the messinian event on the margin of the mediterranean sea in the nice area southern france abstract seismic reflection profiles have been used to map the messinian erosion surface and associated basin margin deposits on the continental margin off nice a palaeovalley extends seaward from the incised var palaeovalley mapped on land the lower part of this valley is filled by an acoustically incoherent unit with a flat top and steep slope into the basin this unit is interpreted as a coarse grained deltaic deposit that accumulated synchronously with the upper messinian evaporites in a ponded lake basin two submersible dives on strategic outcrops supported the interpretation of the seismic profiles we examined and sampled outcrops of probably early tertiary sandstones underlying the messinian erosion surface and of a fining up predominantly conglomeratic sequence that fills messinian channels on the continental slope and probably overlies the deltaic deposits these conglomerates pass up into early pliocene marls and have turbidite sedimentary structures these are prodeltaic deposits formed during the transgression at the end of the messinian based on seismic facies mapping sampling and submersible observations a palaeogeographic reconstruction of the area is proposed a basal erosion surface including the var palaeovalley represents extreme dessication of the western mediterranean and was followed by accumulation of the main messinian salt following this a lake was ponded in the ligurian basin with accumulation of evaporites and shales a gilbert type delta prograded into the basin from the var palaeovalley relative sea lake level lowering is estimated to be about 1200 m at this time there has been little faulting on the margin since the early pliocene transgression but there is estimated to have been about 800 m of flexural subsidence due to both thermal subsidence and water loading

crystallization environment of kazakhstan microdiamond evidence from nanometric inclusions and mineral associations nanometric solid inclusions in diamond incorporated in garnet and zircon from felsic gneiss of the kokchetav massif kazakhstan have been examined utilizing electron microscopy and focused ion beam techniques host garnet and zircon contain numerous pockets of multiple inclusions which consist of 1 3 diamond crystals intergrown with quartz phengite phlogopite albite k feldspar rutile apatite titanite biotite chlorite and graphite in various combinations recalculation of the average chemical composition of the entrapped fluid represented by multiple inclusion pockets indicates that such fluid contained a low wt of sio2 suggesting a relatively low temperature fluid rather than a melt transmission electron microscopy revealed that the diamond contains abundant nanocrystalline inclusions of oxides rare carbonates and silicates within the 15 diamond crystals studied abundant inclusions were found of sio2 tio2 f e xoy c r 2o3 zrsio4 and single grains of thxoy baso4 mgco3 fecr2o4 and a stoichiometric fe rich pyroxene the diversity of trace elements within inclusions of essentially the same stoichiometry suggests that the kokchetav diamond crystallized from a fluid containing variable amounts of si fe ti cr zr ba mg and th and other minor components such as k na p s pb zn nb al ca cl most of the components in crystals included in diamond appear to have their origin in the subducted metasediments but some of them probably originate from the mantle it is concluded that kokchetav diamond most likely crystallized from a coh rich multicomponent supercritical fluid at a relatively low temperature hence the apparently low content of rock forming elements and that the diversity of major and minor components suggests interactions between subducted metasediments and mantle components

fluid rock interactions during uhp metamorphism a review of the dabie sulu orogen east central china comprehensive review on the characteristics of petrology oxygen isotope fluid inclusion and nominally anhydrous minerals nams for many dabie sulu ultrahigh pressure uhp metamorphic rocks including drill hole core samples reveals that fluid has played important and multiple roles during complicated fluid rock interactions attending the subduction and exhumation of supracrustal rocks we have identified several distinct stages of fluid rock interactions as follows 1 the neoproterozoic supercrustal protoliths of uhp rocks experienced variable degrees of hydration through interactions with cold meteoric water with extremely low oxygen isotope compositions during neoproterozoic snow ball earth time 2 a series of dehydration reactions took place during triassic subduction of the yangtze plate beneath the sino korean plate the released fluid entered mainly into volatile bearing high pressure hp and uhp minerals such as phengite zoisite epidote talc lawsonite and magnesite as well as into uhp nams such as garnet omphacite and rutile 3 silicate rich supercritical fluid hydrous melt existed during the uhp metamorphism at mantle depths 100 km which mobilized many normally fluid immobile elements and caused unusual element fractionation 4 the fluid exsolved from the nams during the early exhumation of the dabie sulu terrane was the main source for hp hydrate retrogression and generation of hp veins 5 local amphibolite facies retrogression at crustal depths took place by infiltration of aqueous fluid of various salinities possibly derived from an external source 6 the greenschist facies overprinting and low pressure lp quartz veins were generated by fluid flow along ductile shear zones and brittle faults during late stage uplift of the uhp terrane

seismic evidence for a complex slide near the wreck of the titanic model of an instability corridor for non channeled gravity events abstract the continental rise southeast of the grand banks of newfoundland was surveyed many times during the last 8 years especially during the search area for the wreck of the titanic high resolution sidescan sonar images systeme acoustique remorque sar have shown an area characterised by complex surficial morphology referred to as in instability corridor new seismic reflection profiling has shown that the instability corridor is more extensive than was previously believed and that it is the expression of the distal part of a large sediment slide it consists of upslopedipping imbricated sediment blocks which are tens of metres thick and many kilometres in length downslope from the slide is an acoustically incoherent unit interpreted as comprising debris flow deposits which could represent the final phase of evolution of the slide the slide is blanketed by 5 10 m of younger sediment the upper part of this blanket has been recovered by coring and consists of foram ooze thin sandy turbidites and muddy beds with mudstone clasts radiocarbon dating and foram assemblages show that the upper metre of the core is late holocene in age with about eight resedimented beds forming in the last 4000 years these recent turbidity currents cut erosional furrows and refresh the pre existing steps of the slide three phases characterise the evolution of the instability corridor 1 the major event involving a giant slide of bedded sediments up to 100 m thick with a source probably on the steep continental slope of the grand banks 100 km to the north 2 a draping of normal continental margin terrigenous sediments and 3 erosion by one or a series of high density turbidity currents the giant slide created an instability corridor within which a number of channeled and non channeled events took place during the late holocene

lead and bromine enrichment in eclogite facies fluids extreme fractionation during lower crustal hydration hydration reactions associated with eclogite facies metamorphism of granulites in the norwegian caledonides led to the formation of saline brines with exceptional compositions primary omphacite and garnet hosted fluid inclusions from norwegian eclogites formed by hydration of granulites contain a plethora of solid phases a total of 18 different minerals have been identified in multiphase brines and 12 of these occur at the badsholmen locality in sunnfjord fluid inclusions from this locality are characterized by a high br cl mass ratio 0 03 and extreme pb enrichment as demonstrated by the presence of pb bearing daughter minerals including galena a pb cl bearing phase and a pb cl br bearing phase the fluid compositions may reflect enrichment of elements incompatible with the silicate structure during consumption of h 2 o by eclogite forming hydration reactions pb is believed to have been scavenged from the parent granulite by the increasingly saline brine during k feldspar breakdown

high salinity fluid inclusions formed from recycled seawater in deeply subducted alpine serpentinite abstract the origin of high pressure brines has been investigated in the erro tobbio peridotite western alps a mantle slice that was exposed to the seafloor of the mesozoic ligurian piedmontese tethys and was later involved in alpine subduction hydrothermal alteration by seawater derived fluids led to replacement of the mantle assemblage by cl bearing serpentine 0 35 wt cl brucite 0 2 wt cl and alkali bearing phyllosilicates 0 2 wt cl 0 2 0 55 wt na2o 1 5 wt k2o relics of these hydrous phases occur in olivine titanian clinohumite antigorite assemblages formed at 2 5 gpa and 550 600 c during partial devolatilization and veining of the hydrothermally altered peridotite the high pressure phases lack chlorine and alkalis and are coeval with fluid inclusions trapped in the syn eclogitic veins the inclusions are salt saturated and contain up to 50 wt cl na k mg and fe high fluid chlorinity was probably achieved during rehydration of relict mantle minerals and deposition of hydrous phases in the veins the data presented suggest that the seafloor hydrothermal signature was inherited by the eclogitic fluid due to partitioning of chlorine and alkalis into the fluid phase the presence of salty brines in eclogitized hydrous peridotites can indicate deep recycling of seawater derived fluids hydrous ultramafic systems can therefore act as large scale carriers of seawater into the mantle

advances in marine chemistry 1979 1982 these four years saw advances in many areas further developments in sampling and analytical techniques have opened new avenues of exploration for trace elements and particulate matter the impact of the geosecs expedition was further felt in the field of marine chemistry as the results were still being published a major field effort occurred as a follow on to the geosecs work tto and intensive sampling was performed in the newly discovered submarine hydrothermal vent fields an important and unresolved controversy has arisen regarding the ability to measure preformed co2 in the seawater system in many respects the field of marine chemistry appears to be gaining a momentum spurred by both improvements in analytic techniques and an increasing social and economic relevance

experimental evidence for diamond facies metamorphism in the dora maira massif the peak metamorphic conditions of subducted continental crust in the dora maira massif western alps have been revised by combining experimental results in the kcmash system with petrologic information from whiteschists textural observations in whiteschists suggest that the peak metamorphic assemblage garnet phengite kyanite coesite talc originates from the reaction kyanite talc garnet coesite liquid in the experimentally determined petrogenetic grid this reaction occurs above 45 kbar at 730 c at lower pressures talc reacts either to orthopyroxene and coesite or together with phengite to biotite coesite and kyanite the liberated liquid contains probably similar amounts of h2o and dissolved granitic components the composition of the liquid in the whiteschists at peak metamorphic conditions a major unknown in earlier studies was probably very similar to the liquid composition produced in the experiments therefore the experimentally determined petrogenetic grid represents a good model for the estimation of the peak metamorphic conditions in whiteschists experimentally determined si isopleths for phengite further constrain peak pressures to 43 kbar for the measured si 3 60 of phengite in the natural whiteschists all these data provide evidence that the whiteschists reached diamond facies conditions the fluid absent equilibrium 4 kyanite 3 celadonite 4 coesite 3 muscovite pyrope has been calibrated on the basis of garnet and phengite compositions in the experiments and serves as a geothermobarometer for ultra high pressure uhp metapelites for graphite bearing metapelites and kyanite phengite eclogites forming the country rocks of the whiteschists peak metamorphic pressures of about 44 3 kbar were calculated from this barometer for temperatures of 750 c estimated from garnet phengite thermometry therefore the whole ultra high pressure unit of the dora maira massif most likely experienced peak metamorphic conditions in the diamond stability field while graphite is common in the metapelites diamond has not been found so far the absence of metamorphic microdiamonds might be explained by the low temperature of metamorphism the absence of a free fluid phase in the metapelites and a short residence time in diamond facies conditions resulting in kinetic problems in the conversion of graphite to diamond

