petrology and textural classification of the jericho kimberlite northern slave province nunavut canada the paper presents data on petrology bulk rock and mineral compositions and textural classification of the middle jurassic jericho kimberlite slave craton canada the kimberlite was emplaced as three steep sided pipes in granite that was overlain by limestones and minor soft sediments the pipes are infilled with hypabyssal and pyroclastic kimberlites and connected to a satellite pipe by a dyke the jericho kimberlite is classified as a group ia lacking groundmass tetraferriphlogopite and containing monticellite pseudomorphs the kimberlite formed during several consecutive emplacement events of compositionally different batches of kimberlite magma core logging and thin section observations identified at least two phases of hypabyssal kimberlites and three phases of pyroclastic kimberlites hypabyssal kimberlites intruded as a main dyke hk1 and as late small volume aphanitic and vesicular dykes massive pyroclastic kimberlite mpk1 predominantly filled the northern and southern lobes of the pipe

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

effects of eruption history and cooling rate on lava dome growth to better understand the factors controlling the shapes of lava domes laboratory simulations measurements from active and prehistoric flows and dimensional analysis were used to explore how effusion history and cooling rate affect the final geometry of a dome fifty experiments were conducted in which a fixed volume of polyethylene glycol wax was injected into a tank of cold sucrose solution either as one continuous event or as a series of shorter pulses separated by repose periods when the wax cooling rates exceeded a critical minimum value the dome aspect ratios height diameter increased steadily with erupted volume over the course of a single experiment and the rate at which height increased with volume depended linearly on the time averaged effusion rate thus the average effusion rate could be estimated from observations of how the dome shape changed with time our experimental results and dimensional analyses were compared with several groups of natural lava flows the recently emplaced mount st helens and soufriere domes which had been carefully monitored while active three sets of prehistoric rhyolite domes that varied in eruptive style and shape and two sets of holocene domes with similar shapes but different compositions geometric measurements suggest that dome morphology can be directly correlated with effusion rate for domes of similar composition from the same locality and that shape alone can be related to a dimensionless number comparing effusion rate and cooling rate extrapolation to the venusian pancake domes suggests that they formed from relatively viscous lavas extruded either episodically or at average effusion rates low enough to allow solidified surface crust to exert a dominating influence on the final morphology

ferric iron in catio3 perovskite as an oxygen barometer for kimberlitic magmas i experimental calibration a method to estimate the oxygen fugacity fo2 during the crystallization of kimberlites is developed using the fe content of catio3 perovskite pv a common groundmass phase in these rocks with increasing fo2 more fe exists in the kimberlitic liquid as fe3 and thus partitions into pv experiments to study the partitioning of fe between pv and kimberlite liquid were conducted at 100 kpa on simple and complex anhydrous kimberlite bulk compositions from 1130 to 13008c over a range of fo2 from nno 5 to nno 4 where nno is the nickel nickel oxide buffer and atnb and rare earth element ree contents in the starting materials of 0 5 wt and 1500 ppm respectively the partitioning of fe between pv and kimberlite liquid is influenced mostly by fo2 although the presence of nb increases the partition of fe3 into perovskite at a given t and fo2 multiple linear regression mlr of all the experimental data produces a relationship that describes the variation of fe andnbinpvwith fo2relative to thennobuffer

remarkable cyclic ground deformation monitored in real time on montserrat and its use in eruption forecasting telemetered high resolution tiltmeters were installed in montserrat in summer of 1995 in december 1996 and in may 1997 the 1995 installations several km from the soufriere hills vent were too distant to yield useful data however the 1996 and 1997 installations on the crater rim revealed 6 14 h inflation cycles caused by magma pressurization at shallow depths 0 6 km below the base of dome the tilt data correlated with seismicity explosions and pyroclastic flow activity and were used to forecast times of increased volcanic hazard to protect scientific field workers and the general public

satellite remote sensing of thermal activity at bezymianny and kliuchevskoi from 1993 to 1998 time series trends in thermal advanced very high resolution radiometer avhrr data from 1993 to 1998 provide insight into the active volcanic processes at bezymianny and kliuchevskoi two of the most dangerous volcanoes on the kamchatka peninsula the avhrr time series show differences in these volcanoes pre and postexplosive trends bezymianny exhibited a thermal precursory signal in all recorded explosions between 1993 and 1998 as well as continued postexplosive activity and kliuchevskoi showed only short lived thermal activity and exhibited precursors before the 1994 paroxysmal explosion these contrasting characteristics reflect different magma types and eruption styles at bezymianny a persistent thermal signal and precursory thermal increases are due to the slow ascent of andesitic magma whereas the more rapid rise effusion and cooling of basaltic magmas at kliuchevskoi give rise to a discontinuous thermal pattern documentation analysis and understanding of these characteristics contribute to the understanding of thermal signals and aid the development of monitoring algorithms and early warning techniques

