multiple sources of quaternary tephra layers in the mariana trough abstract tephra layers in quaternary sediments stolper and newman 1994 model of binary mixing of source components with one endmember being the nmorb source of stolper and newman 1994 and the other one being a compositionally variable slab derived h2o rich component similar to the h2o component of stolper and newman 1994 this interpretation implies that the variation in k2o content in the arc derived glasses about a factor of 3 at 60 wt sio2 reflects a magmatic diversity that is inherent to the central mariana arc and is not necessarily reflective of temporal changes of the composition of arc magma sources

contrasting compositions of mariana trough fallout tephra and mariana island arc volcanics a fractional crystallization link discrete quaternary 400 ka tephra fallout layers mostly 1 cm thick within the siliceous oozes of the central mariana trough at 18 n are characterized by medium k to high k subalkalic volcanic glasses k2o 0 8 3 2 wt with high large ion lithophile elements lile high field strength elements hfse ratios and nb depletion ba la 35 ba zr 3 5 la nb 4 typical for convergent margin volcanic rocks compositional zoning within layers ranges from basaltic to dacitic sio2 48 71 wt mgo 0 7 6 5 wt all layers contain basaltic andesites the tephra layers are interpreted as single explosive eruptive events tapping chemically zoned reservoirs the sources being the mariana arc volcanoes mav due to their proximity 100 400 km and similar element ratios mav ba la 36 7 ba zr 3 5 0 9 the glasses investigated however contrast with the contemporaneous basaltic to dacitic lavas of the mav by being more enriched in tio2 1 2 wt mav 0 8 wt feo 10 wt mav 8 9 wt k2o 1 1 wt mav 0 8 wt and p2o5 0 4 wt mav 0 2 wt semi incompatible trace elements including rare earth elements ree of the basaltic andesitic and dacitic glasses match those of the dacitic mav lavas which became enriched by fractional crystallization moreover the glasses follow a tholeiitic trend of fractionation in contrast to mav transitional trends and have a characteristic p2o5 trend that reaches a maximum of 0 6 wt p2o5 at 57 wt sio2 whereas mav lavas increase linearly in p2o5 from 0 1 to 0 3 wt with increasing silica both explosive and effusive series are interpreted to have evolved in common magma reservoirs by convective fractionation similar parental magmas are suggested to have separated into coexisting si andesitic to dacitic and basaltic melts by in situ crystallization the differentiated melt is interstitial in an apatite saturated crystalline mush of plag px ox ol at the cooler chamber margins in contrast to the less differentiated basaltic to basaltic andesitic magmas which are not yet saturated in apatite and occupy the chamber interior reinjection of interstitial melt into the chamber interior and mixing with larger melt fractions of the interior liquid mixing ratios about 1 8 9 can explain the paradoxical behavior of apatite controlled p and mree variation in the basaltic andesite glasses and their mav dacite like fractionation patterns the process may also account for the exclusively tholeiitic trend of fractionation of the glass shard series but in situ crystallization alone cannot cause their absolute enrichment in semi incompatible elements the newly mixed melt is suggested to form the basaltic end member of the glass shard series however it must have become physically separated from the main mav magma body possibly by density driven convective fractionation in order to allow for further evolution of the contrasting geochemical paths as well as differentiation

petrology and geochemistry of lavas from the sumisu and torishima backarc rifts thirteen dredge hauls from the active sumisu and torishima rift grabens west of the izu bonin arc at about 30 31 n 140 e recovered a suite of tholeiitic basalts to sodic rhyolites volcanism occurs along tensional faults within and bounding the rift grabens and along the transfer zones between adjoining rift segments the sumisu and torishima rift lavas differ significantly from the lavas of the adjacent arc volcanic centers in having loweral2o3 na2o ba zr v ti andba ce and higher abundances of the rare earth elements the rift lavas also have characteristics of backarc basin basalts in that they are enriched in al2o3 and depleted in total iron and tio2 relative to mid ocean ridge basalt characteristics which are consistent with a higher water content in the source thus the model of a progressive change in backarc basin basalt composition from arc like to mid ocean ridge like as a function of evolution of the basin as has been suggested from many backarc regions is not generally applicable the comparison of the sumisu and torishima rift lavas with mariana backarc basin lavas indicates that backarc basin basalts differ in composition from one basin to another the comparison of these backarc basin suites with mid ocean ridge suites from similar axial depths indicates that the overall control over the spectrum of backarc basin basalt compositions may be different extents of melting of the mantle the sumisu and torishima rift lavas formed by a slightly higher extent of melting than the mariana backarc basin basalts a phenomenon which is related to the depth of the ridge segments furthermore the data suggest a systematically higher extent of melting in the arc lavas than in the backarc lavas for both of these arc backarc systems consistent with a greater flux of water beneath the arc than beneath the backarc region

mechanism of freeze thaw action in the process of soil salinization in northeast china as a particular mechanism of soil salinization freeze thaw action has an obvious control on soil salinization in northeast china it essentially differs from the present day salinization process by involving violent evaporation a special rule of water salt movement is formed during the process of freezing and thawing and the resultant soil profile is divided into three layers frozen layer semi frozen layer and unfrozen layer it is evident that the salinity in the frozen layer increases along with soil water and salt mass moves towards the frozen layer from the underlying beds through the process of soil freezing the salinity of the frozen layer assembles in the upper soil layer and violent vaporizing occurs the salinization vaporization intensity resembles an eruption in springtime because the unthawed soil layer serves as a waterproof stratum and insulates unconfined water soil salinization in the spring has no direct relation with the groundwater table and is only affected by the thawed perched groundwater above the frozen layer therefore it is not true that the critical depth of groundwater controls the springtime eruption salification in northeast china

mariana trough basalts mtb trace element and srnd isotopic evidence for mixing between morb like and arc like melts abstract mariana trough basalt mtb glasses from zones of of active seafloor volcanism have incompatible trace element compositions which are intermediate between normal morb and basaltic rocks from the active northern mariana island arc miab the chemical variation is observed in trace elemental abundances and ratios such as lil lil and lil hfs mtb glasses with high lil hfs and ba sm ratios and low k rb k ba and sm nd ratios have more enriched sr and nd isotopic compositions comparison of the sr nd isotopic compositions of mtb and miab suggests that the source region within the mantle wedge is heterogeneous the diverse trace element and isotopic compositions of mtb glasses both within and between dredge sites near 18 n imply small scale source heterogeneity correlation between sm nd and143nd 144nd of the mtb glasses is interpreted as due to recent binary mixing rather than closed system evolution of a common homogeneous source mixing of melts at or near the source region between a mantle component with long term lree and lil element depletion morb like and a relatively enriched component with lower integrated143nd 144nd arc like is suggested by trends of the mtb data on ratio ratio ratio element and element element plots

forty million years of magmatic evolution in the mariana arc the tephra glass record tephra glasses retrieved from 10 deep sea drilling project dsdp cores around the mariana arc system make up a remarkable record of explosive volcanism in the marianas over the past 40 m y major element compositions for approximately 1800 tephra glasses from basalt through rhyolite are reported and used to examine the nature and history of this activity three maxima of volcanic explosivity presumably related to especially vigorous volcanism in the mariana arc are identified with the biggest maximum at around 18 11 ma and two other maxima at 35 24 and 6 0 ma the two younger maxima are contemporaneous with peaks in explosive volcanism observed for other western pacific arcs explosive arc volcanism has been predominantly tholeiitic since shortly after arc inception no boninitic glasses were found the tephra glasses belong to the low to medium k suite except during an enigmatic phase of medium to high k explosive volcanism during the late miocene 11 7 ma even though mariana tephra glasses are largely similar in composition to mariana arc lavas the tephra show a much larger compositional range than that found for subaerial mariana arc lavas which totally lack dacitic to rhyolitic volcanic products the tephra glasses define a bimodal population in terms of silica content with a pronounced minimum or daly gap around 65 66 sio2 mariana tephra glasses are fractionated with the least evolved glass being fe rich and having a magnesium number mg 100mg mg fe 2 of 55 basaltic tephra glasses contain 16 a1203 average 14 3 a1203 and are not high alumina basalts this contrasts with the observation that modern mariana arc lavas contain 15 21 average 17 4 a1203 the high alumina basalt lavas of the mariana arc probably reflect plagioclase accumulation and not liquid compositions all tephra glasses plot near low pressure cotectics and reaction curves on the subprojection olivine clinopyroxene quartz mafic and felsic samples define distinct trends the mafic trend reflects fractional crystallization of mantle derived basaltic magma whereas the felsic trend may be due either to anatexis of mariana arc crust or to fractionation of mafic melts the tephra glass data reinforce the model that the magmatic evolution of the mariana arc has been dominated by low pressure fractionation perhaps accompanied by anatexis episodic changes in melting regime to generate miocene potassic tephra may be related to changing mantle sources and processes related to episodes of back arc basin spreading these episodic changes are superimposed on a long term increase in potassium that reflects progressive metasomatism of the mantle source long term increases in k20 contents for mariana arc magmas inferred from the tephra glass record are 0 004 wt m y mafic 0 011 wt m y intermediate and 0 023 wt m y felsic

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

holocene vegetation and climate of the alashan plateau nw china reconstructed from pollen data a set of 55 recent pollen spectra from the alashan plateau and the qilian mountains qilianshan northwestern china has been analyzed the established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by eastern juyan palaeolake 41 89 n 101 85 e 892 m a s l several qualitative approaches e g indicator plant species artemisia chenopodiaceae and ephedra fragilis type s l ephedra distachya type pollen ratios and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the eastern juyan pollen record fossil pollen data reveal pronounced environmental changes in the studied area of the alashan plateau between ca 10 700 and 1700 cal yr b p desert taxa as chenopodiaceae nitraria calligonum reaumuria were abundant in the vegetation cover around the study site through the whole record pollen spectra dated to ca 10 700 5400 cal yr b p are characterised by highest values of chenopodiaceae e fragilis type and other desert indicating taxa suggesting rather dry climate most favourable conditions are reconstructed between 5400 and 3900 cal year b p on the basis of relative increase in abundance of artemisia pollen a return to dry conditions occurred at about 3900 cal yr b p the lake finally desiccated after 1700 cal yr b p reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal yr b p correlate well with similar events found in the published records from northern and western china and central mongolia however eastern juyan record does not show the early holocene humidity maximum as suggested by the sedimentary data from monsoon influenced areas of china

nd and sr isotopes from diamondiferous eclogites udachnaya kimberlite pipe yakutia siberia evidence of differentiation in the early earth nd and sr isotopic data from diamond bearing eclogites found in the udachnaya kimberlite yakutia siberia are interpreted as indicating an early 1 4 ga differentiation event whereby the mantle split into complementary depleted and enriched reservoirs reconstructed whole rock 87sr s6sr ratios present day range from 0 70151 to 0 70315 and are consistent with a mantle origin for these rocks the nd isotopic evolution lines of four samples u 5 u 37 u 41 and u 79 converge at 2 2 2 7 ga sample u 5 is unique in exhibiting the most enriched signature of any of the samples yet analyzed present day end of 20 and this sample points unequivocally to an old enriched component a complementary depleted mantle component is suggested by two of the eclogite samples u 86 and u 25 which yield end values at 2 2 ga of 13 and 7 respectively the two mantle reservoirs possibly formed prior to 4 ga and evolved separately until 2 2 2 7 ga at that time the reservoirs were melted forming eclogites both as residues from the enriched reservoir and as partial melts of peridotite from the depleted reservoir resulting in demonstrably different histories for eclogites from the same locality

