modeling strombolian eruptions of karymsky volcano kamchatka russia a model is proposed to explain temporal patterns of activity in a class of periodically exploding strombolian type andesite volcanoes these patterns include major events explosions which occur every 3 30 min and subsequent tremor with a typical period of 1 s this two periodic activity is thought to be caused by two distinct mechanisms of accumulation of the elastic energy in the moving magma column compressibility of the magma in the conduit and viscoelastic response of the almost solid magma plug on the top a release of the elastic energy occurs during a stick slip dynamic phase transition in a boundary layer along the walls of the conduit this phase transition is driven by the shear stress accumulated in the boundary layer the intrinsic hysteresis of this first order phase transition explains the long periods of inactivity in the explosion cycle temporal characteristics of the model are found to be qualitatively similar to the acoustic and seismic signals recorded at karymsky volcano in kamchatka

progressive infilling of a kimberlite pipe at diavik northwest territories canada insights from volcanic facies architecture textures and granulometry abstract processes responsible for the formation of crater facies kimberlite remain poorly understood because there are few occurrences of well preserved deposits new open pit exposures of the a154n kimberlite pipe at diavik in the lac de gras region of the northwest territories canada reveal well preserved crater facies deposits here we describe the geometries structures and componentry of deposits from the uppermost 130 m of the a154n pipe we then interpret the processes responsible for their emplacement on the basis of these characteristics the base of the section features a poorly sorted primary massive volcaniclastic kimberlite deposit mvk1 grading upward into a better sorted and weakly stratified volcaniclastic kimberlite deposit mvk2 which is itself overlain by 45 m of stratified volcaniclastic kimberlite svk the mvk svk contact is sharp and marks an abrupt transition from sustained eruption of pyroclastic kimberlite to episodic sedimentation from collapse of an unstable volcanic edifice into the open crater the svk deposit is overlain dis conformably by a poorly to well sorted diffusely bedded and graded pyroclastic kimberlite pk1 and pk2 that erupted from another younger kimberlite volcano the pk deposits show a variety of textures supporting a pyroclastic origin including vesiculated juvenile pyroclasts a grain and clast supported fabric and the absence of mud size particles in the matrix vertical clast size grading over 40 50 m and the absence of bedding in the pk2 suggest hydraulic sorting during en masse deposition of pyroclastic kimberlite into a deep water column granulometric analysis shows the pk2 deposit was originally transported as a pyroclastic density current that was sourced from one of the many adjacent pipes in the diavik area and inundated the a154n pipe these observations have implications for kimberlite volcanic processes and grade distribution

elastic reverse time migration elastic prestack reverse time finite difference migration of two component seismic surface data requires data extrapolation and application of an imaging condition data extrapolation involves synchronous driving of the vertical component and horizontal component finite difference meshes with the time reverse of the recorded vertical and horizontal traces respectively extrapolation uses the coupled elastic wave equation for variable velocity solved with a second order explicit finite difference scheme the imaging condition at any point in the grid is the one way traveltime from the source to that point elastic migrations of both synthetic test data and real two component common source gathers produce simpler images than acoustic migrations because of the coalescing of double reflections compressional waves and shear waves into single loci

discrimination of reworked pyroclastics from primary tephra fall tuffs a case study using kimberlites of fort a la corne saskatchewan canada reworked volcaniclastics are traditionally discriminated from primary tephra fall pyroclastics by an absence of features such as blanketing juvenile lapilli grain welding and poor sorting frequently these features are difficult to identify especially in small outcrops ancient or altered successions debris flows and surge deposits crystal rich volcaniclastics such as kimberlites have a large proportion of coarse euhedral crystals and abrasion leading to rounding can be recognised and classified with relative ease a petrographic method of discriminating reworked material has been devised based on the degree of grain roundness and is illustrated using volcaniclastic kimberlite from fort a la corne saskatchewan canada petrographic thin sections of samples at regular intervals throughout the borehole core and from a nearby crater facies kimberlite show that the percentages of rounded subrounded and euhedral grains define two distinct groupings the first group contains a higher percentage of euhedral grains and includes all the samples from the basal 4 8 m of the 14 1 m thick kimberlite section in borehole 004 and all of the crater facies tephra fall tuffs a second group contains more rounded subrounded and fragmental grains and includes all the data from the upper 6 3 m which are interpreted as reworked strata thus point counting concurs with hand sample interpretation and may be used as a verification tool in discriminating reworked pyroclastic sands from primary tephra fall tuffs

