scale dependence of strike and dip in sedimentary basins implications for field measurements and integrating subsurface datasets abstract the measured orientation of geological surfaces such as bedding or fracture planes varies with scale of observation this can be demonstrated by comparing representative orientation of an outcropping surface at centimeter decameter and kilometer scale it can also be verified by tracking variation of dip vectors while generalizing structure maps of subsurface horizons stored as numeric grids the challenge of obtaining meaningful orientation information from outcrops is well known but in practice field geologists intuitively extract orientation information that suits their purposes rather than explicitly recording the scale of observation or even measurement process there is an analogous problem when subsurface structural maps in sedimentary basins made from kilometer scale areas of reflection seismic interpretation are integrated with wells containing image logs that yield strike and dip information at a scale of tens of centimeters in the absence of upscaling guidelines maps are often tied to the correct depth but not to the structural orientation measured in piercing wells the solution at outcrop and wells is to explicitly determine the scale dependent structure then use information at the appropriate length scale as required complete description of strike and dip requires a length scale parameter in addition to the orientation values

balanced section in thrust belts part 1 construction balanced geological cross sections are an important aid to understanding thrust belt structures and to estimating their hydrocarbon bearing potential two approaches to section balancing have been taken in the past construction of retrodeformable sections from raw data and modification of previous interpretations after an evaluation procedure these approaches may be unified by use of a langrangian grid projection of datum locations dips and stratigraphic thicknesses onto the section plane is performed directly by calculation or graphically using plunge lines spline interpolation and parallel fold modeling are the simplest ways of filling gaps in the sectional data but isogon interpolation yields rheologically more realistic results faults are interpolated using cutoff geometries as constraints fault tips are located from distance displacement plots whereas the depth to detachment is obtained by a modified chamberlin construction interpolations made on the section are directed back to the geologic map via plunge lines although these techniques of section construction do not guarantee a balance especially when complexities such as growth structures diapirs or strike slip faults are present they eliminate many potential errors

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

lithium behaviour and isotope fractionation during fluid rock interactions in variscan oceanic suture zones limousin ophiolite and ile de groix high pressure terrane france

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

the role of h 2 o in rapid emplacement and crystallization of granite pegmatites resolving the paradox of large crystals in highly undercooled melts granite pegmatite sheets in the continental crust are characterized by very large crystals there has been a shift in viewing pegmatites as products of very slow cooling of granite melts to viewing them as products of crystal growth in undercooled liquids with this shift there has been a renewed debate about the role of h2o in the petrogenesis of pegmatites based on data on nucleation of minerals and new viscosity models for hydrous granite melts it is argued that h2o is the essential component in the petrogenesis of granite pegmatites h2o is key to reducing the viscosity of granite melts which enhances their transport within the crust it also dramatically reduces the glass transition temperature which permits crystallization of melts at hundreds of degrees below the thermodynamic solidus which has been demonstrated by fluid inclusion studies and other geothermometers published experimental data show that because h2o drastically reduces the nucleation rates of silicate minerals the minerals may not be able to nucleate until melt is substantially undercooled in a rapidly cooling intrusion nucleation starts at its highly undercooled margins followed by inward crystal growth towards its slower cooling hotter core delay in nucleation may be caused by competition for crystallization by several minerals in the near eutectic melts and by the very different structures of minerals and the highly hydrated melts once a mineral nucleates however it may grow rapidly to a size that is determined by the distance between the site of nucleation and the point in the magma at which the temperature is approximately that of the mineral s liquidus assuming components necessary for mineral growth are available along the growth path granite pegmatites are apparently able to retain h2o during most of their crystallization histories within the confinement of their wall rocks pegmatitic texture is a consequence of delayed nucleation and rapid growth at large undercooling both of which are facilitated by high h2o li b f and p contents in granite pegmatite melts without retention of h2o the conditions for pegmatitic textural growth may be difficult to achieve loss of h2o due to decompression and venting leads to microcrystalline texture and potentially glass during rapid cooling as seen in rhyolites in contrast slow cooling within a large magma chamber promotes continuous exsolution of h2o from crystallizing magma growth of equant crystals and final solidification at the thermodynamic solidus these are the characteristics of normal granites that distinguish them from pegmatites

comprehensive chemical analyses of natural cordierites implications for exchange mechanisms abstract cordierite samples from pegmatites and metamorphic rocks have been analysed for major electron microprobe analysis empa and trace elements inductively coupled plasma mass spectrometry icp ms secondary ion mass spectrometry analyses sims as well as for h 2 o and co 2 coulometric titration and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant apart from the homovalent substitutions femg 1 and mnmg 1 on the octahedral site some minor kna 1 on the ch0 channel site and fe 3 al 1 on the t 1 1 tetrahedral site the three most important substitution mechanisms are those for the incorporation of li on the octahedral sites nali 1 mg 1 and of be and other divalent cations on the tetrahedral t 1 1 site nabe 1 al 1 and na mg fe 2 1 al 1 the dominant role of the last vector is clearly demonstrated we propose a new generalized formula for cordierite ch na k 0 1 vi mg fe 2 mn li 2 iv si 5 iv al 3 iv al be mg fe 2 fe 3 o 18 x ch h 2 o co 2 our results show that the population of mg fe 2 on the t 1 1 site is limited to about 0 08 a p f u other exchange mechanisms that were encountered in experiments operate only under p t conditions or in bulk compositions that are rarely realized in nature routine analyses by electron microprobe in which li and be are not determined can be plotted as mg fe mn versus si al to assess whether significant amounts of li and be could be present these amounts can be calculated as li a p f u al na 4 and be a p f u 10 2al m 2 na

lithium in tektites and impact glasses implications for sources histories and large impacts abstract lithium li abundances and isotope compositions were determined in a representative suite of tektites moldavites muong nong type tektites and an australite ivory coast tektites and bediasites impact related glasses libyan desert glass zhamanshinites and irghizites a glass fragment embedded in the suevite from the ries impact crater and sedimentary materials in order to test a possible susceptibility of li to fractionation during hypervelocity impact events and to de convolve links to their potential parental sources the overall data show a large spread in li abundance 4 7 58 ppm li and 7 li values 3 2 to 26 0 but individual groups of tektites and impact glasses have distinctive li compositions most importantly any significant high temperature li isotope fractionation can be excluded by comparing sedimentary lithologies from central europe with moldavites instead we suggest that li isotope compositions in tektites and impact related glasses are probably diagnostic of the precursor materials and their pre impact geological histories the muong nong type tektites and australite specimen are identical in terms of li concentrations and 7 li and we tentatively endorse their common origin in a single impact event evidence for low temperature rayleigh fractionation which must have operated prior to impact induced melting and solidification is provided for a subset of muong nong type tektites although li isotope variations in most tektites are broadly similar to those of the upper continental crust libyan desert glass carries high 7 li 24 7 which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater lithium isotopes in impact related glasses from the zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies which is also consistent with their major and trace element patterns extreme shock pressures and the related extreme post shock temperatures alone appear not to have any effect on the li isotope systematics therefore useful information on parental lithologies and magmatic processes may be retrieved from analyses of martian and lunar meteorites moreover lack of significant li depletion in tektites provides further constraints on the loss of moderately volatile elements during the moon forming impact

