the effects of thermochemical sulfate reduction upon formation water salinity and oxygen isotopes in carbonate gas reservoirs abstract thermochemical sulfate reduction tsr is a well known process that can lead to sour h2s rich petroleum accumulations most studies of tsr have concentrated upon gas chemistry in this study we have investigated palaeoformation water characteristics in a deep anhydrite bearing dolomite sour gas reservoir of permian age in abu dhabi using fluid inclusion stable isotope petrographic and gas chemical data the data show that low salinity isotopically distinct water was generated within the reservoir by reaction between anhydrite and methane the amount of water added to the reservoir from tsr indicated by reduced fluid inclusion salinity and water 18o values varied systematically with the extent of anhydrite reaction with methane water salinity and isotope data show that the original formation water was diluted by between four and five times by water from tsr thus we have shown that large volumes of very low salinity water were generated within the gas reservoirs during diagenesis following gas emplacement the salinity of formation water in evaporite lithologies is therefore not necessarily high modelling based upon a typical khuff gas reservoir rock volume suggests that initial formation water volumes can only be increased by about three times as a result of tsr the extreme local dilution shown by the water salinity and 18o data must therefore reflect transiently imperfect mixing between tsr water and original formation water the creation of large volumes of water has important implications for the mechanism and rate of thermochemical sulphate reduction and the interpretation of gas volumes using petrophysical logging tools

deposition diagenetic and hydrothermal processes in the aptian pre salt lacustrine carbonate reservoirs of the northern campos basin offshore brazil abstract the discovery of large oil accumulations in the rift and sag pre salt sections of the campos and santos basins has revived interest in the exploration of the lacustrine carbonate reservoirs in the brazilian and african marginal basins more than half of brazilian oil production originates from the pre salt reservoirs of these offshore basins a study integrating systematic petrography cathodoluminescence scanning electron microscopy microprobe and x ray diffraction was performed on seven wells in the northern campos basin this study highlights the major primary diagenetic and hydrothermal features of the pre salt succession with the aim to improve our understanding of the factors that influence the porosity and permeability distribution in these important lacustrine carbonate reservoirs the pre salt deposits correspond to bioclastic grainstones and rudstones syngenetic crusts of fascicular calcite and intraclastic grainstones and rudstones of reworked crust fragments and calcite spherulites magnesian silicates are frequently associated with carbonate deposits in the sag phase stevensitic laminations constitute the substrate for the precipitation of calcite crusts and spherulites which displace and replace the syngenetic magnesian clay deposits in the rift section stevensitic ooids are mixed with bioclasts or form ooidal arenites pre salt carbonate reservoirs have undergone a complex and heterogeneous diagenetic evolution eodiagenetic processes include the dissolution neomorphism and cementation of bivalve bioclasts in the rift as well as the dissolution of magnesian silicates and their replacement by calcite spherulites silica and dolomite in the sag section burial alterations are commonly associated with hydrothermal fluids carried through faults and fracture systems these fluids promote dolomitization silicification and dissolution at varying degrees and intensities eodiagenetic precipitation and dissolution owing to variations in the lake water chemistry and the episodic flow of hydrothermal fluids under burial conditions control the creation redistribution and obliteration of porosity in the pre salt reservoirs

external modulation of volcanic activity summary time and again records of seismovolcanic activity that show a diurnal and semi diurnal modulation have been related to the earth s tidal stress field as an external triggering mechanism several seismic data sets from different volcanoes are examined including stromboli volcano italy mt ruapehu new zealand and merapi and batur indonesia where in some cases weather data are also incorporated a comparison with theoretical body tides in the spectral domain reveals strong evidence against a correlation between seismovolcanic activity and tidal stress however other parameters such as temperature and barometric pressure show the same diurnal and semi diurnal modulation and are therefore candidates for a possible external modulation of volcanic activity several mechanisms are discussed for stromboli a clear correlation between volcanic activity and barometric pressure is shown

back arc strain in subduction zones statistical observations versus numerical modeling 1 recent statistical analysis by lallemand et al 2008 of subduction zone parameters revealed that the back arc deformation mode depends on the combination between the subducting vsub and upper vup plate velocities no significant strain is recorded in the arc area if plate kinematics verifies vup 0 5 vsub 2 3 cm a in the hs3 reference frame arc spreading shortening occurs if vup is greater lower than the preceding relationship we test this statistical law with numerical models of subduction by applying constant plate velocities far away from the subduction zone the subducting lithosphere is free to deform at all depths we quantify the force applied on the two converging plates to sustain constant surface velocities the simulated rheology combined viscous non newtonian and brittle behaviors and depends on water content the influence of subduction rate vs is first studied for a fixed upper plate after 950 km of convergence steady state slab pull the transition from extensional to compressive stresses in the upper plate occurs for vs 1 4 cm a the effect of upper plate velocity is then tested at constant subduction rate upper plate retreat advance with respect to the trench increases extension compression in the arc lithosphere and increases decreases the subducting plate dip our modeling confirms the statistical kinematic relationship between vsub and vup that describes the transition from extensional to compressive stresses in the arc lithosphere even if the modeled law is shifted toward higher rates of upper plate retreat using our set of physical parameters e g 100 km thick subducting oceanic plate and short term simulations our results make valid the choice of the hs3 reference frame for assessing plate velocity influence on arc tectonic regime the subduction model suggests that friction along the interplate contact and the mantle stokes reaction could be the two main forces competing against slab pull for upper mantle subductions besides our simulations show that the arc deformation mode is strongly time dependent

controls on back arc basin formation the relationship between subduction and back arc spreading has been well known since the early days of plate tectonics however the reasons why back arc basins are associated with some subduction systems but not all has remained elusive we examine the kinematic controls on subduction and back arc basins for both the present day and cenozoic to differentiate between the major competing hypotheses for back arc basin formation and to explain their temporal and spatial distribution our new data set of subduction and back arc basin parameters uses a new set of paleo oceanic age grids muller et al 2005 associated with a moving atlantic indian ocean hot spot reference frame o neill et al 2005 the plate model includes detailed reconstructed spreading histories of back arc basins based on marine geophysical and satellite gravity data our combined rotation and oceanic paleo age model provides the age distribution of subducting lithosphere through space and time convergence rates and the absolute motion of the downgoing and overriding plates we find that back arc basins develop when the age of subducting normal oceanic lithosphere is greater than 55 million years additionally we establish an age dip relationship showing that the intermediate dip angle of the subducting slab is always greater than 30 with back arc spreading our results suggest that back arc basin formation is always preceded by an absolute motion of the overriding plate away from the subduction hinge thereby creating accommodation space between the overriding and subducting plates once back arc extension is established it continues regardless of overriding plate motion indicating back arc spreading is not a simple consequence of overriding plate behaviour the landward migration of the overriding plate as a precursor to back arc extension may indicate that extension on the overriding plate is influenced by the oceanward lateral flow of the mantle however once back arc extension is established rollback of the subduction hinge appears to be the primary force responsible for the continued creation of accommodation space our analysis indicates the driving mechanism for back arc extension is a combination of surface kinematics properties of the downgoing slab the effect of lateral mantle flow on the slab and mantle wedge dynamics

effects of tidal stresses on volcanic activity at mount etna italy 1 here we model quantitatively the stress and strain induced by tidal forces as possible triggers of mount etna eruptions during 1989 2000 and 2001 by means of 2d numerical analysis by finite difference method applied to the volcano edifice spectral and vectorial analysis of tidal acceleration indicates that the quasi diurnal semi diurnal and ter diurnal constituents may have induced decompressions up to some kpa in the shallow i e 1 500 m gas saturated magma reservoir which controlled magma vesiculation and the timing of lava fountain activity from the south east crater sec we consider the geological heterogeneities in the volcanic edifice i e rock geometries and properties feeder conduit and vent systems volcanic landforms the magma properties i e bulk modulus volatile content and the ongoing volcano tectonic stresses i e volcano flank deformations which strongly influence the response of eruptive activity to tidal forces indeed the tidal factor may act on flank deformation concomitant to shallow magma inflation the implications of our model may help understand the eruptive behaviour and the disequilibrium state of the volcano and may be useful for hazard assessment at mount etna

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

the dynamics of a long lasting effusive eruption modulated by earth tides abstract deciphering eruptive dynamics in near real time is essential when dealing with hazard assessment and population evacuation recognition of specific patterns in time series measured during volcanic activity may help decipher distinctive behavior at active volcanoes providing insights into the underlying driving mechanisms multi parameter data sets usually agree on the overall trend characterizing the temporal evolution of an eruption providing insights into the first order eruptive dynamics however second order variations detected in different data sets remain often poorly understood the 2014 2015 holuhraun eruption iceland offers an excellent opportunity to investigate the dynamics of a long lasting effusive eruption we analyze the seismic tremor and the volcanic radiated power emitted by the lava field during the 6 months of the eruption using singular spectrum analysis ssa in both geophysical time series we identify periods from 5 to 32 days coinciding with periods of earth tides here we show that 50 of both signals are composed of tidal periods suggesting that magma movements follow frequencies imposed by lunisolar forces within the crust and at earth s surface

the role of elasticity in slab bending previous studies showed that plate rheology exerts a dominant control on the shape and velocity of subducting plates here we perform a systematic investigation of the role of elasticity in slab bending using fully dynamic 2 d models where an elastic viscoelastic or viscoelastoplastic plate subducts freely into a purely viscous mantle we derive a scaling relationship between the bending radius of viscoelastic slabs and the deborah number de which is the ratio of maxwell time over deformation time we show that de controls the ratio of elastically stored energy over viscously dissipated energy and find that at de 10 2 substantially less energy is required to bend a viscoelastic slab to the same shape as a purely viscous slab with the same intrinsic viscosity elastically stored energy at higher de favors retreating modes of subduction via unbending while trench advance only occurs for some cases with de 1 where most zones have low de 0 1 slabs with de 10 2 either have very low viscosities or they may be yielding in which case our de estimates may be underestimated by up to an order of magnitude potentially pointing towards a significant role of elasticity in 60 of the subduction zones in support of such a role of elasticity in subduction we find that increasing de correlates with increasing proportion of larger seismic events in both instrumental and historic catalogues

