microstructures mineral chemistry and geochronology of white micas along a retrograde evolution an example from the aar massif central alps switzerland abstract this study investigates gneissic tectonites of different mechanical origins and aims at unravelling the link between microstructures white mica chemistry and k ar data the highest temperature mylonitic deformation which is investigated is dominated by dislocation creep in monomineralic quartz and viscous granular flow in polymineralic domains these mylonites show homogenous mineral chemistry resulting in robust and consistent k ar age data the lowest temperature deformation investigated is that of a retrograde brittle deformation producing cohesionless fault gouges within the cohesionless fault gouges frictional granular flow is considered as the main deformation mechanism the k bearing phases inside the fault gouges record no chemical resetting during this brittle overprint but contain mechanically fragmented k bearing micas and significant amounts of newly produced smectite this yields k ar ages inside of a gouge that are in the range of adjacent mylonite ages and may not represent the timing of gouge formation in an effort to understand these uncertainties in k ar ages detailed observations of the microstructural context of k bearing white mica were made microstructural criteria in combination with quantitative element mapping allowed for the discrimination of five important mica related processes 1 fracturing recrystallization of white mica 2 re precipitation of new fine grained white mica inside the deforming rock matrix 3 pseudomorphic replacement of precursor minerals by white mica and chlorite 4 pseudomorphic replacement of pre existing white mica without grain size reduction and 5 remnant grains the combination of these different processes led to a high variability in mineral chemistry and isotope data for tectonites which relates directly to variations in the size of the equilibrium volumes despite the samples being highly deformed in the presence of fluids inherited sheet silicates may survive if inherited sheet silicates are present they contribute to an increase in both the chemical heterogeneity and the apparent k ar ages of a sample

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

k ar illite age constraints on the proterozoic formation and reactivation history of a brittle fault in fennoscandia k ar ages of authigenic illite from two drill core gouge samples of a fault in the palaeoproterozoic basement of finland record two distinct faulting events the older sample yields apparent ages from 1240 26 to 1006 21 ma for four grain size fractions between 6 and 0 1 m the second sample is structurally younger and yields statistically distinct ages ranging from 978 20 to 886 18 ma we interpret the ages of the 0 1 m fractions which are the youngest as representing the actual time of faulting xrd analysis and age modelling exclude significant age contamination of the finest dated fractions with inherited host rock components these results provide therefore an example of meaningful isotopic dating of illite type clay material formed during precambrian faulting demonstrate and constrain fault reactivation and give evidence for brittle sveconorwegian mesoproterozoic shortening and neoproterozoic extension in fennoscandia

spatial delineation of groundwater salinity using deep time domain electromagnetic geophysical measurements a feasibility study 1 the objective of this study was to delineate the spatial distribution of fresh brackish and saline groundwater bodies as well as brine beneath the judea desert israel we used the deep time domain electromagnetic tdem geophysical system cycle 5m which provides the maximum exploration capability to depths 1 5 2 km below land surface the study was conducted at 21 locations at the desert plateau where fresh groundwater flows through the upper aquifers from the replenishment area at the judea mountains toward the dead sea springs in deeper aquifers brackish and saline groundwater bodies exist which originated from lakes and lagoons that existed at the dead sea rift valley during the pleistocene and pliocene respectively it was found that within carbonate formations fresh groundwater c 103 ppm total dissolved solids tds is characterized by a resistivity of more than 15 m brackish groundwater 103 c 104 ppm tds is characterized by 5 15 m saline groundwater 104 c 105 ppm tds is characterized by 0 5 5 m and brine 105 c ppm tds is characterized by less than 0 5 m

seasonal reversals in groundwater flow direction and its role in the recurrent agwagune landslide problem a geophysical and geological appraisal the character of the shallow subsurface materials in the landslide and flood prone agwagune community has been investigated using geophysical electrical resistivity geological and geotechnical techniques arising from the continuous suffering of the people in the affected areas high occurrence rate and the desire to characterise the surficial materials two dimensional resistivity tomography vertical electrical sounding soil sampling and hydrodynamic monitoring were conducted results show that the surficial materials are dominated by two main lithologic units thin sandy materials with resistivity 30 m and thick argillaceous materials with resistivity 30 m particle size analyses confirm the dominance of argillaceous silty clay 56 2 and very fine 55 3 over arenaceous 9 2 materials bulk and particle densities of the surficial materials vary from 0 99 103 to 1 40 103 and 2 06 103 to 2 50 103 kg m3 respectively ph ec and porosity range from 4 46 to 6 68 8 0 to 23 0 ms cm and 34 0 to 60 0 respectively atterberg limits vary from 15 82 to 38 70 for liquid limit and 18 10 24 00 for plastic limit plasticity index varies from 11 92 to 15 70 shallow groundwater in the coastal area is always in hydrodynamic equilibrium with water inside the cross and efefa rivers and pond fields to sustain this equilibrium condition excess water inside the cross river is usually discharged into efefa river through both surface and underground flow processes however when water inside the cross river dries up a new hydraulic gradient which distorts the existing equilibrium is formed this results in the reversal of groundwater flow direction continuous flow of groundwater into the cross river channel crc without any corresponding recharge results in the formation of voids which gravitational force forces to collapse the collapsed materials usually roll toward the crc resulting in landslides models illustrating the main cause of the repeated landslide problem and suggested measures to minimise its occurrence rate have been included

microstructurally constrained versus bulk fault gouge k ar dating abstract structural mineralogical and geochronological data were collected from two brittle fault zones fault i and ii deforming the ordovician rolvsnes granodiorite in sw norway microstructurally constrained k ar data from cohesive damage zone samples are compared to bulk k ar data from fault gouges from the adjacent fault cores in fault i fluid ingress along the fault core caused pervasive alteration of the host granodiorite plagioclase and biotite are almost completely altered to kaolinite quartz illite and smectite in fault ii a complex deformation history is recorded by multiple fault rock microdomains including an ultracataclasite with 50 authigenic illite and an illite jarosite bearing pseudotachylyte microdomains hosting authigenic illite jarosite from both studied faults were separated characterized mineralogically and dated by k ar results confirm that each domain contains only one generation of authigenic illite jarosite and provide robust time constraints on fault initiation in the carboniferous 339 8 ma and reactivation in the permian 289 6 ma k ar geochronology of the adjacent fault gouges yields inclined age versus grain size relationships the ages of the coarsest grain size fractions are similar to the age range of the damage zone data whereas the ages of the finer fractions are significantly younger our study provides new and important insights into the dynamics of long lived fault zones isotopic signatures and structural features representative of fault initiation are preserved in the damage zones while they are progressively overprinted due to cumulative strain localization in the fault cores finally our study further clarifies the significance of age plateaus in age versus grain size plots which allows for a robust and geologically meaningful interpretation of k ar data

