three dimensional effects causing artifacts in two dimensional cross borehole electrical imaging summary cross borehole electrical resistance tomography ert experiments utilize downhole electrodes typically placed in a borehole filled with material of contrasting resistivity to the host rock the circular geometry of the boreholes is three dimensional and inversion routines are typically two dimensional because of the resistivity contrast artifacts in the form of borehole inversion effects develop in the resistivity images other 3d effects resulting in inversion artifacts are shadow effects caused by use of a 2d code to invert data from a 3d body located outside the image plane in both cases the inversion model misrepresents the spatial change in voltages as a corresponding spatial change in resistivity borehole inversion effects and shadow effects result as the forward solver attempts to resolve the discrepancy in the voltages for numerous electrode pairs into a meaningful resistivity distribution borehole inversion effects are shown to be related to the resistivity contrast between the borehole fill and the host medium and to borehole diameter borehole inversion effects do not materialize with small diameter boreholes e g 0 1 m when the fill resistivity contrast is one order of magnitude or less however a borehole fill resistivity contrast of two orders of magnitude causes artifacts in the form of sheaths near the boreholes and a conductive artifact between the boreholes larger diameter borehole e g 0 2 m induce significant borehole inversion effects with as little as one order of magnitude fill resistivity contrast the general resistivity patterns are similar for the borehole inversion effects however the artifacts are amplified as resistivity contrast and or borehole diameter increase these results are significant because borehole inversion effects may mask a target heterogeneity or an artifact may be confused for an anomaly resulting in improper actions for site characterizations or remediation strategies suggestions of best practices for experimental design to prevent or minimize borehole inversion effects include minimizing borehole diameter minimizing borehole fill resistivity contrast measuring and inputting the resistivity of the borehole fill water into the model and inverting changes in resistivity for time lapse ert data shadow effects are shown to be related directly to the distance of the target heterogeneity out of the image plane our results show that shadow effects become insignificant when the target is between 3 and 5 m outside the 10 m wide image plane because the size of the target and resistivity contrast of the target to the host rock are site specific variables the actual distance at which shadow effects become insignificant will vary from site to site to reduce misinterpretations by shadow effects reduce the dipole length of the four electrode measurements and supplement data from other well pairs and or other methods

upb dating of fe rich phases using a sequential leaching method a sequential leaching method was developed for upb dating of fe rich phases which uses a series of successively stronger acids the method was applied to date fe rich phases of magmatic origin in the kinsman quartz monzonite new hampshire usa and of sedimentary origin in the dales gorge member of the brockman iron formation hamersley basin australia using the composition of major element released by the acid leaching and combining it with x ray and sem analyses of the residues we were able to identify the relatively pure phases released and use these samples for dating magnetite separates from the kinsman quartz monzonite yielded upb age of 372 34 ma which is consistent with smnd and a rbsr isochron ages determined in previous studies leached whole rock samples of the brockman iron formation yielded a 207pb206pb age of 2213 250 ma which agrees with previously determined pbpb smnd and rbsr isochron ages this age is interpreted as the time of redistribution of u and pb associated with the fe rich phases during regional metamorphism while the potential of the sequential leaching method is demonstrated more work is needed in order to improve the precision of the data this requires further investigation of the nature of the pure phases

toward understanding the post collisional evolution of an orogen influenced by convergence at adjacent plate margins late cretaceous tertiary thermotectonic history of the apuseni mountains 1 the relationship between syn to post collisional orogenic shortening and stresses transmitted from other neighboring plate boundaries is important for understanding the kinematics of mountain belts but has received little attention so far the apuseni mountains are an example of an orogen in the interference zone between two other subduction systems located in the external carpathians and dinarides this interference is demonstrated by the results of a combined thermochronological and structural field study that quantifies the post collisional latest cretaceous tertiary evolution the exhumation history derived from apatite fission track and u th he thermochronology indicates that the present day topography of the apuseni mountains originates mainly from latest cretaceous times modified by two tectonic pulses during the paleogene the latter are suggested by cooling ages clustering around 45 ma and 30 ma and the associated shortening recorded along deep seated fault systems paleogene exhumation pulses are similar in magnitude 3 5 km and are coeval with the final collisional phases recorded in the dinarides and with part of the carpathian rotation around the moesian promontory these newly quantified paleogene exhumation and shortening pulses contradict the general view of tectonic quiescence subsidence and overall sedimentation for this time interval the miocene collapse of the pannonian basin did not induce significant regional exhumation along the western apuseni flank nor did the subsequent carpathian collision this is surprising in the overall context of pannonian basin formation and its subsequent inversion in which the apuseni mountains were previously interpreted as being significantly uplifted in both deformation stages

3d crosshole ert for aquifer characterization and monitoring of infiltrating river water the hydrogeological properties and responses of a productive aquifer in northeastern switzerland are investigated for this purpose 3d crosshole electrical resistivity tomography ert is used to define the main lithological structures within the aquifer through static inversion and to monitor the water infiltration from an adjacent river during precipitation events and subsequent river flooding the river water resistivity increases as a consequence the electrical characteristics of the infiltrating water can be used as a natural tracer to delineate preferential flow paths and flow velocities the focus is primarily on the experiment installation data collection strategy and the structural characterization of the site and a brief overview of the ert monitoring results the monitoring system comprises 18 boreholes each equipped with 10 electrodes straddling the entire thickness of the gravel aquifer a multichannel resistivity system programmed to cycle through various four point electrode configurations of the 180 electrodes in a rolling sequence allows for the measurement of approximately 15 500 apparent resistivity values every 7 h on a continuous basis the 3d static ert inversion of data acquired under stable hydrological conditions provides a base model for future time lapse inversion studies and the means to investigate the resolving capability of our acquisition scheme in particular it enables definition of the main lithological structures within the aquifer the final ert static model delineates a relatively high resistivity low porosity intermediate depth layer throughout the investigated aquifer volume that is consistent with results from well logging and seismic and radar tomography models the next step will be to define and implement an appropriate time lapse ert inversion scheme using the river water as a natural tracer the main challenge will be to separate the superposed time varying effects of water table height temperature and salinity variations associated with the infiltrating water

cretaceous to cenozoic thermal evolution of the southwestern south carpathians evidence from fission track thermochronology abstract the southwestern south carpathian orogen is composed of various nappe complexes which were assembled during the cretaceous cenozoic orogeny these are from footwall to hangingwall 1 the danubian nappe complex including a cadomian variscan basement 2 the arjana and severin units with jurassic to early cretaceous rift and oceanic sequences and 3 the getic nappe complex with variscan continental basement fission track ft thermochronology on apatite zircon and sphene from samples collected from various units of the south carpathians in conjunction with field constraints and previous geochronology is used to characterise the alpine tectonic events and to restore the pattern and amount of exhumation since the cretaceous zircon from the flysch unit and the danubian liassic cover sequence yields ft ages around 200 ma suggesting cooling of the rift flanks prior to the opening of the severin rift zircon and sphene from the getic and danubian basement units yield ft ages averaging 110 ma and indicating cooling under 240 c of the basement contemporaneous with or postdating thrusting apatite ft ages display a decreasing age trend from the hangingwall 65 ma to the footwall units 30 ma the age data and corresponding horizontal confined track length distributions suggest that exhumation of the nappe pile occurred in two stages the first is related to the late cretaceous nappe stacking and the second one to the final thrusting of the south carpathians onto the top of the moesian platform apatite ft ages along major brittle wrench faults indicate reheating above ca 120 c during fluid flow associated with fault re activation during oligocene and neogene times thus shear zone rocks experienced a higher temperature overprint during cenozoic time than rocks of the unaffected nappe pile temperatures of hydrothermal flow along these zones decreased below 100 c progressively starting with the late oligocene early miocene when the area began to override the moesian platform

three dimensional p wave velocity image under the carpathian arc abstract an inversion of p wave travel time residuals from selected earthquakes in the distance range 30 98 to two seismic station networks was used to model p wave velocity anomalies down to 250 km depth in the first inversion experiment a region between 43 5 47 5 n and 21 29 e was modelled using 35 seismic stations while in the second one a region between 44 47 n and 25 29 e was modelled using 19 seismic stations the 4 layer block model of the first inversion offers 19 reduction in residual variance while the 5 layer block model of the second one offers 26 reduction the rest being explained by noise and smaller scale heterogeneities the obtained velocity anomalies correlate remarkably well with the gravity anomalies and with the tectonic model for the vrancea region of fuchs et al 1979

