hierarchical segmentation of the malawi rift the influence of inherited lithospheric heterogeneity and kinematics in the evolution of continental rifts we used detailed analysis of shuttle radar topography mission digital elevation model and observations from aeromagnetic data to examine the influence of inherited lithospheric heterogeneity and kinematics in the segmentation of largely amagmatic continental rifts we focused on the cenozoic malawi rift which represents the southern extension of the western branch of the east african rift system this north trending rift traverses precambrian and paleozoic mesozoic structures of different orientations we found that the rift can be hierarchically divided into first order and second order segments in the first order segmentation we divided the rift into northern central and southern sections in its northern section the rift follows paleoproterozoic and neoproterozoic terrains with structural grain that favored the localization of extension within well developed border faults the central section occurs within mesoproterozoic neoproterozoic terrain with regional structures oblique to the rift extent we propose that the lack of inherited lithospheric heterogeneity favoring extension localization resulted in the development of the rift in this section as a shallow graben with undeveloped border faults in the southern section mesoproterozoic neoproterozoic rocks were reactivated and developed the border faults in the second order segmentation only observed in the northern section we divided the section into five segments that approximate four half grabens asymmetrical grabens with alternating polarities the change of polarity coincides with flip over full grabens occurring within overlap zones associated with 150 km long alternating border faults segments the inherited lithospheric heterogeneity played the major role in facilitating the segmentation of the malawi rift during its opening resulting from extension

new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

fault reactivation control on normal fault growth an experimental study field studies frequently emphasize how fault reactivation is involved in the deformation of the upper crust however this phenomenon is generally neglected except in inversion models in analogue and numerical models performed to study fault network growth using sand silicon analogue models we show how pre existing discontinuities can control the geometry and evolution of a younger fault network the models show that the reactivation of pre existing discontinuities and their orientation control i the evolution of the main fault orientation distribution through time ii the geometry of relay fault zones iii the geometry of small scale faulting and iv the geometry and location of fault controlled basins and depocenters these results are in good agreement with natural fault networks observed in both the gulf of suez and lake tanganyika they demonstrate that heterogeneities such as pre existing faults should be included in models designed to understand the behavior and the tectonic evolution of sedimentary basins

basement structure and its influence on the structural configuration of the northern north sea rift the northern north sea rift basin developed on a heterogeneous crust comprising structures inherited from the caledonian orogeny and devonian post orogenic extension integrating two dimensional regional seismic reflection data and information from basement wells we investigate the pre rift structural configuration in the northern north sea rift three seismic facies have been defined below the base rift surface 1 relatively low amplitude and low frequency reflections interpreted as pre caledonian metasediments caledonian nappes and or devonian clastic sediments 2 packages of high amplitude dipping reflections 500 ms thick interpreted as basement shear zones and 3 medium amplitude and high frequency reflections interpreted as less sheared crystalline basement of proterozoic and paleozoic caledonian origin some zones of seismic facies 2 can be linked to onshore devonian shear zones whereas others are restricted to the offshore rift area interpreted offshore shear zones dip s ese and wnw in contrast to w to nw dipping shear zones onshore w norway our results indicate that devonian strain and ductile deformation was distributed throughout the caledonian orogenic belt from central south norway to the shetland platform most of the devonian basins related to this extension are however removed by erosion during subsequent exhumation basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters e g in the stord and east shetland basins pre rift structures with present day dips 15 were reactivated although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift extension direction

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

seismic stratigraphy of the central south china sea basin and implications for neotectonics coring logging data and physical property measurements from international ocean discovery program expedition 349 are integrated with and correlated to reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the south china sea first order sequence boundaries are interpreted which are oligocene miocene middle miocene late miocene miocene pliocene and pliocene pleistocene boundaries a characteristic early pleistocene strong reflector is also identified which marks the top of extensive carbonate rich deposition in the southern east and southwest subbasins the fossil spreading ridge and the boundary between the east and southwest subbasins acted as major sedimentary barriers across which seismic facies changes sharply and cannot be easily correlated the sharp seismic facies change along the miocene pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5ma coeval with the onsets of uplift of taiwan and accelerated subsidence and transgression in the northern margin the depocenter or the area of the highest sedimentation rate switched from the northern east subbasin during the miocene to the southwest subbasin and the area close to the fossil ridge in the southern east subbasin in the pleistocene the most active faulting and vertical uplifting now occur in the southern east subbasin caused most likely by the active and fastest subduction obduction in the southern segment of the manila trench and the collision between the northeast palawan and the luzon arc timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities

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

active normal faulting during the 1997 seismic sequence in colfiorito umbria did slip propagate to the surface in order to determine whether slip during an earthquake on the 26th september 1997 propagated to the surface structural data have been collected along a bedrock fault scarp in umbria italy these collected data are used to investigate the relationship between the throw associated with a debated surface rupture observed as a pale unweathered stripe at the base of the bedrock fault scarp and the strike dip and slip vector previous studies have suggested that the surface rupture was produced either by primary surface slip or secondary compaction of hangingwall sediments some authors favour the latter because sparse surface fault dip measurements do not match nodal plane dips at depth it is demonstrated herein that the strike dip and height of the surface rupture represented by a pale unweathered stripe at the base of the bedrock scarp shows a systematic relationship with respect to the geometry and kinematics of faulting in the bedrock the strike and dip co vary and the throw is greatest where the strike is oblique to the slip vector azimuth where the highest dip values are recorded this implies that the throw values vary to accommodate spatial variation in the strike and dip of the fault across fault plane corrugations a feature that is predicted by theory describing conservation of strain along faults but not by compaction furthermore published earthquake locations and reported fault dips are consistent with the analysed surface scarps when natural variation for surface dips and uncertainty for nodal plane dips at depth are taken into account this implies that the fresh stripe is indeed a primary coseismic surface rupture whose slip is connected to the seismogenic fault at depth we discuss how this knowledge of the locations and geometry of the active faults can be used as an input for seismic hazard assessment

