diapiric transfer of melt in kilauea iki lava lake hawaii a quick efficient process of igneous differentiation kilauea iki lava lake formed in 1959 is a large pond of picritic basalt average mgo content 15 34 by weight which has cooled and crystallized as a small self roofed magma chamber repeated drilling of the upper crust of the lake down to its molten core and more recent 1981 drilling through the thermal maximum and part way through the lower crust have made it possible to monitor the differentiation processes in the lake in detail differentiation processes recognized as active in the lake include rather inefficient settling of the larger 2 10 mm olivine phenocrysts formation of segregation veins and formation of diapir like vertical olivine rich bodies all processes which occur in one or more of the other kilauean lava lakes as well in addition most of the central part of kilauea iki has been affected by diapiric melt transfer in this process relatively low density liquid present at 1145 1160 c rose from within the loose crystal mush at the base of the lens of melt and intruded the equivalent thermal horizon at the top of the lens of melt passing through the hotter but denser melt in the core of the lake without mixing the source volume from which the low density liquid was extracted is depleted in tio 2 and other incompatible elements and enriched in feo and cao the upper part of the lake shows the opposite effects the crystalline assemblage present was olivine augite minor plagioclase the crystallinity of both the source and receiving layers was low enough that no obvious textural imprint was left by the transfer process the principal evidence for its occurrence is the chemical zonation of the lake seen in core from depths of 13 to 80 m diapiric melt transfer was active from 1960 to 1971 and has affected most of the central part of the lake from 13 m to at least 80 m the process ran simultaneously with the other three main differentia tion processes but started and stopped independently of the others calculations suggest that between 21 and 42 wt liquid has been extracted from the depleted zone at 56 78 m in the center of the lake making this a very efficient process of chemical differentiation

contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding abstract as an alternative to classical welding models of fall deposits due to the progressive accumulation of hot tephra which then weld we describe here welded deposits on the northern 1875 caldera rim of askja volcano that have welded due to the influence of hot discrete spatter bombs impacting into and supplying heat to a halo of surrounding tephra this style of welding we term local welding in contrast to regional welding which is described elsewhere carey r j houghton b f thordarson t 2008 contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding j volcanol geotherm res 171 1 19 doi 10 1016 j jvolgeores 2007 11 020 locally welded deposits are associated with the rhyolitic plinian phase of the 1875 eruption of askja volcano two distinct welding units w1 and w2 are interbedded with plinian fall on the northern caldera rim and grade outwards to weakly dispersed non welded fall spatter bombs are found in both welding units but vary in their characteristic sizes and internal features in the w1 unit simple bombs with homogeneous internal characteristics up to 60 cm in diameter are found in the w2 unit large discrete spatter bombs with complex internal features range up to 9 m in diameter we describe here two case studies showing the effects of a single small spatter bombs b multiple small spatter bombs and c large discrete spatter bombs varying in size vertical and lateral profiles through welding zones reveal that the primary controls on local welding are the availability of supplied or added heat and the loading capacity of the spatter bomb local welding grades are much higher than that of regional welding as the combined effects of heat compaction and insulation can provide suitable conditions which lead to dense welding and proximal to the spatter bomb rheomorphic flowage if heating and loading exceed the critical requirement for welding porosity loss via matrix welding and vesicle collapse occurs to a point where further strain must be accommodated as shearing and ductile flowage the spatter bombs are found only within the weakly dispersed welding units and are the final erupted products of each fountaining phase their low viscosities are evident by their deformation on impact and fluidal forms and hold some important clues to eruption dynamics in the shallow conduit and vent regions

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

sub volcanic development of kimberlite pipes evidence from the lace and voorspoed group ii kimberlites south africa abstract the lace and voorspoed kimberlites occur on the kaapvaal craton south africa and form part of the kroonstad group ii kimberlite orangeite cluster the lace kimberlite is composed of a main pipe and a satellite blind pipe the latter of which does not reach the current land surface 30 m below the current land surface and is not observed connecting with the main pipe at depth the main pipe increases in size from 100 m to 250 m in diameter at depth the voorspoed kimberlite pipe is the largest of the cluster and is dominantly infilled with massive layers up to 200 m thick of resedimented volcaniclastic kimberlite rvk coherent kimberlite ck identified at all three pipes is described here in order to constrain their formation distinct volcaniclastic kimberlite vk at the lace main pipe is also described here and is characterised by a highly clastic fragmental quartz rich and mud rich interclast material the vk is interpreted to form by resedimentation of extra crater deposits into a deep 1600 m open vent the ck from both lace occurrences is characterised by coherent to globular segregationary textures generally high proportions of crustal xenoliths and the complete absence of karoo basalt xenoliths which are ubiquitous in vk infilling south african cretaceous kimberlites the increase in pipe size with depth associated with the occurrence of ck at the main pipe and the occurrence of ck within the satellite blind pipe strongly favours an interpretation of formation in a hypabyssal setting rather than by pyroclastic processes ck is also described from the voorspoed kimberlite where it occurs at depth along the south western margin of the pipe the ck is xenolith rich the xenolith population is entirely from the immediate sidewall lithologies and has an incipient globular segregationary texture the contact with the rvk in the centre of the pipe is sharp indicating that the ck was cross cut by a period of eruption prior to the formation of spatially associated rvk the pipe margins at similar depths along the northern and eastern sections of the pipe are characterised by the occurrence of contact breccias which have a gradational change to lower degrees of brecciation away from the pipe the ck at voorspoed is interpreted to form by the intrusion of magmatic kimberlite at depth which invades a previously formed contact breccia and incorporates large proportions of crustal xenoliths from the immediate sidewall the ck occurring at the lace and voorspoed kimberlite are interpreted to form in a sub volcanic hypabyssal setting during a stage of pre conditioning of the country rock prior to eruptive emplacement of the pipe a model for the development of a sub volcanic embryonic pipe is presented for the formation of ck at the kroonstad kimberlite cluster

