tourmaline microboudinage an indicator of its host rheology abstract columnar tourmaline in cenozoic granitic mylonites from the chongshan metamorphic zone cmz yunnan china has deformed at 450 300 c by tensile fractures normal to the foliation and lineation sequential fracturing and separation of the fragments during progressive cooling and exhumation upward the brittle ductile transition produced a series of microboudins with decreasing length width ratios here we present a method to apply the microboudinage paleopiezometry combined with strain analyses microstructural observations and thermochronological data to provide constraints on strain rates e differential stresses and their correlations with temperature for the polycrystalline quartz matrix in which tourmaline grains have been fragmented into microboudins the results yield a flow law of e a nexp q rt with n 4 q 184 kj mol and a 7 180 10 7 mpa ns 1 for naturally deformed quartzite the differential stresses calibrated by this flow law are very close to the geometrical mean of the lower and upper bounds given by luan and paterson 1992 and gleason and tullis 1995 respectively utilization of this flow law to the present day crust of the cmz provides a reliable interpretation for the distribution of focal depths and electrical resistivity structure the microboudinage piezometer also permits to estimate the mechanical strengths of rocks deformed in the elastic brittle regime

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

intersector element partitioning in tourmaline a potentially powerful single crystal thermometer hourglass sector zoning and related polar overgrowths are common features of metamorphic tourmaline developing as a result of variations in element preference on the different growth surfaces for sector zoned crystals three domains are present for each growth zone c c and a with compositional differences most distinct for ca and ti and among c and c sectors intersector differences vary commonly showing decreasing fractionation from core to rim attributed to increasing metamorphic grade here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers based on c c and c a partitioning of ca and ti these thermometers are applicable over a range of temperatures and bulk rock compositions intersector partitioning is not affected by re equilibration and records and preserves complete t histories of individual tourmaline grains from prograde to peak and on to retrograde growth information on element mobility is preserved by tourmaline composition because intersector partitioning is independent of element concentration these factors make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment and tourmaline s refractory nature preserves these signatures even into the sedimentary record

late magmatic controls on the origin of schorlitic and foititic tourmalines from late variscan peraluminous granites of the arbus pluton sw sardinia italy crystal chemical study and petrological constraints abstract tourmalines from the late variscan arbus pluton sw sardinia and its metamorphic aureole were structurally and chemically characterized by single crystal x ray diffraction electron and nuclear microprobe analysis mossbauer infrared and optical absorption spectroscopy to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages the arbus pluton represents a peculiar shallow magmatic system characterized by sekaninaite fe cordierite bearing peraluminous granitoids linked via afc processes to gabbroic mantle derived magmas the fe2 al dominant tourmalines occur in a pegmatitic layers and pods as prismatic crystals b greisenized rocks and spotted granophyric dikes as clots or nests of fine grained crystals in small miaroles locally forming orbicules c pegmatitic veins and pods close to the contacts within the metamorphic aureole structural formulae indicate that tourmaline in pegmatitic layers is schorl whereas in greisenized rocks it ranges from schorl to fluor schorl tourmalines in thermometamorphosed contact aureole are schorl foitite and mg rich oxy schorl the main substitution is na fe2 al which relates schorl to foitite the homovalent substitution oh f at the o1 crystallographic site relates schorl to fluor schorl while the heterovalent substitution fe2 oh f al o relates schorl fluor schorl to oxy schorl tourmaline crystallization in the arbus pluton was promoted by volatile b f and h2o enrichment low oxygen fugacity and fe2 activity the mineralogical evolutive trend is driven by decreasing temperature as follows sekaninaite quartz schorl quartz fluor schorl quartz foitite quartz the schorl foitite evolution represents a distinct trend towards al increase and unit cell volume decrease these trends are typical of granitic magmas and consistent with li poor granitic melts as supported by the absence of elbaite and other li minerals in the arbus pluton tourmaline bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle upper crust

