li and δ7li in himalayan rivers proxies for silicate weathering this paper presents the first systematic survey of lithium and its isotopes in the dissolved load and suspended and bed sediments of tributaries of the ganges both before and after the monsoon locations were chosen in order to cover catchments draining both silicates and carbonates at high 2000 4000 m and low 550 1300 m altitudes modelling of the dissolved composition shows that the li ca ratio of the silicate endmember in himalayan rivers is at least an order of magnitude higher than that of the carbonate endmember most of the dissolved li 90 is derived from silicates even in carbonate dominated catchments while the sr isotope composition of the dissolved load reflects that of the bedrock the main control on its li isotope composition is fractionation during weathering fractionation between the dissolved and suspended load in silicate dominated catchments is greatest at high altitude and lower at low altitude where weathering is more intense tributaries draining silicates have lower dissolved 7li values by 2 3 to 4 2 following the monsoon when weathering is more intense because of higher runoff and elevated temperatures our data suggest that riverine li fluxes largely reflect silicate weathering rates while riverine 7li varies with weathering intensity as rivers presently contribute 50 of the li input to the oceans seawater li concentrations and 7li show potential as proxies for global silicate weathering processes

emplacement and inflation of the al halaq al kabir lava flow field central part of the al haruj volcanic province central libya abstract numerous of lava rise plateaus and tumuli developed in the medial and distal portions of the al halaq al kabir lava flow field during the last holocene eruption in the central part of the al haruj volcanic province ahvp these inflation structures provide important data on the lava emplacement mechanism in this part of the al haruj region where the widespread occurrence of tumuli and lava rise plateaus are good indicators of the mode of emplacement we report the results of detailed measurements of the maximum and minimum diameters in plan view of 551 lava rise plateaus and 289 tumuli from the distal part of the al halaq al kabir lava field using arcgis and field observations tumuli and lava rise plateaus may be divided into subpopulations according to abrupt changes in the scaling exponents on log log plots of their frequency versus diameter using the estimated stiffness young s modulus of the basaltic rocks in the study area of 10 34 gpa numerical and analytical results show that theoretical maximum tensile stresses in the inflated upper solidified crustal layers of the developing tumuli and lava rises at tens of mega pascals mpa this theoretical stress is orders of magnitude higher than typical in situ tensile strengths of rocks 0 5 9 mpa and thus high enough to rupture the crustal layers of the lava rises and tumuli the high tensile stresses are generated during crustal doming driven by a magmatic overpressure of only about 1 mpa our results partly explain the abundance of tension fractures at the surface of the al halaq al kabir lava flow field tumuli observed in the area are remarkably similar in morphology and aspect height width ratios to the flow lobe tumuli in holocene lava flow fields in iceland suggesting an analogous mechanics of formation there appears to be a coincidence between the age of an initial volcanism in the ahvp 7 9 5 3 ma and a local fauna and flora disappearance in the as sahabi area ne sirt basin during messinian zanclean time 7 5 to 5 ma we speculate that the volcanism may have had a local negative environmental impact and contributed to the reported decline in the fauna and flora in the area

joint inversion of regional and teleseismic earthquake waveforms a least squares joint inversion technique for regional and teleseismic waveforms is presented the mean square error between seismograms and synthetics is minimized using true amplitudes matching true amplitudes in modeling requires meaningful estimates of modeling uncertainties and of seismogram signal to noise ratios this also permits calculating linearized uncertainties on the solution based on accuracy and resolution we use a priori estimates of earthquake parameters to stabilize unresolved parameters and for comparison with a posteriori uncertainties we verify the technique on synthetic data and on the 1983 borah peak idaho m 7 3 earthquake we demonstrate the inversion on the august 1954 rainbow mountain nevada m 6 8 earthquake and find parameters consistent with previous studies

faulting processes of the 1956 san miguel baja california earthquake sequence body waveform modeling is used to determine the source processes of three large earthquakes magnitude 6 8 6 4 6 3 occurring between february 9 and 15 1956 along the san miguel fault in northern baja california mexico results of the modeling suggest that the mainshock on february 9 was responsible for the 20 km of surface faulting observed during the sequence although previous researchers have suggested a complex rupture history for the mainshock uncertainty estimates of source time function shape indicate single or double source models fit the observed waveforms equally well the february 15 aftershock however appears to have consisted of two events locations and focal mechanisms obtained for the three events suggest that the rupture process may have been controlled by cross faults to the main trace of the san miguel fault the good correlation between source parameter information and the surficial geology geometry of the san miguel fault zone demonstrates the usefulness of waveform modeling studies in unravelling the complexities of historic multi event earthquake sequences

inversion of regional pn1 and surface wave data for source parameters of a borah peak aftershock we present results of a comparative source study on one of the largest aftershocks of the borah peak idaho earthquake series the mechanism of this event had been previously studied using first motions and teleseismic p wave data and we report here our results from analysis of regional pn1 and surface waves the pn1 waves gave an estimate of the source duration near 5 sec in agreement with the teleseismic p waves both the source duration and the effect of surface wave dispersion through laterally heterogeneous crustal structures must be accounted for in the moment tensor inversions of intermediate period surface waves all data sources both long period and short gave consistent source mechanisms and the long periods also yield three independent and consistent estimates of the seismic moment the results demonstrate the promise of formal source parameter retrieval techniques applied to regional data for the study of earthquakes with magnitudes below the magnitude threshold of teleseismic source determinations

deflection of oceanic transform motion at a continental margin as deduced from waveform inversion of the 1939 accra ghana earthquake abstract waveform inversion of teleseismic p waves of the 1939 accra ghana earthquake m 6 5 suggests that the earthquake was composed of two events the smaller event m 6 1 occurring 9 5 s before the onset of the larger m 6 4 event the smaller event has a focal mechanism that suggests it occurred immediately north of the intersection of the akwapim and coastal boundary fault inversion results also indicate that the larger event could not have occurred on the reactivated akwapim fault system as suggested by previous researchers instead the larger event appears to have occurred along a strike slip fault that parallels the coastline of ghana these results along with the trend of historic earthquakes indicate that not all the motion along the romanche or chain fracture zones is being transmitted inland along the akwapim fault system but that some is being deflected tangentially along a fault that parallels the ghana coastline

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

bleached chondrules evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites we present the first detailed study of a population of texturally distinct chondrules previously described by kurat 1969 christophe michel levy 1976 and skinner et al 1989 that are sharply depleted in alkalis and al in their outer portions these bleached chondrules which are exclusively radial pyroxene and cryptocrystalline in texture have porous outer zones where mesostasis has been lost bleached chondrules are present in all type 3 ordinary chondrites and are present in lower abundances in types 4 6 they are most abundant in the l and ll groups apparently less common in h chondrites and absent in enstatite chondrites we used x ray mapping and traditional electron microprobe techniques to characterize bleached chondrules in a cross section of ordinary chondrites we studied bleached chondrules from semarkona by ion microprobe for trace elements and h isotopes and by transmission electron microscopy chondrule bleaching was the result of low temperature alteration by aqueous fluids flowing through finegrained chondrite matrix prior to thermal metamorphism during aqueous alteration interstitial glass dissolved and was partially replaced by phyllosilicates troilite was altered to pentlandite but pyroxene was completely unaffected calcium rich zones formed at the inner margins of the bleached zones either as the result of the early stages of metamorphism or because of fluid chondrule reaction the mineralogy of bleached chondrules is extremely sensitive to thermal metamorphism in type 3 ordinary chondrites and bleached zones provide a favorable location for the growth of metamorphic minerals in higher petrologic types the ubiquitous presence of bleached chondrules in ordinary chondrites implies that they all experienced aqueous alteration early in their asteroidal histories but there is no relationship between the degree of alteration and metamorphic grade a correlation between the oxidation state of chondrite groups and their degree of aqueous alteration is consistent with the source of water being either accreted ices or water released during oxidation of organic matter ordinary chondrites were probably open systems after accretion and aqueous fluids may have carried volatile elements with them during dehydration individual radial pyroxene and cryptocrystalline chondrules were certainly open systems in all chondrites that experienced aqueous alteration leading to bleaching

seismic exploration scale velocities and structure from ambient seismic noise 1 hz the successful surface waves retrieval in solid earth seismology using long time correlations and subsequent tomographic images of the crust have sparked interest in extraction of subsurface information from noise in the exploration seismology subsurface information in exploration seismology is usually derived from body wave reflections 1 hz which is challenging for utilization of ambient noise we use 11 h of noise recorded in the sirte basin libya first we study the characteristics of the noise we show that the bulk of the noise is composed of surface waves at frequencies below 6 hz some noise panels contain nearly vertically traveling events we further characterize these events using a beamforming algorithm from the beamforming we conclude that these events represent body wave arrivals with a fairly rich azimuthal distribution having body wave arrivals in the noise is a prerequisite for body wave reflections retrieval we crosscorrelate and sum the recorded ambient noise panels to retrieve common source gathers following two approaches using all the noise and using only noise panels containing body wave arrivals likely to contribute to the reflections retrieval comparing the retrieved gathers with active seismic data we show that the two way traveltimes at short offsets of several retrieved events coincide with those of reflections in the active data and thus correspond to apexes of reflections we then compare retrieved stacked sections of the subsurface from both approaches with the active data stacked section and show that the reflectors are consistent along a line the results from the second approach exhibit the reflectors better

