late proterozoic lavas of the central arabian shield evolution of an ancient volcanic arc system a petrological assessment of 11 volcano sedimentary belts in the central arabian shield cas using 118 new analyses is presented the same samples have been used in a rb sr dating programme also reported in this volume the oldest volcano sedimentary belts sequence c 900 ma are chemically immature bimodal suites of low k tholeiites and sodic dacite rhyolite depleted in lithophile elements these lavas have chemical characteristics similar to immature island arcs such as the tonga kermadee and lesser antilles arcs younger lavas of sequence b 900 700 ma are slightly more mature in composition being predominantly calc alkaline and low k arc tholeiite series with higher lithophile element contents they are comparable with pacific island are averages the youngest voluminous lavas sequence a 700 570 ma are generally calc alkaline or high k calc alkaline series lavas with moderately high lithophile element abundances they are comparable to volcanic arcs such as central america and indonesia which are transitional between island arcs and continental margin volcanic arcs the cratonization process in the cas thus involved the superimposition of three volcano sedimentary sequences formed in progressively maturing volcanic arcs early formed immature island arcs were succeeded by chemically more mature island arc deposits and then by deposits formed in volcanic arc s transitional between island arcs and continental margins the evolution ceased at this stage and probably did not advance to the equivalent of an andean continental margin

petrogenesis and tectonic setting of late precambrian ensimatic volcanic rocks central eastern desert of egypt abstract early stages in the geologic evolution of the central eastern desert of egypt ced reflect an intense episode of ensimatic volcanic activity similar to modern magmatism of the ocean floors and island arcs this paper reports results from studies of the petrology and petrogenesis and interprets the significance of these late precambrian volcanic rocks a three fold stratigraphy is preserved in the basement of the ced a basal section of oceanic crust includes ultramafics gabbros and pillowed basalts these older metavolcanics omv are conformably succeeded by dominantly volcanogenic metasediments which are in turn succeeded by a dominantly andesitic calc alkaline sequence of younger metavolcanics ymv the omv and ymv are largely restricted to the ced in egypt but analogous terranes are found in northern arabia 40 400 ppm and ni 30 260 ppm they are poor in k 2 o 0 05 0 92 rb 0 3 5 0 ppm and ba 11 89 ppm on ti zr cr v ni p discriminant diagrams the omv plot in the field of modern abyssal tholeiites high k rb 450 1800 and light ree depletions support this inference although k ba 25 45 is lower than modern mid ocean ridge basalts morb the sum of omv geochemical characteristics requires that these magmas were derived by the fractional fusion of the mantle it is suggested that the omv were generated by 20 25 fractional melting of previously depleted mantle at depths of less than 60 km relatively little fractionation accompanied ascent to the surface where the omv were erupted in a primitive crustal environment either a small oceanic rift or a back arc basin metamorphism of the ymv resulted in little elemental redistribution these andesites have sub alkaline clinopyroxenes and major element geochemical characteristics indistinguishable from modern calc alkaline andesites ymv andesites in the central and western ced have k rb 400 600 k ba 20 40 and are light ree enriched and heavy ree depleted high concentrations of cr 50 150 ppm and ni 20 100 ppm and low initial 87 sr 86 sr ratios 0 7028 0 7030 indicate that these magmas were generated by melting in the mantle modelling studies and consideration of experimental data indicate that these andesites were formed by 2 10 fractional fusion of hydrous undepleted garnet therzolite at depths of 65 km or more in the mantle the data show that an intense episode of instability convection and widespread melting occurred in the mantle beneath afro arabia at the end of the precambrian

m2 baroclinic tide variability modulated by the ocean circulation south of japan we analyze a concurrent simulation result of the ocean circulation and tidal currents using a data assimilative ocean general circulation model covering the western north pacific with horizontal resolution of 1 36 to investigate possible interactions between them four sites of active m2 internal tide variability in open ocean hot spots such as tokara strait izu ridge luzon strait and ogasawara ridge are detected from both the satellite observation and the simulation energy cycle analysis of the simulated m2 baroclinic tide indicates two types of the hot spots dissipation tokara strait and izu ridge and radiation luzon strait and ogasawara ridge dominant sites energy conversion from barotropic to baroclinic m2 tides at the hot spots is modulated considerably by the lower frequency changes in the density field modulation at the two spots tokara strait and izu ridge is affected by the kuroshio path variation together with the seasonal variation of the shallow thermocline at the other two sites influence from changes in the relatively deep stratification through the kuroshio intrusion into south china sea luzon strat and mesoscale eddy activity ogasawara ridge is dominant in the modulation

continental oceanic crustal transition off southwest africa more than 1 426 mi 2 300 km of 48 trace 12 fold seismic reflection profiles were used to examine the nature of the continent ocean boundary off southwest africa south of the orange river faulted blocks which we interpret as rifted continental crust can be traced seaward to the 3 km isobath the transition to oceanic basement occurs in a zone 19 to 25 mi 30 to 40 km wide beneath the continental rise although structural details are obscured by a thick seaward dipping wedge of pre aii pre late early cretaceous overburden oceanic crust at the presumed contact is not older than magnetic anomaly m9 126 to 121 m y b p north of the orange river a pronounced hinge in continental crust correlates with magnetic anomaly g of rabinowitz 1976 seaward of the hinge a complex fault block terrane is evident oceanic basement can not be traced with any certainty landward of anomaly m4 intracontinental stretching and associated volcanism appear to have been important in the early history of the cape basin rifting and local dike intrusion may explain the presence of some lineated magnetic anomalies previously attributed to sea floor spreading related extrusives form at least part of the pre aii wedge just seaward of the hinge zone our interpretation of the seismic data suggests that the initiation of normal spreading in the cape basin postdates by 4 to 9 m y the valanginian age derived from prevailing plate tectonic reconstructions of the south atlantic

open boundary condition for circulation models a persistant difficulty in modeling continental shelf and estuarine circulations is that associated with the correct specification of conditions on the open boundaries this paper deals with the application of a new form of radiation condition on the open boundaries which permits the mean subtidal and tidal forcing to be prescribed and yet allow transients generated inside the region to be transmitted outwards a numerical model of shelf circulation is formulated using vertically integrated equations which accounts for tidal and transient wind forcing as well as the effect of density gradients and the offshore large scale oceanic circulation the shelf model is dynamically linked to a storm model the circulation model is applied to the middle atlantic bight in a study of its response to a migratory storm superimposed on the sub tidal and tidal circulation the major estuaries of the region chesapeake bay delaware bay and long island sound are included in the domain albeit at a resolution coarser than desirable the model results are consistent with those of earlier observational and modeling studies

observations of energetic high wavenumber internal waves in the kuroshio abstract intense and spatially coherent shear layers were detected in and under the kuroshio in an april 2000 survey in the east china sea the sloping layers revealed by shipboard doppler sonars on the r v roger revelle appeared to cross isopycnal surfaces except in a small region near the kuroshio shelfbreak front the rms finescale shear associated with the layers significantly exceeded the geostrophic shear an april 2002 follow on cruise was organized to establish whether these motions were propagating internal waves shipboard and lowered adcps were both operated from the r v melville in addition to ctd sonar transects a 30 h time series of currents and shear was obtained in the core of the kuroshio near the island of kyushu japan the shear structures were indeed found to be propagating with both up and down going internal wave motions present in comparison with the nearby open ocean the finescale 160 m vertical shear variance is increased by a factor of 3 in the kuroshio and by a fact

the structure of the lower crust at the argentine continental margin south atlantic at 44 s abstract it is well established that the argentine passive margin is of the rifted volcanic margin type this classification is based primarily on the presence of a buried volcanic wedge beneath the continental slope manifested by seismic data as a seaward dipping reflector sequence sdrs here we investigate the deep structure of the argentine volcanic margin at 44 s over 200 km from the shelf to the deep oceanic argentine basin we use wide angle reflection refraction seismic data to perform a joint travel time inversion for refracted and reflected travel times the resulting p wave velocity depth model confirms the typical volcanic margin structure an underplated body is resolved as distinctive high seismic velocity vp up to 7 5 km s feature in the lower crust in the prolongation of a seaward dipping reflector sequence a remarkable result is that a second isolated body of high seismic velocity vp up to 7 3 km s exists landward of the first high velocity feature the centres of both bodies are 60 km apart the high velocity lower crustal bodies likely were emplaced during transient magmatic volcanic events accompanying the late rifting and initial drifting stages the lateral variability of the lower crust may be an expression of a multiple rifting process in the sense that the south atlantic rift evolved by instantaneous breakup of longer continental margin segments these segments are confined by transfer zones that acted as rift propagation barriers a lower crustal reflector was detected at 3 to 5 km above the modern moho and probably represents the lower boundary of stretched continental crust with this finding we suggest that the continent ocean boundary is situated 70 km more seaward than in previous interpretations