cr bearing tourmaline associated with emerald deposits from swat nw pakistan genesis and its exploration significance carbonate talc altered ultramafic and mafic rocks of the obducted oceanic lithosphere along the main mantle thrust in the swat valley host emerald deposits and are invaded by quartz veins and stockworks both the quartz veins and carbonate talc altered rocks contain discrete grains and clusters of tourmaline crystals which may be associated with emerald and or chromian muscovite tourmalines from the mingora and gujar kili emerald mines and the spin obo kuh area are ni bearing cr rich dravites and oxy dravites that exhibit substantial chemical variability with 2 0 2 5 atoms per formula unit apfu mg relatively low al 4 8 5 8 apfu high cr 0 5 1 8 apfu high cr cr al ratios of 0 08 0 28 significant amounts of ni up to 0 11 apfu and variable calculated w site o 2 0 2 0 8 apfu the mechanisms that appear to control the tourmaline chemistry at these localites are combinations of the dominant substitution al cr with lesser amounts of the mg oh 1 al cr o 2 and al 3 fe 3 substitutions relative to the mingora gujar kili and spin obo kuh areas the charbagh tourmalines are oxy dravites that have comparable mg contents 2 2 2 3 apfu with variable calculated w site o 2 0 6 0 9 apfu but are more fe rich 0 5 apfu and al rich 6 0 6 3 apfu with low cr 0 00 0 01 apfu and ni contents 0 01 0 02 apfu the mechanism that appears to control the variable chemistry of the charbagh tourmalines is primarily mg oh 1 al o 2 the chemical characteristics of tourmalines from the various localities relate most clearly to differences in host rock chemistry tourmalines from the carbonate talc altered ultramafic mafic rocks and the invasive quartz veins have a common hydrothermal origin associated with emplacement and crystallization of younger granitoids furthermore the occurrence of swat emeralds in quartz tourmaline chromian muscovite veins suggests that the tourmaline is cogenetic with emerald formation the quality and quantity of swat emeralds depend on the 1 host rock composition and 2 nature of the hydrothermal fluids large deposits of gem quality emerald occur in carbonate altered ultramafic rocks which also contain cr rich dravites and oxy dravites this suggests that the presence of high cr magnesian tourmalines particularly in magnesite talc altered ultramafic rocks can represent a criterion for further emerald exploration in the lower swat region of pakistan and comparable ultramafic hosted emerald producing regions

phase relations of peraluminous granitic rocks and their petrogenetic implications peraluminous granitic rocks are magmatic rocks that contain quartz po tassic feldspar and or sodic plagioclase and one or more aluminum rich minerals thus these rocks contain more aluminum than could be accom modated by feldspar in a cipw normative calculation and show normative corundum peraluminous granites are defined by their chemical nature but their recognition is often based on petrography this discrepancy thus may lead to inconsistency although peraluminous granitic rocks are com monly true granite streckeisen 1973 they range from tonalite to granite of special interest are strongly peraluminous as defi ned below granite granodiorite or in rare instances trondhjemite these rocks contain alumi nous minerals almandinic garnet cordierite tourmaline muscovite that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous the origin of peraluminous granite and related intrusive rocks is of much current interest many of these form shallow level intrusions and they can reach enormous sizes examples are the batholiths in the lachlan fold belt in southeastern australia white chappell 1983 the cornub ian batholith in england exley stone 1966 the south mountain batholith in nova scotia mckenzie clarke 1975 the manaslu batho lith in the himalayas lefort 1981 much of the idaho batholith

tourmaline in a low grade clastic metasedimentary rock an example of the petrogenetic potential of tourmaline detrital tourmaline grains and their associated tourmaline overgrowths provide a means to unravel the provenance and petrogenetic history of low grade clastic metasedimentary rocks evidence derives from tourmaline grains found in a lithic wacke metamorphosed to chlorite zone conditions the detrital tourmaline cores are diagnostic indicators of the source rocks of the sediment whereas the overgrowths record both diagenetic and metamorphic reactions in the rock tourmaline grains consist of a detrital core surrounded by asymmetric overgrowths comprised of inner and outer rims abrupt chemical discontinuities between each of these zones implies that volume diffusion within tourmaline was minor under the conditions of formation compositions of the detrital cores vary widely yet can be correlated with source rock types that are consistent with lithic fragments recognizable in the metawacke at either the analogous or antilogous pole inner rim compositions proximal to the detrital cores converge despite the substrate tourmaline composition indicating an approach to chemical equilibrium however significant dufferences in al and x site vacancies at the expense of mg na and ti between the analogous and antilogous poles of the inner rims demonstrate the presence of significant amounts of compositional polarity outer rim compositions at either pole also converge but compositional polarity between the analogous and antilogous poles persists the presence of the inner and outer rims separated by a compositional discontinuity suggests punctuated evolution of the overgrowth this implies that boron was sporadically available during diagenesis and metamorphism based on boron contents of minerals this may correspond to a mechanism such as boron release due to polytypic change of illite or consumption of illite and or muscovite as such tourmaline growth stages may serve as a monitor of chemical reactions in low grade metamorphic rocks

