the metagabbros orthogneisses and paragneisses of the connemara complex western ireland although now largely disappeared within the 400 ma old galway granite the syntectonic connemara metagabbro gneiss complex which crystallized at 490 ma arenig is the largest intrusion into the dalradian rocks it is part of widespread cambro ordovician volcanism and plutonic injection into continental crust in the appalachian caledonide orogenic belt being synchronous in crystallization with the widely obducted 490 ma ophiolites within the orogeny the peridotites and hornblende gabbros were injected broken up and shouldered aside by quartz diorite granodiorite granite and trondhjemite gneisses and it is shown that these orthogneisses are not the in situ differentiation products of the gabbro magma the hornblende in the metagabbros is mainly igneous but is partly metamorphic and replaces olivine fo 75 92 orthopyroxene en 65 92 clinopyroxene wo 48 5 en 50 39 fs 5 14 and plagioclase typically an 80 92 range an 50 96 an aureole at least 10 km wide in the sillimanite zone was imposed and cordierite garnet sillimanite dalradian hornfelses were partially melted at temperatures up to 1000 o c near to the gabbros at 4 5 1 kbar corresponding to c 18 km depth this suggests that the complex forms part of the root of a now eroded batholith of calc alkaline affinities the gabbros corresponding to the transition zone to a basic bottom which is often supposed to underlie many batholiths within the orthogneisses are sheets of paragneiss formed from dalradian metasediments which have been folded up from the floor and down into sides of the magma chamber which process could be illustrative of the means by which basic magma can intimately interact with crustal material the 18 o 16 o d h nd and sr isotope evidence and the existence of inherited zircons in the gneisses indicate that the gabbro and gneiss magmas were significantly contaminated with crustal possibly dalradian material both before and after intrusion with the lowest initial 87 sr 86 sr at 490 ma being 0 708 even in samples far removed from metasediment the metagabbros are tholeiitic to high alumina basalt in character but the gneisses have distinct calc alkaline geochemistry the chemistry igneous hornblende and highly calcic plagioclase match many arc plutons in the western usa the syntectonic nature and the ubiquitous gneissic fabric in the quartz diorites trondhjemites and granites is a consequence of early movements which were probably in part connected with the separation of the connemara massif and which culminated in slicing off the largely inverted complex and carrying it southwards on the mannin thrust which underlies the whole of connemara the complex is thus a fragment of a now disrupted cambro ordovician continental magmatic arc or continent island arc environment which can be traced along the se edge of the laurentian continent

joint inversion of 2d resistivity and seismic travel time data to image saltwater intrusion over karstic areas the simultaneous inversion of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process the main goal of this paper was to develop joint inversion strategies to provide improved resistivity and seismic velocity images for delineating saline water zones in karstic geological formations the cross gradient constraint approach was adopted to jointly invert resistivity and seismic first arrival data the basic idea of this approach is to quantitatively estimate the structural similarity between resistivity and seismic velocity models using the cross product of their gradients and to achieve a unified geological model which satisfies both data sets initially synthetic data were employed to help develop a joint inversion strategy to be used over such complex geological structures the proposed strategy uses a weighting factor for the cross gradient constraints and separate damping factors for the resistivity and seismic data this strategy was applied successfully on field data from the karstic region of stilos crete greece

dynamic analysis and field investigation of a fluidized landslide in guanling guizhou china abstract on june 28 2010 a large catastrophic landslide was triggered by a heavy rainfall in guanling guizhou china this catastrophic event destroyed two villages and caused 99 casualties the landslide involved the failure of about 985 000 m 3 of sandstone from the source area the displaced materials traveled about 1300 m with a descent of about 400 m covering an area of 129 000 m 2 with the final volume being accumulated to be 1 840 000 m 3 approximately to provide information for hazard zonation of similar type of landslides in the same area we used a dynamic model dan3d to simulate the runout behavior of the displaced landslide materials and found that a combined frictional vollemy model could provide the best performance in simulating this landslide and the runout is precisely duplicated with a dynamic friction angle of 30 and a pore pressure ratio r u of 0 55 for the materials at the source area and with vollemy parameters of friction coefficient f 0 1 dimensionless and turbulent coefficient 400 m s 2 the simulated results indicated that the duration of the movement is estimated at about 60 s for a mean velocity 23 m s to examine the effectiveness of simulation by means of dan3d and also to evaluate the reactivation potential of these displaced landslide materials depositing on the valley we used electrical resistivity tomography ert method to survey the depth and internal structure of landslide deposits the ert results showed that dan3d gave a good prediction on the shape and runout distance of the landslide deposits although the predicted maximum depths of landslide deposit on some areas were differing from those obtained by ert method

electrical resistivity tomography applied to groundwater aquifer at downstream of chih ben creek basin taiwan groundwater resource investigations primarily involve inferring groundwater levels and recharge sources from factors such as the distributed location and range subsurface geological structure and flow paths of groundwater sources this study conducted an investigation on the underground aquifer at the downstream of the chih ben creek basin taiwan in addition convenient rapid and accurate two dimensional electrical resistivity tomography ert was employed for evaluations the cross sectional ert image indicates that the low resistivity region in the stratum at survey line cb01 may be a groundwater deposit or fracture zone this region can be divided into three major segments the segment that is 0 50 m from the survey line exhibits a decreasing trend and is thus inferred to be a recharge source survey line cb02 can be generally divided into four layers with the second layer containing a greater amount of groundwater this layer is an aquifer with a depth of approximately 25 100 m below the ground surface and 75 100 m in thickness the base of the aquifer slopes toward the east and primarily possesses a lithological composition of slate and sandstone with explicit and fractured joints

geochronological constraints on the magmatic metamorphic and thermal evolution of the connemara caledonides western ireland the connemara region of the western irish caledonides records the evolution of a short lived mid ordovician c 475 463 ma continental magmatic arc that intruded into dalradian metasedimentary rocks during regional ductile deformation new u pb geochronological data for intermediate intrusive phases and anatexis in southern connemara are consistent with the relative age succession suggested by field relationships calc alkaline plutons quartz diorites were emplaced into the dalradian sequence and into the connemara gabbros at about 467 2 ma coeval with anatexis which was manifested by a 467 2 ma granitic pegmatite and 468 2 ma leucosome formation in a metapelite metasomatic diopside rocks from west central connemara and a calcsilicate rock from southern connemara yield u pb titanite dates of c 462 2 ma and 463 2 ma respectively these dates postdate the metamorphic peak by at least five million years and indicate titanite crystallization at a late stage during the metamorphic history on the basis of u pb and 40 ar 39 ar geochronological data we conclude that the cooling history of southern connemara following anatexis was simple and brief at a minimum rate of 35 c ma 1 between 468 and 460 ma and 14 c ma 1 between 460 and 450 ma

delineation of saltwater intrusion zones using the time domain electromagnetic method the nabeul hammamet coastal aquifer case study ne tunisia the time domain electromagnetic method tdem is applied to monitor to delineate and to map the saltwater intrusion zones in the mediterranean plio quaternary aquifer forty two tdem soundings were carried out in the coastal plain of nabeul hammamet region ne tunisia tdem resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater seawater transition zone the geoelectric sections showing the vertical configuration of seawater intrusion with the brackish salty saturated zones have a resistivity ranging from 0 1 to 5 m and are detected at a depth lower than 1 5 m the salinized zones are located at nabeul sidi moussa sidi el mahrsi al gasba and mrazgua and at hammamet touristic zone of hammamet north and south baraket essahel and reached a distance of 4 km from the coastline indicating a severe state for the aquifer in these zones these tdem results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells moreover in the northeastern part the presence of a saltwater front located far from the coast and along the nw se major surface fault can be explained by two hypothesis i this fault seems to provide a conduit for seawater to move readily towards the water wells and ii the clay and gypsum infiltration of marine messinian deposits through the fault plane leads to low resistivities finally it comes out from this study that tdem survey has successfully depicted salinized zones of this coastal aquifer copyright 2012 john wiley sons ltd

the submarine volcanic system of the errigoiti formation albian santonian of the basque cantabrian basin northern spain stratigraphic framework facies and sequences abstract the errigoiti formation located in the central domain of the basque cantabrian basin is an albian to santonian bathyal submarine volcanic system of alkali basaltic character these volcanics occurred in an extensional geodynamic context generated by the drifting of the iberian plate with respect to the european plate stratigraphic analyses reveal the facies distribution and depositional architecture of a longitudinal cross section of the errigoiti volcanic system four facies groups were distinguished sheet lavas sl derived from low viscosity lava flows at high magma discharge rate pillow lavas pl derived from intermediate viscosity lava flows at moderate discharge rate pillow breccias pb derived either from in situ fragmentation of lavas pb1 or rock falling from pillow lava slopes pb2 and stratified volcaniclastites vc derived from volcaniclast resedimentation through gravity flows either by early remobilization vc1 or post volcanic reworking vc2 the facies groups occur in a predictable repetitive succession essentially from base to top an sl pl pb vc stacking pattern this is interpreted to reflect an upward waning in the magma discharge rate five major volcanic sequences make up the errigoiti formation each comprises packages tens to hundreds of meters thick deposited during short time spans of volcanic activity separated by long time intervals of volcanic inactivity consequently boundaries between sequences are associated with marked hiatuses reworked volcaniclasts and or turbidite pelagic sedimentation analysis of lateral and vertical facies evolution enabled us to propose a depositional model consisting of three depositional environments from proximal to distal settings these are amalgamated pillow volcanoes scattered pillow volcanoes and volcanic fringe basically responding to a proximal to distal pl pb pl vc and sl vc evolution of facies associations contemporaneous fossiliferous turbidite pelagic sequences that surround the volcanic succession allow paleobathymetry to be estimated on the basis of biofacies sites with the highest rate of volcanic emission correspond to an average depth of 900 m sites with thinner volcanic pile accumulated at a minimum depth of 1100 m the facies sequence established in this work and the processes involved in its formation are comparable with the sequences and processes described in other submarine basic volcanic systems consequently the depositional model for the errigoiti formation can perhaps serve as a reference model for this type of volcanic system

