a deep seismic sounding investigation of lithospheric heterogeneity and anisotropy beneath the iberian peninsula abstract the dimensions of the iberian peninsula the facility of firing large charges in the surrounding waters the well known and relatively uniform geology and prior knowledge of the crustal structure resulted in it being chosen as a study area for the investigation of the seismic structure of the lower lithosphere via refraction wide angle reflection seismic profiling the iberian lithosphere heterogeneity and anisotropy experiment iliha with a star shaped arrangement of six long range dss profiles was carried out in october 1989 the models derived from a first interpretation of the recorded data are presented three crustal profiles cover the same western and central part of the hercynian massif as the mantle profiles the resulting interpretations all include a middle as well as a lower crustal layer above the mantle the velocities of the layers in all three models are similar however the layer depths vary beneath the profiles interpretation of the mantle derived data suggests a layered lower lithosphere one reversed line and an intersecting unreversed line indicate the layering penetrates to at least 90 km depth the homogeneity of these layers contrasts strongly with the heterogeneous hercynian surface geology velocities derived from reflected data from the deep layers suggest the constituent materials are either anisotropic or that the layers suffer a slight regional dip

deep structure of fennoscandia from fundamental and higher mode dispersion of rayleigh waves abstract surface wave dispersion for the baltic shield area has been investigated through analysis of phase velocities up to periods of about 250 s for the fundamental rayleigh mode and about 80 s for the first two higher modes this has enabled investigation of the lithosphere asthenosphere system and deeper regions down to about 400 km the shear wave velocitydepth relationship obtained from the inversion of dispersion data for the paths cop kev cop krk can be considered as representative of an average model for the baltic shield moreover the inversion of dispersion data supplemented by previous results from the scandinavian area suggest the presence of significant lateral heterogeneity down to depths of about 350 km moving from the older precambrian shield cop kev cop krk to the peripheral area nur cop models with small if any differences in average shear velocity are consistent with the data in the depth range 350 450 km for the regions studied

pb sr and nd isotopic and chemical evidence for a primitive island arc emplacement of the el arco porphyry copper deposit baja california mexico the el arco porphyry copper deposit is located in central baja california and is a resource containing 600 mt of ore with 0 6 copper it was emplaced within a relatively primitive jurassic island arc and it was subsequently metamorphosed and intruded by the cretaceous peninsular ranges batholith the porphyritic stock intrusion and ore formation at el arco has recently been dated at 165 ma valencia et al geos 24 189 2004 this age is much older than aptian albian k ar ages previously reported from el arco barthelmy geology of el arco calmalli area baja california mexico msc thesis san diego state university ca 1975 baja california geology san diego state university ca pp 127 138 1979 the copper mineralization at el arco is concentrated in a core of potassic alteration in a dioritic porphyritic stock surrounded by propylitic alteration in andesitic lavas mafic dikes that intruded the deposit are not mineralized but they are affected by post ore low grade metamorphism the dikes are compositionally the most primitive rocks while host rock andesites and the porphyry stock display typical volcanic arc characteristics the pb isotope data from sulfides feldspars quartz and whole rock samples indicate that 1 the copper bearing porphyry stock and the surrounding andesites evolved from a similar source with an average value of 9 43 2 no external pb was added during mineralization 3 some pb isotope compositions were slightly disturbed by a later metamorphic event strontium and nd isotopes show that the magmas evolved from a depleted mantle reservoir with no involvement of older continental crust our data favor a model for the formation of the el arco deposit linked to a triassic to jurassic intra oceanic arc system cropping out at the western margin of central baja california in the cedros vizcaino region the intra oceanic arc together with the el arco deposit was accreted to the active continental margin of north america and metamorphosed during the early cretaceous this model is in disagreement to earlier models that favor the el arco deposit formation being linked to the cretaceous continental margin

the fluvial geochemistry of the rivers of eastern siberia i tributaries of the lena river draining the sedimentary platform of the siberian craton abstract the response of continental weathering rates to changing climate and atmospheric pco 2 is of considerable importance both to the interpretation of the geological sedimentary record and to predictions of the effects of future anthropogenic influences while comprehensive work on the controlling mechanisms of contemporary chemical and mechanical weathering has been carried out in the tropics and to a lesser extent in the strongly perturbed northern temperate latitudes very little is known about the peri glacial environments in the subarctic and arctic thus the effects of climate essentially temperature and runoff on the rates of atmospheric co 2 consumption by weathering are not well quantified at this climatic extreme to remedy this lack a comprehensive survey has been carried out of the geochemistry of the large rivers of eastern siberia the lena yana indigirka kolyma anadyr and numerous lesser streams which drain a pristine high latitude region that has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts common to western eurasia and north america the scale of the terrain sampled in terms of area is comparable to that of the continental united states or the amazon orinoco and includes a similarly diverse range of geologic and climatic environments in this paper the chemical fluxes from the western region the very large ancient and geologically stable sedimentary basin precambrian to quaternary of the siberian platform will be presented and compared to published results from analogous terrains in the tropical basins of china while the range in the chemical signatures of the various tributaries included here 60 sampled is large this mainly reflects lithology rather than the weathering environment the areal chemical fluxes are comparable to those of the chinese rivers being dominated by the dissolution of carbonates and evaporites the net consumption of atmospheric co 2 by aluminosilicate weathering is minor as it is in the tropical basins it is much smaller than in active orogenic belts in similar latitudes e g the fraser and yukon but comparable to those of the mackenzie tributaries that drain the eastern slope of the rockies lithology exerts the dominant influence in determining the weathering yield from sedimentary terrains and for a largely carbonate evaporite terrain climate does not have a direct effect

lead isotope compositions of late cretaceous and early tertiary igneous rocks and sulfide minerals in arizona implications for the sources of plutons and metals in porphyry copper deposits porphyry copper deposits in arizona are genetically associated with late cretaceous and early tertiary igneous complexes that consist of older intermediate volcanic rocks and younger intermediate to felsic intrusions the igneous complexes and their associated porphyry copper deposits were emplaced into an early proterozoic basement characterized by different rocks geologic histories and isotopic compositions lead isotope compositions of the proterozoic basement rocks define from northwest to southeast the mojave central arizona and southeastern arizona provinces porphyry copper deposits are present in each pb isotope province lead isotope compositions of late cretaceous and early tertiary plutons together with those of sulfide minerals in porphyry copper deposits and of proterozoic country rocks place important constraints on genesis of the magmatic suites and the porphyry copper deposits themselves the range of age corrected pb isotope compositions of plutons in 12 late cretaceous and early tertiary igneous complexes is 206 pb 204 pb 17 34 to 22 66 207 pb 204 pb 15 43 to 15 96 and 208 pb 204 pb 37 19 to 40 33 these pb isotope compositions and calculated model th u are similar to those of the proterozoic rocks in which the plutons were emplaced thereby indicating that pb in the younger rocks and ore deposits was inherited from the basement rocks and their sources no pb isotope differences distinguish late cretaceous and early tertiary igneous complexes that contain large economic porphyry copper deposits from less rich or smaller deposits that have not been considered economic for mining lead isotope compositions of late cretaceous and early tertiary plutons and sulfide minerals from 30 metallic mineral districts furthermore require that the southeastern arizona pb province be divided into two subprovinces the northern subprovince has generally lower 206 pb 204 pb and higher model th u and the southern subprovince has higher 206 pb 204 pb and lower model th u these pb isotope differences are inferred to result from differences in their respective post 1 7 ga magmatic histories throughout arizona pb isotope compositions of late cretaceous and early tertiary plutons and associated sulfide minerals are distinct from those of jurassic plutons and also middle tertiary igneous rocks and sulfide minerals these differences most likely reflect changes in tectonic setting and magmatic sources within late cretaceous and early tertiary igneous complexes that host economic porphyry copper deposits there is commonly a decrease in pb isotope composition from older to younger plutons this decrease in pb isotope values with time suggests an increasing involvement of crust with lower u pb than average crust in the source s of late cretaceous and early tertiary magmas lead isotope compositions of the youngest porphyries in the igneous complexes are similar to those in most sulfide minerals within the associated porphyry copper deposit this pb isotope similarity argues for a genetic link between them however not all pb in the sulfide minerals in porphyry copper deposits is magmatically derived some sulfide minerals particularly those that are late stage or distal to the main orebody or in proterozoic or paleozoic rocks have elevated pb isotope compositions displaced toward the gross average pb isotope composition of the local country rocks the more radiogenic isotopic compositions argue for a contribution of pb from those rocks at the site of ore deposition combining the pb isotope data with available geochemical isotopic and petrologic data suggests derivation of the young porphyry copper related plutons most of their pb and other metals from a hybridized lower continental crustal source because of the likely involvement of subduction related mantle derived basaltic magma in the hybridized lower crustal source an indiscernible mantle contribution is probable in the porphyry magmas clearly in addition pb was contributed from the local country rocks this is most evident in sulfide minerals in veins that are late stage hosted in proterozoic gneiss and or peripheral to the porphyry copper deposit

deep structure of southeastern europe from rayleigh waves abstract the analysis of rayleigh wave phase velocities up to about 250 s has allowed of deepening structural knowledge down to several hundred kilometers underneath the triangular array formed by the wwssn stations athens istanbul l aquila for the path l aquila istanbul a lid to low velocity channel contrast of variable size is always present while for the other two paths athens istanbul and athens l aquila two alternative patterns are possible one indicating the presence of a contrast between lid and low velocity channel the other suggesting the absence of significant layering down to depths of about 350 km

major ion chemistry of groundwater in a river basin a study from india groundwater is the prime source in the area of varaha river basin andhra pradesh india groundwater samples collected during pre and post monsoon were analyzed for major ion chemistry to understand the operating mechanism of geochemical processes for variation of groundwater quality low ionic concentration is observed in the groundwater occurring at topographic highs and towards the river compared to the rest of the area this is caused by the influence of recharge water geochemistry of groundwater is observed to be mainly controlled by the rock weathering mineral dissolution leaching ion exchange and evaporation and is subsequently modified by the anthropogenic and marine activities contribution of residual soluble salts below the depth of 5 m from the ground surface is high while it is low beyond the depth of 5 m anthropogenic activities cause an accumulation of excess residual soluble salts in the former depth and the content of this soluble matter is reduced by the clay products beyond the latter depth seasonal ionic concentration of groundwater is greatly influenced by the recharge process with reference to topographical features lithological characteristics and anthropogenic activities groundwater quality is classified as mixed and non carbonate alkali groups due to a combined action of geogenic anthropogenic and marine sources respectively the groundwater quality is above the adequacy level for both drinking and irrigation and appropriate management measures are recommended for sustainable development

preliminary magnetotelluric studies along the hellenic volcanic arc implications for the collision between the african plate and the aegea microplate abstract from middle upper miocene time to the present the african plate has subducted under the so called aegea microplate a prominent feature of this continental collision is the past and present volcanic activity along the hellenic volcanic arc hva which is sited 200 km behind the frontal compressional region since 1986 several magnetotelluric mt surveys have been undertaken along the hva and particularly on the islands of milos kos and nisyros to determine their subsurface electrical structure the derived electrical models have indicated very low resistivities less than 30 m for the uppermost 10 km which have been related to known i e milos and nisyros or potential i e kos geothermal anomalies evaluation of the existing electrical models and subsequent 1d modelling of the broadband mt data has revealed some deeper greater than 10 km depth electrical features of the lithosphere below the hva study of the azimuths of the major axes of the rotated impedance ellipses and the parkinson induction arrows in the period range 10 2 10 4 s has led to their association with the subduction and extensional processes taking place in the aegean the mt results are in agreement with the observed gravity values magnetic anomalies and the results from geotectonic deep seismic refraction and seismological studies finally proposal for the future study of the deep electrical structure of the aegean is presented

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region abstract de jonge m r wortel m j r and spakman w 1993 from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 53 65 the seismic velocity structure of the upper mantle and lithosphere in the mediterranean region is very complex many areas with anomalous p wave velocities can be recognized by means of seismic tomography in view of the complicated tectonic evolution of the peri mediterranean orogens and basins this is not surprising in this study we will show results of a modelling approach we have recently developed to predict this structure in this approach we make a quantitative connection between the tectonic evolution on one hand and the present seismic velocity structure on the other our model predicts the evolution of temperature distributions in the lower lithosphere and upper mantle by simulating the flow of material inferred from a kinematic description of lithosphere scale processes from the modelled present thermal state the endpoint of an evolution we calculate expected seismic velocity anomalies that can be compared with results obtained by seismic tomography thus the method enables us to compare the implications of geological reconstructions describing the past tectonic processes with seismological results for the present structure the predicted mantle models show a good correlation with the tomographic results obtained for the mantle this means we can verify many features present in the tectonic scenarios with the seismologically determined deep structure

shear wave velocity variations in the upper mantle beneath central europe summary a new model eur s91 of shear wave velocity variations in the upper mantle beneath central europe and surrounding regions down to a depth of 670km is presented the model is derived from the inversion of the waveforms of 217 seismograms using the partitioned waveform inversion method for the seismogram in the time window from the s wave arrival to the fundamental mode of the rayleigh wave the seismograms were mostly assembled from digitally recording long period and broad band stations in europe the resulting 3 d model accurately predicts most of the observed waveforms in a wide band of frequencies body waves were fit for frequencies up to 60mhz the fundamental rayleigh mode which at high frequencies is more prone to scattering and multipathing was generally low passed at 25 mhz the resolving power of the data set depends strongly on the density of available wave paths and varies as a function of geographical position small scale heterogeneities like the subducted lithosphere in the hellenic collision zone were imaged in the region with the highest density of wave paths which indicates an optimum resolution of better than 200 km the main new results of this study pertain to the transition between east and central europe we present new information about the structure below the tornquist teisseyre zone ttz the ttz is generally regarded as the boundary between the precambrian crust of the baltic shield russian platform and the younger crust of central europe our 3 d s velocity model reveals that below this line a sharp lateral boundary extends down to at least 140 km depth with high velocities beneath the baltic shield and russian platform contrasting to the low velocities beneath the younger regions of europe the observed velocity contrast across the ttz is largest between the pannonian basin and the russian platform where it is equal to 12 per cent at 80 km depth at depths of 300 400 km the ttz is underlain by a zone of low s velocity which indicates a local thinning of the deeply rooted high velocity structure or tectosphere that underlies most of eastern europe in addition to these new results on the transition region between east and central europe a number of features that are present in other tomographic results have been confirmed the precambrian provinces of europe are characterized by high s velocities low velocities are found beneath the pannonian basin the western mediterranean northern aegean sea turkey and a small region south west of the massif central the lithosphere beneath the paris basin has a positive s velocity anomaly the resolution of all these anomalies has been established with sensitivity tests

isotopic and geochemical characteristics of laramide magmatic systems in arizona and implications for the genesis of porphyry copper deposits major element trace element and nd sm and rb sr isotope data are described from igneous rocks in 11 multiphase magmatic complexes of laramide age in arizona eight complexes contain barren stocks as well as productive plutons associated with the formation of porphyry base metal deposits whereas in three complexes porphyry orebodies have not been recognized most of the complexes evolved through similar stages early dominantly intermediate volcanic rocks were intruded by multiphase complexes temporally characterized by increases in sio 2 changes in the ferromagnesian mineral assemblage increasingly porphyritic textures and a progression from barren to subproductive to productive intrusions within complexes the sequence is independent of both the absolute age of initiation of local magmatism and its duration analytical data and field relationships are combined to show elements of the petrogenetic history of these complexes potential relationships between productive and barren magmas and factors which may have influenced formation of the characteristic magmatic hydrothermal sequence the isotopic composition of laramide igneous rocks forms an array from epsilon ndt and 87 sr 86 sr initial values of 0 and 0 704 to 14 and 0 710 respectively early volcanic rocks have a more primitive signature consistent with retention of a significant mantle component subsequent intrusions were derived predominantly from isotopically heterogeneous precambrian lower crust but probably also contain an undefined amount of mantle component individual complexes do not exhibit any consistent isotopic trends over time and unique types of source rocks are not indicated for productive magmas in contrast rare earth elements ree in several complexes display temporally systematic behavior progressively younger intrusions in a given complex follow a path of decreasing concentration of ree steepening profiles greater upward concavity in heavy ree profiles and changes in the eu anomaly from negative to either markedly less negative or positive the ree data from individual complexes suggest an increasing petrogenetic involvement of amphibole either in the restite of the source region or as a fractionating phase and similar paths of petrogenetic evolution in spite of chronologic and trace element evidence which argues against completely comagmatic development productive and barren intrusions cannot be clearly distinguished by the isotopic data but the systematic ree trends parallel increasing productivity of magmas in individual complexes models which reconcile isotopic variation systematic ree behavior protracted local but largely noncomagmatic magmatism and the increasing development of porphyry mineralization include 1 progressive metasomatism of the crustal component 2 increasing assimilation of amphibolitic crust by mantle basalts and 3 migration of crustal anatexis from deep anhydrous rocks to shallower amphibolites the relative importance of these processes cannot yet be clearly assessed from the data but a plausible metallogenic impact of each would be upon the concentration and possibly the composition of magmatic volatiles in the primary melts and or during subsequent fractionation in this light existing models which propose that the principal control upon intrusion productivity is a balance between crystal fractionation and the timing of saturation and release of magmatic hydrothermal fluids may be strongly influenced by processes operative either in their source regions or during their interaction with the crust initiation of such processes may be a response to abrupt changes in tectonic regime in the volcanic are environment

hydrochemical characterization of drinking groundwater with special reference to fluoride in an arid area of china and the control of aquifer leakage on its concentrations the objective of the study is to determine the distribution and origin of fluoride in two confined aquifers within the depth of 80 240 m mid deep confined aquifers in shizuishan city an arid area in northwest china based on geological and hydrogeological conditions the distribution patterns of fluoride in the two confined aquifers were studied correlation analysis was used to reveal the mechanisms and reactions influencing the groundwater chemistry the control of aquifer leakage induced by intense groundwater abstraction on fluoride concentrations was also discussed the results show that the concentration of f in some locations of the study area is beyond the limit of the standards for drinking water quality of china correlation analysis shows that the major reactions occurring in the confined aquifers are dissolution of gypsum fluorite and halite and precipitation of calcite and dolomite groundwater leakage from shallow aquifers is also responsible for the elevation of fluoride in mid deep confined aquifers the research is a scientific basis for the rational development and utilization of groundwater in this area and it may be referenced by international scholars for similar research in other parts of the world

single crystal 40ar 39ar dating of pyrite no fool s clock single crystals of dispersed trace pyrite from two igneous rocks were dated by using the 40 ar 39 ar laser probe method and the resulting ages were compared to step heating ages of associated amphibole and phlogopite the isochron ages for 0 1 0 3 mm cubes of pyrite agree well with the respective amphibole ages of these igneous samples preliminary step heating analyses of single pyrite crystals yield internal isochrons with indistinguishable although less precise ages both pyrite and amphibole are significantly older than associated phlogopite in one sample which has undergone postcrystallization alteration these results suggest that pyrite can give reliable and precise 40 ar 39 ar ages even in the presence of subsequent alteration given the ubiquity of pyrite in many geologic environments this technique has great promise for application to the dating of ores sediments and hydrocarbon migration all of which have been very difficult to date directly

geochemical criteria for a refined tectonic discrimination of orogenic andesites abstract minor trace element and sr isotope data are compiled for tertiary recent orogenic andesites of three tectonic settings 1 oceanic island arcs divided into low k and other andesites 2 continental island arcs and thin continental margins and 3 thick continental margins andean from 1 to 3 there is a steady overlapping increase in la ce ree la yb la y th th u zr y hf yb and ni co and a decrease in k la p la sc cr and sc ni optimum discriminationis achieved with a plots of la yb vs th and la yb vs sc ni and b cluster analysis using the critical parameters listed above shoshonitic andesites and high mg andesites boninites are considered separately orogenic andesites are distinguished from non orogenic andesites by high contents of al low contents of ti zr ree y nb ta and ga and the absence of pronounced negative eu anomalies

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

tectonic history of a jurassic backarc basin sequence the gran canon formation cedros island mexico based on compositional modes of tuffaceous deposits the jurassic gran canon formation cedros island baja california mexico constitutes an unusually well preserved and exposed example of ancient backarc basin fill petrofacies analysis conducted on tuff aceous sandstone and tuff samples from this formation complement and reinforce prior lithofacies interpretations but with some modification when temporal and spatial trends in petrographic data detrital modes are analyzed and compared to mod els based on data collected from deep sea drilling project and ocean drilling pro gram cores the trends indicate a second heretofore unrecognized phase of backarc rifting basalt lavas interstratified with da citic pyroclastic rocks of the primary vol canic lithofacies previously interpreted to record the eruption of differentiated mag mas at the climax of growth of the gran canon island arc are now as a result of this study considered to be the product of arc extension and rifting our method of modal analysis uniquely combines the quantification of textural at tributes of pyroclastic and epiclastic debris that reflect eruption style and magma com position as well as the effects of reworking and mixing in marine settings this study demonstrates that detailed petrographic analysis is useful in the interpretation of ancient volcaniclastic deposits suspected of having formed in backarc basin settings

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

an interpretation of wide angle compressional and shear wave data in southwest germany poisson s ratio and petrological implications shear wave velocity especially when used with compressional wave velocity is an important constraint on estimates of the composition and physical state of the continental lithosphere we present shear velocity s models derived from high quality s wave data along three profiles in southwest germany which combine with existing p wave velocity p models to give poisson s ratio in the crust and uppermost mantle we then construct a laterally varying petrological model of the crust by comparing our p and s models with published laboratory measured rock velocities in general poisson s ratio is 0 25 in the uppermost crust 0 22 0 23 in the mid crust but reaching a low of 0 15 in the black forest low p zone and varies laterally from 0 24 to 0 30 in the lower crust the average poisson s ratio of the whole crust is everywhere about 0 25 the laminated signature of the lower crust prominent on reflection and p wave refraction data is absent on the s wave refraction data implying a strong high low alternation of poisson s ratio in the lower crust this suggests that the lower crustal laminae represent mafic silicic compositional layering for example basic sills in an originally more quartz rich lower crust rather than alternating zones of high and low pore pressure there is no evidence for a shear wave low velocity zone lvz in the black forest mid crust despite the presence of a strong p wave lvz this suggests high quartz content and the presence of pore fluids at low not high pore pressure a clear p to s converted moho reflection pm s is visible on several shots indicating that the moho is at least locally a first order discontinuity no shear wave refractions from the upper mantle are present even where strong p wave refractions are observed possibly indicating an increase of poisson s ratio with depth in the upper mantle the petrological modeling indicates that the upper and middle crust are probably of granitic composition that the mid crustal low p zones have high quartz content and that the lower crust probably consists of granulites of laterally varying bulk composition from granodioritic to gabbroic the lower crust is more mafic in areas of high reflection density on seismic reflection profiles suggesting that the laminations are caused by mafic intrusions into the lower crust either prior to the variscan orogeny or during tertiary volcanic activity

15n isotope biogeochemistry and natural denitrification process in groundwater application to the chalk aquifer of northern france the use of 15n natural isotope tracing in an aquifer contained within chalk rocks in northern france indicates that under certain hydrogeological conditions major denitrification occurs at the boundary where the aquifer becomes confined the nitrate concentrations decrease in the direction of groundwater flow accompanied by an exponential increase in 15n expressed in 15n of the residual nitrate this is characteristic of kinetic isotope effects which accompany the reduction of the nitrate ion during denitrification hydrogeochemical and bacteriological observations confirm this process natural isotope tracing also permits this process to be distinguished from local dilution with nitrate free surface water which would entail a major drop in nitrate values without 15n isotopic enrichment a model is proposed to explain the relatively small observed magnitude of the isotopic fractionation effect

the spatial distribution and hydrogeological controls of fluoride in the confined and unconfined groundwater of tuoketuo county hohhot inner mongolia china insufficient or excessive intake of fluoride can create health problems for humans the objective of this study was to understand the occurrence of fluoride in groundwater as well as its spatiotemporal variation and sources in tuoketuo county hohhot inner mongolia china sixty seven water samples from 34 phreatic and 33 confined sources were collected from hand pumps dug wells and tube wells all samples were analyzed for ph electric conductivity ec total dissolved solids tds total hardness th as well as content of na k ca2 mg2 hco3 so4 2 cl and f the fluoride concentration in water samples varied from 0 40 to 7 20 2 33 1 79 and 0 06 to 12 70 1 65 2 38 mg l in phreatic and confined water respectively an analysis of the hydrogeochemical characteristic of samples indicated that the high fluoride content of groundwater was caused by the alkaline environment with high levels of hco3 na tds ec and with a ca2 deficiency the highest concentration of fluoride 5 mg l in phreatic water was located in the groundwater discharge area because this water was affected by the groundwater flow field in confined aquifers the concentration of fluoride was mainly controlled by lithology a high fluoride content 1 5 mg l was only observed in lacustrine platform zone in confined aquifers

evaluation of hydrogeochemical processes in the pleistocene aquifers of middle ganga plain uttar pradesh india evaluation of major ion chemistry and solute acquisition process controlling water chemical composition were studied by collecting a total of fifty one groundwater samples in shallow 25 m in the varanasi area hydrochemical facies mg hco3 dominated in the largest part of shallow groundwater followed by na hco3 and ca hco3 whereas ca hco3 is dominated in deep groundwater followed by mg hco3 and na hco3 high as concentration 50 g l is found in some of the villages situated in northeastern parts i e adjacent to the concave part of the meandering ganga river of the varanasi area arsenic contamination is confined mostly in tube wells hand pump within the holocene newer alluvium deposits whereas older alluvial aquifers are having arsenic free groundwater geochemical modeling using wateq4f enabled prediction of saturation state of minerals and indicated dissolution and precipitation reactions occurring in groundwater majority of shallow and deep groundwater samples of the study area are oversaturated with carbonate bearing minerals and under saturated with respect to sulfur and amorphous silica bearing minerals sluggish hydraulic conductivity in shallow aquifer results in higher mineralization of groundwater than in deep aquifer but the major processes in deep aquifer are leakage of shallow aquifer followed by dominant ion exchange and weathering of silicate minerals

hydrogeochemical processes of fluoride enrichment in chimakurthy pluton prakasam district andhra pradesh india thirty six groundwater samples were collected from chimakurthy area prakasam district andhra pradesh on hydrogeochemical evaluation it was found to be contaminated based on fluoride concentration the samples were segregated into group a group b and group c fluoride concentration varies from 0 23 to 9 84 mg l with the mean value of 2 01 mg l 44 of the tested samples had f 1 50 mg l apart from f the water was contaminated with no3 and cl implying both geogenic and anthropogenic pollution of the aquifer ionic dominance pattern was unique in samples with low moderate to high f concentrations na and hco3 were progressively increasing along with f from group a to c whereas ca2 and mg2 were depleting groundwater facies were unique among different group samples especially in end members with low and high f concentration suggesting that f dissolution was strongly influenced by the chemical nature of solution na cl molar ratio was 1 whereas na k tz and ca2 mg2 tz ratios were 1 in all samples indicating that na was released from silicate weathering process it also confirms that f was contributed from lithogenic sources of aquifer material mean molecular ratios of 1 for ca2 mg2 in group b samples and 1 1 2 in groups a and c support that the ca2 and mg2 were added into aquatic medium by calcite and dolomite dissolution contradictory distribution of f in north low and south high indicates that availability of f minerals in aquifer matrix influenced the rate of f absorption in accompanying water variation in f concentration in groundwater of the core area south supports the hypothesis of aquatic chemistry acting as catalyst in f dissolution into formation waters even though the aquifer was enriched with f minerals very high f in groundwater in the contact zone of country rock and plutonic intrusive indicates that f mineralization occurred under geothermal conditions the fracture network in disturbed and fragile contact zone has facilitated development of potential aquifers and enhancement in f concentration

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

crust and upper mantle inhomogeneities beneath the central part of the balkan region abstract crustal and upper mantle velocity inhomogeneities are studied by the interpretation of the p wave travel times from local explosions and teleseismic earthquakes recorded in 30 stations on the territory of bulgaria and some neighbouring regions different methods of the solution of inverse 2 d and 3 d kinematic problems are used the established velocity inhomogeneities are discussed in connection with the major characteristics of some geophysical and seismotectonic fields it is noted that the velocity patterns of the crust reflect the configuration of alpine tectonic structures the subcrustal inhomogeneities are discordant to the main features of the near surface structures however these inhomogeneities are concordant to some seismic lineaments inexplicable from the viewpoint of the first order tectonic structures the observed relationship between the seismicity and deep velocity structures show that these lineaments are controlled by the uppermost mantle heterogeneities it is also noted that the high velocity zone in the deeper upper mantle indicates deep seated inhomogeneities beneath the rhodopean massif these inhomogeneities most probably represent palaeo subduction of a lithosphere slab penetrating deeper than 250 km into the asthenosphere

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

seismic tomography of the earth s mantle the analysis of information contained in seismograms is the most promis ing tool for retrieving the three dimensional structure of the earth s mantle and thereby improving our understanding of its dynamics the procedure through which three dimensional images of different parts of the earth s interior arc obtained by inversion of a set of observables measured on the surface of the earth is commonly termed tomography by analogy with the medical procedure with which it shares many aspects of methodology but with much less favorable experimental conditions ideally one would like to be able to model entire seismograms over a wide frequency band for a large number of uniformly distributed sources and stations in order to obtain an optimal illumination of the inhomogeneities appropriate for tomographic inversion in practice a number of difficulties and limitations arise onc is the nonuniform distribution of sources and receivers seis micity is concentrated at plate boundaries and the distribution of con tinental and island areas leaves large portions of the oceans unin strumented another difficulty is our limited ability to accurately forward model the effects of wave propagation in a realistic earth which presents departures from a spherically symmetric referencc model of both elastic anc1astic and isotropic anisotropic nature this is why until now the simplest kind of tomography travel time tomography has prevailed relying on simplifying assumptions concerning the interaction of asphericity with propagating seismic waves ray theory and the laws of geometrical optics in their

understanding hydrological processes in a highly stressed granitic aquifer in southern india the results of a study evaluating the recharge discharge conditions of an unconfined stressed granitic aquifer situated in a semi arid region of andhra pradesh southern india are presented over the last three decades excessive withdrawal of groundwater has drastically lowered the water table to the bedrock the watershed studied was divided into four zones based on geomorphology and hydrogeological conditions using environmental chloride data pertaining to groundwater soil depth profiles and some hydrogeologic and hydrochemical observations a recharge model for the watershed was developed the model revealed that the bulk of the vertical recharge in the western elevated land occurs through preferred pathways and that a small fraction occurs through the soil matrix in addition the watershed has a poor hydrogeologic fabric as indicated by the small range of matrix flow recharge 1 to 1 5 of rainfall among the four zones the dominating preferential flow was high 16 of the annual average rainfall in the valley fills but decreased to 5 5 5 in the plains furthermore although the bulk of the recharge occurs vertically considerable lateral movement of groundwater down the slope indicates that sequential hydrochemical changes occur distinct geomorphological features that exist in the watershed support the proposed model situations similar to those described above may exist in numerous watersheds in the granitic hard rock region therefore information obtained from investigations conducted in this watershed can aid in the development of plans enabling the sustainable exploitation of watersheds that have not yet been developed as well as implementation of appropriate rainwater conservation measures in over exploited watersheds copyright 2009 john wiley sons ltd

mapping the moho of the western alps by wide angle reflection seismics abstract a new picture of the moho beneath the western alps could be obtained using wide angle reflection seismic data this picture in addition to its increased sharpness clearly shows how the moho deepens down to the root zone of the chain 55 km a 25 30 km deep reflector with upper mantle characteristics is discovered under the brianconnais zone where it overlies the autochthonous moho this unit does not seem to connect to the so called ivrea body situated much shallower and farther into the chain it supports a hypothetical flaking of the european lithosphere beneath the western alps farther east the moho beneath the po plain is clearly mapped too with a crustal thickness increasing in steps from 25 to 35 km this p wave moho picture is compared with an s wave picture and major differences appearing in the middle crust are discussed finally the seismic response of the moho is investigated and is shown to be shifted towards low frequencies in the inner zones of the chain this could partly explain why the ecors crop vertical seismic line equipped with high frequency geophones faltered over the identification of the deep alpine moho

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

new geologic mapping and shrimp u pb zircon data in the peninsular ranges batholith baja california mexico evidence for a suture geologic and shrimp u pb zircon studies in the sierra san pedro martir area of northern baja california mexico suggest that the western and eastern parts of the peninsular ranges batholith originated as separate arcs they are now juxtaposed along a well exposed ductile thrust main martir thrust marked by an age discontinuity of at least 10 to 15 m y and sharp changes in rock type metamorphic grade and deformation history the east dipping thrust and adjacent highly deformed rocks were stitched by 108 97 ma plutons that were generated in a region of crustal thickening formed during juxtaposition of the two arcs lack of chemical isotopic and geologic evidence for continentally derived rocks in the western arc may preclude an origin by rifting of the continental margin or development of the arc on a prism of continentally derived sediments adjacent to the continental margin instead the western arc may have originated as an island arc above a subduction zone outboard of north america if so a second concurrent subduction zone along the north american margin must have driven convergence and suturing of the two arcs and the main martir thrust may mark a nonterminal suture within a wider convergence related deformation zone that formed ca 115 108 ma

geochronology of the porphyry copper deposits and related mineralization of mexico k ar dating demonstrates that all but eight of 41 dated porphyry copper and related ore deposits of mexico were emplaced during the laramide episode of maximum plate convergence one older deposit is related to the jurassic volcanic arc of western north america one is pre laramide cretaceous four are oligocene in age and two late cenozoic deposits are within the modern trans mexican chiapenecan volcanic arc thirty three of the deposits lie within a long narrow belt that continues into arizona and new mexico and widens from 100 km to over 300 km in the region of maximum extension in the southern basin and range province eighty five percent of the deposits were emplaced during the eastward transgression of the cordilleran volcanic arc in middle cretaceous through eocene time the occurrence of the porphyry copper deposits of mexico appears to be independent of the terrane intruded and the copper content of the wall rocks where the wall rocks predate the volcanic arc which is syngenetic with the porphy

geochemical evaluation of nitrate and fluoride contamination in varied hydrogeological environs of prakasam district southern india hydrogeochemical controlling factors for high rate of groundwater contamination in stressed aquifer of fractured consolidated rocks belonging to semi arid watershed are examined the groundwater in mid eastern part of prakasam district confining to musi gundlakamma sub basins is heavily contaminated with nitrate and fluoride distinct water chemistry is noticed among each group of samples segregated based on concentration of these contaminants the nitrate is as high as 594 mg l and 57 of the samples have it in toxic level as per bis drinking water standards so also the fluoride which has reached a maximum of 8 96 mq l and 43 of samples are not fit for human consumption nitrate contamination is high in shallow aquifers and granitic terrains whereas fluoride is in excess concentration in deeper zones and meta sediments among the tested wells and 25 of samples suffer from both no3 and f contamination na among cations and hco3 among anions are the dominant species followed by mg2 and cl the no3 rich groundwater is of ca2 mg2 hco3 ca2 mg2 cl and na hco3 type the f rich groundwater is dominantly of na hco3 type and few are of na so4 2 type whereas the safe waters without any contaminants are of ca2 mg2 hco3 and na hco3 types high molecular percentage of na cl so4 2 and k in no3 rich groundwater indicates simultaneous contribution of many elements through domestic sewerage and agriculture activity it is further confirmed by analogous ratios of commonly associated ions viz no3 cl so4 2 and no3 k cl which are 22 56 22 and 42 10 48 respectively the f rich groundwater is unique by having higher content of na 183 and hco3 28 than safe waters the k f ca2 ratio of 10 5 85 and k f so4 2 of 16 7 77 support lithological origin of f facilitated by precipitation of caco3 which removes ca2 from solution the high concentrations of na co3 and hco3 in these waters act as catalyst allowing more fluorite to dissolve into the groundwater the indices ratios and scatter plots indicate that the no3 rich groundwater has evolved through silicate weathering anthropogenic activity evapotranspiration processes whereas f rich groundwater attained its unique chemistry from mineral dissolution water rock interaction ion exchange both the waters are subjected to external infusion of certain elements such as na cl no3 which are further aggravated by evaporation processes leading to heavy accumulation of contaminants by raising the water density presence of no3 rich samples within f rich groundwater group and vice versa authenticates the proposed evolution processes

chronological constraints on the thermal and tilting history of the sierra san pedro martir pluton baja california mexico from u pb 40ar 39ar and fission track geochronology the tectonothermal history of the four major phases of the sierra san pedro martir pluton and surrounding metamorphic rocks of the mesozoic peninsular ranges batholith of baja california is presented on the basis of u pb 40 ar 39 ar step heating and fission track dating in combination with al in hornblende geobarometry a previous model proposed up to 90 of east side up tilting of the pluton exposing 20 km of crustal section to account for its crescent shape asymmetrical zoning internal structure the eastward younging of k ar dates across the intrusion and eastward increase in the metamorphic grade of the country rocks from greenschist to amphibolite facies the u pb data suggest that the different phases of the pluton were emplaced sequentially from west to east between 97 0 4 1 ma and 93 8 1 1 ma all except one of the 105 40 ar 39 ar age spectra have well defined plateaus and are interpreted as cooling ages samples from the pluton give hornblende and biotite 40 ar 39 ar plateau dates and apatite fission track dates that young from west to east thus hornblende dates decrease from 95 to 91 ma biotite dates decrease from 94 to 88 ma and apatite dates decrease from 72 to 57 ma muscovite biotite and plagioclase from the same rock sample collected at the easternmost phase of the pluton yield concordant 40 ar 39 ar dates of 88 ma the exposed part of the pluton underwent rapid cooling approximately equal to 40 c ma down to 250 c in the first 10 m y after intrusion modeling of track length distribution in apatite is consistent with monotonic slow cooling from ca 80 ma to the present the data do not support a history that includes major tilting of the pluton eastward younging of 40 ar 39 ar and fission track dates may be explained by approximately equal to 15 of east side up tilting of the pluton at or after 88 ma about a north south horizontal axis furthermore the fission track data suggest that part or all of this tilting may have taken place at or after 57 ma and therefore may be a consequence of regional scale crustal extension associated with the opening of the gulf of california in neogene time such tilting is in agreement with the al in hornblende geobarometry for the hornblende biotite intrusive phase that yields pressures of 5 2 0 6 kbar an approximately equal to 15 northeast side up tilt of the crustal block containing this pluton would explain the apparent paleomagnetic inclination discrepancies with cratonic north america and militates against large scale northerly transport of baja california

lead isotope systematics of porphyry epithermal spectrum of the birgilda tomino ore cluster in the south urals russia abstract the paper provides the first data on lead isotopic composition of porphyry and epithermal mineralization of the birgilda tomino ore cluster lead isotope characteristics were obtained for 24 sulfide samples representing epithermal au ag bereznyakovskoe ore field and michurino occurrence base metal carbonate replacement biksizak occurrence porphyry copper tomino kalinovskoe and birgilda deposits and four plagioclase samples of the birgilda tomino igneous complex ore samples have lead isotopic signatures similar to neighboring intrusions of the birgilda tomino igneous complex and this confirms genetic relations between epithermal au ag base metal carbonate replacement and porphyry copper mineralization with diorite porphyry intrusions variations in lead isotopic composition are caused by mixing of mantle and crustal lead sources the input of radiogenic 206 pb took place during the post ore phase as a result of a series of tectono magmatic events which include emplacement of at least two phases of the chelyabinsk pluton the latter however could act only as a trigger of hydrothermal activity but not as a lead source

crustal structure of the fennoscandian shield a traveltime interpretation of the long range fennolora seismic refraction profile abstract the 1979 fennoscandian long range project fennolora was aimed at the determination of the detailed structure in the earth s mantle down to a depth of about 400 km observation distances reached almost 2000 km within scandinavia between shotpoints off the north cape and the southern coast of sweden to achieve an unbiased regarding the upper mantle structure a careful crustal survey was carried out along the entire profile at the same time beneath the fennoscandian shield i e the central section of the profile the crust is characterized by quite a smooth increase in p wave velocity down to the moho which lies at a depth of about 50 km in the southern half of the shield and at about 45 km further north the mean crustal velocity is 6 6 6 7 km s at the base of the crust the velocity increases gradually from about 7 km s to 8 0 8 4 km s in a 5 10 km thick crust mantle transition zone both in the south and in the north the relatively homogeneous crust of the baltic shield borders on areas with a more differentiated velocity structure first order discontinuities at shallower depth characterize the crust mantle boundary near the southeastern tip of sweden 38 km and under the caledonides in the north 43 km

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

fluoride dynamics in the granitic aquifer of the wailapally watershed nalgonda district india high concentrations of fluoride up to 7 6 mg l are a recognized feature of the wailapally granitic aquifer of nalgonda district andhra pradesh india the basement rocks provide abundant sources of f in the form of amphibole biotite fluorite and apatite the whole rock concentrations of f in the aquifer are in the range 240 990 mg kg calcretes from the shallow weathered horizons also contain comparably high concentrations of f 635 950 mg kg the concentrations of water soluble f in the granitic rocks and the calcretes are usually low 1 of the total or less but broadly correlate with the concentrations observed in groundwaters in the local vicinity the water soluble fraction of fluoride is relatively high in weathered calcretes compared to fresh calcretes groundwater major ion composition shows a well defined trend with flow downgradient in the wailapally aquifer from na ca hco3 dominated waters in the recharge area at the upper part of the catchment through to na mg hco3 and ultimately to na hco3 and na hco3 cl types in the discharge area in the lowest part the evolution occurs over a reach spanning some 17 km groundwater chemistry evolves by silicate weathering reactions although groundwaters rapidly reach equilibrium with carbonate minerals favouring precipitation of calcite and ultimately dolomite in the lower parts of the watershed this precipitation is also aided by evapotranspiration decreasing ca activity downgradient leads to a dominance of fluorite undersaturated conditions and consequently to mobilisation of f despite the clear downgradient evolution of major ion chemistry concentrations of f remain relatively uniform in the fluorite undersaturated groundwaters most being in the range 3 0 7 6 mg l the rather narrow range is attributed to a mechanism of co precipitation with and or adsorption to calcrete in the lower sections of the aquifer the model may find application in other high f groundwaters from granitic aquifers of semi arid regions

crust and upper mantle models along the active tyrrhenian rim the volcanic complexes from the eolian islands to the campania roman regions and tuscany further north rest on lithospheric sectors which overlie the adriatic continental lithosphere sinking along the apennine maghrebian orogenic belt evidence for this stems from the melting at mantle depth of upper crustal materials as indicated by the widespread interaction of s type and k alkaline melts the genesis of atypical magmas of the roman province central southern italy appears to be the result of an important block faulting and deep lithospheric rifting of the apennine continental margin lying parallel to and above relic sinking slabs intermediate and deep focus earthquakes indicate that the lithospheric slab is still seismically active under the eolian calabrian area and sporadically at the southern end of campania on the other hand in the roman tuscan region it seems to be almost inactive few earthquakes having been located with hypocentral depths not exceeding 150 km the analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shortening in correspondence of tuscany and south tyrrhenian sea which are separated by a tensional region which extends from latium to calabria the existence of distinct lithospheric slabs along the tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as p wave residuals and is confirmed by the trend of long wavelength gravity anomalies bidimensional gravity models along transects in the tyrrhenian sea and italian peninsula interpreted within the geometrical constraints imposed by the results of the interpretation of aeromagnetic seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above mentioned lithospheric slabs

shallow structure of oceanic crust in the western north atlantic from seismic waveform inversion and modeling seismic reflection data from mesozoic oceanic crust in the western north atlantic in the vicinity of the blake spur fracture zone have imaged a number of short subhorizontal events in the upper 1 km of the crystalline crust wide angle expanding spread profile esp data from the same region indicate the presence of first order velocity discontinuities in this depth interval using esp data reprocessed to enhance precritical reflection events we investigate the relationship between the precritical and postcritical reflections with three different approaches amplitude analysis forward modeling and waveform inversion the precritical reflections have high apparent reflection coefficients 0 1 and may be divided into two types those which can be traced out to critical ranges 5 6 km representing velocity steps and those which fade out at ranges of 3 4 km representing shorter wavelength velocity variations synthetic seismogram modeling indicates that the velocity steps occur within a 50 m depth interval while the shorter wavelength features may correspond to high or low velocity zones with a thickness of 20 m 10 of the dominant seismic wavelength or less we investigate the velocity structure in detail by full waveform inversion of a selected portion of esp data transformed into the intercept time slowness domain the inversion method minimizes the sample by sample misfit between the data and reflectivity synthetics in a least squares sense a conjugate gradient algorithm was used starting from a velocity structure derived from forward modeling of wide angle esp data the inversion tightly constrains short wavelength components of the velocity structure and indicates that intracrustal reflections result both from major velocity steps and from zones of alternating high and low velocity synthetic seismograms generated from sonic log data from deep sea drilling project hole 418a show reflections of similar amplitude and character to those seen in the esp data these reflections probably originate from rather subtle features of the velocity depth profile related primarily to changes in porosity in the pillow lava sequence a deeper reflector 800 ms below oceanic basement in the blake spur fracture zone may correspond to the top of a zone of serpentinized upper mantle

eurid a regionalized 3 d seismological model of europe abstract this paper presents a 3 d regionalized model of the european crust and mantle velocity structure down to depths of approximately 300 km the model is entirely based upon the existing geological and geophysical literature and it incorporates topographic and bathymetric features the resulting model which we call eurid european i data set consists of approximately 6400 1 d vertical structures having an average separation of about 100 km eurid is compared quantitatively with eur s91 a recent s wave velocity tomographic model obtained from body and surface wave waveform inversion zielhuis a nolet g 1994 shear wave velocity variations in the upper mantle beneath central europe geophys j int 117 695 715 it is found that the s wave velocities in eurid and in eur s91 zielhuis and nolet 1994 do not differ by more than about 4 over most of the area to validate eurid surface wave dispersion analysis is performed along some selected paths the fundamental mode group velocity curves obtained using 1 d average models derived from eurid are found in good agreement with those determined from observations broadband waveform synthetics are also calculated along the same paths and compared with the observed time series overall we believe that eurid is representative of our current knowledge of the crust upper mantle structure beneath europe and it can be used to model realistically ground motion for periods above 10 s within structurally homogeneous regions the first digital version of this structure database is available for public use

evaluation of hydrogeochemical characteristics of phreatic alluvial aquifers in southeastern coastal belt of prakasam district south india the assessment of hydrogeochemical processes that govern the water quality of inland freshwater aquifers in coastal environment especially in indian sub continent is occasionally attempted to bridge the gap a detail hydrochemical evaluation of groundwater occurring in coastal alluvium is attempted single set of high density water sampling is done from a limited area to gain an in depth knowledge of the processes that govern the water chemistry of the sandy aquifers the water is of weak alkaline nature and less mineralized ec being na ca2 hco3 so42 mg2 no3 na and cl are almost in similar proportions implying the influence of coastal climate on water quality the water shows modest variation in their ionic assemblage among different sample points as evident from schoeller scheme groundwater can be classified into three distinct facies viz cl ca2 mg2 na cl and ca2 mg2 hco3 types the ionic assemblages their indices ratios and cross plots substantiate that multiple processes were involved in the evolution of the water chemistry among them silicate weathering halite dissolution ion exchange and base exchange played prominent role in the ion enrichment of groundwater the aquatic chemistry is further influenced and modified by marine environment evapotranspiration and anthropogenic inputs which is authenticated by good correlation r2 1 among the na cl ec mg2 na and cl gibbs plots established that evaporation is more responsible for contribution of minerals to the groundwater than aquifer material nitrate contamination can be attributed for poor sewerage disposal mechanism which is aggravated by fertilizer inputs irrigation practices and agriculture activity a contrasting correlation r2 90 to 0 40 among select pairs of ions reassures dissimilar source of those ions involvement of multiple processes and limited interaction of formation water with aquifer material

crustal affinities of metallogenesis in the american southwest the source of metals in many lands of ores and ore deposit styles remains uncertain notwithstanding more than a century of field studies scientific advances in concepts and enhancement of analytical capability however numerous geologic research efforts that have addressed many relevant themes in southern arizona have resulted in different kinds of data supporting and consistent with the interpretation of significant association of some ore metals of this region with cratonic crust these themes range in scale from studies of regional geology geophysical interpretations and precious metal production through petrology to trace element and isotope geochemistry the notion of a crustal source for metals contrasts with many long standing ideas of direct mantle sources for this metal province or more recently direct derivation of metals from subducted materials a hundred years of recorded silver and gold production reveal a two fold separation of mining districts in arizona and new mexico on the basis of ranges of produced ag au ratio that correspond in turn with a separation of two distinct geologic domains of the southern cordilleran metal province the produced ag au ratio in districts of different ages ore styles tectonic setting and metal habit are not affected by deposit style or ore control or igneous rock type or vertical zoning and weathering studies of the isotopes and trace element chemistry of related igneous rocks reveal that ore related intrusions have a significant crustal progenitor studies of pb and os isotopes have discovered strong signals of crustal parentage in ore minerals the regional geology metallization history production and chemical and isotopic data strongly support a hypothesis of crustal sources of some of the metal in this large and complex province

tectonic implications of postcontractional magmatism of the alisitos arc segment of the peninsular ranges baja california mexico the alisitos arc segment is the southernmost and only part of the western peninsular ranges batholith accreted during the cretaceous collision related deformation is concentrated along the northern and eastern margins of the arc segment while shortening within the alisitos arc produced similar amounts of crustal thickening throughout the arc suppression of parts of the lower crust of the alisitos arc due to throw across the terrane bounding faults varies substantially geobarometric change across the main martir thrust suggests that 15 km of additional crust was thrust onto the central alisitos arc geochemical and geochronologic data from intrusive rocks of the alisitos arc indicate arc magmatism was active before during and after collision the data suggest that all peninsular ranges batholith intrusive rocks within the alisitos arc were derived from a broadly similar primitive source lacking interaction with evolved continental lithologies postcollisional intrusions from the central alisitos arc adjacent to

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

deep structure of the earth s crust in the contact zone of the palaeozoic and precambrian platforms in poland tornquist teisseyre zone abstract one of the major tectonic problems in europe concerns the southwest margin of the east european platform in the region of the so called polish danish trough in general this margin is assumed to be the tornquist teisseyre t t line running approximately from northwest to southeast in this part of europe determination of deep crustal structure of the contact zone between the precambrian platform and the palaeozoic platform was the main aim of the deep seismic sounding dss programme in poland in 1965 1982 deep seismic soundings of the earth s crust have been made in the t t line zone along nine profiles with a total length of about 2600 km the results of deep seismic soundings have shown that the crust in the marginal zone of the east european platform has highly anomalous properties the width of this zone ranges from 50 km in northwest poland to about 90 km in southeast poland the crustal thickness of the palaeozoic platform in poland is 30 35 km and of the precambrian platform 42 47 km while in the t t tectonic zone it varies from 50 to 55 km above the moho boundary in the t t zone at a depth of 40 45 km there is a seismic discontinuity with p wave velocities of 7 5 7 7 km s boundary velocities mean velocities and stratification of the earth s crust vary distinctly along the t t zone there are also observed high gravimetric and magnetic anomalies in the t t zone the t t tectonic zone determined in this manner is a deep tectonic trough with rift properties the deep fractures delineating the t t tectonic zone are of fundamental importance for the localization of the plate edge of the precambrian platform of eastern europe in the light of dss results the northeastern margin of the t t tectonic zone is a former plate boundary of the east european platform

crustal and upper mantle structure of the mediterranean area derived from surface wave data abstract a summary of results based mainly on the inversion of available surface wave dispersion data is given for the mediterranean area both for crustal and upper mantle structure the results are presented on maps outlining the regionalization of the crust and the lithosphere asthenosphere system in the area it is possible to distinguish several types of crust with average s wave velocities in the range 2 8 3 8 km s 1 and thickness varying from a minimum of about 10 16 km in the western mediterranean to a maximum of about 50 km including a possible transitional layer beneath the ionian sea the average properties of the crust and of the lithospheric part of the mantle indicate a possible continuous structure extending from north africa through the ionian sea to the adriatic sea characterized by the presence of a transitional layer at the crust mantle boundary strong lateral variations are present in the lithosphere asthenosphere system both in thickness from 30 km in the western mediterranean to about 130 km under the alps and in s wave velocity from 4 1 4 2 km s 1 up to 4 7 km s 1 the relatively high position of low resistivity material that seems to characterize the mediterranean area agrees fairly well with the shallower average top of the asthenosphere found in this area from the study of the elastic properties the usefulness of combining seismological and electromagnetic studies is stressed