the origin of dark inclusions in allende new evidence from lithium isotopes aqueous and thermal processing of primordial materials occurred prior to and during planet formation in the early solar system a record of how solid materials were altered at this time is present in the carbonaceous chondrites which are naturally delivered fragments of primitive asteroids it has been proposed that some materials such as the clasts termed dark inclusions found in type iii chondrites suggest a sequence of aqueous and thermal events lithium isotopes 6li and 7li can reveal the role of liquid water in dark inclusion history during aqueous alteration 7li passes preferentially into solution leaving 6li behind in the solid phase and consequently any relatively extended periods of interaction with 7li rich fluids would have left the dark inclusions enriched in the heavier isotope when compared to the meteorite as a whole our analyses of lithium isotopes in allende and its dark inclusions reveal marked isotopic homogeneity and no evidence of greater levels of aqueous alteration in dark inclusion history

elemental and isotopic abundances of lithium in chondrule constituents in the allende meteorite abstract elemental and isotopic abundances of lithium in chondrule constituents in the allende cv3 meteorite were determined using secondary ion mass spectrometry olivines and mesostasis dominated by a feldspathic phase are depleted in li 1 g g 1 and 0 1 0 6 g g 1 respectively in contrast low ca pyroxenes and mesostasis dominated by a na rich phase are enriched in li 1 8 g g 1 and 0 4 3 5 g g 1 respectively and the interchondrule matrix is generally enriched in li 2 0 g g 1 on average the li isotopic abundance of olivine ranges from 7 li 32 to 21 the spatial distributions of elemental and isotopic abundances of li in olivines within individual chondrules exhibit no systematic pattern this suggests that the distribution of li in olivine was not disturbed during aqueous alteration or thermal metamorphism on the allende meteorite parent body although mesostasis is the last crystallizing phase from a chondrule melt and is expected to be enriched in li in the allende meteorite it is generally depleted in li we suggest that during aqueous alteration on the cv asteroid li in mesostasis was leached out by aqueous fluids the li enriched na rich mesostasis was probably produced later by infiltration of na rich fluids it seems likely that aqueous fluids sequestered alkali elements from the allende chondrite region in the cv parent asteroid although significant amounts of li are preserved in ferrous olivine in the interchondrule matrix

oxygen isotopes of chondritic components we review the oxygen isotopic compositions of chondrite components refractory inclusions chondrules and matrix and their inter and intra crystalline oxygen isotopic distributions primary oxygen isotopic compositions acquired before planetesimal accretion are easily disturbed by parent body processes such as aqueous alternation and thermal metamorphism primary or original oxygen isotopic compositions of refractory inclusions ca al rich inclusions and amoeboid olivine aggregates distribute along a slope 1 line on the three oxygen isotope diagram over the range of 60 17 o 18 o 16 o rich and 17 o 18 o rich during refractory inclusion formation on the other hand primary minerals of most chondrules have small isotopic variations and are enriched in 17 o and 18 o relative to refractory inclusions suggesting that chondrule formation occurred in 17 o 18 o rich nebular gas however rare 16 o rich chondrules have been found suggesting some overlap in the timing of formation of chondrules and refractory inclusions in the solar nebula oxygen isotopic compositions of matrix grains distribute along the slope 1 line over the same range as refractory inclusions and chondrules the similarity in oxygen isotopic distributions suggests that matrix was originally a mechanical mixture of nebular dusts co generated with chondrules and refractory inclusions presolar grains with oxygen isotopic compositions that are clearly distinct from those of solar nebular materials are a trace component of chondrite matrices based on these oxygen isotopic characteristics more than 99 5 of the solid materials in the nebula formed locally in the solar nebula and the remainder formed in interstellar space the astrophysical setting of chondrite component formation in the early solar system is also discussed refractory inclusions and 16 o rich matrix dusts formed around the inner edge of the solar nebula on the other hand most chondrules and 17 o 18 o rich matrix dusts seem to have formed elsewhere in the solar nebula efficient large scale radial mixing of the solar nebular materials may have been an essential process in the formation of chondritic planetesimals

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

micromammals from an early holocene archaeological site in southwest china paleoenvironmental and taphonomic perspectives abstract investigations of the well known paleontological and archaeological site of tangzigou in western yunnan province in 2003 and 2006 yielded plentiful mammalian remains and a large number of stone and bone artifacts among the mammalian remains were those of many micromammals representing modern taxa of scandentia insectivora and rodentia the micromammal assemblage is dominated by rodents which constitute 92 of the total number of identifiable elements murids are the most common elements followed by rhizomyids sciurids and hystricids the tangzigou deposits appear to have been created over a period of 200 300 years in the early to middle holocene judging from the tight cluster of ams radiocarbon dates between 9000 and 8745 bp based on the known habitat preferences of the living species most of the tangzigou micromammals were arboreal or dwellers of the forest floor the micromammal assemblage thus indicates that subtropical forest including bamboo dominated the environment around tangzigou the assemblage is remarkable for the near absence of very small micromammal species such as small mice this bias appears to have been introduced by humans who collected the larger bodied species of micromammals for food this interpretation is supported by the presence of a large number of burned elements especially dentaries the analysis of the larger mammals also showed that tangzigou was a place where prehistoric people gathered to butcher the hunted scavenged animals

seismicity of the denali totschunda fault zone in central alaska 1912 1988 and its relation to the 2002 denali fault earthquake sequence i have relocated m 4 5 earthquakes occurring between 1912 and 1988 and smaller magnitude earthquakes occurring between 1971 and 1988 when seismograph stations within central alaska began to increase to examine changes in seismicity preceding the 2002 denali fault earthquake sequence i have also determined focal mechanisms from first motion analysis and waveform modeling for many of the m 5 5 events limited phase and waveform information for the 1912 m s 7 2 earthquake are consistent with rupture at shallow depth on a right lateral strike slip fault although the limited data cannot distinguish between a range of possible mechanisms most other m 4 5 earthquakes occurring within the region prior to 1989 represent thrust reverse faulting or strike slip faulting adjacent to the denali fault system these results highlight the role thrust faulting plays in the deformation of the denali region stress analysis shows continuity in the direction of maximum compressive stress 1 between the western denali fault zone and the castle mountain fault upper cook inlet region suggesting the crust is behaving rigidly to transfer compression to the denali fault zone and faults located to the north

source processes of large m 6 5 earthquakes of the southeastern caribbean 1926 1960 we have conducted body waveform modeling studies of 13 historic earthquakes to provide a better understanding of the long term spatial and temporal pattern of seismicity and deformation within a region extending from barbuda lesser antilles to cumana venezuela our results suggest that shallow earthquakes 50 km deep along the south american caribbean plate margin reflect right lateral and extensional deformation intermediate depth events 100 km show left lateral strike slip motion beneath the paria peninsula of venezuela in the lesser antilles the 1960 barbuda and 1946 martinique earthquakes appear to be interplate thrust events however the greatest moment release in the region has occurred at intermediate depths as a mixture of normal and strike slip faulting generally along trends oblique to the arc the deformation rate estimated from the seismic moment release between 1926 and 1960 is only 1 to 10 of the estimated plate convergence rate for the region

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

lithium isotopes as indicators of meteorite parent body alteration hydrothermal processing on planetesimals in the early solar system produced new mineral phases including those generated by the transformation of anhydrous silicates into their hydrated counterparts carbonaceous chondrites represent tangible remnants of such alteration products lithium isotopes are known to be responsive to aqueous alteration yet previously recognized variability within whole rock samples from the same meteorite appears to complicate the use of these isotopes as indicators of processing by water we demonstrate a new way to use lithium isotopes that reflects aqueous alteration in carbonaceous chondrites temperature appears to exert a control on the production of acetic acid soluble phases such as carbonates and poorly crystalline fe oxyhydroxides temperature and degree of water rock interaction determines the amount of lithium isotope fractionation expressed as the difference between whole rock and acetic acid leachable fractions using these features the type 1 chondrite orgueil 7li whole rock 4 3 7li acetic whole 1 2 can be distinguished from the type 2 chondrites murchison 7li whole rock 3 8 7li acetic whole 8 8 and carbonate poor tagish lake 7li whole rock 4 3 7li acetic whole 9 4 this initial study suggests that lithium isotopes have the potential to reveal the role of liquid water in the early solar system

the fate of moderately volatile elements in impact events lithium connection between the ries sediments and central european tektites lithium abundances and isotope compositions are presented for a suite of sediments from the surroundings of the ries impact structure paralleled by new li data for central european tektites moldavites from several substrewn fields south bohemia moravia cheb basin lusatia including a specimen from the newly discovered substrewn field in poland the data set was supplemented by three clay fractions isolated from sedimentary samples moldavites measured in this study show a very narrow range in 7li values 0 6 to 0 3 relative to l svec and li contents 23 9 48 1 ppm this contrasts with sediments from the ries area which show remarkable range in li isotope compositions from 6 9 to 13 4 and li contents 0 6 256 ppm the osm sediments which based on chemical similarity formed the major part of moldavites show a range in 7li values from 2 0 to 7 9 and li contents from 5 8 to 78 9 ppm therefore the formation of moldavites was apparently accompanied by large scale mixing paralleled by chemical and isotope homogenization of their parent matter the proposed li mixing model indicates that sands clayey sediments and low volumes of carbonates are the major components for tektite formation whereas residual paleokarst sediments could have been a minor but important component for a subset of moldavites striking homogenization of li in tektites combined with limited li loss during impacts may suggest that moderately volatile elements are not scavenged and isotopically fractionated during large scale collisions which is consistent with recent models in general whether homogenization of bodies with distinct li isotope systematics takes place or collision of bodies with similar li systematics operates cannot be resolved at present stage but li isotope homogeneity of solar system planets and asteroidal bodies tentatively implies the latter

