tectonics fluids and ore deposits mobilization and remobilization abstract the mobilization of metals leading to the formation of many known types of metallic resource involves the focussed flow of very large km 3 fluid volumes different types of fluids such as sea water and metamorphic and meteoric fluids with or without biomolecules may be specific for certain metals or suites of metals where large fluid volumes are part of a geologic process there is potential for local metal enrichment examples of such processes within the context of plate tectonics include convective flow of sea water at ocean ridges in relation to ophiolite cu zn mineralization and black smokers subduction of metal enriched sediments and the tectonic recycling of sn w mineralization metamorphic dewatering of subducted oceanic crust in the context of au deposits metamorphic degassing around high level granitic plutons and metamorphic re equilibration of the underthrust plate in relation to continental thrusting in addition during weathering processes short term leaching produces fertile soils whereas long term leaching can result in lateritic ores the large scale remobilization of ore deposits or of mineralization where metal enrichment is currently sub economic is improbable unless large fluid volumes are involved or the crust undergoes major tectonic re arrangement but it is perhaps possible that these situations are more common than we suppose and that such multistage events are indicated by the long term persistence of metallogenic provinces

evidence for early asteroidal collisions prior to 4 15 ga from basaltic eucrite phosphate u pb chronology abstract the late heavy bombardment lhb hypothesis wherein the terrestrial planets are thought to have suffered intense collisions ca 3 9 billion years ago is under debate coupled with new dynamical calculations re examination of geochronological data seem to support an earlier solar system instability and a smooth monotonic decline in impacts as opposed to a cataclysm to better understand this collisional history records from the asteroidal meteorites are required here we report a uranium lead u pb chronological dataset for eucrite meteorites thought to originate from the asteroid 4 vesta this dataset indicates to a continuous history of collisions prior to 4 15 ga our 207pb 206pb model ages of apatite ca5 po4 3 f cl oh and merrillite ca9namg po4 7 from three brecciated basaltic eucrites juvinas 4150 3 11 6 million years ago ma merrillite only camel donga disturbed around 4570 4370 ma and stannern 4143 0 12 5 ma record multiple thermal metamorphic events during the period of 4 4 4 15 ga we interpret this to mean that vesta or the vestoid cluster underwent multiple impacts and moderate high temperature reheating during this time the ages of 4 4 4 15 ga are distinctly younger than the initial magmatic process on vesta 4 5 ga but are significantly older than a later impact peak based on some interpretations of 40ar 39ar chronologies 3 9 3 5 ga the intense collisions prior to 4 15 ga on vesta are at odds with the conventional lhb hypothesis but not inconsistent with the much earlier bombardment and monotonic decline scenario different radiometric chronologies of the asteroid likely represent the different stages of a continual collisional process conversely the model 207pb 206pb ages of apatite in the unbrecciated basaltic eucrite agoult returned an age of 4524 8 9 6 ma this may represent slow cooling from an earlier global reheating of the crust on vesta at 4 55 ga as documented by other radiometric chronologies the apatite in juvinas recorded a coincident timing of 4516 9 10 4 ma which could be due to either slow crustal cooling or impact

spatial and temporal distribution of slip for the 1999 chi chi taiwan earthquake we investigated the rupture process of the 1999 chi chi taiwan earth quake using high quality near source strong motion records broadband teleseismic displacement waveforms and well distributed global positioning system gps data the near source strong motion displacement waveforms recorded significant static offsets of up to 8 m the teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec taking into account the surface displacements observed along the chelungpu fault we considered two fault geometries a single planar fault and a two segment fault with a northeast striking section near the north ern end using the finite fault model with variable slip vectors we derived two models of the temporal and spatial slip distribution of the earthquake the gps data provided good surface displacement constraints for the slip distribution determina tion the spatial slip distribution is generally consistent with field observations the results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m when we use the two segment model the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m a large amount of right lateral slip beneath station tcu068 is necessary to explain its observed large west movement it implies a local converging slip at the corner where the fault bends to the northeast the slip amplitude near the hypocenter is about 3 to 6 m the seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm most of the slip concentrated at shallow depths less than 10 km the total rupture duration is about 28 sec and the rupture velocity is 75 to 80 of the shear wave velocity the slip vector shows a clockwise rotation during the fault rupture the static stress drop of the large asperity region is comparable with the dynamic stress drop as observed directly from the slip velocity at the station near the large slip region

in situ sims u pb dating of phanerozoic apatite with low u and high common pb abstract apatite is a common accessory mineral in various igneous metamorphic and sedimentary rocks it has strong potential to provide important information for geochronology and petrogenesis however precise u th pb dating of apatite especially young samples is difficult due to low abundances of u and less radiogenic pb posing significant challenges for accurate common pb correction an additional issue is the lack of suitable apatite to serve as a standard for in situ analyses here we present both analytical and data reduction protocols for sims in situ u pb analyses on apatite with low u and high common lead with nw 1 apatite as the u pb age standard which was separated from 1160 ma carbonatite in the prairie lake complex in canada apatites from the kovdor carbonatite in the kola peninsula which contains low u mostly 2 5 ppm and high common pb 20 80 yielded weighted average 207pb corrected u pb ages of 375 13 ma kv 8 and kv 18 and 377 11 ma kv a respectively apatites from the quruqtagh ultramafic intrusion in nw china containing low u 2 3 ppm and high common pb 70 yield 207pb corrected u pb age of 805 21 ma the cenozoic durango apatite was dated at 31 2 ma all these new apatite u pb ages are indistinguishable from independently known age constraints to within 2 4 our results demonstrate that a u pb age can be accurately and precisely measured for apatite with low u 50 by sims with a suitable standard and a careful choice of common pb composition

isotopic evidence for trapped fissiogenic ree and nucleogenic pu in apatite and pb evolution at the oklo natural reactor abstract a part of the boundary layer of reactor zone 10 at the oklo natural reactor shows a unique petrologic texture which contains high grade uraninite and massive apatite concretions in order to study distribution behavior of fission products around the boundary between the reactor zone and the wall rock and to clarify the relation of migration mechanisms of fission products with geochemical factors in situ isotopic analyses of nd sm gd pb and u in uraninite and apatite from the sample were performed by sensitive high resolution ion microprobe shrimp sm and gd isotopic ratios of uraninite and apatite show evidence of neutron irradiation with fluence between 4 4 6 8 10 19 n cm 2 judging from the isotopic anomalies of nd and u the apatite coexisting with the uraninite plays an important role in trapping fissiogenic lree and nucleogenic 239 pu into the structure systematic pb isotopic data from apatite uraninite galena and minium suggest the following chronological interpretations 1 the apatite formed 1 92 0 01 ga ago and trapped fissiogenic light ree and nucleogenic 239 pu that migrated from the reactor during the criticality 2 the uraninite around the boundary between reactor and sandstone dissolved once 1 1 1 2 ga ago 3 galena grains were formed by u pb mobilization in association with the intrusion of dolerite dyke 0 45 0 83 ga ago 4 minium was derived from recent dissolution of galena under locally oxidizing conditions

in situ la icp ms u pb dating of metavolcanics of norrbotten sweden records of extended geological histories in complex titanite grains in situ u pb dating of a variety of mineral phases is an important goal in petrology this study reports data chiefly from titanite but also from rutile and apatite obtained using the laser ablation la icp ms methodology on polished thick sections in order to retain as much petrologic information as possible and allowing trace element analyses from adjacent areas to the u pb analyses the samples analysed come from svecofennian intermediate to acid volcanic rocks of the porphyry group within the major iron ore province of norrbotten northern sweden where titanite is a common phase associated with the mineralisation using a laser beam of 30 45 m in diameter accurate and relatively precise 2 3 2 on 206pb 238u ratios data can be obtained on titanite similar precision on pb u ratios can be obtained in rutile but accuracy cannot be assessed because of the lack of well characterised standards however the data are a priori accurate as they are geologically reasonable apatite shows reverse discordance which could be explained by a number of scenarios however the 207pb 206pb ages are fairly precise 1 3 2 and the calculated age is geologically reasonable suggesting that the data may be accurate the titanite grains studied show complex internal structures rare earth element ree analysis by la icp ms demonstrates that the core and rim zones are distinct and supports a model for two stage evolution in two out of three samples with the rims in these samples being enriched in total ree and particularly in lree in one sample and displaying a positive y anomaly in contrast to the cores in situ u pb analysis reveals that core zones from all samples retain distinct older ages of c 2050 ma whereas the reworked rims have either distinct younger or strongly reset ages the older cores are interpreted as representing the first alteration metamorphism of the volcanic pile titanite rims record a u pb age of 1870 24 ma 2 at luossavaara and 1826 15 ma 2 at the smaller fe oxide apatite body at gruvberget in both cases the ages are consistent with previous age determinations from the fe oxide apatite deposits a sample from malmberget records a slightly different scenario where u pb ages spread along concordia from c 1920 to 1708 ma we attribute this pattern to metamorphic reworking of primary metasomatic titanite rutile ages from inclusions within the core of gruvberget titanite essentially mimic the ages obtained from the surrounding titanite and suggest that they have undergone the same history apatite inclusions within titanite at malmberget record a younger age of 1584 12 ma 2 which we attribute to later events known to have affected the area these data indicate that the porphyry group volcanics must be at least c 2050 ma in age in contrast to previous age determinations from zircon which suggested a deposition age of c 1960 to 1880 ma the large grain size of the titanites studied coupled with the ability for the first time to obtain in situ u pb ages from small areas has allowed probing of this hitherto unrecognised event smaller zircon grain size coupled with extremely saline hot pressurised high p t metasomatic fluids relating to regional magnetite apatite mineralisation in the period 1900 to 1800 ma may have resulted in resetting of zircon u pb systematics 2007 elsevier b v all rights reserved

