small scale deformations associated with the 1992 landers california earthquake mapped by synthetic aperture radar interferometry phase gradients the landers earthquake mw 7 3 occurred on june 28 1992 and ruptured nearly 100 km of previously mapped and unmapped faults in the mojave desert we use synthetic aperture radar interferometry insar to examine the cumulative surface deformation between april 24 and august 7 1992 in a 100 100 km region surrounding the northern portion of the earthquake rupture also we introduce a technique for manipulating sar interferograms to extract short wavelength displacement information this technique involves computation and subsequent combination of interferometric phase gradient maps the insar results show significant deformation signatures associated with faults fractures dry lake beds and mountainous regions within 75 100 km of the main rupture using the phase gradient method we are able to extract small scale deformation patterns near the main rupture many of the preexisting mapped faults within 50 km of the main rupture experienced triggered slip these include the old woman lenwood johnson valley west calico and calico faults the insar results also indicate right lateral offsets along secondary fractures trending n ne within the left lateral zone of shear between the main rupture and the johnson valley fault additionally there are interesting interferogram fringe signatures surrounding troy dry lake and coyote dry lake that are related to deformation of dry lake beds

geochemical features of fe mn micronodules in deep sea sediments of the western north pacific ocean potential for co product metal extraction from rey rich mud abstract rare earth element and yttrium rey rich mud around minamitorishima island japan in the western north pacific ocean has received significant attention as a novel rey resource in rey rich muds industrially critical metals such as co ni and mo occur in relatively high concentrations we show that fe mn micronodules separated from rey rich muds are significantly enriched in these elements we measured co contents of almost 3000 ppm and ni contents that exceed 39 000 ppm through experiments we demonstrated that reductive chemical leaching can be used to extract major portions generally 80 of the metals associated with fe mn oxyhydr oxides from rey rich muds the fe mn micronodules were of an oxic diagenetic origin a simple mass balance calculation indicated that the contribution of the fe mn micronodules to the bulk fe mn oxyhydr oxides in the sediment can amount to 8 50 median 18 the other metals associated with fe mn oxyhydr oxides seem to be hosted in mn microparticles probably of a hydrogenetic origin we estimate that the most promising site for rey rich mud development contains 9 3 0 6 102 t 1 6 0 1 103 t and 2 8 0 2 102 t of leachable co ni and mo respectively in 1 km2 0 10 m below seafloor these amounts account for 0 66 0 04 0 061 0 004 and 0 097 0 007 of present annual global productions of co ni and mo respectively the feasibility of extracting these metals as co products during rey rich mud development depends on the cost efficiency of the recovery process which ultimately depends on their market price in the near future

solubilities of some hydrous ree phosphates with implications for diagenesis and sea water concentrations abstract solubility product determinations suggest that the hydrous phosphates of the rare earths repo4 xh 2 o are important in controlling the sea water ree concentrations two of these solids rhabdophane p6222 and hydrous xenotime 141 amd have been synthesized at 100 c via the acid hydrolysis of the respective ree pyrophosphate the solubility products at infinite dilution were determined to be pk 0 24 5 la at 25 c 26 0 pr at 100 c 25 7 nd at 100 c and 25 5 er at 100 c on the basis of calculations involving the reaction of re3 with apatite to form the hydrous phosphate the lanthanum concentration in sea water is predicted to be about 140 pmol l laboratory experiments support the hypothesis that apatite is a substrate for reactions with dissolved ree

near real time radar interferometry of the mw 7 1 hector mine earthquake the hector mine earthquake mw 7 1 16 oc tober 1999 ruptured 45 km of previously mapped and un mapped faults in the mojave desert the ers 2 satellite imagedthemojavedeserton15septemberandagain on20 october just 4 days after the earthquake using a newly developed ground station we acquired both passes and were able to form an interferogram within 20 hours of the second overflight estimates of slip along the main rupture are 1 2 meters greater than slip derived from geological mapping the gradient of the interferometric phase reveals an inter esting pattern of triggered slip on adjacent faults as well as a 30 mm deep sink hole along interstate 40

exchange of neodymium and its isotopes between seawater and small and large particles in the sargasso sea the concentrations and isotopic ratios of nd were measured in small 1 53 m and large 53 m in situ filtered particles sediment trap material sediment and aerosol samples collected during oligotrophic and productive conditions in the sargasso sea atmospheric input is the main source of exogeneous nd into the sargasso sea based on ndal ratios in trapped material we suggest that up to 50 of atmospheric nd could dissolve at the air sea interface the concentration and isotopic composition of nd vary with both depth and the particle size neodymium concentrations of small and large particles increase with depth from 2 9 12 g g and 5 8 11 8 g g respectively at 40 m the nd signature of large particles is significantly more negative nd 0 13 1 0 2 than that of the small ones nd 0 11 7 0 3 and the particles filtered deeper below 237 m the nd 0 values for small particles match the seawater whereas the nd 0 values of large particles remain less radiogenic these differences are related to the different behaviors of the particulate fractions small particles apparently exchange nd with seawater and then sink rapidly to depth as biologically formed aggregates large particles these aggregates isolate the small particles slowing the exchange with the water to produce different signatures between large particles and seawater since these exchange processes modify the particulate nd signature the shallow radiogenic nd 0 signature observed in the surface and subsurface waters in the nw atlantic is not due to external contributions and is likely of advective origin at depth below 800 m the magnitude of the aggregation disaggregation process varies significantly with season the fraction of small particles repackaged into large aggregates can vary from 0 8 to 80 100 in productive and oligotrophic conditions respectively this seasonal variation may correspond to sinking particles of different zooplanktonic origin vertical fluxes of nd into and out of the sargasso sea as well as exchange fluxes in the water column are examined about 50 of the particulate flux from the surface is remineralized at depth a net scavenging flux of 0 8 10 4 g m2 y is required this value corresponds to a scavenging nd residence time of 1900 y considerably longer than previous estimates of global oceanic residence time of nd on the order of 400 y

role of initial stress rotations in rupture dynamics and ground motion a case study with implications for the wenchuan earthquake 1 motivated by observations in the 2008 mw 7 9 wenchuan earthquake we study effects of systematic changes in the principal stress orientation along the fault strike on rupture dynamics and ground motion using a 3 d finite element method based on anderson s theory of faulting we set up the initial stress field with rotations in stress orientations along strike for a dynamic rupture model of a shallow dipping fault we find that initial stress rotations along strike can cause dramatic changes in rupture speed and produce distinct patterns in slip distribution and peak ground motion when a mismatch unfavorable for faulting between fault geometry and initial stress orientations is encountered rupture can spontaneously stop some first order features in the wenchuan event may be partially caused by rotations in the principal stress orientation along strike such as the rupture arrest at the northeast end and two severe destruction zones in the observed seismic intensity distribution these results may have important implications for assessing seismic hazards imposed by faults with changes in the initial stress field along strike worldwide

rare earth elements and neodymium isotopes in sedimentary organic matter abstract we report rare earth element ree and neodymium nd isotope data for the organic fraction of sediments collected from various depositional environments i e rivers n 25 estuaries n 18 open ocean settings n 15 and cold seeps n 12 sedimentary organic matter som was extracted using a mixed hydrogen peroxide nitric acid solution 20 h2o2 0 02 m hno3 after removal of carbonate and oxy hydroxide phases with dilute hydrochloric acid 0 25 m hcl a series of experimental tests indicate that extraction of sedimentary organic compounds using h2o2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates however this contamination is expected to be minor for ree because measured concentrations in h2o2 leachates are about two orders of magnitude higher than in the above mentioned phases the mean ree concentrations determined in the h2o2 leachates for samples from rivers estuaries coastal seas and open ocean settings yield relatively similar levels with ree 109 86 ppm mean s n 58 the organic fractions leached from cold seep sediments display even higher concentration levels 285 150 ppm mean s n 12 the h2o2 leachates for most sediments exhibit remarkably similar shale normalized ree patterns all characterized by a mid ree enrichment compared to the other ree this suggests that the distribution of ree in leached sedimentary organic phases is controlled primarily by biogeochemical processes rather than by the composition of the source from which they derive e g pore river or sea water the nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions in contrast the som extracted from marine sediments display end values that typically range between the end signatures for terrestrial organic matter inferred from the analysis of the sedimentary detrital fractions and marine organic matter inferred from the analysis of local surface seawater a notable exception is the case of organic matter om fractions leached from cold seep sediment samples which sometimes exhibit end values markedly different from both terrigenous and surface seawater signatures this suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes recycling pore water ree characterized by a distinct isotopic composition overall our results confirm that organic matter probably plays an important role in the oceanic ree budget through direct scavenging and remineralization within the water column both the high ree abundances and the shape of shale normalized patterns for leached som also suggest that om degradation in sub surface marine sediments during early diagenesis could control to a large extent the distribution of ree in pore waters benthic fluxes of organic bound ree could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins neodymium isotopes could provide useful information for tracing the origin terrestrial versus marine and geographical provenance of organic matter with potential applications in paleoceanography in particular future studies should further investigate the potential of nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation

rare earth elements in the permian phosphoria formation paleo proxies of ocean geochemistry abstract the geochemistry of deposition of the meade peak member of the phosphoria formation mpm in southeast idaho usa a world class sedimentary phosphate deposit of permian age that extends over 300 000 km2 is ascertained from its rare earth element ree composition ratios of ree al2o3 suggest two sources seawater and terrigenous debris the seawater derived marine fraction identifies bottom water in the phosphoria sea as o2 depleted denitrifying suboxic most of the time and seldom sulfate reducing anoxic this interpretation is supported by earlier research that showed progressively greater ratios in the marine sediment fraction of cr ni v ni mo ni relative to their ratios in seawater for which marine cr v and mo can have a dominantly o2 depleted bottom water source and ni a photic zone largely algal source the water chemistry was maintained by a balance between bacterial oxidation of organic matter settling through the water column determined largely by primary productivity in the photic zone and the flux of oxidants into the bottom water via advection of seawater from the open ocean samples strongly enriched in carbonate fluorapatite the dominant ree host mineral have variable er sm tm sm and yb sm ratios their distribution may represent greater advection of seawater between the phosphoria sea and open ocean during deposition of two ore zones than a center waste and greater upwelling of nutrient enriched water into the photic zone however the mean rate of deposition of marine ni a trace nutrient of algae and po43 a limiting nutrient indicate that primary productivity was probably high throughout the depositional history an alternative interpretation of the variable enrichments of er tm and yb relative to sm is that they may reflect temporally variable carbonate alkalinity of open ocean seawater in permian time a more strongly negative ce anomaly for all phosphatic units than the ce anomaly of modern pelletal phosphate is further indicative of an elevated o2 concentration in the permo carboniferous open ocean as proposed by others in contrast to the depletion of o2 in the bottom water of the phosphoria sea itself the oceanographic conditions under which the deposit accumulated were likely similar to conditions under which many sedimentary phosphate deposits have accumulated and to conditions under which many black shales that are commonly phosphate poor have accumulated a shortcoming of several earlier studies of these deposits has resulted from a failure to examine the marine fraction of elements separate from the terrigenous fraction

inelastic response of compliant fault zones to nearby earthquakes 1 using dynamic rupture models we examine the response of compliant fault zones that surround pre existing faults to nearby earthquakes we find that some portions of a compliant fault zone can experience inelastic deformation due to dynamic stress perturbations while the remaining portions deform elastically inelastic response of the fault zone results in sympathetic fault parallel motion i e consistent with long term geologic slip across the fault while elastic response causes retrograde motion i e opposite to long term geologic slip in the static displacement field inelastic deformation signals along fault zones detected geodetically may be used to constrain the stress state in the crust because inelastic response occurs only when the prestress level is close to material strength which can be measured in the laboratory

variable eocene miocene sedimentation processes and bottom water redox conditions in the central arctic ocean iodp expedition 302 abstract in 2004 integrated ocean drilling program expedition 302 arctic coring expedition acex to the lomonosov ridge drilled the first central arctic ocean sediment record reaching the uppermost cretaceous 430 m composite depth while the neogene part of the record is characterized by grayish yellowish siliciclastic material the paleogene part is dominated by biosiliceous black shale type sediments the lithological transition between paleogene and neogene deposits was initially interpreted as a single sedimentological unconformity hiatus of 26 ma duration separating eocene from miocene strata more recently however continuous sedimentation on lomonosov ridge throughout the cenozoic was proclaimed questioning the existence of a hiatus in this context we studied the elemental and mineralogical sediment composition around the paleogene neogene transition at high resolution to reconstruct variations in the depositional regime e g wave current activity detrital provenance and bottom water redox conditions already below the hiatus mineralogical and geochemical proxies imply drastic changes in sediment provenance and or weathering intensity in the hinterland and point to the existence of another earlier gap in the sediment record the sediments directly overlying the hiatus the zebra interval are characterized by pronounced and abrupt compositional changes that suggest repeated erosion and re deposition of material regarding redox conditions euxinic bottom waters prevailed at the eocene lomonosov ridge and became even more severe directly before the hiatus with detrital sedimentation rates decreasing authigenic trace metals were highly enriched in the sediment this continuous authigenic trace metal enrichment under persistent euxinia implies that the arctic trace metal pool was renewed continuously by water mass exchange with the world ocean so the eocene arctic ocean was not fully restricted above the hiatus extreme positive ce anomalies are clear signs of a periodically well oxygenated water column but redox conditions were highly variable during deposition of the zebra interval significant mn enrichments only occur above the zebra interval documenting the miocene establishment of stable oxic conditions in the arctic ocean in summary extreme and abrupt changes in geochemistry and mineralogy across the studied sediment section do not suggest continuous sedimentation at the lomonosov ridge around the eocene miocene transition but imply repeated periods of very low sedimentation rates and or erosion

marinoan aged red beds at shennongjia south china evidence against global scale glaciation during the cryogenian abstract the continuous existence of the marinoan ice age a late cryogenian panglaciation snowball earth is challenged by the occurrences of widespread glacial marine and nonglacial deposits consisting of stratified diamictite laminated siltstone and claystone and even carbonates which indicate an episode of partial deglaciation red beds that commonly accompany these glacial marine and nonglacial deposits have not received enough attention to date the middle nantuo formation of the cryogenian marinoan epoch in the sanshengtai section shennongjia area is composed of 6 lithofacies i e green massive diamictite green laminated lithic feldspar wacke green laminated siltstone and claystone red laminated lithic feldspar wacke red crudely stratified diamictite and red laminated siltstone among them the last three constitute the red beds and are interpreted as glacial lacustrine and nonglacial deposits which can be found and roughly correlated across several continents high fe2o3 and low ce ce values in the red beds suggest a probable association between the formation of red beds and the neoproterozoic oxygenation events coincidences between the occurrences of red beds and high values of al na ti na and chemical index of alteration cia indicate the favorability of warm intervals with high weathering intensities for the formation of red beds whose presence indicates partial deglaciation during the marinoan ice age and provides a new clue to contradict the worldwide snowball earth hypothesis

influence of shimada seamount on sediment composition in the eastern tropical north pacific abstract shimada seamount is a large young volcanic edifice in the east central pacific that is not associated with any active spreading center or known hot spot the sediments on the abyssal plain surrounding shimada seamount consist of pelagic clay with ferromanganese micronodules and zeolites the pelagic clay is mostly barren of microfossils except for a few occurrences of highly corroded specimens of radiolaria and diatoms eolian terrigenous material is the dominant component of the pelagic clay to a depth of at least 8 m below sea floor with minor contributions from volcanic debris and hydrothermal and hydrogenous sources the average amount of basaltic debris is only 0 25 but concentrations are as high as 10 in some samples the average hydrothermal component metalliferous sediment is 8 8 with a maximum of about 13 at 7 5 m below sea floor in one core the hydrogenous component mostly as ferromanganese micronodules averages 4 1 with a maximum of 5 6 there is no calcareous biogenic debris and essentially no siliceous biogenic debris in the past a decrease in hydrothermal components through time may have been the result of a decrease in relative importance of hydrothermal influences or an increase in the flux of terrigenous debris transported by the northeast trade winds because volcanic activity is still active on shimada seamount or has been in the recent past the observed increase in relative abundance of terrigenous components probably was the result of increased wind transport and not decreased hydrothermal activity shimada seamount may be an important local source of metalliferous sediment in the eastern equatorial north pacific and may have been an even more important source in the past