nd o and sr isotopic constraints on the origin of precambrian rocks southern black hills south dakota abstract the nd o and sr isotopic characteristics of precambrian metasedimentary metavolcanic and granitic rocks from the black hills of south dakota are examined two late archean granites 2 5 2 6 ga have t dm ages of 3 05 and 3 30 ga suggesting that at least one of the granites was derived through the melting of significantly older crust early proterozoic metasedimentary rocks have t dm ages that range from 2 32 to 2 45 ga these model ages in conjunction with probable stratigraphic ages ranging from 1 9 to 2 2 ga indicate that mantle derived material was added to the continental crust of this region during the early proterozoic previous studies of the harney peak granite complex have reported u pb and rb sr ages of about 1 71 ga and most granite samples examined in this study have sr isotopic compositions consistent with that age two granite samples taken from the same sill however give two point rb sr and sm nd ages of 2 08 0 08 and 2 20 0 20ga 2200 nd 15 5 respectively in addition whole rock and apatite samples of the spatially associated tin mountain pegmatite give a sm nd isochron age of 2000 100 ma 2200 nd 5 8 1 8 the sm nd o and rb sr isotopic systematics of these granitic rocks have been complicated to some degree by both crystallization and post crystallization processes and the age of the pegmatite and parts of the harney peak granite complex remain uncertain processes that probably complicated the isotopic systematics of these rocks include derivation from heterogeneous source material assimilation mixing of ree between granite and country rock during crystallization via a fluid phase and post crystallization mobility of sr the nd isotopic compositions of the pegmatite and the harney peak granite indicate that they were not derived primarily from the exposed metasedimentary rocks

coupled lithium and iron isotope fractionation during magmatic differentiation abstract in this study we investigated fe and li isotope fractionation between mineral separates of olivine pheno and xenocrysts including one clinopyroxyene phenocryst and their basaltic hosts samples were collected from the canary islands teneriffa la palma and some german volcanic regions vogelsberg westerwald and hegau all investigated bulk samples fall in a tight range of li and fe isotope compositions 56 fe wr 0 06 0 17 and 7 li ma 2 5 5 2 assuming 7 li of the olivine free matrix is virtually identical to that of the bulk sample for mass balance reasons in contrast olivine phenocrysts display highly variable but generally light fe and mostly light li isotope compositions compared to their respective olivine free basaltic matrix which was considered to represent the melt with 56 fe ol 0 24 to 0 14 and 7 li ol 10 5 to 6 5 respectively single olivine crystals from one sample display even a larger range of 56 fe ol between 0 7 and 0 1 one single clinopyroxene phenocryst displays the lightest li isotope composition 7 li cpx 17 7 but no fe isotope fractionation relative to melt the olivine phenocrysts show variable mg and ni correlated in most cases that range between 0 89 and 0 74 and between 300 and 3000 g g respectively these olivines likely grew by fractional crystallization in an evolving magma one sample from the vogelsberg volcano contained olivine xenocrysts mg 0 89 and ni 3000 g g in addition to olivine phenocrysts this sample displays the highest li and the second highest fe isotope fractionation between olivine and melt 7 li ol melt 13 56 fe ol melt 0 29 our data i e the variable olivine at constant whole rock and matrix isotope compositions strongly indicate disequilibrium i e kinetic fe and li isotope fractionation between olivine and melt for li also between cpx and melt during fractional crystallization 7 li ol melt is correlated with the li partitioning between olivine and melt i e with li ol li melt indicating li isotope fractionation due to preferential faster diffusion of 6 li into olivine during fractional crystallization olivine with low 7 li ol melt also have low 56 fe ol melt indicating that fe isotope fractionation is also driven by diffusion of isotopically light fe into olivine potentially as fe mg inter diffusion the lowest 56 fe ol melt 0 40 was observed in a sample from westerwald germany with abundant magnetite indicating relatively oxidizing conditions during magma differentiation this may have enhanced equilibrium fe isotope fractionation between olivine and melt or fine dispersed magnetite in the basalt matrix may have shifted its fe isotope composition towards higher 56 fe the decoupling of li and fe isotope fractionation in cpx is likely due to faster diffusion of li relative to fe in cpx implying that the large investigated cpx phenocryst resided in the magma for only a short period of time which was sufficient for li but not for fe diffusion the absence of any equilibrium fe isotope fractionation between the investigated cpx phenocryst and its basaltic host may be related to the similar fe 3 fe 2 of cpx and melt in contrast to cpx the generally light fe isotope composition of all investigated olivine separates implies the existence of equilibrium in addition to diffusion driven isotope fractionation between olivine and melt on the order of 0 1

an experimental study of element partitioning among biotite muscovite and coexisting peraluminous silicic melt at 200 mpa h2o

unlocking the spatial dimension digital technologies and the future of geoscience fieldwork the development of affordable digital technologies that allow the collection and analysis of georeferenced field data represents one of the most significant changes in field based geoscientific study since the invention of the geological map digital methods make it easier to re use pre existing data e g previous field data geophysical survey satellite images during renewed phases of fieldwork increased spatial accuracy from satellite and laser positioning systems provides access to geostatistical and geospatial analyses that can inform hypothesis testing during fieldwork high resolution geomatic surveys including laser scanning methods allow 3d photorealistic outcrop images to be captured and interpreted using novel visualization and analysis methods in addition better data management on projects is possible using geospatially referenced databases that match agreed international data standards collectively the new techniques allow 3d models of geological architectures to be constructed directly from field data in ways that are more robust compared with the abstract models constructed traditionally by geoscientists this development will permit explicit information on uncertainty to be carried forward from field data to the final product current work is focused upon the development and implementation of a more streamlined digital workflow from the initial data acquisition stage to the final project output

trackdip a multi scale processing of dipmeter data method tests and field example for 3 d description of gravity driven deformations in the eocene foreland basin of ainsa spain abstract this paper presents trackdip a new method for dipmeter data processing this method selects localizes and measures significant tilts from the comparison at various scales of the changes of orientation of sedimentary beddings we tested this method on simple cases unconformity gradual tilt successive tilts without and with additional random noise and on a field example along three sections in the eocene sobrarbe delta ainsa foreland basin northern spain for synthetic data sets the method clearly identifies and measures the introduced tilts on the field sedimentary and tectonic structures especially three main syn sedimentary sliding surfaces s1 s3 were successfully identified from processed dipmeter data the tilt axis are mainly trending n s in sandstones associated to westward transport of sediments the sliding surfaces s1 and s3 correspond to e w trending tilt axis tentatively correlated either to the flexural subsidence of the basin or to anticline growth during sedimentation south of the studied area combination of these sedimentary and tectonic directions results in a ne sw striking submarine slope which locally controls the gravity driven deformations especially on the s2 sliding surface finally nnw sse trending tilts above the uppermost s3 sliding surface are interpreted as the result of infilling on the side of the scar produced by sliding

the use of dipmeter data to constrain the structural geology of the gullfaks field northern north sea abstract analyses of 23 km of dipmeter data from 48 wells on the gullfaks field northern north sea have helped to constrain and understand the structural geology of the area the analyses have verified the general structure obtained by seismic interpretation i e a main western domino system of rotated fault blocks and non planar bedding and an eastern horst complex separated by a collapsed anticline structure in addition subseismic structures have been revealed by the integrated use of dipmeter data well log correlation seismic data and core data within the domino system dip of bedding decreases towards the main faults to the west large scale drag the effect of such large scale drag decreases with depth probably due to a vertical increase in consolidation and mechanical strength at the time of deformation within the accommodation zone a modified fold structure is seen whereas strata within the horst complex are generally subhorizontal more than half of all faults on the gullfaks field have developed a zone of local drag generally only the northerly trending faults are associated with drag the interval affected by drag is typically some tens of meters wide and is consistently wider in the hanging wall than the footwall due to the effect of drag total offset may be up to one order of magnitude larger than the amount of missing section identified from well log correlation there is no apparent relationship between interval affected by drag and lithology however drag is less abundant in more consolidated rocks at deeper stratigraphic levels minor faults are less abundant than expected from a power law down scaling of seismically detectable faults and are not particularly common within the large scale drag zones it is suggested that a significant amount of subseismic deformation occurs on a scale below resolution of dipmeter data probably by ductile flow rather than discrete faulting north trending minor faults are most common and will restrict fluid flow in an e w direction due to cataclasis and phyllosilicate smear associated with abundant deformation bands micro faults