apatite composition tracing petrogenetic processes in transhimalayan granitoids apatites crystallized from different types of igneous rocks show significant variations in the abundances of some minor and trace elements in this study electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry were used to determine the concentrations of 25 minor and trace elements in apatite separated from three principal rock types of thetranshimalayan igneous plutonic suite s type granites the i type gangdese batholith and postcollisional adakites f mn sr and rare earth elements ree in apatite vary systematically with the composition of the host magma and thus have high potential as petrogenetic tracers more specifically the f and mn contents of apatite can be used as an indicator of magma aluminosity or differentiation index combined with sr and ree data which show significant variations in apatite from different rock types these elements are useful for constructing discrimination diagrams this study also reveals that apatite has the capacity to retain geochemical information about the host magma through the course of magmatic evolution systematic variations of sr and ree in apatite with bulk rock aluminosity are the results of partition competition with pre existing and coexisting major and accessory minerals in silicate melts and thus are useful for more detailed investigations of petrogenetic processes such as fractional crystallization and magma mixing which is signaled by inconsistent eu anomalies sr abundances and ree patterns relative to bulkrock compositions

lead isotope evidence for recent uranium mobility in geological formations of brazil implications for radioactive waste disposal abstract lead lead isotope data from whole rock samples are used to investigate the recent last few million years mobility of u and th the method is based on the comparison of the calculated present day u and th concentrations required to yield the pb isotope composition in the samples with the actual present day concentrations of u and th obtained by direct measurement the geological formations studied include the neoproterozoic carbonate sediments of the bambui group archean paleoproterozoic granite greenstone terrain of the contendas mirante complex and a proterozoic ortho gneisses hosting u deposit in lagoa real all these formations are in the sao francisco craton brazil the data show high u mobility in the carbonate sediments and in the deformed ortho gneisses set in a ductile shear zone infiltration of groundwater through fault zones seems to have facilitated the u mobility the pb isotope approach is a useful technique complementing u series disequilibrium studies and may be included for site characterization studies for radioactive waste disposal

direct ion microprobe u pb dating of fossil tooth of a permian shark abstract we report here direct ion microprobe dating of fossil tooth dentine of a permian fresh water shark orthacanthus senckenbergianus using the shrimp instrument recently installed at hiroshima university fifteen spots on the small sample approximately 2 mm 1 mm indicate a 238 u 206 pb isochron age of 266 18 ma and a tera wasserburg concordia intercept age of 266 24 ma in a three dimensional 238 u 206 pb 207 pb 206 pb 204 pb 206 pb diagram these permian ages are consistent with a 235 u 207 pb age of 453 170 ma and a 232 th 208 pb age of 235 310 ma suggesting indistinguishable depositional and early diagenetic ages of the fossil in its sedimentary sequences the success of the method depends on the chemical fractionation of uranium from lead in a specimen a few hundred microns in size and the consequent variations in lead isotopic compositions due to radioactive decay

high closure temperatures of the u pb system in large apatites from the tin mountain pegmatite black hills south dakota usa abstract the cores of several large 1 2 cm apatites from the early proterozoic tin mountain pegmatite black hills south dakota have concordant u pb ages the age uncertainties of these samples are less than 5 ma the lead isotopic compositions of muscovite and k feldspar coexisting with the apatites were used for initial lead isotopic corrections the resulting u pb concordia ages agree well with u pb and pb pb isochron ages based solely on multiple fragments from single apatites this agreement justifies the use of coexisting muscovite and k feldspar for initial lead corrections the precision of these u pb ages is comparable to those of the u pb systems of more commonly analyzed minerals such as zircon monazite and sphene the estimated u pb closure temperature t c of these apatites is about 620 c this t c is in close agreement with the t c calculated for 0 5 cm diffusion radii and published data for diffusivity and activation energy of lead diffusion in apatite apatite can therefore yield high precision u pb ages that are close to its crystallization age in igneous rocks

a simple mechanism for mid crustal shear zones to record surface derived fluid signatures ion microprobe analyses of garnet porphyroblasts from three separate splays of the mid crustal walter outalpa shear zone curnamona province south australia indicate homogeneous 18 o values of 18 o values in deeply exhumed shear zones may therefore be indicative of fault structures that have a prior history of surface exposure weathering burial and re exposure

elastic reverse time migration elastic prestack reverse time finite difference migration of two component seismic surface data requires data extrapolation and application of an imaging condition data extrapolation involves synchronous driving of the vertical component and horizontal component finite difference meshes with the time reverse of the recorded vertical and horizontal traces respectively extrapolation uses the coupled elastic wave equation for variable velocity solved with a second order explicit finite difference scheme the imaging condition at any point in the grid is the one way traveltime from the source to that point elastic migrations of both synthetic test data and real two component common source gathers produce simpler images than acoustic migrations because of the coalescing of double reflections compressional waves and shear waves into single loci

the oldest zircons in the solar system abstract here we report the occurrence chemistry and u th pb isotopic systematics of three meteoritic zircon assemblages two from the vaca muerta mesosiderite and one from the simmern h5 chondrite one of the vaca muerta zircons occurs in the mesosiderite proper the other in a eucritic clast associated with chromite ilmenite and tridymite whereas the simmern zircon occurs in a chondrule composed predominantly of chromite and feldspar like terrestrial zircons the meteoritic zircons are enriched in the heavy rare earth elements but unlike terrestrial zircons they do not show a positive ce anomaly this feature is also absent in one lunar zircon analyzed and probably reflects the oxidation state of the formation environment under oxidising conditions ce4 which can substitute for zr4 in the zircon structure is stabilized whereas under relatively reducing conditions ce3 is stable the zircon from simmern has depletions in the relative abundances of tm and yb a characteristic of volatility fractionation of the ree the u concentrations of the two vaca muerta zircons are quite different at 1 and 50 ppm respectively both zircons have extremely low initial lead and give radiogenic ages that are the same albeit with relatively large errors on vm 1 zircon because of its much lower u concentration and hence radiogenic pb concentration the mean of the two analyses made on vm 2 zircon is concordant with a207pb 206pb age of 4563 15 ma 2 the simmern zircon has an exceptionally low u concentration of around 180 ppb and only a poorly constrained 207pb 206pb age of 4100 700 ma could be obtained

ion microprobe u th pb dating and ree analyses of phosphates in the nakhlites lafayette and yamato 000593 000749 u th and pb isotopes and rare earth elements rees in individual phosphate grains from martian meteorites lafayette and yamato 000593 000749 were measured using a sensitive highresolution ion microprobe shrimp observed u pb data of 12 apatite grains from yamato y 000593 000749 are well represented by linear regressions in both conventional 2d isochron plots and the 3d u pb plot total pb u isochron indicating that the formation age of this meteorite is 1 53 0 46 ga 2 on the other hand the data of nine apatite grains from lafayette are well represented by planar regression rather than linear regression indicating that its formation age is 1 15 0 34 ga 2 and that a secondary alteration process slightly disturbed its u pb systematics as discussed in the literature regarding nakhla the observed ree abundance patterns of the apatites in lafayette and yamato 000749 normalized to ci chondrites are characterized by a progressive depletion of heavy rees hrees a negative eu anomaly similarity to each other and consistency with previously reported data for nakhla considering the extensive data from other radiometric systems such as sm nd rb sr ar ar and trace elements our results suggest that the parent magmas of the nakhlites including the newly found y 000593 000749 are similar and that their crystallization ages are 1 3 ga

geochronology of the belmont lake metavolcanic complex and implications for crustal development in the central metasedimentary belt grenville province ontario u pb analyses of zircon and titanite were carried out on eight rocks from the belmont lake metavolcanic complex a volcano sedimentary sequence in the central metasedimentary belt of the grenville province of southeastern ontario the ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position the youngest volcanic age is from a rhyolite near the base of the sequence the oldest age is from a dacite in the middle this is overlain by a rhyolite in age a rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 ma old the complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age tectonic emplacement of these segments was most likely along previously unrecognized thrust faults the supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism the earliest event was probably associated with thrusting t

numerical simulation of love wave generation in the ilan basin taiwan during the 1999 chi chi earthquake during the 1999 chi chi taiwan earthquake mw7 6 large amplitude fundamental mode love wave with a predominant period of around 5 sec was observed in the ilan basin northeastern taiwan the love wave was generated near the edge of the basin and propagated toward its center during which its amplitude and duration increased and its phase velocity decreased numerical 2 d modelings of sh wave propagation using a structural model of the ilan basin reproduced the generation process and propagation characteristics of the love wave from multiple sh wave reflections between the free surface and dipping sediment basement interface the simulation results also suggest that long period love wave was not generated during aftershocks because the predominant period of the incident s wave was too short to resonate in the thick sediments of the ilan basin

ion microprobe u pb dating of apatite abstract to illustrate in situ sensitive high resolution ion microprobe shrimp analysis of apatites pb isotopes and pb u ratios of five apatite samples with different ages have been measured using shrimp ii ion microprobe at hiroshima university the prap apatite from a carbonatite complex at prairie lake ontario with a 207 pb 206 pb age of 1156 45 ma 2 was used as the standard for 206 pb 238 u 238 u 16 o 238 u calibration apatites from the poohbah lake alkaline complex give 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages of 2726 145 ma 2 and 2701 86 ma 2 in agreement with a conventional tims 207 pb 206 pb age of 2667 10 ma 2 and a k ar isochron age of 2706 46 ma 2 for the remaining three apatite samples the 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages obtained by shrimp are consistent with radiometric and geological ages in the literature