local vertical seismic profiling vsp elastic reverse time migration and migration resolution salt flank imaging with transmitted p to s waves to avoid the defocusing effects of propagating waves through salt and overburden with an inaccurate overburden velocity model we introduce a vertical seismic profiling vsp local elastic reverse time migration rtm method for salt flank imaging by transmitted p to s waves this method back projects the transmitted ps waves using a local velocity model around the well until they are in phase with the back projected pp waves at the salt boundaries the merits of this method are that it does not require the complex overburden and salt body velocities and it automatically accounts for source side statics in addition the method accounts for kinematic and dynamic effects including anisotropy absorption and all other unknown rock effects outside of this lo cal subsalt velocity model numerical tests on an elastic salt model and offset 2d vsp data in the gulf of mexico using a finite difference time domain staggered grid rtm scheme partly demonstrate the effectiveness of this method over interferometry

a study of clast size distribution ash deposition and fragmentation in a hawaiian style volcanic eruption ash deposits from hawaiian style eruptions are generally of small volume but are important in understanding the mechanisms of these eruptions an analysis of the ash deposit from the 1959 kilauea iki eruption of kilauea volcano is presented and the whole deposit grain size distribution for the eruption is calculated the grain size distribution is found to be heavily skewed towards the coarsest clast sizes and to differ considerably from size distributions for plinian deposits

subsidence breccias in kimberlite pipes an application of fractal analysis abstract a particular variety of volcanogenic country rock breccia is described a contact breccia that has been identified at venetia river ranch and wimbledon kimberlite pipes the contact breccia is clast supported with no juvenile kimberlite component has tightly packed angular fragments with occasional rounding of smaller particles and has a shear fabric dipping towards the center of each kimberlite pipe or volcanic event clasts have preferred orientations parallel to the fabric photographs of the breccia in the open pit face and measured data from drill core are analyzed specifically to quantify the clast size distributions and clast shapes by means of fractal analysis the fractal dimension is one means of characterizing the breccia because the dimension can be specific to a fragmentation mechanism clast size distribution fractal dimensions in the coarser particles greater than circa 3 cm range from greater than 3 for nonsheared breccia down to circa 2 3 for the sheared breccia breccia characterization based on this fractal analysis suggests that fragmentation occurred initially from confined high energy explosions followed by collapse and abrasion by subsequently gravity induced rockmass subsidence all studied contact breccias produced a distinctive fractal signature in the finer particles

beyond receiver functions passive source reverse time migration and inverse scattering of converted waves 1 we present a wave equation prestack depth migration to image crust and mantle structures using multi component earthquake data recorded at dense seismograph arrays transmittedp and swaves recorded on the surface are back propagated using an elastic wave equation solver the wave modes are separated after the reverse time continuation of the wavefield from the surface and subjected to a cross correlation type imaging condition forming an inverse scattering transform reverse time migration rtm does not make assumptions about the presence or properties of interfaces notably it does not assume that interfaces are locally horizontal with synthetic experiments and different background models we show that passive source rtm can reconstruct dipping and vertically offset interfaces even in the presence of complex wave phenomena such as caustics and point diffraction and that its performance is superior to traditional receiver function analysis e g common conversion point ccp stacking in complex geological environments

