climate change during the early paleogene in the bogota basin colombia inferred from paleosol carbon isotope stratigraphy major oxides and environmental magnetism abstract paleosols in the bogota basin colombia record an increase in chemical weathering across the paleocene eocene p e transition rock magnetic properties and major element geochemistry exhibit an abrupt change in an interval identified as including the p e boundary as established by previously published biostratigraphy and a u pb date on volcanic zircons 56 2 1 6 ma during the stratigraphic interval that contains the p e transition magnetic susceptibility increases significantly with an order of magnitude higher concentration of magnetite maghemite and hematite the preponderance of pure stoichiometric magnetite in the paleosols of this interval indicates that the increase in magnetic susceptibility is due to changes in the rate of pedogenesis rather than an increase in the erosion of nearby volcanic rocks which would contribute titanomagnetite pedogenic structures preserved within the paleosols a lack of iron oxides as cement friability of the sandstones and previously published thermochronologic data are not consistent with burial diagenesis as an explanation for the origin of the magnetic mineral assemblage these enhanced pedogenesis and related chemical weathering is also confirmed by increases in the concentration of fe 2 o 3 and al 2 o 3 and loss on ignition values an increase in mean precipitation across this interval is inferred by the lack of carbonate nodules and a decrease in sio 2 in paleosols thus we hypothesize that there was an intensification of chemical weathering during the interval that contains the p e transition

source process of very long period events accompanying long period signals at cotopaxi volcano ecuador abstract renewed seismic activity of cotopaxi ecuador began in january 2001 with the increased number of long period lp events followed by a swarm of volcano tectonic vt earthquakes in november 2001 in late june 2002 the activity of very long period vlp 2 s events accompanying lp 0 5 1 s signals began beneath the volcano the vlp waveform was characterized by an impulsive signature which was accompanied by the lp signal showing non harmonic oscillations we observed temporal changes of both the vlp and lp signals from the beginning until september 2003 the vlp signal gradually disappeared and the lp signal characterized by decaying harmonic oscillations became dominant assuming possible source geometries we applied a waveform inversion method to the observed waveforms of the largest vlp event our inversion and particle motion analyses point to volumetric changes of a sub vertical crack as the vlp source which is located at a depth of 2 3 km beneath the northeastern flank the spectral analysis of the decaying harmonic oscillations of lp events shows frequencies between 2 0 and 3 5 hz with quality factors significantly above 100 the increased vt activity and deformation data suggest an intrusion of magma beneath the volcano a release of gases with small magma particles may have repetitively occurred due to the pressurization which was caused by sustained bubble growth at the magma ceiling the released particle laden gases opened a crack above the magma system and triggered the resonance of the crack we interpret the vlp and lp events as the gas release process and the resonance of the crack respectively

influence of periatlantic climates and paleoclimates on the distribution and mineralogical composition of bauxites and ferricretes

ground deformation caused by magma ascent in an open conduit this study examines magma ascent processes of three basic types prior to intermittent explosions such as vulcanian or strombolian types specifically their relations to volcano ground deformation such repetitive explosions eject magma from an open conduit at short time intervals consequently magma pressure is expected to decrease at the conduit and or reservoir and thereby deflate the volcano then magma within the conduit rises exerting normal and shear stresses on the conduit wall thereby inflating the volcano diffusive mass transfer of water molecules from the melt to bubbles might occur subject to a sudden depressurization by eruption when magma includes numerous small gas bubbles such gas bubble expansion lifts the magma in the conduit calculations of ground deformation on a semi infinite medium for such rising magma show that vertical and radial displacements and tilt motions recorded in the far fields are proportional to the 1 5 power of time for low viscosity magma gas bubbles might rise in the melt because of buoyancy force the gas bubbles expand rapidly with time because of decreased ambient pressure pushing the magma upward in the conduit consequently the volcano slowly inflates initially then the rate of deformation increases over time eventually engendering a rapid inflation immediately before eruption these temporal changes in ground deformations contrast against cases in which magma does not include gas bubbles in such cases amplitudes of ground deformation increase almost linearly or even decrease with time at far fields these differences which are recognized as basic characteristics of temporal changes of ground deformation enable us to know the driving forces of magma in an open conduit and to evaluate the gas bubble behavior quantitatively in magma before eruption

dyke intrusion model for the 1989 seismovolcanic activity off ito central japan in the last 10 years extensive earthquake swarms have occurred intermittently in the region east of izu peninsula central japan in july 1989 an active swarm again took place off ito city and among all past activities it was nearest to land and shallowest this activity eventually became a weak submarine eruption the first of its kind in this region associated with this event a borehole tiltmeter at 92 m depth installed several kilometers from the source area detected distinct continuous tilt change with the following features 1 tilt of 20 rad was observed within 1 week preceding the eruption 2 tilt change showed a good correlation to swarm activity 3 no obvious coeruption tilt change was observed on the basis of the tilt record and swarm distribution we constructed a dislocation model to interpret the seismovolcanic activity the model consists of two tensile faults each of which corresponds to magma intrusions in may and july and a right lateral reverse fault representing the largest earthquake m5 5 at 1109 lt on july 9 this model can simulate not only the above tilt data but also the record of a nearby dilatometer the results from daily laser distance measurements and daily global positioning system monitoring as well as results from other conventional distance surveys and leveling surveys in the surrounding region from this model we conclude that the intersection of the shear fault with the tensile fault caused magma to come up into soft sedimentary layers at the seabottom creating a lava dome later an instability brought about a magma phreatic explosion which did not generate any substantial crustal deformations at deeper levels

multiple levels of magma storage during the 1980 summer eruptions of mount st helens wa transitions in eruptive style explosive to effusive sustained to pulsatory are a common aspect of volcanic activity and present a major challenge to volcano monitoring efforts a classic example of such transitions is provided by the activity of mount st helens wa during 1980 where a climactic plinian event on may 18 was followed by subplinian and vulcanian eruptions that became increasing pulsatory with time throughout the summer finally progressing to episodic growth of a lava dome here we use variations in the textures glass compositions and volatile contents of melt inclusions preserved in pyroclasts produced by the summer 1980 eruptions to determine conditions of magma ascent and storage that may have led to observed changes in eruptive activity five different pyroclast types identified in pyroclastic flow and fall deposits produced by eruptions in june 12 july 22 and august 7 1980 provide evidence for multiple levels of magma storage prior to each event highly vesicular clasts have h2o rich 4 5 5 5 wt melt inclusions and lack groundmass microlites or hornblende reaction rims characteristics that require magma storage at p 160 mpa until shortly prior to eruption all other clast types have groundmass microlites ph20 estimated from both h2o bearing melt inclusions and textural constraints provided by decompression experiments suggest pre eruptive storage pressures of 75 40 and 10 mpa the distribution of pyroclast types within and between eruptive deposits can be used to place important constraints on eruption mechanisms fall and flow deposits from june 12 1980 lack highly vesicular microlite free pyroclasts this eruption was also preceded by a shallow intrusion on june 3 as evidenced by a seismic crisis and enhanced so2 emissions our constraints suggest that magma intruded to a depth of 4 km beneath the crater floor fed the june eruption in contrast eruptions of july and august although shorter in duration and smaller in volume erupted deep volatile rich magma if modeled as a simple cylinder these data require a step wise decrease in effective conduit diameter from 40 50 m in may and june to 8 12 m in july and august the abundance of vesicular intermediate to deep clast types in july and august further suggests that this change was effected by narrowing the shallower part of the conduit perhaps in response to solidification of intruded magma remaining in the shallow system after the june eruption eruptions from july to october were distinctly pulsatory transitioning between subplinian and vulcanian in character as originally suggested by scandone and malone 1985 a growing mismatch between the rate of magma ascent and magma disruption explains the increasingly pulsatory nature of the eruptions through time recent fragmentation experiments spieler et al 2004 suggest this mismatch may have been aided by the multiple levels at which magma was stored and degassed prior to these events

tracking magma volume recovery at okmok volcano using gps and an unscented kalman filter 1 changes beneath a volcano can be observed through position changes in a gps network but distinguishing the source of site motion is not always straightforward the records of continuous gps sites provide a favorable data set for tracking magma migration dense campaign observations usually provide a better spatial picture of the overall deformation field at the expense of an episodic temporal record combining these observations provides the best of both worlds a kalman filter provides a means for integrating discrete and continuous measurements and for interpreting subtle signals the unscented kalman filter ukf is a nonlinear method for time dependent observations we demonstrate the application of this technique to deformation data by applying it to gps data collected at okmok volcano seven years of gps observations at okmok are analyzed using a mogi source model and the ukf the deformation source at okmok is relatively stable at 2 5 km depth below sea level located beneath the center of the caldera which means the surface deformation is caused by changes in the strength of the source during the 7 years of gps observations more than 0 5 m of uplift has occurred a majority of that during the time period january 2003 to july 2004 the total volume recovery at okmok since the last eruption in 1997 is 60 80 the ukf allows us to solve simultaneously for the time dependence of the source strength and for the location without a priori information about the source

model for bauxite formation paragominas brazil abstract samples from a profile of the paragominas bauxite brazil were analyzed extensively principal minerals were determined as well as the concentrations of 56 elements the major element chemistry can be described in terms of the oxides and hydroxides of al si ti and fe bound mineralogically as gibbsite kaolinite and hematite 30 of the 45 minor and trace elements analyzed often maintain their average crustal concentrations depletions are most obvious for the alkali metals the alkaline earths and the metals of the first row transition series enrichment is observed for b sc zr nb sn sb i hf and th differences in concentration patterns for some refractory metals al ti zr hf etc lead to the suggestion that some e g ti zr hf of these metals may be participating in biological reactions the economic bauxite zone is bracketed above and below by kaolinitic horizons and this succession of alteration could be explained by extraordinarily high flow rates of meteoric waters for millions of years through highly permeable terrains the formation and preservation of these highly leached profiles also require a quiescent tectonic setting for 10 100 ma such a model is consistent with conditions which may have prevailed in eastern amazonia for at least 100 ma

geochemical exploration challenges in the regolith dominated igarape bahia gold deposit carajas brazil abstract the igarape bahia situated in the carajas mineral province is a world class example of a lateritic gold deposit it has developed under tropical weathering conditions since at least the eocene and resulted in a regolith cover of at least 100 m thickness the regolith is dominated by 80 m thick ferruginous saprolite containing gossan bodies that constitute the main au ore above saprolite the regolith stratigraphy has been established considering two distinct domains one composed of residual materials and the other transported materials deposited over palaeochannels in the residual domain the ferruginous saprolite grades upwards into a fragmental duricrust interpreted as a collapsed zone and then into different types of ferruginous duricrusts over palaeochannel the ferruginous saprolite is truncated by poorly sorted ferruginous sediment of variable composition that grades upwards into the ferruginous duricrusts formed over transported materials lateritization took place during a marked period that transformed the colluvium of the residual domain and the transported materials accumulated in the channel depressions into the ferruginous duricrust units a later bauxitization event has overprinted all duricrust types but has mostly affected the duricrusts over the palaeochannel forming gibbsitic nodules all duricrusts were finally covered by a transported layer of latosol which flattened the whole landscape in the carajas region gold shows a depletion trend across the regolith but is enriched in the fragmental duricrust below the ferruginous duricrust from which gold is leached gold is also chemically dispersed laterally into the fragmental duricrust but lateral au dispersion in the ferruginous duricrusts of the residual domain is probably also influenced by colluvial transport metals associated with au mineralization cu u mo pb ag lree sn w bi sb and p are generally depleted in the saprolite but most of them are still anomalous the fragmental and ferruginous duricrusts are more leached but the tests performed to estimate the dispersion potential of metals contained in the ferruginous duricrust show that some metals are still significantly anomalous especially au ag and cu however if ferruginous duricrusts are used as an exploration sample media their environment of formation must be considered metal depletion is generally more advanced in the ferruginous duricrusts developed in the vicinities of palaeochannels as oppose to those developed in residual domain on the contrary au over palaeochannel areas is enriched in the upper bauxitized ferruginous duricrusts and in their gibbsitic nodules as a result of lateral chemical transport that is more widespread than in the colluvium over residual domain the latosol is highly depleted in most metals due to its transported nature however the nodular fractions of the latosol show the greatest dispersion potential especially for au ag w u bi and sn it can incorporate magnetic nodules that bring a rich suit of metals associated to the magnetic gossans and non magnetic nodules classified as concretion and pisolites which bring metals enriched or dispersed in the ferruginous duricrusts this suggests that lag constitutes a promising sample medium for geochemical exploration in the lateritic terrains of the carajas region

broadband seismic signals associated with the 2000 volcanic unrest of mount bandai northeastern japan abstract we have observed volcano tectonic vt earthquakes volcanic tremor and very long period events vlpes associated with the volcanic unrest of mount bandai since 2000 using a broadband seismic network closely deployed around the volcano vt earthquakes are characterized by high frequency 10 hz signals with clear onsets of p and s phases whereas volcanic tremor is characterized by a long coda comprising frequencies ranging from a few hertz to more than 10 hz in contrast waveforms of vlpes consist of very long period 10 s signals preceded by short period

mobilities of alkalis alkaline earths and halogens during weathering abstract concentrations of alkali metals alkaline earths and halogens were monitored in an australian weathering profile and in brazilian soils and bauxite the materials analysed are considered to represent a range of chemical weathering histories which are distinguished with respect to their degree of leaching by the dominant aluminosilicate assemblages during initial weathering concentrations of alkalis and alkaline earths are similar or enriched relative to average crustal abundances as weathering proceeds depletion is attenuated by the capacity of a particular element to participate in adsorption and ion exchange processes strong depletion of alkalis and alkaline earths is common as weathering advances and clay minerals are replaced by al oxide phases e g gibbsite with much lower capacities for exchanging and incorporating ions halogen concentration trends are more variable f retention during weathering is likely due to substitution in mineral phases for hydroxyl groups cl and i are commonly observed to accumulate as weathering advances and some of these accumulations may be due to atmospheric additions

source mechanism of vulcanian degassing at popocatepetl volcano mexico determined from waveform inversions of very long period signals 1 the source mechanism of very long period vlp signals accompanying volcanic degassing bursts at popocatepetl is analyzed in the 15 70 s band by minimizing the residual error between data and synthetics calculated for a point source embedded in a homogeneous medium the waveforms of two eruptions 23 april and 23 may 2000 representative of mild vulcanian activity are well reproduced by our inversion which takes into account volcano topography the source centroid is positioned 1500 m below the western perimeter of the summit crater and the modeled source is composed of a shallow dipping crack sill with easterly dip of 10 intersecting a steeply dipping crack northeast striking dike dipping 83 northwest whose surface extension bisects the vent both cracks undergo a similar sequence of inflation deflation and reinflation reflecting a cycle of pressurization depressurization and repressurization within a time interval of 3 5 min the largest moment release occurs in the sill showing a maximum volume change of 500 1000 m3 pressure drop of 3 5 mpa and amplitude of recovered pressure equal to 1 2 times the amplitude of the pressure drop in contrast the maximum volume change in the dike is less 200 300 m3 with a corresponding pressure drop of 1 2 mpa and pressure recovery equal to the pressure drop accompanying these volumetric sources are single force components with magnitudes of 108 n consistent with melt advection in response to pressure transients the source time histories of the volumetric components of the source indicate that significant mass movement starts within the sill and triggers a mass movement response in the dike within a few seconds such source behavior is consistent with the opening of a pathway for escape of pent up gases from slow pressurization of the sill driven by magma crystallization the opening of this pathway and associated rapid evacuation of volcanic gases induces the pressure drop pressure recovery in the magma filling the sill is driven by diffusion of gases from the resulting supersaturated melt into bubbles assuming a penny shaped crack at ambient pressure of 40 mpa the observed pressure and volume variations can be modeled with the following attributes crack radius 100 m crack aperture 5 m bubble number density 1010 1012 m 3 initial bubble radius 10 6 m final bubble radius 10 5 m and net decrease of gas concentration in the melt 0 01 wt

variability in eruption style and associated very long period events at fuego volcano guatemala 1 repeated short term deployments of seismic infrasound video and gas emission instruments at fuego volcano guatemala have revealed three types of very long period vlp events associated with conduit sealing pressure accumulation and release in 2008 ash rich explosions issued from a vent on the western flank and produced one type of vlp type 1 impulsive bomb rich explosions from the summit vent in 2009 produced a shorter period vlp type 2 but also generated ash release type 3 vlp events occurred during ash free exhalations from the summit in 2008 and had waveform shapes similar to type 2 events weak infrasound records for type 1 explosions compared to type 2 suggest lower pressures and higher magma porosity for type 1 type 3 events correlate with spikes in so2 emission rate and are driven by partial sealing and rapid release of ash free gas at the summit vent variations in the vlp period may provide a new tool for monitoring conditions within the conduit

a stable isotope study of lateritic bauxites abstract stable isotope analyses of gibbsitic samples from a number of lateritic bauxites suggest that the accepted oxygen and hydrogen isotope fractionation factors for the mineral at surficial temperatures are incorrect a new ox of 1 0143 0 002 and hy of 0 998 0 015 is proposed for gibbsite and in addition an ox of 1 0175 0 001 and hy of 0 975 0 008 is proposed for boehmite at surficial temperatures application of these fractionation factors suggests that gibbsite from many of the equatorial bauxites analyzed formed in equilibrium with meteoric waters similar to those which commonly accompany monsoon type rainfall these waters are generally depleted in 18o and d compared to precipitation derived from tradewinds the isotopic composition of gibbsite from the mid tertiary weipa bauxite in north queensland indicates equilibrium with waters similar in isotopic composition to modern groundwaters in the region this suggests that a monsoon type climate similar to that of the present has prevailed in the region since at least the mid tertiary the oxygen and hydrogen isotope composition of gibbsite from the paragominas deposit in brazil is markedly out of isotopic equilibrium with modern tradewind derived regional rainfall but in equilibrium with waters comparable to those derived from monsoonal rains this suggests that since the formation of the deposit the climate has changed and the monsoons no longer operate in the region thus the link between the isotopic composition of bauxite minerals and the nature of the climate prevailing during their formation can be used to define tropical regions which have previously experienced a monsoonal climate providing valuable information on the nature of atmospheric circulation in the past

bubble growth processes in magma surrounded by an elastic medium abstract gas bubble growth in magma plays an important role in volcanic explosivity and many previous studies have undertaken theoretical and experimental analyses of gas bubble expansion in melt these previous studies commonly assume constant ambient pressure but it is more natural to assume that the magma is stressed by the crust or volcanic edifices as the volume of gas bubbles increases here we present a bubble growth model that takes into account the elasticity of the surrounding medium we use this model to examine temporal changes in the bubble growth process our model consists of a two dimensional dike filled with compressible viscous melt and numerous tiny gas bubbles we use the cell model proposed by proussevitch et al proussevitch a sahagian d l anderson a t 1993 dynamics of diffusive bubble growth in magmas isothermal case j geophys res 98 22283 22307 to describe the interaction between the numerous gas bubbles and the melt the bubble growth process is formulated by the diffusion equation of volatiles in the melt the mass balance between bubbles and melt and the momentum equation of the melt we also introduce pressure balance equations between the melt and the surrounding elastic medium nishimura t 2004 pressure recovery in magma due to bubble growth geophys res lett 31 using the finite difference scheme we numerically calculate temporal changes in bubble radius and melt pressure within magma subjected to sudden depressurization simulation results show that the elasticity of the surrounding medium strongly controls the bubble growth process under high effective rigidity the final bubble radius is several times smaller than for zero rigidity and the time required for bubble growth is an order of magnitude quicker temporal changes in the melt pressure are particularly dependent on the elasticity of the surrounding medium melt pressure effectively recovers and even exceeds the given pressure drop for conditions of high rigidity and or small initial bubble radius although bubble growth in magma has previously been investigated mainly from geological samples and theoretical perspectives our model can quantitatively evaluate pressure changes in magma that can also be detected by seismic and geodetic measurements

source mechanism of a very long period event at mt ontake central japan response of a hydrothermal system to magma intrusion beneath the summit abstract a very long period vlp volcanic event which occurred on 25 january 2007 beneath mt ontake central japan was recorded by nearby broadband seismometers as well as the japanese nationwide hi net and f net seismic networks the vlp waveforms show a pulse like shape with a duration of approximately 1 min the vlp event was accompanied by a burst sequence of long period lp events we carried out waveform inversion to determine the source mechanism and location of the vlp event our analysis indicates volumetric changes in an inclined crack seismic moment of 10 14 nm at the vlp source which is located at 0 6 km above sea level beneath the summit of mt ontake and above dikes determined from gps data the source time functions of the vlp event showed a pulse like triangular shape indicating inflation followed by deflation of the crack at the source we interpreted the result of the waveform inversion as follows gases released from the intruded magma heated an aquifer system beneath the summit of mt ontake a break of unstable superheated water in a hydrothermal crack in the system caused vaporization of water and associated crack inflation which was followed by discharge of steam from the crack resulting in its collapse these processes caused the vlp event which may have been a precursor of a small phreatic eruption that occurred in late march 2007

geochemical and isotopic studies of bauxitization in the tatun volcanic area northern taiwan the tatun volcanic area in the northern tip of taiwan is composed of pleistocene andesite and andesitic tuff its high relief causes extraordinarily heavy rainfall 3000 mm yr 1 especially during the winter monsoon season bauxite deposits were formed on the windward northern slopes soil samples from two profiles in the bauxite deposits were studied by chemical analysis x ray diffraction differential thermal analysis and hydrogen and oxygen isotopic analyses the soil profiles can be divided into two zones by chemical characteristics in the upper zone zone a the chemical composition of the soil samples undergoes little change except depletion of na and ca due to leaching the major minerals are quartz chlorite and illite in the lower zone zone b all major elements suffer rapid dissolution except al2o3 gibbsite grows drastically at the expense of clays while quartz diminishes sharply fe2o3 and tio2 are enriched at the boundary between the two zones due to coprecipitation of fe and ti as hematite and goethite probably as a result of increasing oxygen fugacity mobilization of fe in zone b is attributed to its low eh thus zone a is inferred as a permeable layer and zone b as an aquifer the weathering rate in this area is estimated to be 12 cm ka 1 the most thoroughly leached soil samples contain up to 80 gibbsite the high gibbsite contents and the analyses of coexisting waters allow hydrogen and oxygen isotopic fractionation factors between gibbsite and water to be calculated as 0 992 0 002 and 1 016 0 001 respectively

very long period signals associated with vulcanian explosions at popocatepetl volcano mexico very long period vlp seismic signals associated with large summit eruptions of popocatepetl volcano in the last four years are investigated using data from a broadband seismometer 0 04 120 s deployed on the north flank of the volcano at a radial distance of 5 km from the active crater the vlp signals associated with individual eruptions share similar waveforms discrete vlp signals accompanying long period lp events also share similar signatures and have dominant periods that are nearly identical to those observed in the vlp waveforms of explosions the vlp particle motions for eruption onsets consistently point to a source located a few km beneath the crater the vlp ground displacement response to each explosion is marked by a compression followed by a dilatation and terminating with another compression suggesting a sequence of pressurization depressurization repressurization of the conduit the repetitive nature of the waveforms points to a non destructive source process which has remained active in the magmatic system of popocatepetl at least since april 1997

beryllium geochemistry in soils evaluation of 10be 9be ratios in authigenic minerals as a basis for age models soils contain a diverse and complex set of chemicals and minerals being an open system both in the chemical and nuclear sense soils have defied quantitative nuclear dating however based on the published studies of the cosmogenic atmospheric 10be in soils its relatively long half life 1 5 ma and the fact that 10be gets quickly incorporated in most soil minerals this radionuclide appears to be potentially the most useful for soil dating we therefore studied the natural variations in the specific activities of 10be with respect to the isotope 9be in mineral phases in eight profiles of diverse soils from temperate to tropical climatic regimes and evaluated the implications of the data for determining the time of formation of soil minerals following an earlier suggestion lal et al 1991 development of cosmogenic nuclear methods for the study of soil erosion and formation rates current sci 61 636 639 we find that the 10be 9be ratios in both bulk soils and in the authigenic mineral phases are confined within a narrower range than in 10be concentrations also the highest 10be 9be ratios in authigenic minerals are observed at the soil rock interface as predicted by the model we present model 10be 9be ages of the b horizon and the corresponding soil formation rates for several soil profiles the present study demonstrates that the 10be 9be ratios in the authigenic phases e g clay and fe hydroxides can indeed be used for obtaining useful model ages for soils younger than 10 15 ma however the present work has to be pushed considerably further to take into account more realistic age models in which for instance downward transport 10be and clays and in situ dissolution of clay minerals at depths altering the 10be 9be ratios of the acidic solutions are included we show that in the case of younger soils 1 ma studied here their 10be inventories and 10be 9be ratios have been significantly disturbed possibly by mixing with transported soils

detailed geochemical studies of the initial stages of weathering of alkaline rocks ilha de sao sebastiao brazil abstract detailed mineral and chemical studies of samples of syenite rocks with thick weathering rinds found in the alkaline massifs on ilha de sao sebastiao illustrate the complex interplay between variables controlling initial weathering processes an array of geochemical information was obtained by optical and electron microscopy x ray analyses mass spectroscopy and optical spectrometry sericite and metahalloysite are the principal phases nucleating and forming as the perthitic feldspar rock matrix disintegrates incipient feldspar dissolution and the formation of submicrometer x ray opaque secondary phases were observed in fresh rock material using transmission electron microscopy pore waters from which secondary phases nucleate and grow are under the constant influence as alteration proceeds of physical e g accessibility of mineral surfaces to percolating fluids and chemical e g chemistry of minerals providing the dominant solutes controls minor and trace element signatures do not vary significantly except for zn rb sr y ree and pb lathanide mobilities appear related to their host mineral stabilities with respect to ambient pore waters

faulting and fracturing in shale and self sourced reservoirs introduction production from self sourced reservoirs relies on natural and induced fracturing for permeability and conductance of hydrocarbons to the producing wellbores thus natural or induced fracturing is often a key to success in unconventional reservoir plays on the other hand fractures may compromise seals and large or well connected fractures or faults may cause undesirable complications for unconventional reservoirs natural and induced fractures are influenced by 1 mechanical stratigraphy 2 pre existing natural deformation such as faults fractures and folds and 3 in situ stress conditions both natural and as modified by stimulation and pressure depletion this special issue of the aapg bulletin elucidates some of these structural geologic and geomechanical controls understanding the occurrence and controls on natural and induced faulting and fracturing in self sourced reservoirs is a key component for developing effective approaches for exploiting self sourced reservoirs

weathering dynamics and geosphere mixing with reference to the potassium cycle abstract continental weathering and erosion are discussed from a planetary perspective as important links in the chain of chemical and physical exchanges between surface geospheres atmosphere hydrosphere crust and the mantle the influence of weathering on geosphere chemistry is explored by considering potassium exchanges between geospheres k is transferred from the continents by weathering and erosion to the oceans from which dissolved k is removed during spilitization and by incorporation into sediments k carried to the mantle by subduction of spilites and sediments 8 10 13 g a 1 could balance the dissolved k added to the oceans from continental river runoff and from seafloor hydrothermal springs the largest k flux is that 2 7 10 14 g a 1 physically carried to the oceans in suspended sediments the weakest link in quantifying geosphere exchanges is the lack of understanding of the construction and restoration of continents and hence in defining the parameters involved in their chemical and physical renewal

source mechanism of vulcanian eruption at tungurahua volcano ecuador derived from seismic moment tensor inversions source mechanisms of explosive volcanic eruptions are critical for understanding magmatic plumbing systems and magma transport tungurahua is a large andesitic stratovolcano where seismoacoustic data has been recorded over several years in may 2010 an energetic eruption cycle began with a midsize vulcanian explosion followed by swarms of explosive eruptions the five station seismoacoustic network recorded significant seismic and infrasonic signals from the explosions source mechanisms of 50 explosion earthquakes associated with vulcanian explosions during this eruptive period are investigated here the source centroid locations and geometries of explosive signals in the 10 2 s band were determined by full waveform moment tensor inversion the observed waveforms are well explained by a combination of volumetric moment tensor components and a single vertical downward force component the source centroids are positioned about 1 5 km below and about 320 m north of the active crater eigenvalue and eigenvector analysis indicates that the source geometries can be described by a subhorizontal thin ellipsoid representing a sill like magma accumulation resultant source time histories show a repetitive sequence of inflation and deflation from event to event indicating identical source processes frequently occurred over the period the inflation deflation in the deep source region may be the result of crack opening volatile bubble growth at depth opens a pathway for gases to escape and triggers shallow explosions at the summit crater the associated downward single force is interpreted as an exchange of linear momentum between the source and the surrounding region during the escaping gas flow

lateritic crusts and related soils in eastern brazilian amazonia abstract the upland soils of carajas and paragominas in eastern brazilian amazonia are made up of yellow to reddish earthy clayey to clayey materials which cover iron aluminum aluminum iron and aluminum lateritic crusts these materials are closely related to each other and to lateritic evolution and are comprised by three horizons described from the base to the top as lower intermediary and upper horizons that are identified by the type amount and size of the lateritc fragments embedded into a matrix that increases towards the top the three horizons show a strong lithological vertical transition into themselves and the degradation degree increases toward the top of the profiles where the main characteristics are the same geochemical signatures between the horizons of every profile and the change in the mineralogical composition from hematite gibbsite to gibbsite al goethite in the n5 and ib and from gibbsite to kaolinite quartz in paragominas these transformations support a lateritic crust chemical reworking which allows for its transformation into a friable and soft in situ matrix and then into soil in a progressively weathering process which started in amazonia probably in the miocene after the formation and exposure of the main lateritic crusts to landsurface

cyclic jerky opening of magma sheet and caldera formation during the 2000 miyakejima volcano eruption 1 nied volcanic observation network at miyakejima volcano central japan repeatedly detected extraordinary step like tilt changes during the 2000 miyakejima eruption associated with these tilt steps broadband seismometers recorded very long pulse waves with a duration of about 50 s during this stage the summit of the volcano collapsed and sank forming a caldera with a depth of about 400 m and a diameter of about 1 6 km in total prior to the tilt steps long period earthquakes were acceleratingly generated in the shallow part of the volcano and the ground tilt changes suggested inflation of the volcanic body the analysis of these data from the tiltmeters and broadband seismometers suggests that the tilt steps and the 50 s pulse packets were caused by the opening of sill sheet like tensile cracks oriented in a se nw direction beneath the volcano with a depth of about 6 8 km and a volumetric change of about 106 107 m3

strain accommodation by slow slip and dyking in a youthful continental rift east africa continental rifts begin and develop through repeated episodes of faulting and magmatism but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented in highly evolved rifts tensile stresses from far field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions1 2 3 these rifting crises are rarely observed in thick lithosphere during the initial stages of rifting here we show that most of the strain during the july august 2007 seismic crisis in the weakly extended natron rift tanzania was released aseismically deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping this event provides compelling evidence for strain accommodation by magma intrusion in addition to slip along normal faults during the initial stages of continental rifting and before significant crustal thinning

triggering of volcanic eruptions by large earthquakes when a large earthquake occurs near an active volcano there is often concern that volcanic eruptions may be triggered by the earthquake in this study recently accumulated reliable data were analyzed to quantitatively evaluate the probability of the occurrence of new eruptions of volcanoes located near the epicenters of large earthquakes for volcanoes located within 200 km of large earthquakes of magnitude 7 5 or greater the eruption occurrence probability increases by approximately 50 for 5 years after the earthquake origin time however no significant increase in the occurrence probability of new eruptions was observed at distant volcanoes or for smaller earthquakes the present results strongly suggest that new eruptions are likely triggered by static stress changes and or strong ground motions caused by nearby large earthquakes this is not similar to the previously presented evidence that volcanic earthquakes at distant volcanoes are remotely triggered by surface waves generated by large earthquakes

the nuclear waste disposal problem an overview from a geological and geochemical perspective abstract in this paper we present a brief review of nuclear waste disposal research from a geological and geochemical perspective examples were chosen to illustrate both laboratory and field aspects of nuclear waste disposal and to show how these could be linked together by geological analogy and observation this strategy of linking geological observations and laboratory experiments and tailoring the disposal concept to simulate the more attractive features of the geology should give greater credence to the overall performance assessment of a nuclear waste disposal system

oxygen isotope dating of the australian regolith australia has had a long and complex history of intense surficial weathering and this has led to the extensive development of laterites bauxites and deeply weathered profiles of a variety of ages across the continent1 2 a detailed knowledge of the age s of such weathering phenomena is of great importance for the reconstruction of australia s post palaeozoic geomorphic and palaeoclimatic history however in many instances absolute geo chronological information is not obtainable using conventional techniques here we describe and evaluate a new method that can provide an estimate of the age of intensely weathered profiles based on the oxygen isotope composition of minerals developed by deep weathering lateritization processes this method allows the definition of four ages of weathering in eastern australia from the late palaeozoic to the present and suggests that some profiles previously thought to be late cretaceous or tertiary in age may be of pre late mesozoic age the oxygen isotope data indicate that the minerals used in this study have retained their original isotopic composition for periods of up to 250 million years despite the continued presence of meteoric waters of progressively higher 18o content during this interval

broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches 1 we systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes one is waveform inversion of very long period vlp signals assuming possible source mechanisms the other is a source location method of long period lp events and tremor using their amplitudes the deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to vlp signals with periods longer than a few seconds the source location method assumes isotropic radiation of s waves and uses seismic amplitudes corrected for site amplifications this simple approach provides reasonable source locations for various seismic signals such as a vlp event accompanying lp signals an explosion event and tremor associated with lahars and pyroclastic flows observed at five or fewer stations our results indicate that a frequency band of about 5 12 hz and a q factor of about 60 are appropriate for the determination of the source locations in this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves the source location method may be categorized as a stochastic approach based on the nature of scattering waves systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes

pressure recovery in magma due to bubble growth 1 pressure recovery in magma subject to sudden depressurization is investigated in terms of the growth of bubbles containing magmatic volatiles assuming conservation of volatile mass and pressure equilibration between the bubbles melt and a surrounding elastic medium the final magma pressure is completely determined by its initial pressure and the magnitude of the pressure drop simulations show that the initial magma pressure is easily recovered or even exceeded when magma containing tiny bubbles is surrounded by a relatively stiff elastic medium under low confining pressure this result suggests that when processes such as magma withdrawal dike intrusion and nearby seismicity decrease the pressure in a magma chamber magma re pressurization can occur without new injection of magma

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

source process of long period seismic events at taal volcano philippines vapor transportation and condensation in a shallow hydrothermal fissure 1 we analyzed observations of a swarm of more than 40 000 long period lp seismic events at taal volcano philippines in 2010 2011 the event waveforms are strongly correlated to each other consistent with a fixed source location and begin with a dilatational first motion they have a peak frequency around 0 8 hz and a quality factor q of 6 waveform inversion of the events pointed to a tensile crack source dipping 30 60 at a shallow 100 200 m depth a simulation using a fluid filled crack model indicated that the complex frequencies of the waveforms are explained by the fundamental longitudinal mode resonance of a vapor filled crack 188 m long a satellite thermal infrared image acquired during the swarm period suggests that the lp events were not accompanied by surface gas releases we considered a vapor transportation model in which vapor exsolved from magma and rose in a fissure extending to the lp source this model yielded estimates that 105 107 m3 of magma was involved in the lp swarm and that the temperature of vapor in the lp source crack was around 600 k we modeled a triggering mechanism of the crack resonance based on sudden condensation of vapor at the crack tip in a cold aquifer this model explained observed characteristics of the events including the dilatational first motion the total volumetric change and the fixed source location

capillary geochemistry in non saturated zone of soils water content and geochemical signatures abstract the unsaturated zone uz retains aqueous solutions against gravity by capillary forces this suction state corresponds to a decreasing internal pressure of the water which modifies its thermodynamic properties accordingly the speciation of solutes and the solubility of solids and gases in such capillary solutions change the volumetric capillary water content of the soil at high suction can be calculated extrapolating the water retention curves wrc with the rossi nimmo model interestingly several tens of liters per cubic meter of soil can be thus suctioned a sufficiently large volume to support that 1 capillary water is not restricted to nanosized pores which means it disobeys the young laplace law and is metastable with respect to vapor superheating and 2 the geochemistry of capillary solutions might significantly influence the subsurface mass transfer two field situations are here interpreted using the capillary thermodynamic properties 1 the trapping of sand grains during the growth of desert roses gypsum and 2 the development of abnormal paragenetic sequences in some saprolites the capillary approach is extended to the soil solids so that the micro mineralogy can be explicitly though sketchily integrated in the calculations the key conclusion is that capillarity changes the saturation indexes and so the reaction rates at given solution composition in a way consistent with the field observations this perspective amounts to geochemically distinguishing the capillary and percolating solutions which is interestingly analogous to the immobile and mobile water distinction already often integrated in uz flow models

stable isotope geochronology of the australian regolith australian regolith profiles can be assigned to one of three post palaeozoic age groups on the basis of the oxygen isotope composition of authigenic clay minerals developed in the profile systematic variations in the isotopic composition of meteoric waters and therefore of the authigenic regolith minerals that formed in equilibrium with them are a result of the continent s drift from high to low latitudes and changes in global climate residual clays collected in situ from regolith profiles of post mid tertiary age have 18o values between 17 5 and 21 3 with the exception of samples from northern australia north of approximately 20 s which have anomalously low values because meteoric waters in northern australia are largely derived from monsoonal rain the high 18o values of post mid tertiary residual clays are consistent with australia s northward drift to low warm latitudes during this time compared with the much higher latitudes it occupied for most of its post palaeozoic history late tertiary residual clays have 18o values that are indistinguishable from all other post mid tertiary clays indicating that further subdivision of the sample groups is not feasible on a continent wide scale comparison with hypothetical modern clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in australia since the mid tertiary pre mid tertiary clays have lower 18o values between 10 0 and 17 5 which are consistently lower than post mid tertiary clays 18o values of less than 14 to 15 are thought to reflect weathering events during much earlier geologic periods perhaps early or mid mesozoic when australia was at high latitude and the australian climate was humid and cool to cold several workers have documented the existence of very old regolith profiles and land surfaces in australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre late mesozoic age which have 18o values between 10 2 and 12 3 regolith profiles composed of low 18o clays 15 are widespread in australia and it is possible that a much greater part of the modern landscape than previously recognized developed in the early or mid mesozoic the 18o values of transported i e sedimentary kaolinites reveals that the major source for many tertiary kaolinitic sediments was this postulated pre late mesozoic low 18o regolith the stableisotope evidence that much of the australian regolith formed in comparatively cold conditions suggests that contrary to some traditional interpretations lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub tropical climates the hydrogen isotope composition of the clays range from 115 to 50 however it is inferred that the majority of clays have undergone some post formational hydrogen isotope exchange which renders their d composition unsuitable for dating purposes

composition and origin of the clay cover on north brazilian laterites the belterra clay in northern brazil is a uniform yellowish unstratified kaolinitic clay with variable contents of gibbsite it is generally 5 10 m thick and covers a lateritic weathering crust on remnants of a dissected table land complete profiles with belterra clay the underlying bauxite laterite and saprolite bed rock were sampled in three areas of the amazon region the chemical and mineralogical data show a distinct affinity between the belterra clay and the underlying layers above all with the saprolite variations in the composition of the underlaying layers are reflected by the belterra clay among the structural and textural features important for the discussion of the origin of the belterra clay are the sharp contact between the clay cover and the underlying laterite as well as conglomeritic brecciate textures and occasional bedding structure in the upper part of the lateritic crust

upper pleistocene amazon deep sea fan muds reflect intense chemical weathering of their mountainous source lands abstract upper pleistocene muds of the amazon deep sea fan contain an abundance of residual weathering products as indicated by their bulk chemical and mineralogical compositions the muds are chemically more mature than average shale average pelagic mud or the surrounding demerara abyssal sediments they are however very similar to the bulk chemical compositions of contemporary suspended sediments of both the amazon estuary and those carried by the major andean tributaries the modern sediment compositions reflect the rapid weathering now occurring in the andean source regions of the basin the major element geochemical signature of the upper pleistocene deep sea fan sediments suggests that intense chemical weathering in the mountainous source lands has controlled the chemistry of amazon river suspended sediments since at least the upper pleistocene minor and trace element signatures appear uniform throughout the fan and element concentrations are in general higher than in the intensely weathered amazon lowland soils but lower than in deep sea sediments

oxygen and hydrogen isotopes in pedogenic minerals implications for paleoclimate evolution in amazonia during the cenozoic stable isotopes in gibbsite and kaolinite were analyzed to reconstruct the amazonia palaeoclimate during the cenozoic and to investigate the environmental conditions of the weathering process and the origin of the oxisol that cover the lateritic bauxite crust at least two types of kaolinite were identified in the oxisol near the surface the kaolinite is less fractionated and was developed at a higher temperature 35 c this is probably due to the effect of vegetation and or evapotranspiration or is a consequence of surface microenvironmental conditions or allochthonous inputs the other kaolinite samples ranged in formation temperatures from 21 c to 26 c and developed under conditions similar to the pleistocene and the modern climate of amazonia at least two types of gibbsite were found one type developed in the modern amazonia climate in a way similar to most kaolinite samples whereas the samples of the other type are more fractionated this is because they may have been formed in low recycling rainwater and or under a low amount of precipitation these two conditions indicate a seasonal climate for bauxite development that can be linked to the low exhumation of the andes cordillera and its geographical position relative to the trombetas region during the period ranging from the late oligocene to the early miocene at the end of the cenozoic the climate was less seasonal and wetter and the temperature was lower in addition there was the probable inland position of the trombetas region which allowed oxisol development the gibbsite developed earlier than the kaolinite of the oxisol but there is a partial inheritance or temporal equivalence among the bauxite horizon and the oxisol as well as multiple generations of gibbsite and kaolinite which is to be expected for materials developing over long periods in hard leaching conditions

transient pore pressure response to confining stress excursions in berea sandstone flooded with an aqueous solution of co2 we measured the pore pressure response due to carbon dioxide co2 gas bubble nucleation and growth in a berea sandstone core flooded with an initially subsaturated aqueous solution of co2 in response to a rapid drop in confining stress under conditions representative of a confined aquifer a portion of the co2 in the earth s crust derived from volcanic magmatic and biogenic sources dissolves in groundwater sudden reductions in confining stress in the earth s crust occur due to dilational strain generated by the propagation of seismic rayleigh and p waves or aseismic slip in the near field of earthquakes a drop in confining stress produces a proportional drop in pore fluid pressure when the pore fluid contains dissolved co2 the pore pressure responds to a drop in confining stress like it does in the dissolved gas free case until the pore pressure falls below the bubble pressure gas bubble nucleation and diffusive growth in the pore space trigger spontaneous transient buildup of the pore fluid pressure and reduction of effective stress we measured the rate of pore fluid pressure buildup in the 100 s immediately following the confining stress drop as a function of the saturation with respect to co2 at the lowest pore pressure realized during the confining stress drop using five different co2 partial pressures the rate scales with the saturation with respect to dissolved co2 from 10 kpa min at 1 25 to 166 kpa min at 1 8 the net pore pressure rise was as large as 0 7 mpa 100 psi over 5 h