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

analysis of scarp profiles evaluation of errors in morphologic dating morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials under the same climatic conditions scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes this morphological evolution can be modelled as the convolution of the initial shape with erosion or degradation function whose width increases with time such modeling applies well to scarps less than 10m high formed in unconsolidated fanglomerates to a good approximation the degradation function is gaussian with a variance measuring the degree of rounding of the initial shape this geometric parameter can be called the degradation coefficient a synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials 30 35 uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically because the degradation coefficient is sensitive to the regional slope and to three dimensional processes gullying loess accumulation stream incision etc a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp the linear diffusion model of scarp degradation is a gaussian model in which the degradation coefficient is proportional to numerical age in that case absolute dating requires only determination of the propotionality constant called the mass diffusivity constant for holocene scarps a few meters high in loose alluvium under arid climatic conditions mass diffusivity constants generally range between 1 and 6 m 2 kyr morphologic analysis is a reliable method to compare ages of different scarps in a given area and it can provide approximate absolute ages of holocene scarplike landforms

contourite drifts on early passive margins as an indicator of established lithospheric breakup the albian cenomanian breakup sequence bs offshore northwest iberia is mapped described and characterised for the first time in terms of its seismic and depositional facies the interpreted dataset comprises a large grid of regional 2d seismic reflection profiles complemented by industry and odp dsdp borehole data within the bs are observed distinct seismic facies that reflect the presence of a black shales and fine grained turbidites b mass transport deposits mtds and coarse grained turbidites and c contourite drifts borehole data show that these depositional systems developed as mixed carbonate siliciclastic sediments proximally and as organic carbon rich mudstones black shales distally on the northwest iberia margin mtds and turbidites tend to occur on the continental slope frequently in association with large scale olistostromes distally these change into interbedded fine grained turbidites and black shales showing widespread evidence of deep water current activity towards the top of the bs current activity is expressed by intra bs erosional surfaces and sediment drifts the results in this paper are important as they demonstrate that contourite drifts are ubiquitous features in the study area after aptian albian lithospheric breakup therefore we interpret the recognition of contourite drifts in northwest iberia as having significant palaeogeographic implications contourite drifts materialise the onset of important deep water circulation marking the establishment of oceanic gateways between two fully separated continental margins as a corollary we postulate the generation of deep water geostrophic currents to have had significant impact on north atlantic climate and ocean circulation during the albian cenomanian with the record of such impacts being preserved in the contourite drifts analysed in this work

controls on early rift geometry new perspectives from the bilila mtakataka fault malawi we use the 110 km long bilila mtakataka fault in the amagmatic southern east african rift malawi to investigate the controls on early rift geometry at the scale of a major border fault morphological variations along the 14 8 m high scarp define six 10 40 km long segments which are either foliation parallel or oblique to both foliation and the current regional extension direction as the scarp is neither consistently parallel to foliation nor well oriented for the current regional extension direction we suggest the segmented surface expression is related to the local reactivation of well oriented weak shallow fabrics above a broadly continuous structure at depth using a geometrical model the geometry of the best fitting subsurface structure is consistent with the local strain field from recent seismicity in conclusion within this early rift pre existing weaknesses only locally control border fault geometry at subsurface

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

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

what are the spratly islands abstract seismic records combined with dredged samples and a core indicate that the spratly islands of the dangerous ground province are constructed of presently active carbonate build ups known to extend back continuously at least to the pleistocene and presumed to have initiated in the miocene most likely upon the crests of sea floor cuestas that trend north east south west parallel to the sea floor spreading magnetic anomalies of the contiguous abyssal plain of the southern part of the south china sea the cuestas range from spectacular to subdued constructed of triassic and cretaceous strata and no older rocks have been identified from dredges the cuesta axes plunge towards the south west away from the islands suggesting that the reefs began colonising their more elevated parts but the timing is uncertain the highest seismically recorded cuesta crest is in 440 m of water and the islands and reefs are generally closely surrounded by water deeper than 1500 m since the so called mid miocene unconformity mmu the region has been undergoing post rift thermal subsidence however the nearby seismic lines show no evidence of drowned carbonate reefs it is suggested that the coral algal reefs colonised the crests of the most elevated cuestas that have maintained stability as shown by the 165 m core of one reef indicating periodic exposure with caliche horizons deepening water has protected the build ups from extinction by post rift draping strata in contrast to the central luconia province and the build ups have been able to keep up with regional thermal subsidence the dredged mesozoic strata indicate that the dangerous ground is not exotic and should be interpreted as an integral part of the pre rift sundaland continent that included south china vietnam peninsular malaysia western sarawak and possibly part of sabah igneous and metamorphic samples have been dredged although individual spot k ar dates cannot be accepted at face value such rocks can also be interpreted as an integral part of sundaland post mmu dredged samples are predominantly deep water calcareous mudstones typified by the draping strata of the ocean drilling program odp site 1143 cored from recent to late miocene

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

relay ramp forms and normal fault linkages canyonlands national park utah fieldwork within a series of mesoscale grabens in southeast utah has revealed a particularly well exposed system of interlinked extensional faults a series of down faulted grabens are developed within a 460 m thick brittle layer of upper paleozoic sandstone and shale which overlies a ductile layer with a high gypsum content all the major grabens consist of two or more overlapping elements which are composed of fault segments these segments may be hard linked fault surfaces are joined or soft linked fault surfaces are isolated but linked by ductile strain of the rock volume between them in map view relay structures are defined as zones connecting the footwalls and hanging walls of overlapping fault segments representing soft linkage of fault segments in the canyonlands grabens the transfer of displacement between soft linked fault segments is characterized by well de fined dipping relay ramps commonly rotated and extended to accommodate the ductile strain between the overlapping fault segments relay ramps develop as ephemeral structures eventually becoming breached by hard linkage of the fault segments breakdown of ramps by breaching is part of the process of fault growth by segment linkage within the canyonlands graben system four orders of segmentation are present this may be a consequence of different scales of mechanical heterogeneity but evidence from the canyonlands grabens and elsewhere points to a fundamental process of discontinuous fault growth by segment linkage

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

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

morphologic dating of scarps formed by repeated slip events along the san andreas fault carrizo plain california morphologic dating of fault scarps determines late cenozoic fault activity by comparing observed topographic profiles with those determined using a calibrated hillslope development model we postulate that the material transport rate along the profile is a function only of local slope and is transport limited morphologic dating of hillslopes bounded by continuously dropping boundaries or cut by continuously slipping faults is used to determine the material transport rate constant the time since the downdrop was initiated or the fault began to slip we calibrated the hillslope development model on the southwest facing scarp southeast of wallace creek along the san andreas fault saf in the carrizo plain california the scarp has been exposed by right lateral offset of a southeast sloping shutter ridge located on the southwest side of the saf and by vertical offset related to secondary deformation we assume that all the observed offset occurs after initial exposure of the scarp by passage of the shutter ridge forward modeling of profile development yielded a mass diffusivity of 8 6 0 8 m2 kyr 1 normal fault slip rates were determined for two graben bounding faults in the northern elkhorn hills in the southeastern carrizo plain by applying the calibrated to the degradation of the scarps to determine the scarp age one fault scarp began to form about 12 kyr ago and the other about 63 kyr ago those ages and estimates of the dip slip along the faults result in slip rates of 1 2 mm yr 1

mesozoic and cainozoic rocks dredged from the south china sea reed bank area and sulu sea and their significance for plate tectonic reconstructions abstract outcrops of pre quaternary rocks were sampled by dredging and coring during two cruises of rv sonne in the south china sea and sulu sea 1982 1983 late triassic deltaic sandstones wih plant remains are the oldest sediments recovered late jurassic early cretaceous regional metamorphism is indicated by gneiss and garnet mica schists exposed in the northwestern flanks of reed bank these rocks and occurrences of gabbro diorite dacite rhyolite and siliceous shale prove that the dangerous grounds and reed bank are underlain by a continental fragment during the period of seafloor spreading in the south china see a late oligocene to early miocene carbonate platform developed on this southwards drifting continental fragment which subsided in the middle miocene middle miocene andesite and early to middle miocene reefal carbonates were recovered from the cagayan ridge in the sulu sea the new data are in accord with the plate tectonic history developed by taylor and hayes 1980 1983 and holloway 1981

