enhanced diapycnal mixing in the south china sea profiles of current velocity temperature and salinity were obtained in the internal wave and mixing experiment in the south china sea scs the luzon strait and the north pacific the observations are examinedforevidenceofenhanceddiapycnalmixinginthescs whichreacheso 10 23 m 2 s 21 inmagnitude resultsfrom independent casts reveal that diapycnal diffusivity in the scs andthe luzon strait is elevatedby two orders of magnitude over that of the smooth bathymetry in the north pacific which are typical of background values in an open ocean the vertical distribution of diapycnal diffusivity is nonuniform in the scs exhibiting higher values at depths greater than about 1000 m this result compares favorably with the direct microstructure measurements at four stations in the scs velocity and density profiles are combined to estimatetheinternaltideenergyfluxgeneratedintheluzonstraitanddirectedintothescs theenergyamounts to 10 gw most of which is rationalized to be the potential energy source for enhanced mixing in the scs

alteration of the damiao anorthosite complex in the northern north china craton implications for high grade iron mineralization abstract the damiao type iron deposit is hosted in a typical proterozoic anorthosite complex in the northern north china craton the types of ores in damiao mainly comprise massive fe ores massive fe p ores and disseminated fe and fe p ores the disseminated fe and fe p ores formed by fractional crystallization are generally hosted in oxide apatite gabbronorite and account for 70 of the proven reserve of the damiao type iron ore the massive fe and fe p ores account for 30 of the proven reserve of the damiao type deposit iron ore and generally occur as irregular dykes or veins filling vertical fractures of the previously consolidated anorthosite showing typical features of hydrothermal mineralization the contact between the massive orebodies and wall rocks is sharp and straight the anorthosite comprises white and dark varieties with the former resulted by the alteration of the latter that occurs as relicts petrographic observation and electron microprobe analyses show abundant fe ti oxide inclusions in plagioclase which impart the dark color to the rock the similar spider diagram patterns between fresh and altered plagioclase and between dark and white colored anorthosite imply a genetic relationship between the dark and white types during the alteration of anorthosite cao and mgo were slightly decreased the sio2 al2o3 and na2o were significantly increased and the tfe2o3 and tio2 were significantly decreased the tfe2o3 and tio2 in the dark colored anorthosite have a range of 4 86 12 18 wt and 0 37 1 65 wt respectively however the tfe2o3 and tio2 in the white colored anorthosite have a range of 1 67 3 1 wt and 0 14 0 31 wt respectively these features suggest that the alteration of the anorthosite led the fe element by leaching from the dark colored anorthosite at highly oxidized condition and then precipitated within the fractures of the anorthosite thus forming the massive fe and fe p orebodies because the estimated amount of transported fe is much more abundant than the proven ore reserve we infer that there should be huge potential for prospecting damiao type iron ores

boundary mixing and the dynamics of three dimensional thermohaline circulations boundary mixing is implemented in an ocean general circulation model such that the vertical mixing coefficient ky is nonzero only near side boundaries and in convection regions the model is used in a highly idealized configuration with no wind forcing and very nearly fixed surface density to investigate the three dimensional dynamics of the thermohaline circulation for ky 5 20 3 1024 m2 s21 and lower the meridional overturning strength to great accuracy is proportional to meridional heat transport is proportional to the circulation 2 3 1 2 kk y y patterns resemble those from runs with uniform vertical mixing but vertical motion is entirely confined to the boundary regions near the western boundary there is upwelling everywhere near the eastern boundary there is a consistent pattern of downwelling above upwelling with downwelling reaching deeper at high latitudes this pattern is explained by convection and vertical advective diffusive balance underneath for ky 5 30 3 1024 m2 s21 and higher no steady solutions have been found the meridional overturning oscillates on a timescale of about 25 years a time averaged thermally direct overturning cell is not supported dynamically because convection extends longitudinally across the entire basin and upwelling near the western boundary does not lead to densities higher than at the eastern boundary assuming uniform upwelling in the west level isopycnals near the equator and level isopycnals along the eastern boundary south of the outcropping latitude permits the analytic determination of convection depth at the eastern wall and hence the density difference between the eastern and western walls this difference is at most one quarter the surface density difference between high and low latitudes and agrees in magnitude and latitudinal dependence with the numerical experiments scaling arguments estimate overturning strength as of the order of 10 3 106 m3 s21 and confirm the 2 3 power dependence onky the derivation also gives a dependence of overturning strength with latitude that agrees qualitatively with the numerical results the scaling for the dependence of meridional heat transport on latitude agrees well with the model results scaling for heat transport amplitude agrees less well but correctly predicts a weaker dependence on ky than maximum overturning

effects of the pacific diapycnal mixing and wind stress on the global and pacific meridional overturning circulation numerical experiments are conducted using an idealized basin to investigate roles of the deep vertical diffusivity and wind stress of the pacific ocean in the global and pacific meridional overturning circulation the pacific middepth diffusivity is found to be enhancing the global meridional overturning circulation when this part of diffusivity is reduced to the background value not only is the layered circulation of the pacific greatly weakened but also the production of the north atlantic deep water nadw and antarctic bottom water aabw is significantly reduced the deeper part of the pacific diffusivity is found to be enhancing the production of the aabw in the model when the wind stress is turned off in the pacific the deep meridional overturning circulation of the pacific is reduced and the production of the nadw and aabw is also significantly reduced this is likely due to the reduction of the wind enhanced upwelling in the subpolar and equatorial regions these results suggest the importance of the diapycnal diffusion and sea surface conditions in the pacific not only to the circulation within the pacific but also to the global meridional overturning circulation

depth imaging of basalt flows in the faeroe shetland basin summary we use a grid of long offset seismic profiles to map the thickness of subsurface basalt flows that extend southeastward across the faeroe shelf offsets of up to 38 000 m were achieved using two seismic acquisition vessels towing multichannel streamers and shooting alternately wide angle reflections and refractions from the basalt and underlying strata allow us to build a velocity model down to the basement lewisian crust the velocity models give a first order picture of the geology of low velocity sediments of presumed early palaeocene and mesozoic age beneath the basalt flows they also provide a control for pre stack depth migration of the entire seismic data set thus allowing us to produce good depth images of the structure pre stack depth migration of selected wide angle arrivals such as those from the base of the basalt and the underlying basement produce strong reflection images that allow these interfaces to be identified unambiguously on the higher resolution images produced from the entire data set in particular we can distinguish between the primary and multiple reflections we thus use the very long offset arrivals to tag the velocities of the geological interfaces from which they are returned and hence to improve both the imaging and the interpretation of the basalt flows and the underlying structure

