ferro andesites in the grande ronde basalt their composition and significance in studies of the origin of the columbia river basalt group flows from the grande ronde basalt of the columbia river basalt group include several with the chemical composition of ferro andesites these flows have sio2 55 mgo 4 and also have higher fe mg than the average value for grande ronde basalt they are also distinctly richer in cs rb k ba la ce th and u than the remainder of the grande ronde basalt flows and possess small negative eu anomalies their pb isotopic compositions define a mixing line with a negative slope on a 206pb 204pb versus 207pb 204pb plot their nd isotopic compositions lie between 143nd 144nd 0 51252 and 0 51264 and their sr isotopic compositions lie between 87sr 86sr 0 7055 and 0 7060 these values define the enriched end of the columbia river basalt group spectrum on a sr nd epsilon diagram excluding the saddle mountains basalt these ferro andesite flows also form a compositional end member of the columbia river basalt group and are sufficiently distinctive to warrant special consideration we compare them with

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

rb cs fractionation a link between granulite metamorphism and the s process abstract high grade metamorphism of pelitic sediments produces large cs losses with little k and rb depletion island arc volcanics contain an enhanced cs component relative to k and rb we suggest a connection between these two processes whereby fluids or melts removed from feldspar bearing subduction assemblages under high grade metamorphic conditions are enriched in cs relative to k and rb these cs enriched components infiltrate subarc mantle and lead to ubiquitous cs enrichment in arc volcanics normal oceanic magmatism is not effective in fractionating rb cs therefore the canonical oceanic basalt value of 85 for rb cs is distinctive relative to processes involving sediments recycling fluid melt metamorphism and arc volcanism

geochemical effects of decoupled fractional crystallization and crustal assimilation most models of crustal assimilation assume that the amount of assimilant added to the magma is proportional to each infinitesimally small amount of solid removed during crystallization afc in some magmatic systems however assimilation and crystallization are not strictly related and the mass assimilated is decoupled from and therefore varies independently of the mass crystallized fca the geochemical consequences of fca are examined and compared to those of afc the behavior of incompatible elements is identical during afc and fca and ratios of these elements do not allow discrimination between the two processes major oxide least squares mass balance models do not discriminate between afc and fca at f 0 7 f fraction of melt remaining however fca yields magmas richer in compatible elements and with higher sr isotopic ratios than afc at a given value of f repeated cycles of fca and afc combined with magma mixing fam may result in unusual geochemical trends such as the evolution of a calc alkaline basaltic parent to a tholeiitic daughter magma or the evolution of low and medium k calc alkaline basalts to high k andesites dacites trachyandesites or trachydacites lavas erupted by the volcano micro profitis ilias on santorini hellenic arc greece provide an example of magmas which evolved by combined fractionation assimilation by fca and mixing

seismic source characteristics of nine strong earthquakes from 1988 to 1990 and earthquake activity since 1970 in the sichuan qinghai xizang tibet zone of china the chinese provinces of sichuan qinghai and xizang tibet are situated in a very active seismic zone from 1988 to 1990 nine strong earthquakes m 5 9 occurred in these provinces a method of analyzing seismic waveforms using apparent source time functions astf and apparent time differences atd is adopted to derive rupture characteristics for the strong earthquakes combining the source characteristics with aftershock data regional tectonics and geology this paper examines the migration of strong earthquakes the qinghai earthquakes in this study were found to have strong reverse slip faulting which is different from the strike slip focal mechanisms of past earthquakes in the region the steepness of compressional axes of sichuan earthquakes is related to the local complicated tectonics finally the single link cluster slc method is used to analyze the spatial temporal behavior of the all strong earthquakes that occurred in the region since 1970 the slc analysis suggests that the patterns of earthquake activity can be identified well and that continental earthquakes occur seemingly with basic regularity

speleothern luminescence intensity and spectral characteristics signal calibration and a record of palaeovegetation change abstract the intensity and spectral characteristics of speleothem luminescence are investigated for signs of any potential palaeoenvironmental signals luminescence in speleothems has been demonstrated to have an organic acid source acids being transported from the overlying soil to the speleothem via the groundwater system luminescence spectral characteristics confirm a humic fulvic acid source of the luminescence but are unable to distinguish between plant acids derived from different vegetation systems spectral characteristics also differ between solid and dissolved speleothem calcite the influence of six factors on luminescence intensity are considered changes in organic acid concentration organic acid structural type depth of the sample below the surface dilution effects through changes in water discharge rate dilution effects through changes in speleothem growth rate and the effects of luminescence quenching due to the presence of metal ions in a holocene stalagmite sample from sutherland a period of low luminescence intensity is observed which is demonstrated to correlate with periods of blanket bog expansion recorded in the regional pollen record this suggestion is supported by a study of 18 recently deposited samples from northwest europe and 5 cave water samples feeding stalagmites in a british cave when a relationship to vegetation is evident with very low luminescence intensity observed from sites overlain by blanket bog deposits this is thought to be due to both low organic acid concentrations in feedwaters and also the low luminescence efficiency of the humic acids from bog sites due to their structural characteristics

cyclic rapid warming on centennial scale revealed by a 2650 year stalagmite record of warm season temperature 1 a 2650 year bc665 ad1985 warm season mjja may june july august temperature reconstruction is derived from a correlation between thickness variations in annual layers of a stalagmite from shihua cave beijing china and instrumental meteorological records observations of soil co2 and drip water suggest that the temperature signal is amplified by the soil organism co2 system and recorded by the annual layer series our reconstruction reveals that centennial scale rapid warming occurred repeatedly following multicentenial cooling trends during the last millennia these results correlate with different records from the northern hemisphere indicating that the periodic alternation between cool and warm periods on a sub millennial scale had a sub hemispherical influence

geochemistry and petrogenesis of amphibolites kolar schist belt south india evidence for komatiitic magma derived by low percentages of melting of the mantle the kolar schist belt of the dharwar craton of south india is an archean greenstone belt dominated by metavolcanic rocks the mafic metavolcanic rocks occur as komatiitic and tholeiitic amphibolites the komatiitic amphibolites occur along the margins of the n s trending synformal belt they are much less abundant than the tholeiitic amphibolites and have 14 to 21 3 wt per cent mgo the komatiitic amphibolites from the west central part of the belt have two distinctive ree patterns 1 those enriched in the middle to light ree but depleted in ce relative to nd and 2 those with patterns that are convex up i e depleted in both light and heavy ree although more depleted in the light ree associated tholeiites have light ree depleted to flat ree patterns komatiitic and tholeiitic amphibolites from the eastern part of the belt have enriched light ree patterns the tholeiitic amphibolites from the kolar schist belt are similar to the th i and th ii types of archean tholeiites of condie 1981 the komatiitic amphibolites are similar to komatiites and komatiitic basalts of barberton mountainland but have higher feo and tio 2 abundances and lower yb gd ratios the petrogenetic interpretations for these rocks are based primarily on a modification of the mgo feo diagram of hanson langmuir 1978 and modelling of zr ni and ree all of the rocks have undergone some fractionation while the modelling does not give accurate temperatures pressures compositions and extents of melting of the mantle sources for the various amphibolites it does present an approach which can be used for estimating these parameters for example the komatiitic amphibolites appear to be derived from melts generated by 10 to 25 per cent melting of the mantle over a range of depths and temperatures greater than 80 km and 1575 c the variation in the p t conditions of magma generation is possibly due to adiabatic melting in mantle diapirs with a range of feo mgo ratios if the tholeiitic amphibolites are derived from similar mantle sources it is not clear that they are their parent melts may have been generated by similar extents of melting but at depths of less than 80 km the komatiitic amphibolites from the west central part of the belt were generated from light ree depleted mantle whereas those from the eastern part of the belt appear to have been generated from light ree enriched mantle the sources for the komatiitic amphibolites in both areas were significantly enriched in feo relative to pyrolite thus a light ree depleted and a light ree enriched source appear to have provided mafic volcanics with similar major element chemistry to this belt during its evolution