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

fault slip and earthquake recurrence along strike slip faults contributions of high resolution geomorphic data article i nfo understanding earthquake eq recurrence relies on information about the timing and size of past eq ruptures along a given fault knowledge of a fault s rupture history provides valuable information on its potential future behavior enabling seismic hazard estimates and loss mitigation stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing eqs analysis of the latter data sets culminated during the mid 1980s in the formulation of now classical eq recurrence models now routinely used to assess seismic hazard within the last decade light detection and ranging lidar surveying technology and other high resolution data sets became increasingly available to tectono geomorphic studies promising to contribute to better informed models of eq recurrence and slip accumulation patterns after reviewing motivation and background we outline requirements to successfully reconstruct a fault s offset accumulation pattern from geomorphic evidence we address sources of uncertainty affecting offset measure ment and advocate approaches to minimize them a number of recent studies focus on single eq slip distribu tions and along fault slip accumulation patterns we put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation cv for eq inter event time and slip per event and find that a single event offsets vary over a wide range of length scales and the sources for offset variability differ with length scale b at fault segment length scales single event offsets are essentially constant c along fault offset accumulation as resolved in the geomorphic record is dominated by essentially same size large offset in crements and d there is generally no one to one correlation between the offset accumulation pattern constrained in the geomorphic record and eq occurrence as identified in the stratigraphic record revealing the higher resolution and preservation potential of the latter while slip accumulation along a fault segment may be dominated by repetition of large nearly constant offset increments timing of surface rupture is less regular

pre existing normal faults have limited control on the rift geometry of the northern north sea abstract many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first phase normal faults and rift related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts however many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data making it difficult to test these models here we integrate recent 3d seismic reflection and borehole data across the entire east shetland basin northern north sea to constrain the long term regional development of this multiphase rift we document the following key stages of basin development i pre triassic to earliest triassic development of multiple sub basins controlled by widely distributed nnw to ne trending east and west dipping faults ii triassic activity on a single major ne trending west dipping fault located near the basins western margin and formation of a large half graben and iii jurassic development of a large e dipping n to ne trending half graben near the eastern margin of the basin which was associated with rift narrowing and strain focusing in the viking graben in contrast to previous studies which argue for two discrete periods of rifting during the permian triassic and late jurassic early cretaceous we find that rifting in the east shetland basin was protracted from pre triassic to cretaceous we find that during the jurassic most pre jurassic normal faults were buried and in some cases cross cut by newly formed faults with only a few being reactivated previously developed faults thus had only a limited control on the evolution and geometry of the later rift we instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere an interpretation supporting the predictions of lithosphere scale numerical models our study indicates that additional regional studies of natural rifts are required to test and refine the predictions of physical and numerical models more specifically our study suggests models not explicitly recognising or including thermal or rheological effects might over emphasise the role of discrete pre existing rift structures such as normal faults

rapid transition from continental breakup to igneous oceanic crust in the south china sea continental breakup represents the successful process of rifting and thinning of the continental lithosphere leading to plate rupture and initiation of oceanic crust formation magmatism during breakup seems to follow a path of either excessive transient magmatism magma rich margins or of igneous starvation magma poor margins the latter type is characterized by extreme continental lithospheric extension and mantle exhumation prior to igneous oceanic crust formation discovery of magma poor margins has raised fundamental questions about the onset of ocean floor type magmatism and has guided interpretation of seismic data across many rifted margins including the highly extended northern south china sea margin here we report international ocean discovery program drilling data from the northern south china sea margin testing the magma poor margin model outside the north atlantic contrary to expectations results show initiation of mid ocean ridge basalt type magmatism during breakup with a narrow and rapid transition into igneous oceanic crust coring and seismic data suggest that fast lithospheric extension without mantle exhumation generated a margin structure between the two endmembers asthenospheric upwelling yielding mid ocean ridge basalt type magmatism from normal temperature mantle during final breakup is interpreted to reflect rapid rifting within thin pre rift lithosphere

extensional hard linkages eastern gulf of suez egypt the araba abu durba area on the eastern margin of the gulf of suez exhibits two superb outcrop examples of extensional hard linkages in a rift basin here three large domino style basement cored northeast dipping fault blocks are formed by a series of major northwest trending normal faults these are offset by two north northeast trending sinistral oblique slip transfer faults that terminate in horsetail normal fault splays the transfer faults do not extend across the entire rift basin detailed mapping and structural analysis show that they developed by breakage of initial low strain relay ramps along reactivated north northeast trending basement fabrics between overlapping northwest trending normal fault segments paleostrain analysis of fault slip indicators shows that both the normal and the sinistral oblique slip transfer faults were formed synchronously in response to northeast southwest extension perpendicular to the main northwest rift trend

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

new insights into the magmatism in the northern margin of the south china sea spatial features and volume of intraplate seamounts the extensive intraplate seamounts are obvious features in the northern south china sea scs however the distribution volume and origin of these seamounts are not well understood which greatly hinders our understanding of magmatism in the scs based on high resolution bathymetric data and 147 seismic profiles and combining gravity and magnetic data we first identify 45 seamounts in the northern margin of the scs and simulate their shape with elliptical cones results show that the total volume of these 45 seamounts above seafloor is estimated at about 1885 3078 km3 and the total volume of intrusive magma above moho is about 0 15 mkm3 which is close to the estimates for classic large igneous provinces across the world these seamounts are mostly located on the continental slope with thin crust approximately 12 18 km which reduces the overlying pressure and shortens the magmatic conduits the dominant azimuth of elliptical major axis in seamounts is consistent with the synrift and synspreading fault strikes ne nee indicating that these pre existing faults provide magmatic conduits for the subsequent postrift intraplate seamounts based on three existing clues i e 1 the intraplate seamounts high velocity layer and hainan mantle plume are contiguous in 3 d space 2 the high velocity layer is thicker beneath the continental shelf but thinner beneath the slope and 3 the basalts dredged from certain seamounts show oib type geochemical features we propose a magmatic upwelling pattern which contains hainan mantle plume to explain the spatial and morphological characteristics of these intraplate seamounts

