a high resolution p wave model for the top 1200 km of the mantle this work attempts to map aspherical velocities in the top 1200 km of the mantle that are illuminated by the international seismological centre p wave data the processing includes summary ray sorting and hypocentral redetermination to cope with the extreme variation of ray coverage a multicell inversion is used to simultaneously constrain anomalies in overlapping cells the multicell solutions are summed after inversion to form the final model named p1200 at cell size of 1 1 and about 50 km in thickness the lateral resolution of the model is about 1 2 in major subduction zones and about 5 15 in most places major features in the model withstood tests on signal coherency and different reference models the long wavelength parts of the p1200 model correlate well with previous global models especially the s12 model of shear wave among the large features in the transition zone and below there are two fast bands one from canada to south america and another from siberia through east asia and the philippine sea to western australia there are also slow patches under the central pacific and from india to eastern africa though most subduction zones have slab like high velocity anomalies they are sandwiched by broad slow velocities at shallow depths some of the slabs appear to penetrate the 660 km discontinuity and stagnant slabs are also seen in the transition zone plume like slow anomalies exist below some prominent hot spots like hawaii iceland yellowstone and french polynesia

p wave tomographic imaging of the crust and upper mantle beneath the japan islands more than 50 000 high accuracy arrival times from 1200 shallow and deep earthquakes selected from the japan university network earthquake catalog are used to investigate the three dimensional 3 d seismic velocity structure beneath japan travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique p wave tomographic images of the crust and upper mantle to a depth of 500 km beneath the japan islands are determined with spatial resolutions of 25 50 km the obtained p wave velocity in the crust and uppermost mantle is slightly higher and relatively homogeneous in western japan in contrast with an average lower velocity and a large heterogeneity in eastern japan where many active volcanoes exist this feature correlates well with the distributions of heat flow and gravity anomalies low velocity low v zones are imaged in the crust and uppermost mantle beneath active volcanoes the low v zones in the mantle wedge dip toward the west and extend continuously to a depth of about 200 km a high velocity high v zone corresponding to the subducted pacific plate is delineated the thickness of the high v zone is estimated to be 80 90 km in southwestern japan the descending philippine sea plate is also delineated its thickness is estimated to be 30 km

experimental study of boron geochemistry implications for fluid processes in subduction zones a comprehensive experimental study utilizing an autoclave hydrothermal apparatus with a 10b isotopic tracer has been conducted to monitor the geochemical behavior of sediment b during early subduction zone processes the partition coefficient of exchangeable b kd was determined over a temperature range of 25 350 c at 800 bars and a water rock ratio of 3 1 5 w w these kd are shown to be a complex function of temperature ph and possibly mineralogy at low temperatures kd is significantly high at 4 in contrast to the value of essentially zero at temperatures higher than 100 c a kd of zero represents no b adsorption implying efficient mobilization of exchangeable b at shallow depths during sediment subduction our experimental results demonstrate high mobilization of bulk b in sediments both exchangeable and lattice bound at elevated temperatures 200 350 c in good agreement with previous observations of b in metasediments indicating progressive depletion during metamorphism in addition this study emphasizes the importance of a possible water rock ratio dependence of b mobilization in other words the degree of sedimentary b mobilization in subduction zones strongly depends on the local thermal structure and porosity distribution in low geothermal gradient areas large amounts of porewater are expelled before significant b mobilization has occurred so that some sedimentary b will survive and get into the deeper parts of the subduction zone our results imply that efficient mobilization of b from the subducted slab must occur and that arc magmatism recycles most of the remaining subducted b back to surface reservoirs a reconsideration of the b budget in subduction zones provides critical information with respect to b sources and sinks in the ocean

petrogenesis of tourmaline rocks associated with fe carbonate graphite metapelite metabasite and strata bound polymetallic sulphide mineralisation peloritani mountains sicily southern italy abstract tourmalinite and tourmaline rich rocks associated with fe carbonate graphite phyllite strata bound polymetallic sulphide deposits metabasite and marble were studied for information on the mechanism of tourmaline formation in the pre hercynian low grade metamorphic sequence of the mandanici unit in the peloritani mountains of sicily southern italy the major and trace element compositions of the tourmaline rocks suggest the existence of a sedimentary protolith with pre metamorphic black shale and bedded chert boron was interpreted to be accumulated in a restricted sedimentary basin between platform carbonate formations with abundant organic matter and fe al ti rich laterite bauxite soil derived clastic supply under a continental volcano tectonic extensional regime accompanied by a local convective hydrothermal system along faults petrographic crystal chemical and 11 b isotopic data are compatible with a model of marine sediment dewatering at temperatures below 200 c which caused the removal of boron from clay metamorphism led to the development of tourmaline in an al ti rich environment in equilibrium with other minerals such as ilmenite albite and muscovite the upper temperature of metamorphism almost 375 c estimated on the basis of 11 b fits geothermometric results from 13 c carbonate graphite on associated rocks the estimated value of 11 b in the tourmalinite protolith 7 5 is also compatible with continental derived al rich sediments

rupture complexity of the mw 8 3 sea of okhotsk earthquake rapid triggering of complementary earthquakes we derive a finite slip model for the 2013 m w 8 3 sea of okhotsk earthquake z 610 km by inverting calibrated teleseismic p waveforms the inversion shows that the earthquake ruptured on a 10 dipping rectangular fault zone 140 km 50 km and evolved into a sequence of four large sub events e1 e4 with an average rupture speed of 4 0 km s the rupture process can be divided into two main stages the first propagated south rupturing sub events e1 e2 and e4 the second stage e3 originated near e2 with a delay of 12 s and ruptured northward filling the slip gap between e1 and e2 this kinematic process produces an overall slip pattern similar to that observed in shallow swarms except it occurs over a compressed time span of about 30 s and without many aftershocks suggesting that sub event triggering for deep events is significantly more efficient than for shallow events

boron isotope variations in nature a synthesis the large relative mass difference between the two stable isotopes of boron 10b and 11b and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes published 11b values relative to the nbs srm 951 standard span a wide range of 90 the lowest 11b values around 30 are reported for non marine evaporite minerals and certain tourmalines the most 11b enriched reservoir known to date are brines from australian salt lakes and the dead sea of israel with 11b values up to 59 dissolved boron in present day seawater has a constant world wide 11b value of 39 5 in this paper available 11b data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects including possible tracer applications of boron isotope geochemistry are summarized

seismic structure of the northeastern japan convergent margin a synthesis many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern japan arc and its relationship to seismic and volcanic activity spatial distributions of the depths to the conrad and the moho discontinuities estimated from shallow earthquake data and seismic explosion data show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the japan sea and the pacific ocean the pn velocity has a lateral variation it is as low as 7 5 km s beneath the land area while that beneath the japan sea and the pacific ocean is 8 0 8 2 km s it changes abruptly at the transition zones which are located along the coastlines precise structure and location of the subducted pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate the pacific plate is composed of a thin 5 km low velocity upper layer and a thick high velocity lower layer its total thickness being 80 90 km the upper plane seismicity of the double seismic zone is confined to the thin low velocity upper layer which probably corresponds to the subducted former oceanic crust the lower plane seismicity lies at the middle of the high velocity lower layer and the lower half of the plate below it is incapable of generating earthquakes the shallower portion of the upper surface of the plate beneath the pacific ocean along which major seismicity with low angle thrust faultings is actually occurring is also located by seismic observations on land and in the sea the pacific plate subducts at an extremely low angle of 5 for the first 25 km depth and then the dip steepens rather abruptly to 30 normal fault type events at the top of the plate have not been detected in the portion where the downward bending is the largest but have been ditected near the trench axis where it is rather small tomographic inversions for seismic velocity structure clearly delineate the inclined high velocity pacific plate with a thickness of 80 90 km and low velocity zones in the crust and the mantle wedge beneath active volcanoes seismic attenuation tomography also shows similar zones of low q value beneath active volcanoes although its spatial resolution is much lower the low velocity zones with 2 6 velocity lows are continuously distributed from the upper crust just beneath active volcanoes to a depth of 100 150 km in the mantle wedge and are approximately parallel to the dip of the underlying pacific plate these low velocity zones probably reflect the pathway of magma ascent from a depth in the mantle wedge to the earth s surface corresponding to a portion of the subduction induced secondary mantle wedge flow

high frequency precursors to p wave arrivals in new zealand implications for slab structure this report revisits the very early high frequency slab phases from earthquakes in the kermadec slab between 25 s and 37 s that arrive as a precursor to the p wave onset at stations in new zealand the analysis of short period digital records for station snzo south karori new zealand for the time period between 1980 and 1986 involved 4 times as many data as in previous studies we confirm most of the earlier observations in particular the relationship between source region and observed waveform numerical waveform modeling using two dimensional slab models confirm that the high frequency precursor can be explained by p wave propagation in a thin 8 10 km high velocity layer hvl the sensitivity of the high frequency phase to source position in the slab is investigated and we demonstrate that the slab phase does not survive interruptions or strong lateral variations of the hvl assuming the shape of the slab from tomographic images and continuity of the hvl we infer that the large negative travel time residuals can be explained if p wave propagation is 4 to 5 faster than in the ambient mantle for depths to 300 km and about 2 faster for depths between 300 and 600 km rather than resorting to regional differences in structure and composition of the hvl we argue that specific source receiver configurations and the shape of the slab explain the observed regional variation in the character of the high frequency slab phases