clay coatings formation in tepetates from texcoco mexico abstract tepetates are common in the mexican highlands and are classified as fragipan duripan pedosediments or saprolite a common feature is the abundance of clay coatings three pedons with red tepetate and grey tepetate were selected at different altitudes and slopes in a small watershed in texcoco mexico physical chemical mineralogical and micromorphological analyses were carried out in soil tepetate and separated clay coatings clay illuviation and neoformation indexes were calculated using micromorphometric techniques red tepetate is composed of basic volcanic glass dust andesitic vitric tuff and has a high clay neoformation and illuviation index in contrast grey tepetate is composed of acid volcanic glass acid vitric tuff and only clay neoformation takes place leading to the formation of a clayey soil although all the tepetates were subject to pedogenesis the intensity and variation of the processes increases on the lower slope and different diagnostic horizons are formed due to tepetate erosion the laterally running waters containing suspensions of particles and soluble silica were deposited or precipitated in sediments or tepetates on the lower slopes giving rise to compound coatings these processes must be older than 20 000 years tepetates from texcoco present several variants which were recognised since pre hispanic times

the thermal stealth flows of santiaguito dome guatemala implications for the cooling and emplacement of dacitic block lava flows thick slow moving block lava flows are associated with extrusive activity in dacitic systems where lava core depressurization during flow front collapse generates devas tating block and ash flows dimensional and rare thermal data collected during jan uary 2000 for an active dacitic block flow at santiaguito guatemala provide insight into cooling and emplacement mechanisms flow velocity was low 12 5 m d 21 in spite ginal shear zones the axial part of the flow front was thicker than the marginal zones and was oversteepened this geometry can be explained by a higher vertical velocity gradient in the axial zone causing more frequent and larger volume flow front col lapses axial zone collapses also penetrate farther up flow but not sufficiently to de pressurize the flow core and generate a block and ash flow for such a block and ash flow to occur we calculate that an in crease in velocity and or thickness due to increased slope or topographic confine ment must occur whereas low surface temperatures make block flows invisible to short wave infrared sensors the low veloc ity also contributes to the stealthy behavior of these flows their stealthy nature how ever masks the fact that they can extend many kilometers moving block and ash flow sources closer to vulnerable communities

the 1996 subaqueous eruption at academii nauk volcano kamchatka and its effects on karymsky lake a subaqueous eruption in karymsky lake in the academii nauk caldera dramatically changed its water column structure water chemistry and biological system in less than 24 h sending major floodwaves down the discharging river and eruption plumes with ash and gases high into the atmosphere prior to the eruption the lake had a ph of about 7 was dominated by bicarbonate and well stocked with fish but turned in early 1996 into a stratified initially steaming waterbody dominated by sulfate with high na and k levels and devoid of fish blockage of the outlet led to rising waterlevels followed by dam breakage and catastrophic water discharge the total energy input during the eruption is estimated at about 1016 j the stable isotope composition of the lake water remained dominated by the meteoric meltwaters after the eruption

satellite thermal observations of the bezymianny lava dome 1993 2008 precursory activity large explosions and dome growth 1 fifteen years worth of advanced very high resolution radiometer avhrr data is presented and used to quantitatively assess processes occurring at bezymianny this andesitic volcano is one of kamchatka s most dangerous volcanoes with 16 eruptions in the last decade that have dispersed ash into north pacific air routes all known episodes of increased activity for which data were available were detected in band 3 3 53 3 93 m avhrr thermal data twenty three peaks can be seen in the data nineteen peaks correspond to known explosions while the remaining three peaks correspond to known phases of dome growth that were not believed to have been accompanied by explosive activity start and end dates of extrusive phases defined by the thermal data are presented repose times between phases of extrusion vary from four months to just over two and half years with an average of just less than a year using rank order statistics a maximum time interval between consecutive explosions of 1288 170 days is determined this could serve as a cut off time for declaring the current dome growth activity over the calculated cumulative erupted volume 0 28 km3 and time averaged extrusion rate 0 6 m3 s 1 from 1993 to 2008 corresponds to values found at bezymianny from 1956 to 1976 showing that the satellite based methodology provides a good way of quantitatively assessing dome growth three different types of precursors to explosive behavior have been identified at bezymianny 1 values that cluster around the mode of the data set prior to explosion potentially due to endogenous dome growth 2 upward trends that commence 15 20 days prior to explosion and reach sensor saturation levels are due to significant extrusion and 3 a gradual upward trend that starts 5 days prior to explosion probably due to ramping up of extrusion this work shows that retrospectively analyzing and modeling of a volcano s thermal signal provides increased insight into its characteristic behavior the methods used in this paper can be used at other dome building volcanoes around the world the insights presented here can be used to improve monitoring capabilities to aid in providing early warnings to large explosions at bezymianny

