advection and dispersion of contaminant in a permeable medium embedding fractures in which advection velocity is comparatively slow abstract this paper concerns the advective migration of an aqueous contaminant in a fractured permeable formation calculation and analysis refer to fractures in which advection velocity is comparatively small the slow advective velocity is created by some local cavities or almost vertical orientation of the fractures it is shown that the advective contaminant transport is characterized by two dimensionless parameters 1 the ratio between the permeable block and fracture flow rates termed the mobility number 2 the ratio between the longitudinal advection velocity of the permeable block flow and that of the fracture flow termed the advection velocity ratio for a sufficiently large domain continuum parameters can be applied to characterization of the fractured permeable formation then the mixing between the permeable block flow and the fracture flow is a mechanism leading to contaminant dispersion for very small values of the advection velocity ratio the effective dispersivity is fully determined by the mobility number its value decreases with increase of the mobility number under such conditions the equivalent porosity is constant and its value is identical to that of the permeable blocks a significant value of the advection velocity ratio increases the equivalent porosity of the fractured permeable formation with regard to the effective dispersivity of the domain if the advection velocity ratio is equal to unity then the effective dispersivity vanishes the larger the deviation of the advection velocity from unity the larger is the effective dispersivity of the fractured permeable medium

nd isotope systematics of coarse and fine grained sediments examples from the middle proterozoic belt purcell supergroup sm nd isotopic compositions are reported for 20 fine and 5 coarse grained samples of the belt purcell supergroup of western north america varepsilon nd and sm nd ratios for fine grained belt purcell sediments are remarkably uniform indicating crustal residence ages ranging only from 1 6 to 2 1 ga varepsilon nd and sm nd ratios for coarse grained sediments however are much more varied and contain evidence of sm nd fractionation during sedimentary recycling assuming that this ree fractionation occurred between the time source areas were eroded and when sediment was deposited a new method of calculating crustal residence age intervals is derived for the coarse grained samples which serves to place constraints on the average time since source materials were extracted from the mantle the nd data from both sample groups provide an average age estimate of 2 0 pm 0 3 ga for the middle proterozoic crust from which most of the belt purcell supergroup was derived the isotopic data toge

magmatic graphite inclusions in mn fe rich fluorapatite of perphosphorus granites the belvis pluton variscan iberian belt three mn fe rich fluorapatite types have been found in the highly evolved peraluminous and perphosphorous granites of the belvis pluton one of these apatite types includes abundant graphite microinclusions suggestive of a magmatic origin for the graphite the belvis pluton is a reversely zoned massif composed by four highly fractionated granite units showing a varied accessory phosphate phases u rich monazite u rich xenotime u rich fluorapatite and late eosphorite childrenite the strong peraluminous character of the granites determines an earlier monazite and xenotime crystallization so the three types of fluorapatite record late stages of phosphate crystallization the earlier type 1 apatite is mostly euhedral small and clear type 2 apatite is dusty large 2800 m and mostly anhedral with strong interlobates interfaces with the main granite minerals more abundant in the less fractionated units and absent in the most evolved unit type 3 is subeuhedral to anhedral shows feathery aggregate texture and only appears in the most evolved unit apatite composition was acquired by electron microprobe analyses laser ablation inductively coupled plasma mass spectrometry and electron energy loss spectroscopy type 1 and type 2 apatite display similar broad compositional ranges showing high mno up to 4 30 wt and feo up to 2 88 wt contents without traces of carbon in apatite structure type 2 differs from type 1 by having slightly higher lree and sr contents ree spectra also differ with type 1 displaying both variable lree slope and negative eu anomaly whereas type 2 shows constant lree slope and higher negative eu anomaly although both display similar hree slope type 3 apatite displays higher feo contents up to 5 09 wt positively correlated with higher cl na li be b zn contents and extremely low y ree contents when compared to the other apatite types cation substitution indicates that part of the fe content is as fe graphite has been found exclusively as abundant microinclusions in type 2 apatite parallel or randomly distributed and heterogeneously grouped in clusters within the crystals high resolution electronic images show that graphite occurs with unusual habits filaments of stacked hexagonal flakes up to 15 m length and up to 0 5 m width textural and chemical features suggest a highly crystallized melt which favor compartmentalizing in compositional microdomains where the apatite types would have crystallized the cocrystallization of type 2 apatite and graphite suggests a c f p rich melt sufficiently saturated to acquire an immiscible character with the highly evolved silicate melt in late magmatic stages as type 2 differs from type 1 apatite by higher lree and sr contents we interpret that fluxing components were favorably concentrated in those residual less depleted lree sr fraction melts once monazite and zircon and xenotime would have crystallized type 3 apatite records a change in the ultimate melt stage an increase of the oxygen fugacity coupled with high undercooling by volatile lost of highly fractionated residual cl richer melts the presence of biogenic carbon in granite peraluminous melts derived from metasedimentary sources and its later crystallization as graphite filaments opens a discussion on the carbon behavior during magma evolution especially in highly polymerized melt framework

trace element characteristics ree patterns and partition coefficients of zircons from different geological environments a case study on indian zircons abstract twelve zircon separates from diverse geological settings in peninsular india have been analyzed for their zr hf sc ree th and u contents employing neutron activation techniques the whole rock samples of acid charnockite and a related rock of syenitic composition were also analyzed for these elements after separation of zircons the study reveals that 1 a the zircons exhibit a wide range of variation in elemental abudances and their ratios 2 b their chondritic normalised ree patterns exhibit negative or positive ce and negative eu anomalies in addition to smooth hree enriched patterns without anomalies and 3 c there are significant differences in the ree partition coefficients of zircons from the charnockite and the associated syenite the overall elemental abundances and ree patterns of the zircons could be explained in terms of crystallochemical factors bulk compositional differences of parent melts and paragenetic histories

a reconnaissance ion probe study of hafnium isotopes in zircons a sims technique for the isotopic analysis of hafnium in zircons using the shrimp ion microprobe has been developed and a precision of typically 0 5 2 achieved in the mean reduced 176hf177hf ratio measured at several spots on a single grain unfractionated chondritic initial hf isotopic compositions have been measured on a number of archaean zircon populations these include the oldest known terrestrial minerals the 4 2 ga old mount narryer detrital zircons thereby confirming their antiquity in contrast positive initial hf relative to the chondritic model composition has been found in several post archaean zircon populations reflecting the increasing involvement of isotopically evolved depleted mantle sources in the formation of younger crust the 570 ma old sri lankan zircon standard sl7 yielded an exceptionally low initial hfof 23 implying a metamorphic origin as a reworked product of ancient crust shrimp u pb analyses of zircons from archaean tonalitic gneiss at watersmeet michigan yield a precise crystallization age of 3636 6 ma 2 and show that a previously reported correlation between 176hf177hf and u pb isotopic discordance in bulk zircon samples patchett 1983 was caused by the addition of radiogenic hf in discrete overgrowths of new zircon ca 2 7 ga ago the original 3 64 ga grains show no evidence of disturbance to their original chondritic hf isotopic composition there is presently no evidence for significant isotopic exchange of hf between zircon and other minerals in crustal rocks

interpretation of field tracer tests of a single fracture using a transient solute storage model the results and interpretation of five induced gradient tracer tests performed at five different average interborehole fluid velocities in a single fracture in monzonitic gneiss are described the experiments were conducted using radioactive 82br and a fluorescent dye as conservative tracers where the tracers were pulse injected into radial convergent and injection withdrawal flow fields the flow fields were established between straddle packers isolating the fracture in three boreholes over distances of 12 7 29 8 m the tracer breakthrough curves were determined from samples of the withdrawn groundwater and were interpreted using residence time distribution rtd theory and two deterministic simulation models the rtd curves of the tracer experiments were interpreted by fitting to the field data a simple advection dispersion model and an advection dispersion model with transient solute storage in immobile fluid zones both models consider the different flow field geometries associated with injection withdrawal and radial convergent tests comparison of the fits obtained by the simulation models suggest that the initial period of solute transport in single fractures is advection dominated and with increasing tracer residence time or decreasing fluid velocity transport progresses toward more fickian like behavior during the advective dominated period the transient solute storage model is shown to adequately describe the asymmetries and long tails characteristic of the fracture rtds interpretation of the tracer experiments using both simulation models further suggests that induced gradient tracer experiments are likely to underestimate the dispersive characteristics of single fractures under natural flow conditions

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

metallogeny in response to lithospheric thinning and craton destruction geochemistry and u pb zircon chronology of the yixingzhai gold deposit central north china craton article magmatism and associated metallogeny provide important constraints on geodynamic processes the hengshan terrain of northern taihang mountains located within the central north china craton is well known for several mesozoic gold deposits here we investigate the yixingzhai quartz vein hosted gold deposit associated with the sunzhuang quartz monzodiorite intrusive complex we present u pb data on zircon grains from the monzodiorite which constrain the timing of emplacement of the pluton as ca 134 ma coeval with the formation of yixingzhai quartz vein gold deposit at ca 131 ma the magmatism and metallogenesis during early creta ceous in the hengshan terrain are part of a major regional magmatic and metallogenic event in the taihang mountains and elsewhere in the north china craton at ca 130 ma ago we characterize the zircon grains from the sunzhuang quartz monzodiorite through morphology internal structures and chemistry and also present data from analyses of the chemistry co and ni and s pb d o isotopes of the minerals from the yixingzhai gold deposit and sunzhuang quartz monzodiorite our results reveal a lower crustal signature with mantle input for the source magma of the sunzhuang pluton the magma was enriched in water and alkalis and shows a wide range of crystallization temperature 850 550 c and mainly 650 to 700 c under high oxygen fugacity the ore minerals and the mineralizing fluids in the yixingzhai gold deposit were derived from magma generated in the lower crust with additional input of mantle components our study links the gold metallogenesis with magmatism in the hengshan terrain based on the new results reported in this study and in conjunction with our interpretation of the ultra broadband high precision magnetotelluric sounding profile from the region we suggest that the lithosphere beneath the hengshan terrain was strongly thinned and decoupled between the crust and mantle in the early cretaceous and that the partly destructed lithosphere was largely preserved through the cenozoic to present the metallogenesis in the hengshan terrain was closely related to the lithosphere thinning and crust mantle decoupling in the north china craton

contaminant advection and spreading in a fractured permeable formation part 1 parametric evaluation and analytical solution abstract this paper concerns contaminant transport phenomena in aquifers comprising fractured permeable formations in contrast to deep rock formations with tight almost impermeable matrix rock we consider fractures embedded in permeable rock blocks it is shown that in many cases e g in sandstone formations the advective transport of contaminants in permeable blocks can be identified as the major process leading to contaminant exchange between fractures and blocks in the framework of the present study a simplified conceptual model of the fractured formation is adopted the conceptual model is formulated by sets of space linear differential equations subject to time dependent boundary conditions a closed form analytical solution of these sets of differential equations is developed calculations of the contaminant distribution along the fracture network are utilized to obtain breakthrough curves concerning the time variation of the average contaminant concentration in certain cross sections of the fractured permeable medium characteristics of the contaminant transport phenomena originating from the contaminant advection and the mixing between the fracture flow and the permeable block flow are determined and possibilities of considering the fractured permeable formation as a continuum are discussed

the oldest zircons in the solar system abstract here we report the occurrence chemistry and u th pb isotopic systematics of three meteoritic zircon assemblages two from the vaca muerta mesosiderite and one from the simmern h5 chondrite one of the vaca muerta zircons occurs in the mesosiderite proper the other in a eucritic clast associated with chromite ilmenite and tridymite whereas the simmern zircon occurs in a chondrule composed predominantly of chromite and feldspar like terrestrial zircons the meteoritic zircons are enriched in the heavy rare earth elements but unlike terrestrial zircons they do not show a positive ce anomaly this feature is also absent in one lunar zircon analyzed and probably reflects the oxidation state of the formation environment under oxidising conditions ce4 which can substitute for zr4 in the zircon structure is stabilized whereas under relatively reducing conditions ce3 is stable the zircon from simmern has depletions in the relative abundances of tm and yb a characteristic of volatility fractionation of the ree the u concentrations of the two vaca muerta zircons are quite different at 1 and 50 ppm respectively both zircons have extremely low initial lead and give radiogenic ages that are the same albeit with relatively large errors on vm 1 zircon because of its much lower u concentration and hence radiogenic pb concentration the mean of the two analyses made on vm 2 zircon is concordant with a207pb 206pb age of 4563 15 ma 2 the simmern zircon has an exceptionally low u concentration of around 180 ppb and only a poorly constrained 207pb 206pb age of 4100 700 ma could be obtained

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

enrichment and distribution of elements in the late permian coals from the zhina coalfield guizhou province southwest china abstract this paper investigates the mineralogy and geochemistry of four coal beds wjb 6 wjb 7 fhs 23 and fhs 27 coals of the late permian in the zhina coalfield western guizhou province china the investigated coals reach the semianthracite anthracite coal rank and have super low to low ash yields the sulfur contents vary considerably through coal sections and are mostly in the range of medium high sulfur coal the mineral assemblage present in the fhs 23 and fhs 27 coals is mainly made up of pyrite and rectorite the wjb 6 and wjb 7 coals have different mineralogy with kaolinite and rectorite dominant in the former as well as quartz and rectorite in the latter these coals contain high concentrations of nb and ta but li is only enriched in the wjb 6 coal rectorite and anatase in these coals are important hosting phases of nb and ta while kaolinite and to a lesser extent chamosite in the wjb 6 coal are dominant carriers for the elevated li concentration the terrigenous material input the marine influence and the effect of circulating hydrothermal solution are the pivotal geological factors causing geochemical anomalies in coals investigated the high sulfur coals were subjected to an enhanced marine influence in the depositional environment as well as to a higher terrigenous influx when compared with the medium sulfur and low sulfur coals resulting in higher concentrations of s fe as mo u hg in the former coals than in the latter ones the anomalous enrichment of nb and ta in these coals as well as of li in the wjb 6 coal is the result of the contributions from ascending hydrothermal solutions although source rocks e g high ti basalt may provide relatively high background abundances of nb ta and li

geological controls on mineralogy and geochemistry of the late permian coals in the liulong mine of the liuzhi coalfield guizhou province southwest china abstract this paper investigates the mineralogical and geochemical compositions of the late permian coals in the liulong mine liuzhi coalfield western guizhou province china by using xrd sem edx icp aes and icp ms both the no 3 and no 7 coals are classified as low volatile bituminous coal however the no 3 coal is a medium ash 29 8 on average and high sulfur 4 76 on average coal while the no 7 coal is a low ash 12 4 on average and medium sulfur 2 16 on average coal major minerals in both coal seams include quartz pyrite marcasite kaolinite calcite and to a lesser extent gypsum and anatase illite chlorite rectorite albite ankerite and siderotil are only present in the no 3 coal the no 3 coal contains higher elemental concentrations than the no 7 coal probably due to the higher mineral contents in the no 3 coal and is enriched in nb and ta and to a lesser extent in k ti li v co cu sr zr mo and ba the mineralogical and geochemical data presented in this study have shown that the no 3 coal was formed under a higher degree of marine influenced coal forming environment than the no 7 coal however the both coals have the kangdian upland made of mafic igneous rocks such as basalt rocks as sediment source region like other coals from guizhou province three geological factors control the geochemical patterns of the no 3 and no 7 coals namely 1 the high detrital input in the no 3 coal causing high ash yields 2 the sediment source region kangdian upland basalt causing high ti nb and ta contents and a minor proportion of co cr v and cu when combined with the high detrital input in the no 3 coal 3 the higher degree of marine influenced depositional environment in the no 3 coal causing a high s sr and ba contents

an experimental study of trace element partitioning between zircon and melt as a function of oxygen fugacity abstract the partitioning of p sc ti sr y nb the rare earth elements ree hf ta th and u between zircon and a synthetic andesitic melt was determined as a function of oxygen fugacity f o 2 over a range of fourteen log units from qfm 8 to qfm 6 where qfm is the quartz fayalite magnetite oxygen buffer at 1300 c and 1 atm using sims and la icp ms the partition coefficients of ce and eu were found to vary systematically with f o 2 relative to those of the other ree producing ce and eu anomalies similar to those that are characteristic of natural igneous zircon these anomalies coexist at terrestrial f o 2 s and were used to quantify eu 3 eu 2 eu 3 and ce 4 ce 3 ce 4 in the melt the partition coefficients of the redox invariant trivalent cations are in excellent agreement with lattice strain theory the values of d ree are related to those determined for natural samples by the expected dependence on temperature the incorporation of ree 3 in zircon was independent of the presence of p d u d th was found to vary systematically with f o 2 indicating the presence of u 4 u 5 and u 6 in the melt at terrestrial conditions d ti was independent of f o 2 despite an expectation of significant ti 3 in the most reduced experiments

magnetostratigraphy and biostratigraphy of an anisian ladinian middle triassic boundary section from hydra greece on the island of hydra the anisian ladinian boundary is exposed in a 24 m thick section of nodular reddish han bulog limestone this paper is focused on the magnetostratigraphy and conodont biostratigraphy of this section the anisian ladinian boundary is defined by the first appearance datum fad of the conodont species gondolella trammeri kozur base of the nevadites ammonoid zone and occurs in a normal polarity zone microfacies analysis has distinguished a lower and upper lithofacies recording gradual shallowing from pelagic conditions to a platform margin paleoenvironment

geochemistry and nd isotope signature of the collserola range palaeozoic succesion ne iberia gondwana heritage and pre mesozoic geodynamic evolution the collserola range includes a representative stratigraphic succession of the palaeozoic of the central part of the catalan coastal ranges ranging from cambro ordovician to carboniferous times in this paper we present an up to date review of the stratigraphy and structure of the palaeozoic of the collserola range and provide geochemical and sm nd isotope data to constrain the pre mesozoic crustal evolution of this sector of the variscan belt geochemical compositions indicate that the palaeozoic siliciclastic rocks of the collserola range were fed by a relatively mature heterogeneous source of sediment comprising quartz rich sediments to intermediate igneous rocks the siliciclastic rocks of the collserola range show great geochemical affinity with the turbidites of passive margins the sm nd signature of the siliciclastic rocks is compatible with those of the palaeozoic and late proterozoic fine grained siliciclastic rocks of the neighbouring terrains of sw europe there is a small decrease of the end t with decreasing age of sedimentation from the cambro ordovician to the carboniferous suggesting an increase of the amount of more juvenile material the presence of small volumes of alkaline basaltic rocks provides evidence for the input of juvenile material in the early palaeozoic basin and suggests that an extensional tectonic regime prevailed during the cambro ordovician sedimentation from a geodynamic point of view the overall analysis of the data implies that the palaeozoic rocks of the catalan coastal ranges were part of the northern gondwana passive margin before the closure of the rheic ocean and the subsequent variscan orogeny

exsolution of thortveitite yttrialite and xenotime during low temperature recrystallization of zircon from new caledonia and their significance for trace element incorporation in zircon recrystallized zircon grains in a phengite epidote chlorite schist from north eastern new caledonia contain as inclusions a mineral assemblage consisting of celadonite kaolinite quartz fe oxy hydroxide smectite chlorite xenotime y thortveitite yttrialite and allanite ce this assemblage formed during low temperature 100 c seafloor alteration of a plagioclase rich mafic rock and represents the first documented evidence of this alteration event in the high p belt of northeastern new caledonia the survival of this low temperature mineral paragenesis in zircon of a rock that has undergone subsequent eclogite facies metamorphism testifies to the strength and value of zircon as a container for mineral inclusions thortveitite sc2si2o7 and yttrialite y2si2o7 inclusions in the altered zircon cores represent a new occurrence for these minerals and suggest that they may be more common than is currently recognized the altered zircon cores generally have lower trace element contents than the pristine igneous zircon cores and we suggest that thortveitite yttrialite and xenotime y formed as a result of trace element expulsion from zircon during low temperature recrystallization trace element concentrations in the zircon cores indicate that trivalent cations ree y sc in zircon cannot be charge balanced by xenotime substitution alone pentavalent cation concentrations nb as are also insufficient for charge balance the presence of thortveitite sc2si2o7 and yttrialite y2si2o7 suggests that trivalent cations in zircon might be charge balanced either by monovalent anions substituting for oxygen or by small monovalent cations such as h occurring interstitially in the zircon lattice

experimental measurements of zircon melt trace element partition coefficients abstract zircon was grown from trace element doped hydrous peralkaline rhyolite melts with buffered oxygen fugacities in cold seal experiments at 0 1 and 0 2 gpa and 800 c and piston cylinder experiments at 1 5 gpa and 900 1300 c zircon and glass were present in all run products and small monazite crystals were present in eight of the 12 experiments average diameters of zircon crystals ranged from 5 to 20 m at 800 c to 30 50 m at 1300 c zircon crystals have thin rims and adjacent glass has a narrow 1 m thick compositional boundary layer concentrations obtained through in situ analysis of cores of run product zircon crystals and melt pools were used to calculate trace element partition coefficients dzircon melt for p sc ti v y la ce pr nd eu gd ho yb lu hf th and u in most cases lu was the most d 12 105 and la the least 0 06 0 95 compatible elements d values from this study fall within the range of previously measured values for rare earth elements ree however d values measured experimentally show less fractionation than those recently measured using natural phenocryst matrix pairs for example dlu dla measured experimentally in this study range between 27 and 206 compared to a value of 706 522 for a natural zircon dacite pair sano y terada k and fukuoka t 2002 high mass resolution ion microprobe analysis of rare earth elements in silicate glass apatite and zircon lack of matrix dependency chem geol 184 217 230 although d values from this study show good agreement with the lattice strain model d values from natural phenocryst matrix pairs combined with measured zircon compositions better reproduce host rock magma compositions of igneous rocks they also yield more reasonable estimates of magma compositions when combined with compositions of out of context zircons for example compositions of the hadean detrital zircons from jack hills australia yield lree enriched magmas when combined with d values from phenocryst matrix pairs yields but yield lree depleted magmas when experimentally determined d values are used we infer that experimentally measured dzircon melt values represent disequilibrium partitioning resulting from rapid zircon growth during short laboratory timescales rapid growth causes development of observed diffusive boundary layers in the melt adjacent to zircon crystals d values from phenocryst matrix pairs are therefore recommended for petrogenetic modeling

contaminant advection and spreading in a fractured permeable formation part 2 numerical simulation abstract in a companion paper referred to as paper i the transport of contaminants in a fractured permeable formation was characterized and formulated it was shown that advective movements in the fracture flow and the permeable block flow as well as mixing between these two types of flow are the most significant factors affecting contaminant transport and spreading in such formations the basic formulation and the closed form analytical solution developed in paper i invite the use of numerical schemes for a further analysis of the contaminant transport processes in the framework of the present paper this target is achieved a numerical solution scheme stemming from the conceptual model of paper i is developed simulations are performed by considering the various properties of the discrete fracture flow and the permeable block flow the results of the present study indicate that fractured permeable formations can be represented by single continuum models provided that a sufficiently large number of sectors is included in the representative elementary volume rev the minimum number of sectors depends on the ratio between the specific discharge of the permeable block flow and that imposed by the fracture presence this ratio is named the mobility number the larger the mobility number the smaller the number of sectors which should be incorporated in the rev equivalent properties of the continuum representing the fractured permeable formation such as the equivalent porosity and dispersivity are determined and evaluated

geochemistry of renuka lake and wetland sediments lesser himalaya india implications for source area weathering provenance and tectonic setting the geochemical investigation of sediments deposited in the renuka lake basin and its adjoining wetland has shown variation in the distribution and concentration of major trace and rees the major elements are depleted in the lake in relation to wetland and that of post archaean australian shale paas except for cao which is strikingly in excess and has a dilution effect on sio2 and other oxides and trace elements the wetland sediments on the other hand are enriched in al2o3 fe2o3 k2o and tio2 and the latter three show a positive correlation with al2o3 in both wetland and lake sediments suggesting their association with phyllosilicates and similar source rocks the enrichment of y zr ni th u and nb in wetland compared to lake and their similarity with paas in the former suggests more clay fractions in the wetland a high zr hf ratio in wetland and lake sediments and a positive correlation of zr with y and hree indicate zr control on hrees however higher zr yb and zr th ratios in wetland compared to lake indicate mineral sorting during the process of lighter particles clays being trapped in wetland soil this is also reflected from negative correlation of gdn ybn with al2o3 and a strong positive correlation with sio2 in wetland sediments the wetland in this context has a control on lake sediment chemistry the chondrite normalized ree patterns are essentially the same for lake as well as wetland sediments but abundance decreases in the former the similarity of pattern with that of paas and negative eu anomaly indicates a cratonic source of sediments in a plot of the individual samples wetland samples cluster while lake samples are separated indicating fractionation of lake sediments a strong positive correlation of lan ybn with al2o3 and a positive correlation of zr lree and zr lan ybn suggest that lrees are controlled by both phyllosilicates and zircon the chemical index of alteration cia indices in lake sediments and in wetland are higher than paas indicating moderate chemical weathering in the source area the petrography lack of felsic magmatic rock fragments and negative correlation between zr gd yb c indicate sedimentary source rocks for the detritus this is in conformity with the lesser himalayan sedimentary sequence belonging to neo proterozoic proterozoic age and constituting lake catchment of renuka the tectonic delineation and discriminant function plots of lake and wetland sediments indicate their cratonic and or quartzose sedimentary orogenic terrain source that has been deposited in a passive margin setting

geological controls on the distribution of rey zr hf nb ta enrichment horizons in late permian coals from the qiandongbei coalfield guizhou province sw china abstract the abnormal enrichment of the rey rare earth elements and yttrium zr hf nb ta assemblage in late permian coals occurring in some coalfields in sw china has been extensively investigated but the geological controlling factors of this assemblage are still under debate this study reports on the mineralogical and geochemical features of coals and noncoal rocks collected from the yudai and jinqi coal mines within the qiandongbei coalfield in guizhou province to elucidate the geological controls on the distribution of rey zr hf nb ta enrichment horizons the studied coals show rather consistent clay mineral assemblage of kaolinite together with varying amounts of quartz gypsum pyrite and calcite notably the coals are anomalously enriched in rey nb ta zr and hf and enriched in other incompatible elements e g ga th and u phosphates e g florencite and to a lesser extent zircon are the primary carriers of rey zirconium and hf are mainly incorporated into zircon and then anatase the latter of which is a predominant carrier of nb and ta the detrital materials originate from a mixture of the erupted felsic volcanic ash resembling a peralkaline rhyolite composition and the eroded materials of emeishan large igneous province elip basalts the studied coals owe their highly enhanced concentrations of the rey zr hf nb ta assemblage to the input of felsic volcanic ash wherein the highly acidic aqueous solutions allowed these elements to become mobile and be redistributed both geological processes governed the distribution of rey zr hf nb ta enrichment horizons the highly acidic solutions were possibly derived from the oxidation of peat bogs and volcanism related acidic rain the concentrations of rey zr and nb in the coal ashes exceed their corresponding cut off grades thus these coals can be considered highly promising raw material sources for the rey zr hf nb ta assemblage

behavior of the rare earth elements and other trace elements during interactions between acidic hydrothermal solutions and silicic volcanic rocks southwestern japan abstract rare earth elements and other trace elements in some roseki deposits mostly pyrophyllite and sericite silicastones alunites and related rocks were determined in order to examine behavior of the trace elements in the acidic hydrothermal alteration of silicic volcanic rocks the analyzed concentrations were normalized to the probable unaltered original rock values inferred from the averaged data of some silicic volcanic rocks the trace element characteristics for those materials are as follows 1 most of the elements such as na fe ba and light ree were leached from the silicastones while heavy ree th hf and zr were retained in them 2 alunite samples have light ree enriched and heavy ree depleted features 3 the typical roseki deposits are characterized by middle ree depletions and have v shaped ree patterns on the normalized concentrations vs atomic number diagram such characteristic patterns of the roseki deposits can be explained by superimposition of the light ree enriched and heavy ree enriched materials such as alunite and silica it is important that trace element behaviors are highly selective and some elements e g yb lu hf and zr were strongly retained in the rocks even under strongly acidic hydrothermal processes

the effect of titanite and other hfse rich mineral ti bearing andradite zircon eudialyte fractionation on the geochemical evolution of silicate melts abstract we present trace element data for hfse rich minerals titanite eudialyte ti bearing andradite zircon from plutonic rocks of the eocene tamazeght complex high atlas mountains morocco in most lithologies significant amounts of titanite are present and as such titanite fractionation played a major role in the evolution of the hfse budget of the whole complex by combining our data with published titanite melt partition coefficients we explore the effects of titanite fractionation on the evolution of geochemical parameters zr hf nb ta la lu and th u ratios during differentiation of silicate melts in detail based upon this we further discuss the genetic relationships between the various rock types present in the tamazeght complex and show that the above mentioned element ratios can potentially be useful for distinguishing geochemically distinct melt reservoirs within a given plutonic rock suite zircon eudialyte and ti bearing andradite are generally rare or are restricted to localized rock units despite their scarcity each of them can have a significant effect upon the hfse budget in their evolving magmas here we derive first estimations of eudialyte melt partition coefficients for ree application of these data to eudialyte bearing rocks of the ilimaussaq complex south greenland and comparing the results to published estimations for the parental melts of these rocks yields consistent results and demonstrates the reliability of our estimations

