three dimensional seismic imaging of paleogene dike fed submarine volcanoes from the northeast atlantic margin we use three dimensional seismic data to describe the architecture of shallow intrusive igneous sill and dike complexes intruded into the upper crust as well as the internal and external geometry of extrusive conical igneous mounds that were fed by the magma conduits the conical mounds accreted on the seabed directly above the tips of the basaltic dikes between 54 9 and 54 6 ma in plan view the mounds are broadly circular 1 1 7 km in diameter and have a relief of 50 300 m they occur above a complex network of linked cuspate shaped sills and dikes intruded into paleocene and cretaceous sediments of the faeroe shetland basin northeast atlantic margin the highly organized internal structure consisting of bulbous layers arranged concentrically around a central axis along with the clear vertical link to the underlying sills and dikes indicates that they most likely represent pillowed basaltic lava and hyaloclastite mounds that were fed by the dikes and extruded onto the seafloor mounds of similar external geometry have been described from sidescan sonar images above active spreading centers in oceanic settings however such structures are rarely recognized in passive margin settings and prior to this investigation our knowledge of their three dimensional internal geometry has been largely speculative

the initial response of a stratified lake to a surface shear stress laboratory experiments are used to study the initial response of a stratified fluid to the action of a wind stress the experiments are described in the context of a parameterization scheme that quantifies the strength of the applied stress relative to the bulk stability of the fluid and also the duration of the wind stress relative to the periods of the waves generated by the stress this study concentrates on the first fundamental internal wave period in experiments where the fluid is considered to have upwelled i e the stratified region of the fluid reaches the surface at the upwind endwall the majority of the experiments use three layer initial density profiles as an approximation to a continuously stratified water column a linear model using normal modes proved successful prior to the commencement of upwelling and this enabled an estimate to be made of the time at which upwelling occurred at this point the wave development ceased and the flows developed via entrainment mechanisms consideration of the energy budget showed that little of the input energy was stored in the system the initial mixing efficiency defined as the ratio of the mean potential energy gained to the energy imparted by the belt never exceeded 30 peak efficiency occurred when the surface stress was just sufficient to bring the interfacial region to the surface

3d seismic interpretation of dissolution pipes in the south china sea genesis by subsurface fluid induced collapse a large suite of remarkable pipe structures has been identified from high resolution 3d seismic data in the dongsha massif northern south china sea the diameters and heights of the collapse structures range from c 100 m to 710 m and c 134 m to 1010 m respectively these pipes vary from cylindrical to a steep conical geometry narrowing upwards they are rooted in a major carbonate succession that was originally deposited as a large carbonate platform system these pipe structures are interpreted as resulting from carbonate diagenesis and dissolution at a deep burial stage i e they are not classical karst collapse structures as suggested in previous studies instead they are analogous to pipe like collapse structures described from the ordovician ellenburger group of west texas the dissolution pipes formed at different times during the neogene with the earliest pipes developing during the early middle miocene 15 0 ma and with at least one peak of pipe formation during the dongsha event began at 5 5 ma this regional event was associated with magma intrusion uplifting and faulting in the study area stable isotope data of reservoir rocks in the area of pipe development suggest that cementation was linked to magmatically driven hydrothermal circulation during the dongsha event small scale pipes are densely clustered above the main oil reservoir and given that petroleum is known to have been generated during the time interval of pipe formation we suggest that corrosive carbonic acid derived from flushing of petroleum reservoirs may have been a contributory factor to the dissolution and collapse process c 2013 elsevier b v all rights reserved

miocene igneous activity in the northern subbasin offshore senegal nw africa abstract more than 70 enigmatic discordant seismic anomalies of limited lateral extent associated with eye shaped structures and folds have been imaged on 2d seismic data from the offshore northern subbasin of the senegal basin nw africa in this paper we define their distribution characterise their morphology and compare them to similar features imaged by seismic data along the ne atlantic margin that have been demonstrated to be igneous sills hydrothermal vents and intrusion related forced folds we propose that the cretaceous and paleogene strata in the northernmost part of the offshore northern subbasin were heavily intruded by igneous sills during the miocene the proposed timing of intrusion is coincident with that previously suggested for the development of the cayar seamount located 100 km nnw of dakar and onshore volcanism in the cap vert area near dakar and in the cape verde islands this stage of miocene igneous activity is interpreted to be closely associated with the coeval collision between africa and europe the interpreted igneous sills give rise to an unexpected soft seismic response the preferred explanation for the soft appearance of the sills is that the majority of sills are thin

modal response of reservoirs to wind stress an analysis of the response of a density stratified reservoir to surface shear stress is presented the reservoir is assumed to be two dimensional and to have a constant depth in the limit that the bulk wedderburn number wb and the bulk richardson number rib are both infinite the resulting equations are linear and solutions can be found in terms of the individual responses of a set of orthogonal normal modes for the case of a steady wind stress the solution consists of periodic motions and steady isopycnal displacements however the steady state isopycnal slope at the base of the mixed layer is infinite implying that upwelling can occur when the wedderburn number is quite large this is attributed to blocking of the stratified fluid below the mixed layer by the endwall the modal theory presented in this paper is compared with experimental observations made using a belt to impart shear stress to a stratified fluid contained in a box the comparison shows that the present theory is qualitatively corr

intrusion and its implication for subsidence a case from the baiyun sag on the northern margin of the south china sea we develop a series of simple numerical models to explain the anomalous subsidence and deposition phenomena on the northern continental margin of the south china sea in particular in the baiyun sag the results suggest that a short period high rate deposition of around 17 ma is related to a rapid subsidence event which may be due to episodic emplacement of a dense intrusion necking and gravity models indicate that in the basement of the baiyun sag there is a dense zone that is 100 200 kg m 3 more dense than the surrounding country rock considering its high magnetic intensity and regional igneous activity the dense zone is thought to be related to a phase of basalt intrusion that may have taken place around 17 ma thermal and subsidence models indicate that a hot denser intrusion can cause significant subsidence immediately after the intrusion the subsidence rate then slows down with cooling thus becoming consistent with the observed subsidence curves at around 17 ma the results also indicate that the lithospheric strength under the baiyun sag is negligible and that the high velocity layer in the lowermost crust may be not an original part of the pre rift crust instead it is thought to be underplated intrusion emplaced at around 30 ma when the continental margin broke up c 2005 elsevier b v all rights reserved

extensional tectonics and post rift magmatism in the southern south china sea new constraints from multi channel seismic data abstract in this study we investigated the extensional tectonics and post rift magmatism in the southern south china sea scs using a newly obtained seismic reflection profile which crosses the southwest sector of the oceanic basin swsob west liyue trough and liyue basin along the southern margin of the scs a wide range of magmatic features was identified in the swsob with a late stage marked by a broad pleistocene unconformity separating horizontal sediment layers from strata deformed by igneous structures along the continental slope most fault activity continued until horizon t4 15 5 ma implying that crustal extension continued during seafloor spreading in the sw oceanic sector of the scs a low angle listric normal fault with a large offset marking the southern boundary of the trough controlled regional crustal extension thick syn rift sedimentary strata and significant crustal thinning in the southern part of the trough reveal relatively strong extension post rift magmatism occurred in this thinned crust and affected sedimentary strata up to the seafloor importantly a series of high angle normal faults rapidly deepened the top of the basement forming a sharp contact between the continental slope and oceanic basin the distal domain is very narrow 20 km with no known detachment faults suggesting rapid continental breakup that may be related to the presence of rigid blocks near the study area

geochemical evolution of oligocene middle miocene sediments in the deep water area of the pearl river mouth basin northern south china sea abstract the deep water area of the pearl river mouth basin in the south china sea has received much scientific attention since the ocean drilling program odp leg 184 in 1999 due to its potential economic prospects and distinct tectono sedimentary evolutionary processes in this study we present the composition of major and trace elements from two newly sampled deep water boreholes by6 and lw3 in the baiyun sag of the southern pearl river mouth basin the geochemical evolution in the oligocene middle miocene as well as potential controlling factors are investigated based on a comparative study with previous data from odp site 1148 and borehole py33 the chemical index of alteration cia and a cn k plot reveal that the observed weathering trends are not compatible for the four discussed boreholes sedimentary sorting is primarily observed in borehole py33 where data trend away from the a apex to the feldspar join in the a cn k plot and show a spread of al 2 o 3 sio 2 and nb zr ratios compared to chemical weathering and hydrodynamic sorting provenance has a greater impact on sediment composition of the deep water area from the north the pearl river was the primary sediment supply however a positive eu anomaly and the provenance discrimination diagrams i e la th versus th yb and zr co versus th co reveal the mafic nature of borehole by6 sediments in the zhuhai lower zhujiang 32 0 18 5 ma and upper hanjiang 13 8 10 5 ma formations these compositions are unusual and differ from the well defined felsic sources in the majority of the baiyun sag these discrepancies are likely related to multistage magmatism the sediments at site 1148 are characterized by slightly enriched heavy rare earth elements and relatively high zr co ratios which could possibly be caused by zircon enrichment from local sources

neogene igneous intrusions in the northern south china sea evidence from high resolution three dimensional seismic data igneous intrusions emplaced within the prospective intervals of sedimentary basins can exert a significant impact on petroleum systems and hence are of considerable interest particularly when risking exploration plays a number of discordant high amplitude seismic anomalies dsas with a range of geometries are documented in high resolution 3d seismic data in the northern south china sea their distribution and seismic characteristics are analysed and compared with similar seismic anomalies documented within sedimentary basins in the atlantic margins and other locations the dsas occur mainly within early miocene strata and are interpreted as igneous intrusions that were emplaced close to the palaeo seabed and are dated as early middle miocene using seismic stratigraphic methods a number of vents are also identified above the intrusions within early middle miocene strata several geometrical forms are observed referred to here as saucer shaped lensoid shaped stacked and composite intrusions the seismic expression of these is increasing complex towards the palaeo seabed with a tendency for the saucer shaped sills to be the deepest intrusive forms the igneous intrusions observed in this study only could be identified using 3d seismic data and they are important for the future evaluations of petroleum systems basin evolution and tectonic analysis in the pearl river mouth basin c 2014 elsevier ltd all rights reserved

the geometry and emplacement of conical sandstone intrusions conical sandstone intrusions with a geometry comparable with that of many igneous sills have been identified using 3d seismic data from large areas of the north sea and faeroe shetland basins these intrusions are of reservoir scale ranging from 100 to 2000 m or so in diameter 50 300 m in height and 1 80 m in thickness aperture they are concentrated in specific stratigraphic intervals in the cenozoic fills of both basins two geometrical end members are recognised and defined here apical cones and flat based bowls the former consist of inward dipping conical inclined sheets meeting at a prominent apex and the latter of similarly dipping discordant margins climbing from the edges of a concordant sheet both end members are associated with domal folds that are interpreted as resulting from the hydraulic elevation of the overburden during intrusion and which are analogous to similar structures associated with bowl shaped igneous sills measurements of aperture versus distance exhibit systematic relationships with the structural relief of these folds offering a potentially predictive method for estimation of sandstone intrusion aperture and reservoir volume prior to drilling a growth model for these end member geometries is presented drawing on existing theory for igneous sill emplacement aperture versus distance plots x are used to illustrate two contrasting models for aperture inflation during propagation but these require much further data before any specific growth model can be adopted

volcanic rocks as prolific gas reservoir a case study from the qingshen gas field in the songliao basin ne china abstract the qingshen gas field with over 100 billion cubic meters bcms of proven gas reserves was discovered recently in the upper jurassic lower cretaceous strata of the songliao basin northeastern china the stratigraphic relationships and gas chemical compositions indicate mixed gas sources dominantly from the upper jurassic lower cretaceous coals and associated dark mudstones underlying the gas reservoirs with minor contribution from deep inorganic sources the gas reservoirs consist mainly of volcanic rocks rhyolite and tuff with some production also from the conglomerate gas charge into these largely volcanic rock reservoirs appears to coincide with the peak gas generation in the deep upper jurassic lower cretaceous coal measures the presence of several thick lacustrine mudstone beds in the upper cretaceous strata as regional caprocks and relatively mild structural deformation since the late cretaceous are among the favorable conditions for the preservation of large volume of natural gases in these relatively deep gas reservoirs the gas yields are the highest in the paleomorphological highs where fractures and secondary porosity are well developed in the gas reservoirs

an experimental study of the upwelling response of stratified reservoirs to surface shear stress an experimental study of the dynamic response of non rotating stratified reservoirs to the application of surface shear stresses is presented the experiments were made using two layered and linear stratifications a moving belt was used to supply a shear stress to the fluid detailed measurements of the density field show that upwelling occurs at all values of the wedderburn number w rather than only occurring when w 1 differences between the two layer theory and the present observations are attributed to the fact that the experimental stratifications were continuous rather than layered shearflow dispersion is observed to be an important mechanism for distributing the effects of localized upwelling over the entire length of the mixed layer a model of mixed layer deepening based on upwelling and shearflow dispersion is presented and is compared to the observations of this and other experimental studies

magma transport through the crust via interconnected sill complexes three dimensional seismic data from the volcanic margin offshore norway have been used to map the complex three dimensional geometry of two major sill complexes these data show that the complexes consist of bowl shaped or inclined sheetlike discordant sills that intersect with one another over a vertical distance of 8 12 km and transect basement and sedimentary rocks of the middle to upper crust using a simple graphical technique we demonstrate the interconnectedness of the sill complex and hence the maximum time for sill emplacement we show that sills are interconnected by junctions occurring systematically at the lowest points of the overlying sills and hence that the sill complex could have acted as a single throughgoing magmatic plumbing system transporting mafic melts from mid lower crustal depths to near surface based on this imaging of the magmatic plumbing system we conclude that sills can form viable and efficient conduits for crustal magma transport in volcanic margins and may play a role in feeding large extrusive complexes

sill related seafloor domes in the zhongjiannan basin western south china sea abstract magmatism can exert significant impact on sedimentary basins such as the zhongjiannan basin zjnb western south china sea we have evaluated multibeam bathymetric and multichannel seismic reflection data acquired by the guangzhou marine geological survey in recent years in order to investigate the distribution the characteristics and the subsurface structures related to seafloor domes found in the northeastern zjnb our data revealed forty two domes at water depths between 2312 m and 2870 m which are clustered around volcanic mounds large seamounts and along the edge of the central depression in the study area these domes are generally circular to elongate or irregular in plan view with large basal areas and they also have gentler flanks dips of 1 46 7 73 with vertical reliefs ranging from tens to hundreds of meters in seismic sections majority of the domes are underlain by variably shaped and complex magmatic sills which provide a cause effect relationship between domes formation and igneous intrusions these intrusions heat surrounding organic rich sediments release hydrocarbons fluidize sediment pore waters and form gas rich fluids which fill in sediment and uplift overlying strata immediately above the sills to form forced folds which are manifested as seafloor domes these sill folds dome structures have important implications for understanding geomorphologic features caused by sills emplaced at depth

the temporal and spatial distribution of volcanism in the south china sea region cenozoic magmatism in the south china sea the associated continental margins coastal south china and indochina is reviewed volcanism contemporaneous with rifting and sea floor spreading in the south china sea was very weak in the margins and adjacent areas there was only very limited magmatic activity most probably after the cessation of sea floor spreading the south china sea has non volcanic margins large basement relief caused by extension formed major basins and a continental oceanic transitional zone in the northern margin reflects high crustal rigidity during rifting and drifting the paucity of a magma supply and presence of rigid fault blocks are unfavorable to the mantle flow model previously proposed to account for the opening of the south china sea which was supposedly linked to the escape of indochina induced by indo eurasia collision c 2005 published by elsevier ltd

prolonged post rift magmatism on highly extended crust of divergent continental margins baiyun sag south china sea three dimensional 3d seismic borehole and geochemical data reveal a prolonged phase of post rift magmatism on highly extended crust of the baiyun sag south china sea two volcanic complexes are identified and described in the context of continental rifting and diachronous continental breakup of the south china sea biostratigraphic data from exploration wells by7 1 and by2 complemented by k ar datings from core samples confirm that magmatic activity in the baiyun sag occurred in two main stages 1 a first episode at the base of the miocene 23 8 ma and 2 a second episode occurring at the end of the early miocene 17 6 ma the relative location of volcanic complexes in the baiyun sag and their stratigraphic position reveals prolonged magmatism inboard of the ocean continent transition zone during continental breakup we suggest that magmatism in the baiyun sag reflects progressive continental breakup in the south china sea with the last volcanic episode marking the end of a breakup sequence representing the early post rift tectonic events associated with the continental breakup process seismic and borehole data from this breakup sequence records diachronous magma emplacement and complex changes in depositional environments during continental breakup c 2016 the authors published by elsevier b v