marginal basin evolution the southern south china sea abstract the southern south china sea is divided into contrasting morphology by the west baram line to the west is the sundaland extinct passive margin in which rifting began in the eocene 46 ma and ceased at 19 21 ma anomaly 6 where sea floor spreading began much later than along the shelf of china the break up hiatus lasted 3 5 ma marked by the mid miocene unconformity also preserved on land sarawak the post rift strata date from 16 ma and drape over the rifted topography to the east is a convergent margin that became a collision zone in the middle miocene the sunda shelf is of uniform 30 km thickness except in localised deep basins and extends to a water depth of 200 m the continental slope is narrow the continental rise dangerous grounds is covered by water ranging from 500 m to 3 5 km depth at the continent ocean transition its width ranges from 170 to 330 km the rajang delta extends over the shelf and continental slope its post rift sediments drape over the rifted proximal topography of the dangerous grounds to the east the drape is thinner and has not completely buried the rifted topography the cuestas appear to have supported the carbonate build up infrastructures of the spratly islands whose slopes rise abruptly from a sea floor of 2 3 km depth the sabah and brunei margin is a collision zone that was formerly convergent the on land geology indicates a mesozoic ophiolitic basement the main collision feature is the western cordillera constructed mainly of sandy eocene to lower miocene turbidites predominantly oligocene to lower miocene in the west crocker 32 18 ma uplifted episodically throughout the upper miocene and pliocene 14 8 ma the 2 km deep northwest borneo trough may be a relict of the convergence phase but could also be a collisional foredeep the oil prolific baram delta resulting from uplift and erosion of the western cordillera has built out as far as the northwest borneo trough it is suggested that the passive margin continental rise dangerous grounds has been underthrust beneath sabah to cause uplift of the western cordillera the west baram line accordingly abruptly separates the collision zone from the western extinct passive margin and is a now extinct major right lateral transform fault

analysis of nonlinear effects on tracer migration in heterogeneous aquifers using lagrangian travel time statistics advective transport in a heterogeneous two dimensional aquifer is simulated and quantified by the statistical moments of tracer travel time and transverse displacement these moments depend on the

oblique extensional tectonics in the malawi rift africa the malawi rift is the southern segment of the western branch of the east african rift system there has been little agreement as to whether this rift is opening perpendicularly or obliquely to its north south axis and little agreement on a mechanism for the formation of the asymmetric basins that make up the rift our analysis combines landsat image interpretation and field measurement of the latest slip direction on faults to produce a kinematic model of rift evolution the fault slip data are consistently compatible with a late cenozoic northwest southeast directed divergence between the nubian and somalian blocks plates across the rift the northwest striking livingstone fault at the northern limit of the malawi rift and the northwest striking zambezi fault zone to the south serve as dextral intracontinental transform zones between left stepping segments of the western branch of the east african rift system within the rift second order northwest striking transfer faults separate adjacent asymmetric basins the transform and transfer faults form a pattern that is similar to overlapping right stepping strike slip faults with a releasing geometry fault surfaces with two sets of striations indicate a progression from predominantly strike slip toward oblique normal faulting we hypothesize that during initial rift formation most northwest striking faults were dextral and that fault interaction between these structures resulted in curved stress trajectories and a pull apart component arcuate north to northeast striking border faults and subsiding basins then formed between these northwest striking faults in response to the right stepping dextral shear the maximum distance over which fault interaction is significant may control basin dimensions as opening of the rift proceeds slip partitioning and gravity failure result in increasing normal slip perpendicular to major escarpments and decreasing strike slip parallel to them

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

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

the structure and evolution of deepwater basins in the distal margin of the northern south china sea and their implications for the formation of the continental margin abstract although it is generally accepted that the south china sea margin can be classified as a magma poor rifted margin little is known about the structural style of the distal margin and how the distal deep basins evolved observations and data from the northern south china sea margin suggest that the deepwater basins distal margin domain are commonly underlain by a highly extended continental crust and detachment fault systems have been interpreted in places we have interpreted a large seismic data set covering deepwater basins in the northern south china sea the interpreted moho on reflection seismic profiles indicates that the crustal thickness varies along sections perpendicular to the coast which is the first order criterion to divide the whole margin into a proximal domain necking zone and distal domain furthermore the underlying extremely stretched crust

different expressions of rifting on the south china sea margins abstract rifting of continental margins is generally diachronous along the zones where continents break due to various factors including the boundary conditions which trigger the extensional forces but also the internal physical boundaries which are inherent to the composition and thus the geological history of the continental margin being opened quite recently in the tertiary in a scissor shape manner the south china sea scs offers an image of the rifting structures which varies along strike the basin margins the scs has a long history of extension which dates back from the late cretaceous and allows us to observe an early stretching on the northern margin onshore and offshore south china with large low angle faults which detach the mesozoic sediments either over triassic to early cretaceous granites or along the short limbs of broad folds affecting palaeozoic to early cretaceous series these early faults create narrow troughs filled with coarse polygenic conglomerate grading upward to coarse sandstone because these low angle faults reactivate older trends they vary in geometry according to the direction of the folds or the granite boundaries a later set of faults characterized by generally e w low and high angle normal faults was dominant during the eocene associated half graben basement deepened as the basins were filling with continental or very shallow marine sediments this subsequent direction is well expressed both in the north and the sw of the south china sea and often reactivated earlier detachments at places the intersection of these two fault sets resulting in extreme stretching with crustal boudinage and mantle exhumation such as in the phu khanh basin east of the vietnam fault a third direction of faults which rarely reactivates the detachments is ne sw and well developed near the oceanic crust in the southern and southwestern part of the basin this direction which intersects the previous ones was active although sea floor spreading was largely developed in the northern part and ended by the late miocene after the onset of the regional mid miocene unconformity known as mmu and dated around 15 5 ma latest miocene is marked by a regional basement drop and localized normal faults on the shelf closer to the coast the se margin of the south china sea does not show the extensional features as well as the northern margin detachments are common in the dangerous grounds and reed bank area and may occasionally lead to mantle exhumation the sedimentary environment on the extended crust remained shallow all along the rifting and a large part of the spreading until the late miocene when it suddenly deepened this period also corresponds to the cessation of the shortening of the nw borneo wedge in palawan sabah and sarawak we correlate the variation of margin structure and composition of the margin mainly the occurrence of granitic batholiths and mesozoic broad folds with the location of the detachments and major normal faults which condition the style of rifting the crustal boudinage and therefore the crustal thickness

nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions abstract in the neves area the pre alpine intrusive protolith of the zentralgneise unit tauern window eastern alps is well preserved in a kilometric scale low strain domain without pervasive alpine deformation it is compositionally heterogeneous consisting predominantly of granodiorites with lesser leucocratic granites and different generations of lamprophyres and aplites the intrusive rocks are crosscut by fractures that were locally infiltrated by fluids and surrounded by alteration haloes incipient alpine amphibolite facies ductile deformation is strongly localized on these precursor fractures and on lithological planar heterogeneities resulting in the development of several different types of shear zones fractures without alteration haloes initially accommodate slip entirely on the fracture itself with increasing deformation a foliation is progressively developed in the adjacent host rock eventually producing a single heterogeneous ductile shear zone with the typical sigmoidal foliation pattern strong layers aplite dykes and bleached alteration haloes developed to either side of precursor fractures localize shear on their boundaries to produce characteristic paired shear zones shearing is more evenly distributed within weak layers lamprophyres and quartz veins with a marked discontinuity in shear strain against the adjacent little deformed granodiorite shear zone development was accompanied by the formation of new fractures and quartz rich veins in the host rock which in turn also localized shear magmatic contacts fractures and quartz veins are mostly steeply dipping and effectively span the complete range of strike orientations the kinematics of the overprinting strike slip shear zones was determined by the orientation of the initial discontinuities relative to the local principal compressive stress axis 1 here oriented ca 345 discontinuities of almost all orientations show shear reactivation even in the case of very low resolved shear stress indicating an overall viscous response of the system without a specific yield stress the geometry and kinematics of the shear zone network suggest that the overall deformation in low strain domains was close to coaxial during deformation along the shear zone network compatibility was maintained by fracturing with the development of new quartz veins and by distributed ductile deformation of the host rock especially within contractional domains of the shear network and at shear zone intersections deformation never propagates into the undeformed homogeneous granodiorite as discrete ductile shear zones but is limited by the original extent of the precursor discontinuities shear zone development in intact rock is always preceded by fracturing which localizes subsequent shear reactivation

seismic stratigraphy and tectonic structure from a composite multi channel seismic profile across the entire dangerous grounds south china sea abstract we interpret a more than 500 km long composite multi channel seismic reflection profile across the entire dangerous grounds the south china sea five tectonostratigraphic units are determined together with seven sequence boundaries detailed analysis of extensional features based on measurements of fault heaves revealed two major phases of extension separated by a distinct unconformity which likely correspond with the beginning of sea floor spreading in the south china sea early extension occurred during continental rifting late cretaceous early oligocene and resulted in formation of half grabens and rotated blocks controlled by a deeply rooted detachment system extension continued in our study area during the drifting phase of the east subbasin of the south china sea late oligocene early miocene until the subsequent opening of the southwest subbasin at about 25 ma but its intensity decreased markedly thereafter deeply rooted detachment systems evolved possibly during this second phase of extension at the continent ocean transition area from a coincidence of the lowermost reflections and moho depth as derived from gravity inversion we tentatively interpret the flattened part of this detachment system as the crust mantle boundary it is suggested that the dangerous grounds reflect a magma poor rift system at the initial stage of mantle unroofing we suggest that a widespread carbonate platform developed across the dangerous grounds concurrent with the period of seafloor spreading in the southwest subbasin of the south china sea fault related stretching factors f along the line show discrepancies with the whole crustal stretching factors c the continental crust of the dangerous grounds may have experienced nonuniform thinning

deep crustal structure of the conjugate margins of the sw south china sea from wide angle refraction seismic data abstract the south china sea is the largest marginal basin of se asia yet its mechanism of formation is still debated a 1000 km long wide angle refraction seismic profile was recently acquired along the conjugate margins of the sw sub basin of the south china sea over the longest extended continental crust a joint reflection and refraction seismic travel time inversion is performed to derive a 2 d velocity model of the crustal structure and upper mantle based on this new tomographic model northern and southern margins are genetically linked since they share common structural characteristics most of the continental crust deforms in a brittle manner two scales of deformation are imaged and correlate well with seismic reflection observations small scale normal faults grabens horsts and rotated faults blocks are often associated with a tilt of the velocity isocontours affecting the upper crust the mid crust shows high lateral velocity variation defining low velocity bodies bounded by large scale normal faults recognized in seismic reflection profiles major sedimentary basins are located above low velocity bodies interpreted as hanging wall blocks along the northern margin spacing between these velocity bodies decreases from 90 to 45 km as the total crust thins toward the continent ocean transition the continent ocean transitions are narrow and slightly asymmetric 60 km on the northern side and no more than 30 km on the southern side indicating little space for significant hyper stretched crust although we have no direct indication for mantle exhumation shallow high velocities are observed at the continent ocean transition the moho interface remains rather flat over the extended domain and remains undisturbed by the large scale normal faults the main decollement is thus within the ductile lower crust

a phase of transient subsidence sediment bypass and deposition of regressive transgressive cycles during the breakup of iberia and newfoundland abstract seismic outcrop and well data from west iberia and newfoundland are used to investigate sediment stacking patterns during continental breakup as a function of tectonic subsidence in west iberia two breakup sequences are revealed on seismic data by marked strata offlap oceanwards from the present day continental shelf this character is similar to newfoundland where correlative strata comprise lower cretaceous cenomanian coarse grained siliciclastics accumulated around local sediment source areas the interpreted data reveal that the two breakup sequences 1 materialise sediment bypass onto continental slope depocentres that experienced important tectonic subsidence during continental breakup but without showing typical syn rift growth packages 2 generate specific forced regressive stratigraphic intervals that relate to uplift and exhumation of the proximal margin subsidence and sediment stacking patterns in both west iberia and newfoundland reflect similar continental breakup processes as they evolved from the upper lithosphere to their mantle breakup stages on both margins coarse grained siliciclastic units on the proximal margin give rise to thick shaley successions in deep water basins this work also confirms that in a setting dominated by a significant sediment influx yet lacking the burial rates of continental slope basins in newfoundland west iberia comprised accommodation driven basins during continental breakup not necessarily sediment starved as a corollary of our analysis we classify breakup sequences around the world based on the characteristic lithologies of their regressive transgressive depositional cycles

the breakup sequence and associated lithospheric breakup surface their significance in the context of rifted continental margins west iberia and newfoundland margins north atlantic regional 2d seismic reflection profiles and borehole data are used to characterise the syn to post rift transition in the shallow offshore porto basin and in deep offshore regions of west iberia and newfoundland east canada the interpreted data highlight the development of a regional stratigraphic surface at the time of complete lithospheric breakup between west iberia and newfoundland this surface usually called breakup unconformity is renamed in this work as lithospheric breakup surface lbs on the basis that 1 it is not always developed as an unconformity and 2 all lithosphere is involved on the breakup process not only the continental crust depositional changes occur across the lbs in association with late aptian lithospheric breakup which is marked by the deposition of a breakup sequence bs rather than a single stratigraphic surface stratigraphic correlations between strata in shallow and deeper parts of the two margins lead us to propose the breakup sequence bs as representing the transitional period between lithospheric breakup and the establishment of thermal relaxation as the main process controlling subsidence on divergent continental margins the results in this work are important for other continental margins as they demonstrate that during lithospheric breakup significant quantities of sediment bypassed the inner proximal margins of west iberia and newfoundland on their way to the outer proximal margin in addition the interpreted data show that complete lithospheric breakup between conjugate margins is recorded by similar tectono stratigraphic events in iberia and newfoundland these events are associated with reservoir successions in sediment overfilled basins and with carbon rich strata black shales in sediment starved basins

lateral crustal variation and post rift magmatism in the northeastern south china sea determined by wide angle seismic data abstract the northeastern margin of the south china sea experienced continental rifting followed by magmatism in the cenozoic this evolution has strongly influenced the heterogeneity of its crustal structure to gain insights into the spatial variation in crustal structure data from 30 ocean bottom seismometers were used to forward model ten p wave velocity models along both dip and strike directions the cenozoic strata 1 7 3 5 km s the mesozoic strata 3 5 5 5 km s the crystalline crust 5 5 7 5 km s and high velocity lower crust 7 0 7 5 km s were identified based on p wave velocities overall the crust thins from 25 km on the continental shelf to 15 km on the slope with thicker crust underneath the dongsha basin a mesozoic basin but thinner crust underneath the pre cenozoic nw trending fault zones this difference in thickness is possibly controlled by different strength of inherited structures i e the dongsha basin and the fault zones furthermore a widespread high velocity lower crust layer which resulted from the intrusion of a mafic sill complex was observed over the shelf to slope mafic intrusions within the lower crust have uplifted the caprock on the shelf and magma eruptions have formed many post rift seamounts on the slope the evidence suggests that post rift magmatism overprinted the vertical crustal structure we therefore propose that the heterogeneous crustal structures in this passive margin are an integrated result of segmental extension followed by magmatic overprinting

reactivation of intrabasement structures during rifting a case study from offshore southern norway abstract pre existing structures within crystalline basement may exert a significant influence over the evolution of rifts however the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood using borehole constrained 2d and 3d seismic reflection data from offshore southern norway we identify and constrain the three dimensional geometry of a series of enigmatic intrabasement reflections through 1d waveform modelling and 3d mapping of these reflection packages we correlate them to the onshore caledonian thrust belt and devonian shear zones based on the seismic stratigraphic architecture of the post basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events reactivation preferentially occurs along relatively thick c 1 km relatively steeply dipping c 30 structures with three main styles of interactions observed between them and overlying faults i faults exploiting intrabasement weaknesses represented by intra shear zone mylonites ii faults that initiate within the hangingwall of the shear zones inheriting their orientation and merging with said structure at depth or iii faults that initiate independently from and cross cut intrabasement structures we demonstrate that large scale discrete shear zones act as a long lived structural template for fault initiation during multiple phases of rifting

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

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

rifting and magmatism in the northeastern south china sea from wide angle tomography and seismic reflection imaging we present a new travel time tomography velocity model and seismic reflection images that delineate the rift architecture and magmatic features of the rifted margin in the northeastern south china sea these data reveal moderately stretched crust 25 km thick along the continental shelf and thin but laterally variable crustal thickness in the distal margin along the continental slope crust rapidly thins to 4 km in a basin characterized by tilted fault blocks that sole into a low angle detachment strain was localized to a degree within the highly stretched basin but failed to progress to breakup and seafloor spreading crust in the distal margin is 12 15 km thick few extensional structures are apparent in the distal margin but seismic velocities are suggestive of highly thinned and magmatically intruded continental crust the magmatic features we interpret include volcanic zones at the top of the basement that deform or disrupt overlying postrift strata sills intruded into the postrift sedimentary section and a high velocity 6 9 7 5 km s lower crustal layer that we take to be magmatic underplating or pervasive lower crustal intrusions these features primarily occur in the distal margin and may have been emplaced during postrift seafloor spreading the postrift magmatism may have been induced by convective removal of continental lithosphere following breakup and the onset of seafloor spreading in the south china sea

extensional styles of the conjugate rifted margins of the south china sea abstract to elucidate continental rifting mechanism of the south china sea scs we characterize crustal structures of the two conjugate rifted margins and calibrate the continental ocean transition zone cot with multi channel reflection seismic gravimetric and magnetic data narrower than those found in many other magma poor margins the cot in the scs coincides well with a positive negative gravity boundary and shows moho reflection gaps basement highs and seaward normal faults post rifting spreading volcanic bodies and igneous intrusions often complicate the structures of the cot rifted basins here are often bounded by listric normal faults the majority of which terminate at the upper lower crust interface i e the brittle ductile transition boundary this observation suggests that the lower crust was weak and played a dominant role in the continental breakup we propose that the scs lower crust acted as a decouple layer during extension but the normal oceanic crust began to establish soon after crustal breakup we also show how thermal regime affected the extent and timing of continental rifting of the scs

styles of extension offshore mid norway and implications for mechanisms of crustal thinning at passive margins 1 eocene magmatic breakup along the mid norway rifted margin was preceded by extreme jurassic cretaceous crustal thinning in a magma poor environment along the se borders of the rift top basement detachment faults with heaves on the order of 15 40 km evolved in at least two stages to become the boundaries between moderately thinned 20 30 km thick crust and a 100 200 km wide highly extended area with crustal thicknesses generally between 2 and 12 km under the present day more and voring basins in the footwalls of the basin flank detachments lower and middle crust was exhumed in extensional domes that became incised by a younger set of normal faults under the most highly thinned areas a more distal set of deep seated basin floor detachments incised and extended remnant crust and probably the upper mantle leaving as little as 5 km of continental crust to be preserved under thick synrift and postrift deposits we suggest that basin flank detachments such as the ones described above hold the potential to reduce the crustal thickness down to the critical value required for embrittlement of continental crust thus they prepare the ground for incision by the basin floor detachments which may become responsible for exhumation of deep crust or continental mantle if extension is allowed to proceed

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

velocity weakening behavior of plagioclase and pyroxene gouges and stabilizing effect of small amounts of quartz under hydrothermal conditions 1 we investigated properties of frictional sliding of plagioclase pyroxene and their mixture gouges with a small amount of hornblende biotite and quartz as accessory minerals under hydrothermal conditions with an effective normal stress of 200 mpa pore pressure of 30 mpa and temperatures from 100 c to 600 c axial loading rate was stepped between 0 001 and 0 0001 mm s to acquire the rate dependence both plagioclase and pyroxene gouges showed velocity weakening behavior in the whole temperature range except the velocity strengthening behavior of pyroxene at 200 c for temperatures above 400 c both plagioclase and pyroxene gouges showed oscillatory slips as a result of small dc values of 3 4 m which make the critical stiffness rise remarkably and approach the system stiffness above 300 c the direct effect of plagioclase shows an increasing trend with temperature indicating control of the deformation process by thermally activated mechanisms as the difference of a and b values here are only 20 at most this trend also applies to the evolution effect our analytical derivation based on the theory of pressure solution shows a log linear contact area growth with time that corresponds to an evolution effect and estimations based on this encompass the plagioclase data though the identification of actual mechanisms is not easy finally it is found that a little quartz 3 5 added to the plagioclase 60 62 pyroxene 35 mixture has a strong stabilizing effect leading to a transition from velocity weakening to velocity strengthening these results may help constrain the depth range of seismic slips on deep faults in the lower crust of gabbroic composition