salt rich aqueous fluids formed during eclogitization of metabasites in the alpine continental crust austroalpine mt emilius unit italian western alps abstract the metabasite bodies of the mt emilius continental unit western italian alps underwent a stage of alpine eclogite facies metamorphism 1 1 1 3 gpa and 450 550 c accompanied by polyphase deformation and recrystallization the metabasites consist of two main rock types 1 eclogites omphacite garnet glaucophane epidote phengite paragonite preserving no relics of their precursors 2 eclogitized granulites i e rocks whose incomplete eclogitic recrystallization clinopyroxene ii garnet ii epidote amphibole chlorite allowed survival of textural and mineralogical relics of pre alpine granulitic assemblages clinopyroxene i garnet i plagioclase amphibole in this latter case the pre alpine granulites were converted to eclogites as the result of infiltration of aqueous fluids during eclogitization in both eclogites and eclogitized granulites hydrated high pressure foliations are cut by eclogitic metamorphic veins the bulk rock chemistry of the metabasites influenced the compositions of both the vein and rock forming clinopyroxenes and the compositional correlation between the vein and rock forming clinopyroxenes indicates that the syn eclogitic fluids have re equilibrated with the metabasite hosts the predominant vein minerals omphacite epidote and garnet contain primary high salinity fluid inclusions the fluids consist of two phase liquid vapour and of multiphase liquid vapour salt additional quartz salty aqueous inclusions containing nacl cacl 2 and mgcl 2 as the main chloride species the vein inclusions show a salinity range from 17 to 45 wt salts in eclogites and from 20 to 50 wt salts in eclogitized granulites in contrast fluid inclusions in matrix minerals of the eclogitized granulites contain primary two phase inclusions displaying a salinity range between 10 and 25 wt salts the marked difference in fluid salinities recorded by the inclusions in the eclogitic veins and those in the partially re equilibrated eclogitized granulites is interpreted in terms of progressive hydration during eclogitization of granulite facies rocks which caused an increase in the salt content of the residual inclusion fluids

microdiamond daughter crystals precipitated from supercritical coh silicate fluids included in garnet erzgebirge germany microdiamonds associated with phlogopite quartz paragonite phengite apatite and rutile are found as regular constituents of minute polyphase inclusions in garnet of ultrahigh pressure p metamorphic gneiss lenses within migmatites of the gneiss eclogite unit erzgebirge germany these aggregates are interpreted to represent original inclusions of a supercritical dense coh fluid rich in k na and sio 2 from this fluid diamond was precipitated as a daughter crystal due to cooling at ultrahigh p conditions brittle failure of the garnet host due to overpressure during release of confining pressure is demonstrated by healed radial cracks during further cooling the silicate phase assemblage of the inclusions crystallized at reduced internal pressures outside the stability field of diamond as indicated by the presence of quartz paragonite and plagioclase it is proposed that the mica dominated mineral assemblage of the inclusions formed by reaction between the fluid and the garnet host the previously formed diamond daughter crystals being preserved metastably these diamond bearing inclusions provide an unequivocal record of dense supercritical coh fluids rich in alkalies and silica within subducted continental crust during ultrahigh p metamorphism

multiphase solid inclusions in uhp rocks su lu china remnants of supercritical silicate rich aqueous fluids released during continental subduction abstract primary multiphase solid ms inclusions without preserved fluid are found within peak minerals in kyanite quartzite topaz and kyanite phengite epidote eclogite from donghai area su lu terrane typical mineral association in inclusions is paragonite muscovite anhydrite corundum alunite type sulphate zircon calcite chlorite sio 2 barite pyrite apatite in quartzites and paragonite rutile apatite amphibole zn staurolite magnetite plagioclase zircon pyrite alunite type sulphate zn mg fe al ti spinel in eclogites on the basis of the fluid inclusion textures and of the daughter phase assemblage calculated fluid composition is as follows in quartzites 24 wt sio 2 30 wt al 2 o 3 9 wt cao 5 wt k 2 o 3 wt na 2 o 11 wt so 3 18 wt h 2 o with traces of tio 2 fe 2 o 3 feo mgo bao p 2 o 5 cl f and co 3 2 and in eclogites 26 wt sio 2 21 wt tio 2 20 wt al 2 o 3 2 wt mgo 4 wt feo 6 wt fe 2 o 3 7 wt cao 3 wt na 2 o 3 wt p 2 o 5 7 wt h 2 o 1 wt cl and traces of zno mno k 2 o so 3 and f originally trapped chloride poor aqueous fluids contained very high amounts in the order of tens of wt of si 4 al 3 and ti 4 solute species reflect the chemical composition of the host rocks mg 2 fe 2 ti 4 p 5 and na are abundant in the fluids present in eclogites while fluids are enriched in al 3 k na so 4 2 co 3 2 in quartzites we propose that multiphase solid inclusions represent remnants of high density supercritical silicate rich aqueous fluids that were in equilibrium with peak minerals at uhp conditions these fluids show characters which are transitional between aqueous fluids and silicate melts and were probably produced by dehydration reactions of the host rocks during the latest stages of subduction