the variation of heat generation density and seismic velocity with rock type in the continental lithosphere abstract the petrophysical properties radioactive heat generation compressional wave velocity and density are related to rock type in crystalline rocks the cation fraction in the rock forming minerals is applied to determine the relationships quantitatively heat generation exhibits considerable variation with rock type as well as with the geologic age of the rocks therefore the relation between heat generation and rock type has been split into a relation for phanerozoic rocks and another for precambrian rocks which exhibit significantly lower heat generation only 1 3 of that of phanerozoic rocks the interrelations between the petrophysical properties are applied to fennoscandia precambrian terrane and southern bavaria northern alpine foreland phanerozoic rocks to estimate the heat generation by radioactivity in the crust and the heat flow density from the upper mantle

the evolution of the carpathians pannonian system interaction between neotectonics deep structure polyphase orogeny and sedimentary basins in a source to sink natural laboratory abstract the carpathians pannonian basin system provides a natural laboratory for analysing lithospheric to surface controls on tectonic topography development in a coupled source to sink environment to link processes taking place at depth and at the surface recent research focused on the interplay between basin evolution active tectonics topography evolution and intraplate folding mechanisms neotectonic processes control landscape development and natural hazards in particular the seismicity during the late stage late neogene quaternary evolution of both the carpathians pannonian basin system and its interaction with the adjacent dinarides and balkans the deep structure of the se carpathians exerts a strong control on the post collisional evolution of the system new constraints are available from seismic tomography deep seismic reflection and refraction profiling and detailed studies of the vreancea seismicity inherited orogenic fabric and structure of the active black sea sink has a strong influence on the localisation of the neogene sediment pathways a close relationship has been established between the timing and mechanisms of stress changes in the pannonian and transylvania basins and structural episodes in the surrounding thrust belts pointing to an intrinsic mechanical coupling with these basins the orogen and its foredeep basin inversion taking place during the pliocene quaternary times in the entire carpathians pannonian system is related to changes in the regional stress field leading to differential vertical movements associated with a laterally variable folding mechanism active in the entire system short crustal folding patterns alternate with lithospheric wavelengths in the se carpathians foreland east and south carpathians transylvania and pannonian basins the lateral variability is the result of a marked contrast in rheology between these areas directly related to the crustal configuration thermal properties and late stage collision kinematics with the carpathians foreland lateral variations in the properties of the downgoing plates largely control the collision mode in the carpathians and the post collisional evolution of the entire system

a geodynamic model of the southern apennines accretionary prism the apennines comprise a neogen quaternary accretionary prism that shows several anomalies with respect to classic alpine type mountain belts namely i low elevation ii a shallow new moho below the core of the belt iii high heat flow in the internal parts iv mainly sedimentary cover involved in the prism v a deep foredeep and vi a fully developed back arc basin the suction exerted by a relatively eastward migrating mantle can determine the eastward retreat of the subduction zone and an asthenospheric wedging at the retreating subduction hinge heat flow geochemical and seismological data support the presence of a hot mantle wedge underlying the western side of the apenninic accretionary prism a thermal model of the belt with foreland dipping isotherms fits with deepening of the seismicity toward the east mantle volatiles signatures are also widespread in springs along the apennines

geothermal models for the east carpathians abstract in order to explain the high heat flow 73 126 mw m 2 observed at the inner part of the east carpathians a model which takes into account the radiogenic heat generation and the descent of a lithospheric plate has been elaborated calculated geotherms indicate the presence of a high temperature anomaly exceeding 1000 c localized in the upper mantle the geothermal data suggest that both the high heat flow and the building up of the neo volcanic chain are consequences of the lithospheric alpine subduction in the carpathians area

on the thermal regime of some tectonic units in a continental collision environment in romania an analysis of the evolution of the main tectonic units in romania shows that the thermal regime of the lithosphere should be derived according on the one hand to the particular tectonic interactions the various tectonic units have been involved in and on the other hand to the investigated depth interval a steady state conduction model of the crustal temperature field based on the heat flow distribution and information on the structure is presented for the romanian territory it shows large lateral thermal variations between tectonic units as a result of different geological and thermal histories within the frame of a complex modelling of the thermal evolution of the lithosphere in the east carpathians as proposed in this study the zero order thermal effects of the pre miocene oceanic subduction of the eurasian plate are evaluated the deep thermal structure of the subducted slab is derived and shown to be compatible with the velocity structure of the lithosphere and the intermediate depth seismicity of the vrancea area

40ar 39ar laser dating of a single grain of magnetite abstract we have determined an 40 ar 39 ar age spectrum for a single grain of magnetite using laser step heating a 300 m magnetite grain from a grenville front gneiss was heated in 14 steps to 1600 c excess 40 ar resulted in a saddle shaped age spectrum with an integrated age of 1962 39 ma however the minimum of the saddle gave an age of 1144 107 ma consistent with typical grenvillian cooling ages of 1100 900 ma we have also dated a single grain of biotite from the same hand sample as the magnetite the spectrum yielded an integrated age of 1261 3 6 ma the thermal release patterns of 40 ar and of ca k 37 ar 39 ar were very different for the magnetite and biotite thus 40 ar can be retained in measurable quantities in magnetite our results are a first step toward the attempted direct dating of different components of nrm in paleomagnetism

evaluation of known boundary and resistivity constraints for improving cross borehole dc electrical resistivity imaging of discrete fractures abstractthere is a need to better characterize discrete fractures in contaminated hard rock aquifers to determine the fate of remediation injections away from boreholes and also to evaluate hydraulic fracturing performance a synthetic cross borehole electrical resistivity study was conducted assuming a discrete fracture model of an existing contaminated site with known fracture locations four boreholes and two discrete fracture zones assumed to be the dominant electrical and hydraulically conductive pathways were explicitly modeled within an unstructured tetrahedral mesh we first evaluated different regularization constraints starting with an uninformed smoothness constrained inversion to which a priori information was incrementally added we found major improvements when 1 smoothness regularization constraints were relaxed or disconnected along boreholes and fractures 2 a homogeneous conductivity was assumed along boreholes and 3 borehole conductivity constraints that could be determined

magnetism of biotite crystals abstract we report mossbauer spectra magnetic hysteresis acquisition and demagnetization of isothermal remanent magnetization irm and low temperature irm warming curves of biotite crystals as well as a summary of domain observations on magnetic extracts the biotites are from 1 0 to 1 2 ga gneisses and 1 85 ga plutons of the grenville churchill and bear provinces canada most have paramagnetic susceptibilities in the range 0 45 1 2 10 3 si similar to reported values for iron rich biotites magnetite identified by its 120 k verwey transition is an inclusion in all the biotites sizes and domain states of inclusions correlate with magnetite content as measured by saturation magnetization ms the higher ms is the lower are the domain state indicators mrs ms mrs is saturation irm and coercive force hc added to a base population 0 003 0 1 of pseudo single domain psd grains with mrs ms from 0 1 to 0 3 and hc from 7 to 20 mt is 1 in two exceptional cases 7 and 14 of coarse grained multidomain md magnetite with much softer hysteresis properties the underlying psd magnetite fraction in biotites potentially retains useful paleomagnetic remanence in the more magnetic micas this stable fraction may be swamped by md magnetite with less stable behavior

lithosphere thermal structure and evolution of the transylvanian depression insights from new geothermal measurements and modelling results the surface heat flow density pattern of the transylvanian depression td represents a marked high amplitude short wavelength low in a region of elevated heat flow detailed temperature depth profiles obtained by continuous temperature logging combined with a finite element modelling of topographic and fluid flow effects support the conclusion that the observed thermal gradient in the td truly represents the rate of heat loss of the subsurface the surface heat flux is 30 mw m 2 in the centre of the depression increasing to about 60 mw m 2 at margins climatic correction is of the order of 2 10 mw m 2 depending on the investigated depth interval the measured temperatures are compatible with the cooling of the earth surface during the weichselian glaciation followed by the climate warming which started 10 11 000 years ago the transient effects of neogene sedimentation and erosion mean an overall 2 3 mw m 2 reduction in surface heat flux a low mantle heat flux 30 mw m 2 and a low crustal heat production rate in the td 0 5 wm 3 in the centre are necessary to explain the heat flux anomaly the surface heat flux pattern of the td and the extreme low value in the centre of the depression point to an exceptionally cold and strong lithosphere in the transylvanian region as shown by strength envelopes characteristic to the entire depression the evolution of the td generally can be understood in terms of an exceptionally strong lithosphere block caught in a compressive tectonic environment 2001 elsevier science b v all rights reserved