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

oligocene miocene carbonates and their role for constraining the rifting and collision history of the dangerous grounds south china sea abstract the attenuated continental crust of the dangerous grounds is located in the southeastern part of the south china sea it was affected by unconformities as identified by several authors cullen et al 2010 hinz and schluter 1985 hutchison 2010 hutchison and vijayan 2010 in the northeastern dangerous grounds a prominent reflector in seismic data is associated with the top of a widespread oligocene to early miocene 18 20 ma carbonate platform this reflector and the underlying carbonates can be used to constrain the timing of the unconformities and the rifting history of the dangerous grounds by carefully interpreting seismic reflection lines we trace the platform carbonates based upon their appearance in the seismic image this platform is continuous in the palawan borneo trough and gets patchy toward the dangerous grounds in the dangerous grounds the image of this key reflector changes and here it merely forms the top of a clastic layer carbonates remain abundant but mainly as isolated reefs that grew on top of tilted fault blocks in the southwestern dangerous grounds the prominent unconformity sealing the tectonic activity is known as the middle miocene unconformity this in fact is an early miocene unconformity which represents a sequence boundary in the borneo palawan trough and in various parts of the dangerous grounds while in other parts of the dangerous grounds it represents a major angular unconformity the unconformity characteristics supplemented with tentative ages indicate that luconia and the southern dangerous grounds were sub aerial during the early miocene while the reed bank the northern dangerous grounds and parts of the central dangerous grounds were mostly submerged except for some islands concentrated on the western edge of the borneo palawan trough this trough is interpreted as a foreland basin where the flexural forebulge provided shallow marine conditions that promoted reef growth as the carbonate deposition migrated from the borneo palawan trough toward the dangerous grounds we suggest that the flexural forebulge provided shallow water conditions for further reef growth on the eastern dangerous grounds

african stress pattern from formal inversion of focal mechanism data abstract the kinematic models and the associated orientation of extensional stress of the east african rift system have been subjected to much debate since a long time in the past decades the proposed models relied on the interpretation of the overall rift geometry geological fault slip data and the few focal mechanisms available these models generally suffer of a poor time control and an underestimation of the possible changes in the stress field and geodynamic regime with time and space in the recent years there has been a significant increase in the number of focal mechanisms available for the entire rift system and it is now possible to estimate the present day stress field in relative detail based on seismotectonic data alone we compile 347 focal mechanism data from the global harvard cmt catalogue and various other sources and grouped 332 of them in 24 distinct regions boxes on the basis of their geographical proximity kinematic homogeneity and tectonic setting for each box and for the same data set reduced stress tensors have been obtained by formal stress inversion using both the tensor program delvaux sperner 2003 and the slick method michael 1984 1987 both inversion methods show in comparable results in terms of horizontal stress axes orientations and tectonic stress regimes which stem for the robustness of the approach the obtained stress pattern reflects a complex interaction between 1st order effects as different driving forces including plate boundary forces and 2nd and 3rd order effects as gravitational potential of topography intra lithospheric processes and the influence of structural heterogeneities of the rift structures the evidence present in the stress orientations of the 2nd and 3rd order stress pattern as the variations in the horizontal stress axes along the axis of the rift are of particular interest as they were not yet captured or shown in earlier numerical models of the stress field additional sources of tectonic forces in supplement to the gravitational potential energy forces as considered in the earlier models are necessary to explain the observed patterns

the continent ocean transition at the mid northern margin of the south china sea the northern margin of the south china sea scs has particular structural and stratigraphic characteristics that are somewhat different from those described in typical passive margin models the differences are attributable to poly phase tectonic movements and magmatic activity resulting from the interaction among the eurasian philippine sea and indo australian plates based on several crustal scale multi channel seismic reflection profiles and satellite gravity data across the northetn scs margin this paper analyzes the structures volcanoes and deep crust of the continent ocean transition zone cot at the mid northern margin of the scs to study the patterns and model of extension there

comparison of surface slip and focal mechanism slip data along normal faults an example from the eastern gulf of corinth greece abstract focal mechanism and surface slip data are used to investigate whether kinematics are similar at depth and at the surface along an active normal fault in the gulf of corinth greece we present a new database of slip data from the lateral termination of the south alkyonides fault segment safs and the en echelon stepover between it and an adjacent fault and use published data on surface slip and focal mechanism data pertaining to slip at depth during the 1981 alkyonides earthquake sequence the focal mechanisms exhibit similar fault plane orientations and kinematics to those measured at the surface within the stepover both data sets show that contemporaneous c n s and c e w extension is being accommodated by c e w and c n s oriented normal faults and the overall deformation is distributed oblate vertical flattening the deviation of the surface slip direction from 350 increases with distance from the centre of the safs the deviation of the focal mechanism t axes from 350 fit well with the surface data implying that the coseismic slip on the safs at depths of 7 10 km exhibits a similar kinematic pattern as that observed at the surface our results imply that it is critical to know the along strike position of data on a fault if either focal mechanisms or surface slip are to be used to infer regional strain and stress trajectories

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

geodynamic significance of the trm segment in the east african rift w tanzania active tectonics and paleostress in the ufipa plateau and rukwa basin abstract the tanganyika rukwa malawi trm rift segment in western tanzania is a key sector for understanding the opening dynamics of the east african rift system ears in an oblique opening model it is considered as a dextral transfer fault zone that accommodates the general opening of the ears in an nw se direction in an orthogonal opening model it accommodates pure dip slip normal faulting with extension orthogonal to the rift segments and a general e w extension for the entire ears the central part of the trm rift segment is well exposed in the ufipa plateau and rukwa basin within the paleoproterozoic ubende belt it is also one of the most seismically active regions of the ears we investigated the active tectonic architecture and paleostress evolution of the ufipa plateau and adjacent rukwa basin and in order to define their geodynamic role in the development of the ears and highlight their pre rift brittle tectonic history the active fault architecture fault kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the trm segment two pre rift brittle events are evidenced an older brittle thrusting is related to the interaction between the bangweulu block and the tanzanian craton during the late pan african early paleozoic it was followed by a transpressional inversion during the early mesozoic this inversion stage is the best expressed in the field and caused dextral strike slip faulting along the fault systems that now control the major rift structures it has been erroneously interpreted as related to the late cenozoic ears which instead is characterized by pure normal faulting our third and last stress stage