forecasting large explosions at bezymianny volcano using thermal satellite data large volcanic explosions pose a severe risk to life and cargo by injecting ash into local and international air traffic routes prior to exploding bezymianny kamchatka commonly shows an increase in lava extrusion rate which can be detected by satellites as an increase in thermal radiance here we present the first method of forecasting explosive eruptions based solely on satellite data a pattern recognition algorithm using advanced very high resolution radiometer avhrr data has been developed based on known precursory trends of increasing radiance prior to 19 explosions at bezymianny volcano in 1993 2008 the algorithm retrospectively forecasts 89 of the explosions 100 of the explosions that show precursory increases in thermal radiance with 71 of alerts issued in the 30 days beforehand the method also provides the probability of an explosion occurring within a given number of days after an alert is triggered by the algorithm when applied to independent data the algorithm correctly provided alerts before the 16 december 2009 31 may 2010 and 13 april 2011 explosions

petrology and petrogenesis of mesoproterozoic lamproites from the ramadugu field nw margin of the cuddapah basin eastern dharwar craton southern india abstract petrography mineral chemistry and major and trace element data are presented for the newly discovered mesoproterozoic 1 33 1 43 ga lamproites from the ramadugu field rlf at the nw margin of the paleo mesoproterozoic cuddapah basin in the eastern dharwar craton edc southern india rlf lamproites are emplaced as dykes have a nw se trend and their petrography reveal the effects of low temperature alteration however their textural features mineralogy and geochemistry are closely similar to other well characterised lamproites worldwide including examples from the eastern dharwar craton leucite hills west kimberley smoky butte and labrador the rlf magmas have undergone varying degrees of olivine clinopyroxene fractionation yet their compatible and incompatible trace element concentrations are sufficiently high to signal a primitive character incompatible element ratios suggest limited contamination by continental crust geochemical evidence indicates the derivation of rlf magmas from metasomatised harzburgite within the garnet stability field rare earth element inversion modelling further highlights substantial involvement of the sub continental lithospheric mantle in their genesis the rlf lamproites are geochemically similar to the well known extension related ultrapotassic lavas from eastern virunga and western anatolia and exclude an affinity with orogenic lamproites such as those from the mediterranean region bulk rock geochemical models recently developed to infer diamond potential reveals that rlf lamproites are non prospective lamproites of the rlf together with those from the krishna lamproite field and cuddapah basin are interpreted as an expression of extensional events in the eastern dharwar craton possibly related to the break up of the supercontinent of columbia between 1 5 and 1 3 ga

magma budgets and steady state activity of vulcano and stromboli we present three models for magma budget during steady state volcanic activity by which non erupted magma is emplaced as dykes or cumulates or crystallises in place using gas and thermal data we apply our models at vulcano to calculate degassing cooling and crystallisation of magma at a rate of 40 375 kg s 1 within a magma body with an upper surface at a 2 km depth at stromboli we calculate a steady magma supply of 300 1300 kg s 1 to shallow 1 km depths

degassing explosions at karymsky volcano kamchatka during the summer of 1997 karymsky vol cano produced summit explosions about six times each hour typical explosive episodes lasted between 30 seconds and three minutes produced gas and ash columns several hun dred meters high and ejected some incandescent material to better understand the physical source mechanisms re sponsible we recorded hundreds of explosions with a three component broad band seismometer and microphone lo cated 1650 meters from the active vent nearly every explo sion is recorded as an emergent yet identical seismic wavelet which is followed 4 15 s later by an impulsive acoustic ar rival we interpret the signals as a near surface gas volume burst which fractures the vent plug lowers the lithostatic pressure within the magma column and often induces fur ther degassing when degassing continues it is generally manifested as either a series of regular one second chug ging 1 explosions steady higher frequency jetting or a hy brid combination we believe that the seismic signature for chugs short duration harmonic tremor with integer over tones is the result of repeated gas volume bursts at the vent in contrast seismograms for jetting are non harmonic and contain higher frequencies we believe that the competing degassing behaviors are influenced by the gas flux as well as the plug conduit characteristics we propose that a plug exists due to a viscosity gradient caused by volatile depletion in the upper conduit