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey summary we discuss the subsurface structure of the karadere duzce branch of the north anatolian fault based on analysis of a large seismic data set recorded by a local passcal network in the 6 months following the mw 7 4 1999 izmit earthquake seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long period oscillations in both p and s wave trains that do not exist in nearby off fault stations examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone the anomalous features in fault zone seismograms produced by events not necessarily in the fault may be referred to generally as fault zone related site effects the oscillatory shear wave trains after the direct s arrival in these seismograms are analysed as trapped waves propagating in a low velocity fault zone layer the time difference between the s arrival and trapped waves group does not grow systematically with increasing source receiver separation along the fault these observations imply that the trapping of seismic energy in the karadere duzce rupture zone is generated by a shallow fault zone layer traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3 4 km the synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m a velocity decrease relative to the surrounding rock of approximately 50 per cent and an s wave quality factor of 10 15 the results are supported by large 2 d and 3 d parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones the inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower type structure the motion amplification associated with fault zone related site effects increases the seismic shaking hazard near fault zone structures the effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large

nonlinear dynamic failure process of tunnel fault system in response to strong seismic event strong earthquakes and faults have significant effect on the stability capability of underground tunnel structures this study used a 3 dimensional discrete element model and the real records of ground motion in the wenchuan earthquake to investigate the dynamic response of tunnel fault system the typical tunnel fault system was composed of one planned railway tunnel and one seismically active fault the discrete numerical model was prudentially calibrated by means of the comparison between the field survey and numerical results of ground motion it was then used to examine the detailed quantitative information on the dynamic response characteristics of tunnel fault system including stress distribution strain vibration velocity and tunnel failure process the intensive tunnel fault interaction during seismic loading induces the dramatic stress redistribution and stress concentration in the intersection of tunnel and fault the tunnel fault system behavior is characterized by the complicated nonlinear dynamic failure process in response to a real strong seismic event it can be qualitatively divided into 5 main stages in terms of its stress strain and rupturing behaviors 1 strain localization 2 rupture initiation 3 rupture acceleration 4 spontaneous rupture growth and 5 stabilization this study provides the insight into the further stability estimation of underground tunnel structures under the combined effect of strong earthquakes and faults

geochemistry of ferromanganese nodules from domes site a northern equatorial pacific multiple diagenetic metal sources in the deep sea abstract the major and minor element composition of ferromanganese nodules from domes site a has been determined by x ray fluorescence methods three phases appear to control the bulk compositions mn and fe oxyhydroxides and aluminosilicates relatively wide compositional variations are evident throughout the area nodules with high mn fe ratios high cu mg mo ni and zn concentrations and high todorokite mno 2 ratios have granular surface textures and are confined to an east west trending depression with thin quaternary sediment cover nodules with low mn fe ratios high concentrations of as ca ce co la p sr ti v y and zr and low todorokite mno 2 ratios have smooth surfaces and are confined to shallower areas with relatively thick quaternary sediment to the north and south of the depression all nodules in the area have compositions which are influenced by diagenesis but those with the most marked diagenetic signature high mn fe and cu ni ratios low ce la ratios and more todorokite are found in areas of very slow or non existent sedimentation many of these nodules are actually in contact with outcropping tertiary sediment this paradox may be resolved by postulating by analogy with some shallow water occurrences that the nodules accrete from bottom waters which have enhanced particulate and dissolved metal contents derived from diagenetic reaction in areas remote from the site of nodule formation the metals are supplied in a bottom flow probably antarctic bottom water which also erodes or prevents modern sedimentation in the depression nodules on the flanks of the depression are not evidently affected by this flow and derive at least pan of their constituent metals from diagenetic reaction in the underlying quaternary sediment apparently abyssal diagenetic nodules can have an immediate and a remote diagenetic metal source metal fluxes derived from pore water dissolved metal gradients may not be relevant to particular accreting nodules if a significant fraction of their metals is derived from outside the area in which they form

fish debris as chemical scavengers of zirconium and lanthanum in oceanic environments zr and hf fractionation in marine phosphates abstract red clays foraminifer oozes and clayey carbonaceous oozes from the southeastern pacific ocean have been analyzed for p mn fe zr hf th and la in sediments located far from continental areas considerable amounts of la and zr 20 60 are carried in fish debris carbonate fluorapatite whereas hf and th are taken up preferentially by micronodules and fe mn oxyhydroxides red clays far from the continents exhibit the highest zr hf ratios 75 150 significantly higher than continental rocks and oceanic basalts 30 60 zr is concentrated relative to hf in fish debris the causes of this enrichment of zr in apatite and consequently its separation from its twin element hf are to be found in the greater complexing of hf which somewhat interferes with its incorporation in apatite relative to zr the ability of trace elements to enter carbonate fluorapatite decreases in the order la zr th hf

geochemistry and origin of ferruginous nodules in weathered granodioritic gneisses mysore plateau southern india fe nodules occur within saprolites formed from weathering of granodioritic gneisses in the rain shadow region of the mysore plateau adjacent to the sahyadri mountains in southern india these nodules and their host saprolites were studied for their geochemistry including chemical speciation to understand nodule formation and chemical redistribution processes during rock weathering from their mode of occurrence and mineralogical and geochemical data we infer that the nodules originated by a two stage process in which the initial extensive weathering of gneisses likely facilitated subsequent ferrolysis weathering and nodule formation nodules originated by precipitation of goethite hematite and gibbsite along with several amorphous phases within the matrix of weathered gneisses this is possible only under hydromorphic conditions suggesting that parts of the plateau must have gone through a humid phase prior to the present aridity in the saprolites al fe and ti become enriched because of the removal of si ca na and k however within the nodule fe ti cr and ni are deposited after their chemical transport from the saprolite titanium known for its immobile nature was also mobilized and concentrated under the conditions of nodule formation the most important elements in the nodule constitution are fe al ti and mn each having both crystalline and amorphous phases fe ti and mn oxyhydroxides grain coatings in the saprolites and discrete amorphous mn and ti phases in the nodules seem to have scavenged trace elements from the weathering profile ree were mobilized during weathering and nodule genesis in which ce and ti show a strong geochemical coherence the enrichment of only hree in saprolite and both hree and lree with significant ce in the nodule indicate the control of evolving secondary minerals in the ree redistribution during rock weathering strong enrichment of ce in the weathering profile and in nodules has important implications to the ree chemistry of river waters

oxygenation variations in the atmosphere and shallow seawaters of the yangtze platform during the ediacaran period clues from cr isotope and ce anomaly in carbonates abstract the late neoproterozoic era witnessed a significant oxygenation in earth s surface in line with the naissance and diversity of early animals however detailed variations of the oxygenation during this period remain controversial chromium isotope in ancient carbonates has shown its ability to trace the oxygenation history of the atmosphere hydrosphere system in this study we analyzed cr isotope and ce anomaly data of carbonates from the ediacaran doushantuo and dengying formations in the yangtze gorges area south china in order to reconstruct oxygenation variations in the atmosphere and shallow seawaters of the yangtze platform during the ediacaran period after evaluating and excluding detrital and diagenetic effects well preserved 53crauth signatures were obtained post marinoan carbonates record slightly positive 53crauth values 0 18 0 43 and slightly negative ce anomaly suggesting generally oxidizing conditions in the atmosphere with po2 over 1 pal and in shallow seawaters of the yangtze platform during the post marinoan phase which may have been related to the diversity of early ediacaran organisms shuram wonoka correlative carbonates are characterized by the fluctuations of 53crauth values 0 25 to 0 97 and a significant negative 13c excursion which may have resulted from partial oxidation of the large deep water doc reservoir under enhanced oxidative weathering conditions this process released 13c depleted carbon into dic pool and isotopically unfractionated cr iii into water columns the latter of which immediately precipitated by adsorption onto the detrital materials meanwhile an increase in local anoxia and even euxinia in the intrashelf basin of the yangtze platform driven by enhanced microbial sulfate reduction and the resultant h2s possibly limited regional biological evolution during this phase late ediacaran carbonates record elevated 53crauth values 0 40 0 96 together with the decreasing trend in ce ce values indicating a more oxygenated environment in the atmosphere and shallow seawaters of the yangtze platform during the late ediacaran phase which may have been beneficial to the diversification of late ediacaran animals

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

geochemistry of the rare earth elements in ferromanganese nodules from domes site a northern equatorial pacific abstract the distribution of rare earth elements ree in ferromanganese nodules from domes site a has been determined by instrumental neutron activation methods the concentrations of the ree vary markedly low concentrations characterize samples from a depression the valley in which quaternary sediments are thin or absent high concentrations are found in samples from the surrounding abyssal hills the highlands where the quaternary sediment section is relatively thick moreover the valley nodules are strongly depleted in the light trivalent ree lree and ce compared with nodules from the highlands some of the former showing negative ce anomalies the ree abundances in the nodules are strongly influenced by the ree abundances in coexisting bottom water some controls on the ree chemistry of bottom waters include a the more effective removal of the lree relative to the hree from seawater because of the greater degree of complexation of the latter elements with seawater ligands b the very efficient oxidative scavenging of ce on particle surfaces in seawater and c the strong depletion of both ce and the lree in or a larger benthic flux of the hree into the antarctic bottom water aabw which flows through the valley the distinctive ree chemistry of valley nodules is a function of their growth from geochemically evolved aabw in contrast the ree chemistry of highland nodules indicates growth from a local less evolved seawater source

deformation on nearby faults induced by the 1999 hector mine earthquake interferometric synthetic aperture radar observations of surface deformation due to the 1999 hector mine earthquake reveal motion on several nearby faults of the eastern california shear zone we document both vertical and horizontal displacements of several millimeters to several centimeters across kilometer wide zones centered on pre existing faults portions of some faults experienced retrograde that is opposite to their long term geologic slip motion during or shortly after the earthquake the observed deformation likely represents elastic response of compliant fault zones to the permanent co seismic stress changes the induced fault displacements imply decreases in the effective shear modulus within the kilometer wide fault zones indicating that the latter are mechanically distinct from the ambient crustal rocks

