high silicon self diffusion coefficient in dry forsterite silicon self diffusion coefficients dsi in dry synthetic forsterite single crystals were measured at temperatures of 1600 and 1800 k from ambient pressure up to 13 gpa using an ambient pressure furnace and kawai type multi anvil apparatus the water contents in the samples were carefully controlled at 1 g g diffusion profiles were obtained by secondary ion mass spectrometry sims in depth profiling mode small negative pressure dependence of dsi is determined with an activation volume of 1 7 0 4 cm3 mol the activation energy is found to be 410 30 kj mol logdsi values dsi in m2 s at 1600 and 1800 k at ambient pressure are determined to be 19 7 0 4 and 18 1 0 3 respectively these values are 2 4 orders of magnitude higher than those reported by jaoul et al 1981 we speculate that their low dsi might reflect the effects of a horizontal migration of the isotopically enriched thin films applied on the sample surfaces which may inhibit diffusion into the substrate during annealing our results for dsi resolve the inconsistency between dsi measured in diffusion experiments and those deduced from creep rates measured in deformation experiments

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

channel axis overbank and drift sediment waves in the southern hikurangi trough new zealand abstract in the southern apex of the hikurangi trough east of new zealand swath bathymetry and backscatter seismic profiles and cores from the proximal part of the 2000 km long hikurangi channel show different types of sediment waves in the channel axis and on the levee backslopes these represent different responses to large turbidity currents locally backslope sediment waves merge into sediment waves formed by a deep geostrophic flow in the channel axis and on channel walls sediment waves that have wavelengths of 1 4 km and heights of less than 6 m occur where cores show gravelly and coarse sandy turbidites they are not apparent in layering below the channel axis they are inferred to be thin transitory surface sand bodies migrating across coarser substrates and may have formed in a recent perhaps the last turbidity current their geometry suggests that they probably formed as antidunes in high velocity flows that were much thicker than the channel depth overbank sediment waves also have similar wavelengths of 1 4 km but heights of up to 45 m they have conspicuous sub seabed layering to a depth of at least 400 m beneath the seabed seismic stratigraphy indicates that they have developed for most of the last 2 ma during near vertical aggradation of the channel its levees and overbank slopes at average rates of 0 4 0 7 m ka the sediment waves migrate up levee backslopes towards the levee crest at rates of 3 20 m ka and are inferred to be formed beneath lee waves initiated in overbank flows by the linear perturbation of the levee they are best developed on the outsides of bends where centrifugal outflow of upper overspill parts of large turbidity currents might be concentrated they are particularly well developed at right hand bends on the left bank where centrifugal and southern hemisphere coriolis effects combine poorly developed sediment waves on the inside of some left hand bends may be the result of coriolis effects only overbank sediment waves decrease in height and wavelength away from the channel and continue into a depression along the slope toe deformation front at the landward edge of the turbidite plain where the channel intersects the slope toe depression the absence of a left bank levee suggests that overbank flows re enter the channel along the toe of the chatham rise sediment waves up to 5 m high and 2 5 km in wavelength migrate away from the channel and towards a slope toe moat they are inferred to be part of a drift deposit perhaps associated with a branch of the pacific deep western boundary current

si and o diffusion in mg fe 2sio4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone si and o diffusion rates on polycrystalline mg fe 2 sio 4 wadsleyite and ringwoodite have been determined at pressures between 16 and 22 gpa and temperatures between 1400 and 1600 c using a kawai type multi anvil high pressure apparatus pre synthesized polycrystalline wadsleyite or ringwoodite was used as starting materials diffusing sources of 29 si and 18 o enriched mg fe 2 sio 4 thin film were deposited on the surface of wadsleyite and ringwoodite by pulsed laser deposition the diffusion profiles were obtained using secondary ion mass spectrometry in the depth profiling mode all measured diffusion profiles were composed of volume and grain boundary diffusion regimes arrhenius relations for volume and grain boundary diffusion rates of si and o in wadsleyite and ringwoodite have been determined the results show that si is the slowest diffusing element among the major elements in both wadsleyite and ringwoodite under mantle transition zone as well as slab conditions therefore si should be the rate controlling species for high temperature creep in wadsleyite and ringwoodite comparisons with si and o diffusion rates obtained in this study and those in olivine and silicate perovskite suggest that si and o diffusion rates are enhanced at both 410 and 660 km seismic discontinuities the deformation mechanism maps constructed from si diffusion data in wadsleyite and ringwoodite suggest that the dominant deformation mechanism operating in the mantle transition zone is dislocation creep which may be the origin of the observed global seismic anisotropy under cold subduction zone conditions grain size sensitive diffusion creep becomes dominant when the grain size is reduced to less than 10 100 m below the metastable olivine wedge

mixing of heterogeneities in the mantle effect of viscosity differences the effect of viscosity variations associated with large scale chemical heterogeneities on mixing in the mantle is studied for a model two dimensional problem low viscosity regions are rapidly deformed develop long tendrils and are entrained towards regions of surface divergence very viscous regions are only slowly stretched thus geochemical reservoirs can persist relatively undisturbed for long periods of time if they are o 10 100 times more viscous than the surrounding mantle high viscosity ratio blobs have a tendency to aggregate leading to the formation of large scale heterogeneities from smaller ones

seismic evidence for a chemical heterogeneity in the midmantle a strong and slightly dipping seismic reflector beneath the mariana subduction zone 1 a clear later phase 80 s after the direct p wave is observed in most of individual seismograms recorded by a short period seismometer network in japan j array from a cluster of deep earthquakes that occurred at the northern mariana subduction zone this phase 1 shows a p wave particle motion 2 arrives later from earthquakes with shallower focal depths 3 has a steeper incident angle than that of p wave and 4 shows a deviation of a few degrees in the arrival azimuth from that of p wave we interpret it as an s to p converted wave which takes off downward from the source and is reflected at a velocity discontinuity reflector below the earthquakes travel time inversion shows that the seismic reflector dips southwest by 20 at 24 25 n 144 75 e and at a depth of 1115 km with a lateral extension at least 100 100 km the location corresponds to the lower edge of a high velocity anomaly in global tomographic models amplitude and waveform analyses suggest a decrease of s wave velocity by 2 6 and an increase of density by 2 9 within the reflector there is almost no difference in p wave velocity 1 between the reflector and the surrounding mantle the estimated thickness of the reflector is 12 km these observations indicate that the observed seismic structure is more likely to be a chemical reservoir rather than a purely thermal anomaly the seismic reflector might be a piece of subducted oceanic crust as suggested by a previous study it also could be related to the break down of the d phase of dense hydrous magnesium silicates at midmantle pressure condition reported by recent mineral physics studies both scenarios imply that mechanical chemical segregation might occur within the subducted slab at midmantle condition

mid pliocene to recent abyssal current flow along the antarctic peninsula results from odp leg 178 site 1101 abstract sediments recovered from a drift deposit located on the pacific side of the antarctic peninsula odp leg 178 site 1101 give a physical record of a bottom current sourced from the weddell sea deep water for the past 3 ma sediment grain size and magnetic fabric analyses indicate a contourite depositional environment and little change in the average intensity of this current terrigenous fluxes decreased around the time of the onset of northern hemisphere glaciation which we interpret as a freezing of the base of the antarctic peninsula ice cap terrigenous fluxes have increased since 1 7 ma implying a possible return of the antarctic peninsula ice cap to a more wet based ice sheet

seismic scatterers at the shallowest lower mantle beneath subducted slabs abstract data from a western united states short period seismic network are analyzed in order to investigate anomalous later phases within a time window from about 10 s to 120 s after direct p waves for deep and intermediate depth earthquakes in circum pacific subduction zones the anomalous phases are best interpreted as s to p scattered waves wavelengths of 10 km from heterogeneities in the shallow lower mantle depths 950 km several s to p scatterers where elastic properties of the rocks must substantially change within several kilometers are detected in the shallowest 300 km of the lower mantle beneath four circum pacific regions kuril bonin fiji and peru around most of the observed scatterers the seismic tomography models have delineated high seismic velocity anomalies which are associated with recently subducted pacific slab or nazca slab the most likely origin of the scatterers would be basalt which used to form the oceanic crust interestingly enough the majority of the scatterers are located near the bottom boundaries of the slabs given rather moderate degrees of folding and or buckling of the pacific and nazca slabs in the shallowest lower mantle at the study areas the existence of the oceanic crust associated with the most recent slab subduction at the scattering sites is unlikely alternative and more likely explanations include the presence of ancient basaltic rocks localized dehydration of hydrous minerals or a sharp boundary between different rock fabrics such as isotropic and anisotropic lower mantle rocks associated with mantle flow dragged by the slab subduction

