blade and bifacial technology in mid holocene occupations at deseado massif santa cruz province argentina abstract in the deseado massif there are many stratified archaeological sites located in caves and rockshelters the cultural sequences proposed in the past century include an occupational hiatus and cultural changes that were developed on the basis of large tools from archaeological sites without debitage analysis the aim of this paper is to review the current debate on lithic technology and human occupations of this area during the mid holocene integrating new data as well as the latest environmental interpretations the contribution of new information from blade and bifacial technologies is central to discussion of the models proposed by other authors the new baseline information generated in the last decade allow original interpretations the evidence of coexistence between blade and bifacial technologies during the mid holocene constitutes the main contribution of this paper

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

crystalline inclusions and c isotope ratios in diamonds from the snap lake king lake kimberlite dyke system evidence of ultradeep and enriched lithospheric mantle abstract u type paragenesis inclusions predominate 94 7 among the crystalline inclusion suite of 115 diamonds 4 2 mm obtained from the recently discovered snap lake king lake skl kimberlite dyke system southern slave canada the most common inclusions are olivine 90 and enstatite 22 sulfide cr pyrope chromite and cr diopside inclusion are less abundant 15 10 5 and 1 respectively results of the inclusion composition study demonstrate the following a the relatively enriched character of the mantle parent rocks of the u type diamonds the average mg of olivine inclusions is 92 1 and of enstatite inclusions average 93 3 cao content in cr pyrope inclusions is relatively high 3 73 5 75 wt b four of ten u type cr rich pyrope inclusions contain a majoritic component up to 16 8 mol which requires pressures of 110 kbar carbon isotopes compositions for 34 diamonds with u type inclusions have a 13c range from 3 2 to 9 with a strong peak around 3 5 this is much heavier than the ratios of u type diamonds from siberia and south africa 4 5 diamonds with olivine inclusions can be divided into two groups based on their 13c values as well as the mg and ni fe ratio in the olivines most show a narrow range of 13c values from 3 2 to 4 8 average 3 72 and have olivine inclusions with mg less than 92 3 and relatively high fe ni ratios a second group is characterized by a much wider variation of c isotope composition 13c varies from 3 8 to 9 0 average 5 97 and the olivine inclusions having a higher mg up to 93 6 and relatively low fe ni ratios this difference in the c isotope composition may have several explanations a peculiarities of asthenosphere degassing coupled with an abnormal thickness of lithosphere b the abnormal thickness and enriched character of lithospheric mantle c involvement of subducted c of crustal origin in the processes of the diamond formation the presence of subcalcic cr rich majorite up to 17 mol pyropes of low ca harzburgite paragenesis among the crystalline inclusion suite of skl diamonds is strong evidence for the existence of diamondiferous depleted peridotite in lithospheric mantle at depth near 300 km beneath southern slave area and is postulated to be one of the main reasons for the much heavier c isotope composition of skl u type diamonds in comparison with those from siberian and south african kimberlites

mineral chemistry and density of subducted basaltic crust at lower mantle pressures subducted slabs are less dense than the surrounding mantle near the base of the transition zone 660 km depth because of the survival of garnet in former basaltic crust by this depth mantle peridotite has transformed to denser perovskitite1 2 the buoyancy of the former basaltic crust may contribute to the observed accu mulation or horizontal displacement of many slabs at the base of the transition zone3 here we report experimental confirmation of the widely held belief that the basaltic crust of slabs eventually transforms to a dense perovskititic lithology stable in the lower mantle synthetic mid ocean ridge basalt more glass subjected to pressures of 45 80 and 100 gpa in a laser heated diamond anvil cell transforms to an assemblage of aluminous mg fe silicate perovskite non quenchable casio3 perovskite stishovite and a sodic aluminous phase with the ca ferrite structure fig 1 per ovskititic more is about 0 06 g cm 3 more dense than a model lower mantle prem derived from seismological data thus even thermally equilibrated perovskititic slabs should encounter no sig nificant hindrance to subduction and convection in the lower mantle

