selenium in volcanic environments a review abstract selenium is a chemical element with major environmental implications due to the extremely narrow range between essential and toxic concentrations volcanoes emit significant amounts of se which has an enormous impact on the se cycle and potentially human and animal health this paper presents a broad overview of the current state of knowledge of major aspects of volcanic derived se focussing on the processes in soils and aquifers volcanic soils formed when volcanic products weather rapidly display peculiar characteristics selenium contents can be relatively high 1 2 orders of magnitude higher compared to the worldwide average 0 4 mg kg but often with low mobility the soils can be impacted by local deposition of volcanic emissions which are enriched in se due to volatilization in the magma chamber it seems that the chemical fate of se in volcanic soils is controlled by sorption processes on poorly crystalline phases which presence depends on the parental materials and weathering these sorption processes also determine leaching to groundwaters some volcanic aquifers have se concentrations above the who guideline of 10 g l this might also be related to geothermal activity in spite of the well documented interest on se during the last decades a significant number of uncertainties exist on the behavior of this fascinating element a preliminary model of the se cycle around volcanoes can be constructed but the well known analytical problems associated with se determinations have produced a lack of reliable information on some processes involved in the chemical interaction between soils and water this review therefore also aims to identify the processes where new efforts are needed to produce good quality data to be compared and integrated in global models

metamorphosed gabbroic dikes related to opening of iapetus ocean at the st lawrence promontory blair river inlier nova scotia canada abstract metamorphosed mafic dikes in the laurentian blair river inlier of northern cape breton island nova scotia are related to the opening of the iapetus ocean during the breakup of the supercontinent rodinia the dikes were metamorphosed during a paleozoic likely silurian thermal event related to appalachian orogenesis but were not deformed significantly two dikes yielded u pb zircon ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 581 pm 6 end document and documentclass aastex usepackage amsbsy usepackag

the caldwell group lavas of southern quebec morb like tholeiites associated with the opening of iapetus ocean the caldwell group belongs to the internal nappe domain of the humber zone and consists of basaltic lavas quartzo feldspathic sandstones and mudslates the lavas are clinopyroxene plagioclase olivine phyric tholeiites and are typically altered to epidote chlorite carbonate and or hematite rich secondary assemblages in most cases the high field strength elements do not appear to have been perturbed by the alteration and preserve magmatic signatures most caldwell basalts exhibit coupled major and trace element variations compatible with low to medium pressure 10 kbar where 1 kbar 100 mpa fractional crystallization paleotectonic discriminants imply an ocean floor or normal mid ocean ridge basalt n morb affinity most basalts have flat n morb normalized profiles except for the highly incompatible elements ba th nb which show slight relative enrichment melting models suggest that most of these lavas formed by about 20 melting from a mantle slightly less depleted than fertil

environmental problems at the nevsehir kozakli geothermal field central turkey the kozakli nevsehir geothermal field extends a long a nw se direction at se of the centrum of kozakli the area is not rugged and average elevation is 1 000 m the kozanozu creek flows towards north of the area in the kozakli thermal spa area thermal waters are manifested along a valley with a length of 1 5 km and 200 m width in this resort some hot waters are discharged with no use the thermal water used in the area comes from wells drilled by mta in addition these waters from wells are also utilized by hotels baths and motels belonging to city private management municipality and private sector the measured temperature of kozakli waters ranges from 43 51 c in springs and 80 96 c in wells waters are issued in a wide swampy area as a small group of springs through buried faults electrical conductivity values of thermal spring and well waters are 1 650 3 595 s cm and ph values are 6 72 7 36 kozakli cold water has an electrical conductivity value of 450 s cm and ph of 7 56 all thermal waters are dominated by na and cl so4 while cold waters are dominated by ca 2 and hco3 the aim of this study was to investigate the environmental problems around the kozakli geothermal field and explain the mechanisms of karstic depression which was formed by uncontrolled use of thermal waters in this area and bring up its possible environmental threats at the kozakli geothermal field a sinkhole with 30 m diameter and 15 m depth occurred in january 17th 2007 at the recreation area located 20 m west of the geothermal well which belongs to the government of nevsehir province the management of the geothermal wells should be controlled by a single official institution in order to avoid the creation of such karstic structures affecting the environment at the source area

a model for the simulation of combined major and trace element liquid lines of descent abstract variations of major and trace element partition coefficients as functions of temperature and composition have severely limited the range of composition for quantitative modeling of the differentiation of natural magmatic systems application of a two lattice melt model greatly reduces compositional dependence for trace elements this allows the temperature dependence of isobaric trace element partitioning to be evaluated independently thus making it possible to model an expanded range of conditions and compositions the first goal of this investigation was to construct a model to simulate major and trace element systematics of natural differentiation processes by combining trace element partitioning with a major element phase equilibrium model nielsen 1985b the second goal was the application of this model to the simulation of magma chamber recharge assimilation eruption and fractional crystallization these simulations indicate that the proportions of minerals fractionating from an open system are not necessarily the same as those in a closed system recharge or assimilation will drive a magma composition off the cotectic along which it is evolving however fractionation will drive the liquid back towards the cotectic in a recharged magma chamber as the recharge flux increases the fractionating mineral proportions will be increasingly biased towards those phases which appear first from the primitive magma the bulk partition coefficient for an open system can be considerably different 5 10 or more for some elements compared to a closed system paired assimilation and fractional crystallization are often cited as the mechanisms responsible for the origin of high al basalts and andesites however the addition of an al rich assimilant into a fractionating basaltic magma will increase the proportion of plagioclase to the extent that al in the derived liquids will be effectively buffered or even decrease the assimilation of forsteritic olivine by reaction keleman and ghiorso 1986 increases the proportions of pyroxene and olivine thus reducing the fe enrichment and al depletion characteristic of low pressure basalt fractionation

forward potential field modeling of the appalachian orogen in the gaspe peninsula quebec canada implications for the extent of rift magmatism and the geometry of the taconian orogenic wedge the nature and extent of potential source bodies associated with prominent regional scale gravity and magnetic anomalies in the northern quebec appalachians are investigated through forward modeling potential field anomalies are interpreted to be the geophysical expression of basalt flows extruded during the neoproterozoic to cambrian rifting of laurentia prior to opening of iapetus geophysi cal modeling provides substantial new constraints on seismic and structural cross sections and the map distribution of volcanism this study indicates that the volcanism was significantly more widespread than previously recognized basaltic rocks form a sheet up to 4 kilometers thick transported on the main taconic decollement most of this sheet is deeply buried and overlain by a thick pile of paleozoic sediments later tectonic modifications by backthrusting and hinterland directed normal faulting as well as by acadian strike slip faulting substantially changed the geometry of the transported volcanic rocks and the structural style both across and along the strike of the orogen the extension of the gravity anomaly under the st lawrence river also suggests that the ordovician deformation front is 20 to 30 kilometers further to the north than previously interpreted

the use of mixing models and chemical geothermometers for estimating underground temperatures in geothermal systems abstract application of various chemical geothermometers and mixing models indicate underground temperatures of 260 c 280 c and 265 c in the geysir hveravellir and landmannalaugar geothermal fields in iceland respectively mixing of the hot water with cold water occurs in the upflow zones of all these geothermal systems linear relations between chloride boron and 18o constitute the main evidence for mixing which is further substantiated by chloride silica and sulphate relations in the geysir and hveravellir fields a new carbonate silica mixing model is proposed which is useful in distinguishing boiled and non boiled geothermal waters this model can also be used to estimate underground temperatures using data from warm springs this model as well as the chloride enthalpy model and the na li and co2 gas geothermometers invariably yield similar results as the quartz geothermometer sometimes also does by contrast the na k and the na k ca geothermometers yield low values in the case of boiling hot springs largely due to loss of potassium from solution in the upflow the results of these geothermometers are unreliable for mixed waters due to leaching subsequent to mixing

the marnet radiolinked seismometer network spanning the marmara sea and the seismicity of western turkey summary the marnet telemetered seismic network spanning the marmara sea supplements the isk network of conventional seismic stations and increases the resolution for monitoring the seismicity in western turkey seismicity maps for the period 1976 to 1981 display pronounced swarm type activity where small earthquakes cluster in the same locality three types of seismic activity can be identified and related to present day tectonic deformation normal earthquake episodes associated with the main line of the north anatolian fault continuous swarm activity but with marked fluctuations and bursts of activity in the tensional regime south of a line from izmir to adapazari and continuous activity with only minor fluctuations within the marmara region as it is sheared by the westward movement of the main anatolian plate

the thermal springs of jordan the thermal springs alongside wadi araba dead sea and jordan valley jordan were investigated and sampled in a comprehensive field study of 2 weeks conventional physicochemical properties were measured in situ dissolved solids and isotopic composition were analyzed two main spring locations on the east side of the dead sea were mapped it became evident that the hottest springs are among the closest to prominent faults some springs are controlled by gas lift jordan s hot springs are described by means of a broad hydrochemical and physicochemical data set and several figures are presented based on their hydrochemistry the thermal springs are classified into four thermal provinces water genesis is discussed several geothermometers are applied to estimate reservoir temperatures observed discharge rate water temperature and isotopic composition are compared with data from the literature although discharge and water temperature are reported to be constant over the last decades groundwater overexploitation led to a shift of the isotopic composition what is documented for the first time in jordan thus the effect of groundwater mining on jordan s hot springs can be stated as a fact

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

the turkish dilatancy project tdp3 multidisciplinary studies of a potential earthquake source region the section of the north anatolian fault lying near the city of izmit at the east of the marmara sea has been identified as a seismic gap and the possible site of a future major earthquake previously published studies of records from an earthquake swarm within the gap tdpl and tdp2 provided the first evidence that shear wave splitting occurs in earthquake source regions a conclusion since verified by many studies at other locations a third field study tdp3 was mounted in the izmit region during the summer of 1984 observations were made over an eight month period and included geomagnetic and geoelectric measurements in addition to a series of observations utilising dense arrays of three component seismometers earthquake activity in the principal study area was monitored over a period of eight months records showed features similar to those observed in the earlier studies in particular 1 almost all shear waves emerging within the shear wave window displayed shear wave splitting 2 the polarizations of the first arriving faster split shear waves showed sub parallel alignments characteristic of propagation through a distribution of parallel vertical cracks striking perpendicular to the minimum compressional stress these and other observations support the conclusion of earlier studies that the upper crust is pervaded by distributions of micro cracks aligned by stress known as extensive dilatancy anisotropy a search for time dependence in shear wave phenomena has revealed temporal variations in the delays between the split shear waves throughout the course of the tdp3 study but as yet this has not been correlated wi th specific earthquake activity

taconian orogenesis sedimentation and magmatism in the southern quebec northern vermont appalachians stratigraphic and detrital mineral record of iapetan suturing cambrian ordovician units of the southern quebec appalachians oceanic domain include obducted ophiolites and an overlying syncollisional sedimentary basin represented by the saint daniel melange and flysch units of the magog group these terrains were thrust onto the laurentian continental margin during the taconian orogeny and are unconformably overlain by silurian devonian successor basins this contribution presents and discusses new stratigraphic data acquired in the oceanic domain as well as u pb and 40ar 39ar geochronological data on detrital zircons and muscovites sampled at various stratigraphic levels from the base of the sedimentary units of the oceanic domain and the silurian devonian units of the gaspe belt this work combined with the compilation of existing data for southern quebec and western new england allows a better definition of the tectono stratigraphic evolution of the area and are used to propose correlations with different rock units of the northern new england appalachians which represents a collage of laurentian margin and oceanic units it is shown that cambrian ordovician rocks of southern quebec and northern vermont have undergone a similar tectonic evolution the ophiolites were obducted onto the laurentian margin as a more or less coherent slab of oceanic lithosphere both the ophiolites and continental margin rocks were uplifted eroded and unconformably overlain by middle to late ordovician units of the saint daniel melange and magog group in a forearc setting the presence of mafic and felsic volcanic flows that are interstratified within the saint daniel melange can be correlated with an episode of delamination and slab breakoff during the final stages of obduction and exhumation of the orogenic wedge the magog group was deposited during the emplacement of the taconian nappes as the outboard volcanic arc was still active but progressively shutting down the provenances suggested by the age of the dated detrital minerals can be entirely reconciled with the peri laurentian context of the studied rock units and testify of the tectonic evolution and sedimentary recycling of the taconian orogen from ophiolite obduction onto the laurentian margin to the collapse of the orogenic belt and the formation of successor basins

calculable fluid rock interactions this paper introduces a model of rock deformation anisotropic poro elasticity or ape where the response of fluid saturated rock to changing conditions prior to fracturing can be calculated the driving mechanism for deformation is fluid migration along pressure gradients between neighbouring intergranular microcracks and pores at different orientations to the stress field the parameters that control changes to microcrack geometry also control the splitting birefringence of seismic shear waves so that changes in deformation can be directly monitored by analysing the shear wave splitting which is observed in almost all rocks analysis of shear wave splitting in the earth9s crust and ape modelling show that distributions of mostly intergranular cracks in the crust are always geometrically close to fracturing with the implication that shear wave splitting is sensitive to comparatively minor changes of stress and minor changes of in situ conditions this has important implications for the state of criticality of the rockmass and as a consequence changes in shear wave splitting have been observed before larger earthquakes on those few occasions when suitable source receiver geometry coincides with appropriate seismic activity ape also has implications for monitoring changing conditions in reservoirs during hydrocarbon recovery

shear wave polarizations near the north anatolian fault i evidence for anisotropy induced shear wave splitting summary the turkish dilatancy projects tdp1 in 1979 and tdp2 in 1980 recorded small earthquakes near the north anatolian fault with closely spaced networks of three component seismometers in order to investigate the possibility of diagnosing dilatancy from its effects of shear wave propagation this paper examines the polarizations of shear wavetrains recorded in the shear wave window immediately above the earthquake foci abrupt changes in the orientation and or ellipticity of the shear wave polarizations are almost always observed during the first few cycles following the initial shear wave arrival on each seismogram the horizontal projections of the polarizations of the first shear wave arrivals at any given station show nearly parallel alignments with approximately the same orientations at each of the recording sites with one exception it is difficult to explain this uniform alignment over a wide area in terms of scattering at the irregular surface topography or by earthquake focal mechanisms we demonstrate that the shear wave splitting is likely to be the result of anisotropy in the region above the earthquake foci which could produce polarizations displaying the observed alignments the temporal change of the azimuth of alignment observed at one locality between 1979 and 1980 may be due to the release of a local stress anomaly by a very near earthquake

effects of the free surface on shear wavetrains summary the behaviour of shear waves is of great importance in identifying and investigating seismic anisotropy in the earth however shear wavetrains recorded at the earth s surface do not always reflect the motion at depth introducing practical problems of interpretation shear wavetrains incident on the surface of an isotropic half space at angles less than critical about 35 are broadly preserved but at greater angles substantial distortions can occur for stations situated close to the source as in local earthquake studies the local sp phase a radially polarized precursor to s may occur the behaviour at the surface of an anisotropic half space is further complicated by the divergence of phase and energy propagation vectors all of these complications suggest that detailed seismogram modelling is essential to any study of shear wave propagation in the earth and in particular to investigations of anisotropy induced shear wave splitting

the boron isotope systematics of icelandic geothermal waters 1 meteoric water charged systems we have measured the boron isotope composition and boron and chloride concentrations of 27 icelandic geothermal fluids from both high and low temperature systems the 11b values range from 6 7 in the krafla system to 25 0 in a warm spring from the southern lowlands in addition we have also determined the 11b values of basaltic glass from nesjavellir 5 3 1 4 and travertine from snaefellsnes 22 0 5 the b isotope and cl b systematics of the high temperature systems are dominated by the composition of the local basalts the lower temperature systems show evidence for mixing with b and cl of a marine origin together with some uptake of b into secondary mineral phases the data from the snaefellsnes geothermal system indicate that the fluids have undergone interaction with basalts that have undergone significant low temperature alteration by seawater

geochemistry and u pb zircon age of comenditic metafelsites of the tibbit hill formation quebec appalachians metafelsites in waterloo area quebec represent the only known silicic volcanic rocks in the predominantly basaltic tibbit hill formation low grade metamorphism accompanied by hydration and albitization has converted the felsic volcanic rocks mainly to muscovite quartz albite schists the volcanic parent of these metafelsites was formed partly as lava flows and partly as tuffs the principal compositional type was a comendite a component of intermediate rocks is also present but its extent is undetermined and probably minor u pb zircon studies of the metafelsites have yielded a reliable age of this early cambrian age is probably representative of the age of the tibbit hill formation as a whole the tibbit hill formation accumulated at one of the clearest examples of a rrr rift rift rift triple junction the sutton mountains triple junction of the continental rift system formed as a prelude to the opening of the iapetus ocean its volcanic rocks are products of the youngest major episode of rift rela

geochemistry origin and provenance of upper proterozoic to upper cambrian alkaline to transitional basaltic rocks in and contiguous to a sector of the appalachian humber zone canada

the basis for earthquake prediction summary recent advances in understanding the behaviour of shear waves propagating in the crust make the routine prediction of earthquakes seem practicable accumulating evidence suggests that most of the earth s crust is pervaded by distributions of fluid filled cracks and microcracks that are aligned by the contemporary stress field so that the cracked rockmass is effectively anisotropic to seismic waves this causes shear waves to split and shear wave splitting is observed whenever shear waves propagating along suitable raypaths in the crust are recorded by three component instruments these distributions of cracks are known as extensive dilatancy anisotropy or eda many characteristics of the crack and stress geometry can be monitored by analyzing shear waves propagating through the cracked rockmass observations of temporal variations of the behaviour of shear wave splitting in seismic gaps confirm these hypotheses and suggest that stress changes before earthquakes may be monitored by analyzing shear waves in particular monitoring earthquake preparation zones with three component shear wave vertical seismic profiles could lead to techniques for the routine prediction of earthquakes

inversion of arrival times in a region of dilatancy anisotropy shear wave splitting has been identified in many three component seismograms from two separate field experiments on a section of the north anatolian fault in north west turkey these observations are consistent with shear wave propagation through a zone of extensive dilitancy anisotropy a preliminary attempt has been made to confirm this interpretation by simultaneously inverting suites of arrival times for hypocentral locations and for parameters describing an anisotropic halfspace although the inversion procedure is not globally convergent it is possible to recognize the true solution by systematically varying the initial conditions applied to selected data sets the inversion defines several anisotropic models that fit the data significantly better than a simple isotropic model and display the anisotropy required by the shear wave splitting however most of these anisotropic models are not superior when they are used to individually locate events in a much larger data set however for each experiment there is a single model that produces clearly superior locations for the larger data sets than those of other anisotropic or simple isotropic models both models display similar velocity variations which are characteristic of propagation through distributions of biplanar cracks displaying orthorhombic symmetry the principal axes of the two models are oriented in similar directions and are within 20 of the principal axis of regional stress derived from fault plane solutions the solutions indicate low velocities close to the tensional axis as would be expected in extensive dilatancy anisotropy

sm nd and trace element characterization of shales from the abitibi belt labrador trough and appalachian belt consequences for crustal evolution through time nd isotopic compositions and sm nd li k rb sr ba ni and cr abundances are reported for 25 shale samples from the canadian shield late archean abitibi greenstone belt and the mid proterozoi

neotectonics of the marmara sea region of turkey seismological investigations in western anatolia nw turkey have identified linear patterns of earthquake epicentres outlining a wedge shaped block in the area of the marmara sea this block shows different seismic characteristics from the rest of western anatolia and appears to act as a separate tectonic unit earthquake fault plane mechanisms show that the marmara block is being rotated and sheared in order to accommodate the right lateral motion of the north anatolian fault and the extensional tectonics of the southwestern anatolia investigations of the behaviour of seismic shear waves suggest that neotectonic stress aligns water filled microcracks throughout the upper brittle 10 20 km of the crust and that in situ stress directions can be monitored by analysis of shear waves recorded on three component instuments