petrology of the axial ridge of the mariana trough backarc spreading center abstract the axial ridge of the mariana trough backarc basin between 17 40 n and 18 30 n rises as much as 1 km above the floor of a 10 15 km wide rift valley physiographic segmentation with minor ridge offsets and overlaps coincides with a petrologic segmentation seen in trace element and isotope chemistry analyses of 239 glass and 40 aphyric basalt samples collected with alvin and by dredging show that the axial ridge is formed largely of olivine hypersthene normative tholeiitic basalt about half of these are enriched in both lil elements and volatiles but are depleted in hfs elements like other rocks found throughout much of the mariana trough the lil enrichments distinguish these rocks from n morb even though nd and sr isotope ratios indicate that much of the crust formed from a source similar to that for n morb in addition to lil enriched basalt there is lil depleted basalts even more closely resembling n morb in major and trace elements as well as sr nd and pb isotopes both basalt varieties have higher al and lower total fe than morb at equivalent mg level mg ranges from relatively primitive e g mg 65 70 to more highly fractionated e g mg 45 50 highest parts of the axial ridge are capped by pinnacles with elongated pillows of basaltic andesite e g 52 56 sio 2 these are due to extreme fractional crystallization of basalts forming the axial ridge active hydrothermal vents with chimneys and mats of opaline silica barite sphalerite and lesser amounts of pyrite chalcopyrite and galena formed near these silicic rocks the vents are surrounded by distinctive vent animals polychaete worms crabs and barnacles isotope data indicate that the mariana trough crust was derived from a heterogeneous source including mantle resembling the morb source and an arc source component the latter was depleted in hfs elements in previous melting events and later modified by addition of h 2 o and lil elements

origin of k2o sio2 trends in volcanoes of the mariana arc lavas from volcanoes in the mariana arc show a range of k 2 o sio 2 trends even though the volcanoes are all nearly the same distance above the benioff zone the preferred petrologic explanation for the k 2 o sio 2 variations invokes differences in the degree of partial melting required to produce lavas for each volcano from a relatively homogeneous source material the mariana arc volcanoes appear to evolve chemically in a manner similar to oceanic volcanoes e g hawaii with early and late alkalic stages dominated by an intermediate tholeiitic stage if volcanoes in other arcs also undergo this evolution many of the anomalies in k 2 o depth relations in modern arcs could be explained

carbon isotopic composition nitrogen content and inclusion composition of diamonds from the roberts victor kimberlite south africa evidence for 13c depletion in the mantle the c isotopic composition and n content of a suite of diamonds of known inclusion mineral composition from the roberts victor kimberlite have been measured the mean 13c content of diamonds containing peridotitic minerals x 5 4 vs pdb s 0 9 n 65 does not differ significantly from those containing sulfides x 4 9 s 0 9 n 20 diamonds containing eclogitic minerals can be subdivided into two groups based on their carbon isotopic composition group a x 15 5 s 0 4 n 10 and group b x 5 6 s 0 6 n 4 the clinopyroxenes occluded by the group a diamonds are depleted in sio2 mgo and cao and significantly enriched in al2o3 feo and mno compared to clinopyroxenes occluded by group b diamonds carbon in two graphite diamond eclogites has a mean isotopic composition of 5 31 in both samples graphite shows a slight enrichment in 13c compared to the coexisting diamond the range of n concentrations of diamonds containing peridotitic or eclogitic minerals is essentially the same 0 to 750 ppm while it is considerably larger for sulfide containing diamonds 0 to 1700 ppm there is no difference in the c isotopic composition between type i and type ii diamonds for sulfide and peridotitic minerals occluding diamonds all type ii diamonds containing eclogitic minerals belong to group a no correlation between n content and c isotopic composition could be established although a large range in both variables is observed for the sample suite the composition of eclogitic minerals included in diamonds of low 13c content differs from that of eclogite xenoliths characterized by 18o depletions which have been related to subduction processes hence the data available do not suggest a common cause for the depletion of the heavy isotopes of the two elements the chemical and isotopic characteristics of the suite of diamond samples reflect different mantle environments diamonds depleted in 13c 13c 15 to 16 come from a region at greater depth than those of 13c contents of 5 to 6 the source region of the former is characterized by higher fe mn al and lower mg ca si and n contents than that of the latter

nd and sr isotopic compositions of lavas from the northern mariana and southern volcano arcs implications for the origin of island arc melts nd and sr isotopic data are reported for lavas from 23 submarine and 3 subaerial volcanoes in the northern mariana and southern volcano arcs values of end range from 2 4 to 9 5 whereas 87sr 86sr ranges from 0 70319 to 0 70392 these vary systematically between and sometimes within arc segments the nd and sr isotopic compositions fall in the field of ocean island basalt oib and extend along the mantle array lavas from the volcano arc mariana central island province and the southern part of the northern seamount province have end to 10 and 87sr 86sr 0 7032 to 0 7039 these are often slightly displaced toward higher 87sr 86sr at similar end in contrast those lavas from the northern part of the mariana northern seamount province as far north as iwo jima show oib isotopic characteristics with end and 87sr 86sr 0 7035 to 0 7039 plots of 87sr 86sr and end versus ba la and la yb n support a model in which melts from the mariana and volcano arcs are derived by mixing of oib type mantle or melts therefrom and a metasomatized morb type mantle or melts therefrom an alternate interpretation is that anomalous trends on the plots of nd and sr isotopic composition versus incompatible element ratios found in some s nsp lavas suggest that the addition of a sedimentary component may be locally superimposed on the two component mixing of mantle end members

subducting oceanic crust the source of deep diamonds inclusions of majoritic garnet in diamonds from the jagersfontein kimberlite formed at unusually great depths of 250 to 500 km in the asthenosphere and transition zone the original host rocks were derived from a much shallower basaltic eclogitic source the presence of negative eu anomalies in all majoritic garnets requires a crustal origin thereby linking these very deep diamond sources to subducting oceanic crust the carbon isotope values 13c of the host diamonds fall within a narrow range at 20 which is fundamentally different from the broad range 24 to 2 and bimodal distribution of carbon isotopes of jagersfontein diamonds that formed in the shallower lithosphere this indicates that majoritic garnet bearing diamonds at jagersfontein inherited their light carbon isotopic composition directly from organic matter contained in a subducting slab these diamonds were likely formed by direct conversion from graphite well within the diamond stability field

multi stage metasomatism of diamondiferous eclogite xenoliths from the udachnaya kimberlite pipe yakutia siberia the primary garnet pyrope almandine omphacite cpx 1 6 5 7 wt na2o sulfide fe ni co mss assemblage of the two diamondiferous eclogite xenoliths studied u33 1 and ux 1 experienced two mantle metasomatic events the metasomatic event i is recorded by the formation of platy phlogopite 10 wt k2o prior to incorporation of the xenoliths in the kimberlite the bulk of the metasomatic alteration consisting of spongy textured clinopyroxene cpx 2a 1 3 wt na2o coarser grained clinopyroxene cpx 2b 2 5 wt na2o pargasitic amphibole 0 8 wt k2o 3 3 5 wt na2o kelyphite cpx 3 mostly 1 wt na2o and zoned mg fe al spinel sodalite calcite k feldspar djerfisherite k5 95na0 02fe18 72ni2 36co0 01cu4 08s26cl and a small amount of k ca fe mg glass is ascribed to the metasomatic event ii that occurred also in the upper mantle but after the xenoliths were incorporated in the kimberlite a pervasive chloritic alteration mainly clinochlore magnetite that overprints earlier assemblages probably took place in the upper crustal environment the diamonds are invariably associated with secondary clinopyroxene and chlorite but the diamonds formed before the entrainment of the xenoliths in the udachnaya kimberlite

physical volcanology of the submarine mariana and volcano arcs narrow beam maps selected dredge samplings and surveys of the mariana and volcano arcs identify 42 submarine volcanos observed activity and sample characteristics indicate 22 of these to be active or dormant edifices in the volcano arc are larger than most of the mariana arc edifices more irregularly shaped with numerous subsidiary cones and regularly spaced at 50 70 km volcanos in the mariana arc tend to be simple cones sets of individual cones and volcanic ridges are elongate parallel to the trend of the arc or at 110 counterclockwise from that trend suggesting a strong fault control on the distribution of arc magmas volcanos in the mariana arc are generally developed west of the frontal arc ridge on rifted frontal arc crust or new back arc basin crust volcanos in the central mariana arc are usually subaerial large 500 km3 and spaced about 50 70 km apart those in the northern and southern marianas are largely submarine closer together and generally less than 500 km3 in volume there is a shoaling of the arc basement around iwo jima accompanied by the appearance of incompatible element enriched lavas with alkalic affinities the larger volcanic edifices must reflect either a higher magma supply rate or a greater age for the larger volcanos if the magma supply estimated at 10 20 km3 km of arc per million years at 18 n has been relatively constant along the mariana arc we can infer a possible evolutionary sequence for arc volcanos from small irregularly spaced edifices to large over 1000 km3 edifices spaced at 50 70 km the volcano distribution and basal depths are consistent with the hypothesis of back arc propagation into the volcano arc

shoshonitic magmas in nascent arcs new evidence from submarine volcanoes in the northern marianas volcanoes in the northern mariana arc between uracas lat 20 n and minami iwo jima 24 n are very active yet entirely submarine in contrast to the predominantly low k basaltic magmas of the central mariana arc the northern mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north the northern arc melts have enrichments in ba 800 ppm rb 70 ppm sr 1000 ppm ce 50 ppm and ce yb n 24 which increase to the north as far as iwo jima lavas from volcanoes north of iwo jima lack these enrichments and are indistinguishable from those of the central maranas the shoshonites are unusual in occurring along the magmatic front of a primitive intra oceanic arc we hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the mariana trough spreading center northward through the volcano arc shoshonites thus may characterize the initial stages of arc construction after an episode of back arc rifting and need not be restricted to the mature stages of arc evolution this situation contrasts with subduction zone initiation where first melts may be boninites or low k tholeiites these differing initial melts converge toward tholeiitic and calc alkaline compositions as arcs evolve

eclogites with oceanic crustal and mantle signatures from the bellsbank kimberlite south africa part 2 sr nd and o isotope geochemistry the sr nd and o isotopic compositions of garnet and clinopyroxene mineral separates from nine eclogite xenoliths from the bellsbank kimberlite erupted at 120 ma define three groups group a eclogites considered to be mantle cumulates are characterized by 6180 and 87sr srsr values typical of mantle derived materials 5 1 to 5 6 o and 0 7042 0 7046 respectively and very low sm nd ratios apparent rb sr ratios and nallz01 values 0 057 0 078 0 00005 0 00136 and 14 to 16 respectively the ree and isotopic data for these eclogites can be modelled in terms of crystallization from a group ii kimberlite magma at 1 1 5 ga group b and c eclogites believed to be the metamorphosed products of ancient subducted oceanic crust are characterized by low 3180 2 9 to 4 7 extremely high nd a20 40 to 219 and radiogenic 87sr s6sr ratios 0 708 0 710 the sm nd ratios of the group b eclogites are very high up to 1 6 the data for group b and c eclogites define a linear correlation on sm nd and 1 nd vs nal 201 diagrams these relationships are consistent with mixing of the bellsbank kimberlite cno 1201 10 sm nd 0 10 with a depleted eclogite end member end 120 219 sm nd 1 6 during a cryptic metasomatic event the sr isotopic variations in group b and c eclogites cannot be generated by simple two component mixing the st nd and o isotope data for group b and c eclogites probably reflect a complex sequence of depletion and enrichment events in both crust and mantle settings enrichments which possibly affected the group b and c eclogites include seawater alteration of a morb like protolith which lowered the 6180 and raised the svsr 86sr ratio but left the nd isotopic compositions unchanged and cryptic metasomatism by the magmatism that produced the bellsbank kimberlite the high sm nd ratio of the depleted eclogite end member cannot be generated by extraction of a melt from a modern morb composition rather it is argued that such high sm nd ratios are produced as a result of partitioning during the recrystallization of a morb like component to eclogite during subduction nd model ages suggest that this process occurred 2 3 2 4 ga

