observations of seismic reflectors in the lower lithosphere beneath the skagerrak the lithosphere the rigid outer shell of the earth includes both the crust and the upper mantle in the past decade the complex continental crust and underlying shallower mantle lithosphere have been extensively studied using reflection seismology but the lower lithosphere has not been successfully imaged here we report the observation of continuous and virtually horizontal reflectors in the lower continental lithosphere down to depths of 100 110 km below the skagerrak scandinavia these are apparently not structurally associated with the crust whereas previously reported mantle reflectors such as those observed by the birps group around the british isles1 2 are often located near large faults in the overlying crust like the crust the mantle lithosphere shows a seismically transparent upper and a reflective lower part thus the processes that form seismic reflectors seem to have an affinity for ductile rheological environments in the mantle as well as in the crust our observations are consistent with a model consisting of a mechanically strong upper lithosphere underlain by a thermal boundary layer which separates it from the convecting asthenosphere

petrology and geothermobarometry of granulite facies metapelites from the hisoy torungen area south norway new data on the sveconorvegian p t t path of the bamble sector the high grade rocks metapelite quartzite metagabbro of the hisoy torungen area represent the south westernmost exposures of granulites in the proterozoic bamble sector south norway the area is isoclinally folded and a metamorphic p t t path through four successive stages m1 m4 is recognized petrological evidence for a prograde metamorphic event m1 is obtained from relict staurolite chlorite albite staurolite hercynite ilmenite cordierite sillimanite fine grained felsic material quartz and hercynite biotite sillimanite within metapelitic garnet the phase relations are consistent with a pressure of 3 6 0 5 kbar and temperatures up to 750 850 c m1 is connected to the thermal effect of the gabbroic intrusions prior to the main m2 sveconorwegian granulite facies metamorphism the main m2 granulite facies mineral assemblages quartz plagioclase k feldspar garnet biotite sillimanite are best preserved in the several metre wide al rich metapelites which represent conditions of 5 9 9 1 kbar and 790 884 c these p t conditions are consistent with a temperature increase of 80 100 c relative to the adjacent amphibolite facies terranes no accompanying pressure variations are recorded up to 1 mm wide fine grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction bt sil qtzgrt lq this dehydration reaction together with the absence of large scale migmatites in the area suggests a very reduced water activity in the rocks and xh2o 0 25 in the c o h fluid system was calculated for a metapelitic unit a low but variable water activity can best explain the presence or absence of fine grained felsic material representing a former melt in the different granulitic metapelites the strongly peraluminous composition of the felsic veinlets is due to the reaction grt former melt silcrd bt qtz h2o which has given poorly crystalline cordierite aggregates intergrown with well crystalline biotite the cordierite and biotite producing reaction constrains a steep first stage retrograde relative to m2 uplift path decimetre to metre wide strongly banded metapelites quartz plagioclase biotite garnet sillimanite inter layered with quartzites are retrograded to m3 amphibolite facies assemblages a p t estimate of 1 7 5 6 kbar 516 581 c is obtained from geothermobarometry based on rim rim analyses of garnet biotite plagioclase sillimanite quartz assemblages and can be related to the isoclinal folding of the rocks m4 greenschist facies conditions are most extensively developed in millimetre wide chlorite rich calcite bearing veins cutting the foliation

the potential acid producing capacity and factors controlling oxidation tailings in the guryong mine korea a detailed characterization of the site is crucial to designing an efficient method of managing the risks associated with tailings from abandoned mines therefore samples collected from various depths within tailings in guryong mine korea were analyzed for their chemical physical and mineralogical characteristics all samples of the guryong tailings had acid generating potential however in the oxidation zone the net acid generation nag was low 30 kg h2so4 t 1 although the acid neutralization potential anp was less than zero the anp values in the unoxidation zone were higher 56 0 kg caco3 t 1 than in the other zones as a result the amount of alkali ions that are needed to neutralize the acid needs to be considered in this experiment g3 g4 and g6 drill cores containing fine tailings particles near the unoxidation zone were observed to contain calcite caco3 with acid neutralizing capacity a low ph 2 4 in the oxidation zone of the tailings changed to a neutral ph in the unoxidation zone of the tailings these results suggest that the acid neutralizing capacity of the tailings was controlled by particle and mineral composition of tailings