magmatic tectonic evolution of a volcanic rifted margin abstract many north atlantic continental margins are underlain by huge volcanic edifices near the continent ocean boundary a deep crustal hole drilled on the voring plateau odp leg 104 has provided important constraints on the initial breakup history and the subsequent margin evolution by penetrating more than 900 m of igneous rocks and interbedded sediments below a post early eocene cover the rocks constitute two distinct different volcanic series the upper series comprising a seaward dipping reflector wedge consists of transitional mid oceanic tholeiitic lava flows and thin volcaniclastic sediments dacitic flows some dikes and thicker interbedded sediments constitute the lower series the margin evolved by paleocene crustal extension accompanied by uplift and pervasive intrusion of the rift zone just prior to breakup magma from shallow crustal melts produced the lower series the upper series was constructed during an intense rapidly waning subaerial volcanic surge following breakup near the paleocene eocene transition it covers both the new oceanic crust and large areas of the continental crust the dipping wedge was formed by subsidence due to loading and thermal contraction possibly amplified by tectonism when the surge abated the injection center rapidly subsided and normal oceanic crust was formed there is a direct temporal and compositional relationship between the onshore north atlantic volcanic province and the margin volcanism compared to the transverse part of the province including the iceland hotspot which has been active over 60 m y the volcanic margins reflect a 2500 km long transient segment related to continental breakup lasting only about 3 m y the volcanic surge and uplift at breakup are related to a modest regional increased temperature at the base of the lithosphere this mode of margin formation has had important paleoenvironmental implications

three dimensional imaging of miocene volcanic effusive and conduit facies implications for the magmatism and seafloor spreading of the south china sea abstract an integrated and practical seismic based three dimensional 3d visualization technique of volcanic effusive and conduit facies is proposed in the miocene lower zhujiang formation of the baiyun sag pearl river mouth basin prmb south china sea scs the technique is based mainly on the 3d visualization to separately described the strong amplitude reflection volcanic effusive facies and the weak amplitude chaotic reflection volcanic conduit facies with different seismic cube attributes instantaneous amplitude attribute and variance cube attribute the detail work flow of the method has been proposed with eight steps including the original data type seismic attributes selection the visualizing skills and the final validation with borehole and thin sections it is convenient to operate and describe the spatial distribution and interrelation of various volcanic facies effectively and intuitively the 3d imaging result of different volcanic facies described in the baiyun sag can be viewed from any perspectives and better understand the related genesis mechanism which associated with the nw se trend normal fault system during the breakup stage the two volcanic facies indicate that the spatial distribution of the volcanic rocks is parallel to the normal faults strike and the magma probably flows along the normal fault plane and then feds into the volcanic mounds with eruption the volcanic mounds are mostly belonged to the central fissure eruption types and mainly correspond to the second magmatic episode 23 8 ma of early miocene in the prmb and were induced associated with the seafloor spreading of the northern scs we may easier to find effective volcanic reservoirs or other volcano related metallic minerals based on the proposed new method this significant work can also serve as a useful reference for other continental margins or sedimentary basins with typical volcanic influence

the three dimensional geometry and growth of forced folds above saucer shaped igneous sills forced folds formed at the seabed immediately overlying shallow 1 km saucer shaped sills along the ne atlantic margin during the early paleogene examples of this sill fold relationship are exceptionally well imaged by high resolution 3d seismic datasets from the ne rockall basin the forced folds are domal in shape 2 4 km in diameter exhibit a structural relief of up to 350 m and comprise sediment volumes of ca 1 km3 a comparison of the thickness distribution across and volume of a saucer shaped sill with a high intrusion diameter to depth ratio and the structural relief and volume of its associated forced fold shows a remarkable equivalence this has the important implication that the structural relief on intrusion related forced folds can be used as an estimate of the thickness of the underlying sill the analysed forced folds are interpreted to have formed through three continual growth stages that are directly linked to the mechanical emplacement of the underlying saucer shaped sills their growth was associated with an increase in faulting of the overlying strata and influenced coeval or subsequent development of polygonal fault systems within the overburden these structures represent a new type of four way dip closed hydrocarbon trap

crustal plumbing system of post rift magmatism in the northern margin of south china sea new insights from integrated seismology abstract the origin and evolution of magmatism in rifting margins are a fundamental geological subject and remain the focus of intense studies unlike the classical magma poor and magma rich rifting margins the northern margin of the south china sea scs exhibits a strong post rift magmatism but the evolution and mechanism of this behavior are still poorly understood in this work we investigate the detailed structural features of the post rift magmatism in the crust of the scs northern margin our analysis is based on wide angle and multichannel reflection seismic data combined with previous seismological results our results show a wide distribution of shallow igneous sills and intrusions these features are spatially and tectonically linked to the lower crustal high velocity bodies hvbs and submarine volcanism indicating a causative connection between the three features considering the existence of an obvious low velocity branch of the hainan plume in the northern scs and uplift of the lithosphere asthenosphere boundary we propose that the hvbs reflect consolidated mafic intrusions which formed the lower crustal reservoirs feeding the overlying igneous sills and intrusions in the scs northern margin where abundant extensional and detachment faults can act as magmatic channels such a dynamic process might cause post rift volcanism our results suggest that the crustal magmatic system of post rift volcanism has a multilevel upward migration mode and the hvbs in the lower crust could be the product of post rift magmatism further indicating that the scs northern margin had a magma poor property at the rifting phase but has undergone a strong magmatic rejuvenation by the subsequent mantle plume

seismic characteristics and evolution of post rift igneous complexes and hydrothermal vents in the lingshui sag qiongdongnan basin northwestern south china sea abstract the study of morphology distribution and characteristics of igneous complexes has great significance to the understanding of magma plumbing processes geodynamics and tectonic evolution of continental margins previous studies concentrated partly on the magma rich rifted basins where the lateral magma transport mainly affects the igneous complexes connection and distribution however due to seismic wave shielding effects of the large shallow magmatic bodies the underlying igneous complexes and their corresponding magma plumbing systems in the magma poor rifted margins are still in debate in this study 2d 3d seismic data and well data are utilized to describe the morphology architecture and spatial temporal distribution of igneous complexes in the lingshui sag of the qiongdongnan basin northwestern south china sea margin the identified igneous complexes include 98 intrusive sills and feeder dykes beneath some of the isolated sills twenty six cone shaped mounds that overlie intruded sills through internal disturbed conduits were also described drilled well samples and seismic expressions suggest that these mounds are hydrothermal vents a uniform bottom mounds horizon of these vents suggests that they probably formed at the same time constrained by biostratigraphic data and sedimentation rate of underlying and overlying sedimentary layers the magma emplacement was dated to the middle miocene ca 14 6 ma most of the hydrothermal vents are distributed along the f2 fault zone and have direct linkage with the underlying sills while the large sill complexes that are connected with limited vents are mainly present above the hyperextended continental crust where the crust thins to 6 10 km the sills intruded into different layers from the lower oligocene to the lower miocene and the emplaced depth of sills is 1 2 6 3 km whether or not they feed any vents above unlike most of the large volume and laterally linked sills found in the magma rich rifted margins the scattered distribution of sills at different levels indicates that dykes probably play an important role in magma transport which might coexist with numerous polygonal or small faults and interference reflections this work highlights the critical role of basin structures in controlling the distribution of post rift igneous complexes in magma poor margins including thinned continental crust sedimentary thickness and faults

continental rifting and sediment infill in the distal part of the northern south china sea in the western pacific region challenge on the present day models for the passive margins abstract well known difficulties in imaging structures and sediment infill in the distal margins covered by deepwater and thick sediment in the western pacific have limited our ability to interpret rifting to drifting processes of these margins we used a wealth of multi channel seismic profiles and drilling data to construct a regional stratigraphic framework for the cenozoic strata in the xingning jinghai subbasin which is now located to the north of the apparent oceanic crust in the south china sea eight sequence bounding unconformities segmented seven sequence stratigraphy can be confidently recognized in our survey using mostly standard criteria for identification the particular arrangement of strata elements in the syn rift succession presents two contrast geometry sedimentary packages whose pattern is different with that bounded by high angle faults on the continental shelf observed by the previous studies in the xingning jinghai subbasin strata pattern on the hangingwall of the low angle faults shows that the faults bounding the depocenters were initially formed by high angle faults which is similar to the present day high angle faults on the continental shelf subsequently the high angle faults in the deepwater region were rotated to be extensional detachment low angle faults which extremely thinned the crust from 33 km to 8 10 km the low angle detachment fault systems can be used to explain the magmatic addition during the post rift stage on the hyper extended crust in the northern margin the hyper extended crust of the south china sea with the characteristics of landward dipping low angle faults high velocity lower crust and moderately magmatism challenges the magma poor or magma rich models constructed from the atlantic margins

geometry and controls on the development of igneous sill related forced folds a 2 d seismic reflection case study from offshore southern australia emplacement of magma in the shallow subsurface can result in the development of dome shaped folds at the earth s sur face these so called forced folds have been described in the fi eld and in subsur face data sets although the exact geometry of the folds and the nature of their relation ship to under lying sills remain unclear and in some cases controversial in this study we use high quality two dimensional 2 d seismic refl ection and borehole data from the ceduna sub basin offshore southern australia to describe the structure and infer the evolution of igneous sill related forced folds in the bight basin igneous complex thirty three igneous sills which were em placed 200 1500 m below the paleo seabed in upper cretaceous rocks are mapped in the ceduna sub basin the intrusions are expressed as packages of high amplitude refl ections which are 32 250 m thick and 7 19 km in diameter we observe fi ve main types of intrusion type 1 strata concordant sills type 2 weakly strata discordant trans gressive sills type 3 saucer shaped sills type 4 laccoliths and type 5 hybrid intru sions which have geometric characteristics of intrusion types 1 3 these intrusions are overlain by dome shaped folds which are up to 17 km wide and display up to 210 m of re lief the edges of these folds coincide with the margins of the underlying sills and the folds display the greatest relief where the underly ing sills are thickest the folds are therefore interpreted as forced folds that formed in response to emplacement of magma in the shallow subsurface the folds are onlapped by lutetian middle eocene strata indicat ing they formed and the intrusions were em placed during the latest ypresian ca 48 ma we demonstrate that fold amplitude is typi cally less than sill thickness even for sills with very large diameter to depth ratios suggest ing that pure elastic bending forced folding of the overburden is not the only process ac commodating magma emplacement and that supra sill compaction may be important even at relatively shallow depths based on the ob servation that the sills intruded a shallowly buried succession the discrepancy between fold amplitude and sill thickness may refl ect loss of host rock volume by fland pore fl uid expulsion from poorly lithifi ed water rich beds this study indicates that host rock composition emplacement depth and deformation mechanisms are important controls on the style of deformation that oc curs during intrusive igneous activity and that forced fold amplitude may not in all cases refl ect the thickness of an underlying igneous intrusion in addition the results of this study suggest that physical and numeri cal models need to model more complex host rock stratigraphies and rheologies if they are to capture the full range of deformation mechanisms that occur during magma em placement in the earth s shallow subsurface

geometric characterization of igneous intrusions 3 d seismic insights from the campos basin se brazil abstract igneous intrusions are important for the exploration and appraisal phases of an oilfield due to their impact on petroleum systems their presence can be associated with the generation migration accumulation and entrapment of hydrocarbons in particular 1 sills with low permeability might form barriers to fluid flow and migration 2 sills may re use fracture networks providing insights on fluid migration and interaction s 3 sills may influence source rock maturation 4 sill induced uplifting of overburden and faulting may generate traps and 5 their geometric complexities enables the understanding of the interconnectedness of sill complexes which is the focus of this study therefore we provide a systematic characterization of sill geometries and their morphometric parameters we used three dimensional seismic data calibrated with well logs to interpret sills in the southern campos basin brazil throughout the late cretaceous until the paleogene sills intruded into the cretaceous to the eocene post salt sedimentary sequence including shallow platform carbonates transgressive marls and shales a morphometric analysis assisted by seismic attributes allowed the geometric characterization of sills namely 1 saucer shaped 2 slightly saucer shaped 3 climbing saucer shaped 4 transgressive and 5 rough layer parallel the documented sills comprise a wide range of sizes 0 43 14 35 km2 that increase with depth up to 3 18 km extend vertically from 0 06 to 0 23 km and vary from low 1 82 3 31 to high dip 6 05 15 74 the sill complex area extends over 67 35 km2 this study suggests that a thorough characterization of sill intrusions may have a substantial influence on the prediction of other igneous occurrences the mapped sills might have implications not just on the acoustically similar shallow platform albian carbonates of the macae group but may also provide insightful geometric constraints on the brazilian pre salt igneous intrusions

ne atlantic continental rifting and volcanic margin formation the ne atlantic rift system which has been under extensional deformation since the caledonian orogeny experienced a series of rift episodes in late paleozoic to early cenozoic times fig 1 late paleozoic rifting is poorly constrained particularly with respect to timing however rifted basin geometries inferred to be of this age are observed at depth in seismic data from the flanks of the younger rift structures

submarine volcanic mounds in the pearl river mouth basin northern south china sea a number of enigmatic km scale mound structures have been discovered in the baiyun sag of the pearl river mouth basin using high resolution 2d and 3d seismic data combined with multi beam bathymetry based on detailed seismic characterization we interpret these as sill fed volcanic mounds associated structures include igneous sills trans tensional faults lava flows and compactional drape folds the igneous intrusions and associated mounds were emplaced in the late early miocene c 18 5 ma or shortly thereafter constrained by the onlap relationship between the mounds and their overburden the volcanic mounds are preferentially developed above or adjacent to basement highs indicating a structural control on the igneous plumbing system we propose that the fractures and tectonic faults above the raised basement follow pre existing zones of weakness and may have acted as feeding conduits for the magmatic material the discovery of the early miocene igneous province has important implications for the understanding of the evolution of the pearl river mouth basin and for regional hydrocarbon prospectivity c 2014 elsevier b v all rights reserved

neotectonic regime on the passive continental margin of the northern south china sea abstract between 1989 and 1994 more than 6600 km of reflection seismic profiles were obtained in the south china sea off hong kong with the german research vessel sonne during cruises so 50b so 72a and so 95 a seismo stratigraphic interpretation of this data set leads to a new age assignment of the unconformity t0 which we place within the pleistocene both neogene unconformities t1 and t0 are generated by uplift of the dongsha rise and truncation of their overlying strata this uplift is caused by intrusion of magma into the upper crust our seismic profiles show plutons which have penetrated the sedimentary cover whereby their original stratification in the contact zone is eliminated these magmato tectonic events may be correlated to the two main collision phases between taiwan and the continental margin of east china 5 3 and 3 0 ma ago the collisional events subsequent to the nnw to wnw drift of taiwan transformed the compression into strike slip movements along the continental margin of southeastern china the accompanying stress regime is transtensional with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the manila trench providing the extensional stress the strike slip movements remobilized many of the rift and drift faults providing pathways for magma ascent the tectonic framework of the northern south china sea is characterized by miocene faults trending ne sw these faults are scarce but are distributed throughout the study area pliocene faults striking ene wsw to ne sw are concentrated west of the dongsha islands and are mostly strike slip in character recent faults are generally oriented ne sw subparallel to the synrift faults they result in part from local uplifts where they are normal in character but strike slip motion also occurs most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases

lead pb profiles in red coral skeletons as high resolution records of pollution in the mediterranean sea 26 lead concentrations in long lived corallium species of known age from the mediterranean 27 sea atlantic and pacific oceans were determined by laser ablation inductively coupled 28 plasma mass spectrometer la icpms lead concentrations in a 2000 year old sub fossil 29 mediterranean c rubrum are ca 0 09 0 03 g g for the period 1894 1955 lead 30 concentrations in c rubrum skeletons from the mediterranean are stable within the range 0 2 31 0 4 g g concentrations increase to about 1 1 2 g g during the period 1960 1978 then 32 decrease progressively to stabilize and reach values in the range 0 2 0 4 g g in present day 33 corals these variations can be related to the lead gasoline pollution event that 1 started in 34 the early 1950s with the increase of the numbers of cars in the world and 2 was mitigated 35 by the implementation of new regulations starting in 1975 leading to a return to pre 1950 36 levels in 2000 in the pacific lead concentrations in c japonicum and c konojoi are lower 37 than in the mediterranean c rubrum with values close to 0 17 0 03 g g the lowest lead 38 concentrations in present day samples 0 11 g g are found in c johnsoni and c niobe from 39 the azores islands in the atlantic and in a mediterranean c rubrum from montecristo island 40 one of the least accessible and most protected areas in the mediterranean sea using lead 41 concentrations in c rubrum and in the mediterranean seawaters a partition coefficient kd 42 pb ca calcite pb ca seawater of 13 3 is estimated it allows calculating past and present lead 43 contents in seawater in which corals grew application to corallium species indicates that 44 values endangering human health or threatening the preservation of aquatic ecosystem on 45 long terms were nearly reached or exceeded in mediterranean seawaters at the maximum of 46 the lead gasoline pollution event in the 1980s measurements in c rubrum from different 47 places in the mediterranean indicate that present day seawater concentrations vary between 48 2 40 and 200 pmol kg as expected the lowest concentrations come from protected areas 49 insulated from human activities while the highest come from places close to lead mining or 50 processing sites 51

past and potential tsunami sources in the south china sea a brief synthesis abstract extending across some 3 5 million square km and with coastlines populated by in excess of 80 million people the south china sea scs is bordered by seven independent states understanding the risk of tsunamis in the scs is therefore an imperative especially given the new priorities for the science community following the endorsement by the un general assembly of the sendai framework for disaster risk reduction 2015 2030 our review presents a synthesis of existing literature on the current state of knowledge concerning known tsunamigenic threats but also highlights a number of other potential sources that have so far received less attention or gone largely un or under recognised an overview of the geological evolution of the scs is presented in order to appreciate how the existing structural configuration of the ocean basin is responsible for the presence of a variety of potential tsunamigenic mechanisms traditional thinking places the generation of a large magnitude earthquake at the manila trench subduction zone at the top of the spectrum for tsunami potential with several simulations already available in the literature illustrating wave characteristics resulting from the worst case rupture in addition to the manila trench and other possible earthquake sources however volcanic activity and submarine landsliding of sediment burden on continental shelves on the scs margins represent hitherto fundamentally unquantified tsunami threats although revealed nonetheless by for example the existence of the giant brunei and baiyun submarine slides furthermore in the central scs previously considered essentially devoid of tsunami sources numerous near surface carbonate platforms and coral atolls show evidence of arcuate bight like structures in their planform geometry likewise suggesting their propensity for possible tsunamigenic lateral flank collapse in the current absence of well constrained tsunami probability estimates and scenarios of wave size and propagation features for non earthquake tsunami sources future research priorities lie in two main areas these are 1 improvement of modelling for tsunamigenic submarine failures as well as for earthquakes and 2 a greater focus on geomorphic investigation to identify palaeotsunami deposits on coastlines considered likely to have been impacted in the past and where good preservation potential exists this is needed to establish the magnitude timing frequency of events on holocene timescales the last 10 000 years well beyond historical records thereby improving our capabilities for understanding and forecasting the likelihood and severity of future tsunami risk in the south china sea

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

saucer shaped sill with lobate morphology revealed by 3d seismic data implications for resolving a shallow level sill emplacement mechanism we use 3d seismic data to describe the 3d geometry of a large igneous intrusion the solsikke compound sill and address a number of issues related to sill emplacement the solsikke compound sill formed by amalgamation of a number of sills and exhibits a complex internal morphology dominated by saucer shaped depressions and linear discontinuities one of the saucer shaped sub elements of the compound sill the solsikke lobate sill has a previously unrecognized morphology it has a basal feeder and consists of a bifurcating network of interlinked lobe shaped sill segments we propose two models for the development of this intrusive style based on analogues from igneous systems and hydrofracturing experiments the lobate pattern indicates that the solsikke lobate sill was fed at its deepest point and adopted its geometry through outwards and upwards propagation the feeder location is coincident with a fault intersection suggesting that magma transport from the underlying source exploited the zone surrounding the intersection

new technique for dating igneous sills three dimensional seismic interpretation of tertiary sills within the northeast atlantic margin demonstrates that shallow level 20 km long the fill of the minibasin is dated biostratigraphically as 54 6 55 ma which fits well with radiometric dates for the timing of intrusion of sills around this basin ca 53 55 ma the recognition and dating of onlap fill seismic reflector packages that are delimited by forced folds form a new and useful method for dating shallow level igneous intrusions in sedimentary basins a method that provides independent constraints on radiometric dating techniques similar forced folds are recognized from other basins that have shallow level sills suggesting that the technique presented here may be similarly applicable in comparable geologic settings

geometry internal architecture and evolution of buried volcanic mounds in the northern south china sea abstract high resolution seismic and borehole data were used to characterize a volcanic mound in the northern south china sea including its internal architecture lithological characteristics and evolutionary history on seismic profiles the mound shows a convex geometry similar to an isolated carbonate buildup it was therefore previously seen as a carbonate buildup and a significant hydrocarbon target until an industrial well by7 1 proved its volcanic nature ten seismic facies are identified to analyze the internal architecture of the mound under the constraint of borehole data petrologic analysis based on cuttings and thin sections reveals that the mound is composed of volcanic tuffs siliciclastics carbonates and basalt layers depositions and architecture of the mound are interpreted as a result of an interplay between tephra accumulation during volcanic eruptions wave induced re deposition of volcaniclastics when the volcanic mound emerged above sea level and subsequent siliciclastic carbonate deposition when the volcanic mound was flooded during the phases of volcanic quiescence furthermore the correlation of seismic and well data allows us to reconstruct the entire evolutionary history of the mound from its formation to its demise and final burial this work presents a detailed description of the mound architecture and its genesis and thus provides an analogue for detailed interpretations of similar structures encountered during petroleum explorations in the south china sea or elsewhere

submarine erosional troughs in the northern south china sea evidence for early miocene deepwater circulation and paleoceanographic change abstract the paleoceanography of the south china sea scs is poorly understood although recent cruises and an odp expedition leg 184 have provided a useful general framework here we report previously unrecognized multi km scale sedimentary structures consisting of coupled ridges and troughs within the early miocene strata using high resolution 3d seismic data from the northern scs margin the troughs are interpreted as linear and or arcuate erosional features which truncate the underlying strata they range in orientation from e w in the southern part of the study area to nearly ne sw in the northwestern part of the study area the spacing of erosional troughs varies from less than 0 1 km in the southern part to more than 3 km in the northern part and they are about 50 1500 m in width with a relief of 10 90 m the erosional troughs are parallel to the regional strike of the early miocene slope of the northern scs from their internal geometry context regional distribution and most importantly their orientation relative to the paleo slope gradient at the time of their formation it is argued that they formed due to the action of bottom currents linked to the broader paleo circulation regime in the basin we infer that the paleo bottom currents intruding from the pacific flowed along the northern scs slope resulting in the occurrence of localized erosional troughs as deep water masses impinged on and interacted with the sea floor topography this study provides new insights into the early miocene paleoceanography of the scs and demonstrates the utility of 3d seismic data to enhance our understanding of paleo bottom current circulation regimes

characteristics of surface heat flow in the south china sea a total of 592 heat flow measurements ranging from 8 to 192 mw m 2 78 percent of which are between 50 and 100 mw m 2 have been collected in the south china sea scs to overcome shortcomings such as the uneven distribution of the measurements and the occurrence of abnormal heat flow values the tectonic evolution of different areas and their crustal thickness have been combined in analyzing geothermal characters the results show that the oceanic basins where they are floored by oceanic crust the western part of the southern margin and the western fault system have high heat flow values heat flow along the northern margin of the scs increases from 61 mw m 2 on the shelf to 73 80 mw m 2 in the slope area and in the xisha zhongsha area increases from about 70 mw m 2 to about 85 mw m 2 from the nw to the se heat flow in the nansha spratley islands is about 60 mw m 2 or even higher and decreases from the nw to se the average heat flow of the mekong basin is about 60 mw m 2 which is similar to that of the beibuwan basin on the northern margin heat flow on the eastern margin and on the eastern part of the southern margin is lower especially in the luzon trough where the average heat flow is lower than 40 mw m 2 observed heat flow values in the sw subbasin are generally lower than predicted theoretically from the age of the ocean floor unlike values in the eastern subbasin a high heat flow zone in the lower slope area of the northern margin is recognized for the first time c 2003 elsevier ltd all rights reserved

biogenic mineralization in the ferromanganese nodules and crusts from the south china sea abstract global marine ferromanganese fe mn nodules and crusts host immense metal resources and the metal enrichment mechanism is still in dispute the south china sea scs is one of the largest marginal seas in the western pacific and its northern slope is a passive continental margin with high sedimentary rate a large amount of ferromanganese nodules and crusts have been discovered in the scs northern slope previous investigations shown that the scs nodules crusts are often smaller and thinner and contain higher si and al but lower mn co and ni than the western pacific nodules and crusts in this study high resolution scanning electron microscope hr sem and energy dispersive spectrometer eds were performed to explore the microorganism activities with respect to the nodules crusts formation various biogenic signature and microfossils in the scs fe mn nodules crusts are recorded these bio marks and microfossils present several morphological types tubiform burrows bulbiform organism fossils mould structures cylindrical protozoan globular growth structures isolated spheroidal bacteria and biofilms these mineralized bio marks and microfossils are mostly protozoans belonging to various bacteria biofilm diatoms and coccoliths with mn and or fe on their surface using the electron probe micro analyzer epma the microfossil rich areas contain higher mn than the surrounding microfossil poor areas are observed the abundance of bio marks and microfossils and their geochemical features support a dominant role of microorganism activities in the scs nodule crustal formation we proposed that microorganisms may have served as seeds templates to induce mineral deposition in the nodules and crusts and chemical oxidation and other abiotic mechanisms also contribute to the fe mn oxide formation the biogenic hypothesis provides another perspective to further understand the formation of deep marine fe mn nodules crusts and will be important for exploration of fe and mn metals in the future

geometry and growth of sill complexes insights using 3d seismic from the north rockall trough doleritic sill complexes which are an important component of volcanic continental margins can be imaged using 3d seismic reflection data this allows unprecedented access to the complete 3d geometry of the bodies and an opportunity to test classic sill emplacement models the doleritic sills associated with basaltic volcanism in the north rockall trough occur in two forms radially symmetrical sill complexes consist of a saucer like inner sill at the base with an arcuate inclined sheet connecting it to a gently inclined commonly ragged outer rim bilaterally symmetrical sill complexes are sourced by magma diverted from a magma conduit feeding an overlying volcano with an elongate concave upwards trough like geometry bilaterally symmetrical sills climb away from the magma source from which they originate both sill complex types can appear as isolated bodies but commonly occur in close proximity and consequently merge producing hybrid sill complexes radial sill complexes consist of a series of radiating primary flow units with dimensions up to 3 km each primary flow unit rises from the inner saucer and is fed by primary magma tube primary flow units contain secondary flow units with dimensions up to 2 km each being fed by a secondary magma tube branching from the primary magma tube secondary flow units in turn are composed of 100 m scale tertiary flow units a similar branching hierarchy of flow units can also be seen in bilaterally symmetrical sill complexes with their internal architecture resembling an enlarged version of a primary flow unit from a radial sill complex this branching flow pattern as well as the interaction between flow units of varying orders provides new insights into the origin of the structures commonly seen within sill complexes and the hybrid sill bodies produced by their merger the data demonstrate that each radially symmetrical sill complex is independently fed from a source located beneath the centre of the inner saucer grows by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature these features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening the branching hierarchy of flow units within bilaterally symmetrical sill complexes is broadly similar to that of primary flow units within a radially symmetrical sill complex suggesting that the general features of the laccolith emplacement model also apply

high velocity breakup related sills in the voring basin off norway multichannel seismic reflection profiles in the hel graben v0ring basin reveal a sill complex at approximately 5 km depth it is associated with exceptionally high 7 4 km s 1 seismic wide angle velocities the existence of observable wide angle arrivals shows that the sills act as efficient waveguides seismic reflection data and amplitude modeling constrain the thickness of individual sills to approximately 100 m sonic logs from sills of similar thickness on the nearby utgard high show an average velocity of 7 0 km s 1 such high velocities require an olivine gabbroic sill composition and emplacement under conditions which allowed growth of relatively large crystal sizes a possible reason for such an emplacement environment is the hei graben s role as an intrusion center during breakup volcanism this would provide the necessary duration of the magmatic activity as well as locally increased melt volumes and cooling times sill complexes of this kind decrease the accuracy of determined velocity fields and crustal geometries below the top of the sill complex affecting depth conversion and gravity modeling furthermore the results question the concept of lower crustal bodies as large scale homogeneous accumulations of mafic melt

a crustal structure profile across the northern continental margin of the south china sea an ocean bottom seismometer obs geophysical experiment was carried out across the northern continental margin of the south china sea two dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the obs profile according to the calculation and interpretation of refracted p wave phases the crustal thickness decreases from 22 km obs 1 in littoral area to 8 km obs 15 in deep sea the lower slope structured by volcanism changes sharply in moho depth from 22 to 9 km the volcanoes over the lower slope were markers of ocean continental transition zone a high velocity layer hvl with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope the south china sea was originated by the passive rifting of south china continent and seafloor spreading however geological and geophysical data collected in the northern margin of the south china sea show a small amount of magma intruded into or erupted onto the crust during pull apart and breakup further analysis shows that the hvz in the base of the thinned continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the south china sea magmatism during the crustal extension and breakup is very weak therefore the northern continental margin of the scs is classified as non volcanic passive margin the southern margin of the south china sea has a crust with a steady thickness of 18 24 km which is different from the nor them margin of the south china sea with a gradually thinned crust they constitute an asymmetrically conjugated pair of passive margins c 2001 elsevier science b v all rights reserved

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago

dynamics of sill and laccolith emplacement in the brittle crust role of host rock strength and deformation mode igneous intrusions in sedimentary basins exhibit a great diversity of shapes from thin sheets e g sills cone sheets to massive intrusions e g laccoliths plugs presently none of the established models of magma emplacement have the capability to simulate this diversity because they account for either purely elastic or purely plastic or purely viscous host rocks whereas natural rocks are complex elasto plastic materials in this study we investigate the effects of elasto plastic properties of host rock on magma emplacement using laboratory experiments made of dry granular materials of variable cohesion our results show how the deformation mechanism of the host rock controls the emplacement of magma thin sheet sills form in high cohesion materials which dominantly deform by elastic bending whereas massive intrusions such as punched laccoliths form in low cohesion materials which dominantly deform by shear failure our models also suggest that combined elastic shear failure deformation modes likely control the emplacement of cone sheets our experiments are the first to spontaneously produce diverse geologically relevant intrusion shapes our models show that accounting for the elasto plastic behaviour of the host rock is essential to filling the gap between the established elastic and plastic models of magma emplacement and so to reveal the dynamics of magma emplacement in the earth s brittle crust

seismic reflection imaging and controls on the preservation of ancient sill fed magmatic vents two dimensional seismic reflection data from offshore southern australia image a series of 2 13 km wide by 50 800 m high sub circular middle eocene age mounds the majority of the mounds occur above tips of igneous bodies intruded into the underlying upper cretaceous succession the mounds are interpreted as the seismic expression of submarine volcanic vents which are amongst the largest and oldest examples ever documented these vents are pristine and have been preserved because of their submarine environment of emplacement and burial in a post eruption sediment drape supplementary material uninterpreted version of the seismic sections presented in figure 3 is available at www geolsoc org uk sup18545

crustal structure north of the taiping island itu aba island southern margin of the south china sea abstract based on the multi channel seismic mcs and gravity data offshore north of taiping island itu aba island in the spratly islands nansha islands we revisited the crustal structures in the northern part of the southern margin of the southwest sw sub basin of the south china sea scs the mcs data suggest that the basement structural highs in the southwest margin of the scs are dominated by both fault blocks and volcanic basement structures that probably formed along with the basement faults the gravity modeling results reveal that these volcanic basement structures were probably associated with the high velocity or density lower crust hvdlc suggesting that the southern margin of the sw sub basin serves as an intermediate margin based on the tectonic features in the scs margins including 1 the transition between the magma poor margins of the northwest nw sub basin and intermediate margins of the east and sw sub basins 2 the cessation of the seafloor spreading in the nw sub basin being succeeded by a major ridge jump event which was very likely to reflect an active mantle upwelling event 3 the extensive distribution of the hvdlc beneath in the well investigated northern margin of the east sub basin and as explored in the sw sub basin in this study and 4 basement faulting and volcanism shown in this study that may be related to the hvdlc and hyper extension we proposed a conceptual model to interpret the origin of the hvdlc in the southern margin of the sw sub basin the margin of the scs basin was magma poor at the time it occurred an active mantle upwelling event caused by small scale mantle convection possibly related to the influence of the nascent hainan mantle plume was formed subsequently resulting in a southward ridge jump and the hvdlc beneath the current margins of the east and sw sub basins the east and sw sub basins continued to spread latitudinally dividing their hvdlcs as the margins separated accordingly afterwards the hyper extension in the distal margins may also be responsible for a crust weakening zone wherein the subsequent volcanic events could occur

subsurface fluid flow at an active cold seep area in the qiongdongnan basin northern south china sea abstract the active haima cold seep sites were discovered by the remotely operated vehicle on the western part of the northern slope of south china sea in 2015 and 2016 however the subsurface structures in the seep area are not well studied which prevents the further understanding of the evolution of fluid venting system in the active cold seep area in 2017 a high resolution 2d seismic line transecting the two main seep sites was acquired and processed in this study the subsurface structures were well resolved on the seismic profile the new observations include the widespread subsurface fluid flow features i e chimney structures and pockmarks and the pervasively distributed magmatic activities seismic indicators for hydrothermal vents were also observed on the seismic section this new discovery confirms the contribution of magmatic activities to the evolution of subsurface fluid flow in the study area minor faults under the recognizable resolution of seismic profile which can act as conduits for the subsurface fluid flow were also identified in the fine grained sediment sequences overall these results provide new insights into the evolution of subsurface fluid flow in the study area

plio quaternary sedimentation processes and neotectonics of the northern continental margin of the south china sea abstract analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the south china sea permit the recognition of four quaternary high frequency type 1 sequences of the 4th order deposited during the past ca 690 kyr at the present day shelf edge only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved the prograding complexes can be considered as regressive units accumulated during relative sea level falls they exhibit internal discontinuities which might point to minor sea level fluctuations of the 5th order a preliminary regional relative sea level curve for the past 630 kyr is established using the present positions of the delta fronts mapped the neotectonics curve derived by subtracting eustatic sea level changes from the relative sea level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea level our seismo stratigraphic interpretation documents that the area off hong kong and around the dongsha islands experienced two uplift episodes during the past 5 ma namely at the miocene pliocene boundary and at the end of the lower middle pleistocene respectively these uplift events which are centred on the dongsha rise led to its subaerial exposure and to the erosion of the pliocene and most of the pleistocene strata the change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato tectonic uplift was caused by a reorientation of the tectonic regime the recent depositional environment on the northern continental margin of the south china sea is dominated by sediment accumulation within the inner shelf and the zhujiang pearl river estuary the outer shelf and upper slope especially around the dongsha islands are characterised by bypass of terrigenous material the sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits it overlies oceanic as well as transitional crust

seismic analysis of polygonal fault systems in the great south basin new zealand abstract polygonal fault systems pfs consisting of networks of layer bound normal faults are analyzed for eocene strata in the great south basin new zealand an advanced fault enhancement and skeletonization method is applied to delineate faults using 3d seismic data from the great south basin the process sharpens structural and stratigraphic discontinuities and smears the incoherent noise on coherence to obtain a skeletonized fault probability volume which can be directly used to extract and map fault geometries the characteristics of the polygonal faults in cross section planform and 3d space were studied the faults dip approximately 50 with displacements on a single fault ranging from tens of meters to a hundred meters the fault planform patterns are polygonal but also related to the regional horizontal stress anisotropy caused by slope changes of the basal unit the patterns vary from linear for high slopes rectangular for moderate slopes and polygonal for low slopes two preferred orientations may reflect the superposition of deep cretaceous trends on the polygonal system in the eocene strata a local concentric pattern with outward dipping normal faults is related to passive or active draping above a circular plutonic volcanic structure the genetic mechanism of the polygonal fault systems is interpreted to be related to volume loss and shear failure related to opal a ct transition within the sediments

deep seismic structure of the northeastern south china sea origin of a high velocity layer in the lower crust we present a 2 d seismic tomographic image of the crustal structure along the obs2012 profile which delineates the moho morphology and magmatic features of the northeastern south china sea margin the image was created by forward modeling rayinvr and traveltime tomographic inversion tomo2d overall the continental crust thins seaward from 27 km to 21 km within the continental shelf across the zhu i depression and dongsha rise with slight local thickening beneath the dongsha rise accompanying the increase in the moho depth the dongsha rise is also characterized by 4 7 km thick high velocity layer hvl 7 0 7 6 km s in the lower crust and exhibits a relatively high velocity 5 5 6 4 km s in the upper crust with a velocity gradient lower than those of the zhu i depression and tainan basin across the continental slope and continent ocean transition cot which contain the tainan basin the crust sharply thins from 20 km to 10 km seaward and a 2 3 km thick hvl is imaged in the lower crust we observed that volcanoes are located only within the cot but none exist in the continental shelf the dongsha rise exhibits a high magnetic anomaly zone and different geochemical characteristics from the cot based on those observations we conclude that the hvl underlying the cot is probably extension related resulting from the decompression melting in the cenozoic whereas the hvl beneath the dongsha rise is probably arc related and associated with the subduction of the paleo pacific plate these findings are inconsistent with those of some previous studies

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

tectonic characteristics and evolution history of the pearl river mouth basin abstract on the basis of the new understandings from tens of thousand of kilometres of geophysical material and over 60 exploration and evaluation wells providing data on the pearl river mouth basin prmb this paper analyses the special tectonic position of the prmb where three major plates i e the eurasian the pacific and the indo australian plates meet and interact the characteristics of the basin geological structure and its tectonic evolution are also discussed situated on continental and transitional crust the prmb is a mesozoic cenozoic oil and gas bearing basin developed on caledonian folding basement which was reformed during the mesozoic in the process of its formation and evolution the prmb underwent extension slight compression and re extension with the eruption of intermediate acid and basic magma meanwhile it formed double structural layers with faulting below and depression above and sediments were laid down with marine facies following continental facies hydrocarbons accumulated from continental source rocks in the marine reservoir rocks by using a fracture structure model of the uplift and depression the mechanism of the prmb and its evolution history have been interpreted

constraining the depth and timing of large scale conical sandstone intrusions kilometer scale sandstone intrusions a recently recognized end member of the spectrum of soft sediment deformation structures are important components of many deep water sandstone reservoirs they result from the remobilization of considerable volumes of sand during early stages of burial this paper uses three dimensional seismic data calibrated to nearby wells to describe an extensive system of large downward tapering conical sandstone intrusions from the faeroe shetland basin on the uk atlantic margin the intrusions are derived from a middle eocene submarine fan and are injected vertically upward through overlying highly faulted claystones to form conical bodies that interconnect across the 700 m thick claystone interval to feed a set of shallow intrusions located within a few hundred meters of the paleoseabed the forcible intrusion of these shallow sandstone bodies produced complementary folding of the contemporaneous seabed the subsequent onlap of these seabed domal folds took place immediately after the intrusion event and by correlation to biostratigraphic data from nearby wells we date these intrusions as late miocene this is the first time that both the age and emplacement depth range of a system of large scale sandstone intrusions have been constrained

structure stratigraphy and basin subsidence of tertiary basins along the chinese southeastern continental margin abstract in southeastern china offshore tertiary basins extend along the broad continental shelf from taiwan to hainan island these basins share similar characteristics of structure stratigraphy and tectonics based on their age and tectonic framework these tertiary basins can be divided into paleogene basins and neogene basins however observations of extensional structures indicate that the paleogene basins are rift basins with predominant structural features of ne sw trending half grabens and fault blocks on a regional scale these half grabens and adjacent uplifts represent a horst and graben structural style neogene basins are downwarp basins lying on the tilting continental shelf upper tertiary sequences are relatively undeformed but locally exhibit minor pliocene pleistocene folding and faulting seismic stratigraphy and well data indicate that the early tertiary strata are commonly tilted and were structurally disturbed as nonmarine to marginal marine facies that were deposited in the wedge shaped half grabens late tertiary strata are generally undisturbed marine facies which accumulated in the enlarged downwarp basins overlying the infilled half grabens the tectonic history of these basins shows two stages of basin subsidence first early basement rifting and basin subsidence accompanying displacement along the border faults formed the half grabens which received sediments in the late cretaceous to middle eocene second late thermal subsidence owing to cooling of the continental crust predominated and resulted in a tilting and subsiding continental shelf upon which relatively flat marine facies were deposited in the late tertiary

hybrid flow sills a new mode of igneous sheet intrusion three dimensional 3 d seismic mapping of the vigra sill complex has revealed a series of shallow level lobate sills this complex was emplaced ca 55 ma as part of the igneous activity associated with breakup of the northeast atlantic margin the complex consists of discordant sheets some of which are remarkable in that they have an axial seismic amplitude anomaly along their lengths the anomalies are interpreted as evidence for the development of magma tubes that formed in the subsurface at depths between 200 and 400 m and that fed the lobate sill segments we argue that this sill complex represents a hybrid between expansion of sheets by flow and fracture propagation these hybrid flow sills are suggested to result from magma emplacement into high porosity and water saturated sediments at low confining pressures where the coalescence of flow lobes results in the formation of magma tubes capable of propagating 8 km and terminating in the formation of new flow lobes

post rift submarine volcanic complexes and fault activities in the baiyun sag pearl river mouth basin new insights into the breakup sequence of the northern south china sea abstract post rift volcanisms and fault activities are significant for understanding the tectonic sedimentary evolution of rifted continental margins and associated hydrocarbon entrapments in this study a series of post rift fault associated volcanic activities have been found in the northern continental margin of the south china sea scs however their episodes and relationships with the progressive continental breakup are still doubtful here new 2d 3d seismic borehole dating and biostratigraphic data are used to investigate the characteristics of the post rift volcanism and fault activities in the baiyun sag bys pearl river mouth basin the newly found fault associated volcanic complexes include thirteen submarine volcanic mounds and associated lava flows together with igneous sills that are mainly composed of basalts and tuffs seismic stratigraphic analysis combined with k ar dating from cores confirms that post rift volcanism in the bys climaxed along with the breakup of the scs mainly in three episodes 1 the first episode near oligocene miocene boundary 23 3 ma 2 the second at the middle early miocene 17 6 ma and 3 the new found third episode at the late early miocene 17 1 ma also fifty three syn sedimentary faults are interpreted which are characterized by a wnw trending normal fault group separated by an ene trending transcurrent fault group and there is evidence that these fifty three faults were long lived from ca 32 17 1 ma and served as important conduits for the upward migration of the magma the three episodes of volcanism and tectonic fault activities are related to the progressive continental breakup in the northern scs margin and they represent the tectonic signature of the early stage of the post rift subsidence after the lithospheric breakup which extends to the top of a hypothetical breakup sequence 32 17 1 ma in the bys furthermore this study proves that the diachronous continental breakup in the scs margin can result in corresponding changes in depositional architectures along with a breakup sequence characterized by the deposition of a sandstone carbonate shale regressive transgressive cycle the sedimentological changes and associated tectonic features recorded in the baiyun sag suggest an exceptionally active tectonic setting in the time of the formation of the breakup sequence early oligocene early miocene along the northern scs margin

eocene sandstone intrusions in the tampen spur area norwegian north sea quad 34 imaged by 3d seismic data the eocene of the northern north sea is characterised by fine grained mudstones and isolated sandbodies three dimensional 3d seismic data reveal that the eocene mudstones are intensely deformed by polygonal faulting and contain numerous discordant amplitude anomalies the anomalies identified in the tampen spur area are similar to discordant anomalies previously described from the eocene in the south viking graben and the outer moray firth detailed mapping shows that the anomalies are often conical in three dimensions with dimensions ranging from 100 to 200 m height and a few hundred metres to a few kilometres lateral extent well calibrations show that the anomalies arise from sandstones tens of metres thick encased in mudstone the discordant amplitude anomalies are interpreted as large scale conical sandstone intrusions fed from deeper paleocene sandbodies individual conical intrusions may contain millions of cubic metres of sandstone and may provide fluid migration paths potential reservoirs and pose a drilling risk when exploring for deeper targets

saucer shaped intrusions occurrences emplacement and implications abstract magmatic intrusions and fluidized injected sands represent the two main types of sheet intrusions in the earth s crust in this paper we show that both intrusion types often display a saucer like geometry as revealed by 3d seismic imaging and field observations saucer shaped intrusions are fairly common in sedimentary basins as for example offshore in the norwegian and north sea basins and onshore in the karoo basin of south africa the formation of the saucer geometry is controlled by the low viscosity of the injected fluid and by the interaction between a growing shallow hydraulic fracture and overburden deformations statistics gathered from observations and modelling show a linear relationship between the depth of emplacement and the size of the saucer shaped intrusions we anticipate future cross disciplinary studies aiming to discover other occurrences of saucer shaped intrusions and to identify the physical processes controlling the development of this fundamental geometry

volcano growth mechanisms and the role of sub volcanic intrusions insights from 2d seismic reflection data abstract temporal and spatial changes in volcano morphology and internal architecture can determine eruption style and location however the relationship between the external and internal characteristics of volcanoes and sub volcanic intrusions is often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data we use high quality 2d seismic reflection data from the ceduna sub basin offshore southern australia to quantitatively analyse 56 pristinely preserved eocene age volcanogenic mounds and a genetically related network of sub volcanic sills and laccoliths detailed seismic mapping has allowed the 3d geometry of each mound to be reconstructed and distinct seismic facies within them to be recognised forty six continental basaltic shield volcanoes have been identified that have average flank dips of 3 parallel seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material suggesting that a series of temporally separate eruptions emanated from a central vent the shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill complex eight volcanogenic hydrothermal vents which are also associated with the lateral tips of sills were also recognised and these appear to have formed from the seepage of intrusion related hydrothermal fluids onto the seafloor via emplacement induced fractures this work highlights that deformation patterns preceding volcanic eruptions may i be offset from the eruption site ii attributed to intrusions with complex morphologies and or iii reflect magma movement along pre existing fracture systems these complexities should therefore be considered in eruption forecasting models that link pre eruption ground deformation to subterranean magma emplacement depth and volume more generally our study highlights the key role that seismic reflection data can play in understanding the geometry distribution and evolution of ancient and modern volcanic systems

paleogene igneous intrusion and its effect on thermal maturity of organic rich mudstones in the beibuwan basin south china sea abstract the seismic drilling and logging data reveal that a large scale igneous intrusion with a width of 14 km and a maximum thickness of 170 m intruded within the paleogene liushagang formation in the fushan depression beibuwan basin south china sea scs in this study we report the geochemistry and sr nd pb hf isotopic compositions of the igneous rocks and evaluate the thermal effect induced by this large scale igneous intrusion on the host rocks the analyzed igneous samples exhibit strong enrichment in light rare earth elements lree and large ion lithophile elements lile having characteristics similar to intra plate oceanic island basalts oib the sr nd pb hf isotopic data display narrow ranges e g 87sr 86sri 0 7042 0 7044 143nd 144ndi 0 5128 0 5129 206pb 204pbi 18 90 18 94 ehf t 7 56 9 60 geochemical and isotopic compositions suggest a mixed mantle source between depleted mid ocean ridge basalt morb mantle dmm like mantle and enriched mantle type ii emii possibly the hainan mantle plume vitrinite reflectance values major mineralogical changes together with a maturity related biomarker ts ts tm all reveal significant thermal effect induced by the igneous intrusion vitrinite reflectance values of the host rock are up to 2 5 in the intrusion region whereas lower reflectance values 0 62 0 73 occur in the unaffected area of the same strata moreover our results suggest that the host rocks above the igneous intrusion are characterised by higher maturity than below which should be attributed to the different behavior of hydrothermal fluids these observations suggest that the thermal effect of large scale thick igneous intrusions is much more intense than that of thin igneous intrusions and the behavior of hydrothermal fluids induced by magmatic intrusive events should be a critical impact factor during heat transfer process