law for the distance between successive earthquakes 1 discovery of a new law for the three dimensional spatial distance between the foci of successive earthquakes is reported analyzing the seismic data taken between 1984 and 2001 in southern californian it is found that the cumulative distribution of the distances follows the modified zipf mandelbrot law showing complexity of geometry of the events

development of the eastern california shear zone walker lane belt the effects of microplate motion and pre existing weakness in the basin and range abstract the role that the motion of microplates has played in the development of the eastern california shear zone in western north america is unclear it was previously proposed that shear related to baja california motion has propagated from the gulf of california northward into nevada however there is evidence that the formation of the eastern california shear zone predates the inception of baja california motion thus either baja california began to move northwestward prior to 6 ma or the eastern california shear zone formed by shear strain resulting from different microplate motion than baja california the role of sierra nevada motion on the development of an adjacent shear zone remains untested we present a numerical modeling study that examines the deformational response of western north america to baja california and or sierra nevada microplate motion in particular we study if and under what condition of microplate motion shear strain can localize in the northern and southern part of the eastern california shear zone separated by the garlock fault we find that given the pre existing weakness from miocene basin and range extension a lithospheric strength contrast or normal faults shear strain from either the baja california or sierra nevada microplates can lead to the formation of the eastern california shear zone furthermore the presence of a pre existing weakness explains the earlier initiation of strike slip faulting north of the garlock fault our models suggest that today baja california microplate motion is the major player for present day deformation rates along the eastern california shear zone and was in the past 6 myrs also a major driver of strain localization in southern eastern california shear zone within the mojave block

palaeomagnetism and magnetic anisotropy of proterozoic banded iron formations and iron ores of the hamersley basin western australia abstract rock magnetic properties and palaeomagnetism of weakly metamorphosed banded iron formations bifs of the palaeoproterozoic hamersley group western australia and proterozoic bif derived iron ores have been investigated the bif units sampled here are slightly younger than 2500 ma at paraburdoo mount tom price and mount newman iron ore formation was completed before 1850 ma sampling was mainly from the mount tom price and paraburdoo mining areas and for the first time a palaeomagnetic fold test on fresh unweathered and unaltered bif samples has allowed the nature of the remanence of the bifs to be defined the remanence of the bifs is carried by late diagenetic low grade metamorphic magnetite after primary haematite this remanence is pre folding and is unlikely to be greatly affected by the high anisotropy because the palaeofield inclination was demonstrably low determination of palaeofield directions from measured remanence directions is complicated by self demagnetization effects in strongly magnetic highly anisotropic bif specimens we present a method for correcting measured directions for the effects of self demagnetization and anisotropy for typical bifs the effect of magnetic anisotropy on measured remanence inclinations and inferred palaeolatitudes is minor for low palaeolatitudes but can lead to large errors in calculated palaeopoles for intermediate to moderately steep palaeolatitudes anisotropy also causes cones of confidence to be underestimated due to compression of the range of inclinations in principle deflection of post folding remanence towards the bedding plane by high magnetic anisotropy can produce an apparent syn folding signature with best agreement between directions from different fold limbs after partial unfolding thus high anisotropy cannot only bias estimated palaeofield directions and cause underestimation of errors but can also mislead interpretation of the time of remanence acquisition the anisotropy of anhysteretic remanent magnetization arm probably yields an upper limit to the anisotropy of the chemical remanent magnetization crm carried by the bifs therefore from the anisotropy of arm a maximum inclination deflection of 9 is suggested for the sampled bifs this corresponds to less than 5 change of palaeolatitude the palaeomagnetic pole position calculated for bifs at paraburdoo is 40 9 s 225 0 e dp 2 9 dm 5 8 after tilt correction but without correction for anisotropy other pole positions reported include that from flat lying bifs from wittenoom at 36 4 s 218 9 e dp 4 6 dm 9 1 from mount tom price iron ore at 37 4 s 220 3 e dp 5 7 dm 11 3 and from paraburdoo ore at 36 4 s 209 9 e dp 4 7 dm 8 8 the poles from the bifs the paraburdoo ore and the part of the tom price deposit that was sampled in this study are indistinguishable from each other and from the mount jope volcanics overprint pole the magnetization of the bifs was probably acquired during burial metamorphism of the hamersley group soon before the main folding and uplift event in the southern part of the hamersley province this tectonic event exposed magnetite rich bifs to near surface oxidizing conditions producing extensive martite goethite orebodies and also appears to have produced the syn folding overprint magnetization recorded by the mount jope volcanics of the underlying fortescue group ages of magnetization are tentatively interpreted as 2200 100 ma for the bifs 2000 100 ma for the supergene enrichment of bif to martite goethite ore recorded by the parabudoo and mount tom price orebodies and 1950 100 ma for the metamorphic martite microplaty haematite ore recorded as an overprint by the tom price orebody and as the only surviving magnetization of the mount newman orebody

abundance and fractionation patterns of rare earth elements in streams affected by acid sulphate soils abstract the abundance and shale normalised fractionation patterns of rare earth elements rees were studied in 121 streams of first and second order in an area where acid sulphate soils developed on oxidised sulphide bearing marine sediments are abundant during high water flow events in autumn on which this study focuses the leaching of rees from the acid sulphate soils is extensive resulting in high total ree concentrations up to 1 mg l in streams draining such soils exclusively in these streams there is a general depletion of the heavy rees explained by preferential scavenging of the latter by oxyhydroxides in the deepest soil profile horizons in streams draining areas of glacial till and peat the ree concentrations are several orders of magnitude lower in these streams in contrast to the ree enriched streams there is a depletion of light rees explained most likely by preferential complexation of the middle and heavy rees by dissolved humic substances

geochemistry of the rare earth elements in hypersaline and dilute acidic natural terrestrial waters complexation behavior and middle rare earth element enrichments rare earth element ree speciation was modelled in acid 2 9 ph 3 5 hypersaline groundwaters from australia and from the palo duro basin in texas usa using a combined specific ion interaction pitzer model and ion pairing model the free metal ion species i e ln3 is the dominant form of dissolved rees in these systems accounting for 40 70 of the dissolved metal in groundwater from lake tyrrell victoria australia 50 90 of the rees in groundwater from lake gilmore western australia and always 90 of each ree in the texas groundwaters lakes tyrrell and gilmore are actually dry lakes that act as groundwater discharge zones the abundance of the free metal ion species increases in these waters with increasing ionic strength and with decreasing ph the free metal ion species is followed in abundance by ree sulfate and ree chloride complexes that account for 20 50 and 10 15 respectively of the dissolved rees in the groundwaters from lake tyrrell 15 30 and 5 20 respectively in the groundwaters from lake gilmore and 3 and 7 respectively in the palo duro basin groundwaters the groundwaters of the lake tyrrell system and the palo duro basin are enriched in the middle rees mrees compared to both the light rees lrees and the heavy rees hrees only nd sm and dy were determined in the lake gilmore groundwaters and consequently it is unclear whether these acid groundwaters are also enriched in the mrees previous investigators suggested that fe rich organic flocs ree phosphate complexation and solid liquid exchange reactions between terrestrial waters and mree enriched surface fe mn coatings suspended particulates or secondary mineral phases within aquifer materials may promote the development of mree enrichments in natural waters we propose that organic colloids and ree phosphate complexes are insignificant in acidic natural waters in regards to mree enrichments instead solid liquid exchange reactions or dissolution of surface coatings suspended particulates and or secondary phases as well as sulfate complexation more likely controls the development of mree enrichments in acidic natural terrestrial waters

petrography and sedimentology of the 2490 ma ds4 impact spherule layer revisited brockman iron formation hamersley group western australia

volcanic nutrient inputs and trophic state of lake caviahue patagonia argentina the strategies for eutrophication control remediation and policy management are often defined for neutral to alkaline freshwater systems as they are most suitable for human use the influence of nutrients on eutrophication in a naturally acidic lake is poorly known the main purpose of the present work is to evaluate the significance of volcanic nutrients in the control of the trophic state of the acidic lake caviahue located at north patagonia argentina acidic water systems were most studied on artificial acidified lakes such as mining lakes in germany or pit lakes in the united states lake caviahue received a very high p load 42 192 ton p yr and low n load 14 ton n yr mainly as ammonium with quite low n p ratios 1 0 the magmatic activity of the copahue volcano represents the main natural contribution of nutrients and acidity to the lake caviahue the lake is oligotrophic in terms of chla neither the transparency nor the nutrient dissolved or particulate contents are to date representative of the trophic state of the lake high p loads do not imply the eutrophication of the lake we suggest that nitrogen and not phosphorus represents the key control nutrient in volcanically acidified lakes as ton was better related to chla observed 0 13 036 mg m 3 in the lake the ph increased around one unit ph 2 0 3 0 during the last five years suggesting that the lake has not yet returned to a stable state

dissolved rare earth elements in the southern ocean cerium oxidation and the influence of hydrography abstract analysis of dissolved ree distributions in the southeastern atlantic ocean has revealed that progressive oxidative removal of dissolved ce from deepwater 1 km occurs over the mixing time of the oceans ce anomaly ce ce values measured in deep waters from the southeastern atlantic are similar to but slightly higher than those from deep ocean stations throughout the indian and pacific oceans typically falling in the range 0 08ce ce 0 12 only deepwater samples from the north atlantic exhibit values greater than ce ce 0 12 with the exception of southeastern atlantic bottomwaters which are influenced by antarctic bottomwater covariation of dissolved ree concentrations with salinity and or dissolved si concentrations at this site has allowed dissolved ree compositions for various southern ocean water masses to be predicted end member concentrations for antarctic bottom water aabw derived in this way indicate high dissolved ree concentrations similar to average pacific deep water but with significantly enhanced dissolved ce concentrations and less pronounced hree enrichment this result is consistent with the proximity of our study site to active aabw deepwater formation and evolution of that water mass during transport to the pacific ocean

rare earth elements in chloride rich groundwater palo duro basin texas usa rare earth element ree data for groundwater samples from the deep basin brine aquifer of the palo duro basin texas usa illustrates the potential use of ree for inferring groundwater flow paths through different geologic materials the ree content of the groundwaters range over 2 5 orders of magnitude and are depleted by 102 to 105 relative to aquifer materials the shale normalized ree patterns for groundwater that have primarily interacted with arkosic sandstones granite wash are flat with similar heavy ree hree enrichments lula n 0 60 to 0 80 the samples with highest ree contents and ree patterns which are enriched in the intermediate rees irees sm tb reflect variable degrees of interaction with carbonate rocks the iree enrichment is the result of fluid interaction with fe mn coatings on carbonate minerals and or secondary minerals in fractures and vugs the chloride complex lncl2 and free ions are the predominant ree species accounting for over 95 of the rees carbonate and sulfate species account for the other 5 and have very little influence on the behavior of the rees although this study indicates a potentially important role for the rees in understanding geochemical transport and groundwater movement it also indicates the necessity for developing a better understanding of ree speciation in high ionic strength solutions

earthquake locations in the inner continental borderland offshore southern california the inner continental borderland region offshore southern california is tectonically active and contains several faults that are potential seismic hazards to nearby cities however fault geometries in this complex region are often poorly constrained due to a lack of surface observations and uncertainties in earthquake locations and focal mechanisms to improve the accuracy of event locations in this area we apply new location methods to 4312 offshore seismic events that occurred between 1981 and 1997 in seven different regions within the borderland the regions are defined by either temporal or spatial clustering of seismic activity in the southern california seismic network scsn catalog obtaining accurate locations for these events is difficult due to the lack of nearby stations the limited azimuthal coverage and uncertainties in the velocity structure for this area our location procedure is based on the l 1 norm grid search waveform cross correlation method of shearer 1997 except that we use a nearest neighbor approach astiz et al 2000 to identify suitable event pairs for waveform cross correlation and we explore the effect of different velocity models on the locations and associated station terms in general our relocated events have small estimated relative location errors and the events are more clustered than the scsn catalog locations a quarry on the south tip of catalina island provides a test of our location accuracy and suggests that under ideal conditions offshore events can be located to within 1 to 2 km of their true locations our final locations for most clusters are well correlated with known local tectonic features we relate the 1981 santa barbara island m l 5 3 earthquake with the santa cruz fault the 13 july 1986 oceanside m l 5 3 sequence with the san diego trough fault zone and events near san clemente island with the known trace of the san clemente fault zone over 3000 of the offshore events during this time period are associated with the 1986 oceanside earthquake and its extended aftershock sequence our locations define a northeast dipping fault plane for the oceanside sequence but in cross section the events are scattered over a broad zone about 4 km thick this could either be an expression of fault complexity or location errors due to unaccounted for variations in the velocity structure events that occur near coronado bank in the scsn catalog are relocated closer to the san diego coast and suggest a shallow angle northeast dipping fault plane at 10 to 15 km depth manuscript received 12 february 1999