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

development of a positive eu anomaly during diagenesis diagenetic remobilization of eu is possible under conditions of reduction to eu2 at low oxidation potential and near neutral solution producing pore waters relatively enriched in eu2 as distinct from its trivalent ree neighbours eu is reprecipitated in the 3 state in environments of high oxidation potential these processes have produced positive eu anomalies in highly oxidized pleistocene muds of the amazon deep sea fan similar occurrences should be rare but where found they do provide valuable information on local diagenetic processes and conditions

seismic and geodetic evidence for extensive long lived fault damage zones during earthquakes slip is often localized on preexisting faults but it is not well understood how the structure of crustal faults may contribute to slip localization and energetics growing evidence suggests that the crust along active faults undergoes anomalous strain and damage during large earthquakes seismic and geodetic data from the calico fault in the eastern california shear zone reveal a wide zone of reduced seismic velocities and effective elastic moduli using seismic traveltimes trapped waves and interferometric synthetic aperture radar observations we document seismic velocities reduced by 40 50 and shear moduli reduced by 65 compared to wall rock in a 1 5 km wide zone along the calico fault observed velocity reductions likely represent the cumulative mechanical damage from past earthquake ruptures no large earthquake has broken the calico fault in historic time implying that fault damage persists for hundreds or perhaps thousands of years these fi ndings indicate that faults can affect rock properties at substantial distances from primary fault slip surfaces and throughout much of the seismogenic zone a result with implications for the amount of energy expended during rupture to drive cracking and yielding of rock and development of fault systems

the origin of the calcites from pb zn veins in the harz mountains federal republic of germany abstract studies of the ree distribution in calcites from hydrothermal banded pb zn mineralizations as well as in calcites from pelitic and psammitic unmetamorphosed rocks and magmatites of the harz mountains revealed that the calcite of the banded ores crystallized from hybrid magmatic metamorphic solutions these were rather rich in ree3 fe3 and probably zn2 and pb2 ion concentrations the absence of any negative eu anomalies points to oxidizing conditions the sulphides have crystallized from a different solution it is suggested that the necessary hs rich solutions stem from near surface hydrothermal convection cells set up by nearby granitic intrusions the alternating deposition of calcite and sulphide banded ores may be explained by assuming that farther away from the intrusions the hs rich solutions were intermittedly admixed with the hybrid fluids this caused a decrease in temperature an interruption of calcite deposition and sulphide mineralization near the intrusion continuous mixing of these two fluids became more common and consequently banded ores are rather rare

age determinations and growth rates of pacific ferromanganese deposits using strontium isotopes abstract 87 sr 86 sr ratios trace element and ree compositions and textural characteristics were determined for three hydrogenetic fe mn crusts one hydrothermal deposit and two mixed hydrothermalhydrogenetic crusts from the pacific the sr isotope data are compared to the sr seawater curve for the cenozoic to determine the ages and growth rates of the crusts the 87 sr 86 sr in the crusts does not increase monotonically with depth as expected if the sr were solely derived from seawater and perfectly preserved since deposition this indicates post depositional exchange of sr or heterogeneous sources for the sr originally contained in the crusts textures of hydrogenetic crusts generally correlate with sr isotopic variations the highest porosity intervals commonly exhibit the highest 87 sr 86 sr ratios indicating exchange with younger seawater intervals with the lowest porosity commonly have lower 87 sr 86 sr and may preserve the original sr isotopic ratios minimum ages of crust growth inception were calculated from dense low porosity intervals growth of the hydrogenetic crusts began at or after 23 ma although their substrates are cretaceous estimated average growth rates of the three hydrogenetic crusts vary between 0 9 and 2 7 mm ma consistent with published rates determined by other techniques within the marshall islands crust growth rates for individual layers varied greatly between 1 0 and 5 4 mm ma for one crust very low 87 sr 86 sr ratios occurred in detrital rich intervals hydrothermal fe mn oxide from the active lau basin back arc spreading axis valu fa ridge has an 87 sr 86 sr ratio with a predominantly seawater signature 87 sr 86 sr 0 709196 indicating a maximum age of 0 9 ma one crust from an off axis seamount west of gorda ridge may have begun precipitating hydrogenetically at 0 5 ma 0 709211 and had increasing hydrothermal or volcanic input in the top half of the crust indicated by a significantly lower 87 sr 86 sr ratio 0 709052

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

rupture dynamics with energy loss outside the slip zone 1 energy loss in a fault damage zone outside the slip zone contributes to the fracture energy that determines rupture velocity of an earthquake a nonelastic two dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a coulomb yield condition in a mode 2 crack like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point coulomb yielding occurs on the extensional side of the fault plastic strain is distributed with uniform magnitude along the fault and it has a thickness normal to the fault proportional to propagation distance energy loss off the fault is also proportional to propagation distance and it can become much larger than energy loss on the fault specified by the fault constitutive relation the slip velocity function could be produced in an equivalent elastic problem by a slip weakening friction law with breakdown slip dc increasing with distance fracture energy g and equivalent dc will be different in ruptures with different initiation points and stress drops so they are not constitutive properties they are determined by the dynamic solution that arrives at a particular point peak slip velocity is however a property of a fault location nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium

seismic structures of the calico fault zone inferred from local earthquake travel time modelling author posting the authors 2011 this article is posted here by permission of john wiley sons for personal use not for redistribution the definitive version was published in geophysical journal international 186 2011 760 770 doi 10 1111 j 1365 246x 2011 05055 x

manganese micronodules a possible indicator of sedimentary environments abstract manganese micronodule distribution size internal features and chemical composition as well as the composition of associated sediments have been determined in eight sediment cores taken from the siliceous ooze area of the central indian basin cib micronodule abundance expressed as the number of micronodules per gram of dried sediment 0 375 n g and size 75 1000 m show considerable variation with core depth and are directly related to each other the morphology surface texture and internal features of the micronodules are similar to those of surface macronodules from the same basin micronodules have high contents of mn 35 02 cu 1 6 ni 1 4 and zn 0 37 high mn fe ratios 5 101 and very low fe 1 8 al 2 o 3 1 3 tio 2 0 30 sio 2 2 7 and rare earth element 522 ppm contents compared to surface and buried macronodules micronodule abundance size and composition depend on the redox characteristics of the sedimentary environment and can therefore be used as indicators of the sedimentary environment

hydrothermal sediments as a potential record of seawater nd isotope compositions the rainbow vent site 36 14 n mid atlantic ridge 1 geochemical compositions and sr and nd isotopes were measured in two cores collected 2 and 5 km from the rainbow hydrothermal vent site on the mid atlantic ridge overall the cores record enrichments in fe and other metals from hydrothermal fallout but sequential dissolution of the sediments allows discrimination between a leach phase easily leachable and a residue phase refractory the oxy anion and transition metal distribution combined with rare earth element ree patterns suggest that 1 the leach fraction is a mixture of biogenic carbonate and hydrothermal fe mn oxy hydroxide with no significant contribution from detrital material and 2 99 5 of the ree content of the leach fraction is of seawater origin in addition the leach fraction has an average 87sr 86sr ratio indistinguishable from modern seawater at 0 70916 although we lack the nd value of present day deep water at the rainbow vent site we believe that the ree budget of the leach fraction is predominantly of seawater origin we suggest therefore that the leach fraction provides a record of local seawater nd values nd isotope data from these cores span the period of 4 14 ka 14c ages and yield nd values for north east atlantic deep water neadw that are higher 9 3 to 11 1 than those observed in the nearby madeira abyssal plain from the same depth 12 4 0 9 this observation suggests that either the iceland scotland overflow water isow and lower deep water contributions to the formation of neadw are higher along the mid atlantic ridge than in the surrounding basins or that the relative proportion of isow was higher during this period than is observed today this study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water nd values and hence deepwater circulation patterns in the oceans than is possible from other types of sediments

origin of detrital fluxes in the southeast indian ocean during the last climatic cycles because of a close relationship between detrital flux variations and magnetic susceptibility ms flux ms cm 3 of bulk sediment multiplied by the linear sedimentation rate variations in the southeast indian basin of the southern ocean ms flux profiles have been used to examine the spatial and temporal detrital flux changes in this basin during the last climatic cycle results indicate a general increase in detrital material input during the coldest periods suggesting a widespread phenomenon at least on the basin scale mineralogical data geochemical data and 87sr 86sr isotopic ratios have been used to determine the origin and transport mechanisms responsible for increased detrital flux during glacial periods mineralogical and geochemical data show that these glacial highs are due to increases in both kerguelen crozet volcanic and antarctic detrital inputs the 87sr 86sr isotopic composition of the 45 m fraction indicates that the kerguelen crozet province contributes to at least 50 of the coarse particule input to the west this contribution decreases eastward to reach less than 10 these tracers clearly indicate that the crozet kerguelen province was a major source region of detrital in the western part of the basin during glacial times in contrast material of antarctic origin is well represented in the whole basin fine and coarse fractions because of the minor amount of coarse particles in the sediments volcanic particles from kerguelen and crustal particles from antarctica have most probably been transported by the antarctic bottom water current and or the circumpolar deepwater current during glacial periods as is the case today nevertheless the presence of coarse particles even in low amount suggests also a transport by ice rafting sea ice and icebergs originated from both kerguelen and antarctic sources however the relative importance of both hydrographic and ice rafting modes of transport cannot be identified accurately with our data during low sea level stands glacial maximum periods increasing instability and erosion of the continental platform and shallow plateaus could have resulted in a more efficient transfer of crustal and volcano detrital material to the southeast indian basin at the same time extension of the grounded ice shelves over the continental margins and increase in the erosion rate of the antarctic ice sheet could have induced a greater input of ice rafted detritus ird to southern ocean basins enhancement of the circumpolar deepwater current strength might have also carried a more important flux of detrital material from kerguelen however an increase in the bottom water flow is not necessarily required

reply to comment by y fialko on deformation of compliant fault zones induced by nearby earthquakes theoretical investigations in two dimensions 1 fault zone structure and properties may contain important information about past earthquake rupture and subsequent healing processes damaged fault zones are observed geologically in the field e g chester and chester 1998 ben zion and sammis 2003 seismic studies have revealed the existence of low velocity fault zones around active faults e g li et al 1998 ben zion et al 2003 compliant fault zones are inferred from insar observations of the displacement field of recent earthquakes e g fialko et al 2002 fialko 2004 however the width and depth extent of fault zones are still under debate in the community 2 duan et al 2011 conduct detailed theoretical investigations of the response of compliant fault zones to nearby earthquakes using spontaneous rupture models with offfault elastoplastic rheology in a 2 d plane strain framework built upon an earlier study by duan 2010 they call for a reexamination of existing observations based on possible constraints on the in situ stress state by the inelastic response of compliant fault zones revealed by their theoretical studies and possible deficiencies in previous studies in deducing the structure and properties of compliant fault zones fialko 2011 hereafter referred to as fialko11 provides a comment to duan et al 2011 and refutes the call although primarily defending the previous studies fialko et al 2002 fialko 2004 which considered only the elastic response of compliant fault zones to static stress changes fialko11 also downplays significance of the possible inelastic response of compliant fault zones to dynamic stress changes i will first discuss significance of both the previous studies on elastic response to static stress changes and the recent studies on inelastic response to nearby ruptures then i will reply in some details to the comments made by fialko11

nd sr o isotopic and chemical evidence for a two stage contamination history of mantle magma in the central alpine bergell intrusion two different contamination processes have been identified as having been operative in the genesis of a plutonic suite initial contamination of a mantle source and subsequent crustal contamination of uprising partial melts from the mantle these processes are indicated by a detailed analyses of nd sr and oxygen isotopes together with major and trace elements of the 32 30 ma calc alkaline bergell intrusion this intrusion is located at the suture of the alpine continental collision zone and contains rock types capable of discriminating between mantle and intracrustal processes a range from basaltic andesitic dykes in the surrounding country rocks cumulitic hornblendites gabbros tonalite granodiorite and lamprophyres to pegmatites and aplites is exposed in this single intrusion the results of ree modelling and isotopic compositions of the basic members suggest that the cumulates were fractionated from a picrobasaltic liquid originating by partial melting of enriched subcontinental mantle end 4 increases in 87sr 86sr 0 7055 and 18o 6 7 in these samples relative to the mantle array and compositions of other periadriatic intrusions are most likely the result of an initial contamination of the mantle source by dehydration or partial melting of altered subducted oceanic crust slight differentiation of such a picrobasaltic liquid produced the basaltic andesitic dykes simultaneous fractional crystallization and contamination of the uprising magma by continental crust produced crustal isotopic signatures which increase with acidity to values of end 7 6 87sr 86sr 0 716 and 18o 10 the crustal imprint and lree enrichment in the dominating tonalite increase with decreasing crystallization depth which indicates that the tonalites were emplaced in several distinct batches with different degrees of contamination shoshonitic lamprophyres which intruded into the partly solidified granodiorite were generated in a deep strongly contaminated mantle source the posttectonic 26 ma novate leucogranite is not cogenetic with the main bergell body but rather formed from a predominantly crustal source if the described features are indeed due to mantle source contamination processes which are well known for volcanic arcs it must be concluded that these may also play a significant role in the genesis of calcalkaline plutonic suites

settling particles with positive ce anomalies from the japan sea rare earth element patterns of settling particles collected at five water depths 890 to 3 240 m of the japan sea show significant positive ce anomalies the very surface sediment exhibits a slightly positive one excess ce content over the ce la ratio of average shale increases with increasing excess mn content from 890 to 1 870 m and it possibly remains constant below this depth these results give evidence for the removal of ce in association with the removal of mn from seawater by settling particles

inelastic response of compliant fault zones to nearby earthquakes in three dimensions abstract using dynamic modeling of earthquake rupture on a strike slip fault and seismic wave propagation in a three dimensional inhomogeneous elastoplastic medium we investigate the inelastic response of compliant fault zones to nearby earthquakes we primarily examine the plastic strain distribution within the fault zone and the displacement field that characterizes the effects of the presence of the fault zone we find that when the fault zone rocks are close to failure in the prestress field plastic strain occurs along the entire fault zone near the earth s surface and some portions of the fault zone in the extensional quadrant at depth while the remaining portion deforms elastically plastic strain enhances the surface displacement of the fault zone and the enhancement in the extensional quadrant is stronger than that in the compressive quadrant inelastic response may be distinguished from elastic response by sympathetic motion or reduced retrograde motion exhibited in the fault parallel horizontal surface displacement in conjunction with enhanced vertical surface displacement in a strike slip faulting environment these findings suggest that taking into account both elastic and inelastic deformation of fault zones to nearby earthquakes may improve our estimations of fault zone structure and properties from small scale surface deformation signals furthermore identifying the inelastic response of nearby fault zones to large earthquakes may allow us to place some constraints on the absolute stress level in the crust

redox condition in the nanhua basin during the waning of the sturtian glaciation a chromium isotope perspective abstract the neoproterozoic oxygenation event noe is often considered to be synchronously and possibly causally associated with the cryogenian glaciations reconstructing early cryogenian redox conditions is therefore essential for understanding the onset of the noe we analyzed cr isotope compositions 53cr as well as major and rare earth element ree concentrations of the banded iron formations bifs in the basal fulu formation of the xiajiajiang section nanhua basin which are thought to have been deposited during the waning stage of the sturtian glaciation strongly positively fractionated authigenic 53cr values were obtained after detrital correction ranging from 0 64 to 1 22 and averaging at 0 91 0 40 2 n 10 or after detrital evaluation 0 71 this suggests extensive oxidative cr cycling occurred at the earth s surface and implies that the po2 was probably higher than 1 pal during this period the lack of ce anomalies 0 90

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

geochemistry of late permian to early triassic pelagic cherts from southwest japan implications for an oceanic redox change major trace and rare earth element abundances were determined for the southwestern japanese pelagic chert sequence from the early late permian to early early triassic to investigate a redox change in deep sea pelagic environments before and at the permo triassic boundary ptb 251 ma the sequence was primarily deposited in the deep sea of the superocean panthalassa and then was accreted to japan in the middle jurassic a remarkable lithostratigraphic change from red chert to siliceous carbonaceous claystone through gray chert is observed in this sequence constituent elements for these sedimentary rocks are essentially derived from two sources 1 an ancient seawater via biogenic mainly radiolarian hydrothermal and authigenic materials and 2 an average shale like terrigenous material the present measurement demonstrates significant stratigraphic changes of the ce cenon ter value estimated ce anomaly value of non terrigenous component recalculated by subtraction of terrigenous rees from bulk rees and the mn te sample mn te paas value excess mn component other than terrigenous one te terrigenous elements including ti al nb hf th paas post archean average australian shale in the permian chert the ce cenon ter values increase from 0 2 to 1 and the mn te sample mn te paas values decrease up section suggesting that the redox condition of deep sea open ocean changed from oxic to suboxic in an interval of approximately 10 myr the fe te sample fe te paas and mn te sample mn te paas values of carbonaceous claystone near or at the ptb are less than unity suggesting that reductive dissolution of iron and manganese occurred under an anoxic condition this supports the idea of the ptb oceanic anoxia in the superocean panthalassa the present data suggest that the anoxic condition prevailed in the deep sea pelagic regions for an extremely long period much more than 10 myr from the middle late permian to early early triassic this long term development of widespread oceanic anoxia may have been linked to the greatest mass extinction of the phanerozoic