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

elasticity of subducted basaltic crust at the lower mantle pressures insights on the nature of deep mantle heterogeneity abstract the origin of the large low velocity structures observed in the lowermost mantle is still unclear to make new insights into deep mantle heterogeneity we performed ab initio modeling of the elasticity of representative petrology with the pyrolitic and basaltic compositions based on the elasticities of the following mineral phases magnesium silicate perovskite post perovskite ferropericlase calcium silicate perovskite stishovite cacl 2 and calcium ferrite titanate type mgal 2 o 4 calculations elucidated that the basalt composite is 2 denser than the pyrolitic one through all of the pressures in the lower mantle in addition the shear v s and bulk sound v velocities were found to be 2 slower and faster in the basalt composition in particular at 30 gpa and 120 gpa respectively while both the pyrolitic and basaltic composites have almost the same compressional wave speed v p thermochemically distinct piles which are thought to be related to accumulated hot and dense subducted crusts would therefore be expected to produce as much as a 5 to 6 low velocity anomaly in the s wave but only 1 in the p wave these suggest that the basaltic pile seems less compatible to the seismological signatures of the large low velocity structures if accompanied by thermal anomalies reaching 1000 to 1500 k

effects of pressure and temperature on the silicon diffusivity of pyrope rich garnet abstract we have determined the pressure and temperature dependencies of si volume diffusion rates in a single crystal of pyp75alm15gr10 garnet at 6 25 gpa and 1400 1800 c by the 29si tracer diffusion method high pressure experiments were conducted using the kawai type multi anvil high pressure apparatus diffusion profiles were obtained using secondary ion mass spectrometry in the depth profiling mode the si diffusion coefficient in garnet dgt is expressed by the arrhenius equation dgt d0 exp e pv rt with log10d0 7 1 1 7 m2 s e 345 56 kj mol and v 4 7 0 5 cm3 mol si diffusion seems to be the slowest in the major constituent elements in a pyrope rich garnet and control rates of plastic deformation the comparison between si diffusion rates in garnet and wadsleyite ringwoodite suggests that garnet has similar or slightly lower strength at most 2 times compared with wadsleyite and has similar or slightly higher strength at most 3 times compared with ringwoodite at temperatures ranging from 900 to 1300 c thus strength contrast between subducted oceanic crust and underlying peridotite layer may be small at the mantle transition zone conditions this result suggests that the separation of subducted oceanic crust from an underlying peridotite layer may not occur

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

magnetic storm response of lower thermosphere density measurements of atmospheric density near 200 km from the satellite electrostatic triaxial accelerometer seta experiment are used to delineate the temporal seasonal latitudinal and day night dependences of the response to magnetic storm related perturbations in high latitude energetic inputs five periods of geomagnetic activity are analyzed and yield consistent results which can be interpreted within the framework of recent thermosphere ionosphere simulations by fuller rowell et al 1995 in response to a change in magnetic activity level from quiet kp 1 2 to active kp 4 7 conditions an increase in daytime 1030 lt density of order 50 70 occurs between 60 and 80 geographic latitude in the summer hemisphere with about half the maximum response in the winter hemisphere this difference is mainly due to the difference in ionization conductivity levels and hence joule heating rates between the hemispheres on the dayside penetration of the disturbance at about the 50 intensity level is realized at the equator whereas in the winter hemisphere equatorward penetration is much weaker these effects are connected with the prevailing solar driven circulation the net summer to winter meridional flow facilitates equatorward advection of the disturbance bulge in the summer hemisphere but hinders advection in the winter hemisphere in both hemispheres the daytime component of the solar driven diurnal circulation tends to oppose equatorward penetration to the same degree however on the nightside 2230 lt penetration at nearly the 100 level of both summer and winter disturbance bulges are realized to within 20 of the geographic equator this behavior is associated with the equatorward advection in both hemispheres consistent with the nighttime component of the solar driven circulation comparisons with the msise90 model hedin 1991 show it to capture the salient features of the daytime behavior but exhibits little day night asymmetry in contrast to the experimental results

simulation of low latitude ionospheric response to 2015 st patrick s day super geomagnetic storm using ionosonde derived pre vertical drifts over indian region

some mineral physics constraints on the rheology and geothermal structure of earth s lower mantle we explore the implications of recent mineral physics measurements of diffusion coefficients and melting temperatures of lower mantle materials on the rheological and geothermal structure of earth s lower mantle we show that mgsio3 perovskite is significantly stronger than mgo periclase and therefore the rheology of the lower mantle depends strongly on the geometry of a weaker phase periclase we calculate viscosities of the lower mantle for two cases 1 where periclase occurs as isolated grains and 2 where periclase occurs as continuous films using mineral physics data and models of two phase rheology we find that the effective viscosity for the former is about 10 1000 times higher than the latter we therefore suggest that the rheology of the lower mantle is structure and hence strain dependent leading to weakening at large strains due to the formation of continuous films of periclase overall depth variation of viscosity depends not only on the pressure dependence of creep but also on the geothermal gradient both mgsio3 perovskite and periclase have relatively small activation energies e g r t m with g 10 14 where r is the gas constant and t m is melting temperature and therefore the depth variation of viscosity is rather small even for a nearly adiabatic temperature gradient however the geothermal gradients consistent with the geodynamical inference of nearly depth independent viscosity are sensitive to the pressure dependence of viscosity which is only poorly understood a superadiabatic gradient of up to 0 6 k km is also consistent with mineral physics and geodynamical observations

late cretaceous and paleogene tectonic evolution of the north pacific ocean the late cretaceous history of the northern pacific ocean has not been adequately deciphered largely because a major plate reorganization occurred during the cretaceous magnetic quiet interval using primary data to reconstruct plate motions from fracture zone trends and late cretaceous seafloor spreading magnetic anomalies allows formulation of a reasonable sequence of events that accounts for all the geologic features of that region especially the emperor and chinook troughs the primary event in our reconstruction is the subduction of the old northwest pacific triple junction new relative plate motions imposed by formation of convergent boundaries along both the northern pacific and farallon plates caused the farallon plate to crack this subdivision occurred 82 m y ago and resulted in the formation of the kula and chinook plates the chinook plate was bounded on the north by the chinook kula ridge the western arm of the great magnetic bight on the west by the southern emperor trough a slowly spreading rift valley on the south by the mendocino transform and on the east by the chinook farallon ridge the northern emperor trough formed the initial western boundary of the kula plate from 82 m y ago to 50 m y ago this configuration was stable the chinook plate expanded the chinook kula ridge migrated north and the kula plate was subducted with the subduction of this ridge the chinook plate adhered to the pacific plate and the pacific farallon ridge became the north south trending feature reflected by anomalies 22 and younger this reconstruction obviates the awkward late cretaceous shifting of triple junctions found in other proposed histories and provides reasonable explanations for the several structural features of the region to achieve closure of vector triangles representing the relative late cretaceous plate motions some extension must occur presumably across the eastern mendocino fracture zone between the northern and southern portions of the farallon plate these two plates apparently were independent units between 105 and 50 m y ago the initiation and cessation of rapid north farallon north american convergence 82 and 50 m y ago may have determined the nature and duration of the laramide orogeny