imaging of intrabasalt and subbasalt structure with full wavefield seismic tomography 1 the imaging of subsurface structure using conventional seismic reflection methods is problematic across areas where high velocity basaltic rocks are intercalated with sedimentary layers of low velocity in this study we use an approach that combines wavefield inversion of both normal incidence and wide aperture seismic data to constrain velocity structure within and beneath the basalt our field data are a two ship long offset profile acquired in the faeroe basin a conventional traveltime inversion of the wide angle data is performed to obtain a starting model for the wavefield inversion synthetic tests are used to explore resolution and to determine a strategy for inversion of the field data our final velocity model shows a high velocity basaltic layer underlain by an intermediate velocity layer that is presumably sedimentary the basalts appear highly heterogeneous in velocity and the degree of heterogeneity increases significantly with depth within the layer a prestack depth migration using the final velocity model reveals a number of new features despite the velocity heterogeneity within the basalts strong reflections are seen within and immediately beneath the basaltic section and these reflectors are more clearly imaged on the final depth migrated section than hitherto the transition from sediments to basalt does not appear to be sharp uniquely defined or locally subhorizontal the data suggest that velocity heterogeneity and the complexity of the transition from basalt to sediment may explain the difficulties of imaging beneath basalts west of britain wavefield tomography can resolve this complexity and hence improve both imaging and confidence of interpretation within and beneath basalts

iron and magnesium isotopic constraints on the origin of chemical heterogeneity in podiform chromitite from the luobusa ophiolite tibet we present high precision measurements of iron fe and magnesium mg isotopic compositions of olivine orthopyroxene and chromite separates from harzburgites dunites and chromitites in the mantle section of the luobusa ophiolite southern tibet to investigate the origins of podiform chromitite two harzburgites in the zedong ophiolite southern tibet are also reported for comparison the olivine and orthopyroxene in the luobusa and zedong harzburgites have similar fe and mg isotopic compositions with fe 56 values ranging from 0 to 0 083 in olivine from 0 034 to 0 081 in orthopyroxene and mg 26 values ranging from 0 25 parts per thousand to 0 20 parts per thousand in olivine from 0 29 parts per thousand to 0 26 parts per thousand in orthopyroxene respectively the olivines of two dunites from the luobusa display small fe and mg isotopic variations with fe 56 values of 0 014 parts per thousand and 0 116 parts per thousand and mg 26 values of 0 21 parts per thousand and 0 29 parts per thousand all chromites in the luobusa chromitites have lighter fe isotopic compositions than the coexisting olivines with fe 56 values ranging from 0 247 parts per thousand to 0 043 parts per thousand in chromite and from 0 146 parts per thousand to 0 215 parts per thousand in olivine fe 56 chr ol 0 294 to 0 101 parts per thousand the chromite mg 26 values span a significant range from 0 41 parts per thousand to 0 14 parts per thousand large disequilibrium fe and mg isotope fractionation between chromite and olivine as well as positive correlation of chromite fe 56 values with their mgo contents could be attributed to fe mg exchange between chromite and olivine in the disseminated chromitites the higher modal abundances of olivine than chromite would result in a more extensive fe mg exchange whereas chromite in the massive chromitite where olivine is rare could not be affected by this process

the regulation of northern overturning by southern hemisphere winds abstract coarse resolution models are used to study the interaction of zonal wind stress at the latitude of drake passage and the production of northern deep water a nearly linear response to wind stress at the tip of south america is seen in northern deep water production in both one and two basin configurations a comparison of steady state circulations forced by different wind stress strengths over the southern hemisphere westerlies shows the changes in circulation away from the southern ocean largely confined to western boundary currents the change in circulation accompanying stronger winds is similar to that predicted by the southern upwelling northern sinking couplet discussed by stommel transient studies are conducted in which wind stress is increased over the region of the southern hemisphere westerlies in an ocean initially stratified and at rest forced only by the southern hemisphere westerlies the development of the flow is similar to that observed by kawase in a two layer model barocli

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

the use of vertical seismic profiles in seismic investigations of the earth during the past 8 years the u s geological survey has conducted an extensive investigation on the use of vertical seismic profiles vsp in a variety of seismic exploration applications seismic sources used were surface air guns vibrators explosives marine air guns and downhole air guns source offsets have ranged from 100 to 7800 ft well depths have been from 1200 to over 10 000 ft we have found three specific ways in which vsps can be applied to seismic exploration first seismic events observed at the surface of the ground can be traced level by level to their point of origin within the earth thus one can tie a surface profile to a well log with an extraordinarily high degree of confidence second one can establish the detectability of a target horizon such as a porous zone one can determine either before or after surface profiling whether or not a given horizon or layered sequence returns a detectable reflection to the surface the amplitude and character of the reflection can also

an experimental study of the influence of oxygen fugacity on fe ti oxide stability phase relations and mineral melt equilibria in ferro basaltic systems

remote wind driven overturning in the absence of the drake passage effect zonal wind stress over the southern ocean may be responsible for a significant fraction of the meridional overturning associated with north atlantic deep water numerical experiments by tsujino and suginohara imply that the zonal periodicity of the southern ocean is not necessary for midlatitude westerly winds to drive strong remote meridional overturning here idealized numerical experiments examine the importance of zonal periodicity and other factors in setting the sensitivity of this overturning to the wind stress these experiments support the conclusion that the wind can drive remote overturning in the absence of zonal periodicity however making the subpolar ocean zonally periodic roughly doubles the strength of the overturning induced by the wind there tsujino and suginohara s experiments are especially sensitive to wind stress because their basin has a relatively small meridional range which increases the ekman transport associated with the wind stress depending on the stratification in the wind forcing region the heating associated with the westerly winds can occur almost exclusively near the surface or deeper in the thermocline as well subsurface cooling in the wind forcing region reduces the remote effects and can occur through both vertical or horizontal diffusion a scale analysis of the heat budget suggests that sufficiently strong subpolar westerlies produce remote overturning because there is no way for local cooling to balance wind induced surface heating tsujino and suginohara suggested that wind increases the overturning by enhancing the mixing driven thermohaline circulation however an increase in thermohaline circulation is associated with increased conversion of turbulent kinetic energy to potential energy this increase in the energy conversion is absent in the wind driven case indicating an important qualitative difference between mixing driven thermohaline overturning and remote wind driven overturning

experimental evidence for the exsolution of ilmenite from titaniferous spinel microintergrowths of titaniferous spinel and ilmenite have been experimentally produced in the system feti cr o by annealing in vacuo at constant temperatures in the range 700 1100 c of spinel ilmenite assemblages previously synthesized at 1300 c under controlled low f02 depending on the original f02 of synthesisat 1300 c annealing produces three types of micro intergrowths type i lowest f02 10 11 has rims and trellislike lamellae of ilmenite as well as small blebs of metallic iron type ii f02 10 10 10 9 shows spinel with rims and a few lamellae of ilmenite type iii highest f02 10 8 5 displays both spinel with rims and lamellae of ilmenite and ilmenite with rims and lamellae of spinel on the basis of microprobe analysis including precise determination of the 0 contents it is shown that the synthetic microintergrowths did not form by a redox process rather the textures represent ex solution caused by vacancy relaxation in spinel and for the most reduced samples in ilmenite according to the substitution scheme