anomalously high sc contents in ore minerals from sn w deposits possible economic significance and genetic implications abstract an investigation on sn w and w deposits and associated granites in the erzgebirge region central kazakhstan mongolian altai and central mongolia reveals anomalously high sc contents up to several thousands of parts per million in wolframite and cassiterite from sn w deposits in the eastern erzgebirge even though whole rock samples of granites from these localities have low sc contents typical of high silica granitic rocks it is possible to trace the distribution of sc in rocks and veins using data on accessory and ore minerals enriched in sc columbite rutile cassiterite wolframite zircon scheelite and mica there are no indications for an enrichment of sc during the magmatic evolution of the granite intrusions magmatic fractionation causes rather low sc contents in evolved granites on the other hand sc enrichment in zircon found in these rocks is clearly related to processes of secondary alteration leading to high u ca and fe besides sc enrichment in the mineral enhanced sc contents were also found in whole rock samples from the greisen the occurrence of sc rich wolframite and cassiterite is mainly restricted to endocontact orebodies greisen and veins outside the rare metal bearing granites the sc content in wolframite drops off if host rocks are formed by schist and gneiss correlation between sc and nb concentrations in wolframite found in endocontact orebodies also disappears in the exocontact veins except if the vein system provides a focused fluid flow sc enrichment in sn w mineralisation is accompanied by strong y sc y yb and th u fractionation in sc bearing minerals as indicated by trace element contents in wolframite and scheelite y sc ratios in wolframite below 0 1 are typical of sn deposits it is suggested that certain conditions of complexation ph and eh in f rich fluids are necessary prerequisites for sc enrichment and deposition our results hint for a sc input into the ore forming system by an external f rich fluid carrying also u and heavy ree and possibly derived from a mantle related source although whole rock samples of rare metal bearing topaz granite have low sc contents the related sn w ores may represent an interesting source for sc extraction because of their enrichment in sc

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

temperature effect over garnet effect on uptake of trace elements in zircon of ttg like rocks abstract to assess the garnet effect on uptake of rare earth elements in ttg petrogenesis zircon trace elements were analyzed for ttg like rocks in a neoproterozoic composite batholith at huangling in the yangtze gorge south china a ttg like suite has higher whole rock la yb and sr y ratios lower whole rock nb la ratios and e nd t values and lower zircon e hf t values than the other three non ttg suites zircons from this suite have higher hf nb and ta contents than those from the other three non ttg suites however ree profiles and ratios cannot be unambiguously distinguished between residued cores and co magmatic domains despite significant differences in their u pb ages and lu hf isotopes all zircons from the four suites are enriched in hree but depleted in lree with positive ce anomalies they display no to very weak eu anomalies contrasting to the typical zircon of magmatic origin this suggests that plagioclase was neither a stable phase during partial melting nor a removed phase during fractional crystallization most of the zircons from the ttg like rocks have ti contents lower than 30 ppm yielding a range of ti in zircon temperatures from 600 to 880 c while a part of zircons from all granitoids show various degrees of lree enrichment the absence of flat hree patterns is evident for all zircons including both residued cores and co magmatic domains in the ttg like rocks this suggests that there is no preferential uptake of hree in garnet relative to zircon even if garnet could exist as a stable phase during partial melting to form the ttg and their source rocks because partition coefficients for garnet melt zircon melt and zircon garnet decrease with increasing temperature during partial melting comparison of calculated apparent d hree values with experimental d hree values between zircon and melt allows estimate of temperatures for zircon crystallization this yields a range of 750 to 800 c for the ttg like rocks which is consistent with whole rock zircon saturation temperatures of 756 to 793 c however they are significantly lower than the crossover temperatures of 900 to 950 c for preferential partition of hree in the zircon garnet melt system thus the temperature is suggested as a key cause for the lack of garnet effect on the uptake of hree in zircons from the ttg like rocks therefore the temperature effect can play a critical role in dictating the partition of hree in the zircon garnet melt system of adakitic and ttg type rocks

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

tajik basin and southwestern tian shan northwestern india asia collision zone 3 preorogenic to synorogenic retro foreland basin evolution in the eastern tajik depression and linkage to the pamir hinterland

the dhala structure bundelkhand craton central india eroded remnant of a large paleoproterozoic impact structure the newly discovered dhala structure madhya pradesh state india is the eroded remnant of an impact structure with an estimated present day apparent diameter of about 11 km it is located in the northwestern part of the archean bundelkhand craton the pre impact country rocks are predominantly granitoids of 2 5 ga age with minor 2 0 2 15 ga mafic intrusive rocks and they are overlain by post impact sediments of the presumably 1 7 ga vindhyan supergroup thus the age for this impact event is currently bracketed by these two sequences the dhala structure is asymmetrically disposed with respect to a central elevated area cea of vindhyan sediments the cea is surrounded by two prominent morphological rings comprising pre vindhyan arenaceousargillaceous and partially rudaceous metasediments and monomict granitoid breccia respectively there are also scattered outcrops of impact melt breccia exposed towards the inner edge of the monomict breccia zone occurring over a nearly 6 km long trend and with a maximum outcrop width of 170 m many lithic and mineral clasts within the melt breccia exhibit diagnostic shock metamorphic features including multiple sets of planar deformation features pdfs in quartz and feldspar ballen textured quartz occurrences of coesite and feldspar with checkerboard texture in addition various thermal alteration textures have been found in clasts of initially superheated impact melt the impact melt breccia also contains numerous fragments composed of partially devitrified impact melt that is mixed with unshocked as well as shock deformed quartz and feldspar clasts the chemical compositions of the impact melt rock and the regionally occurring granitoids are similar the ir contents of various impact melt breccia samples are close to the detection limit 1 1 5 ppb and do not provide evidence for the presence of a meteoritic component in the melt breccia the presence of diagnostic shock features in mineral and lithic clasts in impact melt breccia confirm dhala as an impact structure at 11 km dhala is the largest impact structure currently known in the region between the mediterranean and southeast asia

eocene tectonometamorphism on serifos western cyclades deduced from zircon depth profiling geochronology and mica thermochronology abstract phengite bearing metasedimentary sequences preserving relict glaucophane from serifos western aegean are indicative of high pressure conditions during cycladic blueschist metamorphism depth profiling and conventional sims u pb geochronology and o isotope analysis on zircon from highly strained orthogneisses at the base of the sequence reveal xenocrystic zircon with varying degrees of recrystallization one end member population has needle like or prismatic morphologies is internally oscillatory zoned with little to no rim material created during recrystallization these zircons yield triassic to carboniferous ages elevated th u and 18 o mostly ranging between 4 and 11 in marked contrast a separate zircon population has a spongy structure created by complete recrystallization of the pre existing crystal these zircons possess low th u and flat hree patterns and yield eocene ages with 18 o 7 chondrite normalized ree profiles are extremely depleted within this spectrum other zircons show variable states of recrystallization and mixed ages regression of u pb data from three mylonitic orthogneiss samples that exhibit near complete recrystallization and similar age depth profiles yields c 40 ma ages these new data are the first geochronological constraints that successfully demonstrate an eocene metamorphic event in the western cyclades and new 40 ar 39 ar phengitic mica ages of 38 32 ma presented here suggest the metamorphic wedge was exhumed into the shallow crust shortly thereafter

the origin and response of zircon in eclogite to metamorphism during the multi stage evolution of the huwan shear zone china insights from lu hf and u pb isotopic and trace element geochemistry abstract the huwan shear zone hsz is an eclogite bearing transpressive wrench zone located along the shangdan suture that juxtaposes the paleozoic qinling and mesozoic hong an dabie orogenic terrains the region preserves a complex history that bridges the gap between adjacent orogenic terrains simultaneous in situ trace element u th pb and lu hf isotope analysis of zircon grains from samples of the xiongdian and sujiahe eclogite identify a late carboniferous to early permian period of high pressure metamorphism ca 283 to 306 ma zircon grains are observed to respond to metamorphic overprint via a two stage process 1 an initial prograde stage of fluid catalyzed interface coupled dissolution reprecipitation involving exsolution of a non ideal solid solution thorite thsio 4 end member and loss of highly incompatible components lree and pb 2 a second stage of coupled zircon dissolution coarsening and new rim growth in equilibrium with garnet at high pressure conditions we identify proterozoic whole rock sm nd and zircon grain lu hf isotopic evidence which challenges the traditional interpretation that the xiongdian and sujiahe eclogite formed in response to early paleozoic mantle melting and oceanic crust generation we argue the huwan shear zone contains no conclusive evidence of early middle paleozoic oceanic crust but rather proterozoic crustal components analogous to those found in the northern qinling terrain and associated with formation of the shangdan suture we present a simpler geodynamic model involving continuous convergence and accretion of terrains onto the southern margin of the north china block during the paleozoic qinling and mesozoic dabie orogenies

slow cooling of deep crustal granulites and pb loss in zircon abstract we attempted to obtain the magmatic crystallization age of a metamorphosed granulite facies t 800 90 c p 8 1 kbar massif type anorthosite from the ankafotia body of southwest madagascar the sample studied is a coarse grained leuconorite with good preservation of igneous texture and mineralogy although plagioclase which contains abundant rutile and zircon inclusions has been slightly recrystallized thirty three isotope dilution u pb analyses of zircons representing single grain fragments 29 analyses and multi grain fractions 4 analyses yield a spectrum of concordant ages from 631 to 549 ma a time span of more than 80 myr back scattered electron and cathodoluminescence images show that most grains are either homogeneous structureless fragments 35 or are permeated to a variable degree by anastamosing cracks occupied by relatively u and or th enriched zircon 45 a smaller percentage of grains show relict magmatic zoning 20 thin u and or th rich overgrowths occur on about 25 of grains raman spot analyses demonstrate that all fragments are highly crystalline and non metamict there are marked correlations between zircon grain size and internal features such that the oldest grains are larger and show relict magmatic zoning the youngest grains are small fragments containing high u crack networks ion microprobe spot analyses show that each zircon grain preserves a distinct trace element signature rare earth element patterns show heavy ree enrichment with negative eu anomalies and positive ce anomalies we suggest that the ca 80 myr spread in concordant u pb ages in this sample is indicative of high temperature pb loss during one or more protracted periods of granulite facies metamorphism with only minor episodic or continuous metamorphic zircon growth volume diffusion and or fracture assisted diffusion seems to be the dominant mechanism of pb loss cooling curves calculated using recently measured pb diffusion parameters conform to the age size relationship and imply very slow cooling rates 1 2 c myr or less as might be expected for a terrane in which granulite conditions were maintained for an extended period of time our results therefore suggest a note of caution for interpretation of concordant zircon ages in meta igneous rocks affected by high grade metamorphism of long duration

a continuum approach for modeling mass transport in fractured media a continuum approach has been developed for modeling mass transport in fractured rocks it involves a new application of a particle tracking method in which physical transport is simulated in terms of velocity and the variations in velocity statistics describing the particle motion come from observing the actual pattern of particle motion in a discrete subdomain this subdomain is a small but representative piece of the much larger continuum in effect particle motion in the continuum is forced to mimic that in the discrete subdomain the model successfully duplicates patterns of anisotropic dispersion predicted by de josselin de jong 1972 and breakthrough curves simulated with a discrete fracture model applications demonstrate that the de josselin de jong approach for estimating dispersivities for idealized networks cannot generally be applied to networks formed from sets of finite irregularly spaced fractures in addition this study reinforces indications from earlier studies about the complexity of dispersion in fractured media factors that contribute to spreading in the major and minor principal directions change with the orientation of the network relative to the mean hydraulic gradient

distribution of rare earth elements in lunar zircon an investigation of rare earth elements ree in 15 zircon grains from lunar breccia sample 14321 combined with published analyses has allowed lunar zircon grains to be separated into four distinctive types type 1 zircon is characterized by the relative depletion of light ree lree resulting in a steep chondrite normalized pattern type 2 zircon shows relative enrichment in the lree compared to type 1 grains type 3 zircon also shows relatively high concentrations of lree as well as a relative depletion in the heavy ree hree which results in a relatively flat chondrite normalized pattern type 4 zircon grains are characterized by the steepest chondrite normalized ree pattern with the lowest lree and the highest hree as well as by a distinctive positive ce anomaly multiple analyses of ree in a complex impact modified zircon from breccia sample 73235 suggest a possibility that the very light ree from la to nd were mobilized during impact however the main differences between the identified zircon types appear to be primary and reflect the original crystallization environment of zircon grains these differences are not linked to major changes associated with the different suites of plutonic rocks such as mg and alkali suites and quartz monzodiorites qmd but instead reflect small scale variations in residual pockets of melt where zircon grains crystallized for example the presence of plagioclase in the immediate vicinity of zircon was responsible for the type 1 zircon ree pattern whereas type 2 zircon was formed in the presence of pyroxene the only exception is type 4 zircon which was probably associated with some felsite and granite samples representing very late differentiates of lunar mafic magmas

an integrated microtextural and chemical approach to zircon geochronology refining the archaean history of the napier complex east antarctica integrated textural and chemical characterisation of zircon is used to refine the u pb geochronology of the archaean ultra high temperature napier complex east antarctica scanning electron microscope characterisation of zircon and the rare earth element compositions of zircon garnet and orthopyroxene are integrated to place zircon growth in an assemblage context thereby providing tighter constraints on the timing of magmatic and metamorphic events data indicate that magmatism occurred in the central and northern napier complex at ca 2 990 ma a regional relatively low pressure metamorphic event occurred at ca 2 850 2 840 ma mineral ree data from garnet bearing orthogneiss indicate that ca 2 490 2 485 ma u pb zircon ages provide an absolute minimum age for the ultrahigh temperature uht foliation preserved in this rock internal zircon zoning relationships and estimated zircon garnet dree values from paragneiss suggest that an absolute minimum age of ultra high temperature metamorphism is ca 2 510 ma but that it is more likely to be older than ca 2 545 ma we suggest that the high proportion of published zircon u pb data with ages between ca 2 490 2 450 ma reflects late post peak zircon growth and does not date the timing of peak uht metamorphism

rare earth element mobility during conversion of nepheline syenite into lateritic bauxite at passa quatro minais gerais brazil abstract in a lateritic bauxite formed by weathering of nepheline syenite at passa quatro minas gerais state brazil bauxites on the hill tops directly develop from the syenite bed rock while downslope a kaolinitic layer occurs between bauxite and synetie a petrological investigation was performed on undisturbed weathered rock samples collected from a representative upslope pit the undisturbed weathered rocks were chemically analysed for major trace elements including ree and zr mass balance calculations were applied and the behaviour of the ree in the passa quatro weathering system was established compared to ree reference chondrite and to ree reference parent rock in the lateritic bauxite the results suggest that the first stages of weathering induce a volumetric change of 50 i e collapse with respect to the parent rock and remove ree with a slightly larger loss of the lree except ce compared to the hree in the upper layers where bauxite is more mature a net mass gain in ree is observed relative to the underlying layers this gain takes place during the reduction of the upper layer during the downward progression of the weathering front very significant ree losses occurs during the bauxitization processes throughout the upslope profile in addition the downslope kaolinitic system is demonstrated to be depleted in ree in the same proportions as the upslope bauxite we proposed that the ree exported in solution from the whole weathering mantle have enriched neighbouring watershed sediments

zircon petrochronology and 40ar 39ar sanidine dates for the mesa falls tuff crystal scale records of magmatic evolution and the short lifespan of a large yellowstone magma chamber

distribution of ree and trace elements in size and mineral fractions of high purity quartz sands eight sample sets raw quartz sand quartz fraction 2 m clay fraction 2 20 m fraction and heavy minerals of the cretaceous quartz sand deposits of haltern and weferlingen central germany and the tertiary quartz sand of frechen western germany were studied to characterize the distribution of ree and trace elements and to get genetic information about provenance and sedimentologic history of the sediments the quartz sand samples from different localities have rather similar trace element distribution and ree patterns with enriched lree and negative eu anomalies however these relations can be modified by local changes in syn or postsedimentary geochemical conditions adsorption of ree and trace elements on humic substances under reducing conditions and postsedimentary weathering in the quartz sand of weferlingen resulted in significantly modified element abundances the concentration of trace elements is most important in the 2 m fraction and in the heavy mineral fraction where they may be enriched by a factor of up to 100 the chondrite normalized ree distribution of the 2 m fraction is quite similar to those in the north american shale nas with average eu sm ratios of 0 21 and layb cn of 6 1 low trace element abundances in the 2 and 2 20 m fractions were attributed to quartz dilution and quantified among the common minerals in the heavy mineral fractions especially zircon and the fe 1bti oxides rutile ilmenite magnetite influence the trace element distribution investigations concerning the provenance of the quartz sands illustrate that the host sediments have a rather homogeneous geochemical signature due to their sedimentological history taking into account th ta variations the quartz sands of weferlingen and haltern can be distinguished from the frechen quartz sand additionally discriminations based on element ratios within the quartz fraction th sc ba sc ba co cs sc or li sc seem to be promising

geochemistry of precambrian and paleozoic siliciclastic rocks from the iberian range ne spain implications for source area weathering sorting provenance and tectonic setting abstract the major and trace element chemical composition of precambrian and paleozoic shales and sandstones from the iberian range spain has been investigated to determine the provenance and tectonic setting of these rocks as well as to appraise the influence of the weathering hydraulic sorting and recycling processes upon source rock signature the samples studied belong to a prograde sequence from diagenesis to anchizonal grade and are mainly composed of quartz illite mica phases and or kaolinite with chlorite feldspars and carbonates as minor components the major element distribution chemical index of alteration cia indices reflects that recycling processes have been important in homogenizing the composition of shales and sandstones the higher cia indices observed in the silurian and devonian shales 80 and 85 respectively compared with those of precambrian to ordovician and the carboniferous age about 70 indicate that their source area underwent more intense chemical weathering processes possibly due to climatic and or tectonic variations alternatively the source area of the silurian and devonian shales may have been composed of recycled sedimentary materials mineral fractionation is mainly observed in coarser rocks through zircon apatite and xenotime accumulation although the shales are not free of these phases the zircon content of the fine grained rocks is not high enough to affect rare earth element ree contents but phosphate minerals apatite and xenotime at least partially control the ree distribution the influence of apatite and xenotime are slightly higher in the precambrian shales as the phosphate concentration produces a decrease in the la sm ratios chondrite normalized ree patterns and negative eu anomaly size of the studied rocks are similar to that of post archean australian shales paas indicating that they originally come from a differentiated silicic source the higher ree contents in the studied shales in relation to paas indicate that recycling processes in the iberian range sources were probably more intense than that of paas the slight differences among the ree patterns of the different groups of shales probably do not reflect changes in source area composition but instead suggest variations in mineral sorting chemical weathering and or sediment recycling the th sc co th cr th cr v v ni ratios support a primitive silicic source for these rocks with the higher th sc and lower co th in cambrian and ordovician shales indicating a higher proportion of felsic material in their primitive source area the compositional maturity of analyzed sandstones is typical of cratonic environments and their la sc th and zr contents reflect their passive continental margin setting

zircon inclusions in corundum megacrysts i trace element geochemistry and clues to the origin of corundum megacrysts in alkali basalts abstract zircons enclosed in corundum megacrysts from basalts have a short prismatic habit with the prism slightly more developed than the pyramidal faces the 110 prism is dominant compared with 100 indicating crystallisation from alkaline peralkaline environments rare zircon decomposition reactions suggest the possible presence of a primary sio 2 phase in the source paragenesis for corundum megacrysts the zircon inclusions are geochemically distinctive high y up to 1 2 u uo 2 up to 1 7 wt th tho 2 up to more than 2 wt hf up to 3 4 wt and ree ree up to 5000 ppm they form a cogenetic group that is characterised by extreme ree fractionation with preference for the hree varying from 30 100 chondritic sm to 5000 20000 chondritic lu ree partitioning between zircon and silicate liquid is evaluated the parental melts calculated for the zircon inclusions and other corundum related zircons using zircon melt partition coefficients derived in the present paper show concave down ree patterns with a maximum sm concentration close to 100 chondritic sm abundance such ree patterns represent highly evolved melts after extensive fractionation of low ca feldspar prior to and throughout the crystallisation of zircon the characteristics of zircon inclusions provide evidence that corundum megacrysts must have crystallised from alkaline and highly evolved melts under very reducing conditions implying that the corundum is unlikely to have formed as high pressure phenocrysts in the host mafic magmas

ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern dabie shan u pb zircon geochronology the dabie shan contains two rare geologic features one the occurrence of ultra high pressure metamorphic rocks peak p 2 7 gpa uhp in the east central part of this belt and two some of these uhp rocks are characterized by anomalously 18o depleted oxygen isotopic compositions geochronological data are presented that constrain the age of the uhp metamorphism the ages of protoliths and potentially the age of hydrothermal alteration believed to be responsible for the anomalous oxygen isotopic compositions the age of uhp metamorphism in the eastern dabie shan is dated at 218 5 1 7 ma using u pb in zircon separated from host gneisses this age is identical within uncertainty with a less precise age using u pb in zircon separated from uhp eclogite 225 5 3 6 ma and with previously published ages from uhp eclogites of the dabie shan map relationships strongly support an in situ as opposed to exotic orgin of the uhp eclogites in this region the identical ages of uhp metamorphism in the gneisses and eclogites provides additional support for this interpretation the age of the protolith gneisses is dated as 772 5 9 5 ma based on the upper intercept of the zircons which accords well with other dates of granitic gneisses in the qinling belt the association of mafic and felsic magmatism is interpreted to reflect rifting along the northern margin of the yangtze block at this time these upper intercept ages may date the hydrothermal circulation of 18o depleted meteoric water which gave rise to the anomalously 18o depleted uhp protoliths of the dabie shan and sulu region the coincidence of these protolith ages with the early sinian glaciation of south china is consonant with the suggestion that the highly anomalous oxygen isotopic compositions in this region date from this time the upper intercept age of the eclogite is imprecisely determined at 447 82 79 ma but is younger than the host gneisses and is not characterized by anomalous oxygen isotopic compositions

geochemical study of laterites of the jamnagar district gujarat india implications on parent rock mineralogy and tectonics abstract the laterite deposits occur in a linear stretch along the northern arabian sea coast in the jamnagar and porbandar districts of gujarat state india these deposits are characterised by presence of gibbsite kaoline calcite quartz anatase natroalunite goethite and hematite and relicts of mafic minerals and plagioclase on the basis of petro mineralogy and geochemistry these deposits are grouped as aluminous laterites fe2o3 1 45 3 84 av 3 13 al2o3 39 31 57 24 av 45 80 and laterites fe2o3 9 84 32 21 av 25 13 al2o3 34 74 49 59 av 41 27 the major trace and ree characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic andesitic composition and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation the correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements the jamnagar laterite deposits occur as capping over the deccan trap basaltic lava flows and pyroclasic deposits lateritisation prevailed during palaeocene age when india was separated from the seychelles and passing over the equator during this time climate morphology and drainage conditions were favourable for lateritisation that result in the formation of jamnagar and other laterite deposits within the deccan province flood basaltic provinces of deccan columbia north australia and hawaii appear good location for hosting laterite deposits due to their wide areal extent small geological time span and uniform chemical composition however comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate morphology and drainage are equally important factors for facilitating lateritisation

transport of a tracer slug in a fractured permeable formation abstract this paper concerns the migration of a tracer slug injected into a fractured permeable formation basic transport processes are formulated dimensionless parameters governing transport phenomena in the domain are identified and their effects are determined a simplified conceptual model is employed for the quantitative evaluation of the physical phenomena associated with tracer migration in the domain the analytical approach applied in this study provides some basic characteristics concerning the build up and decay of tracer breakthrough curves characteristics of fracture networks incorporating a large number of fracture sectors are evaluated using a numerical finite difference scheme it is shown that various time and length scales characterize the phenomena involved in tracer slug migration in a fractured permeable formation it is found that in cross sections located at a small distance from the tracer injection point two maximum values of tracer concentration are expected in the breakthrough curves in cross sections located at comparatively large distances from the tracer injection point the breakthrough curves are similar to those characterizing an ideal porous media

zircon morphology geochronology and trace element geochemistry of the granites from the huangshaping polymetallic deposit south china implications for the magmatic evolution and mineralization processes abstract the huangshaping polymetallic deposit is a large scale deposit located in the central nanling region south china different types of mineralization have been classified in the area which are attributed to three types of granitoids from the composite granitic pluton quartz porphyry granophyre and granite porphyry in order to study the magmatic genesis and evolutionary process as well as constrain the crystallization and mineralization events 100 zircon separates from different intrusive stages of the pluton have been analyzed for trace element contents and u pb isotopic concentrations the results show that zircons from the huangshaping granitoids are enriched in th u hf ti ree and other trace elements indicating hydrothermal fluid alteration and transformation additionally there is a large variation between different types of granitoids in terms of trace element concentrations compared to the zircons from the quartz porphyry and the granophyre zircons from the granite porphyry are more enriched in th u hf ti and p but strongly depleted in eu this suggests that the magma that formed the granite porphyry possessed higher temperatures possibly experienced stronger crystal fractionation and originated from a more evolved complex magmatic source region with higher degree of crustal maturity combined with characteristics of crystal morphology and internal texture hydrothermal zircons were distinguished from magmatic zircons in each granitoid to reveal mineralization processes the u pb geochronology results show that there are two major stages of mineralization 190 ma weak cu pb zn mineralization related to the quartz porphyry and the granophyre and 155 ma strong w sn mo pb zn mineralization associated with the granite porphyry compositions of these hydrothermal zircons suggest that the earlier stage mineralization could be close to single relatively cold reduced and quickly ascended fluids whereas the later stage might be related to hot oxidized strongly fractionated and highly evolved mixed fluids this study also indicates that hydrothermal zircons from typical composite granitic plutons could be a good tool to reveal the multi stage magmatic and mineralization process in middle to late jurassic south china

geology and geochemistry of shallow drill cores from the bosumtwi impact structure ghana the 1 07 ma well preserved bosumtwi impact structure in ghana 10 5 km in diameter formed in 2 ga old metamorphosed and crystalline rocks of the birimian system the interior of the structure is largely filled by the 8 km diameter lake bosumtwi and the crater rim and region in the environs of the crater is covered by tropical rainforest making geological studies rather difficult and restricted to road cuts and streams in early 1999 we undertook a shallow drilling program to the north of the crater rim to determine the extent of the ejecta blanket around the crater and to obtain subsurface core samples for mineralogical petrological and geochemical studies of ejecta of the bosumtwi impact structure a variety of impactite lithologies are present consisting of impact glass rich suevite and several types of breccia lithic breccia of single rock type often grading into unbrecciated rock with the rocks being shattered more or less in situ without much relative displacement autochthonous and lithic polymict breccia that apparently do not contain any glassy material allochtonous the suevite cores show that melt inclusions are present throughout the whole length of the cores in the form of vesicular glasses with no significant change of abundance with depth twenty samples from the 7 drill cores and 4 samples from recent road cuts in the structure were studied for their geochemical characteristics to accumulate a database for impact lithologies and their erosion products present at the bosumtwi crater major and trace element analyses yielded compositions similar to those of the target rocks in the area graywacke phyllite shale and granite graywacke phyllite and granite dikes seem to be important contributors to the compositions of the suevite and the road cut samples fragmentary matrix with a minor contribution of pepiakese granite the results also provide information about the thickness of the fallout suevite in the northern part of the bosumtwi structure which was determined to be 15 m and to occupy an area of 1 5 km2 present suevite distribution is likely to be caused by differential erosion and does not reflect the initial areal extent of the continuous bosumtwi ejecta deposits our studies allow a comparison with the extent of the suevite at the ries another well preserved impact structure

a large scale flow and tracer experiment in granite 1 experimental design and flow distribution this paper describes the stripa three dimensional experiment where water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the experiment was performed in a specially excavated drift 100 m long at the 360 m level in granite the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock this paper describes the experimental techniques the fracture mapping the tracer and flow rate measurements and the results of the flow rate measurements the detailed observations made possible by the plastic sheeting technique have given some qualitative as well as quantitative information on flow rate distribution in fractured rock which previously has not been available these observations may be of importance for assessing the transport of dissolved species such as radionuclides through fractured rock

a connection between the neoproterozoic dom feliciano brazil uruguay and gariep namibia south africa orogenic belts evidence from a reconnaissance provenance study abstract a provenance study of neoproterozoic siliciclastic successions in the stratigraphically and tectonically lowermost and uppermost parts of the pan african gariep belt stinkfontein subgroup and oranjemund group respectively in southwestern africa as well as in the rocha group of the punta del este terrane dom feliciano belt in uruguay revealed that the oranjemund and rocha groups can be correlated and most likely formed in the same basin thus the rocha group is considered to represent the fill of the westernmost part of a re activated ediacaran gariep basin the lower parts of the oranjemund and rocha groups reflect erosion of mafic rocks whereas the upper parts are derived from a predominantly felsic source area first major and trace element geochemical data are consistent with oceanic islands of within plate geochemistry in the immediate vicinity as the most likely source of the mafic input into the lower part of the oranjemund group whereas a combination of continental margin and island arc is indicated as source for the bulk of the younger sediments in the upper oranjemund group age spectra obtained by shrimp u pb analyses of detrital zircon grains from the stinkfontein subgroup port nolloth group the oranjemund group and the rocha group are very similar except for a lack of the youngest age group around 600 ma in the stinkfontein subgroup in all three units zircon grains of 1000 1200 ma dominate with a further peak in the age distribution between 1700 and 2000 ma these ages compare well with the pre gariep basement geology in southwestern africa where the former age range corresponds to magmatic and high grade metamorphic activity in the mesoproterozoic namaqua natal belt and the latter to an extensive palaeoproterozoic andean type volcanic arc richtersveld terrane comparable ages are conspicuously absent in the basement of the rio de la plata craton in south america derivation of the rocha group sediments from a similar source as the contemporaneous oranjemund group sediments is therefore suggested the most likely source of the youngest detrital zircon grains in these two stratigraphic units is the 640 590 ma magmatic arc of the dom feliciano belt this interpretation explains the continental island arc component in the sediment provenance and takes into account the absence of comparable magmatism in the gariep belt two stages of basin evolution are distinguished for the gariep basin an early failed continental rift that subsequently became re activated as back arc basin related to the cryogenian dom feliciano arc consequently the gariep basin does not represent the main suture between the rio de la plata and the kalahari cratons this suture is now suspected to be west of the dom feliciano volcanic arc and might be connected with the sierra ballena major gercino lineament