tectonics of the acadian orogeny in new england and adjacent canada paleogeographic analysis of post taconian rocks in new england and adjacent parts of canada has revealed the existence of two volcanic arcs which shut off at the time of the acadian orogeny one was built on arc basement previously accreted to north america during the taconic orogeny the other on precambrian continental basement of avalonia in the intervening merrimack fredericton trough metamorphosed and poly deformed turbidites and black shales record deep water conditions in silurian following mckerrow and ziegler 1971 this tract is interpreted as the site of an ocean which closed in siluro devonian by simultaneous subduction beneath both continental margins in the molucca sea in indonesia a comparable arc arc collision is in an early stage of development moore et al 1982 suggested that an accretionary prism built against one arc is overthrusting its counterpart which developed on the other side of the ocean an identical geometry with an avalonian accretionary prism overriding the conve

a rare garnet tourmaline sillimanite biotite ilmenite quartz assemblage from the granulite facies region of south central massachusetts a rare lithology consisting of garnet tourmaline sillimanite biotite ilmenite quartz has been found within the granulite facies region of south central massachusetts the homogeneous ti rich oxy dravitic tourmaline x mg mg mg fe 0 72 0 77 falls into the alkali group and is similar in composition to lower grade tourmaline found in corresponding metapelitic rocks in maine charge balancing calculations and binary diagrams suggest that like biotite in the region tourmaline has undergone deprotonation by means of the exchange vectors alor 1 oh 1 and tio 2 r 1 oh 2 where r represents fe mg the restriction of a concordant tourmaline rich horizon in otherwise tourmaline free rocks of this granulite facies region suggests that either 1 b released during prograde fluid absent dehydration reactions of muscovite and biotite was locally available in a fluid phase or melt for later crystallization near the peak of granulite facies metamorphism along pathways that provided a conduit for fluid migration or 2 that this is simply a b rich compositional horizon tourmalinite that survived anatexis and granulite facies metamorphism and that records the incipient conditions of tourmaline breakdown and subsequent recrystallization near or post peak metamorphism

assessing detrital garnet chemical composition as a quantitative provenance tool a multivariate statistical approach abstract chemical analysis of detrital garnet is a widely utilized quantitative tool for determining the provenance of sediments the goal of this study is to investigate the ability of the compositions of detrital garnet to provide a direct linkage to the specific source rocks from which the garnet was derived to achieve this goal we analyzed detrital garnet isolated from alluvial samples collected from the french broad river and several of its tributaries a watershed that drains portions of the multiply deformed southern appalachian orogen usa to test whether potential linkages between detrital and potential source rock garnet could be achieved garnet crystals were chemically characterized from a wide variety of lithologies that crop out in the french broad watershed and thus are the most likely local sources of detrital garnet mahalanobis distances measured on canonical discriminant functions successfully differentiated garnet compositions among the 18 analyzed source rocks these metrics were then applied to 2 300 detrital garnet compositions to link each grain to its potential source rock approximately 94 of the detrital garnet crystals were linked to their potential source regions thus only 6 of the detrital crystals were treated as unclassified we interpret the unclassified high ca garnets to have been derived from minor sub map scale lenses and boudins of calc silicate or skarns from exposed ocoee or ashe metaclastic units within the french broad river watershed the unclassified high mn detrital garnet grains are interpreted to have been derived from the various felsic granitiods and pegmatites that intrude the region of study

the formation of fluidized ejecta on mars by granular flows a simple granular flow model is used to investigate some of the conditions under which ejecta may flow as a granular media the purpose of this investigation is to provide some bounds as to when either volatiles or an atmosphere are required to explain the fluid like morphology of many martian ejecta deposits we consider the ejecta deposition process from when an ejecta curtain first strikes a target surface via ballistics and possibly flows thereafter a new finding is that either hard smooth surfaces or slightly erodible surfaces allow ejecta to flow readily as a granular medium neither volatiles nor an atmosphere are required to initiate flow a low friction coefficient between ejecta grains can also generate flow and would be analogous to adding volatiles to the ejecta the presence of either a rough or a densely packed erodible surface does not permit easy ejecta flow high friction coefficients between ejecta grain also prevent flow while changes in the coefficient of restitution a measure of how much energy is retained after collisions between particles plays a minor role in the flow dynamics of ejecta a hard smooth or a somewhat erodible surface could be generated by past fluvial activity on mars which can either indurate a surface erode and smooth a surface or generate sedimentary terrains that are fairly easy to erode no ramparts or layered ejecta morphologies are generated by our model but this may be because several simplifying assumptions are used in our model and should not be construed as proof that either volatiles or an atmosphere are required to form fluidized ejecta morphologies

an experimental study on k and na incorporation in dravitic tourmaline and insight into the origin of diamondiferous tourmaline from the kokchetav massif kazakhstan tourmaline was synthesized in the system mgo al2o3 b2o3 sio2 kcl nacl h2o from an oxide mixture and excess fluid at 500 700 c and 0 2 4 0 gpa to investigate the effect of pressure temperature and fluid composition on the relative incorporation of na and k in dravitic tourmaline incorporation of k at the x site increases with pressure temperature and kcl concentration a maximum of 0 71 k pfu leaving 0 29 x vacant sites pfu was incorporated into k dravite synthesized at 4 0 gpa 700 c from a 4 78 m kcl na free fluid in contrast na incorporation depends predominately on fluid composition rather than pressure or temperature dravite with the highest na content of 1 00 na pfu was synthesized at 0 4 gpa and 700 c from a 3 87 m nacl and 1 08 m kcl fluid all synthesized crystals are zoned and the dominant solid solution in the na and k bearing system is between magnesio foitite mg2al al6si6o18 bo3 3 oh 3oh and dravite namg3al6si6o18 bo3 3 oh 3 oh with the dravitic component increasing with the concentration of na in the fluid in the k bearing na free system the dominant solid solution is between magnesio foitite and k dravite kmg3al6si6o18 bo3 3 oh 3 oh with the k dravitic component increasing with pressure temperature and the concentration of k in the fluid the unit cell volume of tourmaline increases with k incorporation from 1555 1 3 to 1588 1 2 a3 reflecting the incorporation of the relatively large k ion comparison of our results to the compositional data for maruyamaite k dominant tourmaline from the ultrahigh pressure rocks of the kokchetav massif in kazakhstan suggests that the latter was formed in a k rich na poor environment at ultrahigh pressure conditions near the diamond stability field

diverse tourmaline compositions from orogenic gold deposits in the hutti maski greenstone belt india implications for sources of ore forming fluids the late archean hutti maski greenstone belt hosts the largest operational gold mine in india at hutti as well as two satellite mines at hira buddini and uti tourmaline is a common accessory mineral in the auriferous altered wall rocks proximal to the gold bearing veins of these orogenic gold deposits we report here major rare earth element ree and selected trace element compositions of tourmalines from these alteration zones at hutti and hira buddini and from spatially associated volcaniclastic rocks at uti in order to compare and evaluate possible fluid sources related to tourmaline precipitation and gold mineralization tourmalines at hutti occur as tourmaline calcite microveins within proximal alteration zones and as disseminated grains along the biotite chlorite defined mylonitic foliation these tourmalines belong to the dravite oxydravite group with an evolutionary trend towards magnesio foitite and commonly are mg rich up to 2 06 apfu with low na 0 61 apfu and up to 53 x site vacancies characteristics are low abundances of total ree 0 25 0 67 chondrite and a flat trend with minor hree enrichment accompanied by strong positive eu anomalies at hira buddini tourmalines of the oxydravite povondraite series replace amphiboles and hydrothermal biotite based on textural and chemical characteristics three generations of tourmalines are present at hira buddini earliest type i tourmaline has moderate fe content up to 1 46 apfu high na average 0 80 apfu and moderate x site vacancies up to 22 type ii tends to be relatively enriched in fe up to 2 08 apfu have similar na contents average 0 79 apfu and low x site vacancies up to 8 these tourmalines contain higher total ree 0 93 2 23 chondrite and display a flat trend with slight middle rare earth element mree depletion accompanied by a small positive eu anomaly the latest tourmalines type iii are fe poor up to 1 52 apfu and na poor average 0 67 apfu with relatively high x site vacancies up to 21 this tourmaline type has relatively low total rees 0 21 1 05 chondrite and similar abundance patterns to those of hutti tourmalines accompanied by large positive eu anomalies similarity in tourmaline compositions with evolutionary trends in compositional space from different textural associations suggests that a single low salinity and reduced metamorphogenic fluid with inherently low ree was responsible for proximal alteration and gold mineralization at hutti the type i and type ii tourmalines from hira buddini display oxydravite povondraite trends with compositional overlap that suggests fluid mixing at a paragenetically early stage the early hydrothermal fluid was more saline oxidizing and likely had a granite derived component with high ree contents a later evolved relatively low salinity and reduced fluid is recorded by the last generation type iii tourmalines at hira buddini the tourmalines from uti metapelites are characterized by dravitic composition low na contents high x site vacancies 31 47 and an evolutionary trend toward magnesio foitite these tourmalines have higher ree contents 1 16 2 08 chondrite lree enriched patterns together with large positive eu anomalies and low concentrations of most trace elements all features that suggest a metamorphic origin