global thermospheric neutral density and wind response to the severe 2003 geomagnetic storms from champ accelerometer data 1 measurements of atmospheric density near 410 km from the star accelerometer on the champ satellite are used to illustrate the spatial temporal dependence of the thermospheric response to the severe solar storms occurring during 29 october to 1 november 2003 this interval includes periods of elevated magnetic activity with kp values of 5 9 as well as undisturbed intervals that serve to define quiet time baseline densities measurements are available from 87 to 87 latitude during both day and night at local times near 1300 and 0100 hours respectively during times of maximum geomagnetic activity for this study density measurements exhibit enhancements of 200 300 northern hemisphere daytime responses are much larger than in the southern hemisphere the origins of this effect are unknown nighttime density disturbances more readily propagate to equatorial latitudes possibly facilitated by the predominant equatorward flow in both hemispheres due to the diurnal tides driven by in situ euv heating the champ density measurements are compared with density predictions from the nrl msise00 empirical density model and demonstrate some model shortcomings measurements of cross track accelerations provide the opportunity to estimate zonal winds from the equator to about 60 latitude transitioning to a measure of purely meridional winds at the turning point of the orbit near 87 latitude a periodic variation in cross track winds with an apparent period of 24 hours appears at high latitudes and exhibits similar amplitudes and temporal latitudinal structures to the empirical hwm 93 wind model when projected into the cross track direction this periodicity is due to the displacement of geomagnetic and geographic coordinates at low latitudes champ and hwm 93 both yield westward winds of order 100 ms 1 during midday under quiet magnetic conditions however during severely disturbed periods the hwm 93 winds generally show a greater westward intensification to 250 ms 1 than the champ measurements at night champ winds are near zero under quiet conditions whereas hwm 93 indicates eastward winds of order 50 100 ms 1 under disturbed conditions the champ winds shift to westward values of order 200 to 250 ms 1 while hmw 93 values do not exceed about 50 ms 1 in the westward direction the physical origins of the observed effects are difficult to isolate and unequivocal interpretation will require sophisticated numerical modeling taking into account self consistent interactions between the neutral winds drifts and ionization densities

on the motion of hawaii and other mantle plumes abstract the hawaiian hotspot and its prominent bend at 47 ma have figured prominently in the development of ideas on the nature of mantle plumes and plate motion here i review paleomagnetic analyses associated with ocean drilling program odp leg 197 which together with studies of plate circuits and geodynamic modeling results indicate southward motion of the hawaiian hotspot during formation of the emperor seamounts these analyses confirm the long posited idea that mantle plumes should be influenced by mantle flow moreover these results indicate that late cretaceous early paleogene hotspot motion was the dominant factor in forming the emperor track and thus the famous bend morphology an important corollary of this finding on hotspot motion is that long term polar wander of earth which has been inaccurately assessed by viewing paleomagnetic data in a fixed hotspot reference frame has been far less than previously thought salient points for future research raised by the odp leg 197 paleomagnetic results include the scale of mantle flow recorded by hotspot track segments and the underlying processes that cause track segments to be dominated by mantle flow rather than plate motion for given time intervals

a deep sea thermohaline flow path in the northwest pacific abstract a recent reevaluation of the bathymetry of the northwest pacific accompanied by an analysis of reflection profiler records and deep sea drilling sites provide geological evidence for a 2000 km long north south flow path east of the emperor seamounts the geological evidence is similar to that associated elsewhere with thermohaline currents as there are no present day physical oceanographic observations of a north south flowing thermohaline current i conclude that the inferred bottom current is either presently inactive or has not been observed by the methods of investigation used to determine its presence

silicon and oxygen self diffusion in stishovite implications for stability of sio2 rich seismic reflectors in the mid mantle abstract diffusion of si and o in single crystal stishovite was examined at pressures of 14 0 21 5 gpa and temperatures of 1673 2073 k self diffusion coefficients of si dsi and o d o were determined as dsi m 2 s 2 4 10 12 exp 237 kj mol 6 0 cm 3 mol p r t and d o m 2 s 7 2 10 11 exp 263 kj mol 4 8 cm 3 mol p r t respectively where p is pressure in gpa t is absolute temperature in k and r is the ideal gas constant it was revealed that diffusion of si is approximately one order of magnitude slower than that of o and thus si is the rate controlling element for plastic deformation of stishovite si diffusion in stishovite is assessed to be at least three orders of magnitude slower than that in bridgmanite under mid mantle conditions therefore it is anticipated that highly viscous sio2 rich components subducted into the lower mantle persist as the seismic reflectors for long term without mixing up with the bridgmanite dominated surrounding mantle

a speculation on the structure of the d layer the growth of anti crust at the core mantle boundary through the subduction history of the earth abstract the growth curve of the continental crust shows that large amounts of continental crust formed in the early part of the earth history are missing in order to test a hypothesis that the former crust was subducted to the deep mantle we performed phase assemblage analysis in the systems of mid oceanic ridge basalt morb anorthosite and tonalite trondhjemite granite ttg down to the core mantle boundary cmb conditions results show that all these materials can be subducted to the cmb leading to the development of a compositional layering in the d layer we speculate that there could be five layers of feo enriched melt from partial melting of morb morb crust anorthosite ttg and slab or mantle peridotite in ascending order although the polymorphic transformation of perovskite to post perovskite in mg fe sio3 may explain the seismic discontinuity at the top of the d layer d discontinuity the effects of solid solution on the sharpness of the transformation suggest that the compositional layering is more plausible for the origin of the d discontinuity the d layer can be an anti crust made up mostly of ttg anorthosite derived from the former continental crust tectonic style of the anti crust at the cmb is similar to that at the surface at both places chemically distinct layers are density stratified and are also characterized by the processes of accretion magmatism and metasomatism

radiometric ages for basement rocks from the emperor seamounts odp leg 197 1 the hawaiian emperor seamount chain is the type example of an age progressive hot spot generated intraplate volcanic lineament however our current knowledge of the age distribution within this province is based largely on radiometric ages determined several decades ago improvements in instrumentation sample preparation methods and new material obtained by recent drilling warrant a reexamination of the age relations among the older hawaiian volcanoes we report new age determinations 40ar 39ar incremental heating method on whole rocks and feldspar separates from detroit sites 1203 and 1204 nintoku site 1205 and koko site 1206 seamounts ocean drilling program odp leg 197 and meiji seamount deep sea drilling project dsdp leg 19 site 192 plateaus in incremental heating age spectra for site 1203 lava flows give a mean age of 75 8 0 6 2 ma which is consistent with the normal magnetic polarity directions observed and biostratigraphic age assignments site 1204 lavas produced discordant spectra indicating ar loss by reheating and k mobilization six plateau ages from lava flows at site 1205 give a mean age of 55 6 0 2 ma corresponding to chron 24r drilling at site 1206 intersected a n r n magnetic polarity sequence of lava flows from which six plateau ages give a mean age of 49 1 0 2 ma corresponding to the chron 21n 22r 22n sequence plateau ages from two feldspar separates and one lava from dsdp site 192 range from 34 to 41 ma significantly younger than the cretaceous age of overlying sediments which we relate to postcrystallization k mobilization combined with new dating results from suiko seamount dsdp site 433 and volcanoes near the prominent bend in the lineament sharp and clague 2002 the overall trend is increasing volcano age from south to north along the emperor seamounts consistent with the hot spot model however there appear to be important departures from the earlier modeled simple linear age progression which we relate to changes in pacific plate motion and the rate of southward motion of the hawaiian hot spot

