structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

the cooling of frontal flow ramps a calorimetric study on the rocche rosse rhyolite flow lipari aeolian islands italy relaxation geospeedometry using differential scanning calorimetry dsc has been applied to quantify the cooling history across the glass transition of flow ramps at the front of the calcalkaline rhyolite rocche rosse flow of lipari aeolian islands italy modelled cooling rates for the obsidian retrieved from two profiles range between 0 2 and 0 03 k min 1 cooling at the flow front appears to be dominated by conductive heat loss of individual flow ramps forming individual cooling units cooling rates of tens of kelvins per day appear to have controlled the last stage of viscous deformation before the entire flow came to rest it is inferred that cooling rates slower than those modelled are required to sustain flow in highly viscous rhyolitic lavas

evolution of thermal and mechanical properties of mine tailings and fly ash mixtures during curing period fly ash is often used as a binder for modifying the properties of geomaterials such as organic and expansive soils sludge from water treatment dredged sediments mine tailings etc changes in t

cooling rate correction of paleointensity determination for volcanic glasses by relaxation geospeedometry the influence of the cooling rate on paleointensity estimates was investigated for samples from a vertical profile across a 600 a d obsidian lava flow ramp from lipari italy the natural cooling rates at the glass transition which were previously determined for the seven investigated samples by relaxation geospeedometry vary by a factor of more than 4 rock magnetic investigations indicate a magnetic microlite fraction in the single domain grain size range and strong magnetic anisotropy the thermoremanence anisotropy tensor was determined for each specimen to correct the paleointensity results for this anisotropy the cooling rate dependency of the thermoremanence was determined experimentally extrapolation to natural cooling rates indicate an overestimate of the paleointensity by 13 to 20 during experiments with typical laboratory cooling rates correcting for the different cooling rates and the cooling rate dependencies within the vertical profile significantly reduces the standard deviation of the average flow paleointensity the average paleointensity for the 543 19 a d flow ramp results in 52 4 1 1 t corresponding to a virtual axial dipole moment of 9 2 0 2 am2 uncertainties introduced by anisotropy correction and cooling rate extrapolation are considered by error propagation

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

evaluation of sample quality of sensitive clay using intrinsic compression concept a simple index the degree of sample disturbance is proposed in this study to quantitatively evaluate the quality of sensitive clay samples based on the concept of void index proposed by burland in 1990 the degree of sample disturbance is defined as the ratio of the difference between the in situ void index and the void index of the undisturbed sample tested in the laboratory to the difference between the in situ void index and the void index of the completely remolded clay all these indices are determined at the same effective overburden stress theoretically the degree of sample disturbance varies from 0 perfect undisturbed sample to 100 completely remolded sample the proposed index is used in this study to evaluate the sensitive ariake clay in japan oedometer tests on undisturbed samples of natural ariake clay obtained from the field using the current sampling practice in japan show the degree of sample disturbance ranging from approximately 5 to 38 the clay sample with an in situ void index closer to the intrinsic compression line has a lower degree of sample disturbance in addition a series of consolidation and unconfined compression tests were conducted on artificially disturbed samples in the laboratory to demonstrate the change of consolidation yield stress unconfined compressive strength and compression index with the degree of sample disturbance a simple method is proposed in this paper to correct the mechanical parameters measured in a laboratory setting considering the degree of sample disturbance

cooling rates of lunar orange glass beads abstract it is widely accepted that the apollo 17 orange glass beads are of volcanic origin the degree of degassing of the glass beads depends on their cooling rates so the estimation of volatile contents in the parental magmas of these lunar pyroclastic glasses also depends on the cooling rates the cooling rate can be estimated using the calorimetric properties of the glass across the glass transition in this study a series of heat capacity measurements were carried out on hand picked lunar volcanic orange glass beads during several cycles of heating to temperatures above their glass transition using a differential scanning calorimeter the cooling rate of orange glass beads sample 74220 867 was calculated to be 101 k min using the correlation between glass cooling rates and fictive temperatures estimated from their heat capacity temperature paths this cooling rate is close to the lower end of the range that best fits the diffusion profiles of several volatile species in the glass beads and at the upper end of the cooling rate range recorded in glasses quenched subaerially on earth the cooling rate is likely to be controlled by the cooling environment cooling medium such that the lunar volcanic glass beads could have been cooled in a gaseous medium released from volcanic eruptions on the moon but not during free flight in vacuum the existence of a gas medium suggests in turn that there may have been at least a short lived or episodic atmosphere on the early moon at around 3 5 ga

mercury intrusion and permeability of louiseville clay several theories have been proposed to correlate the permeability hydraulic conductivity with the pore size distribution of soils and it seemed interesting to determine if these theories could be applied to natural clays for this purpose permeability and mercury intrusion porosimetry tests were performed on a champlain sea clay for both intact and remoulded conditions after compression of the specimens to strains varying from 0 to 42 the results show that for either intact or remoulded soil conditions there is a relationship between the pore size parameters and the permeability of the clay however there is no unique relationship for both intact and remoulded clays and for the silt and clay considered in previous studies consequently mercury intrusion porosimetry alone cannot be usepto evaluate the permeability of soils in general plusieurs thkories ont ctc proposces pour corrcler la permiabilite conductivitk hydraulique avec la distribution des grosseurs de pore des sols et il a semblc intiressant de verifier si ces theories pourraient 2tre appliquees aux argiles naturelles a cette fin des essais de permcabilitc et de porosimctrie a intrusion de mercure okt ctc rcaliscs sur l argile de la mer champlain dans des conditions tant intactes que remanikes apris la compression des specimens a des dcformations variant de 0 a 42 les rcsultats demontrent que pour des conditions soit intactes ou remanices il existe une relation entre les paramitres de grosseur de pore et la permcabilitc de l argile cependant il n existe pas de relation unique pour les argiles tant intactes que remanices et pour le limon et l argile ctudics antkrieurement en conscquence la porosimctrie a intrusion de mercure ne peut pas a elle seule tre utilisce pour cvaluer la permcabilitc des sols en general mots clds permcabilitc argile porosimctrie a intrusion de mercure structure traduit par la rcdaction

investigation of land subsidence with the combination of distributed fiber optic sensing techniques and microstructure analysis of soils abstract land subsidence is a global phenomenon caused by a variety of factors and there are still many challenges in land subsidence monitoring the results of an investigation of land subsidence using the combination of distributed fiber optic sensing dfos techniques and microstructure analysis of soil are here presented two dfos techniques brillouin optical time domain reflectometry botdr and fiber bragg grating fbg were developed in two boreholes namely gm03 and sz01 in su xi chang area china to monitor movement of strata crossed by the borehole and pore pressure in some specific strata scanning electron microscope sem and mercury intrusion porosimetry mip were employed to quantify and characterize the microstructures of undisturbed soils from the boreholes based on the botdr monitoring results the annual levels of land subsidence in gm03 and sz01 are 1 2 mm and 2 9 mm respectively and the movement history of strata were clearly tracked for both boreholes the main contributors to subsidence are two aquitards ad2 and ad3 that exist adjacent to the second aquifer af2 the results obtained by fbg based sensors indicate good agreement with botdr and it confirms that the deformation of aquifer is significantly controlled by pore pressure sem images were analyzed with pore particle and crack analysis system pcas three statistical parameters including average form factor ffavg fractal dimension df and area probability distribution index b were used to describe the geometric characteristics of pores it is found that larger average form factor larger fractal dimension and higher proportion of large pores in soil microstructures favors land subsidence mip results confirm that area probability distribution index can be used for the estimation of strata compression potential in land subsidence investigations

palynofloral palynofacies and carbon isotope of permian coal deposits from the godavari valley coalfield south india insights into the age palaeovegetation and palaeoclimate abstract palynological studies of the present permian sediments play a vital role in biostratigraphic and palaeoecological interpretations additionally the palynofacies analysis total organic carbon toc content and 13c value in the present study focus largely for the palaeoenvironmental and palaeoclimatic reconstruction and also provides information about processes responsible for sedimentary deposits along with their lithological counter parts the palynological investigation of 306 m deep borehole msm 25 from the somavaram area of the godavari valley coalfield has led to infer five distinct palynofloral assemblages the artinskian palynofloral assemblage i and ii guadalupian palynofloral assemblage iii and iv and lopingian palynofloral assemblage v ages have been assigned to the palynofloral assemblages based on the palynofloral evidence the distinct stable carbon isotope ratios also comprehend these ages with extreme climatic events the artinskian age 22 4 is characterized by relatively higher average 13c values whereas lowest average 13c values are observed at the lopingian age 24 0 with intermediate average 13c value 23 2 during guadalupian age in the present study the permian triassic p t transition is marked by the distinct negative carbon isotope excursion followed by a distinct recovery during the early triassic time period the relative variability of palynofacies components such as palynomorphs structured terrestrial phytoclasts opaque phytoclasts degraded organic matter om and amorphous om is related to hydrodynamic perturbations during the deposition time based on the dominance and sub dominance of the palynofacies three distinct depositional phases have been identified representing differential environmental settings the palynomorphs and structured terrestrial phytoclasts dominate the palynofacies assemblage a suggesting forest swamp environment while in the palynofacies assemblage b the dominance of degraded om and amorphous om characterize reed marshes lakeshore setting and the abundance of opaque phytoclasts in the palynofacies assemblage c indicate oxidized swamp environment

sheet hyaloclastite density current deposits of quench and bubble burst fragments from thin glassy sheet lava flows seamount six eastern pacific ocean abstract new observations with the submersible alvin and deep tow camera show that bedded sheet hyaloclastites are common deposits between 2024 and 1723 m depth on the upper flank of seamount six located on the cocos plate at 12 45 n 102 35 w the individual sheets are highly localized and of small areal extent 2 though no vent sites were found several facies associations of hyaloclastite with pillow talus knobbly fist sized lava fragments and thin sheet lava deposition of hyaloclastites occurred from lateral density currents formed by transformation from convective suspension settling grain size distribution settling behaviour of different co deposited shard types and sedimentary structures together with pelagic ooze in the matrix and geochemically mixed shard populations indicate some erosion traction reworking and turbulence during transport critical observations are that contorted sheet lava protrudes through hyaloclastite and that sheet lava flow vugs commonly contain pelagic ooze facies associations plus consideration of limu formation allow the establishment of a new multi component model of hyaloclastite formation it is inferred that the formation of limu bearing sheet hyaloclastite involves entrapment of pelagic sediment beneath or within lava this leads to limu bubble formation and suppressed tephra jetting together with convectively rising water heated by the lava flow these processes loft shards slightly into the water column from which they settle singly or in vertical sediment gravity flows that are redirected to flow along the seafloor

crystal rich mass flow deposits related to the eruption of a sublacustrine silicic cryptodome early permian collio basin italian alps abstract sedimentological granulometric and petrographic data are presented from a detailed study on a crystal rich mass flow deposit which is presumably related to the eruption of a sublacustrine cryptodome the deposit forms a prominent intercalation in the lower permian collio formation in the italian alps north of brescia outcrops of the 10 20 m thick volcaniclastic deposit dasdana i beds db can be traced over 12 km from east to west the db consists of a thick crystal rich sandy gravelly lower subunit representing a sequence of amalgamated bouma a b divisions overlain by a thin well bedded sandy muddy subunit that is rich in outsize porphyritic silicic fragments modal and computer aided image analyses reveal that the crystal rich lower subunit contains up to 80 of volcanogenic crystals some samples contain up to 60 of porphyritic fragments which have a phenocryst content of about 20 the wide textural range from cryptocrystalline poikilomosaic to rarer medium grained granophyric groundmass the irregular to lensoid shapes of the porphyritic fragments and the presence of basement and sedimentary clasts suggest that the db originated from a sublacustrine eruption of a partially extrusive cryptodome ca 1 6 km3 two other porphyritic felsic cryptodomes dosso dei lupi dosso del bue described briefly here emplaced into the collio formation sometime after the db event and expose flat bases and tilted sediments at their sides textures observed in these domes are comparable to those found in the db porphyritic fragments

compaction behaviour of clay this paper presents an experimental study of the compaction behaviour of non active clay one dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using trento high capacity tensiometers at lower water contents a transistor psychrometer was used to measure post compaction suction samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses three water content regions were identified in the compaction plane depending on whether post compaction suction increased decreased or remained constant as the degree of saturation was increased at constant water content hydraulic paths of specimens subjected to loading unloading cycles at constant water content have clearly shown that post compaction suction may increase as the degree of saturation increases this non intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour to this end a coupled mechanical water retention model was formulated irreversible one dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress modified suction and void ratio irreversible hydraulic wetting paths were modelled by a boundary surface in the space suction degree of saturation and void ratio this study was completed by investigating the pore size distribution of compacted samples through mip tests

feldspar alteration and diagenetic characteristics of the parsora sandstones son basin india reply see shah and bandyopadhyay 2005 gondwana research gnl v 8 pp 258 265 figure references in the reply are in the context of this paper

mineralogy chemistry and physical properties interrelationships of some sensitive clays from eastern canada this paper describes the use of quantitative mineralogy and specific surface area in interpreting the index properties of clayey soils from nine sites in eastern canada samples representative of t

generation of fine hydromagmatic ash by growth and disintegration of glassy rinds 1 the deposits of mafic hydromagmatic eruptions are more fine grained and variable in vesicularity than dry magmatic deposits blocky equant shapes of many hydromagmatic clasts also contrast with droplet thread and bubble wall morphology of dry magmatic fragments small 180 m blocky hydromagmatic pyroclasts have traditionally been interpreted to result from discrete vapor explosions although such explosions tend to occur only under certain conditions this paper considers a process of hydromagmatic ash formation that involves repeated growth and disintegration of glassy rinds on pyroclast surfaces as they deform within turbulent flows this process termed turbulent shedding may occur during the expansion phase of vapor explosions or during turbulent but nonexplosive mixing of magma with water steam or water sprays the occurrence of turbulent shedding and the resulting fragment sizes depend on the timescale for rind growth and the timescale between disturbances that remove or disintegrate glassy rinds turbulent shedding is directly observable in some small littoral jets at kilauea calculations suggest that in the presence of liquid water or water sprays glassy rinds having a thickness of microns to millimeters should form in milliseconds to seconds this is similar to the timescale between turbulent velocity fluctuations that can shred lava globules and remove such rinds the fraction of a deposit consisting of fine ash should increase with the duration of this process large scale surtseyan jets generate hundreds or thousands of shedding events bubble bursts or tephra jets at kilauea s coast may produce only a few

cooling dynamics of spatter fed phonolite obsidian flows on tenerife canary islands abstract relaxation geospeedometry has been applied to two series of clastogenic obsidian flows on tenerife to determine their thermal history across the glass transition the phonolite flows investigated were both generated by lava fountaining activity followed by rheomorphism of the deposits the detailed sampling resolution within the two series enabled an accurate quantification of their thermal history cooling rates within the investigated spatter fed flows vary over more than two orders of magnitude the highest cooling rates of 0 39 k min were modeled for the central vesiculated part of one flow the dense basal obsidian layers of both flows were cooled at substantially lower rates of 0 0042 and 0 0028 k min respectively there appears to be an influence of in situ vesiculation processes on the thermal budget of the investigated flows in addition the slow cooling rates for the basal portions of both flows seem to be associated with a stage of thermal buffering continual advective heat transport of hot material along a basal shear plane may sustain elevated temperatures associated with quasi isothermal annealing within this decollement numerical simulations based on conductive heat loss concepts fail to resolve the cooling history quantified through relaxation geospeedometry for the investigated flows the effects of vesiculation and thermal annealing on the cooling behavior of the clastogenic flows across the glass transition are discussed in the light of these new data in addition viscometric data on these phonolites are used to correlate the known cooling rates to viscosities at the glass transition

alluvial sandstone composition and paleoclimate ii authigenic mineralogy abstract various empirical and theoretical arguments suggest that early formed cement in sandstone is a product of meteoric water whose chemistry is controlled by climate the nature and distribution of early silicate cement in gondwana fountain and cutler sandstone support this supposition sandstones from all three units have experienced a broadly similar diagenetic history characterized by two stages of authigenesis stage i was typified by neomorphic development of kaolinite chlorite smectite quartz and additionally in the cutler formation laumontite stage ii was dominated by replacement reactions involving the production mostly of illite iron oxide carbonate minerals and mostly in the gondwana sandstone a second generation of quartz thermodynamic relations hydrologic constraints and radiometric dating of the late stage illite indicate that early authigenesis took place within a few million years of deposition at burial depths measured in hundreds of meters consequently the nature of the silicate cement was a function of the groundwater chemistry as controlled by climate during times of relative aridity ionic concentration of the groundwater was high and high proportions of smectite chlorite and more rarely laumontite formed such was the case in petrofacies i iv v of the gondwana supergroup for a definition of gondwana petrofacies see part i of this study in the cutler fm and in the upper 150 m of the fountain fm during times of high precipitation pore water was dilute which promoted authigen c formation of kaolinite and quartz this is represented by sandstones in petrofacies ii and vi of the gondwana and by sandstones in the lower 200 m of the fountain fm illite is especially abundant as a pseudomorphic replacement of kaolinite in the older gondwana sandstones illitization apparently began at burial depths of about 1 600 m at a temperature of about 75 c illite is not common in the cutler formation and is present only in subordinate amounts in the fountain formation from the study area the 18o values of early clay cement in the gondwana sandstones range systematically from base to top from 5 00 to 13 20 the systematic variation in 18o value of gondwana clay reflects the gradual migratory drift of the gondwana harm toward lower latitudes through time average 18o values for cutler cement 13 23 and fountain cement 19 82 are greater than the analogous values for gondwana cements this is consistent with the lower latitude setting of deposition for the cutler and fountain relative to the latitudinal location of the gondwana basins however the values are anomalously lower than what have been observed in modern day neoformed clays in weathering profiles from low latitudes

solidification and morphology of submarine lavas a dependence on extrusion rate the results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity the experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter the ratio of the time taken for the surface to solidify and a time scale for lateral flow for submarine basalts a solution of the cooling problem which is dominated by conduction in the lava but convective heat transfer in the water and estimates of lava viscosities place this parameter within the empirically determined pillowing regime over a wide range of extrusion rates this result is consistent with the observation that pillow basalts are the most common products of submarine eruptions smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusions of basaltic magma still higher eruption rates in regions of low topographic relief may produce submarine lava lakes minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type

the role of external water on rapid cooling and fragmentation of magma abstract the cooling rate of magma in the presence of external water during phreatomagmatic and submarine eruptions is one of the key parameters governing non explosive to explosive magma fragmentation and eruption transitions but remains poorly constrained combining results from laboratory experiments with realistic eruptive temperatures of magma cooling in ambient water of variable temperatures and numerical modeling of transient heat transfer we find that magma to water heat flux can be up to 4 10 6 w m 2 the experiments exhibit two distinct water boiling regimes a film boiling regime defined by the presence of a coherent water vapor film between magma surface and ambient water and a nucleate boiling regime below a critical magma surface temperature known as the leidenfrost temperature where the vapor film breaks and numerous bubbles form at the magma water interface in general the vapor film was stable in our experiments for time scales of 5 s indicating that this might be a limiting factor in pre explosion magma water mixing for energetic molten fuel coolant interaction and explosive volcanic eruptions the time scale of vapor film stability increases and the leidenfrost temperature 1223 to 948 k decreases with increasing water temperature 276 to 366 k we show that for the empirically obtained large heat flux to external water the cooling rate of magma can reach up to 106 k s 1 at length scales of few microns thus magma may undergo fine fragmentation due to quench induced large thermal stresses our experimental and modeling results demonstrate that the time scales of various water boiling regimes and erupting magma and ambient water temperatures determine the magma to water heat transfer rates which in turn determine the transition to explosivity under subaqueous eruption conditions

evaluation of a relaxation geospeedometer for volcanic glasses abstract the cooling of silicate melts influences the character of volcanic processes primarily through the effect of temperature on melt viscosity but also through the derivative thermal properties expansivity and heat capacity if the cooling rates of volcanic facies can be established then the undoubtedly complex processes of erupting cooling and degassing magmas can be more readily understood the frozen structure of every glass volcanic or synthetic is influenced by the previous cooling history moreover the relaxation of the glass structure back to equilibrium during reheating across the glass transition is also dependent on the quenched in structure and thus can be used to determine the cooling rate history in this study differential scanning calorimetry dsc measurements have been used to determine the enthalpic relaxation of four volcanic glasses each glass has been heated at known heating rates in the calorimeter to temperatures above the glass transition interval the first heating of the glass involves the relaxation of the structure frozen in during the volcanic cooling subsequent controlled heating and cooling in the calorimeter enables the determination of a set of kinetic parameters which can be used to model the heat capacity curves by modeling the transient values of heat capacity across the glass transition interval the relaxation of enthalpy and the volcanic cooling rate across the glass transition interval can be obtained from our study we can demonstrate four different cooling rates for volcanic glasses over a range of three orders of magnitude from 4 c min 1 to 2 c day 1 we propose that the enthalpic relaxation of silicate melts can be applied as a geospeedometer to the study of volcanic rocks from a variety of occurrences

na k ion exchange reaction between rhyolitic glass and na k c1 aqueous solution under hydrothermal conditions abstract hydrothermal experiments on ion exchange reactions were carried out using synthetic and natural rhyolitic glasses and na k cl aqueous solution at 200 300 c and 1000 bars the rhyolitic glass did not crystallize during the reaction even under hydrothermal conditions and it behaved as a na k ion exchanger the na k ion exchange properties of the glass were strongly influenced by its thermal history quenched glass preferentially fixed k rather than na and glass obtained by slow cooling showed the opposite trend the present experimental results show clearly that glass as well as minerals can control the composition of the coexisting aqueous solution in hydrothermal systems the present results also suggest that the chemical composition of coastal thermal waters in japan is controlled by the two stage episode of reaction between acidic volcanic rocks and seawater

high and highly variable cooling rates during pyroclastic eruptions on axial seamount juan de fuca ridge abstract we present a calorimetric analysis of pyroclastic glasses and glassy sheet lava flow crusts collected on axial seamount juan de fuca ridge ne pacific ocean at a water depth of about 1400 m the pyroclastic glasses subdivided into thin limu o pele fragments and angular blocky clasts were retrieved from various stratigraphic horizons of volcaniclastic deposits on the upper flanks of the volcanic edifice each analysed pyroclastic sample consists of a single type of fragment from one individual horizon the heat capacity c p was measured via differential scanning calorimetry dsc and analysed using relaxation geospeedometry to obtain the natural cooling rate across the glass transition the limu o pele samples 1 mm grain size fraction and angular fragments 0 5 mm grain size fraction exhibit cooling rates of 10 4 3 to 10 6 0 k s 1 and 10 3 9 to 10 5 1 k s 1 respectively a coarser grain size fraction 2 mm for limu o pele and 1 mm for the angular clasts yields cooling rates at the order of 10 3 7 k s 1 the range of cooling rates determined for the different pyroclastic deposits presumably relates to the size or intensity of the individual eruptions the outer glassy crusts of the sheet lava flows were naturally quenched at rates between 63 k s 1 and 10 3 k s 1 by comparing our results with published data on the very slow quenching of lava flow crusts we suggest that 1 fragmentation and cooling appear to be coupled dynamically and 2 ductile deformation upon the onset of cooling is restricted due to the rapid increase in viscosity lastly we suggest that thermally buoyant plumes that may arise from rapid heat transfer efficiently separate clasts based on their capability to rise within the plume and as they subsequently settle from it

the equivalence of enthalpy and shear stress relaxation in rhyolitic obsidians and quantification of the liquid glass transition in volcanic processes abstract the relaxation of enthalpy and shear stress has been investigated for six silicic volcanic obsidians calc alkaline rhyolitic obsidians from ben lomond dome new zealand erevan dry fountain armenia and little glass butte usa peralkaline obsidians from mayor island new zealand and eburru kenya and a macusanite obsidian from se peru the temperature dependences of enthalpy and shear stress relaxation are obtained from the dependence of the calorimetric heat capacity peak temperature on heating rate and the dependence of shear viscosity on temperature respectively both processes enthalpy relaxation and shear stress relaxation can be approximated to be arrhenian in the investigated temperature ranges relevant to volcanological processes activation energies derived for enthalpy and shear stress relaxation for each sample are equal this equality permits the calculation of viscosity at the glass transition as a function of cooling rate of a volcanic melt the relationship between viscosity at the glass transition and the cooling rate is given by log10 s at tg k log10 q where s the shear viscosity at the glass transition q is the cooling rate in c s 1 and k is a constant the six melt compositions investigated here exhibit a value of k 10 49 0 31 for the modeling of volcanic processes this equation allows the prediction of the viscosity at the glass transition temperature for a given value of cooling rate taken together with the maxwell relation an effective relaxation time can be obtained for the cooling rate prediction of the glass transition temperature permits the allotment of temperature ranges for the liquid and glassy segments of the cooling history of the volcanic melt and thus for the correct assignment of glassy and liquid values of the derivative thermodynamic properties such as expansivity and heat capacity in thermodynamic modeling of late stage volcanic processes

cooling process recorded in subglacially erupted rhyolite glasses rapid quenching thermal buffering and the formation of meltwater the thermal histories of two subglacial rhyolite glasses from torfajokull complex of south central iceland have been determined from changes in the relaxation of enthalpy in the calorimetric glass transition interval heat capacity measurements of bulk glass samples from rau ufossafjoll sample number js 1 1 and blahnukur sample number js 2 1 by differential scanning calorimetry show marked differences in the temperature of the onset of glass transition tg on reheating the average tg is 750 k for js 1 1 whereas it is 850 k for js 2 1 these differences in the onset of tg are related to quench rate through considerations of the activation energy and timescales for structural relaxation modeled using the kohlrausch williams watt function multiple glass samples from the two torfajokull locations recover different average values and distributions of a fictive temperature t f which we interpret in terms of differences in the thermal histories of the glasses in both glass samples the range of fictive temperatures and by implication apparent cooling rates is lower than those estimated for a glass rapidly quenched by contact with cold glacial melt water and requires that the glass was annealed at temperatures in the glass transition interval associated with relaxation times of the order of 1000 10 000 s the complex cooling histories of the torfajokull samples show that the products of subglacial eruptions may be held at elevated temperatures for several hours and as a result may drive vigorous convection in the ice bound vaults above erupting rhyolite deposits

a microstructural investigation of osaka bay clay the impact of microfossils on its mechanical behaviour a recent microstructural investigation of osaka bay clay sediments has revealed the presence of abundant microfossils particularly in the marine layers which appear to influence directly the micr

the water retention properties of a natural unsaturated loess from northern france the water retention properties of a natural loess from northern france were investigated on intact block samples that were excavated along a high speed train line tgv that experienced stability problems during heavy rain episodes suction measurements were made by using the filter paper method and an in house constructed high capacity tensiometer hct so as to determine the water retention curve of the loess the results showed that an alternative approach using a previously wetted filter paper could fruitfully be used with suction values reasonably compatible with the hct measurements the water retention curve obtained exhibited a peculiar form with no hysteresis observed around the natural water content 14 4 and two hysteresis loops on both the wet and dry sides of the curve it is hypothesised that this zone with no hysteresis corresponds to the natural variations of the water content under seasonal changes providing a range of natural suction between 20 and 80 kpa and it is suggested that th

study of the structure of a sensitive champlain clay and of its evolution during consolidation scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity champlain clay the clay structure is observed firstly on intact remolded and oven dried soils and secondly on soils consolidated at various levels in one dimensional compression both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra aggregate porosity remolding affects interaggregate links but does not destroy aggregates the observation of clay structure at various levels of one dimensional compression shows that the collapse of the structure is progressive the largest interaggregate pores being the first affected as the consolidation proceeds smaller and smaller pores are affected for a given pressure increment only the largest existing pores are affected a structure anisotropy has been seen to develop with increasing compression the scanning electron microscope and the me

biomarker signatures of permian gondwana coals from india and their palaeobotanical significance abstract coal samples belonging to the lower permian barakar formation and the upper permian raniganj formation collected from damodar valley basin of eastern india have been analysed for understanding their organic geochemical characteristics using rock eval pyrolysis gas chromatography mass spectrometry gc ms and comprehensive two dimensional gas chromatography coupled with time of flight mass spectrometry gc gc tofms the rock eval pyrolysis parameters suggest that the coals from both the formations contain a mixture of type ii and type iii kerogen the rock eval tmax values of the analysed coals vary from 417 to 451 c n alkanes ranging from c12 to c31 predominate the aliphatic hydrocarbons present in the coal extracts the carbon preference indices cpi as well as the odd to even preference oep values of the n alkanes are 1 suggesting input from higher vascular land plants c29 steranes predominate over c27 and c28 steranes which corroborates contribution from terrestrial higher plants aliphatic diterpanes like ent beyerane isopimarane abietane phyllocladanes and ent kaurane as well as aromatic diterpanes like simonellite bisnorsimonellite retene methylretenes and tetrahydroretene which are mainly known to originate from conifers are detected in the studied coals the lower gondwana floral assemblage of peninsular india is mainly represented by glossopteris flora pteridospermatophyta however some primitive conifers have also been reported from this succession we propose that the diterpanes detected in the studied coals were possibly derived from the primitive conifers this implies that the biosynthetic pathways to produce these diterpanes had evolved in the gondwana flora during the permian period

effects of thermal maturity on biomarker distributions in gondwana coals from the satpura and damodar valley basins india abstract organic geochemistry of gondwana coals especially the distribution of molecular fossils or biomarkers is not well constrained throughout the world in this study we have therefore evaluated biomarker signatures along with bulk organic matter and petrographic characteristics in coal samples collected from two gondwana basins in india satpura basin kanhan coalfield and damodar valley basin jharia coalfield from both coalfields the samples were collected from the lower permian barakar formation which is one of the major coal bearing strata in india a significant variation in thermal maturity levels in the samples is indicated by rock eval pyrolysis and petrographic analysis with the kanhan samples generally belonging to immature to early mature stage while the jharia samples display characteristics of overmature coals this variation in the thermal maturity strongly affects the biomarker distributions especially the terpenoids hopanes and steranes were considerably degraded due to thermal maturation and were below detection limit in the overmature samples presence of aliphatic diterpanes ent 16 h kaurane 16 h phyllocladane as well as aromatic diterpanes retene methylretenes tetrahydroretene simonellite and bisnorsimonellite in low maturity samples indicate terrestrial input possibly from the primitive conifers however the aliphatic and aromatic diterpanes were below detection limit in overmature samples making it difficult to infer their source distributions of polycyclic aromatic hydrocarbons pahs are also controlled by thermal maturity levels as evident from difference in pah ratios in the low and high maturity samples

cooling rate effects on paleointensity estimates in submarine basaltic glass and implications for dating young flows 1 cooling rate effects on the intensity of thermoremanent magnetization trm have been well documented in ceramics in that case laboratory cooling is generally more rapid than the initial cooling leading to an overestimate of the paleofield by 5 10 in thellier type paleointensity experiments the reverse scenario however has never been tested we examine the effects of cooling rate on paleointensity estimates from rapidly quenched submarine basaltic glass sbg samples from 13 sites at 17 30 18 30 s on the east pacific rise absolute cooling rates determined by relaxation geospeedometry at five of these sites range from 10 to 330 c min 1 at the glass transition 650 c over the dominant range of remanence blocking temperatures 200 400 c the natural cooling rates are approximately equal to or slightly slower than the laboratory cooling rates during the thellier experiment these results suggest that while the cooling rate effect might introduce some within site scatter it should not result in a systematic bias in paleointensity from sbg paleointensity estimates from the 15 sites range from 29 to 59 t with an average standard error of 1 t comparison with models of geomagnetic field intensity variations at the site indicate the youngest group of samples is very recent indistinguishable from present day and the oldest is at least 500 and probably several thousand years old these age estimates are consistent with available radiometric ages and geologic observations

felsic fire fountaining beneath archean seas pyroclastic deposits of the 2730 ma hunter mine group quebec canada abstract the lapilli tuff breccias ltb 1 and ltb 2 of the archean hunter mine group in the south central part of the abitibi greenstone belt are inferred to be the product of subaqueous lava fountaining intercalated sub wave base iron formations interstratified turbiditic tuffs the absence of wave induced sedimentary structures and the stratigraphic position of lapilli tuff breccias beneath basaltic komatiites support this contention a complete eruptive sequence shows a tripartite division into a massive breccia b stratified lapilli tuff and c turbiditic tuff lapilli tuff division the massive breccia division is characterized by clusters of isolated and compressed irregular shaped clasts inferred to be deposited directly from the hot magmatic lava fountain abundant vesicular pyroclasts with a vesicle content of up to 60 exhibit locally coalescing vesicles indicating bubble nucleation prior to eruption the prevalence of irregular to amoeboid clast shapes suggests transport from the vent in a steamy rich high density current to the site under a self generated steam cupola ubiquitous subequant lapilli size pyroclasts of the stratified lapilli tuff division suggest that significant ingress of water into the fountain changed the prevalent fragmentation process from magmatic to hydrovolcanic the turbiditic tuff lapilli tuff division composed of pumice lithic fragments and vitric ash is envisaged to have formed by gravitational collapse of a subaqueous turbulent eruptive plume this type of eruptive mechanism constituted a minor but important process of volcanic construction on the ocean floor during the archean and possibly during incipient arc and backarc formation in modern day settings

ageing effects in a compacted bentonite a microstructure approach it is suspected that the as compacted state of heavily compacted clays used as possible engineered barriers for nuclear waste disposal is time dependent and that further change may occur in the material even at constant water content and density this paper presents an investigation of the time dependent microstructure changes of an mx80 clay bentonite compacted at various dry densities and water contents microstructure investigation is based on mercury intrusion pore size distribution measurements and scanning electron microscopy sem results obtained by other researchers by using x ray diffraction at low angles are also used statically compacted samples of mx80 were kept at constant volume and water content for various periods of time 1 30 and 90 days prior to mercury intrusion and sem micro structure investigation a significant change in micro structure with time was observed characterised by a decrease in the inter aggregate porosity and an increase in the very thin porosity not intruded by

proprietes caracteristiques des argiles de l est du canada the compilation of numerous geotechnical data has allowed the definition of the main physical mechanical and hydraulic properties of marine and lacustrine clays of eastern canada as well as the establishment of correlations between some of these properties the possible uses of these correlations are described this study shows that the clays of eastern canada exhibit a behaviour similar to that of other clays but that they are characterized by a higher degree of structuration keywords physical properties mechanical properties hydraulic properties clays canada correlations journal translation

hyaloclastite fragmentation below the glass transition an example from el barronal submarine volcanic complex spain this research has been funded by projects cgl2005 03511 bte hi2006 0073 prin2009 prin 2009h37m59 and prin 2010 11 2010tt22sc and 2010tt22sc 003

recent hydrothermal explosion craters in an old hyaloclastite flow central iceland abstract hundreds of small diameter 2 50 m hydrothermal explosion craters are dispersed across the top plateau of a hyaloclastite ridge in central iceland the craters are undisturbed by erosion and must be of recent age the ridge dyngjufjoll ytri is a tectonic horst separated from the dyngjufjoll volcanic center and the askja caldera by a narrow graben the ridge is 20 km by 6 km with a flat top partly covered with glacial sediments and air fall tephra it is composed of two major volcanic units a lower hyaloclastite flow and an upper complex series containing pillow lavas air fall and surge tephra deposits and water lain sediments large max 9 m diameter cylindrical gas pipes coated with calcite are locally exposed in the hyaloclastite flow evidence suggests that volcanism contributing to the formation of the ridge was long extinct when its surface was broken by the hydrothermal explosions the elevated position of the ridge and its narrow form make unlikely the existence of a long lived hydrothermal system this is also borne out by the absence of intense thermal alteration of the material blown out in the explosions the ridge is surrounded by postglacial lavas one of these lavas issued from a fissure with the same strike as the ridge that terminates in a small crater at the base of its southern slope it is suggested that the fissure continues as an intrusion into the basal hyaloclastite flow where water in gas pipes of the hyaloclastite was converted into high pressure steam that exploded through the overlying unconsolidated formations

gondwana lithostratigraphy of peninsular india abstract the controversy regarding the stratigraphic interpretation of the indian gondwana succession in the peninsular basins has continued for more than a century with the exception of the damodar and satpura basins while the stratigraphic reconstruction in damodar and satpur was based on the order of superposition of strata elsewhere the relative ages were based on paleontological evidence that disregarded various physical criteria including the order of superposition overlying the precambrian crystalline basement the gondwana succession of late permian to early jurassic age can be classified into four sedimentary facies a glaciogenic facies facies a a coal bearing facies facies b a red shale sandstone facies facies c and a hill forming coarse sandstone conglomeratic facies facies d the stratigraphic order of these four facies in ascending order from facies a at the bottom to facies d at the top is well established in the damodar and satpura regions in both areas facies d overlies the underlying older sediments as well as the crystalline basement with a pronounced unconformity however in the pranhita godavari and son basins and elsewhere the stratigraphic relations between facies b facies c and facies d are controversial one such enigma is where the sequence of facies c and facies d are repeated several times in the geological column this interpretation contrasts with the supposed genesis of climatically controlled lithic fill in gondwana basins overturning the standard stratigraphic relation between facies c and facies d was based on fragmentary fossil evidence where the lower gondwana flora seems to be present in upper gondwana rocks turning the stratigraphy upside down was done without establishing the order of superposition between strata throughout the 20 th century most stratigraphers working in the pranhita godavari and son basins worked within a fossil based stratigraphic paradigm this resulted in still more confusion the magnitude of which can be appreciated as one browses through various interpretations presented in innumerable publications in this paper we attempt to offer a lithostratigraphic interpretation of the peninsular gondwana basins based only on physical criteria such as lithological association their petrographical characteristics and the most fundamental tool of stratigraphy the order of superposition

the thermal history of a spatter fed lava flow the 8 ka pantellerite flow of mayor island new zealand the thermal history of the 8 ka spatter fed lava flow of mayor island new zealand has been investigated via relaxation geospeedometry cooling rates extant during the vitrification of the clastogenic pantellerite flow have been quantified cooling rates modelled for two obsidian layers at the top and the base of the flow vary over four orders of magnitude the flow base defined by a lower obsidian layer shows a gradual increase in cooling rates from 0 00072 k min adjacent to the crystalline core of the flow to 0 017 k min at the contact to a basal crumble breccia cooling rates of flow ridges formed by an upper obsidian layer vary between 0 001 and 6 k min based on field observation and thermal modelling cooling rates of kelvins to tens of kelvins per day for both upper and lower obsidians are difficult to interpret as simple cooling processes instead we propose a thermal history involving thermal annealing as an alternative explanation for these slow effective cooling rates such thermal annealing appears to have facilitated welding and rheomorphism of the spatter deposit leading to the development of a coherent lava sheet based on the results obtained here we present a quantitative scenario of the thermal history during the final stages of flow emplacement as a contribution to understanding the rheology of rheomorphic spatter deposits associated with explosive peralkaline rhyolitic volcanism and briefly address the hazard potential of such deposits

lava balloons peculiar products of basaltic submarine eruptions between december 1998 and april 2001 a submarine basaltic eruption occurred west of terceira island azores portugal in water depths between 300 and 1 000 m physical evidence for the eruption was provided by the periodic occurrence of hot lava balloons floating on the sea surface the balloons consisted of a large gas filled cavity surrounded by a thin shell a few centimetres thick the shells of the collected balloons are composed of two layers termed the outer layer and the inner layer defined by different bubble number density bubble sizes and crystal content the inner layer is further divided into three sublayers defined by more subtle differences in vesicularity the outer layer is glassy golden coloured and highly porous it shows signs of fluidal deformation and late stage extension cracks interstitial glass contains 0 29 wt h2o and co2 is below detection melt inclusions contain up to 1 18 wt h2o and 1 500 ppm co2 from different inclusions cooling rates of the outermost glass of the outer layer are found to be as high as 1 259 k s during ascent of low viscosity magma to the ocean floor volatiles dominated by co2 exsolved from the magma melt crystals the buoyancy of the vapour phase that accumulated below a thin crust on lava ponded at the vent caused bulging and ultimately cracking of the crust this allowed large bubbles central cavity surrounded by a film of vesicular magma balloon shell to leak into the water column on contact with the seawater the outermost part of the outer layer of the shell hyperquenched if an entirely closed shell was produced during detachment the trapped gas inside allowed buoyant rise only balloons with the right balance of physical properties e g size and bulk density rose all the way to the sea surface

quantification of submarine lava flow morphology through analog experiments we developed a technique for determining paleoeffusion rates and emplacement times for submarine lava flows using observations of flow morphology and estimates of eruption volume eruption temperature lava viscosity and preflow topography using laboratory simulations and correlating these results with sea floor observations four submarine lava flow morphologies are considered to be diagnostic of specific effusion rates jumbled folded and lineated sheets and striated pillows we applied this approach to the coaxial flow emplaced in less than 14 days on the juan de fuca ridge in early summer 1993 and we calculated an effusion rate of 100 m3 s giving an emplacement time of 10 days

cooling rates of hyaloclastites applications of relaxation geospeedometry to undersea volcanic deposits glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits we found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0 15 k min 1 the most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples the very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition because of the onset of crystallization instead they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures the thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models

pore size distribution of a compacted silty soil after compaction saturation and loading soil microstructure is an important feature that controls soil behaviour at the macroscale this microstructure depends on the sample preparation method and evolves during saturation and loading this paper investigates the effects of compaction water content drying techniques adopted prior to performing porosimetry saturation and loading on the evolution of the microstructure of a silty soil mercury intrusion porosimetry is used to obtain the pore size distribution at different states of soil presenting single and double porosity it is observed that in presence of aggregates obtained from a compaction on the dry side of optimum the bimodal pore size distribution is not significantly affected by the saturation process at zero stress this feature of behaviour is quite specific to low plasticity silty soil conversely loading under saturated conditions has a more significant effect on the pore size distribution this bimodal distribution converges into a single mode of pore size when the stress is

gondwana lithostratigraphy of peninsular india reply see pradip dutta 2002 gondwana research gnl v 5 pp 540 553

incorporation of seawater into mid ocean ridge lava flows during emplacement evidence for the interaction between seawater and lava during emplacement on the deep seafloor can be observed in solidified flows at a variety of scales including rapid quenching of their outer crusts and the formation of lava pillars through the body of the flow recently an additional interaction incorporation of heated seawater vapor into the body of a flow has been proposed large voids and vesicles beneath the surface crusts of mid ocean ridge crest lobate and sheet lava flows and lava drips found within those cavities have been cited as evidence for this interaction the voids resulting from this interaction contribute to the high porosity of the shallow ocean crust and play an important role in crustal permeability and hydrothermal circulation at mid ocean ridges and thus it is important to understand their origin we analyze lava samples from the fast spreading east pacific rise and intermediate spreading galapagos spreading center to characterize this process identify the source of the vapor and investigate the implications this would have on submarine lava flow dynamics we find that lava samples that have interacted with a vapor have a zone of increased vesicularity on the underside of the lava crust and a coating of precipitate minerals i e crystal fringe that are distinct in form and composition from those crystallized from the melt we use thermochemical modeling to simulate the reaction between the lava and a vapor and find that only with seawater can we reproduce the phase assemblage we observe within the crystal fringes present in the samples model results suggest that large scale contamination of the lava by mass exchange with the vapor is unlikely but we observe local enrichment of the lava in cl resulting from the incorporation of a brine phase separated from the seawater we suggest that high eruption rates are necessary for seawater incorporation to occur but the mechanism by which seawater enters the flow has yet to be resolved a persistent vapor phase may be important in inhibiting the collapse of lava flow roofs during natural waxing and waning of lava levels during emplacement allowing lava pathways to be maintained during long lived eruptions in addition we illustrate the potential for a persistent vapor layer to increase local flow rates within submarine flows by up to a factor of three thereby influencing how lava is distributed across the ridge crest

measurements of the cooling at the base of pahoehoe flows temperature measurements were made in august and october of 1994 at the base of small active pahoehoe flow lobes on kilauea volcano hawai i surprisingly after about 2 minutes of initial rapid cooling the basal temperatures increased significantly before resuming a slower cooling trend the recorded temperatures are also warmer than those predicted by simple conductive cooling models preliminary calculations suggest that these observations can be explained by the insulating effect of microfractures in the underlying flow and the kinetics of crystallization the initial cooling may be rapid enough to super cool the lava such that the onset of crystallization is delayed when crystallization does begin it is initially rapid releasing sufficient latent heat to re heat the lava as the system equilibrates the flow resumes a slow cooling

contrasting siliciclastic evaporite strata in subsurface and outcrop an example from the permian nippewalla group of kansas u s a abstract geologists tend to expect that rocks as they appear in outcrop are a very good approximation of the same strata in the subsurface but this is not the case in mixed siliciclastic evaporite units strata that contain both a siliciclastic and an evaporite mineral component distinct differences in lithologic and stratigraphic descriptions of ancient siliciclastic evaporite strata exist between outcrop and core these differences present challenges in stratigraphic nomenclature lithologic correlation age determinations and interpretations about past depositional environments diagenetic history and paleoclimate an example of siliciclastic evaporite strata is the middle permian to early triassic gypsum and or anhydrite hereby referred to as gypsum anhydrite and halite bearing red beds throughout the midcontinent of north america and equivalent strata from other pangean deposits here we use core and field observations of the middle permian nippewalla group in kansas to show the range of similarities and differences in lithologies and thicknesses of specific lithofacies in outcrop and at various depths for example the displacive halite lithology consisting of red mudstones dominated by randomly oriented halite crystals is abundant in cores and interpreted as saline mudflat deposits the outcrop counterpart is less common friable massive red mudstones with some gypsum anhydrite pseudomorphs after displacive halite crystals we interpret these lithologic differences of this saline mudflat lithofacies as the result of excellent preservation of buried displacive halite and late stage dissolution of near surface halite additionally bedded halite and intergranular halite cements in siltstones and sandstones are also vulnerable to late stage dissolution near the surface further modifying lithologies and thicknesses thickness of the nippewalla group in the amoco rebecca k bounds core of western kansas is 931 feet 284 meters thick but it is estimated to be only half as thick in the outcrop belt of south central kansas to estimate amount of rock lost to late stage dissolution we conducted dissolution experiments on displacive halite units from cores which resulted in 60 95 loss of rock thickness and mass due to dissolution of halite the unconsolidated red sediment resulting from these dissolution experiments compares favorably with much of the fine massive red siliciclastics that make up the greater part of the nippewalla group outcrops we propose that major lithologic differences resulting from near surface diagenetic processes must be expected in any evaporite bearing siliciclastic unit besides guiding correlation attempts between surface and subsurface this knowledge is vital for making accurate interpretations of depositional and diagenetic history of siliciclastic evaporite units

cooling rate variation in natural volcanic glasses from tenerife canary islands silicate melts form glasses in a variety of geological environments the relaxation equilibration of the frozen glass structure provides a means of investigating the quench rates of natural glasses and this cooling history provides an important constraint for models of melt dynamics phonolite glasses from the central volcanic edifice of tenerife canary islands indicate a range of five orders of magnitude cooling rate determined by modeling the relaxation of the structure dependent property enthalpy h across the glass transition the relaxation of enthalpy is determined by heat capacity c p h t measurement of natural glass samples by differential scanning calorimetry dsc upon heating the heat capacity curve in the vicinity of the glass transition has a geometry characteristic of the previous cooling rate a series of thermal treatments applied to each individual sample results in a set of sample specific parameters which are used to model the heat capacity curve of the naturally cooled glass the cooling rate is then derived the equivalence of shear and enthalpic relaxation enables the relaxation of enthalpy for these volcanic samples to be described by a general term for the evolution of fictive temperature quench rates for thirty one glasses are calculated to be within the range 10 c s 1 to 7 c per day the cooling rates quoted are linear approximations across the glass transition within different volcanic facies cooling rates depend on several factors the most rapidly cooled glasses occur where samples lose heat by radiation from the surface our analyses indicate that in certain environments a natural annealing process results in slow quench rates this is interpreted as either a slow initial cooling process or the reheating of a glass to an annealing temperature within the glass transition interval the latter results in relaxation to a lower temperature structure controls on these processes include the initial temperature and dissipation of thermal energy from the volcanic body our results are consistent with an influence of volatiles on quench rates in volcanic bombs where glass adjacent to vesicular layers is relatively rapidly quenched we interpret this as a rapid quench rate frozen into the glass resulting from a change in viscosity due to volatile degassing in lava flows the conduction of heat from the hot flow interior controls the cooling process and diminishes the effect of volatile exsolution relaxation geospeedometry can be applied to glass samples from a variety of geological environments where cooling rates cannot be measured directly such measurements provide a means of determining cooling rates for a variety of volcanic processes an independent calibration for existing temperature and time data and a means for testing cooling rate dependent models

gondwana lithostratigraphy of peninsular india comment see prodip dutta 2002 gondwana research gnl v 5 p p 540 553

feldspar alteration and diagenetic characteristics of the parsora sandstones son basin india abstract moderate to poorly sorted immature parsora sandstones rich in k feldspar show much of the feldspar during early diagenesis transformed to kaolinite after prolonged interaction with acidic pore solutions the kaolinitic epimatrix formed and was later partially or wholly converted as an orthomatrix producing chert phyllosilicate assemblage ferric oxide bleached biotite kaolinite and quartz cement denote an oxy acidic early diagenetic environment late diagenesis involved neoformation of primary or secondary matrix illitisation of montmorillonite and muscovite authigenesis the high pressure temperature regime required for these transitions resulted from tectonic activity during triassic jurassic times carbonate chlorite appeared late in the sediments denoting an alkaline reducing condition at the late part of the diagenesis finally the secondary porosity developed through carbonate dissolution was later filled up with allochemical ferric iron cement receiving ions from the percolating meteoric water

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

effects of open and closed system oxidation on texture and magnetic response of remelted basaltic glass as part of an experimental and observational study of the magnetic response of submarine basaltic glass sbg we have examined using ion backscattering spectrometry rbs transmission and scanning electron microscopy energy dispersive x ray spectrometry and surface x ray diffraction the textures wrought by the controlled open and closed system oxidation of glasses prepared by the controlled environment remelting and quenching of natural sbg initial compositions with 9 wt feo were melted at 1430 c with the oxygen fugacity buffered at fayalite magnetite quartz melts were cooled at a rate of 200 c min 1 near the glass transition tg 680 c in open system experiments where chemical exchange is allowed to occur with the surrounding atmosphere polished pieces of glass were reheated to temperatures both below and above tg for times 1 5000 h undercooled melts were oxidized at 900 c and 1200 c for 18 and 20 h respectively rbs demonstrates unequivocally that the dynamics of open system oxidation involves the outward motion of network modifying cations oxidation results in formation of a fe ca and mg enriched surface layer that consists in part of ti free nanometer scale ferrites a divalent cation depleted layer is observed at depths 1 m specimens annealed oxidized above tg have magnetizations elevated by 1 2 orders of magnitude relative to the as quenched material this does not appear to be related to the surface oxidation quenched glass closed system i e no chemical exchange between sample and atmosphere exhibits very fine scale chemical heterogeneities that coarsen with time under an electron beam this metastable amorphous immiscibility is the potential source for the nucleation of ferrites with a wide range of ti contents ferrites not anticipated from an equilibrium analysis of the bulk basalt composition

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

behaviour of a sensitive marine sediment microstructural investigation the aim of this study is to characterise along various stress paths the microstructural evolution of a deep water marine sediment from the gulf of guinea gog results obtained at the macroscopic level have shown that the phenomenological behaviour of the gog sediment is explained by the properties of remoulded samples given by the isotropic and critical state lines and by the properties of the intact samples given by the damage evolution of the inter aggregate bonds microstructural investigations conducted by mercury intrusion porosimetry and scanning electron microscopy demonstrate that the volumetric strains measured at the macroscopic level come from inter aggregate pore variations associated with the degrading of the inter aggregate bonds the mechanism responsible for reorienting the particles appears to apply in the case of the remoulded sediment as for the natural sediment it is first necessary to increase the isotropic consolidation stress towards higher values in order to break the bonds between the aggregates before it becomes possible to activate the particle reorientation mechanism and thus approach the remoulded behaviour

effect of soil microstructure on the compressibility of natural singapore marine clay the effect of soil microstructure on the compressibility of natural singapore marine clay is studied in this paper it was found that natural singapore marine clay can sustain higher void ratio than reconstituted singapore marine clay at the same effective stress in one dimensional compression this difference is most noticeable between yield stress and two times the yield stress this void ratio difference is commonly attributed to soil microstructure and the decrease in this difference at higher stresses is attributed to progressive destructuration as a consequence of progressive destructuration the virgin compression curve is nonlinear and the compression index along the virgin compression range is variable which is only noticeable during the constant rate of strain consolidation test on high quality samples in the absence of high quality samples and constant rate of strain consolidation tests an empirical method is proposed to obtain a first order estimation of a nonlinear virgin compression cur

hyperquenched volcanic glass from loihi seamount hawaii abstract explosive submarine basaltic eruptions occurring in water depths of several kilometres commonly result in the formation of layered volcaniclastic deposits in order to quantify the cooling of such volcaniclastics we have identified and separated two types of glassy fragments from these deposits on loihi seamount 1 fine 30 80 m limu o pele bubble wall fragments and 2 coarser 0 8 1 2 mm dense angular fragments these pristine basaltic glasses have been subjected to differential scanning calorimetry dsc from room temperature up to temperatures above their glass transition heat capacity c p in j g 1 k 1 data reveal glassy and liquid regimes separated by clear hysteresis behaviour within the glass transition the transient c p in the glass transition interval exhibits a deep trough before the peak indicating very high cooling rates it is a classic feature of so called hyper quenching having been observed in dsc experiments on glasses produced using the splat quench d b dingwell p courtial d giordano and a r l nichols viscosity of peridotite liquid earth and planetary science letters 226 1 2 127 138 2004 and cascade fibre spinning y z yue j d christiansen and s l jensen determination of the fictive temperature for a hyperquenched glass chemical physics letters 357 1 2 20 24 2002 techniques the trough is deepest for the limu o pele fragments energy matching methods developed for the estimation of cooling rates for such glasses yield a rate of 10 5 31 k s 1 for the cooling of the fine sieve fraction of limu glass on the sea floor at loihi thus limu o pele volcaniclastics believed to be formed during mild submarine pyroclastic eruptions have experienced the fastest cooling of any natural volcanic glass measured to date such extreme cooling rates are likely to impact on many chemical and physical aspects of the stability of these glasses on the sea floor as well as their use as proxies for field variables of the earth s physical state and as monitors of the efficiency of chemical lithosphere hydrosphere exchange

a microstructure approach to the sensitivity and compressibility of some eastern canada sensitive clays investigation of micro macro relationships in soils most often concerns granular soils in which both the elemental unit the grain and the physical laws governing inter grain interactions appear to be better known the situation is different for clays because the elementary unit and the inter unit interactions at the micro scale are more difficult to characterise in fine grained soils it has been shown that an intermediate level corresponding to the way clay and fine grained particles are arranged together had to be considered so as to link microscopic features to macroscopic behaviour an investigation of the change in microstructure during compression carried out some time ago on a sensitive clay from canada demonstrated that studying the changes in pore size distribution provides a satisfactory description of microstructure changes during compression the analysis is applied here to six other sensitive clays first a careful examination of the intact and remoulded microstructure is conducted in o

glass transition temperatures of natural hydrous melts a relationship with shear viscosity and implications for the welding process abstract glass transition temperatures tg have been determined for natural multicomponent melts using differential scanning calorimetry trachytic dacitic phonolitic and basaltic base compositions have been analysed over a range of water contents up to 3 75 wt for each sample tg has been obtained over a range of cooling heating rates using the extrapolated onset and the peak temperatures in heat capacity temperature curves tg of all compositions are strongly reduced by increasing water content particularly for the first 1 wt added base composition also has an effect with the lowest tg occurring in the peralkaline phonolite suite for all samples a clear dependence on the cooling heating rate has been recorded these results have been compared with rheological investigations on the same samples on the basis of the equivalence of the shear and enthalpic relaxation process timescales we provide a method to predict the shear viscosity at the glass transition for all the melts investigated in this study both dry and hydrous our determinations of tg provide a lower limit for the time temperature envelope that gives rise to densely welded deposits and constraints on their emplacement temperature furthermore by using the viscosity values predicted at the glass transition we suggest that welding processes may occur over timescales on the order of tens of seconds to tens of minutes at tg

no depth limit to hydrovolcanic limu o pele analysis of limu from lō ihi seamount hawai i deep sea limu o pele are shards of basaltic glass commonly described as bubble walls when first identified they were inferred to form in submarine fire fountains but were then reinterpreted as the products of hydrovolcanic volcanism formed when submarine lava flows entrapped and vaporised seawater limu discovered below the c 3 km critical depth of seawater where superheated water exists as a supercritical fluid instead of a vapour led to the hydrovolcanic model of limu o pele formation being discarded in favour of a magmatic co2 driven strombolian like model this revised magmatic mechanism has been widely accepted by the scientific community we describe a newly discovered limu o pele rich deposit at 1 052 mbsl on the northeast summit plateau region of l ihi seamount hawai i the limu at this site is concentrated in a chemically monomict ash lens interbedded with thin lava sheets that are separated from overlying volcaniclastic material by a discontinuity the geometry and geochemistry of the deposit provide compelling evidence for a hydrovolcanic sheet flow related origin the exceptional abundance and preservation of limu at this site allows 4 morphologic subtypes of limu thin film plateau border convex film and pele s hair to be identified and linked to portions of the isolated rupturing bubbles from which they are derived we extend our discussion to beyond this new l ihi deposit by including a review of limu o pele occurrences and thermodynamic considerations that demonstrate the hydrovolcanic model of limu formation to be more tenable than the magmatic model at all depths including below the critical depth of seawater

incipient melt segregation as preserved in subaqueous pyroclasts melt segregation is the extraction of residual melt from the rigid but permeable network of growing crystals with which it co evolved it is recognized as an effective mechanism of igneous differentiation that acts over many geologic time and length scales here we present evidence for rapid melt segregation in subaqueous basaltic pyroclasts segregation produced intravesicular extrusions i e partly hollow balloons of glass penetrating the walls of earlier formed vesicles set in a microcrystalline groundmass the segregation process can be described as a form of gas filter pressing where microlite crystallization produced local gradients in volatile supersaturation and vapor pressure that drove melt extrusion into adjacent vesicles unlike in previously described segregation features the structures presented here are shown to have formed after the extruded melt became enriched in fast diffusing h2o but before it became measurably enriched or depleted in slower diffusing major elements we show that melt segregation of this embryonic type must occur in seconds rather than in the days to centuries required for similar processes to occur in lava flows or magma chambers and that it occurs within the short time scales that characterize explosive fragmentation of basaltic melt

quantification of the pore structures of malan loess and the effects on loess permeability and environmental significance shaanxi province china an experimental study the pore microstructures of loess control the porosity and permeability of the loess affecting the patterns of groundwater flow and the transport of contaminants in the present study the pore microstructure of malan loess was investigated quantitatively in samples from five different loess layers specimens were examined via sem and pore microstructure parameters were determined using the digital image analysis method pore structures including pore area ratio par pore size distribution pore shape and pore morphology the effects of the pore structure on loess permeability and the environmental significance of these factors are discussed in this paper the results indicate that the samples of five loess layers in this study are considered to be porous soil according to both the par and porosity values the number of micropores small pores mesopores and macropores decreased significantly the differences in number were mainly due to the significant reduction in the number of round pores indicating that round pores tend to be small in terms of area micropores small pores mesopores and macropores were dominated by elongated and irregular pores the macro and mesopore structural characteristics of loess determined the transfer characteristics of groundwater and pollutants in the loess additionally the 62 area reduction in the area of elongated or irregular macro and mesopores and the decreasing connectivity from top to bottom layers caused by the deformation and destruction of the pores due to the overlying soil reduced the permeability and the water pollutant migration rate with depth

cooling rates of mid ocean ridge lava deduced from clinopyroxene spherulites abstract we present a compositional analysis of spherulites and their surrounding groundmass in basaltic andesite lava samples collected from the pacific antarctic ridge the spherulites consist of radiating dendritic branches of clinopyroxene and contain abundant vesicles that are stretched parallel to the branches stretched vesicles require that the spherulites grew when the groundmass was liquid and thus while it was hotter than its glass transition although chemical components incompatible in clinopyroxene should have been enriched in the melt by spherulite growth no compositional variations occur at a scale larger than the 10 m wide slit aperture used for laser ablation icp ms the absence of large scale gradients implies that the spherulites grew faster than the elements could diffuse 10 m because diffusion is temperature controlled cooling must have been rapid enough to prevent movement if the spherulites nucleated when the melt was at between 1380 and 1223 k i e undercooled by 0 to 157 k then the constant concentrations of li na and k the fastest diffusing elements analyzed require temperature to have cooled faster than 10 6 7 k min 1 if instead the spherulites nucleated at undercoolings of 357 to 465 k or as cold as 915 k equal to the glass transition temperature then the cooling rate could have been as slow as those inferred for glassy rinds on submarine lavas by relaxation geospeedometry at all possible cooling rates however the spherulites must have grown as fast as 10 3 5 m s 1 to reach their final sizes of 1 4 to 3 2 mm we speculate that the rapid growth resulted from low kinetic barriers to clinopyroxene growth in the basaltic andesite melt

lava bubble wall fragments formed by submarine hydrovolcanic explosions on lō ihi seamount and kīlauea volcano glassy bubble wall fragments morphologically similar to littoral limu o pele have been found in volcanic sands erupted on l ihi seamount and along the submarine east rift zone of k lauea volcano the limu o pele fragments are undegassed with respect to h2o and s and formed by mild steam explosions angular glass sand fragments apparently form at similar and greater depths by cooling contraction granulation the limu o pele fragments from l ihi seamount are dominantly tholeiitic basalt containing 6 25 7 25 mgo none of the limu o pele samples from l ihi seamount contains less than 5 57 mgo suggesting that higher viscosity magmas do not form lava bubbles the dissolved co2 and h2o contents of 7 of the limu o pele fragments indicate eruption at 1200 300 m depth 120 30 bar these pressures exceed that generally thought to limit steam explosions we conclude that hydrovolcanic eruptions are possible with appropriate pre mixing conditions at pressures as great as 120 bar