phase equilibria in a volatile free kimberlite at 0 1 mpa and the search for primary kimberlite magma abstract phase relations at 0 1 mpa over a range of oxygen fugacities f o 2 from 1130 to 1350 c on a volatile free synthetic kimberlite analog composition show the crystallization sequence of olivine monticellite akermanite perovskite clinopyroxene ulvopsinel and kirschteinite at low pressures kimberlite liquids show limited change in ca si al and ti but a large variation in fe mg from the liquidus to 90 crystallization we observe low kd femg ol liq for kimberlite liquids 0 15 to 0 25 there is limited low pressure differentiation of kimberlites affecting mostly only feo and mgo by olivine fractionation or accumulation the low kd femg ol liq for kimberlite liquids require they crystallize higher mg olivine compared to most other mantle derived magmas olivine phenocrysts in kimberlite are dominantly more magnesian fo 92 94 than typical mantle olivine fo 90 and with a low kd femg ol liq necessitates the large amounts of this phase in kimberlites precipitated and accumulated at low pressure by decompression induced degassing of h 2 o or co 2 the comparison of experimental with natural data suggest that kimberlites can be viewed as essentially carbonate liquids with only 10 to 25 sio 2 nearly carbonatites that have accumulated olivine

the influence of whitecapping waves on the vertical structure of turbulence in a shallow estuarine embayment abstract the vertical distribution of the turbulent kinetic energy dissipation rate was measured using an array of four acoustic doppler velocimeters in the shallow embayment of grizzly bay san francisco bay california owing to the combination of wind and tide forcing in this shallow system the surface and bottom boundary layers overlapped whitecapping waves were generated for a significant spectral peak steepness greater than 0 05 or above a wind speed of 3 m s 1 under conditions of whitecapping waves the turbulent kinetic energy dissipation rate in the upper portion of the water column was greatly enhanced relative to the predictions of wind stress wall layer theory instead the dissipation followed a modified deep water breaking wave scaling near the bed bottom 10 of the water column the dissipation measurements were either equal to or less than that predicted by wall layer theory stratification due to concentration gradients in suspended sediment was identified as the likely cause for t

importance of pre existing oceanic conditions to upper ocean response induced by super typhoon hai tang 1 this study investigates upper ocean response to super typhoon hai tang the most intense typhoon in 2005 in the western north pacific using multi satellite microwave data typhoon data and argo profiles sequential merged microwave sea surface temperature sst images show that hai tang induced four separately cooling responses after its trail in the western north pacific during 11 18 july comparison between upper ocean responses of cooling sst and pre typhoon sea surface height suggests that these cooling responses of the upper ocean to hai tang are closely associated with pre existing cyclonic circulation denoted by pre existing negative sea surface features furthermore applying argo profiles the physical mechanism is confirmed to be associated with pre existing cyclonic circulations provide a relatively unstable thermodynamic structure and therefore cold water would be brought up readily this paper provides the rather convincing evidence that cyclonic flow and uplifted thermocline are the pre existing conditions for intensive cooling following the typhoon passage

numerical simulations of tropical cyclone ocean interaction with a high resolution coupled model the tropical cyclone ocean interaction was investigated using a high resolution tropical cyclone ocean coupled model the model design consisted of the noaa geophysical fluid dynamics laboratory tropical cyclone prediction model which was coupled with a multilayer primitive equation ocean model coupling between the hurricane and the ocean models was carried out by passing into the ocean model the wind stress heat and moisture fluxes computed in the hurricane model the new sea surface temperature sst calculated by the ocean model was then used in the tropical cyclone model a set of idealized numerical experiments were performed in which a tropical cyclone vortex was embedded in both easterly and westerly basic flows of 2 5 5 and 7 5 m s 1 with a fourth experiment run with no basic flow specified initially the profile of the tangential wind for hurricane gloria at 1200 utc 22 september 1985 was used as the initial condition of the tropical cyclone for each of the experiments the model ocean was initially horizontally homogenous and quiescent to clarify the impact of the ocean response to the hurricane s behavior analogous experiments were also carried out with the sst kept constant control cases the experiments indicated that the cooling of the sea surface induced by the tropical cyclone resulted in a significant impact on the ultimate storm intensity due to the reduction of total heat flux directed into the tropical cyclone above the regions of decreased sst the sea surface cooling produced by the tropical cyclones was found to be larger when the storms moved slower in the experiments run without an initial basic flow the maximum sst anomaly was about 5 6 c with a resulting difference in the minimum sea level pressure and maximum surface winds of 16 4 hpa and 7 m s 1 respectively in contrast in the experiments run with the 7 5 m s 1 basic flow the maximum sst anomalies ranged from about 2 6 to 3 0 c with a difference in the minimum sea level pressure and maximum surface winds of about 7 3 hpa and 2 7 m s 1 the tropical cyclone ocean coupling significantly influenced the storm track only for the case with no basic flow and the 2 5 m s 1 easterly flow in these cases the storm with the ocean interaction turned more to the north and east no basic flow or the north 2 5 m s 1 easterly flow of the experiments with constant sst in the first case the storm by 72 hours was located over 70 km to the east southeast of the control case a possible explanation for this track deviation is related to a systematic weakening of the mean tangential flow at all radii of the storm due to the interaction with the ocean and resulting alteration of the beta drift

the 3d oceanic mixed layer response to hurricane gilbert upper ocean heat and mass budgets are examined from three snapshots of data acquired during and after the passage of hurricane gilbert in the western gulf of mexico measurements prior to storm passage indicated a warm core eddy in the region with velocities of o 1 m s21 based upon conservation of heat and mass the threedimensional mixed layer processes are quantified from the data during and subsequent to hurricane passage horizontal advection due to geostrophic velocities is significant in the eddy regime suggesting that prestorm oceanic variability is important when background flows have the same magnitude as the mixed layer current response storm induced near inertial currents lead to large vertical advection magnitudes as they diverge from and converge toward the storm track surface fluxes estimated by reducing flight level winds to 10 m indicate a maximum wind stress of 4 2 n m22 and a heat flux of 1200 w m 22 in the directly forced region the upward heat flux after the passage of the storm has a maximum of 200 w m22 corresponding to a less than 7 m s21 wind speed entrainment mixing across the mixed layer base is estimated using three bulk entrainment closure schemes that differ in their physical basis of parameterization entrainment remains the dominant mechanism in controlling the heat and mass budgets irrespective of the scheme depending on the magnitudes of friction velocity surface fluxes and or shear across the mixed layer base the pattern and location of maximum entrainment rates differ in the directly forced region while the general area of maximum entrainment is in the right rear quadrant of the storm shear induced entrainment scheme predicts a narrow region of cooling compared to the the stressinduced mixing scheme and observed sst decreases after the storm passage the maximum contribution to the mixed layer dynamics is associated with shear induced entrainment mixing forced by near inertial motions up to the third day as indicated by bulk richardson numbers that remained below criticality thus entrainment based on a combination of surface fluxes friction velocity and shear across the entrainment zone may be more relevant for three dimensional ocean response studies