differentiating induced and natural seismicity using space time magnitude statistics applied to the coso geothermal field a remarkable characteristic of earthquakes is their clustering in time and space displaying their self similarity it remains to be tested if natural and induced earthquakes share the same behavior we study natural and induced earthquakes comparatively in the same tectonic setting at the coso geothermal field covering the preproduction and coproduction periods from 1981 to 2013 we analyze interevent times spatial dimension and frequency size distributions for natural and induced earthquakes individually these distributions are statistically indistinguishable determining the distribution of nearest neighbor distances in a combined space time magnitude metric lets us identify clear differences between both kinds of seismicity compared to natural earthquakes induced earthquakes feature a larger population of background seismicity and nearest neighbors at large magnitude rescaled times and small magnitude rescaled distances local stress perturbations induced by field operations appear to be strong enough to drive local faults through several seismic cycles and reactivate them after time periods on the order of a year

the development of acidic groundwaters in coal bearing strata part i rare earth element fingerprinting abstract this study examines the rare earth element ree pattern of acidic mine discharges in the durham basin ne england as a means of fingerprinting their sources and understanding the water rock interactions although whole rock compositions proved to be unhelpful mimicking acid mine water generation in a series of selective leachates of the coal and coal bearing strata gave ree patterns similar to those measured in the emergent waters ree ratios and anomalies were used as indicators of specific interactions in the development of acidic groundwater the implications of the findings for the classification and evolution of acid mine discharges are discussed

predictability in the epidemic type aftershock sequence model of interacting triggered seismicity 1 as part of an effort to develop a systematic methodology for earthquake forecasting we use a simple model of seismicity on the basis of interacting events which may trigger a cascade of earthquakes known as the epidemic type aftershock sequence model etas the etas model is constructed on a bare unrenormalized omori law the gutenberg richter law and the idea that large events trigger more numerous aftershocks for simplicity we do not use the information on the spatial location of earthquakes and work only in the time domain we demonstrate the essential role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source we offer an analytical approach to account for the yet unobserved triggered seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of seismicity beyond a few minutes we find a strong predictability if one accepts to predict only a small fraction of the large magnitude targets specifically we find a prediction gain defined as the ratio of the fraction of predicted events over the fraction of time in alarms equal to 21 for a fraction of alarm of 1 a target magnitude m 6 an update time of 0 5 days between two predictions and for realistic parameters of the etas model however the probability gains degrade fast when one attempts to predict a larger fraction of the targets this is because a significant fraction of events remain uncorrelated from past seismicity this delineates the fundamental limits underlying forecasting skills stemming from an intrinsic stochastic component in these interacting triggered seismicity models quantitatively the fundamental limits of predictability found here are only lower bounds of the true values corresponding to the full information on the spatial location of earthquakes

aftershock zone scaling we investigate the distribution of aftershock zones for large earthquakes scalar seismic moment m 10 19 5 n m moment magnitude m 7 mainshocks are selected from the harvard centroid moment tensor catalog and aftershocks are selected from the preliminary determination of epicenters neic catalog the aftershock epicenter maps are approximated by a two dimensional gaussian distribution the major ellipse axis is taken as a quantitative measure of the mainshock focal zone size the dependence of zone length l on earthquake size is studied for three representative focal mechanisms thrust normal and strike slip although the numbers of mainshocks available for analysis are limited maximum a few tens of events in each case all earthquakes show the same scaling m l 3 no observable scaling break or saturation occurs for the largest earthquakes m 10 21 n m m 8 therefore it seems that earthquake geometrical focal zone parameters are self similar

u pb geochronology and paleomagnetism of the westerberg sill suite kaapvaal craton support for a coherent kaapvaal pilbara block vaalbara into the paleoproterozoic precise geochronology combined with paleomagnetism on mafic intrusions provides first order information for paleoreconstruction of crustal blocks revealing the history of supercontinental formation and break up these techniques are used here to further constrain the apparent polar wander path of the kaapvaal craton across the neoarchean paleoproterozoic boundary u pb baddeleyite ages of 2441 6 ma and 2426 1 ma for a suite of mafic sills located on the western kaapvaal craton in south africa herein named the westerberg sill suite manifests a new event of magmatism within the kaapvaal craton of southern africa these ages fall within a ca 450 myr temporal gap in the paleomagnetic record between 2 66 and 2 22 ga on the craton our older westerberg suite age is broadly coeval with the woongarra magmatic event on the pilbara craton in western australia in addition the westerberg suite on the kaapvaal craton intrudes a remarkably similar archean proterozoic sedimentary succession to that on the pilbara craton supporting a stratigraphic correlation between kaapvaal and pilbara i e vaalbara the broadly coeval westerberg woongarra igneous event may represent a large igneous province the paleomagnetic results are more ambiguous with several different possibilities existing a virtual geomagnetic pole obtained from four sites on the westerberg sills is 18 9 degrees n 285 0 degrees e a 95 14 1 degrees k 43 4 sample based vgp n 34 16 8 degrees n 2879 9 degrees e dp 4 4 degrees dm 7 7 degrees if primary i e 2441 2426 ma it would provide a further magmatic event within a large temporal gap in the kaapvaal craton s paleoproterozoic apparent polar wander path it would suggest a relatively stationary kaapvaal craton between 2 44 ga and 2 22 ga and ca 35 degrees of latitudinal drift of the craton between ca 2 66 ga and 2 44 ga this is not observed for the pilbara craton suggesting breakup of vaalbara before ca 2 44 ga however it is likely that the woongarra paleopole represents a magnetic overprint acquired during the ophtalmian or capricorn orogeny invalidating a paleomagnetic comparison with the westerberg sill suite alternatively our westerberg virtual geographic pole manifests a 2 22 ga magnetic overprint related to ongeluk volcanism the similarity between ongeluk and westerberg paleopoles however may also infer magmatic connections if both are primary directions despite the apparent 200 million year age this difference c 2015 elsevier b v all rights reserved less

paleomagnetism of the marble bar chert member western australia implications for apparent polar wander path for pilbara craton during archean time abstract the archean biosphere drilling project abdp drilled a continuous 270 m long oriented core from the towers formation which includes the marble bar chert member 3456 1 3476 0 ma in the pilbara craton northwestern australia a paleomagnetic study of 261 discrete specimens collected from a 158 5 to 182 0 m section of the marble bar chert member revealed two distinct magnetic components lt and mt the mt component yields seven different mean paleomagnetic directions clustered as mb1 to mb7 these together with the published paleomagnetic poles of early archean rocks from the pilbara craton draw a continuous paleomagnetic pole path which likely to be regarded as the early to late archean apparent polar wander path apwp for the pilbara craton the apwp implies that the pilbara craton underwent a latitudinal drift of about 21 during the interval when the magnetization of the marble bar chert member was acquired the estimated speed of the lateral drift is 12 112 cm yr 120 1120 km myr which is large compared with current plate motion velocities suggesting that continents might have moved during the archean faster than in the phanerozoic

the hydrogen and oxygen isotopic composition of precipitation evaporated mine water and river water in montana usa summary the isotopic composition of 42 samples of rain and snow collected in 2004 were used to construct a local meteoric water line lmwl for butte montana the derived equation d 7 31 18 o 7 5 r 2 0 987 represents one of the first published lmwls based on direct precipitation for any location in the northern rocky mountains samples of underground and surface mine waters in butte including the berkeley pit lake and a nearby tailings pond define a linear trend with a much lower slope and intercept than the lmwl d 5 00 18 o 49 5 r 2 0 991 consistent with non equilibrium evaporation at an average relative humidity of roughly 65 detailed evaporation calculations are presented which indicate that the shallow berkeley pit lake was approximately 25 evaporated in october 2003 whereas the surface of the tailings pond was at least 50 evaporated the intersection of the lmwl and mine water evaporation trend was used to calculate the average composition of recharge water to the flooded mine complex d 139 18 o 18 0 these values are considerably lighter than the weighted total of precipitation for the 2004 calendar year d 118 18 o 15 3 which is partly explained by the unusually low snowfall that montana experienced in 2004 based on this study the lmwl recently proposed by kendall and coplen 2001 kendall c coplen t b 2001 distribution of oxygen 18 and deuterium in river waters across the united states hydrological processes 15 1363 1393 from regression of isotopic data from a number of montana rivers is more accurately interpreted as an evaporation line isotopic trends based on river data should be treated with caution particularly in a semi arid region such as montana where rivers are often influenced by dams and irrigation withdrawals

paleomagnetism of the north american precambrian a look at the data base more than half of the approximately 650 paleopoles reported from all precambrian cratons have been obtained from north america the observations have spurred a proliferation of apparent polar wander paths to support different hypotheses for the tectonic evolution of the continent many of the reasons for this development can be traced to the inadequacy of the data base with its average of only 1 6 poles 10 ma 1 as compared to 7 poles 10 1 ma for the last 300 ma even when it is assumed that a primary pole has been derived from each rock unit sampled the total number of primary poles excluding the 900 1200 ma interval yields an average of only 0 4 pole 10 ma 1 an inspection of the data base shows a non systematic sampling of a non continuous fragmented paleomagnetic record with gaps as large as tens and even hundreds of ma more importantly a search through the literature reveals that very few poles have an age known to better than 50 ma and for many poles the age bracket could be as large as a few hundreds of ma this is partly owing to the fact that radiometric and paleomagnetic sites rarely originate from the same localities it is shown that this limited data base with all its deficiencies and uncertainties cannot be used to support certain hypotheses or for the drawing of a meaningful apparent polar path for the whole of the precambrian it appears that because of the enormous time scale precambrian paleomagnetism should rather be directed towards the construction of segments of polar paths such as those in the 900 1200 ma interval comparison of well dated contemporaneous segments from different parts or structural provinces could be used most effectively to delineate relative movements if any and reconstruct the mosaic of the past continent for certain time intervals one of the recent developments of precambrian paleomagnetism has been to show that the apparent pole did not remain constrained to the equatorial region but made several excursions into high latitudes

a kinematic model of southern california we propose a kinematic model for southern california based on late quaternary slip rates and orientations of major faults in the region internally consistent motions are determined assuming that these faults bound rigid blocks relative to north america most of california west of the san andreas fault is moving parallel to the san andreas fault through the transverse ranges and not parallel to the motion of the pacific plate this is accomplished by counterclockwise rotation of california south of the san andreas fault and by the westward movement of central california north of the gar lock fault the velocities of the blocks are calculated along several paths in southern california that begin in the mojave desert and end off the california coast a path that crosses the western transverse ranges accumulates the accepted relative north america pacific plate velocity whereas paths to the north and south result in a significant missing component of motion this implies the existence of a zone of active deformation in southern california that is interpreted to include the western transverse ranges and northwest trending predominately strike slip faults close to the coast both north and south of the transverse ranges strain on this system accounts for about a third of the total north america pacific plate motion

evidence for a neoarchean lip in the singhbhum craton eastern india implications to vaalbara supercontinent abstract we report eight new pb pb baddeleyite ages and paleomagnetic results on a series of hitherto unknown neoarchean nne ssw trending mafic dyke swarms intruding the paleoarchean basement rocks in the singhbhum craton eastern india being the most dominant dyke swarms in the region they occur over the entire singhbhum craton with an areal distribution extending to about 30 000 km 2 of the eight dyke samples analysed across the entire dyke swarm six were emplaced at 2762 4 2 0 ma weighted mean of 6 dyke ages two with similar strike directions yielded older and younger ages of 2800 2 0 7 ma and 2752 0 0 9 ma respectively the older 2800 2 0 7 ma dyke event appears to be coeval with several other magmatic events reported earlier from the singhbhum craton emplacement of dacite tuffs within the malaigiri basin on the southern margin of the craton the budhapal and rengali granite from the south western and southern parts of the craton along with the temperkola granite activity and associated acid volcanics in the western part of the craton and perhaps the mayurbhanj granite fine grained phase are also contemporaneous suggesting a fairly wide spread thermal event in the region at this time well defined craton wide magmatic events contemporaneous to the 2762 4 2 0 ma singhbhum dyke activity have been reported from the pilbara the younger 2752 0 0 9 ma age dyke event occurring in the singhbhum is also know from the eastern pilbara an older event at 2783 1 2 ma gaborone kanye plantation porphyry derdepoort modipe episode was identified in the kaapvaal craton comparison of paleomagnetic data obtained on the singhbhum neoarchean dyke swarms with the pilbara and kaapvaal data show all these continents were located at steep latitudes and could have been proximal to each other during this time if pilbara and kaapvaal formed supercraton vaalbara during the neoarchean time we propose singhbhum with similar archean geology could also have had its ancestry in the same supercraton

spatial distribution of aftershocks and background seismicity in central california we examine the spatial distribution of earthquake hypocenters in four central california areas the aftershock zones of the 1 1984 morgan hill 2 1979 coyote lake and 3 1983 coalinga earthquakes as well as 4 the aseismically creeping area around hollister the basic tool we use to analyze these data are frequency distributions of interevent distances between earthquakes these distributions are evaluated on the basis of their deviation from what would be expected if earthquakes occurred randomly in the study areas we find that both background seismic activity and aftershocks in the study areas exhibit nonrandom spatial distribution two major spatial patterns clustering at small distances and anomalies at larger distances are observed depending on tectonic setting while both patterns are seen in the strike slip environments along the calaveras fault morgan hill coyote lake and hollister aftershocks of the coalinga event a thrust earthquake seem to be characterized by clustering only the spatial distribution of earthquakes in areas gradually decreasing in size does not seem to support the hypothesis of a self similar distribution over the range of scales studied here regardless of tectonic setting spatial distributions are independent of magnitude for the coalinga aftershocks but events in strike slip environments show increasing clustering with increasing magnitude finally earthquake spatial distributions vary in time showing different patterns before during and following the end of aftershock sequences

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

paleothermometry of the sydney basin evidence from overprinting of magnetizations of late permian and mesozoic rocks and from the rank of permian coals and mesozoic phytoclasts coal particles suggests that surface rocks in the sydney basin eastern australia have been raised to temperatures of the order of 200 sup 0 c or higher as vitrinite reflectance an index of coal rank or coalification is postulated to vary predictably with temperature and time estimates of the paleotemperatures in the sydney basin based on observed vitrinite reflectance measurements can be made in conjunction with reasonable assumptions about the tectonic and thermal histories of the basin these estimates give maximum paleotemperatures of present day surface rocks in the range 60 249 sup 0 c depending on factors such as location in the basin the thickness of the sediment eroded and the maximum paleogeothermal gradient higher coal rank and consequently larger eroded thicknesses and paleogeothermal gradients occur along the eastern edge of the basin and may be related to seafloor spreading in the tasman sea on the basin s eastern margin a theory of thermal activation of magnetization entailing the dependence of magnetic viscosity on the size distribution of the magnetic grains is used to obtain an independent estimate of the maximum paleotemperaturesmore in the sydney basin this estimate places the maximum paleotemperature in the range 250 300 sup 0 c along the coastal region both coalification and thermal activation of magnetization models provide strong evidence of elevated paleotemperatures which in places exceed 200 sup 0 c and the loss of sediment thicknesses in excess of 1 km due to erosion less

an experimental study of water rock interaction and acid rock drainage in the butte mining district montana this paper summarizes a laboratory study of water rock interaction and the generation of acidic mine drainage in the butte mining district montana the butte district includes two large open pit mines exploiting different portions of the same porphyry cu mo system 1 the well known berkeley pit which is abandoned and flooding with acidic mine water and 2 the nearby continental pit which is active the two pits are separated by a normal fault with several thousand feet of vertical displacement and consequently the styles of alteration and mineralization are quite different humidity cell and recirculating leachate experiments of crushed rock exposed on the walls of the berkeley pit produced effluent waters very similar in composition to the flooded berkeley pit lake in contrast the same experiments on crushed ore from the continental pit generated circum neutral leachates with low metal concentrations caused by the presence of calcite in the alteration assemblage because carbonate is being depleted at a faster rate than pyrite during weathering the quality of mine drainage in the continental pit could eventually degrade

evidence for stabilization of the pilbara block australia the stabilization of continental crust to form cratons represents one of the major features of earth history1 major structural geochemical2 3 and to a lesser extent sedimentological changes4 associated with the development of stable crustal blocks are recorded mainly around 2 500 myr ago1 this change however appears to have been globally diachronous and cratonic sequences as old as 3 100 myr are recorded5 i now present the results of a recent regional stratigraphical and sedimentological study on the 2770 myr old lower fortescue group6 7 previously classified lithologically as proterozoic8 but following the recent recommendation of a 2 500 myr archaean proterozoic chronological boundary9 is referred to as archaean in the pilhara block10 western australia a major stabilization of the underlying granitoid greenstone terrain appears to have pre dated fortescue basin formation this event which available geochronology suggests was relatively rapid marked a major changing point in the tectonic evolution of the pilhara block

vaalbara earth s oldest assembled continent a combined structural geochronological and palaeomagnetic test the only remaining areas of pristine 3 6 2 7 ga crust on earth are parts of the kaapvaal and pilbara cratons general similarities of their rock records especially of the overlying late archean sequences suggest that they were once part of a larger vaalbara supercontinent here we show that the present geochronological structural and palaeomagnetic data support such a vaalbara model at least as far back as 3 1 ga and possibly further back to 3 6 ga vaalbara fragmented prior to 2 1 ga and possibly as early as 2 7 ga suggesting supercontinent stability of at least 400 myr consistent with neoproterozoic and phanerozoic analogues

the fold test in palaeomagnetism summary the fold test suggested by mcelhinny is shown to be inappropriate more correctly one should determine whether the mean direction of a group of sites from one limb of a fold may be distinguished statistically from the mean direction of a group of sites from another limb details of the application of this test are given with examples it is shown that the test indicates significance under far less severe folding than does the test suggested by mcelhinny

palaeomagnetism of red beds from the kimberley group western australia implications for the palaeogeography of the 1 8 ga king leopold glaciation abstract the 1 8 ga king leopold glaciation in northwestern australia is recorded in the kimberley basin by subglacial erosional forms cut in an unconformity surface at the top of the speewah group and buried by glaciofluvial deposits at the base of the king leopold sandstone the lowest formation of the kimberley group the glaciofluvial deposits are conformably overlain by texturally mature locally glauconitic quartzarenite of shallow marine origin implying that glaciation occurred near sea level palaeomagnetic data for five sites 29 specimens in the hematite bearing elgee siltstone of the upper kimberley group in the northeastern kimberley basin gave a dip corrected mean direction of declination d 95 4 inclination i 13 8 95 9 7 indicating a palaeolatitude 7 0 5 3 5 0 results for red beds from five sites 28 specimens in the conformably overlying pentecost sandstone gave a dip corrected mean direction of d 94 1 i 13 0 95 11 7 6 6 6 4 5 9 combining our data for the elgee siltstone and pentecost sandstone with results for the elgee siltstone in the southeastern kimberley basin li z x 2000 palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia geophysical journal international 142 173 180 yielded a dip corrected mean direction for 17 sites of d 93 5 i 15 1 95 4 4 palaeolatitude 7 7 2 3 and an overall pole position at latitude p 5 4 s longitude p 211 8 e with confidence semi axes dp 2 3 and dm 4 5 a positive fold test at 99 confidence was obtained for the combined data for the 17 sites the basinwide concordance of results for the elgee siltstone and the positive fold test argue for an early magnetisation acquired prior to late palaeoproterozoic initial folding of the kimberley group and close to the time of deposition our results imply a low palaeolatitude for the kimberley group and the king leopold glaciation palaeomagnetic data for the 1 822 ga plum tree creek volcanics in the pine creek orogen to the east of the kimberley basin are consistent with northwestern australia being in low palaeolatitudes during the late palaeoproterozoic hence the enigma of glaciation near sea level in low palaeolatitudes which marks the neoproterozoic and early palaeoproterozoic applies also to the late palaeoproterozoic red beds from the lansdowne arkose of the speewah group also were studied but only directions ascribable to tertiary regolith weathering processes were found similar findings for the late palaeoproterozoic mcarthur basin in northern australia suggest some units in that basin also record tertiary regolith processes

rare earth element geochemistry of colour lake an acidic freshwater lake on axel heiberg island northwest territories canada a lake column profile was collected in 24 m of water from colour lake axel heiberg island northwest territories canada in early june of 1991 beneath 1 8 m of lake ice the rare earth element ree concentrations of the acidic fresh waters of colour lake were analyzed along with the major solute chemistry in order to investigate ree distribution and speciation in the low ph waters previous studies indicate the lake is dominated by ca2 mg2 and so42 and has no measurable carbonate alkalinity shale normalized ree patterns for the lake waters are all enriched in the middle ree s mree s as compared to the light ree s lree s and heavy ree s hree s dissolved ree concentrations in colour lake e g 2 3 22 nmol kg 1 for nd mean value of 20 nmol kg 1 are typically less than values obtained for the acid saline waters of the lake tyrrell playa system in australia as well as the slightly acidic groundwaters of the carnmenellis region of england but greater than ree concentrations measured in the alkaline saline waters of mono lake california u s a the speciation of the ree s in colour lake was modelled based on the major solute chemistry using a combined specific ion interaction and ion pairing model these calculations suggest that in the relatively high sulfate low ph waters of colour lake the ree s exist as either free metal so42 or f complexes our calculations indicate that so42 complexes dominate over the free metal and fluoride species for the majority of the ree s in the lake water and that in general for acidic high sulfate waters sulfate complexes with the ree s may increase the dissolved concentrations of the ree s over natural waters where relatively low sulfate concentrations prevail

acid drainage at the inactive santa lucia mine western cuba natural attenuation of arsenic barium and lead and geochemical behavior of rare earth elements abstract a detailed geochemical study was conducted at the inactive zn pb mine of santa lucia in western cuba the studied mine wastes are characterized by high total concentrations of potentially toxic elements pte with average values of 17 4 fe 5 47 ba 2 27 pb 0 83 zn 1724 mg kg as and 811 mg kg cu oxidation of sulfide minerals in mine waste dumps and in the open pit produces acid mine effluents ph 2 5 2 6 enriched in dissolved so 4 2 up to 6754 mg l fe up to 4620 mg l and zn up to 2090 mg l low ph values 2 5 2 8 and high dissolved concentrations of the same pte were found in surface waters up to 1500 m downstream from the mine nevertheless concentrations of as ba and pb in acid mine effluents and impacted surface waters are relatively low 0 01 0 3 mg l as 0 002 0 03 mg l ba and 0 3 4 3 mg l pb analysis by x ray diffraction and electron microscopy revealed the occurrence of lead bearing barite and beudantite and the more common solid phases reported elsewhere in similar environments including fe oxyhydroxides jarosite anglesite and plumbojarosite because the reported solubilities for barite and beudantite are very low under acidic conditions these minerals may serve as the most important control in the mobility of as ba and pb in contrast fe oxyhydroxides are relatively soluble under acidic conditions and therefore they may have a less significant role in pte on site immobilization mine wastes and stream sediments show a light ree lree and middle ree mree enrichment relative to heavy ree hree in contrast acid mine effluents and surface waters are enriched in hree relative to lree these results suggest that the lree released during the oxidation of sulfides are captured by secondary weathering minerals while the mree are removed from the altered rocks the low concentrations of lree in acid stream water suggest that these elements can be retained in the sediments more strongly than hree and mree one possible explanation for the sharp decrease in dissolved lree might be their retention by low solubility secondary minerals such as anglesite barite and jarosite

