the most conductive direction of the sea oor this enhancement is opposite to what one would expect based on naive isotropic theory we also show that it is possible in certain circumstances to extract the along strike electrical conductivity from marine controlled source electromagnetic data using only isotropic modelling the extraction of across strike conductivity however requires full anisotropic modelling the physical insight into electromagnetic induction in uniaxial media that is presented here should greatly assist the geological interpretation of marine csem experimental data applying our algorithm to the pegasus data set csem data collected over 40 ma paci c ocean lithosphere produces a model with conductivity in the fossil spreading direction that is seven times greater than the conductivity perpendicular to spreading strain aligned mineralogical fabric as predicted by tectonic modelling would explain our result with enhanced conductivities caused by hydrogen conduction along the olivine a axis or connected accumulations of trace conductors such as graphite or magnetite

formation of epizonal gold mineralization within the latimojong metamorphic complex sulawesi indonesia evidence from mineralogy fluid inclusions and raman spectroscopy abstract the gold deposits within the latimojong metamorphic complex of sulawesi indonesia including awak mas and salu bulo are estimated to host 50 tonnes au with an average grade of 1 41 g t they are located within the metamorphic basement consisting of pumpellyite to greenschist facies metasedimentary and metavolcanic rocks where gold precipitated in quartz veins that fill north south striking normal faults and extensional fractures the mineral assemblage is dominated by pyrite chalcopyrite galena minor tetrahedrite tennantite and sphalerite gold is electrum with a low silver content au ag ratio of 8 5 to 9 1 albite dolomite ankerite siderite chlorite and white mica are the main alteration minerals quartz albite and carbonate veins hosting h2o bearing fluid inclusions with minor aqueous carbonic phases co2 n2 were detected mole fraction

fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising fluids the naturally occurring noble gas isotopes 40ar 36ar 84kr and 129xe and halogens cl br i have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits pcd bingham canyon utah and silverbell ray mission pinto valley and globe miami in arizona in addition analyses of 3he 4he have been obtained from sulphide minerals hosted by the quartz veins at silverbell ray pinto valley and globe miami the majority of pcd fluids studied have br cl and i cl ratios that overlap those of fluids included in mantle diamond suggesting that the salinity had a juvenile origin the high i cl 121 10 6 mole m in samples from the propylitic zone of silverbell is attributed to the presence of sedimentary formation water 3he 4he ratios have r ra values in the range 0 3 to 1 72 and provide evidence for the involvement of a crustal component in addition to mantle volatiles 40ar 36ar ratios vary from meteoric values of 317 in the propylitic zone of bingham canyon and 323 in the skarn alteration of mission up to 3225 in the potassic zone of pinto valley fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end member comprising meteoric water and air and a high salinity end member consisting of a mixed mantle and crustal fluid the 40ar cl ratio of fluid inclusions at pinto valley 10 4 m is similar to values obtained previously for mantle fluids the 40ar cl value is two orders of magnitude lower at bingham canyon where a depleted 36ar concentration 0 2 10 6 cm3 g below that of air saturated water asw and a range of highly fractionated noble gas compositions f84kr 13 and f129xe 160 indicate that boiling and pulsed fluid flow have occurred

buried paleo channels on the new jersey continental margin channel porosity structures from electromagnetic surveying abstract we report on a marine electromagnetic em survey across two portions of the new jersey continental margin that have been previously shown to contain buried paleo channels the em method used provides bulk porosity estimates to depths of around 20 m below the seafloor and is thus able to place porosity constraints on the nature of the channel infill and the contrast in physical properties across the channel boundaries our data show that a key condition for the channels to have an electrical signature is that they incise an underlying regional unconformity r thought to represent a subaerially eroded surface exposed during the late wisconsinan glaciation channels that cut r are seen through increases in apparent porosity another seismically imaged channel sequence which lies within the outer shelf sediment wedge sequence above r does not have an electrical signature indicating that the sediments above and below the channel boundaries have similar physical properties

analyses of unusual long period earthquakes with extended coda recorded at katmai national park alaska usa 1 a swarm of six long period lp events with slowly decaying coda wave amplitudes and durations up to 120 s was recorded by seismic stations located in the proximity of mt griggs a fumarolically active volcano in the katmai national park alaska during december 8 21 2004 spectral analyses reveal the quasi monochromatic character of the waveforms dominated by a 2 5 hz mode frequently accompanied by a weaker high frequency onset 6 0 9 0 hz particle motion azimuths and inclination angles show a dominant wnw ese direction of polarization for all the signals and suggest that seismic energy is radiated by a stable source at shallow depth damping coefficients between 0 0014 and 0 0063 are estimated by fitting an exponential decay model to the signal s coda corresponding quality factors range from 78 to 351 the source of the waveforms is modelled as a resonant cavity filled with a fluid gas mixture

neogene sutures in eastern indonesia five suture zones are described from the zone of collision between the eurasian indian australian and pacific philippine sea plates within the eastern indonesia region these are the molucca sorong sulawesi banda and borneo sutures each of these sutures has a relatively short history compared to most pre neogene orogenic belts but each preserves a record of major changes in tectonics including subduction polarity reversals elimination of volcanic arcs changing plate boundaries and important extension within an overall contractional setting rapid tectonic changes have occurred within periods of less than 5 ma many of these events although important would be overlooked in older orogenic belts because the age resolution required to identify them even when the evidence is preserved is simply not possible q 2000 elsevier science ltd all rights reserved