u th pb systematics of individual perovskite grains from the allende and murchison carbonaceous chondrites ion microprobe u th pb isotopic measurements have been made of individual perovskite grains from the allende cv3 and murchison cm2 chondrites these are the first chronological data reported for murchison refractory inclusions several generations of perovskite were identified in polished thin sections of fluffy type a inclusions 3529 44 and 4691 from allende of which only the largest anhedral perovskites 20 m were analysed with the ion microprobe the allende perovskites are characterised by low u typically 3 ppm but ranging up to 12 ppm in grain 7 1 from 3529 44 and th u of around 4 in 3529 44 and 10 in 4691 the204pb concentrations in the allende perovskites range from 6 to 140 ppb a precise age measurement could be obtained on grain 7 1 only the u pb systematics of this grain are concordant with a207pb 206pb age of 4565 34 2 ma two of the murchison perovskites occurred as individual 20 m inclusions in spinel grains 7 309 7 a52 while the third perovskite bearing inclusion was a spherule dominated by perovskite with interstitial spinel 7 396 u concentrations range from 3 6 to 15 ppm with th u less than 0 5 and204pb concentrations ranging from 61 to 369 ppb all analyses of the murchison perovskites are consistent with a single formation age of 4569 26ma the ages determined by ion microprobe from these perovskites show good agreement with previous age estimates of allende refractory inclusions measured by conventional mass spectrometric techniques there is no evidence in the u pb systematics of allende and murchison refractory inclusions for material that substantially predates the formation of the solar system

u pb rb sr and sm nd chronology of granitic basement hydrothermal albitites and uranium mineralization lagoa real south bahia brazil the granites orthogneisses hydrothermal albitities and rocks which have suffered uranium mineralization from the lagoa real district south state of bahia brazil have been investigated by u pb rb sr and sm nd techniques u pb values on zircons from the granitic protolith give an age of 1725 ma u pb on u mineralization dates the primary mineralization at 1395 ma and indicates a reworking at 480 ma which may represent the age of the thrusting of the lagoa real complex over espinhaco metasediments during the brazilian orogeny these two dates are given by rb sr on albitites but from sparse information and are not supported by unequivocal arguments the uranium deposition and sodium metasomatism however cannot be linked either with the thermal history of the granite or with brazilian thrusting sm nd gives scattered results which are suggestive of autochtonous reworkings of rees these results lead to the following suggestions 1 magmatic activity of subalkaline affinity existed within the sao francisco craton at about 1 7 ga 2 such subalkaline plutons are likely sources for u mineralization 3 at about 1 4 ga an unknown event caused hydrothermal activity leading to u deposition at lagoa real 4 brazilian overthrusting at about 480 ma did not play any genetic role in the hydrothermal activity

an 40ar 39ar geochronological study of the elzevir batholith and its bearing on the tectonothermal history of the southwestern grenville province canada results of 40ar 39ar step heating for muscovite potassium feldspar and plagioclase from the ca 1240 ma elzevir trondhjemite in the central metasedimentary belt of the canadian grenville province have been combined with earlier data and used to deduce a thermal history for the eastern elzevir terrane following the ottawan orogeny 1050 950 ma muscovite yielded precise plateau dates of ca 900 ma whereas the potassium feldspar displayed disturbed age spectra with ca 730 760 ma dates for broad plateau regions this age difference could be explained by slow cooling or by thermal overprinting at 760 800 ma that has updated the microcline the plagioclase spectra provide evidence for a low temperature hydrothermal event ca 380 ma ago that has generated sericite in saussurite and has caused partial argon loss from the microcline this result agrees with the other plagioclase thermochronometry and paleomagnetism on the cordova gabbro 25 km to the west but provides a lower estimate for the upper age brac

toward real time regional earthquake simulation ii real time online earthquake simulation ros of taiwan earthquakes abstract we developed a real time online earthquake simulation system ros to simulate regional earthquakes in taiwan the ros uses a centroid moment tensor solution of seismic events from a real time moment tensor monitoring system rmt which provides all the point source parameters including the event origin time hypocentral location moment magnitude and focal mechanism within 2 min after the occurrence of an earthquake then all of the source parameters are automatically forwarded to the ros to perform an earthquake simulation which is based on a spectral element method sem a new island wide high resolution sem mesh model is developed for the whole taiwan in this study we have improved sem mesh quality by introducing a thin high resolution mesh layer near the surface to accommodate steep and rapidly varying topography the mesh for the shallow sedimentary basin is adjusted to reflect its complex geometry and sharp lateral velocity contrasts the grid resolution at the surface is about 545 m which is sufficient to resolve topography and tomography data for simulations accurate up to 1 0 hz the ros is also an infrastructural service making online earthquake simulation feasible users can conduct their own earthquake simulation by providing a set of source parameters through the ros webpage for visualization a shakemovie and shakemap are produced during the simulation the time needed for one event is roughly 3 min for a 70 s ground motion simulation the ros is operated online at the institute of earth sciences academia sinica http ros earth sinica edu tw our long term goal for the ros system is to contribute to public earth science outreach and to realize seismic ground motion prediction in real time

cenozoic and mesozoic metamorphism in the longmenshan orogen implications for geodynamic models of eastern tibet new zircon u pb and mica 40ar 39ar dating combined with structural studies in the longmenshan orogen confirm that most of the upper crustal deformation in the eastern margin of tibet is mesozoic however at lower structural levels apatite u pb and monazite electron microprobe dating reveals a previously unknown domain of cenozoic ca 65 ma barrovian type metamorphism and deformation this discovery shows that the crust in the eastern margin of tibet was already a substantial thickness around the time of the india asia collision associated deformation has a n s oriented stretching lineation implying that deformation was not driven by topographic gradients in the tibetan plateau the observed moderate amounts of distributed postmetamorphic e w shortening can probably explain the present thickness of the continental crust in the area these results do not support models of crustal thickening caused by solid state lateral flow of midcrustal metamorphic rocks

thin skinned tectonics in the northern rhenish massif germany a network of profiles in the hercynian mountain system geo traverse rhenoherzynikum is needed to determine details of the geological structure and find the reasons for tectonic movements outstanding features within the mountain system such as the large fault zone along the southern boundary of the hunsruck1 and the left flank of the rhinegraben have already been investigated by reflection seismology2 3 we describe here a new reflection refraction experiment carried out in 1978 in the most northern part of the rhenish massif across the stavelot venn massif near aachen fig 1 while layers in the lower crust dip to the nnw a strong upper reflector at 3 4 km depth shows a slight dip to the sse and indicates a prominent fault zone near aachen known in belgium as the faille du midi here a comparable and apparently identical reflector was found some 100 and 175 km to the west of our profile we interpreted this reflector as a prominent and well lubricated thrust fault along which a huge horizontal nappe displacement took place during the last stages of the variscan orogeny

mineral chemistry and in situ upb geochronology of the mare basalt northwest africa 10597 implications for low ti mare volcanism around 3 0 ga abstract unbrecciated mare basalts are rare in the lunar meteorite collection found in 2015 northwest africa nwa 10597 is a medium grained low ti mare basalt with a subophitic texture the meteorite consists mostly of mm sized pyroxene and plagioclase with minor olivine spinel ilmenite phosphates silica and trace zr rich minerals such as baddeleyite zirconolite and tranquillityite a portion of plagioclase and silica has been transformed to their high pressure polymorphs due to shock metamorphism nwa 10597 has a low tio2 content 2 9 wt but is relatively enriched in rare earth elements ree laaverage 65 ci with an overall unfractionated pattern except for a negative eu anomaly calculated ree concentrations of parent melts in equilibrium with mg rich pyroxene and ca rich plagioclase suggest no significant assimilation of ree rich melts after the onset of pyroxene crystallization in situ u pb analyses of baddeleyite and apatite reveal a mutually consistent age of 3 0 ga which is also in excellent agreement with that of low ti mare basalts nwa 4734 and lapaz icefield lap 02205 dated with other independent techniques the concordance suggests no significant thermal disturbance in the u pb isotopic system of nwa 10597 although it was heavily shocked nwa 10597 closely resembles nwa 4734 in terms of petrographic texture mineral chemistry and geochronology indicating a pairing relationship

constraints on average taiwan reference moho discontinuity model receiver function analysis using bats data summary by analysing teleseismic waveform data we propose a large scale taiwan reference moho discontinuity model trmdm through coherent stacking and h analysis of receiver functions rfs tectonic structural features are determined from accurate crustal thickness h and reliable vp vs ratio consequently poisson s ratio estimations for taiwan the best estimated regional average moho depth is 33 5 2 9 km noted is a westward crustal thinning from 39 3 0 km in eastern taiwan to 30 1 5 km in southeastern china the averaged moho depth is 23 0 2 5 km in northern taiwan and increases to 33 5 2 0 km in the south the markedly thin crust and high vp vs ratio in northern taiwan are mainly associated with backarc opening and magmatic activities based on h estimations and associated seismicity patterns beneath suang long sslb and adjacent four stations we propose two moho reference models that exhibit distinctive crustal thickening in central taiwan the spatial variations of crustal thickness models show strong lateral change in the moho topography the thick crust in the south thin crust in the north and transition in central taiwan mark the different tectonic units between the subduction wedge and the collision prism onshore in view of the following list of constraints thicker crust in the south than in the north eastward crust thickening significant moho depth changes clear 9 11 s subcrustal boundaries from five stations the compelling thickening of crust and upper mantle beneath the central mountain belt seismicity patterns with the absence of mantle earthquake in the wadatibenioff zone regional geological features the occurrence of the inland chi chi earthquake the compelling low at yulb 1 58 0 13 that may extend to central taiwan at sslb 1 59 0 23 relatively thick crust at yulb 39 5 1 6 km and sslb 40 5 1 3 km or 52 5 1 5 km and finally the apparent horizontal offset between highest yu shan mountain and the deepest moho at sslb we are able to suggest that the initial subduction of the eurasian plate occurred in southern taiwan and most likely extended to the transition zone in central taiwan although the current rf study is limited by large interstation distance our analysis provides more notable constraints than previous studies to explicitly determine the characteristic features of moho discontinuity this detailed approach means that rather than treating the tectonic framework as a whole heterogeneous lithospheric feature clear moho boundary geometry variations indicate that active orogenic processes and differential tectonic stress loading create separate and complex crustal and subcrustal to upper mantle structural features caused by the arc continent collision