internal tidal energy fluxes in the south china sea from density and velocity measurements by gliders 1 internal tidal energy fluxes were obtained from june 2011 to august 2011 using underwater gliders in the south china sea spray gliders profiled every 2 h to 500 m which is deep enough given the shallow thermocline to compute mode 1 fluxes from vertical mode fits to tidal displacements and currents westward mode 1 diurnal and semidiurnal fluxes exceeded 40 and 30 kw m 1 to our knowledge these flux observations are the first from both velocity and density measurements by gliders fluxes compare well with a mooring near a generation site in southern luzon strait and a regional model furthermore the zonal depth structure of the internal tide is obtained by binning measurements which cover four spring neap cycles and over 100 km along 20 39 n westward phase propagation is found for currents and displacements while roughly constant phase is found along beams both these features of the phase suggest a narrow banded internal tide semidiurnal energy density is largest along a raypath which coincides with generation sites on both the eastern and western ridges in luzon strait diurnal energy density is surface intensified consistent with relatively shallower diurnal raypaths emanating from the eastern ridge

single zircon dating constraining the maximum age of the barberton greenstone belt southern africa one of the central issues in early precambrian crustal evolution is the age and genetic relationship between greenstone belt supracrustal assemblages and nearby high grade gneiss terranes the crucial question in most cases is which of the two is older we report zircon ages using the new single grain evaporation technique from a metaquartzite and a felsic volcanic flow of the onverwacht group in the barberton greenstone belt bgb south africa and swaziland that constrain the age of this basal part of the greenstone sequence between 3451 15 and 3438 6 ma this is almost 100 ma younger than previous age estimates assigned to the onverwacht and agrees well with recent sm nd pb pb and zircon ion microprobe dating tonalitic orthogneisses of the ancient gneiss complex agc adjacent to the bgb have ages up to 3644 4 ma and are thus demonstrably older than the greenstones also they cannot be derived from them by partial melting as has been proposed previously this age relationship as well as the presence of metaquartzites and thrust slices of pregreenstone tonalite in the onverwacht tectonic sequence rule out an entirely oceanic evolution for the early history of the bgb and suggest that continental crust was either below or nearby

deep structure of the western south african passive margin results of a combined approach of seismic gravity and isostatic investigations abstract the passive margin of the south atlantic shows typical features of a rifted volcanic continental margin encompassing seaward dipping reflectors continental flood basalts and high velocity density lower crust at the continent ocean transition probably emplaced during initial seafloor spreading in the early cretaceous the springbok profile offshore western south africa is a combined transect of reflection and refraction seismic data this paper addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives the velocity modelling revealed a segmentation of the margin into three distinct parts of continental transitional and oceanic crust as observed at many volcanic margins the lower crust is characterised by a zone of high velocities with up to 7 4 km s the conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities found to be 3100 kg m 3 both approaches identified the body to have a thickness of about 10 km yet the gravity modelling predicted the transition between the high density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal finally isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced the results imply isostatic equilibrium over large parts of the profile smaller deviations are supposed to be compensated regionally the calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km

east west asymmetry in nonlinear internal waves from luzon strait the nonhydrostatic regional ocean modeling system is applied to study the effects of thermocline shoaling deepening bathymetry and asymmetric modulated tides on the soliton growth to the west and east of luzon strait in the south china sea and western pacific ocean luzon strait comprises a shallow east ridge and a deep west ridge and its interaction with barotropic tidal currents yields strong westward internal tides that disperse into solitons satellite imagery indicates that the westward solitons are more numerous and better defined than the eastward solitons the model results show that the eastward solitons are 45 39 28 and 23 smaller than the westward solitons due to asymmetric modulated barotropic tides at the east ridge a deeper pacific ocean westward thermocline shoaling related to the kuroshio current and internal tide resonance in a double ridge configuration respectively due to the westward location of the kuroshio little thermocline deepening occurs east of the east ridge hence the influence of thermocline deepening on counteracting eastward soliton growth is small the kuroshio mainly enhances westward soliton growth the dispersion of internal tides into solitons is governed by the balance between the nonlinearity parameter on the one hand and the nonhydrostatic and coriolis dispersions on the other it is shown that this balance favors soliton growth for thermocline shoaling while it counters it for a deeper ocean a series of double ridge experiments is performed in which the distance between the ridges and the height of the west ridge are varied for a semidiurnal tidal forcing and two gaussian ridges separated by 100 km barotropic to baroclinic energy conversion is enhanced at both ridges causing larger westward internal tides and solitons the combination of coriolis forcing thermocline shoaling and a double ridge configuration enhances the distinctiveness of the so called type a and b solitons when a modulated tide occurs

birth of a volcanic margin off argentina south atlantic 1 based on a dense grid of multichannel reflection seismic lines we study the evolution of a volcanic rifted margin segment off argentina the segment under study is located between 44 s and 41 s we describe in detail the facies of the extrusive basaltic complexes across the margin these include single and multiple inner seaward dipping reflectors sdrs with varying architecture along the margin outer highs and outer sdr wedges a detailed interpretation of a transitional zone between the inner and outer sdr wedges is presented multiple inner sdrs are concentrated at the southern part of the margin segment while in the north only one steeply dipping wedge is present the dip of the inner sdr wedges changes along the margin and we propose subsidence by loading as main cause the transitional zone between the inner and outer sdr wedges becomes narrower toward the north by correlating with magnetic data we conclude that the emplacement of the 30 100 km wide multiple inner sdrs occurred episodically we propose an injection center which migrated in a seaward direction with proceeding extension as the origin for the multiple inner sdrs a scissor like opening of the margin segment resulted in different amounts of stretching along strike of the margin segment and is likely the cause for the varying distribution of the extrusive basaltic complexes the varying extension rates within the margin segment contribute to decreasing volumes of melts generated in a northward direction within this rift segment

three dimensional double ridge internal tide resonance in luzon strait abstractthe three dimensional 3d double ridge internal tide interference in the luzon strait in the south china sea is examined by comparing 3d and two dimensional 2d realistic simulations both the 3d simulations and observations indicate the presence of 3d first mode semi diurnal standing waves in the 3 6 km deep trench in the strait as in an earlier 2d study barotropic to baroclinic energy conversion flux divergence and dissipation are greatly enhanced when semidiurnal tides dominate relative to periods dominated by diurnal tides the resonance in the 3d simulation is several times stronger than in the 2d simulations for the central strait idealized experiments indicate that in addition to ridge height the resonance is only a function of separation distance and not of the along ridge length that is the enhanced resonance in 3d is not caused by 3d standing waves or basin modes instead the difference in resonance between the 2d and 3d simulations is attributed to the topographic blocking

internal tides recorded at ocean bottom off the coast of southeast taiwan an ocean bottom experiment consisting of an array of four ocean bottom seismometers obs was conducted off the coast of southeast taiwan during may july 2011 we develop comprehensive analyses of the space time kinematics of the tidal signals recorded in the compact high sensitivity temperature loggers chtl and the obs geophones at the ocean bottom with depths ranging from 1254 to 1610 m the evidence suggests that internal tides are responsible for the recorded signals baroclinic internal waves mainly the m2 tide are generated by barotropic tidal currents in the luzon strait the internal tides exhibit gradual phase changing and irregularly fluctuating strength leaving signatures in the chtl as ambient temperature variations signifying low mode wave motions within the stratified water layers and in obs geophones as intermittent tremor agitations signifying high mode turbulent flows on the seafloor the m2 internal tides across our array are found to propagate in the northeast direction at speeds ranging from 1 to 2 m s 1 furthermore the internal tides are identified at the ocean bottom based on an operational hydrodynamic hindcast forecast model the simulations show good agreement with the observed temperature variation on the seafloor and substantiate the vertical velocity and displacement of the water parcel driven by the internal tides the joint detection of the temperature and tremor signals provides further information about the interactions of internal tides with the seafloor topography and the associated energy dissipation our results elucidate the space time ubiquity of the internal tides at the ocean bottom which is an important interface of dynamic oceanography

magmatic unmixing in spinel from late precambrian concentrically zoned mafic ultramafic intrusions eastern desert egypt abstract spinel is widespread in the ultramafic core rocks of zoned late precambrian mafic ultramafic complexes from the eastern desert of egypt these complexes gabbro akarem genina gharbia and abu hamamid are precambrian analogues of alaskan type complexes they are not metamorphosed although weakly altered each intrusion is composed of a predotite core enveloped by pyroxenites and gabbros at the margin silicate mineralogy and chemistry suggest formation by crystal fractionation from a hydrous magma relatively high cr 2 o 3 contents are recorded in pyroxenes up to 1 1 wt and amphiboles up to 1 4 wt from the three plutons the chrome spinel crystallized at different stages of melt evolution as early cumulus inclusions in olivine inclusions in pyroxenes and amphiboles and late magmatic intercumulus phase the intercumulus chrome spinel is homogenous with narrow range of chemical composition mainly fe 3 rich spinel spinel inclusions in clinopyroxene and amphibole reveal a wide range of al 27 44 wt al 2 o 3 and mg 6 13 wt mgo contents and are commonly zoned the different chemistries of those spinels reflect various stages of melt evolution and re equilibration with the host minerals the early cumulus chrome spinel reveals a complex unmixing structures and compositions three types of unmixed spinels are recognized crystallographically oriented irregular and complete separation unmixing products are al rich type i and fe 3 rich type ii spinels with an extensive solid solution between the two end members the compositions of the unmixed spinels define a miscibility gap with respect to cr al fe 3 extending from the fe 3 al join towards the cr corner spinel unmixing occurs in response to cooling and the increase in oxidation state the chemistry and grain size of the initial spinel and the cooling rate control the type of unmixing and the chemistry of the final products causes of spinel unmixing during late magmatic stage are analogous to those in metamorphosed complexes the chemistry of the unmixed spinels is completely different from the initial spinel composition and is not useful in petrogenetic interpretations spinels from oxidized magmas are likely to re equilibrate during cooling and are not good tools for genetic considerations