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

geology of the victor kimberlite attawapiskat northern ontario canada cross cutting and nested craters abstract the pipe shapes infill and emplacement processes of the attawapiskat kimberlites including victor contrast with most of the southern african kimberlite pipes the attawapiskat kimberlite pipes are formed by an overall two stage process of 1 pipe excavation without the development of a diatreme sensu stricto and 2 subsequent pipe infilling the victor kimberlite comprises two adjacent but separate pipes victor south and victor north the pipes are infilled with two contrasting textural types of kimberlite pyroclastic and hypabyssal like kimberlite victor south and much of victor north are composed of pyroclastic spinel carbonate kimberlites the main features of which are similar clast supported discrete macrocrystal and phenocrystal olivine grains pyroclastic juvenile lapilli mantle derived xenocrysts and minor country rock xenoliths are set in serpentine and carbonate matrices these partly bedded juvenile lapilli bearing olivine tuffs appear to have been formed by subaerial fire fountaining airfall processes the victor south pipe has a simple bowl like shape that flares from just below the basal sandstone of the sediments that overlie the basement the sandstone is a known aquifer suggesting that the crater excavation process was possibly phreatomagmatic in contrast the pipe shape and internal geology of victor north are more complex the northwestern part of the pipe is dominated by dark competent rocks which resemble fresh hypabyssal kimberlite but have unusual textures and are closely associated with pyroclastic juvenile lapilli tuffs and country rock breccias volcaniclastic kimberlite current evidence suggests that the hypabyssal like kimberlite is in fact not intrusive and that the northwestern part of victor north represents an early formed crater infilled with contrasting extrusive kimberlites and associated breccias the remaining main part of victor north consists of two macroscopically similar but petrographically distinct pyroclastic kimberlites that have contrasting macrodiamond sample grades the juvenile lapilli of each pyroclastic kimberlite can be distinguished only microscopically the nature and relative modal proportion of primary olivine phenocrysts in the juvenile lapilli are different indicating that they derive from different magma pulses or phases of kimberlite and thus represent separate eruptions the initial excavation of a crater cross cutting the earlier northwestern crater was followed by emplacement of phase i a low grade olivine phenocryst rich pyroclastic kimberlite and the subsequent eruption of phase ii a high grade olivine phenocryst poor pyroclastic kimberlite as two separate vents nested within the original phase i crater the second eruption was accompanied by the formation of an intermediate mixed zone with moderate grade thus the final pyroclastic pipe infill of the main part of the victor north pipe appears to consist of at least three geological macrodiamond grade zones in conclusion the victor kimberlite was formed by several eruptive events resulting in adjacent and cross cutting craters that were infilled with either pyroclastic kimberlite or hypabyssal like kimberlite which is now interpreted to be of probable extrusive origin within the pyroclastic kimberlites of victor north there are two nested vents a feature seldom documented in kimberlites elsewhere this study highlights the meaningful role of kimberlite petrography in the evaluation of diamond deposits and provides further insight into kimberlite emplacement and volcanism

geology of the mwadui kimberlite shinyanga district tanzania abstract the mwadui pipe represents the largest diamondiferous kimberlite ever mined and is an almost perfectly preserved example of a kimberlitic crater in fill albeit without the tuff ring the geology of mwadui can be subdivided into five geological units viz the primary pyroclastic kimberlite pk re sedimented volcaniclastic kimberlite deposits rvk granite breccias subdivided into two units the turbidite deposits and the yellow shales listed in approximate order of formation the pk can be further subdivided into two units lithic rich ash and lapilli tuffs which dominate the succession and lithic poor juvenile rich ash and lapilli tuffs the lower crater is well bedded down to at least 684 m from present surface extent of current drill data the bedding is defined by the presence of juvenile rich lapilli tuffs vs lithic rich lapilli tuffs and the systematic variation in granite content and clast size within much of the lithic rich lapilli tuffs four distinct types of bedding have been identified in the pyroclastic deposits diffuse zones characterised by increased granite abundance and size and upward fining units represent the dominant types throughout the deposit lateral heterogeneity was observed in addition to the vertical changes suggesting that the eruption was quite heterogeneous or that more than one vent may have been present the continuous nature of the bedding in the pyroclastic material and the lack of ash partings suggest deposition from a high concentration ejecta sustained eruption column at times e g the massive very diffusely stratified deposits the paucity of tractional bed forms suggest near vertical particle trajectories i e a clear air fall component but the poorly sorted matrix supported nature of the deposits suggest that pyroclastic flow and or surge processes may also have been active during the eruption available diamond sampling data were examined and correlated with the geology data derive from the old 120 37 m 200 61 m 300 92 m and 1200 ft 366 m levels pits sunk during historical mining operations drill logs as well as more recent bench mapping correlating macro diamond sample data and geology shows a clear relationship between diamond grade and lithology localised enrichment and dilution of the primary diamond grade has taken place in the upper reworked volcaniclastic deposits due to post eruptive sedimentary in fill processes clear distinction can be drawn between upper re sedimented and lower pyroclastic crater deposits at mwadui both from a geological and diamond grade perspective finally an emplacement model for the mwadui kimberlite is proposed geological evidence suggests that little or no sedimentary cover existed at the time of emplacement the nature of the bedding within the pyroclastic deposits and the continuity of the bedding in the vertical dimension suggest that the eruption was continuous but that the eruption column may have been heterogeneous both petrologically as well as geometrically volcanic activity appears to have ceased thereafter and the crater was gradually filled with granite debris from the unstable crater walls and re sedimented volcaniclastic material derived from the tuff ring the mwadui kimberlite exhibits marked similarities compared to the orapa kimberlite in botswana

