experimental study of boron geochemistry implications for fluid processes in subduction zones a comprehensive experimental study utilizing an autoclave hydrothermal apparatus with a 10b isotopic tracer has been conducted to monitor the geochemical behavior of sediment b during early subduction zone processes the partition coefficient of exchangeable b kd was determined over a temperature range of 25 350 c at 800 bars and a water rock ratio of 3 1 5 w w these kd are shown to be a complex function of temperature ph and possibly mineralogy at low temperatures kd is significantly high at 4 in contrast to the value of essentially zero at temperatures higher than 100 c a kd of zero represents no b adsorption implying efficient mobilization of exchangeable b at shallow depths during sediment subduction our experimental results demonstrate high mobilization of bulk b in sediments both exchangeable and lattice bound at elevated temperatures 200 350 c in good agreement with previous observations of b in metasediments indicating progressive depletion during metamorphism in addition this study emphasizes the importance of a possible water rock ratio dependence of b mobilization in other words the degree of sedimentary b mobilization in subduction zones strongly depends on the local thermal structure and porosity distribution in low geothermal gradient areas large amounts of porewater are expelled before significant b mobilization has occurred so that some sedimentary b will survive and get into the deeper parts of the subduction zone our results imply that efficient mobilization of b from the subducted slab must occur and that arc magmatism recycles most of the remaining subducted b back to surface reservoirs a reconsideration of the b budget in subduction zones provides critical information with respect to b sources and sinks in the ocean

petrogenesis of tourmaline rocks associated with fe carbonate graphite metapelite metabasite and strata bound polymetallic sulphide mineralisation peloritani mountains sicily southern italy abstract tourmalinite and tourmaline rich rocks associated with fe carbonate graphite phyllite strata bound polymetallic sulphide deposits metabasite and marble were studied for information on the mechanism of tourmaline formation in the pre hercynian low grade metamorphic sequence of the mandanici unit in the peloritani mountains of sicily southern italy the major and trace element compositions of the tourmaline rocks suggest the existence of a sedimentary protolith with pre metamorphic black shale and bedded chert boron was interpreted to be accumulated in a restricted sedimentary basin between platform carbonate formations with abundant organic matter and fe al ti rich laterite bauxite soil derived clastic supply under a continental volcano tectonic extensional regime accompanied by a local convective hydrothermal system along faults petrographic crystal chemical and 11 b isotopic data are compatible with a model of marine sediment dewatering at temperatures below 200 c which caused the removal of boron from clay metamorphism led to the development of tourmaline in an al ti rich environment in equilibrium with other minerals such as ilmenite albite and muscovite the upper temperature of metamorphism almost 375 c estimated on the basis of 11 b fits geothermometric results from 13 c carbonate graphite on associated rocks the estimated value of 11 b in the tourmalinite protolith 7 5 is also compatible with continental derived al rich sediments

boron isotope variations in nature a synthesis the large relative mass difference between the two stable isotopes of boron 10b and 11b and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes published 11b values relative to the nbs srm 951 standard span a wide range of 90 the lowest 11b values around 30 are reported for non marine evaporite minerals and certain tourmalines the most 11b enriched reservoir known to date are brines from australian salt lakes and the dead sea of israel with 11b values up to 59 dissolved boron in present day seawater has a constant world wide 11b value of 39 5 in this paper available 11b data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects including possible tracer applications of boron isotope geochemistry are summarized

