generation of leucogranites via fractional crystallization a case study of the jurassic bengbu granite in the southeastern north china craton abstract the magmatic processes that form leucogranites are closely related to plate collision as the products of crustal anatexis leucogranites provide clues to intracrustal differentiation and the regional tectonic evolution the bengbu area is located along the southeastern margin of the north china craton ncc 150 km north of the dabie orogen and is bounded by the tancheng lujiang fault zone to the east late jurassic leucogranites are widely distributed in the bengbu area we collected samples of the bengbu leucogranite blg and analyzed data on whole rock geochemistry zircon u pb geochronology zircon in situ lu hf isotopes quartz in situ o isotopes and total bulk sr nd pb isotopes zircon u pb dating yielded formation ages for these leucogranites of 160 ma the samples are characterized by high sio2 72 4 wt 76 9 wt alkali 7 3 wt 9 4 wt and al2o3 13 4 wt 15 5 wt contents in addition to two samples exhibiting the rare earth element tetrad effect all rocks have high differentiation index values 95 99 extremely low iron magnesium titanium oxide contents total fe2o3

the origin and evolution of low δ18o magma recorded by multi growth zircons in granite we for the first time reported low 18o granites within craton in bengbu uplift southeast margin of north china craton integrated ion microprobe study of 18o and u pb age on single zircon grains and zircon populations gives direct evidence for the origin and later magmatic evolution of the low 18o granites three types of zircon domains are recognized inherited magmatic core type i inherited metamorphic core mantle type ii and overgrown magmatic rim type iii type i zircons were formed in neoproterozoic and have the average 18o values of 5 3 0 6 around mantle value triassic type ii zircons have extremely low and highly heterogeneous 18o values ranging from 9 4 to 8 6 consistent with the values and variations exhibited by metamorphic zircons from dabie sulu orogen this feature argues for a triassic metamorphic origin for the 18o depletion signature of zircons from ultrahigh pressure metamorphic rocks in dabie sulu orogen jurassic type iii zircons have isotopically homogeneous 18o values of 3 3 0 5 collectively zircon populations recorded the 18o variations from source to low 18o granite the primary protolith of jurassic granites in bengbu uplift is a neoproterozoic granitic intrusion in south china block later high temperature meteoric hydrothermal alteration has lowered the whole rock 18o values in various degrees the low 18o protolith was then buried to the middle lower crust by triassic continental subduction and jurassic anatexis produced the low 18o granitic magma moreover 18o values of type iii zircons are isotopically lighter than previously reported values of magmatic garnets in jurassic granites indicating later magmatic evolution of low 18o magma toward high 18o values probably as a result of infiltration of high 18o fluid from wall rocks

a lithium isotopic study of sub greenschist to greenschist facies metamorphism in an accretionary prism new zealand article i nfo to investigate the behavior of li during low grade metamorphism and fluid flux in an accretionary prism we

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

experimental zircon melt and zircon garnet trace element partitioning and implications for the geochronology of crustal rocks garnet is the most commonly used mineral in thermobarometry whereas zircon is the most robust chronometer to date high grade metamorphic rocks to provide a basis for correlation of zircon and garnet growth we determined experimentally the trace element partitioningbetweenzircon ahydrousgraniticmeltandgarnetat20kbarand800 1000 cforp y rareearthelements ree zr hf th andu inrespecttomelt zirconpreferentiallyincorporatesallinvestigatedelementsapartfromreewithatomicnumberlowerthansm at this pressure and in the chosen composition the distribution coefficient between zircon and melt d zrn melt for ree increases with increasingatomicnumberofthereeandwithdecreasingtemperature dyb is 20at1000 c butmorethananorderofmagnitude higher at800 c the solubilityofzrinhydrousgraniticmelts buffered by zirconisabouta factoroftwo lower at20kbar than what has been previously established for mid crustal pressures large garnet produced in the experiments allowed determination of garnet melt trace element partitioning d grt melt at temperatures of 800 1000 c conditions relevant for partial melting of crustal rocks there is a systematic increase indree with decreasing temperature zircon contains significantly more heavy ree than garnet at temperatures of 800 850 c zircon garnetpartitioncoefficientsofheavy reedecreasewithincreasingtemperaturefromdlu of12at800 cto 1 4at1000 c middle reepartitioningisclosetounityforthewholeinvestigatedtemperaturerange differentempiricallydetermined zircon garnet partition coefficients from granulites and ultra high temperature granulites can potentially be explained by the experimentallydeterminedchangeofpartitioningasafunctionoftemperature thesedatacanassistinestablishingequilibriumbetween garnetandzirconzonesinnaturalrocks andintheconstructionofdetailedpressure temperature timepathsinhigh grademetamorphic rocks

chronology and geochemistry of mesozoic granitoids in the bengbu area central china constraints on the tectonic evolution of the eastern north china craton abstract we performed zircon u pb dating and analyses of major and trace elements and sr nd pb isotopes for granitoids in the bengbu area central china with the aim of constraining the magma sources and tectonic evolution of the eastern north china craton ncc the analyzed zircons show typical fine scale oscillatory zoning indicating a magmatic origin zircon u pb dating reveals granitoids of two ages late jurassic and early cretaceous 206pb 238u ages of 160 ma and 130 110 ma respectively the late jurassic rocks jingshan intrusion consist of biotite syenogranite whereas the early cretaceous rocks huaiguang xilushan nushan and caoshan intrusions are granodiorite syenogranite and monzogranite the late jurassic biotite syenogranites and early cretaceous granitoids have the following common geochemical characteristics sio2 70 35 74 56 wt k2o na2o 0 66 1 27 mainly the occurrence of neoproterozoic magmatic zircons 850 ma and inherited early mesozoic 208 228 ma metamorphic zircons within the late jurassic biotite syenogranites together with the occurrence of neoproterozoic magmatic zircons 657 and 759 ma and inherited early mesozoic 206 231 ma metamorphic zircons within the early cretaceous nushan and xilushan granitoids suggests that the primary magmas were derived from partial melting of the yangtze craton yc basement in contrast the occurrence of paleoproterozoic and paleoarchean inherited zircons within the huaiguang granitoids indicates that their primary magmas mainly originated from partial melting of the ncc basement the occurrence of yc basement within the lower continental crust of the eastern ncc indicates that the yc was subducted to the northwest beneath the ncc along the tan lu fault zone during the early mesozoic

selective entrainment of peritectic garnet into s type granitic magmas evidence from archaean mid crustal anatectites entrainment of restite is commonly invoked to explain both the origin of relatively mafic granites and granodiorites as well as the chemical connection between granite magmas and their sources this concept has become linked to models for magma migration out of the source as restite entrainment is considered to take place when diatexitic sources mobilise en masse this is at odds with the common occurrence of relatively mafic granites as high level intrusions in the crust or their eruptive equivalents that must have formed from markedly water undersaturated magmas that ascended through narrow conduits we investigate pelitic migmatites from the mkhondo valley metamorphic suite mvms in swaziland where a mid crustal heating event produced metatexitic migmatites with minimal post anatectic recrystallisation in these rocks all the garnet is peritectic having arisen through biotite fluid absent melting which produced garnet poikiloblasts characterised by inclusions of melt quartz and biotite leucosomes that represent sites of melt transfer carry similar smaller typically 1 mm entrained garnet poikiloblasts which were capable of amalgamating to form larger composite grains in anatectic structures where melt was present for longer entrained garnet was extensively recrystallised via a dissolution precipitation process to adopt a more magmatic character the peritectic garnet in the pelitic source appears to have grown out of equilibrium with feldspar and hree rich accessory phases while the recrystallised garnet in the larger melt filled structures became progressively better equilibrated with these minerals thus peritectic garnet in the source grew sufficiently rapidly to prevent trace element equilibrium with the bulk rock composition and concurrent rapid magma segregation prevented the development of diatexitic source conditions the segregated magma consisted of melt the peritectic assemblage principally garnet and the accessory minerals monazite and zircon these rocks illustrate that mafic granites may arise purely as mixtures of melt and the peritectic assemblage produced by the incongruent melting reaction importantly under the circumstances which produced the mvms anatectites peritectic garnet is entrained as 1 mm poikiloblasts demonstrating how mafic granitic magmas can migrate out of the source without the source becoming diatexitic