thermochronologic constraints on evolution of the linglong metamorphic core complex and implications for gold mineralization a case study from the xiadian gold deposit jiaodong peninsula eastern china abstract the nne trending linglong metamorphic core complex hosts the majority of the gold deposits in the jiaodong peninsula of eastern china many of the deposits are hosted by the 163 155 ma linglong granite in the footwall of the linglong detachment fault argon thermochronology suggests that the granite had cooled to 400 c by 143 1 5 ma possibly as a result of normal movement on the detachment nine zircon fission track zft ages from samples collected along a nw se transect perpendicular to the central part of the linglong detachment fault at the 652 m level in the xiadian deposit constrain the subsequent thermal evolution of linglong metamorphic core complex which overlapped the period of major gold deposition the zft ages vary from 136 9 3 3 ma 1 to 130 1 2 2 ma 1 the unaltered linglong granite in the footwall and amphibolite in the hangingwall have similar ages at 136 9 3 3 ma 1 and 135 0 3 0 ma 1 whereas ages for the disseminated and stockwork style ores appear to be younger at ca 131 130 ma although there is an overlap of ages when considering the 1 precision interestingly zft ages show no marked differences between the hangingwall and footwall of the linglong detachment fault although significant movement along the fault occurred the results are best interpreted to indicate that the linglong granite was emplaced at 160 ma and cooled to 240 50 c at 135 ma as recorded by unaltered rocks in the footwall hydrothermal alteration along the linglong detachment fault led to annealing of zircon fission tracks and the consistent younger ages of 131 ma quartz aggregates associated with gold mineralization show evidence of recrystallization suggesting that the hydrothermal event was initiated at temperatures of at least 300 350 c near the brittle ductile transition but cooled rapidly to zft closure temperatures within a country rock environment that was already relatively cool therefore these zft ages suggest that the timing of mineralization at the xiadian deposit was post 135 ma and likely very close to 131 ma the mineralization and cooling occurred in the footwall of a major detachment fault under an extensional regime possibly related to the progressive slab rollback of the paleo pacific plate and controlled by the linglong metamorphic core complex

influence of deformation and fluids on ar retention in white mica dating the dover fault newfoundland appalachians abstract white mica 40ar 39ar analyses may provide useful constraints on the timing of tectonic processes but complex geological and thermal histories can perturb ar systematics in a variety of ways ductile shear zones represent excellent case studies for exploring the link s between dynamic re neo crystallization of white mica and coeval enhanced fluid flow and their effect on 40ar 39ar dates white mica 40ar 39ar dates were collected from compositionally similar granites that record different episodes of deformation with proximity to the dover fault a terrane bounding strike slip shear zone in the appalachian orogen newfoundland canada 40ar 39ar data were collected in situ by laser ablation and by step heating single crystals results were compared to each other and against complementary u pb zircon and monazite and k ar fault gouge analysis although step heat 40ar 39ar is a widely applied method in orogenic settings this dataset shows that relatively flat step heat 40ar 39ar spectra are in contradiction with wide spreads in in situ 40ar 39ar dates from the same samples and that plateau dates in some cases yielded mixed dates of equivocal geological significance this result indicates that the step wise release of ar from white mica likely homogenizes and obscures spatially controlled ar isotope reservoirs in white mica from sheared rocks in contrast in situ laser ablation 40ar 39ar analysis preserves the spatial resolution of 40ar reservoirs that have been variably reset by deformation and fluid interaction this study therefore suggests that laser ablation is the best method for dating the timing of deformation recorded by white mica final interpretation of results should be guided by microstructural analysis estimation of deformation temperature chemical characterization of white mica and complementary chronometers overall the dataset shows that granitic protoliths were emplaced between 430 and 422 ma u pb zircon high strain deformation along the wing pond shear zone occurred between ca 422 405 ma u pb monazite and 40ar 39ar subsequent patchy ar loss in white mica occurred locally during low t shear

patterns of mineral transformations in clay gouge with examples from low angle normal fault rocks in the western usa abstract neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto frictional regime but neither the conditions nor the processes which wall rock is transformed into clay minerals are well understood yet understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults we therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low angle normal faults lanf s in the american cordillera to demonstrate the range and type of clay transformations in natural fault gouges the sampled faults juxtapose a wide and representative range of wall rock types including sedimentary metamorphic and igneous rocks under shallow crustal conditions clay mineral transformations were observed in all but one of 28 faults one fault contains only mechanically derived clay rich gouge which formed entirely by cataclasis clay mineral transformations observed in gouges show four general patterns 1 growth of authigenic 1m d illite either by transformation of fragmental 2m 1 illite or muscovite or growth after the dissolution of k feldspar illitization of fragmental illite smectite is observed in lanf gouges but is less common than reported from faults with sedimentary wall rocks 2 retrograde diagenesis of an early mechanically derived chlorite rich gouge to authigenic chlorite smectite and saponite mg rich tri octahedral smectite 3 reaction of mechanically derived chlorite rich gouges with mg rich fluids at low temperatures 50 150 c to produce localized lenses of one of two assemblages sepiolite saponite talc lizardite or palygorskite chlorite quartz and 4 growth of authigenic di octahedral smectite from alteration of acidic volcanic wall rocks these transformation groups are consistent with patterns observed in fault rocks elsewhere the main controls for the type of neoformed clay in gouge appear to be wall rock chemistry and fluid chemistry and temperatures in the range of 60 180 c