estimating abundances of volatile and other mobile components in evolved silicic melts through mineral melt equilibria to variable degrees of accuracy from source partitioning between and earths residual minerals and anatectic melts through melt fractionation partitioning between igneous minerals and residual melts to the end stages of magma solidification where higher concentrations of normally trace elements may promote saturation in their crystalline phases the magmatic abundance of rare alkalis and alkaline earths

tourmaline at diagenetic to low grade metamorphic conditions its petrologic applicability article i nfo tourmaline developed under low temperature conditions b 300 c typically has distinctive morphological and chemical characteristics that reveal significant information about the environments in which they crys tallize under diagenetic conditions tourmaline can develop as overgrowths on detrital tourmaline cores or as new authigenic crystals tourmaline as monopolar crystal overgrowths is found in sandstones shales conglomerates dolostones and limestones nucleating exclusively at the positive end of the c axis cpole on the detrital grain a feature related to the mineral s polar nature these overgrowths tend to have compo sitions dominated by x site vacant tourmaline species e g foitite and can be linked to growth in aqueous environments low in na with other chemical characteristics related to the host rocks as temperature in creases tourmaline overgrowths develop at both the cpole andc pole but continue to exhibit a signif icant degree of morphological and chemical asymmetries these differences at either pole diminish as a function of increasing temperature such that it can be used as an intramineral geothermometer authigenic tourmalines without detrital tourmaline nuclei are found in many sedimentary or weakly meta morphosed metasedimentary rocks as well as fluid dominated geothermal systems here tourmalines are commonly foititic but have mg fe contents influenced by the host rock composition low temperature tour malines developed in hypersaline environments e g salt domes have distinct chemical characteristics high na fe 3 and w o and follow a trend between oxy dravite and povondraite o p trend this composi tional trend can be used as a guide to indicate tourmaline development within low temperature hypersaline environments and appears to be diagnostic of an oxidizing environment with high na in the fluid and high sa linity with the resulting reduction of the activity of h2o the o p trend is retained in some meta evaporite de posits that are relatively high grade and is found in tourmaline from some types of economically important metal deposits although tourmalines in low temperature environments are largely overlooked they have po tential to be a useful indicator of the chemical and thermal environments in a regime largely absent of such indicators

boron in metapelites controlled by the breakdown of tourmaline and retrograde formation of borosilicates in the yanai area ryoke metamorphic belt sw japan tourmaline out isograd formed by the breakdown of tourmaline is defined in the upper amphibolite facies metapelites in the yanai area ryoke metamorphic belt sw japan the rim composition of tourmaline progressively becomes aluminous with ascending metamorphic grade and the chemical zoning of tourmaline is controlled by x alna 1mg 1 and mgtiyal 2 vectors in low to medium grade zones where muscovite is stable whereas it is controlled by mg oh yal 1o 1 camgox 1 yal 1 oh 1 and mgtiyal 2 vectors in further higher grade muscovite unstable zones the size of tourmaline increases drastically where breakdown of muscovite quartz takes place probably due to the growth of tourmaline during breakdown of muscovite on the high temperature side of the tourmaline out isograd depletion of whole rock boron is observed escape of boron bearing melt or the fluid evolved from the melt during its crystallization probably caused this depletion although locally trapped boron bearing melt or fluid formed irregularly shaped tourmaline and dumortierite during retrograde metamorphism

hourglass sector zoning in metamorphic tourmaline and resultant major and trace element fractionation a new type of sector zoning with an hourglass shape has been identified in metamorphic tourmalines that formed under a wide variety of physical and chemical conditions the two sectors in the c direction are not equivalent due to asymmetry in the crystal structure of tourmaline along the c axis the c sector is characterized by low concentrations of ti ca mg and na although al is high and has a pale commonly blue or pale green color conversely the c sector is low in mg and al and high in ca fe and ti the latter two causing the dark brown color of this sector the a sector has intermediate characteristics and probably approximates a sector free tourmaline thin sectioning of these sector zoned tourmalines perpendicular to the c axis can produce three types of apparent radial zoning patterns blue green cores dark brown cores or no distinct cores these apparent cores will further vary in relative diameter depending on the sectioning level furthermore core boundaries can be straight or ragged depending on whether the relative growth speeds for the different faces was constant or variable these textures have been used to argue for a prograde or detrital origin of tourmaline cores however sector zoning is a more appealing explanation for most of these textures and can further explain the textural resemblance among metamorphic tourmalines from highly variable bulk rock composition metamorphic history and mineral paragenesis the sector zoning that is described here develops by preferential uptake of elements on the r growth plane resulting from a combined effect of differences in surface charge and morphology of this plane in the c and c directions this leads to the preferential incorporation of more positively charged elements in the c direction and a preference for a vacant x site in the c direction because the compositional differences among the sectors are pronounced in both major and trace elements and in the same order of magnitude as growth zoning variability the presence of sector zoning must be established and taken into account when making inferences from tourmaline chemistry

insight into diagenetic processes from authigenic tourmaline an example from carboniferous and permian siliciclastic rocks of western poland abstract authigenic tourmaline is a rare and minor component of siliciclastic rocks however once it occurs it can be used to interpret a number of subsurface parameters and processes such as fluid composition redox state salinity ph and fluid migration paths notwithstanding the conditions of tourmaline authigenesis still need to be recognize with greater clarity carboniferous and permian siliciclastic rocks in the subsurface of western poland in the vicinity of the dolsk fault show unusually high boron contents at places surpassing 1000 g g which are associated with the presence of authigenic tourmaline the mineral forms fine elongated crystals of nano to micrometer width grouped in radiating or semi parallel aggregates which are dispersed in the clay matrix of shales and graywackes coat grain surfaces and line secondary pores in porous sandstones replace some grains in volcaniclastic breccia and overgrow detrital tourmalines in quartzarenites regardless of host rock compositions the tourmaline is si deficient moderately al rich and shows significant x site vacancies and highly variable mg mg fetot ratios in rare zoned tourmaline the mg mg fetot ratios distinctly decrease and vacancies slightly increase towards the growth direction the results suggest that the tourmaline nucleated rapidly under a strong driving force at high boron concentration and high temperature the fluids which enabled the process were acidic reducing b and mg bearing and of low na and ca contents the tourmaline grew primarily at the expense of kaolinite possibly of other clay minerals and k feldspar in the temperature range 150 200 c its crystallization was a short episode in the diagenetic history of the host rocks tourmaline authigenesis across the carboniferous permian unconformity in the proximity of a prominent fault zone is evidence for fluid and heat migration along faults and for temporarily open geochemical system during late diagenesis the source of boron has been unproven yet the circulation of bitterns originated from upper permian evaporites was highly probable

on the applicability of oil shale to palaeomagnetic investigations abstract samples of oil shales of autunian age from the krkonose riesengebirge piedmont basin northern bohemia which represent rocks with fossil micro organic matter in the initial stage of carbonification were subjected to palaeomagnetic investigations the palaeomagnetic data obtained from these rocks are fully in accordance with those derived previously on rocks of the red bed facies in the same area preliminary results obtained on lower carboniferous coal bearing shales collected from the upper silesian basin ostrava karvina region indicate also that these rocks characterized by a higher degree of carbonification are suitable for palaeomagnetic investigations these results with those of laboratory carbonification indicate that such rocks as bituminous rocks black shales oil shales coal bearing shales or generally rocks containing micro organic matter at different stages of natural carbonification are worthy of being studied palaeomagnetically