tourmalines from appalachian caledonian massive sulfide deposits textural chemical and isotopic relationships tourmaline is a common gangue mineral in several strata bound massive sulfide deposits of the appalachian caledonian orogen most of the tourmaline rich deposits occur in dominantly metasedimentary terranes such as bleikvassli norway black hawk maine ore knob north carolina and elizabeth vermont minor amounts of tourmaline are also known in association with volcanic hosted deposits in the appalachians and in the trondheim district of norway the tourmaline forms isolated euhedral crystals or crystal aggregates in massive sulfide and adjacent wall rocks in a few areas it is found in conformable tourmaline rich layers tourmalinites associated minerals may include quartz plagioclase phlogopite and dolomite with pyrrhotite chalcopyrite galena and sphalerite many of the tourmaline crystals are optically zoned in which brown zones concentrically alternate with pale yellow or green zones a few specimens of tourmaline intergrown with massive sulfide e g ore knob display fine delicate growth lamellae similar to those commonly observed in hydrothermal vein sphalerites skarn garnets and sphalerites from the massive sulfide deposits of the kuroko district japan detailed geochemical studies indicate that the tourmalines have characteristic major and trace element compositions electron microprobe analyses show that with rare exception the tourmalines are mg rich dravites avg feo feo mgo 0 21 abrupt transitions between color zones within some tourmaline are accompanied by relative variations in feo feo mgo of as much as 30 percent yellow brown zones are more mg rich than blue or green zones in contrast the fine growth lamellae are not characterized by such variations in chemistry spectrographic analyses of pure mineral separates indicate that the tourmalines also contain high average contents of cr 78 ppm cu 77 ppm pb 114 ppm sr 98 ppm and v 195 ppm while uniformly low in li 7 ppm and mn 382 ppm in all analyzed samples fluorine is much more abundant than chlorine the average f cl ratio is 33 tourmalines from tourmalinites and massive sulfide deposits are typically characterized by heavier delta 18 o values 9 5 15 5ppm and less variable heavier delta d values generally 45 to 60ppm than tourmalines from unmetamorphosed igneous pegmatites the latter typically have delta 18 o 9 5 per mil and delta d or 60 per mil oxygen isotope fractionations between quartz and tourmaline delta 1 27 4 01 do not correlate directly with inferred grade of subsequent metamorphism although in areas of high metamorphic grade the delta values approach those of igneous quartz tourmaline pairs the delta 18 o values of quartz and tourmaline are believed to reflect variation in the oxygen isotope compositions of the host lithologies the similar narrow range in hydrogen isotope composition for tourmaline in all studied deposits is compatible with a modified seawater origin for the tourmaline and sulfide forming fluids the distinctive textural and chemical characteristics of the tourmalines reported here have both exploration and genetic significance though it may have undergone recrystallization and some accompanying chemical and isotopic exchange during regional metamorphism tourmaline in the massive sulfide deposits is an early formed perhaps diagenetic mineral in which fine lameliar zoning may be a preserved premetamorphic feature in any case the tourmalines from the massive sulfide deposits are mg rich dravites with trace element and stable isotope compositions substantially different from those of the fe rich schorls typical of most granitic rocks these geochemical and isotopic signatures are attributed to the original environment of formation of the associated sulfide deposits and suggest that mg rich tourmaline may be a valuable prospecting guide in the search for massive sulfide deposits

a least squares approach to mass transport calculations using the isocon method a statistically rigorous approach based on the isocon method grant 1986 to evaluate mass transport is presented chemical analyses of multiple samples of unaltered parent and altered rock are used to calculate the average oxide or element concentration and its standard deviation for each rock population in a typical application the uncertainties in element concentration associated with the lack of homogeneity in each population outweigh the analytical uncertainty an efficient algorithm is presented to select the immobile elements by identifying the maximum number of elements that are within their uncertainties compatible with the same isocon the actual isocon is constructed by forcing a line through the origin and optimizing its slope using a weighted least squares procedure for the selected immobile elements thus individual uncertainties for each immobile element are taken into account as an illustration the procedure is applied to a published set of data on potassic and sericitic alterations of quartz monzonite of the bingham porphyry copper system the surprising result indicates that the apparent increase of potassic alteration phases is a consequence of acid leaching of calcium and sodium no mass transport of potassium is indicated silica water and sulfur were added during alteration the best fit isocon requires a small mass increase during each alteration process which however is within the uncertainty obtained for the slope of the isocon a software package is available from the authors in the form of a fortran 77 source code

