hydrogeochemical conditions and evolution at the aspo hrl sweden abstract the overall hydrogeochemical conditions at and in the near vicinity of the underground experimental aspo hard rock laboratory hrl in se sweden have been investigated groundwater data from more than 400 samples have been compiled and evaluated the groundwater samples represent depths down to 1700 m below sea level and sampling has been performed prior to and during the hrl tunnel excavation episodic events have to a great extent influenced the hydrochemical evolution since the last glaciation which ended some 13 ka ago at that time glacial melt water was flushed under hydraulic pressure down into the fracture system to a depth of at least several hundred metres the next episodic event took place when the baltic freshwater lake transformed into the brackish litorina sea some 7 ka ago at this time aspo was covered by the sea and these denser more saline waters partly replaced the glacial water down to a depth where the density equilibrated with the replacement sea water at some time around 3 4 ka ago aspo started to rise above sea level and meteoric water began to infiltrate the rock the overall trend of increasing salinity with depth may easily be misinterpreted as a fairly simple groundwater system evolving from a two component evolution path between non saline and saline groundwaters however when combining the results from environmental isotopes and the chemical parameters using a new modelling tool named m3 multivariate mixing and mass balance calculations a higher resolution was obtained and a more complex groundwater pattern which reflects the present and paleo hydrogeological events can be recognised the measured groundwater composition was modelled to be a mixture of meteoric past and present baltic seawater glacial or cold climate recharge and brine type of waters the modelling result shows that the processes considered to have a dominating impact on the present aspo groundwater chemistry are mixing both in disturbed and undisturbed systems calcite dissolution and precipitation redox reactions and biological processes the undisturbed groundwater conditions prior to the hrl tunnel construction at aspo consisted of 1 a dominating proportion of meteoric fresh water in the upper 250 m of the aquifer 2 a brackish saline water consisting of mixing proportions of present and ancient baltic sea water and glacial melt water present to a depth of 250 600 m 3 saline water still containing proportions of glacial water which could represent even older glaciations and brines a large portion of which have been stagnant for perhaps millions of years below a depth of 600 m during the hrl tunnel construction there were changes in the composition of the water flowing into the tunnel at different locations although the variation in salinity was relatively small the variations in the mixing proportions of the different water types were substantial

investigation by multivariate analysis of groundwater composition in a multilayer aquifer system from north africa a multi tracer approach abstract a multi tracer approach has been carried out in the sbeitla multilayer aquifer system central tunisia to investigate the geochemical evolution the origin of groundwaters and their circulation patterns it involves statistical data analysis coupled with the definition of the hydrochemical and isotopic features of the different groundwaters principal components analysis pca of geochemical data used in conjunction with bivariate diagrams of major and trace elements indicate that groundwater mineralization is mainly controlled by water rock interaction and anthropogenic processes in relation to return flow of irrigation waters the pca of isotopic data and bivariate conventional diagrams of stable and radiogenic isotopes i e 18o vs 2h and 18o vs 14c provide valuable information about the origin and the circulation patterns of the different groundwater groups they permit classifying groundwaters into three groups the first group is characterized by low 3h concentrations low 14c activities and depleted stable isotope contents it corresponds to an old end member in relation with palaeoclimatic recharge which occurred during the late pleistocene and the early holocene humid periods the second group is distinguished by high to moderate 3h concentrations high 14c activities and enriched heavy isotope signatures it corresponds to a modern end member originating from a mixture of post nuclear and present day recharge in relation to return flow of irrigation waters the third group is characterized by an average composition of stable and radiogenic isotope signatures it provides evidence for the mixing between the upward moving palaeoclimatic end member and the downward moving present day end member

survival of ancient landforms in a collisional setting as revealed by combined fission track and u th he thermochronometry a case study from corsica france abstractthe age of high elevation planation surfaces in corsica is constrained using new apatite u th he data field observations and published work zircon fission track apatite fission track aft data and landform stratigraphical analysis thermal modeling results based on aft and u th he data and the eocene sediments uncomformably overlapping the variscan crystalline basement indicate that present day elevated planation surfaces in corsica are the remnants of an erosion surface formed on the basement between 120 and 60 ma during the alpine collision in the paleocene eocene the variscan crystalline basement was buried beneath a westward thinning wedge of flysch and the eastern portion was overridden by the alpine nappes resetting of the apatite fission track thermochronometer suggests an overburden thickness of 4 km covering variscan corsica protected by soft sediment the planation surface was preserved in the latest oligocene to miocene times the surface was re exposed and offset by

fracture roughness and gouge distribution of a granite shear band 1 localization of deformation during fracture mechanical tests leads to the development of shear bands we performed triaxial tests using sidobre granite at four different confining pressures from 20 to 80 mpa we compared two sets of tests one set was stopped immediately after the formation of the shear band a second one included additional shear deformation from the analysis of thin sections of these laboratory samples we characterize the typical microstructures in the shear band mode i and ii cracks riedel cracks cataclastic flow statistical properties of rupture surface roughness and gouge grain size reveals scaling invariance using a mechanical profiler the fracture roughness is measured along parallel profiles and shown to be correctly described over up to 3 orders of magnitude by self affine geometry with a roughness exponent close to 0 80 this property is very similar to tensile crack even if local processes are different the influence of the slip is observed fracture surfaces are rougher along the slip direction 0 74 than perpendicular to it 0 80 the confining pressure is shown to have a weak effect on the fracture roughness it smoothes the surface slight increase of the roughness exponent gouge particles extracted from the shear band present a power law distribution with an exponent ranging from 1 44 to 1 91 this exponent appears to increase with the shearing displacement and the confining pressure when a significant shear of the band is combined with a high confining pressure i e impeded dilation of the band the hallmark of fragmentation is observed for the particle distribution and related to a smoothing of the band boundary

shallow slip deficit due to large strike slip earthquakes in dynamic rupture simulations with elasto plastic off fault response summary slip inversions of geodetic data from several large magnitude 7 strike slip earthquakes point to coseismic slip deficit at shallow depths 3 4 km that is coseismic slip appears to decrease towards the earth surface while the inferred slip distribution may be consistent with laboratory derived rate and state friction laws suggesting that the uppermost brittle crust may be velocity strengthening there remains a question of how the coseismic slip deficit is accommodated throughout the earthquake cycle the consequence of velocity strengthening fault friction at shallow depths is that the deficit of coseismic slip is relieved by post seismic afterslip and interseismic creep however many seismic events with inferred shallow slip deficit were not associated with either resolvable shallow interseismic creep or robust shallow afterslip hence the origin of shallow slip deficit remains uncertain in this study we investigate whether inelastic failure in the shallow crust due to dynamic earthquake rupture can explain the inferred deficit of shallow slip evidence for such failure is emerging from geologic seismic and geodetic observations we find that the amount of shallow slip deficit is proportional to the amount of inelastic deformation near the earth surface such deformation occurs under a wide range of parameters that characterize rock strength in the upper crust however the largest magnitude of slip deficit in models accounting for off fault yielding is 2 4 times smaller than that inferred from kinematic inversions of geodetic data to explain this discrepancy we further explore to what extent assumptions in the kinematic inversions may bias the inferred slip distributions inelastic deformation in the shallow crust reduces coseismic strain near the fault introducing an additional artificial deficit of up to 10 per cent of the maximum slip in inversions of geodetic data that are based on purely elastic models the largest magnitude of slip deficit in our models combined with the bias in inversions accounts for up to 25 per cent of shallow slip deficit which is comparable but still smaller than 30 60 per cent deficit inferred from kinematic inversions we discuss potential mechanisms that may account for the remaining discrepancy between slip deficit predicted by elasto plastic rupture models and that inferred from inversions of space geodetic data

apatite fission track analysis of neogene exhumation in northern corsica france apatite fission track analyses along a w e orientated transect across northern corsica indicate an important episode of crustal exhumation in late early miocene time samples taken from the alpine orogenic wedge from the adjacent foreland basin and from the crystalline basement complex flooring the basin are completely reset this implies that a 2 0 2 3 km thick crustal section made of thrust sheets and or autochthonous foreland deposits has been removed by erosion since early miocene time a geometric projection of this lost cover towards the west indicates that all of northern corsica was covered either by alpine nappes or middle eocene foreland deposits fission track ages are the same across the main boundary fault system separating the alpine orogenic wedge and the foreland indicating the absence of significant differential vertical displacement between upper and lower plates during neogene unroofing

asperity failure control of stick slip along brittle faults stick slips are spontaneous unstable slip events during which a natural or man made system transitions from a strong sticking stage to a weaker slipping stage stick slips were proposed by brace and byerlee science 153 990 992 1966 as the experimental analogue of natural earthquakes we analyze here the mechanics of stick slips along brittle faults by conducting laboratory experiments and by modeling the instability mechanics we performed tens of shear tests along experimental faults made of granite and gabbro that were subjected to normal stresses up to 14 3 mpa and loading velocities of 0 26 617 m s we observed hundreds of spontaneous stick slips that displayed shear stress drops up to 0 66 mpa and slip velocities up to 14 1 mm s the pre shear and post shear fault surface topography were mapped with atomic force microscopy at pixel sizes as low as 0 003 m2 we attribute the sticking phase to the locking of touching asperities and the slipping phase to the brittle failure of these asperities and found that the fault asperities are as strong as the inherent strength of the host rock based on the experimental observations and analysis we derived a mechanical model that predicts the relationships between the measured stick slip properties stress drop duration and slip distance and asperity strength

multivariate indications between environment and ground water recharge in a sedimentary drainage basin in northwestern china abstract a paucity of studies on the interaction between environment and ground water recharge severely restricts the ability of people to assess future water resources under changing environment in this study an effort to explore the relationship between the arid environment and ground water recharge was carried out using multivariate statistical techniques in a sedimentary drainage basin the jungar in northwestern china hierarchical cluster analysis hca and principal components analysis pca were performed based on hydrogeochemical data to assess the ground water recharge and its governing factors observation of the hca and pca analytical results revealed a division of seven clusters c1 to c7 and three principal components pc1 to pc3 which explained 59 6 16 6 and 10 9 of the variance respectively and thus accounted for the majority of the total variance in the original dataset based on these q mode hca clusters and r mode pac scores dominant environmental processes influencing recharge regimes were identified i e geogenic geomorphoclimatic and anthropogenic which separated the recharge regimes into four zones zone i to zone iv zones i and ii c4 c1 were associated to elevated hydroclimate degree coupled to low salinity zone iii c2 c3 was associated to moderately elevated salinity and evidently elevated contamination but coupled to low hydroclimate degree zone iv c5 c6 c7 was associated mainly to elevated salinity coupled to low or inverse hydroclimate degree it revealed that the geogenic processes are more significant 60 than the geomorphoclimatic 17 and anthropogenic 11 processes as a result the overall recharge process is rather heterogeneous and is strongly environment dominated in the jungar drainage system compared with other watersheds in arid environment a distinctive feature of the jungar waters is that they are affected by a combination of natural and non natural events rather than following a steady and continuous geological evolution these will continue to influence the recharge regime of the jungar for a long time due to its steady tectonics and arid climate however changing rainfall but not snow is becoming the key factor driving changes in ground water resources in this drainage system as results of the decades of warming and humidification in northwestern china