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

imaging of subducted lithosphere beneath south america tomographic images are produced for the deep structure of the andean subduction zone beneath western south america the data used in the imaging are the delay times of p pp and pwp phases from relocated teleseismic earthquakes in the region regionally structural features larger than about 150 km are resolved by the data presentations of layer anomaly maps and cross sections reveal 1 the nazca slab is probably continuous laterally and at depth over most regions 2 the offset between the north and south deep earthquake zones containing the 1994 deep bolivia main shock and its aftershocks can be modelled by a northwest striking and steeply northeast dipping slab structure and 3 the nazca slab clearly penetrates the lower mantle beneath central south america but is partly deflected in the southern deep zone

tourmalines from appalachian caledonian massive sulfide deposits textural chemical and isotopic relationships tourmaline is a common gangue mineral in several strata bound massive sulfide deposits of the appalachian caledonian orogen most of the tourmaline rich deposits occur in dominantly metasedimentary terranes such as bleikvassli norway black hawk maine ore knob north carolina and elizabeth vermont minor amounts of tourmaline are also known in association with volcanic hosted deposits in the appalachians and in the trondheim district of norway the tourmaline forms isolated euhedral crystals or crystal aggregates in massive sulfide and adjacent wall rocks in a few areas it is found in conformable tourmaline rich layers tourmalinites associated minerals may include quartz plagioclase phlogopite and dolomite with pyrrhotite chalcopyrite galena and sphalerite many of the tourmaline crystals are optically zoned in which brown zones concentrically alternate with pale yellow or green zones a few specimens of tourmaline intergrown with massive sulfide e g ore knob display fine delicate growth lamellae similar to those commonly observed in hydrothermal vein sphalerites skarn garnets and sphalerites from the massive sulfide deposits of the kuroko district japan detailed geochemical studies indicate that the tourmalines have characteristic major and trace element compositions electron microprobe analyses show that with rare exception the tourmalines are mg rich dravites avg feo feo mgo 0 21 abrupt transitions between color zones within some tourmaline are accompanied by relative variations in feo feo mgo of as much as 30 percent yellow brown zones are more mg rich than blue or green zones in contrast the fine growth lamellae are not characterized by such variations in chemistry spectrographic analyses of pure mineral separates indicate that the tourmalines also contain high average contents of cr 78 ppm cu 77 ppm pb 114 ppm sr 98 ppm and v 195 ppm while uniformly low in li 7 ppm and mn 382 ppm in all analyzed samples fluorine is much more abundant than chlorine the average f cl ratio is 33 tourmalines from tourmalinites and massive sulfide deposits are typically characterized by heavier delta 18 o values 9 5 15 5ppm and less variable heavier delta d values generally 45 to 60ppm than tourmalines from unmetamorphosed igneous pegmatites the latter typically have delta 18 o 9 5 per mil and delta d or 60 per mil oxygen isotope fractionations between quartz and tourmaline delta 1 27 4 01 do not correlate directly with inferred grade of subsequent metamorphism although in areas of high metamorphic grade the delta values approach those of igneous quartz tourmaline pairs the delta 18 o values of quartz and tourmaline are believed to reflect variation in the oxygen isotope compositions of the host lithologies the similar narrow range in hydrogen isotope composition for tourmaline in all studied deposits is compatible with a modified seawater origin for the tourmaline and sulfide forming fluids the distinctive textural and chemical characteristics of the tourmalines reported here have both exploration and genetic significance though it may have undergone recrystallization and some accompanying chemical and isotopic exchange during regional metamorphism tourmaline in the massive sulfide deposits is an early formed perhaps diagenetic mineral in which fine lameliar zoning may be a preserved premetamorphic feature in any case the tourmalines from the massive sulfide deposits are mg rich dravites with trace element and stable isotope compositions substantially different from those of the fe rich schorls typical of most granitic rocks these geochemical and isotopic signatures are attributed to the original environment of formation of the associated sulfide deposits and suggest that mg rich tourmaline may be a valuable prospecting guide in the search for massive sulfide deposits

observations of body wave multipathing from broadband seismograms evidence for lower mantle slab penetration beneath the sea of okhotsk we present observations of anomalously broad and complex sh waveforms from two deep focus earthquakes in the southern kurils to digital world wide standard seismograph network and regional seismic test network stations in north america by making use of broadband three component seismograms and relying on a variety of phases one can limit the class of possible explanations for these phases in particular it is shown that the anomalous arrivals are not due to source complexity near receiver structure a triplication from a lower mantle velocity gradient a low q zone in the mid lower mantle or shear wave splitting we show that these arrivals correspond to relatively fast paths and have enhanced amplitudes indicating that they are most probably caused by multipathing due to interaction with a high velocity lower mantle feature below the source region we examine the hypothesis that this feature may be a lower mantle extension of the kuril slab ray tracing experiments show that multipathing is indeed expected along the azimuths corresponding to the north american stations used in this study for a realistic slab model observations of reversed polarity arrivals are consistent with such an explanation where it appears that two rays comprising the arrival emerge from different points on the focal sphere one test of this explanation is that slab induced multipathing should not be seen along back of slab oceanic azimuths examinations of seven events for which the stations are in this azimuth range do not exhibit the same broadening and complexity of the sh waveforms identification of slab induced multipathing associated with deep focus events has two important consequences first it appears to require slab penetration beyond the 650 km discontinuity at least 300 400 km into the lower mantle under the sea of okhotsk second these phases may act as a contaminant when attempting to study other seismic phenomena such as discontinuities low q zones near receiver structure or source complexity

a least squares approach to mass transport calculations using the isocon method a statistically rigorous approach based on the isocon method grant 1986 to evaluate mass transport is presented chemical analyses of multiple samples of unaltered parent and altered rock are used to calculate the average oxide or element concentration and its standard deviation for each rock population in a typical application the uncertainties in element concentration associated with the lack of homogeneity in each population outweigh the analytical uncertainty an efficient algorithm is presented to select the immobile elements by identifying the maximum number of elements that are within their uncertainties compatible with the same isocon the actual isocon is constructed by forcing a line through the origin and optimizing its slope using a weighted least squares procedure for the selected immobile elements thus individual uncertainties for each immobile element are taken into account as an illustration the procedure is applied to a published set of data on potassic and sericitic alterations of quartz monzonite of the bingham porphyry copper system the surprising result indicates that the apparent increase of potassic alteration phases is a consequence of acid leaching of calcium and sodium no mass transport of potassium is indicated silica water and sulfur were added during alteration the best fit isocon requires a small mass increase during each alteration process which however is within the uncertainty obtained for the slope of the isocon a software package is available from the authors in the form of a fortran 77 source code

structural trends and palaeogeography of the central and western sicily belt new insights the geology of the sicilian mainland is summarized by n s geological sections a continuous late cenozoic orogenic belt through central and western sicily resulted from a complex deformative history recorded by several tectonic events the deformation mainly involved the sedimentary cover of the old african continental margin formed in a large basinal area bordered at its southern margin by a shallow water carbonate environment attached to gondwana the orogenic belt involves a complex architecture of thrust systems of different size geometry and palaeogeographical origin deformation which mainly developed in the earlier stages of thrusting in the basinal rock assemblages mainly gave rise to a stack of three different duplex structures respectively composed of palaeozoic mesozoic palaeogene and neogene strata large scale clockwise rotation of the thrusts predated transpressional movements in the hinterland during the latest miocene to pliocene high angle reverse faults with lateral components modified earlier tectonic contacts within the allochthons contemporaneous southwards directed imbrications affected the external southern areas progressively incorporating foreland and piggyback basirts the stratigraphic relationships of basin fills to the tectonic structures reveals that reactivation processes have been active during the last plio pleistocene