melting experiments on the enstatite diopside join at 70 224 kbar including the melting of diopside melting relations on the enstatite diopside en mg2si2o6 di camgsi2o6 join including the compositions of crystalline phases and melts coexisting along the solidi were experimentally determined in the pressure range 70 224 kbar with a split sphere anvil apparatus ussa 2000 melting is peritectic in enstatite rich compositions at 70 124 kbar 1840 2100 c and eutectic at higher pressures while the diopside rich clinopyroxene melts azeotropically at 70 165 kbar and up to 300 c lower temperatures than the eutectic orthopyroxene is replaced with enstatite rich clinopyroxene at 120 kbar and 2090 c first garnet with 17 mol di forms on the solidus at 158 kbar and 2100 c two garnets coexist on the solidus at 165 183 kbar and 2100 c garnet coexists with casio3 perovskite at 183 224 kbar 2100 2230 c and two coexisting perovskites are stable at higher pressures the melting curve of diopside was determined at 80 170 kbar the slope becomes negative at 140 kbar and 2155 c at 170 kbar and 2100 c diopside with 96 di breaks down to garnet with 89 di and casio3 perovskite the new data were used to calculate an improved temperature pressure phase diagram for the cmas system which can be useful for estimating the mineralogy of the earth s upper mantle

high pressure transformations in naalsio4 and thermodynamic properties of jadeite nepheline and calcium ferrite type phase abstract phase transitions in naalsio 4 were examined at 3 5 27 gpa and 950 1600 c using a multianvil type and a bridgman anvil type high pressure apparatus the results show that naalsio 4 nepheline first dissociates into an assemblage of naalsi 2 o 6 jadeite and naalo 2 with distorted zincite structure at about 4 gpa at about 7 gpa this assemblage changes to jadeite plus naalo 2 with distorted rocksalt structure jadeite and naalo 2 react to form an naalsio 4 phase with calcium ferrite structure at 18 20 gpa and this boundary has a negative slope enthalpies of nepheline and calcium ferrite type naalsio 4 jadeite and and naalo 2 were measured by high temperature oxide melt solution calorimetry the enthalpy for transition of naalsio 4 nepheline to jadeite plus naalo 2 was 6 2 4 4 kj mol and that for the transition in naalo 2 was 23 6 2 4 kj mol at 298 k the enthalpy of formation of naalsio 4 calcium ferrite from jadeite plus naalo 2 was 79 6 6 9 kj mol at 298 k the calculated boundaries of these transitions from the measured enthalpy data are generally consistent with those by experimental determination considering the errors of the measured enthalpies and thermophysical properties of the relevant phases and the uncertainty of pressure in the high pressure experiments the calculated boundary for dissociation of jadeite to calcium ferrite plus stishovite has a positive slope the present calculation of the transition boundaries involving naalsio 4 calcium ferrite may suggest that configurational entropy of calcium ferrite possibly due to al si disorder could contribute to the slopes of the boundaries

phase transformations in subducted oceanic crust and buoyancy relationships at depths of 600 800 km in the mantle abstract phase transformations in a representative oceanic crust composition morb have been studied at pressures up to 28 gpa at 1200 c and 1500 c using a multi anvil apparatus the assemblage of majorite casio 3 rich perovskite stishovite which is displayed by the morb composition at pressures above 20 gpa was found to transform further into an assemblage containing a new aluminous phase at pressures above 25 gpa this al phase has a complex composition and is also relatively sodium rich its x ray diffraction pattern is similar to that observed for mgal 2 o 4 calcium ferrite type and is tentatively indexed on the basis of an orthorhombic cell yielding a zero pressure density of 3 87 2 g cm 3 majorite garnet was found to remain as the most abundant phase at the highest pressure studied 28 gpa and does not appear likely to transform to perovskite until pressures exceed 29 30 gpa these results imply that the basaltic crust component of subducted oceanic lithosphere would be 0 1 0 2 g cm 3 less dense than surrounding mantle pyrolite between the depths of 660 800 km thereby confirming an earlier hypothesis of anderson moreover the underlying layer of harzburgite would be 0 05 g cm 3 less dense than pyrolite throughout most of this depth interval these buoyancy relationships contribute to a barrier which impedes and may sometimes prevent the entry of slabs into the lower mantle

