chemical and boron isotopic compositions of tourmaline from the paleoproterozoic houxianyu borate deposit ne china implications for the origin of borate deposit abstract the houxianyu borate deposit in northeastern china is one of the largest boron sources of china hosted mainly in the paleoproterozoic meta volcanic and sedimentary rocks known as the liaohe group that are characterized by high boron concentrations the borate ore body has intimate spatial relationship with the mg rich carbonates silicates of the group with fine grained gneisses meta felsic volcanic rocks as main country rocks the presence of abundant tourmalinites and tourmaline rich quartz veins in the borate orebody provides an opportunity to study the origin of boron the nature of ore forming fluids and possible mineralization mechanism we report the chemical and boron isotopic compositions of tourmalines from the tourmaline rich rocks in the borate deposit and from the tourmaline bearing fine grained gneisses tourmalines from the fine grained gneisses are chemically homogeneous showing relatively high fe and na and low mg with 11b values in a narrow range from 1 22 to 2 63 tourmalines from the tourmaline rich rocks however commonly show compositional zoning with an irregular detrital core and a euhedral overgrowth and have significantly higher mg ree and more pronounced positive eu anomalies v 229 1852 ppm and sr 208 1191 ppm than those from the fine grained gneisses they show varied b isotope values ranging from 4 51 to 12 43 which plot intermediate between those of the terrigenous sediments and arc rocks with low boron isotope values as represented by the 11b 1 22 to 2 63 of the fine grained gneisses of this study and those of marine carbonates and evaporates with high boron isotope values in addition the rim of the zoned tourmaline shows notably higher mg ti v sn and pb and ree particularly lrees but lower fe co cr ni zn mn and lower 11b values than the core these data suggest that 1 the sources of boron of the borate ore body are mainly the paleoproterozoic meta volcanic and sedimentary rocks and 2 the ore forming fluids should be the high temperature metamorphic fluids related to the amphibolite facies metamorphism of the paleoproterozoic foldbelt which leach boron from the boron rich meta volcanic and sedimentary rocks of the liaohe group and the boron rich metamorphic fluids subsequently interacted with the marine mg rich carbonates and evaporates forming borate deposit the tourmaline overgrowth in the rim and the tourmaline rich rocks

petrochemistry and sr pb and nd isotopic geochemistry of the paleoproterozoic kuandian complex the eastern liaoning province china abstract a geochemical and isotopic study has been carried out on the paleoproterozoic kuandian complex and some associated granitoids in the eastern liaoning province china the kuandian amphibolite and granite give an imprecise 1 9 0 4 ga all errors are 2 rb sr errorchron with 87 sr 86 sr o 0 711 0 006 a 2 11 0 06 ga pb pb isochron with a first stage growth 8 43 and a 2 31 0 10 ga smnd isochron with 143 nd 144 nd o 0 50970 0 00009 or nd t 1 1 nd depleted mantle model dates tdm of amphibolite are 2 75 to 2 46 ga those of granite are 2 53 to 2 36 ga zircons from the kuandian granite give a minimum 2 14 0 05 ga upper intercept date the kuandian amphibolite is chemically similar to the high mg member of columbia river basalts and the kuandian granite is an anorogenic granite they are genetically related and formed 2 4 to 2 3 ga ago fractional crystallization of olivine pyroxene and plagioclase from precursor magma of the kuandian amphibolite can produce magma with composition of the kuandian granite the paleoproterozoic mantle source in the eastern liaoning province is less depleted than that inferred from the average mantle evolution curve in contrast with the archean mantle in the sino korean craton which is more depleted than the average this study also reveals that the lishan granite of the eastern liaoning province is older than 3 ga and that some granites and dykes previously mapped as proterozoic are of mesozoic age