detecting hydrothermal graphite deposition during metamorphism and gold mineralization fourier transform ir analyses of carbonaceous material from the otago and alpine schists and the macraes gold deposit of the south island new zealand show the progressive effects of graphitization during metamorphism and suggest that the majority of carbonaceous material identified at the macraes deposit precipitated from hydrothermal fluids given that the distinction of sedimentary carbonaceous material from fluid precipitated graphite is a key to better understanding the redox state of crustal rocks ore depositional processes and the extent of carbon cycling in the crust this study highlights the importance of ir spectroscopy in the characterization of reduced carbon bearing rocks

a carbonaceous sedimentary source rock model for carlin type and orogenic gold deposits this paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for au and as in sediment hosted orogenic and carlin type gold deposits and develops a corresponding genetic model in this two stage basin scale model gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis stage 1 and concentrated to ore grades by later hydrothermal structural or magmatic processes stage 2 in reduced continental margin basin settings organic matter sedimented under anoxic to euxinic conditions immobilizes and concentrates gold arsenic and a range of trace elements particularly v ni se ag zn mo cu u present in marine bottom waters into fine grained black mudstone and siltstone of slope and basin facies during early diagenesis gold and certain other trace elements ni se te ag mo cu pge are preferentially partitioned into arsenian pyrite that grows in the muds these processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic commonly from 5 to 100 ppb au and 10 to 200 ppm as rare organic and sulfide rich metalliferous black shales may contain up to 1 to 2 ppm au and over 1 000 ppm as present as refractory gold in arsenian pyrite and nanoparticles of free gold during late diagenesis and early metamorphism stage 2 the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations and the organic matter is cooked to bitumen under higher grade metamorphism lower greenschist facies and above arsenian pyrite in carbonaceous shales is converted to pyrrhotite these processes release gold arsenic sulfur and other elements sb te cu zn mo bi tl and pb from the source rocks to become concentrated by hydrothermal processes locally to produce gold ores in structural sites such as fold hinge zones shear or breccia zones within or above the black shale sequence la icp ms analyses of diagenetic pyrite in carbonaceous sediments both associated and not associated with gold deposits suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits application of this sedimentary source rock model enables a systematic exploration approach for sediment hosted gold deposits based on the distribution composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite

porosity formation factor relationships for high porosity siliciclastic sediments from amazon fan the electrical resistivity of siliciclastic rocks is a function both of pore fluid resistivity and of formation factor ff an intrinsic rock property for low porosity rocks ff depends on clay conduction and porosity in contrast we find that ff of high porosity sediments fractional porosities of 0 3 0 6 from amazon fan is controlled primarily by porosity and pore geometry clay conduction is a minor effect porosity vs formation factor ff plots for amazon fan well logs demonstrate two distinct trends which are dependent on the amount of shale present muds with more than about 0 4 shale fraction follow a trend that increases to much higher ff as porosity decreases compared to sands and slightly muddy sands this separation is of opposite sign to the separation between low porosity sandstones and shales attributable to clay conduction we conclude that in high porosity muds presence of clays reduces formation conductivity by increasing the tortuosity of pores

conversion of carbonaceous material to graphite within the greywacke zone of the eastern alps morphology and reflectance of carbonaceous material cm in late carboniferous metasediments of the eastern greywacke zone eastern alps indicate a mixture of vitrinite grainy textured and lamellar shaped particles as imaged by high resolution atomic force microscopy vitrinite and the grainy textured particles show mesophase structures which can be described as facetted nanocrystals within the carbon matrix high resolution transmission electron microscopy has revealed two types of microtextures representing different degrees of graphitization the first type is characterized by elongated ring shaped microtextures whereas the second type is characterized by graphite lamellae and polygonal flakes with long range ordered aromatic layers in spite of the heterogeneity of the cms the geographical distribution of quantitative metamorphic parameter raman spectra parameter x ray diffraction pattern microscopic reflectance suggests a graphitization process which is promoted by advective heat transport during post collisional processes in a tentative pressure time path late cretaceous thrusting results in a turbostratic ordering of the aromatic layer ordering to long range ordered aromatic layers was achieved during the late cretaceous paleogene exhumation of mid crustal rocks beneath the eastern greywacke zone

vulcan a deep towed csem receiver we have developed a three axis electric field receiver designed to be towed behind a marine electromagnetic transmitter for the purpose of mapping the electrical resistivity in the upper 1000 m of seafloor geology by careful adjustment of buoyancy and the use of real time monitoring of depth and altitude we are able to deep tow multiple receivers on arrays up to 1200 m long within 50 m of the seafloor thereby obtaining good coupling to geology the rigid body of the receiver is designed to reduce noise associated with lateral motion of flexible antennas during towing and allows the measurement of the vertical electric field component which modeling shows to be particularly sensitive to near seafloor resistivity variations the positions and orientations of the receivers are continuously measured and realistic estimates of positioning errors can be used to build an error model for the data during a test in the san diego trough offshore california inversions of the data were able to fit amplitude and phase of horizontal electric fields at three frequencies on three receivers to about 1 in amplitude and 1 in phase and vertical fields to about 5 in amplitude and 5 in phase the geological target of the tests was a known cold seep and methane vent in 1000 m water depth which inversions show to be associated with a 1 km wide resistor at a depth between 50 and 150 m below seafloor given the high resistivity 30 m and position within the gas hydrate stability field we interpret this to be massive methane hydrate

tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait indonesia evidence for a miocene continent continent collision