the continental margin of uruguay crustal architecture and segmentation abstract the uruguayan continental margin comprises three sedimentary basins the punta del este pelotas and oriental del plata basins the genesis of which is related to the break up of gondwana and the opening of the atlantic ocean herein the continental margin of uruguay is studied on the basis of 2d multichannel reflection seismic data as well as gravity and magnetic surveys as is typical of south atlantic margins the uruguayan continental margin is of the volcanic rifted type large wedges of seaward dipping reflectors sdrs are clearly recognizable in seismic sections sdrs flat lying basalt flows and a high velocity lower crust hvlc form part of the transitional crust the sdr sequence subdivided into two wedges has a maximum width of 85 km and is not continuous parallel to the margin but is interrupted at the central portion of the uruguayan margin the oceanic crust is highly dissected by faults which affect post rift sediments a depocenter over oceanic crust is reported deepwater pelotas basin and volcanic cones are observed in a few sections the structure of continental crust sdrs flat flows oceanic crust is reflected in the magnetic anomaly map the positive free air gravity anomaly is related to the shelf break while the most prominent positive magnetic anomaly is undoubtedly correlated to the landward edge of the sdr sequence given the attenuation interruption and or sinistral displacement of several features most notably sdr sequence magnetic anomalies and depocenters we recognize a system of nw se trending transfer faults here named rio de la plata transfer system rpts two tectono structural segments separated by the rpts can therefore be recognized in the uruguayan continental margin segment i to the south and segment ii to the north

trace elements and isotope data of the um garayat gold deposit wadi allaqi district egypt trace element composition of sulfides and o c sr and s isotopic data are assessed to constrain the evolution and potential fluid and metal sources of the um garayat gold deposit ore microscopy and bse investigations of quartz veins show blocky arsenopyrite and pyrite replaced in part by pyrrhotite chalcopyrite sphalerite galena and gersdorffite free milling gold occurs commonly in close association with the late sulfides and along fractures in pyrite on the other hand recrystallized pyrite is disseminated in host metavolcaniclastic metasedimentary rocks that commonly contain carbonaceous material in situ la icp ms analysis of sulfides shows the recrystallized pyrite enriched in most trace elements while blocky pyrite contains only some traces of arsenic detected concentrations of gold up to 17 ppm were only reported in arsenopyrite disseminated in quartz veins the 34s values of blocky pyrite and pyrrhotite in quartz veins define a narrow range 1 6 to 3 7 suggesting a homogenous sulfur source which is consistent with the dominantly mafic host rocks the recrystallized pyrite has a distinctive sulfur isotope composition 34s 9 3 to 10 6 which is rather comparable to diagenetic sulfides hydrothermal carbonate in quartz veins and wallrock have nearly constant values of 18o 10 5 to 11 9 and 13c 4 2 to 5 5 based on constraints from mineral assemblages and chlorite thermometry data of six samples indicate that carbonate precipitation occurred at 280 c from a homogenous hydrothermal fluid with 18oh2o 4 4 0 7 and 13c 3 7 0 8 strontium isotope values of two samples 87sr 86sr 0 7024 and 0 7025 are similar to the initial 87sr 86sr ratios of island arc metabasalts 710 ma in the south eastern desert the generally homogenous sulfur c o sr isotope data are suggestive of metamorphogenic fluids likely produced from dominantly mafic volcanic rocks at the greenschist amphibolite facies transition

island arc character and late precambrian age of volcanics at wadi shwas hijaz saudi arabia geochemical and sr and nd isotopic evidence abstract a summary description of two volcanic sequences named the surgah and the shwas formation situated in the wadi shwas area at long 42 0 lat 20 0 in the arabian shield is given major and trace element concentrations including ree abundances are presented as well as sr and some nd isotope results one sequence the surgah formation shows a tholeiitic differentiation trend from basaltic to rhyolitic rocks whereas the shwas formation has calc alkaline affinities both sequences have low concentrations of incompatible elements notably rb nb zr and ti the coexistence of a tholeiitic and a calc alkaline suite along with these low concentrations is strongly reminiscent of some present day island arc environments an rb sr errorchron age of 721 55ma was obtained on the surgah formation with high initial87sr 86sr ratios around 0 705 the rare earth abundances are overall very low and the patterns show a relative depletion of the light ree in the least evolved rocks indicating a relatively light ree depleted mantle source a time integrated light ree depleted source is also indicated by the fairly radiogenic143nd 144nd ratios end values around 8 the nd model age of source depletion tchurnd is around 2 2 ga

seismic stratigraphic analysis of the punta del este basin offshore uruguay south america the punta del este basin of offshore uruguay is one of a series of mesozoic sedimentary basins along the eastern seaboard of south america the basin resulted from continental rifting of an older gondwana landmass this rifting led to the initiation of the south atlantic ocean the tectonic and stratigraphic history of the basin can be characterized by a three phase evolution with each phase involving a separate and distinct basin geometry style of faulting and lithostratigraphic succession the rift phase deposited predominantly continental siliciclastics of neocomian age arranged in a number of syndepositional assymetric trap door grabens this phase is overlain by a largely unfaulted succession of continental to marine rocks of the sag basin phase of aptian to maastrichtian age these rocks record an overall marine transgression the passive margin phase is represented by a thick sequence of tertiary sediments that postdate rift related tectonism and correspond to sedimentation along the margin of the newly opened south atlantic ocean the punta del este part of the greater salado basin is relatively unexplored with only two wells having been drilled both in the updip part of the basin these two wells have contributed some understanding of the stratigraphic succession but have failed to adequately assess the basin s true hydrocarbon potential this paper constitutes one of the first detailed comprehensive published accounts of this basin and is a prerequisite for future exploration in the area

coral record of variability in the upstream kuroshio current during 1953 2004 the kuroshio current kc one of the most important western boundary currents in the north pacific ocean strongly affects regional hydroclimate in east asia and upper ocean thermal structure limited by few on site observations the responses of the kc to regional and remote climate forcings are still poorly understood here we use monthly coral 18o data to reconstruct a kc transport record with annual to interannual resolution for the interval 1953 2004 the field site is located in southern taiwan on the western flank of the upstream kc increased reduced kc transport would generate strong weak upwelling resulting in relatively high low local coral 18o the upstream kc transport and downstream transport off tatsukushi bay japan covary on interannual and decadal timescales this suggests common forcings such as meridional drift of the north equatorial current bifurcation or zonal climatic oscillations in the pacific the intensities of kc transport off southeastern and northeastern taiwan are in phase before 1990 and anti phase after 1990 this difference may be due to a poleward shift of the subtropical western boundary current as a response to global warming

generation and propagation of m 2 internal tides modulated by the kuroshio northeast of taiwan the variability and energetics of m 2 internal tides during their generation and propagation through the kuroshio flows northeast of taiwan are investigated using a high resolution numerical model the corrugated continental slopes particularly the i lan ridge and mien hua canyon are first identified as the energetic sources of m 2 internal tides the domain integrated m 2 barotropic to baroclinic conversion rate under the kuroshio influence is similar to 2 35gw similar to 0 9gw of which is generated at the i lan ridge similar to 0 93gw at the mien hua canyon and similar to 0 52gw at the north shelf the m 2 internal tide generation is influenced by the horizontally varying zonally tilting stratification associated with the kuroshio in this situation the conversion rate decreases by similar to 30 at the i lan ridge but increases to within similar to 10 at the mien hua canyon and north shelf in comparison to the simulation initiated with horizontal homogeneous stratification internal tides from multiple sources interfere to form a three dimensional baroclinic field the interference by the internal tides from the mien hua canyon and north shelf is refracted by the kuroshio and exhibits a mesoscale gyre pattern which can explain the frequent occurrence of internal solitary waves an energetic along slope tidal beam tbkc from the i lan ridge radiates southward against the northward kuroshio flows causing strong vertical displacement which favorably compares with recently reported field measurements the m 2 internal tide energy dissipates primarily near the source sites and the remaining energy radiates outward over limited distances complex topographic features and background currents enhance the internal tide dissipation which induces strong inhomogeneous diapycnal mixing

