analysis of the mesoscale structure in the imecocal region off baja california from hydrographic adcp and altimetry data we present geostrophic velocities obtained using hydrographic altimeter data and direct measurements of currents from 11 cruises offshore of baja california from january 2000 to july 2002 the study area was dominated by meanders and eddies in geostrophic balance two mechanisms of eddy generation were observed the first associated with the geometry of the coastline and the second a product of the cooling of the california current and the california undercurrent from the south there were two persistent eddies observed during the study the first eddy was offshore of bahia vizcaino and had an anticyclonic circulation situated in the southern region the rotation of the second eddy was dependant on which current was first to enter the transition zone along the coast spring was a transition period characterized by the formation of meanders the summer brought a period of eddy generation along the coast autumn and winter were marked by a separation of eddies from the coast and their subsequent drift towards the west the phase velocity of the mesoscale eddies was in accordance with the theory of the linear propagation of a rossby wave

correlation scales objective mapping and absolute geostrophic flow in the california current the spatial covariances of the time dependent density and geostrophic velocity fields off southern california are determined from a unique set of repeated hydrographic observations 44 cruises made by the california cooperative oceanic fisheries investigations from 1984 to 1994 the covariances and objective analysis are used to combine direct velocity observations from shipboard acoustic doppler current profiler adcp measurements made on a recent survey october 1993 with hydrographic observations the analysis reduces ageostrophic noise in the adcp velocities by smoothing and enforcing horizontal nondivergence additionally the velocities are mapped over scales that are dynamically consistent with the hydrography maximum surface geostrophic flow in the california current in october 1993 is about 35 cm s 1 50 larger than that estimated assuming a 500 m level of no motion absolute flow at 500 m is o 10 cm s 1 and indicates that the surface eddy field penetrates through the thermocline uncertainty in the geostrophic reference calculated from the adcp measurements is of o 4 cm s 1 the velocity residual objectively analyzed minus raw adcp estimates exhibits smaller correlation scales than the geostrophic flow

seismic constraints on a remnant mesozoic forearc basin in the northeastern south china sea abstract the northeastern of the south china sea scs has undergone tectonic inversion from a mesozoic convergent continental margin to a cenozoic divergent continental margin the remnant subduction related structures such as volcanic arc and forearc basin likely preserve key clues to reveal the dynamic mechanism of this tectonic inversion we applied ocean bottom seismometers obs data combining with multi channel seismic data gravity data drilling data and petrologic observations to reveal geophysical and structural features of the dongsha basin a mesozoic basin in the northeastern scs the mesozoic strata are characterized by large thickness 1 8 km relatively high p wave velocities 3 5 5 5 km s high densities 2 55 2 65 g cm3 alternating folds and thrust faults which are significantly different from the features of cenozoic strata the dongsha basin is flanked by a mesozoic granitic arc to the northwest and an inferred palaeo pacific subduction zone to the southeast indicating that it is geographically located in the mesozoic forearc region considering the similar mesozoic strata detected in the southern margin of the scs and the contemporaneous accretionary complex outcrops observed in the palawan continental terrane we propose that the mesozoic strata in these two regions originated from a common mesozoic forearc basin which was broken by the forearc rifting and subsequently separated by the spreading of cenozoic scs accordingly a continuous palaeo pacific subduction system is reconstructed including the arc forearc accretionary wedge tectonic sequences reviewing the mechanisms of forearc rifting globally and the retreat of volcanic arcs onshore south china we speculate that rollback of the palaeo pacific subduction slab might be one of the causes for the forearc rifting and the initial extension of the scs

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

balances of heat and momentum at 33 5 n 127 w in the upper ocean during the mixed layer dynamics experiment the balances of momentum and heat were studied for an 18 day period in october november 1983 during the mixed layer dynamics experiment at a site 650 km off central california data were collected from a drifting platform from which surface winds air temperature and ocean currents from a string of vector measuring current meters were measured the position of the unattended drifter was determined by loran c on the platform currents in the surface layers were partially wind driven and partially coherent with low frequency currents at deeper levels the latter currents though coherent were sheared turned significantly with depth and were presumably nearly geostrophically balanced vertically differencing velocity in the mixed layer improved the balance between wind and current by removing a portion of the geostrophic flow the complex correlation coefficient between wind stress and current integrated to 38 m was 0 76 for current relative to 38 m yet only 0 36 for the undifferenced case surface heat flux magnitudes were not clearly reflected in the heat content of the near surface layers although variability was over the first 13 days of the experiment the correlation coefficient between daily averaged heat flux and heat content change was 0 89 but average net surface heating was 60 w m 2 while the average heat content change in the top 38 m was only 10 w m 2 heat balance must have been restored by advection vertical advection was rejected as an explanation because heat content changes in layers defined by isotherm depths showed similar imbalances with regard to surface heating horizontal advection was estimated by two methods 1 by using sparse thermistor chain tows around the current meter drifter to construct a history of horizontal temperature gradients and 2 by using current profiles at moderate depths to estimate pressure gradients essentially through geostrophy hence buoyancy gradients by the hydrostatic relation hence temperature gradients the two methods gave very different estimates though both tended to redress the imbalance between surface heat flux and local heat storage