structural trends and palaeogeography of the central and western sicily belt new insights the geology of the sicilian mainland is summarized by n s geological sections a continuous late cenozoic orogenic belt through central and western sicily resulted from a complex deformative history recorded by several tectonic events the deformation mainly involved the sedimentary cover of the old african continental margin formed in a large basinal area bordered at its southern margin by a shallow water carbonate environment attached to gondwana the orogenic belt involves a complex architecture of thrust systems of different size geometry and palaeogeographical origin deformation which mainly developed in the earlier stages of thrusting in the basinal rock assemblages mainly gave rise to a stack of three different duplex structures respectively composed of palaeozoic mesozoic palaeogene and neogene strata large scale clockwise rotation of the thrusts predated transpressional movements in the hinterland during the latest miocene to pliocene high angle reverse faults with lateral components modified earlier tectonic contacts within the allochthons contemporaneous southwards directed imbrications affected the external southern areas progressively incorporating foreland and piggyback basirts the stratigraphic relationships of basin fills to the tectonic structures reveals that reactivation processes have been active during the last plio pleistocene

differential mobility of elements in burial diagenesis of siliciclastic rocks abstract mass balance calculations involving smectite rich siliciclastic mudstones sampled from boreholes show that significant k2o addition and cao loss correlate strongly with the progress of illitization of smectite and with the dissolution of calcite the calculations are based on the immobility of al2o3 and require a chemically homogeneous sediment at deposition such that the shallower samples represent protolith compositions of deeper samples constancy of ratios of tio2 al2o3 are used to 1 establish that both tio2 and al2o3 have similarly low differential mobilities and 2 identify stratigraphic sections available in the literature that are sufficiently homogeneous to allow the calcu ations our calculations show that most major oxide components are immobile at the 5 limit of resolution of the calculations exceptions are k2o which is almost universally added to mudstones and cao which is commonly removed from mudstones during diagenesis the addition of up to 50 k2o correlates with percent illite in mixed layer illite smectite indicating that illitization of smectite involves fixation of k2o from diagenetic fluids removal of 40 cao from some sections correlates with decreasing calcite mode and is attributed to dissolution of calcite together these reactions lead to a 10 15 loss of mineral volume a volume loss that must be added to porosity loss when modeling compaction illitization and carbonate dissolution may be linked because k fixation during illitization decreases the ph of the local fluid a reverse weathering reaction which enhances carbonate dissolution addition of up to 20 na2o in some rocks may be caused by albitization of plagioclase but na2o addition is not pervasive the apparent lack of mass transfer associated with dissolution of kaolinite and feldspars or precipitation of chlorite implies that these reactions are balanced by other reactions such that their oxide components in mudstones are conserved limited data from sandstone mudstone pairs are consistent with transfer of k2o from sandstones to mudstone via rising diagenetic fluids except for cao and the alkalis diagenesis of siliciclastic mudstones appears isochemical 5 relative for most major oxide components the much larger changes recorded in some reservoir sandstones are clearly exceptions and may not reflect changes occurring at the scale of kilometers

boron isotope variations in tourmaline from hydrothermal ore deposits a review of controlling factors and insights for mineralizing systems abstract tourmaline group minerals are typically the predominant host of boron in hydrothermal mineral deposits boron is a fluid mobile element whose isotopic composition reflects many factors that are relevant to understanding mineralizing processes including fluid source s fluid rock interaction and formational temperature a new compilation of 2622 published 11b values for tourmaline from diverse types of hydrothermal ore deposits is presented here with the focus 2215 analyses on seven main types porphyry cu mo au deposits granite related sn w deposits iocg deposits orogenic au deposits stratabound vms and sedex deposits and sediment hosted u deposits the total range of 11b values for the seven types is 26 8 to 35 0 four granite sn w orogenic au stratabound vms and sedex have median 11b values close to the continental crustal average of about 10 the median values for iocg and porphyry cu mo au deposits are higher 3 9 and 2 1 respectively whereas sediment hosted u deposits have distinctly high 11b median 25 3 importantly a considerable range of 11b values exists for tourmaline within each deposit type the smallest 17 8 for granite sn w deposits and the largest 48 0 for iocg deposits the boron isotope variations in tourmaline from different deposits are suggested reflect three levels of controlling factors and how these factors operated is illustrated with selected number of case studies the primary factor is the composition of the boron source secondary effects relate to fluid tourmaline fractionation equilibrium or rayleigh there are commonly also tertiary factors that depend on evolution of the specific deposit these include fluid mixing changing water rock ratio and or depositional temperature influences of other boron bearing minerals and where relevant post ore metamorphism separating the effects of these factors is rarely possible from boron isotopes alone however the growth of multi isotope studies of tourmaline and coexisting phases such as mica as well as developments in modelling experimentation of boron isotopes and element partitioning suggest that this limitation will be overcome

geochronology of the medium to high grade metamorphic units of the peloritani mts sicily the peloritani mountains are a fragment of an orogen variably attributed to the alpine or hercynian orogeny on the basis of 39ar 40ar u pb and rb sr dating the main metamorphism of the two medium high grade metamorphic units the mela and aspromonte units and most of the thrusting responsible for stacking the orogenic edifice are seen to be hercynian the main thrusting of the aspromonte unit over the lower grade units took place at 301 2 ma brittle deformation during tertiary reactivation of hercynian thrust planes did not generate any rejuvenation of white micas in the studied sector our dataset shows a great complexity and we propose to unravel it by considering different levels of information to first order the mela and aspromonte units differ in their metamorphic paths and their geochronological evolution the mela unit shows generally younger ages carboniferous than the aspromonte unit and unlike the latter was extensively retrogressed in greenschist facies the aspromonte unit is itself geochronologically heterogeneous proterozoic ages are preserved both in titanite and in amphibole relics of one tectonic subunit devonian to carboniferous amphibole ages are found in different other subunits tertiary overprint is minor and spatially limited we propose to consider the chronologically heterogeneous subunits as accreted pre hercynian terranes amalgamated late during the hercynian orogeny micas in both units give scattered mesozoic 39ar 40ar and rb sr ages with evidence for heterochemical mica generations we interpret them as a result of widespread hydrothermal circulation event s tertiary overprint is generally absent with the exception of a small area near messina where biotite and muscovite underwent a complex recrystallisation history in the interval between 48 and 61 ma

the augen gneisses of the peloritani mountains ne sicily granitoid magma production during rapid evolution of the northern gondwana margin at the end of the precambrian abstract the medium to high grade polymetamorphic basement rocks of the peloritani mountains northern sicily include large volumes of augen gneiss of controversial age and origin by means of a geochemical and shrimp zircon study of representative samples the emplacement age of the original granitoid protoliths of the augen gneisses and the most likely processes and sources involved in that granitoid magmatism have been determined u pb dating of three samples from widely spaced localities in the peloritani mountains yielded igneous protolith ages of 565 5 545 4 and 545 4 ma respectively these late ediacaran early cambrian ages are much older than was previously assumed on geological grounds and are typical of the peri gondwanan terranes involved in the geodynamic evolution of the northern gondwana margin at the end of the avalonian cadomian orogeny major and trace element compositions and sr nd isotopic data in combination with zircon inheritance age patterns suggest that the granitoid protoliths of the sicilian and coeval calabrian augen gneisses were generated by different degrees of mixing between sediment and mantle derived magmas the magmas forming the ca 545 ma inheritance rich granitoids appear to have had a significant contribution from partial melting of paragneiss that is the dominant rock type in the medium to high grade peloritanian basement the closeness of the inferred deposition age of the greywacke protoliths of the paragneisses with the intrusion age of the granitoids indicates rapid latest precambrian crustal recycling involving erosion burial metamorphism to partial melting conditions and extensive granitoid magmatism in less than ca 10 ma

petrology and geochemistry of silurian triassic sedimentary rocks in the tongling region of eastern china their roles in the genesis of large stratabound skarn ore deposits abstract this paper describes the petrology and geochemistry of the silurian triassic sedimentary rocks in the tongling area in eastern china aiming to establish a genetic link between different stratabound skarn deposits and sedimentary lithologies the results from this study show that some devonian triassic transitional lithological units with compositions varying between siliceous rock and carbonate especially thinly layered impure carbonate control the distribution of some large stratabound skarn ore deposits in the tongling region interlayer detachment faults in the transitional lithology rocks are particularly important controlling the final locations of the deposits the transitional lithological zones may have also served as source rocks likely providing some ore forming metals to the deposits gypsum evaporites in rocks from carboniferous sources may have supplied some sulphur to the hydrothermal systems five of such transitional lithological units enriched in organic matter are spatially and closely associated with some large stratabound skarn ore deposits in the tongling region suggesting that organic matter may have served as an absorbent or reducing agent during ore formation

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

the salt dome problem a multilayered approach the dynamical evolution of buoyancy driven geological systems is mainly influenced by two physical parameters density and equivalent viscosity salt structures are an appropriate geological representation of these systems important variations of these parameters are directly related to changes in mass and thus the internal structures themselves and their changes in time become significant parameters in order to decipher these structures in nature by means of experiments it is therefore necessary to extend model calculations on intrusion processes to multilayer systems a two dimensional finite element program has been developed to simulate the rise of individual diapirs through multi layered overburdens exhibiting newtonian viscous rheologies this program includes the following features arbitrarily shaped interfaces between different fluid boundaries layers of finite thickness and subsidence of the model within the model frame as well as time and depth dependent material properties this paper is concerned with single diapirs intruding upbuilt multilayered overburdens the effect of a subsiding salt base due to pure downbuilding and differential loading of gravitationally unstable distributions of mass variable density and viscosity of the overburden with depth control the shape and ascent rates of diapiric bodies the subsidence history of salt structures dominates the development of maximum horizontal pressure gradients with time and thus the ascend histories of diapirs

formation of laminite deposits in anaerobic dysaerobic marine environments abstract vraconian sediments from the bandol area var southeastern france are characterized by alternations of thin dark laminae in which organic matter is concentrated and light calcareous silt grained laminae the dark laminae black shales are regarded as the result of autochthonous i e in place hemipelagic sedimentation the light laminae calcareous silt result from the partial reworking of turbiditic influxes by deep marine currents comparison with modern marine environments suggests that the vraconian laminite deposits from the bandol area were formed by sedimentation from deep marine circulations the laminated structures formed in a deep marine environment subjected to periodic variations in the physicochemical conditions organic productivity and thus the nature of organic matter the dark laminae were deposited in an anaerobic marine environment in which the organic matter was preserved during the deposition of the light laminae the depositional environment changed to dysaerobic conditions allowing the development of a peculiar benthic fauna responsible for the decreasing organic matter content source rock characteristics of these deposits are inferred from their laminated structure and fine texture coupled with the occurrence of organic rich layers

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

boron isotope systematics of marine sediments abstract boron contents and boron isotopic compositions were determined for modern and ancient permian to miocene marine sediments including pelagic clay calcareous ooze siliceous ooze and neritic clay sediments 11b values of modern marine sediments range from 6 6 to 4 8 isotopic variation is controlled by the simple mixing of four major constituents detritus of continental origin marine smectite biogenic carbonates and biogenic silica detritus of continental origin with an average 11b value of 13 to 8 is the low 11b end member constituent of marine sediments and its boron is largely controlled by the concentration of illite which originates from wind or fluvial transport marine smectite biogenic carbonate and biogenic silica on the other hand represent the high 11b end members with 11b values of 2 3 to 9 2 8 0 to 26 2 and 2 1 to 4 5 respectively these high 11b values are the result of the equilibrium uptake of boron from seawater spatial variations in boron isotopes in the pacific sediments are essentially due to the distribution of the above four constituents although ancient argillaceous sediments shale and slate have boron contents that are identical with those of modern equivalents boron contents of limestone and chert are distinctly lower than those of modern calcareous and siliceous oozes ancient marine sediments have systematically lower 11b values 17 0 to 5 6 than those of the modern sediments the lower 11b values can be caused by diagenesis which induces 1 preferential removal of high 11b boron in calcium carbonate and silica during recrystallization and 2 boron isotopic exchange in the course of the smectite illite transition the observed boron isotopic compositions of ancient argillaceous sediments are distinctly different from those of fresh and altered morb therefore boron isotope systematics will be useful in identifying components from the descending oceanic slab involved in the formation of island arc magma and in investigating mantle crust recycling through subduction processes

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

mineralogy geochemistry and geological significance of tourmaline rich rocks from the paleozoic cinco villas massif western pyrenees spain tourmaline rich rocks associated with clastic metasedimentary rocks of carboniferous age occur in the cinco villas massif western pyrenees three types of tourmaline rich rocks were distinguished 1 fine grained stratiform tourmaline rich rocks which are associated with carbonaceous metapelites tr1 2 stratabound tourmaline rich rocks associated with metapelites in the contact aureole of the aya granitoid pluton tr2 3 stratabound to massive tourmaline rich rocks associated with psammopelites in contact with granites and pegmatites tr3 tourmalines belong to the schorl dravite solid solution series and have a wide compositional range from nearly end member dravite for tr1 tourmalines to schorl for tr3 tourmalines tr2 tourmalines have intermediate compositions the fe fe mg typically varies between 0 02 and 0 55 increasing from tr1 to tr3 the tr1 tourmalines commonly display a discontinuous chemical zoning with fe rich green cores 8 8 5 feo and mg rich colorless rims 10 11 mgo in contrast crystals that exhibit fine growth lamellae appear to lack significant chemical zoning oxygen and hydrogen isotope compositions also reveal major differences between tr1 and tr3 tourmalines the former displaying heavier 18o values 17 7 19 and d values 35 to 42 than tr3 tourmalines 11 to 13 and 47 to 76 respectively the tr2 tourmalines show intermediate values of 11 3 to 14 6 for 18o and 40 to 55 for d linear and continuous chemical variations obtained for major and trace elements of the whole rocks reflect mixing between clay rich and quartz rich end members indicative that some tourmaline rich rocks contain a significant detrital component chondrite normalized ree rare earth element patterns of tourmaline rich rocks are similar to those of surrounding unaltered clastic metasediments except for some tr1 rocks which are characterized by low contents of ree mass balance calculations show that tourmaline forming processes plus metamorphism led to mass and volume changes at mesoscopic scales 10 for the tr1 tourmalinites silicon fe mn and ree elements were partially lost from sedimentary rocks whereas mg and particularly b were added to pelitic sediments available data nevertheless do not allow an assessment of the boron source formation of the tr1 tourmaline rich rocks probably was the net result of several processes including direct precipitation from b rich hydrothermal fluids or colloids early diagenetic reactions of carbonaceous pelitic sediments with these fluids and subsequent recrystallization during regional metamorphism the tr2 tourmaline rich rocks mainly developed by metamorphic recrystallization of tr1 tourmaline rich rocks and veins adjacent to pegmatites and granitic rocks tr3 are the result of boron metasomatism the primary boron having been recycled from stratiform tourmalinites during regional metamorphism and magmatism

carbon isotopic thermometry calibrated by dolomite calcite solvus temperatures abstract the temperature dependence of carbon isotopic fractionations between calcite and graphite and between dolomite and graphite are calibrated by the calcite dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the kasuga area central japan the carbon isotopic fractionations 13ccc gr and 13cdo gr systematically decrease with increasing metamorphic temperature the concordant relationships between the fractionations and solvus temperatures are approximately linear with t 2 over the temperature range 400 to 680 c 13ccc gr 5 6 106 t 2 k 2 4 13cdo gr 5 9 106 t 2 k 1 9 these systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases the equation for the calcite graphite system has a slope steeper than bottinga s 1969 results it is however in good agreement with that of valley and o neil 1981 in the temperature range from 600 to 800 c because of the relatively high sensitivity to temperature these isotopic geothermometers are useful for determining the temperatures in moderate to high grade metamorphosed carbonate rocks