calcareous nannofossil biostratigraphic dating of a ferromanganese crust from schumann seamount abstract calcareous nannofossil biostratigraphy was employed to determine the age and growth rates of the different layers within ferromanganese crusts from schumann seamount 200 miles north of the island of kauai hawaii this work is part of a study to reconstruct the paleoceanographic history of crusts using various geochemical indicators the methods are based on the identification of coccolith imprints not actual coccolith remains age constraints on the time span of a particular horizon are defined either 1 by the presence of a species which was extant for only a limited geological time interval or 2 by the presence of two organisms whose time ranges overlapped age resolution is optimized by short time ranges or narrow overlaps in the crust studied there was considerable inter horizon variability in the preservation of coccolith imprints in imprint abundance and in species diversity some of the crust layers examined were narrowly constrained temporally 1 4 myr while others were less so 10 myr our results indicate that the minimum age for the interval at 27 mm depth is at least eocene this is the maximum age many believe any crust can be the position of this interval however is only about one half of the way through the crust while the data support previous estimates of average crust growth rates 0 5 mm myr the actual apparent growth rate appears to have varied by an order of magnitude 0 1 to 2 mm myr

anomalies in rare earth distributions in seawater gd and tb we have measured profiles of the rare earth elements ree in atlantic and pacific ocean waters the data normalized versus shales exhibit a pronounced anomaly in gd relative to its neighbors eu and tb in the ree series such that the gd concentrations are high by 30 50 closer inspection reveals that the anomaly is made up of both elevated gd and depressed tb concentrations likely associated with solution chemistry shifts in the transition from an exactly half filled 4f electron shell anomalies in gd and tb solution complexation are also indicated by the turner whitfield dickson speciation model the overall trend of heavy ree iii enrichment in seawater and the gdtb anomaly described here tend to support scavenging as an important removal mechanism for the ree from seawater

a physical model for widespread near surface and fault zone damage induced by earthquakes 1 i present a rigorous unifying interpretation of the well documented widespread near surface and fault zone damage induced by earthquakes by simulating three dimensional dynamic rupture propagation on a vertical strike slip fault stresses in the crust are depth dependent and material response is governed by the drucker prager yielding criterion i show that material yielding induced by seismic waves under the low confining pressure causes widespread near surface damage because the confining pressure increases with depth the yielding zone at depth is narrowly confined near the fault but its thickness broadens dramatically near the surface forming a flower like damage zone the fault zone damage at depth is induced by large dynamic stresses associated with the rupture front while is induced by strong seismic waves ahead of the rupture front near the earth s surface these results have important implications for the formation and evolution of fault zones and possibly for the dynamic triggering of earthquakes as well

triggered slip observations of the 17 august 1999 izmit turkey earthquake using radar interferometry we use synthetic aperture radar interferometry insar to map the displacement field of the 17 august 1999 izmit earthquake which largely conforms to that predicted for an elastic upper crust we determine the earthquake source parameters and show that slip continues farther west than the mapped fault ruptures we also show that additional sub surface displacements occurred on parallel strands of the north anatolian fault zone we argue that this was caused by changes in static stress accompanying the mainshock or by the dynamic release of regional stresses

off fault plasticity and earthquake rupture dynamics 1 dry materials or neglect of fluid pressure changes 1 we analyze inelastic off fault response during earthquakes spontaneous crack like rupture with slip weakening is modeled in 2 d plane strain using an explicit dynamic finite element procedure a mohr coulomb type elastic plastic description describes the material bordering the fault we identify the factors which control the extent and distribution of off fault plasticity during dynamic rupture those include the angle with the fault of the maximum compressive prestress the seismic s ratio and the closeness of the initial stress state to mohr coulomb failure plastic response can significantly alter the rupture propagation velocity delaying or even preventing a transition to supershear rupture in some cases plastic straining also alters the residual stress field left near the fault in part 1 we consider dry materials bordering the fault or at least neglect pore pressure changes within them part 2 addresses the effects of fluid saturation showing that analysis procedures of this part can describe undrained fluid saturated response elastic plastic laws of the type used are prone to shear localization resulting in an inherent grid dependence in some numerical solutions nevertheless we show that in the problems addressed the overall sizes of plastic regions and the dynamics of rupture propagation seem little different from what are obtained when we increase the assumed plastic hardening modulus or dilatancy parameter above the theoretical threshold for localization obtaining a locally smooth numerical solution at the grid scale evidence for scaling of some localization features with a real nongrid length scale in the model is also presented

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

anoxic to suboxic mesoproterozoic ocean evidence from iron isotope and geochemistry of siderite in the banded iron formations from north qilian nw china abstract banded iron formations bifs provide important constraints on geochemical cycling of fe and ancient marine environment globally the formation of bifs peaked during late archean and early paleoproterozoic with limited reappearance during neoproterozoic here we investigate a rare example of mesoproterozoic ca 1 3 ga bifs from jingtieshan in the north qilian region of nw china we present rare earth element and yttrium ree y compositions together with iron isotope features of siderite from the bifs and integrate these with our published data on carbon isotope compositions from the siderite rich bifs including carbonate facies bifs and mixed carbonate oxide facies bifs siderite from the bifs shows ree y characteristics that are consistent with submarine hydrothermal fluids mixed with seawater including positive eu eu anomalies and high y ho ratios the siderite also displays homogeneous iron isotope compositions 56fe range from 0 71 to 0 41 one sample down to 1 62 and moderate negative carbon isotope compositions 13c values 8 40 to 3 0 these findings argue against the traditional view that siderite associated with bifs was formed through microbial dissimilatory iron reduction dir instead siderite from jingtieshan bifs is in equilibrium with submarine hydrothermal fluids and seawater suggesting an inorganic origin and was directly precipitated from the co2 and fe oversaturated water column with only insignificant role for dir these mesoproterozoic bifs are also characterized by ce anomalies and the siderite falls within the pe log s t and po2 pco2 stability fields suggesting that the bifs were deposited in an anoxic to suboxic ocean the results from our study suggest the presence of iron rich mesoproterozoic deep ocean in the north qilian area

coupling between suboxic condition in sediments of the western bay of bengal and southwest monsoon intensification a geochemical study abstract reconstruction of paleo redox conditions in a radiocarbon 14c dated sediment core sk 218 1 covering the past 45 ka thousand calendar years collected from the western bay of bengal lat 14 02 n long 82 00 e at a water depth of 3307 m has been made based on redox sensitive element geochemistry the high u th ratio mo enrichment mo u enrichment factor ratio ce ce we also provide the first record of the nitrogen isotopic composition 15n of sedimentary organic matter in the western bay of bengal a region where the mesopelagic oxygen minimum zone omz is just short of being suboxic denitrifying today the sedimentary 15n fluctuated considerably in the past especially during the marine isotope stage 3 oscillations in 15n were apparently in concert with those in organic carbon and nitrogen contents and could be related to climatic changes heinrich and dansgaard oeschger events in the north atlantic the dansgaard oeschger 12 event appears to have exerted the most intense effect on bay of bengal biogeochemistry when surface productivity as inferred from the organic carbon and nitrogen contents was the highest recorded in the core and the 15n reached up to 6 3 considering the probable dilution by isotopically light terrigenous organic matter it would appear that omz of the bay of bengal had turned denitrifying however the absence of suboxic conditions in the sediments at this time suggests a decoupling of the benthic processes with those in the mesopelagic water column

the whole rock cerium anomaly a potential indicator of eustatic sea level changes in shales of the anoxic facies abstract the whole rock cerium anomaly tested for outer shelf upper slope stratigraphic sections from the middle ordovician through the lower silurian of scotland is proposed as an empirical technique to develop a eustatic 3rd order or finer scale sea level curve this interval was chosen as it straddles the well documented late ordovician glaciation and can be defined by graptolite zones the anomaly is calculated from neutron activation analysis of low carbonate phosphate free fossil free field identified shales of the graptolite facies by comparison of the normalized cerium content with the linearized trend of the normalized composition of other rare earth elements in order of atomic number for sections originally deposited in the main pycnocline below the surface mixed layer values of the anomaly for a given sample would indicate its position on the redox curves developed for the early paleozoic by wilde 1987 changes in the anomaly that are positive with time would indicate a lowering of sea level as the apparent depth on the redox curve would reflect more oxic conditions relative changes negative with time would indicate a rise in sea level as the apparent depth reflects more anoxic conditions depending on the vertical sample spacing and the time interval sampled resolution of the order of 1 m y might be achieved thus the vail et al 1977 curves of the 3rd order 1 to 10 m y or of finer scale could be obtained by this technique with the proper choice of section accordingly for the early through middle paleozoic when the main pycnocline was anoxic this geochemical technique could be used to develop eustatic sea level curves and additionally offer an independent calibration for seismic stratigraphy as well as an indicator of glacial interglacial climatic sequences or eustatic changes due to fluctuations in global ridge crest volumes

can compliant fault zones be used to measure absolute stresses in the upper crust 1 geodetic and seismic observations reveal long lived zones with reduced elastic moduli along active crustal faults these fault zones localize strain from nearby earthquakes consistent with the response of a compliant elastic layer fault zone trapped wave studies documented a small reduction in p and s wave velocities along the johnson valley fault caused by the 1999 hector mine earthquake this reduction presumably perturbed a permanent compliant structure associated with the fault the inferred changes in the fault zone compliance may produce a measurable deformation in response to background tectonic stresses this deformation should have the same sense as the background stress rather than the coseismic stress change here we investigate how the observed deformation of compliant zones in the mojave desert can be used to constrain the fault zone structure and stresses in the upper crust we find that gravitational contraction of the coseismically softened zones should cause centimeters of coseismic subsidence of both the compliant zones and the surrounding region unless the compliant fault zones are shallow and narrow or essentially incompressible we prefer the latter interpretation because profiles of line of sight displacements across compliant zones cannot be fit by a narrow shallow compliant zone strain of the camp rock and pinto mountain fault zones during the hector mine and landers earthquakes suggests that background deviatoric stresses are broadly consistent with mohr coulomb theory in the mojave upper crust with 0 7 large uncertainties in mojave compliant zone properties and geometry preclude more precise estimates of crustal stresses in this region with improved imaging of the geometry and elastic properties of compliant zones and with precise measurements of their strain in response to future earthquakes the modeling approach we describe here may eventually provide robust estimates of absolute crustal stress

damage to the shallow landers fault from the nearby hector mine earthquake crustal faults have long been identified as sites where localized sliding motion occurs during earthquakes which allows for the relative motion between adjacent crustal blocks although there is a growing awareness that we must understand the evolution of fault systems on many timescales to relate present day crustal stresses and fault motions to geological structures formed in the past fault zone damage and healing have been documented quantitatively in only a few cases we have been monitoring the healing of damage on the shallow johnson valley fault after its rupture in the 1992 magnitude 7 3 landers earthquake and here we report that this healing was interrupted in 1999 by the magnitude 7 1 hector mine earthquake rupture which occurred 20 30 km away the hector mine earthquake both strongly shook and permanently strained the johnson valley fault adding damage discernible as a temporary reversal of the healing process the fault has since resumed the trend of strength recovery that it showed after the landers earthquake these observations lead us to speculate that fault damage caused by strong seismic waves may help to explain earthquake clustering and seismicity triggering by shaking and may be involved in friction reduction during faulting

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

hydrogeochemistry of continental brackish waters in the southern coastal plain israel abstract the southern coastal plain in israel incorportates a transitional fringe of the desert in which three different chemical types of groundwater are found 1 near surface waters from springs along the besor river course 2 shallow to moderate depth waters from the slightly westward dipping pleistocene coastal aquifer this aquifer which consists of sandstone layers of the kurkar group is recharged in the coastal plain and 3 deep waters of the westward dipping upper cretaceous judea group carbonates which are recharged in the mountains in the east a thick aquiclude of upper cretaceous tertiary rocks separates the judea group aquifer from the overlying coastal aquifer in the southern coastal plain isotopically light oxygen and depleted deuterium characterize the judea group waters as expected from high altitude recharge the isotopic composition of the coastal plain waters is variable but for the most part enriched in 18o and d within the southern coastal plain aquifer a southern subgroup comprises waters more depleted in heavy isotopes than those of either the northern or eastern subgroups the besor waters are isotopically similar to the judea group waters reflecting their origin in the mountain region and flow through the surficial river gravels and sands it is suggested that leakage of the besor waters into the underlying southern coastal plain aquifer results in mixing of the two water types the most prominent chemical feature characterizing the groundwater of the southern coastal plain is na cl 1 this na cl ratio can be maintained only by a continuous input from a non marine source of na the most plausible source of this na is the dissolution of feldspar derived from the windblown loess deposits which cover the area and or leaching of trona minerals found in the unsaturated zone combined with base exchange processes

isotopic and trace element constraints on mixing and melting models of marginal basin volcanism bransfield strait antarctica bransfield strait is a narrow marginal basin separating the south shetland islands from the northern end of the antarctic peninsula quaternary volcanism occurs in the strait as subaerial and submarine volcanoes aligned on the inferred axis of rifting and as two subaerial off axis volcanoes on the northern margin of the strait the bransfield strait lavas are similar to published analyses from other marginal basins ranging from basalts and basaltic andesites to trachytes they exhibit moderate enrichments in alkali and alkaline earth elements relative to high field strength elements that are typical of many back arc basin basalts the seamount basalts have trace element chemistry similar to enriched mid ocean ridge basalts e morb but with variously higher alkali and alkaline earth element concentrations and frequently lower nb low pressure fractional crystallization accounts for most of the compositional variation within individual volcanoes but it does not explain intervolcano differences even though the volcanoes are closely spaced and presently or recently active melting of depleted mantle mixed with 0 5 2 crust or sediment explains the isotopic and trace element variations not accounted for by magma chamber processes the off axis volcanoes are the products of less partial melting than the on axis volcanoes one of the off axis volcanoes also contains more of an enriched component in its source some of the lavas have rb sr too low to account for their 87sr 86sr perhaps due the loss of rb during mantle metasomatism or interaction between slab derived fluids and the mantle source of the basalts strontium neodymium and 207pb 204pb isotopic signatures remained constant during the transition from tertiary island arc volcanism to quaternary marginal basin volcanism but 206pb 204pb increased high cen smn of basalts from some volcanoes requires residual garnet in the source thus the young 15 25 ma at the trench subducted slab is either deeper than 60 km beneath the volcanoes or it has fractured and is no longer a coherent barrier to melts generated below it

effects of low velocity fault zones on dynamic ruptures with nonelastic off fault response 1 using a finite element method for elastoplastic dynamic analysis we examine the effects of a low velocity fault zone lvfz surrounding a fault on a spontaneous dynamic earthquake rupture a mohr coulomb failure criterion is used to characterize nonelastic off fault response to earthquake ruptures we find that the presence of a lvfz alters the distribution of off fault plastic strain and results in larger final slip and larger peak slip velocities on the fault these effects show a lvfz width dependency a supershear relative to the shear wave velocity of country rocks rupture transition is observed with a lvfz width of 400 m or larger up to 2 km the presence of a lvfz increases the amplitude of ground shaking at stations within the lvfz and induces high frequency oscillations at stations within and near the lvfz

distinct asymmetry in rupture induced inelastic strain across dipping faults an off fault yielding model 1 off fault stresses associated with rupture propagation cause material yielding under a mohr coulomb condition leaving irrecoverable deformation in the fault zone 2d dynamic rupture simulations for a 30 reverse fault and a 60 normal fault in a depth dependent stress environment show that the yielding inelastic zone off the fault broadens as it nears the surface with decreasing confining pressure forming a skewed flower like structure bounded at the top by the free surface the inelastic strain in the hanging wall is significantly larger and broader than the footwall for both reverse and normal faults the occurrence of inelastic strain however significantly reduces ground motion especially on the hanging wall and gives rise to a reduced asymmetry in ground motion on the hanging wall and footwall compared to elastic solutions these results provide theoretical predictions for fault zone structure of dipping faults that can be tested by future observational experiments

the rare earth element geochemistry of surface sediments in four transects in the south china sea and its geological significance seventy five samples of surface sediment were collected from four transects in the south china sea scs for analyses of rare earth element ree geochemistry total ree abundance ree in the scs varies from 45 to 195 ppm average 128 ppm lower than that of the upper continental crust the spatial distribution of ree is strongly dependent upon the geographical location and depositional environment low ree concentrations are observed on the continental slope e g xisha and nansha islands while high ree concentrations are present in the deep basin sediments on the slope are also characterized by lower lree hree la yb n eu eu and ce ce ratios relative to deep basin sediments there is a positive correlation between al2o3 and ree and a negative correlation between cao and ree conversely the relatively insignificant fe mn oxide accumulation in the scs suggests that manganese nodules do not make a significant contribution to the bulk ree composition of sediments therefore the sediment ree geochemistry is mainly controlled by terrigenous and biogenic sources biogenic carbonate has a diluting effect on ree concentrations but a significant influence on lree hree ce ce and la yb n values is found only in sediments with especially high biogenic carbonate levels the ree geochemistry of scs surface sediments indicates that their source is mainly post archean felsic rocks in the eastern sub basin the relatively low lree hree ratios and high eu eu values of the sediments indicate that significant terrigenous materials are derived from young volcanic rocks e g rocks in the luzon arc

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

origin of negative ce anomalies in mixed hydrothermal hydrogenetic fe mn crusts from the central indian ridge abstract layered fe mn crusts from the off axis region of the first segment of the central indian ridge north of the rodrigues triple junction were studied geochemically and mineralogically vernadite mno2 is the main mineral oxide phase 230thxs and co concentrations suggest high growth rates of up to 29 mm myr and a maximum age of the basal crust layer of 1 ma whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation co pb ni and ti concentrations are strikingly lower concentrations and distribution of the strictly trivalent rare earths and yttrium rey are typical of hydrogenetic ferromanganese oxide precipitates but in marked contrast the crusts are characterized by negative cesn shale normalized anomalies and ce pr sn ratios less than unity profiles through the crusts reveal only minor variations of the rey distribution and ce pr sn ratios range from 0 45 to 0 68 compared to ratios of up to 2 for typical hydrogenetic crusts from the central indian basin the apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent rey the adsorption desorption equilibrium has been reached positive ce anomalies in the partition coefficient patterns reveal preferential uptake of ce but to a lesser extent than in normal hydrogenetic crusts a new parameter excess ce cexs to quantify the degree of decoupling of ce from rey iii is established on the basis of partition coefficients cexs cebulk ratios suggest that the cir crusts formed by precipitation of fe mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of ce results from the same oxidative sorption process the growth rates calculated with 230thxs data as well as with the co formula are inversely related to cexs

isotopic compositions of ce nd and sr in ferromanganese nodules from the pacific and atlantic oceans the baltic and barents seas and the gulf of bothnia abstract ferromanganese nodules from the pacific and atlantic oceans the barents and baltic seas and the gulf of bothnia were analyzed for the isotopic compositions of ce nd and sr and the abundances of ree ba and sr ree patterns of barents baltic and bothnian samples show no ce anomaly or even a negative one in contrast to the positive anomaly observed for the pacific and atlantic samples moreover the baltic and bothnian samples have distinctly low end values average end values of the four regions are as follows pacific 5 barents 10 atlantic 11 and baltic inclusive of gulf of bothnia 19 the characteristic low end values of the baltic samples are indicative of the influence of precambrian rocks from the baltic shield of particular interest is the feature of the ce isotopic composition that ece values of the samples from the pacific are negative and those from the other three regions positive this novel finding might suggest a difference in sources of ce between the pacific and other regions these results demonstrate that ce isotopic ratios can be a useful tracer in marine geochemistry in combination with isotopic compositions of nd and sr

cerium a chemical tracer for paleo oceanic redox conditions abstract the ce anomalies found in marine carbonates provide a sensitive indicator for the study of paleo oceanic redox conditions the dependency of cce the observed ce concentration and cepo04 the activity of the cepo4 complex to the po2 ph and pco2 of seawater can be used for deciphering some aspects of the paleo ocean chemistry and is log c ce log cepo 0 4 13 2 0 25 log p o 2 3 0 ph 1 95 0 25 log p o 2 1 50 log p co 2 1 50 log ca the ph which is related to pco2 and po2 are major factors for controlling the ce concentration in seawater therefore ce anomalies ceas ce observed ce interpolated between la and pr or nd serve as indicators for ph or pco2 or po2 changes nearly uniform ce abundances found in pacific 5000 m water columns piepgras and jacobsen 1988 and the ceas in ichthyoliths can be explained using this model a general cea shift in sediments from d s d p holes 525a 530a b 516 516f suggest that the entire south atlantic water redox condition changed from reducing to oxidizing at 56 my in the north atlantic the galicia margin samples show a redox change between 132 148 my indicating active surface currents between the atlantic ocean and the shallow sea off the iberian peninsula the carbonate samples from d s d p hole 316 in the central pacific yielded an average cea of 0 15 0 01 which is 2 3 the ceas observed in deep pacific seawater by piepgras and jacobsen 1988 the relative enrichment of ce in these samples is ascribed to coprecipitation of ce oh 4 onto fe mn o coatings the striking similarities in the trace element profiles of ree sc hf th and ceas and the low u abundances 0 08 ppm in many marine carbonates indicate insignificant ce redox and trace elemental concentration changes for the pacific ocean over the past 95 my no significant ce redox change occurred in the pacific ocean within k t boundary one 240 my china limestone deposited under oxic sedimentary conditions yielded a cea of 0 53 calculations indicate a pco2 of 1 9 present value prevailed over the 240 my tethyan ocean u th ratios and low u concentrations are diagnostic indicators for obtaining reliable ceas in marine carbonates and perhaps for biogenic apatites and conodonts as well

nonuniform prestress from prior earthquakes and the effect on dynamics of branched fault systems 1 to examine the effects of branched fault geometry on the dynamics of fault systems in the long term we perform multicycle simulations on generic faulting models an explicit finite element algorithm is used to simulate spontaneous dynamic rupture of earthquakes the fault stress during the interseismic period is evaluated by an analytical viscoelastic model we find that the fault prestress field becomes highly nonuniform near the branch point and on the two branch segments over multiple earthquake cycles owing to the branched fault geometry and stress interaction between the two segments the principal prestress on faults rotates over multiple earthquake cycles and departs from the regional stress field significantly near the branch point after a number of earthquake cycles the branched fault systems evolve to a steady state in which several patterns of the fault prestress and earthquake rupture repeat the nonuniform prestress developed from previous earthquakes has large effects on the rupture and slip patterns several different rupture scenarios can occur on a given branched fault system in addition backward branching can occur in the nonuniform prestress field either driven by slip on the stem of the fault system or through a triggering mechanism these modeling results may have important implications for understanding fault branching behavior observed in the 1992 landers the 1999 hector mine and the 2002 denali fault earthquakes and for seismic hazard analysis in the areas where branched fault systems exist

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

deformation of compliant fault zones induced by nearby earthquakes theoretical investigations in two dimensions 1 using spontaneous rupture models with off fault elastoplastic material response we investigate the deformation of compliant fault zones induced by nearby earthquake ruptures in a two dimensional plane strain framework we find that dynamic stresses from nearby ruptures can produce inelastic strain along some portions of a fault zone that experience dilatational stress changes if the fault zone rock is close to failure in the prestress field accumulation of inelastic strain causes dramatic variations in particle velocity across the fault zone reversing the sense of fault parallel relative motion from retrograde opposite to the long term geologic slip to sympathetic consistent with the long term slip during the dynamic process in the static displacement field of a roughly parallel strike slip fault system the inelastic response of a fault zone results in sympathetic motion while the elastic response generally gives rise to retrograde motion our theoretical investigations reveal that some deficiencies may exist in applying an elastic inhomogeneity model to infer fault zone properties in previous studies including the assumption of negligible fault normal motion and ignorance of changes in some components of the stress tensor these deficiencies and possible constraints on the in situ stress state by inelastic strain signals in the static displacement field call for a reexamination of existing observations of fault zone deformation induced by recent large earthquakes

rare earth geochemistry of phosphorites abstract the abundance of rare earth elements ree s in francolite increases with increasing age as a result of post depositional enrichment abundances are higher in pelletal samples than in non pelletal ones because the higher surface mass ratio of pelletal francolite promotes enrichment during diagenesis onshore francolite has higher ree abundances than that found offshore distribution patterns in francolite may be similar to those reported for open ocean water or shale depending upon the dominant source of the ree s different patterns result from weathering and deep burial diagenetic modification of the original patterns and abundances negative ce anomalies occur in francolites containing structural sulphur that is isotopically indistinguishable from seawater of the same age zero or positive anomalies occur in francolites which contain sulphur that is isotopically lighter than seawater

assessment of seawater nd isotope signatures extracted from foraminiferal shells and authigenic phases of gulf of guinea sediments the radiogenic neodymium nd isotope composition of foraminiferal shells provides a powerful archive to investigate past changes in sources and mixing of water masses however seawater nd isotope ratios extracted from foraminiferal shells can be biased by contaminant phases such as organic matter silicates or ferromanganese coatings the removal of which requires rigorous multiple step cleaning of the samples here we investigate the efficiency of flow through and batch cleaning methods to extract seawater nd isotope compositions from planktonic foraminifera in a shelf setting in the gulf of guinea that is strongly influenced by riverine sediment inputs nd isotope analyses of reductively and oxidatively cleaned mono specific planktonic foraminiferal samples and reductively cleaned mixed benthic foraminifera were complemented by analyses of non reductively cleaned mono specific planktonic foraminiferal samples fe mn coatings of de carbonated bulk sediment leachates and the residual detrital fraction of the same sediment al ca and mn ca ratios of fully cleaned foraminiferal samples reveal indistinguishable levels of cleaning efficiency between the batch and the flow through methods and the nd isotope compositions obtained from application of both methods are identical within error furthermore non reductively cleaned foraminiferal samples have the same nd isotope composition as reductively cleaned foraminifera at our study sites close to the niger river mouth the nd isotope composition of the foraminifera agree with the seawater nd isotope composition of nearby stations based on the combined extracted nd isotope signatures and element to calcium ratios as well as rare earth element distribution patterns we infer that the planktonic foraminiferal nd isotope signatures reflect bottom water pore water signatures the isotopic composition of the bulk de carbonated sediment leachates fe mn coatings differs significantly from the foraminiferal data at this site and probably reflects particles that acquired their ferromanganese pre formed pre formed ferromanganese coatings in nearby rivers therefore in such river influenced shelf settings foraminiferal shells should be used to obtain unbiased bottom seawater signatures

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time