lithium isotopic systematics of hydrothermal vent fluids at the main endeavour field northern juan de fuca ridge vent fluids issuing from the main endeavour field mef juan de fuca ridge were analyzed for 7li to help constrain subseafloor hydrothermal alteration and phase separation processes magmatic activity prior to sampling of the fluids in 1999 enhanced heat and mass transfer as indicated by the large scale but temporary changes in vent fluid chemistry in particular dissolved chloride concentrations indicate formation of supercritical cl poor vapors which affected alteration throughout the mef system 7li of fluids however ranges from 7 2 to 8 9 and reveals no significant correlation with dissolved chloride being consistent with results of hydrothermal experiments that show no lithium isotope fractionation during supercritical phase separation on a chloride normalized basis li concentration data indicate relatively short residence times or high fluid rock mass ratios of vent fluids most impacted by phase separation effects reaction path models involving li isotope data also show elevated fluid rock mass ratios boron data in contrast suggest direct input from degassing magma enhanced heat flow associated with magmatic injection at depth inhibits penetration of seawater derived hydrothermal fluid into fresh basalt particularly in those systems where magmatic volatile input is most active the inverse correlation between li cl and b cl in vapor rich vent fluids may be a useful indicator of recent subseafloor magmatic activity

crystallographic control on lithium isotope fractionation in archean to cenozoic lithium cesium tantalum pegmatites the age distribution of lct pegmatites largely overlaps with major phases of collisional orogenic events and assembly of super continents some of the largest known lct pegmatite deposits formed in very short intervals 2 7 2 5 and 1 9 1 8 billion years ago ga corresponding to two major pulses of continental crust growth however the exact process of generation and segregation of large volumes of li bearing pegmatite liquids perhaps involving disequilibrium fractional crystallization and leaving residual melts enriched in fluxing elements such as b f h2o li and p remains largely obscure the new data on li contents and isotope compositions in major mineral phases from temporally and geographically separated pegmatite bodies document extreme variations in d7li values among individual large lct pegmatites in particular archean occurrences the observed 10 variations in d7li values for the same mineral phases from different localities i e beryl petalite spodumene lepidolite amblygonite muscovite contrast with globally homogeneous li isotope systematics of major mineral phases from unmodified mantle rocks consistent li isotope offsets between coexisting mineral phases are best explained by li isotope fractionation as a function of the bond length between li and neighboring ions o oh f we suggest that spatially distinct li isotope patterns act as fingerprints for different pegmatites and can be explained by the pre existing li isotope differences of their crustal sources at the time of pegmatite formation owing to differences in crustal age and evolution this would imply secular evolution of the continental crust over earth history toward present day globally broadly uniform crustal 7li 6li ratios d7li 0 the differences among archean occurrences could reflect possible archean paleogeography and perhaps be linked with different thermal regimes of individual cratons as a consequence of variations in crustal thickness

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

a lithium isotope study of hot springs and metabasalts from mid ocean ridge hydrothermal systems the li isotopic compositions of seawater and of fresh and altered basalts are distinct and therefore applicable to the study of the hydrothermal processes in the oceanic crust and the li balance in the ocean high temperature fluids from seven vents on the east pacific rise epr at 21 n and 11 13 n have 6li values ranging between 6 and 11 i e 3 7 heavier than fresh basalt values the intervent variations in li concentration and isotopic composition correlate well with water rock ratios no temporal change in the isotopic value was observed between 1981 and 1985 metabasalts show both li depletion and enrichment relative to fresh basalt they display light li isotopic values which reflect incorporation of li mobilized from fresh basalt from these observations we conclude that the li isotopic composition of submarine hot springs is controlled by a path dependent process involving dissolution of primary minerals and precipitation of li with alteration phases 6li values of fluids from the mid atlantic ridge 6 to 8 fall in the range of the epr indicating similar reaction controls at the two ridge systems the lack of 7li enrichment in the fluids from slower spreading ridges indicates that li is not recycled from older weathered crust thus the difference between the 3he and 87sr 86sr based hydrothermal flux and the crustal transfer rate of li cannot be reconciled by the inclusion of secondary li from older crust

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 review on the applications of image logs in structural analysis and sedimentary characterization abstract image logs provide important information on lithology sedimentary textures paleoflow directions fractures and in situ stress analysis lacking of criteria used for establishing the image log facies limits the applications of image logs in sedimentary reservoir interpretation this paper provides a thoroughgoing review focusing on the recent applications of borehole image logs for sedimentological and structural description and interpretation and aims to establish image log facies which can provide guidelines in sedimentary reservoir interpretation this paper firstly summarizes the principles and basic characteristics of various imaging logging tools and then briefly introduces the pre processing workflow of the image log data then the generated images are used for depth and orientation shifts of cores by calibrating individual sedimentary and structural features descriptive and concise image log facies are established based on combinations of image textures including dip type dip pattern and color scheme and the characteristics as well as physical criteria for each individual image facies are summarized the established image log facies are then interpreted in terms of structural and sedimentological features such as lithology sedimentary structures vugs fractures and faults the image log facies and its stacking patterns are then used to interpret the lithofacies associations by calibrating with cores and conventional logs natural fractures and induced fractures are recognized by image logs and the principles of breakouts and drilling induced fractures for in situ stress analysis are reviewed then the applications of image logs in investigation of fracture attitudes and states as well as in computation of fracture parameters are summarized the procedures to evaluate fracture effectiveness through image logs are discussed at last the application of image logs for structural dip analysis is reviewed and image logs are used for recognizing faults fracture sets and attitudes of stratum through the dip patterns the basic procedures for paleocurrent reconstruction which includes dip picking of cross beddings structural dip determination and structural dip removal are reviewed then the paleocurrent directions of the lower cretaceous bashijiqike formation in the kuqa depression were reconstructed which could help further understanding of the depositional systems this review will help extend the utility of image logs in interpreting small to large scale sedimentary and structural features and bridges the gaps between well log analysis and sedimentary and structural interpretation

an experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures 51 to 350 c insights as to chemical processes in near shore ridge flank hydrothermal systems studies of hydrothermal circulation within partly buried basement on the eastern flank of the juan de fuca ridge jfr have shown that ridge flank geochemical fluxes are potentially important for the global budgets of some elements there are major uncertainties in these flux calculations however because the composition of these basement fluids is strongly dependent on temperature and because they may be modified by interaction with the overlying terrigenous sediments either by diffusive exchange with basement or during upwelling to the seafloor to better understand the nature and temperature control of basalt fluid and sediment fluid reactions at the jfr flank we have conducted laboratory experiments between 51 and 350 c and at 400 bars pressure k rb and si are leached from basalt between 150 and 351 c and sr and u are taken up the direction of exchange of li and ca with basalt varies with temperature li and sr are removed from fluid at 150 c but isotope studies show that there is simultaneous release of both elements from basalt indicating that uptake is controlled by the formation of secondary minerals moreover our experiments confirm that sr isotope exchange with oceanic crust occurs at moderate temperature and is not confined to high temperature axial hydrothermal systems our data and field data from the jdr flank indicate that uptake of u into basalt at moderate temperature could remove between 9 9 and 15 106 mol u yr 1 from the oceans this is higher than a recent estimate based on measurements of u in altered ocean crust 5 7 3 3 106 mol yr 1 which concords with arguments that the element heat ratios of jdr flank fluids are too large to be representative of average global flank fluids k ca sr ba li si and b are leached from terrigenous sediments between 51 and 350 c and u is taken up cs and rb are removed from the fluid below 100 c and leached from the sediment at higher temperature sr isotope data show that sr is preferentially mobilised from volcanic components within terrigenous sediments which may lead to an overestimation of the ridge flank sr isotope flux at the jdr if there is exchange of sediment pore fluids with basement