le canyon du var case study of a modern active proximal channel the var canyon and the continental slope along the french riviera were investigated using sar a new deeply towed high resolution side scan sonar and 3 5 khz subbottom profiler package later on a ground truth operation using the cyana submersible and kuellenberg cores provided in situ observations and samples the main characteristics of this area are the narrow shelf the steep continental slope and very coarse superficial materials during the pliocene an alluvial cone was built on the floor of a deep ria located at the present var alluvial plain this detritic cone overlies the messinian erosion surface it is totally submarine and formed by pudding stones conglomerates and marls since the early quaternary this large sedimentary body has been dismantled by gravity processes mass wasting debris flows turbidites the bed form at the head of the var valley 500 m depth is marked by an anastomosed network eroding the spurs that give the typical herringbone facies of the canyon s flanks downslope from this area begins a gravel wave field extending to a water depth of 2 100 m wavelength and height appear to be directly controlled by the topography downward and according to a break in the slope the sea floor is characterized by amore rhythmic alternance of gravel fields and mud fields to 2 400 m the muddy areas are always located on relatively high points of the sea bottom the significance of these bed forms will be discussed and related to the sedimentary processes which may have operated in this area less

halogen contents of eclogite facies fluid inclusions and minerals caledonides western norway primary multiphase brine fluid inclusions in omphacite and garnet from low to medium temperature eclogites have been analysed for cl br i f li and so4 halogen contents and ratios provide information about trapped lower crustal fluids even though the major element na k ca contents of inclusion fluids have been modified by fluid mineral interactions and step daughter crystal formation after trapping halogens in the inclusion fluids were analysed with crush leach techniques cl br and cl i mass ratios of eclogite fluids are in the range 31 395 and 5000 33 000 respectively most fluids have a cl br ratio lower than modern seawater and a cl i ratio one order of magnitude lower than modern seawater fluids with the lowest cl br and highest cl i ratios come from an eclogite that formed by hydration of granulite facies rocks and may indicate that br and i are fractionated into hydrous minerals reconstructions indicate that the inclusion fluids originally contained 500 4000 ppm br 1 14 ppm i and 33 438 ppm li electron microprobe analyses of eclogite facies amphibole biotite phengite and apatite indicate that f and cl fractionate most strongly between phengite f cl mass ratio of 1469i1048 and fluid f cl mass ratio of 0 008 and the least between amphibole and fluid the chemical evolution of cl and br in pore fluids during hydration reactions is in many ways analogous to cl and br in seawater during evaporation the cl br ratio remains constant until the ah2o value is sufficiently lowered for cl to be removed from solution by incorporation into hydrous minerals

antipathetic magnesium manganese relationship in basal metalliferous sediments abstract basal metalliferous sediments from sites 77b 80 and 81 of the deep sea drilling project represent mixtures of pelagic clay biogenic ooze and a metalliferous component of hydrothermal origin the metalliferous end member of the sediments displays a strong inverse relationship r 0 88 between mg and mn mg is most likely tied up in an x ray amorphous mg silicate sepiolite whereas mn occurs almost exclusively in an oxide phase precipitation of the mg rich phase is favored by high flow rates and limited mixing of the hydrothermal end member source of silica with seawater source of mg under those conditions much of the hydrothermal mn2 with its slow oxidation kinetics may escape to the free water column in contrast in highly diluted hydrothermal fluids which provide a source solution for mn rich sediments dissolved silica is diluted below saturation with respect to sepiolite the separation of the mn and mg phases may be further compounded by hydraulic fractionation

trace element rich brines in eclogitic veins implications for fluid composition and transport during subduction primary and pseudosecondary fluid inclusions occur in oscillatory and sector zoned omphacite in eclogitic veins from the monviso ophiolitic complex in the western alps the inclusions contain aqueous brines and daughter crystals of halite sylvite calcite dolomite albite anhydrite and or gypsum barite baddeleyite rutile sphene fe oxides pyrite and monazite this daughter mineral suite indicates high solubilites of na k ca mg fe zr ti p ba ce la th and s species and provides direct evidence for transport of high fieldstrenght large ion lithophile and light rare earth elements as dissolved species during subduction fluid inclusion heterogeneities preserved within and between adjacent grains in the veins however suggest that the scale of fluid equilibration was small a crack seal geometry in some of the veins implies that fluid release in pulses rather than steady flow controlled mineral deposition and growth in the veins from these observations we develop a model of fluid release and entrapment in which pulses of fluid are associated in time with increments of shear and tensile failure the rate of fluid release and the reduction in porosity both depend on the rate of plastic flow vein fluids may initially be derived from decreptitation of early fluid inclusions in the host eclogites small scale fluid heterogeneities implied by the fluid inclusions in the veins are best interpreted in terms of limited fluid flow and hence limited metasomatism we conclude that element recycling into the mantle wedge during subduction will depend at least as strongly on fluid transport mechanisms as on element solubilities in the fluid phase at monviso despite evidence for high trace element solubilities in saline brines the elements were not removed from the downgoing slab prior to teaching depths of 40 km

fluid melt rock interaction in mafic eclogites and coesite bearing metasediments constraints on volatile recycling during subduction the question as to whether the metasomatizing slab agent needed to form island arc magmas is an aqueous fluid or a hydrous melt requires a knowledge of fluid melt rock interaction during high pressure low temperature metamorphism in the western alps typical anhydrous mafic eclogites monviso massif and coesite bearing metasediments dora maira massif have experienced a prograde p t path characteristic of a mature cold subduction zone microstructural petrologic geochemical and fluid inclusion studies show that fluid flow was limited during eclogite and high grade blueschist facies metamorphism most of the fluids were driven off the rocks at pressures lower than 1 and 1 6 gpa respectively with increasing pressure and temperature the remaining fluid phase was released during crystal plastic flow processes or devolatilisation reactions but retain the host rocks to form veins partial melts or dense hydrous silicates tectonic erosion at modern convergent margins delivers large amounts of terrigenous sediments kmash system in subduction zones in contrast to the basalt and peridotite systems the kmash system is characterized by a wide range of pressure sensitive reactions which allow the reconstruction of dehydration hydration depths in the subducted slab independently of the thermal structure of subduction zones terrigenous sediments will begin to melt at pressures 2 gpa the melt phase can absorb tremendeous quantities of water and represent major sinks for devolatilisation fluids dense hydrous silicates will form in any subducted sediments at all depths these silicates can store significant amount of water in their structure in the subducted oceanic crust and upper mantle heterogeneous distribution of fluids inherited from hydrothermal alteration at mid ocean ridges will cause contemporaneous dehydration and hydration reactions on a local scale rather than large scale fluid infiltration in the overlying mantle wedge the situation where a cold competent and fluid rich subducted slab is bounded above by a hot relatively weak and anhydrous material is likely to act against buoyant rise of devolatilisation fluids by forcing the fluids to flow downwards at sub arc depths 50 10 to 80150 km and for any geothermal gradient continuous internal buffering of volatile activities will retain the fluid phase in the slab this is in contrast with shallow sub forearc depths 20 to 50 10 km where tectonic vein arrays localized thrust faults serpentine diapirs mud volcanoes and boninite magmas attest to the release of large volume of fluids into the overriding mantle wedge

multiphase solid inclusions in zoisite bearing eclogite evidence for partial melting of ultrahigh pressure metamorphic rocks during continental collision abstract multiphase solid ms inclusions in both garnet and omphacite were investigated for zoisite bearing eclogite from the ultrahigh pressure uhp metamorphic zone in the sulu orogen the results provide petrological evidence for local anatexis during exhumation of deeply subducted continental crust there are three types of ms inclusions 1 plagioclase quartz 2 plagioclase quartz k feldspar and 3 barite plagioclase k feldspar zoisite epidote the host minerals mostly exhibit radial fractures surrounding the ms inclusions the first and second types of ms inclusions were analyzed for their bulk compositions yielding high sio 2 and na 2 o but very low feo mgo tio 2 with variable k 2 o for the second type trace element analyses of representative ms inclusions yield generally very low concentrations except such large ion lithophile elements as sr ba and rb these features suggest different origins for the three types of ms inclusions the first type of ms inclusions would be primarily derived from dehydration melting of paragonite whereas the second type of ms inclusions would be derived from dehydration melting of both paragonite and phengite the third type of ms inclusion may result from the interaction between metamorphic fluid and host mineral in view of the occurrence of barite as a filling phase in the fractures of host minerals zoisite breakdown is also indicated by its highly cuspate shape in coexistence with quartz providing components for growth of garnet during the exhumation therefore the anatexis of zoisite bearing uhp eclogite is primarily driven by the breakdown of hydrous minerals such as phengite and paragonite the major and trace element compositions of ms inclusions in the eclogites mainly depend on the species of hydrous minerals involved in the mineralogical reactions of dehydration melting in subduction channel

fluid composition and evolution in coesite bearing rocks dora maira massif western alps implications for element recycling during subduction fluid inclusions and f cl concentration of hydrous minerals were analysed in the coesite pyrope quartzite the interlayered jadeite quartzite and their country rock gneiss from the dora maira massif using a combination of microthermometry raman spectrometry synchrotron x ray microfiuorescence and electron microprobe analysis three populations of fluid inclusions were recognized texturally and can be related to distinct metamorphic stages a low salinity aqueous fluid occurs in the retrogressed country gneiss and as late secondary inclusions in jadeite quartzite and chloritized pyrope an earlier secondary population is found in matrix quartz of the jadeite and pyro pe quartzites this population can be related to the early decompression and so to incipient breakdown of garnet into phlogopite bearing assemblages the inclusion fluid is highly saline up to 84 wt equivalent nacl and contains na ca fe cu and zn as major cations in pyrope quartzite additional k was found in these brines which locally coexist with co2 rich inclusions the oldest fluid inclusions are preserved in kyanite grains included in fresh pyrope and in pyrope itself in pyrope all inclusions have decrepitated and contain magnesite an mg phosphate sheet silicate s a chloride and an opaque phase with no fluid preser ved in contrast the kyanite inclusions in pyrope preserve primary h2o co2 low salinity fluid inclusions probably owing to the low compressibility of the kyanite inclusions and host garnet in spite of in situ re equilibration these inclusions can be interpreted as relics of the dehydration fluid that attended pyrope growth these correlations between textural and chemical fluid inclusion data and metamorphic stages are consistent with the fluid composition calculated from the halogen content of different generations of phlogopite and biotite the preservation of different fluid compositions both in time and space is evidence for local control and possibly origin of the fluids in agreement with isotopic data these results in particular the absence of co2 in the jadeite quartzite are best interpreted in terms of a fluid melt system evolution with increasing metamorphism partitioning of h2o na ca fe and heavy metals into melt jadeite quartzite and mg na k f co2 and p into a residual aqueous fluid can account for depletion in na ca and fe of the pyrope quartzite during the retrograde path a h 2 o rose as melt crystallized generating the two populations of hypersaline and water rich fluids that were highly reactive to pyrope the process of fluid melt interaction envisioned here coupled with models of melt extraction in subduction zones provides an attractive opportunity for the instantaneous 1 ma and selective transport of elements between a downgoing slab and the overlying mantle wedge

petrology of ultrahigh pressure rocks from the southern su lu region eastern china abstract in the su lu ultrahigh p terrane eastern china many coesite bearing eclogite pods and layers within biotite gneiss occur together with interlayered metasediments now represented by garnet quartz jadeite rock and kyanite quartzite in addition to garnet omphacite rutile coesite other peak stage minerals in some eclogites include kyanite phengite epidote zoisite talc nyboite and high al titanite the garnet quartz jadeite rock and kyanite quartzite contain jadeite quartz garnet rutile zoisite apatite and quartz kyanite garnet epidote phengite rutile omphacite assemblages respectively coesite and quartz pseudomorphs after coesite occur as inclusions in garnet omphacite jadeite kyanite and epidote from both eclogites and metasediments study of major elements indicates that the protolith of the garnet quartz jadeite rock and the kyanite quartzite was supracrustal sediments most eclogites have basaltic composition some have experienced variable crustal contamination or metasomatism and others may have had a basaltic tuff or pyroclastic rock protolith the su lu ultrahigh p rocks have been subjected to multi stage recrystallization and exhibit a clockwise p t path inclusion assemblages within garnet record a pre eclogite epidote amphibolite facies metamorphic event ultrahigh p peak metamorphism took place at 700 890 c and p 28 kbar at c 210 230 ma the symplectitic assemblage plagioclase hornblende epidote biotite titanite implies amphibolite facies retrogressive metamorphism during exhumation at c 180 200 ma metasedimentary and metamafic lithologies have similar p t paths several lines of evidence indicate that the supracrustal rocks were subducted to mantle depths and experienced in situ ultrahigh p metamorphism during the triassic collision between the sino korean and yangtze cratons

dehydration melting of ultrahigh pressure eclogite in the dabie orogen evidence from multiphase solid inclusions in garnet several types of multiphase solid ms inclusions are identified in garnet from ultrahigh pressure uhp eclogite in the dabie orogen the mineralogy of ms inclusions ranges from pure k feldspar to pure quartz with predominance of intermediate types consisting of k feldspar quartz silicate plagioclase or epidote barite the typical ms inclusions are usually surrounded with radial cracks in the host garnet similar to where garnet contains relict coesite barite aggregates display significant heterogeneity in major element composition with total contents of only 57 73 and highly variable sio2 contents of 0 32 25 85 that are positively correlated with bao and so3 contents the occurrence of ms inclusions provides petrographic evidence for partial melting in the uhp metamorphic rock the occurrence of barite aggregates with variably high sio2 contents suggests the coexistence of aqueous fluid with hydrous melt under hp eclogite facies conditions thus local dehydration melting is inferred to take place inside the uhp metamorphic slice during continental collision this is ascribed to phengite breakdown during hot exhumation of the deeply subducted continental crust as a consequence the aqueous fluid is internally buffered in chemical composition and its local sink is a basic trigger to the partial melting during the continental subduction zone metamorphism

polyphase growth of accessory minerals during continental collision geochemical evidence from ultrahigh pressure metamorphic gneisses in the sulu orogen abstract an integrated study of petrology geochronology and geochemistry was performed for ultrahigh pressure metamorphic gneisses in the sulu orogen the results are used to elucidate the polyphase growth of such metamorphic minerals as zircon titanite and garnet in response to pressure temperature changes and fluid melt action during continental collision this provides insights into the property of metamorphic fluid melt and their effects on trace element mobility a combined result from ree patterns mineral inclusions and ti in zircon temperatures indicates three stages of zircon growth prograde growth occurred at 237 ma primarily at eclogite facies retrograde growth at 222 ma mostly at eclogite facies and the last growth at 205 ma at granulite facies the three stages of zircon growth are deciphered by distinct ree patterns and trace element compositions reflecting the differences in the property of metamorphic fluid melt the episodic growth of metamorphic zircon is primarily dictated by the episodic concentration of zr and si in metamorphic fluid melt relict domains of magmatic titanite are distinguished from metamorphosed and metamorphic domains by their distinctive ree patterns and trace element compositions the metamorphic titanite exhibit variably elevated nb contents and nb ta ratios suggesting nb ta fractionation due to breakdown of amphibole and or biotite during metamorphism polyphase growth of garnet is suggested by an integrated analysis of mineral inclusions and major and trace elements in large garnet grains trace element abundances vary in different zones of garnet which is ascribed to changes in the paragenesis and composition of matrix minerals involved in garnet forming reactions at different p t conditions therefore the metamorphic growth of zircon titanite and garnet would have occurred not only during prograde subduction but also during retrograde exhumation in the continental collision zones both metamorphic dehydration and partial melting would have taken place episodically during the collisional orogeny the breakdown of hydrous minerals at high to ultrahigh pressure conditions is a key to fluid liberation and element supply for the growth of these accessory minerals

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

fluids in deeply subducted continental crust petrology mineral chemistry and fluid inclusion of uhp metamorphic veins from the sulu orogen eastern china abstract the complex vein associations hosted in southern sulu ultrahigh pressure uhp eclogites contain quartz omphacite or jadeite kyanite allanite zoisite rutile garnet these minerals have chemical compositions similar to those of host eclogites inclusions of polycrystalline quartz pseudomorphs after coesite were identified in vein allanite and garnet and coesite inclusions were found in vein zircon these facts suggest that the veins together with host eclogites have been subjected to synchronous uhp metamorphism the vein minerals contain relatively high concentrations of rare earth elements ree high field strength elements hfse and transition metal elements tme a kyanite quartz vein has a whole rock composition similar to adjacent uhp metamorphic granitic gneisses abundant primary multi solid fluid inclusions trapped within uhp vein minerals contain complex daughter minerals of muscovite calcite anhydrite magnetite pyrite apatite celestite and liquid and gas phase of h 2 o with solids up to 30 70 of the inclusion volume the presence of daughter minerals anhydrite and magnetite indicates the subduction fluids were oxidizing and provides a possible interpretation for the high oxygen fugacity of subduction zone magmas these characteristics imply that the uhp vein minerals were crystallized from supercritical silicate rich aqueous fluids that were in equilibrium with peak uhp minerals and that the fluids in deeply subducted continental crust may contain very high concentrations of silicate as well as hree hfse and tme such fluids might have resulted in major fractionation between nb and ta i e the uhp fluids have subchondritic nb ta values whereas the host eclogites after extraction of the fluids have suprachondritic nb ta values therefore voluminous residual eclogites with high nb ta ratios may be the complementary suprachondritic reservoir capable of balancing the subchondritic depleted mantle and continental crust reservoirs

hydrothermal clay mineral formation of east pacific rise and bauer basin sediments samples of surface metalliferous sediment recovered from the crest of the east pacific rise at 6 s and 10 s latitudes and from the adjacent bauer basin are characterized by an authigenically formed fe rich montmorillonite that dominates the non carbonate mineralogy of the clay fraction 2 m oxygen isotopic formation temperatures indicate that the fe montmorillonites are created by low temperature hydrothermal processes 30 50 c in the 10 s region of the east pacific rise and bauer basin possibly as a result of cooling and oxidation of unstable high temperature 380 30 c sulfide assemblages or as a result of the percolation of hydrothermally altered seawater solutions through underlying basalt and sediments the widespread sedimentation of the clay mineral is suggested to be caused by colloidal transport possibly as a result of erosion of hydrothermal mounds by bottom currents hydrothermal fe montmorillonite nontronite formation may act as a direct and significant oceanic sink for si and fe released by the high temperature hydrothermal alteration of basalt at ocean spreading centers

complete miscibility between silicate melts and hydrous fluids in the upper mantle experimental evidence and geochemical implications the phase relationships between silicate melts and hydrous fluids were studied by direct visual observation in an externally heated diamond anvil cell complete miscibility of silicate melt and water was observed for a wide range of melt compositions including nepheline jadeite dacite haplogranite and ca bearing granite some evidence for complete miscibility was also observed in the system basalt h2o the critical temperatures in all systems decrease rapidly with pressure at 15 kbar the critical temperature for nepheline is around 550 c for jadeite around 800 c and for granitic compositions it is close to 900 c in general the critical temperatures appear to increase with silica content in the system our results suggest that there is complete miscibility between silicate melts and water in most of the upper mantle except at very shallow depths this means that a water saturated solidus cannot be defined any more in the deeper parts of the upper mantle very silica rich melt inclusions found in spinel lherzolites associated with fluid inclusion are probably the result of the unmixing of a supercritical fluid containing comparable amounts of water and silicate components the decomposition of amphibole in a subducted slab occurs at conditions where the miscibility gap between fluid and silicate melt is not yet closed while the decomposition of phengite and lawsonite occurs far beyond the critical curve accordingly the fluids released by the breakdown of these minerals should have very different properties highly mobile hydrous fluids containing little dissolved silicate should be produced by amphibole breakdown while the decomposition of lawsonite and phengite will lead to much more silicate rich and less mobile fluid phases

syn exhumation partial melting and melt segregation in the sulu uhp terrane evidences from leucosome and pegmatitic vein of migmatite abstract in order to investigate partial melting and melt evolution during exhumation of deeply subducted continental crust we carried out a combined study on layered leucosomes and pegmatitic veins from the weihai rongcheng migmatites in the sulu ultra high pressure uhp metamorphic terrane eastern china the leucosomes are millimetric to centimetric in thickness and mainly consists of k feldspar quartz plagioclase the pegmatitic veins emplace along the compositional layers or crosscut them and are mainly composed of k feldspar quartz cl images show that most zircon grains of the leucosomes have a core rim zoning structure whereas zircons of the pegmatitic veins are mostly new growth grains with rarely preserved relict domains the inherited zircon domains ca 750 ma are of a magmatic origin with zircon ehf t values between 5 7 and 5 3 mean 0 8 1 5 suggesting that the protolith rock is a mid neoproterozoic juvenile crust the zircon overgrowth rims 223 3 ma of the leucosomes and the new zircon grains 217 2 ma of the pegmatitic veins formed in equilibrium with melt and are similar to magmatic zircons in terms of their cl images and trace element compositions e g heavy enriched ree patterns i e very low gd lu n ratios with positive ce and variably negative eu anomalies high y contents and low hf y ratios compared with the inherited protolith zircon domains the triassic zircon domains of the leucosomes and the pegmatitic veins have obviously high u but low th contents resulting in very low th u ratios

genesis of microdiamonds from melt and associated multiphase inclusions in garnet of ultrahigh pressure gneiss from erzgebirge germany abstract the common association of microdiamonds with the phase assemblage phlogopite apatite paragonite and quartz containing amorphous na al silicate inclusions as inclusions in garnets of quartzofeldspathic rocks from the saxonian erzgebirge germany was studied by analytical electron microscopy the assemblage implies a precedent melt which coexisted with the microdiamonds before and after entrapment in the garnet host and subsequently crystallized the formation of microdiamonds in this metamorphic rock could be explained by cotectic induced partial melting of a subducted continental slab at about 4 6 gpa and 1000 c as constrained by the occurrence of tio 2 with an pbo 2 type structure at the peak metamorphic conditions and by the catalytic effect of siderophile and chalcophile elements

experimental constraints on phase relations in subducted continental crust synthesis piston cylinder experiments were carried out in the range 2 0 4 5 gpa and 680 1 050 c to investigate phase relations in subducted continental crust a model composition kcmash has been used because all major ultrahigh pressure uhp minerals of the whole range of rock types typical for continental crust can be reproduced within this system the combination of experimental results with phase petrologic constraints permits construction of a uhp petrogenetic grid the phase relations demonstrate that the most important uhp paragenesis consists of coesite kyanite phengite clinopyroxene and garnet in subducted continental crust below 700 c talc is stable instead of garnet as most of these minerals are also stable at much lower pressure and temperature conditions it is thus not easy to recognize uhp metamorphism in subducted crust a general feature however is the absence of feldspars at h2o saturated conditions plagioclase is never stable at uhp conditions but k feldspar can occur in h2o undersaturated rocks mineral compositions in the experiments are fully buffered by coexisting phases the si content of phengite and biotite increase with increasing pressure at 4 0 gpa 780 c biotite contains 3 28 si per formula unit which is most probably caused by solid solution of biotite with talc above 800 c the caal2sio6 component in clinopyroxene buffered with kyanite coesite and a mg phase increases with increasing temperature providing a tool to distinguish between cold and hot eclogites up to 10 ca eskolaite ca0 5 0 5alsi2o6 in clinopyroxene has been found at the highest temperature and pressure investigated 900 c 4 5 gpa garnet buffered with coesite kyanite and clinopyroxene displays an increase of grossular component with increasing pressure for a given temperature although the investigated system represents a simplification with respect to natural rocks it helps to constrain general features of subducted continental crust the observed phase relations and phase compositions demonstrate that at pressures 3 0 gpa and temperatures 800 c continental crust can retain significant amounts of h2o 1 wt whereas k free mafic or ultramafic rocks are dry at these conditions uhp parageneses are only preserved if the whole exhumation path is situated within the stability field of phengite i e if there is cooling during exhumation or if the whole exhumation occurred at t 700 c in contrast break down of phengite and concomitant partial melting in terranes that show isothermal decompression may lead to a complete recrystallization of the subducted crust during exhumation the density of uhp rocks can be estimated on the basis of the established phase relations pelitic rocks are likely to have a density close to mantle rocks 3 3 g cm3 because of significant amounts of dense garnet and kyanite whereas granitic rocks are less dense 3 0 g cm3 hence subducted average continental crust is most probably buoyant with respect to mantle rocks and tends to get exhumed as soon as it is detached from the down going slab electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00410 001 0336 3

the stability and composition of phengitic muscovite and associated phases from 5 5 to 11 gpa implications for deeply subducted sediments abstract the stability and composition of phengitic muscovite was investigated from 5 5 11 gpa 700 1150 c in synthesis experiments performed in a multianvil apparatus starting materials consisted of natural minerals with a bulk composition similar to that of a k deficient intermediate dioctahedral trioctahedral mica phengitic muscovite was found to be stable from 5 5 11 gpa at 900 c phengite melting occurs between 1075 1150 c at 7 8 gpa and 1000 1050 c at 10 gpa at 10 11 gpa 800 c octahedral cation deficient ocd muscovite and k hollandite are observed rather than phengite the average phengite content of muscovite is positively correlated with pressure ranging from 3 65 si pfu at 5 5 gpa to 3 81 si pfu at 11 gpa the maximum phengite content of stable muscovite appears to be 3 80 3 85 si pfu most phengite examined exhibits at least minor solid solution towards phlogopite averaging 2 04 0 06 2 octahedral cations pfu the hydrous phases phengite lawsonite topaz oh and mg pumpellyite occur between 6 8 gpa 700 900 c with increasing pressure lawsonite and mg pumpellyite dehydrate to form garnet between 8 9 gpa with increasing temperature mg pumpellyite lawsonite and topaz oh devolatilize to form garnet and kyanite between 900 1000 c at 7 8 gpa phengitic muscovite and topaz oh would be stable in hydrous sediments in cool mature subduction zones to depths exceeding 360 km while lawsonite and mg pumpellyite would be stable to 240 300 km allowing the transport of h2o contained in these phases deep into the upper mantle in warmer subduction zones the dehydration of mg pumpellyite lawsonite and topaz oh as well as the melting of phengite would result in fluid release at depths of 180 240 km the presence of phengite at far greater depths than the zone of melt generation beneath arcs 100 150 km requires a mechanism such as the partitioning of k be b ba and rb into migrating fluids rather than the simple dehydration of phengite beneath arcs in order to provide for the transfer of these slab signature elements from phengite into arc magmas

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