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

the relation between regionally consistent stretching lineations and plate motions abstract regional stretching lineations in the himalayas and southern tibet coincide with the known relative motions of the converging plates this relation is used to infer plate motions from the stretching lineations in the variscan and caledonian belts of europe and in the late proterozoic belts of northeast and east africa in each region high angle convergence of plates produced transverse stretching lineations and high angle collision was followed by or combined with large displacements first by ductile shear and later by brittle fractures parallel to the plate boundaries apparent stretching as a result of volume loss ramsay wood 1973 is common but recognisable as such reorientation by later deformations must be allowed for ramsay 1967 in ductile shear zones simple shearing leads to the progressive approach towards the shear plane of the xy plane of the strain ellipsoid and progressive approach of x the extension axis to the shear line ramsay graham 1970 thus large extensions approximate to the shear line large extensions tend to produce sheath folds whose acutely curved axes approach the stretching direction quinquis et al 1978 also the pre existence of a strong linear fabric predisposes the development of later folds with axes parallel to the earlier linear fabric for all of these reasons the extension axis x rather than the fold axis is of prime significance

trapped near inertial waves and enhanced chlorophyll distributions waves with near inertial frequencies were observed along a front associated with a large mesoscale feature in the sargasso sea during the late summer of 1987 high subsurface chlorophyll concentrations occurred on the edge of this front coincident with the wave packets the amplitude of the waves increased with time and kinetic energy propagated downward reducing 20 m richardson numbers in the thermocline to 1 or less chlorophyll levels were episodic showing no periodicity coincident with wave dynamics however on two occasions chlorophyll concentration increased from 1 mg chl m 3 several hours after the waves penetrated the thermocline it was hypothesized that mixing associated with shear instabilities stimulated new production a diffusivity model combined with nutrient data produced a phytoplankton bloom that accounted for only one of the maxima the other increase in chlorophyll may have been the result of horizontal advection of the wave packets near the front

eastward tectonic migration and transition of the jurassic cretaceous andean type continental margin along southeast china abstract a mesozoic andean type active continental margin is believed to have developed along the southeast china continental margin which has been investigated in detail however the architecture and evolution of its retroarc arc forearc system which is important for us to understand the interaction or connection between continental and oceanic lithospheres are ambiguous using multiple disciplinary data comprising seismic profiles field observations and numerical paleo topographies this study synthetically focused on the jurassic cretaceous evolution and geodynamics of the andean type southeast china continental margin subduction of the paleo pacific plate was initiated during the early jurassic 200 ma generating a nne striking jurassic magmatic arc along the east china sea bounded by imbricate thrust faults on both sides and coinciding with a paleo topographic coastal mountain range while the jurassic arc erupted along an ene striking triassic suture zone in the northern south china sea dominated by the tethyan tectonic domain and overprinted by the pacific tectonic domain the jurassic coastal mountain range began to collapse and transited into a rift basin at 135 ma and then the andean type continental margin gradually switched to the western pacific type during the late cretaceous 100 72 ma accompanied by jurassic thrust faults inverting into cretaceous detachment faults and magmatic arc migrated eastward to the taiwan rukyu areas such eastward tectonic migration and transition is associated with the eastward retreat of the subducted paleo pacific slab then a regional latest cretaceous 72 66 ma compression prevailed southeast china probably related to ridge subduction when the pacific plate replaced the paleo pacific plate to subduct beneath east asia

internal inertial waves in a surgasso sea front abstract this work examines the presence of internal inertial waves in a front in the north atlantic subtropical convergence zone results of doppler shear profiler and towed thermistor chain surveys are displayed to document the position and magnitude of the front objective maps of the total measured velocity are computed and subtracted from the observed velocity fields the remaining wave signal is processed to yield horizontal towed and vertical dropped kinetic energy spectra across the front from these rotary spectra are also computed along the line of tow and in the vertical to determine the horizontal and vertical anisotropy it is found that several nearly monochromatic waves are propagating northward and southward from the front with horizontal length scales of 32 50 km it was also discovered that the region of anticyclonic frontal vorticity exhibits an excess of downgoing energy at the longest vertical wavelength thus sampled 50 m while the region of cyclonic vorticity possesses more

plate convergence measured by gps across the sundaland philippine sea plate deformed boundary the philippines and eastern indonesia summary the western boundary of the philippine sea ph plate in the philippines and eastern indonesia corresponds to a wide deformation zone that includes the stretched continental margin of sundaland the philippine mobile belt pmb extending from luzon to the molucca sea and a mosaic of continental blocks around the ph australia sunda triple junction the gps geodyssea data are used to decipher the present kinematics of this complex area in the philippines the overall scheme is quite simple two opposing rotations on either side of the left lateral philippine fault clockwise to the southwest and counterclockwise to the northeast transfer 55 per cent of the ph sundaland convergence from the manila trench to the northwest to the philippine trench to the southeast further south 80 per cent of the ph sunda convergence is absorbed in the double subduction system of the molucca sea and less than 20 per cent along both continental margins of northern borneo finally within the triple junction area between the sundaland ph and australia plates from sulawesi to irian jaya preferential subduction of the celebes sea induces clockwise rotation of the sulu block which is escaping toward the diminishing celebes sea oceanic space from the eastwardadvancing ph plate to the south we identify an undeformed banda block that rotates counterclockwise with respect to australia and clockwise with respect to sundaland the kinematics of this block can be defined and enable us to compute the rates of southward subduction of the banda block within the flores trench and of eastward convergence of the makassar straits with the banda block the analysis made in this paper confirms that this deformation is compatible with the eastward motion of sundaland with respect to eurasia determined by the geodyssea programme but is not compatible with the assumption that sundaland belongs to eurasia as was often assumed prior to this study

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

mineralization controls in island arc settings insights from philippine metallic deposits abstract a review of the gold copper volcanogenic massive sulfide and ultramafic hosted i e chromitite nickel sulfide platinum group minerals deposits in the philippines is presented it is critical that a thorough understanding of the spatial and temporal relationship among magmatism structures and mineralization must be gained if the correct evaluation of the economic potential of a particular deposit is to be done structural features conducive to precious and base metal mineralizations are associated with shear zones extensional jogs and collision zones in northern luzon alkali and adakitic magmatism are considered good markers for gold copper mineralization volcanogenic massive sulfide deposits are hosted by either ophiolites of marginal basin origin or metamorphic terranes exploration works on these deposits have been geared in determining the gold content of the massive sulfides chromitite deposits are related with ultramafic rock hosted deposits their occurrence is attributed to crystallization magma mixing and mantle melt interaction processes in subduction related settings the multiple stages of partial melting responsible for the formation of supra subduction zone ophiolites result in the generation of second to third stage melts that are enriched in nickel sulfides and platinum group minerals on the basis of structural geochemical and tectonic controls panay mindoro and central mindanao and the sierra madre leyte and samar are good exploration targets for precious and base metal deposition in the western and eastern sides of the philippines respectively

3 d mapping of permeable structures affecting a deep granite basement using isotropic 3c vsp data summary this paper illustrates the efficiency of vertical seismic profiling vsp for the investigation of dipping and hydraulically conductive structures affecting a granitic basement covered by sediments a three component 3c vsp data set has been acquired in the gpk1 and eps1 wells of the soultz sous forets enhanced geothermal system egs located within the upper rhine graben urg our study focuses on the isotropic processing of profiles acquired with vertical vibrator p and their subsequent interpretation mainly p s converted reflections are identified from the analysis of the 3c records these p s conversions occur on steep permeable faults that are positioned in space by traveltime modelling these faults cut the granite basement in several hectometric scale blocks and represent the main fluid paths between the boreholes these faults are thought to be inherited from late variscan and alpine deformation periods reactivated by the current stress field when properly processed and interpreted vsp allow the scale gap between surface and borehole data to be bridged

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

wind forced internal waves in the north pacific and sargasso sea abstract the three dimensional structure of the near inertial frequency internal wave field was measured at two open ocean sites using expendable velocity profilers both wave fields appear to be dominantly wind forced although their vertical structure and horizontal scales are quite different the hydro 79 data were taken in the sargasso sea in september 1979 the internal wave field is predominantly downward propagating and vertically uniform when wkb scaled in the upper 800 m of the ocean the energy density is roughly equal to munk s 1981 universal value the stkex data were taken during a period of strong storms in the northeastern pacific ocean in november 1980 in the upper few hundred meters the wave field is five times larger horizontally and five times more energetic when wkb scaled than the hydro 79 wave field measurements made after the passage of a strong cold front show an even more energetic and larger scale wave field extending to 500 m comparison with the simulations of price 198

