geobarometry geothermometry and late archean geotherms from the granulite facies terrain of south india geobarometry and geothermometry of garnet bearing chamockitic and metapelitic assemblages from the high grade terrain from south india indicate three fields of equilibration high pressure granulites p 8 3 pm 1 0 kb t 760 pm 40 circ c are restricted to the charnockites and mafic granulites of the north slopes of the nilgiris these place a minimum constraint of 30 km on the maximum thickness of late archean crust medium pressure granulites p 6 4 pm 1 0 kb t 735 pm 40 circ c characterize the charnockites of the central nilgiris and the madras granulites to the east low pressure granulites p 5 0 pm 1 0 kb t 700 pm 20 circ c characterize the charnockites and metapelites south of the bhavani shear zone although migmatites from the kodaikanal massif may reflect somewhat higher temperatures all three granulite fields lie on a metamorphic geotherm piezothermic array which is strongly convex to the temperature axis and characteristic of convective heat transfer

the oxygen isotopic compositions of silica phytoliths and plant water in grasses implications for the study of paleoclimate abstract information about climatic conditions during plant growth is preserved by the oxygen isotope composition of biogenic silica phytoliths deposited in grasses the oxygen isotope composition of phytolith silica is dependent on soil water 18 o values relative humidity and evapotranspiration and temperature during plant growth phytolith and plant water 18 o values for c3 a breviligulata and c4 c longifolia grasses from natural and greenhouse sites in southwestern ontario were used to compare the isotopic fractionation between biogenic silica and water in various parts of these living plants for non or weakly transpiring tissues rhizomes stems sheaths in both grass species the 18 o silica plant water remained constant at 34 and the 18 o and d values of plant water collected from pre dawn and mid day samplings showed little variation these plant waters were only slightly enriched in 18 o and d relative to water provided to the grasses isotopic temperatures calculated from the silica and plant water isotopic data matched measured growing temperatures for the region by comparison the upper leaf water was extremely enriched in oxygen 18 and deuterium at maximum rates of transpiration relative to water from non transpiring tissues as were the calculated steady state values for leaf water 18 o and d silica produced in the transpiring tissues leaf inflorescence has higher 18 o values than silica from non transpiring tissues but the enrichment is modest compared to upper leaf water under mid day conditions leaf phytoliths have formed from plant water typical of average conditions in the lower leaf where the extreme 18 o enrichment is not encountered c longifolia was also collected from alberta and nebraska where growing conditions are different from southwestern ontario phytoliths at all three sites have a similar pattern of 18 o values within the plants but the isotopic separation between leaf and stem silica increases from 4 to 8 as average relative humidity decreases the difference between actual growing temperature and that calculated using measured 18 o values for stem silica and local meteoric water became progressively larger as relative humidity decreased likely because of evaporative 18 o enrichment of soil water such effects are most pronounced in arid environments and pertinent in grasslands where much of the active rooting zone can be situated at the shallower depths most affected by the 18 o enrichment of soil water

rare earth thhfta and large ion lithophile element variations in metabasites from the proterozoic amphibolite granulite transition zone at arendal south norway abstract the proterozoic arendal metabasites are minor intrusions which possess wholly metamorphic textures and mineral assemblages data are presented for eight selected samples chondrite normalised ree patterns are relatively flat between 10 and 20 chondrite abundances they are characterised by 1 ce n yb n n nd n 1 normalised to primordial mantle values the incompatible elements reveal variable enrichment in the large ion lithophile elements except th and low ta they are similar to many destructive plate margin basalts on a th hf ta diagram the rocks plot in a sub linear trend reflecting variation in th hf samples with high th hf ratios come from the zone of highest metamorphic grade where the host gneisses are deficient in th consequently the patterns in the metabasites could not have been produced by any secondary metamorphic fractionation or by bulk contamination by the country rocks there is no evidence for any post magmatic mobility of any of the elements except rb which is depleted in the highest grade rocks relative to their lower grade counterparts the trace element distributions are largely reflecting those of the parental magmas but consideration of bulk distribution coefficients shows how they may have been modified in some aspects e g ce n nd n by the imposition of the metamorphic mineralogies the data are consistent with a model involving a derivation from a mantle source region which had been affected by subduction related hydrous metasomatism or partial melting and b crystallisation of the magmas directly under the high grade conditions

fluids preserved in variably altered graphitic pelitic schists in the dufferin lake zone south central athabasca basin canada implications for graphite loss and uranium deposition the athabasca basin canada contains the highest grade unconformity type uranium deposits in the world underlying the athabasca group sedimentary rocks of the dufferin lake zone are variably graphitic pelitic schists vgps altered to chlorite and hematite red green zone rgz they were locally bleached near the unconformity during paleoweathering and or later fluid interaction overall graphite was lost from the rgz and the bleached zone relative to the original vgps fluid inclusions were examined in different generations of quartz veins using microthermometry and raman spectroscopy to characterize and compare the different fluids that interacted with the rgz and the vgps in the vgps ch4 and n2 rich fluid inclusions which homogenize into the vapor phase between 100 and 74 c and 152 and 125 c respectively and co2 rich fluid inclusions homogenizing either into vapor or liquid between 20 and 28 c are present carbonic fluids could be the result of the breakdown of graphite to ch4 co2 whereas n2 rich fluid is interpreted to be the result of breakdown of feldspars micas to nh4 n2 in the rgz the presence of fluid inclusions with low ice melting temperature 38 to 16 c reflect the presence of cacl2 and fluid inclusions with halite daughter minerals that dissolve between 190 and 240 c indicate the presence of highly saline fluids these fluids are interpreted to be derived from the athabasca basin the circulation of carbonic fluids and brines occurred during two different events related to different p t conditions of trapping the carbonic fluids interacted with basement rocks during retrograde metamorphism of the basement rocks before deposition of the athabasca basin whereas the brines circulated after the deposition of the athabasca basin these latter fluids are similar to brines related to uranium mineralization at mcarthur river and thus in addition to possibly being related to graphite depletion in the rgz they could be linked to uranium mineralization

magma chamber scale liquid immiscibility in the siberian traps represented by melt pools in native iron magma unmixing i e separation of a homogeneous silicate melt into two or more liquids is responsible for sudden changes in the evolution of common melts element fractionation and potential formation of orthomagmatic ore deposits although immiscible phases are a common phenomenon in the mesostasis of many tholeiitic basalts evidence of unmixing in intrusive rocks is more difficult to record because of the transient nature of immiscibility during decompression cooling and crystallization in this paper we document a clear case of liquid immiscibility in an intrusive body of tholeiitic gabbro in the siberian large igneous province using textures and compositions of millimeter sized silicate melt pools in native iron the native iron crystallized from a metallic iron liquid which originated as disseminated globules during reduction of the basaltic magma upon interaction with coal bearing sedimentary rocks in the siberian craton the silicate melts entrapped and armored by the native iron are composed of two types of globules that represent the aluminosilicate 60 77 wt sio2 and silica poor fe ti ca p rich in wt sio2 15 46 feo 15 22 tio2 2 7 cao 11 27 p2o5 5 30 conjugate liquids different proportions and the correlated compositions of these globules in individual melt pools suggest a continuously evolving environment of magmatic immiscibility during magma cooling these natural immiscible melts correspond extremely well to the conjugate liquids experimentally produced in common basaltic compositions at 1025 c our results show that immiscibility can occur at large scale in magma chambers and can be instrumental in generating felsic magmas and fe ti ca p rich melts in the continental igneous provinces

atmospheric oxygenation caused by a change in volcanic degassing pressure around two and a half billion years ago following the end of the archaean eon the atmosphere turned from anoxic to weakly oxic in what is known as the great oxidation event using a model of volcanic degassing gaillard et al demonstrate that a preceding period of continental crust formation may have been the trigger they propose that as continents emerged and volcanoes became increasingly subaerial rather than submarine magmatic volatiles were degassed at lower pressures leading to a progressive oxidation of the gases released this shift to a release of sulphur as sulphur dioxide rather than as hydrogen sulphide could then have fed marine sulphate reduction and the eventual oxygenation of earth s atmosphere the precambrian history of our planet is marked by two major events a pulse of continental crust formation at the end of the archaean eon and a weak oxygenation of the atmosphere the great oxidation event that followed at 2 45 billion years ago this oxygenation has been linked to the emergence of oxygenic cyanobacteria1 2 and to changes in the compositions of volcanic gases3 4 but not to the composition of erupting lavas geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3 5 billion years ago5 6 here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation using thermodynamic calculations simulating gas melt equilibria in erupting magmas we suggest that mostly submarine archaean volcanoes produced gases with so2 h2s 1 and low sulphur content emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late archaean then led to widespread subaerial volcanism which in turn yielded gases much richer in sulphur and dominated by so2 dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere

studies of late prehistoric and modern opal phytoliths from coastal sand dunes and machair in northwest britain abstract this paper investigates the possibilities of identifying the origins of and classifying modern and prehistoric sand samples from coastal dune environments based on a study of their phytolith content a simple conservative classification of phytolith morphotypes has been developed for specimens from this type of sedimentary environment this classification has facilitated the recognition of anthropogenic and non anthropogenic depositional levels in ancient sand dunes on the basis of their contained phytolith suites areas of ancient human occupation and activity are shown to be characterized by phytolith concentrations which are larger by orders of magnitude than those that occur naturally in these coastal dune systems correspondence analysis has been used to investigate the extent to which some specific aspects of past human activity can be distinguished specifically the introduction of cut peat plant and animal waste and possible differences in the character of grazing or pasture in the dune systems

submarine palaeoenvironments during emeishan flood basalt volcanism sw china implications for plume lithosphere interaction during the capitanian middle permian end guadalupian extinction event abstract plume induced lithospheric uplift and erosion are widely regarded as key features of large igneous province lip emplacement as is the coincidence of lip eruption with major extinction and oceanic anoxic events oae the emeishan lip which erupted during the capitanian previously termed end guadalupian extinction event has provided the most widely discussed example of axisymmetric doming above a rising mantle plume advocates have argued that in excess of 500 m of uplift occurred over 30 000 km 2 causing extensive radially distributed erosion and alluvial fan formation however the recognition of submarine hydromagmatic and phreatomagmatic style volcanism as well as syn volcanic marine sediments interbedded in the eruptive succession now requires further examination to this simple plume uplift model here we present data from newly discovered sections from the center of the putative uplifted area around lake er hai sw yunnan province that provide a more complete history of the emeishan volcanism these reveal that platform carbonate deposition was terminated by rapid subsidence followed quickly by the onset of volcanism importantly these eruptions also coincide with widespread losses amongst fusulinacean foraminifera and calcareous algae for at least the lower two thirds of the 4 5 km thick lava pile eruptions continued at or below sea level as testified by the presence of voluminous mafic volcaniclastic deposits pillow lavas and development of syn volcanic reefal limestones in the emeishan inner zone only in the later stages of eruption did terrestrial lava flows become widely developed this onset of volcanism in a submarine setting and the consequent violent phreatomagmatic style eruptions would have had a profound effect on marine fauna and exacerbated any volcanically induced climate effects during the capitanian the late permian of sw china at the time of the emeishan was an extended area of thinned lithosphere with epeiric seas which appear to have been sustained through the onset of lip emplacement therefore while there remains substantial geochemical support of a plume origin for emeishan volcanism lip emplacement cannot be ubiquitously associated with regional pre eruption uplift particularly where complex lithospheric structure exists above a plume

geo fo 2 integrated software for analysis of magmatic oxygen fugacity oxygen fugacity fo 2 is a fundamental thermodynamic property governing redox potential in solid earth systems analysis of magmatic fo 2 aids our understanding of the valence state and solubility of multivalent elements during magma evolution specialized software geo fo 2 was developed for calculating magmatic fo 2 on the basis of oxybarometers and thermobarometers for common minerals amphibole zircon and biotite in intermediate silicic magmas with user friendly interfaces it is easy to input files csv or excel files output data in excel files and plot results as binary diagrams that can be saved as vector graphics and modified using image processing software

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

environmental change and tephra deposition the strath of kildonan northern scotland pollen analysis tephra counts and geochemical data are presented from the upper 200 cm of a core from a basin mire in the strath of kildonan northern scotland three main tephra concentrations are located and tentatively dated to c 7650bp k1 c 4250 bp k2 and 3250 bp k3 by cross correlation with the regional pollen chronology the identity of the tephra layers is unknown but the peak at 4250 bp may be from the hekla 4 eruption the associated changes in catchment soils and vegetation are highly variable k1 is associated with a major vegetation disturbance but no significant change occurs at k3 k2 is correlated with a large regional rise in pine pollen these results conflict with previous studies on distal impacts of volcanic activity during the holocene and demonstrate the diversity of environmental changes associated with holocene volcanic activity

assimilation of sulfate and carbonaceous rocks experimental study thermodynamic modeling and application to the noril sk talnakh region russia most of the intrusions in the noril sk talnakh region siberia are hosted in thick sedimentary sequences including abundant evaporitic and terrigenous sedimentary rocks three mafic ultramafic intrusions in this region contain unusually thick massive sulfide deposits which represent one of the world s largest economic concentrations of ni cu and pge the interaction of siberian magmas with sulfate and organic matter rich sedimentary rocks has been proposed as a possible mechanism for the origin of these exceptional sulfide deposits but the interaction process and the reaction paths have never been fully investigated here we clarify by both experimental petrology and thermodynamic modeling how sulfate and organic matter assimilation occur in mafic ultramafic magmas affecting magma composition crystallization and sulfide saturation interaction experiments were conducted at conditions relevant to the emplacement of noril sk type intrusions 1200 c 80 mpa to simulate the assimilation of sulfate and or organic compounds by ultramafic magmas we used a picrite from noril sk1 intrusion and coal and anhydrite from the area as starting materials the experimental results show that the incorporation of anhydrite into the magma occurs by chemical dissolution in the melt which increases the magma s sulfur content but suppresses sulfide saturation and reduces olivine crystallization extreme assimilation leads to sulfate saturation in the magma and high dissolved sulfur contents of 0 9 0 1 wt s conversely coal assimilation promotes sulfide segregation and magma crystallization while decreasing the dissolved h2o content of the melt and increasing the amount of coexisting fluid phase we also employed gas melt thermodynamic calculations to quantify the effect of these assimilations on the redox conditions and the s content of the magma and investigate the role of temperature pressure and initial gas content of the magma in the assimilation process we quantify how sulfate assimilation strongly oxidizes the magma and increases its s content both effects are intensified by increasing pressure from 50 to 100 mpa in this study decreasing temperature from 1350 to 1200 c in this study and decreasing amounts of fluid phase initially coexisting with the magma from 2 to 0 wt the interaction with organic matter ch in this study induces a strong reduction of the magma even for extremely low degrees of assimilation few tenths of wt and the dehydration of the melt we therefore suggest that in the noril sk talnakh district 1 additional s was supplied to mantle derived magmas by the assimilation of evaporitic rocks and was transported during magma ascent in the form of dissolved oxidized s 2 a substantial reduction of the magma inducing sulfide segregation and important crystallization then occurred due to the interaction with carbonaceous sediments this mechanism can potentially produce massive sulfide deposits by important sulfate assimilation locally higher than 3 wt caso4 and minor organic matter assimilation few tenths of wt ch however if one of the two steps does not occur or the assimilation in 1 is not large enough disseminated sub economic or no sulfide deposits are produced we conclude that exceptional conditions favoring substantial assimilation of sediments are needed to generate exceptional ore deposits like those of the noril sk talnakh district

fluid inclusions in high grade anatectic metamorphites fluid inclusions have been studied by microthermometry in metapelites and metabasites which have undergone partial melting in the transition zone from amphibolite to granulite facies mobilizates contain far more abundant and larger fluid inclusions than non mobilized or restite layers and these inclusions occur as several generations of well defined and chemically contrasted fluids carbonic co 2 ch 4 and hydrocarbon aqueous h 2 o nacl and n 2 a garnet bearing mobilizate in amphibolite contains 4 generations of relatively pure fluids most of them trapped after peak metamorphic conditions in the following p t domains co 2 and n 2 p 2 8 kbar t 550 850 c ch 4 p 1 2 kbar t 400 550 c h 2 o p t 120 400 c

magnetic properties of tektites and other related impact glasses we present a comprehensive overview of the magnetic properties of the four known tektite fields and related fully melted impact glasses aouelloul belize darwin libyan desert and wabar glasses irghizites and atacamaites namely magnetic susceptibility and hysteresis properties as well as properties dependent on magnetic grain size tektites appear to be characterized by pure fe2 paramagnetism with ferromagnetic traces below 1 ppm the different tektite fields yield mostly non overlapping narrow susceptibility ranges belize and darwin glasses share similar characteristics on the other hand the other studied glasses have wider susceptibility ranges with median close to paramagnetism fe2 and fe3 but with a high susceptibility population bearing variable amounts of magnetite this signs a fundamental difference between tektites plus belize and darwin glasses and other studied glasses in terms of oxygen fugacity and heterogeneity during formation thus bringing new light to the formation processes of these materials it also appears that selecting the most magnetic glass samples allows to find impactor rich material opening new perspectives to identify the type of impactor responsible for the glass generation

the transformation of amphibolite facies gneiss to charnockite in southern karnataka and northern tamil nadu india amphibolite facies metamorphic grade gives way southward to the granulite grade in southern karnataka as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes petrologic investigations in the transitional zone south of mysore have established the following points 1 the transition is prograde amphibole bearing gneisses intimately associated with charnockite at kabbal and several similar localities are not retrogressive after charnockite as proved by patchy obliteration of their foliation by transgressive very coarse grained charnockite high fluorine content of biotite and amphibole in gneisses and high large ion lithophile element contents in gneisses and charnockites these features are in contrast to very low fluorine in retrogressive amphiboles and biotites very low large ion lithophile element contents and zonal bleaching of charnockite in clearly retrogressive areas as at bhavani sagar tamil nadu 2 metamorphic temperatures in the transitional areas were 700 800 c pressures were 5 7 kbar and h2o pressures were 0 1 0 3 times total pressures based on thermodynamic calculations using mineral analyses dense co2 rich fluid inclusions in the kabbal rocks confirm the low h2o pressures at the first appearance of orthopyroxene farther to the south in the nilgiri hills and adjacent granulite massif areas peak metamorphic temperatures were 800 900 c pressures were 7 9 kbar and water pressures were very low so that primary biotites and amphiboles those with high f contents are rare 3 the incipient granulite grade metamorphism of the transitional areas was introduced by a wave of anatexis and k metasomatism this process was arrested by drying out under heavy co2 influx charnockites so formed are hybrids of anatectic granite and metabasite of metabasite and immediately adjacent gneiss or are virtually isochemical with pre existing gneiss despite gross recrystallization to granulite mineralogy these features show that partial melting and metasomatism are attendant rather than causative in charnockite development copious co2 from a deep crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis granulite metamorphism of both neosome and paleosome followed the process is very similar to that deduced for the madras granulites by weaver 1980 the massif charnockites for the most part extremely depleted in lithophile minor elements show many evidences of having gone through the same process

low density carbonic fluids in the archean granulite facies terrain of the jequie complex bahia brazil the 2 7 ga old high grade metamorphic rocks of the jequi complex of bahia include charnockites enderbites and late pink potassic granites mineralogic p t determinations for the granite terrain yield 4 5 kb 750 850c for the peak of metamorphism microthermometry of fluid inclusions in quartz was performed on different rock types early co 2 rich fluids have densities around 0 85 g cm 3 and may represent synmetamorphic fluids since the isochores cross the inferred p t box late fluids are of lower density and correspond to the waning phase of metamorphism the correspondence in the jequte complex of the relatively low p t conditions with the low density co 2 rich fluids provides evidence that the trapped fluids are to some degree representative of the granulite facies metamorphism though they may have been modified by post metamorphic processes

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

deep crustal carbonates as co 2 fluid sources evidence from metasomatic reaction zones metasomatic reaction zones which developed at marble pelitic schist contacts in a granulite facies terrane in west greenland contain a consistent sequence of five mineralogical zones outward from the carbonates the zones are characterized by the assemblages grossular diopside meionite i meionite anorthite diopside ii anorthite diopside edenitic hornblende iii anorthite enstatite iv plagioclase almandine sillimanite v sphene is superceded by ilmenite between zones ii and iii quartz is present in all zones except zone i scapolite plagioclase clinopyroxene and mica exhibit a small degree of compositional variation which correlates with distance from the carbonate these small compositional variations are superimposed on a strong cao chemical potential gradient compositional features zone distributions and cao activity calculations demonstrate that the zones developed in response to cao diffusion along a chemical potential gradient of 2 kcal m the cao source appears to be carbonate rocks which release calcium as decarbonation reactions proceed the maximum volume of co2 released in this process and that released during discontinuous reactions in the marbles will contribute a total volume of co2 approximately equivalent to the volume of carbonate in the rock calculations demonstrate that a terrane consisting of as little as 8 carbonate will release sufficient co2 to result in complete dehydration of an amphibolite terrane at deep crustal conditions dehydration through co2 release will be accomplished either through rapid burial which would prevent both equilibration of mineral assemblages and co2 release at intermediate crustal levels or through diffusion driven metasomatic reactions which would lead to co2 release primarily at the high temperatures of deep crustal environments the latter process would be the dominant co2 source at deep crustal levels if carbonate rocks occur predominately as relatively thin layers

solidification history of the kitdlit lens immiscible metal and sulphide liquids from a basaltic dyke on disko central west greenland

phytolith taphonomy and distributions in archeological sediments from panama abstract this paper presents the results of research into the nature distribution and significance of phytoliths in archeological sediments from panama four sites are investigated that span a time period dated by radiocarbon from 6600 bc to ad 500 and which encompass a range of human adaptations and ecological settings the strengths and limitations of phytolith analysis are evaluated in relation to a diverse set of paleoecological issues the results indicate that panamanian archeological deposits contribute silicified structures from a large number of plant taxa phytoliths appear to be horizontally and vertically stable after deposition there are problems in human paleoecology such as the evolution of root cropping systems that are not amenable to study with phytolith data however a considerable amount of information can be generated about some components of prehistoric seed cropping systems wild plant usage and landforms

fluid inclusions in granulite facies metapelites of the hercynian ancient lower crust of the serre calabria southern italy investigations of fluid inclusions in granulitefacies metapelites of southern calabria enable characterization of the fluid composition of these lower crustal rocks and constrain the petrologically deduced retrograde p t path characterized by isothermal uplift prior to isobaric cooling in middle crustal levels fluid inclusions in cordierite garnet and sillimanite have a co2 rich composition inclusions in cordierite rarely contain minor amounts of n2 and h2o and in garnets some co2 ch4 n2 inclusions have been analyzed by raman microprobe quartz reveals the most complex fluid melusion compositions 1 co2 rich 2 co2 ch4 n2 3 ch4 n2 4 h2o mgcl2 cacl2 nacl 5 h2o nacl and 6 h2o co2 the earliest fluid inclusions after peak metamorphism are rich in co2 with minor amounts of n2 and h2o an early co2 h2o n2 fluid composition has been confirmed by detection of co2 h2o and n2 in the channels of the cordierite structure most of the early co2 rich fluid inclusions were modified during the uplift from the lower to the middle crustal level resulting in a density decrease with co2 still dominant the subsequent isobaric cooling led to further modifications of the fluid inclusions high density inclusions around implosion textures or scattered amongst lower density ones must have formed during this cooling episode aqueous inclusions in quartz are mostly formed late and are consistent with trapping during retrograde rehydration

oxygen index as an indicator of early organic maturity abstract most maturity indices can be used during catagenesis and metagenesis but there are only a few indicators to show the degree of organic maturation within the diagenesis zone a previous study has already demonstrated that the oxygen index oi measured by rock eval analysis provides reliable information about the early evolution stages of coals and type iii kerogens the main purpose of this study was to investigate the conditions of oi application in both natural and artificial evolution the results of experiments presented here revealed that the accuracy of oi in estimating the evolution level depended on the amount and chemical composition of the organic matter natural series of low rank coals showed oi to be a valuable rank parameter not only during diagenesis but in early catagenesis also oi appeared to be a sensitive indicator during both simulated diagenesis and the entire oil window for gas prone coal having a substantial humic contribution to its precursor material in contrast the oi of oil prone coal and coal with mixed oil and gas potential proved to be a valuable rank parameter only up to the beginning of the oil window though it could be utilized successfully for describing depth profiles in organic rich intervals of early maturity in wells its use in determining natural maturity was restricted by the organic richness of rocks as well as by the effect of the mineral matrix providing humic material is present oi can be used to follow the artificial thermal maturation of type ii kerogen in the absence of mineral matrix

forecasting etna eruptions by real time observation of volcanic gas composition it is generally accepted but not experimentally proven that a quantitative prediction of volcanic eruptions is possible from the evaluation of volcanic gas data by discussing the results of two years of real time observation of h2o co2 and so2 in volcanic gases from mount etna volcano we unambiguously demonstrate that increasing co2 so2 ratios can allow detection of the pre eruptive degassing of rising magmas quantitative modeling by the use of a saturation model allows us to relate the pre eruptive increases of the co2 so2 ratio to the refilling of etna s shallow conduits with co2 rich deep reservoir magmas leading to pressurization and triggering of eruption the advent of real time observations of h2o co2 and so2 combined with well constrained models of degassing represents a step forward in eruption forecasting

scapolite phase equilibria and carbon isotopes constraints on the nature and distribution of co2 in the lower continental crust abstract recent applications of scapolite phase equilibria and carbon isotopes are reviewed in order to evaluate the role played by co2 in the genesis of granulites in the lowermost crust scapolite occurs mainly in mafic granulites from exposed high grade terranes most of which have had a prior upper crustal history before equilibration at 9 10 kbar and in high pressure 11 15 kbar xenoliths and orthogneisses which likely represent mantle derived material that has not interacted with supracrustal lithologies calculated equilibrium co2 activities are sufficiently high 0 7 to be consistent with the presence of a co2 rich fluid phase accounting for the low h2o activities in scapolite bearing granulites and some xenoliths co2 activities less than ca 0 5 or the absence of scapolite are consistent with fluid absent metamorphism the measured isotopic composition of carbon 13cpdb in scapolite is only a tight constraint on the source of carbon in scapolite for mafic xenoliths and high pressure orthogneisses carbon isotope values for these lithologies 7 to 2 overlap the range of values for co2 dissolved in or exsolved from basalts and are consistent with a magmatic origin for the co2 the carbon isotope composition of scapolite in granulites from exposed terranes 10 to 4 is more equivocal and may instead be related to pregranulite facies carbonate present in the rock minimum values of volumetric fluid rock calculated to account for the modal abundance and composition of scapolite in granulites on the order of 0 001 to 0 1 are much lower than those required for the desiccation of amphibolites to granulites 0 1 to 0 5 thus scapolite should form in response to infiltration of such large volumes of co2 if p t and bulk compositional constraints are met however only seven of twenty granulite occurrences contain primary carbonate bearing scapolite in mafic granulites it appears that co2 occurs in the lower crust only locally in a co2 rich fluid phase or dissolved in mafic melts and not on a pervasive scale or at the high volumetric fluid rock required the model of carbonic metamorphism

abrupt hydrographic changes in the equatorial pacific and subtropical atlantic from foraminiferal mg ca indicate greenhouse origin for the thermal maximum at the paleocene eocene boundary 1 the paleocene eocene boundary peb was marked by an extraordinary climatic event hypothesized to originate from a large perturbation to the carbon cycle which fueled global warming the rapid dissociation of oceanic methane hydrates the pattern of surface warming interpreted from existing sea surface temperature records is not consistent with a greenhouse origin for this event which would have fueled sea surface warming globally although oxygen isotope 18o based reconstructions indicate polar warming results for the tropics and subtropics are ambiguous because of uncertainties associated with interpreting planktonic foraminiferal 18o to remedy this we have constructed high resolution temperature records based on mg ca of multiple species of both surface and thermocline dwelling planktonic foraminifera across the peb in the equatorial pacific and subtropical atlantic during the carbon isotope excursion cie surface temperatures increased by 3 5 4 c and thermocline temperatures warmed by 3 c estimates of surface water and thermocline salinity based on paired mg ca and 18o data indicate a pattern of hydrographic changes in the equatorial and subtropical oceans that is different from previously proposed with a more vigorous hydrologic cycle during warming the pattern of warming and salinity changes are consistent with this being a greenhouse induced global warming event and the timing of hydrographic changes relative to the cie supports the hypothesis that gradual warming of intermediate deep waters triggered methane hydrate dissociation

chemical weathering mass loss and dust inputs across a climate by time matrix in the hawaiian islands we determined the total mass loss and rate of chemical weathering from three minimally eroded hawaiian lava flows that are 10 170 and 350 ka old using a backhoe we sampled the entire weathering zone at 28 sites and measured the depletion or enrichment of each major element in each soil horizon relative to parent material we were able to assess the influence of both climate and substrate age on chemical weathering because each flow crosses a precipitation gradient from 600 to 2500 mm yr 1 mass loss rates were highest for the 0 10 ka interval under the wettest climatic conditions 54 t km 2 yr 1 and decreased to near zero in the wet sites during the 10 170 and 170 350 ka intervals not surprisingly weathering rates were lower in drier sites 24 t km 2 yr 1 from 0 10 ka to b 2tk m 2 yr 1 thereafter however the effects of precipitation were non linear there was a precipitation threshold below which mass loss was relatively small and above which mass loss was substantial but insensitive to increased rainfall chemical weathering rates depend on tectonic uplift erosion climate rock type or some combination thereof by working on stable uneroded surfaces of a single rock type across a well constrained precipitation gradient we were able to identify another potential driver the rate of dust deposition although hawai i is one of the least dusty places in the northern hemisphere dust inputs reached 82 of the total mass loss from the weathering zone at some sites and averaged 30 on the 170 ka flow this highlights the potential importance of dust as a component of observed weathering fluxes from catchments worldwide

rapid magma emplacement in the karoo large igneous province abstract understanding the dynamics of continental large igneous provinces lips relies on precise dating of basaltic rocks lip research has traditionally focused on dating lavas often neglecting the volumetrically important sill intrusions in underlying sedimentary basins here we present u pb zircon and baddeleyite ages for fourteen new samples of karoo lip sills and dykes spaced by as much as 1100 km across the half million square kilometer karoo basin the samples yield remarkably coherent ages ranging from 183 0 0 5 to 182 3 0 6 myr probability modeling indicates that basin scale emplacement took place within an interval of about 0 47 myrs less than 0 90 myrs with 95 confidence and could even have represented a single magma emplacement event combining the new ages with the estimated volume of sills in the karoo basin gives an emplacement rate of 0 78 km3 yr which is higher than previous estimates upper crustal magma storage may account for these high rates the results challenge the view that melt emplacement in a sedimentary basin is a prolonged process support a scenario of pulsating catastrophic events within a narrow time frame and strengthens the hypothesis linking lips and sill emplacement to global environmental crises