earth tides and etnean volcanic eruptions an attempt at correlation of the two phenomena during the 1983 1985 and 1986 eruptions abstract an attempt has been made to correlate volcanic events on mt etna and moon sun attraction during the eruptions of 28 march 6 august 1983 12 march 13 july 1985 and 30 october 1986 the possibility of a trigger effect has been supposed for eruptive phenomena that originate by small and continuous external forces under particular stress conditions on the volcanic structure the parameters compared for the two phenomena are the hourly mean tremor amplitude recorded at serra la nave station and the hourly value of the vertical and of the two partial horizontal north south and east west components of the tidal acceleration induced by the moon sun system the relationship between two series of values the former for the tremor amplitude and the latter for one of the tidal acceleration components were then tested by statistical methods based on the information theoretic measure of interdependence between any pair of signal sequences the results show an effect of the horizontal tidal components on well known tectonic structures which may be widened or closed in contrast there is little evidence that the uprise of magma masses might depend on the vertical tidal attraction

burial cementation in the devonian kaybob reef complex alberta canada abstract detailed analysis of the petrography and distribution of compositionally zoned ferroan calcite and dolomite cements in the devonian kaybob reef complex of alberta canada has demonstrated that porosity occlusion is predominantly a result of burial diagenesis to depths in excess of 4 km different but temporally related mechanisms of formation are indicated for the two cement types coarsely crystalline dolomite and coarsely crystalline calcite calcite cement precipitational history determined by correlation of compositional zones demonstrates that pressure solution along stylolites was the essential mechanism of calcite cementation in the reef interior and to a lesser extent in the reef slope facies zoned dolomite cements are in contrast the major cement type in the reef margi and reef slope facies a basinal source for dolomite precipitating fluids is indicated it is suggested that the composition of basin derived pore waters was controlled by temperature dependent clay mineral reactions as a function of progressive burial

linking so2 emission rates and seismicity by continuous wavelet transform implications for volcanic surveillance at san cristobal volcano nicaragua san cristobal volcano is the highest and one of the most active volcanoes in nicaragua its persistently high activity during the past decade is characterized by strong degassing and almost annual vei 1 2 explosions which present a threat to the local communities following an eruption on 8 september 2012 the intervals between eruptions decreased significantly which we interpret as the start of a new eruptive phase we present here the results of semi continuous so2 flux measurements covering a period of 18 months obtained by two scanning uv doas instruments installed as a part of the network for observation of volcanic and atmospheric change project and the results of real time seismic amplitude measurements rsam data our data comprise a series of small to moderately explosive events in december 2012 june 2013 and february 2014 which were accompanied by increased gas emissions and seismicity in order to approach an early warning strategy we present a statistical method for the joint analysis of gas flux and seismic data by using continuous wavelet transform and cross wavelet transform xwt methods this analysis shows that the xwt coefficients of so2 flux and rsam are in good agreement with the occurrence of eruptive events and thus may be used to indicate magma ascent into the volcano edifice such multi parameter surveillance efforts can be useful for the interpretation and surveillance of possible eruptive events and could thus be used by local institutions for the prediction of upcoming volcanic unrest

fault controlled dolomitization at swan hills simonette oil field devonian deep basin west central alberta canada the partly dolomitized swan hills formation middle upper devonian in the simonette oil field of west central alberta underwent a complex diagenetic history which occurred in environments ranging from near surface to deep 2500 m burial five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post date stylolites in limestones depths 500 m these include early planar varieties and later saddle dolomites fluid inclusion data from saddle dolomite cements th 137 190 c suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data tpeak 160 c thus at least some dolomitizing fluids were hydrothermal fluorescence microscopy identified three populations of primary hydrocarbon bearing fluid inclusions and confirms that saddle dolomitization overlapped with upper cretaceous oil migration the source of early dolomitizing fluids probably was devonian or mississippian seawater that was mixed with a more 87sr rich fluid fabric destructive and fabric preserving dolostones are over 35 m thick in the swan hills buildup and basal platform adjacent to faults thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults this plume like geometry suggests that early and late dolomitization events were fault controlled late diagenetic fluids were in part derived from the crystalline basement or palaeozoic siliciclastic aquifers based on 87sr 86sr values up to 0 7370 from saddle dolomite calcite and sphalerite cements and 206pb 204pb of 22 86 from galena samples flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m both vertically along reactivated faults and laterally in the buildup along units that retained primary and or secondary porosity

stratigraphic control on facies and diagenesis of dolomitized oolitic siliciclastic ramp sequences pinda group albian offshore angola pervasively dolomitized oolitic to siliciclastic ramp sequences are prolific oil reservoirs in the albian pinda group of northern angola during the late cretaceous this reservoir series was segmented by salt tectonic gravitational gliding into halokinetic turtle back and raft structures that provide hydrocarbon traps today the albian ramp sequences contain a large variety of reservoir facies reaching from littoral sandstones with interparticle porosity to various types of dolomitized marine shelf to shoreline carbonates with moldic vuggy and intercrystalline porosity reservoir prediction is substantially improved by an integrated approach combining high resolution sequence stratigraphy with carbonate geochemistry as high resolution stratigraphy documents most of the important sandstone reservoirs formed at the base of stratigraphic sequences during shoreface transgression pisolitic dolostones with moldic porosity are the best carbonate reservoirs they developed as transgressive shoreface sand sheets above the basal sandstone reservoirs regressive facies tracts contain oolitic and pisolitic dolomites with intercrystalline and moldic porosity that originated in progradational barrier and sand belt settings the combined stratigraphic and geochemical approach allowed us to determine the pinda group dolomites as early diagenetic in origin whereas fluid inclusion and oxygen isotope analysis alone suggested a late burial dolomite formation dolomite neomorphism at higher burial temperatures modified most of the original geochemical signatures of early near surface dolomitization cathodoluminescence data and trace element analysis suggest that dolomitization was associated with gradually decreasing pore water salinity accordingly barrier oolites were completely dolomitized and developed intercrystalline porosity during the earliest stages of diagenesis at a later phase of early diagenesis as waters became less saline and undersaturated with respect to calcium carbonate fabric selective dissolution of the remaining calcareous components occurred the decrease in pore water salinity and associated porosity generation are genetically linked with high frequency events of relative sea level lowering this possible relationship implies that high resolution sequence stratigraphy can be a valid reservoir prediction tool even in pervasively dolomitized series

correlations between so2 flux seismicity and outgassing activity at the open vent of villarrica volcano chile 1 the characteristics of the open vent activity of villarrica volcano chile were studied in detail by integrating visual observations of the lava lake analysis of the seismic tremor and measurements of so2 flux the outgassing activity comprises a persistent gas plume emission from the bottom of the crater as well as frequent explosive events three main styles of bubble bursting were identified at the surface of the active lava lake seething magma small short lived lava fountains and strombolian explosions seething magma consists of continual burst of relatively small bubbles a few meters in diameter with varying strength over the entire surface of the lava lake small lava fountains seen as a vigorous extension of seething magma commonly have durations of 20 120 s and reach 10 40 m high above the lava lake correlations between seismicity and visual observations indicate that the seismic tremor is mostly caused by the explosive outgassing activity furthermore for different periods between 2000 and 2006 during which the activity remained comparable the real time seismic amplitude measurement system rsam and so2 emission rates show a very good correlation higher so2 emissions appeared to be related to higher levels of the lava lake stronger bubble bursting activity and changes in the morphology and texture of the crater floor background low levels of activity correspond to a lava lake located 80 m below the crater rim small and or blocky morphology of the roof seismic amplitude rsam lower than 25 units few volcano tectonic earthquakes and daily averages of so2 emissions lower than 600 mg d

kaolin cements in limestones potential indicators of organic rich pore waters during diagenesis abstract kaolin dickite and or kaolinite cement occurs locally in the chalk group upper cretaceous lower tertiary in the north sea and the derbyhaven beds lower carboniferous on the isle of man united kingdom stable isotope and petrographic data indicate that the kaolin cements in both the chalk group and derbyhaven beds precipitated during late diagenesis in either marine or modified marine pore waters kaolin cements in both formations are associated with hydrocarbons which suggests that organic complexing of aluminum may be responsible for precipitation of kaolin cement published experimental studies have demonstrated that the mobility of aluminum is greatly increased by complexing with organic acids in such systems aluminum would be released and made available for clay mineral precipitation when the organo aluminum complexes are destabilized increased whole rock 13c values in chalk group limestones from the eldfisk field where kaolin cement was widespread provides corroborating evidence for the late diagenetic decarboxylation of organic acids which would have released complexed aluminum the presence of kaolin cement may thus be an indicator of the former presence of organic rich pore fluids in limestones and provide an additional tool for determination of the pore water history of limestones and sedimentary basins

cement distribution in a carbonate reservoir recognition of a palaeo oil water contact and its relationship to reservoir quality in the humbly grove field onshore uk abstract the distribution of mineral cements total porosity microporosity and permeability have been determined for the humbly grove oolitic carbonate reservoir middle jurassic great oolite formation weald basin onshore uk using a combination of optical petrography electron microscopy fluid inclusion analysis quantitative xrd wireline data analysis and core analysis data grainstone reservoir facies have porosities ranging between 5 and 24 but are mostly between 11 and 24 permeabilities vary from