neodymium isotope systematics of the mantle beneath the baltic shield evidence for depleted mantle evolution since the archaean abstract more than 300 published and unpublished nd isotopic analyses of mantle derived rocks from the baltic shield have been compiled the rocks range in age from archaean to phanerozoic within any given age interval the mantle derived rocks range in nd t from depleted mantle values at or above the growth curves of the global depleted mantle reservoirs of depaolo 1981 and depaolo et al 1991 to negative values initial neodymium isotopic compositions below the de paolo curve are best explained by interaction between depleted mantle derived magmas and local crustal contaminants the data now available lend no support to the existence of isolated less depleted or undepleted mantle domains beneath the baltic shield as was suggested by mearns et al 1986 and valbracht 1991a b

comparative oxygen barometry in granulites bamble sector se norway oxygen fugacities have been estimated for the high grade portion of the bamble granulite facies terrane se norway using both titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers the two oxygen barometers show good agreement for samples indicating high titaniferous magnetite ilmenite temperatures whereas agreement is poor for low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably lower than those estimated from orthopyroxene titaniferous magnetite quartz this discrepancy increases with a decrease in temperature which appears to reflect preferential resetting of the hematite content in the ilmenite grains without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains the mean temperature for the non reset samples 795 60 c 1 agrees well with temperatures obtained from garnet orthopyroxene k d exchange thermometry in the same region 785 60 c 1 most non reset o

juvenile co2in enderbites of tromoy near arendal southern norway a fluid inclusion and stable isotope study the enderbites from tromoy in the central granulite facies part of the proterozoic bamble sector of southern norway contain dominantly co2 and n2 fluid inclusions co2 from fluid inclusions in quartz segregations in enderbites was extracted by mechanical crushing and thermal decrepitation and the 13c measured measurement was also made on samples washed in 10 hcl oxidized with cuo at high temperatures and step wise extracted with progressive heating results between the different techniques are systematic the main results show 13c of 4 5 1 5 for crushing and 7 2 for thermal decrepitation 13c is about constant for co2 extracted at different temperatures and points to a homogeneous isotopic composition due to the presence of carbonate particles and or induced contaminations for the extraction by thermal decrepitation the results for the crushing experiments are assumed the most reliable for fluid inclusion co2 very low values of 13c have not been found in enderbite samples and 13c combined with 18o of the host quartzes 8 11 indicates juvenile values in addition the fluid inclusions were examined by microthermometry and raman analysis and host quartz by acoustic emission and cathodoluminescence co2 fluid inclusions have varying densities with a frequency maximum of 0 92 g cm 3 and generally do not concur with trapping densities at granulite conditions textures show that co2 must have been trapped in fluid inclusions in one early event but transformed to different extents during late isothermal uplift without important fractionation of isotope compositions the present data support a model of intrusion and crystallization of a co2 rich enderbitic magma at granuiite conditions

low pressure granulite facies metapelitic assemblages and corona textures from macrobertson land east antarctica the importance of fe2o3and tio2in accounting for spinel bearing assemblages low pressure granulite facies metasedimentary gneisses exposed in macrobertson land east antarctica include hercynitic spinel bearing metapelitic gneisses peak metamorphic mineral assemblages include spinel rutile ilmenite sillimanite garnet spinel ilmenite sillimanite garnet cordierite ortho pyroxene magnetite ilmenite garnet spinel cordierite biotite ilmenite and orthopyroxene cordierite biotite each with quartz k feldspar and melt the presence of garnet biotite and cordierite orthopyroxene bearing assemblages implies crossing tie lines in afm projection for the k2o feo mgo al2o3 sio2 h2o kfmash system this apparent contradiction and the presence of spinel rutile and ilmenite in the assemblages is acounted for by using the kfmash tio2 o2 system i e afm tio2 fe2o3 we derive a petrogenetic grid for this system applicable to low pressure granulite facies metamorphic conditions retrograde assemblages are interpreted from corona textures on hercynitic spinel and fe ti oxides the relative positions of the peak and retrograde metamorphic assemblages on the petrogenetic grid suggest that corona development occurred during essentially isobaric cooling