slab temperature and thickness from seismic tomography 1 method and application to tonga delay times of compressional body wave phases from both teleseismic and local events are used to invert for a high resolution p wave velocity model in the tonga subduction zone the images obtained show a high velocity subducting slab with velocity deviations of the order of 3 4 assuming to first order that the positive velocity anomalies within the slab are caused by a temperature effect a theoretical slab temperature model based on the diffusion equation is used to explain velocity anomalies within the tomographic slab temperature differences between the interior of the slab and the ambient mantle are converted to velocity perturbations using the scaling parameter dvp dt 4 8 10 4 km s 1 c 1 for lithosphere material the optimal values for the parameters in the temperature model are found using a nonlinear optimization that compares the integrated velocity anomalies in the tomographic slab region to integral of high velocities in a synthetic slab derived from a temperature model the parameters for slab thickness and mantle potential temperature are not uniquely determined therefore a fixed value for the mantle potential temperature based on laboratory values for the temperature of the spinel to perovskite transition at 660 km is used using 1180 c as the potential temperature the theoretical temperature model gives an optimal slab thickness of 82 km for a region near 29 s in tonga the uncertainty in the thickness is dominated by the uncertainty in the mantle temperature and would be 8 km for an uncertainty of 100 in mantle temperature but nonsystematic errors are less in order to enhance the tomographic result the velocity model is biased towards the theoretical slab model however a posteriori changes made to the tomogram will most likely violate the fit to the delay time data to prevent this the difference between the tomogram and the predicted slab model is projected onto the null space of the inversion to remove components which do not satisfy the seismic data using only null space components to modify the minimum norm solution an enhanced model is obtained which has been biased toward the theoretical solution but has the same data misfit as the minimum norm solution the final image shows a very narrow and continuous slab with maximum velocity anomalies of the order of 6 7 many of the gaps within the slab as well as artifacts around the slab which were present in the minimum norm solution are absent in the biased image

intermediate term prediction of occurrence times of strong earthquakes pattern recognition procedures for infrequent events are adapted to the problem of identifying patterns of clustering of small and intermediate scale seismicity before large earthquakes identification procedures derived from analysis of large california and nevada earthquakes yield a high success rate when applied to other parts of the world

the role of volatiles in the transition zone phase relations in the system mgo sio2 with low volatile contents of h2o f2 and cl2 were experimentally investigated at 100 234 kbar pressures and 850 2050 c temperatures using a split sphere anvil apparatus ussa 2000 superphase b mg10si3o14 oh f 4 was observed at 160 234 kbar fluorous phase b mg12si4o19f2 at 178 kbar and hydrous phase f mg4si7o16 oh 4 also at 178 kbar at lower pressures the volatiles were present in phase a mg7si2o8 oh f 6 phase c mg 7 x si 2 x o 9 x oh f 4 and phase e mg 2 x si 1 x o 4 x y oh f 2y with the exception of the fluorous phase b all these phases can coexist with stishovite at pressures above 130 kbar in a purely hydrous system the dehydration temperatures of the assemblage superphase b stishovite increase from 1200 c at 160 kbar to 1400 c at 234 kbar dehydration produces beta phase mg2sio4 possibly containing up to 7 wt of structural h2o about 3 wt of h2o in beta phase expands the stability of the assemblage beta phase stishovite at the expense of ilmenite by 30 kbar in more complex compositions the volatile solidus is below 1350 c thus at the temperatures which are much lower than the expected mantle temperatures at the relevant depths consequently most of the mantle is in a partially molten state the volatile bearing phases can only be present in the colder subducted slabs but not in the rest of the transition zone 400 670 km hydrous beta phase and stishovite are the most likely constituents of the slabs incongruent melting of the hydrous beta phase coexisting with stishovite producing garnet and melt could be the cause of deep focus earthquakes evidence for a mineralogically and chemically stratified upper mantle is reviewed and its structure is discussed in the context of the present results

differential mobility of elements in burial diagenesis of siliciclastic rocks abstract mass balance calculations involving smectite rich siliciclastic mudstones sampled from boreholes show that significant k2o addition and cao loss correlate strongly with the progress of illitization of smectite and with the dissolution of calcite the calculations are based on the immobility of al2o3 and require a chemically homogeneous sediment at deposition such that the shallower samples represent protolith compositions of deeper samples constancy of ratios of tio2 al2o3 are used to 1 establish that both tio2 and al2o3 have similarly low differential mobilities and 2 identify stratigraphic sections available in the literature that are sufficiently homogeneous to allow the calcu ations our calculations show that most major oxide components are immobile at the 5 limit of resolution of the calculations exceptions are k2o which is almost universally added to mudstones and cao which is commonly removed from mudstones during diagenesis the addition of up to 50 k2o correlates with percent illite in mixed layer illite smectite indicating that illitization of smectite involves fixation of k2o from diagenetic fluids removal of 40 cao from some sections correlates with decreasing calcite mode and is attributed to dissolution of calcite together these reactions lead to a 10 15 loss of mineral volume a volume loss that must be added to porosity loss when modeling compaction illitization and carbonate dissolution may be linked because k fixation during illitization decreases the ph of the local fluid a reverse weathering reaction which enhances carbonate dissolution addition of up to 20 na2o in some rocks may be caused by albitization of plagioclase but na2o addition is not pervasive the apparent lack of mass transfer associated with dissolution of kaolinite and feldspars or precipitation of chlorite implies that these reactions are balanced by other reactions such that their oxide components in mudstones are conserved limited data from sandstone mudstone pairs are consistent with transfer of k2o from sandstones to mudstone via rising diagenetic fluids except for cao and the alkalis diagenesis of siliciclastic mudstones appears isochemical 5 relative for most major oxide components the much larger changes recorded in some reservoir sandstones are clearly exceptions and may not reflect changes occurring at the scale of kilometers

three dimensional p wave velocity structure beneath central japan low velocity bodies in the wedge portion of the upper mantle above high velocity subducting plates abstract the three dimensional 3 d p wave velocity structure beneath central japan has been investigated in detail by an inversion method 7490 p wave arrival times from 120 shallow and intermediate depth earthquakes that have occurred in this region are used to estimate velocity anomalies in 3 d subdivided blocks and hypocentral perturbations simultaneously the results reveal complex 3 d structures with low velocity zones in the wedge portion of the upper mantle above the high velocity philippine sea and pacific plates subducting beneath this region prominent low velocity bodies exist just beneath active volcanoes particularly in the hida mountain range low velocity bodies are spatially correlated with the low q zones estimated from seismic intensity data one low velocity body coincides with an anisotropic body detected from the study of shear wave splitting dome shaped low velocity masses seem to represent partially melted mantle diapirs no clear evidence on velocity contrast has been identified across the fossa magna which is a tectonic boundary between northeast and southwest japan

boron isotope variations in tourmaline from hydrothermal ore deposits a review of controlling factors and insights for mineralizing systems abstract tourmaline group minerals are typically the predominant host of boron in hydrothermal mineral deposits boron is a fluid mobile element whose isotopic composition reflects many factors that are relevant to understanding mineralizing processes including fluid source s fluid rock interaction and formational temperature a new compilation of 2622 published 11b values for tourmaline from diverse types of hydrothermal ore deposits is presented here with the focus 2215 analyses on seven main types porphyry cu mo au deposits granite related sn w deposits iocg deposits orogenic au deposits stratabound vms and sedex deposits and sediment hosted u deposits the total range of 11b values for the seven types is 26 8 to 35 0 four granite sn w orogenic au stratabound vms and sedex have median 11b values close to the continental crustal average of about 10 the median values for iocg and porphyry cu mo au deposits are higher 3 9 and 2 1 respectively whereas sediment hosted u deposits have distinctly high 11b median 25 3 importantly a considerable range of 11b values exists for tourmaline within each deposit type the smallest 17 8 for granite sn w deposits and the largest 48 0 for iocg deposits the boron isotope variations in tourmaline from different deposits are suggested reflect three levels of controlling factors and how these factors operated is illustrated with selected number of case studies the primary factor is the composition of the boron source secondary effects relate to fluid tourmaline fractionation equilibrium or rayleigh there are commonly also tertiary factors that depend on evolution of the specific deposit these include fluid mixing changing water rock ratio and or depositional temperature influences of other boron bearing minerals and where relevant post ore metamorphism separating the effects of these factors is rarely possible from boron isotopes alone however the growth of multi isotope studies of tourmaline and coexisting phases such as mica as well as developments in modelling experimentation of boron isotopes and element partitioning suggest that this limitation will be overcome

mantle transition zone structure beneath the changbai volcano insight into deep slab dehydration and hot upwelling near the 410 km discontinuity we study the detailed mantle transition zone structure beneath the active changbai intraplate volcano in northeast china by using a receiver function method a total of 3005 teleseismic receiver functions recorded by 70 broadband stations are obtained by using a common conversion point stacking method for conducting the time to depth conversion we use a three dimensional velocity model of the study region so as to take into account the influence of structural heterogeneities our results reveal significant depth variations of the 410 520 and 660 km discontinuities a broad depression of the 410 km discontinuity and a low velocity anomaly are revealed beneath the changbai volcano which may reflect a large scale hot mantle upwelling around the 410 km discontinuity with a positive clapeyron slope the 520 km discontinuity is identified clearly and its uplift occurs above the stagnant pacific slab we also find a prominent depression of the 660 km discontinuity which is elongated along the trend of deep earthquake clusters in a range of 39 n 44 n latitude and the depression area has a lateral extent of about 400 km because the 520 and 660 km discontinuities correspond to positive and negative clapeyron slopes respectively we think that the 520 uplift and the 660 depression are caused by the cold subducting pacific slab a part of the pacific slab may have penetrated into the lower mantle and so caused the large scale 660 depression in front of the deep earthquake clusters our results also reveal a part of the upper boundary of the subducting pacific slab in the mantle transition zone

simultaneous determination of the three dimensional crustal structure and hypocenters beneath the kanto tokai district japan abstract a new method is proposed for determining the two dimensional depth distributions to the conrad and the moho together with station corrections and source parameters from first arrival time data in the present study the velocity structure is modelled by a hyperbolic function tanh and the configuration of each interface is expressed in a series of chebyshev functions with coefficients which are unknown parameters a non linear inversion method by tarantola and valette is applied for inversion an approximate ray tracing method with sufficient accuracy for a complex region is adopted for computation of seismic ray paths and travel times the method is applied to p wave first arrival time data from local earthquakes and explosions gathered in the seismological network by the national research center for disaster prevention to reveal the crustal structure beneath the kanto tokai district japan the results obtained in this study are very interesting and show the usefulness of the present method for the study of the crustal structure the distribution of station corrections is reasonable where there is information on the shallow structure low velocity zones appear around tokyo bay and the cape of omae and high velocity zones appear in the mountainous regions the depth to the conrad is about 12 16 km and its lateral change is gentle while the lateral change in the depth to the moho is comparatively large and there is a narrow region where the depth to the moho exceeds 40 km except for this region the central mountainous region the agreement of the crustal structure obtained in the present study with those by the previous refraction studies is fairly good in comparing our results to fractional velocity perturbation in layer 1 0 32 km derived with aki and lee s method by ishida and hasemi our work provides good information on the features causing the crustal velocity anomalies which have been unable to be constrained in ishida and hasemi s work

the fate of the juan de fuca plate implications for a yellowstone plume head beneath the pacific northwest the juan de fuca plate a remnant of the farallon plate continues subducting beneath the north american continent to the east of the cascadia subduction zone lies the yellowstone hotspot track the origins of this track can be traced back to the voluminous basaltic outpourings in the columbia plateau around 17 ma if these basalts are the result of a large melting anomaly rising through the mantle to the base of the north american continent such as a mantle plume head the anomaly would need to punch through the subducting juan de fuca slab here we use teleseismic body wave travel time tomography to investigate the fate of the subducted slab and its possible interaction with a plume head our dataset is derived from the oregon array for teleseismic study oats deployment in oregon and all other available seismic data in this region during the same period in our jdf07 models we image the subducted juan de fuca plate in the mantle east of the cascades beneath oregon where the slab has not been imaged before to a depth of 400 km but no deeper the slab dips similar to 50 degrees e and has a thickness of similar to 75 km immediately beneath the slab we image a low velocity layer with a similar geometry to the slab and extending down to at least similar to 575 km depth in the v model the total length of the high velocity slab is similar to 660 km about 180 km longer than the estimated length of slab subducted since 17 ma assuming similar slab geometry to today this 180 km length of slab would reach similar to 60 km depth comparable to the thickness of continental lithosphere we propose that the absence of the slab below 400 km today is due to the arrival of the yellowstone plume head similar to 17 ma which destroyed the juan de fuca slab at depths greater than the thickness of the continental lithosphere given this scenario the low velocity anomaly beneath the slab is likely the remnant plume head material which has been pulled down by traction with the subducting plate the amplitude of the observed low velocity anomaly is comparable with that expected for plume head material 100 300 degrees c hotter than the surrounding asthenosphere c 2007 elsevier b v all rights reserved

slab temperature and thickness from seismic tomography 2 izu bonin japan and kuril subduction zones delay times from teleseismic and local p wave arrivals are used to invert for a high resolution three dimensional velocity model beneath the northwest pacific the model shows high velocity slabs with average velocity anomalies of the order of 3 4 assuming the positive velocity deviations in the subducting lithosphere are to first order due to a temperature anomaly the results of a theoretical slab temperature profile based on the diffusion equation are converted to a synthetic slab velocity model temperature variations between the ambient mantle and the interior of the slab are converted to p wave velocity perturbations using dvp dt 4 8 10 4 km s 1 c 1 a nonlinear optimization scheme compares the tomograms obtained via tomography to the theoretically predicted models in order to determine the optimal values for slab thickness and mantle potential temperature using 1180 100 c as the potential temperature thickness estimates of 88 8 km 85 8 km and 84 8 km are obtained for the izu bonin japan and kuril slabs respectively a correlation exists between slab thickness and age which is strong if mantle temperature variations along the slab strike can be ruled out in the process of estimating slab thickness the predicted slab velocity model is used as a filter to enhance the initial minimum norm tomographic result the initial tomogram is modified to closely resemble the synthetic slab tomogram by using only null space components the use of the null space components guarantees that the enhanced solution will satisfy the original seismic delay times the enhanced slab images show very continuous and narrow slabs compared to the initial tomographic results

low s velocities under the tornquist teisseyre zone evidence for water injection into the transition zone by subduction a strong low s velocity anomaly at 300 500 km depth coincides with the western boundary of the russian platform the anomaly is too large to be explained by a simple temperature anomaly or by compositional variations nor is it an artifact induced by seismic anisotropy we present a model that explains the anomaly through the injection of water at the time of closure of the tomquist ocean that separated the continents of avalonia and baltica in the early paleozoic dense hydrous magnesium phases are the most likely agents for transporting water to the transition zone but an important role may also be played by nominally anhydrous clinopyroxene when these minerals are brought out of their stability field water is released it may accumulate in spinel or k amphibole and may be released when the mantle warms up after subduction halts the effect of this water is to induce weakening of the shear modulus or even creation of a heavy melt by a conservative estimate a subduction episode lasting 85 m y would inject enough water to saturate a large volume of mantle rock with 0 3 h2o low velocities or low q anomalies have also been observed in the transition zones near currently active slabs

geochronology of the medium to high grade metamorphic units of the peloritani mts sicily the peloritani mountains are a fragment of an orogen variably attributed to the alpine or hercynian orogeny on the basis of 39ar 40ar u pb and rb sr dating the main metamorphism of the two medium high grade metamorphic units the mela and aspromonte units and most of the thrusting responsible for stacking the orogenic edifice are seen to be hercynian the main thrusting of the aspromonte unit over the lower grade units took place at 301 2 ma brittle deformation during tertiary reactivation of hercynian thrust planes did not generate any rejuvenation of white micas in the studied sector our dataset shows a great complexity and we propose to unravel it by considering different levels of information to first order the mela and aspromonte units differ in their metamorphic paths and their geochronological evolution the mela unit shows generally younger ages carboniferous than the aspromonte unit and unlike the latter was extensively retrogressed in greenschist facies the aspromonte unit is itself geochronologically heterogeneous proterozoic ages are preserved both in titanite and in amphibole relics of one tectonic subunit devonian to carboniferous amphibole ages are found in different other subunits tertiary overprint is minor and spatially limited we propose to consider the chronologically heterogeneous subunits as accreted pre hercynian terranes amalgamated late during the hercynian orogeny micas in both units give scattered mesozoic 39ar 40ar and rb sr ages with evidence for heterochemical mica generations we interpret them as a result of widespread hydrothermal circulation event s tertiary overprint is generally absent with the exception of a small area near messina where biotite and muscovite underwent a complex recrystallisation history in the interval between 48 and 61 ma

p and s wave travel time inversions for subducting slab under the island arcs of the northwest pacific we have observed slablike high p and s velocity anomalies around the wadati benioff zone under island arcs of the northwest pacific through travel time tomographic inversions nineteen years of international seismological centre travel time residuals for events and stations in this large region are used analyses of resolution and noise show that the images are generally well resolved the images illustrate that slab anomalies are continuous along strike in most parts of the upper mantle of the region and become contorted and generally broadened with depth near the bottom of the upper mantle fingering of the slabs including segmenting and spreading is indicated the fast anomalies associated with the japan izu bonin and mariana subduction zones tend to flatten to subhorizontal at depth while downward spreading may occur under parts of the mariana and kurile arcs the fast anomalies below 700 km are not in the shape of a single coherent sheet the principal compressional axes of focal mechanisms in the region consistently follow the downdip direction of the high velocity slab even when it bends to subhorizontal at depth the depth at which compression begins to dominate the downdip stress regime in the slab apparently depends on bending of the slab and its dip slab fingering and intense deep seismicity probably are the consequence of the slab encountering a barrier of some form around the 670 km discontinuity

the augen gneisses of the peloritani mountains ne sicily granitoid magma production during rapid evolution of the northern gondwana margin at the end of the precambrian abstract the medium to high grade polymetamorphic basement rocks of the peloritani mountains northern sicily include large volumes of augen gneiss of controversial age and origin by means of a geochemical and shrimp zircon study of representative samples the emplacement age of the original granitoid protoliths of the augen gneisses and the most likely processes and sources involved in that granitoid magmatism have been determined u pb dating of three samples from widely spaced localities in the peloritani mountains yielded igneous protolith ages of 565 5 545 4 and 545 4 ma respectively these late ediacaran early cambrian ages are much older than was previously assumed on geological grounds and are typical of the peri gondwanan terranes involved in the geodynamic evolution of the northern gondwana margin at the end of the avalonian cadomian orogeny major and trace element compositions and sr nd isotopic data in combination with zircon inheritance age patterns suggest that the granitoid protoliths of the sicilian and coeval calabrian augen gneisses were generated by different degrees of mixing between sediment and mantle derived magmas the magmas forming the ca 545 ma inheritance rich granitoids appear to have had a significant contribution from partial melting of paragneiss that is the dominant rock type in the medium to high grade peloritanian basement the closeness of the inferred deposition age of the greywacke protoliths of the paragneisses with the intrusion age of the granitoids indicates rapid latest precambrian crustal recycling involving erosion burial metamorphism to partial melting conditions and extensive granitoid magmatism in less than ca 10 ma

step wise relocation of isc earthquake hypocenters for linearized tomographic imaging of slab structure a vast volume of seismic phase data computed from routinely determined hypocenter locations is presently available for seismic imaging techniques such as tomographic inversion and residual sphere analysis routinely reported earthquake hypocenters however can be in error by several tens of kilometers these biases in hypocenter location can result in the misidentification of seismic phases and the loss of structural signal in the seismic phase data thus the value of these data in constraining seismic images is significantly reduced furthermore hypocenter mislocations degrade the linearization of the tomographic problem and map into the images produced by tomographic inversion to obtain adequate reference hypocenters for linearized inversion we used iasp91 software and reported arrival times to reprocess isc hypocenters and phase data for northwest pacific earthquakes subsequently we inverted p and pp wave residuals for earth structure and source mis location we describe this step wise relocation of isc hypocenters which underlies the linearization of the tomographic inversion and compare the relocation vectors before and after inversion the hypocenter relocations determined prior to inversion are of the order of 10 km which is significant with regard to both the estimated standard errors and the effect on travel time residuals and systematic with regard to earthquake position in the subducted slab in contrast the spatial components of the relocation vectors determined upon inversion of p and pp residuals are up to an order of magnitude smaller do not reveal a correlation with location in the seismic zone and do not generally exceed the noise level the incorporation of pp data in the relocation was essential to remove the depth bias prior to inversion to retrieve slab signal that might have been absorbed in mislocation and to constrain the focal depth upon seismic inversion non linear inversion schemes will not be efficient in removing the depth bias or in retrieving lost slab signal unless seismic phases that contain additional information about the depth bias like the depth phase pp are used

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

resolution experiments for nw pacific subduction zone tomography we investigate the resolving power of isc neic p travel time data in tomographic inversions for the geometry of the subduction zones in the nw pacific from thermal models for the kurile japan izu bonin mariana and ryukyu slabs we generate three dimensional synthetic velocity anomalies for subducting slabs which are then projected onto a cell model for the uppermost 1400 km of the mantle using these synthetic models we compute synthetic delay times for ray paths corresponding to the source and receiver locations used for the actual data add gaussian noise invert the synthetic data and compare the resulting velocity structure to the initial synthetic models this comparison is illustrated for sections through the kuriles and the mariana arcs a variety of resolution artifacts are observed which in many cases resemble features visible in the tomographic results obtained from inverting the actual isc neic data

petrology and geochemistry of silurian triassic sedimentary rocks in the tongling region of eastern china their roles in the genesis of large stratabound skarn ore deposits abstract this paper describes the petrology and geochemistry of the silurian triassic sedimentary rocks in the tongling area in eastern china aiming to establish a genetic link between different stratabound skarn deposits and sedimentary lithologies the results from this study show that some devonian triassic transitional lithological units with compositions varying between siliceous rock and carbonate especially thinly layered impure carbonate control the distribution of some large stratabound skarn ore deposits in the tongling region interlayer detachment faults in the transitional lithology rocks are particularly important controlling the final locations of the deposits the transitional lithological zones may have also served as source rocks likely providing some ore forming metals to the deposits gypsum evaporites in rocks from carboniferous sources may have supplied some sulphur to the hydrothermal systems five of such transitional lithological units enriched in organic matter are spatially and closely associated with some large stratabound skarn ore deposits in the tongling region suggesting that organic matter may have served as an absorbent or reducing agent during ore formation

formation of laminite deposits in anaerobic dysaerobic marine environments abstract vraconian sediments from the bandol area var southeastern france are characterized by alternations of thin dark laminae in which organic matter is concentrated and light calcareous silt grained laminae the dark laminae black shales are regarded as the result of autochthonous i e in place hemipelagic sedimentation the light laminae calcareous silt result from the partial reworking of turbiditic influxes by deep marine currents comparison with modern marine environments suggests that the vraconian laminite deposits from the bandol area were formed by sedimentation from deep marine circulations the laminated structures formed in a deep marine environment subjected to periodic variations in the physicochemical conditions organic productivity and thus the nature of organic matter the dark laminae were deposited in an anaerobic marine environment in which the organic matter was preserved during the deposition of the light laminae the depositional environment changed to dysaerobic conditions allowing the development of a peculiar benthic fauna responsible for the decreasing organic matter content source rock characteristics of these deposits are inferred from their laminated structure and fine texture coupled with the occurrence of organic rich layers

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

random stress and earthquake statistics spatial dependence summary we calculate the 3 d stochastic rotations of focal mechanisms disorientations caused by stresses arising from the presence of many small random point defects that may surround the tip of an earthquake fault these random stresses can be shown to be distributed according to a cauchy distribution as a consequence the next episode of fracture of a fault cannot be planar the disorientation of focal mechanisms of these new rupture episodes is closely approximated by a rotational cauchy distribution as observed previously the geometry of fault systems for natural earthquakes is consistent with these observations since it too can be modelled by the cauchy distribution these observations indicate how the 3 d rupture process in rocks and other materials can be modelled we also calculate distributions of disorientations caused by a uniformly random 3 d rotation of sources these distributions are governed by symmetry properties of earthquake focal mechanisms to take into account the source symmetry we compare the cauchy distribution which is due to influence of random stresses to the distributions caused by random rotations

stochastic slip predictable model for earthquake occurrences recent geophysical studies have indicated that an earthquake recurrence interval and the size of the preceding event are positively correlated this observation is the basis for the deterministic time predictable recurrence model of shimazaki and nakata using the basic assumptions of the time predictable recurrence model we develop a stochastic model of earthquake occurrence that incorporates temporal dependence this paper discusses the formulation of the model and the effect of including temporal dependence hazard estimates for a section of the san andreas fault near parkfield where data has suggested time predictable behavior are obtained for illustrative purposes comparisons are made with the poisson model results indicate that currently used poisson models may give lower estimates of the seismic hazard when there has been a seismic gap of the various sensitivity analyses performed it is observed that slip rate has the largest effect on exceedence probabilites computed from the stochastic time predictable model therefore accurate determinations of slip rates both seismic and aseismic can substantially reduce the uncertainty in seismic hazard estimates

3 d seismic velocity structure of the crust and the uppermost mantle in the northeastern japan arc 3 d seismic velocity structure of the crust and the uppermost mantle beneath the northeastern japan arc is investigated by using arrival time data from local earthquakes we use a velocity model composed of three layers corresponding to the upper crust the lower crust and the uppermost mantle respectively taking into account the observed regional variation of pn velocity the uppermost mantle is further divided into three parts by two pn velocity boundaries near the coasts of the japan sea and the pacific ocean the velocities within the upper crust the lower crust and the three parts of the uppermost mantle are assumed to be constant locations of two pn velocity boundaries and depth distributions of the conrad and the moho discontinuities are expressed by continuous functions of unknown parameters station corrections and hypocenters are also introduced to be unknowns these unknown parameters are determined by inverting arrival time data of p and s wave first arrivals and clear later arrivals of pg and p waves the pn velocity boundary between the land and the pacific ocean is located approximately along the pacific coastline and that between the land and the japan sea is nearly along the japan sea coastline the conrad and the moho discontinuities are at depths ranging from 14 to 20 km and from 27 to 36 km respectively the conrad and the moho depths have similar spatial distributions they are deep beneath the land and become shallower toward the western and the eastern coastlines beneath the land they are shallow in the central part of the tohoku district and become deeper toward both the north and the south directions in the north they become shallow again