doppler sonar observations of internal waves the wavenumber frequency spectrum abstract in may 1980 an 18 day sequence of velocity profiles of the top 600 m of the sea was collected off the coast of southern california the measurements were obtained using a pair of doppler sonars mounted on the research platform flip from these data estimates of the wavenumber frequency spectrum of the oceanic internal wavefield are obtained the spectra are characterized by a series of ridges which occur at near internal and tidal frequencies as well as higher harmonics and sums of these fundamentals the ridges run parallel to the wavenumber axis there is a pronounced near inertial spectral peak the near inertial motions are dominated by a few identifiable wave groups there is a net downward energy propagation in the near inertial frequency band the vertical wavenumber dependence of a the spectrum is decidedly asymmetric in this region the asymmetry extends to five times the inertial frequency making much of the so called continuum asymmetric a high wavenumber cutoff at approximately 60

vsp in crystalline rocks from downhole velocity profiling to 3 d fracture mapping abstract vsp surveys have been carried out at several potential nuclear waste disposal sites in finland since the mid 1980s to date more than 200 three component profiles have been measured the main purpose of the surveys was to detect fracture zones in the crystalline bedrock and to determine their positions most seismic events could be linked to zones of increased fracturing observed in the borehole logs the more pronounced seismic reflectors could be correlated with hydro geologically significant zones which have been the main targets in the investigations processing and interpretation methods have been developed specifically for vsp surveys in crystalline rocks weak reflections from thin fracture zones are enhanced by multi channel filtering techniques based on the radon transform the position and orientation of the fracture zones are determined by polarisation analysis and by combining data from several shot points the compilation of the results from several boreholes gives a comprehensive image of the fracture zones at the scale of the whole site the discussion of the methodology is based on examples from the olkiluoto site in sw finland

geologic and paleomagnetic evidence for a possible miocene collision in western panay central philippines the palawan metamorphic terrane represented by paleozoic basement on the northwestern tip of panay central philippines collided with the remainder of the island between late oligocene and middle miocene time subduction continued north and south of the collision zone along the manila and negros trenches respectively evidence for the collision is 1 the juxtaposition along a major fault of old melange terrane against highly metamorphosed paleozoic continental sediments similar to those exposed on palawan island itself and 2 miocene thrusting in the melange terrane oriented parallel to the suture paleomagnetic studies show that since the early miocene the island of panay has rotated 20 clockwise declination 20 9 inclination 22 1 for six sites whereas the northern philippines has rotated counterclockwise these contrasting rotations are consistent with a collision of the philippine arc with a northeastward converging palawan block

processes of allochthonous terrane evolution mindoro island philippines on mindoro two tectonostratigraphic terranes the north palawan block and the mindoro block are separated by a steeply dipping shear zone the north palawan block was rifted off southern china in the oligocene and comprises most of the shallow southern end of the south china sea the eastern part of this terrane exposed on mindoro includes jurassic and paleogene strata probable rift basalts of oligocene age and oligo miocene graben fill deposits in the late oligocene and early miocene the eastern north palawan block underwent crustal stretching with grabens oriented at a high angle to synchronous spreading anomalies in the south china basin we hypothesize that grabens formed in an overall transtensional environment near a transform boundary at the eastern margin of the opening south china basin the mindoro block consists of a pre upper cretaceous low grade metamorphic basement overlain by upper cretaceous and upper eocene strata the mindoro block records several episodes of intense deformation of mesozoic and tertiary age and contrasts with the north palawan block both in terms of stratigraphy and structural evolution the mindoro suture which separates the mindoro and north palawan blocks is a complex structural boundary comprising slices of diverse lithologies separated by steeply dipping anastomosing faults deformed tectonic slices in the suture zone include serpentinized ultramafic rock amphibolite and rocks derived from both of the bounding terranes we interpret this suture as a zone of mostly transcurrent faulting that was active through much of mid tertiary time paleogeographic considerations for early and middle miocene time support the premise that the west side of the central philippine archipelago was a left lateral transform boundary the mindoro and north palawan blocks were initially juxtaposed along the transcurrent mindoro suture by late miocene time subsequent deformation on mindoro includes crustal shortening associated with the southern end of the manila trench which projects onshore on southwest mindoro the onset of shortening here probably reflects a late miocene change in philippine eurasian plate motion the mindoro suture zone is now locked and it acts as a rigid buttress against which strata of the north palawan block have been structurally stacked the mindoro suture zone is similar to other terrane boundaries in the northern philippines the history of terrane transport in this region was apparently dominated by strike parallel shuffling of terranes along major transcurrent boundaries within the philippine arc transcurrent motion has taken place in extensional and compressional regimes and it is ongoing today this may be a dominant process by which complex island arc systems are disrupted prior to accretion onto a continental margin