effusion rate trends at etna and krafla and their implications for eruptive mechanisms abstract using effusion rates obtained from ground and satellite based data we build a data set of 381 effusion rate measurements during effusive activity at etna and krafla between 1980 and 1999 this allows us to construct detailed effusion rate curves for six fissure fed eruptions at etna and krafla and four summit fed eruptions at etna these define two trends type i and ii type i trends have effusion rates that rise rapidly to an initial peak before declining more slowly resulting in an exponential decrease in eruption rate and declining growth in cumulative volume type ii trends are characterised by steady effusion and eruption rates and hence a linear increase in cumulative volume the former is typical of fissure eruptions and can be explained by tapping of an enclosed pressurised system the latter are typical of persistent etnean summit eruptions plus one persistent effusive eruption at stromboli 1985 1986 examined here and can be explained by overflow of the time averaged magma supply we use our effusion rate data to assess the magma balance at etna 1980 1995 and krafla 1975 1984 between 1980 and 1995 etna was supplied at a time averaged rate of 6 8 2 3 m 3 s 1 of which 13 was erupted at krafla 817 30 10 6 m 3 was erupted and intruded during 1975 1984 and the ratio of erupted to intruded volume was 0 3 at etna there is evidence for intrusion of the unerupted magma within and beneath the edifice as well as storage in the central magma column at krafla unerupted magma was intruded into a rift zone but an increasing proportion of the supply was erupted from 1980 onwards a result of the rift zone capacity being reached magma intruded prior to an eruptive event may also be entrained and or pushed out during eruption to contribute to the initial high effusion rate phases of type i events the detail in our effusion rate curves was only possible using a thermal approach which estimates effusion rates using satellite data we look forward to analysing satellite derived effusion rate trends in real time using data from current and soon to be launched sensors

numerical modelling of the growth dynamics of a simple silicic lava dome 1 two dimensional axisymmetrical computational models have been developed using finite element techniques to represent the rheological stiffening due to degassing induced crystallisation and the effects of a brittle carapace within a simple lava dome the dome is modelled numerically considering the effects of temperature pressure and rate of extrusion using these state variables the bulk viscosity is derived from empirical equations and the bulk rheology approximated using a solidification viscosity dividing the dome into solid dominated and fluid dominated domains elastoplastic equations for the solid component and fluid mechanical equations for the fluid domain are solved simultaneously allowing continuous stress across the fluid solid interface to ensure the two components move in unison we apply this model a hookean solid carapace model and a purely fluid lava dome model to the case of the october 1980 lava dome at mount st helens the results show that dynamic growth models involving a solid carapace are required to simulate this lava dome

the 1996 eruption of karymsky volcano kamchatka historical record of basaltic replenishment of an andesite reservoir the simultaneous eruption in 1996 of andesite from karymsky volcano and of basalt from the academy nauk vent 6km away appears to provide a case of mafic recharge of an andesite reservoir for which the time of recharge is exactly known and direct samples of the recharging magma are available the explosive phreato magmatic eruption of basalt was terminated in less than 24h whereas andesite erupted continuously during the following 4 years detailed petrological study of volcanic ash bombs and lavas of karymsky andesite erupted during the period 1996 1999 provides evidence for basaltic replenishment at the beginning of the eruptive cycle as well as a record of compositional variations within the karymsky magma reservoir induced by basaltic recharge shortly after the beginning of the eruption the composition of the matrix glass of the karymsky tephra became more mafic and then within 2 months gradually returned to its original state and remained almost constant for the following 3 years further evidence for basaltic replenishment is provided by the presence of xenocrysts of basaltic origin in the andesite of karymsky a conspicuous portion of the plagioclase phenocrysts in the karymsky andesite has calcic cores with compositions and textures resembling those of plagioclases in the academy nauk basalt similarly the earlier portion of the andesite of the eruption sequence contains rare olivines which occur as resorbed cores in pyroxenes the composition of the olivine matches that of olivines in the academy nauk basalt the sequence of events appears to be 1 injection of basaltic magma into the karymsky chamber with immediate compensating expulsion of pre existing chamber magma from the karymsky central vent 2 direct mixing of basaltic and andesitic magmas with dispersal of phenocrysts associated with the basalt throughout the andesite so that newly mixed magma appeared at the vent within 2 months 3 re establishment of thermal and chemical equilibrium within the reservoir involving crystallization in the new hybrid liquid which returned the melt composition to normal formed rims on inherited calcic plagioclase and caused the resorption of dispersed olivine xenocrysts taken together these findings indicate that the karymsky magma reservoir was recharged by basalt at the onset of the 1996 eruptive cycle the rapidity and thoroughness of mixing of the basalt with the preexisting andesite probably reflects the modest contrast in temperature viscosity and density between the two magmas