deep water renewal by turbidity currents in the sulu sea the ventilation of the intermediate and deep layers of the ocean is governed by convection dense water formed at the sea surface through air sea interaction processes mainly at high latitudes sinks to great depths convection determines the heat salt and dissolved gas budgets of the ocean s interior and therefore exerts a significant influence on the earth s climate convective processes can also be initiated by the flow of dense water over submarine sills separating ocean basins with water masses of different buoyancy here we report the observation of relatively light deep water in the overflow region near the sill in the northern part of the 5 000 m deep sulu sea because of its buoyancy this water could not have reached the sea floor of its own accord turbidity currents induced by changes in water density that result from sediment influx occur in this region at intervals of several decades as indicated by the frequent deposition of graded sequences of silty mud on the abyssal plain we suggest that such turbidity currents combined with the effects of classical hydrological plume convection are capable of bringing light water to large depths in tropical regions where normal oceanic convection is relatively weak this mechanism may contribute significantly to the ventilation of deep basins

experimental evidence against co2 promoted deep crustal melting there has been considerable controversy regarding the role of carbon dioxide in the metamorphism and melting of the earth s crust fuelled principally by reports of experimental evidence for co2 enhanced partial melting of the assemblage phlogopite mica quartz in the model system kalo2 mgo sio2h2o co21 2 the analogous process in the crust would lead to the formation of granulite facies rocks at temperatures characteristic of amphibolite facies metamorphism the granulite fades3 5 would thus be indicative not of unusually high temperatures but of the influx of carbonic fluids4 6 moreover the similarity of their low temperature melts to the compositions of some calc alkaline lamprophyres led peterson and newton2 to suggest that such magmas might be generated by the introduction of co2 rich fluids providing a means of large scale mass transfer in the deep crust these ideas have been highly influential6 but there are aspects of peterson and newton s results that are hard to reconcile with other available data i have accordingly tried to replicate the results of refs 1 and 2 but as i report here have been unable to do so the present results thus cast doubt on the general idea of melt fluxing by co2 and the formation of magnesium and co2 rich magmas at crustal pressures

isotopic constraints on the timing of crustal accretion of the bamble sector norway as evidenced by coronitic gabbros abstract this paper presents the first sm nd data for coronitic gabbros hyperites from the high grade proterozoic bamble sector norway sm nd whole rock isochron ages of the vestre dale gabbro 1 11 0 14 ga the jomasknutene gabbro 1 77 0 19 ga and the flosta gabbro 1 64 0 23 ga indicate that contrary to earlier ideas intrusion of these gabbros is not exclusively bound to the sveconorwegian orogeny 1 2 0 9 ga some of the gabbros were already emplaced at the onset of or during the gothian orogeny 1 75 1 5 ga initial nd values of about 5 5 of jomasknutene and flosta gabbros provide clear evidence of a depleted mantle reservoir beneath this part of the southwest scandinavian domain this highly positive value differs from the nd isotope evolution curve for the southwest scandinavian mantle as postulated by mearns et al 1986 which assumes that depletion of the mantle beneath this part of scandinavia started at c 1 74 ga however the initial nd value of the vestre dale gabbro plots close to this curve whereas 143nd 144nd ratios of the mantle sources of the tromoy and arendal gabbros evolved with approximately chondritic 144sm 144nd ratios their nd 1 1 ga values range from 5 1 0 3 to 6 0 0 3 gothian metasomatism of a depleted mantle source by lile and lree bearing fluids provides a mechanism to obtain low nd isotope ratios in magmas represented by the vestre dale gabbro examples of low nd isotope magmas have also been found in the telemark sector and in southern sweden the marked depletion in nb indicates that the metasomatic fluids were possibly related to gothian subduction