borehole cylindrical noise during hole surface and hole hole resistivity measurements drilled boreholes generally are the only feasible means to access the subsurface for the emplacement of downhole electrodes for most hole hole and hole surface resistivity experiments however the very existence of the borehole itself creates the potential for significant noise due to the inevitable conductivity contrast that develops between the borehole walls and the formation borehole cylindrical noise develops whenever a current source is placed in a drilled borehole borehole geometries may range from nearly perfect cylinders to highly irregular rugose holes in consolidated rock to relatively minor collapsed disturbed zones in caving sediments boreholes in non caving formations generally are filled with artificial conductive materials to afford crucial electrical continuity between downhole electrodes and the borehole walls filled boreholes form cylindrically shaped heterogeneities that create significant noise due to preferential current flow up and down the conductive columns selected conditions are simulated with a finite difference model to illustrate the significance of borehole cylindrical noise on hole hole and hole surface mise a la masse electrical potentials near a current electrode mise a la masse electrical potentials measured during a field tracer experiment also are presented these measurements are used to illustrate significant errors may develop in the interpretation of apparent resistivity estimates out to a distance of several meters from the current source if borehole cylindrical noise is not recognized and accounted for in the analysis of electrical potential data

new seismic and tomography data in the southern part of the harghita mountains romania southeastern carpathians connection with recent volcanic activity the southern part of the southeastern carpathians represents the site of the most recent volcanic eruptions of the entire carpathian pannonian region the products of these eruptions range from 42 to 10 ka radiocarbon ages in the south harghita mountains high k calc alkaline rocks with adakite like features and at 1 2 0 6 ma k ar ages in the persani mountains alkali basalts they were emplaced in a post collisional regime ciomadul volcano is located at the southernmost part of the nw se oriented c limani gurghiu harghita range crossing the inner part of the southeastern carpathians and in the rough proximity of the vrancea seismic zone at ca 60 km toward nw its magma generation is attributed to geodynamic events closely related to the seismogenic area a number of particular geophysical and geochemical features located in the study region including 1 the abrupt attenuation of the seismic waves originating from the vrancea intermediate depth foci 2 the most intense heat flow anomaly in romania 3 the most prominent 3he 4he anomaly measured in natural postvolcanic gas emanations are all in favor of the hypothesis of a still existing hot local magma chamber data acquired during recent seismic monitoring of the vrancea zone and its neighborhoods suggest an enhancement of the local seismicity beneath the southern edge of the south harghita mts both at crustal and subcrustal levels at the same time recent tomography images obtained using local earthquake data correlate well with the presence of a vertically extended low velocity zone coming from the upper mantle to the assumed magmatic chambers located in the crust the present data supporting the presence of an active crustal magma chamber beneath ciomadul allow us to consider that future volcanic activity at this volcano cannot be discarded

active deformation in the vrancea region rumania recent and historical seismicity as well as reliable fault plane solutions are used to study the active deformation caused by the occurrence of intermediate depth 60 170 km earthquakes of the vrancea region rumania in this area located in the southeastern part of the carpathian arc the westward subduction of the carpathian trench has terminated leaving continental lithosphere at present at the arc the principalt axis of the intermediate depth events trends n159 e and has a plunge of 74 which is the same as the dip of the subducted plate thep axis has a trend of 314 and a shallow plunge of 15 the analysis of the moment tensor of six focal mechanisms showed that the dominant mode of deformation of the subducted lithosphere is a down dip extension at a rate of about 2 cm yr based on seismicity data

estimating traveltimes and groundwater flow patterns using 3d time lapse crosshole ert imaging of electrical resistivity fluctuations induced by infiltrating river water abstractthe infiltration of river water into aquifers is of high relevance to drinking water production and is a key driver of biogeochemical processes in the hyporheic and riparian zone but the distribution and quantification of the infiltrating water are difficult to determine using conventional hydrological methods e g borehole logging and tracer tests by time lapse inverting crosshole ert electrical resistivity tomography monitoring data we imaged groundwater flow patterns driven by river water infiltrating a perialpine gravel aquifer in northeastern switzerland this was possible because the electrical resistivity of the infiltrating water changed during rainfall runoff events our time lapse resistivity models indicated rather complex flow patterns as a result of spatially heterogeneous bank filtration and aquifer heterogeneity the upper part of the aquifer was most affected by the river infiltrate and the highest groundwater velocities and possible preferential flow occurred at shallow t

are systematic variations in thrust belt style related to plate boundary processes the western alps versus the carpathians within the mediterranean region cenozoic deformation of the western alps and the west to east carpathians has resulted in two different styles of foreland fold and thrust belt the most prominent difference between the two belts is the presence carpathians or absence western alps of contemporaneous back arc extension but other important differences in structure topography and metamorphism also exist these differences in thrust belt style developed mainly during the final stages of thrust belt evolution and appear to reflect fundamental differences in the tectonic settings of the western alps and the carpathians in middle and late cenozoic time in particular they appear to be the result of convergence that is in the first case driven primarily by major plate motions and in the second case only by local motions of small lithospheric flakes or fragments we suggest that the structural styles developed in these two mountain belts may be useful in identifying mountain belts that have evolved in similar tectonic settings elsewhere in the world in this respect the western alps and the carpathians can be regarded as typical examples of two different styles of foreland fold and thrust belt or more properly as end member examples within a broad spectrum of foreland fold and thrust belt styles we propose that continental subduction zones and orogenic belts can be loosely divided into segments that show no major back arc extensional deformation adjacent to the belt the western alps and segments that exhibit back arc extension contemporaneously with thrusting the carpathians the former are found in areas where the rate of overall plate convergence exceeds the rate of subduction and are commonly typified by extensive involvement of crystalline basement in thrusting exposure of high grade metamorphic rocks at the surface high topographic elevation and large amounts of erosion tens of kilometers the latter are found in areas where the rate of subduction exceeds the rate of overall plate convergence and are commonly typified by thrust belts with little to no involvement of crystalline basement in thrusting low grade to no metamorphism low topographic elevation little erosion and in some instances an anomalously deep foredeep basin system

a statistical procedure for the analysis of seismotectonically induced hydrochemical signals a case study from the eastern carpathians romania changes in the stress field of an aquifer system induced by seismotectonic activity may change the mixing ratio of groundwaters with different compositions in a well leading to hydrochemical signals which in principle could be related to discrete earthquake events due to the complexity of the interactions and the multitude of involved factors the identification of such relationships is a difficult task in this study we present an empiric statistical approach suitable to analyse if there is an interdependency between changes in the chemical composition of monitoring wells and the regional seismotectonic activity of a considered area to allow a rigorous comparison with hydrochemistry the regional earthquake time series was aggregated into an univariate time series this was realized by expressing each earthquake in form of a parameter beq taking into consideration both energetic magnitude of a seismic event and spatial parameters position of epi hypocentrum relative to the monitoring site the earthquake and the hydrochemical time series were synchronised aggregating the e parameters into bearthquake activityq functions e which takes into account the time of sampling relative to the earthquakes which occurred in the considered area for the definition of the aggregation functions a variety of different beq parameters were considered the set of earthquake functions e was grouped by means of factor analysis to select a limited number of significant and representative earthquake functions e to be used further on in the relation analysis with the multivariate hydrochemical data set from the hydrochemical data a restricted number of hydrochemical factors were extracted factor scores allow to represent and analyse the variation of the hydrochemical factors as a function of time finally regression analysis was used to detect those hydrochemical factors which significantly correlate with the aggregated earthquake functions this methodological approach was tested with a hydrochemical data set collected from a deep well monitored for two years in the seismically active vrancea region romania three of the hydrochemical factors were found to correlate significantly with