reply to wolff and turbeville s comment on a reappraisal of ignimbrite emplacement progressive aggradation and particulate to non particulate flow transitions during emplacement of high grade ignimbrite by mj branney and p kokelaar branney and kokelaar 1992 emphasized that many features of pyroclastic flow deposits largely record the last processes involved in their formation so wolff and turbeville s glib reminder of this philosophy at the end of their comment is quite unnecessary many structures in high grade ignimbrites record non particulate flow that occurred some considerable time after particulate aggradation ceased this is not in question and we pointed this out in our paper it is the earlier deposition and deformation history of rheomorphic ignimbrites that is at issue this is the aspect that bears more widely on the nature of pyroclastic flows and related eruptive phenomena in another paper branney and kokelaar 1994 we have documented evidence for hotstate remobilization and deformation of some stationary rheomorphic ignimbrites by post emplacement disturbance caldera collapse however in branney and kokelaar 1992 we provided evidence that shows that for most rheomorphic ignimbrites it is inappropriate to assume a twofold flow history of hot remobilization after an initial flow came to rest progressive aggradation and agglutination provide the most straightforward explanation for many of the markedly irregular vertical variations in welding intensity characteristic of high grade ignimbrites just as progressive aggradation best accounts for vertical variations in sedimentary lithofacies and or in chemical composition in other ignimbrites

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

the geology and emplacement history of the pigeon kimberlite ekati diamond mine northwest territories canada abstract the pigeon kimberlite is located approximately 6 km to the northwest of the koala cluster of the ekati diamond mine and is presently one of ten kimberlite occurrences in the ekati resource development plan it was emplaced along a regional lithological contact between syn yellowknife supergroup granitoid rocks and yellowknife supergroup metasedimentary rocks that were covered by a now eroded veneer of poorly consolidated muddy sediments detailed age dating has not been undertaken however the emplacement age is inferred from sedimentary xenoliths present within the pipe to range between 45 75 ma pigeon is a small kimberlite body estimated to be approximately 3 5 ha at surface consisting of a steep sided pipe that can be separated into four main geological domains that are characterized by contrasting textures different diamond characteristics and unique mineral abundance and compositional signatures the uppermost portion of the body consists of mud rich resedimented volcaniclastic kimberlite that was formed by the deposition of extra crater deposits by debris flow type processes into an open diatreme texturally complex kimberlite is present within the lower portion of the kimberlite and includes rocks that display a range of features consistent with coherent magmatic and less common volcaniclastic fragmental rocks this texturally complex zone is interpreted to represent a clastogenic deposit formed by a low energy eruption within an open diatreme

on the first experimental phreatomagmatic explosion of a kimberlite melt abstract detailed field investigations of kimberlite pipes of the upper cretaceous gibeon kimberlite field in southern namibia revealed geologic features which do neither agree with extensive nor with explosive vesiculation in the pipe hanaus 2 vesicle free magmatic kimberlite intruded the diatreme as a plug here we report on the first experiments in which phreatomagmatic explosions were produced with remolten natural non fragmental magmatic kimberlite from the hanaus 2 central plug as a best fit model kimberlite magma system after water was injected into the melt under controlled conditions the resulting water melt mix was triggered by a low energy shock wave 400 m s

the economic implications of kimberlite emplacement abstract the economic potential of kimberlite bodies is defined by the volume and diamond content of all their internal units which are summarised in three dimensional geological models canadian geological models reveal distinct types of kimberlite bodies characterised by fundamentally different emplacement processes and products data for representative samples of canadian kimberlites are used to show that qualitative and quantitative macroscopic petrography olivines and xenoliths are powerful and practical techniques in assessing the economic implications of emplacement within individual phases of kimberlite kimberlite bodies result from the near surface emplacement of multiple discrete batches of mantle derived magmas each carrying different diamond populations and in some instances subsequent resedimentation processes magmas containing 25 modal of olivine macrocrysts the average maximum load of solids that can be carried to surface by a kimberlite magma have the greatest potential to be significantly diamondiferous modifications to the abundance and size distribution of the olivine macrocrysts in each batch of magma commonly occur during emplacement the modifications to the olivine macrocrysts which vary with different emplacement processes and products are mirrored in the macrodiamond content dilution by xenoliths is important in predicting diamond contents but it is also reflected in reduced olivine contents thus olivine macrocrysts can act as a proxy for macrodiamonds the abundance and size distribution data for olivine can improve the prediction of diamond grade and distribution within and between kimberlite units summary geological models and macroscopic petrography together improve the evaluation of newly discovered bodies resulting in enhanced resource estimates and increased degrees of confidence

mineralogy of primary carbonate bearing hypabyssal kimberlite lac de gras slave province northwest territories canada abstract a suite of fresh late cretaceous to eocene hypabyssal kimberlites from the lac de gras field were studied in order to understand better carbonate silicate and oxide paragenesis the samples have excellent preservation of textures and primary mineralogy and are archetypal or group 1 kimberlite five kimberlite localities are identified as calcite bearing based on the presence of high sr ba calcite as phenocrysts microphenocrysts and in segregations three kimberlite localities are identified as dolomite bearing based on the presence of mixed calcite dolomite segregations containing oscillatory and banded textures of calcite dolomite solid solution and dolomite magnesite sr ba calcite are characterized by high xca 0 95 and are enriched in sr 4900 11 100 ppm and ba 3200 14 200 ppm the calcite dolomite and dolomite magnesite solid solution compositions span the xca range from 0 42 to 0 95 and typically have sr and ba contents in the range of 1000 4000 ppm the carbonate silicate and oxide mineral compositions suggest that the origin of the calcite bearing versus dolomite bearing kimberlites studied is related to subtle differences in parent magma composition in particular the co2 h2o ratio formation of the carbonates reflects the latter part of a protracted magmatic crystallization sequence in which sr ba calcite precipitates from an evolved kimberlite melt subsequently calcite dolomite solid solution and dolomite is precipitated from localized mg rich carbonate fluids at relatively high temperatures higher than serpentine stability