prefolding and overprint magnetic signatures in precambrian 2 9 2 7 ga igneous rocks from the pilbara craton and hamersley basin nw australia a total of 446 oriented samples have been collected from an archaean intrusion and the fortescue group volcanics and intrusions in the pilbara and hamersley regions of northwestern australia the paleomagnetism and rock magnetism of these samples have been investigated using susceptibility and hysteresis properties and both alternating field af and thermal demagnetization the most consistent paleomagnetic results were achieved by first applying af demagnetization and then stepwise thermal demagnetization evidence of the effects of lightning are widespread which accounts for the efficacy of this particular demagnetization strategy application of the fold test has resulted in placing significant constraints on the acquisition ages of some of the magnetizations and their corresponding pole positions a prefolding pole position from the millindinna complex is latitude 11 9 s longitude 161 3 e dp 6 8 dm 8 4 and is correlated with a radiometric age of 2 86 0 02 ga folding in the millindinna complex occurred prior to the deposition of the fortescue group new geochronological data indicate that the extrusion of the flood basalts commenced about 2 8 ga this provides a minimum age for the magnetization of the millindinna complex deformation responsible for the formation of the mobile belt separating the pilbara and yilgarn blocks during the ophthalmian orogeny has affected the fortescue group and produced a moderate degree of folding in the southern part of the hamersley basin in the region of millindinna complex outcrop the fortescue group is generally flat lying prefolding pole positions from the fortescue group are for the mount roe basalt latitude 52 4 s longitude 178 0 e dp 6 4 dm 9 1 and for the mount jope volcanics latitude 40 5 s longitude 128 7 e dp 19 9 dm 20 8 the overprint magnetization in the mount jope volcanics yields a pole position latitude 35 0 s longitude 211 5 e dp 2 8 dm 5 5 and is interpreted as having been acquired during folding relating to the formation of the ophthalmian fold belt

diel behavior of rare earth elements in a mountain stream with acidic to neutral ph abstract diel 24 h changes in concentrations of rare earth elements ree were investigated in fisher creek a mountain stream in montana that receives acid mine drainage in its headwaters three simultaneous 24 h samplings were conducted at an upstream station ph 3 3 an intermediate station ph 5 5 and a downstream station ph 6 8 the ree were found to behave conservatively at the two upstream stations at the downstream station ree partitioned into suspended particles to a degree that varied with the time of day and concentrations of dissolved ree were 2 9 to 9 4 fold 190 to 830 higher in the early morning vs the late afternoon the decrease in dissolved ree concentrations during the day coincided with a corresponding increase in the concentration of ree in suspended particles such that diel changes in the total ree concentrations were relatively minor 27 to 55 increase at night across the lanthanide series the heavy ree partitioned into the suspended solid phase to a greater extent than the light ree filtered samples from the downstream station showed a decrease in shale normalized ree concentration across the lanthanide series with positive anomalies at la and gd and a negative eu anomaly as the temperature of the creek increased in the afternoon the slope of the ree profile steepened and the magnitude of the anomalies increased the above observations are explained by cyclic adsorption of ree onto suspended particles of hydrous ferric and aluminum oxides hfo hao conditional partition coefficients for each ree between the suspended solids and the aqueous phase reached a maximum at 1700 hours and a minimum at 0700 hours this pattern is attributed to diel variations in stream temperature possibly reinforced by kinetic factors i e slower rates of reaction at night than during the day estimates of the enthalpy of adsorption of each ree onto suspended particles based on the field results averaged 82 kj mol and are similar in magnitude to estimates in the literature for adsorption of divalent metal cations onto clays and hydrous metal oxides the results of this study have important implications to the use of ree as hydrogeochemical tracers in streams

behavior of rare earth elements in acid coal mine drainage in shanxi province china rare earth element ree concentrations were determined in acid mine drainage amd bedrock pyrite and coal samples from the sitai coal mine and the malan coal mine in shanxi province china the amd displayed high ree concentrations with typical convex shale normalized patterns the ree concentrations in the bedrock samples are one order of magnitude higher than those found in pyrite and coal samples the high ree concentrations in amd most likely come from the acidic solution leached out ree in bedrock results from laboratory and field experiments show that ph is the most important factor controlling the fractionation of ree but fe al and mn colloids and secondary minerals also affects their fractionation as the ph increased from 4 to 6 the concentrations of total dissolved ree decreased from 520 to 0 875 g l 1 fe and al in amd has less influence on the fractionation of dissolved ree than low concentrations of mn hree were preferentially removed by secondary minerals and colloids followed by mree rare earth element s speciation modeling indicates that sulfate complexes lnso4 and ln so4 2 79 91 and free metal species ln3 8 8 21 are the dominant ree species in the amd but the ree sulfate complexation could not explain the mree enriched patterns

the aqueous geochemistry of the berkeley pit butte montana u s a water levels in the berkeley pit butte montana are currently rising approximately 22m per year following the cessation of pumping in 1982 projections suggest that the pit may be filled to capacity at the 5520 ft 1682 m elevation by the year 2009 if remedial action is not implemented in addition as the water level in the pit continues to rise there is the potential for encroachment of contaminated water into the alluvial aquifer and subsequent transport of metals downgradient to silver bow creek geochemical measurements and aqueous samples collected during october 1987 indicate that water in the berkeley pit is moderately oxidizing eh 460mv below 30 m acidic ph 3 0 cafe sulfate solution the principal ions are al as ca cd cu fe k mg na so4 and zn which typically increase in concentration from the surface to the bottom of the pit arsenic occurs mainly as as v in total metal concentrations up to 1 mg l fe as fe iii in the top 3 m and as fe ii below this depth in concentrations up to 1000 mg l sulfate was measured in concentrations up to 6780 mg l from the deepest 130 m sample copper and zn were found in total metal concentrations of 202 and 512 mg l respectively at the 130 m sampling depth to verify the field eh measurements minteq was used to calculate a theoretical eh based on the fe ii fe iii couples the results suggest that the ratio fe ii fe iii is representative of the system eh when both species occur in measurable quantities 0 25mg l and when the minor species constitutes at least 5 of the total concentration data from this study were used in the geochemical computer code phreeqe to evaluate potential remediation of the water body through the addition of alkaline tailings fluid produced at the current milling operation on site five cases were evaluated two representative of conditions under ice cover pco2 not fixed and three open system simulations pco2 10 3 5 mineral controls included fe oh 3 gypsum caso4 2h2o jurbanite alohso4 and jarosite kfe3 so4 2 oh 6 the addition of three volumes of alkaline slurry to the existing volume of acidic fluid would raise the ph to 5 0 this option would take approximately 7 a at the current rate of production 11 6 million gallons per day 43 9 ml d at this time the fluid level would be approximately 20 m above the alluvial bedrock contact

syn deformational remanent magnetization of the mount eclipse sandstone central australia summary the palaeomagnetism of the latest devonian early carboniferous mount eclipse sandstone in central australia reveals samples from 16 out of 31 sites having a consistent hightemperature component of natural remanent magnetization site mean directions from the two limbs of the most detailed studied syncline attain their best grouping after 75 per cent of unfolding and further unfolding causes a cross over feature mineralogical studies using microscope and electron microprobe show that this remanance is most likely to be carried by secondary haematite formed by alteration of fe rich minerals during the midcarboniferous deformation four different models are examined to reconstruct the palaeohorizontal for the syn deformational remanence the best estimate of the palaeomagnetic south pole position is lat 33 8 s and long 121 2 e dp 19 2 drn 19 7 close to australia this result indicates a rapid polanvard movement of eastern gondwanaland during the first half of the carboniferous we also suggest that the widespread alice springs orogeny related overprints in central australia were acquired during the beginning of the main phase of deformation in the mid carboniferous

geochemistry of the rare earth elements and uranium in the acidic berkeley pit lake butte montana abstract filtered 0 45 m and nonfiltered concentrations of rare earth elements ree u zr th ba sc and y were measured as a function of depth in the berkeley pit lake a large acidic mining lake in butte mt the ree show very little variation with depth apart from a slight concentration near the surface presumably due to evaporation the ree profiles of the pit waters show a depletion in light ree when normalized against nasc and the host butte quartz monzonite bqm and a possible enrichment in middle ree vs heavy ree when normalized against bqm all of the ree partitioned weakly into secondary ferric precipitates formed by aging of deep berkeley pit water the measured distribution coefficients increased across the lanthanide series from la kd 7 7 to nd kd 10 3 and then decreased steadily to lu kd 1 4 under the conditions of the berkeley pit lake the aqueous speciation of ree and u is dominated by sulfate complexes because the stability constants of ree sulfate complexes show very little variation across the lanthanide series the observed trends in kd cannot be explained by aqueous complexation despite high concentrations of dissolved ree e g 1 1 mg l ce and u 0 85 mg l saturation indices for all solid phases were strongly negative due to the low ph of the berkeley pit lake 2 3 2 6 the mobility of ree and u is more likely constrained by adsorption or co precipitation with strengite jarosite schwertmannite or other secondary minerals forming in the lake

palaeomagnetic cleaning strategies abstract cleaning is a term used in palaeomagnetism to refer to laboratory methods designed to demagnetize preferentially the less stable components of magnetization although the diversity of methods suggests that there is a wide choice available this is illusory except in simple cases the wrong cleaning strategy may yield misleading results cleaning methods include thermal magnetic alternating field or a f low temperature chemical shock and microwave cleaning a cleaning strategy involves one or more cleaning methods applied in a specific sequence the design of a strategy is made easier with the a priori knowledge of magnetic mineralogy and granulometry or in other words rock magnetic properties although not a substitute for other rock magnetic experiments the variation of low field susceptibility with temperature k t not only provides information on magnetic mineralogy and granulometry but it also draws attention to chemical alteration that may occur during thermal cleaning apart from the rapid though reversible decrease of k associated with curie temperatures other diagnostic k t features include the low temperature about 140 c peak typical of multidomain md magnetite the high temperature hopkinson peak typical of fine grained magnetite and other magnetic minerals and the classic lepidocrocite maghemite haematite profile which is irreversible examples are given where the remanence caused by lightning can be effectively eliminated only by applying a f or low temperature lt pre treatment such remanence may be an isothermal remanent magnetization irm or a combination of irm and anhysteretic remanent magnetization arm as the unblocking temperature of relatively low coercivity md grains may extend to high temperature it is often desirable to suppress md remanence an example is given of palaeointensity determination with the without lt pre treatment the nature of the lt transition is briefly addressed in the light of a rare double low temperature peak which may reflect both the isotropic point and the verwey transition

determination of amplitude and duration magnitudes and site residuals from short period seismographs in northern california abstract equations for determining amplitude magnitude mx and duration magnitude mf that employ all calibrated instruments in the usgs short period telemetered seismic network in northern california ncsn were developed and tested against a set of 1276 earthquakes from 1986 to 1990 that were analyzed on the caltech usgs processing system cusp the expressions for decay of amplitude and record duration in these equations are functions of distance alone sensitivity corrections for both mx and mf are simply the logarithms of the ratios of the magnification of the reference instrument to that of the instrument actually used component corrections were chosen so as to minimize the dependence of instrument site residuals on instrument component mf site residuals were found to be closely linked to mx site residuals in a manner that suggests both depend primarily on site amplification both mx and mf site residuals vary systematically with bedrock lithology older well consolidated rocks produce negative residuals smaller amplitudes and shorter durations and younger unconsolidated rocks produce positive residuals larger amplitudes and longer durations average station magnitude residuals are virtually independent of distance from the epicenter to at least 800 km and mx mf averaged over 0 5 unit magnitude intervals is less than 0 05 from m 0 5 to m 5 5 comparison of mx and mbk m l uc berkeley for 293 events in both the cusp data set and the berkeley catalog shows that calculated mx s are marginally larger than the corresponding mbk s mx mbk averages about 0 04 the characteristics of the standard wood anderson seismograph employed to calculate mx are free period 0 8 sec damping constant 0 8 and static magnification 2080

precursory seismic activation and critical point phenomena in this paper we relate the behavior of seismicity prior to a characteristic earthquake to the excitation in proximity to a spinodal instability we illustrate the spinodal instability as the upper limit of superheated water prior to a steam explosion we draw an analogy between the steam explosion and a characteristic earthquake and show that the power law activation associated with the spinodal instability is essentially identical to the power law increase in benioff strain observed prior to characteristic earthquakes we find that theory and actual data give very similar results

on the plate boundary forces that drive and resist baja california motion the driving forces of microplate transport remain one of the major unknowns in plate tectonics our hypothesis postulates that the baja california microplate is transported along the north america pacific plate boundary by partial coupling to the pacific plate and low coupling to the north america plate to test this idea we use numerical modeling to examine the interplate coupling on a multiple earthquake cycle time scale along the baja california pacific plate boundary and compare the modeled velocity field with the observed geodetic motion of the baja california microplate we find that when the strain can localize along a weak structure surrounding microplate faults high interplate coupling produced by frictional tectonic stresses can reproduce the observed kinematics of the baja california microplate as seen from geodetic rigid plate motions we also find that the northward motion of baja california can influence the fault slip partitioning of the major faults in the north america pacific plate boundary region north of baja california

rapid development of negative ce anomalies in surface waters and contrasting ree patterns in groundwaters associated with zn pb massive sulphide deposits ground and surface waters collected from two undisturbed zn pb massive sulphide deposits the halfmile lake and restigouche deposits and active mines in the bathurst mining camp bmc nb canada were analysed for the rare earth elements ree ree contents are highly variable in waters of the bmc with higher contents typical of waters with higher fe and lower ph there are significant differences between ground and surface waters and between groundwaters from different deposits the ree contents of surface waters are broadly similar within and between deposit areas although there are spatial variations reflecting differences in ph and redox conditions surface waters are characterised by strong negative ce anomalies ce ce nasc as low as 0 08 produced by oxidation of ce3 to ce4 and preferential removal of ce4 from solution upon leaving the shallow groundwater environment groundwaters and seeps typically lack significant ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that ce oxidation is a rapid process in the surface waters deeper groundwaters at the halfmile lake deposit are characterised by ree patterns that are similar to the host lithologies whereas most groundwaters at the restigouche deposit have lree depleted patterns compared to nasc halfmile lake deposit groundwaters have generally lower ph values whereas restigouche deposit groundwaters show greater heavy ree complexation by carbonate ions shallow waters at the halfmile lake and stratmat main zone deposits have unusual patterns which reflect either the adsorption of light ree onto colloids and fracture zone minerals and or precipitation of ree phosphate minerals middle ree enrichment is typical for ground and surface waters and is highest for neutral ph waters the labile portion of stream sediments are generally more middle ree enriched than total sediment and surface waters indicating that the ree are removed from solution by adsorption to fe and mn oxyhydroxides in the order middle ree light ree heavy ree

revisiting the age and paleomagnetism of the modipe gabbro of south africa abstract the modipe gabbro is a precambrian intrusive unit hosted by the kaapvaal craton of south africa and provides one of the oldest records of geomagnetic field behavior in the late archean earlier paleomagnetic research into the modipe gabbro provided valuable insight into its magnetic properties and mineralogy but predate the development of paleomagnetic tools that are important in unraveling potentially complex histories of precambrian rocks further a lack of information about the precise age of the intrusion prevented this earlier paleomagnetic study from being used to evaluate the tectonic history of the kaapvaal craton here we present a comprehensive paleomagnetic and geochronologic study of the modipe gabbro that complements and builds upon the existing work the emplacement age of the gabbro 2784 0 1 0 ma established using the u pb id tims method on baddeleyite links the intrusion to nearby igneous bodies in the kaapvaal craton establishing one of the oldest fully differentiated magmatic events in the geologic record the precise age of the modipe gabbro and field observations about its strike allow us to perform a tilt correction using the both the attitude and paleomagnetism of the nearby derdepoort basalts the tilt corrected data allow a comparison of kaapvaal craton s paleolatitude with that of the pilbara craton at 2 78 ga with implications for the existence of the supercraton vaalbara

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

continuing evolution of the pacific juan de fuca north america slab window system a trench ridge transform example from the pacific rim abstract many subduction margins that rim the pacific ocean contain complex records of cenozoic slab window volcanism combined with tectonic disruption of the continental margin the series of slab windows that opened beneath california and mexico starting about 28 5 ma resulted from the death of a series of spreading ridge segments and led to piecewise destruction of a subduction regime the timing and areal extent of the resultant slab window volcanism provide constraints on models that depict the subsequent fragmentation and dispersal of the overlying continental margin the initial pioneer slab window thermally weakened the overlying western transverse ranges and california borderlands region starting about 28 5 ma a second thermal pulse occurred in the same region starting about 19 ma during growth of the monterey slab window this additional heating combined with the capture of a partially subducted monterey plate fragment by the cocos plate initiated the pulling apart and rotation of the adjacent continental margin similarly the capture of guadalupe and magdalena plate fragments by the pacific plate and initiation of the guadalupe magdalena slab window about 12 5 ma are coeval with baja california pulling away from the mexico continental margin with the break along the comondu arc in crust already thermally weakened by about 10 my of volcanism in coastal california distributed crustal extension and subsidence accompanied the new transform plate boundary and continued until the slab windows cooled and plate motion coalesced along a through going system of strike slip faults the transform boundary continues to evolve and forward modeling predicts an instability with the current configuration as a result of convergence between the sierra nevada and peninsular ranges batholiths starting about 2 my in the future the instability may be resolved by a shift in the locus of transform motion from the san andreas fault to the eastern california shear zone or by breaking off another fragment of the mojave or southern sierra nevada crustal blocks and translating it northward

palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia summary a palaeomagnetic study of the elgee formation red siltstones and shales in the palaeoproterozoic kimberley basin of northwestern australia has been carried out all seven sampling sites revealed an extremely stable magnetic remanence carried by haematite the age of the formation is confined by precise shrimp u pb ages of early diagenetic xenotime from rocks both above and below it to be 1704 7 14 ma but this may represent a minimum age the youngest detrital zircon grains in the underlying formation provide a maximum age of 1786 14 ma for the formation the extreme stability of the remanence the dissimilarity of the remanent direction from expected younger palaeomagnetic directions and the lack of regional overprint in the 1790 4 ma hart dolerite just north of the study region support a primary origin for the remanence a marginally positive fold test also supports a primary origin the mean direction of d 92 2 i 14 9 a 95 6 4 gives a palaeopole at 4 4 s 210 0 e with dp 3 3 dm 6 5 this pole a previously reported palaeopole from the hart dolerite and ca 1700 ma overprint poles from the pilbara craton all agree with palaeopoles of similar ages from the mcarthur basin of northern australia palaeomagnetic results thus suggest that the north and west australian cratons were possibly joined together by approximately 1 7 ga

chemical evolution of rare earth elements fractionation between colloidal and solution phases of filtered river water abstract within the dissolved fraction of connecticut river water there is large scale fractionation of rare earth elements between colloidal and solution phases colloidal particles carry a large part of the dissolved ree pool filtration through filters with progressively smaller pore size 0 45 0 22 and 0 025 m results in filtrates with lower absolute concentrations of ree and more fractionated compositions with decreasing pore size the filtrates have shale normalized abundances which become systematically more depleted in the lree relative to the hree hence both the solution and colloidal phases are significantly fractionated with respect to the dissolved fraction these conclusions are consistent with previous studies of ree in rivers estuaries and soils and with surface solution speciation models colloids play an important role in the aquatic geochemistry of rare earth elements they are responsible for the fractionation of ree during the estuarine removal of ree the removal of suspended and colloidal particles from river water leaves the solution phase of river water with compositions of ree as evolved as those of surface seawater hence the evolution of the composition of ree in river water and seawater is significantly influenced by colloid formation during chemical weathering on the continents

geometrical impact of the san andreas fault on stress and seismicity in california 1 most large earthquakes in northern and central california clustered along the main trace of the san andreas fault saf the north american pacific plate boundary however in southern california earthquakes were rather scattered here we suggest that such along strike variation of seismicity may largely reflect the geometrical impact of the saf using a dynamic finite element model that includes the first order geometric features of the saf we show that strain partitioning and crustal deformation in california are closely related to the geometry of the saf in particular the big bend is shown to reduce slip rate on southern saf and cause high shear stress and strain energy over a broad region in southern california and a belt of high strain energy in the eastern california shear zone

linearity spectrum analysis of multi component magnetizations and its application to some igneous rocks from south eastern australia summary a method that enables the objective resolution of almost parallel multi component magnetizations is described and demonstrated a feature distinguishing this method from others is its simultaneous analysis of demagnetization data from a group of specimens rather than the analysis of data from one specimen at a time the only prerequisite is that the specimens are derived from a homogeneous source thus for a formation carrying a simple single component magnetization all specimens from the formation may be simultaneously reduced for a more complicated two component magnetization it is shown that only specimens from a particular site can be considered homogeneous and for a complex three component system each sample often requires undivided attention thus the workload is proportionally increased to achieve analyses of comparable reliability from data of variable quality new pole positions from mesozoic intrusions of the sydney basin nsw are from the marsden park breccia pipe 48 s 127 e a95 6 the st marys breccia pipe 46 s 150 e a95 8 the prospect dolerite 60 s 142 e a95 13 and 53 s 180 e a95 6 and from the dundas breccia pipe 58 s 162 e a95 36 and 31 s 195 e a95 16 the last two formations possess multi component magnetizations these pole positions are consistent with previous results from south eastern australia

inception of the eastern california shear zone and evolution of the pacific north american plate boundary from kinematics to geodynamics 1 the san andreas fault saf is the transform boundary between the pacific and the north american plates yet up to 25 of the relative plate motion is now accommodated by the eastern california shear zone ecsz here we investigate the inception of the ecsz and its geodynamic interactions with the saf using a 3 d viscoelastoplastic finite element model for a given fault configuration of the plate boundary zone the model simulates long term slip on the faults and plastic strain outside the faults our results show that the formation of the big bend of the saf around 5 12 ma impeded fault slip and localized strain along the ecsz causing its inception development of the ecsz was further enhanced by the activation of the garlock fault gf and lithospheric weakening caused by the encroachment of the basin and range extension similarly the san jacinto fault sjf in southern california developed along a belt of localized strain which resulted from the formation of the restraining bend along the san bernardino mountains segment of the saf 2 myr ago once activated the sjf reduced slip on both the southern saf and the ecsz across the mojave desert these results indicate causative relationship between the saf and the ecsz the inception of the ecsz and other young faults is the consequence of the evolving saf plate boundary zone that continuously adjusts itself to accommodate the relative plate motion

rare earth element fractionation during the precipitation and crystallisation of hydrous ferric oxides from anoxic lake water abstract an enrichment of light rare earth elements lree is characteristic for most of the acidic fe and so 4 rich pit lakes and groundwaters in the lignite mining area of lower lusatia germany one of these acidic lakes the pit lake rl 1223 has a strong thermal and chemical stratification the upper water layer 0 9 m shows ph values of about 3 during all seasons the monimolimnion 10 17 m of the lake is anoxic and has ph values of about 7 the rare earth element ree patterns of the upper lake water show enriched lree la n yb n 1 6 whereas the opposite patterns depletion of lree la n yb n 0 4 are found in the anoxic water of the monimolimnion experiments were conducted to observe the behaviour of ree during fe oxidation in water from the monimolimnion depth 14 m the sampled monimolimnion water was placed in plastic bottles and the changing water chemistry was observed for 40 weeks after sampling due to the initial anoxic conditions almost all fe precipitated in the investigated water and the ph value decreased from about 7 to 3 during the oxidation the fe precipitates are identified as ferrihydrite which is transformed into goethite within the oxidation process stable ph conditions ph 3 0 were reached after about 10 weeks of oxidation the original ree patterns of the investigated water are generally reflected in the fe precipitates collected at the beginning of the experiment as well as after up to 40 weeks of oxidation however in the corresponding water lree were temporally enriched with a maximum la n yb n ratio of 1 0 and a maximum la n sm n ratio of 2 3 after 6 weeks of oxidation time ph 3 8 4 9 although complex geochemical changes took place between the start and the end of the experiment ree patterns observed at these points in time are nearly identical these differences of the ree pattern can be explained by the sampling procedure the experimental findings can be transmitted to the mining dump aquifers of the study area where geochemical conditions comparable to the experimental oxidation time from 3 to 6 weeks are found and hydrous ferric oxides are precipitating groundwater passing through the mining dumps can preferentially desorb lree from the fe precipitates and display the typical lree enrichment and carry it to the epilimnion of the acidic pit lakes in lower lusatia

rare earth element geochemistry of groundwaters from a thick till and clay rich aquitard sequence saskatchewan canada rare earth elements ree were determined in groundwater samples collected from a thick till and clay rich aquitard sequence located in southern saskatchewan canada the groundwaters are na mg so4 type waters that range from highly concentrated brines e g i up to 2 moles kg near the ground surface to relatively dilute waters i 0 04 moles kg at depth the majority of these groundwaters have ph values between 7 and 8 although the deepest samples are more alkaline 9 ph 9 6 groundwater ree concentrations are relatively constant in the overlying till but increase by up to a factor of 50 in the underlying clay bedrock shallow groundwaters have heavy ree hree enriched shale normalized patterns whereas the ree patterns of the deep groundwaters are relatively flat solution complexation modelling indicates that variations in ree patterns reflect differences in solution complexation across the ree suite in the shallow groundwaters strongly adsorbed positively charged carbonate complexes lnco3 sulfate complexes lnso4 and free metal ion species ln3 dominate the speciation of light rees lree whereas hrees occur chiefly as more stable negatively charged dicarbonato complexes i e ln co3 2 for the deepest groundwaters however all of the rees are predicted to occur in solution as dicarbonato complexes the large hree enrichments of the shallow groundwaters reflect the greater affinity of the positively charged lree solution species to adsorb to clay minerals or coatings on clay minerals in the aquitard sequence compared to the more stable negatively charged hree dicarbonato complexes on the other hand the flat ree patterns of the deep groundwaters reflect the dominance of the negatively charged dicarbonato complex for all rees the solution complexation model along with the strong positive correlation between rees and co32 f 0 79 r 0 95 and to a lesser extent ph 0 57 r 0 72 indicates that carbonate ion concentrations and thus ph exert important controls on aqueous ree concentrations in these groundwaters

constraints on fault slip rates of the southern california plate boundary from gps velocity and stress inversions summary we use global positioning system gps velocities and stress orientations inferred from seismicity to invert for the distribution of slip on faults in the southern california plate boundary region of particular interest is how long term slip rates are partitioned between the indio segment of the san andreas fault saf the san jacinto fault sjf and the san bernardino segment of the saf we use two new sets of constraints to address this problem the first is geodetic velocities from the southern california earthquake center s scec crustal motion map version 3 by shen et al which includes significantly more data than previous models the second is a regional model of stress field orientations at seismogenic depths as determined from earthquake focal mechanisms while gps data have been used in similar studies before this is the first application of stress field observations to this problem we construct a simplified model of the southern california fault system and estimate the interseismic surface velocities using a backslip approach with purely elastic strain accumulation following meade et al in addition we model the stress orientations at seismogenic depths assuming that crustal stress results from the loading of active faults the geodetically derived stressing rates are found to be aligned with the stress orientations from seismicity we therefore proceed to invert simultaneously gps and stress observations for slip rates of the faults in our network we find that the regional patterns of crustal deformation as imaged by both data sets can be explained by our model and that joint inversions lead to better constrained slip rates in our preferred model the sjf accommodates 15 mm yr 1 and the indio segment of the saf 23 mm yr 1 of right lateral motion accompanied by a low slip rate on the san bernardino segment of the saf anomalous fault segments such as around the 1992 m w 7 3 landers surface rupture can be detected there observed stresses deviate strongly from the long term loading as predicted by our simple model evaluation of model misfits together with information from palaeoseismology may provide further insights into the time dependence of strain accumulation along the san andreas system

focal mechanisms and the state of stress on the san andreas fault in southern california focal mechanisms have been determined from p wave first motion polarities for 138 small to moderate 2 6 m 4 3 earthquakes that occurred within 10 km of the surface trace of the san andreas fault in southern california between 1978 and 1985 on the basis of these mechanisms the southern san andreas fault has been divided into five segments with different stress regimes earthquakes in the fort tejon segment show oblique reverse sup on east west and northwest striking faults the mojave segment has earthquakes with oblique reverse and right lateral strikesup motion on northwest strikes the san bernardino segment has normal faulting earthquakes on north south striking planes while the banning segment has reverse strike sup and normal faulting events all occurring in the same area the earthquakes in the indio segment show strike slip and oblique normal faulting on northwest to north south striking planes these focal mechanism data have been inverted to determine how the stresses acting on the san andreas fault in southern california vary with position along strike of the fault one of the principal stresses is vertical in all of the regions the vertical stress is the minimum principal stress in fort tejon and mojave the intermediate principal stress in banning and indio and the maximum principal stress in san bernardino the orientations of the horizontal principal stresses also vary between the regions the trend of the maximum horizontal stress rotates over 35 from n15 w at fort tejon to n20 at indio except for the san bernardino segment the trend of the maximum horizontal stress is at a constant angle of about 65 to the local strike of the san andreas fault implying a weak fault the largest change in the present stress state occurs at the end of the rupture zone of the 1857 fort tejon earthquake it appears that the 1857 rupture ended when it propagated into an area of low stress amplitude possibly caused by the 15 angle between the strikes of the san jacinto and san andreas faults the strong correlation between present state of stress and segmentation in previous earthquakes suggests that the stress state is important in controlling rupture propagation

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

prefolding and premegakinking magnetizations from the devonian comerong volcanics new south wales australia and their bearing on the gondwana pole path palaeomagnetic results from the late middle to early late devonian comerong volcanics in the budawang synclinorium lachlan fold belt lfb new south wales australia satisfy a fold test and support the hypothesis that foliated parts of the lfb have been folded by megakinks during the terminal mid carboniferous orogenic phase the preferred pole position is at 76 9 s 330 7 e a95 7 2 allowing calibration of the australian pole path at around 370 ma ago an alterative pole position at 71 3 s 283 1 e same a95 takes into account a possible rotation of the megakinked terrane by 15 clockwise with respect to the australian craton although there are still problems unravelling previously published results from silurian rocks in the lfb both because of unreliability and uncertainty as to where the lfb crustal units lay in relation to the australian craton there is no geological reason to suspect any large relative movement between the lfb and the craton since the middle devonian and thus the comerong volcanics pole position is representative of the late devonian for australia the new pole requires reassessment of many other poles that have previously been accepted as representing the siluro devonian for australia and gondwanaland we present reasons for believing that the magnetization or remagnetization of many rock units e g mereenie sandstone and mulga downs group australia and the gneigura supergroup africa was later than sedimentation probably during widespread early carboniferous deformation another rock unit msissi norite africa could be of early carboniferous rather than late devonian age

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

mobility and speciation of rare earth elements in acid minesoils and geochemical implications for river waters in the southwestern iberian margin abstract this paper discusses the abundance fractionation and chemical speciation of the rare earth elements ree released during two contrasting water soil interactions using acid sulfate and circumneutral soil samples from an abandoned mine land watershed in sw spain our simulative experiment shows that the ree mobility is strongly dependent on the soil solution acidity the acid solution extracts ph 3 1 3 7 extracted from the minesoils display overall ree concentrations much higher up to three orders of magnitude than those of the near neutral soil extracts the middle ree mree were preferentially removed when compared to light ree lan smn 0 07 and heavy ree gdn ybn 2 49 the origin of this mree enriched signature is attributed to dissolution and or solid liquid exchange reactions involving iron oxy hydroxides particles and surface coatings the ree were found to behave conservatively under the strong acid conditions of the soil solutions with sulfate complexes mainly lnso4 being the largely dominant aqueous species 75 80 despite the competitive effects of aluminium free metal ions ln3 accounted for most other species in solution 12 16 all other ligands analysed phosphate nitrate chloride fluoride and bicarbonate were not predicted to be significant complexers of ree according to speciation calculations the results of this study have implications for the ree geochemistry of the rivers draining the mine sites of the iberian pyrite belt the acid sulfate soils represent a major readily leachable mree reservoir for the tinto odiel fluvial system which reflect the geochemical signature of the soil water interaction in the mine lands watersheds

an examination of the nature and dynamics of seismogenesis in south california usa based on non extensive statistical physics abstract we examine the nature of the seismogenetic system in south california usa by searching for evidence of complexity and non extensivity in the earthquake record we attempt to determine whether earthquakes are generated by a self excited poisson process in which case they are independent or by a critical process in which long range interactions in non equilibrium states are expected correlation emphasis is given to background seismicity i e to the rudimentary expression of the seismogenetic system we use the complete and homogeneous earthquake catalogue published by the south california earthquake data centre in which aftershocks are either included or have been removed by a stochastic declustering procedure we examine multivariate cumulative frequency distributions of earthquake magnitudes interevent time and interevent distance in the context of non extensive statistical physics which generalizes the additive boltzmann gibbs thermodynamics to non additive non extensive dynamic systems our results indicate that the seismogenetic systems of south california are generally sub extensive complex and certainly non poissonian background seismicity exhibits long range interaction as evidenced by the overall increase of correlation observed by declustering the earthquake catalogues as well as by the high correlation observed for earthquakes separated by long interevent distances the results compare very well with those obtained in previous work for the seismogenetic systems of north california specifically the walker lane eastern california shear zone on one hand and the san andreas fault system south california continental borderland region on the other appear to comprise fault networks with different dynamics and expression the former exhibits persistent very high correlation and has attributes of stationary self organized criticality soc the latter exhibits high correlation mainly at long ranges and has attributes of evolutionary of self organized criticality all in all our results are compatible with simulations of small world fault networks in which free boundary conditions at the surface allow for self organization and criticality to develop

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

palaeomagnetism of flood basalts in the pilbara craton western australia late archaean continental drift and the oldest known reversal of the geomagnetic field 1 a late archaean circa 2775 2715 ma succession of terrestrial continental flood basalts mafic tuffs felsic volcanic rocks and clastic sedimentary rocks in the nullagine synclinorium and meentheena centrocline of the east pilbara basin western australia has been sampled for a palaeomagnetic study over 500 oriented mostly basalt drill cores were collected from the supracrustal succession and associated dykes thermal and alternating field demagnetization revealed two distinct components positive fold conglomerate and reversal tests confirm that the primary natural remanent magnetization nrm is still preserved the secondary component is interpreted as the record of remagnetization during a major thermal event possibly in the early proterozoic analysis of the primary nrm directions results in a magnetostratigraphy and an apparent polar wander path apwp for the 60 myr interval covered by the sampled succession assuming a geocentric axial dipole during this time interval the apwp shows that the pilbara craton was drifting during the late archaean and that drift rates probably varied significantly in particular a mean 27 2 shift in palaeolatitude is recorded across an unconformity that represents a relatively short time period and that marks a significant change in basalt geochemistry this study suggests that continents moved horizontally during the late archaean and that the rates of movement were significantly faster than in the phanerozoic in addition a reversed polarity interval with a positive reversal test is recorded we argue that it documents the oldest known geomagnetic reversals of the geomagnetic field

recent advances in fine particle magnetism implications for paleomagnetism it is becoming increasingly obvious in paleomagnetism that the older practice of using large numbers of samples to improve statistical measures of accuracy is often not adequate to reveal the signal of greatest geological importance blanket demagnetization treatments are now largely outdated except for the most ideally behaved samples a rapidly vanishing phenomenon in many locales variations in characteristic remanent directions between neighboring and supposedly contemporaneous but lithogically distinct rock units can no longer be simply treated as noise we now recognize that such differences may actually reflect rock magnetic effects rather than such factors as the short term behavior of the geomagnetic field or local variations in structure multiple overprints often the result of moderate reheating and or chemical alteration can result in an uncertain relationship between the timing of emplacement and the acquisition of remanence in the past rocks which presented such problems could often be avoided in favor of more straightforward units much of that geological cream has been skimmed however further progress in many areas particularly the determination of the apw path and reversal stratigraphy in the paleozoic will require a better understanding of magnetization processes in order to resolve the above mentioned problems and produce accurate and reliable results

hydrogeochemistry and rare earth element behavior in a volcanically acidified watershed in patagonia argentina abstract the rio agrio watershed in northern patagonia argentina is naturally acidic due to discharges of volcanic h 2 so 4 hcl and hf at its headwaters near the summit of copahue volcano a suite of water samples was collected from the summit of the volcano to a point roughly 40 km downstream where the ph of the rio agrio rose above 6 0 this suite included a sample of the hyperacidic ph the concentrations of ree in the rio agrio decreased by several orders of magnitude through the study area as a result of dilution and chemical attenuation a subtle shift in the slope of shale normalized profiles of dissolved ree concentration was observed from being weakly positive near the source of the rio agrio to showing a weak middle ree enrichment trend in lake caviahue to being weakly negative in the lower reaches of the river the trend to a negative slope across the lanthanide series in the lower river is explained by selective partitioning of the heavier ree to hydrous oxides of fe and al suspended in the water column and accumulating on the riverbed most of the decrease in ree load occurred immediately downstream of the confluence with a tributary that increased the ph of the rio agrio from 4 3 to 6 1 although the mixed water was supersaturated with ree phosphate compounds precipitation of lnpo 4 is not believed to have been a dominant process because the predicted pattern of inter element fractionation from phosphate deposition is inconsistent with the observed trends instead ree attenuation most likely occurred from adsorption onto freshly precipitated hydrous aluminum oxide the behavior of ree in the rio agrio watershed is broadly similar to what has been observed in watersheds that owe their acidity to oxidation of sulfide minerals

mineralogy and geochemistry of trace metals and ree in volcanic massive sulfide host rocks stream sediments stream waters and acid mine drainage from the lousal mine area iberian pyrite belt portugal abstract acid mine drainage represents a major source of water pollution in the lousal area the concentrations of trace metals and the rare earth elements ree in the host rocks stream sediment surface waters and acid mine drainage amd associated with abandoned mine adits and tailings impoundments were determined in order to fingerprint their sources and to understand their mobility and water rock interaction the results show that the fe so4 rich acid waters vary substantially in composition both spatially and seasonally these waters include very low ph mostly in the range 1 9 3 0 extreme so4 concentrations 4635 20 070 mg l 1 so 4 2 high metal contents fe al cu zn and mn and very high ree contents the trace metal concentrations decrease downstream from the discharge points either due to precipitation of neoformed phases or to dilution the north american shale composite nasc normalized patterns corresponding to sediment from one stream corona stream show a flat tendency or are slightly enriched in light ree lree the nasc normalized patterns corresponding to acidic mine waters show enrichment in the middle ree mree with respect to the lree and heavy ree hree moreover the ree concentrations in acidic mine waters are 2 or 3 orders of magnitude higher than those of the surface waters changes of ree concentrations and variation of eu anomaly show two spatially distinct patterns a pond and spring waters with higher ree concentrations ranging from 375 to 2870 g l 1 that records conspicuous negative eu anomaly and b seeps from tailings impoundments corresponding to lower ree concentrations than the first pattern ranging from 350 to 1139 g l 1 with typically negative eu anomaly the stream water samples collected from the impacted stream during the spring show a low ph 2 8 3 1 and contain high concentrations of fe and trace elements up to 61 mg l 1 also temporal variations of the ree concentrations were observed in the corona waters the results obtained show that the ree concentrations increase during the winter spring transition stream waters draining the lousal mine area show high ree concentrations reaching a maximum value of about 2846 g l 1 spring the mree concentrations are usually enriched with respect to both the lree and hree a decrease in ree concentrations and a ph increase from 3 to 6 was observed downstream of the confluence of a tributary stream the geochemistry of the waters strongly influenced the mineralogy and geochemistry of efflorescent sulfates precipitated on the banks of the streams polluted by amd the mineralogy is dominated by hexahydrite rozenite szomolnokite alunite gypsum halotrychite coquimbite copiapite and schwertmannite the ree concentrations determined in the efflorescent sulfates suggest a selective partitioning of the hree onto mg al oxyhydroxides

records of geomagnetism climate and tectonics across a paleoarchean erosion surface abstract paleomagnetism has provided key constraints on the evolution of earth s climate geomagnetic field and continental geography through phanerozoic and proterozoic time extending these constraints into the archean eon has been particularly challenging due to the paucity of the ancient rock record here we report paleomagnetic measurements on the nasa astrobiology drilling project abdp 8 core drilled through one of the world s least deformed and least metamorphosed paleoarchean 3200 3600 million year old ma rock successions located in the east strelley belt of the eastern pilbara craton australia our results show that the 3350 ma euro basalt preserves a shallow magnetic inclination that appears to have formed as a result of early seafloor hydrothermal alteration suggesting that the evaporitic carbonate platform of the conformably underlying strelley pool formation was deposited in a near equatorial location this is consistent with although does not require late paleoarchean climatic zoning low orbital obliquity and a geocentric axial dipole gad field geometry similar to that of the phanerozoic the euro basalt paleopole overlaps with previously published paleoarchean poles from the east pilbara craton and with time equivalent poles reported from the barberton greenstone belt of the kaapvaal craton supporting the existence of a paleoarchean vaalbara continental aggregation

mineralogical control of rare earth elements in acid sulfate soils abstract major trace and rare earth element concentrations were measured in porewater surface water and sediments at an acid sulfate soil site the concentrations of la and ce in porewater are up to 1 3 ppm there is a strong correlation between ree concentration and acidity except that the maximum concentrations were consistently found below the horizon of maximum acidity associated with an increase in ph to ca 4 and change in mineralogy from jarosite dominated to goethite dominated mottles jarosite replacement by goethite is as expected with the rise in ph which in turn is due to the occurrence of a fossil shell bed just below the rare earth element patterns in the porewaters are enriched in the mree with respect to post archaean australian shale paas measurements and calculations show that this is in accord with experiments on low degree partial dissolution of jarosite even when the jarosite itself is highly enriched in lree there is a clear fractionation in the patterns between the clay rich soil matrix which is slightly depleted in the lree when normalized to paas la ybpaas 0 5 and the secondary mineral phase jarosite which is enriched in the lree la ybpaas 15 50 the ree pattern in the porewater changes with the transition from jarosite to goethite rich mottles becoming relatively more enriched in the lree compared to the hree which is consistent with the incongruent dissolution of jarosite to form goethite and the release of greater amounts of jarosite ree to solution including proportionately more of the jarosite compatible lree maximum surface water ree concentrations in acidic water were 100 200 ppb la and ce ree patterns in surface water were very similar to the porewater transition zone enriched in the mree but asymmetric relatively enriched in the lree compared to the hree

revisiting the paleomagnetism of the neoarchean uaua mafic dyke swarm brazil implications for archean supercratons abstract the original connections of archean cratons are becoming traceable due to an increasing amount of paleomagnetic data and refined magmatic barcodes the uaua block of the northern sao francisco craton may represent a fragment of a major archean craton here we report new paleomagnetic data from the 2 62 ga uaua tholeiitic mafic dyke swarm of the uaua block in the northern sao francisco craton eastern brazil our paleomagnetic results confirm the earlier results for these units but our interpretation differs we suggest that the obtained characteristic remanent magnetization for the 2 62 ga swarm is of primary origin supported by a provisionally positive baked contact test the corresponding paleomagnetic pole 25 2 n 330 5 e a95 8 1 n 20 takes the present northern part of the sao francisco craton to moderate latitudes based on the comparison of the paleolatitudes of cratons with high quality paleomagnetic data and magmatic barcodes we suggest that the northern part of the sao francisco craton could have been part of the proposed supervaalbara supercraton during the archean supervaalbara is proposed as including but not limited to the part of the sao francisco craton as well as the superior wyoming kola karelia zimbabwe kaapvaal tanzania yilgarn and pilbara cratons

palaeomagnetism of iron formation from the late palaeoproterozoic frere formation earaheedy basin western australia palaeogeographic and tectonic implications abstract oriented cores of unweathered frere formation 1 9 1 8 ga including shaly and peloidal iron formation were obtained from two holes drilled to 116 m depth on opposite limbs of an anticline in the southern earaheedy basin at the northeastern margin of the yilgarn craton anisotropy of magnetic susceptibility measurements indicated that the frere formation in this area was unaffected by regional metamorphism the predominant magnetic mineral in the iron formation is hematite but a small amount of magnetite also is present in some samples stepwise thermal demagnetisation was conducted for 263 specimens many specimens acquired spurious components of magnetisation after treatment to 300 500 c ascribable to the oxidation of siderite to magnetite on heating however other specimens displayed a stable high temperature 680 c dual polarity component a carried by hematite that gave a bedding dip corrected direction of d 314 3 i 24 8 k 38 5 95 2 6 n 78 a fold test was positive at 99 level of confidence indicating acquisition of remanence prior to stanley folding in the earaheedy basin that occurred at 1 78 ga near the end of capricorn orogenesis the presence of polarity reversals in the stratigraphic section from one drill hole and within some specimens argues for the identification of a dipole field axis and the sufficient averaging of secular variation to define a palaeopole for the frere formation located at 45 2 s 220 0 e dp 1 3 dm 2 4 component a is ascribed to a chemical remanent magnetisation crm acquired soon after deposition and indicates a palaeolatitude of 13 0 1 5 for the frere formation the frere pole plots adjacent to but is still significantly different from late to post capricorn orogeny overprint poles from the hamersley province of the southern pilbara however vertical axis relative anticlockwise rotation of 10 15 for the frere pole brings it close to these pilbara overprint poles the data imply that the earaheedy basin and possibly the yilgarn craton underwent clockwise rotation of 10 15 relative to the pilbara craton during stanley folding this finding accords with evidence for tectonic settings marked by sinistral strike slip deformation adjacent to the yilgarn pilbara cratonic boundary during deposition and subsequent folding in the earaheedy basin the data also imply that the west australian and north australian cratons were in close proximity by 1 8 ga

geochemistry and stable isotope composition of the berkeley pit lake and surrounding mine waters butte montana abstract samples of mine water from butte montana were collected for paired geochemical and stable isotopic analysis the samples included two sets of depth profiles from the acidic berkeley pit lake deep groundwater from several mine shafts in the adjacent flooded underground mine workings and the acidic horseshoe bend spring beginning in july 2000 the spring was a major surface water input into the berkeley pit lake vertical trends in major ions and heavy metals in the pit lake show major changes across a chemocline at 10 20 m depth the chemocline most likely represents the boundary between pre 2000 and post 2000 lake water with lower salinity modified horseshoe bend spring water on top of higher salinity lake water below based on stable isotope results the deep pit lake has lost approximately 12 of its initial water to evaporation while the shallow lake is up to 25 evaporated the stable isotopic composition of so 4 in the pit lake is similar to that of horseshoe bend spring but differs markedly from so 4 in the surrounding flooded mine shafts the latter is heavier in both 34 s and 18 o which may be due to dissolution of hypogene so 4 minerals anhydrite gypsum barite in the ore deposit the isotopic and geochemical evidence suggests that much of the so 4 and dissolved heavy metals in the deep berkeley pit lake were generated in situ either by leaching of soluble salts from the weathered pit walls as the lake waters rose or by subaqueous oxidation of pyrite on the submerged mine walls by dissolved fe iii laboratory experiments were performed to contrast the isotopic composition of so 4 formed by aerobic leaching of weathered wallrock vs so 4 from anaerobic pyrite oxidation the results suggest that both processes were likely important in the evolution of the berkeley pit lake

water rock interaction in an acidic mine discharge as indicated by rare earth element patterns abstract the rare earth element ree composition of an acidic spring discharging at ph 2 7 was studied in relation to the ree composition of selected extracts of the coal bearing strata hydrologically above the discharge the low ph of the discharge and the access to the strata through which it flows provides an excellent opportunity to study the use of rees as tracers of water rock interaction extraction techniques were used to mimic the process of acidic groundwater generation in coal bearing strata samples were treated to remove exchangeable ions and then treated sequentially with solutions buffered at ph 5 5 3 6 and 1 6 in order to mimic the natural buffering systems of groundwaters finally samples were oxidised with hydrogen peroxide in an attempt to remove the pyrite the results show that the composition of the spring is controlled by pyrite oxidation and buffering by fe oxy hydroxides the latter with compositions inherited from carbonates from within the sequence the similarity of ree patterns of the carbonate and the silicate extracts tends to obscure information concerning the relative roles of carbonate or silicate phases the source strata of the spring has evolved over time and shows that different coal seams have a unique contribution this distinct contribution appears more related to the mixture of sedimentary components i e carbonates silicates etc in the coal seam and the combination of shale and sandstone layers surrounding coal seams than the composition of the components themselves the similarity between ree compositions of the sequential extracts suggests that relationships discovered for this spring will be applicable elsewhere in the basin however this very property will hamper the use of such lithophilic elements in cases where characterisation of the source area is not possible

pre and post folding magnetizations from the early devonian snowy river volcanics and buchan caves limestone victoria summary multicomponent magnetizations of the snowy river volcanics have been resolved into pre folding dec 340 1 inc 59 2 and post folding dec 10 5 inc 72 3 elements the former is attributed to initial cooling of the volcanics while the latter is probably related to the waning stages of the deformational episode which was presumably accompanied by cooling we argue that the pole position from the pre folding magnetizations lat 74 3 s long 222 7 e represents the australian palaeopole for the early devonian a reassessment of other australian pole positions determined from rocks of about this age suggests that remagnetization during the carboniferous may be common interpretation of the pole path prior to the devonian is equivocal and awaits further study the post folding magnetizations from the volcanics are similar in stability and direction to those from the buchan caves limestone dec 27 8 inc 75 6 which appears to be completely remagnetized the age of this remagnetizing event appears to be mid carboniferous if our interpretation of the pole path for this time is correct it is noted that a much unappreciated attribute of the fold test lies with identifying not just the relative age of magnetization but also the palaeohorizontal only when the palaeohorizontal is established can the calculation of a palaeopole be justified

spatial separation of large earthquakes aftershocks and background seismicity analysis of interseismic and coseismic seismicity patterns in southern california we associate waveform relocated background seismicity and aftershocks with the 3 d shapes of late quaternary fault zones in southern california major earthquakes that can slip more than several meters aftershocks and near fault background seismicity mostly rupture different surfaces within these fault zones major earthquakes rupture along the mapped traces of the late quaternary faults called the principal slip zones pszs aftershocks occur either on or in the immediate vicinity of the pszs typically within zones that are 2 km wide in contrast the near fault background seismicity is mostly accommodated on a secondary heterogeneous network of small slip surfaces and forms spatially decaying distributions extending out to distances of 10 km from the pszs we call the regions where the enhanced rate of background seismicity occurs the seismic damage zones one possible explanation for the presence of the seismic damage zones and associated seismicity is that the damage develops as faults accommodate bends and geometrical irregularities in the pszs the seismic damage zones mature and reach their finite width early in the history of a fault during the first few kilometers of cumulative offset alternatively the similarity in width of seismic damage zones suggests that most fault zones are of almost equal strength although the amount of cumulative offset varies widely it may also depend on the strength of the fault zone the time since the last major earthquake as well as other parameters in addition the seismic productivity appears to be influenced by the crustal structure and heat flow with more extensive fault networks in regions of thin crust and high heat flow

environmental geochemistry of rare earth elements in cu porphyry mine tailings in the semiarid climate conditions of sarcheshmeh mine in southeastern iran abstract sarcheshmeh mine is one of the largest oligo miocene porphyry cu deposits in the world it is located in the kerman cenozoic magmatic arc in southeastern iran this paper discusses the geo environmental behavior of rare earth elements rees in the sarcheshmeh dammed tailing pond situated in semiarid climate for this purpose solid and water samples were collected to consider 1 weathering oxidation reactions and upward migration of soluble elements 2 super saturation and formation dissolution of the secondary evaporative phases 3 hydro geochemical changes of the surface and groundwater resources 4 flotation of the cu sulfide ore and tailing management strategies the mean values of the rees for fresh and weathered tailings and the evaporative phases were 113 0 103 7 and 74 6 mg kg respectively when compared with the fresh and weathered tailings the evaporative phases showed significant enrichment of hrees and a well depleted pattern of lrees except for that of eu this geochemical pattern suggests a higher solubility and mobility potential of hrees and eu compared with lrees resulting in good fractionation and enrichment of these elements in the surface evaporative layer formed on top of the weathered tailings the water samples showed a range of hydro geochemical features under acidic ph of 2 5 to 4 7 near neutral ph of 6 4 to 7 9 alkaline ph of 8 to 10 and highly alkaline ph 10 conditions the maximum concentration of rees was observed in the acidic waters produced by the weathered tailings after rainfall rees of 489 to 1903 g l although rees decreased as the ph value increased the general trend was compatible with the highest concentration of hrees rather than lrees the speciation calculations indicate that lnso4 ln so4 2 and ln3 are the primary forms of dissolved rees at acidic and near neutral ph and the dominant species was lnso4 lnco3 40 78 ln co3 2 31 68 and lnso4 31 07 were the dominant species under alkaline conditions at high alkaline ph the speciation pattern changed to lnoh2 53 15 ln co3 2 44 88 and lnco3 2 61 where ln denotes lanthanide based on the results and considering previous works it appears that ionic potential plays an important role in the geo environmental behavior of rees of adsorption tendency mobility potential and ionic substitution

ree fractionation during the gypsum crystallization in hyperacid sulphate rich brine the poas volcano crater lake costa rica exploited as laboratory abstract the critical role of rare earth elements lanthanides plus yttrium hereafter ree in high tech technologies and consequently their increasing demand from the industry in addition to the capability of ree to trace water rock interaction processes boosted the study of ree in unconventional extreme environments this study is focused on the geochemical behaviour of ree in the hyperacid sulphate rich brine of the crater lake of poas volcano costa rica where the precipitation of gypsum occurs this system can hence be considered as a natural laboratory to evaluate the fractionation of ree between the lake water mother brine and the precipitating gypsum mineral total ree concentrations dissolved in waters range from 1 14 to 2 18 mg kg 1 calculated distribution coefficients kd for ree between the gypsum and the mother brine indicate a preferential removal of the light ree lree with respect to the heavy ree hree with kd values mainly decreasing from la to lu during the observation period 2007 2009 the distributions of ree concentrations dissolved in lake water normalized to the average local volcanic rock show two different trends i lree depleted patterns and ii flat patterns the identification of the lree depleted pattern is justified by the kd calculated in this study we demonstrate that the precipitation of gypsum is able to strongly fractionate the ree in hyperacid sulphate rich brine inducing changes in ree concentrations and distributions over time x ray computed tomography imaging was performed on gypsum crystal precipitated from the lake waters to gain insights on crystal scale processes possibly controlling the ree geochemistry i e surface processes vs structural substitution accordingly the heavy metals and possibly the ree seem to be mainly located on the crystal surface rather than inside the crystal suggesting that a surface process could be the major process controlling ree removal from the water to the crystal

palaeomagnetic studies of fold development and propagation in the pembrokeshire old red sandstone abstract the geometry of two folds in lower devonian old red sandstone in pembrokeshire deformed in the hercynian has been defined at intermediate stages during their evolution by this preliminary palaeomagnetic study this is possible because remagnetization appears to have occurred in discrete episodes during deformation and the shape can be reconstructed by restoring the fold limbs to an angle at which the remagnetization directions coincide the plunge of the folds is shown to vary considerably during evolution one fold having an early easterly plunge which changed to the present westerly plunge the other fold having an early plunge which was more steeply to the west than its present attitude clockwise rotation of the whole of southern pembrokeshire by 40 towards the end of or since the hercynian deformation is indicated by the palaeomagnetic data and a structural model for this is proposed

kinematics of the northern walker lane an incipient transform fault along the pacific north american plate boundary in the western great basin of north america a system of dextral faults accommodates 15 25 of the pacific north american plate motion the northern walker lane in northwest nevada and northeast california occupies the northern terminus of this system this young evolving part of the plate boundary offers insight into how strike slip fault systems develop and may reflect the birth of a transform fault a belt of overlapping left stepping dextral faults dominates the northern walker lane offset segments of a w trending oligocene paleovalley suggest 20 30 km of cumulative dextral slip beginning ca 9 3 ma the inferred long term slip rate of 2 10 mm yr is compatible with global positioning system observations of the current strain field we interpret the left stepping faults as macroscopic riedel shears developing above a nascent lithospheric scale transform fault the strike slip faults end in arrays of n striking normal faults suggesting that dextral shear diffuses into extension in the great basin coeval extension and dextral shear have induced slight counterclockwise fault block rotations which may ultimately rotate riedel shears toward the main shear zone at depth thus facilitating development of a throughgoing strike slip fault

mobility and fractionation of rare earth elements during supergene weathering and gossan formation and chemical modification of massive sulfide gossan primary massive sulfide gossans msg in the bathurst mining camp bmc new brunswick canada are characterized by relative enrichment of au sb and as formation of jarosite group minerals jarosite plumbojarosite and argentojarosite and little or no fractionation in the rare earth elements ree including preservation of large positive eu anomalies average eu eu nasc 4 14 in msg 6 61 in massive sulfide mineralization 0 60 in host rocks the chemical and mineralogical characteristics of msg e g halfmile lake deposit imply low ph 3 and relatively oxidizing conditions during gossan formation oxidation of a volcanogenic massive sulfide body comprising pyrite pyrrhotite sphalerite galena and chalcopyrite with a falling water table the lack of light ree or heavy ree fractionation and preservation of positive eu anomalies characteristic of the original 465 ma hydrothermal fluid is consistent with relatively large water rock ratios during massive sulfide mineralization oxidation and removal of the ree predominantly as sulfate complexes lnso4 ln so4 2 low ph groundwaters recovered from past producing mines in the bmc display ree patterns reflecting those inferred to have occurred during gossan formation gossan at the restigouche deposit in contrast to the halfmile lake deposit displays mineralogical and chemical evidence for having been chemically reworked since primary gossan formation evidence for chemical reworking includes loss of primary massive sulfide mineralization textures replacement of plumbojarosite with anglesite almost complete removal of jarosite minerals loss of au sb and as and apparent preferential removal of eu resulting in loss of positive eu anomalies for most samples average eu eu nasc 1 21 in the gossan with many displaying strong negative anomalies 3 65 in massive sulfide mineralization 0 54 in host rocks based on geochemical modeling conditions inferred for the chemical reworking of the restigouche deposit include near neutral conditions and either relatively oxidizing conditions with eu2 hosted in a preferentially weathered mineral host possibly through substitution for pb in plumbojarosite and beudantite or cycling between reduced and oxidized conditions during gossan reworking

paleomagnetism of late archean rocks of hamersley basin western australia and the paleointensity at early proterozoic we report the results of paleomagnetic and rock magnetic measurements of late archean rocks from hamersley basin western australia and the paleointensity determination for early proterozoic basalts and banded iron formations have two to four components of remanent magnetization and have consistent directions for different localities indicative of geomagnetic origin rock magnetic measurements of basalts reveal that the main magnetic mineral is a fine grained magnetite present in 10 ppm in mass which do not alter when heated up to its blocking temperature we interpret the stable component up to 390 c as the post tilting thermal overprint from uplift at 2 0 ga and the higher temperature component as the pre tilting thermoviscous remanence during burial metamorphism from the thellier type paleointensity experiments using the thermal overprint component we obtain a mean virtual dipole moment vdm estimate of 1 8 3 6 10 22 am 2 this suggests that early proterozoic was characterized by a 1 weak geomagnetic field of less than one half of the present 2001 elsevier

opening of the red sea constraints from a palaeomagnetic study of the as sarat volcanic field south western saudi arabia summary four stratigraphic sections through alkali basalt flows of oligocene to miocene age 29 24ma in the as sarat volcanic field south western saudi arabia were sampled for palaeomagnetic study after systematic alternating field demagnetization 42 magnetically acceptable flows 139 samples yield a mean direction of magnetization of d 355 3 i 15 2 ag5 4 3 which defines a palaeomagnetic pole at 78 8 n 247 8 e of these acceptable flows 24 are normally and 18 reversely magnetized part of one section was apparently erupted during the early phases of a polarity reversal of the earth s field the mean direction derived from the 24 normally magnetized flows is significantly different after inverting 180 from that derived from the 18 reversed flows supporting the hypothesis of a displaced dipole source for the earth s field in late oligocene to early miocene time a comparison of the results from as sarat with palaeomagnetic results from upper tertiary rocks in africa indicates that the red sea has opened 12 estimated 8 at the 95 per cent confidence level these results indicate that most of the counter clockwise rotation of arabia relative to africa occurred since the eruption of the as sarat volcanics in disagreement with proposed models for main stage red sea spreading from late eocene to early oligocene time the palaeomagnetic results also indicate that the arabian peninsuia was more equatorial in late oligocene to early miocene time than it is now by an amount compatible with the opening of the gulf of aden