impact of dia and catagenesis on sulphur and oxygen sequestration of biomarkers as revealed by artificial maturation of an immature sedimentary rock hydrous pyrolysis of an immature ro 0 25 sulphur rich marl from the gessoso solfifera formation messinian in the vena del gesso basin was carried out at 160 c t 330 c for 72 h to study the effect of progressive diagenesis and early catagenesis on the abundance and distribution of sulphur containing and sulphur and oxygen linked carbon skeletons in low molecular weight and high molecular weight fractions e g kerogen to this end compounds in the saturated hydrocarbon fraction monoaromatic hydrocarbon fraction polyaromatic hydrocarbon fraction alkylsulphide fraction and ketone fraction were quantified as well as compounds released after desulphurisation of the polar fraction and hilialh4 treatment of the desulphurised polar fraction sulphur bound phytane and 20r 5 14 17 h and 20r 5 14 17 h c27 c29 steranes in the polar fraction become less abundant with increasing maturation temperature whereas the amount of their corresponding hydrocarbons increases in the saturated hydrocarbon fraction carbon skeletons that are bound in the kerogen by multiple bonds e g c38n alkane and isorenieratane are first released into the polar fraction and then as free hydrocarbons these changes occur at relatively low levels of thermal maturity ro 0 6 as evidenced by the immature values of biomarker maturity parameters such as the c35 hopane ratio and the 22s 22s 22r 17 21 h c35 hopane ratio sulphur and oxygen bound moieties present in the polar fraction are not stable with increasing thermal maturation however alkylthiophenes ketones 1 2 di n alkylbenzenes and free n alkanes seem to be stable thermal degradation products of these sulphur and oxygen bound moieties thus apart from free n alkanes which are abundantly present in more mature sedimentary rocks and crude oils alkylthiophenes 1 2 di n alkylbenzenes and ketones can also be expected to occur the positions of the thiophene moiety and the carbonyl group coincide with the original positions of the functional groups of their precursors thus important information about palaeobiochemicals is retained throughout the sequestration degradation process

rates of li diffusion in garnet coupled transport of li and y rees numerical simulation of stranded diffusion profiles in partially resorbed garnet crystals from the aureole of the makhavinekh lake pluton labrador canada yields quantitative rates of intracrystalline diffusion for li in garnet diffusion coefficients for li at 700 900 c and 0 53 gpa are 0 5 1 5 log10 units lower than those for divalent cations in the same samples and match those for y and yb this correspondence likely stems from coupled substitution of li and y or ree ions in the garnet structure the requirement of local electroneutrality limits li mobility to be no faster than that of y rees because of this coupling li zoning in garnet is retained to comparatively high temperatures making garnet a valuable monitor of the behavior of li in deep crustal systems

reappraisal of anoxia and organic richness with emphasis on cretaceous of north atlantic accumulation of anoxic sediments in the north atlantic during barremian through turonian time early to middle cretaceous was controlled mainly by local conditions although global climatic and oceanographic factors played a supporting role evidence does not support the popular hypothesis developed over the past few years of global or oceanwide anoxia data which contradict this hypothesis are based on 1 a reevaluation of criteria for identifying sediments that accumulated in anoxic water 2 a critical reappraisal of reported worldwide occurrences of anoxic sediments of these ages and 3 an examination of the spatial and temporal distribution of anoxic sediments in the north atlantic and elsewhere a model is proposed in which the earliest anoxic sediments of cretaceous age in the north atlantic were deposited in deep restricted basins by middle cenomanian time about 97 m y ago sluggish circulation had led to a gradual expansion of the oxygen minimum layer permitting deposition of anoxic sediment in nonbasinal settings as well expansion of the oxygen minimum layer caused the calcite compensation depth to rise promoting oxidation of organic carbon and causing contraction of the oxygen minimum layer development of anoxia was thus self damping anoxia effectively disappeared by early senonian time 88 m y ago when improved circulation created oceans more like those of the present some evidence indicates that enhanced biologic productivity and upwelling may have been local factors in fostering anoxia but the early and middle cretaceous were generally not highly productive times

lithium isotopic systematics of a type granites and their mafic enclaves further constraints on the li isotopic composition of the continental crust article i nfo lithium concentrations and isotopic compositions of 39 a type granites and mafic enclaves from 11 plutons in northeast china and the north china craton are used to constrain their genesis and to characterize further the average composition of the continental crust lithium concentrations 2 8 to 80 ppm in 29 a type granites are slightly higher than those of average i type granites and lower than those of average s type granites reflecting source differences lithium isotopic compositions 7 li 1 8 to 6 9 of a type granites fall within the range of worldwide i type and s type granites by contrast 10 mafic enclaves have significantly higher li concentrations 32 to 179 ppm and less variation in li isotopic compositions 7 li

organic rich sedimentation at the cenomanian turonian boundary in oceanic and coastal basins in the north atlantic and tethys one of the most striking results of the deep sea drilling project is the proof that organic rich sediments have a widespread geographical distribution during the period from upper cenomanian to middle turonian such sediments were drilled at north atlantic dsdp sites 105 135 137 138 367 398 551 603 they are also present from outcrops or oil wells on the shelf of the african continental margin senegal tarfaya and agadir basins in the tethys former alboran block southern spain algeria tunisia and umbrian apennines italy and in the north sea although these sediments have different lithologies and depositional environments from shelf areas to the deep sea their study mainly based on organic geochemistry with additional data on sedimentology biostratigraphy and palaeo bathymetry suggests that a unique pulse of organogenic accumulation characterizes the cenomanian turonian boundary event ctbe the content and type of organic matter are related to the depositional environment and organic preservation the organogenic accumulation is distributed according to various trends off the african continental margin the organic content increases from onshore areas to the shelf casamance area and moreover increases also in deep sea areas with a gradual transition from terrestrial type iii to marine type ii the best preservation of the organic matter being in the deepest areas i e site 367 off the american continental margin site 603 shows the same toc and type of organic matter as at site 105 the ctbe is also well recorded in the northern part of the atlantic celtic margin north sea by a drastic lithological change black shales within chalks but the type of organic matter is mainly terrestrial in the tethyan area the organic matter is of marine origin and well preserved results are compared with those of pratt 1984 from the western interior basin of the usa different hypotheses to explain this synchronous widespread accumulation of organic matter are discussed 1986 the geological society

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

rates of hydrothermal cooling of new oceanic upper crust derived from lithium geospeedometry episodic emplacement and cooling of lavas and dikes at mid ocean ridges leads to large fluctuations in hydrothermal fluxes and biological activity however the processes operating beneath the seafloor during these transient events such as permeability creation and dike cooling are poorly understood we have developed a new approach to determine the cooling rate of the sheeted dike complex based on the extent of diffusion of lithium from plagioclase into clinopyroxene during cooling we have calibrated this li geospeedometer using new high temperature experiments to determine both the temperature dependence of the partitioning of li between plagioclase and clinopyroxene and the diffusion coefficient for li in clinopyroxene application of this method to lavas and dikes from odp hole 504b shows that cooling rates vary dramatically with depth in the upper oceanic crust extremely rapid cooling rates 450 c hr 1 in the upper part of the sheeted dike complex are sufficient to power hydrothermal megaplume formation within the overlying water column

elemental and major biochemical changes across an oxidation front in a relict turbidite an oxygen effect abstract the elemental and major biochemical compositions of the relict f turbidite sampled in two cores from the madeira abyssal plain were determined this fine grained distal sequence occurs at ca 9 m core depth and includes a surficial oxidized horizon defined by a distinct color change oxygen diffused downward through sediments above this interface and in ca 10 kyr destroyed 80 of the organic substances that below the front had survived degradation in the presence of porewater sulfate for ca 140 kyr these deposits provide an opportunity to establish the extent and selectivity of oxic sedimentary degradation under natural conditions without the usual complications of bioturbation and varying sources or sedimentation rates in both cores a sample from the upper oxidized layer was compared to two samples from the underlying unoxidized layers the unoxidized sequences of both turbidities contained 0 93 1 02 wt organic carbon oc and 0 10 0 11 wt total nitrogen tn approximately 20 of the initial oc and 40 of the initial tn remained in the oxidized horizons with a consequent decrease in atomic c n ratio from ca 11 to ca 5 all samples gave very low yields of lignin phenols and comparable oc normalized yields of total aldoses and amino acids and indicated predominantly marine organic matter om and nonselective oxic degradation of these biochemical classes compositions of individual aldoses and amino acids generally were also similar in surface and deep sediments except that the oxidized horizons yielded markedly elevated 3 5x percentages of nonprotein amino acids this study clearly demonstrates that prolonged exposure to oz can lead to organic matter alteration which is far more extensive than that obtained with sulfate alone in comparison to early diagenesis however alteration of the measured biochemicals was largely nonselective such oxidation reactions could control the distribution and composition of organic matter in slowly accumulating continental rise and deep ocean environments