rainfall induced volcanic activity on montserrat 1 dome forming volcanic eruptions cyclically extrude bodies of lava over several months which then become gravitationally unstable and collapse generating pyroclastic flows on 29 july 2001 extreme rainfall over montserrat coincided with a major collapse of the soufriere hills lava dome we present rainfall and seismic records that demonstrate for the first time a relationship between intense rainfall and lava dome collapse with associated pyroclastic flow generation after seven months of little rain and a period of sustained dome growth the onset of intense rain was followed within hours by dome collapse and pyroclastic flows the large scale weather system responsible for the rain was identifiable in satellite images and predicted by meteorological forecasts issued 60 hours prior to the volcanic activity it is suggested that weather prediction of intense rainfall be incorporated with existing geophysical and geochemical measurements to improve warnings of these hazardous events

variation in sulfur dioxide emissions related to earth tides halemaumau crater kilauea volcano hawaii variation in so2 emissions from halemaumau crater kilauea volcano hawaii is analyzed using a set of techniques known as exploratory data analysis so2 flux was monitored using a correlation spectrometer a total of 302 measurements were made on 73 days over a 90 day period the mean flux was 171 t d with a standard deviation of 52 t d a significant increase in flux occurs during increased seismic activity beneath the caldera so2 flux prior to the this change varies in a systematic way and may be related to variation in the tidal modulation envelope

comparison of seismic activity for llaima and villarrica volcanoes prior to and after the maule 2010 earthquake llaima and villarrica are two of the most active volcanoes in the chilean southern volcanic zone and presently show contrasting types of activity llaima is a closed vent edifice with fumarolic activity while villarrica has an open vent with a lava lake continuous degassing and tremor activity this study is focused on characterizing the relationships between volcanic and seismic activity in the months before and after the 2010 m8 8 maule earthquake which was located in nnw direction from the volcanoes time series for tremors long period and volcano tectonic events were obtained from the catalogue of the volcanic observatory of the southern andes ovdas and from the sfb 574 temporary volcanic network an increase in the amount of tremor activity long period events and degassing rates was observed at villarrica weeks before the mainshock and continued at a high level also after it this increase in activity is interpreted to be caused by enhanced magma influx at depth and may be unrelated to the maule event in llaima an increase in the volcano tectonic activity was observed directly after the earthquake the simultaneous post earthquake activity at both volcanoes is consistent with a structural adjustment response since this enhanced activity lasted for more than a year we suggest that it is related to a medium term change in the static stress thus the maule earthquake may have affected both volcanoes but did not trigger eruptions from which we assume that none of the volcanoes were in a critical state

anomalous emissions of so2 during the recent eruption of santa ana volcano el salvador central america santa ana volcano in western el salvador central america had a phreatic eruption at 8 05 am local time on october 1 2005 101 years after its last eruption however during the last one hundred years this volcano has presented periods of quiet degassing with fumarolic activity and an acidic lake within its crater this paper presents results of frequent measurements of so2 degassing using the minidoas differential optical absorption spectroscopy system and a comparison with the volcanic seismicity prior to the eruption during and after the eruption vehicle measurements of so2 flux were taken every hour during the first nine days of the eruption and daily after that the period of time reported here is from august to december 2005 three periods of degassing are distinguished pre eruptive eruptive and post eruptive periods the intense activity at santa ana volcano started in july 2005 during the pre eruptive period up to 4306 and 5154 ton day of so2 flux were recorded on october 24 and september 9 2005 respectively these values were of the same order of magnitude as the recorded values just after the october 1st eruption 2925 ton day at 10 01 am hourly measurements of so2 flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase in so2 flux and that this parameter reaches a peak after the explosion took place this behavior suggests that increasing accumulation of exsolved magmatic gases occurs within the magmatic chamber before the explosions increasing the pressure until the point of explosion a correlation between so2 fluxes and rsam real time seismic amplitude measurements is observed during the complete sampling period periodic fluctuations in the so2 and rsam values during the entire study period are observed one possible mechanism explaining these fluctuations it that convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels allowing increasing degasification and then decreasing degasification as the batch of magma lowers its gas content becomes denser and sinks to give space to a new magma pulse these results illustrate that the measurements of so2 flux can provide important warning signals for incoming explosive activity in active volcanoes

an upper bound for the tidally rectified current at one location on the southern flank of georges bank abstract long term current observations at 45 and 75 m at one location on the southern flank of georges bank in water 85 m deep were examined for evidence of tidal rectification loder has shown analytically that rectification of the strong semidiurnal tidal current can cause a mean along bank flow and thus may partially drive the observed clockwise circulation around georges bank the amplitude of the tidally rectified along bank flow is proportional to the squared amplitude of the cross bank tidal current a simply extension of loder s model to include the weaker n2 and s2 tidal components suggests that fortnightly 354 h and monthly 661 h variations of the square of the cross bank tidal current should cause a modulation of the subtidal along bank flow the predicted ratio r of the fortnightly and monthly modulation of the along bank flow to the mean along bank flow on the southern flank was a function of position and ranged from 0 1 0 5 the amplitude of modulation of the along bank flow at 360

accurately measuring volcanic plume velocity with multiple uv spectrometers a fundamental problem with all ground based remotely sensed measurements of volcanic gas flux is the difficulty in accurately measuring the velocity of the gas plume since a representative wind speed and direction are used as proxies for the actual plume velocity there can be considerable uncertainty in reported gas flux values here we present a method that uses at least two time synchronized simultaneously recording uv spectrometers flyspecs placed a known distance apart by analyzing the time varying structure of so2 concentration signals at each instrument the plume velocity can accurately be determined experiments were conducted on k lauea usa and masaya nicaragua volcanoes in march and august 2003 at plume velocities between 1 and 10 m s 1 concurrent ground based anemometer measurements differed from flyspec measured plume speeds by up to 320 this multi spectrometer method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic or industrial gas flux measurements

prevention of carbonate cementation in petroleum reservoirs by the time a carbonate unit has been buried to the depths of most petroleum reservoirs the significant question is often not how did the pores originate but rather why are they still there preservation of porosity regardless of its origin is a consequence of one or more of the following mechanisms 1 minimal burial 2 reduced burial stress generally due to overpressured pore fluids 3 increased framework rigidity which prevents compaction 4 exclusion of pore waters by petroleum entry 5 stable mineralogy 6 permeability barriers isolating porous intervals from diagenetic fluids and 7 pore resurrection a consequence of the temporary filling of pores with cement that is subsequently removed examples from the stratigraphic record demonstrate that each of these pore preserving mechanisms may control reservoir quality

comparison of differential diagenesis of two oolites on the lower triassic platform margin ne sichuan basin implications for the co evolution of rock structure and porosity abstract two oolites of the lower triassic feixianguan formation on the margins of the kaijiang liangping k l trough in the ne sichuan basin were deposited in the upper parts of similar shallowing upward sequences and are capped by a subaerial exposure surface however they have contrasting diagenetic histories and reservoir qualities the sour oolitic dolostone reservoirs on the eastern side of the k l trough have significantly higher porosities than the sweet oolitic limestone reservoirs on the western side a petrologic and geochemical comparison of the two oolites was carried out so as to investigate the role of diagenetic processes on the co evolution of oolite structure and pore network on both sides of the k l trough eogenetic meteoric digenesis led to an inversion of texture with ooid dissolution and interparticle cementation in the oolite layers close to the exposure surface the layers relatively far from the exposure surface mostly underwent recrystallization in association with connate seawater resulting in neomorphic fabrics in the ooid cortices and less interparticle calcite cement during the subsequent dolomitization the early formed oolite structure were mostly inherited by the dolostones on the eastern side with fabric retentive textures in the layers close to the exposure surface and fabric destructive textures in the layers far from the exposure surface during deeper burial the oolitic limestones were subjected to extensive calcite cementation and porosity loss whereas the dolostones generally retained more porosity and have better connectivity of the micropore network the higher porosity of the dolostones is ascribed to lesser chemical compaction and associated cement precipitation rather than the creation of new pores porosity enhancement is closely dependent on the absence of the calcite cement related to pressure solution the heterogeneity of the dolostone fabrics and the porosity was further enhanced by the subsequent recrystallization and the dissolution reprecipitation process induced by thermochemical sulfate reduction during which small amounts of net porosity are calculated to have been created the oolitic limestones are the best reservoirs close to the exposure surface whereas the most porous dolostones with the highest degree of fabric destruction are commonly some distance from the exposure surface these results provide some insights into the diagenetic controls on oolite structure and porosity and have implications for predicting the porosity of deeply buried oolitic reservoirs so have global theoretical and practical significance

porosity loss fluid flow and mass transfer in limestone reservoirs application to the upper jurassic smackover formation mississippi ooid grainstones of the upper jurassic smack over formation are buried to a depth of over 6 km and exposed to temperatures in excess of 200 c at black creek field mississippi combined effects of mechanical compaction intergranular pressure solution and cementation have reduced intergranular porosity of these ooid grainstones to 0 indicating that porosity reduction has gone to completion modal analysis of 24 samples lacking preburial cements indicates that from the original 40 porosity 13 porosity units range 4 to 21 were lost by mechanical compaction 15 porosity units range 8 to 23 were reduced by intergranular pressure solution and 12 porosity units range 1 to 26 were destroyed by cementation intergranular pressure solution caused an average of 28 range 15 to 51 vertical shortening in smackover ooid grainstones under ideal conditions the 28 vertical shortening will generate enough calcium carbonate to precipitate 10 calcite cement this is close to the measured volume of cements in smackover grainstones 12 suggesting that intergranular pressure solution provided most of the calcite cement present no external sources of calcium carbonate are required fine grained samples that experienced high degrees of intergranular pressure solution and contain only small amounts of cement occur at the top of the reservoir whereas coarse grained samples with abundant cement and low degrees of pressure solution occur in the middle and basal parts of the reservoir suggesting that the fine grained intervals acted as sources and the coarse grained intervals as sinks for calcium carbonate mass transfer of pressure solution generated calcium carbonate from the top of the unit to precipitation sites in the middle and basal parts of the reservoir could have occurred by a non rayleigh type convection cell due to calcite s reverse solubility with respect to temperature the cooling upward moving limb of the convection cell would become progressively more undersaturated and hence able to transport more dissolved calcium carbonate released by intergranular pressure solution in the upper portion of the reservoir pore fluids descending in the downward moving limb of the cell would become progressively more supersaturated and calcium carbonate would tend to precipitate as cement in the middle and basal parts of the reservoir as fluids become progressively hotter