illite and hydrocarbon exploration illite is a general term for the dioctahedral mica like clay mineral common in sedimentary rocks especially shales illite is of interest to the petroleum industry because it can provide a k ar isotope date that constrains the timing of basin heating events it is critical to establish that hydrocarbon formation and migration occurred after the formation of the trap anticline etc that is to hold the oil illite also may precipitate in the pores of sandstone reservoirs impeding fluid flow illite in shales is a mixture of detrital mica and its weathering products with diagenetic illite formed by reaction with pore fluids during burial k ar ages are apparent ages of mixtures of detrital and diagenetic end members and what we need are the ages of the end members themselves this paper describes a methodology based on mineralogy and crystallography for interpreting the k ar ages from illites in sedimentary rocks and for estimating the ages of the end members

three dimensional geophysical anatomy of an active landslide in lias group mudrocks cleveland basin uk a geoelectrical investigation of a slow moving earth slide earth flow in lower jurassic lias group rocks of the cleveland basin uk is described these mudrock slopes are particularly prone to failure and are a major source of lowland landslides in the uk but few attempts have been made to spatially or volumetrically characterise the subsurface form of these slides the primary aim of this study was to consider the efficacy of fully three dimensional geoelectrical imaging for landslide investigation with reference to a geological setting typical of lias group escarpments the approach described here included a reconnaissance survey phase using two dimensional electrical resistivity tomography ert resistivity mapping self potential sp profiling and mapping followed by a detailed investigation of an area of the landslide using three dimensional 3d ert and self potential tomography spt interpretation of the geophysical data sets was supported by surface observations aerial lidar and differential gps geomorphological surveys and intrusive investigations boreholes and auger holes the initial phase of the study revealed the existence of a strong sp signature at the site consistent with a streaming potential source and established the relationships between the main geological units the geomorphologic expression of the landslide and the resistivity of the materials in and around the study area the 3d spt model generated during the second phase of the study indicated drainage patterns across the landslide and preferential flow from the low permeability mud rocks into the underlying more permeable sandstone formation because of favourable resistivity contrasts between the clay rich whitby mudstone formation landslide material and the underlying staithes sandstone formation the volumetric 3d ert image allowed a number of surface and subsurface landslide features to be identified and spatially located these included the lateral extent of slipped material and zones of depletion and accumulation the surface of separation and the thickness of individual earth flow lobes and the dipping in situ geological boundary between the whitby mudstone and staithes sandstone bedrock formations

using dc resistivity method to characterize the geometry and the salinity of the plioquaternary consolidated coastal aquifer of the mamora plain morocco the direct current resistivity method was applied to the consolidated coastal plioquaternary aquifer of mamora plain located on the atlantic coast of morocco the aim is to determine the depth of the base of the saturated zone in the aquifer and to help in imaging lateral and vertical distribution of groundwater salinity the geoelectric survey showed four geoelectric formations with the following electrical resistivities from top to bottom 20 80 200 2000 200 300 and 5 70 ohm m the latter designates the basement of the aquifer constituted of marls and sandy marls the mean resistivity of 250 ohm m designates the aquifer formation it decreases to less than 25 of its initial values for the soundings near the shore reflecting the oceanic impact on the aquifer formation resistivity the contour map shows that the basement of the saturated zone in the aquifer is deeper in the northwest near the sebou river estuary with values up to 70 m below sea level this results in a larger thickness of the saturated zone of the aquifer leading to a consequent hydraulic potential on the other hand it has been deduced that the extent of marine intrusion inside the continent can be governed by human activities natural properties and substratum geometry of the aquifer as well as by ecological factors an optimal network of electrical soundings has been proposed for the monitoring of saltwater intrusion

k ar illite and apatite fission track constraints on brittle faulting and the evolution of the northern norwegian passive margin abstract determining the timing of post caledonian brittle faulting in northern norway is important for the understanding of the extensional tectonic evolution of the north norwegian continental margin fault gouges from the troms and vesteralen regions of northern norway yield carboniferous to permian and carboniferous to cretaceous k ar illite ages respectively the results show a contrast in fault activity and exhumation between the troms and the vesteralen regions while major faulting in the troms region appears to have ceased after the permian faulting event faulting continued into at least the cretaceous in the vesteralen region the findings highlight the importance of a widespread permian tectonic event followed by a distinct southwestward migration of post permian tectonic activity on the north norwegian passive margin late triassic to early jurassic apatite fission track ages do not show significant age offsets across major fault zones in troms indicating that most or all of fault activity took place prior to the late triassic the thermal history models are consistent and indicate continuous cooling to about 60 c in the late permian triassic

evolution of saline waters and brines in the benue trough nigeria abstract hydrogeochemical assessment of 40 saline waters and brines from 20 locations within the lower southern and middle regions of the benue trough nigeria are presented and discussed in terms of genesis of the primary salinity and subsequent hydrochemical evolution the total dissolved ions range from 5263 to 88 800 mg l and 5148 to 47 145 mg l in the lower and middle region respectively the saline waters and brines are characteristically na cl type enriched in ca and sr on the one hand and depleted in mg and so 4 on the other relative to the seawater evaporation trend ionic ratios na cl br systematic and divalent cations suggest two likely sources of primary salinity a fossil seawater source and dissolution of halite however water rock interaction involving mg uptake by clay minerals and possibly dolomitization during diagenesis appear to be responsible for further modification of the primary chemistry a conceptualized hydrogeological flow model for the brines is presented