lithium isotopes in global mid ocean ridge basalts abstract the lithium isotope compositions of 30 well characterized samples of glassy lavas from the three major mid ocean ridge segments of the world spanning a wide range in radiogenic isotope and elemental content and sea floor physical parameters have been measured the overall data set shows a significant range in 7li 1 6 to 5 6 with no global correlation between li isotopes and other geochemical or tectonic parameters the samples with the greatest lithophile element depletion n morb k2o tio2

arrested kinetic li isotope fractionation at the margin of the ilimaussaq complex south greenland evidence for open system processes during final cooling of peralkaline igneous rocks li contents li and isotopic composition 7 li of mafic minerals mainly amphibole and clinopyroxene from the alkaline to peralkaline ilimaussaq plutonic complex south greenland track the behavior of li and its isotopes during magmatic differentiation and final cooling of an alkaline igneous system li in amphibole increase from b10 ppm in caamphiboles of the least differentiated unit to n3000 ppm in na amphiboles of the highly evolved units in contrast li in clinopyroxene are comparatively low b85 ppm and do not vary systematically with differentiation the distribution of li between amphibole and pyroxene is controlled by the major element composition of the minerals ca rich and na rich respectively and changes in oxygen fugacity due to li incorporation via coupled substitution with ferric iron during magmatic differentiation 7 li values of all minerals span a wide range from 17 to 8 with the different intrusive units of the complex having distinct li isotopic systematics amphiboles which dominate the li budget of whole rocks from the inner part of the complex have constant 7 li of 1 8 2 2 2 n 15 this value reflects a homogeneous melt reservoir and is consistent with their mantle derivation in agreement with published o and nd isotopic data clinopyroxenes of these samples are consistently lighter with 7 liamph cpx as large as 8 and are thus not in li isotope equilibrium these low values probably reflect late stage diffusion of li into clinopyroxene during final cooling of the rocks thus enriching the clinopyroxene in 6 li at the margin of the complex 7 li in the syenites increases systematically from 2 to high values of 14 this coupled with the observed li isotope systematics of the granitic country rocks reflects post magmatic open system processes occurring during final cooling of the intrusion although the shape and magnitude of the li isotope and elemental profiles through syenite and country rock are suggestive of diffusion driven isotope fractionation they cannot be modeled by one dimensional diffusive transport and point to circulation of a fluid having a high 7 li value possibly seawater along the chilled contact in all this study

lithium isotope geochemistry of the hawaiian plume results from the hawaii scientific drilling project and koolau volcano 1 we determined lithium isotopic compositions of mauna loa and mauna kea basalts from the 3 1 km drill hole of the hawaiian scientific drilling project hsdp for comparison li isotopic ratios were also determined for basalts from koolau volcano these two suites of samples define geochemical extremes in the range of hawaiian shield lavas the 400 ka record of mauna kea in the hsdp core shows temporal fluctuations between low 7li 4 relative to the l svec standard and high 7li 5 6 suggesting that the source components in the hawaiian plume are heterogeneous in li isotopic composition based on sio2 content and isotopic ratios of he li nd hf and pb three geochemical groups are identified in mauna kea lavas mauna kea basalts between 1900 and 2500 mbsl have relatively low 7li of about 4 they are low sio2 lavas distinguished by the highest 3he 4he and 208pb 204pb and low 176hf 177hf and 143nd 144nd like basalt from loihi seamount this mauna kea group is considered to originate from the core of the plume above 1900 mbsl high 7li lavas with high sio2 contents appear in both the submarine and subaerial sections they are marked by low 3he 4he and high 176hf 177hf the 7li rich signature of some samples 7li up to 5 7 is indicative of recycled oceanic crust in the plume this magma group defines the kea component the low sio2 lavas in the subaerial section have low 7li 4 3he 4he and 208pb 204pb their 7li values overlap the range of 7li in unaltered mid ocean ridge basalt morb and are consistent with upper mantle material entrained by the plume or contamination of plume derived magmas by the pacific lithosphere the 7li of koolau lavas mostly fall within the range of 4 5 0 3 exceptions are two samples that have 7li of 2 3 the lightest isotopic values may indicate subducted li that was isotopically fractionated during slab dehydration in contrast to other isotopic systems most koolau samples however resemble mauna kea samples in li isotopic composition mauna loa samples have 7li values of 3 5 to 4 9 within the range of the koolau and mauna kea lavas based on these data the loa trend volcanoes and kea trend volcanoes have largely overlapping li isotopic compositions in summary the hawaiian plume is not highly variable in li isotopic composition 7li is typically 4 with perturbations by subducted components to lower and higher ratios 2 5 to 5 7 the overlap of most hawaiian basalt and morb in their range of li isotopic ratios suggests minor influence of recycled oceanic crust in the plume and perhaps similar li isotopic ratios in the upper and lower mantle

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

a euxinic southern north atlantic ocean during the cenomanian turonian oceanic anoxic event abstract during mid cretaceous times large amounts of organic carbon corg became sequestered in black shales possibly due to oceanic anoxic events characterized by the development of an extended oxygen minimum zone omz here we provide the first direct evidence for an open ocean omz in the cenomanian turonian c t southern north atlantic and in fact show that the base of the photic zone was euxinic as revealed by molecular fossils from photosynthetic green sulfur bacteria in c t black shales this together with evidence for bottom water anoxia and accumulation of redox sensitive trace metals and hydrogen rich organic matter indicates a continuously euxinic water column concurrent with the high corg accumulation rates which are 15 150 times greater in the southern than in the northern north atlantic and the low biological productivity this suggests that preservation controlled the accumulation of corg in c t black shales

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

sm nd and rb sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at shuanghe in the dabie mountains central china abstract ultrahigh pressure metamorphic uhpm rocks at shuanghe area in the dabie mountains occur as a uhpm block within the regional granitic gneiss a sm nd isochron defined by garnet omphacite rutile from coesite bearing eclogite yield an age of 226 3 3 2 ma another sm nd isochron defined by garnet two phengites form uhp gneiss yield a similar age of 226 5 2 3 ma the two consistent sm nd ages defined by three uhpm minerals suggest that nd isotopic equilibrium between uhpm minerals in these rocks during uhp metamorphism has been achieved this may correspond to the age of peak metamorphism with an average metamorphic temperature of 800 c it is demonstrated that the retrograde metamorphism of uhpm rocks occurred in an open chemical system whereas the nd and sr isotopic systematics of uhpm minerals may have remained closed nd and sr isotopic disequilibrium between uhpm minerals and retrograde metamorphic minerals has been observed therefore the tie line of garnet or phengite and whole rock containing retrograde metamorphic minerals gives an old sm nd age and a young rb sr age respectively with no geologic significance however a rb sr ages of 219 0 6 6 ma defined by phengite garnet from a uhpm gneiss indicates that the uhpm rocks at shuanghe cooled down to 500 c at that time it suggests that the uhpm rocks at shuanghe experienced the first rapid cooling during 226 219 ma on the other hand the rb sr ages of 174 7 8 to 169 2 3 3 ma defined by retrograde minerals amphibole or biotite with closure temperature ranging from 450 to 300 c and intensely retrograded metamorphic rocks reflect a second rapid cooling during this time interval this is consistent with the rapid cooling time of 190 170 ma of the orthogneiss in the dabie su lu uhpm belt obtained by ar ar dating method in contrast to uhpm rocks the nd isotopic composition of the garnet in granitic gneiss has been reset during retrograde metamorphism and is in equilibrium with those of retrograde epidote and biotite which yields a sm nd isochron age of 213 5 ma indicating the retrometamorphic time corresponding to amphibolite facies in addition the biotites from the granitic gneiss yield rb sr ages of 171 173 ma similar to those of the uhpm rocks these data suggest that the country rocks granitic gneiss may have a similar cooling history to the uhpm rocks at shuanghe two stages of rapid cooling of uhpm rocks at shuanghe may correspond two stages of fast uplift the initial rapid uplifting and cooling of uhpm rocks during 226 219 ma may be caused by compression tectonics during subducting time of the continental crust whereas the later rapid cooling may reflect the exhumation of the entire subducted continental crust by extension during the early middle jurassic

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

lithium isotopes as a probe of weathering processes orinoco river abstract lithium isotopes have the potential to be effective tracers of weathering processes due to their large relative mass difference and therefore fractionation in this study an attempt is made to fill a major gap in the knowledge of li isotope fractionation during continental weathering and of the mechanisms involved finally the relationship between the suspended and dissolved material is made on a basin wide scale the orinoco basin provides a clear contrast in reaction limited and transport limited weathering regimes that has already been documented by a comprehensive study on its fluvial geochemistry edmond et al geochim cosmochim acta 60 1996 2949 2976 edmond et al geochim cosmochim acta 59 1995 3301 3325 conspicuous in our new results is the difference in 6li of the dissolved load between the andean 30 to 22 and shield 22 to 7 tributaries while the 6li of the suspended load is similar between the two to a first approximation during superficial weathering in high relief tectonically active terrains the dissolved load is high in li and isotopically heavy more negative 6li whereas in stable shield regions the concentrations are low and isotopically light in proportion to the increasing degree of weathering

lithium and nd isotopic constraints on the origin of li poor pegmatite with implications for li mineralization abstract although volumetrically minor in the upper continental crust pegmatites host lots of rare metal mineralization e g li be pegmatites and associated mineralization were generally thought to originate from extreme differentiation of a parent granite system we propose an alternative model to interpret the genesis of pegmatite and factors controlling li mineralization based on combined nd and li isotopic studies on the li poor pegmatites barren from the qinghe pegmatite field of the altai orogen nw china the qinghe pegmatites show significantly varied nd isotopic compositions end t 4 3 1 7 which overlap the surrounding schists 6 5 1 5 but lower than the granites 2 2 9 of the orogen these data together with the low ree 3 3 41 ppm and absence of biotite in the pegmatites suggest they were not derived from extreme differentiation of a parent granite as traditionally thought but from low degrees of partial melting of the schists involving muscovite dehydration melting under amphibolite facies conditions the pegmatites are characterized by heavy li 7li 4 1 14 5 and low li abundance 3 6 50 ppm which contrast to that of local schist 7li 0 9 3 0 li 24 123 ppm and granite 7li 0 9 3 0 li 24 70 ppm and also to that of global li rich pegmatites 7li 1 0 10 li 500 ppm modeling study indicates that li poor pegmatites always have heavy li signature compared with li rich pegmatites due to the abundance of biotite in the source the formation of li rich pegmatite with li mineralization is attributable to the distinct source characteristics with abundant fluxing components like li na co32 and hco3 and sufficient alumina rich clay phases and the fluxing components probably originated from evaporate interlayers in the source

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

ocean wide stagnation episode in the late cretaceous in this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid cretaceous here called the cenomanian turonian black shale horizon ctbsh the occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments the stratigraphic record above and below the ctbsh in environments as different as the deep north atlantic ocean and marginal and epicontinental seas over enormous areas in north america north africa and northwestern europe is characterized by a stratigraphic gap a disconformity or a continuous but strongly condensed stratigraphic section the anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2 no simple model has yet been found to explain the occurrence of the ctbsh in such a wide range of depth and palaeoenvironmental conditions

geochemical age and isotopic constraints on the location of the sino korean yangtze suture and evolution of the northern dabie complex east central china the northern dabie complex in east central china lies between the sino korean plate to the north and the yangtze plate to the south the northern dabie complex has been variously proposed to represent a paleozoic magmatic arc on the sino korean plate an exhumed piece of subducted yangtze plate crust or crust produced almost entirely by cretaceous extension related magmatism trace element compositions of northern dabie complex orthogneisses and granites show arc signatures similar to those of ultra high pressure rocks in the central dabie but no mineralogical evidence of ultra high pressure metamorphism is present in the samples investigated here field relationships textures major and trace element compositions and ion microprobe u pb zircon protolith crystallization ages reveal three distinct types of gneiss diorite gneiss xenoliths 770 6 26 ma 95 confidence limit those within first genation highly deformed migmatitic grey gneisses 747 6 14 ma and those cross cut by secondgeneration cretaceous weakly foliated felsic gneisses 127 6 4 ma unfoliated cretaceous granites 117 6 11 ma monazite th pb age 5 117 6 1 ma intrude secondgeneration gneisses cretaceous second corresponding author e mail john c ayers vanderbilt edu generation gneisses and granites yield zircon inheritance ages of ca 2 ga 700 800 ma and rarely 227 271 ma indicating that the northern dabie complex is not simply a cretaceous extensional terrane the 700 800 ma zircon ages are similar to those of granitic gneisses from the central ultra highpressure zone 698 6 47 ma and are characteristic of the yangtze craton nd values suggest that cretaceous rocks in the northern dabie complex formed by partial melting of basement with very low nd and not by melting of first generation or diorite gneisses nd depleted mantle model ages are consistent with the time of formation of the yangtze craton at 1 4 2 5 ga the northern dabie complex is interpreted to be an extension of the yangtze craton that was unaffected by ultra high pressure metamorphism the sino korean yangtze suture must lie to the north of the northern dabie complex

temperature dependent isotopic fractionation of lithium between clinopyroxene and high pressure hydrous fluids the fractionation of lithium isotopes between synthetic spodumene as representative of li bearing clinopyroxene and cl and oh bearing aqueous fluids was experimentally determined between 500 and 900 c at 2 0 gpa in all the experiments 7li was preferentially partitioned into the fluid the fractionation is temperature dependent and approximated by the equation 7li clinopyroxene fluid 4 61 1 000 t k 2 48 r 2 0 86 significant li isotopic fractionation of about 1 0 exists even at high temperatures of 900 c using neutral and weakly basic fluids revealed that the amount of fractionation is not different the li isotopic fractionation between altered basalt and hot spring water 350 c in natural samples is in good agreement with our experimentally determined fractionation curve the data confirm earlier speculations drawn from the li isotopic record of dehydrated metamorphic rocks that fluids expelled from a dehydrating slab carry heavier li into the mantle wedge and that a light li component is introduced into the deeper mantle li and li isotopes are redistributed among wedge minerals as fluids travel across the wedge into hotter regions of arc magma production this modifies the li isotopic characteristics of slab derived fluids erasing their source memory and explains the absence of cross arc variations of li isotopes in arc basalts

global geochemical cycles of carbon sulfur and oxygen time resolved data on the carbon isotopic composition of carbonate minerals and the sulfur isotopic composition or sulfate minerals show a strong negative correlation during the cretaceous carbonate minerals are isotopically heavy during this period while sulfate minerals are isotopically light the implication is that carbon is being transferred from the oxidized carbonate reservoir to the reservoir of isotopically light reduced organic carbon in sedimentary rocks while sulfur is being transferred from the reservoir of isotopically light sedimentary sulfide to the oxidized sulfate reservoir these apparently oppositely directed changes in the oxidation state of average sedimentary carbon and sulfur are surprising because of a well established and easy to understand correlation between the concentrations of reduced organic carbon and sulfide minerals in sedimentary rocks rocks rich in reduced carbon are also rich in reduced sulfur the isotopic and concentration data can be reconciled by a model which invokes a significant flux of hydrothermal sulfide to the deep sea at least during the cretaceous

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

lithium isotope behaviour during partial melting of metapelites from the jiangnan orogen south china implications for the origin of ree tetrad effect of f rich granite and associated rare metal mineralization abstract we carried out combined nd and li isotopic studies on the neoproterozoic biotite granites late mesozoic evolved two mica muscovite granites and associated the shuangqiaoshan group metapelites from the jiangnan orogen south china which along with petrological and geochemical data were used to constrain the lithium isotopic behavior during partial melting of metapelites the origin of the ree tetrad effect in evolved granites and implications for related rare metal mineralization the neoproterozoic biotite granites show features typical of s types e g high a cnk ratios and have end 6 9 to 10 and 7li 2 2 4 comparable to the shuangqiaoshan group metapelites with end 6 to 11 and 7li 2 3 7 respectively suggesting that the biotite granites were derived from melting of the metapelites and the li isotopic fractionation during the melting process appears negligible the two late mesozoic shimensi and zengjialong granites occur as small stocks showing high silica peraluminous low cao and sr contents variably enrichment in volatiles f b and are accompanied by w cu and sn mineralization the shimensi granites have end t values of 7 0 8 6 and 7li 2 7 3 9 similar to the shuangqiaoshan group metapelites whereas the zengjialong granites have relatively high end t values 5 1 7 3 and heavy li isotopic features mostly 7li 0 18 1 53 and particularly ree tetrad effect is seen in the latter we argue that the late mesozoic evolved granites formed as a result of re melting of the granulitic residues left in the lower crust after extraction of the neoproterozoic biotite granites from the metapelites such re melting of the residues was triggered by underplating of basaltic magma with more mantle input and f b as well in the source of the zengjialong granites the elevated 7li values of the zengjialong granites were probably caused by intense interaction between melt and external fluids during magma emplacement which in turn resulted in the formation of the ree tetrad effect in the granites isotopic modeling suggests that fluid exsolution from evolved granites is minor and is less likely to have been responsible for the extensive rare metal mineralization as traditionally thought

the absence of lithium isotope fractionation during basalt differentiation new measurements by multicollector sector icp ms we report measurements of the isotopic composition of lithium in basalts using a multicollector magnetic sector plasma source mass spectrometer mc icp ms this is the first application of this analytical technique to li isotope determination external precision of multiple replicate and duplicate measurements for a variety of sample types averages 1 1 2 population the method allows for the rapid 8 min sample analysis of small samples 40 ng li relative to commonly used thermal ionization methods the technique has been applied to a suite of samples from kilauea iki lava lake hawaii the samples range from olivine rich cumulitic lava to sio2 and k2o enriched differentiated liquids and have 7li per mil deviation of sample 7li 6li relative to the l svec standard of 3 0 to 4 8 the data indicate a lack of per mil level li isotope fractionation as a result of crystal liquid fractionation at temperatures greater than 1050 c this conclusion has been tacitly assumed but never demonstrated and is important to the interpretation of li isotope results from such geochemically complex environments as island arcs

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

lithium isotopic composition and concentration of himalayan leucogranites and the indian lower continental crust abstract the lithium isotopic compositions of adakitic rocks and k rich volcanic rocks in southern tibet range from 1 3 to 7 5 and 4 9 to 3 5 respectively the subduction of the indian plate beneath the lhasa terrane means that traditional lithium isotopic compositions of various reservoirs are unable to explain the aforementioned 7 li data therefore it is necessary to determine the li isotopic compositions of the different geological endmembers underneath southern tibet here we report the lithium isotopic composition and concentration of indian upper and lower continental crust on the basis of whole rock major and trace element data and sr nd pb isotope data leucogranites from luozha and longzi are considered as representative of indian upper crust whereas two mica granites from quedang and dala and granulites and gneisses from nyalam are considered as representative of indian lower crust the li concentration of indian upper crust varies from 23 to 45 ppm with a mean of 34 ppm consistent with a weighted mean li concentration for the upper crust of 35 11 ppm in contrast the li abundance of indian lower crust is estimated to be 33 84 ppm with a mean of 58 ppm much higher than the average li concentration for the lower crust of 8 ppm because of the high modal abundance of biotite and muscovite the li isotopic compositions 0 9 to 5 6 of indian upper continental crust are relatively heavy compared with the average li isotopic composition of upper continental crust on the other hand the li isotopic compositions of indian lower continental crust 4 4 to 0 1 are lighter than those of indian upper continental crust the isotopically heavy signature of indian upper crust is produced by high 7 li fluids released from the indian lower crust slab whereas the lighter signature of indian lower crust is generated by the partial melting of residual indian lower crust slab during metamorphic dehydration of indian lower crust

lithium and lithium isotope profiles through the upper oceanic crust a study of seawater basalt exchange at odp sites 504b and 896a abstract ocean drilling program odp hole 504b near the costa rica rift is the deepest hole drilled in the ocean crust penetrating a volcanic section a transition zone and a sheeted dike complex the distribution of li and its isotopes through this 1 8 km section of oceanic crust reflects the varying conditions of seawater alteration with depth the upper volcanic rocks altered at low temperatures are enriched in li 5 6 27 3 ppm and have heavier isotopic compositions 7li 6 6 20 8 relative to fresh mid ocean ridge basalt morb due to uptake of seawater li into alteration clays the li content and isotopic compositions of the deeper volcanic rocks are similar to morb reflecting restricted seawater circulation in this section the transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization li enrichment in this zone is accompanied by relatively light isotopic compositions 0 8 2 1 which signify influence of basalt derived li during mineralization and alteration li decreases with depth to 0 6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high temperature reaction zone rocks in the dike complex have variable isotopic values that range from 1 7 to 7 9 depending on the extent of hydrothermal recrystallization and off axis low temperature alteration hydrothermally altered rocks are isotopically light because 6li is preferentially retained in greenschist and amphibolite facies minerals the 7li values of the highly altered rocks of the dike complex are complementary to those of high temperature mid ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage the inventory of li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of li in the ocean on balance the upper 1 8 km of oceanic crusts remains a sink for oceanic li the observations at 504b and an estimated flux from the underlying 0 5 km of gabbro suggest that the global hydrothermal flux is at most 8 109 mol yr compatible with geophysical thermal models this work defines the distribution of li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle

zircon age and nd hf isotopic composition of the yunnan tethyan belt southwestern china the baoshan block of the tethyan yunnan southwestern china is considered as northern part of the sibumasu microcontinent basement of this block that comprises presumably greenschist facies neoproterozoic metamorphic rocks is covered by paleozoic to mesozoic low grade metamorphic sedimentary rocks this study presents zircon ages and nd hf isotopic composition of granites generated from crustal reworking to reveal geochemical feature of the underlying basement dating results obtained using the single zircon u pb isotopic dilution method show that granites exposed in the study area formed in early paleozoic about 470 ma pingdajie granite and in late yanshanian about 78 61 ma late cretaceous to early tertiary huataolin granite the early paleozoic granite contains archean to mesoproterozoic inherited zircons and the late yanshanian granite contains late proterozoic to early paleozoic zircon cores both granites have similar geochemical and nd hf isotopic charateristics indicating similar magma sources they have whole rock tdm nd values of around 2 000 ma and zircon tdm hf values clustering around 1 900 1 800 and 1 600 1 400 ma the nd hf isotopic data imply paleoproterozoic to mesoproterozoic crustal material as the major components of the underlying basement being consistent with a derivation from archean and paleoproterozoic terrains of india or nw australia both granites formed in two different tectonic events similarly originated from intra crustal reworking temporally the late yanshanian magmatism is probably related to the closure of the neotethys ocean the early paleozoic magmatism traced in the baoshan block indicates a comparable history of the basements during early paleozoic between the se asia and the western tethyan belt such as the basement outcrops in the alpine belt and probably in the european variscides that are considered as continental blocks drifting from gondwana prior to or simultaneously with those of the se asia

lithium isotope fractionation during incongruent melting constraints from post collisional leucogranite and residual enclaves from bengbu uplift china abstract lithium li elemental and isotopic compositions of the jurassic jingshan leucogranites including garnet rich mafic enclaves and wall rock wuhe gneisses from the southeast margin of north china craton ncc were investigated to understand the behavior of li isotopes during post collisional magmatism the jingshan leucogranites have distinct u shape ree patterns with y and ree concentrations significantly lower yet sr y ratios higher than their presumed source rocks i e the dabie sulu gneisses trace element modeling of ree and sr y suggests these elemental signatures of the jingshan leucogranites can be consistently explained by a fluid present crustal incongruent partial melting bt qz pl h 2 o grt melt leaving mainly grt bt with minor allanite in the residuum the mafic enclaves show identical sr nd isotopic compositions with their host leucogranites contrasting with the wuhe gneiss and the exposed regional lower crust the garnet rich mafic enclaves are thus interpreted as entrained residual phases formed by this incongruent partial melting the jingshan leucogranites show relatively high 7 li values 4 0 to 9 0 and low li concentrations 4 7 11 3 ppm in comparison to published data for worldwide granites in contrast the residual enclaves show low 7 li values as low as 0 6 and high li concentrations as high as 118 ppm garnet separated from residual enclaves is characterized by a narrow range of low 7 li values 1 5 to 0 1 with high li concentrations from 32 9 to 81 7 ppm by contrast coexisting quartz shows relatively high 7 li values 15 0 to 16 6 with very low li concentrations 1 ppm biotite from both leucogranite and residual enclaves shows high li concentrations 195 382 ppm and relatively heavy li isotope compositions 3 2 to 7 5 the li elemental and isotopic signatures of the residual enclaves can be modeled as a grt bt rich residuum mixed with leucogranite melt in various proportions this work indicates that the li isotopic compositions for magmatic rocks that are derived from anatexis of mid to lower crustal gneisses may not be a faithful source indicator as commonly suggested

alkali diffusion in plagioclase feldspar tracer diffusion kinetics at 1 atm pressure under dry conditions using 6li 41k and 87rb in four plagioclase feldspars have been determined diffusion profiles were measured using an ion microprobe sims the arrhenius parameters and 2 uncertainties for li k and rb respectively in albite are pre exponential factor log do 3 8 1 0 3 4 1 4 and 5 8 3 8 in m2 s and activation energies 146 14 296 30 and 283 85 kj mol the diffusion rate of k in albite at 700 c and 100 mpa water pressure equals that at 1 atm dry suggesting that diffusion of k is not dependent on water fugacity between 0 004 and 100 mpa the k diffusion rate depends on plagioclase anorthite content and is approximately 20 times slower in labradorite than albite li diffusion rates in albite and anorthite are identical a linear relation between log d for the alkalis measured and their ionic radius squared permits an estimate of cs diffusion kinetics diffusion rates are isotropic or nearly so in albite

diffusion driven extreme lithium isotopic fractionation in country rocks of the tin mountain pegmatite abstract lithium concentrations and isotopic compositions in the country rocks amphibolites and schists of the tin mountain pegmatite show systematic changes with distance to the contact both li and 7 li decrease dramatically along a 10 m traverse from the pegmatite into amphibolite with li concentration decreasing from 471 to 68 ppm and 7 li decreasing from 7 6 to 19 9 rubidium and cs also decrease from the pegmatite contact into the country rock but only within the first 2 m of the contact after which their concentrations remain constant neither mixing between pegmatite fluids and amphibolite nor li isotope fractionation by rayleigh distillation during fluid infiltration is a likely explanation of these observations due to the extremely light isotopic composition required for the amphibolite end member in the mixing model 7 li 20 and the similarly extreme isotopic fractionation required in a rayleigh distillation model rather these variations are likely due to isotopic fractionation accompanying li diffusion from the li rich pegmatite li 450 to 730 ppm into amphibolites li 20 ppm the fact that other alkali element concentrations vary only within 2 m of the contact reflects the orders of magnitude faster diffusion of li relative to heavier elements quartz mica schists in contact with the pegmatite also show large variations in both li and 7 li as a function of distance from contact 1 wt to 70 ppm and 10 8 to 18 6 respectively but over a longer distance of 30 m lithium concentrations of the schist decrease from 1 wt adjacent to the contact to 70 ppm 300 m from the contact the latter is a typical concentration in metapelites the nature of the 7 li variations in the schists is different than in the amphibolites schists within the first 2 m of the contact have nearly identical 7 li of 10 which mimics that of the estimated bulk pegmatite 8 to 11 at a distance of 30 m the 7 li reaches the lowest value in the schists of 18 6 similar to the lowest amphibolite measured at a distance of 300 m the 7 li climbs back to 2 5 which is within the range of 7 li of other schists in the region and metapelites worldwide the behavior of li in the schists can also be modeled by li diffusion with the effective diffusion coefficient in the schist being 10 times greater than that in the amphibolite the effective diffusion coefficients of li in the amphibolite and schist are 2 orders of magnitude greater that those in minerals which implicates the importance of fluid assisted grain boundary diffusion over solid state diffusion in transporting li through these rocks

lithium isotopic compositions of post collisional mafic ultramafic rocks from dabieshan china implications for recycling of deeply subducted continental crust abstract lithium li isotopes are potential tracers of processes related to crust mantle interaction and recycled crustal materials previous studies have reported that li isotopic compositions of island arc lavas are similar to those of fresh mid ocean ridge basalts morbs although the former are expected to record high slab derived 7li values caused by fluid metasomatism however it is unclear whether li isotopic signatures of subducted continental crust were transported to mantle depths and preserved there for clarification we determined whole rock major and trace element and li isotopic compositions of post collisional mafic ultramafic rocks from northern dabieshan china the analyzed samples have high mgo up to 20 67 wt and low sio2 41 06 56 20 wt contents and arc like trace element distribution patterns suggesting derivation by partial melting of fertile mantle sources the samples have 7li values of 2 9 to 7 2 average 2 7 n 42 and li concentrations of 2 50 to 28 1 g g average 9 20 g g both of which are beyond the relatively limited ranges of mantle values 7li 2 9 to 4 3 average 3 5 1 0 and li 1 20 0 10 g g excluding possible effects of wall rock assimilation and contamination magmatic crystallization and li isotopic fractionation during subduction exhumation processes the observed li isotopic heterogeneity is most likely related to the recycling of crustal materials based on a comparison with li isotopic compositions of ultrahigh pressure uhp metamorphic rocks from the dabie sulu orogenic belt and terrestrial sediments we suggest that the recycled continental crustal materials likely comprised gneisses sediments eclogites and or minor carbonate rocks i e marbles our study demonstrates that li isotopes may provide a novel means of tracing deeply subducted continental materials

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

lithium isotope fractionation between li bearing staurolite li mica and aqueous fluids an experimental study abstract we determined the lithium isotope fractionation between synthetic li staurolite and aqueous fluids containing excess licl or lioh at 3 5 gpa between 670 and 880 c and between li mica and similar fluids at 2 0 gpa and 300 to 500 c in all experiments for the system li staurolite fluid 7 li was weakly partitioned into li staurolite whereas for li mica fluid 7 li preferentially fractionated into the fluid the difference in the li isotope fractionation behaviour results from different li coordination in staurolite li 4 and mica li 6 for the system li mica fluid fractionation is about half as large along the same t range as for spodumene fluid wunder b meixner a romer r l heinrich w 2006 t dependent isotopic fractionation of lithium between clinopyroxene and high pressure hydrous fluids contrib mineral petrol 151 112 120 this behaviour is consistent with differences in the bonding strengths of the li octahedra in li mica and spodumene subduction and concomitant dehydration of metabasic oceanic crust containing chlorite and clinopyroxene with li in six fold coordination releases fluids enriched in li and 7 li into the fore arc and arc mantle and thus introduces a light li component into the deeper mantle ongoing dehydration and li loss along the subduction path produces fluids with increasingly lower li concentrations and lighter lithium isotope compositions however as staurolite is the most important carrier of li in metapelitic assemblages the inverse fractionation of li isotopes relative to fluids enables staurolite to transport high li concentrations in combination with an isotopic composition enriched in 7 li into the mantle thus depending on the li contents and li isotope signature of the protolite breakdown of li bearing staurolite at high p and t can release fluids with high li contents and isotopically heavy li into the deep mantle wedge

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

lithium and its isotopes in major world rivers implications for weathering and the oceanic budget abstract the outstanding problem in the lithium geochemical cycle is the lack of an isotopic mass balance in the ocean the 6li compositions of fresh basalts 4 the hydrothermal fluids derived from them average 9 and seawater significantly heavier at 32 are well understood but only very sparse river input data are available for li mass balance calculations in an attempt to rectify the situation we have measured the lithium concentrations and isotopic compositions of major world rivers draining representative geological terrains this helps both to constrain the river endmember and to understand the behavior of lithium isotopes in the continental weathering environment fluvial isotopic compositions display a very large range 6 0 to 32 2 there is no definitive relationship between 6li and lithology but in general rivers draining marine evaporites are 20 to 22 carbonates 26 to 32 black shales 26 shields 6 6 to 19 and mixed siliceous terrains 6 to 28 the flow weighted mean concentration of the measured rivers is 215 nm at 23 this updated riverine 6li value responsible for 30 of the global riverine discharge does not solve the isotopic imbalance if the measured li concentrations and isotopic compositions are representative of all rivers the presence of a yet unidentified sink with a higher fractionation factor 1 023 than determined for low temperature basalt alteration 1 019 is required for an isotopic steady state of li in the ocean authigenic clays are a possible candidate as clays are known to be enriched in both lithium and in the light isotope preferentially alternatively the hydrothermal flux must be much less than half of that estimated by the 3he inventory and the oceanic budgets for 87sr 86sr and mg the relationship of 6li to the major ions and 87sr 86sr suggests that the important processes affecting river dissolved lithium isotopic compositions are fractionation between solution and secondary minerals and thus the intensity of weathering

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

anatomy of garnets in a jurassic granite from the south eastern margin of the north china craton magma sources and tectonic implications abstract the late jurassic jingshan granite located at the south eastern margin of the north china craton contains abundant garnets which can be subdivided into three types based on texture and composition i euhedral garnet in mafic biotite and garnet rich enclave grt i ii coarse grained garnet grt ii in the host granite and iii small euhedral garnet in aplite grt iii in general grt i has higher feo cao and lower mno contents than grt ii grt iii has higher mn but lower ca contents than others grt i has lower mree and hree contents than grt ii grt iii has prominent and distinctly negative eu anomaly as well as higher mree composition compared to the others systematic variations in oxygen isotope compositions are observed among the three garnet types with 18 o values of 4 7 in grt iii some of the grt ii and grt iii display two distinct zonings with cores having similar major and trace element compositions to grt i cathodoluminescence cl images revealed that the zircons from different garnet bearing samples possess fine scale oscillatory zoned magmatic rims with inherited cores in situ zircon u pb dating and trace element analyses show that the dark luminescent magmatic rims all have jurassic concordia ages 160 ma and similar trace element patterns most of the inherited cores also display similar triassic ages of 210 236 ma which is similar to the ages of ultrahigh pressure uhp metamorphic rocks of the dabie sulu orogen 230 ma in addition jurassic concordia ages were also found in a zircon inclusion in grt i implying that the grt i was formed shortly before the main magmatic event the age data suggest that the three different garnet types may be genetically related and modified by cogenetic magmatic events based on the zircon u pb ages from different garnet bearing samples the major element trace element oxygen isotope and zoning textures of the three kinds of garnet we suggest that grt i may be peritectic garnet whereas grt ii and iii are probably the results of magmatic dissolution precipitation processes and re equilibration of garnets with changing magmatic conditions during melting differentiation crystallization and cooling within the granite we conclude from the oxygen isotopic character of the garnets and ages of the zircons that the source rocks for the jingshan granites are from dabie sulu orogen representing the south china craton

lithium isotopic systematics of granites and pegmatites from the black hills south dakota to study li isotopic fractionation during granite differentiation and late stage pegmatite evolution li isotopic compositions and concentrations have been measured for the s type harney peak granite the spatially associated tin mountain pegmatite and possible metasedimentary source rocks in the black hills south dakota the harney peak granite is isotopically heterogeneous with 7 li varying from 3 1 to 6 6 the 7 li values of proterozoic metasedimentary rocks that are possible sources of the harney peak granite range from 3 1 to 2 5 and overlap with post archean shales and the harney peak granite for the granite suite there is no correlation between 7 li and elements indicative of degrees of granite differentiation sio2 li rb etc the li isotopic composition of the harney peak granite therefore appears to res ect the source composition minerals from the zoned tin mountain pegmatite have extremely high li contents and heavier li isotopic compositions than the granite or surrounding black hills metasedimentary rocks the heavier compositions may res ect li isotopic fractionation resulting from extensive crystal melt fractionation lithium concentrations decrease in the order spodumene 3 7 wt muscovite 0 2 to 2 0 wt plagioclase 100 1100 ppm quartz 30 140 ppm plagioclase muscovite and spodumene in all zones display a relatively narrow range in 7 li of 7 9 to 11 4 in contrast quartz is isotopically heavier and more variable 14 7 to 21 3 with 7 li showing an inverse correlation with li concentration this correlation res ects the mixing of isotopically heavy li in quartz and lighter li in s uid inclusions as documented by s uid inclusion compositions

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

lithium and boron in late orogenic granites isotopic fingerprints for the source of crustal melts abstract geochemically diverse late and post variscan granites of the erzgebirge vogtland the saxon granulite massif and thuringia germany formed by anatectic melting of palaeozoic sedimentary successions and associated mafic to felsic volcanic rocks the compositional diversity of the least evolved of these granites is largely inherited from the protoliths we present li and b isotopic data of these granites and compare them with the isotopic composition of their protoliths to investigate whether i there exist systematic differences in the li and b isotopic composition among different granite types and ii li and b isotopic compositions provide information on the granite sources complementary to information from the isotopic composition of sr nd and pb and the trace element signatures low f biotite and two mica granite types have flat upper continental crust ucc normalized trace element pattern with variable enrichments in li rb cs sn and w and depletions in sr ba and eu these signatures are least pronounced for the niederbobritzsch biotite granite which has the largest contribution of mafic material and most pronounced for the two mica granites the granites show a relatively narrow range of 7li values 3 0 to 0 5 and a broad range of 11b values 13 4 to 20 1 the 11b values are lower in rocks with distinctly higher contents of li rb cs and sn the high 11b of the niederbobritzsch granite may be explained by the melting of former altered oceanic crust in its source relative to ucc intermediate f to high f low p granites show strong depletions in sr ba eu as well as zr and hf strong enrichments in li rb and cs as well as nb sn ta and w and ree pattern with stronger enrichments for hree than for lree these granites show narrow ranges of 7li 2 0 to 1 6 and 11b values 14 7 to 9 1 reflecting the smaller variability of the li and b isotopic composition in their source lithologies the anomalously high 7li value 14 7 of one granite sample burgberg which is similar to 7li values of its wall rocks up to 14 5 may indicate late magmatic fluid rock interaction with external wall rock derived fluids because of the small compositional range of most source lithologies the li and b isotopic variation in the granites is also small indicating that the isotopic composition of li and b does not represent a particularly sensitive source tracer with the exception of source lithologies characterized by extreme 7li or 11b values

lithium isotope geochemistry of sediments and hydrothermal fluids of the guaymas basin gulf of california abstract lithium isotopic compositions of hydrothermally altered sediments of deep sea drilling project dsdp site 477 477a as well as high temperature vent fluids of the guaymas basin have been determined to gain an understanding of lithium exchange during fluid sediment interaction at this sediment covered spreading center unaltered turbidite of the basin has a 6 li value of 10 5 7 heavier than fresh oceanic basalts contact metamorphism induced by a shallow sill intrusion results in a decrease of the lithium content of the adjacent sediments and a lighter isotopic value 8 below the sill sediments altered by a deep seated hydrothermal system show strong depletions in lithium while lithium isotopic compositions vary greatly ranging from 11 to 1 the shift to lighter composition is the result of preferential retention of the lighter isotope in recrystallized phases after destruction of the primary minerals the complexity of the isotope profile is attributed to inhomogeneity in mineral composition the tortuous pathway of fluids and the temperature effect on isotopic fractionation the range of lithium concentration and 6 li values for the vent fluids sampled in 1982 and 1985 overlaps with that of the sediment free mid ocean ridge systems the lack of a distinct expression of sediment input is explained in terms of a flow through system with continuous water recharge the observations on the natural system agree well with the results of laboratory hydrothermal experiments the experimental study demonstrates the importance of temperature pressure water rock ratio substrate composition and reaction time on the lithium isotopic composition of the reacted fluid high temperature authigenic phases do not seem to constitute an important sink for lithium and sediments of a hydrothermal system such as guaymas are a source of lithium to the ocean the ready mobility of lithium in the sediment under elevated temperature and pressure conditions also has important implications for lithium cycling in subduction zones

serpentinite derived low δ7li fluids in continental subduction zones constraints from the fluid metasomatic rocks whiteschist from the dora maira massif western alps abstract whole rock lithium li and li isotopic compositions of coesite bearing whiteschists and their country rock metagranites from the dora maira massif in the western alps were investigated to understand their behavior during fluid rock interaction in mantle depths of continental subduction zones the whiteschists reveal relatively low 7li values 6 4 to 2 4 with an average value of 2 1 in comparison to the country rock metagranites 7li 1 2 to 3 6 with an average value of 1 4 the 7li values of whiteschists do not show any correlations with major elements e g mg fe li or isotopes i e 26mg and 18o values and cannot be explained by kinetic fractionation hence the low 7li values of whiteschists result from interactions with metasomatic fluids containing isotopically light li that occurred in deep portions of a continental subduction zone fluid rock interaction modeling suggests that the metasomatic fluids contain low 7li values down to 4 and moderate li concentrations 50 to 150 ppm which were probably derived from the dehydration of serpentinites in the subduction channel the presence of such low 7li fluids in deep subduction zones could cause li isotopic heterogeneity in the earth s interior

chemostratigraphy versus biostratigraphy data from around the cenomanian turonian boundary a detailed isotopic profile is presented for a stratigraphically expanded cenomanian turonian boundary section in chalk facies exposed at eastbourne sussex and compared with data from pueblo colorado in both sections macro and micropalaeontological markers first appearances and disappearances are well constrained and their relative positions and relationship to the structure of the carbon isotope curve are identical this consistent relationship between two independent phenomena one geochemical the other biostratigraphical is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon isotope excursion in these two areas this interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon isotope excursion in europe and north america

lithium isotope fractionation during fluid exsolution implications for li mineralization of the bailongshan pegmatites in the west kunlun nw tibet abstract granitic pegmatites are considered significant host rocks for the rare metal deposits however the enrichment mechanisms for the rare metal elements e g li be nb and ta remain debated here we report the whole rock and mineral e g muscovite and spodumene major trace elements and li isotopic compositions of the bailongshan granitic pegmatites in the west kunlun nw tibet to address this issue the bailongshan pegmatites hosting a super large li rb polymetallic deposit are composed of li poor and li rich pegmatites the li poor pegmatites display high 7li values in the whole rock 2 30 4 94 and muscovite 2 22 7 55 in contrast the li rich pegmatites show low 7li values in the whole rock 1 89 to 0 35 muscovite 3 39 to 4 49 and spodumene 2 83 to 1 87 these results together with the variations of the elements suggest that the li poor and li rich pegmatites were produced by the melt fluid separation during the late stage of granitic magma evolution this means that the li poor pegmatites were formed in a h2o poor silicate rich melt system while the li rich pegmatites were generated in a h2o rich silicate poor melt supercritical fluid system the melt fluid separation can lead to significant li isotope fractionation with 7li enriched in the strongly bonded residual silicate melt and 6li preferring to weaker hydrated bonds in the fluid alternatively the li rich pegmatites enriched in 6li could have been induced by preferential accumulation of the faster diffusing 6li in the supercritical or near critical fluid the li rich pegmatites experienced extensive crystal fluid interaction in a relatively closed magmatic hydrothermal system which resulted in the leaching and reprecipitation of ore forming elements but produced restricted li isotope fractionation the exsolved supercritical fluid is more enriched in alkali fluxing components li rb cs p and f by the continuous interaction with the residual silicate melt therefore the supercritical fluid exsolution plays an important role in the li isotope fractionation and rare metal mineralization

end cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the northwestern pacific ocean abstract the second largest cretaceous extinction event coincided with an oceanic anoxic event at the cenomanian turonian c t boundary this high resolution analysis of upper bathyal benthic foraminifera in central hokkaido japan indicates that the extinction event occurred in the latest cenomanian over a period of 0 2 m y 93 6 93 4 ma analysis of the dissolved oxygen index based on calcareous benthic foraminiferal wall thickness size and morphology shows that low oxygen 0 1 1 5 ml l conditions developed during a period of 0 15 m y before the c t boundary and 1 5 m y after the minimum oxygen condition 0 1 1 ml l prevailed twice during this interval similarly benthic foraminiferal extinctions occurred twice in concert with initiation of the two minimum oxygen levels coincidence of the two extinction horizons with developemt of low oxygen conditions suggests that the main cause of the extinctions was formation of dysoxic intermediate water this report suggests that the global c t boundary extinction event occurred in a stepwise fashion during the latest cenomanian 0 2 0 5 m y due to development of widespread oceanic anoxic dysoxic conditions within intermediate water masses

fingerprinting sources of orogenic plutonic rocks from variscan belt with lithium isotopes and possible link to subduction related origin of some a type granites lithium li elemental and isotope data are presented for a suite of plutonic rocks i s a and ss type coexisting mafic bodies from the western carpathians slovakia that were generated throughout the complete variscan orogenic cycle i type granites show a limited range of 7li contrasting with the large variations found in s type granites and orthogneisses of distinct ages this contradicts previous reports of predominantly light li s type granites sourcing metasedimentary lithologies and isotopically heavier i type granites derived from meta igneous sources an almost exclusively heavy li isotope signature 7li 4 7 found in four out of five a type granites rules out several commonly accepted petrogenetic scenarios such as remelting of granulitic residue after formation of i type granitic melts anatexis of calc alkaline meta igneous crust or extensive closed system fractional crystallization of mantle derived magmas instead it most probably reflects a derivation of a type granites from a mantle wedge modified by slab derived fluids during an early variscan or pan african subduction episode in contrast the distinct and lower 7li values 1 2 in the contemporaneous ss type granites can be related to their likely pelitic parentage mafic rocks gabbros and diorites associated with several occurrences of granites are uniformly li rich and isotopically light 0 5 precluding a direct derivation from the mantle these signatures testify to their cumulate origin whereby kinetic effects may be a viable explanation for the light li isotope compositions associated with diffusive redistribution of li between mantle derived mafic melts and acid magmas this corroborates recent studies on faster diffusion of 6li compared with 7li in natural systems taken together the presumed dichotomy between the sources and processes leading to generation of s and i type granitic magmas does not seem to be reflected by li isotope signatures in a simple and globally valid manner interpretation of li isotope compositions thus needs to be paralleled by other available information on petrology whole rock geochemistry and the magmatic context

strontium isotopic composition of mid cretaceous seawater the 87sr 86sr ratio in fish teeth separated from mid cretaceous marl and black shale from the northeastern apennines and venetian alps italy define three periods of low 87sr 86sr ratio at 121 to 124 million years ago ma 110 to 115 ma and 89 to 91 ma the 87sr 86sr excursions correspond to oceanic anoxic events represented by the livello selli livello 113 livello urbino and livello bonarelli black shale marker beds and probably reflect an increase in the low 87sr 86sr hydrothermal strontium flux associated with the emplacement of the ontong java and kerguelen plateaus 120 to 110 ma and the caribbean plateau 89 to 91 ma the modeled flux is consistent with the volumes and eruption rates of the oceanic plateaus but is far smaller than expected from the proposed cretaceous crustal production rates of 50 to 100 percent greater than modern

lithium isotope fractionation during continental weathering processes a comprehensive understanding of lithium isotope fractionation during terrestrial weathering is necessary in order to use lithium isotopes to trace chemical cycles climatic changes and igneous processes this study investigates lithium isotope fractionation in two laboratory experiments and by analyses of natural basalt weathering products partial dissolution of basalts in the laboratory does not result in fractionation of lithium isotopes but similar dissolution of a granite sample causes significant fractionation this may reflect dissolution of secondary minerals from the granite or differences in the li isotope composition of primary minerals in this more evolved igneous rock significant li isotope fractionation was also observed during sorption onto mineral surfaces in the laboratory although this was highly dependent on sample mineralogy no fractionation accompanies the outer sphere physisorption of li to smectite surfaces some fractionation accompanies sorption onto ferrihydrite and significant fractionation with 0 986 is seen during inner sphere chemisorption to gibbsite surfaces repeat experiments with varying amounts of sorption demonstrate that li remains in an exchangeable site on the gibbsite surface the extent of fractionation onto gibbsite observed in this study 13 is about half that required in order for clay surface removal to balance the ocean li isotope budget isotopic fractionation of li was found to occur on a 300 yr timescale in both cold and warm natural environments a minimally altered rock surface from iceland was found to be two lighter in 7li than the sample interior probably due to the preferential incorporation of 6li in clay or oxide rich alteration products on the sample surface soil samples from hawaii also demonstrate li fractionation during weathering in this environment rainwater 7li 10 contributes a significant flux of isotopically heavy li to the developing soil despite this soils have similar li isotope compositions to the primary basalt 7li 4 indicating that 6li is preferentially retained during weathering this conclusion is supported by isotopically heavy river water on hawaii 7li 22 and by the correlation between li concentration and 7li in the soil the lab and field based measurements of this study clearly demonstrate that lithium fractionates during weathering potentially providing information about the weathering environment now and in the past