the influence of geological factors on the concentration of boron in australian and canadian coals abstract the concentration of boron in australian and canadian coals determined using atomic emission spectrometry aes inductively coupled plasma spectrometry icp aes and prompt gamma ray spectrometry is summarized in order to assess the variation of b content in coal with respect to rank age geological setting in seam and stratigraphic and the degree of paleosalinity of the coal forming environment this study indicates that no or very complex relations exist between boron and rank subbituminous to anthracite variations of b with ash content for canadian coals of different age devonian to oligocene eocene indicate that the b content of coals is not governed by the age of the coal there is some evidence of variation of b with maceral content in canadian coals particularly as related to the inertinite and vitrinite content of coals the b content of coal seams is sensitive to the environment of deposition with b contents remaining relatively stable and within the range of values designated for each depositional setting however b values may show variation in the same seam laterally due to changes of the environment of deposition and or the enrichment of b by a secondary source the vertical variation of b in a coal bearing section or strata is related to depositional environment and lithology of rock there is often little variation in b content for coal layers as compared to the partings dirt bands the b content of partings in a coal bearing strata may vary greatly as compared to the coal seams after reappraising earlier work and on the basis of more recent studies on australian and canadian coals it is proposed that the following ranges of values for b in coal indicate the degree of marine influence during the early stages of coalification up to 50 ppm b freshwater influenced coals 50 110 ppm b mildly brackish water influenced coals 110 ppm b brackish water influenced coals using these criteria assessments are given for the degree of marine influence on canadian and australian coals

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

a reconnaissance of the boron isotopic composition of tourmaline abstract a preliminary investigation of the boron isotopic composition of tourmaline from some boron rich associations has been made the results for tourmaline from metasedimentary parageneses n 12 range from 11b 22 to 22 per mil these data mainly fall between the boron isotopic compositions of normal marine sediments with 11b 2 to 5 per mil and seawater with 11b 39 5 per mil tourmaline samples from granitic pegmatites n 6 on the other hand range from 11b 12 to 5 per mil the data provide a rudimentary indication of the range of boron isotopic variation in tourmaline some of the processes leading to this range and some possible geochemical tracer applications

interelement relationship in abyssal pacific ferromanganese nodules and associated pelagic sediments abstract by r mode factor analysis and enrichment factor calculations most of the elements in abyssal ferromanganese nodules and associated pelagic sediments excluding common authigenic minerals like apatite barite opal and carbonates are found to be preferentially concentrated in one of the following three major phases aluminosilicates e g al si sc ga cr be na k rb and cs fe oxides e g fe p s v se te as b sn u hg pb ti ge y zr nb pd in rare earths hf th pa pu am ru and bi and mn oxides e g mn tl ag cd mg ca ba ra co ni cu zn mo sb and probably w the specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties e g the ph of zero point of charge and dieletric constant of these three phases

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

source composition and distribution of the fluid in the kurile mantle wedge constraints from across arc variations of b nb and b isotopes b and nb concentrations and b isotope composition were determined for lavas covering the entire length of the kurile arc b nb and 11b of these lavas show clear across arc variations in which both are highest at the trench side and continuously decrease as the slab depth increases b nb in the volcanic front lavas 8 25 is significantly higher than those of morb and oib indicating that the mantle wedge is extensively metasomatized by b rich fluid derived from the subducting slab the frontal 11b values are also out of the range of morb and oib and systematic difference exists between northern kurile nk 5 4 0 5 and central and southern kurile csk 4 3 0 3 however these two parameters approach or coincide with mantle values at the most back arc side the 11b and 87sr 86sr linearly correlate with nb b suggesting control by simple mixing of two isotopically homogeneous components that is slab derived fluid and mantle wedge the estimated 11b and 87sr 86sr of the fluid are 7 0 0 6 and 0 70326 0 00005 for nk and 6 3 0 3 and 0 7033 for csk respectively these fluid compositions are consistent with a source constituted by 95 altered oceanic crust and 5 oceanic sediment with the slight difference between nk and csk resulting from the different lithologies of subducting sediments the mantle wedge beneath the kurile arc has b sr and nd isotope compositions identical with morb but shows significantly higher b nb the above trends bear a close resemblance to those observed in the izu arc strongly suggesting their universality in the arc system the across arc decline of b nb observed both in kurile and izu implies that the fluid flux from the slab continuously decreases as the slab depth increases however this relates only to a final stage of slab dehydration since most of the volatile components are lost at the fore arc region in contrast to b k is uniformly enriched across the arc this requires control by a k bearing mineral phase either in the slab phengite or the mantle wedge phlogopite although such a mineral is responsible for only a small part of the whole fluid transport