the impact of subtidal circulation on internal tide generation and propagation in the philippine sea abstractthis study examines the effects of the subtidal circulation on the generation and propagation of the m2 internal tide in the philippine sea using a primitive equation model barotropic to baroclinic conversion at the luzon strait is found to vary due to the background circulation changes over the generation site and the changing influence of remotely generated internal tides from the mariana arc the varying effect of remotely generated waves results from both changing generation energy levels at the mariana arc and variability in the propagation of the internal tides across the philippine sea the magnitude and direction of the depth integrated baroclinic energy fluxes vary temporally due to a combination of changing generation propagation and dissipation spatial patterns of internal tide propagation near the luzon strait are influenced by the locations of mesoscale eddies to the east and west of the strait the results provide insight into the mechanisms of variability of the baroclinic tide

rb sr isotope study of latest proterozoic volcano sedimentary belts in the central arabian shield five new rb sr whole rock isochrons for volcanic successions assigned to 9sequence9 a in the central arabian shield indicate that very late precambrian c 690 570 ma volcanicity was an important event in the evolution of the shield the following ages are considered to define or approximate to the age of lava extrusion fatimah group 688 30 ma jahhad unit 616 13 ma juqjuq formation 612 22 ma arfan formation 608 9 ma hummah unit 572 23 ma initial 87 sr 86 sr ratios range from 0 7027 to 0 7036 and rb sr ratios are uniformly low 87 srl 86 sr ratio for the jahhad and hummah samples reflects the involvement of less depleted mantle or possibly slight crustal contamination

age and chemical characteristics of some pre pan african rocks in the egyptian shield abstract u pb ages on zircons from several types of sialic rocks together with a variety of geochemical data on one sample of early plutonic activity within the egyptian shield are presented the earliest autochthonous granitic rocks in the egyptian shield are probably quartz diorites tonalites emplaced just prior to the main peak of pan african igneous activity 550 650 ma the studied example has an age of 711 ma 7 ma and is characterized by very low initial sr ratio 87sr 86sr 0 7026 and very low abundances of k2o and related large ion lithophile trace elements ree contents are low less than 20 chondritic abundances abundance patterns show only moderate light rare earth enrichment la yb 4 5 these characteristics are inconsistent with any models requiring fractional fusion of pre existing continental crustal material granitic and arkosic cobbles occur in rare conglomerate beds within volcanoclastic and greywacke sedimentary sequences the cobbles show a wide range in ages 1 1 2 3 ga and have no obvious source within the egyptian shield it is suggested that they are not indicative of any sialic plutons in the egyptian shield which might predate deposition of the enclosing immature sediments more probably they were derived from adjacent continental areas such as the uweinat region to the west and were deposited in an evolving arc ocean basin complex

gravimetric determination of the continental oceanic boundary of the argentine continental margin from 36 s to 50 s fil arecco maria alejandra universidad de buenos aires facultad de ingenieria argentina

role of subaerial volcanic rocks and mantle plumes in creation of south atlantic margins implications for salt tectonics and source rocks abstract seaward dipping reflectors sdrs represent flood basalts rapidly extruded during either rifting or initially subaerial sea floor spreading evaporites can form on this basaltic proto oceanic crust as in the afar triangle today evidence for sdrs in south atlantic deep water regions comes from proximity to the uniquely large parana etendeka volcanic province onshore the tristan and gough hot spots drilled volcanic rocks and seismic profiles showing sdr provinces more than 100 km wide as much as 7 km thick and thousands of kilometers long sdrs are clearest adjoining the aptian salt basins however we speculate that sdrs are also present but seismically obscured below the salt basins we argue that the conjugate aptian salt basins are post breakup not pre breakup they were separated from the start by a mid oceanic ridge distal salt accumulated on proto oceanic crust not rift basins this hypothesis is supported by seismic stratigraphy and structure magnetic anomalies plate reconstructions and hydrothermal potash evaporites an important implication for exploration is that thick basalts rather than rift age source rocks may underlie distal parts of the salt basins

three dimensional numerical simulation of m2 internal tides in the east china sea the east china sea and adjacent seas are one of the most significant generation regions of the m 2 internal tide in the world s oceans in the present study we investigate the distribution and energetics of the m 2 internal tide around the continental shelf edge in the east china sea using a three dimensional numerical model the numerical experiment shows that m 2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the bashi luzon and tokara straits the ridges along the ryukyu island chain and the continental shelf slope in the east china sea the former particularly so all of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the m 2 barotropic tide is almost normally incident the m 2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern it is found that the calculated pattern of the m 2 internal tide agrees well with topex poseidon altimeter observations the conversion rate from m 2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 gw roughly 10 of the energy in the m 2 surface tide incident on the prominent topographic features is converted to the m 2 internal tide although about half of the m 2 internal tidal energy is subject to local dissipation in close proximity to the generation sites

numerical assessment of factors affecting nonlinear internal waves in the south china sea abstract nonlinear internal waves in the south china sea exhibit diverse characteristics which are associated with the complex conditions in luzon strait such as the double ridge topography the earth s rotation variations in stratification and the background current induced by the kuroshio these effects are individually assessed using the mitgcm the performance of the model is first validated through comparison with field observations because of in phased ray interaction the western ridge in luzon strait intensifies the semidiurnal internal tides generated from the eastern ridge thus reinforcing the formation of nonlinear internal waves however the ray interaction for k 1 forcing becomes anti phased so that the k 1 internal tide generation is reduced by the western ridge not only does the rotational dispersion suppress internal tide generation it also inhibits nonlinear steepening and consequent internal solitary wave formation as a joint effect the double ridges and the rotational dispersion result in a paradoxical phenomenon diurnal barotropic tidal forcing is dominant in luzon strait but semidiurnal internal tides prevail in the deep basin of the south china sea the seasonal variation of the kuroshio is consistent with the seasonal appearance of nonlinear internal waves in the south china sea the model results show that the westward inflow due to the kuroshio intrusion reduces the amplitude of internal tides in the south china sea causing the weakening or absence of internal solitary waves winter stratification cannot account for the significant reduction of nonlinear internal waves because the amplitude growth of internal tides due to increased thermocline tilting counteracts the reduced nonlinearity caused by thermocline deepening

a tectonostratigraphic synthesis of the sub andean basins inferences on the position of south american intraplate accommodation zones and their control on south atlantic opening it has been shown in the accompanying paper that the sub andean foreland can be subdivided longitudinally into a number of tectonostratigraphic domains to test the hypothesis that changes in palaeo depositional setting rely on the presence of a series of transverse zones of structural accommodation data have been digitally compiled from across the south american continent spatial and temporal geological relationships have been analysed and evaluated as a means of identifying the position of tectonostratigraphic domain boundaries structural accommodation zones and patterns of subsidence and intraplate deformation the results suggest that individually these structural accommodation zones represent a composite of deep crustal fractures which on a regional scale interlink to form a transcontinental belt or zone that can accommodate intraplate deformation during episodes of plate reorganization their strong spatial relationship with mesozoic intraplate alkaline igneous activity suggests that they exerted an important control on lithospheric melt siting during gondwana breakup these localized zones of high heat flow have important implications for source rock maturity in the interior phanerozoic intracratonic basins of south america on the south atlantic margin the majority of these crustal lineaments correlate with failed arms of triple junction rifts and define the boundaries to tectonostratigraphic domains recognized along the south atlantic rift system

variability of nonlinear internal waves in the south china sea affected by the kuroshio and mesoscale eddies long term observations of nonlinear internal waves in the south china sea reveal seasonal to interannual variability during two selected segments of inverted echo sounder observations tidal forcing in luzon strait is almost identical but the observed amplitudes of nonlinear internal waves in the south china sea are very different the effects of the kuroshio and mesoscale eddies reproduced by hybrid cooridnate ocean model hycom reanalysis simulation are then investigated the kuroshio can enhance the zonal tilt of the thermocline and induce intruding flow in luzon strait during the two selected segments different thermocline slopes did not significantly change the internal tide generation but the intruding flow may result in a 11 difference in the amplitude of generated m2 internal tides during the two selected segments mesoscale eddies appeared on the path of internal wave propagation a cold eddy in one case and a warm one in the other the eddies changed local stratification and induced additional background currents thus affecting the nonlinear evolution of internal tides in addition wave front steering due to the mesoscale eddies dramatically affected the observed amplitude changes of the nonlinear internal waves the edge rather than the center of the nonlinear internal wave front passed through the observational stations resulting in reduced amplitude in the observations