early mid holocene climatic variations in tasmania australia multi proxy records in a stalagmite from lynds cave mass spectrometric uranium series dating and c o isotopic analysis of a stalagmite from lynds cave northern tasmania australia provide a high resolution record of regional climate change between 5100 and 9200 yr before present bp combined delta 18 o delta 13 c growth rate initial u 234 u 238 and physical property color transparency and porosity records allow recognition of seven climatic stages stage i 9080 yr bp a relatively dry period at the beginning of stalagmite growth evidenced by elevated u 234 u 238 stage ii 9080 8600 yr bp a period of unstable climate characterized by high frequency variability in temperature and bio productivity stage 111 8600 8000 yr bp a period of stable and moderate precipitation and stable and high bio productivity with a continuously rising temperature stage iv 8000 7400 yr bp the warmest period with high evaporation and low effective precipitation rainfall less evaporation stage v 7400 7000 yr bp the wettest period with highest stalagmite growth and enhanced but unstable bio productivity stage vi 7000 6600 yr bp a period with a significantly reduced precipitation and bio productivity without noticeable change in temperature stage vii 6600 5100 yr bp a period of lowest temperature and precipitation marking a significant climatic deterioration overall the records suggest that the warmest climate occurred between 8000 and 7400 yr bp followed by a wettest period between 7400 and 7000 yr bp these are broadly correlated with the so called mid holocene optimum previously proposed using pollen and lake level records however the timing and resolution of the speleothem record from lynds cave are significantly higher than in both the pollen and lake level records this allows us to correlate the abrupt change in physical property delta 18 o delta 13 c growth rate and initial u 234 u 238 of the stalagmite at similar to8000 yr bp with a global climatic event at early mid holocene transition c 2001 elsevier science b v all rights reserved

enso controlled rainfall variability records archived in tropical stalagmites from the mid ocean island of niue south pacific niue island is located in close proximity to the epicenter of the south pacific convergence zone spcz and its rainfall variability is controlled by changes in the phase of the el nino southern oscillation enso phenomenon four actively growing stalagmites displaying couplets of light and dark calcite layers were sampled from a flank margin cave on niue island in order to determine the dominant climate factor controlling lamina thickness and establish the usefulness of the stalagmites as archives of enso variability records couplets counting ams radiocarbon assays and growth rates analysis mean growth rate 0 34 0 04 mm yr for n 604 support the premise that these couplets are annually deposited and their stalagmites contain records of up to two centuries long comparison of band thickness records with instrumental records of air temperature and rainfall kept on the island since 1930 and 1906 respectively suggests that rainfall variability is the dominant controlling factor coherency between the spectral power of the annual layers unraveling periodicities at 2 4 and 5 4 years and that of annual and monsoon rainfall at 2 4 2 7 and 5 2 years corroborates the rainfall control on the band thickness variability of the niuean stalagmites phase lags and amplitude discrepancies between rainfall and stalagmite records are attributed to the impact of torrential rains accompanying cyclones that occasionally struck the island the excellent agreement between the periodicities prominent in the niuean stalagmites and those typical of the enso phenomenon 2 4 and 4 3 6 0 years suggests the latter exerts a dominant control on the stalagmite growth rates via rainfall variability interdecadal periodicities at 10 14 and 30 years contained in the niuean stalagmites spectral power are tentatively attributed to enso phase changes driven by the inter decadal pacific oscillation ipo the niuean stalagmites exhibiting relative fast growth rates and prominent layered sequences hold promise to provide continuous century to millennium long high resolution atmospheric records of enso history that will complement and expand the sea surface temperature records archived in tropical pacific corals

regional o sr and pb isotope relationships in late cenozoic calc alkaline lavas of the andean cordillera quaternary recent volcanism in the andes has occurred in three regions 45 33 s 28 16 s and 2 s 5 n each of which has a distinct plate tectonic setting and contains volcanic suites with different chemical and isotopic characteristics isotope ratios of o and sr are lowest and those of pb least variable in the southern volcanic zone svz where medium k lavas have isotopic characteristics equivalent to volcanics from intraoceanic arcs where continental crust is absent the svz lavas were probably derived from an asthenospheric mantle source above a shallow benioff zone parental basaltic magmas rose largely unmodified through thin continental crust where differentiation occurred by low pressure crystal fractionation without concurrent modification of isotopic composition the slight enrichment of 206 pb in the northern volcanic zone nvz where the crust is thin and the benioff zone deep suggests a greater subduction zone component for parental medium k magmas the slight 18 o enrichment suggests a small amount of lower crustal interaction isotope ratios of o and sr are highest and those of pb most variable in the central volcanic zone cvz parental magmas in the cvz were probably generated within the same mantle source region as those in the svz and nvz subsequently during transit through the exceptionally thick continental crust of the central andes high k magmas were produced by a combination of bulk contamination in the lower crust and later low pressure fractional crystallization assimilation processes in the upper crust which altered both chemical and isotopic compositions

testing theoretically predicted stalagmite growth rate with recent annually laminated samples implications for past stalagmite deposition annually laminated stalagmites deposited over the last 30 160 years are analysed to determine their growth rate three natural and artificial cave sites in england france and belgium were chosen for their wide range of variability in growth rate determining variables and multiple samples were taken from each site the annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave void opening 14c analyses or by using dated event horizons measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction a good agreement is observed between empirical observations and theoretical predictions although two complicating factors variations in calcite porosity and seasonal cessation of the water supply to the samples both affect the growth rate implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed

the mineral chemistry of new titanates from the jagersfontein kimberlite south africa implications for metasomatism in the upper mantle new members of the crichtonite mineral series are described in which k ba ca and ree are in significant concentrations 5 wt oxides filling the a formula position in am21o38 these phases are chromium 16 wt cr2o3 titanates 58 wt tio2 enriched in zro2 5 wt and constitute a mineral repository for refractory and large ion lithophile elements in the upper mantle the mineral senes coexists with mg cr ilmenite nb cr rutile and ca cr nbzr armalcolite that have equally unusual chemistries kimberlitic crichtonites are depleted in the intermediate lanthanides but highly enriched in lree and hree with chondrite normalized abundances of 103 to 105 crichtonite armalcolite and nb cr rutile occupy a compositional range in tio2 contents bridging the gap between ilmenite and rutile two minerals having a widespread distribution in kimberlites and mantle derived nodule suites in common with other associations and based on similarities in mineral chemistry it is concluded that these minerals formed at p 20 30 kb 900 1100 c by reaction of peridotite with metasomatizing fluids kimberlitic crichtonite may be expressed as spinel cr ferropseudobrookite and armalcolite is equivalent to cr geikielite rutile in the system femg tio2 cr2o3 this system contains a number of cr ti compounds not found as minerals but it is proposed that the ubiquitous occurrence of ilmenite intergrowths in kimberlitic rutile results from decomposition of high pressure pbo2 type crystallographic shear structures the new minerals have exotic chemistries and the high k affinities broaden the scope for the origin of alkalic rocks the generation of highly potassic magmas in the upper mantle and suggest that alkali metasomatism may be pervasive

mantle convection and early crustal evolution abstract the existence of peridotitic komatiites in the archaean suggests that the archaean mantle was significantly hotter than the modern mantle this evidence is contradicted by estimates of archaean continental geothermal gradients based on the pressure and temperature recorded in metamorphic rocks which suggest that there is no marked difference between archaean and modern continental geothermal gradients numerical modelling shows that small changes in the mantle temperature can have an important influence on convection if the average temperature of the upper mantle is increased by 200 c convection within the mantle becomes chaotic and an upper mantle partial melt zone encircles the globe the crust formed during this period will be komatiitic in composition but will be unstable and will be mixed back into the mantle by subduction later when the mantle temperature falls to 100 c above its present level the upper mantle partial melt zone contracts away from subduction areas it is suggested that the first primitive felsic magmas were generated at subduction zones the appearance of these magmas at 3 8 ga permitted the formation of buoyant continents and eventually led to crustal thickening as a consequence of this thickening the proto continents consisting of a bimodal suite of basalts and sodic granodiorites contained two types of latent energy 1 radioactive energy held in elements such as th k and u and 2 potential energy resulting from the elevation of the continents above sea level the potential energy of the continents led to sedimentation the increase in the rate of sedimentation during the archaean resulted from increased crustal buoyancy at the same time heat released by radioactive elements in the deep crust built up under the insulating blanket of the upper crust this caused a major metamorphic metasomatic and crustal melting event which produced the potassic granites of the late archaean once the radioactive elements had been removed from the lower crust that region of the continent become tectonically stable the proterozoic shelf sediments were deposited at the margins of these stable cratons convection models of the archaean mantle show hot diapirs rising from the boundary layer above the core mantle interface we suggest that these diapirs began to melt at a depth of 450 km giving rise to komatiitic magmas this model requires the average temperature of the archaean upper mantle to be 100 c above that of the modern mantle the similarity between archaean and modern continental geothermal gradients can be explained if archaean continents formed above subduction zones raising the temperature of the archaean mantle by 100 c 1 halves the thickness of the oceanic lithosphere 2 increases the oceanic geothermal gradient at the mid point of a convection cell 3 decreases the viscosity of the mantle by at least an order of magnitude the combination of these effects produces a marked decrease in the strength of the archaean lithosphere and mantle thus the form of archaean tectonics can be expected to have been very different from modern tectonics