dolomite overgrowths suggest a primary origin of cone in cone a long debated aspect of cone in cone structures is whether the mineral aggregates composing the structure precipitated with their conical form primary cone in cone or whether the cones formed after precipitation secondary cone in cone a calcite deposit from the cretaceous of jordan bears all the defining characteristics of the structure trace dolomite within the sample supports the primary cone in cone hypothesis the host sediment is a biosiliceous mudstone containing abundant rhombohedral dolomite grains dolomite rhombohedra are also distributed throughout the calcite of the cone in cone the rhombohedra within the calcite locally have dolomite overgrowths that are aligned with calcite fibres evidence that dolomite co precipitated with calcite and did not replace calcite includes i preferential downward extension of dolomite overgrowths in the presumed growth direction of the cone in cone from the dolomite grains on which they nucleate and ii planar vertical borders between dolomite crystals and calcite fibres because dolomite overgrows host sediment rhombohedra and forms part of the cones it follows that the host sediment was incorporated into the growing cone in cone as the calcite precipitated and not afterward the host sediment was not injected into the cone in cone along fractures as the secondary origin theory suggests this finding implies that cone in cone in general does not form over multiple stages and thus has greater potential to preserve the chemical signature of its original precipitation

development of long period ground motions from the nankai trough japan earthquakes observations and computer simulation of the 1944 tonankai mw 8 1 and the 2004 se off kii peninsula mw 7 4 earthquakes strong ground motions recorded in central tokyo during the 1944 tonankai mw8 1 earthquake occurring in the nankai trough demonstrate significant developments of very large 10 cm and prolonged 10 min shaking of long period t 10 12 s ground motions in the basin of tokyo located over 400 km from the epicenter in order to understand the process by which such long period ground motions developed in central tokyo and to mitigate possible future disasters arising from large earthquakes in the nankai trough we analyzed waveform data from a dense nation wide strong motion network k net and kik net deployed across japan for the recent se off kii peninsula mw 7 4 earthquake of 5 september 2004 that occurred in the nankai trough the observational data and a corresponding computer simulation for the earthquake clearly demonstrate that such long period ground motion is primarily developed as the wave propagating along the nankai trough due to the amplification and directional guidance of long period surface waves within a thick sedimentary layer overlaid upon the shallowly descending philippine sea plate below the japanese island then the significant resonance of the seismic waves within the thick cover of sedimentary rocks of the kanto basin developed large and prolonged long period motions in the center of tokyo the simulation results and observed seismograms are in good agreement in terms of the main features of the long period ground motions accordingly we consider that the simulation model is capable of predicting the long period ground motions that are expected to occur during future nankai trough m 8 earthquakes

effectiveness of geophysical surveys for water wells relocation in overexploited aquifers the example of maggiore and traversola valleys northwestern italy aquifer overexploitation is a common problem in drinking water management this will become more and more important given the general reduction of water resources to overcome overexploitation one of the most adopted solutions is the relocation of extraction wells to establish the positions of new wells a precise knowledge of the hydrogeological setting is required specific surveys are therefore necessary to obtain information over wide investigation zones geophysical methods particularly electromagnetic and electrical can be useful with this aim in the present paper a case history on the combined use of electric resistivity tomography and time domain electromagnetic soundings is reported surveys have been performed within the maggiore and traversola valleys to investigate the uppermost part of the quaternary deposits hosting the near surface aquifer the electromagnetic data have been inverted with a spatially constrained approach by assuming a quasi 1d model of the subsurface geophysical surveys allowed for depicting the depth and lateral continuity of the supposed aquifer level in the surveyed area up to a depth of about 200 m and proposing potential positions for well relocation

relationships between hornblende k ar ages chemical composition and hydrogen isotopes connemara western ireland evidence for a massive extinct hydrothermal system major element compositional analyses k ar ages d and 18 o values for 30 zoned and unzoned hornblendes from dalradian amphibolites and metagabbros mostly in north connemara are reported although the cooling ages are expected from previous u pb zircon studies to be c 475 450 ma the results obtained are from 556 6 to 410 9 ma with an average of 470 ma fluid movements probably at 275 15 c i e much below ar closure temperature for hornblende erratically reset the ages as is shown by a negative correlation of hornblende d and age and a wide scatter of ages even within 2 m the changes were implemented by h d exchange between fluid and hornblendes in which ionic porosity z influenced the loss of ar and possibly its gain from the fluid to give the excess ar found in some samples z is controlled by hornblende chemical composition high mg si and mg fe and low fe al ti na and particularly low k amphiboles giving low z values retained ar more firmly and gained ar more readily than compositions which had higher z values which gave younger ages these range down to c 400 ma being the age of the intrusion of the galway granite suite that initiated the fluid circulation the scatter of ages is a consequence of incomplete equilibration mainly because of the slow h d exchange rate below 350 c and partly because the fluid permeated erratically in different areas and down cracks of all kinds promoting irregular ar movement the meteoric fluid circulated through connemara the galway granite and at least some of the contiguous silurian sediments of the south mayo trough these overlying sediments may have contributed to the water circulated in north connemara which was slightly less negative d than in central connemara for hornblende k ar ages to be a reliable measure of times of uplift and cooling they need to be demonstrated to be free from the influence of hot fluids by showing no correlation of age with d

on the arrangement of solid inclusions in fibrous veins and the role of the crack seal mechanism the arrangement of solid inclusions in veins was examined in three different rock types and tectonic settings common to all samples is a new type of sinusoidal inclusions associated with inclusion bands oriented parallel to the vein wall and inclusion trails at high angle to the vein wall crosscutting relationships of inclusion bands and the sinusoidal inclusions imply that inclusion bands do not reflect individual crack seal increments in our veins inclusion bands are not a sufficient criterion to infer the crack seal mechanism further evidence for solid inclusions not formed by the classic crack seal mechanism is given by inclusion bands in gypsum crystals grown in soft clay during incorporation solid inclusions can become folded or boudinaged depending on their orientation with respect to the opening direction the complex displacement field within the vein is recorded by curved crystal fibres which track the opening direction based on the arrangement of solid inclusions within the vein we suggest that our veins grew continuously during syntectonic vein formation solid inclusions formed by a fluctuation of adhesion at the vein wall interface rather than by crack sealing and vein growth was at least partly driven by the force of crystallisation q 2005 elsevier ltd all rights reserved

shatter cones branched rapid fractures formed by shock impact 1 shatter cones are rock discontinuities known only from sites of extraterrestrial impacts and they are assumed to be formed by impact induced shock waves here we characterize the structure of shatter cones by field and microanalyses and explain their formation by dynamic fracture mechanics our analyses reveal that shatter cones always occur as multilevel three dimensional networks 0 01 100 m in size with hierarchal branched fractures a typical individual shatter cone is a curved oblate branch that bifurcates from its parent fracture e g a larger shatter cone and expands to form a spoon like surface the unique shatter cone striations are arranged in v shaped pairs whose enclosed angle is constant for a given sample we propose that shatter cones are the natural consequence of tensile rock fracturing at extreme velocities first the structure of shatter cone networks is strikingly similar to the structure of branched networks of experimental dynamic fractures that propagate at high velocities velocities that approach the rayleigh wave speed vr second fracture front waves generated experimentally by the interaction of a rapidly moving tensile fractures and material inclusions create tracks on the fracture surface that correspond to the v shaped striations of shatter cones third applying the front wave concept to our field measurements vredefort impact south africa shows that the shatter cones propagated at velocities of 0 98 0 90vr with a systematic velocity decrease from the impact center these extreme asymptotic velocities require the intense energy flux of impacts our model explains all of the structural features of shatter cones curved surfaces cone directivity unique striations hierarchic multilevel structure and their exclusive occurrence at impact sites

electrical imaging of the groundwater aquifer at banting selangor malaysia a geophysical study was carried out in the banting area of malaysia to delineate groundwater aquifer and marine clay layer of the alluvial quaternary deposits of beruas and gula formations the beruas formation is formed by peat and clayey materials as well as silt and sands whereas the gula formation consists of clay silt sand and gravels both formations were deposited on top of the carboniferous shale of the kenny hill formation a 2 d geoelectrical resistivity technique was used resistivity measurement was carried out using an abem sas 4000 terrameter the 2 d resistivity data of subsurface material for each survey line was calculated through inverse modelling and then compared with borehole data the resistivity images of all the subsurface material below the survey lines show similar pattern of continuous structure of layering or layers with some lenses with resistivity ranging from 0 1 to 50 m the upper layer shows resistivity values ranging from 0 1 to 10 m representing a clay horizon with a thickness up to 45 m the second layer with depth varies from 45 to 70 m below surface and has resistivity values ranging from 10 to 30 m borehole data indicate coarse sand with some gravels for this layer which is also the groundwater aquifer in the study area the lowermost layer at a depth of 70 m below ground level shows resistivity values ranging from 30 50 m and can be correlated with metasedimentary rocks consisting of shale and metaquartzite

obtaining geologically meaningful 40ar 39ar ages from altered biotite biotite is the most used 40ar 39ar geochronometer yet two significant problems arise from ar ar step heating dating altered biotite can be problematic producing disturbed age spectra that reflect 39ar recoil however unaltered biotite can yield disturbed ages with apparently meaningful plateau ages as a result of mineral breakdown during stepped heating obtaining meaningful ages from such spectra is very difficult because alteration of biotite is common and widespread in nature and because many biotites affected by alteration are nonetheless unique geologically and or representative of key localities the capability to obtain reliable ages from altered material is extremely important in this study the effects of alteration progress on biotite age spectra were tested using both ir laser step heating and uv laser microprobe 40ar 39ar dating techniques our aims were to extract geologically meaningful ages from altered biotite and to identify cases where the ages had been influenced by alteration three variably altered biotites from the precambrian metamorphic terrain of southwestern montana were selected for argon isotopic analysis sample a is an unaltered rock containing pristine biotite sample b is a highly altered rock with chlorite and prehnite interlayers within biotite and sample c contains biotite with only incipient alteration for each sample the biotite ages obtained with ir and uv laser techniques were compared and the validity of the apparent ages was assessed ir step heating analysis of biotite from sample a yielded a well defined plateau of 1776 6 ma uv laser microprobe analysis of the same biotite yielded a concordant weighted mean age of 1771 8 ma based upon 65 spot analyses of eight grains that ranged in age from 1819 54 to 1722 62 ma in contrast ir step heating of biotite from sample b resulted in disturbed spectra with two separate fragments yielding total gas ages of 1505 12 and 1540 16 ma whereas uv laser microprobe analysis yielded 14 spot ages ranging from 1806 72 to 1565 78 ma uv laser analysis of sample c produced apparent ages ranging from 1772 52 to 1359 200 ma detailed analysis of age variations occurring perpendicular to 001 cleavage planes of biotite in sample b was accomplished by depth profiling using the uv laser microprobe depth profiling of single grains revealed considerable age variation among the biotite layers with profiles 1 and 2 yielding apparent ages ranging from 1730 226 to 1511 186 ma and from 1741 290 to 956 230 ma respectively in both samples b and c younger apparent ages correspond to higher 36ar 39ar ratios the youngest ages therefore are believed to have derived from altered layers whereas the oldest ages are related to layers with relatively little or no alteration in summary incremental step heating of altered biotite single grains yields 40ar 39ar age spectra that are compromised by recoil and variable release patterns however extraction of small samples via the uv laser microprobe provides a simpler pattern of apparent ages all younger than the true cooling age yet inversely correlated with atmospheric argon this result suggests that true biotite ages can be recovered from areas of pristine material if they are sufficiently large to be ablated by the uv laser