integrated wide angle and near vertical subbasalt study using large aperture seismic data from the faeroe shetland region acquiring large aperture seismic data 38 km maximum offset along a profile crossing the faeroe shetland basin in the north atlantic enables us to use wide angle reflections and refractions in addition to conventional streamer data 0 6 km for subbasalt imaging the wideangle results are complemented and confirmed by images obtained from the conventional near vertical offset range traveltime tomography applied to the wide angle data shows a low velocity layer 3 5 4 5 km s underneath southeastward thinning lava flows suggesting a 2 5 3 0 km thick sedimentary layer the velocity model obtained from traveltime tomography is used to migrate wide angle reflections from large offsets that arrive ahead of the water wave cone the migrated image shows base basalt and sub basalt reflections that are locally coincident with the tomographic boundaries application of a new multiple suppression technique and controlled stacking of the conventional streamer data produces seismic sections consistent with the wide angle results prestack depth migration of the near vertical offsets shows a continuous base basalt reflection and a clearly defined termination of the basalt flows

magnesium isotopic evidence for chemical disequilibrium among cumulus minerals in layered mafic intrusion abstract magnesium isotopic compositions of olivine clinopyroxene and ilmenite from the baima intrusion sw china for the first time are investigated to constrain the magnitude and mechanisms of mg isotope fractionation among cumulus minerals in layered mafic intrusions and to evaluate their geological implications olivine and clinopyroxene have limited mg isotope variations with 26 mg ranging from 0 33 to 0 05 and from 0 29 to 0 13 respectively similar to those of mantle xenolithic peridotites by contrast ilmenites display extremely large mg isotopic variation with 26 mg ranging from 0 50 to 1 90 the large inter mineral fractionations of mg isotopes between ilmenite and silicates may reflect both equilibrium and kinetic processes a few ilmenites have lighter mg isotopic compositions than coexisting silicates and contain high mgo contents without compositional zoning indicating equilibrium fractionation the implication is that the light mg isotopic compositions of lunar high ti basalts may result from an isotopically light source enriched in cumulate ilmenites on the other hand most ilmenites have heavy mg isotopic compositions coupled with high mgo concentration and chemical zoning which can be quantitatively modeled by kinetic mg isotope fractionations induced by subsolidus mg fe exchange between ilmenite and ferromagnesian silicates during the cooling of the baima intrusion the extensive occurrence of kinetic mg isotope fractionation in ilmenites implies the possibility of widespread compositional disequilibrium among igneous minerals in magma chambers consequently disequilibrium effects need to be considered in studies of basaltic magma evolution magma chamber processes and magmatic fe ti oxide ore genesis

the damping effect of bottom topography on internal decadal scale oscillations of the thermohaline circulation by comparing the response of flat and bowl shaped basins to fixed heat fluxes of various magnitudes it is determined that coastal topography has a considerable damping influence upon internal decadal oscillations of the thermohaline circulation it is proposed that this is because the adjustment of baroclinic currents to the no normal flow boundary condition at weakly stratified coasts is aided in the topography case by the generation of substantial barotropic flow

iron isotope fractionation during crystallization and sub solidus re equilibration constraints from the baima mafic layered intrusion sw china abstract to better understand fe isotope fractionation between mafic minerals and oxides during crystallization of mafic magma and sub solidus re equilibration the fe isotopes of whole rocks and separated minerals olivine clinopyroxene magnetite and ilmenite of the baima mafic layered intrusion sw china have been investigated the separated minerals show a systematical decrease in 57 fe values from magnetite 0 15 to 0 51 to olivine 0 11 to 0 15 and clinopyroxene 0 35 to 0 05 and then to ilmenite 0 82 to 0 10 demonstrating regular fractionation between these minerals except for a few of samples most of the olivine and clinopyroxene are similar to those of mantle xenoliths in fe isotopes indicating that fe isotope equilibrium reached during magma crystallization was well preserved by contrast the fe isotopes of the magnetite and ilmenite may be evidently modified by sub solidus re equilibration via the fe 3 versus ti 4 and fe 2 exchange between the oxides furthermore the sub solidus re equilibration in fe isotope is strongly controlled by the proportions of magnetite and ilmenite in rocks therefore although the 57 fe ilm of the lower zone rocks with magnetite ilmenite ratios as high as 6 10 was reduced evidently by the sub solidus re equilibration the magnetite preserved their original fe isotope compositions by contrast the fe isotopes of both most magnetite and ilmenite in the middle zone had been markedly modified by sub solidus re equilibration owing to the moderate magnetite ilmenite ratios 4 7 the decreases of both 57 fe mt and 57 fe ol upwards in the cyclic units of the lower zone reveal that extensive early fractional crystallization of the magnetite resulted in depletion of heavier fe isotopes in the magma on the other hand early crystallization of olivine and clinopyroxene gave rise to the slight elevation of 57 fe ol values upwards in the cyclic units of the middle and upper zones the stratigraphic reversals in the 57 fe mt and 57 fe ol values suggest multiple magma recharges additionally the 57 fe ol values in the base of the lower zone 0 10 to 0 15 indicate that the parental magma were heavy in fe isotope due to extensive silicate mineral fractionation at depth this study indicates fractionation in fe isotope between silicates and oxides during magma crystallization and sub solidus re equilibration

disequilibrium iron isotopic fractionation during the high temperature magmatic differentiation of the baima fe ti oxide bearing mafic intrusion sw china abstract iron isotopic compositions of olivine clinopyroxene and titanomagnetite of the baima fe ti oxide bearing layered mafic intrusion sw china are used to investigate fe isotopic fractionation during the formation of the fe ti oxide ore bodies and to constrain the origin of silicate minerals and fe ti oxides the baima intrusion comprises the lower zone of interlayered troctolite clinopyroxenite and oxide ores and the upper zone of gabbros significant differences of fe isotope values between olivine fe 56 0 01 to 0 11 clinopyroxene fe 56 0 11 to 0 22 and titanomagnetite fe 56 0 20 to 0 31 were observed in rocks and ores of the lower zone iron isotopic fractionation between olivine and clinopyroxene olivine and titanomagnetite and clinopyroxene and titanomagnetite exhibits large variations of 0 06 to 0 22 0 12 to 0 27 and 0 00 to 0 20 respectively suggesting disequilibrium fractionation this disequilibrium cannot be explained by thermal or chemical gradient induced kinetic fractionation or by possible subsolidus exsolution of granular ilmenite from titanomagnetite instead it could be attributed to crystallization of silicates and titanomagnetite from two immiscible si rich and fe rich liquids continuous segregation of the fe rich liquid changed the fe isotopic composition of the si rich liquid and thus the fe isotopic compositions of olivine and clinopyroxene crystallized from it resulting in disequilibrium fe isotopic fractionation between them the effect of oxygen fugacity on the crystallization order of titanomagnetite and ilmenite from the fe rich melts on the other hand gave rise to the disequilibrium fe isotope fractionation between titanomagnetite and olivine clinopyroxene