a fifty year climatic signal in three holocene stalagmite records from mato grosso brazil abstract three stalagmites were collected in the perolas cave 150 km nw of cuiaba mato grosso brazil in order to reconstruct the climate history of the surrounding region these stalagmites were similarly formed by stacking of thousands of calcitic pairs of laminae microphotographs of polished thin sections were used to count the laminae pairs and measure their width a reasonable fit was found between the counting results and u th and 14c geochronological data proving that these pairs are annually deposited and correlations were also found between the annual growth rate of the stalagmites and the annual water excess in the perolas region proving that the former parameter could be used as a climatic proxy three files of climatic proxy data covering 256 years were thus obtained and statistically treated to restore the historical fluctuations of the climate apart from well documented periodicities a still poorly known but very strong half century climatic oscillation appeared in the results

teleseismic estimates of the energy radiated by shallow earthquakes the energy flux contained in the p wave groups p pp sp or the s wave groups s ps ss radiated by a shallow earthquake is modeled assuming that the energy flux in the direct and depth phases adds incoherently by defining generalized radiation patterns which incorporate this neutral interference the wave groups are analyzed as though they were comprised of a single phase measurements of the energy flux in the wave groups are corrected in the frequency domain for both the body wave attenuation and the frequency band of the recording the corrected measurements are then used to estimate the seismic energy radiated by the earthquake this analysis is applied to digital recordings of the teleseismic wave groups radiated by the may 2 1983 coalinga california earthquake and the october 28 1983 borah peak idaho earthquake for the coalinga earthquake an estimate of es 1 6 0 4 1021 dyn cm was determined from six p wave groups while the sh wave group recorded at station col returned an estimate of es 1 2 1021 dyn cm for the borah peak earthquake an estimate ofes 3 2 0 5 1021 dyn cm was determined from seven p wave groups the distribution of the isoseismals for the borah peak earthquake indicate that the energy radiated by this event was focussed to the northwest in the direction of rupture propagation correcting the teleseismic estimate for this focussing gives es 3 6 0 5 1021 dyn cm combining these estimates of the radiated energy with broad band estimates of the seismic moment yields estimates of the apparent stress of 17 and 7 bars for the coalinga and the borah peak earthquakes respectively

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

geochemical records of qionghai lake sediments in southwestern china linked to late quaternary climate changes abstract knowledge of the chemical weathering history under the subtropical monsoonal climate will help to resolve the discrepancies regarding how climate conditions constrain chemical weathering major element and rare earth element ree compositions of the qionghai lake sediments in sichuan province southwestern china were analyzed aiming to provide information on sediment source discrimination and history of chemical weathering intensities and its responses to variations of indian summer monsoon ism and paleoclimate conditions as revealed by the a cn k diagram and other provenance proxies including tio2 zr ratio th sc vs zr sc and la th vs hf diagrams as well as the ree characteristics the source of qionghai lake sediments was felsic rocks additionally these sediments were subjected to small changes in provenance sedimentary sorting and recycling and weak diagenesis after deposition and or metasomatism indicating original signals were maintained on the intensity of chemical weathering of source area the chemical weathering intensities inferred from cia chemical index of alteration values have significantly fluctuated over the past 28 kyr reflecting three stages of paleoclimate evolution which is consistent with grain size characteristics carbonate contents low frequency magnetic susceptibilities toc and biomarker proxy paq the cia values changed significantly during the typical warm and cold climate events including the last glacial maximum heinrich 1 cold event younger dryas and holocene climatic optimum and generally exhibited an increasing trend in amplitude correspondingly in concert with the climate shifting from cold and dry to warm and humid conditions generally warm and humid climate conditions suggest enhanced chemical weathering intensity whereas weak chemical weathering denotes cold and dry climate in the ism region in addition sequential variations of the cia values during the past 28 kyr may reflect changing chemical weathering processes in responses to the varying intensities of indian summer monsoon and the climate conditions forced by the northern hemisphere solar insolation

pb and nd isotope constraints on the origin of high mg and tholeiitic amphibolites kolar schist belt south india the late archean north south trending kolar schist belt in south india 4 km wide by 80 km long is thought to be a suture between two gneiss terranes krogstad et al 1989 within this volcanics dominated belt are recognized both tholeiitic and high mg komatiitic and picritic amphibolites which make up some 70 and 5 respectively of the exposed outcrops a massive tholeiitic amphibolite separates the belt into western and eastern parts a pb pb whole rock age of 2732 155 ma on samples from a single outcrop of massive tholeiite is a minimum age for this rock samples of this rock have nd values at 2700 ma that range between 3 8 and 6 8 1 initial 238u 204pb of 7 5 and k1 initial 232th 238u of about 4 two different types of high mg amphibolites are recognized from the western part of the belt a picritic or p type and a komatiitic or k type the p type have highly variable ce al ratios all greater than chondritic nd yb ratios greater than chondritic nd at 2700 ma of 1 5 to 8 and pb isotope compositions variable in 207pb 204pb with 1 of about 8 0 and k1 of about 4 the trace element data suggest that the light ree enrichment is a character of the mantle source and is not due to residual garnet the k type amphibolites have near chondritic ce al and nd yb ratios nd at 2700 ma of 1 5 to 8 and 1 of about 8 and k1 of about 4 although the p type is light ree enriched compared to the k type both types have similar ce nd ratios as well as initial pb and nd isotopes if the 2696 136 ma age for the sm nd isochron which includes both types of high mg amphibolite has any significance it dates the time of light ree enrichment of the mantle source for the p type komatiitic amphibolites the high mg amphibolites in the eastern part of the belt are light ree enriched have pb isotopic compositions that are variable in 207pb 204pb with a 1 about 8 5 and nd at 2700 ma of 1 8 to 4 5 hydrothermal fluids associated with metamorphism and shearing prior to about 2400 ma ago were responsible for the introduction of gold quartz carbonate veins into the kolar schist belt the pb isotope composition of galena in these veins suggests that these fluids may have also introduced extraneous pb from adjacent older granitoid gneisses into the amphibolites which could be responsible for the variability in the 207pb 204pb ratios of the samples this extraneous pb probably is not responsible for the distinct pb isotope character of each type of amphibolite

gold mineralisation and alteration of penakacherla schist belt india constraints on archaean subduction and fluid processes abstract in the dharwar craton southern india gold deposits are found mostly along the six arcuate shear zones passing through late archaean greenstone belts 2 7 ga one such shear zone complex extends for about 400 km within and along the ramagiri hungund schist belt the penakacherla sector of this shear zone is excellently exposed enabling a detailed investigation of synorogenic gold mineralisation and its relationship to associated hydrothermal alteration metamorphism and deformation under ne sw compression associated with archaean subduction processes converted mafic volcanic rocks into amphibolites and intermediate to felsic volcanic rocks into quartz mica schists continued compression generated a 50 100 m wide shear zone complex consisting of mafic phyllonites advection of hydrothermal fluids through this shear zone and reaction between fluids and the mafic phyllonites resulted in a silicified k metasomatic assemblage mainly consisting of chlorite amphibole k mica plagioclase ankerite quartz fe oxides pyrite chalcopyrite and arsenopyrite networks of quartz and carbonate veinlets a few millimeters to a few centimeters thick formed along the foliation planes giving rise to microscopic alteration envelope in which individual veinlet systems are merged into one another to form a composite alteration system gold is found within these quartz veinlets mafic phyllonites and at their mutual contacts hydrothermal fluids have modified the primary major minor trace and lree compositions of host rocks such that their mutual behaviour became non systematic some hfse and hree also show minor mobility but the overall ree pattern generally resembles that of the precursor mafic volcanic rocks mass and volume loss gain by si and ca has made significant impact on al ti and zr abundances which are generally immobile during hydrothermal alteration however element pairs such as zr hf v sc and nb ta maintain primary inter element ratios although their absolute abundances are drastically diluted similarly ree in highly silicified and carbonatised samples are reduced but patterns remain similar to those of relatively least altered mafic phyllonites with la n yb n between 1 and 3 in some samples lree enrichment is observed elevating in la n yb n from 3 to 11 pathfinder elements and base metals such as as cd cu pb zn and sb have been added along with the au and ag 13 c of carbon varies from 16 to 21 suggesting a biogenic origin whereas coexisting pyrite 34 s ranges from 1 to 3 pointing towards the involvement of magmatic or average crustal sulphur overall concentrations of k rb sr ba nb ta ti cs cr co v y and sc and many of the ratios such as k rb la sc la yb indicate that metamorphism devolatilisation and dehydration of an oceanic subducting slab might have partially contributed the mineralising fluids and generated the alteration assemblage observed in the host rocks fluid sources were mantle and greenstone belt dehydration and devolatilisation generating observed compositional and alteration diversity