carbon and isotopic mass balance models of oasis valley fortymile canyon groundwater basin southern nevada environmental isotopes and carbon chemistry provide means of differentiating various recharge areas flow paths and ages of ground water in portions of the nevada test site and vicinity regional delta d delta sup 18 o trends are offset from the present day meteoric line by a deuterium depletion of 5 per thousandth suggesting paleoclimatic changes partial pressures of co sub 2 and the sup 18 o and sup 13 c data indicate solubility and isotopic equilibrium between the gas and water in the soil zone with progressive exchange with underlying ground water in the shallow alluvium of oasis valley application of a closed system co sub 2 model using the eq3nr eq6 reaction path simulator successfully reproduces chemical compositions observed in the alluvium in the amargosa desert and in the deep tuff aquifer beneath pahute mesa and yucca mountain initial p sub co sub 2 input to the soil zone during recharge was calculated to range from 0 03 to 0 10 atm which is comparable to measured soil co sub 2 pressures in oasis valley results are compared for sup 14 c ages using the delta sup 13 c dilution correction and a mass action correction term relating predicted and calculated ionic activity products of caco sub 3 results are generally comparable with discrepancies attributed to anomalous delta supmore 13 c values less

principal component chemical bacteriological and isotopic analyses of oued souf groundwaters revised oued souf city located in the northwestern part of algeria has rapidly grown and been urbanized the city and surrounding areas depend heavily on groundwater as a water source for drinking as well as domestic industrial and agricultural uses comprehensively understanding the chemistry of the groundwater provides insight into the interaction of water with the environment and contributes to better overall resource management the phreatic groundwaters are so4 ca in character these waters are hard with a high salinity which poses a distinct danger for plants furthermore major chemical elements in the water have concentrations above the values recommended by world health organization the phreatic groundwaters display bacteriological germs in sampled waters and high concentrations of nitrates were detected in the samples due to the absence of a formal sanitation network in this work stable and radioactive isotopes are used to understand the water origin of the phreatic groundwaters the present isotopic study suggests that the groundwaters from the oued souf phreatic aquifer are composed of two primary components one from infiltrating recent rain waters and the other one from deep captive groundwaters herein descriptive statistics correlation matrices and factor analyses were employed to understand the hydrochemistry of the groundwater in the phreatic aquifer in the oued souf area

conservative behavior of arsenic and other oxyanion forming trace elements in an oxic groundwater flow system summary groundwater samples were collected along a flow path in a shallow fractured tuffaceous aquifer from the oasis valley beatty wash region of southern nevada usa and analyzed for a number of oxyanion forming trace elements including arsenic as antimony sb selenium se molybdenum mo and tungsten w in addition ancillary geochemical parameters including ph major solute compositions dissolved silica dissolved oxygen and iron and manganese concentrations were quantified in the groundwaters arsenic concentrations range from 70 nmol kg up to 316 nmol kg in groundwaters of the oasis valley beatty wash flow system and generally exhibit increasing concentrations with flow down gradient along the flow path antimony w and to a lesser extent mo exhibit similar increasing concentration trends with flow down gradient in the aquifer albeit at lower concentrations levels e g mean sd for sb w and mo are 2 3 0 9 nmol kg 7 4 3 7 nmol kg and 101 19 nmol kg respectively selenium concentration which range between 4 and 11 nmol kg generally decrease in groundwaters with flow down gradients in the oasis valley beatty wash groundwater flow systems inverse modeling of groundwater chemistry evolution from the lower reaches of the oasis valley flow path using phreeqc indicate that the groundwater composition is consistent with mixing of nearly equal proportions of groundwater from upper reaches of oasis valley and beatty wash groundwater along with dissolution of volcanic glass potassium feldspar and gypsum followed by calcite precipitation and formation of secondary zeolites analcime clay minerals ca montmorillonite and cristobalite the geochemical modeling indicates that the concentrations of as and the other oxyanion forming trace elements are controlled by dissolution of volcanic glass water rock interaction with mineralized zones within the aquifer i e sulfide oxidation desorption from aquifer surface sites and mixing of oasis valley and beatty wash groundwaters

direction changes in thrusting of the schistes lustres in alpine corsica abstract the direction of thrusting contemporaneous with high pressure low temperature hp lt metamorphism of the ophiolite schistes lustres nappes in cap corse alpine corsica has changed from being towards the northwest to towards the southwest during upper cretaceous obduction similar anticlockwise changes in thrusting have been observed in other regions of alpine corsica calabria and southern betic cordilleras a model is proposed for the alpine evolution of this part of the western alps involving a sinistral component of transcurrent movement added to the northwest thrusting these events have been followed by eocene backthrusting of nappe of southern alpine origin in northwest cap corse towards the southeast with associated backfolding of the underlying schistes lustres

origin of rare earth element signatures in groundwaters of circumneutral ph from southern nevada and eastern california usa concentrations of the rare earth elements ree were measured in circumneutral ph groundwaters from southern nevada and death valley ca groundwaters from the regional lower paleozoic carbonate rock aquifer cambrian devonian have flat shale normalized patterns that closely resemble the shale normalized patterns of the aquifer rock samples principally cambrian groundwaters associated with younger carbonate rocks chiefly permian in the study region exhibit heavy ree hree enriched shale normalized ree patterns with substantial negative ce anomalies that also mimic these carbonate rocks in addition groundwaters from the felsic volcanic rock aquifers have the same flat to light ree lree enriched shale normalized patterns with large negative eu anomalies as the felsic volcanic rocks the similar ree patterns of all the groundwaters and associated aquifer rocks studied suggest that the groundwaters inherited ree signatures from the host rocks through which they flow because negative ce anomalies are not an uncommon feature of carbonate rocks of marine origin the negative ce anomalies reported here for these groundwaters may reflect a permian marine ce signature previously we demonstrated that carbonate complexes dominate ree speciation in southern nevada and death valley groundwaters moreover solid liquid partitioning coefficients kd indicate that the affinity of lrees to sorb to aquifer surface sites is substantially greater than for the hrees in the southern nevada carbonate and felsic volcanic rock alluvial aquifers consequently the hrees enrichments reported here for groundwaters associated with younger paleozoic carbonate rocks compared to these source rocks is consistent with ree carbonate complexation and preferential removal of lrees to aquifer surface sites

the geochemistry of rare earth elements in groundwater from the carnmenellis area southwest england shallow groundwater samples from the carnmenellis area of southwest england collected from wells boreholes springs adits and stream baseflow represent recently recharged waters of low salinity their major ion concentrations closely reflect the lithology of their host rocks which comprise the carnmenellis granite and devonian metasediments and metabasite of greenschist grade groundwaters from the granite are predominantly na cl or na ca cl type whilst those from the metasediment are na ca mg cl hco3 waters with a larger range of compositions the major ion compositions are predominantly a function of water rock interaction processes and the larger range of metasediment water compositions probably reflects the greater lithological variation the ph of groundwater samples circulating through granite is typically lower than that of groundwater in the metasediments the range being 4 3 to 7 2 median 5 7 and 4 7 to 8 0 median 6 6 respectively rare earth element ree concentrations of 0 45 m filtered groundwater samples have been determined by inductively coupled plasma mass spectrometry icp ms a large range of concentrations exists and many are below detection limits but levels reach up to 229 g 1 1 6 m total rees the rees are strongly controlled by ph with higher levels in groundwaters of ph 6 chondrite normalised profiles are light rare earth element lree enriched compared to heavy rare earths hrees with a common slight negative eu anomaly both features reflecting the compositions of their host rocks ree profiles therefore appear to be controlled by water rock interactions involving predominantly ree enriched minerals in the granite the rees are probably derived mainly from the accessory minerals monazite and apatite as well as the high ree framework minerals biotite and muscovite the source of rees in groundwater from the metasediments is more uncertain but probably includes clay minerals chlorite and carbonate ree compositions normalised to shale have flatter profiles although many are slightly convex with higher normalised sm eu and gd values a few metasediment derived waters with high total ree concentrations have lree enriched shale normalised patterns it is suggested that the bulk of the rees in these few samples is colloidal rather than totally dissolved groundwaters from the metasediments have a notable depletion in ce which is distinct from waters in the granite this depletion is problematic in that it is difficult to see how redox processes could be the dominant control since groundwaters from the metasediments are unlikely to be more oxidising than those from the granite likewise variations in ph fail to totally explain the distinctions in ce concentration and la ce ratios between the two water types it is therefore suggested that the ce contents are largely source related rather than process related the observed ree compositions of granite and metasedimentderived groundwaters from the carnmenellis area are so distinctive that the rees in general and ce in particular might be useful as future tracers in studies of water rock interaction and groundwater provenance

geochemical and statistical evidence of recharge mixing and controls on spring discharge in an eogenetic karst aquifer summary information about sources of recharge distributions of flow paths and the extent of water rock reactions in karst aquifers commonly result from monitoring spring chemistry and discharge to investigate the relationship between spring characteristics and the complexities of karst aquifers we couple variations in surface and groundwater chemistry to physical conditions including river stage precipitation and evapotranspiration et within a sink rise system through a 6 km portion of the upper floridan aquifer ufa in north central florida principal component analysis pca of time series major element compositions suggests that at least three sources of water affect spring discharge including allogenic recharge into a swallet diffuse recharge through a thin vadose zone and water upwelling from deep within the aquifer the deep water source exerts the strongest influence on water chemistry by providing a majority of na mg2 k cl and so 4 2 to the system anomalously high temperature at one of several monitoring wells reflects vertical flow of about 1 m year mass balance calculations suggest diffuse recharge and deep water upwelling can provide up to 50 of the spring discharge however their contributions depend on head gradients between the conduit and surrounding aquifer matrix which are influenced by variations in precipitation et and river stage our results indicate that upwelling from deep flow paths may provide significant contributions of water to spring discharge and that monitoring only springs limits interpretations of karst systems by masking critical components of the aquifer such as water sources and flow paths these results also suggest the matrix in eogenetic aquifers is a major pathway for flow even in a system dominated by conduits