unusual low frequency volcanic seismic events with slowly decaying coda waves observed at galeras and other volcanoes abstract events with slowly decaying coda waves are observed in active andesitic volcanoes associated mainly with vulcanian type eruptions or large gas emissions however these signals are also recorded in some quiescent volcanoes these unusual signals are considered to be related to magmatic activity and generally occur beneath the active crater the signals have been observed to be a short term precursor galeras volcano colombia 1992 1993 asama yama volcano japan 1983 after eruption tokachi dake volcano japan 1989 during seismic swarms meakan dake volcano japan 1982 and during quiescence puracevolcano colombia 1994 1995 tarumai volcano japan 1970 1971 1975 spectral analysis reveals common characteristics for this type of signal the spectrum is characterized by one or several sharp frequency peaks fundamental frequencies are not affected by epicentral distance azimuth or travel time indicating a source effect the damping coefficient for coda waves ranges from 0 002 to 0 02 and is related to large values of the quality factor q c ranging from 250 to 25 respectively these parameters may be the result of large amounts of gas bubbles in the magma body

time space variation of volcano seismic events at la fossa vulcano aeolian islands italy new insights into seismic sources in a hydrothermal system we investigated the relationship between volcano seismic events recorded at la fossa crater of vulcano aeolian islands italy during 2004 2006 and the dynamics of the hydrothermal system during the period of study three episodes of increasing numbers of volcano seismic events took place at the same time as geothermal and geochemical anomalies were observed these geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids three classes of seismic events long period high frequency and monochromatic events characterised by different spectral content and various similarity of the waveforms have been recognised these events clustered mainly below la fossa crater area at depths of 0 5 1 1 km b s l were space distributed according to the classes based on their features we can infer that such events at vulcano are related to two different source mechanisms 1 fracturing processes of rocks and 2 resonance of cracks or conduits filled with hydrothermal fluid in the light of these source mechanisms the increase in the number of events at the same time as geochemical and geothermal anomalies were observed was interpreted as the result of an increasing magmatic component of the hydrothermal fluids implying an increase of their flux indeed such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids increased pore pressures gave rise to fracturing processes while the increased fluid flux favoured resonance and vibration processes in cracks and conduits finally a gradual temporal variation of the waveform of the hybrid events one of the subclasses of long period events was observed likely caused by heating and drying of the hydrothermal system

tornillos modeled as self oscillations of fluid filling a cavity application to the 1992 1993 activity at galeras volcano colombia abstract tornillos are quasi monochromatic seismic signals with a slowly decaying coda that are observed near active volcanoes and geothermal areas worldwide in this work a lumped parameter model describing the tornillo source process as the self oscillations of fluid filling a cavity is investigated a nonlinear ordinary differential equation is derived that governs the behavior of the model taking into account viscous and nonlinear damping as well as the reaction force of the fluid inside the cavity this equation is numerically integrated both for different cavity sizes and different fluids of volcanological interest such as gas h2o co2 h2o so2 and gas particle mixtures ash so2 water droplets h2o this cavity model predicts that when the filling fluid is a mixture of ash and so2 the signal duration will increase until the mixture becomes enriched in ash and then the duration exhibits a decrease additionally the damping coefficients 1 2q of the synthetic signals are estimated in the range between 0 002 and 0 014 both results agree well with the temporal variation of tornillos duration and the estimated q quality factors damping coefficients observed at galeras volcano in the context of the cavity model tornillo frequency variations from 4 hz to 1 hz observed prior to eruptions can be interpreted as the result of fluid composition changes as more ash particles are added this is in agreement with the observation that gas accumulation at galeras was a steady rather than an episodic process and that tornillos were most likely triggered after a fluid pressure threshold had been exceeded

raman characterization of carbonaceous material in the macraes orogenic gold deposit and metasedimentary host rocks new zealand abstract raman spectroscopic and petrographic analyses were performed on samples collected from zones distal and proximal to the macraes gold deposit in the otago schist of new zealand to characterize the features and possible origins of carbonaceous material cm and to assess the potential role of cm in the formation of gold deposits cm is a common component in meta sedimentary orogenic gold deposits and it has been proposed that cm contributes to gold mineralization processes but the details of the mechanisms responsible are not fully understood documentation of the origins of the otago schist cm will improve our understanding of the role of cm in gold deposits this work has identified four types of cm of varying thermal maturity and origins from prehnite pumpellyite grade to lower greenschist grade samples in prehnite pumpellyite and pumpellyite actinolite grade rocks low maturity cm 1 coexists with framboidal pyrite indicating an in situ sedimentary origin with a potential association with the source of gold low crystallinity cm 2 is also found in low grade samples and is likely to have been deposited from fluids unrelated to gold mobilization cm 3 is the highest maturity cm recognized cm 3 is found in samples from the highest metamorphic grades studied lower greenschist facies where bands of cm 3 cross cut the foliation cm 3 is therefore thought to have been transported by fluids though possibly only at short length scales cm 4 is less mature than cm 3 and is found in mineralized rocks in association with sulfide minerals and gold cm 4 is likely to have a depositional origin but its precise role with respect to gold mineralization has not been identified

tornillo type seismic signals at galeras volcano colombia 1992 1993 abstract unusual low frequency seismic events called tornillos screws at the observatorio vulcanologico y sismologico de pasto ovsp have been observed at galeras volcano during 1992 1993 of six eruptions that occurred between july 1992 and june 1993 five were preceded by episodes of tornillo signals these signals are characterized by 1 a waveform having a homogeneous distribution of frequencies 2 a long coda lasting up to several minutes 3 a small amplitude compared to the duration and 4 a slow decay of the coda the tornillo signals have been grouped into thirteen principal forms the 1992 1993 tornillos showed four main periods of occurrence each of which was followed by an eruption episode i occurred from 11 to 16 july 1992 and consisted of nine events episode ii lasted from 23 december 1992 to 14 january 1993 with twenty events episode iii was observed from 13 february to 23 march 1993 with 74 events episode iv lasted from 10 april to 7 june 1993 with 109 events the seismic activity at galeras in april may 1993 was characterized mainly by the occurrence of tornillo signals the behavior of these signals was similar to that before previous episodes ending with eruptions these observations permitted us to forecast the 7 june 1993 eruption several days to weeks beforehand the occurrence of tornillos is the most important criterion for determining the probability of an eruption at galeras in the current period of reactivation the maximum daily number of tornillos and the longest duration of individual events occur near the end of each episode within an individual episode the durations of single events increase progressively near to the point of eruption a positive correlation is observed between the total number of pre eruptive tornillo signals during an episode and the volume of material ejected by the eruption these observations may suggest that the presence of tornillos is an indication of variations in the physical conditions between the fluid and the surrounding solid material within the volcano and they constitute an important tool for forecasting future eruptions at galeras

archaean au ag mineralisation at racetrack near kalgoorlie western australia a high crustal level expression of the archaean composite lode gold system the racetrack au ag deposit in the archaean yilgarn block western australia is hosted by a porphyritic basalt in a low greenschist facies setting and is associated with a brittle strike slip fault system three distinct and successive stages of hydrothermal activity and late quartz carbonate veining resulted in multiple veining and or brecciation stages i and ii are au bearing whereas stage iii and late veins are barren the ore shows features of both classic epithermal and mesothermal deposits alteration assemblages typified by sericitization carbonization silicification and chloritization are similar to those of mesothermal gold deposits wheras the quartz vein textures including comb rosette plumose and banded ore mineralogyof arsenopyrite pyrite chalcopyrite sphalerite galena freibergite tetrahedrite tennantite fahlore electrum and gold and metal associations cu as ag sn sb w au and pb are more characteristics of epithermal deposits fluid inclusions related to stage ii are two phase and aqueous with 1 8 average 4 wt nacl equiv and co2 content of 0 85 molal pressure corrected homogenisation temperatures range from 190 c to 260 c mineral assemblages indicate that ore fluid ph ranged between 4 2 and 5 3 fo 2 between 10 38 8 and 10 39 6 bars and m s between 10 3 2 and 10 3 6 calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the mineralisation but evidence for deep crustal pb indicates that deeply sourced fluids were also involved the deposit is interpreted to have formed in a shallow environment via mixing of deeply sourced fluids from at least as deep as the base of the greenstone belt with surface waters it therefore represents the upper crustal end member of the crustal depth spectrum of archaean lode gold mineralisation

review of electromagnetic induction for mapping barrier island framework geology abstract the geologic framework controls on modern barrier island transgression and the relationship of these controls to subsurface structure hydrology and island geomorphology are not well understood recent evidence suggests that alongshore variations in pre holocene geology of barrier islands modify nearshore hydrodynamic processes and sediment transport ultimately affecting how barrier islands will respond to relative sea level rise explorations of holocene barrier island geology are usually based on cores to supplement bathymetric onshore offshore seismic and or ground penetrating radar gpr surveys the advantages and limitations of these methods with respect to barrier island investigations are briefly described in this review alternative near surface geophysical methods including electromagnetic induction emi sensors are increasingly being used for coastal research because they are non invasive provide continuous subsurface information across a variety of sub environments and are capable of characterizing large areas in a short time although these emi sensors have shown promise in coastal applications a number of issues primarily related to subsurface hydrology need to be addressed to fully assess the limitations of this technique this paper reviews the theory methodology and applications of emi in support of geologic framework studies with particular reference to barrier islands resolution of these issues will allow emi sensors to complement and offer significant advantages over traditional methods in support of an improved understanding of large scale barrier island evolution

the role of paleochannels in groundwater seawater exchange relict fluvial channels that are infilled with high permeability sediments act as preferred pathways for groundwater flow and solute transport in coastal regions such paleochannels can provide a hydraulic connection between freshwater aquifers and the sea facilitating saltwater intrusion landward or freshwater discharge offshore although paleochannels have been implicated in several instances of saltwater intrusion there has been little direct study of these channels to confirm their role in this work simulation modeling of a general multi layered coastal plain aquifer setting indicates that when a paleochannel breaches a confining unit offshore submarine groundwater discharge of intermediate salinity occurs this discharge is largely concentrated along the margins of the channel conversely seawater inflow occurs along the channel axis resulting in higher salinity in the middle of the channel relative to the flanks chirp seismic and electromagnetic data collected offshore wrightsville beach nc usa confirm these simulation results and indicate fresher porewater along channel flanks and slightly higher porewater salinity along the channel axis hence paleochannels contribute to the spatial variability in submarine groundwater discharge by serving as conduits of focused fluid exchange simulations also reveal that the freshwater saltwater transition zone is closer to land below paleochannels than in locations with a continuous confining unit this indicates that such channels are likely to be significant modes of saltwater intrusion into confined aquifers when excess freshwater extraction occurs on land

parameterization of multichromatic tornillo signals observed at galeras volcano colombia in the past decade several of the ash eruptions at galeras volcano colombia have been preceded by tornillos these unusual tremor wavelets have quasi sinusoidal waveforms with screw like envelope profiles and can last up to several minutes a swarm of tornillos occurred at galeras volcano between 8 december 1999 and 12 february 2000 these tornillos appear to be more complex than those previously recorded with the broadband instruments or with the short period network of the observatorio vulcanologico y sismologico in pasto they are multichromatic with a varying number of narrow spectral peaks between 1 and 20 hz we describe a procedure for parameterizing the tornillo signals in the time and frequency domains to determine signal parameters in addition to wavelets like the tornillos the procedure can be applied to random signals such as volcanic tremor we derive distribution and correlation functions for the signal parameters determined from the swarm these provide along with the signal signature constraints for modelling variations of the source process from these observations we derive qualitative conclusions about the characteristics of differential equations which describe the underlying processes and excitation mechanisms as forced or self excited oscillators

fluid evolution in the baia mare epithermal gold polymetallic district inner carpathians romania the baia mare district romania represents a complex segment of the neogene quaternary subduction related volcanic chain of the carpathians in this province the calc alkaline volcanism and associated mineralization are closely related to a major strike slip fault and an underlying pluton the ore deposits of the district have many features typical of low sulfidation or adularia sericite epithermal deposits the combination of fluid inclusion microthermometry raman spectroscopy bulk crush leach analysis laser ablation optical emission spectrometry la oes of individual fluid inclusions and stable isotope data has been used to characterize the ore forming solutions involved with gold polymetallic mineralization in three of the largest deposits ore fluids at baia sprie cavnic and sasar deposits had temperatures of 320 to 150 c and salinities in the range 0 21 wt nacl equiv during phreatomagmatic activity fracturing and periods of vein dilation the pressure fluctuations may have caused boiling the hydrothermal fluids were na k li ca chloride solutions with lesser amounts of so4 and f the na k ratios and the stable isotope compositions are consistent with equilibration of the fluids with country rocks at progressively lower temperatures the halogen ratios br cl 103 in the range 0 13 1 21 together with sulfur isotopic systematics 34s 0 3 5 2 per mil are consistent with a dominantly magmatic origin of the solutes and probably of the ore fluids themselves

impact of low salinity porewater on seafloor electromagnetic data a means of detecting submarine groundwater discharge submarine groundwater discharge has been recognized as an important process in coastal and shelf environments but due to the diffuse nature of the process methods to identify and map zones of discharge still need development vertical profiles of subseafloor salinity from two locations off the east coast of the u s and from a coastal embayment in cape cod ma have been used to model seafloor electromagnetic em responses to changes in porewater salinity ordinarily porewaters of salinity close to that of seawater will be electrically conductive replacement of this conductive porewater by a body of fresh groundwater will reduce the electrical conductivity of the porewater and hence that of the seafloor based on in situ measurements of porewater salinity and reasonable estimates of sediment porosity our modelling quantifies the changes in em apparent porosity measurements that might be expected over coastal and nearshore regions of fresh water discharge given the results obtained we demonstrate that existing em technology might be used to map zones of fresh water in conjunction with other methods

tectonostratigraphic evolution of cenozoic marginal basin and continental margin successions in the bone mountains southwest sulawesi indonesia abstract the bone mountains located in southwest sulawesi along the se margin of sundaland are composed of oligocene to possibly lower miocene marginal basin successions bone group that are juxtaposed against continental margin assemblages of eocene miocene age salokalupang group three distinct units make up the latter i middle upper eocene volcaniclastic sediments with volcanic and limestone intercalations in the upper part matajang formation reflecting a period of arc volcanism and carbonate development along the sundaland margin ii a well bedded series of oligocene calc arenites karopa formation deposited in a passive margin environment following cessation of volcanic activity and iii a series of lower middle miocene sedimentary rocks in part turbiditic which interfinger in the upper part with volcaniclastic and volcanic rocks of potassic affinity baco formation formed in an extensional regime without subduction the bone group consists of morb like volcanics showing weak to moderate subduction signatures kalamiseng formation and a series of interbedded hemipelagic mudstones and volcanics deko formation the deko volcanics are in part subduction related and in part formed from melting of a basaltic precursor in the overriding crust we postulate that the bone group rocks formed in a transtensional marginal basin bordered by a transform passive margin to the west sundaland and by a newly initiated westerly dipping subduction zone on its eastern side around 14 13 ma an extensional tectonic event began in sw sulawesi characterized by widespread block faulting and the onset of potassic volcanism it reached its peak about 1 ma year later with the juxtaposition of the bone group against the salokalupang group along a major strike slip fault walanae fault zone the latter group was sliced up in variously sized fragments tilted and locally folded potassic volcanism continued up to the end of the pliocene and locally into the quaternary

tornillos beneath tongariro volcano new zealand abstract unusual low frequency seismic events have recently begun to occur beneath tongariro volcano new zealand because the seismic waveforms appear similar to waveforms called tornillos which have been recorded at galeras volcano in colombia and have been found to precede small to medium sized ash eruptions there by several weeks to months we are monitoring them closely at tongariro these events are characterised by small amplitude monochromatic or multichromatic waveforms that decay slowly with time features that suggest a source involving magmatic or hydrothermal fluids within a zone surrounded by hard rock the frequency content of monochromatic events is typically between 1 and 3 hz and is often found to be peaked at f 1 2 hz event durations range from about 10 to 80 s the appearance of the shorter duration events is identical to so called lp or long period events the lps and tornillos appear to be co located so that the only difference between lps and tornillos is the extended duration of the latter these events have been identified in the seismograms of the permanent monitoring station kavz since at least january 2001 occurring at a rate of about one per month during june august 2001 the rate of occurrence gradually increased peaking in september 2001 at several events per day we deployed two broadband and several short period seismometers at close distances to the expected source location the resulting seismograms show a complex mixture of seismic waves originating from shallow depth beneath the area of the te maari craters located approximately 0 5 km from the nearest station the close range broadband records reveal some interesting details about the tornillo source the tornillo waveform is found to consist of two parts a low frequency f 1 2 hz part and a higher frequency f 3 hz part the high frequency energy travels at body wave speeds c 3 0 km s while the low frequency energy travels at the speed of shear or surface waves in the shallow crust c 1 km s interestingly for some events the low frequency waves arrive before the high frequency body waves at the closest station this and comparison with several lp events suggests a spatial separation of the high and low frequency sources with the low frequency energy originating at shallow depth and acting as a trigger for the release of tectonic stress at greater depth in the form of high frequency body waves

a time domain electromagnetic survey of the tag hydrothermal mound a conductivity survey of the tag mound was made using innovative transient electric dipole dipole instrumentation the receiver was deployed on the sulfide mound 30 m south of the central black smoker while the submersible alvin carried the transmitter on a survey path around the receiver at a radius of approximately 70 m conductivity measurements of the seafloor between the transmitter and receiver were made at 5 minute intervals the survey lasted 4 hours measurements made at 12 sites are initially interpreted in terms of an apparent conductivity of a uniform seafloor a more complex model in which the seafloor has two layers is then used apparent conductivities range from 1 4 to 15 9 s m generally higher than that of seawater the results suggest possible focusing of hydrothermal convection in the northern quadrant of the mound adjacent zones of anhydrite accumulation and fluid convection in the north eastern quadrant heterogeneity and layering in the kremlin zone and unexpected spatial variability in the western quadrant the data from several sites show evidence of distortion attributed to 3 d anomalies

review paper instrumentation for marine magnetotelluric and controlled source electromagnetic sounding we review and describe the electromagnetic transmitters and receivers used to carry out magnetotelluric and controlled source soundings in the marine environment academic studies using marine electromagnetic methods started in the 1970s but during the last decade these methods have been used extensively by the offshore hydrocarbon exploration industry the principal sensors magnetometers and nonpolarizing electrodes are similar to those used on land but magnetotelluric field strengths are not only much smaller on the deep sea floor but also fall off more rapidly with increasing frequency as a result magnetotelluric signals approach the noise floor of electric field and induction coil sensors 0 1 nv m and 0 1 pt at around 1 hz in typical continental shelf environments fluxgate magnetometers have higher noise than induction coils at periods shorter than 500 s but can still be used to collect seafloor magnetotelluric data down to 40 100 s controlled source transmitters using electric dipoles can be towed continuously through the seawater or on the sea bed achieving output currents of 1000 a or more limited by the conductivity of seawater and the power that can be transmitted down the cables used to tow the devices behind a ship the maximum source receiver separation achieved in controlled source soundings depends on both the transmitter dipole moment and on the receiver noise floor and is typically around 10 km in continental shelf exploration environments the position of both receivers and transmitters needs to be navigated using either long baseline or short baseline acoustic ranging while sea floor receivers need additional measurements of orientations from compasses and tiltmeters all equipment has to be packaged to accommodate the high pressure up to 40 mpa and corrosive properties of seawater usually receiver instruments are self contained battery powered and have highly accurate clocks for timekeeping even when towed on the sea floor or in the water column behind a transmitter

a porosity mapping survey in hecate strait using a seafloor electro magnetic profiling system abstract a newly developed marine electromagnetic e m system was used to create apparent porosity maps of the uppermost 20 m of sediments on the seafloor measurements of electrical conductivity were interpreted to give the porosity of the bottom sediments and underlying units the data were collected continuously in a surveying mode using two receivers at different spacings to improve the resolution of porosity as a function of depth the variations in apparent porosity over the area correlate well with information obtained from cores and acoustic profiles acoustic profiles indicated the presence of biogenic gas in the central region of the survey area the absence of distinct changes in apparent porosity over regions of gas allows us to conclude that the concentration of gas trapped within the queen charlotte muds does not exceed about 4 of the sediment by volume if we assume that the gas displaces fluid in the sediment a buried lower porosity layer was detected its position reflecting changes in the depth to the glaciomarine layer mapped variations in apparent porosity are well correlated with features on the acoustic record this illustrates the system s ability to obtain continuous profiles of apparent porosity over seafloor features the marine e m survey provided rapid areal coverage and combined with the acoustic profiles information on the porosity of deeper units

towards an automatic monitoring system of infrasonic events at mt etna strategies for source location and modeling active volcanoes characterized by open conduit conditions generate sonic and infrasonic signals whose investigation provides useful information for both monitoring purposes and studying the dynamics of explosive processes in this work we discuss the automatic procedures implemented for a real time application to the data acquired by a permanent network of five infrasound stations running at mt etna volcano the infrasound signals at mt etna consist in amplitude transients called infrasound events the adopted procedure uses a multi algorithm approach for event detection counting characterization and location it is designed for an efficient and accurate processing of infrasound records provided by single site and array stations moreover the source mechanism of these events can be investigated off line or in near real time by using three different models 1 strombolian bubble 2 resonating conduit and 3 helmholtz resonator the infrasound waveforms allow us to choose the most suitable model to get quantitative information about the source and to follow the time evolution of the source parameters

modelling low frequency volcanic earthquakes in a viscoelastic medium with topography summary magma properties are fundamental to explain the volcanic eruption style as well as the generation and propagation of seismic waves this study focusses on magma properties and rheology and their impact on low frequency volcanic earthquakes we investigate the effects of anelasticity and topography on the amplitudes and spectra of synthetic low frequency earthquakes using a 2 d finite difference scheme we model the propagation of seismic energy initiated in a fluid filled conduit embedded in a homogeneous viscoelastic medium with topography we model intrinsic attenuation by linear viscoelastic theory and we show that volcanic media can be approximated by a standard linear solid sls for seismic frequencies above 2 hz results demonstrate that attenuation modifies both amplitudes and dispersive characteristics of low frequency earthquakes low frequency volcanic earthquakes are dispersive by nature however if attenuation is introduced their dispersion characteristics will be altered the topography modifies the amplitudes depending on the position of the seismographs at the surface this study shows that we need to take into account attenuation and topography to interpret correctly observed low frequency volcanic earthquakes it also suggests that the rheological properties of magmas may be constrained by the analysis of low frequency seismograms

magmatic evolution of sulawesi indonesia constraints on the cenozoic geodynamic history of the sundaland active margin abstract tertiary and quaternary magmatic rocks from west sulawesi record the complex history of part of the sundaland margin where subduction and collision have been and are still active the present study based on petrographic data major and trace element chemistry and 40 k 40 ar dating aims to document the age and chemical characteristics of the magmatic formations from west sulawesi and to determine the corresponding constraints on the geodynamic evolution of the sundaland border the west sulawesi magmatic province includes the south arm of sulawesi ujung pandang area the western part of central sulawesi with the toraja and palu areas and finally the north arm extending from palu to manado which includes the tolitoli and manado areas paleocene magmatic activity seems to be restricted to an episode of calc alkaline magmatism in the ujung pandang area 61 59 ma the major eocene 50 40 ma magmatic event is tholeiitic and is documented in all areas except in ujung pandang it led to the emplacement of tholeiitic pillow lavas and basaltic dykes of back arc basin bab affinity these rocks are potential equivalents to the celebes sea basaltic basement from oligocene to miocene magmatic eruptions produced successively island arc tholeiitic iat and calc alkaline ca rock series the youngest iat activity occurred around 18 ma in the central part palu area and around 14 ma in the north arm tolitoli area while ca magmas were emplaced in the north arm at ca 18 ma tolitoli and manado areas typical calc alkaline activity resumed only in the north arm tolitoli and manado areas during the late miocene 9 ma and is still active in the manado region in other areas palu toraja and ujung pandang areas an important and widespread magmatic event occurred between 13 and 10 ma and emplaced k rich magmas either silica undersaturated alkali potassic basalts ak ultrapotassic basanites uk or shoshonites sh k rich activity continued in the south until the pleistocene 0 77 ma with alkali potassic ultrapotassic and shoshonitic magmas in central sulawesi toraja and palu areas the most recent magmatic event occurred between 6 5 and 0 6 ma the corresponding products are granitic rocks and widely distributed rhyolitic pyroclastic flow deposits all these rocks are acidic in character sio 2 60 with trace element and isotopic signatures sr nd pb typical of a strong continental imprint the most striking tectonic implication of this magmatic evolution is that west sulawesi can no longer be considered as a typical magmatic arc as previously assumed with the exception of the manado area beneath which subduction is still active calc alkaline and island arc tholeiitic lavas and plutonics are volumetrically minor with respect to k rich magmas their occurrence through time is also fairly restricted mostly to the period between 30 and 15 ma another important feature is the occurrence of island arc tholeiitic and calc alkaline magmas crosscutting an older terrane of bab affinity the tinombo formation manado tolitoli and palu areas as this formation is being regarded as an equivalent to the celebes sea floor the most likely explanation for this feature is the hypothesis of tectonic erosion linked to the nw dipping subduction beneath the north arm the late miocene high k magmatic activity in central and south sulawesi reflects the prevalence of a post collisional tectonic regime following the docking of microcontinents of australian origin to central sulawesi during neogene times the incompatible element enriched character of these high k rocks might reflect their derivation from a mantle source enriched through metasomatism related to a previous subduction event such a model cannot account for the plio pleistocene cak magmatism of central sulawesi the acidic composition of which does not support a derivation from an ultrabasic source the trace element patterns of the cak rocks are very similar to those of the high grade metamorphics of central sulawesi suggesting that the latter might represent their possible source such an anatectic model implies a collisional to post collisional tectonic regime limited to central sulawesi while a post subduction regime prevailed in the south

metabasalts as sources of metals in orogenic gold deposits although metabasaltic rocks have been suggested to be important source rocks for orogenic gold deposits the mobility of au and related elements as sb se and hg from these rocks during alteration and metamorphism is poorly constrained we investigate the effects of increasing metamorphic grade on the concentrations of au and related elements in a suite of metabasaltic rocks from the otago and alpine schists new zealand the metabasaltic rocks in the otago and alpine schists are of morb and wpb affinity and are interpreted to be fragments accreted from subducting oceanic crust gold concentrations are systematically lower in the higher metamorphic grade rocks average au concentrations vary little between sub greenschist 0 9 0 5 ppb and upper greenschist facies 1 0 0 5 ppb but decrease significantly in amphibolite facies samples 0 21 0 07 ppb the amount of au depleted from metabasaltic rocks during metamorphism is on a similar scale to that removed from metasedimentary rocks in otago arsenic concentrations increase with metamorphic grade with the metabasaltic rocks acting as a sink rather than a source of this element the concentrations of sb and hg decrease between sub greenschist and amphibolite facies but concentration in amphibolite facies rocks are similar to those in unaltered morb protoliths and therefore unaltered oceanic crust cannot be a net source of sb and hg in a metamorphic environment the concentrations of au as sb and hg in oceanic basalts that have become integrated into the metamorphic environment may be heavily influenced by the degree of seafloor alteration that occurred prior to metamorphism we suggest that metasedimentary rocks are much more suitable source rocks for fluids and metals in orogenic gold deposits than metabasaltic rocks as they show mobility during metamorphism of all elements commonly enriched in this style of deposit

origin of ore fluids in the muruntau gold system constraints from noble gas carbon isotope and halogen data abstract hydrothermal vein minerals directly associated with native gold mineralization in the muruntau vein system uzbekistan have been studied for noble gas carbon isotope and halogen chemistry of the trapped ore related fluids helium trapped in early arsenopyrite 1 which has preserved the original fluid signature better than associated scheelite and quartz indicates a small input from a mantle source 5 of total he however the overwhelming majority of the he in the fluid 95 is from crustal sources the noble gases ne kr and xe in the sample fluids are dominated by gases of atmospheric origin the carbon isotope 13 c 2 1 to 5 3 and halogen characteristics of the fluids log br cl 2 64 to 3 23 lend further support for the activity of juvenile fluids during the main ore stage the high proportion of crustal components in the ore forming fluids may be explained by intense fluid rock interaction and is also supported by previous nd and sr isotope studies the involvement of a juvenile fluid component during the main stage of hydrothermal activity at muruntau 275 ma can be linked to the emplacement of lamprophyric dikes at muruntau due to apparently overlapping ages for high temperature alteration related ore vein formation and intrusion of the dikes the input of mantle derived fluids possibly related to the hercynian collisional event in the western tien shan stimulated intense fluid rock interaction in the crust in this context the mantle derived fluid should be considered as one possible carrier of metals significant amounts of external meteoric fluids circulating in fracture systems are interpreted to have modified the noble gas signature of fluid in quartz mostly during late low temperature fluid circulation

evaluating raman spectra of carbonaceous matter by automated iterative curve fitting abstract raman spectroscopy of carbonaceous material rscm estimates the maximum metamorphic temperature of coal graphite and cm enclosed in metapelites however the evaluation of cm raman spectra is often biased by subjectivity which reduces the overall comparability of rscm results to decrease subjectivity an automated evaluation software is presented it is based on the iterative and simultaneous modeling of signal and baseline functions two new rscm parameters are introduced termed raman area ratio rar and scaled total area sta these parameters are tested on a sample suite of organic rich shales and slates of the teuschnitz syncline thuringia germany of well constrained very low to low metamorphic grade defined by illite crystallinty and vitrinite reflectance a correlation of both rscm parameters with vitrinite reflectance verifies that the rscm parameters reflect the metamorphic conditions this correlation prevails at different excitation wavelengths 488 nm 633 nm 785 nm used for the raman measurements

on the theory of sea floor conductivity mapping using transient electromagnetic systems the electrical conductivity of the sea floor is usually much less than that of the seawater above it a theoretical study of the transient step on responses of some common controlled source electromagnetic systems to adjoining conductive half spaces shows that two systems the horizontal in line electric dipole dipole and horizontal coaxial magnetic dipole dipole are capable of accurately measuring the relatively low conductivity of the sea floor in the presence of seawater for these systems the position in time of the initial transient is indicative of the conductivity of the sea floor while at distinctly later times a second characteristic of the transient is a measure of the seawater conductivity the diagnostic separation in time between the two parts of the transient response does not occur for many other systems including several systems commonly used for exploration on land a change in the conductivity of the sea floor produces a minor perturbation in what is essentially a seawater response some transient responses which could be observed with a practical deep towed coaxial magnetic dipole dipole system located near the sea floor are those for the half space the layer over a conductive or resistive basement and the half space with an intermediate resistive zone the system response to two adjoining half spaces representing seawater and sea floor respectively is derived analytically the solution is valid for all time provided the conductivity ratio is greater than about ten or less than about one tenth the analytic theory confirms the validity of numerical evaluations of closed form solutions to these layered earth models a lateral conductor such as a vertical infinite conductive dike outcropping at the sea floor delays the arrival of the initial crustal transient response the delay varies linearly with the conductance of the dike this suggests that time delay could be inverted directly to give a measure of the anomalous integrated conductance of the sea floor both between and in the vicinity of the transmitter and the receiver dipoles

the archean lode gold deposits at wiluna western australia high level brittle style mineralization in a strike slip regime the wiluna lode hosted gold deposits comprise a group of individual archean lode hosted gold deposits located in the northern part of the norseman wiluna belt western australia collectively they are the fifth largest gold producer in the yilgarn block the deposits are hosted in a series of very low grade metamorphosed prehnite pumpellyite facies mafic and ultramafic lava flows with abundant primary igneous textures preserved lode hosted gold mineralization is controlled by the wiluna strike slip fault system which consists of north and northeast trending and west and east dipping sets of principal displacement faults and associated subsidiary structures the movement on all faults was dextral with minor oblique reverse or oblique normal motion and maximum apparent displacement of 1 350 m the lode deposits are centered on structural inhomogeneities in the principal displacement faults e g divergent bends and dilational jogs including horsetail splays and or subsidiary structures e g overstepping and intersecting faults the plunge of the ore shoots is generally moderately to steeply to the south and is controlled by the intersections between 1 lithologic layering and fault planes 2 two or more fault planes 3 a fault plane and an earlier formed barren or weakly mineralized quartz reef that is semiconcordant to the regional stratigraphy and 4 a fault plane and a felsic intrusion the shape and orientation of ore shoots becomes more complex downdip where they are controlled by additional features such as drag folds and link structures fault hosted ore breccias including implosion and net veined breccias and brecciated veins are significant loci of gold mineralization in all lode deposits they contain mainly quartz chalcedony carbonates fuchsite and arsenopyrite pyrite and or stibnite mineralization occurs also in shear veins and extensional veins and finely disseminated along foliation planes of the mineral fabric formed oblique to the principal displacement faults textures of implosion breccias at wiluna indicate a history of incremental extensional opening across dilational sites and multiple episodes of brecciation and hydrothermal recementation quartz textures such as vugs cavities comb textures and cockade textured quartz are ubiquitous indicating the preservation of open space due to low effective confining pressure geologic relations indicate that the mineralized strike slip fault system was generated late in the tectonic history of the greenstone belt and that high grade ore zones formed late in the strike slip deformation event the very low grade metamorphic facies and the brittle style of deformation in the host rocks combined with the style of mineralization indicate that the fault and mineralizing system formed in a shallow near surface crustal environment textural evidence combined with the tectonic setting of the lode deposits favors the suction pump mechanism as a fluid infiltration mechanism for the lode hosted gold deposits within the wiluna strike slip fault system