geochemistry of tertiary igneous rocks of northern luzon philippines evidence for a back arc setting for alkalic porphyry copper gold deposits and a case for slab roll back oligocene to early miocene volcanic rocks are preserved in the central cordillera range and cagayan valley of northern luzon philippines basaltic and andesitic rocks of the pugo formation in the baguio district of the central cordillera were intruded by the 27 to 20 ma calc alkaline central cordillera diorite complex in the southern cagayan valley the subalkaline to alkaline late oligocene mamparang formation overlies the cretaceous caraballo formation and has been intruded by the didipio igneous complex the cordon syenite complex and the palali batholith the didipio complex comprises an early suite of diorites which were intruded by the strongly mineralized stocks of the dinkidi cu au porphyry deposit whole rock geochemical data for intrusive and extrusive rocks of the baguio district range from low k calc alkaline to shoshonitic basalts to dacites with rare earth element ree and high field strength element hfse characteristics of suprasubduction zone magmas and are all interpreted to have been sourced from the same parent melt samples from didipio display higher alkali contents but similar trace element characteristics new age dates for the didipio area range from 25 7 to 24 8 ma the potassic magmas of the cagayan valley are interpreted to have formed in a back arc coeval to the mainarc sequence that is preserved in the baguio miocene rocks this contradicts earlier models which invoke an early miocene arc reversal in the northern luzon archipelago with the switch from early westward subduction to later eastward subduction attributed to a variety of causes the lack of a single compelling trigger for arc reversal combined with the coeval emplacement of arc magmas in the west and back arc magmas in the east in northern luzon is best interpreted as the result of eastward subduction since the late oligocene the presence of 20 ma adakitic magmas in the baguio district may indicate that flattening of the downgoing slab resulted in a hiatus in magmatism and termination of back arc rifting

the macolod corridor a rift crossing the philippine island arc abstract the macolod corridor in southwestern luzon is an approximately 40 km wide zone of still active intense quarternary volcanism which perpendicularly crosses the island in a ne sw direction the tectonic setting of the corridor is still somewhat questionable due to several not yet well understood major structural elements affecting southwestern luzon based on the presently available information we believe that the corridor is a pull apart zone formed by a diffuse system of nw se oriented shearing

measurements of shoaling internal waves and turbulence in an estuary 1 the shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas including such effects in numerical models demands improvements in the understanding of several aspects of the energetics especially those relating to turbulence generation and observations are needed to build this understanding to address some of these issues in the estuarine context we undertook an intensive field program for 10 days in the summer of 2008 in the st lawrence estuary the sampling involved shore based photogrammetry ship based surveys and an array of moorings in the shoaling region that held both conventional and turbulence resolving sensors the measurements shed light on many aspects of the wave shoaling process wave arrivals were generally phase locked with the m2 tide providing hints about far field forcing in the deeper part of the study domain the waves propagated according to the predictions of linear theory in intermediate depth waters the waves traversed the field site perpendicularly to isobaths a pattern that continued as the waves transformed nonlinearly acoustic doppler velocimeters permitted inference of the turbulent energetics and two main features were studied first during a period of shoaling internal waves turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude second the evolving spectral signatures associated with a particular wave shoaling event suggest that the turbulence is at least partly locally generated overall the results of this study suggest that parameterizations of wave induced mixing could employ relatively simple dynamics in deep water but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions

accumulation of particles in propagating fronts field observations imply that accumulation and advection of invertebrate larvae and other plankton by propagating fronts provides an efficient mechanism for the cross shelf transport and subsequent coastal settlement of larvae and plankton gravity currents propagating into a heavier uniform density fluid are known to have near surface velocities u that exceed the propagation speed c of the gravity current nose it is shown by simple dam break laboratory experiments and through corresponding numerical solutions of two dimensional stratified flow and lagrangian particle advection that this characteristic of gravity currents can lead to accumulation in the gravity current nose of particles that originate well behind the gravity current head however efficient particle accumulation and transport with the speed c only occurs for particles with sufficient vertical buoyancy or vertical swimming capability weakly buoyant or neutral particles are swept down and back away from the gravity current head by the circulation in this region a dam break into an ambient fluid with stratification two layered could result in the transport of some particles that are initially trapped in the forepart of the leading disturbance an undular bore however this situation does not result in significant accumulation of particles at the leading edge of the disturbance the numerical solutions show that particles that originate in the dense fluid ahead of the gravity current are much less likely to be accumulated at the gravity current nose a simple scaling criterion for the minimum vertical buoyancy velocity for efficient accumulation and transport of buoyant particles based on the gravity current and particle characteristics is developed and compares favorably with the numerical results the implications of these results for transport of larvae in coastal environments are discussed the dynamics of marine benthic invertebrate populations are greatly affected by larval transport for near shore populations larval transport prior to settlement includes at least three processes cross shore advection because larvae are generally very small and cannot control their cross shore position by swimming alone larval behavior because by swimming vertically larvae might be able to exploit some depth dependent cross shore flows and accumulation by convergent circulation in propagating features because cross shore advection of larvae is often dependent on the retention of larvae at the propagating features several hypotheses of onshore larval transport namely surface slicks over linear internal waves shanks 1983 internal bore warm fronts pineda 1994 and upwelling relaxation fronts farrell et al 1991 invoke concentration of larvae at propagating features these hypotheses state that larvae become concentrated at convergent features aligned parallel to the coastline and that larval transport occurs as these linear features propagate shoreward the interplay between transport and accumulation is poorly understood issues include 1 the dependency of transport on accumulation and of accumulation on larval behavior and 2 whether the frontal larvae originate onshore or off

structure and evolution of the intracratonic basins of central australia summary the central australian geology is dominated by a series of parallel sedimentary intracratonic basins whose history spans time from the late proterozoic to the carboniferous the basins are separated by regions of exposed proterozoic crust that have a history of significant uplift the formation of the basins cannot be explained by conventional thermal or stretching mechanisms nor does the foreland basin model provide an adequate explanation for their occurrence the geophysical observations particularly gravity point to a structure whereby the crust is considerably thicker under the basins than it is under the regions where basement rock is exposed this suggests that the crust as a whole is involved in the process that led to the basin formation a mechanical model is developed which is based on the supposition that the lithosphere has been in a state of horizontal compression for long time intervals the lithosphere is considered as a viscoelastic plate that has been subjected to a small normal load distributed in an irregular manner under compression initial deflections due to this load are magnified according to the plate s physical properties the magnitude of the compressive force and the wavelength spectrum of the initial perturbations because of the viscosity the deflections grow with time at a rate that is determined by the balance of forces acting on the plate and by the lithosphere s rheology both the elastic and viscous deformations are much enhanced if erosion of the uplifted areas occurs with the sediments deposited into the downwarps these deformations take place at stresses that are much less than the buckling stresses as bending stresses increase with time failure by thrust faulting is predicted to occur within the basins with the exposed basement being thrust over the basins the model has been applied to the central australian region starting at about 900myr ago the first basins to develop are the officer and amadeus basins with uplift occurring in the intervening musgrave block initial rates of uplift and basin subsidence are small but they can increase rapidly with time if the compressive force is main