stratigraphy of the intra crater volcaniclastic deposits of the victor northwest kimberlite northern ontario canada abstract the victor northwest vnw kimberlite is one of several steep sided pipes in the victor kimberlite complex in this paper detailed logging of 4 2 km of drill core and petrographic studies of hundreds of samples and thin sections are used to reconstruct the intra crater stratigraphy of the vnw kimberlite and to constrain the emplacement history of the pipe the results show that the vnw pipe comprises numerous contrasting small volume volcanic facies including dark and competent kimberlite sedimentary country rock breccias pyroclastic kimberlite and resedimented volcaniclastic kimberlite we interpret that the vnw pipe was formed by two separate eruption cycles during the first eruption cycle the main vnw crater is excavated and partly filled the second eruption cycle excavates a smaller nested crater within the existing lithified pipe fill both eruption cycles can be subdivided into three comparable stages the first stage in both cycles comprises a highly explosive eruption involving crater excavation and deposition of pyroclastic kimberlite the eruption products contain abundant broken olivines small angular country rock fragments and kimberlite ash all these features indicate high degrees of fragmentation resulting from high eruption intensities the high proportion of country rock fragments in these deposits suggests continuous pipe wall erosion the second stage in both cycles is represented by dark and competent deposits which have low country rock fragment abundances and mostly intact olivines based on contact relationships and textures within these units it is suggested that these rock types are formed by lower energy eruptions during which no major pipe wall erosion took place the eruption came to an end during the third and last stage in both cycles the uppermost deposits record resedimentation of kimberlite by water major pipe wall collapse results in the formation of voluminous sedimentary country rock breccia deposits that cap all previous deposits

a new approach to kimberlite facies terminology using a revised general approach to the nomenclature of all volcanic rocks and deposits descriptive to genetic although kimberlite pipes bodies are usually the remains of volcanic vents in vent deposits and subvolcanic intrusions the terminology used for kimberlite rocks has largely developed independently of that used in mainstream volcanology existing kimberlite terminology is not descriptive and includes terms that are rarely used used differently and even not used at all in mainstream volcanology in addition kimberlite bodies are altered to varying degrees making application of genetic terminology difficult because original components and depositional textures are commonly masked by alteration this paper recommends an approach to the terminology for kimberlite rocks that is consistent with usage for other volcanic successions in modern terrains the eruption and emplacement origins of deposits can often be readily deduced but this is often not the case for old variably altered and deformed rock successions a staged approach is required whereby descriptive terminology is developed first followed by application of genetic terminology once all features including the effects of alteration on original texture and depositional features together with contact relationships and setting have been evaluated because many volcanic successions consist of both primary volcanic deposits as well as volcanic sediments terminology must account for both possibilities

the crater facies kimberlite system of tokapal bastar district chhattisgarh india abstract discovery of diamondiferous kimberlites in the mainpur kimberlite field raipur district chhattisgarh in central india encouraged investigation of similar bodies in other parts of the bastar craton the earlier known tokapal ultramafic intrusive body located beyond the 19 km milestone in tokapal village along the jagdalpur geedam road was reinterpreted as crater facies kimberlite its stratigraphic position in the meso neoproterozoic intracratonic sedimentary indravati basin makes it one of the oldest preserved crater facies kimberlite systems ground and limited subsurface data dug tube wells and exploratory boreholes have outlined an extensive surface area 550 ha of the kimberlite the morphological and surface color features of this body on enhanced satellite images suggest that there is a central feeder surrounded by a collar and wide pyroclastic apron exploration drilling indicates that the central zone probably corresponds to a vent overlain by resedimented volcaniclastic epiclastic rocks that are surrounded by a 2 km wide spread of pyroclastic rocks lapilli tuff tuff ash beds and volcaniclastic breccia drill holes also reveal that kimberlitic lapilli tuffs and tuffs are sandwiched between the kanger and jagdalpur formations and also form sills within the sedimentary sequence of the indravati basin the lapilli tuffs are commonly well stratified and display slumping base surges and lava flows occur in the southern part of the tokapal system the geochemistry and petrology of the rock correspond to average group i kimberlite with a moderate degree of contamination however the exposed rock is intensely weathered and altered with strong leaching of mobile elements ba rb sr layers of vesicular fine grained glassy material represent kimberlitic lava flows tuffs containing juvenile lapilli with pseudomorphed olivine macrocrysts are set in a talc serpentine carbonate matrix with locally abundant spinel and sphene garnet has not been observed and phlogopite is very rare very limited microdiamond testing two 18 kg samples proved negative however the composition of chromite grains indicate crystallization in the diamond stability field