salinity mapping of coastal groundwater aquifers using hydrogeochemical and geophysical methods a case study from north kelantan malaysia integrated hydrogeochemical and geophysical methods were used to study the salinity of groundwater aquifers along the coastal area of north kelantan for the hydrogeochemical investigation analysis of major ion contents of the groundwater was conducted and other chemical parameters such as ph and total dissolved solids were also determined for the geophysical study both geoelectrical resistivity soundings and reflection seismic surveys were conducted to determine the characteristics of the subsurface and groundwater contained within the aquifers the ph values range from 6 2 to 6 8 indicating that the groundwater in the study area is slightly acidic low content of chloride suggests that the groundwater in the first aquifer is fresh with an average concentration of about 15 8 mg l and high geoelectrical resistivity 45 ohm m on the other hand the groundwater in the second aquifer is brackish with chloride concentration ranging from 500 mg l to 3 600 mg l and very low geoelectrical resistivity 1 000 mg l the groundwater in the third aquifer is fresh with chloride concentrations generally ranging from 2 mg l to 210 mg l and geoelectrical resistivity of greater than 45 ohm m fresh and saltwater interface in the first aquifer is generally located directly in the area of the coast but for the second aquifer both hydrogeochemical and geoelectrical resistivity results indicate that the fresh water and saltwater interface is located as far as 6 km from the beach the considerable chloride ion content initially suggests that the salinity of the groundwater in the second aquifer is probably caused by the intrusion of seawater however continuous monitoring of the chloride content of the second aquifer indicated no significant changes with time from which it can be inferred that the salinity of the groundwater is not affected by seasonal seawater intrusion schoeller diagrams illustrate that sulphate concentrations of the groundwater of the second aquifer are relatively low compared to those of the recent seawater therefore this result suggests that the brackish water in the second aquifer is probably from ancient seawater that was trapped within the sediments for a long period of time rather than due to direct seawater intrusion

groundwater investigation in kuala selangor using vertical electrical sounding ves surveys integrated geoelectrical and hydrochemical surveys were used to investigate and delineate different types of groundwater in the kuala selangor alluvial aquifer previous hydrogeological borehole investigation showed that this aquifer contains several types of groundwater in relation to its salinity the high salinity of the groundwater in some areas is believed to be due to either saltwater intrusion from the nearby sea or river infiltration during high tide season the vertical electrical sounding ves method was employed to study and map the subsurface variation of resistivity in the area for each sounding measurement a total spread length of 300 m was obtained with a vertical depth penetration of about 60 to 75 m chemical analysis of the groundwater samples taken from both shallow and deep boreholes was carried out for the water quality determination a total of 45 ves stations were succesfully established along three parallel roads with a direction almost perpendicular to the coastal line the distance between stations varies from 1 to 2 km with a maximum length of about 60 km surveyed line results of the vertical electrical soundings as well as the hydrochemistry of the groundwater samples show that the soil and groundwater in the study area can be grouped into fresh and brackish water zones the subsurface resisitivity sections derived from the ves study suggest that the area is dominated by brackish soil and groundwater zones especially in the area towards the coast this result appears to agree well with the groundwater pumped from boreholes scattered around in the area water drawn from boreholes near the coast showed higher salinity compared to the water pumped from inland boreholes chloride values greater than 250 mg l are considered to represent the brackish zones whilst values less than 250 mg l represents zones of fresh soil and groundwater

precise dating of low temperature deformation strain fringe analysis by 40ar 39ar laser microprobe pyritized graptolites from the welsh basin united kingdom slate belt acted as rigid bodies during cleavage formation and epizonal white micas formed within the resulting strain shadows orthogonal to the principal stress orientation although the quantities of mica are small they are a pure synkinematic mineral and have been dated by ar 40 ar 39 infrared laser microprobe as a means to dating cleavage four samples of strain fringe mica from different hand samples yielded ages ranging from 394 4 3 1 to 397 8 1 8 ma 2sigma with a mean age of 396 1 1 4 ma 2sigma by focusing on minerals that are unequivocally synkinematic this technique provides a novel solution to the problems of isotopically dating slaty cleavage previous studies have predominantly relied on dating whole rock slate samples or separated illite grains by ar 40 ar 39 techniques problems encountered included 1 separating the effects of isotopic contamination by detrital phases 2 ar 39 loss during the irradiation of illite mineral separates and 3 thermally induced ar 40 loss in nature from fine grained minerals by circumventing these problems this new method provides the first unequivocal and high precision age data for acadian deformation in the well characterized welsh basin slate belt with such precision the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent continent collision

constraining deformation phases in the aar massif and the gotthard nappe switzerland using th pb crystallization ages of fissure monazite ce abstract fissure monazite ce hereafter called monazite commonly crystallizes during deformation at low metamorphic grade and offers the possibility to date protracted deformation over several millions of years and to identify distinct deformation phases we performed th pb geochronology at the microscale on 10 samples of fissure monazite from two alpine crystalline massifs aar massif and gotthard nappe ion microprobe ages show that the earliest stage of crystallization recorded by fissure monazite domain ages occurred around 15 9 ma in the gotthard nappe and about 1 my later in the aar massif with the latest crystallization event recorded at 6 ma protracted monazite crystallization in fissures indicates that deformation datable with fissure monazite lasted about 10 ma comparison of th pb crystallization ages of fissure monazite to existing thermochronological data shows that early monazite crystallization coincide with zircon fission track ages whereas the youngest monazite crystallization overlaps with apatite fission track ages monazite also grows contemporaneous with muscovite illite crystallization k ar ages in fault gouges as monazite can grow during dissolution precipitation cycles induced by tectonic activity their chronology allows to further constrain in the aar massif the final handegg phase at 12 11 5 ma and the coeval activity of the pfaffenchopf 11 5 9 ma and the oberaar and rhone simplon phases 11 5 and 6 ma in the gotthard nappe monazite crystallization constrains a major portion of the chiera backfolding phase at 14 13 ma and confirms that the south western termination of the nappe was affected by the rhone simplon phase

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

constraining the timing of brittle deformation and sedimentation in southern finland implications for neoproterozoic evolution of the eastern fennoscandian shield abstract sheared sedimentary clay was found in a faulted fracture in crystalline bedrock in a tunnelling site at 60 m depth in southern finland brittle faults are numerous in the fennoscandian palaeoproterozoic bedrock but only some of them have relative age constraints while absolute ages are nearly lacking sedimentary rocks altogether are uncommon in finland and only sparsely dated by micropaleontological studies this study reports k ar data of fresh non weathered authigenic illite and constrains a time framework for the local faulting and sedimentation the neoproterozoic tonian to cryogenian ages derived from the grains in diminishing grain size order are c 967 947 809 and 697 ma results indicate that the formation of the extension fracture is related to the collapse of sveconorwegian orogeny c 1000 ma clay and mature quartz sand were deposited in this extension fracture in shallow water in an intracratonic basin followed by early diagenetic processes and neocrystallization of illite around 967 947 ma the neoproterozoic 1000 700 ma sedimentation documented in this study is rare in the fennoscandian shield as a whole neocrystallization of authigenic illite in the finest 0 4 and

k ar dating of synkinematic clay gouges from neoalpine faults of the central western and eastern alps abstract with ongoing alpine convergence and deformation during exhumation there is a general progression from ductile to brittle behaviour on the periadriatic fault and kinematically related faults farther north e g the simplon rhone fault and a diffuse discontinuous zone of generally dextral strike slip movement on the southern boundary of the aar massif k ar dating of fine grained illite from clay fault gouges provides a reliable method for establishing the maximum age of this transition to brittle faulting and for short lived faults the approximate time of faulting itself the new results establish that brittle faulting on the northeastern segment of the canavese fault i e the part of the periadriatic fault southwest of lago maggiore occurred around 20 ma with south side up kinematics a k ar age of ca 17 ma for the crosscutting giudicarie fault in the eastern alps is effectively identical with an already published pseudotachylyte age and places a lower limit on major and continuous strike slip movements of the periadriatic fault the age of brittle faulting farther north on the southern border of the aar massif is from 13 6 0 3 to 8 3 1 1 ma consistent with the younger cooling and exhumation in this area the dominantly dextral brittle faulting becoming younger to the north reflects the continued indentation and anticlockwise rotation of adria as alpine units become exhumed and progressively welded to the southern block in contrast to the eastern alps there is no field evidence for westward lateral extrusion of alpine units relative to adria and the european foreland

inversion of self potential data from the cerro prieto geothermal field mexico self potential sp data from the cerro prieto geothermal field in baja california mexico have been inverted using a model consisting of a vertical contact separating regions of different electrical properties a temperature source is assumed to coincide with the vertical contact between materials with different thermoelectric coupling coefficients a derivative free levenberg marquardt algorithm is used to estimate values for the depth vertical extent length and intensity of the source region the depth to the top of the source is estimated to be about 1 3 0 2 km which agrees quite well with the depth to the top of the production zone determined from drilling the vertical extent and length of the source region are estimated to be 11 3 km and 9 9 0 4 km respectively there appears to be geologic evidence for the presence of a fault or fault zone within the geothermal field that roughly coincides in location with the self potential source region the conductivity on the east side of the produc

40ar39ar dating of very fine grained samples an encapsulated vial procedure to overcome the problem of 39ar recoil loss 40ar39ar dating of very fine grained materials is compromised by the loss of 39ar by recoil and also sometimes other ar isotopes during irradiation an encapsulated sample 40ar39ar procedure is described which overcomes this problem and which produces a k ar equivalent date measurements indicate that the procedure yields reliable and reproducible results it offers the potential for dating small amounts of material of many types for example very fine grained authigenic sheet silicates from rock cores which may suffer ar loss during irradiation

40ar 39ar dating of cataclastic k feldspar a new approach for establishing the chronology of brittle deformation abstract constraining the timing of brittle deformation such as in high angle normal or strike slip faulting is technically challenging in this study we present a new approach of age determinations from cataclastic k feldspars of brittle faults developed in rocks of the tan lu fault zone and from louzidian and liaonan metamorphic core complexes in ne china the attempt is based on field investigations microstructural observations back scattered electron bse imaging electron microprobe analyses x ray diffraction scanning electron microscope sem results and 40ar 39ar step heating of k feldspar separated from brittle fault zones of cataclastic mylonite granite and gneiss sem and bse images of individual k feldspar crystals reveal distinct grain deformation features including grain scale faults fractures and microfractures that occur parallel or perpendicular to each other the 40ar 39ar dating results provide well defined plateau spectra for the cataclastic k feldspar grains in the tan lu fault zone 74 5 1 3 ma and of brecciated gneisses and mylonites that formed at depth in the louzidian and liaonan metamorphic core complexes 120 129 ma and 116 2 ma these data suggest complete resetting of the ar isotope system of the cataclastic k feldspars allowing to constrain the timing of their deformation

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

dating of shallow faults new constraints from the alptransit tunnel site switzerland methods for dating shallow faults in the earth9s crust are still evolving and their reliability remains controversial based on results from well preserved fault gouge samples from the alptransit deep tunnel site in switzerland we propose a simplified and readily applicable approach to investigate and date clay rich gouge zones we collected 10 samples covering a north south section of 15 km all sampled faults are developed in orthogneiss host rock have a rather consistent approximately northwest southeast strike are mainly normal and are related to northeast southwest orogen parallel extension during alpine exhumation fine grained clay separates from the fault gouges consist of illite 1m 1m d and 2m 1 polytypes smectite and chlorite with minor amounts of feldspar in some sample fractions the k ar ages for

the effect of sub seismic fault slip processes on the isotopic signature of clay minerals implications for k ar dating of fault zones abstract clay minerals are abundant in fault gouges and isotope dating of the radiogenic noble gases that they contain may be used to constrain timing of fault initiation reactivation and to estimate recurrence intervals of earthquakes the potential influence of fault slip and ambient temperature on the isotope signature of authigenic clay minerals however remains unknown this study reports measurements of the k ar isotope signature of samples that have been sheared experimentally at sub seismic slip rates within a range of ambient temperatures as well as of samples undergoing standardised clay heating degas experiments in the investigation and comparison of the influence of sub seismic frictional slip and external heating on clay gouge the age data confirm that the sub seismic frictional slip of clay gouge affects the clay microstructures and releases radiogenic 40ar the experimental data indicate that radiogenic 40ar release due to external heating can be disregarded until 350 c which is supported by ar diffusion modelling frictional slip at sub seismic slip rates and at room temperature results in a significant radiogenic 40ar loss of 56 and the remaining clay will inherit 44 of radiogenic 40ar sub seismic frictional slip experiments at imposed elevated temperatures from 150 to 450 c increase the amount of radiogenic 40ar loss and decrease the amount of inherited radiogenic 40ar at a relatively high temperature of 450 c about 16 of radiogenic 40ar will be present in the remaining sample portion reinforcing the importance of rigorous clay grain size separation processes required prior to fault gouge dating