recognition of contrasting magmatic processes using sb systematics an example from the western central luzon arc the philippines abstract the western central luzon volcanic system is associated with eastward subduction along the manila trench two arcs the bataan ba and the mindoro ma arcs have resulted from this subduction and are separated by a ne sw oriented rift related zone of volcanism called the macolod corridor mc the ba consists of volcanism related to partial melting of the mantle wedge initiated by fluids from the subducted slab the ma volcanics are also related to the subduction process but lile and radiogenic sr isotope data compared with the western part of the ba are significantly higher the mc also has high lile data compared with the western section of the ba but lower radiogenic sr isotope values than the ma trace element modelling has been used to explain sb systematics sr ca vs ba ca observed in geochemical data from volcanoes worldwide these trends and their sense of curvature are most probably the result of variations in plagioclase and clinopyroxene crystal fractionation sb systematics have been examined from four volcanoes mt natib and mt mariveles within the western section of the ba mt maquiling within the mc and the mt san cristobal banahaw complex within the ma the results suggest that crystal fractionation was a dominant process during the evolution of the magma chambers below the various volcanoes in addition initial melt compositions suggest that the source of the ma magmas has been enriched in a crustal component the original magma composition s from the mc volcano mt maquiling appears to have been generated by smaller degrees of partial melting compared with the ba volcanoes studied

on isostasy at atlantic type continental margins cross spectral techniques have been used to analyze the relationship between free air gravity anomalies and topography of approximately 100 profiles over the continental margins of eastern north america southwest africa and the coral sea lord howe rise the resulting admittance functions for these margins have been interpreted in terms of the flexure model of isostasy the relatively young coral sea lord howe rise margin is associated with the lowest value of the effective elastic thickness te 5 km while the relatively old eastern north american margin is associated with the highest value 10 te 20 km thus te appears to increase with the age of the margin these results which are consistent with flexure studies from the major ocean basins have been interpreted in terms of a simple model in which the flexural strength of the lithosphere increases with age the model suggests that a low rigidity plate or airy type model is most applicable early in rifting history while a high rigidity plate is more applicable later in margin evolution thus sediments at a margin initially load a relatively thin and hot plate while sediments later in margin evolution load a relatively thick and cold plate the model explains a number of features of the tectonic stratigraphic evolution of margins these include a change in flexural style from a narrow and deep basin to a broad and shallow basin coastal plain onlap and uplift in the continental interior furthermore the flexure model of isostasy contributes in a major way to observed free air gravity anomalies at continental margins in particular the model explains the existance of airy isostatic gravity anomalies at margins the amplitude and wavelength of these anomalies are a function of the sediment supply the type of mechanisms controlling sediment deposition up building and or out building and the thermal structure history and age of the margin

heat flow on the hawaiian swell and lithospheric reheating most oceanic volcanic centres caused by hotspot activity are surrounded by sea floor that is unusually shallow for its age1 2 there is increasing evidence that swells found on older sea floor like the hawaiian swell have formed from a broad scale reheating and thinning of the lithosphere as it passes over a mantle hotspot3 4 if the formation and subsequent disappearance of these swells are controlled by thermal processes they should have an above normal heat flux we present here the results from 95 new heat flow measurements on the hawaiian swell along the older part of the swell the heat flow is 20 25 higher than the normal heat flow for crust of this age this anomaly is consistent with the observed swell uplift the shape and amplitude of the heat flow anomaly require that the reheating be largely confined to the lower half of the lithosphere

winds between san diego and san clemente island dense ship observations off san diego were used to capture the diurnal and seasonal wind trends the land breeze regime extends to 40 km off san diego in the winter but goes to less than 10 km when averaged for the winter significant diurnal variations in wind speed occur in all seasons from the coast to beyond 140 km ship observations were averaged over 0 2 of latitude and longitude these have significant structure that is obscured in other studies based upon 1 averages wind speeds decrease by a factor of 2 or more from 140 km offshore to the coast in both the northerly and westerly component the mean flow has a weak summer southerly component this is in opposition to earlier studies which indicated northerly mean monthly flow all year ship observations were compared to san diego airport and san clemente island measurements in order to check the accuracy of allowing land measurements to substitute for over water measurements san diego winds were found to be very representative of the nearest 10 km of ocean in wind speed and direction on the diurnal and seasonal scales san diego would be a good proxy station from which to infer the long term near shore meteorlogical conditions san clemente island wind speeds are systematically less than the ship observed wind speeds in the easterly component but the correspondence between the northerly component at san clemente and ships is irregular in the diurnal and monthly means this station could not be used to infer the northerly component without an uncertain and elaborate correction

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

some comments on two layer extensional models for the evolution of sedimentary basins simple extensional models that involve listric faulting in the brittle upper crust and plastic flow in the lower lithosphere have been shown to account for the subsidence history of various continental sedimentary basins and continental shelves in this paper we present structural evidence that extension in the continental lithosphere during rifting is not uniform we review evidence that the rifting process in major intracratonic rift basins is spasmodic rather than continuous that extension and subsidence within the rift during a tectonic phase is generally accompanied by uplift and erosion of the rift flanks that subcrustal heat input during rifting occurs over an area much broader than the rift proper and that there may be broad regional uplift before and or during rifting to explain the uplift of the flanks during rifting and their postrift subsidence we invoke two mechanisms subcrustal thinning by extension below the flanks and tilted major normal faults in the crust between graben and flanks the uplift and erosion of the flanks due to tilted faults probably do not significantly affect estimates of extension from subsidence analysis but uplift due to both sources can in certain cases be incorrectly attributed to regional uplift or doming we present a simplified analysis of the two layer extensional model for the elementary case in which extension is instantaneous and the crust is thinned by a different amount from the subcrustal lithosphere we provide a simple graphical method of data analysis to obtain the parameters that describe thinning of the crust and lithosphere during extension from the subsidence history application of this method to the central part of the pattani trough in the intracratonic gulf of thailand shows that extension and thinning of the lithosphere of a factor of 2 since late eocene can account for much of the subsidence history and the present day heat flow our analysis suggests that thinning of the crust in this area is 20 greater than thinning of the whole lithosphere assuming that none of the lithosphere is removed from the region of extension during rifting we show by simple geometric examples that a process of nonuniform extension implies that much greater thicknesses of sediment can be deposited in the center of a young basin than in the case of uniform extension of both crust and subcrustal lithosphere such an extensional process produces significant uplift of the flanks of the rift and as a result of erosion of the uplifted areas the effective cross sectional area of the basin can be increased by as much as 10 20 depending on the rate of erosion compared to the area that would have been created by a process of uniform extension finally we show that it may ultimately be possible to compute erosion rates from seismic cross sections of basins

statistics of internal tide bores and internal solitary waves observed on the inner continental shelf off point sal california abstractmoored observations of temperature and current were collected on the inner continental shelf off point sal california between 9 june and 8 august 2015 the measurements consist of 10 moorings in total 4 moorings each on the 50 and 30 m isobaths covering a 10 km along shelf distance and an across shelf section of moorings on the 50 40 30 and 20 m isobaths covering a 5 km distance energetic highly variable and strongly dissipating transient wave events termed internal tide bores and internal solitary waves isws dominate the records simple models of the bore and isw space time behavior are implemented as a temperature match filter to detect events and estimate wave packet parameters as a function of time and mooring position wave derived quantities include 1 group speed and direction 2 time of arrival time duration vertical displacement amplitude and waves per day and 3 energy density energy flux and propagation loss in total over 1000 bore events and over 9000 isw events