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

source parameters of earthquakes along the coastal margin of west africa and comparisons with earthquakes in other coastal margin settings abstract the coastal margins of western africa and most of the eastern americas are considered to be stable continental interiors where large earthquakes occur infrequently since these regions have similar geologic and tectonic histories it might seem reasonable to expect similarities between their large earthquakes on the other hand current plate forces acting on these regions differ and may lead to regional differences in earthquakes to examine the similarities of coastal margin earthquakes we first determined the source parameters for six earthquakes of m 5 5 occurring along the coastal margin of west africa a region that has not previously been studied in detail results of this analysis indicate that the earthquakes are shallow 8 15 km strike slip events along high angle faults dips generally 80 with nodal planes having orientations similar to those of faults mapped in the exposed precambrian basement five out of seven events show complexities in their source time functions east of the cameroon line most p axes trend northeast southwest to east west earthquakes west of the cameroon line show less coherency of stress field with p axes for onshore events trending northwest southeast and for offshore events north south to northeast southwest in contrast m 5 5 earthquakes of the eastern coastal margin of north and south america have reverse mechanisms with more moderate dips on nodal planes 45 70 and over 50 have east west oriented p axes which reflect stresses caused by the motion of north and south america relative to europe and africa in north america earthquakes appear to occur on faults that cannot be associated with surficial geology occur shallower or deeper than west african events and have shorter rupture lengths for the equivalent moment these differences suggest that west african events may not serve as useful analogs for events expected along the american coastal margin

developments in the understanding and application of lithium isotopes in the earth and planetary sciences the significant relative mass difference c 16 between the two stable isotopes of li approximately 6li 7 5 7li 92 5 coupled with broad elemental dispersion in earth and planetary materials makes this a system of considerable interest in fingerprinting geochemical processes determining mass balances and in thermometry natural mass fractionation in this system is responsible for c 6 variation among materials examined to date fig 1 although the modern era of li isotope quantification has begun there are still many questions about the li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered e g hoefs 1997 figure 1 summary of lithium isotopic compositions of earth and planetary materials filled bars are solid samples open bars are liquids see text for references and details the purpose of this chapter is to summarize the current understanding of li isotopes in geo and cosmochemical systems and to indicate 1 where li isotopes have a high probability of adding new understanding of these systems 2 where some of the more significant deficits in knowledge exist the small but burgeoning li isotope community has not yet compiled the volume of peer reviewed literature needed to adequately assess even that which has been studied to date as a result significant portions of this chapter are based on data reported in abstracts and as such are more than normally subject to revisions over time this chapter is anticipated to serve as a starting point for those interested in research incorporating li isotope geochemistry or in understanding the state of extant research experiments in li isotope fractionation knowledge of significant li isotopic fractionation during basic chemical processes is long standing the early experiments by taylor and urey 1938 in which li isotopes were fractionated by incomplete extraction of an aqueous solution from a zeolite exchange

bridging onshore and offshore present day kinematics of central and eastern mediterranean implications for crustal dynamics and mantle flow we present a new kinematic and strain model of an area encompassing the calabrian and hellenic subduction zones western anatolia and the balkans using haines and holt s 1993 method we derive continuous velocity and strain rate fields by interpolating geodetic velocities including recent gps data in the balkans relative motion between stable eurasia and the western aegean sea is gradually accommodated by distributed n s extension from southern balkans to the eastern corinth gulf so that the westward propagation of the north anatolian fault naf throughout continental greece or peloponnesus is not required we thus propose that the naf terminates in north aegean and that n s extension localized in the corinth gulf and distributed in southern balkans is due to the retreat of the hellenic slab the motion of the hyblean plateau apulia peninsula south adriatic sea ionian basin and sirte plain can be minimized by a single rigid rotation around a pole located in the sirte plain compatible with the opening the pelagian rifts 2 2 5 mm yr and seismotectonics in libya we interpret the trenchward ultraslow motion of the calabrian arc 2 2 5 mm yr as pure collapse the calabrian subduction being now inactive in the absolute plate motion reference frame our modeled velocity field depicts two toroidal crustal patterns located at both ends of the hellenic subduction zone clockwise in nw greece and counter clockwise in western anatolia we suggest the nw greece toroidal pattern is the surface expression of a slab tear and consequent toroidal asthenospheric flow

oxygen isotopic compositions of low feo relicts in high feo host chondrules in acfer 094 a type 3 0 carbonaceous chondrite closely related to cm with one exception the low feo relict olivine grains within high feo porphyritic chondrules in the type 3 0 acfer 094 carbonaceous chondrite have 17o 17o 0 52 18o values that are substantially more negative than those of the high feo olivine host materials these results are similar to observations made earlier on chondrules in co3 0 chondrites and are consistent with two independent models 1 nebular solids evolved from low feo low 17o compositions towards high feo more positive 17o compositions and 2 the range of compositions resulted from the mixing of two independently formed components the two models predict different trajectories on a 17o vs log fe mg olivine diagram but our sample set has too few values at intermediate fe mg ratios to yield a definitive answer published data showing that acfer 094 has higher volatile contents than co chondrites suggest a closer link to cm chondrites this is consistent with the high modal matrix abundance in acfer 094 49 vol acfer 094 may be an unaltered cm chondrite or an exceptionally matrix rich co chondrite chondrules in acfer 094 and in co and cm carbonaceous chondrites appear to sample the same population textural differences between acfer 094 and cm chondrites are largely attributable to the high degree of hydrothermal alteration that the cm chondrites experienced in an asteroidal setting

the 16 august 1931 valentine texas earthquake evidence for normal faulting in west texas the 1931 valentine texas earthquake occurred in a region near the transition from the southern basin and range rio grande rift physiographic province to the southern great plains province previous studies of this earthquake have presented focal mechanisms from first motion data supporting either pure normal or strike slip faulting with extension oriented in a southwest northeast direction nearly perpendicular to the physiographic boundary between the provinces this study presents the results of an inversion of regional and teleseismic body wave phases to determine earthquake source parameters results of the inversion suggest that the earthquake occurred at a depth of 10 km along a fault dipping 54 to the east with a strike of 10 to 20 and a rake of 155 the strike is similar to that of the southern segment of the nearby mayfield fault a fault that shows evidence for repeated movement during the quaternary seismic and geodetic information suggest unilateral rupture toward the south during the earthquake the t axis for the earthquake shows extension oriented in a northwest southeast direction a direction in agreement with the direction given by geologic stress indicators

lithium isotopes as a probe of weathering processes orinoco river abstract lithium isotopes have the potential to be effective tracers of weathering processes due to their large relative mass difference and therefore fractionation in this study an attempt is made to fill a major gap in the knowledge of li isotope fractionation during continental weathering and of the mechanisms involved finally the relationship between the suspended and dissolved material is made on a basin wide scale the orinoco basin provides a clear contrast in reaction limited and transport limited weathering regimes that has already been documented by a comprehensive study on its fluvial geochemistry edmond et al geochim cosmochim acta 60 1996 2949 2976 edmond et al geochim cosmochim acta 59 1995 3301 3325 conspicuous in our new results is the difference in 6li of the dissolved load between the andean 30 to 22 and shield 22 to 7 tributaries while the 6li of the suspended load is similar between the two to a first approximation during superficial weathering in high relief tectonically active terrains the dissolved load is high in li and isotopically heavy more negative 6li whereas in stable shield regions the concentrations are low and isotopically light in proportion to the increasing degree of weathering

seismotectonics and relative plate motions in the scotia sea region source parameter inversion of p and sh waveforms and amplitudes for 20 shallow earthquakes using a singular value decomposition technique provides important constraints on the tectonics and relative plate motions of the scotia sea region the derived focal mechanisms show both thrust and strike slip faulting along the north scotia ridge and normal and strike slip faulting along the south scotia ridge two thrust faulting mechanisms south of tierra del fuego indicate diffuse convergence of the antarctic plate along the western margin of the scotia plate earthquakes are consistent with active subduction and back arc spreading along the south shetland trench and bransfield strait the depths of two earthquakes 35 km and 55 km and one shallow thrust faulting event suggest continued subduction along the south shetland trench but the underthrusting is largely aseismic due to the young plate age and slow subduction rate the magnitude and depth of normal faulting earthquakes along bransfield strait and the south scotia ridge are suggestive of diffuse extension rather than typical organized mid ocean spreading which is generally associated with smaller and shallower earthquakes eight strike slip and thrust faulting events provide well constrained slip vectors showing scotia plate motion relative to the surrounding larger plates using a four plate model scotia sc south sandwich ss antarctica an and south america sa and a fixed sa an euler vector we inverted these data together with published centroid moment tensor slip vectors along the south sandwich trench and published marine magnetic data from the ss back arc spreading center to derive the first quantitative plate motion model for the scotia region the sc sa euler pole is located in the south atlantic and shows large latitudinal uncertainties the sc an pole is better constrained and located in the weddell sea these results predict left lateral strike slip motion with a component of compression along the north scotia ridge left lateral strike slip with a component of extension along the south scotia ridge and east west compression in drake passage although no rate data have been published connecting the scotia plate with the global plate system euler vector magnitudes are obtained through closure the results though poorly constrained suggest relative motion rates of 0 5 cm yr along the north scotia ridge and 1 0 cm yr along the south scotia ridge and in drake passage

a re examination of the 1947 manix california earthquake sequence and comparison to other sequences within the mojave block the 10 april 1947 manix california earthquake m l 6 2 is the largest earthquake to have occurred in the mojave block in historic time left lateral movement was observed along the manix fault strike of n70 e following the earthquake however the large aftershocks of the sequence as located by richter and nordquist 1951 align themselves along a trend of n30 w this led richter 1958 to conclude that rupture during the main shock was along the trend of the aftershocks and that the surface faulting was a secondary feature in this study relocation of the larger aftershocks of the sequence verifies the previously observed trend of n30 w suggesting the aftershocks occurred along a fault conjugate to the manix fault body waveform modeling of the main shock indicates that it was composed of two subevents the location of the second subevent with respect to the first subevent suggests unilateral rupture to the southwest along the manix fault although the focal mechanisms of both events are consistent with either faulting along the manix fault or a conjugate fault both subevents occurred at relatively shallow depths 5 to 7 km a study of other recent earthquakes of m l 3 0 within the mojave block indicates that the majority of earthquakes in the region occur at shallow depths 7 km although the heat flow in the area is 10 to 20 mw m2 lower than in surrounding regions where deeper seismicity is present

micromammal taphonomy of el wad terrace mount carmel israel distinguishing cultural from natural depositional agents in the late natufian a taphonomic analysis of micromammal remains from the late natufian deposits of el wad terrace mount carmel israel was conducted in order to test the long standing premise of owl deposition as the primary accumulating agent the inferred taphonomic sequence was modeled within an actualistic recent comparative framework incorporating a locally derived barn owl pellet collection and an off site control assemblage of micromammal remains from the cliff overhanging the terrace the sequence was reconstructed based on multiple types of recorded taphonomic data comprising skeletal modifications breakage digestion weathering gnawing and charring and age structure evidence for post depositional processes including fluvial transport trampling and weathering was isolated and consequently the typical owl imprints were traced through the two actualistic and the archaeological assemblages based on the extent of breakage and patterning in skeletal element frequencies it was also possible to scale the preservation potential of primary data in el wad terrace as a discrete site type intermediate between true cave and open air depositional environments verifying the role of owls as principal agents of accumulation of the el wad terrace micromammal remains enabled the detection of two minor superimposed cultural patterns consumption of mole rats spalax sp by the natufians and commensalism of mice mus spp

oxygen isotopic compositions of relict and host grains in chondrules in the yamato 81020 co3 0 chondrite we report the oxygen isotope compositions of relict and host olivine grains in six high feo porphyritic olivine chondrules in one of the most primitive carbonaceous chondrites co3 0 yamato 81020 because the relict grains predate the host phenocrysts microscale in situ analyses of o isotope compositions can help assess the degree of heterogeneity among chondrule precursors and constrain the nebular processes that caused these isotopic differences in five of six chondrules studied the 17o 17o 0 52 18o compositions of host phenocrysts are higher than those in low feo relict grains the one exception is for a chondrule with a moderately high feo relict both the fayalite compositions as well as the o isotope data support the view that the low feo relict grains formed in a previous generation of low feo porphyritic chondrules that were subsequently fragmented it appears that most low feo porphyritic chondrules formed earlier than most high feo porphyritic chondrules although there were probably some low feo chondrules that formed during the period when most high feo chondrules were forming

the seismicity of chihuahua mexico and the 1928 parral earthquake abstract studies of the seismicity of chihuahua mexico and determination of source parameters for the 1928 parral earthquake suggest that the eastern portion of chihuahua is currently undergoing extension the parral earthquake has similar source parameters to other southern basin and range rio grande rift events the focal mechanism for the parral event however indicates northeast southwest oriented extension a direction that is parallel to neither the east west oriented extension seen near the us mexican bordern nor to the physiographic province boundary between the sierra madre occidental and the southern basin and range where the earthquake occurred intensity information for the parral event and the 1931 valentine texas earthquake suggests that attenuation within the region lies somewhere between relationships developed for the eastern and cordilleran portions of the usa

comparison of seismic and geodetic scalar moment rates across the basin and range province scalar moment rates estimated from a 146 year seismicity catalog agree within uncertainties with the deformation rate of the basin and range province determined by using space geodesy seismic moment rates have been estimated from a new catalog of earthquakes complete for m 5 the catalog was compiled from 15 preexisting catalogs supplemented by the review of 44 journal articles throughout the catalog compilation care was taken to obtain the moment magnitude or a reasonable and not inflated equivalent seventy six percent of the moment release occurred during 10 earthquakes of magnitude m w 6 79 the spatial distribution of earthquakes and their moment release matches the geodetic pattern of deformation all three are concentrated in a 200 km wide zone along the western boundary of the great basin with this zone widening to the north several techniques ultimately traceable to kostrov and brune are used to translate the geodetic strain rates into rates of seismic moment release the agreement between geodetic and seismic moment rate suggests that within uncertainties the rate of historic earthquakes within the basin and range province taken as a whole provides a reasonable estimate for the future rate of seismicity these results support the hypothesis that even a few years of detailed geodetic monitoring can provide a good constraint on earthquake occurrence rate estimates for large enough regions

the absence of lithium isotope fractionation during basalt differentiation new measurements by multicollector sector icp ms we report measurements of the isotopic composition of lithium in basalts using a multicollector magnetic sector plasma source mass spectrometer mc icp ms this is the first application of this analytical technique to li isotope determination external precision of multiple replicate and duplicate measurements for a variety of sample types averages 1 1 2 population the method allows for the rapid 8 min sample analysis of small samples 40 ng li relative to commonly used thermal ionization methods the technique has been applied to a suite of samples from kilauea iki lava lake hawaii the samples range from olivine rich cumulitic lava to sio2 and k2o enriched differentiated liquids and have 7li per mil deviation of sample 7li 6li relative to the l svec standard of 3 0 to 4 8 the data indicate a lack of per mil level li isotope fractionation as a result of crystal liquid fractionation at temperatures greater than 1050 c this conclusion has been tacitly assumed but never demonstrated and is important to the interpretation of li isotope results from such geochemically complex environments as island arcs

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

seismicity of the kodiak island region 1964 2001 and its relation to the 1964 great alaska earthquake earthquake relocation first motion and waveform modeling studies of m 5 5 earthquakes are used to examine the seismicity associated with the kodiak island region since the 1964 great alaska earthquake our results indicate that the most intense seismicity and moment release in this region occurred within the pacific plate and along the plate interface of the southwestern edge of the kodiak segment where slip during the 1964 mainshock was less than 5 m few earthquakes have occurred within the north american plate the intense seismicity correlates well with the northern edge of a zone of high plate interface coupling detected by global positioning system geodesy studies our studies suggest that during 1964 1974 faulting within the pacific plate was characterized by normal and normal oblique faulting however since 1974 reverse oblique faulting has become more common in the pacific plate seismic moment release has been over 6 times greater in the kodiak region than in the prince william sound cook inlet region during the past 37 years unlike the prince william sound region there is also a lack of down dip migration of seismicity since 1964 manuscript received 23 october 2001

earthquakes in the pamplona zone yakutat block south central alaska the pamplona zone is a region of complex deformation and moderate seismicity located within the yakutat block a region that has been relatively aseismic since a series of large m 7 8 earthquakes in 1899 in 1970 a sequence of moderate to large sized earthquakes occurred within the pamplona zone largest event of mw 6 7 together with a mw 6 1 event in 1958 these events are the only m 5 5 events known to have occurred in the pamplona region since 1900 thus these events give important information on internal deformational processes within the yakutat block waveform modeling of three earthquakes in april 1970 showed rupture complexity along low angle thrust faults focal depths indicate that two of the events occurred above the wrangell aleutian megathrust while the largest event may have occurred on the megathrust events in 1958 and february 1970 indicate that deformation within the western pamplona zone is occurring along high angle 60 faults with reverse oblique motion we believe the pamplona spur the easternmost part of the pamplona zone may have behaved as an asperity during the 1899 sequence the location of the spur may be influenced by a north south trending fault zone in the subducting pacific plate that appears to be responsible for the 1987 1992 gulf of alaska sequence occurring 50 to 200 km south of the pamplona zone

extensional tectonics in northern utah southern idaho u s a and the 1934 hansel valley sequence abstract the hansel valley pocatello valley region of northern utah and southern idaho is one of the most seismically active areas of the eastern basin and range study of the seismicity of this region provides insight into the crustal processes taking place near the physiographic boundary between the basin and range and the middle rocky mountains this study presents source parameters determined for the march 12 1934 hansel valley utah mainshock and largest aftershock these results are then integrated with studies of regional and local seismicity to determine better the tectonic processes currently active in the region