how deep can we see the high velocity anomalies beneath the japan islands high velocity anomalies are found in the lower mantle beneath the japan islands and their vicinity through an analysis of detailed three dimensional p wave velocity structure based on a tomographic inversion of isc data beneath the sea of japan the high velocity anomalies in the lower mantle are slab like and appear to extend below the deep focus earthquakes of the high velocity pacific slab descending from the japan trench this slab like high velocity body extending into the lower mantle steepens below a depth of 500 600 km resolution analyses confirms the existence of a slab like high velocity region in the lower mantle though the depth extent is not well resolved on the other hand the pacific slab descending from the izu bonin trench seems to be fingering that is high velocity anomalies are penetrating into the lower mantle beneath latitude 26 n and not penetrating but horizontally bending in the deeper portion of the upper mantle around 29 n

u th systematics of dispersed young volcanoes in ne china asthenosphere upwelling caused by piling up and upward thickening of stagnant pacific slab abstract young 300 to 5500years old dispersed intraplate volcanism characterized by small volume of melt and large compositional variability occurred over ne china at jingbohu long gang tianchi and wudalianchi these young volcanic rocks provide ideal opportunities for investigating the mechanism of dispersed continental volcanism using short lived uranium series isotopes we present systematic u series nd sr pb isotope and trace element analyses of the young lavas from ne china jingbohu lavas display variable extents of 230th excesses 10 to 28 and moderately depleted nd isotopic compositions end 1 5 to 3 3 long gang lavas have pronounced 33 to 35 230th excesses and slightly depleted nd isotopic compositions end 0 5 to 0 7 the tianchi lavas display moderate 12 230th excesses and slightly enriched nd isotopic compositions end 1 0 to 1 1 230th enrichments in all these volcanic rocks are uncharacteristic of melts generated by subduction the strongest evidence against the involvement of subduction related fluids is derived from the long gang lavas having more than 30 230th excesses low u th sr th and ba th ratios and positive nb and ta anomalies the fluids released from the subduction of the pacific plate under the eurasian plate might have already been completely lost before the slab reached the mantle beneath ne china we postulate that in addition to the convective circulation process the continuous piling up and upward thickening of stagnant pacific slab in the mantle transition zone may help drive a broad asthenosphere upwelling far from the trench leading to mantle partial melting and the formation of the young volcanoes in ne china in addition our u th disequilibrium data provide constraints on magma evolution time the magma evolution time from low sio2 47 5 basalt to higher sio2 50 4 basalt at long gang is within 10 thousand years 10ka the magma evolution time from trachyte to rhyolite at tianchi volcano is also less than 10ka if the tianchi silicic rocks were evolved from long gang basaltic magmas with minor crustal assimilation then the magma evolution time from basaltic magma to silicic magmas is less than 110 thousand years

boron isotope systematics of marine sediments abstract boron contents and boron isotopic compositions were determined for modern and ancient permian to miocene marine sediments including pelagic clay calcareous ooze siliceous ooze and neritic clay sediments 11b values of modern marine sediments range from 6 6 to 4 8 isotopic variation is controlled by the simple mixing of four major constituents detritus of continental origin marine smectite biogenic carbonates and biogenic silica detritus of continental origin with an average 11b value of 13 to 8 is the low 11b end member constituent of marine sediments and its boron is largely controlled by the concentration of illite which originates from wind or fluvial transport marine smectite biogenic carbonate and biogenic silica on the other hand represent the high 11b end members with 11b values of 2 3 to 9 2 8 0 to 26 2 and 2 1 to 4 5 respectively these high 11b values are the result of the equilibrium uptake of boron from seawater spatial variations in boron isotopes in the pacific sediments are essentially due to the distribution of the above four constituents although ancient argillaceous sediments shale and slate have boron contents that are identical with those of modern equivalents boron contents of limestone and chert are distinctly lower than those of modern calcareous and siliceous oozes ancient marine sediments have systematically lower 11b values 17 0 to 5 6 than those of the modern sediments the lower 11b values can be caused by diagenesis which induces 1 preferential removal of high 11b boron in calcium carbonate and silica during recrystallization and 2 boron isotopic exchange in the course of the smectite illite transition the observed boron isotopic compositions of ancient argillaceous sediments are distinctly different from those of fresh and altered morb therefore boron isotope systematics will be useful in identifying components from the descending oceanic slab involved in the formation of island arc magma and in investigating mantle crust recycling through subduction processes

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

mineralogy geochemistry and geological significance of tourmaline rich rocks from the paleozoic cinco villas massif western pyrenees spain tourmaline rich rocks associated with clastic metasedimentary rocks of carboniferous age occur in the cinco villas massif western pyrenees three types of tourmaline rich rocks were distinguished 1 fine grained stratiform tourmaline rich rocks which are associated with carbonaceous metapelites tr1 2 stratabound tourmaline rich rocks associated with metapelites in the contact aureole of the aya granitoid pluton tr2 3 stratabound to massive tourmaline rich rocks associated with psammopelites in contact with granites and pegmatites tr3 tourmalines belong to the schorl dravite solid solution series and have a wide compositional range from nearly end member dravite for tr1 tourmalines to schorl for tr3 tourmalines tr2 tourmalines have intermediate compositions the fe fe mg typically varies between 0 02 and 0 55 increasing from tr1 to tr3 the tr1 tourmalines commonly display a discontinuous chemical zoning with fe rich green cores 8 8 5 feo and mg rich colorless rims 10 11 mgo in contrast crystals that exhibit fine growth lamellae appear to lack significant chemical zoning oxygen and hydrogen isotope compositions also reveal major differences between tr1 and tr3 tourmalines the former displaying heavier 18o values 17 7 19 and d values 35 to 42 than tr3 tourmalines 11 to 13 and 47 to 76 respectively the tr2 tourmalines show intermediate values of 11 3 to 14 6 for 18o and 40 to 55 for d linear and continuous chemical variations obtained for major and trace elements of the whole rocks reflect mixing between clay rich and quartz rich end members indicative that some tourmaline rich rocks contain a significant detrital component chondrite normalized ree rare earth element patterns of tourmaline rich rocks are similar to those of surrounding unaltered clastic metasediments except for some tr1 rocks which are characterized by low contents of ree mass balance calculations show that tourmaline forming processes plus metamorphism led to mass and volume changes at mesoscopic scales 10 for the tr1 tourmalinites silicon fe mn and ree elements were partially lost from sedimentary rocks whereas mg and particularly b were added to pelitic sediments available data nevertheless do not allow an assessment of the boron source formation of the tr1 tourmaline rich rocks probably was the net result of several processes including direct precipitation from b rich hydrothermal fluids or colloids early diagenetic reactions of carbonaceous pelitic sediments with these fluids and subsequent recrystallization during regional metamorphism the tr2 tourmaline rich rocks mainly developed by metamorphic recrystallization of tr1 tourmaline rich rocks and veins adjacent to pegmatites and granitic rocks tr3 are the result of boron metasomatism the primary boron having been recycled from stratiform tourmalinites during regional metamorphism and magmatism

mapping of p wave slab anomalies beneath the tonga kermadec and new hebrides arcs abstract p wave velocity anomalies of several per cent fast relative to the jeffreys bullen jb model are seen around subduction zones under the tonga kermadec and new hebrides trenches from inversion of international seismological centre isc travel time residuals from intermediate and deep focus earthquakes mantle heterogeneities outside the model are corrected using previous velocity models ray paths inside the model region are traced allowing two dimensional velocity variations the rays of similar source and receiver locations are combined into summary rays and the hypocenters are relocated as part of the inversion iterations the resulting images are interpreted in conjunction with resolution and error estimations the slab like anomalies are generally continuous in places of high seismicity and decrease in amplitude with depth most coherent slab anomalies are surrounded by large slow patches between the surface and 350 km depth the fast slab beneath the tonga arc appears to end at 550 km depth before the seismicity ends but there is a fast band at 750 1000 km depths below the deepest tongan earthquakes the fast slab like anomaly beneath the kermadec arc tends to flatten to subhorizontal near the bottom of upper mantle and it occurs aseismically near new zealand down to 500 550 km depth interpretations in the lower mantle in many places such as kermadec and new hebrides arcs however are hampered by poor resolution

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

carbon isotopic thermometry calibrated by dolomite calcite solvus temperatures abstract the temperature dependence of carbon isotopic fractionations between calcite and graphite and between dolomite and graphite are calibrated by the calcite dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the kasuga area central japan the carbon isotopic fractionations 13ccc gr and 13cdo gr systematically decrease with increasing metamorphic temperature the concordant relationships between the fractionations and solvus temperatures are approximately linear with t 2 over the temperature range 400 to 680 c 13ccc gr 5 6 106 t 2 k 2 4 13cdo gr 5 9 106 t 2 k 1 9 these systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases the equation for the calcite graphite system has a slope steeper than bottinga s 1969 results it is however in good agreement with that of valley and o neil 1981 in the temperature range from 600 to 800 c because of the relatively high sensitivity to temperature these isotopic geothermometers are useful for determining the temperatures in moderate to high grade metamorphosed carbonate rocks

the influence of geological factors on the concentration of boron in australian and canadian coals abstract the concentration of boron in australian and canadian coals determined using atomic emission spectrometry aes inductively coupled plasma spectrometry icp aes and prompt gamma ray spectrometry is summarized in order to assess the variation of b content in coal with respect to rank age geological setting in seam and stratigraphic and the degree of paleosalinity of the coal forming environment this study indicates that no or very complex relations exist between boron and rank subbituminous to anthracite variations of b with ash content for canadian coals of different age devonian to oligocene eocene indicate that the b content of coals is not governed by the age of the coal there is some evidence of variation of b with maceral content in canadian coals particularly as related to the inertinite and vitrinite content of coals the b content of coal seams is sensitive to the environment of deposition with b contents remaining relatively stable and within the range of values designated for each depositional setting however b values may show variation in the same seam laterally due to changes of the environment of deposition and or the enrichment of b by a secondary source the vertical variation of b in a coal bearing section or strata is related to depositional environment and lithology of rock there is often little variation in b content for coal layers as compared to the partings dirt bands the b content of partings in a coal bearing strata may vary greatly as compared to the coal seams after reappraising earlier work and on the basis of more recent studies on australian and canadian coals it is proposed that the following ranges of values for b in coal indicate the degree of marine influence during the early stages of coalification up to 50 ppm b freshwater influenced coals 50 110 ppm b mildly brackish water influenced coals 110 ppm b brackish water influenced coals using these criteria assessments are given for the degree of marine influence on canadian and australian coals

subducting plate boundary beneath the northeastern japan arc estimated from sp converted waves abstract in the tohoku district the northeastern part of honshu japan a conspicuous phase is frequently observed between p and s phases in seismograms for events in the lower seismic plane of the double planed deep seismic zone this phase is dominant in the vertical component and has an apparent velocity almost equal to or slightly smaller than the p phase we have never found this phase in seismograms for events in the upper seismic plane from these characteristics the phase is interpreted as sp converted from s to p at the upper boundary of the descending oceanic plate ubp using the travel times of the sp waves we estimated the location of the ubp beneath the tohoku district to be just above the upper seismic plane of the double planed deep seismic zone this position is consistent with those determined from the analyses of the travel times of the scsp and ps waves which are respectively the seismic wave converted from scs to p and that from p to s at the ubp

a reconnaissance of the boron isotopic composition of tourmaline abstract a preliminary investigation of the boron isotopic composition of tourmaline from some boron rich associations has been made the results for tourmaline from metasedimentary parageneses n 12 range from 11b 22 to 22 per mil these data mainly fall between the boron isotopic compositions of normal marine sediments with 11b 2 to 5 per mil and seawater with 11b 39 5 per mil tourmaline samples from granitic pegmatites n 6 on the other hand range from 11b 12 to 5 per mil the data provide a rudimentary indication of the range of boron isotopic variation in tourmaline some of the processes leading to this range and some possible geochemical tracer applications

perceptible earthquakes in the broad aegean area abstract a probabilistic estimate of seismic hazard can be obtained from the spatial distribution of earthquake sources their frequency magnitude distribution and the rate of attenuation of strong ground motion with distance we calculate the earthquake perceptibility i e the annual probability that a particular level of ground shaking will be generated by earthquakes of particular magnitude by weighting frequency magnitude data with the predicted felt area for a given level of ground shaking at a particular magnitude this provides an earthquake selection criterion that can be used in the anti seismic design of non critical structures we calculate the perceptibility at a particular value of isoseismal intensity peak ground acceleration and velocity as a function of source magnitude and frequency for the broad aegean area using local attenuation laws we use frequency magnitude distributions that were previously obtained by combining short term catalogue data with tectonic moment rate data for 14 tectonic zones in greece with sufficient earthquake data and where contemporary strain rates are available from satellite data many of the zones show a characteristic earthquake distribution with the most perceptible earthquake equal to the maximum magnitude earthquake but a relatively flat perceptibility between magnitudes 6 and 7 the maximum perceptible magnitude is in the fastest deforming region in the middle of the aegean sea and tends to be systematically low on the west in comparison to the east of the aegean sea the tectonic data strongly constrain the long term recurrence rates and lead to low error estimates 0 2 in the most perceptible magnitudes

interelement relationship in abyssal pacific ferromanganese nodules and associated pelagic sediments abstract by r mode factor analysis and enrichment factor calculations most of the elements in abyssal ferromanganese nodules and associated pelagic sediments excluding common authigenic minerals like apatite barite opal and carbonates are found to be preferentially concentrated in one of the following three major phases aluminosilicates e g al si sc ga cr be na k rb and cs fe oxides e g fe p s v se te as b sn u hg pb ti ge y zr nb pd in rare earths hf th pa pu am ru and bi and mn oxides e g mn tl ag cd mg ca ba ra co ni cu zn mo sb and probably w the specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties e g the ph of zero point of charge and dieletric constant of these three phases

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

a stochastic model for spatially and temporally dependent earthquakes site specific hazard estimation requires modeling the occurrences of earthquakes on faults that can potentially impact the site evidence for large magnitude earthquakes approximately moment magnitude 6 5 and above occurring infrequently on long faults indicates that the assumptions of temporal and spatial independence are not valid thus a new stochastic model that captures the temporal and spatial characteristics of earthquake recurrence is introduced this model uses a generalized semi markovian process gsmp to provide the complex framework required for describing space time earthquake dependence the objective of this model is to estimate the hazard over time periods of engineering significance e g 50 to 200 yr the model is applied to the northern san andreas fault the portion of the fault that ruptured in 1906 mean recurrence rates obtained from the model application are in good agreement with actual observations events are also simulated over a long time period to observe the fault behavior based on the results obtained from the simulation two distinct processes are observed to be at work in that section of the san andreas the north coast segment generates large earthquakes approximately moment magnitude 7 7 to 8 1 and the south santa cruz mountains segment generates somewhat smaller earthquakes approximately moment magnitude 6 8 to 7 4 the san francisco peninsula segment represents a transition between these two behaviors sensitivity studies of the model parameters reveal that the results are relatively sensitive primarily to the slip rate and the mean and standard deviation of the interarrival time distribution the model appears to be relatively insensitive to the remaining parameters of the model

source composition and distribution of the fluid in the kurile mantle wedge constraints from across arc variations of b nb and b isotopes b and nb concentrations and b isotope composition were determined for lavas covering the entire length of the kurile arc b nb and 11b of these lavas show clear across arc variations in which both are highest at the trench side and continuously decrease as the slab depth increases b nb in the volcanic front lavas 8 25 is significantly higher than those of morb and oib indicating that the mantle wedge is extensively metasomatized by b rich fluid derived from the subducting slab the frontal 11b values are also out of the range of morb and oib and systematic difference exists between northern kurile nk 5 4 0 5 and central and southern kurile csk 4 3 0 3 however these two parameters approach or coincide with mantle values at the most back arc side the 11b and 87sr 86sr linearly correlate with nb b suggesting control by simple mixing of two isotopically homogeneous components that is slab derived fluid and mantle wedge the estimated 11b and 87sr 86sr of the fluid are 7 0 0 6 and 0 70326 0 00005 for nk and 6 3 0 3 and 0 7033 for csk respectively these fluid compositions are consistent with a source constituted by 95 altered oceanic crust and 5 oceanic sediment with the slight difference between nk and csk resulting from the different lithologies of subducting sediments the mantle wedge beneath the kurile arc has b sr and nd isotope compositions identical with morb but shows significantly higher b nb the above trends bear a close resemblance to those observed in the izu arc strongly suggesting their universality in the arc system the across arc decline of b nb observed both in kurile and izu implies that the fluid flux from the slab continuously decreases as the slab depth increases however this relates only to a final stage of slab dehydration since most of the volatile components are lost at the fore arc region in contrast to b k is uniformly enriched across the arc this requires control by a k bearing mineral phase either in the slab phengite or the mantle wedge phlogopite although such a mineral is responsible for only a small part of the whole fluid transport

spatial and temporal evolution of the subducting pacific plate structure along the western pacific margin 1 tomographic images of the subducting pacific plate beneath the izu bonin mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western pacific island arcs but reasons for the variation in geometry and morphology are still poorly understood by comparing high resolution tomographic images of the western pacific and updated paleogeographic reconstructions we are able to link the spatiotemporal evolution of the subducting pacific plate back to the mid miocene we have reconstructed tectonic motions along the kurile japan izu bonin mariana arc system and the ryukyu arc to provide an independent additional interpretation of the subducting pacific plate using the most current plate motion data we then investigate the plausibility of our model and three other proposed models based on the interpreted slab structure from tomographic images the new reconstruction agrees with the basic characteristics of former trench retreat models but illustrates the importance of the collision of the ogasawara plateau with the trench in the mid miocene and its subsequent effect on the slab structure at depth and the impact of other aseismic ridge collisions along the plate boundary the combination of evidence in changed physical properties imaged with tomography and the current interpreted slab morphology can be analyzed with the past plate motions to understand subduction zone processes