developments in the understanding and application of lithium isotopes in the earth and planetary sciences the significant relative mass difference c 16 between the two stable isotopes of li approximately 6li 7 5 7li 92 5 coupled with broad elemental dispersion in earth and planetary materials makes this a system of considerable interest in fingerprinting geochemical processes determining mass balances and in thermometry natural mass fractionation in this system is responsible for c 6 variation among materials examined to date fig 1 although the modern era of li isotope quantification has begun there are still many questions about the li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered e g hoefs 1997 figure 1 summary of lithium isotopic compositions of earth and planetary materials filled bars are solid samples open bars are liquids see text for references and details the purpose of this chapter is to summarize the current understanding of li isotopes in geo and cosmochemical systems and to indicate 1 where li isotopes have a high probability of adding new understanding of these systems 2 where some of the more significant deficits in knowledge exist the small but burgeoning li isotope community has not yet compiled the volume of peer reviewed literature needed to adequately assess even that which has been studied to date as a result significant portions of this chapter are based on data reported in abstracts and as such are more than normally subject to revisions over time this chapter is anticipated to serve as a starting point for those interested in research incorporating li isotope geochemistry or in understanding the state of extant research experiments in li isotope fractionation knowledge of significant li isotopic fractionation during basic chemical processes is long standing the early experiments by taylor and urey 1938 in which li isotopes were fractionated by incomplete extraction of an aqueous solution from a zeolite exchange

the geochemical differentiation of s type pegmatites constraints from major trace element and li b isotopic composition of muscovite and tourmaline pegmatites often exhibit regional as well as internal zonation in this study we use major and trace element and li b isotopic composition of muscovite and tourmaline from internally zoned and un zoned s type pegmatites and their host granites to characterize the geochemical and isotopic fractionation associated with their formation the internally zoned pegmatites comprise three distinct textural zones namely wall intermediate and core muscovite and tourmaline occur in all the zones of these pegmatites the trace element concentrations ratios of muscovite from the three zones form well defined differentiation trends marked by enrichment of incompatible elements such as rb cs sr b zn nb ta p and the depletion of ni co v sc ti ba from the wall zone through the intermediate zone to the core zone this is suggestive of a strong role of fractional crystallization in producing the compositional diversity in the internally zoned pegmatites alkali element ratios such k rb and k cs in muscovite exhibit near exponential decline from the wall to the core zone which is suggestive of rayleigh type fractional crystallization fractional crystallization modelling reveals that the formation of the wall zone requires 69 crystallization the intermediate zone 85 95 and the core zone ca 99 crystallization leading to extreme enrichment of rb and cs and other incompatible elements muscovites and tourmaline from the un zoned pegmatites display similar compositional trends as the internally zoned ones but with a significant compositional gap between the host granite and the pegmatite lithium isotopic composition of muscovites and b isotopic composition of tourmalines become progressively lighter from wall to core zone of the internally zoned pegmatite and from the granite to the pegmatite for the un zoned pegmatites this is suggestive of an important role of vapour exsolution in the formation of the pegmatites taken together the geochemical and isotopic trends in the pegmatites can be explained by rayleigh fractional crystallization operating in tandem with vapour exsolution

crystallization conditions and evolution of magmatic fluids in the harney peak granite and associated pegmatites black hills south dakota evidence from fluid inclusions abstract a microthermometric study of inclusions in granites and pegmatites in the proterozoic harney peak granite system identified four types of inclusions type 1 inclusions are mixtures of co2 and h2o and have low salinities on average 3 5 wt nacleq type 2 inclusions are aqueous solutions of variable salinities from 0 to 40 wt nacleq type 3 inclusions are carbonic dominated by co2 with no detectable water and type 4 inclusions consist of 20 to 100 solids with the remaining volume occupied by a co2 h2o fluid many inclusions have a secondary character however a primary character can be unambiguously established in several occurrences of the type 1 inclusions these inclusions were trapped above the solidus and represent the exsolved magmatic fluid the secondary populations of types 1 2 and 3 probably formed as a result of reequilibration and unmixing of the type 1 fluid that progressively changed composition and density with decreasing temperature and pressure and was finally trapped along healed microfractures under subsolidus conditions type 4 inclusions are primary and are interpreted to be trapped fluid bearing complex silicate melts that subsequently solidified or underwent other posttrapping changes it is demonstrated that primary type 1 fluid inclusions that coexist with crystallized melt inclusions in the complex li bearing tin mountain pegmatite were trapped along the two fluid phase boundary in the system co2 h2o nacleq consequently the temperature and pressure conditions of trapping are identical to the bulk homogenization conditions on average 340 c and 2 7 kbar these conditions indicate that this li cs rb p and b rich pegmatite crystallized at some of the lowest known temperatures for a silicate melt in the crust an internally consistent empirical solvus surface in p t xco2 coordinates was generated for the pseudobinary co2 h2o 4 3 wt nacleq pegmatite fluid system distribution coefficients for the major species co2 h2o nacl and ch4 between the immiscible co2 rich and h2o rich fluid phases as a function of pressure and temperature were extracted from data for the two cogenetic fluid inclusions types

lithium abundance and isotope systematics of forearc serpentinites conical seamount mariana forearc insights into the mechanics of slab mantle exchange during subduction 1 variable lithium contents and contrasting li isotopic signatures are evident in the serpentininite muds and clasts extruded at conical seamount in the mariana forearc the muds have high li contents compared to mantle values 3 7 ppm and a mean 7li value of 6 the clasts are generally lower in li and 7li varies from 6 to 10 with higher 7li correlating broadly to higher lithium contents the diverse 7li in the serpentinite clasts suggests li exchanges between mantle rocks and evolving slab derived fluids from different depths producing a subarc mantle that is zoned in terms of li abundances and 7li mariana forearc li isotopic signatures reach values as high as those reported in mariana arc lavas but neither mariana lavas nor lavas from other mature arcs show the variability observed in the serpentinites although elevated serpentinite li contents indicate forearc releases of li large differences in 7li are not evident in the slab outputs at forearc versus arc depths in the marianas despite evidence for changes in other alkaline species e g ba sr k it is thus possible that the li sampled by mariana arc volcanoes is in large part li which was released in the forearc and transported in the mantle via convection to arc depths as has been proposed to explain b isotopic variations straub and layne 2002 the uniform 7li signatures observed in mature volcanic arcs tomascak et al 2002 are consistent with higher overall fluxes of slab fluids which generate larger melting anomalies including both modified and nonmodified mantle wedge domains high or low 7li in lavas from anomalous arcs e g panama tomascak et al 2000 may indicate that the volumes of mantle sampled in these magmatic events are smaller and thus more likely to reflect the signatures of hydrated plums e g allegre and turcotte 1986 phipps morgan and morgan 1999 with extremely high or low 7li