stable isotope composition of magmatic and deuteric carbonate phases in hypabyssal kimberlite lac de gras field northwest territories canada abstract the oxygen and carbon isotope compositions of carbonates from thirteen late cretaceous to paleogene hypabyssal intrusions from the lac de gras kimberlite field indicate that the carbonates are well preserved and have a complex paragenetic formation history kimberlites at ten localities studied are calcite bearing based on the presence of phenocrysts microphenocrysts and or millimeter scale calcite only segregations of sr rich calcite the calcite bearing kimberlites also contain large cm scale sr poor calcite serpentine segregations that are texturally distinct from the smaller sr rich calcite only segregations kimberlites at three other localities studied are dolomite bearing based on the presence of calcite dolomite segregations some of which preserve complex oscillatory and banded textures of calcite dolomite and magnesian calcite 18 o values for whole rock calcite in calcite bearing kimberlite and for micro samples of calcite from individual segregations in calcite and dolomite bearing kimberlite generally vary from 6 to 9 consistent with their formation at magmatic temperatures e g 750 c from a kimberlite melt in contrast higher 18 o values of 9 to 14 characterize micro samples of calcite from calcite serpentine segregations in calcite bearing kimberlite as well as whole rock dolomite and micro samples of dolomite from segregations in dolomite bearing kimberlite these data are consistent with formation from deuteric fluids late stage magmatic at sub solidus temperatures e g 500 to 100 c these higher 18 o values for whole rock calcite also correlate with increased intensity of forsterite alteration increased abundance of calcite serpentine segregations textural overprint of primary groundmass minerals by anhedral calcite and serpentine and development of atoll spinels all interpreted as a result of deuteric fluids in contrast whole rock calcite in dolomite bearing kimberlite has notably lower 18 o values of 1 5 to 5 5 interpreted to have formed from or been overprinted by locally derived high co 2 h 2 o deuteric fluids at 500 to 100 c 13 c values of the various types of calcite and dolomite 8 to 3 have no systematic variation with 18 o values and therefore there is no isotopic record of volatile degassing from these hypabyssal bodies

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

co magmatic sulfides and sulfates in the udachnaya east pipe siberia a record of the redox state and isotopic composition of sulfur in kimberlites and their mantle sources kimberlites of the udachnaya east pipe siberia include a uniquely dry and serpentine free rock type with anomalously high contents of chlorine cl 6 1 wt alkalies na2o k2o 10 wt and sulfur s 0 50 wt referred to as a salty kimberlite the straightforward interpretation is that the na k cl and s rich components originate directly from a carbonate chloride kimberlitic magma that is anhydrous and alkali rich however because brines and evaporites are present on the siberian craton previous studies proposed that the kimberlitic magma was contaminated by the assimilation of salt rich crustal rocks to clarify the origin of high cl alkalies and s in this unusual kimberlite here we determine its sulfur speciation and isotopic composition and compare it to that of non salty kimberlites and kimberlitic breccia from the same pipe as well as potential contamination sources hydrothermal sulfides and sulfates country rock sediment and brine collected in the area the average 34s of sulfides is 1 4 2 2 in the salty kimberlite 2 1 2 7 in the non salty kimberlites and 14 2 5 8 in the breccia the average 34s of sulfates in the salty kimberlites is 11 1 1 8 and 27 3 1 6 in the breccia in contrast the 34s of potential contaminants range from 20 to 42 for hydrothermal sulfides from 16 to 34 for hydrothermal sulfates 34 for a country rock sediment chukuck suite and the regional brine aquifer our isotope analyses show that 1 in the salty kimberlites neither sulfates nor sulfides can be simply explained by brine infiltration hydrothermal alteration or the assimilation of known salt rich country rocks and instead we propose that they are late magmatic phases 2 in the non salty kimberlite and breccia brine infiltration lead to sulfate reduction and the formation of secondary sulfides this explains the removal of salts alkali carbonates and sulfates as well as the minor olivine serpentinization 3 hydrothermal sulfur was added to the kimberlitic breccia but not to the massive kimberlites in situ measurements of sulfides confirm this scenario clearly showing the addition of two sulfide populations in the breccia pyrite pyrrhotites with average 34s of 7 9 3 4 and chalcopyrites with average 34s of 38 0 0 4 whereas the salty and non salty kimberlites preserve a unique population of djerfisherites cl and k rich sulfides with 34s values within the mantle range this study provides the first direct evidence of alkaline igneous rocks in which magmatic sulfate is more abundant than sulfide although sulfates have been rarely reported in mantle materials sulfate rich melts may be more common in the mantle than previously thought and could balance the sulfur isotope budget of earth s mantle

djerfisherite in kimberlites and their xenoliths implications for kimberlite melt evolution djerfisherite k6 fe ni cu 25s26cl occurs as an accessory phase in the groundmass of many kimberlites kimberlite hosted mantle xenoliths and as a daughter inclusion phase in diamonds and kimberlitic minerals djerfisherite typically occurs as replacement of pre existing fe ni cu sulphides i e pyrrhotite pentlandite and chalcopyrite but can also occur as individual grains or as poikilitic phase in the groundmass of kimberlites in this study we present new constraints on the origin and genesis of djerfisherite in kimberlites and their entrained xenoliths djerfisherite has extremely heterogeneous compositions in terms of fe ni and cu ratios however there appears to be no distinct compositional range of djerfisherite indicative of a particular setting i e kimberlites xenoliths or diamonds rather this compositional diversity reflects the composition of the host kimberlite melt and or interacting metasomatic medium in addition djerfisherite may contain k and cl contents less than the ideal formula unit raman spectroscopy and electron backscatter diffraction ebsd revealed that these k cl poor sulphides still maintain the same djerfisherite crystal structure two potential mechanisms for djerfisherite formation are considered 1 replacement of pre existing fe ni cu sulphides by djerfisherite which is attributed to precursor sulphides reacting with metasomatic k cl bearing melts fluids in the mantle or the transporting kimberlite melt 2 direct crystallisation of djerfisherite from the kimberlite melt in groundmass or due to kimberlite melt infiltration into xenoliths the occurrence of djerfisherite in kimberlites and its mantle cargo from localities worldwide provides strong evidence that the metasomatising infiltrating kimberlite melt fluid was enriched in k and cl we suggest that kimberlites originated from melts that were more enriched in alkalis and halogens relative to their whole rock compositions

parental carbonatitic melt of the koala kimberlite canada constraints from melt inclusions in olivine and cr spinel and groundmass carbonate abstract this study of the hypabyssal kimberlite with particularly fresh olivine from the palaeogene koala pipe ekati cluster slave craton canada is focused on reconstruction of the kimberlite parental melt the koala kimberlite sample is a typical ultramafic rock archetypal or group i kimberlite containing large abundance of forsteritic olivine set in a carbonate rich matrix the euhedral olivine ii shows significant zoning in terms of forsterite content and trace elements only the rims of olivine ii are considered to be magmatic they are uniform in terms of fo 91 5 0 2 mol and host primary crystal apatite cr spinel and melt inclusions the magmatic spinel phenocrysts are strongly zoned from titanian magnesian chromite to pleonaste with the cores having the same composition as spinel inclusions in olivine the primary and pseudo secondary melt inclusions in both magmatic cr spinel and olivine comprise a complex assemblage of daughter phases dominated by carbonate minerals dolomite eitelite na 2 mg co 3 2 shortite na 2 ca 2 co 3 3 nyerereite na 2 ca co 3 2 zemkorite na k 2 ca co 3 2 and fairchildite k 2 ca co 3 2 in addition to the dominant carbonates the melt inclusions contain phosphates chlorides and sulphates bradleyite na 3 mg po 4 co 3 halite sylvite aphthitalite na 0 25 k 0 75 2 so 4 but the silicate component is represented by tetraferriphlogopite only the melt inclusions in olivine studied in heating experiments show immiscibility of two carbonate liquids on heating and cooling and homogenise at low temperature 2 o sro and bao in wt 0 37 0 65 1 17 2 40 2 37 4 18 respectively such compositions are compared to secondary calcite replacing nyerereite and shortite in the natrocarbonatite lavas of the modern oldoinyo lengai volcano the results on mineralogy composition and homogenisation temperature of melt inclusions and the groundmass of the koala kimberlite imply that the parental kimberlite liquid was a si poor ca mg carbonate enriched in alkali elements lithophile trace elements phosphorus chlorine and sulphur

on the response of the ocean to a moving storm the nonlinear dynamics abstract a novel and efficient numerical method is used to investigate the nonlinear equations of motion for the upper layer of a two layer ocean in which the lower layer is infinitely deep and at rest the efficiency is achieved by seeking solutions that are in a steady state translating in equilibrium with the storm oscillations are found in the wake of the storm two features of the response are attributed to the nonlinear terms in the equation of motion 1 a rapid transition from a maximum in the downwelling phase to a maximum in the upwelling phase of each oscillation followed by a gradual relaxation to the next downwelling maximum and 2 a displacement of the maximum response usually to the right of the storm track by 40 km it is shown that the horizontal pressure gradient terms can be neglected from the momentum equations for fast large storms in which case a lagrangian integration can be performed following fluid particles this enables feature 1 to be attributed to the along tra

constraints on kimberlite ascent mechanisms revealed by phlogopite compositions in kimberlites and mantle xenoliths abstract kimberlite magmas are of economic and scientific importance because they represent the major host to diamonds and are probably the deepest magmas from continental regions in addition kimberlite magmas transport abundant mantle and crustal xenoliths thus providing fundamental information on the composition of the sub continental lithosphere despite their importance the composition and ascent mechanism s of kimberlite melts remain poorly constrained phlogopite is one of the few minerals that preserves a history of fluid migration and magmatism in the mantle and crust and is therefore an invaluable petrogenetic indicator of kimberlite magma evolution here we present major and trace element compositional data for phlogopite from the bultfontein kimberlite kimberley south africa i e the kimberlite type locality and from entrained mantle xenoliths phlogopite macrocrysts 0 3 0 5 mm and microcrysts between 0 1 and 0 3 mm in the bultfontein kimberlite display concentric compositional zoning patterns the cores of these phlogopite grains exhibit compositions typical of phlogopite contained in peridotite mantle xenoliths however the rims of some grains show compositions analogous to kimberlite groundmass phlogopite i e high ti al and ba low cr whereas other rims and intermediate zones between cores and rims exhibit unusually elevated cr and lower al and ba concentrations the latter compositions are indistinguishable from matrix phlogopite in polymict breccia xenoliths considered to represent failed kimberlite intrusions and from ti rich overgrowth rims on phlogopite in other mantle xenoliths consequently it is likely that these phlogopite grains crystallized from kimberlite melts and that the high ti cr zones originated from earlier kimberlite melts at mantle depths we postulate that successive pulses of ascending kimberlite magma progressively metasomatised the conduit along which later kimberlite pulses ascended producing progressively decreasing interaction with the surrounding mantle rocks in our view these processes represent the fundamental mechanism of kimberlite magma ascent our study also indicates that in addition to xenoliths xenocrysts and magmatic phases kimberlite rocks incorporate material crystallized at various mantle depths by previous kimberlite intrusions mantle derived antecrysts

composition and emplacement of the benfontein kimberlite sill complex kimberley south africa textural petrographic and melt inclusion constraints abstract the benfontein kimberlite is a renowned example of a sill complex and provides an excellent opportunity to examine the emplacement and evolution of intrusive kimberlite magmas we have undertaken a detailed petrographic and melt inclusion study of the benfontein upper middle and lower sills these sills range in thickness from 0 25 to 5 m new perovskite and baddeleyite u pb dating produced ages of 85 7 4 4 ma and 86 5 2 6 ma respectively which are consistent with previous age determinations and indicate emplacement coeval with other kimberlites of the kimberley cluster the benfontein sills are characterised by large variations in texture e g layering and mineral modal abundance between different sill levels and within individual samples the lower sill is characterised by carbonate rich diapirs which intrude into oxide rich layers from underlying carbonate rich levels the general paucity of xenogenic mantle material in the benfontein sills is attributed to its separation from the host magma during flow differentiation during lateral spreading the low viscosity is likely responsible for non explosive emplacement of the benfontein sills while the rhythmic layering is attributed to multiple magma injections the benfontein sills are marked by the excellent preservation of olivine and groundmass mineralogy which is composed of monticellite spinel perovskite baddeleyite ilmenite apatite calcite dolomite along with secondary serpentine and glagolevite namg6 si3alo10 oh o 8 h2o this is the first time glagolevite is reported in kimberlites groundmass spinel exhibits atoll textures and is composed of a magnesian ulvospinel magnetite mum or chromite core surrounded by occasional pleonaste and a rim of mg al magnetite we suggest that pleonaste crystallised as a magmatic phase but was resorbed back into the residual host melt and or removed by alteration analyses of secondary inclusions in olivine and primary inclusions in monticellite spinel perovskite apatite and interstitial calcite are largely composed of ca mg carbonates and to a lesser extent alkali carbonates and other phases these inclusions probably represent the entrapment of variably differentiated parental kimberlite melts which became progressively more enriched in carbonate alkalis halogens and sulphur during crystal fractionation carbonate rich diapirs from the lower sill contain more exotic phase assemblages e g ba fe titanate barite ancylite pyrochlore which probably result from the extreme differentiation of residual kimberlite melts followed by physical separation and isolation from the parental carbonate rich magma it is likely that any alkali or halogen rich minerals crystallising in the groundmass were removed from the groundmass during syn post magmatic alteration or in the case of na remobilised to form secondary glagolevite the benfontein sill complex therefore provides a unique example of how the composition of kimberlites may be modified after magma emplacement in the upper crust

87sr 86sr in kimberlitic carbonates by ion microprobe hydrothermal alteration crustal contamination and relation to carbonatite carbonates in a 30 cm wide zoned kimberlite dyke from the de beers mine kimberley s africa were studied by cathodoluminescence and electron microprobe techniques and their 87sr 86sr ratios were measured using an aei im20 ion microprobe primary carbonates including calcite dendrites rhombohedral calcites in segregation vesicles and mosaic dolomite have high sr 0 69 1 35 wt sro and ba 0 24 0 44 bao and 87sr 86sr ratios in the range 0 7046 to 0 7056 secondary sparry calcite in amygdales and veins is characterised by low ba 0 05 bao and 87sr 86sr near 0 72 rhombohedral calcite 0 5 cm from a contact with 2 900 my old biotite gneiss has minor element chemistry like that of primary carbonate but an elevated 87sr 86sr ratio of 0 7103 possibly indicating crustal contamination in a boundary layer of the kimberlite magma amygdale like segregations of carbonate and or serpentine originated as gas cavities and were not formed by liquid immiscibility they are now filled either by secondary calcite or by minerals precipitated from residual kimberlite liquid however dendritic calcite and primary dolomite and calcite with high sr ba and low 87sr 86sr demonstrate shared chemical characteristics between these carbonates and carbonatite the primary kimberlite magma had initial 87sr 86sr close to 0 7046

upper ocean thermal structure and the western north pacific category 5 typhoons part ii dependence on translation speed abstract using new in situ ocean subsurface observations from the argo floats best track typhoon data from the u s joint typhoon warning center an ocean mixed layer model and other supporting datasets this work systematically explores the interrelationships between translation speed the ocean s subsurface condition characterized by the depth of the 26 c isotherm d26 and upper ocean heat content uohc a cyclone s self induced ocean cooling negative feedback and air sea enthalpy fluxes for the intensification of the western north pacific category 5 typhoons based on a 10 yr analysis it is found that for intensification to category 5 in addition to the warm sea surface temperature generally around 29 c the required subsurface d26 and uohc depend greatly on a cyclone s translation speed it is observed that even over a relatively shallow subsurface warm layer of d26 60 70 m and uohc 65 70 kj cm 2 it is still possible to have a sufficient enthalpy flux to intensify the storm to category 5

mechanically disrupted and chemically weakened zones in segmented dike systems cause vent localization evidence from kimberlite volcanic systems deformation and alteration zones along kimberlite dikes hold clues as to how point source volcanic vents can localize along sheet like intrusions brittle deformation zones occur in host rock adjacent to kimberlite intrusions of the swartruggens kimberlite dike swarm south africa deformation includes local fracturing and brecciation and is associated with relay zones between offset dike segments breccia zones indicate dilation and hydraulic fracturing and some zones along the dikes were affected by chemical corrosion forming fresh cores surrounded by onion skin concentric shells of altered rock the alteration was caused by either exsolved magmatic volatiles moving in advance of the magma through the fracture or by hydrothermal fluids consideration of the time scales needed for chemical corrosion of host rock requires intrusions to stall at depth prior to transport to higher crustal levels highly disrupted offsets could be preferred locations for explosive activity and initial vent formation as dikes approach the surface a kimberlite pipe forms after magma breaks through to the surface the altered zones are reamed out and fresh cores in spheroidally altered rock are incorporated into the pipe fill along with more angular country rock material as observed in layered volcanic breccias in kimberlite pipes at the venetia mine south africa this model may have wider implications for the localization of conduits along dikes in other volcanic systems dike segmentation provides weak zones where hydrothermal fluids and magmatic volatiles can be preferentially channeled chemical corrosion can further weaken these zones which may then become the locus for initial phreatic and phreatomagmatic explosions creating shallow vents that can then channel magma to the surface during eruption

the volatile content of hypabyssal kimberlite magmas some constraints from experiments on natural rock compositions kimberlites are volatile rich magmas that ascend from deep in the mantle at high velocities then as they reach a root zone at 1 3 km in depth they either discharge explosively through to the surface or stall to form dykes and sills understanding this eruptive behaviour is difficult due to a lack of data on volatile solubility particularly at conditions where the magmas enter the root zone 30 80 mpa in this study we perform experiments on some putative primary kimberlite magma compositions to assess the amount of co2 and h2o retained if these compositions represent magma as it enters the root zone at the conditions investigated 100 200 mpa and 1 275 1 100 c the results suggest that none of these particular kimberlite compositions reproduce a magma that can retain the observed high volatile content when intruded at these pressures 4 8 km in our experiments the low volatile retention is due to a combination of factors including a high proportion of solid phases none of which are volatile bearing and inadequate volatile solubilities in the subordinate amounts of melt present modelled solubilities also suggest that the dissolved volatile contents remain too low even at super liquidus temperatures i e 100 melt for water the higher values observed in natural rocks can be explained by the addition of h2o associated with ubiquitous post emplacement serpentinization the high co2 contents in hypabyssal rocks are unlikely to be related to alteration we suggest that most kimberlites originally had lower sio2 contents and as such may have been transitional between silicate and carbonate melts this results in both higher co2 solubilities and lower liquidus temperatures for such compositions it is possible that both co2 and water solubility may first decrease and then increase as magmas decompress and crystallize such unusual behaviour can help explain why kimberlite magmas can be very explosive or form shallow hypabyssal intrusions

orthopyroxene survival in deep carbonatite melts implications for kimberlites kimberlites are rare diamond bearing volcanic rocks that originate as melts in the earth s mantle the original composition of kimberlitic melt is poorly constrained because of mantle and crustal contamination exsolution of volatiles during ascent and pervasive alteration during and after emplacement one recent model russell et al in nature 481 7381 352 356 2012 doi 10 1038 nature10740 proposes that kimberlite melts are initially carbonatitic and evolve to kimberlite during ascent through continuous assimilation of orthopyroxene and exsolution of co2 in high temperature high pressure experiments designed to test this model assimilation of orthopyroxene commences between 2 5 and 3 5 gpa by a reaction in which orthopyroxene reacts with the melt to form olivine clinopyroxene and co2 no assimilation occurs at 3 5 gpa and above we propose that the clinopyroxene produced in this reaction can react with the melt at lower pressure in a second reaction that produces olivine calcite and co2 which would explain the absence of clinopyroxene phenocrysts in kimberlites these experiments do not confirm that assimilation of orthopyroxene for the entirety of kimberlite ascent takes place but rather two reactions at lower pressures 3 5 gpa cause assimilation of orthopyroxene and then clinopyroxene evolving carbonatitic melts to kimberlite and causing co2 exsolution that drives rapid ascent

controls on the explosive emplacement of diamondiferous kimberlites new insights from hypabyssal and pyroclastic units in the diavik mine canada abstract kimberlites are mantle derived magmas that either crystallise as hypabyssal intrusions erupt explosively after rapid ascent to the surface or less commonly form lava lakes and flows thereby creating texturally distinct kimberlite units efforts to fully understand the processes responsible for the explosive eruption of kimberlite magmas have been hindered by the widespread alteration and crustal contamination of most volcaniclastic kimberlites to address this issue we have undertaken a detailed petrographic and mineral chemical study of fresh i e minimally altered pyroclastic and hypabyssal kimberlites hk from the ca 55 56 ma a154 north and south kimberlite pipes in the diavik mine lac de gras canada these localities host exceptionally fresh kimberlites and are therefore ideally suited to this study kimberlite emplacement at a154 north and south initiated with the intrusion of hypabyssal kimberlite external dykes and was followed by the explosive formation of kimberlite pipes and volcaniclastic kimberlite infill subsequent kimberlite magmas intruded the volcaniclastic kimberlite units forming multiple cross cutting internal dykes the studied volcaniclastic units feature abundant rounded magmaclasts and massive textures suggestive of primary deposits these units are classified as pyroclastic kimberlites pk pyroclastic and hypabyssal kimberlite units at diavik exhibit subtle mineral compositional differences samples from both internal hk units and pk units feature identical compositions for liquidus olivine rims mg 90 5 0 1 and 90 7 0 2 respectively with a marginally lower mg of 90 2 0 2 in olivine rims from the external hk dykes similarly early formed chromite compositions are the same for internal hk and pk units cr 79 1 3 4 and 78 3 5 7 mg 60 0 1 3 and 60 0 2 2 but differ in the external hk units cr 86 9 2 7 mg 52 8 1 9 the internal hk and pk units also exhibit lower carbonate contents than the internal hk units these compositional differences indicate that the external dykes were probably derived from slightly different primitive melt compositions to those parental to the internal hk and pk units spinel evolutionary trends from chromite to magnesian ulv spinel magnetite mum compositions are indistinguishable in internal hk and pk samples fe3 47 2 5 8 and 49 7 9 3 cr 25 7 11 0 and 17 0 14 0 these results demonstrate that the primitive melt compositions and early magmatic evolution processes are identical for the internal kimberlite units regardless of whether the kimberlite melts erupted explosively or were emplaced as shallow intrusions however magmaclasts in the pk units contain higher abundances of phlogopite

the origin of high hydrogen content in kimberlitic olivine evidence from hydroxyl zonation in olivine from kimberlites and mantle xenoliths abstract olivine macrocrysts in kimberlites are the most h rich natural olivines known their xenocrystic provenance makes unclear whether h enrichment occurred in the mantle prior to entrainment in kimberlite magma or during ascent we present a fourier transform infrared ftir spectroscopy based study of h zonation in kimberlite derived olivine macrocrysts and or olivine in xenoliths from the kimberlites jericho nunavut canada beartooth northwest territories canada and pipe 200 and matsoku lesotho the objective of the study was to determine whether changes in the concentration or speciation of h defects in proximity to the host kimberlite could yield insights into the origin of h enrichment within the group 1 region of the ftir spectrum 3420 3700 cm 1 we find that olivines within xenoliths and macrocrysts show weak zonation or significant h depletions in rims peaks in the group 2 region 3260 3420 cm 1 in beartooth olivines show marked decrease in the crystal margins in comparison to group 1 peaks we find no preserved evidence for kimberlite related h enrichment in our dataset we ascribe h depletion to diffusive h loss to infiltrating kimberlitic media diffusion models using coefficients previously applied to dehydrogenation of olivine and assuming a dry environment produce extremely short ascent durations incompatible with the results of other geospeedometers this mismatch suggests that the poorly developed zonation in jericho and beartooth olivines indicates water enrichment and or faster ascent of these melts in comparison to pipe 200 and matsoku resulting in greater retention of mantle derived h a further significant factor in the mismatch is the differing speciation of h in most natural mantle derived olivines in comparison to those used in diffusion experiments we argue that the presence of presumably mantle derived group 2 h in olivine macrocrysts indicates rapid ascent of magma exsolving water rich fluid permitting preservation of these faster diffusing defects only in particularly rapidly ascending kimberlite magmas this interpretation explains empirical correlations between the presence of group 2 bands water derived diamond resorption features and volcaniclastic kimberlite facies

geological constraints on the eruption of the jwaneng centre kimberlite pipe botswana abstract geological mapping has allowed constraints to be placed on the eruption mechanisms involved in the formation of the late permian early triassic jwaneng centre kimberlite pipe botswana twelve lithofacies and three lithofacies associations lfa 1 3 are recognised lfa 1 comprises massive to bedded volcaniclastic kimberlite and marginal shale breccias and outcrops over 65 of the surface area of the pipe it is characterised by a lithic population dominated by transvaal shale clasts lfa 1 grades into lfa 2 which comprises massive and bedded volcaniclastic kimberlite and volcaniclastic breccias and outcrops over 19 of the surface area of the pipe the lithic population of lfa 2 is dominated by contorted and fluidal outlined karoo age mudstones and siltstones lfa 3 comprises a wedge shaped unit in the north of the pipe and consists of a series of allochthonous megablocks of sedimentary and volcaniclastic strata the juvenile clast type and matrix mineral assemblages of the volcaniclastic deposits in the centre pipe differ from those in many other southern african kimberlite pipes various emplacement models for kimberlite pipes are discussed and evaluated in the light of the new geological data both a maar diatreme model and an explosive volatile driven eruption model could account for much of the geology of the centre pipe and distinguishing between the two models based on deposits alone is difficult there is strong circumstantial evidence for ambient conditions favourable to phreatomagmatism at the time of the eruption and the influence of external water may explain the differences between the jwaneng centre pipe and the class 1 kimberlites common across southern africa in terms of both the juvenile clasts and of the inter clast cement however low abundances of some types of lithic inclusions derived from major country rock units pose an unresolved problem for a classic maar diatreme model of pipe formation

petrology of hypabyssal kimberlites relevance to primary magma compositions abstract hypabyssal kimberlites are similar in their mineralogy and geochemistry across the world and thus form a distinct magma type that is produced repeatedly in time and space this small volume magma is derived from the asthenosphere 200 650 km and as it nears the surface consists of olivine macrocrysts i e xenocrysts 25 vol olivine phenocrysts 25 vol entrained in a ba ti mg rich al poor carbonate silicate liquid containing high but unknown amounts of dissolved co2 ch4 and h2o hypabyssal kimberlites are shown to be hybrid rocks formed by mixing with and assimilation of mantle derived lherzolite and harzburgite orthopyroxene is not stable in these magmas and its resorption leads the precipitation of primary liquidus olivine the magma crystallizes rapidly at crustal levels to uniform holocrystalline rocks that do not contain glass in addition to spinel perovskite monticellite apatite and phlogopite kinoshitalite primary carbonates are typically present as low pressure liquidus phases serpentines primary polygonal serpentine and chrysotile and carbonate commonly crystallize together from volatile rich co2 h2o deuteric residua as a polycrystalline mesostasis or discrete segregations the latter are not in filled vesicles kimberlite magmas have a very long crystallization interval ranging from 1200 to 300 c and there is a continuum from the magmatic crystallization of silicate and oxide minerals to carbo hydrothermal residua forming the calcite serpentine mesostasis it is concluded that there are no hypabyssal kimberlites which are representatives of the initial primary magma all kimberlites are hybrid and contaminated magmas which have undergone crystallization in the mantle prior to crystallization of the groundmass mesostasis assemblages

decrease of hydrogen incorporation in forsterite from co2 h2o rich kimberlitic liquid to test if hydrogen incorporation by ionic diffusion can occur between a volatile rich kimberlitic liquid and forsterite results of high pressure and high temperature experiments using a piston cylinder apparatus at 1200 1300 c and 1 gpa for durations of 1 min 5 h and 23 h are reported here kimberlitic liquid in the system cao mgo al2o3 sio2 co2 h2o and synthetic forsterite single crystals were chosen as a first simplification of the complex natural kimberlite composition unpolarized fourier transform infrared spectroscopy was used to quantify the concentrations of oh in the crystallographically oriented forsterite scanning electron microscopy electron backscattered diffraction electron microprobe analyses and transmission electron microscopy were performed to identify the run products after 5 and 23 h a forsterite overgrowth crystallized with the same orientation as the initial forsterite single crystal the kimberlitic liquid has crystallized as micrometer scale euhedral forsterite neocrystals with random crystallographic orientations as well as a nanoscale aluminous phase and a calcic phase despite theoretical water saturation of the system and long duration none of the initial forsterite single crystals display signs of hydration such as hydrogen diffusion profile from the border toward the center of the crystal most likely the presence of co2 in the system has lowered the h2o fugacity to such an extent that there is no significant hydration of the starting forsterite single crystal or its overgrowth also the presence of co2 enhances rapid forsterite crystal growth forsterite growth rate is around 2 108 m3 h at 1250 c these experimental results suggest a deep mantle origin of the high oh content found in natural mantle derived xenoliths transported in kimberlites as reported from the kaapvaal craton in agreement with previous studies it also points out to the fact that significant hydration must take place in a co2 poor environment

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

estimate of ocean mixed layer deepening after a typhoon passage over the south china sea by using satellite data abstractthe ocean responses to typhoon cimaron which influenced the south china sea scs from 1 to 8 november 2006 are analyzed based on satellite observed sea surface temperature sst and climatological temperature profiles in the scs mixed layer deepening an important parameter characterizing turbulent mixing and upwelling driven by strong typhoon winds is derived corresponding to the sst drop of 4 4 c on 3 november 2006 the mixed layer deepened by 104 5 m relative to the undisturbed depth of 43 2 m which is consistent with a simulation result from a mixed layer model furthermore baroclinic geostrophic velocity and vorticity are calculated from the surface temperature gradient caused by the typhoon the negative vorticity associated with the typhoon cooling indicated an anticyclonic baroclinic circulation strongest at the base of the mixed layer and at the depth of 50 m the geostrophic speed reached as high as 0 2 m s 1 typhoon cimaron proceeded slowly 1 7 m s 1 when it was making a s

geology of the orion south kimberlite fort a la corne canada abstract a wide variety of primary pyroclastic volcaniclastic and re sedimented volcaniclastic deposits derived from multiple kimberlite eruptions are exceptionally well preserved at the orion south kimberlite body in the fort a la corne field in central saskatchewan construction of this kimberlite complex involved episodic kimberlite volcanic events punctuated by periods of volcanic quiescence erosion and sedimentary deposition within the western canadian sedimentary basin the orion south kimberlite complex erupted into deltaic coastal plain transitional estuarine mannville group cantuar and pense formations and shallow marine lower colorado group joli fou viking and westgate formations environments at orion south eight distinct kimberlite phases erupted over 6 to 7 million years from ca 106 ma cantuar formation equivalent to ca 99 ma viking formation equivalent detailed core logging geochemistry chronostratigraphy petrography and geophysics were undertaken to define distinct eruptive phases and reconstruct the depositional environment volcanic styles and 3 d architecture of the complex the eight main kimberlite deposits record eruptive styles ranging from magmatic to wet and dry phreatomagmatic to submarine eruptions a consequence of the varying interaction between kimberlite magma and seawater and or groundwater

temperature changes in ascending kimberlite magma abstract we present a thermodynamical model of kimberlite magma ascent from 200 km depth and from 400 km depth we model four different magma compositions a basalt and a carbonatite to bound kimberlite behaviour and two intermediate cases that represent kimberlite 1 has properties intermediate to carbonatite and basalt and kimberlite 2 has properties that are closer to basalt the results show that adiabatic expansion of the melt phase can be a large cooling effect during kimberlite melt ascent accounting for 140 c cooling of kimberlite 1 and 90 c cooling of kimberlite 2 melts with high volatile contents are more corrosive during magma ascent enriching the melts in mgo as olivine xenocrysts are assimilated kimberlite magma temperatures decrease during ascent up to the onset of rapid pressure induced olivine crystallization the models show that little olivine assimilation occurs during kimberlite ascent 2 o models where 5 wt h 2 o 5 wt co 2 is exsolved are consistent with observations of approximately 25 phenocrysts and 25 xenocrysts in many kimberlites

the molecular structure of melts along the carbonatite kimberlite basalt compositional joint co2and polymerisation transitional melts intermediate in composition between silicate and carbonate melts form by low degree partial melting of mantle peridotite and might be the most abundant type of melt in the asthenosphere their role in the transport of volatile elements and in metasomatic processes at the planetary scale might be significant yet they have remained largely unstudied their molecular structure has remained elusive in part because these melts are difficult to quench to glass here we use ftir raman 13c and 29si nmr spectroscopy together with first principle molecular dynamic fpmd simulations to investigate the molecular structure of transitional melts and in particular to assess the effect of co2on their structure we found that carbon in these glasses forms free ionic carbonate groups attracting cations away from their usual depolymerising role in breaking up the covalent silicate network solution of co2in these melts strongly modifies their structure resulting in a significant polymerisation of the aluminosilicate network with a decrease in nbo si of about 0 2 for every 5 mol co2dissolved this polymerisation effect is expected to influence the physical and transport properties of transitional melts an increase in viscosity is expected with increasing co2content potentially leading to melt ponding at certain levels in the mantle such as at the lithosphere asthenosphere boundary conversely an ascending and degassing transitional melt such as a kimberlite would become increasingly fluid during ascent hence potentially accelerate carbon rich transitional melts are effectively composed of two sub networks a carbonate and a silicate one leading to peculiar physical and transport properties

satellite observations of sea surface cooling by hurricanes sea surface cooling associated with 13 hurricanes in the western north atlantic between september 1981 and december 1984 is examined using satellite derived sea surface temperature fields some surface cooling is observed in all cases however because of cloud cover and the fairly weak signal in some cases we see pronounced cooling along an extensive and continuous portion of the storm path for only three strong hurricanes the persistence of cooling following the passage of a hurricane varies from a few days to at least 16 days the amplitude of cooling is moderately well correlated with hurricane strength and is as large as 3 5 c when the hurricanes move rapidly the maximum cooling occurs well to the right of the track approximately 70 km whereas for slowly moving hurricanes the maximum cooling occurs near or on the track because western north atlantic hurricanes are often found in close proximity to high pressure systems daytime satellite images must be made with some care because of diurnal warming

a reply to the comment by gernon et al on the petrography of the snap lake kimberlite dyke northwest territories canada and its interaction with country rock granitoids by fulop et al 2018

a co2 solubility model for silicate melts from fluid saturation to graphite or diamond saturation abstract a model based on a thermodynamic framework for co2 concentrations and speciation in natural silicate melts at graphite diamond saturated to fluid saturated conditions is presented the model is simultaneously calibrated with graphite saturated and fluid saturated conditions allowing for consistent model predictions across the cco buffer the model was calibrated using water poor 1 wt h2o silicate melts from graphite to co2 fluid saturation over a range of pressure p 0 05 3 gpa temperature t 950 1600 c composition foidite rhyolite nbo 0 02 0 92 wt sio2 39 77 tio2 0 1 5 8 al2o3 7 5 18 feo 0 2 24 mgo 0 1 24 cao 0 3 14 na2o 1 5 k2o 0 6 and fo2 qfm 1 5 to qfm 6 the model can predict co2 concentrations for a wide range of silicate melt compositions from ultramafic to rhyolitic compositions i e melts that dissolve carbon only as carbonate anions co32 and those that dissolve carbon both as co32 and as molecular co2mol as a function of pressure temperature and oxygen fugacity the model also does a reasonable job in capturing co2 solubility in hydrous silicate melts with 2 3 wt h2o new co2 solubility experiments at pressures 3 gpa suggest that the newly developed co2 solubility model can be satisfactorily extrapolated to 4 5 gpa above 5 gpa the model poorly reproduces experimental data likely owing to structural change in silicate melt at pressures above 5 gpa an excel spreadsheet and a matlab function are provided as online supplementary materials for implementing the new co2 solubility model presented here

root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar diatreme volcanoes abstract the understanding of processes within the root zone of maar diatreme volcanoes is important for the interpretation of the geology volcanology and even hazard assessment of these volcanoes in the phreatomagmatic model of pipe formation the irregularly shaped root zone is the site of the phreatomagmatic explosions and thus functions as the engine for pipe formation in this model the root zone grows over a period of time in a series of many single thermohydraulic i e phreatomagmatic explosions the explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels the ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole like fashion into the root zone many phreatomagmatic eruptions consequently result in the formation of a cone shaped diatreme thus with ongoing eruptions the cone shaped diatreme has to grow systematically both in depth and diameter during its growth processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone at the surface the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter thermohydraulic explosions which fragment both magma and the surrounding country rocks mostly occur within the bottom part of the root zone violent explosions in small pipes may clear the overlying diatreme for a short period of time before tephra fall and collapse of the walls of the new crater refill the small initial diatreme in larger pipes via expansion of the mixture of highly pressurized water vapor juvenile gas phases and explosively produced tephra the confined and expanding eruption cloud has to pierce through the diatreme fill in a feeder conduit in order to erupt diatreme clearing events in large pipes are difficult or impossible to maintain since the explosive force in the root zone is only in exceptional instances strong enough to lift or entrain the entire diatreme tephra knowledge of the genetic relationships between root zones and diatremes is critical to understand pipe growth processes the combination of such processes can lead to substantial variation in volcanic behavior and thus produce fundamentally different volcano and rock types it is the purpose of this paper to outline important features of root zones and suggest their significance for the genesis and evolution of maar diatreme and related volcanoes

asthenospheric kimberlites volatile contents and bulk compositions at 7 gpa abstract during ascent kimberlites react with the lithospheric mantle entrain and assimilate xenolithic material loose volatiles and suffer from syn and post magmatic alteration consequently kimberlite rocks deviate heavily from their primary melt experiments at 7 gpa 1300 1480 c 10 30 wt co 2 and 0 46 wt h 2 o on a proposed primitive composition from the jericho kimberlite show that saturation with a lherzolitic mineral assemblage occurs only at 1300 1350 c for a carbonatitic melt with 2 and 35 wt co 2 at asthenospheric temperatures of 1400 c where the jericho melt stays kimberlitic this composition saturates only in low ca pyroxene garnet and partly olivine we hence forced the primitive jericho kimberlite into multiple saturation with a lherzolitic assemblage by adding a compound peridotite saturation in olivine low and high ca pyroxene and garnet was obtained at 1400 1650 c 7 gpa melts are kimberlitic with 18 29 wt sio 2 al 2 o 3 22 1 24 6 wt mgo 15 27 wt co 2 and 0 4 7 1 wt h 2 o with a trade off of h 2 o vs co 2 and temperature melts in equilibrium with high ca pyroxene with typical mantle compositions have 2 5 wt na 2 o much higher than the commonly proposed 0 1 0 2 wt the experiments allow for a model of kimberlite origin in the convective upper mantle which only requires mantle upwelling that causes melting at the depth where elemental carbon in metal diamond or carbide converts to co 2 at 250 km if primary melts leading to kimberlites contain a few wt h 2 o then adiabatic temperatures of 1400 1500 c would yield asthenospheric mantle melts that are kimberlitic 18 wt sio 2 al 2 o 3 but not carbonatitic 2 al 2 o 3 in composition carbonatites only forming 100 200 c below the adiabat these kimberlites represent small melt fractions concentrating co 2 and h 2 o and then acquire part of their chemical signature by assimilation fractionation during ascent in the subcratonic lithosphere

apatite compositions and groundmass mineralogy record divergent melt fluid evolution trajectories in coherent kimberlites caused by differing emplacement mechanisms kimberlites are pipe like igneous bodies consisting of a pyroclastic crater and diatreme commonly underlain by coherent root zone rocks and with associated dyke sill complexes the processes that control the different modes of coherent kimberlite emplacement remain uncertain in addition late evolution of kimberlite melts during emplacement into the upper crust remains poorly constrained therefore it is unclear whether there is a link between melt composition evolution and the emplacement mechanism of coherent kimberlites i e planar dykes sills vs irregular bodies in the root zone an absence of comparative studies on late stage magmatic phases across the different emplacement modes of coherent kimberlite from the same locality hamper resolution of these issues therefore we report petrographic and mineral chemical data for groundmass apatite in samples of dyke sill and root zone kimberlites from the kimberley cluster south africa early crystallised phases olivine spinel mg ilmenite in dyke sill and root zone kimberlites have indistinguishable compositions and hence crystallised from similar primitive melts conversely apatite compositions are generally distinct in dyke sill low sr high and variable si and root zone kimberlites high and variable sr low si the si enrichment of apatite in dykes sills is attributed to the coupled incorporation of co32 and sio44 for po43 reflecting higher co2 contents in their parental melts and potentially higher si contents due to the preferential crystallisation of carbonates over mica monticellite the low sr contents of apatite in dyke sill kimberlites reflect equilibrium with a kimberlite melt i e dsr is close to unity for carbonate and silicate melts whereas the higher sr contents of apatite in root zone kimberlites require crystallisation from or overprinting by a h2o co2 fluid significantly higher dsr the relative enrichment of co2 in kimberlite dykes sills is evident from the abundance of carbonates the presence of mesostasis dolomite and calcite phenocrysts in some samples and concomitant reduced proportions of other groundmass phases e g serpentine mica monticellite during late alteration of kimberlite dykes sills monticellite is typically replaced by carbonates whereas olivine and pleonaste are relatively stable indicating the melts which form dykes sills evolve to higher co2 h2o ratios it is unlikely that these two distinct evolutionary paths were caused by crustal contamination before or during near surface magma emplacement because crustal assimilation is not recorded in the o and sr isotopic composition of late crystallising olivine rinds or carbonates respectively we suggest that higher concentrations of co2 are retained in kimberlite dykes sills due to higher confining pressures i e lack of breakthrough to the surface in contrast exsolution of co2 from root zone kimberlites increased melt h2o co2 ratios and promoted the crystallisation of mica and monticellite at the expense of dolomite and calcite apatite compositions have the potential to aid in the discrimination of kimberlites from lamproites higher lree sr f and s lower si contents and carbonatites higher lree f cl and s lower fe contents however the compositions of kimberlitic apatite overlap those from aillikites probably due to similar late stage melt compositions

ferric iron in catio3 perovskite as an oxygen barometer for kimberlite magmas ii applications we apply an oxygen barometer based on the fe content of catio3 perovskite to estimate the oxygen fugacity fo2 during the crystallization and emplacement of kimberlites in different eruptive phases of a single pipe or between different pipes clusters or provinces mineral chemical data for perovskite were compiled from the literature and obtained in our detailed study of perovskites from 11 kimberlites at somerset island and lac de gras canada perovskite compositions in kimberlites record a range in fo2 of many orders of magnitude from nno 5 to nno 6 where log fo2 is given relative to the nickel nickel oxide nno buffer the range of fo2 recorded by different parageneses of perovskite within a single pipe can vary up to three orders of magnitude with trends toward both oxidation and reduction during crystallization kimberlites record some of the greatest ranges and the highest known fo2 conditions for any terrestrial magma this is attributed to the presence of deep and oxidized source regions and the variable interplay of ferric ferrous vs carbon fluid equilibria during ascent of kimberlite magmas three kimberlite pipes from the lac de gras field show that higher fo2 values correlate with higher proportions of more resorbed diamonds suggesting that this variable has a measurable effect on the physical properties of diamonds in a pipe

the ascent of kimberlite insights from olivine olivine xenocrysts are ubiquitous in kimberlite deposits worldwide and derive from the disaggregation of mantle derived peridotitic xenoliths here we provide descriptions of textural features in xenocrystic olivine from kimberlite deposits at the diavik diamond mine canada and at igwisi hills volcano tanzania we establish a relative sequence of textural events recorded by olivine during magma ascent through the cratonic mantle lithosphere including xenolith disaggregation decompression fracturing expressed as mineral and fluid inclusion rich sealed and healed cracks grain size and shape modification by chemical dissolution and abrasion late stage crystallization of overgrowths on olivine xenocrysts and lastly mechanical milling and rounding of the olivine cargo prior to emplacement ascent through the lithosphere operates as a kimberlite factory wherein progressive upward dyke propagation of the initial carbonatitic melt fractures the overlying mantle to entrain and disaggregate mantle xenoliths preferential assimilation of orthopyroxene opx xenocrysts by the silica undersaturated carbonatitic melt leads to deep seated exsolution of co2 rich fluid generating buoyancy and supporting rapid ascent concomitant dissolution of olivine produces irregular shaped relict grains preserved as cores to most kimberlitic olivine multiple generations of decompression cracks in olivine provide evidence for a progression in ambient fluid compositions e g from carbonatitic to silicic during ascent numerical modelling predicts tensile failure of xenoliths disaggregation and olivine cracks over ascent distances of 2 7 km and 15 25 km respectively at velocities of 0 1 to 4 m s 1 efficient assimilation of opx during ascent results in a silica enriched olivine saturated kimberlitic melt i e sio2 20 wt that crystallizes overgrowths on partially digested and abraded olivine xenocrysts olivine saturation is constrained to occur at pressures 1 gpa an absence of decompression cracks within olivine overgrowths suggests depths 25 km late stage 25 km resurfacing and reshaping of olivine by particle particle milling is indicative of turbulent flow conditions within a fully fluidized gas charged crystal rich magma

quantitative modelling of the apparent decoupling of mg and ni in kimberlitic olivine margins comment on cordier et al journal of petrology 56 1775 1796 2015

gyrolithes from the ediacaran cambrian boundary section in fortune head newfoundland canada exploring the onset of complex burrowing abstract the beginning of the cambrian explosion is characterized by the onset of infaunalization and the appearance of systematic patterns of burrowing the trace fossil gyrolithes is common in the ediacaran cambrian global stratotype section and point where it shows a higher diversity and burrow depth than previously reported from any cambrian spiral vertical burrows two ichnospecies are present g scintillus isp nov exhibits a small burrow radius to whorl radius ratio whereas g gyratus hofmann exhibits an exceptionally large ratio that formerly led to its identification as an aberrant ichnospecies of skolithos the helical morphology of these cambrian gyrolithes is interpreted as having served two purposes as an anchor in a relatively high energy environment and as an optimal shape for maximizing surface area for bacterial gardening these shallow marine gardening burrows share a similar feeding strategy as graphoglyptids suggesting that shallow early cambrian sediments may have been relatively poor in organics and thus further supporting the model for onshore offshore migration of gardening burrows

hurricane forced upwelling and chlorophyll a enhancement within cold core cyclones in the gulf of mexico 1 clear skies subsequent to hurricane ivan s passage across the gulf of mexico in september 2004 provided a unique opportunity to investigate upper ocean responses to a major hurricane oceanic cyclonic circulation was rapidly intensified by the hurricane s wind field 59 62 m s 1 maximizing upwelling and surface cooling 3 7 c in two large areas along ivan s track upward isothermal displacements of 50 65 m computed from wind stress and sea surface height changes caused rapid ventilation of thermoclines and nutriclines leading to phytoplankton blooms with peak concentrations 3 4 days later wind speed changes along ivan s track demonstrated that the cool waters 20 26 c provided immediate negative feedback to the hurricane s intensity although our study focused on a relatively small ocean area it revealed that mesoscale cyclones in addition to warm anticyclones may play an important role in producing along track hurricane intensity changes

comment on the ascent of kimberlite insights from olivine by brett r c et al earth planet sci lett 424 2015 119 131 brett et al 2015 proposed a kimberlite factory model that involves carbonatitic proto kimberlite melts preferentially assimilating opx xenocrysts as they transit the cratonic mantle lithosphere to evolve into silicic hydrous melts that reach olivine saturation during ascent p 130 a cornerstone of this model is a specific carbonatitic composition of proto kimberlite melts ascending through the subcratonic lithospheric mantle whereby parental carbonatitic magmas are progressively converted to kimberlite e g russell et al 2012 2013 bussweiler et al 2015 p 120 the model by brett et al 2015 is based on observations of the carbonate sealed cracks in olivine that strongly support to the hypothesis that all kimberlite magmas originate as carbonatitic melts e g russell et al 2012 2013 kamenetsky et al 2013 pilbeam et al 2013 kamenetsky and yaxley 2015 bussweiler et al 2015 p 129 while the major thrust of the study by brett et al 2015 hinges on the premise that the parental kimberlite melt is carbonatitic the overwhelming majority in the kimberlite community still prefers a carbonated ultramafic ultrabasic composition for parental kimberlite melts thus the suggestion that kimberlites have an initial carbonatite composition is not less than a paradigm shift in the kimberlite petrology it appears that a carbonatite origin for kimberlites has been proposed in many studies that significantly pre date the publications starting from 2012 that they cite but which unfortunately are overlooked by brett et al 2015 it is therefore worth acknowledging the research which has previously advanced this unorthodox idea