origins of stratiform and stratabound fe cu zn horizons in the lower proterozoic moran lake group labrador central mineral belt zn cu and fe are concentrated as stratiform and stratabound sulphide rich beds in the lower proterozoic warren creek formation moran lake group central labrador upper member sedimentary rocks have a hydrothermal like fe enrichment but a dominantly hydrogenous signature as indicated by high al2o3 relative to sio2 and high al and fe relative to mn the upper member shales and sulphide rich beds were deposited as fe rich pelagic sediments the paucity of mn and abundance of fe in typical shale samples and lack of cu pb and zn fractionation in stratiform massive sulphide beds that contain up to 4702 ppm zn 533 ppm cu and 15 ppm pb suggest that deposition occurred in restricted brine pools i e cu and zn were precipitated rapidly and were not fractionated stratabound sphalerite mineralization containing 3 7 zn and 121 ppm cu but no pb was deposited in a porous lithology at the top of the warren creek formation and represents a unique style of metal concentration the stratiform deposits proba

petrogenesis and source characteristics of metatholeiites from the archean ramagiri schist belt eastern part of dharwar craton india the n s trending 2 4 km wide ramagiri schist belt is made up of three blocks dominated by metavolcanic rocks separated and surrounded by granitic rocks of distinct characteristics the metavolcanic rocks are tholeiitic in composition and are very similar in their major element composition as well as in their abundances of some trace elements however the rare earth elements ree require distinct sources the rocks of the amphibolite facies eastern block have lree depleted ree patterns ce yb 0 7 0 9 requiring derivation from depleted mantle like sources the greenschist facies metatholeiitic rocks of the central block have lree enriched ree patterns ce yb 3 6 reflecting the nature of their source s the nd isotopic data require that the lree enriched nature could not have been attained significantly prior to its melting the fine grained upper greenschist facies metatholeiites of the western block have flat to slightly lree depleted patterns ce yb 0 8 0 95 minor fractional crystallization of rock forming minerals may relate a few samples to each other among samples from each of the three blocks different extents of partial melting of distinct mantle sources have played a dominant role in the generation of the parent magmas to the central versus eastern and western block metatholeiites

the influence of the de vries 200 year solar cycle on climate variations results from the central asian mountains and their global link long term climatic changes related to solar forcing were examined using millennium scale palaeoclimatic reconstructions from the central asian mountain region i e summer temperature records for the tien shan mountains and precipitation records for the tibetan plateau the reconstructions were based on juniper tree ring width records i e juniperus turkestanica for the tien shan and sabina przewalskii for the tibetan plateau the data were processed using spectral and wavelet analysis and filtered in the frequency range related to major solar activity periodicities the results obtained for various tree ring chronologies indicate palaeoclimatic oscillations in the range of the de vries similar to 210 year solar cycles through the last millennium the quasi 200 year variations revealed in the palaeoclimatic reconstructions correlate well r 2 0 58 0 94 with solar activity variations delta c 14 variations the quasi 200 year climatic variations have also been detected in climate linked processes in asia europe north and south america australia and the arctic and antarctica the results obtained point to a pronounced influence of solar activity on global climatic processes analysis has shown that climate response to the long term global solar forcing has a regional character an appreciable delay in the climate response to the solar signal can occur up to 150 years in addition the sign of the climate response can differ from the solar signal sign the climate response to long term solar activity variations from 10s to 1000s years manifests itself in different climatic parameters such as temperature precipitation and atmospheric and oceanic circulation the climate response to the de vries cycle has been found to occur not only during the last millennia but also in earlier epochs up to hundreds of millions years ago c 2007 elsevier b v all rights reserved

mafic and ultrapotassic rocks from the canyon domain central grenville province geochemistry and tectonic implications the canyon domain and the banded complex in the manicouagan area of the grenville province preserve a re cord of magmatic activity from 1 4 to 1 ga this study focuses on 1 4 1 2 ga mafic rocks and 1 ga ultrapotassic dykes geochemistry and sm nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the laurentian margin to the grenvillian orogeny in the manicouagan area the mafic rocks include layers inferred to represent flows homogeneous bodies in mafic migma tite and deformed dykes all of which were recrystallized under granulite facies conditions during the grenvillian orogeny in spite of the complexities inherent in these deformed and metamorphosed mafic rocks we were able to recognize suites with distinctive geochemical and isotopic signatures integration of this data along with available ages is consistent with a 1 4 ga continental arc cut by 1 2 ga non arc basalts derived from depleted asthenospheric mantle with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment the 1 ga ultrapotassic dykes postdate the grenvillian metamorphism they are extremely enriched in incompatible elements have negative nb anomalies relatively unradiogenic sr isotopic compositions initial 87 sr 86 sr 0 7040 and nd 3t o 15 some dykes have composi tional characteristics consistent with derivation from the mantle ruling out crustal contamination as a major process in their petrogenesis the most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric man tle with thermal input from the asthenosphere in association with post orogenic delamination

tectonic stress field of china inferred from a large number of small earthquakes mean principal tress axes were inferred for china using 9621 p wave first motion polarity readings from 5054 small earthquakes 1 ml 5 the area studied was divided into 76 subregions the mean p compressive b intermediate and t relatively tensional axes corresponding to composite focal mechanism solutions of multiple earthquakes for each subregion were determined by a grid test to all possible orientations of the p b and t axes with a step of 5 or 10 in order to get a relatively homogeneous sampling in space we have avoided using the readings from spatially and temporally clustered earthquakes we have rechecked most of the polarity readings by inspection of original seismograms the focal mechanism solutions of large m 6 individual earthquakes are also presented for comparison the results indicate the existence of an overall radial pattern of the present day maximum horizontal stress orientations throughout the continental area of china this pattern is thought to be closely related to indentor models of continental collision between the indian ocean and the eurasian plate

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

solar influence and hydrological variability during the holocene from a speleothem annual record molinos cave ne spain this study is a contribution to the ctm2013 48639 c2 1 r opera cgl2009 10455 and hidropast cgl2010 16376 projects spanish government european regional development fund the uz2014 cie 04 project university of zaragoza the ga lc 030 2011 project aragon government la caixa and the e 28 and s 97 research groups aragon government

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

fe rich archean tholeiites derived from melt enriched mantle sources evidence from the kolar schist belt south india tholeiitic amphibolites in the circa 2700 ma kolar schist belt south india are intimately interlayered with minor komatiitic amphibolites the tholeiitic amphibolites which are similar to other archean tholeiitic rocks are fe enriched with feo total varying from about 9 to 13 wt olivine and plagioclase have similar calculated saturation surface temperatures ranging from about 1125 to 1225 c on many trace and major element plots there is a distinct compositional gap between the komatiitic and tholeiitic amphibolites that cannot be explained by density filtering because the calculated melt densities for the komatiitic 2 73 2 79 and tholeiitic 2 61 2 72 amphibolites nearly overlap the rare earth element ree patterns for the tholeiites are flatter and have lower light ree abundances than those for many of the associated komatiitic rocks modeling of major and trace element data suggests that the tholeiitic rocks are not related to the komatiitic rocks by 1 differentiation of magmas of

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

uranium thorium systematics of two canadian coals abstract a detailed study of u th distribution in two lower cretaceous coals in canada shows that for these coals formed in a continental fluvial and deltaic environment with no marine influence the u contents are in the range 0 07 7 5 ppm with th in the range 0 3 11 0 ppm average th u ratios are near 2 which indicates slight uranium enrichment the environments of the two coals show different degrees of weathering montmorillonite illite and kaolin gibbsite and u values are lowest in the more weathered environment in sedimentary profiles associated with the coals the maximum uranium values are not in the coals but in carbonaceoss clay sediments above and below coal seams uranium distribution patterns can be correlated cith ni cu rb pb sr and zr indicating contributions from heavy minerals plus more mobile species possibly simple organic compounds which are adsorbed or bonded onto claysor organic matter

little ice age climate near beijing china inferred from historical and stalagmite records four data sets yield information about holocene climatic change in china at different scales of space and time a 120 yr ground temperature and precipitation measurements covering eastern china b two noaa 10 yr 850 hpa wind records that highlight features of data set a c an 1100 year record of annual calcite accumulation on a stalagmite near beijing and d lamb type average wetness and temperature data from chinese historical records back to a d 1470 and 1450 respectively dry wet fluctuations and cold warm oscillations are inferred using the long term stalagmite thickness series quasi 70 140 450 and 750 yr oscillations have been detected using a wavelet transform technique a phase relationship between temperature and precipitation oscillations has been identified based on modern observations and historical records in northern china relatively lower temperatures correlate with periods when precipitation shifted from above to below normal three colder periods during the little ice age lia in china are inferred centered in the late 14th century 750 yr oscillation the early 17th century 450 yr and the 19th century 140 yr the latest cool period 1950s 1970s is found at the 70 yr oscillation interdecadal drought flood and cold warm differences are explained using modern circulation patterns lia climate in china was likely controlled by east asian monsoon circulation anomalies that were affected by variations in continent ocean thermal contrast