exploration of groundwater flowpaths and effective recharge in the amargosa desert nevada using multivariate statistical analysis and elevation dependent chloride mass balance method estimation of groundwater flowpaths and effective recharge was performed in the vicinity of amargosa desert nevada usa using multivariate statistical methods msms and a simple elevation dependent chloride mass balance method modified by estimating a minimum effective recharge elevation mere msms were applied to major ion data to explain the relationships among different groundwater chemical species define hydrochemical facies needed to determine groundwater flowpaths and evolution and identify the influence of surface and geologic features on groundwater for each defined watershed an average groundwater chloride concentration is used and the chloride deposition rate is assessed in the subject watersheds over all land elevations above the estimated mere by assuming two constant spatial and temporal concentrations of chloride in precipitation which is a function of elevation the mere for the amargosa desert was appraised as 1200 m above mean sea level m amsl based upon the elevation of the orifice of cane spring 1237 m amsl one of the lowest elevation permanent springs on the nevada national security site this minimum elevation is the cutoff altitude for our calculations at which precipitation is considered to make a significant contribution to recharge elevation dependent precipitation was evaluated relating elevation data from the online mapping software acme labs mapper 2 1 and precipitation data from the prism climate group s prism these analyses provide further insight into the hydrology of the region and demonstrate the strong impact surface and geologic features can have on surface water infiltration and groundwater in arid regions specifically evidence is presented of past focused recharge around the ephemeral fortymile wash and interaction between geologic faults and groundwater infiltration and flowpaths in addition groundwater flow based upon water chemistry appears to be segmented by major faults groundwater recharge in the vicinity of the amargosa desert has been estimated around 15 280 acre ft year

is internal friction friction mogi 1974 proposed a simple model of the incipient rupture surface to explain the coulomb failure criterion we show here that this model can plausibly be extended to explain the mohr failure criterion in mogi s model the incipient rupture surface immediately before fracture consists of areas across which material integrity is maintained intact areas and areas across which it is not cracks the strength of the incipient rupture surface is made up of the inherent strength of the intact areas plus the frictional resistance to sliding offered by the cracked areas although the coefficient of internal friction slope of the strength versus normal stress curve depends upon both the frictional and inherent strengths the phenomenon of internal friction can be identified with the frictional part the curvature of the mohr failure envelope is interpreted as a consequence of differences in damage cracking accumulated in prefailure loading at different confining pressures

high pressure low temperature metamorphism and polyphase alpine deformation at sant andrea di cotone eastern corsica france abstract a quarry located in the schistes lustres of eastern corsica has been studied in detail for both structural geology and metamorphic petrology the superimposed structures belong to three successive generations for each generation folds foliations lineations and behaviour of metamorphic minerals are briefly described attention is devoted to the connection between deformation recrystallization processes of minerals in thin section and macroscopic contrasts in ductility typical hp lt metamorphic minerals were developed during the two first generations of structures and were little transformed during the third clinopyroxenes garnets blue amphiboles phengites chlorites stilpnomelane piemontite lawsonite pumpellyite and deerite occur in different lithologies p t conditions of metamorphism are estimated to 8 kbar and 300 c fo2 and xco2 in metamorphic fluids are specified furthermore evolution and behaviour of metamorphic fluids are described in this example of hp lt metamorphism with emphasis on interactions between these fluids deformation processes and mineral assemblages

the external massifs relics of variscan basement in the alps chemical and structural data give new insight into the complex metamorphic evolution of crystalline basement of the helvetic realm central and western alps the relics of pre carboniferous basement the so called external massifs may be subdivided into an older basement unit with a younger cover which together suffered the following metamorphic evolution from late caledonian until variscan times 1 a late caledonian high pressure grade metamorphic event with formation of kyanite bearing mineral assemblages conditions of 8 10 kb 550 c may have been attained it is not excluded that the high pressure evolution has been accompanied by formation of late caledonian nappe structures crustal thickening due to collision or ductile thrusts 2 depending on the maximum temperature attained the later geothermal evolution probably of early variscan age led to at least one of the following stages a mineral assemblages of biotite sillimanite garnet b mineral assemblages of sillimanite cordierite k feldspar c second regional anatexis with formation of cordierite bearing granitoids conditions of about 4 5 kb 600 650 c have been attained 3 during the late cooling history alpine type tension gaps of variscan age with quartzk feldspar andalusite were formed latest joints were covered by muscovite andalusite

in situ and step heating 40ar 39ar dating of white mica in low temperature shear zones tenda massif alpine corsica france in order to clarify the link between 40ar 39ar record in white mica and deformation we performed in situ and bulkwise 40ar 39ar dating over the east tenda shear zone tenda massif alpine corsica white micas from 11 samples were selected and extensively analyzed using in situ techniques across nested scales of strain intensity gradients developed at the expense of a late variscan protolith 40ar 39ar systematics are unaffected by inherited ar and directly linked to deformation with little or no ar lattice volume diffusion extensive sampling allows constraining the end of deformation related to burial and exhumation respectively at 34 and 22 ma bracketing the duration of regional extensional shear to 12 myr results also highlight a regional strain localization toward the upper contact of the unit with smaller scale localization in specific lithologies notably meta aplites second order complications exist such as local ill defined correlations between ages and finite strain microstructures thus the use of a strain gradient as a proxy for strain localization in time is regionally valid but sometimes locally too complex to track or resolve strain partitioning localization trends at the meter outcrop scale and below age mixing and incomplete isotopic homogenization by dissolution precipitation are identified as the main causes of local discrepancies that complicate the link between age and microstructure and the derivation of strain localization rates tracking temporal trends in shear distribution across regional scale deformation gradients in such settings is possible but requires a multi scale approach as implemented here to reveal younging patterns associated to strain localization

multivariate mixing and mass balance m3 calculations a new tool for decoding hydrogeochemical information to support and help hydrochemical evaluation a multivariate mathematical tool named m3 multivariate mixing and mass balance calculations has been created within the aspo hard rock laboratory research programme the computer code can be used to trace the origin of the groundwater and calculate the mixing portions and mass balances from ambiguous groundwater data groundwater composition data used traditionally to describe the reactions taking place in the bedrock can now be used to trace the effect from present and past groundwater flow with increased accuracy the m3 model consists of the following 3 steps multivariate analysis called principal component analysis pca is used to summarise the information from the data set the summarised information shown in the pca plots is used for finding relationships patterns extreme waters and for further m3 modelling from the pca plot mixing calculations are used to calculate the effect of the groundwater mixing on the obtained groundwater composition this so called ideal mixing model is used to calculate the mixing proportions given in for all the groundwater samples the final step in m3 calculations is the mass balance calculations deviations from the ideal mixing model are used to trace the sources and sinks of elements given in mg l which can be due to mass balance reactions the tested margin of error of the model is 10 for the aspo site data but depends on the data to be modelled a mixing portion of less than 10 is regarded as under the detection limit of the model and such calculations are therefore uncertain this method can be used to trace the origin and calculate the mixing portions and effects from the reactions on the observed groundwater composition with a higher resolution and convenience compared to many standard methods

geochemical and statistical evidence of deep carbonate groundwater within overlying volcanic rock aquifers aquitards of southern nevada usa abstract samples collected from springs and wells in southern nevada were analyzed for major solutes and trace elements as part of a larger study to characterize the geochemical signatures of these groundwaters in this study principal component analysis pca was used to reduce the large data sets including the four major cations ca mg na k and 27 trace elements analyzed in these groundwater samples principal components analysis of the major cation data indicates that groundwaters from cenozoic felsic volcanic rock aquifers aquitards of southern nevada exhibit strong chemical associations to each other but weak relationships to groundwaters from the regional carbonate aquifer which were instead chemically similar to each other however pca of the trace element data demonstrates that some groundwaters from the volcanic aquifers aquitards are chemically similar to those of the underlying regional carbonate aquifer the pca also reveals that these groundwaters from the volcanic aquifers aquitards have significantly different trace element compositions than perched groundwaters contained within similar felsic volcanic rocks moreover rare earth element ree data from groundwaters collected from wells finished in the volcanic aquifers aquitards of southern nevada have similar concentrations and similar shale normalized patterns to the carbonate aquifer groundwaters as well as local carbonate rocks these same southern nevada well waters do not exhibit ree concentrations or shale normalized signatures that resemble the perched volcanic groundwaters or the tuffs of southern nevada the ree data and trace element pca along with previous carbon isotope analyses water temperature data hydraulic head relations and results of a recent pump test of a well near yucca mountain suggest close contact of the regional carbonate groundwaters and groundwaters from the overlying volcanic rocks of southern nevada and possible upwelling of the carbonate groundwaters into the overlying volcanic rock units in the vicinity of yucca mountain

cold subduction and the formation of lawsonite eclogite constraints from prograde evolution of eclogitized pillow lava from corsica a new discovery of lawsonite eclogite is presented from the lancone glaucophanites within the schistes lustres nappe at defile du lancone in alpine corsica the fine grained eclogitized pillow lava and inter pillow matrix are extremely fresh showing very little evidence of retrograde alteration peak assemblages in both the massive pillows and weakly foliated inter pillow matrix consist of zoned idiomorphic mg poor 0 8 wt mgo garnet omphacite lawsonite chlorite titanite a local overprint by the lower grade assemblage glaucophane albite with partial resorption of omphacite and garnet is locally observed garnet porphyroblasts in the massive pillows are mn rich and show a regular prograde growth type zoning with a mn rich core in the inter pillow matrix garnet is less manganiferous and shows a mutual variation in ca and fe with fe enrichment toward the rim some garnet from this rock type shows complex zoning patterns indicating a coalescence of several smaller crystallites matrix omphacite in both rock types is zoned with a rimward increase in xjd locally with cores of relict augite numerous inclusions of clinopyroxene lawsonite chlorite and titanite are encapsulated within garnet in both rock types and albite quartz and hornblende are also found included in garnet from the inter pillow matrix inclusions of clinopyroxene commonly have augitic cores and omphacitic rims the inter pillow matrix contains cross cutting omphacite rich veinlets with zoned omphacite si rich phengite si 3 54 apfu ferroglaucophane actinolite and hematite these veinlets are seen fracturing idiomorphic garnet apparently without any secondary effects pseudosections of matrix compositions for the massive pillows the inter pillow matrix and the cross cutting veinlets indicate similar p t conditions with maximum pressures of 1 9 2 6 gpa at temperatures of 335 420 c the inclusion suite found in garnet from the inter pillow matrix apparently formed at pressures below 0 6 0 7 gpa retrogression during initial decompression of the studied rocks is only very local late veinlets of albite glaucophane without breakdown of lawsonite indicate that the rocks remained in a cold environment during exhumation resulting in a hairpin shaped p t path

very low temperature record of the subduction process a review of worldwide lawsonite eclogites abstract lawsonite eclogites preserve a record of very low temperature conditions in subduction zones all occur at active margin settings typically characterized by accretionary complexes lithologies and as tectonic blocks within serpentinite matrix melange peak lawsonite eclogite facies mineral assemblages garnet omphacite lawsonite rutile typically occur in prograde zoned garnet porphyroblasts their matrix is commonly overprinted by higher temperature epidote bearing assemblages greenschist or amphibolite facies conditions erase former lawsonite eclogite relics various pseudomorphs after lawsonite occur particularly in some blueschist eclogite transitional facies rocks coesite bearing lawsonite eclogite xenoliths in kimberlitic pipes and lawsonite pseudomorphs in some relatively low temperature ultrahigh pressure eclogites are known using inclusion assemblages in garnet lawsonite eclogites can be classified into two types l type such as those from guatemala and british columbia contain garnet porphyroblasts that grew only within the lawsonite stability field and e type such as from the dominican republic record maximum temperature in the epidote stability field formation and preservation of lawsonite eclogites requires cold subduction to mantle depths and rapid exhumation the earliest occurrences of lawsonite eclogite facies mineral assemblages are early paleozoic in spitsbergen and the new england fold belt of australia this suggests that since the phanerozoic secular cooling of earth and subduction zone thermal structures evolved the necessary high pressure temperature conditions buoyancy of serpentinite and oblique convergence with a major strike slip component may facilitate the exhumation of lawsonite eclogites from mantle depths