elements of the archean thermal history and apparent polar wander of the eastern kaapvaal craton swaziland from single grain dating and paleomagnetism abstract single grains of zircon hornblende biotite and feldspar have been dated to define the thermal history of the archean mbabane pluton swaziland coincident207pb 206pb zircon and40ar 39ar hornblende ages suggest that the pluton underwent rapid cooling to about 450 c at the time of emplacement at 2690 ma because the mbabane pluton is one of a suite of granites which represent the last major archean intrusive event in the eastern kaapvaal craton this time of emplacement marks the end of cratonization much younger biotite and feldspar ages indicate argon loss perhaps due to several low temperature events related to dike intrusion at 2000 2300 ma from such a thermal history the age of magnetization of a paleomagnetic pole polelatitude 19 7 n polelongitude 105 7 e a95 9 4 k 67 obtained from 5 sites can be determined based on the unblocking temperature of the magnetic carrier and the consistent direction seen in several sites it appears that the hornblende age and coincidently the207pb 206pb zircon age most accurately represents this age of magnetization thus the mbabane pluton yields a precisely dated archean 2687 6 ma 2 hornblende plateau age paleomagnetic pole which is different than other archean poles such as that from the nearby usushwana complex 2875 40ma although the two intrusions are separated by less than 12 km and there is no evidence of relative structural rotation between them the paleomagnetic poles from the two bodies are 65 apart this implies that there was significant apparent polar wander during the late archean

40ar 39ar laser dating of biotite inclusions in a single crystal of magnetite the iron oxide mineral magnetite is widely used to study the past geomagnetic field because of its ability to record the ancient field at the time of its crystallization or cooling and because of its common occurrence in continental and oceanic rocks we present here the 40ar 39ar laser dating of one half of a 2 mm octahedral crystal of magnetite from an ultramafic rock near bush s corner harford county maryland in the appalachian piedmont the other half was examined by scanning electron microscopy sem to characterize the inclusions in the crystal laser step heating separates the argon isotopes released into three distinct phases a three dimensional isotope correlation plot illustrates the existence of a pure radiogenic component corresponding to an age of 323 5 ma this is the age of argon closure of minute biotite inclusions identified in the magnetite by sem and therefore is a precise estimate of the minimum age of the magnetite

differential rotation between lithosphere and mantle a consequence of lateral mantle viscosity variations the description of plate motions in the so called hotspot reference frame introduces a global rotation of the lithosphere with respect to the mantle this rotation called toroidal field of degree 1 is roughly westward it reaches an amplitude of about 2 cm yr and has been consistently found in the different generation of plate tectonic models various authors have tried to relate this observation to the deceleration of the earth s rotation to polar wander or to tidal drag however these different physical mechanisms cannot explain the requested amplitude in this paper we compare the values of this rotation vector using different relative plate motion models expressed in the hotspot reference frame in a model earth with lateral viscosity variations a differential rotation is predicted the observed net lithospheric rotation is consistent with the dynamics of a model earth where the asthenospheric viscosity below the oceans is at least one order of magnitude lower than underneath the continents this relative westward drift of the lithosphere may account for the significant structural differences between east or west dipping subduction zones

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

thermal modeling of the geometry of subduction with implications for the tectonics of the overriding plate the path which subducting lithosphere follows can be broken into three zones zone i a subhorizontal region of nearly constant dip near the trench zone ii a region of rapidly increasing dip and zone iii a region generally deeper than 125 km again of nearly constant dip we have modeled the thermal evolution of slabs as they pass through these three zones using the method of lines a numerical technique well suited to the solution of time dependent partial differential equations by use of appropriate initial conditions and time dependent boundary conditions we can simulate subduction with variations in age of subducting lithosphere slab velocities and paths followed by the slab thermal modeling results indicate that the geometry of the slab in region ii can be empirically related directly to the thermal structure of the slab in that region and thus indirectly to age and velocity it follows that low angle subduction can extend several hundred kilometers inland only in cases of high convergent velocities 15 cm yr 1 and old 120 m y lithosphere we further suggest that rapid variations in the convergence velocities can provide an enabling mechanism for back arc spreading while slow changes in convergence velocities and or age variations in the subducting lithosphere lead to migration of volcanic arcs

tertiary evolution of the intra carpathian area a model abstract the outer carpathian flysch nappes encircle an intra carpathian domain which can be divided into two megatectonic units north pannonian and tisza mostly on the basis of contrasting mesozoic and palaeogene facies development we see two major kinematic problems to be solved 1 1 the present distribution of the mesozoic and palaeogene facies is mosaic like and some belts form exotic bodies within realms of austroalpine affinity 2 2 late eocene palinspastic reconstruction of the outer carpathian flysch nappes suggest that the entire intra carpathian area must have been located several hundreds of kilometres to the south and to the west of its present position neogene extension can account for shortening in the external carpathian nappes but is unable to explain mesozoic facies anomalies and offsets of palaeogene formations we suggest that evolution of the intra carpathian area involved first late palaeogene early miocene juxtaposition of the north pannonian and tisza megatectonic units accompanied by the closure of the external carpathian flysch troughs thereafter extension of this amalgamated unit occurred which was compensated by thrusting of flysch nappes onto the european foreland and formation of molasse foredeeps eastward escape of the north pannonian unit from the alpine collisional belt involved left lateral shear along the pieniny klippen belt and right lateral shear along the mid hungarian zone parts of the late palaeogene basin and an early miocene volcanic edifice were dissected offset and elongated by several 100 kms the driving mechanism of the eastward escape of the intra carpathian area can be related to the collision of apulia and europe and the subduction of the external carpathian crust under the pannonian units the escape ceased gradually in the early miocene when oblique collision between the north pannonian unit and european continent occurred neogene extension of the pannonian region was an areal deformation the extension at locally variable rate resulted in the break up of the heterogenous floor of the neogene basin the driving mechanism of basin extension and contemporaneous compressional deformation of the external carpathians is thought to be related to ongoing subduction involving the marginal part of the attenuated european continental crust tectonic activity in the carpathians and basin subsidence and volcanism shifted in time and in unison from the west toward the east southeast

a note on the depth recurrence and strain release of large vrancea earthquakes the large 1940 vrancea event with body wave magnitude mb 7 3 was investigated in terms of the depth of rupture initiation and extent it was found that the rupture started at 150 km depth and propagated downwards the ruptured zones of the 1977 1986 and 1990 vrancea events were estimated from the distribution of aftershocks located with the joint hypocentre determination method their depth ranges are 90 110 km 130 150 km and 70 90 km respectively because the body wave magnitudes mb were saturated for the last three events and the surface wave magnitudes ms were underestimated not being corrected for depth we chose the moment magnitudes to quantify the four events 7 7 1940 7 4 1977 7 1 1986 and 6 9 1990 respectively the depth interval 110 130 km is found to be unbroken since at least 1838 or 1802 and therefore is expected to accommodate the next large moment release mw 7 0 to 7 4 the strain in the vertical and in the se nw directions is about 0 0003 giving a moderate strain rate of about 10 13 s 1 a correlation between the depth interval of the large events and the year of occurrence in a century is suggested offering a physical basis to the observed quasi cyclicity

geothermometry from 40ar39ar dating experiments abstract we have selected a variety of minerals from three basic intrusions within the high grade metamorphic terrane near haliburton ontario for k ar dating by application of 40 ar 39 ar incremental heating experiments we conclude that the discordant k ar mineral dates can best be explained by a slow cooling history from the stepwise heating experiments we calculated isotopic closure temperatures using dodson s theory for slow cooling and from these constructed a cooling curve this curve was then compared to independent constraints to test the overall validity of our procedures and assumptions the results are geologically reasonable insofar as 1 a the maximum calculated temperatures from hornblendes of 700 c are consistent with independent approximate metamorphic grid arguments 2 b the ar closure temperatures for biotites 350 400 c are consistent with independent evidence and 3 c minerals with older k ar dates have higher calculated closure temperatures the resultant geological cooling curve implies that a maximum temperature of 700 c was reached before 1000 ma ago and thereafter the temperature decreased via changes in uplift and cooling rates to below 200 c by 700 ma ago we have discovered that plutonic plagioclases are very sensitive indicators comparable to k felds pars of ar loss and therefore can usefully extend the range of application of the 40 ar 39 ar stepwise heating method we also describe experiments in which we have tested the effects on the ar systematics of acid leaching of plagioclases

