influences of the depth dependence of thermal conductivity and expansivity on thermal convection with temperature dependent viscosity in this paper we carried out numerical experiments of a time dependent thermal convection in a two dimensional cartesian box of aspect ratio width height of 6 in order to study the influences on the convecting flow patterns of the spatial variations in physical properties viscosity thermal conductivity k and expansivity a series of calculations by systematically varying the magnitude of spatial variations in these properties showed that the strongly temperature dependent induces the change in flow pattern into the stagnant lid st regime regardless of the increase in k and or decrease in with depth where the convection occurs only beneath a stagnant lid of cold fluid at the top surface in particular we found that the increase in thermal conductivity k with depth significantly affects the convecting flow patterns in the presence of strong temperature dependence in compared with those with uniform k the patterns of st convection with non uniform k are characterized by i thinner top thermal boundary layers or lids and ii larger horizontal length scales of convection cells beneath the stagnant lid in addition the variation in k with depth decreases the threshold values of the temperature dependence in above which the st mode of convection takes place which may also help stabilize the convection cells of large horizontal length scales beneath stagnant lids our results may highlight the potential importance of the increase in thermal conductivity with depth or pressure in controlling the planforms of thermal convection in the mantle of terrestrial planets

illite neoformation in plagioclase during weathering evidence from semi arid northeast brazil illite minerals in soils and weathered rocks are usually interpreted as secondary clays derived from the transformation of primary rock forming minerals with similar properties e g muscovite or as direct products of hydrothermal alteration after feldspar i e sericite with the help of detailed investigations involving x ray diffraction scanning electron microscopy and x ray element mapping this study testifies to the neoformation of illite inside plagioclase feldspar crystals after their partial dissolution in the weathering zone of luvisols in semi arid northeast brazil our results thus reveal that meteoric weathering can produce illite not only from mica i e by a transformation process but also within non alkali feldspar by a neoformation process at least under the semi arid conditions that have long prevailed in the study area given that illite in weathering mantles has recurrently been attributed often by default to hydrothermal processes results shown here provide new focus to an alternative pathway of illite formation primarily controlled by climate

thermal histories of the core and mantle recognition that the cooling of the core is accomplished by conduction of heat into a thermal boundary layer d at the base of the mantle partly decouples calculations of the thermal histories of the core and mantle both are controlled by the temperature dependent rheology of the mantle but in different ways thermal parameters of the earth are more tightly constrained than hitherto by demanding that they satisfy both core and mantle histories we require evolution from an early state in which the temperatures of the top of the core and the base of the mantle were both very close to the mantle solidus to the present state in which a temperature increment estimated to be 800 k has developed across d the thermal history is not very dependent upon the assumption of newtonian or non newtonian mantle rheology the thermal boundary layer at the base of the mantle i e d developed within the first few hundred million years and the temperature increment across it is still increasing slowly in our preferred model the present temperature at the top of the core is 3800 k and the mantle temperature extrapolated to the core boundary without the thermal boundary layer is 3000 k the mantle solidus is 3860 k these temperatures could be varied within quite wide limits without seriously affecting our conclusions core gravitational energy release is found to have been remarkably constant at 3 1011 w nearly 20 of the core heat flux for the past 3 109 y although the total terrestrial heat flux has decreased by a factor of 2 or 3 in that time this gravitational energy can power the chemical dynamo in spite of a core heat flux that is less than that required by conduction down an adiabatic gradient in the outer core part of the gravitational energy is used to redistribute the excess heat back into the core leaving 1 8 1011 w to drive the dynamo at no time was the dynamo thermally driven and the present radioactive heating in the core is negligibly small the dynamo can persist indefinitely into the future available power 1010 y from now is estimated to be 0 3 1011 w if linear mantle rheology is assumed or more if mantle rheology is non linear the assumption that the gravitational constant decreases with time imposes an implausible rate of decrease in dynamo energy with conventional thermodynamics it also requires radiogenic heating of the mantle considerably in excess of the likely content of radioactive elements

a model for fibrous illite nucleation and growth in sandstones we have developed a model for the formation of fibrous illite in sandstones where kaolinite is a primary reactant and potassium is derived from in situ k feldspar grain dissolution or imported into the model reference frame illite fiber nucleation and growth are modeled using arrhenius expressions that consider saturation state in addition to temperature and time nucleation occurs on pore walls and muscovite and detrital illite may be defined as energetically favorable substrates the model is integrated with other touchstone models to account for the influence of other diagenetic processes on surface area and reactant volumes and to provide input for permeability simulations we evaluated the illite model performance on two data sets 1 jurassic quartzose samples from offshore mid norway with maximum temperatures ranging from 108 to 173c 226 to 343f and 2 miocene lithic samples from offshore southeast asia that have maximum temperatures ranging from 157 to 182c 315 to 360f the model matches measured abundances of illite kaolinite and k feldspar in both data sets using identical kinetic parameters predicted k ar ages are consistent with available data given uncertainties associated with detrital contaminants although no illite particle size data are available from the analyzed samples modeled crystallite thicknesses from the norway data set are comparable to published measurements of 0 004 to 0 012 m from north sea samples with similar temperature histories

self consistent thermodynamic description of silicate liquids with application to shock melting of mgo periclase and mgsio3 perovskite summary we develop a self consistent thermodynamic description of silicate liquids applicable across the entire mantle pressure and temperature regime the description combines the finite strain free energy expansion with an account of the temperature dependence of liquid properties into a single fundamental relation while honouring the expected limiting behaviour at large volume and high temperature we find that the fundamental relation describes well previous experimental and theoretical results for liquid mgo mgsio3 m g2sio4 and sio2 we apply the description to calculate melting curves and hugoniots of solid and liquid mgo and mgsio3 for periclase we find a melting temperature at the core mantle boundary cmb of 7810 160 k with the solid hugoniot crossing the melting curve at 375 gpa 9580 k and the liquid hugoniot crossing at 470 gpa 9870 k for complete shock melting of periclase we predict a density increase of 0 14 g cm 3 and a sound speed decrease of 2 2 km s 1 for perovskite we find a melting temperature at the cmb of 5100 100 k with the perovskite section of the enstatite hugoniot crossing the melting curve at 150 gpa 5190 k and the liquid hugoniot crossing at 220 gpa 5520 k for complete shock melting of perovskite along the enstatite principal hugoniot we predict a density increase of 0 10 g cm 3 with a sound speed decrease of 2 6 km s 1

geothermometry geochronology and mass transfer associated with hydrothermal alteration of a rhyolitic hyaloclastite from ponza island italy abstract a rhyolitic hyaloclastite from ponza island italy was hydrothermally altered producing four distinct alteration zones based on x ray diffraction mineralogy and field textures 1 nonpervasive argillic zone 2 propylitic zone 3 silicic zone and 4 sericitic zone the unaltered hyaloclastite is volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli incomplete alteration of the hyaloclastite resulted in the nonpervasive argillic zone characterized by smectite and disordered opal ct the other three zones exhibit more complete alteration of the hyaloclastite the propylitic zone is characterized by mixed layer illite smectite i s with 10 to 85 i mordenite opal c and authigenic k feldspar akspar the silicic zone is characterized by i s with 90 i pure illite quartz akspar and occasional albite the sericitic zone consists primarily of i s with 66 i pure illite quartz and minor akspar and pyrite k ar dates of i s indicate hydrothermal alteration occurred at 3 38 0 08 ma oxygen isotope compositions of i s systematically decrease from zones 1 to 4 in the argillic zone smectite has 18o values of 21 7 to 22 0 and i s from the propylitic silicic and sericitic zones ranges from 14 5 to 16 3 12 5 to 14 0 and 8 6 to 11 9 respectively 18o values for quartz from the silicic and sericitic zones range from 12 6 to 15 9 by use of isotope fractionation equations and data from authigenic quartz hosted primary fluid inclusions alteration temperatures ranged from 50 to 65 c for the argillic zone 85 to 125 c for the propylitic zone 110 to 210 c for the silicic zone and 145 to 225 c for the sericitic zone fluid inclusion data and calculated 18owater values indicate that hydrothermal fluids were seawater dominated mass transfer calculations indicate that hydrothermal alteration proceeded in a relatively open chemical system and alteration in the sericitic zone involved the most extensive loss of chemical species especially si systematic gains in mg occur in all alteration zones as a result of i s clay mineral formation and systematic losses of na ca and k occur in most zones with the exception of ca calculations of mass transfer associated with hydrothermal alteration on ponza agree with chemical fluxes observed in laboratory experiments involving hydrothermal reactions of rhyolite and seawater the anomalous ca loss at ponza may be due to hydrothermal formation of anhydrite and later low temperature dissolution on the basis of mg enrichments derived from circulating seawater we estimate the following minimum water rock ratios 9 3 6 and 9 for the argillic propylitic silicic and sericitic zones respectively hydrothermal fluid ph for the propylitic and silicic zones was neutral to slightly basic and relatively acidic for the sericitic zone as a result of condensation of carbonic and perhaps other acids

a doubling of the post perovskite phase boundary and structure of the earth s lowermost mantle a new model of the deep earth allows geophysicists to measure variations in earth s temperature near the boundary between the rocky mantle and core using a recently discovered phase change in the lowest part of the earth s mantle where atoms rearrange themselves in crystals under extreme pressure and temperature the model also explains odd features of this part of the mantle such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting combined with observations the results imply very large variations in temperature providing further evidence for circulation of material throughout the earth s mantle the thermal structure of the earth s lowermost mantle the d layer spanning depths of 2 600 2 900 kilometres1 is key to understanding the dynamical state and history of our planet earth s temperature profile the geotherm is mostly constrained by phase transitions such as freezing at the inner core boundary or changes in crystal structure within the solid mantle that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory a recently discovered phase transition at pressures of the d layer2 3 4 is ideally situated to reveal the thermal structure of the lowermost mantle where no phase transitions were previously known to exist here we show that a pair of seismic discontinuities observed in some regions of d can be explained by the same phase transition as the result of a double crossing of the phase boundary by the geotherm at two different depths this simple model can also explain why a seismic discontinuity is not observed in some other regions and provides new constraints for the magnitude of temperature variations within d

thermodynamics of silicate liquids in the deep earth article i nfo we discuss the geophysical implications of recent first principles molecular dynamics simulations of mgsio3 liquid in particular the findings that the gruneisen parameter increases by a factor of three on two fold compression and the predicted melting curve the predicted melting temperature of mgsio3 perovskite at 136 gpa is 5400 600 k which if lowered by freezing point depression by 1300 k yields a mantle solidus temperature of 4100 k identical to recent estimates of the temperature at the base of the mantle we argue on this basis that partial melting at the base of the mantle is plausible while mgsio3 perovskite is denser than the isochemical liquid reasonable values of iron partitioning and bulk iron contents leads to the conclusion that a melt at the base of the multi component mantle would be denser than its surroundings and therefore buoyantly stable we predict the bulk sound velocity of this melt to be 10 9 km s 1 less than that of ultra low velocity zones and consistent with the explanation of these regions as being due to partial melting the increase on compression of the gruneisen parameter in the liquid state yields isentropes that are much hotter than previously thought a potential temperature of only 2450 k is sufficient to melt the entire mantle and a magma ocean will begin crystallization at mid mantle depths rather than at the base of the mantle

k ar illite dating to constrain multiple events in shallow crustal rocks implications for the late phanerozoic evolution of ne asia abstract a recently developed illite age analysis iaa approach was applied to determine the multiple events for the chugaryeong fault belt korea each event was determined by a combined approach of the optimized illite polytype quantification and the k ar age dating of clay fractions separated from the fault clays the late cretaceous to paleogene events 76 5 0 8 69 1 0 6 59 3 0 7 and 48 2 0 7 ma were recognized by calculating the authigenic 1m 1m d illite ages on the iaa plots of the fault clays the early cretaceous ages 121 7 124 7 and 112 4 1 5 ma were also obtained from the convergent intercepts of 100 2m 1 illite on the iaa plots the absence of the 2m 1 illites in the host rock indicates that the early cretaceous ages represent the timings of high t hydrothermal events of 280 c the 2m 1 illites in the fault clays should be pre formed by a fluid rock interaction under a relatively high t subsurface condition and be mechanically reworked into the near surface along the fault by post tectonic events this is the first report determining the absolute age constraints of multi activated tectonic events from a fault these geochronological determinations of the multiple events recorded in the chugaryeong fault belt are crucial to establish the tectonic evolution of the korean peninsula since the late cretaceous

thermally induced alterations of minerals during measurements of the temperature dependence of magnetic susceptibility a case study from the hydrothermally altered soultz sous forets granite france identification of magnetic minerals using the temperature dependence of magnetic susceptibility in low field t combined with optical microscopy microprobe x ray diffraction and chemical analysis provided new constraints on the alteration of fe bearing minerals of the magnetite bearing soultz sous forets granite from the eps 1 borehole upper rhine graben france while relatively fresh granite shows largely reversible t curves typical of magnetite the altered granite revealed a wide variety of irreversible heating and cooling curves which allowed an assignment to different alteration stages under specific geochemical conditions though paramagnetic minerals like fe bearing carbonates pyrite or antiferromagnetic hematite could not be detected according to their curie or neel temperature they were identified due to reactions to new ferrimagnetic phases during the heating cooling experiments at specific temperatures mineral reactions were proved by measurements of the single mineral phases hematite fe carbonates and illite our mineralogical results combined with the thermomagnetic measurements imply that first faulting of the granite occurred already during cooling of the magma which caused a first magnetite oxidation event during uplift of the granitic body and exposure to a paleo erosion surface strongly acidic fluids emerged from pyrite oxidation caused a decomposition of fe bearing minerals like martite hematite derived from magnetite oxidation and fe carbonates and an ongoing transformation of magnetite to martite subsequently precipitation of fine grained hematite was restricted only to the upper part of the pluton in the deeper part of the borehole pyrite was preserved from oxidation in an active fault zone martite was reduced back to magnetite which can be explained with the occurrence of organic matter transported by fluids

living dead slabs in 3 d the dynamics of compositionally stratified slabs entering a slab graveyard above the core mantle boundary abstract segregation of subducted mid ocean ridge basalt morb at the cmb has been identified as a potentially important mechanism in the long term evolution of the mantle and core here three dimensional 3 d and two dimensional 2 d simulations of a compositionally stratified slab reaching the cmb are presented with the goals of characterising the resulting thermo chemical structures for comparison with seismic studies and of quantifying the fraction of morb that is able to segregate and remain near the cmb compositional stratification of the slab results in a strong torque due to the relatively high density of basalt and low density of harzburgite which tends to rotate the slab such that the basalt side faces down slab cmb interaction is characterised by heating up of the slab followed by separation of the basalt and harzburgite layers with harzburgite rising in vigorous plumes plumes form at the edges and sides of slabs at the cmb as well as in their interiors as previously observed for purely thermal slabs with plume heads dominated by depleted harzburgitic material sometimes with small amounts of entrained basalt while plume tails entrain basaltic material segregation of basalt depends strongly on the presence or absence of a preexisting dense layer at the cmb and by dimensionality a preexisting dense layer greatly increases the fraction of basalt that segregates from the slab in 3 d this fraction is in the range 0 5 0 7 with a layer present compared to 0 25 0 45 with no preexisting layer two modes of basalt segregation are observed for slabs that land basalt side up i hot harzburgite extruding from the sides and edges and ii hot harzburgite rich plumes bursting through the basalt layer as previously observed in laboratory experiments whereas for a slab that lands basalt side down iii hot basalt can peel off from its underside displaying fingering instabilities in 3 d furthermore basalt harzburgite segregation is sometimes observed in slab segments that have already been heated at the cmb and risen a few hundred km by a folding mechanism a range of interesting structures are observed in the model cmb region which may be useful in interpreting seismic observations strong lateral gradients in composition and temperature are quite common structures include plumes next to vertical slab segments inverted slab sections perched above the cmb and harzburgite curtains the presence of a stratified layer above the cmb as observed in global simulations in which a layer builds up by basalt segregation strongly suppresses plume formation 2 d simulations give a good first order guide to the dynamics obtained in fully 3 d geometry but inherently 3 d structures are missed plumes versus sheets fingering and there is a quantitative difference in the fraction of basalt segregated

need for re apprehension of basin tectono depositional set up during initial stage of himalayan orogeny from pedogenic evidences abstract the collision and suturing of indian and eurasian plates about 50 ma ago closed the tethys ocean initiated himalayan orogen and a foreland basin developed towards its south the last phase of marine sedimentation in indian sub continent during paleocene eocene is represented by subathu formation overlain by continental dagshai sediments and nature of this transition named as passage beds sensu bhatia and mathur 1965 is controversial further it is poorly understood both in terms of depositional environment and age surprisingly these beds show evidences of pedogenesis but no such palaeopedological studies have been reported so far the degree and nature of pedogenesis is widely used in solving diverse geological problems in complex geological settings therefore pedogenesis of these beds exposed in the shimla hills of subathu sub basin has been worked out morphological and micromorphological studies divide them into older green greenish grey pedofacies gp and younger red reddish brown pedofacies rp units pedons are up to tens of centimeters thick structure largely comprises sub angular to sub rounded blocky peds a suite of pedogenic features include burrows root traces infillings mottling cutans segregations and nodules which vary in dominance from gp to rp unit greenish grey pedons are characterized by mottles fe mn oxide segregations whereas reddish brown pedons by root traces commonly filled with carbonates presence of carbonate segregations and cutans detailed field and laboratory studies at various local and regional exposures can reveal the nature and extent of pedogenesis which will be significant to enact depositional environment as well as stratigraphic position of passage beds co relatable at different localities throughout length of the himalaya from pakistan to nepal because of their distinctive lithology and stratigraphic position such studies bear global significance in demonstrating the use of palaeosols as a geologic archive in complex geological settings

calcimetry as a useful tool for a better knowledge of flow pathways in the soultz sous forets enhanced geothermal system the soultz sous forets granite located in the rhine graben france has been chosen for the european enhanced geothermal system egs three wells have been drilled to a minimum depth of 5000 m in order to reach a temperature of 200 c at soultz the main fracture network in the basement is orientated approximately n s with moderate to steep dip its geometrical relationship with the in situ stress field suits fluid circulation hence the egs project however fractures are firmly sealed due to natural fluids fossil and or possibly present the main sealing minerals as identified during previous studies are clay minerals calcite and quartz however some fractured zones remain permeable due to the high porosity developed in the wall rocks through hydrothermal alteration a circulation test was carried out from july to december 2005 to test the performance of the soultz geothermal reservoir this test showed a significant difference in the production rate between the two outflow wells gpk2 and gpk4 in order to improve the fluid circulation within the underground heat exchanger chemical stimulations have been scheduled in this framework quantifying the calcite content of the granite provides a basis for identifying the calcite rich zones as well as choosing the most suitable chemical stimulation measurement of calcite ponderal concentration was carried out in the cutting samples of the 3 deep wells gpk2 gpk3 gpk4 between 4000 and 5000 m depth using manocalcimetry based on detailed measurements in the 3 wells this study shows that calcite is not only a very common and ubiquitous hydrothermal mineral but that its content seems to be also spatially correlated with most of the fracture zones bearing natural flow the conductivity of these natural flow pathways seems anti correlated with the calcite content calcimetry has proved to be an easy efficient and low cost method for a better knowledge of hydrothermal sealing of the soultz reservoir this method can be applied with great benefit to all types of basement reservoirs oil gas water heat overlain by sedimentary rocks for a better understanding of the fracture network permeability

complex hydrothermal alteration and illite k ar ages in upper visean molasse sediments and magmatic rocks of the variscan badenweiler lenzkirch suture zone black forest germany post collisional upper visean molasse sediments and magmatic rocks of the badenweiler lenzkirch zone reveal by microscopy of thin sections different degrees of hydrothermal illitization of feldspar and mica particles and xrd ir and xrf data of the 2 m fractions show illitic material as the dominant clay mineral consisting of a mixture of 1m and 2m1 polytypes moreover small amounts of illite smectite mixed layer minerals of r1 ordering are proved in the granites in the separates two illite mixing lines with different fe mg contents are verified between authigenic illite from feldspar alteration and detrital illite in the molasse sediments as well as between authigenic illite from feldspar alteration and altered mica flakes in the granites fe rich detrital chlorite is present within the molasse sediments while mixtures of high aluminous fe poor dioctahedral di trioctahedral chlorite with randomly interstratified chlorite smectite mixed layer minerals are formed from feldspar alteration in the granites illite k ar dating of the 2 and 0 63 m fractions yields hydrothermal illitization of feldspar and partial resetting of the k ar system of detrital illite and mica flakes in the molasse sediments at 200 c during upper permian to middle triassic times while the granites in the eastern part of the study area were not altered contemporaneously in contrast hydrothermal activity at 200 c during upper jurassic to lower cretaceous times occurred in the granites whereas these temperatures were too low for resetting the older permo triassic illite k ar ages in the molasse rocks within both k ar age clusters the data are seen to decrease with grain size and portion of illite 2m1 polytype the alteration phenomena indicate multiple hydrothermal episodes in the study area and they match those from the central and western european crust as fluid supply was controlled geodynamically by episodic break up of pangea

plume capture by divergent plate motions implications for the distribution of hotspots geochemistry of mid ocean ridge basalts and estimates of the heat flux at the core mantle boundary abstract the coexistence of stationary mantle plumes with plate scale flow is problematic in geodynamics we present results from laboratory experiments aimed at understanding the effects of an imposed large scale circulation on thermal convection at high rayleigh number 106 ra 109 in a fluid with a temperature dependent viscosity in a large tank a layer of corn syrup is heated from below while being stirred by large scale flow due to the opposing motions of a pair of conveyor belts immersed in the syrup at the top of the tank three regimes are observed depending on the ratio v of the imposed horizontal flow velocity to the rise velocity of plumes ascending from the hot boundary and on the ratio of the viscosity of the interior fluid to the viscosity of the hottest fluid in contact with the bottom boundary when v 1 and 1 large scale circulation has a negligible effect on convection and the heat flux is due to the formation and rise of randomly spaced plumes when v 10 and 100 plume formation is suppressed entirely and the heat flux is carried by a sheet like upwelling located in the center of the tank at intermediate v and depending on established plume conduits are advected along the bottom boundary and ascending plumes are focused towards the central upwelling heat transfer across the layer occurs through a combination of ascending plumes and large scale flow scaling analyses show that the bottom boundary layer thickness and in turn the basal heat flux q depend on the peclet number pe and when 10 q pe1 2 and when 1 q pe 1 3 consistent with classical scalings when applied to the earth our results suggest that plate driven mantle flow focuses ascending plumes towards upwellings in the central pacific and africa as well as into mid ocean ridges furthermore plumes may be captured by strong upwelling flow beneath fast spreading ridges this behavior may explain why hotspots are more abundant near slow spreading ridges than fast spreading ridges and may also explain some observed variations of mid ocean ridge basalt morb geochemistry with spreading rate moreover our results suggest that a potentially significant fraction of the core heat flux is due to plumes that are drawn into upwelling flows beneath ridges and not observed as hotspots

origin of illite in the lower paleozoic of the illinois basin evidence for brine migrations in the lower paleozoic of the illinois basin three illite polytypes are found 2m 1 of detrital origin and 1m d and 1m of diagenetic origin illite polytype quantification of detrital 2m 1 illite and diagenetic 1m d and 1m illite combined with k ar age dating allows extrapolation to apparent detrital and diagenetic illite ages kinetic modeling of smectite illitization combined with the calculated age of illitization can evaluate different origins of illite the diagenetic illite in the lower paleozoic of the illinois basin is interpreted not to have formed solely by burial diagenesis but mainly during multiple brine events the upper ordovician maquoketa group contains diagenetic illite dominantly 1m d with minor 1m with an extrapolated age of 360 m y 356 377 m y and formed from smectite at temperatures of 50 100 c this age falls within the span of dates for illite smectite i s in k bentonites from the upper mississippi valley and is interpreted to be a combined result of illitization by burial diagenesis and either a hydrothermal brine from the southern and deeper part of the basin or a k rich brine from the michigan basin upper mississippi valley area or forest city basin in ordovician and cambrian shale partings and sandstone older than the maquoketa group the diagenetic illite 1m d in shale and 1m in sandstone has an age of 300 m y and formed at temperatures 140 c this late paleozoic age falls within the range of illites from sandstone in the upper mississippi valley and k bentonites of the appalachian basin it coincides with the alleghany orogeny and is interpreted as having formed by gravity driven flow from the uplifted alleghanian ouachita orogenic belt that drove hot 140 c fluids through the illinois basin

clay minerals related to the circulation of geothermal fluids in boreholes at rittershoffen alsace france abstract two geothermal wells grt 1 and grt 2 were drilled into the granite at rittershoffen alsace france in the upper rhine graben to exploit geothermal resources at the sediment basement interface brine circulation occurs in a permeable fracture network and leads to hydrothermal alteration of the host rocks the goal of the study was to characterize the petrography and mineralogy of the altered rocks with respect to the permeable fracture zones in the granitic basement as clay minerals are highly reactive to hydrothermal alteration they can be used as indicators of present day and paleo circulation systems special attention has been paid to the textural structural and chemical properties of these minerals the fine grained clay fraction

k ar dating of magmatic sericite crystallites for determination of cooling paths of metamorphic overprints a combined optical and x ray characterisation of fine grained micas in granodioritic to tonalitic dikes and intrusions of the eastardennes eifel nappe linksrheinisches schiefergebirge germany belgium was completed with k ar dating of separated size fractions from these rocks in each sample the k ar ages decrease with decreasing size fraction but the same size fractions of the different samples yield different ages application of the closure temperature concept to the k ar ages of the various size fractions indicates that the crystallite size expressed as cis fwhmser001ad and coherent scattering domain csd thickness acts as the effective radius of ar diffusion a linear model may describe the correlation between k ar ages and crystallite thickness the ages younger than the model prediction are caused by the occurrence of microcline as an accessory k bearing mineral phase the obtained k ar ages were interpreted as representative of the cooling path of the magmatic components in the eastardennes eifel nappe below 330 c the k ar age of the largest size fraction of the tonalitic dike v11 313 6 7 2 ma is the closest value for the age of the variscan cleavage development the oldest age of the hydrothermally altered tonalitic dike 300 2 8 4 ma might represent an episode of hydrothermal fluid migration after cleavage development it represents at least a minimum age the microcline age 242 8 6 0 ma of the hill intrusion may represent the closure temperature of this mineral at about 140 c

interpretation of the d zone at the base of the mantle dependence on assumed values of thermal conductivity a common assumption in modeling dynamic processes in the earth s lower mantle is that thermal conductivity is sensibly constant throughout the lower mantle and equal to approximately 4 w m 1 k 1 this value is the result of extrapolation using a linearized theory with estimated parameters for lattice contributions to thermal conductivity furthermore this value is highly dependent on the assumed geotherm excluding theoretical uncertainties in the extrapolation recent experimental data for the pressure dependence of conductivity coupled with a revised geotherm lead to substantially higher estimated values for the lower mantle the hypothesis that the seismically resolved anomalous zone at the base of the mantle d is a thermal boundary layer can be questioned in this case of a higher estimation for thermal conductivity

onset and orientation of convection in the inner core summary thermal convection is an effective mechanism for producing seismic anisotropy in many regions of the earth however it is not known whether this mechanism is relevant for the anisotropy observed in the inner core here we establish the requirements for convection in the inner core by combining a simple model for inner core growth with a solution for conductive cooling thermal convection is likely during the early stages of inner core growth but becomes less probable as the volume of the inner core increases the transition to a non convecting state is driven by changes in both the thermal and compositional stratification a decrease in the vigour of convection near the transition to a non convecting state isolates the pattern of flow with the lowest critical rayleigh number rac we apply a perturbation method based on rayleigh s principle to calculate rac in a hydrostatically flattened inner core we find that the final pattern of flow is characterized by a degree l 1 mode in which the axis of upwelling aligns with the rotation axis this pattern of flow has the symmetry required to explain the distribution of anisotropy at the largest scales the extent of crystal alignment depends on the level of stress during this final convective state one possible interpretation of the observed anisotropy is that the final convective state establishes the large scale crystal alignment without completely erasing a more complicated texture that developed when convection was more vigorous

characterization of neoformed illite from hydrothermal experiments at 250 degrees c and p sub v soln an hrtem atem study solid products from hydrothermal experiments conducted at 250 c and p sub v soln were characterized by powder x ray diffraction xrd and atem hrtem experiments were conducted with muscovite kaolinite and quartz or amorphous silica in 2m kcl solutions for 43 to 176 d post experiment solution compositions lie either within the illite 0 88 k stability field or on the illite 0 88 k kaolinite or illite 0 88 k diaspore univariant boundaries in log a sub k sup a sub h sup vs log a sub h sub 4 sio sub 4 activity space transmission electron microscopy tem observations of muscovite grain edges reveal the neoformation of illite crystals with a range of compositions atem from 0 31 to 0 89 k o sub 10 oh sub 2 the range of k contents appears to narrow toward 0 88 k o sub 10 oh sub 2 with increased experiment duration hrtem suggests the presence of 2 to 11 layer fundamental particles composed of illitic layers with 10 a periodicity fundamental particle thicknesses increase toward an average of 8 layers particle with increased experiment duration in the longer duration experiments fundamental particle thicknesses were normally distributed about thicknesses of 4 and 8 layers whereas fundamental particles with thicknesses 4 layers were common in a shorter duration experiment the compositions and structure of the illites are consistent with the multiphase model which more states that the smectite to illite transition occurs through the step wise formation of solubility controlling phases consisting of fundamental particles with thicknesses of 1 2 4 and le 8 layers the increase in k content and fundamental particle thickness with the extent of reaction suggests that the illite crystals underwent a prograde reaction culminating in the formation of end member illite 0 88 k o sub 10 oh sub 2 this reaction in conjunction with the previously observed retrograde reaction from muscovite to end member illite demonstrates the stability of end member illite in the system k sub 2 o al sub 2 o sub 3 sio sub 2 h sub 2 o at 250 c less

time constraints for the tectono thermal evolution of the cantabrian zone in nw spain by illite k ar dating abstract contrasting sedimentary facies and tectonic structures diversely distributed and affected by diagenetic to low grade metamorphic activity form a complex pattern in the northwestern spanish cantabrian area of the variscan orogen the distribution of these metamorphic features is based on field observations clay mineralogy mineral crystallinity indices vitrinite reflectance data and observation of rock microtextures k ar dating of fine grained illite rich size fractions provides a complete set of ages for the episodic deformation and thermal overprints in the southeastern cantabrian area the usual k ar isochron plotting was combined with the bench type age distribution to unravel the successive illite crystallization episodes several tectono thermal episodes occurred in the southeastern pisuerga carrion province initially during the early permian at 293 4 ma in the ruesga line valsurvio dome and sierra del brezo area a further mid permian event was detected at 268 6 ma in the palentine nappes and during the mid triassic at 243 5 ma again in the valsurvio and sierra del brezo areas and along the ruesga line a later reactivation of the ruesga line was detected during mid jurassic time at 175 6 ma

illite polytype quantification for accurate k ar age determination polyquant a new method to quantify illite polytypes in physical mixtures has been coupled with illite age analysis iaa pevear 1992 to determine accurate k ar ages of the individual polytypes k ar radioisotope dates from illite in shales and sandstones are typically meaningless because these rocks are mixtures of diagenetic and detrital components in unknown proportions iaa uses linear extrapolation to unmix measured k ar ages and establish the end member ages this procedure requires samples to have a diagenetic illite smectite i s component mixed with a detrital discrete illite component because they are separable and quantifiable using x ray diffraction xrd of oriented aggregate samples we extend iaa for use in mixtures of diagenetic and detrital illite with no i s component by coupling a genetic algorithm ga with the wildfire programs 1993 of reynolds in a new computer program polyquant which quantifies illite polytypes in a natural sample based on first principles of xrd wildfire is a forward model that calculates hkl reflections by varying parameters such as rotational disorder octahedral cation occupancy i e cis and trans vacancies chemical substitutions k and fe orientation and crystallite thickness polyquant executes several forward models using the ga to vary the parameters and weight percents of each polytype to automatically achieve a best fit with an experimental xrd pattern sensitivity tests reveal that changes in the weight percent of an illite polytype disorder p 0 p cv and the orientation function affect the pattern more than other parameters in addition polyquant successfully quantified illite components in prepared mixtures of 1 m illite and 2 m 1 muscovite and 1 m d illite and 2 m 1 muscovite we show examples to validate iaa from prepared mixtures of end members with known ages and also to obtain end member ages of highly illitic clay fault gouge using k ar ages and polyquant to quantify the 1 m and 2 m 1 components from mixtures of rm 30 25 1 ma and a 2 m 1 muscovite from wards 428 9 ma iaa determined end member ages of 19 9 ma 0 44 ma and 429 ma 408 459 ma in reasonable agreement with the measured results in addition we use clay gouge from the canadian rockies to date movement along thrust faults regional geologic data indicate movement along these faults occurred between 73 and 48 ma iaa determined the ages of faulting to be from 79 2 to 53 5 ma in good agreement with the known range of fault dates our results indicate that neoformation of illite in the fault zone must have modified the ages to younger dates

first principles calculations of the lattice thermal conductivity of the lower mantle abstract the temperature variations on top of the core mantle boundary are governed by the thermal conductivity of the minerals that comprise the overlying mantle estimates of the thermal conductivity of the most abundant phase mgsio3 perovskite at core mantle boundary conditions vary by a factor of ten we performed ab initio simulations to determine the lattice thermal conductivity of mgsio3 perovskite finding a value of 6 8 0 9 w m 1 k 1 at core mantle boundary conditions 136 gpa and 4000 k consistent with geophysical constraints for the thermal state at the base of the mantle thermal conductivity depends strongly on pressure explaining the dynamical stability of super plumes the dependence on temperature and composition is weak in the deep mantle our results exhibit saturation as the phonon mean free path approaches the interatomic spacing combining our results with seismic tomography we find large lateral variations in the heat flux from the core that have important implications for core dynamics

interpretation of k ar dates of illitic clays from sedimentary rocks aided by modeling k ar dates of illitic clays from sedimentary rocks may contain mixed ages i e may have ages that are intermediate between the ages of end member events two phenomena that may cause mixed ages are 1 long lasting reaction during the burial illitization of smectite and 2 physical mixing of detrital and diagenetic components the first phenomenon was investigated by simulation of illitization reactions using a nucleation and growth mechanism these calculations indicate that values for mixed ages are related to burial history for an equivalent length of reaction time fast burial followed by slow burial produces much older mixed ages than slow burial followed by fast the type of reaction that occurred in a rock can be determined from the distribution of ages with respect to the thickness of illite crystals dating of artificial mixtures confirms a non linear relation between mixed ages and the proportions of the components vertical variation of k ar age dates from gulf coast shales can be modeled by assuming diagenetic illitization that overprints a subtle vertical trend presumably of sedimentary origin in detrital mineral content

thermal conductivity of mgo periclase at high pressure implications for the d region abstract the thermal conductivity of the lowermost mantle determines the rate at which heat flows across the core mantle boundary and consequently plays a central role in the thermal evolution of both the mantle as well as the core in an effort to test and improve model estimates of thermal conductivity in the deep mantle we perform first principles computations of the lattice conductivity for mgo periclase the method uses the peierls boltzmann transport equation via a combination of first principles molecular dynamics and first principles lattice dynamics phonon lifetimes are found to be inversely proportional to temperature and increases 3 fold as the density is increased from 3 37 to 5 49 g cm 3 thermal conductivities increase nearly 6 fold over the same density interval and show excellent agreement with the available experimental measurements we use these results to assess how conductivity measurements of mantle minerals can be reliably extrapolated to conditions characteristic of the lowermost mantle and find debye theory to be superior for this task we then apply this insight to estimate the conductivity of mgsio 3 perovskite in the lowermost mantle and combine this with our computational results for mgo periclase to construct a model estimate for a representative lower mantle assemblage we find the mantle conductivity to be 5 9 0 6 w m k at the top of the thermal boundary layer and 4 0 0 5 w m k at its base implying core mantle boundary heat flux values at the lower end of geophysical estimates

lattice thermal conductivity of mgsio3 perovskite and post perovskite at the core mantle boundary abstract thermal conductivity is essential for controlling the rate of core heat loss and long term thermal evolution of the earth but it has been poorly constrained at the high pressures of earth s lowermost mantle we measured the lattice component of thermal diffusivity heat transport by scattering of phonons of both mgsio 3 perovskite pv and post perovskite ppv at high pressures of up to 144 gpa and at room temperature lattice thermal conductivity of pv dominant lowermost mantle assemblage obtained in this study is about 11 w m k while ppv bearing rocks exhibit 60 higher conductivity since such pv value is comparable to the conventionally assumed lowermost mantle conductivity our findings do not significantly alter but support the recent notion of high core mantle boundary heat flow along with a young inner core and high temperatures in the early deep earth

mineralogical and geochemical features of karst bauxites from poci western henan china implications for parental affinity and bauxitization abstract the poci bauxite deposits in western henan china are hosted in the lower member of upper carboniferous benxi formation unconformably overlying upon the paleokarst surface of the ordovician majiagou formation the orebodies comprise a high grade bauxite horizon characterized by the association of diaspore illite anatase and a basal iron rich horizon diaspore goethite hematite illite anatase sandwiched between the overlying clayey layer illite diaspore goethite anatase and the underlying clayey layer illite diaspore microcline goethite geochemical investigations reveal that rb cs ba cu zn are depleted while b ga bi v sc zr hf nb ta w u and th are enriched in bauxite horizons b is highly enriched in bauxite ores and clays contents 176 1061 ppm and positively associated with sio2 indicating b is mainly hosted in clay components e g dominantly illite which are considered a mixture of authigenic minerals transformed from kaolinites during diagenesis and unaltered detrital minerals mass change calculations reveal that hf zr nb ta u th sc cr and ga are stable relative to tio2 during the bauxitization process indicating these elements are mainly associated with anatase and diaspore the bauxite horizons and the underlying clays are more enriched in total ree contents rees and display more intense lree hree fractionation than the overlying clays provenance analysis shows that parental materials of poci bauxites were mainly derived from felsic dominated igneous rocks along the southern margins of the north china craton with minor contribution from siliciclastic sedimentary rocks and argillaceous components of underlying carbonates a conceptual model is proposed for the formation and evolution of poci bauxites uplift caused by the north qinling orogenesis along the southwestern margin of ncc led to the formation of karstic topography allowing aluminum rich source materials to be transported to the low karst plain and transformed into incipient bauxites under hot and humid tropical conditions when the platform was submerged fe2 ions were released from fe al oxides hydroxides under the reducing conditions associated with bacteria activity in an organic rich environment and redeposited as pyrites and siderites generating a high grade bauxite horizon and an iron rich bauxite horizon this marine modification resulted in further aluminum enrichment of bauxite ores

estimates of heat flow in the deep mantle based on the power requirements for the geodynamo 1 regeneration of the magnetic field by convection in the core places demands on heat flow into the base of the mantle if the heat flow is too low thermal convection is shut off and the rate of generation of compositional buoyancy by the solidification of the core becomes too low to sustain the geodynamo conversely a large heat flow causes rapid growth of the inner core so that convection prior to the appearance of the inner core must be sustained by thermal buoyancy alone the attendant requirements on primordial heat become more severe as the age of the inner core decreases we show that estimates of the present day heat flow satisfy the power requirements for the geodynamo however the resulting thermal history is incompatible with estimates of mantle temperatures prior to 3 ga this discrepancy can be resolved by accumulating radioactive isotopes in d or adding heat sources to the core

thermal conductivity of ferropericlase in the earth s lower mantle abstract mg fe o ferropericlase fp is one of the important minerals comprising earth s lower mantle and its thermal conductivity could be strongly influenced by the iron content and its spin state we examined the lattice thermal conductivity of mg fe o fp containing 19 mol iron up to 111 gpa and 300 k by means of the pulsed light heating thermoreflectance technique in a diamond anvil cell we confirmed a strong reduction in the lattice thermal conductivity of fp due to iron substitution as reported in previous studies our results also show that iron spin crossover in fp reduces its lattice thermal conductivity as well as its radiative conduction we also measured the electrical conductivity of an identical fp sample up to 140 gpa and 2730 k and found that fp remained an insulator throughout the experimental conditions indicating the electronic thermal conduction in fp is negligible because of the effects of strong iron impurity scattering and spin crossover the total thermal conductivity of fp at the core mantle boundary conditions is much smaller than that of bridgmanite bdg our findings indicate that bdg and post perovskite is the best heat conductor in the earth s lower mantle and distribution of iron and its valence state among the lower mantle minerals are key factors to control the lower mantle thermal conductivity

variation of thermal conductivity and heat flux at the earth s core mantle boundary the two convective systems that dominate earth s internal dynamics meet at the boundary between the rocky mantle and metallic liquid core energy transfer between processes driving plate tectonics and the geodynamo is controlled by thermal conduction in the lowermost mantle d we use atomic scale simulations to determine the thermal conductivity of mgsio3 perovskite and post perovskite under d conditions and probe how these two convective systems interact we show that the thermal conductivity of post perovskite 12 w mk is 50 larger than that of perovskite under the same conditions 8 5 w mk and is anisotropic with conductivity along the a axis being 40 higher than conductivity along the c axis this enhances the high heat flux into cold regions of d where post perovskite is stable strengthening the feedback between convection in the core and mantle reminiscent of the situation in the lithosphere there is potential for deformation induced texturing associated with mantle convection to modify how the mantle is heated from below we test this by coupling our atomic scale results to models of texture in d and suggest that anisotropic thermal conductivity may help to stabilise the roots of mantle plumes over their protracted lifetime

phanerozoic polyphase orogenies recorded in the northeastern okcheon belt korea from shrimp u pb detrital zircon and k ar illite geochronologies abstract we present the shrimp u pb detrital zircon and k ar illite 1m d 1m and 2m 1 ages suggesting new insight into the phanerozoic polyphase orogenies preserved in the northeastern okcheon belt korea since the initial basin formation during neoproterozoic rifting through several successive contractional orogens the u pb detrital zircon ages from the early paleozoic strata of the taebaeksan zone suggest a cambrian maximum deposition age and are supported by trilobite and conodont biostratigraphy although the age spectra from two sedimentary groups the yeongwol and taebaek groups show similar continuous distributions from the late paleoproterozoic to early paleozoic ages a grenville age hiatus 1 3 0 9 ga in the continuous stratigraphic sequence from the taebaek group suggests the existence of different peripheral clastic sources along rifted continental margin s in addition we present the k ar illite 1m d 1m ages of the fault gouges which confirm fault formation reactivation during the late cretaceous to early paleogene ca 82 62 ma and the early miocene ca 20 18 ma the 2m 1 illite ages at least those younger than the host rock ages provide episodes of deformation metamorphism and hydrothermal effects related to the tectonic events during the devonian ca 410 ma and permo triassic ca 285 240 ma these results indicate that the northeastern okcheon belt experienced polyphase orogenic events namely the okcheon middle paleozoic songrim late paleozoic to early mesozoic daebo middle mesozoic and bulguksa late mesozoic to early cenozoic orogenies reflecting the phanerozoic tectonic evolution of the korean peninsula along the east asian continental margin

characterization of the waukesha illite a mixed polytype illite in the clay mineral society repository the waukesha illite is an excellent example of the illites found in argillaceous rocks typical for paleozoic shales that have undergone significant burial diagenesis during their geologic history it consists of a mixture of detrital 2 m 1 interpreted to be a residuum of karstification within silurian carbonates and diagenetic 1 m and 1 m d illite the chemistry and the age of the illite polytypes are different extrapolating to 100 the 1 m and 1 m d polytypes have an apparent diagenetic age between 295 and 325 ma the chemistry of the 1 m polytype could not be determined because of its low abundance the approximate chemical composition of the 1 m d polytype is 0 67 k 3 6 si and 1 9 al per half unit cell the 2 m 1 polytype has an apparent detrital age between 440 and 520 ma and an approximate chemical composition per half unit cell of 0 78 k 3 4 si and 2 1 al all within our margin of error x ray diffraction xrd results of both random powder and oriented preparations both indicate that the waukesha illite consists of a mixture of illites the xrd patterns of the random powder preparation indicate it is a physical mixture of three different illite polytypes this result was confirmed using 3 different methods 1 by measuring illite polytype specific reflections 2 by mixing illite polytype reference samples and 3 by mixing wildfire calculated xrd patterns decomposition of the illite 001 xrd peak from oriented preparations also indicates mixtures of illites however the proportions of the three illitic components derived from the oriented 001 peak decomposition differ from those results derived from the analysis of the random powder data therefore the shape of the 001 reflection of the waukesha illite cannot be explained by mixing the three different illite polytypes

burial diagenesis of paleosols in the giant yacheng gas field people s republic of china bearing on illite reaction pathways abstract sixty percent of the supratidal deposits of a well in the giant yacheng gas field show evidence of pedogenic alteration pedogenic features of these mid tertiary sediments include porphyroskelic and lattisepic textures argillans embayed quartz grains peds horizonation high carbonaceous content pedotubules and mottling yacheng sediments presently occur in a high grade diagenetic setting depth of approximately 4 km and temperatures of about 180 c despite mineralogical transformations induced by burial much of the pedogenic and burial diagenetic history of yacheng sediments is revealed by detailed mineralogical and geochemical analysis this analysis also reveals the co existence of authigenic illite formed by different reaction pathways over differing timetables analytical data indicate that although the clay mineral suite includes only chlorite and illite each mineral has formed by a variety of processes most chlorite in yacheng sediments is of detrital origin this is indicated by the similarity in the amount and distribution of fe and al in chlorite from schist cobbles and in the sediment clay fraction as determined by quantitative x ray diffraction xrd and analytical electron microscopy aem authigenic chlorite while comparatively rare in the studied interval grew from solution in pore spaces and tends to be significantly poorer in fe and mg than detrital chlorite three varieties of illite were recognized by their textural morphological and structural characteristics detrital illite the least abundant component exhibits 2m1 stacking order by powder xrd macroscopic muscovite flakes the probable parent of clay sized detrital illite were dated by k ar methods at 207 35 3 95 ma authigenic illite formed by precipitation in pore spaces and by replacement of smectite of pedogenic origin these two varieties of illite have distinctive textural morphological and chemical characteristics pore growth illite displays euhedral textures in scanning sem and transmission tem electron microscopes and post dates authigenic quartz and feldspar formation this type of illite has 1m stacking order and electron diffraction images show that individual particles have a single coherently diffracting domain down the c crystallographic axis by contrast authigenic illite particles that formed by replacement of smectite have anhedral morphologies in tem and exhibit a texture similar to that of smectite in petrographic thin sections sem and lattice fringes imaged by high resolution electron microscopy hrtem matrix illite also displays 1m order by powder xrd but electron diffraction shows that submicron particles are aggregates of coherently diffracting domains that are rando ly stacked along the c axis hrtem lattice fringe images indicate that these diffracting domains average 8 10 unit cells thick anhedral illite particles show on average higher al and fe and lower si and k by aem than co existing pore growth illite k ar age dates suggest that the integrated time of formation of pore filling illite is significantly later than the mean illitization time of smectite derived illite

microscopic features of quartz and clay particles from fault gouges and infilled fractures in granite discriminating between active and inactive faulting abstract to assist in identifying faults that have a significant potential for displacement at or near the ground surface we carried out in depth investigations on fault gouges and a fracture infilled with clay clay vein in the kojaku granite on the tsuruga peninsula central japan we sampled several fault gouges at different stages of evolutions and clay rich infilling of a fracture with no evidence of offset based on our field observations gouge in an active fault is characterized by 1 stacked layers of different colors made up of comminuted fragments and clays and 2 injection of the fragments and clays from the gouge into the surrounding rocks indicating an accumulation of seismic induced shearing our thin section observations and x ray diffraction analyses show that all our samples are similar in the degree of fragmentation and mineral composition and because of this our study became focused mainly on microscopic features using laser diffraction particle size analysis scanning electron microscopy sem and transmission electron microscopy tem we identified the mineralogical and textural characteristics of the samples in order to improve our ability to discriminate between active and inactive faulting particle size distribution analysis showed that the gouge in the active fault contains the greatest abundance of finer particles due to multiple slip events which contrasts with the clay rich infilling of a fracture sem examination of the quartz particles showed that the gouge in the active fault contains more particles that have retained sharp and smooth crystal surfaces formed by fracturing than do either the gouges in minor faults that show no evidence of recent shear or the clay rich infilling of a fracture in contrast tem observations of very fine clay minerals approximately

how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones observations and experiments observations and hydrothermal experiments were used to derive new information about how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones samples of deeply buried porous sandstones with different types of clay coats were split in two coats removed from one of each pair of splits and grain surfaces inspected with scanning electron microscopy quartz grains in a fluvial deltaic sandstone buried to 115c had no visible authigenic quartz on grain surfaces cleaned of diagenetic chlorite coats though well developed overgrowths occurred on nearby naturally uncoated grains however in similar sandstones buried to 164c quartz grain surfaces exposed by chlorite coat removal were covered with small 5 m mainly anhedral syntaxial quartz overgrowths similar overgrowths were observed under various detrital and diagenetic clay coats in porous eolian sandstones buried to temperatures up to 215c we conclude that clay coats may retard quartz nucleation at moderate temperatures but at high temperatures many coats permit quartz nucleation and preserve porosity by limiting cement growth to investigate cement growth limitation mechanisms samples with coats removed were subjected to quartz cementing conditions in a hydrothermal reactor during experiments the naturally occurring small overgrowths on clay cleaned grains coalesced and grew suggesting that clay particles in coats inhibit cement growth by forming barriers to early overgrowth coalescence although the fraction of grain surface coverage is the primary control on cement inhibition by coats cement growth interference textures vary with coat type providing a mechanism by which coat composition may be a secondary control on inhibitory effectiveness in deeply buried sandstones quartz cement can fill significant microporosity within diagenetic chlorite coats potentially affecting mechanical and petrophysical rock properties

mantle regulation of core cooling a geodynamo without core radioactivity abstract the case for radioactivity in the core based on the power requirements of the geodynamo is re evaluated previous calculations of mantle regulation of core thermal evolution have used an inappropriate formula new calculations with a more appropriate formula yield lower core heat loss in the past thus mitigating the implication of unreasonably high past core and mantle temperatures multiple thermal evolutions leading to present heat flows are also demonstrated depending on the efficiency of mantle removal of core heat some with moderately high past core heat loss and some with low and steady core heat loss the latter would permit a low or moderate power dynamo without core radioactivity key uncertainties are the efficiency of core cooling by the mantle the thermal conductivity of the core and the energy or entropy flow required to maintain the dynamo the present rate of heat loss from the core is argued to be still rather uncertain and a commonly used estimate of the thermal conductivity of the core is shown plausibly to be too high and in any case to be uncertain by perhaps a factor of 2 the geochemical difficulties associated with postulating radioactive heat sources in the core are stressed

porosity and thermal conductivity of the soultz sous forets granite the success of the soultz sous forets hot dry rock project depends on the ability to maintain fluid circulation in a fractured granite fractures represent the main fluid pathways to understand the behavior of this granite in respect to thermal fluid rock interaction the important aspects are 1 the porous network around these fractures and 2 the thermal conductivity of the rock this granite is altered and composed of different weathered facies variations of porosity and thermal conductivity take place in regard to the alteration and fracturing of the granite two types of porosity measurements were performed mercury injection and water porosity on two samples sizes the two methods give similar porosity values between 0 3 and 10 thermal conductivity measurements were performed in two perpendicular directions to look at anisotropy with two methods at different scale and value ranges from 2 3 to 3 9 w m 1 k 1 optical scanning provides us with a good knowledge of local increase of thermal conductivity due to sealed fracture or quartz cemented matrix

episodic mineralization of hydrothermal illite in the soultz sous forets granite upper rhine graben france episodic and localized illite mineralization is documented in the hydrothermally altered soultz sous forets granite upper rhine graben france separated grain size fractions of altered granite and argillite vein samples contain mixtures of 2m1 and 1m trans vacant illite varieties the platy pseudohexagonal 2m1 illite phases dominate the vein fillings whereas the 1m illite occurs largely as a fibrous pore filling variety which is particularly abundant in the granite matrix multiple phases of fluid injections into the granite body have resulted in different illite assemblages each sample containing a mixture of polytype generations formed during different crystal growth events on the basis of mineralogical and k ar isotopic constraints the ages of these vein mineralizing events are determined by plotting the k ar values of the various grain size fractions against polytype abundance and the fitted volume weighted crystallite thickness distributions the results suggest a permian age for the formation of the studied argillite veins characterized by successive injections of hydrothermal fluids secondary episodes of illite crystallization occurred during jurassic and cretaceous or even younger times in both the veins and the granite matrix there are indications that the polytype structure and composition of illite were strongly influenced by variations in fluid chemistry and the degree of fluid rock interaction as the granite was progressively sealed during post variscan episodic hydrothermal activity

blocked radiative heat transport in the hot pyrolitic lower mantle abstract the heat flux across the core mantle boundary q cmb is the key parameter to understand the earth s thermal history and evolution mineralogical constraints of the q cmb require deciphering contributions of the lattice and radiative components to the thermal conductivity at high pressure and temperature in lower mantle phases with depth dependent composition here we determine the radiative conductivity k rad of a realistic lower mantle pyrolite in situ using an ultra bright light probe and fast time resolved spectroscopic techniques in laser heated diamond anvil cells we find that the mantle opacity increases critically upon heating to 3000 k at 40 135 gpa resulting in an unexpectedly low radiative conductivity decreasing with depth from 0 8 w m k at 1000 km to 0 35 w m k at the cmb the latter being 30 times smaller than the estimated lattice thermal conductivity at such conditions thus radiative heat transport is blocked due to an increased optical absorption in the hot lower mantle resulting in a moderate cmb heat flow of 8 5 tw on the lower end of previous q cmb estimates based on the mantle and core dynamics this moderate rate of core cooling implies an inner core age of about 1 gy and is compatible with both thermally and compositionally driven ancient geodynamo

the effect of sub seismic fault slip processes on the isotopic signature of clay minerals implications for k ar dating of fault zones abstract clay minerals are abundant in fault gouges and isotope dating of the radiogenic noble gases that they contain may be used to constrain timing of fault initiation reactivation and to estimate recurrence intervals of earthquakes the potential influence of fault slip and ambient temperature on the isotope signature of authigenic clay minerals however remains unknown this study reports measurements of the k ar isotope signature of samples that have been sheared experimentally at sub seismic slip rates within a range of ambient temperatures as well as of samples undergoing standardised clay heating degas experiments in the investigation and comparison of the influence of sub seismic frictional slip and external heating on clay gouge the age data confirm that the sub seismic frictional slip of clay gouge affects the clay microstructures and releases radiogenic 40ar the experimental data indicate that radiogenic 40ar release due to external heating can be disregarded until 350 c which is supported by ar diffusion modelling frictional slip at sub seismic slip rates and at room temperature results in a significant radiogenic 40ar loss of 56 and the remaining clay will inherit 44 of radiogenic 40ar sub seismic frictional slip experiments at imposed elevated temperatures from 150 to 450 c increase the amount of radiogenic 40ar loss and decrease the amount of inherited radiogenic 40ar at a relatively high temperature of 450 c about 16 of radiogenic 40ar will be present in the remaining sample portion reinforcing the importance of rigorous clay grain size separation processes required prior to fault gouge dating

thin section analysis of lithified paleosols from dagshai formation of the himalayan foreland identification of paleopedogenic features and diagenetic overprinting and implications for paleoenvironmental reconstruction abstract in the present study we report micromorphology of diagenetically altered paleosols 31 ma old from dagshai formation himalayan foreland the fluvial sequence exposed along the koshaliya river nw himalaya contains four types of paleosols with decreasing abundance of well developed paleosols from basal to upper part of the dagshai formation burial diagenesis at 7 5 km depth caused compaction 54 78 current thickness compared to pre burial thickness and cementation of the paleosols accompanied by internal reorganization of groundmass within peds staining of ped walls with iron oxide plugging of voids disruption of textural pedofeatures fracturing of large mineral grains and nodules coarsening of pedogenic calcite crystals redoximorphic features and mineralization of root channels despite diagenetic alteration evidence of paleopedogenic processes is still well preserved in these fossil soils in the form of microstructures b fabrics pedogenic calcite bioturbation and textural pedofeatures thin section analysis helped to distinguish pedogenic and diagenetic features of lithified paleosols and to infer the paleoenvironment of the dagshai paleosols the paleopedological characteristics of the fossil soils suggest humid to sub humid conditions during their formation in early oligocene the paleoclimate inferred here is consistent with prevalence of tropical paleovegetation cf ficus l reported from dagshai sediments

smectite to illite reactions in salton sea shales a transmission and analytical electron microscopy study tem aem study of a sequence of shales from the salton sea geothermal field revealed that the mechanism for the reaction of smectite to form illite is markedly different from that for gulf coast sediments illite in salton sea shales occurs principally as individual euhedral to subhedral pseudohexagonal crystals in open pore space smectite was not observed by tem in proximity to such illite and is shown by xrd data to decrease in amount with depth as the proportion of illite increases illite is thus implied to be derived by complete dissolution of smectite and other phases transport of components and crystallization of illite from solution however in shallow sediments detrital smectite is also observed to be in part directly replaced by illite in a manner duplicating gulf coast textures the mechanism by which smectite undergoes complete dissolution to allow precipitation of illite at a distant site is compatible with an open system such as the salton sea sediments characterized by high water rock ratio and relatively high permeability in contrast the mechanism involving a reaction front where the smectite is directly replaced by illite such as occurred in gulf coast shales is compatible with relatively impermeable shales

numerical evaluation of mantle plume spacing size flow rates and unsteadiness predictions of several characteristics of mantle plumes from boundary layer theory have been tested and calibrated with numerical models in cylindrical coordinates instability spacing in the initial stages of the numerical models is well predicted as are the lift off time of plume heads the size of plume heads at lift off and the heat flow of individual plume tails however since the prediction quality for the instability spacing and the lift off time of plume heads deteriorates in the presence of larger heterogeneities in the thermal boundary layer these predictions seem not very useful for mantle plumes predictions for the plume head size at lift off appear to be largely independent of the degree of boundary layer heterogeneity and therefore may provide reasonable estimates for mantle plumes the predictions for the heat flow of a plume tail seem to yield usable results for both stationary plume tails and those that show at least periods of quasi stationary heat flow assuming that mantle plumes are reasonably steady the prediction formula is used to derive estimates for the temperature difference t across the thermal boundary layer at the core mantle boundary this depends on the fraction of the core surface that is presumed to be occupied by plume feeding areas taking this fraction to be greater than 1 2 yields t 400 c too low to be compatible with petrological constraints on plumes smaller fractions yield larger t but this seems to be incompatible with the geophysical distribution of hotspots

a vertic paleosol at the archean proterozoic contact from the singhbhum orissa craton eastern india abstract we report on an inferred paleoproterozoic soil horizon from the singhbhum orissa craton near keonjhargarh orissa eastern india which preserves vertic vertisol like features the 2 10 m thick white shale consists of quartz muscovite pyrophyllite interpreted as a paleosol overlies 3 32 ga granite and is covered by pre 2 0 ga sandstones kolhan group deposited in marginal marine environments the paleosol passes downwards through a partly altered granite saprolith zone to fresh granite abundant pedogenic slickensides ped structures gilgai topography reddish stain on ped surfaces and sepic plasmic microfabric in the paleosol were probably related to shrink and swell processes driven by marked seasonal precipitation in a well drained landscape an observed decrease of alkali elements and an increase of silica alumina and cia values from granite to paleosol together with relatively constant ti al ratios suggest in situ weathering of granite protolith however a paleo vertisol necessitates a mafic parent rock either directly igneous or reworked through alluvium the c 2 25 ga malangtoli jagannathpur basaltic rocks are relatively widespread and close to the inferred paleosol occurrences and provide a logical solution geochemistry of the highly depleted paleosol in contrast particularly when applying the isochon method strongly supports a granitic parent the apparent conundrum can possibly be solved through repeated alluvial reworking of both granitic and mafic detritus and accumulation of weathered material with varying proportions of these two components yet enough smectitic clays 30 to form a paleo vertisol this pre 2 0 ga weathering event in the singhbhum craton is consistent with a global scenario of paleoproterozoic weathering which followed an extended global glaciation and thus has the potential to contribute to understanding of pre 2 0 ga amalgamation of regional and global cratonic blocks

thermal conductivity of mgo mgsio3 perovskite and post perovskite in the earth s deep mantle abstract we report lattice thermal conductivities of mgo and mgsio3 in the perovskite and post perovskite structures at conditions of the earth s lower mantle obtained from equilibrium molecular dynamics simulations using an advanced ionic interaction potential the full conductivity tensor was calculated by means of the green kubo method and the conductivity of mgsio3 post perovskite was found to be significantly anisotropic the thermal conductivities of all three phases were parameterized as a function of density and temperature assuming a fe free lower mantle composition with mole fractions x mgsio 3 0 66 and x mgo 0 34 the conductivity of the two phase aggregate was calculated along a model geotherm it was found to vary considerably with depth rising from 9 5 w m k at the top of the lower mantle to 20 5 w m k at the top of the thermal boundary layer above the core mantle boundary extrapolation of experimental data suggests that at deep mantle conditions the presence of a realistic amount of iron impurities lowers the thermal conductivity of the aggregate by about 50 manthilake et al 2011a from this result and our thermal conductivity model we estimate the heat flux across the core mantle boundary to be 10 8 tw for a fe bearing mgo mgsio3 perovskite aggregate and 10 6 tw for a fe bearing mgo mgsio3 post perovskite aggregate

thermal transport properties of major archean rock types to high temperature and implications for cratonic geotherms abstract the thermal structure of archean terranes depends in part on the thermal transport properties of their distinctive rock types we determined thermal diffusivity d of a suite of 14 greenstone mafic granulite and tonalite trondhjemite granodiorite ttg rocks at temperatures up to 1000 c at atmospheric pressure using laser flash analysis which lacks systematic errors associated with conventional contact techniques at room temperature d ranges from 3 8 mm 2 s 1 for banded iron formation to 0 8 mm 2 s 1 for a quartz poor trondjhemite for all samples thermal diffusivity decreases with increasing temperature such that d for the suite converges around 0 7 0 1 mm 2 s 1 at 700 c combining these results with measured density and heat capacity calculated from modal mineralogy provides thermal conductivity as a function of temperature for each rock suite whereas near surface thermal conductivity varies from 2 7 to 4 2 w m 1 k 1 depending on rock type thermal conductivity of the lower crust is 2 w m 1 k 1 and only weakly dependent on lithology which is more thermally resistive than the uppermost mantle 3 5 w m 1 k 1 use of temperature dependent thermal transport properties in numerical models reveals that surface geotherms can be relatively insensitive to crustal heat production because high heat producing ttg rocks typically have high thermal diffusivity and conductivity at low temperatures and consequently are more efficient conductors of the heat they produce this finding implies that calculations of crustal heat production from surface borehole measurements may entail significant uncertainties

the age of the inner core abstract the energy conservation law when applied to the earth s core and integrated between the onset of the crystallization of the inner core and the present time gives an equation for the age of the inner core in this equation all the terms can be expressed theoretically and given values and uncertainties of all relevant physical parameters the age of the inner core can be obtained as a function of the heat flux at the core mantle boundary and the concentrations in radioactive elements it is found that in absence of radioactive elements in the core the age of the inner core cannot exceed 2 5 ga and is most likely around 1 ga in addition to have an inner core as old as the earth concentrations in radioactive elements needed in the core are too high to be acceptable on geochemical grounds

kar systematics of clay to mica minerals in a multi stage low grade metamorphic evolution the behavior of the ar isotopic system of clay to mica fractions was studied in cambrian greywacke samples along a transect of northwestern morocco these rocks were affected by a progressively increasing metamorphic overprint spanning from diagenetic to epizonal metamorphic conditions k ar isotopic data of 0 2 10 m size fractions recovered from seven samples allowed to recognized three episodes of illite crystallization 1 during an upper ordovician thermal event at 445 ma which is characterized by an illite chlorite mineral paragenesis in the northernmost part of the transect 2 during a carboniferous low grade overprint at 305 ma which is characterized by a similar mineral paragenesis and 3 during a triassic to liassic hydrothermal activity at 205 ma which generated a smectite dominated paragenesis the ages were examined in combining x ray mineralogic and k ar isotopic data in terms of linear arrays in both isochron and harper diagrams to differentiate true isochrons from mixing lines it could also be shown that mixtures of two generations of micaceous minerals can induce different trends in the k ar dates depending whether the first generation of minerals was either or not affected by the event inducing the later generation

dating of anatase forming diagenetic reactions in rotliegend sandstones of the north german basin diagenetic conditions controlling authigenic formation of anatase and in situ la icp ms u pb isotope dating of this phase are studied in upper rotliegend ii sandstones from two wells in nw germany anatase grew after breakdown of detrital ti phases e g ilmenite although local scale ti transport and mobilization from detrital clay hematite coats or condensed hydrocarbons cannot be ruled out the anatase forming reaction marks the change from a regime of reducing conditions imposed by first hydrocarbon generation to oxidizing conditions probably caused by influx of a fluid from evaporitic zechstein rocks this change in fluid influx is interpreted as response to enhanced normal faulting and halokinesis during accelerated burial in triassic times isotope data of u and pb indicate incorporation of crustal common pb from mesozoic pore fluids but precisely mark diagenetic growth of anatase at 224 3 5 1 5 6 ma in a tera wasserburg plot locally u pb isotope signatures are consistent with either additional incorporation of u and pb from detrital precursor phases or with uptake of uranogenic pb from hydrocarbons generated prior to 224 ma anatase is shown to be a valuable authigenic phase suitable for u pb chronometry of diagenetic events which appears to be unaffected by protracted burial and temperatures exceeding temperatures of crystallization

discrete clay diagenesis in a very low permeable sequence constrained by an isotopic k ar and rb sr study multimethod analyses of several size fractions of clays were used to reconstruct the diagenetic history of the shallow buried claystones within the paris basin a systematic decrease occurred in k ar dates relative to the decrease in size of the clay fractions signifying higher amounts of newly formed clay material in the finer fractions we suggest that the authigenic clay minerals occurring in the fine fractions had an al montmorillonite composition by assuming that the isotopic k ar and rb sr dates obtained on a bentonite layer in the sedimentary sequence stand for pure authigenic clay minerals one may interpret all k ar dates as mixtures of one authigenic and two detrital end members the results imply that a period of low sea level favoured diagenetic smectite type clay formation about 10 15 million years after deposition of the sediments signatures of limited scale chemical and isotopic homogenisation mean that the rock volumes affected by the diagenetic modifications had to be quite limited the study of clay minerals extracted from some stylolites further suggests that any overpressure related to the origin of stylolites had no effect on clay authigenesis

dynamical consequences in the lower mantle with the post perovskite phase change and strongly depth dependent thermodynamic and transport properties article i nfo we have carried out numerical simulations of large aspect ratio 2 d mantle convection with the deep phase change from perovskite pv to post perovskite ppv using the extended boussinesq approximation for a fluid with temperature and pressure dependent viscosity we have investigated the effects of various ppv phase parameters on the convective planform heat transport and mean temperature and viscosity profiles since ppv is expected to have a relatively weak rheology with respect to pv and a large thermal conductivity we have assumed that the transition from pv to ppv is accompanied by both a reduction in viscosity by 1 to 2 orders of magnitude and by an increase in thermal conductivity by a factor of 2 furthermore we have analyzed the combined effects of a strongly decreasing thermal expansivity in pv and steeply increasing thermal conductivity according to recent evidence from high pressure experiments and first principle calculations as long as the thermal expansivity and conductivity are constant ppv exerts a small but noticeable effect on mantle convection it destabilizes the d layer causes focusing of the heat flux peaks and an increase of the average mantle temperature and of the temporal and spatial frequency of upwellings when the latest depth dependent thermal expansivity and conductivity models are introduced the effects of ppv are dramatic on the one hand without ppv we obtain a very sluggish convective regime characterized by a relatively cool mantle dominated by large downwellings that tend to stagnate beneath the transition zone with ppv on the other hand we observe an extremely significant increase of the average mantle temperature due to the formation of large sized and vigorous upwellings that in some cases tend to cluster thus forming superplumes if a very large thermal conductivity at the core mantle boundary is assumed k 20 wk 1 m 1 we obtain a quasi steady state regime characterized by large and stable plumes with long lifetimes the combination of strongly depth dependent expansivity and conductivity is a viable mechanism for the formation of long wavelength long lived thermal anomalies in the deep mantle even if a low viscosity ppv atop the core mantle boundary is included

fibrous illite in oilfield sandstones a nucleation kinetic theory of growth fibrous illite is one of the most important cements that grows within sandstones during burial and the only one which is commonly dated using the k ar age technique a small quantity of illite can dramatically reduce porefluid flow rates within a sandstone thus making oil recovery uneconomic illite ages potentially correspond to geological events such as hydrocarbon filling of a sandstone reservoir providing calibration to basin models yet the fundamental processes controlling fibrous illite growth are not understood this contribution presents a new theory for illite growth within sandstones that explains the fibrous morphology of illite the restricted range of illite k ar age dates compared to the age of the host sandstones and the lack of 0 myr old illite reported the growth of fibrous illite as an authigenic cement may be controlled by nucleation kinetics and not by thermodynamic or growth kinetic considerations as has been previously assumed

metallogeny of the large scale carboniferous karstic bauxite in the sanmenxia area southern part of the north china craton china abstract above two billion tons of bauxite were formed during the exposure of the north china craton ncc in 445 300 ma mineralogical geochemical and isotopic analyses of karstic bauxite deposits in the sanmenxia area situated within southern ncc were conducted to explore the genetic processes of carboniferous bauxite the bauxite contains three layers a lower fe bearing claystone layer a middle bauxite ore layer and an upper claystone layer fe bearing claystone is dominated by illite and hematite in the uplift and illite siderite and pyrite in the depression bauxite ore is composed of diaspore illite pyrite and anatase and the upper claystone consists of illite diaspore and anatase distinct pyrite 34s values 11 7 15 2 and 11 5 to 1 0 illite 87sr 86sr i 0 711917 0 713588 and 0 708000 0 711057 and end t 12 2 to 11 4 and 11 8 to 9 7 values and the immobile elemental ratios were obtained between the lower fe bearing claystone and upper bauxite ore and claystone together with chemistry of detrital rutile it is denoted the fe bearing claystone was formed from the underlying limestone whereas the bauxite ore and claystone were derived from both igneous rocks along craton margin and regional precambrian metamorphic rocks the visible microorganisms and wide development of framboidal pyrite with negative 34s within the bauxite ore provide evidences of microbial activity during bauxite formation bio leaching process after the deposition of allochthonous source materials caused the downward migration of ions al3 fe2 ti4 ree3 etc these ions encountered an alkaline and reducing condition in the karstic depression forming diaspore pyrite and anatase and ree enrichment at the bottom of bauxite ore this large input of raw materials warm and humid climate and microorganisms led to large scale bauxite formation in the ncc during late carboniferous

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

the effect of variable thermal diffusivity on kinematic models of subduction 1 we examine the influence of variable thermal properties on the thermal state of a subducting slab in the upper mantle and the transition zone by combining a kinematic slab model with models of thermal conductivity thermal diffusivity and conductivity models for major mantle minerals in the mgo sio2 system are developed based on experimental measurements on these minerals at high pressure and temperature the models show significantly higher thermal conductivity for stishovite and clinopyroxene compared to the mg2sio4 polymorphs and majorite garnet in our subduction model we consider scenarios with a differentiated slab basalt harzburgite pyrolite in a pyrolite mantle and uniform composition for both the slab and the mantle pyrolite or a pure mg2sio4 based system the role of highly conductive pyroxene is examined by taking it into account in some models and replacing it in others with majorite garnet this choice has a strong influence on the thermal state of the slab shifting the depth of the 1000 k temperature anomaly by as much as 100 km this is caused by faster cooling of the plate at the surface and thermal insulating effects once subducted temperature differences between models with variable thermal diffusivity and those with constant parameters can reach 125 k i e 10 of total thermal anomalies of the slab relative to an average geotherm taking into account the stable mineral phases we evaluate density variations between different models and find that variable thermal diffusivity results in a modest increase of negative buoyancy of the slab

pedogenesis of late quaternary deposits northern kyonggi bay korea implications for relative sea level change and regional stratigraphic correlation abstract late pleistocene and early holocene paleosols are described from construction pits and boreholes in the northern kyonggi bay west coast of korea thin section petrography chemistry clay mineralogy and geotechnical properties of the paleosols were examined to infer relative sea level fluctuations during the late quaternary relict laminae and gradational contacts with underlying tidal rhythmites confirm that the late pleistocene paleosol is a pedogenically altered tidal deposit illuvial clay coatings rootlets and enrichment of kaolinite and chemically stable oxides indicate that pedogenesis occurred on a well drained stable surface during the last glacial period redoximorphic features such as drab colored root traces and sphaerosiderite however suggest that waterlogged conditions developed temporarily due to a rise of the water table at the end of the last glacial period as sea level rose an early holocene paleosol formed in freshwater bog deposits burying the late pleistocene paleosol the early holocene paleosol has abundant sphaerosiderites and organic material the presence of weakly developed illuvial clay coatings oxidized siderites and pellets however indicates oxidizing condition associated with water table fall occurred during the early holocene despite the similarity in the degree of chemical and clay mineralogical weathering the late pleistocene paleosol is distinguished from its early holocene counterpart by thicker and more abundant illuvial clay coatings more fe 2 o 3 and a greater degree of consolidation duration of pedogenesis might be a primary cause for the difference of the pedofeatures with climate playing a secondary role the widespread presence of similar late pleistocene paleosols highlights its significance as a key stratigraphic marker for regional correlations along the west coast of korea

transport properties of mg2sio4 liquid at high pressure physical state of a magma ocean abstract we use a flexible potential model to perform large scale molecular dynamics simulations on self diffusivity and viscosity of mg 2 sio 4 melt up to pressures of 32 gpa and over a temperature range of 2600 to 3200 k we find that self diffusivity decreases and viscosity increases uniformly with pressure the latter from values of 10 2 pa s at 0 gpa to 10 1 pa s at 32 gpa 2600 k both transport properties can be readily fit with a closed arrhenius expression over the whole pressure and temperature range considered independent estimates of self diffusivities and viscosity allow us to examine their relation through the stokes einstein and the eyring equations while at low pressures the sio 4 tetrahedron seems to be the viscous flow unit bare ion diffusion becomes more dominant at high pressure combining previous simulation results on thermodynamic properties with the current viscosity simulations we compute a magma ocean adiabat and the associated viscosity profile we find that viscosity in the magma ocean is 2 10 2 pa s near the surface and that it increases by less than 0 5 log unit up to 35 gpa combining scenarios for magma ocean dimensions in the young earth with thermodynamic properties and viscosity of mg 2 sio 4 melt we compute a magma ocean rayleigh number ra in the range of 10 28 and 10 29 putting the magma ocean in the dynamic regime of hard turbulence using scaling relations for the nusselt number nu at very high ra we estimate the heat flux of the magma ocean to be in the range of 10 18 to 10 19 w

mantle plumes and flood basalts enhanced melting from plume ascent and an eclogite component new numerical models of starting plumes reproduce the observed volumes and rates of flood basalt eruptions even for a plume of moderate temperature arriving under thick lithosphere these models follow the growth of a new plume from a thermal boundary layer and its subsequent rise through the mantle viscosity structure they show that as a plume head rises into the lower viscosity upper mantle it narrows and it is thus able to penetrate rapidly right to the base of lithosphere where it spreads as a thin layer this behavior also brings the hottest plume material to the shallowest depths both factors enhance melt production compared with previous plume models the model plumes are also assumed to contain eclogite bodies inferred from geochemistry to be recycled oceanic crust previous numerical models have shown that the presence of nonreacting eclogite bodies may greatly enhance melt production it has been argued that the eclogite derived melt would react with surrounding peridotite and refreeze however recent experimental studies indicate that eclogite derived melts may have reached the earth s surface with only moderate or even minor modification combined with an assumed 15 vol component of eclogite our models yield a sharp peak in melting of about 1 3 myr duration and volumes of melt that encompass those observed in flood basalt provinces

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

water rock interaction processes in the triassic sandstone and the granitic basement of the rhine graben geochemical investigation of a geothermal reservoir saline fluids have been collected in the rhine graben over the last two decades both from the triassic sandstone aquifer and the granitic basement down to a depth of 3500m their salinities and location are compared in order to distinguish the respective influences of temperature and host rock mineralogy in the water rock interaction processes the comparison shows that sulphates in the sedimentary formations were dissolved by the fluids which also led to br enrichment mica dissolution has strongly increased the rb and cs contents which then provide an indication of the degree of water rock interaction the sr isotopic ratios are used to compare the fluids with the granite minerals two relationships are revealed for the fluids in the sandstone and the granite one related to widespread mica dissolution which could have affected both the buntsandstein and the granite and the other to subsequent plagioclase dissolution which is observed only in the granite computations showed that 12 5g of mica and 1 658 of plagioclase per liter of fluid have been dissolved the nature of these two relationships suggests two different evolutions for the fluids and the individualization of the two reservoirs during the graben s history the cation concentrations are mainly controlled by temperature and are independent of the type of host rock equilibrium with the rock mainly caused ca and k concentration variations which has induced clear ca k and ca 18o k 18o correlations geothermometric computations indicate that with increasing depth the cations the silica and the 18o so4 geothermometers evolve towards a value close to 230 c this demonstrates the existence of a hot reservoir in the granite of the graben at a depth estimated at 4 5 5 km

fossil soils as grounds for interpreting long term controls on ancient rivers abstract the main factors controlling fluvial systems are time initial topographic relief geology climate vegetation base level upland runoff upland drainage network hillslope morphology downstream deliveries channel behavior and pattern of deposition similar factors control soil formation in drainage basins climate organisms topographic relief parent material and time effects of these factors may be preserved as well or better in fossil soils of alluvial sequences as in sedimentary structures facies and mineralogy of paleochannels for example former rainfall may be interpreted from depth to the top of the calcic horizon from percent clay from percent of different kinds of clay minerals from quartz feldspar ratio from hue and from identification of fossil soils interpretation of the role of these factors in producing a particular stratigraphic section should take into account its resolution the proportion of geological time represented temporal completeness of original sediment preserved lithological completeness and of original fossils preserved paleontological completeness temporal and lithological completeness can be estimated by comparison with the most likely rates of sediment accumulation and most likely thicknesses respectively for pertinent sedimentary environments and time scales paleontological completeness can be estimated by comparing the preserved fossils with expectations based on former ecosystems indicated by fossil soils likely controls and resolution of a sequence of eocene and oligocene fossil soils from badlands national park south dakota were studied as a guide to the periodicity and causes of episodic sedimentation there short term episodicity and filtering of sedimentation events of particular magnitude were apparent from superposition of paleosols but resolution of the sequence was not sufficient to permit a detailed analysis of their individual causes long term paleoenvironmental changes and four episodes of erosional downcutting could be recognized all four occasions of landscape instability and erosion were times of drier climate and sparser vegetation than usual local uplift and supply of volcanic ash were contributing factors in some episodes of erosion when allowances are made for time scales and completeness of sequences of fossil soils they can be useful indicators of changes in former environment biota and fluvial regimen