the effect of fluid and deformation on zoning and inclusion patterns in poly metamorphic garnets within the bergen arcs of w norway caledonian eclogite facies assemblages t 650 c p 15 kbar have formed from grenvillian granulites t 800 900 c p 10 kbar along shear zones and fluid pathways garnets in the granulites grti pyr56 40 alm45 25gro19 14 are unzoned or display a weak ca 1 wt feo over 1000 m zoning the eclogite facies rocks contain garnets inherited from their granulite facies protoliths these relict garnets have certain areas with compositions identical to the garnets in their nearby granulite but can be crosscut by bands of a more almrich composition grtii pyr31 41alm40 47gro17 21 formed during the eclogite facies event these bands orientated preferentially parallel or perpendicular to the eclogite foliation may contain mineral filled veins or trails of eclogite facies minerals omphacite amphibole white mica kyanite quartz and dolomite steep compositional gradients up to 9 wt feo over 40 m separate the two generations of garnets indicating limited volume diffusion the bands are interpreted as fluid rich channels where element mobility must have been infinitely greater than it was for the temperature controlled volume diffusion at mineral interfaces in the granulites the re equilibration of granulite facies garnets during the eclogite facies event must therefore be a function of fracture density deformation and fluid availability the results cast doubts on modern petrological and geochronological methods that assume pure temperature controlled chemical re equilibration of garnets

the stability of sapphirine quartz and hypersthene sillimanite quartz assemblages an experimental investigation in the system feo mgo al 2 o 3 sio 2 under h 2 o and co 2 conditions phase relations and mineral chemistry involving the phases garnet gt spinel sp hypersthene hy sapphirine sa cordierite cd sillimanite sil and quartz qz have been experimentally determined in the system fmas feo mgo al2o2 sio2 under low fo2 and for various h2o co2 conditions several compositions were studied with 100 mg mg fe ratio ranging from 64 to 87 with excess quartz and sillimanite our data do not show any differences in gt cd stability and composition as a function of h2o co2 and h2o co2 ch4 content in good agreement with a previous experimental study at lower temperature aranovich and podlesskii 1983 at 1 000 c and 11 kbar under co2 saturated conditions cordierite grew from a crystalline mix unseeded with cordierite thus under water absent conditions cordierite will have a high p stability field in the presence of co2 if water has a pressure stabilizing effect on cordierite then our results would indicate that the effects of h2o and co2 are of the same magnitude at high temperature our data support the theoretical p t grid proposed by hensen 1986 for high t metapelites and are largely consistent with the high temperature experimental data of hensen and green 1973 the univariant boundary gt cd hy sil qz which marks the disappearance of hy sil qz assemblages has a negative dp dt slope above 1 000 c and a positive one below this temperature extrapolation of our data to iron free systems shows that the high p breakdown limit of mg cordierite has a negative slope in the range 1 025 1 300 c and probably positive below 1 000 c this indicates a maximum of stability for mg cordierite at around 1 000 c and 13 kbar because of the curvature of the univariant reactions en sil py qz mg cd en sil qz and gt cd hy sil qz the iron free invariant point involving the phases py en cd sil and qz probably does not exist sapphirine qz bearing assemblages are stable only at temperatures above 1 050 c at 1 075 c the joint gt sa is stable up to 11 kbar at higher pressure garnet sapphirine and quartz react according to the reaction gt sa qz hy sil reequilibrated sapphirines are more aluminous than the theoretical endmember mg2al4sio10 due to alal mgsi substitutions 100 al2o3 al2o3 feo mgo in experimental sapphirines ranges from 50 5 to 52 2 sapphirine in the assemblage sa cd sil qz shows a decrease in al content with decreasing temperature and pressure such that the alumina isopleths for sapphirine have a slight negative dp dt slope a similar decrease in al content of sapphirine with temperature is also observed in sa sil qz assemblages

evidence for prograde metamorphic evolution of sri lankan pelitic granulites and implications for the development of continental crust petrological evidence for prograde metamorphic evolution is obtained for pelitic granulites of the newly defined highland complex in sri lanka it includes the occurrences of relict kyanite quartz staurolite corundum kyanite hercynite kyanite and sapphirine kyanite spinel within garnet in the sillimanite quartz rich rocks of special interest is the mineralogy of khondalites graphitic garnet sillimanite k feldspar quartz gneisses the matrix of which is free of hydrous minerals indicating that dehydration reactions have been completed in this kind of rocks however relict hydrous minerals such as al ti rich more than 58 wt al2o3 and more than 1 wt tio2 staurolite and extremely ti rich up to 9 8 wt tio2 biotine occur as inclusions within garnet the local relict mineral assemblages within garnet in khondalites indicate the following continuous staurolite breakdown reactions which may have progressed as temperature increased and pressure decreased staurolite quartz kyanite garnet h2o staurolite corundum kyanite garnet h2o staurolite kyanite hercynite garnet h2o staurolite sillimanite hercynite garnet h2o some of these dehydration reactions are inferred to have also taken place in other widespread pelitic granulites of the highland complex moreover garnet in the highland complex pelitic granulites occasionally preserves growth zoning though modified slightly to extensively by post growth volume diffusion based on the evidence a clockwise prograde p t path of evolution is inferredfor meta sedimentary granulites belonging to the highland complex on the other hand no evidence for prograde metamorphism has so far been obtained in lower grade rocks of the wanni complex to the northwest of the highland complex such a difference between these complexes may be the first petrological feature which supports the new geotectonic division of the sri lankan basement rocks based virtually on the distinctly different neodymium model ages it suggests that these two complexes were amalgamated during the very last part of prograde metamorphism of the highland complex rocks that is during decompression and heating probably by the lower crustal lateral flow after tectonic overthickening and delamination the clockwise prograde p t t path followed by the meta sedimentary granulites of the highland complex is in marked contrast with the near isobaric cooling path for meta igneous granulites suggested by some authors it is proposed that both types of p t t paths albeit for different rock types are possible and resulted from diverse deep crustal processes such as underplating of continental crust by sediments and magmas or near convergent plate boundaries

whiteschists and orthoamphibole cordierite rocks and the p t t path of the modum complex south norway abstract this paper describes the second known occurrence of whiteschist from norway whiteschists and orthoamphibole cordierite rocks which can both be described in the m f ash system are found in the modum complex together with albitites in contact zones between metagabbros and supracrustals they are formed due to extensive hydrothermal activity bulk rock and mineral chemistry define a bimodal fe mg distribution talc kyanite schists and fe poor orthoamphibole cordierite rocks form a leucocratic group and fe rich orthoamphibole cordierite rocks a melanocratic group the break down of an early orthoamphibole cordierite paragenesis to a later talc kyanite paragenesis indicates a cooling path at isobaric conditions or under increasing pressure the temperature pressure regime is of the order of 600 750 c and 6 8 kb reaction textures with talc albite kyanite forming pseudomorphs after gedrite indicate excess albite these nonisochemical reactions indicate the presence of an active na bearing fluid at deep levels in the crust

metagabbros in the modum complex southern norway an important heat source for sveconorwegian metamorphism abstract the precambrian modum complex in southern norway is characterized by supracrustal rocks penetrated by numerous gabbro intrusions occurring as elongated bodies subparallel with the regional foliation these gabbroic bodies show a partial alteration to amphibolites the best preserved parts of the metagabbros show a subophitic texture with olivine and plagioclase as the major cumulus phases and clinopyroxene orthopyroxene and ilmenite as the major intercumulus phases subsequent alteration of these igneous phases has led to formation of coronas around olivine in contact with plagioclase and recrystallization of clinopyroxene the igneous phases indicate intrusion temperatures in the range of 1100 1000 c and pressures below 5 8 kbar formation of coronas and recrystallization of clinopyroxene occurred in the pressure temperature range of 7 10 kbar and 800 600 c a 1224 15 ma sm nd mineral isochron obtained from igneous phases indicates emplacement at the start of the sveconorwegian metamorphism a complex evolution is suggested for the sveconorwegian metamorphic event involving both magmatism and high grade metamorphism

mobilization of gold in the deep crust evidence from mafic intrusions in the bamble belt norway abstract the location of mesothermal gold deposits in the upper part of major transcurrent shear zones suggests that gold was derived from the deep wider portions of the shears the 30 km wide bamble belt south norway is a deep shear belt metamorphosed to upper amphibolite and granulite grade at about 1 1 ga preliminary studies showed that its rocks are strongly depleted in gold and other chalcophile elements mafic rocks were chosen for more detailed study of the mobilization of gold during metamorphism gold in mafic rocks largely partitions into the sulphide phase which is mainly comprised of pyrrhotite modification of this phase was required to liberate gold bamble has two main groups of mafic rock the first metabasites intruded before peak metamorphism are uniformly low in gold their o2 at peak metamorphism obtained from ilmenite orthopyroxene equilibria indicates a strongly oxidized mineral assemblage well above fmq pyrrhotite was stable at peak temperature of 800 c but on cooling below 600 c internal mineralogical buffering by the oxidized assemblage caused the o2 to cross into the stability field of pyrite following conversion of pyrrhotite to pyrite the latter was partly replaced by magnetite these serial changes in the mineralogical form of iron sulphide was conducive to the extraction of gold as was the oxidized nature of the mineral assemblage that would have buffered metamorphic fluids to high o2 the second group of mafic rocks hyperites intruded after peak metamorphism record intermediate steps in the extraction of gold these intrusions of coronitic gabbro were metamorphosed in whole or in part to amphibolite there is a decrease in gold and other chalcophile elements across a hyperite dyke from the pyrrhotite bearing coronitic gabbro interior to the pyrite bearing amphibolite margin

petrology of granulite facies metapelites of the highland complex sri lanka implications for the metamorphic zonation and the p t path in the pan african granulite facies highland complex of sri lanka the metamorphic grade increases from the central northwestern part towards boththe east and the southeast in metapelites the following prograde changes in metamorphic assemblage are recognized biotite ilmenite garnet or co cordierite sillimanite alkali feldspar quartz in the central northwestern part give way to garnet rutile sillimanite ilmenite or biotite alkali feldspar quartz in the e and se and are replaced by gar garnet cordierite biotite magnetite ilmenite alkali feldspar quartz bearing assemblages in the southwest cordierite coexisting with garnet is restricted to the western highland complex where metamorphic pressures of 5 7 kbar havebeen determined in the eastern highland complex where garnet clinopyroxene quartz is stable in metabasic rocks metamorphic pressures of 8 10 kbar have been obtained from barometers on metapelites phase relations of metapelites as well as geobarometry point to a continuous metamorphic transition between the eastern and the western part of the highland complex a clockwise p t path for the whole highland complex is indicated by the succession kyanite sillimanite andalusite an even earlier stage of the prograde metamorphism documented by sillimanite needles older than kyanite inclusions in garnet hhave been found in two samples of the eastern highland complex this points to a strong pressure increase at amphibolite facies conditions probably due to tectonic thickening of the crust during prograde metamorphism other inclusion assemblages in garnet and reaction textures indicate the breakdown of staurolite to kyanite spinel garnet and subsequent continued garnet growth in the sillimanite field at the expense of biotite sillimanite and quartz during further heating ternary feldspars in metapelites bear evidence of extreme metamorphic temperatures of about 900 c previously only indicated by coexisting pyroxenes in metabasic and charnockitic rocks within a few garnets inclusions of staurolite which are ti rich 1 34 wt tio2 and richer in fe xfe 0 745 than the enclosing garnet have survived the very high grade metamorphism the high grade stage of the prograde metamorphism was accompanied by strong flattening and a general n s stretching which is many metapelites ceased after peak temperatures but proceeded in others tectonic uplift of the whole highland complex occurred only after a phase of near isobaric cooling in the lower crust zircon 610 ma and biotite cooling ages 460 ma holzl et al 1991 as well as retrograde p t paths which passed the andalusite stability field are similar in the eastern and western part of the highland complex this suggests that the lower crustal cross section exposed in the highland complex was already tilted during cooling

co 2 melts and granulite metamorphism the discovery that granulites contain co2 rich fluid inclusions while amphibolites in the same terrane contain h2o rich or mixed co2 h2o inclusions1 has led to a debate over the processes that produce granulite metamorphism one theory2 4 maintains that granulites form as the result of a massive influx of co2 from lower crustal or mantle sources such an influx could be responsible for the marked depletion many granulite terranes show in large ion lithophile elements2 5 others however maintain that granulite facies metamorphism is a necessary complement of crustal melt ing6 9 recently lamb and valley10 11 have argued that granulite metamorphism may be a product of any one of three processes co2 streaming partial melting or recrystallization of originally dry rocks here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust