on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 2 applicability of a u leach model to mineral separates abstract preliminary u series data are presented on the disequilibria of mineral separates of surface samples from the eye dashwa lakes granite canada most analyses of the ferromagnesian quartz plus feldspar and zircon plus sphene grains show that leaching of u has taken place such that 234 u 239 u 1 and 230 th 234 u 1 the simple leach model presented in a companion paper was used to explain these characteristic ratios it is suggested that the leach model may be used on zircon and sphere grains to estimate u leach rates and this is relevant to the suggestion of using sphene like hosts as the primary barrier in the safe disposal of nuclear waste a full analysis of u mobility within a given rock volume was not possible due to our limited data base and to our inability to monitor labile u directly

postseismic and interseismic displacements near a strike slip fault a two dimensional theory for general linear viscoelastic rheologies 1 we present an analytic solution for the deformation near an infinite strike slip fault in an elastic layer overlying a linear viscoelastic half space the theory is valid for any linear viscoelastic rheology and any earthquake sequence this is a generalization of the work of j c savage and colleagues which only holds for models with a uniform shear modulus maxwell viscoelastic lower half space and periodic rupture recurrence we demonstrate the theory for models of an elastic layer over a maxwell standard linear solid burgers and triviscous half space for each of these models we calculate example postseismic displacements interseismic displacements in a periodic earthquake sequence and interseismic displacements for a nonperiodic earthquake sequence our solution is for a simple geometry however the model presents an elegant tool to explore the evolution of displacements for relatively complex rheologies and rupture recurrence histories

effect of water on the rheology of experimentally deformed quartzite empirical flow laws have been determined for simpson quartzite samples deformed to mechanical steady state in the quartz stability field using griggs blacic solid medium deformation apparatus experiments were conducted on samples both as received dry and with water added via the dehydration of a talc confining medium wet best fits of the power law type yield a stress exponent of 2 72 0 19 an activation enthalpy of 134 32 kj mol 1 and a preexponential constant of 1 16 1 15 0 58 10 7 mpa 2 72 s 1 for the dry quartzite law and are 2 61 0 15 145 17 kj mol 1 and 5 05 5 00 10 6 mpa 2 61 s 1 for the wet quartzite the enhanced hydrolytic weakening of the wet experiments appears to affect the flow laws mostly in the preexponential constants possibly as a defect concentration term that is higher in the wet than in the dry law over the range of experimental conditions 750 900 c 10 7 to 10 4 s 1 and 1 0 1 25 gpa confining pressure dry specimens are 1 5 2 5 times stronger than wet samples deformed at the same conditions the microstructures produced are analogous to those observed in many natural quartz tectonites recrystallization is well developed in the wet but not the dry specimens at flow stresses below 500 mpa microstructures indicative of recovery are well developed a comparison of our creep activation enthalpies with those determined from diffusion experiments are consistent with deformation of wet simpson quartzite that is limited by oxygen self diffusion inconsistencies between the present study and previous studies are probably the result of differences in sample material sample treatment and sample assemblies chemical environment

heat flow heat production and crustal structure in peri atlantic regions abstract a linear relationship is commonly observed between heat flow and heat generation it provides information about the distribution of radioelements with depth over large regions the linear relationship is no more tenable but points still cluster within an elongated trend in which a regression analysis provides the bulk reduced heat flow and a gross estimate of the heat production distribution with depth over the whole considered region when geological provinces share an identical heat flow heat generation relation they form a geothermal province data measurements in western europe suggest that at least two provinces should be considered one can be related to the hercynian crust and the second to the older caledonian crust we suggest that the depth obtained from thermal data corresponds to the depth of the mafic granulite layer western france south and central england share identical geothermal parameters which can be correlated with the depth of the granulitic layer down to 17 18 km data from scotland do not fit the relationship of south and central u k and present a lower slope indicating that the radiogenic enriched layer is shallow 8 10 km this correlates with the seismic structure of the caledonian crust where the granulite layer is observed at this depth data from scotland can be compared to those from norway newfoundland new hampshire and eastern appalachian crust where the same crustal composition is observed

depositional models for fine grained sediment in the western hellenic trench eastern mediterranean sediment in tectonically active topographically restricted settings of the western hellenic arc eastern mediterranean consists primarily of clayey silt and silty clay failure of metastable sediment temporarily stored on relatively steep slopes is triggered by earthquake tremors and eustatic oscillations redeposition of these materials by gravitative transport has resulted in markedly different lithofacies from site to site most piston cores include three late quaternary stratigraphic units that can be correlated with sections in other parts of the eastern mediterranean numerous radiocarbon age determinations enhance the correlation seven fine grained sediment types are identified in cores from eight distinct depositional environments some muds are closely related to specific environments slump and debris flow deposits on slope and high relief environments or to time well laminated mud during the latest pleistocene mid holocene or to both uniform and faintly laminated muds restricted to trench basins turbiditic and hemipelagic muds are common throughout the study area mud distribution patterns correlate closely with calculated sedimentation rates we propose two depositional models for these sediments the first emphasizes downslope transformations resulting in progressively reduced flow concentration during transport from slump and debris flow turbidity current low density turbidity current or turbid layer mechanisms the distal end member deposits settling from low concentration flows are thick rapidly emplaced fine grained uniform muds closely associated with faintly laminated muds these were ponded in flat trench basin plains planktonic and terrigenous fractions in the turbiditic finely laminated and uniform muds record mixing of materials of gravitative and suspension origin during redeposition this sequence prevails under conditions of minimal stratification of water masses as characterized by the present mediterranean in the second model developed for conditions of well developed water mass stratification well laminated rather than uniform mud prevails as the end product of low concentration flows these very finely laminated and graded muds record particle by particle settling from detached turbid layers concentrated along density interfaces they include material from turbid layers complemented by the normal rain of pelagic material stratification barriers resulted in region wide distribution of such deposits in both slope and trench environments

tsunami induced sediment transport in the abyssal mediterranean sea an unusual stratigraphic unit nicknamed homogenite fills topographic lows in the complex ridge and trough bathymetry at two survey sites on the western mediterranean ridge and the calabrian ridge on near bottom 4 khz seismic reflection profiles this unit us an acoustically transparent near surface flat lying layer whereas in cores it is a homogeneous gray marl as much as 7 m thick grain size decreases upcore within the unit implying that it was deposited in a single event controlled by gravitational settling the stratigraphic position of the homogenite relative to a firmly dated sapropel bed suggests emplacement between 4400 and 3100 yr b p the source of the homogenite is inferred to be the nearby basin walls farther east two other sites with similar rugged topography lack homogenite entirely a triggering mechanism is required which is capable of initiating massive sediment transport simultaneously in many separate basins at the western two survey sites but which is not effective at the eastern sites a large archeologically recorded earthquake of the correct age is considered and rejected because its epicenter is closer to the nonhomogenite bearing sites than to the sites where this sediment type was observed and because several other earthquakes of comparable magnitude have since been recorded in the area whereas the homogenite is unique the 3 500 yr b p collapse of the caldera of the volcano of santorini caused a huge tsunami which is recorded archeologically and geologically around the eastern mediterranean because of refraction of the tsunami by the bathymetry and because the caldera collapsed in its southwest corner a disproportionate amount of tsunami energy was directed toward the western area where homogenite is observed in contrast the homogenite free sites were relatively sheltered an order of magnitude calculation shows that the near bottom oscillating currents accompanying the santorini tsunami were at or above the threshold erosion velocity at the homogenite bearing sites in addition the near bottom pressure pulse under the tsunami at the homogenite bearing sites was sufficient to cause liquefaction of sediments neither mechanism was adequate to cause sediment transport or slope failure at the homogenite free sites

deformation during the 12 november 1999 duzce turkey earthquake from gps and insar data only 87 days after the mw 7 5 17 august 1999 izmit earthquake the duzce earthquake ruptured a ca 40 km long adjoining strand of the north anatolian fault naf system to the east we used displacements of 50 global positioning system gps sites together with interferometric synthetic aperture radar insar range change data spanning the event to estimate the geometry and slip distribution of the coseismic rupture postseismic deformation transients from the duzce earth quake and the preceding i zmit event that are included in some of the measurements are corrected for using dislocation models fit to gps data spanning the various time periods nonlinear inversions for fault geometry indicate that the rupture occurred on a ca 54 north dipping oblique normal right lateral fault distributed slip inver sions indicate maximum strike slip near the center of the duzce fault close to the earthquake hypocenter slip magnitude and depth of faulting decrease to the west and east of the hypocenter both gps and insar data suggest that normal slip is restricted to the shallow portion of the rupture the duzce earthquake had the highest slip to rupture length ratio of any historic earthquake along the naf

short term afterslip in the 1994 sanriku haruka oki earthquake the sanriku haruka oki earthquake that occurred on december 28 1994 at the japan trench as a typical interplate thrust event was followed by year long afterslip as large as the slip in the high speed rupture heki et al 1997 here we report on the transition between these inferred from crustal movements during the five days interval before and after the earthquake since this timescale is too long for seismometers but not suitably long for global positioning system gps we rely primarily on strainmeter data taken 200 km southwest of the epicenter to confirm that the recorded strain changes are not local disturbances we compare them with crustal movements derived by high time resolution analyses of gps data in the same period the transition to the long term afterslip was gradually achieved by slow fault slip with a time constant of a few hours the cumulative slow slip in 24 hours amounts to 1 3 of the coseismic slip i e we may overestimate the coseismic displacement if we look at gps data time series composed of daily solutions the result presented here indicates that a single earthquake could have multiple aspects in its slowness visible with different seismological and geodetic tools and we need to use all such data to understand fully such a hybrid earthquake

sediment residence times constrained by uranium series isotopes a critical appraisal of the comminution approach abstract quantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments we present uranium isotope data for cooper creek palaeochannel sediments from the lake eyre basin in semi arid south australia in order to attempt to determine the formation ages and hence residence times of the sediments to calculate the amount of recoil loss of 234u a key input parameter used in the comminution approach we use two suggested methods weighted geometric and surface area measurement with an incorporated fractal correction and typical assumed input parameter values found in the literature the calculated recoil loss factors and comminution ages are highly dependent on the method of recoil loss factor determination used and the chosen assumptions to appraise the ramifications of the assumptions inherent in the comminution age approach and determine individual and combined comminution age uncertainties associated to each variable monte carlo simulations were conducted for a synthetic sediment sample using a reasonable associated uncertainty for each input factor and including variations in the source rock and measured 234u 238u ratios the total combined uncertainty on comminution age in our simulation for both methods of recoil loss factor estimation can amount to 220 280 ka the modelling shows that small changes in assumed input values translate into large effects on absolute comminution age to improve the accuracy of the technique and provide meaningful absolute comminution ages much tighter constraints are required on the assumptions for input factors such as the fraction of recoil lost 234th and the initial 234u 238u ratio of the source material in order to be able to directly compare calculated comminution ages produced by different research groups the standardisation of pre treatment procedures recoil loss factor estimation and assumed input parameter values is required we suggest a set of input parameter values for such a purpose additional considerations for calculating comminution ages of sediments deposited within large semi arid drainage basins are discussed

plagioclase preferred orientation in layered mylonites evaluation of flow laws for the lower crust thesis s m joint program in marine geology and geophysics massachusetts institute of technology dept of earth atmospheric and planetary sciences and the woods hole oceanographic institution 2008

geochemical baselines for the radioelements k u and th in the campania region italy a comparison of stream sediment geochemistry and gamma ray surveys abstract this paper presents new data on the baseline concentrations of u th and k in 2389 stream sediments over the whole campania region these data based on systematic sampling and analysis are compared with those obtained by gamma ray spectrometry surveys variations in the u th and k concentration in the surficial environment of the campania region appear to be related to bedrock lithology generally high u th and k values in stream sediments correspond well with the occurrence of volcanic rocks in the central western part of the region whereas low values are found in areas characterized by silico clastic and carbonate deposits occurring mostly in the southern and eastern part of the region gamma ray spectrometry maps show a similar pattern although the distribution of the highest radioactivity levels define more restricted areas than the ones resulting from mapping stream sediment geochemistry particularly high 40k radioactivity levels delimit all the known eruptive centers roccamonfina campi flegrei and somma vesuvius including the fissural sources of campania ignimbrites much better than u and th radioactivity one of the concerns for human health in the campania region is the total gamma radiation and rn potential related mostly to alkaline volcanics of the neapolitan volcanological province in particular geothermal activity occurring in all the campanian volcanic areas represents a potential hazard for rn gas

elevated stresses and creep rates beneath the brittle ductile transition caused by seismic faulting in the upper crust 1 large faults in the brittle upper continental crust are envisaged to terminate near the brittle ductile transition zone at a depth that is a complex function of material properties temperature stress and strain rate here we investigate the effect of coseismic displacement along a fault in the upper crust on the adjacent middle and lower crust using a two dimensional numerical model of faulting within an elastic frictional viscous rheology results demonstrate that a major displacement event can cause a dramatic increase in differential stress and creep strain rates in the crust near and below the lower termination of the fault a transient deflection of the brittle ductile transition zone and a zone of elevated strain rates down to the base of the crust the perturbation decays over timescales consistent with postseismic relaxation the stresses and strain rates predicted in such models are in accord with those inferred from microstructural damage analysis of exhumed metamorphic rocks indicating short term deformation at decaying stress and strain rates

uranium series disequilibrium in tuffs from yucca mountain nevada as evidence of pore fluid flow over the last million years abstract samples of tuff from boreholes drilled into fault zones in the exploratory studies facility esf and relatively unfractured rock of the cross drift tunnels at yucca mountain nevada have been analysed by u series methods this work is part of a project to verify the finding of fast flow paths through the tuff to esf level indicated by the presence of bomb 36cl in pore fluids secular radioactive equilibrium in the u decay series i e when the radioactivity ratios 234u 238u 230th 234u and 226ra 230th all equal 1 00 might be expected if the tuff samples have not experienced radionuclide loss due to rock water interaction occurring within the last million years however most fractured and unfractured samples were found to have a small deficiency of 234u weighted mean 234u 238u 0 95 0 01 and a small excess of 230th weighted mean 230th 234u 1 10 0 02 the 226ra 230th ratios are close to secular equilibrium weighted mean 0 94 0 07 these data indicate that 234u has been removed from the rock samples in the last 350 ka probably by pore fluids within the precision of the measurement it would appear that 226ra has not been mobilized and removed from the tuff although there may be some localised 226ra redistribution as suggested by a few ratio values that are significantly different from 1 0 because both fractured and unfractured tuffs show approximately the same deficiency of 234u this indicates that pore fluids are moving equally through fractured and unfractured rock more importantly fractured rock appears not to be a dominant pathway for groundwater flow otherwise the ratio would be more strongly affected and the th and ra isotopic ratios would likely also show disequilibrium application of a simple mass balance model suggests that surface infiltration rate is over an order of magnitude greater than the rate indicated by other infiltration models and that residence time of pore fluids at esf level is about 400 a processes of u sorption precipitation and re solution are believed to be occurring and would account for these anomalous results but have not been included in the model despite the difficulties the u series data suggest that fractured rock specifically the sundance and drill hole wash faults are not preferred flow paths for groundwater flowing through the topopah spring tuff and by implication rapid flow within 50 a from the surface to the level of the esf is improbable

tectonic setting and provenance of the neoproterozoic uinta mountain and big cottonwood groups northern utah constraints from geochemistry nd isotopes and detrital modes abstract the neoproterozoic uinta mountain group was deposited in an east trending intracratonic rift bounded on the north by an active fault system and opening into a shallow sea on the west where the big cottonwood group was deposited in an estuary although this rift may have been associated with the early stages in the breakup of rodinia it was not an aulacogen geochemical nd isotope and detrital mode studies indicate that uinta mountain group sediments were derived from mixed archean and paleoproterozoic sources with the former dominating big cottonwood group sediments appear to have been derived predominantly from paleoproterozoic sources the archean sediment source is the wyoming craton and source rocks comprised dominantly granites enriched in th u y zr hf and ree the relative abundance of enriched granite implied by sedimentary rocks of the uinta mountain group indicates that the wyoming craton is anomalous compared to other archean cratons cia values and a cn k relationships in shales of the uinta mountain and big cottonwood groups indicate high degrees of weathering of sources probably in subtropical to tropical climates supporting a near equatorial location for southwestern laurentia at about 800 ma differences in the nd isotopic composition between the big cottonwood group and neoproterozoic sedimentary rocks in western utah and northeast nevada suggest a northwest striking uplift in northwest utah possibly ancestral to the paleozoic toole uinta arch

234u 238u evidence for local recharge and patterns of ground water flow in the vicinity of yucca mountain nevada usa uranium concentrations and 234u 238u ratios in saturated zone and perched ground water were used to investigate hydrologic flow and downgradient dilution and dispersion in the vicinity of yucca mountain a potential high level radioactive waste disposal site the u data were obtained by thermal ionization mass spectrometry on more than 280 samples from the death valley regional flow system large variations in both u concentrations commonly 0 6 10 g l 1 and 234u 238u activity ratios commonly 1 5 6 are present on both local and regional scales however ground water with 234u 238u activity ratios from 7 up to 8 06 is restricted largely to samples from yucca mountain data from ground water in the tertiary volcanic and quaternary alluvial aquifers at and adjacent to yucca mountain plot in 3 distinct fields of reciprocal u concentration versus 234u 238u activity ratio correlated to different geographic areas ground water to the west of yucca mountain has large u concentrations and moderate 234u 238u whereas ground water to the east in the fortymile flow system has similar 234u 238u but distinctly smaller u concentrations ground water beneath the central part of yucca mountain has intermediate u concentrations but distinctive 234u 238u activity ratios of about 7 8 perched water from the lower part of the unsaturated zone at yucca mountain has similarly large values of 234u 238u these u data imply that the tertiary volcanic aquifer beneath the central part of yucca mountain is isolated from north south regional flow the similarity of 234u 238u in both saturated and unsaturated zone ground water at yucca mountain further indicates that saturated zone ground water beneath yucca mountain is dominated by local recharge rather than regional flow the distinctive 234u 238u signatures also provide a natural tracer of downgradient flow elevated 234u 238u in ground water from two water supply wells east of yucca mountain are interpreted as the result of induced flow from 40 a of ground water withdrawal elevated 234u 238u in a borehole south of yucca mountain is interpreted as evidence that natural downgradient flow is more likely to follow southerly paths in the structurally anisotropic tertiary volcanic aquifer where it becomes diluted by regional flow in the fortymile system

determination of recent 238u 234u and 230th mobility in granitic rocks application of a natural analogue to the high level waste repository environment abstract the isotope activity ratios 234u 238u and 230th 234u have been investigated in drill core samples up to 1300 m depth in three granitoids from australia to identify the nature of possible recent 1 0 which has generated excess 230th these enriched ground waters do not appear to have penetrated below 530 m depth and 230th excess indicates bulk loss of u the observed disequilibria indicate that significant radionuclide mobilisation has occurred in these rocks during the recent past

review of the modelling of radionuclide transport from u series disequilibria and of its use in assessing the safe disposal of nuclear waste in crystalline rock abstract u series disequilibia from crystalline rocks and u deposits have been used to estimate the timing of hydrogeological events for u and ra mobility and to model the transport rates of u and ra both with some sucess unfortunately activity ratio data alone are not unique to a given process or model and it is shown how inappropriate choice of the model can have quite diverse consequences for interpretation of the data information from other sources is needed to help minimise these non uniqueness problems but as yet the state of methodology is unadequate to assess completely the validity of the models in particular the rate of deposition of u in fractures seems highly dependent upon the availability of trivalent fe and other low temperature minerals whose rates of formation are largely unknown this review reinforces the need to assess closely the suggestion that chemisorption is an effective retardant of fracture borne borne repository source radionuclides

considerations for u series dating of sediments insights from the flinders ranges south australia abstract uranium isotope ratios have been determined for the fine grained detrital fraction of pleistocene wilkawillina valley fill sediments four local proterozoic bedrock samples and fine grained aeolian material from a sand dune deposit of the flinders ranges south australia the aim was to quantify the comminution age i e the time elapsed since physical weathering of the bedrock and residence time of the valley fill sediments and to place tighter constraints on input parameters for the comminution age calculation despite using two independent approaches for determination of the recoil lost fraction of 234 u from the sediment weighted geometric and surface area estimates samples fail to produce realistic comminution ages and hence residence times the issues involved in the ability to determine sediment comminution ages are discussed the 234 u 238 u activity ratio of the local bedrock is not in secular equilibrium despite the bedrock being much older than 1 ma i e the timeframe for 234 u and 238 u to reach secular equilibrium in a closed system using the average flinders ranges bedrock 234 u 238 u ratio instead of an assumed 234 u 238 u activity ratio of unity for the source would significantly reduce calculated residence times this result warrants concern for future studies using the comminution approach for which a secular equilibrium source 234 u 238 u activity ratio is assumed significant input of aeolian material may modify the measured 234 u 238 u activity ratios such input may be more tightly constrained in future studies using rare earth element and radiogenic isotopic data future comminution studies would benefit from further consideration of the importance of 1 leaching lost 234 u from source rock and bulk sediment samples 2 wind deposition of fine grained material and 3 the appropriateness and robustness of sample pre treatment procedures