scale invariant sheath folds in salt sediments and shear zones abstract sheath folds are developed in a broad spectrum of geological environments in which material flow occurs including gravity driven surficial deformation in ignimbrites unconsolidated sediments and salt together with deeper level ductile shear zones in metamorphic rocks this study represents the first geometric comparison of sheath folds in these different settings across a wide range of scales elliptical closures defining eye folds represent y z cross sections through highly curvilinear sheath folds our analysis of the published literature coupled with field observations reveals remarkably similar ellipticities r yz for sheath folds in metamorphic shear zones r yz 4 23 salt r yz 4 29 sediment slumps r yz 4 34 glaciotectonites r yz 4 48 and ignimbrites r yz 4 34 nested eye folds across this range of materials n 1800 reveal distinct and consistent differences in ellipticity from the outer r yz to the inner most r y z elliptical rings of individual sheath folds the variation in ratios from outer to inner rings r r yz r y z in gravity driven surficial flows typically displays a relative increase in ellipticity to define cats eye folds r r yz that are remarkably constant r 2 0 99 across 9 orders of magnitude sheath y axes range from 0 1 mm to 75 km our findings lead us to conclude that the geometric properties of sheath folds are scale invariant and primarily controlled by the type and amount of strain with r also reflecting the rheological significance of layering associated with original buckle fold mechanisms the scaling pattern of sheath folds reflects the length scales of the precursor buckle folds and width of deformation zones across a broad range of materials and environments with continued deformation the layering marking the original folds may become increasingly passive to define sheath folds these empirical relationships suggest sheath folding is a fundamental mode of viscous response across a broad spectrum of materials strain rates and scales encompassing a variety of deformation settings

the cooling history of connemara western ireland from k ar and rb sr age studies k ar age determinations are reported on 26 hornblendes 17 coexisting muscovites and biotites nine muscovites and nine biotites from the dalradian connemara schists metagabbros and gneisses these are supplemented by 19 rb sr whole rock mica ages and four 40 ar 39 ar incremental heating ages on micas a long at least 75 ma and complex cooling history without a simple pattern of ages has been obtained the ages are not correlated with the grain sizes or the chemical compositions of the analysed minerals or the topographic elevation from which the samples came but there is an irregular increase of hornblende k ar ages to 480 10 ma with increase of metamorphic grade southwards towards the metagabbros and gneiss the preservation of the complex cooling pattern is ascribed to the action of syn and post metamorphic slides or faults which moved slices of the massif upwards by varying amounts closely spaced samples give results which rule out simple tilting of the massif rapid cooling c 30 ma 1 at 480 10 ma arenig llanvirn during the f3 fold phase was followed by slower cooling until 455 10 ma caradoc when renewed rapid uplift occurred possibly correlated with the southward thrusting of connemara and with synchronous renewed uplift in the scottish dalradian rocks widespread biotite k ar and rb sr ages of 440 5 ma end ordovician throughout connemara and the dalradian rocks of scotland are ascribed to the major taconic tectonic event which docked the dalradian rocks against the flanking folded ordovician successions of the midland valley and the south mayo trough biotites giving k ar ages of about 415 ma may have been reset during the late silurian folding of the cover rocks the importance of very close sampling integrated with structural studies is emphasized

paleomagnetic evidence for 4000 km of crustal shortening across the 1 ga grenville orogen of north america paleomagnetic data from the grenville province of north america suggest that laurentia underwent 4000 1000 km of crustal shortening from ca 1040 1020 ma to 980 ma as a result of the grenville orogeny in which laurentia was in collision with amazonia a corollary is that the size and scale of shortening affect the assembly of continental fragments that include laurentia which before 1 ga may have been significantly larger in area than now by thousands of square kilometers caused by crustal shortening in a broadly northwest southeast direction by the grenville orogeny

how hard are hard rock deformations abstract the study of soft rock deformations has received increasing attention during the past two decades and much progress has been made in the understanding of their genesis it is also recognized now that soft rock deformations which show a wide variety in size and shape occur frequently in sediments deposited in almost all types of environments in spite of this deformations occurring in lithified rocks are still relatively rarely attributed to sedimentary or early diagenetic processes particularly faults in hard rocks are still commonly ascribed to tectonics commonly without a discussion about a possible non tectonic origin at a stage that the sediments were still unlithified misinterpretations of both the sedimentary and the structural history of hard rock successions may result from the negligence of a possible soft sediment origin of specific deformations it is therefore suggested that a re evaluation of these histories keeping the present day knowledge about soft sediment deformations in mind may give new insights into the geological history of numerous sedimentary successions in which the deformations have not been studied from both a sedimentological and a structural point of view

a stable isotope study of retrograde alteration in sw connemara ireland dalradian metamorphic rocks lower ordovician meta igneous rocks mgs and caledonian granites of the connemara complex in sw connemara all show intense retrograde alteration alteration primarily involves sericitization and saussuritization of plagioclase the alteration of biotite and hornblende to chlorite and the formation of secondary epidote the alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs and was the result of a phase of fluid influx into these rocks in hand specimen k feldspar becomes progressively reddened with increasing alteration mineralogical alteration in the mgs and caledonian granites took place at temperatures 275 15 c and in the mgs pfluid is estimated to be 1 5 kbar during alteration the d values of alteration phases are 18 to 29 fluid inclusions 47 to 61 chlorites and 11 to 31 epidotes chlorite 18o values are 0 2 to 4 3 while 18o values for quartz k feldspar pairs show both positively sloped mgs and highly unusual negatively sloped caledonian granites arrays diverging from the normal magmatic field on a plot the stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200 140 c the retrograde fluid had d 20 to 30 in all lithologies but the fluid 18o varied both spatially and temporally within the range 4 to 7 the fo2 of the fluid that deposited the epidotes in the mgs varied with its 18o value with the most 18o depleted fluid being the most oxidizing the d values together with low 0 18o values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin this meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration the variation in retrograde fluid 18o values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid rock interaction infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the galway granite soon after intrusion at 400 ma however convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later

dynamic fracture by large extraterrestrial impacts as the origin of shatter cones a large impact by a comet or meteorite releases an enormous amount of energy which evaporates melts and fractures the surrounding rocks distinctive features of such impacts are shatter cones deformed rocks characterized by hierarchical striated features although such features have been used for decades as unequivocal fingerprints of large body impacts the process by which shatter cones form has remained enigmatic here we show that the distinctive shatter cone striations naturally result from nonlinear waves front waves that propagate along a fracture front this explains the observed systematic increase of striation angles with the distance from the impact shatter cone networks typically spanning many scales can be understood as hierarchical bifurcations of the fracture front which is generated by the immense energy flux carried by the initial impact generated shock waves our quantitative predictions based on this theory are supported by field measurements at the kentland and vredefort impact sites these measurements indicate that shatter cones near to the impact site were formed by fractures propagating at nearly the rayleigh wave speed of the host rocks whereas the furthest shatter cones observed about 40 km from the impact site were formed by fronts moving more slowly these results provide insight into impact dynamics as well as dissipative mechanisms in solids subjected to sudden extremely intense fluxes of energy

integrated geophysical studies at ancient itanos greece the results of an integrated geophysical survey at the archaeological site of itanos crete are presented and discussed at hellenistic itanos which is located near the seashore the buried ruins are partially under the saline water table the purpose of this geophysical survey was to map buried relics of buildings streets and walls of ancient itanos in particular the usefulness of combining conventional geophysical mapping techniques and high resolution imaging methods in delineating shallow targets of archaeological interest at such complex archaeological sites is studied magnetic gradient soil resistance and electromagnetic measurements were taken in grids covering an area of approximately 16 000 m2 processing of geophysical maps included filtering with the gradient and first derivative operators in the space domain and the upward continuation and butterworth filters in the wavenumber domain emphasis is given to the mathematical description of the processing steps the integration of the geophysical measurements revealed the existence of a well and three parallel walls verified by excavation ground probing radar and electrical tomography sections crossing the parallel walls showed the vertical extent of these features ground penetrating radar time slices and 3d electrical tomography depth slices were used for the verification of specific anthropogenic anomalies which were detected on the geophysical maps a shallow seismic survey was carried out in an effort to locate and map the ancient port the combination of a wide spectrum of geophysical prospecting techniques was successful in delineating the buried relics enhancing the information context regarding the hellenistic settlement of itanos together with its port and necropolis the geophysical survey at itanos demonstrates that the integrated approach is appropriate for archaeological investigations at complex sites like itanos

early overpressuring in organic rich shales during burial evidence from fibrous calcite veins in the lower jurassic shales with beef member in the wessex basin uk field petrographic and geochemical analysis of fibrous calcite veins in the lower jurassic shales with beef member in the wessex basin was conducted to investigate the formation mechanism of the veins bedding parallel fibrous calcite veins including beef veins and tabular cone in cone structures are widespread in the black shales the calcite veins consist of subvertical fibrous crystals and a dark median zone the median zone contains scattered clays pyrite microcrystals skeletal fragments and amorphous organic matter the veins exhibit moderate carbon isotope values ranging from 1 515 to 2 732 the oxygen isotope composition ranges from 8 872 to 4 521 which is possibly too negative to reflect the primary porewater oxygen isotope signatures and indicates a porewater modification it is interpreted that the veins mainly derive carbonates from seawater inorganic carbon and bioclasts the veins formed as closed system hydraulic fractures in overpressured cells during sediment degassing in the methanogenic zone the shale beds with a high total organic carbon content could have generated abundant co 2 which may have resulted in either the cementing of the pores in the matrix or overpressure buildup the skeletal fragments provide a control on the spatial distribution of veins as nuclei for calcite precipitation from supersaturated pore fluids