physical modeling of sedimentation adjacent to diapirs and comparison with late precambrian oratunga breccia body in central flinders ranges south australia the interaction of sedimentation with the change in shape of a developing diapir is modeled in a series of simple sandbox experiments this model replicates the pillow diapir and postdiapir stages of salt movement modeling produced rim synclines crestal unconformities and turtle structure anticlines all features known to be associated with diapirs by changing experimental parameters such as diapir shape sedimentation was simulated around various diapiric situations one experiment closely matches the sediment distribution around the oratunga diapir one of the controversial breccia bodies in the late precambrian cambrian adelaide geosyncline exposed in the flinders ranges of south australia rim synclines unconformities and bedding attitude around oratunga resemble those described around salt domes in addition the distribution size orientation and lithology of breccia within the oratunga diapir resemble breccia associated with active salt diapirs in iran these data suggest the breccia was emplaced as a salt diapir

li b rich rhaetian metabauxite tuscany italy reworking of older bauxites and igneous rocks abstract li b rich metabauxite layers occur in two outcrops of talus metabreccias intercalated between norian and liassic marbles in the alpi apuane tuscany italy field evidence petrographical geochemical and paleogeographic paleoclimatologic considerations suggest that bauxitic material was derived from a multistage reworking of late carboniferous early autunian primary deposits now completely removed the identified lithotypes are cookeite rich metabauxite cookeite bearing metabreccia chloritoid schist and chloritoid phyllite the mg content of calcite and the si content of muscovite and mineral assemblages indicate temperatures of 350 380 c pressures of f o 2 values of 10 30 to 10 24 for the alpine metamorphism in comparison with the average mesozoic bauxite of bronevoy et al 1985 the metabauxite is strongly enriched in si k ca mg li b be ni and ce it shows comparable contents of co la eu tb ta and th it is depleted in ga cr v zn mn hf u and is strongly depleted in sr f cu a metabauxite layer shows decreasing abundance of fe and ga from bottom to top with a pattern opposite to that of primary bauxite deposits inverted profile the strong enrichment of li and b is not related to evaporitic conditions since the mgo na 2 o and sr contents are too low and indicator minerals such as dravitic tourmaline albite and scapolite are missing during the permian volcanic products similar to the coeval peralkaline peraluminous rocks of corsica sardinia were widespread in tuscany b li rich minerals were produced by circulation of hot hydrothermal fluids within the permian volcanic rocks during and soon after their emplacement the erosion of such hydrothermal products supplied detrital material to the talus metabreccia

the association of tourmalinite with stratiform scheelite deposits three types of stratiform scheelite deposits are recognised they all commonly have a close spatial association with tourmalinite regional prograde calc silicate rocks in precambrian rift settings commonly contain 100 ppm wo3 with enrichment to 0 5 1 wo3 in retrograde metamorphic assemblages at fold hinges joints faults shears and granite and pegmatite dyke contacts the calc silicate progenitor was probably a impure dolomitic carbonate sediment amphibolite hosted scheelite deposits occur in metamorphosed altered mafic volcanics formed in a narrow rift graben scheelite occurs both as stratiform and stratabound footwall stringer ore which has undergone minor remobilization during tectonism tourmalinites are rarely the host for stratabound quartz scheelite wolframite veins remobilized from the host tourmalinite and associated metavolcanics during tectonism

numerical simulation of rayleigh taylor instability for single and multiple salt diapirs abstract the diapiric ascent of light rocks through a denser oberburden is simulated using a new numerical method based in part on finite differences rocks are modelled as viscous newtonian liquids and the internal interfaces are located with the help of passive markers these markers are relocated using a new algorithm equivalent to a cellular automaton rule this allows the markers to be redistributed very rapidly this new method appears to be well adapted to quickly resolving geological problems simulations of the growth of a single dome are performed under various viscosity ratios for the salt and the overburden the effect of asymmetrical initial deformations of the salt layer is to produce diapiric structures that slowly return to symmetry as the diapir matures and rises in an isotropic medium simulations involving continuous sedimentation of the overburden are also performed an initial geometry on a basin margin in which multiple diapirs eventually develop is studied diapirs grow relatively rapidly near the centre while on the margins the salt layer flows upward following the basement simulations with salt that is more viscous than sediments show the development of previously unnoticed asymmetrical structures