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

the etendeka igneous province magma types and their stratigraphic distribution with implications for the evolution of the parana etendeka flood basalt province detailed geochemical and field data for the volcanic sequence and intrusions of the etendeka igneous province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the etendeka parana continental flood volcanic event geochemical and petrographic characterization of over 1 000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized both silicic and mafic types can be grouped into high ti and low ti suites on the basis of elevated ti relative to other elements the mafic magmas are khumib high ti tafelberg kuidas horingbaai huab tafelkop albin and esmeralda all low ti amongst the silicic types the goboboseb springbok wereldsend grootberg and beacon low ti quartz latites and the nil desperandum high ti latite have been described previously in addition the hoas low ti nadas sechomib and hoarusib all high ti latites and the fria low ti sarusas ventura khoraseb naude and elliott all high ti quartz latites are described for the first time here there is a marked provinciality in the distribution of the high and low ti suites with the former concentrated in the northern etendeka region and the latter dominant in the southern etendeka stratigraphic distribution of magma types allows two new formations to be defined in the northern etendeka the khumib formation of basaltic flows and the skeleton coast formation dominated by silicic sheets the geochemical provinciality hampers precise correlations between northern and southern etendeka available evidence suggests that the lower part of the awahab formation in the southern etendeka is coeval with the lower part of the khumib formation and that the silicic units in the upper part of the tafelberg formation probably correlate with the skeleton coast formation the paucity of khumib dykes in relation to tafelberg dykes and their field relationships with regard to the volcanic sequence in the northern etendeka suggests that the main khumib eruptive centers lay further north consistent with southward thinning of the khumib basalts in the southern etendeka the doros complex is the eruptive center of the plume derived tafelkop basalts which probably built a shield volcano within the regional flood lava field this work indicates that the etendeka has a greater variety of both silicic and low ti mafic magma types than are known from the se parana detailed comparisons reveal that all the important silicic types in the parana have geochemical equivalents in the etendeka new correlations are santa maria fria ourinhos khoraseb guarapuava sarusas thus extending the previously recognized correlations between southern etendeka quartz latites and the caixas do sul and anita garibaldi rhyolites these correlations emphasize that very large volume silicic systems develop with pronounced lithospheric rifting in continental flood basalt provinces

hydrothermal cu ni au ag mineralization in a granodiorite sill north of cradock republic of south africa an undulating sheet like granodiorite body is intrusive into sedimentary rocks and dolerite of the karoo supergroup north of cradock the top of this sheet where in contact with dolerite is characterised by the presence of graphite containing nodules of sedimentary origin and by sulphide arsenide mineralization ree and other geochemical evidence indicate that the granodiorite and the ore bearing horizon are genetically related but the latter is more altered by hydrothermal fluids similarities in ree distribution patterns also imply very little assimilation of sedimentary material the granodiorite displays plume like features signifying that the material was plastic or semi molten when segregation of the plume like features took place the ni mineralisation in the ore bearing horizon is not linked to the mgo or fe2o3 of the granodiorite or of the ore bearing zone and is regarded as a separate event of hydrothermal origin

rare helical spheroidal fossils from the doushantuo lagerstatte ediacaran animal embryos come of age a small quantity of helically coiled spheroidal fossils has been recovered from acid digestion of phosphorite samples from the ediacaran doushantuo formation south china these fossils consist of an internal body enclosed in a sculptured envelope that is very similar to that of doushantuo animal eggs and blastula embryos such as megasphaera ornata a hallmark of these fossils is a three dimensional spiral structure which always consists of three clockwise coils and occurs on both the envelope and the internal body the spiral structure consists of a spiral tunnel or canal flanked by two raised levees and it is punctured by a series of holes some specimens show evidence of uncoiling invagination along the spiral structure or bipectinate furrowing on the band between canals a possible ontogenetic link between these helical spheroidal fossils and megasphaera ornata is suggested by similar size similar envelope sculptures and co occurrence we tentatively interpret these fossils as postblastula embryos related to megasphaera ornata thus they may represent the most advanced embryonic fossils so far known from the ediacaran although their adult morphologies and phylogenetic affinity remain unknown

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

alpine glacial topography and the rate of rock column uplift a global perspective abstract the present study investigates the influence of alpine glacial erosion on the morphology and relief distribution of mountain regions associated with varying rock column uplift rates we take a global approach and analyse the surface area distribution of all mountain regions affected by glacial erosion between latitudes 60 s and 60 n most surface area in glaciated mountain ranges is concentrated below the modern snowline as predicted by the glacial buzzsaw hypothesis above the modern snowline the analysed mountain regions all exhibit an exponential decay of surface area with height on the basis of this decay the analysed mountain regions fall within three distinct groups primarily reflecting variations in average values of rock column uplift rates mountain ranges affected by rapid rock column uplift display high above snowline relief and large decay lengths whereas inactive orogens have little relief above the modern snowline we find a surprisingly simple relation between hypsometry above the local snowline and regional tectonic activity

carbonic fluid inclusions in granulites from tanzania a comparison of geobarometric methods based on fluid density and mineral chemistry abstract high density carbonic fluid inclusions with well developed negative crystal shape occur in host quartz plagioclase and garnet in intermediate to high pressure granulites from the furua granulite complex southern tanzania they are most abundant in intercalated metapelitic units detailed microthermometric data on inclusions in combination with electron microprobe analyses of associated solid phases are presented for a kyanite bearing garnet granulite and a garnet two pyroxene granulite both selected from the same locality the inclusions contain virtually pure co2 and are believed to be of primary syngenetic origin this is indicated by their distribution in the host minerals and by the homogenization temperatures which give well defined single maxima between 30 and 50 c the corresponding fluid pressures are only 1 3 kbar lower than the pressure range of 10 13 kbar that is inferred from the solid phase geobarometers based on element partitioning in garnet kyanite plagioclase and orthopyroxene clinopyroxene garnet plagioclase assemblages associated temperature estimates of 770 870 c are based on the compositions of garnet biotite garnet clinopyroxene and orthopyroxene clinopyroxene pairs although the co2 density data fit within the regional pressure regime of 7 12 kbar for the metamorphism in the furua area the detailed comparison with solid phase geobarometers at the scale of a single outcrop reveals a small underestimate of pressure which may be explained by minor adjustment of the inclusions after peak metamorphism or by partial h2o pressures in the order of 0 1ptot to 0 2ptot

a comparison of three methods for the extraction of phytoliths from sediments abstract this paper compares three methods commonly used to extract fossil phytoliths from sediments a basic procedure using heavy liquid flotation and oxidation is compared with two other procedures across a range of sediment types commonly encountered in archaeological studies the three procedures are 1 a heavy liquid flotation method hlf 2 a burning method pow and 3 another heavy liquid flotation method hlfpol similar to hlf but adapted to allow the extraction of pollen and spores as well as phytoliths within a single process comparisons of the resulting output using these three techniques for phytolith extraction show that different methods can produce different results and therefore basic techniques should be modified according to the characteristics of the sediments for which they are used while all the techniques showed similarities in assemblage results there were problems associated with disaggregation and effective separation of light and heavy fractions in particular with the pow procedure the evidence suggests that morphotype selection occurred both within the physical sorting process and in the process of inverting slides to shed excess residue in both cases it is difficult to suggest a solution to the problem the results show clearly that the advantages gained by using the pow procedure are largely outweighed by the problems encountered with its use and because of possible size shape selection it is not recommended for general extraction procedures the heavy liquid flotation procedures on the other hand are shown to produce more concentrated residues with higher levels of clarity and less potential than the pow procedure for sample bias the use of a non toxic heavy liquid sodium polytungstate now allows the process to be used in relative safety it is recommended that analysts use heavy liquid flotation procedures with chemical treatments specific to sediment requirements

gas emissions due to magma sediment interactions during flood magmatism at the siberian traps gas dispersion and environmental consequences we estimate the fluxes of extremely reduced gas emissions produced during the emplacement of the siberian traps large igneous province due to magma intrusion in the coaliferous sediments of the tunguska basin using the results of a companion paper iacono marziano et al submitted to epsl and a recent work about low temperature interaction between magma and organic matter svensen et al 2009 we calculate co ch4 dominated gas emission rates of 7 1015 2 1016 g yr for a single magmatic volcanic event these fluxes are 7 to 20 times higher than those calculated for purely magmatic gas emissions in the absence of interaction with organic matter rich sediments we investigate by means of atmospheric modelling employing present geography of siberia the short and mid term dispersion of these gas emissions into the atmosphere the lateral propagation of co and ch4 leads to an important perturbation of the atmosphere chemistry consisting in a strong reduction of the radical oh concentration as a consequence both co and ch4 lifetimes in the lower atmosphere are enhanced by a factor of at least 3 at the continental scale as a consequence of 30 days of magmatic activity the short term effect of the injection of carbon monoxide and methane into the atmosphere is therefore to increase the residence times of these two species and in turn their capacity of geographic expansion the estimated co and ch4 volume mixing ratios i e the number of molecules of co or ch4 per cm3 divided by the total number of molecules per cm3 in the low atmosphere are 2 5 ppmv at the continental scale and locally higher than 50 ppmv the dimension of the area affected by these high volume mixing ratios decreases in the presence of a lava flow accompanying magma intrusion at depth complementary calculations for a 10 year duration of the magmatic activity suggest i an increase in the mean ch4 volume mixing ratio of the whole atmosphere up to values 3 to 15 times higher than the current one and ii recovery times of 100 years to bring back the atmospheric volume mixing ratio of ch4 to the pre magmatic value thermogenic methane emissions from the siberian traps has already been proposed to crucially contribute to end permian early triassic global warming and to the negative carbon isotopic shift observed globally in both marine and terrestrial sediments our results corroborate these hypotheses and suggest that concurrent high temperature co emissions also played a key role by contributing to increase i the radiative forcing of methane and therefore in its global warming potential and ii the input of isotopically light carbon into the atmosphere that generated the isotopic excursion we also speculate a poisoning effect of high carbon monoxide concentrations on end permian fauna at a local scale

titaniferous magnetite ilmenite thermometry and titaniferous magnetite ilmenite orthopyroxene quartz oxygen barometry in granulite facies gneisses bamble sector se norway implications for the role of high grade co 2 rich fluids during granulite genesis oxygen fugacities have been estimated for a wide distribution of samples from the granulite facies terrane region c of the bamble sector se norway using both the titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers these oxygen fugacities are estimated using temperatures calculated from the titaniferous magnetite ilmenite thermometer of ghiorso and sack 1991 and are both internally consistent with each other as well with the thermometer in samples for which the estimated temperature is high the two oxygen barometers show good agreement whereas agreement is poor for low temperature samples in these low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably less than those estimated from orthopyroxene titaniferous magnetite quartz an increase in this discrepancy with decrease in temperature appears to reflect preferential resetting of the hematite component in the ilmenite grains without significant alteration of the more numerous titaniferous magnetite grains this is due in part to greater re equilibration of the ilmenite grains during retrograde interoxide resetting between the ilmenite grains and the titaniferous magnetite grains the mean temperature for the non reset samples 791 17 c 1 is in good agreement with temperatures obtained from garnet orthopyroxene kd exchange thermometry in the same region 785 795 c 1 harlov 1992 2000a most non reset oxygen fugacities range from log10 f o2 14 to 11 8 or approximately 0 5 1 5 log units above quartz fayalite magnetite at 7 5 kbar both these temperatures and the range of oxygen fugacities are in good agreement with those estimated using the titaniferous magnetite ilmenite thermometer oxygen barometer of andersen et al 1991 the quilp equilibrium quartz ulvospinel ilmenite pyroxene is used to project self consistent equilibrium temperatures and oxygen fugacities for samples reset due to hematite loss from the ilmenite grains these projected temperatures and oxygen fugacities agree reasonably well with the non reset samples the mean projected quilp temperature is 823 6 c 1 this result supports the conclusion that low titaniferous magnetite ilmenite temperatures down to 489 c and accompanying low oxygen fugacities are the result of hematite loss from the ilmenite grains non reset oxygen fugacities lie approximately 1 5 log10 units above the upper graphite stability curve indicating that the stable c o h fluid phase interacting with these gneisses whether regionally or locally was co2 this is borne out by the presence of numerous co2 rich fluid inclusions in these rocks