cohesion versus friction in controlling the long term strength of a self healing experimental fault the coulomb s failure criterion which postulates that failure occurs along a fault plane when the applied shear stress overcomes a resistance made of two parts of different nature cohesion and friction remains the standard conceptual framework of faulting mechanics more recently rate and state friction laws became the main modelling tool of the seismic cycle these laws implicitly assume that only frictional resistance sets the fault strength and its evolution we therefore raise the question of the role of cohesion and related healing sealing mechanisms on fault mechanics we designed an original laboratory experiment based on a model material an ice thin layer sitting on top of a water tank and mechanically deformed at various rates with a circular couette like geometry this allowed sliding along the fault plane over arbitrarily large slip distances and analyzing the competition between faulting and cohesion healing rates whereas frictional resistance resulting from the fault roughness is limited in magnitude we show that cohesion healing plays an essential role in the time evolution of the interface strength under constant loading rate in particular the magnitudes of shear stress fluctuations are observed to be temperature and velocity weakening the present experiment shares several properties similar to that of active faults during seismic cycles suggesting that cohesive healing could control some of these features scale invariance properties gutenberg richter law of rupture events size distribution omori s law of energy dissipation at least after major ruptures time asymmetry in energy dissipation and periods of creep under high shear stress alternating with major earthquake like ruptures

evaluation of pleistocene groundwater flow through fractured tuffs using a u series disequilibrium approach pahute mesa nevada usa abstract groundwater flow through fractured felsic tuffs and lavas at the nevada national security site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at pahute mesa to help evaluate fracture flow and matrix water exchange we have determined u series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces breccia zones and interiors of unfractured core the u series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium series decay chain due to preferential mobilization of 234 u relative to 238 u and u relative to th samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays silica fe mn oxyhydroxides and zeolite intact core interiors and breccia fragments were sampled in bulk in addition profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture matrix water exchange samples of rock matrix have 234 u 238 u and 230 th 238 u activity ratios ar closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix greater u mobility was observed in welded tuff matrix with elevated porosity and in zeolitized bedded tuff samples of brecciated core were also in secular equilibrium implying a lack of long range hydraulic connectivity in these cases samples of discrete fracture surfaces typically but not always were in radioactive disequilibrium many fractures had isotopic compositions plotting near the 230 th 234 u 1 1 line indicating a steady state balance between u input and removal along with radioactive decay numerical simulations of u series isotope evolution indicate that 0 5 to 1 million years are required to reach steady state compositions once attained disequilibrium 234 u 238 u and 230 th 238 u ar values can be maintained indefinitely as long as hydrological and geochemical processes remain stable therefore many pahute mesa fractures represent stable hydrologic pathways over million year timescales a smaller number of samples have non steady state compositions indicating transient conditions in the last several hundred thousand years in these cases u mobility is dominated by overall gains rather than losses of u

solution deposition processes and mass transfer in the deformation of a minor fold abstract deformation occurred by solution deposition processes in a decimeter scale fold from siliceous marbles in the corsican schistes lustres as argued from a set of consistent data analysis of fold shape modal analysis microstructures metamorphic parageneses and mineral fluid equilibria mass transfer is evidenced between the limbs and the hinge zone and between adjacent lithologies with volume changes locally exceeding 50 at the metamorphic conditions of deformation 300 c and 8 kbar such a mass transfer may account for the inferred high ductility of the schistes lustres nappes model calculations for this deformation mechanism predict strain rates of 3 1 10 10 s 1 to 5 7 10 11 for quartz and calcite rich rocks respectively

review of the physical basis of laboratory derived relations for brittle failure and their implications for earthquake occurrence and earthquake nucleation a laboratory derived crack growth based constitutive relation for brittle faulting is developed the relation consists of two rheologic components a nonlinear arrhenius dependence of strain rate on temperature and stress corresponding to subcritical crack growth and a linear slip weakening behavior associated with dilatancy crack coalescence and supercritical crack growth the implications of this general behavior for the onset of rapid slip earthquake nucleation are considered laboratory observations of static fatigue and time dependent failure from rock fracture and rock friction experiments are consistent with this simple constitutive description as are the predictions of rate and state dependent equations for the onset of rapid frictional slip between bare rock surfaces i argue that crack growth is the physical process that controls time dependent rock fracture and the time dependent onset of unstable frictional sliding some similar and related arguments made in the past 1 2 century in the fields of rock mechanics and earthquake seismology are reviewed for stressing rates appropriate for the san andreas fault system the simple constitutive relation with lab derived constants predicts a minimum time for nucleation of 1 yr general predictions are a minimum nucleation patch radius of 0 06 to 0 2 m and a minimum earthquake moment of 8 5 x 107nm

how strong is an asperity a recent study of repeating earthquakes on the san andreas fault in central california by nadeau and johnson 1998 found that the smallest events occurred on patches having a linear dimension of the order of 0 5 m displacements of about 2 cm and stress drops of the order of 2000 mpa roughly 10 times larger than rock strengths measured in the laboratory the stress drop for larger events was observed to decrease as a power law of the seismic moment reaching the commonly observed value of 10 mpa at about magnitude 6 these large strengths are shown here to be consistent with laboratory data if the preexisting microcracks are all healed a hierarchical fractal asperity model is presented which is based on recent laboratory observations of contact distributions in sliding friction experiments this cantor dust model is shown to be consistent with the observed power law decrease in stress drop and increase in displacement with increasing event size the spatial distribution of hypocenters in the parkfield area is shown to be consistent with this simple fractal model and with a hierarchical clustering of asperities having a fractal dimension of d 1 and discrete rescaling factor of about 20

volcanic settings and their reservoir potential an outcrop analog study on the miocene tepoztlan formation central mexico abstract the reservoir potential of volcanic and associated sedimentary rocks is less documented in regard to groundwater resources and oil and gas storage compared to siliciclastic and carbonate systems outcrop analog studies within a volcanic setting enable to identify spatio temporal architectural elements and geometric features of different rock units and their petrophysical properties such as porosity and permeability which are important information for reservoir characterization despite the wide distribution of volcanic rocks in mexico their reservoir potential has been little studied in the past in the valley of mexico situated 4000 m above the neogene volcanic rocks groundwater is a matter of major importance as more than 20 million people and 42 of the industrial capacity of the mexican nation depend on it for most of their water supply here we present porosity and permeability data of 108 rock samples representing five different lithofacies types of the miocene tepoztlan formation this 800 m thick formation mainly consists of pyroclastic rocks mass flow and fluvial deposits and is part of the southern transmexican volcanic belt cropping out south of the valley of mexico and within the two states of morelos and mexico state porosities range from 1 4 to 56 7 average porosity is 24 8 generally permeabilities are low to median 0 2 933 3 md with an average permeability of 88 5 md the lavas are characterized by the highest porosity values followed by tuffs conglomerates sandstones and tuffaceous breccias on the contrary the highest permeabilities can be found in the conglomerates followed by tuffs tuffaceous breccias sandstones and lavas the knowledge of these petrophysical rock properties provides important information on the reservoir potential of volcanic settings to be integrated to 3d subsurface models

characterization of the groundwater flow regime and hydrochemistry of groundwater from the buem formation eastern ghana this study demonstrates the application of multivariate statistical methods in definition of groundwater recharge and discharge areas in a sedimentary basin in ghana q mode hierarchical cluster analysis hca was applied to 57 hydrochemical data from the buem formation in the northern part of the volta region in ghana r mode hca and r mode factor analysis were then applied to the same dataset to reveal the processes controlling the hydrochemistry of groundwater from this hydrogeological formation results of both the q and r mode analyses were backed by graphical methods the analyses revealed two major water types differentiated by salinity levels into four spatial groundwater associations the characteristics of the four groundwater types are discussed the recharge areas are characterized by cahco3 low salinity waters which evolve through rock water interactions to nahco3 high salinity waters in the discharge areas this study finds that the hydrochemistry of groundwater from this formation is mainly controlled by the weathering of minerals principally silicates in the aquifer matrix the effects of the chemistry of recharging precipitation are higher in the recharge areas while mineral weathering tends to be severe close to the discharge areas in the groundwater flow regime all the four spatial groundwater associations have low sodium content but salinity levels increase towards the discharge areas such that some of wells in the discharge areas may not be acceptable for irrigation on grounds of high salinities which might affect the osmotic potentials of plants copyright 2011 john wiley sons ltd

multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system summary the study of groundwater hydrogeochemistry of the paleozoic basses laurentides sedimentary rock aquifer system in quebec produced a large geochemical dataset groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions the large number of data can lead to difficulties in the integration interpretation and representation of the results two multivariate statistical methods hierarchical cluster analysis hca and principal components analysis pca were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry this subgroup consisted of 144 samples and 14 parameters ca2 mg2 na k hco 3 cl so 4 2 fe2 mn2 br sr2 f ba2 hs seven geochemically distinct clusters c1 c7 resulted from the hca samples from clusters c3 c4 c6 and c7 are mostly located in preferential recharge areas the majority of these samples have ca mg hco3 recharge groundwater c3 c6 c7 and na hco3 evolved groundwater c4 samples from the other three clusters c1 c2 c5 are characteristic of an aquifer system under confined conditions the majority of these samples have na hco3 evolved groundwater c1 c5 and na cl ancient groundwater that exhibits elevated concentrations in br c2 in addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry the distribution of clusters also showed the importance of the geological formations on minor and trace elements such as fe2 mn2 sr2 f and ba2 the first five components of the pca account for 78 3 of the total variance in the dataset component 1 is defined by highly positive loadings in na cl and br and is related to groundwater mixing with champlain sea water and solute diffusion from the marine clay aquitard the high positive loadings in ca2 and mg2 of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system from their characteristic loadings the first two components are defined as the salinity and hardness components respectively components 3 5 are related to more local and geological effects the integration of the hca and the pca with conventional classification of groundwater types as well as with the hydrogeological and geological contexts allowed the division of the region into four main geochemical areas providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater the following factors were recognized as influencing the evolution of groundwater identified in every geochemical area 1 geological characteristics including sedimentary rock type and till mineralogy 2 hydrogeological characteristics represented by the level of confinement and the hydraulic gradient and 3 the geological history including the latest glaciation and the champlain sea invasion with its integrated approach this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems and provides an example of the long term geochemical evolution of hydrogeological systems after a major perturbation in this case seawater invasion