a geophysical study of the manila trench luzon philippines 1 crustal structure gravity and regional tectonic evolution the manila trench subduction zone is an active convergent plate margin between the south china sea and the northern philippines the trench trends northerly and is associated with a volcanic arc an east dipping benioff zone beneath luzon and a well developed fore arc basin system the luzon trough fore arc basins lie landward of the manila trench and contain up to 4 5 km of cenozoic sediments offscraping and accretion of turbidite sediments deposited in the manila trench have resulted in the upbuilding and outbuilding of an accretionary prism which forms the seaward margin of the fore arc basin system the uplifted zambales ophiolite and its offshore extension form the landward side of the fore arc basin multichannel seismic reflection profiles reveal that folding and thrust faulting of trench strata occur at the base of the trench slope the major structural decollement at the manila trench usually forms near the unconformity separating the hemipelagic sediments from the turbidite sediments subduction and perhaps underplating of the basal hemipelagic trench sediments accompany the deformation and accretion of the overlying clastic deposits faulting and uplift occur within a narrow zone of the fore arc where seamounts associated with the relict spreading center of the south china sea basin have presumably been subducted north of lingayan gulf the fore arc is disrupted by active fault systems that trend north and northwest offshore from the luzon central valley and from the southern cordillera central based on regional geological and tectonic observations we infer that subduction probably began at the manila trench in late oligocene to middle miocene time the long term average convergence rate at the manila trench is estimated to be between 10 and 20 mm yr and may be slowing in the north owing to the collision of taiwan with eurasia

evolution of a forearc basin luzon central valley philippines the cenozoic history of the 14 km thick luzon central valley sequence illustrates the development of a forearc basin forearc basins are important both as major sediment traps and as sites of hydrocarbon accumulations the luzon basin is floored by oceanic crust on the seaward western side and older accreted terranes on the arc eastern side initial sedimentation on this oceanic crust occurred during early tertiary northward translation and emplacement of the crust as an ophiolite along a strike slip or oblique slip zone the basal sediments consist of pelagic limestones and thin ash layers overlain by sandy turbidites derived from uplift and progressive dissection of the ophiolite a sequence of arc derived sediments at least 26 000 ft 8 km thick was shed into the astern arc side of the basin during late paleogene to quaternary convergence along the western margin of luzon by the middle miocene the central valley became a continuous elongate basin fringed by extensive shelf deposits along both the uplifted seaward and arc sides of the basin detritus shed from both flanks filled the subsiding basin and resulted in progressively shallower depths nonmarine deposition began in central portions of the basin in the pliocene and migrated with time both north and south along the basin axis late miocene to holocene movement along the philippine fault zone caused uplift and folding of adjacent parts of the basin exploration models for the central valley predict gas prone hydrocarbon generation in central portions of the basin at times that coincide with and postdate the formation of both structural and stratigraphic traps previous drilling in the basin has either been in areas with thermally immature source rocks or has failed to reach prospective intervals where thermal maturation is inferred the hydrocarbon potential of the central valley has not been determined adequately

rift tectonics on the passive continental margin off galicia spain abstract new migrated multichannel seismic profiles on the starved passive continental margin off galicia spain illustrate the tectonic style of the early cretaceous rifting event which preceded the separation of iberia and north america the main episode of rifting was preceded by other tensional episodes probably of earliest cretaceous and late jurassic age listric faulting associated with rifting was accompanied by large scale mass movements from the crests of the tilted blocks two subaerial erosional surfaces are visible one of late jurassic or earliest cretaceous age was affected by the final faulting episode the other was synchronous with the main phase of rifting and is present only on the upper part of the margin because the central trough was under deep water the significance of a ridge near the ocean continent boundary where altered lherzolite has been dredged and cored is discussed below the tilted blocks which include the basement rocks the seismic horizon s is visible as on the armorican margin its significance is also discussed

sr isotopic and trace element variations in oligocene to recent igneous rocks from the philippine island arc evidence for recent enrichment in the sub philippine mantle oligocene miocene plutonic rocks from the philippine island arc are characterized by uniform87sr 86sr isotopic ratios of 0 7035 0 7039 in contrast volcanics erupted in the past 5 ma in central luzon marinduque and mindoro have higher radiogenic sr 0 7042 0 7054 and show regional variations in their sr isotopic compositions volcanics of the pliocene recent bicol volcanic chain of southern luzon have87sr 86sr in the same range 0 7034 0 7040 as the mid tertiary plutonics increases in radiogenic sr are coupled with increases in rb sr ba and th abundances in the central luzon mindoro marinduque volcanic belt while no such correlation exists for the mid tertiary plutonics we consider the low values observed for mid tertiary plutonics and bicol volcanics to be controlled by fluids released from the subducting philippine sea plate basalt that have87sr 86sr of the same range sr isotopic compositions of the volcanics in the northern part of the central luzon volcanic belt may be controlled by fluids generated from the subducted south china sea crust the highest values of radiogenic sr 0 7051 0 7054 and highest lil abundances which are observed in the southern part of the central luzon volcanic arc appear to be the result of source contamination by slivers of the continental crust of the north palawan mindoro terrane that collided with the philippine arc in the miocene

seamounts as recorders of hot spot epeirogeny observations in the central pacific suggest that older seamounts are uplifted if plate motion carries them over mantle hot spots a depth anomaly map of the area reveals several volcanic chains now located on younger hot spot swells uplift is estimated by comparing the observed depth of a seamount summit or the observed stratigraphic section in an atoll with that predicted assuming standard subsidence of the sea floor after the seamount formed cretaceous seamounts on the margin of the hawaiian swell have standard summit depths whereas those on the crest of the swell are at least 1 100 m shallower summit depth correlates with sea floor depth anomaly implying that the hawaiian swell has caused the uplift eocene fossils are exposed at the surface in the tuamotu atolls whereas according to the standard subsidence relation eocene deposits should be covered by 1 000 to 2 000 m of more recent material the inferred uplift is consistent with the atoll9s present position atop the society swell possible evidence for 600 m of uplift in the southern cook islands however is unexplained by swell height the observed uplifts of the cretaceous seamounts near hawaii and of the tuamotu atolls put a limit on when the hawaiian and society swells formed at their present locations of maximum elevation the swells must have developed within the past several million years and probably formed at the same time as did the younger volcanic edifices on their summits

evidence for magmatic hydrothermal fluids and ore forming processes in epithermal and porphyry deposits of the baguio district philippines the baguio district contains a diverse array of epithermal porphyry and skarn deposits together with a large broadly strata bound advanced argillic lithocap magmatism mineralization and alteration occurred in response to subduction of the south china sea plate and the scarborough ridge beneath northern luzon over the past 3 m y rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry cu au deposits most of the epithermal au ag deposits of the baguio district including antamok and acupan the two largest au deposits are intermediate sulfidation state quartz carbonate adularia illite base metal sulfide veins that contain electrum and minor au ag tellurides in contrast high sulfidation mineralization at kelly includes enargite tennantite electrum and precious metal tellurides and is associated with advanced argillic alteration although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type the epithermal mineralizing fluids were dilute generally 600 c hypersaline brines 30 to 70 wt nacl equiv and low density vapor sulfur isotope compositions of sulfides in the porphyry skarn and intermediate sulfidation epithermal veins of the southern and central baguio district are mostly between 1 and 6 per mil consistent with a predominance of h2s in the mineralizing fluids i e reducing conditions in contrast sulfides from the high sulfidation porphyry and intermediate sulfidation deposits located adjacent to the baguio lithocap mostly have negative sulfur isotope values 6 9 to 0 8 consistent with oxidizing so42 predominant mineralizing fluids intermediate sulfidation epithermal veins at acupan have crosscut a well mineralized porphyry cu au stock work at ampucao the two deposits cannot be distinguished on the basis of radiometric age determinations ampucao 0 51 0 26 ma acupan 0 65 0 07 ma and are interpreted to be cogenetic with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction measured 34ssulfide 1 1 to 6 6 34ssulfate 10 4 to 31 8 values and initial strontium ratios of anhydrite 0 70378 0 70385 are consistent with identical and predominantly magmatic sources of these components for the ampucao porphyry and acupan epithermal veins helium isotopes provide further evidence of mantle derived components in the epithermal veins r ra values of 6 0 and 6 7 oxygen deuterium and carbon isotopes provide evidence for predominantly magmatic water at ampucao and for hybrid magmatic meteoric waters at acupan that precipitated precious metals due to boiling the proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at acupan the common observation of cross cutting relationships between porphyry and epithermal veins observed throughout the baguio district imply that the evolution of porphyry style to intermediate sulfidation style mineralization was a common phenomenon in this region and contributed significantly to its rich metal endowment

late cenozoic uplift of stable continents in a reference frame fixed to south america a reference frame fixed to south america may approximate to an absolute reference frame for the past 100 myr in this frame otherwise stable continents that have moved onto the former positions of oceanic ridges have experienced rapid plateau uplift probably caused by phase changes in the continental mantle and occasional volcanism with time lags of up to 70 myr

observations of the semidiurnal internal tide on the southern california slope and shelf 1 we give a detailed description of the semidiurnal band current and temperature variability observed during the internal waves on the continental margin iwaves field experiments of 1996 and 1997 off of mission beach california this variability was dominated by the internal tide and the structure of the internal tide on the slope and shelfbreak region was different from that on the narrow shelf on the slope and shelfbreak the internal tide was dominated by alongshore propagating coastal trapped waves in this region semidiurnal band currents were predominantly oriented in the alongshore direction in the lower half of the water column at a water depth h of 350 m current and temperature variability were consonant with a short wavelength 8 km bottom trapped wave propagating in the alongshore direction to the north in the upper 120 m of the water column above the depth of the shelfbreak slope and shelfbreak currents were highly coherent with a zero phase lag that is there was no phase propagation in the cross shore direction on the narrow 10 km shelf cross shore currents u were much more energetic than on the slope and had the structure of a mode one internal wave the alongshore currents v decreased monotonically from the surface to the bottom of the water column with a phase that did not change with depth the near bottom u signal propagated toward the coast during all mooring deployments faster in the summer than in the fall the near bottom u and mid column temperature relative phase was neither consistent with a purely progressive nor a purely standing mode one internal wave we conclude that the internal tide on the shelf was partially reflected

determining an age for the inararo tuff eruption of mt pinatubo based on correlation with a distal ash layer in core md97 2142 south china sea abstract the largest known eruption of mt pinatubo in the late quaternary was the inararo tuff formation itf eruption roughly estimated as five times larger than the 1991 eruption the precise age of the itf eruption has been uncertain here a correlative of the itf eruption layer d is identified in marine sediments and an age obtained tephras were identified in core md97 2142 of leg ii of the images iii cruise in northern offshore of palawan southeastern south china sea 12 41 33 n 119 27 90 e on the basis of the geochemical and isotopic fingerprints layer d can be correlated with the itf eruption of the modern pinatubo eruption sequence by means of the md97 2142 specmap chronology layer d was dated at around 81 2 ka this estimated age of the itf eruption and tephra layer d coincides with an anomalously high so4 2 spike occurring within the 5 millennia from 79 to 84 ka in the gisp2 ice core record

the negative gravity field over the 85 e ridge an isopach map made from seismic reflection and refraction data in the bay of bengal shows two prominent n s trending features in the basement topography one is the northernmost portion of the ninetyeast ridge which is totally buried by sediments north of 10on the other buried ridge trends roughly n s for 1400 km at 85oe to the latitude of sri lanka and then curves toward the west it has basement relief up to 6 km two free air gravity anomaly profiles across the region show a strong gravity low 60 mgal over the 85oe ridge while the ninetyeast ridge shows a gravity high to understand the negative free air gravity anomaly over the 85oe ridge we model the lithosphere as a thin elastic plate and calculate its flexural and gravitational response to an uneven sediment load a plausible formation history for a buried ridge consists of at least two major episodes the first is the formation of the ridge on a lithosphere with a flexural rigidity of d i at some later time the ridge is buried by an influx of sediments the lithosphere is cooler and the flexural rigidity has increased to d 2 the character of the gravity field depends primarily upon the initial and final values of flexural rigidity these d1 and d2 values are varied to obtain good agreement between the model and observed gravity anomalies best fitting models have a 180 times increase in flexural rigidity between ridge formation and sediment burial an approximate relationship between flexural rigidity and crustal age shows that the 85oe ridge was formed on relatively young lithosphere 5 15 m y old and that it was buried when the lithosphere was 40 80 m y old

significance of slab derived partial melts and aqueous fluids for the genesis of tholeiitic and calc alkaline island arc basalts evidence from mt arayat philippines abstract mt arayat an inactive stratovolcano is located behind the volcanic front of the bataan segment of the taiwan luzon arc in the central valley of luzon the philippines volcanism in this arc segment results from subduction of south china sea basin crust along the manila trench eruption products of mt arayat comprise pyroclastics and porphyritic basalt and andesite lavas of high k calc alkaline affinity compared to typical oceanic island arc volcanics the basalts display slightly elevated abundances of ta and nb relative to zr and hf and of ta nb zr hf and light rare earth elements lree s relative to y and heavy rare earths hree s their ree distribution suggests mixing between high hree low lree hree and low hree high lree hree components the latter suggesting the presence of residual garnet in the source region of mt arayat basalts enrichment of lree s relative to hree s is typical of calc alkaline and high k calc alkaline island arc basalts but is usually missing or small in island arc tholeiites lree enrichment is often attributed to a metasomatizing aqueous fluid generated during dehydration of the subducted slab for this model to be applicable extremely low abundances in the fluid of agents like f oh and or co2 3 which form hard complexes with the ree s are a prerequisite due to the temperature dependence of the eu 3 eu 2 redox potential divalent eu predominates in aqueous fluids of low complex forming capacity in the subduction zone environment whereas the other ree s with the possible exception of yb are still trivalent a lree enriched aqueous fluid generated by slab dehydration should therfore display a positive eu anomaly however lree enriched island arc basalts generally do not show positive eu anomalies implying that this lree enrichment is unlikely to result from ree transfer by an aqueous fluid instead a model is favoured which assumes contributions from both slab derived aqueous fluids and partial melts in the source region for island arc tholeiites the mantle wedge is only affected by a lile enriched aqueous fluid whereas the source region for calc alkaline and high k calc alkaline basalts is additionally metasomatized by small volumes of melt generated by small degrees of partial melting of the subducted slab with garnet as a residual phase these lree enriched partial melts may react with the depleted peridotite of the mantle wedge to produce domains of refertilized garnet peridotite subsequent partial melting produces calc alkaline melts whose trace element compositions display signatures of both depleted peridotite and more fertile garnet peridotite

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

detrital zircon record from major rivers of luzon island implications for cenozoic continental growth in se asia the significance of continental crustal growth in the phanerozoic has long been debated as an active accretionary orogenic belt se asia has been proposed to be one of the best archives for studying juvenile continental growth in the cenozoic despite the limited availability of data therefore we conducted for the first time a comprehensive u pb and hf isotopic analysis of detrital zircons separated from major rivers of luzon island the largest landmass of the philippine archipelago u pb ages of these zircons are predominantly supplementary material u pb ages and hf isotopic results for detrital zircons from all samples are available at https doi org 10 6084 m9 figshare c 4481882

the shear wave velocity structure of the crust and uppermost mantle beneath tagaytay philippines inferred from receiver function analysis depths of the partially melted zone and the moho discontinuity are probably at 18 kilometers and 34 kilometers respectively beneath tagaytay seismic station luzon philippines this conclusion is based on the shear wave velocity structure determined in this study which indicates the presence of a low velocity zone and high velocity zone at these depths the shear wave velocity model was derived from the inversion of five receiver functions of teleseismic earthquakes recorded by the broadband seismometer at tagaytay however due to the very limited information to constrain our initial model other models with comparable waveform fit were also obtained but with deeper low velocity zone and shallower moho

uplift and strength evolution of passive margins inferred from 2 d conductive modelling summary post breakup vertical motions of passive margins are seen here as a result of the post rift 2 d thermal evolution a 2 d finite element numerical model is performed to evaluate both the vertical and horizontal conduction that drive the thermal evolution of continental passive margins from breakup to post breakup states initial temperature configurations corresponding to non volcanic and volcanic margins are tested and lead to different thermal evolution of the lithosphere for both margins a thermal thickening is observed in the stretched lithosphere whereas the unstretched lithosphere undergoes first 0 80 ma a thermal thinning and secondly after 80 ma a thermal thickening in comparison with non volcanic margins volcanic margins show a slower thermal thickening and a greater thermal thinning in stretched and unstretched lithosphere respectively the variations with time of lithosphere thickness are then translated into isostatic vertical movements and reveal seaward thermal induced subsidence and landward thermal induced uplift the estimated uplift reaches up to 250 m in volcanic margins and 120 m in non volcanic margins the modelled timing and amount of uplift in both margins are consistent with present day topography of volcanic passive margins that stand two to three times higher than non volcanic margins using these thermal models we finally show that the 2 d strength of the margins drastically evolves with time from a seeward dominant strength 0 80 ma toward a landward dominant strength time larger than 80 ma these lateral strength evolution could have strong effect on the flexural response of the margin through time

erosion isostatic rebound models for uplift an application to south eastern australia summary a mountain s history includes two distinctive phases one of active tectonism and construction followed by one of erosion and passive isostatic rebound in the first phase uplift is driven by tectonic mechanisms while in the second phase base levels of the terrain are regionally uplifted it is this latter phase that is modelled here the starting model is a mountain range initially in isostatic equilibrium on a viscoelastic plate defined by the effective flexural rigidity d and relaxation time 7 the rate of erosion at any time t is assumed to be proportional to the elevation at that time with an erosional time constant 7 for a given present day topography the uplift erosion gravity and stress can be computed through time as functions of d 7 7 and the time to at which the erosional rebound mechanism became the dominant landscaping process the model has been applied to the highlands of south eastern australia which we assume to be an erosional residue of the palaeozoic lachlan fold belt observations of rivers cutting through cainozoic basalts and other geomorphological indicators of uplift can then be interpreted in terms of the isostatic rebound and there is no need to invoke active tectonic uplift mechanisms the model parameters that fit the observations are t 150 3 50myr dt 2 5 x ioz4nmmyr and to 180 200myr the predicted late palaeozoic fold belt topography is about 75 per cent greater than the present day values topographic depressions are predicted to have occurred along the margins of the formerly elevated areas and the model is relevant to understanding the evolution of basins flanking the highlands within the highland area erosion generally exceeds uplift but in some regions the two are approximately equal in keeping with recent geomorphological observations the flexural stresses associated with the erosion initially increase with time and maximum values in south eastern australia are predicted to occur in late cainozoic time with the stress state near the surface being mainly tensional

isotopic constraints on the role of subducted sialic material in indonesian island arc magmatism the island arcs of indonesia exhibit a range of subduction related tectonic environments and consequently are of particular interest in studying the relationship between the nature of the subducted plate and volcanism the sunda arc in java manifests the underthrusting of oceanic lithosphere beneath the newly accreted margin of asia in the banda arc continental material appears to be subducting beneath a volcanic arc that is underlain by oceanic crust 87sr 86sr ratios 0 7040 to 0 7059 in holocene andesitic lavas from java are higher than those from other volcanic arcs except those arcs where sialic contamination has been inferred a group of anomalous calc alkaline lavas characterized by high 87sr 86sr ratios 0 7054 to 0 7059 and relatively high abundances of k and related elements appear to be the result of sialic contamination of a mantle derived melt high 87sr 86sr ratios as large as 0 7095 together with values of 18o as large as 9 2 smow in lavas from the banda arc imply mixing of mantle derived and sialic components because of the tectonic peculiarities of the region the most likely source of contamination is from subduction of terrigenous material derived from the northwest continental shelf of australia lead isotopic ratios in lavas from java are generally transitional to the trends defined by other arc lavas and are characterized by higher 207pb 206pb ratios than oceanic basalts the anomalous calc alkaline lavas in particular are characterized by relatively high 207pb 206pb ratios interpreted to result from subduction and melting of sediments derived from the precambrian shields of australia and india during the opening of the indian ocean neodymium isotope ratios lie within the range defined from other volcanic arcs in terms of 143nd 144nd and 87sr 86sr the banda arc samples lie on a mixing line between compositions typical of the mantle and the upper continental crust that subducted sediments appear as a component in at least some of the holocene indonesian lavas implies melting at the top of the subducted lithospheric slab and provides constraints on the thermal structure of the descending plate

spatial patterns in dense algal blooms lntricatc and striking patterns are often created in dense algal blooms by the interaction of sinking floating or swllmming algae and local physical dynamics the structure of these patterns can reveal a great deal about the processes underlying the pattern formation here i explore three common patterns in dense algal blooms chaotic mixing internal wave banding and sharp fronts for each of these patterns i develop a simple model to simulate the qualitative aspects of the patterns the models are then analyzed to better understand the time and spacedependent processes involved in pattern formation and to suggest ways in which we might better sample such patterns to more accurately quantify the dynamics one significant result of this analysis is that complicated patterns of ilagrangian tracers need not be driven by similarly complicated patterns of the flow among the most striking manifestations of biological oceanographic dynamics are exceptionally dense algal blooms such blooms can color the water bright opaque hues often forming fantastic patterns with unexpectedly sharp boundaries these patterns typically arise through the interaction of the organism s behavior sinking floating or swimming and the ambient physical flows neutrally buoyant particles will not accumulate through physical biological dynamics as discussed by franks 1992a but may form patches driven by differential growth or grazing populations with any ability to move themselves independent of the water to any degree have the potential of forming dense accumulations in certain flow regimes a great deal can be learned about the local physical dynamics and the behavioral and physiological responses of the organisms by examining the structure of dense algal blooms certain accumulation patterns are characteristic of particular flows observation of only the surface expression of such patches may reveal much about the underlying dynamics here i present three examples of recurrent patterns in dense algal blooms chaotic mixing patterns internal wave banding and dense stripes forced by ageostrophic fronts fig 3 for each case i develop a simple illustrative model to elucidate the main features of the flow and behavior while the models reproduce the qualitative aspects of the patterns i e they look similgr i cannot claim that they have accurately captured the underlying dynamics in general insufficient sampling was performed at the time the photographs were taken to definitively identify the dominant physical and biological dynamics the models are useful vehicles however to identity the range of potential patterns and the types

numerical simulations of larval transport into a rip channeled surf zone competent larvae of intertidal invertebrates have to migrate toward shore for settlement however their migration through the surf zone is not understood we investigated larval transport mechanisms at a ripchanneled beach because tracking larvae in the surf zone is infeasible we used a three dimensional biophysical model to simulate the processes the coupled model consists of a physical module for currents and waves and a biological module for adding larval traits and behaviors as well as stokes drift to lagrangian particles model calculations were performed with and without onshore wind forcing without wind wave driven onshore streaming occurs in the bottom boundary layer outside the surf zone with onshore wind onshore currents occur near the surface in the surf zone offshore directed rip currents and compensating onshore directed currents over shoals are formed in both no wind and wind cases in the biological module neutral negative and positive buoyant particles were released offshore additionally particles either sank in the presence of turbulence or not two scenarios achieved successful onshore migration negatively buoyant larvae without wind forcing sink in the turbulent bottom boundary layer and are carried onshore by streaming positively buoyant larvae drift toward shore in wind driven surface currents to the surf zone then sink in the turbulent surf zone and remain near the bottom while transported shoreward in both cases the larval concentration is highest in the rip channel consistent with field data this successful result is only obtained if turbulence dependent sinking behavior and stokes drift are included in the transport of larvae

strontium isotopic characteristics of arc volcanic rocks at the initial stage of subduction in western japan abstract in western japan the philippine sea plate subducts northwestward from the ryukyu trench and the nankai trough to form two volcanic arcs the ryukyu and southwest japan arcs respectively these arcs are thought to be in the initial stage of subduction because microearthquake data show that the subducting slab extends only a short distance from the trenches in the southwest japan arc volcanoes are aligned parallel to the nankai trough although the leading edge of the subducted slab does not reach under the volcanic arc to the south the subducted slab reaches just under the ryukyu volcanic arc we determined 87sr 86sr ratios and rb and sr contents for 39 volcanic rock samples from 14 quaternary volcanoes of both arcs and summarized the spatial distribution of the ratios the ranges of 87sr 86sr ratios of volcanic rocks from the ryukyu and southwest japan arcs are 0 7040 0 7069 and 0 7035 0 7066 respectively in the ryukyu arc the regional variation in 87sr 86sr ratios of volcanic rocks is hidden under the wide scatter of ratios of different volcanic rocks from each one volcano in the southwest japan arc the ratios of volcanic rocks from volcanoes on the volcanic front vary in the along arc direction 0 7040 0 7048 for the western part 0 7035 0 7039 for the central part and 0 7048 0 7066 for the eastern part the across arc variations in the ratios are different from place to place these isotopic features suggest the absence of slab derived components in the source mantle and reflect the heterogeneous nature of 87sr 86sr ratios in the upper mantle modified by crustal processes this coincides with the seismological observation that the subducting philippine sea slab does not reach under the volcanic arc at all

physical and biological processes underlying the sudden surface appearance of a red tide in the nearshore the sudden appearance at the surface of an alongshore parallel band of red tide near huntington beach california is described in high spatial and temporal resolution using novel instrumentation including a global positioning system tracked jet ski the scale of the surface chlorophyll a chl a band was small 200 m crossshore and ephemeral 3 h compared with the subsurface extent of the red tide 2 km 7 d the red tide was dominated by the regionally common dinoflagellate lingulodinium polyedrum f stein and had developed as a subsurface chl a layer during the 7 d prior to the surface appearance a few hours before the surface appearance a subsurface patch of elevated chl a chl a 30 m gl 21 was observed in 13 m total depth in the trough of a shoreward propagating internal wave consistent with dinoflagellate vertical swimming interacting with the internal wave driven convergence internal wave breaking induced vertical mixing in 8 m water depth vertically spread the chl a patch to the surface creating the alongshore surface band 500 m from shore both the subsurface chl a patch and the surface chl a band were prevented from entering the surf zone by a density barrier of warm water adjacent to the beach these high resolution observations emphasize the role of nearshore physical dynamics in controlling the duration and intensity of red tide exposure to coastal habitats

simulation of the transformation of internal solitary waves on oceanic shelves abstract internal solitary waves transform as they propagate shoreward over the continental shelf into the coastal zone from a combination of the horizontal variability of the oceanic hydrology density and current stratification and the variable depth if this background environment varies sufficiently slowly in comparison with an individual solitary wave then that wave possesses a soliton like form with varying amplitude and phase this stage is studied in detail in the framework of the variable coefficient extended korteweg de vries equation where the variation of the solitary wave parameters can be described analytically through an asymptotic description as a slowly varying solitary wave direct numerical simulation of the variable coefficient extended korteweg de vries equation is performed for several oceanic shelves north west shelf of australia malin shelf edge and arctic shelf to demonstrate the applicability of the asymptotic theory it is shown that the solitary wave may maintain its sol

the geochemistry and tectonic setting of the northern section of the luzon arc the philippines and taiwan abstract the luzon arc consists of a 1200 km chain of stratovolcanoes and volcanic necks stretching from mindoro 13 n to the coastal range of taiwan 24 n this study is concerned with three of the five major segments along the arc the northern luzon babuyan and taiwan segments the late tertiary to quaternary volcanics of these segments are primarily andesitic but range in composition from basalt to rhyolite and are typical arc volcanics porphyritic plagioclase textures primarily calc alkaline with a few tholeiitic volcanic centers low tio 2 concentrations and low high field strength element hfse to large ion lithophile element lile ratios there is a large range in k 2 o and other liles from low k tholeiites to high k calc alkaline suites calayan island and mt tabungon volcanic substratum of mt cagua volcanics in the babuyan segment and most rocks from the taiwan coastal range are low k tholeiites e g nearly flat ree patterns low lree and lile concentrations and low th u ratios the dominant calc alkaline series ranges from medium k to high k rocks the high k calc alkaline rocks are mainly young and are found on batan and lutao islands when the low k tholeiitic and medium and high k calc alkaline rocks are associated in the same region the low k rocks are usually older there is a general relationship between k 2 o and other lile concentrations and k ar radiometric dates to some extent 87 sr 86 sr ratios also increase with time throughout the arc there is a correlation between latitude and 87 sr 86 sr and a positive correlation between 87 sr 86 sr and la sm cn an increase in both these geochemical parameters has been associated with an increase in the input of continental crustal material in other arc regions the lowest 87 sr 86 sr ratios found along the entire luzon arc the samples from baguio are equivalent to those found in samples from mid tertiary plutons from northern luzon and the bicol arc both groups of rocks are associated with westward subduction along the philippine trench where presumably deep oceanic sediments with little or no continental crustal component have been subducted the absence of continental crust below the arc in the northern luzon and babuyan segments has been suggested by several groups of researchers this together with the fact that metasomatized ultramafic nodules probably of mantle origin in disequilibrium with their batan host lavas but with similar 87 sr 86 sr and la sm cn ratios to the host rocks suggests that upper level assimilation afc processes does not appear to be the major influence on the geochemical signatures a collision zone between the upper crustal block of eastern china and taiwan and the manila trench has been recorded in the northern section of the arc taiwan sediments have also been shown to decrease in thickness along the south china sea basin nearly parallel to the manila trench from north to south the sediment source region is most probably taiwan and perhaps eastern china this latitudinal in variation sediment thickness may explain the crustal signature related to both geochemical and age parameters we suggest that this crustal input has taken place via subduction of sediment rich in a crustal component

a new isostatic model for the east pacific rise crest we have developed a new isostatic model for the east pacific rise epr that explains the origin of both the axial topographic high and the rise crest gravity anomaly our model involves a thin elastic plate with a constant thickness crust that is broken at the ridge crest we assume that a buoyant force beneath the plate bends the free edge of the plate upward at the rise axis forming the topographic high and the rise crest gravity anomaly we have used this model and two conventional isostatic models to examine the isostasy of three segments of the epr at 9 l4 n 6 11 s and 16 21 s rather than modeling individual profiles we have stacked summed the gravity and bathymetry data in each area and computed a single 200 km long mean mirrored profile for each different ridge segment these stacked profiles are a remarkable improvement over even the best individual profiles and clearly show both the axial topographic high and its associated free air gravity anomaly in all three areas the best fitting model parameters are similar and give average compensation depths of about 6 7 km below the seafloor near the base of the oceanic crust and an upper limit on the flexural rigidity of the plate that increases from about 1018 n m at the ridge axis to about 3 1019 n m 5 km from the axis and 1020 n m 25 km or more from the rise crest these results indicate that the epr crest is compensated at much shallower depths than suggested by previous investigators our results are consistent with the presence of a small low density magma chamber in the lower crust although at least part of the compensating root for the axial high must extend into the upper mantle we interpret the low upper mantle densities below the rise crest as a zone of partial melt which accumulates at the base of the oceanic crust between episodic rifting events when the overlying crustal magma chamber is replenished

prototypical solitons in the south china sea 1 surface signatures associated with non linear internal waves are often seen in satellite images of the western south china sea scs slope and shelf observation in the deep sea to the east are rare here we report on the evolution of an energetic packet as it propagated through the deep central basin of the scs toward the western slope and shelf the waves have amplitudes estimated at 170 m half widths of 3 km and phase speeds of 2 9 0 1 m s faster than the mode 1 linear phase speed of 2 6 m s the shape and observed phase speed were consistent with the korteweg devries kdv model over the 65 km path that they were tracked the intrinsic velocity shear of the waves is small compared to pre existing shears and the waves exhibit weak turbulence the kdv fit and a satellite derived estimate of horizontal wave extent imply a westward energy flux of 4 5 gw for each crest

silica standardization a discriminant technique applied to a volcanic arc system abstract a classic tholeiitic calc alkaline and shoshonitic island arc sequence has developed in western luzon the philippines as a result of subduction defined by an eastward dipping benioff zone a simple technique of standardizing the data allows chemical concentrations to be recast to andesite equivalent compositions based on the excellent linear correlations that exist between sio2 and other elements individual analyses were standardized to 55 sio2 by projecting parallel to least squares regression lines raw and sio2 standardized data were then treated by an univariate one factor analysis of variance and a multivariate discriminant function analysis results of the analysis of variance indicate that at the 99 confidence level 20 of the 27 chemical variates discriminate between at least two of the three geographically distinct magma series sio2 standardized data generally discriminate better than do raw data and k2o ba rb sr and zr provide the best discrimination better classification of samples into the appropriate series is obtained from results of the discriminant function analysis using the sio2 standardized data rather than results using the raw data with this standardizing technique it was possible to detect offsets of sio2 standardized k2o isopleths along the manila bay fracture zone that correspond to offsets in contours of depths for earthquake foci

thermally induced residual topography within oceanic lithosphere the lithosphere following a thermal event should subside isostatically to its pre event configuration however if the thermal event is sufficient to reset the rigidity of the lithosphere then the subsidence is forced to follow a different path to the initial uplift lithospheric rigidity decrease during uplift allows flexural deformation resetting while during subsidence an increasing rigidity with time results in flexural interference this thermo mechanical hysteresis effect may be responsible for anomalous bathymetry and free air gravity anomalies associated with hotspot traces extinct spreading centres and the ocean continent boundary of rifted passive continental margins

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

tertiary arc rifting in northern luzon philippines the north luzon terrane nlt comprising the section of luzon north of the philippine fault is one of the largest arc terranes in the philippine archipelago numerous features suggest that the nlt is a late oligocene to early miocene analogue for the processes in the modern intra arc rift zone at the northern end of the mariana trough first the nlt has bifurcating magmatic arcs sharing similar magmatic histories these include the northern sierra madre nsm and cordillera central cc magmatic arcs which are separated by the cagayan basin but which are linked in the caraballo range to the south the rock record indicates that the nsm cc and caraballo ranges were active arcs in late eocene to late oligocene time second seismic reflection and well data indicate that the cagayan basin formed by extensional faulting in late oligocene to early miocene time third alkalic arc magmatism recognized to be a precursor of intra arc rifting in modern settings occurred at the juncture of the nsm and cc arcs in late oligocene to early miocene time fourth oceanic crust represented by the itogon ophiolite formed at the southwestern end of the cagayan basin in late oligocene to early miocene time major and trace element chemistry show that the itogon sheeted dikes have tholeiitic arc and backarc basin basalt affinities the rock record and geophysical offshore data suggest that the nlt was developing in an island arc system above the subducting west philippine plate in late eocene time rifting occurred in the island arc from late oligocene to early miocene time but did not mature into backarc spreading most likely because of the collision of the benham rise a basaltic rise in the west philippine basin with the nlt the arc rifting in the nlt may be another manifestation of the extensional tectonism that affected most of southeast asia in late oligocene to early miocene time during which the south china and southeast sulu basins formed subsequent to arc rifting the history of the nlt has been linked to the subduction of the south china plate along the manila trench the structural history of the cagayan basin and magmatic history of the southern cc suggest that the subduction in the manila trench at the latitude of the nlt began about 15 ma

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

observations of nonlinear internal wave run up to the surfzone abstractthe cross shore evolution of nonlinear internal waves nliws from 8 m depth to shore was observed by a dense thermistor array and adcp isotherm oscillations spanned much of the water column at a variety of periods at times nliws propagated into the surfzone decreasing temperature by 1 c in 5 min when stratification was strong temperature variability was strong and coherent from 18 to 6 m depth at semidiurnal and harmonic periods when stratification weakened temperature variability decreased and was incoherent between 18 and 6 m depth at all frequencies at 8 m depth onshore coherently propagating nliw events had associated rapid temperature drops t up to 1 7 c front velocity between 1 4 and 7 4 cm s 1 and incidence angles between 5 and 23 front position t and two layer equivalent height ziw of four events were tracked upslope until propagation terminated front position was quadratic in time and normalized t and ziw both decreased collapsing as a linearly decaying funct

flexural models of continental lithosphere based on the long term erosional decay of topography summary the most easily observed geophysical characteristic of continents is their surface topography topographic power in the spectral range 1000 100 km has been computed for north american geological provinces and is found to decrease systematically as the tectonic age of the underlying crust increases these data have been quantitatively modelled in terms of topographic erosion and stress relaxation within the continental lithosphere through geological time spans the lithosphere is treated as a thin maxwell viscoelastic plate which deforms flexurally in response to the vertical surface loads of topography and its erosion effective rheological model parameters are flexural rigidity d a measure of the lithosphere s elastic strength and viscous relaxation time constant a measure of its viscosity erosion is assumed to occur at a rate linearly proportional to the height of topography at any given time the proportionality being determined by the erosion time constant the models are constructed in space and time frequency domains using simple linear systems theory two loading schemes are considered model 1 assumes that a flexurally competent lithosphere is suddenly loaded by topography which subsequently erodes whereas model 2 ignores the emplacement and erosion of topography during orogenesis when the lithosphere is thermally activated and considers only the load effected by erosion beginning some time later when the lithosphere has cooled and strengthened both models predict that the remnant topography of very old regions such as the canadian shield can be maintained in fact is favoured by a viscoelastic lithosphere with as small as 1 10ma the continued existence of such topography does not necessarily imply significant long term lithospheric strength model 1 results indicate low values of the flexural rigidity d 1021 1022nm which are interpreted to characterize not so much presentday d but that which was effective when topography was formed model 2 more successfully reproduces the data and constrains the product d to values 1024 1025nm ma which compare very favourably to those found from studies of individual loads on continental lithosphere the model results show that the erosion time constant is probably wavenumber dependent and falls in the range 200 400ma for the topographic wavelengths under consideration

seafloor spreading history of the western north atlantic basin derived from the keathley sequence and computer graphics abstract an analysis of sea surface magnetic profiles and an aeromagnetic contour chart west of bermuda yields a new tectonic framework for the keathley m series seafloor spreading magnetic anomaly sequence changes in spreading direction derived from the western keathley sequence occur at times corresponding to m24 m21 and m11 of which m11 is a time of continental breakup the models facilitate new identifications of the anomalies between m16 and m4 obviating the need for anomalously slow spreading between m11 and m4 previously suggested by other workers and by us and placing the location of the well defined rough smooth basement boundary at m11 the models show that spreading rates contemporaneously vary among profiles collected between flowlines as determined by a recently presented kinematic history this strongly suggests that individual ridge axis segments act independently of another in detail our reconstruction technique records in map form where the ridge crest has made significant departures from perfect symmetry and a predictable spreading rate during its evolutionary history among eight profiles collected parallel to seafloor spreading flowlines in the western north atlantic encompassing only 2700 km of normal oceanic crust we can identify more than fourteen ridge jump events there is evidence for a small 30 km ridge jump to the east of many ridge axis segments at m24 this is supported in the eastern north atlantic conjugate crust of the canary basin where m25 and m24 are poorly represented a series of four ridge jumps to the east along one paleoridge axis segment now located at 36 n 65 w is related to the passage of the mesozoic mid atlantic ridge crest over the verde hotspot at 137 m y b p the project magnet magnetic anomaly contour chart for the area between 29 n and 40 n has been used to determine stage poles of motion for processes occurring at the ridge crest related to its segmentation which have a component oblique to spreading between chrons m21 and m11 these trends may relate to the motion of the ridge crest over the mantle

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

a 2 ma record of explosive volcanism in southwestern luzon implications for the timing of subducted slab steepening 1 new chemical and isotopic analyses of the tephra layers plus deep sea tephrostratigraphic record from two cores from either side of luzon island philippines have allowed the identification of two periods of explosive volcanic activity originating from the macolod corridor in the southwestern part of the luzon the first period extended from prior to 1355 ka to 1977 ka and the second period extended from 478 ka to the present separated by a period of relative quiescence the time intervals between large explosive eruption events in each period were 31 15 ka and 156 52 ka respectively combined with published chronological and geochemical data from onshore volcanic deposits the tephrostratigraphic record shows that the locus of large explosive eruptions has migrated southwestward from the northeastern section to the middle and southwestern sections of the macolod corridor the period of relative quiescence is characterized by monogenetic volcanism in the central section of the corridor the migration of active volcanism across the southwestern part of luzon during the quaternary is used to infer the evolution of the subducting south china sea crust the period of relative quiescence represents a period of adjustment of the subducted slab by steepening which began around 1355 ka or shortly thereafter and finished at around 478 ka

the western central luzon volcanic arc the philippines two arcs divided by rifting abstract the western central luzon arc is apparently a complex zone of volcanism and tectonism the volcanoes of the northern segment of the arc the bataan arc ba fall along two semi parallel lineaments the western bataan lineament wbl and the eastern bataan lineament ebl this northern segment is cut off from the southern extension of the arc by a ne sw cross arc zone of volcanism the macolod corridor mc the volcanoes of the southern segment of the arc mindoro arc ma fall along two parallel lineaments the western mindoro lineament wml and the eastern mindoro lineament eml samples collected from the mc ebl and ma are alkali and lil enriched compared with the wbl the enrichment of the ebl is believed to be the result of the release of smaller amounts of hydrous rich fluids within the mantle below the ebl than below the wbl this process generated smaller degrees of partial melting below the ebl as compared to the wbl which resulted in the higher concentrations of lil elements in the ebl magmas as compared to the wbl magmas the alkali and lil enriched nature of the mc is believed to be the result of small degrees of partial melting during rifting the enriched nature of the ma is thought to be due to slivers of crustal material from the palawan mindoro block being incorporated into the mantle during subduction this region has the highest radiogenic sr values found in the philippines the mc may represent a pull apart rift zone between the philippine and west luzon shear zones and the transform between the manila and philippine trenches

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

circulation and larval distribution in internal tidal bore warm fronts internal tidal bore warm fronts were observed during the summer of 1996 off the coast of southern california warm bore fronts had concentrating currents resulting from high frequency internal motions and from a larger two way flow the two way flow featured surface currents onshore and bottom currents offshore a sharp thermocline depression and high frequency large amplitude internal motions followed the leading edge of the bore with downwelling currents on the trailing side of the crest of the nonlinear internal waves and upwelling currents in front of the crest warm bores propagated onshore with a propagation speed c that ranged from 10 6 to 19 6 cm s 1 while time averaged frontal currents varied from 11 2 to 17 6 cm s 1 in the shallowest bin in one out of three cases c which implied that there were faster currents than the rate of advance of the front and which implied that the origin of surface frontal material is behind the front not in front of it three invertebrate larval taxa were found at all sites across fronts but only two intertidal barnacles pollicipes polymerus and chthamalus spp were concentrated at the front s surface while the subtidal bryozoan membranipora spp was not frontal pollicipes were more concentrated than were chthamalus the frontal downwelling currents observed suggested that concentrated larvae would have to swim upward in order to maintain depth pollicipes were abundant on the offshore warm side of the fronts but were absent or rare on the onshore colder side suggesting that the origin of frontal pollicipes was behind the front although an alternative cannot be ruled out conclusively chthamalus were more abundant at depth than at the surface at all sites except at the front where this pattern was reversed the origin of frontal chthamalus is uncertain membranipora were more abundant on the onshore colder side of the fronts and abundances were usually higher at depth than at surface lack of accumulation in this species may be due to its limited swimming capability

the sulu sea internal soliton experiment abstract we present the results of a comprehensive study of large amplitude internal solitons generated in the sulu sea in the philippines by intense tidal flow over a sharp bathymetric feature surface signatures of these waves have been observed in images from the dmsp landsat and nimbus 7 satellites and the space shuttle sir a synthetic aperture radar a two week experiment was conducted in the sulu sea in may 1980 from r v oceanograher during which a three mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea vertical profiles of density temperature and acoustic backscatter as well as radar and photographic surface signatures were obtained from the ship data from satellites moorings and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves which ha