geochemistry of the neoarchaean high mg basalts boninites and adakites from the kushtagi hungund greenstone belt of the eastern dharwar craton edc implications for the tectonic setting abstract volcanic rocks of the kushtagi hungund greenstone belt from the eastern dharwar craton edc show extreme diversity due to the presence of high mg high fe high mg fe basalts high mg dacites and andesites boninitic affinities and sodic plagioclase quartz rich felsic rocks adakites with na2o 4 6 wt the adakites drummond and defant 1990 martin 1999 and high mg dacites andesites are being reported for the first time from greenstone belts of the dharwar craton trace elements in these different types of volcanic rocks have distinct characteristics for example the basalts have 1 al2o3 tio2 16 pm value of 17 2 la yb n 1 3 3 low order negative anomalies of nb nb zr zr hf hf and ti ti 4 zr nb 4 10 and 5 ce nb 3 4 two samples of andesites having mg enrichment and al2o3 tio2 ratios of 31 35 are interpreted to have boninitic affinities other dacites and andesites are characterized by 1 high mg 8 10 wt 2 high al2o3 tio2 22 27 3 zr nb 8 14 4 la yb n 2 7 5 negative nb nb zr zr hf hf and ti ti anomalies and 6 sc lu 67 172 the adakites are characterized by 1 a narrow range of sio2 67 70 wt 2 enriched na2o 4 6 wt with very high na2o k2o 2 5 7 7 3 low mg 0 38 0 48 4 high la yb n 13 31 with fractionated patterns no eu anomaly and gd yb n 2 4 5 very high al2o3 tio2 50 80 and 6 enriched ni cr and co total 50 ppm these adakites resemble 3 0 ga tonalite trondhjemite gneisses of the dharwar craton which are interpreted as products of partial melting of the basaltic slab the available data suggests that partial melting of the different mantle and slab sources generated this collage of compositionally different rocks within an island arc setting

the f zone a negative velocity gradient near the inner outer core boundary might be adequately explained by the existence of heat producing elements in the region geochemically there should be about one third to more than a half of the earth s total resources of heat producing elements present below the upper mantle which is also consistent with observations of heat flux at the earth s surface the results of high pressure experiments further suggests that the heat producing elements would exist as dioxides which are chemically incompatible with the major mantle silicates under the temperature and pressure conditions prevailing in the lower mantle the great density of these heat producing dioxides probably greater than the liquid iron nickel core may cause them to be transported to the inner outer core boundary the f zone

trace element variation in speleothem aragonite potential for palaeoenvironmental reconstruction trace element variation in annually laminated stalagmites has the potential to record long term high resolution palaeoclimatic data provided both 1 the relationship between trace element content in the carbonate and the climate and 2 the mechanism of stalagmite growth are understood here we report a secondary ion mass spectrometry sims study of an aragonitic speleothem t7 from cold air cave southern africa which achieves small m spatial resolution and ppm precision t7 has a series of fine visible laminae believed to be annual to subannual this article establishes 1 the usefulness of sims in analyzing speleothem aragonite at the spatial resolution and precision relevant to climatic studies 2 the distribution of trace elements in aragonite on micron scales and their relationship to models for speleothem growth and 3 the potential of aragonite speleothems to encode climatic data at subannual resolution complex reproducible oscillations in sr ca and ba ca are observed parallel to the growth direction of the speleothem however in addition to this variability we observe trace element oscillations perpendicular to the growth direction and infer that aragonite crystallites in the speleothem are laterally as well as vertically zoned stepscans parallel to the growth direction demonstrate complex zoning patterns from which simple climatic data are difficult to extract due to small scale lateral heterogeneity in the aragonite however time series analysis of the whole data set reveals regular cycles in sr ca and ba ca at a scale that matches the magnitude of the visible laminae on this basis it appears that within the complex geochemical variability there resides a regular environmental control possibly variation in water throughput hence rainfall

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

multi stage crustal growth and neoarchean geodynamics in the eastern dharwar craton southern india abstract the dharwar craton is a composite archean cratonic collage that preserves important records of crustal evolution on the early earth here we present results from a multidisciplinary study involving field investigations petrology zircon shrimp u pb geochronology with in situ hf isotope analyses and whole rock geochemistry including nd isotope data on migmatitic ttg tonalite trondhjemite granodiorite gneisses dark grey banded gneisses calc alkaline and anatectic granitoids together with synplutonic mafic dykes along a wide northwest southeast corridor forming a wide time window in the central and eastern blocks of the dharwar craton the dark grey banded gneisses are transitional between ttgs and calc alkaline granitoids and are referred to as transitional ttgs whereas the calc alkaline granitoids show sanukitoid affinity our zircon u pb data together with published results reveal four major periods of crustal growth ca 3360 3200 ma 3000 2960 ma 2700 2600 ma and 2570 2520 ma in this region the first two periods correspond to ttg generation and accretion that is confined to the western part of the corridor whereas widespread 2670 2600 ma transitional ttg together with a major outburst of 2570 2520 ma juvenile calc alkaline magmatism of sanukitoid affinity contributed to peak continental growth the transitional ttgs were preceded by greenstone volcanism between 2746 ma and 2700 ma whereas the calc alkaline magmatism was contemporaneous with 2570 2545 ma felsic volcanism the terminal stage of all four major accretion events was marked by thermal events reflected by amphibolite to granulite facies metamorphism at ca 3200 ma 2960 ma 2620 ma and 2520 ma elemental ratios la yb n sr y nb ta hf sm and hf nd isotope data suggest that the magmatic protoliths of the ttgs emplaced at different time periods formed by melting of thickened oceanic arc crust at different depths with plagioclase amphibole garnet titanite ilmenite in the source residue whereas the elemental ba sr la yb n sr y nb ta hf sm and hf nd isotope data ehf t 0 67 to 5 61 end t 0 52 to 4 23 of the transitional ttgs suggest that their protoliths formed by melting of composite sources involving mantle and overlying arc crust with amphibole garnet clinopyroxene plagioclase ilmenite in the residue the highly incompatible and compatible element contents ree k ba sr mg ni cr together with hf and nd isotope data ehf t 4 5 to 3 2 end t 1 93 to 1 26 of the sanukitoids and synplutonic dykes suggest their derivation from enriched mantle reservoirs with minor crustal contamination field elemental and isotope data ehf t 4 3 to 15 0 end t 0 5 to 7 0 of the anatectic granites suggest their derivation through reworking of ancient as well as newly formed juvenile crust secular increase in incompatible as well as compatible element contents in the transitional ttgs to sanukitoids imply progressive enrichment of neoarchean mantle reservoirs possibly through melting of continent derived detritus in a subduction zone setting resulting in the establishment of a sizable continental mass by 2700 ma which in turn is linked to the evolving earth the neoarchean geodynamic evolution is attributed to westward convergence of hot oceanic lithosphere with continued convergence resulted in the assembly of micro blocks with eventual slab break off leading to asthenosphere upwelling caused extensive mantle melting and hot juvenile magma additions to the crust this led to lateral flow of hot ductile crust and 3d mass distribution and formation of an orogenic plateaux with subdued topography as indicated by strain fabric data and strong seismic reflectivity along an e w crustal profile in the central and eastern blocks of the dharwar craton

plate tectonics 2 5 billion years ago evidence at kolar south india the archean kolar schist belt south india is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accrted amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics sugesting that their volcanic protoliths were derived from dint mantle sources the amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago ma along a zone marked by the kolar schist belt this history of accretion of discrete crustal terranes resembles those of phanerozoic convergent margins and thus suggests that plate tectonics operated on earth by 2500 ma

a 3 1 billion year old marble and the 87sr 86sr of late archean seawater a marble band in the 2 75 gyr old ramagiri schist belt in the dharwar craton of south india gave a pb pb age of 3 075 0 095 gyr the geochemical data including high sr and low ba and mn indicate seawater origin for the parent rock and that there was insignificant geochemical exchange between the marble and the surrounding rocks the calculated initial nd isotopic composition and 1 indicate an older continental crustal source for the nd and pb the initial 87sr 86sr of the marble is 0 70128 which is higher than the calculated mantle value at 3 ga although pre 3 gyr old marine carbonate rocks are thought to be buffered by mantle sr the ramagiri marble contains evolved crustal sr despite this the marble has the lowest measured 87sr 86sr among carbonates and represents one of the least radiogenic periods in seawater sr isotope composition

