the erzgebirge germany a subducted part of northern gondwana geochemical evidence for repetition of early palaeozoic metasedimentary sequences in metamorphic thrust units one of the major metamorphic terranes of the bohemian massif the erzgebirge is interpreted to record a subducted part of a palaeozoic margin of gondwana a geochemical study on non calcareous metasediments from the various metamorphic units from lower greenschist to granulite facies metamorphism supports a recently established thrust model geochemical discrimination and correlation from the metasediments of the erzgebirge suggest repetition of an early palaeozoic metasedimentary sequence in metamorphic thrust units this new finding is in line with recent radiometric dating of intercalated metarhyolitic rocks which yielded ages of around 480 ma it is furthermore supported by correlation with a low grade standard section in thuringia which represents the transition from an orogenic belt to a passive margin setting with highly mature sediments significant geochemical signatures have been identified in three different lithotypes which reappear in at least three metamorphic units of the erzgebirge geochemical correlation of these units was established using simple comparison of averages and with statistical techniques the identification of significant geochemical signatures from different lithotypes in metamorphic suites has important implications for terrane analysis and reconstruction of ancient tectonic settings the repetition of lithologies and their distinct chemical compositions in progressively metamorphosed units is useful for examining element mobility during barrovian metamorphism statistical comparison implies that li is progressively depleted from the greenschist to amphibolite facies whereas ca exhibits some enrichment all the other elements studied are considered to be immobile

trace element modelling of pelite derived granites the presence or absence of a vapour phase during incongruent melt reactions of muscovite and biotite together with the composition of the protolith determines the trace element characteristics of the resulting melt provided that equilibrium melting occurs for those phases that host the tracc elements of interest for granitic melts rb sr and ba provide critical constraints on the conditions that prevailed during melting whereas ree are primarily controlled by accessory phase behaviour mass balance constraints for eutectic granites that are formed by the incongruent melting of muscovite in pelites indicate that melting in the presence of a vapour phase will result in a large melt fraction and deplete the restite in feldspar hence the melt will be characterized by low rb sr and high sr ba ratios in contrast vapour absent melting will result in a smaller melt fraction and an increase in the restitic feldspar consequently high rb sr and low sr ba ratios are predicted vapour absent melting will also enhance the negative eu anomaly in the melt granites that result from the incongruent melting of biotite in the source will be characterized by higher rb concentrations than those that result from the incongruent melting of muscovite the himalayan leucogranites provide an example of unfractionated crustally derived eutectic melts that are enriched in rb but depleted in sr and ba relative to their metasedimentary protoliths these compositions may be generated by the incongruent melting of muscovite as a low melt fraction f 0 1 from a pelitic source under vapour absent conditions

oceanic molybdenum drawdown by epeiric sea expansion in the mesoproterozoic abstract molybdenum is a bioessential micronutrient whose abundance in the global oceans may have played a primary role in evolution of the earth s nitrogen cycle and ultimately in the timing of the ecologic expansion of early eukaryotes because molybdenum mo is delivered to the ocean under conditions of oxic weathering and is removed in suboxic and euxinic environments the concentration of mo in the oceans reflects a complex function of global redox and the hydrologic conditions that influence the areal extent of euxinic sedimentation recent compilations of mo within euxinic shales scott et al 2008 och and shields zhou 2012 sahoo et al 2012 indicate that the oceanic reservoir of mo did not rise substantially above crustal values until the great oxidation event 2 3 ga and a modern mo cycle did not develop until the contraction of ocean euxinia in the latest proterozoic at present a paucity of data from euxinic shales of the late mesoproterozoic 1 3 to 1 0 ga limits our ability to relate marine redox evolution to biological innovation during a critical interval of eukaryotic development here we present data from marine shales of the 1 1 ga atar and el mreiti groups mauritania which were deposited during sea level highstand when shallow epeiric seas covered much of the west african craton epicratonic strata of the el mreiti group were deposited under fluctuating redox conditions near a shallow chemocline as evidenced by iron speciation and record generally low mo concentrations

crustal reworking in southern africa constraints from sr nd isotope studies in archaean to pan african terrains abstract isotopic data for crustal rocks from southern africa indicate that significant crustal growth occurred prior to 2 5 ga and crustal growth since 1 0 ga was negligible orogenic events since about 2 0 ga appear to have reworked progressively larger proportions of pre existing crustal material and the last major orogenic event the damara of namibia resulted in no detectable increase in crustal mass model age ratios dm nd t dm sr refect intracrustal fractionation of rb sr relative to sm nd and so constrain models for intracrustal reworking data from sedimentary rocks suggest that rb sr ratios are increased at average rates of between 1 2 and 2 2 per billion years by processes of erosion and sedimentation metamorphism and intracrustal melting in the continuously reworked upper crust these inferred rates of rb sr fractionation can account for the present day 87 sr 86 sr ratios in modern river particulates and the restricted range of depositional 87 sr 86 sr ratios in upper proterozoic sediments

origin of mineralizing fluids of the sediment hosted navachab gold mine namibia constraints from stable o h c s isotopes the navachab gold mine in the damara belt of central namibia is characterized by a polymetallic au bi as cu ag ore assemblage including pyrrhotite chalcopyrite sphalerite arsenopyrite bismuth gold bismuthinite and bismuth tellurides gold is hosted by quartz sulfide veins and semimassive sulfide lenses that are developed in a near vertical sequence of shelf type metasedimentary rocks including marble calcsilicate rock and biotite schist the sequence has been intruded by abundant syntectonic lamprophyre aplite and pegmatite dikes documenting widespread igneous activity coeval with mineralization the majority of quartz from the veins has 18o values of 14 to 15 per mil v smow the total variations in 18o values of the biotite schist and calcsilicate rock are relatively small 12 14 whereas the marble records steep gradients in 18o values 17 21 the lowest values being recorded at the vein margins despite this there is no correlation between 18o and 13c values and the carbonate content of the rocks indicating that fluid rock interaction alone cannot explain the isotopic gradients in addition the marble records increased 13c values at the contact to the veins possibly related to a change in the physicochemical conditions during fluid rock interaction gold is interpreted to have precipitated in equilibrium with metamorphic fluid 18o 12 14 d 40 to 60 at peak metamorphic conditions of ca 550 c and 2 kbars consistent with isotopic fractionations between coexisting calcite garnet and clinopyroxene in the alteration halos the most likely source of the mineralizing fluid was a midcrustal fluid in equilibrium with the damaran metapelites that underwent prograde metamorphism at amphibolite to granulite facies grades although there is no isotopic evidence for the contribution of magmatic fluids they may have been important in contributing to the overall hydraulic regime and high apparent geothermal gradients ca 80 c km 1 in the mine area

assessment of pyrite composition by la icp ms techniques from massive sulfide deposits of the bathurst mining camp canada from textural and chemical evolution to its application as a vectoring tool for the exploration of vms deposits abstract pyrite is ubiquitous throughout the massive sulfide deposits of the bathurst mining camp canada pyrite locally preserves primary pseudo primary textures as well as secondary textures that formed in response to the hydrothermal metamorphic and deformation processes to which the host sequence was exposed in the bathurst mining camp most forms of pyrite are arsenian up to 3 13 wt as with considerable enrichment in tl sb sn bi ag se and to a lesser extent cd ga te hg ge in and au la icp ms analyses of primary pyrite show significant enrichment in fluid mobile elements in particular tl sb as and hg as well as bi pb and sn in contrast secondary pyrite syn to post deformation varieties is not enriched in these elements superimposed metamorphism typically causes loss of fluid mobile elements to different degrees except for se pyrite chemical variations have the potential to monitor ore petrogenesis at inter and intra deposit scales pyrite from the cu zone is enriched in se relative to pyrite from zn pb zone in which tl is elevated throughout the host sequence fluid mobile element concentrations of pyrite vary by several orders magnitude with the highest fluid mobile element abundances in footwall rocks immediately proximal to the deposit moreover elevated fluid mobile element concentrations of pyrite are recognized in footwall felsic volcanic and sedimentary rocks as much as several hundred metres away from the deposit hanging wall zones contain pyrite with fluid mobile element contents comparable to pyrite from sulfide horizon the fluid mobile element concentrations of pyrite are higher in exhalative sedimentary rocks than pyrite from the sulfide mineralization itself the spatial variation in fluid mobile element concentrations in pyrite as identified using la icp ms can be used to identify otherwise cryptic deposit related haloes ultimately this technique when combined with traditional exploration tools can be used to vector toward vms mineralization in the bathurst mining camp and possibly a useful indicator in a prospect scale base metal exploration

origin of rare element mineralized damara belt pegmatites a geochemical and light stable isotope study abstract neoproterozoic li cs ta lct pegmatites and pegmatitic sheeted leucogranites slgs of the damara belt namibia although coeval are variably mineralized and have intruded multiple tectono stratigraphic units major and trace element data together with oxygen and hydrogen isotopes were used to identify possible sources for these pegmatite melts two groups of pegmatites can be identified on the basis of o isotopes group a pegmatites which include u enriched pegmatitic slgs with a nb y f nyf pegmatite affinity kinnaird and nex 2007 and li be rich lct pegmatites with 18o 11 2 12 9 are metaluminous to peraluminous suggesting that they evolved from a partial melt of a mixed metasedimentary and igneous source group b pegmatites which contain sn li sn and tourmaline mineralization have higher 18o values 14 16 consistent with their derivation from a purely s type source with possible incorporation of or exchange with carbonates crystallization temperatures calculated using ti in quartz and o isotope thermometry are in agreement with each other and range from 420 to 575 c for lct pegmatites and 650 c for pegmatitic slgs the juxtaposition of coeval post tectonic lct pegmatites and pegmatitic slgs with an nyf affinity in the damara belt precludes tectonic setting as the only source of compositional variability in lct and nyf pegmatite melts

timescales of disequilibrium melting in the crust constraints from modelling the distribution of multiple trace elements and a case study from the lesser himalayan rocks of sikkim a numerical code has been developed to track the distribution of trace elements in crustal rocks undergoing melting the model handles diffusion with moving boundaries and accounts for the processes of diffusion dissolution and precipitation in a partially molten system among the various input parameters for modelling source composition i e modal abundance variations diffusion coefficients and partition coefficients are found to exert a significant control on the melt chemistry the other inputs such as melt reaction stoichiometry kinetics of melting and grain size of protolith have lesser influence exploration of the general behaviour indicates that for systems in which disequilibrium melting of the kind considered in this paper occurs trace element concentrations may be used to constrain the composition of the protolith or the timescales of melting depending on the specific circumstances after exploring some general features of melting in a pelitic system the model is applied to calculate trace element distributions in migmatites from the lesser himalayan rocks in sikkim india we focus on the distribution of trace elements during the initial stages of melt formation these partially molten rocks show disequilibrium distribution of trace elements and the numerical code is capable of quantitatively reproducing many of the observed patterns the results of the modelling indicate that the observed melts in this zone were formed within 50 000 years and that segregation of melts into leucosome and restite was complete between 50 000 and 250 000 years these short timescales may point to deformation enhanced melt segregation at least on a hand specimen scale it is important to distinguish between timescales of segregation over these scales and timescales of removal of melt on an outcrop scale to form plutons the latter requiring higher degrees of melting and larger distances of migration take longer

porosity of late paleocene ornitholithus eggshells tremp fm south central pyrenees spain palaeoclimatic implications eggshell fragments of ratite type ornitholithus oofamily elongatoolithidae attributed to giant birds are described from upper paleocene deposits in the pyrenean provence region we study the porosity of a rich ornitholithus sample from claret 4 locality tremp fm lleida spain closely related to the global warming event which took place at the paleocene eocene boundary petm in order to infer relations between egg conductance nesting habits and palaeoenviromental conditions an egg mass of around 3 kg is inferred for the large ornitholithus eggs in agreement with the values previously estimated by touraine touraine f 1960 oeufs d oiseaux de tres grande taille dans l eocene inferieur de provence pp 783 789 but lower than those obtained by dughi and sirugue dughi r sirugue f 1962 distribution verticale des oeufs d oiseaux fosiles de l eocene de basse provence bull soc geol fr 7 69 78 o arquatus group 8 7 kg porosity observed in ornitholithus eggshells is extremely reduced in comparison to bird eggs and even much more reduced in relation to theropod dinosaurs pore number is similar to that of bird eggs but most ornitholithus pores are exceedingly small micropores thus pore radius and total pore area is much lower than in recent birds moreover ornitholithus micropores lack connectivity between them thus decreasing functional pore area and permeability the function of micropores could be related to weight spare favorable hatching and or thermal isolation ornitholithus eggshells are the most compact of all bird or theropod eggshells studied so far consequently calculated water vapor conductance values in ornitholithus eggs are in average 8 times lower than that for recent birds the relation between egg conductance and nesting environment shown in recent birds suggests in the case of ornitholithus an open and extremely dry nest environment anomalous compact ornitholithus eggshells could help to keep eggs inner relatively constant temperature and humidity in the extremely warm and dry palaeoenvironment inferred for the pyrenean region at the paleocene eocene thermal maximum

the influence of source rock type chemical weathering and sorting on the geochemistry of clastic sediments from the quetico metasedimentary belt superior province canada abstract the geochemistry of clastic sediments is controlled by at least four factors source rock composition weathering of the source rocks sorting of the weathered detritus and post depositional alteration during diagenesis and metamorphism in order to evaluate the relative importance of these factors major trace and rare earth element contents were determined for distal and proximal clastic turbidites from the archaean quetico metasedimentary belt the degree of metamorphism of the samples ranges from middle greenschist to upper amphibolite facies simple mixing of archaean mafic and acidic rocks of similar composition to those found in the adjacent granite greenstone terrains will account for the tio2 feot mgo cr sc y and hree contents of the clastic turbidites the metasediments are enriched in lree relative to the mafic acidic rock mixing line indicating that the acidic source was enriched in the lree compared to archaean terrains from other parts of the world some quetico turbidites have an additional fe rich source component possibly a chemical sediment incorporated at the time of turbidite slumping cao na2o k2o rb and sr form trends on bivariant plots that are oblique to the mafic acidic rock mixing line and hence cannot be accounted for by simple mixing of the source rocks chemical weathering of feldspars prior to deposition can account for cao na2o k2o rb and sr trends since cao na2o and sr are lost to the weathering solutions and k2o and rb are retained on the product clays the higher na 2 o cao k 2 o na 2 o rb k 2 o and sr cao ratios but lower cao content of the distal samples suggest that they were derived from a bulk sediment that had experienced a greater degree of chemical weathering than the proximal sediments sorting is the factor that most strongly influences the composition of individual samples within the proximal sample group the coarse grained metagraywackes with their higher quartz feldspar and heavy mineral contents are enriched in sio2 cao na2o sr lree zr and hf relative to the fine grained clay rich metapelites metapelites are enriched in tio2 al2o3 feot mgo k2o cr zn sc y hree cs and rb as a result of their higher clay contents thus the use of clastic sediment compositions in determining average crustal compositions e g for the ree can only give satisfactory results when all grain size fractions are sampled in their correct relative proportions the chemical differences observed between the high and low grade samples can be accounted for by source rock type chemical weathering of the source rocks or sorting post depositional element mobility does not appear to be an important factor in determining the composition of the quetico metasediments

petrology and k ar ages of rift related basaltic rocks offshore northern brazil 3 n tholeiitic basaltic rock in three cores from petrobras drill site aps 21 1960 2480 m depths amapa basin offshore brazil is compositionally similar to rift related basaltic rock associated with the opening of both the north and south atlantic oceans sio 2 52 54 wt k 2 o 0 7 1 3 tio 2 1 3 2 whole rock k ar ages are 185 4 183 2 and 126 5 m y if these represent crystallization ages then the older samples correspond to north atlantic tectonism as represented by the liberian dike system and the younger correlates with south atlantic rift related magmatism of which serra geral flood basalts are the best example trace and ree elements identify t type mantle source areas la sm n 2 zr nb 8 11 that feasibly were mixes of n type and p type components metasomatized or veined upper mantle these amapa basin mafic rocks document the southernmost magmatism related to north atlantic rifting as well as early mesozoic mantle source areas and processes beneath gondwanaland such

geochemical changes accompanying the mylonitization of diverse rock types from the grenville front zone eastern labrador the relationship between mineralogy and bulk composition was examined in mylonites developed in a variety of rock types from the grenville front zone of eastern labrador mylonites developed from o

fluid evolution during burial and variscan deformation in the lower devonian rocks of the high ardenne slate belt belgium sources and causes of high salinity and c o h n fluids fluid inclusions in quartz veins of the high ardenne slate belt have preserved remnants of prograde and retrograde metamorphic fluids these fluids were examined by petrography microthermometry and raman analysis to define the chemical and spatial evolution of the fluids that circulated through the metamorphic area of the high ardenne slate belt the earliest fluid type was a mixed aqueous gaseous fluid h2o nacl co2 ch4 n2 occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic area in the central part of the metamorphic area epizone in addition to this mixed aqueous gaseous fluid primary and isolated fluid inclusions are also filled with a purely gaseous fluid co2 n2 ch4 during the variscan orogeny the chemical composition of gaseous fluids circulating through the lower devonian rocks in the epizonal part of the slate belt evolved from an earlier co2 ch4 n2 composition to a later composition enriched in n2 finally a late variscan aqueous fluid system with a h2o nacl composition migrated through the lower devonian rocks this latest type of fluid can be observed in and outside the epizonal metamorphic part of the high ardenne slate belt the chemical composition of the fluids throughout the metamorphic area shows a direct correlation with the metamorphic grade of the host rock in general the proportion of non polar species i e co2 ch4 n2 with respect to water and the proportion of non polar species other than co2 increase with increasing metamorphic grade within the slate belt in addition to this spatial evolution of the fluids the temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of the basin in addition to the maturity of the metamorphic fluids the salinity of the aqueous fluids also shows a link with the metamorphic grade of the host rock for the earliest and latest fluid inclusions in the anchizonal part of the high ardenne slate belt the salinity varies respectively between 0 and 3 5 eq wt nacl and between 0 and 2 7 eq wt nacl while in the epizonal part the salinity varies between 0 6 and 17 eq wt nacl and between 3 and 10 6 eq wt for the earliest and latest aqueous fluid inclusions respectively although high salinity fluids are often attributed to the original sedimentary setting the increasing salinity of the fluids that circulated through the lower devonian rocks in the high ardenne slate belt can be directly attributed to regional metamorphism more specifically the salinity of the primary fluid inclusions is related to hydrolysis reactions of cl bearing minerals during prograde metamorphism while the salinity of the secondary fluid inclusions is rather related to hydration reactions during retrograde metamorphism the temporal and spatial distribution of the fluids in the high ardenne slate belt are indicative for a closed fluid flow system present in the lower devonian rocks during burial and variscan deformation where fluids were in thermal and chemical equilibrium with the host rock such a closed fluid flow system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform 180 values of both the veins and their host rock demonstrate a rock buffered fluid flow system

trace element partitioning between coexisting biotite and muscovite from metamorphic rocks western labrador structural compositional and thermal controls coexisting biotite and muscovite in ten metapelitic and quartzofeldspathic rocks from western labrador have been analyzed by electron microprobe for major and minor elements and by a laser ablation microprobe coupled to icp ms lam icp ms for selected trace elements li sc v cr mn co ni cu zn rb sr y zr nb cs ba ree hf and ta the samples have experienced a single prograde grenvillian metamorphism ranging from 490 to 680 c and from 7 to 12 kbar the trace element compositions of coexisting micas in the metamorphic rocks are used to assess the effects of crystal structure major element composition and temperature on the partitioning of each element between biotite and muscovite overall trace element distributions are systematic across the range of metamorphic grade and bulk composition suggesting that chemical equilibrium was approached most distribution coefficients biotite muscovite show good agreement with published data however distribution coefficients for co and sr are significantly different from previous determinations probably because of contamination associated with older data obtained by bulk analysis techniques the sequence of distribution coefficients is governed mainly by the ionic radii and charges of substituting cations compared to the optimum ionic radius of each crystallographic site in the micas in particular distribution coefficients exhibit the sequence cr3 0 615 a v3 0 64 a sc3 0 745 a in vi sites and ba2 1 61 a sr2 1 44 a and cs 1 88 a k 1 64 a rb 1 72 a na 1 39 a in xii sites the distributions of li sc sr and ba appear to be thermally sensitive but are also controlled by major element compositions of micas v and zr partitioning is dependent on t and may be used to cross check thermometry calculations where the latter suffer from retrograde re equilibration and or high concentrations of fe3 the ranges and dependence of distribution coefficients on major element compositions provide important constraints on the values that can be used in geochemical modeling

geochronology and petrology of migmatites from the proterozoic damara belt importance of episodic fluid present disequilibrium melting and consequences for granite petrology abstract the oetmoed granite migmatite complex ogmc central damara orogen namibia consists of grt and crd bearing s type granites and hbl and titanite bearing a type granites that intruded into crd sil kfs bearing metasedimentary rocks stromatic migmatites and nebulites stromatic migmatites formed by limited in situ partial melting of metapelites under h2o saturated conditions at 700 c and 4 5 kbar this partial melting event took place close to the peak of regional metamorphism at 510 ma as revealed by sm nd garnet whole rock ages as well as u pb monazite ages the newly formed melt remained more or less at the site of origin melanosomes of the stromatic migmatites do not resemble true residues instead they represent reaction zones between in situ melt and the metasedimentary host rock leucosomes from the stromatic migmatites are lree and hfse depleted which is typical for the low melt fractions generally observed in migmatite terranes mass balance calculations suggest that these leucosomes may be disequilibrium melts similar 18 o whole rock values between 13 and 14 observed in leucosomes and corresponding melanosomes suggest homogenization of oxygen isotopes between the different rock types via the melt and an internal fluid phase during melting other leucosomes with a major element chemistry similar to the leucosomes from the stromatic migmatites but higher ree contents suggest significant incorporation of lree enriched phases monazite from the country rocks for these leucosomes sm nd garnet whole rock ages are 473 ma indicating a second phase of melting nebulites mainly result from injection of granitic melts into the country rocks but their residual chemistry indicates that partial melting and limited melt removal must have occurred monazites from these nebulites record concordant u pb ages between 540 ma and 470 ma indicating episodic migmatization during high grade regional metamorphism intrusive peraluminous granites are likely generated by partial melting of pelitic sources in the lower crust and different source rocks are probably not the controlling factor for the different chemistry of leucosomes and granites therefore different melting conditions fluid absent vs fluid present and different modes of entrainment and solubilities of accessory phases control the elemental budgets of the leucosomes large scale migmatite granite complexes are a substantial part of some high grade terrains but the distinctive geochemical composition of some leucosomes make these rocks unlikely precursors of large scale granitic bodies

the provenance of low calcic black shales the elemental concentration of sedimentary rocks depends on the varying reactivity of each element as it goes from the source through weathering deposition diagenesis lithification and even low rank metamorphism however non reactive components of detrital particles ideally are characteristic of the original igneous source and thus are useful in provenance studies to determine the source of detrital granitic and volcanic components of low calcic 1 caco3 marine black shales the concentrations of apparently non reactive i e unaffected by diagenetic redox and or low rank metamorphic processes trace elements were examined using standard trace element discrimination diagrams developed for igneous rocks the chemical data was obtained by neutron activation analyses of about 200 stratigraphically well documented black shale samples from the cambrian through the jurassic a la th sc ternary diagram distinguishes among contributions from the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 all the low calcic black shales cluster within the region of the upper crust th hf co ternary diagrams also are commonly used to distinguish among the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 as co is redox sensitive in black shale environments it was necessary to substitute an immobile element i e example rb in the diagram with this substitution of black shales all cluster in the region of the upper continental crust to determine the provenance of the granitic component pearce et al 1984 plots of ta vs yb and rb vs yb ta shows a cluster at the junction of the boundaries separating the volcanic arc granite vag syn collision granite syn colg and within plate granite wpg fields the majority fall within the vag field there are no occurrences of ocean ridge granite org the minimal contribution of basalts to marine black shales is confirmed by the ternary wood diagram th hf 3 ta wood et al 1979 the black shales plot in a cluster in a high th region outside the various basalt fields which suggests contribution from the continental crust

experimental silicate phosphate equilibria in peraluminous granitic magmas with a case study of the alburquerque batholith at tres arroyos badajoz spain with the actual mineralogy and whole rock p in the granite experimental results presented here establish the p2o5 content of aplite pegmatite facies at tres arroyos peraluminous silicic melt for three potential buffering reactions at 200 mpa h2o and t from 525 to 850 c 1 biotite sarcopside 2 spessartine sarcopside 3 petalite amblygonite montebrasite quartz the first two equilibria are moderately insensitive to t and buffer the p content of melt between 1 30 1 57 wt

intraformational redistribution of selected trace elements in the posidonia shale hils syncline nw germany caused by the thermal influence of the vlotho massif selected samples of nw german posidonia shale hils syncline area were separated into five fractions bitumen kerogen pyrite carbonates silicates and chemically analyzed for trace element concentration using icp oes analyses in immature posidonia shale 0 53 ro co cu mo ni and zn occur mainly in the kerogen and pyrite fractions in mature posidonia shale 1 45 ro these trace elements are mainly fixed in the silicate fractions we postulate a thermally induced intraformational redistribution of co cu mo ni and zn caused by heat from a deep seated igneous intrusion the vlotho massif

cl br and i analyses of metamorphic and sedimentary rocks by isotope dilution mass spectrometry isotope dilution mass spectrometry with negative thermal ions was applied to determine cl br and i in rocks which in part contained less than 100 ppb of br and i two sets of samples have been investigated a a series of al rich metapelites of increasing metamorphic grade from the damara orogen namibia and b fresh and hydrothermally altered greywackes from the pb zn deposit bad grund in germany it was found that regional metamorphism of al rich metapelites causes no strong fractionation of the halides the br cl ratios in the metapelites are similar to those of sea water the i cl and i br ratios however are 500 times higher the i depleted in the ocean most probably is associated with organic matter stored in sediments the unaltered greywackes from near the pb zn vein have about the same concentrations of halides as the metamorphic al rich pelites by contrast the hydrothemally altered greywackes contain about twice as much cl and i and about 2 5 times as much br as the unaltered samples the element ratios however are similar for all three categories of rocks thereby indicating that sea water played no role in the hydrothermal system

fluid inclusion systems in metaplaya deposits and their relationships to mineralization and tectonics abstract fluid inclusions have been analysed along traverses through the upper proterozoic damara orogen south west africa namibia two genetically different fluid systems of regional importance could be distinguished 1 a fluid system with 25 50 gross salinity nacl kcl cacl2 source continental evaporitic sequences and 2 another fluid system with 4 16 gross salinity nacl source metamorphic fluids derived from pelitic geosynclinal sediments further fluid systems of local importance are bound to numerous late tectonic granite and alaskite intrusions residual hypersaline solutions caused mineralization of stratiform cu deposits and numerous giant quartz reefs the two fluid systems have played an important role in the development of thrusts and nappes

the metamorphic behaviour and petrogenetic significance of zinc in amphibolite facies staurolite bearing mica schists puolankajarvi formation central finland abstract whole rock analyses and mineral analyses were performed on 24 samples of mica schists from the early proterozoic puolankajarvi formation pjf the whole rock zn content 36 127 ppm mean 77 ppm was at the normal level for pelitic and crustal rocks staurolite being the only mineral phase to contain zinc in measurable amounts 0 0 1 33 wt zno mean 0 28 wt when staurolite was present it contained nearly all of the zinc of the rock the zn content does not vary between the rocks in which staurolite has never been generated those in which staurolite is present and those from which staurolite has been destroyed this suggests that despite the fact that staurolite is a very strong acceptor of zn the generation of staurolite under reducing conditions log f o 2 22 5 t 545 c p 3 7 kbar did not increase the content of zn in the whole rock neither did the destruction of staurolite under more oxidizing conditions log f o 2 22 2 21 0 t 500 520 c p 2 1 3 5 kbar reduce it because there is evidence of considerable fluid flow through the rock during certain stages of the metamorphism of the pjf it is concluded that zn is an immobile element in amphibolite facies metamorphism in petites zinc should be treated as an additional component in metamorphic reactions of staurolite which increases the degrees of freedom of these reactions because of the immobility of zn and the increase in degrees of freedom these reactions will become dependent upon the concentration of zn in the rock

loss of metals from pelites during regional metamorphism in aluminous metapelites the ratio h2o k2o decreases with increasing metamorphic grade and degree of reaction this ratio is a very practical indicator for the progress of the mineral reconstitution during progressive metamorphism with decreasing values of the ratio h2o k2o the cu concentration and the following element ratios also decrease either continuously or in stepwise fashion tl k2o ba k2o pb k2o bi k2o hg k2o sr na2o zn fe2 mg cd fe2 mg rb k2o remains approximately constant in the aluminous metapelites of the damara orogen in namibia the following losses occur between the biotite isograd and anatexis 61 cu 20 tl 34 ba 59 pb 86 bi 46 hg 30 sr 25 zn 31 cd thus the potential of regional metamorphism to form hydrothermal deposits in the low grade environment should not be neglected

the end cretaceous dinosaur succession in europe the tremp basin record spain abstract the succession of maastrichtian deposits in the tremp basin south pyrenean area spain has provided long sections with numerous dinosaur sites found in the aren and tremp formations the dinosaur record consists on titanosaur sauropods dromaeosaurid theropods hadrosaur ornithopods including lambeosaurines and nodosaurid ankylosaurians correlation of the sections enabled a clear succession of dinosaur localities to be established and thereby the succession of dinosaur faunas titanosaur remains are present throughout the series but are particularly abundant in the basal strata theropods and hadrosaur ornithopods are found all through the series lambeosaurine hadrosaur remains are restricted to sandstone channel beds close to the k t boundary the palaeoenvironmental conditions in each site were deduced from the sedimentological study which allows establishing a relationship between environments and dinosaur taxa and thus the over or under representation of taxa in the vertical succession to be unravelled titanosaurs and ornithopods are common in but not exclusive to marine to continental transitional and continental environments respectively ankylosaurians are so far restricted to marine to continental transitional environments but the sample is scarce the fossil richness and the possibility of correlations among the different local sections make the tremp basin one of the best places in europe to understand the final history on non avian dinosaurs the fossil record from the tremp basin suggests that they were well diversified during the whole maastrichtian until their extinction as observed in north america and asia sauropods were still present at the end of the maastrichtian and lambeosaurines occurred at least in the upper part of the maastrichtian

generation of porphyritic and equigranular mafic enclaves during magma recharge events at unzen volcano japan mafic to intermediate enclaves are evenly distributed throughout the dacitic 1991 1995 lava sequence of unzen volcano japan representing hundreds of mafic recharge events over the life of the volcano this study documents the morphological textural chemical and petrological characteristics of the enclaves and coexisting silicic host lavas the eruptive products described in this study appear to be general products of magma mingling as the same textural types are seen at many other volcanoes two types of magmatic enclaves referred to as porphyritic and equigranular are easily distinguished texturally porphyritic enclaves display a wide range in composition from basalt to andesite are glass rich spherical and porphyritic and contain large resorbed plagioclase phenocrysts in a matrix of acicular crystals and glass equigranular enclaves are andesitic non porphyritic and consist of tabular medium grained microphenocrysts in a matrix glass that is in equilibrium with the host dacite magma porphyritic enclaves are produced when intruding basaltic magma engulfs melt and phenocrysts of resident silicic magma at their mutual interface equigranular enclaves are a product of a more prolonged mixing and gradual crystallization at a slower cooling rate within the interior of the mafic intrusion

basinal brines at the origin of the imiter ag hg deposit anti atlas morocco evidence from la icp ms data on fluid inclusions halogen signatures and stable isotopes h c o the imiter ag hg deposit is located in the precambrian volcano sedimentary formations of the saghro inlier eastern part of the anti atlas mountains morocco the orebodies consist of northeast southwest to east west veins and lenses hosted by cryogenian black shales and gray wackes and neoproterozoic conglomerates and are controlled by an east west fault network the so called imiter fault mineralogical and paleo fluid geochemistry investigations microthermometry raman spectroscopy la icp ms on individual inclusions bulk crush leach analyses and stable isotope data o h show that the main ag ore stage is related to circulation of deep basinal sedimentary brines na k mg salinity 16 7 to 26 wt nacl equiv molar cl br 330 18 o 2 15 2 35 smow and d 53 8 to 65 5 smow at temperatures of about 180 to 220 c and hydrostatic pressures the main driving mechanism for silver ore deposition is the dilution of ore bearing brines by a low salinity meteoric fluid containing a low density volatile component n 2 ch 4 co 2 t h 180 to 220 c 18 o 1 4 smow and d of about 28 2 smow silver content of the brines ranges from 2 to 30 mmol kg solution up to 3 200 ppm ag avg ag concentration about 900 ppm whereas the maximum ag content found in dilute waters is about 0 4 mmol kg solution 40 ppm the ore forming model proposed for the imiter deposit is 1 ag extraction from the basement by the penetration of deep basinal brines and 2 deposition in a structural trap through fluid mixing with recharge fluids this model is comparable to that described worldwide for the origin of pb zn f ba and u deposits near unconformities between basement and sedimentary basins similarities among the major ag deposits from the anti atlas imiter zgounder bou azzer strongly suggest that they resulted from a unique event likely related to the opening of the atlantic ocean the silver ores are superimposed on the same lineament as a preexisting uneconomic pan african co ni as system linked to magmatic intrusions but ag ores have no genetic relationship with them

dinosaur demise in light of their alleged perennial polar residency the end cretaceous biological crisis is represented by the demise of the non avian dinosaurs however most crucial biologically was the elimination of the photosynthesizing marine phyto and zooplankton forming the base of the marine food chain their abrupt demise attests to sunlight screening darkening the atmosphere for a few years alvarez et al science 208 1095 1108 1980 doi 10 1126 science 208 44 noticed in deep marine end cretaceous sediments an anomalous rise in the chemical element iridium ir which is rare on planet earth and thus suggests an extraterrestrial origin through an impact of a large asteroid this impact would have ejected enormous quantities of particles and aerosols shading the solar illumination as attested to by the elimination of the marine photosynthesizing plankton such a dark period must have affected life on land the apparent cold blooded non avian dinosaurs which were used to living in open terrains to absorb the solar illumination became inactive during the dark period and were incapable of withstanding predators this was in contrast to cold blooded crocodilians turtles and lizards that could hide in refuge sites on land and in the water dinosaur relics discovered in cretaceous polar regions were attributed to perennial residents surviving the nearly half year long dark winter despite their ability to leave the polar concentrations of disarticulated dinosaur bones were suggested as having resulted from a catastrophic burial of a population by floods however this should have fossilized complete skeletons alternatively herds of dinosaurs living in high latitudes might have been sexually driven to spend the half year of continuously illuminated polar summer for mating rather than for nourishment in which the lower latitudes provided as well the aggressive mating competitions would have left victims among the rivals and of young ones incidentally trampled over all being consumed and their skeletons disarticulated accordingly the alleged polar dinosaurs do not challenge the logical conclusion that the non avian dinosaurs were cold blooded as a result of which they became inactive and subjected to predation during the end cretaceous dark period

dinosaurs nesting on tidal flats abstract the discovery of a dinosaur clutch in upper cretaceous tidal flat deposits in the tremp formation in biscarri isona lleida spain provides insight into the mode of life of some dinosaurs the clutch occurs in grey marls that were originally waterlogged muddy sediments the seven elongated eggs are parallel to each other and with their long axis almost vertically oriented a mound nest is inferred in contrast to hole nest described so far for similar eggshell types the permeability of the eggshell oospecies megaloolithus siruguei was highly enhanced by a braided network of multicanaliculate pore canals the nest style eggshell porosity and tidal flat environment point to a periaquatic habitat for these dinosaurs a modern analogue occurs in crocodiles alligators and some birds living in periaquatic environments with nesting on plant mounds above waterlogged soils or even on floating vegetation

stable isotope evidence for fluid present and fluid absent metamorphism in metapelites from the damara orogen namibia a large difference of about 5 in the o isotopic composition of quartz characterizes the transition from very low grade or even anchimetamorphic slates to pelites metamorphosed at greenschist facies conditions a further increase in temperature does not result in systematic isotopic shifts mean around 15 5 however immediately at the isograds marking the transition from greenschist to amphibolite facies and amphibolite facies to higher amphibolite facies the quartz 18o values are significantly higher by 1 this increase is restricted to the area immediately at the isograds

zn and pb mobility during metamorphism of sedimentary rocks and potential implications for some base metal deposits comprehension of the genesis of pb zn ore systems is currently limited by a poor understanding of where these metals are sourced from our study of metal mobility during regional metamorphism in the mt lofty ranges south australia demonstrates that in staurolite absent siliciclastic metasedimentary rocks biotite contains 80 of the bulk rock zn as well as a considerable proportion of the total pb fluid flow through these metasedimentary rocks led to a continuous depletion of pb and zn on a mineral and bulk rock scale during prograde regional metamorphism we calculate that 80 of the bulk rock zn and 50 of the bulk rock pb were mobilised mainly through reactions involving biotite these reactions led to a calculated pb and zn loss of 2 7 and 27 mt respectively in the high grade metamorphic zone halogen contents of apatite and biotite and bulk rock zn isotope data provide evidence that cl rich metamorphic fluids were important for metal transport hence fluid flow accompanying prograde metamorphism of typical sedimentary rocks can mobilise base metals to the degree required to potentially supply significant pb zn ore systems

geochemical constraints on crustal anatexis a case study from the pan african damara granitoids of namibia major and trace element models of recently published vapour absent mica dehydration melting experiments are used to identify granitoids generated by muscovite and biotite dehydration melting and to distinguish between plagioclase limited and biotite limited biotite dehydration melting in the case of granitoids from the pan african damara mobile belt namibia many of the leucogranites and salem type granitoids may be modelled by biotite dehydration melting the low rb sr granitoids e g donkerhuk onanis salem onanis donkerhuk nomatsaus salem goas probably reflect feldspar limited biotite dehydration melting a pelitic source whereas the high rb sr suites e g bloedkoppie leucogranite stinkbank leucogranite salem swakopmund leucocratic stink bank granite reflect biotite limited biotite dehydration melting a greywacke source alaskites from the damara belt have major element compositions which are consistent with muscovite dehydration melting and their positive eu anomalies are linked to high k2o reflecting k feldspar entrainment combined zr and lree light rare earth element solubility models indicate that insufficient time probably less than 104 years had elapsed between melt generation and melt extraction to ensure that the alaskite melts attained their equilibrium concentrations of zr and the lrees in contrast the leucogranites and salem type granites have attained their equilibrium inventories of these trace elements combined fe2o3 and mgo contents in some samples from two granitoids the salem goas and donkerhuk onanis intrusions are higher than those readily attainable by biotite dehydration melting indicating either 1 that they contain a contribution from melts generated by incipient garnet breakdown or 2 that they contain small amounts of an entrained ferromagnesian phase

the petrogenesis of some migmatites and granites central damara orogen namibia evidence for disequilibrium melting wall rock contamination and crystal fractionation

lead contents of s type granites and their petrogenetic significance an evaluation of pb and ba contents in s type granites can provide important information on the processes of crustal partial melting primary low t s type granites which form mainly by fluid absent muscovite melting may acquire a significant enrichment in pb when compared to higher t s type granites for a given ba content we consider the following factors are responsible for this enrichment muscovite is a major carrier of pb in amphibolite facies metapelites and thus large quantities of pb can be liberated upon its breakdown the typical restite assemblage of qz bt sil pl grt kfsp that forms during low t fluid absent muscovite melting can take up only minor amounts of this pb this is because the crystal melt pb distribution coefficients for these restite minerals are low to very low only k feldspar is moderately compatible for pb with a crystal melt distribution coefficient of 3 but its modal content in restites is usually low at the same time the restite assemblage will retain much ba owing to the very high ba uptake in both biotite and k feldspar which is an order of magnitude higher than for pb thus during a low t anatectic event involving a low degree of crustal melting pb as an incompatible element can become strongly enriched in the partial melt relative to ba and also relative to source rock values in the case of higher t anatexis and larger partial melt amounts the pb becomes less enriched and the ba less depleted or even enriched relative to source rock values during fractional crystallization of a s type granite magma ba behaves strongly compatibly and pb weakly compatibly the concentrations of both elements decrease along the liquid line of decent owing to this sympathetic fractionation behavior the primary source related pb ba fingerprint with weak or strong pb enrichment remains in evolved s type granites this facilitates a distinction between primary low t s type granites which are related to muscovite melting and secondary low t s type granites that evolve through fractional crystallization from a higher t parental magma we show in this paper that a simple logarithmic pb versus ba diagram can be a valuable aid for interpreting the petrogenesis of s type granite suites

an example of trondhjemite genesis by means of alkali metasomatism rockford granite alabama appalachians a model for trondhjemite genesis is proposed where granite is transformed to trondhjemite via infiltration by a na rich metamorphic fluid the rockford granite of the northern alabama piedmont serves as the case example for this process and is characterized as a synmetamorphic peraluminous trondhjemite granite suite the major process operative in the conversion of granite to trondhjemite involves cation exchange of na for k in the feldspar and mica phases through a volatile fluid medium whole rock 18o values for the trondhjemites are negatively correlated with atomic proportion k na ratio indicating a partial reequilibration of the altered granitoids with a na and18o rich metamorphically derived fluid biotite decomposition to an al epidote paragonitic muscovite secondary quartz assemblage is also associated with the sodium metasomatism as are apatite replacement by al epidote and secondary zircon crystallization rare albitization of primary magmatic plagioclase and discontinuous grossularite reaction rim growth on magmatic garnet are present in the trondhjemites indicating the mobility of ca during alkali metasomatism the replacement of magmatic phases by me tasomatic phases exemplifies the chemical changes produced during infiltration metasomatism where the trondhjemites are depleted in p2o5 th rb u k2o v sn f mgo pb tio2 feo and li and enriched in cao na2o zr and sr relative to the granites other elements such as cr mno cu zn co ba sio2 ni al2o3 are shown to be relatively immobile during the metasomatism the infiltration metasomatism probably occurred during prograde regional metamorphism when a discrete fluid phase was produced in the surrounding amphibolite grade metasediments foliation planes in the granite apparently served as conduits for fluid flow with reaction enhanced permeability accompanying the 8 molar volume reduction during na for k exchange in the feldspars a source for the na and sr in the metamorphic fluid may have been paragonitic muscovite in the metasedimentary country rocks rubidium and k were probably retained in metasedimentary biotite the silent lake pluton in southeastern ontario is a possible analogue to the alkali metasomatic processes affecting the rockford granite