uranium series nuclides in the golden fault colorado u s a dating latest fault displacement and measuring recent uptake of radionuclides by fault zone materials abstract concentrations and isotopic ratios of u th and ra were measured in a fault zone near golden colorado where major displacement occurred between about 190 and 615 ka faulting created new surfaces for leaching and provided the pathways for u rich ground water uranium and230th the latter produced by the decay of dissolved234u are adsorbed by fault gouge hematite stained sand and brecciated sand and claystones the observed u enrichment is as much as six times baseline value and the simultaneous enrichment of230th is estimated at about ninefold relative to238u the adsorption of radionuclides chemically analogous to th such as pu iv and np and237np decay products on fault zone materials would contribute to the immobilization of high level radioactive waste in the vicinity of a repository in the event of leakage from engineered barriers into fractured rock mass

investigation of the tectonics of the main marmara fault by means of deep towed seismic data abstract we report a study of the active principal deformation zone pdz of the main marmara fault mmf in the sub basins of the sea of marmara by means of deep towed seismic pasisar as well as multi beam bathymetry data collected by ifremer s r v le suroit in september 2000 our main objective is to investigate the active deformation within the uppermost sedimentary layers with a much higher resolution than hitherto has been available to the west of the sea of marmara the pdz is located along the southern flank of the tekirdag basin where the sediments are affected by steep reverse faults dipping toward the north e w strike slip faults are also observed in the central part of the tekirdag basin and thrusting occurs along its n50 trending margin we interpret these structures in terms of a slight clockwise rotation in the basin north of the pdz to the east the pdz enters the central basin and follows a steep scarp along the southern flank of a tectonic depression the scarp consists of an en echelon fault system with a normal component these faults are combined with small parallel anticlines and synclines that extend along the southern portion of the depression the northern scarp of the depression is made of a mixed system of faults with both normal and reverse components associated with anticlines and synclines these faults are best interpreted as right lateral strike slip faults with a vertical component that is dominantly normal these faults and the sigmoid shape of the depression are compatible with a clockwise rotation above the pdz this recent tectonic structure appears to be superimposed over a pre existing graben that is now essentially deactivated the pdz continues eastwards out of the central basin as a n50 e trending nw verging thrust system toward the kumburgaz basin that is located on a restraining bend of the pdz this shortening zone consists of two main n60 e trending branches the northern one is more pronounced and composed of two successive restraining bends the southern branch is smoother and forms a gently curved connection between the two segments of the pdz this suggests that the pdz migrates southward to cut through this restraining bend further east the pdz enters the cinarcik basin along its northern scarp active deformation observed on the pasisar profiles along the 290 trending eastern portion of this scarp consists of n110 5 trending dextral strike slip faults connecting short segments of active n130 140 normal faults that control elongated depocenters along the southern flank of the cinarcik basin the e w izmit fault enters the basin from the east pasisar data confirm the extension of the izmit strike slip fault into the cinarcik basin and the large development of normal faulting along the southern flank of the basin some of the normal faulting observed here may be related to horse tail termination of the izmit fault while most of it is the expression of strain partitioning

regional wave propagation in turkey and surrounding regions this paper was published by the american geophysical union agu copyright 2000 agu see also http www agu org journals gl gl0003 1999gl008375 pdf 1999gl008375 pdf http atlas geo cornell edu turkey publications gok et al 2000 htm

the influence of different rheological parameters on the surface deformation and stress field of the aegean anatolian region the aegean anatolian region is characterised by an inhomogeneous deformation pattern with high strain rates and a high seismicity both at the boundaries and in the plate interior this pattern is controlled by the geometry and rheology of the structural units involved and their tectonic setting a numerical analysis with a finite element model of the region is used to quantify the influence of different rheological parameters viscoelastic material behaviour is implemented for the mantle lithosphere whereas the crust is modelled with an elastic plastic rheology the variation of the inelastic material properties viscosity and plastic strength quantifies the influence of these material parameters on the deformation stress and strain patterns comparison of the modelled results with geodetic and geophysical observations reveals that the viscosity of the mantle lithosphere is the key to explaining the inhomogeneous deformation pattern the best fit model yields a viscosity of 1020 pa s beneath anatolia whereas adjacent regions have viscosities between 1021 and 1023 pa s the model also explains the intra plate seismicity and the stress field as well as its partitioning into regions with strike slip and normal faulting the final model is in good agreement with seismological geodetic and geological observations local deviations can be tracked down to small scale structures which are not included in the model

a thick holocene homogenite from the ionian abyssal plain eastern mediterranean abstract a homogenite layer thicker than 12 m holocene in age occurs in the ionian abyssal plain the graded sandy base is 1 3 m thick most of the layer is structureless and homogeneous in grain size and mineral composition the most remarkable components are siltsized grains composed of aragonite needles they are interpreted as skeleton fragments of the green alga halimeda sp the homogenite covers an area of at least 1100 km 2 and assuming a minimum thickness of 10 m comprises a volume of 11 km 3 the source of the material of the homogenite is a matter of speculation very likely it has been remobilized from different areas around the ionian abyssal plain as triggering event a tsunami generated by the collapse of the santorini caldera about 3500 yrs b p is assumed

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

infilling history of a neoproterozoic intracratonic basin nd isotope provenance studies of the uinta mountain group western united states abstract neodymium isotope and selected trace element concentration data were obtained from 27 samples of shales and arkosic sandstones comprising the neoproterozoic uinta mountain group umg in north eastern utah and northwestern colorado to determine the provenance of siliciclastic detritus deposited in this region and to reconstruct aspects of the proterozoic geologic history of the southern margin of the archean wyoming province in the east lobe of the uinta mountains coarse grained components of the jesse ewing canyon formation the oldest recognized formation of the umg have measured nd values of 23 to 28 and were most probably derived from archean basement of the wyoming province to the north fine grained sediment in the southern portions of the jesse ewing canyon formation and shales and quartz arenites from overlying undifferentiated umg all contain at least a component of detritus derived from proterozoic crust in the west lobe the oldest members of the umg the red castle lake gilbert peak and moosehorn lake formations and arkosic arenite comprising the northern portions of the overlying mount watson formation were also derived exclusively from archean sources however as in the east lobe the more mature sandstones that dominate the southern sections of the mount watson formation have isotopic compositions that require a significant proterozoic crust derived detrital component our data support a model in which sedimentary rocks with an archean provenance represent the preserved remnants of alluvial fans marking the northern margin of the basin in which the umg was deposited a source for these sediments within the archean wyoming province is consistent with the high light rare earth element lree and th abundances of finegrained low nd sedimentary rocks given that late archean granitic rocks within the wyoming province have similar trace element characteristics sediments with proterozoic components in both the east and west lobes were apparently deposited from a fluvial system that transported sediment along the basin axis the proterozoic detrital component in these sediments originated either through direct erosion of the colorado province in the neoproterozoic or through erosion of mixed archean and proterozoic crust located to the east of the umg basin that originally formed during the paleoproterozoic accretion of the colorado province to the southern margin of the wyoming craton

quaternary mud turbidites from the south shetland trench west antarctica recognition and implications for turbidite facies modelling a piston core from the basinal part depth of 5188 m of the south shetland trench west antarctica yielded a terrigenous mud section 11 m long which can be subdivided with great precision into turbidite and hemipelagite layers mud turbidites mean bed thickness 44 cm alternate regularly with and are best distinguishable from their hemipelagite host mean bed thickness 17 cm by the following features i sharp basal contacts ii terrigenous sand free textures except basal well sorted silt laminae and the absence of outsized ice rafted components iii a laminated little to non bioturbated internal structure iv distinct textural and compositional grading and v marked steps on water content and sediment density logs mud turbidites recovered from the south shetland trench differ from an earlier model mud turbidite sequence by their i excessive about six times larger bed thickness ii complex internal organization manifested in multiple repetitions up to four of the same structural interval s in sequential or nonsequential order iii distinctive very fine grained cap of highly porous clay rich in fragments of siliceous biogenics iv widespread zones of penesyndepositional deformation and v evidence of flow reversals these features are interpreted to record deposition from large muddy turbidity currents subjected to flow transformations including soliton and or seiche related reversals induced by ponding and interactions of the flow with the topographical confinements of the trench it is concluded that contained muddy turbidites cannot be adequately modelled using published sequences differentiation of single model and contained mud turbidites offers obvious advantages in basin analysis and in understanding the plethora of turbidity current related depositional mechanisms of deep sea mud

isotopic composition of uranium and thorium in crystalline rocks the 238u 234u 230th 232th system has been investigated in 84 silicic crystalline rocks obtained from drill cores surface and near surface samples in california wyoming colorado and illinois results of these analyses displayed on ternary diagrams with apexes for 238u 234u and 230th indicate five predominant geochemical processes that affected uranium in the rock 1 bulk uranium leaching where 238u and 234u were removed with little or no fractionation 2 preferential 234u leaching by alpha recoil displacement 234u recoil loss with lesser 238u loss 3 234u recoil loss with little or no 238u loss 4 uranium assimilation where both 238u and 234u were added with present day 234u 238u activity ratios varying from 0 8 to 1 2 and 5 addition of 234u and 230th by daughter emplacement processes 234u 230th recoil gain evidence for the existence of 234u and 230th recoil gain in rocks is the most important finding of this investigation radioactive disequilibrium occurs in the majority of rocks analyzed where 234u recoil loss is the predominant process associated with incipient weathering u assimilation and 234u 230th recoil gain occur under conditions of substantial water penetration along fractures and into weathered zones in the rocks relatively unfractured and petrographically fresh rocks from the uph 3 drill hole in northern illinois are closest to being in radioactive equilibrium for any suite of rocks included in this study and they demonstrate that equilibrium during the last 0 5 m y can be maintained over a substantial vertical distance where there has been little or no movement of water in the basement rock the 238u 234u 230th system can be a sensitive indicator of geologically recent u mobility and rock water interaction both in petrographically fresh core samples and in sealed fracture zones

the shochary ridge sequence southeastern pennsylvania a possible ordovician piggyback basin fill abstract the central appalachian orogen of eastern pennsylvania is underlain in part by three fault bounded deep water clastic sequences the windsor township formation of the hamburg klippe greenwich slice the martinsburg formation and the shochary ridge sequence deep water sandstones of the windsor township formation were deposited in a trench on oceanic lithosphere in early middle ordovician time clastic detritus of the late middle early late ordovician martinsburg formation accumulated as part of a longitudinal deep sea clastic system in the central appalachian foreland basin deposits of the coeval shochary ridge sequence comprise a 1500 m thick coarsening upward sequence of hemipelagic mudstone and siltstone turbidites although devoid of the type of bedding cyclicity implicit to published submarine fan models the shochary ridge sequence may have accumulated as part of a morphologically poorly developed deep sea fan in which submarine channels and depositional lobes never formed or were poorly developed at best the coarsening upward nature of the shochary ridge sequence probably reflects progradation of its depositional system in response to either an inferred late middle early late ordovician glacially induced reduction in sea level and or an increase in tectonic activity in the hinterland sedimentologic and paleocurrent data suggest that deposits of the shochary ridge sequence did not accumulate as part of the martinsburg depositional system palinspastic restoration places the shochary ridge depocenter to the southeast of the martinsburg basin i e on the orogen side of the foreland basin accordingly the shochary ridge sequence is interpreted to reflect gradual filling of a basin that existed within the active thrust terrane to the southeast of the martinsburg depocenter this basin a piggyback or slope basin formed on martinsburg strata that had been tectonically incorporated into the northwest migrating thrust terrane as the frontal thrust advanced into the foreland basin

postseismic deformation following the 1991 racha georgia earthquake 1 the 1991 ms 7 0 racha earthquake is the largest ever recorded in the caucasus mountains approximately three months after this thrust faulting earthquake a gps network was set up to measure postseismic surface deformation we present an analysis of these data which indicate accelerated postseismic motions at several near field sites we model this deformation as either afterslip on the rupture surface or viscoelastic relaxation of the lower crust we find that the postseismic motions are best explained by shallow afterslip on the earthquake rupture plane the minimum postseismic moment release is estimated at 6 0 1018 n m which is over 200 times the moment released by aftershocks in this same period and about 20 of the coseismic moment we also show that the effective viscosity of the lower crust in the western greater caucasus region exceeds 1018 pa s

coseismic and early postseismic slip for the 2003 tokachi oki earthquake sequence inferred from gps data 1 early afterslip following the 2003 tokachi oki earthquake is investigated using subdaily gps time series afterslip results are compared with the coseismic slip for the m8 mainshock and the m7 4 aftershock afterslip between those two earthquakes is inferred at the southwestern adjacent region of the mainshock between two epicentral regions which possibly triggered the aftershock in the southwest subsequently deeper slip occurs the afterslip loci are distinct from the rupture regions the non uniform propagation of afterslip may reflect the depth dependence of the effective normal stress and the distance between the closest unstable slip patches

the possible bearing of the granite of the uph deep drill holes northern illinois on the origin of mississippi valley ore deposits the pb pb th pb and u pb systems of whole rock drill core samples of the granite of uph record at least one postcrystallization event treatment of the data on a concordia plot indicate the timing of this disturbance was probably 260 35 m y ago and probably no older than 400 m y ago the upper intercept age on concordia is 1416 20 m y and the pb pb isochron age for the four least disturbed rocks plus the four potassium feldspars is 1451 19 m y these ages are in close agreement with rb sr whole rock and u pb zircon ages determined by others and should be the age of granite formation considerable pb loss is indicated for many of the shallower samples that have a more red rather than pink color probably to a factor of two to three or more as a result of the disturbance although the granite remains pb rich today 40 80 ppm in some other studies of disturbed u th pb systems the radiogenic lead has been taken up by potassium feldspars however the pb for most samples seems to have been lost from the system for the granite of uph one sample with an unusually high pb content of about 195 ppm has the most radiogenic pb of any sample but normal values of th u this sample has obviously gained radiogenic pb by more than a factor of four and confirms that pb was indeed mobilized in parts of the system within the limits of the uncertainties equal amounts of pb were lost or gained in both the u pb and th pb systems which is compatible with mobilization being restricted to lead there is some tendency however for the more affected samples to have lower th u values and higher u contents a complex model in which u is gained pb lost and 208pb lost preferentially to 207pb and 206pb cannot be ruled out u and th have somewhat different crystallographic locations and decay energies so that 208pb might be in more accessible sites than the other pb isotopes fission track mapping of the samples indicates most of the u today is located in submicroscopic sites along edges and cleavages of biotite and iron oxides so u is readily available for remobilization lead extraction with only minor u or th removal may have been accomplished by chloride rich brines lead isotope data on the granite of uph indicates that some of the pb in the ore in the nearby upper mississippi valley lead zinc district may have been derived from these granites an even better match is made with the ores of southeastern missouri although a granite like that of uph would only be one end member most likely the radiogenic end member of a mixed source curiously similar aged and heavy metal rich granites from southeastern missouri are not a good match for theckn nearby ores basement rocks such as the granite of uph must be reconsidered as an important contributor to the ores of the mississippi valley but it is unlikely that they constitute the sole source

evidence of power law flow in the mojave desert mantle studies of the earth s response to large earthquakes can be viewed as large rock deformation experiments in which sudden stress changes induce viscous flow in the lower crust and upper mantle that lead to observable postseismic surface deformation laboratory experiments suggest that viscous flow of deforming hot lithospheric rocks is characterized by a power law in which strain rate is proportional to stress raised to a power n refs 2 3 most geodynamic models of flow in the lower crust and upper mantle however resort to newtonian linear stress strain rate relations here we show that a power law model of viscous flow in the mantle with n 3 5 successfully explains the spatial and temporal evolution of transient surface deformation following the 1992 landers and 1999 hector mine earthquakes in southern california a power law rheology implies that viscosity varies spatially with stress causing localization of strain and varies temporally as stress evolves rendering newtonian models untenable our findings are consistent with laboratory derived flow law parameters for hot and wet olivine the most abundant mineral in the upper mantle and support the contention that at least beneath the mojave desert the upper mantle is weaker than the lower crust

an analogue validation study of natural radionuclide migration in crystalline rocks using uranium series disequilibrium studies abstract concentrations and isotope ratios of natural decay series radionuclides have been studied in three contrasting crystalline rock drillcore sections intersecting water conducting fractures deep in the bedrock radioactive disequilibria resulting from rock water interactions were observed in two of the cores these indicated u migration along distances of 40 cm or more on a time scale of 1 myr in conjunction with th immobility under the same conditions fracture surface minerals showed a high affinity for radionuclide retardation and a limit of 3 cm is suggested for the migration of radionuclides from fracture fluids into the saturated rock this limit may correspond to enhanced matrix porosities resulting from earlier hydrothermal activity along the same channels

uranium isotopic evidence for the origin of the bahariya iron deposits egypt abstract the economic iron ore deposits of egypt are located at bahariya oasis in the lower middle eocene limestone the main iron minerals are goethite hematite siderite pyrite and jarosite manganese minerals are pyrolusite and manganite gangue minerals are barite glauconite gibbsite alunite quartz halite kaolinite illite smectite palygorskite and halloysite geochemical comparison between the ore and the nubia sandstone showed that the ore is depleted in the residual elements al ti v and ni and enriched in the mobile elements fe mn zn ba and u which indicates that the bahariya iron ore is not a lateritic deposit despite the deep weathering in this area on the other hand the nubia sandstone showed depletion in the mobile elements which demonstrates the leaching process in the nubia aquifer the presence of such indicator minerals as jarosite alunite glauconite gibbsite palygorskite and halloysite indicate that the ore was deposited under strong acidic conditions in fresh water isotopic analyses of the uranium in the amorphous and crystalline phases of the ore in the country rocks and dissolved in the nubia aquifer water all support the conclusion that u and fe were precipitated together from warm ascending groundwater u and fe display strong co variation in the ore and the 234u 238u activity ratio of the newly precipitated u in the country rock and the leached component of u in the groundwater are identical there is only slightly more uranium in the amorphous phase than in the crystalline and only a slightly lower 234u 238u activity ratio suggesting that the iron in the two phases have a similar origin comparison of the excess 234u in the water and in the total ore leads to the conclusion that the precipitation of the u and by inference the iron occurred within the last million years however that both precipitation and leaching of u have occurred over the last 300 000 years is evidenced by the extreme 230th 234u disequilibria observed in some of the samples some of the amorphous depositional events have been very recent perhaps within the last 10 000 years

volcanism sedimentation and massive sulfide mineralization in a late cretaceous arc related basin eastern taurides turkey abstract late cretaceous arc volcanism and associated massive sulfide mineralizations occur in the eastern taurus mountains the mineralizations are related to felsic dacitic rhyolitic volcanic rocks which together with basement rocks form the lowermost levels of a 5000 m thick volcano sedimentary sequence and are restricted to a few levels within the sequence basaltic rocks which are intruded by tonalite and dacite form the base of the volcano sedimentary sequence the dacitic rhyolitic rocks are overlain by a volcano sedimentary succession with andesitic dacitic flows the flows do not contain any mineralization this succession starts with volcanic breccia and tuffs at the base passing into crystal rich sandstone and pelagic mudstone with tuffite intercalations and ends with marls intercalated with sandstones basalt and peridotite olistoliths the felsic rocks bear stockwork and disseminated types of mineralization the massive sulfide mineralization has a simple mineral assemblage of pyrite chalcopyrite bornite and sphalerite optical microscopic examination of pyrites from derince massive sulfide deposits reveals that the pyrites are commonly seen in framboidal and cubic forms the geochemistry of the magmatic rocks and sedimentary facies associations indicate that the mineralizations in the derince were developed in an intra arc environment

izmit earthquake postseismic deformation and dynamics of the north anatolian fault zone 1 we have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 izmit and duzce earthquake ruptures using a three dimensional viscoelastic finite element method our models confirm earlier findings that surface deformation within the first few months of the izmit earthquake is principally due to stable frictional afterslip on and below the izmit earthquake rupture a second deformation process is required however to fit the surface deformation after several months viscoelastic relaxation of lower crust and or upper mantle with a viscosity of the order of 2 to 5 1019 pa s improves the models fit to later gps site velocities however for a linear viscous rheology this range of values is inconsistent with highly localized interseismic deformation around the north anatolian fault zone nafz that was well observed prior to the earthquake sequence the simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes that is that it has a power law or burger s body transient rheology a burger s body rheology with two characteristic viscosities 2 to 5 1019 pa s and at least 2 1020 pa s in the mantle is consistent with deformation around the nafz throughout the earthquake cycle

the pleistocene glaciolacustrine sediments in the belchatow mine central poland endogenic and exogenic controls abstract the quaternary overburden of belchatow outcrop contains five glaciolacustrine units the three most widespread are presented they originated during the advance of the sanian elsterian odranian drenthian and wartanian warthian ice sheets the following lake environments are distinguished lake bottom plain tectonically active subaqueous slope subaqueous fan terminoglacial subaqueous fan and prodelta fan the lakes formed under changing conditions the most significant tectonic activity of the graben took place during the odranian and the lake deposits from this glaciation represent terminoglacial conditions the wartanian lake deposits are the only ones that show a shallow water facies that has not been eroded because it has not been overridden by an ice sheet sedimentation conditions changed during the succeeding glaciations endogenic factors affecting sedimentation i e tectonic activity of the graben complemented some exogenic controls such as the distance from the ice sheet the thermal conditions of the lake and the type of sediment supply tectonics changed the style of deposition so much that the lakes although situated in a lowland area displayed characteristics of deep valleys

slope apron deposition in an ordovician arc related setting the vuelta de las tolas member suri formation famatina basin northwest argentina abstract the ordovician suri formation is part of the infill of the famatina basin of northwest argentina which formed in an active setting along the western margin of early paleozoic gondwana the lower part of this formation the vuelta de las tolas member records sedimentation on a slope apron formed in an intra arc basin situated on a flooded continental arc platform the coincidence of a thick arenig llanvirn sedimentary succession and volcanic plutonic arc rocks suggests an extensional or transtensional arc setting and is consistent with evidence of an extensional regime within the volcanic are in the northern puna region the studied stratigraphic sections consist of volcanic rocks and six sedimentary facies the facies can be clustered into four facies associations association 1 composed of facies a laminated siltstones and mudstones and b massive mudstones and siltstones is interpreted to have accumulated from silty muddy high and low density turbidity currents and highly fluid silty debris flows with subsequent reworking by bottom currents and to a lesser extent hemipelagic suspension in an open slope setting facies association 2 is dominated by facies c current rippled siltstones strata these deposits are interpreted to record overbank sedimentation from fine grained turbidity currents facies e matrix supported volcanic breccias interbedded with andesitic lava units comprises facies association 3 deposition was contemporaneous with subaqueous volcanic activity and accumulated from cohesive debris flows in a coarse grained wedge at the base of slope facies association 4 is typified by facies d vitric fine grained sandstones and siltstones and f channelized and graded volcanic conglomerates and breccias deposits these strata commonly display thinning and fining upward trends indicating sedimentation from highly concentrated volcaniclastic turbidity currents in a channelized system the general characteristics of these deposits of fresh pyroclastic detritus suggest that their accumulation was contemporaneous with or post dated shallow water or subaereal explosive volcanism the vuelta de las tolas member tends to show an overall random facies patterns reflecting the strong influence of non cyclical episodic processes related to arc volcanism and slope sedimentation the scarcity of resident ichnofaunas and the presence of thick packages of uniform mudstones suggest deposition under oxygen depleted conditions in a topographically confined ponded sub basin interbasinal correlations favor comparison with middle arenig slope apron successions formed in the northern puna basin and suggest a southward prolongation of the arenig volcanic arc

applications of uthpb isotope systematics to the problems of radioactive waste disposal abstract concentrations of u th and pb and the isotopic composition of pb for whole rock samples of granitoids show 1 that open system behavior is nearly universal in the surface and near surface environment and 2 that elemental mobility is possible to depths of several hundred meters several identified or at least postulated factors that control u and or pb mobility include 1 the mineralogical sites for u and its daughter products 2 access of groundwater to these sites 3 the volume of circulating water and 4 the chemistry of the groundwater studies of granitic samples from peralkaline complexes in the arabian shield have shown that most samples lost less than 20 of their u during recent exposure to the near surface environment most of the u in these samples appears to be firmly bound in zircons in contrast most surface and shallow drill core samples of the granite of lankin dome granite mountains wyoming have lost 70 of their u most of the u in these samples is weakly bound in biotite and epidote family minerals the granite recovered during the illinois deep drill hole project stephenson county illinois is mineralogically similar to the granite of lankin dome but this granite lost radiogenic pb rather than u probably as a result of exposure to groundwater that had a markedly different chemistry from that in the granite mountains studies of the sherman granite wyoming and the gotemar granite southeastern sweden have shown that u and or pb mobility is greatest in and near fractured rock the greater mobility is interpreted to be the result of both a larger water rock ratio in the fractured rock and exposure to water over an increased surface area and consequently a greater number of uranium sites several types of geochemical and mineralogic data can be used to identify rock water interaction in granites however if rock samples have favorable radiogenic to common pb ratios both the amount and approximate timing of u or pb mobility can be obtained through the use of isotopic studies such information can be extremely important in the search for favorable hosts for containment of radioactive waste rocks such as the gotemar granite have undergone considerable rock water interaction most of which occurred 400 myr ago and little in recent times thus a search for zones that have experienced only a little interaction with water may provide a misleading prediction as to the ability of such zones to shield radioactive wastes from the modern biosphere from an isotopic point of view an ideal candidate for evaluation as a host rock for radioactive wastes would have the following characteristics 1 a high ratio 2 of radiogenic to common pb in order to optimize precision of the results 2 a simple two stage geologic history so that results could be interpreted without multiple working hypotheses and 3 an originally high percentage 50 of labile u so that the results would be highly sensitive to even small amount of rock water interaction these characteristics should produce rocks with marked radioactive disequilibrium in surface samples the disequilibrium should grade to radioactive equilibrium with increasing depth until zones in which water has not circulated are found extensive regions of such zones must exist because u th pb systematics of most analyzed granitoids demonstrate closed system behavior for almost all of their history except for their recent history in the near surface environment

seven years of postseismic deformation following the 1999 m 7 4 and m 7 2 izmit duzce turkey earthquake sequence 1 we report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode gps observations for the 1999 izmit duzce earthquake sequence resolvable time dependent postseismic changes to the preearthquake interseismic velocity field extend at least as far as the continuous gps station in ankara 200 km southeast of the izmit rupture seven years after the earthquake sequence the relative postseismic velocity across the north anatolian fault naf reaches 10 12 mm a roughly 50 of the steady state interseismic rate with the highest postseismic velocities within 40 km of the coseismic ruptures we use a sequence of logarithmic time functions to fit gps site motions up to three logarithmic terms with decay constants of 1 150 and 3500 days are necessary to fit all the transient motion observed at the continuous gps stations the first term is required for the component of site motion parallel to the naf at near field sites strongly implicating rapid shallow afterslip the intermediate and longer term postseismic velocity components reflect more broadly distributed strain with a symmetric double couple pattern suggestive of either localized deep afterslip or viscoelastic relaxation of the upper mantle and or lower crust in two areas including the marmara sea this pattern is superimposed on north south extension centered on the naf we speculate that this extension may result from aseismic dip slip along coseismically weakened faults driven by the background tectonic stress

introduction to the illinois deep hole project commonwealth edison recently drilled 3 engineering test holes in n w illinois the 3 holes uph 1 2 and 3 were 0 6 1 6 and 1 6 km deep respectively and the latter 2 penetrated nearly one kilometer of precambrian granitic basement in 1980 continuous core from all 3 holes and access to uph 3 were made available for scientific investigations through the illinois deep hole project the principal study of these holes was an integrated investigation of surface and in hole experiments plus detailed petrologic geochemical and physical property studies of the core samples 50 references

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

the chemical and isotopic record of rock water interaction in the sherman granite wyoming and colorado chemical isotopic radiographic and rock leaching data are combined to describe the effects of rock water interactions in core samples of petrographically fresh 1 43 b y old sherman granite the data serve to identify sensitive indicators of incipient alteration and to estimate the degree pathways and timing of element mobilization unfractured core samples of sherman granite are remarkably fresh by most chemical or isotopic criteria but incipient alteration is indicated by the abundance and distribution of uranium and the degree of radioactive equilibration of uranium with its decay products uranium abundances which are out of equilibrium with lead decay products indicate remobilization of a portion 3 to 60 percent of original uranium in late phanerozoic time association of uranium with minor but pervasive secondary alteration products also indicates some remobilization the amount of apparent uranium mobility in unfractured sherman granite 3 to 60 percent is small compared to the results of similar studies of archean granites from nearby localities chemical and isotopic data evaluated as a function of core sample depth suggest a uranium migrational pathway involving near surface leaching and reconcentration at depth movement of solutions through the upper 200 ft 60 m of sherman granite is fracture controlled and brecciated granite shows more obvious petrographic chemical and isotopic evidence of alteration and multi element redistribution laboratory experiments using freshly crushed sherman granite confirm that uranium is leached in preference to elements such as si mg ca and k and that leachable uranium is situated close to the solid liquid interface perhaps as uranium along grain boundaries in crystal defects or on cleavage traces of minerals that exclude uranium from their structure

the block like behavior of anatolia envisaged in the modeled and geodetic strain rates 1 the geodetic velocity and strain rate patterns in anatolia constrain the rheology of the lithosphere once compared with thin shell finite element tectonic model predictions geodetic and modeled deformation favors a hard lithospheric rheology responsible for the high east west horizontal velocities in the center of anatolia between 39 41 n in proximity of the north anatolian fault the block like behavior of anatolia due to the hard lithospheric rheology is responsible for the low geodetic and modeled strain rates in the center of the peninsula the low strain rate is well correlated with the region of low release of seismic energy between 33 36 e and 38 40 n the high seismic and geodetic strain rate region in the far west part of the naf is also well reproduced by the modeling

rapid afterslip following the 1999 chi chi taiwan earthquake 1 postseismic displacements of as much as 14 cm were recorded by gps measurements in the 3 months following the mw 7 6 1999 chi chi taiwan earthquake data from 35 continuous and 90 campaign surveyed stations which show continued east over west thrusting are analyzed to estimate the postseismic slip distribution and fault geometry assuming the shallow fault dips 24 e as determined by numerous studies of the mainshock we invert for the deeper fault structure our results show that the fault dip shallows with depth below the hypocenter merging into a nearly horizontal decollement at a depth of 8 12 km the afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7 12 km depth as well as significant slip on the lower decollement afterslip is notably absent in the region of maximum coseismic slip consistent with the afterslip being driven by the mainshock stress change

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

history of actinide and minor element mobility in an archean granitic batholith in manitoba canada abstract surface and borehole core samples from the lac du bonnet granite manitoba canada have been analysed for major element concentrations fe 3 fe total ratios rare earth element ree content and actinide isotopic abundances this work forms part of the geological investigations of the canadian nuclear fuel waste management program performed by atomic energy of canada limited aecl the study attempts to understand the history of and processes governing mobilisation of elements and naturally occurring radionuclides during high and low temperature alteration events in fluid bearing fractures in the granite one surface sample and two core samples from 150 m and 730 m are each in contact with fractures in the granite and show evidence of alteration events that penetrated the rock matrix over distances of at least 3 cm loss of ca and na is seen in cores from a depth of 150 m from the highly altered hematite rich rock adjacent to sub horizontal fracture zones at the underground research laboratory url of aecl near lac du bonnet in contrast k fe fe 3 fe and u concentrations increase towards the fracture surface due to formation of illite and association of u with hematite and the illite at the fracture surface u continues to increase but fe and thefe 3 fe ratio decrease indicating fe removal by reduction the ree also show some enrichment in more altered rock at intermediate depths but the total ree concentration is lower than in the surface and deep core samples no clear trends are visible for parent and fracture surface ree in surface and deep core samples however disequilibrium values of 234 u 238 u and 230 th 234 u ratios in surface and intermediate depth core samples indicate that u has been mobilised in recent geological time the last ma but th has remained relatively immobile high th u and 230 th 234 u ratios in surface samples are indicative of rapid leaching of u but little isotopic fractionation probably within the last 10 5 a apparently unaltered rock several centimetres distant from the fracture in surface and intermediate depth samples has lost appreciable u but evidence from u series disequilibrium studies suggests that this process occurred more than one million years ago perhaps during deuteric or hydrothermal alteration core from a fracture at depth in the granite shows little hematite or clay formation and lacks evidence of ree and recent or ancient actinide mobilisation the u series results are correlated with the observed concentrations and isotope activity ratios of u in groundwaters sampled from the same or adjacent fractures analyses of samples of highly altered rubble recovered from centre portions of fracture zones at the url show both excesses and deficiencies of 234 u and 230 th in neighbouring locations possibly due to the presence of a redox front whose position is controlled by modern groundwater composition the implications of these results are discussed for the concept of disposal of nuclear fuel waste at depth in plutonic rock on the canadian shield

the migration of radionuclides in granite a review based on natural analogues abstract the characterization of a geological formation for nuclear waste disposal should be carried out on a site by site basis however the study of analogous granitic formations all around the world gives a few general guidelines for a better understanding of elemental migration processes in this review focused on mineralogical petrological and geochemical phenomena it is shown that fractures should play a dominant role in transport through granites moreover mineralogical transformations as well as their textural and petrophysical consequences e g permeability changes should be reliably predicted finally this review confirms that water rock interactions do mobilize many elements including analogues of actinides u th ree however most alteration minerals of granite e g clay minerals carbonates exhibit a high capability for efficiently trapping these heavy elements it is concluded that natural analogues are very useful for specifying the appropriate approach for the characterization of a geological site they have also proved essential for developing and validating geochemical models of mass transfers around a repository in granite

dating of archean basement in northeastern wyoming and southern montana rb sr whole rock and u pb zircon ages of granite and gneiss cores from three deep drill holes extend known occurrences of archean rocks in the subsurface of northeastern wyoming and southern montana rb sr and k ar mineral ages are discordant and reflect early or middle proterozoic disturbance highly altered rocks occur in a thin zone immediately below the sub cambrian unconformity samples from a few metres deeper in the basement are much fresher but show the effects of this alteration in filled fractures and thin adjacent alteration haloes whole rock rb sr systems have retained a fair degree of integrity in spite of increased susceptibility to modification because of the disturbed mineral systems interaction of the rocks with water a few metres below the sub cambrian unconformity probably occurred for only a relatively short time fractures filled rapidly with secondary minerals such as chlorite anhydrite and carbonate to maintain a relatively impermeable crystalline basement in which the silicates and their contained isotopic systems were preserved ages of cores from two wells extend the archean basement to the nacp anomaly a possible suture related to early proterozoic tectonism these and published ages limit a possible ensimatic mobile belt to a zone 300 km wide beneath the williston basin however the possibility remains that archean crust was continuous between the wyoming age province and the superior province

u th pb systematics of morphologically characterized zircon and allanite a high resolution isotopic study of the alpine rensen pluton northern italy abstract the rensen pluton is a typical member of the tertiary calc alkaline plutonic suite structurally connected to the periadriatic lineament it intrudes the austroalpine polymetamorphic basement of the eastern alps southwest of the tauern window northern italy zircons and allanites from tonalitic quartz dioritic and monzogranitic lithologies were studied systematically on the basis of refined grain by grain microanalytical techniques high resolution isotope analyses show that morphology and u pb systematics of zircon are highly correlated with magma evolution zircons from the main tonalitic part of the intrusion display a gradual increase of u content from early stage s type morphology to late stage g1 type morphology most of the zircon crystals include premagmatic seeds derived from old crustal sources unevolved s type zircons contain inherited components of late proterozoic early paleozoic apparent age whereas late stage g1 type zircons show inheritance of early proterozoic apparent age both types of inherited components are present in zircons from a fine grained tonalitic domain located at the center of the pluton which shows restitic structures the crustal affinity of this rock is corroborated by its relatively low e nd value 6 0 as compared to values obtained for the main tonalite 3 9 and the quartz diorite 3 5 the accuracy of cainozoic zircon ages is affected by initial radioactive disequilibrium in the u pb decay chains particularly uncertain is the fractionation behavior of protactinium which could be enriched in zircon due to the high stability of the pa 5 oxidation state because the th pb system is devoid of long lived intermediate radioactive nuclides the best approximation to the emplacement age of the rensen pluton is given by allanite th pb ages of 31 70 0 25ma 95 c l for the main tonalite and by a slightly younger age of 31 09 0 32ma for quartz diorite

representative uranium deposits and occurrences exclusive of sandstone impregnations and quartz conglomerates abstract all the known non sandstone and non quartz conglomerate types of uranium deposits and occurrences were reviewed to focus on geologic environments from which unknown large economic types might be expected one or more representative examples of each type was selected and its major occurrence characteristics identified following a new limited genetic classification potential significance was judged by capacity of the mineralization process to produce large deposits rather than by the size and grade of known examples the precedent for this approach is set by uranium exploration history exploration occurred in spurts stimulated by demand beyond the capability of known deposits and distinguished by recognition of new types of larger richer deposits which could supply the demand stagnation in the 1960 s and 1970 s of the discovery rate for conventional sandstone impregnations and quartz pebble conglomerates which contributed the bulk of uranium production illustrated the need for another innovative spurt the study encompassed the then unconventional types of uranium deposits however during the investigation exploration discovered so many large rich unconventional deposits that the connotation conventional on the production basis embraced them this included the rossing late magmatic replacement dissemination and a number of impregnation replacement masses related to proterozoic unconformities in canada and australia these types were included in the original project and are retained in this discussion but their inclusion reduces the significance precision and impact originally intended by designating the entire range of considered deposit types as unconventional accordingly the designation conventional unconventional has been removed or subdued however the principle that surprising discoveries introduce new economic types of deposits which were subtly evidenced in known occurrences and shift the designation of conventional was emphatically confirmed by both this project and concurrent exploration recognition of this principle lends potential significance to the remaining unconventional deposits and occurrences discussed their occurrence parameters may contain clues to yet other unknown types of large rich deposits however little effort was made in this paper to identify specific potentially economic exploration targets

high temperature transient creep in olivine rocks abstract the transient creep behaviour of two natural dunites has been investigated at temperatures between 1373 and 1573 k and a confining pressure of 300 mpa in a high resolution gas medium deformation apparatus the specimens were deformed in constant stress experiments in the presence of an aqueous phase and were oriented perpendicular to foliation the results confirm the finding of earlier workers that the high temperature transient flow properties of olivine rocks can be effectively modelled in terms of a burgers body rheology observations of time dependent strain recovery after unloading further support this model the viscosity in the transient regime 1 is found to have the same sensitivity to temperature and stress within the errors of each estimate as has been found previously for steady state creep viscosity 2 thus the ratio 2 1 is found to be relatively insensitive to temperature and stress with values between 0 17 and 0 67 these values are higher than the 2 1 0 1 that has generally been assumed in geophysical modelling of upper mantle transient deformation but are similar to the results of previous experiments with olivine single crystals the ratio of the shear moduli in the transient and steady state regimes 2 1 is found to be weakly sensitive to temperature at 250 mpa stress and 300 mpa confining pressure the value of 2 1 decreases slowly as temperature increases for the present experiments 0 05 2 1 which is comparable to the range of values reported in previous studies

subaqueous sediment gravity flow deposits practical criteria for their field description and classification a new method for the description and classification of subaqueous sediment gravity flow deposits is proposed the classification scheme employs a convenient letter code and divides deposits individual beds into descriptive categories of two hierarchical levels facies and subfacies facies as the higher rank categories are distinguished chiefly on the basis of sediment type i e bed grain size texture a total of 13 facies have been distinguished g gravel gs gravel sand couplet gys gravelly sand s sand sm sand mud couplet ms mud sand couplet tm silt mud couplet mt mud silt couplet m mud mys muddy sand sym sandy mud myg muddy gravel gym gravelly mud subfacies as the lower rank categories are distinguished within the individual facies on the basis of the bed s internal structures the number of subfacies is unlimited and their labelling code includes particular facies symbols see above preceded by lower case letters denoting specific sedimentary structures and their vertical arrangement subfacies thus refer to the bed s intervals or divisions which are labelled as follows m massive unstratified and ungraded g graded unstratified and graded s plane stratified x cross stratified 1 parallel and or cross laminated q liquefied for example subfacies gsg graded to plane stratified gravel are gravel beds that have a lower graded interval and an upper plane stratified interval subfacies xg cross stratified gravel are gravel beds that are cross stratified throughout subfacies sls plane stratified to laminated sand are sand beds that have a lower plane stratified interval and an upper laminated parallel and or cross laminated interval

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

sediment residence times in catchments draining to the gulf of carpentaria northern australia inferred by uranium comminution dating abstract uranium u isotopes are useful for constraining the timescales of weathering and erosion processes the 234u 238u activity ratio parentheses denote activity ratio of fine grained detrital minerals is proposed to record the time elapsed since mineral grains were reduced to

gps and geologic estimates of the tectonic activity in the marmara sea region nw anatolia a dense network of 52 global positioning system gps sites is used to determine the velocity field and strain rate pattern at the western end of the north anatolian fault zone nafz in the marmara sea region nw anatolia based on four gps campaigns carried out biannually between 1990 and 1996 the detailed kinematic field of crustal motion is calculated the southernmost station shows an average rate of 22 3 mm yr oriented westward relative to istanbul eurasia this value is indicative of the dextral strike slip motion of nw anatolia relative to the black sea the gps velocity field reveals that the sites located on the thrace black sea block show negligible motion relative to istanbul the gps based deformation pattern of three sections crossing the westward prolongation of the nafz is compared with neotectonic data both the gps and the neotectonic data give clear evidence that most of the deformation occurs along a relatively narrow e w oriented zone this belt extends from the single fault trace of the nafz through the gulf of izmit the marmara sea the arkoy region and the gulf of saros into the north aegean trough nat in addition the cross sections show the increasing influence of the n s oriented extension in the aegean sea region from the comparison of the directions and rates of shear and normal strain deduced from gps data with geologic and seismic observations we conclude that the most active zone of dextral shear follows a line along mudurnu valley the northern marmara sea and the saros trough where it joins the nat

use of u isotopes in exploring groundwater flow and inter aquifer leakage in the south western margin of the great artesian basin and arckaringa basin central australia abstract the distribution of uranium isotopes 238u and 234u in groundwaters of the south western margin of the great artesian basin gab australia and underlying arckaringa basin were examined using groundwater samples and a sequential extraction of aquifer sediments rock weathering the geochemical environment and recoil of daughter products control the 238u and 234u isotope distributions giving rise to large spatial variations generally the shallowest aquifer j aquifer contains groundwater with higher 238u activity concentrations and 234u 238u activity ratios close to secular equilibrium however the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238u activity concentrations other locations in the j aquifer that receive little or no recharge contain higher 238u activity concentrations because uranium from localised uranium rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution the geochemical conditions of the deeper aquifers generally result in lower 238u activity concentrations in the groundwater accompanied by higher 234u 238u activity ratios the sequential extraction of aquifer sediments showed that recoil of 234u from the solid mineral phases into the groundwater rather than dissolution of or exchange with the groundwater accessible minerals in the aquifer caused enrichment of groundwater 234u 238u activity ratios in the boorthanna formation decay of 238u in uranium rich coatings on j aquifer sediments caused resistant phase 234u 238u activity ratio enrichment the groundwater 234u 238u activity ratio is dependent on groundwater residence time or flow rate depending on the flow path trajectory thus uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers however spatial heterogeneity and the lack of clear regional correlations made it difficult to identify recharge and inter aquifer leakage

distribution of uranium thorium and rare earth elements in the eye dashwa lakes pluton a study of some analogue elements abstract the distribution of u th and rare earth elements ree s in the eye dashwa lakes pluton near atikokan ontario is examined materials analysed include a unaltered granite b altered granite c highly altered granite adjacent to open fractures and d fracture filling minerals distinct distribution patterns are noted for u and some ree s among the four types of samples th shows higher concentrations in materials c and d compared with unaltered and altered granite the highly altered granite and some fracture fillings have greater concentrations of u th and ree s the large concentrations of u th and ree s in these materials are due to both sorption on selective materials and precipitation as mineral phases containing these elements the occurrence of uraninite bastnaesite and thorogummite coatings on fracture fillings are examples of this precipitation

the erosion response to quaternary climate change quantified using uranium isotopes and in situ produced cosmogenic nuclides abstract studying how catchment erosion has responded to past climate change can help us better understand not only how landscape evolution operates but also predict the consequences of future climate change on soil resource availability recent years have seen the development of tools that allow a quantitative assessment of past changes in catchment erosion this work reviews the principles of the application of in situ produced cosmogenic nuclides and uranium isotopes to quantifying past erosion rates results highlight the role of periglacial processes and mass wasting in dictating how catchment erosion responds to climatic variability at the 10 kyr scale at the million year scale it is more difficult to untangle the role of climate and tectonics a strong coupling exists at the 10 kyr to 100 kyr scales between climatic cycles and the transfer time of regolith from source to sink this coupling reflects changes in sediment source that are either set by changes in vegetation cover at the catchment scale or by the storage of sediments on continental shelves at a larger scale although further analytical developments are required for these tools to reach their full potential existing works suggest that in the near future they will provide unprecedented quantitative insights on how soil and fluvial systems adapt to external perturbations climatic tectonic and or anthropic

kinematics of the mw 7 2 12 november 1999 duzce turkey earthquake the november 12 1999 duzce earthquake ruptured a 40 km long fault segment of the north anatolian fault system immediately to the east of the august 17 1999 izmit rupture we use displacements of 32 sites derived from gps measurements immediately before and after the duzce earthquake to estimate the geometry and slip distribution of the coseismic rupture the 51 northward dipping rupture plane the rake of the slip vector average 3 76 0 04 m right lateral 0 76 0 04 m normal slip and the slip distribution inferred from the gps data are consistent with seismic observations and the distribution of surface offsets measured in the field the geodetically determined moment magnitude is mw 7 2 the duzce earthquake had the highest slip to rupture length ratio of any historic earthquake along the north anatolian fault this is consistent with the duzce earthquake being a part of a composite rupture with the preceding izmit event

radioactive disequilibria in mineralised fracture samples from two uranium occurrences in northern sweden abstract mineralised fractures from two uranium occurrences in northern sweden were examined mineralogically and isotopically to establish the presence or absence of radioactive equilibrium that may indicate recent rock water interaction processes based on the natural mobility of uranium i e during the last 0 5 ma the results show evidence of radioactive disequilibrium in six of the nine samples investigated disequilibria are attributable to solution to solid 234 u recoil gain weakly mineralised zones adjacent to the main mineralisation and solid to solution 234 u recoil loss moderate to highly mineralised zones the absence of significant 238 u loss in the samples emphasises the reducing conditions at the sampled depths

sedimentology and evolution of the martinsburg formation upper ordovician fine grained turbidite depositional system central appalachians the upper ordovician martinsburg formation of eastern pennsylvania consists of mudstone siltstone and sandstone turbidites that accumulated in a tectonically active foreland basin the mudstone rich bushkill member the stratigraphically lowest unit of the martinsburg in this area grades upward into approximately equal proportions of mudstone siltstone and sandstone of the ramseyburg member many of the turbidites of these units are arranged in small scale 1 9 m fining upward sequences that are interpreted as reflecting the influence of external or allocyclic controls such as variations in the local rate of sea level rise and or variations in the intensity of tectonic activity in shelf nearshore or hinterland areas rather than more commonly cited autocyclic mechanisms the thick approximately 2000 m bushkill ramseyburg coarsening upward sequence records progradation of a muddy turbidite depositional system along the axis of the foreland basin although this sequence accumulated during a caradocian eustatic rise in sea level sedimentation rates landward of the shoreline were apparently great enough to allow for long term seaward progradation of the shelf source the paucity of depositional lobe like facies coarsening upward sequences in the bushkill member allows for tentative comparison of the progradational bushkill ramseyburg system with the active fan lobe of the mississippi fan progradation of the bushkill ramseyburg system ceased abruptly when mudstone turbidites and laminated black shale of the upper unit of the martinsburg the pen argyl member accumulated the great thickness of some mudstone turbidite beds of the pen argyl member is interpreted to record topographic confinement of the central appalachian foreland basin which may have helped to preclude continued progradation of the bushkill ramseyburg turbidite system

sedimentology and possible paleoceanographic significance of mudstone turbidites and associated deposits of the pen argyl member martinsburg formation upper ordovician eastern pennsylvania abstract the pen argyl member the stratigraphically highest unit of the upper ordovician martinsburg formation of eastern pennsylvania consists of the three mudstone facies laminated mudstone uniform mudstone and black shale these deposits conformably overlie a coarsening upward sequence of fine grained and classic sandstone turbidites of the underlying bushkill and ramseyburg members respectively petrographic and x radiographic analysis suggests that laminated and uniform mudstone facies beds accumulated from muddy turbidity currents interbedded black shale facies beds however are interpreted to reflect slow gravitational settling of sediment in a density stratified anoxic basin the marked transition from sandstone and siltstone turbidite deposits of the ramseyburg member to mudstone turbidite and black shale deposits of the pen argyl member may reflect the combined effects of a caradocian rise in sea level increased organic carbon production lack of sand size sediment and a tropical to subtropical location of the basin density stratification such a model however does not explain adequately the very thick laminated and uniform mudstone facies beds common only to the pen argyl member an alternative hypothesis involves amplification of global eustatic and climatic related oceanographic effects by local or basinal influences the very thick beds of the laminated and uniform mudstone facies by comparison with lithologically similar deposits of the eastern mediterranean are interpreted to have been ponded in a topographically restricted basin accordingly deposition of the pen argyl member may record a significant change in basin morphology from a wide extensive basin to a topographically restricted or enclosed anoxic basin

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

rapid postseismic transients in subduction zones from continuous gps 1 continuous gps time series from three of four recently measured large subduction earthquakes document triggered rapid postseismic fault creep representing an additional moment release upward of 25 over the weeks following their main shocks data from two mw 8 0 and mw 8 4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep time series for another mw 7 7 event show 30 postseismic energy release but here we cannot differentiate between afterslip and triggered deeper creep a fourth mw 8 1 event which occurred in the broad chilean seismogenic zone shows no postseismic deformation despite coseismic offsets in excess of 1 m for the three events which are followed by postseismic deformation stress transferred to the inferred centroids at 34 60 and 36 km depths by their respective main shock asperities increased reverse shear stress by 0 5 0 8 and 0 2 bar with a comparatively small decrease in normal stress 0 01 bar constraining the coulomb stress increase required to force slip along the metastable plate interface deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins these events captured by some of the first permanent gps networks show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes index terms 7209 seismology earthquake dynamics and mechanics 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158 8150 tectonophysics plate boundary general 3040 7230 seismology seismicity and seismotectonics keywords subduction zone earthquake postseismic moment release

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 1 a u leach model and its applicability to whole rock data the removal of u from granitic rocks is characterised by234u 238u 1 and 230th 234u 1 it is notable from weathered eye dashwa lakes canada granite samples and from the published data that230th 234u ratios seldom exceed a limiting value of about 2 a u leach model is discussed in detail which may account for these observations the model assumes that 230th is practically immobile and that the removal of u can then be measured against the decay rate of the unsupported230th a property of the model is that the isotope ratios reach constant values reflecting a kind of secular equilibrium and this implies that u is seldom removed faster than the decay of230th if the limited230th 234u ratios from the data correspond to secular equilibrium ratios then this allows simple calculation of u leach rates from any given subsurface sample a test for the model using235u 231pa ratios is suggested a comparison of leach rates derivable from u th pb systematics of colorado and wyoming granite samples with the corresponding estimates from the model shows that the latter are high by a factor of 10 50 data from rapidly weathered surface rinds suggests that the presence of labile u restricts the application of the model to subsurface low weathered zones

reorientation mechanisms of phyllosilicates in the mudstone to slate transition at lehigh gap pennsylvania abstract the mudstone to slate transition of the martinsburg formation at lehigh gap pennsylvania was re examined using a new transmission mode x ray texture goniometer supplemented by sem xrd and optical studies three mesoscopic zones are recognized in the outcrop i mudstone ii transition and iii slate zone in the mudstone zone the mica basal planes are parallel to bedding whereas the preferred orientation of the chlorite basal planes is up to 30 shallower than bedding the angular difference between chlorite and mica decreases towards the transition zone becoming subparallel at ca 50 m from the contact with the overlying shawangunk formation in the transition zone the preferred orientations of both mica and chlorite are intermediate to bedding and cleavage orientations which is consistent with mechanical reorientation of phyllosilicates this is supported by a decrease in march strain with a minimum at ca 95 m from the contact for both mica and chlorite sem observations similarly show the importance of grain rotation in large detrital grains in the slate zone both chlorite and mica orientations are parallel to cleavage chlorite and mica in the cleavage orientation of the slate zone have high fe contents whereas low fe mica and mg fe chlorite dominate in the mudstone and transition zone which indicates that dissolution neocrystallization is the dominant mechanism in the slate zone thus mechanical rotation of large detrital grains is important in the early stages of cleavage development with dissolution neocrystallization occurring at all stages and becoming dominant in the more evolved stages

u series in fe u rich fracture fillings from the oxidised cap of the mina fe uranium deposit spain implications for processes in a radwaste repository abstract within the framework of the enresa spain natural analogue programme the u ore deposit of mina fe is being studied as a natural analogue of radioactive spent fuel behaviour in this context the knowledge of the role played by fracture minerals as scavengers of certain analogue elements mainly u and the establishment of the time scale of the rock water interaction processes controlling the uptakes or losses of u in the system are two relevant objectives fracture infill materials from the site have first been mineralogically characterised then the upper part of the u series determined in both bulk samples and u rich leachates obtained by sequential leaching uranium series of the bulk samples indicate that most of the fractures remained as closed systems in the last 1 6 ma while in other fractures water rock interaction processes affecting the upper part of the u series have been identified these processes indicate recent or rapid u accumulation or losses 102 ka or 234u 230th recoil gain the apparently random distribution in depth of fractures where these processes occurred corroborates the different hydraulic behaviour of fractures as a result of their varying degree of sealing uranium concentrations and 234u 238u ars of the leachates obtained with morgan s solution and 6n hcl indicate that minerals dissolved with these reagents u iv vi oxyhydroxides and goethite clays respectively are responsible for the retention of almost all of the u in the bulk samples furthermore the 234u lost by the u minerals dissolved with morgan s solution seems to be fixed onto goethite clay mixtures the intersticial water being the vehicle for the isotopic transfer which in turn is a recent or recent past process

the evolution of the seismic aseismic transition during the earthquake cycle constraints from the time dependent depth distribution of aftershocks 1 using the example of the 1992 m 7 3 landers earthquake we show that in the aftermath of a large earthquake the depth extent of aftershocks shows an immediate deepening from pre earthquake levels followed by a time dependent postseismic shallowing we use these seismic data to constrain the change in the depth of the seismic aseismic transition with time throughout the earthquake cycle most studies of the seismic aseismic transition have focussed on the effects of temperature and or lithology on the transition either from brittle faulting to viscous flow or from unstable to stable sliding a strain rate dependent transient deepening of the brittle ductile transition following a major earthquake is predicted by geological and laboratory observations by analyzing the time dependent depth distributions of aftershocks we identify and quantify the temporal evolution of this transition in the example of the landers earthquake its depth changes by as much as 3 km over the course of 4 years

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

226ra 238u and 228th 228ra disequilibrium as weathering indices in beach sand sediments associated with granitoids from cyclades greece abstract radioactive secular disequilibrium measured as the absolute difference from 1 of the 226ra 238u and 228ra 228th ratios have been used to determine weathering extent twenty eight samples from beach sands of cyclades islands all of them being the weathering products of the local granitic plutons are studied for their secular disequilibrium in both 238u and 232th series 226ra 238u and 228th 228ra respectively the results are compared to weathering indices already in use worldwide and suggest a significant linear correlation of u series disequilibrium with wip alkaline and alkaline earth element leaching and pwi silica leaching for the beach sands studied and significant non linear correlations with cia chemical index of alteration and pia plagioclase index of alteration considering only the heavy mineral enriched samples significant correlations exist between u series disequilibrium and cia ciw chemical index of weathering and pia therefore with an appropriate choice of the weathering index and samples both u series and weathering index can recover the extent of chemical weathering on the other hand the use of th series disequilibrium as a weathering index is limited due to 228th and 228ra geochemistry and especially due to their short radionuclide half lives u series disequilibrium can therefore be used as a relatively sensitive weathering index in sediments consistent with cia ciw and pia indices however the mineralogical composition must be considered more specifically the mineral content of the sediments should involve considerable amounts of sensitive to weathering minerals e g fe mg minerals as well as feldspars

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

the strain rate field in the eastern mediterranean region estimated by repeated gps measurements we use the combined gps velocity field of the eastern mediterranean for the period 1988 to 1996 to determine crustal deformation strain rates in a region comprising the hellenic arc the aegean sea and western anatolia we interpret the velocity field and determine the strain rate tensor by the spatial derivatives of the collocated motion vectors the region following the line marmara sea north aegean trough northern central greece and the central ionian islands is associated with strong right lateral shear motion with maximum shear strain rates of 180 nano strain a 180 10 9 a in the central aegean sea n s oriented extensional processes prevail reaching 100 nano strain a the southern aegean is characterized by relatively small strain rates maximum extensional components of the strain rate tensor reaching 150 nano strain a in a n s direction are found in central greece the hellenic arc is associated with moderate arc parallel extension and strong compression perpendicular to it projections of the strain rates parallel to the major fault zones reveal that the northern aegean is governed by the westward continuation of the north anatolian fault zone which is associated with strong dextral shearing maximum 220 nano strain a accompanied by numerous large earthquakes in this century

analogous tectonic evolution of the ordovician foredeeps southern and central appalachians new stratigraphic data suggest that the diachronous evolution of the ordovician foredeeps in the southern and central appalachians was remarkably similar stratigraphic features that characterize the middle ordovician sevier basin in tennessee and the middle and late ordovician martinsbuirg basin in pennsylvania are in identical ascending order 1 disconformity on the knox group beekmantown group 2 shelf carbonates 3 slope deposits 4 submarine fan turbidites and 5 contourites and muddy turbidites we propose that diachronous attempted subduction of the north american craton beneath southeastern microplates and or volcanic arcs resulted in uplift and erosion of the western shelf followed by its rapid subsidence basinward migration of eastern and northeastern terrigenous source areas and associated submarine fan turbidites resulted from continued convergence and filled the basins finally tectonic stabilization and lowering of the source area is recorded by contourites and muddy turbidites the evolutionary model proposed for the sevier and martinsburg basins closely resembles present day tectonics of the timor foredeep and the adjoining sahul shelf north of australia similar comparisons have also been made for ordovician basins in the northern appalachians analogous tectonic mechanisms therefore appear to have operated diachronously along the eastern margin of north america from tennessee to new england and possibly to newfoundland during ordovician time

experimental intracrystalline plastic flow in hot pressed synthetic quartzite prepared from brazilian quartz crystals samples of synthetic ultrafine grained quartzite were prepared by hot pressing aggregates of crushed clear brazilian quartz of mean grain size 0 4 m at 300 mpa and 1373 and 1473 k the samples displayed rapid grain growth to ca 12 20 m with 2 porosity at 1473 k facilitated by the 0 6 wt of water adsorbed onto the grain boundaries during sample preparation this water could be driven off by preheating thereby preventing grain growth sufficient water was incorporated during growth into the coarsened samples to render them weak and ductile these were deformed experimentally in the quartz field using an argon gas medium apparatus at 300 mpa confining pressure at temperatures mainly between t 1273 and 1473 k ductile flow was described by the flow law 10 4 9 3 2 9 7 f h 2 o exp 242000 rt with stress a in mpa and grain size d in microns and strain rate in s 1 r is the gas constant and f h 2 o is water fugacity based on observation of grain flattening optical strain features shapes and densities of dislocation arrays and flow law parameters samples deformed dominantly by dislocation creep with some contribution from grain boundary sliding bearing in mind possible changes in the flow law parameters over the extrapolation interval and possible effects of the phase transition extrapolation to natural strain rates and temperatures predicts plastic flow at higher flow stresses at the same water fugacity at greenschist facies temperatures than previously published flow laws

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

uranium and microcracks in a 1 000 meter core redstone new hampshire the spatial distribution and mineralogical association of uranium in 30 samples of a 1 000 meter core from the redstone nh quarry were examined with fission track techniques backscattered electron imaging and energy dispersive x ray spectrometry with the following results for the conway and mount osceola granites 1 uranium occurs in microcracks sealed with siderite and or with ca re fluorocarbonate minerals the uranium contents of siderite and the re fluorocarbonates are 1 to 30 ppm and 500 1 500 ppm respectively 2 siderite and to a lesser extent re fluorocarbonate minerals occur as replacement minerals of amphibole and biotite the re fluorocarbonates are the main alteration minerals of allanite 3 the degree of alteration and the extent of uranium redistribution are greater in samples with major uraniferous microcracks 4 the contents of ca and mn are approximately constant for siderite in sealed cracks throughout the conway and mount osceola granites for the entire section penetrated by the corehole approximately 700 meters from these observations we conclude that an extensive set of fractures throughout a significant volume of the mount osceola and conway granties were the conduits through which hydrothermal fluids containing co2 uranium and res circulated microcracks facilitated fluid rock interactions resulting in alteration and uranium redistribution certain primary uraniferous accessory minerals i e allanite and ilmenorutile may have been the source for at least part of the uranium and res that now occur in secondary minerals in these granites

contained reflected turbidity currents from the middle ordovician cloridorme formation quebec canada an alternative to the antidune hypothesis the parautochthonous cloridorme formation is a syn orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle fan outer fan and basin floor deposits the basin floor deposits about 1 5 km thick are confined to members 1 2 and 1 and are characterized by graded thick 1 10 m mud rich calcareous greywacke beds previously interpreted as deposits of concentrated muddy unidirectional turbidity currents that locally generated backset antidune lamination in internally stratified flows the dominant flow directions were from east to west but west to east transport also occurred as seen in the orientation of ripples climbing ripples flutes consistently overturned flames and grain imbrication we believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180 one or more times during deposition of the lower sandy part of the beds flow reversals are consistent with the sharp grain size breaks and mud partings within sandy divisions measurement of grain fabric relative to stratification in the most celebrated antidune bedforms indicates flow from west to east thus the bedforms were produced by west to east migration of megaripples not by the upcurrent migration of antidunes the thick muddy beds were deposited by large volume muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor much like the contessa and similar beds of the italian apennines large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed because of their mode of emplacement we propose that these beds be called contained turbidites