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

non destructive multi method internal analysis of multiple inclusions in a single diamond first occurrence of mackinawite fe ni 1 xs a single gem lithospheric diamond with five sulfide inclusions from the udachnaya kimberlite siberia russia has been analyzed non destructively to track the growth conditions of the diamond sulfides are the most abundant mineral inclusions in many lithospheric diamond crystals and are the most favorable minerals to date diamond crystals by re os isotope systematics our investigation used non destructive micro techniques combining x ray tomography x ray fluorescence x ray powder diffraction and raman spectroscopy this approach allowed us to determine the spatial distribution of the inclusions their chemical and mineralogical composition on the microscale and finally the paragenetic association leaving the diamond host completely unaffected the sample was also studied by x ray diffraction topography to characterize the structural defects of the diamond and to obtain genetic information about its growth history the x ray topographic images show that the sample investigated exhibits plastic deformation one set of 111 slip lamellae corresponding to polysynthetic twinning affects the entire sample chemical data on the inclusions still trapped within the diamond show they are monosulfide solid solutions of fe ni and indicate a peridotitic paragenesis micro x ray diffraction reveals that the inclusions mainly consist of a polycrystalline aggregate of pentlandite and pyrrothite a thorough analysis of the raman data suggests the presence of a further fe ni sulfide never reported so far in diamonds mackinawite the total absence of any oxides in the sulfide assemblage clearly indicates that mackinawite is not simply a late alteration of pyrrhotite and pentlandite due to secondary oxidizing fluids entering diamond fractures after the diamond transport to the surface instead it is likely formed as a low temperature phase that grew in a closed system within the diamond host it is possible that mackinawite is a more common phase in sulfide assemblages within diamond crystals than has previously been presumed and that the percentage of mackinawite within a given sulfide assemblage could vary from diamond to diamond and from locality to locality

geochemical data as indicators of environmental change and human impact in sediments derived from downstream marshes of an ephemeral river northeast china recent sedimentary history of natural environmental change and anthropogenic influence in an ephemeral river catchment has been reconstructed using selected major and trace elements element ratios and their different geochemical phases tessier sequential extraction methods pollen and grain size combined with 210pb and 137cs dating method in marsh sedimentary cores attempts were made to use selected element ratios with different geochemical phases residual phase of ti al v cr ni rb k sr and ba mobile sr and ba combined with 210pb and 137cs chronology to interpret certain time information of environmental changes saved within the marsh sediments results indicate that there were two marked humid periods during 1850 1860 ad and 1890 1920 ad and sand storm activities prevailed during 1920 1930 ad after about 1900 ad soil erosion has increased with the extensive agricultural activities in the huolin river catchments and further intensified after 1950s after 1980 soil erosion has become even more intense which is consistent with the reinforcement of human activities the drastic loss of vegetation cover in the upstream lands especially the exploitation of the open cast coalmine in the upstream of huolin river at that time influenced by the inundation of the huolin river the heavy metal pollution historical trends in xianghai marsh wetland could be roughly divided into three periods by analysis of sediment enrichment factor ksef and the index of geoaccumulation igeo 1760 1880 ad 1880 1980 ad and 1980 now human activities accelerate the inputs of heavy metal which leads to degradation of the marsh this study also investigated on source of marsh sediments by ti al redox condition by v cr and v v ni and salinization indicators by sr ba and rb k the results demonstrate that sources of sediments and redox conditions were partly similar for both riparian and depressional marshes besides some differences in degree of salinization between two types of marsh were also identified especially after 1880

metasomatic diamond growth a multi isotope study 13c 15n 33s 34s of sulphide inclusions and their host diamonds from jwaneng botswana abstract the formation of diamond through metasomatic events from volatiles enriched fluids melts brought into pre existing mantle rocks has been suggested from a series of independent studies however the link between these hypothetical volatile rich fluids and deep seated mineral inclusions mostly silicate and sulphides entrapped in diamonds remains unclear yet the relationship between these two species may provide the key to our understanding of diamond crystallization in order to address the relationship between the origin and formation of diamonds and their mineral inclusions we carried out the first coupled stable isotopic study 13 c 15 n and multiple s isotopes as 34 s 33 s 33 s of diamonds containing sulphide inclusions using samples from the jwaneng kimberlite as our model system sulphides extracted from the present collection of 55 diamonds belong to either eclogitic e type 52 diamonds or peridotitic p type 3 diamonds paragenetic suites as attested by their cr and ni content cr 0 18 wt and ni 14 wt for p types sulphur isotopic compositions have been measured in situ by multicollector secondary ion mass spectrometry and reveal that peridotitic sulphide inclusions in diamonds n 4 lie on the terrestrial fractionation line whereas mass independent sulphur isotope fractionations mif are preserved inside eclogitic sulphides inclusions 0 5 33 s n 33 such large mif values extended here to the negative values recorded in archean sediments are thought to be produced through photochemical reactions in the archean atmosphere which implies that sulphides inclusions contain an archean sedimentary sulphur component that was transferred to the earth s mantle in contrast to this isotopic dichotomy between e type and p type sulphides the geochemical characteristics of their host diamonds 13 c 15 n n content n speciation are largely homogeneous throughout the population and differ from silicate bearing diamonds previously studied in the same locality sulphide bearing diamonds appear to define a distinct population which might reflect a different crystallization process characterized by carbon and nitrogen isotopic compositions falling within the range of unfractionated mantle values the lack of a distinct isotopic signature of recycled sedimentary nitrogen and carbon in sulphide bearing diamonds leads us to infer that sulphide bearing jwaneng diamonds were not derived from the same chemical reservoir as their inclusions one possible formation mechanism that is compatible with our observations is diamond crystallization from a mantle derived carbon bearing fluid associated with pre existing sedimentary sulphide minerals this model has important implications for the interpretation of diamond ages obtained from sulphide inclusions using re os systematics here we suggest that the incorporation of a significant amount of mantle related sulphur during a diamond growth event into the original sulphide could lead to a re equilibration of the re os isotope composition in any inclusion and accordingly account for some scatter on re os isochrons

archean mantle heterogeneity and the origin of diamondiferous eclogites siberia evidence from stable isotopes and hydroxyl in garnet data are presented for the o isotopic composition of clinopyroxene and garnet the c isotopic composition of diamond and the oh content of garnet from eclogite xenoliths brought to the surface by the udachnaya kimberlite pipe yakutia siberia radiogenic isotopic data suggest that the eclogites could have been derived from an ultradepleted mantle at approximately 2 9 ga pearson et al 1995 snyder et al in preparation o isotopic compositions generally show equilibration between the eclogitic minerals cpx grt 0 11 0 41 and have 18 o smow for both garnet and clinopyroxene that lie near the range of accepted mantle values of 5 7 0 7 however several eclogites indicate significant deviations from this range at higher values of 6 8 7 0 also two eclogites lie at the lower end of the mantle range at values of 4 8 and 5 0 all in clinopyroxene c isotopic compositions of diamonds all have 13 c pdb in the range of 1 to 7 and are centered at approximately 5 also within the range of accepted mantle values the oh contents of the garnet are generally between 0 and 22 ppm as h 2 0 although two samples exceed 70 ppm this range of oh is similar to eclogitic garnet from the kaapvaal craton of southern africa the mantle c isotopic values of associated diamonds the majority of o isotopic data and the low oh content of the minerals although suggesting a general lack of crustal participation in the formation of the udachnaya eclogites do not rule out the participation of some ancient crustal material that these eclogites include both 18 o enriched and 18 o depleted types suggests that the protoliths may have been overprinted by both low and high temperature hydrothermal events cf jacob et ai 1994 a positive correlation between 18 o and 87 sr 86 sr allows the interpretation of these eclogites as representing a cross section of an archean ophiolite however the lack of a single coherent grouping on a plot of 18 o vs 87 sr 86 sr suggests that if the udachnaya eclogites were derived from oceanic crust they cannot be cogenetic and must represent at least two separate ophiolite sequences conversely if the eclogites are found to be cogenetic then a totally different process affected their formation and a probable metasomatic mechanism was operative because of the total lack of correlation of 18 o with other geochemical parameters we find no compelling evidence that all eclogites are derived ultimately from oceanic crust

