formation and deformation of hyperextended rift systems insights from rift domain mapping in the bay of biscay pyrenees the bay of biscay and the pyrenees correspond to a lower cretaceous rift system including both oceanic and hyperextended rift domains the transition from preserved oceanic and rift domains in the west to their complete inversion in the east enables us to study the progressive reactivation of a hyperextended rift system we use seismic interpretation gravity inversion and field mapping to identify and map former rift domains and their subsequent reactivation we propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen this study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation two spatially and temporally distinct rift systems can be distinguished the bay of biscay parentis and the pyrenean basque cantabrian rifts while the offshore bay of biscay represent a former mature oceanic domain the fossil remnants of hyperextended domains preserved onshore in the pyrenean cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain both domains accommodated most of the shortening the final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes the complex 3 d architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system these results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the bay of biscay and pyrenean domains

new models for evolution of magma poor rifted margins based on a review of data and concepts from west iberia and the alps direct observation and extensive sampling in ancient margins exposed in the alps combined with drill hole and geophysical data from the present day iberia margin result in new concepts for the strain evolution and near surface response to lithospheric rupturing at magma poor rifted margins this paper reviews data and tectonic concepts derived from these two margins and proposes that extension leading to thinning and final rupturing of the continental lithosphere is accommodated by three fault systems each of them characterized by a specific temporal and spatial evolution during rifting of the margin by its fault geometry and its surface response the data presented in this paper suggest that margin architecture and distribution of rift structures within the future margin are controlled first by inherited heterogeneities within the lithosphere leading to a contrasting behaviour of the future distal and proximal margins during an initial stage of rifting the place of final break up appears to be determined early in the evolution of the margin and occurs where the crust has been thinned during a first stage to less than 10 kilometres during final break up the rheology of the extending lithosphere is controlled by the thermal structure related to the rise of the asthenosphere and by serpentinization and magmatic processes

structural style formation of low angle normal fault and its controls on the evolution of baiyun rift northern margin of the south china sea abstract recent studies of high resolution seismic reflection profiles in the northern rifted margin of the south china sea revealed that low angle normal faults dominated the structural evolution of deepwater basins rather than high angle normal faults solely as was previously assumed however none of the studies proposed kinematic restorations of the fault system and the relationship to continental margin formation the baiyun rift is located in the slope of the northern margin of the south china sea underlain by extremely thinned continental crust it is filled with a relatively complete sequence of cenozoic sediments up to 10 km and has been considered the best documented deepwater basin basin wide 3d seismic data together with the available deepwater well data have allowed the structural framework to be built and tectono stratigraphic history of the baiyun rift to be traced in detailed from the rift stage a quantitative study of the primary geometry and kinematics of the major faults can be performed consequently results show the inception of the rift is characterized by faults slipped at high angles the later stage mid eocene of intensive extension is dominated by a fault system with large horizontal displacements 10 km and initial low dips

hyper extended rift systems in the xisha trough northwestern south china sea implications for extreme crustal thinning ahead of a propagating ocean abstract from the apex of the nw sub basin of the south china sea we present new long cable deep penetration seismic profiles and deepwater drillings together with corrected seismic interpretations from previous studies structural mapping demonstrates that the xisha trough is characterized by a hyper extended rift system that shows evidence of extremely thinned crust and rotated fault blocks a series of ne nee and w e striking listric normal faults along the xisha trough which merge at depth into moho reflection record strongly extensional deformation based on the absence of an acoustic basement beneath a wedge shaped rifted sequence we document three diapiric magma structures exiting the moho and penetrating into the extremely thinned continental crust which is covered by a cenozoic sequence for the xisha trough we can demonstrate based on seismic data and calculated fault slip rates the faults bounding the xisha trough were initially formed by distributed rifting and were reactivated and focused on faulting along the axis of the xisha trough however the peak faulting migrated along the margin strike from east to west and terminated at the apex of the xisha trough one of the key processes controlling the evolution of the xisha trough is depth dependent extension which may arise from differential lithospheric stretching by regional dynamic lower crustal mantle flow

40ar 39ar geochronological constraints on the tectonothermal evolution of the eastern segment of the sveconorwegian orogen south central sweden

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

different expressions of the crustal structure across the dongsha rise along the northeastern margin of the south china sea abstract this study presents two long cable deep penetration multi channel seismic reflection images and associated gravity modeling to delineate structures and magmatic features that occur along the margins of the eastern and western dongsha rise in the northeast south china sea scs these data show approximately symmetrical sags imaged on the shelf but the structures begin to vary in multiple ways along the eastern and western dongsha rise after crossing the continental shelf at the slope break an anticline with two thrust faults and a mesozoic unconformity are imaged on the eastern dongsha rise whereas negative flower structures are detected on the western dongsha rise most large scale normal faults sole into a mid or lower crustal detachment below the lower slope on the eastern dongsha rise whereas some uplifts with small fault offsets were imaged at the lower slope and seaward dipping tilted fault blocks were imaged between the lower slope and oceanic basin on the western dongsha rise magmatism expressed by different types such as intrusions volcanoes and sills was active since at least 5 5 ma and magmatic deposits appear to be well developed on the eastern dongsha rise of the northeastern scs margin gravity modeling showed that the crust below the lower slope oceanic basin in the eastern dongsha rise is hyper extended continental crust underplated by a high velocity layer with a maximum thickness of 9 4 km below the slope break rather than thickened oceanic crust the continent ocean transition zone cot has a broader extent on the eastern dongsha rise compared to the western dongsha rise pure shear deformation and lower crustal flow have led to the formation of the crustal structural contrasts and the wide northeastern continental margin of the scs

anisotropic rayleigh wave phase velocity maps of the sunda plate abstract we explore the rayleigh wave phase velocity and shear velocity structures beneath sunda plate over a broad period range of 30 150 s and 5 100 km the two stations technique was used to measure dispersion curves from the waveforms of 19 233 teleseismic events 1998 2018 recorded worldwide by 75 broadband seismic stations spread around the sunda plate the interstation path specific dispersion curves are then inverted for high resolution isotropic and azimuthally anisotropic phase velocity maps in the frequency range 30 150 s as well as for shear velocity model between 5 and 100 km main findings include a strong dichotomy with fast velocities located beneath the south china sea and the sunda shelf compared with slow velocities found beneath the surrounding regions at short periods our model also exhibits very slow velocities beneath the hainan plume at lithospheric and asthenospheric depths the complex anisotropy in the region at shorter periods contrasts with the pattern observed at longer periods sampling the asthenosphere and is consistent with the absolute plate motions in the region

stable isotope stratigraphy of holocene speleothems examples from a cave system in rana northern norway high precision tims u series dates and continuous stable oxygen and carbon isotope profiles of a 4000 year stalagmite record from rana northern norway are presented and compared with data from two other speleothems from the same cave the dating results yield ages from 3875 34 to 296 3 years before ad2000 with 2s errors from 0 5 to 1 the overall growth rate is 35 mm ka corresponding to a temporal resolution of 29 years mm the stalagmite is tested for isotopic equilibrium conditions where all hendy tests except one indicate isotopic equilibrium or quasi equilibrium deposition both the stable oxygen and carbon isotope records reveal a strong and abrupt enrichment in the near top measurements this corresponds in time to the opening of a second cave entrance in the late 1960s which caused changes in the cave air circulation the stable oxygen isotope signal is enriched compared to the modern value over the last 300 years indicating a negative response to temperature changes likewise the stable carbon isotope record is enriched in this period however both of the stable isotope records are shown to be significantly enriched compared to the isotope ranges displayed by other stalagmites in the same cave and this questions the reliability of the proxy records derived from the presented stalagmite still a general good correspondence of large scale fluctuations is found between the three stable oxygen isotope records from this cave the stable carbon isotope records show large variations within the cave and are believed to be governed by soil zone conditions percolation pathways and possibly driprates q 2001 elsevier science b v all rights reserved

numerical modeling of failed rifts in the northern south china sea margin implications for continental rifting and breakup abstract failed rifts record important information of continental extension and breakup process in the northern south china sea scs margin the tainan southern depression and the baiyun sag to the east are characterized with lower crust high velocity anomalies lchva and intracrust detachment faults whereas the xisha trough to the west develops on a larger scale with crust cutting normal faults and absence of lchva these contrasts indicate different rifting processes between the northeastern and northwestern scs 2d numerical modeling is performed to understand the formation mechanism of these failed rifts two types of mechanisms are proposed i syn rift competitive type and ii rift migration type with a half extension rate of 2 cm yr and 1 5 cm yr respectively in type i two rifts develop initially on the shoulders of the weak zone but they compete with each other during extension one rift becomes dominant to furnish the final breakup whereas the other one is abandoned the crust structure of this type fits the observations in the baiyun sag and the tainan southern depression however in type ii only one rift develops at the beginning the initial rifting center will migrate and the final continental breakup will occur at a place far from the initial rifting location in this type normal faults cut through whole crust and wide extensional margins will form such as observed in the xisha trough our results suggest that the depth dependent extension of the scs is strongly heterogeneous resulting primarily from varying extensional rates

large scale erosional response of se asia to monsoon evolution reconstructed from sedimentary records of the song hong yinggehai and qiongdongnan basins south china sea

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

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

crustal structure and inferred rifting processes in the northeast south china sea abstract taiger project deep penetration seismic reflection profiles acquired in the northeastern south china sea scs provide a detailed view of the crustal structure of a very wide rifted continental margin these profiles document a failed rift zone proximal to the shelf a zone of thicker crust 150 km from the shelf and gradually thinning crust toward the cob spanning a total distance of 250 300 km such an expanse of extended continental crust is not unique but it is uncommon for continental margins we use the high quality images from this data set to identify the styles of upper and lower crustal structure and how they have thinned in response to extension and in turn what rheological variations are predicted that allow for protracted crustal extension upper crustal thinning is greatest at the failed rift uc 7 5 but is limited farther seaward uc 1 2 we interpret that the lower crust has discordantly thinned from an original 15 17 km to possibly less than 2 3 km thick beneath the central thick crust zone and more distal areas this extreme lower crustal thinning indicates that it acted as a weak layer allowing decoupling between the upper crust and the mantle lithosphere the observed upper crustal thickness variations and implied rheology lower crustal flow are consistent with large scale boudinage of continental crust during protracted extension

the sedimentary and tectonic evolution of the yinggehai song hong basin and the southern hainan margin south china sea implications for tibetan uplift and monsoon intensification 1 the yinggehai song hong basin is one of the world s largest pull apart basins lying along the trace of the red river fault zone in the south china sea south of hainan island this basin crosscuts the rifted margin of the northern south china sea in this paper we present for the first time a regional compilation of multichannel seismic reflection data from both the strike slip and rifted margins the basins started to open after similar to 45 ma especially after similar to 34 ma the yinggehai basin was folded and inverted in the middle miocene after 21 ma in the north and 14 ma in the south before rapidly subsiding again after similar to 5 ma because of continued tectonism this subsidence has caused shale diapirism especially driven by associated sedimentation in the late pliocene 2 6 2 0 ma extension along the adjacent south hainan margin shows preferential lower crustal extension suggestive of lower crustal flow increasing toward the continent ocean transition during breakup sediment supply is reconstructed to peak in the middle miocene then falls between 14 and 10 3 ma to reach a low in the late miocene however rates rose again in the pliocene pleistocene the red river sediment budget is incompatible with climate models that propose stronger monsoon rains starting at 8 ma or with large scale river capture away from the red river after similar to 10 ma both lines of evidence point to major uplift in the red river drainage being middle miocene or older the recent preindustrial red river carried much more sediment than the average pleistocene accumulation rate indicating modest sediment buffering onshore at least in recent geologic time

geochemistry of coeval mesozoic plutonic and volcanic suites in hong kong middle jurassic to lower cretaceous intermediate to silicic plutonic and volcanic rocks of hong kong record a transition from calc alkaline through high k calc alkaline to transitional shoshonitic compositions with time close spatial and temporal associations among comagmatic volcanic plutonic pairs indicate that magmatism occurred in discrete episodes mostly of less than one million years duration synchronous high k calc alkaline and transitional shoshonitic magmatic activity during at least one pulse suggests a relatively rapid transition from a subduction related to an extension related tectonic setting geochemical signatures indicate that the magmatic suites have a mantle origin with a decreasing crustal contribution from two distinct sources the earliest mantle derived magmas interacted strongly with a dominantly archaean crustal protolith younger magmas show evidence for interaction with a dominantly proterozoic crustal protolith the strongest mantle influence is shown by magmas which were intruded along the boundary between the two dominant crustal sources this interface marks a deep crustal discontinuity which promoted the passage of magmas to the surface

the structure and formation of diapirs in the yinggehai song hong basin south china sea abstract the occurrence of shale diapirs in the yinggehai song hong ygh sh basin is well documented as is their association with big petroleum fields in order to better understand how and why the diapirs form we performed a detailed geophysical analysis using a new regional compilation of high resolution two and three dimensional seismic reflection data as well as drilling data that cover the diapirs in ygh sh basin as many as 18 diapirs were identified and are arranged in six n s striking vertical en echelon zones on seismic reflection sections gas chimney structures diapiric faults and palaeo craters are genetically linked with the process of diapirism here we use geophysical and geological observations to propose a three stage model for diapirism initiation emplacement and collapse during these three stages different diapiric structure styles are formed which we describe in detail these include buried diapirs piercing diapirs and collapsed diapirs we link the diapirism to activity on the offshore continuation of the red river fault as shown on our high resolution seismic reflection data which is also related to a high paleogeothermal gradient caused by crustal thinning we also recognize the role of loading by the very large volume of sediment eroded from the edges of the tibetan plateau and delivered by the red river to the basin

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

imaging a lithospheric detachment at the continent ocean crustal transition off morocco abstract the sismar seismic survey on the moroccan atlantic margin recorded deep penetration images of the continent ocean boundary this paper focuses on the 3d observation of a landward dipping reflector overlaid by a layered unit the deep part of the reflector plunges towards the continent beneath thinned continental crust whereas its upper part finishes at the top of the basement in a transition zone where likely volcanics dipping reflectors are visible and where a magnetic anomaly named s1 marks the continent ocean boundary location as the landward dipping reflector crosses the moho it is interpreted as a lithospheric detachment with associated volcanic material originating from the asthenospheric mantle observations are used i to build a 2d model to explain the mechanisms of the lithospheric breaking off between moroccan margin and its conjugate canadian margin the landward dipping reflector allowing mantle exhumation ii to propose an ene wnw trend for the initial rifting extension in this part of atlantic during late triassic direction compatible with that of the southern grand banks transform margin

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

geodynamics of the south china sea abstract the beginning of seafloor spreading in the south china sea scs is now established from iodp drilling leg 349 at 33 ma chron 12 32 ma is the oldest chron identified in the scs the nature of the crust of the northeastern part of the scs located north of chron c12 where chrons 15 to 17 were previously identified is not oceanic but thinned continental crust intruded by volcanic elongated features emplaced 17 22 ma ago based on magnetic anomaly identifications the end of the scs spreading could be either 15 5 20 5 ma briais et al 1993 barckhausen et al 2014 or something else however as post spreading magmatic activity 13 3 5 ma largely masks the spreading fabric in particular near the axis of the east sub basin published locations of the axial magnetic anomaly extinct spreading axis and spreading rates are not reliable a contoured map of the extremely dense set of magnetic data shows that a few magnetic lineations belonging to the magnetic seafloor spreading fabric are still preserved and parallel to the n055 bathymetric seafloor spreading trends identified on swath bathymetric maps in the central part of the scs suggesting that the extinct ridge axis is n055 trending with potential n145 transform faults based on published swath bathymetric data oceanic domains with different seafloor spreading lineaments have been delimited n055 n075 and n085 and provide important constraints used to propose a kinematic sketch of the scs opening as a consequence the zhongnan faults zone located between the east and southeast sub basins acted as a major fracture zone system during the scs opening with horizontal offsets varying from 50 km to 140 km the flow line pattern defined from the seafloor spreading lineaments and the few identified fzs have been used to highlight conjugate segments of continental margins during the first phases of opening of the scs from the fit of continents to chron c10 30 ma the n175 extension observed in the xisha trough and eventually south of the macclesfield bank extends to the qui nhon ridge located along the eastern margin of vietnam in the southward prolongation of the red river fault system normal faults curve toward the south with a horsetail geometry interpreted as evidence for a few tens of kilometers of dextral motion along the qui nhon ridge since chron 10 and until the end of scs opening the plate boundary located between the southern south china sea sscs and eu plates jumped westward several times from the location of the ulugan fault near palawan to the western limit of the southwest basin explaining the progressive formation of the scs from east to west and giving the characteristic v shape of the scs the opening of the whole scs is linked and occurred simultaneously with the northward subduction of the proto scs whose suture is located south of palawan and extends westwards in north borneo

spatial and temporal evolution of rifting and continental breakup in the eastern black sea basin revealed by long offset seismic reflection data the age and distribution of the syn rift and early post rift infill records the spatial and temporal distribution of extension and breakup processes in a rift basin the eastern black sea basin ebsb is thought to have formed by back arc extension during cretaceous to early cenozoic time however a lack of direct constraints on its deep stratigraphy leaves uncertainties over the time duration and location for rifting and breakup processes in the basin here we use the enhanced imaging provided by 2d long offset seismic reflection profiles to analyze the deep structural and stratigraphic elements of the ebsb based on these elements we infer the presence of two distinct late cretaceous syn rift units recording initial extension rift stage 1 over the continental highs shatsky ridge and the mid black sea high followed by strain localization along the major basin bounding faults and rift migration towards the basin axis rift stage 2 overlying these units palaeocene eocene and oligocene units show a syn kinematic character in the nw with evidence for ongoing extension until oligocene time towards the se these sequences are instead post kinematic directly overlaying a basement emplaced during breakup we interpret the palaeocene oligocene units to record the time spanning from the initiation of breakup late cretaceous palaeocene in the se to the end of extension oligocene in the nw the first ubiquitously post rift infill is the lower miocene maykop formation our results highlight the along strike temporal variability of extension and breakup processes in the ebsb

seismic imaging of the transitional crust across the northeastern margin of the south china sea abstract crustal structure across the passive continental margin of the northeastern south china sea scs is presented based on a deep seismic survey cooperated between taiwan and china in august 2001 reflection data collected from a 48 hydrophone streamer and the vertical component of refraction reflection data recorded at 11 ocean bottom seismometers along a nw se profile are integrated to image the upper 1 6 2 4 km s lower 2 5 2 9 km s and compacted 3 4 5 km s sediment the upper 4 5 5 5 km s middle 5 5 6 5 km s and lower 6 5 7 5 km s crystalline crust successively the velocity model shows that the thickness 0 5 3 km and the basement of the compacted sediment are strongly varied due to intrusion of the magma and igneous rocks after seafloor spreading of the scs furthermore several volcanoes and igneous rocks in the upper middle crust 7 10 km thick and a high velocity layer 0 5 km thick in the lower crust of the model are identified as the ocean continent transition oct below the lower slope in the northeastern margin of the scs a thin continent nw of the oct and a thick oceanic crust se of the oct in the continental margin of the northeastern scs are also imaged but these transitional crusts cannot be classified as the oct due to their crustal thickness and the limited amount of the volcano the magma and the high velocity layer the extended continent next to the gravity low and a sag zone extended from the sw taiwan basin may have resulted from subduction of the eurasian plate beneath the manila trench whereas the thick oceanic crust may have been due to the excess volcanism and the late magmatic underplating in the oceanic crust after seafloor spreading of the scs

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

continental lithospheric thinning and breakup in response to upwelling divergent mantle flow application to the woodlark newfoundland and iberia margins abstract depth uniform stretching is not the dominant deformation process for thinning continental lithosphere leading to breakup it cannot explain the observed depth dependent lithosphere stretching and mantle exhumation at rifted continental margins depth dependent lithosphere thinning in which stretching of the lower crust and lithosphere mantle greatly exceeds that of the upper crust has been observed at many non volcanic and volcanic rifted continental margins including conjugate margin pairs passive continental margins show a paucity of brittle deformation in the upper crust during continental lithosphere thinning leading to breakup and sea floor spreading initiation a new model of rifted continental margin formation has been developed that assumes that deformation and thinning of continental lithosphere leading to breakup occurs in response to an upwelling divergent flow field within continental lithosphere and asthenosphere and that this deformation evolves into sea floor spreading the new model successfully predicts depth dependent stretching of continental margin lithosphere for both non volcanic and volcanic margins and mantle exhumation at non volcanic margins both of which are observed but are not explained by existing depth uniform continental lithosphere stretching models the new model provides a balance of extensional strain supplies an explanation for the paucity of synrift brittle deformation and offers a simple transition from prebreakup lithosphere thinning to sea floor spreading the observed diversity of rifted continental margin structure and width of the ocean continent transition can be explained by variability in the form of the upwelling divergent flow field the new upwelling divergent flow model of continental lithosphere thinning leading to continental breakup successfully predicts the observed bathymetry and margin geometry for the most recent segment of sea floor spreading initiation in the woodlark basin in the western pacific and the observed bathymetry and free air gravity anomaly for the newfoundland and iberian margins

lower crustal extension across the northern carnarvon basin australia evidence for an eastward dipping detachment asymmetry and strain partitioning along conjugate margins are often explained in terms of detachment faults nevertheless cogent evidence for their existence remains limited furthermore even when inferred detachment faults are imaged seismically it is difficult to demonstrate that differential displacement has occurred across these surfaces we present tectonic and stratigraphic evidence from the northern carnarvon basin northwest australia that documents the existence of an intracrustal eastward dipping detachment by integrating sequence stratigraphy with kinematic and isostatic models of basin development we conclude that the northern carnarvon basin was formed as a consequence of four extension events 1 a broadly distributed late permian event 2 a predominantly localized rhaetian event responsible for the inception of the barrow and dampier subbasins 3 a localized callovian fault reactivation within the barrow dampier subbasins and 4 a tithonian valanginian event that generated large post valanginian regional subsidence across the northern carnarvon basin with only minor accompanying brittle deformation and erosional truncation the regional distribution and amplitude of the post valanginian subsidence are not consistent with the minor amounts of tithonian valanginian brittle upper crustal extension observed on the margin large portions of the platform were emergent or at very shallow water depths prior to the tithonian valanginian extension to match the distribution and magnitude of the post valanginian thermal type subsidence requires significant lower crustal and mantle extension across the northern carnarvon basin such a distribution of extension implies the existence of an eastward dipping intracrustal detachment having a ramp flat ramp geometry that effectively thinned the lower crust and lithospheric mantle the detachment breached the surface close to the position of the continent ocean boundary west of the exmouth plateau the flat component of the detachment occurred at midcrustal depths 15 km across the plateau and ramped beneath the australian continent lower crustal ductile extension provides a viable mechanism to generate large regional subsidence with little attendant brittle deformation which may explain the paradox that both sides of many conjugate margins appear to be the upper plate

seismic evidence of hyper stretched crust and mantle exhumation offshore vietnam abstract we study the evolution of the eocene recent phu khanh basin opened during the rifting of the south china sea scs this sub basin formed when continental crust ruptured along the east vietnam boundary fault evbf at the western edge of the scs using high quality long streamer seismic lines we interpret structures that highlight the different phases of the scs rifting and processes related to crustal boudinage extreme crustal thinning and mantle uplift that sometimes places sediments in contact with the moho discontinuity mark the central part of the basin the mantle is shallowest there and marks the final rupture of the continental crust during an intense phase of mantle upwelling there a low angle detachment fault separates several crustal blocks from the moho the cylindrical axis of the moho rise is roughly parallel to the trend of the south china sea propagator above the mantle the upper and lower crusts form large crustal boudins the network of normal faults is dense in the upper crust and occasionally propagates into the lower crust however the lower crust is missing at some places the seismic facies above the moho rise is poorly stratified and might have been affected by a certain degree of metamorphism at the apex of mantle uplift there are frequent indications of fluid circulations including volcanic edifices and gas escapes features three stages of extension are clearly identifiable with ages of the two youngest constrained by well calibration the first and oldest rift sequence is situated between the tilted pre rift basement and the oligocene horizons 32 ma the second is delimited by the oligocene to the mid miocene 15 5 ma horizons and the third is bound by the mid miocene and the upper miocene before 10 5 ma horizons these three rift episodes formed in at least two extension directions the first n s and the second nw se the distinct mid miocene 15 5 ma horizon is tilted and the above layers show a diverging reflection these are in turn sealed by an erosional unconformity before 10 5 ma although tectonic activity appears diachronous from north to south we suggest that cessation of rifting did not occur before 12 10 5 ma this differs from models derived from magnetic anomalies observed in the south china sea 15 5 to 20 ma

crustal stretching style variations in the northern margin of the south china sea linking deep seismic profiles with regional scale gravity inversion is a powerful tool to deduce the architecture of rifted margins and their structural evolution here we map upper and lower crustal thicknesses of the northern south china sea scs margin in order to investigate the occurrence of depth dependent crustal extension from the proximal to the distal margin by comparing upper and lower crustal stretching factors we find that the northern margin of the scs is segmented in three parts 1 sedimentary basins where upper crust is stretched more than lower crust 2 distal margin where lower crust is stretched more than upper crust 3 mostly proximal margin regions where the two layers have similar stretching factors our results suggest that sedimentary basins and distal margin prominently feature depth dependent extension however accommodated by different processes while differential thinning within sedimentary basins appears to be governed by lateral pressure variations inducing lower crustal flow we suggest the distal margin to be affected by a combination of mantle flow induced lower crustal shearing and sequential fault activity during crustal hyper extension

interactions between continental breakup dynamics and large scale delta system evolution insights from the cretaceous ceduna delta system bight basin southern australian margin 1 the interpretation of two regional seismic reflection profiles and the construction of a balanced cross section through the southern australian margin bight basin are designed to analyze the influence of the australia antarctica continental breakup process on the kinematic evolution of the cretaceous ceduna delta system the data show that the structural architecture of this delta system consists of two stacked delta systems the lower white pointer delta system late albian santonian is an unstable tectonic wedge regionally detached seaward above late albian ductile shales sequential restoration suggests that the overall gravitational sliding behavior of the white pointer delta wedge 45 km of seaward extension i e 27 is partially balanced by the tectonic denudation of the subcontinental mantle we are able to estimate the horizontal stretching rate of the mantle exhumation between 2 and 5 km ma 1 the associated uplift of the distal part of the margin and associated flexural subsidence in the proximal part of the basin are partially responsible for the decrease of the gravitational sliding of the white pointer delta system lithospheric failure occurs at 84 ma through the rapid exhumation of the mantle the upper hammerhead delta system late santonian maastrichtian forms a stable tectonic wedge developed during initial slow seafloor spreading and sag basin evolution of the australian side margin lateral variation of basin slope related to the geometry of the underlying white pointer delta wedge is associated with distal raft tectonic structures sustained by high sedimentation rates finally we propose a conceptual low angle detachment fault model for the evolution of the australian antarctic conjugate margins in which the antarctic margin corresponds to the upper plate and the australian margin to the lower plate

morphotectonics of rifted continental margins in embryo east africa youth africa arabia and maturity australia rifted margin s develop through embryonic youthful and mature stages and some diversity is attributable to the along strike position of the embryonic rift valley stage between the extremes of the crest of a rifted arch and the saddle between arches in east africa arabia an embryonic stage of arches and saddles cleft by rift valleys is connected with the youthful 20 m y red sea gulf of aden in australia the 53 m y southern margin represents early maturity and the 125 to 160 m y western margin late maturity the dominant morp ho tectonic feature of the embryo is the arch 2000 km long and 1000 km across cleft by rift valleys and separated along strike from its neighbour by a saddle with the emplacement of oceanic litho sphere the arch splits into half arches or rims along the newly formed margins the rims subside about a hinge situated 500 km landward of the continent ocean boundary the rim along the saddle becomes submerged soon after breakup whereas the rim along the crest initially s

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

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

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

3d analogue modeling of the south china sea a discussion on breakup pattern the opening of the south china sea is one of the most important cenozoic events in se asia in order to investigate its tectonic evolution three analogue modeling experiments were compared the modeling results suggest that rifting pattern and orientation change of the rift zone were related to initial theological stratification affected by the ductile flow of silicone lower crust and honey asthenosphere the faults became flattened especially close to the breakup area we conjecture that the slope area may bear relatively hotter and thinner lithosphere than the shelf area from the beginning of rifting due to stretching and mantle upwelling associated with this regional extension which in turn lead to the change in initial rheological stratification and therefore the rifting pattern from shelf to slope in the experiments breakup developed first at isolated points which grew and coalesced to become a single spreading area the conjugate boundaries were either all concave or all convex where a rigid massif was located at the divergent boundary stretching history was different in this case the northern and southern areas thinned rapidly and developed into two deep troughs which may finally evolve into spreading centers the shape of the massif controls the orientation and boundary shape of the spreading area it is interpreted that crustal breakup was more viscous in style and the nw sub sea basin developed along the northern trough of the zhongsha xisha massif macclesfield bank c 2008 elsevier ltd all rights reserved

phanerozoic growth of asia geodynamic processes and evolution abstract accretion processes often obscured in mountain belts can be documented with great detail in se asia where these have taken place during the tertiary the resulting configuration showing accreted continental strips and tectonised wedges is illustrated by the tethysides jammed between the northern laurasian cratons baltica and siberia and gondwanian cratons africa arabia india and australia eurasia increased progressively in size due to the amalgamation of crustal and sedimentary belts at places where the processes are documented in the recent times they can be included within a collision factory which displays the opening of basins by rifting and sea floor spreading within the upper plate until they undergo a process of shortening both stages being subduction controlled in se asia the early stages are illustrated in the eastern sunda arc where the subduction of the sunda trench is blocked in sumba and timor region and flipped into the flores trough in less than 2 my the incipient shortening is at present taking place in the pliocene damar basins another stage where half of the upper plate basin has disappeared is documented in the celebes sea the examples of deformation being transferred further inland exist in the northern celebes sea and the makassar basin the next important stage is the complete consumption of the marginal basin where both margins collide and the accretionary wedge is thrust over the margin as illustrated in nw borneo and palawan each of these stages is responsible for a single short lived tectonic event the succession of several events composes an orogen which may last for over 10 my these events predate the arrival of the conjugate margin of the large ocean which marks the beginning of continental subduction as observed in the himalaya tibet region these examples show that the closure is generally diachronous through time as illustrated in the philippines we observe that the ophiolite obducted in such context is generally of back arc origin upper plate rather than the relict of the vanishing large ocean which is rarely preserved in the philippines once the crust is accreted the subduction zone progressively moved southward until its present position we propose that the lithospheric mantle of the accreted block is delaminated and rolls back in a continuous manner whereas the crust is deformed and accreted

the basins of sundaland se asia evolution and boundary conditions abstract most of the basins developed in the continental core of se asia sundaland evolved since the late cretaceous in a manner that may be correlated to the conditions of the subduction in the sunda trench by the end of mesozoic times sundaland was an elevated area composed of granite and metamorphic basement on the rims which suffered collapse and incipient extension whereas the central part was stable this promontory was surrounded by a large subduction zone except in the north and was a free boundary in the early cenozoic starting from the palaeogene and following fractures initiated during the india eurasia collision rifting began along large faults mostly n s and nnw sse strike slip which crosscut the whole region the basins remained in a continental fluvio lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust phu khanh natuna n makassar or even reached the ocean floor spreading stage celebes flores western sundaland was a combination of basin opening and strike slip transpressional deformation the configuration suggests a free boundary particularly to the east trench pull associated with the proto south china sea subduction java sulawesi trench subduction rollback in the early miocene australian blocks reached the sunda subduction zone and imposed local shortening in the south and southeast whereas the western part was free from compression after the indian continent had moved away to the north this suggests an important coupling of the sunda plate with the indo australian plate both to se and nw possibly further west rollback had ceased in the java sumatra subduction zone and compressional stress was being transferred northwards across the plate boundary the internal compression is expressed to the south by shortening which is transmitted as far as the malay basin in the late miocene most of the sunda plate was under compression except the tectonically isolated andaman sea and the damar basins in the pliocene collision north of australia propagated toward the north and west causing subduction reversal and compression in the short lived damar basin docking of the philippine plate confined the eastern side of sundaland and created local compression and uplift such as in nw borneo palawan and taiwan transpressional deformation created extensive folding strike slip faulting and uplift of the central basin and arakan yoma in myanmar minor inversion affected many thailand rift basins all the other basins record subsidence the uplift is responsible for gravity tectonics where thick sediments were accumulated sarawak ne luconia bangladesh wedge

crustal structure and extension mode in the northwestern margin of the south china sea combining multi channel seismic reflection and gravity modeling this study has investigated the crustal structure of the northwestern south china sea margin these data constrain a hyper extended crustal area bounded by basin bounding faults corresponding to an aborted rift below the xisha trough with a subparallel fossil ridge in the adjacent northwest sub basin the thinnest crust is located in the xisha trough where it is remnant lower crust with a thickness of less than 3 km gravity modeling also revealed a hyper extended crust across the xisha trough the postrift magmatism is well developed and more active in the xisha trough and farther southeast than on the northwestern continental margin of the south china sea and the magmatic intrusion extrusion was relatively active during the rifting of xisha trough and the northwest sub basin a narrow continent ocean transition zone with a width of 65 km bounded seaward by a volcanic buried seamount is characterized by crustal thinning rift depression low gravity anomaly and the termination of the break up unconformity seismic reflection the aborted rift near the continental margin means that there may be no obvious detachment fault like that in the iberia newfoundland type margin the symmetric rift extreme hyper extended continental crust and hotter mantle materials indicate that continental crust underwent stretching phase pure shear deformation thinning phase and breakup followed by onset of seafloor spreading and the mantle lithosphere may break up before crustal necking in the northwestern south china sea margin

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

the growth and propagation of synsedimentary faults abstract offset of each syn fault horizon across a synsedimentary i e growth fault records the throw subsequent to its deposition allowing successive growth stages of a fault to be determined this technique has been applied to synsedimentary faults mapped on 3d seismic datasets to distinguish between faults which propagated laterally during growth faults which did not propagate laterally for significant growth periods and faults in which the lateral dimensions of the active surface decreased during their growth these different fault tip line behaviours result in characteristic lateral and dip parallel fault displacement variations fault propagation rates have been measured for 10 fault tips the maximum propagation rate is 15 km my for gravity driven faults and 3 km my for tectonically driven faults rates of fault propagation decrease with elapsed time from the initiation of faulting with tip line stasis and retreat becoming dominant in the later stages of fault growth static and retreating lateral tip lines are associated with overlap of the fault strain field with that of a neighbouring fault most often with the formation of a fault relay zone

depositional architecture and structural evolution of a region immediately inboard of the locus of continental breakup liwan sub basin south china sea new 3d seismic data and regional 2d seismic profiles from the northern south china sea the most extensive dataset imaging a distal rifted margin in the world are used to characterize a region located immediately inboard of the locus of cenozoic continental breakup the interpreted dataset images a 6 km thick continental crust in which the moho and the base of syn rift sediment are observed as clear well resolved seismic reflections this extremely thinned continental crust was offset at its base by a complex detachment fault system from which oceanward dipping listric faults propagated vertically to bound six separate tilted blocks in a style akin to tectonic rafts the seismic reflection data in this work allowed us to investigate the thickness of synand post rift strata above tilt blocks to reveal that the early middle eocene syn rift topography was gradually blanketed in the late eocene 38 ma after 33 ma earliest oligocene the main depocenter on the margin migrated to the south of the liwan sub basin i e oceanward as recorded by the thickening of strata within a breakup sequence this work is important as it demonstrates how closely structures and sedimentation within the liwan sub basin were controlled by a basal rift related detachment system which is imaged in detail by 3d seismic data for the first time on a rifted continental margin continental breakup was marked by a shift in the locus of subsidence and crustal stretching toward ocean crust within a time period spanning 16 m y we extrapolate our findings from the south china sea to the development of asymmetric passive margins across the world

crustal structure across the xisha trough northwestern south china sea located at the northwestern part of the south china sea scs between the hainan and xisha paracel islands the xisha trough represents a failed rift in conjunction with the opening of the scs between 32 and 17 ma from west towards east within a scale of several hundred kilometers it presents all major stages of the rifting process and thus provides an ideal place to study the rifting process in great details in the autumn of 1996 a joint team of sino german scientists carried out a wide angle seismic experiment across the xisha trough with 10 ocean bottom hydrophones obh along a 237 km nnw sse oriented profile which was surveyed in 1987 with multi channel seismic mcs method by bgr of germany and soa of china favorable weather conditions and the powerful 4 x 12 1 air gun array rendered very good quality data with seismic signals observed at the offset of up to 110 km a detailed velocity depth model was obtained by using an interactive trial and error 2d ray tracing method interpretation of the nics data published by bgr provides very good geometrical constraints of the complex upper crustal structure which is characterized by fault blocks half horsts and half grabens filled with syn and post rift cenozoic sediments the velocity model in turn confirms the major structure outlined by the interpretation of the mcs data showing a varying sedimentary layer between i and 4 km of thickness and velocities between 1 7 and 4 5 km s the p wave velocity of 5 5 km s on the top of the crystalline basement is relatively low suggesting strong weathering within the crystalline crust the velocity increases downward continuously to 6 8 km s at the bottom of the crust without a clear differentiation in the middle crust showing clearly its continental nature even beneath the xisha trough the moho is marked by a sharp first order interface with a velocity of 8 0 8 1 km s at the uppermost mantle the moho depth is 15 km beneath the center of the trough and increases gradually to more than 25 kin towards north and south corresponding to an extreme thinning of the pre rift continental crust from more than 25 kin under the coast line to only 8 kin beneath the xisha trough the similar velocity structure of the continental nature on both sides of the xisha trough suggests a homogeneous pre rift continental setting the sharp moho and the lack of high velocity body hvb in the lower crust imply no magmatic underplating which is very different to interpretations across the eastern part of the continental margin in northern south china sea the intense faulting in the upper crust the strong but rather symmetrical crustal thinning centered at the xisha trough and the close neighborhood to the open scs nw subbasin suggest a pure shear rifting which failed most likely at the phase shortly before the continental breakup c 2001 elsevier science b v all rights reserved

geological development of the central and south vietnamese margin implications for the establishment of the south china sea indochinese escape tectonics and cenozoic volcanism abstract the vietnamese margin forms a key region to the understanding of escape tectonics and the development of the south china sea scs the existing geological reconstructions of the region are restricted to studies of single basins are based on limited amounts of geophysical data or analysis of onshore geological features these models are critically assessed on the basis of interpretation of the most comprehensive 2 d digital seismic database published to date within the area combined with a thorough analysis of existing literature and a new model is presented the vietnamese margin is underlain by a series of paleogene rift basins established through southeastward extrusion of indochina the east vietnam boundary fault evbf forms the almost 1000 km long seaward continuation of the left lateral ailao shan red river shear zone asrrsz toward the southern half of the phu khanh basin the evbf breaks up into discrete segments and splays into the se directed tua hoa fault zone paleogene faults splayed from the evbf and the mae ping shear zone and accommodated the coeval motion of these two major left lateral structural lineaments during the late oligocene basin inversions offshore occurred contemporaneously with initial right lateral inversion along the mae ping shear zone and the onset of major uplift of the metamorphic core complexes along the asrrsz it is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of india and the effective coupling of the west burma block and india the later resulting in broadening of the indenting continental mass after the mid oligocene left lateral movements across the offshore evbf decreased and eventually ceased later onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the shan thai terrain renewed rifting offshore south vietnam resulted from the jump of the scs spreading axis and subsequent neogene southwestward propagation of continental break up the neogene opening of the scs is viewed as a consequence of a slab pull associated with subduction of the proto scs underneath borneo as offshore neogene escape tectonism had virtually ceased during this phase of rifting right lateral transtension is inferred along n to nw oriented fault zones in the phu khanh and the nam con son basins rifting and by inference seafloor spreading continued until the end of middle miocene time although at significantly reduced rates during the final 5 10 ma termination of seafloor spreading is marked by a distinct latest middle miocene unconformity in the nam con son and the southern phu khanh basins neogene volcanism resulted in the build up of several magmatic structures across the central and south vietnamese margin and induced reactivation of older faults in the phu khanh basin the offshore magmatism heralded widespread volcanism onshore southern indochina associated with a latest neogene uplift and denudation event the uplift led to significantly increased siliciclastic accumulation rates offshore which repressed widespread carbonate deposition

ages and magnetic structures of the south china sea constrained by deep tow magnetic surveys and iodp expedition 349 combined analyses of deep tow magnetic anomalies and international ocean discovery program expedition 349 cores show that initial seafloor spreading started around 33 ma in the northeastern south china sea scs but varied slightly by 1 2 myr along the northern continent ocean boundary cob a southward ridge jump of approximate to 20 km occurred around 23 6 ma in the east subbasin this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the southwest subbasin which propagated for about 400 km southwestward from approximate to 23 6 to approximate to 21 5 ma the terminal age of seafloor spreading is approximate to 15 ma in the east subbasin and approximate to 16 ma in the southwest subbasin the full spreading rate in the east subbasin varied largely from approximate to 20 to approximate to 80 km myr but mostly decreased with time except for the period between approximate to 26 0 ma and the ridge jump approximate to 23 6 ma within which the rate was the fastest at approximate to 70 km myr on average the spreading rates are not correlated in most cases to magnetic anomaly amplitudes that reflect basement magnetization contrasts shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers in addition to large vertical intensity variations these complexities are caused by late stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0 5 which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization the primary contribution to magnetic anomalies of the scs is not in the top 100 m of the igneous basement

structure and sediment budget of yinggehai song hong basin south china sea implications for cenozoic tectonics and river basin reorganization in southeast asia the temporal link between offshore stratigraphy and onshore topography is of key importance for understanding the long term surface evolution of continental margins here we present a grid of regional high quality reflection seismic and well data to characterize the basin structure we identify fast subsidence of the basin basement and a lack of brittle faulting of the offshore red river fault in the yinggehai song hong basin since 5 5 ma despite dextral strike slip movement on the onshore red river fault we calculate the upper crustal whole crustal and whole lithospheric stretching factors for the yinggehai song hong basin which show that the overall extension observed in the upper crust is substantially less than that observed for the whole crust or whole lithosphere we suggest that fast basement subsidence after 5 5 ma may arise from crustal to lithospheric stretching by the regional dynamic lower crustal mantle flow originated by collision between india eurasia and indian oceanic subduction below the eurasian margin in addition we present a basin wide sediment budget in the yinggehai song hong basin to reconstruct the sedimentary flux from the red river drainage constrained by high resolution age and seismic stratigraphic data the sediment accumulation rates show a sharp increase at 5 5 ma which suggests enhanced onshore erosion rates despite a slowing of tectonic processes this high sediment supply filled the accommodation space produced by the fast subsidence since 5 5 ma our data further highlight two prominent sharp decreases of the sediment accumulation at 23 3 ma and 12 5 ma which could reflect a loss of drainage area following headwater capture from the paleo red river however the low accumulation rate at 12 5 ma also correlates with drier and therefore less erosive climatic conditions

tectono stratigraphic terranes and detachment faulting of the south china sea and sulu sea abstract geoscientific data acquired from the south china sea and sulu sea areas by bgr since 1977 are compiled and interpreted as comprehensive data sets together with available information of commercial wells and drillsites of the ocean drilling program odp generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles on the basis of the stratigraphic and structural analysis 5 main tectono stratigraphic terranes are defined for the south china sea and 4 main terranes for the sulu sea respectively the dangerous grounds reed bank palawan nw borneo trough and palawan island represent terranes of continental origin which developed on the proto china margin by uniform sense low angle simple shearing within the crust in late cretaceous to early paleocene this rift was abandoned and a new westward propagating rift system developed north of the dangerous grounds reed bank area from the middle eocene to the oligocene early miocene together with seafloor spreading in the south china sea basin the leading edge of the southward drifting continental terranes collided with the late cretaceous to early eocene subduction complex of the northernmost terrane of the proto sulu sea continuous convergence of these terranes back arc spreading creating the se sulu sea terrane and the assumed anti clockwise rotation of borneo are responsible for the complex collision compression structures of the sulu sea terranes including the formation of splinters of oceanic crust major right lateral wrench systems are nnw sse running up to 500 km long and cut across most of the identified terranes wrenching presumably ceased 12 to 16 myr ago

seismic structure in the northeastern south china sea s wave velocity and vp vs ratios derived from three component obs data a nearly 500 km long seismic profile with reflective and refractive wide angle ocean bottom seismometer obs data and multi channel seismic mcs data was acquired across the northeastern continental margin of the south china sea scs the s wave crustal structure and vp vs ratios have been obtained based on a previously published p wave model using the software raylnvr modeling of vertical and horizontal component obs data yields information on the seismic crustal velocities lithology and geophysical properties along the obs 2001 seismic profile s wave velocities in the model increase generally with depth but exhibit high spatial variability particularly from the shelf to the upper slope of the northeastern scs margin vp vs ratios also reveal significant lithological heterogeneity dongsha penghu uplift dpu is a tectonic zone with a thicker crust than adjacent areas and a high magnetic anomaly with a vp vs of 1 74 and a p wave velocity of 5 0 5 5 km s the dpu primarily consists of felsic volcanic rocks in the upper crust and is similar to the petrology of zhejiang fujian volcanic provinces which perhaps is associated with a mesozoic volcanic arc the ocean continent transition oct in the northeastern scs is characterized by a thinning continental crust volcanoes in the upper crust and a high velocity layer hvl in the lower crust the s wave velocity and vp vs ratio suggest that the hvl has a mafic composition that may originate from underplating of the igneous rocks beneath the passive rifted crust after the cessation of seafloor spreading c 2009 elsevier b v all rights reserved

complex rifted continental margins explained by dynamical models of depth dependent lithospheric extension observations from a number of rifted margins e g south atlantic salt basin mid norwegian margin exmouth plateau reveal wide regions of extremely attenuated crust and depositional environments that indicate depth dependent lithospheric extension although the one dimensional thermal kinematic consequences of depth dependent extension are understood no comprehensive process based explanation for the complex style of these margins exists here we present self consistent numerical models of passive margin formation that explain the depth dependent extension the width of the margin its characteristic tripartite nature and why such margins are prone to deposition of evaporites under appropriate climatic conditions some features that are important to reproducing the observed characteristics include decoupling between upper and lower parts of the lithosphere during stretching contrasting wide and narrow extensional styles above and below the decoupling level and progressive focusing of crustal extension toward the rift axis

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

symmetry of the south china sea conjugate margins in a rifting drifting and collision context abstract the symmetry of conjugate rifted margins is a first order observable feature reflecting the geodynamic processes acting during and after continental rifting the symmetry of the south china sea scs rifted margins can be deduced from comprehensive geophysical datasets on a continental margin scale here we combine three key approaches 1 lateral fault distributions are delineated according to free air gravity anomalies 2 crustal stretching styles are mapped based on gravity inversion constrained by deep seismic profiles and 3 total extension of conjugate margins is estimated according to margin restorations and tectonic settings we infer a predominantly symmetric rifting style caused by pure shear extension with only narrow domains of asymmetric deformation in continent ocean transition cot regions that have undergone simple shear and where the lower crust of the highly thinned distal margin is embrittled before continental breakup however our analysis also suggests that this symmetry has been modified by post rift geodynamic processes southward lower crustal flow which occurred only on the southern margin due to the low viscosity of the lower crust and the slab pull induced by the subducting proto scs plate during seafloor spreading shifted the crustal stretching styles from symmetric to asymmetric the collision between the southern margin and borneo thickened the lower crust more than the upper crust at the southern end of the southern margin and shortened the southern margin this event had a large impact on the se margin but a small impact on the sw margin we conclude that 1 for the se and ne margins the crustal stretching styles shifted from asymmetric to approximately symmetric and the total extension shifted from symmetric to asymmetric 2 for the sw and nw margins the crustal stretching and total extension remained asymmetric and symmetric respectively

geological evolution regional perspectives and hydrocarbon potential of the northwest phu khanh basin offshore central vietnam abstract seismic stratigraphic and structural analyses of the northwest phu khanh basin offshore central vietnam based on 2 d seismic data indicate that the initial rifting began during the latest cretaceous or palaeogene controlled by left lateral transtension along the east vietnam boundary fault zone evbfz and northwest southeast directed extension east of the evbfz rifting stopped due to transpression during middle oligocene times but resumed by left lateral transtension during the late oligocene thick sequences of lacustrine and alluvial sediments were deposited during the palaeogene rift periods the late oligocene rifting ended due to inversion triggered by right lateral wrenching near the palaeogene neogene boundary following the onset of this inversion regional uplift and volcanism took place in the southern half of the study area and contemporaneous subsidence and transgression took place farther north leading to widespread carbonate deposition as the right lateral wrenching decreased during the early neogene thermal subsidence and siliciclastic sedimentation became dominant resulting in the buildup and southward propagation of the shelf slope sediment accumulation and subsidence rates increased after the middle miocene times due to eastward tilting of central vietnam and the adjacent offshore area potential direct hydrocarbon indicators dhis in the phu khanh basin include common amplitude anomalies gas chimney like features and seafloor gas seeps in addition oil seeps are found at dam thi nai immediately landward of the basin geochemical analyses of the oil seeps indicate the existence of at least two early to peak mature source rocks maturation modelling combined with the seismic analysis suggests the likely presence of oil kitchens 40 50 km downdip in the basin and a fairly simple oil migration route the basin is probably charged from lacustrine syn rift mudstones humic coals and fore reef marls potential reservoirs are turbidite lowstand delta shelf and coastal sandstones as well as platform and reef carbonates and fractured basement various structural and stratigraphic traps formed during the palaeogene and early neogene prior to the main stage of petroleum generation

low velocity layers in the northwestern margin of the south china sea evidence from receiver functions of ocean bottom seismometer data abstract the receiver function method was applied to teleseismic recordings of an active source ocean bottom seismometer array in the northwestern margin of the south china sea forward modeling of the receiver functions was used to derive velocity interfaces beneath the stations two main groups of low velocity layers were imaged the first group in the reef area with a thickness of 7 10 km exhibits a seaward uptrend of the buried depth but poor continuity the second group with a thickness of 3 4 km is more continuous along the zhongsha trough the buried depth decreases asymmetrically from the flanks to the rift center a high shear wave velocity layer of 4 0 km s is imaged at the crust bottom beneath the zhongsha trough with thickness of 3 km the average vp vs in the cenozoic sediment is 2 0 3 0 and was affected by high fluid activity induced by intensive faults the vp vs of the crust varies between 1 77 and 1 88 suggesting an intermediate to basic composition under the continental extension together these results suggest a two stage evolution model of the continental crust in the first stage the crust deformed in a ductile manner and thus created considerable shearing structures with high anisotropy that caused the obvious decrease of the shear wave velocity in the second stage the shearing structures connected asymmetrically driven by detachment faults in the upper crust and upwelling of the lower crust the zhongsha trough then formed probably with magmatic underplating due to lithospheric extension or rising of hot mantle materials