trace element mobility and lithium isotope exchange during hydrothermal alteration of seafloor weathered basalt an experimental study at 350 c 500 bars abstract the relative mobility of trace incompatible elements and exchange of lithium isotopes during alteration of basalt previously altered by exposure to seawater at low temperatures seafloor weathered were experimentally determined at 350 c 500 bars these data are important as a means to test models calling for hydrothermal alteration of weathered basalt as a source of alkali elements for hot spring vent fluids at mid ocean ridges weathered basalt used for the experiment was characterized by high cs rb b k and li concentrations high cs rb and low k rb and ba rb ratios respectively relative to fresh basalt the basalt is enriched in 7li consistent with a history involving li uptake during seafloor weathering the experiment involved a na ca k cl fluid and flexible cell hydrothermal equipment which permitted periodic sampling of the fluid phase at experimental conditions the extraction efficiency of all trace incompatible elements was significant and ranged from 40 to 80 cesium rubidium lithium and boron were particularly mobile whereas ba sr and to a lesser degree k were taken up by alteration minerals early stage release of li was dominated by 7li most probably as a consequence of the dissolution of low temperature alteration phases in the weathered basalt that were rendered unstable at the elevated temperatures of the experiment subsequently however an increase in 6li in solution was observed owing to a combination of mineral dissolution from li bearing components in fresh basalt and isotopic equilibration effects owing to the mobility of li during hydrothermal alteration of weathered basalt it is unlikely that dissolution of weathered basalt components in subseafloor reaction zones 350 400 c could occur without noticeably affecting the lithium isotope composition of vent fluids as inferred previously from field studies thus the relatively high cs rb ratios of some vent fluids which were thought to be the result of hydrothermal alteration of weathered basalt may be caused by other effects such as partitioning of rb relative to cs into hydrothermal minerals at temperatures in excess of 400 c cs rb ratios in vent fluids from a wide range of pacific and atlantic ridge localities however reveal relatively large variations in space and time which suggest that a single process is unlikely to account for all of the data the relative mobility of trace alkali elements in weathered basalt not only constrains models of alkali element enrichment in hot spring vent fluids at mid ocean ridges but also provides data bearing on potential sources of alkali elements for arc magmas in subduction zones

assessing uncertainties in balanced cross sections abstract balanced structural cross sections are models that are fit to incomplete data the models are under constrained with respect to any particular two dimensional line length model but enough data generally exists to yield a well constrained area balance solution furthermore the area balance encompasses all possible line length solutions therefore where the primary objective of section balancing is the determination of horizontal shortening magnitude area balancing provides an analytical solution we use this analytical solution to develop a comprehensive robust analysis of the uncertainty in shortening estimates resulting from cross section balancing the analytical solution allows us to propagate errors formally on the input parameters stratigraphic thicknesses depth to decollement eroded hanging wall cutoffs through the equations and produce the resulting uncertainty on the magnitude of shortening balanced cross sections from the subandean belt of the central andes are used to demonstrate the relative importance of stratigraphy and eroded hanging wall cutoffs in the contribution to the overall error

an enthalpy formulation for glaciers and ice sheets polythermal conditions are ubiquitous among glaciers from small valley glaciers to ice sheets conventional temperature based cold ice models of such ice masses cannot account for that portion of the internal energy which is latent heat of liquid water within temperate ice so such schemes are not energy conserving when temperate ice is present temperature and liquid water fraction are however functions of a single enthalpy variable a small enthalpy change in cold ice is a change in temperature while a small enthalpy change in temperate ice is a change in liquid water fraction the unified enthalpy formulation described here models the mass and energy balance for the three dimensional ice fluid for the surface runoff layer and for the subglacial hydrology layer together in a single energy conserving theoretical framework it is implemented in the parallel ice sheet model results for the greenland ice sheet are compared with those from a cold ice scheme this paper is intended to be an accessible foundation for enthalpy formulations in glaciology

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

petrologic and geochemical links between the post collisional proterozoic harney peak leucogranite south dakota usa and its source rocks abstract the proterozoic terrane of the black hills south dakota includes the composite harney peak leucogranite and associated pegmatites that were emplaced into metamorphosed pelites and graywackes available dates indicate that granite generation post dated regional metamorphism and deformation that have been attributed to collision of the wyoming and superior cratons at 1760 ma previous radiogenic and stable isotope work indicates that the exposed metasedimentary rocks are equivalent to sources of the leucogranites in this study whole rock and mineral compositions of the metasedimentary rocks were used to calculate the likely average residue mineralogies and melt fractions that would be generated by muscovite dehydration melting of the rocks these were then used to model observed trace element compositions of the granites using published mineral melt distribution coefficients model trace element melt compositions using pelitic and graywacke protoliths yield similar results the models reproduce well the observed depletion of transition metals and ba in the granites relative to metasedimentary protoliths the depletion is due mainly to high proportion of biotite with variable amounts of k feldspar in the model residue sr is also depleted in the granites compared to source rocks but to a lesser relative extent than ba this is because of the low biotite melt distribution coefficient for sr and because high proportion of plagioclase in the residue is compensated by high sr concentrations in protoliths rubidium cs and ta behaved as slightly compatible to incompatible elements and therefore were not strongly fractionated during melting of the considered elements only b appears to have been highly incompatible relative to residue during melting the protoliths had sufficient b to allow tourmaline crystallization in those parts of the harney peak granite in which ti concentration was sufficiently low not to enhance crystallization of biotite the reproducibility of observed trace element concentrations in the harney peak granite by the models supports the often made proposition that metapelites and metagraywackes are common sources for leucogranites this argues against mass input from the mantle into metagraywacke and metapelitic crustal sources or melting of amphibolites to generate the post collisional harney peak and other similar peraluminous granite suites

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 generation and crystallization conditions of the proterozoic harney peak leucogranite black hills south dakota usa petrologic and geochemical constraints the mineralogy petrology and geochemistry of the proterozoic harney peak granite black hills south dakota were examined in view of experimentally determined phase equilibria applicable to granitic systems in order to place constraints on the progenesis of peraluminous leucogranites and commonly associated rare element pegmatites the granite was emplaced at 3 4 kbar as multiple sills and dikes into quartz mica schists at the culmination of a regional high temperature low pressure metamorphic event principally along the periphery of the main pluton and in satellite intrusions the sills segregated into granite pegmatite couplets the major minerals include quartz k feldspar sodic plagioclase and muscovite biotite mg no molar mgo mgo feo 0 32 0 38 is the predominant ferromagnesian mineral in the granite s core whereas at the periphery of the main pluton and in the satellite intrusions tourmaline mg no 0 18 0 48 is the dominant ferromagnesian phase almandine spessartine garnet is also found in the outer intrusions there is virtually a complete overlap in the wide concentration ranges of sio2 cao mgo feo sr zr w of the biotite and tourmaline bearing granite suites with no discernable differentiation trends on harker diagrams precluding the derivation of one suite from the other by differentiation following emplacement this is consistent with the oxygen isotope compositions which are 11 5 0 6 for the biotite granites and 13 2 0 8 for the tourmaline granites suggesting derivation from different sources the concentrations of tio2 and possibly ba are higher and of mno and b are lower in the biotite granites the normative orthoclase albite ratio is extremely variable ranging from 0 26 to 1 65 in the biotite granites to 0 01 1 75 in the tourmaline granites very few sample compositions fall near the high pressure watersaturated haplogranite minima eutectic trend indicating that the granites for the most part are not minimum melts generated under conditions with a text h text 2 text o 1 instead most biotite granites are more potassic than the water saturated minima and eutectics and in analogy with experimentally produced granitic melts they are best explained by melting at 6 kbar a text h text 2 text o 1 and temperatures 800 c such high temperatures are also indicated by oxygen isotope equilibration among the constituent minerals nabelek et al 1992 several of the tourmaline granite samples contain virtually no k feldspar and have oxygen isotope equilibration temperatures 716 775 c therefore they must represent high temperature accumulations of liquidus minerals crystallized under equilibrium conditions from melts more sodic than the water saturated haplogranite minima or during fractionation of intruded melts into granite pegmatite couplets accompanied by volatile aided differentiation of the alkali elements the indicated high temperatures a text h text 2 text o 1 the relatively high tio2 and ba concentrations and the relatively low partial 18 text o values of the biotite granites suggest that they were generated by high extent biotite dehydration melting of an immature archean metasedimentary source the ascent of the hot melts may have triggered low extent muscovite dehydration melting of schists higher in the crust producing the high b low ti melts comprising the periphery of the main pluton and the satellite intrusions alternatively the different granite types may be the result of melting of a vertical section of the crust in response to the ascent of a thermal pulse with the low partial 18 text o biotite granites generated at a deeper hotter region and the high partial 18 text o tourmaline granites at a higher cooler region of the crust the low ti and high b concentrations in the high partial 18 text o melts resulted in the crystallization of tourmaline rather than biotite which promoted the observed differentiation of the melts into the granitic and pegmatitic layers found along the periphery of the main pluton and the satellite intrusions