seismic anisotropy and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

lateral variations in mantle velocity structure and discontinuities determined from p pp s ss and ss sds travel time residuals on the basis of p pp s ss arrival times and ss s410s ss s660s differential times we construct models of mantle p and s velocity structure and boundary topography of the 410 km and 660 km discontinuities events from the catalog of the international seismological centre isc are relocated relative to the international association of seismology and physics of the earth s interior 1991 iasp91 velocity model using both p and s arrival times the arrival times are corrected for ellipticity and the pp and ss residuals are corrected for the topography at the bounce point the cap averaged pp p and ss s differential time residuals plotted at the pp and ss surface reflection points form broad coherent patterns the geographic distribution of the cap averaged residuals agrees quite well with pp p and ss s differential time residuals derived from long period global digital seismograph network gdsn data a robust lp inversion scheme is used to infer global mantle structure synthetic tests indicate that for regions well sampled by ss s410s and ss s660s differential times the velocity estimates are not seriously contaminated by the topography of the 410 and 660 km discontinuities however estimates of boundary deflections may be influenced by extensive p and s velocity variations of 3 or greater we find the 410 km discontinuity to be depressed by as much as 24 km beneath north america conversely the discontinuity is deflected upward underneath eurasia in some regions the topography of the 660 km discontinuity is quite distinct from that of the 410 km discontinuity but the two appear to be positively correlated a series of depressions are found at several intersections of the 660 km discontinuity with known subduction zones the elevated topography in the 410 km discontinuity beneath europe is underlain by a trough in the 660 km discontinuity a number of subduction zones are characterized by a thinning of the transition zone negative p and s velocity anomalies underlying back arc basins and tectonically active continental regions encircle the pacific where they are resolved the stable continental cratons are systematically positive velocity features that extend below 200 km with the inclusion of pp and ss travel time residuals we are better able to constrain midmantle structure most notably in the depth range 35 660 km beneath the northwest pacific we observe high p velocity where they are resolved mid ocean ridges are most clearly imaged as low velocity features in the s model the northern portion of the mid atlantic ridge is underlain by negative s velocity anomalies in the pacific the east pacific rise is an extensive low s velocity anomaly

li b rich rhaetian metabauxite tuscany italy reworking of older bauxites and igneous rocks abstract li b rich metabauxite layers occur in two outcrops of talus metabreccias intercalated between norian and liassic marbles in the alpi apuane tuscany italy field evidence petrographical geochemical and paleogeographic paleoclimatologic considerations suggest that bauxitic material was derived from a multistage reworking of late carboniferous early autunian primary deposits now completely removed the identified lithotypes are cookeite rich metabauxite cookeite bearing metabreccia chloritoid schist and chloritoid phyllite the mg content of calcite and the si content of muscovite and mineral assemblages indicate temperatures of 350 380 c pressures of f o 2 values of 10 30 to 10 24 for the alpine metamorphism in comparison with the average mesozoic bauxite of bronevoy et al 1985 the metabauxite is strongly enriched in si k ca mg li b be ni and ce it shows comparable contents of co la eu tb ta and th it is depleted in ga cr v zn mn hf u and is strongly depleted in sr f cu a metabauxite layer shows decreasing abundance of fe and ga from bottom to top with a pattern opposite to that of primary bauxite deposits inverted profile the strong enrichment of li and b is not related to evaporitic conditions since the mgo na 2 o and sr contents are too low and indicator minerals such as dravitic tourmaline albite and scapolite are missing during the permian volcanic products similar to the coeval peralkaline peraluminous rocks of corsica sardinia were widespread in tuscany b li rich minerals were produced by circulation of hot hydrothermal fluids within the permian volcanic rocks during and soon after their emplacement the erosion of such hydrothermal products supplied detrital material to the talus metabreccia

the association of tourmalinite with stratiform scheelite deposits three types of stratiform scheelite deposits are recognised they all commonly have a close spatial association with tourmalinite regional prograde calc silicate rocks in precambrian rift settings commonly contain 100 ppm wo3 with enrichment to 0 5 1 wo3 in retrograde metamorphic assemblages at fold hinges joints faults shears and granite and pegmatite dyke contacts the calc silicate progenitor was probably a impure dolomitic carbonate sediment amphibolite hosted scheelite deposits occur in metamorphosed altered mafic volcanics formed in a narrow rift graben scheelite occurs both as stratiform and stratabound footwall stringer ore which has undergone minor remobilization during tectonism tourmalinites are rarely the host for stratabound quartz scheelite wolframite veins remobilized from the host tourmalinite and associated metavolcanics during tectonism

simulation of earthquake sequences an earthquake sequence can be considered to be a complex extension of a shear crack in a viscoelastic medium under the influence of non uniform stresses because of these inhomogeneous stresses the crack grows rapidly at rates comparable to seismic body wave velocities during some intervals of time during other intervals which punctuate the episodes of rapid expansion the major mode of slip and growth is one of creep under suitable pre stress and frictional conditions the post seismic creep phase of one earthquake may become the pre seismic creep phase of a succeeding earthquake thus inhomogeneity of the pre stress and or the static and dynamic frictional stresses combined with viscoelasticity of the medium provides a mechanism that accounts for not only the pre seismic and the post seismic creep and the stopping of the crack but also the various types of earthquake sequences that occur in nature by increasing the amplitude of the fluctuations in the spatial distribution of these stresses the type of earthquake sequence can be varied progressively from an isolated earthquake to a sequence with foreshocks main shock and aftershocks and finally to an earthquake swarm as the wavelengths of the fluctuations in the stresses decrease the frequency of earthquake occurrence increases the type of earthquake sequence is also controlled by the general level of the stresses a silent earthquake or aseismic creep event will occur if the pre stress is sufficiently high

long term seismic potential of the san andreas fault southeast of san francisco california the long term decade or longer seismic potential of the peninsular san andreas fault the 125 km long segment southeast of san francisco has been assessed by comparing the slip accompanying the 1906 mw 7 7 earthquake with the amount of this slip deficit made up since 1906 of particular importance is the longstanding factor of 2 inconsistency between 1906 surface offsets 1 5 m and geodetically determined coseismic slip 2 7 m on the southern 90 km of the peninsular san andreas in reexamining this issue we find that the discrepancy cannot be attributed to either large observational uncertainties in the geodetic data or shortcomings in fault modeling rather the problem lies in the complexity of this 90 km long fault reach where the san andreas trend changes by 6 the zone of recent deformation is 0 5 2 km wide and much of the fault is heavily vegetated and inaccessible farther northwest on the 1906 rupture where the fault geometry is much simpler evidence from deformed fences shows that right lateral coseismic slip was commonly distributed across a zone 20 600 m wide with only about 70 of the total slip occurring at the main fault trace the general importance of distributed coseismic deformation and the evidence for fault zone complexity indicate that the best estimate of 1906 slip on this 90 km fault segment is the geodetically constrained value of 2 6 0 2 m farther northwest on the peninsular san andreas the coseismic slip ranges from 3 4 to 4 4 m and geodetic slip and surface offsets show considerably better agreement following previous work we have assessed the risk posed to the southern peninsular san andreas by two broad classes of earthquakes these appraisals use the geodetic slip distribution apply a long term slip rate of 15 mm yr suggested by geologic and geodetic studies and assume the approximate correctness of the time predictable recurrence model the possibility of an m 6 1 2 earthquake on the 30 km long segment northwest of san juan bautista cannot be completely precluded but the evidence bearing on its likelihood is contradictory in contrast with several previous assessments we find that the risk of an earthquake of m 7 rupturing the southern 90 km of the peninsular san andreas during the next several decades is quite low

the linked stress release model for spatio temporal seismicity formulations procedures and applications summary the linked stress release model is based on the build up of stress through elastic rebound and its dissipation in the form of earthquakes in addition stress can be transferred between large scale geological or seismic features the model can be statistically fitted to both historical and synthetic seismicity catalogues and through simulation can be used to create probabilistic forecasts of earthquake risk we review the genesis of the model provide some observations on forecasting using the model and follow with a comprehensive review of applications to date a systematic procedure for identification of the best model is illustrated by data from the persian region we then consider the evaluation of fitted models using residual point processes and information gains implications of the use of benioff strain rather than seismic moment are discussed the sensitivity of the model to regionalization magnitude errors catalogue incompleteness catalogue size and declustering magnitude cut off is then considered in detail with reference to data from north china the latter data are also used to illustrate the model evaluation techniques introduced earlier some technical material on numerical fitting simulation and calculation of the information gain is given in an appendix