seismological study of the kliuchevskoi flank eruption of 1983 kamchatka abstract a flank eruption called the predskazanny eruption occurred at an altitude of 2875 m on the east flank of the kliuchevskoi volcano from march 8 to june 27 1983 the eruption was largely effusive with a constant chemical composition of the lavas calc alkaline aluminium basalts their volume is estimated at 0 11 km 3 the seismic precursors of the predskazanny eruption was concentrated beneath the new eruption center first at depths of between 10 and 15 km earthquake of february 28 k s 8 3 m 3 5 and then at depths between 5 km b s l and 3 km a s l earthquake swarm of march 1 7 volcanic tremor during the earthquake swarm of march 1 7 was absent with the approach of an eruption the depth of earthquake foci in the swarm decreased an analysis of the seismicity implies that the magma was apparently ascending in the newly formed channel from a depth of at least 5 km the feeding area of the predskazanny eruption was apparently connected with the major magma channel of kliuchevskoi at depths between 5 and 10 km but not deeper than 15 km

satellite thermal infrared data of shiveluch kliuchevskoi and karymsky 1993 2008 effusion explosions and the potential to forecast ash plumes this paper presents an analysis of advanced very high resolution radiometer avhrr thermal data from shiveluch kliuchevskoi and karymsky kamchatka russia from 1993 to 2008 these different volcanoes show contrasting and variable patterns in their thermal data and lack reliable precursory thermal trends prior to large explosions pixel integrated temperatures pirt at shiveluch were above background during three phases 1 1993 1995 2 2001 2005 and 3 2006 time of writing each of which was associated with growth of an andesitic dome punctuated by explosions the coarse spatial resolution of the avhrr may have prevented observation of precursory thermal patterns at this volcano kliuchevskoi showed five phases these show a rapid days or gradual weeks to months increase in temperature followed by rapid drop offs suggesting these basaltic eruptions start explosively followed by lava effusion or vice versa fast magma ascent rates probably prevent the generation of thermal precursors at karymsky elevated pirt values cluster into seven phases showing three trends 1 persistently high pirt 2 a gradual increase and decrease and 3 gradual increase followed by steep drop offs these trends are due to the extrusion of viscous andesitic dacitic lava not to strombolian vulcanian activity and show no consistent pattern prior to large explosions pirt values at karymsky lake reflect the dyke intrusion that started the 1996 eruptive cycle at karymsky the values obtained here provide a baseline against which to monitor these volcanoes and karymsky lake in the future

unusually high electrical conductivity of phlogopite the possible role of fluorine and geophysical implications phlogopite is an accessory mineral often found in mantle samples from various tectonic settings of continental regions considerable effort has been expended on the effect of phlogopite on some key chemical and petrological processes of the upper mantle such as the recycling of k f and h2o and the generation of k rich fluids melts in contrast less attention has been devoted to its physical properties in this study the orientation related electrical conductivities of phlogopite single crystals have been experimentally determined at 1 gpa and 200 900 c with an end loaded piston cylinder press and a solartron 1260 impedance gain phase analyzer in the frequency range of 106 0 1 hz the results demonstrate that phlogopite can have unusually high conductivity 0 01 s m above 600 c and 1 s m at 900 c significant electrical anisotropy by a factor of 6 above 900 c and large activation enthalpies 134 204 kj mol along different directions the main charge carriers are probably k and f and fluorine may play a critical role in electrical conduction the regional enrichment of k and f rich phlogopite above subduction zones or in normal shields for example could result in remarkable anomalies of electrical conductivity this provides a new mechanism for explaining some locally resolved electrical anomalies in the continental upper mantle

temporal trends in lava dome extrusion at santiaguito 1922 2000 we present a means of extracting lava dome extrusion rates from data provided by the thematic mapper and enhanced thematic mapper plus instruments flown on the landsat satellites extrusion rates derived from the landsat data for santiaguito dome complex guatemala during november 1987 and january 2000 of 0 72 0 08 and 0 48 0 09 m3 s 1 compare favorably with ground based estimates of 0 63 0 28 and 0 48 0 17 m3 s 1 a satellite data derived set of 18 extrusion rate estimates between 1987 and 2000 along with ground based volume estimates prior to 1987 allow us to infer volumes of magma erupted since 1922 these data reveal cyclic extrusion at santiaguito each cycle begins with a 3 6 year long phase of high extrusion rate 0 5 2 1 m3 s 1 followed by a longer 3 11 years phase of low extrusion rate 0 2 m3 s 1 the 8th cycle began in 1996 and was still in its high extrusion rate phase during january 2000 with time however the durations of the low extrusion rate phases have increased peak extrusion and time averaged extrusion rates for each cycle have decreased and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased these trends may be the result of depressurization and exhaustion of the source in this case the current eruption may be expected to end around 2020 alternatively santiaguito may be entering a period of persistent activity maintained by a stable magma supply in this case we may expect extrusion to become less cyclic and to stabilize at 0 2 0 4 m3 s 1 however a 2 wt decrease in sio2 content of erupted products since 1970 appears to be consistent with chamber exhaustion as well as an increase in block lava flow lengths during 1970 2000

a genetic relationship between magnesian ilmenite and kimberlites of the yakutian diamond fields abstract we present new major element geochemical data and review the existing data for ilmenite macrocrysts megacrysts as well as ilmenite in mantle xenoliths from four diamondiferous kimberlite fields in the yakutian province this combined data set includes 10 874 analyses of ilmenite from 94 kimberlite pipes in the studied samples we identify various different ilmenite compositional distributions e g haggerty s parabola or step like trends in mgo cr2o3 bivariate space which are common to all kimberlites from a given cluster but the compositional distributions differ between clusters we propose three stages of ilmenite crystallization 1 mg cr poor ilmenite crystallising from a primitive asthenospheric melt the base of haggerty s parabola on mgo cr2o3 plots 2 this primitive asthenospheric melt was then modified by the partial assimilation of lithospheric material which enriched the melt in mgo and cr2o3 left branch of haggerty s parabola 3 ilmenite subsequently underwent sub solidus recrystallization in the presence of an evolved kimberlite melt under increasing oxygen fugacity o2 conditions right branch of haggerty s parabola in mgo cr2o3 plots significant differences in the ilmenite compositional distribution between different kimberlite fields are the result of diverse conditions during subsequent ilmenite crystallization in a kimberlite melt ascending through the lithospheric mantle which have different textures and compositions beneath the studied kimberlite fields we propose that a tio2 fluid formed due to immiscibility of an asthenospheric melt with low cr and high ti contents this fluid infiltrated lithospheric mantle rocks forming mg ilmenite these features indicate a genetic link between ilmenite and the host kimberlite melt

magmatic evolution and ascent history of the aries micaceous kimberlite central kimberley basin western australia evidence from zoned phlogopite phenocrysts and uv laser 40ar 39ar analysis of phlogopite biotite the neoproterozoic aries kimberlite was emplaced in the central kimberley basin western australia as a n nne trending series of three diatremes infilled by lithic rich kimberlite breccias the breccias are intruded by hypabyssal macrocrystic phlogopite kimberlite dykes that exhibit differentiation to a minor high na si olivine phlogopite richterite kimberlite and late stage macrocrystic serpentine diopside ultramafic dykes mineralogical and geochemical evidence suggests that the high na si olivine phlogopite richterite kimberlite was derived from the macrocrystic phlogopite kimberlite as a residual liquid following extended phlogopite crystallization and the assimilation of country rock sandstone and that the macrocrystic serpentine diopside ultramafic dykes formed as mafic cumulates from a macrocrystic phlogopite kimberlite chemical zonation of phlogopite biotite phenocrysts indicates a complex magmatic history for the aries kimberlite with the early inheritance of a range of high ti phlogopite biotite xenocrysts from metasomatized mantle lithologies followed by the crystallization of a population of high cr phlogopite phenocrysts within the spinel facies lithospheric mantle a further one to two phlogopite biotite overgrowth rims of distinct composition formed on the phlogopite phenocrysts at higher levels during ascent to the surface ultra violet laser 40ar 39ar dating of mica grain rims yielded a kimberlite eruption age of 815 4 4 3 ma 95 confidence 40ar 39ar laser profiling of one high ti phlogopite biotite macrocryst revealed a radiogenic 40ar diffusive loss profile from which a kimberlite magma ascent duration from the spinel facies lithospheric mantle was estimated assuming an average kimberlite magma temperature of 1000 c yielding a value of 0 23 2 32 days for the north extension lobe of the aries kimberlite

mantle and crustal sources of magmatic activity of klyuchevskoy and surrounding volcanoes in kamchatka inferred from earthquake tomography

thirty years of satellite derived lava discharge rates at etna implications for steady volumetric output 1 we present a 30 year long data set of satellite derived time averaged lava discharge rates tadr for mount etna volcano sicily italy spanning 1980 2010 and comprising 1792 measurements during 23 eruptions we use this to classify eruptions on the basis of magnitude and intensity as well as the shape of the tadr time series which characterizes each effusive event we find that while 1983 1993 was characterized by less frequent but longer duration effusive eruptions at lower tadrs 2000 2010 was characterized by more frequent eruptions of shorter duration and higher tadrs however roughly the same lava volume was erupted during both of these 11 year long periods so that the volumetric output was linear over the entire 30 year period increasing at a rate of 0 8 m3 s 1 between 1980 and 2010 the cumulative volume record can be extended back in time using data available in the literature this allows us to assess etna s output history over 5 centuries and to place the current trend in historical context we find that output has been stable at this rate since 1971 at this time the output rate changed from a low discharge rate phase which had characterized the period 1759 to 1970 to a high discharge rate phase this new phase had the same output rate as the high discharge rate phase that characterized the period 1610 1669 the 1610 1669 phase ended with the most voluminous eruption of historic times

volcanology of the aries micaceous kimberlite central kimberley basin western australia abstract the neoproterozoic 815 4 4 3 ma aries kimberlite intrudes the king leopold sandstone and the carson volcanics in the central kimberley basin northern western australia aries is comprised of a n nne trending series of three diatremes and associated hypabyssal kimberlite dykes and plugs the diatremes are volumetrically dominated by massive clast supported accidental lithic rich kimberlite breccias that were intruded by hypabyssal macrocrystic phlogopite kimberlite dykes and plugs with variably uniform to globular segregationary textured groundmasses lower diatreme facies accidental lithic rich breccias probably formed through fall back of debris into the vent with a major contribution from the collapse of the vent walls these massive breccias are overlain by a sequence of bedded volcaniclastic breccias in the upper part of the north lobe diatreme abundant poorly vesicular to nonvesicular juvenile kimberlite ash and lapilli with morphologies that are indicative of phreatomagmatic fragmentation processes occur in a reversely graded volcaniclastic kimberlite breccia unit at the base of this sequence this unit and overlying bedded accidental lithic rich breccias are interpreted to be sediment gravity flow deposits including possible debris flows derived from the collapse of the crater walls and or tephra ring deposits that surrounded the crater diatreme forming eruptions may have been initiated by magma water interactions along fracture and joint controlled aquifers within the king leopold sandstone the current level of exposure of the diatremes probably extends from the lower diatreme facies up into the base of a bedded upper diatreme sequence

mineralogy of the tk1 and tk4 kimberlites in the timmasamudram cluster wajrakarur kimberlite field india implications for lamproite magmatism in a field of kimberlites and ultramafic lamprophyres abstract a mineralogical study of the hypabyssal facies late cretaceous macrocrystic pulse of tk1 intrusion and the mesoproterozoic aphanitic pulse of tk4 intrusion in the wajrakarur kimberlite field of southern india shows that the rocks contain macrocrysts of forsteritic olivine phenocrysts and microphenocrysts of al na poor diopside and phlogopite set in a groundmass mainly of al na poor diopside and phlogopite other groundmass minerals are spinel perovskite and fluorapatite in tk1 and spinel titanite chlorite calcite and gittinsite in tk4 k richterite and perovskite occur only as inclusions in phlogopite and titanite respectively in tk4 late stage deuteric phases include pyrite and barite in tk1 and strontianite chalcopyrite galena and pentlandite in tk4 diopside microphenocrysts in tk4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth tk1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite whereas tk4 spinels are less evolved with magnesiochromite composition only tk1 phlogopites show a simple compositional trend that is typical of lamproite micas while four distinct growth zones are observed in tk4 phlogopites with the following compositional characteristics zone i high cr 2 o 3 and tio 2 and low bao zone ii low cr 2 o 3 zone iii low tio 2 and high bao zone iv low bao forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for tk1 olivines mineralogically both tk1 and tk4 are classified as diopside phlogopite lamproites rather than archetypal kimberlites the two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions with elevated content of fe 3 in phlogopite spinel and perovskite tk1 appears to have crystallised in a relatively high oxygen fugacity environment multiple growth generations of phlogopite spinel and fluorapatite in tk4 indicate a complex evolutionary history of the magma close spatial and temporal associations of mesoproterozoic kimberlites and lamproites in southern india can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting

causes and consequences of pressurisation in lava dome eruptions abstract high total and fluid pressures develop in the interior of high viscosity lava domes and in the uppermost parts of the feeding conduit system as a consequence of degassing two effects are recognised and are modelled quantitatively first large increases in magma viscosity result from degassing during magma ascent strong vertical gradients in viscosity result and large excess pressures and pressure gradients develop at the top of the conduit and in the dome calculations of conduit flow show that almost all the excess pressure drop from the chamber in an andesitic dome eruption occurs during the last several hundred metres of ascent second microlites grow in the melt phase as a consequence of undercooling caused by gas loss rapid microlite growth can cause large excess fluid pressures to develop at shallow levels theoretically closed system microlite crystallization can increase local pressure by a few tens of mpa although build up of pressure will be countered by gas loss through permeable flow and expansion by viscous flow microlite crystallization is most effective in causing excess gas pressures at depths of a few hundred metres in the uppermost parts of the conduit and dome interior some of the major phenomena of lava dome eruptions can be attributed to these pressurisation effects including spurts of growth cycles of dome growth and subsidence sudden onset of violent explosive activity and disintegration of lava during formation of pyroclastic flows the characteristic shallow level long period and hybrid seismicity characteristic of dome eruptions is attributed to the excess fluid pressures which are maintained close to the fracture strength of the dome and wallrock resulting in fluid movement during formation of tensile and shear fractures within the dome and upper conduit

the 2001 2004 dome forming eruption of shiveluch volcano kamchatka observation petrological investigation and numerical modelling there have been three episodes of lava dome growth at shiveluch volcano kamchatka since the plinian explosive eruption in 1964 the episodes in 1980 1981 1993 1995 and 2001 2004 have discharged at least 0 27km 3 of silicic andesite magma a time averaged mean extrusion rate of 0 2m 3 s is thus estimated for the last 40years here the 2001 2004 activity is described and compared with the earlier episodes the recent activity involved three pulses in extrusion rate and a transition to ongoing lava extrusion estimated magma temperatures are in the range 830 to 900 c with 850 c as the best estimate using the plagioclase amphibole phenocryst assemblage and fe ti oxides melt inclusions in amphibole and plagioclase have maximum water contents of 5 1wt implying a minimum pressure of 155mpa for water saturated conditions the magma chamber depth is estimated to be about 5 6km or more a result consistent with geophysical data the thicknesses of opx mt amph reaction rims on olivine xenocrysts are used to estimate the residence time of olivine crystals in the shallow chamber in the range 2 months to 4 years suggesting replenishment of deeper magma into the shallow chamber contemporaneous with eruption the absence of decompression driven breakdown rims around amphiboles indicates ascent times of less than 7days volcanological observations of the start of the 2001 2004 episode suggest approximately 16 days for the ascent time and a conduit equivalent to a cylinder of diameter approximately 53 71m application of a conduit flow model indicates that the magma chamber was replenished during the 2001 2004 eruption consistent with the results of olivine reaction rims and that the chamber has an estimated volume of order 7km 3

crystallization of groundmass spinel in kimberlite groundmass spinel grains in 46 kimberlite and related rocks have been analyzed and compared the majority of the spinel analyses are classified as high chromium chromite chr and magnesioulvo spinel magnetite mum and represent two significant stages of spinel growth there are also a significant number of spinel grains that are classified as xenocryst spinel xen pleonaste spinel ple and magnetite mag eight different spinel zoning trends are identified the majority of the chr spinel grains are interpreted as a primary phase that crystallized as small octahedra from kimberlite magma on the journey from the upper mantle to the final resting place in the upper crust three zoning trends lead directly away from primary chromite the major zoning trend trend 1 is from chromite to magnesio ulvo spinel magnetite this zoning trend is unique to spinel in kimberlite carbonatites and lamprophyres we suggest that this somewhat oxidizing and more magnesian trend was influenced by the high carbonate content of group i kimberlites and the rapid crystallization of the minerals during the evolution of volatiles the zoningtrend 2 involves increasing titanium and ferric iron as a function of increasing fe 2 fe 2 mg this trend is similar to the zoning of spinel in basalt and is thought to be due to co crystallization of magnesium and aluminum rich silicate minerals such as olivine and phlogopite in kimberlites or pyroxene and plagioclase in basalt zoning trend 3 in kimberlite leads away from primary chromite and towards an aluminous pleonaste ple spinel this trend is characterized by a large decease of cr cr al parallel to so called olivine spinel iso potential lines similar trends of lesser magnitude and cyclic al cr zoning have been identified in basaltic spinel this trend is thought to be due to very rapid crystallization under conditions of supersaturation where the crystallization of spinel affects the local environment ahead of the growing spinel crystal i e diffusion controlled crystallization the tendency for immiscibility between ferrite or titanate rich spinel and aluminate rich spinel pleonaste has a great influence on trends 1 and 3 zoning and also on atoll spinel formation very local conditions such as nucleation or lack of nucleation of other minerals can influence both the textural environment and composition of kimberlitic spinel