shear wave polarizations near the north anatolian fault iii observations of temporal changes summary almost all shear waves from local earthquakes recorded on closely spaced three component seismometer networks deployed near the north anatolian fault turkey in two experiments in 1979 and 1980 display shear wave splitting the observations are consistent with the presence of eda extensive dilatancy anisotropy distributions of fluid filled cracks and microcracks aligned by the regional stress field temporal changes in the stress field which may occur before an earthquake may modify the geometry and possibly the orientation of the eda microcracks and lead to corresponding changes in the behaviour of the split shear waves a third experiment was undertaken in 1984 to investigate eda further and to search for possible temporal variations of the polarization of the leading split shear wave and the time delay between split shear waves observations indicate that the polarization alignments which are parallel to the strike of the parallel vertical eda cracks are unaltered between 1979 and 1984 implying that the direction of the regional stress field has not changed significantly temporal changes in the stress field are more likely to cause changes in the crack density and or aspect ratio which would result in a corresponding change in time delay between the split shear waves we examine observations of time delay in relation to their propagation path with respect to the crack geometry since it is then possible to separate the effects of changes in crack density and changes in aspect ratio with this procedure a small temporal variation of time delays is found between 1979 and 1984 consistent with a decrease in crack density and consequently a relaxation of stress in this time period no evidence was found for any observable variation of time delay over a six month observation span in 1984 we suggest that analysis of repeated shear wave vsps offers a technique for monitoring stress changes before earthquakes

late neoproterozoic to permian tectonic evolution of the quebec appalachians canada abstract due to the unique location of the quebec appalachians in a re entrant of the paleo north american margin and to the fact that the area largely escaped late paleozoic deformation this segment of the orogen preserves evidence of the early orogenic stages that are partly obscured elsewhere despite diachronicity both along and across strike of the orogen five tectonic events of regional significance are recognized 1 the earliest event is mainly recorded by neoproterozoic to early ordovician normal faults associated with extension of the laurentian craton and the establishment of a passive continental margin 2 the second event the ordovician taconian orogeny is marked by foreland directed deformation and corresponds to the principal deformational and metamorphic events recorded by the laurentian margin 3 the third event early salinic is early silurian it is restricted to the southern part of the quebec appalachians and consists of hinterland se directed thrusts folds and retrograde metamorphism 4 the fourth event late salinic is recorded by regional scale late silurian to early devonian normal or transtensional faults and is associated with the formation of the connecticut valley gaspe trough and 5 the last event the devonian acadian orogeny affects with variable intensity all the pre carboniferous lithologies this tectonic synthesis implies that the subdivision of the peri laurentian oceanic tracts proposed in other segments of the appalachians should be applied with caution in quebec and that the structural style the number of oceanic domains and possibly the vergence of subduction change along the strike of the orogen in particular the similarities of the thetford mines and boil mountain ophiolitic complexes and sedimentary covers and the lack of evidence for a major intervening suture are consistent with the maximum allochtony hypothesis i e the assumption that the southern quebec ophiolites are rooted east of the chain lake massif a geodynamic model involving the taconian obduction of a large ophiolitic nappe s the docking of a peri gondwanan gander medial new england terrane in early salinic the formation of large sedimentary basins connecticut valley gaspe and merrimack troughs due to trench rollback and or delamination during the late salinic event and collision at the outer margin of composite laurentia during the acadian orogeny can account for the protracted structural and metamorphic history of the quebec appalachians

aftershock activity of the 1999 izmit turkey earthquake revealed from microearthquake observations an accurate aftershock distribution of the 1999 izmit turkey earthquake was obtained by using the data from a local seismic network izinet and 10 temporary seismic stations more than 2000 aftershocks were relocated for the period of about 2 months following the mainshock from this aftershock distribution we obtained several pieces of information on the characteristics of the mainshock first the mainshock initiated fault rupture from a place adjacent to an active swarm area where many microearthquakes had been occurring for more than 20 yr prior to the mainshock second the aftershock region extended in the east west direction along the north anatolian fault zone nafz this confirms that the mainshock was caused by a slip on the nafz third the western end of the rupture caused by the mainshock is likely to have reached up to about 29 2 e in the izmit bay and hence the total length of the fault rupture caused by the mainshock amounts to about 150 km as long as the estimate of the fault rupture length is based on the aftershock distribution this information is important for the discussion on the possibility of future large earthquakes in the west of the source region of the izmit earthquake we also found a clear tendency that aftershocks occur in clusters which implies strong heterogeneity in both the rupture process and the medium along the fault zone manuscript received 7 october 2000

analysis of records of local earthquakes the turkish dilatancy projects tdp1 and tdp2 summary this is the introduction to a series of papers analysing records from three component seismometers immediately above a swarm of small earthquakes near the north anatolian fault in turkey the networks were set up to investigate the possibility of estimating dilatancy induced adisotropy by monitoring shear wave splitting in shear waves from local earthquakes as suggested by the hypothesis of extensive dilatancy anisotropy eda these networks were among the first closely spaced digital three component seismometers to be deployed in the shear wave window immediately over a seismic source zone where the polarizations of incident shear waves can be recognized from surface recordings consequently the seismograms display several new phenomena that have not been previously observed 1 the polarizations of almost all shear waves arriving within the shear wave window showed abrupt changes in direction characteristic of shear wave splitting in synthetic seismograms modelling wave propagation through anisotropic rocks 2 the polarizations of the faster split shear waves are in patterns characteristic of propagation through distributions of cracks aligned by the principal axes of stress but not characteristic sf shear waves propagating through isotropic rock from a double couple source oriented by the same stress axes 3 many characteristics of the observed polarization patterns are similar to synthetic polarization diagrams for wave propagation through vertical parallel cracks 4 the orientation of the anisotropy derived from the shear wave polarizations is consistent with the common axes of stress of the fault plane mechanisms 5 the orientation of the shear wave anisotropy is also similar to the orientation of the anisotropy derived independently from inverting p and s wave arrival times and 6 there is some indication of a temporal change in polarization in one locality such as might be expected if a change in a local stress anomaly altered the crack geometry

hydrogeochemical and isotopic study of thermal and mineralized waters from the nevsehir kozakli area central turkey abstract in the kozakli geothermal province thermal waters are manifested along a valley 1 5 km long and 200 m in width thermal waters utilised by the resort and some other hotels are mostly discharged from bore wells the issuing temperatures of the thermal waters vary from 40 50 c in thermal springs and 45 96 c in bores and open wells the geochemical and isotopic signatures of the thermal water suggest mixing of thermal waters with formation waters and cold near surface groundwaters before emerging to the surface and hence geochemical indicators fail to indicate the near true reservoir temperatures however the oxygen and hydrogen isotopic signatures strongly suggest a high temperature reservoir 220 c in the crystalline basement rocks long circulation of meteoric waters within the basement rocks is indicated by low tritium values in the thermal waters major involvement of miocene marls in modifying the chemical signatures of the thermal waters is inferred from the trace element concentrations

tectonics of the marmara sea region of turkey new evidence from micro earthquake fault plane solutions summary composite and single event fault plane solutions for microearthquakes in the izmit bay area of the marmara sea indicate right lateral strike slip motion and tension on this extension of the north anatolian fault this interpretation is consistent with teleseismically determined fault plane solutions obtained for larger earthquakes on the marmara sea seismic lineation consideration of the microplate geometry of north western turkey inferred from seismicity as well as earthquake mechanisms suggests that the region comprises two seismotectonic units with differing styles of deformation the anatolid structures of south and central western anatolia are undergoing major extension whereas the pontid structures of the marmara sea region are being sheared resulting in a mixed regime of both strike slip and extensional faulting

age of the grenville dyke swarm ontario quebec implications for the timing of lapetan rifting u pb baddeleyite and zircon ages for three diabase dykes from widely spaced localities within the grenville dyke swarm indicate a single age of emplacement at ma the 700 km long grenville dyke swarm located in the southeastern part of the canadian shield was emplaced syntectonically with the development of the ottawa graben this graben may represent a plume generated lapetan failed arm that developed at the onset of the breakup of laurentia other precisely dated lapetan rift related units such as the callander alkaline complex and the tibbit hill formation volcanic rocks indicate a protracted 36 ma period of rifting and magmatism prior to volcanism along this segment of the lapetan margin the age of the grenville dykes is the youngest in a progression of precisely dated mafic magmatic events from the 723 ma franklin dykes and sills to the 615 ma long range dykes along the northern and northeastern margins of laurentia respectively thus the age for these dykes represents a key time marker for

timing of tectonic events in the menderes massif western turkey implications for tectonic evolution and evidence for pan african basement in turkey the menderes massif forms the western of the two large metamorphic culminations within the turkish alpide orogen it has three major lithologic units with a gneissic core at the base and a schist and a marble envelope overlying it successively although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the massif we present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the massif to constrain the timing of major tectonic events that shaped the massif since the late proterozoic pt3 in the southern part of the massif sensu stricto three episodes of deformation and metamorphism are distinguished whereas in its northern part there are four the first episode occurred at 500 10 ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis in the central part of the massif the 470 9 ma old now highly deformed tonalitic and granitic intrusions mark the end of this episode on a cambrian reconstruction of continents around the eastern mediterranean the menderes massif forms the southern end of the pan african orogenic collage of northeastern africa and arabia the area of earliest palaeozoic deformation in the menderes may connect with the northwest african orogenic collage along the strike via the bozburun and saricicek diabases arkoses and schists in the center of the karacahisar dome interpreted herein as fragments of a pan african suture the earliest palaeozoic deformations to affect the rocks were probably related to the last pan african collisions and associated postcollisional convergence the southern part of the massif was undeformed from early ordovician to the early later eocene whereas the northern part was deformed metamorphosed and intruded possibly during the late triassic related to the closure of the karakaya marginal basin of palaeo tethys the next major event affecting the whole of the massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts and only greenschist grade in the outermost envelope this metamorphism here called the main menderes metamorphism mmm is biostratigraphically constrained between early eocene and early oligocene time rb sr isotopic data show a spread of ages between 60 ma and 25 ma with the greatest number of determinations around 35 5 ma this number is in excellent agreement with the stratigraphic evidence and shows that mmm took place during latest eocene time or at the transition from eocene to oligocene time along the northern border of the massif deformation and metamorphism had already taken place during the late cretaceous in a high pressure low temperature hp lt metamorphic belt northernmost part of menderes massif sensu lato which was then covered by palaeocene molasse the evolution of the hp lt belt was probably related to the obduction of the bozkir ophiolites from the izmir ankara branch of the neo tethys ocean and preceded terminal collision in the evolution of the massif the mmm was a product of the latest palaeocene collision across neo tethys and the consequent internal imbrication of the menderes taurus block that resulted in the burial of the menderes massif area beneath the lycian nappe complex a low grade metamorphic event dated at 10 to 5 ma is interpreted to be related to the extensional deformation in the aegean and western turkey which has been dated stratigraphically to have begun during the tortonian 11 5 ma

the role of hydrogeology in solution subsidence development and its environmental impacts a case study for sazlica nigde turkey solution subsidence and other types of collapse failures developed in the vicinity of sazlica have been a major source of environmental problems such as groundwater pollution soil erosion and foundation failures extensive pumping of water from the lake dipsiz during irrigation seasons creates landslide developments at the shores of the lake five stages of landslide development were observed in the unconsolidated soils around lake dipsiz bowl shaped solution subsidence features with depths from 1 to 3 m and diameters between 1 and 60 m were formed due to excess pumping and recharge and discharge features of unconfined aquifer the pumping activities must be controlled to prevent further environmental problems lake dipsiz and other subsidence developments are the groundwater exposure areas highly vulnerable to contamination the proposed remedies for overcoming the environmental problems are the establishment of conservation areas around such natural features ceasing the removal of top soil controlling the urbanization and keeping the livestock farming away from the areas susceptible to pollution

the saint daniel melange evolution of an accretionary complex in the dunnage terrane of the quebec appalachians the saint daniel melange is part of a series of melanges located along the baie verte brompton line in the northern appalachians this line marks the suture between rocks of oceanic affinities and those of the ancient passive margin of north america with which they collided during the taconian middle to late ordovician orogeny the saint daniel melange contains a wide variety of lithologies including well bedded to dismembered sedimentary sequences pebbly mudstone olistostromes and slivers of igneous and metamorphic rocks black shales with interbeds of green shale calcareous siltstone or sandstone are the dominant units they exhibit various stages of melange formation such as those present in shallow parts of an accretionary complex units of oceanic origin include sediments derived from the forearc basin and slivers of an ophiolite and of a magmatic arc units derived from sediments of the passive margin of north america are also present the ratio between these various lithologies changes greatly within the melange on a kilometric scale along strike the saint daniel melange is a structural complex in which the various units were assigned a sequential order mimicking a stratigraphic order the saint daniel melange is interpreted as the relict of an accretionary complex because of its actual structural position within the northern appalachians and because all its lithologies and their structural fabric can be found in modern accretionary complexes

shear wave splitting in the anza seismic gap southern california temporal variations as possible precursors shear wave splitting above small earthquakes in the anza seismic gap on the san jacinto fault southern california displays the effective anisotropy of vertical fluid filled microcracks the delays between the split shear waves increase significantly over the 3 years of available records at the only station with arrivals from a wide range of azimuths and angles of incidence these changes can be modeled by increasing the aspect ratio bowing of stressoriented microcracks which is one of the expected elastic effects of an increase of stress on a rock mass containing a distribution of fluid filled microcracks this is the first time that temporal variations of shear wave splitting have been observed and suggests that shear wave splitting can be used to monitor the detailed changes in the buildup of stress before an earthquake

stress in the earth s crust the link between crustal fluids and extensive dilatancy anisotropy observations of seismic shear wave splitting birefringence along almost all raypaths in the earth9s crust have led to the recognition that the fluid filled cracks microcracks and pores known to pervade most rocks in the crust have been preferentially aligned by the prevailing stress field this phenomenon is known as extensive dilatancy anisotropy or eda and the fluid filled microstructures as eda cracks because the seismic effects can be modelled by distributions of parallel cracks the effects of these stress aligned eda cracks have been observed in many different areas and they appear ubiquitous in the upper 10 to 20 km of the crust many details of the crack geometry and the current stress field can be readily determined from records of the shear waves which have propagated through these aligned cracks in separate studies geochemists have confirmed the presence of microscopic fluid filled cavities in almost all geological material these are referred to as fluid inclusions and provide unequivocal evidence of crustal fluid circulation often along stress controlled fractures different stress episodes can be recognized in many rock samples and studies of fluid inclusions can be used to interpret the palaeo stress history of a rock where the in situ morphology of these inclusions is related to the current regional stress field this paper discusses the relationship between the fluid inclusions of the geochemical literature and eda cracks and concludes that the former may be regarded as one of the constituent inclusion types of extensive dilatancy anisotropy

microearthquakes in the tdp swarm turkey clustering in space and time summary the third occupation experiment tdp3 of recording sites above a persistent swarm of microearthquakes near the north anatolian fault with a larger seismic network and over a longer period of time confirms and refines previous observations with greater resolution the greater resolution in earthquake locations has revealed marked clustering in time and space many perhaps most of the earthquakes belong to clusters where successive earthquakes originate in a very small volume and have similar fault mechanisms such studies allow the progression of seismic activity of small earthquakes to be followed in some detail and may reveal features which are hidden in larger and more complex earthquake sequences

mesozoic east north american alkaline magmatism part 1 evolution of monteregian lamprophyres quebec canada abstract the cretaceous monteregian alkaline igneous province is composed of shallowly emplaced plutonic complexes and cogenetic dykes and sills the mafic dykes are principally camptonites monchiquites and alnoites and sample the magmas that fed the plutons the three principal dyke suites have different incompatible trace element ratios y ce zr nb and are not interrelated by closed system fractional crystallization zonation of pyroxene grains imply a polybaric crystallization history indicating that magmas ascended as mafic crystal charged mushes intrasuite chemical variations among monchiquites are broadly consistent with segregation of the suspended phenocrysts from interstitial syenitic melts partial resorption of suspended amphibole megacrysts assimilation of syenitic material 5 8 and exsolution of carbonatitic melt are required to explain the variations of ba rb k 2 o th la and tio 2 chemical variations among mafic camptonites are acceptably modelled by fractionation of pyroxene and olivine only implying that their amphibole rich character is the result of postfractionation crystallization under volatile rich conditions high zr nb camptonites and rb rich ac monchiquites could not unequivocably be linked to the main lineages and may represent distinct sources or have been affected by crustal contaminants

temporal changes in shear wave splitting during an earthquake swarm in arkansas shear wave splitting has been observed in seismograms of two aftershock and one foreshock sequence recorded over 12 days by a local network of nine three component digital seismometers during the 1982 enola arkansas earthquake swarm polarizations of the faster split shear wave show alignments within the shear wave window which correlate with the regional stress field the time delay between split shear waves appears to increase before and to decrease at or after the time of each main shock this behavior is similar to observations before and after a m 6 0 event near the anza seismic gap southern california and may correspond to variations in crack geometry caused by changes in the stress field before and after the earthquakes there are indications that the decrease in delay may occur a few hours before the main shock and could be a possible precursor for earthquake prediction

seismic and electrical anisotropy in the mornos delta gulf of corinth greece and its relationship with gps strain measurements shear wave splitting studies on seismo grams from local earthquakes at the site of the mornos delta gulf of corinth greece has revealed a clear seismic anisotropy with a fast s polarization striking n55 25 o magneto telluric soundings in the frequency range 0 01 to 100 hz on the delta showed a clear electric anisotropy with a n55 o 10 o direction for the highest frequency this anisotropy spans through the whole layer of sediments about 1 km thick comparison of the 1966 1972 triangulations and the 1991 1995 gps positions of geodetic points in and around the delta showed rapid extension strain 2x10 s year in the direction n340o 30 o perpendicular to the fast s and the highest conductivity directions suggestive of a causal relationship between these observations we thus propose that this strain controls the two reported anisotropies by the formation and maintaining of fluid filled steeply dipping antithetic faults and fractures and fluid filled vertical cracks all striking n55 o 4 20 o the source of strain is likely to be active normal faulting near and under the delta as independently evidenced by the recent discovery of nearby offshore faults striking about n60 o significantly different from the dominant e w strike of the major faults of the gulf

the age of the sept iles layered mafic intrusion canada implications for the late neoproterozoic cambrian history of southeastern canada the large sept iles layered mafic intrusion of eastern canada has been precisely dated by u pb zircon methods at 565 4 ma consideration of other magmatic events at that time in southeastern canada reveals three different phases of magmatism the first phase was composed of two tholeiitic dike swarms at 615 ma and 590 ma the second including the sept iles intrusion comprised a widespread series of mostly alkaline intrusions emplaced around 575 565 ma along the rift faults of the st lawrence graben the last phase was composed predominantly of alkali and transitional basalts now exposed in the appalachians erupted during the latest neoproterozoic and early cambrian the second and third phases are best accounted for by the arrival of a major mantle plume near the town of sept iles 565 million years ago the widespread but volumetrically minor alkali magmatism that peaked 10 m y earlier is typical of other plumes elsewhere the plume model is reinforced by sedimentological evidence for a crusta

comparative evolution of the iapetus and rheic oceans a north america perspective abstract differences in the origin and evolution of the iapetan and rheic oceans profoundly affected the development of the ouachitan appalachian variscan orogen the iapetus ocean was initiated in the late neoproterozoic early cambrian by the separation of large continental landmasses laurentia baltica gondwana whereas the rheic ocean originated in the late cambrian early ordovician as the result of the separation of several ribbon continents collectively termed peri gondwanan terranes from the northern margin of gondwana compared to the classic passive margin developed along the laurentian margin of iapetus passive margin successions to the rheic ocean are more limited in extent during convergence both margins of the iapetus ocean developed western pacific type arc back arc systems whereas subduction of the rheic ocean was primarily directed beneath laurentia and was andean in style closure of iapetus involved a number of arc back arc accretionary events and had occurred by the middle silurian as a result of laurentia baltica collision to form laurussia and the accretion of the peri gondwanan terranes rheic ocean closure occurred in the carboniferous by way of continent continent collision between laurussia and gondwana with gondwana on the lower plate within iapetus the formation of ophiolites occurred early in the orogenic cycle and was followed soon after by obduction hp lt metamorphism and foreland directed thrusting that is intimately related to accretionary events these features dominate the northern appalachian orogen where ht lp metamorphism is attributed to post accretionary slab break off events in contrast hp lt metamorphism within the rheic ocean reflects a type subduction during laurussia gondwana collision and is rapidly succeeded by ht lp metamorphism attributed to orogenic collapse ophiolites are rare and were formed either very early early ordovician or very late devonian carboniferous in the evolution of the ocean the early ordovician ophiolites were not obducted until the carboniferous at least 100 million years after their protoliths were formed rheic ocean closure resulted in the formation of large scale bivergent structures within the orogen with symmetry changing on either side of the rheic suture comparison of the evolution of the iapetus and rheic oceans suggests that differences in rift configuration passive margin development and subduction zone geometry within the two oceans profoundly influenced the subsequent style of orogenesis within the ouachita appalachian variscan orogen

