inclusions of nanocrystalline hydrous aluminium silicate phase egg in superdeep diamonds from juina mato grosso state brazil abstract inclusions in alluvial diamond from juina mato grosso brazil have been investigated by tem methods electron diffraction hrtem aem haadf eels and raman spectroscopy the inclusion paragenesis of juina diamonds is dominated by ultrahigh pressure superdeep phases one of these diamonds sample 1 1 4 contains several micrometer sized approximately 200 m by 50 70 m inclusions which have been studied tem foils prepared applying focused ion beam fib technique revealed that these inclusions consist of a porous nanocrystalline groundmass which is composed of nanometre sized crystals of a hydrous aluminium silicate phase with al si approximately 1 1 and chemical composition of phase egg alsio 3 oh a minor volume fraction of nanocrystalline stishovite and pore space which was originally filled with a fluid or gas the nanocrystalline hydrous aluminium silicate phase is idiomorphic randomly oriented approximately 20 30 nm in size predominantly with tetragonal crystal structure a 0 0 743 nm c 0 0 706 nm the monoclinic structure of synthetic phase egg determined at ambient conditions m w schmidt l w finger r j ross r e dinnebier synthesis crystal structure and phase relations of alsio 3 oh a high pressure hydrous phase american mineralogist 83 1998 881 888 is only occasionally observed the fluid filling in the porosity has been released into the vacuum of the fib during tem specimen preparation quench products of the fluid containing minor concentrations of f p s cl k ca and ba were detected at the walls of the pores in addition phase egg is identified by raman spectroscopy within a second sample rs 43a from the same location the presence of phase egg in the inclusions in diamond may suggest that crustal material has been subducted to a depth of the lower transition zone although metastable growth of nanocrystalline high pressure phases or extension of their respective stability fields to lower pressure can not ruled out completely

geologic controls of hydrothermal discharge on the northern gorda ridge an investigation of a 10 x 10 km area near an axial high of the rift valley of the northern gorda ridge by using bathymetry side scan sonar and bottom photography where prior water column surveys indicated ongoing high temperature hydrothermal discharge reveals that the discharge is localized by specific tectonic and volcanic conditions the discharge occurs where faults having a predominant ridge parallel and an anomalous subsidiary ridge oblique tectonic trend intersect at the southern end of a linear ridge on the east wall and at another site at the base of the east wall of the rift valley hydrothermal alteration of basalt talus and stratiform hydrothermal precipitates produced by past activity occur where faults and fissures with the same two tectonic trends intersect near a fault having a third ridge transverse trend at a 1 x 1 km zone of sheet flows on the floor of the rift valley present and past hydrothermal discharge in this area is controlled by the intersection of an axis parallel tectonic trend common to all spreading centers having axis oblique trends related to the regional stress field near the shallowest and volcanically most productive part of the ridge segment

amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

fast and slow spreading ridges structure and hydrothermal activity ultramafic topographic highs and ch4 output different parts of the world ridge system have quite different morphologies which reflect different constructional processes it appears that hydrothermal circulation at all spreading centers is an important exchange process between the ocean and the newly formed oceanic crust this hydrothermal circulation may vary according to morphology and crustal composition and may also affect ridge constructional processes the tag 26 n and snake pit 23 n hydrothermal sites on the mid atlantic ridge mar display mn ch4 ratios in overlying seawater similar to those of nonsedimented east pacific rise sites i e about 0 2 mol l in contrast large methane anomalies with very low mn ch4 ratios of 0 005 mol l are associated with ultramafic topographic highs near 15 n close to the axis and on ultramafic walls of the rift valley the association of ultramafic bodies and ch4 anomalies in seawater indicates active serpentinization processes ch4 is produced during serpentinization according to the fisher tropsch reaction charlou et al 1991 many ultramafic rock assemblages have been sampled on the mar away from fracture zones in particular by the deep sea drilling project changes of mechanical properties and of density of uplifted deep material in the accreting plate boundary zone caused by serpentinization may play an important role in the construction of slow spreading ridges

remobilization in the cratonic lithosphere recorded in polycrystalline diamond polycrystalline diamonds framesites from the venetia kimberlite in south africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption chemical variations within the garnets correlate with carbon isotopes in the diamonds indicating contemporaneous formation trace element radiogenic and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt derived by remobilization of material that had been stored for a considerable time in the lithosphere these results indicate more recent formation of diamonds from older materials within the cratonic lithosphere

nanometric inclusions of carbonates in kokchetav diamonds from kazakhstan a new constraint for the depth of metamorphic diamond crystallization abstract previous studies have revealed that microdiamonds from the kokchetav ultra high pressure metamorphic terrane of kazakhstan contain nanometric scale inclusions of si fe ti and cr oxides because the structure of sio 2 inclusions was not confirmed to be coesite or stishovite due to their very small size such diamonds formerly served only as an indicator of a minimum pressure ca 4 gpa geothermobarometry applied to kokchetav diamond bearing rocks yielded a wide range of conditions t 700 c 1250 c and p 4 9 gpa our paper presents transmission electron microscopy studies with focused ion beam assistance that indicate that diamonds from marbles contain inclusions of aragonite caco 3 and magnesite mgco 3 and that aragonite and nitrogen bearing nanometric particles are associated with dislocations reflecting diamond growth at relatively high temperature conditions we determined the boundary of dolomite stability using the reaction camg co 3 2 dolomite caco 3 aragonite mgco 3 this allowed us to utilize available experimental data to evaluate the pressure at which diamond was crystallized taking into consideration uncertainties existing between experimental data produced in different laboratories we propose the pressure for kokchetav diamond crystallization to be 6 to 9 gpa this evaluation is based on the assumption that temperature was determined correctly as 980 c minimum and 1250 c maximum for diamond grade dolomitic marbles our data provide strong evidence that the metasedimentary rocks of the kokchetav massif containing diamonds were subducted to the depth of 190 280 km

the distribution of geothermal fields on the juan de fuca ridge near bottom water temperatures were mapped along 400 km of the strike of the juan de fuca ridge as part of a combined sea marc seabeam experiment to image the variability of morphology and structure along a spreading center segment the water temperature data collected by a continuously towed thermistor chain in addition to salinity data indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the cobb propagator and one field just to the north of the propagator on the endeavor ridge segment each thermal region is located above a morphological dome on the spreading center these domes are an average of 100 200 m shallower than the rest of the axis the structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0 06 sup 0 c up to 300 m above the bottom two simple models are used to estimate the heat flux associated with these features

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

relict hydrothermal zones in the tag hydrothermal field mid atlantic ridge 26 n 45 w two relict hydrothermal zones were delineated between water depths of 3400 and 3500 m at the lower part of the east wall of the rift valley of the mid atlantic ridge in the tag hydrothermal field using a deep towed side scan sonar tow and a camera temperature tow along the northern 3 km of the wall and a submersible transect named the north and mir relict zones they are located about 4 km and 2 km northeast respectively of the known active high temperature sulfide mound between water depths of 3625 and 3670 m on the rift valley floor near the base of the east wall the north zone extends about 2 km along the northern end of the lower east wall the zone includes two moundlike features up to 30 m high by 200 m in diameter imaged by side scan sonar within a 2 km long line of discontinuous hydrothermal deposits comprising inactive toppled and standing chimneys layered material and patchy dark stains on sediment photographed by the camera temperature tow several other moundlike features were imaged with the side scan sonar outside of the photographic coverage the mir relict hydrothermal zone 2 km south of the north zone named after the mir submersible used to investigate it consists of three subzones 1 a 200 m wide area of diverse types of hydrothermal materials exposed by normal faulting at its western margin 2 a 400 m wide by 700 m long central area of discrete groups of toppled and standing inactive sulfide chimneys up to 25 m high on a substrate of red metalliferous sediment and carbonate lutite spires sampled on the highest chimneys are composed of coarse grained recrystallized sulfides dominated by pyrite and chalcopyrite which contain the first primary free gold grains 2 3 m diameter found at a hydrothermal site on a mid ocean ridge and 3 a 150 m wide hummocky area of layered hydrothermal material with the appearance of low temperature precipitates and carbonate lutite with patchy dark stains at its eastern margin the active sulfide mound the north zone and the mir zone are each located on the fractured western margins of gentle dome shaped areas of pillow flows typically 500 m in diameter interpreted as summits of volcanic centers that may have supplied heat to drive adjacent hydrothermal activity the distribution and size of the active and inactive hydrothermal zones of the tag field the chronology and the characteristics of relict samples recovered indicate a history of at least 100 103 years of high temperature hydrothermal episodes with multiple overprinting stages of mineralization accompanied by alteration

mantle fluid evolution a tale of one diamond abstract microinclusions analyzed in a coated diamond from the diavik mine in canada comprise peridotitic minerals and fluids the fluids span a wide compositional range between a carbonatitic melt and brine the diamond is concentrically zoned the brine microinclusions reside in an inner growth zone and their endmember composition is k19na25ca5mg8fe3ba2si4cl32 mol the carbonatitic melt is found in an outer layer and its endmember composition is k11na21ca11mg26fe7ba2si10al3p2cl5 the transition in inclusion chemistry is accompanied by a change in the carbon isotopic composition of the diamond from 8 5 in the inner zone to 12 1 in the outer zone we suggest that this transition reflects mixing between already evolved brine and a freshly introduced carbonatitic melt of different isotopic composition the compositional range found in diamond on dvk 294 is the widest ever recorded in a single diamond it closes the gap between brine found in cloudy octahedral diamonds from south africa and carbonatitic melt analyzed in cubic diamonds from zaire and botswana thus all microinclusions analyzed to date fall along two arrays connecting the carbonatitic melt composition to either a hydrous silicic endmember or to a brine endmember this connection suggests that many diamonds are formed from fluids derived form a mantle source not significantly influenced by local heterogeneities

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

east pacific rise near 13 n geology of new hydrothermal fields abundant massive sulfide deposits are present at the crest of the east pacific rise near 13 north where the opening rate is about 12 centimeters per year large manganese and helium 3 anomalies in seawater samples evidence of intense present day activity of hydrothermal springs indicate that sulfides are still being produced along this segment of the rise massive sulfides also occur on adjacent off axis seamounts

mineral inclusions in diamonds from the sloan kimberlites colorado mineral inclusions have been recovered from 40 small 1 5 mm diamonds from the sloan 1 and 2 kimberlite pipes in northern colorado primary inclusions i e proto or syngenetic are olivine clinopy roxene sanidine rutile and possibly native fe and some phlogopite phases interpreted as epigenetic are acmite richterite most phlogopite perovskite mn ilmenite cr spinel magnetite calcite serpentine and possibly mg ilmenite acmite richterite and perovskite have not previously been reported in diamond the epigenetic minerals commonly occur as inclusion assemblages such as phlogopite richterite phlogopite perovskite ilmenite magnetite serpentine and phlogopite clinopyroxene spinel magnetite calcite the majority of the primary inclusions have an eclogitic suite affinity which is uncommon but similar to diamonds in the premier orapa and mbuji mayi kimberlites of southern and central africa and from a few sites in russia and western australia secondary inclusions reflect

spatial and temporal distribution of seismicity along the northern mid atlantic ridge 15 35 n 1 a detailed investigation of the relationship between the spatial and temporal patterns of the seismic activity recorded by six autonomous hydrophones and the structure of the northern mid atlantic ridge between 15 and 35 n is presented two years of monitoring yielded a total of 3485 hydroacoustically detected events within the array recorded by four or more hydrophones the seismically active zone extends 20 km to either side of the ridge axis consistent with earlier results from studies of fault morphology along the axis hydrophone recorded activity shows important variations areas with intense and persistent seismic activity stripes stand in sharp contrast to areas that lack seismicity gaps the regions of persistent activity are a new observation at mid ocean ridges in general the patterns of seismically active inactive regions are also recognized in the 28 year teleseismic record implying that these patterns are maintained at timescales between a few years and a few decades we find no simple relationship between individual segment variables e g length or trend of the segment maximum offset of discontinuities or along axis change in mantle bouguer anomaly mba and water depths and number of hydrophone recorded events there does appear to be a correlation between axial thermal structure and seismicity regions of low and high numbers of events would thus correspond to thinner hotter and thicker colder lithosphere respectively seismicity may reflect thermal structure at short timescales decadal or longer while relief and inferred crustal thickness may integrate this structure over longer periods of time order of 1 myr

melting of continental crust during subduction initiation a case study from the chaidanuo peraluminous granite in the north qilian suture zone the chaidanuo granite batholith is a similar to 500 km 2 homogeneous high level intrusion in the north qilian oceanic suture zone three types of enclaves have been recognized including 1 supracrustal xenoliths 2 biotite gneiss that represents restite of the upper crustal melting and 3 coeval mantle derived mafic magmatic enclave mme the batholith consists dominantly of peraluminous biotite monzogranite with sio2 69 73 wt and a cnk 1 05 1 28 and shows geochemical affinity with the upper continental crust e g enrichment of large ion lithophile elements liles k rb u th pb depletion of high field strength elements hfses nb ta ti p eu and sr and enriched sr sr 87 sr 86 i 0 731 to 0 744 nd epsilon nd t 6 0 to 7 1 isotopes zircon u pb dating indicates that this batholith formed at 516 505 ma coeval with the mmes 510 ma which represent the early stage of seafloor subduction in the north qilian suture zone the hf isotopic composition of the mme epsilon hf t 6 0 to 2 1 is more depleted than that of the host granite epsilon hf t 14 8 to 4 7 suggesting mixing of mantle and crust derived melts the inherited zircon cores in the host granite yield an age peak at similar to 750 ma with a few detritals of 591 1683 ma zircons from a biotite gneiss enclave yield a protolith age of 744 ma and a metamorphic melting event at 503 ma sr nd isotopic modeling reveals that the batholith was generated by melting of neoproterozoic granitic rocks with the addition of 10 18 mantle derived magma therefore peraluminous granite can be produced by melting of crustal materials heated by mantle derived magmas during the early stage of subduction initiation at the site of a prior passive continental margin c 2014 elsevier ltd all rights reserved

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

syn collisional adakitic granodiorites formed by fractional crystallization insights from their enclosed mafic magmatic enclaves mmes in the qumushan pluton north qilian orogen at the northern margin of the tibetan plateau the qumushan qms syn collisional granodiorite which is located in the eastern section of the north qilian orogen at the northern margin of the greater tibetan plateau has typical adakitic characteristics and also contains abundant mafic magmatic enclaves mmes this recognition offers an unprecedented insight into the petrogenesis of both the adakitic host granodiorite and the enclosed mmes the mmes and their host granodiorites share many characteristics in common including identical crystallization age similar to 430 ma same mineralogy similar mineral chemistry and whole rock isotopic compositions indicating their genetic link the mmes are most consistent with being of cumulate origin formed at earlier stages of the same magmatic system that produced the qms adakitic granodiorite subsequent replenishment of adakitic magmas could have disturbed the cumulate piles as mmes dispersed in the adakitic granodiorite host during emplacement the geochemical data and petrogenetic modeling of trace elements suggest that the qms adakitic host granodiorite is most consistent with fractional crystallization dominated by the mineral assemblage of the mmes the parental magma for the qms granodiorite is best explained as resulting from partial melting of the ocean crust together with recycled terrigenous sediments during continental collision which may have also experienced interaction with mantle peridotite during ascent c 2016 elsevier b v all rights reserved

geochronological and geochemical constraints on the petrogenesis and tectonic significance of paleozoic dolerite dykes in the southern margin of alxa block north china craton abstract dolerite dykes are common in the southern margin of alxa block which is the westernmost part of north china craton the ages and petrogenesis of the dolerite dykes which are important for a better understanding of tectonic magmatic evolution in the region are uncertain this paper reports the results of an integrated geochronological and geochemical study of the dolerite dykes in the jinchuan area previously these dolerite dykes were considered to be coeval with the 831 ma jinchuan ultramafic intrusion by some researchers despite a cross cutting relationship for the dykes our new zircon u pb dating indicates that the dolerite dykes were emplaced at 424 ma 400 ma younger than the jinchuan intrusion the jinchuan dolerite dykes contain 5 9 wt mgo and 47 51 wt sio 2 and are characterized by light ree rare earth elements enrichments relative to heavy ree pronounced negative nb anomaly elevated initial 87 sr 86 sr from 0 7056 to 0 7068 negative end from 2 to 5 and zircon ehf from 2 to 20 the trace element and isotope data are consistent with an asthenosphere derived parental magma that experienced 10 25 crustal contamination prior to final emplacement since the jinchuan dolerite dykes are 20 40 ma younger than the subduction related basaltic volcanic rocks blueschists and eclogites in the nearby north qilian orogenic belt to the south we propose that the jinchuan dolerite dykes are the products of basaltic magmatism induced by delamination of previously subducted oceanic lithosphere and the associated asthenosphere upwelling in a post subduction setting the occurrence of 424 ma post subduction dolerite dykes in the jinchuan area and the 450 ma arc basalts to the south indicate that the southwestern margin of north china craton was an active plate margin in early paleozoic

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

geochronology petrogenesis and tectonic significance of huashugou granitoids in north qilian nw china abstract north qilian orogenic belt nqob is a typical early paleozoic orogenic belt in china however the tectonic setting of nqob remains controversial especially the post subduction processes in this study we report whole rock geochemistry zircon u pb ages and hf nd isotopic compositions of huashugou granitoids in the western segment of the nqob nw china la icp ms u pb dating of zircon from huashugou granitoids indicate magmatic crystallization ages of ca 420 ma with late paleoproterozoic captured zircons of ca 1700 ma the huashugou granitoids show enrichment in light rare earth elements and large ion lithophile elements e g rb th and u depletion of heavy rare earth elements and high field strength elements e g nb ta and ti negative eu anomalies and a cnk

petrogenesis of the early paleozoic low mg and high mg adakitic rocks in the north qilian orogenic belt nw china implications for transition from crustal thickening to extension thinning abstract the petrogenesis and geodynamic implications of the early paleozoic adakitic rocks in the north qilian orogenic belt remain topics of debate in this study petrology zircon u pb age and lu hf isotopic composition whole rock geochemistry and sr nd isotopes were carried on both low mg and high mg adakitic rocks from the north qilian orogenic belt these results will provide significant constraints on the evolution of the north qilian orogenic belt in general the low mg adakitic granites mainly consist of plagioclase 50 55 alkali feldspar 20 25 quartz 20 25 and biotite 5 in contrast the high mg adakitic granodiorites are generally composed of alkali feldspar 30 35 plagioclase 30 45 quartz 20 25 and amphibole 10 the low mg adakitic granitoids 446 457 ma are characterized by high sio2 69 72 wt low mg 39 42 and low cr and ni contents however the high mg adakitic granitoids 430 431 ma have relatively lower sio2 65 66 wt higher mg 50 59 and higher cr and ni contents the low mg adakitic rocks have high initial 87sr 86sr ratios 0 7068 0 7080 negative end t 2 3 to 3 3 and ehf t values 6 8 to 1 9 with old zircon hf model ages 1 2 1 6 ga however the high mg adakitic rocks show lower initial 87sr 86sr ratios 0 7044 0 7066 higher end t 1 8 to 3 0 and positive ehf t values 2 3 7 7 with younger zircon hf model ages 0 9 1 1 ga these results suggest that the low mg rocks were generated by partial melting of thickened crust whereas the high mg rocks were derived from anatexis of delaminated lower crust which subsequently interacted with mantle magma upon ascent the data obtained in this study provide significant information about the geological and tectonic processes after the closure of the qilian ocean the continent continent collision and thickening probably occurred during 440 467 ma with formation of low mg adakitic rocks and the transition of the tectonic regime from compression to extension probably occurred at 430 ma with formation of high mg adakitic rocks

an atlantic hydrothermal plume trans atlantic geotraverse tag area mid atlantic ridge crest near 26 n the physical characteristics of an atlantic hydrothermal plume and its seafloor sources are described from the first data set of water column properties associated with a high temperature source area at a slow spreading oceanic ridge the observations comprise five near bottom tows of a camera color video and still temperature sensor array through the buoyant portion and 23 conductivity temperature depth ctd profiles through the neutrally buoyant portion of the plume made at the trans atlantic geotraverse hydrothermal field in the rift valley of the mid atlantic ridge at 26 08 n 44 49 w in july 1985 the source area is a mound up to 250 m wide and 50 m high constructed primarily of massive sulfides between depths of 3620 and 3670 m at the base of the east wall flow and discharge regimes systematically changed from the center to the edge of the mound high temperature black smokers vented at fast rates 1 m s from discrete sulfide chimneys and at slow rates from fractures and clear solutions vented at slow rates from diffuse sources in the inner zone of the mound intermediate temperature blue white and white smokers vented at slow rates from discrete sulfide sulfate chimneys and clear solutions vented from diffuse sources in the middle zone patchy diffuse discharge of clear solutions through sulfide talus occurred in the outer zone the diffuse discharge of clear solutions and the discrete discharge from the white smokers were observed to turbulently rise up to several meters above the seafloor where the discharge was laterally advected in prevailing laminar flow at several centimeters per second a convective heat flux of 8 8 106 w for only the black smokers that vented from fractures was estimated by applying a buoyant plume model to temperature anomalies measured with the towed array this value is intermediate between values estimated for entire vent fields at the fast spreading east pacific rise discharge from the black smokers rose to form the neutrally buoyant portion of the plume that was cold and fresh relative to surrounding seawater where it attained density equilibrium between 190 and 350 m above the mound in contrast hydrothermal plumes observed in the pacific were warm and salty relative to surrounding seawater the difference is attributed to the effect on plume density of entrainment during rise through opposite salinity profiles that decrease downward in the atlantic and increase downward in the pacific resulting in different temperature salinity compensations at neutral buoyancy the temperature difference between the neutrally buoyant portion of the plume and surrounding seawater negative for the atlantic positive for the pacific is not a unique function of convective heat flux from a source area as a consequence of both the effect of the entrainment of salinity on plume density and the separation of diffuse and discrete components of discharge the hydrothermal plume and the hydrothermal mound are inferred to have grown in size and complexity in response to the development of hydrothermal flow and discharge regimes for at least the past 104 years

collision driven slab breakoff magmatism in northwestern anatolia turkey abstract postcollisional eocene magmatism in northwestern anatolia produced two e w trending linear belts of plutons along and north of the izmir ankara erzincan suture zone iaesz whose geochemical features and age relations support a slab breakoff model for their petrogenetic oinevolution the suture zone granitoids szgs in the southern belt have ages around 54 48 ma are intrusive into blueschist rocks of the iaesz and are composed of diorite quartz diorite granodiorite and syenite the marmara granitoids mgs in the northern belt are slightly younger 48 35 ma intrusive into the paleozoic mesozoic crystalline basement rocks of the sakarya continent and composed of monzogranite granite and granodiorite both szgs and mgs have moderately to highly evolved medium to high k calc alkaline compositions and are predominantly metaluminous i type granitoids nd sr isotope systematics documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepacka

diffuse venting and background contributions to chemical anomalies in a neutrally buoyant ocean hydrothermal plume plumes originating in high temperature hydrothermal discharges entrain background water and often entrain diffuse source fluids during convective ascent the mixing of fluid from those three different sources determines the chemical composition of the ensuing neutrally buoyant plumes here convection models and aluminum data from the trans atlantic geotraverse tag site are used to examine relative contributions of focused diffuse and background sources to anomalies in the plume our analysis shows that anomalously high al values observed just above the seafloor at tag which we assume stem from diffuse flows can contribute as much as 50 to the al anomaly in the neutrally buoyant plume found 350 m above bottom background water contributes nearly an equal fraction of al to the anomaly more generally entrained contributions depend on gradients in profiles external to the rising plume entrainment also depends on effective source area distributed high temperature vents entrain more fluid than a single composite high temperature vent larger effective source area is particularly significant for entrainment of diffuse source or other tracers trapped within a few tens of meters of the seafloor downstream cross stream and temporal variabilities exhibited in the three dimensional model plume also underscore problems of sampling and interpreting actual plume data

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

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

theory applied to the mid atlantic ridge hydrothermal plumes the finite difference approach a system of differential equations describing the entrainment of ambient seawater during the rise of a buoyant hydrothermal plume has been solved by an explicit finite difference method chosen for its ease of application an equation for tracer concentration has been added so that concentrations in the neutrally buoyant plume can be calculated for those elements whose background profiles vary over the depth range of the buoyant plume the height of plume rise can be related directly to the thermal and hydrothermal vent flux for the tag vent field 26 n mar five plume layers have been identified the calculated heat flux is 500 940 mw and the fluid flux is 0 210 0 392 m3 s 1 the fluid flux to the neutrally buoyant plume is 1460 2740 m3 s 1 calculated plume concentrations of mn compared with measurements made at tag in 1988 indicate that there is either 50 removal of manganese in the buoyant plume or that low temperature vent fluids contribute about 50 of the total thermal output of the tag vent field

manganese and methane in hydrothermal plumes along the east pacific rise 8 40 to 11 50 n abstract in november 1991 we surveyed the water column for hydrothermal plumes along 350 km of the east pacific rise axis from 8 40 to 11 50 n using a combination of physical and chemical measurements our survey included the two major ridge segments north and south of the clipperton transform fault at about 10 10 n both limbs of the overlapping spreading centers osc s at 9 03 n and 11 45 n and a 30 km section of the next ridge segment to the south we found vigorous plumes along most of this ridge axis in keeping with its magmatically robust cross section axial summit caldera and shallow magma related seismic reflector these plumes were detectable by both physical temperature and light attenuation and chemical dissolved mn and ch4 measurements although the chemical measurements were more sensitive the least active sections were the southern third of the northern segment from 10 20 to 52 n and the oscs especially the osc at 11 45 n plumes there had weak mn and ch4 signals and were barely detectable by physical methods these axial sections were the only ones surveyed that lie deeper than 2600 m and appear to be magma starved the most active sections on the northern segment gave stronger signals for mn and temperature than for ch4 and light attenuation whereas the opposite was true on the southern segment which was the site of a volcanic eruption at 9 45 52 n only seven months prior to our cruise on the northern segment the four physical and chemical plume tracers correlated positively and linearly with one another suggesting that the segment was fed by relatively uniform end member fluids with a mean ch 4 mn molar ratio of 0 075 the southernmost section surveyed from 8 42 to 9 08 n closely resembled the northern segment the rest of the southern segment fell into three sections with different ch 4 mn ratios 9 39 to 53 n with ch 4 mn as high as 10 9 08 to 39 n with ch 4 mn of 0 51 and 9 53 to 10 07 n with ch 4 mn of 0 85 the section with the highest ch 4 mn was the site of the volcanic eruption which produced high temperature low salinity gas rich vent fluids carrying abundant bacterial particles the high ch4 concentrations are clearly associated with the volcanic eruption but the origin of the ch4 is unclear

composition and dissolution of black smoker particulates from active vents on the juan de fuca ridge during two atlantis ii alvin cruises to the juan de fuca ridge in 1984 active high temperature 140 284 c vents were sampled for black smoker particulates using the grassle pump individual mineral phases were identified using standard x ray diffraction and petrographic procedures in addition elemental compositions and particle morphologies were determined by x ray energy spectrometry and scanning electron microscope x ray energy spectrometry techniques the vent particulates from the southern juan de fuca ridge vent sites were highly enriched in s si fe zn and cu and were primarily composed of sphalerite wurtzite pyrite pyrrhotite barite chalcopyrite cubanite hydrous iron oxides and elemental sulfur two additional unidentified phases which were prevalent in the samples included an fe si phase and a ca si phase the grain sizes of the individual particle phases ranged from 100 m for the fe si particles grain size and current meter data were used in a deposition model of individual phase dispersal for many of the larger sulfide and sulfate particles the model predicts dispersal to occur over length scales of only several hundreds of meters the high temperature black smokers from the more northerly endeavour segment vents were highly enriched in fe s ca cu and zn and were primarily composed of anhydrite chalcopyrite sphalerite barite sulfur pyrite and other less abundant metal sulfide minerals the grain sizes of the individual particles ranged from 10 m to slightly larger than 500 m the composition and size distributions of the mineral phases are highly suggestive of high temperature mixing between vent fluids and seawater a series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals the dissolution rates ranged over more than 3 orders of magnitude from 3 2 10 8 cm s 1 for anhydrite to 1 2 10 12 cm s 1 for chalcopyrite the results indicate that for some minerals particularly anhydrite and marcasite total dissolution occurs within a few hours to a few weeks of their formation for other more stable minerals including pyrite sphalerite and chalcopyrite the time required for total dissolution is much longer and consequently individual crystals may be expected to persist in the sediments for considerable periods of time after deposition

a model of an atlantic and pacific hydrothermal plume a turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields owing to the stably stratified salinity field in the pacific relatively warm salty water spreads at an equilibrium level where the plume density equals the ambient density in contrast the unstable salinity profile in the atlantic gives the plume added buoyancy and it continues to rise to an equilibrium level where it is relatively cool and fresh these attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer the equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient the net entrainment of surrounding seawater is greater in the atlantic plume model than in the pacific plume model for the same buoyancy flux recent data from the tag hydrothermal field at 26 n on the mid atlantic ridge and data from a vent field on the endeavor segment of the juan de fuca ridge are compared to model results the model predicts the penetration height and s characteristics of the atlantic plume and it explains some of the differences between the observed atlantic and pacific hydrothermal plumes

mid atlantic ridge hydrothermal events recorded by deep sea corals trace element and stable isotope analyses were performed on azooxanthellate corals from the north atlantic at two different tectonic settings one set was from orphan knoll near newfoundland 1700 m depth 50 25 57 n 46 22 05 w the other from the mid atlantic ridge 1200 m depth 45 14 12 n 28 34 12 w the mid atlantic ridge corals contain significantly greater quantities of fe mn cu ni and zn within their skeletons than the orphan knoll corals the metal concentrations are not homogeneous within the mid atlantic ridge coral skeletons but occur as episodic pulses during a decade or two of each coral s lifetime we believe these metals originated in a hydrothermal discharge zone associated with the mid atlantic spreading centre if so it is evidence that the duration of an individual hydrothermal event is from a decade up to 30 years or so with more specimens of known ages it may be possible to reconstruct the history of a particular segment of an oceanic spreading centre resume les elements en traces et des isotopes stables ont ete analyses sur des coraux sans zooxanthelles de l atlantique nord cueillis dans deux contextes tectoniques differents une serie d echantillons provenaient d orphan

mean temperature salinity salinity depth and temperature depth curves for the north atlantic and the north pacific abstract all available hydrographic data are used to compute average temperature salinity salinity depth and temperature depth curves for 5 squares in the north atlantic and north pacific 10 s to 60 n both objective and subjective methods are used to filter out obviously erroneous data summary maps of all 5 square mean curves and their corresponding standard deviations are used to select regions of spatial homogeneity over which the curves are averaged scatter diagrams of each parameter pair are used to identify 5 squares containing a variety of water masses the area average curves and their standard deviations are presented individually along with tables of the parameter values these curves in conjunction with the 5 square summary maps provide a comprehensive picture of the distributions of these properties in the upper and mid depth portions of these oceans this well resolved picture of the water mass structure both confirms and adds new insights into the traditional concepts of these property distributions the application of the mean temperature salinity and salinity depth curves to the inference of salinity from observed temperature profiles is examined shallow 0 500 db dynamic heights calculated from observations of temperature and salinity true dynamic height are compared with dynamic heights computed from observed temperature profiles and salinities inferred from the mean property curves maps of the rms differences between true and inferred dynamic heights by 5 square reveal those areas where salinities inferred from either temperature salinity or salinity depth curves yield reliable dynamic heights

systematic regional variations in diamond carbon isotopic composition and inclusion chemistry beneath the orapa kimberlite cluster in botswana abstract the carbon isotopic composition nitrogen content and aggregation state of 95 inclusion bearing diamonds collected from the production of damtshaa kimberlites were investigated the damtshaa kimberlites belong to the group of southern african kimberlites showing 12c enrichment in eclogitic compared to peridotitic diamonds the results were compared with similar studies of the nearby orapa and letlhakane kimberlites providing the opportunity to examine variations in mantle composition on the kilometer scale while orapa letlhakane and damtshaa diamonds may share some overall similarities in their 13c distribution there are significant differences among them these differences support the concept that diamonds from different kimberlite pipes have distinctive features in their 13c distribution and that this is true for kimberlite occurrences which are spatially separated by only a few tens of km compared to orapa peridotitic garnet inclusions from damtshaa and letlhakane are derived in part from highly depleted dunitic harzburgitic reservoirs extending to greater depth in all three kimberlites diamonds with eclogitic garnet inclusions displaying comparatively low al2o3 cr2o3 ratios characteristic for mantle compositions show a wide range in carbon isotopic composition from about 4 to 18 vs pdb the observed relationship between 13c and al2o3 cr2o3 ratios indicates the presence of 13c depleted mantle sources that cannot be explained by subduction estimates of possible pressure temperature conditions based on the fe mg distribution coefficients of coexisting eclogitic garnets and clinopyroxenes and the ca mole fraction in garnets lead to the conclusion that beneath the orapa letlhakane and damtshaa kimberlites there is a mantle zone depleted in 13c approximately 20 30 km thick and extending over an area of at least 200 km2

hydrothermal anomalies in the lucky strike segment on the mid atlantic ridge 37 17 n abstract as part of the fara french american ridge atlantic project the northern mid atlantic ridge mar was surveyed for hydrothermal activity between 33 and 40 n during the fazar cruise in august october 1992 after detection of hydrothermal activity in the lucky strike segment 37 17 n a detailed water column survey was undertaken in this region during a follow up cruise with the dsrv alvin several active high temperature vents were found on the summit of an central seamount here we focus on the results of the water column survey undertaken during the fazar cruise the influence of mediterranean water and the site s shallow depth complicates the hydrography at lucky strike background temperature and salinity gradients are usually too complex to indicate hydrothermal anomalies clearly light transmission anomalies within the lucky strike region were small but were detected throughout the segment from mid depth 1500 m all the way to the valley seafloor 2300 m depth the large depth range covered by these anomalies probably results from vertical mixing as well as the presence of multiple vent sources at various depths methane anomalies and a temperature anomaly observed deeper than the vents documented by alvin further support the idea of additional deeper vents within this segment particle samples of the deep particle layer are enriched in fe and trace metals

deformation microstructures reveal a complex mantle history for polycrystalline diamond 1 detailed quantitative electron backscatter diffraction ebsd analysis of polycrystalline diamond rocks diamondites provides insights into their formation and significance the fine grain size of diamondites is usually attributed to rapid crystallization however ebsd reveals significant intragrain bending distinct low angle boundaries and straight to highly irregular high angle grain boundaries highly deformed grains may be in contact with others showing little or no deformation these features are typical for crystal plastic deformation in which differential stress generates dislocations according to the dominant slip systems in diamond dislocations accumulate to form subgrain boundaries with grain size reduction by rotation of subgrains nucleation and growth of new grains and migration of grain boundaries such features are seen in other polygranular materials such as deformed metals and quartzite deformed at high temperatures during this process interaction with fluids produced interstitial garnets with compositions different from those of the primary inclusions oscillatory cl zoning in diamonds developed through diffusion along subgrain boundaries rather than being a primary growth feature diamondites are thus not simply products of primary crystallization but may be strongly deformed recrystallized and modified integrated ebsd cl and in situ chemical and isotopic analysis provide the spatial control and new insights into mantle processes

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

the changing vision of marine minerals abstract non fuel marine minerals are reviewed from the perspective of resources and their value as active analogs that can advance understanding of types of ancient ore deposits that formed in marine settings the theory of plate tectonics is the largest influence in expanding our vision of marine minerals and in developing our understanding of geologic controls of mineralization in space and time prior to the advent of plate tectonics we viewed the ocean basins as passive sinks that served as containers for particulate and dissolved material eroded from land this view adequately explained marine placer deposits heavy minerals and gems aggregates sand and gravel and precipitates phosphorites and manganese nodules although numerous sites of placer mineral deposits are known on continental shelves worldwide current activity pertains to diamond mining off southwestern africa tin mining off southeastern asia and intermittent gold mining off northwestern north america which are all surpassed economically by worldwide recovery of marine sand and gravel in turn dwarfed by offshore oil and gas with the advent of plate tectonics plate boundaries in ocean basins are recognized as active sources of mineralization in the form of hydrothermal massive sulfide deposits and proximal lower temperature deposits hosted in oceanic crust mafic at ocean ridges and felsic at volcanic island arcs and of magmatic ni cu sulfide chromite and pge deposits inferred to be present in the oceanic upper mantle lower crust based on their occurrence in ophiolites some 300 sites of hydrothermal active and relict mineralization most of them minor are known at this early stage of seafloor exploration on ocean ridges in fore arc volcanoes at back arc spreading axes and in arc rifts deposits formed at spreading axes and transported off axis by spreading are present in oceanic lithosphere but are virtually unknown the tag trans atlantic geotraverse hydrothermal field in the axial valley of the mid atlantic ridge latitude 26 n is considered to exemplify a major volcanogenic massive sulfide vms deposit forming at a spreading axis the most prospective of these occurrences lie within the 200 nautical mile 370 km wide exclusive economic zone eez of the nations of the volcanic island arcs of the western pacific where metal content of massive sulfides ag au ba cu pb sb zn exceeds that at ocean ridges plate tectonics early provided a framework for mineralization on the scale of global plate boundaries and is providing guidance to gradually converge on sites of mineralization through regional scales of plate reorganization with the potential to elucidate the occurrence of individual deposits e g eocene carlin type gold deposits investigation of the spectrum of marine minerals as active analogs of types of ancient mineral deposits is contributing to this convergence consideration of questions posed by brian skinner 1997 of what we do and do not know about ancient hydrothermal mineral deposits demonstrates the ongoing advances in understanding driven by investigation of marine minerals

volcanism and metallogenesis of axial and off axial structures on the east pacific rise near 13 degrees n a fast spreading segment 12 cm yr super 1 of the east pacific rise near 12 degrees 50 n explored in detail by surface ship and manned submersible displays intense hydrothermal activity the rise crest about 1 500 m in width with a regional depth of 2 600 m is occupied at its center by an axial graben 1 3 titania alkali enriched olivine ti k basalts with high tio 2 1 4 and high alkali content na 2 o 3 0 k 2 o 0 3 occur on the southeastern seamount the fractionated tholeiites are believed to have been derived from primitive melts during differentiation which took place within a magma reservoir asymmetrical with respect to the axis of the graben which supplied both axial and off axial lava flows the ti k enriched basalts are believed to have been produced from an alkali enriched magmatic source

geochemistry of sediments from the tag hydrothermal field m a r at latitude 26 n abstract sediments from the tag hydrothermal field show evidence of hydrothermal inputs in the form of fe cu zn and mn enrichments the fe cu and zn are thought to have been introduced as finely divided sulphides precipitated from suspension after dispersion away from now inactive hydrothermal vents and have since been oxidised by contrast the manganese is believed to be in the form of primary oxide precipitate the processes of metal enrichment have been variably active during discrete intervals in the past geochemical partition analysis has demonstrated that the elements determined can be distributed differently between various phases in the different types of sediments studied and that diagenetic transfer of elements from one phase to another occurs on burial the general lack of metal enrichments in the sediments of the intensity sometimes found on the east pacific rise is thought to be largely the result of major metal precipitation subsurface

focused ion beam technique and transmission electron microscope studies of microdiamonds from the saxonian erzgebirge germany a focused ion beam of ga ions is a relatively new technique that has been developed for microelectronic industries now researchers of the earth sciences find it to be a promising tool for studying various geological materials using the fib technique and an fei strata db 235 dual beam system we have successfully prepared several electrontransparent foils which crossed wm sized diamonds included in host minerals such as zircon and garnet from quartzofeldspathic rocks of the saxonian erzgebirge germany scanning and transmission electron microscopy applied to these foils revealed that the diamonds contain crystalline nanometric inclusions these inclusions consist of minerals of known stoichiometries such as sio2 and al2sio5 whereas others are characterized by different combinations of si k p ti and fe in the presence of oxygen stoichiometries are not clear at this stage of research one suite of inclusions is assumed to be represented by archerite kh2po4 which is known to be stable at pressures of 4 22 gpa and one nanocrystal containing pb oxygen and carbon is interpreted to be pbxoy or pbco3 along with solid crystalline inclusions the diamonds contain cavities filled by liquid gas that escaped during sample preparation these are associated with dislocations of diamond growth our data are consistent with the concept of diamond crystallization from a coh rich multicomponent supercritical fluid and suggest that the composition of such a fluid is more consistent with a local crustal source rather than that of a mantle origin 2003 elsevier science b v all rights reserved

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

geologic form and setting of a hydrothermal vent field at lat 10 56 n east pacific rise a detailed study using angus and alvin a hydrothermal vent field here called the feather duster site occurs on the eastern marginal high near the edge of a narrow 95 m and shallow 15 20 m axial graben within an area dominated by sheet flows and collapse features the sheet flows are intermediate in relative age between younger fluid flow lavas on the floor of the axial graben and older pillow constructional lavas on the marginal highs hydrothermal activity occurs in two zones within a 65 by 45 m area the main zone is located where a fissure system and sulfide sulfate chimneys vent warm 9 47 sup 0 c and hot 347 sup 0 c hydrothermal fluids here two mounds of massive sulfide totaling about 200 t are forming one occurs at the base of a 3 m high scarp which is the wall of a drained lava lake the other is perched on top of the scarp 19 references 4 figures

nanoinclusions in microdiamonds from neogenic sands of the ukraine samotkan placer a tem study abstract mineral and fluid inclusions in seven microdiamonds ca 0 2 mm in diameter from the neogene samotkan placer of the ukrainian shield were investigated by tem various types of submicron or nanometre sized inclusions such as olivine and orthopyroxene fe sn oxide and assemblages of mineral multi phases were observed in an octahedral microdiamond crystal numerous olivine and enstatite micro and nanocrystals were observed their composition is close to that of other olivine and enstatite inclusions found in kimberlitic diamonds worldwide an unusual feature of these minerals in the samples studied however is a relatively high nio content 0 50 0 80 wt in olivine fo 91 3 92 1 and 0 40 0 70 wt in enstatite fo 94 1 95 4 these peridotitic mineral associations represent the host possibly lherzolitic mantle in which the diamonds grew the mean mg values of olivine and enstatite inclusions in samotkan s microdiamond are respectively 91 43 and 94 83 which are closer to mg values of these minerals in lherzolite rather than in harzburgite assemblages included in diamond in addition enstatite clinoenstatite k richterite graphite and fe sn oxide were also identified as nanoinclusions in samotkan diamond the fe sn oxides and magnetite were found in two microdiamonds of the transitional 111 110 form the k richterite and graphite have been attributed to epigenetic inclusions the origin of fe sn oxide is not clear assemblages of multi phase minerals were observed in four microdiamonds of variable morphology octahedron transitional 111 110 form cube and cube coated diamond these phases belong to fluid bearing inclusions and are enclosed in cavities which as a rule are not filled completely by the solid phases the remainder of the volume is occupied by a fluid that for the most part has been released during sample preparation in the majority of cases the multi phase assemblages consist of carbonate mica rutile ilmenite apatite and sylvite carbonates are the most abundant phases in the fluid inclusions they are calcium rich carbonates frequently with admixtures of fe mg and sr the mica inclusions are enriched in silicon with si varying from ca 6 7 to 7 0 a p f u the multi phase mineral assemblages present in samotkan s microdiamond are similar to fluid bearing microinclusions found previously in other diamond types e g fibrous diamonds the fibrous coat of coated diamonds or the internal clouds of octahedral diamonds from kimberlites of different provinces worldwide they represent the carbonate alkali and chlorine rich mantle fluid composition present during crystallisation of the samotkan s microdiamond judging from the composition of the multi phase assemblages it may be assumed that the samotkan s microdiamond grew from a carbonatitic to a slightly silicic melt rich in alkali and volatile components

tectonics of the mid atlantic rift valley between the tag and mark areas 26 24 n evidence for vertical tectonism abstract a segment of the mid atlantic ridge between the tag and mark areas between 26 and 24 n was studied during march april of 1988 from the r v akademik mstislav keldysh using mir submersibles the rift valley is depressed here to depths of 3200 4700 m and includes seven independent magmatic cells which are in different phases of their evolution some of them are now in the constructive phase whereas others are in the destructive phase and are strongly fractured slopes of two types flank the rift valley the normal slopes similar to the famous area are block faulted terrains with small elevations above the neovolcanic ridge crest in the center of the rift valley the abnormal slopes are elevated from 1 to 3 km above the neovolcanic ridge crest an almost undisturbed section of the upper oceanic crust from gabbro through sheeted dikes to pillow lavas outcrops on the abnormal slopes as the dikes are dipping nearly vertically and pillow lavas preserve their initial inclinations no block rotation or back tilting occurred during the development of rift mountains pure vertical uplift was responsible for rift mountain growth speculations are made that serpentinization of the uppermost mantle peridodite can be considered as the main process leading to oceanic crust uplift serpentinization takes place during the nonvolcanic destructive phases when seawater can easily penetrate into the deeper crust and uppermost mantle reaching the peridodites as a result serpentinites are added to the oceanic crust of slow spreading ridges

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

three dimensional numerical simulation of the hydrothermal system within tag like sulfide mounds a 3 d finite element algorithm with incorporated explicit pipe like elements is developed to solve the coupled time dependent heat transport and fluid flow differential equations and yield the internal temperature and fluid velocity fields for tag like mounds a range of models with permeable and impermeable upper boundaries and different thermal conductivities are investigated the solutions have three common features a central high temperature zone which coincides with a non magnetic zone inferred from magnetic data fluid upflow along the vertical high permeability column surrounding a central pipe and a maximum fluid velocity of the order of the observed maximum value at the central black smokers thermal conductivity variations strongly influence the temperature distribution but not the fluid velocity pattern

helium and methane measurements in hydrothermal fluids from the mid atlantic ridge the snake pit site at 23 n methane and helium isotopes concentrations have been measured in hydrothermal fluids of black smoker vents at the snake pit area mar 23 n as part of the hydrosnake cruise with the submersible nautile the samples contain large quantities of helium and methane with endmember values of 4 6 10 5 cm3 stp g for helium and 1 38 10 3 cm3 stp g for methane the helium isotopic ratio 3he 4he is 8 4 times the atmospheric ratio these values are strikingly similar to those already obtained on the east pacific rise the ch4 3he ratio is also quite similar ch4 3he 2 6 106 suggesting a non biogenic origin of this gas in the fluids assuming that the range of variation of the 3he concentration data obtained so far from various tectonic settings is close to the genuine range of values encountered on mid ocean ridges the global mass flow involved in the hydrothermal circulation at the ridge s axis is estimated between 1000 and 3000 m3 of water sec leading to a residence time of the global ocean with respect to the hydrothermal circulation between 15 and 45 million years this estimate implies that in addition to the individual vents smokers there is an extensive diffuse circulation of hydrothermal fluids along the ridges in agreement with recent observations concerning heat budgets at hydrothermal sites in the eastern pacific

new insight into polycrystalline diamond genesis from modern nanoanalytical techniques abstract technical developments in analytical methods that reach nanometer spatial resolution have enabled the interrogation of smaller submicron sized inclusions in diamond that had previously been elusive this has inspired and enabled studies of non classical diamond species from different geological settings resulting in a strongly faceted and dynamic picture of diamond formation this article reviews the leap of knowledge achieved by employing state of the art analytical methods with high spatial resolution to polycrystalline diamonds from different settings i e from kimberlite from crustal ultra high pressure metamorphic terranes and alluvial carbonados while crustal metamorphic diamonds are generally formed under oxidizing conditions polycrystalline diamond from the earth s mantle and carbonado have inclusion suites reflecting variable and sometimes extreme redox conditions diamond fluid compositions however fall in the same compositional field for worldwide diamond fluids regardless of their geodynamic environment on the basis of thermodynamic equilibrium data for c h o fluids in the mantle we argue that submicron inclusions in diamonds are products of local remobilization connected to fluid fluxed partial melting and redox freezing thus evidence from these inclusions complements information from classical work on larger inclusions and allows a unique direct insight into the medium in which diamond formed

acoustic imaging of hydrothermal plumes east pacific rise 21 n 109 w we report the first observations based on acoustic imaging of large scale structure and time variability of buoyant plumes emanating from black smoker type seafloor hot springs three dimensional plume reconstructions were made from a digital data set of acoustic backscattering information recorded on a prototype submersible mounted sonar system the acoustic images of two adjacent black smokers depict volume and show zones of flow organization meters to tens of meters in the lower 40 m of the buoyant plumes the two plumes coalesce bend in the prevailing current exhibit short term minutes variation in cross section and rapid seconds turbulent eddy variations at small scales 1 m the plume imaging system is being developed for determination of plume dynamics flux determinations when combined with chemical and thermal measurements and long term monitoring of the activity of seafloor hydrothermal fields

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

geochemical and physical structure of the hydrothermal plume at the ultramafic hosted logatchev hydrothermal field at 14 45 n on the mid atlantic ridge abstract the hydrothermal plume generated in deep waters above the logatchev hydrothermal field lhf about 15 n on the mid atlantic ridge was investigated and mapped for its 3d distributions using a combination of in situ optical light scattering data temperature and salinity data as well as concentrations of hydrogen methane total dissolvable fe and total dissolvable mn based on the results obtained for these meaningful parameters we report the geochemical and physical characteristics of the fluids expelled from the ultramafic lhf and the chemical structure of its hydrothermal plume in the water column the hydrothermal plume is sourced by at least seven distinct vent sites and possibly additional diffusive fluid and gas discharge it comprises a water body characterized by strong nephelometric anomalies expressed as ntu nephelometric turbidity units and high concentrations of fe and mn 5 times seawater concentration and the gas plume with several times the h 2 and ch 4 concentrations of normal seawater up to three plume levels with a total vertical extension of about 350 m from the seafloor were classified in the hydrothermal plume the ntu plume could be followed to approximately 2 5 km to the north and to the south from the vent site while the gas plume spread several km farther from the hydrothermal source high concentrations of h 2 up to 1598 nmol l 1 and ch 4 up to 323 nmol l 1 accompanied by relatively low dissolvable fe concentrations up to 270 nmol l 1 as well as low concentrations of dissolvable mn 112 nmol l 1 compared to basaltic hydrothermal systems are the characteristics of the plume the low metal gas ratios showed a decrease with increasing distance from the vent site our data demonstrate that ultramafic systems such as the lhf serve both as sources and sinks for elements with respect to metal and gas inputs into the oceanic water column the relevance of such systems is underlined by the discovery and postulated frequency of further ultramafic hosted hydrothermal systems on slow spreading ridges

evidence of fluid inclusions in metamorphic microdiamonds from the kokchetav massif northern kazakhstan abstract microdiamonds from garnet clinopyroxenites of the kokchetav massif northern kazakhstan and associated alluvial diamonds have been investigated using infrared spectroscopy all diamonds have high nitrogen contents from 747 up to 4488 20 at ppm and are of type ib iaa nitrogen data are consistent with a diamond formation over a narrow temperature range microdiamonds from garnet clinopyroxenites are characterized by water and carbonate inclusions similar to those ocurring in fibrous coated diamonds from kimberlite which suggest that diamonds grew from a c h o fluid in contrast alluvial microdiamonds do not contain any carbonate inclusions and h2o is absent or present in only minor amounts alluvial diamonds are considerably more n rich but have a similar range of nitrogen aggregation states it is suggested that alluvial diamonds belong to a separate diamond population compared with the microdiamonds from garnet clinopyroxenites the kokchetav microdiamonds are distinct from kimberlitic fibrous diamonds in that they contain abundant ib centres have high nitrogen contents and show different populations depending on host rock type these characteristics support a metamorphic origin for the microdiamonds from the uhpm rocks of the kokchetav massif

geochemistry and re os geochronology of the organic rich sedimentary rocks in the jingtieshan fe cu deposit north qilian mountains nw china abstract the jingtieshan group in the north qilian mountains nw china is dominantly composed of banded iron formations bifs copper deposits and organic rich sedimentary rocks ors carbonaceous phyllite x ray diffraction analysis of the ors shows the mineral assemblage to be quartz clay minerals the total organic carbon contents show a range of 0 44 1 72 here we present the results of the geochemistry and re os geochronology of the ors from the jingtieshan group the high values of chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and th u ratio indicate intense weathering the al 2 o 3 tio 2 zr sc th sc la th ratios high rare earth elements abundances light rare earth elements enrichment normalized to chondrite and distinctly negative eu anomalies suggest that the jingtieshan group ors were derived mainly from felsic volcanic units the new re os isochron age of 1308 100 ma 2 n 6 mswd 23 broadly overlap with the previous published ages determined using sm nd and u pb isotope systems the new age represents the depositional age of the jingtieshan group as well that of bif in the jingtieshan area furthermore the initial 187 os 188 os ratios 0 44 0 07 indicate that the os in the seawater was dominantly derived from hydrothermal fluids 75 the ce anomaly ce ce 0 95 1 00 and v v ni ratios 0 71 0 86 as well as the lack of enrichment in redox sensitive trace elements such as u v zn pb cu ni cr co and mn together with the presence of overlying bif suggest that the jingtieshan area represents a ferruginous deep water succession this and intense submarine hydrothermal activities contributed to the deposition of the jingtieshan bif

discrete and diffuse heat transfer atashes vent field axial volcano juan de fuca ridge abstract heat fluxes of discrete and diffuse components of hydrothermal discharge are estimated from submersible measurement in the ashes vent field located in the caldera of axial volcano on the central juan de fuca ridge the discrete component comprises discharge from individual vents and the diffuse component comprises seepage from large areas of the seafloor the investigation centered on the high temperature portion of the field a 100 100 m area of fractured lobate and sheet lava flows encompassing discrete discharge 326 c from seven individual vents and diffuse flow from intervening areas a total of 4 4 2 10 6 w was estimated for the discrete heat flux based on measurements of effluent temperature flow rate and orifice diameter at all the known individual vents by d s v alvin in september 1987 a total of 15 75 10 6 w was calculated with a standard plume model for the diffuse flux based on a grid of temperature measurements at altitudes of 1 m and 20 m above the study area using a 1 m long vertical array of temperature sensors mounted at the front of alvin s instrument platform the study indicates that 1 the diffuse component rises separately from the discrete component of hydrothermal discharge and is laterally advected by a prevailing current below the discrete component and that 2 the diffuse component of convective heat flux is approximately an order of magnitude greater than the discrete component in the high temperature portion of the ashes vent field

black smokers massive sulphides and vent biota at the mid atlantic ridge the discovery of black smokers massive sulphides and vent biota in the rift valley of the mid atlantic ridge demonstrates that this assemblage of hydrothermal phenomena is not limited to intermediate to fast spreading oceanic ridges hydrothermal exchange processes may thus be important at the ridges which extend through the atlantic ocean and western indian ocean comprising more than half of the 55 000 km global length of seafloor spreading centres

h type hybrid granitoids a proposed revision of the granite type classification and nomenclature abstract recent studies on calc alkaline plutonic rocks reveal field and petrographic relationships with strong implications for the processes involved in their genesis the presence of magmatic inclusions and magma mingling zones in these rocks supports an origin by magma mixing compositional variations and isotopic anomalies are a good test for such petrogenetic models most of these calc alkaline plutonic rocks which characterize both collision related and active plate margin environments have been classically identified as i igneous type granitoids following chappell and white s 1974 classification and then interpreted as derived from partial melting of older igneous rocks restite model if the magma mixing origin of a type of granitoids can be demonstrated from field and petrographic evidence and supported by chemical and isotopic variations the nomenclature must be changed in this sense the new category of h hybrid type is tentatively introduced it includes most of the so called i type granitoids and some of the s type as deduced from field relationships of magma mingling zones a mixing model is suggested that can operate on a large scale to explain the petrogenesis of the hercynian calc alkaline granodiorites of iberia finally a modified classification of common plutonic rocks in orogenic environments is proposed

sulfide mineralogy and redox conditions in some shergottites magmatic sulfide mineralogy has been studied in 2 olivine phyric shergottites dag 476 and sau 005 and 4 basaltic shergottites zagami shergotty los angeles and nwa 480 modal abundances of magmatic sulfides as estimated by image analysis on thin section are high 0 16 to 0 53 area percent and correlate positively with abundances of fe ti oxides sulfides are mesostasis minerals being mostly interstitial grains or locally enclosed in post cumulus melt inclusions e g sau 005 in olivine sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of cu sulfides chalcopyrite and or cubanite hot desert finds e g dag 476 show abundant fracture filling iron oxy hydroxides of probable terrestrial origin unaltered sulfides show metal rich hexagonal pyrrhotite compositions with metal sulfur m s ratio ranging between 0 936 0 005 and 0 962 0 01 this compositional range corresponds to the two phase structural domain 2c nc of the fe s system however the high temperature disordered hexagonal 1c pyrrhotite structure would be in better agreement with magnetic properties of shergottites ni contents in pyrrhotite increase from los angeles 0 05 at to shergotty zagami and nwa 480 0 2 0 5 at and dag 476 and sau 005 up to 3 at the higher ni values of pyrrhotite in olivine phyric shergottites correlate with the abundance of pentlandite exsolutions both reflecting more primitive ni rich sulfide liquids where abundant olivine crystallized this result and the strong correlation between sulfide abundances and fe ti oxides argue for a primary magmatic origin of these sulfides although they reproduce the trend of magmatic oxygen fugacity conditions determined from fe ti oxide pairs observed pyrrhotite compositions are systematically more metaldeficient compared to those calculated from the fe s o system this suggests post magmatic oxidation during cooling on mars followed by terrestrial weathering for hot desert finds

unusual upper mantle beneath guaniamo guyana shield venezuela evidence from diamond inclusions the geochemistry of mineral inclusions in diamond is an important source of information about the composition of the continental lithospheric mantle at depths exceeding 120 150 km at these depths two main types of geochemical environment support diamond formation they are ultramafic or peridotitic u type and eclogitic e type environments as shown by minerals that occur as inclusions in diamonds in primary diamond bearing kimberlite or lamproite rock the ratio of diamonds from these two geochemical environments varies widely between localities the u type environment dominates for the majority of diamond occurrences worldwide whereas the e type environment dominates for a very limited number of localities in south africa north america and australia the present study shows that an uncommonly high percentage 99 4 of e type diamonds with extremely variable inclusion assemblages is found in kimberlites in the northwestern part of the guyana shield at guaniamo venezuela these variations range from previously unknown silica undersaturated corundum eclogite to abundant silica rich coesite eclogite assemblages representing 22 of all e type diamonds some of which contain syngenetic ilmenite and magnetite the compositional variations of garnet and omphacite inclusions are extremely broad the wide variability of the eclogitic source in which diamonds formed beneath the guyana shield indicates a broadly basaltic chemistry in this environment which may represent ancient subducted oceanic crust such specific features have not been reported for any other diamond occurrence and reflect an unusual composition of the deep lithospheric mantle in this area

geochemistry zircon u pb dating and hf isotopies composition of paleozoic granitoids in jinchuan nw china constraints on their petrogenesis source characteristics and tectonic implication abstract granitoids are widely distributed in jinchuan at the southwestern margin of the north china plate which is also an important area of mineral deposits the research subject of this article are two paleozoic granitoids a cataclastic syenogranite and a granodiorite porphyry this study presents whole rock geochemistry and zircon u pb hf isotope data for the two granitoids to determine their petrogenesis source characteristics and tectonic significance the cataclastic syenogranite is characterized by metaluminous composition with high potassium and la n yb n from 39 to 48 the composition with strong negative eu anomalies and zircon saturation temperatures t zr from 947 to 1072 c classify this intrusion as an a type granite the granodiorite porphyry is metaluminous with high sodium sub alkaline la n yb n ratios from 27 to 32 these i type intrusions have no eu anomalies and t zr ranges from 818 to 845 c both the cataclastic syenogranite and granodiorite porphyry show enrichment of lree and lile and depletion of hree and hfse except hf and zr using single zircon la icp ms u pb dating the emplacement age of the cataclastic syenogranite and granodiorite porphyry are determined at 433 4 3 7 ma and 361 7 4 6 ma respectively zircons from the cataclastic syenogranits have uniform negative e hf t values 11 0 5 to 9 0 5 implying the involvement of an old palaeoproterozoic crustal source in magma genesis the zircons from the granodiorite porphyry have e hf t values that range from 8 1 0 to 10 0 6 suggesting heterogeneous source materials involving both juvenile and ancient crust reworked crustal components based on the geological significance of granites at the southwestern margin of the north china plate the closure of the north qilian ocean occurred at 444 ma geochemical features suggest that the cataclastic syenogranite and granodiorite porphyry formed in an intraplate extensional and compressional setting respectively hence after a period of extensional post collisional intraplate evolution strong compressive forces affected the area

blueschists in major suture zones of china blueschist facies rocks and c type eclogites occur as allochthonous terranes or as small tectonic blocks in almost all the accretionary fold belts and major suture zones within the interior of china and along the circum pacific and tethys himalayan belts at least forty blueschist localities have been described blueschists around the pacific margins and the himalaya alpine belts are mostly mesozoic in age only those in taiwan and new caledonia are cenozoic intracratonal blueschists of china are older than late permian when the collision amalgamation presumably occurred several alleged precambrian blueschist localities ye 1987 are shown in the recently published metamorphic map of china a precambrian blueschist belt in anhui hubei central china extends for about 2300 km however except for the pre sinian blueschist terrane in aksu the age determination for precambrian blueschist metamorphism elsewhere has not been confirmed characteristic features of chinese blueschists include the following 1 blueschist facies metamorphism predates the continental collision amalgamation 2 most blueschists have undergone multistage metamorphism commonly with increasing temperature and or decreasing pressure for later events 3 assemblages include sodic amphibole epidote albite quartz phengite chlorite sphene lawsonite jadeitic pyroxene and aragonite are not common and 4 protoliths are mainly mafic pelagic and clastic rocks blueschist facies metamorphism in china may be divided into two types on the basis of the imposed geothermal gradient hence the progressive change in mineral assemblage the rare lawsonite bearing blueschists produced at lower temperatures and higher pressures are confined to the inner mongolia and yarlung zangbo suture zones where aragonite and possibly jadeitic pyroxene quartz occur and the blueschists are associated with subgreenschist facies rocks most other blueschists of china formed at higher temperatures along the transitional blueschist greenschist facies boundary where epidote sodic and calcic amphiboles are ubiquitous and the blueschists are interlayered with greenschist facies rocks the common occurrence of intracratonal blueschists in major suture zones of china and elsewhere in eurasia indicates pre mesozoic subduction accretion of oceanic crust and flysch sediments these zones of accretion represent growth around the periphery of major precambrian cratons this fact together with the distribution of ophiolite belts and available paleomagnetic data provides evidence for an extremely mobile history of plate movement in eurasia however the paleozoic intracontinental blueschists and ophiolites of china have formed before rather than during final closure between cratons they do not usually mark the location of terminal sutures but are the result of earlier accretion and continental growth by subduction underplating and imbrication of oceanic materials similar to the accretion history of westernmost north america

unusual micro and nano inclusions in diamonds from the juina area brazil abstract a series of uncommon micro and nano inclusions has been identified in diamonds from the rio soriso placer deposit in mato grosso state brazil the micro inclusions are variable in size from 1 to 300 m usually they are polymineralic being formed predominantly by intergrowths of carbonates silicates and other minerals carbonates are represented mostly by dolomite and occasionally by calcite silicates found are coesite wollastonite ii cuspidine and monticellite sulphides and ilmenite form micro inclusions as well nano inclusions are different from micro inclusions not only in size not exceeding 200 nm they are usually included in micro inclusions among nano inclusions halides nacl kcl cacl2 and pbcl2 anhydrite spinel phlogopite pbo2 tio2 with an pbo2 structure native fe and other phases are identified all these minerals are of the eclogitic association they are either associated with coesite or are included in a diamond with a light organic carbon isotopic composition with 13c from 14 to 25 pdb this confirms our earlier conclusion that diamonds from the juina area may have formed as a result of subduction of the crustal material to depths of at least the lower transition zone or even the lower mantle the pressure estimates for the investigated diamonds vary in a range from 3 to 10 gpa an interesting assemblage of calcite cuspidine wollastonite monticellite fluid identified in one of the studied diamonds is considered as a product of a reaction of wollastonite fluid forming cuspidine monticellite the presence of numerous pores cavities and bubbles in mineral inclusions and identification of an association of volatile containing mineral inclusions such as halides nacl kcl cacl2 and pbcl2 fluorine containing silicate cuspidine and phlogopite emphasize the important role of volatiles particularly chlorine and fluorine in the formation of the diamonds

micrometer scale cavities in fibrous and cloudy diamonds a glance into diamond dissolution events abstract micrometer sized internal cavities in diamonds preserve evidence of diamond dissolution events combining the methods of focused ion beam fib sample preparation and transmission electron microscopy tem enables these features to be studied in detail micrometer scale cavities are found in the inner parts of fibrous and cloudy kimberlitic diamonds their filling consists of amorphous matrix secondary nano crystals volatiles and in some cases larger resorbed crystals trapped minerals include corundum kappa alumina quartz olivine moissanite 6h and ca mg carbonates this is the first observation of kappa alumina in nature secondary nano minerals are observed within the amorphous matrix and include carbonates al oxide fluorite ilmenite and secondary diamond crystals the amorphous matrix is spongy and its composition is dominated by amorphous carbon nitrogen chlorine and also contains water when no crystalline phases are observed the matrix is also enriched in alumina silica and in some cases calcium we propose that micrometer scale cavities in diamonds form during dissolution events induced by the introduction of oxidizing hydrous fluids into the diamond growth area hydrous fluids are the main dissolving agents for most kimberlitic diamonds fedortchouk y canil d semenets e 2007 mechanisms of diamond oxidation and their bearing on the fluid composition in kimberlite magmas am mineral 92 1200 1212 at diamond forming conditions silica and alumina are enriched in hydrous fluids that are in equilibrium with eclogites kessel r ulmer p pettke t schmidt m w thompson a b 2005 the water basalt system at 4 to 6 gpa phase relations and second critical endpoint in a k free eclogite at 700 to 1400 c earth planet sci lett 237 873 892 this is consistent with the increased solubility of alumina with increased pressure and temperature in the na cl bearing fluids manning c e 2006 mobilizing aluminum in crustal and mantle fluids j geochem explor 89 251 253 manning c e 2007 solubility of corundum kyanite in h2o at 700c and 10 kbar evidence for al si complexing at high pressure and temperature geofluids 7 258 269 additionally hydrous fluids may leach grain boundaries that are enriched in alumina in peridotitic environments hiraga t anderson i m kohlstedt d l 2004 grain boundaries as reservoirs of incompatible elements in the earth s mantle nature 427 699 703 wirth r 1996 thin amorphous films 1 2 nm at olivine grain boundaries in mantle xenoliths from san carlos arizona contrib mineral petrol 124 44 54 diamond dissolution will form oxidized carbon species and may decrease the solubility of silica and alumina in the dissolving agent leading to their precipitation diamond forming fluids that are trapped in sub micrometer inclusions in the same fibrous diamonds are the dominant fluid component in the diamond growth area corrosive hydrous fluids are less common and appear as short discrete events followed by the return of the common diamond forming fluids and continued diamond precipitation

nano inclusion suite and high resolution micro computed tomography of polycrystalline diamond framesite from orapa botswana abstract a single polycrystalline diamond aggregate from the orapa kimberlite botswana contains a syngenetic micro and nano inclusion suite of magnetite pyrrhotite omphacite garnet rutile and c o h fluid in order of abundance this suite of inclusions is distinctly different from those in fibrous diamonds although the presence of sub micrometer fluid inclusions provides evidence for a similarly important role of fluids in the genesis of polycrystalline diamond it is the first study of polycrystalline diamond by high resolution ct computed tomography reaching a resolution of 1 3 m using polychromatic x rays combined with focused ion beam assisted transmission electron microscopy the method reveals epigenetic replacement coatings of hematite and late stage sheet silicates around the magnetites showing that magnetites are often but not always interstitial to the diamond and thus were open to late stage overprinting it is proposed that the polycrystalline diamond formed by a redox reaction between a small scale carbonatitic melt and a sulfide bearing eclogite the water released from the melt during diamond precipitation fluxed local melting of the surrounding eclogite and oxidation of sulfide phases to magnetite which mingled with the carbonatitic melt and re precipitated locally

characteristics of hydrothermal plumes from two vent fields on the juan de fuca ridge northeast pacific ocean deep ctd transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally buoyant plumes emanating from each of two major vent fields on the southern symmetrical segment sss and endeavour segment es of the juan de fuca ridge at both vent fields emissions from point and diffuse hydrothermal sources coalesced into a single 200 m thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0 02 0 05 c and light attenuation anomalies of 0 01 0 08 m 1 10 80 g l above background temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped 10 15 km downcurrent light attenuation trends were non uniform and differed between plumes apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates vent fluids from the sss are metal dominated and mostly precipitate very fine grained hydrous fe oxides that remain suspended in the plume vent fluids from the es are sulfur dominated and precipitate a high proportion of coarser grained fe sulfides that rapidly settle from the plume the integrated flux of each vent field was estimated from measurements of the advective transport of each plume heat flux was 1700 1100 mw from the es and 580 351 mw from the sss particle flux varied from 546 312 g s to 204 116 g s at the es depending on distance from the vent field and was 92 48 g s from the sss

diamond inclusions in garnets from metamorphic rocks a new environment for diamond formation diamonds commonly occur in kimberlites lamproites and alluvial sediments derived from these rocks more recently diamonds or their graphite pseudomorphs have been discovered in ultramafic massifs1 and picrites2 here we report the occurrence of diamonds in situ in crustal rocks highly retrograded high pressure metamorphic garnet pyroxene and pyroxene carbonate garnet rocks biotite gneisses and schists from the kokchetav massif northern kazakhstan ussr the diamonds are cubo octahedral averaging 12 m in size and occur in zircons and with euhedral graphite as inclusions in unzoned garnets we believe that the zircon and garnet matrices protected these diamonds from retrogressive transformation to graphite mica rutile titanite clinopyroxene kyanite and zircon also occur as inclusions in garnet often intergrown with the diamonds equilibration relations of inclusions and host garnets indicate that both diamonds and graphite crystallized from a fluid phase under static conditions at pressures of 40 kbar and temperatures 900 1 000 c

hydrothermal activity and sulphide formation in axial valleys of the east pacific rise crest between 18 and 22 s abstract deep grabens some 90 m in depth occur on the crest of the east pacific rise between 17 9 and 18 6 s and between 21 1 and 21 7 s and are found within the topographic highs in these regions along the rise axis these axial valleys mark areas of recent faulting and intensive hydrothermal activity which is associated with the formation of metalliferous sediments and of massive sulphides of iron copper and zinc most iron and manganese released from the ore fluids continues to be deposited outside the grabens preferentially on the western flank of the rise a tendency which can be recognised also in older sediments of this area

trace elements in sulfide inclusions from yakutian diamonds sulfide inclusions in diamonds may provide the only pristine samples of mantle sulfides and they carry important information on the distribution and abundances of chalcophile elements in the deep lithosphere trace element abundances were measured by proton microprobe in 50 sulfide inclusions sdi from yakutian diamonds about half of these were measured in situ in polished plates of diamonds providing information on the spatial distribution of compositional variations many of the diamonds were identified as peridotitic or eclogitic from the nature of coexisting silicate or oxide inclusions known peridotitic diamonds contain sdis with ni contents of 22 36 consistent with equilibration between olivine monosulfide solid solution mss and sulfide melt whereas sdis in eclogitic diamonds contain 0 12 ni a group of diamonds without silicate or oxide inclusions has sdis with 11 18 ni and may be derived from pyroxenitic parageneses eclogitic sdis have lower ni cu and te than peridotitic sdis the ranges of the two parageneses overlap for se as and mo the mo and se contents range up to 700 and 300 ppm respectively the highest levels are found in peridotitic diamonds among the in situ sdis significant zn and pb levels are found in those connected by cracks to diamond surfaces and these elements reflect interaction with kimberlitic melt significant levels of ru 30 1300 ppm and rh 10 170 ppm are found in many peridotitic sdis sdis in one diamond with wustite and olivine inclusions and complex internal structures have high levels of other platinum group elements pges as well and high chondrite normalized ir pd comparison with experimental data on element partitioning between crystals of monosulfide solid solution mss and sulfide melts suggests that most of the inclusions in both parageneses were trapped as mss while some high cu sdis with high pd rh may represent fractionated sulfide melts spatial variations of sdi composition within single diamonds are consistent with growth histories shown by cathodoluminescence images in which several stages of growth and resorption have occurred within magmatic environments that evolved during diamond formation

measurements of plume flow from a hydrothermal vent field simultaneous velocity temperature and conductivity data were taken in the convective flow emanating from a hydrothermal vent field located at 10 56 n 103 41 w on the east pacific rise the horizontal profiles obtained indicate that the flow field approaches an ideal plume in the temperature and velocity distribution such parameters as total heat flow and maximum plume height can be estimated using either the velocity or the temperature information the results of these independent calculations are in close agreement yielding a total heat flow from this vent site of 3 7 0 8 mw and a maximum height of 150 10 m the nonlinear effects of large temperature variations on heat capacity and volume changes slightly alter the calculations applied to obtain these values

manganese geochemistry near high temperature vents in the mid atlantic ridge rift valley in july 1985 the first high temperature hydrothermal vents ever discovered on the mar were found at 26 n tag a transponder navigated survey of a 4 8 km area was begun when on board measurements of manganese revealed concentrated hydrothermal plumes in the water column comparable in size and intensity to those found over geothermal fields on the epr these plumes also possess anomalously high light scattering properties and anomalously warm potential temperatures using relay transponder navigation with a rosette ctd system it was possible to sample bottom waters with temperature anomalies of several decidegrees samples collected near vent orifices possessed silica anomalies of up to 17 m and dissolved manganese anomalies as large as 360 nmol kg these manganese and silica anomalies are linearly related and predict amn si ratio of 20 mmol mol for these mar vent fluids a value essentially identical to that measured in 350 c fluid from the epr at 21 n the distribution of temperature anomalies in the water column over this area requires the presence of more than one active vent site a rough estimate of the convective heat loss from this section of the mar based on z profiles is 1 2 108 cal s which is similar to the heat loss estimated for the vent field on the epr at 21 n

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

first find of polycrystalline diamond in ultrahigh pressure metamorphic terrane of erzgebirge germany this article describes polycrystalline diamond from the erzgebirge ultrahigh pressure metamorphic uhpm terrane of the bohemian massif related to the variscan 340 ma continent continent collision the foils polycrystalline diamond included in zircon were prepared with focused ion beam fib and studied with transmission electron microscopy tem each domain of the polycrystalline diamond consisted of a series of diamond monocrystals from 1 to 4 up to 15 containing numerous nanometric fluid and crystalline inclusions of sio2 caco3 kcl and kalsi3o8 the integrated chemistry of the nanoinclusions suggests that the polycrystalline diamond was crystallized from a mixture of two end members which includes a carbon rich hydrous silicic fluid containing si al k and a hydrous saline fluid rich in cl k na traces of carbonate sulphate and phosphate coupled with the presence of metallic cations such as fe mg ti cr co zn zr pb as and hg found in the diamond are coherent with the local geochemical diversity of the host metasedimentary rocks the oxidation state of the diamond forming fluid was close to c co buffer for example fo2 6 log units which is at the upper limit of the diamond stability region the presence of dislocation arrays indicating low angle grain boundaries together with zig zag features or kinks at diamond grain boundaries reflects rapid crystallization of the polycrystalline diamond triangular fluid pockets with steps at the surface related to 110 and 111 planes of diamond could promote the formation of c h and c oh bonds that probably could facilitate the process of diamond graphitization the microstructural features of polycrystalline diamond from the erzgebirge uhpm terrane as well as their undisputed formation from crustal organic carbon can be used for better understanding of the origin of any polycrystalline diamond formation from both kimberlitic and alluvial sources including enigmatic polycrystalline black diamond commonly called carbonado

high pressure fluids in the system mgo sio 2 h 2 o under upper mantle conditions fluids and melts have been trapped and analysed in high pressure experiments in the model mantle system mgo sio2 h2o at 6 to 10 5 gpa and 900 to 1 200 c the fluid melt traps consisted of a diamond layer that was added to the experimental charge and was separate from the silicate phases the recovered diamond traps were analysed by laser ablation icp ms starting materials were synthetic mixtures of brucite talc and silica with variable mg si containing 11 31 wt h2o experiments on a serpentine starting composition mg3si2o5 oh 4 result in mgo sio2 weight ratios in the subsolidus fluids close to 1 at 6 gpa and close to 2 at 9 gpa melt compositions at 6 and 9 gpa have mgo sio2 ratios close to that of forsterite at a single pressure the amount of dissolved silicate in the fluid increases steadily with increasing temperature up to 1 150 c where a sudden increase of both sio2 and mgo is observed this discrete step marks the solidus which is more clearly developed at 6 than at 9 gpa thus hydrous melts within the model mantle subsystem mg2sio4 mg2si2o6 h2o are chemically distinct from aqueous fluids up to at least 9 gpa corresponding to 300 km depth extrapolation of the current data set implies that total convergence between fluid and melt along the solidus probably occurs at 12 13 gpa 400 km i e close to the earth s mantle transition zone beneath cratons interactions of hydrous fluids with upper mantle lithologies cause relative silica depletion olivine enrichment at depths greater than 200 km and silica orthopyroxene enrichment at shallower depths