magnetotelluric imaging of upper crustal convection plumes beneath the taupo volcanic zone new zealand 1 broadband mt magnetotelluric data were recorded that form an array of measurements at the south eastern margin of the tvz taupo volcanic zone in the central north island of new zealand these array data are used to investigate mechanisms by which the tvz s extraordinarily high heat flux is transported to the surface taken together with seismological data these mt data show compelling evidence that support a model of hydrothermal convection within the brittle upper 6 7 km part of the crust both 2 d and 3 d inversion models of these mt data show vertical low resistivity zones that connect surface geothermal fields to an inferred magmatic heat source that lies below the brittle ductile transition

nitrogen aggregation in metamorphic diamonds from kazakhstan microdiamonds that occur in high grade metamorphic rocks of the kokchetav massif in kazakhstan have been interpreted as part of the metamorphic mineral assemblage implying previously unrecorded pressures for the metamorphism of crustal rocks analysis of the infrared and visible absorption spectra from kokchetav microdiamonds extracted from recent stream sediments draining the metamorphic rocks shows roughly 48 63 aggregation of single n substitution to a centres but no measurable further aggregation calculated residence times assuming peak metamorphic temperatures of 800 900 c are from 0 5 ma to 40 ma and support the petrographic evidence that these diamonds formed during the high pressure metamorphism rather than being inherited from premetamorphic sediments

two sulphur isotope provinces deduced from ores in the mount isa eastern succession australia the sulphur isotopic characteristics of ore deposits in the australian mount isa eastern succession are not well known unlike those of the western succession in this study new detailed analyses are provided for recently discovered eastern succession mineralisation such as the starra and osborne bif hosted cu au ores the dugald river sediment hosted pb zn prospect and four vein hosted cloncurry style cu au deposits hampden mt elliot swan mt cobalt and the answer mine all of the deposits of the eastern succession have 34ssulphide between 8 and 9 regardless of their genesis empirically a moderate 34s range averaging close to 0 characterises starra style cu au and pegmont pb zn bif ores whereas shear and vein style cu mineralisation populations are tighter and do not average close to 0 this is a particularly surprising result for dugald river where a larger isotopic variation more typical of stratiform sediment hosted pb zn ores in the region might have been expected by comparison western succession stratiform pb zn and vein style cu deposits span a huge range of 15 to 51 large sulphur isotope ranges typify sulphate evaporite or organic sulphur rich sedimentary successions the lack of such variation in the eastern succession in turn suggests that primary evaporite sequences there were halite dominated but sulphate poor and or contained only limited volumes of organic sulphur rich sediment eastern succession sequences were therefore less likely hosts for giant stratiform pb zn deposits because of their paucity of sulphur although local sulphur sources permitted small deposits such as dugald river to develop sedimentary conditions were more favourable for the development of sulphur poor synsedimentary hydrothermal systems such as starra osborne and pegmont although sulphur isotope evidence is equivocal about the origin of these epigenetic deposits close to the williams batholith mt dore hampden owe their clustering around 0 to their granitic fluid source

h2o in olivine and garnet inclusions still trapped in diamonds from the siberian craton implications for the water content of cratonic lithosphere peridotites abstract we investigated the h2o content of olivine and garnet inclusions still trapped in seven uncut and unpolished kimberlitic diamonds from udachnaya siberain craton fourier transform infrared ftir spectroscopy analyses of the inclusions show spectra similar to those observed for the same minerals in mantle xenoliths the olivine inclusions are found to contain 0 5 to 5 ppm wt h2o while the garnets do not show any clear absorption bands and therefore are considered to be dry these data contrast with h2o contents reported for olivines and garnets in xenoliths 300 and 20 ppm wt h2o respectively as well as olivine xenocrysts up to 400 ppm wt h2o from the same kimberlite we interpret the high h2o concentrations in xenolithic minerals or xenocrysts to be the result of interactions with either the kimberlitic magmas or metasomatic fluids melts and believe that the inclusions in diamonds investigated here preserve their mantle signature which is not altered during ascent to the surface based on the data collected in this study we conclude that the deep roots of the siberian craton were essentially dry when the diamond formed and that this was possibly the reason for making this portion of the lithosphere stable with respect to the convective mantle finally using h2o partition coefficient data we estimate that the diamond forming melts in this cratonic lithosphere contain below 0 1 wt h2o