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

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

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

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

b and li in proterozoic metapelites from the black hills u s a implications for the origin of leucogranitic magmas the abundance and distribution of b and li in metasedimentary rocks and in the harney peak granite hpg in the black hills south dakota u s a elucidate the behavior of these two elements during 1 regional metamorphism that began at 1760 ma 2 subsequent contact metamorphism associated with emplacement of the hpg and associated pegmatites at 1715 ma and 3 anatexis leading to production of the granite there is no clear evidence for changes in b and li concentrations with progressive regional metamorphism of the metapelites from chlorite biotite grade up to staurolite grade rocks outside the pegmatite aureole that surround the hpg have average b contents of 80 ppm there is no correlation of b with other elements in the pelitic schists which indicates that none of the major phases is the dominant host for b boron content is mainly controlled by small amounts of randomly distributed tourmaline that was identified in alpha track maps of thin sections in the aureole of the granite b concentrations are depleted in many samples the depletion is attributed to consumption of tourmaline during interaction of the rocks with alkalic fluids the average li contents in metapelites far away from the hpg are also 80 ppm near the hpg li concentrations reach roughly 190 ppm indicating significant metasomatism by fluids that emanated from the granite and pegmatites the concentrations of b and li in the low grade metapelites are sufficient to explain their abundances in the hpg if the granite formed by partial melting of the metapelites and if there was total breakdown of tourmaline stabilization of tourmaline in leucogranites is not necessarily related to sources enriched in b but may be related to its competition for fe and mg with biotite

limited lithium isotopic fractionation during progressive metamorphic dehydration in metapelites a case study from the onawa contact aureole maine the major trace element and li isotopic compositions of granodiorite and metapelites from the onawa pluton and surrounding contact aureole have been measured to document the behavior of li and its isotopes during progressive metamorphic dehydration major andtraceelementconcentrationsinmetapelitesofthecontactaureolechangelittle whilelossonignition loi decreaseswithincreasing metamorphic grade which ranges from regional chlorite zone metamorphism far removed from the pluton to partially melted rocks adjacent to the pluton lithium concentrations in metapelites from all zones correlate with loi and abundances of the main li bearing minerals chlorite biotite muscovite decreasing by a factor of two from 130 ppm far removed from the pluton to 64 ppm adjacent to thepluton incontrast liisotopiccompositionsremainrelativelyunchangedacrosstheaureole 7 li 3 5to 1 0 andarecomparable to the range observed in schists and unmetamorphosed shales compared to the surrounding metasediments the granodiorite has a lower li content 45 ppm and a comparable 7 li value of 0 2 similar to those of other granites and the average upper crust 0 2 these observations are consistent with the removal of li from metapelites via rayleigh distillation during progressive metamorphic dehydration with isotopic fractionation factors between fluids and rocks ranging between 1 001 and 1 004 these values are similar to thoseofarecentexperimentalstudyandproduceisotopicfractionationthatisbarelybeyondanalyticaluncertainty 1 fortheobserved degree ofli depletion the good correlationsbetweenli concentrations and loiwithmineralogicalabundancesreflecttheimportanceof mineralogyincontrollingliconcentrationsandisotopiccompositionsofmetamorphicrocks comparisonoftheseresultswiththosefrom a study of a contact halo around the tin mountain pegmatite suggests that the nature of the intrusion plays a critical role in controlling the behavior of li in country rocks large diffusive driven isotopic fractionation over a small scale is expected to occur when rocks are infiltrated by li rich magmatic fluids while metamorphic devolatilization results in minor isotopic fractionation on the aureole scale published by elsevier b v

information from folds a review abstract folds are spectacular geological structures that are seen in layered rock on many different scales to mark 30 years of the journal of structural geology we review the information that can be gained from studies of folds in theory experiment and nature we first review theoretical considerations and modeling from classical approaches to current developments the subject is dominated by single layer fold theory with the assumption of perfect layer parallel shortening but we also review multilayer fold theory and modeling and folding of layers that are oblique to principal stresses and strains this work demonstrates that viscosity ratio degree of non linearity of the flow law anisotropy and the thickness and spacing distribution of layers of different competence are all important in determining the nature and strength of the folding instability theory and modeling provide the basis for obtaining rheological information from natural folds through analysis of wavelength thickness ratios of single layer folds and fold shapes they also provide a basis for estimating the bulk strain from folded layers information about folding mechanisms can be obtained by analysis of cleavage and fabric patterns in folded rocks and the history of deformation can be revealed by understanding how asymmetry can develop in folds by how folds develop in shear zones and how folds develop in more complex three dimensional deformations

stable isotope evidence for the petrogenesis and fluid evolution in the proterozoic harney peak leucogranite black hills south dakota abstract oxygen and hydrogen isotope systematics of the proterozoic harney peak granite black hills south dakota were examined in order to constrain its petrogenesis and to examine the role of fluids in a peraluminous granite pegmatite magmatic system the leucogranite and its satellite intrusions were emplaced as hundreds of sills and dikes which are texturally heterogeneous ranging from aplitic to pegmatitic the dominant ferromagnesian mineral in the core of the granite is biotite while along its perimeter and in satellite intrusions it is tourmaline biotite and tourmaline are for the most part mutually exclusive oxygen isotopes among minerals in non pegmatitic rocks from throughout the pluton equilibrated for the most part at magmatic temperatures between 800 to 650 c in the pegmatitic samples quartzfeldspar oxygen isotope fractionations point to disequilibrium probably a result of the sequential crystallization of these minerals the isotopic composition of most pegmatites suggests local derivation by differentiation of emplaced batches of magma the whole rock 18 o values of the granites are heterogeneous ranging from 10 4 to 14 3 however there is a pronounced difference in the isotopic composition of the biotite containing granites from the core of the pluton 11 5 0 6 and the tourmaline rich granites from its perimeter and the satellite intrusions 13 2 0 8 the average oxygen isotopic composition of the surrounding schists is identical to that of the latter granites biotite muscovite and tourmaline muscovite d values vary from 20 to 10 and from 0 to 10 respectively although these values differ from theoretical values the narrow ranges suggest that the minerals are in isotopic equilibrium and that their isotopic compositions record the composition of the magmatic fluid the calculated d value of the magmatic fluid is 67 to 58 well within the magmatic water range however somewhat elevated mineral d values in the southern part of the harney peak granite where the metasediments reached the second sillimanite isograd suggest that limited interaction with fluids derived from the dehydrating metasediments may have occurred alternatively the elevated values could reflect a hydrogen isotope heterogeneity in the source or interaction with another magmatic system to the south of the harney peak granite it is shown that fractional crystallization or subsolidus interaction of the harney peak granite with the magmatic fluid or a fluid derived from the schist cannot explain the difference between the 18 o values of the core and perimeter granites although some oxygen isotope heterogeneity in the granite could be explained by assimilation of the country rocks assimilation cannot explain all of the difference between the two granite types instead it is proposed that intrusion of the magma which led to the biotite granites in the core of the pluton at the culmination of regional metamorphism initiated melting of the schists at a depth somewhat greater than the present level of erosion the melts were emplaced into the overlying schist and differentiated into the many tourmaline rich granite pegmatite sills and dikes comprising much of the perimeter of the harney peak granite and its satellite plutons alternatively the different melts may have resulted from melting along an isotopically heterogeneous vertical section of the crust in response to the ascent of a thermal pulse

three dimensional structural model of the cantarell and sihil structures campeche bay mexico the cantarell and sihil fields are located in a complex system of compressive structures in the offshore campeche bay province in mexico the geometry of the cantarell sihil structure varies along trend from a simple fault related structure in the south to a duplex consisting of the cantarell and sihil structures in the central part to a more complex system consisting of compressive blocks separated by tertiary normal faults in the north the cantarell sihil structures formed during three main episodes of deformation 1 jurassic to early cretaceous extension resulting in the formation of normal faults that displace tithonian kimmeridgian and lower cretaceous units 2 miocene compression during which the cantarell sihil thrust system was formed and 3 pliocene to holocene extension during which several of the preexisting jurassic normal faults were reactivated the cantarell field produces out of three separate fault bounded allochthonous blocks the akal nohoch and kutz blocks the main field is located in the akal structure secondary fields in the allochthonous block include kutz which formed on the crest of a downthrown fault block and nohoch which formed above a west vergent backthrust the recently discovered sihil field is located in a subthrust compressive structure and consists of two structural lobes formed above the sub sihil fault the chac structure is formed at the updip edge of a tilted fault block in the autochthonous block the detailed three dimensional structural model is being used for future production of the remaining reserves in the cantarell field as well as for the delineation of the sihil field

terrestrial laser scanning in geology data acquisition processing and accuracy considerations terrestrial laser scanning or lidar is a recent innovation in spatial information data acquisition which allows geological outcrops to be digitally captured with unprecedented resolution and accuracy with point precisions and spacing of the order of a few centimetres an enhanced quantitative element can now be added to geological fieldwork and analysis opening up new lines of investigation at a variety of scales in all areas of field based geology integration with metric imagery allows 3d photorealistic models to be created for interpretation visualization and education however gaining meaningful results from lidar scans requires more than simply acquiring raw point data surveys require planning and typically a large amount of post processing time the contribution of this paper is to provide a more detailed insight into the technology data collection and utilization techniques than is currently available the paper focuses on the workflow for using lidar data from the choice of field area and survey planning to acquiring and processing data and finally extracting geologically useful data because manufacturer specifications for point precision are often optimistic when applied to real world outcrops the error sources associated with lidar data and the implications of them propagating through the processing chain are also discussed

evaluation analysis and prediction of geologic structures abstract balanced cross sections claim to be better because they apply a rigorous set of rules to develop the conceptual model of the structures present in an area balanced cross sections can be further improved and become more useful to understanding real physical problems by collection of additional data such as seismic reflection surveys collection of additional stratigraphic data or collection of rock fabric information the additional information validates the initial model and provides details on deformation conditions and on local rock responses to the deformation although individual cross sections are two dimensional the objective of evaluation and analysis of deformed regions should be three dimensional whenever possible to recognize the challenges of the real world subsurface system analysis derived from the hydrologic community emphasizes conceptual model development through model verification validation uncertainty quantification benchmarking and meta analysis their approach includes many steps informally used by the structural geology community but in a much more explicit way newer geological applications of structural geology would benefit from this more rigorous approach for designing and doing performance predictions as technological needs become more socially sensitive such as for carbon storage sites new areas of energy exploration in higher population density areas or for nuclear waste storage facilities

experimental partitioning of be cs and other trace elements between cordierite and felsic melt and the chemical signature of s type granite the trace element signature that cordierite crd imparts to silicic magmas was evaluated by experiment using metapelite mineral mixtures to produce cordierite bearing peraluminous granitic melts at 200 mpa ph2o from 700 to 850 c most elemental partition coefficients vary with t beryllium is strongly compatible with dbecrd melt values decreasing linearly from 202 0 to 6 7 as t rises from 700 to 850 c manganese is compatible dmncrd melt 7 67 to 1 92 over the same range of t and shows similar values to those reported for biotite in silicic melts incompatible components include li rb b f and p although cs is nearly compatible in cordierite especially at higher t dcscrd melt 0 19 to 0 60 where the large alkalis are better accommodated structurally cordierite appears to be the most effective crystalline reservoir of be and cs in metapelites and their anatectic melts natural data support the hypothesis that crd when present in granitic melts sequesters be cs and in the absence of garnet mn s type granitic rocks containing crd show consistently low be contents mean 0 8 ppm be with an average range of 1 to 1 20 whereas crd free granites e g containing accessory garnet exhibit distinctly higher be contents mean 6 ppm be with an average range of 3 to 12 these values increase further in evolved facies mean 69 ppm be with a an average range of 11 to 145 which commonly give rise to beryl bearing pegmatites whole rock signatures of be discriminate source environments of silicic magmas at a resolution equal to the boundaries of the cordierite stability field e g at the p t x conditions where cordierite gives rise to garnet aluminum silicate cordierite bearing granitic rocks contain low cs contents mean 1 8 ppm cs compared to the crd free equivalents mean 18 ppm cs mn contents also correlate with the presence mean 0 01 wt mno or absence of crd mean 0 09 wt mno depending on its contribution to anatexis cordierite may either give or take s type chemical character from granitic liquids resulting in a distinctive crd associated group of s type elements this signature is different from that of micas high li f and to a lesser degree be and mn whole rock compositions of granites coupled with notable absences of beryl in their associated pegmatites indicate that a sizable population of s type granites originated from crd bearing sources the normative crd component of silicic peraluminous melts is 4 wt to 850 c higher modal contents of cordierite reflect either restite entrainment or peritectic reactions which produce crd after magma ascent to shallow depths the distinctive trace element signature of cordierite now provides improved resolution of the source mineralogy for s type magmas

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

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

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

improving curvature analyses of deformed horizons using scale dependent filtering techniques fractures which are common structural heterogeneities in geological folds and domes impact the charge seal and trapping potential of hydrocarbon reservoirs because of their effects on reservoir quality the numerical prediction of fractures has recently been the focus of petroleum geoscientists a horizon s curvature is commonly used to infer the state of deformation in those strata it is assumed that areas of elevated calculated curvatures underwent elevated deformation resulting in a concentration of fractures and faults there usually curvatures are calculated from spatial data after sampling the continuous horizon at discrete points this sampled geometry of the horizon includes surface undulations of all scales which are then also included in the calculated curvatures including surface undulations of all scales in the curvature analysis leads to noisy and questionable results we argue that the source data must be filtered prior to curvature analysis to separate different spatial scales of surface undulations such as broad structures faults and sedimentary features only those surface undulations that scale with the problem under consideration should then be used in a curvature analysis for the scale dependent decomposition of spatial data we test the suitability of four numerical techniques fourier spectral analysis wavelet transform filtering singular value decomposition factorial kriging on a seismically mapped horizon in the north sea for surfaces sampled over a regular grid e g seismic data fourier spectral analysis extracts meaningful curvatures on the scale of broad horizon features such as structural domes and basins