sedimentologic and stratigraphic constraints on emplacement of the star kimberlite east central saskatchewan abstract diamond bearing kimberlites in the fort a la corne region east central saskatchewan consist primarily of extra crater pyroclastic deposits which are interstratified with lower cretaceous albian and cenomanian marine marginal marine and continental sediments approximately 70 individual kimberlite occurrences have been documented the star kimberlite occurring at the southeastern end of the main fort a la corne trend has been identified as being of economic interest and is characterized by an excellent drill core database integration of multi disciplinary data sets has helped to refine and resolve models for emplacement of the star kimberlite detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex micropaleontologic and biostratigraphic analysis of selected sedimentary rocks and u pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at star the oldest kimberlite in the star body erupted during deposition of the predominantly continental strata of the lower mannville group cantuar formation kimberlites within the cantuar formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate successive eruptive events occurred contemporaneous with deposition of the marginal marine upper mannville group pense formation kimberlites within the pense formation consist primarily of terrestrial airfall deposits fine to medium grained cross stratified kimberlitic olivine dominated sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression the location of the source feeder vents of the cantuar and pense kimberlite deposits has not been identified the youngest and volumetrically most significant eruptive events associated with the star kimberlite occur within the predominantly marine lower colorado group joli fou and viking formations kimberlite beds which occur at several horizons within these units consist of subaerial and marine fall deposits the latter commonly exhibiting evidence of wave reworking black shale encased resedimented kimberlite beds likely deposited as subaqueous debris flows and turbidites are particularly common in the lower colorado group during its multi eruptive history the star kimberlite body is interpreted to have evolved from a feeder vent and overlying positive relief tephra ring into a tephra cone initial early joli fou volcanism resulted in formation of a feeder vent 200 m diameter and tephra ring subsequent eruptions dominated by subaerial deposits partly infilled the crater and constructed a tephra cone a late joli fou eruption formed a small 70 m diameter feeder pipe slightly offset to the nw of the early joli fou feeder vent deposits from this event further infilled the crater and were deposited on top of early joli fou kimberlite proximal to the vent and sediments of the joli fou formation distal to the vent the shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the lower colorado group resulting in wave reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits tempestites turbidites debris flows in more distal settings

3d particle size distributions from 2d observations stereology for natural applications abstract we have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution not limited to log normal unimodal etc we have applied numerical techniques to define intersection probability distributions for any shapes previously only known for spheres and quantified the errors involved in using spherical coefficients for various non spherical particles this stereological technique is based on knowing the probability distribution of random cross sections through various particles so that small circle cross sections can be subtracted from an observed population to provide the 3d size distribution of particles the results indicate that the most important parameter controlling calculated size distribution is particle aspect ratio for a distribution of particles with a specific aspect ratio or range of aspect ratios variations of particle form spherical vs cubic rectangular vs elliptical do not alter the results so the technique can be applied to a range of particle shapes applications can be made in a petrology volcanology and other fields only a few of which can also be treated using expensive x ray techniques

the influence of conduit processes on changes in style of basaltic plinian eruptions tarawera 1886 and etna 122 bc basaltic volcanism is most typically thought to produce effusion of lava with the most explosive manifestations ranging from mild strombolian activity to more energetic fire fountain eruptions however some basaltic eruptions are now recognized as extremely violent i e generating widespread phreatomagmatic subplinian and plinian fall deposits we focus here on the influence of conduit processes especially partial open system degassing in triggering abrupt changes in style and intensity that occurred during two examples of basaltic plinian volcanism we use the 1886 eruption of tarawera new zealand the youngest known basaltic plinian eruption and the only one for which there are detailed written eyewitness accounts and the well documented 122 bc eruption of mount etna italy and present new grain size and vesicularity data from the proximal deposits these data show that even during extremely powerful basaltic eruptions conduit processes play a critical role in modifying the form of the eruptions even with very high discharge and presumably ascent rates partial open system behaviour of basaltic melts becomes a critical factor that leads to development of domains of largely stagnant and outgassed melt that restricts the effective radius of the conduit the exact path taken in the waning stages of the eruptions varied in response to factors which included conduit geometry efficiency and extent of outgassing and availability of ground water but a relatively abrupt cessation to sustained high intensity discharge was an inevitable consequence of the degassing processes