metamorphic response and crustal architecture in a classic collisional orogen the damara belt namibia abstract the damara belt is a well exposed mid crustal section through a collisional orogen of cambrian age that closed the khomas ocean basin between passive margins on the congo and kalahari cratons collision resulted in a bi vergent orogen with a distinct paired metamorphic pattern of foreland vergent high p low t orogenic margins and a broad high grade low p high t orogen core spatial and temporal patterns of the metamorphic response to collision have been characterized for all parts of the belt using a large dataset n 240 of internally consistent quantitative pt determinations evolution of mineral parageneses and semi quantitative p t paths metamorphic mapping and quantitative metamorphic field gradients integration with deformation history structural profiles metamorphic chronology magmatic history and stratigraphy constrains a dynamic model of crustal architecture during peak metamorphic events the pattern of zonal metamorphic response is demarcated by three major metamorphic discontinuities md with steep pressure gradients inferring crustal scale structures that accommodated lateral exhumation of crustal wedges discontinuities are confirmed by deformation features in the field and metamorphic mineral growth indicates that vertical flattening at the peak of metamorphism progressing through ductile to brittle extensional structures crustal wedges along the orogenic margins experienced steep clockwise p t paths with peak pt conditions terminated by isothermal decompression during rapid exhumation in isostatic response to deep burial metamorphic chronology and over printing metamorphic fabrics constrain a sequence of foreland propagating out wedging of crustal thrust wedges that resulted in telescoping of the orogenic margins peak metamorphism at a geothermal gradient of 20 25 c km and 8 9 kb in the southern zone wedge i was attained between 517 530 ma followed by south directed out wedging at the uis pass suture accommodated by relative extension md1 at high structural levels near the boundary with the high grade orogen core out wedging of the southern zone further buried the southern margin zone wedge ii in the footwall below the uis pass suture peak metamorphism at 17 c km and 9 5 11 5 kb in the southern margin zone was attained at 517 4 ma and followed by out wedging on basal thrusts accommodated by vertical flattening and extensional reactivation of the uis pass suture md2 peak metamorphism at 17 c km and 10 5 kb in a high p low t crustal wedge in the northern margin wedge iii occurred at 510 4 ma peak metamorphism in this wedge was terminated by isothermal decompression during north directed thrusting accommodated by extension at higher structural levels near the high grade orogen core md3 granulite facies metamorphism in the high grade orogen core which formed the upper plate to the deeper thrust wedges occurred at significantly lower pressures 4 3 6 0 kb higher t depth ratios 38 47 c km and low p t clockwise p t paths indicating only moderate burial and protracted high grade conditions metamorphic chronology confirms high grade conditions 540 505 ma persisted beyond isostatic adjustment of the high p low t orogenic margins high heat flow conditions and long thermal lag are best explained by lithospheric breakoff during collision in contrast to the high p low t margins that experienced lateral exhumation in a convergent system the high grade orogen core was exhumed vertically as a broad core complex during extensional collapse of the orogen peak metamorphic conditions in the central part of the orogen core record higher pressures than marginal lower grade zones to both the north and south indicating vertical exhumation as a broad massif this post peak vertical exhumation of the central core occurred after 505 ma was accommodated by brittle extensional detachments at high stratigraphic levels with km scale omission of crustal section

rare earth elements as reactive tracers of biogeochemical weathering in forested rhyolitic terrain article rareearthelements rees were evaluatedaspotentialtracers of biogeochemicalweathering atpedon hillslope and catchment scales in the jemez river basin critical zone observatory jrb czo valles caldera national pre serve nm usa we investigated time series of ree patterns in precipitation soil pore water groundwater and stream water and related these data to ree composition of soil rock and atmospheric dust ree signatures in stream waters are dynamic reflecting processes that occur along hydrologic flowpaths during transport to the stream including organic matter complexation primary and secondary mineral weathering water soil bedrock interaction and atmospheric deposition strong compositional similarities for the ree between soil waters and stream waters during the initial snowmelt are consistent with shallow subsurface flows to streams most bio

crustal structure of the paleozoic kunlun orogeny from an active source seismic profile between moba and guide in east tibet china abstract we herein present a new seismic refraction wide angle reflection profile that crosses the songpan ganzi terrane the animaqing suture zone and the eastern kunlun mountains comprised of the south kunlun and middle kunlun blocks separated by the middle kunlun fault the profile is 380 km long and extends from moba to guide in eastern tibet the crustal thickness is about 62 km under the songpan ganzi terrane 62 64 km under the south kunlun and 60 km under the middle kunlun block the songpan ganzi flysch seems to be present up to a depth of 15 km south of the animaqing suture zone and up to a depth of 10 km in the middle kunlun block with thicknesses elsewhere that depend on assumptions about the likely lithologies the profile exhibits clear lateral variations both in the upper and lower crust which are indicative of different crustal blocks juxtaposed by the kunlun fault system whether or not the songpan ganzi flysch was originally deposited on oceanic crust at the longitude of our profile 100 e it is now underlain by continental crust and the presence of continental crust beneath the songpan ganzi terrane and of a continental arc under the south kunlun block suggest paleozoic continent continent arc collision in the eastern kunlun mountains comparison of crustal velocity columns from all wide angle seismic profiles across the eastern kunlun mountains indicates a remarkable west to east change in the moho topography across the kunlun fault system 15 20 km moho step at 95 e but only 2 5 km along our profile at 100 e lower crustal thickness of the kunlun terranes is rather uniform about 35 km from 80 95 e which suggests that similar thrust thickening processes have played a role where the qaidam basin abuts the kunlun fault but thins to 20 25 km at 100 e east of the qaidam basin the increased crustal thickness from 93 to 98 e compared to that at 100 e may be due to the differences in the thickness of the crust of the two plates before their collision and or largely achieved by thickening of the lower crust perhaps indicating a crustal flow mechanism operating more strongly in the western region

origin of granites in an archean high grade terrane southern india archean deep level granites in southern india are similar geochemically to young granites from continentalmargin arc systems they exhibit light ree enriched patterns with variable but chiefly positive eu anomalies this is in striking contrast to the negative eu anomalies typical in high level archean granites in addition the deep level granites are relatively enriched in ba and sr and depleted in total ree and high field strength elements hfse one pluton the sankari granite has unusually low contents of ree and hfse most of the deep level granites appear to represent cumulates with variable amounts of trapped liquid and of minor phases resulting from fractional crystallization of a granitic parent such parental granitic magmas can be produced by batch melting of archean tonalite at middle to lower crustal depths the sankari granite requires a tonalitic source depleted in ree and hfse archean tonalites and tonalitic charnockites exhibit original igneous geochemical signatures and their average composition does not show a significant eu anomaly hence they cannot represent the positive eu anomaly complement to the negative eu anomaly high level granites our results suggest that archean deep level granites may represent this complement such granite may form in waterrich zones in the middle or lower crust and be produced in response to dehydration of the lower crust by a rising co2 rich fluid phase

paleoprecipitation record from coral sr ca and δ18o during the mid holocene in the northern south china sea coupled high resolution sr ca and delta o 18 records of a modern and a mid holocene coral from sanya in the southern hainan island northern south china sea scs were reported and the residual delta o 18 delta delta o 18 were calculated to indicate precipitation change in this region unlike other paleoclimate studies this study focused on changes of precipitation time rather than precipitation amount as negative delta delta o 18 peaks in coral generally correspond to peak precipitations or rainy seasons in the surrounding region the time offsets between negative delta delta o 18 peaks and other seasonal indicators such as sea surface temperature sst can well indicate the time of rainy seasons and the precise time offsets can be estimated by the method of cross spectral analysis the results of the modern coral indicate that the variation of the coral delta delta o 18 lags that of the instrumental measured precipitation by about 2 months and about 3 months to the sst derived from coral sr ca ratios this agrees well with the modern observation that the salinity change in the southern coastal regions generally lags that of the precipitation in hianan island by about 2 months and the precipitation change lags about 1 month behind the sst in this region thus coral delta delta o 18 records can be a reliable proxy for the change of rainy seasons in this region the results of the mid holocene coral show about 2 5 months leading of the delta delta o 18 variation ahead of the sst by compensating the approximate 3 months lag of the delta delta o 18 variation behind the sst in modern time the occurrence of rainy seasons during the mid holocene may have advanced about 5 6 months in detail it may start around december and end around april to may with maximum occurring around february therefore rainy seasons mainly occur in winter through early spring during the mid holocene compared with that from may through october in modern times such precipitation patterns appear to agree with the mid holocene pollen records in this region variations of large scale circulation may possibly result in such a different precipitation pattern further studies in particular climate model studies collaborated with meteorologists are required for a better understanding of the mechanism

impact glasses from zhamanshin crater u s s r chemical composition and discussion of origin three silica rich zhamanshinites and one irghizite from the zhamanshin impact crater northern aral area u s s r have been analyzed for up to 40 major minor and trace elements all data point to a clear distinction between these impact glasses and other tektites or impact glasses e g from the australasian strewn field halogens are generally enriched in the irghizites and zhamanshinites when compared to normal splash for tektites with zhamanshinites enriched more than irghizites the same holds also for the alkali metals and a number of other volatile elements like sb and as nickel and cobalt are enriched in the irghizite sample to a considerable degree suggesting meteoritic contamination this view is also supported by gold and selenium data but for quantifications other siderophile elements need to be considered chromium is not a valid indicator of meteoritic contamination because smallamounts of ultra basic igneous material may completely alter the picture the rare earth elements do show a sedimentary pattern consistent with two or three different source materials and a variation which is probably mostly due to dilution with silica rich materials the peak pressure and temperature experienced by the irghizites was lower than for australites or other splash form tektites and even lower for zhamanshinites which is revealed by the content of volatile elements and lesser homogeneity

applications of stalagmite laminae to paleoclimate reconstructions comparison with dendrochronology climatology abstract laminated stalagmites observed in either ultra violet or visible light or recognized via trace elements are now widely recognized as a common deposition form annually laminated stalagmites should be expected in caves which have an overlying climate that has a strong seasonality similar climate zones to where trees grow with distinct annual rings continuous laminated stalagmite chronologies up to several thousand years should be expected where some mixing of stored water occurs such stalagmites can be used to reconstruct climate particularly through variations in lamina width such climate records would be relatively damped by mixing of event water with stored groundwater constraining the amount of high frequency climate signals contained in the stalagmite but relatively long continuous lamina sequences permit the preservation of low frequency centennial scale climate signals this contrasts with numerous tree ring climate records which are frequently limited in preserving multi centennial trends due to the necessary removal of age related noise from relatively short tree segments laminated stalagmites and tree rings should therefore to some degree provide complementary climate information appropriate methods for compiling stalagmite layer chronologies and climatologies are presented

spectral analysis of a 1000 year stalagmite lamina thickness record from shihua cavern beijing china and its climatic significance stalagmite laminae provide a high resolution geological record of climate change in this paper moving spectral analysis is used to analyse a stalagmite lamina thickness record to study climatic v

microbes in caves agents of calcite corrosion and precipitation abstract diverse biogenic and abiogenic processes produce calcite speleothems from a biogenic perspective cave microbes mediate a wide range of destructive and constructive processes that collectively influence the growth of calcite speleothems and their internal fabrics destructive processes include substrate breakdown by dissolution boring and residue micrite production whereas constructive processes include microbe calcification trapping and binding of detrital particles to substrates and microbial induced calcite precipitation biogenesis can be established from 1 the presence of mineralized microbes 2 fabrics such as stromatolite like structures that can be attributed to microbial activity and or 3 geochemical proxies carbon and oxygen isotopes lipid biomarkers considered indicative of microbe activity such criteria have for example been used to demonstrate microbial involvement in the formation of pool fingers stalactites stalagmites cave pisoliths and moonmilk nevertheless absolute proof of microbial biogenesis in calcitic speleothems is commonly difficult because taphonomic processes and or diagenetic processes commonly mask evidence of microbial activity the assumption that calcitic speleothems are abiogenic which has been tacitly assumed in many studies is dangerous as there is clear evidence that microbes thrive in most caves and can directly and indirectly influence calcite precipitation in many different ways

rupture complexity of a moderate sized mb 6 0 earthquake broadband body wave analysis of the north yemen earthquake of 13 december 1982 abstract the occurrence of the north yemen earthquake of 13 december 1982 provides an important opportunity to study source properties of earthquakes in the southern arabian peninsula although moderate in size m b 6 0 this earthquake is the largest to have occurred in the region since the deployment of the global digital seismograph network p waves recorded at teleseismic distances can be obtained from stations of this network and of the graefenberg array that are flat to displacement and velocity in the frequency range from 0 01 to 5 0 hz the broad bandwidth of the data is necessary for deriving a dynamic description of the earthquake as well as the static properties of the source in contrast inversions using only long period data provide much less insight into the complexity of rupture by fitting the displacement pulse shapes with synthetics we find that the yemen earthquake was a complex rupture consisting of two events that occurred about 3 0 sec apart the depth of both hypocenters is estimated to be 7 km the focal mechanisms of the events each have a nodal plane that strikes 340 and dips 60 to the east however the slip directions of the focal mechanisms are in slightly different directions 230 and 300 respectively the total moment of the earthquake is 3 0 10 25 dyne cm with the second event having three times the moment of the initial event by inverting p wave arrival time differences at each station we find the second hypocenter is located 7 5 km from the initial hypocenter in a direction that is nearly colinear with the nnw striking nodal plane of the focal mechanisms of each event the trend of extensional ground cracks in the epicentral region and the predominant strike of composite focal mechanisms of locally recorded aftershocks are also in a nnw direction from the consistency of these observations we infer that the east dipping nnw striking nodal planes are the fault planes the static stress drop of the first and second events are 44 and 31 bars respectively inverting the energy flux in the velocity waveforms we find the energy radiated by the earthquake is 4 8 10 20 dyne cm this implies an average apparent stress of 4 bars at different times during the aftershock sequence seismicity tended to cluster about one or another of two different planes which although having roughly the same strike had conjugate dips one of these planes delineated late in the aftershock sequence coincides with the inferred fault plane for the main shock the complexity of the main shock and of the aftershock sequence suggests that strain accumulated on a system of strongly interdependent faults as the region became critically loaded the effect of a major rupture was to critically stress faults adjacent to the initial nucleation the second event of the main shock represents the rapid release of stress from the fault system while the ensuing aftershock sequence represents the gradual release of stress

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

annually laminated sequences in the internal structure of some belgian stalagmites importance for paleoclimatology abstract fifteen stalagmites from four caves and one sealed tunnel in southern belgium are composed of alternations of annually deposited white porous and dark compact laminae this is demonstrated by comparing the number of laminae with the local history of the site for modern stalagmites and with radioisotopic ages for late glacial and holocene stalagmites annual cyclicity in the internal structure of these speleothems is explained by the highly seasonal variations of the water excess which influences underground water flow comparison between climatic data and modern stalagmites of a closed tunnel shows that growth laminae can record climatic variations 1 there is a good correlation r 0 84 between lamina thickness in a stalagmite and water excess 2 during years with a high water excess dark compact laminae are more developed which makes the speleothem darker vertical successions of several laminae represent microsequences that may have recorded climatic variations with a time resolution of 1 2 year in a late glacial stalagmite successive laminae microsequences form very regular cycles of 11 years separated by a thick darkcompact lamina it is supposed that as for modern stalagmites the thick dark compact lamina corresponds to a period of high water excess hence this 11 year cycle may reflect a climatic cycle

the silurian passamaquoddy bay mafic dyke swarm new brunswick petrogenesis and tectonic implications the volcanic and sedimentary rocks of the passamaquoddy bay pb area of southeastern new brunswick are part of the silurian devonian coastal volcanic belt cvb an extensive belt of bimodal volca

intracrustal recycling and upper crustal evolution a case study from the pan african damara mobile belt central namibia abstract clastic sediments from the pan african damara mobile belt show a wide range in depositional nd nd 0 18 to 1 and several key trace element ratios notably th nd and la sm increase from 0 2 to 0 7 and 4 0 to 8 0 respectively with decreasing nd 0 such trace element ratio nd 0 data arrays are attributed to binary mixing within the sedimentary mass and the data array defined by the damara sediments is consistent with data from other regions the low nd 0 end member is characterised by high th nd th y la sm and hf zr ratios and reflects highly differentiated upper crust dominated by granitoids pb isotope data suggest that the low nd 0 end member also had relatively high time integrated th u 4 by contrast the high nd 0 end member reflects juvenile upper crust but this end member has la sm th nd and hf zr ratios 4 0 0 2 and 0 02 respectively slightly lower than those of taylor and mclennan s preferred model for bulk crust and significantly lower than those of the andesite model intracrustal differentiation is discussed in terms of bulk crust present day average upper crust post archaean shale and a highly differentiated low nd 0 end member trace element ratios which are not significantly fractionated during erosion and sedimentation e g th nd th y and la sm show relatively smooth increases between these reservoirs whereas other trace element ratios which are fractionated both by sedimentary and magmatic processes e g rb sr and rb zr increase dramatically in the more differentiated crustal reservoirs