giant mounded drifts in the argentine continental margin origins and global implications for the history of thermohaline circulation abstract partially buried giant drifts are located in the southern most sector of the argentine continental margin generating a bathymetric jump at the base of the slope they are characterised as giant asymmetrical elongated mounded contourite drifts and are described in detail here for the first time this description is mainly based on the bathymetric and multichannel seismic reflection profiles data their origin and evolution in the argentine basin are decoded and their implications in an area crucial for geologic and palaeoceanographic reconstruction between the atlantic and antarctica are discussed the buried giant drifts are divided into two zones by a large seamount the major giant drift 50 km wide 300 km long and having a sedimentary thickness of nearly 1 km is located to the south of this seamount and oriented to the north where its summit outcrops at present seafloor here its asymmetric external shape is characterised by a steep western side and a gently dipping smooth eastern side with internal reflections prograding eastward based on its position morphology and internal characteristics it has been deduced that this giant drift was generated in the argentine basin by the southward branch of a confined large loop of the antarctic bottom deep water from the eocene oligocene boundary coevally with the drake passage opening until the middle miocene however after a major palaeoceanographic change in the mid to late miocene a new oceanographic scenario was established that fossilised these giant drifts these changes produced a new depositional style in the margin resulting in initiation of the present contourite depositional system and morphologic features over the slope extension of north atlantic deep water circulation into the southern hemisphere and deepening of antarctic bottom water circulation in the argentine basin are herein postulated as the factors that controlled said changes these giant drifts show strong seismic evidence of hydrates and free gas that are ripe for energy resources exploration thus demonstrating the economic potential of contourite deposits in deep marine environments

silver and silver bearing minerals at the um samiuki volcanogenic massive sulphide deposit eastern desert egypt the um samiuki zn cu pb ag mineralisation south eastern desert egypt is hosted by felsic volcanic rocks which form part of the 712 ma old east west trending shadli volcanic belt two major occurrences of massive sulphides are present at the top of rhyolitic breccia in the western and eastern mine areas in each occurrence a bornite bearing zone is overlain by a pyrite chalcopyrite bearing zone and underlain by a disseminated cu depleted zone in the massive sulphide ore sphalerite chalcopyrite pyrite galena bornite and tetrahedrite tennantite are major minerals whereas arsenopyrite pyrrhotite molybdenite and magnetite are accessory phases covellite and digenite are common secondary minerals bornite tetrahedrite tennantite and covellite contain high amounts of silver averages of 1 97 1 39 and 1 82 wt respectively based on mineralogical balance calculations bornite and covellite accommodate 80 of silver in the um samiuki deposit ag was incorporated in the crystal structure of the early crystallised copper sulphides and sulphosalts and silver minerals the temperature sequential precipitation of the fluids and the structure of the crystallising phases control the distribution of silver post depositional deformation and metamorphic processes caused liberation remobilisation and redeposition of silver within the massive sulphides

u pb zircon geochronology and geological evolution of the halaban al amar region of the eastern arabian shield kingdom of saudi arabia u pb zircon model ages for eleven major units from the halaban al amar region of the eastern arabian shield indicate three stages of evolution 1 plate convergence 2 plate collision and 3 post orogenic intracratonic activity convergence occurred between the western afif and eastern ar rayn plates that were separated by oceanic crust remnants of oceanic crust now comprise the ophiolitic complexes of the urd group the oldest plutonic unit in the study is from one of these complexes and gave an age of 694 8 ma detrital zircons from the sedimentary abt formation of the urd group which is intercalated with the ophiolitic rocks were derived from source rocks with a mean age of 710 ma the abt formation may be an accretionary wedge on the western margin of the ar rayn plate plate convergence was terminated by collision of the afif and ar rayn plates during the al amar orogeny which began about 670 ma during collision the urd group rocks were deformed and in part obducted on to one or both plates synorogenic leucogranitoid rocks were intruded from 670 to 640 ma from about 640 to 630 ma widespread unfoliated dioritic plutons were emplaced in the ar rayn block and represent the end of orogenesis related to collision there is no definitive evidence for a significantly older basement beneath the study region

timing and characteristics of late pleistocene and holocene wetter periods in the eastern desert and sinai of egypt based on 14c dating and stable isotope analysis of spring tufa deposits abstract there is very little dated evidence on wet periods in the eastern desert and sinai peninsula of egypt during the late pleistocene and holocene to obtain such information we have studied the petrography isotope geochemistry and ams radiocarbon ages of mostly relict tufas deposited by springs draining perched ground water bodies in metamorphic and volcanic rocks the tufas unconformably overly precambrian basic igneous rocks basalt diabase and gabbro as the ages of tufa carbonate are frequently older than the true ages of the deposits because of the incorporation of old 14c dead carbon we have dated both the carbonate matrix and insoluble organic material of the tufas these ages show that the tufas were largely formed during two broad time periods the most recent from 12 058 to 6678 cal yr bp african humid period and the other from 31 200 22 500 cal yr bp with preferential growth during the coldest times of this period namely during heinrich events 2 and 3 h2 and h3 and the last glacial maximum lgm the time span between 19 000 9000 cal yr bp including the yd and h1 appears to have been relatively more arid than the earlier lgm or h2 periods or the later holocene the late pleistocene tufas are depleted in 18o relative to the holocene tufas and were deposited at a lower temperature 14 0 20 8 c vs 18 4 23 4 c we believe that the holocene tufas in the sinai were formed by rainfall from the mediterranean and those in the southern part of the eastern desert by african monsoon rainfall derived from the red sea gulf of aden and indian ocean in contrast the moisture that fed the late pleistocene tufas which are depleted in 18o relative to holocene deposits and progressively depleted from north to south was probably brought by the westerlies from the atlantic mediterranean sea when the westerly circulation was pushed southwards during the coldest periods of the late pleistocene periods of tufa deposition correlate with major documented paleoclimatic events in north africa during the late pleistocene and holocene such as the nile floods high sea level and the formation of sapropels in the mediterranean

margin segmentation and volcano tectonic architecture along the volcanic margin off argentina uruguay south atlantic abstract some 25 000 kilometers of regional multichannel seismic data acquired by bgr along the continental margins off argentina and uruguay document that the early cretaceous south atlantic continental breakup and initial sea floor spreading were accompanied by large scale transient volcanism emplacing voluminous extrusives manifested in the seismic data by huge wedges of seaward dipping reflectors sdrs the emplacement of the deeply buried 60 120 km wide sdrs was probably episodic as documented by at least three superimposed sdrs units distinct along margin variations in architecture volume and width of the sdrs wedges are probably related to margin segmentation it is suggested that the margin can be divided at least in four compartments bounded by the falkland fracture zone falkland transfer the colorado transfer the ventana transfer and the salado transfer the individual margin segments reflect in the distribution and thickness of the post rift sediments the individual transfer zones may have acted as rift propagation barriers selectively directing rift segments in left stepping patterns along the western south atlantic margin although we found extensive variations in the architecture style and extent of the seaward dipping reflector sequences a general trend is that the largest volumes are emplaced close to the proposed transfer zones and the width of the sdrs wedges decreases northward within the individual margin segments we suggest that mainly adiabatic decompression and melt generation from shallow sources can explain distinct along margin variations in the volcano tectonic architecture and volumes of extruded magmas

seismic stratigraphy and subsidence analysis of the southern brazilian margin campos santos and pelotas basins abstract the campos santos and pelotas basins have been investigated in terms of 2d seismo stratigraphy and subsidence the processes controlling accommodation space e g eustacy subsidence sediment input and the evolution of the three basins are discussed depositional seismic sequences in the syn rift barremian to the drift holocene basin fill have been identified in addition the subsidence uplift history has been numerically modeled including i sediment flux ii sedimentary basin framework iii relation to plate tectonic reconfigurations and iv mechanism of crustal extension although the initial rift development of the three basins is very similar basin architecture sedimentary infill and distribution differ considerably during the syn rift sag to the drift basin stages after widespread late aptian early albian salt and carbonate deposition shelf retrogradation dominated in the campos basin whereas shelf progradation occurred in the santos basin in the tertiary these basin fill styles were reversed since the paleogene shelf progradation in the campos basin contrasts with overall retrogradation in the santos basin in contrast long term cretaceous paleogene shelf retrogradation and intense neogene progradation characterize the pelotas basin its specific basin fill and architecture mainly resulted from the absence of salt deposition and deformation these temporally and spatially varying successions were controlled by specific long term subsidence uplift trends onshore and offshore tectonism in the campos and santos basins affected the sediment flux history distribution of the main depocenters and occurrence of hydrocarbon stratigraphic structural traps this is highlighted by the exhumation and erosion of the serra do mar serra da mantiqueira and ponta grossa arch in the hinterland as well as salt tectonics in the offshore domain the pelotas basin was less affected by changes in structural regimes until the eocene when the andean orogeny caused uplift of the source areas flexural loading largely controlled its development and potential hydrocarbon traps are mainly stratigraphic

observed enhanced internal tides in winter near the luzon strait seasonal characteristics and nonlinear interaction of internal tides its near the luzon strait in the northeastern south china sea are investigated using 285 day in situ observation data it is found that its which are dominated by the first mode wave throughout the year are the strongest in subsurface layer baroclinic incoherent diurnal semidiurnal variance accounts for about 85 7 78 3 of diurnal semidiurnal its the amplitude and seasonal variation of the diurnal its are more prominent than those that are semidiurnal e g the largest kinetic energy densities of diurnal and semidiurnal baroclinic tidal currents are 2 81 and 0 83 kj m2 in winter respectively it is considered that there are two reasons for the significantly enhanced its in winter 1 it may be due to the kuroshio intrusion and 2 the enhanced diurnal its may be due to the enhanced diurnal barotropic tidal currents while the enhanced semidiurnal its may be caused by the strong nonlinear interaction between diurnal it constituents o1 and k1 due to their high vertical shears in subsurface layer thus harmonic semidiurnal constituent d2 with a similar frequency of constituent m2 is induced it subsequently enhances the semidiurnal its in this subsurface layer and the associated energy is carried downward to enhance the semidiurnal its in the upper and lower layers