classification of rifted sedimentary basins of the pannonian basin system according to the structural genesis evolutionary history and hydrocarbon maturation zones abstract we apply the concept that sedimentary basins can be classified according to their structural genesis and evolutionary history to the tertiary rifts of the pannonian basin of eastern europe we have approached the classification by breaking the basins down into the cycles or stages that they comprise this approach helps us to understand the basin evolution better and allows us to compare the basins more easily the drivers that define the cycles of basin history are 1 basin forming tectonics 2 sedimentary processes and 3 basin modifying tectonics we link common elements of petroleum systems and plays to these natural cycles or stages in basin evolution to improve the prediction of which plays could be expected to occur in a particular basin or region this concept is constructed through several steps these steps are 1 to identify standard evolutionary patterns related to geodynamic drivers 2 to group the basins with similar tectono stratigraphic evolution and correlate these with petroleum system development 3 to relate basin trap types to basin history and 4 to calculate characteristic hydrocarbon maturation zones by thermal modeling we present an application to the pannonian basin system of eastern europe an area formed by miocene back arc extension and affected by compressional reactivation during its late stage evolution the sub basins of the pannonian basin system appear to have experienced comparable magnitudes of deformation to have developed similar trap types and to have experienced a characteristic hydrocarbon maturation history in a way that supports play prospectivity

the thermal regime of a three dimensional subducting lithospheric slab and its electromagnetic response a numerical model abstract a three dimensional subducting lithospheric slab is simulated by a numerical technique and its temperature regime investigated a single slab model or models with multiple slab sections can be considered an example is shown of two slab sections that dip at different angles the near surface heat flow above the slab is considered and compared with a two dimensional model the temperature changes of particular points within the slab are monitored as it subducts and compared with the two dimensional case considerable differences exist between the two and three dimensional cases depending on the location of the point considered an electromagnetic model is derived from the thermal model and the perturbations of time varying electromagnetic fields caused by the electrical resistivity variations associated with the temperature variations are investigated

main differences between thrust belts it is useful to differentiate between thrust belts that are related to east e dipping or west w dipping subduction more precisely these either follow or resist the overall eastward mantle flow detected by the hot spot reference frame because of the overall westward drift of the lithosphere we find in e dipping subduction that the basal decollement underlying the eastern plate reaches the surface and involves deep crustal rocks with w dipping subduction however we find that the basal decollement of the eastern plate is warped as well as subducted consequently thrust belts related to e or ne dipping subduction show conspicuous structural and morphologic relief involve deep crustal rocks and are associated with shallow foredeeps on the other hand thrust belts related to w or sw dipping subduction show relatively low structural and morphological relief involve only shallow upper crustal rocks and are associated with deep foredeeps as well as back arc extension the accretionary wedge foredeep back arc basin association is visualized as an overall eastward propagating tectonic wave the accretionary wedge forms in the frontal parts and generally below sea level this is followed by forward migrating extension that cuts the earlier accretionary wedge typically such a system occurs in the context of overall w dipping subduction and is characterized by an arcuate shape e g carpathians apennines barbados etc along the branches of the arc external transpression and internal transtension co exist but with different sense i e sinistral transpression contrasting with dextral transtension we also observe that with w dipping subduction the tangent to a pre deformation marker is descending into the foredeep at an angle in the range of 1 10 while with e or ne dipping subduction the same marker would rise towards the hinterland with typical angles of about 5 10 foredeep subsidence is mainly controlled by the load of the thrust sheets in thrust belts due to e or ne dipping subduction and by the roll back of the subduction hinge in accretionary wedges due to w dipping subduction subsidence or uplift rates in the foredeeps and accretionary wedges related to the two different types of subduction are very different providing different p t t paths in the two geodynamic realms the present shape and structure of the thrust belts belonging to one of these two general types may help us in reconstructing the location of thinned lithosphere and basin evolution in the past

s wave attenuation characteristics beneath the vrancea region in romania new insights from the inversion of ground motion spectra the s wave attenuation characteristics beneath the vrancea region in romania are analyzed from the spectra frequency range 0 5 20 hz of more than 850 recordings at 43 accelerometric stations of 55 intermediate depth earthquakes m 4 0 7 1 that occurred in the vrancea seismogenic zone the method commonly chosen for this type of investigation in the case of crustal earthquakes is the generalized inversion technique git e g andrews 1986 castro et al 1990 yet the vrancea dataset is entirely different from common crustal datasets because of the strong clustering of the hypocenters within a very small focal volume there are only few crossing ray paths from sources to receivers as a consequence inhomogeneities in the attenuation properties are not averaged out which leads to unphysical results if the standard git approach is adopted the problem is discussed qualitatively by performing tests with synthetic data and solved quantitatively by adapting the git technique in view of these peculiarities with the optimally adapted inversion scheme it is possible to unravel differences in the attenuation characteristics between two or more sets of stations the results show that the attenuation of seismic waves is roughly comparable in the low frequency range 4 5 hz but stronger by up to an order of magnitude at higher frequencies within the carpathian mountain arc as compared with the foreland area modeling this strongly frequency dependent lateral variation of seismic attenuation by a significantly lower q beneath vrancea 1 provides a very good fit of observed strong motion characteristics 2 sheds new light on the distribution of intensities of the previous strong earthquakes 3 will have strong implications for future hazard assessment and 4 is fully compatible with structural models from deep seismic sounding tomography and teleseismic attenuation

thermal structure of the crust and upper mantle of romania abstract a synthesis of the heat flow data for romania enabled a study of the thermal regime of the crust and upper mantle to be made this showed lateral thermal differences between various tectonic units the thermal structure of the crust and upper mantle appears to be mainly the result of mantle convection and plate interaction in the studied area

challenges and opportunities for fractured rock imaging using 3d cross borehole electrical resistivity abstractthere is an increasing need to characterize discrete fractures away from boreholes to better define fracture distributions and monitor solute transport we performed a 3d evaluation of static and time lapse cross borehole electrical resistivity tomography ert data sets from a limestone quarry in which flow and transport are controlled by a bedding plane feature ten boreholes were discretized using an unstructured tetrahedral mesh and 2d panel measurements were inverted for a 3d distribution of conductivity we evaluated the benefits of 3d versus 2 5d inversion of ert data in fractured rock while including the use of borehole regularization disconnects brds and borehole conductivity constraints high conductivity halos inversion artifacts surrounding boreholes were removed in static images when brds and borehole conductivity constraints were implemented furthermore applying these constraints focused transient changes in conductivity resulting from solute transport on the bedding plane pr

thermal evolution and geometry of the descending lithosphere beneath the se carpathians an insight from the past abstract mantle heterogeneities imaged by seismic tomography in the se carpathians contain information on the present thermal state of the mantle based on p wave seismic velocity anomalies we develop a model of the present mantle temperature beneath the region and combine the model with a model of crustal temperature constrained by heat flow data the modeled temperatures are assimilated into the geological past using the information on the regional movement in the early and middle miocene prominent thermal states of the lithospheric slab descending in the region are restored from its diffuse present state in miocene times the slab geometry clearly shows two portions of the sinking body the northwest southeast oriented portion of the body is located in the vicinity of the boundary between the east european and scythian platforms and this portion of the sinking body may be a relic of cold lithosphere that has traveled eastward another portion has a northeast southwest orientation and is related to the present descending slab above a depth of 60 km the slab had a concave thermal shape confirming the curvature of the carpathian arc and a convex surface below that depth the slab maintained its convex shape until it split into two parts at a depth of about 220 km we propose that this change in the slab geometry which is likely to be preserved until the present can cause stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region also we hypothesize that either the processes of dehydration and partial melting of the descending lithospheric slab or dragging down of hotter rocks from the adjacent uppermost mantle by the slab are possible causes of the reduction in seismic velocities beneath the transylvanian basin

imaging high stage river water intrusion into a contaminated aquifer along a major river corridor using 2 d time lapse surface electrical resistivity tomography the hanford 300 area is located adjacent to the columbia river in south central washington state usa and was a former site for nuclear fuel processing operations waste disposal practices resulted in persistent unsaturated zone and groundwater contamination the primary contaminant of concern being uranium uranium behavior at the site is intimately linked with river stage driven groundwater river water exchange such that understanding the nature of river water intrusion into the 300 area is critical for predicting uranium desorption and transport in this paper we use time lapse electrical resistivity tomography ert to image the inland intrusion of river during high stage conditions we demonstrate a modified time lapse inversion approach whereby the transient water table elevation is explicitly modeled by removing regularization constraints across the water table boundary this implementation was critical for producing meaningful imaging results we inverted approximately 1200 data sets 400 per line over 3 lines using high performance computing resources to produce a time lapse sequence of changes in bulk conductivity caused by river water intrusion during the 2011 spring runoff cycle over approximately 125 days the resulting time series for each mesh element was then analyzed using common time series analysis to reveal the timing and location ofmore river water intrusion beneath each line the results reveal non uniform flows characterized by preferred flow zones where river water enters and exits quickly with stage increase and decrease and low permeability zones with broader bulk conductivity break through curves and longer river water residence times the time lapse ert inversion approach removes the deleterious effects of changing water table elevation and enables remote and spatial continuous groundwater river water exchange monitoring using surface based ert arrays under conditions where groundwater and river water conductivity are in contrast less

testing the apatite magnetite geochronometer u pb and 40ar 39ar geochronology of plutonic rocks massive magnetite apatite tabular bodies and iocg mineralization in northern chile abstract detailed zircon and apatite u pb dating and 40 ar 39 ar dating of actinolite have been carried out on the carmen sierra aspera kiruna type magnetite apatite and iron oxide cu au iocg district in the coastal cordillera of northern chile 26 s they define a precise succession of magmatic and hydrothermal events associated with early cretaceous andean magmatism apatite and magnetite from a magnetite apatite tabular body with intergrowth texture in the carmen deposit yield a total pb u isochron age of 131 0 1 0 ma this result is the first direct dating of magnetite apatite mineralization in an early andean deposit and the age coincides with zircon ages of a quartz diorite stock that partially hosts mineralization 130 6 0 3 ma magnetite from the studied tabular body contains only small amounts of radiogenic pb and serves to constrain the initial common pb isotopic composition the high degree of correlation suggests that both minerals closed for pb diffusion at essentially the same time and at a relatively high temperature close to that of zircon making the apatite magnetite pair a reliable geochronometer for igneous or hydrothermal crystallization zircon from the sierra aspera composite pluton yields ages between 131 3 0 3 ma and 127 4 0 1 ma clearly resolving the timing of intrusion of discrete intrusive phases actinolite 40 ar 39 ar ages partially overlap the ages of plutonic phases of the sierra aspera pluton but are younger than the magnetite apatite tabular body the initial pb isotopic composition of the melts and or fluids from which the magnetite apatite tabular bodies crystallized is very similar to the primitive pb isotopic composition of granitic magmas associated with early cretaceous plutons measured in k feldspar the pb isotopic correspondence combined with the temporal and spatial association between magnetite apatite mineralization and the dioritic quartz dioritic magmatism strongly suggests a genetic relationship between early cretaceous continental arc magmatism massive magnetite apatite deposits and iocg mineralization

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

three dimensional numerical modeling of contemporary mantle flow and tectonic stress beneath the earthquake prone southeastern carpathians based on integrated analysis of seismic heat flow and gravity data the principal purpose of the study is to understand the interplay between intermediate depth large earthquakes in the southeastern carpathians vrancea and tectonic stress induced by a high velocity body lithospheric slab descending into the mantle beneath the region to analyze processes of stress generation and localization in and around the descending slab we develop a three dimensional 3d numerical model of contemporary mantle flow and stress beneath the vrancea region the input data of the model consist of i temperatures derived from seismic p wave velocity anomalies and surface heat flow ii crustal and uppermost mantle densities converted from p wave velocities obtained from seismic refraction studies iii geometry of the vrancea crust and slab from tomography and refraction seismic data and iv the estimated strain rate in the slab as a result of earthquakes to constrain the model viscosity we find that major crustal uplifts predicted by the model coincide with the east carpathian orogen and surround the transylvanian basin and that predicted areas of subsidence are associated with the moesian and east european platforms we show a correlation between the location of intermediate depth earthquakes and the predicted localization of maximum shear stress modeled tectonic stresses predict large horizontal compression at depths of about 70 220 km beneath the vrancea region which coincides with the stress regime defined from fault plane solutions for the intermediate depth earthquakes this implies that buoyancy driven descent of the lithospheric slab beneath the vrancea region is directly linked to intermediate depth seismicity 2004 elsevier b v all rights reserved

crustal phases in earthquake location for crustal earthquakes of moderate or large size the first reported phases at distant stations are usually the first predicted by the crustal model used for smaller events however or for stations at larger distances the first phase detected is often a later crustal phase of larger amplitude this may be eitherpg which travels entirely in the upper crustal layer with a velocity of about 5 6 km s orp with a path mainly in the lower crustal layer at a velocity of about 6 7 km s many earthquake location programs do not take account of these phases and treat their arrivals as if they were the earlier phasepn at the international seismological centre we re identify up to 200 crustal phases each month this often results in significant improvement in position the direct determination of depth or even the obtaining of a formal solution where none was possible before we find that these re identifications are needed in most continental areas of the world and that the original crustal model of jeffreys and bullen still remains a useful standard

crosshole gpr full waveform inversion of waveguides acting as preferential flow paths within aquifer systems high contrast layers caused by porosity or clay content changes can have a dominant effect on hydraulic processes within an aquifer these layers can act as low velocity waveguides for gpr waves we used a field example from a hydrological test site in switzerland to show that fullwaveform inversion of crosshole gpr signals could image a subwavelength thickness low velocity waveguiding layer we exploited the full information content of the data whereas ray based inversion techniques are not able to image such thin waveguide layers because they only exploit the first arrival times and first cycle amplitudes this lowvelocity waveguide layer is caused by an increase in porosity and indicates a preferential flow path within the aquifer the waveguide trapping causes anomalously high amplitudes and elongated wavetrains to be observed for a transmitter within thewaveguide and receivers straddling thewaveguide depth range the excellent fit of amplitudes and phase between the measured and modeled data confirms its presence this new method enables detailed aquifer characterization to accurately predict transport and flow and can be applied to a wide range of geologic hydrological and engineering investigations

surface downhole electrical resistivity tomography applied to monitoring of co2 storage at ketzin germany abstractsurface downhole electrical resistivity tomography sd ert surveys were repeatedly carried out to image co2 injected at the pilot storage ketzin germany the experimental setup combines surface with downhole measurements by using a permanent electrode array that has been deployed in three wells two baseline experiments were performed during the site startup and three repeat experiments were performed during the first year of co2 injection by the time of the third repeat approximately 13 500 tons of co2 had been injected into the reservoir sandstones at about 650 m depth field data and inverted resistivity models showed a resistivity increase over time at the co2 injector the lateral extent of the related resistivity signature indicated a preferential co2 migration toward the northwest using an experimental resistivity saturation relationship we mapped co2 saturations by means of the resistivity index method for the latest repeat co2 saturations show values of up to 70 near the injectio

the borehole fluid effect in electrical resistivity imaging fluid that fills boreholes in crosswell electrical resistivity investigations provides the necessary electrical contact between the electrodes and the rock formation but it is also the source of image artifacts in standard inversions that do not account for the effects of the boreholes the image distortions can be severe for large resistivity contrasts between the rock formation and borehole fluid and for large borehole diameters we have carried out 3d finite element modeling using an unstructured grid approach to quantify the magnitude of borehole effects for different resistivity contrasts borehole diameters and electrode configurations relatively common resistivity contrasts of 100 1 and borehole diameters of 10 and 20 cm yielded for a bipole length of 5 m apparent resistivity underestimates of approximately 12 and 32 when using ab mn configurations and apparent resistivity overestimates of approximately 24 and 95 when usingam bn configurations effects are generally more severe at shorter

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

quantification of carbon dioxide emissions of ciomadul the youngest volcano of the carpathian pannonian region eastern central europe romania abstract we provide the first high resolution co 2 flux data for the neogene to quaternary volcanic regions of the entire carpathian pannonian region eastern central europe and estimate the co 2 emission of the seemingly inactive ciomadul volcanic complex the youngest volcano of this area our estimate includes data from focused and diffuse co 2 emissions from soil the co 2 fluxes of focused emissions range between 277 and 8172 g d 1 corresponding to a co 2 output into the atmosphere between 0 1 and 2 98 t per year the investigated areas for diffuse soil gas emissions were characterized by wide range of co 2 flux values at apor baths ranging from 1 7 10 1 to 8 2 10 4 g m 2 d 1 while at l z re ti ranging between 1 43 and 3 8 10 4 g m 2 d 1 the highest co 2 focused gas fluxes at ciomadul were found at the periphery of the youngest volcanic complex which could be explained either by tectonic control across the brittle older volcanic edifices or by degassing from a deeper crustal zone resulting in co 2 flux at the periphery of the supposed melt bearing magma body beneath ciomadul the estimate of the total co 2 output in the area is 8 70 10 3 t y 1 and it is consistent with other long 10 kyr dormant volcanoes with similar age worldwide such as in italy and usa taking into account the isotopic composition of the gases that indicate deep origin of the co 2 emissions this yields further support that ciomadul may be considered indeed a dormant or pams volcano volcano with potentially active magma storage rather than an inactive one furthermore hazard of co 2 outpourings has to be taken into account and it has to be communicated to the visitors finally we suggest that co 2 output of dormant volcanic systems has to be also accounted in the estimation of the global volcanic co 2 budget

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

geophysical analysis of major geothermal anomalies in romania the romanian segment of the eastern pannonian basin and the moesian platform are known for their geothermal and hydrocarbon bearing structures we used seismic gravity and geothermal data to analyze the geothermal behavior in the oradea and timisoara areas from the romanian segment of eastern pannonian basin and the craiova bals optasi area from the moesian platform we processed 22 seismic reflection data sets recorded in the oradea and timisoara areas to obtain p wave velocity distributions and time seismic sections the p wave velocity distributions correlate well with the structural trends observed along the seismic lines we observed a good correlation between the high areas of crystalline basement seen on the time seismic sections and the high heat flow and gravity anomaly values for the craiova bals optasi area we computed a three dimensional 3d temperature model using calculated and measured temperature and geothermal gradient values in wells with an irregular distribution on the territory the high temperatures from the craiova bals optasi area correlate very well with the uplifted basement blocks seen on the time seismic sections and high gravity anomaly values

lithosphere asthenosphere interaction at the southeastern carpathian arc bend implications for anisotropy abstract the vrancea region in the southeastern carpathians romania represents a unique case among the seismic areas in the world taking into account the extreme concentration and persistence of seismicity and the tectonic stress field subduction in a post collisional phase is still active in a narrow area located at the sharp bend of the mountain belt our goal is to show that the particular shape of the shear wave splitting can be interpreted in the light of the decoupling and slab retreat processes which hypothetically induce a specific configuration of the upper mantle flow shear wave splitting of sks phases shows a relatively coherent pattern outside the epicentral area suggesting a prominent ne sw anisotropy in agreement with previous estimations performed in central and eastern europe and following the trends of the deformation field as outlined by the gps measurements a clear change is pointed out inside the vrancea area where strike parallel polarization is emphasized toward the nw wedge side the polarization turns to a strike perpendicular direction in agreement to an upwelling asthenospheric flow in the back arc region i e polarization aligned to the local strike of the slab these shear wave splitting attributes are not consistent with conventional models of 2 d mantle flow near subduction zones nor with a sub vertical down dipping flow driven by the sinking of the slab they correlate well with lateral inhomogeneities outlined by the tomography image heat flow seismic wave attenuation and thermal field we suggest that the eastward slab retreat and decoupling between the underlying asthenosphere and the slab itself have induced strike parallel mantle flow likely favoring detachment of the slab along the arcuate mountain belt these processes are directly related to the strong anisotropy observed in the se carpathians the anisotropy and gps data suggest a strong coupling of the surface and mantle processes

characterization of a contaminated wellfield using 3d electrical resistivity tomography implemented with geostatistical discontinuous boundary and known conductivity constraints abstractcontinuing advancements in subsurface electrical resistivity tomography ert are increasing its capabilities for understanding shallow subsurface properties and processes the inability of ert imaging data to resolve unique subsurface structures and the corresponding need to include constraining information remains one of the greatest limitations yet provides one of the greatest opportunities for further advancing the utility of the method we propose a new method of incorporating constraining information into an ert imaging algorithm in the form of discontinuous boundaries known values and spatial covariance information we demonstrated the approach by imaging a uranium contaminated wellfield at the hanford site in southeastern washington state usa we incorporate into the algorithm known boundary information and spatial covariance structures derived from the highly resolved near borehole regions of a regularized ert inversion the resulting inversion provides a solution which fits the ert d

recognition of extraneous argon components through incremental release 40ar39ar analysis of biotite and hornblende across the grenvillian metamorphic gradient in southwestern labrador 40ar39ar incremental release ages have been determined for 15 hornblende and 20 biotite concentrates separated from rocks collected across the garnet and kyanite zones of grenvillian metamorphism in southwestern labrador most hornblende spectra from the kyanite zone are slightly discordant with low temperature increments yielding ages older than the ca 1000 ma date suggested for culmination of grenvillian metamorphism in the area however all the hornblende concentrates record well defined plateau ages these range from 968 to 905 ma across the kyanite zone and date times of diachronous post metamorphic cooling the discordant spectra are interpreted to result from low temperature liberation of excess 40ar components from grain margins two hornblende concentrates from the garnet zone display very discordant spectra total gas ages of 2100 and 3017 ma in which incremental dates systematically decrease during analysis this pattern of discordance suggests that excess argon components are inhomogeneously distributed throughout these hornblende grains most biotites from the garnet and kyanite zones record total gas or plateau ages in excess of 1000 ma 2066 857 ma reflecting the widespread presence of excess argon components because most of the 40ar39ar age spectra are internally concordant the ratios of excess 40ar relative to radiogenic 40ar must have been uniform in the various gas fractions liberated from each sample this is also reflected in the inability of isotope correlation diagrams to differentiate between excess radiogenic and atmospheric argon components the biotite total gas or plateau dates show marked local variation this is interpreted to indicate that the biotite grains were in contact with a post metamorphic intergranular vapor phase that was characterized by large and variable 40ar36ar ratios such ratios most likely resulted from widespread diffusion of the argon liberated from adjacent archean basement gneisses during the grenvillian metamorphic overprint

zonation for 3d aquifer characterization based on joint inversions of multimethod crosshole geophysical data predictive groundwater modeling requires accurate information about aquifer characteristics geophysical imaging is a powerful tool for delineating aquifer properties at an appropriate scale and resolution but it suffers from problems of ambiguity one way to overcome such limitations is to adopt a simultaneous multitechnique inversion strategy we have developed a methodology for aquifer characterization based on structural joint inversion of multiple geophysical data sets followed by clustering to form zones and subsequent inversion for zonal parameters joint inversions based on cross gradient structural constraints require less restrictive assumptions than say applying predefined petrophysical relationships and generally yield superior results this approach has for the first time been applied to three geophysical data types in three dimensions a classification scheme using maximum likelihood estimation is used to determine theparameters of a gaussian mixture model that defines zonal geometries

strategies for characterization of fractured rock using cross borehole electrical tomography there is an increasing need to characterize fractured rock systems and to monitor the movement of fluids in these systems fractured rock aquifers are increasingly exploited for water resources and are subject to contamination from industrial activities at the earth s surface deep rock repositories of hazardous waste must be carefully characterized in terms of fracture transport characteristics more recently there has been a surge in technologies designed to increase permeability of shale reservoirs by creating fractures to promote fluid removal however fractured rock systems present unique challenges for characterization and monitoring technologies fracturing typically generates highly heterogeneous and anisotropic systems making the evaluation of the distribution of physical properties from sparse subsurface measurements particularly problematic geophysical imaging technologies are increasingly applied in an effort to overcome the limitations of sparsely located direct observations of subsurfac

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

the evolution of the pannonian depression romanian sector as derived from subsidence and heat flow data abstract a quantitative analysis of subsidence sedimentation and thermal evolution of the romanian sector of the pannonian depression is presented based on subsidence data from 75 boreholes uniformly distributed over the study area and on heat flow data the hydrocarbon generation window for neogene sedimentary formations is also estimated borehole heat flow and crustal thickness data support an extension of the lithosphere of 0 40 the excess heat in lithosphere was estimated to be 15 30 mw m 2 the result of lithospheric material ascending during extension the lithosphere thickness is at least 15 20 greater than the 65 75 km currently estimated by steady state conduction models in the case of the badenian 16 5 13 ma sarmatian 13 11 5 ma and early pannonian 11 5 5 1 ma formations conditions for hydrocarbon generation are fulfilled in certain areas

40ar 39ar ages of precambrian manganese ore minerals from sweden india and morocco in order to test their chronometric potential 40ar 39ar stepheating and 4he analyses have been carried out on five manganese ore minerals of the hollandite cryptomelane series from three precambrian manganese deposits ultevis sweden sitapar india bachkoun morocco samples from the metamorphic occurrences ultevis and sitapar yielded ar ages of 1 8 ga and 0 95 ga interpreted as the age of postmetamorphic cooling hollandites ultevis and of an early k introducing alteration process subsequent to amphibolite facies metamorphism cryptomelanes sitapar both data are consistent with known chronologies of the svecokarelian and satpura orogenic cycles a date of 670 ma obtained for a hollandite from a volcanogenic vein deposit bachkoun however contrasts with published extrusion ages of 580 560 ma for the volcanic host rocks ouarzazate series probably due to incorporation of excess argon the use of the 40ar 39ar technique together with multiple isotope systematics made it nevertheless possible to establish a reasonable estimate of a mineralization age close to 580 ma measurement of fractional ar losses during vacuum step heating 500 1600 c although indicating good ar retentivities failed to define model diffusion parameters because of non linear arrhenius arrays helium diffusion results 200 1200 c indicated retention of radiogenic 4he by the samples corroborated by u he mineral dates between 0 96 and 0 31 ga potassium bearing manganese oxides are therefore able to retain argon possibly also 4he through geological times and may thus provide ages of ore forming processes and perhaps later cooling and alteration stages

partial delamination of continental mantle lithosphere uplift related crust mantle decoupling volcanism and basin formation a new model for the pliocene quaternary evolution of the southern east carpathians romania abstract a geodynamic model is proposed for the mid miocene to quaternary evolution of the southern east carpathians in order to explain the relationships between shallow and deep geological phenomena that occurred synchronously during late collision tectonics in this area an active volcanic zone cross cuts since 2 my the suture between the overriding tisza dacia and subducting european continental plates mafic calc alkaline and alkaline magmas south harghita and persani volcanoes erupted contemporaneously these magmas were supplied by partial melting of the mantle lithosphere of the subducting and not of the overriding plate in an effort to decipher this geodynamically a typical setting of magma generation the spatial and temporal distribution of shallow and deep phenomena was successively examined in order to establish the degree of their interdependence our model indicates that intra mantle delamination of the subducting european plate is the principal cause of a succession of events it caused upwelling of the hot asthenosphere below a thinned continental lithosphere of the carpathians inducing the uplift of the lithosphere and its internal decoupling at the moho level by isostatic and mostly thermal effects during this uplift the crust deformed flexurally whilst the mantle deformed in a ductile way this triggered decompressional partial melting of the uppermost mantle lithosphere flexural deformation of the crust induced its fracturing allowing for the rapid ascent of magmas to the surface as well as reactivation of an older detachment horizon at the base of the carpathian nappe stack above which the brasov ciuc and gheorghieni hinterland basins formed by extension and gravity spreading the rapid subsidence of the focsani foreland basin is controlled by the load exerted on the lithosphere by the delaminated mantle slab that is still attached to it in this model crust mantle decoupling magma genesis and volcanism local near surface hinterland extension are consequences of uplift induced by asthenospheric upwelling triggered by intra mantle delamination this model enables to conceive that delamination induced decoupling began to be efficient 9 4 my ago at the northern end of the east carpathians when the mantle slab dipped westwards since then intra mantle delamination migrated laterally normal to the slab strike and follows the arcuate shape nw se sw of the carpathians nowadays whereas the mantle slab is still actively foundering below the vrancea seismic zone to the se of the most recent volcanic area south harghita persani a significant southwestward shift of the delamination process can be discerned

time dependent thermal state of the lithosphere in the foreland of the eastern carpathians bend insights from new geothermal measurements and modelling results summary the time dependent heat budget thermal evolution and rheology of the lithosphere in the last 13myr along a 120 km long profile in the foreland of the eastern carpathians bend is presented the study area a complex tectonic environment in the vicinity of the wellknown intermediate depth seismogenic vrancea zone includes the deepest sedimentary basin in romania 18 km with a recent rapid evolution in the last 13myr 8 km of sediments detailed high resolution temperature logs in the depth ranges from 0 700 m to 0 2400 m in eight thermally stabilized boreholes together with logging and geological information on structure lithology and time evolution of the sedimentary pile have been used to model the thermal evolution by means of a 2 d finite element model which includes sedimentation history sediment compaction lateral and vertical variation of thermal properties of sediments and consolidated crust modelling results have been compared to measured temperatures corrected for palaeoclimate effects in a trial and error iterative approach sedimentation palaeoclimate undercompaction and heat refraction effects on one hand and the heat generated in the upper crust on the other combine to explain the observed subsurface temperature field and in particular the pronounced curvature of the vertical temperature profiles the neogene quaternary sedimentation resulted in a rather uniform deficit of the surface heat flux of about 12 mw m 2 in the study area in spite of the marked lateral variation of the sedimentary pile thickness the palaeoclimate effect is responsible for a surface heat flux depression of 7 8 mw m 2 uniform along the study profile unlike older sedimentary basins in the study area transient sedimentation thermal effects add to palaeoclimate effects in establishing the temperature field in the depth range of geothermal measurements the lateral variation of the palaeoclimatically corrected surface heat flux from the centre of the focsani depression 40 mw m 2 to its margin and the foreland platform 70 mw m 2 is mainly the result of the lateral variation of the heat produced in the upper crust where thickness varies from 7 to 21 km respectively a heat production of 2 3 wm 3 for the southeastern end of the profile and of 2 15 wm 3 for the rest of it has been modelled as a result of the sedimentation process temperature variations as large as 70 100 c occurred in the pre neogene sediments and the crystalline crust immediately under the sedimentary pile with consequences on the metamorphic state and rheological behaviour of the foreland

outer space sensitivities in geoelectrical tomography geoelectrical imaging is the preferred method for resolving a wide range of problems associated with the subsurface barker 1997 rubin and hubbard 2005 modern multielectrode arrays griffiths and turnbull 1985 stummer et al 2002 allow geoelectrical data to be acquired efficiently in diverse environments and user friendly inversion software e g loke 1999 can be used to convert the recorded data to meaningful subsurface models

tomographic imaging of deep velocity structure beneath the eastern and southern carpathians romania implications for continental collision the vrancea seismic zone located beneath the elbow of the eastern and southern carpathians is characterized by intermediate depth seismicity associated with subduction and plate collision among many strong earthquakes that have occurred in the region the 1977 vrancea earthquake march 4 1977 ms 7 1 depth of 86 km caused extensive damage and fatalities the vrancea seismic zone is defined by a tabular region of seismicity that extends from the surface to a depth of 200 km the small size about 80 km in length and 40 km in width and geometry of the seismic zone have made it difficult to interpret the kinematics of subduction and continental collision in the romanian carpathians to better understand the collision subduction environment body wave seismic tomography was used to image the deep structure beneath the eastern and southern carpathians in romania a total of 7837 p and 2292 s arrival times from 433 shallow and intermediate depth earthquakes recorded by local and regional seismic stations were inverted for the three dimensional 3 d seismic velocity structure the travel times and ray paths were calculated by an efficient 3 d ray tracing technique by utilizing the lsqr algorithm p and s wave velocity perturbations were determined from the surface down to a depth of 200 km the high resolution p wave tomographic images reveal a pattern of broad heterogeneity in the velocity structure of the region one of the most important features is a high velocity body existing beneath the carpathian arc at depths between 100 and 170 km this high velocity body outlines a slab dipping near vertically where most of the intermediate depth earthquakes occur beneath the transylvanian basin a high velocity zone is dipping toward the se and may represent the base of lithosphere which is in convergence with the subducted slab low velocity bodies are found along the forearc of the carpathian foredeep down to depths of 70 to 80 km these low velocity bodies may be correlated with the shallow sedimentary layer in the foreland and may represent crustal materials wedged and underthrust along with the subducted lithosphere