origin of fe ti oxide ores in mafic intrusions evidence from the panzhihua intrusion sw china economicconcentrationsof fe ti oxidesoccuras massive conform able lenses or layers in the lower part of the panzhihua intrusion emeishan large igneous province sw china mineral chemistry textures and quilfequilibria indicate that oxides in rocks of theintrusion were subjected to extensive subsolidus re equilibration andexsolution the primary oxide reconstructed from compositions oftitanomagnetite in the oresand associated intergrowths isan alumi nous titanomagnetite usp

seismic structure of basalt flows from surface seismic data borehole measurements and synthetic seismogram modeling we use the wide angle wavefield to constrain estimates of the seismic velocity and thickness of basalt flows overlying sediments wide angle means the seismic wavefield recorded at offsets beyond the emergence of the direct wave this wide angle wavefield contains arrivals that are returned from within and below the basalt flows including the diving wave through the basalts as the first arrival and p wave reflections from the base of the basalts and from subbasalt structures the velocity structure of basalt flows can be determined to first order from traveltime information by ray tracing the basalt turning rays and the wide angle base basalt reflection this can be refined by using the amplitude variation with offset avo of the basalt diving wave synthetic seismogram models with varying flow thicknesses and velocity gradients demonstrate the sensitivity to the velocity structure of the basalt diving wave and of reflections from the base of the basalt layer and below the diving wave amplitudes of the

thermohaline circulation enhanced by wind forcing abstract a thermohaline circulation enhanced by wind forcing is demonstrated in an idealized basin model and a mechanism that provides a connection between wind forcing and a thermohaline circulation is clarified a rectangular ocean that extends over the northern and southern hemispheres is driven by differential heating and wind stress at the sea surface the differential heating is so distributed that the deep water is formed at the southern end of the model ocean the wind stress is so distributed that there are three wind driven gyres in the northern hemisphere and it is not imposed in the southern hemisphere comparison is made between the cases with and without the wind stress when the wind forcing is imposed the basin scale meridional circulation increases in intensity this is due to the enhanced surface heating in the cyclonic wind driven gyre with the ekman upwelling and the accompanying enhanced surface cooling in the deep water formation region in the cyclonic wind driven gyre the ekman

exploration beneath volcanics snake river plain idaho coincident gravity magnetotelluric mt and seismic reflection refraction surveys were conducted along a line traversing the boundary between the volcanic covered eastern snake river plain idaho and the sediment covered western overthrust belt one dimensional mt and seismic refraction analysis away from the immediate boundary between sediments and volcanics successfully maps the depths to units of igneous and sedimentary or metasedimentary rock substantially different models of the volcanic covered terrain and of the sediment covered terrain are linked by a gravity anomaly and by an elongation and rotation of mt anisotropy ellipses which indicate a fault fault dip depth extent and motion are constrained by marked changes in the first arrival apparent velocities and by an electrical marker layer the analysis shows that metasediments extend laterally at least 16 km beneath the volcanic cover the two terrains are connected by a boundary zone which is a major normal fault

sensitivity of the gfdl ocean general circulation model to a parameterization of vertical diffusion abstract a coarse resolution primitive equation general circulation model with idealized geometry and forcing is used to explore sensitivity to the assumption that vertical diffusion depends upon local stability a case with constant diffusivity is compared with a case in which the diffusivity is inversely proportional to the local brunt v frequency the stability dependent parameterization of vertical diffusivity yields a poleward heat flux similar to that of a small constant diffusivity however this parameterization increases the mean temperature in the deep ocean by about 0 8 c and the strength of the meridional circulation by over 40 in addition the stability dependent diffusivity is found to increase the stratification in the deep ocean the experiments suggest that it may be possible to calibrate the rate of deep water formation of general circulation models without affecting the poleward heat transport by varying the magnitude of the vertical diffusivity below the thermocline the explicit

can eddies set ocean stratification abstract a simple theory is presented for the buoyancy anomaly and depth of penetration of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous rotating fluid it is assumed that the overturning of isopycnals induced by pumping and differential heating balances the counteroverturning tendency of baroclinic instability baroclinic eddies not only develop on the stratified lens but also play a fundamental role in setting its stratification the theory is successfully tested against numerical and laboratory experiments in which the mechanically induced deepening of a buoyant lens is arrested by its baroclinic instability finally the possibility is discussed that the eddy transfer process studied here might play a role in setting the stratification and depth of the main thermocline in the ocean

interpretation of a vertical seismic profile conducted in the columbia plateau basalts seismic reflection data are often of poor quality when recorded in areas where volcanic rocks are present at or near the surface in order to investigate this phenomenon a vertical seismic profiling vsp experiment was conducted in the columbia plateau basalts so that the behavior of seismic energy in subsurface volcanic rocks could be observed directly thus giving insight into data acquisition in volcanic terrains the lithologic section at the vsp site consists of low velocity 400 m s to 900 m s alluvium in the uppermost 50 m beneath which are layers of high velocity about 5800 m s high density basalts interbedded with clay layers with much lower velocities about 1700 m s and densities these large velocity and density contrasts dramatically influence wave generation and propagation in spite of the small source borehole offset 61 m large amplitude s waves are generated by the downgoing p waves when they reach a shallow 250 m clay basalt boundary these s waves in turn generate strong

importance of the eastern indian ocean for the abyssal pacific 1 the role of the eastern indian ocean in controlling the abyssal circulation in the pacific is examined using a 1 1 world ocean model thanks to the improvement of bottom topography and the incorporation of a bottom boundary layer model the bottom water formation off the adelie coast is produced this bottom water is not only the source of the abyssal water in the eastern indian but also has a great influence on the whole abyssal pacific the lower part of circumpolar deep water cdw which enters the abyssal pacific passing through south of new zealand changes its property through mixing with this bottom water flowing underneath cdw in the australian antarctic basin and the south australia basin the tracer experiments show that the water ventilated off the adelie coast occupies about 20 of the abyssal pacific whereas north atlantic deep water nadw occupies about 50 the weddell sea bottom water about 20 and the ross sea bottom water about 10 the flux of the ventilated water estimated by the tracer experiments is 17 1 sv for nadw 6 3 sv from the weddell sea 6 2 sv from off the adelie coast and 3 5 sv from ross sea in this model the total flux of 33 1 sv is not far from the estimate from observations though it may overestimate by 1 4 sv this does not directly indicate that the real world ocean should have the large amount of the bottom water sources in the pacific indian sector however the model offers a picture of the water properties consistent with the observation