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

crustal structure across the kunlun fault from passive source seismic profiling in east tibet abstract the crust beneath the northeastern ne tibetan plateau records the imprints on paleozoic kunlun orogen and far field effects from continental collision and convergence between the indian and eurasian plates a passive source seismic profile was conducted across eastern kunlun mountains also called animaqing suture belt receiver function imaging and h k stacking results with this dataset demonstrate that 1 crust slightly thins from about 64 km under the songpan ganzi terrane to about 56 62 km under the qaidam kunlun block and the qilian block 2 moho topography is relatively smooth with gradual undulation beneath east kunlun orogeny belt in contrast to 2 5 km moho step at the akms kunlun fault from previous deep seismic soundings or even no moho topography variation from recent deep seismic reflection profiling 3 the average crustal vp vs ratios display an increasing trend to the kunlun fault belt from 1 76 to 1 85 in songpan ganzi terrane while decreases from 1 83 to 1 65 away from the fault belt in qaidam kunlun block 4 the high vp vs ratio in songpan ganzi terrane is similar to previous results from the profile across longmenshan fault belt the normal to low vp vs ratio distribution in qaidam kunlun block supports the viewpoint that the deformation occurring in ne tibet is predominated by upper crustal thickening and 5 the thickness of non seismogenic layer varies slightly about 40 km between 90 and 100 e then decreases to less than 20 km around 106 e along the kunlun fault the change of the non seismogenic layer thickness is consistent with the change of the lower crust thickness derived from deep seismic sounding the increased crustal thickness may be due to the differences in the thickness of the crust of the two plates before their collision and or largely achieved by thickening of the lower crust perhaps indicating a crust flow mechanism operating more strongly in the western region

petrograph a new software to visualize model and present geochemical data in igneous petrology a new software petrograph has been developed to visualize elaborate and model geochemical data for igneous petrology purposes the software is able to plot data on several different diagrams including a large number of classification and petrotectonic plots petrograph gives the opportunity to handle large geochemical data sets in a single program without the need of passing from one software to the other as usually happens in petrologic data handling along with these basic functions petrograph contains a wide choice of modeling possibilities from major element mass balance calculations to the most common partial melting and magma evolution models based on trace element and isotopic data results and graphs can be exported as vector graphics in publication quality form or they can be copied and pasted within the most common graphics programs for further modifications all these features make petrograph one of the most complete software presently available for igneous petrology research

geodynamic setting of mesothermal gold deposits an association with accretionary tectonic regimes mesothermal gold provinces of phanerozoic age are characteristically associated with regional structures along which allochthonous terranes have been accreted onto continental margins or arcs a recurring sequence of transpressive deformation uplift late kinematic mineralization and shoshonitic magmatism is consistent with thermal reequilibration of tectonically thickened crust mesothermal gold camps in the superior province are spatially associated with large scale structures that have been interpreted as zones of transpressive accretion of individual subprovinces or allochthonous terranes these boundary structures are characterized by the sequence of significant horizontal shortening uplift late kinematic mineralization and shoshonitic lamprophyres and therefore may have the same geodynamic significance as phanerozoic counterparts in this model thermal re equilibration of underplated and subducted oceanic lithosphere and sediments in a transpressive regime over time scales of 10 to 40 m y is a necessary precursor to gold mineralization hydrothermal fluids are released along boundary faults and their splays during uplift the uniform temperature low salinity and mole co2 signify uniform source conditions whereas the variable o c sr and pb isotopic compositions of fluids reflect lithological complexity of the source regions and conduits ou the basis of this model it is suggested that mesothermal lode gold deposits are the product of subduction related crustal underplating and deep late metamorphism rather than magmatic or metamorphic events in the supracrustal rocks secular variations in the generation of archean proterozoic and phanerozoic mesothermal au provinces reflect the timing of collisional orogenies within terranes of these eras

annual to sub annual resolution of multiple trace element trends in speleothems this study aims to establish evidence for the widespread existence of preserved high resolution trace element variations in speleothems that may have climatic significance ion microprobe analysis of speleothems reveals that annual to sub annual variations in element chemistry exist at five shallow western european cave sites crag cave county kerry and ballynamintra county waterford ireland uamh an tartair sutherland scotland grotte pere noel belgium grotta di ernesto ne italy with widely varying climatic geomorphic and geological settings the variations are not restricted to species mg sr and ba known to substitute directly for ca in the calcite lattice but include h f na and p phosphorus as phosphate displays the greatest variability and may have the most significance as a proxy for the seasonal temperature cycle because of its role as a nutrient element the technique allows estimation of growth rate of speleothems at any interval of interest which is one of several possible uses in palaeoclimatology

fluid interaction and geochemical mobility in metabasalts an example from the central appalachians deformation of metabasalts in the central appalachians has produced contrasting zones of fabric development within individual flows more schistose zones reflect metamorphic textures and mineralogies while more massive zones still retain igneous textures and locally relict igneous clinopyroxene samples from a single flow show chemical variations that appear to be a function of fabric development composition volume relationships indicate that more massive zones were least affected by greenschist facies metamorphism and their geochemical signatures are therefore closest to that of the original magmas more schistose zones may have acted as conduits for metamorphic fluids most likely nacl rich brines which transported components into and out of the system these more schistose zones therefore may have lost or gained material during metamorphism cation exchange reactions and silica solubility are used to measure reaction progress and to estimate fluid rock ratios in different zones within a flow the

neoarchean greenstone volcanism and continental growth dharwar craton southern india constraints from sims u pb zircon geochronology and nd isotopes abstract we present sims u pb zircon ages and nd isotope data for the felsic volcanic rocks from seven neoarchean greenstone belts of the eastern dharwar craton edc and from the chitradurga greenstone belt in the western dharwar craton wdc zircon ages show bimodal age distribution of felsic volcanism the ca 2 70 2 65 ga felsic volcanic event is contemporaneous with 2 7 ga mafic greenstone volcanism and emplacement of juvenile tonalitic to granodioritic crust while 2 58 2 54 ga felsic volcanics are coeval and spatially and probably genetically in some cases linked to the major episode calc alkaline magmatic accretion in the edc the chitradurga and veligallu greenstone belts host felsic volcanics of the first generation the latter showing inheritance at ca 2 95 ga four of the five greenstone belts hosting the second generation of felsic volcanics chitradurga kolar kadiri hutti show crustal inheritance at ca 2 6 2 7 2 9 3 0 3 1 and 3 3 ga ndt indicate derivation of the felsic volcanics from juvenile sources or short lived crustal sources with minor influence of older crust the new and existing data are consistent with two stage growth of the dharwar craton in the neoarchean first stage accretion led to the growth of a 2 7 2 6 ga juvenile crustal province of mafic volcanics and felsic plutons along the eastern margin of the wdc second stage accretion 2 58 2 52 ga led to the emplacement of ttg and calc alkaline plutons and felsic volcanics throughout the eastern dharwar craton an active margin context could apply for the two stage accretion scenario considering a west dipping subducting slab beneath the craton in the framework of long lived ultra hot accretionary orogen but the great width of influence of magmatic accretion and or reworking particularly during the second stage would suggest large scale mantle flow reorganization that would have generated large plume s

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved

multielement geochemistry of offshore sediments in the southeastern yellow sea and implications for sediment origin and dispersal abstract in total 116 surface sediments were collected from an offshore area of the southeastern yellow sea including a large mud belt southeastern yellow sea mud seysm and analyzed for grain size and geochemical composition organic carbon and 42 elements principal component analysis revealed that elemental compositions of the offshore sediments were mostly controlled by common aluminosilicate clay minerals and quartz most elements heavy minerals hf zr u th rare earth elements rees biogenic calcium carbonates ca sr feldspar and mica k ba pb and mn oxides mn oxide coatings on sand grains notably total ree concentrations may be associated with heavy minerals possibly zircon and monazite especially in silty grains even though heavy ree hrees concentrations are more strongly controlled by clay minerals in muddy sediments the diagnostic discrimination plots of geochemical compositions e g fe vs al mg vs al light ree vs hree and la lu ucc vs la y ucc suggested that the offshore sediments especially in seysm deposits were composed of a mixture of korean river derived silts and chinese river derived clays this demonstrated that chinese river sediments especially clay particles largely contributed to the formation of the giant mud belt in the korean coastal area furthermore the observed geochemical end members provide new markers of sediment provenance which can be used to track dispersal patterns and sediment limits from chinese and or korean rivers