deformation controlled cation diffusion in tourmaline a microanalytical study on trace elements and boron isotopes abs tract plastic deformation of variable intensity has modified primary textures composition and element distribution in tourmaline from a mylonitic pegmatite from the nw argentinean sierras pampeanas the primary concentric tourmaline zonation has been overprinted and partly destroyed by synkinematic cation diffusion that occurred under amphibolite facies p t conditions textural changes include bending of crystals formation of subgrains and subgrain rotation leading locally to recrystallization of tourmaline some parts of deformed crystals were less affected or unaffected by plastic deformation and secondary cation diffusion two principal processes intracrystal trace element diffusion and matrix exchange of trace elements caused the compositional variations in deformed tourmaline domains intracrystal diffusion partly or completely destroyed the primary trace element zonation by cation diffusion from zones of high to low concentration small cations occupying the y position are readily mobilized even by weak deformation whereas large cations on the x site require higher deformation intensity to be mobilized and show less pronounced or no homogenization of the primary zonation matrix exchange between tourmaline and co existing solid or fluid phases generally leads to trace element loss from deformed tourmaline domains the extent of the matrix exchange is primarily controlled by the compatibility of mobilized cation species with matrix phases during mylonitization in contrast the b isotopic compositions in deformed and undeformed crystal domains are uniform indicating absence of significant b diffusion and isotope fractionation during crystal growth and plastic deformation i e the activation energy to move b in tourmaline must be too high even for intense plastic deformation to overcome

primary diagenetic copper carbonate at the malbunka copper deposit amadeus basin northern territory australia abstract the malbunka copper deposit located about 220 km west of alice springs in the northern territory of australia may be a rare example of primary formation of copper carbonate mineralization this deposit consists of unusual azurite disks up to 25 cm diameter and lesser amounts of secondary azurite crystals and malachite carbon isotope values of the copper carbonate minerals are consistent with formation from groundwater dissolved inorganic carbon oxygen isotope thermometry formation temperature estimates are 5 16 c above ambient temperatures suggesting the copper carbonates formed at a depth between 0 3 and 1 6 km in the amadeus basin azurite fluid inclusion waters are rich in boron chlorine and other elements suggestive of dilute oil basin formation fluids in addition presence of euhedral tourmaline with strong chemical zonation suggest that this was a low temperature diagenetic setting the strong correlation of structures associated with hydraulic fracturing and rich copper carbonate mineralization suggest a strongly compartmentalized overpressure environment it is proposed that copper carbonates of the malbunka deposit formed when deep copper rich formation fluids were released upward by overpressure induced failure of basin sediments permitting mixing with carbonate rich fluids above this work bears directly upon exploration for a new type of primary copper deposit through understanding of the conditions of genesis

epigenetic to low grade tourmaline in the gdoumont metaconglomerates belgium a sensitive probe of its chemical environment of formation abstract this study reports the first observation and compositional data of tourmaline overgrowths in the post caledonian basal gdoumont conglomerates of the belgian part of the rhenohercynian basin authigenic tourmaline occurs as monopolar hemimorphic and bipolar asymmetrical foitite overgrowths within fractures and along the margins of detrital tourmaline grains and tourmalinite pebbles formulae calculated from electron microprobe analyses reveal high amounts of vacancies in the x site 61 to 84 placing this tourmaline amongst the most alkali deficient tourmaline recorded to date besides the alkali deficiency gdoumont overgrowths are characterized by high al low na and ca and low to moderate mg fe mg ratios these characteristics reflect the composition of the host conglomerates and suggest local derivation of the chemical components slightly differing zoning patterns sample scale and differences between localities regional scale indicate heterogeneity of the low grade host rock host tourmaline grains as well as tourmaline occurring in quartz veins crosscutting the gdoumont metasediments have distinctly different compositions the absence of discontinuous zoning suggests growth of the authigenic tourmaline in just one stage it is most likely that tourmaline formed from boron released by metamorphic breakdown of detrital minerals e g illite and or k feldspar based on their crystal chemistry and the observed optical properties the overgrowths must have developed during diagenetic to lower greenschist facies conditions scarce concurrency of bipolar overgrowths isolated neoblasts and cryptocrystalline nests of tourmaline indicates limited growth until middle greenschists facies conditions

provenance of late palaeozoic metasediments of the patagonian proto pacific margin southernmost chile and argentina in this provenance study of late palaeozoic metasediments of the eastern andean metamorphic complex eamc along the south patagonian proto pacific margin of gondwana the palaeogeological setting of the continental margin in devonian carboniferous and permian times is reconstructed the study is based on detrital heavy mineral contents chemical compositions of tourmaline grains and whole rock element and nd sr isotopic compositions element and isotopic compositions reveal that devonian carboniferous metaturbidites deposited before the development of a late carboniferous permian magmatic arc along the margin were mainly fed from felsic recycled old continental rocks the last recycling phase involved erosion of metasediments that were exposed in patagonia feeder systems to the basin cut either through epidote rich or garnet rich metasediments in permian time eamc metaturbidites were deposited next to the evolving magmatic arc and were derived from felsic crustal rocks two provenance domains are recognised the metasediments of the northern one are chemically similar to those of the devonian carboniferous metasediments this domain was fed from the metasedimentary host rocks of the magmatic arc the southern domain probably was fed from the arc proper as indicated mainly by the dominance of metaplutonic lithic fragments abundant detrital biotite and the major element composition of the metasediments