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

source parameters of montana earthquakes 1925 1964 and tectonic deformation in the northern intermountain seismic belt waveform modeling and first motion analysis are used to determine the source parameters of six 5 8 m 6 8 earthquakes that occurred between 1925 and 1964 within the northern intermountain seismic belt of montana results of this study suggest that the 1925 clarkston earthquake occurred along an oblique normal fault with a trend similar to the southern end of the clarkston valley fault the two largest earthquakes of the 1935 helena sequence occurred along right lateral strike slip faults with trends similar to the bald butte and helena valley faults the 1947 virginia city earthquake occurred along a northwest southeast trending segment of the madison fault movement at depth was along a fault with strike similar to that of the 1959 hebgen lake main shock a reanalysis of a m 6 0 aftershock of the 1959 hebgen lake sequence suggests the earthquake occurred at a depth of 8 km along a fault that is not seen at the surface an m 5 8 earthquake in 1964 located about 10 km from the 1959 aftershock may have occurred along steeply dipping fault planes 48 to 80 at depths of 8 to 14 km most events could be modeled as simple ruptures

historical seismicity and implications for diffuse plate convergence in the northeast indian ocean large historical earthquakes provide constraints on the geographical extent and kinematics of the slow diffuse plate boundary extending from the central indian ridge to the sumatra trench the fault parameters of pre 1963 earthquakes are derived using a grid search for the best fit between observed and synthetic body waveforms surface wave spectral amplitudes and polarity and polarization constraints and location uncertainties are determined using a bootstrap resampling method the march 9 1928 ninetyeast ridge m 7 7 event shows left lateral strike slip faulting along a plane approximately coincident with the orientation of the ninetyeast ridge two small events which occurred at the location of the 1928 event in 1980 show focal mechanisms nearly identical to that determined for the 1928 earthquake and apparently reactivated the same fault the 1928 waveforms can also be fit by a thrust faulting solution with ene striking fault planes but a variety of evidence including the recent strike slip earthquakes at the same location suggest the strike slip solution these earthquakes are located along the western scarp of the ridge and do not represent reactivation of the ninetyeast fracture zone to the east of the edifice which was a major plate boundary in the early cenozoic the january 23 1949 m 6 75 and march 22 1955 m 7 0 wharton basin earthquakes although only 350 km apart show different strike slip and thrust faulting mechanisms all earthquakes show a regionally consistent pattern of horizontal compressional stress which changes from nw se in the wharton basin to n s in the central indian basin the compressional axes are oriented perpendicular to linear gravity anomalies associated with lithospheric flexure indicating little change in stress orientation since the onset of folding seismic deformation along the diffuse boundary consists of sinistral strike slip faulting associated with n s features such as the ninetyeast ridge and the 86 e fracture zone and thrust or reverse faulting in regions between fracture zones assuming transform motion the approximate slip rate along the northern ninetyeast ridge calculated from the summed moments of earthquakes is 2 8 mm yr this value is an order of magnitude less than previous estimates and suggests that at most only a small fraction of the current relative plate motion 7 mm yr occurs along the ridge the geographic distribution of seismicity suggests that the wharton basin east of the ninetyeast ridge is nearly as seismically active as the central indian basin to the west this result along with observed long wavelength gravity anomalies in the wharton basin indicates that the india australia plate boundary intersects the sumatra trench along a diffusely deforming region several thousand kilometers long rather than along a discrete transform zone

identifying the collector evidence for human processing of the cape dune mole rat bathyergus suillus from blombos cave southern cape south africa the remains of cape dune mole rats are commonly found in archaeological sites in the cape but identifying the agents responsible for their introduction namely humans raptors or other carnivores has until now been largely speculative an examination of mole rats caught and cooked by contemporary farmworkers in the southern cape showed distinctive burning patterns on the incisors and premaxillae similar charring is observable on mole rat post cranial bones recovered from the later stone age layers at blombos cave suggesting that mole rats were brought to this site by humans cooked in the ethnographically observed manner and eaten extending this study to other archaeological sites in the cape may help identify the prehistoric collectors of these animals

indicators of aqueous alteration and thermal metamorphism on the cv parent body microtextures of a dark inclusion from allende abstract an unusual dark clast in the allende cv3 chondrite termed allende af which was previously interpreted as a primary aggregate formed in the solar nebula kurat et al 1989 palme et al 1989 was re examined our study reveals abundant evidence suggesting that it probably experienced extensive aqueous alteration and subsequent thermal metamorphism on the meteorite parent body allende af contains numerous rounded to oval shaped inclusions embedded in a dark matrix the inclusions consisting predominantly of fine grains of fe rich olivine have internal textures suggesting that they are pseudomorphs after chondrules several inclusions appear to be replaced cais veins filled with fibrous olivine grains occur abundantly in both inclusions and matrix some veins up to 4 mm in length penetrate several inclusions providing strong evidence that aqueous alteration occurred after accretion the fibrous morphology of olivine in veins and inclusions suggests that the olivine was produced by dehydration and thermal transformation of phyllosilicate that had been formed by aqueous alteration olivine grains in the matrix contain numerous micro inclusions of fe ni sulfide which were probably incorporated during transformation from phyllosilicate allende af is probably related to the fine grained variety of dark inclusions reported from cv3 chondrites that has been described as the type containing abundant porous aggregates of fe rich olivine by johnson et al 1990 many dark inclusions previously described appear to be similar in texture and mineralogy to allende af and probably experienced similar secondary process on the meteorite parent body the wide variation in texture of dark inclusions can be explained by different degrees of aqueous alteration that preceded thermal metamorphism the size distribution of chondrule pseudomorphs and the abundance of cai pseudomorphs suggest that the precursor of allende af is a cv type chondrite probably allende itself oxygen isotopic and chemical compositions are consistent with this interpretation the cv parent body has been commonly thought to have escaped major secondary processing however allende af provides evidence that extensive aqueous alteration and thermal metamorphism have occurred locally on the cv parent body

source parameters of large historical 1918 1962 earthquakes south island new zealand we have studied 18 earthquakes of m w 5 5 within the north island new zealand region to determine fault parameters for earthquake hazards and regional tectonic studies since most large m w 6 5 earthquakes in the north island occurred prior to 1961 these events provide important information to supplement studies of more recent seismicity our results indicate that no large plate interface earthquakes have occurred in the central and southern north island for the past 80 years although six strike slip earthquakes of m w 6 8 occurred within the australian upper plate during an extremely active 25 year period that began in 1917 only the m w 7 2 strike slip events were associated with surface faulting indicating the difficulties that may arise in attempting to identify active faults within this region two earthquakes m w 6 9 7 1 off the northeastern north island in 1947 appear to have occurred along the plate interface and were associated with local tsunamis having runup heights of up to 10 m two m w 6 8 events also occurred within the pacific lower plate highlighting the hazards related to intraslab events slip vectors for the earthquakes studied suggest that the majority of transcurrent motion along the plate margin is accommodated within the australian plate similar to the results obtained from studies of more recent smaller earthquakes pure thrusting occurs along the plate interface and t axes of intraslab events indicate downdip tension in the pacific plate

lithium and its isotopes in major world rivers implications for weathering and the oceanic budget abstract the outstanding problem in the lithium geochemical cycle is the lack of an isotopic mass balance in the ocean the 6li compositions of fresh basalts 4 the hydrothermal fluids derived from them average 9 and seawater significantly heavier at 32 are well understood but only very sparse river input data are available for li mass balance calculations in an attempt to rectify the situation we have measured the lithium concentrations and isotopic compositions of major world rivers draining representative geological terrains this helps both to constrain the river endmember and to understand the behavior of lithium isotopes in the continental weathering environment fluvial isotopic compositions display a very large range 6 0 to 32 2 there is no definitive relationship between 6li and lithology but in general rivers draining marine evaporites are 20 to 22 carbonates 26 to 32 black shales 26 shields 6 6 to 19 and mixed siliceous terrains 6 to 28 the flow weighted mean concentration of the measured rivers is 215 nm at 23 this updated riverine 6li value responsible for 30 of the global riverine discharge does not solve the isotopic imbalance if the measured li concentrations and isotopic compositions are representative of all rivers the presence of a yet unidentified sink with a higher fractionation factor 1 023 than determined for low temperature basalt alteration 1 019 is required for an isotopic steady state of li in the ocean authigenic clays are a possible candidate as clays are known to be enriched in both lithium and in the light isotope preferentially alternatively the hydrothermal flux must be much less than half of that estimated by the 3he inventory and the oceanic budgets for 87sr 86sr and mg the relationship of 6li to the major ions and 87sr 86sr suggests that the important processes affecting river dissolved lithium isotopic compositions are fractionation between solution and secondary minerals and thus the intensity of weathering

lithium systematics in howardite eucrite diogenite meteorites implications for crust mantle evolution of planetary embryos we present lithium li abundances and isotope compositions in a suite of howardites eucrites and diogenites heds these meteorites most likely originated from asteroid vesta and were delivered to earth by a series of independent impact events the li concentrations show striking differences between li poor diogenites plus cumulate eucrites and li enriched eucrites whilst howardites have li abundances intermediate between eucrites and diogenites contrary to li elemental inter group differences li isotope compositions are irresolvable among these individual groups of hed meteorites despite their wildly distinct petrography attesting to insignificant li isotope fractionation during formation of a thick basaltic crust by melting of the vestan mantle the mean li isotope composition of bulk silicate vesta is estimated at 3 7 0 6 1 intermediate to that of the earth versus mars and moon but identical with these terrestrial bodies within uncertainty this further validates largely homogeneous inner solar system solids from the li isotope perspective and supports the lack of loss of moderately volatile elements from planetary embryos during their magmatic histories because li does not follow depletion trends inferred from more volatile elements pasamonte eucrite has the same li isotope composition as other eucrites although it may not be directly linked to vesta these observations are also important for generating li elemental and isotope signatures in juvenile basaltic crusts of large terrestrial planets and numerous planetary embryos in the early solar system a combination of cv l chondrites may be less suitable for building vesta from li perspective but this may face sampling bias of available data and only further analyses may resolve this issue alternatively significant shift of 1 towards heavier li isotope compositions must have occurred during thermal processing of cv l 2 2 2 8 mixture in order to account for the observed li isotope systematics in hed meteorites no correlation is observed between li versus zn fe or si isotopes respectively implying unrelated processes of forming stable isotope variations observed in hed meteorites

a study of historic earthquakes of the prince william sound alaska region we have investigated the character of seismicity that occurred in the prince william sound cook inlet region during 40 years prior to the 1964 great alaskan earthquake we have relocated all events of magnitude 5 5 focal mechanisms have been determined from body waveform modeling and first motion analysis for the larger generally magnitude 6 3 events the results suggest a number of similarities and differences between pre and post 1964 mainshock seismicity similarities include the persistence of normal faulting at depths of 40 to 60 km within the subducted slab in both the tazlina glacier and columbia bay regions north of prince william sound and among deeper events within northern cook inlet differences include a higher level of shallow seismicity 40 km depth in the upper cook inlet region and north of cook inlet prior to 1964 higher levels of seismicity within the subducting plate in the south central and eastern kenai peninsula prior to 1964 and a lower level of seismicity in the offshore prince william sound region prior to 1964 much of the lower plate seismicity for the past 70 years appears to cluster immediately downdip of the 1964 asperity two of the events in this study caused notable damage modified mercalli intensity vii to viii in the anchorage area the first in 1933 m w 6 9 appears to have occurred at 9 km depth along a strike slip fault within northern cook inlet the second in 1954 m w 6 7 occurred within the subducting plate at 60 km depth beneath the northern kenai peninsula analysis of these events as well as smaller events we have studied will greatly improve models of seismic hazard for the anchorage region manuscript received 18 september 2000

mechanical interaction between volcanic systems in libya abstract the spatial distributions of monogenetic volcanoes primarily volcanic craters within the four principal volcanic provinces of libya are examined and presented on a volcano density map six main volcanic clusters have been identified referred to as volcanic systems remarkably the al haruj ahvp and nuqay nvp volcanic provinces have double peak volcano density distributions while the gharyan gvp and as sawda svp volcanic provinces have single peak volcano density distributions we interpret each volcano density peak as corresponding to a separate volcanic system so that there is a total of six systems in these four provinces there was an overlap in volcanic activity in these provinces with at least three simultaneously active we propose that each of the 6 volcanic systems was is supplied with magma from a large sill like reservoir similar in lateral dimensions to the systems clusters themselves numerical results show zones of high tensile and shear stresses between the reservoirs that coincide roughly with the main swarms of extension dykes and volcanic fissures and shear faults fractures in the areas the most recent volcanic eruptions in libya fall within the modelled high stress concentration zones primarily eruptions in the volcano waw an namus and the holocene al mashaqaq lava flow there are no known eruptions in libya in historical time but some or all the volcanic systems may have had one or more arrested historical dyke injections in particular part of the recurrent seismic events in the hun graben in the northwest libya may be related to dyke propagation and arrest if some of the inferred magma reservoirs are still fluid as is likely they pose earthquake and volcanic hazards to parts of libya particularly to the city of gharyan and zallah town as well as to many oil field operations

blombos cave southern cape south africa preliminary report on the 1992 1999 excavations of the middle stone age levels the later and middle stone age levels at blombos cave bbc were excavated over four field seasons between 1992 and 1999 here we report on the results from the middle stone age msa levels the taphonomy and depositional history of the msa levels is complex due to faulting folding and spalling careful observations during excavation have assisted in understanding some of these taphonomic and site formation processes microstratigraphic analysis currently in progress will add to this information the uppermost msa level the still bay phase contains high densities of bifacial points the fossile directeur of the still bay industry placing the still bay within the msa culture sequence has been problematic in the past because still bay assemblages are rarely found in situ and previous excavations were inadequately recorded however with the regional data discussed in the text the still bay can be securely placed before the howiesons poort dated at 65 70 ka flaked stone makes up the greatest proportion of all artefacts with the highest incidence of retouch and use of fine grained non local materials found in the still bay levels the ochre assemblage is remarkable for the mass of material compared to other msa sites finds uncommon in an msa context are two pieces of ochre from the still bay phase engraved with a geometric design a fragment of deliberately engraved bone also 28 shaped and polished bone tools recovered mainly from a phase just below the still bay blombos cave is the first site where well preserved faunal remains have been recovered in association with the still bay allowing for unique insights into human subsistence behaviour and palaeoenvironmental reconstruction large fish bones marine shells seals and dolphins attest to extensive exploitation of aquatic resources and a wide range of terrestrial animals were hunted and gathered the few human teeth recovered are heavily worn and damaged thus the issue of morphological modernity cannot be addressed the bbc findings are a useful adjunct to findings from other msa coastal sites in the southern cape especially klasies river kr and die kelders cave 1 dk1 uniquely bbc provides insights into human behaviour during a phase of the msa never before studied in detail

the 1911 m 6 6 calaveras earthquake source parameters and the role of static viscoelastic and dynamic coulomb stress changes imparted by the 1906 san francisco earthquake the occurrence of a right lateral strike slip earthquake in 1911 is inconsistent with the calculated graphic 1 static stress decrease imparted by the 1906 rupture at that location on the calaveras fault and 5 yr of calculated post 1906 viscoelastic rebound does little to reload the fault we have used all available first motion body wave and surface wave data to explore possible focal mechanisms for the 1911 earthquake we find that the event was most likely a right lateral strike slip event on the calaveras fault larger than but otherwise resembling the 1984 m w 6 1 morgan hill earthquake in roughly the same location unfortunately we could recover no unambiguous surface fault offset or geodetic strain data to corroborate the seismic analysis despite an exhaustive archival search we calculated the static and dynamic coulomb stress changes for three 1906 source models to understand stress transfer to the 1911 site in contrast to the static stress shadow the peak dynamic coulomb stress imparted by the 1906 rupture promoted failure at the site of the 1911 earthquake by 1 4 5 8 bar perhaps because the sample is small and the aftershocks are poorly located we find no correlation of 1906 aftershock frequency or magnitude with the peak dynamic stress although all aftershocks sustained a calculated dynamic stress of 3 bar just 20 km to the south of the 1911 epicenter we find that surface creep of the calaveras fault at hollister paused for 17 yr after 1906 about the expected delay for the calculated static stress drop imparted by the 1906 earthquake when san andreas fault postseismic creep and viscoelastic relaxation are included thus the 1911 earthquake may have been promoted by the transient dynamic stresses while calaveras fault creep 20 km to the south appears to have been inhibited by the static stress changes 1 embed inline graphic 1 gif

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

sodium metasomatism in chondrules in co3 chondrites relationship to parent body thermal metamorphism we have studied the mineralogy and petrology of mesostases of 783 type i chondrules in seven co3 chondrites that range in petrologic subtype from 3 0 to 3 7 chondrule mesostases in the co chondrite of subtype 3 0 consist mainly of primary glass and plagioclase while chondrule mesostases in the co chondrites of higher subtypes 3 2 3 7 contain various amounts of nepheline in addition to glass and plagioclase nepheline has replaced glass and plagioclase forming finegrained aggregates and thin parallel lamellar intergrowths with plagioclase the nephelinization has proceeded preferentially from the outer margins of chondrules toward the inside although the degree of nephelinization differs widely among chondrules in each of the metamorphosed chondrites our modal analyses and bulk chemical analyses of individual mesostases indicate that the amounts of nepheline in chondrules systematically increase with the increasing petrologic subtype of the host chondrites nepheline also has a tendency to increase in grain size with increasing petrologic subtype we conclude that nepheline in chondrules in the co3 chondrites has formed largely as a result of effects related to heating on the meteorite parent body we suggest that nepheline initially formed as hydrous nepheline under the presence of aqueous fluids and subsequently was dehydrated after exhaustion of aqueous fluids the degree of hydrothermal activity must have increased with increasing degree of heating and thus chondrules in more thermally metamorphosed chondrites produced larger amounts of nepheline the results imply that co3 chondrites have gone through lowgrade aqueous alteration and subsequent dehydration at the early stage of heating on the meteorite parent body

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

graben hydrocarbon occurrences and structural style major hydrocarbon occurrences types of traps and structural styles have been synthesized from the sirte basin the suez and viking grabens and from other normal faulted regions hydrocarbons occur in a stacked succession of one or more basins pregraben graben fill and interior sag preservation of pregraben accumulations depends on late initiation of crustal arching and limitation of uplift to the graben shoulders furthermore a stable pregraben tectonic environment is required to ensure internal continuity of subsequent fault block closures hydrocarbon traps in the pregraben and graben fill sediments are primarily dependent on the multidirectional orientation of normal faults tilting of fault blocks and in many cases flexing or erosion parallel with block edges the fault pattern is dominated by longitudinal faults subparallel with the graben axis and secondarily by oblique faults the direction and degree of block rotation are influenced by fault profile planar or listric degree of extension fault pattern doglegs junctions terminations downwarping of the subsequent sag basin and isostatic adjustments between large blocks fold closures result from the upward termination of faults into forced folds which may be accentuated by drag during renewed faulting passive drape and differential compaction extend he folds to shallower depths because they form along block edges the flexures have trends that mimic the multidirectional fault patterns truncation traps are usually developed from the erosional retreat of fault scarps and they can also mimic the fault patterns where the sedimentary succession is complete an interior sag basin is superimposed across the graben its lower part is structured mostly by drape and differential compaction across the underlying graben fault blocks and fault block topography the upper part is usually an unsegmented syncline and hydrocarbon traps at this level include depositional buildups reefs turbidite mounds and salt diapirs or other structures caused by superimposed deformation unrelated to graben tectonics

the seismicity seismotectonics and earthquake hazards of libya with detailed analysis of the 1935 april 19 m 7 1 earthquake sequence summary we have investigated the seismicity of libya in order to understand better the earthquake hazards the tectonics of the region and the present day evolution of the sirt basin we first relocated all events occurring between 1931 and 1988 using a bootstrap location technique we then determined focal mechanisms from firstmotion data finally we used waveform modelling techniques to determine source parameters for the 1935 main shock and its two largest aftershocks relocation of the 1930s events are in some cases significantly different from those given by the international seismological summary iss the first motion results suggest a combination of strike slip and normal faulting for the 1935 and 1939 sequences the waveform modelling results of the 1935 mainshock suggest a strike slip mechanism with one fault plane similar to the strike of the eastern edge of the hun graben about 5 hr after the mainshock an aftershock mb 6 0 occurred about 40 km to the south which was followed about 9 hr later by another aftershock mb 6 4 in the same area waveform modelling results for this earthquake sequence suggest focal depths ranged from 15 21km with rupture lengths of 14 16 km an average displacement of 1 8 m is estimated for the mainshock but no surface rupture has been noted for the event in the vicinity of the hun graben area the number of large earthquakes that have been reported through history is an indication that the area is seismically active most of the activity appears to be concentrated along the eastern margin of the nw se trending hun graben the focal mechanisms suggest that the maximum compressive stress in northwestern libya is oriented wnw in the north eastern part of the country the stress direction changes to a more ne sw orientation as evidenced by the 1963 february 21 al marj and the 1967 al jabal al akhdar mainshocks

cyrenaican shock absorber and associated inversion strain shadow in the collision zone of northeast africa far field compressional stresses resulting from arc collisions with the northeast coast of africa arabia propagated across the african plate in the santonian ca 84 ma and later similar pulses occurred through much of the cenozoic waves of inversion related features including folds thrusts and igneous activity developed during the compressional events structures generated were uneven in intensity and distribution and were commonly concentrated in existing rifts because of the irregular shapes of the north african continental margin and associated inboard basins cyrenaica underwent the most severe shortening although deformation extended eastward from libya to the levant areas south and southeast of cyrenaica the sirt basin and the far western desert of egypt underwent very little shortening because they occupied a regional strain shadow the eastern region of the western desert and sinai which were not sheltered by the stress absorbing cyrenaica inversion recorded strong compressional deformation synchronous with that in cyrenaica as closure of the mediterranean continues cyrenaica will become an indenter comparable to those of other orogenic belts the detailed tectonic evolution of individual northeast african basins has depended on their positions in relation to the cyrenaican strain shadow no single subsidence and paleostress history reflects the complete regional development of the converging mediterranean north african margin

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

origin of magnetite in oxidized cv chondrites in situ measurement of oxygen isotope compositions of allende magnetite and olivine magnetite in the oxidized cv chondrite allende mainly occurs as spherical nodules in porphyritic olivine po chondrules where it is associated with ni rich metal and or sulfides to help constrain the origin of the magnetite we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in po chondrules of allende by an in situ ion microprobe technique five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18o values from 4 8 to 7 1 and delta 17o values from 2 9 to 6 3 seven coexisting olivine grains have oxygen isotopic compositions from 0 9 to 6 3 in delta 18o and from 4 6 to 7 9 in delta 17o the delta 17o values of the magnetite and coexisting olivine do not overlap they range from 0 4 to 2 6 and from 4 0 to 5 7 respectively thus the magnetite is not in isotopic equilibrium with the olivine in po chondrules implying that it formed after the chondrule formation the delta 17o of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas we infer that the magnetite formed on the parent asteroid by oxidation of metal by h2o which had previously experienced minor o isotope exchange with fine grained silicates

evidence for high temperature fractionation of lithium isotopes during differentiation of the moon lithium isotope and abundance data are reported for apollo 15 and 17 mare basalts and the lapaz low ti mare basalt meteorites along with lithium isotope data for carbonaceous ordinary and enstatite chondrites and chondrules from the allende cv3 meteorite apollo 15 low ti mare basalts have lower li contents and lower 7li 3 8 1 2 all uncertainties are 2 standard deviations than apollo 17 high ti mare basalts 7li 5 2 1 2 with evolved lapaz mare basalts having high li contents but similar low 7li 3 7 0 5 to apollo 15 mare basalts in low ti mare basalt 15555 the highest concentrations of li occur in late stage tridymite 20 ppm and plagioclase 11 3 ppm with olivine 6 1 3 8 ppm pyroxene 4 2 1 6 ppm and ilmenite 0 8 0 7 ppm having lower li concentrations values of 7li in low and high ti mare basalt sources broadly correlate negatively with 18o 16o and positively with 56fe 54fe low ti 7li 4 56fe 0 04 18o 5 7 high ti 7li 6 56fe 0 18 18o 5 4 lithium does not appear to have acted as a volatile element during planetary formation with subequal li contents in mare basalts compared with terrestrial martian or vestan basaltic rocks observed li isotopic fractionations in mare basalts can potentially be explained through large degree high temperature igneous differentiation of their source regions progressive magma ocean crystallization led to enrichment in li and 7li in late stage liquids probably as a consequence of preferential retention of 7li and li in the melt relative to crystallizing solids lithium isotopic fractionation has not been observed during extensive differentiation in terrestrial magmatic systems and may only be recognizable during extensive planetary magmatic differentiation under volatile poor conditions as expected for the lunar magma ocean our new analyses of chondrites show that they have 7li ranging between 2 5 and 4 the higher 7li in planetary basalts than in the compilation of chondrites 2 1 1 3 demonstrates that differentiated planetary basalts are on average isotopically heavier than most chondrites

seismicity of the prince william sound region for over thirty years following the 1964 great alaskan earthquake in this paper we present results of body wave form modeling of 19 earthquakes generally m b 5 7 occurring from 1964 to 1983 in the vicinity and down dip of the large asperity within the prince william sound region that ruptured in 1964 these data are supplemented with source parameters from studies of more recent post 1980 events our results suggest that moderate earthquakes which occurred in the region between 1964 and 1984 were predominantly located in the vicinity of the prince william sound asperity and could be assigned to two groups the first group consists of events occurring above the plate interface within prince william sound along reverse faults or low angle thrusts the second group occurs at 35 to 60 km depth in the region north of prince william sound and represents normal to normal oblique faulting within the subducted pacific crust or upper mantle these earthquakes occur below the northern edge of the 1964 asperity in a region where the subducting plate undergoes a rapid change in strike and dip a third group of events occurs in cook inlet well down dip of the 1964 asperity and below the plate interface these events exhibit a variety of mechanisms and many at depths of 50 to 70 km may be associated with complexities in the shape of the downgoing slab most of the cook inlet events occurred after 1984 whereas a few events of similar magnitude have occurred in the vicinity of the prince william sound asperity since 1984

a taphonomic investigation of small vertebrate accumulations produced by the snowy owl bubo scandiacus and its implications for fossil studies abstract the action of predators such as diurnal raptors owls mammals or humans influence the nature of small vertebrate fossil assemblages but currently their taphonomic features are still poorly understood in this study we investigate the taphonomic signature of the snowy owl bubo scandiacus based on an analysis of pellets collected at breeding sites located in greenland and the canadian arctic this taxon is widely distributed through the north hemisphere and was an important predator in pleistocene times taphonomic parameters suggest that contrary to previous assumptions b scandiacus produces on average moderate digestion of incisors molars and post cranial elements and should be classed as a category 3 or category 3 4 predator according to the terminology established by andrews significant inter site variability was observed for some of the damage considered in particular digestion on incisors and a key finding is that variability and the associated statistical confidence intervals are crucial notions that should be taken into account when assessing taphonomical features in order to reliably identify the potential predator s responsible for small vertebrate fossil accumulations

faulting within the eastern baikal rift as characterized by earthquake studies earthquake relocations focal mechanism determinations waveform modeling and stress analyses using focal mechanism information are used to examine the faulting processes within the western baikal rift 95 to 108 5 results of the study show that high angle dip 70 faulting is most likely to occur in the more youthful parts of the rift and is most likely to be associated with m 4 5 events like the eastern rift nearly all earthquakes occurred on faults dipping 30 suggesting that in no part of the rift is significant deformation occurring on low angle structures focal mechanism information does not indicate there is a sharp boundary to the western rift as observed in the eastern rift less normal faulting rakes 60 to 120 occurs in the western rift than the eastern rift waveform modeling of the two largest earthquakes 1950 mondy and 1959 srednebaikal in the western rift gives focal depths of 10 to 15 km the 1959 event appears to have occurred along the eastern boundary fault on lake baikal just to the north of proval bay a feature created a m 7 1 earthquake in 1862 the 1950 event may have occurred along the southern boundary fault of the tunka depression stress orientation information indicates a near horizontal nw se to wnw ese striking 3 in the eastern part of the western rift

classification of seismic strain estimates in the mediterranean region from a bootstrap approach summary the uncertainty that may affect seismic strain estimates in the mediterranean is investigated using a distribution free numerical approach based on the bootstrap resampling technique applied to more than 2000 seismic source mechanisms of shallow earthquakes that occurred from the azores to iran in the period 1905 1999 this analysis shows that the short time interval covered by the available data set may be the main source of uncertainty on long term strain estimates since it could imply a biased representation of contributions from large earthquakes our results also indicate that as a possible consequence of this bias the condition of strain field uniformity is poorly verified in most of the zones considered the confidence limits obtained for scalar strains and directions of principal strain axes indicate that both the amount and the style of seismic deformation are poorly defined for roughly half of the zones considered mostly located in the western and central mediterranean area these results suggest that one should be cautious in using seismic strain estimates when not accompanied by satisfactorily uncertainty evaluation

contrasts between source parameters of m 5 5 earthquakes in northern baja california and southern california summary earthquake source processes are determined for four historic events that occurred in baja california between 1915 and 1954 these results are combined with previous studies of recent and historic seismicity to compare earthquake processes along the san jacinto imperial cerro prieto and northern baja fault systems of southern california and northern mexico observed regional differences in rupture complexity fault rupture lengths and aftershock foreshock activity appear to be related to variations in heat flow and total fault offset there appear to be no systematic variations in stress drop as measured from far field observations between earthquakes along the imperial cerro prieto fault zone and those within the peninsular ranges of northern baja california slip rates estimated from historical seismicity between 1915 and 1992 fall 1 5 cm yr 1 short of the estimated relative plate motion between the pacific plate and north america for this region

modeling the pnl waveforms of the fairview peak dixie valley nevada u s a earthquake sequence 1954 1959 abstract the 1954 1959 fairview peak dixie valley earthquakes produced one of the most complex and extensive sequences of faulting in the intermountain u s during historic time study of this sequence provides insight into the processes of crustal extension that are currently taking place in the basin and range province we have modeled the pnl waveforms of earthquakes of this sequence to 1 determine the source parameters for smaller m m 6 3 with the results of teleseismic studies 3 determine whether strainmeter records of pn1 waveforms can also be used to estimate source parameters source parameters obtained for the larger events from pn1 modeling are in agreement with previous studies source parameters estimated from strainmeter records also agree well with results of teleseismic analysis suggesting the pn1 strainmeter records may provide a useful addition to other studies of large earthquakes in the western u s focal mechanisms obtained from modeling the smaller earthquakes varied 10 20 in strike and rake from fault plane solutions determined from first motion studies the pn1 data support the results of previous studies that suggest the earthquakes of this sequence occurred along high angle faults dip of 40 70 with significant components of right lateral strike slip motion rakes of 135 to 145

lithium isotope compositions of chondrules cai and a dark inclusion from allende and ordinary chondrites abstract bulk carbonaceous and ordinary chondrites have distinct li isotope compositions indicating the existence of local reservoirs and distinct formation conditions in the early solar system these differences may be also recorded in the components that compose chondrites here li concentrations and li isotope compositions of 89 chondrules 10 cai and 1 dark inclusion di from the allende cv3 meteorite and from 5 ordinary chondrites of low petrologic types semarkona bishunpur saratov bjurbole and bremervorde are presented in general chondrules have highly variable li isotope compositions ranging from 7li of 8 5 to 10 whereby the mean isotope composition of chondrules separated from a single chondrite is slightly lighter than its bulk remarkable however are the differences in li concentrations between bulk chondrite and chondrules of the entire set studied here 98 of the chondrules have significantly lower li abundances in the range of 0 2 to 0 75 g g than their hosts typically around 1 5 g g our results indicate that li elemental and isotopic fractionation has not occurred extensively during chondrule formation low but highly variable li abundances as well as the relatively large range in li isotopes point to small scale heterogeneities in the chondrule forming reservoir with respect to li such a non chondritic reservoir is unique to all chondrules the compositional differences in li isotopes between bulk carbonaceous and ordinary chondrites seitz et al 2007 are likely to be the result of mixing chondrules cai and matrix in different proportions

historic earthquakes 1918 to 1923 and an assessment of source parameters along the san jacinto fault system body waveform modeling is used to determine the source parameters of two earthquakes that occurred along the northern san jacinto fault system in 1918 and 1923 the 1918 earthquake parameters are consistent with a 20 to 25 km rupture along the claremont fault at a depth of 7 5 km limited data for the 1923 event are more consistent with rupture on the san jacinto fault than rupture along the san andreas fault or a buried cross fault although the greatest damage associated with the earthquake occurred closer to the san andreas fault using the results of this study and previous studies of historic earthquakes along the southern san jacinto fault the relationships between rupture length and magnitude focal depth and heat flow and other parameters are examined in an effort to estimate the source properties of future events that are expected along currently quiescent portions of the fault zone one important observation is that rupture lengths along the san jacinto fault are shorter for an equivalent moment magnitude than those along the imperial valley mexicali fault system the higher heat flow of the imperial valley region may be responsible for this difference

source characteristics of earthquakes along the southern san jacinto and imperial fault zones 1937 to 1954 abstract body waveform inversion techniques are used to study the source parameters of four earthquakes occurring between 1937 and 1954 along the southern san jacinto and imperial faults 1937 buck ridge 1940 imperial valley 1942 borrego mountain and 1954 salada wash events all earthquakes had simple rupture histories with the exception of the 1940 imperial valley main shock which consisted of at least four subevents whose relative locations indicate unilateral rupture toward the southeast earthquakes in regions of high heat flow 80 mw m 2 had focal depths near the base of the seismogenic zone 8 to 10 km the 1937 buck ridge earthquake located in a region of lower heat flow however appears to have occurred at a shallow 3 2 km depth the location mechanism and aftershock distribution for the 1942 borrego mountain earthquake suggest it could have occurred along the split mountain fault a recently identified northeast trending cross fault located between the elsinore and coyote creek faults or along an unnamed fault that parallels the trend of the coyote creek fault moment and rupture length estimates obtained from this study agree well with estimates obtained in previous studies that used different data sets

behaviour of li isotopes during continental weathering the bidar laterite profile india weathering of large basaltic provinces is a major sink of atmospheric carbon dioxide and is also an important part of the geochemical cycle of many other elements this study aims to improve our understanding of basaltic weathering by analysis of trace elements and li isotopes in a lateritic profile developed upon the deccan traps flood basalt at its base the profile consists of unaltered basalt that has a li concentration and 7li value of 5 ppm and 2 5 respectively which is upwards progressively altered to a highly weathered laterite iron rich residuum at the surface high concentrations of fe2o3 85 wt at 11 m depth indicate the presence of a palaeowatertable the transition metals the rare earth elements rees and u are also strongly enriched in this horizon whereas fluid mobile elements such as li and rb are depleted relative to the precursor basalt and the bulk 7li value is very low 5 5 a high proportion of leachable li is found in this horizon and this is enriched in 6li relative to the bulk we suggest that leaching extracts the labile weathering products and these have high 6li as 7li has been preferentially mobilised during basalt weathering throughout the rest of the profile li concentrations and li isotope values are best explained by two component mixing between the precursor basalt and aeolian material with high li and low 7li mass balance calculations show that at least 50 of the li present in the profile could have been supplied by a mineral aerosol that has a 7li value between 0 and 1 3 the depth integrated 7li value of the profile is 0 6 which suggests that 7li has been preferentially leached from the aerosol after its deposition the source of this aeolian material is most likely to be ancient continental crust it is possibly derived from archaen proterozoic terrain to the south and southeast of the deccan and or material from central asia similar to that which forms chinese loess and which is supplied to the north pacific basin

the primitive matrix components of the unique carbonaceous chondrite acfer 094 a tem study the mineralogical and chemical characteristics of the fine grained matrix 53 m of the unique primitive carbonaceous chondrite acfer 094 have been investigated in detail by scanning electron microscopy sem and analytical transmission electron microscopy atem generally the fine grained matrix represents a highly unequilibrated assemblage of an amorphous material small forsteritic olivines 200 300 nm low ca pyroxenes 300 400 nm and fe ni sulfides 100 300 nm the matrix is basically unaffected by secondary processes only minor amounts of serpentine and ferrihydrite as products of hydrous alteration are present texturally the amorphous material acts as a groundmass to olivines pyroxenes and sulfides mostly exhibiting rounded or elongated morphologies only very few clastic mineral grains have been found the texture and chemical composition of the amorphous material are consistent with an origin by disequilibrium condensation in either the cooling solar nebula or a circumstellar environment as such the amorphous material may be considered as a possible precursor of matrix materials in other types of chondrites the non clastic matrix olivines fo98 99 and pyroxenes en97 100 are suggested to have formed either by condensation in the solar nebula under highly oxidizing conditions or by recrystallization from the amorphous material the formation of these grains by fragmentation of chondrule components is unlikely due to chemical and microstructural reasons rapid cooling caused the observed intergrowths of clino orthoenstatite in the mg rich matrix pyroxenes although some similarities exist comparing the fine grained matrix of acfer 094 with the matrices of the unequilibrated c03 chondrite alha77307 and the unique type 3 chondrite kakangari acfer 094 remains unique since it contains the highest measured concentrations of circumstellar sic and the second highest of diamond highest is orgueil it seems reasonable to suggested that at least parts of the amorphous material in the fine grained matrix may be of circumstellar origin