fractals chaos self organized criticality and tectonics some geological structures have simple geometrical forms and can be analysed using deterministic equations examples include alluvial fans and many sedimentary basins but most geological structures are complex and appear to defy mathematical analyses yet in the complexity there is an order complex geological structures generally obey fractal statistics examples include topography distributions of earthquakes and faults and mineral deposits an unresolved question is whether the fractal order is simply the result of scale invariance or the result of governing equations that yield deterministic chaos in order to try to answer this question a variety of slider block models have been considered the stick slip behaviour of slider block models is a simple analogy to earthquakes a pair of slider blocks has been shown to behave chaotically models that use many slider blocks exhibit self organized criticality and generate fractal statistics similar to the statistics of regional seismicity

metamorphic amphiboles composition and coexistence amphiboles have long been key players in metamorphic petrology the concept of facies was developed for rocks of basaltic composition eskola 1920 1939 fyfe et al 1958 and within this concept amphiboles had a leading role the first appearance of amphiboles the presence of amphiboles of certain compositions or last appearance of amphiboles that are replaced by pyroxene bearing assemblages mark a number of major facies boundaries the transition from greenschist to amphibolite facies is marked in part by hornblende replacing actinolite and the granulite facies is defined by the breakdown of hornblende to orthopyroxene bearing assemblages the blueschist facies is defined by the appearance of glaucophane while the transition from blueschist facies to eclogite facies conditions is indicated by the breakdown of glaucophane to omphacitic pyroxene bearing assemblages references to amphibole names actinolite glaucophane or rocks characterized by certain amphiboles amphibolite hornblende figure prominently in six facies names turner 1981 liou et al 1985 oh et al 1988 evans 1990 peacock 1993 a large part of the literature that is devoted to metamorphic petrology of amphiboles concerns reactions which produce amphiboles from more hydrated mafic igneous rocks or lead to the destruction of amphiboles as they break down to form anhydrous or nearly anhydrous mineral assemblages consequently amphiboles can be thought of as occupying the wide intermediate portion of p t xfluid space in which metamorphic rocks are found the number of citations of the published amphibole nomenclature serves as a yardstick meterstick of the interest in amphiboles and a minimum estimate of the amount of literature devoted to this mineral two versions of the nomenclature of amphiboles have appeared 1978 and 1997 leake 1978 leake et al 1997 and they have been cited a over 2300 times in the past 28 years this works out to a minimum

methods for calculating frechet derivatives and sensitivities for the non linear inverse problem a comparative study1 a fundamental step in the solution of most non linear inverse problems is to establish a relationship between changes in a proposed model and resulting changes in the forward modelled data once this relationship has been established it becomes possible to refine an initial model to obtain an improved fit to the observed data in a linearized analysis the frechet derivative is the connecting link between changes in the model and changes in the data in some simple cases an analytic expression for the frechet derivative may be derived in this paper we present three techniques to accomplish this and illustrate them by computing the frechet derivative for the id resistivity problem for more complicated problems where it is not possible to obtain an expression for the frechet derivative it is necessary to parameterize the model and solve numerically for the sensitivities partial derivatives of the data with respect to model parameters the standard perturbation method for computing first order sensitivities is discussed and compared to the more efficient sensitivity equation and adjoint equation methods extensions to allow for the calculation of higher order directional and objective function sensitivities are also presented finally the application of these various techniques is illustrated for both the 1d and 2d resistivity problems

the relationship of argon retentivity and chemical composition of hornblende k ar ages of 26 hornblende separates from connemara western ireland do not show any correlation with the chemical composition of the hornblendes including their iron contents it is suggested that this is the usual pattern as there are only rare reports of compositional control of k ar ages

bedding parallel fibrous veins beef and cone in cone worldwide occurrence and possible significance in terms of fluid overpressure hydrocarbon generation and mineralization abstract bedding parallel fibrous veins are common worldwide in sedimentary basins especially within strata of low permeability the term beef refers to bedding parallel veins of fibrous minerals where the fibres are mutually parallel and have formed quasi vertically more complex on a smaller scale are cone in cone structures yet these are also common within bedding parallel veins for both beef and cone in cone we have compiled a worldwide catalogue 157 localities typically the veins consist mainly of white gangue minerals for example calcite gypsum or quartz but may also contain accessory minerals of economic interest for example bitumen sulphides emerald pitchblende or gold fluid inclusions may contain oil or gas calcite beef 110 localities is common in organic rich shale of marine carbonate origin especially of 1 cambrian ordovician 2 devonian carboniferous 3 early jurassic or 4 cretaceous to palaeogene ages gypsum beef 30 localities is common in evaporitic or lacustrine strata of continental origin especially of triassic or neogene ages quartz beef 17 localities is common within meta turbidite sequences especially of ordovician or proterozoic ages because these modal ages seem to reflect climatic controls we infer that the fibre forming mineral species have not travelled far vertically the same conclusion holds for accessory minerals typical temperatures of formation are 1 up to 60 c for gypsum beef 2 70 c to 120 c for calcite beef and 3 200 c to 350 c for quartz beef hydrocarbon bearing calcite beef may be a good indicator of a petroleum system in which oil or gas migrate together with aqueous solutions we argue that beef and cone in cone layers result from tensile fracturing and vertical dilation coeval with fibre growth possible causes are either 1 force of crystallization or 2 seepage forces due to fluid overpressure for layers that form at depths of several km fluid overpressure is the more likely cause

velocity estimation by the common reflection surface crs method using ground penetrating radar data in this paper we describe the use of the common reflection surface crs method to estimate velocities from ground penetrating radar gpr data applied to multicoverage data the crs method provides as one of its outputs the time domain rms velocity map which is then converted to depth by the familiar dix algorithm combination of the obtained depth converted velocity map with electrical resistivity in situ measurements enables us to estimate both water content and water conductivity these quantities are essential to delineate infiltration of contaminants from the surface after industrial or agricultural activities the method was applied to gpr data and compared with the classical nmo approach the results show that the crs method provides a physically more meaningful velocity field thus improving the potential of gpr as an investigation tool for environmental studies

on the salt water intrusion into the durusu lake istanbul a joint central loop tem and multi electrode ert field survey durusu lake is the biggest and most important freshwater source supplying drinking water to the european side of istanbul in this study electrical resistivity tomography ert and transient electromagnetic tem measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of durusu lake the ert and tem measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier tem data were interpreted using different 1 d inversion methods such as occam marquardt and laterally constrained inversion lci ert data were interpreted using 2 d inversion techniques the inversion results of ert and tem data were shown as resistivity depth sections including topography the sand layer spreading over the basin has a resistivity of 150 400 omega m with a thickness of 5 10 m the sandy layer with clay silt and gravel has a resistivity of 15 100 omega m and a thickness of 10 40 m followed by a clay layer of a resistivity below 10 omega m when the inversion of these data is interpreted along with the hydrogeology of the area it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close using information from boreholes around the lake it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses

an 40 ar 39 ar investigation of the contact effects of a dyke intrusion kapuskasing structural zone ontario an 40ar 39ar study on biotite and hornblende from baked tonalite gneiss adjacent to a 14 m wide kapuskasing dyke in the chapleau block of the kapuskasing structural zone employed resistance furnace step heating of bulk mineral separates single grain laser step heating and laser spot dating of individual grains in thick section all three methods yielded concordant results for the biotite indicating that it has been uniformly overprinted at ca 2 05 ga this date is probably a close estimate of the age of the dyke intrusion the argon data from the hornblende are more difficult to interpret all three methods suggest that the hornblende was partially overprinted and then affected by a later influx of excess argon from the external environment laser spot dates record an apparent age gradient extending radially outward from 2 25 ga in the grain cores to 2 4 2 7 ga in the grain rims corresponding 37ar 39ar values show no systematic variation across the hornblende although 38ar 39ar ratios display a similar pattern to the age distribution with lower values in the cores than in the rims the bulk separate and single grain step heating spectra mimic a volume diffusion ar loss profile that would appear to be inconsistent with the laser spot dates three possible interpretations to explain this apparent discrepancy may involve either experimental difficulties an effective radius of diffusion which is much smaller than the actual grain radius or an effective radius of diffusion that is of the order of the grain radius it is clear that for the 40ar 39ar dating of samples that have experienced complex geologic histories it is important to utilize both resistance furnace and laser techniques

the jettencave southern harz mountains germany geophysical observations and a structural model of a shallow cave in gypsum anhydrite bearing rocks abstract gypsum and anhydrite are soluble rocks where fissures and bedding partings can be enlarged with time by the dissolution of the mineral species through water the selective enlargement results in sub surface voids acting as preferential flow path for the drainage of the rock with time larger cavities develop and a network of cave passages can evolve if the enlarged cave voids are not too deep under the surface geophysical measurements can be used to detect identify and trace these structures we have used gravity measurements grav electrical resistivity imaging eri self potential measurements sp electrical conductivity measurements ec and ground penetrating radar gpr above the cave jettenhohle a cave located in the southern harz mountains in germany the jettencave is developed in the hauptanhydrit formation of the permian zechstein sequence characterised by large breakdown rooms and an exposed water table the overburden of the cave is only around 10 15 m and dolomitic rocks are located in close vicinity we present results from our geophysical surveys in vicinity of the cave we are able to identify the cave geometry from grav eri and gpr measurements which distinguish the local lithology of the permian zechstein rocks in the area from the eri and ec measurements we derive information on the void volume in the soluble rocks we finally present a three dimensional structural model of the jettencave and its surroundings based on our geophysical results and the hydrological interpretation

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

shape of the shallow aquifer at the fresh water sea water interface on a high energy sandy beach abstract inland aquifers are connected to the ocean through permeable coastal sediments the mixing zone between sea water and fresh groundwater forms a so called subterranean estuary the dynamics and the shape of this interface influence fluxes of fresh water to the coastal zone on tidal sandy beaches tide and waves actions lead to the formation of an intertidal saline circulation cell that complements the structure of the subterranean estuary between sea water and fresh water the upper beach corresponds to the recharge zone where large volumes sea water penetrate the sediment at high tide whereas the lower beach corresponds to the discharge zone of older pore water that remains in the sand for several tidal cycles the objective of our study was to characterize the shape and the evolution of this saline cell in a high energy macro tidal beach the truc vert beach sw france in order to assess the distribution of saline brackish and fresh water in this high energy beach aquifer we conducted electrical resistivity tomography ert measurements from the lower beach face to the sand dune in winter 2012 2013 we also measured water table elevation and salinity in three piezometers situated at the base of the dune and in pore waters at low tide on tidal cross shore transects results show that the intertidal saline plume can be identified and localized with the ert method the fresh saline water interface is almost vertical in the upper beach the saline circulation cell occupies the upper part of the tidal beach over a thickness of 5 m deep below this saline cell a brackish water flows to the ocean about 30 of fresh water was found in pore water in the lower part of the beach shifting of the vertical front between saline and fresh waters of about 2 5 m occurred during the spring neap tidal cycle this migration is small relative to the beach size suggesting that the transition zone is relatively stable the variations in salinity of the circulation cell suggest that the position of the saline plume is controlled by the spring tide level our results differ slightly from studies based on modelling and piezometric measurement made in less exposed micro tidal sandy beaches our data would allow to better constrain numerical models that would enable to quantify water residence time and solute fluxes in subterranean estuaries of high energy beaches

a fluid inclusion and stable isotope study of 200 ma of fluid evolution in the galway granite connemara ireland fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the caledonian galway granite these fluids were examined by petrography microthermometry chlorite thermometry fluid chemistry and stable isotope studies the earliest fluid was a h2o co2 nacl fluid of moderate salinity 4 10 wt nacl eq that deposited late magmatic molybdenite mineralised quartz veins v1 and formed the earliest secondary inclusions in granite quartz this fluid is more abundant in the west of the batholith corresponding to a decrease in emplacement depth within veins and to the east this fluid was trapped homogeneously but in granite quartz in the west it unmixed at 305 390 c and 0 7 1 8 kbar homogeneous quartz 18o across the batholith 9 5 0 4 n 12 suggests v1 precipitation at high temperatures perhaps 600 c and pressures 1 3 kbar from magmatic fluids microthermometric data for v1 indicate lower temperatures suggesting inclusion volumes re equilibrated during cooling the second fluid was a h2o nacl kcl low moderate salinity 0 10 wt nacl eq moderate temperature 270 340 c high d 18 2 low 18o 0 5 2 0 fluid of meteoric origin this fluid penetrated the batholith via quartz veins v2 which infill faults active during post consolidation uplift of the batholith it forms the most common inclusion type in granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of biotite and hornblende sericitization and saussuritization of plagioclase and reddening of k feldspar the salinity was generated by fluid rock interactions within the granite within granite quartz this fluid was trapped at 0 5 2 3 kbar having become overpressured this fluid probably infiltrated the granite in a meteoric convection system during cooling after intrusion but a later age cannot be ruled out the final fluid to enter the granite and its host rocks was a h2o nacl cacl2 kcl fluid with variable salinity 8 28 wt nacl eq temperature 125 205 c d 17 to 45 18o 3 to 1 2 13cco2 19 to 0 and 34ssulphate 13 23 that deposited veins containing quartz fluorite calcite barite galena chalcopyrite sphalerite and pyrite v3 correlations of salinity temperature d and 18o are interpreted as the result of mixing of two fluid end members one a high d 17 to 8 moderate 18o 1 2 2 5 high 13cco2 4 low 34ssulphate 13 high temperature 205 230 c moderate salinity 8 12 wt nacl eq fluid the other a low d 61 to 45 low 18o 5 4 to 3 low 13c 10 high 34ssulphate 20 23 low temperature 80 125 c high salinity 21 28 wt nacl eq fluid geochronological evidence suggests v3 veins are late triassic the high d end member is interpreted as a contemporaneous surface fluid probably mixed meteoric water and evaporated seawater and or dissolved evaporites whereas the low d end member is interpreted as a basinal brine derived from the adjacent carboniferous sequence this study demonstrates that the galway granite was a locus for repeated fluid events for a variety of reasons from expulsion of magmatic fluids during the final stages of crystallisation through a meteoric convection system probably driven by waning magmatic heat to much later mineralisation concentrated in its vicinity due to thermal tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic heat has abated

high temperature memory in calcic amphiboles and constraints on compositional control of their 40ar 39ar ages well characterized calcic amphiboles from an incompletely mixed magmatic rock association of mainly intermediate dioritic composition were studied by incremental heating experiments of 40 ar 39 ar the rocks in question were thermally overprinted by late hercynian granites microprobe and scanning electron microscopy analyses show that the amphibole grains consist of two different calcic hornblende varieties 1 a si and mg rich variety and 2 a variety enriched in al ti fe k and na the mg si rich hornblende can be further characterized by its higher cao k 2 o ratios 30 50 compared to the al ti fe k na rich hornblende 12 15 three hornblende separates that previously had yielded conventional k ar ages of 320 317 and 302 ma have been dated by the 40 ar 39 ar step heating technique the low and medium temperature parts of the 40 ar 39 ar age spectrum show discordant ar systematics with single step ages generally younger than 325 ma the gas released at the highest temperature steps preserves an exceptional record of old and remarkably similar integrated ages 342 346 and 344 ma the high temperature ages correspond to phases with higher apparent cao k 2 o ratios 30 45 and are interpreted to result from ar release from mg si hornblende domains that are assumed to have been very resistent to ar loss during the late hercynian thermal events the results of this study suggest that ar retentivity differs among calcic amphiboles and mg si rich hornblendes are more ar retentive than their al ti fe k na rich counterparts

stress sensitivity of stylolite morphology abstract stylolites are rough surfaces that form by localized stress induced dissolution using a set of limestone rock samples collected at different depths from a vertical section in cirque de navacelles france we study the influence of the lithostatic stress on the stylolites morphology on the basis of a recent morphogenesis model we measured the roughness of a series of bedding parallel stylolites and show that their morphology exhibits a scaling invariance with two self affine scaling regimes separated by a crossover length l at the millimeter scale consistent with previous studies the importance of the present contribution is to estimate the stylolite formation stress from the sample position in the stratigraphic series and compare it to the crossover length l using the expected relationship l 2 we obtained a successful prediction of the crossover behavior and reasonable absolute stress magnitude estimates using relevant parameters depth of stylolite formation between 300 to 600 m with corresponding normal stress in the range of 10 18 mpa accordingly the stylolite morphology contains a signature of the stress field during formation and we thus suggest that stylolites could be used as paleo stress gauges of deformation processes in the upper crust

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

salt water intrusion mapping by geoelectrical imaging surveys the geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore water salinity a new field survey technique that can be used for environmental and geotechnical investigations has been developed this study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt water intrusion boundary in yan state of kedah northwest malaysia the technique was incorporated into these surveys and it has proved to be a robust method for accurately mapping the fresh water saline water boundary the resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the geological survey of malaysia at those sites

structural analysis of shatter cones from the slate islands northern lake superior shatter cones an unusual type of fracturing produced by intense shock are found widespread on the slate islands in northern lake superior the islands have been interpreted as the central uplift of an eroded meteorite impact crater about 30 km in diameter the cones are best developed in certain rock types keweenawan basalt flows and chilled margins of associated feeder dikes and archean diorite and foliated feldspar porphyry at certain sites cones show an elongate cross section and anomalous orientation caused by foliation induced elastic anisotropy in the host rock in general the cones point upward and inward toward the centre of the slate islands group after structural correction of some sites according to paleomagnetic data there is increased convergence of cone axes to a central focus the inferred impact point that occurs at a height of about 1 km above the present land surface

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

argon retentivity of hornblendes a field experiment in a slowly cooled metamorphic terrane hornblende from samples of amphibolite and granitic gneiss collected within a single outcrop in the central adirondacks yield significantly different sup 40 ar sup 39 ark sub k dates of 948 plus minus 5 and 907 plus minus 5 ma assuming that this terrane cooled slowly following high grade metamorphism and that the samples have experienced the same thermal history the difference in dates apparently reflects a corresponding difference in blocking temperature for diffusion of radiogenic argon in these hornblende samples the fe fe mg mn of the hornblende samples are 0 8 and 0 6 the higher ratio corresponding to the younger sup 40 ar sup 39 ar sub k date transmission electron microscopy observations indicate that both hornblende samples are homogeneous and devoid of any exsolution but contain zones of fibrous phyllosilicates approximately 0 1 to 2 mu m wide parallelling 100 and 110 these alteration zones probably formed during post metamorphic cooling as a result of the migration of fluids through the hornblendes and are obvious pathways for argon escape from hornblende as these features are more abundant in the hornblende sample with the younger sup 40 ar sup 39 ar date and higher fe fe mg mn they may influence the argon blocking temperature by effectively partitioning the hornblende grains intomore diffusion domains of varying size biotite from the granitic gneiss yields an sup 40 ar sup 39 ar sub k date of 853 plus minus 2 ma with a mildly discordant step heating spectrum that in part reflects the degassing of submicroscopic inclusions precipitated during alteration of the host biotite plagioclase from the amphibolite yields a sup 40 ar sup 39 ar sub k integrated date of 734 plus minus 3 ma less

potential formation mechanisms of early diagenetic displacive veins in the permian boda claystone formation abstract the boda claystone formation is the most promising host rock for the disposal of high level radioactive waste in hungary the formation has several properties obstructing the migration of radionuclides however structural heterogeneities may nonetheless act as migration pathways therefore understanding the tectonic evolution of the formation is vital previous research has identified four different vein generations in the baf 2 well this study deals with the generation of veins that contain characteristic microstructures such as curved wall rock inclusions in bands trails and cone in cone arrangements based on optical cathodoluminescence and electron microscopy together with x ray fluorescence and raman microspectroscopy these veins appear to have potentially formed during early diagenetic processes vein development was continuous and occurred along horizontal surfaces the abovementioned structural elements were formed by growing crystals however primary crystal morphologies were presumably replaced during diagenetic and hydrothermal processes a theoretical model is described which could be responsible for the horizontal and continuous vein opening and simultaneous crystallisation in sediments with high but easily degraded effective porosity according to this model compaction pressure solution elevated pore fluid pressures seepage forces and the force of crystallisation can all play important roles in the formation of these types of veins

identifying seawater intrusion in coastal areas by means of 1d and quasi 2d joint inversion of tdem and ves data abstract seawater intrusion is an increasingly widespread problem in coastal aquifers caused by climate changes sea level rise extreme phenomena like flooding and droughts and groundwater depletion near to the coastline to evaluate and mitigate the environmental risks of this phenomenon it is necessary to characterize the coastal aquifer and the salt intrusion geophysical methods are the most appropriate tool to address these researches among all geophysical techniques electrical methods are able to detect seawater intrusions due to the high resistivity contrast between saltwater freshwater and geological layers the combination of two or more geophysical methods is recommended and they are more efficient when both data are inverted jointly because the final model encompasses the physical properties measured for each methods in this investigation joint inversion of vertical electric and time domain soundings has been performed to examine seawater intrusion in an area within the ferragudo albufeira aquifer system algarve south of portugal for this purpose two profiles combining electrical resistivity tomography ert and time domain electromagnetic tdem methods were measured and the results were compared with the information obtained from exploration drilling three different inversions have been carried out single inversion of the ert and tdem data 1d joint inversion and quasi 2d joint inversion single inversion results identify seawater intrusion although the sedimentary layers detected in exploration drilling were not well differentiated the models obtained with 1d joint inversion improve the previous inversion due to better detection of sedimentary layer and the seawater intrusion appear to be better defined finally the quasi 2d joint inversion reveals a more realistic shape of the seawater intrusion and it is able to distinguish more sedimentary layers recognised in the exploration drilling this study demonstrates that the quasi 2d joint inversion improves the previous inversions methods making it a powerful tool applicable to different research areas

vredefort shatter cones revisited shatter cones have been described from a number of circular and polygonal structures worldwide the origin of which has been alternatively ascribed to the impacts of large extraterrestrial projectiles or to catastrophic endogenic processes despite their association with enigmatic catastrophic processes the nature of shatter cones and the physics involved in their formation have not been comprehensively researched results of detailed field and laboratory studies of shatter cones from three areas in the collar of the vredefort dome in south africa are presented vredefort shatter cones are directly related to a widely displayed fracture phenomenon termed multiply striated joint sets msjs msjs are planar to curviplanar fractures occuring at spacings of 1 to several millimeters the joint sets have a fractal character when a new measurement protocol is used in the field involving study of all joint surfaces and all steps and striae exposed on these surfaces new information is gained on the genesis and significance of the msjs and on their relationship to striated conical fractures the internal constitution of a rock specimen with msjs was examined in detail by documenting the precise geometry of many fractures in a suite of parallel thin sections transecting the specimen the steps and striae on shatter cone surfaces have the characteristics of displacement fractures microfaults along which evidence of melting is observed shatter cone and msjs surfaces are often covered with glassy films we evaluate whether these fracture phenomena are linked to the formation of pseudotachylitic friction melt our field and petrographic observations can be interpreted as consistent with the generation of shatter cones msjs relatively late in the formation of the vredefort structure this scenario contrasts sharply with the widely held view that shatter cones are formed during the early compression phase of a shock event that affected horizontal strata

cone in cone and beef mineralization associated with triassic growth basin faulting and shallow shale diagenesis edgeoya svalbard cone in cone cic and beef bf carbonate lenses ornament detachment zone faults underlying triassic growth basins on edgeoya field relationships place cic and bf growth as during early diagenesis and a transition from hydroplastic to a later brittle style of faulting that is marked by coarser calcite veining deformation is constrained to have occurred at 300 m depth multiple models exist for cic formation for the edgeoya example textural analysis of thin sections suggests that small tensile fractures and carbonate shell fragments nucleated development of calcite aggregates with cic and bf morphology within unconsolidated to poorly consolidated sediment to form asymmetric antitaxial tensile aggregates subparallel to bedding and fault surfaces the conical forms result from differential growth on stepped cleavage parallel faces of fibres facing host sediment with preferential inclusion incorporation at inner corners the preferred directions of calcite growth are attributed to local stresses and seepage flow associated with pore pressure gradients substantial framboidal pyrite in the sediments represents an early phase of microbially driven sulphate reduction which may have induced calcite mineralization the transition to brittle style faulting was marked by development of deformation twins in cic bf fibres and a transition to coarse blocky calcite growth in relay arrays of steeply oriented microveins this indicates local fault related stresses substantially changed during shallow diagenesis and lithification an evolution attributed to changing pore pressures seepage forces and material moduli calcite mineralizations at edgeoya track the very significant changes in mechanical properties and stress states that occur during synlithification deformation at very shallow crustal levels

the influence of microstructures on the relationship between argon retentivity and chemical composition of hornblende this paper discusses isotope dating of hornblende separates from the connemara western ireland the dating is based on potassium argon dates and the author provides a rebuttal of an earlier paper which dismisses any correlation between iron content in the hornblende and the argon isotope dates for the same mineral

investigation of seawater intrusion in the dibdibba aquifer using 2d resistivity imaging in the area between al zubair and umm qasr southern iraq electrical resistivity surveying for delineating seawater intrusion was performed in the dibdibba aquifer in the area between the cities of al zubair safwan and al zubair umm qasr in the vicinity of khor al zubair channel basrah governorate southern iraq fourteen 2d resistivity profiles with a total length of 14 km were collected in the study area the resistivity sections were compared with lithological data extracted from 11 boreholes thirty nine groundwater samples were collected within the area and analyzed for chemical constituents internal hydrogeological reports and unpublished studies were also evaluated results reveal the existence of three major resistivity layers ranging from 0 1 to 130 m at various depths and locations the first layer has very low electrical resistivity 0 1 5 m representing a layer saturated with saltwater intruded from khor al zubair channel the second layer shows resistivity in the range of 5 130 m attributed to a transition zone and an unaffected zone saturated with brackish groundwater the last resistivity layer 3 m represents coarse grain sediments saturated with saline groundwater furthermore a hard clay bed jojab appears with a resistivity of 3 7 m in all 2d imaging lines within a depth of 20 28 m electrical conductivity ec measurements from seven wells collected in 2014 and 2016 show a positive ec difference increasing landward with an average increase of 1927 s cm in addition six chemical relationships na cl ca mg hco3 so4 so4 hco3 so4 cl mg ca and cl hco3 co3 are used to detect the source of salinity in groundwater this study proves that extensive use of high resolution 2d imaging sections alongside lithological and hydrogeological data can serve as a useful tool to delineate the boundaries between aquifers identify hydraulic boundaries between groundwater with different salinities and allocate hard clay layers between the upper and lower dibdibba aquifer in general the combination of 2d imaging and hydrochemistry enables conceptualization of the hydrogeological situation in the subsurface and characterization of the salinity source here seawater intrusion in the study area there have been no studies published so far on the characteristics of saltwater intrusion in the study area and this study is considered to be important for monitoring and studying the intrusion and regression of seawater

sinkhole structure imaging in covered karst terrain 1 ground penetrating radar gpr and resistivity techniques have been widely used to map the locations of sinkholes in covered karst terrain to determine whether a sinkhole is a likely preferential conduit for groundwater flow however requires higher resolution imaging than that used in conventional sinkhole mapping surveys field observations combined with simulated surveys for a 15 m diameter 3 m deep sinkhole in west central florida are used to assess the resolution of gpr and resistivity surveys targeting the semiconfining unit that floors the sinkhole depression 2d resistivity surveys clearly show the central depression as well as resistivity contrasts between the cover sediments within and outside of the sinkhole but are inadequate for resolving breaches in the semiconfining unit or underlying conduits a 3d gpr survey resolves vertical structure on the order of tens of centimeters within the semiconfining unit as well as indicators of conduits that extend several meters beneath the central depression 3d gpr thus holds promise for imaging hydrologically significant features of sinkholes

sheath folds as discriminators of bulk strain type abstract nested elliptical closures defining eye folds represent classic y z cross sections through highly curvilinear sheath folds generated during intense ductile deformation in metamorphic rocks systematic analysis of 1425 such eye folds based on our own field observations and examples from the published literature reveals distinct and consistent differences in ellipticites measured from the outer r yz to the inner most r y z elliptical rings of individual sheaths the variation in overall aspect ratios from outer to inner rings is defined as r where r r yz r y z and may display a relative increase or decrease in ellipticity to define cats eye r bulls eye r 1 fold patterns respectively layer thicknesses may also be measured along the y axis parallel to the axial surface t y and at 90 to this along the z axis t z to define the ratio of t yz sheath folds generated during broadly simple shear deformation k 1 display mean r yz 4 61 t yz 3 31 and cats eye folds r 0 69 sheath folds generated during general shear also display cats eye folds with identical mean r 0 69 values but greater thickness variations and elliptical ratios t yz 4 35 r yz 5 76 thus within both simple and general shear dominated deformations the overall variation in layer thickness t yz and ellipticity of eye folds r yz increases with increasing deformation and a greater component of pure shear whilst the r value remains constant and reflects original fold patterns sheath folds formed during constrictional k 1 deformation display markedly lower aspect ratios r yz 2 42 and thickness variations t yz 2 94 together with distinctive bulls eye folds r 1 23 these empirical relationships suggest fundamental and universal constraints on curvilinear fold generation across this broad spectrum of deformation types and allow sheath folds to act as both effective 95 consistent and robust discriminators of bulk strain type

geophysical characterization of the complex dynamics of groundwater and seawater exchange in a highly stressed aquifer system linked to a coastal lagoon se spain anthropogenic pressure influences the two way interactions between shallow aquifers and coastal lagoons aquifer overexploitation may lead to seawater intrusion and aquifer recharge from rainfall plus irrigation may in turn increase the groundwater discharge into the lagoon we analyse the evolution since the 1950s up to the present of the interactions between the campo de cartagena quaternary aquifer and the mar menor coastal lagoon se spain this is a very heterogeneous and anisotropic detrital aquifer where aquifer lagoon interface has a very irregular geometry using electrical resistivity tomography we clearly identified the freshwater saltwater transition zone and detected areas affected by seawater intrusion severity of the intrusion was spatially variable and significantly related to the density of irrigation wells in 1950s 1960s suggesting the role of groundwater overexploitation we distinguish two different mechanisms by which water from the sea invades the land a horizontal advance of the interface due to a wide exploitation area and b vertical rise upconing caused by local intensive pumping in general shallow parts of the geophysical profiles show higher electrical resistivity associated with freshwater mainly coming from irrigation return flows with water resources mostly from deep confined aquifers and imported from tagus river 400 km north this indicates a likely reversal of the former seawater intrusion process

cooling and inferred uplift erosion history of the grenville orogen ontario constraints from 40ar 39ar thermochronology stepwise 40ar 39ar degassing experiments of 57 mineral separates of hornblende muscovite biotite and perthitic microcline have been used in conjunction with petrologic observations to place regional constraints on the postmetamorphic cooling and the inferred uplift and erosion history of the grenville orogen in ontario the 40ar 39ar data support an interpretation of slow nearly uniform cooling 1 4 c m y from temperatures of 500 c to below 150 c in the central gneiss belt cgb hornblendes cooled through ar closure between 930 and 1025 ma whereas in the central metasedimentary belt cmb hornblendes record the following range in 40ar 39ar cooling ages 1104 ma in the frontenac terrane 1007 1067 ma in the sharbot lake terrane 919 1026 ma in the elzevir terrane and 972 ma in the central metasedimentary belt boundary zone regional uplift erosion rates of 0 03 0 14 km m y have been estimated for the grenville orogen in ontario based on the 40ar 39ar data a model retrograde p t path for rocks of the cgb and an upper time constraint provided by flat overlying cambrian and ordovician sediments these erosion rates are consistent with rates estimated for other proterozoic or archean granulite terranes but are an order of magnitude slower than active orogens such as the alps and himalayas a regular variation in hornblende 40ar 39ar cooling ages is observed in rocks that traverse highly strained often mylonitic shear zones that separate the four major terranes of the cmb the pattern of 40ar 39ar ages is interpreted to reflect late tectonic extension consistent with field observations in the central metasedimentary belt boundary zone and elsewhere in the cmb up to 13 km of vertical displacement is inferred for some rocks in the cmb between the time they cooled below closure to argon diffusion in hornblende 500 c and their exposure at the surface 25 c

propagating solitary waves along a rapidly moving crack front a rapidly moving crack in a brittle material is often idealized1 as a one dimensional object with a singular tip moving through a two dimensional material however in real three dimensional materials tensile cracks form a planar surface whose edge is a rapidly moving one dimensional singular front the dynamics of these fronts under repetitive interaction2 3 4 with material inhomogeneities asperities and the morphology5 6 7 8 9 10 11 of the fracture surface that they create are not yet understood here we show that perturbations12 to a crack front in a brittle material result in long lived and highly localized waves which we call front waves these waves exhibit a unique characteristic shape and propagate along the crack front at approximately13 14 15 the rayleigh wave speed the speed of sound along a free surface following interaction counter propagating front waves retain both their shape and amplitude they create characteristic traces along the fracture surface providing cracks with both inertia and a new mode of dissipation front waves are intrinsically three dimensional and cannot exist in conventional two dimensional theories of fracture1 because front waves can transport and distribute asperity induced energy fluctuations throughout the crack front they may help to explain how cracks remain a single coherent entity despite repeated interactions with randomly dispersed asperities

investigation of the nature of slip surface using geochemical analyses and 2 d electrical resistivity tomography a case study from lapseki area nw turkey the nature and subsurface structure of the slip surface of a landslide was studied on the basis of geochemical analyses and 2 d electrical resistivity tomography ert survey head scarp and lateral slip surfaces of the landslide marked by clear slickensided shear planes were composed of the average amounts of clayey silt 32 5 and sand 67 5 energy dispersive x ray spectroscopy edx data revealed the enrichment of si 23 24 fe 12 2 al 9 51 and c 8 34 in the elemental composition of the disturbed slip surface from x ray diffractometry xrd data six main clay types were determined such as volkonskoite halloysite ferrosilite saponite illite and nontronite the ert survey displayed that the landslide developed as a reactivation on the upper part of an old landslide body

evaluating freshwater lens morphology affected by seawater intrusion using chemistry resistivity integrated technique a case study of two different land covers in carey island malaysia freshwater lenses are vital to small island communities but are susceptible to seawater intrusion due to the physical changes in the shoreline land cover the effect of seawater intrusion and irrigation water on a coastal unconfined aquifer beneath naturally preserved mangrove and deforested mangrove barren belt was investigated in carey island analysis of the total dissolved solids tds and earth resistivity er using a geochemistry electrical integrated technique gave a tds er relationship capable of predicting freshwater lens morphology affected by sea irrigation water the study result shows freshwater was fourfold thicker in close proximity of the mangrove forest than the mangrove barren area the further the shoreline from the mangrove thickest section the less vulnerable was the seawater intrusion and the more fresh the irrigation water and hence the greater the freshwater availability potential

effect of volcanic dykes on coastal groundwater flow and saltwater intrusion a field scale multiphysics approach and parameter evaluation volcanic dykes are common discrete heterogeneities in aquifers however there is a lack of field examples of and methodologies for comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport we have applied an integrated multi physics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer the approach involved ground geophysical imaging passive magnetics and electrical resistivity tomography well hydraulic testing and tidal propagation analysis which provided constraints on the geometry of the dyke network the subsurface saltwater distribution and the sandstone hydrodynamic properties and connectivity a three dimensional variable density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations a good agreement of model simulations with tide induced head fluctuations geophysically derived pore water salinities and measured apparent resistivities was obtained when dykes hydraulic conductivity storativity and effective porosity are respectively about three one and one orders of magnitude lower than the host aquifer the presence of the dykes results in barrier like alterations of groundwater flow and saltwater intrusion preferential flowpaths occur parallel to observed dyke orientations freshwater inflows from upland recharge areas concentrate on the land facing side of the dykes and saltwater penetration is higher on their sea facing side this has major implications for managing groundwater resources in dyke intruded aquifers including in coastal and island regions but also provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems this article is protected by copyright all rights reserved

reconstructing palaeochannel morphology with a mobile multicoil electromagnetic induction sensor abstract field methods to map and reconstruct the morphology of buried river systems are highly dependent on spatial interpolation conventional methods such as standard borehole survey allow a detailed vertical reconstruction of the shallow subsurface but leave lateral connections between sample locations open to interpretation geophysical survey techniques have recently introduced more detail mobile electromagnetic induction emi survey combines high density sampling with full lateral coverage but fails to produce detailed information about vertical facies changes recently multicoil emi survey added vertical discrimination potential to this lateral continuity in this study we present an integrated approach for reconstructing the morphology of a known palaeochannel segment by modelling the depth to the sandy substrate in addition a calibration method based on a limited number of auger data is proposed in a first phase the modelling procedure was evaluated along two transects on a test site showing palaeochannel depths ranging from 1 to 4 m beneath the surface in a second phase the morphology of the entire site was reconstructed these three resulting depth models were then compared with auger observations and electrical resistivity tomography ert data the high correlation coefficients 0 9 between observed and modelled depths showed that even in complex pedological environments palaeochannel morphology could be predicted precisely using multicoil emi data therefore we concluded that a multicoil emi survey proves to be an efficient and reliable solution for mapping and reconstructing the morphology of the shallow subsurface

electrical resistivity in support of geological mapping along the panama canal abstract dredging and widening of the panama canal is currently being conducted to allow larger vessels to transit to and from the americas asia and europe dredging efficiency relies heavily on knowledge of the types and volumes of sediments and rocks beneath the waterway to ensure the right equipment is used for their removal to aid this process a waterborne streaming electrical resistivity survey was conducted along the entire length of the canal to provide information on its geology within the confines of the canal a total of 663 line kilometers of electrical resistivity data were acquired using the dipole dipole array the support of the survey data for dredging activities was realized by calibrating and qualitatively correlating the resistivity data with information obtained from nearby logged boreholes and geological maps the continuity of specific strata was determined in the resistivity sections by evaluating the continuity of similar ranges of resistivity values between boreholes it was evident that differing geological units and successions can have similar ranges of resistivity values for example quaternary sandy and gravelly alluvial fill from the former river channel of the chagres river had similar resistivity ranges generally from 40 to 250 m to those characteristic of late miocene basalt dikes from 100 to 400 m but for quite different reasons similarly competent marine based sedimentary rocks of the caimito formation were similar in resistivity values ranging from 0 7 to 10 m to sandstone conglomerate of the bohio formation consequently it would be difficult to use the resistivity data alone to extrapolate more complex geotechnical parameters such as the hardness or strength of the substrate a necessary component for such analyses requires detailed objective information regarding the specific context from which the geotechnical parameters were derived if these data from cored boreholes and detailed geological surveys are taken into account however then waterborne streaming resistivity surveying can be a powerful tool in this case it provided inexpensive and highly resolved quantitative information on the potential volume of loose suctionable material along the gamboa sub reach which could enable large cost savings to be made on a major engineering project involving modification of one of the most important navigable waterways in the world

a re examination of the influence of composition on argon retentivity in metamorphic calcic amphiboles abstract the effect of composition on argon retention in metamorphic hornblende has been re evaluated by the 40 ar 39 ar step heating method utilizing the same samples from a k ar study in which a relationship between hornblende composition and argon retention was inferred incremental heating of the hornblendes yields 40 ar 39 ar age plateaus or near plateaus between 1081 3 and 1112 3 ma these data support a simple cooling history through argon closure following high grade metamorphism consistent with recent geochronological studies of the bamble sector of norway no clear evidence of extraneous argon is preserved in the 40 ar 39 ar data nor is there any sign of a thermal disturbance following argon closure contrary to the k ar results the 40 ar 39 ar data show no relationship between hornblende cooling age and composition the results of this investigation together with those from other studies suggest that the composition of metamorphic hornblende is not an important factor in controlling its argon closure temperature published studies inferring a compositional dependence on the argon closure temperature in metamorphic hornblende are commonly based on analytical data from impure retrogressed altered recrystallized or microstructurally complex hornblendes which are not representative of the diffusive properties of a pure hornblende such mineralogical and structural complexities may form both above and below the closure temperature of hornblende which may give rise to variable hornblende ages from rocks that have experienced the same geologic history such complexities forming at high temperature may contribute to a modified or variable characteristic grain size s of diffusion resulting in a modified complex hornblende closure temperature these complexities may contribute to low apparent hornblende ages if formed below its true closure temperature in addition variable hornblende ages may be obtained if fine grained mineral intergrowths are present and undergo recoil related phenomena during irradiation geologically meaningful hornblende ages are possible only when proper care is taken in sample selection and characterization

evaluation of landfill disposal boundary by means of electrical resistivity imaging this paper deals with an employment of electrical resistivity imaging eri for survey of leachate content on the waste disposal site in northern israel the research consisted of conducting ten eri lines and drilling investigation wells data simulation used a 2d earthimager inversion program analysis of 2d eri interpretation results shows that determination of the boundary between the landfill body bottom intensively saturated with leachates and underlying layers of highly water saturated fat nonconsolidated clays presents a challenge however statistical analysis of eri data indicates that standard deviation and confidence interval of a set of resistivity data measured in the landfill body are significantly larger than those in underlying clays moreover maximum changes of these parameters are found on the boundary between landfill body and underlying soil thus reflecting natural differences in scattering of resistivity data measured in these two objects

major southward thrusting of the dalradian rocks of connemara western ireland the connemara schists are of dalradian late precambrian cambrian age and since the work of kilburn et al 1 it has been apparentthat they occupy an anomalous geographical position south southeast of the strike continuation of the dalradian rocks of scotland and ireland and south of the inferred position of the highland boundary fault fig 1 also the connemara schists are unusual in having reached a higher metamorphic grade and having had a different metamorphic history from most other parts of the dalradian the model which we propose here for the connemara dalradian that of an allochthonous thrust sheet offers an explanation for these anomalies and highlights hitherto unsuspected similarities between the tectonic histories of the south east margins of the metamorphic caledonides in the british isles and scandinavia

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

latest cretaceous cone in cone structures and soft sediment deformation basque cantabrian basin north spain a record of deep marine paleoseismicity unusual cone in cone structures are preserved in fibrous celestite veins hosted by carbonatic rocks the veins are early diagenetic features formed near the water sediment interface in a deep marine environment of latest cretaceous early maastrichtian age new field and microscopic evidence on the veins and their host rocks indicates that they predate sediment compaction and were related to synsedimentary soft sediment deformation structures the mechanism of cone in cone formation has been related to fluid pressure drops following sediment overpressurization but instantaneous loading during emplacement of submarine slides or other mechanisms might be viable alternatives we argue that this cone in cone structure is an overprinting feature penetrative conical fractures that resulted from seismic wave propagation through a mechanically anisotropic medium submarine amplification of seismic surface waves rayleigh waves induced shock wave formation in the contacts between veins and the bounding lithified calcarenite and unlithified marl sediment layers fracture front wave propagation normal to the seafloor and the rayleigh source across the veins and along the celestite crystal fibers induced crack nucleation in heterogeneities and penetrative conical fracturation the cone in cone structure might thus be regarded as a new paleoseismological indicator in deep sea sediments

proximate environmental forcing in fine scale geochemical records of calcareous couplets upper cretaceous and palaeocene of the basque cantabrian basin eastern north atlantic abstract calcareous couplets are key elements in reconstructing the evolution of a sedimentary basin due to the influence of forcing mechanisms such as climate sea level and tectonism on their depositional patterns proposed forcing mechanisms however are often not mutually exclusive and even constraining the relative importance of different processes is problematic added to the question of discriminating forcing mechanisms a major challenge is to produce high sampling density so that observations lie within temporal resolutions equal to or finer than the timescales on which different forcing operates here we show fine scale 1 sample 2 cm caco3 18o and 13c records and sedimentological observations from three different sites isla de castro sopelana ma and sopelana da with calcareous couplets in the basque cantabrian basin eastern north atlantic to illustrate the potential of fine sampling strategies to help distinguish proximate environmental forcing partial redistribution of carbonate during burial diagenesis has been proposed for these sediments our caco3 18o and 13c data could thus be dismissed as diagenetic signals if only one sample was collected from each bed detailed observations of the fine scale geochemical records however challenge purely diagenetic explanations combined with sedimentology the caco3 18o and 13c values partially altered by diagenesis are interpreted to have resulted from alternating climates the proximate forcing through which alternating climates caused the geochemical patterns though was different in each section due to their specific palaeogeographic positions in the basin and the properties of the seawater masses the proximity of continental areas of high relief to the isla de castro section supported a high continental influence during its deposition the sopelana ma sediments are assigned to a transgressive system tract a condition that is interpreted to have promoted a high influence of oceanic processes in its depositional setting finally a relatively cool oxygen rich water mass with high oxidation potential influenced the geochemical and depositional patterns of sopelana da beyond the climatic and oceanographic dynamics inferred for a basin that linked the western tethys with boreal domains during major marine transgressions of the late cretaceous to palaeocene an implication of our work is that if similar fine scale geochemical records were applied to calcareous couplets spanning major events in earth s history e g ocean anoxic events alternative forcing scenarios leading to and out of these events could be discriminated

fluid disturbed hornblende k ar ages from the dalradian rocks of connemara western ireland the results of k ar age determinations and hydrogen and oxygen stable isotope measurements on hornblendes from the poly metamorphic dalradian schists of connemara western ireland indicate that the hornblende k ar systems have been significantly disturbed by low temperature fluid reaction correlations between k ar ages d values structural water contents and the occupancy of the hornblende structural a sites suggest that excess water as h 3 o occupies vacant a site positions during stable isotope exchange and displaces ar causing lowering of the k ar ages this process occurs below the normally accepted closure temperature for ar in hornblende and is not detectable by optical or x ray investigation of the mineral this process may not be unique to connemara hornblendes and so is of potential importance to geochronology in other metamorphic terranes

parallel psm fdm hybrid simulation of ground motions from the 1999 chi chi taiwan earthquake a new technique for the parallel computing of 3 d seismic wave propagation simulation is developed by hybridizing the fourier pseudospectral method psm and the finite difference method fdm this psm fdm hybrid offers a good speed up rate using a large number of processors to show the feasibility of the hybrid a numerical 3 d simulation of strong ground motion was conducted for the 1999 chi chi taiwan earthquake mw 7 6 comparisons between the simulation results and observed waveforms from a dense strong ground motion network in taiwan clearly demonstrate that the variation of the subsurface structure and the complex fault slip distribution greatly affect the damage during the chi chi earthquake the directivity effect of the fault rupture produced large s wave pulses along the direction of the rupture propagation slips in the shallow part of the fault generate significant surface waves in coastal plain along the western coast a large velocity gradient in the upper crust can propagate seismic waves to longer distances with minimum attenuation the s waves and surface waves were finally amplified further by the site effect of low velocity sediments in basins and caused the significant disasters

internal structure and conditions of permafrost mounds at umiujaq in nunavik canada inferred from field investigation and electrical resistivity tomography a systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at umiujaq in nunavik canada to assess their internal structure and conditions prior information under the form of a geocryologic model of the permafrost mounds was integrated in the inversion of the pseudo section of apparent electrical resistivity the geocryologic model was developed from the synthesis of previous field investigations including shallow and deep sampling temperature and electrical resistivity logging and cone penetration tests performed in the permafrost mounds values of electrical resistivity were ascribed to the different layers making of the geocryologic model to define a synthetic resistivity model of the permafrost mounds used as a reference model to constrain the inversion the constrained resistivity model clearly show the presence of ice rich cores in the permafrost mounds underscored by high resistivity values in excess of 30 000 m while t

cross validation of geo electrical and hydrogeological models to evaluate seawater intrusion in coastal aquifers 1 the validation of variable density flow models simulating seawater intrusion in coastal aquifers requires information about concentration distribution in groundwater electrical resistivity tomography ert provides relevant data for this purpose however inverse modeling is not accurate because of the non uniqueness of solutions such difficulties in evaluating seawater intrusion can be overcome by coupling geophysical data and groundwater modeling first the resistivity distribution obtained by inverse geo electrical modeling is established second a 3 d variable density flow hydrogeological model is developed third using archie s law the electrical resistivity model deduced from salt concentration is compared to the formerly interpreted electrical model finally aside from that usual comparison validation the theoretical geophysical response of concentrations simulated with the groundwater model can be compared to field measured resistivity data this constitutes a cross validation of both the inverse geo electrical model and the groundwater model

seismic evidence of alpine crustal thickening and wedging from the western pyrenees to the cantabrian mountains north iberia 1 the alpine collision between the iberian and european plates resulted in a complex crustal structure beneath the northern iberian peninsula as revealed from a new set of seismic refraction wide angle reflection profiles the study area is characterized by two major e w ranges the cantabrian mountains and the pyrenees which are relayed to the south by the iberian chain important variations in crustal thickness and velocity distribution are found in a 560 km long e w transect in contrast to the typical 30 to 32 km thick european variscan crust of the western end of the profile a continuous alpine crustal root is evidenced from the cantabrian mountains to the central pyrenees with a moho depth of 46 48 km locally rising to 40 km depth in between beneath the basque cantabrian basin another outstanding feature is the inferred presence of high velocities of 6 40 6 75 km s at midcrustal depths which can be associated with portions of a lower crustal wedge from the northern european domain indenting the southern iberian crust during the alpine stage of compression this indentation produces the delamination of the iberian crust with northward underthrusting of its lower half and the consequent crustal thickening the indenting wedge has a discontinuous presence along the longitudinal section as it was controlled and or affected by n s to ne sw structures further evidence of the northward subduction of the iberian plate is provided by another profile toward the aquitaine basin while a n s profile across the iberian chain reveals an alpine midcrustal thickening beneath this belt with moho depths of 42 km

the geometry and topology of natural sheath folds a new tool for structural analysis abstract curvilinear sheath folds are classically depicted as displaying symmetrical geometries about two orthogonal mirror planes centred along the x y axial surface and the x z medial culmination depression surface which bisects the fold nose however 10 000 geometric analyses of minor folds and fabrics formed during ductile thrusting in the caledonides of northern scotland reveals that major dome and basin sheath folds can display distinct and predictable asymmetries across both axial and medial surfaces the strain is typically heterogeneous so that structural fabrics and younging evidence are preserved within sheath folds at varying stages of development this allows an analysis of the evolution of such structures from tongue folds to more extreme tubular forms geometric relationships between measured orientations of fold hinges axial planes extension lineations and foliations are compared on fabric topology plots ftps which provide an effective tool for monitoring planar and linear fabric rotations with increasing progressive non coaxial deformation they consistently display systematic variation from regions of lower to higher strain on passing from upper to lower fold limbs across major axial surfaces and on crossing medial surfaces from short to long hinge line segments axial and medial surfaces effectively therefore divide major sheath folds into quadrants with different amounts senses and combinations of planar and linear fabric rotation within each domain such heterogeneous deformation implies that models of intense non coaxial deformation uniformly affecting pre existing folds may overestimate bulk displacement and shear strain variable fold hinge line rotation about medial surfaces also provides an effective mechanism for the closure of major sheaths which may otherwise project for unfeasible distances in the x direction bedding cleavage intersections are developed at greater angles to the transport direction than fold hinges which they transect in a consistent and predictable sense thereby confirming the direction of fold rotation even in areas which lack information on fold facing in cross section asymmetric tear drop eyes indicate the sense of fold hinge line vergence whilst fold limb and hinge line asymmetry may be combined on 3 d vergence ranking and rotation grids which allow location and relative strain states of minor structures to be accurately predicted within the overall sheath framework systematic fabric analysis on ftps may be applied to the investigation of ductile deformation across a broad range of scenarios

application of time domain electromagnetic method in investigating saltwater intrusion of santiago island cape verde santiago island the biggest and most populated island of the cape verde republic is characterised by limited surface waters and strong dependence on groundwater sources as the primary source of natural water supply for extensive agricultural activity and human use however as a consequence of the scarce precipitation and high evaporation as well as the intense overexploitation of the groundwater resources the freshwater management is also in a delicate balance with saltwater at coastal areas the time domain electromagnetic tdem method is used to locate the extent of saltwater intrusion in four important agricultural regions in santiago island sao domingos santa cruz sao miguel and tarrafal the application of this method in santiago island proves it to be a successful tool in imaging the fresh saltwater interface location depths to the saline zones and extensions of saline water are mapped along eight tdem profiles