3 d x ray tomography of diamondiferous mantle eclogite xenoliths siberia a review abstract diamonds form over billions of years hundreds of kilometers beneath the earth s surface and in combination with inclusions trapped within provide important constraints on the evolution of the mantle over geological time diamonds are generally studied as individual crystals sourced from highly explosive kimberlite pipes which entrain and subsequently disaggregate mantle fragments xenoliths en route to the surface this has resulted in a general absence of robust textural descriptions of diamonds relative to their hosting mantle protolith the textural associations of diamonds within their mantle host rocks are reviewed here on the basis of a compilation of x ray tomographic data for 17 diamondiferous eclogite xenoliths from siberian kimberlites this review represents a comprehensive description of diamonds relative to their host silicates the lack of such descriptions in previous studies is largely due to the rarity of these xenoliths the difficulty in preparing petrographic thin sections containing diamonds and their high monetary value high resolution computed x ray tomography hrcxt produces up to 1200 sequential 2 d slices through individual xenoliths each of which represents a pseudo thin section with a resolution on the order of 5 20 m the improved resolution of x ray imaging in recent studies allows for the identification of not only primary minerals but metasomatic minerals assemblages including spongy textured clinopyroxene phlogopite k richterite and hercynitic spinel allowing for the delineation of distinct metasomatic pathways through the xenoliths and their relationship to diamonds diamonds are observed in three distinct textural settings potentially representing several temporally distinct diamond growth events these setting includes 1 diamonds completely enclosed in garnet 2 diamonds associated with highly embayed silicate grain boundaries and 3 diamonds contained within distinct metasomatic plumbing systems diamonds observed completely enclosed in garnets suggest an early diamond forming event prior to major re crystallization and eclogite formation during subduction the occurrence of diamond in association with embayed garnets suggests that diamond grew at the expense of the hosting silicate protolith in addition the spatial relationships of diamonds with metasomatic pathways which are generally interpreted to result from late stage proto kimberlitic fluid percolation indicate a period of diamond growth occurring close to but prior to the time of kimberlite emplacement furthermore the paragenesis of sulfides within eclogite xenoliths are described using 3 d models for entire xenoliths volumes providing important constraints of the timing of sulfide mobilization within the mantle three d animations created using x ray tomography data for ten of the xenoliths can be viewed at the following link http eps utk edu faculty taylor tomography php

constraining the internal variability of the stable isotopes of carbon and nitrogen within mantle diamonds the carbon and nitrogen isotope values of mantle xenoliths and xenocrysts are used to trace the cycling of volatiles in the deep earth for example to place empirical constraints on the origin of diamond forming carbon in the mantle the global database for diamond shows that the 13c value of peridotitic diamonds is very narrow typically around 5 whereas eclogitic diamonds can show positive and very negative 13c values resembling crustal carbonates and crustal organic carbon 2 commonly interpreted to reflect a relationship between eclogitic diamond formation and subduction zone planet tectonics curiously diamonds from both parageneses can show positive crust like and negative mantle like 15n values from 20 most of these data are derived from single stage combustion gas sourced mass spectrometry which produces simplistic datasets by fragmenting single diamonds or using in situ ion beam techniques it is known that single diamonds can show large scale heterogeneity for their carbon isotope values and nitrogen abundances sometimes as large as entire populations of diamond across a few hundred micrometres what is less well known is the scale of nitrogen isotope heterogeneity within single diamonds and if the nitrogen isotope heterogeneity of single diamonds can provide an insight into why diamonds that show very restricted 13c values show a much large range of 15n values to investigate the scale and to determine the origin of the nitrogen isotope heterogeneity source vs fractionation during diamond formation shown for populations of mantle diamonds we have determined multiple 13c 15n values and nitrogen abundances from 14 monocrystalline mcds and 25 polycrystalline diamonds pcds using step wise oxidation gas sourced mass spectrometry these data show that the heterogeneity shown for carbon and nitrogen isotope values from single diamond samples presented here is typically 5 and 8 respectively both of which are comparable to the standard deviation for the mean mantle 13c and 15n values 3 and 4 however there are samples that show much larger heterogeneities for 13c and 15n values 23 and 33 respectively which cannot be generated by equilibrium stable isotope fractionation during or prior to diamond formation these data suggest that isotopic heterogeneity may be present within the diamond forming fluid on sub mm scale or that these diamonds formed during multiple diamond formation events from isotopically distinct sources from these 39 samples there are only 5 pcds that show a larger range of carbon isotopes relative to nitrogen isotopes but of these 5 samples only 2 show a range of 13c values outside of analytical uncertainty the remaining 34 samples show a greater isotopic heterogeneity for 15n relative to 13c values the samples with the largest carbon and nitrogen isotopic heterogeneity are also the samples with low bulk 13c values 10 whilst there is no relationship between the ranges of nitrogen isotope values for a given sample and the corresponding bulk 15n value or nitrogen content these data show that 15n values recorded in mantle diamonds are relatively heterogeneous and can show both mantle like negative and crustal sedimentary like positive 15n values within the same sample we conclude that the large range of nitrogen isotope values seen within individual diamonds means that the observation of negative mantle like nitrogen in mantle diamonds acquired by single stage bulk combustion isotope ratio mass spectrometry cannot be used as a conclusive indicator for a mantle origin for the entirety of the diamond forming carbon and vice versa also the behaviour of 15n 14n is not coupled with the behaviour of 14n 12c during diamond formation instead it appears that diamond forming fluids can have positive and negative 15n values irrespective of their 13c value s these data suggest that subduction induced nitrogen isotope heterogeneity may not be coupled with subduction induced carbon isotope heterogeneity in diamond forming fluids

submarine arc volcanism in the southern mariana arc as an ophiolite analogue supra subduction zone ssz ophiolites are being recognized more and more frequently in the geologic record submarine volcanism in intra oceanic arcs is one tectonic setting in which such ophiolites might form the southern seamount province of the mariana arc represents the best documented example of an active intra oceanic submarine arc which can serve as a modern analogue for some ssz ophiolites the southern seamount province comprises nine submarine volcanoes at least seven of which are active or dormant these edifices have erupted plagioclase clinopyroxene olivine phyric basalts andesites dacites and dacitic pumices these lavas are similar to those of the subaerial edifices in the central marianas sio2 49 70 tio2 0 4 1 3 mgo 1 2 5 9 ba 140 450 ppm 87sr 86sr 0 70346 0 70354 but are somewhat more enriched in the light rare earth elements the geochemical characteristics of subaerial mariana arc lavas are preserved in the submarine lavas and the ssp lavas are slightly enriched in incompatible elements relative to those of the subaerial edifices we are ignorant of the composition of any lavas erupted between the principal edifices which may be expected to dominate the volcanic section of ssz ophiolites nevertheless the characteristic high ratio lil hfsc low ti ni and cr and diagnostic mineral compositions calcic plagioclase relatively fe rich olivine are likely to be preserved in unaltered submarine arc lavas the mariana active arc is built on back arc or thinned frontal arc crust and any ophiolite formed from such an arc is likely to exhibit complex intrusive and eruptive relationships of plutonic hypabyssal and volcanic rocks of back arc frontal arc and active arc origin such complicated intrusive relationships if preserved in structurally disrupted ophiolites will make it difficult to reconstruct the geologic history of an ssz ophiolite

abundance and distribution of diamonds in eclogite revealed by volume visualization of ct x ray scans a diamond bearing eclogite has been studied using industrial high energy computed tomography and volume visualization techniques using this non destructive technique in which distinction between phases is based on density differences seven diamonds five completely enclosed in the rock have been isolated and viewed in three dimensions six diamonds appear to be single crystals of well formed to malformed octahedra one is a spinel twin macle partial to complete rimming by secondary barite provides sufficient density contrast with surrounding silicates to allow the diamonds to be easily recognized by their morphology they appear to be confined to a 1 cm wide layer diamonds range in size from 0 9 to 2 4 mm in maximum dimension and are estimated to constitute 0 19 wt of the sample equivalent to a grade of 9500 carats per metric ton several models for diamond genesis can be ruled out for this sample e g pseudomorphs of graphite by diamond precipitation as glomeroporphyritic aggregates from

the siberian lithosphere traverse mantle terranes and the assembly of the siberian craton abstract the kimberlite fields scattered across the ne part of the siberian craton have been used to map the subcontinental lithospheric mantle sclm as it existed during devonian to late jurassic time along a 1000 km traverse ne sw across the archean magan and anabar provinces and into the proterozoic olenek province 4100 garnets and 260 chromites from 65 kimberlites have been analysed by electron probe major elements and proton microprobe trace elements these data and radiometric ages on the kimberlites have been used to estimate the position of the local paleo geotherm and the thickness of the lithosphere and to map the detailed distribution of specific rock types and mantle processes in space and time a low geotherm corresponding approximately to the 35 mw m2 conductive model of pollack and chapman tectonophysics 38 279 296 1977 characterised the devonian lithosphere beneath the magan and anabar crustal provinces the devonian geotherm beneath the northern part of the area was higher rising to near a 40 mw m2 conductive model areas intruded by mesozoic kimberlites are generally characterised by this higher but still cratonic geotherm lithosphere thickness at the time of kimberlite intrusion varied from ca 190 to ca 240 km beneath the archean magan and anabar provinces but was less 150 180 km beneath the proterozoic olenek province already in devonian time thinner devonian lithosphere 140 km in parts of this area may be related to riphean rifting near the northern end of the traverse differences in geotherm lithosphere thickness and composition between the devonian toluopka area and the nearby mesozoic kimberlite fields suggest thinning of the lithosphere by ca 50 60 km related to devonian rifting and triassic magmatism a major conclusion of this study is that the crustal terrane boundaries defined by geological mapping and geophysical data extended from outcrops in the anabar shield represent major lithospheric sutures which continue through the upper mantle and juxtapose lithospheric domains that differ significantly in composition and rock type distribution between 100 and 250 km depth the presence of significant proportions of harzburgitic and depleted lherzolitic garnets beneath the magan and anabar provinces is concordant with their archean surface geology the lack of harzburgitic garnets and the chemistry of the lherzolitic garnets beneath most of the other fields are consistent with the proterozoic surface rocks mantle sections for different terranes within the archean portion of the craton show pronounced differences in bulk composition rock type distribution metasomatic overprint and lithospheric thickness these observations suggest that individual crustal terranes of both archean and proterozoic age had developed their own lithospheric roots and that these differences were preserved during the proterozoic assembly of the craton data from kimberlite fields near the main archean proterozoic suture the billyakh shear zone suggest that reworking and mixing of archean and proterozoic mantle was limited to a zone less than 100 km wide

metasomatic origin of diamonds in the world s largest diamondiferous eclogite article i nfo the world s largest diamondiferous eclogite 8 8 kg ud 111 02 from the udachnaya kimberlite siberia is the subject of this investigation high resolution x ray computed tomography hrxct chemistry of host minerals and diamond inclusions stratigraphy of the diamonds cathodoluminescence zoning and carbon isotopes have been obtained hrxct images 3 d models and subsequent detailed dissection of this group b eclogite revealed linear distributions of diamonds along alteration zones both unusual multiple diamond clusters with dodecahedral morphologies and distinctive internal zoning recorded by cathodoluminescence analyses are indicative of multiple stages of diamond growth and resorption in ud 111 02 carbon isotope ratios 13 c of 16 diamonds have a total range of 7 2 0 to 9 2 with the majority at 5 4

lithological and geochemical record of mining induced changes in sediments from macquarie harbour southwest tasmania australia macquarie harbour in southwest tasmania australia has been affected severely by the establishment of mines in nearby queenstown in the 1890s as well as heavy metal laden acid rock drainage from the mount lyell mine area over 100 mt of mine tailings and slag were discharged into the queen and ring rivers with an estimated 10 mt of mine tailings building a delta of ca 2 5 km2 and ca 10 mt of fine tailings in the harbour beyond the delta coring of sediments throughout macquarie harbour indicated that mine tailings accreted most rapidly close to the king river delta source with a significant reduction in thickness of tailings and heavy metal contamination with increasing distance from the king river source close to the king river delta the mine tailings are readily discriminated from the background estuarine sediments on the basis of visual logging of the core laminations colour sediment grain size sediment magnetic susceptibility and elemental geochemistry especially concentrations of the heavy metals cu zn and pb the high heavy metal concentrations are demonstrated by the very high contamination factors cf 6 for cu and zn with cf values mostly 50 for cu for the mine impacted sediments although the addition of mine waste into the king river catchment has ceased the catchment continues to be a source of these heavy metals due to acid rock drainage and remobilisation of mine waste in storage in the river banks river bed and delta the addition of heavy metals to the harbour sourced from the mount lyell mines preceded the advent of direct tailings disposal into the queen river in 1915 with the metals probably provided by acid rock drainage from the mount lyell mining area

paleolimnological records of climatic change in north america lacustrine fossil records provide long time series of data on limnological and climatic conditions these data are useful for establishing natural patterns of climate variability and for generating testable hypotheses about atmospheric circulation and climate ecosystem linkages shoreline features can indicate past lake level fluctuations that may reflect changes in moisture balance but often these records are discontinuous and are evidence of only extreme conditions the organisms geochemistry and sedimentology of lake sediments may provide a more continuous sequence of direct and indirect lake climate interactions in the past the most clearly interpretable paleolirnnological records of climatic change are those that use several lines of evidence to corroborate a climatic hypothesis and are from sites near an ecotone or in regions of extreme climate in all cases hydrologic setting mediates a lake s response to climate and must be considered in interpreting sedimentary sequences discussion of the impact of recent and future climatic changes necessitates a baseline against which the magnitude of observed or predicted changes can be measured commonly we look to recent history as a reference point for comparison however the landscape of recent decades or in some cases even centuries has been altered greatly by human activities thus to determine whether recent or future climatic change is unique or unusual we need long natural preanthropogenic time series against which observed or predicted climatic states and variability can be compared paleolimnological archives are a tool for looking at environmental patterns prior to anthropogenic impact and show a range of climatic states far greater than those documented by written records former strand lines of pluvial lakes bonneville and lahontan in the western u s for example testify to moisture extremes unsurpassed in recent centuries or even millennia in addition one can us the paleolimnological record as an independent climatic proxy against which patterns and rates of terrestrial response to climatic change can be compared here i present a broad overview of paleoclimatic reconstruction in north america from lacustrine records with a focus on the late quaternary the review is limited to climatic inference from paleolirnnological records a term i use in a restrictive sense to refer to records of past lake states physical biological and geochemical as opposed to records of past stream hydrology e g ely et al 1993 knox 1993 or terrestrial conditions i summarize paleolimnological tools available for reconstruction of past climate the capabilities and limitations of these tools

pore structure and fractal characteristics of ordovician majiagou carbonate reservoirs in ordos basin china fractal analysis was performed on carbonate core plug samples from the ordovician majiagou carbonate reservoirs in the ordos basin using mercury intrusion capillary pressure micp nuclear magnetic resonance nmr and the x ray computed tomography ct measurements to improve our understanding of the pore structure characteristics the relationships between pore structure parameters and the fractal dimensions were investigated the pore systems are dominated by secondary intercrystalline pores and enlarged dissolution pores as well as microfractures the fractal curves from micp analysis break into two segments at the swanson s parameter the small pore throat systems can be described by the fractal theory whereas pores connected by relatively large throats greater than the pore throat radius at the pittman s hyperbola s apex are not cylindrical in shape cannot be described by a capillary tube model and tend to have apparent fractal dimensions larger than 3 0 the fact that the entirety of the capillary curve cannot be fit by a single fractal dimension implies that there are multiple pore systems present with different fractal dimensions the ct analysis shows that the pores are dispersed in the three dimensional spaces mainly with elliptical shapes the nmr measurements are sensitive to pore body size and micp probes pore throat dimensions the latter being complementary to the pore body size distribution none of the ct micp and nmr techniques provide right or wrong answers to the pore throat systems but they probe different aspects of the pore systems this study assumes the pore shapes to be spherical in general and then the fractal dimension is calculated from the nmr transverse relaxation time t2 spectrum the fractal dimensions of all the samples are calculated and the accuracy of the fractal model is verified by the high regression coefficients almost all the pore systems can be described by fractal theory and the fractal dimensions are strongly correlated with the t2 values separating the immovable fluid and the free fluid microfractures may bias t2 toward larger values making it hard to derive fractal dimensions from nmr measurements the coexistence of small pores pore radius 50 m results in a heterogeneous pore distribution and a high fractal dimension reservoir quality increases with the complexity degree of the microscopic pore structure conversely samples that are dominated by small pore systems tend to have a lower fractal dimension and a less complex pore structure

use of floodplain sediment cores to investigate recent historical changes in overbank sedimentation rates and sediment sources in the catchment of the river ouse yorkshire uk abstract floodplain sediment cores collected from seven sites in the catchment of the river ouse in yorkshire uk have been used to provide information on recent historical changes in both rates of overbank sedimentation and sediment sources the environmental radionuclides 137 cs and unsupported 210 pb have been used to establish chronologies for each core and to estimate average sediment accumulation rates for the last ca 30 and 100 years respectively average sedimentation rates for the individual cores ranged from 0 11 to 1 04 g cm 2 yr 1 in all but one case the estimates of average sedimentation rate during the last ca 30 years for the individual cores are broadly similar to those for the last ca 100 years suggesting that overbank sedimentation rates have been essentially uniform over the longer time period composite fingerprints based on a combination of geochemical and mineral magnetic properties and a numerical mixing model have been used to investigate downcore changes in sediment source in the case of source type most of the cores reflect a primarily topsoil source although there have been periods with increased contributions from subsoil channel bank sources within the ouse basin in general the period commencing in the late 19th and early 20th century and extending through to the 1960s was characterised by increased contributions from topsoil sources however contributions from subsoil channel bank sources have increased over the last few decades the source tracing results relating to sediment contributions from the three main geological topographic zones are in broad agreement with the proportion of the area of the catchment underlain by each rock type temporal variations in the contributions from the three geological topographic zones vary from site to site but for the lower reaches of the river ouse contributions from areas underlain by permian and triassic rocks which mainly outcrop in the vale of york have increased since the turn of the century the changes in sediment source identified are probably a reflection of changes in land use and management and possibly changes in climate these results enable estimates of contemporary suspended sediment fluxes and sources to be placed into a historical context and provide a means of considering the likely impact of potential future changes in land use and climate in the study basin

eclogitic inclusions in diamonds evidence of complex mantle processes over time the first ion probe trace element analyses of clinopyroxene garnet pairs both included within diamonds and from the eclogite host xenoliths are reported these diamondiferous eclogites are from the udachnaya and mir kimberlite pipes yakutia russia the major and trace element analyses of these diamond inclusion and host rock pairs are compared in order to determine the relative ages of the diamonds confirm or deny genetic relationships between the diamonds and the eclogites evaluate models of eclogite petrogenesis and model igneous processes in the mantle before during and after diamond formation the most striking aspect of the chemical compositions of the diamond inclusions is the diversity of relationships with their eclogite hosts no single distinct pattern of variation from diamond inclusion minerals to host minerals is found for all four samples garnet and clinopyroxene inclusions in the diamonds from two samples u 65 3 and u 66 3 have lower mg s lower mg and higher fe contents and lower lree than those in the host eclogite we interpret such variations as due to metasomatism of the host eclogite after diamond formation one sample u 41 3 shows enrichment in diamond inclusion mree enrichment relative to the eclogite host and may indicate a metasomatic event prior to or during diamond formation bulanova 2 found striking differences between inclusions taken from within different portions of the very same diamond clinopyroxene inclusions taken from the central early portions of yakutian diamonds were lower in mg and mg contents by up to 25 than those later inclusions at the rims of diamonds these trends are parallel to those between diamond inclusions and host eclogites determined for four of the five samples from the present study and may merely represent changing magmatic and or p t conditions in the mantle garnet trace element compositions are similar in relative proportions but variable in abundances between diamond inclusions and host eclogites this is probably due to the rapid diffusion of trace elements in garnet under mantle temperatures and consequent alteration of the garnet and not due to juvenile diamonds locking in source heterogeneities c f 3 trace element compositions of clinopyroxenes included in diamonds are generally similar to those in the host eclogite however one host clinopyroxene does show enrichment in the lree compared to that in the inclusion and may be attributed to mantle metasomatism not related to kimberlite transport in another eclogite m 46 the host clinopyroxene is depleted in the lree and fe and enriched in the hree and mg relative to the inclusion and is consistent with partial melting of the eclogite subsequent to diamond formation smnd ratios in clinopyroxenes appear to be little affected by these processes for most samples allowing sm nd isotopic studies to yield important information about ancient protoliths eclogitic mineral inclusions in yakutian diamonds appear consanguineous with the diamonds a contention supported by the observations of bulanova 2 therefore re os whole rock and smnd clinopyroxene age determinations of the udachnaya eclogites also yield the time of diamond formation approximately 2 9 ga 32 33

experimental study on diamond dissolution in kimberlitic and lamproitic melts at 1300 1420 c and 1 gpa with controlled oxygen partial pressure to evaluate the dissolution processes of diamond crystals in kimberlitic and lamproitic magmas a series of diamond dissolution experiments were carried out in the graphite stability field at 1300 1420 c and 1 gpa under the wi mw and hm buffers dissolution agents used include an aphanitic kimberlite from wesselton mine south africa and a lamproite from mount north west kimberley australia with increasing run duration diamond morphology changed from a sharp octahedron through combinations of octahedron and tetrahexahedroidal forms to spherical tetrahexahedroid having rounded faces negatively oriented trigons were formed on the octahedral 111 face as the degree of diamond dissolution increased the trigons changed from smaller shallow types to larger deep types the dissolution rate in the kimberlitic solvent at 1300 c was 0 12 mm h under the hm buffer 0 0034 mm h under the mw buffer and 0 0017 mm h under the wi buffer whereas that at 1420 c was 0 014 mm h under the wi buffer in the lamproitic solvent the dissolution rate was 0 0024 mm h at 1420 c under the wi buffer the data indicate that diamond dissolves in silicate melts as carbonate ions through an oxidizing reaction the degree of dissolution strongly depends on temperature oxidation state and the compositional dependence of co 2 solubility in the melts

crystal accumulation and magma mixing in the petrogenesis of tholeiitic andesites from fukujin seamount northern mariana island arc

the origins of yakutian eclogite xenoliths owing to the association with diamonds eclogite xenoliths have samples were derived from typical depleted mantle however two groups of three samples each indicate both enriched mantle and received disproportionate attention given their low abundance in kimberlites several hypotheses have been advanced for the origin of possible ultra depleted mantle present beneath yakutia during the late archean and early proterozoic the vast majority of eclogites eclogite xenoliths from the subduction and high pressure melting of oceanic crust to cumulates and liquids derived from the upper studied from the obnazhennaya pipe also exhibit characteristics of mantle we have amassed a comprehensive data set including group a eclogites and are probably derived directly from the mantle majorand trace element mineral chemistry carbon isotopes in however the eclogites from the mir kimberlite are more typical of diamonds and rb sr sm nd re os and oxygen isotopes in other eclogites world wide and show convincing evidence of a recycled ultrapure mineral and whole rock splits from eclogites of the udoceanic crustal affinity we concur with the late ted ringwood achnaya kimberlite pipe yakutia russia furthermore eclogites that eclogites can be formed in a variety of ways both within the from two other yakutian kimberlite pipes mir and obnazhennaya mantle and from oceanic crustal residues have been studied in detail and offer contrasting images of eclogite protoliths relative to eclogites from southern africa and other yakutian localities udachnaya eclogites are notable in the absence of chemical zoning in mineral grains as well as the degree of light

extreme crustal oxygen isotope signatures preserved in coesite in diamond the anomalously high and low oxygen isotope values observed in eclogite xenoliths from the upper mantle beneath cratons have been interpreted as indicating that the parent rock of the eclogites experienced alteration on the ancient sea floor1 recognition of this genetic lineage has provided the foundation for a model of the evolution of the continents whereby imbricated slabs of oceanic lithosphere underpin and promote stabilization of early cratons2 early crustal growth is thought to have been enhanced by the addition of slab derived magmas leaving an eclogite residuum in the upper mantle beneath the cratons3 but the oxygen isotope anomalies observed in eclogite xenoliths are small relative to those in altered ocean floor basalt and intermediate stage subduction zone eclogites and this has hindered acceptance of the hypothesis that the eclogite xenoliths represent subducted and metamorphosed ocean floor basalts we present here the oxygen isotope composition of eclogitic mineral inclusions analysed in situ in diamonds using an ion microprobe secondary ion mass spectrometer the oxygen isotope values of coesite a polymorph of sio2 inclusions are substantially higher than previously reported for xenoliths from the subcratonic mantle but are typical of subduction zone meta basalts and accordingly provide strong support for the link between altered ocean floor basalts and mantle eclogite xenoliths

early proterozoic oceanic crust and the evolution of subcontinental mantle eclogites and related rocks from southern africa seven eclogitic nodules from kimberlites in southern africa have been studied in detail for whole rock major and trace element geochemistry petrography and mineral chemistry by electron microprobe high purity mineral separates from six of these samples have been analyzed for trace elements and for the isotopic composition of sr nd and oxygen three eclogite groups are recognized group a eclogites have very high mg fe low na in pyroxene moderate 18o 4 7 to 5 3 and low 87sr 86sr and 143 144nd olivine and enstatite may also be present as accessory phases in this group group b eclogites have moderate to high mg fe ratios high na in pyroxene low 18o 3 0 to 3 4 high 87sr 86sr and 143nd 144nd ratios and extremely lree depleted hree enriched garnets with no eu anomalies group c eclogites have low mg fe ratios high na in pyroxene and variable sr nd and o isotope compositions accessory feldspar is present in one sample that may be of crustal origin mineral separates of garnet and pyroxene have positive eu anomalies the group a eclogites are too refractory to represent magma compositions and must have formed as cumulate dike rocks in the upper mantle that contain a minor trapped liquid component this is supported by the presence of accessory olivine and enstatite and by their ksm and knd which are similar to empirical pyroxene garnet partition coefficients the group b eclogites are extremely depleted in incompatible elements and have ndvalues 10x to 20x morb the high 87sr 86sr of these eclogites is not consistent with their strongly depleted lree and high nd and cannot be primary it must have been imposed on the protolith the low 18o of these eclogites cannot form by mantle fractionation processes and must also be inherited from the protolith both the sr and oxygen isotope data are consistent with high temperature hydrothermal alteration of a basaltic protolith followed by partial melting to form the refractory compositions observed now the hydrothermal fluid may have been sea water but secondary enrichment of the protolith in rb is required to generate the observed high sr ratios the high na content of the pyroxenes supports a spilitic alteration event the major and trace element characteristics of the group c eclogites are consistent with recrystallization of a cumulate gabbro protolith one group c rock is probably a garnet granulite derived from the lower crust the other may represent the plutonic portion of oceanic crust a reconstructed whole rock isochron for the three bellsbank eclogites yields an age of 2 1 0 1 b y this implies that plate tectonic processes involving the generation and subduction of oceanic crust have been active since the early proterozoic the early proterozoic ocean crust consisted of two components a plutonic section of gabbro cumulates group c eclogites and a volcanic section of basalt group b eclogites the volcanic component has undergone substantial hydro thermal alteration and subsequent partial melting to form a refractory residue the plutonic component is less modified

minor and trace elements as indicators of solute provenance and flow routing in a subglacial hydrological system mitchell a c brown g h fuge r 2006 minor and trace elements as indicators of solute provenance and flow routing in a subglacial hydrological system hydrological processes 20 4 877 897 sponsorship university of wales aberystwyth studentship am university of wales aberystwyth research grants 56 95 and 36 96 ghb and rf and nerc grant no gr3 11216

recycling of crustal materials through study of ultrahigh pressure minerals in collisional orogens ophiolites and mantle xenoliths a review abstract newly recognized occurrences of ultrahigh pressure uh p minerals including diamonds in ultrahigh temperature uh t felsic granulites of orogenic belts in chromitites associated with ophiolitic complexes and in mantle xenoliths suggest the recycling of crustal materials through deep subduction mantle upwelling and return to the earth s surface this circulation process is supported by crust derived mineral inclusions in deep seated zircons chromites and diamonds from collision type orogens from eclogitic xenoliths in kimberlites and from chromitities of several alpine himalayan and polar ural ophiolites some of these minerals contain low atomic number elements typified by crustal isotopic signatures ophiolite type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone in addition to ringwoodite and inferred stishovite a number of nanometric minerals have been identified as inclusions employing state of the art analytical tools reconstitution of now exsolved precursor uh p phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier uh p conditions for example tibetan chromites containing exsolution lamellae of coesite diopside suggest that the original chromitites formed at p 9 10 gpa at depths of 250 300 km the precursor phase most likely had a ca ferrite or a ca titanite structure both are polymorphs of chromite and at 2000 c would have formed at minimum pressures of p 12 5 or 20 gpa respectively some podiform chromitites and host peridotites contain rare minerals of undoubted crustal origin including zircon feldspars garnet kyanite andalusite quartz and rutile the zircons possess much older u pb ages than the time of ophiolite formation these uh p mineral bearing chromitite hosts evidently had a deep seated evolution prior to extensional mantle upwelling and partial melting at shallow depths to form the overlying ophiolite complexes these new findings together with stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere recycling of surface organic carbon into the lower mantle and ascent to the earth s surface through mantle upwelling intensified study of uh p granulite facies lower crustal basement and ophiolitic chromitites should allow a better understanding of the geodynamics of subduction and crustal cycling

fallout of pyroclastic debris from submarine volcanic eruptions volcanic fallout deposits on land being widespread and accessible for study have received much attention and have revealed a great deal about subaerial eruption mechanisms in contrast virtually nothing is known about equivalent deposits produced by submarine volcanoes despite the probable abundance of such material in today s oceans and in accreted volcanic arc terrains many submarine deposits may form by the fallout of debris to the sea floor downcurrent from the umbrella region of submarine eruption columns experiments on water saturated pumice and pieces of rock lithics show that particles settling to the sea floor at terminal velocities of 10 to 50 centimeters per second will display conspicuous bimodality of particle diameters pieces of pumice may be five to ten times as large as codeposited lithic fragments similar material erupted into the air and deposited on land displays less well developed bimodality pumice diameters are generally two to three times as large as associated lithics submarine fallout deposits are therefore distinctive and may be used to indicate a subaqueous origin for some of the great thicknesses of nonfossiliferous volcanic debris contained in ancient volcanic terrains worldwide whose environment of deposition has been uncertain

dominants and accumulation of rare earth elements in sediments derived from riparian and depressional marshes the rare earth elements rees in the sediments of the xianghai wetlands were measured by inductively coupled plasma spectrometry the rees accumulation rates in two sedimentation cores derived from the riparian and depressional marshes were determined by 210pb method the results showed that rees concentrations in the xianghai wetland sediments rees 116 mg kg 1 were lower than the corresponding values in chinese soils 181 mg kg 1 and river sediments rees 158 191 mg kg 1 under alkaline conditions with ph 8 2 10 3 the light rees were more enriched than the heavy rees cerium is the predominant element and accounts for 30 33 of the total rees rees in the depressional marsh sediments were relatively high rees 127 vs 104 mg kg 1 especially light rees contents a significantly positive correlation was found between the neighboring elements except pr and dy the different types of vertical distribution of rees between the riparian and the depressional marsh can partly result from long term differing hydrological regimes generally depressional marsh had accumulated much more rees than riparian marsh the mean accumulation rates of rees 102 98 vs 48 89 g cm 2 year 1

the carbon isotopic composition and nitrogen content of lithospheric and asthenospheric diamonds from the jagersfontein and koffiefontein kimberlite south africa asthenospheric diamonds from the jagersfontein kimberlite south africa have a 13c range from 8 9 to 24 4 vs pdb deep diamonds from the nearby koffiefontein mine have 13c values between 2 9 and 6 1 at these two locations asthenospheric diamonds are more frequently nitrogen type ii than type i if they are type i the nitrogen content is low and its state of aggregation is high diamonds from the jagersfontein kimberlite have a bimodal 13c distribution on the basis of the carbon isotopic composition of the hosts and their mineral inclusion composition one can suggest that as many as six distinct diamond source regions were sampled by the kimberlite in the mantle beneath jagersfontein the relative abundance of low 13c diamonds may be higher in the asthenosphere than in the lithosphere in the koffiefontein sample suite asthenospheric and lithospheric diamonds are indistinguishable in 13c the differences in the nature of the relationships between isotope and inclusion chemistry demonstrated by deep diamonds from two diatremes which are very closely associated in space and time indicate a high degree of complexity in mantle carbon geochemistry even within the asthenosphere

oxygen isotopes in coexisting garnets clinopyroxenes and phlogopites of roberts victor eclogites implications for petrogenesis and mantle metasomatism abstract 18 o values of coexisting garnet clinopyroxene and phlogopite for twelve compositionally and texturally diverse roberts victor eclogite xenoliths range from 3 8 to 7 1 4 0 to 7 4 and 5 9 to 7 4 respectively differences between the 18 o values of coexisting garnets and clinopyroxenes are normally zero however there is some variation in the 18 o values of different fractions of the same mineral in four samples which suggests the presence of isotopic zonation and inhomogeneity possibly resulting from the introduction of a secondary fluid which metasomatized the eclogites and resulted in the formation of phlogopite amphibole and celsian the 18 o value of the metasomatic fluid is generally buffered by the isotopic composition of the primary garnet and clinopyroxene as indicated by a correlation between the isotopic composition of phlogopite and the primary pyroxene and garnet the large range in 18 o values of the eclogites and the similarity in the isotopic composition of coexisting pyroxene and garnet support the interpretation that the roberts victor eclogites represent metamorphosed altered basalts the eclogites were subjected to infiltration metasomatism in the mantle prior to their incorporation in the kimberlite and the source of this fluid was probably unrelated to the eclogite

depths and water content of magma chambers in the aleutian and mariana island arcs on pseudoternary diagrams locations of experimentally produced melt compositions that coexist with plagioclase and anhydrous mafic minerals vary as functions of pressure a geobarometer and water content a geohygrometer projection of rock compositions onto diagrams allows constraints to be placed on magma chamber depths and meltwater content application of the experimentally calibrated geobarometer and gehygrometer to aleutian and mariana rock suites suggests aleutian magma chambers to be at depths of 7 to 17 km pressures from 2 to 5 kbar and meltwater content of andesites near 2 wt mariana magma chambers are at shallow depths pressure less than 2 kbar and their water content is less than 2 wt probably near 1 wt magma chamber depths can be interpreted to be controlled by density differences between crystallizing magmas and crust which in turn may be controlled by crustal thermal structure differences in water content are correlated with amounts of sediment incorporated into basaltic magmas formed near the subducting oceanic slab

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

effects of partial melting on the uranium decay series distinction between possible partial melting processes using stable incompatible trace elements depends largely on the mass fraction of liquid produced at low degrees of melting less than 5 both incompatible element concentrations and interelement fractionations are greater for batch fractional and accumulated fractional melting than for dynamic or continuous melting at higher degrees of melting uncertainty in initial source composition and small fractionations between incompatible elements make it unlikely that the most realistic melting models batch and dynamic could be discriminated however it is possible for these melting processes to be distinguished by the magnitude of radioactive disequilibria that is produced within the 238u decay series even for durations of partial melting much longer than the half lives of 230th and 226ra both230th 238u and 226ra 230th disequilibria can occur because of differences in the bulk solid liquid partition coefficients for these elements the magnitude of these disequilibria depends on melting process the 230th 232th of a dynamic melt can differ significantly from that of a batch melt and will not necessarily indicate the original 238u 232th of the source if morb is formed by a dynamic melting process then the th u of the upper mantle near ridge axes may be higher than that calculated from the 230th 232th of the basalts

nature of diamonds in yakutian eclogites views from eclogite tomography and mineral inclusions in diamonds abstract we have performed dissections of two diamondiferous eclogites ux 1 and u33 1 from the udachnaya kimberlite yakutia in order to understand the nature of diamond formation and the relationship between the diamonds their mineral inclusions and host eclogite minerals diamonds were carefully recovered from each xenolith based upon high resolution x ray tomography images and three dimensional models the nature and physical properties of minerals in direct contact with diamonds were investigated at the time of diamond extraction polished sections of the eclogites were made containing the mould areas of the diamonds to further investigate the chemical compositions of the host minerals and the phases that were in contact with diamonds major and minor element compositions of silicate and sulfide mineral inclusions in diamonds show variations among each other and from those in the host eclogites oxygen isotope compositions of one garnet and five clinopyroxene inclusions in diamonds from another udachnaya eclogite u51 span the entire range recorded for eclogite xenoliths from udachnaya in addition the reported compositions of almost all clinopyroxene inclusions in u51 diamonds exhibit positive eu anomaly this feature together with the oxygen isotopic characteristics is consistent with the well established hypothesis of subduction origin for udachnaya eclogite xenoliths it is intuitive to expect that all eclogite xenoliths in a particular kimberlite should have common heritage at least with respect to their included diamonds however the variation in the composition of multiple inclusions within diamonds and among diamonds from the same eclogite indicates the involvement of complex processes in diamond genesis at least in the eclogite xenoliths from yakutia that we have studied

the application of c isotope measurements to the identification of the sources of c in diamonds a review abstract in the past decade the isotopic compositions of c in 600 inclusion bearing diamonds have been determined such analyses have revealed the following isotopic characteristics 1 peridotitic diamonds which typically contain garnet chromite olivine and or orthopyroxene inclusions with refractory compositions high mg cr have 13 c values predominantly between 10 and 1 with a sharp peak in the distribution near 5 2 eclogitic diamonds which commonly contain inclusions of omphacitic clinopyroxene cr poor pyrope and or eclogitic accessory minerals such as rutile kyanite coesite or sanidine have 13 c values between 34 and 3 with a smaller peak near 5 3 the isotopic compositions obtained for suites of diamonds from individual occurrences are in general unique and do not resemble the range and distribution obtained by amalgamating the diamond isotope data from a number of localities 4 isotopic zoning patterns and heterogeneities are found in some diamonds cores of coated diamonds tend to be depleted in 13 c relative to the rims and within single octahedral diamonds 13 c variations of nearly 6 have been reported because expected c isotope fractionations at mantle temperatures are small attempts to model the full range of diamond isotope values through fractionating a homogeneous mantle c source have been unsuccessful nevertheless fractionation is probably responsible for some of the observed variation in 13 c values two other models have also been proposed to account for the diamond characteristics outlined above the primordial model suggests that the range and distribution of c isotope compositions are inherited from primordial c in the mantle which has an inhomogeneous isotopic composition such as that found in meteorites the subduction model suggests that subducted crustal c is the source of c in diamonds as organic and inorganic c compounds in the crust exhibit a range of 13 c values similar to that observed in diamonds this paper reviews the c isotope characteristics of diamonds and compares the models which have been proposed to explain the origins of these characteristics

are arc type rocks the products of magma crystallisation observations from a simple oceanic arc volcano raoul island kermadec arc sw pacific raoul island is the emergent summit of a large intra oceanic strato volcano in what is globally one of the simplest of subduction settings in this simple setting erupted magmas span the compositional range from basalt to dacite but none have the high mg numbers and high ni and cr expected of primitive mantle derived melts the lavas range from aphyric to highly porphyritic and are characterised by phenocryst assemblages dominated by plagioclase accompanied by clinopyroxene olivine orthopyroxene and spinel phenocryst core compositions and zoning profiles are remarkably uniform irrespective of total phenocryst content or geochemical composition indicating a decoupling of melt and crystal components in the system a consistent model for the raoul magmatic system is that primitive high mg magma generated in a melt column within the underlying mantle wedge is transformed into a series of derivative low mg magmas by fractional crystallisation within the lower crust low mg magma accumulates variable quantities of crystal cargo as it ascends toward the surface through a crystal mush zone these processes are essentially those that characterise continental subduction related magmatic systems but differ only in the absence of an evolved crustal component

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

cross arc geochemical variations in the kurile arc as a function of slab depth lavas from transects across the kurile islands arc showed geochemical variations related to changes in the compositions of fluids derived from the subducting slab enrichment factors for boron cesium arsenic and antimony all elements with strong affinities for water decreased across the arc this decrease is presumably related to losses of water rich fluids during the dehydration of the subducting plate enrichments of potassium barium beryllium 10 and the light rare earth elements remained constant these species may move in silica rich fluids liberated from the slab at greater depths

archaean re os age for siberian eclogites and constraints on archaean tectonics considerable uncertainty surrounds the nature and evolution of the earth s mantle in archaean times 2 5 gyr ago mantle derived eclogite xenoliths erupted by kimberlites provide important clues in this regard because their basaltic composition suggests that they may be remnants of an early 4 gyr magma ocean1 2 subducted archaean oceanic crust3 5 or crystallized high pressure mantle melts6 9 better constraints on the age and origin of mantle eclogites are thus important for our understanding of early earth processes here we present rhenium osmium isotope data for diamond bearing eclogites from the udachnaya kimberlite pipe in siberia which indicate formation in the archaean 2 9 0 4 gyr this age is too young for the eclogites to be remnants of early earth differentiation but overlaps the age range for crust generation and craton stabilization on both the aldan and anabar shields of the siberian craton 2 85 3 2 gyr 10 11 these data together with 3 1 gyr re os model ages for diamond bearing udachnaya peridotites12 show that the siberian craton lithosphere was at least 150 km thick the minimum required for diamond stability by the mid archaean

esmeralda bank geochemistry of an active submarine volcano in the mariana island arc esmeralda bank is the southernmost active volcano in the izu volcano mariana arc this submarine volcano is one of the most active vents in the western pacific it has a total volume of about 27 km3 rising to within 30 m of sea level two dredge hauls from esmeralda recovered fresh nearly aphyric vesicular basalts and basaltic andesites and minor basaltic vitrophyre these samples reflect uniform yet unusual major and trace element chemistries mean abundances of tio2 1 3 and feo 12 6 are higher and cao 9 2 and al2o3 15 1 are lower than rocks of similar silica content from other active mariana arc volcanoes mean incompatible element ratios k rb 488 and k ba 29 of esmeralda rocks are indistinguishable from those of other mariana arc volcanoes on a ti zr plot esmeralda samples plot in the field of oceanic basalts while other mariana arc volcanic rocks plot in the field for island arcs

recent history of sediment deposition in marl and sand based marshes of belize central america there are two contrasting types of wetlands in belize marl and sand based marshes we measured accumulation rates of sediment in six cores from marl and sand based marshes of northern belize and compared biogeochemical characteristics to assess recent wetland history f1850 to present sediment depth increments were analysed for bulk density loi nutrients c n p s ca mg k and na and snail shell density and species diversity cores were dated using 210 pb and a constant rate of supply model unsupported 210 pb inventories of the cores ranged from 6 16 to 8 92 pci cm 2 marl based marshes showed the maximum peak of 210 pb activity from 4 to 10 cm below the sediment surface 210 pb peaks corresponded with the bottom of a marl layer containing chlorophyll a and we suggest that this relationship reflects the high growth and decomposition rates of cyanobacterial mat inorganic carbon ca mg k na s and pb contents and accumulation rates were much greater in the marl based marshes than in the sand based marshes average dry mass accumulation rates in the six marshes ranged from 113 to 572 g m 2 year 1 over the past 100 years average linear sedimentation rates during the last 100 years in the two types were not significantly different 0 93 and 1 08 mm year 1 respectively increased sediment accumulation by human activities such as soil washout from adjacent roads was recorded in a sand based marsh near roads sediment cores in the marl based marshes display changes of marsh vegetation apparently caused by water level changes the vegetation change occurred at the end of the 1800s and the beginning of 1900s and is represented by a band of dark peat in otherwise marl dominated sediments overall the sediment cores show that conditions were relatively undisturbed by human activities in the recent past d 2002 elsevier science b v all rights reserved

shoshonitic volcanism in the northern mariana arc 1 mineralogic and major and trace element characteristics petrographic and geochemical characteristics of samples dredged from 23 submarine volcanic edifices in the northern mariana and southern volcano arcs define two distinct rock series the central and northern mariana arc to 23 n and the northern volcano arc north of iwo jima are characterized by plagioclase clinopyroxene orthopyroxene titantomagnetite bearing subalkaline rocks including both low k and medium k series the northern mariana arc and southern volcano arc from 23 n to iwo jima are erupting rocks of a shoshonitic series with phenocrysts of plagioclase clinopyroxene olivine and biotite these rocks are less saturated than those of the subalkaline provinces and are substantially enriched in ba 400 900 ppm sr 600 1000 ppm k2o 1 4 5 and k2o na2o 0 4 1 2 relative to the subalkaline lavas ba y and ba zr increase by a factor of 3 to 4 in the shoshonitic rocks but k rb ba sr and k ba are relatively constant throughout the arc there is no relationship between degree of enrichment and volcano volume or degree of fractionation seamounts and islands within each province have the same range of compositions much of the intra edifice variation in lava composition can be modeled by 10 70 crystallization of plagioclase and clinopyroxene with smaller amounts of olivine orthopyroxene and titanomagnetite or by accumulation of 10 40 phenocrysts dominantly plagioclase the differences between parental lavas in the alkalic and subalkalic provinces require melting of two distinct mantle sources the occurrence of this enriched mantle in the northern marianas may be a consequence of the propagation of the mariana trough spreading center into the volcano arc

multiple growth events processes and fluid sources involved in diamond genesis a micro analytical study of sulphide bearing diamonds from finsch mine rsa abstract twenty one sulphide inclusion bearing diamonds from the finsch mine south africa were analysed for nitrogen abundances and carbon isotope compositions by microbeam methods on the basis of sulphide ni contents one diamond is of peridotitic affinity the rest belongs to the eclogitic suite ftir analyses show nitrogen abundances and aggregation states from 21 to 1093 at ppm and 0 to 83 iab statistically indistinguishable from previous results for finsch eclogitic silicate inclusion bearing diamonds appleyard et al 2004 but significantly higher than observed before for diamonds of the peridotitic suite deines et al 1989 detailed analyses revealed marked variations in nitrogen characteristics within individual diamonds demonstrating a complex mantle residence consistent with multiple episodes of diamond growth over time linked to the growth stratigraphy of the diamond sims micro analyses show variations in 13 c from 8 90 to 2 80 with a mean value of 5 54 1 80 1 standard deviation closely overlapping the typical worldwide value the c isotopic variability within individual diamonds ranges up to 3 26 sims based nitrogen abundances are 3 2221 at ppm with heterogeneous distribution within individual diamond from the 13 c n co variations within individual diamonds three major processes of diamond growth for sulphide inclusion bearing samples at finsch are proposed 1 some diamonds were precipitated during a single event of open system isotopic fractionation in fluids that varied from oxidised carbonatitic to reduced ch 4 rich in this growth scenario nitrogen is either compatible or incompatible during diamond growth 2 other diamonds show abrupt 13 c n changes indicative of diamond growth involving mixing of several fluid sources 3 some diamonds grow from a combination of the two previous processes the models are consistent with metasomatic diamond growth involving single and multiple fluid sources multiple growth stages for individual diamonds may have taken place over extended time periods and which have important implications for diamond dating studies

the eruption of mount pagan volcano mariana islands 15 may 1981 a major explosive eruption occurred 15 may 1981 at mount pagan volcano the larger of two historic eruptive centers on pagan island mariana islands the eruption was preceded by increased numbers of locally felt earthquakes beginning in late march or early april and by new ground cracks new sublimates and increased gas emissions a swarm of felt earthquakes began at 0745h local time uct 10 hours 15 may and at 0915 h closely following a loud sonic boom a strong plinian column issued from the volcano the high altitude ash cloud at least 13 5 km travelled south southeast but ash and scoria deposits were thickest 2 m in the nw sector of the island because of the prevailing low altitude southeasterly winds the early activity of 15 may probably involved magmatic eruption along a fissure system oriented about n10 e however the eruption became hydromagmatic possibly within minutes and was largely restricted to three long lived vents the northernmost of these built a substantial new scoria ash cinder cone flows and air fall deposits consisting almost entirely of juvenile material exceeded 105 106 m3 in volume 75 106 m3 of magma on land and at least 70 100 606 m3 at sea an unknown volume was carried away by stratospheric winds lithic blocks and juvenile bombs as large as 1 m in diameter were thrown more than 2 km from the summit and evidence for base surge was observed in restricted corridors as low as 200 m elevation on the north and south slopes of the volcano neither of these events resulted in serious injuries to the 54 residents of the island nor did the eruption produce serious chemical hazards in their water supply weak eruptions occurred during the ensuing month and some of these were monitored by ground observations seismic monitoring and deformation studies precursory seismicity and possibly deformation occurred with some of the observed eruptions more vigorous eruptions were reported by visiting residents in late 1981 and early 1982 but these were of lesser magnitude than the 15 may 1981 event the 15 may lava is predominantly aa and ranges from 3 to 30 m in thickness in composition it is a high alumina basalt with small 1 mm long phenocrysts of plagioclase and clinopyroxene 7 that is more or less typical of basalt of the northern marianas volcanoes it contains slightly more sio2 52 k2o tio2 and less al2o3 and cao than does the basalt of the last eruptive event of mount pagan volcano in 1925 gas analyses indicate that a large portion of air was introduced into the vent system through the porous volcanic edifice and that the carbon gases were not in equilibrium with the magma or each other

a late holocene record of environmental changes from coastal wetlands abel tasman national park new zealand abstract article size organic content loss on ignition loi geochemistry radiocarbon and 137cs analyses were carried out on paired cores taken from wainui totaranui and awaroa inlets abel tasman national park a 1700 year record of long and short term environmental changes was produced representing a sedimentary and geochemical sequence from tidal flat to mature salt marsh the sequence is punctuated by a series of short term environmental changes namely tsunami establishment of salt marsh and european settlement long term environmental changes include fluctuating accretion rates and relative sea level rise tsunami signatures include i a peak in fines ii contemporaneous or delayed peak in organic content and or loi iii contemporaneous peaks in fe and or s iv dilution of anthropogenic contaminants and v visible change in the sediments ruptures of the wellington and west wairarapa faults are considered to be the tsunamigenic sources pre european sediment accretion rates in abel tasman national park range from 0 5 to 1 7 mm a with post european settlement rates increasing to 1 6 2 7 mm a in the past 30 years rates have increased to 2 3 3 3 mm a the component of relative sea level rise is estimated to be about 1 3 2 2 mm a which compares favourably with the nearest tidal records from wellington

petrology and geochemistry of the island of sarigan in the mariana arc calc alkaline volcanism in an oceanic setting isotopic studies of rocks from oceanic island arcs such as the marianas indicate that little if any recycling of continental material e g oceanic sediments occurs in these arcs because oceanic arcs are on the average more mafic than the dominantly andesitic continental arcs an important question is whether the andesites of continental arcs are produced by a fundamentally different more complex mechanism than the lavas of oceanic arcs an excellent opportunity for study of this question is provided by the island of sarigan in the mariana active arc on which calc alkaline andesites including hornblende bearing types are exposed along with more mafic lavas

diamondiferous eclogites from yakutia siberia evidence for a diversity of protoliths major element and ree compositions of 14 diamondiferous eclogites from the udachnaya kimberlite in yakutia siberia have been determined by electron microprobe and secondary ion mass spectrometer sims based on previous clinopyroxene classification schemes e g taylor and neal 1989 all of these eclogite xenoliths belong to group b c although some of the garnet compositions and mineral ree abundances are inconsistent with the indicated groups this demonstrates the inadequacy of the classification scheme based on african eclogites for application to siberian samples because of the coarse grain size of the udachnaya nodules meaningful modal abundances could not be obtained however reconstructed ree compositions using various garnet clinopyroxene ratios demonstrate relative insensitivity to changes in mode for common eclogitic assemblages many of these reconstructed ree compositions show lree depletions some depletions are consistent with an origin either directly or through partial melting as normal or type i ocean floor basalt others however require material of eclogitic or pyroxenitic affinities to undergo partial melting this facilitates the depletion of lree while leaving the hree at nearly original levels many of the eclogites of south africa are consistent with a protolith of anomalous or type ii ocean floor basalt this fundamental difference between the two regions is the likely cause of the inconsistencies with the chemicallybased classification

archean emplacement of eclogitic components into the lithospheric mantle during formation of the kaapvaal craton re os data for selected whole rock eclogites and eclogitic sulfide inclusions in diamonds from seven kimberlites on the kaapvaal zimbabwe cratons yield ages around 3 ga the presence of such old eclogitic components in the subcontinental lithospheric mantle is more common than previously thought overlap of these ages with those of many cratonic peridotites demonstrates that incorporation of eclogitic materials accompanied or closely followed cratonic lithosphere stabilization many of these eclogitic components have fractionated c n o and s isotopic compositions which could have been created at low temperatures implying that some style of archean subduction involving emplacement of oceanic lithosphere was part of craton keel development

geochemical data as indicators of palaeosalinity in coastal organic rich sediments abstract a geochemical study of extractable major minor and trace elements peatlands from e spain elucidated variations in salinity related to the interpretation of relative sea level change samples were taken from different peatlands from the subsiding valencia castellon quaternary basin e spain these correspond to back barrier marshes with brackish and freshwater influence containing carex juncus typha and phragmites samples from a highland sphagnum moss freshwater peat bog were also included for comparison this paper categorizes palaeosalinity indicators in this coastal peat deposits as follows b br i na s ge u this compares with low rank coal which shows the following relationship b br i s na ge u the formulation of an index for characterising the organic detrital content using k or al concentration is also proposed this resulted in the following salinity index for peat b k br k i k na k s k ge k u k and for low rank coal b k br k i k s k na k ge k u k

stable and radiogenic isotope study of eclogite xenoliths from the orapa kimberlite botswana eclogite xenoliths from orapa can be accurately classified as group i or group ii on the basis of na2o in garnet and k2o in clinopyroxene group i xenoliths are commonly diamondiferous while group ii xenoliths are diamond free both xenolith varieties may contain graphite isotopic character is to some degree correlated with major and trace element chemistry group ii samples with ca poor garnet have clinopyroxenes with radiogenic 87sr86sr 0 705 0 709 and the least radiogenic 143nd144nd 0 5122 0 5125 group i eclogites with higher ca and fe in garnets have less radiogenic 87sr86sr 0 702 0 7066 and bulk earth or higher 143nd144nd ratios group i eclogites have more radiogenic 206pb204pb 18 6 19 than group ii xenoliths 16 5 18 6 in contrast group ii xenoliths have more variable and in some cases more radiogenic 206pb204pb 36 6 39 3 than group i xenoliths 38 3 38 4 the sr sm nd and pb concentrations of minerals in orapa group i eclogite xenoliths are much lower than in group ii samples all the group ii xenoliths are inferred to be enriched in light rare earth elements while group i xenoliths are probably characterised in many cases by light rare earth element depletion constituent garnet and clinopyroxene in both group i and ii eclogite xenoliths are essentially in isotopic equilibrium at the time of pipe emplacement mineral as well as calculated whole rock 143nd144nd compositions of most of the group i eclogites are too close to bulk earth and depleted mantle estimates in order to obtain useful model age information depleted mantle model ages derived from the much lower 143nd144nd compositions of the group ii eclogite xenoliths range from 661 to 1248 my with an average clinopyroxene model age of 908 my and an average whole rock model age of 1016 my on the basis of an observed covariation of o and sr isotopic compositions the entire orapa group i eclogite xenolith suite can be modelled as mixtures of oceanic basalt with or without a few percent of ocean floor sediment the group ii xenoliths might have crystallised from a melt which derives from a protolith with time averaged lree depletion their radiogenic sr isotope character could be due to interaction of the melt with metasomatised lithosphere or might be a superimposed metasomatic signature