dynamics of plate bending at the trench and slab plate coupling 1 the bending strength of subducting lithosphere plays a critical role in the earth s plate tectonics and mantle convection modulating the amount of slab pull transmitted to the surface and setting the boundary conditions under which plates move and deform however it is the subject of a lively debate how much of the potential energy of the downgoing plate is consumed in bending the plate and how the lithospheric strength is defined during this process we model the subduction of a viscoelastic lithosphere driven solely by the downgoing plate s buoyancy freely sinking in a passive mantle represented by drag forces to investigate the dynamics of bending 1 we vary the density and the viscosity profile within the plate from isoviscous where strength is distributed to strongly layered where strength is concentrated in a thin core and 2 we map the stress strain and dissipation along the downgoing plate the effective plate strength during bending is not a simple function of average plate viscosity but is affected by rheological layering and plate thinning earth like layered plates allow for the transmission of large fractions of slab pull 75 80 through the bend and yield a net slab pull of fspnet 1 to 6 1012 n m 1 which varies with the buoyancy of plates in all models only a minor portion of the energy is dissipated in the bending surprisingly bending dissipation hardly varies with lithospheric viscosity because in our dynamic system the plates minimize overall dissipation rate by adjusting their bending curvature as a result bending dissipation b is mainly controlled by the bending moment work rate exerted by slab pull we propose a new analytical formulation that includes a viscosity dependent bending radius which allows for assessment of the relative bending dissipation in the earth s subduction zones using parameters from a recent global compilation this yields estimates of b tot 20 these results suggest that plates on earth weakly resist bending yet are able to propagate a large amount of slab pull

the dual beam mini doas technique measurements of volcanic gas emission plume height and plume speed with a single instrument the largest error in determining volcanic gas fluxes using ground based optical remote sensing instruments is typically the determination of the plume speed and in the case of fixed scanning instruments also the plume height we here present a newly developed technique capable of measuring plume height plume speed and gas flux using one single instrument by simultaneously collecting scattered sunlight in two directions the angle between the two measurement directions is fixed removing the need for time consuming in field calibrations the plume height and gas flux is measured by traversing the plume and the plume speed is measured by performing a stationary measurement underneath the plume the instrument was tested in a field campaign in may 2005 at mt etna italy where the measured results are compared to wind fields derived from a meso scale meteorological model mm5 the test and comparison show that the instrument is functioning and capable of estimating wind speed at the plume height

triggering of volcanic eruptions although earthquakes and volcanic eruptions are each manifestations of large scale tectonic plate and mantle motions it is usually thought that the occurrences of these events are not directly related there have been some studies however in which triggering of volcanic eruptions by earthquakes remote from the volcano has been proposed1 2 the 1992 landers southern california earthquake caused triggered seismicity at very large distances3 including the magmatically active4 long valley caldera region which also experienced a significant coincident deformation transient5 motivated by this demonstration of the ability of a distant earthquake to disturb a volcanic system and the earlier studies of specific cases of eruption triggering we examine here the historical record of eruptions and earthquakes to see if there are indeed significantly more eruptions immediately following large earthquakes we find that within a day or two of large earthquakes there are many more eruptions within a range of 750 km than would otherwise be expected additionally it is well known6 that volcanoes separated by hundreds of kilometres frequently erupt in unison the characteristics of such eruption pairs are also consistent with the hypothesis that the second eruption is triggered by earthquakes associated with the first

reservoir quality textural evolution and origin of fault associated dolomites fault associated dolomitized carbonates are proven hydrocarbon reservoirs in the subsurface yet their origins and spatial variability in reservoir quality are poorly understood fault associated dolomitization has affected a 4 8 km 2 5 5 mi wide strip of inner platform carbonates of the oligocene miocene taballar limestone exposed onshore northeastern borneo where they are juxtaposed against deep marine shales of the eocene maliu mudstone on textural grounds planar dolomites postdating compaction and from the predominance of monophase aqueous inclusions replacive dolomite rhombs and later dolomite cements appear to have formed at about 50 60c and at shallow burial depths up to 0 5 1 km 0 3 0 6 mi isotopic and inclusion data indicate that the most likely dolomitizing fluid was dominated by neogene seawater for dolomites 18ov pdb 5 9 to 10 3 consistent with the precipitation from southeast asian oligocene miocene seawater 18o 1 5 to 4 2 at temperatures of 40c up to a maximum of about 50 75c 87sr 86sr 0 708566 0 708697 from tm 2 1 3 4 wt nacl however replacement and remobilization of the precursor limestone also contributed to the isotopic signature of the dolomites 87sr 86sr 0 708115 0 708197 whereas an evolved formation water component cannot be ruled out dolomitizing fluids used faults and fractures as conduits to move into and alter the limestone migrating farthest into the most permeable strata the likely driver for fluid movement was convective flow caused by nearby neogene igneous activity perhaps in combination with tectonically induced hydrologic drive related to fault reactivation close to the main fault late stage dolomite cements occlude pore throats reducing porosity 5 and permeability 5 md the best reservoir quality occurs in medium to coarsely crystalline idiotopic mosaics of dolomite that have completely replaced the limestone 0 5 2 km 0 3 1 2 mi away from the main fault where the late stage cements did not form these dolomites have 12 20 intercrystalline porosity and moderate to good permeability tens of millidarcys fracturing has had variable impact on reservoir quality where late fractures remained open permeability is enhanced tens to hundreds of millidarcys whereas brecciation and fault gouges result in sealing and reduced permeability the textures reservoir quality characteristics and mechanisms of dolomitization show similarities to the few other detailed studies in the literature this study refines the types of predictive reservoir models used in hydrocarbon exploration for subsurface faulted and dolomitized carbonates and increases the understanding of dolomitizing mechanisms of equatorial carbonates

hydrocarbon bearing fluid inclusions in fluorite associated with the windy knoll bitumen deposit uk abstract hydrocarbon bearing fluid inclusions in fluorite associated with an outcropping bitumen deposit at windy knoll derbyshire have been analysed in situ using a combination of microthermometry fourier transform infrared ftir microspectrometry and ultraviolet uv microscopy the inclusions in these samples can be considered as a series with two endmembers aqueous inclusions containing a low density vapour phase and inclusions containing liquid oil with no detectable aqueous phase the majority of the inclusions are mixed types containing both aqueous and liquid hydrocarbon phases although microthermometry distinguishes at least two different aqueous fluids with varying homogenization temperatures and salinities the oil fraction is cogenetic and trapped together with just one fluid a low salinity low calcium brine with an average homogenization temperature of 134 c the majority of the liquid hydrocarbon bearing inclusions fluoresce bright blue under uv illumination with peaks around 475 nm characteristic of paraffinic oils the ftir spectra of these inclusions are dominated by peaks assigned to aliphatic c h bonding however inclusions have also been found which display a fluorescence typical of the red shift associated with less mature oils the ftir spectra display peaks assigned to c o c o and o ch2 bonding this study presents new data on the in situ analysis of hydrocarbon bearing fluid inclusions from this important area of natural petroleum seepage and ore mineralization the results suggest a direct link between the fluid inclusion populations the outcropping bitumens and fluorite deposition

contrasting diagenetic evolution patterns of platform margin limestones and dolostones in the lower triassic feixianguan formation sichuan basin china abstract deeply buried carbonate reservoirs from the lower triassic feixianguan formation in the sichuan basin of china host extensive natural gas resources these reservoirs are predominantly found in oolitic shoals with the reservoir quality of dolomitized zones being higher than that of undolomitized limestone counterparts here we present a combination of petrographic isotopic fluid inclusion and quantitative porosity data in order to understand and predict the diagenetic processes that have impacted the reservoir quality of dolostones and limestones the porosity of limestones has been reduced to 7 5 due to calcite cementation whereas the porosity in oolitic dolostones is not cemented with calcite and typically has 23 5 porosity dolomitization and concurrent early diagenetic gypsum growth played crucial roles on the development and preservation of high porosity in the oolitic dolostone first by stabilizing the rock fabric to inhibit loss of porosity during burial and secondly through the generation of new porosity by dissolution of carbonate and anhydrite a negative shift of 18 o and salinity values 13 c values 20 vpdb and 18 o 10 vpdb together with elevated calcite precipitation temperatures 110 c it is likely that tsr was responsible for the formation of enlarged dissolution vugs that increased porosity by 2 in dolostones due to i anhydrite dissolution ii production of significant amounts of water resulting in formation water undersaturated with respect to calcite and dolomite iii generation of h 2 s and co 2 and the consequent reaction of h 2 s with the siderite feco 3 component in calcite and dolomite this study demonstrates the importance of diagenesis in the formation of deeply buried high quality reservoirs in ooid dominated grainstones influenced by the presence of evaporites our results should be useful for guiding future exploration and reservoir developments in similar paleogeographic and diagenetic settings