the geology of kimberlite pipes of the ekati property northwest territories canada abstract this paper reviews key characteristics of kimberlites on the ekati property nwt canada to date 150 kimberlites have been discovered on the property five of which are mined for diamonds the kimberlites intrude archean basement of the central slave craton numerous proterozoic diabase dykes intrude the area the precambrian rocks are overlain by quaternary glacial sediments no phanerozoic rocks are present however mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late cretaceous and tertiary cover likely

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

local migration with extrapolated vsp green s functions we have developed a novel vertical seismic profile vsp imaging method that requires only a local velocity model around the well this method is denoted as a local migration where the model based forward propagation and backward propagation operators are computed using a local velocity model between the well and the target body the velocity model for the complex overburden and salt body is not needed and the source side statics are automatically accounted for in addition kinematic and dynamic effects including anisotropy absorption and other unknown undefined rock effects outside of this local velocity model are mostly accounted for numerical tests on an acoustic 2d sigsbee vsp data set an elastic salt model and offset 2d vsp data in the gulf of mexico partly validate the effectiveness of this method by accurately imaging the sediments next to the vertical well

migration by extrapolation of time dependent boundary values migration of an observed zero offset wavefield can be performed as the solution of a boundary value problem in which the data are extrapolated backward in time this concept is implemented through a finite difference solution of the two dimensional acoustic wave equation all depths are imaged simultaneously at time 0 the imaging condition and all dips right up to vertical are correctly migrated numerical examples illustrate this technique in both constant and variable velocity media

geology and diamond distribution of the 140 141 kimberlite fort a la corne central saskatchewan canada abstract the cretaceous age fort a la corne falc kimberlite province comprises at least 70 bodies which were emplaced near the edge of the western canadian interior seaway during cycles of marine transgression and regression many of the bodies were formed during a marine regression by a two stage process firstly the excavation of shallow but wide craters and then subsequent infilling by xenolith poor crater facies subaerial primary pyroclastic kimberlite the bodies range in size up to 2000 m in diameter but are mainly less than 200 m thick and thus comprise relatively thin but high volume pyroclastic kimberlite deposits each body is composed of contrasting types of kimberlite reflecting different volcanic histories and therefore are considered separately the 140 141 kimberlite is the largest delineated body in the province estimated to have an areal extent below glacial quaternary sediments in excess of 200 ha the infilling of the 140 141 crater is complex resulting from multiple phases of kimberlite the central part of the infill is dominated by several contrasting phases of kimberlite one of these phases is a primary pyroclastic airfall mega graded bed up to 130 m in thickness the constituents grade in size from very fine to coarse macrocrystic kimberlite through to a basal breccia the mega graded bed is a widespread feature within parts of the body examined to date and at this current stage of evaluation appears to explain a variable diamond distribution within a tested portion of the pipe a second different phase of kimberlite is interpreted as representing a younger nested crater within the mega graded bed centrally located thicker intersections 450 m of this younger kimberlite may indicate a vent for the kimberlite crater the thickness of the mega graded bed increases with proximity to the younger kimberlite in the study area macrodiamond minibulk sample grades from the mega graded bed have been obtained from nine large diameter drill holes located within the northwest part of the body from an area of 20 ha which represents approximately 10 of the currently modeled kimberlite outline diamond grade increases with depth within the mega graded bed and also increases within the same unit towards the centrally positioned younger kimberlite macrodiamond sample grades vary from low at the top of the mega graded bed to considerably higher grades near the base total sample grade per drill hole varies from moderate near the vent feature to lower grades 200 300 m from the vent feature macrodiamond stone frequency measured in stones per tonne shows a pronounced relationship with depth and proximity to the vent feature within the mega graded bed there is a strong correlation between depth and increased stones per tonne and a similar correlation between stones per tonne and proximity to the vent feature the data supports the emplacement model of the mega graded bed and in turn this information is useful in understanding the macrodiamond distribution within this bed