the contour current flow along the southern iceland faeroe ridge as documented by its bedforms and asymmetrical channel fillings abstract the iceland faeroe ridge is a natural barrier to the exchange of water masses between the norwegian greenland sea and the north atlantic basin the main overflow of cold and dense water from the norwegian greenland sea through the faeroe channels results in the generation of an intense contour current flow below 600 m water depth along its southern flank side scan sonar surveys revealed an extensive pattern of various bedforms with current indicators matching well with contour flow directions previously inferred from oceanographic measurements in the shallow ridge crest area only minor current induced bedforms were observed reflecting the relatively weaker intensities of overflow across the ridge in addition to the observed bedforms surveys of a nearby ridge parallel channel system also located on the southern flank of the iceland faeroe ridge document an asymmetrical sedimentation pattern with northern channel flanks displaying condensed sedimentation this asymmetrical sedimentation pattern is attributed to the influence of the coriolis force which is the ultimate driving mechanism for the generation of contour current systems

dipping low velocity layer in the mid lower mantle evidence for geochemical heterogeneity data from western united states short period seismic networks reveal a conversion from an s to a p wave within a low seismic velocity layer greater than or equal to the 4 percent velocity difference compared to the surrounding mantle in the mid lower mantle 1400 to 1600 kilometers deep east of the mariana and izu bonin subduction zones the low velocity layer about 8 kilometers thick dips 30 to 40 southward and is at least 500 kilometers by 300 kilometers its steep dip large velocity contrast and sharpness imply a chemical rather than a thermal origin ancient oceanic crust subducted into the lower mantle is a plausible candidate for the low velocity layer because of its broad thin extent

eustatic control of calciclastic turbidites abstract global changes in sea level can be recognized in seismic sections by establishing the relationship between sea level changes and the timing of potential deep sea carbonate reservoir facies of turbidity current and debris flow origin their occurrence may be predicted prior to drilling compilation of published data suggests that throughout the phanerozoic most calciclastic turbidites tend to correspond to lowering episodes of sea level calciclastic turbidites therefore should occur primarily in association with major uncorformities caused by lowstands of sea level the data also suggest a possible lowstand of sea level during the late cretaceous campanian maastrichtian

reworking in upper mesozoic and cenozoic central pacific deep sea sediments data from deep sea drilling cores from upper mesozoic and cenozoic central pacific ocean sediments have been used to estimate the frequency with which pelagic microfossils in sediments of different ages include species which have been displaced from older deposits intruding microfossils which include planktonic foraminifera and calcareous nannofossils and to a minor degree also radiolarians and diatoms are most easily distinguished by not being contemporaneous with the sediments in which they are found presumably their occurrence arises from the mechanical reworking of oceanic sediments by bottom water currents the data suggest that there were pulses of intensive reworking around 40 myr bp 30 myr bp 15 myr bp 5 10 myr bp and during the plio pleistocene these pulses were interrupted by phases of only modest erosion on the pacific ocean floor the absence of reworking of non contemporaneous fossils in sediments older than 70 myr suggests relatively sluggish deep sea currents which were not able to erode deeply into the underlying cretaceous and in certain areas jurassic sediments

reworked neritic fossils in upper mesozoic and cenozoic central pacific deep sea sediments monitor sea level changes upper mesozoic and cenozoic pelagic sediments in the central pacific ocean contain occasional horizons with reworked and displaced fossils produced by organisms that once lived in neritic shallow water environments the flux of neritic fossils was restricted to eight intervals of low eustatic sea level during late mesozoic and cenozoic times they were eroded from shoals along the flanks of volcanic highs which often supported tropical islands and which since then have subsided

16 m y of hotspot and nonhotspot volcanism on the patton murray seamount platform gulf of alaska age progressive linear seamount chains in the northeast pacific appear to have formed as the pacific plate passed over a set of stationary hotspots however some anomalously young ages and the lack of an enriched isotopic signature in basalts from the seamounts do not fit the standard hotspot model for example published ages 28 30 ma for basalts dredged from the patton murray seamount platform in the gulf of alaska are 2 4 m y younger than the time when the platform was above the cobb hotspot however the lowermost basalt recovered by ocean drilling on patton murray yielded a 40 ar 39 ar age of 33 ma this age exactly coincides with the time when the seamount platform was above the cobb hotspot consistent with a stationary long lived mantle plume a 27 ma alkalic basalt flow recovered 8 m above the 33 ma basalt is similar in age and composition to the previously dredged basalts and may be the alkalic capping phase typical of many hotspot volcanoes a 17 ma tholeiitic basalt sill recovered 5 m above the 27 ma basalt was emplaced long after the seamount platform moved away from the hotspot and may be associated with a period of intraplate extension anomalously young phases of volcanism on this and other hotspot seamounts suggest that they can be volcanically rejuvenated by nonhotspot causes but this rejuvenation does not rule out the hotspot model as an explanation for the initial creation of the seamount platform the lack of an enriched isotopic signature in any of these basalts shows that enriched compositions are not necessary characteristics of plume related basalts the isotopic compositions of the lower basalts are slightly more depleted than the 0 9 ma products of the cobb hotspot despite the fact that the hotspot was closer to a spreading ridge at 0 9 ma it appears that this hotspot like several others has become more enriched with time

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

eustatic and tectonic controls on deposition of hybrid siliciclastic carbonate basinal cycles discussion with examples changes in sea level represent one of the dominant controls on basinal sedimentation adjacent to mixed carbonate siliciclastic sediment source areas sedimentary responses to sea level change of the siliciclastic and carbonate components of these hybrid systems commonly result in deposition of alternating siliciclastic and shelf derived carbonate basinal deposits such deposition is particularly pronounced adjacent to carbonate platforms where alternate immersion exposure of the flat platform top results in carbonate highstand deposition and siliciclastic lowstand deposition in contrast small to moderate amplitude sea level drops in distally steepened ramp settings may expose only the inner part of the gently sloping shelf resulting in lowstand deposition of mixed sil ciclastic allodapic footnote 3 carbonate sediments along active margins tectonic uplift and subsidence of sediment source areas act as additional major controls on deposition of siliciclastic carbonate basinal cycles two of the most important tectonic effects are 1 uplift of siliciclastic sediment source areas resulting in increased erosion and swamping of carbonate shelf sources and 2 exposure or immersion of shelf carbonate sediment source areas due to vertical tectonic movements most published seismic stratigraphic studies of sea level control on deep sea sedimentation focus on lowstand deposition of siliciclastic sediment and commonly neglect the contribution of allodapic carbonate sediment deposited during sea level highstands however the examples discussed in this paper indicate that highstand carbonate deposits may make up a significant proportion of many hybrid carbonate siliciclastic basinal sequences

average daytime f region disturbance neutral winds measured by uars initial results thermospheric neutral winds play important roles on the dynamics of the upper atmosphere we use extensive f region zonal and meridional wind data measured by the wind imaging interferometer windii instrument on board the upper atmosphere research satellite uars to study the mid and low latitude daytime average perturbation winds during magnetically disturbed periods we have determined the perturbation winds by subtracting the quiet time wind values along the satellite orbits our data indicate large changes in the latitudinal profiles of both the zonal and meridional disturbance winds from morning to afternoon hours the early morning zonal disturbance winds are eastward near the equator and at upper mid latitudes above 50o and westward at lower mid latitudes the mid morning and afternoon zonal disturbance wind patterns show very small amplitudes at low latitudes and increasing westward winds at mid latitudes these latitudinal profiles are in excellent agreement with the patterns derived from zonal wind measurements on board the de 2 satellite the meridional daytime perturbation winds are equatorward and have magnitudes increasing linearly with latitude with largest values in the early morning sector the

new zealand and australian cenozoic sedimentary cycles and global sea level changes a global sea level history determined by vail et al consists of 23 sea level cycles between the base of the cenozoic and the pliocene pleistocene boundary 65 to 1 8 ma we have examined the relation between this global sea level history and the new zealand and australian continental margin shallow marine sedimentary record sedimentary cycles in the australian cenozoic marginal marine sequences are bounded by unconformities of various durations the tectonic stability and aridity of the western and southwestern margin of australia during the cenozoic produced a sedimentary record dominated by hiatuses this contrasts with the relatively complete sequences of the tectonically more active southeastern marginal basins the four major sedimentary cycles in the australian cenozoic paleocene to early eocene middle to late eocene latest oligocene to late middle miocene and latest miocene to quaternary correlate with the supercycles ta tb tc td and te of vail et al in new zealand most of the cenozoic stages represent classic sedimentary cycles bounded by unconformities or correlative conformities formed as a result of large rapid eustatic sea level changes the marine tertiary sequence in new zealand consists of 23 stages of the 18 stage boundaries between the end of the paleocene 53 ma and the end of the miocene 5 ma 16 appear to correlate with the boundaries of eustatic sea level cycles eustatic sea level lowstands are well recorded as unconformities in new zealand as a result of its unique tectonic setting during the cenozoic for most of the early cenozoic until the middle oligocene 30 ma new zealand was generally subsiding after the middle oligocene this region began to be uplifted as the pacific australian plate boundary migrated onto new zealand climaxing in the latest cenozoic late pliocene quaternary thus exposing a nearly complete sequence of marine cenozoic strata well suited for the study of sedimentary cycles unconformities which form as a result of eustatic sea level changes represent a very useful correlation tool especially on continental margins with a sufficiently high terrigenous sediment supply and can be used to supplement paleontologic correlations their ultimate usefulness for correlation depends on the rapidity of the sea level changes or the speed at which sedimentary facies change in response to sea level changes if sea level changes rapidly 10 m 1 000 years stratigraphic resolution will be high 105 years but resolution decreases as the speed of sea level change decreases unconformities may well prove to be a vital tool linking the classic land based sections around the world with deep sea sections

storm time meridional wind perturbations in the equatorial upper thermosphere 1 we present observations from the coupled ion neutral dynamics investigation cindi of storm time meridional winds in the neutral atmosphere near the magnetic equator at 400 km altitude observations near the magnetic equator in the southern geographic hemisphere are dominated by energy inputs from the southern polar regions that produce south to north equatorward wind perturbations to accompany perturbations in the neutral density and temperature in one exceptional case when observations are made near midnight and the north magnetic pole rotates through the midnight sector north to south poleward meridional wind perturbations are observed just south of the magnetic equator accompanying perturbations in the neutral density on the dayside and the nightside are consistent with observed increases in the ion temperature and inferred increases in the neutral temperature in accord with hydrostatic equilibrium

glacial interglacial sediment transport to the meiji drift northwest pacific ocean evidence for timing of beringian outwashing abstract a large sediment deposit known as the meiji drift located in the northwestern pacific ocean is thought to have formed from deep water exiting the bering sea although no notable deep water forms there presently we determine the terrigenous sources since 140 ka to the drift using bulk sediment 40ar 39ar and nd isotopic analyses on the silt sized 20 63 m terrigenous fraction from ocean drilling program odp site 884 to reconstruct paleo circulation patterns there are large changes in both isotopic tracers varying on glacial interglacial cycles during glacial intervals bulk sediment 40ar 39ar ages range between 40 and 80 ma while nd isotopic values range from end 1 to 2 during interglacial intervals sediments become much younger and more radiogenic with bulk sediment ages falling to 2 15 ma and nd isotopic values ranging between end 5 and 9 these data and quantitative comparison to potential source rocks indicate that the young kamchatkan and aleutian arcs lying nw and ne of the meiji drift contribute the majority of sediment during interglacials conversely older source rocks such as those drained by the yukon river and northeast russia are the dominant origin of sediments during glacials mixing model calculations suggest that as much as 35 45 of the sediment deposited in the meiji drift during glacials is from the bering sea it remains unclear whether thermohaline type circulation or focussing of bering sea flow lead to the glacial interglacial sediment source changes observed here

abyssal bedforms as indicators of changing bottom current flow examples from the u s east coast continental rise direct indications of circulation patterns in the deep sea especially along continental rises and sediment drifts can be obtained through the analysis of abyssal bedforms such as furrows and mud waves such direct evidence of current flow will supplement indirect indicators of circulation provide by paleochemical indicators preserved in ocean sediments water that sinks in the northern north atlantic forms part of the western boundary undercurrent along the continental rise of eastern north america and the understanding of temporal changes in the speed and depth of flow along this continental rise can provide important information on how the speed at which the global conveyor system is operating changes with time studies of furrows and mud waves along the blake bahama outer ridges show that they are active sedimentary features today and that bottom flow speeds near the time of the younger dryas were increased over later intervals a more detailed analysis of bedform structure and sediments is needed to more clearly show the timing and reason for this change in sedimentation pattern

phase transition and density of subducted morb crust in the lower mantle abstract phase relations mineral chemistry and density of a natural mid oceanic ridge basalt morb composition were investigated up to 134 gpa and 2300 k by a combination of in situ x ray diffraction measurements and chemical analyses using transmission electron microscope tem results demonstrate that the morb composition consists of mgsio 3 rich perovskite stishovite casio 3 perovskite and cafe 2 o 4 type al phase in the upper part of the lower mantle the most abundant mineral of mgsio 3 rich perovskite undergoes phase transition to a cairo 3 type post perovskite phase above 110 gpa and 2500 k post perovskite phase is similar in composition to perovskite except considerably high na 2 o content stishovite transforms to cacl 2 type sio 2 phase above 62 gpa and 2000 k and further to pbo 2 type phase above 110 gpa pbo 2 type sio 2 phase includes large amount of al 2 o 3 which significantly expands its stability relative to cacl 2 type phase phase transition of casio 3 perovskite from tetragonal to cubic was also observed with increasing temperature cafe 2 o 4 type al phase is stable to the bottom of the mantle the density of morb crust was calculated using volume data combining with measured chemical compositions and calculated mineral proportions the former morb crust is denser than the average lower mantle at all depths greater than 720 km contrary to earlier predictions the subducted basaltic crust may have accumulated at the base of the mantle

tectonic evolution of the north pacific during the cretaceous quiet period the cretaceous quiet period ended with a significant reorganization of the plate tectonics of the north pacific the farallon plate broke into three primary pieces 1 the kula plate 2 a large fragment transferred to the pacific plate and 3 the continued farallon plate the time of the rearrangement is constrained to just before magnetic anomaly 34 by its presence contrasts in tectonic spreading fabric tsf the emperor trough and the chinook trough our model is based on 1 a complete reevaluation of primary bathymetric and magnetic data 2 the distribution of major troughs emperor chinook hokkaido and krusenstern 3 mapping and analysis of tsf orientation and amplitude on quiet zone crust and 4 available deep sea drilling project drill hole data east west trending magnetic reversal lineations and tsf south of the aleutian trench are bounded on the west by the buldir fracture zone at 175 e the major troughs mark the abandonment and initiation of spreading in the reorganization their absence elsewhere precludes other long distance boundary relocations emperor trough is the abandoned pacific farallon spreading center rift initiation and early slow spreading have created the high amplitude topography of the chinook trough we believe that the hokkaido trough is the initiation site of a failed oceanic rift the incorporation of large amounts of farallon plate into the pacific plate obviates the need for the very rapid pacific farallon spreading rates of previous models and significantly alters the interpretation of mid pacific geology

rapidity of freshwater calcite cementation implications for carbonate diagenesis and sequence stratigraphy abstract in less than 10 years subaerially exposed holocene oolitic sand on eleuthera island bahamas was completely case hardened by freshwater vadose calcite cementation this phenomenon demonstrates the rapidity of freshwater carbonate diagenesis and explains in part why carbonate platforms preferentially shed unconsolidated sediment during highstands and not during lowstands when they are subaerially exposed it further proves contrary to what the exxon conceptual sequence stratigraphic models imply that carbonate deposits do in fact respond differently to subaerial exposure than siliciclastic deposits case hardening of unconsolidated carbonate sediment in response to subaerial exposure and early near surface freshwater diagenesis helps explain why shallow water platform sediments are preferentially shed into adjacent basins during highstands of sea level and not during lowstands during lowstands rapid subaerial lithification of carbonate sediments retards their reworking by wind or water once lithified these deposits are further stabilized by vegetation and karstification inhibiting their transport as unconsolidated sediment into adjacent deeper water basins observations from eleuthera island also document the reciprocal processes associated with freshwater carbonate diagenesis calcium carbonate released by partial dissolution of aragonitic ooids was locally reprecipitated as pore filling low magnesian calcite cement this reciprocity is confirmed by the confinement of freshwater dissolution and cementation to the upper 10 20 cm of the subaerially exposed body of oolitic sand below this case hardened surface oolitic sands remained unconsolidated only very minor amounts of calcite cement were required for effective casae hardening

subparallel dipping heterogeneities in the mid lower mantle 1 data from western u s short period seismic networks show anomalous later phases which we interpret as s to p converted waves from heterogeneities in the mid lower mantle depths of 1000 1850 km northeast of the mariana subduction zone the geometry of the objects is mapped by a two step approach 1 computing the s to p scattering likelihood with the arrival time slowness and azimuth of the later arrivals measured by array techniques relative to direct p waves and 2 by direct use of the waveforms using semblance at least three subparallel objects are detected in the lower mantle study region with the dips of 30 to 40 southward and with a lateral extent larger than 500 km by 300 km the elastic properties associated with the heterogeneous objects appear to change within several kilometers considering their high efficiency at converting short period waves wavelengths of 5 10 km previous seismic tomography studies have not predicted significant velocity anomalies around the heterogeneities this is probably because they are below the resolution limit of present methods the three major heterogeneities are separated from each other nearly 300 km vertically and significant anomalies seem absent between each object nevertheless semblance cross sections with a finer grid size 0 1 0 1 10 km of the clearest intermediate object at 1400 1600 km show a hint that the object is not a single interface but is actually composed of double interfaces nearly 50 km apart purely thermal anomalies of kilometers scale must be transient features in the mantle and thus are highly unlikely to be the cause of the heterogeneities they should rather represent either sharp chemical variations in major element composition or sharp changes in preferred orientations of anisotropic lattice of the lower mantle minerals thermal anomalies however may be superimposed on such variations because of heat generation either by concentrated radioactive nuclei or by viscous shear heating due to deformations a plausible tectonic interpretation of these dipping objects is that they represent remnants of subducted lithospheric plates which preceded the current subduction of the pacific plate although we cannot make conclusive arguments on what the mechanism of creating such heterogeneities from these observations alone we suggest that they may represent stretched thinned and duplexed rocks within chaotic mantle flows

seismic stratigraphy of detroit seamount hawaiian emperor seamount chain post hot spot shield building volcanism and deposition of the meiji drift 1 detroit seamount one of the northernmost seamounts of the hawaiian emperor seamount chain was formed at ca 76 ma new seismic data suggest renewed volcanism as late as 25 m y after initial seamount formation we use high resolution single channel seismic scs data acquired over the summit of detroit seamount in 2001 on ocean drilling program odp leg 197 supplemented by older scs data acquired as part of the gloria mapping program of the u s geological survey to characterize the seismic stratigraphy of detroit seamount volcanic edifices occur on the summit of the seamount and are older than the oldest beds of the meiji drift early oligocene ca 34 ma on the basis of ash layers in odp drill holes we suggest the edifices were active throughout much of the eocene ca 52 34 ma with activity possibly extending into the early oligocene 34 ma hence the age difference between the shield building lavas and the postshield cones on detroit is far greater than the shield postshield age differences observed on the hawaiian islands suggesting that renewed volcanic activity and tectonic collapse may be possible on any of the hawaiian islands we confirm earlier assertions that the thick sediment cap oligocene and younger in age was deposited by an ocean bottom current with a southeastward flow direction along the northeast facing flank of the emperor seamount chain this sediment cap the meiji drift was deposited by a lower velocity current than many other sediment drifts a low angle normal fault dipping 19 suggests topographic collapse of detroit seamount sometime during the eocene or late cretaceous

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

oxygen diffusion rates in quartz exchanged with co2 oxygen self diffusion rates were determined in quartz samples exchanged with18o enriched co2 between 745 and 900 c and various pressures and the diffusion profiles were measured using an ion microprobe the activation energy q and preexponential factor d0 at p co2 p tot 100 bar for diffusion parallel to the c axis are 159 13 kj g atom and 2 10 0 75 0 55 10 8 cm2 s this rate is approximately 100 times slower than that obtained from hydrothermal experiments and 100 times faster than a previous 1 bar quartz o2 exchange experiment the oxygen diffusion rate measured at 0 6 bar 888 c and at 900 c in vacuum is in agreement with the previous 1 bar exchange experiments with18o2 the effect of higher co2 pressures is small at 900 c the diffusion rate exchanged with co2 is 2 35 10 15 cm2 s at 100 bar 2 24 10 15 cm2 s at 3 45 kbar and 8 13 10 15 cm2 s at 7 2 kbar there is probably a diffusing species other than oxygen that enhances the oxygen diffusion rate in these quartz co2 systems relative to that occurring at very low pressures or in a vacuum the effect of this diffusing species however is not as strong as that associated with h2o preserved oxygen isotope fractionations between coexisting minerals in a slowly cooled high grade metamorphic terrane will vary depending upon whether a water rich phase was present or not closure temperatures will be approximately 100 c higher in rocks where no water rich phase was present during cooling the measured fractionations between coexisting minerals in metamorphic rocks may potentially be used as a sensor of water presence during retrogression

high hydrogen solubility in al rich stishovite and water transport in the lower mantle abstract stishovite is an important phase in subducting oceanic crust the post garnet assemblage from a precursor eclogite lithology contains up to 25 stishovite at pressures above 25 gpa this stishovite may contain up to 5 wt al 2 o 3 we measured the hydrogen contents of stishovite samples synthesized at 20 25 gpa and 1200 1800 c from several starting materials containing up to 10 wt al 2 o 3 ftir spectra of stishovite show major bands at 3111 3134 cm 1 with the frequencies increasing as h 2 o and al 2 o 3 contents increase and several minor bands at 2659 2667 3240 3261 3312 3334 and 3351 cm 1 the h 2 o content of al free stishovite is in the range of 16 30 wt ppm the maximum h 2 o content of al bearing stishovite 4 4 wt al 2 o 3 synthesized at 20 gpa and 1400 c is 3010 300 wt ppm most hydrogen in stishovite is associated with al 3 substitutional defects on the octahedral si 4 site the hydrogen can occupy 40 of vacancies created by incorporation of al 3 at 20 gpa this observation along with some anomalies in the ftir spectra may indicate an alternative mechanism of al 3 incorporation into stishovite via the formation of oxygen vacancies or interstitial al i defects we report the highest h 2 o concentrations in al stishovite to date and argue that it is the most important carrier of water into the lower mantle post garnet eclogitic assemblages

posterosional volcanism in the cretaceous part of the hawaiian hotspot trail multibeam bathymetry and seismic reflection profiling shows the cretaceous products of the hawaiian hotspot to be a ridge of coalesced guyots that prolong the n nw trend of the more isolated paleocene emperor seamounts a 10 000 km2 plateau detroit plateau where the trail changes strike to nw and the obruchev rise hotspot ridge which extends to the kamchatka trench the northernmost guyots were submerged and tilted southeast by the load of new shield volcanoes added to the end of the chain then secondary volcanism built small cones on their summit platforms and in a gap between two guyots dredged rock samples and the distribution of the cones indicates that on one guyot these submarine eruptions were in the alkalic postshield stage of hawaiian volcanism and at another were probably in the alkalic rejuvenated stage seamount building eruptions at detroit plateau produced lavas nepheline melilitites that belong geochemically to the alkalic rejuvenated stage and are very similar to pleistocene lavas in the hawaiian islands however these eruptions postdated passage off the hotspot plume by a much longer time than the 0 5 2 5 m y observed in the hawaiian islands and were probably initiated by different tectonic processes

the hawaiian emperor bend older than expected the kink in the hawaiian emperor seamount chain in the pacific ocean was initiated 50 million years ago at a time when major plate motion changes occurred

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

a physical record of the antarctic circumpolar current late miocene to recent slowing of abyssal circulation abstract sediments recovered from a drift deposit lying along the pacific margin of the antarctic peninsula odp leg 178 site 1095 provide a physical record of the antarctic circumpolar current since late miocene time determination of the strength of the magnetic fabric anisotropy of magnetic susceptibility provides a proxy for current strength fabric strength declines throughout the record from high values in the late miocene a pronounced step occurs between 5 0 and 5 5 ma and values decrease more gradually since about 3 0 ma the mass accumulation rate of terrigenous sediment derived from the antarctic peninsula indicates stabilization of the antarctic peninsula ice cap prior to about 8 5 ma

self diffusion of oxygen and silicon in mgsio3 perovskite abstract we present results of simultaneous measurements of self diffusion of oxygen and silicon in magnesium silicate perovskite oxygen diffusion is 2 orders of magnitude faster than si self diffusion and fe mg interdiffusion in perovskite with d0 9 16 10 4 0 16 9 2 10 6 m2 s and q 501 80 kj mol at 25 gpa despite this high o diffusivity however the electrical conductivity of the lower mantle will be dominated by electronic conduction and the present day core is likely to be out of redox equilibrium with the mantle

bipolar atlantic deepwater circulation in the middle late eocene effects of southern ocean gateway openings we present evidence for antarctic circumpolar current acc like effects on atlantic deepwater circulation beginning in the late middle eocene modern ocean circulation is characterized by a thermal differentiation between southern ocean and north atlantic deepwater formation regions in order to better constrain the timing and nature of the initial thermal differentiation between northern component water ncw and southern component water scw we analyze benthic foraminiferal stable isotope 18obf and 13cbf records from ocean drilling program site 1053 upper deep water western north atlantic our data compared with published records and interpreted in the context of ocean circulation models indicate that progressive opening of southern ocean gateways and initiation of a circum antarctic current caused a transition to a modern like deep ocean circulation characterized by thermal differentiation between scw and ncw beginning 38 5 ma in the initial stages of drake passage opening in addition the relatively low 18obf values recorded at site 1053 show that the cooling trend of the middle late eocene was not global because it was not recorded in the north atlantic the timing of thermal differentiation shows that ncw contributed to ocean circulation by the late middle eocene 1 4 myr earlier than previously thought we propose that early ncw originated in the labrador sea based on tectonic reconstructions and changes in foraminiferal assemblages in this basin finally we link further development of meridional isotopic gradients in the atlantic and pacific in the late eocene with the tasman gateway deepening 34 ma and the consequent development of a circumpolar proto acc

models of hawaiian volcano growth and plume structure implications of results from the hawaii scientific drilling project the shapes of typical hawaiian volcanoes are simply parameterized and a relationship is derived for the dependence of lava accumulation rates on volcano volume and volumetric growth rate the dependence of lava accumulation rate on time is derived by estimating the eruption rate of a volcano as it traverses the hawaiian plume with the eruption rate determined from a specified radial dependence of magma generation in the plume and assuming that a volcano captures melt from a circular area centered on the volcano summit the timescale of volcano growth is t 2 r plate where r is the radius of the melting zone of the circular plume and plate is the velocity of the pacific plate the growth progress of a volcano can be described by a dimensionless time t t plate 2r where t 0 is chosen to be the start of volcano growth and t 1 approximates the end of shield growth using a melt generation rate for the whole plume of 0 2 km 3 yr a plume diameter of 50 km and a plate velocity of 10 cm yr we calculate that the lifetime of a typical volcano is 1000 kyr for a volcano that traverses the axis of the plume the standard dimensions are a volume of 57 000 km 3 a summit thickness of 18 km a summit elevation of 3 6 km and a basal radius of 60 km the volcano first breaches the sea surface at t 0 22 when it has attained only 5 of its eventual volume 80 of the volume accumulates between t 0 3 and t 0 7 typical lava accumulation rates start out over 50 m kyr in the earliest stages of growth from the seafloor and level out at 35 m kyr from t 0 05 until t 0 4 from t 0 4 to t 0 9 the submarine lava accumulation rates decrease almost linearly from 35 m kyr to 0 subaerial accumulation rates are about 30 lower the lava accumulation rate is a good indicator of volcano age a volcano that passes over the plume at a distance 0 4r off to the side of the plume axis is predicted to have a volume of about 60 of the standard volcano a lifetime about 8 shorter and lava accumulation rates about 15 20 smaller the depth age data for mauna kea lavas cored by the hawaii scientific drilling project are a good fit to the model parameters used given that mauna kea appears to have crossed the plume about 15 20 km off axis the lifetime of mauna kea is estimated to be 920 kyr mauna loa is predicted to be at a stage corresponding to t 0 8 kilauea is at t 0 6 and loihi is at t 0 16 the model also allows the subsurface structure of the volcanoes the interfaces between lavas from different volcanoes to be modeled radial geochemical structure in the plume may be blurred in the lavas because the volcanoes capture magma from a sizeable cross sectional area of the plume this inference is qualitatively born out by available isotopic data the model predicts that new hawaiian volcanoes are typically initiated on the seafloor near the base of the next older volcano but generally off the older volcano s flank

a possible mechanism for epeirogenic uplift continental geology is dominated by vertical movements some of these are the result of crustal shortening and extension associated with large horizontal displacements involving processes which are now understood at least in outline however both uplift and subsidence can occur without associated shortening or extension of the continental crust most investigations of such epeirogenic movements have been concerned with subsidence partly because of the economic importance of the resulting sedimentary basins and partly because of the existence of a simple model for the process1 which can account for the development of several basins in some detail2 4 however uplift has been relatively neglected and cannot be produced by the same mechanism the purpose of this paper is to examine whether epeirogenic uplift can result from the intrusion of large thicknesses of basic magma into the lower part of continental crust this suggestion was considered as a possible mechanism for the regional uplift of the colorado plateau by gilbert5 more than 100 years ago and also by holmes6 though both rejected the idea however a recent discussion of no less than 14 different mechanisms for generating uplift7 did not include this process even though it seems able to produce the observed vertical motions and also to account for some of the features of the evolution of sedimentary basins that cannot be explained by the uniform stretching model3 8 9 although the suggestion is not new the argument used here to support it is and depends on an understanding of the relationship between ocean island volcanoes and mantle circulation

silicon self diffusion in single crystal natural quartz and feldspar abstract silicon diffusion was measured in natural quartz and anorthitic feldspar under dry low pressure 0 1 mpa conditions using a 30 si tracer sources of diffusant consisted of 30 si enriched silica powder for experiments on quartz and microcrystalline 30 si doped synthetic feldspar of composition comparable to the feldspar specimens distributions of 30 si were measured with rutherford backscattering spectrometry and nuclear reaction analysis using the reaction 30 si p 31 p the following arrhenius relations were obtained for anneals at 1 atm in air for quartz transport normal to c d qtz c 7 97 10 6 exp 447 31 kj mol 1 rt m 2 s 1 transport parallel to c d qtz c 6 40 10 6 exp 443 22 kj mol 1 rt m 2 s 1 for anorthitic feldspar an 93 d an 3 79 10 7 exp 465 50 kj mol 1 rt m 2 s 1 the few successful experiments on diffusion in plagioclase of more albitic compositions an 67 and an 23 reveal si diffusivities a few orders of magnitude faster than that in the anorthite the results for these feldspars bracket the determination of caal nasi interdiffusion under dry conditions by grove et al geochim cosmochim acta 48 1984 2113 2121 suggesting that the rate limiting process is indeed si diffusion si diffusion in quartz under more reducing conditions nno is slightly slower by about half an order of magnitude than diffusion in samples annealed in air this is consistent with observations made in studies of synthetic quartz bejina and jaoul phys earth planet inter 50 1988 240 250

hawaiian xenolith populations magma supply rates and development of magma chambers hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types magma supply rates and xenolith populations magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage these magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained during the earliest and latest stages no magma storage zone exists and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava during the tholeiitic second stage magma storage reservoirs develop and persist both at the base of the ocean crust and 3 7 km below the caldera only xenoliths of shallow origin are carried to the surface by differentiated lava during the alkalic third stage magma in the shallow subcaldera reservoir solidifies and crustal xenoliths including oceanic crustal rocks are carried to the surface in lava that fractionates in an intermediate depth reservoir worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

mudwaves on the gardar sediment drift ne atlantic small amplitude 15 m mudwaves were mapped on the gardar sediment drift using the hydrosweep ds multibeam echosounder system on the r v maurice ewing improved data processing techniques allowed the swath mapped bathymetry to image features smaller than the nominal resolution 14 m of hydrosweep mudwave heights wavelengths and orientations were determined from the hydrosweep data and in conjunction with 3 5 khz profiles these mudwave fields were analyzed with regard to present models of mudwave formation mudwave crest orientation was clockwise to mean bottom flow direction and migration was to the right of measured currents for two areas on the drift this is consistent with models developed on large amplitude mudwaves using mudwave orientation and migration direction in a third area bottom current directions were inferred

the mid oligocene marshall paraconformity new zealand coincidence with global eustatic sea level fall or rise the marshall paraconformity is a regional mid oligocene unconformity that occurs widely in shelf sequences from the eastern new zealand passive continental margin the paraconformity represents a break in sedimentation of at least 3 m y and coincided with a regional sea level highstand in contrast to the prediction of global lowstand at 29 m y b p similar paraconformities are widespread on other southern continents deep sea hiatuses of similar age occurred in the adjacent southwest pacific ocean basins they may or may not have a common origin with the hiatus associated with the marshall paraconformity possible causes for the paraconformity and its associated glauconitic and bioclastic sediments are sea level fluctuations including those related to local geoidal effects or erosive bottom waters stemming from the development of antarctic glaciation or from splitting of the southern continents

bottom current sediment waves sediment drifts and contourites in the northern rockall trough four types of large scale sediment bedform occur in the northeast rockall trough broad sheeted drifts elongate drifts sediment waves and thin contourite sheets a large sheeted drift occupies the northern basin its crest can be traced for 40 km perpendicular to the bottom current flow direction elongate drifts occur adjacent to steep areas of continental slope separated from the break of slope by a moat drift crests are oriented alongslope parallel to bottom current flow elongate drifts are asymmetric with the steeper flank facing upslope sedimentation rates are higher on the downslope flank sediment waves with a wavelength of 1 2 km and wave height up to 20 m occur locally on the flanks of sheeted and elongate drifts larger waves wavelength of 3 4 km and wave height of 50 100 m occur on the flank of the wyville thomson ridge wave crests are oblique to bathymetric contours to drift crests and to bottom current flow the association of sediment waves and drifts their orientation oblique to regional slopes and the presence of contourite sediments in cores indicate that these are bottom current rather than turbidity current waves a contourite sheet typically 10 25 cm in thickness and composed of well sorted sand covers the present day seafloor along the lower slope bedform evolution through time has involved a complex interaction between bottom currents of variable intensity sea level change and sediment input the present sea level highstand is characterised by minimal sediment input and redistribution of sediments by strong bottom currents giving active bedform growth and contourite development variability of sediment input is the main factor affecting sedimentation during sea level lowstands where input was high as when ice sheets reached the shelf edge downslope sediment transport dominated overwhelming any bottom currents that were active when input was low such as during the last lowstand some evidence for active currents can be observed although these were less energetic than those during highstands

constraints on past plate and mantle motion from new ages for the hawaiian emperor seamount chain 1 estimates of the relative motion between the hawaiian and louisville hot spots have consequences for understanding the role and character of deep pacific mantle return flow the relative motion between these primary hot spots can be inferred by comparing the age records for their seamount trails we report 40ar 39ar ages for 18 lavas from 10 seamounts along the hawaiian emperor seamount chain hesc showing that volcanism started in the sharp portion of the hawaiian emperor bend heb at 47 5 ma and continued for 5 myr the slope of the along track distance from the currently active hawaiian hot spot plotted versus age is constant 57 2 km myr between 57 and 25 ma in the central 1900 km of the seamount chain including the heb this model predicts an age for the oldest emperor seamounts that matches published ages implying that a linear age distance relationship might extend back to at least 82 ma in contrast hawaiian age progression was much faster since at least 15 ma and possibly as early as 27 ma linear age distance relations for the hawaii emperor and louisville seamount chains predict 300 km overall hot spot relative motion between 80 and 47 5 ma in broad agreement with numerical models of plumes in a convecting mantle and paleomagnetic data we show that a change in hot spot relative motion may also have occurred between 55 ma and 50 ma we interpret this change in hot spot motion as evidence that the heb reflects a combination of hot spot and plate motion changes driven by the same plate mantle reorganization

evolution of pliocene to recent abyssal sediment waves on bounty channel levees new zealand abstract levees bordering bounty channel 900 km east of new zealand accommodate a 400 m thick sequence maximum of sediment waves that have formed since pliocene times these bedforms with amplitudes of 2 17 m and wavelengths of 0 6 6 km occur in 4100 4900 m of water and were formed by turbidity currents as indicated by their restriction to levee backslopes the frequent occurrence of turbidites in cores and the preferential but not exclusive development of waves on the left bank levee in accord with the southern hemisphere coriolis deflection the wave field was instigated in the late pliocene when glacially lowered sea level allowed rivers draining the southern alps of south island to discharge directly into bounty channel and its attendant canyons the field grew vertically through the coalescence of small waves into larger bedforms that continually migrated across and up levee backslopes at an average rate of 5 6m 100 yrs wave growth decreased into the late pleistocene probably in response to progressive containment of turbidity currents as the relief of bounty channel increased to 200 m or more the glacial periods of wave growth were interrupted by interglacial interludes of quiescence when the field was draped mainly by pelagic calcareous ooze

precise determination of post stishovite phase transition boundary and implications for seismic heterogeneities in the mid lower mantle abstract the phase transition boundary between stishovite and cacl2 type structure in pure sio2 was investigated at 45 75 gpa and 300 2490 k based on the in situ x ray diffraction measurements in a laser heated diamond anvil cell lhdac results show that the boundary has a positive dp dt slope of 11 1 mpa k and the transition occurs about 70 gpa at 2200 k along the typical mantle geotherm this corresponds to a depth of 1700 km somewhat shallower than the previous estimate seismic heterogeneities have been found in a wide depth range from 800 to 1850 km in the upper to middle layers of the lower mantle the post stishovite phase transition is known to be ferroelastic type which causes a considerable reduction in shear modulus leading to a large slow shear velocity anomaly the almost pure sio2 phase included in subducted crustal materials may be therefore responsible for the relatively deep mid lower mantle seismic heterogeneities the shallow lower mantle anomalies are possibly caused by the similar phase transition in sio2 phase containing al2o3 and h2o or by the phase transition in al bearing casio3 perovskite from cubic to tetragonal structure

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined