geochemistry and provenance of the middle ordovician austin glen member normanskill formation and the taconian orogeny in new england the austin glen member of the upper middle ordovician normanskill formation is a sandstone shale ysch succession deposited in the foreland of the taconian orogen petrographic major and trace element and nd pb isotopic data provide substantial constraints on its provenance lack of k feldspar and paucity of plagioclase in addition to the dominance of sedimentary rock fragments indicate that the source was dominated by recycled sedimentary components major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same no evidence of an ophiolitic or volcanic component was observed interpretation of nd isotopic characteristics are complicated by a partial resetting of the nd isotope system at about the time of sedimentation but indicate that the provenance of the austin glen member had a long term history of light rare earth element lree enrichment average tdm 1a8 ga furthermore nd isotopic compositions are extremely homogeneous end 8a1 0a6 1 s d n 23 at 450 ma the approximate depositional age indicating either a single source or very well mixed sources 207pb 204pb ratios are variable but within the range of pb isotopic compositions typically described as grenvillian the range of 207pb 204pb is greater than expected for the range of 206pb 204pb and suggests an additional component of pb possibly introduced during diagenesis the immediate source of the austin glen member may have been the accretionary prism that developed as older sediments of the laurentian margin were scraped off the basin oor incorporated within the accretionary prism and shed into the basin no evidence indicating the arrival of an undifferentiated island arc or continental fragment during the taconian orogeny has been found the data acquired during this study can be explained almost exclusively by grenville province source components but with possible additional contributions from older laurentian terranes and late proterozoic rift volcanics that are not readily quanti ed but likely to have been minor accordingly we conclude that the taconian orogeny in new england involved either 1 a continental arc that involved exclusively laurentia 2 collision of a continental block with identical geochemical characteristics as laurentia or 3 essentially no detritus from any exotic colliding block island arc or continental fragment reached the foreland basin at the time of austin glen deposition

adjustment of the electromagnetic field distorted by 3 d heterogeneities summary the 3 d adjustment distance of electromagnetic fields distorted by lateral contrasts of conductivity was studied with applications to conductivity anomalies occurring near coasts or islands investigations of the electrical conductivity structure of the mantle depend critically on whether the distortion of the electromagnetic data is caused by local or by remote contrasts of conductivity with the help of simple models it is shown that the actual adjustment distance of the electric field along the off strike direction to the conductivity contrast is a balance between an adjustment distance related to the galvanic coupling of the upper layer to the substratum and a distance describing the horizontal scale of the electric currents deviated by the contrast in conductivity it is shown that this adjustment distance cannot exceed the effective dimension of the conductivity contrast consequently published adjustment distances of several thousand kilometres are unlikely to exist as a result sea floor electromagnetic soundings carried out at large distances from coastlines are useful for probing the local conductivity structure of the oceanic mantle the 2 d interpretation of the electric field in the offshore direction at stations perturbed by the coastal effect has a high probability of bias because the field is affected by the combination of the 2 d galvanic coupling and the effect of the horizontal short cut by the closest conductive channels of the electric current flowing in the ocean

geomagnetic variation anomalies and deflection of telluric currents summary we show that most of the abnormal variations of the transient magnetic field have deflection and canalization of telluric currents as main sources in order to do so we develop a formalism which is valid in a limited frequency range which satisfies the following hypotheses a the thickness of the laterally inhomogeneous upper layer is small with respect to the penetration depth of the transient field b self induction of the heterogeneities of conductivity can be neglected theoretical results and observations performed at mid latitudes are in good agreement the main result we establish is that deviation and canalization of the current responsible for the transient abnormal field do not affect their temporal variations the study of temporal variations of the abnormal field thus provides us with information about the structure of the crust in the region where the deviated and canalized currents are induced

possible electrokinetic origin of large magnetic variations at la fournaise volcano abnormal time variations of the geomagnetic field related to volcanic activity have been reported for several decades1 10 two main candidates have been considered for the source mechanism of these volcanomagnetic variations piezomagnetism and electro kinetic effects we considered both of these mechanisms in our attempts to interpret the most spectacular volcanomagnetic variations observed on piton de la fournaise volcano reunion island 11 but now new analysis of the latest data which covers a time span of more than three years leads us to think that water circulation is the main agent of the strong magnetic signals observed on the volcano in addition to the signals that we correlated with the volcano activity11 12 longer period components also exist as shown here with amplitudes and characteristics that have not been reported before we propose that these magnetic variations are generated by electrokinetic effects in which case the water circulation system into this massif would be a sensor for detecting stress changes linked to the volcano activity

sandstone petrography and geochemistry of late proterozoic sediments of the armorican massif france a key to basin development during the cadomian orogeny abstract brioverian late proterozoic sediments of the armorican massif in northwest france are contained within isolated basins whose development is linked to cadomian orogenesis these basins were formed between c 650 and 530 ma ago mainly by gravitational flow processes petrographical study and geochemical analysis of major and trace elements show that the sandstone formations of north brittany are characterized by great immaturity 10 20 feldspar 10 20 lithic fragments and high concentrations of na2o ba sr v and cr the formations from western and central brittany as well as the southern part of normandy are compositionally more mature 1 petrographical and geochemical data for north brittany formations yield plots which suggest a mixed source region composed of a continental active margin island arc and ancient basement material sedimentation of the brioverian group was influenced by a distensive tectonic regime towards the south sedimentary formations are characterized by continental source areas and were laid down in a passive tectonic environment however ree distribution patterns for sediments of this southern domain preserve evidence for the contribution of magmatic arc material such formations could have been deposited in a marginal basin

geomagnetic induction soundings over the michigan basin abstract geomagnetic variation sounding and magnetotelluric results from six sites on an east west long period profile across the michigan basin are presented a strongly conductive zone on the western flank of the presumed underlying keweenawan rift system in the precambrian basement is shown to exist near cadillac michigan this zone is perhaps similar in character to the flambeau anomaly exposed at the surface in wisconsin also on the flank of the keweenawan rift whose conductivity resides in iron formations and in massive and disseminated graphite and sulphides no clear expression of the michigan basin itself or of the presumed keweenawan rift in the basement is seen in the results the limited magnetotelluric sounding results correspond to a surface conducting layer over a resistive deeper crust over a rise in conductivity at mantle depths they show several hundred seimens of crustal conductance in excess of that provided by the phanerozoic sediments of the basin but do not determine whether the excess crustal conductivity is associated with the underlying keweenawan clastics and volcanics or whether some of that conductivity is in a deeper crustal layer like that found under the adirondack dome by connerney et al

sediment provenance within subduction complexes an example from the aleutian forearc abstract the ultimate composition of any sandstone is affected by a host of primary and secondary factors including the lithologies present in source terranes climate depositional environment and diagenesis in the case of a subduction complex however unequivocal identification of detrital provenance may be impossible because of the cumulative effects of tectonic and sedimentary transport long distance sedimentary transport 1000 km is common within trenches and abyssal plain turbidites can be tectonically transported for long distances as the underlying oceanic basement drifts towards a subduction front post accretionary displacement can occur as a consequence of strike slip faulting and the total distance of tectonic dislocation may reach several thousand kilometers the present day aleutian forearc region north pacific ocean illustrates many of the problems which typify subduction zones several petrologic suites can be identified and there are significant variations in detrital modes in both time and space the aleutian region serves as a sobering modern analog for accreted rock units such as the franciscan complex of california where intercalations of discrete sandstone suites have been noted in the absence of paleomagnetic control interpretations of sediment provenance within ancient subduction complexes probably should be restricted to the generic level

sand composition in an iberian passive margin fluvial course the tajo river the tajo river the 10th largest river in europe drains part of the western passive margin of europe that includes multiple tectonic elements of the iberian plate modern fluvial sand composition in the tajo river drainage basin reflects the nature of the source region which lies in the central part of the iberian peninsula four fluvial petrographic provinces a b c and d can be established in the tajo drainage basin corresponding well with the four principal structural units drained 1 the iberian range 2 the hesperian massif 3 the tertiary tajo basin and 4 the neogene santarem lisboa basin province a corresponds to the tajo river head and is characterized by quartzolithic sedimenticlastic sands qm67f4lt29 and rs79rg3rm18 these sands have been derived from diverse mesozoic siliciclastics and carbonates of the iberian range province b appears in the upper reaches of the tajo river course and is quartzofeldspathic qm57f34lt9 with diverse rock fragments rs34rg23rm43 sources are hercynian granitoids and metasediments and neogene clastics and minor carbonates of the tertiary tajo basin province c extends along the middle course of the tajo river with quartzofeldspathic metamorphiclastic sand modes qm60f33lt7 rs4rg21rm75 the sources are metamorphic rocks intruded by plutonites of the hesperian massif province d is quartzofeldspathic qm55f39lt6 with a dominance of phaneritic rock fragments rs5rg33rm62 and corresponds to the lower reaches of the tajo river where siliciclastic deposits of the neogene santarem lisboa basin are the main sources sands plot on provenance discrimination diagram qmflt within the recycled orogen field tajo river head and continentalblock fields upper middle and lower course in addition we have proven the usefulness of the rsrgrm diagram to discriminate the defined fluvial provinces originating from heterogeneous parent rock textures and mineralogy climate does not exert any strong influence on the petrogenesis of the tajo river drainage basin sand and erosion in the source areas may be described in terms of weathering limited denudation regime by contrast mixing with tributary supplies is the main process that modifies composition in the tajo river sand the establishment of fluvial provinces related to the main bedrock structural units reflects the great relevance of tributaries from each province in the generation of the tajo river sand and the low significance of inherited sandy load from previous provinces the abundance of granitoid rock fragments rsrgrm rg in fluvial sand of both tributaries and main channel of the tajo river drainage basin faithfully represents the relative abundance of granodiorite monzogranite bedrock exposure in each subbasin metasedimentary and metamorphic bedrock outcrop area is overrepresented by metamorphic rock fragments rsrgrm rm in both sand from tributaries and from the tajo main trunk river this is manifested by differences of 18 23 between means of metasedimentary outcrop area and the rsrgrm rm mean in the sand from provinces b and c d respectively sedimentary mainly carbonate outcrop area is underrepresented or not represented by sedimentary rock fragments rsrgrm rs in sand of the tajo river this underrepresentation causes a difference between means of sedimentary outcrop area and the rsrgrm rs mean of 21 17 1 and 10 7 in sands from province a b and c d respectively this fact confirms the rapid loss of these grains during transport because of their labile nature

detrital modes of recent deep sea sands and their relation to tectonic setting a first approximation complete petrographic analyses of modern deep sea sands are surprisingly rare but are needed if problems such as the influence of tectonics on petrology or changes in petrology due to diagenesis are to be understood in ancient sandstones this paper is a first attempt using data from our own study of 80 sands plus data from the literature to establish a baseline for modern deep sea sands with which ancient sandstones can be compared we assigned sands to five plate tectonic categories each of which has a distinct average petrologic composition 1 basins associated with trailing edge continental margins q62f26l12 2 with leading edge continental margins either subduction q16f53l31 or 3 strike slip q34f39l27 4 back arc basins q20f29l51 5 fore arc basins q8f17l75 the amount and type of lithic fragments and the type of feldspar are particularly important discriminators the amount of quartz less so trailing edge and fore arc basins have quite distinctive compositions but back arc basins and basins near the two types of leading edge margins show some overlap and thus may be hard to differentiate in ancient sandstones

lower crustal and upper mantle electrical conductivity contrasts in the central north island of new zealand abstract magnetotelluric soundings made in the central north island of new zealand over the last 20 years have been reanalysed together with more recent soundings in an attempt to detect any electrical conductivity contrast associated with a known boundary in other geophysical properties invariant apparent resistivity curves from 11 sites in all have been compared and curves which appear to be representative of the different regions have been selected one dimensional modelling has led to the identification of a good conductor at lower crustal or upper mantle depths in the northwest of the north island no such conductor is identified in the south and east modelling of a single site in the taupo volcanic zone has led to the first indication yet obtained of a deeper conductor beneath the geothermal region

petrography and geochemistry of the lower silurian sandstones from the angzanggou formation in the north qilian belt china implications for provenance weathering and tectonic setting the north qilian orogenic belt is on the northeastern margin of the tibetan plateau it is connected with the alxa block in the north and the tethyan orogenic assemblage in the south the lower silurian angzanggou formation deposited in the northern area of the north qilian orogenic belt is the most important for revealing the architecture and orogenic processes of the north qilian belt provenance analysis of the angzanggou formation can reveal not only the tectonic evolution of the central orogenic belt of china but also palaeozoic asia plate reconstructions petrographic analysis indicated that the compositional and textural maturity of the sandstones was low the detrital composition of the angzanggou formation samples consists of quartz 8 14 feldspar 6 29 and lithic fragments 56 86 the sandstones could be classified as litharenites or feldspathic litharenites the detrital modal composition suggests that these sandstones were probably deposited in a fore arc basin the element ratios and some discrimination diagrams based on geochemistry indicate that felsic and intermediate rocks were the main source rocks the sio 2 al 2 o 3 ratio the index of chemical variability and the th sc versus zr sc discrimination diagram suggest that the compositional maturity and degree of recycling were moderate to low the index of alteration cia and the a cn k diagram indicate the intensity of weathering was moderate the discrimination diagrams based on major and trace elements and petrographic discrimination diagrams imply that the angzanggou formation rocks were derived from a continental island arc and a sedimentary cover probably overlaid the volcanic arc therefore we infer that during early silurian time the north qilian belt sediments accumulated in a fore arc basin

geochemistry of the archaean and proterozoic clastic and carbonate rocks of rajasthan india abstract the late archaean sediments in rajasthan occur either as enclave suites within mangalwar complex or vast spreads of volcanics and volcaniclastic turbidites with quartzwacke of hindoli group the lower proterozoic cover sequence of aravalli fold belt and jahajpur group were deposited in ensialic aborted rift basins dominated by shelf type clastic and carbonate sediments archaean clastics are essentially potassic sandstones characterised by higher lree n hree n and low eu eu ratios and greater concentrations of total ree than proterozoic counterparts the archaean carbonates have low ree total higher co cr and higher eu eu eu n sm n la th and la sc ratios compared to the proterozoic carbonates a passive margin setting basin support the rift related clastic and carbonate deposition

petrologic binary diagrams for characterizing and comparing arenites abstract point counting according to the gazzi dickinson method was performed on 136 samples of several paleocene to early miocene turbidite units of the central northern apennines the main components of the siliciclastic fraction are plotted on binary diagrams in which the coordinates are dimensionless ratios the following petrographic parameters have been used qm q monocrystalline quartz total quartz q q f total quartz total quartz total feldspar k f k feldspar total feldspar mw m white micas total micas for each pair of ratios binary diagrams can be drawn in which each sandstone formation occupies a fairly restricted field the simultaneous use of two or more diagrams allows two formations to be distinguished in at least one of the diagrams

detrital modes of the ionian forearc basin fill oligocene quaternary reflect the tectonic evolution of the calabria peloritani terrane southern italy abstract during oligocene neogene time the calabria peloritani terrane cpt a small block of continental lithosphere rifted from the southern margin of the eurasian continent and drifted southeastward to collide with the african continent along the leading edge of the cpt a late oligocene to quaternary mostly siliciclastic succession 2 000 meters thick was deposited in the ionian forearc basin the detritus forming the succession was derived directly from the erosion of the nearby cpt composed of hercynian plutons intruding metasedimentary host rocks contrary to most modern and ancient forearc basins penecontemporaneous volcanic detritus is virtually absent this results from rift related topographic barriers which separated the forearc basin from the associated volcanic arc in spite of an overall quartzofeldspathic continental block provenance the analysis of a large sandstone and conglomerate petrological dataset 228 samples points to three discrete detrital inputs of aphanitic lithic fragments in i late oligocene early miocene ii late messinian and iii quaternary times these petrological variations can be linked to independently determined tectonic events in the western mediterranean which likely modified the lithologic composition of the sediment source terranes input i documents the progressive widespread unroofing of the continental basement of the southern european margin when northwestward subduction of the remnants of the ligurian ocean began input ii is related to widespread intra messinian tectonism possibly due to out of sequence thrusting induced by isostatic readjustments of the perimediterranean orogenic wedges following the messinian drawdown input iii reflects the rapid vertical uplift experienced by the cpt since mid pleistocene time possibly the result of slab detachment along the ionian subduction zone this study indicates that detailed statistical analysis of the detrital modes of ancient terrigenous deposits can be used to identify the tectonic events affecting somewhat petrologically monotonous sediment source areas within small lithospheric terranes

proterozoic tectonic evolution and metallogenesis in the aravalli delhi orogenic complex northwestern india abstract the proterozoic aravalli delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits a few w sn deposits associated with granites are also known in the complex based on tectono lithological features the following domains are distinguished the archaean basement consisting of the banded gneissic complex and granites the early proterozoic bhilwara aravalli jharol and north delhi belts and the middle to late proterozoic south delhi belt and the vindhyan basin intra cratonic rifting of the archaean basement commencing 2 2 ga ago resulted in the rock association of the bhilwara belt a thick pile of detritus derived largely from felsic sources and to a minor extent from tholeiitic sills with the geochemical characteristics of ocean floor basalts stratiform zn pb cu sulphide deposits at rajpura dariba rampura agucha and also possibly those at pur banera and jahazpur formed 1 8 0 04 ga ago by convective seawater circulation in zones of crustal extension the metal content of exhalative brines was precipitated in troughs where biologic activity was prolific the shelf sediments of the aravalli belt characterized by dolomites with stromatolitic phosphorites were deposited on a passive continental margin at the rifted western edge of the archaean basement complex the monotonous pelitic pile of the jharol belt represents deep pelagic continental rise sediments the rakhabdev lineament delineates the shelf rise boundary the mafic ultramafic bodies along this lineament represent aravalli oceanic crust which subducted westward and eventually obducted as a consequence of an initial collision of the aravalli continental margin with an incipient arc to the west around 1 5 ga ago in the aravalli belt at zawar strongly radiogenic stratabound pb zn deposits were formed close to the basement in second order basins with biologic activity by hydrothermal solutions convecting through a heterogeneous source the north delhi belt comprises three sedimentation domains the khetri sub basin the alwar sub basin and the lalsot bayana sub basin sedimentation in this belt commenced with shelf carbonates followed by coarse clastic sediments and volcanites finally pelites and semi pelites were deposited in a multi lagoonal shallow water locally evaporitic environment synkinematic granitic intrusives in the north delhi rocks are in the age range of 1 7 1 5 ga the stratabound cu sulphide deposits of the khetri belt and the pyrite pyrrhotite deposits at saladipura with a pb pb model age of 1 8 ga were formed from hydrothermal seawater and partly bacteriogenic sulphur in small shallow rift related basins the south delhi belt with extensive mafic volcanism localized felsic volcanism argillaceous arenaceous carbonate accumulations in successive elongated basins and conspicuous felsic plutonism is interpreted as an island arc the geochemistry of pillowed and massive metavolcanites and an ophiolite assemblage indicate subduction in the western side of the arc part of the rocks of the delhi belt may also have formed in rift related back arc basins as suggested by the ocean floor characteristics of metavolcanic rocks subduction on the western side of the arc ultimately led to its terminal collision with the aravalli continental margin around 1 0 ga involving intense progressive strain and oblique convergence small cu zn deposits were formed within sedimentary intercalations in calc alkaline basalts close to the hypothetical subduction zone extensional tectonics in the back arc basins produced stratiform zn pb cu deposits ambaji deri around 1 1 ga ago by high temperature reduction of seawater convecting through multiple sources sn w mineralizations are apparently related to the malani felsic igneous phase of 735 ma rb sr age

assessing the hydrogeochemistry and water quality of the aji chay river northwest of iran aji chay river is one of the most important surface reservoirs of northwest of iran because it passes through tabriz city and discharges to urmia lake one of the largest permanent salty lakes in the world the main objectives of the present study are to evaluate its overall water quality and to explore its hydrogeochemical characteristics including the potential contamination from heavy metals and metalloids such as co pb zn cd cu cr al and as for this purpose 12 water samples were collected from the main river body and its tributaries within tabriz plain the piper diagram classified water samples mainly into na cl and secondary into ca hco3 and mixed ca mg cl types denoting a profound salinization effect the cross plots showed that natural geochemical processes including dissolution of minerals e g carbonates evaporites and silicates as well as ion exchange are the predominant factors that contribute to fluvial hydrogeochemistry while anthropogenic activities industrial and agricultural impose supplementary effects cluster analysis classified samples into two distinct clusters samples of cluster b appear to have elevated electrical conductivity ec values and trace metals concentrations such as co pb and cd while sio2 and zn are low in comparison with the samples of the cluster a the main processes controlling aji chay river hydrogeochemistry and water quality were identified to be salinization and rock weathering both are related with geogenic sources which enrich river system with elevated values of na cl ca2 mg2 k so4 2 and ec as a direct effect of evaporites leaching and elevated values of pb and cd as an impact from the weathering process of volcanic formations according to the us salinity diagram all of the water samples are unsuitable for irrigation as having moderate to bad quality

implications of the geochemistry of the pelitic granulites of the delhi supergroup aravalli mountain belt northwestern india abstract an isolated granulite terrain occurs within the linear zone of schists and amphibolites of the proterozoic delhi supergroup in the aravalli mountain belt of nw india the geochemistry of the pelitic granulites of such terrains suggests the arkosic to shaley nature of the protolith these rocks are characterized by a high maturity index low to intermediate fe2o3 mgo values 5 78 high la sc 8 3 th sc 4 0 and ni co 1 4 ratios and low ti zr 16 sc cr 0 16 and sc ni 0 16 ratios which imply a passive continental margin nature of the basin the high k2o value 3 0 high k 2 o na 2 o ratio 1 96 lree enrichment flat hree pattern consistent negative eu anomaly high la cn yb cn 10 6 and th sc 4 0 ratios and low la th 2 4 ratio low ni 30 ppm and cr 47 ppm contents and uniform zr hf ratio largely reflect continental provenance and probable proterozoic age these rocks also differ from archaean granulites of the fold belt with regards to k2o and th u values and deformational history

petrological characteristics of archean graywackes abstract in terms of qfr and alkali element k na relationships most archean graywackes are similar to phanerozoic quartz intermediate graywackes however a number of important differences preclude direct comparisons felsic volcanic rock fragments greatly outweigh andesitic rock fragments in archean graywackes whereas the reverse is seen in phanerozoic examples in comparison to phanerozoic quartz intermediate graywackes archean graywackes tend to have about 5 lower silica contents a dominantly volcanogenic provenance can be documented for several archean graywacke suites in almost all examples plagioclase dominates over k feldspar but this alone cannot be taken as evidence for a volcanic source because early archean granitic rocks are typically sodium rich tonalites trondhjemite the abundance of quartz in most archean graywackes q typically 40 is indicative of a major granitic component archean graywackes tend to have high feo mgo values typically 8 0 and in this respect are similar to quartz poor graywackes or modern sands deposited in fore arc basins it is suggested that these high values represent moderate amounts of mafic volcanic debris which have degraded to form part of the matrix thus many archean graywackes appear to have been derived from the well established igneous bimodal suite mafic volcanics na granites felsic volcanics characteristic of many archean terranes the petrological differences between archean graywackes and their younger counterparts preclude direct interpretations of tectonic setting but the petrology of many archean graywackes is consistent with deposition at the edge of continents

a model for the influence of local inhomogeneities on the magnetotelluric variations at two van stations in greece abstract the magnetotelluric impedance tensor has been measured for the stations thiva and loannina of the van network in greece a model is suggested that can explain the distortion of the tensor by near surface structure if a 3 d near surface local structure and a 1 d regional one are considered the values calculated for the ratio ew ns are in reasonable agreement with the experimental ones the calculated values for the strike direction are 40 and 15 for thiva and ioannina respectively these values are comparable to the experimental ones of 40 5 and 15 5

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

fluid flow near reservoir lakes inferred from the spatial and temporal analysis of the electric potential electric self potential sp variations have been monitored continuously from 1995 to 1998 at 14 points on a ridge separating the roselend and la gittaz reservoir lakes in the french alps the lakes have level variations of at least 50 m over yearly cycles seasonal variations of sp associated with lake level variations are observed on five points of the array for three points located on the banks of the lakes a positive correlation to the lake level variations is observed with a maximal amplitude of about 180 mv corresponding to an average response of 2 4 mv per meter of water for two points located on the bottom of each lake the correlation is negative with a maximal magnitude of about 50 mv corresponding to an average response of 1 1 mv per meter of water two independent temporary electrical arrays located on the banks of each lake confirm these measurements and allow a better spatial characterization of the sources associated with the observed sp variations in particular near the roselend lake the electrical response to lake level variations is increasing for decreasing altitude the measured sp variations are proposed to result from the electrokinetic coupling associated with a vertical groundwater flow connecting a constant pore pressure source to the bottom of the lakes numerical modeling indicates that the spatial variation of the response and the nonlinear response observed at one point can be explained by leakage currents in the conductive lake water the values of the streaming potential coefficient spc measured in the laboratory with crushed rock samples from the site range from 14 to 50 mv 0 1 mpa for an electrolyte resistivity of 40 m and are compatible to first order with the magnitude of the observed seasonal sp variations a detailed quantitative electrokinetic modeling is currently limited mainly by the poor knowledge on the contribution of electrical leakage currents and the local variability of the spc this experiment indicates that spatial and temporal variations of the electric potential are promising tools to characterize and monitor shallow groundwater flow and provide practical data for the investigation of groundwater flow associated with volcanic or tectonic activity

quartz arenites review and interpretation abstract quartz arenites orthoquartzites are exceptional sands pettijohn et al 1972 that in the past have formed extensive and commonly thick formations they are somewhat enigmatic in that they do not appear to be forming at the present time this paper examines the origin of quartz rich sands documents the range of environments in which they are found and suggests a model for their genesis quartz sand is most commonly formed by tropical weathering of coarse grained quartz bearing rocks such as granite it may be deposited as texturally immature fluvial sandstones generally under a humid climate with drying of the climate quartz rich bauxitic soils and sandy alluvium can be a substantial source of poorly rounded dune sands for major deserts quartz sand when transported into shallow marine environments becomes very well rounded through reworking by tidal currents such sand may spill into deep oceanic environments and by sedimentary or tectonic transport may come to rest in both stable and active tectonic settings quartz rich sandstones can also be formed by diagenetic destruction of labile framework grains of immature sandstones precambrian orthoquartzites are commonly thick and widespread when compared to younger examples the thinness of post silurian quartz arenites may be largely due to the trapping effect of land vegetation and solution of quartz by organic acids in weathering profiles there is an abundance of shallow marine and fluvial quartz arenites in the early paleozoic and the cretaceous this is due to widespread continental flooding and a humid world climate following the disintegration of supercontinents the shallow marine examples are commonly associated with bituminous sometimes phosphatic shale glauconite and possibly chamositic ironstone there is an abundance of eolian quartz arenites in the permo triassic this is related to a widespread dry continental climate during assembly of the pangean supercontinent

evolution of a provenance as revealed by petrographic analyses of cretaceous formations in the queen charlotte islands british columbia canada two contrasting marine sedimentary facies the haida formation of sandy and argillaceous sediments and the conformably overlying honna formation of gravelly sediments were formed within different types of tectonic basins during mid to late cretaceous time the sediments of both formations were derived from the east sandstones from the two formations show characteristics of mature magmatic arc provenance and are classified as lithic and feldspathic arenites however the honna sandstones are more feldspathic and less quartzose than the haida sandstones the honna sandstones have many volcanic rock fragments vrf but the haida sandstones do not feldspars of the vrf rich honna sandstones however do not seem to have been derived from the breakdown of volcanic rocks the observed petrographic differences between the two formations can be ascribed to a process in which the volcanic cover and the basement rock denudation took place simultaneously in the source area during deposition of the honna formation

from cadomian arc to ordovician passive margin geochemical records preserved in metasedimentary successions of the orlica śnieznik dome in sw poland the chemical composition of metamorphosed siliciclastic rocks in the orlica nieznik dome bohemian massif identifies the main sources for the neoproterozoic the mlynowiec formation mf early cambrian the stronie formation sf and late cambrian early ordovician the goszow quartzites gq sediments the mf developed from erosion of a cadomian magmatic arc along the northern gondwana margin the variegated sf with supra subduction affinities shows chemical characteristics pointing to erosion of the freshly exhumed cadomian orogen and detritus deposition in the back arc basin the very different chemical features of the gq indicate deposition in a basin sited on a passive continental margin the explanation proposed for the observed changes in chemical composition involves three main stages 1 the pre 540 ma evolution of an active continental margin and related back arc basin ceased with the collision and accretion of the magmatic arc to the gondwana margin 2 early cambrian rift to drift transition 540 500 ma and development of a depositional basin filled with detritus derived from remnants of the magmatic arc 3 peri gondwana break up leading to the formation of shallow water passive margin depositional basins filled with quartz rich detritus resembling early ordovician armorican quartzites known from other parts of the variscan belt

electromagnetic induction in new zealand analogue model and field results abstract the behaviour of electric and magnetic variations over north island new zealand is studied with the aid of a laboratory analogue model the source field frequencies used in the analogue modelling simulate naturally occurring geomagnetic variations of 5 120 min periods in phase and quadrature magnetic and electric fields for a selection of traverses for the modelled region of north island are presented since north island is of a relatively narrow cross section the field responses even for inland locations are expected to show strongly the effects of the surrounding ocean the irregular coastlines as well as the strait between north and south islands lead to coastal and inland field anomalies due to induced currents being deflected and channelled to produce localized current densities the comparison of model results with field station measurements obtained earlier individually by ingham and by midha for sites in the northeastern central and southern near cook strait regions of north island demonstrates the large role the ocean has in the observed field responses differences in the model and field results at some sites are expected and should reflect the effects of the local geology and the conductive substructure related to the complex tectonics of the region not simulated in the model

geochemistry of archean shales from the pilbara supergroup western australia archean clastic sedimentary rocks are well exposed in the pilbara block of western australia shales from turbidites in the gorge creek group ca 3 4 ae and shales from the whim creek group ca 2 7 ae have been examined the gorge creek group samples characterized by muscovite quartzchlorite mineralogy are enriched in incompatible elements k th u lree by factors of about two when compared to younger archean shales from the yilgarn block alkali and alkaline earth elements are depleted in a systematic fashion according to size when compared with an estimate of archean upper crust abundances this depletion is less notable in the whim creek group such a pattern indicates the source of these rocks underwent a rather severe episode of weathering the gorge creek group also has fairly high b content 85 29 ppm which may indicate normal marine conditions during deposition rare earth element ree patterns for the pilbara samples are characterized by light ree enrichment lanybn 7 5 and no or very slight eu depletion eueu 0 82 0 99 a source comprised of about 80 felsic igneous rocks without large negative eu anomalies felsic volcanics tonalites trondhjemites and 20 mafic ultramafic volcanics is indicated by the trace element data very high abundances of cr and ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for

the sandstone memory of the evolution of a triassic volcanic arc in the southern alps italy the erosion of a southern volcanic belt provided the bulk of the fine grained and moderately sorted siliciclastic detritus in the whole deltaic to lagoonal carnian upper triassic sequence of the bergamasc alps volcanic input began in the early carnian calcare metallifero bergamasco and became prominent in early middle val sabbia sandstone and late carnian times s giovanni bianco fm after an intervening period of diminished supply gorno fm the mineralogical and chemical composition of the sandstones compares closely with that of siliciclastics derived from modern pacific type magmatic arcs and it testifies to an evolution of the source rocks from andesites and dacites during the deposition of the val sabbia sandstone towards rhyodacitic ignimbrites for the s giovanni bianco fm the marked reduction in feldspars at the top of the sequence contrasts with the classical trend from undissected to dissected magmatic arc provenance and is ascribed to the progressive deepening of erosion into middle triassic felsic volcanics an increase in undulatory and polycrystalline quartz grains in the late carnian shows that the erosion did reach deeper into the crystalline roots of the arc although non volcanic detritus never exceeded 10 after a terminal pyroclastic event in middle late carnian times suggested by the sudden appearance of pumiceous vitric clasts at the top of the val sabbia sandstone the mid triassic orogenic magmatism ended and was followed by the tensional stage which led to the birth of neotethys

water in the mantle results from electrical conductivity beneath the french alps 1 a deep magnetotelluric sounding in the french alps provided a vertical electrical conductivity profile between 200 1000 km two prominent features are observed first the conductivity in the depth range 400 800 km is smaller than the conductivity of a pyrolite mantle obtained from laboratory results for a normal geotherm second the data do not require the conductivity to change throughout the transition zone 410 660 km in this part of the mantle a temperature of 350 450 c less than normal explains the magnetotelluric conductivity profile at 200 400 km our model favors a cold mantle with 1000 1500 ppm of water dissolved in olivine if correct this model suggests that the subducted slab is dehydrated before reaching the transition zone

petrology and geochemistry of greywackes from the aravalli supergroup rajasthan india and the tectonic evolution of a proterozoic sedimentary basin the proterozoic aravalli supergroup in south central rajasthan western india is predominantly composed of coarse low grade meta arenites carbonates greywackes interbedded fine grained silty arenites and metapelites resting on an archaean basement complex of gneisses schists and high grade metasediments we have differentiated four lithofacies a b c and d within the greywacke suite each with characteristic qfl composition grain size and major trace and rare earth element concentrations tectonic setting for each facies type could only be discriminated using qmflt plots greywackes of facies a and d were derived from a recycled orogen and facies b was derived from arc related andesitic source rocks a continental block provenance is indicated for the silty arenites of facies c this petrofacies based interpretation shows good agreement with environmental reconstructions based on lithofacies and sedimentary structure analyses the only exception is facies b whose andesitic parentage as deduced from petrofacies analysis could not be demonstrated at its outcrop these provenance discriminations were tested through tectonic setting interpretations based on major trace and rare earth elements the geochemical data broadly confirmed the tectonic interpretations made on the basis of the petrological attributes use of these laboratory based methods in conjunction with field measurements of primary sedimentary structures allow us to discriminate provenance and tectonic setting fairly precisely a proterozoic plate model with subduction to the west has been proposed to explain the sedimentological variation in the aravalli supergroup

petrography of modern marine sands from the peru chile trench and adjacent areas sand samples from piston cores taken in the peru chile trench and adjacent areas were examined petrographically in an attempt to characterize sands from the oceanward side of a continent margin volcanic arc framework composition averaged q18f44l38 close to the average reported for this type of setting but showed wide variation in the ratio of feldspar to lithic fragments quartz was uniformly low less than 30 samples rich in lithic grains were from sites that lie off areas of recent volcanism on the adjacent continent samples from off southern central america had compositions more like those found in island arc settings averaging q3f21l76 whereas those from the straits of magellan increased in quartz and decreased in lithic fragments toward the atlantic plagioclase was greatly predominant over k feldspar in all samples and averaged an28 a considerable portion of the plagioclase was close to end member albite suggesting recycling from pre existing sedimentary rocks climate had no obvious effect on the framework proportions or the feldspar composition but the volume of sediment in the trench increases with increasing rainfall on the continent

geochemistry characterization of groundwater in an agricultural area of razan hamadan iran this study was conducted to evaluate factors regulating groundwater quality in an area with agriculture as main use thirty groundwater samples have been collected from razan area hamadan iran for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater the chemical compositions of the groundwater are dominated by na ca2 hco3 cl and so42 which have been derived largely from natural chemical weathering of carbonate gypsum and anthropogenic activities of fertilizer s source the production of so42 has multiple origins mainly from dissolution of sulphate minerals oxidation of sulphide minerals and anthropogenic sources the major anthropogenic components in the groundwater include na cl so42 and no3 with cl and no3 being the main contributors to groundwater pollution in razan area

direct observation of channelling of induced currents summary the cook strait between the two main islands of new zealand affords an excellent opportunity to study the channelling of induced oceanic electric currents between regions of much lower conductivity we report here on simultaneous recordings of magnetic field variations on both islands and the voltage in a cable across the strait which enabled us to determine the magnitude and direction of the channelled current the observation of large currents approximately perpendicular to the direction expected in a homogeneous medium clearly demonstrates the dominance of channelling over local induction in the strait

evolution of lower proterozoic epicontinental deposits stromatolite bearing aravalli rocks of udaipur rajasthan india abstract the aravalli rocks 2060 ma old which crop out around udaipur western india comprise a thick sequence of metasediments with stromatolites and basal volcanics resting unconformably over a peneplained basement known as the banded gneissic complex ca 2585 ma old the rocks have undergone a very low grade of metamorphism and display a complex structure resulting from two major and several minor episodes of folding there are two distinctly different facies sequences in the aravalli rocks indicating deep sea and nearshore shelf environments the stratigraphic sequence of the rocks deposited under the shelf environment starts with basic volcanics and tuffs altered to greenschists and quartizites with arkosic conglomerate in the next sequence carbonates predominate in association with orthoquartzites carbonaceous phyllites phyllites and stromatolitic rock phosphate the carbonate sequence passes upward into greywacke phyllite lithic arenite in the distal parts and conglomerate arkose orthoquartzite in proximal areas the youngest sequence comprises orthoquartzite with silty arenite the distribution of different facies particularly that of dolomite with stromatolitic rock phosphate is controlled by sea floor topography suggesting the presence of an epicontinental sea bounded by a landmass to the west and a series of islands and shoals sedimentation in the shelf and epicontinental sea was presumably triggered by development of fault controlled troughs along craton margins terrigenous debris was deposited in newly developed troughs with contemporaneous volcanicity along trough margins with the erasing of the ephemeral relief in the provenance carbonate deposition was initiated the environment encouraged algal growth and formation of stromatolitic rock phosphate carbonaceous phyllites developed in areas of restricted circulation rapid influx of terrigenous detritus with renewed tectonism in the next phase resulted in the deposition of a turbidite sequence of greywacke phyllite and lithic arenite in the deeper parts of the epicontinental sea and conglomerate arkose orthoquartizite in the marginal areas the final phase of sedimentation was presumably under fluvial conditions which marked the completion of epicontinental trough filling the nature of the terrigenous clasts indicates a predominantly granitic source of sediments supply of sediment was mainly from the continent to the east and partly from a landmass to the west the cycle of sedimentation noted in the epicontinental aravalli sea is broadly similar to the model of tectonic stages suggested by krynine 1942

magnetovariational measurements in the cook strait region of new zealand abstract magnetovariational measurements have been made at 10 sites on the northern side of the cook strait new zealand single station transfer functions have been calculated for the sites and indicate that the effect of induction in the shallow water of the cook strait is most important at around 1000 s period at longer periods the effect of induced currents in the pacific ocean predominates a two dimensional electrical conductivity model including local conductivity structure has been shown to satisfy the measured responses at sites about 60 80 km distance from the strait closer to the strait the inductive process is strongly three dimensional a simple d c line current model of current flow has been shown to reproduce some of the features of the observed responses induction arrows indicate the existence of conductivity anomalies associated with a known lateral seismic boundary and with one of the two principal faults in the region

2 d or 3 d interpretation of conductivity anomalies example of the rhine graben conductivity anomaly summary evidence of a conductivity anomaly in the rhine graben was first given about 15 years ago and consequently led to the definition of various models of induction in the region for periods ranging from a few minutes to a few hours these models reflect two antagonistic ways of explaining the observed anomalous variations of the magnetic field direct induction in a two dimensional 2 d structure or static distortion of telluric currents by the resistive crystalline vosges france and schwarzwalde germany massifs we discuss the two approaches using a simple formalism in particular we show that the self induction related to the anomalous currents flowing in the rhine graben is negligible for periods larger than 1000 s and that even though the static distortion of telluric currents does account for the observed anomaly 2 d models can explain some of its features we also show how the channelled currents are induced in the large sedimentary basins surrounding the area under study an experimental verification of this result is given

critical evaluation of six tectonic setting discrimination diagrams using geochemical data of neogene sediments from known tectonic settings abstract an attempt is made to evaluate 6 tectonic setting discrimination diagrams 1 discriminant function and 5 bivariate diagrams frequently used by many researchers for this purpose an extensive database was established for major element geochemistry derived from miocene to recent sand and sandstone medium to fine grained samples collected from a variety of tectonic settings including 1 passive margin pm setting 2 active continental margin acm setting and 3 oceanic island arc oia setting our results suggest that the discrimination fields proposed to infer tectonic settings for six commonly used discrimination diagrams do not work properly for the analyzed miocene to recent sediments the success for these diagrams varies from 0 to about 62 we therefore recommend that these diagrams be used with prudence

age source and stratigraphic implications of pb isotope data for conformable sediment hosted base metal deposits in the proterozoic aravalli delhi orogenic belt northwestern india abstract stratiform sediment hosted base metal deposits in the aravalli delhi orogenic belt of northwestern india are hosted by the sediment dominated bhilwara aravalli and delhi sequences of proterozoic age pb isotope data for 36 samples from five ore districts provide useful stratigraphic and approximate age information model pb ages using a newly developed proterozoic model are 1800 ma for the rampura agucha rajpura dariba and saladipura deposits 1700 ma for the zawar deposits and 1100 ma for the ambaji and deri deposits mineralization in this orogenic belt thus occurred at three stages in middle to upper proterozoic times the oldest of these reflected by deposits in the bhilwara sequence was of broad regional extent the rampura agucha deposit is thus hosted by highly metamorphosed rocks that belong to the bhilwara belt and not to an older supracrustal component of the archean banded gneissic complex the host rocks to the saladipura deposit are bhilwara equivalent and are not part of the delhi supergroup as previously mapped and therefore stratigraphic assignments in the area must be re examined model ages of 1100 ma for the ambaji deri deposits are the only evidence obtained in this study regarding the age of the delhi supergroup and are in apparent conflict with much older ages indicated by previous studies rocks of such late upper proterozoic age may be restricted to the southwestern segment of the orogenic belt or alternatively thrust stacking and or interfolding of lithologically similar sequences of a wide range of ages throughout the belt may not yet be evident because of the limited age and isotopic data presently available all the data can be readily explained by the extraction of pb from sediments derived from an upper crustal basement the isotopic compositions of the zawar deposits provide the clearest evidence for an ancient u enriched upper crustal source the ambaji deri pb data suggest a mature status of the delhi are when these deposits were formed

grain size control of mineralogy and geochemistry in modern river sediment new guinea collision papua new guinea the new guinea collision includes diverse sediment source areas associated with arc continent collision to the west of the solomon sea triple junction and with subduction of oceanic crust to the southeast and northeast of the triple junction twenty seven sediment suites each comprising up to seven gravel sand and mud samples from the same locality were analysed to determine mineralogical and geochemical variation with changing grain size this paper deals primarily with the mineralogical variation compositional variation from coarse to fine grained fractions is generally 50 of each variable s abundance with many variables showing greater than 100 variation in contrast variation due to analytical error is generally less than 10 between year variation generally ranges from 15 to 25 and downstream variation is generally less than 50 petrographic results indicate that sediment composition is fundamentally dependent on grain size the principal control on sediment composition is mechanical weathering of rock fragments and compositional sorting of the constituent mineral phases while the gazzi dickinson method for point counting sediment reduces modal variability and in most cases provides robust provenance discrimination it is unsuitable for discerning faint source rock signatures often revealed by grain size dependent compositional variation only the upper plate magmatic arc provenance signature is evident from recalculated modal and geochemical data and that signature does not reflect the modern upper plate magmatic arc detailed petrographic analysis of grain types as opposed to recalculated modal or geochemical data is required to elucidate both upper and lower plate provenances and discriminate between ancient and contemporary arc provenances

composition and weathering conditions of paleoproterozoic upper crust of bundelkhand craton central india records from geochemistry of clastic sediments of 1 9ga gwalior group abstract the 1 9 ga gwalior group represents one of the major paleoproterozoic depositional basin of bundelkhand craton and is comprised of 1 km thick unmetamorphosed and undeformed sedimentary succession with basal clastic sequence of sandstone shale association par formation and an upper chemogenic bif rich sequence morar formation the geochemical examinations of the basal clastic rocks are the subject of present study the compositional maturity and extreme quartz enrichment in sandstones of gwalior group suggest slow upliftment and high in situ weathering of basement terrains in a stable platformal setting these clastic sediments are characterized by strong depletion of mobile constituents like ca sr and na high plagioclase index of alteration pia values and strong positive correlation between al 2 o 3 and tio 2 indicating severe weathering of upper crust positive correlation between feo t and tio 2 suggests fe retention in paleoweathering profiles and is attributed to oxygenated atmosphere post depositional potash metasomatism is indicated in a cn k systematics of these sediments and k enrichment from near zero to as high as 38 is inferred with most of the shale samples show 30 extraneous k 2 o additions depleted transition element ni cr co sc contents elevated large ion lithophile element lile k rb ba th light rare earth elements lree contents fractionated rare earth element ree patterns strong negative eu anomalies in these sediments point toward k rich intracrustal granitic source component steeper ree patterns avg la yb n 12 57 compared to basement granites and conspicuous depletion of y over other liles in auc normalized spidergram also suggest a heavy rare earth element hree depleted ttg source component minor contribution from tholeiitic mafic rock is evidenced from th sc sc la sc sc th systematics and positive correlation of transition elements with feo t and tio 2 mixing calculations on the ree data suggest that upper continental crust of bundelkhand craton was constituted of 40 granite 40 ttg and 20 mafic rocks this is in contrast with the present day composition of bundelkhand granite gneiss complex bggc that contains 90 high k granite the data suggest unroofing of granite batholiths by means of erosion and upliftment of supracrustal ttg cover

a study of diurnal variation of the electromagnetic field in northern france using ancient recordings summary from 1883 to 1901 magnetic elements were continuously recorded at the french saint maur observatory from 1893 to 1895 earth potentials along two 15 km long orthogonal lines were also recorded moreover from 1884 to 1885 blavier ingenieur des telegraphes used several some hundred kilometre long telegraphic lines to measure and record earth potentials using this set of data we will study the daily variations of the telluric and magnetic fields and the way according to which these two fields are correlated the observed magnetotelluric tensor is antisymmetric when the long telluric lines are considered it is not the case for the short lines but making use of a correction derived from the formalism developed by le mouel menvielle in the static distortion approximation one can derive an impedance whose phase is equal to the phase of the impedance derived from the long line data

south african modern beach sand and plate tectonics south america is the ideal continent for baseline studies on how the framework composition of modern sands relates to reconstruction of palaeoplates it has well defined active and passive margins great contrasts in climate and relief and is free of continental glaciation fig 1 i report here petrographical studies of its beach sands which show two active margin associations rich in volcanics and plagioclase one along its pacific coast and one along the argentine coast and two associations rich in quartz a passive margin association from argentina to trinidad and a moderately quartz rich association along the caribbean coast tectonic control is thus overwhelming but complications exist along the argentine coast where a dry narrow continent permits active margin sand to mantle a passive margin another surprising result is that quartz rich sands border the crystalline rocks of much of the sera do mar in brazil

south america and a few grains of sand part 1 beach sands to study correlations between petrography and provenance of modern sands and thus contribute to improved interpretation of ancient sandstones this study reports on the petrography of 218 modern south american beach sands obtained from a shoreline of 25 300 km judged by quartz feldspar rock fragment ratios there are five major associations pacific 24 16 60 argentina 28 14 58 brazil 91 4 5 caribbean east 59 8 23 and caribbean west 54 17 29 study of potash feldspar volcanic rock fragments and the sio 2 al 2 o 3 ratio supplement q f rf ratios tectonics are the dominant control on the mineralogy both the pacific and brazilian associations which form 75 of south america s coastline identify correctly tectonic setting that is active margin composition for the pacific and passive margin for the brazilian however the argentine association would yield a serious error because sand with active margin composition overprints a passive margin variation of total quartz and feld

pb zn deposits and salt bearing diapirs in southern europe and north africa many diapirs with triassic evaporite successions in southern europe and north africa are accompanied by strata bound pb zn mineral deposits these are of two types 1 epigenetic mineralization filling cavities exhibiting analogies with mississippi valley type deposits and 2 syndiagenetic mineralization in sediments rich in organic materials this second type is very similar to the so called volcanic exhalative type in most of these ore deposits diapirism seems to be a determining factor in the development of base metal concentrations diapir growth can be divided into four distinct stages initiation ascent piercement and subsequent deformation study of north african and southern european deposits has led to a genetic model of diapir emplacement and associated pb zn mineralization the source of these metals is unknown the transport of the metals is provided or facilitated by the brine from adjacent triassic evaporites deposition of sulfides occurs where the deep fluids meet the upper beds these deposits can be remobilized with each new phase of diapir growth

composition of modern deep sea sands from arc related basins summary petrographic and chemical examination of modern deep sea sands shows a clear distinction between active and passive plate tectonic settings among active settings sands from forearc basins of island arcs and basins from strike slip continental margins can be distinguished but those from other arc related settings overlap considerably in composition in particular sands from continental margin subduction zones and those from the backarc of island arcs appear to be indistinguishable chemically arc related sands are very close in composition to ancient greywacke sandstones for instance sodium almost always exceeds potassium thus it is not necessary for sodium to be added to sands diagenetically to make greywackes as has been suggested the influence of tectonics on the composition of sandstones has long been a central feature of sandstone petrology the geosynclinal model of global tectonics stimulated much thought on this subject probably the best known ideas are those of krynine e g 1942 subsequently such research declined but the plate model for global tectonics has produced a new wave of interest e g crook 1974 schwab 1975 potter 1978 dickinson suczek 1979 much of this work has relied on data from ancient sediments where diagenetic changes and difficulty in de ciphering the tectonic setting limit the useful ness of the conclusions much more work is needed on recent sediments to establish a base line against which ancient sediments can be compared we have previously reported valloni maynard 1981 the results of our work on the petrography of a set of recent deep sea sands from piston cores in this paper we shall com pare this petrographic information with bulk chemistry and attempt to relate these to tecto nics in arc related settings

compositional suites of terrigenous deep sea sands of the present continental margins the compositional variability shown by sands of present continental margins was determined through conventional microscopic techniques this allowed the establishment of a descriptive classification of deep sea terrigenous sands based on a restricted number of commonly used parameters the fundamental sand types include 1 qf suite sands in which quartzose and or feldspathic grains predominate carbonate l bearing sands on average richer in lithics occur within this suite 2 ql suite in which quartzose and or lithic grains predominate little compositional diversification is apparent within this suite 3 fl suite in which lithic and or feldspathic grains predominate two compositional members can be identified based on the k feldspar plagioclase ratio 4 lv suite consists of sands in which volcanic grains largely dominate the lithic types vitric and serpentine sands occur within this suite the suites are related to distinct source area types defined as follows 1 cratonic block 2 sedimentary orogenic belt 3 volcanic orogenic belt 4 volcanic arc some sands cannot be easily assigned to a single compositional suite because petrologic parameters overlap with an adjacent suite such critical compositions are commonly arkosic using roundness of the framework components it is possible to define a category identified as matured sands which are greatly enriched in resistates

composition provenance and tectonic setting of eze aku sandstone facies in the afikpo synclinorium southern benue trough nigeria field study petrographic and major element geochemical composition of the eze aku sandstone facies outcropping in the afikpo synclinorium southeastern nigeria were utilized in this study the aim is to interpret the provenance and tectonic setting for sandstones in the sedimentary basin field observation shows alternating sequence of parallel sandstone ridges trending ne sw and shales which represent the low lying plains in the area four major sandstone facies were identified massive conglomeritic sandstone facies laminated sandstone facies bioturbated sandstone facies and cross bedded sandstone facies ternary plots for framework elements quartz feldspar and rock fragments from petrography of the sandstones indicate the sandstones as arkosic and subarkosic arenites tectonic setting discrimination diagrams plotted based on major element oxides revealed continental block provenance dominantly in a passive continental margin petrographic and geochemical results indicate large amounts of detritus were derived principally from plutonic igneous rocks with minor contribution from metamorphic source region probably from obudu plateau oban and cameroon massifs

geology geochemistry and tectonic setting of archaean greywackes from karnataka nucleus india more than 80 of the area covered by the chitradurga and shimoga schist belts 3 0 2 6 ga of karnataka nucleus india is made up of greywackes feldspathic lithic and quartzose greywackes are deposited respectively along the western northern and the eastern margin of the chitradurga schist belt greywackes of the shimoga schist belt show a large compositional scatter between feldspathic and lithic types compositional differences indicate variable provenance for the different localities tonalite trondhjemite gneisses ttg mafic ultramafic schists basic intermediate acid volcanic rocks sedimentary rocks like banded iron formation quartzites and cherts and k granites in minor quantity were exposed in the source area volcanic debris was also contributed from contemporaneous volcanism in the basin greywackes in this region are invariably interbedded with fine grained biotite rich phyllites and schists marked compositional differences are observed between the greywackes and the interbedded phyllites the greywackes have k2o na2o 1 whereas phyllites show large variation in k2o na2o ratios ranging from 1 5 to 15 0 high cr ni content of the greywackes and phyllites of the chitradurga belt are indicative of an important contribution from ultramafic rocks light ree enrichment and negative eu anomalies are particularly pronounced in the mudpacks of the greywackes represented by phyllite the ree and other chemical data such as la th ti zr and k2 mgo ratios indicate that these greywackes were supplied from a juvenile continental nucleus and were laid down on a simatic and converging active continental margin an archaean miniplate model with low angle subduction and sedimentary basins of moderate size is proposed to explain the geochemical and tectonic features of the schist belts

bacterial effects on the mobilization of cations from a weathered pb contaminated andesite abstract mobilization of contaminant pb and other cations from a weathered andesite was examined by conducting water rock leaching experiments to measure release rates of the major and minor elements found in the bulk rock experiments were conducted for over 600 h at ph 3 and 6 5 as a function of grain size and in the presence and absence of a common subsurface bacterial species bacillus subtilis the acid leaching experiments exhibited enhanced pb mobilities the contact area between mineral surfaces and water controlled the amount of most elements leached into solution typically bacteria accelerated the leaching of trace elements however major element levels were inversely correlated with bacterial content and generally lower major element concentrations were observed in the presence of bacteria relative to the bacteria free systems this effect was likely caused by bacterial enhancement of secondary mineral precipitation rates extremely low concentrations of pb were leached into solution during the course of the experiments under conditions most closely approximating natural conditions i e near neutral ph moreover the release rate of pb relative to other elements was low pb was associated with iron oxides precipitated in the rock pore spaces and the experiments suggest that the iron oxides dissolved to a lesser extent than did other minerals in the rock matrix the mobility of the pb associated with these iron oxides was less than that of other heavy metals that were likely associated with the surrounding matrix

geochemical characteristics of the triassic tethys turbidites in northwestern sichuan china implications for provenance and interpretation of the tectonic setting the triassic tethys graywacke slate turbidites in the northwestern sichuan china have been analysed for major and trace elements and petrographically studied compared to phanerozoic turbidites the turbidites in this study are quartz intermediate average 55 in composition and are characterized geochemically by their moderate fe2o 3 mgo 9 28 2 84 tio2 0 72 0 17 contents and al2o3 sio2 0 25 0 10 ratios moderate abundances of ferromagnesian trace elements co 15 8 ppm cr 113 72 ppm ni 14 9 ppm sc 12 4 ppm etc and moderate contents of incompatible elements such as th 11 3 ppm u 3 0 7 ppm zr 170 64 ppm hf 4 1 ppm and total rees 159 33 ppm in general the slates show systematically higher fe2o 3 mgo sc co and eueu but lower sollasc and thsc than the associated graywackes suggesting that various provenance components may separate into different grain size fractions during sedimentary sorting processes that is the more mafic materials tended to incorporate into the sedimentary record for the clay size fraction framework modes and geochemical data indicate that the turbidites were mainly derived from a recycled orogenic provenance characterized chiefly by sedimentary metasedimentary rocks and granite gneisses similar to the upper continental crust but with a variable admixture of continental island arc volcanic components flysch deposition took place in a back arc basin situated between an active continental margin the kunlun qinling fold belt and a continental island arc the yidun island arc weathering conditions in the source area significantly influenced the composition and distribution of elements in the sediments with the elapse of time during sedimentation the degree of chemical weathering in the provenance became intense while the tectonic activity decreased gradually

evolution of the taupo hikurangi subduction system abstract the present day taupo hikurangi subduction system is a southward extension of the tonga kermadec arc system into a sediment rich continental margin environment it consists of a shallow structural trench the hikurangi trough a 150 km wide imbricate thrust controlled accretionary borderland the continental slope shelf and coastal hills of eastern north island a frontal ridge the main greywacke ranges of north island and a volcanic arc and marginal basin the taupo volcanic zone structural elements become progressively more elevated and subduction more oblique towards the south the whole nne trending system is truncated at a largely strike slip transform boundary that extends along the southwestern part of the hikurangi trough and the hope fault of south island to the main alpine fault the volcanic arc is 200 270 km from the structural trench and comprises a nne trending chain of andesite dacite volcanoes extending along the eastern side of the taupo volcanic zone most of the andesites are olivine bearing and have been erupted within the last 50 000 years it is suggested the taupo hikurangi margin has evolved by rotation of accretionary elements from an original nw trending subduction system north of new zealand the older elements of the prism were associated with subduction of a re entrant of the pacific plate and perhaps the south fiji basin in mid tertiary times they subsequently became separated from their nw trending volcanic arc by dextral strike slip movement along curved faults east of the main greywacke ranges during the plio pleistocene oblique subduction and accretion intensified as the taupo hikurangi margin rotated into line with the nne trending kermadec system and a marginal basin was developed along a similar trend to form the taupo volcanic zone within the last 50 000 years olivine bearing andesite volcanism has commenced along the eastern side of the taupo volcanic zone

useful characteristics of shallow and deep marine csem responses inferred from 3d finite difference modeling hydrocarbon reservoirs can be mapped if sufficient resistivity contrastsexistbetweenthemandtheirconfininglayers butpractical problems remain in target discrimination in deep and shallowwaters especiallyinthepresenceofheterogeneousoverburden wehavedevelopedanefficient3dstaggered gridfinite difference controlled source electromagnetic csem modeling code that enables study of the physics underlying some practical problems we undertook a comparative analysis of reservoir detection in 2000 m and 300 m deep waters using the simulated electric and magnetic field responses of a simple 3d reservoir we examined the effect of two types of near surface heterogeneitymimickingdisconnectedgascloudsand orpatchygeochemicalalterationhalosonthe3dreservoirresponse wefoundthat small scale shallowheterogeneitiescausedistortionsthatarealmost independent of the source frequency these persist at all source receiver offsets in the electric amplitude response in deep and shallow waters and phase response in shallow water they decrease in magnitude with increasing offset in deepwater phase response large scale near surface heterogeneities distort the horizontal electric field response more significantly than the small scale ones but the near surface response gets smaller in amplitude as the offset increases the distortions in shallow water are much smaller in magnitude than those for the deepwater case so that the reservoir signatures still are visible on the responseprofiles thismightbeconsideredasapositivefeaturefor shallow water inline electric field exploration the magnetic field responses for the orthogonal direction provide diagnostic target signatures that are similar to the inline electric field responsesindeepwaterbutthataredifferentinshallowwater the magnetic responses are affected by the airwave in a different manner from the electric field suggesting that combined 3d electric and magnetic field analysis might be vital for handling theairwaveproblem

electrical resistivity structures of the kunlun qaidam qilian system at the northern tibet and their tectonic implications abstract the northern tibetan plateau is characterized by northwest southeast trending basin range systems such as the kunlun shan ranges qaidam basin qilian shan ranges the cenozoic evolution and deformation of the qaidam basin and its neighboring ranges are important indications for the northward growth of the tibetan plateau the latest magnetotelluric data were collected along a profile in n16 5 e from the songpan ganzi block across the kunlun shan ranges east section of the qaidam basin and ending in the qilian shan ranges both two dimensional and three dimensional inversions of the data along the profile were performed and the results provided new evidence for lithospheric structures in the northern tibetan plateau with three dimensional isotropic inversion codes we are able to model the phase roll out of quadrant proq magnetotelluric data which exist at low frequencies in a number of continuous sites at the northern qaidam basin sensitivity studies of the three dimensional models indicate that the qaidam basin with low resistivity upper crust is the major contributor for the proq effect while a south north striking low resistivity gap intersecting with the qaidam basin at its northern part affects the range of the proq effect in the magnetotelluric resistivity models the qaidam basin is not in symmetric structure at upper crust level with its depocenter near the northern qaidam fault at mid lower crust level the compositions of both the kunlun shan ranges and the southern qaidam basin are of generally high resistivity which does not support large scale lower crust materials of the songpan ganzi block flow below the kunlun shan ranges or the qaidam basin instead the unsymmetrical qaidam basin and the shovel shape high resistivity anomalies in crust below the kunlun shan ranges and the southern qiadam basin indicate the regional northward push from the songpan ganzi block the south deepening low resistivity anomalies in the crust of the qilian shan ranges support the existence of an intracrustal detachment which controls the thrusts in northern qaidam basin and the qilian shan ranges the crustal deformation in northern tibetan plateau is consistent with mantle convergence or collision between the kunlun qaidam lithospheric mantle and the asian lithospheric mantle

upper mantle lateral heterogeneities and magnetotelluric daily variation data we use telluric and magnetic data of the diurnal variation recorded in europe australia and north america to study the magnetotelluric tensor in the 6h 24h period range we use associate directions and we eliminate the effects of deviation of telluric currents we thus obtain for each observatory reliable phases and apparent resistivity values representative of the neighbouring stratified substratum it appears that the values obtained in the four european observatories saint maur france ebro spain toledo spain nagycenk hungary give similar results and that these results are different from those obtained either in tucson usa or in watheroo australia

magnetic measurements on la soufriere volcano guadeloupe lesser antilles 1976 1984 a re examination of the volcanomagnetic effects observed during the volcanic crisis of 1976 1977 abstract during the seismovolcanic crisis of 1976 1977 at la soufriere on guadeloupe a magnetic network of 12 reference markers was set up measurements of the intensity of the earth s magnetic field carried out up to once a day at each marker showed volcano magnetic variations of several nanoteslas nt the variations at certain markers were more or less concealed by transient magnetic variations due to anomalies in conductivity as early as 1978 measurements were resumed and a telemetering network was coupled with the network of reference markers to which 4 new markers were added a detailed study of conductivity anomalies was carried out on the entire volcano contrasts in conductivity linked to the existence of a superficial conducting surface on a ssw nne axis located south of the volcano caused a great lack of homogeneity in the field variations measured at the surface variations greater than about 10 nt appeared in the difference in intensity of the earth s magnetic field between two stations no long term magnetic variation was observed between 1978 and 1984 on the network of markers the accuracy of measurements of volcanic effects was at best 2 nt measurements carried out on the telemetering network during the night refined these results since their accuracy was 1 nt the only significant volcanic crisis between 1978 and 1984 5 7 january 1981 seems to be observed by telemetering stations all the measurements carried out in periods of volcanic inactivity make it possible to re examine the crisis of 1976 1977 though volcanomagnetic effects over short periods cannot be accurately determined variations with a time constant of several weeks were present over the entire volcano these variations were as high as 7 8 nt in remote stations and they can be linked to the three major phases of eruptive activity at la soufriere during the crisis of 1976 1977

geochemistry of the headwaters of the yangtze river tongtian he and jinsha jiang silicate weathering and co2 consumption water and sediment samples were collected from the headwaters of the yangtze river tongtian he and jinsha jiang upstream of the yangtze river which flows on the eastern qinghai tibet plateau a detailed geochemical study of the river system was carried out to determine i temporal and spatial variations of the major ions and their implications ii contribution of carbonate silicate and evaporite to the river dissolved load and iii co2 consumption via silicate weathering results show that cations derived from evaporite dissolution account for 44 7 82 8 of the total cations in the headwaters of the yangtze river and increasing from se to nw of the drainage basin the contribution from silicate weathering gradually increases from the headwaters due to exposure of intrusive rocks and volcanic rocks in the jinsha jiang suture belt proportion of cations derived from silicate weathering to the total cations in river waters reaches a maximum at panzhihua city which is consistent with the abundant exposure of cenozoic granitoids and precambrian high grade metamorphic rocks around panzhihua the jinsha jiang basin has higher silicate weathering rates but lower carbonate weathering rates than the middle and lower reaches of the yangtze river the calculated enrichment factors of potentially harmful metals in the river sediments are within the range of 0 33 2 59 indicative of level 1 or 2 contamination the highest enrichment factor for co cr and v is found in panzhihua city indicating that it has been influenced by anthropogenic sources

trace element geochemistry and sedimentary provinces a study from the tasman geosyncline australia abstract the abundances of la th u and hf have been determined in flysch sequences of the tasman geosyncline australia the arc derived graywackes differ from those of rifted continental margins and marginal basins in containing low abundances of la th u and hf la 9 2 1 7 ppm th 1 4 0 6 ppm u 0 52 0 2 ppm hf 2 1 0 6 ppm reflecting similar low abundances in the andesitic source rocks graywackes of rifted continental margins and marginal basins in contrast are mature and characterised by high abundances of la th u and hf la 39 9 9 ppm th 16 0 6 ppm u 3 40 0 5 ppm hf 7 9 ppm mirroring increased abundances in the granitic and sedimentary source rocks sedimentary rocks deposited in inter arc basins show wide dispersion but have characteristics intermediate between these two types the th u ratio for magmatic arc sediments is 2 7 for most other sedimentary rocks it remains uniform at 4 5 0 3 for sediments having andesitic and dacitic rocks as provenance the la th ratios are 6 7 and 4 5 respectively this ratio remains constant at 2 6 for most quartzose sedimentary rocks

geochemistry of metasediments from the precambrian hapschan series eastern anabar shield siberia abstract the precambrian hapschan series in the anabar shield in northern siberia is composed of garnet paragneisses pelitic graywackes marbles calciphyres and calc silicate rocks carbonates and carbonate rich clastic sediments and a minor amount of enderbite and mafic granulite trace element distributions in the paragneisses especially ree patterns and low cr and ni suggest felsic sources for the graywacke protoliths with exception of mn pb and sr trace elements in hapschan carbonates and calc silicates are housed chiefly in chiefly silicate contaminant phases when normalized to al2o3 to partially compensate for trace elements contained in al silicates most trace elements are depleted in hapschan carbonates relative to average phanerozoic marine limestone pml rb cr ni and ti are strikingly depleted in hapschan as well as other precambrian high grade carbonates relative to pml the element depletions in hapschan marbles may be explained by some combination of loss during granulite facies metamorphism or by removal in another depository such as bif geologic and geochemical data are consistent with deposition of the hapschan series in a cratonic or passive continental margin setting during the early proterozoic basement to this series may be the high grade rocks of the daldyn and upper anabar series from which a zircon u ion probe age of 3 3 ga has been reported

major ion chemistry in the headwaters of the yamuna river system chemical weathering its temperature dependence and co 2 consumption in the himalaya abstract the yamuna river and its tributaries in the himalaya constitute the yamuna river system yrs the yrs basin has a drainage area and discharge comparable in magnitude to those of the bhagirathi and the alaknanda rivers which merge to form the ganga at the foothills of the himalaya a detailed geochemical study of the yrs was carried out to determine i the relative significance of silicate carbonate and evaporite weathering in contributing to its major ion composition ii co2 consumption via silicate weathering and iii the factors regulating chemical weathering of silicates in the basin the results show that the yrs waters are mildly alkaline with a wide range of tds 32 to 620 mg l 1 in these waters the abundances of ca mg and alkalinity which account for most of tds are derived mainly from carbonates many of the tributaries in the lower reaches of the yamuna basin are supersaturated with calcite in addition to carbonic acid sulphuric acid generated by oxidation of pyrites also seems to be supplying protons for chemical weathering silicate weathering in yrs basin contributes on average 25 molar basis of total cations on a basin wide scale silicate weathering however does not seem to be intense in the basin as evident from low si na k in the waters 1 2 and low values of chemical index of alteration cia in bed sediments 60 co2 drawdown resulting from silicate weathering in the yrs basin in the himalaya during monsoon ranges between 4 to 7 105 moles km 2 y 1 this is higher than that estimated for the ganga at rishikesh for the same season the co2 consumption rates in the yamuna and the ganga basins in the himalaya are higher than the global average value suggesting enhanced co2 drawdown in the southern slopes of the himalaya the impact of this enhanced drawdown on the global co2 budget may not be pronounced as the drainage area of the yrs and the ganga in the himalaya is small the co2 drawdown by silicates in the yrs basin is marginally higher than the reported values of co2 release from oxidation of organic rich sediments estimated using re as a proxy this comparison shows the need to constrain co2 sources and sinks better to balance its budget in a regional scale the results also show that silicate weathering rate in the yrs basin is 10 mm ky 1 and on the ganga basin it is 5 mm ky 1 which are several times lower than the carbonate weathering rates the significantly higher silicate weathering rate observed in the yrs basin seems to be governed by rapid physical erosion in this region the apparent activation energy for overall silicate weathering in the yrs basin derived from na and si concentrations and water temperature ranges from 50 to 80 kj mol 1 these values are comparable to those reported for granitoid weathering in natural watersheds and feldspar weathering in laboratory experiments this study brings to light the sources contributing to major ions enhanced chemical weathering rates in the yamuna river basin and interdependence of silicate weathering on physical erosion and temperature

detrital modes and provenance of the stilo capo d orlando formation miocene southern italy the stilo capo d orlando formation sco fm is a miocene clastic unit nonconformably covering the basement of the southern portion of the calabria peloritani arc cpa a small scale terrane which was accreted onto the apennines maghrebides orogenic system during neogene time the sco fm is composed of conglomerate sandstone and mudrock deposited in a marine environment through the action of gravity currents detrital modes of sandstones and conglomerates of the sco fm indicate a local provenance in fact petrological parameters can be matched directly with nearby basement lithologies two petrofacies with distinctive parameters are present a northern petrofacies is predominantly composed of plutonic and low grade metamorphic detritus and was derived from the serre massif which is mostly made of late hercynian plutons intruded into metasedimentary rocks a southern petrofacies is mostly composed of metamorphic detritus and was derived from the aspromonte and the peloritani mountains which are predominantly composed of middle to high grade metamorphic rocks petrological results place important constraints on the geodynamic evolution of the cpa according to several authors the arc is composed of two sectors microterranes with different geological histories and partly composed of contrasting rock types whose timing of juxtaposition is debated early cretaceous against middle late miocene that is much before or soon after deposition of the sco fin the sco fm crops out only in the southern sector of the cpa and does not contain any detritus derived from the northern sector in spite of a favourable sediment palaeodispersal system this fact indicates that the amalgamation of the two sectors probably took place after deposition of the sco fm

diagenesis of sandstones in the back arc basins of the western pacific ocean sandstones occur in back arc basins of the western pacific at dsdp sites 299 sea of japan 297 northern shikoku basin 445 and 446 daito ridge and basin province 453 mariana trough 286 new hebrides basin and 285 south fiji basin these sandstones are dominantly volcaniclastic arenites derived from andesitic island arcs the degree of sandstone diagenesis is dependent on original composition burial rate heat flow history of the basin and timing of sandstone deposition with respect to rifting processes and associated high heat flow sandstones containing a larger proportion of volcaniclastic components showed more diagenetic effects than sandstones containing a significant volume of other rock fragments and mineral components sandstones deposited during early stages of rifting sites 445 446 with a slow burial rate and high crustal heat flow showed the greatest degree of downhole diagenetic change these diagenetic changes include early pore space reduction and rim cementation by clay minerals followed later by calcite and subsequent pore fill cementation by clinoptilolite heulandite analcite and later calcite replacement of recognizable volcanic rock fragments by chert calcite and zeolites was observed in the deepest part of the hole sandstones deposited after rifting under conditions of associated lower heat flow showed considerably less diagenetic changes particularly if burial was rapid the high heat flow associated with earliest rifting associated fluid circulation driven by thermal convection and slow burial rate controlled the diagenetic history of these sandstones thus timing of sandstone deposition with rifting stage and associated burial rates were key factors in controlling sandstone diagenesis in back arc basins

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

volcanomagnetic effects observed on piton de la fournaise volcano reunion island 1985 1987 a permanent network of four to six telemetered magnetic stations has been installed on piton de la fournaise volcano in october 1985 and 1986 eight eruptive sequences have occurred since then some of which affected only the summit whereas others affected the whole massif volcanomagnetic variations are observed with each of these volcanic events the geomagnetic field intensity is measured simultaneously every minute at each station with a precision of 0 25 nt nanotesla the main results are the following volcanomagnetic variations observed with eruptions have amplitudes of several nanoteslas to more than 10 nt with characteristic time durations ranging from l min or less to several months a good correlation between the magnetic variations recorded at the different stations is observed spatial and temporal properties of the volcanomagnetic field appear to be controlled by the features of the eruptions several days before the beginning of the december 1985 march july november december 1986 and january 1987 eruptions changes in the intensity differences are observed with amplitudes of a few nanoteslas up to 5 nt at stations located close to the active part of the rift zone variations are also observed in the most remote stations for larger eruptions in march 1986 november december 1986 and january 1987 correlations between magnetic variations ground deformations and seismic activity have been observed for the december 1985 march 1986 november december 1986 and january 1987 events three main mechanisms could account for the observed volcanomagnetic variations piezomagnetic effects electrokinetic effects and electrical resistivity changes since variations in the stress field in the surroundings can modify the induced and natural magnetizations of magnetized rocks the circulation of water through the interconnected pore network microcracks faults aquifers and also the electrical resistivity of geological structures through the modification of the properties of the pore network

composition of plagioclase feldspar in modern deep sea sands relationship to tectonic setting microprobe analysis of plagioclase in deep sea sands from various tectonic settings gives averages ranging from 19 an for trailing edge continental margins to 56 an for basins on the ocean side of an island arc for each setting except island arcs anomalously high amounts of pure albite are found these albitic grains may be recycled from pre existing sedimentary rocks potassium rich plagioclase thought to be indicative of a volcanic provenance is less abundant than would be expected from the proportion of volcanic rock fragments perhaps such high k plagioclases are less resistant to weathering than low k plagioclase

detrital supply from subduction accretion complexes to the eocene oligocene post collisional southern thrace basin nw turkey and ne greece abstract the thrace basin is a large mostly eocene oligocene post collisional sedimentary basin which developed following the closure of the vardar izmir ankara oceanic domain latest cretaceous paleocene sandstone petrologic data framework and heavy mineral analyses and the synthesis of preexisting and new sedimentological observations along representative stratigraphic sections show that the basin fill of the southern thrace basin was mostly derived from the izmir ankara and biga intra pontide subduction accretion complexes to the south proximal facies consistently show northward paleocurrents whereas most paleocurrent indicators measured downcurrent point to an eastward paleoflow likely the result of the deflection of primary gravity flows originated along the southern margin of the basin detrital contributions from the rhodopian basement complex to the west are virtually absent within the southern thrace basin fill conversely rhodopes derived eocene proximal facies in northeastern greece are characterized by a series of coarse grained fan deltas prograding eastward and likely feeding the basin plain turbidites of the depocentral portion of the thrace basin now concealed in the subsurface to the north of our study area arenites of the southern thrace basin are mostly lithic arkoses and arkosic litharenites provenance from the izmir ankara and biga suture zones to the south is characterized by ophiolitic granitoid gneissic low grade metamorphic and extrabasinal carbonate rock fragments as well as by picotite and glaucophane the application of detailed petrographic observations for discriminating paleo vs neovolcanic and penecontemporaneous vs noncoeval terrigenous sands lead to a substantial revision of the geodynamic interpretation of the thrace basin formerly considered a forearc basin a significant penecontemporaneous volcanic component is common in the upper eocene lower oligocene section and can be related to extensive post collisional volcanism following the closure of the vardar izmir ankara ocean the coexistence of pure neovolcanic layers crystal tuffs and cinerites and hybrid arenites rich in penecontemporaneous carbonate grains with sands derived from a continental basement and ophiolitic suites indicates the presence of episutural basins where shallow water carbonates were deposited on top of the exhuming subduction accretion prism these carbonates were mixed with penecontemporaneous neovolcanic and terrigeneous components and redeposited in deeper marine environments

water chemistry and control of weathering of pichola lake udaipur district rajasthan india the water chemistry of pichola lake revealed that it is dominated by na and hco3 the lake water chemistry strongly reflects the dominance of continental weathering aided by anthropogenic activity such as tourist influx developmental activities in the catchment area and disposal of untreated municipal and domestic sewage into the lake basin the supply of major ions is mainly through weathering of the silicate rock exposed in the drainage basin and the contribution from saline and alkaline soils groundwater because of the semiarid conditions of the region the increase in phosphate loading and consequent depletion of silica suggests biological consumption of the latter the observed chemical data of pichola lake was used to predict the mineral assemblages in the carbonate and aluminosilicate system it demonstrates that calcite and dolomite are the possible minerals that are in equilibrium with the lake water system and that the lake water chemistry is in the range of stability of kaolinite

petrography and geochemistry of the cambro ordovician wajid sandstone southwest saudi arabia implications for provenance and tectonic setting abstract the wajid sandstone of probable cambro ordovician age rests unconformably on peneplained precambrian crystalline rocks on the southeastern margin of the arabian shield the sandstone is composed of varicolored siliciclastic rocks mainly coarse to fine grained sandstones with granule conglomerate and siltstone interbeds displaying diverse sedimentary primary structures such as planar and trough cross bedding and flat bedding they form repeated fining upward cycles typical of deposition from braided streams current indicators indicate that flow was from sw to nne petrographically all samples of the wajid sandstone are of quartz arenite type highly enriched in quartz but poor in heavy minerals feldspar and lithic fragments the provenance and tectonic setting of the wajid sandstone have been assessed using integrated petrographic and geochemical studies petrographic analysis reveals that mono and poly crystalline quartz grains and heavy minerals from metamorphic and igneous rocks of a craton interior setting were the dominant sources chemically major and trace element concentrations in the rocks of the wajid sandstone indicate deposition in a passive continental margin setting petrographic and geochemical data suggest that the sediments were derived from metamorphic and igneous rocks forming the adjacent precambrian basement rocks of the arabian shield and were deposited on a passive continental margin deposition took place after stabilization of the arabian shield following the late precambrian pan african orogeny the wajid sandstone can be correlated with similar deposits elsewhere in arabia and north africa which were deposited on a low lying landmass forming the stable continental margin of the arabian nubian shield flanking the southern margin of the paleo tethys ocean

electromagnetic induction in the new zealand south island abstract laboratory magnetic field measurements for a scaled analogue model of new zealand and the surrounding oceans are used to provide induction arrows for simulated geomagnetic variations of 5 120 min periods for a series of traverses over the south island as the island is relatively narrow the field responses for all on land locations show significant effects of the surrounding oceans the model simulates a uniformly resistive island the oceans and a conductive asthenosphere at depth and thus discrepancies between the model and field results for sites on the island are attributed to anomalous geological structures not simulated in the model removing the coast effects before interpretation by subtracting the model induction arrows from the field site arrows at eyrewell permits an obvious reinterpretation that attributes a significant component of the field responses to the nearby alpine and marlborough faults rather than to the channelled current in cook strait

evolution of the western continental margin french italian alps sandstone mineralogy as an index of plate tectonic setting most plate tectonic developmental models for the western or french italian alps show that the western or french continental margin of the tethyan locally piedmont ocean exhibited several contrasting types of structural behavior from late paleozoic through tertiary time initially this margin acted as a rifted passive progressively subsiding atlantic type margin from late paleozoic through jurassic time during the cretaceous and tertiary active volcanism blueschist metamorphism and indications of rapid uplift and erosion suggest that active subduction of the piedmont and valais ocean basin s occurred producing a himalayan like sutured orogenic highland local island arc trench inland sea systems and possibly even transform faults all characteristics of orogenically active continental margins like those of the modern mediterranean and around the perimeter of the present day pacific ocean compiled analyses of modern sands from present day ocean basins and continental margins have been used

the 2 7 2 0 ga volcano sedimentary record of africa india and australia evidence for global and local changes in sea level and continental freeboard abstract the 2 7 2 0 ga volcano sedimentary records of the african indian and australian cratons indicate two broadly defined periods of extensive drowning of the emergent continental areas concomitant with lowered freeboard carbonate banded iron formation bif platforms characterised the first such event at ca 2 6 2 4 ga africa and australia to 2 7 ga india these earlier globally enhanced sea levels are ascribed to increased mid ocean ridge activity possibly related to breakup of a postulated late archaean southern supercontinent alternatively a transition from global scale catastrophic mantle overturn events to the onset of plate tectonics may have occurred in the late archaean nelson 1998 earth planet sci lett 158 109 119 both explanations of increased mid ocean ridge activity are compatible with significant early to middle archaean crustal growth armstrong 1981 phil trans r soc london a 301 443 472 with the emergent high freeboard cratons being subjected to aggressive weathering and erosion enhanced continental crustal growth near the archaean proterozoic boundary mclennan and taylor 1982 j geol 90 347 361 related to the development of significant island arc complexes would have resulted in common lowered freeboard enhanced sea level conditions at the passive margins of the southern cratons the diachronous nature of these earlier transgressions in the various cratons may reflect the effect of local tectonic movements and or the thermal state of the cratons from ca 2 4 2 2 ga cratons that make up the present day continents of india africa and australia had relatively high continental freeboard and lowered sea levels glacigenic deposits are preserved on the kaapvaal africa singhbhum india and pilbara australia cratons the second broadly defined drowning event at ca 2 15 ga was probably due to post glacial climatic amelioration freeboard was reduced by the combination of eustatic rise and the reestablishment of aggressive weathering as warmer palaeoclimates returned in india carbonates were more prominent than the siliciclastic sediments including prominent black shales seen in africa and australia

effects of sedimentary sorting on neodymium isotopes in deep sea turbidites the study of neodymium model ages of sedimentary rocks has added considerably to our understanding of crustal growth and evolution so far however the possible effects of various sedimentary processes on nd isotope distributions have not been fully evaluated here we present nd isotope data for a series of sand mud pairs in modern deep sea turbidites from different tectonic settings which show that sands and muds commonly have significantly different nd isotope compositions that in only some cases are associated with differences in sm nd ratio differences are as great as 7 ndunits corresponding to nd model ages that differ by up to 0 44 gyr and may be explained by separation or unmixing of components from different sources during sedimentary transport and sorting for one sample heavy mineral fraction ation may be indicated these results have implications for studies of nd model ages in sedimentary rocks and for the interpretation of provenance from sedimentary petrography and geochemistry

compositions of sandstones in circum pacific subduction complexes and fore arc basins arc trench systems of the circum pacific orogenic belt contain voluminous sandstones within fore arc terranes that include complexly deformed subduction complexes and relatively undeformed fore arc basins of several types turbidites incorporated within subduction complexes include not only axially transported trench fill but also abyssal plain sediments deposited on the sea floor beyond the trench and slope basin deposits perched on the accretionary trench slope mean framework modes of circum pacific sandstone suites can be expressed adequately by the use of qfl and qmflt plots supplementary qmpk and qplvls plots depict partial modes of mineral grains alone and polycrystalline lithic fragments respectively source rocks were mainly volcanic and plutonic terranes of he circum pacific magmatic arcs although some recycled sedimentary and metasedimentary debris is also present analysis of point counts for 2 587 rocks grouped into 104 suites from california the pacific northwest southern alaska southwest japan and new zealand indicates that the characteristic fore arc sandstones display similar compositional ranges everywhere and can be termed the circum pacific volcano plutonic graywacke suite knowledge of their petrology may aid the recognition of analogous tectonic settings in the geologic past frameworks vary across a compositional spectrum that ranges chiefly from feldspatholithic sands derived mainly from volcanic cover in undissected magmatic arcs to lithofeldspathic sands derived largely from plutonic batholiths in dissected magmatic arcs quartz contents are typically intermediate and the feldspar to quartz ratio is semiconstant plagioclas is the dominant feldspar and volcanic rock fragments are commonly the most abundant lithic fragments interpretations of compositional trends within subduction complexes and adjacent fore arc basins imply that simple transverse delivery of sediment from the arc orogene to the fore arc region is not the rule instead sand evidently is distributed along subduction zones by longitudinal turbidity currents initiated at widely spaced sediment delivery points where sediment derived from tectonic culminations along the arc trench system can bypass the sediment traps of fore arc basins moreover turbidites shed from dormant or transform segments of arc orogenes are locally spread far into the ocean basin as abyssal plains which are later rafted bodily into the subduction zone finally no sedimentologic explanations of compositional contrasts across fore arc graywacke terranes can be acce ted without considering the alternative of postdepositional tectonic transport by strike slip

etude du champ magnetique anormal d origine intralithospherique the separation of the anomalous magnetic field with respect to the depth of lateral contrasts of conductivity is discussed in this paper it is shown that for most geophysical cases this separation is very simply performed for periods greater than 1800 s the anomalous field of an intralithospheric source is the difference between the observed anomalous field and the one related to the lateral contrasts of conductivity in the superficial part of the crust mostly the coast effect electromagnetic data observed in california are analysed using this method an anomalous field of intralithospheric source is shown to exist the study of this field provides us with indications about lateral variations of the physical and chemical conditions in the lithosphere the obtained results are in good agreement with data drawn from other earth sciences finally we show that such results can be obtained in other tectonically active areas japan and peruvian andes

a note on the use of statistics in reporting detrital clastic compositions error polygons and error bars are commonly used graphical methods for showing the precision associated with means on triangular diagrams and orthogonal plots respectively if the error or precision associated with a mean based either upon counts of individual components or upon count ratios is to be defined using basic statistics the confidence interval method should be used standard deviation alone which has been frequently in the literature is not an appropriate statistic to use for this purpose the graphical use of confidence intervals permits a rapid visualization of statistically significant differences between means and thus more quantitative description of detrital clastic composition previous investigators using the standard deviation method have underestimated the precision of their data when sample sizes are large and overestimated precision with small samples

tectonic versus chemical weathering controls on the composition of fluvial sands in tropical environments the compositions of fluvial sands collected in mountainous regions along the volcanic front in central america and along the andean front in venezuela and colombia correlate with the tectonic setting of their source terrains the sands derived from the central american volcanic arc are compositionally distinct from those derived from the andean terrains and minor variations in tectonic style can also be discriminated subtle differences in tectonic setting and source rock composition are recognizable only when modification by chemical weathering is slight they are strongest in sands from low order streams draining mountainous areas with modest alluvial plain development sands that have been exposed to weathering for extended periods during alluvial storage are progressively enriched in chemically stable phases with increased weathering sands from continental terrains converge toward a supermature quartz arenite end member and the imprint left by source rock composition and tectonic setting is obscured in intraoceanic terrains a similar but much less pronounced enrichment in stable phases relative to less stable phases is observed similarly overprinting the tectonic signal although detailed tectonic information is easily lost sands derived from intraoceanic terrains are distinguishable from those derived from continental terrains even after long exposure to intense chemical weathering conditions

provenance of the palaeocene eocene clastic rocks of the komandorsky islands the palaeocene eocene sequence on the komandorsky islands is represented by sediments and minor volcanics with a total thickness of more than 3000 m sandstone siltstone mudstone siliceous rocks and conglomerate which have accumulated in the upper and middle parts of a deep water fan prevail all the debris was delivered from the north east from the side of the contemporary komandorsky basin in the bering sea products of volcanic denudation and fresh tephra dominate its composition however at some levels the sandstone contains fragments of jasper quartzite slate schist gabbro and granite as well as non volcanic quartz along with a volcanic component the heavy minerals fraction of the sandstone contains considerable quantities of apatite zircon garnet and chromite as well as pyroxenes amphiboles and magnetite the chemical composition of the garnet is specific to metamorphic rocks a significant admixture of chromite is indicative of denudation from an ophiolite complex the folded and partly metamorphosed pre palaeogenic rocks were a source of these fragments their most likely source terrane was the shirshov bowers chain cretaceous palaeoarc the komandorsky block originally was the forearc part of the aleutian arc where the latter was superimposed on the shirshov bauers chain a subsequent north west displacement of forearc structures in response to the transform fault at the boundary between the pacific and north american plates could have resulted in the separation of the komandorsky block from its early palaeogene debris source area

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

petrography and geochemistry of cenozoic sedimentary sequences of the southern samar island philippines clues to the unroofing history of an ancient subduction zone abstract the cenozoic sedimentary sequences of southern samar island in eastern philippines were examined to understand the unroofing history of an ancient arc terrane petrographic and geochemical data revealed varying degrees of inputs from the ophiolite basement and differences in modal compositions the sedimentary units are mostly made up of lithic fragments the late oligocene to early miocene daram formation contains more chert and volcanic fragments whereas the late middle miocene to early pliocene catbalogan formation is dominantly composed of ultramafic components these variances are correspondingly reflected in the geochemical signatures of these two sedimentary formations the catbalogan formation clastic rocks have higher volatile free mgo and fe2o3 values average 8 4 for both oxides compared to the daram formation samples average 5 1 and 6 3 respectively geochemical variations are also reflected in the co cr and ni values the catbalogan formation samples reflect higher concentrations co 15 57 ppm cr 231 1094 ppm ni 84 484 ppm compared to the daram formation samples co 24 32 ppm cr 234 418 ppm ni 212 323 ppm these observations suggest that the daram formation eroded and transported more of the crustal portions of the ophiolite while the younger catbalogan formation represents a later exhumation and subsequent erosion of the ultramafic section an oceanic island arc oia setting is proposed for the two formations based on several tectonic discrimination diagrams e g th la sc la vs th the oia signature is further supported by their smooth chondrite normalized rare earth element ree patterns with no obvious eu anomaly as well as lree enrichment which are typical of sediments deposited in oia setting based on the dominantly ophiolitic provenance of the daram and catbalogan formations the post emplacement history of the nearby samar ophiolite is constrained during the late oligocene to early pliocene period