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

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

the palaeoproterozoic boron deposits in eastern liaoning china a metamorphosed evaporite abstract we have carried out a field study of the palaeoproterozoic borate deposits of eastern liaoning province china the borates are hosted within mg silicate and mg carbonate rocks and have previously been interpreted as either skarns or metamorphosed volcanogenic exhalative deposits the deposits contain textures that are compatible with a sedimentary origin of the borates and there is a lack of the associated mineralization that is characteristic of magnesian skarns in addition preliminary boron isotope data indicate that the boron within the borates was not derived from the footwall rocks that have been proposed as the source of the skarn fluids a purely exhalative model can be dismissed on the basis of geochemical arguments and comparison with modern environments which show that borates are too soluble to precipitate directly from hydrothermal fluids the geology and field relationships show a number of similarities with recent non marine evaporite settings and young continental rifts in arid environments we conclude therefore that the liaoning deposits are metamorphosed evaporites in which the boron was originally present as primary evaporite borate minerals this model places the liaoning borates in the same category as the majority of other economic borate deposits in the world

integration of detrital gold microchemistry heavy mineral distribution and sediment geochemistry to clarify regional metallogeny in glaciated terrains application in the caledonides of southeast ireland regional exploration for rare and precious metal enrichment traditionally uses multielement geochemical analysis of the fines 150 m fraction of stream sediments however these data can be misleading in glaciated regions with complex geology here we compare the spatial distributions of data from sediment fines with distributions of heavy mineral concentrates including detrital gold in the same region gold grains are characterized according to abundance and morphology plus a microchemical signature from the combination of alloy analysis and systematic identification of mineral inclusions revealed in polished sections these inclusions survive indefinitely and are indicative of hypogene mineralogy whereas the metal loadings of fines may be affected by weathering or anthropogenic activity all three approaches are mutually supportive sediment fines analyses provide a basis for more labor intensive targeted gold grain studies which in turn highlight specific gold element associations useful for interpretation of geochemical data sets spatial distributions of resistate heavy mineral suites constrain the directions and extents of glacial transport which facilitates more confident interpretations of placer lode relationships from gold grain studies characterization of 2 160 gold grains from 40 localities in the auriferous region of southeast ireland provided a clear indication of proximity of gold to source and identified gold derived from different episodes of mineralization a distinction is apparent between gold in the south of the region wexford likely derived from widespread stratabound au as fe s mineralization and that in the north wicklow where the historical placer mining district of the goldmines river yielded gold with inclusions exhibiting a distinctive pb bi as association the goldmines river placers formed by the efficient accumulation and preservation of detrital gold derived from several discrete intravalley sources we recommend that a combination of classic stream sediment geochemistry heavy mineral analysis and gold grain studies is used more widely to provide additional insights on the location and nature of gold mineralization and regional metallogeny in regions of poor exposure and complex geology

early to middle holocene silicic tephra horizons from the katla volcanic system iceland new results from the faroe islands comparatively few icelandic tephra horizons dated to the early part of the holocene have so far been detected outside iceland here i present several tephra horizons that have been recorded in a holocene peat sequence on the faroe islands geochemical analyses show that at least two dacitic and one rhyolitic tephra layers were erupted from the katla volcanic system on southern iceland between ca 8000 and 5900 cal yr bp the upper two layers can be correlated with the silk tephras described from southern iceland whereas the third dated to ca 8000 cal yr bp has a geochemistry virtually identical to the rhyolitic component of the vedde ash the results suggest that the late weichselian and early holocene eruption history of the katla volcano was probably more complex than inferred from iceland a new early holocene rhyolitic tephra dated to ca 10 500 cal yr bp probably originates in the snaefellsnes volcanic centre in western iceland these new findings may play an important role in developing a holocene tephra framework for northwest europe copyright 2002 john wiley sons ltd

geochemistry and boron isotopic compositions of tourmaline from the paleoproterozoic amphibolites ne china implications for the origin of borate deposit abstract the paleoproterozoic metasediments and metavolcanics in the jiao liao ji belt northeastern china host a large number of borate deposits to trace the source of boron in these borate deposits we carried out in situ chemical and boron isotopic studies on tourmalines of amphibolites from the lieryu formation of the liaohe group in the jiao liao ji belt the petrology and the chemical compositions of tourmalines of amphibolites show that these tourmalines formed by influx of b rich fluids during different stages of metamorphism the 11b values of tourmaline continue to decline during the successive metamorphism tourmalines that formed during the prograde metamorphism show higher 11b values 9 52 10 18 than those formed during the peak metamorphism of amphibolite facies 7 22 9 43 subsequently tourmalines with lower 11b values formed during the retrograde metamorphism of greenschist facies which have slightly different boron isotopic compositions in cores 4 18 5 50 and rims 2 66 4 66 mainly due to the temperature effect the boron isotopic variations of tourmalines of amphibolites match well with our modeling study of boron isotope the results suggest that tourmalines may be precipitated from fluids released from dehydration of marine sediments with relative high 11b values 9 during prograde metamorphism in the same way the borate deposits formed from the liberated b rich fluids that interacted with the mg rich carbonates and or silicates

trace element systematics of tourmaline in pegmatitic and hydrothermal systems from the variscan schwarzwald germany the importance of major element composition sector zoning and fluid or melt composition article an extensive data set on the compositional variation of tourmaline from granitic pegmatites from migmatitic gneisses and from various types of hydrothermal veins from the schwarzwald germany is provided the investigated tourmalines are members of the alkali and x vacant groups representing mostly dravite schorl solid solutions with some analyses belonging to the foitite mg foitite series oxygen isotope data on quartz tourmaline pairs indicate formation temperatures between 550 and 350 c for most of the quartz tourmaline veins most of the tourmalines show strong sector zonation fractionating certain major e g na mg minor e g ti ca and trace elements e g sr pb ree among the different crystallographic sectors of the crystals we conclude that comparison of tourmaline compositions for petrogenetic interpretations must be based on the concentrations in the neutral a sector in order to eliminate the effects of intra crystalline fractionation most trace element contents vary over several orders of magnitude with median concentrations generally be tween 0 1 and 10 g g the highest concentrations are found for zn v sr sc sn and li median concentrations of several tens to hundreds of g g whereas very low median concentrations b0 1 g g were found for u th bi tl and cs the concentration of several trace elements e g sr ree co correlates with the major element composition of the tourmaline which implies potential crystal chemical effects on their incorporation conse quently the general assumption that tourmaline is a passive monitor for the chemical compositions of the melts or fluids from which it crystallizes has to be questioned nevertheless our study demonstrates that the trace element composition of tourmaline allows to distinguish between geochemically distinct fluid sources and the trace element composition of tourmaline may therefore be used to unravel the chemical complexity of granite related hydrothermal systems

la icp ms u pb zircon ages of the liaohe group in the eastern block of the north china craton constraints on the evolution of the jiao liao ji belt abstract as a major lithostratigraphic unit of the palaeoproterozoic jiao liao ji belt in the eastern block of the north china craton the liaohe group consists of an assemblage that is transitional from a lower arkose and volcanic rich sequence langzishan li eryu and gaojiayu formations through a middle carbonate rich sequence dashiqiao formation to an upper argillaceous sequence gaixian formation tectonically associated with the liaohe group are large volumes of granitoid rocks named the liaoji granite whose emplacement age has been dated at about 2 1 2 2 ga regionally the liaohe group and the associated liaoji granite extend along a nee trending belt that is flanked by 2 45 2 55 ga basement gneisses u pb zircon data and cathodoluminescence cl imaging are used to constrain the maximum depositional and metamorphic ages of the liaohe group which are critical in understanding the tectonic setting and history of the jiao liao ji belt cathodoluminescence images reveal that most detrital zircon grains from the liaohe group are characterized by concentric oscillatory zoning with comparatively low luminescence and high th u ratios suggesting magmatic origin but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low th u ratio indicating metamorphic origin results of this study show that the detrital zircon grains of the langzishan formation the lowest sequence of the liaohe group have concordant u pb ages ranging from 2 05 to 2 24 ga suggesting that the liaohe group was deposited at some time after 2 05 ga although most overgrowth or recrystallization rims are too narrow to be analyzed some rims yield concordant or upper intercept ages around 1 93 ga interpreted as the peak metamorphic age of the liaohe group detrital zircon grains from the dashiqiao formation in the middle sequence of the liaohe group have concordant u pb ages ranging from 2 25 to 2 53 ga some of which are similar to those of the basement gneisses in the area this study indicates that the liaohe group was deposited after the emplacement of the liaoji granite and the latter may be a major component of the provenance for the langzishan formation in contrast the protoliths of the middle sequence of the liaohe group were most probably derived from the basement gneisses these new zircon ages for the liaohe group and recent data for the liaoji granite combined with lithological structural and metamorphic considerations support a rifting model for the evolution of the jiao liao ji belt

shrimp u pb zircon geochronology of the liaoji granitoids constraints on the evolution of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton abstract the paleoproterozoic jiao liao ji belt lies at the eastern margin of the eastern block of the north china craton and is composed mainly of the liaohe group and the liaoji granitoids the liaoji granitoids are divisible into pre tectonic magnetite and hornblende biotite monzogranitic gneisses and post tectonic or anorogenic porphyritic monzogranites and alkaline syenites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the paleoproterozoic jiao liao ji belt shrimp u pb zircon analyses reveal that the pre tectonic magnetite monzogranitic gneisses were emplaced in the period 2176 2166 ma and metamorphosed at 1914 ma and the pre tectonic hornblende biotite monzogranitic gneisses were emplaced at 2150 2143 ma these data demonstrate that the pre tectonic monzogranitic gneisses of the liaoji granitoids were not younger than the deposition of the liaohe group as previously considered since the latter contains a large amount of 2100 2000 ma detrital zircons in contrast the pre tectonic monzogranitic gneisses of the liaoji granitoids or similar aged granitoids may have been an important component of the provenance for the liaohe group shrimp u pb zircon analyses also reveal that the post tectonic porphyritic monzogranites and granites in the jiao liao ji belt were emplaced at 1875 10 and 1856 31 ma respectively simultaneously with the emplacement of the alkaline syenites that was dated at 1857 20 and 1843 23 ma similar post tecotnic or anorogenic granites are not only limited to the jiao liao ji belt but are also found in the north and south korea suggesting that the 1 85 ga post tectonic or anorogenic granitic magmatic event may have occurred in both the korean peninsula and the eastern block of the north china craton the shrimp zircon ages of this study combined with lithological structural metamorphic and geochemical data is consistent with a rift closure model which suggests that the archean complexes on the northern and southern sides of the jiao liao ji belt were originally situated on a single continental block that underwent paleoproterozoic rifting associated with the formation of the liaohe group and liaoji granitoids and closed upon itself at 1 9 ga

chemical and stable isotopic compositions of proterozoic metamorphosed evaporites and associated tourmalines from the houxianyu borate deposit eastern liaoning china an integrated major element trace and rare earth element and stable isotope b si o and s study has been carried out on the houxianyu borate deposit eastern liaoning china the present day mineralogy of the deposit is closely similar to that of magnesian skarn deposits and the borates are underlain by granite however the geochemical and isotopic evidence does not favour a skarn type origin in particular the boron isotopic compositions of the borate minerals and associated tourmalines preclude their origin from fluids derived from the granite rather the data are compatible with the borate deposit being a metamorphosed evaporite the mineralogy and chemistry of the deposit are most compatible with a non marineorigin although the high 34s and 11b values suggest that there may have been some marine components to the evaporitic brines overall the premetamorphic origin of the houxianyu borate deposit is similar to that of the tertiary non marine evaporite borate deposits of western turkey there are also similarities with other proterozoic early rifting environments e g the upper proterozoic damaran orogen of south africa that have implications for the structural evolution and mineral potential of the region

the boron isotopic composition of altered oceanic crust samples of drilled oceanic crust from dsdp holes 417a 417d and 418a and odp hole 735b and oceanic crust from the oman and cyprus ophiolites were analyzed for b contents and 11b composite samples from dsdp holes 417a 417d and 418a were used to represent the upper 550 m of altered oceanic crustal layer 2a whole rock samples from the troodos ophiolite cyprus and the oman ophiolite wer selected to represent crustal layer 2b dikes composite samples from odp hole 735b were used to represent crustal layer 3 the b content of the dsdp composites ranges from 7 2 ppm to 104 ppm and correlates with both 18o and k showing that it is a good indicator of the extent of low temperature alteration the 11b of the dsdp composites varies between 2 5 and 5 4 the b content of the samples from the troodos ophiolite ranges from 2 4 ppm to 8 1 ppm 11b varies from 0 9 to 7 8 the b content of the oman ophiolite samples ranges from 5 0 ppm to 11 1 ppm 11b varies from 1 6 to 16 9 the b content of the samples from odp hole 735b ranges from 1 1 ppm to 7 1 ppm 11b varies from 4 3 to 24 9 the general pattern displayed by these samples is one of greatest and most variable b enrichment at the top of the crust and least enrichment at the bottom of the section all of these samples are enriched compared to unaltered morb which is believed to have a b content of approximately 0 5 ppm the 11b values of deeper samples from layers 2b and 3 are more variable and generally higher than those from layer 2a boron contents and 11b are not correlated the data from the dsdp site 417418 composites indicate that the 11b of fluid circulating in the upper crust changes only slightly during alteration increasing by an average of 5 1 with an accompanying decrease in b concentration of 7 low temperature alteration appears to be a water dominated process resulting in minor modification of circulating seawater a minimum water rock ratio of 400 is calculated for these samples implying a minimum low temperature seawater flux through the upper oceanic crust of 3 4 1014 l y the average b content of altered oceanic crust as represented by these samples is 5 2 1 7 ppm and the average 11b is 3 4 1 1 this average isotopic composition is measurably different from the apparent average of oceanic sediments supporting the idea that 11b could be useful for identifying the source s of b in island arcs

detrital metamorphic and metasomatic tourmaline in high pressure metasediments from syros greece intra grain boron isotope patterns determined by secondary ion mass spectrometry the boron isotopic composition of zoned tourmaline in two metasediments from the island of syros determined by secondary ion mass spectrometry sims reflects the sedimentary and metamorphic record of the rocks tourmaline from a silicate bearing marble contains small 20 m detrital cores with highly variable 11b values 10 7 to 3 6 pointing to a heterogeneous protolith derived from multiple sources the sedimentary b isotopic record survived the entire metamorphic cycle with peak temperatures of 500 c prograde to peak metamorphic rims are homogeneous and similar among all analysed grains 11b 0 9 the varying 11b values of detrital cores in the siliceous marble demonstrate that in situ b isotope analysis of tourmaline by sims is a potentially powerful tool for provenance studies not only in sediments but also in metasediments a meta tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin 11b 3 3 and prograde to peak metamorphic overgrowth zones 1 6 fe rich rims formed during influx of b bearing fluids under retrograde conditions show strongly increasing 11b values up to 7 7 towards the margins of the grains the 11b values of metamorphic tourmaline from syros formed in mixed terrigenous marine sediments reflect the b signal blended from these two different sources and was probably not altered by dehydration during subduction

boron isotope geochemistry of metasedimentary rocks and tourmalines in a subduction zone metamorphic suite abstract in order to understand the behavior of boron b and its isotope fractionation during subduction zone metamorphism b contents and isotopic compositions together with major element compositions were determined for metasedimentary rocks and tourmalines from the sambagawa metamorphic belt central shikoku japan no systematic changes in whole rock b content and isotope composition of the metasediments were observed among the different metamorphic grades indicating the lack of a bulk fluid rock b isotope fractionation as a result of devolatilization both modal abundance and grain size of tourmaline increase with increasing metamorphic grade in contrast b contents in muscovite and chlorite decrease with increasing metamorphic grade these observations combined with mass balance calculations of b suggest the formation of tourmaline during progressive metamorphism from metamorphic fluids containing b mainly derived from muscovite and subordinately from chlorite without allowing significant net removal of b from the metasedimentary rocks tourmalines in the higher grade metasedimentary rocks have zonal structure of b isotope and major element composition with decreasing 11 b and increasing mg mg fe from the inner rim core to the outer rim the change of mg mg fe in the tourmalines with increasing grade is paralleled by similar variation in chlorite these observations suggest that the growing tourmalines record the progressive evolution of the b isotopic composition of the metamorphic fluid in the outermost rims preserving the isotope signature of peak metamorphic p t fluid conditions based on the above observations the 11 b of the tourmaline is thought to have been nearly identical to that of the metamorphic fluid resulting in the apparent b isotopic fractionation factor between metamorphic fluid and whole rock 11 b 10 b fluid 11 b 10 b whole rock which decreases from 1 007 0 003 to 1 001 0 003 from chlorite to biotite zone metamorphism such results together with the formation of tourmaline from and sequestering of b in metamorphic fluids may lead to less b isotopic fractionation as a result of subduction zone devolatilization than noted in suites containing less tourmaline this therefore makes it possible to transport b isotopic signatures which ultimately reflect earth s surface materials to the deep mantle perhaps resulting in mantle b isotope anomalies near convergent margins

timing of metamorphism in the paleoproterozoic jiao liao ji belt new shrimp u pb zircon dating of granulites gneisses and marbles of the jiaobei massif in the north china craton abstract the paleoproterozoic jiao liao ji belt lies in the eastern block of the north china craton with its southern segment extending across the bohai sea into the jiaobei massif high pressure pelitic and mafic granulites have been recently recognized in the paleoproterozoic jingshan group jiaobei massif new shrimp u th pb geochronology combined with cathodoluminescence cl imaging of zircon has been applied to the determination of the timing of the metamorphism of the high temperature and high pressure granulites and associated gneisses and marbles metamorphic zircons in these high pressure granulites gneisses and marbles occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores metamorphic zircons are all characterized by nebulous zoning or being structureless with high luminescence and relatively low th u values metamorphic zircons from two high pressure mafic granulites yielded 207pb 206pb ages of 1956 41 ma and 1884 24 ma one metamorphic zircon from a garnet sillimanite gneiss also gave an apparent 207pb 206pb age of 1939 15 ma these results are consistent with interval of ages of c 1 93 1 90 ga already obtained by previous studies for the north and south liaohe groups and the laoling group in the northern segment of the jiao liao ji belt metamorphic zircons from a high pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207pb 206pb ages of 1837 8 ma 1821 8 ma and 1836 8 ma respectively two diopside olivine phlogopite marbles yielded weighted mean 207pb 206pb ages of 1817 9 ma and 1790 6 ma these paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c 1 85 ga produced from the ji an group in the northern segment of the jiao liao ji belt and c 1 86 1 80 ga obtained for the high pressure pelitic granulites from the jingshan group in the southern segment as this metamorphic event was coeval with the emplacement of a type granites in the jiao liao ji belt and its adjacent areas it is interpreted as having resulted from a post orogenic or anorogenic extensional event

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

boron isotope systematics of tourmaline formation in the sullivan pb zn ag deposit british columbia canada abstract we report here the results of 54 boron isotope analyses of tourmaline associated with the giant sullivan pb zn ag deposit in southeastern british columbia canada the 11 b values range from 11 1 to 2 9 which is almost as great as the range found worldwide in tourmalines from 33 massive sulfide deposits and tourmalinites in dominantly clastic metasedimentary terranes the major control on the overall 11 b values of the sullivan tourmalinites is the boron source potential controls over the large range of the data also include 1 differences in formation temperatures of the tourmalinites 2 different stages of tourmaline formation 3 variations in the proportions of dissolved boron incorporated into the tourmaline rayleigh fractionation 4 seawater entrainment and 5 post depositional metamorphism the boron isotope data at sullivan are consistent with boron derivation from leaching of footwall clastic sediments however the great abundance of tourmaline in the sullivan deposit suggests that the local clastic sediments were not the sole source of boron and we argue that non marine evaporites buried deep below the orebody are the most viable source of this additional boron it is likely that some of the variation in tourmaline 11 b values reflect mixing of boron from these two sources comparison of the potential effects of these controls with geologic and other geochemical evidence suggests that major causes for the wide range of 11 b values measured at sullivan are seawater entrainment and rayleigh fractionation although in places post depositional alteration and thermal metamorphism were important in determining 11 b values of some of the recrystallized tourmalinites

water and the viscosity of andesite melts the viscosity of a synthetic andesite like melt has been measured between 1010 and 1014 p for water contents in the range 0 3 5 wt the very slow kinetics of water exsolution over this viscosity range allowed the measurements to be made at 1 bar with a high precision after a steep viscosity decrease of 5 orders of magnitude for 1 wt h2o an additional 2 5 wt h2o causes a further viscosity decrease of only 2 orders of magnitude these viscosity decreases are qualitatively similar to those observed previously for more silica rich compositions the new data join smoothly with available high temperature measurements made at high pressures on water bearing andesite melts because the intrinsic effects of pressure are as small for water bearing as for water free samples the depressing effect of water on the viscosity of natural andesite melts can be estimated changes in water speciation as a function of either temperature or pressure do not seem to have marked effects on the viscosity although quantitative applications are not yet possible the configurational entropy theory accounts qualitatively for these features

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

isotopic and elemental partitioning of boron between hydrous fluid and silicate melt the fractionation of b and its isotopes between aqueous fluid and silicate melt has been studied from 550 to 1100 c and 100 500 mpa fluid melt partition coefficients are 1 for rhyolite melt this shows that b is not always strongly extracted from melts into hydrous fluids boron isotopic fractionation is large compared with the carbon and oxygen stable isotopic systems especially at high t and is most simply explained by differences in coordination trigonal vs tetrahedral among coexisting phases combined with earlier measurements on illite water 300 350 c b isotopic fractionation defines a temperature dependent trend from 300 to 1100 c because of the large magnitude and apparent low sensitivity to bulk composition b isotopic fractionation can be readily applied to studies of diagenesis hydrothermal alteration of planetary bodies subduction zone processing and arc magma generation and magma chamber evolution

adsorption and desorption controlled magnesium isotope fractionation during extreme weathering of basalt in hainan island china magnesium isotopic compositions of a set of clay rich saprolites developed on the neogene tholeiitic basalt from hainan island in southern china have been measured in order to document the behavior of mg isotopes during continental weathering compared with unaltered basalts 26mg 0 36 the overlying saprolites are strongly depleted in mg i e th mg 99 1 to 92 9 and display highly variable 26mg ranging from 0 49 to 0 40 magnesium concentration and 26mg value of the saprolites display a general increasing trend upwards in the lower part of the profile but a decreasing trend towards the surface in the upper part the variations of mg concentration and isotopic composition in this weathering profile can be explained through adsorption and desorption processes 1 adsorption of mg to kaolin minerals kaolinite and halloysite with preferential uptake of heavy mg isotopes onto kaolin minerals and 2 desorption of mg through cation exchange of mg with the relatively lower hydration energy cations in the upper profile evidence for adsorption is supported by the positive correlation between 26mg and the modal abundance of kaolin minerals in saprolite of the lower profile while negative correlations between 26mg and concentrations of lower hydration energy cations e g sr and cs in the upper profile support the desorption process our results highlight that adsorption and desorption of mg on clay minerals play an important role in behavior of mg isotopes during extreme weathering which may help to explain the large variation in mg isotopic composition of river waters

the geochemical cycle of boron constraints from boron isotope partitioning experiments between mica and fluid abstract the fractionation of boron isotopes between synthetic boromuscovite and fluid was experimentally determined at 3 0 gpa 500 c and 3 0 gpa 700 c for near neutral fluids 11b mica fluid 11b mica 11b fluid is 10 9 1 3 at 500 c and 6 5 0 4 at 700 c this supports earlier assumptions that the main fractionation effect is due to the change from trigonal coordination of boron in neutral fluids to tetrahedrally coordinated boron in micas clays and melts the t dependence of this effect is approximated by the equation 11b mica clay melt neutral fluid 10 69 1000 t k 3 88 r2 0 992 valid from 25 c for fluid clay up to about 1000 c for fluid silicate melt experiments at 0 4 gpa that used strongly basic fluids produced significantly lower fractionations with 11b mica fluid of 7 4 1 0 at 400 c and 4 8 1 0 at 500 c showing the reduced fractionation effect when large amounts of boron in basic fluids are tetrahedrally coordinated field studies have shown that boron concentrations and 11b 10b ratios in volcanic arcs systematically decrease across the arc with increasing distance from the trench thus reflecting the thermal structure of the subducting slab our experiments show that the boron isotopic signature in volcanic arcs probably results from continuous dehydration of micas along a distinct p t range continuous slab dehydration and boron transport via fluid into the mantle wedge is responsible for the boron isotopic signature in volcanic arcs

a comparison of u pb and hf isotopic compositions of detrital zircons from the north and south liaohe groups constraints on the evolution of the jiao liao ji belt north china craton the jiao liao ji orogenic belt is one of the important paleoproterozoic mobile belts in the north china craton ncc and its central segment consists of the north and south liaohe groups and the liaoji granitoids the north and south liaohe groups consist of sedimentary and volcanic successions metamorphosed from greenschist to lower amphibolite facies and the liaoji granitoids are divisible into 2 2 2 1 ga pre tectonic monzogranitic gneisses and 1 88 1 85 ga post tectonic porphyritic monzogranites and alkaline syenites combined with cathodoluminescence cl imaging we report la icp ms laser ablation inductively coupled plasma mass spectrometry u pb and hf isotopic data for detrital zircons from the north and south liaohe groups zircons grains from both groups have igneous zircon cores that yielded two u pb age populations at 2 0 2 2 ga major and 2 5 ga minor indicating that their provenances were similarly dominated by paleoproterozoic liaoji granitoids and late archean basement rocks some structureless zircon rims in both groups yield concordant or upper intercept ages 1 9 ga interpreted as the peak metamorphic age of the two groups these results suggest that both groups were deposited in the period 2 0 1 9 ga shortly after the emplacement of the liaoji granitoids moreover zircons from both groups have similar hf model age peaks t c dm peaks at 2 66 2 75 ga and 2 80 3 00 ga

extremely high solubility of rutile in chloride and fluoride bearing metamorphic fluids an experimental investigation rutile tio 2 is an important high field strength element sequestering phase and thus understanding its solubility in metamorphic fluids is important if we are to understand terrestrial trace element cycling titanium is often assumed to be fluid immobile and previous experimental data suggest that rutile has very low solubility in h 2 o however fluids in high temperature metamorphic rocks are known to be more complex in composition the solubility of rutile in chloride and fluoride rich hydrous fluids was determined experimentally at 0 5 gpa and high temperatures the experimental results indicate much higher rutile solubility in brines compared to pure h 2 o in chloride brines solubility was 2 4 times higher than in h 2 o and in fluoride brines solubility was elevated 20 100 times the results imply that titanium may be much more mobile in metamorphic fluids than previously anticipated as solubility is critically dependent on fluid chemistry we also present a possible mechanism for rutile precipitation in metamorphic veins due to a change in fluid chemistry following the precipitation of halogen rich minerals such as apatite

boron isotopic composition of tourmalines from the 3 8 ga old isua supracrustals west greenland implications on the δ11b value of early archean seawater abstract the boron isotope composition of different occurrences of tourmalines in the 3 8 ga old isua west greenland supracrustals has been analysed by ion microprobe tourmalines in the mafic volcaniclastics have 11 b values between 12 6 and 5 8 with a mean at 3 2 5 1 these values are close to the values previously reported for tourmalines in the isua acid volcanic tuffs 6 7 1 4 and indicate no difference in 11 b value of the mantle or the continental crust between the present day and early archean times in contrast tourmalines in a marine conglomerate have low and homogeneous 11 b values of 20 2 2 2 for these tourmalines which are of authigenic origin having formed through metamorphism of pre existing marine clays a 11 b of 8 7 can be calculated for the unmetamorphosed marine sediments deposited before 3 8 ga at isua a value of 27 11 is calculated for the 11 b value of seawater at 3 8 ga the large error arises because the 11 b value of marine sediments are controlled by 1 the ratio of detrital to chemically precipitated boron and 2 the boron isotope fractionation between precipitated boron and dissolved boron in seawater a high 11 b similar to the present day value of 40 seems rather unlikely unless the fraction of detrital b in marine sediments was as high as today a lower value of 27 11 for early archean seawater is consistent with mass balance of boron between seawater mantle and continental crust

early proterozoic tectonic styles and associated mineral deposits of the north china platform abstract the remarkable change in tectonic style from archean granite greenstone belts and high grade terrains to linear sedimentary basins marks the beginning of the early proterozoic in china the different evolutionary histories of and accumulations in the early proterozoic basins result in different archean early proterozoic boundaries two time limits 2 8 and 2 5 ga are significant for the boundary in eastern china early proterozoic basins displaying different tectonic styles contain different mineral deposits the liaodong peninsula type of early proterozoic basin contains the most abundant mineral resources and deposit types including stratabound b fe and pb zn deposits in the eugeosynclinal facies of the liaojitite suite and pyrite p and magnesite deposits in miogeosynclinal facies rocks the magnesite deposits in liaodong peninsula are the largest in the world and were formed in a unique geological setting

boron isotopic composition of subduction zone metamorphic rocks abstract many arc lavas contain material derived from subducted oceanic crust and sediments but it remains unresolved whether this distinctive geochemical signature is transferred from the subducting slab by aqueous fluids silicate melts or both boron isotopic measurements have the potential to distinguish between slab transfer mechanisms because 11 b fractionates preferentially into aqueous fluids whereas little fractionation may occur during partial melting previous studies have shown that 11 b values of island arc lavas 6 to 7 overlap the range of 11 b values for altered oceanic crust 5 to 25 and pelagic sediments and turbidites 7 to 11 secondary ion mass spectrometry sims analyses of minerals in subduction zone metamorphic rocks yield 11 b 11 to 3 suggesting that slab dehydration reactions significantly lower the 11 b values of subducted oceanic crust and sediments in order to explain the higher 11 b values reported for arc lavas as compared to subduction zone metamorphic rocks the b bearing component derived from the metamorphosed slab must be enriched in 11 b relative to the slab favoring an aqueous fluid as the slab transfer mechanism