benue trough and benue chain it is suggested that the benue trough may have been initiated by the extension of the equatorial oceanic fracture zones onto the continent during the early stages of the separation of africa and south america a transcurrent movement along deep seated faults of the basement is responsible for the structure of the trough after a period of extension characterized by the sedimentary infilling of the trough and igneous activity the trough is turned into a chain through a short phase of compression a discrete pattern of en echelon folds and the strain pattern deduced from the analysis of large scale and microfracturing correspond to a n s to n160 e direction of compression coupled to a sinistral transcurrent movement along a ne sw direction the difference in age of the folding phase in the northern and southern parts of the chain indicates a diachronous nature for this tectonic event in relation to the wrench regime the tertiary evolution of the trough marked by a tensional regime resulting in an e w extension is to be related to the cameroon volcanic line

time constrained illitization in gas bearing rotliegende permian sandstones from northern germany by illite potassium argon dating permian rotliegende sandstone cores were collected from an area of about 14 800 km2 5710 mi2 mostly to the east southeast of the city of bremen in northern germany at depths between 4596 and 5330 m 15 079 17 487 ft the separated size fractions 0 2 0 2 1 0 and 1 0 2 0 m consist of illite 90 100 with small to minute amounts of chlorite and detectable quartz and feldspars in the coarser fractions scanning electron microscopic and transmission electron microscopic observations showed two types of illite morphologies flakes coating detrital framework minerals and laths and fibers invading the pore space the data points of most size fractions fit two isochrons with slopes providing ages of 191 8 and 178 1 ma with initial 40ar 36ar ratios reasonably close to the atmospheric value microthermometric fluid inclusion determinations in quartz and calcite characterize two types of percolating fluids a highly saline 19 nacl equivalent fluid at variable temperatures depending on the reservoirs 185 to 150c and a slightly saline one 2 6 nacl equivalent again at varied temperatures 170 to 145c also depending on the locations these temperatures are higher than paleotemperatures calculated on the basis of a present day burial gradient of 30 5c km therefore favoring hydrothermal illitization with the oldest illite crystallizing at a generally higher temperature than that of the younger illite however if illite coincidently precipitated with quartz which is supported by petrographic observation then illite with ages of about 200 ma in the eastern to central rotliegende sandstones of the area formed at a lower temperature but in more saline fluids than that of about 155 ma alternatively illite crystallization temperature and salinity of the interacting fluids could have been activated by the same hydrothermal activity at different locations in the studied area and could have decreased and changed respectively when the fluids moved in the sandstone reservoirs the potassium argon data fit a regional model of recurrent thermal activity with the oldest occurrence of authigenic illite in the eastern imbrock ganderkesee area and a time dependent trend of the hydrothermal activity toward the west previous results from northern germany central netherlands and the southern north sea complete the model with an initial activity at the same 200 ma time in the western offshore and central netherlands and an activity trend toward the east

fault dating in the canadian rocky mountains evidence for late cretaceous and early eocene orogenic pulses fault rocks from the classic rocky mountain foreland fold and thrust belt in southwestern canada were dated by ar analysis of clay grain size fractions using x ray diffraction quantification of the detrital and authigenic component of each fraction these determinations give ages for individual faults in the area illite age analysis the resulting ages cluster around 72 and 52 ma here called the rundle and mcconnell pulses respectively challenging the traditional view of gradual forward progression of faulting and thrust belt history of the area the recognition of spatially and temporally restricted deformation episodes offers field support for theoretical models of critically stressed wedges which result in geologically reasonable strain rates for the area in addition to regional considerations this study highlights the potential of direct dating of shallow fault rocks for our understanding of upper crustal kinematics and regional tectonic analysis of ancient orogens

the use of vertical electrical sounding resistivity method for the location of low salinity groundwater for irrigation in chaj and rachna doabs a geoelectrical resistivity survey using vertical electrical sounding ves was conducted at chaj doab land between rivers jhelum and chenab pakistan and rachna doab land between rivers chenab and ravi pakistan with the objective of investigating groundwater conditions a total of 90 sites were selected with 43 sites in chaj and 47 sites in rachna doabs the resistivity meter abem terrameter sas 4000 sweden was used to collect the ves data by employing a schlumberger electrode configuration with half current electrode spacings ab 2 ranging from 2 to 180 m and the potential electrode mn from 1 to 40 m the field data were interpreted using the interpex ix1d computer software and the resistivity versus depth models for each location was estimated the outputs of subsurface layers with resistivities and thickness presented in contour maps and 3 d views by using surfer software were created a total of 102 groundwater samples from nearby hydrowells at different depths were collected to develop a correlation between the aquifer resistivity of ves and the electrical conductivity ec of the groundwater and to confirm the resulted geophysical resistivity models from the correlation developed it was observed that the groundwater salinity in the aquifer may be considered low and so safe for irrigation if resistivity 45 m and marginally fit for irrigation having resistivity between 25 and 45 m the study area has resistivities from 3 9 to 2 222 m at the top of the unsaturated layer between 1 21 and 171 m in the shallow aquifers and 0 14 152 m in the deep aquifers of the study area the results indicate that the quality of groundwater is better near the rivers and in the shallow layers compared to the deep layers

direct dating of folding events by 40ar 39ar analysis of synkinematic muscovite from flexural slip planes abstract timing of folding is usually dated indirectly with limited isotopic dating studies reported in the literature the present study investigated the timing of intracontinental multi stage folding in upper proterozoic sandstone limestone and marble near beijing north china and adjacent regions detailed field investigations with microstructural backscattered electron bse images and electron microprobe analyses indicate that authigenic muscovite and sericite crystallized parallel to stretching lineations striations or along thin flexural slip surfaces both developed during the complex deformation history of the study area involving repeated compressional extensional and strike slip episodes muscovite sericite separates from interlayer slip surfaces along the limbs and from dilatant sites in the hinges of folded sandstones yield muscovite 40 ar 39 ar plateau ages of 158 159 ma whereas those from folded marble and limestone samples yield ages of 156 1 ma muscovite from thin flexural slip planes on fold limbs and hinges yields ages within analytical error of 155 165 ma further muscovite samples collected from extensionally folded limestone and strike slip drag folds yield younger ages of 128 125 ma with well defined plateaus to assess the potential influence of the detrital mica component of the host rock on the age data two additional muscovite samples were investigated one from a folded upper proterozoic cambrian sandstone outside the western hills of beijing and one from a folded sandstone sampled 20 cm from folding related slip planes muscovite separates from these samples yield significantly older ages of 575 2 ma and 587 2 ma suggesting that the timing of folding can be directly determined using the 40 ar 39 ar method this approach enables the identification and dating of distinct deformation events that occur during multi stage regional folding 40 ar 39 ar dating can be used to constrain the timing of muscovite and sericite growth at moderate to low temperatures

assessment of the state of soils shallow sediments and groundwater salinity in abi cross river state nigeria abi area in nigeria borders the salinity enriched lower benue trough lbt and plans are currently underway to extend large scale irrigation facilities under construction in the lbt to abi area in order to generate baseline soil and water salinity information about abi area under non irrigation condition integrated information from constrained analyses of vertical electrical sounding data two dimensional electrical resistivity tomographies and laboratory analyses of soil and water samples were used to assess and map the spatial salinity distribution existence of widespread heterogeneities in the distribution of soil and water salinity between the shaly and sandy materials that dominate the shallow geology of the area was observed minimum values of water electrical conductivity wec and total dissolved solids tds were observed to be 19 2 s cm and 13 mg l respectively in the sandstone dominated areas maximum values of wec and tds were observed to be 931 0 s cm and 624 mg l respectively within the shale dominated areas soil electrical conductivity was observed to vary from 5 0 s cm in the sandstone areas to 14 0 s cm in the shale dominated areas minimum and maximum soil ph observations were 4 53 in the shale dominated area and 6 55 in the sandstone dominated area respectively these results show that the water and soil resources in the area vary from fresh to slightly saline and non saline to high salinity levels respectively consequently both resources are still good for agricultural purposes

electrical resistivity and seismic refraction tomography to detect buried cavities near surface cavities can pose serious hazards to human safety especially in highly urbanized town centres the location of subsurface voids the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse in this study electrical resistivity tomography ert and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of rome ert is a well established and widely employed method for cavity detection however additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation we propose that the structure of the cavities defined by ert can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time herein the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics the cavity location inferred by geophysical non invasive methods has been subsequently confirmed by direct inspection

assessment of the reliability of 2d inversion of apparent resistivity data the reliability of inversion of apparent resistivity pseudosection data to determine accurately the true resistivity distribution over 2d structures has been investigated using a common inversion scheme based on a smoothness constrained non linear least squares optimization for the wenner array this involved calculation of synthetic apparent resistivity pseudosection data which were then inverted and the model estimated from the inversion was compared with the original 2d model the models examined include i horizontal layering ii a vertical fault iii a low resistivity fill within a high resistivity basement and iv an upfaulted basement block beneath a conductive overburden over vertical structures the resistivity models obtained from inversion are usually much sharper than the measured data however the inverted resistivities can be smaller than the lowest or greater than the highest true model resistivity the substantial reduction generally recorded in the data misfit during the least squares inversion of 2d apparent resistivity data is not always accompanied by any noticeable reduction in the model misfit conversely the model misfit may for all practical purposes remain invariant for successive iterations it can also increase with the iteration number especially where the resistivity contrast at the bedrock interface exceeds a factor of about 10 in such instances the optimum model estimated from inversion is attained at a very low iteration number the largest model misfit is encountered in the zone adjacent to a contact where there is a large change in the resistivity contrast it is concluded that smooth inversion can provide only an approximate guide to the true geometry and true formation resistivity

clay quantification and ar ar dating of synthetic and natural gouge application to the miocene sierra mazatan detachment fault sonora mexico direct dating of brittle fault rocks has been predicated on the assumption that illite in fault gouge is a mixture of two populations of clays one detrital derived from the wall rock and the other authigenic forming in the brittle fault zone during faulting owing to complex diagenetic histories of wallrock shales in previous fault dating studies this assumption has remained largely untested we demonstrate the validity of our clay quantification technique using calculated wildfire patterns to accurately model both artificial mixtures of 2m1 and 1md illite and natural mixtures in young fault gouges using our quantification approach we obtain well defined detrital and authigenic ages from the sierra mazatan metamorphic core complex in sonora mexico because the age population of the wall rock is well constrained by cooling ages we confirm that the detrital component in the gouge is the age of the footwall granite while the age of the authigenic component is the time at which faulting ceased which is in agreement with field constraints based on the ar ar age and the thermal conditions for the growth of the authigenic illite we also conclude that the sierra mazatan detachment continued slipping in the brittle regime at strain rates similar to those for the plastic regime on the order of 10 14 s 1

delineation of saltwater intrusion into the freshwater aquifer of lekki peninsula lagos nigeria recently the deterioration of water quality in the coastal zones of lekki peninsula area of lagos due to saltwater infiltration into the freshwater aquifer has become a major concern with the aim of providing valuable information on the hydrogeologic system of the aquifers the subsurface lithology and delineating the groundwater salinity vertical electrical resistivity ves sounding survey was carried out utilizing surface schlumberger electrode arrays and electrode spacing varying between 1 and 150m the dc resistivity surveys revealed significant variations in subsurface resistivity also the ves resistivity curves showed a dominant trend of decreasing resistivity with depth thus increasing salinity in general the presence of four distinct resistivity zones were delineated viz the unconsolidated dry sand a having resistivity values ranging between 125 and 1 028 m represent the first layer the fresh water saturated soil zone b having resistivity values which correspond to 32 256 m is the second layer the third layer zone c is interpreted as the mixing transition zone of fresh with brackish groundwater the resistivity of this layer ranges from 4 to 32 m while layer four zone d is characterized with resistivities values generally below 4 m reflecting an aquifer possibly containing brine the rock matrix salinity and water saturation are the major factors controlling the resistivity of the formation moreover this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface dc resistivity method