thermal maturity evaluation of dispersed organic matter inclusions from kimberlite pipes lac de gras northwest territories canada abstract dispersed organic matter dom inclusions have been recovered from crater diatreme and diatreme xenoliths within hypabyssal facies of diamondiferous kimberlite pipes in the lac de gras region of northwest territories canada incident white and fluorescent light microscopy has been used to study vitrinite and liptinite dom xenoliths in the pipes percent reflectance in oil ro of wood derived vitrinite visible light region fluorescence properties of sporinite cutinite and resinite and changes in maceral morphology have been used to evaluate thermal alteration within the kimberlite pipes temperature estimates for different thermal zones in the kimberlite pipes have been inferred by comparing vitrinite reflectance with data from rapid pyrolysis experiments conducted on low rank vitrinites crater facies dom consists of very low reflecting 20 to 200 c to a maximum of 650 c the presence of petroleum derived cokes are consistent with estimates of 400 450 c for samples recovered close to and within hypabyssal dykes and macrocrystic breccia and massive hypabyssal facies below this zone tuffisitic kimberlites are marked by a reduction in vitrinite reflectance 0 5 to 1 8 ro and a lower inferred alteration temperature estimated at 200 to 450 c anomalous populations of very low reflecting partially devolatilized vitrinite 0 50 to 0 84 ro in this zone may have suppressed reflectance possibly a consequence of liquefaction like conditions and impregnation by oily bitumens produced during pyrolysis of associated liptinite macerals

the role of fluidisation in the formation of volcaniclastic kimberlite grain size observations and experimental investigation abstract deep steep sided kimberlite pipes in southern africa are normally partially filled with multiple units of a characteristically massive structureless volcaniclastic rock here termed massive volcaniclastic kimberlite mvk these units can be arranged in a pseudo concentric nested pipes within pipes structure several key observations on typical mvk from the venetia kimberlite pipes south africa indicate that fluidisation may have been an important process during its emplacement these include 1 the thorough mixing together of juvenile components and of lithic components derived from all stratigraphic levels of the country rock and 2 a matrix composed of void filling minerals related to hydrothermal metamorphism mainly diopside and serpentine which indicates that the primary deposit had a high porosity 50 and 3 particle size distributions poor in fine ash 10 cm analogue experiments utilising a sand bed laced with marker horizons were conducted in order to investigate the role of fluidisation in the formation of mvk high pressure gas fed through the bed from a point source resulted in the formation of an upwardly diverging pipe structure of thoroughly mixed fluidised material bounded by undisturbed sand strong upward gas flow along the centre of the pipe is characteristically bubbly and results in internal circulation with downward moving regions at the pipe margins analysis of the experimental results suggests that the gas velocity decreases linearly with height and has a gaussian distribution of vertical velocity in the cross flow direction a decrease in the gas flow rate resulted in the development of nested pipes reminiscent of the pipes within pipes structures in kimberlite pipes the results suggest that fluidisation could be a major control on the structure and sorting of deposits in kimberlite pipes we propose that the fluidisation of particles in a kimberlite pipe occurs during the final stages of the eruption when erupting pyroclasts and incorporated fragmented lithic material can no longer be ejected out of the deep wide conduit this bed is subject to quasi sustained fluidisation by the erupting gas particle flow which imparts on it the distinctive characteristics of a massive well mixed poorly sorted deposit

separation of p and s waves in combined p and sv observations with vertical and in line horizontal geophones recognition and separation of the individual p and s arrivals may form a considerable problem due to the geophone receiving characteristics p and s waves are observed on both horizontal and vertical geophones a new method of separating p and s waves is presented that inverts the geophone records for the receiving characteristics thereby separating the two wavetypes the filter coefficients are determined from the near surface p and s wave velocity and from the geometry of the geophone groups the p s separation filter was tested on synthetic data with good results even ps and sp converted reflections which are completely coinciding for horizontal reflectors could be well separated the filter appears to be stable and to have low sensitivity to noise in the data or to errors in the near surface p and s wave velocity the filter is superior to other separation methods which were applied to the same dataset for comparison this method can also be applied to vsp data