progressive changes in volcanism during lapetan rifting comparisons with the east african rift red sea system mafic dikes and metamorphosed basaltic flows of late proterozoic to early paleozoic age in western vermont and northeastern new york have geochemical signatures consistent with their origin during progressive rifting of the ancient north american continent the basalts change from being enriched in ti and fight rare earth elements rees to being depleted in ti and light rees from west to east across the western appalachians western samples are similar to early stage rift basalts as seen in the main ethiopian rift whereas easternmost samples are like mid ocean ridge basalt morb produced in axial parts of the red sea samples from intermediate geographic areas can be either enriched or depleted by analogy with the east african rift red sea system the chemical changes in basalts across the western appalachians probably reflect a changing source from trace element enriched mantle ocean island basalt asthenosphere or continental lithosphere to depleted morb type asthenosphere as rifting progressed

microearthquake activity before the izmit earthquake in the eastern marmara region turkey 1 january 1993 17 august 1999 a telemetered seismic network izinet consisting of 13 stations has been in operation since 1993 in the western extension of the north anatolian fault zone nafz in the eastern marmara region the network was established to study microearthquake activity in this region which had been known as a seismic gap until the occurrence of the 17 august 1999 izmit kocaeli earthquake m w 7 4 for the last 7 yr about 3250 events were recorded and located local magnitudes of these events which were determined based on the duration of seismic coda waves were generally smaller than 4 0 seismicity in the time period studied clusters in five areas most of the events are found to be shallower than 20 km it turned out that before the 17 august 1999 izmit earthquake the izmit adapazari region was seismically more active than the other regions in the western extension of the nafz manuscript received 30 august 2000

tectonic setting of outer trench slope volcanism pillow basalt and limestone in the taconian orogen of eastern new york the only pillow basalt in synorogenic sedimentary rocks at the exterior margin of the taconic orogen in eastern north america is at stark s knob in eastern new york earlier reported as extrusive into allochthonous ordovician slope and rise facies this small lens ca 125 m long 39 m thick is a fault bounded block in upper ordovician melange under the taconian frontal thrust its n morb normal mid ocean ridge basalt basalt geochemistry and spinel composition are characteristic of oceanic ridge settings at a water depth of 2 km or more abundant limestone lenses on pillows and lava shelves within pillows yielded a middle late ordovician gastropod the limestones are reconciled with this extrusion depth and with limited early paleozoic pelagic carbonate production by lime mud transport from the laurentian platform or abiotic carbonate precipitation with sea water heating during basalt extrusion a genetic relationship between the parautochthonous stark s knob basalts and the allochthonous jonestown volcanics in slope and rise facies of the hamburg klippe eastern pennsylvania is likely both are ordovician morb basalts that reflect volcanism on the subducting outer trench slope prior to the taconic arc laurentia collision taconic orogenesis may have led to basalt production on the subducting plate by 1 the setting up of orogen parallel predominantly strike slip motion on the subducting slab with morb basalt generated at offsets in a setting analogous to the gulf of california or 2 development of faults in a flexure induced extensional regime by either process mafic volcanism appears to be a rare but tectonically significant process on outer trench slopes as continental margins or oceanic plates enter subduction zones resume l unique basalte a coussinet dans les roches sedimentaires syntectoniques a la bordure exterieure de

processes controlling the distribution of boron and chlorine in natural waters in iceland abstract the concentrations of b and cl in natural waters in iceland lie in the range 0 001 10 and 1 20 000 ppm respectively lowest concentrations occur in surface and groundwaters in the central highlands highest cl concentrations are found in high temperature waters on the reykjanes peninsula and highest b concentrations in well waters from high temperature geothermal systems in the axial zones of the active volcanic belts the b and cl contents of icelandic basalts are 0 1 6 6 and 75 750 ppm respectively these large variations are considered to result from variable degassing during consolidation as well as concentration variations in the initial magma tholeftes are lowest in both elements av 1 2 ppm b and 170 ppm ci transitional basalts intermediate av 2 1 ppm b and 240 ppm ci and alkali basalts highest av 3 8 ppm b and 340 ppm cl cl b ratios in tholeiites are most often within 25 50 but somewhat lower in alkali basalts most geothermal waters contain b and cl within 0 05 1 and 10 100 ppm respectively these rather low values are attributed to the low content of b and cl in the basaltic rock the b and cl distribution in the icelandic natural waters indicate that these elements act as essentially incompatible their sources of supply include 1 the atmosphere seawater spray and aerosols 2 the rock with which the water interacts 3 seawater groundwater and 4 magma intrusions in surface water and nonthermal groundwater the dominant source of supply of cl is seawater spray and aerosols but the soil and rock contribute often significantly to the b in these waters their cl b ratio is similar to that of seawater 1330 or somewhat lower boron and cl concentrations generally increase with water temperature warm waters cl b ratios intermediate between those of seawater and basalt with increasing temperature this ratio decreases and gradually approaches that of the rock some high temperature geothermal waters have as low cl b ratios as 1 and b concentrations as high as 10 ppm the cause is either b degassing of the magmatic intrusive heat source or phase separation in the producing aquifer some low temperature waters

contrasting secondary mobility of ti p zr nb and y in two metabasaltic suites in the appalachians substantial mobility of high field strength hfs elements ti y p zr and nb during greenschist facies metamorphism of two metabasaltic suites from the appalachians the ascot formation of southeastern quebec and the arbuckle brook formation of nova scotia is attributed to the presence of co2 in the fluid phase during metamorphism the style of the mobility exhibited by these two suites is different in the ascot formation metasomatism affected rocks rich and poor in carbonates it led to enrichment in some hfs elements and depletion in others in contrast in the arbuckle brook formation there was depletion in co2 rich rocks of all hfs elements and consequently much less fractionation between hfs elements these differences may be explained by the relative effectiveness of buffering in the two suites in the ascot formation buffering was ineffective and several different mineral assemblages were developed reflecting a range in mobility of hfs elements was controlled by chemical potential diffe

shear wave splitting above small earthquakes in the kinki district of japan abstract we have identified shear wave splitting diagnostic of the effective anisotropy induced by aligned microcracks in the wavetrains of micro earthquakes at four stations of the abuyama network in the kinki district of japan we find that the directions of polarization of the faster split shear waves are nearly parallel for all azimuths of arrival and for all angles of incidence less than the critical angle at three of the four stations these directions of polarization are consistent with the axis of maximum compression obtained from earthquake fault plane mechanisms and also agree with the directions of the general trends of geological structures which represent the orientations of the cleavage or lamination these results suggest that crack induced anisotropy is present in the brittle upper crust beneath japan as has been found elsewhere but we could not distinguish whether this reflects the distributions of cracks induced by the present stress field or results from the general trends of surface geology although the delay times between faster and slower shear waves are difficult to estimate reliably because of their high sensitivity to internal interfaces the delay times can be interpreted as the result of a distribution of parallel vertical cracks with a crack density of about 0 04 the consistency or lack of consistency of the directions of the shear wave polarizations at the four stations demonstrates the effects of surface topography and near surface layering on the shear wave polarizations

obduction of tethyan type ophiolites a case study from the thetford mines ophiolitic complex quebec appalachians canada abstract oceanic plagiogranites and peridotite hosted granites phg of the thetford mines ophiolite tmo yield mean u pb zircon ages of 479 2 1 6 ma and 469 5 2 8 ma and are interpreted to be the products of fractionation of basaltic magma and melting of the laurentian margin respectively the existing 40ar 39ar age for the ophiolitic metamorphic sole of the tmo is a hornblende isochron age of 477 5 ma for amphibolite facies rocks sites previously sampled for u pb and 39ar 40ar analyses were resampled for more accurate 39ar 40ar dating in order to better constrain the thermo tectonic evolution of the ophiolite and underlying laurentian margin rocks on which they were overthrust and quantify the time required for obduction of tethyan type ophiolites in the canadian appalachians amphiboles from tmo gabbro and plagiogranite yield 39ar 40ar plateau ages of 477 475 ma in contrast muscovites from phg yield cooling ages of 466 465 ma and show evidence for thermal resetting at ca 460 ma for both a granitic mylonite and a crosscutting pegmatite facies the amphibolitic metamorphic sole yields 39ar 40ar ages of ca 471 ma in amphibole and high temperature ages of ca 466 ma in muscovite with evidence for recrystallization to ages as young as 457 ma muscovites from the sub ophiolitic laurentian metasedimentary basement and micaschist clasts in supraophiolitic debris flows of the tmo yield similar pseudo plateau and high temperature ages of ca 463 464 ma the u pb and 39ar 40ar data suggest that the obduction of peri laurentian oceanic crust lasted approximately 5 to 10 m y since both facies formed approximately m y after the ophiolitic crust this supports models whereby the still hot ophiolitic mantle provided the heat needed to generate the phg and the metamorphic sole between ca 475 and 470 ma muscovite ages of phg record cooling below ca 450 500 c by ca 465 ma but 39ar 40ar ages from both a mylonitized phg facies and micaschist clasts suggest that the emplacement of the oceanic lithosphere on the laurentia margin had nearly ended by ca 460 ma likely due to foreland directed downward thrust propagation and related exhumation of the collisional wedge the new age data imply that the southern quebec ophiolites were thrust 100s of km over the laurentian margin which has major implications for the location of the subduction suture and the early stages of the taconic orogeny in the northern appalachians

subsurface thermal conductivity assessment in calabria southern italy a regional case study determining the suitability of a local area at a regional or local scale for the geothermal application of low enthalpy systems requires the knowledge of rock thermal conductivity values to evaluate the possibility of low enthalpy heat exchange a digital cartographic tool is also needed to synthesize the thermal properties of the underground this tool should be easily accessible and upgradeable and thus suitable for territorial planning and environmental control in order to address these key issues a methodological approach was developed within the framework of the national vigor project dedicated to evaluating the geothermal potential in southern italy in this paper the region of calabria was selected as a case study around 70 samples that were representative of the main geological formations were collected from all over the area thermal property tests were carried out both in dry and wet conditions using a thermal device in accordance with the modified transient plane source method the thermal conductivity values were then compared with data from the international literature in order to consider the influence of the entire stratigraphic sequence on the thermal conductivity parameters a geostatistical analysis of the available lithostratigraphic data was performed using the matlab toolbox modalstrata specially developed for this purpose a comprehensive geothermal subsurface characterization of calabria was thus obtained

shear wave polarizations near the north anatolian fault ii interpretation in terms of crack induced anisotropy summary the polarizations of shear waves recorded by networks of digital thxee component seismometers immediately above small earthquakes near the north anatolian fault in turkey display shear wave splitting on almost all shear wave seismograms recorded within the shear wave window this splitting is incompatible with source radiation patterns propagating through simple isotropic structures but is compatible with effective anisotropy of the internal structure of the rock along the ray paths this paper interprets the phenomena in terms of widespread crack induced anisotropy distributions of stress induced cracks model many features of the observations and synthetic polarization diagrams calculated for propagation through simulated cracked rock are similar to the observed patterns this evidence for widespread crack induced anisotropy lends strong support to the hypothesis of extensive dilatancy anisotropy eda suggested by laboratory experiments in subcritical crack growth the crucial evidence confirming some form of eda would be observations of temporal changes in shear wave splitting as the stress field alters the crack density and crack geometry there is some weak evidence for such temporal changes at one site but further analysis of suitable digital three component seismometer networks in seismic areas is required to confirm eda

shear wave polarizations in the peter the first range indicating crack induced anisotropy in a thrust fault regime summary three component seismograms of small local earthquakes recorded in the peter the first range of mountains near garm tadzhikistan ssr display shear wave splitting similar to that previously observed near the north anatolian fault in turkey the peter the first range is in a region of compressional tectonics whereas the north anatolian fault is a comparatively simple strike slip fault detailed analysis of the turkish records suggests that the splitting is diagnostic of crack induced anisotropy caused by vertical microcracks aligned parallel to the direction of maximum compression preliminary examination of paper records from garm shows that most shear waves arriving within the shear wave window display shear wave splitting and that the polarizations of leading shear waves are consistently aligned in a ne sw direction the area is complicated and the tectonics are not well understood but the ne sw direction is approximately perpendicular to the compressional axis in many of the fault plane mechanisms of the earthquakes these earthquakes are usually at depths between 5 and 12 km although there are some deeper events nearby parallel shear wave polarizations such as those observed are expected to indicate the strike of nearly vertical parallel microcracks which would be aligned parallel to the direction of maximum compression thus the shear wave polarizations in the peter the first range indicate that the directions of principal stress are reversed in the rock above the earthquake foci where thrust faulting is taking place

geochemistry of early mesozoic tholeiites from morocco abstract mesozoic dolerites from two areas of morocco the high atlas fold belt between marrakech and demnat and the anti atlas belt in the area of foum zquid are most high ti quartz normative tholeiites whichi in many respects resemble mesozoic dolerite dikes from eastern north america the dolerites display a wide range of major and trace element compositions some of which are due to fractional crystallization the doleritic sequences from high atlas also show vertical stratigraphic zonation which is characterized by a progressive depletion of lithophile elements toward the top this trend together with regularities of trace element ratio variations are indicative of a dynamic melting of an initially homogeneous source it is suggested that the continental upper mantle source for dolerites of morocco was enriched in several incompatible elements in comparison with the upper mantle source for ocean floor tholeiites