deep structures of the palawan and sulu sea and their implications for opening of the south china sea abstract compared to the northern south china sea continental margin the deep structures and tectonic evolution of the palawan and sulu sea and ambient regions are not well understood so far however this part of the southern continental margin and adjacent areas embed critical information on the opening of the south china sea scs in this paper we carry out geophysical investigations using regional magnetic gravity and reflection seismic data analytical signal amplitudes asa of magnetic anomalies are calculated to depict the boundaries of different tectonic units curie point depths are estimated from magnetic anomalies using a windowed wavenumber domain algorithm application of the parker oldenburg algorithm to bouguer gravity anomalies yields a 3d moho topography the palawan continental block pcb is defined by quiet magnetic anomalies low asa moderate depths to the top and bottom of the magnetic layer and its northern boundary is further constrained by reflection seismic data and moho interpretation the pcb is found to be a favorable area for hydrocarbon exploration however the continent ocean transition zone between the pcb and the scs is characterized by hyper extended continental crust intruded with magmatic bodies the nw sulu sea is interpreted as a relict oceanic slice and the geometry and position of extinct trench of the proto south china sea pscs is further constrained with additional age constraints from inverted moho and curie point depths we confirm that the spreading of the se sulu sea started in the early oligocene late eocene due to the subduction of the pscs and terminated in the middle miocene by the obduction of the nw sulu sea onto the pcb

3d seismic investigation of the structural and stratigraphic characteristics of the pagasa wedge southwest palawan basin philippines and their tectonic implications abstract the pagasa wedge is a poorly imaged deepwater orogenic wedge that has been variously interpreted as representing an accretionary prism a former accretionary prism modified by thrusting onto a thinned continental margin and a gravity driven fold thrust belt this study using 2d and 3d seismic data together with well information indicates that at least the external part of the wedge is dominantly composed of mass transport complexes capped by syn kinematic sediments that have thrusts and normal faults superimposed upon them drilling shows that despite stratigraphic repetition of eocene middle miocene units there is stratigraphic omission of oligocene and early miocene units this absence suggests that mass transport processes have introduced the eocene section into the wedge rather than tectonic thrusting the accretionary prism stage oligocene of the central palawan ophiolite history appears to be marked by predominantly north vergent deformation the deep regional unconformity 17 ma likely indicates the approximate time when obduction ceased in palawan the pagasa wedge is a late stage product of the convergence history that was active in its final phase sometime above the top of the nido limestone 16 ma and the base of the tabon limestone in the aboabo a1x well 9 ma the top of the wedge is traditionally associated with the middle miocene unconformity mmu however the presence of multiple unconformities diachronous formation tops local tectonic unconformities and regional diachronous events e g migrating forebulges all suggest simply giving a single age or assigning a single unconformity such as the mmu as defining the top of the pagasa wedge is inappropriate the overall ne sw trend of the wedge and the dominant nw transport of structures within the wedge diverge from the more northerly transport direction determined from outcrops in palawan and also from the nido limestone in the sw part of the pagasa wedge possibly this nw transport direction is more related to gravity driven structures responding to uplift of ne sw dangerous grounds margin during the middle miocene related to slab breakoff than it is to thrusting rooted in a plate boundary the final modification of the wedge occurred when the effects of compression deformation on the wedge had largely ended but gravity processes in particular mass transport and normal faulting still operated

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

the advection of submesoscale thermal features in the alboran sea gyre abstract noaa 7 infrared and nimbus 7 multi spectral visible imagery of the alboran sea collected as part of the donde va experiment during the period 6 20 october show the advection of submesoscale cold water features about the alboran sea gyre continuous monitoring of thew cold water features using satellite imagery is possible because of the twice daily every 12 h spacing of the noaa 7 coverage of the area after registration to a mercator projection and atmospheric correction analysis of the displacement of the cold water features in successive images shows their apparent origin to be just east of gibraltar their movement at average speeds of 0 4 m s 1 around the gyre and their apparent re entrainment into the incoming atlantic water east of gibraltar the nimbus 7 czcs imagery supplements the analysis by adding details of the movement and the theory on where the cold water features originate during the 15 day period nine cold water features were thermally distinct enough to be tracked for

upstream control of the frontal jet regulating plankton production in the alboran sea western mediterranean using a coupled physical biological model we document that a 30 km wide meandering jet constitutes a major source of biological enrichment in the alboran sea western mediterranean even in the absence of wind forcing and tidal dynamics the level of enrichment is shown to vary markedly during the year depending on the upstream characteristics of the jet as it exits from the gibraltar strait when its intensity is sufficiently low and characterized by weaker cross frontal density gradients during winter spring the jet is weakly nonlinear and may not fulfill the necessary conditions for frontogenesis it then remains weakly productive in the case of stronger jet intensity 1 1 sv accompanied by stronger cross frontal density and velocity gradients within the alboran sea during summer autumn the frontal jet becomes strongly nonlinear and ageostrophic with large cross frontal vorticity changes on the order of planetary vorticity under these conditions upward vertical velocities in the range 10 50 m d 1 supply nutrients into the euphotic layer more effectively and support high level frontogenesis induced phytoplankton production on the anticyclonic side of the main jet axis the strong eddy pumping mechanism also provides a comparable level of plankton production within strongly nonlinear elongated cyclonic eddies along the outer periphery of the frontal jet the plankton biomass is advected partially by the jet along its trajectory and dispersed within the basin by mesoscale eddies and meanders

a laboratory study of gyres and uplift near the strait of gibraltar laboratory experiments were conducted in which a rotating basin of stratified salty water in a field of gravity with a free surface was connected to a basin of fresh water by a narrow shallow channel the resulting density driven flow in the channel consisted of two currents a freshwater flow at the top from the fresh basin to the salty basin and a saltwater flow at the bottom in the opposite direction it models the flow in the strait of gibraltar which connects the atlantic ocean to the saltier mediterranean sea selective withdrawal of deep water up to and over the sill depth is observed in the stratified salty mediterranean basin the governing dimensionless numbers are the ratio of the rossby radius of deformation within the strait to the width of the strait and the ratio of rossby radius in the stratified med water to rossby radius of deformation within the strait the experiments were deliberately scaled to correspond to the parameters of the real mediterranean gibraltar region or not as we wished with the most correct parameters the water at a depth corresponding to 700 m in the mediterranean was selectively withdrawn up to sill depth and out of the salty basin the water at a depth corresponding to 900 m was not with double the correctly scaled stratification the water at a depth corresponding to 500 m was drawn out and the water at a depth corresponding to 700 m was not with no stratification water of a depth corresponding to 1200 m was drawn out the results are qualitatively consistent with the ideas of stommel et al 1973 that water at great depth in the mediterranean is drawn up and out at the strait of gibraltar although quantitatively the scaled experimental depths of withdrawal are not as great there are some indications that the gyre of atlantic water corresponding to the alboran sea gyre may enhance the selective withdrawal process but the mechanism is unclear

shear wave velocity structure of reed bank southern continental margin of the south china sea abstract the shear wave velocity structure of a wide angle seismic profile obs973 2 across reed bank in the southern continental margin of the south china sea scs is simulated by 2 d ray tracing method based on its previous p wave model this profile is 369 km long and consists of fifteen three component ocean bottom seismometers obs the main results are as follows 1 the model consists of seven layers and the shear wave velocity increases from 0 7 km s at the top of sediment layer to 4 0 km s in the lower crust 2 the moho depth decreases from 20 22 km at the reed bank to 9 11 km at the deep oceanic basin with the shear wave velocity of 4 2 km s below the moho 3 the v p v s ratio decreases with depth through the sedimentary layers attributed to increased compaction and consolidation of the rocks 4 in the continental upper crust at model distance 90 170 km s wave velocity 2 5 3 2 km s is relatively low and v p v s ratio 1 75 1 82 is relatively high compared with the other parts of the crust corresponding to the lower p wave velocity in the previous p wave model and normal faults revealed by mcs data indicating that a strong regional extensional movement had occurred during the formation process of the scs at the reed bank area 5 the s wave structures indicate that reed bank crust has different rock compositions from that in the east section of the northern margin denying the presence of conjugate relationship of reed bank with dongsha islands according to p wave models and other data we inferred that reed bank and macclesfield were separated from the same continental crust during the rifting and break up process

development patterns and controlling factors of tertiary carbonate buildups insights from high resolution 3d seismic and well data in the malampaya gas field offshore palawan philippines abstract the comprehensive subsurface database of the malampaya buildup late eocene to early miocene offshore nw palawan provides a rare insight into the development of south east asian cenozoic carbonate systems and their controlling factors the newly acquired high resolution three dimensional seismic survey combined with facies and well log analysis allowed a better understanding of the internal architecture of a carbonate platform whose development was largely controlled by tectonic deformation the malampaya carbonate system was initiated in the late eocene as an attached shelf influenced by significant clastic input the late eocene early oligocene shelf was subject to syn depositional extensional tectonics eastward tilting and block faulting that favoured the development of small size buildups on structural highs after a stage of eastward reef progradation an aggrading carbonate shelf frequently affected by subaerial exposure developed from the earliest late oligocene to the early miocene during this period recurrent reactivation of highs along the western and northeastern buildup margins determined the asymmetric morphology and internal architecture of the carbonate system the final demise of the carbonate buildup occurred in the late early miocene it resulted from an increase in subsidence rate and or a sharp increase in nutrient input additional parameters like eustacy oceanographic conditions and the type of carbonate producers played a subordinate role in the buildup development and ultimate demise

slow dense replenishments of a basic magma chamber the layered series of the newark island layered intrusion nain labrador the newark island layered intrusion is a composite layered intrusion within the nain anorthosite complex labrador the intrusion comprises a lower layered series ls dominated by troctolites olivine gabbros and oxide rich cumulates and an upper hybrid series hs characterized by a wide range of mafic granitic and hybrid cumulates and discontinuous layers of chilled mafic rocks wiebe 1988 the hs crystallized from a series of replenishments of both silicic and basic magmas the ls crystallized from periodically replenished basic magmas the ls has a lower zone that consists mainly of olivine plagioclase cumulates and contains minor cryptic reversals in mineral compositions that resulted from replenishments of relatively primitive magma an upper zone is dominated by olivine plagioclaseaugite ilmenite cumulates cumulus titanomagnetite and pyrrhotite occur within some oxide rich cumulates and the stratigraphically highest layers contain cumulus apatite at intermediate levels in the sequence cumulus inverted pigeonite occurs in place of olivine several prominent regressions in the stratigraphy of the upper zone are marked by fine grained troctolitic layers with much higher mg no 100 mgo mgo feo and anorthite than underlying cumulates these layers coarsen upward and grade back to oxide bearing olivine gabbros within thicknesses ranging from 10 cm to 15 m dikes that cut the ls have major and trace element compositions that strongly suggest that they are feeders for the replenishments in the lower zone when olivine and plagioclase were the only cumulus phases replenishments were less dense than the resident magma and rose as plumes and mixed with it precipitation of cumulus oxides in the upper zone lowered the density of resident magma so that subsequent replenishments were more dense than resident magma replenishments that occurred after oxides began to precipitate had small injection velocities these post oxide injections flowed along the interface between resident magma and the cumulate pile and precipitated flow banded fine grained troctolites

meteorologically forced subinertial flows through the strait of gibraltar the observed transport due to subinertial flows with periods ranging from days to a few months through the strait of gibraltar reaches values up to 106 m3 s 1 and is well correlated with atmospheric pressure fluctuations over the mediterranean sea this transport is barotropic and accounts for 84 of the variance observed at these frequencies a second mode accounts for 12 of the variance and is characterized by a node zero amplitude located at the mean depth of the interface between atlantic and mediterranean waters this baroclinic mode is modulated by the spring neap tidal cycle corresponding to an increased exchange of waters between atlantic and mediterranean at neap tides a simple model of the mediterranean which includes two basins and two straits indicates that the system has two resonant frequencies at periods of 1 2 and 5 6 days the 1 2 day resonance corresponds to the eastern and western basins oscillating through the strait of sicily while that at 5 6 days is the resonance of the mediterranean sea with the north atlantic ocean a good approximation to the observed flows is obtained when this model is forced with the most energetic mode of the atmospheric pressure over the eastern and the western mediterranean and a friction term is included to limit the flow through the strait of gibraltar restricting the flow through the strait of sicily does not improve the agreement between the model and the observations for the flows at gibraltar

sensitivity of mediterranean thermohaline circulation to gateway depth a model investigation 1 the neogene sedimentary record of the mediterranean sea holds evidence for changes in water properties and circulation these paleoceanographic changes have been attributed to changes in the flow through the ocean gateway between the mediterranean sea and the atlantic ocean we use an oceanic general circulation model to achieve quantitative physics based understanding of the effect of changes in the depth of the gateway such as may result from tectonic activity or variation in sea level to isolate these effects we use idealized basin geometry and impose simplified atmospheric forcing a reference experiment with present day sill depth demonstrates that the model simulates reasonably well the main features of the present day mediterranean thermohaline circulation as inferred from observations and previous numerical studies subsequently a series of sensitivity simulations is performed with different sill depths the model results show that mediterranean temperature salinity and thermohaline circulation depend strongly on sill depth as the sill depth decreases the upper overturning cell is quasi linearly reduced in strength while contrary to what one would expect the deep cell intensifies and does so in a nonlinear way we find that a shoaling of the sill depth induces a blocking effect on the outflow waters which creates a strong recirculation in the deep layers strengthening the deep cell nevertheless deep water formation is reduced and as a consequence the ventilation of the deep layers diminishes we identify three different circulation modes of the mediterranean thermohaline circulation depending on the sill depth shallow sill moderate sill and deep sill modes coupled with strong weak and negligible blocking effects respectively our results are consistent with the pre messinian paleoceanographic record of the mediterranean sea and may be useful to understanding the behavior of other land locked basins both extant and from the geological past

high fertility in the alboran sea since the last glacial maximum based on the glacial to postglacial 13c differences between endobenthic uvigerina peregrina species from the alboran basin and from other mediterranean basins changes in the fertility of the western part of this basin during the last deglaciation are reconstructed as a result of particulate organic carbon poc rain from the highly productive upwelling cell along the northwestern margin of the alboran basin u peregrina is presently depleted by about 1 6 with respect to the measured 13c values of bottom water co2 and by about 0 9 with respect to specimens from other areas of the western mediterranean or from the gulf of cadiz within the mediterranean outflow water the uvigerina 13c difference between the alboran sea and the gulf of cadiz 13c was close to 0 at the beginning of the last deglaciation and during the late glacial time this suggests that highly fertile systems set in the alboran sea near 16 kyr b p two rapid increases in the 13c offset are recorded near 15 kyr and 11 kyr b p fluctuations around 1 1 to 1 2 occurred during the early holocene and a maximum was reached near 9 kyr b p after 4 kyr the 13c offset decreased to its present day average value of 0 9 changes in the intensity of surficial production cannot account for all the observed fluctuations especially in the early holocene time a strong decrease in the intermediate and deep water ventilation of the alboran basin may have occurred near 8 9 kyr in phase with the last stagnant phase in the eastern mediterranean and the deposition of sapropel s1 as a result the redistribution and remineralization at depth of the produced organic matter was incomplete the poc rain reaching the sediment was locally intensified and caused the lowering of the 13c values of endobenthic foraminifers such as u peregrina the benthic 13c signal suggests that the difference between the alboran sea and the gulf of cadiz was at its maximum at the same time an important modification in the water masses structure may have occurred near 9 8 kyr b p the deepening of the permanent pycnocline probably related to a thicker atlantic jet at a stage of high sea level stand is recorded by the replacement of the right coiling n pachyderma dominance coincident with a shallow pycnocline by the g inflata dominance coincident with a deep pycnocline diatom abundances were strongly reduced indicating an important modification of the productive system the glacial postglacial evolution of productivity within the alboran basin was therefore more complex than in the adjacent atlantic ocean and opposite to the global one which displays a general increase in productivity during glacial time although it is the global budget of paleoproductivity that would drive the partitioning of carbon within the ocean local or regional discrepancies with the global glacial interglacial model must be addressed local winds and regional atmospheric pressure systems which are the forcing factors for circulation and exchange with the atlantic control the fertile systems of the alboran basin

experimental effects of pressure and fluorine on apatite saturation in mafic magmas with reference to layered intrusions and massif anorthosites apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic complexes we investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes apatite saturation gives information about the formation of silicate rocks and is of interest in explaining the formation of apatite oxide rich rocks e g nelsonites comprising approximately one third apatite and two third fe ti oxide two models of formation are proposed for this rock type crystal fractionation followed by accumulation of apatite and fe ti oxides and liquid immiscibility new experiments carried out with mafic compositions at 500 mpa confirm that the most important variables on phosphate saturation are sio2 and cao fluorine addition leads to apatite saturation at lower sio2 and higher cao concentrations comparison of our results with those of previous experimental studies on liquid liquid immiscibility at upper to mid crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid liquid immiscibility in the petrogenesis of nelsonites and similar rocks the liquid line of descent of three natural examples studied the sept iles intrusive suite the anorthositic complex of the lac st jean and the skaergaard layered intrusion do not cross the liquid liquid immiscibility field before they reach apatite saturation thus the apatite oxide rich rock associated with these three intrusive suites are best explained by crystal fractionation followed by accumulation of apatite and fe ti oxides

on the upper layer circulation in the alboran sea we present new experimental results and assemble them with previous results in order to develop an improved picture of the upper layer circulation in the alboran sea it is suggested that the key idea to understanding this upper layer circulation is the tendency of the atlantic jet aj to have negative curvature local interactions with the western alboran gyre wag or the african coast can however counterbalance this tendency and modify the anticyclonic path of the aj it is also proposed that the density gradients in the wag can be maintained in part by means of an intermittent surface cross gyre current which results in an input mixing and renewal of atlantic water the static stability at the bottom of the gyre increases because of the mixing of atlantic water with western mediterranean deep water which is uplifted close to the african coast this mixing process thereby acts as a local source of potential vorticity we also report the existence in the alboran sea of subsurface anticyclonic eddies located between 100 and 400 m of relatively cold water that appear to be detached from the iberian shelf regarding the large scale variability of the aj wag system we present evidence of an eastward migration of the wag and the subsequent formation of a new anticyclonic gyre in the western alboran basin on a timescale of 1 month this eastward gyre migration process temporarily allows the simultaneous presence of three anticyclonic gyres in the alboran sea

characteristics and evolution of cenozoic sediments in the liyue basin se south china sea the liyue basin in southeastern south china sea is considered to be a cenozoic basin superimposed on the mesozoic erathem the present account is based on comprehensive analysis of seismic profiles dragnet and core samples cenozoic deposits in the basin are characterized by a sequence of marine detrital and carbonate rocks there are two regional unconformities t 70 and t 40 corresponding to the commencement and termination of sea floor spreading in the south china sea in the late oligocene and late early miocene respectively the cenozoic sedimentary evolution of the basin recorded different sedimentary responses to sea floor spreading in the south china sea and reflected differences in the basin structure paleogeographic pattern and sedimentary characteristics before 30 ma late oligocene and after 30 ma the evolution of sea floor spreading changes in sea level and sediment sources controlled the cenozoic sedimentary infill c 2012 elsevier ltd all rights reserved

formation of thick stratiform fe ti oxide layers in layered intrusion and frequent replenishment of fractionated mafic magma evidence from the panzhihua intrusion sw china 1 the panzhihua intrusion is one of the largest layered intrusions that hosts huge stratiform fe ti oxide layers in the central part of the emeishan large igneous province sw china up to 60 m thick stratiform massive fe ti oxide layers containing 85 modal of magnetite and ilmenite and overlying magnetite gabbro compose cyclic units of the lower zone of the intrusion the cyclic units of the middle zone consist of magnetite gabbro and overlying gabbro in these cyclic units contents of fe2o3 t tio2 and cr and fe3 ti4 ratio of the rocks decrease upward cr content of magnetite and forsterite percentage of olivine decrease as well the upper zone consists of apatite gabbro characterized by enrichment of incompatible elements e g 12 18 ppm la 20 28 ppm y and increasing of fe3 ti4 ratio from 1 3 to 2 3 upward these features indicate that the panzhihua intrusion was repeatedly recharged by more primitive magma and evolved magmas had been extracted calculations using melts indicate that extensive fractionation of olivine and clinopyroxene in deep level resulted in increasing fe and ti contents in the magma when these fe ti enriched magmas were emplaced along the base of the panzhihua intrusion fe ti oxides became an early crystallization phase leading to a residual magma of lower density we propose that the unusually thick stratiform fe ti oxide layers resulted from coupling of gravity settling and sorting of the crystallized fe ti oxides from fe ti enriched magmas and frequent magma replenishment along the floor of the magma chamber

association of cumulus apatite with compositionally unusual olivine and plagioclase in the taihe fe ti oxide ore bearing layered mafic ultramafic intrusion petrogenetic significance and implications for ore genesis in many large layered mafic ultramafic intrusions worldwide cumulus apatite commonly occurs in the highly fractionated fe ti oxide rich lithological units at the top of the intrusions and the associated plagioclase and olivine if present have an content 50 mol and fo content 40 mol these are not true for several fe ti oxide ore bearing mafic mafic intrusions in the emeishan large igneous province sw china a good example is the taihe intrusion which is described in this paper in this intrusion the associated olivine and plagioclase are significantly more primitive containing 69 mol fo and 59 mol an respectively melts simulation reveals that such unusual association is the result of previous cotectic crystallization of fe ti oxides with silicate minerals during magma evolution under oxidizing condition close to that of nickel nickel oxide buffer supports for this new model include the observed upward decrease in plagioclase an contents coupled by lack of significant change in original olivine fo contents in the fe ti oxide ore bearing sequence below the apatite rich horizon which is in turn supported by the facts that fe ti oxide crystallization has a counter effect on mgo feo but no effect on cao na2o in the residual magma and that the addition of fe ti oxides in the cumulus assemblage expedites the arrival of apatite on the liquidus our new findings support the interpretation that the oxide ores in the taihe intrusion formed by gravitational accumulation of fe ti oxides crystallizing from a basaltic magma not a fe ti p rich immiscible liquid segregated from such magma

a strait outflow circulation process study the case of the alboran sea abstract a three dimensional primitive equation model is used to investigate the physical processes governing the exchanges of water between the mediterranean sea and the atlantic ocean at the level of the strait of gibraltar the circulation is driven by connecting two reservoirs filled with waters of different densities the motion starts from rest and is initiated by removing the dam separating them at the initial time the results are in agreement with observations in the strait the light atlantic water flows into the mediterranean basin in the surface layer while the denser mediterranean water moves toward the ocean as a deep current after a spinup time interval of three days the flow transport in the strait reaches a quasi stationary value of 0 9 sv sv 106 m3 s 1 as it enters the alboran sea the flow of atlantic water experiences a transition regime where the surface current is transformed into a shallow buoyant jet after several days of integration this flow intrudes into the alboran bas

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

the relationship between the taihe fe ti oxide ore bearing layered intrusion and the adjacent peralkaline a type granitic pluton in sw china constraints from compositions of amphiboles and apatite hosted melt inclusions abstract the taihe igneous complex which is located in the inner zone of the emeishan large igneous province elip consists of an fe ti oxide ore bearing layered gabbroic unit and a silicic enclave bearing peralkaline a type granitic unit the apatite hosted melt inclusions in the gabbroic unit and the amphiboles in both the gabbroic unit and the granitic unit were used to investigate the relationship between the two units the apatite hosted melt inclusions have 32 3 68 3 wt sio2 0 51 23 9 wt feot 0 7 19 wt tio2 8 87 19 0 wt al2o3 2 39 19 5 wt cao 1 70 7 27 wt na2o 0 24 5 60 wt k2o and 0 13 6 83 wt p2o5 such a large compositional range is difficult to be achieved through fractional crystallization but can be accounted for by silicate liquid immiscibility developed during the differentiation of the gabbroic unit the weighted bulk composition of the taihe gabbroic unit is extremely rich in fe and poor in si 17 2 wt feot and 36 2 wt sio2 indicating that some si rich components must have been removed a significant compositional gap in the amphiboles in the gabbroic rocks and the adjacent peralkaline a type granitoids i e calcic amphibole in the gabbros and apatite hosted inclusions and sodic calcic to sodic amphiboles in the granites and their silicic enclaves was observed this cannot be explained by the previously suggested differentiation of a common basaltic parental magma from gabbros to silicic enclaves and granites indicating a sudden change in the physical chemical conditions of the related magmas we propose that the silicic enclaves enclosed in the peralkaline a type granitic pluton represent the missing si rich components of the taihe layered gabbroic unit the continuous expulsion of immiscible si rich melts from the lower crystal mush into the upper main magma body caused the crystallization of large amounts of fe ti oxides in the gabbroic unit then the residual si rich magmas in the upper part of the taihe mafic magma chamber were drawn into the subsequently intruding peralkaline granitic magmas during the magmatic transgression process forming the silicic enclaves within the adjacent contemporaneous peralkaline a type granitic pluton

remotely sensed sea surface thermal patterns in the gulf of cadiz and the strait of gibraltar variability correlations and relationships with the surface wind field satellite image sequences covering periods of a few days throughout the annual cycle of the waters off southern iberia have been analyzed in conjunction with concurrent surface wind speed data from coastal stations qualitative analysis reveals a large degree of temporal and spatial variability in the thermal signature of the sea surface over periods of both a few days and several months during the summer a cool seasurface temperature signature extends from the western iberian coast around cape st vincent and eastward as far as faro at the same time a warm signature originating on the iberian coast between faro and cadiz extends into the strait of gibraltar these two features are shown to sometimes adopt more westerly positions and the strait experiences regions of cool thermal signature originating at its southern side during winter the surface flow into the mediterranean through the strait of gibraltar is anomalously warm and appears to come from the interior of the gulf of cadiz quantitative measurements show that temporal variability over timescales of a few days at individual sites is maximum in midsummer spatial thermal variability over the whole region is found to peak toward the end of the summer statistical analyses of the data reveal the coupling between the surface wind field in the gulf of cadiz and the surface thermal pattern especially during the summer wind induced across stream upwelling in the strait of gibraltar although dynamically subordinate to tidal and density driven processes is shown to occasionally dominate the surface thermal signature

abundant fe ti oxide inclusions in olivine from the panzhihua and hongge layered intrusions sw china evidence for early saturation of fe ti oxides in ferrobasaltic magma abundant fe ti oxide inclusions in cumulus olivine fo77 81 from the panzhihua and hongge intrusions emeishan large igneous province sw china document the first evidence for early crystallization of fe ti oxides in ferrobasaltic systems in nature the intrusions also contain significant stratiform fe ti v oxide ores the oxide inclusions are sub rounded or irregular range from 5 to 50 m in diameter and are dominated by either titanomagnetite or ilmenite the fact that the inclusions are either titanomagnetite or ilmenite dominant suggests that they are trapped crystals instead of immiscible oxide melt formed during growth of the host olivine the absence of other silicate phases in the inclusion bearing olivine is difficult to reconcile with a possible xenocrystic origin of the oxide inclusions these oxide inclusions are thus interpreted to be cumulus minerals crystallized together and trapped in olivine from the same parental magma in addition to fe ti oxides some inclusions contain amphibole biotite fluorapatite that might have formed by reaction of trapped hydrous liquid with the host olivine numerical modeling of high ti emeishan basalts using the melts program successfully simulates early crystallization of olivine fo81 and fe ti spinel in the presence of a moderate amount of h2o 1 5 wt under pressure and fo2 conditions generally pertinent to the panzhihua and hongge intrusions the modal mineralogy of the oxide inclusions is in good agreement with the bulk compositions of the ore as inferred from whole rock data in a given intrusion this is consistent with the interpretation that the stratiform oxide ores in the intrusions formed by accumulation of fe ti oxide crystals that appeared on the liquidus with olivine and clinopyroxene

tectonic stratigraphic division and blind fold structures in nansha waters south china sea extensive multiple channel reflection seismic data have been collected in the nansha spratley islands waters the southern margin of the south china sea stratigraphic correlation is shown with focus on a comprehensive geophysixcal survey line run front offshore nw sabah to offshore se vietnam according to the varying tectono stratigraphy from southeast to northwest five tectonic belts can be determined i e the palawan borneo nappe nansha trough nanwei liyue compressive belt zheng he extensional belt and the circum southwest subbasin belt in the palawan borneo nappe neogene quaternary deposits were highly upthrust northwestwards resulting in a series of moderately to tightly folded anticlines separated by open synclines the nansha trough was a narrow deep water belt filled with thick undisturbed neogene quaternary deposits the nanwei liyue compressive bell was dominated by strongly folded paleo anticlines overlain by an undeformed sedimentary cap with a pronounced hiatus of paleogene sediments the zheng he extensional belt consisted of a rugged topography and paleogene half grabens bounded by listic faults the major extensional faults were reactivated to cut through the overlying neogene quaternary deposits over the circum southwest subbasin belt neogene quaternary deposits draped on the largely subsided fault blocks related to the late oligocene mid miocene seafloor spreading based on the regional stratigraphic correlation the prominent paleo anticlines found within the nanwei liyue compressive belt are deduced to consist of mainly mesozoic marine sediments that were compressed in the late mesozoic era therefore the nansha microcontinent block is shown to be a collision complex assembled during late mesozoic era c 2004 elsevier ltd all rights reserved

on the relative vorticity of the atlantic jet in the alboran sea abstract it is shown from hydrographic data that the eastward flowing atlantic jet aj in the alboran sea has zero or positive relative vorticity this holds even when the aj curves anticyclonically around the western and eastern alboran gyres this feature is due to the presence of large positive shear vorticity mainly caused by the interaction between the aj and the slow westward flow of mediterranean water on the northern side of the aj it is also shown that the aj acquires negative curvature vorticity at the same time that it acquires positive shear vorticity at the exit of the strait of gibraltar this feature is described in terms of a shear and curvature conversion it is found that the cross stream variation of alongstream geopotential differences is the main term in this vorticity interchange description of the aj in the western alboran sea

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

sea surface velocities in shallow seas extracted from sequential coastal zone color scanner satellite data sequential images of visible wavelength reflectance from channel 3 540 560 nm of the coastal zone color scanner czcs have been used for computing advective velocities in the eastern english channel using the maximum cross correlation technique the computation method known as matched filtering is widely used by meteorologists and has recently been applied by oceanographers to detect sea surface motion from satellite infrared images provided accurate coregistration of images is achieved by matching ground control points significant correlation is obtained when the technique is applied to czcs data and coherent velocity distributions are obtained for united kingdom shelf waters the residual circulation patterns for the english channel are found to be consistent with previous studies and recent observations

anomalous lower crustal structure and origin of magmatism in the southeastern margin of the south china sea abstract late cenozoic continental rifting and breakup separated the southern margin of the south china sea scs from the northern margin it remains unknown whether the high density velocity zones hvzs in the lower crust extend southwards from the northeastern margin of the scs to the conjugate southern margin we integrated two newly acquired and processed multichannel seismic reflection profiles with gravity and magnetic data across the liyue reed bank and north palawan basin to clarify the characteristics of crustal structure and their relationship to post rift magmatism our results show an asymmetric distribution of the hvzs in the conjugate margins the lower crust anomalous reflections are isolated and mostly restricted in the areas of the ocean continent transition oct and the distal sag in gravity modeling the crustal thickness decreases from 20 km in the proximal sag to a minimum of 6 km in the distal sag and these anomalous reflections spatially correspond to high density zones no more than 4 km in thickness the magmatic features are presented by igneous intrusions at the top of the basement that deform post rift strata in the early miocene these hvzs above which the crustal stretching factor is 3 3 5 8 support that an anomalously hot asthenospheric mantle persisted during lithospheric thinning resulting in magmatic underplating and density drop in the uppermost mantle during early breakup

whole rock and mineral composition constraints on the genesis of the giant hongge fe ti v oxide deposit in the emeishan large igneous province southwest china the hongge giant fe ti v oxide ore deposit is hosted by a layered intrusion located in the central part of the emeishan large igneous province sw china the intrusion is relatively small in comparison with other typical oxide bearing intrusions worldwide it consists of a lower olivine clinopyroxenite zone a middle clinopyroxenite zone and an upper gabbro zone herein referred to as the lower middle and upper zones most of the economic fe ti v oxide ore layers occur within the middle zone the hongge oxide ores are depleted in ree and enriched in zr hf nb and ta as compared to the associated clinopyroxenites this enrichment of elements that are compatible in titanomagnetite is consistent with the interpretation that the ores formed by accumulation of magnetite and ilmenite as in the nearby coeval panzhihua fe ti v oxide deposit described previously by others mafic silicates in the hongge deposit have much higher mgo contents than those in other oxide deposits associated with large layered intrusions in the world this highlights the importance of relatively primitive parental magma becoming saturated in titanomagnetite at an early stage in the genesis of the giant fe ti v oxide deposits in the emeishan large igneous province phase equilibrium constraints suggest that the parental magma of the hongge deposit is similar to that of some of the most primitive high ti basalts in the emeishan large igneous province the ferrobasaltic parental magma and the ferropicritic primary magma of the hongge intrusion are similar in major and trace element composition to the ferropicritic ferrobasaltic magma in the pechenga belt kola peninsula russia depletion of incompatible trace elements in the oxide ores and associated rocks in the hongge intrusion as compared to the coeval high ti basalts suggest that not all the magma involved in the development of the hongge intrusion has been retained in the intrusion the occurrence of multiple fe ti oxide layers alternating with fe ti oxide bearing silicate layers within a single zone and the repetitive appearance of sulfides olivine and cr rich layers suggest that multiple pulses of magma were involved in the formation of the hongge intrusion and related fe ti v oxide deposit we propose that the middle zone of the hongge intrusion was a magma stepwise flow through system and that some of the liquid was lost to the peripheral lavas to form the basalt

geochemistry petrogenesis and metallogenesis of the panzhihua gabbroic layered intrusion and associated fe ti v oxide deposits sichuan province sw china the panzhihua gabbroic layered intrusion is associated with the 260ma emeishan large igneous province in sw china this sill like body hosts a giant fe ti v oxide deposit with 1333 million ton ore reserves which makes china a major producer of these metals the intrusion has a marginal zone of fine grained hornblende bearing gabbro and olivine gabbro followed upward by lower middle and upper zones the lower and middle zones consist of layered melanogabbro and gabbro composed of cumulate clinopyroxene plagioclase and olivine these zones also contain magnetite layers the upper zone consists chiefly of leucogabbro composed of plagioclase and clinopyroxene with minor olivine most rocks in the body show variable scale rhythmic modal layering in which dark minerals primarily clinopyroxene dominate in the lower parts of each layer and lighter minerals primarily plagioclase dominate in the upper parts the oxide ores occur as layers and lenses within the gabbros and are concentrated in the lower parts of the intrusion ore textures and associated mineral assemblages indicate that the ore bodies formed by very late stage crystallization of v rich titanomagnetite from an immiscible oxide liquid in a fluidrich environment the rocks of the panzhihua intrusion become more evolved in chemistry upward and follow a tholeiitic differentiation trend with enrichment in fe ti and v they are enriched in light rare earth elements relative to heavy rare earth elements and exhibit positive nb ta and ti anomalies and negative zr and hf anomalies the silicate rocks and oxide ores of the panzhihua intrusion formed from highly evolved fe ti v rich ferrobasaltic or ferropicritic magmas the textures of the ores and the abundance of minor hydrous phases indicate that addition of fluids from upper crustal wall rocks induced the separation of the immiscible oxide melts from which the fe ti v oxide ore bodies in the lower part of the intrusion crystallized

mineral compositional constraints on petrogenesis and oxide ore genesis of the late permian panzhihua layered gabbroic intrusion sw china a systematic study of mineral compositions has been carried out on stratigraphic sections through the panzhihua intrusion a layered gabbroic sill of late permian age that hosts significant magmatic fe ti v oxide deposits in the emeishan large igneous province sw china the intrusion which is 19 km long and 2 km thick is divided into a marginal zone mgz lower zone lz middle zone sub zones mza and mzb and upper zone uz from the base upwards compositions of the most primitive cumulus olivine fo81 and plagioclase an73 found in the intrusion suggest that the parental magma was similar to the mg rich end member of the coeval high ti basalts in the region two reversals in terms of mineral compositions are found in the intrusion one in the lower mza and the other at the transition between the mzb and the uz the first reversal is marked by a gradual increase in the an content of plagioclase an60 to an70 over a 100 m vertical interval the other is characterized by abrupt changes in the compositions of olivine fo28 to fo70 clinopyroxene mg 51 to 75 and plagioclase an24 to an51 over a 20 m vertical interval these suggest that the panzhihua intrusion opened at least twice for recharge of more primitive magmas strong depletion of incompatible trace elements such as zr in the cumulate sequence without corresponding enrichment in any border series is suggested to be evidence for significant loss of residual liquid at a late stage during solidification of the intrusion compared to other well studied layered intrusions the panzhihua intrusion contains fe ti oxides crystallized at a high temperature consistent with evidence obtained in earlier studies early appearance of liquidus fe ti oxides in the panzhihua magma is most likely a combined effect of a rather high degree of initial oxidation and elevated volatile fugacity

sea surface flow estimation from advanced very high resolution radiometer and coastal zone color scanner satellite imagery a verification study a refined technique for estimating surface currents from the displacement of features in sequential advanced very high resolution radiometer avhrr and coastal zone color scanner czcs images is presented it is used to calculate flow fields in two regions along the california coast and the results are compared to concurrent drifter drogue observations there is overall agreement to within approximately 6 cm s with somewhat better agreement at velocities less than 40 cm s the poorer performance of the technique at high velocities was due to difficulties in identifying and tracking features in areas of rapid flow the accuracy of the measurements is primarily affected by the analyst s precision in tracking each feature which in turn depends on how well the 2 to 6 km features preserve their identity from one image to the next a 12 to 24 hour interval yielded the best results in this study the directional component of the satellite derived flow field was representative of subsurface flow patterns down to at least 100 m although velocities obtained from avhrr infrared and czcs visible images may not always represent flow at the same depth the measurements were practically identical with the data used

mesoscale dynamics and vertical motion in the alboran sea abstract the inflow of atlantic water through the strait of gilbraltar usually exhibits a stationary wavelike pattern in the alboran sea we use an objective analysis technique for quantitative scale separation to investigate the interaction of scales in the region the large scale is clearly dominated by an anticyclonic gyre smaller scale analysis shows the existence of several mesoscale cyclonic eddies along the northern boundary of the western alboran sea anticyclonic gyre the relationship between the large scale mesoscale variability and the induced ageostrophic vertical motion is established using the q vector formulation we find that on the macroscale upward motion occurs upstream of the anticyclonic gyre upstream of a wave crest while downward motion takes place downstream upstream of a trough we also show that the vertical motion associated with the mesoscale eddies is an order of magnitude higher than the large scale vertical motion these patterns of large scale and mesoscale vertical m

crystallization of apatite in natural magmas under high pressure hydrous conditions with particular reference to orogenic rock series two separate series of hydrous experiments involving 1 imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite and 2 crystallizing similar natural rock compositions progressively until apatite appears demonstrate a close dependence between apatite saturation and silica content of the magma and determine p2o5 levels at a given silica value and temperature at which that composition may be expected to crystallize apatite the effect of pressure on apatite solubility is not great and is most significant for silicic compositions

deep sea circulation in the alboran sea alboran sea circulation between 220 and 1100 m depth is studied interaction between three types of water masses in this area causes a complicated flow pattern atlantic water flowing as a jet through the strait of gibraltar into the mediterranean often forms an anticyclonic gyre to the depth of 200 m and its features are now well documented a few works based on geostrophic calculations and bernoulli s equation treat the deep flow nine free floats were released at different depths and locations from january to may 1982 and acoustically tracked every 2 hours for 40 to 90 days acoustical tracking was done from three listening stations moored in the area the tracks of the floats at all depths from 220 to 1100 m revealed broad and slow approximately 2 5 cm s cyclonic circulation located under the surface anticyclonic gyre part of the flow following the bottom topography turned near the moroccan continental slope as a jet approximately 5 cm s to gibraltar and part turned to the east following the southern boundary of the deep channel to the isle of alboran

an integrated geophysical study on the mesozoic strata distribution and hydrocarbon potential in the south china sea abstract a series of drilling dredge and seismic investigations indicate that mesozoic sediments exist in the south china sea scs which shows a bright prospect for oil and gas exploration in order to study the distribution of mesozoic strata and their residual thicknesses in the scs we carried out an integrated geophysical study based mainly on gravity data gravity basement depth and distribution of residual mesozoic thickness in the scs were obtained using gravity inversion constrained with high precision drilling and seismic data in addition the fine deep crustal structures and distribution characteristics of mesozoic thicknesses of three typical profiles were obtained by gravity fitting inversion mesozoic strata in the scs are mainly distributed in the south and north continental margins and have been reformed by the later tectonic activities they extend in ne trending stripes are macro controlled by the deep and large ne trending faults and cut by the nw trending faults which were active in later times the offset in nw direction of mesozoic strata in nansha area of the southern margin are more obvious as compared to the north margin in the pearl river mouth basin and southwest taiwan basin of the north continental margin the mesozoic sediments are continuously distributed with a relatively large thickness in the nansha area of the south margin the mesozoic strata are discontinuous and their thicknesses vary considerably according to the characteristics of mesozoic thickness distribution and hydrocarbon potential analyses from drilling and other data dongsha uplift chaoshan depression southwest taiwan basin peikang uplift and liyue bank have large thickness of the mesozoic residual strata have good hydrocarbon genesis capability and complete source reservoir cap combinations show a bright prospect of mesozoic oil gas resources

circulation in the alboran sea as determined by quasi synoptic hydrographic observations part i three dimensional structure of the two anticyclonic gyres abstract the circulation and dynamics of the modified atlantic water have been studied using data from an intensive field experiment carried out between 22 september and 7 october 1992 data included 134 ctd casts adcp and satellite imagery a well defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern alboran sea smaller scale cyclonic eddies were also observed the front separates the more saline older modified atlantic water s 38 in the northern region from the fresher more recent modified atlantic water s 36 8 in the south the associated baroclinic jet had a mean transport of 1 sv and maximum geostrophic velocities of 1 0 ms 1 the three dimensional structure and spatial scales of both gyres were similar that is 90 km long and 220 m deep in the eastern alboran northeast of oran the origin of the algerian current was also detected with an eastward transport of 1 8 sv the general picture can be presented as a structure formed by a wavelike

the impact of eustatic sea level fluctuations temperature variations and nutrient level changes since the pliocene on tropical carbonate platform xisha islands south china sea abstract sedimentological paleontological and geochemical data from core xk 1 in the xisha islands south china sea allow a detailed documentation of the evolution of the reef bank system from the early pliocene to the late pleistocene and of the aeolianite deposits from the late pleistocene to the holocene a bank characterized by heterozoan carbonates occurred until 1 7 ma between 1 7 and 0 2 ma the system turned into a reef dominated by photozoan carbonates after 0 2 ma the aeolianite deposits composed of heterozoan skeletal grains occupied this area a pliocene to pleistocene decrease in the abundance of planktonic foraminifera and some benthic foraminifer species generally associated with deep water settings indicates a long term shallowing upwards trend resulting from the large scale eustatic sea level falls seven exposure horizons are recorded in core xk 1 due to high frequency sea level changes the thickness of the reef body in the individual cycles increased after the middle pleistocene transition this is interpreted as a consequence of the increase in duration of the short term sea level highstands the formation of heterozoan aeolianite deposits after 0 2 ma is probably caused by climate cooling related with the intensification of east asian winter monsoon the rapid increase in coral abundance at 1 7 ma correlates well with a sharp decline in nutrient level recorded by decreases in geochemical nutrient indexes values declines in bryozoan and red algae rhodolith abundance and decreases in the abundance of foraminifer species indicative of elevated nutrient level this correlation indicates that the carbonate factory turnovers were also affected by nutrient level fluctuations which could be linked to a paleoceanographic reorganization these results demonstrate that together with sea level fluctuations also paleoceanographic changes had a significant effect on the pliocene holocene tropical carbonate system

calcareous plankton and the mid brunhes climate variability in the alboran sea odp site 977 abstract quantitative calcareous plankton analyses have been performed at the ocean drilling program site 977 in the alboran sea through the mid brunhes interval 300 540 ka the results evidence orbital suborbital and millennial scale climate variability which primary reflects temperature change the patterns of increase decrease of coccolithophore and planktonic foraminifera warm water taxa reproduce the stage and substage climate variability in the planktonic 18o in good agreement with other planktonic isotope records from mediterranean sea and atlantic ocean variable conditions characterized by alternating cool nutrient rich or warm and stable sea surface waters occurred during interglacial marine isotope stage mis 13 in response to high amplitude oscillations of insolation during obliquity maximum and to north africa monsoon strength influencing distribution of taxa mis 13a resulted warmer than mis 13c based on the higher abundances of warm water taxa they increase just after insolation maxima suggesting a primary response of calcareous plankton to precessional orbital control following short term warm mis 11e and more humid mis 11d phases a climate optimum lasting about 16 kyr is recognized during mis 11c when major tropical subtropical water arrival into the alboran sea occurred as evidenced by the presence of trilobatus sacculifer mis 11c records unstable climate condition that persisted up to the late mis 11 indicating multiple pulses of southward migrations of subpolar front following the full interglacial mis 11c warm and oligotrophic conditions occurred during mis 9 as during mis 11 especially in mis 9e although without a climate optimum reduced abundance of warm water taxa and decrease of globorotalia inflata highlight colder surface water conditions and decreased atlantic mediterranean water exchange during glacials especially during the prominent sea level low stand of mis 12 short term prominent peaks of the polar subpolar neogloboquadrina pachyderma and coccolithus pelagicus ssp pelagicus and additional key taxa preferring fresher and turbid water together with minima in total nannofossil accumulation rate and enhanced coccolith reworking sustain a correlation with the north atlantic heinrich type ht events ht1 ht1a ht3 ht4 6 thus documenting the sensitiveness of the alboran sea in recording european and laurentide ice sheet dynamics the comparable chronology of most of these cold spells in the available balearic and ionian calcareous plankton records highlights that atlantic melt water entering alboran basin through gibraltar strait may have reached the central mediterranean preserving some of its original polar signature

the petroleum potential of deep water northwestpalawan block gsec 66 abstract this paper presents the results of the evaluation of the petroleum potential of thedeep water acreage of philodrill gsec 66 or what the authors call the northwest malampaya block all the elements necessary for a major hydrocarbon accumulation are believed to be present in the block probable source rocks are the deep water nido limestone the pre nido early tertiary syn rift section and pre tertiary sediments potential reservoirs include the nido reefal buildups nido and pre nido detrital and or fractured carbonates early miocene galoc elastic equivalent turbidites and pre nido sediments the principal play types recognized in the area are the late oligocene to early miocene reefs and the erosional karsted carbonate highs after evaluation of available pre 1982 seismic data an acquisition program of 1625 km was undertaken eleven leads prospects were delineated in the area after the interpretation of this new seismic data two prospects were upgraded to drillable status the santa monica prospect and the ipil prospect the santa monica prospect is a well defined four way dip closure on the nido limestone with a vertical closure of over 1500 feet and an areal closure of over 20 500 acres the ipil prospect is a gently closed feature developed at the nido limestone platform level with an areal closure of over 11 600 acres and a vertical relief of 400 feet the technical merits of the delineated huge prospects combined with the very favorable deep water exploration terms of the philippines and their proximity to the soon to be developed malampaya camago field make this block a very promising area for further exploration work

tide at the eastern section of the strait of gibraltar from october 1995 to april 1996 three mooring lines were deployed at the eastern entrance of the strait of gibraltar the spatial coverage of the mooring array allows for a good description of the tides they exhibit a dominant semidiurnal nature and a noticeable baroclinic structure that matches the one of the mean exchange tidal currents in the upper layer are irregular and usually too weak to reverse the mean upper layer flow that keeps on flowing east lower layer flow reverses with semidiurnal periodicity because of the smallness of the mean flow and the appreciable amplitude of the regular semidiurnal oscillation of tidal currents in this layer tidal transports can be satisfactorily compared with previous estimates of bryden et al 1994 if we allow for strong internal divergences associated with the internal tide no significant eddy flux of water transport tidal rectification is observed at the eastern section contrary to the almost 50 of the total layer transport found by bryden et al 1994 in camarinal sill section time dependent hydraulic theory provides a good scenario for interpreting these two independent sets of observations despite the fact that the composite froude number does not reach the critical values predicted in the hydraulic models most of the time

key factors controlling the accumulation of the fe ti oxides in the hongge layered intrusion in the emeishan large igneous province sw china abstract the hongge layered intrusion hosts the largest fe ti v oxide ore deposit in the central part of the emeishan large igneous province sw china it is divided into lower zone lz middle zone mz and upper zone uz from the bottom to the top for the lz relatively higher cr 250 3000 ppm and ni 50 200 ppm contents of clinopyroxene lower end259ma and higher 87sr 86sr 259ma values 2 82 to 0 07 and 0 7057 0 7076 respectively and plenty of hornblende demonstrate a more primitive parental hydrous magma in contrast relatively low cr

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

cyclicity in the main and upper zones of the bushveld complex south africa crystallization from a zoned magma sheet the major element composition of plagioclase pyroxene olivine and magnetite and whole rock sr sr data are presented for the uppermost 2 1 km of the layered mafic rocks upper main zone and upper zone at bierkraal in the western bushveld complex initial sr sr ratios are near constant 0 7073 0 0001 for 24 samples and imply crystallization from a homogeneous magma sheet without major magma recharge or assimilation the 2125 m thick section investigated in drill core comprises 26 magnetitite and six nelsonite magnetite ilmenite apatite layers and changes up section from gabbronorite an72 plagioclase mg 74 clinopyroxene to magnetite ilmenite apatite fayalite ferrodiorite an43 mg 5 clinopyroxene fo1 olivine the overall fractionation trend is however interrupted by reversals characterized by higher an of plagioclase higher mg of pyroxene and olivine and higher v2o5 of magnetite in the upper half of the succession there is also the intermittent presence of cumulus olivine and apatite these reversals in normal fractionation trends define the bases of at least nine major cycles we have calculated a plausible composition for the magma from which this entire succession formed forward fractional crystallization modeling of this composition predicts an initial increase in total iron near constant sio2 and an increasing density of the residual magma before magnetite crystallizes after magnetite begins to crystallize the residual magma shows a nearconstant total iron an increase in sio2 and decrease in density we explain the observed cyclicity by bottom crystallization initially magma stratification developed during crystallization of the basal gabbronorites once magnetite began to crystallize periodic density inversion led to mixing with the overlying magma layer producing mineralogical breaks between fractionation cycles the magnetitite and nelsonite layers mainly occur within fractionation cycles not at their bases in at least two cases crystallization of thick magnetitite layers may have lowered the density of the basal layer of melt dramatically and triggered the proposed density inversion resulting in close but not perfect coincidence of mineralogical breaks and packages of magnetitite layers

experiments on liquid immiscibility along tholeiitic liquid lines of descent crystallization experiments have been conducted on compositions along tholeiitic liquid lines of descent to define the compositional space for the development of silicate liquid immiscibility starting materials have 46 56 wt sio2 11 7 17 7 wt feotot and mg number between 0 29 and 0 36 these melts fall on the basaltic trends relevant for mull iceland snake river plain lavas and for the sept iles layered intrusion where large scale liquid immiscibility has been recognized at one atmosphere under anhydrous conditions immiscibility develops below 1 000 1 020 c in all of these compositionally diverse lavas extreme iron enrichment is not necessary immiscibility also develops during iron depletion and silica enrichment variations in melt composition control the development of silicate liquid immiscibility along the tholeiitic trend elevation of na2o k2o p2o5 tio2 promotes the development of two immiscible liquids increasing melt cao and al2o3 stabilizes a single liquid field new data and published phase equilibria show that anhydrous low pressure fractional crystallization is the most favorable condition for unmixing during differentiation pressure inhibits immiscibility because it expands the stability field of high ca clinopyroxene which reduces the proportion of plagioclase in the crystallizing assemblage thus enhancing early iron depletion magma mixing between primitive basalt and fe ti p rich ferrobasalts can serve to elevate phosphorous and alkali contents and thereby promote unmixing water might decrease the temperature and size of the two liquid field potentially shifting the binodal solvus below the liquidus leading the system to evolve as a single melt phase

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

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

architecture development and geological control of the xisha carbonate platforms northwestern south china sea newly acquired seismic data allow improved understanding of the architecture and evolution of isolated carbonate platforms on the continental slope of the northern south china sea the xisha carbonate platforms were initiated on a basement high the xisha uplift in the early miocene and have remained active up to the present their distribution is limited to pre existing localized fault bounded blocks within the xisha uplift so individual platforms were small in size at the beginning of the miocene however during the middle miocene the platform carbonate factories flourished across an extensive area with 55 900 km 2 the platforms began to backstep in response to a relative sea level rise in the late miocene platform edge reefs patch reefs pinnacle reefs atoll reefs and horseshoe reefs all developed on various platforms the distribution of platform carbonates shrank significantly during pliocene quaternary time to isolated carbonate platforms represented today by xuande atoll and yongle atoll tectonics and eustasy were the two main controls on platform development tectonics controlled both the initial topography for reef growth and the distribution of platforms including those that survived the drowning event associated with the late miocene rapid relative sea level rise eustasy controlled high frequency carbonate sequence development crown copyright c 2014 published by elsevier b v all rights reserved

a sensitivity study of the general circulation of the western mediterranean sea part ii the response to atmospheric forcing abstract this paper investigates the influence of sea surface thermohaline fluxes and wind stress on the circulation of the western mediterranean sea using a high resolution 3d primitive equation model an 18 year experiment was forced with the daily output of a fine grid mesh numerical weather prediction model the major characteristics of the circulation are well reproduced the basin surface circulation is cyclonic over all of the basin the two anticyclonic alboran gyres are present the instabilities of the algerian current generate large anticyclonic eddies that invade the whole algerian basin the liguro provencal catalan current is well marked deep water convection down to the bottom only occurs during the first 3 years then winter intermediate water is produced the north south gradient of the atmospheric thermohaline fluxes induces a northward surface transport of water from the algerian basin into the liguro provencal basin this pattern can be associated with the balearic front sensitivity

stratigraphic well correlations for 3 d static modeling of carbonate reservoirs the principles and purposes of stratigraphic well correlation in carbonate sedimentary systems are defined and discussed within the context of static reservoir modeling the challenge of well correlations is to relate the heterogeneities measured at core and well scales to the spatial heterogeneities at reservoir and flow unit scales the introduction of a priori knowledge in the process of stratigraphic well correlation is critical to support the stratigraphic rules and to establish a coherent geological and petrophysical concept the links between well correlation and geostatistics are discussed with regard to the stationarity hypothesis and property trend analysis we stress that wells are incomplete and biased samples of the geological reality which is not dependent unlike the dynamic reservoir behavior on the well numbers location and spacing stratigraphic rules are applied as a function of the well spacing relative to the geological reality a simple trigonometric method combining angle of base profile paleobathymetry and well spacing is introduced to check the validity of the well correlation in carbonate ramp like systems two models based respectively on outcrop and subsurface with seismic data are discussed in detail to show the combined influence of the data set sedimentary systems and diagenetic transformations on stratigraphic well correlations

an explanation for the curvature of the atlantic jet past the strait of gibraltar abstract a consistent explanation for the anticyclonic curvature of the atlantic jet as it passes through the strait of gibraltar and flows into the mediterranean sea eastern side of the strait is provided the anticyclonic curvature of the atlantic jet which is the key feature to understand the upper layer circulation in the western alboran sea is simply related to the positive net evaporation over the mediterranean the result of this positive net evaporation that mainly occurs in areas of the mediterranean far from the strait of gibraltar is a net inflow transport through the strait it is proposed that the positive net evaporation is able to produce such a net inflow in the strait because of an anomalous large scale pressure gradient this anomalous pressure gradient is found to be approximately collinear to the strait orientation the time averaged inflow of atlantic water at the eastern side of the strait of gibraltar must therefore be supergeostrophic and hence it must have anticyclonic curv

south china continental margin signature for sandstones and granites from palawan philippines abstract we report results of heavy mineral analysis and u pb dating of detrital zircons from metasediments and cenozoic sandstones and u pb dating of zircons from cenozoic granites of the north palawan continental terrane npct and the south palawan terrane spt the npct metasediments are derived mainly from granitic and metamorphic rocks of continental character they contain zircons that indicate a maximum depositional age of late cretaceous and other age populations indicating a south china origin the sediments were deposited on the south china margin before rifting of the continental margin during opening of the south china sea miocene spt sandstones contain similar heavy mineral assemblages suggesting sources that included npct metasediments metamorphic basement rocks at the contact between the spt and the npct south china sea rift volcanic and or minor intrusive rocks and the palawan ophiolite complex the spt sandstones are very similar to lower miocene kudat formation sandstones of northern borneo suggesting a short lived episode of sediment transport from palawan to borneo in the early miocene following arc continent collision u pb dating of zircons shows that the central palawan granite is eocene 42 0 5 ma the capoas granite was intruded during a single pulse or as two separate pulses between 13 8 0 2 ma and 13 5 0 2 ma inherited zircon ages from the capoas granite imply melting of continental crust derived from the south china margin with a contribution from cenozoic rift related and arc material

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

geological significance of seismic reflections and imaging of the reservoir architecture in the malampaya gas field philippines the integration of petrographic analyses of cores and thin sections petrophysical measurements and well logs demonstrates that variations in acoustic impedance in the malampaya buildup upper eocene to lower miocene offshore northwest palawan are related to vertical changes in porosity and pore type which are dominantly controlled by diagenetic processes the nido limestone was subdivided into 10 50 m 30 150 ft thick units characterized by specific diagenetic patterns and petrophysical properties diagenetic units the alternation between tight and porous diagenetic units is mainly controlled by meteoric diagenesis leaching and pedogenesis and by late burial cementation and leaching well to seismic ties show that the main seismic reflectors within the buildup interior reflect the boundaries between diagenetic units most of the negative amplitude reflectors are related to unconformities whereas positive amplitude reflectors have a more questionable chronostratigraphic value and may represent the bases of cemented lenses that can crosscut time lines comparison with other southeast asian tertiary buildups indicates different origins of seismic reflections related to distinct patterns of diagenetic evolution the identification of such seismodiagenetic units and of their controlling factors is of paramount importance for the architecture and the petrophysical characterization of carbonate reservoirs

in situ and satellite observations of the eastward migration of the western alboran sea gyre during october 2003 an intensive oceanographic survey biomega was carried out in the alboran sea coinciding with a migration event of the western alboran sea gyre wag the observations gathered during that cruise constitute the first field evidence of a migrated stage of the wag in this work we present the main differences between the 3d hydrodynamic fields observed during biomega and those corresponding to a wag located at its usual position the migration of the gyre was followed by satellite altimetry and sea surface temperature imagery the causes of the gyre migration are explored in terms of the quasi geostrophic tendency equation in particular of the dynamics governing scales larger than the rossby radius of deformation it is shown that the steady state gyre must be almost equivalent barotropic and that the key process to break down the stationarity would be a density advection at gyre scale the mechanisms to explain the migration of the wag proposed by previous authors are discussed in light of the explanation proposed in this work

a study of the balance of horizontal momentum in a vertical shearing current abstract horizontal current and density data fields are analyzed in order to validate from an experimental point of view the contribution of the advective and coriolis accelerations and the hydrostatic pressure gradient term to the balance of horizontal momentum the relative importance of the vertical advection of horizontal velocity in this balance is estimated by solving the quasigeostrophic qg omega equation the analysis of the balance of horizontal momentum is carried out using data from three consecutive high resolution samplings of the atlantic jet aj and western alboran gyre wag on the eastern side of the strait of gibraltar the horizontal velocity reached maximum values of 1 30 m s 1 in the aj at the surface the ageostrophic velocity field reaches maximum absolute values of 30 cm s 1 at the surface thus confirming the supergeostrophic nature of the aj at the surface the pressure gradient term reaches absolute values of 8 10 10 5 m s 2 the coriolis acceleration 10 12 10 5 m s 2

evidence for internal hydraulic control in the northern oresund new observations of mainly flow velocity salinity and temperature are used to show and discuss some of the physical conditions in oresund the strait between denmark and sweden one of three connections between the brackish baltic sea and the saline north sea the main geometric features are a contraction in the northern oresund and the shallow drogden sill at the entrance to the baltic the observations show that the two layer flows through the contraction are often hydraulically controlled the observations also reveal details of the transition from subcritical to supercritical flow in terms of the composite froude number on the basis of local flow parameters these details are that the flow may be subcritical as well as supercritical in different areas of some cross section existing theories on rotating hydraulics are unable to account for these circumstances which are due to the strong influence of the earth s rotation and the curvature of the streamlines in the present study it is not attempted to explain these conditions but the probable effects of rotation and curvature on the controlled flow rate are discussed briefly also the possible effects of hydraulic control on the exchange of the baltic are discussed it is argued that the stratification in the kattegat the sea to the north is more important than the presence of the drogden sill for the amount of high saline water to enter the baltic through oresund this result is supported by observations of the stratification in oresund and the flow at the sill the observations show that the interface in oresund rises significantly during flow to the baltic and that the transport of saline water into the baltic is closely connected to the shallowness of the interface in oresund

rhenium osmium isotope and platinum group elements in the xinjie layered intrusion sw china implications for source mantle composition mantle evolution pge fractionation and mineralization abstract the xinjie mafic ultramafic layered intrusion in the emeishan large igneous province elip hosts cu ni platinum group element pge sulfide ore layers within the lower part and fe ti v oxide bearing horizons within the middle part the major magmatic cu ni pge sulfide ores and spatially associated cumulate rocks are examined for their pge contents and re os isotopic systematics the samples yielded a re os isochron with an age of 262 27 ma and an initial 187 os 188 os of 0 12460 0 00011 os t 0 5 0 1 the age is in good agreement with the previously reported u pb zircon age indicating that the re os system remained closed for most samples since the intrusion emplacement they have near chondritic os t values ranging from 0 7 to 0 2 similar to those of the lijiang picrites and song da komatiites exceptionally two samples from the roof zone and one from upper sequence exhibit radiogenic os t values 0 6 to 8 6 showing minor contamination by the overlying emeishan basalts the pge rich ores contain relatively high pge and small amounts of sulfides generally less than 2 and the abundance of cu and pge correlate well with s implying that the distribution of these elements is controlled by the segregation and accumulation of a sulfide liquid some ore samples are poor in s mostly t and cr tio 2 ratios immediately below units 2 4 together with high cu zr ratios decreasing from each pge ore layer within these cyclic units are consistent with multiple magma replenishment episodes the sulfides in the cumulate rocks show little evidence of pge depletion with height and thus appear to have segregated from successive inputs of fertile magma this suggests that the xinjie intrusion crystallized from in an open magma system e g a magma conduit the compositions of the disseminated sulfides in most samples can be modeled by applying an r factor silicate sulfide mass ratio of between 1000 and 8000 indicating the segregation of only small amounts of sulfide liquid in the parental ferropicritic magmas thus continuous mixing between primitive ferropicritic magma and differentiated resident magma could lead to crystallization of chromite cr bearing magnetite and subsequently abundant fe ti oxides thereby the segregation of pge rich cu sulfide when considered in the light of previous studies on plume derived komatiites and picrites worldwide the close to chondritic os isotopic composition for most xinjie samples lijiang picrites and song da komatiites suggest that the ferropicritic magma in the elip were generated from a plume this comprised recycled neoproterozic oceanic lithosphere including depleted peridotite mantle embedded with geochemically enriched domains the ascending magmas thereafter interacted with minor possibly

three fe ti oxide ore bearing gabbro granitoid complexes in the panxi region of the permian emeishan large igneous province sw china the permian 260 ma emeishan large igneous province of sw china contains three nearly identical gabbro granitoid complexes that host giant fe ti oxide deposits the fe ti oxide deposits are within the lower portions of evolved layered gabbroic intrusions and are spatially and temporally associated with a type granitic plutons the 264 3 ma taihe layered gabbroic intrusion hosts a large magmatic fe ti oxide deposit and is coeval with the taihe peralkaline a type granitic pluton which is dated at 261 2 ma within the a type granitic pluton are microgranular enclaves which have compositions intermediate between the gabbro and host granite primitive mantle normalized incompatible element plots show corresponding reciprocal patterns between the mafic and felsic rocks the chondrite normalized ree patterns show eu anomalies changing from positive eu eu 1 5 to 5 9 in the gabbroic intrusion to negative in the enclaves eu eu 0 4 to 0 6 and granites eu eu 0 2 to 0 5 whole rock end t values of the gabbroic intrusion end t 2 5 to 3 3 are similar to those of the enclaves end t 1 0 to 2 0 and granite end t 1 5 to 1 9 whereas the zircon ehf t values of the gabbro ehf t 8 1 0 8 are indistinguishable from those of the granites ehf t 9 2 1 0 suggesting that the parent magmas for all rock types originated from the same mantle source geochemical modeling indicates that the gabbros and granites can be generated by fractional crystallization of a common parental magma similar to high ti emeishan flood basalt the compositional jump from the gabbro to the enclaves is attributed to the crystallization of fe ti oxide minerals the results of this study and other studies suggest that the magmatic conditions for example pressure composition fo2 which led to the formation of at least three fe ti oxide bearing gabbro granitoid complexes were relatively common during the development of the emeishan large igneous province

middle to late cenozoic tectonic events in south and central palawan philippines and their implications to the evolution of the south eastern margin of south china sea evidence from onshore structural and offshore seismic data abstract using recently gathered onland structural and 2d 3d offshore seismic data in south and central palawan philippines this paper presents a new perspective in unraveling the cenozoic tectonic history of the southeastern margin of the south china sea south and central palawan are dominated by mesozoic ophiolites palawan ophiolite distinct from the primarily continental composition of the north these ophiolites are emplaced over syn rift eocene turbidites panas formation along thrust structures best preserved in the ophiolite turbidite contact as well as within the ophiolites thrusting is sealed by early miocene 20 ma sediments of the pagasa formation isugod formation onland constraining the younger limit of ophiolite emplacement at end late oligocene 23 ma the onset of ophiolite emplacement at end eocene is constrained by thrust related metamorphism of the eocene turbidites and post emplacement underthrusting of late oligocene early miocene nido limestone this carbonate underthrusting at end early miocene 16 ma is marked by the deformation of a seismic unit corresponding to the earliest members of the early middle miocene pagasa formation within this formation a tectonic wedge was built within middle miocene from 16 ma to 12 ma forming a thrust fold belt called the pagasa wedge wedge deformation is truncated by the regionally observed middle miocene unconformity mmu 12 ma a localized post kinematic extension affects thrust fold structures the mmu and late miocene to early pliocene carbonates e g tabon limestone this structural set up suggests a continuous convergent regime affecting the southeastern margin of the south china sea between end eocene to end middle miocene the ensuing structures including juxtaposed carbonates turbidites and shallow marine clastics within thrust fold belts have become ideal environments for hydrocarbon generation and accumulation best developed in the northwest borneo trough area the intensity of thrust fold deformation decreases towards the northeast into offshore southwest palawan

diagnosing mesoscale vertical motion from horizontal velocity and density data the mesoscale vertical velocity is obtained by solving a generalized omega equation equation using density and horizontal velocity data from three consecutive quasi synoptic high resolution surveys in the alboran sea the atlantic jet aj and the northern part of the western alboran gyre wag were observed as a large density anticyclonic front extending down to 200 230 m the horizontal velocity uh in the aj reached maxima of 1 2 m s 1 for the three surveys with extreme rossby numbers of f 0 9 in

mean sea level and surface circulation variability of the mediterranean sea from 2 years of topex poseidon altimetry we describe the circulation and mean sea level variations of the mediterranean sea from 2 years of topex poseidon altimetric data it is first shown that the response of the mediterranean sea to atmospheric pressure forcing is close to an inverse barometer except at high frequencies which means that the adjustment is accompanied by a flow through the straits of sicily and gibraltar we then use topex poseidon to study the mean sea level variations representing steric effects and integrated large scale changes of the mass of the mediterranean sea we observe an annual cycle with a fast drop during winter steric effects account for about half of the observed variations the remaining signal is believed to be driven by evaporation minus precipitation e p forcing and internal hydraulic control in the straits of gibraltar using suboptimal space time objective analysis the classic components of the mediterranean surface circulation are recovered despite low signal to noise ratio the rms of sea level variability is less than 10 cm the variable mediterranean circulation is seen as a complex combination of mesoscale and large scale variations the surface circulation is more complex in the eastern basin than in the western basin in the east it is composed of subbasin scale gyres such as the so called mersa matruh and shikmona gyres which do not have an obvious recurrence period we also observe an intensification of the large scale cyclonic winter circulation in the western and in the ionian basins several mesoscale structures such as the alboran gyres and the ierepetra gyre show a clear seasonal cycle with a maximum in summer the good qualitative and quantitative agreement of the results with previous data from the mediterranean illustrates the improved accurary of topex poseidon over its predecessors

the continent ocean transition at the southeastern margin of the south china sea abstract the south china sea formed by magma poor or intermediate volcanic rifting in the paleogene we investigate the structure of the continent ocean transition cot at its southern margin off nw palawan between the continental blocks of reed bank and the islands of palawan and calamian several surveys recorded by the bgr from 1979 to 2008 established a comprehensive database of regional seismic lines accompanied with magnetic and gravity profiles we interpret two major rifted basins extending in the ne direction across the shelf and slope separated by a structural high of non volcanic origin the continent ocean transition is interpreted at the seaward limit of the continental crust when magnetic spreading anomalies terminate some 80 100 km farther north the area in between displays extensive volcanism as manifest by extrusions that occasionally reach and cut the seafloor by dykes and by presumed basaltic lava flows occurring after break up the cot is highly variable along the nw palawan slope one type shows a distinct outer ridge at the cot with a steep modern seafloor relief the other type is characterised by rotated fault blocks bounded by listric normal faults ramping down to a common detachment surface half grabens developed above a strongly eroded pre rift basement the seafloor relief is smooth across this other type of cot we suggest the pre rift lithospheric configuration had major influence on the formation of the cot besides transfer zones volcanic domains confined to the north of competent crustal blocks correlate with the style of the cot gravity modelling revealed an extremely thinned crust across the shelf we propose a depth dependent extension model with crust being decoupled from mantle lithosphere explaining the discrepancy of subsidence observed across the south china sea region

seismic evidence for mesozoic strata in the northern nansha waters south china sea abstract according to previous studies mesozoic deposits have been unequivocally identified in the northeastern nansha waters southern margin of the south china sea scs thick lower structural layers in the north nansha waters have not clearly been identified as either mesozoic or cenozoic strata these strata are characterized by strong top erosion tilted layer or folded anticlines new long offset multi channel seismic data show refracted phases from the top of the lower structural layer in the northern nansha waters a major velocity leap approximately from 1 6 km s to 3 8 km s or 2 9 km s to 5 3 km s calculated from the refraction wave of seismic data is found across a prominent angular unconformity indicating a major sedimentary hiatus according to the stratigraphic characteristics and velocity range of the lower structural layer velocity leap at the top of lower structural layer and ubiquitous absence of upper cretaceous strata in the nansha waters the lower structural layer of the northern nansha waters are interpreted as mesozoic based on the similarities in stratigraphic characteristics of the lower structural layers between the northern and central nansha waters previous studies from gravity data and multi channel seismic data we propose that lower structural layers over central nansha waters may also mesozoic this further suggests that the intensity of upper crustal extension was moderate in nansha waters during the cenozoic which related to a combination of the cenozoic slab pull of the proto scs and lithosphere delamination over an ancient orogenic belt between the northern and southern continental margins of the scs which may weaken extension of upper crust over the nansha waters

the genesis of the newly discovered giant wuben magmatic fe ti oxide deposit in the emeishan large igneous province a product of the late stage redistribution and sorting of crystal slurries a giant fe ti oxide deposit hosted by the wuben mafic intrusion has recently been discovered in the pan xi area of the emeishan large igneous province elip the evolved compositions of the gangue minerals within the fe ti oxide ores indicate that they formed during later stages of magma differentiation than those within the neighboring panzhihua intrusion or other ore bearing intrusions in this area the rocks from the wuben intrusion and mzb of the panzhihua intrusion contain compositionally similar silicate minerals and have similar titanomagnetite ilmenite ratios suggesting that the former is related to and probably connected to the latter by subsurface magmatic conduits this indicates that unconsolidated minerals that formed in the mzb flowed as crystal slurries into the wuben magma chamber during the later stages of evolution of the parental magma the later secondary enrichment of fe ti oxides by mechanical redistribution and the sorting of crystals as a result of density and size differences generated the wuben massive fe ti oxide bodies the ilmenite was commonly saturated in the magma at late stage of differentiation in the elip thereby the associated deposit contains much higher contents of ilmenite this indicates that future exploration for fe ti oxide mineralization in the elip should not merely focus on the lower parts of large layered intrusions but should also include nearby relatively small intrusions or even the upper parts of large intrusions especially as ilmenite enriched fe ti oxide deposits may have greater economic value than ilmenite poor deposits

the formation of p rich fe ti oxide ore layers in the taihe layered intrusion sw china implications for magma plumbing system process abstract the taihe intrusion is one of the layered intrusions that host giant fe ti oxide deposit in the central part of the emeishan large igneous province sw china different from the other layered intrusions the taihe intrusion has a massive fe ti oxide ore layer at the top of the lower zone lz particularly the rocks of both middle and upper zones contain as much as 5 12 apatite and the most important fe ti oxide ore layers apatite magnetite clinopyroxenite occur at the bases of cyclic units in the middle zone mz rather than in the lower zone lz high cr and ni concentrations of clinopyroxene 65 263 ppm and 66 83 ppm respectively and high an contents of plagioclase 79 80 of the lz rocks indicate their more primitive parental magmas the clinopyroxene and plagioclase of the mz rocks are characterized by low cr and ni contents 1 21 ppm and 0 4 10 ppm respectively and low an 51 67 indicating more evolved parental magma the fe ti oxide ore layers in the mz are not only high in fe and ti but also enriched in p2o5 and rare earth elements indicating an unusual fe ti p rich parental magma it is speculated that the mz represents a later intrusion of fe ti p rich magmas that were produced by the fe ti enriched magma from a deep seated magma chamber mixing with the extensively evolved p rich magma in a middle level magma chamber early crystallization and cumulation of fe ti oxide and apatite together with clinopyroxene from the fe ti p rich magmas from the middle level magma chamber resulted in the formation of fe ti oxide ore layers in the mz fe ti p rich magma and apatite magnetite clinopyroxenites occur in the base of cyclic units whereas apatite gabbros are presented at the upper parts of each cyclic unit the upper zone uz is the product of the crystallization of highly differentiated magma consists chiefly of apatite gabbro and minor intercalated apatite clinopyroxenite

sea level changes and carbonate platform evolution of the xisha islands south china sea since the early miocene abstract analyses of the biogeochemical branched and isoprenoid tetraether bit index and elemental geochemistry from well xk1 provide insight into the development of the xisha islands carbonate platform in the south china sea scs since the early miocene bit is the ratio of branched glycerol dialkyl glycerol tetraethers bgdgts to isoprenoid glycerol dialkyl glycerol tetraethers igdgts which are derived from meteoric and marine environments respectively bit serves as a novel proxy for tracking sea level changes the bit curve of well xk1 is characterized by low high low high alternating stages indicating the superposition of sea level changes on carbonate platform evolution in the scs following the rapid expansion of the scs in the early stages of the early miocene biogenic reefs began to form and bit oscillated intensely the scs started to regress after its initial expansion during the middle miocene at which time global sea level was also falling significantly the combination of both tectonic activity and eustatic variation has resulted in the deposition of strata with reef beach facies which are characterized by high bit values relative sea level reached its lowest point in the late stages of the middle miocene 11 6 ma subsequent sea level rise between the late miocene and pliocene induced a negative shift in bit and lagoonal facies formed under optimal warm marine conditions periodic exposure caused the reefs of the xisha islands to suffer from erosion during the pleistocene which is consistent with a second elevation in the bit index however modern trends show increasing regional water depths again major and trace element curves na si p b ga mo zn as well as the associated ratios na2o k2o na2o sio2 b ga ti sr zr sr al sr th u accurately record sea level variations several significant discontinuities correlate with sea level shifts and provide important details about the geomorphology sedimentation patterns and diagenesis types on the scs carbonate platform the agreement between organic and inorganic geochemical data demonstrates that our reconstructions of scs sea level changes and modes of carbonate platform development are robust our findings also demonstrate that carbonate evolution in the xisha islands was shaped by relative sea level changes implying that sea level fluctuations in the scs were controlled by global eustatic factors in addition to regional tectonic subsidence

paleosecular variation of brunhes age lava flows from british columbia canada 1 brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern british columbia silverthrone garibaldi lake mt meager clearwater wells gray park and kelowna area a total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site previous radiometric studies indicate that the ages of these lava flows range from 2 3 to 760 ka stepwise thermal demagnetization 14 to 21 steps was carried out for all the samples in each site and af demagnetization was performed on one sample per site forty five sites were selected based on rigorous criteria 95 5 to calculate a mean direction d 356 9 i 70 2 95 2 8 that is statistically indistinguishable from the direction of the dipole field at the area i 68 3 virtual geomagnetic poles vgps do not show the far sided effect and the angular standard deviation is 17 5 a value in agreement with the paleomagnetic field dispersion for that latitude these high quality results are expected to improve the time averaged field taf and secular variation models

stable isotopic constraints on fluid rock interaction and cu pge s redistribution in the sonju lake intrusion minnesota the sonju lake intrusion part of the 1 1 ga midcontinent rift related beaver bay complex is a 1 200 m thick strongly differentiated layered sequence of mafic cumulates located in northeastern minnesota basal melatroctolite and dunite layers are overlain by troctolite gabbro fe ti oxide rich gabbro apatite diorite and monzodiorite stratigraphic intervals rich in pt pd cu and s occur over 500 m in the fe ti oxide rich gabbro and apatite diorite units peak concentrations show offsets that are similar to those found in other tholeiitic layered intrusions concentrations of pd in excess of 100 ppb are confined to the lowermost 25 m of the interval copper shows a sharp increase to 630 ppm above the pd rich interval sulfur contents are low 375 ppm in the cu rich interval but they increase to values as high as 3 150 ppm above in the apatite diorite disseminated sulfides in the intrusion have 34s values that range from 2 2 to 3 per mil vienna canyon diablo troilite v cdt and suggest that contamination by country rock sulfur was not an important process in the formation of the metal rich interval 18o values of plagioclase from the intrusion range from 5 6 to 12 0 per mil v smow and indicate that a relatively low 18o fluid 18o 3 5 interacted with the rocks of the intrusion at temperatures less than 275 c clinopyroxene and fe ti oxides ilmenite with minor amounts of titanomagnetite show much more restricted ranges in 18o values 4 6 5 7 and 5 5 6 7 per mil respectively and attest to the kinetic control of the oxygen isotope exchange process the externally derived fluid that interacted with rocks now enriched in platinum group elements pge cu and fe sulfide minerals locally liberated sulfur and replaced chalcopyrite and pyrite with goethite in the cu rich zone goethite that replaces chalcopyrite may contain up to 8 5 weight percent cu it is evident that hydrothermal alteration resulted in a decoupling of copper and sulfur with sulfur being transferred out of the cu rich interval interaction between rocks in the pge cu s interval of the sonju lake intrusion and an externally derived fluid at low temperatures modified what appears to have been a primary stratigraphic metal sulfur zonation the effects of hydrothermal alteration on pge and base metal sulfide mobility and redistribution must be understood before models of primary zonation processes can be meaningfully applied

variations in the structure of the anticyclonic gyres found in the alboran sea historical satellite aircraft and in situ data have shown that two anticyclonic gyres the western and eastern alboran gyres are major ocean features of the alboran sea an examination of several years of satellite imagery indicates that large variations in the surface expression of these two gyres occur and that on occasion one or the other gyre disappears the disappearance of both gyres at the same time was not seen the initial disappearance of either gyre occurs on a time scale of a week to 2 weeks whereas the return may take from 3 weeks to 2 months various forcing mechanisms i e winds mass flux inflow through the straits of gibraltar and sicily and or density have been used in numerical ocean circulation models to study the dynamics of the western mediterranean sea various model results show relationships similar to those shown by the satellite imagery however no single forcing mechanism has been positively identified as the source of the disappearances and the events may be a result of a combination of forcing mechanisms

observation of a western alboran gyre migration event abstract in the western alboran sea light atlantic water and dense mediterranean waters meet this gives rise to intense density fronts and energetic mesoscale features such as two semi permanent anticyclonic vortices the western and eastern alboran gyres however the circulation in the alboran sea is strongly varying in time with episodes where neither the western alboran gyre nor the eastern alboran gyre are present in october 1996 four consecutive high resolution surveys of the western alboran gyre wag were carried out and lagrangian floats were released during the first survey the western alboran sea was occupied by the wag surrounded by the atlantic jet the following surveys showed the wag drifting eastward beginning a wag migration event as confirmed 15 days later by the lagrangian float tracks and the sst images to replace the old gyre one month later a new gyre was formed analysis of adcp velocities sst images and ts properties show a change between the first and the second survey in the atlantic inflow through the strait of gibraltar the relationships between this change in the atlantic inflow a drop in the atmospheric pressure at ceuta the tidal regime and the wag migration are discussed the existence of a high resolution sampling in space together with the possibility of addressing the temporal variability has allowed us to describe in detail and for the first time the time evolution of the western alboran sea during a wag migration event relating the migration to changes in the inflow through the strait of gibraltar

the meandering path of a drifter around the western alboran gyre abstract an accidentally released drifter in the eastern section of the strait of gibraltar whose successive positions were tracked by the argos surveillance system was advected more than 170 km around the western alboran gyre in the alboran sea of the western mediterranean sea during four days the drifter trajectory along the gyre s periphery was wavelike around a hypothetical smoothed streamline with a period of 35 h and an amplitude of approximately 2 km temperature observations confirm the wavelike nature of the trajectory neither tidal currents within the alboran basin nor wind related forcing are able to explain the observed path the interaction of the incoming atlantic jet and the western alboran gyre at the place where they meet together with the existence of relative vorticity pulses of the atlantic jet associated with tidal currents in the strait is put forward as a likely mechanism that generates short scale eddies in which the drifter could have been trapped the subsequent advection of

do fe ti oxide magmas exist probably not many fe ti oxide bodies associated with anorthosite suites and with some tholeiitic plutonic bodies have cross cutting relationships with their host rocks suggesting that they may have been emplaced as oxide melts pure fe ti oxides melt at temperatures much higher than is considered to be geologically realistic so various fluxes mainly apatite fluorine or carbon have been called upon to stabilize the melts down to plausible temperatures this review traces our experimental attempts to test the effectiveness of proposed fluxes and therefore to demonstrate the existence of such melts at geologically realistic temperatures neither f apatite nor carbon act to stabilize ti rich fe ti oxide melts at 1300 c and below and we conclude that unless some totally unforeseen material does serve as a flux fe ti oxide magmas almost certainly do not exist although our data are not conclusive it appears that increasing contents of feo and possibly tio 2 and p 2 o 5 mutually enhance their solubilities in silicate melts allowing extensive buildup of those components in melts residual to anorthosite we interpret that oxide orebodies form by gravitational accumulation of crystalline oxides from such liquids once those melts become saturated with either fe ti oxides or apatite both phases will tend to co precipitate thus explaining the common occurrence of apatite with oxide orebodies nelsonites cross cutting oxide bodies were probably emplaced as crystalline oxides possibly lubricated by small amounts of residual silicate liquid oxidation of the fe 2 tio 4 component in initially ulvospinel rich spinel and concomitant formation of ilmenite grains by granule oxy exsolution may have weakened the crystalline oxide and facilitated its flow during emplacement it seems clear though that the presence of carbon does stabilize ti poor iron oxide melts to very low temperatures at and even below 1000 c consistent with the disputed magmatic origin of the magnetite lavas at el laco chile

the dynamics of the sicily strait a comprehensive study from observations and models abstract the dynamics of the sicily strait are investigated in a comprehensive study using recent in situ observations ocean general circulation model ogcm simulations and process model results in particular results of a very high resolution mediterranean model med16 developed in the context of the mercator project are described the circulation in the sicily strait can be described as a two layer exchange of atlantic water aw and eastern mediterranean outflow water eow the algerian current brings aw the upper layer eastwards and splits into two branches at the entrance to the sicily strait one flowing to the tyrrhenian sea the other into the sicily strait the later is composed of two streams referred to as the atlantic ionian stream ais and the atlantic tunisian current atc in winter the atc signature is more pronounced in summer the ais is associated with a number of well known semi permanent features including the intermittent northward extension of the ais called nais at the ionian shelf break which seems to be driven by the surface density contrast between waters of the sicilian and the ionian basins new intermittent patterns are shown by the med16 simulations for example an anticyclonic eddy called mca south of the malta channel and an anticyclonic gyre associated to the nais called naisa upwelling is well developed in august with temperature lower than 24 c along the western and southern coasts of sicily the seasonal transport of the aw through the strait has a maximum value 1 4 sv in winter and a minimum value at the end of summer 0 8 sv in the lower layer at the exit of the sicily strait the eow mainly composed of levantine intermediate water liw outflows into the tyrrhenian sea and veers to the right then as well known the liw flows along the northern coast of sicily before reaching the sardinia channel a new liw path from the sicily strait towards the sardinia channel is shown by the med16 model and is due to intermediate eddy shedding at the exit of the sicily strait the topography of the sill in the sicily strait plays a major role in the circulation a combination of barotropic baroclinic double kelvin waves on both side of the sill provides a mechanism for splitting the algerian current

contrasting parental magma compositions for the hongge and panzhihua magmatic fe ti v oxide deposits emeishan large igneous province sw china many 260 ma mafic ultramafic layered intrusions including hongge and panzhihua in the emeishan large igneous province southwestern china host world class fe ti v oxide ore deposits these two most important ore bearing intrusions show differences in lithology and mineral chemistry the most important orebodies in the hongge intrusion occur as concordant layers in the middle part of the intrusion closely associated with clinopyroxenites titanomagnetite and mg rich ilmenite are the major ore minerals of the hongge deposit coexisting clinopyroxene contains 1 7 wt tio2 these data indicate high ti parental magma for the hongge ore bearing clinopyroxenites in the panzhihua intrusion the most important orebodies also occur as concordant layers but in its lower part instead of middle part in contrast with the hongge deposit the most important host rocks of the panzhihua deposit are gabbros not clinopyroxenites in addition ilmenite is rare and titanomagnetite is predominant in the panzhihua deposit coexisting clinopyroxene in the panzhihua deposit contains 1 6 wt tio2 the contrasting lithologic and mineral compositions indicate that the parental magma for the hongge deposit has higher tio2 than that for the panzhihua deposit the compositions of clinopyroxene from the panzhihua and hongge deposits indicate that their parental magmas are also different in mgo feo and trace element ratios as well calculations using average experimental mg fe exchange coefficient and trace element partition coefficients between clinopyroxene and magma show that the hongge parental magma has higher mgo feo ratios and more fractionated mantle normalized trace element patterns than the panzhihua parental magma the estimated compositions of the parental magmas for the hongge and panzhihua ore bearing lithologies resemble the average compositions of the longzhoushan type high ti basalts and ertan type intermediate ti basalts in the emeishan large igneous province respectively the new trace element data from this study together with available sr nd isotope data for the ore bearing intrusions from literature support a new petrogenetic model involving selective assimilation of newly subducted stagnant oceanic gabbroic slab above the deep seated emeishan mantle plume this process and subsequent contamination with the upper crust played an important role in the variation of parental magma compositions between the hongge and panzhihua magmatic oxide ore deposits abundant fe ti oxide ore deposits associated with less evolved basaltic magma in the emeishan large igneous province than elsewhere in the world are attributed to selective assimilation of newly subducted stagnant oceanic lithospheric slab by the ascending mantle plume derived picritic magma that was originally undersaturated with fe ti oxides