compressional wave attenuation in oceanic basalts to understand better the seismic attenuation in the upper volcanic regions of the oceanic crust compressional wave attenuations of oceanic basalts have been measured as a function of confining pressure using an ultrasonic pulse echo spectral ratio technique capable of measuring attenuations to pressures of 500 mpa seven basalts five from deep sea drilling project cores and two from dredge samples have wide ranges of densities porosities and alterations making possible an analysis of the parameters influencing basalt attenuation attenuation increases with the volume of secondary minerals present and with increasing porosity thus vesicularity and compositional changes associated with basalt alteration will produce variations in attenuation with the application of hydrostatic pressure cracks close thereby reducing attenuations this pressure dependence should be manifested in oceanic layer 2 by decreasing attenuation with depth an inverse relationship between velocity and attenuation is observed at high hydrostatic pressures water saturation increases attenuation at pressures below 200 mpa and enhances the sensitivity of attenuation to pressure thus making the state of saturation important in the 40 to 100 mpa range generally found in layer 2 these results provide a framework for interpreting marine attenuation data

identification and inversion of converted shear waves case studies from the european north atlantic continental margins summary wide angle shear wave arrivals converted from compressional to shear waves at crustal interfaces enable crustal vp vs ratios to be determined which provide valuable constraint on geological interpretations analysis of the converted shear wave phases represents the next logical step in characterizing the crustal structure and composition following multichannel seismic structural imaging and tomographic inversion of the wide angle compressional wave phases in this offshore study across two passive margins extending from stretched continental to fully oceanic crust the high data density 2 10 km ocean bottom seismometer obs spacing and a consistent efficient conversion interface produced shear wave data sets suitable for traveltime inversion the shear waves were recorded by three orthogonal geophones in each obs arrival phases visible to 180 km offset were identified using their arrival times moveout velocities and particle motions across the north atlantic volcanic rifted continental margins studied breakup was accompanied by the eruption of large volumes of basalts of the north atlantic igneous province the interface between post volcanic sediments and the top of the basalts provides the dominant conversion boundary across the oceanic crust and the continent ocean transition however the shear wave data quality was significantly diminished at the continental ends of the profiles where the thick basalt flows and hence this conversion interface feathers out and crustal attenuation increases initial modelling of the converted shear wave phases was carried out using a layer based approach with arrivals converted on the way up used to constrain the vp vs ratio of the post volcanic sedimentary sequence beneath each obs to produce a model with continuous crustal s wave velocities the compressional wave velocities beneath the sediment top basalt interface were transformed into starting shear wave velocities using a constant value of vp vs and the inversion carried out by specifying the appropriate ray path once the data set had been fully interpreted correction of the traveltimes to effective symmetric ray paths enabled us to apply a regularized grid inversion such inversions are less subjective than the layer based approach and yield more robust minimum structure results with quantifiable errors except in the vicinity of a known subbasalt low velocity zone encountered on the faroes margin monte carlo analyses were performed for this approach the average model from multiple inversions using randomized starting models and traveltimes shows the structure required by the traveltimes and the model standard deviation gives an estimate of uncertainty model and inversion parametrizations were fully tested and optimum parameters chosen for compressional and shear wave inversions this allows after appropriate model smoothing an estimate to be made of the spatial variation of the vp vs ratio within the crust there are marked gradients in vp vs and vp vs ratio across the continent ocean transition which may result from intrusion of high magnesium mafic igneous material into the crystalline continental crust the vp vs ratio used in conjunction with vp also provides constraints on the subbasalt lithologies forming the low velocity zone we conclude from such an analysis that this zone is unlikely to be composed entirely of igneous hyaloclastite material some proportion of clastic sedimentary rocks is likely to be present the vp vs and vp properties of the units underlying the low velocity zone are inconsistent with crystalline

tidally induced diapycnal mixing in the kuril straits and its role in water transformation and transport a three dimensional nonhydrostatic model experiment 1 baroclinic processes generated by the k1 tidal flow around the kuril straits and their role in the linkage between the okhotsk sea and the north pacific are investigated using a three dimensional nonhydrostatic model large amplitude unsteady lee waves are generated around sill tops all along the kuril island chain and induce significant density inversions from the sea surface down to the 27 6 density layer along with this wave breaking a large flow of energy takes place from the swift tidal flow regions to greater depths as a result of the clockwise propagation of both the topographically trapped waves around the islands and the remaining unsteady lee waves such wave generation and energy exchange eventually cause intense diapycnal mixing over the shallow topographic features and near the bottom leading to a maximum diapycnal diffusivity of over 103 cm2 s 1 even in the deep bussol strait which is thought to be the main exit of the okhotsk sea water considerable mixing corresponding to diapycnal diffusivity values of between 10 50 cm2 s 1 occurs vigorous mixing in the shallow regions produces low potential vorticity pv water in the upper layer and high pv water below accordingly pv fronts are formed along the island chain and sustain instabilities that in turn release baroclinic eddies with low core pv values these features are indicated in recent satellite imagery and in situ observations suggesting that the tide is the controlling factor in the formation of fronts observed in the kuril straits tidally induced mean transport across the straits is estimated to reach 26 sv 1 sv 106 m3 s 1 which is much larger than in the barotropic case however most of the exchanged water tends to circulate around the islands due to the effect of bottom topography whereas eddies pinched off from the tidal fronts carry the exchanged water offshore the amount of eddy driven offshore transport away from the islands reaches 14 sv with roughly half being directed to the north pacific this significant offshore transport spreads the effect of the diapycnal mixing taking place in the straits over wider areas of the north pacific and the okhotsk sea for example the pv values generated in the eddies differ by 30 40 from the ambient water on average whereas sea surface salinity within the eddies is 0 1 psu higher than the surroundings corresponding to the density increase of 0 08 thus the eddy transport provides significant pv and salinity fluxes to both the north pacific and the okhotsk sea hence we infer that a combination of tidally driven processes taking place at the passages leads to the formation of eddies that play a central role in water transport and transformation and are an essential aspect of the physical interplay between the okhotsk sea and the north pacific

geochemical and nd hf isotopic constraints on the origin of the 1 74 ga damiao anorthosite complex north china craton abstract the 1 74 ga damiao complex in the north china craton consists of anorthosite 85 norite 10 mangerite 4 and minor troctolite 75 would have been required to form the parental high al gabbroic magma from the lower crust we propose that the crustal rocks were dragged into the upper mantle during amalgamation of the north china craton where the ambient temperature was high enough 1271 c at 12 kbar to cause extensive melting producing a deep seated magma chamber the melt then evolved through polybaric crystallization producing anorthositic magmas with abundant suspended plagioclase that were finally injected at mid crustal depth to form the damiao complex

iron isotope systematics of the panzhihua mafic layered intrusion associated with giant fe ti oxide deposit in the emeishan large igneous province sw china

vertical energy flux at enso time scales in the subthermocline of the southeastern pacific the question of how energy is redistributed in the ocean has renewed the interest for the processes leading to midlatitude subthermocline variability at low frequency here we investigate a process that has been disregarded although potentially relevant for climatic studies dealing with the planetary energy budget the focus is on the southeastern pacific where an efficient oceanic teleconnection takes place linking the remote surface equatorial momentum forcing with the subthermocline through the vertical propagation of low frequency long wavelength extratropical rossby waves etrw a high resolution model is used to document the vertical energy flux associated with etrw at interannual to decadal time scales the analysis of a long term 1958 2008 simulation reveals that the vertical energy flux can be interpreted to a large extent as resulting from the coastally forced etrw as far south as 35 s so that heat content variability can be predicted along theoretical trajectories originating from the coast below the thermocline it is shown that the vertical energy flux associated with the el nino southern oscillation forms beams below the thermocline that account for a large fraction of the total vertical energy flux at interannual time scales extreme el nino events are the dominant contributor to this flux which is hardly impacted by mesoscale activity the energy beams experience a dissipation processes in the ocean below 1000 m that is interpreted as resulting from vertical turbulent diffusion our results suggest that the etrw at enso time scales are strongly dissipated at the surface but still can modulate the heat content in the deep ocean of the southeastern pacific

modeling layered structure in deep pacific circulation the layered structure of the deep pacific circulation is investigated using a multilevel numerical model with idealized geometry the circulation is driven by sea surface heating and newtonian body cooling at the southwest corner of the basin the latter forcing is intended to incorporate thermohaline forcing in the southern ocean a layered structure forms in the zonally averaged meridional circulation when the reference density for the body cooling varies vertically the density balance between vertical advection and vertical diffusion holds in the zonally averaged field as well as in the interior this balance combined with the reference density for the body cooling determines the zonally averaged vertical velocity and hence the zonally averaged meridional circulation from the zonally averaged continuity equation this two dimensional mechanism for describing the layered structure for this three dimensional rotating fluid model is identical to that for a two dimensional nonrotating fluid model the increased vertical structure is accompanied by the enhancement of some higher vertical modes which brings about various changes in the three dimensional structure such as the formation of a broad diffusive deep western boundary current

dynamics of the atlantic meridional overturning circulation and southern ocean in an ocean model of intermediate complexity abstract a steady state variable density 2 layer ocean model vlom is used to investigate basic dynamics of the atlantic meridional overturning circulation and southern ocean the domain consists of idealized rectangular representations of the atlantic southern and pacific oceans the model equations represent the depth averaged layer 1 response except for one solution in which they represent the depth integrated flow over both layers to allow for overturning water can cross the bottom of layer 1 at the velocity w e w d w m w n the three parts representing interior diffusion w d that increases the layer 1 thickness h throughout the basin mixed layer entrainment w m that ensures h is never less than a minimum value h m and diapycnal cooling processes external to the basin w n that adjust h to h n for most solutions horizontal mixing has the form of rayleigh damping with coefficient which we interpret to result from baroclinic instability through the closure v f 2 p where p 1 2 g h 2 is the depth integrated pressure gradient g is the reduced gravity coefficient and is a mixing coefficient with this interpretation the layer 1 flow corresponds to the sum of the eulerian mean and eddy mean v transport widths that is the residual circulation finally layer 1 temperature cools polewards in response to a surface heat flux q and the cooling can be strong enough in the southern ocean for g 0 south of a latitude y 0 in which case layer 1 vanishes and the model reduces to a single layer 2 solutions are obtained both numerically and analytically the analytic approach splits fields into interior and boundary layer parts from which a coupled set of integral constraints can be derived the set allows properties of the circulation upwelling driven transport out of the southern ocean m downwelling transport in the north atlantic transport of the antarctic circumpolar current and stratification atlantic thermocline depth and the latitudes y and y 0 where h thins to h m or layer 1 vanishes in the southern ocean to be evaluated in terms of model forcings southern ocean wind strength a q entrainment due to w d processes v in the southern ocean northern sinking upwelling within the atlantic subpolar gyre and to the presence of the pacific ocean a hierarchy of solutions is reported in which forcings and processes are individually introduced the complete solution set includes a wide variety of solution types with m 0 and m 0 with and without wind forcing with without and for two parameterizations of northern boundary sinking that represent cooling external to and within the north atlantic for a wide range of and a and for different closures novel aspects of the model and solutions include the following use of vlom which allows q forcing to be introduced realistically the aforementioned closure which allows v to be determined when layer 1 represents both the surface mixed layer h h m and the depth of subsurface isopycnals h h m latitude y where layer 1 outcrops in the southern ocean being internally determined rather than externally specified and a boundary layer based on gill s 1968 solution that smoothly connects the southern and atlantic ocean responses across the latitude of the southern tip of south america finally some solutions in the set are comparable to solutions to idealized ocean general circulation models ogcms in these cases our solutions provide insight into the underlying dynamics of the ogcm solutions for example pointing toward processes that may be involved in eddy saturation and compensation

fe ti v p ore deposits associated with proterozoic massif type anorthosites and related rocks abstract magmatic rocks containing economic concentrations of iron titanium vanadium and phosphorous are commonly associated with massif type anorthosites and related rocks this rock association is part of the anorthosite mangerite charnockite rapakivi granite suites that are restricted to the proterozoic understanding the geochemistry and emplacement mechanisms of ilmenite magnetite and apatite ore deposits is crucial for exploration efficient mining operations and ore processing this review discusses the controlling factors on the grade of an ore its mineralogy and its major and trace element distribution we present petrogenetic models of currently mined deposits lac tio tellnes damiao and discuss the characteristics of minor ore bodies from anorthosite provinces worldwide grenville north china craton east european craton rogaland laramie models of formation of anorthosite and related rocks are presented as well as the nature of the possible parental magmas of the suite a mineralogical classification of fe ti ores is proposed 1 gabbro noritic ilmenite ore apatite magnetite 2 ti magnetite dominated ore 3 nelsonite fe ti oxides apatite and 4 rutile ilmenite ore the stability of ilmenite and magnetite is then critically reviewed and the influence of various factors particularly oxygen fugacity and crystallization pressure is examined we discuss liquidus compositions of fe ti oxides and the behavior of important trace elements such as cr and v both of which are sensitive to fo2 variations post cumulus evolution of both oxides can occur due to re equilibration with trapped liquid re equilibration with ferromagnesian silicates exsolution oxidation reaction between ilmenite and magnetite and metamorphic overprinting these various processes are described and their effects on the oxide geochemistry are emphasized several potential ore forming processes have been invoked and can explain the formation of huge concentration of ilmenite magnetite apatite fractional crystallization can be combined with crystal sorting and plagioclase buoyancy to produce relative enrichment of dense ore minerals silicate liquid immiscibility can segregate conjugate si rich and fe rich melts the latter being enriched in fe ti p magma mixing can produce hybrid magmas located in a single phase field of the phase diagram and precipitate a pure ilmenite cumulate alternative processes are also described such as ejection of fe ti enriched residual melts by filter pressing and compaction solid state remobilization of ilmenite in veins and hydrothermal transport of fe and ti from the host anorthosite followed by concentration in veins and lenticular ore bodies the magnetic properties of fe ti ore deposits present contrasting signatures depending on whether the natural remanent magnetization is dominated by hemo ilmenite or multi domain magnetite micro and macro scale deformation features of ore rocks are intimately correlated with magma emplacement and with ballooning of the anorthosite diapir associated with gravitational sagging of dense ore bodies exploration perspectives show that oxide apatite gabbronorites are interesting targets because ilmenite in these rocks is poorer in cr and mg and because the ti resource may be combined with apatite and vanadiferous magnetite

q estimation from vertical seismic profile data and anomalous variations in the central north sea four different methods of estimating q from vertical seismic profile vsp data based on measurements of spectral ratios pulse amplitude pulse width and zeroth lag autocorrelation of the attenuated impulse are described the last procedure is referred to as the pulse power method practical problems concerning nonlinearity in the estimating procedures uncertainties in the gain setting of the recording equipment and the influence of structure are considered in detail vsp data recorded in a well in the central north sea were processed to obtain estimates of seismic attenuation these data revealed a zone of high attenuation from approximately 4 900 ft to 5600 ft with a value of 25 3 results of the spectral ratio analysis show that the data conform to a linear constant q model in addition since the pulse width measurement is dependent upon the dispersive model adopted it is shown that a nondispersive model cannot possibly provide a match to the real data no unambiguous evidence is presented that e

seismic wave attenuation in volcanic rocks from vsp experiments seismic wave attenuation in the columbia plateau basalts and snake river plain volcanics was analyzed using vertical seismic profiling vsp data the computation of attenuation coefficients is based on fitting a straight line to the logarithm of amplitude ratios computed for fixed values of frequency and variable depth this approach does not require any assumptions on the dependence of q on frequency for the columbia plateau basalts the attenuation coefficients obtained from the field data are smaller than those computed from the synthetic vsp generated using the sonic and density logs indicating that the observed attenuation is related to scattering effects and is substantially larger than the intrinsic attenuation of basalt therefore it is concluded that only a lower bound for q can be established in agreement with recent findings by other authors the effective attenuation of seismic energy in basalts about 1 1 10 4dbs m for the peak frequency is comparable to the effective attenuation observ

hydrocarbon traces in the tertiary basalts of the faeroe islands abstract hydrocarbons in the form of gases oils and waxes have been observed in the basalts of the faeroe islands in the north atlantic gases and traces of oil were observed in the outflowing water of the deep lopra 1 well drilled in 1981 the hydrocarbon gas was fairly dry with stable isotopic ratios of 13c1 3 41 4 32 4 26 5 respectively typical of a thermogenic gas high temperature gas chromatography of the oil showed that it consisted mostly of c13 60 n alkanes biomarker distribution observed by gc ms indicates that the oil was derived from a mature source rock deposited in an anoxic environment this suggests that the source rock must lie beneath the known basalts waxes exhibiting bright yellow fluorescence under uv light were observed as coatings on zeolite minerals widely distributed on the faeroe islands the waxes consist predominantly of higher n alkanes shown by htgc the fluorescence indicates the presence of aromatic compounds biomarker distribution indicated that the waxes were derived at least in part from a source rock containing some terrestrial organic matter astestified by the low amounts of oleanane present the waxes were probably deposited from traces of oil present in deeply circulating waters in fractures within the basalts coals which had been suspected to generate some of the hydrocarbons observed in the faeroese basalts were also examined vitrinite values of ro 0 5 as well as gc ms analyses of the suduroy coal extracts showed that these coals are immature and have not generated significant hydrocarbons

the validity of q estimates from borehole data using spectral ratios the measurement from borehole sonic data of q the acoustic attenuation coefficient of an earth section can be achieved in three ways forward modeling chuen and toksoez 1981 spectral ratios gladwin and stacey 1974 and inversion cheng et al 1986 the spectral ratio technique has been applied to real data goldberg et al 1985 but is unstable and not very reliable experiments have shown that the spectral ratio technique applied to waveforms gives q estimates which are lower than those measured from cores in the laboratory goldberg and zinszner 1989 we investigate this phenomenon using synthetic and real data

how much deep water is formed in the southern ocean three tracers are used to place constraints on the production rate of ventilated deep water in the southern ocean the distribution of the water mass tracer po4 phosphate star in the deep sea suggests that the amount of ventilated deep water produced in the southern ocean is equal to or greater than the outflow of north atlantic deep water from the atlantic radiocarbon distributions yield an export flux of water from the north atlantic which has averaged about 15 sv over the last several hundred years cfc inventories are used as a direct indicator of the current production rate of ventilated deep water in the southern ocean although coverage is as yet sparse it appears that the cfc inventory is not inconsistent with the deep water production rate required by the distributions of po4 and radiocarbon it has been widely accepted that the major part of the deep water production in the southern ocean takes place in the weddell sea however our estimate of the southern ocean ventilated deep water flux is in conflict with previous estimates of the flux of ventilated deep water from the weddell sea which lie in the range 1 5 sv possible reasons for this difference are discussed

origin of nelsonite and fe ti oxides ore of the damiao anorthosite complex ne china evidence from trace element geochemistry of apatite plagioclase magnetite and ilmenite abstract nelsonite and fe ti oxides ore are common in proterozoic massif type anorthosites and layered intrusions their geneses have long been controversial with existing hypotheses including liquid immiscibility between si rich and fe ti p rich melts and gravitational fractionation among apatite magnetite ilmenite and silicates in this paper we report detailed field geology and mineral geochemical studies of the nelsonite and fe ti oxides ore from the damiao anorthosite complex ne china geological observations indicate that the nelsonite and fe ti oxides ore occur as irregularly inclined stratiform like or lensoid or veins and are in sharp contact with the anorthosite and gabbronorite the widespread veins and lenses structure of the damiao nelsonite and fe ti oxides ore in the anorthosite indicates their immiscibility derived origin the apatite in the nelsonite and gabbronorite shows evolution trends different from that in the gabbronorite in the diagrams of sr versus rees and eu eu suggesting that petrogenesis of the nelsonite and gabbronorite is different from the gabbronorite compared with the gabbronorite the nelsonite and fe ti oxides ore have magnetite high in cr plagioclase high in sr and low in an and apatite high in sr low in rees with negative eu anomaly the evidence permits us to propose that the damiao fe ti oxides ore nelsonite and gabbronorite were derived from different parental magmas the gabbronorite was formed by solidification of the interstitial ferrodioritic magma in the anorthosite which was the residual magma after extensive plagioclase and pyroxene crystallization and was carried upward by the plagioclase crystal mesh in contrast the fe ti oxides ore and nelsonites and mangerite were produced by crystallization of the fe ti p rich and sio2 rich magmas respectively due to the liquid immiscibility that occurred when the highly evolved ferrodioritic magma mixed with newly replenished magmas the variation from fe ti oxides ore to nelsonite and gabbro nelsonite upwards as apatite content increases with height in the steeply inclined fe ti oxides orebodies suggest that gravity fractionation may have played important roles during the crystallization of the fe ti p rich magma

in situ investigation of seismic body wave attenuation in heterogeneous media field experiments have been carried out to study the nature and magnitude of seismic wave attenuation for a variety of lithologies in each survey two three component sets of geophones with wall clamping mechanisms were lowered down boreholes and signals originating from surface compressional and shear wave sources were recorded the data collected were corrected for spherical divergence and analyzed to determine intrinsic attenuation for situations of anomalous wavefront expansion and in cases where multiple reflection losses may be significant corrections were supplied by a synthetic seismogram programme to improve the estimates of intrinsic attenuation values of attenuation were obtained for pure sandstone sandstone marl sequences and fissured unfissured chalk sequences these formations were all near surface and relatively porous significant differences in the relative values of compressional and shear wave attenuation in the various lithologies were noted in particular compressional absorption in the fissured zones of chalk was twice the absorption associated with the seismic velocities and the absorption of shear waves fluctuated much less a large contrast in p wave attenuation was also observed between pure bunter sandstone and the sandstone marl sequence absorption was over three times as small in the former a smaller contrast was noted for shear attenuation the results obtained suggest that for the relatively homogeneous formations such as pure sandstone and unfissured chalk shear absorption was dominant over bulk absorption in contrast bulk absorption was larger than shear absorption for other formations e g the fissured chalk sequences and a partially saturated chalk section attenuation was found to be approximately proportional to frequency in all experiments

geochemistry and iron isotope systematics of coexisting fe bearing minerals in magmatic feti deposits a case study of the damiao titanomagnetite ore deposit north china craton abstract geochemical and iron isotopic compositions of magnetite ilmenite and pyrite separates from the fe ti oxide ores hosted in the damiao anorthosite type fe ti ore deposit were analyzed to investigate sub solidus cooling history of the titanomagnetite the fe ti oxides form two series of solid solutions namely ulvospinel magnetite usp mtss and hematite ilmenite hem ilmss solid solutions the magnetite separates have 14 27 mol ulvospinel while the ilmenite separates have 5 8 mol hematite major element compositions of the mineral separates suggest that the ilmenites were mainly exsolved from the usp mtss by oxidation of ulvospinel in the temperature range of 820 600 c and experienced inter oxide re equilibration with the magnetites associated with the exsolution is the substantial inter mineral iron isotope fractionation the magnetite separates are characterized by high 57fe 0 27 0 65 whereas the ilmenite separates have lower 57fe 0 65 to 0 28 two types of pyrite are petrographically observed each of which has a distinctive iron isotope fingerprint type i pyrite pyritei with higher 57fe 57fe 0 63 0 95 is consistent with magmatic origin and type ii pyrite pyriteii with lower 57fe 57fe 0 90 to 0 11 was likely to have precipitated from fluids iron isotopic fingerprints of the pyritei probably indicate variations of oxygen fugacity whereas those of the pyriteii may result from fluid activities the iron isotopic fractionation between the magnetite and ilmenite is the net result of sub solidus processes including ulvospinel oxidation and inter oxide re equilibration without needing varying oxygen fugacity albeit its presence although varying composition of magnetite ilmenite pairs reflects variations of oxygen fugacity inter oxide iron isotopic fractionation does not

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

differentiation of nelsonitic magmas in the formation of the 1 74 ga damiao fe ti p ore deposit north china the 1 74 ga damiao anorthosite complex north china is composed of anorthosite and leuconorite with subordinate melanorite mangerite oxide apatite gabbronorite perthite noritic i e jotunitic and ferrodioritic dykes the complex hosts abundant vein pod and lens like fe ti p ores containing variable amounts of apatite 10 60 modal and fe ti oxides in addition to fe ti p ores there are also abundant fe ti ores which are closely associated with fe ti p ores in the deposit most of fe ti p ores are dominated by fe ti oxides and apatite devoid of silicate minerals mineralogically similar to the common nelsonites elsewhere in contrast fe ti ores are dominated by fe ti oxides with minor apatite 5 modal the parental magma of these ores estimated from olivine and apatite compositions using mineral melt partition coefficients has composition similar to the ferrodioritic dykes fe ti p ores have variable fe ti oxides and apatite proportions indicating that they are cumulates their simple assemblage of fe ti oxides and apatite and local net texture suggest that the fe ti p ores in damiao have formed from nelsonitic melts immiscibly separated from the ferrodioritic magma during late stage differentiation fe ti ores are also cumulates and have mineral compositions similar to fe ti p ores the close association between fe ti and fe ti p ores indicates that the fe ti ores may have also formed from the nelsonitic melts we proposed that differentiation of nelsonitic melts accompanied by gravity settling is responsible for the formation of fe ti and fe ti p ores such a differentiation process in nelsonitic melts is well supported by variations of sr y th u ree and eu eu of apatite in fe ti p ores using oxides apatite ratio of 2 1 and compositions of apatite and calculated primary oxides we estimate the composition of the nelsonitic melt as 52 0 wt fe2o3t 18 5 wt cao 14 2 wt p2o5 8 7 wt tio2 4 0 wt al2o3 and 1 1 wt mgo with minor sio2 k2o na2o and f such a nelsonitic melt is suggested to be possibly conjugated with si rich melts compositionally similar to the damiao jotunitic dykes 50 wt sio2 and 15 wt fe2o3t which may subsequently evolve to mangeritic rocks in damiao our modeling also indicates that the onset of immiscibility occurs at a time when the evolved melt has 44 wt sio2 21 wt fe2o3t 3 0 wt tio2 and 2 6 wt p2o5 high oxygen fugacity and phosphorous content in magmas may play important roles in the immiscibility of nelsonitic magmas including promoting iron enrichments and widening the two liquid field

parameter sensitivity of primitive equation ocean general circulation models abstract experiments with a low resolution primitive equation ocean general circulation model with idealized basin geometry and surface forcing have been carried out in order to identify the processes controlling the climatically important aspects of the circulation emphasis was placed on the sensitivity of the model solutions to the magnitude of the vertical diffusivity scaling arguments suggest and the numerical experiments confirm that the solutions are most sensitive to the magnitudes of the wind stress curl and the vertical diffusivity for small vertical diffusivity wind forcing dominates the solution the vertical scale of the thermocline is set by the strength of the ekman pumping and there is a multiple gyre circulation in the upper layers for large vertical diffusivity diabatic surface forcing dominates the solution vertical diffusion controls the vertical scale of the thermocline and there is a single large anticyclonic gyre in the upper layers both the meridionally and zonally inte