accelerated pacific plate subduction following interplate thrust earthquakes at the japan trench interplate thrust earthquakes are usually followed by afterslips and they let the fore arc move slowly trenchward however we do not know if the subducting oceanic plate is accelerated landward after such earthquakes the westward velocity of global positioning system gps stations in ne japan show gradient decreasing from east to west reflecting the e w contractional strain built up by the inter plate coupling here we show that such coupling significantly enhanced 1 5 times after the 2003 tokachi oki earthquake mw 8 0 hokkaido in the segments adjacent to the ruptured fault the coupling seems to be further enhanced 3 times after the 2011 tohoku oki earthquake mw 9 0 it is unlikely that interplate friction suddenly increased over such a large region and relatively strong pre 2003 coupling there would not allow such enhancements even if full coupling is attained hence they are attributable to the temporary acceleration of the pacific plate subduction we propose a simple 2 dimensional model in which down dip acceleration of the slab let the force balance rapidly recover promoted by a thin low viscosity layer on the slab surface the accelerated subduction would account for temporary activations of regional interplate seismicity after megathrust earthquakes

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

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

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

global positioning system gps and gps acoustic observations insight into slip along the subduction zones around japan the global positioning system gps is one of the most powerful tools available for observation of earth s surface deformation in particular coseismic postseismic slow transient and interseismic deformation have all been observed globally by gps over the past two decades especially in subduction zones moreover gps acoustic techniques have been developed for practical use in the past decade allowing observation of offshore deformation immediately above slip regions here we describe the application of gps and gps acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around japan where geodetic data coverage is particularly dense the data demonstrate temporally variable strain accumulation in the source region of the 2011 mw 9 0 tohoku oki earthquake and observation of the huge slip of the tohoku oki earthquake near the trench using gps acoustic methods has considerably advanced o

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

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

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

brightness temperature calculation of lunar crater interpretation of topographic effect on microwave data from chang e in order to quantitatively interpret topographic effect on chang e ce microwave data a detailed method to compute brightness temperature tb over a lunar crater is proposed which incorporated the effect of surface tilts the method improves the effective solar irradiance model of the lunar surface to obtain the temperature profile of the lunar crater the calculated tb at 37 ghz with the proposed computation method which is based on three digital elevation models dems from different sources are consistent with the observed tb from the ce 2 microwave radiometer the simulated behavior of tb across crater hercules reproduces the tb undulation observed by ce in a single swath tb is significantly affected by the lunar dust of a lunar crater and affected by albedo and emissivity in a lesser degree based on the explanation with simplified models the tb variation over a crater is proved to be significantly affected through physical temperature by the crater shape described by dems with the simplified crater model the amplitude of the tb oscillatory curves is proved to depend on the crater shape

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

long term seismic quiescences and great earthquakes in and around the japan subduction zone between 1975 and 2012 an earthquake catalog created by the international seismological center isc was analyzed including 3898 earthquakes located in and around japan between january 1964 and june 2012 shallower than 60 km with the body wave magnitude of 5 0 or larger clustered events such as earthquake swarms and aftershocks were removed from the isc catalog by using a stochastic declustering method based on epidemic type aftershock sequence etas model a detailed analysis of the earthquake catalog using a simple scanning technique zmap shows that the long term seismic quiescences lasting more than 9 years were recognized ten times along the subduction zone in and around japan the three seismic quiescences among them were followed by three great earthquakes the 1994 hokkaido toho oki earthquake m w 8 3 the 2003 tokachi oki earthquake m w 8 3 and the 2011 tohoku earthquake m w 9 0 the remaining seven seismic quiescences were followed by no earthquake with the seismic moment m 0 3 0 1021 nm m w 8 25 which are candidates of the false alarm the 2006 kurile islands earthquake m w 8 3 was not preceded by the significant seismic quiescence which is a case of the surprise occurrence as a result when limited to earthquakes with the seismic moment of m 0 3 0 9 1021 nm four earthquakes occurred between 1976 and 2012 in and around japan and three of them were preceded by the long term seismic quiescence lasting more than 9 years

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

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

distribution of seismic coupling on the subducting plate boundary in northeastern japan inferred from gps observations abstract many global positioning system gps stations of the geographical survey institute and tohoku university in northeastern japan observed clear coseismic and postseismic deformations associated with the m7 5 1994 far off sanriku earthquake applying the geodetic inversion algorithm given by yabuki and matsu ura geophys j int 1992 109 363 376 to the observed gps data we estimate in this paper the spatial distributions of the coseismic and postseismic slip on the boundary between the subducting pacific plate and the overriding continental plate it is noted that the coseismic slip estimated in this paper denotes the slip for a period between the day before and the day after the main shock the inversion for coseismic slip shows that the main shock was thrust faulting typical for interplate earthquakes which is consistent with the results of other seismological studies the short term postseismic deformation std observed for a period of ca 10 days between the main shock and its largest aftershock shows that the initially high deformation rate was lowered rather rapidly in comparison with the subsequent long term deformations ltd lasting longer than 1 year which decreased at an almost constant low rate the observed data of std can be explained by postseismic slip distributed approximately on the same region as the faulting area of the main shock where the moment release during this period is ca 16 of that estimated for the coseismic slip the region of the sliding causing ltd is found to have significantly expanded southward and downward or westward on the plate boundary the moment released by the postseismic sliding for nearly 1 year amounts approximately to 80 of that released by the coseismic slip in addition to the contribution from uniform steady sliding due to the relative plate motion furthermore we find from the inversion analysis a locked region to the south of the long term postseismic sliding region on the plate boundary the amount of nominal back slip estimated is so large that the locked region of the plate boundary is considered to have been tightly coupled for the year of 1995 this study demonstrates that the gps observation only for ca 1 year can distinguish the decoupled region due to the postseismic sliding around the source area of the main shock from the coupled one of the plate boundary

quasi periodic slow slip events in the afterslip area of the 1996 hyuga nada earthquakes japan 1 the time evolution of afterslip on a plate boundary experiencing interplate earthquakes is expected to show logarithmic decay the global positioning system network in japan has been monitoring transient deformation since the occurrence of two large interplate earthquakes with moment magnitudes of 6 8 and 6 7 in the hyuga nada area southwest japan in 1996 the spatial and temporal evolution of aseismic interplate slip based on crustal deformation data indicates that afterslip followed the two earthquakes and gradually declined to background rates by around 2004 with total moment magnitude of 7 3 however quasi periodic slow slip events suddenly began within the afterslip area in 2005 with approximately one year duration and two year recurrence interval the moment magnitudes of the three slow slip events since january 2005 range from 6 7 to 6 8 this differs greatly from the expected behavior of logarithmic decay over time both velocity strengthening and velocity weakening rate and state modes have been implicated as the cause of afterslip whose location is complementary to the main shock area of velocity weakening while a slow slip event occurs in the velocity weakening area with different frictional properties from those of an afterslip area in light of the seemingly different frictional properties the coexistence of afterslip and slow slip events in the same area would provide additional information about precisely how the plate interface is behaving the monitoring of these slow slip events should give the clues to understanding the coexistence of long term afterslip and slow slip events and the increasing risk of earthquakes in neighboring areas

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

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

time dependent inversion study of the slow thrust event in the nankai trough subduction zone southwestern japan we estimate time variation of interplate coupling between the subducting philippine sea and the overriding continental plates along the western part of the nankai trough japan during the period between 1996 and 1999 after subtracting annual components and average annual velocities deviation from steady crustal deformation in the shikoku and kyushu islands is examined around 15 gps stations facing the bungo channel detected the following three stage ground displacements of up to 3 cm in 1997 with a duration of 1 year 1 increased displacement rate associated with the 1996 hyuga nada earthquakes 2 an increasingly rapid anomalous period of deformation from june 1997 to the end of 1997 and 3 a slowdown period and return to normal rates of deformation after the end of 1997 linearized least squares locate the slip area of this slow event near the plate boundary beneath the bungo channel the estimated slip is opposite the motion of the philippine sea plate these results support the hypothesis that the observed anomalous caistal deformation is due to a rebound process of the philippine sea plate time dependent inversion analysis shows the following slip history during the initial period of increased displacement rate a visible slip area is resolved beneath the coastal area of southwestern shikoku in the next stage of accelerated displacements the slip area expanded southwestward to the bungo channel beginning around june 1997 when postseismic slip of the 1996 hyuga nada earthquakes almost ended after this accelerated period the estimated thrust slip ends with time

temporal change of interplate coupling in northeastern japan during 1995 2002 estimated from continuous gps observations summary temporal change of deformation in northeastern japan is clarified by continuous global positioning system gps observations from 1995 april to 2002 march the observed gps velocity is approximately parallel to the direction of plate convergence on east and west plate boundaries of northeastern japan and shows post seismic transient deformation around source regions of the mw 7 8 1993 hokkaido nansei oki and the mw 7 7 1994 sanriku haruka oki earthquakes we interpret the source of the observed deformation as contemporary interplate coupling on the east subducting boundary to the pacific plate and the west collision boundary to the amurian plate using elastic dislocation theory we inverted horizontal and vertical velocities of 212 gps stations to estimate interplate coupling on both boundaries the estimated coupling during 1995 2002 is spatially heterogeneous however it is temporally almost constant except for the region around the 1993 and 1994 earthquakes after slip of the 1994 earthquake occurred over the coseismic rupture area and its downdip extension on the plate boundary for 0 3 1 3 yr after the earthquake after slip continued only in the downdip extension for later periods and decayed with time weak coupling was recovered in the eastern part of the coseismic rupture area 3 3 yr after the earthquake interplate coupling on the pacific plate was strong in two regions miyagi oki and tokachi oki the west plate boundary is tightly coupled except for the source areas of three large earthquakes that occurred in 1964 1983 and 1993 the apparent decoupling of the source areas of these earthquakes implies long term post seismic deformation as a result of viscoelastic relaxation in the subseismogenic lithosphere

interaction of slip on asperities numerical simulation of seismic cycles on a two dimensional planar fault with nonuniform frictional property 1 numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes a planar square fault in an infinite uniform elastic medium is considered and the frictional stress on the fault is assumed to obey a rate and state dependent friction law nonuniformity in a frictional constitutive parameter is introduced on the model fault on the fault plane one or two circular patches with velocity weakening frictional property are surrounded by velocity strengthening areas unstable slip may occur for velocity weakening friction and aseismic sliding occurs for velocity strengthening friction velocity weakening patches correspond to asperities because intense seismic slip may occur there simulation results indicate that episodic aseismic slip events slow earthquakes occur when the velocity weakening patch size is close to the critical size of earthquake nucleation propagation of postseismic sliding on the velocity strengthening region follows an earthquake at a velocity weakening patch when the postseismic sliding reaches another velocity weakening patch an earthquake may be triggered at the patch resulting in a double earthquake the time delay between two events of the double earthquake increases with the distance between the two velocity weakening patches or the degree of velocity strengthening in the region between the patches when the distance between the two velocity weakening patches is long an earthquake at one patch does not directly cause an earthquake at the other patch in these cases complex earthquake recurrence may appear due to the interaction between ruptures at the two patches and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity weakening patch

possibility of recovery of slip deficit rate between the north american plate and the pacific plate off sanriku northeast japan 1 the analysis of global positioning system gps data shows an increase in the westward ground velocity in iwate northeast japan from around 2003 after a period of roughly constant crustal deformation rate the spatiotemporal study of time series of displacements reveals that the westward slip deficit rate increased slightly from 2001 to 2003 at the deeper part of the source region of the 1994 sanriku oki earthquake the increase has been considerable since january 2003 and the area of increased slip deficit rate has expanded and now covers the source region of the 1994 sanriku oki earthquake this indicates that the restoration of the slip deficit rate which was affected by the 1994 earthquake was not completed in the period from 1994 to 2003