tool production processes in lithic quarries from the central plateau of santa cruz argentina abstract lithic resources at the central plateau of santa cruz argentina are abundant ubiquitous and of very good quality for knapping they have been exploited by hunter gatherer societies since the latest pleistocene until the late holocene the study of their distribution availability and ways of exploitation at the quarries together with the information stemming from the archaeological sites enable the understanding of the first stages of tool production and consumption in this paper two quarries from la maria archaeological locality cantera de silex de cdm and cantera bosque petrificado are studied and compared their geomorphologic location is described the lithological characteristics of the outcrops the size of the stones and the variability of raw materials available at them are also addressed the accessibility and visibility of the quarries are analyzed the way raw materials were exploited at the sources is evaluated taking into consideration their relationship with the local and regional structure of lithic resources the information generated for the quarries is complemented and compared with the local trends identified for the habitation sites this enabled the formulation of a general model about the first stages of production although the quarries have different types of raw materials flint and silicified wood results show that similar technological strategies were implemented in them these are in agreement with the general trend at the local and regional levels both sources are easily accessible from the surrounding landscape they are visible from nearby areas probably they were exploited mainly from nearby sites at the quarries the first stages of tool production were performed core decortication and preparation and the production of blanks the acquisition of raw material involved the selection of good quality nodules and boulders and the production of polyhedral cores knapped in multiple directions these cores could be transported to the habitation sites or could be discarded in situ while still presenting active platforms on the other hand differences in some procurement practices might be related to decisions and variations linked to the particular characteristics of the resources in both outcrops

density of morb eclogite in the upper mantle in order to study the role of eclogite subducted oceanic crust in geodynamics we carried out high pressure experiments on natural mid oceanic ridge basalt morb using a multi anvil apparatus we determined phase relations of morb as a function of pressure and temperature in the temperature range of 1200 1700 c and pressures from 5 to 14 gpa the present results differ from a previous high pressure study of morb earth planet sci lett 77 1986 245 conducted at 1200 c as follows 1 coesite coe or stishovite st appears throughout the studied pressure range and 2 the clinopyroxene garnet cpx gar ratio is smaller particularly in the low pressure range 12 gpa our results show that the calculated bulk density of subducted oceanic crust increases discontinuously at around 9 gpa due to the coesite stishovite phase transition the density is considerably higher than estimates based on the previous experiments at pressures less than 12 gpa thus the role of eclogite in driving subduction should be more important than previously thought on the other hand the density difference between peridotite and eclogite in ascending mantle plumes becomes smaller as temperature increases a result of the increase in clinopyroxene garnet sio2 ratio in eclogite with increasing temperature as eclogite is still denser than peridotite even under subsolidus conditions recycled oceanic crust entrained in ascending plumes must be sustained by the upward flow of ambient peridotite in mantle plumes