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

ranking welding intensity in pyroclastic deposits welding of pyroclastic deposits involves flattening of glassy pyroclasts under a compactional load at temperatures above the glass transition temperature progressive welding is recorded by changes in the petrographic e g fabric and physical e g density properties of the deposits mapping the intensity of welding can be integral to studies of pyroclastic deposits but making systematic comparisons between deposits can be problematical here we develop a scheme for ranking welding intensity in pyroclastic deposits on the basis of petrographic textural observations e g oblateness of pumice lapilli and micro fabric orientation and measurements of physical properties including density porosity point load strength and uniaxial compressive strength our dataset comprises measurements on 100 samples collected from a single cooling unit of the bandelier tuff and parallel measurements on 8 samples of more densely welded deposits the proposed classification comprises six ranks of welding intensity ranging from unconsolidated rank i to obsidian like vitrophyre rank vi and should allow for reproducible mapping of subtle variations in welding intensity between different deposits the application of the ranking scheme is demonstrated by using published physical property data on welded pyroclastic deposits to map the total accumulated strain and to reconstruct their pre welding thicknesses

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

rheology of welding inversion of field constraints at present the mechanisms and rheological behaviour of pyroclastic deposits during welding and compaction are poorly understood here we explore the extent to which the rheological properties of pyroclastic deposits are constrained by physical property distributions in welded ignimbrite physical properties of samples from a 20 m section of the bandelier tuff new mexico are used as proxies for strain the observed strain et is ascribed to a combination of a time dependent viscous compaction ev and a time independent mechanical compaction em described by

distinct kimberlite pipe classes with contrasting eruption processes abstract field and scott smith field m scott smith b h 1999 contrasting geology and near surface emplacement of kimberlite pipes in southern africa and canada proc 7th int kimb conf eds gurney et al 1 214 237 propose that kimberlite pipes can be grouped into three types or classes classical or class 1 pipes are the only class with characteristic low temperature diatreme facies kimberlite in addition to hypabyssal and crater facies kimberlite class 2 and 3 pipes are characterized only by hypabyssal and crater facies kimberlite in an increasing number of class 1 pipes a new kimberlite facies transitional facies kimberlite is being found in most cases this facies forms a zone several metres wide at the interface between the hypabyssal and diatreme facies the transitional facies exhibits textural and mineralogical features which are continuously gradational between the hypabyssal and the diatreme types the textural gradations are from a coherent magmatic texture to one where the rock becomes increasingly magmaclastic and this is accompanied by concomitant mineralogical gradations involving the decline and eventual elimination of primary calcite at the expense of microlitic diopside both transitional and diatreme facies kimberlites are considered to have formed in situ from intruding hypabyssal kimberlite magma as a consequence of exsolution of initially co 2 rich volatiles from the volatile rich kimberlite magma the transitional facies is initiated by volatile exsolution at depths of about 3 km below the original surface with subsequent cracking through to the surface and resultant rapid decompression the further catastrophic exsolution of volatiles and their expansion leads to the formation of the diatreme facies thus diatreme facies kimberlite and class 1 pipes are emplaced by essentially magmatic processes rather than by phreatomagmatism distinctly different petrographic features characterize crater facies kimberlite in each of the three pipe classes in crater facies kimberlites of class 1 pipes small pelletal magmaclasts and abundant microlitic diopside are characteristic these features appear to reflect the derivation of the crater facies material from the underlying diatreme zone most class 2 pipes have shallow craters and the crater facies rocks are predominantly pyroclastic kimberlites with diagnostic amoeboid lapilli which are sometimes welded and have vesicles as well as glass possible kimberlite lava also occurs at two class 2 pipes in n angola the possible presence of lava as well as the features of the pyroclastic kimberlite is indicative of hot kimberlite magma being able to rise to levels close to the surface to form class 2 pipes most class 3 kimberlites have very steep craters and crater facies rocks are predominantly resedimented volcaniclastic kimberlites in some cases characterized by the presence of abundant angular magmaclasts which are petrographically very similar to typical hypabyssal facies kimberlite found in class 1 pipes the differences in crater facies kimberlite of the three classes of pipe reflect different formation and depositional processes as well as differences in kimberlite composition specifically volatile composition kimberlite forming pipe classes 1 and 3 is thought to be relatively water rich and is emplaced by processes involving magmatic exsolution of volatiles the kimberlite magma forming class 2 pipes is co 2 rich can rise to shallow levels and can initiate phreatomagmatic emplacement processes

a rare occurrence of a crater filling clastogenic extrusive coherent kimberlite victor northwest ontario canada kimberlite pipes can contain significant proportions of dark and dense kimberlite that have mostly been interpreted as intrusive coherent hypabyssal in origin this study reports a well documented occurrence of a fresh intra crater clastogenic extrusive coherent kimberlite that is concluded to have formed as a result of lava fountaining this paper focuses on a dark dense competent generally crystal rich massive kimberlite unit within the victor northwest kimberlite pipe ontario canada using a comprehensive volcanological and petrographic analysis of all available drill cores it is shown that this unit has a fresh well crystallised coherent groundmass and is extrusive and pyroclastic in origin the proposed clastogenic coherent extrusive origin is based on deposit morphology gradational contacts to enveloping pyroclastic units as well as the presence of remnant pyroclast outlines and angular broken olivines this paper and an increasing number of other studies suggest that fragmental extrusive coherent kimberlite in intra crater settings may be more common than previously thought the emplacement history and volcanology of these pipes need to be reconsidered based on the emerging importance of this particular kimberlite facies

characteristics and alteration origins of matrix minerals in volcaniclastic kimberlite of the muskox pipe nunavut canada abstract the matrix of volcaniclastic kimberlite vk from the muskox pipe northern slave province nunavut canada is interpreted to represent an overprint of an original clastic matrix muskox vk is subdivided into three different matrix mineral assemblages that reflect differences in the proportions of original primary matrix constituents temperature of formation and nature of the altering fluids using whole rock x ray fluorescence xrf whole rock x ray diffraction xrd microprobe analyses back scatter electron bse imaging petrography and core logging we find that most matrix minerals serpentine phlogopite chlorite saponite monticellite fe ti oxides and calcite lack either primary igneous or primary clastic textures the mineralogy and textures are most consistent with formation through alteration overprinting of an original clastic matrix that form by retrograde reactions as the deposit cools or in the case of calcite by precipitation from ca bearing fluids into a secondary porosity the first mineral assemblage consists largely of serpentine phlogopite calcite fe ti oxides and monticellite and occurs in vk with relatively fresh framework clasts alteration reactions driven by deuteric fluids derived from the juvenile constituents promote the crystallisation of minerals that indicate relatively high temperatures of formation 400 c lower temperature minerals are not present because permeability was occluded before the deposit cooled to low temperatures thus shielding the facies from further interaction with fluids the other two matrix mineral assemblages consist largely of serpentine phlogopite calcite diopside and chlorite they form in vk that contains more country rock which may have caused the deposit to be cooler upon emplacement most framework components are completely altered suggesting that larger volumes of fluids drove the alteration reactions these fluids were likely of meteoric provenance and became heated by the volcaniclastic debris when they percolated into the vk infill most alteration reactions ceased at temperatures 200 c as indicated by the absence or paucity of lower temperature phases in most samples such as saponite recognition that muskox vk contains an original clastic matrix is a necessary first step for evaluating the textural configuration which is important for reconstructing the physical processes responsible for the formation of the deposit

on the welding of pyroclasts from very low viscosity magmas examples from kimberlite volcanoes abstract lithofacies in kimberlite pipes in southern africa exhibit features consistent with welded pyroclastic rocks these include flared conduit filling geometries abundant lithic clasts lithic clast layers subhorizontal clast fabrics gradational contacts with volcaniclastic rocks and sintered and coalesced globular ash and lapilli and melt coated particles the welding dynamics of kimberlite pyroclasts differ from those of glassy vesiculated pyroclasts in silicic volcanic systems low melt viscosity 0 1 pa s results in the efficient separation of volatiles and melt and the breakup of magma into nonvesicular spherical droplets the glassy state is difficult to form in silica deficient magmas because the crystallization kinetics are fast in low viscosity melts three pyroclastic lithofacies are recognized that primarily relate to the state of the initial melt phase in the pyroclasts on deposition 1 densely welded kimberlite forms where the initial melt phase in pyroclasts remains as pure mel

geochemical trends in kimberlites of the ekati property northwest territories canada insights on volcanic and resedimentation processes abstract the ekati property northwest territories canada hosts in excess of 150 volcanic kimberlite pipes occupied by a wide variety of rock types including coherent magmatic material and a range of fragmental volcaniclastic deposits of both pyroclastic and resedimented origin geochemical analysis of a suite of samples from several of these bodies provides valuable insight into the nature of their components and the processes by which they form observed variations in the bulk composition of coherent kimberlites correlate with their mode of emplacement and petrographic characteristics high volume bodies of coherent kimberlite occurring within and in several cases dominating volcanic pipes pipe fill ck are depleted in co2 and key incompatible elements e g ti and nb but enriched in ni and sio2 relative to samples from narrow kimberlite dyke intrusions the composition and certain textural features of pipe fill ck can be interpreted to reflect formation by pyroclastic processes that involved a loss of volatiles and fines and a concentration of olivine crystals relative to intrusive magmatic kimberlite if this is the case then the apparent coherent character of these rocks suggests that they represent coalescence of hot fluidal pyroclasts i e spatter generated by fire fountain style eruptions samples of massive pyroclastic kimberlite pk are geochemically similar to pipe fill ck but generally show a greater degree of depletion of incompatible elements suggestive of more explosive eruption processes and a greater degree of physical fractionation the geochemical data support petrographic observations that ekati pk contains very little xenolithic material resedimented volcaniclastic kimberlite rvk shows variable degrees of enrichment in al2o3 relative to pk the extent of al enrichment correlates with the proportion of dark fine grained clastic matrix material in the rvk samples and their composition can be explained as a mixture of a very olivine rich fines depleted juvenile component with varying amounts of argillaceous sediment likely derived from surface deposits present at the time of kimberlite eruption however the increased al2o3 content in rvk is also positively correlated with nb concentration indicating that the matrix consistently includes a small amount of kimberlitic ash geochemical trends in massive volcaniclastic kimberlite mvk and fine grained volcaniclastic kimberlite vk from the fox pipe are very different to those of other vk samples from ekati and appear to reflect mixing of juvenile kimberlitic material with granodiorite the data suggest very little if any incorporation of exotic fine grained sediments into these rocks geochemical modelling suggests that the eruption s forming fox mvk involved a significant loss of fines similar to that interpreted for pk in other ekati kimberlites however the large quantity of fragmented granodiorite 30 to 45 within fox mvk indicates that in contrast to other localities the fox eruption was unable to completely clear its vent and disperse the excavated granodiorite prior to infilling the pipe the composition of fox vk provides no evidence for a loss of fines and suggests that these were either retained during eruption or reintroduced by mixing with ash deposits from previous eruptions

evaluation of experimentally measured and model calculated ph for rock brine co2 systems under geologic co2 sequestration conditions abstract reliable ph estimation is essential for understanding the geochemical reactions that occur in rock brine co 2 systems when co 2 is injected into deep geologic formations for long term storage due to a lack of reliable experimental methods most laboratory studies of co 2 rock brine interactions conducted under geologic co 2 sequestration gcs conditions have relied on thermodynamic modeling to estimate ph however the accuracy of these model predictions is typically uncertain in this study we expanded the measurement range of a spectrophotometric method for ph determination and we applied the method to measure the ph in batch reactor experiments at 75 c and 100 atm utilizing rock samples from five ongoing gcs demonstration projects a combination of color changing ph indicators bromophenol blue and bromocresol green was shown to enable measurements over the ph range of 2 5 5 2 in situ ph measurements were compared with ph values calculated using geochemical models calculations with four different thermodynamic databases resulted in a maximum difference of 0 16 ph units among these databases the phrqpitz database generally provided the most accurate ph predictions for rocks comprised of carbonate siltstone and sandstone with phrqpitz the differences between measured and calculated ph values were within 0 03 ph units for these three rocks however for basalt significant differences 0 10 0 25 ph units were observed even with phrqpitz these discrepancies may be due to the models failure to fully account for certain proton consuming and producing reactions that occur between the basalt minerals and co 2 saturated brine solutions

variations of olivine abundance and grain size in the snap lake kimberlite intrusion northwest territories canada a possible proxy for diamonds abstract the snap lake hypabyssal kimberlite is a 15 inclined intrusion that intrudes archaean rocks of the slave craton mapping has identified two main lithofacies within the intrusion olivine rich kimberlite ork and olivine poor kimberlite opk extensive bulk sampling has demonstrated that diamonds vary in both abundance and size across the intrusion since fresh forsteritic olivine and diamond possess similar densities they can be expected to be hydraulically equivalent this study investigates the local scale variation of olivine grain size and content using image analysis and whether olivine can be used as a proxy for diamond concentration and size direct measurement of diamonds is made difficult by extremely low concentrations of around 0 4 ppm and by the inability of the sampling methodology to sample selectively olivines from the two kimberlite varieties possess distinctly different crystal size distributions and this together with contrasting groundmass textures mineralogy and phlogopite compositions indicates that the opk and ork represent two distinct batches of kimberlite magma the general lack of sorting of olivine grains and the presence of decussate phlogopite textures in the ork indicate that this magma crystallized rapidly but was probably preceded by the opk which had a more complex crystallization history as revealed by complex zoning patterns of its phlogopite grains a methodology for comparing olivine and diamond size distributions has been developed and a strong correlation between diamond and olivine size distributions is demonstrated the correlation is used to demonstrate that diamond size distributions can be predicted from the proportions of opk and ork that comprise each bulk sample it can be concluded that the two textural varieties of kimberlite possess distinctly different olivine and diamond populations and that olivines are a good proxy for understanding diamond distributions at a local scale in the snap lake intrusion

time scales of compaction in volcanic systems we used 12 high temperature deformation experiments on fabricated cores of rhyolite ash to explore the effect of porosity on the rheology of pyroclastic deposits during deformation the cores of ash accommodate strain mainly by shortening and reduction of porosity porosity loss creates a strain dependent rheology expressed by a marked and continuous increase in effective viscosity the effective viscosity graphic 1 of pyroclastic materials is predicted as a function of porosity graphic 2 and melt viscosity graphic 3 o by graphic 4 the optimal value for the parameter based on the experimental data is 0 78 0 15 these experiments provide constraints on the time scales of compaction and flow processes in volcanic systems under variable conditions i e temperature load stress our results indicate that welding and compaction processes in pyroclastic deposits e g ignimbrites conduits can occur on time scales of tens of minutes to hours at these time scales welding is fully decoupled from cooling of the deposits and may be coupled to depositional processes within volcanic conduits welding processes operate on fragmented magma rapidly enough to eliminate porosity in a matter of hours thereby sealing off permeability and supporting cyclical vulcanian style explosive eruptions 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif

miocene lamproite volcanoes in south eastern spain an association of phreatomagmatic and magmatic products abstract a series of small miocene 8 3 6 7 ma lamproite rock occurrences as monogenetic volcanoes and or dykes cover a large area in southeastern spain these rocks are associated with extensional basins filled by neogene deposits in the betic and subbetic structural units at cancarix sierra de las cabras calasparra barqueros cerro de monagrillo jumilla and vera eruptions occurred whereas at fortuna mula and zeneta there were only small scale intrusions mainly dykes this paper describes volcanic centers at cancarix calasparra and barqueros which show initial phreatomagmatic eruptions driven by interaction of rising lamproite magma with groundwater tuff ring formed during this volcanic activity subsequent activity consisted of dome extrusion in the vent areas of cancarix and calasparra and by explosive to effusive magmatic activity accompanied by extensive lava flows at barqueros calasparra and cancarix are relatively symmetric monogenetic tuff rings filled by late stage massive vertical plug extruded as degassed crystalline high viscosity magma along the volcanic conduit barqueros was initially a tuff ring whose late stage hawaiian style fountaining generated spatter and clastogenic lavas that built the intra tuff ring cone of cabezo del morron finally extensive lava flows spread from the base of the cone toward the northern part of the edifice variations in the tectonic extensional regime and local hydrogeologic conditions shallow aquifers influenced the occurrence of these lamproite volcanoes late stage magma rise was dependent on the magmatic volatile regime being already degassed at calasparra and cancarix by showing higher viscosity high crystallization rate of intra tuff ring dome extrusions or still rich in volatiles at barqueros displaying lower viscosity lava fountaining and then lava flows