aerosol size confines climate response to volcanic super eruptions extremely large volcanic eruptions have been linked to global climate change biotic turnover and for the younger toba tuff ytt eruption 74 000 years ago near extinction of modern humans one of the largest uncertainties of the climate effects involves evolution and growth of aerosol particles a huge atmospheric concentration of sulfate causes higher collision rates larger particle sizes and rapid fall out which in turn greatly affects radiative feedbacks we address this key process by incorporating the effects of aerosol microphysical processes into an earth system model the temperature response is shorter 9 10 years and three times weaker 3 5 k at maximum globally than estimated before although cooling could still have reached 12 k in some midlatitude continental regions after one year the smaller response plus its geographic patchiness suggests that most biota may have escaped threshold extinction pressures from the eruption

fluid inclusions in high grade gneisses of the kapuskasing structural zone ontario metamorphic fluids and uplift erosion path fluid inclusions in quartz grains from five samples of high grade rocks two paragneisses an amphibolite a mafic gneiss and a tonalite dike from the 2 7 ga kapuskasing structural zone ksz ontario were examined with petrographic microthermometric and laser raman techniques three types of fluid inclusions were observed co2 rich h2o rich and mixed co2 h2o co2 rich fluid inclusions are pseudosecondary or secondary in nature and are generally pure co2 a few contain varying amounts of ch4 h2o rich fluid inclusions are secondary in nature contain variable amounts of dissolved salts and generally contain daughter crystals mixed co2 h2o fluid inclusions occur where trails of h2o rich inclusions intersect trails of co2 rich inclusions isochores for high density p 1 03 g cm3 pseudosecondary pure co2 inclusions intersect the lower pressure portion of the estimated p t field for high grade metamorphism implying that pure co2 was the peak metamorphic fluid the variable ch4 content of co2 inclusions within graphite bearing samples suggests that ch4 was introduced locally after the formation of the co2 inclusions however the origin of the ch4 remains problematic an aqueous fluid clearly penetrated the gneisses after the peak metamorphism during uplift erosion forming secondary inclusions and contributing to the minor retrogressive hydration observed in these rocks the presence of the pseudosecondary high density co2 inclusions in quartz crystals in the ksz rocks constrains the uplift erosion path for the ksz to one of simultaneous decrease in pressure and temperature

limestone assimilation and the origin of co2 emissions at the alban hills central italy constraints from experimental petrology abstract the alban hills volcanic region 20 km south of rome in the roman province emitted a large volume of potassic magmas 280 km 3 during the quaternary chemical interactions between ascending magmas and the 7000 8000 m thick sedimentary carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been frequently corroborated by geochemical surveys in this paper we characterize the effect of carbonate assimilation on phase relationships at 200 mpa and 1150 1050 c by experimental petrology calcite and dolomite addition promotes the crystallization of ca rich pyroxene and mg rich olivine respectively and addition of both carbonates results in the desilication of the melt furthermore carbonate assimilation liberates a large quantity of co 2 rich fluid a comparison of experimental versus natural mineral glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different alban hills eruptions a maximum of 15 wt assimilation is suggested by some melt inclusion and clinopyroxene compositions however most of the natural data indicate assimilation of between 3 and 12 wt carbonate current high co 2 emissions in this area most likely indicate that such an assimilation process still occurs at depth we calculate that a magma intruding into the carbonate basement with a rate of 1 2 10 6 m 3 year estimated by geophysical studies and assimilating 3 12 wt of host rocks would release an amount of co 2 matching the current yearly emissions at the alban hills our results strongly suggest that current co 2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate hosted reservoir at 5 6 km depth with important consequences for the present day volcanic hazard evaluation in this densely populated and historical area

rapid phytolith extraction for analysis of phytolith concentrations and assemblages during an excavation an application at tell es safi gath israel abstract a rapid phytolith extraction procedure is described that allows phytolith concentrations and morphotype assemblages to be analyzed within hours this procedure enables the results of these analyses to be used during an archaeological excavation in order to better understand how plants were used the new procedure was tested using a standard phytolith extract and two experimental phytolith sediment blends and found to be both accurate and precise the reliability of partial slide counting was evaluated and found to be as accurate and precise as existing phytolith quantification methods the new extraction and counting procedures were applied to an archaeological site tell es safi gath israel the results demonstrate how information on phytolith concentrations in sediments that are available from one day to the next can be used during an excavation to more effectively document the local features of interest and obtain better information

extremely reducing conditions reached during basaltic intrusion in organic matter bearing sediments redox conditions in magma are widely interpreted as internally buffered and closely related to that of their mantle source regions we use thermodynamic calculations to show that high temperature interaction between magma and organic matter can lead to a dramatic reduction of the magma redox state and significant departure from that of the original source field studies provide direct evidence of the process that we describe with reported occurrences of graphite and native iron in igneous mafic rocks implying very reducing conditions that are almost unknown in average terrestrial magmas we calculate that the addition of 0 6 wt organic matter in the form of ch or ch2 to a standard basalt triggers graphite and native iron crystallization at depths of few hundred meters interaction with organic matter also profoundly affects the abundance and the redox state of the gases in equilibrium with the magma which are co dominated with h2 as the second most abundant species on a molar basis h2o and co2 being minor constituents the assimilation of only 0 1 wt organic matter by a basalt causes a decrease in its oxygen fugacity of 2 orders of magnitude the assimilation of 0 6 wt organic matter at depths 500 m implies minimum co content in the magma of 1 wt other gas components being less than 0 1 wt in the light of our calculations we suggest that the production of native iron bearing lava flows and associated intrusions was most likely accompanied by degassing of co rich gases whose fluxes depended on the magma production rates

increased subaerial volcanism and the rise of atmospheric oxygen 2 5 billion years ago the hypothesis that the establishment of a permanently oxygenated atmosphere at the archaean proterozoic transition approximately 2 5 billion years ago occurred when oxygen producing cyanobacteria evolved is contradicted by biomarker evidence for their presence in rocks 200 million years older to sustain vanishingly low oxygen levels despite near modern rates of oxygen production from approximately 2 7 2 5 billion years ago thus requires that oxygen sinks must have been much larger than they are now here we propose that the rise of atmospheric oxygen occurred because the predominant sink for oxygen in the archaean era enhanced submarine volcanism was abruptly and permanently diminished during the archaean proterozoic transition observations are consistent with the corollary that subaerial volcanism only became widespread after a major tectonic episode of continental stabilization at the beginning of the proterozoic submarine volcanoes are more reducing than subaerial volcanoes so a shift from predominantly submarine to a mix of subaerial and submarine volcanism more similar to that observed today would have reduced the overall sink for oxygen and led to the rise of atmospheric oxygen

deep crustal granulites with migmatitic and mylonitic fabrics from the zambezi belt northeastern zimbabwe abstract high p granulites contained in two allochthonous tectonic units were thrust southwards onto the northern margin of the zimbabwe craton during the pan african zambezi orogeny in the lower sheet the masoso metamorphic suite contains mafic garnet granulite assemblages formed during a high p t metamorphic event although the suite as a whole is predominantly granitic the garnet granulites occur as relicts within narrow mafic layers characterized by migmatitic and mylonitic fabrics the annealed mylonites represent surfaces of deep crustal tectonic imbrication that formed immediately before the pan african orogeny gabbros which intruded the granulites after the main phase of migmatization have formed corona textures that document a low p t metamorphic event at mid crustal levels the style of deformation then changed and the masoso suite with its mylonitic layers was folded and thrusted southwards onto the archaean zimbabwe craton

climate changes caused by degassing of sediments during the emplacement of large igneous provinces most mass extinctions during the last 500 m y coincide with eruptions of large igneous provinces lips the cretaceous tertiary extinction was synchronous with the deccan flood volcanism the permian triassic extinction with the eruption of the enormous siberian traps and the end guadalupian extinction with the emeishan volcanic province the causal link remains disputed however and many lips apparently had no significant impact on the biosphere here we show that a key control on the destructive consequences of lip emplacement is the type of sedimentary rock in basins beneath the flood basalts contact metamorphism around intrusions in dolomite evaporite coal or organic rich shale generates large quantities of greenhouse and toxic gases co 2 ch 4 so 2 which subsequently vent to the atmosphere and cause global warming and mass extinctions the release of sediment derived gases had a far greater impact on the environment than the emission of magmatic gases

p t conditions for the arendal granulites southern norway implications for the roles of p t and co2in deep crustal lile depletion the orthopyroxene clinopyroxene garnet orthopyroxene and garnet clinopyroxene geothermometers and the garnet orthopyroxene plagioclase garnet clinopyroxene plagioclase and anorthite ferrosilite grossular almandine quartz geobarometers are applied to metabasites and the garnetplagioclase sillimanite quartz geobarometer is applied to a metapelite from the proterozoic arendal granulite terrain bamble sector norway p t conditions of metamorphism were 7 3 0 5 kbar and 800 60 c this terrain shows a regional gradation from the amphibolite facies into normal lile content granulite facies rocks and finally strongly lile deficient granulite facies gneisses neither p nor t vary significantly across the entire transition zone the change in grade parallels the increasing dominance of co2 over h2o in the fluid phase lile depletion is not a pre condition of granulite facies metamorphism granulites may have either depleted or normal chemistries the results presented herein show that lile deficiency in granulite facies orthogneisses is not necessarily related to variations in either p or t the important mechanisms in the arendal terrain were a direct synmetamorphic crystallization from magma with primary lile poor mineralogies imposed by the prevailing fluid regime and b metamorphic depletion involving scavenging of liles during flushing by mantle derived co2 rich fluids the latter process is constrained by u pb and rb sr isotopic work to have occurred no later than 50 ma after intrusion of the acid intermediate gneisses and was probably associated with contemporary basic magmatism in a tectonic environment similar to a present day cordilleran continental margin

the ilugissoq graphite andesite volcano nuussuaq central west greenland abstract the ilugissoq graphite andesite volcano on nuussuaq belongs to the asuk member of the paleocene vaigat formation it is the largest eruption site within the vaigat formation and is recognized as the source of the majority of the graphite andesite tuffs found in marine sediments in central nuussuaq the volcano consists exclusively of pyroclastic rocks containing a diverse lithic assemblage including sediment xenoliths the primary pyroclastic fragments consist of magnesian andesite with several weight percent of graphite which formed when mafic magma established a shallow level magma reservoir beneath the eruption site and within older clastic sediments from the nuussuaq basin magma modified mudstone is completely dominant in the xenolith assemblage and attests that the graphite andesite originated through prolonged high temperature assimilation of mudstone the eruptions took place on a marine shelf consisting of picritic hyaloclastites and subaqueous crater mounds the volcano consists of four overlapping crater cones aligned along a more than 4 km long nnw sse oriented fissure system two cones barely reached sea level whereas the other two reached up to 200 m above the sea the morphology of the pyroclastic rocks demonstrates that the volcano evolved through phreatomagmatic activity which diminished with time the magma never degassed sufficiently to reach a subaerial lava stage a moderate primary gas pressure well in excess of 100 bars in the graphite andesite magma facilitated the phreatomagmatic explosions which created the ilugissoq volcano the rocks of the volcano are rich in graphite and contain little or no native iron in comparison the contemporaneous and chemically similar subaerial lavas and breccias from disko and nuussuaq contain less graphite and more iron the differences are considered to be due to the extremely pressure dependent redox sensitivity of carbon oxygen equilibria in the range 1 bar the lavas to 500 bars the ilugissoq volcano eruptions in the ilugissoq volcano must have been accompanied by intense co and co2 emanations which would have represented a lethal hazard for all animal life in the volcano s surroundings

an infrared spectroscopic ir and light element li be na study of cordierites from the bamble sector south norway abstract infrared absorption spectra and light element contents of several natural cordierites across the arendal amphibolite granulite facies transition bamble sector south norway are presented the infrared spectra record h2o both type i and type ii and co2 as fluid constituents in the channels co and hydrocarbons were not detected type ii water and ca na k are correlated and show a 2 1 molar ratio the infrared and light element data indicate a decrease of na type ii h2o co2 and li with metamorphic grade while type i h2o and be are variable the decrease of these volatiles and alkalies and the low total volatile contents of the granulite facies cordierites are best explained by progressive dehydration and decarbonation processes possibly related to partial melting a progressive change of the x h 2 o h 2 o h 2 o co 2 ratio in the cordierites across the transition as suggested by previous studies is not observed greenschist to low amphibolite facies re equilibrated cordierites show a significant increase in either co2 or h2o co2 na is introduced at some localities the retrograde fluid phase is calculated to be co2 rich

reduced magmatic fluids in basalt from the island of disko central west greenland abstract fluid and melt inclusions in minerals of two native iron bearing dyke rocks from disko greenland were investigated using heating and cooling microscopic techniques the melt inclusions in olivine are homogenized at temperatures of 1170 1200 c the melts are characterized by high sio 2 k 2 o and tio 2 and low mgo contents the co existence of combined melt fluid gas inclusions in olivine implies that the olivine phenocrysts crystallized from a heterogeneous magma at low pressure gas bubbles were investigated in the glass of the rock water and four crystalline phases were observed at room and low temperatures on the walls of the bubbles serpentine naphthalene clathrate and an unknown phase the complex composition of trapped volatiles is reflected in considerable ranges of clathrate melting and solidus temperatures 20 to 7 5 c and 82 6 to 73 c respectively melt equilibrium with metallic iron at t 1450 k suggests that log f o 2 13 95 the calculated composition of c o h fluid in equilibrium with fe fe 3 c and fes is characterized by high ch 4 and h 2 contents during cooling at the postmagmatic stage polymerization proceeds and heavy hydrocarbons are formed inside vesicles the presence of organic compounds in inclusions trapped at a magmatic stage is a natural consequence of unusual reducing condition during crystallization

the thermotectonic evolution of a proterozoic low pressure granulite dome west uusimaa sw finland three fold generations have been recognized in svecofennian rocks 1 800 ma from west uusimaa sw finland the first one f1 might be related to thrusting and imbrication tectonics at plate collision contacts the main generation f2 is due to a n s horizontal crustal shortening which created at first e w trending upright folds in the whole region and later tightened these f2 folds in the western part of the belt whereas conjugate shear zones and tectonic lenses of competent rock bodies developed in the eastern part simultaneously the metamorphic conditions rose from amphibolite to granulite facies in this eastern part which is known as the west uusimaa complex the amphibolite to granulite facies transition zone along the western boundary of the granulite facies complex is studied in detail a number of prograde mineral reactions are telescoped in this transition zone the breakdown of biotite and amphibole to ortho clino pyroxene in metaigneous rocks the appearance of garnet in cordierite bearing metapelites and the appearance of scapolite in calcareous rocks distinct mineralogical changes also occur in this zone which cross cuts all major structures and rock units and are only affected by late f3 folding open disharmonic folds with approximately n s trending axial planes and young shear zones associated with pseudotachylite generation the absence of any evidence of block faulting and tilting of the crust that could be associated with the granulite complex suggests that the whole region represents one crustal level

ulvospinel in native iron bearing assemblages and the origin of these assemblages in basalts from ovifak greenland and buhl federal republic of germany euhedral crystals of ulvospinel are found in many of the native iron bearing xenoliths from the basalt of buhl near kassel west germany and ovifak on disko island west greenland the typical assemblage of these xenoliths at both localities is native fe troilite cohenite ulvospinel ilmenite olivine and plagioclase as well as silicate glass containing droplets of former fe and troilite melt the ulvospinel subsolidus textures and intergrowths also indicate identical cooling histories for the xenoliths in both cases ulvospinel crystallized after the formation of iron but still above the fe fes eutectic at 988 c a subsequent strong drop in oxygen fugacity revealed partial breakdown of ulvospinel according to the reaction text fe text 2 text tio text 4 text fetio text 3 text fe tfrac text 1 text 2 text o text 2 microprobe analyses of a buhl xenolith indicate that ulvospinel contains up to 4 7 w t mno while olivine compositions correspond to fa64 74fo12 24te12 15 the entire xenolith contains 1 9 w t mno this fact together with the geological evidence and the occurrence of corroded quartz relicts within some of the xenoliths provides clear evidence for reduction under near surface conditions in a blast furnace like process the reducing agent was coal from the tertiary seams cut by the erupting basalt while the xenolith source material most probably was spherosiderite which is very common in the coals and would explain the high mno content consequently the presence of cohenite is not necessarily an indicator of high pressure the analogies between the buhl and ovifak localities and their xenoliths strongly suggest a similar formation through near surface reduction and not derivation from the mantle

global temperature response to century scale degassing from the siberian traps large igneous province abstract the siberian traps large igneous province was a key player in the end permian extinction and climatic change due to degassing from lavas and heated sedimentary rocks although the specific degassing scenarios from the province are debated this implies that gas release on a timescale tuned to the cooling of lava flows and subvolcanic intrusions i e decades to centuries must have been sufficient to affect the atmospheric chemistry here we test this assumption by using simple box model calculations to constrain century scale degassing of co2 and ch4 from high end volumes of individual lava flows and sills from the siberian traps the model includes gas fluxes of ch4 and co2 their atmospheric lifetimes and radiative forcing as well as the climate sensitivity in a global average climate system calibrated to end permian time the fluxes are estimated based on lava degassing and contact aureole volumes and devolatilization during the first 100 years following emplacement we test the sensitivity to extreme emissions of up to 25 gtc yr ch4 fractions from 0 to 100 wide ranges of climate sensitivities 1 5 6 0 c for co2 doubling pre event concentrations and atmospheric lifetimes we find that the global annual mean temperature perturbation is 7 0 c in our baseline case using a 10 gtc yr emission and a 60 ch4 fraction assuming 4 5 c as the climate sensitivity even for low emission scenarios 0 7 1 2 gtc yr the temperature response is 1 5 c we conclude that sporadic individual large scale volcanic events in large igneous provinces have the potential to cause a strong global warming on very short timescales in addition to the emission strength the ch4 fraction and the climate sensitivity have the strongest impact on the century scale temperature perturbation

methane release from igneous intrusion of coal during late permian extinction events abstract unusually large and locally variable carbon isotope excursions coincident with mass extinctions at the end of the permian period 253 ma and guadalupian epoch 260 ma can be attributed to methane outbursts to the atmosphere methane has isotopic values 13c low enough to reduce to feasible amounts the carbon required for isotopic mass balance the duration of the carbon isotopic excursions and inferred methane releases are here constrained to 10 000 yr by counting annual varves in lake deposits and by estimating peat accumulation rates on paleogeographic maps the most marked carbon isotope excursions form linear arrays back to plausible methane sources end permian siberian traps and longwood bluff intrusions of new zealand and end guadalupian emeishan traps of china intrusion of coal seams by feeder dikes to flood basalts could create successive thermogenic methane outbursts of the observed timing and magnitude but these are unreasonably short times for replenishment of marine or permaf

the effects of large igneous provinces on the global carbon and sulphur cycles abstract the correlation between large igneous provinces lips extinction events and rapid climate change suggests that volcanism can have a detrimental impact on earth surface conditions changes in atmospheric and ocean chemistry particularly the climate sensitive carbon and sulphur cycles are among the most probable processes for inducing global environmental stress however the interactions and feedbacks between volcanism and these cycles are numerous and complex making the characterisation of the response to a lip challenging here we summarise the sources and sinks of carbon and sulphur from large scale volcanism and magmatism using information from modern and ancient systems for the sources we review the current understanding of volcanic emissions and explore the relative contributions and importance of magma derived degassing versus volatile release from sediments affected by igneous intrusions and lava in addition we explore the various ways in which lips can reduce atmospheric concentrations of these same elements the relative influences of each source and sink are in part determined by the mode of lip emplacement and eruption style along with the subsequent timescales of such effects we focus on a few key examples including the siberian traps the parana etendeka and the central atlantic magmatic province camp to demonstrate how the environmental impact can vary considerably with differing modes of emplacement lip duration and eruption styles in particular we show that the host rocks can have a dominant role as a source or sink of emissions depending on the lithologies affected by the lip emplacement

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

oxygen buffering of kilauea volcanic gases and the oxygen fugacity of kilauea basalt volcanic gases collected during episode 1 of the puu oo eruption along the east rift zone of kilauea volcano hawaii have uniform c o h s cl f compositions that are sharply depleted in co2 the co2 poor gases are typical of type ii volcanic gases gerlach and graeber 1985 and were emitted from evolved magma stored for a prolonged period of time in the east rift zone after releasing co2 rich gases during an earlier period of temporary residence in the summit magma chamber the samples are remarkably free of contamination by atmospheric gases and meteoric water thermodynamic evaluation of the analytical data shows that the episode 1 gases have equilibrium compositions appropriate for temperatures between 935 and 1032 c open and closed system equilibrium models of species distributions for the episode 1 gases show unequivocally that coexisting lavas buffered the gas oxygen fugacities during cooling these models indicate that the fo2 buffering process occurs by transfer of oxygen from the major species in the gas phase h2o co2 so2 to the lava during cooling and that the transfer of oxygen also controls the fugacities of several minor and trace species h2 co h2s s2 cl2 f2 in addition to o2 during cooling gas lava exchanges of other components are apparently insignificant and exert little influence compared to oxygen exchange during cooling oxygen transfer during cooling is variable presumably reflecting short term fluctuations in gas flow rates higher flow rates restrict the time available for gas lava oxygen transfer and result in gases with higher equilibrium temperatures lower flow rates favor fo2 constrained equilibration by oxygen transfer down to lower temperatures thus the chemical equilibrium preserved in these gases is a heterogeneous equilibrium constrained by oxygen fugacity and the equilibrium temperatures implied by the compositions of the gases reflect the temperatures at which gas lava oxygen exchange ceased this conclusion challenges the common assumption that volcanic gases are released from lava in a state of chemical equilibrium and then continue equilibrating homogeneously with falling temperature until reaction rates are unable to keep pace with cooling no evidence is found moreover that certain gas species are kinetically more responsive and able to equilibrate down to lower temperatures than those of the last gas lava oxygen exchange homogeneous reaction rates in the gas phase are apparently slow compared to the time it took for the gases to move from the last site of gas lava equilibration to the site of collection an earlier set of data for higher temperature co2 rich type i volcanic gases which come from sustained summit lava lake eruptions supplied by magma that experienced substantially shorter periods of crustal storage shows fo2 buffering by oxygen transfer up to 1185 c oxygen fugacity measurements in drill holes into ponded lava flows suggest that buffering by oxygen transfer may control the fo2 of residual gases down to several hundred degrees below the solidus in the early stages of cooling although the details of the fo2 buffering mechanisms for oxygen transfer are unknown the fact that fo2 buffering is effective from molten to subsolidus conditions suggests that the reaction mechanisms must change with cooling as the reactants change from predominantly melt to melt plus crystals to glass plus crystals mass balance calculations suggest that redox reactions between the gas and ferrous ferric iron in the lava are plausible mechanisms for the oxygen transfer and that the fo2 of the gases is buffered by sliding ferrous ferric equilibria in the erupting lavas contrary to expectations based on models predicting the oxidation of basalt by h2 and co escape during crustal storage co2 rich type i gases and co2 poor type ii gases have identical oxygen fugacities despite greatly different crustal storage and degassing histories volcanic gas data give a tightly constrained log fo2 of nno 0 5 0 05 for subaerially erupted kilauea basalt from liquidus to solidus temperatures consistent with recent fo2 determinations for the mantle source regions of ocean island basalts because the oxygen fugacities of volcanic gases emitted by subaerial lavas imply that the fo2 of kilauea basalt is unchanged during crustal storage kilauea basalt either arrives in the crust with an oxygen fugacity between nno and fmq or it develops an oxygen fugacity in this range immediately upon arrival in the summit chamber

fluid inclusions in rocks from the amphibolite facies gneiss to charnockite progression in southern karnataka india direct evidence concerning the fluids of granulite metamorphism fluid inclusion studies of rocks from the late archaean amphibolite facies to granulite facies transition zone of southern india provide support for the hypothesis that co2 rich h2o poor fluids were a major factor in the origin of the high grade terrain charnockites closely associated leucogranites and quartzo feldspathic veins contain vast numbers of large co2 rich inclusions in planar arrays in quartz and feldspar whereas amphibole bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed facies quarries contain no large fluid inclusions inclusions in the northernmost incipient charnockites as at kabbal karnataka occasionally contain about 25 mol of immiscible h2o lining cavity walls whereas inclusions from the charnockite massif terrane farther south do not have visibile h2o microthermometry of co2 inclusions shows that miscible ch4 and n2 must be small probably less than 10mol combined densities of co2 increase steadily from north to south across the transitional terrane entrapment pressures calculated from the co2 equation of state range from 5 kbar in the north to 7 5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750 c in quantitative agreement with mineralogic geobarometry this agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions calculations on the stability of the charnockite assemblage biotite orthopyroxene k feldspar quartz show that an associated fluid phase must have less than 0 35 h2o activity at the inferred p and t conditions which agrees with the petrographic observations high tio2 content of biotite stabilizes it to lower h2o activities and the steady increase of biotite tio2 southward in the area suggests progressive decrease of ah2o with increasing grade oxygen fugacities calculated from orthopyroxene magnetite quartz are considerably higher than the graphite co2 o2 buffer which explains the absence of graphite in the charnockites the present study quantifies the nature of the vapours in the southern india granulite metamorphism it remains to be determined whether co2 flushing of the crust can by itself create large terranes of largeion lithophile depleted granulites or whether removal of h2o bearing anatectic melts is essential

electrical conductivity distribution of the lithosphere in the central fennoscandian shield abstract geoelectric information on the crustal structures of the central fennoscandian shield consists of magnetovariational mv and magnetotelluric mt data mv data are obtained from magnetometer arrays devised to map lateral variations of subsurface resistivity mt data are obtained from soundings yielding knowledge on vertical resistivity distribution in the form of cross sections the electromagnetic data base for fennoscandia includes data from about 350 magnetometer sites and about 600 magnetotelluric soundings the results show that the crustal resistivity of the archaean and palaeoproterozoic crust varies greatly both laterally and vertically the model resistivities range from several tens of thousands of m to below 1 m which are extreme values amongst those normally observed in crustal rocks several large elongated and inclined crustal conductors which mark fossil tectonic boundaries have been discovered in the shield these include 1 the lake ladoga outokumpu kainuu schist belt and oulu conductors that form a discontinuous conductive boundary between the domains of archaean and palaeoproterozoic crust 2 the southern finland conductor caused partly by nearly vertical several kilometres deep graphite bearing metasedimentary layers that were tilted and deeply buried in a svecofennian collision 3 the kokkola bothnian skelleftea storavan and oulu conductors representing a collisional belt in a northwards accreted palaeoproterozoic terrain and 4 the lapland granulite belt conductors imaging a sequence of sheared thrust sheets that developed as the granulites were upthrusted southwestwards onto the archaean craton zones of enhanced electrical conductivity delimit more resistive and homogeneous crustal blocks including the archaean kuhmo block in eastern finland and the svecofennian central finland granitoid complex cfgc highly resistive upper crust 30 000 m in the cfgc coincides with the granitoid intrusions groundwater which fills the fractures and pores of the granitoids is non conductive 100 m and is thus not able to enhance the bulk conductivity therefore the resistivity of the upper crust approaches that of dry rocks at depths of 10 to 14 km a decrease in resistivity by one order of magnitude coincides with a seismic low velocity vp zone that appears related to a porous fractured zone filled with saline water a lower crustal conductor beneath the cfgc at depths of 30 to 40 km has a thickness of 10 to 15 km and a resistivity of 20 to 100 m it is most probably caused by graphite that can have been precipitated from co2 rich fluids during the peak metamorphism of the svecofennian orogeny and the subsequent cooling period free fluids trapped in the lower crust appear less plausible magnetotelluric soundings in the resistive cfgc in the central fennoscandian shield have not provided indications of a well developed electrical asthenosphere within the uppermost 300 km

magma and volatile supply to post collapse volcanism and block resurgence in siwi caldera tanna island vanuatu arc v24c 04 allen s r 2005 complex spatterand pumice rich pyroclastic deposits from an andesitic caldera forming eruption the siwi pyroclastic sequence tanna vanuatu bulletin of volcanology 67

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

subsurface fluid flow at an active cold seep area in the qiongdongnan basin northern south china sea abstract the active haima cold seep sites were discovered by the remotely operated vehicle on the western part of the northern slope of south china sea in 2015 and 2016 however the subsurface structures in the seep area are not well studied which prevents the further understanding of the evolution of fluid venting system in the active cold seep area in 2017 a high resolution 2d seismic line transecting the two main seep sites was acquired and processed in this study the subsurface structures were well resolved on the seismic profile the new observations include the widespread subsurface fluid flow features i e chimney structures and pockmarks and the pervasively distributed magmatic activities seismic indicators for hydrothermal vents were also observed on the seismic section this new discovery confirms the contribution of magmatic activities to the evolution of subsurface fluid flow in the study area minor faults under the recognizable resolution of seismic profile which can act as conduits for the subsurface fluid flow were also identified in the fine grained sediment sequences overall these results provide new insights into the evolution of subsurface fluid flow in the study area

the mineralogy and petrology of i type cosmic spherules implications for their sources origins and identification in sedimentary rocks abstract i type cosmic spherules are micrometeorites that formed by melting during atmospheric entry and consist mainly of iron oxides and feni metal i types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time we report the results of a study of the mineralogy and petrology of 88 i type cosmic spherules recovered from antarctica in order to evaluate how they formed and evolved during atmospheric entry to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks two textural types of i type cosmic spherule are recognised 1 metal bead bearing met spherules dominated by ni poor 100 and suggest that metal from h group ordinary cm cr and iron meteorites may form the majority of particles oxidation during entry heating increases in the series met 80 wt ni comprising a particle mass fraction of

charnockite geobarometers based on coexisting garnet pyroxene plagioclase quartz numerous geothermometers based on compositions of coexisting minerals have been calibrated experimentally or theoretically during the past 10 yr in contrast few continuous reaction geobarometers exist which have had wide application one based on the reaction of cordierite to garnet sillimanite and quartz is limited by a relatively narrow pressure range of application and also by conflicting calibrations1 2 because the mixing relations of mg and fe and the role of h2o in cordierite3 are not understood another successful barometer uses the assemblage garnet plagioclase al2sio5 and quartz4 5 continuous geobarometers based on the reaction of orthofer rosilite to fayalite plus quartz6 and on the aluminium content of enstatite in equilibrium with garnet7 have been used to a lesser extent the former barometer is limited by rarity of the requisite assemblage and the latter by uncertain experimental calibration for crustal rocks we calibrate here two mineralogical geobarometers from measured thermodynamic data the participating minerals pyroxenes garnet plagioclase and quartz are frequently associated in high grade metamorphic rocks calculation of pressures for several terrains show that the geobarometers yield reasonable and consistent results for the entire range of crustal pressures

a petrologic and fluid inclusion study of charnockites from the lutzow holm bay region east antarctica evidence for fluid rich metamorphism in the lower crust abstract the proterozoic terrain of lutzow holm bay in east antarctica comprises an amphibolite to granulite facies progression from north to south exposing an oblique section of the lower crust the granulite terrain is represented dominantly by orthopyroxene bearing anhydrous granulites charnockites garnet and biotite bearing gneisses leptynites and garnet sillimanite and graphite bearing aluminous metapelites khondalites thus it is petrographically identical with its gondwanian counterparts in sri lanka and southern india charnockite formation is characterized by the consumption of garnet biotite and quartz to produce orthopyroxene alkali feldspar and plagioclase under isothermal conditions and at reduced water activities a number of mineral reaction textures including orthopyroxene plagioclase symplectites around clinopyroxene relics in intermediate charnockites and spinel rims between adjacent garnet and sillimanite in khondalites suggest near isothermal conditions of equilibration mineral phase equilibria barometry traverse across the granulite terrain indicates an increase in pressure from c 5 kbar in the north to c 8 9 kbar in the south the temperature gradient of c 100 c is less pronounced fluid inclusion studies indicate abundant co 2 trapped within the charnockite minerals the systematic variation in fluid densities with a garnet feldspar quartz succession within individual samples argues against post metamorphic fluid infiltration and fits a scenario of mineral equilibration during near isothermal uplift following a clockwise pressure temperature time path along the pressure gradient the fluid densities show an increase from c 0 98 to c 1 10 g cm 3 this strengthens other evidence of a synmetamorphic entrapment of co 2 preliminary carbon isotope measurements of co 2 extracted from inclusions yield 13 c values of c 5 to 6 suggesting a sub continental mantle source the gondwanan lutzow holm bay terrain had undergone substantial extension during the late proterozoic with displacement along megafaults and emplacement of several alkaline subalkaline granite and syenite plutons and also k basalts it is therefore envisaged that the abundant co 2 in the charnockites could have been derived from an attenuated continental lithosphere and transferred through magmatic conduits

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

a simple preparation technique for the study of opal phytoliths from archaeological and quaternary sediments abstract this note describes a simple and inexpensive method for the extraction and counting of opal phytoliths from archaeological and quaternary sediments

fluids in granulites since the discovery of co2 fluid inclusions in granulites the role of fluids in the formation of these rocks has been widely studied owing to the complexity of the tectono metamorphic history of granulite terrains fluid inclusion data alone are not sufficient they need to be integrated with geochemical and mineralogical studies done on the same rock samples a clear understanding of the tectono metamorphic history of granulite terranes is also indispensable the widespread occurrence of co2 and the later discovered high salinity aqueous fluid inclusions support the idea that the lower crust underwent fluid flow and that both carbonic and brine fluids played a role in its formation both low h2o activity fluids play a similar role in destabilizing hydrous mineral phases furthermore experimental studies have shown that brine fluids have a much larger geochemical effect on granulites than initially expected these fluids are far more mobile in the lower crust compared with co2 and also have the capability for dissolving numerous minerals as in the example of the limpopo complex fluid inclusions and many metasomatic features observed in granulite terranes can thus be explained only by large scale movement of high salinity aqueous fluids and to a lesser extent co2 implying that lower crustal granulites are not as dry as previously assumed similar brines and co2 rich fluids are also found in mantle material most likely derived from deeply subducted supracrustal protoliths

precious metal enrichment at low redox in terrestrial native fe bearing basalts investigated using laser ablation icp ms primary native fe is a rare crystallizing phase from terrestrial basaltic magmas requiring highly reducing conditions fo2 iron wustite buffer in order to form reducing conditions in basaltic magmas can be achieved through assimilation of carbonaceous crustal material which leads to formation of an immiscible molten c rich native fe alloy liquid if this liquid also contains sufficient sulfur it can undergo further division into conjugate fe c rich and a fe s rich immiscible melts that can effectively scavenge the highly siderophile elements hse re au and the platinum group elements pge pd pt rh ru ir os as well as ni and cu to economic abundances three localities are known globally where native fe bearing mafic rocks occur 1 paleocene basalts of disko island west greenland 2 a miocene lava of the buhl basalts germany and 3 mafic intrusions associated with the late permian siberian flood basalts in this contribution we report major and minor element compositions and hse concentrations for the main alloy phases feni metal and cohenite and sulfide for all three known global occurrences of native fe bearing basalt total hse abundances in metal grains obtained by laser ablation inductively coupled plasma mass spectrometry la icp ms are lowest in the buhl basalt 0 05 ppm intermediate in the disko island basalts 4 8 ppm and highest the siberian khungtukun and dzhaltul intrusions 10 30 ppm these differences demonstrate that while native fe formation is the result of carbonaceous crustal assimilation hse enrichment is not ubiquitous during this process the siberian occurrences are characterized by pt pge ppge pt pd enrichment relative to the ir pge ipge rh ru ir os consistent with models of early stage fractionation of olivine chromite and metallic ipge in staging magma reservoirs prior to the addition of c rich crustal materials in the shallow crust relative to noril sk ni cu pge sulfide ores the siberian native fe basalts are enriched in the ppge relative to the ipge but exhibit ru enrichments in contrast disko island native fe rocks do not show significant fractionation of the ppge from the ipge but have positive re and ru anomalies and high os ir ratios to reconcile these observations we present a general model where some parental melts experienced early stage crustal assimilation in staging magma reservoirs prior to reduction by carbon rich materials e g khungtukun dzhaltul whereas basaltic parental melts to disko island and buhl solely experienced interaction with carbonaceous material resulting in extensive devolatilization native fe segregation and native fe formation

bootstrap inversion for vertical and lateral variations of the s wave structure and the υp υs ratio from shallow earthquakes in the rhinegraben seismic zone germany using s wave arrival times of 400 earthquakes in the southern rhinegraben 1 d and 3 d inversions for the shear s wave crustal structure of that region are performed these models are then combined with previously obtained 1 d and 3 d p wave models to compute vertical and lateral variations of the p s poisson s ratio such an independent p and s wave inversion approach circumvents many of the limitations of the classical wadati diagram method usually used for the determination of crustal p s ratios for the statistical evaluation of the 1 d models we have used a new monte carlo bootstrap resampling technique which has been found useful in many statistical estimation problems where the underlying statistics of the data is poorly known the 1 d bootstrap p s crustal models exhibit significant vertical variations whereas the upper sedimentary and crystalline layer of the crust is characterized by a significant increase of p s over the reference value p s in the upper and middle crust is lowered this correlates well with several findings from wadati diagrams for p s in other seismically active zones and might be explained through the gradual closing of saturated microcracks in that depth range however the p s reduction can also be interpreted in terms of a particular petrological composition such as orthoclase feldspar without the indispensable need for fluids a lowering of p gus is also observed for the lower crust which might reflect the strong lamination found here from previous deep seismic sounding experiments for the upper mantle a strong increase of p s is observed which is primarily triggered by a decrease of s and is best explained by an eclogite petrological assemblage for the 3 d s wave models significant reductions of more than 100 were obtained for the unexplained travel time residuals variations of p s in the upper and middle crust are mostly induced by changes in p rather than s for the upper crust slight decreases of p s are observed for the rhinegraben but increases are detected for the adjacent vosges and black forest areas in the middle crust the refraction seismic deduced reduction of p s under parts of the black forest can neither be corroborated nor rejected however because of some experimental ambiguity on the effects of petrological composition and interstitial pore fluids this does not rule out the presence of the latter in the lower crust a local reduction of p s is observed under the kaiserstuhl and graben black forest shoulder and has been explained in terms of a metamorphic dehydrating phase change of the hydrous amphibolite facies to the anhydrous granulite facies depending on the pore pressure of the dehydrated water and the fractional amount of interstitial co2 granulite facies metamorphism occurs in the 650 800 c temperature range temperatures at the upper end of this interval can be generated by the mechanism of accretionary magmatic underplating as it has been proposed for some extensional rift zones where asthenospheric upwelling as in the rhinegraben occurs

fluid heterogeneity during granulite facies metamorphism in the adirondacks stable isotope evidence the preservation of premetamorphic whole rock oxygen isotope ratios in adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived hot co2 h2o fluids during granulite facies metamorphism this conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations the data suggest that these rocks were not an open system during metamorphism that fluid rock ratios were in many instances between 0 0 and 0 1 that externally derived fluids as well as fluids derived by metamorphic volatilization rose along localized channels and were not pervasive and thus that no single generalization can be applied to metamorphic fluid conditions in the adirondacks

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

estimating phytolith influx in lake sediments abstract so far no phytolith extraction protocols have been tested for accuracy and repeatability here we aim to display a phytolith extraction method combining the strengths of two widely used protocols supplemented with silica microspheres as exogenous markers for quantifying phytolith concentrations phytolith concentrations were estimated for samples from two sedimentary sequences in which numerical age depth models make it possible to calculate phytolith influxes phytolith numbers per cm2 per yr analysis of replicates confirmed the statistical robustness the repeatability and the very few biases of our extraction technique for small phytoliths since the relationship between grass silica short cells and microspheres was kept stable furthermore we demonstrated that silica microspheres are robust exogenous markers for estimating phytolith concentrations the minimum number of items i e phytoliths plus silica microspheres that must be counted to estimate phytolith concentrations and thus influxes depends on the ratio of phytoliths to microspheres r and is minimized when r 1 nevertheless we recommend using ratios r 1 in order to avoid having the counting process become excessively time consuming because microspheres are easier to identify and count than phytoliths

lower crustal petrology from wide angle p and s wave measurements in the black forest abstract the lower crust of the black forest in southwest germany is strongly reflective for compressional waves but almost non reflective for shear waves if the reflectivity for p waves is caused by alternating high and low velocity rocks the s wave observations require that the low velocity rocks have a low poisson s ratio and vice versa a purely compositional petrological model for lower crustal rocks can fit the observed p and s wave velocity data provided a rather high quartz content 50 is acceptable for the lower crust

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago

petrology and geochemistry of the neoproterozoic guaxupe granulite facies terrain southeastern brazil abstract geochemical and oxygen isotopic data on the neoproterozoic granulite facies rocks enderbites charnockite and charnokitic augen gneisses of guaxupe brazil are assembled geochemical discrimination function calculations show an igneous origin for majority of the rock types in the area major and trace element data especially ree are similar to tonalite and granodiorite oxygen isotope composition for charnockitic gneisses and mafic granulites yield 18o values in the range of 8 8 to 11 and fall in the range of quartzofeldspathic rocks of medium to high grade terrains elsewhere a small scale variation of 18o values compatible with the chemical data imply the preservation of pre metamorphic oxygen isotope compositions minimum peak pressure temperature conditions are 8 5 kbar and 850 c the high grade metamorphism did not appear to have altered significantly the geochemical and oxygen isotope compositions of the protoliths approximately 2 5 kbar of pressure decrease accompanied by 200 c cooling has been recorded for a portion of the cooling path the p t path is consistent with a single event namely the formation and uplift of the guaxupenappe in the neoproterozoic brasiliano cycle