the crust mantle boundary beneath cratons and craton margins a transect across the south west margin of the kaapvaal craton lower crustal suite xenoliths occur in on craton and off craton kimberlites located across the south western margin of the kaapvaal craton southern africa rock types include mafic granulite plagioclase bearing assemblages eclogite plagioclase absent assemblages with omphacitic clinopyroxene and garnet pyroxenite orthopyroxene bearing eclogite the mafic granulites are subdivided into three groups garnet granulites cpx grt plag qtz two pyroxene garnet granulites cpx opx grt plag kyanite granulites cpx grt ky plag qtz reaction microstructures preserved in many of the granulite xenoliths involve the breakdown of plagioclase by a combination of reactions 1 cpx plag grt qtz 2 plag grt ky qtz 3 plag cpx jd rich qtz compositional zoning in minerals associated with these reactions records the continuous transition from granulite facies mineral assemblages and pressure p temperature t conditions to those of eclogite facies two distinct p t arrays are produced 1 off craton granulites away from the craton margin define a trend from 680 c 7 5 kbar to 850 c 12 kbar 2 granulite xenoliths from kimberlites near the craton margin and on craton granulites produce a trend with similar geothermal gradient but displaced to lower t by 100 c both p t fields define higher geothermal gradients than the model steady state conductive continental geotherm 40 mwm2 and are not consistent with the paleogeotherm constructed from mantle derived garnet peridotite xenoliths a model involving intrusion of basic magmas around the crust mantle boundary followed by isobaric cooling is proposed to explain the thermal history of the lower crust beneath the craton margin the model is consistent with the thermal evolution of the exposed namaqua natal mobile belt low pressure granulites and the addition of material from the mantle during the namaqua thermal event c 1150 ma the xenolith p t arrays are not interpreted as representing paleogeotherms at the time of entrainment in the host kimberlite they most likely record p t conditions frozen in during various stages of the tectonic juxtaposition of the namaqua mobile belt with the kaapvaal craton

compositional change of majoritic garnet in a morb composition from 7 to 17 gpa and 1400 to 1600 c experimental phase relations of an average normal mid ocean ridge basalt n morb composition from 7 gpa to 17 gpa and 1400 to 1600 c reveal the compositional variation of garnet in equilibrium with pyroxene the na2o content of majoritic garnet in equilibrium with pyroxene and stishovite increases up to 2 5 wt with increasing pressure and temperature na enters the garnet structure via the substitution mg fe ca al na si ti the pyroxene garnet partition coefficient dcp ga for na decreases with increasing pressure however clinopyroxene coexisting with garnet becomes more na rich as pressure increases these relationships are independent of the feo content in garnet our experiments confirm that rare majoritic and na rich garnet inclusions in diamonds have formed at transition zone pressure in lithologies of basaltic bulk composition

phase relations on the diopside jadeite hedenbergite join up to 24 gpa and stability of na bearing majoritic garnet abstract phase relations on the diopside di hedenbergite hd jadeite jd system modeling mineral associations of natural eclogites were studied for the compositions mol di70jd30 di50jd50 di30jd70 di20hd80 and di40hd10jd50 using a toroidal anvil with hole 7 gpa and a kawai type 6 8 multianvil apparatus 12 24 gpa we established that di hd and jd form complete series of solid solutions at 7 gpa and melting temperatures of pure di 1980 c and jd 1870 c for that pressure were estimated experimentally the melting temperature for the di50jd50 composition at 15 5 gpa is 2270 c the appearance of garnet is clearly dependent on initial clinopyroxene composition at 1600 c the first garnet crystals are observed at 13 5 gpa in the jadeite rich part of the system di30jd70 whereas diopside rich starting material di70jd30 produces garnet only above 17 gpa the proportion of garnet increases rapidly above 18 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites are produced from diopside rich starting materials in all experiments garnet coexists with stishovite st at a pressure above 18 gpa pyroxene is completely replaced by an assemblage of majorite maj st casio3 perovskite ca pv in ca rich systems whereas maj is associated with almost pure jd up to a pressure of 21 5 gpa above 22 gpa maj and st are associated with naalsio4 with calcium ferrite structure cf we established that an hd component also spreads the range of pyroxene stability up to 20 gpa in the di70jd30 system at 24 gpa an assemblage of maj ca pv mgsio3 with ilmenite structure mg il was obtained the experimentally established correlation between na si and al contents in maj and pressure in grt maj pyroxene assemblages may be the basis for a majorite geobarometer the results of our experiments are applicable to the upper mantle and the transition zone of the earth 400 670 km and demonstrate a wide range of transformations from eclogite to perovskite bearing garnetite in addition the mineral associations obtained from the experiments allowed us to simulate parageneses of inclusions in diamonds formed under the conditions of the transition zone and the lower mantle

enrichment processes at the base of the archean lithospheric mantle observations from trace element characteristics of pyropic garnet inclusions in diamonds trace element concentrations of peridotitic garnet inclusions in diamonds from two chinese kimberlite pipes were determined using the ion microprobe garnet xenocrysts from the same two kimberlite pipes were also analyzed for comparison in contrast to their extremely refractory major element compositions all harzburgitic garnets showed enrichment in light rare earth elements ree relative to chondrite resulting in sinuous ree patterns both normal and sinuous ree patterns were observed from the lherzolitic garnets concentrations of ree in garnets changed significantly from diamond to diamond and no specific correlations were observed with their major element compositions analyses of randomly selected two to three points within every grain of a large number of garnet inclusions by the ion microprobe demonstrated that there was no evident compositional heterogeneity and multiple grains of one phase from a single diamond host also exhibit very similar compositions this implies that the trace element heterogeneity within one grain or among multiple inclusions from the same diamond host as reported from siberian diamonds is not a common feature for these chinese diamonds concentrations of na ti and zr tend to decrease when garnets become more refractory but variations of sr and li are more complex compositions rich in light ree and relatively poor in high field strength elements hfse of the harzburgitic garnet inclusions in diamonds are generally consistent with metasomatism by carbonatite melts the trace element features observed from the garnet inclusions in chinese diamonds may be caused by carbonatite melt infiltration and partial melt extraction spatial and temporal gradients in melt rock ratio and temperature are the main reasons for the large variations of ree patterns and other trace element concentrations

high pressure and high temperature phase relations in diopside camgsi2o6 abstract phase transformations in diopside ca 0 92 mg 1 08 si 2 o 6 were studied by quench experiments at pressures of 18 24 gpa and temperatures of 1000 2400 k using an ma8 type multi anvil apparatus at moderate temperatures diopside decomposed into the assemblage of two components one with mgsio 3 stoichiometry and the other with casio 3 stoichiometry the mgsio 3 component crystallized into mg 2 sio 4 stishovite then transformed into mg 2 sio 4 stishovite mgsio 3 ilmenite and mgsio 3 perovskite with increasing pressure the casio 3 component was observed always as a glass in the recovered samples it is likely that casio 3 formed the cubic perovskite type structure under pressure at higher temperature diopside transformed into mg ca sio 3 garnet and casio 3 perovskite and then to mgsio 3 and casio 3 perovskites the solubility of ca into mg ca sio 3 garnet decreases with increasing pressure the stability field of ca bearing garnet is expanded to lower temperature range compared to that of pure mgsio 3 garnet the present results clarify the phase relations of diopside to the uppermost part of the lower mantle

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

high pressure transitions of diopside and wollastonite phase equilibria and thermochemistry of camgsi2o6 casio3 and casi2o5 catisio5 system abstract phase transitions of camgsi2o6 diopside and casio3 wollastonite were examined at pressures to 23 gpa and temperatures to 2000 c using a kawai type multiavil apparatus enthalpies of high pressure phases in casio3 and in the casi2o5 catisio5 system were also measured by high temperature calorimetry at 17 18 gpa diopside dissociates to casio3 rich perovskite mg rich mg ca sio3 tetragonal garnet gt above about 1400 c the solubilities of casio3 in garnet and mgsio3 in perovskite increase with temperature at 17 18 gpa below about 1400 c diopside dissociates to ca perovskite mg2sio4 stishovite the mg si phases coexisting with ca perovskite change to mg2sio4 stishovite to ilmenite and finally to mg perovskite with increasing pressure casio3 wollastonite transforms to the walstromite structure and further dissociates to ca2sio4 larnite casi2o5 titanite the latter transition occurs at 9 11 gpa with a positive clapeyron slope at 1600 c larnite titanite transform to casio3 perovskite at 14 6 0 6 gpa calibrated against the transition pressure of mg2sio4 the enthalpies of formation of casio3 walstromite and casi2o5 titanite from the mixture of cao and sio2 quartz at 298 k have been determined as 76 1 2 8 and 27 8 2 1 kj mol respectively the latter was estimated from enthalpy measurements of titanite solid solutions in the system casi2o5 catisio5 because casi2o5 titanite transforms to a triclinic phase upon decompression the enthalpy difference between titanite and the triclinic phase is only 1 5 4 8 kj mol using these enthalpies of formation and those of larnite and casio3 perovskite the transition boundaries in casio3 have been calculated the calculated boundaries for the wollastonite walstromite larnite titanite transitions are consistent with the experimental determinations within the errors the calculated boundary between larnite titanite and ca perovskite has a slope of 1 3 1 8 0 4 mpa k and is located at a pressure about 2 gpa higher than that determined by am mineral 79 1994 1219

the eclogite garnetite transformation in the morb h2o system abstract to decipher phase relations of oceanic crust in the coldest slab at the mantle transition zone multi anvil experiments were conducted in the morb h 2 o system at pressures of 10 19 gpa and temperatures of 700 1500 c garnet and stishovite were recognized in all run charges above 15 gpa garnet drastically increases nasi na 2 msi 5 o 12 component m ca mg fe 2 jadeite occurs instead of omphacite na k hollandite containing 7 mol naalsi 3 o 8 and ca perovskite with 60 mol catio 3 were observed at p 17 gpa with decomposition of omphacite and increase of modal ratio of garnet there is a sharp increase of density at 440 km the density increase due to appearance of ca perovskite at 570 km is estimated approximately 100 km shallower than that of previous estimation

combining remote sensing geophysics and lithic provenance and reduction to understand long term continuity in paleo inuit chert quarrying and seasonal inland travels on southern baffin island nu abstract in 2013 we identified a large chert quarry located in the intermediate zone between southern baffin island s coast and interior in 2015 we used a combination of remote sensing and geophysical technology to assess how intensively pre dorset and dorset populations collectively known as paleo inuit used the site this paper presents the results of those investigations and explains how they articulate with geochemical and lithic reduction data from two large inland paleo inuit habitation sites on southern baffin island our findings suggest that despite a dramatic shift in the arctic climate c 5000 2500 bp human populations in this region maintained seasonal patterns of intensive resource exploitation in the interior regions of baffin island this was likely a result of ongoing need for vital resources only available in the interior including chert toolstone

phase relations in the transition zone phase relations in the systems mgo al2o3 sio2 and cao mgo sio2 have been investigated experimentally at 166 226 kbar pressures and 1350 2500 c temperatures with a split sphere anvil apparatus ussa 2000 mgsio3 ilmenite is stable to lower pressures 175 kbar than found previously casio3 perovskite forms at p bar 15t c 151 000 three new high pressure phases are reported a phase with the diopsidic composition the cm phase a high pressure polymorph of al2o3 and superphase b with the tentative composition mg10si3o14 oh f 4 the invariant point for coexisting majorite mg4si4o12 perovskite mgsio3 beta phase mg2sio4 and liquid has been located at 224 kbar 2430 c with the eutectic melt composition on the enstatite forsterite join at 40 44 wt of forsterite the melting temperature of mgsio3 perovskite at 225 kbar is predicted to be 2600 c the new data made possible the calculation of a temperature pressure phase diagram for the system cao mgo al2o3 sio2 cmas in the pressure range 0 280 kbar the mineralogy of the earth s mantle and the possible mechanisms for producing large seismic velocity gradients in the transition zone are discussed on the basis of the derived phase relations

high pressure phase transformation in camgsi2o6 and implications for origin of ultra deep diamond inclusions the decomposition of diopside to casio3 cubic and mgsio3 orthorhombic perovskites was demonstrated by in situ x ray diffraction measurements under simultaneous high pressure and high temperature conditions using a combination of synchrotron radiation and a multianvil apparatus at spring 8 quench experiments also confirmed the decomposition of diopside in a wide temperature range of 1000 1900 c and at pressures 23 27gpa these results strongly support the idea that some mineral inclusions with pyroxene stoichiometry discovered in natural diamonds may have been originated from the lower mantle moreover observed temperature dependence of mgsio3 content dissolved in casio3 perovskite suggests that some of the inclusions were formed at relatively low temperatures 1200 c in the deep mantle presumably related to slab subductions

inclusions in diamonds from the k14 and k10 kimberlites buffalo hills alberta canada diamond growth in a plume analyses of mineral inclusions carbon isotopes nitrogen contents and nitrogen aggregation states in 29 diamonds from two buffalo hills kimberlites in northern alberta canada were conducted from 25 inclusion bearing diamonds the following paragenetic abundances were found peridotitic 48 eclogitic 32 eclogitic websteritic 8 websteritic 4 ultradeep 4 and unknown 4 diamonds containing mineral inclusions of ferropericlase and mixed eclogitic asthenosphericwebsteritic and eclogitic websteritic mineral associations suggests the possibility of diamond growth over a range of depths and in a variety of mantle environments lithosphere asthenosphere and possibly lower mantle eclogitic diamonds have a broad range of c isotopic composition d 13 c y21 x to y5x peridotitic websteritic and ultradeep diamonds have typical mantle c isotope values d 13 c y4 9 x av except for two 13 c depleted peridotitic d 13 c y11 8 x y14 6 x and one 13 c depleted websteritic diamond d 13 c y11 9 x infrared spectra from 29 diamonds identified two diamond groups 75 are nitrogen free type ii or have fully aggregated nitrogen defects type iab with platelet degradation and low to moderate nitrogen contents av 330 ppm n 25 have lower nitrogen aggregation states and higher nitrogen contents f30 iab 1600 ppm n the combined evidence suggests two generations of diamond growth type ii and type iab diamonds with ultradeep peridotitic eclogitic and websteritic inclusions crystallised from eclogitic and peridotitic rocks while moving in a dynamic environment from the asthenosphere and possibly the lower mantle to the base of the lithosphere mechanisms for diamond movement through the mantle could be by mantle convection or an ascending plume the interaction of partial melts with eclogitic and peridotitic lithologies may have produced the intermediate websteritic inclusion compositions and can explain diamondsofmixedparageneses andtheoverlapinc isotopevaluesbetweenparageneses strongdeformationandextremelyhigh nitrogen aggregation states in some diamonds may indicate high mantle storage temperatures and strain in the diamond growth environment a second diamond group with type iaa iab nitrogen aggregation and peridotitic inclusions crystallised at the base of the cratonic lithosphere all diamonds were subsequently sampled by kimberlites and transported to the earth s surface crown copyright d 2004 published by elsevier b v all rights reserved

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

ultradeep greater than 300 kilometers ultramafic upper mantle xenoliths geophysical discontinuities in earth s upper mantle and experimental data predict the structural transformation of pyroxene to garnet and the solid state dissolution of pyroxene into garnet with increasing depth these predictions are indirectly verified by omphacitic pyroxene exsolution in pyropic garnet bearing xenoliths from a diamondiferous kimberlite conditions for silicon in octahedral sites in the original garnets are met at pressures greater than 130 kilobars placing the origin of these xenoliths at depths of 300 to 400 kilometers these ultradeep xenoliths support the theory that the 400 km seismic discontinuity is marked by a transition from peridotite to eclogite