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

the transition between blueschists and lawsonite bearing eclogites based on observations from corsican metabasalts abstract syntectonic eclogites associated with blueschist parageneses have recrystallized in metabasalts from eastern corsica under very low temperatures 420 c the evolution of these eclogites is recorded by the order of development of metamorphic minerals as demonstrated by helicitic inclusions of lawsonite and actinolite in fe rich garnets and the occurrence of fibrous na pyroxenes in the pressure shadows and cracks of boudinaged garnets within a foliated matrix composed of glaucophane ca fe garnets and lawsonite a schreinemakers analysis has been completed on the lawsonite ferroglaucophane actinolite almandine grossular ferro omphacite chlorite system in a t p h 2 o space the resulting three dimensional relationships are applied to the studied samples they are consistent with a prograde increase in temperature at low h 2 o producing eclogites from blueschists and with a subsequent retrogressive decrease in pressure

asperity model of an earthquake dynamic problem a previous study that presented the static solution for an asperity model of an earthquake is extended to solve the dynamic problem that develops when failure occurs on the boundary of an asperity patch and then spreads over the surrounding displacement shadow region the boundary integral equation method is coupled with basic constitutive equations for failure and friction to solve the dynamic problem with different parameters used for the strong asperity patch and weak shadow region no friction displacement weakening friction and velocity strengthening friction are all investigated depending on the type and amount of friction that is present the dynamic solutions for slip on the fault exhibit a range of different features including overshoot of the static solution and oscillation rupture front velocities that may be greater than or less than the s velocity and change with position and either total or partial release of the static moment common characteristics of the solutions are that failure on the asperity patch is almost independent of failure on the shadow region and that the displacement deficit on the shadow region is released by propagating slip pulses the stress concentrations of the asperity model are sufficient to produce nonlinear elastic effects in a region extending outward from the fault to distances comparable with the dimensions of the shadow region beginning with the solutions for slip on the fault waveforms are simulated for an earthquake of magnitude m w 1 44 and compared with data recorded at a distance of 8 65 km simulations that contain both source and propagation effects are capable of explaining most of the basic features of the observational data including general agreement with the shape of the waveforms in the time domain the levels and slopes of the spectra at low frequencies less than 10 hz and at high frequencies greater than 100 hz and some of the interference effects present in both the time and frequency domains

the occurrence of deerite in highly oxidizing conditions within the schistes lustres of eastern corsica a deerite bearing rock occurs at the boundary between quartzite and metabasites within the schistes lustres of eastern corsica it contains the typomorphic assemblage pyroxene blue amphibole hematite and magnetite pyroxene shows homogeneous composition close to the aegirine end member and blue amphibole is zoned from crossite core to riebeckite rim the bulk chemical analysis of the rock is remarkable by its very high iron content and the presence of an unusually large amount of zn which is concentrated in both deerite and amphibole electron microprobe analyses of the corsican deerite are compared with those published in the literature as shown by deerite from the fransciscan iron formation the principal substitution for fe2 is mn whereas the amount of substitution for fe3 is low in the system sio2 feo fe2o3 al2o3 na2o mgo h2o the typomorphic paragenesis can be described by an univariant reaction interpreted as the result of a pressure decrease p t conditions of metamorphism previously estimated to be 8 kbar and 300 c are in good agreement with present knowledge of the deerite stability field the occurrence of hematite and magnetite in equilibrium permits an estimation of the oxygen fugacity log fo2 29 41 bar oxidation conditions are higher than those previously mentioned in the literature for similar assemblages

contribution of correlation and spectral analyses to the regional study of a large karst aquifer charente france the purpose of the study is to demonstrate that correlation and spectral analyses can contribute to the regional study of a large karst aquifer an example is presented for the la rochefoucauld karst aquifer charente france different types of spatially distributed time series provide valuable spatio temporal information for the karst aquifer the available time series consist of the spring flow rates the flow rates at different locations in sinking streams the piezometric levels the electrical conductivity and temperature of the water the atmospheric pressure and the precipitation the analysis of the flow rates at the springs shows that the aquifer empties very slowly and has a large storage capacity hydrodynamic links were established between three of the four rivers flowing on the aquifer and the springs the results also demonstrate the important spatial heterogeneity of the aquifer and indicate that the most rapid flow occurs in the northern part of the aquifer hourly piezometric and electrical conductivity time series indicate that the transmissivity of the aquifer varies when some conductive channels become desaturated during the low water period the delays between the distributed recharge and the piezometric level between the localized river input and the flow rates at the springs and between the electrical conductivities in rivers and the main spring provide information on the travel times in the aquifer the observation of earth tides and barometric effects indicate that this apparently unconfined aquifer has a confined behaviour

rhenium molybdenum and uranium in groundwater from the southern great basin usa evidence for conservative behavior abstract dissolved re mo and u concentrations and the concentrations of the major cations and anions were measured in groundwaters from twenty three springs in the southern great basin usa from june 1992 through march 1994 rhenium concentrations ranged from 5 1 pmol kg to 190 20 pmol kg the highest re values were observed in the saline groundwater of saratoga spring in death valley and cold spring in ash meadows whereas the lowest re concentrations were found in nevares spring in death valley the mean re concentration for all of the spring waters sampled is 44 33 pmol kg the concentrations of re differs dramatically for groundwaters that discharge from the regional paleozoic carbonate aquifer and for local groundwaters from felsic volcanic rocks the mean re concentration for groundwaters issuing from the carbonate aquifer is 37 14 pmol kg which is similar to the average re value reported for seawater i e 39 8 0 2 pmol kg whereas for the spring waters that discharge from the felsic volcanic aquifers the mean re concentration is 18 3 5 pmol kg the overall mean concentrations of u and mo in these groundwaters are 18 12 nmol kg and 120 60 nmol kg respectively differences in the u and mo concentrations for groundwaters from the carbonate aquifer and those from the volcanic aquifer are also observed such that the mean u and mo concentrations in the carbonate groundwaters are 13 5 nmol kg and 106 40 nmol kg respectively and the mean u and mo concentrations in the volcanic spring waters are 31 5 4 nmol kg and 94 12 nmol kg respectively by comparison u and mo concentrations reported for seawater are 13 9 nmol kg and 107 nmol kg respectively in the oxygenated groundwaters of the great basin re mo and u appear to be acting conservatively as in seawater as evidenced by the covariance observed between re mo and u with chloride sodium and sulfate groundwaters discharging from the regional carbonate aquifer in ash meadows typically exhibit a u re ratio of about 300 while groundwaters that discharge in death valley from local felsic volcanic sources have ratios of about 1700 waters in the remainder of the death valley springs are intermediate and may result from the mixing of the carbonate and volcanic derived waters the re mo and u concentrations in addition to the major solute chemistry indicates that dissolution of carbonate rocks is of primary importance in the groundwaters from ash meadows whereas the weathering of felsic volcanic rocks contributes substantially to the chemical signatures of the death valley groundwaters the differences between u re ratios and different aquifer materials suggest that there is a relationship between the dissolved u re ratios and the aquifer materials similar re mo u ratios for the groundwaters from the carbonate aquifer and seawater are strongly suggestive of quantitative uptake of these trace elements from seawater by carbonate mineral precipitation and subsequent quantitative release of these trace elements during dissolution of the carbonate rocks by groundwater the substantially larger salinity normalized re mo and u concentrations in the groundwaters compared to seawater rule out the possibility that these groundwaters represent simple mixing of dilute terrestrial waters and seawaters or reconstitution of evaporite deposits by groundwater dissolution

assessment of groundwater quality for irrigation and drinking purposes and identification of hydrogeochemical mechanisms evolution in northeastern tunisia oligocene and mio plio quaternary siliciclastic deposits constitute the most important deep aquifers of the kairouanai sahel region considering the over exploitation and contamination of the surface groundwater recourse to use deep groundwater was crucial these aquifers revealed three major hydrochemical facies hco3 mg hco3 na and so4 mg water types rock water interaction showed the main mechanisms are rock weathering and evaporation different parameters such as water quality index wqi sodium absorption ratio sar percentage of sodium residual sodium carbonate rsc magnesium hazard mh and permeability index pi were used to evaluate groundwater suitability for drinking and irrigation purposes results highlighted that groundwater is unsafe for irrigation based on pi mh rsc and salinity diagram according to the wqi values 10 25 of the water samples had good water quality 69 23 were considered as poor water 12 82 were very poor water and 7 69 were considered unsuitable for drinking purpose

hydrothermal contamination of public supply wells in napa and sonoma valleys california groundwater chemistry and isotope data from 44 public supply wells in the napa and sonoma valleys california were determined to investigate mixing of relatively shallow groundwater with deeper hydrothermal fluids multivariate analyses including cluster analyses multidimensional scaling mds principal components analyses pca analysis of similarities anosim and similarity percentage analyses simper were used to elucidate constituent distribution patterns determine which constituents are significantly associated with these hydrothermal systems and investigate hydrothermal contamination of local groundwater used for drinking water multivariate statistical analyses were essential to this study because traditional methods such as mixing tests involving single species e g cl or sio2 were incapable of quantifying component proportions due to mixing of multiple water types based on these analyses water samples collected from the wells were broadly classified as fresh groundwater saline waters hydrothermal fluids or mixed hydrothermal fluids meteoric water wells the multivariate mixing and mass balance m3 model was applied in order to determine the proportion of hydrothermal fluids saline water and fresh groundwater in each sample major ions isotopes and physical parameters of the waters were used to characterize the hydrothermal fluids as na cl type with significant enrichment in the trace elements as b f and li five of the wells from this study were classified as hydrothermal 28 as fresh groundwater two as saline water and nine as mixed hydrothermal fluids meteoric water wells the m3 mixing model results indicated that the nine mixed wells contained between 14 and 30 hydrothermal fluids further the chemical analyses show that several of these mixed water wells have concentrations of as f and b that exceed drinking water standards or notification levels due to contamination by hydrothermal fluids

current tufa sedimentation in a changing slope valley the river anamaza iberian range ne spain abstract a three year study of modern carbonate sedimentation was conducted through analysis of sedimentological and hydrochemical parameters measured every six months at 10 sites along a high slope river in northeastern spain river anamaza three stretches of the river were characterised the dominant water inputs from the upstream karstic springs primarily from the jurassic rock aquifer determined the so4 hco3 ca composition of the river water from this area decreasing trends in alkalinity calcium and total dissolved inorganic carbon occurred downstream in both the warm and cool periods as a result of calcite precipitation tufa thickness variations were consistent with such hydrochemical evolution deposition rates increased downstream primarily where the gradient is steeper middle stretch and subsequently decreased at the downstream gently sloped stretch therefore the slope along the river and the distance from the main upstream springs conditioned the spatial distribution of tufa deposits by determining the chemical characteristics of the water the monitored sites represent four primary fluvial subenvironments with distinct sedimentary facies the highest carbonate deposition rates were measured in fast flow conditions stromatolites facies a deposits with calcite coated algae and mosses facies c formed in cascades and small jumps with very fast flowing water exhibited lower deposition rates and typical erosion lower rates corresponded to slow flow conditions in which thin stromatolite crusts and or filamentous and calcareous algae and tufa fragments facies b accumulated in slow flowing water areas near springs upstream stretch calcite was absent linked to the higher pco2 of water microbial films and aquatic flora composed the biofacies facies d in such subenvironment therefore tufa deposition rates in each fluvial subenvironment were controlled by the amount of co2 outgassing linked to local flow conditions the biological substrate type and the chemical attributes of the water along each stretch a six month pattern of deposition rates best marked in the steeper stretch was recorded from thickness measurements spring summer periods 4 30 mm autumn winter periods 1 22 mm parallel variations were recorded using pwp plummer wigley parkhurst and calcite mass balance calculations multivariate statistical analyses hca and pca clearly separated hydrochemical and sedimentological attributes in samples from warm and cool periods exceptions to this pattern were related to changes in the water discharge high discharge events caused the dilution of the chemical composition and erosion of the tufa deposits therefore temperature dependent factors i e physico chemical and biological processes coupled with discharge changes controlled the seasonal variations in deposition rates the stable isotope composition of calcite and river water also reflected the discharge effects however the seasonal variation signature of temperature was preserved in the 18o of sediment