contourite depositional system on the argentine slope an exceptional record of the influence of antarctic water masses a significant contourite depositional system cds on the continental slope of the southern argentine margin is described here for the first time this system contains both erosive and depositional features that have resulted from several factors including topographic intensification of the antarctic sourced water masses the systematic northward decrease in speed of these water masses a northward increase of downslope sedimentary processes and local tectonic influences this system is an exceptional example of a cds that started to develop at the time of the eocene oligocene boundary potentially coeval with the opening of the drake passage however a new margin morphology characterized by a complex terraced slope lacking any continental rise developed after a major paleoceanographic change in the middle to late miocene we infer that this change resulted from the extension of north atlantic deep water circulation into the southern hemisphere and the deepening of antarctic bottom water circulation in the argentine basin

energy of nonlinear internal waves in the south china sea 1 four sets of adcp measurements were taken in the south china sea scs these results were combined with previous satellite observations and internal tide numerical model results analysis suggests that strong internal tides are generated in luzon strait propagate as a narrow tidal beam into the scs are amplified by the shoaling continental slope near tungsha island become nonlinear and evolve into high frequency nonlinear internal waves niw internal waves in the scs have geographically distinct characteristics 1 west of luzon strait the total internal wave energy eiw is 10 that predicted by garrett munk spectra egm levine 2002 there is no sign of niw 2 near tungsha island eiw 13 egm strong nonlinear and high harmonic tides are present repetitive trains of large amplitude niw appear primarily at a semidiurnal periodicity with their amplitudes modulated at a fortnightly tidal cycle the rms vertical velocity of niw shows a clear spring neap tidal cycle and is linearly proportional to the barotropic tidal height in luzon strait with a 1 85 day time lag consistent with the travel time of internal tides from luzon strait to tungsha island 3 at the northern scs shelfbreak eiw 4 egm single depression waves are found but no multiple waves packets are evident 4 on the continental shelf eiw 2 egm both depression and elevation niw exist

on the generation and evolution of nonlinear internal waves in the south china sea the nonhydrostatic regional ocean modeling system is applied to the nonlinear internal waves or solitons that are generated at the luzon ridge in the south china sea the luzon ridge near the batan islands is represented by an idealized ridge with a height of 2 6 km on a flat bottom model runs are performed for various ridge shapes and a symmetric tidal forcings the model is in the mixed tidal lee wave regime the barotropic tide over the ridge generates first mode waves through the internal tide release mechanism westward traveling solitons emerge from these first mode waves through nonlinear steepening in the internal tide release mechanism asymmetric tides with strong eastward currents can generate strong westward solitons the eastward current creates an elevation wave with a higher energy density west of the ridge and as soon as the current slackens the wave is released westward on its backslope strong solitons develop the energy density is further enhanced by nonlinearities such as differences in phase speeds and energy fluxes related to lee waves a modal and harmonic decomposition shows the generation of vertical modes and higher temporal harmonics and indicates significant wave wave interaction e g triads in the mixed tidal lee wave regime more energy is contained in the first mode compared to the higher modes hence linear internal tide beams are less well defined and strong solitons develop

crustal scale architecture and segmentation of the argentine margin and its conjugate off south africa summary integration of regional seismic reflection and refraction profiles and potential field data across the argentine margin and its conjugate off south africa complemented by crustal scale gravity modelling is used to reveal and illustrate the whole crust architecture onshore offshore crustal structure correlations the character of the continent ocean boundary transition and the relationship of crustal structure to regional variation of potential field anomalies the study reveals within these two provinces distinct along margin structural and magmatic changes that are spatially related to a number of conjugate transfer systems governing the margin segmentation and evolution clearly implying structural inheritance in particular the colorado transfer system on the argentina margin marks a distinct along margin boundary in the distribution and volume of breakup related magmatism similarly the hope transfer system on the conjugate south africa margin also marks a distinct along margin transition from a zone of relative magnetic quiescence to a zone of prominent magnetic anomalies furthermore the study indicates that the g magnetic anomaly along the south africa margin probably defines the eastern limit of the continent ocean transition cot rather than a discrete continent ocean boundary cob potential field plate reconstructions of the south atlantic suggest conjugate margin asymmetry characterized by a rather broad argentine margin conjugate to a narrow south africa margin in detail the argentine margin is characterized by a sharp and relatively constant cot whereas the cot along the conjugate south africa margin is considerably wider an along strike tectonomagmatic asymmetry variation is also observed and is expressed by the northward increase in width of the cot on the south african margin the study clearly shows that integration of regional seismic reflection and refraction profiles potential field data and gravity modelling provide a powerful resource for testing and validating alternative seismic profile structural interpretations and plate tectonic reconstructions as well as geodynamic models for lithospheric breakup and early drift

summer kuroshio intrusion through the luzon strait confirmed from observations and a diagnostic model in summer 2009 abstract based on current measurements recorded at mooring station n2 20 40 441 n 120 38 324 e hydrographic data and argo observations in the period starting from july 2009 a diagnostic model with a modified inverse method is used to study the circulation in the luzon strait ls a number of new circulation features in the ls are found as follows 1 both observed and modeled currents show that the intruded kuroshio flow northwestward through the ls into the south china sea scs in the upper 400 m during july 2009 2 the diagnostic model confirms that the kuroshio is located in the area east of 121 20 e and west of 122 20 e at 20 00 n there is a meso scale cyclonic eddy at both the surface and 1000 m depth in the area west of the kuroshio near 20 00 n the meso scale cyclonic eddy forced the argo float 1 to make the cyclonic trajectory then the argo float 1 went into the area of the western kuroshio the argo float 1 was tracked as the flow moved northwestward into the scs across the ls in july and august 2009 reflecting the northwestward flow at both the surface and 1000 m depth which coincided with modeled currents these results confirm the northwestward kuroshio intrusion into the scs across the ls in summer 2009 for the first time 3 from the dimensional analysis for the equation of stream function it is seen that the joint effect of the baroclinity and relief jebar and the effect are two important mechanisms on the kuroshio intrusion into the scs in this period this summer kuroshio intrusion results from the weaker upstream kuroshio transport in summer 2009 el nino initiating period due to inertia effects and is associated with a weak volume transport across the ls 2 15 106 m3 s 1 westward 4 after comparison of the dynamics of the kuroshio intrusion during october 2008 and summer 2009 it is clear that these were influenced by the seasonal variability due to the monsoon winds and the interannual variation resulting from the weak upstream kuroshio transport affected by the enso due to inertia effects

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

effects of kuroshio intrusions on nonlinear internal waves in the south china sea during winter 1 during winter the kuroshio tends to cross luzon strait penetrating the northeastern south china sea where it forms energetic mesoscale structures luzon strait is also a site where westward propagating large amplitude internal waves are generated we describe observations of these waves acquired in the deep basin of the south china sea during the winter of 2010 2011 with the goal of assessing the influence of mesoscale variability on their properties combining tidal current simulations with an internal wave generation and evolution model we obtain time series of deviations between our observations and the model simulations these deviations are analyzed in terms of mesoscale variability based on the data assimilated hybrid coordinate ocean model hycom simulations we find that simplified models of nonlinear internal wave response to changes in horizontal stratification gradients and vertical shear provide at best weak simulations of amplitude modulation in contrast to these results deviations of internal wave arrival time occurring up to 2 h early during kuroshio inflows are quite well simulated when derived from integration of the first internal mode phase speed along two dimensional ray traced paths using hycom simulations of velocity and density fields together with bathymetry refraction of the internal waves by kuroshio intrusions can lead to substantial distortion of the paths sufficient to provide a potential explanation for the apparent suppression of waves during previous winter measurements our results suggest that the internal wave field can be a sensitive indicator of mesoscale variability in luzon strait and the northeastern south china sea

a review of internal solitary wave dynamics in the northern south china sea abstract the current research into internal solitary waves isws and the related dynamic processes in the northern south china sea scs are reviewed in this paper this unique wave phenomenon did not draw much interest until about one decade ago and is now one of the hot topics in the field of wave dynamics three methods of investigation are summarized in the paper namely remote sensing images in situ measurements and numerical simulations previous works have primarily been based on one or two of these methods and have provided great insights into such wave phenomena the lifetime of an isw in the northern scs from its origin in the luzon strait ls through to its formation and evolution in the deep basin and its transformation near the shelf break up until its dissipation on the continental shelf is summarized with the illustration of different investigation approaches various factors that can affect the wave generation processes are summed up as well such factors as are barotropic tides in the ls kuroshio intrusion temporal and spatial variation of stratification and the modulation of the western ridge in the ls can significantly alter the wave fields and are extensively discussed

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

late proterozoic transpression on the nabitah fault system implications for the assembly of the arabian shield abstract the longest proposed suture zone in saudi arabia the nabitah suture can be traced as a string of ophiolite complexes for 1200 km along the north south axis of the arabian shield results of a field study in the north central shield between 23 and 26 n indicate that the nabitah suture is indeed a major crustal discontinuity across which hundreds of kilometers of displacement may have occurred on north south trending subvertical faults of the nabitah fault system although not a unique solution many structures within and near these faults can be reconciled with transpression i e convergent strike slip and syntectonic emplacement of calc alkaline plutonic rocks transcurrent motion on the nabitah fault system appears to have began prior to 710 ma was active circa 680 ma and terminated prior to significant left lateral strike slip on the najd fault system which began sometime after 650 ma northwest directed subduction in the eastern shield could have produced the observed association of calc alkaline magmatism and left lateral transpressive strike slip and is consistent with interpretation of the abt schist and sedimentary rocks of the murdama group as relics of the associated accretionary wedge and fore arc basin

seismicity and stresses in the brazilian passive margin abstract seismicity and stresses along the brazilian continental margin show different patterns between the northeastern and southeastern regions in the northeastern margin earthquakes tend to occur onshore under a strike slip regime with horizontal compression parallel to the northern coast line in the southeastern margin higher seismicity is observed offshore in areas where the continental crust was highly extended during the south atlantic rifting in the mesozoic three new events in the southeast continental shelf are shown to have reverse faulting mechanisms from waveform modeling of short period teleseismic p waves multiple depth phases reflections from the top and bottom of the water layer and double reflections in the water layer could be identified and better constrained the hypocenters to middle and upper crustal depths in south america models of intraplate stresses caused by plate boundary forces and spreading effects due to the continental oceanic crustal transition indicate higher compressional stresses in the se offshore area as compared with the continental area in agreement with the observed higher seismicity and reverse faulting mechanisms the combination of regional stresses local flexural effects from thick sedimentary loads and a presumably weaker crust from mesozoic thinning explains the main patterns of seismicity in the northeastern and southeastern brazilian margins

propagation of low mode internal waves through the ocean abstract the baroclinic tides play a significant role in the energy budget of the abyssal ocean although the basic principles of generation and propagation are known a clear understanding of these phenomena in the complex ocean environment is only now emerging to advance this effort a ray model is developed that quantifies the effects of spatially variable topography stratification and planetary vorticity on the horizontal propagation of internal gravity modes the objective is to identify baroclinic shoals where wave energy is spatially concentrated and enhanced dissipation might be expected the model is then extended to investigate the propagation of internal waves through a barotropic mesoscale current field the refraction of tidally generated internal waves at the hawaiian ridge is examined using an ensemble of mesoscale background realizations derived from weekly ocean topography experiment topex poseidon altimetric measurements the path of mode 1 is only slightly affected by typical cur

generation and propagation of baroclinic tides modified by the kuroshio in the luzon strait 1 using a three dimensional model with idealized settings this study evaluated the effect of the kuroshio on the generation and propagation of semidiurnal m2 and diurnal k1 baroclinic tides bcts in the luzon strait ls the influences of the varied kuroshio transport the location of the kuroshio and the separation distance of the two meridional ridges were investigated the absence of the kuroshio in the model leads to 30 decreases in the westward baroclinic energy flux fbcx emanating from the west slope of the east ridge compared to the fbcx with the presence of the kuroshio compared to the fbcx without the kuroshio s influence the westward fbcx is increased by 20 40 when the kuroshio is located in either the middle or the west portions of the ls whereas both the westward and eastward fbcx are 25 40 decreased as the kuroshio is moved to the east of the east ridge the wavelength of the mode 1 m2 bct is similar to the separation distance of the two ridges favoring a resonance generation for m2 rather than k1 bcts the increase of the kuroshio transport from 20 to 30 sv 1 sv 106 m3 s 1 enhances the density front but weakens the westward fbcx owing to the effects of energy advection and lateral friction from the kuroshio the influence of the kuroshio on the westward fbcx of k1 is opposite of that on m2 the characteristic slope of k1 is closer to the isopycnal slope across the kuroshio than m2 thereby causing the discrepancy

a late precambrian 710 ma high volcanicity rift in the southern eastern desert of egypt the late precambrian shadli metavolcanics of se egypt constitute a slightly metamorphosed bimodal sequence that has been previously interpreted as manifesting volcanic activity at an island arc we report the first rb sr geochronologic trace element including ree and nd isotopic data for these rocks two types of basalt are recognized the stratigraphically lower suite having compositions like n morb ferrobasalt while the overlying basalt is similar to slightly fractionated e morb the two basalt types were derived from melting of a strongly depleted source most likely within the upper 60 75 km of the upper mantle the origin of the felsic melts is problematic and these could either have fractionated from a mafic melt or resulted from melting of juvenile crust the mafic and felsic lavas yield a rb sr isochron age of 712 24 ma that probably represents the time of volcanic eruption the trace element characteristics of both mafic and felsic members of the shadli metavolcanics show few of the hallmarks of subduction related melts and we reject the hypothesis that these formed at an island arc instead the field and geochemical data are most consistent with the hypothesis that these rocks originated in a magmatic rift where the eruption of large volumes of lava accompanied large scale lithospheric extension this inference suggests that the tectonic setting of the important 700 715 ma crust forming event in ne africa and arabia needs to be critically reexamined

speed and evolution of nonlinear internal waves transiting the south china sea abstract in the south china sea scs 14 nonlinear internal waves are detected as they transit a synchronous array of 10 moorings spanning the waves generation site at luzon strait through the deep basin and onto the upper continental slope 560 km to the west their arrival time speed width energy amplitude and number of trailing waves are monitored waves occur twice daily in a particular pattern where larger narrower a waves alternate with wider smaller b waves waves begin as broad internal tides close to luzon strait s two ridges steepening to o 3 10 km wide in the deep basin and o 200 300 m on the upper slope nearly all waves eventually develop wave trains with larger steeper waves developing them earlier and in greater numbers the b waves in the deep basin begin at a mean speed of 5 greater than the linear mode 1 phase speed for semidiurnal internal waves computed using climatological and in situ stratification the a waves travel 5 10 faster than b waves until they reach

a late proterozoic bimodal volcanic subvolcanic suite from wadi araba southwest jordan abstract geotectonic setting age relationships petrography and geochemistry of a pan african bimodal volcanic subvolcanic suite have been examined the volcanic phase terminated the pan african molasse evolution and spans the time interval 550 540 ma the volcanics forming a 70 km nne ssw trending belt are distributed predominantly as rhyolitic lava flows and subordinately as trachybasalts and trachyandesites the composition of the numerous dikes varies from basalt to trachyandesite and rhyolite the rhyolites are typified as alkali rhyolites and comendites geochemical criteria characterize a bimodal suite which is not of cogenetic origin the basalts are mantle derived fractionation controlled products whereas the alkali rhyolites and comendites were generated by partial melting of continental crustal rocks the investigated magmatic suite has been compared with equivalent suites from the arabian nubian shield

the argentine continental margin north of 48 s sedimentary successions volcanic activity during breakup abstract new seismic data and geophysical results from the outer argentine continental margin and from seismic flow line transects across the oceanic argentine brazil and cape angola basins are presented the results document that the early cretaceous south atlantic continental breakup and initial sea floor spreading were accompanied by large scale transient volcanism emplacing voluminous extrusive constructions on the conjugate outer continental margins of the south atlantic on the argentine margin we interpret three major tectono volcanic crustal units beneath a thick and tectonically undisturbed sedimentary succession of cretaceous and tertiary age 1 syn rift basins and even pre rift features are present on the outer shelf 2 a deeply buried 60 120 km wide and several thousand metres thick volcanic wedge occupies most of the slope the wedge is characterized by seaward dipping reflectors and is associated with the distinct magnetic anomaly g 3 the seaward adjacent oceanic crust of cretaceous age shows isochronous changes of the seismic images along our flow line transects suggesting some form of episodicity of rich magma and poor to moderate magma supply at the pre existing mid ocean ridge of the south atlantic during cretaceous time

internal tide radiation from the luzon strait the m2 k1 and o1 internal tides originating in the luzon strait are investigated using the sea surface height measurements by multiple satellites ers 2 envisat topex poseidon jason 1 2 and geosat follow on a plane wave fit method is used to resolve multiple internal tides in arbitrary horizontal directions the luzon strait is an energetic internal tide generation site and radiates internal tides both westward into the south china sea scs and eastward into the western pacific wp in the scs the k1 and o1 internal tides propagate over 1600 km reaching the vietnam coast in the wp they propagate over 2500 km and arrive to the mariana ridge and guam the k1 and o1 internal tides refract toward the equator during propagation the m2 internal tides in the scs bifurcate into two beams the northwestward beam is coincident with the frequent occurrence of internal solitary waves in this region implying their causative relation the phase speeds inferred from the altimetric along beam propagation agree with the theoretical values due to the influence of the earth s rotation the k1 and o1 phase speeds decrease remarkably from high to low latitudes for the diurnal internal tides the eastward radiation is about 50 greater than the westward radiation for m2 the westward radiation is about two times the eastward radiation the altimetric energy fluxes are about 50 of those in numerical model simulations

south atlantic volcanic margins the early cretaceous south atlantic continental break up and initial sea floor spreading were accompanied by large scale transient volcanism emplacing the parana etendeka continental flood basalts and voluminous extrusive constructions on the conjugate margins south of the torres arch abutment plateau on the north namibia margin we interpret four main tectono magmatic crustal units 1 oceanic crust 2 thickened oceanic crust covered by huge seaward dipping wedges 3 a c 150 km wide break up related rift zone partly covered by the dipping wedges and 4 thicker continental crust partly deformed by palaeozoic extension east of the early cretaceous rift similar settings also characterize other south atlantic margin segments we infer an up to 300 km wide and 2400 km long rift zone representing lithospheric extension leading to breakup and formation of the south atlantic volcanic margins comparison with other volcanic margins demonstrates in spite of local and regional differences gross similarities in tectono magmatic style crustal units and dimensions

progress on the formation dynamics of the layered circulation in the south china sea abstract in the south china sea scs an alternating cyclonic anticyclonic cyclonic cac circulation is recognized in the upper middle deep layers based on the principle of stokes theorem the cac circulation is driven extrinsically by the east asia monsoonal winds a vertical sandwich like inflow outflow inflow through luzon strait ls and intrinsically by the slope current topography interaction the understandings on the formation mechanisms of cac circulation have been achieved based on different principles and the physically solid interpretation on the cac circulation need to be further clarified in this paper we review different dynamic perspectives from recent researches that describe the combined effects of surface wind forcing lateral external forcing and the intrinsic coupling among different layers our aim is to obtain a consistent understanding of the dynamics of the circulation in the scs the cac circulation forms largely from the planetary vorticity flux that is extrinsically induced by the inflow outflow inflow through ls which is predominantly balanced by the interaction between the cac flow and bottom topography inside basin the vertical motion dynamically links the circulation in three layers and its spatial pattern has a strong impact on the basin circulation particularly in the middle and deep layers vertical coupling of the layers occurs mainly over the slope because of the cross slope motion due to interaction between strong slope current and topography the internal layered circulation and intensified mixing in turn affect and maintain the layered current structure in ls based on the review of the forcing mechanisms we offer perspectives for further investigations

samarium neodymium data on two late proterozoic ophiolites of saudi arabia and implications for crustal and mantle evolution whole rock and mineral samples from the jabal al wask and jabal ess ophiolites northwestern saudi arabia yield sm nd isochron ages of 743 24 ma and 782 38 ma respectively these formation ages which provide maximum limits for possible obduction ages are in broad but not precise agreement with the previously known geologic history of the arabian shield they indicate that the ophiolitic rocks are roughly coeval with nearby volcanic and plutonic rocks supporting a back arc origin for the two ophiolites we suggest that the jabal al wask and jabal ess ophiolites were parts of the same northeast southwest trending ophiolite belt now offset along the najd fault system initial nd values range from 6 6 to 7 6 indicating derivation from a mantle source that has been lil depleted for at least 2 ga reported nd values from the arabian shield that are lower than this suggest the presence of older reworked continental crust

extension of the najd shear system from saudi arabia to the central eastern desert of egypt based on integrated field and landsat observations the najd shear system in saudi arabia extends over 1200 km in a nw se direction and has a width of approximately 300 km a digital color mosaic compiled from seven landsat thematic mapper scenes was used to delineate characteristic structural features of the najd system in the midyan region of saudi arabia and to search for similar features in the egyptian eastern desert the digital mosaic was generated using ratios of landsat thematic mapper bands bands 5 4 3 4 5 1 5 7 that are sensitive to the rock content of fe bearing aluminosilicates spectrally opaque phases and hydroxyl bearing or carbonate minerals respectively the mosaic covers approximately 130 000 km of late proterozoic exposures of the arabian nubian shield and has the eastern desert and the midyan region placed in their approximate pre red sea locations the ajjaj shear zone ajz marks the termination of the najd system against the eastern margin of the red sea in the midyan region the ajz aligns with the central eastern desert based on analysis of pre red sea locations analyses of landsat data and field observations show that the ajjaj shear zone and the central eastern desert exhibit the following features in common 1 outcrops that are generally elongate in a nw se direction as a result of folding with fine scale lithologic heterogeneity at the outcrop scale related to deformation associated with faulting 2 nw trending left lateral faults and ductile shear zones 3 subhorizontal nw trending mineral lineations and variably dipping nw trending foliations with local changes in attitude around large competent e g granitic bodies and 4 lithologic contacts that are generally tectonic in nature and related to faulting these features are less common to the north and south of both the ajjaj shear zone and the central eastern desert results are consistent with the najd shear system extending into the eastern desert and dominating the structural patterns within the central part of the eastern desert

geochronology of the late precambrian hamisana shear zone red sea hills sudan and egypt the hamisana shear zone hsz is a broad zone of deformation approximately 50 km wide and at least 300 km long making it one of the largest basement structures in ne africa it has been interpreted as a precambrian suture as a zone of strike slip displacement or as a zone of crustal shortening the results of new rb sr and u pb zircon geochronological studies indicate that the northern hsz was thermally active during the pan african event until c 550 mg ago initiation of the structure may have begun 40 110 ma earlier all units have low initial 87 sr 86 sr ratios indicating juvenile derivation the timing of activity in the hsz is 50 150 ma younger than collisional suturing and terrane assembly in the arabian nubian shield but is similar to the 655 540 ma najd fault system of egypt and arabia deformation and metamorphism along the hsz clearly post date terrane accretion and probably are closely related to the najd tectonic cycle the most important deformation of the hsz is unrelated to suturing and at least one late precambrian suture must extend west from arabia into the interior of n africa

the late proterozoic ophiolite of sol hamed ne sudan abstract the sol hamed complex a sequence from ultramafics through gabbros thin sheeted dykes to pillow lavas is an ophiolite it was obducted tilted nearly to vertical eroded and covered unconformably by the nafirdeib series this is a volcaniclastic series dated at 712 58 ma the lower part of which includes conglomerates with ophiolitic clasts olistostromes one with large oolitic limestone slabs felsitic and dacitic tuffs turbidites and black shales with andesites above some of the structures in the ophiolite are attributed to sub oceanic deformation deformation after the deposition of the nafirdeib series produced folds and cleavage trending about ne sw and more locally a cleavage trending nw in a shear zone where the ophiolite was thrust northeastwards over the nafirdeib series the ophiolite and the nafirdeib series were intruded by the batholithic granite dated elsewhere at ca 669 ma the ophiolite is thought to occur on a suture with the nafirdeib series representing part of an island arc sequence

numerical and analytical estimates of m2 tidal conversion at steep oceanic ridges abstract numerical calculations of the rate at which energy is converted from the external to internal tides at steep oceanic ridges are compared with estimates from analytic theories the numerical calculations are performed using a hydrostatic primitive equation ocean model that uses a generalized s coordinate system as the vertical coordinate the model regional ocean modeling system roms estimates of conversion compare well with inviscid and nondiffusive theory in the sub and supercritical regimes and are insensitive to the strength of viscosity and diffusivity in the supercritical regime the nondissipative analytic solution is singular all along the internal tide beams because of dissipation the roms solutions are nonsingular although the density gradients are strongly enhanced along the beams the agreement between model and theory indicates that the prominent singularities in the inviscid solution do not compromise the estimates of tidal conversion and that the linearization used in derivi

internal solitary waves induced by flow over a ridge with applications to the northern south china sea 1 the generation of internal solitary waves by barotropic tides over a ridge is studied in a nonhydrostatic numerical model under idealized oceanographic settings the experiments examine the effects of ridge width barotropic tidal strength and stratification on wave generation the barotropic tidal flow produces internal wave beams emitting from the ridge top if the slope of the ridge exceeds a critical value equal to the slope of the wave beam reflection and refraction of a wave beam in an upper ocean waveguide associated with a strong shallow thermocline produce horizontally propagating internal tides when the local froude number over a ridge is not small lee waves generated on the ridge convert enough energy from the barotropic tides to the internal tides to form tidal bores and solitary waves increasing stratification at ridge depths enhances the generation of internal waves particularly at the diurnal periods in the luzon strait the slope of the wave beam decreases in spring and summer as stratification at the ridge depths increases favoring the generation of internal tides without the presence of a strong shallow thermocline internal solitary waves are not observed east of the luzon strait in the northern south china sea internal solitary waves are likely observed from april to july when a strong shallow thermocline is present a deep mixed layer in winter suppresses the production of internal solitary waves