constraints on the age and halogen composition of mantle fluids in siberian coated diamonds extension of the ar ar stepped heating technique has been used to characterise the ar halogen cl br i ca and k components in seven coated diamonds from the aikhal kimberlite siberia at least three components have been identified with different ar isotope compositions the major component is characterised by high 40ar 36ar 11 000 and constant 40ar cl 527 22 10 6 br cl 1 74 0 18 10 3 and i cl 22 0 3 4 10 6 indicative of a mantle fluid phase this component is widespread in coated diamonds having been previously reported in samples from africa and canada estimates of halogen abundances in the sub continental mantle based on data from african and siberian coated diamonds are 3 ppm cl 11 ppb br and 0 4 ppb i these low abundances which are in good agreement with values derived for the depleted asthenospheric mantle derived from morb data imply that the upper mantle is 90 degassed of its halogens a second ar component in coated stones is most simply understood by in situ decay of 40k and is consistent with the coat forming event occurring close to the time of host kimberlite eruption 350 380 ma ago a third ar component has a low 40ar 36ar ratio 300 is unassociated with release of k or halogens and is most likely to be atmospheric blank

re os dating of sulphide inclusions zonally distributed in single yakutian diamonds evidence for multiple episodes of proterozoic formation and protracted timescales of diamond growth the timing of diamond formation in the siberian lithospheric mantle was investigated by re os isotope dating of sulphide inclusions from eclogitic and lherzolitic diamonds from the mir 23rd party congress and udachnaya kimberlite pipes in yakutia the diamonds contained multiple sulphide inclusions distributed over their core to rim zones cathodoluminescence carbon isotope and nitrogen aggregation studies demonstrate that the diamonds are zoned and that the distinct zones are associated with different diamond growth episodes there are coherent relationships between carbon isotope composition nitrogen concentration and aggregation state of the diamond hosts and major and trace element compositions re os compositions and initial os isotope ratios of the included sulphides this suggests that the different diamond and sulphide populations formed at different times from fluids melts with different chemical compositions based on the re os isochron ages and the nitrogen aggregation states we conclude that the sulphides are co genetic with their diamond hosts the ages obtained for the different diamond populations demonstrate two major periods of yakutian diamond formation for both eclogitic and lherzolitic suites i e 2 1 1 8 ga mir 23rd party congress and udachnaya and 1 0 0 9 ga mir and 23rd party congress these two episodes correspond to major tectono magmatic events collision between the different terranes of the siberian craton during the formation of the palaeoproterozoic supercontinent 2 0 1 8 ga and accretion leading to formation of the supercontinent rodinia 1 1 ga importantly re os isotope dating demonstrates that some single diamonds have protracted timescales of growth with different ages associated with core and rim zones zoned single eclogitic crystals from mir and 23rd party congress in the current study crystallised over intervals that were irresolvable 200 ma up to 1 ga apart the very radiogenic initial os isotope ratios of the eclogitic and lherzolitic sulphides 187os 188os 0 14 2 22 imply incorporation of radiogenic os from subducted oceanic lithosphere a conclusion that is also supported by the anomalously light carbon isotope compositions of some diamonds subducted lithosphere is therefore considered a significant component in proterozoic diamond formation beneath the siberian craton

isotope evidence for the involvement of recycled sediments in diamond formation diamonds as chemically robust containers of material from the mantle have provided important information regarding the evolution of the earth s interior1 yet despite much effort2 9 the origins of diamonds themselves have remained controversial10 13 sulphur isotope ratios measured in most mantle or meteoritic samples exhibit minimal deviation from the meteoritic standard whereas the ratios in crustal materials deviate by as much as 70 ref 14 for this reason isotopic studies of sulphide mineral inclusions in diamonds and mantle material are an attractive means of investigating the possible role of crust mantle interaction in the formation of diamonds15 recent ion microprobe studies have found departures from mantle values in the sulphur isotope compositions of individual diamond inclusions16 and some mantle rocks17 which would be consistent with subduction of altered ocean crust into the region of diamond growth here we present new sulphur and lead isotope data from diamond sulphide inclusions which suggest that sedimentary material might also be subducted into the mantle and that the crustal recycling process has been operative for at least 1 000 million years

antiquity of peridotitic diamonds from the siberian craton diamonds erupted by kimberlites traversing ancient continental tectosphere 1 provide a window into the evolution of continents and their mantle keels however the vintage of this window that is the timing of crystallization of peridotitic mineral inclusion bearing diamonds beneath different cratons has proved controversial because of the model age arguments involved 2 12 isochron age data for peridotitic garnets in combination with nitrogen aggregation data for host diamonds from the udachnaya kimberlite on the siberian craton show that such diamonds are ancient and could not have crystallized as recently 70 ka before eruption as proposed 10 12 the garnets yield a smnd isochron age of 2 0 ga and the diamonds display nitrogen aggregation characteristics requiring lithospheric mantle storage at temperatures of 1100 1200 c for a comparable period the crystallization age of these peridotitic diamonds is similar to that of equivalent diamonds from the premier kimberlite on the kaapvaal craton which postdate the massive 2 05 ga old bushveld complex and represent a diamond generation unrelated to craton keel stabilization 3 2 ga ago 3 9 10

high resolution seismic tomography of compressional wave velocity structure at newberry volcano oregon cascade range compressional wave velocity structure is determined for the upper crust beneath newberry volcano central oregon using a high resolution active source seismic tomography method newberry volcano is a bimodal shield volcano east of the axis of the cascade range it is associated both with the cascade range and with northwest migrating silicic volcanism in southeast oregon high frequency 7 hz crustal phases nominally pg and a midcrustal reflected phase travel upward through a target volume beneath newberry volcano to a dense array of 120 seismographs this arrangement is limited by station spacing to 1 to 2 km resolution in the upper 5 to 6 km of the crust beneath the volcano s summit caldera the experiment tests the hypothesis that cascade range volcanoes are underlain only by small magma chambers a small low velocity anomaly delineated about 3 km below the summit caldera supports this hypothesis for newberry volcano and is interpreted as a possible magma chamber of a few to a few tens of km3 in volume a ring shaped high velocity anomaly nearer the surface coincides with the inner mapped ring fractures of the caldera it also coincides with a circular gravity high and we interpret it as largely subsolidus silicic cone sheets the presence of this anomaly and of silicic vents along the ring fractures suggests that the fractures are a likely eruption path between the small magma chamber and the surface

modeling of craton stability using a viscoelastic rheology archean cratons belong to the most remarkable features of our planet since they represent continental crust that has avoided reworking for several billions of years even more it has become evident from both geophysical and petrological studies that cratons exhibit deep lithospheric keels which equally remained stable ever since the formation of the cratons in the archean dating of inclusions in diamonds from kimberlite pipes gives archean ages suggesting that the archean lithosphere must have been cold soon after its formation in the archean in order to allow for the existence of diamonds and must have stayed in that state ever since yet although strong evidence for the thermal stability of archean cratonic lithosphere for billions of years is provided by diamond dating the long term thermal stability of cratonic keels was questioned on the basis of numerical modeling results we devised a viscoelastic mantle convection model for exploring cratonic stability in the stagnant lid regime our modeling results indicate that within the limitations of the stagnant lid approach the application of a sufficiently high temperature dependent viscosity ratio can provide for thermal craton stability for billions of years the comparison between simulations with viscous and viscoelastic rheology indicates no significant influence of elasticity on craton stability yet a viscoelastic rheology provides a physical transition from viscously to elastically dominated regimes within the keel thus rendering introduction of arbitrary viscosity cutoffs as employed in viscous models unnecessary

young peridotitic diamonds from the mir kimberlite pipe mineral inclusions in diamonds contained in the explosive volcanic rocks known as kimberlites provide an important record of geochemical processes in the continental lithosphere samarium neodymium model ages as old as 3 2 gyr have been obtained for many peridotitic mineral inclusions1 4 pointing to the great antiquity of the host peridotitic diamonds relative to the age of the associated kimberlites and hence an extended period of residence in the sub continental mantle here we report trace element data from garnet inclusions in peridotitic diamonds from the mir kimberlite pipe siberia which appear to be inconsistent with this interpretation the heterogeneous distribution of the trace elements both within and among discrete garnets from single diamonds are indicative of rapid crystal growth leading to solid melt disequilibrium on a local scale the conditions for survival of these heterogeneities within individual garnet crystals are tightly constrained by diffusion kinetics which would rapidly homogenize the trace element distributions in the sub continental mantle thus while it seems clear that peridotitic diamonds and their inclusions are derived from ancient lithospheric material our data require that they crystallized shortly before the eruption of the kimberlite 360 myr ago5

multiple origins of obsidian pyroclasts and implications for changes in the dynamics of the 1300 b p eruption of newberry volcano usa the pyroclastic deposits of the 1300 b p eruption of newberry volcano or usa contain minor amounts of obsidian 1 6 wt the volatile h2o and co2 contents and textures of these clasts vary considerably ftir measurements of h2o in obsidian pyroclasts range from 0 1 to 1 5 wt indicating equilibration pressures 20 mpa co2 contents are low 10 ppm except in clasts that also contain xenolith powder that provided a local co2 source obsidian clasts exhibit a range of color and textural types that changed in relative proportion as the eruption progressed together these data indicate that there were multiple origins of obsidian and that the dominant source changed during the eruption early in the eruption obsidian was almost entirely black or grey microlite bearing and probably derived from dikes or wall rock fractures filled with vanguard magma or tuffisite that together with wall rocks were eroded and incorporated into the eruption column as the vent widened later in the eruption following a brief cessation of activity the proportion of obsidian to wallrock lithic clasts increased and new types of obsidian dominated types that represent remnants of a shallow conduit plug welded fallback material from within the conduit and sheared and degassed magma from near the conduit walls analysis of bubble shapes preserved within obsidian indicates that shear stresses and shear rates varied by over two orders of magnitude with maxima of 88 kpa and 10 2 3 s 1 respectively based on an assumed magma temperature of 850 c furthermore the highest shear rates and stresses and the shortest flow times 10 20 min are preserved in clasts that also contain wall rock the longest deformation times 5 and 8 h correspond to two microlite rich clasts suggesting that the higher microlite content results from slower ascent rates and or longer magma residence times at shallow levels differences between obsidian pyroclasts from the newberry eruption and those of the mono craters may relate to the nature of the conduit feeding the two events from this comparison we conclude that obsidian can provide information on time scales and mechanisms of pre fragmentation magma ascent

identification of molybdenite in diamond hosted sulphide inclusions implications for re os radiometric dating abstract sulphide inclusions are common features of natural diamonds they can provide an insight into the nature of diamond forming reactions and are especially important for re os dating of diamond formation a discrete molybdenite mos2 phase has been identified for the first time by raman spectroscopy in 73 out of 80 syngenetic sulphide inclusions in 7 eclogitic diamonds from the mir kimberlite yakutia russia the sulphide inclusions were chemically and texturally characterised by electron probe microanalyses epma focused ion beam scanning electron microscopy fib sem and synchrotron based x ray tomographic microscopy sxrtm our observations suggest the molybdenite has unmixed from an original sulphide melt or monosulphide solid solution it occurs as sub micron sized grains commonly in association with the chalcopyrite rims of the inclusions and sometimes within surrounding decompression cracks molybdenite has also been identified by raman spectroscopy in at least 50 of sulphide inclusions in preliminary studies of eclogitic diamonds from argyle nw australia orapa letlhakane damtshaa botswana and dachine french guiana and peridotitic diamond hosted inclusions from udachnaya yakutia russia and murowa zimbabwe we have modelled the effects that different amounts of re loss through its segregation into an unrecovered molybdenite phase could have on the radiometric ages of diamonds dated using the re os system in general re loss through this process will lead to isochron ages older than the true age and variable degrees of re loss will lead to increased scatter around the apparent isochron for model age calculations the effects would depend on the 187re 188os ratio of the inclusions if their compositions evolved above or below that of the chondritic mantle evolution curve but re loss could generate unrealistically old or future ages particularly in eclogitic inclusions

synchrotron mossbauer source technique for in situ measurement of iron bearing inclusions in natural diamonds abstract we describe a new methodology to collect energy domain mossbauer spectra of inclusions in natural diamonds using a synchrotron mossbauer source sms measurements were carried out at the nuclear resonance beamline id18 at the european synchrotron radiation facility grenoble france we applied this non destructive approach to collect sms spectra of a ferropericlase inclusion still contained within its diamond host from juina brazil the high spatial resolution of the measurement 15 m enabled multiple regions of the 190 105 m 2 inclusion to be sampled and showed that while fe 3 fe tot values in ferropericlase were below the detection limit 0 02 overall there was a magnetic component whose abundance varied systematically across the inclusion hyperfine parameters of the magnetic component are consistent with magnesioferrite and the absence of superparamagnetism allows the minimum particle size to be estimated as 30 nm bulk fe 3 fe tot values are similar to those reported for other ferropericlase inclusions from juina and their variation across the inclusion can provide constraints on its history

diamond growth history from in situ measurement of pb and s isotopic compositions of sulfide inclusions in a continuing effort to understand crust mantle dynamics we have determined the s and pb isotopic compositions of mantle sulfides encapsulated within diamonds from under the siberian craton and compared these results to those of previously investigated african counterparts because diamond inclusions are isolated from exchange with surrounding mantle they may preserve the history of diamond growth and act as direct tracers of the origins of mantle materials study of these inclusions may thus offer the best chance of recognizing global scale interaction between earth9s crust and mantle although 34 s values of the siberian sulfides do not deviate significantly from the mantle value of 0 3 pb isotopic compositions are highly variable pb isotopic compositions of sulfides from peridotitic suite diamonds generally plot near the terrestrial pb growth curve with model ages ranging between 0 and 2 ga whereas sulfides from eclogitic suite diamonds have radiogenic compositions plotting beyond the growth curve these results which are similar to those for sulfides in african diamonds suggest that the sulfides from eclogitic suite diamonds were derived from a source with an unusually high u pb ratio and may indicate a common process such as subduction of crystal materials into the mantle operating beneath africa and siberia the absence of extremely radiogenic pb in sulfides from eclogite xenoliths suggests that the radiogenic material from which eclogitic suite diamonds grew was a transient feature of the mantle associated with diamond growth the ultimate origin of this high u pb signature however remains enigmatic large variations in pb isotopic composition of sulfides from different zones in a single peridotitic suite diamond document 1 crystallization of the diamond9s core near 2 0 ga 2 growth of its outer zone in an environment with a high u pb ratio similar to the growth environment of eclogitic suite diamonds and 3 growth of the diamond rim near the time of kimberlite emplacement

three dimensional cathodoluminescence imaging and electron backscatter diffraction tools for studying the genetic nature of diamond inclusions as a step towards resolving the genesis of inclusions in diamonds a new technique is presented this technique combines cathodoluminescence cl and electron backscatter diffraction ebsd using a focused ion beam scanning electron microscope fib sem instrument with the aim of determining in detail the three dimensional diamond zonation adjacent to a diamond inclusion ebsd reveals that mineral inclusions in a single diamond have similar crystallographic orientations to the host within 0 4 the chromite inclusions record a systematic change in mg and cr from core to the rim of the diamond that corresponds with a 80 c decrease of their formation temperature as established by zinc thermometry a chromite inclusion positioned adjacent to a boundary between two major diamond growth zones is multi faceted with preferred octahedral and cubic faces the chromite is surrounded by a volume of non luminescent diamond cl halo that partially obscures any diamond growth structures the cl halo has apparent crystallographic morphology with symmetrically oriented pointed features the cl halo is enriched in 200 ppm cr and 80 ppm fe and is interpreted to have a secondary origin as it overprints a major primary diamond growth structure the diamond zonation adjacent to the chromite is complex and records both syngenetic and protogenetic features based on current inclusion entrapment models in this specific case a syngenetic origin is favoured with the complex form of the inclusion and growth layers indicating changes of growth rates at the diamond chromite interface combined ebsd and 3d cl imaging appears an extremely useful tool in resolving the ongoing discussion about the timing of inclusion growth and the significance of diamond inclusion studies

a study of eclogitic diamonds and their inclusions from the finsch kimberlite pipe south africa previous studies of diamonds from finsch have shown that eclogitic inclusions are rare at finsch and that the eclogitic garnet and clinopyroxenes are iron and manganese rich in order to expand the current database of information 93 eclogitic diamonds were selected for this study eight diamonds were polished into plates for cathodoluminescence studies and infrared examination of diamond growth and 31 diamonds were cracked to retrieve inclusions the eclogitic garnets analysed in this study are enriched in fe and are relatively depleted in ca and mg relative to worldwide data feo contents for garnet range from 15 to 27 wt and mno contents reach a maximum value of 1 6 wt the eclogitic clinopyroxenes have relatively high feo contents up to 14 8 wt and k2o contents are low 0 4 wt three non touching garnet clinopyroxene mineral pairs produce equilibration temperatures of 1138 1179 c at an assumed pressure of 50 kb no type ii diamonds were found during this study all diamonds are of type iaab total nitrogen contents of type iaab diamonds range from 11 to 1520 ppm with variable aggregation states up to 84 nitrogen aggregated as b defects distinct infrared characteristics suggest that the finsch kimberlite sampled either more than one mantle source region of similar age but differing temperature or two different populations of diamonds with different ages the diamonds provide evidence of changing mantle conditions during crystallisation continuous diamond growth is illustrated by the presence of regular octahedral growth zones although in some diamonds cubic growth is noted one diamond shows evidence of platelet degradation suggesting exposure to high temperatures and or shearing stresses

diamonds through time diamonds form in the upper mantle during episodic events and have been transported to the earth s surface from at least the archean to the phanerozoic small diamonds occur as inclusions in robust minerals in tectonically activated ultrahigh pressure metamorphosed crustal rock establishing an association with subduction processes and recycled carbon but providing no economic deposits diamonds in economic deposits are estimated to be mainly 99 derived from subcontinental lithospheric mantle and rarely approx 1 from the asthenosphere harzburgite and eclogite are of roughly equal importance as source rocks followed by lherzolite and websterite diamonds which provide evidence of extensive residence time in the mantle are with minimal exceptions smooth surfaced crystalline diamonds scd with potential commercial value the oldest prolific scd formation event documented on the world s major diamond producing cratons occurs in archean lithospheric mantle harzburgite metasomatized by likely subduction related potassic carbonatitic fluids disaggregation of the diamondiferous carbonated peridotite on decompression during volcanic transit gives rise to the association between diamonds g10 garnets and diamond inclusion type chromites well used in diamond exploration within the mantle domains of diamond stability there have been repeated episodes of further diamond crystallization and or growth these are associated with old often proterozoic subduction related melt generation metasomatic fluid migration and reaction with preexisting mantle eclogite websterite and peridotite using improved methods of isotope analysis diamond formation ages can be correlated with specific major processes such as craton accretion craton edge subduction and magmatic mantle refertilization fibrous cuboid diamond and fibrous coats on scd are rough surfaced diamonds with abundant fluid inclusions they have low mantle residence time forming rapidly from late stage metasomatic fluids in diamond stable domains that may already contain scd the symbiotic relationship between formation of fibrous diamond and magmatic sampling and transport of diamonds into the crust suggest that the associated fluids contribute diamond friendly volatile loading of the deep lithospheric mantle shortly before the triggering of a volcanic eruption continuing a process of volatile enrichment in the lithospheric mantle already identified in the archean harzburgite diamond event mantle derived scd commonly shows evidence of resorption illustrating that diamond unfriendly processes including lamproite and kimberlite generation are also active and may have a substantial negative effect in extreme cases on scd crystal size exposure of scd to a long period of changing conditions during mantle residence contributes to the difficulty of assigning specific parageneses and ages to individual inclusion free diamonds with our current state of knowledge