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

using multivariate statistical analysis of groundwater major cation and trace element concentrations to evaluate groundwater flow in a regional aquifer groundwater samples were collected from 11 springs in ash meadows national wildlife refuge in southern nevada and seven springs from death valley national park in eastern california concentrations of the major cations ca mg na and k and 45 trace elements were determined in these groundwater samples the resultant data were subjected to evaluation via the multivariate statistical technique principal components analysis pca to investigate the chemical relationships between the ash meadows and death valley spring waters to evaluate whether the results of the pca support those of previous hydrogeological and isotopic studies and to determine if pca can be used to help delineate potential groundwater flow patterns based on the chemical compositions of groundwaters the results of the pca indicated that groundwaters from the regional paleozoic carbonate aquifers all of the ash meadows springs and four springs from the furnace creek region of death valley exhibited strong statistical associations whereas other death valley groundwaters were chemically different the results of the pca support earlier studies where potentiometric head levels 18o and d geological relationships and rare earth element data were used to evaluate groundwater flow which suggest groundwater flows from ash meadows to the furnace creek springs in death valley the pca suggests that furnace creek groundwaters are moderately concentrated ash meadows groundwater reflecting longer aquifer residence times for the furnace creek groundwaters moreover pca indicates that groundwater may flow from springs in the region surrounding scotty s castle in death valley national park to a spring discharging on the valley floor the study indicates that pca may provide rapid and relatively cost effective methods to assess possible groundwater flow regimes in systems that have not been previously investigated copyright 1999 john wiley sons ltd

statistical approach to determine the salinized ground water flow path and hydrogeochemical features around the underground lpg cavern korea the ground water flow path of the coastal area in the yellow sea korea was interpreted using both the cross correlation analysis of hydraulic properties and the principal component analysis pca of ground water chemistry data was obtained from observation wells in the underground liquefied petroleum gas lpg cavern constructed in the coastal area of pyeongtaek cross correlation results showed that the operating pressure became more influenced on artificial factors for the variation of the groundwater level of the study area 45 66 of correlation coefficient even though its affecting area was limited to the region with fractures or faults and also showed that the delay time from the variation of operating pressure to the fluctuation of ground water level were relatively long periods 28 31 days three hydrogeochemical events encrusted cement dissolution host rock dissolution and seawater intrusion which were dominantly influenced on ground water quality could be induced from the result of pca quantitative evaluation for these events using the mixed equation with principal component scores suggest that the dissolution of encrusted cement materials was the predominant factor 39 0 of the total mixed proportion to change the chemical composition of the seepage water during the ground water flow from the observation wells to the cavern integration of the statistical results also imply that ground water flow and hydrogeochemistry were predominantly affected by artificial factors such as cavern operation pressure and dissolution of encrusted cement materials which were interdependent factors on the observation wells with high cross correlation coefficients and ph copyright 2007 john wiley sons ltd

evolutionary model for alpine corsica mechanism for ophiolite emplacement and exhumation of high pressure rocks a tectonic model of alpine corsica is proposed based on geological studies its evolution starts after the jurassic with intraoceanic subduction followed by mid cretaceous subduction of the european continental margin under the oceanic segment of the adriatic plate after subduction of the continental crust to a depth of 150 km slices of crustal material are buoyantly uplifted together with high pressure oceanic rocks ophiolites and schistes lustres high pressure low temperature continental gneiss units overthrust the outer segments of the european crust while producing a normal sense motion along the upper surface of the rising crustal body during the eocene the closure of the remnant ligurian oceanic basin separating the proto corsican belt and adria resulted in a second orogenic phase with the emplacement of unmetamorphosed ophiolitic nappes which overthrust the previously exhumed and eroded hp belt this corsican model suggests an original evolutionary path for orogenic belts when continental collision is preceded by intraoceanic subduction

microstructural criteria for reliable thermometry in low temperature eclogites abstract two alpine eclogite bodies sampled in metaophiolitic complexes of the piemonte zone have been studied for geothermometry it is demonstrated that temperature estimates by both exchange thermometry and sizes of antiphase domains in omphacites give rise to erratic results when the defect structures of the minerals are not taken into account microstructural criteria by means of both optical and tem microscopy for reliable thermometry in low temperature eclogites are disscussed the dynamically recrystallized grains are the more suitable sites for the application of exchange thermometry while only low strained omphacites can be used for thermometry based on apd s

application of mass balance and flow simulation calculations to interpretation of mixing at aspo sweden the hydrogeology of a vertical fracture zone at 70 m depth at the access tunnel to the aspo hard rock laboratory was monitored over 3 a for hydrochemical changes that could be effected by construction of a deep repository for high level nuclear waste tunnel construction dramatically disturbed the hydrogeological system but this provided an opportunity to integrate hydrogeochemical and hydrological evaluation of the zone the objective of this study was to evaluate hydrogeochemical evolution groundwater flow and surface water intrusion during the experiment using an integrated approach of geochemical mass balance calculations and numerical flow simulations the dilution of major ions was the dominant hydrochemical trend however hco3 and so4 showed significant enrichment increasing activity of 14c suggested that oxidation of organic c was the likely source of hco3 any mineral source dissolving during the experiment seemed insufficient to account for changes in so4 and current intrusion of sea water was excluded according to the data cation exchange as well as minor calcite reactions in fractures were assumed probable in such temporary chemical conditions conservative two end member mixing models with shallow groundwater in the zone and initial groundwater at tunnel level also assumed remarkable mass transfer several mmol l therefore a third so4 rich end member a regional shallow groundwater type which may mix by lateral flow in the system was tested this was also expected from hydraulic measurements and preliminary flow simulations assuming homogeneity three end member mixing calculations using cl and so4 as conservative tracers give a constant proportion of lateral water in all boreholes after 300 days which is consistent with the steady state character of the flow field in the late part of the experiment to predict reactions on plausible levels needs significant adjustments of initial and final waters indicating uncertainties in the hydrochemical information of the fracture zone in the flow simulations the transmissivities were selected so that the chemical mixing proportions would match simulated portions of flow as closely as possible the simulated total recoveries drawdowns differ from the measurements mainly due to overly simple parametrisation of the transmissivity in the fracture zone however integrating hydrochemistry in flow modelling is considered encouraging in producing additional information of the heterogeneity of a flow structure

a case of obduction related high pressure low temperature metamorphism in upper crustal nappes arabian continental margin oman p t paths and kinematic interpretation in the southeastern oman mountains the saih hatat tectonic window reveals arabian continental material beneath the oceanic sensu lato nappes i e the hawasina sedimentary units and the huge sumail ophiolite the northeastern internal half of the window suffered an intense deformation associated with a high pressure low temperature hp lt metamorphism approximately dated at 80 75 ma according to the available stratigraphie data after the deformation due to the absence of collision the obduction inherited structural and metamorphic pattern was virtually unmodified a metamorphic map is established based on mineral assemblages in metapelites and metabasites low grade assemblages occur in the highest units muscat nappes quryat unit characteristic minerals are femg carpholite lawsonite associated with kaolinite or pyrophyllite and locally sudoite in the metapelites while lawsonite and blue amphiboles are found in the metabasites high grade rocks outcrop in the deepest and easternmost units as sifah antiform and are typified by an epidote glaucophane bearing eclogite assemblage intermediate units hulw show assemblages of intermediate grade chloritoid schists and glaucophane bearing metabasites higher grade assemblages such as talc chloritoid were not found inverted gradients are observed locally in the muscat nappes pyrophyllitebearing units above kaolinite quartz bearing units and these are ascribed to late metamorphic thrust displacements which are demonstrated by microstructures a complex p t evolution is fairly well documented by the mineral assemblages prograde evolution in the subophiolitic continental rocks began with a rather hot gradient of about 30 35 c km with chloritoid growth in the higher units thereafter pressure increased with the temperature remaining constant or even decreasing chloritoid replaced by kaolinite oxides and carpholite growth in synkinematic conditions the peak p t conditions are close to 8 kbar 270 c for the muscat nappes and 11 kbar 400 c for the as sifah unit the corresponding surface related gradient is low 10 15 c km during the retrograde evolution pressure and temperature generally decreased concomitantly but in some of the upper units temperature remained constant or increased slightly for some time at which point sudoite growth from carpholite took place the metamorphic pattern and mineral evolution are interpreted in the framework of the late cretaceous obduction the already cold oceanic lithosphere was thrust upon a relatively hot thinned passive margin with coeval basaltic volcanism pressure progressively increased in the passive margin due to the wedge shape of the advancing ophiolite the maximum thickness of which was about 25 km in the as sifah area in this area the overburden was also attributable to the accumulation of continental material up to 5 km thick by means of a complex set of synmetamorphic often conjugated folds and thrusts the basal peridotites of the obducted slab were probably not hotter than 300 c during its thrusting upon the continental margin the temperature of the tectonic pile below the ophiolite remained low because it was thrust above more external and still colder continental areas late thrusting in the same southerly direction controlled the retrograde evolution together with erosional and gravity driven tectonic unloading

statistical analysis of the hydrogeochemical evolution of groundwater in hard rock coastal aquifers of thoothukudi district in tamil nadu india the study of groundwater hydrogeochemistry of a hard rock aquifer system in thoothukudi district has resulted in a large geochemical data set a total of 100 water samples representing various lithologies like horn blende biotite gneiss alluvium marine alluvium fluvial quartzite charnockite granite and sandstone were col lected for two different seasons and analyzed for major ions like ca 2 m g 2 n a k hco3 c l s o 4 2 no3 p o 4 f and h4sio4 statistical analysis of the data has been attempted to unravel the hidden relationship between ions correlation analyses and factor analyses were applied to classify the groundwater samples and to identify the geochemical processes controlling groundwa ter geochemistry factor analysis indicates that sea water intrusion followed by leaching of secondary salts weath ering and anthropogenic impacts are the dominant factors controlling hydrogeochemistry of groundwater in the study area factor score overlay indicate major active hydrog eochemical regimes are spread throughout the eastern northwestern and southeastern parts of the study area the dominant ions controlling the groundwater chemistry irre spective of season are cl n a m g 2 c a 2 s o 4 2 k and no3 an attempt has also been made to note the seasonal variation of the factor representations in the study area this study also illustrates the usefulness of statistical analysis to improve the understanding of groundwater systems and estimates of the extent of salinity salt water intrusion

estimation of volume changes by comparative chemical analyses in heterogeneously deformed rocks folds with mass transfer abstract this paper presents a method for calculating the volume change between the various sectors of the same heterogeneously deformed layer fold shear zone by comparing the chemical composition of deformed sectors with that of a reference sector the principle consists of considering some minerals as being insoluble illite chlorite and passively concentrated in deformed zones because of the loss of more soluble minerals quartz calcite dolomite by pressure solution simple observations can be used to test the validity of the assumptions required to calculate volume change in the analysis of a slaty matrix around a ptygmatic fold a map of values is drawn and these values are shown to be compatible with the general strain pattern for several limb hinge pairs of straight limbed folds the relations between volume change elongation parallel to limb layering l l o and the angle between limb and hinge are determined the influence of various parameters such as temperature pressure initial composition and structure of the rock on these relations is also pointed out

paleoenvironmental interpretations of rare earth element signatures in mosasaurs reptilia from the upper cretaceous pierre shale central south dakota usa abstract rare earth elements were analyzed from fossil marine reptile mosasauridae bones collected from five superposed members sharon springs gregory crow creek degrey and verendrye of the upper cretaceous pierre shale at localities along the missouri river in brule buffalo hughes and hyde counties in central south dakota fossil bones from each member of the pierre shale have different rare earth element ree signatures that may be distinctive over wide geographic areas fossils from the sharon springs member have distinctive ree signatures that may be further subdivided into three superposed groups that correspond with the upper middle and lower sharon springs member ree signatures are distinctive from each stratigraphic unit therefore fossils eroded from their stratigraphic context may be assigned to their proper depositional unit based on ree signature comparisons differences in ree compositions of bones among members appear to result from differential mixing of oxygenated and anoxic seawaters if differences in mixing are interpreted as depth differences the lower sharon springs member was deposited in deep anoxic water water depths decrease in the middle and upper sharon springs and the overlying gregory and crow creek members were deposited in even more shallow water finally according to this interpretation the overlying degrey and verendrye members were deposited in progressively deeper marine waters but not as deep as the lower sharon springs these interpretations are generally consistent with those based on faunal diversity and eustatic sea level curves

assessing hydrochemical evolution of groundwater in limestone terrain via principal component analysis this paper describes the use of multivariate statistical analysis to trace hydrochemical evolution in a limestone terrain at zagros region iran the study area includes a deep confined aquifer overlaid by an unconfined aquifer the method involves the use of principal component analysis pca to assess and evaluate the hydrochemical evolution based on chemical and isotope variables of 12 piezometers drilled in both the unconfined and confined aquifers first pca on all variables shows that water rock interaction under different conditions with respect to the atmospheric co2 is the main process responsible for chemical constituents as a result combinations of several ratios such as ca tds so4 tds and mg tds with physico chemical and isotope variables reveal different hydrochemical evolution trend in the aquifers second pca on the selective samples and variables reveals that displacement of the unconfined samples from dry to wet season follows a refreshing trend towards river samples that is characterized by reducing electrical conductivity and increasing sulphate and tritium contents however the refreshing trend cannot be traced in the confined aquifer samples suggesting no recharge from river to the confined aquifer third pca reveals that chemical composition of water samples in the unconfined aquifer tends to have considerable difference from each other in the end of recharge period in contrast the confined aquifer samples have a tendency to show similar chemical composition during recharge period in comparison to end of dry period this difference is caused by different mechanism of recharge in the unconfined aquifer through the whole aquifer surface and the confined aquifer through the limited recharge area

exhumation of deep crustal metamorphic rocks and crustal extension in arc and back arc regions we adress the problem of exhumation of metamorphic rocks in arc and back arc positions based on observations of the aegean and tyrrhenian back arc regions in both regions back arc extension has been active for 25 ma at least while convergence and crustal thickening was going on at the thrust front compressional structures are reworked in the back arc domain as extensional flat lying detachments which allow unroofing of the metamorphic pile metamorphic rocks suffer first a dynamic burial during nappe stacking and then fast exhumation when they reach the extensional region we describe a continuous process of burial and exhumation that is contemporaneous with the migration of the thrust front toward external zones the front of extension follows behind at approximately one hundred kilometers at the convergence front continuous subduction of a cold oceanic slab or continuous accretion of continental units keeps a cool p t gradient and hp lt metamorphic rocks are formed at depth the overall cool environment leads to a deep brittle ductile transition and thus to a resistant crust which can sustain its large thickness while the thrust front propagates forward parts of the accretionary wedge which were formed earlier enter the back arc domain which can be already under extension and which is warmer because of a greater distance to the cold slab and the presence of the volcanic arc the brittle ductile transition rises in the thick crust which then becomes unstable and subsequently collapses the exhumation history of metamorphic rocks below detachments is two fold 1 a constantely thickening crust is unroofed by flat lying detachments which rework early thrusts this first period is characterized by a good preservation of hp lt parageneses 2 the second period is when rocks are in the zone of crustal scale extension of the back arc region deep crustal metamorphics are exhumed below flat lying detachements which affect the whole crust

hydro geochemical processes in an area with saline groundwater in lower shire river valley malawi an integrated application of hierarchical cluster and principal component analyses abstract our ability to adapt to changes in groundwater quality arising from a changing climate and or local pressures is dependent on comprehension of the governing controls of spatial variation in groundwater chemistry this paper presents results of an assessment of dominant hydro geochemical processes controlling groundwater chemical composition using an integrated application of hierarchical cluster analysis hca and principal component analysis pca of a major ion dataset of groundwater from lower shire river valley malawi the area is in the southernmost part of the western section of the east african rift system ears and has localised occurrence of saline groundwater hca classified samples into three main clusters c1 c3 according to their dominant chemical composition c1 dominant composition na cl median tds 3436 mg l 1 c2 dominant composition na hco 3 median tds 966 mg l 1 and c3 dominant composition alkali earths hco 3 median tds 528 mg l 1 these clusters were in turn described by the principal components pc1 pc3 and pc2 respectively resulting from the pca the results of the pca and geochemical interpretation suggest that the spatial variation of groundwater quality in the area is influenced by the following processes c3 samples result mainly from h 2 co 3 weathering of aluminosilicate minerals by percolating water supersaturated with co 2 in addition to aluminosilicate weathering c2 samples are influenced by the processes of cation exchange of ca 2 and mg 2 in the water for na on clay minerals and carbonate precipitation the increase in ionic strength of c2 samples is attributed to mixing with high tds groundwater in proximity with c2 samples the saline brackish c1 groundwater results from the processes of evaporation for samples with high water table close to the shire marshes and dissolution of cl and so 4 evaporative salts followed by mineralised seep from sedimentary karoo and cretaceous lupata sandstones

integrated investigation of seawater intrusion around oil storage caverns in a coastal fractured aquifer using hydrogeochemical and isotopic data summary seawater intrusion can be activated by the construction of underground caverns which act as groundwater sinks near a coastal area in an environment complicated with such artificial structures seawater intrusion is not simple and thus needs to be evaluated by means of multiple analytical approaches this study uses geochemical and isotopic indicators to assess the characteristics of salinized seepage into an underground oil storage cavern in yeosu korea cl br ratios principal component analysis pca of chemical data and stable isotope data were used to determine the origin and the extent of salinization indications of seawater intrusion into the cavern through fractured bedrocks were observed however it was highly probable that another source may have contributed to the observed salinity the pca results revealed that the seepage water chemistry was predominantly affected both by seawater mixing and cement material dissolution the maximum seawater mixing ratio in the seepage water was estimated on the basis of the cl br mixing ratio and the cl 18o relation with the results showing considerable variation ranging from less than 1 to as high as 14 depending on the cavern location the spatial variations in the chemical characteristics and in mixing ratios are believed to have resulted from the hydrogeological heterogeneity of the study site as caused by both fractured aquifer and the cavern facilities

lithostratigraphy tephrochronology and rare earth element geochemistry of fossils at the classical pleistocene fossil lake area south central oregon abstract one of the most famous fossiliferous pleistocene sites in the pacific northwest is fossil lake oregon until recently fossil collections from the area were not stratigraphically controlled owing to the lack of a detailed stratigraphic and chronologic framework our field studies reveal at least nine exposed thin rhythmic fining upward depositional packages most separated by disconformities analysis of interbedded tephras reveals that the rye patch dam 646 ka dibekulewe 610 ka tulelake t64 95 ka marble bluff 47 ka and trego hot springs 23 2 ka tephra layers are present in the section indicating deposition from more than 646 ka to less than 23 ka which includes both the late irvingtonian and rancholabrean north american land mammal ages a much longer time span than previously believed bones analyzed from eight of the defined units have distinctly different rare earth element ree signatures fossils obtain ree during early diagenesis and signatures are probably closely

brittle ductile transition and associated seismicity experimental and numerical studies and relationship with the b value the acoustic emission ae and the mechanical behavior of granite samples during triaxial compression tests have been analyzed the size of ae events displays power law distributions conforming to the gutenberg richter law observed for earthquakes which is characterized by the b value as the confining pressure increases the macroscopic behavior becomes more ductile for all different stages of the rock mechanical behavior linear nonlinear prepeak nonlinear postpeak shearing there is a systematic decrease of the b value with increasing confining pressure a numerical model based on progressive elastic damage and the finite element method allows simulations of the main experimental observations on ae and of a wide range of macroscopic behaviors from brittleness to ductility the model reproduces a decrease in the b value that appears to be related to the type of macroscopic behavior brittle ductile rather than to the confining pressure both experimental and numerical results suggest a relationship between the b value and the brittle ductile transition moreover these results are consistent with recent earthquake observations and give new insight into the behavior of the earth s crust

groundwater flow system inferred from hydraulic stresses and heads at an underground lpg storage cavern site underground liquefied petroleum gas lpg storage caverns were constructed below the groundwater table to contain pressurized gas by groundwater pressure continuous and regular groundwater monitoring data were used to analyze whether the gas containment condition was satisfied or not the monitoring data included time series analysis of hydraulic heads gas and groundwater pressures and groundwater chemistry through cross correlation analyses of the time series data the major factors causing hydraulic head fluctuation were found to be groundwater recharge from precipitation and cavern gas pressures hydraulic head and hydrochemical data indicate that a fault zone acts as the groundwater recharge zone and water curtain tunnels reduce head fluctuations