comparative study of lahars generated by the 1961 and 1971 eruptions of calbuco and villarrica volcanoes southern andes of chile abstract the villarrica and calbuco volcanoes of the andean southern volcanic zone are two of the most active volcanoes in chile and have erupted several times in the xx century the 1961 eruption at calbuco volcano generated lahars on the north east and southern flanks while the 1971 eruption at villarrica volcano generated lahars in almost all the drainages towards the north west and south of the volcano the deposits from these eruptions in the voipir and chaillupen river villarrica and the tepu river calbuco are studied the 1971 lahar deposits on villarrica volcano show a great number of internal structures such as lamination lenses grading of larger clasts and a great abundance of large floating blocks on top of the deposits the granulometry can be unimodal or bimodal with less than 5 by weight of silt clay material sem images reveal a great variety of forms and compositions of clasts the 1961 lahar deposits on calbuco volcano have a scarce number of internal structures steeper margins and features of hot emplacement such as semi carbonized vegetal rests segregation pipes and a more consolidated matrix the granulometry usually is bimodal with great quantities of silt clay material 10 by weight sem images show a uniformity of composition and forms of clasts differences on deposits reveal different dynamics on both lahars the villarrica lahar was generated by sudden melt of ice and snow during the paroxysmal phase of the 1971 eruption when a high fountain of lava was formed the melted water flowed down on the flanks of the volcano and incorporated sediments to become transition flows highly energetic and were emplaced incrementally dilution of the flows occurs when the lahars reached unconfined and flatter areas in cases where the lahar flow found large water streams dilution is enhanced the calbuco lahars were generated by the dilution of block and ash pyroclastic flows by flowing over the ice or snow or by entering active rivers transforming to debris flows the differences on dynamics of both flows show the importance to understand initiation processes of lahars in order to make better hazard assessment due to laharics flows

a new global mode of earth deformation seasonal cycle detected we have detected a global mode of earth deformation that is predicted by theory precise positioning of global positioning system sites distributed worldwide reveals that during february to march the northern hemisphere compresses and the southern hemisphere expands such that sites near the north pole move downward by 3 0 millimeters and sites near the equator are pulled northward by 1 5 millimeters the opposite pattern of deformation occurs during august to september we identify this pattern as the degree one spherical harmonic response of an elastic earth to increased winter loading of soil moisture snow cover and atmosphere data inversion shows the load moment s trajectory as a great circle traversing the continents peaking at 6 9 1022 kilogram meters near the north pole in winter indicating interhemispheric mass exchange of 1 0 1016 0 2 1016 kilograms

so2 degassing from turrialba volcano linked to seismic signatures during the period 2008 2012 in 1996 after 150 years of relative calm turrialba volcano was reawakening a visible plume and serious damage to surrounding vegetation due to acid rain are the most obvious signals as part of the network for observation of volcanic and atmospheric change project four gas monitoring stations were initially installed on the west flank of the volcano with the purpose of measuring sulphur dioxide emissions during this period of increased activity using the scanning differential optical absorption spectroscopy technique we present here the results of semicontinuous gas flux measurements over a period of 5 years from 2008 to 2012 providing a novel data set that documents a relatively rapid increase in so2 fluxes from around 350 t day 1 to around 4 000 t day 1 leading up to an eruptive period followed by a gradual return to the former baseline values gas flux data were also compared with seismic data for selected periods of interest providing insights into the link between degassing and seismicity the most important result from this comparison is the identification of an inflexion point in the gas emissions followed by a clearly increasing trend in seismic activity distinguishable 6 months prior to a phreatic eruptive event that occurred on 5 january 2010 this signal can be interpreted as a possible indicator of future eruptive events monitoring of so2 thus complements seismic monitoring as a forecasting tool for eruptive events such monitoring is critical considering the proximity of turrialba to the central valley an area inhabited by more than 50 of costa rica s population

recent unrest 2002 2015 imaged by space geodesy at the highest risk chilean volcanoes villarrica llaima and calbuco southern andes abstract villarrica llaima and calbuco volcanoes are the most active and dangerous volcanoes in the southern andes and we use interferometric synthetic aperture radar insar observations from multiple satellites ers 2 envisat alos radarsat 2 cosmo skymed terrasar x sentinel 1a and alos 2 to constrain ground deformation that spans episodes of unrest and eruption at all three volcanoes between 2002 and 2015 we find episodes of ground deformation at each volcano which we invert using analytic elastic half space models to make some of the first geophysical inferences about the source depths of potential magma chambers at llaima we interpret that the vei 2 april 3 2009 eruption was preceded by 6 15 cm of precursory ground uplift one month before from a source 5 km below the surface on the western side of the edifice the vei 2 march 3 2015 villarrica eruption was followed by a short lived uplift of 5 cm in the se part of the volcano from a source depth of 6 km the vei 4 april 22 23 2015 calbuco eruption produced 12 cm of coeruptive subsidence from a source depth 8 11 km and offset 2 km s from the summit importantly we do not find clear evidence that the january 1 2008 the march 3 2015 and april 22 2015 eruptions at llaima villarrica and calbuco volcanoes were preceded by either transient or continuous ground uplift there are several possible explanations for the lack of precursory deformation at each volcano it is possible that any precursory deformation occurred only hours before the eruption e g at calbuco pre eruptive inflation was canceled by co eruptive subsidence as we inferred happened during the april 2009 llaima eruption the pre eruptive deformation was too small to be detectable in areas with persistent topography correlated phase delays pressurized source are deep or that open vent volcanoes like villarrica and llaima do not pressurize at all three volcanoes x and c band interferograms decorrelate in a few weeks due to vegetation snow and ice and have persistent atmospheric phase delays that we find cannot be reliably removed with available global weather models the low number of sar acquisitions therefore makes it challenging to reliably measure unaliased deformation we recommend a multi satellite observing strategy with short repeat periods frequently acquired high resolution digital elevation models and with acquisitions during every satellite overflight that may improve the temporal resolution of measurements

synchronous degassing patterns of the neighbouring volcanoes llaima and villarrica in south central chile the influence of tidal forces the neighbouring volcanoes villarrica and llaima are two of the most active volcanoes in chile and both currently degas continuously we present a semi continuous time series of so2 fluxes for villarrica and llaima volcanoes the time series was obtained using five scanning mini differential optical absorption spectrometers mini doas uv spectrometers over 6 months 13 february to 31 july 2010 and is based on 6 829 scans for villarrica and 7 165 scans for llaima statistical analyses of the so2 flux time series reveal a periodicity of degassing maxima about every 7 days and further a conspicuous synchronicity of the degassing maxima and minima between the two volcanoes intra day variations in so2 fluxes also show a striking correlation between villarrica and llaima all these patterns correlate well with the trend of the modelled solid earth tide curves where the 7 day degassing maxima correspond with both the fortnightly tidal maxima and minima the intra day degassing peaks mostly correlate well with the periods of maximum deformation rates during the diurnal tidal cycle and further with semidiurnal minima in atmospheric pressure a phenomenon we refer to as the tidal pump as there is little time lag between the tidal action and the changes in degassing rates we infer that degassing at both volcanoes is controlled by conduit convection involving physical separation between gas and magma at comparatively shallow levels variations in daily degassing rates were up to a factor of ca 12 and 10 for villarrica and llaima respectively without any noticeable changes in the periodicity we thus suggest that the described cyclic variations must be taken into account for all comparable volcanoes when using gas monitoring as a tool for volcanic hazard mitigation

experimental simulation of chemomechanical processes during deep burial diagenesis of carbonate rocks chemomechanical processes involved in the deep burial diagenesis of carbonate petroleum reservoirs are still poorly understood to better understand these processes and explain how porosity and permeability can be preserved at the great depth of dbrs deeply buried reservoirs we developed an experimental device allowing both the simulation of high pressure stresses temperature conditions 80 c 60 mpa of confining pressure and differential stress up to 40 mpa of dbr and the circulation of different fluids in rock samples we tested triaxial multistep creep tests four core samples of a cemented limestone and analyzed creep deformations fluids chemistry and petrographical and petrophysical properties of samples different flow conditions no flow and flow through and chemical compositions natural meteoric water with and without phosphate ions were considered our study showed that the precipitation of calcite on free pore walls of micrites blocks the microporosity between micrite crystals thus rendering the microporosity inaccessible to fluids hence the connected porosity decreased strongly after experimentation this is due to the psc pressure solution creep which is the main process implied in the porosity reduction of a carbonate rock during deep burial the preservation of macropores during psc allows the preservation of permeability in addition calcite solubility is positively dependent on mechanical parameters axial compaction and axial stress thus suggesting that calcite can precipitate during decompression of deep basinal fluids resulting in changes in porosity a comparison of experimental results with theoretical calculations showed that the integration of the psc process into calculation databases would greatly improve the modeling of dbr

deep burial hydrothermal alteration of the pre salt carbonate reservoirs from northern campos basin offshore brazil evidence from petrography fluid inclusions sr c and o isotopes abstract petrographic mineralogical elemental isotopic and fluid inclusion analyses were integrated to unravel the diagenetic evolution of brazilian pre salt lacustrine carbonate reservoirs of northern campos basin southeast brazilian margin detailed thin section and cathodoluminescence petrography scanning electron microscopy and electron microprobe analyses established a paragenetic evolution of diagenetic processes and products comprising extensive dolomitization silicification and dissolution a paragenesis including saddle dolomite macrocrystalline calcite mega quartz sr barite celestine fluorite dickite sphalerite galena and other metallic sulfides filling fractures and dissolution porosity and aqueous fluid inclusions with homogenization temperatures of 92 152 c and salinities between 13 and 26 wt eq nacl characterized a hydrothermal system with some analogy to carbonate hosted pb zn mississippi valley mvt and irish type deposits petroleum inclusions and solid bitumen testify atypical oil generation and migration associated with the hydrothermal flow the host pre salt spherulitic and fascicular carbonates present highly radiogenic 87sr 86sr ratios indicating strong interaction with continental crust materials hydrothermal phases show 18o values more negative than syngenetic and diagenetic carbonates the 13c values are interpreted as result of interaction between the hydrothermal fluids and the host rocks the combined data set provides clear evidence of intense hydrothermal alteration of northern campos basin pre salt reservoirs at deep burial conditions 2 km possibly related to late cretaceous or more probably paleogene magmatic activity mixed sourced fluids bearing a basinal signature fed the hydrothermal system and promoted dissolution of the host rocks the hydrothermal alterations had strong impact on the porosity permeability and heterogeneity contributing together with the associated fracturing to the excellent production performance of the pre salt reservoirs