boron isotope and light element sector zoning in tourmaline implications for the formation of b isotopic signatures hourglass sector zoning in metamorphic tourmaline is known to effectively fractionate the major and trace elements between different sectors producing three distinct compositions at the growth surface here we show that the light elements li be h and b as well as the 11 b signature are also affected by sector zoning the sector enrichment in elements is controlled by a dual process of initial preference due to growth surface charge and morphology followed by consecutive charge balance controlled enrichment the light elements especially b and h appear to act as charge balance cations in this mechanism with a preferred b 3 for si 4 and o 2 for oh substitution in the c sector a lighter 11 b signature d c c 1 8f0 6x accompanies this increase in b iv in the c sector in line with the lighter signatures for b iv compared to b iii in minerals however it exceeds this theoretical fractionation by a factor of 10 although we have not identified a definite process that is responsible for this fractionation it may be related to local variations in host medium along the growth surface resulting from preferred uptake of elements these observations show that 11 b signatures in tourmaline are not an independent measure of its host environment but also a function of mineral composition and the 3 dimensional zoning variations herein 2007 elsevier b v all rights reserved

the geothermobarometric potential of tourmaline based on experimental and natural data the geothermobarometric potential of tourmaline has been assessed by investigating element exchange among tourmaline and coexisting minerals in metamorphosed pelites and graywackes and in experimental exchange between tourmaline and biotite in the natural samples a temperature dependence of tourmaline mg fe exchange with biotite staurolite garnet chlorite and muscovite and ca na exchange with plagioclase is observed equilibrium calculations for the complete mineral assemblage show that tourmaline is in compositional equilibrium with all coexisting phases which would allow for an internally consistent set of thermometers among all these phases to be defined however a prohibitively large spread is present in the k d vs t relations this is not caused by analytical effects compositional zoning or disequilibrium among the minerals the experimental results show that it is the result of inter site partitioning of elements over the y and z octahedral sites of tourmaline variations in the element distribution over these sites their relative participation in the exchange and differences in the temperature dependence of exchange with each site strongly affects the k d vs t relation observed with the slope actually changing sign depending on the elements residing at each site non ideal interactions among the elements at each site will also affect this and furthermore link every exchange to the bulk tourmaline composition and hence the element mobility in the rock the promising potential of tourmaline geothermobarometry can therefore not be fulfilled until effects of inter site partitioning and non ideal interactions are known

provenance of cretaceous synorogenic sandstones in the eastern alps constraints from framework petrography heavy mineral analysis and mineral chemistry abstract the detrital components of cretaceous sedimentary rocks in the northern calcareous alps reflect the early alpine geodynamic evolution of the austroalpine microplate two contrasting source areas are distinguished on the base of light and heavy mineral analysis the first source area is located at the southeastern margin of the austroalpine and is composed of palaeozoic sediments and metamorphic rocks mesozoic carbonate rocks and ultrabasic rocks derived from the suture zone of the vardar meliata ocean the second source area is located in the northwest in a lower austroalpine position near the transpressive plate margin that juxtaposes austroalpine and penninic units this source area comprises palaeozoic low grade metamorphic rocks including high pressure hp rocks late palaeozoic meta sediments mesozoic carbonate rocks and ultrabasic rocks from obducted slices of penninic oceanic crust chemical analyses of detrital white mica amphibole and garnet support the discrimination between the two source areas tourmaline chemistry calls for a significant amount of metasedimentary rocks in the source area granitoid rocks and high grade metamorphic rocks are rare blue amphibole phengite and chloritoid composition suggest the erosion of lower blueschist facies rocks in the northwestern source area we suggest a modified model of austroalpine valanginian to coniacian tectono sedimentary evolution which is based on 1 an onset of subduction of the penninic ocean no earlier than late cretaceous 2 deposition of the analyzed sedimentary rocks in piggyback basins and 3 a reconstruction of provenance as proposed in this study