formation of clastogenic lava flows during fissure eruption and scoria cone collapse the 1986 eruption of izu oshima volcano eastern japan the 1986 eruption of b fissure at izu oshima volcano japan produced among other products one andesite and two basaltic andesite lava flows locally the three flows resemble vent effused holocrystalline blocky or aa lava however remnant clast outlines can be identified at most localities indicating that the flows were spatter fed or clastogenic the basaltic andesite flows are interpreted to have formed by two main processes a reconstitution of fountain generated spatter around vent areas by syn depositional agglutination and coalescence followed by extensional non particulate flow and b syn eruptive collapse of a rapidly built spatter and scoria cone by rotational slip and extensional sliding these processes produced two morphologically distinct lobes in both flows by a earlier non particulate flow of agglutinate and coalesced spatter which formed a thin lobe of rubbly aa lava ca 5 m thick with characteristic open extension cracks revealing a homogeneous holocrystalline interior and b later scoria cone collapse which created a larger lobe of irregular thickness 20 m made of large detached blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter the source regions of these lava flows are characterized by horseshoe shaped scarps 30 m high with meso blocks ca 30 m in diameter of bedded scoria at the base one lava flow has a secondary lateral collapse zone with lower ca 7 m scarps backward tilted meso blocks are interpreted to be the product of rotational slip and forward tilted blocks the result of simple toppling squeeze ups of coalesced spatter along the leading edge of the meso blocks indicate that coalescence occurred in the basal part of the scoria cone this low viscosity coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone occurred rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera floor squeeze ups concentrated at the distal margin indicate that the extensional regime changed to one of compression probably as a result of cooling of the flow front sliding material piled up behind the slowing flow front and coalesced spatter was squeezed up from the interior of the flow through fractures and between rafted blocks the andesite flow although morphologically similar to the other two flows has a slightly different chemical composition which corresponds to the earliest stage of the eruption it is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased this lava is interpreted to have been formed by post depositional coalescence of spatter under the influence of the in situ cooling rate and load pressure of the deposit extrusion occurred through the lower part of the scoria cone and subsequent non particulate flow of coalesced material produced a blocky and aa lava flow the mechanisms of formation of the lava flows described may be more common during explosive eruptions of mafic magma than previously envisaged

some major problems with existing models and terminology associated with kimberlite pipes from a volcanological perspective and some suggestions five significant problems hinder advances in understanding of the volcanology of kimberlites 1 kimberlite geology is very model driven 2 a highly genetic terminology drives deposit or facies interpretation 3 the effects of alteration on preserved depositional textures have been grossly underestimated 4 the level of understanding of the physical process significance of preserved textures is limited and 5 some inferred processes and deposits are not based on actual modern volcanological processes these issues need to be addressed in order to advance understanding of kimberlite volcanological pipe forming processes and deposits the traditional steep sided southern african pipe model class i consists of a steep tapering pipe with a deep root zone a middle diatreme zone and an upper crater zone if preserved each zone is thought to be dominated by distinctive facies respectively hypabyssal kimberlite hk descriptively called here massive coherent porphyritic kimberlite tuffisitic kimberlite breccia tkb descriptively here called massive poorly sorted lapilli tuff and crater zone facies which include variably bedded pyroclastic kimberlite and resedimented and reworked volcaniclastic kimberlite rvk porphyritic coherent kimberlite may however also be emplaced at different levels in the pipe as later stage intrusions as well as dykes in the surrounding country rock the relationship between hk and tkb is not always clear sub terranean fluidisation as an emplacement process is a largely unsubstantiated hypothesis modern in vent volcanological processes should initially be considered to explain observed deposits crater zone volcaniclastic deposits can occur within the diatreme zone of some pipes indicating that the pipe was largely empty at the end of the eruption and subsequently began to fill in largely through resedimentation and sourcing of pyroclastic deposits from nearby vents classes ii and iii canadian kimberlite models have a more factual descriptive basis but are still inadequately documented given the recency of their discovery the diversity amongst kimberlite bodies suggests that a three model classification is an over simplification every kimberlite is altered to varying degrees which is an intrinsic consequence of the ultrabasic composition of kimberlite and the in vent context few preserve original textures the effects of syn to post emplacement alteration on original textures have not been adequately considered to date and should be back stripped to identify original textural elements and configurations applying sedimentological textural configurations as a guide to emplacement processes would be useful the traditional terminology has many connotations about spatial position in pipe and of process perhaps the traditional terminology can be retained in the industrial situation as a general lithofacies mining terminological scheme because it is so entrenched however for research purposes a more descriptive lithofacies terminology should be adopted to facilitate detailed understanding of deposit characteristics important variations in these and the process origins for example every deposit of tkb is different in componentry texture or depositional structure however because so many deposits in many different pipes are called tkb there is an implication that they are all similar and that similar processes were involved which is far from clear

the emplacement history of a remarkable heterogeneous chemically zoned rheomorphic and locally lava like ignimbrite tl on gran canaria abstract ignimbrite tl on gran canaria is a complex compositionally zoned rheomorphic tuff that locally exhibits features previously considered to be diagnostic of lavas it is made up of two locally overlapping lobes of ignimbrite that were emplaced during a single eruptive episode the eastern lobe is high grade with rheomorphic zones and localised patches that are lava like the western lobe is extremely high grade more extensively lava like and welded to its top surface both parts are zoned with a basal comendite rich zone grading up through a mixed zone into an upper trachyte rich zone lithic contents and the relative proportions of comendite and trachyte pyroclasts vary with height each comendite rich zone is vitroclastic whereas each trachyte rich zone is partly lava like with local gradations into vitroclastic ignimbrite mixed zones are intermediate in character and locally show compositional banding gradational zoning in massive ignimbrite best seen in lower strain zones and welding fabrics that are pervasively lineated and oblique to bedding suggest that deposition was sustained agglutination was rapid and rheomorphic deformation began during the sustained deposition the viscosity and porosity of the agglutinate varied with height because successively deposited pyroclast populations varied in grainsize composition and temperature the hot agglutinate continued to compact and shear downslope after the density currents had dissipated causing further rheomorphic folding thrusting attenuation and autobrecciation the western lobe locally overlies the partly welded top of the eastern lobe in part because it advanced rheomorphically across it for at least 300 m hot state loading and auto intrusion occurred due to unstable density layering in the chemically zoned agglutinate deformation behaviour changed during cooling and degassing and because of heat transfer between juxtaposed agglutinates and localised retention of dissolved volatiles where there was an overlying impermeable cap

geology of a complex kimberlite pipe k2 pipe venetia mine south africa insights into conduit processes during explosive ultrabasic eruptions k2 is a steep sided kimberlite pipe with a complex internal geology geological mapping logging of drillcore and petrographic studies indicate that it comprises layered breccias and pyroclastic rocks of various grain sizes lithic contents and internal structures the pipe comprises two geologically distinct parts k2 west is a layered sequence of juvenile and lithic rich breccias which dip 20 45 inwards and k2 east consists of a steep sided pipe like body filled with massive volcaniclastic kimberlite nested within the k2 pipe the layered sequence in k2 west is present to 900 m below present surface and is interpreted as a sequence of pyroclastic rocks generated by explosive eruptions and mass wasting breccias generated by rock fall and sector collapse of the pipe walls both processes occurred in tandem during the infill of the pipe several breccia lobes extend across the pipe and are truncated by the steep contact with k2 east dense pyroclastic rocks within the layered sequence are interpreted as welded deposits k2 east represents a conduit that was blasted through the layered breccia sequence at a late stage in the eruption this phase may have involved fluidisation of trapped pyroclasts with loss of fine particles and comminution of coarse clasts we conclude that the k2 kimberlite pipe was emplaced in several distinct stages that consisted of an initial explosive enlargement followed by alternating phases of accumulation and ejection

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

formation of composite pyroclasts by welding inside a lithic rich mafic eruption column los marteles caldera canary islands abstract the tuff ring of the los marteles phreatomagmatic maar gran canaria canary islands includes a particular unit that comprises abundant composite spheroidal clasts however these clasts differ from cored clasts elsewhere that consist of erupted lithic pyroclasts with an adhering rim of coherent chilled magma the composite clasts here studied range from lapilli to bombs and are cored or concentrically banded among the welded components several types of primary clasts are discerned that include i juvenile clasts resultant of the magma inertial fragmentation and ii cognate or accessory lithic clasts juvenile clasts include glass spheres nano and microachneliths and crystals lithic clasts include lava fragments scoriae and olivine xenocrysts primary clasts are interpreted to have been produced by the explosion of a partially crystallized mafic sio 2 50 55 magma that erupted into a maar filled up with scoriae plus lava fragments the explosion would have originated as a dense and turbulent gas thrust into which the repeated collisions of melt droplets with solid clasts generated droplet coated crystals lithic clasts and single glass spheres we interpret the cored and concentrically banded pyroclasts to be made of coalesced and or agglutinated particles coated with a melt rim to the rest of the components these composite clasts developed spheroidal shapes during transport within a violent strombolian eruption column due to spin effect and finally landed in solid state

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass

h2o and co2 in kimberlitic fluid as recorded by diamonds and olivines in several ekati diamond mine kimberlites northwest territories canada abstract surface dissolution features on diamonds and fourier transform infra red spectroscopy ftir of phenocrystal and xenocrystal olivines from kimberlites contain a record of magmatic fluid in kimberlite magmas we investigated composition and behavior of kimberlitic fluid and the effect of volatiles on the eruption style and geology of kimberlites using microdiamonds and olivine concentrates from six kimberlite pipes with different lithologies and the character of diamond resorption ekati diamond mine northwest territories canada the study showed a clear correlation between the resorption style of diamond population of the kimberlites and the type of infrared ir spectra of their olivines four kimberlites have high quality diamonds with smooth regular surface features and high h 2 o content of the olivines indicating the presence of h 2 o rich fluid during the emplacement fast ascent rates of fluid rich magma can explain explosive eruption and filling the pipes with volcaniclastic kimberlite facies conversely grizzly and leslie kimberlites have diamonds with complex sharp features diminishing diamond quality and indicating loss of the fluid the slower ascent rates and less explosive eruption of the fluid free magmas produced kimberlite pipes filled with magmatic facies kimberlite distinctive peaks in olivine ir spectra at 3356 and 3327 cm 1 were found to correlate with the presence of hydrous magmatic fluid character of diamond morphology suggests that during the whole ascent of all six kimberlites the magmatic fluid when present had a high h 2 o co 2 ratio

carbon and oxygen stable isotope values in shells of mytilus edulis and modiolus modiolus from holocene raised beaches at the outer coast of the varanger peninsula north norway the amplitudes of isotopic temperatures based on the stable isotope values of the calcite in profiles from shells of mytilus and modiolus from holocene raised beaches earlier dated and in recent modiolus shells were shown to correspond to the observed annual amplitude of the surface water in the area the relation between 13c and 18o values shows that the ocean water has been mixed with fresh water from the rivers at the coast where the molluscs lived the isotopic temperatures were therefore based on this ratio no clear differences in annual temperatures could be demonstrated within the period studied of about 4500 years

physical processes in volcanic eruptions mechanisms are modeled in terms of dynamic physico chemical processes in this respect volcanology shares with much of earth science in general the benefits that accrue from the application of the methods and concepts of other disciplines to its problems basic concepts from the fields of thermo dynamics fluid mechanics and rheology have been particularly impor tant in fostering new insights recent developments have been so numerous as to make it necessary to limit the scope of this review and thus we concentrate here on the basic physical processes involved in the rise of magma to the surface and the distribution of cruption products on thc ground or in the atmosphere the perspective of planetary volcanism wilson hcad 1983 underlines the fact that volcanoes can be regarded as probes of the composition and structure of a planetary interior as a function of position depth and time

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