late hercynian u vein mineralization in the alps fluid inclusion and c o h isotopic evidence for mixing between two externally derived fluids late hercynian u bearing carbonate veins within the metamorphic complex of la lauziere are characterized by two parageneses the first is dominated by dolomite or ankerite and the second by calcite and pitchblende fluids trapped in the dolomites and ankerites at 350 400 c are saline waters 20 to 15 wt eq nacl with d 34 to 49 in the calcite they are less saline 17 to 8 wt eq nacl and trapped at 300 350 c with d 50 to 65 all fluids contain trace n2 co2 and probably ch4 the carbonates have 13c 8 to 14 and derived their carbon from organic matter evolution of the physico chemical conditions from dolomite ankerite to calcite deposition was progressive h and o isotope studies indicate the involvement of two externally derived fluids during vein development a d rich 35 low fo2 saline fluid is interpreted to have come from underlying sediments and entered the hotter overlying metamorphic slab and mixed with more oxidizing and less saline u bearing meteoric waters during regional uplift this evidence for a sedimentary formation water source for the deep fluid implies that the metamorphic complex overthrusted sedimentary formations during the late hercynian

explosive tephra emissions at mount st helens 1989 1991 the violent escape of magmatic gas following storms from 24 august 1989 until 18 june 1991 mount st helens produced at least 28 shallow explosion like seismic events with signatures similar to those produced by gas explosions on the dome during the mid 1980s at least six were accompanied by violent emission off non juvenile tephra ejection of blocks of rock nearly 1 km from the vent and avalanching of debris off the north side of the dome four produced no emission of tephra and the remainder occurred when the crater could not be observed although later crater visits found no new tephra deposits all six confirmed emissions and most although not all other seismic events took place hours to days after storms over time periods ranging from 2 to 15 days statistical goodness of fit tests give a probability of 1 x 10 2 to 1 x 10 5 that the precipitation prior to emissions was fortuitously greater than normal similar tests for precipitation prior to all 28 events give probabilities of 3 x 10 2 to 1 x 10 3 the short delay between storms and emissions suggests that the events that follow storms originate at very shallow depth probably within the dome itself although the exact causal mechanism is not known it is speculated that slope instability or accelerated growth of cooling fractures following storms may have released gas trapped within or at the base of the dome of the events that did not follow storms three were located seismically between 1 4 and 2 1 km depth thus the events as a group are not confined to shallow depth and probably record gas transport from a deeper magmatic source a deep source is also suggested by an unprecedented 4 yr long increase in background seismicity at 2 to 9 km depth that peaked in 1989 and 1990 calculations indicate that the energy content of gas exsolved from the crystallizing conduit was probably sufficient to power the emissions

origin of dissolution vugs caverns and breccias in the middle devonian presqu ile barrier host of pine point mississippi valley type deposits mississippi valley type lead zinc ore deposits at pine point occur in dissolution vugs caverns and breccias which previously were interpreted to be related to meteoric karstification during middle devonian sub watt mountain exposure studies of open pits at pine point and core samples from 34 wells from the subsurface presqu9ile barrier revealed that dissolution related to the sub watt mountain exposure was relatively minor and differed from the large scale hydrothermal dissolution that occurred prior to or was contemporaneous with the emplacement of mississippi valley type deposits dissolution vugs caverns and breccias related to the sub watt mountain exposure are 1 commonly filled in with green shale and locally with pendant calcite cements 2 preserved both in limestones and dolomites 3 restricted to the strata immediately beneath the unconformity and 4 formed prior to stylolitization dolomitization and mineralization diagnostic meteoric karst features such as rundkarren dolina calcrete terra rossa and speleothems are not observed in the presqu9ile barrier the limited evidence of meteoric water during sub watt mountain exposure is possibly due to an arid climate and relatively short periods of exposure in contrast hydrothermal dissolution vugs caverns and breccias that host mississippi valley type ore deposits at pine point are filled with laminated dolomites saddle dolomites sulfide minerals late stage calcite and pyrobitumen that are associated with hydrothermal fluids occur both above and below the watt mountain unconformity follow the regional conduit system that parallels the barrier postdate stylolites suggesting that dissolution must have occurred during burial and occur only in dolomites interpreted to have been formed from burial fluids fluid inclusion measurements indicate that the saddle dolomites precipitated from fluids between 92 degrees and 178 degrees c having salinities between 11 and 29 wt percent nacl equiv thus the majority of dissolution vugs caverns and breccias that host mississippi valley type ore deposits at pine point appear to be related to hydrothermal brines not meteoric fluids and formed before and or during late stage dolomitization and pb zn mineralization several mechanisms have been proposed to account for the hydrothermal dissolution including acid basinal fluids generated by thermochemical sulfate reduction diagenesis of organic matter and or cooling of co 2 rich brines during their updip movement all of which may have been active at pine point

diagenesis of the palaeo oil water transition zone in a lower pennsylvanian carbonate reservoir constraints from cathodoluminescence microscopy microthermometry and isotope geochemistry abstract oil water transition zones in carbonate reservoirs represent important but rarely studied diagenetic environments that are now increasingly re evaluated because of their potentially large effects on reservoir economics here data from cathodoluminescence and fluorescence microscopy isotope geochemistry microthermometry and x ray tomography are combined to decipher the diagenetic history of a 5 m long core interval comprising the oil water transition zone in a lower pennsylvanian carbonate reservoir the aim is to document the cementation dynamics prior during and after oil emplacement in its context of changing fluid parameters intergrain porosity mean values of 7 are present in the upper two sub zones of the oil water transitions zone but values sharply increase to a mean of 14 in the lower sub zone grading into the water saturated portions of the reservoir and a very similar pattern is observed for permeability values in the top of the water filled zone cavernous porosity with mean values of about 24 is found carbonate cements formed from the earliest marine to the late burial stage five calcite ca 1 through 5 and one dolomite dol phase are recognized with phase ca 4b recording the onset of hydrocarbon migration carbon and oxygen cross plots clearly delineate different paragenetic phases with ca 4 representing the most depleted 13c ratios with mean values of about 21 during the main phase of oil emplacement arguably triggered by far field alpine tectonics carbonate cementation was slowed down and eventually ceased in the presence of hydrocarbons and corrosive fluids with temperatures of 110 140 c and a micro hiatal surface formed in the paragenetic sequence these observations support the oil inhibits diagenesis model the presence an earlier corrosion surface between phase ca 3 and 4 is best assigned to initial pulses of ascending corrosive fluids in advance of hydrocarbons the short lived nature of the oil migration event found here is rather uncommon when compared to other carbonate reservoirs the study is relevant as it clearly documents the strengths of a combined petrographic and geochemical study in order to document the timing of oil migration in carbonate reservoirs and its related cementation dynamics

eruptions of pavlof volcano and their possible modulation by ocean load and tectonic stresses all nine magmatic eruptions at pavlof volcano in six of the years from 1973 to 1984 have occurred between september 9 and november 20 volumes of erupted material range from 0 1 to 15 9 106 m3 dense rock equivalent at an average rate of 3 106 m3 yr 1 the volumes are estimated from eyewitness reports for two eruptions the others are estimated from a relationship that we derive between eruption volume and harmonic tremor duration and amplitude the volume of lava erupted is approximately time predictable a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 2 times eruption volumes and we postulate that the volcano acts as a long period several month volume strain meter with lava being preferentially erupted when strain beneath the volcano is compressive the volcano did not erupt during the period 1978 1980 when tilt seismic data and sea level data indicate that deep aseismic slip may have occurred models of this event predict a volume increase beneath the volcano that might have compensated strain from magma injection these observations indicate that pavlof volcano may be responsive to small slow changes in ambient stresses or strains and that these changes may modify or trigger eruptions

sulfur and halogen gases at masaya caldera complex nicaragua total flux and variations with time santiago crater of masaya caldera complex near managua nicaragua entered a phase of intense magmatic degassing in late 1979 the flux of so2 increased rapidly from a previous average of 380 t d 1 to approximately 1200 t d 1 in february 1980 we report on results of a study of the gas flux and geochemistry conducted as part of a broader interdisciplinary study of the volcano and its impact on the adjacent environment masaya is an unusual volcano because of its low shield like form consistent tholeiitic basaltic composition frequent activity and especially because of the approximately 25 year cycle of major non eruptive degassing crises we have used a combination of techniques involving remote sensing using a correlation spectrometer cospec of the flux of so2 and direct filter sampling of the ratios of the sulfur and halogen gases and aerosols to quantify the flux of all of these species the three stage filters successively trap aerosols halogen acid gases and sulfur dioxide and are analyzed by ion chromatography we have used the ratios of various species with the cospec measurements of the flux of so2 to calculate that the average flux of so2 is 1275 t d 1 hcl is 830 t d 1 hf is about 16 t d 1 and hbr is at most 1 t d 1 h2s and so4 are only minor sulfur species the flux of so2 and hcl represents the largest reported noneruptive sustained volcanic release of these species in the world masaya contributed 7 of the total so2 estimated to have been released by volcanoes worldwide in 1981 the flux of so2 has declined by about 9 each year since 1979 and can be modeled as a first order kinetic rate law with a decay constant of approximately 0 04 yr 1 approximately 2 2 106 tons of so2 has been released between september 1979 and september 1985 the ratio s cl has declined more rapidly than the flux of so2 reflecting the greater solubility of hcl than so2 in the magma the so2 flux at santiago varies more widely within a single day than observed at other degassing volcanoes and may be controlled at least in part by effects of the solid earth tide an area larger than 500 km2 has been severely impacted downwind of the volcano downwind ground level concentrations of so2 of 0 25 ppm are frequently encountered acid rain unusually chloride rich has a ph as low as 2 63 s cl ratios in the gas plume increase downwind probably as a result of the high solubility and dry deposition velocity of hcl preliminary analyses of primary concentrations of sulfur and chlorine in the magma of the present lava lake are used to calculate that at least 1 2 km3 has been completely degassed with respect to sulfur to provide the observed flux this implies that 10 km3 have been degassed by previous crises in the past century and further suggests a magma supply rate of approximately 0 1 km3 yr comparable with kilauea or etna volcanoes during historic time only two lava flows have been extruded implying an unusually low ratio of extrusion intrusion of only 0 0007