burial and exhumation of corsica france in the light of fission track data 1 the mesozoic and cenozoic exhumation and cooling history of corsica is reconstructed by fission track ft data on basement and sedimentary rocks apatite ages are 105 16 ma zircon ages are 160 145 ma the jurassic and cretaceous ages show that parts of the variscan basement escaped alpine influence the basement was thermally affected by rifting prior to jurassic opening of the ligurian piedmont ocean then it cooled to near surface temperatures in paleocene eocene times subduction buried parts of the basement and overlying flysch to greater depth in the oligocene both collapse of the nappe stack and rifting prior to opening of the ligurian provencal basin affected the apatite ft system of the basement in different partly overlapping areas causing a complex age pattern the study shows that thorough analysis of ft data and thermal modeling allow to assign age populations to distinct cooling processes even when several thermotectonic events contributed to generate an intricate age pattern

fault permeability near yucca mountain a deep paleozoic carbonate aquifer is of special concern for the proposed high level nuclear repository at yucca mountain nevada it provides a potential pathway for groundwater transport of contaminants from the repository back to the biosphere the map of groundwater temperature at the water table has been interpreted by several investigators to indicate upwelling groundwater along major fault zones both east and west of yucca mountain of particular concern is the permeability of these fault zones the deep carbonate aquifer has been penetrated by only one test hole in the vicinity of yucca mountain ue 25pl in this borehole the hydraulic head in the deep carbonate aquifer was 20 m higher than head in the overlying tuff aquifer observations in ue 25pl show good earth tide water level fluctuations in the deep carbonate aquifer both the large 2 cm amplitude of the tidal signal and the fact that it is in phase with the tidal potential indicate that the deep aquifer is well confined by a layer of low hydraulic conductivity an estimate of the maximum hydraulic permeability of a fault zone that penetrates the confining is made by simulating the tidal response given a maximum permeability and the head difference one can calculate the upward flow from the deep carbonate aquifer into the overlying tuffs this analysis supports the interpretation of upward flow from the deep carbonate to the overlying tuffs this is a favorable condition for the proposed repository the upward potential for flow from the deep carbonate aquifer protects it from the downward movement of contaminants further deep drilling is necessary to confirm that the high head persists beneath the entire proposed repository nothing should be done either through construction of the repository or through groundwater development to reduce heads in the carbonate aquifer the higher heads protect the carbonate aquifer

application of factor analysis to study contamination of a semi confined aquifer wielkopolska buried valley aquifer poland groundwater chemistry is controlled by many natural processes as well as anthropogenic processes the identification of the influence of anthropogenic processes on groundwater chemistry is difficult particularly in cases of early phase of groundwater anthropogenic transformation the present study shows the application of factor analyses fa for the identification of anthropogenic processes affecting groundwater chemistry of a semi confined aquifer wielkopolska buried valley aquifer poland the results of this study clearly demonstrate that fa is a reliable method for differentiation of natural and anthropogenic processes affecting groundwater chemistry particularly during the early phase of anthropogenic groundwater chemistry transformations

back arc extension and denudation of mediterranean eclogites eclogite facies rocks exposed in mediterranean back arcs are delimited from above by low angle normal faults and detachments nevertheless our work demonstrates that these extensional structures associated with back arc extension played only a limited role in removing the overburden from above the eclogites extension in mediterranean back arcs began in the late oligocene or early miocene but the pressure temperature time p t t paths of eclogite facies rocks exposed in these areas indicate that a major part of the overburden several tens of kilometers has been removed from above these rocks prior to the oligo miocene we show that the time period bracketed between the peak of eclogite metamorphism eocene in the central aegean probably upper cretaceous in corsica and the betics and the onset of back arc extension in the oligo miocene was characterized by thrust faulting in the central aegean corsica and the betics eclogite bearing units were partly unroofed and then overthrusted lower pressure units we emphasize that with one exception tinos island greece the entire inventory of extensional contacts operated subsequently to the overthrusting of the eclogites above the lower grade sequences thus mediterranean back arc extension lags behind a major part of the denudation process and is superposed on orogenic wedges that contain eclogite facies rocks at relatively shallow structural levels we emphasize that the mode of occurrence of eclogites in mediterranean back arc regions involves a continuum of in situ crustal accretion below the eclogites widespread p t paths that show cooling or isothermal decompression and lower grade rocks at the bottom of the structural pile thus instead of reflecting whole crust back arc extension the tectonic style associated with the denudation of mediterranean eclogites better fits an active accretionary wedge setting this is similar to the mode of occurrence of eclogite facies rocks in mountain belts such as the western alps where decompression was synorogenic and back arc extension played no role

manganese in monoclinic members of the epidote group piemontite and related minerals according to mayo 1932 who provided a brief historical review of the names used for piemontite the first researcher who described this mineral has been cronstedt in 1758 who named it rod magnesia in 1790 chevalier napione analyzed the sample described by cronstedt and termed it manganese rouge on the basis of his chemical data hauy designated the substance as manganese oxide violet silicifere in 1801 later in his traite de mineralogie hauy 1822 adopted the name proposed by cordier 1803 who first recognized the mineral as an epidote manganesifere the name piedmontite was proposed in 1853 by kenngott the basis of the type locality and more recently transformed into piemontite according to the standard guidelines for mineral nomenclature the name piemontite should be reserved to members of the ternary solid solution ca2al2 mn fe al si2o7 sio4 o oh that basically contains mn3 dominant at one site nonetheless the use of this name for any monoclinic manganiferous epidote group members showing the characteristic strong red yellow violet pleochroism is very common and probably convenient with special regard to petrographic purposes indeed the color of manganian i e mn3 bearing epidote or clinozoisite ranges to red to pinkish while manganoan i e mn2 bearing members do not exhibit the characteristic reddish hue the discredited name withamite was used to describe poorly manganiferous piemontite hutton 1938 yoshimura and momoi 1964 but corresponds on the basis of the current nomenclature to a manganian clinozoisite the name thulite sometimes erroneously used for pinkish clinozoisite should be reserved to mn3 bearing orthorhombic members in this chapter we focus on piemontite sensu stricto with the ideal formula ca2al2mn3 si2o7 sio4 o oh but also include for the reasons explained above those members of the clinozoisite epidote piemontite

discrimination between different water bodies from a multilayered aquifer kaluvelly watershed india trace element signature in the multilayered aquifer of kaluvelly india comprising various sedimentary layers overlying a charnockitic basement concentrations of trace elements were measured in aquifer formations and in groundwaters to identify geochemical tracers for water bodies the two main sandstones cuddalore and vanur originate from the charnockites and the cuddalore sandstone has experienced lateritization in the studied area two charnockite end members were identified a dioritic and a granitic one mineralogical composition and whole rock ti concentrations confirmed the charnockite which displayed the granitic composition as the parent rock of the two sandstones titanium distribution indicates that the cuddalore sandstone originates from a more intense weathering of the parent material than the vanur sandstone despite extensive differences in trace element contents recorded in aquifer formations only a few trace elements were suitable to distinguish the water bodies among soluble elements li in the vanur aquifer and ba in the charnockite and carbonaceous aquifers can be used as tracers as the input of these elements in solution is mainly regulated by the available stock for a given mineralogical origin there is a direct link between the aquifer formation composition and water signature with the exception of as concentrations of redox sensitive elements were not preserved during pumping because of oxidation preventing their use as tracers low mobility elements such as la ce th zr nb hf or ta were too insoluble to be detected in waters and or to record the aquifer formation signature their input in solution was not regulated by the available stock but by the dissolution rate of rock forming minerals only ti can be used to distinguish between two out of the three aquifers charnockite and vanur the specific behavior of ti recorded in these waters may be linked to rutile inclusions within plagioclases and to the influence of climate on ti solubility

multivariate statistical analysis for identifying water quality and hydrogeochemical evolution of shallow groundwater in quaternary deposits in the lower kelantan river basin malaysian peninsula a long term hydrogeochemical data set is used in this study to evaluate the water quality and hydrogeochemical evolution of shallow groundwater in a quaternary deposit a multivariate statistical method hierarchical cluster analysis hca is applied to overcome the problem of a large number of data points in the integration interpretation and representation of the results hca is applied to a subgroup of the hydrogeochemical data set to evaluate their usefulness to classify the groundwater bodies this subgroup consists of 27 groundwater wells and 15 variables ph total dissolved solids electrical conductivity ec na ca2 mg2 k hco3 cl so42 fe mn nh4 no3 and sio2 only 12 chemical variables were used for the analysis four clusters have been identified c1 c4 with two main prevalent facies na hco3 and ca hco3 the hydrogeochemical evolution of shallow groundwater is governed by the processes of precipitation weathering dissolution and ion exchange

analysis of continental midcrustal strain localization induced by microfracturing and reaction softening 1 low angle extensional shear zones which often characterize the brittle ductile transition of the continental crust are seen here to result from strain localization the potentially destabilizing deformation mechanism is assumed to be the progressive transformation of fractured coarse feldspar grains into white mica as observed in the east tenda shear zone alpine corsica the coupling between microfracturing and feldspar to mica reaction is coeval with strain localization that occurred in that field case at a depth close to 15 km this reaction is proposed as the main destabilizing factor responsible for the onset of localization with feldspar having a stationary dislocation creep flow stress larger than mica to test this hypothesis a rheological model is constructed based on the field observations for a mixture of three phases mica quartz and feldspar deforming at a common strain rate the phase concentrations change with time according to the feldspar to mica reaction which takes place only if feldspar grains are fractured a condition detected with the mohr coulomb criterion the tendency for the strain to localize is assessed by numerical means for the structure composed of an upper crust gliding rigidly over the lower crust which sustains an overall simple shear the onset of strain localization is defined by an increase of at least two orders of magnitude in strain rate over part of the lower crust the upper crust gliding velocity has to be increased by at least a factor of 5 for localization to occur the time lapse for this velocity change determines the depth of the shear zone 15 17 km the kinetics of the metamorphic reaction and the final amount of white mica control its width 1 4 km the time of the shear zone formation is less than half a million years

modeling of geochemical processes and multivariate statistical analysis for hydrochemical assessment of spring water of the outer himalaya india water resources in the himalayan region are under stress because of the changes in land use and land cover pattern and climate in the recent past the region has encountered extreme events such as cloud burst and widespread flooding in this reference this study was conducted on the spring water resources in the outer himalayan region to assess their quality and quantity the main geochemical processes and the impact of anthropogenic forcing on water chemistry were deciphered using geochemical modeling tools multivariate statistical analysis and graphic plots the hierarchical cluster analyses were used to categorize the springs in two clusters based on their chemical characteristics the principal component analysis was used to evaluate the effective loading of spring water hydrochemical data ionic ratios and geochemical modeling using phreeqc were used to confirm the processes that govern the chemistry of the spring water the results indicate that silicate weathering and anthropogenic activities are the dominant processes controlling the chemical evolution of spring water in the region this study will provide a better insight for understanding the spring water resources and their sustainable management in the himalayan region