fluids and thrusting abstract recent studies of the structure of the continental crust by cocorp and birps have shown that major thrust structures in the lower crust are ubiquitous plate tectonic processes of continental crust destruction or construction at sites where subduction or collision occurs the himalayas or the andes involve thrusting of continental materials or ocean crust beneath continents and local overthrusting may accompany transcurrent motion in all such cases massive fluid flow must occur as first stressed by m k hubbert and w w rubey thrusting mechanisms require that fluid pressures are close to or greater than lithostatic pressures when thrusting occurs compaction of the underplate must occur rapidly expelling pore water crustal thickening leads to gradual heating of the underplate with prograde metamorphism near the top and even melting at the base if the overthrust plate is thick and hot at the base retrograde metamorphism will occur at the base of the overthrust plate and rising fluids will encounter inverted thermal gradients in such a region veins need not occur but leaching phenomena may dominate if an underthrust plate is hydrated and or contains sedimentary aquifers large fluid volumes are expelled through shear zones into the overthrust plate the scale of fluid release processes can be large thus in thin skinned tectonics where the overthrust plate is 10 15 km thick induced fluid release can easily reach 4 109 g m 2 of thrust surface the flow of such fluids will be controlled by the thrust surface and lithology both of which will influence hydraulic fracture mechanisms and spacing of fractures the chemistry of thrust derived fluids may be highly variable depending on lithology and the time constants of thrusting vertical thermal and redox environments will be similarly dependent in the subduction process impressive quantities of fluids must pass back up the thrust surface and such fluids have recently been directly observed during drilling dewatering of spilites serpentinites and sediment layers of the underthrust oceanic lithosphere must produce massive fluid flow back to the surface but some of these fluids may form hydrated minerals in the overlying mantle and at great depth flux mantle melting extreme metasomatism in blueschist belts must result from such fluids a case of particular interest involves the cessation of subduction when a high level slab reaches thermal equilibrium in general flow regimes in the thrust and fault zones associated with collisions follow a sequence from conditions of high t p with locally derived fluids at low water rock ratios during initiation of the structures to high fluxes of reduced metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs later in the tectonic evolution and at shallower crustal levels there may be incursion of oxidizing near surface fluid reservoirs into the faults these fluids may have extremely low 18o values where mountain ranges form on rebound faults and high altitude depleted fluids penetrate down the rebound structure extensive mineralization may be associated with such thrust derived fluids examples which will be discussed include the mother lode au deposits of california u s a and the large u deposits of lagoa real brazil

uranium enrichment in archaean crustal basement associated with overthrusting uranium deposits cumulatively in the 100 000 tonne u3o8 range occur within ductile shear zones transecting archaean basement gneisses at lagoa real north east of caetite state of bahia brazil1 3 fig 1 the gneisses dated at 2 600 3 000 myr are at amphibolite to granulite facies of meta morphism there is a general concensus that such rocks form near the base of the crust and typically exhibit pronounced depletion of u relative to the upper crust5 6 to the east and west of lagoa real the archaean gneisses overlie proterozoic meta sediments and volcanics of the espinhaco supergroup along well documented thrust surfaces7 8 limited u pb dating of the deposits indicates that u mineralization occured at 820 myr ref 9 involving removal of si and k coupled with na addition in oxidizing conditions v pb and light rare earth elements lree were introduced along with uranium from hypersaline co2 hydrocarbon rich fluids with 18o 4 at temperatures of 540 c depths of 15 km and pfluid pload we show here that the geological constraints are consistent with release through hydrofracturing of 1 000 km3 of over pressurized meteoric water recharged formation brines in the proterozoic sediments up through the hot overriding gneisses

ion microprobe u pb dating of quaternary zircon implication for magma cooling and residence time abstract an ion microprobe u pb dating method of quaternary zircon is developed using the sensitive high resolution ion microprobe shrimp and applied to igneous rocks from japan total pb u isochron age of 1 36 0 23 ma 95 confidence limit cl mswd 1 03 was obtained for zircons extracted from takidani granodiorite in central japan this may provide a constraint on magma cooling when coupled with fission track ages of the zircon as well as rb sr and k ar ages on co existing minerals the closure temperature determined by each method has lead to exponentially declining cooling history the history is consistent with a simple conductive cooling model of a small magma body 10 2 10 3 km 3 a pb u isochron age of 271 58 ka 95 cl mswd 0 85 has been determined for volcanic zircons from torihama dacite sw japan the age is significantly older than the 238 u 230 th ionium age of 145 33 ka and fission track age of 163 8 ka found in the literature suggesting either the magma residence time of 100 kyr or a rapid cooling rate of about 6 c kyr in contrast a tephrochronological estimate of 240 10 ka agrees well with the observed pb u age implying that the ionium and fission track ages are incorrect the pb u isochron age of 90 29 ka 95 cl mswd 1 04 is obtained for zircons in pyroclastic rocks from the unzen eruption in 1991 sw japan the age is again older than the eruptive age which suggests a magma residence time of 90 kyr in a shallow reservoir

effects of fault geometry and slip style on near fault static displacements caused by the 1999 chi chi taiwan earthquake we investigated the fault geometry effects and the corresponding coseismic slip distribution using various proposed earthquake fault models for the chi chi earthquake of 21 september 1999 the types of fault geometries are threefold a simple planar fault plane a two segmented planar fault plane and a three dimensional 3d curved fault surface rupture propagation model we derived the estimated spatial slip distribution from an inversion analysis of gps coseismic displacement data and show that the 3d fault model is the preferred solution the simple and segmented fault models lead to significant artificial slip distributions associated with the pre defined fault geometry and the spatial distribution of gps stations the spatial distribution of coseismic slip deduced from the 3d fault model has three observable features 1 the overall slip is concentrated at depth of less than 12 km which may well correspond to a shallow dipping detachment 2 the maximum slip of about 10 m is located 45 km to the north of the epicenter and 3 the slip vector is dominated by the dip slip component in addition the results from the inversion of gps data are consistent with those from the inversion analysis of teleseismic broadband data a resolution analysis further demonstrates that the results are highly correlated with field gps data studies when we used synthetic test data the inversion of spatially distributed gps data is highly sensitive to fault geometry we conclude that the use of the 3d fault model is not only necessary but also certainly competent enough to well explain the inferred slip style and the observed static coseismic displacements d 2005 elsevier b v all rights reserved

3d velocity structure around the source area of the 1999 chi chi taiwan earthquake before and after the mainshock 3d v p and v p v s models for the source area before and after the chi chi earthquake are derived from a tomographic inversion of seismic travel time data from the taiwan central weather bureau seismic network cwbsn resulting 3d velocity models reveal a strong lateral variation in the crust particularly at a depth range of 5 to 25 km along the trend of the dipping chelungpu thrust in general low v p and high v p v s anomalies are found in and around the source volume of the chi chi earthquake a volume centered around the entire 100 km 40 km chelungpu rupture surface we pay special attention to the crustal properties and their changes due to the chi chi event and the association of the crustal anomalies with seismicity combining the results with those of other geological and geophysical surveys the crustal anomalies are interpreted as images of a highly fractured and fluid filled chi chi source region fluid overpressure is known to reduce the strength of the fault zone and in this case may have initiated the nucleation of the chi chi earthquake the v p models obtained before and after the chi chi event show some interesting heterogeneities regions of low v p anomaly appear to have further expanded with the occurrence of the chi chi earthquake the v p v s model shows high anomalies near the source rupture especially near where the rupture is believed to have nucleated after the chi chi event the v p v s model shows a substantial change that may reflect an outward shift of the fluid filled fractured source region this shift is shown by a general expansion in v p v s anomalies to a broader region e g where two intensive aftershock clusters occurred and a significant v p v s reduction to more normal values near the chelungpu rupture we attribute these changes in v p and v p v s anomalies as well as the expansion and shift of the anomalous regions to be a response to the localized stress change caused by the slip of the chi chi rupture the location of the seismic events is correlated with that of the crustal v p and v p v s anomalies large events appear to occur in the transition zones of both v p and v p v s anomalies this finding may be of use in the identification of weakened crustal regions in a seismic zone thus suggesting where impending large earthquakes are likely to occur all input data and initial and final models of this article are given as electronic files in the cd attached to the end of this issue