modelling the permeability evolution of carbonate rocks abstract diagenesis is a major control on the distribution of porosity and permeability in carbonate rocks and therefore impacts fluid flow in the subsurface while changes in porosity can be directly related to diagenetic petrographic characteristics such as cement distribution and dissolution features quantifying how these textures relate to attendant changes in permeability is more challenging here we demonstrate for the first time how pore scale models representing typical carbonate sediments and their diagenetic histories can be used to quantify the evolution of petrophysical properties in carbonate rocks we generate 3d pore architecture models i e the spatial distribution of solid and pores from 2d binarized images representing the typical textural changes of carbonate sediments following hypothetical diagenetic pathways for each 3d rock model we extract the pore system and convert this into a network representation that allows flow properties to be calculated the resulting porosity and permeability evolution scenarios display several diagenetic tipping points where the decrease in permeability is dramatically larger than expected for the associated decrease in porosity the effects of diagenesis also alter the capillary entry pressures and relative permeabilities of the synthetic cases providing trends that can be applied to real rocks indeed values of porosity and absolute permeability derived from these synthetic 3d rock models are within the range of values measured from nature such diagenetic pathway models can be used to provide constraints on predicted flow behaviour during burial and or uplift scenarios using diagenetic back stripping of real carbonate rocks

gas souring by thermochemical sulfate reduction at 140 c reply natural gas in the permian triassic khuff formation of abu dhabi contains variable amounts of h2s gas souring occurred through thermochemical sulfate reduction of anhydrite by hydrocarbon gases sour gas is observed only in reservoirs hotter than a critical reaction temperature 140 c petrographic examination of core from a wide depth range showed that the anhydrite reactant has been replaced by calcite reaction product only in samples deeper than 4300 m gas composition data show that only reservoirs deeper than 4300 m contain large quantities of h2s i e 10 at present day geothermal gradients 4300 m is equivalent to 140 c fluid inclusion analysis of calcite reaction product has shown that calcite growth only became significan at temperatures greater than 140 c thus three independent indicators all show that 140 c is the critical temperature above which gas souring by thermochemical sulfate reduction begins the previously suggested lower temperature thresholds for other sour gas provinces 80 130 c derive from gas composition data that may not allow adequately either for the reservoir temperature history or for the migration of gas generated at higher temperatures into present traps conversely published proposals for higher threshold temperature 180 200 c derive from short duration experimental data that are not easily extrapolated to geologically realistic temperatures and time scales therefore the temperature of 140 c derived from our study of the khuff formation may be th best estimate of temperature required for in situ thermochemical sulfate reduction to produce the high h2s concentrations encountered in deep carbonate gas reservoirs

the relationship between petroleum exotic cements and reservoir quality in carbonates a review exotic minerals i e those that do not have an obvious source of components within the host rocks can be major porosity occluding cement and replacement phases in subsurface carbonate reservoirs here we present and discuss petrographic and fluid inclusion data from a number of petroleum systems these have had different geological histories but a common factor is the presence of exotic mineral cements and late stage dissolution the effect of these cements and late stage dissolution on reservoir quality is also considered petroleum filling does not appear to inhibit the precipitation of exotic cements in the way that it appears to inhibit the precipitation of calcite burial dolomite and anhydrite are the most important of these volumetrically but they are often accompanied by other late stage cements such as fluorite kaolin quartz barite celestite sphalerite and galena generally in much smaller quantities in accounting for the concentration of the material contained in these cements compared with the host rocks stylolitisation is a possible mechanism in some cases but in many others import from sources external to the reservoir is required

impact of stylolitization on fluid flow and diagenesis in foreland basins evidence from an upper jurassic carbonate gas reservoir abu dhabi united arab emirates

earthquake size distribution power law with exponent beta 1 2 we propose that the widely observed and universal gutenberg richter relation is a mathematical consequence of the critical branching nature of earthquake process in a brittle fracture environment these arguments though preliminary are confirmed by recent investigations of the seismic moment distribution in global earthquake catalogs and by the results on the distribution in crystals of dislocation avalanche sizes we consider possible systematic and random errors in determining earthquake size especially its seismic moment these effects increase the estimate of the parameter beta of the power law distribution of earthquake sizes in particular we find that estimated beta values may be inflated by 1 3 because relative moment uncertainties decrease with increasing earthquake size moreover earthquake clustering greatly influences the beta parameter if clusters aftershock sequences are taken as the entity to be studied then the exponent value for their size distribution would decrease by 5 10 the complexity of any earthquake source also inflates the estimated beta value by at least 3 7 the centroid depth distribution also should influence the beta value an approximate calculation suggests that the exponent value may be increased by 2 6 taking all these effects into account we propose that the recently obtained beta value of 0 63 could be reduced to about 0 52 0 56 near the universal constant value 1 2 predicted by theoretical arguments we also consider possible consequences of the universal beta value and its relevance for theoretical and practical understanding of earthquake occurrence in various tectonic and earth structure environments using comparative crystal deformation results may help us understand the generation of seismic tremors and slow earthquakes and illuminate the transition from brittle fracture to plastic flow

curvature of subducted lithosphere from earthquake locations in the wadati benioff zone estimates of slab curvature from 133 profiles across 12 major subduction zones are obtained by fitting splines through earthquakes locations several geometric quantities are computed from the spline fits including the minimum radius of curvature we also introduce a quantity called the equivalent radius of curvature to precisely define the bending dissipation in either a viscous or a plastic slab the minimum and equivalent radius of curvature are approximately equal in slabs with simple geometry i e a single bend but deviate substantially when the geometry is more complicated a compilation of estimates shows that the equivalent radius of curvature is insensitive to the age of the plate at the trench mean values are 175 km or 191 km depending on the rheology of the slab when bending occurs by viscous deformation the resulting dissipation can exceed the power available from subduction with reasonable choices for viscosity a more consistent description of the energetics is obtained by assuming a plastic rheology

geochemical variations in andean basaltic and silicic lavas from the villarrica lanin volcanic chain 39 5 s an evaluation of source heterogeneity fractional crystallization and crustal assimilation at 39 5 s in the southern volcanic zone of the andes three pleistocene recent stratovolcanoes villarrica quetrupillan and lanin form a trend perpendicular to the strike of the andes 275 to 325 km from the peru chile trench basalts from villarrica and lanin are geochemically distinct the latter have higher incompatible element abundances and la sm but lower ba la and alkali metal la ratios these differences are consistent with our previously proposed models involving a a west to east decrease in an alkali metal rich high ba la slab derived component which causes an across strike decrease in degree of melting or b a west to east increase in the contamination of subduction related magma by enriched subcontinental lithospheric mantle silicic and mafic lavas from the stratovolcanoes have overlapping sr nd and o isotopic ratios silicic lavas also have geochemical differences that parallel those of their associated basalts e g rhyolite from villarrica has lower la sm and incompatible element contents than high sio2 andesite from lanin at each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing apparently crustal contamination was not an important process in deriving the evolved lavas basaltic flows from small scoria cones 20 35 km from villarrica volcano have high incompatible element contents and low ba la like lanin basalts but trend to higher k rb 356 855 and lower 87sr 86sr 0 70361 0 70400 than basalts from either stratovolcano however all basalts have similar nd pb and o isotope ratios the best explanation for the unique features of the cones is that the sources of svz magmas e g slab derived fluids or melts of the subcontinental lithospheric mantle have varying alkali metal and radiogenic sr contents these heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing this model is preferable to one involving crustal contamination because it can account for variable sr isotope ratios and uniform nd and pb isotope ratios among the basalts and the divergence of the cones from across strike geochemical trends defined by the stratovolcanoes

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally

model for how microbial methane generation can preserve early porosity in dolomite and limestone reservoirs in some dolomite and limestone hydrocarbon reservoirs protection from cementation is a primary factor in porosity preservation we present a model in which methanogens methane producing microorganisms produce methane gas ch4 g that outgasses from solution in pore space creating a two phase system that reduces effective hydraulic conductivity k protecting pore space from cementation methanogens have been implicated in dolomite formation and can generate methane to fill pore space of a model near surface carbonate sediment 37 5 primary porosity with ch4 g in 180 to 4650 yr depending on nutrient levels gas generation results in occlusion of the aqueous phase from pore spaces and throats creating a two phase flow regime reducing the effective hydraulic conductivity of model marine carbonate sand by about 50 from 2 8 to 1 2 cm day in as little as 55 yr therefore reducing aqueous fluid flow necessary for cementation despite rapid burial and complete cessation of methanogenesis effective hydraulic conductivity could take more than 100 000 yr to return to its original value if methanogenesis continues with burial the effective hydraulic conductivity is reduced to zero after 250 yr dolomites can preserve more primary porosity with depth than other carbonates we propose that in addition to increased structural resistance a biogenic model exists for porosity preservation in dolomites that is linked to the activity of methanogens this model represents specific end member cases and illustrates the effect of methane buildup in relationship to the extent of reservoir diagenesis

rheologic controls on slab dynamics several models have been proposed to relate slab geometry to parameters such as plate velocity or plate age however studies on the observed relationships between slab geometry and a wide range of subduction parameters show that there is not a simple global relationship between slab geometry and any one of these other subduction parameters for all subduction zones numerical and laboratory models of subduction provide a method to explore the relative importance of different physical processes in determining subduction dynamics employing 2 d numerical models with a viscosity structure constrained by laboratory experiments for the deformation of olivine we show that the observed range in slab dip and the observed trends between slab dip and convergence velocity subducting plate age and subduction duration can be reproduced without trench motion i e slab roll back for locations away from slab edges successful models include a stiff slab that is 100 1000 times more viscous than previous estimates from models of plate bending the geoid and global plate motions we find that slab dip in the upper mantle depends primarily on slab strength and plate boundary coupling with a small dependence on subducting plate age once the slab sinks into the lower mantle the primary processes controlling slab evolution are 1 the ability of the stiff slab to transmit stresses up dip 2 resistance to slab descent into the higher viscosity lower mantle and 3 subduction induced flow in the mantle wedge corner

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

underwater and drone based photogrammetry reveals structural control at geysir geothermal field in iceland abstract geysers are local hydrothermal vents with periodic gas bubble driven explosions at the surface little is known however on the control on distribution the dynamics and the geometry of the conduits of geysers to better understand the link between the deep and surface expression at the geysir geothermal field iceland a detailed analysis of the spatial distribution of the thermal expressions and their relationship to the tectonic framework was carried out by use of high resolution unmanned aerial vehicle uav based optical and radiometric infrared cameras we are able to identify 364 distinct thermal spots distributed over the area close analysis of their arrangement yields a clustered appearance following a preferred direction that is found to be consistent with the assumed tectonic trend in the area furthermore by using underwater cameras we are able to obtain for the first time detailed images from the two largest geysers at depths exceeding 20 m near to the surface the conduit of the geysers are near circular but at a depth of 9 12 m the shape changes into a crack like elongated fissure the elongation direction of these deep cracks is consistent with the identified thermal expression at the surface highlighting a structural or even tectonic control at the geysir geothermal field which may also explain the susceptibility for seismically triggered activity changes

modal distribution of pore throat size in sandy conglomerates from an alluvial fan environment lower karamay formation junggar basin west china abstract alluvial fan exhibits various modal distribution of pore throat size which effectively control the oil displacement efficiency and fluid movement however the genetic mechanism of the modal distribution of the pore throat size and its macroscopic distribution within alluvial fan is poorly understood based on core analysis this paper which take the sandy conglomerate reservoir within the alluvial fan in junggar basin as an example aims to study the variations in modal distribution of pore throat size and controlling mechanisms the results reveal that 1 the modal distribution types of the pore throat size are complicated and can be classified into six subtypes including unimodal type uni unimodal type uni unimodal type uni bimodal type bi bimodal type bi and multimodal type multi uni uni and uni is dominated by intergranular pores intragranular dissolved pores and micropores respectively bi bi and multi are characterized by the combination of several pore types 2 diagenesis including compaction cementation and dissolution rock composition the mudstone fragment content and rock texture the clay content control the volume of each pore throat type which significantly influences the modal distribution of the pore throat size lithofacies with low mudstone fragment and clay content and great grain sorting tend to have experienced weak compaction thereby retaining a large volume of intergranular pores and have been subjected to strong dissolution when adequate acidic ions occur in the porewater resulting in a large volume of intragranular dissolved pores strong dissolution reduced the rock compressive strength and further enhanced the degree of mechanical compaction during the burial process cementation occurred later than compaction and dissolution and its intensity is controlled by the supply of co2 and ca2 and compaction intensity thus reducing the volume of intergranular pores the content of mudstone fragment and clay varies among different lithofacies of different origins for traction current deposits lithofacies with smaller median grain size contain fewer mudstone fragments resulting in fewer micropores the clay content decreased first and then increased with decreasing median grain size and lithofacies with lower clay content cause less volume of micropores 3 lithofacies types combined with porewater condition for dissolution and lithofacies location affect the diagenetic intensity rock composition and rock texture variations thus resulting in various modal distribution of pore throat size within the alluvial fan moreover the rock texture especially grain sorting is very important for compaction and facilitates percolation of meteoric water and dissolution

villarrica volcano chile characteristics of the volcanic tremor and forecasting of small explosions by means of a material failure method villarrica volcano chile 39 42 s 71 93 w is one of the most active volcanoes in the andes it shows persistent strombolian activity in a small lava lake situated at the bottom of the summit crater from september to december 2000 the volcano exhibited anomalous behaviour after a regional tectonic seismic event on 22 september the eruption of a small volume of lava apparently plugged the conduit this situation then lasted for ten days on 5 and 8 october a series of explosions reopened the system this eruption behaviour has allowed us to study the evolution of the characteristic tremor in the open and closed states of the conduit a shift in the peak frequency from 1 hz open to 2 hz closed the explosions related to the opening of the conduit were forecasted by means of a material failure method

kinematics and flow patterns in deep mantle and upper mantle subduction models influence of the mantle depth and slab to mantle viscosity ratio 1 three dimensional fluid dynamic laboratory simulations are presented that investigate the subduction process in two mantle models an upper mantle model and a deep mantle model and for various subducting plate mantle viscosity ratios sp m 59 1375 the models investigate the mantle flow field geometrical evolution of the slab sinking kinematics and relative contributions of subducting plate motion and trench migration to the total rate of subduction all models show that the subducting plate is always moving trenchward resulting from slab pull furthermore all deep mantle models show trench retreat as do upper mantle models in the initial stage of subduction before slab tip transition zone interaction upper mantle models with a low sp m 66 217 continue to show trench retreat after interaction upper mantle models with a high sp m 378 709 show a period of trench advance after interaction followed by trench retreat upper mantle models with a very high sp m 1375 show continued trench advance after interaction the difference in trench migration behavior and associated slab geometries is attributed to both sp m and the mantle depth to plate thickness ratio tm tsp which both affect the slab bending radius to mantle thickness ratio rb tm four subduction regimes can be defined regime i with rb tm 0 3 trench retreat slab draping and a concave trench regime ii with 0 3 rb tm 0 5 episodic trench migration slab folding and a concave trench regime iii with rb tm 0 5 trench advance slab rollover geometries and minor trench curvature and regime iv with rb tm 0 8 trench retreat slab draping and a rectilinear trench in all models slab parallel downdip motion induces poloidal mantle flow structures in addition trench retreat and rollback motion of the slab induce quasi toroidal return flow around the lateral slab edges toward the mantle wedge rollback induced poloidal flow around the slab tip is not observed in any of the experiments finally comparison between the slab geometries observed in the upper mantle models and slab geometries observed in nature imply that the effective viscosity ratio between slab and ambient upper mantle in nature is less than 103 and of the order 1 7 102 with a best estimate of 1 3 102

the relationship between petroleum emplacement and carbonate reservoir quality examples from abu dhabi and the amu darya basin abstract the relative importance of petroleum emplacement in inhibiting diagenetic processes and preserving porosity and permeability in lower cretaceous thamama group kharaib formation carbonate reservoirs of abu dhabi uae and in callovian kimmeridgian carbonate reservoirs of the amu darya basin in uzbekistan and turkmenistan has been evaluated by combining geologic petrophysical and geochemical data when petroleum emplacement is synchronous with and prior to significant burial cementation in carbonates primary petroleum inclusions are trapped in the cements the process appears to be characterised by steep intra field porosity depth trends within a more gradual regional decline in porosity with depth this has profound implications for the prediction of porosity in carbonate reservoirs reservoir quality is better in grainstones and packstones compared to adjacent wackestones and lime mudstones in the kharaib formation because of preserved macroporosity intergranular vuggy mouldic the pore system in the finer units is dominated by micropores these features indicate a primary textural control on porosity and permeability within the grainstones and packstones macroporosity is variably filled by late equant sparry calcite cements porosity and permeability variations in grainstones and packstones at a reservoir scale are therefore controlled by the variation in amount of equant sparry calcite cement this in turn depends on the timing of the precipitation of this cement relative to petroleum emplacement as shown by fluid inclusion data where petroleum emplacement has occurred relatively early at migration foci prior to significant burial cementation by equant sparry calcite reservoir quality is preserved where it has occurred after significant burial cementation reservoir quality has been destroyed in the amu darya sequences primary macroporosity is commonly preserved down to depths of 11 000 ft 3 5 km with differences in the porosity and permeability characteristics of grainstones being controlled by variations in the amount of early probably freshwater cement and the extent of associated dissolution small volumes of burial cements do occur but they do not contain petroleum inclusions consequently there is no firm evidence that petroleum emplacement has inhibited diagenesis in this area this part of the study has shown that it is not always possible to obtain conclusive evidence from the diagenesis to pin down the processes responsible for the preservation of reservoir quality and that petroleum filling may not always be the primary cause the relationships documented here show that the race for space between diagenetic waters and petroleum is a major control on reservoir quality in the thamama group carbonate reservoirs but is not so important for the jurassic carbonates in the amu darya basin

bending stress and dissipation in subducted lithosphere 1 oceanic lithosphere undergoes permanent deformation during subduction once the stresses exceed the elastic limit departures from elastic behavior occur by brittle failure in the shallow lithosphere and by a combination of low and high temperature creep at greater depths we combine laboratory based rheological models with estimates of slab shape from earthquake hypocenters to quantify the bending stress and dissipation in subduction zones the peak stress occurs at the depth of the brittle ductile transition which is controlled mainly by lithospheric age integrals of the stress over the thickness of the plate are used to evaluate the resistive bending force and the bending moment a representative value for the resistive force on old oceanic lithosphere is 3 1012 n m 1 which is comparable in magnitude to ridge push but opposite in direction both the bending force and moment are remarkably insensitive to the rate of subduction in fact the bending moment can be approximated using a simple power law rheology and a stress exponent of n 14 such a large exponent implies that the lithosphere behaves like a perfectly plastic solid for most subduction zones the bending moment saturates along the entire plate as a consequence the bending stress does not influence the development of curvature during subduction this behavior may explain why the curvature of subducted lithosphere is nearly independent of age

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk