magnesium isotope fractionation in biogenic and abiogenic carbonates implications for paleoenvironmental proxies abstract geochemical variations in marine biogenic carbonates that are preserved in the geological record serve as proxies of past environmental change however interpreting most proxies is complicated by biologically mediated vital effects highlighting the need to develop new tools for reconstructing paleoenvironmental change recently magnesium mg isotope variability in carbonates has been explored extensively to determine its utility as a paleoenvironmental proxy we review the results of these works which have yielded valuable information on the factors affecting mg isotope fractionation between carbonates and solution 26mgcarb sol in biogenic and abiogenic carbonate minerals strong evidence exists for a mineralogical control on 26mgcarb sol with the negative offset from 0 following the sequence aragonite 3 mol mol and saturation states 3 that are similar to seawater suggest that 26mgcarb sol has a temperature dependence of 0 01 c 1 and is insensitive to precipitation rate in contrast a significant precipitation rate dependence is observed in calcites precipitated from solutions with relatively low mg ca ratios

relative ages of loess and till in two quaternary palaeosols in gorges valley mount kenya east africa two compound palaeosol profiles formed in loess and till were studied in the oldest early quaternary end moraine gorges age system on mount kenya although both tills appear to have similar weathering histories the overlying loessic sediments serving as secondary parent materials for the palaeosols are considered to have different ages on the basis of colour presence or absence of clay films and field texture especially percentage of silt palaeomagnetic determinations showed both tills to have reversed remanent magnetism suggesting that they were emplaced during the matuyama chron the overlying loessic sediments in profiles gor55 and gor58 show normal magnetism and grade upward into the lower zone of bioturbation in the a horizon complex however in gor58 the surface loessic sediments have normal remanent magnetism with considerable secular variations suggesting it was emplaced over a longer time frame during the brunhes chron i e 0 78 ma profile gor55 contains larger amounts of gibbsite indicating more aggressive leaching over time and an absence of secular magnetic variations suggests deposition over a shorter time interval the study of volcanic feldspars and ash using scanning electron microscopy in the two profiles shows that sand grain 63 250 m weathering is slightly different in the two tills relative weathering effects e g corrosion of grain surfaces and neoformation of clay minerals are greater in profile gor55 than in profile gor58 overall the data indicate that some sites in the lower tropical afroalpine timberline environment may have aeolian covers that are considerably younger than the deposits they overlie 1997 by john wiley sons ltd

effect of mineralogy salinity and temperature on li ca and li isotope composition of calcium carbonate li ca and li isotope ratios in marine and freshwater calcium carbonates are potential tracers of past environmental variables such as weathering intensity and temperature to make use of their potential requires full understanding of the fractionation of li ca and 7 li 6 li during growth of calcium carbonate this study improves such understanding with two sets of new measurements on inorganic calcites and aragonites precipitated over a range of salinity and on the test of benthic foraminifera formed at a range of temperatures li ca in inorganic calcite increases by a factor of four as salinity increases from 10x to 50x inorganic aragonite demonstrates no significant change in li ca over the same salinity range the difference in behaviour is probably due to the incorporation mechanism of li substitution of li in the ca 2 site in aragonite makes growth solution li ca the key variable while interstitial incorporation of li in calcite means that the growth solution li concentration is more important compared to the growth solution 7 li 6 li is c3x lower in calcite and c11x lower in aragonite with no relationship to salinity for either mineral similar isotope fractionation to these inorganic experiments are observed for biogenically produced calcite foraminifera and aragonite corals this suggests little biological control during li incorporation into biogenic calcium carbonates the difference in fractionation between calcite and aragonite is consistent with an equilibrium isotope fractionation reflecting different incorporation mechanisms for li into the two minerals four samples of the benthic foraminifera uvigerina precipitated over a temperature range of 14 8c have li ca ranging from 18 5 to 13 1 amol mol the ratio is inversely related to temperature with a sensitivity of 2 5f0 8 per 8c this sensitivity is similar to that observed in a previous study of foraminiferal li ca but about half that observed during inorganic calcite growth the large variability in both li ca and temperature sensitivity exhibited between various foraminifera species suggests an additional control on calcite li ca apart from those of salinity and temperature observed in this study d 2004 elsevier b v all rights reserved

stoneley wave propagation in a fluid filled borehole with a vertical fracture the propagation of stoneley waves in a fluid filled borehole with a vertical fracture is investigated both theoretically and experimentally the borehole propagation excites fluid motion in the fracture and the resulting fluid flow at the fracture opening perturbs the fluid solid interface boundary condition at the borehole wall by developing a boundary condition perturbation technique for the borehole situation we studied the effect of this change in the boundary condition on the stoneley propagation cases of both hard and soft formations have been investigated the fracture has minimal effects on the stoneley velocity except in the very low frequency range in which the stoneley velocity drastically decreases with decreasing frequency significant stoneley wave attenuation is produced because of the energy dissipation into the fracture the quantitative behavior of these effects depends not only on fracture aperture and borehole radius but also on the acoustic properties of the formation and fluid

extensional and strike slip tectonics across the monte amiata monte cetona transect northern apennines italy and seismotectonic implications abstract this paper deals with the structural evolution along a transect across the inner northern apennines monte amiata volcano geothermal area monte cetona mainly focussing on the post orogenic middle miocene quaternary structures the tectonic setting of the study area derives from the superimposition of three main faulting events the first and second events developed during the middle late miocene and early middle pliocene respectively and took place in response to extensional tectonics the third faulting event developed in a transcurrent transtensional setting during the quaternary quaternary faults mainly strike ne sw and show left lateral kinematics with a minor dip slip normal component they caused the monte amiata volcanic eruptions 300 190 ka and controlled the widespread pleistocene and present hydrothermal fluids circulation quaternary strike slip faults have been documented in the monte amiata monte cetona area for the first time in this paper correlation with the adjoining areas e g vulsini region identifies the quaternary strike slip faulting recognised in the study area as a feasible source for the seismic activity in the monte amiata region where the origin of diffuse low magnitude seismicity is still under debate and poorly understood

geological structure of a long living geothermal system larderello italy we have examined the data of 600 geothermal wells and re interpreted approximately 500 km seismic profiles through the field of larderello italy we conclude that the two main seismic reflectors present below the geothermal area host two different fluids 1 superheated steam in the upper h horizon reached by drillholes and 2 supercritical fluid in the deeper k horizon reached by few unproductive or damaged wells the superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at larderello whereas the supercritical fluid represents a potential unconventional deep seated resource still to be assessed the high temperatures existing in correspondence of the k horizon suggest that the silica rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks unless occasional fluid overpressure and abrupt high strain rates occur

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

neogene marine isotopic evolution and the erosion of lesser himalayan strata implications for cenozoic tectonic history abstract an extensive northward deepening blanket of neoproterozoic and cambrian sedimentary rocks once extended from the himalayan margin far onto the indian craton cambrian deposits of this upper lesser himalayan succession which include deposits of the outer lesser himalaya tectonic unit are enriched in radiogenic 187os they make up part of a proximal marine facies belt that extends onto the craton and along strike from india to pakistan by contrast age equivalent facies in the tethyan himalaya are more distal in nature neoproterozoic to cambrian strata of the upper lesser himalayan succession are now missing in much of the lesser himalaya with their erosion exposing older precambrian lesser himalayan strata we suggest that exhumation and weathering of the upper lesser himalaya and related strata caused dramatic changes in the 187os 188os and 87sr 86sr neogene record of seawater starting at 16 ma first order estimates for the volume of upper himalayan strata as well as the volume of all lh rock eroded since this time and geochemical box modeling support this idea exhumation at 16 ma is a fundamental event in the evolution of the himalayan orogeny and the geochemical evolution of the oceans and will be a critical part of the construction of future models of himalayan thrust belt evolution

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

late neogene volcanics and interbedded palaeosols near mount kenya abstract two lava flows with interbedded palaeosols outcrop c 40 km sw of mount kenya near the amboni river north of mweiga kenya along the nyeri thompson falls road at 0 18 s 37 48 e these flows overlain by loess are principally trachyandesite and form the base of the mount kenya volcanic series which in the early literature is described as being of probable miocene pliocene age here we report 39 ar 40 ar dates c 5 2 5 5 ma and reversed magnetizations which establish a latest miocene to earliest pliocene age for these flows weathering characteristics of palaeosols interbedded with the lavas indicate generally dry climatic conditions during the late miocene punctuated with humid events during the pliocene and quaternary these late miocene quaternary palaeosols depict a relatively long and complex weathering history followed by loess deposition the palaeosols appear to have been episodically deflated initially in phase with the deposition of lavas when surfaces were devoid of vegetation and later during periods of climatic deterioration when wind systems intensified such weathering histories within palaeosol profiles are also documented on nearby mount kenya where well weathered lower palaeosol horizons developed on matuyama age tills are overlain by much younger less weathered horizons developed on brunhes age loess the geochronology of late miocene lavas reported here provides maximum ages for weathering histories of palaeosols formed in a xeric tropical highland climate

complex seismic trace attributes interpretation of seismic reflection records is a blend of quantitative science and visual art an interpreter uses the rules of wave propagation realistic limits on impedances of rocks and accepted principles of stratigraphic deposition and structural deformation to arrive at a geologic understanding of a seismic section this application of science however seldom produces a unique answer and the obligation to consider alternative interpretations provides plenty of latitude for creative imagining

correlation between seismic reflectivity and rheology in extended lithosphere southern tuscany inner northern apennines italy abstract in southern tuscany inner zone of the northern apennines the lithosphere has been affected by extensional deformation since the middle miocene and is characterized by high heat flow 120 mw m 2 both local shallow and regional deep seismic reflection profiles clearly show the occurrence of a sharp reflector k horizon within the upper crust which is probably located at the top of a shear zone acting as the decollement horizon for the latest pliocene quaternary normal faults its depth varies between 3 and 6 km in geothermal areas and 9 and 12 km elsewhere borehole control in the geothermal areas shows that it occurs at a temperature of approximately 450 c the hypothesis that the k horizon represents the top of the brittle ductile transition agrees with two lines of evidence a it approximately follows the same isotherm over the whole region and b its depth coincides with rheological predictions of the brittle ductile transition for the range of high pore fluid pressures and strain rates estimated for southern tuscany it appears therefore that at least under specific conditions very high pore fluid pressures strain concentration the brittle ductile transition may have a seismic signature

element ca c and o isotope ratios in modern brachiopods species specific signals of biomineralization fossil brachiopods are of major importance for the reconstruction of palaeoenvironmental conditions particularly of the paleozoic in order to better understand signals of ancient shell materials modern analogue studies have to be conducted here we present c and o isotope data in conjunction with mg ca sr ca mn ca and fe ca data for nine modern rhynchonellid and terebratulid brachiopod species from tropical to intermediate latitudes and shallow to very deep marine settings c and o isotope signals of most species suggest formation of secondary shell layers near or in isotopic equilibrium with ambient seawater some species especially in the suborder terebratellidina show partly distinct disequilibrium signals suggesting some degree of phylogenetic control on the expression of vital effects mn ca and fe ca ratios measured in the modern species form a baseline to assess fossil preservation but also yield environmental information mg ca and sr ca ratios follow previously observed patterns with all studied brachiopod species comprising low mg calcite strong covariation of sr ca ratios with mg ca ratios is only observed in rhynchonellids and possibly one terebratulid species potentially linking the incorporation behaviour of alkaline earth metals to phylogeny sr ca show a strong negative correlation with 13c values in terebratellidinid species which exhibit major isotopic disequilibrium and also combined data from three localities for which two species were studied indicate such a negative relation the observed covariation of sr ca ratios with 13c values may therefore become a useful tool to detect 13c disequilibrium and to robustly estimate 13c values of ambient dic in deep time

temperature dependence of δ 7 li δ 44 ca and li ca during growth of calcium carbonate abstract lithium and calcium isotope ratios together with the li ca element ratio have been measured in calcites precipitated inorganically at temperatures ranging from 5 to 30 c and on seasonal growth bands from a coral these measurements indicate the potential uses of these three environmental proxies carbonate li isotopes are lighter than the solution from which they grow probably due to equilibrium fractionation this fractionation is not significantly influenced by temperature and because li is not involved in any known biological process this suggests that carbonates will provide a recorder for the past li isotope composition of natural waters and hence for past weathering conditions as has been observed previously for inorganic aragonite the ca isotopes in inorganic calcite are lighter than the growth solution and are only weakly dependent on temperature this confirms that the temperature dependence observed in some species of foraminifera geochem geophys geosyst 1 2001 reflects additional isotope fractionation due to biological processes during mineralization ca isotopes may therefore provide a powerful tool with which to investigate the processes of biomineralization finally li ca ratios in inorganic and biogenic carbonates increase as temperatures decrease with a sensitivity of 4 per c this temperature dependence of li ca may prove useful to assess past temperatures in cold environments such as the deep ocean

acoustic measurements in unconsolidated sands at low effective pressure and overpressure detection shallow water flows and over pressured zones are a major hazard in deepwater drilling projects their detection prior to drilling would save millions of dollars in lost drilling costs i have investigated the sensitivity of seismic methods for this purpose using p wave information alone can be ambiguous because a drop in p wave velocity vp can be caused both by overpressure and by presence of gas the ratio of p wave velocity to s wave velocity vp vs which increases with overpressure and decreases with gas saturation can help differentiate between the two cases since p wave velocity in a suspension is slightly below that of the suspending fluid and vs 0 vp vs and poisson s ratio must increase exponentially as a load bearing sediment approaches a state of suspension on the other hand presence of gas will also decrease vp but vs will remain unaffected and vp vs will decrease analyses of ultrasonic p and s wave velocities in sands show that the vp vs ratio especially at low effective pressures

seismicity and velocity structures along the south alpine thrust front of the venetian alps ne italy abstract in this paper we show the seismicity and velocity structure of a segment of the alpine retro belt front along the continental collision margin of the venetian alps ne italy our goal is to gain insight on the buried structures and deep fault geometry in a silent area i e an area with poor instrumental seismicity but high potential for future earthquakes as indicated by historical earthquakes 1695 me 6 7 asolo and 1936 ms 5 8 bosco del cansiglio local earthquakes recorded by a dense temporary seismic network are used to compute 3 d vp and vp vs tomographic images yielding well resolved images of the upper crust underneath the south alpine front we show the presence of two main distinct high vp s verging thrust units the innermost coincides with the piedmont hill and the outermost is buried under a thick pile of sediments in the po plain background seismicity and vp vs anomalies interpreted as cracked fluid filled volumes suggest that the ne portion of the outermost blind thrust and its oblique lateral ramps may be a zone of high fluid pressure prone to future earthquakes three dimensional focal mechanisms show compressive and transpressive solutions in agreement with the tectonic setting stress field maps and geodetic observations the bulk of the microseismicity is clustered in two different areas both in correspondence of inherited lateral ramps of the thrust system tomographic images highlight the influence of the paleogeographic setting in the tectonic style and seismic activity of the region

thermal modelling of the larderello geothermal field tuscany italy we present a 3 d thermal model of the larderello geothermal field tuscany to evaluate 1 the extent and contribution of the heat transfer mechanisms conduction vs convection at the intermediate upper crust levels 2 the variability of the heat and mass fluxes entering from below and 3 the crucial role of the formation permeability the model composed by three main layers considers the upper 10 km of the crust to better constrain the simulations with experimental data from borehole fluid inclusion studies and hypocentral distributions several sets of simulations were carried out with different bottom boundary temperatures and different formation permeabilities for the two deeper layers the results indicate that the present temperature t and pressure distributions in the larderello field require deep reservoir rocks with higher permeability than the overlying capping units and underlying intermediate crust permeability values of 1 mdarcy for the reservoir rocks are enough to allow fluid convection if the temperature at 10 km depth is as high as 500 50 c the presence of localized zones with formation permeability 50 100 times higher than the surrounding rocks strongly favours the migration of over pressurized fluids which episodically break through the overburden feeding the presently exploited geothermal fields

geochronology of the larderello geothermal field new data and the closure temperature issue the larderello geothermal field is generally accepted to have been produced by a granite intrusion at 4 9 km depth hydrothermal parageneses and fluid inclusions always formed at temperatures greater than or equal to the current ones which implies that the field has always undergone a roughly monotonic cooling history fluctuations 40 k since intrusion of the granite at 4 ma the heat required to maintain the thermal anomaly over such a long period is supplied by a seismically anomalous body of 32000 km3 rooted in the mantle borehole minerals from larderello are thus a unique well calibrated natural example of thermally induced ar and sr loss under geological conditions and time spans the observations biotites retain ar above 450 c agree well with other albeit less precise geological determinations but contrast with laboratory determinations of diffusivity from the literature we therefore performed a hydrothermal experiment on two larderello biotites and derived a diffusivity dlab 370 c 5 3 10 18 cm2s 1 in agreement with published estimates of diffusivity in annite from dlab and the rejuvenation of the k ar ages we calculate maximum survival times at the present in hole temperatures they trend smoothly over almost two orders of magnitude from 352 ka to 5 3 ka anticorrelating with depth laboratory diffusivities are inconsistent not only with geological facts but also among themselves from the geologically constrained lifetime of the thermal anomaly we derive a diffusivity dg 370 c 3 81 1021 cm2s 1 3 1 orders of magnitude lower than dlab the cause of these discrepancies must be sought among various laboratory artefacts overstepping of a critical temperature t enhanced diffusivities in wet experiments presence of fast pathway dislocation and pipe diffusion and of dissolution reprecipitation reactions which we imaged by scanning electron microscopy these phenomena are minor in geological settings in the absence of mineral transformation reactions complete or near complete resetting is achieved only by volume diffusion therefore laboratory determinations will necessarily result in apparent diffusivities that are too high compared to those actually effecting the resetting of natural geochronometers

evolution of cenozoic seawater lithium isotopes coupling of global denudation regime and shifting seawater sinks abstract the li isotopic record of seawater shows a dramatic increase of 9 over the past 60 million years here we use a model to explore what may have caused this change we focus particularly on considering how changes in the reverse weathering sinks that remove li from seawater can contribute to explain the observed increase our interpretation is based on dividing the oceanic sink which preferentially removes light li into two components i removal into marine authigenic clays in sediments at low temperatures with associated high fractionation factors and ii removal into altered oceanic basalt at higher temperatures and resulting lower fractionation factors we suggest that increases in the flux of degraded continental material delivered to the oceans over the past 60 ma could have increased removal of li into sedimentary authigenic clays versus altered basalt because altered basalt is associated with a smaller isotopic fractionation an increasing portion of the lower temperature authigenic clay associated sink could contribute to the rise of the seawater li isotope value this effect would moderate the extent to which the isotopic value of continental inputs must have changed in order to explain the seawater record over the cenozoic nonetheless unless the magnitude of fractionation during removal differs significantly from current understanding substantial change in the li 7 of inputs from continental weathering must have occurred our modeling suggests that dissolved riverine fluxes in the early eocene were characterized by li 7 of 0 to 13 with best estimates of 6 6 12 6 these values imply increases over the past 60 myrs of between 10 and 24 and we view a 13 increase as a likely scenario these changes would have been accompanied by increases in both the dissolved li flux from continental weathering and the removal flux from seawater into marine authigenic clays increases in li 7 of continental input are consistent with a change in the global denudation regime as a result of increasing continental erosion rate through the cenozoic changes in denudation may have meant increasing climate sensitivity of weathering over time but do not require globally supply limited and thus entirely climate insensitive weathering in the early cenozoic

mapping capable faulting hazard in a moderate seismicity high heat flow environment the tuscia province southern tuscany northern latium italy abstract this study is focused on potential evidence of capable faulting affecting southern tuscany northern latium a region of high heat flow and moderate to low seismicity here we refer to this region as tuscia the latin name for the land of the etruscans the review of the evidence for active tectonics in this area has allowed us to identify several potentially active capable faults mapped using a combination of analysis of digital terrain models with remote sensing and local geological information derived from bibliographic data and different scale maps active and capable faulting is certainly more evident in the eastern sector of tuscia chianti cetona ridge pienza amiata and bolsena caldera however even in the western tuscia e g colline metallifere and tyrrhenian coast capable faulting may be hypothesized along numerous structural elements the characterization of active faulting potential in terms of geometry slip types and rates in such a high heat flow environment beyond its usefulness in improving the assessment of fault displacement and earthquake hazard also helps to improve knowledge of the stress field and structural setting of the many geothermal fields in the area this allows new useful insights into geothermal exploitation and hazard e g induced triggered seismicity moreover this new knowledge of active tectonics and capable faults of the hinterland sector of the northern apennines may also provide useful insights into the siting processes of highly hazardous and strategic structures and more generally in land use planning and management of infrastructures especially during emergencies

advanced three dimensional seismic imaging of deep supercritical geothermal rocks in southern tuscany the seismic k horizon is the key to gaining understanding on the deep supercritical geothermal rocks in southern tuscany the k horizon is hosted in metamorphic rocks which cause strong seismic wavefield scattering resulting in a poor signal to noise ratio our study aims to reveal high resolution seismic images of the k horizon below a geothermal field in southern tuscany using an advanced threedimensional seismic depth imaging approach the key seismic pre processing steps in the time domain include muting a large amount of persistent noise based on the statistical analysis of the seismic amplitudes and tomostatics technique to correct for static effects we carried out seismic depth imaging using kirchhoff pre stack depth migration and fresnel volume migration techniques each migration technique was tested with constant and heterogeneous three dimensional velocity models due to the difficulties in determining emergent angles for this low signal to noise ratio data set the migration results with the heterogeneous three dimensional velocity model show less coherent reflections compared to the migration results using the constant velocity model both velocity models however lead to relatively the same structure and depth of the k horizon indicating the similarity of the average velocities along the wave propagation paths in both velocity models with both velocity models fresnel volume migration yields the k horizon with better reflection coherency and higher signal to noise ratio than standard kirchhoff pre stack depth migration nevertheless both migration techniques have been able to reveal the k horizon with relatively high resolution and provide a reliable basis for geothermal rock characterization as well as steering of the first geothermal well penetrating the k horizon

upper crustal structure of the larderello geothermal field as a feature of post collisional extensional tectonics southern tuscany italy abstract reflection seismic profiles crossing the larderello geothermal field permit the distinction of three different seismic facies units in the upper continental crust the upper 3 4 km of the crust is characterized by low reflectivity its base corresponding to a reflector referred to as the k horizon and recognized in many other areas of southern tuscany beneath this reflector a seismic facies of 0 8 1 0 twt thickness is characterized by strong convergent and divergent reflections forming a lozange shaped geometry the lowermost seismic facies is characterized by almost horizontal reflections based on the distribution of the hypocentral microearthquakes temperature data recorded in deep boreholes and the geometry of normal faults the k horizon is explained here as a kinematically active rheological boundary which separates a brittle upper part from a ductile lower part according to this hypothesis the k horizon and the lozange reflections could originate from a mylonite band located at the contact between two geological bodies characterized by different rheological behavior it is inferred that this horizon acts as a decoupling plane in the upper continental crust it developed as a consequence of the extensional tectonics and the high heat flow which characterize southern tuscany

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

three dimensional p wave velocity structure of mt etna italy the three dimensional p wave velocity structure of mt etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs results show a near vertical low velocity zone that extends from beneath the central craters to a depth of 10 km this low velocity region is coincident with a band of steeply dipping seismicity suggesting a magmatic conduit that feeds the summit eruptions the most prominent structure is an approximately 8 km diameter high velocity body located between 2 and 12 km depth below the southeast flank of the volcano this high velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting

glacial stratigraphy and paleomagnetism of late cenozoic deposits of the north central united states the north central united states preserves one of the best continental records of late pliocene and early middle pleistocene glaciations in the northern hemisphere the glaciogenic sequences of this region consist of multiple tills interbedded with paleosols and volcanic ashes here we present results on paleomagnetic measurements and till compositional data from glacial sedimentary sequences in iowa nebraska kansas and missouri periods of normal polarity brunhes chron and reverse polarity matuyama chron were identified in the sedimentary sequences investigated this chronology is further constrained by the presence of three volcanic ashes derived from dated eruptions of the yellowstone caldera which indicate that the oldest till was deposited 2 0 ma based on these results we identify three groups of tills representing at least seven pre illinoian glaciations two older groups of reverse polarity tills containing low and intermediate proportions of crystalline clasts respectively and one younger group of normal polarity tills enriched in crystalline lithologies the clay mineralogy of the reverse polarity tills is enriched in kaolinite and depleted in expandable clays relative to the normal polarity tills which are also characterized by a minor amount of chlorite the silt fraction of tills also shows mineralogical contrasts whereby the normalpolarity tills are characterized by increases in calcite dolomite and feldspar whereas the older tills show depletion in these minerals and a relative enrichment in quartz these petrographic and mineralogic changes are indicative of an increase with time in the areal distribution of unweathered igneous and metamorphic source bedrock

weathering and geochronology of a quaternary paleosol sequence in lower teleki valley mount kenya summary a sequence of paleosols including residual regolith saprolite till aeolian volcaniclastic colluvial and slope wash deposits dating from the lower brunhes chron

sub surface geology and velocity structure of the krafla high temperature geothermal field iceland integrated ditch cuttings wireline and zero offset vertical seismic profile analysis abstract the krafla geothermal area in northern iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone of key importance to improved resource exploration and development in volcanic areas such as krafla is the interpretation and understanding of the subsurface geology within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the k 18 borehole within the krafla caldera based on combined wireline ditch cuttings and zero offset vsp vertical seismic profile analyses this study presents the first published sonic log velocity data from a high temperature geothermal borehole in iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations the shallow subsurface geology of the k 18 site from c 0 380 m comprises an inter layered sequence of sub aerial basaltic lavas hyaloclastites and tuffaceous lithologies of both felsic and basic composition which are progressively replaced by basaltic sheet intrusions with increasing depth an interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis gamma and sonic velocities between c 790 1120 m depth discrete high sonic vp units cut the lower c 100 m of this interval and are interpreted as either sheet intrusions or lava interiors at c 1800 m a sharp increase in p wave velocity from c 4 5 to c 5 5 km s represents the transition from a mixed lava and sheet intrusion dominated sequence into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c 2215 m reduced travel time analysis of processed zero offset vsp results reveal good correspondence with the major stratigraphic boundaries in the borehole supporting the potential for vsp studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields finally the application of percentage based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential

the deep structure of the larderello travale geothermal field from 3d microearthquake traveltime tomography 1 with the aim of exploring the deep structure of the larderello travale lt geothermal field a high resolution 3 d tomographic inversion of microearthquake traveltimes has been performed results show that the deep part of the larderello travale field is characterized by the presence of a structure having a velocity range of 6 0 6 5 km s and a convex shape deepening towards the northeastern and the southeastern sides of the field earthquakes are mostly concentrated on the top of the high velocity structure and below the k horizon implying a transition of rheological properties at depth the reported dependence on time of ts tp observed at one station located above an earthquake cluster suggests that the variation in pore fluid pressure might be responsible for the transition of rheological properties along the contact in such an area changes in pore fluid pressure might be related to time dependent hydraulic mechanisms that are very effective in crustal rocks at elevated temperatures index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8045 structural geology role of fluids 8180 tectonophysics tomography 8424 volcanology hydrothermal systems citation vanorio t r de matteis a zollo f batini a fiordelisi and b ciulli 2004 the deep structure of the larderello travale geothermal field from 3d microearthquake traveltime tomography geophys res lett 31 l07613

temporal record of lithium in seawater a tracer for silicate weathering abstract this paper presents multi species records of the li ca ratio and li isotopic composition 7 li of planktonic foraminifera from the pacific and atlantic oceans for the past 18 ma the li ca record is corrected for interspecific offsets determined from recent holocene foraminifera interspecific offsets in 7 li are not significant despite different diagenetic histories the records produced from both oceans are remarkably consistent corrected planktonic foraminiferal li ca ratios range from 6 3 to 10 9 mol mol while planktonic foraminiferal 7 li ranges from 25 to 31 both records are interpreted in terms of long term changes in seawater li ca and 7 li enabling issues related to higher resolution variability in li ca and 7 li to be ignored by assuming that the hydrothermal flux of li into the oceans and the flux of li removed from the oceans during low temperature uptake by marine basalts and sediments have not changed significantly since 18 ma and using published records for the seawater calcium concentration the seawater li ca and 7 li records can be used to estimate global average river 7 li and li fluxes our records indicate that the river flux of dissolved li decreased between 16 and 8 ma while the 7 li value of the river input increased these data imply that both silicate weathering rates and weathering intensity decreased over this interval which may have been responsible for putative increases in levels of atmospheric co 2 in contrast the riverine flux of li has increased since 8 ma while its 7 li value has increased this implies that the silicate weathering rate has increased while weathering intensity has decreased since that time

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

lithium isotope evidence for enhanced weathering during oceanic anoxic event 2 the ocean anoxic event 2 oae2 about 93 5 million years ago was marked by high atmospheric co2 concentration rapid global warming and marine anoxia and euxinia the event lasted for about 440 000 years and led to habitat loss and mass extinction the marine anoxia is thought to be linked to enhanced biological productivity but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery here we use lithium isotope measurements from carbonates spanning the interval including oae2 to assess the role of silicate weathering we find the lightest values of the li isotope ratio 7li during oae2 indicating high levels of weathering and therefore atmospheric co2 removal which we attribute to an enhanced hydrological cycle we use a geochemical model to simulate the evolution of 7li and the ca sr and os isotope tracers our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric co2 concentrations and rapid global warming which initiated oae2 the simulated warming was accompanied by a roughly 200 000 year pulse of accelerated weathering of mafic silicate rocks which removed co2 from the atmosphere the weathering also delivered nutrients to the oceans that stimulated primary productivity we suggest that this process together with the burial of organic carbon allowed the rapid recovery and stabilization from the greenhouse state

pore fluid pressure effects in anisotropic rocks mechanisms of induced seismicity and weak faults many observations and studies indicate that pore fluid pressure in the crustal rocks plays an important role in deformation faulting and earthquake processes conventional models of pore pressure effects often assume isotropic porous rocks and yield the nondeviatoric pressure effects which seem insufficient to explain diverse phenomena related to pore pressure variation such as fluid extraction induced seismicity and crustal weak faults we derive the anisotropic effective stress law especially for transversely isotropic and orthotropic rocks and propose that the deviatoric effects of pore fluid pressure in anisotropic rocks not only affect rock effective strength but also cause variation of shear stresses such shear stress variations induced by either pore pressure buildup or pore pressure decline may lead to faulting instability and trigger earthquakes and provide mechanisms for the failure of crustal weak faults with low level of shear stresses we believe that the deviatoric effects of pore fluid pressure in anisotropic rocks are of wide application in studies of earthquake precursors and aftershocks oil and gas reservoir characterization enhanced oil recovery and hydraulic fracturing

paleomagnetic evidence for multiple late pliocene early pleistocene glaciations in the klondike area yukon territory the late pliocene early pleistocene terraces of the klondike area provide a conformal record of sedimentation which marks the transition from preglacial to glacial conditions and is one of the most complete records of glaciation and interglaciation in the northern cordillera preglacial sedimentation is recorded in the lower white channel gravel that contains a reverse normal polarity sequence a re aggradation of the nonglaciated valleys of the goldfields in response to late pliocene cooling is recorded by the upper white channel gravel which is characterized by a dominant normal polarity with a lower reversal likely associated with the first ice wedge casts klondike gravel interfingers with upper white channel and is normally magnetized indicating an equivalent magnetostratigraphic unit this glaciofluvial gravel provides evidence of extra basinal clasts marking a major reorganization of drainage associated with the first advance of the cordilleran ice sheet in western yukon territory correlated

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

overpressure detection from compressional and shear wave data by analyzing experimental data we show that in many room dry rocks the poisson s ratio pr decreases with decreasing differential pressure confining minus pore pressure this means that in gas saturated rocks pr decreases with increasing pore pressure we confirm the generality of the observed effect by theoretically reproducing it via effective medium modeling this effect can be used as a new tool for overpressure detection from surface seismic cross well sonic logs and measurements ahead of the drill bit

weathering rinds as mirror images of palaeosols examples from the western alps with correlation to antarctica and mars weathering rinds have been used for decades as relative age indicators to differentiate glacial deposits in long quaternary sequences but only recently has it been shown that rinds contain long and extensive palaeoenvironmental records that often extend far beyond mere repositories of chemical weathering on both earth and mars when compared with associated palaeosols in deposits of the same age rinds often carry a zonal weathering record that can be correlated with palaeosol horizon characteristics with respect to both abiotic and biotic parameters as demonstrated with examples from the french and italian alps rinds in coarse clastic sediment contain weathering zones that correlate closely with horizon development in associated palaeosols of presumed late glacial age in addition to weathering histories in both rinds and palaeosols considerable evidence exists to indicate that the black mat impact 12 8 ka reached the european alps a connection with the younger dryas readvance supported by both mineral and chemical composition preliminary metagenomic microbial analysis using density gradient gel electrophoresis suggests that the eubacterial microbial population found in at least one ah palaeosol horizon associated with a rind impact site is different from that in other late glacial and younger dryas surface palaeosol horizons

fresnel volume migration of single component seismic data standard implementations of kirchhoff prestack depth migration psdm distribute the recorded wavefield along two way traveltime isochrons and an image is generated by constructive interference of these isochrons along the actual reflector elements beside the recent developments of wave equation based approaches kirchhoff psdm is still considered widely as a state of the art technique in obtaining high quality images of the subsurface particularly for highly irregular survey layouts and target oriented imaging tasks however for sparse sampling or limited aperture the resulting image is affected by significant migration noise as a result of limited constructive interference of the back propagated wavefield some modifications have been proposed to reduce these artifacts these modifications include constructing a specular path of wave propagation derived from estimates of the emergent angle of coherent phases in the seismogram section and the mainly heuristic restriction of the imaging operator to the neighborhood of that wavepath our approach uses fresnel volumes to restrict the migration operator in a physically frequency dependent way using the emergent angle at the receiver determined by a local slowness analysis a ray is propagated into the subsurface the back propagation of the wavefield is restricted to the vicinity of this ray according to its approximated fresnel volume this so called fresnel volume migration approach enhances image quality significantly compared with standard kirchhoff psdm because of the inherent focusing and the restriction of the back propagation to the region around the actual reflection point

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

migration of common shot gathers three depth migration methods which operate on common shot data are presented the first migration method maps digitized horizons from the x t domain to the x z domain because this method is based on ray tracing its computation time is short it is suggested for iterative velocity analysis the other two migration methods map the entire common shot gather into a depth section the common shot migration requires calculation of the arrival time of the direct wave from the source to all the depth points and is done through a direct solution of the eikonal equation all three methods are suitable for areas with both lateral and vertical velocity variation

improved structural characterization of the earth s crust at the german continental deep drilling site using advanced seismic imaging techniques this paper describes the principles of three novel seismic imaging techniques and their application to two deep seismic reflection data sets from the vicinity of the german continental deep drilling site ktb these imaging techniques are based on kirchhoff prestack depth migration and use an inherent restriction of the migration operator to focus the wavefield to its actual reflection point for fresnel volume migration the emergent angle at the receivers is estimated and then used to propagate the wavefield back into the subsurface along which the fresnel volume is determined the migration operator is restricted to this volume thereby focusing the image to the part of the isochrone which physically contributes to the reflection for coherency migration the coherency of the wavefield at neighboring traces is calculated and used as a weighting factor within the migration integral leading to a comparable focusing to the reflection point for coherency based fresnel volume migration both approaches are combined resulting in an even more focused seismic image with significantly increased image quality we applied these methods to two seismic data sets from the area around the ktb a survey with standard split spread geometry ktb8502 and a sparse data set with a small number of source points in combination with short receiver lines instruct93 the focusing approaches yield major improvements in the final images for both data sets incoherent noise and migration artifacts are reduced and the visibility of crustal structures is strongly enhanced allowing for an improved geologic and tectonic characterization

in situ measurements of li isotopes in foraminifera in situ measurement of li isotope ratios in foraminifera has been developed using a cameca ims 1270 ion microprobe in situ 7li analyses have been performed in biogenic calcite of planktonic foraminifera from various locations results show that for west pacific mixed globigerinoides and globorotalia 22 s161 e the isotopic variability between tests and within a single test respectively is not significantly greater than estimated analytical uncertainty 1 5 mean 7li for several planktonic foraminifera tests corresponds to the seawater value strongly suggesting negligible li isotope fractionation relative to seawater as previously inferred by hall et al 2005 using thermo ionization mass spectrometer and multicollector inductively coupled plasma mass spectrometry techniques combined with scanning electron microscopy and ion microprobe imaging micron sized grains enriched in lithium silica and aluminum have been found in the foraminifera calcite matrix a simple mixing model shows that 0 3 2 wt of marine clays incorporated within the analyzed calcite would lower the foraminifera 7li value by 3 to 10 relative to the isotopic composition of the pure calcite by comparison no such grains have been detected in corals the presence of micron sized silicate grains embedded within the foraminifera calcite is consistent with the erez 2003 biomineralization model involving calcite precipitation from seawater vacuoles by contrast coral calcium carbonate is instead precipitated from ions which have been pumped or diffused through several membranes impermeable to micrometric grains ion microprobe in situ 7li measurements in biogenic calcite present new methods for investigating both biomineralization processes and the past record of the ocean composition by exploring geochemical variations at a scale that is smaller in space and in time

sand coatings in paleosols evidence of weathering across the plio pleistocene boundary to modern times on mt kenya abstract a comparison of younger post olduvai paleosol horizons with older buried horizons of plio pleistocene age shows that primary and secondary minerals and organic molecules in sand coatings in these paleosols remain intact and provide a record of past weathering events from ir spectra concentrations of organic and some inorganic constituents within these coatings reveal supporting evidence of variable weathering trends from late pliocene to holocene time with some variability hematite and goethite concentrations in sand coatings parallel similar variable concentrations of secondary fe extractable concentrations previously determined for pre and post olduvai paleosols in these mt kenya sections negative correlations between metahalloysite and gibbsite previously determined to result from aggressive leaching of si from metahalloysite in paleosols tend to follow similar distributions in the sand coatings reported here similarly additions of gibbsite in selected paleosol horizons are followed by reductions of lesser concentrations of metahalloysite suggesting that individual horizons within paleosols have independent leaching histories different from the entire paleo pedon as with these paleosols analyzed previously quartz exists in greater proportion within sands recovered from ah and ahb horizons and this mineral has previously been considered to be sourced from the older surrounding african crust rather than from local neogene volcanic sources the presence of vermiculite in sand coatings previously not detected in mt kenya paleosols may be related to the presence of cedar stands juniperus procera within the timberline zone of the mountain a forest species clay mineral correlate that may relate to past forest biome evolution specifically in the pre olduvai paleosols the occurrence of vermiculite in these older paleosols a clay species with a known affinity for conifers birkeland 1999 may indicate a higher timberline during pre olduvai time the outcome of this analysis shows that certain horizons act as a singular open weathering system responding to the throughput of either meteoric or groundwater in selective ways to produce a range of weathering products sourced from primary minerals and selective allochthonous mineral inputs from near and far more importantly sand coatings are shown to provide important paleoenvironmental data parallel to that recovered from macro paleosol systems moreover the wealth of paleoenvironmental data recovered from sand coatings rivals that in weathering rinds and the combined data are applicable to other paleoenvironments both on earth and mars

halloysite characteristics and formation in the northern golan heights the mineralogy of alteration products of late pleistocene basaltic scoriae and that of a paleosol from the northern golan heights was examined these products had relatively high specific surface areas ssas and cation exchange capacities cecs that were attributed to kaolinite smectite mixed layers 10a halloysite traces of smectite and illite the latter is attributed to aeolian deposition using specific surface area data from 18 to 59 clay were calculated to have formed in the weathered scoria the 10a halloysite was particularly well preserved in the paleosol the absence of significant amounts of short rage ordered minerals allophane ferrihydrite is attributed to the long dry summers and to the relatively old age of the parent materials sem observations of weathered rock and of mildly dispersed clay revealed two types of clay particles a hexagonal or prism like idiomorphic suggesting kaolinite and b rounded composite of a diameter approx 0 5 um appearing to be made up of spherical segments joined together by one or more flat faces hrtem of the 10a particles in the paleosol showed elongated ellipsoids tapered at one end and with internal layering or spiraling and spheroids with spiraling layering with a diameter 130 150 nm less common are sheet like crinkly films sio2 al2o3 molar ratios vary between 1 9 and 3 0 the particles have high fe up to 5 5 and ti up to 3 1 contents ti contents were higher in the peripheral parts of the spheroidal and in the crinkly sheet like particles sem observations suggest that while spheroidal and ellipsoidal 10a halloysite formed by solid phase transformation of volcanic glass the crinkly sheet like particles formed by precipitation on vesicle walls morphological features also suggest transformation of halloysite particles into kaolinite the absence of significant amounts of 10a halloysite in the modern soils indicates their xeric moisture regime

seismic exploration in complex terrains a processing experience in the southern apennines we discuss a data processing sequence adopted to reprocess a seismic line that crosses the italian southern apennines from the tyrrhenian sea to the adriatic margin and investigate both the overthrust and foreland areas we first determine the main causes of the very low s n ratio in the field data and then propose a processing sequence aimed at exploiting the signal content also making use of a priori geological knowledge of this area our work indicates a combination of causes for the very low quality of the seismic data these include length of the spread about 20 km that is unfavorable because of the rapid variation in the near surface geology tectonic complexity crooked line acquisition and the rough topography associated with outcropping rocks characterized by highly variable velocities based on the outcome of this data analysis we present a processing sequence driven by knowledge of the regional tectonic setting and by knowledge of the shallow subsurface geology the main effort is in remov

nonlinear refraction traveltime tomography a few important issues for performing nonlinear refraction traveltime tomography have been identified they include the accuracy of the traveltime and raypath calculations for refraction the physical information in the refraction traveltime curves and the characteristics of the refraction traveltime errors consequently we develop a shortest path ray tracing method with an optimized node distribution that can calculate refraction traveltimes and raypaths accurately in any velocity model we find that structure ambiguity caused by short and long rays in the seismic refraction method may influence the inversion solution significantly therefore we pose a nonlinear inverse problem that explicitly minimizes the misfits of the average slownesses ratios of traveltimes to the corresponding ray lengths and the apparent slownesses derivatives of traveltimes with respect to distance as a result we enhance the resolution as well as the convergence speed to regularize our inverse problem we use the tikhon

seismic depth imaging of a geothermal system in southern tuscany this work represents a case study concerning the application of reflection seismic imaging methods in the context of geothermal exploration our goal is to obtain accurate structural images of a geothermal active area in southern tuscany these images will be required in subsequent studies as the input for geological model building and numerical simulation of the heat transport and fluid flow the target region exhibits great geologic complexity including strong velocity contrasts lateral nearsurface inhomogeneities fracture zones and significant topography those features are typical for a volcanic hard rock environment and pose significant challenges to conventional seismic imaging methodology therefore we apply a sophisticated and robust depth imaging workflow to previously acquired surface seismic data within our workflow we focus on estimating the seismic velocities of the predominant rock units and subsequently carry out kirchhoff pre stack depth migration and fresnel volume migration to obtain high resolution images of the subsurface our results demonstrate that the applied methodology provides a valueable tool for imaging in a complex environment such as a volcano geothermal area in detail the resulting reflector images show the main horizons that delineate the tuscan sedimentary rocks in the target region the images from standard kirchhoff migration can be significantly enhanced by utilizing fresnel volume migration which eliminates migration artefacts and provides a better result moreover we obtain the migration velocities and depths for an important regional reflector known as the k horizon which is of major interest for geothermal characterization

buried palaeosols of the nevado de toluca an alternative record of late quaternary environmental change in central mexico buried palaeosols of central mexico not previously analysed from a palaeopedological standpoint have helped to develop a reliable regional model of late quaternary climatic change this paper focuses upon morphological and micromorphological properties particle size distribution and extractable fe al and si of seven palaeosols named pt1 pt7 in the vicinity of the nevado de toluca volcano the characteristics of andic cambisol pt1 similar to those of modern soils in semi arid environments indicate a drier climate in the first half of the holocene humic andosols pt2 pt4 are analogous to modern volcanic soils of humid forest environments they show evidence that a moist palaeoclimate prevailed during marine oxygen isotope stages ois 2 and 3 luvisols pt5 and pt6 which are assumed to have formed at the end of marine ois 5 to marine ois 4 also indicate humid conditions we attribute the differences between andosols pt2 pt4 and luvisols pt5 pt7 to variations in the duration in the pedogenesis rather than to changes in palaeoclimate micromorphological features of andosol to luvisol transition confirm that these soils form an evolutionary sequence being for the most part consistent with lacustrine records the palaeosol properties do not reflect the episodes of drier climate during the last glacial maximum however as shown by diatom and palynological data from lake sediments mesoclimate variations and or incompleteness of soil memory reflecting mostly periods of humid pedogenesis probably provide the reason for this disagreement copyright 2001 john wiley sons ltd

riverine li isotope fractionation in the amazon river basin controlled by the weathering regimes we report li isotope composition 7li 7li of river borne dissolved and solid material in the largest river system on earth the amazon river basin to characterize li isotope fractionation arl a continental scale the 7li 7li in the dissolved load 1 2 to 32 is fractionated toward heavy values compared to the inferred bedrock 1 to 5 and the suspended sediments 6 8 to 0 5 as a result of the preferential incorporation of 66li into secondary minerals during weathering despite having very contrasted weathering and erosion regimes both andean headwaters and lowland rivers share similar ranges of dissolved 7li 7li 1 2 to 18 correlations between dissolved 7li 7li and li na and li mg ratios suggest that the proportion of li incorporated in secondary minerals during weathering act as the main control on the 7lidiss 7lidiss across the entire amazon basin a batch steady state fractionation model for andean and lowland rivers satisfactorily reproduces these variations with a fractionation factor between weathering products and dissolved load sec dis sec dis of 0 983 two types of supply limited weathering regimes can be identified for the lowlands clearwaters with dominant incorporation of li in secondary minerals and black waters e g rio negro where dissolution of secondary minerals enhanced by organic matter produces low 7li 7li apart from the black waters the 7li 7li of andean and lowland rivers is negatively correlated to the denudation rates with the lowest 7li 7li corresponding to the rivers having the highest denudation rates in contrast the main tributaries draining both the andes and the lowlands have higher 7li 7li compared to other rivers we propose that part of the dissolved li derived from weathering in the andes is re incorporated in sediments during transfer of water and sediments in floodplains and that this results in an increase of the dissolved 7li 7li along the course of these rivers unlike other rivers the dissolved 7li 7li in the main tributaries is best described by a rayleigh fractionation model with a fractionation factor sec dis sec dis of 0 991 altogether the control imposed by residence time in the weathering zone and floodplain processes results in i a non linear correlation between dissolved 7li 7li and the weathering intensity defined as w d and ii a positive relationship between the dissolved li flux and the denudation rate these results have important implications for the understanding of past ocean 7li 7li and its use as a paleo weathering proxy

tomostatics turning ray tomography static corrections applications of tomographic velocities to static corrections have drawn much attention recently in computing field statics with the help of seismic tomography geophysical prospecting 1987 w n de amorin et al showed that the waves refracted at the base of a low velocity layer can be used successfully for computing and refining field static corrections in tomographic inversion for velocity plus statics seg expanded abstracts 1991 livia squires et al pointed out that velocity variations and static shifts caused by near surface effects and positional uncertainties can be solved simultaneously using constraint tomography

local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints

determination of the lithium isotopic composition of planktic foraminifera and its application as a paleo seawater proxy to investigate the potential use of li isotopes in foraminifera as a paleo lithium seawater proxy the li isotopic compositions of planktic foraminifera orbulina universa globigerinoides sacculifer globorotalia menardii a ndgloborotalia truncatulinoides were determined by thermal ionization mass spectrometry tims using phosphate as an ion source and multi collector inductively coupled plasma mass spectrometer mc icp ms rigorous cleaning procedures were employed to purify foraminiferal tests of detrital metal oxide and organic phases in single species analyses data generated using both methods reveal that d 7 li in planktic foraminifera resemble seawater such that the isotopic fractionation from the precipitation of foraminiferal calcite appears to be minimal down core measurements indicate that the d 7 li of o universa has remained constant over the last 44 ka in the north atlantic suggesting little change of li isotopic composition of ocean water during the last glaciation consistent with the long mean residence time of li results suggest that planktic foraminifera may provide a reliable record of the lithium isotopic composition of ocean water in the past the first measurements of seawater d 7 li from the indian ocean average 33 0f1 2x 2r throughout the water column this value is within error of values previously reported for the atlantic and pacific oceans as is expected based on the long mean residence time of li in the ocean there is no evidence for a significant decrease in li cl ratios as reported by some workers with indian ocean waters averaging 9 10f0 11 ag g d 2005 elsevier b v all rights reserved

lithium to calcium ratios in modern cenozoic and paleozoic articulate brachiopod shells li ca ratios in modern brachiopod shells generally correlate inversely with growth temperature ranging from 20 mol mol at 30 c to 50 mol mol at 0 c with no apparent interspecific offsets causes of the temperature effect on li ca ratios are not yet understood cenozoic brachiopod li ca ratios average 30 mol mol similar to the average observed in modern brachiopods relatively constant li ca ratios for eocene to pleistocene nonluminescent brachiopod shells consistent with previous observations of cenozoic planktonic foraminifera support the conclusion of little variation in cenozoic seawater li ca nonluminescent portions of permian and carboniferous brachiopods have li ca ratios substantially lower generally 10 mol mol than modern cenozoic or devonian samples mass balance considerations constrained by 18o of brachiopods suggest that low li concentrations in permo carboniferous seawater could be the result of a lower flux of dissolved li from the continents and or a higher flux of li from seawater to clastic marine sediments nonluminescent devonian brachiopods from a single hand specimen have li ca ratios around 70 of the modern average these li ca ratios can be explained by either somewhat higher temperature with constant seawater li ca somewhat lower seawater li ca at constant temperature or a combination of slightly elevated temperature and slightly lower seawater li ca

precise magnesium isotope measurements in core top planktic and benthic foraminifera 1 this study presents a new methodology to obtain highly precise measurements 0 1 of magnesium isotope ratios in very small samples of foraminiferal carbonate 40 50 g here this technique is used to examine mg isotopic variation among different species of core top foraminifera over a range of different ambient conditions despite the high degree of temperature control on the abundance of elemental mg incorporated into foraminiferal tests analyses of surface dwelling globigerinoides ruber and g sacculifer from five cores with associated sea surface temperatures ranging from 20 to 31 c show no significant temperature dependent variations in their mg isotope ratios analyses of different size fractions of g sacculifer show an increase in mg ca with test size but no variation of mg isotope ratio in all nine planktic and benthic species were analyzed all show identical mg isotope ratios with a mean of 26mg 4 72 apart from small differences in three species namely o universa g sacculifer which are both 0 4 lighter than the average and p obliquiloculata which is 0 4 heavier these results highlight the constancy of foraminiferal mg isotope ratios despite changing environmental conditions which dominate mg ca variation and arguably affect ca isotope fractionation this is an important observation which needs to be included in any model of foraminiferal calcification the insusceptibility of 26mg values to external parameters makes mg isotopes ideally suited to constraining past variations in the mg isotope budget of the oceans and the information this carries about the history of oceanic dolomitization continental weathering and hydrothermal behavior

extensional shear zones as imaged by reflection seismic lines the larderello geothermal field central italy the larderello geothermal field is located in the inner northern apennines in an area which has been subject to extension since the early miocene the latest extensional episode pliocene present has resulted in the formation of nw trending nedipping listric normal faults whose geometry is controlled down to f3 km by borehole data in this paper we integrate a new interpretation of seismic reflection lines with existing seismic field and borehole data to analyse the relations among listric normal faults the top of the brittle ductile transition and the migration of geothermal fluids in accordance with previous interpretations we consider the strong reflector k horizon marking the top of the reflective mid lower crust and located at a depth of 3 5 km in the geothermal area to represent the top of the brittle ductile transition its reflectivity most probably derives from the presence of overpressured fluids we identify three main nw trending nedipping extensional brittle shear zones showing listric geometry and soling out in the vicinity of the k horizon the latter appears to be dislocated in correspondence of the soling out of the shear zones these shear zones because of the associated intense fracturing represent the most natural channels of upward migration of geothermal fluids from the magmatic sources located below the k horizon we suggest that these two conclusions that listric normal faults root at or near the brittle ductile transition and that they act as preferential upward migration paths for magmatic fluids may be of general validity for geothermal fields located in extensional settings d 2002 elsevier science b v all rights reserved

andosol to luvisol evolution in central mexico timing mechanisms and environmental setting abstract surface and buried andosols and buried luvisols of the nevado de toluca late quaternary tephra paleosol sequence central mexico were studied to show whether these soils present an evolutionary sequence and to determine the pedogenic mechanisms and environmental factors involved in the evolutionary process micromorphological observations and mineralogical composition of fine sand and clay fractions were used to detect type and succession of soil forming process some of the buried andosols defined as intergrade andosols have a predominantly blocky structure humus depleted areas redoximorphic features and thin clay coatings in ah horizons clay fractions of buried andosols contain halloysite besides amorphous components whereas in modern andosols allophane is dominant luvisols have micro areas with granular structure and abundant phytoliths in the groundmass of bt horizons assumed to be the relict andosol features luvisol clay fractions are dominated by halloysite and kaolinite primary minerals show micromorphological weathering features in all studied soils being stronger in luvisols however even in luvisols sand fractions consist mostly of unstable volcanic silicates we hypothesise that the studied profiles form an evolutionary sequence andosols intergrade andosols luvisols the soil transformation is supposed to be linked to progressive crystallisation of 1 1 clay minerals comparing the nevado de toluca paleosol properties with the existing data on volcanic soil climo and chronesequences and assessing the regional paleopedological and lacustrine records of quaternary paleoclimates we concluded that wet dry climatic oscillations took place during the formation of the studied paleosols rapid crystallisation of 1 1 minerals occurred during dry phases which speeded up the andosol to luvisol transformation and made it independent from the primary mineral weathering status the andosol to luvisol transformation accelerated by climatic fluctuations is thought to be a common soil evolutionary pathway in the subtropical and tropical regions of recent volcanism which suffered contrasting precipitation oscillations in the quaternary

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

fresnel volume migration of multicomponent data if the aperture of a seismic reflection experiment is strongly limited kirchhoff migration suffers from strong artifacts attributable to incomplete summation this can be overcome by restricting the migration operator to the region that physically contributes to a reflection event examples of such limited aperture experiments include data acquisition in boreholes tunnels and mines we present an extension to three component 3c kirchhoff prestack depth migration where the migration operator is restricted to the fresnel volume of the specular reflected raypath we use the measured polarization direction at a 3c receiver to determine points of specular reflection in homogeneous media the polarization angle of 3c data can be used directly to decide whether a certain image point belongs to the fresnel volume of a specular reflection in heterogeneous media the fresnel volume around an image point is approximated by means of paraxial ray tracing the method is tested on a synthetic vertical seismic profiling experiment with strongly limited aperture migration artifacts and crosstalk effects from converted waves are strongly reduced compared with standard migration schemes the method is successfully applied to seismic data acquired in a tunnel

three dimensional tomography and rock properties of the larderello travale geothermal area italy in a geothermal area a detailed knowledge of the three dimensional velocity structures aids the management of the field and the further development of the geothermal source here we present a high resolution study of the three dimensional s wave velocity structures from microearthquake travel times for the larderello travale geothermal field italy we have also deduced the vp vs and vp vs parameters for this area to emphasize the deep variations in the physical rock properties due to fluid content and porosity furthermore effective porous medium modelling has been performed for site relevant lithologies to improve our interpretation of the results in terms of rock physics signatures this has allowed us to estimate the variation range of the seismological parameters investigated as well as their sensitivity for suitable rock under specific physical conditions low vp vs anomalies arising from a lower vp compared to vs dominate the geothermal field of larderello travale these have been interpreted as due to steam bearing formations on the contrary analysis of vp vs images provides information on the relative changes in rock porosity at depth comparison of tomographic section images with previously interpreted seismic lines suggests that the reflective k horizon delineates a transition between zones that have different porosities or crack gatherings the k horizon also lies on low vp vs anomalies which suggests a steam saturation zone despite the reduced porosity at this depth

the effects of diagenesis on lithium isotope ratios of shallow marine carbonates in this study we present new data on the 7li values and li ca mg ratios of carbonate cores from the great bahama bank clino unda a deep water core off of the bank top odp leg 166 site 1007 and the coralline key largo limestone we use these samples to evaluate the influence of meteoric diagenesis marine burial diagenesis and dolomitization on the li isotope system in carbonates we find that recrystallization of aragonite to low mg calcite in the presence of meteoric fluids results in a systematic decrease of the li ca mg ratio in clino unda and key largo samples due to the lower li ca mg ratio in meteoric fluids compared to seawater for li isotopes we observe that the 7li of meteorically altered low mg calcite is 22 0 3 8 n 28 1 which is coincidentally similar to the original aragonite rich sediments 22 1 in the bahamas 18 1 in key largo but with a larger variability from 15 to 27 we interpret these features as reflecting the overprinting of primary li during meteoric alteration with a highly variable isotope signature that may be controlled by a combination of local porewater and or global climatic conditions in either case meteoric diagenesis produces isotopic signatures that are unrelated to seawater composition in contrast marine burial diagenesis and dolomitization of clino and unda sediments under fluid buffered conditions result in li isotope composition that is similar 30 2 1 5 n 36 1 to modern seawater 31 for site 1007 the 7li values range between 23 permil and 31 permil we interpret this range as reflecting a combination of varying diagenesis style fluid to sediment buffered and varying contribution of calcite derived from pelagic sediments with distinct isotopic composition due to primary mineralogy altogether our results show that diagenesis does not invalidate the use of bulk carbonates for deriving li isotope paleo records but the reliability of past carbonates as recorders of seawater 7li values will depend on carefully characterizing their diagenetic history

mineralogy and chemistry of late pliocene early pleistocene paleosols on mount kenya weathering indices of relative age and paleoenvironmental reconstruction abstract iron and al extracts as weathering indices in paleosols have been used in many localities to determine relative age transformation of total chemical element concentrations to secondary forms translocation of organically complexed al and long standing inundation of soils with groundwater on mt kenya a succession of paleosols straddling the olduvai subchron are here analyzed to determine the degree to which fe al extracts assist paleoenvironmental reconstruction especially relative age determination genesis and translocation of alteration products and the effect of paleoclimatic deterioration with the advent of glaciation ca 2 0 ma and possibly before warmer humid climate from the onset of the plio pleistocene to the olduvai subchron thereafter reverting to a long episode of oscillating drier wetter ice age perturbations is written into the profile morphologies mineralogies and chemistries supporting earlier stratigraphic interpretations

distributions of halloysite metahalloysite and gibbsite in tropical mountain paleosols relationship to quaternary paleoclimate abstract paleosol profile available water varied during the quaternary and when high was accompanied by increased leaching and loss of sio 2 this mechanism controlled the formation of gibbsite and halloysite metahalloysite in paleosols on mount kenya during the time they were exposed to subaerial weathering the available data for distributions of weathering products in paleosols support a reconstruction of high energy paleoclimate and wetness during the first two interglacials lake ellis gorges naro moru lake ellis followed by reduced energy lower precipitation in the teleki naro moru interglaciation lower brunhes and ending with increased paleoclimatic energy during the liki teleki interglaciation isotope stage 5 based on the data available weathering during the present postglacial interval fails to achieve even the magnitude of a low energy interglaciation using relative amounts of gibbsite halloysite it is possible to contruct a model of relative paleoclimatic energy for each of the interglacial on mount kenya