fault gouge dating in the southern appalachians usa illite age analysis iaa the method of comparing radiometric ages of successive size fractions with varying percentages of detrital illite has been successfully applied to several rock types including fault gouge shales and argillaceous limestones iaa results are presented for fi ve fault rocks including four clay gouges and one cataclasite from the exhumed southern appalachian foreland fold thrust belt eastern united states determining detrital versus authigenic illite is now an established procedure utilizing x ray analysis to quantify illite polytypes less established however is how to interpret 40 ar 39 ar ages as a function of diagenetic grade both a total gas age incorporating the recoiled argon fraction after irradiation and a retention age omitting the recoiled fraction are obtained for a sample we relate their respective use to diagenetic grade and specifi cally the crystallite thickness of illite when measured crystallite sizes are equal to or smaller than that calculated from ar recoil we use total gas ages here 5 nm while for crystallites greater than 10 nm we use retention ages the four clay gouge ages are all the same within error and much younger than that of the cataclasite we conclude that a major period of frontal appalachian fault activity occurred during the early permian cisuralian 276 280 ma and that these foreland faults were active simultaneously as part of an internally deforming regional thrust wedge

constraining the timing of brittle deformation and faulting in the toki granite central japan abstract constraining of the timing of fault zone formation is of fundamental geotectonic importance to understand structural evolution and brittle fault processes here we present authigenic illite k ar age data from brittle fault zones comprising two gouges within the toki granite central japan the gouge samples were collected at depths of 252 9 and 403 7 m from a shaft at the mizunami underground research laboratory and were separated into five grain size fractions

fault dating in the canadian rocky mountains evidence for late cretaceous and early eocene orogenic pulses comment comment the bold assertions by van der pluijm et al 2006 1 do not survive close scrutiny the technologically advanced procedures employed involve great ingenuity but the results of the fault dating are suspect because 1 2 1 beaumont c 1981 foreland basins geophysical journal

potassium argon timing of episodic mica and illite crystallization in highly indurated hassi messaoud algeria hydrocarbon bearing sandstones nanometer to micrometer mica and illite separates of indurated cambrian and ordovician oil bearing sandstones from the hassi messaoud field algeria were extracted x rayed observed by scanning and transmission electron microscopy and k ar dated electron microscope observations revealed typical euhedral shapes for the mica to illite particles of most size fractions almost no odd shaped detrital crystals were detected the combined results document several generations of mineralogical and morphological identical mica to illite crystals that could not be differentiated by the traditional identification methods illite and mica genesis was multiphased with crystallization episodes at 340 10 ca middle mississippian 280 10 ma ca early permian and 170 10 ma ca middle jurassic younger than the stratigraphic age of the host rocks which is incompatible with a detrital origin the two older mica ages confirm that the hydrocarbon generation and emplacement had to start after the variscan tectonothermal event and before exhumation of the meta sediments the younger k ar ages at 135 to 110 ma ca early cretaceous relate to further crystallization episodes whereas those at circa 295 265 and 210 ma probably correspond to variable mixtures of the older and younger mica to illite end members three average k ar values are statistically significant the oldest at 340 10 ma corresponds to the start of the variscan tectonic activity and the intermediate at 280 10 ma sets its end both episodes probably modifying the reservoir capacities of the potential hydrocarbon host rocks the ages at 170 10 ma identify a further diagenetic activity characterized by illitization of dickite type precursors in local reservoirs these younger ages could correspond to the hydrocarbon charge into reservoirs which stopped diagenetic illitization at a present day depth of approximately 4000 m 13 000 ft

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use

a new tectonic model for the cameroon line central africa abstract the cameroon line a major geological feature in central africa has been considered successively as a series of horsts and grabens a continental rift and a mega shear zone it is marked out by about 60 anorogenic complexes and a dozen volcanic centres all of which have alkaline affinity remote sensing allows us recognition of the main lineament trends n70 n s n135 and e w while autocorrelation analysis reveals a major fault zone striking n30 in western cameroon and n15 in the northern region a mega left lateral shear zone is the model that best accounts for the fracture pattern and associated features such as linear and circular structures alignment of subvolcanic complexes syntectonic leucogranites marking out older shear zones and vein dykes the n70 adamawa fault zone a pan african fracture reworked during albian aptian times is the only shear zone of continental scale that could have initiated en echelon mega tension gashes within the cameroon line during a cainozoic left lateral transcurrent movement

electrical methods ves and ert for identifying mapping and monitoring different saline domains in a coastal plain region alt emporda northern spain summary the spatial variability through time of the degree of salinity of soils and groundwater is a major issue concerning the sustainable management of water resources the problem is accentuated in coastal plain areas where saline bodies of different origin coexist we present an extensive geoelectrical resistivity dataset collected in the alt emporda clastic coastal aquifer system ne spain integrating the results of field campaigns undertaken within a period of more than two decades the dataset is unique in the literature and comprises highly valuable information for the investigation of saline domains the joint application of vertical electrical sounding ves and electrical resistivity tomography ert methods allowed the identification of saline domains and monitoring their evolution through time geophysical data gathered during field campaigns in 1982 2002 and 2010 were calibrated and interpreted on the basis of soil and groundwater physico chemical analyses and hydrogeological stratigraphic and geomorphological data the results illustrate the potential of electrical resistivity methods at differentiating saline domains in coastal aquifer areas and at modelling their configuration and evolution although the ves data processing allows solving the one dimensional resistivity structure of the subsurface the inversion imposes a 1d layered model thus interpretation of two dimensional structures is subject to the interpolation between discrete measures in contrast ert data offer a continuous 2d image of the resistivity distribution both laterally and in depth given that the bulk resistivity of the medium is extremely sensitive to salt content the ert profiles permitted identifying and determining the geometry of hyper saline areas characterized by resistivities of less than 5 m the study demonstrates the efficiency of the electrical methods to map subsurface conductive zones and illustrates how the accurate knowledge of the hydrogeological pattern results critical to meet this objective