episodic rifting and subsidence in the south china sea the south china sea experienced at least three stages of rifting and two intervening stages of sea floor spreading since the early cretaceous its evolution can be described by an episodic model of tectonism one of thermal cooling and subsidence pulsed by temporally and spatially confined heating events analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the late cretaceous the late eocene and the late early miocene the rift system corresponding to the first episode trends northeast southwest whereas those of the second and third trend east west these two trends coincide with the orientations of the major tectonic lineations within the basin age estimates from heat flow and bathymetric data suggest the oceanic crust in the southwest subbasin is considerably older 55 ma than that in the northwest 35 36 ma or east 32 ma subbasins the episodic tectonic model is supported by basin subsidence analysis subsidence especially subsidence rate curves derived from the regional well data demonstrates that unlike a classic atlantic passive margin thermal subsidence in the south china sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes in terms of hydrocarbon potential the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs separated by widespread unconformities the thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating

spreading direction in the central south china sea recent work1 2 indicates that the south china sea is an atlantictype marginal basin of late tertiary age magnetic anomalies in the eastern part of the sea are consistent with seafloor spreading directed approximately north south1 2 we present here a new morphostructural study based on coupled seabeam mapping and single channel seismic reflection profiling which reveals dominant normal fault scarps striking n50 e between 113 and 119 e longitude near the axis of this basin such a structural fabric implies a nw se spreading direction at least in the 150 200 km wide axial region of the south china sea and places new constraints on geodynamic models for the formation of this basin in the tectonic and palaeogeographic framework of south east asia and the south west pacific

the upper ocean internal wave field influence of the surface and mixed layer a model is developed to calculate the upper ocean internal wave spectrum as modified by the surface boundary and mixed layer the garrett munk spectrum is assumed to describe the deep ocean wave field the main effect of the surface and mixed layer is to align the vertical structure of the waves forming vertically standing waves locally this contrasts with the assumption of random alignment in the garrett munk model model spectra and coherences are calculated for idealized buoyancy frequency profiles and compared with the garrett munk model measurements in the upper 200 m from the mixed layer dynamics experiment in the northeast pacific in 1983 are also compared with the model results the most striking success of the model is predicting the observed high coherence and 180 phase difference across the mixed layer of horizontal velocity

north palawan block philippines its relation to asian mainland and role in evolution of south china sea the island of mindoro the northern part of palawan island and the reed bank area southwestern philippines together constitute a continental fragment the north palawan block lying within an island arc oceanic setting the permian to paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the philippine archipelago these rocks also suggest that the north palawan block once occupied a pre drift position contiguous with the south china mainland four prominent pre neogene regional unconformities are recognized both onshore and offshore the china mainland in taiwan and in the north palawan block the synchrony of these unconformities and the facies relation of the unconformity bounded sedimentary units strongly suggest a common pre neogene history for all these areas by contrast an important regional unconformity occurring at the top of the middle miocene throughout the palawan area is absent from the asian mainland extension in the south china sea basin since the mesozoic which has separated the north palawan block from the asian mainland has been approximately uniform from west to east however there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea floor spreading from the foregoing observations and using the most recent magnetic spreading anomaly data for the south china sea a suite of palinspastic reconstructions has been prepared which shows the evolution of the south china sea area from the late triassic to the pliocene the reconstructions illustrate 1 the convergent continental margin setting of the north palawan block during much of the jurassic and cretaceous 2 the late cretaceous inception of the philippine island arc system 3 the subsequent counter clockwise rotation of the arc system from the late eocene onward 4 the paleocene to middle miocene opening of the south china sea and 5 the early to middle miocene collision between the north palawan block and the palawan subduction system

geology and geochemistry of the clastic sequences from northwestern panay philippines implications for provenance and geotectonic setting abstract whole rock geochemical analysis of samples from the clastic sequences in northwestern panay revealed different compositional ranges for the buruanga peninsula and antique range the results provide additional evidence that northwestern panay consists of two distinct terranes as a result of the arc continent collision between the palawan microcontinental block and the philippine mobile belt major element compositions of clastic rocks from the buruanga peninsula saboncogon formation revealed that they belong to a continental margin tectonic setting whereas the antique range sedimentary rocks lagdo formation show an affinity to an oceanic island arc setting the fragante formation of the antique range shows some similarities in tectonic setting and provenance with buruanga peninsula clastic rocks which suggests a buruanga peninsula sediment contribution during its time of formation furthermore provenance analyses from combined major and trace element data indicate a more silicic source for the buruanga peninsula clastics and a more mafic derivation for the sedimentary rocks of the antique range these findings are consistent with previous studies suggesting that the buruanga peninsula forms part of the palawan microcontinental block and the antique range belongs to the philippine mobile belt the palawan microcontinental block is believed to be a drifted continental fragment from the mesozoic east asian accretionary complex in the southern part of the eurasian mainland which represents the continental margin setting and felsic source of the buruanga peninsula clastic rocks meanwhile the oceanic island setting and mafic source of the antique range clastic rocks represent the volcanic rocks of the philippine mobile belt that were formed as a result of the subduction of the leading oceanic edge of the palawan microcontinental block

middle oligocene oceanic crust of south china sea jammed into mindoro collision zone philippines mindoro island south of luzon philippines is a complex junction between the manila trench and the collision zone of the north palawan block with the western philippines mobile belt middle oligocene ophiolites recognized in this suture are coeval with the oldest magnetic anomalies of the south china sea basin these ophiolites are part of a complex pile of terranes thrust above the north palawan block at the lower middle miocene boundary these ophiolites are interpreted as fragments of south china sea oceanic crust jammed between two distinct continental blocks during the counterclockwise rotation of luzon

middle eocene low paleolatitude radiolarian evidence for the cabog formation central east luzon philippine mobile belt abstract the cabog formation newly established herein and exposed in central east luzon philippine mobile belt is defined in age by the occurrence of radiolarians the radiolarian assemblage is correlative with the middle eocene and suggests a low paleolatitude affinity the correlation sedimentary environment and the tectonic significance are discussed the cabog formation is correlative with the distal part of the middle late eocene caraballo formation which is exposed in the northeastern side of the philippine fault zone the sandstone composition and radiolarian age suggest that the cabog formation represents the first depositional stage in the early arc setting the northward migration of the formation is also estimated in relation with the philippine sea plate motion along the older philippine fault from the equatorial area

geodynamic evolution of the taiwan luzon mindoro belt since the late eocene abstract the structural framework of the taiwan luzon mindoro belt or festoon is described following three major transects the luzon transect with active subduction and active island arc the taiwan transect with active collision the mindoro transect with active subduction and inactive collision based on this geological study and on available geophysical data a model for the geodynamic evolution of this portion of the philippine sea and eurasia plates boundary is proposed in a succession of reconstructions between the late eocene and the present the major geodynamic events are 1 1 beginning of the opening of the south china sea s c s in lower oligocene times contemporaneous with obduction of the zambales and angat ophiolites on luzon 2 2 subduction of a mesozoic oceanic basin along the proto manila trench from the upper oligocene to the lower miocene 3 3 obduction of the south china sea oceanic crust onto the chinese and reed bank calamian passive margins in middle miocene time 14 15 ma related to a major kinematic reorganization end of opening of the s c s 4 4 beginning of collision between the luzon microblock and the two margins of the s c s in the upper miocene 7 ma collision is still active in taiwan whereas it stopped in mindoro during the pliocene

shallow to near surface vein type epithermal gold mineralization at lalab in the sibutad gold deposit zamboanga del norte mindanao philippines abstract the sibutad vein type epithermal gold deposit is the most promising economically feasible gold mineralization found in recent years in zamboanga del norte province in zamboanga peninsula mindanao island the sibutad gold deposit occurs in pliocene to pleistocene volcanic rocks resting on a deformed island arc block to the east of the tectonically active sindangan cotabato daguma lineament the host rocks are the malindang volcanics composed of lower and upper members which are both intruded by andesite porphyry the lower member is made up of andesite flows dacite tuff and tuffite whereas volcanic breccia and tuff breccia characterize the upper member the sibutad gold deposit is subdivided into the larayan and lalab prospects in lalab which is the prospect studied hydrothermal activity and gold mineralization occur in the andesite flows the geology alteration and mineralization of the lalab orebody are of adularia sericite type that suggests the gold was precipitated from reduced near neutral ph solutions within a shallow to near surface environment the following events produced the lalab orebody 1 pre breccia wallrock alteration 2 hydrothermal brecciation 3 post breccia wallrock alteration and 4 gold mineralization gold precipitated in quartz veins was a response to boiling followed by fluid mixing prolific gold zones occur between 30 m below sea level and 200 m above sea level

structural evolution of bondoc burias area south luzon philippines from seismic data abstract recently acquired 2 d seismic profiles in the offshore area between bondoc peninsula and burias island south luzon philippines are interpreted in the context of known structural styles observed onshore and in relation to paleo and neo tectonic regimes in the region two distinct seismic sequences can be distinguished relative to their structural style and tectonic significance the top of a lower sequence shows strongly reflective properties this unit correlative to late oligocene to early miocene limestone bodies observed onshore in bondoc peninsula and burias island is affected by intense to moderate superposed folding and thrust faulting an upper sequence correlative to a two member turbiditic and shallower marine clastic deposit widely exposed in bondoc peninsula is affected by thrust faulting and deformation associated with overturned tight folding the onshore equivalents of these two seismic sequences form the core of a bent anticlinorium that twists from a nw se axis in onshore bondoc into a n s axis southwards into the southern tip of the peninsula then back to a nw se axis in the offshore region further to the south overlying this structural core is a relatively less deformed sequence where syn sedimentary half grabens are still preserved in places this complex structural style is the result of a series of several tectonic events occurring from the eocene to the present involving carbonate build up deep water turbidite deposition consequent compression folding and faulting and late event half graben controlled deposition some resulting structures are indicative of tectonic inversion processes positive and negative which may prove to be potentially favorable in the search for structural plays in the area

sr isotopic composition of marbles from the puerto galera area mindoro philippines additional evidence for a paleozoic age of a metamorphic complex in the philippine island arc the sr isotopic composition of marbles from the puerto galera area mindoro philippines is compatible with either a tertiary or a paleozoic age the former is considered as unlikely because nonmetamorphic sediments of that age overlie the metamorphic complex this implies that the metamorphic complex does not represent the basement of the philippine arc but is an accreted terrane

inertial oscillations in the upper ocean during the mixed layer dynamics experiment mildex surface currents in the near inertial frequency band were analyzed from 18 day long measurements taken in october november 1983 as part of the mixed layer dynamics experiment the currents below two drifting platforms separated by 55 km were found to have differed in their inertial response to a frontal passage on november 1 by 10 cm s 1 wind records from the two platforms were used to compute the predicted inertial currents with a simple slab model of the wind driven flow the model currents reproduced most of the features of the observed inertial currents including the disparity between the two locations following the november 1 frontal passage the disparity was due to differences in the weak winds preceding the frontal passage which account for inertial currents of 5 cm s 1 in opposing directions at the two platforms at the time of the front these differences or small scale 50 km structure in the wind field were responsible for the disparity rather than the slight difference in the arrival time 2 hours of the front at the two locations

observations of near inertial waves in acoustic doppler current profiler measurements made during the mixed layer dynamics experiment measurements of upper ocean shear made during the mixed layer dynamics experiment mildex provide evidence of large horizontal scale motion at near inertial frequency the measurements consist of shipboard acoustic doppler current profiles four large scale spatial surveys of 2 4 days duration were made by the r v wecoma as a set of boxes approximately 60 km per side around a drifting current meter buoy velocity time series from the drifting buoy and from sonar measurements made from flip also indicated the presence of motions at near inertial frequency horizontal length and time scales of the motion are estimated from the phase of the shear vector measured during the spatial surveys estimates of the length scale of the waves range from 500 to 1000 km and the frequency is approximately 1 1f the behavior of the phase is found to be consistent with a model of narrow band inertial waves with vertical structure such that there is a zero crossing in velocity at the base of the mixed layer 40 60 m

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

imaging the high temperature geothermal field at krafla using vertical seismic profiling abstract geophysical exploration and in particular active source seismic imaging of geothermal fields is important to assess and optimize the exploitation of natural heat sources for energy production and direct use the first multi offset moving source vertical seismic profiling vsp experiment over the high temperature geothermal field in krafla iceland was carried out in spring 2014 with the aim to test whether vsp is a suitable method to map volcanic stratigraphy fractures dykes steam zones and magmatic bodies at this site and for volcanic environments in general in this study we present a workflow for processing the sparse krafla vsp dataset recorded with receivers in either of two boreholes the analysis involved first arrival traveltime inversion and seismic reflection processing the seismic velocity model obtained by traveltime tomography reveals structural information between the two boreholes and can be linked to an existing geological model showing that the seismic velocities are mainly controlled by lithology the zero offset seismic reflection data were processed into two corridor stacks walk away vsp reflection data were migrated with a novel multicomponent kirchhoff migration algorithm that includes p and s wave isolation to obtain separate pp ps and ss migrated images the reflections imaged in the corridor stacks can be linked to the main lithological units known from borehole logging information migrated images from the walk away data reveal reflectors below and to the sides of the two boreholes considering a priori information such as hypocenter locations from earthquake seismology studies the reflectors can be related to changes in lithology fault zones dykes and possibly the top of the krafla magma chamber we found that vsp is potentially a useful method to image the key lithological boundaries and volcanic stratigraphy in the complex magmatic environment at krafla but a priori information proved to be essential to constrain the processing and interpretation of the sparse array dataset

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

pre eocene synmetamorphic structure in the mindoro romblon palawan area west philippines and implications for the history of southeast asia the structure of the pre eocene rocks considered as the basement of the philippines has been investigated in the mindoro lubang romblon tablas sibuyan and north palawan areas in the former two areas the same pre eocene succession of units is recognized from top to bottom 1 a pre eocene olistostrome 2 an ophiolitic nappe 3 a schistose sequence pelites sandstones basic schists and marbles and 4 a gneissic unit the nature of the contact between the olistostrome and the underlying units is unclear but the ophiolite and the schistose sequence form two thrust sheets of oceanic origin thrust upon the gneissic unit that is considered a part of a continental basement called the west philippines block small scale structures show that the early deformation stage is characterized by a submeridian 0 n40 e lineation formed in greenschist to amphibolite facies conditions during the thrusting kinematic analysis show that the thrusting was from north to south in north palawan metamorphic rocks with similar microtectonic and kinematic characteristics are found they are overlain by a late jurassic olistostrome which is correlated with the olistostromes found in calamian north mindoro carabao and buruanga peninsula north panay the microstructural features and the presence of the olistostrome suggest that the north palawan mindoro tablas romblon sibuyan and carabao islands belong to the same north palawan block of hamilton 1979 which is a continental fragment rifted from asia in cenozoic times it is assumed that the western panay and zamboanga areas which are characterized by mesozoic ophiolites and metamorphic rocks also belong to the north palawan block all these islands experienced to some extent the same mesozoic geohistory the south verging thrusting is interpreted as the result of an oblique collision of the west philippines block with asia the contemporaneous left lateral strike slip faulting and the calc alkaline magmatism widespread along the chinese margin are also included in the geodynamic model

internal wave observations from flip in mildex abstract during 0ctober november 1983 the research platform flip participated in the mixed layer dynamics experiment mildex off the coast of southern california included among the equipment on board was an array of six doppler sonars and a repeatedly profiling ctd the sonars operate at frequencies between 67 and 80 khz with peak transmitted power of order 2 kw each four of the sonars were directed downward 53 obtaining velocity profiles to depths in excess of 1100 m the ctd was profiled to a depth of 320 m every 3 minutes approximately 6000 ctd profiles were obtained during mildex the mildex internal wavefield is slightly less energetic than the garrett munk canonical standard except in the near inertial frequency band here very low energy levels are seen the semidiurnal baroclinic tide dominates the spectra of both horizontal and vertical velocity in this work slant velocity estimates from back to back sonar beam are combined to form estimates of horizontal velocity and its vertical der

near inertial current oscillations in the vicinity of the bering sea marginal ice zone near inertial current oscillations with 10 20 cm s amplitudes were prevalent over the bering sea shelf during november 1982 and again in march and april 1983 and also evident at reduced amplitudes during the intervening winter spectral peak frequencies were consistently within 1 of the local inertial frequency in contrast to the more superinertial 5 above frequencies commonly reported elsewhere a superinertial secondary energy peak at 1 038 was evident corresponding to the first mode wave amplitudes decreased with distance shoreward from the shelf break consistent with the effects of decreasing bottom depth and increasing mixed layer depth the oscillations were highly coherent over 100 km distances similar to observations reported by thomson and huggett 1981 for the british columbia coast whereas near inertial oscillations have been commonly reported to be uncoupled over much shorter 10 km distances in other regions vigorous near inertial ringing was associated with rapidly passing weather systems the decline in near inertial oscillation amplitudes during winter was partially due to a significant reduction in both cyclone frequency and occurrence of wind events causing clockwise wind shifts the decline was enhanced by reduction in the vertical stratification needed to support inertio gravity internal waves as the shelf waters apparently became mixed from top to bottom the loose mobile sea ice in the winter marginal ice zone miz did not appear to inhibit wind generation of the inertial oscillations the presence of sea ice appears in fact to have contributed to the spring increase of near inertial current amplitudes through restratification of the water column caused by melting ice our observations particularly the spatial coherency and spectral properties were generally consistent with kundu and thomson s 1985 model for inertio gravity waves generated in the wake of a translating weather front the half wavelength typical of these waves forced by transiting weather fronts on the bering shelf appears to be 150 km or approximately the width of the winter miz the associated near inertial currents are 180 out of phase with those a half wavelength away in the direction of phase propagation thus a storm passing perpendicular to the ice edge can excite waves at near inertial frequencies which compress deform and dilate the ice pack by up to a few percent of the miz width we suggest that this mechanism in conjunction with near inertial interfacial shear which can increase upward heat flux influences the width scale of the miz