ion microprobe pb pb dating of carbonado polycrystalline diamond abstract we report in situ ion microprobe pb pb dating of quartz rutile and clay mineral inclusions and matrix part of polycrystalline diamonds carbonado derived from a proterozoic conglomerate in diamond bearing deposit of minas gerais in brazil together with u pb ages of zircons also extracted from the deposit thirty four spots on seven quartz grains located in the cavity of the gm01 carbonado yield 207pb 206pb isochron age of 3247 800 ma 2 mswd 0 75 and six spots on three rutile inclusions give the age of 3916 1300 ma 2 mswd 0 092 seven spots on three clay mineral inclusions of the do3 carbonado show common lead compositions while four spots on matrix define 207pb 206pb isochron age of 3811 1800 ma 2 mswd 0 012 seventy six spots on seventy zircon grains derived from the same conglomerate show three major u pb concordant ages of 2151 17 ma 2692 20 ma and 2931 22 ma with two concordant zircon outliers of 1726 58 ma and 3599 12 ma the youngest age is consistent with the formation age of 1750 1700 ma in the proterozoic conglomerate estimated by other workers the 3 6 ga zircon is the oldest record in the south american platform it may be detrital in origin and reflect the remnant of an archean craton the pb pb age of quartz and rutile inclusions in gm01 carbonado and that of do3 carbonado matrix are 3315 720 ma and 3811 1800 ma the matrix age is consistent with pb pb age of 2 6 3 8 ga of central african carbonados in the literature suggesting a close genetic relationship between brazilian and african carbonados

assessing the geochemical and tectonic impacts of fluid rock interaction in mid crustal shear zones a case study from the intracontinental alice springs orogen central australia the reynolds anmatjira ranges central australia form part of a high grade basement terrane dissected by intensely metasomatized transpressional shear zones active during the ordovician carboniferous alice springs orogeny unlike typical retrograde structures associated with discrete fluid flow the mid crustal setting and intracontinental nature of these shear systems present significant problems for the source and ingress mechanism of the fluid involved in their rehydration to address these issues we describe two detailed traverses across deformed and metasomatized basement rocks in this region and interrogate their record of fluid rock interaction from various perspectives both traverses combine structural and petrological observations with zr in rutile and ti in quartz thermobarometry oxygen and hydrogen stable isotope analysis and major trace and rare earth element mobility trends each technique is critically evaluated for its utility in this study and its more widespread applicability to alternative field areas providing a strategic framework for the general investigation of fluid affected shear zones ultimately the integrated data sets specify pressure temperature conditions of 530 c and 4 5 kbar implying average apparent thermal gradients of 29 36 c km 1 and depths of 14 18 km other characteristic features to emerge include strongly variable element mobilities and pronounced isotopic depletion fronts consistent with the alteration effects of an externally derived non equilibrium fluid this is confirmed by calculated fluid compositions indicative of contributions from a fluid of meteoric origin with estimated 18o and d values as low as 2 3 and 59 8 respectively we propose that these surficial fluid signatures are imposed on the mid crust by the prograde burial and dehydration of hydrothermally altered fault panels produced during pre orogenic basin formation progressive fluid release with continued subsidence then leads to the accumulation of increasing fluid volumes in the vicinity of the brittle ductile transition promoting extensive hydration metasomatism and reaction softening at the locus of stress transmission from plate boundary sources the sustained injection of externally derived fluids into refractory crustal material may thus stimulate a critical reduction in the long term strength of the lithosphere providing strong impetus for the initiation and advancement of intracontinental orogenesis

the age and pb loss behaviour of zircons from the isua supracrustal belt as determined by ion microprobe ion microprobe uthpb analyses of zircons from a conglomeratic metavolcanic unit in the isua supracrustal belt of west greenland show that their magmatic age is3807 1ma and failed to detect any older zircon cores or xenocrysts low u areas within zircons at a 30 m scale lost only small amounts of radiogenic pb and only in the recent past whereas high u areas within grains lost much greater proportions of their pb both recently and as early as the archaean some areas in the zircons have concordant upb and thpb ages the ion probe results agree with earlier determinations for the isua supracrustals and clarify minor discrepancies between previous multigrain and single crystal analyses

diagenetic apatite character and in situ ion microprobe u pb age keeseville formation potsdam group new york state an occurrence of diagenetic fluorapatite cement is documented within the cambro ordovician keeseville formation potsdam group near chateaugay in new york state the fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites which have been reworked by aeolian processes prior to burial the paragenetic sequence includes the following compaction of dust rimmed grains quartz cementation minor kaolinite fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation the fluorapatite occurs as elongated bladed crystals that characteristically contain ladder like inclusion rich cores running parallel to crystal length surrounded by clearer rims and larger blocky crystals towards the middle of interstices in situ shrimp analyses of blocky fluorapatite crystals yield a u pb age of 486 29 ma indicating that the cement for

uranium lead systematics of phosphates in lunar basaltic regolith breccia meteorite hills 01210 chronological studies of brecciated lunar meteorites have proved difficult because they are mixtures of materials from various sources and the radiometric clocks are sometimes affected by the subsequent impact events on the moon here we report the in situ u pb dating of phosphates in lunar meteorite meteorite hills met 01210 which is a regolith breccia consisting of low ti mare basalt clasts and mineral fragments with a minor anorthositic component in situ analyses of four merrillite and four apatite grains in met 01210 which are resistant to secondary events resulted in a 207pb 206pb 204pb 206pb isochron age of 3904 85 ma 95 confidence limit this phosphate formation age when considered as the crystallisation age of this low ti basalt is similar to crystallization ages of 3 8 3 9 ga for unbrecciated low ti basalt meteorites asuka 881757 and yamato 793169 this result reinforces the hypothesis that all these three meteorites originated from the same area on the moon and were launched by a single impact event consistent with the similarity of launch ages mineralogical and geochemical signatures

in situ u pb dating of monazite xenotime and zircon from the lantian black shales time constraints on provenances deposition and fluid flow events abstract the lantian formation located in eastern south china block scb forms the lower sequence of the ediacaran period at the transition from proterozoic to paleozoic the fossils of lantian formation have been proposed to predate the avalon biota about 579 565 ma the earliest known fossil assemblages with complex morphologies based largely on stratigraphy mineral chemistry and in situ u pb dating of monazites xenotimes and zircons from the black shale in fossil rich zone are studied for the first time to provide critical age constraints for provenance early diagenesis and fluid flow events detrital zircons and monazites give age populations similar to that of the doushantuo formation indicative of the same provenances for ediacaran basins throughout the scb the low y monazites formed during early diagenesis yield a weighted mean age of 612 29 ma n 9 mswd 3 1 age spectrum of analyzed monazites demonstrated that the sedimentation started from at least around 645 ma subsequently the overprinting events could be recorded by xenotimes and zircons precipitated from fluids during late diagenesis age results from xenotimes ranging from 441 ma and 585 ma were contemporaneous with the timing of collision of scb with gondwanaland and a weighted mean age of 394 8 3 7 ma n 23 mswd 2 8 obtained from diagenetic zircons could be correlated to the post tectonic granites widespread on the scb the pre existing monazites generally remain pristine and the multi staged fluids were locally interacted with the samples to form th rich domains in monazites

thermal and pore fluid pressure history on the chelungpu fault at a depth of 1111 m during the 1999 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan in 2005 the taiwan chelungpu fault drilling project was launched to drill two deep holes holes a and b cutting across the fault plane the heat strength 7 0 c m within a heated layer of 5 mm on the fault at hole a due to frictional faulting is evaluated from the values of shear stress and thermal and mechanical parameters measured from the core samples based on a 1 d heat conduction equation and 2 d faulting model with the values of thermal diffusivity evaluated within a representative temperature range the thermal and pore fluid pressure history at depths 1110 37 1111 34 m in hole a is constructed results show that the peak temperature at the center of the heated layer could have been higher than 1100 c during faulting and temperature rise decreased with increasing distance and time the possible relationships between the temperatures and chemical reactions of clay minerals are discussed in detail in the heated layer pseudotachylites have been formed and quartz plasticity might also have been operative during faulting outside this slip zone the temperature rise was low and thus clay minerals were stable during faulting the evaluated pore fluid pressure is 22 5 mpa this suggests the existence of a suprahydrostatic state in the fault zone during the earthquake indirect evidence of the existence of fluids in the fault zone during faulting is described additionally rock physics is applied to interpret the observations

retrograde fluid infiltration in the high grade modum complex south norway evidence for age source and ree mobility the high grade metamorphic basement of the modum complex south norway exhibits retrogradation and alteration due to late stage fluid infiltration extensive alteration zones of albite and calcite rich veining occur especiallywithin and around numerous metagabbros the gabbros intruded at 1224 15ma are now partly altered to amphibolites due to the subsequent high grade metamorphism two generations of albite rich rocks have been recognized 1 a fine grained foliated type 2 a coarse grained crosscutting type both types show a typical greenschist facies mineralassemblage albite actinolite chlorite talc the calcite veins dykesrepresent a younger generation of veins than both albite rich types u pb data for spheneof type 1 yielded an age of 1080 3 ma determining a point on the retrogradep t t path of the modum complex increasing albitisation of themetagabbros leads to a decrease in 143nd 144nd oand an increase in 87sr 86 o albite and calcite rich samples show negative nd and positive sr suggesting that fluids which interacted with the metagabbros originated from a crustal reservoir the nd and sr isotopic data show disequilibrium at the microscale as well as at the macroscale negative sm nd model ages of the albite rich rocks demonstrate that rare earth elements rees were mobile and fractionated during albitisation

in situ ion microprobe u pb dating and ree abundances of a carboniferous conodont we report here in situ ion microprobe u pb dating of a conodont micro fossil using an ion microprobe method thirteen spots on the single fragment of the carboniferous conodont size approximately 800 m 100 m yield a 238u 206pb isochron age of 323 36 ma and a tera wasserburg concordia intercept age of 332 44 ma in a three dimensional 238u 206pb 207pb 206 pb 204pb 206pb diagram these ages are consistent with the depositional and early diagenetic ages of the fossil in its host mississippian sedimentary sequence within experimental error the success of the method depends on the chemical fractionation of u from pb within a hundred m length scale and the consequent variations in pb isotopic compositions due to radioactive decay shale normalized rare earth element ree abundances of two spots on the same sample show flat patterns from light ree to middle ree and decreases from middle ree to heavy ree with negative anomalies of both ce and eu the ree characteristics are significantly different from those of devonian conodonts reported by other workers suggesting discrepant redox states and or formation environments

the proterozoic albitite hosted valhalla uranium deposit queensland australia a description of the alteration assemblage associated with uranium mineralisation in diamond drill hole v39 the valhalla uranium deposit located 40 km north of mount isa queensland australia is an albitite hosted mesoproterozoic u deposit similar to albitite hosted uranium deposits in the ukraine sweden brazil and guyana uranium mineralisation is hosted by a thick package of interbedded fine grained sandstones arkoses and gritty siltstones that are bound by metabasalts belonging to the ca 1 780 ma eastern creek volcanics in the western succession of the mount isa basin alteration associated with u mineralisation can be divided into an early main and late stage the early stage is dominated by laminated and intensely altered rock comprising albite reibeckite calcite titano magnetite brannerite the main stage of mineralisation is dominated by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite apatite uranoan zircon uraninite anatase albite reibeckite calcite and hematite the late stage of mineralisation comprises uraninite red hematite dolomite calcite chlorite quartz and pb fe cu sulfides brannerite has u pb and pb pb ages that indicate formation between 1 555 and 1 510 ma with significant pb loss evident at ca 1 200 ma coincident with the assemblage of rodinia the oldest ages of the brannerite overlap with 40ar 39ar ages of 1 533 9 ma and 1 551 7 ma from early and main stage reibeckite and are interpreted to represent the timing of formation of the deposit these ages coincide with the timing of peak metamorphism in the mount isa area during the isan orogeny lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater mount isa district reveals that mineralisation involved the removal of k ba and si and the addition of na ca u v zr p sr f and y u th ratios indicate that the ore forming fluid was oxidised whereas the crystal chemistry of apatite and reibeckite within the ore zone suggests that f and text po 3 4 were important ore transporting complexes 18o values of co existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380 c and involved a fluid having 18ofluid values between 6 5 and 8 6 reibeckite d values reveal that the ore fluid had a dfluid value between 98 and 54 the mineral assemblages associated with early and main stages of alteration plus 18ofluid and dfluid values and timing of the u mineralisation are all very similar to those associated with na ca alteration in the eastern succession of the mount isa basin where a magmatic fluid is favoured for this style of alteration however isotopic data from valhalla is also consistent with that from the nearby mount isa cu deposit where a basinal brine is proposed for the transport of metals to the deposit based on the evidence to hand the source fluids could have been derived from either or both the metasediments that underlie the eastern creek volcanics or magmatism that is manifest in the mount isa area as small pegmatite dykes that intruded during the isan orogeny

slip distribution and tectonic implication of the 1999 chi chi taiwan earthquake we report on the fault complexity of the large m w 7 6 chi chi earthquake obtained by inverting densely and well distributed static measurements consisting of 119 gps and 23 doubly integrated strong motion records we show that the slip of the chi chi earthquake was concentrated on the surface of a wedge shaped block the inferred geometric complexity explains the difference between the strike of the fault plane determined by long period seismic data and surface break observations when combined with other geophysical and geological observations the result provides a unique snapshot of tectonic deformation taking place in the form of very large 10m displacements of a massive wedge shaped crustal block which may relate to the changeover from over thrusting to subducting motion between the philippine sea and the eurasian plates

source characteristics of the northern longitudinal valley taiwan derived from broadband strong motion simulation the 2014 m l 5 9 fanglin earthquake occurred at the northern end of the aftershock distribution of the 2013 m l 6 4 ruisui event and caused strong ground shaking and some damage in the northern part of the longitudinal valley we carried out the strong motion simulation of the 2014 fanglin event in the broadband frequency range 0 4 10 hz using the empirical green s function method and then integrated the source models to investigate the source characteristics of the 2013 ruisui and 2014 fanglin events the results show that the dimension of strong motion generation area of the 2013 ruisui event is smaller whereas that of the 2014 fanglin event is comparable with the empirical estimation of inland crustal earthquakes which indicates the different faulting behaviors furthermore the localized high pgv patch might be caused by the radiation energy amplified by the local low velocity structure in the northern longitudinal valley additional study issues are required for building up the knowledge of the potential seismic hazard related to moderate large events for various seismogenic areas in taiwan

three dimensional qp and qs tomography beneath taiwan orogenic belt implications for tectonic and thermal structure summary we determined the 3 d qp and qs structure of the taiwan orogenic belt to enhance understanding of the related tectonic and thermal structure beneath the collision zone the inversion used t values measured from the spectra of p and s waves from the dense taiwan strong motion network for moderate size earthquakes ml 4 5 5 5 to avoid source complexity the time period 1991 2007 includes the aftershock sequence of the 1999 chi chi earthquake that provides good ray coverage in central taiwan over 18 000 velocity spectra from 883 earthquakes were analysed a non linear least square technique is applied to the spectra for t determination by assuming a 2 source model for the frequency band of 1 30 hz a frequency independent q was assumed in this study the corner frequency of a specific event was fixed for the corresponding stations and a quality index was defined to assure good quality data for the inversion the results reveal the sharp variation of qp and qs across the recently ruptured chelungpu fault and the kaoping and chaochou faults in pingtung plain the q values in the hangingwall are smaller by about 85 and 110 for qp and qs respectively relative to the footwall the fault geometry is distinctly delineated by the contour of qp qs of 1 2 that extends to the depth of the geologically identified decollement structure beneath the central range the low qp low qs and high qp qs features coincide well with the aseismic zone comparison to the recent thermomechanical numerical models of taiwan shows that the low q zone corresponds to the exhumation of the lower crust the low qs regime high attenuation beneath the central ranges at the depth of 5 22 km coincides with predicted temperatures of 400 600 c the qs comparison with the major tectonic and thermal mechanical models of taiwan reveals that the shear wave attenuation model contains comprehensive rheological and thermal information of relevance to understanding mountain building processes this technique appears particularly useful for distinguishing strong and weak crustal regions in the absence of other constraints

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

dynamic simulation of the 1999 chi chi taiwan earthquake 1 we apply a modified three dimensional finite difference method to investigate the dynamics of the 1999 chi chi earthquake we determine the dynamic source rupture process and simulate the strong ground motions over a frequency range of 0 05 0 5 hz our dynamic source model reveals that the rupture process of the chi chi earthquake is much more complex than that described in the classical propagation rupture models the chi chi earthquake rupture process includes the jumping phenomenon the northern parts on the fault plane have a longer slip duration than the southern parts the motions on the hanging wall are larger than those on the footwall side which is a consequence of the asymmetry of the fault with respect to the free surface in general the synthetics calculated by the dynamic source model agree well with the observed data our dynamic source model reproduces distinctive velocity pulses at stations located in the forward rupture direction and at stations close to the fault surface breaks the apparent rupture directivity propagating from south to north then produces noticeably larger peak ground velocity to the north these results demonstrate that the dynamic rupture model reproduces the main features of long period ground motions these results may lead to improved understanding of rupture processes accompanying large earthquakes the dynamic modeling scheme may produce more reasonable and reliable strong ground motion predictions for assessment of seismic hazard

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

the saricicek howardite fall in turkey source crater of hed meteorites on vesta and impact risk of vestoids the saricicek howardite meteorite shower consisting of 343 documented stones occurred on september 2 2015 in turkey and is the first documented howardite fall cosmogenic isotopes show that sarici

uranium lead systematics of low ti basaltic meteorite dhofar 287a affinity to apollo 15 green glasses article i nfo dhofar 287 is a lunar meteorite found in oman in 2001 which consists of a major portion 95 of low ti mare basalt dho 287a and a minor attached part 5 of regolith breccia dho 287b here we report the u pb systematics of dho 287a using data collected with a sensitive high resolution ion microprobe shrimp in situ analyses of five merrillite and three apatite grains which are resistant to secondary petrologic events resulted in a total pb u isochron age of 3 34 0 20 ga in 238 u 206 pb 207 pb 206 pb 204 pb 206 pb 3 d space 95 confidence level the observed pb pb isochron of these eight phosphates coupled with four plagioclase grains alsoyieldeda 207 pb 206 pbageof3 35 0 13ga thisformationage whenconsideredasthecrystallizationageof

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

continental underthrusting beneath the southern alps of new zealand both the inferred thermal regime and the variation in crustal thickness beneath the southern alps suggest that the mode of crustal shortening changes substantially along the length of the alpine fault north of mt cook crustal shortening is being accommodated predominantly by uplift and erosion of pacific plate continental crust as postulated in the wellman adams tectonic model however south of mt cook the absence of high heat flow and a large crustal root that is not in isostatic equilibrium may have resulted from underthrusting of as much as 100 km of indian plate continental crust

geochronology of the martian meteorite zagami revealed by u pb ion probe dating of accessory minerals abstract the precise chronology of geological events on mars is hampered by the lack of absolute ages for the martian timescale and the significant uncertainties that result from the extrapolation of the lunar timescale to mars hartmann and neukum 2001 martian meteorites represent the only samples of mars currently available attempts to identify source craters for the meteorites have thus far proven inconclusive hamilton et al 2003 lang et al 2009 mouginis mark and boyce 2012 precluding their use in constraining the absolute martian timescale the majority of the known martian meteorites are basalts shergottites all dated shergottites have mineral separate rb sr or sm nd ages of borg et al 2005 here we report a 238u 206pb age of 182 7 6 9 ma by ion microprobe analysis of baddeleyite zro2 grains in the zagami shergottite there is no correlation between discordancy and baddeleyite grain location relative to shock metamorphism mineral petrography demonstrates that baddeleyite is the result of late stage igneous crystallization and raman spectroscopy shows that baddeleyite has not been transformed by shock into preservable high pressure polymorphs supported by an age of 153 81 ma for phosphate grains obtained using the same method we conclude that zagami crystallized at 180 ma in agreement with previous results from mineral separate geochronology therefore the shergottites represent igneous rocks preferentially ejected from young terrains on mars in a small number of ejection events

fault rupture process of the 20 september 1999 chi chi taiwan earthquake we modeled the source rupture process of the 20 september 1999 chi chi taiwan earthquake mw 7 6 using an integrated dataset of near field strong ground motion and global positioning system observations this large inland thrust earthquake produced a surface break more than 80 km long along the chelungpu fault the event triggered over 700 strong motion instruments on the island of tai wan this large ground motion dataset provides the best opportunity to date to un derstand earthquake source processes in a major earthquake first we develop a 3d curved fault model consistent with the surface rupture data and aftershock distribu tion the subsurface fault plane has an average dip of 30 to the east and measures 96 km along strike and 40 km down dip next we applied a genetic algorithm to reconstruct the source rupture process the inversion results indicate a complex slip distribution with a generally broad triangular shaped slip zone that points down dip most of the displacement occurred over a 15 km depth range in the northern segment of the fault with the maximum slip exceeding 20 m the average slip is 3 8 m and the average rupture velocity is 2 6 km sec the mainshock slip distribution clearly complements the aftershock location distribution slip rise times range from 8 to 6 sec over most of the primary slip area and decrease slightly as rupture propagates south to north this relatively long rise time resulted in a low dynamic stress drop and low peak ground accelerations observed at surface stations the rake angle rotates across the rupture plane from predominantly dip slip in the southern segment to mostly left lateral oblique slip in the north we find that geometrical irregularities over the fault plane played an important role in controlling the temporal rupture behavior at fault bends rupture tends to decelerate the rake angle rotates to a near dip slip orientation and the shear stress increases as rupture tries to overcome the bending barriers the total seismic moment from our inversion is 2 9 10 27 dyne cm in good agreement with the harvard and the u s geological survey moment estimation

regional wave propagation from mexican subduction zone earthquakes the attenuation functions for interplate and inslab events the seismic waves from subduction zone earthquakes are significantly affected by the presence of 3d variation in crust and upper mantle structure around the source area these heterogeneous structures also profoundly modify the character of seismic waves as they propagate from the source area to regional distances this is illustrated by studying shallow interplate earthquakes along the mexican subduction zone and deeper inslab normal faulting earthquakes in the subducted cocos plate beneath mexican mainland the strong motion recordings of these earthquakes are used to evaluate the character of wave propagation along the path between the source region and mexico city we compare the wavefield from two large earthquakes of different source type during the shallow h 17 km interplate 1995 guerrero earthquake m w 7 3 the lg phase is the most prominent feature at regional distances of about 150 to a few hundred kilometers from the source the presence of a lateral velocity gradient in the crust caused by the subduction of the cocos plate enhances the lg wave amplitude which is then amplified further in the mexican volcanic belt by amplification in the low velocity volcanic rocks both effects lead to very large ground motions along the path from the coast to the mexican inland in the frequency band from 0 2 to 4 hz however for the deeper h 40 km inslab normal faulting 1999 oaxaca earthquake m w 7 5 the amplitude of the lg phase is too small to produce the abnormal wave propagation and the direct s wave and its multiple sms reflections between the free surface and moho show a simple attenuation with increasing distance we compare these observations with numerical simulations of seismic wave propagation using the fourier spectral method the results provide a key to the understanding of seismic wave field generated by shallow interplate and deeper inslab earthquakes in a realistic 3d heterogeneous structure

ion microprobe uranium thorium lead dating of shergotty phosphates we report ion microprobe u th pb dating of shergotty phosphates by means of the sensitive high resolution ion microprobe shrimp recently installed at hiroshima university japan ten analyses of whitlockite merrillite and three analyses of apatite indicate a 238u 206pb isochron age of 225 200 ma and a tera wasserburg concordia constrained linear three dimensional isochron age of 217 110 ma in the 238u 206pb 207pb 206pb204pb 206pb diagram these ages agree well with the 232th 208pb age of 189 83 ma which suggests that primary crystallization or a shock metamorphic event defined the formation age of the phosphate minerals the average of the later two ages 204 68 ma is consistent with the previously published rb sr age of 165 11 ma and u th pb age of 200 ma these show marginal agreement with the 40ar 39ar age of 254 10 ma but are significantly different from the sm nd age of 360 16 ma taking into account the closure temperature of the u pb system in apatite we suggest the time that shergotty last experienced a temperature of 900 c was 204 68 ma

isotropic events observed with a borehole array in the chelungpu fault zone taiwan shear failure is the dominant mode of earthquake causing rock failure along faults high fluid pressure can also potentially induce rock failure by opening cavities and cracks but an active example of this process has not been directly observed in a fault zone using borehole array data collected along the low stress chelungpu fault zone taiwan we observed several small seismic events i type events in a fluid rich permeable zone directly below the impermeable slip zone of the 1999 moment magnitude 7 6 chi chi earthquake modeling of the events suggests an isotropic nonshear source mechanism likely associated with natural hydraulic fractures these seismic events may be associated with the formation of veins and other fluid features often observed in rocks surrounding fault zones and may be similar to artificially induced hydraulic fracturing

palaeoproterozoic thermal events recorded in the 4 0 ga acasta gneiss canada evidence from shrimp u pb dating of apatite and zircon u pb isotopes of apatites and zircons extracted from a sample of the acasta gneisses that occurs along the western margin of the slave craton in northwest territories of canada have been measured using a shrimp ii ion microprobe eleven apatite analyses 30 m spot give 238u 204pb 206pb 204pb and 204pb 206pb 207pb 206pb isochron ages of 1905 86 ma 2 and 1936 28 ma 2 respectively analyses 20 m spot on the partly recrystallised central portions of fourteen zircons mostly define a mixing array on a 238u 206pb 207pb 206pb concordia plot with concordia intercepts at 4014 25 ma 2 and 1967 93 ma 2 the former agrees with 3 96 4 02 ga protolith ages obtained on the oldest components of the acasta gneisses by other workers the lower concordia intercept for the zircon data is consistent with the u pb age of apatites and may be related to a 500 c thermal event perhaps early in the palaeoproterozoic wopmay orogeny

wavefield extrapolation of body waves for 3 d imaging of earthquake sources summary reverse time imaging of earthquake source parameters is extended from two to three spatial dimensions and from two to three component recordings provided that the recording aperture is sufficiently large and the data are not spatially aliased source radiation patterns in both time and space can be reconstructed by elastic reverse time propagation of body waves such reconstructions are necessarily partial as only the energy that was recorded is available for reconstruction for a point source the origin time and the 3 d spatial location of an event can be reconstructed by extracting the time and position of the best focused energy from the backward propagating wavefield for a spatially and temporally extended source biased estimates of fault position and rupture slip time history can be estimated if the recording aperture is sufficient for smaller recording apertures the time history can still be estimated if the fault location and geometry are known a priori the latter is viable for a reasonable number 200 of three component recordings and so is potentially applicable to real data all these processes assume that a smoothed representation of the 3 d velocity distribution in the volume containing the source and receivers is available

strong ground motion simulation of the 1999 chi chi taiwan earthquake from a realistic three dimensional source and crustal structure 1 we simulate the strong ground motion of 1999 chi chi taiwan earthquake mw 7 6 by considering a three dimensional source rupture model in a full waveform three dimensional wave propagation study the strong ground motion records during the 1999 chi chi earthquake show various characteristics at different sites in taiwan we adopt a three dimensional source model derived from an inversion study with identical path effects as considered in this three dimensional forward study comparisons between the simulation results and observed waveforms from dense island wide strong motion stations demonstrate that the fault geometry lateral velocity variation and complex source rupture process greatly influence the distribution of strong ground shaking the simulation has reproduced the heavy damage area that is mainly concentrated in the hanging wall especially close to the surface break of the chelungpu fault the source directivity effect is also reproduced and shows serious shaking along the northward rupture direction low velocity material in the shallow part of the western plain is found to generate significantly amplified ground motions in the central range the shaking is relatively weak owing to the energy radiation characteristics of a low angle thrust of the chelungpu faulting system the wavefield is then amplified by a high velocity gradient under the coastal range our simulation results in the frequency range of 0 01 0 5 hz give good agreement with the extensive strong motion observations of the chi chi earthquake we find that adequate source representation good three dimensional crustal velocity structures and careful numerical work are necessary to make the ground motion prediction feasible

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

the origin of retrograde shear zones in the napier complex implications for the tectonic evolution of enderby land antarctica abstract retrograde shear zones rszs in granulites at fyfe hills in the napier complex east antarctica formed during a late proterozoic or early palaeozoic reactivation event these rszs preserve a structural and metamorphic record of excavation from depth equivalents of 6 8 kbar 20 26 km to depth equivalents of 3 5 kbar 10 17 km excavation was essentially isothermal suggesting that the rszs formed in an allochthonous terrain during crustal thickening by low angle thrusting rehydration of the rszs was accompanied in part by large ion lithophile element enrichment and reduction in k rb features which are attributed to 1 the retrograde fluid having originated in continental crust that had not previously undergone granulite facies metamorphism and 2 the fluid having been introduced into the rszs by the intrusion of granitic dykes and pegmatites the saturation of these rsz pegmatites in components characteristically depleted in deep crustal and mantle sources such as boron and beryllium supports a low grade source for the retrograde fluid furthermore a rehydration mechanism involving intrusion of pegmatites suggests that the fyfe hills granulites are underlain by a significantly lower grade hydrous terrain

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

ion microprobe u pb dating and ree analyses of phosphates in h4 chondrite yamato 74371 1 u and pb isotopes and rare earth elements rees in individual phosphate grains from h4 chondrites y 74371 were measured by using an ion microprobe nine analyses of whitlockite merrillite and five analyses of apatites indicate a total pb u isochron age of 4533 40 ma 2 sigma which are consistent with the results from previous using thermal ionization mass spectrometer tims the observed apatites age of 4525 30 ma 2 sigma however is younger than those of previous works on the other hand the time difference between the whitlockite age of 4601 94 ma 2 sigma and those of apatites are not observed because of the large uncertainties the ree abundance patterns of the whitlockites normalized to ci chondrite are characterized by an almost constant enrichment of 200 800 times ci abundance and a striking negative eu anomaly the ree abundances of the apatites are lower than those of whitlockite grains and vary appreciably among different grains the remarkable correlation between the eu anomaly eu eu and total concentration of ree is confirmed but significant correlation with eu anomaly and formation age of individual grains are not observed

fluids tectonics and crustal deformation abstract in the plate tectonic process lithosphere creation at ocean ridges and its cooling leads to volatile fixation in the oceanic crust the outer 10 km or so of all crust contains abundant water in pores and fractures and variable amounts of volatiles in minerals when surface rocks are buried by tectonic processes fluids must be released and modify the mechanical properties in the subduction process hydrated oceanic crust may be decoupled from the remaining oceanic lithosphere at depth rising aqueous fluids or melts lead to a complex series of mass energy transfer processes which may decouple continental crust near the moho continental crust if subducted may also be decoupled from its lithosphere by degassing fluid release processes which create gas solid mixtures beneath impermeable cover create low strength systems subject to facile deformation hydraulic fracture processes and diapiric phenomena

hydrodynamic pressures on arch dam during earthquakes a complete three dimensional finite difference scheme has been developed and used to analyze the nonlinear hydrodynamic pressures on arch dam during earthquakes both free surface waves and nonlinear convective acceleration are included in the analysis various dam shapes and reservoir banks were studied and the characteristic of nonlinear contribution due to curved geometry and free surface waves are discussed numerical experiments have been made to determine the desirable mesh size arrangements and time increments the effects of surface wave and convective acceleration on hydrodynamic pressure could augment the hydrodynamic pressure to 10 larger than that of a linear analysis for an earthquake with large ground displacement a large rise of the water surface could probably happen and be a severe threat to human safety in recreational areas and even cause overflow to affect the safe operation of the arch dam an empirical formula is given to predict approximate hydrodynamic force

a metamorphic history from micron scale 207pb 206pb chronometry of archean monazite ion microprobe measurements of pb isotope ratios in monazites have been obtained in situ from thin sections using the cambridge isolab 120 molecular interferences are sufficiently resolved at an rp of 6500 to allow 2 7pb z 6pb dating of monazite with precisions as low as 4 5 ma 2 r the results presented here provide important information on the chronological history of the late archean metamorphism of the wind river range wyoming usa matrix monazites and monazite inclusions in garnets from a metapelite from the northern wind river range have been analysed by sims in a previous study peak metamorphic conditions t 800 c p 8 1 kb were estimated using inclusion assemblages in garnets from this same sample isolated monazite inclusions in garnet yield 2 7pb z 6pb age estimates of 2781 6 to 2809 10 ma those along fractures yield lower ages 2603 2687 ma which are similar to tims and sims ages of matrix monazites a single large 500 xm monazite grain locally preserves growth zoning but has a recrystallised core and a resorbed recrystallised rim age estimates for these three regions are 2788 9 ma 2663 4 and 2523 6 ma respectively thus the inclusion assemblages of sharp and essene may record peak metamorphic conditions at ca 2 8 ga and indicate a phase of metamorphism that predates by over 100 ma the emplacement of the bridget batholith the major lithologic component of the northern wind river range the analysed monazite grains appear to preserve ca 300 ma history even within a single grain monazite inclusions in garnet that are fully armoured may provide estimates for the time of garnet growth even in high grade terranes where most chronometers are reset the age pattern preserved by the large monazite grain cannot be simply related to diffusion controlled closure instead a chronology is preserved which can be related to the petrographic setting of individual grains through in situ analysis

three dimensional dense strong motion waveform inversion for the rupture process of the 1999 chi chi taiwan earthquake 1 we inverted the high resolution spatiotemporal slip distribution of the 21 september 1999 chi chi taiwan earthquake utilizing data from densely distributed island wide strong motion stations for a three dimensional 3 d fault geometry and 3 d green s functions calculations based upon parallel nonnegative least squares inversion the 3 d fault geometry consistent with high resolution reflection profile is determined from gps inversion and aftershocks distribution this 3 d fault model presents the dip angle gradually becoming shallower from south to north along the fault and near flat at the deeper portion of the fault the 3 d green s functions are calculated through numerical wavefield simulation from three dimensional heterogeneous velocity structure derived from tomography studies the green s functions show significant azimuthal variations and suggest the necessity of lateral heterogeneity in velocity structure considering complex fault geometry and green s functions in full 3 d scale we invert the spatial temporal slip distribution of the 1999 chi chi earthquake using the best available and most densely populated strong motion waveform data we perform the inversion under a parallel environment utilizing multiple time window to manage the large data volume and source parameters results indicate that most slip occurred at the shallower portion of the fault above the decollement two major asperities are found one in the middle of the fault and another one at the northern portion of the fault near the bend in the fault trace the slip in the southern portion of the fault shows a relatively low slip rate with longer time duration while the slip in the northern portion of the fault shows a large slip rate with shorter time duration the synthetics explain the observations well for the island wide distributed strong motion stations this comprehensive study emphasizes the importance of realistic fault geometry 3 d green s functions and parallel inversion technique in correctly accounting for both the detailed source rupture process and its relationship with the strong ground motion of this intense earthquake

corundum cr muscovite rocks at o briens zimbabwe the conjunction of hydrothermal desilicification and lil element enrichment geochemical and isotopic evidence monomineralic domains of chlorite corundum and cr muscovite coexist over a kilometer scale within ultramafic schists of the harare greenstone belt 2 73 ga this exotic lithological association includes the conjunction of some of the most aluminous al2o3 88 wt and potassic k2o 10 wt rocks known the paragenetic sequence developed from chlorite corundum corundum diaspore cr muscovite variably overprinted both the corundum and chloritite domains terminal stages were marked by sporadic production of andalusite quartz and finally margarite

source process of the chi chi earthquake a joint inversion of strong motion data and global positioning system data with a multifault model the chi chi taiwan earthquake of 21 september 1999 was a large thrust earthquake that caused disastrous damage the surface fracture trace runs along the chelungpu fault which strikes n5 e along most of the faulting area but turns to the northeast while approaching its northern end it finally presents a horsetaillike faulting system and bends to an east northeast direction at the northern end both strong motion and global positioning system gps data recorded large displace ments in the northern part in this study we use a multifault model to simulate the observed large strong motion and gps data the results of the joint inversion reveal that in the southern part slip occurred mainly in the shallow portion reaching a maximum about 20 m on the ene fault where the rupture propagated to the deep part of the fault there was obviously slip vector rotation from south to north such that the slip on the branched fault plane was almost purely reverse faulting the seismic moment a total of 2 7 10 20 n m was released in less than 40 sec during the mainshock aftershocks occurred mainly in areas where little or no slip occurred slip vector rotation can be explained by the complexity of regional tectonic stress changes in tectonic stress at the northern end of the fault inhibited the northward propagation of the rupture and favored the rupturing of the ene fault

tomographic imaging of lithospheric structures under taiwan abstract tomographic images of the crustal and mantle velocity structures under taiwan are obtained by simultaneous inversion of local earthquake p wave arrival times for hypocenters and p wave velocity structures in northern taiwan a high velocity zone coinciding with the wadati benioff zone can readily be identified as the subducted philippine sea plate the imaged zone dips toward the north at an angle of 40 from a depth range of 20 55 to 100 130 km an upper mantle low velocity wedge ranging from 40 to 80 km in depth exists above the subducted slab above this wedge is the ilan plain of northern taiwan which lies at the west end of the okinawa trough a well recognized back arc basin the crustal velocities under the plain are also relatively low the well defined high velocity zone and the low velocity wedge provide some constraints on the thermal structures of the subduction system under northern taiwan in tomographic images across the central section of taiwan thickening of the crust and up arching of the lower crustal materials under the central range are commonly observed the crust under the western foothills region is clearly thinner and the near surface low velocity layers are well developed the structures under the central range show that although the taiwan orogeny is quite young a root deeper in the north and shallowing to the south has formed the results of our tomography show that a significant portion of the lithosphere is involved in the taiwan orogeny

geometallurgy of australian uranium deposits abstract australian uranium ores are often composed of complex mineral assemblages differences in ore compositions and textures are seen between deposits as well as within a single deposit which can host a range of ore types such a wide variety of uranium ores make it impossible for a single extraction or treatment process to be developed that will accommodate all of the ores from a mineralogical perspective key issues confronting the australian uranium mining industry include the prevalence of low grade ores a lack of detailed chemical and mineralogical information uranium speciation texture grainsize for the various ore deposit types and the presence of refractory uranium bearing minerals and highly acid consuming gangue minerals this paper reviews some of the main controls on uranium geometallurgy by linking concepts relating to ore genesis and the resulting ore mineralogy with the processing behaviour of specific australian uranium ore types emphasis is placed on the value of detailed ore mineralogical analysis and the insight this provides into the factors of importance when considering uranium extraction