crustal melts below 400 c we propose that the internally zoned li bearing tin mountain pegmatite in the harney peak granite pegmatite system of the black hills south dakota crystallized from fluid rich compositionally complex melts at 400 350 c the low crystallization temperatures resulted from the combined fluxing effects of li b p h 2 o and carbonate anions the presence of hydrous silicate melts at temperatures of 350 c is revealed by microthermometric data on primary fluid inclusions cogenetic with crystallized melt inclusions mineral assemblages of the crystallized melt inclusions and chemistry of bulk fluid leachates indicate that the melts and fluids contained significant amounts of li and na as carbonates and or borates that acted as powerful fluxes the low temperatures give a new perspective on the stability of silicate melts in the crust

trace element constraints on pegmatite genesis tin mountain pegmatite black hills south dakota the tin mountain pegmatite is a small zoned granitic body that is extremely enriched in rb and li but has moderate concentrations of sr and ba these trace elements are modelled using granitic distribution coefficients in order to test the potentials of partial melting of metasedimentary rocks and fractionation of a less evolved granitic melt to have produced the parental liquid to the tin mountain pegmatite batch melting of any reasonable metasedimentary source rock would likely have yielded melts that were either insufficiently enriched in rb and li to be the parental liquid or that had sr and ba concentrations that were much higher than those estimated for the parental liquid the modelling of simple fractional crystallization and equilibrium crystallization of a granitic melt within the compositional range of the spatially associated harney peak granite gives calculated melt compositions with either lower sr and ba concentrations or inadequate rb and li enrichments to be the parent liquid of the pegmatite at least two variants from simple crystal liquid fractionation models can however successfully account for the derivation of the parent liquid 1 generation of a rb li ba and sr rich granitic melt outside of the compositional range of the sampled portions of the harney peak granite complex by low degrees of partial melting of metasedimentary rocks found in the black hills followed by moderate extents of fractional or equilibrium crystallization 2 derivation from harney peak granite via a complex multi stage crystal liquid fractionation process such as progressive equilibrium crystallization

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

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

estimating bedding orientation from high resolution digital elevation models a high resolution digital elevation model dem generated from airborne light detection and ranging lidar remote sensing data is used here to estimate the 3 d orientation of bedding planes methods for enhancement manual identification and extraction of lineaments and estimation of best fit planes representing bedding are presented and evaluated for a study area in folded metasedimentary rocks in northeast tasmania australia estimated bedding plane dip directions are shown to be accurate and reliable when compared with field based observations the same cannot be said for dip angle estimates it is likely that small errors in the location of a manually digitized lineament will affect dip estimation more than dip direction estimation particularly for steeply dipping structures fold axis orientations calculated from the stereographic analysis of estimated bedding closely correspond to orientations determined from field data the mean absolute differences pm standard error for 12 of the 14 regularly spaced domains located within the study area were 8 7 circ pm 1 2 circ for the fold plunge and 4 9 circ pm 0 9 circ for the fold trend the techniques described here for the extraction of bedding plane orientations from high resolution dems complement field based geological mapping and can assist structural interpretations

behavior of lithium and its isotopes during weathering of hawaiian basalt 1 we examined the pedogenic behavior of lithium li and its isotopes in hawaii by sampling same age lava flows under mean annual rainfall ranging from 18 to 300 cm lithium concentrations in these soils vary from 1 to 29 ppm whereas na k and ca are completely leached from the soil at the most humid and severely weathered site li mg si and al show significant retention due to their association with secondary clay minerals in these soils allochthonous li delivered in marine and mineral aerosol mixes with basalt derived li modifying the isotopic composition of the li pool the ability of soil to retain li is related to its effective cation exchange capacity which in turn is governed by rainfall and leaching intensity and their resulting effect on mineralogy lithium isotope ratios have a large range 7li of 0 4 to 14 well beyond the intershield or temporal variation of the lavas of hawaiian volcanoes 2 5 to 5 7 the most unweathered samples have 7li 5 6 comparable to that of mauna kea and mauna loa lavas the li concentrations and isotope ratios together suggest that in arid to subhumid sites there is a net addition of isotopically heavier lithium from marine aerosol but that under greater rainfall there is a net loss of li and isotopically light li is preferentially retained thus during incongruent weathering of primary minerals li especially 6li is adsorbed and sequestered by the clay mineral fraction of high cation exchange capacity soils in drier regions but lost from highly weathered low cation exchange capacity acidic soils in the wetter regions

behaviour of li isotopes during continental weathering the bidar laterite profile india weathering of large basaltic provinces is a major sink of atmospheric carbon dioxide and is also an important part of the geochemical cycle of many other elements this study aims to improve our understanding of basaltic weathering by analysis of trace elements and li isotopes in a lateritic profile developed upon the deccan traps flood basalt at its base the profile consists of unaltered basalt that has a li concentration and 7li value of 5 ppm and 2 5 respectively which is upwards progressively altered to a highly weathered laterite iron rich residuum at the surface high concentrations of fe2o3 85 wt at 11 m depth indicate the presence of a palaeowatertable the transition metals the rare earth elements rees and u are also strongly enriched in this horizon whereas fluid mobile elements such as li and rb are depleted relative to the precursor basalt and the bulk 7li value is very low 5 5 a high proportion of leachable li is found in this horizon and this is enriched in 6li relative to the bulk we suggest that leaching extracts the labile weathering products and these have high 6li as 7li has been preferentially mobilised during basalt weathering throughout the rest of the profile li concentrations and li isotope values are best explained by two component mixing between the precursor basalt and aeolian material with high li and low 7li mass balance calculations show that at least 50 of the li present in the profile could have been supplied by a mineral aerosol that has a 7li value between 0 and 1 3 the depth integrated 7li value of the profile is 0 6 which suggests that 7li has been preferentially leached from the aerosol after its deposition the source of this aeolian material is most likely to be ancient continental crust it is possibly derived from archaen proterozoic terrain to the south and southeast of the deccan and or material from central asia similar to that which forms chinese loess and which is supplied to the north pacific basin

lead isotopic evidence for mixed sources of proterozoic granites and pegmatites black hills south dakota usa abstract the lead isotopic compositions of k feldspars separated from the ca 1700 ma harney peak granite complex and spatially associated granitic pegmatites indicate that these rocks were derived from at least two sources it has been reported previously that the core of the harney peak granite complex is dominated by relatively lower gd18o avg 11 5 granites whereas higher gd18o avg 13 2 granites occur around the periphery of the complex the higher 18 o granites and one simple pegmatite have low values of 207 pb 204 pb for their 206 pb 204 pb thus they likely were derived from a source with a short crustal residence time this source may have been the pelitic schists into which the harney peak granite complex and pegmatites were intruded feldspars from granites with lower gd18o values have significantly higher 207 pb 204 pb for their 206 pb 204 pb the data define a linear array with a slope equivalent to an age of ca 2 6 ga with t2 defined to be 1 7 ga such a slope could represent a mixing array or a secondary isochron for the source these low 18o granites could have been derived from a source with a high u pb and with a crustal residence beginning before the proterozoic the source s of these granites may have been a sediment derived from late archean continental crust the highly evolved tin mountain pegmatite has lead isotopic systematics intermediate between those of the two granite groups suggesting either a mixed source or contamination two late archean granites the little elk granite and the bear mountain granite had precursors with high u pb and low th u histories the th u history of the bear mountain granite is too low for this rock to have been an important component of the source of the proterozoic granites however crustal rocks with lead isotopic compositions similar to those of the little elk granite were an important source of lead for some of the proterozoic granitic rocks

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