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

spreading dynamics and sedimentary process of the southwest sub basin south china sea constraints from multi channel seismic data and iodp expedition 349 abstract neotectonic and sedimentary processes in the south china sea abyssal basin are still debated because of the lack of drilling evidence to test competing models in this study we interpreted four multi channel seismic profiles across the southwest sub basin swsb and achieved stratigraphic correlation with new drilling data from integrated ocean discovery program iodp expedition 349 neogene sediments are divided into four stratigraphic units each with distinctive seismic character sedimentation rate and lithology variations suggest climate controlled sedimentation in the late miocene winter monsoon strength and increased aridity in the limited accumulation rates in the swsb since the pliocene summer monsoons and a variable glacial interglacial climate since have enhanced accumulation rates terrigeneous sediments in the swsb are most likely derived from the southwest three basement domains are classified with different sedimentary architectures and basement structures including hyper stretched crust exhumed subcontinental mantle and steady state oceanic crust the swsb has an asymmetric geometry and experienced detachment faulting in the final stage of continental rifting and exhumation of continental mantle lithosphere mantle lithospheric breakup post dates crustal separation delaying the establishment of oceanic spreading and steady state crust production

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

the south china sea margins implications for rifting contrasts abstract implications regarding spatially complex continental rifting crustal extension and the subsequent evolution to seafloor spreading are re examined for the northern and southern rifted margins of the south china sea previous seismic studies have shown dramatic differences in the present day crustal thicknesses as the manifestations of the strain experienced during the rifting of the margin of south china although the total crustal extension is presumed to be the same along the margin and adjacent ocean basin the amount of continental crustal extension that occurred is much less along the east and central segments of the margin than along the western segment this difference was accommodated by the early formation of oceanic crust creating the present day south china sea basin adjacent to the eastern margin segment while continued extension of continental crust was sustained to the west using the observed cross sectional areas of extended continental crust derived from deep penetration seismics two end member models of varying rift zone widths and varying initial crustal thicknesses are qualitatively examined for three transects each model implies a time difference in the initiation of seafloor spreading inferred for different segments along the margin the two models examined predict that the oceanic crust of the south china sea basin toward the west did not begin forming until sometime between 6 12 my after its initial formation 32 ma toward the east these results are compatible with crustal age interpretations of marine magnetic anomalies assuming rifting symmetry with conjugate margin segments now residing along the southern portions of the south china sea basin implies that the total width of the zone of rifting in the west was greater than in the east by about a factor of two we suggest the most likely causes of the rifting differences were east west variations in the rheology of the pre rift crust and associated east west variations in the thermal structure of the pre rift lithosphere the calculated widths of rifted continental crust for the northern and southern margins when combined with the differential widths of seafloor generated during the seafloor spreading phase indicate the total crustal extension that occurred is about 1100 km and is remarkably consistent to within 10 for all three eastern central western segments examined

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

re orientation of the extension direction and pure extensional faulting at oblique rift margins comparison between the main ethiopian rift and laboratory experiments in this study we draw on a unique combination of well resolved fault slip data and earthquake focal mechanisms to constrain spatial variations in style of faulting in the obliquely extending main ethiopian rift east africa these data show that both boundary and internal faults oblique and orthogonal to the plate divergence pd respectively exhibit almost pure dip slip motion and indicate significant local deflection in orientation of the extension direction at rift margins scaled analogue models closely replicate the multidisciplinary observations from the rift and suggest that the process is controlled by the presence of a deep seated pre existing weakness oblique to the direction of pd that is able to cause a local rotation in the orientation of the extension direction at rift margins minor counterclockwise block rotations are required to accommodate the difference in slip direction along the different fault systems as supported by existing and new palaeomagnetic data from the rift

overlapping faults intrabasin highs and the growth of normal faults normal fault systems bounding extensional basins are typically adjoined by a series of subbasins separated by intrabasin highs the strata within these basins form syndepositional anticlines and synclines whose axes are transverse to the strike of the main bounding fault one possible explanation for these intrabasin highs is that they result from persistent along strike deficits in fault displacement such deficits are incompatible with scaling relationships observed between fault displacement and length based on large populations of faults we present data from active normal faults within the basin and range province and from inactive normal faults of the newark basin of eastern north america demonstrating a clear correlation between the along strike position of overlapping splay faults and the location of intrabasin highs as well as syndepositional transverse folds summed displacements for all faults within an intrabasin high are comparable to the displacements on faults bounding flanking subbasins o

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

breaking up the hanging wall of a rift border fault the 2009 karonga earthquakes malawi 1 the southern east african rift has an unusually large seismogenic thickness 35 40 km which is responsible for wide tilted basins and extremely long faults with the potential for m7 8 normal faulting earthquakes from 6 19 december 2009 a shallow earthquake sequence four of mw 5 5 hit the karonga region of northern lake malawi the location is 50 km west of the rift bounding livingstone fault within the hanging wall we used seismology and insar to obtain source parameters and combined this with information on rift structure from geomorphology and seismic profiles the deformation is consistent with rupture of a shallow west dipping fault with no evidence for the involvement of magmatic fluids although the livingstone fault dominates local geomorphology the karonga earthquakes demonstrate that the hanging wall block is actively breaking up reflecting temporal and spatial migration of activity or the release of stresses within it

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

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

along strike segmentation of the south china sea margin imposed by inherited pre rift basement structures abstract multibeam bathymetric seismic and borehole data are used to investigate a large scale strike slip structure the baiyun liwan fault zone in the northern south china sea this fault zone comprises nw to ne striking faults and negative flower structures that were generated by oblique extensional displacement notably the interpreted data reveals that the baiyun liwan fault zone was active during the cenozoic recording intense magmatism and accommodating significant intraplate deformation during progressive continental rifting and ocean spreading it bounds two distinct crustal segments and played a significant role in segmenting the northern margin of the south china sea the geometry of faults and strata within the baiyun liwan fault zone also controlled local sediment routing and depocentre evolution during the cenozoic as basement and syn rift structures change markedly across the baiyun liwan fault zone we propose this structure to be inherited from a lithospheric scale fault zone separating the mesozoic arc from forearc related terrains we therefore stress the importance of pre existing structures in the development of rifted margins with the example provided by the baiyun liwan fault zone having profound implications for palaeogeographic reconstructions in the south china sea at present the baiyun liwan fault zone is incised by the pearl river canyon and eroded by recurrent submarine landslides forming a major area of sediment bypass towards the abyssal plain

an alternative model for the growth of faults conventional growth models suggest that faults become larger due to systematic increases in both maximum displacement and length we propose an alternative growth model where fault lengths are near constant from an early stage and growth is achieved mainly by increase in cumulative displacement the model reconciles the scaling properties of faults and earthquakes and predicts a progressive increase in fault displacement to length ratios as a fault system matures this growth scheme is directly applicable to reactivated fault systems in which fault lengths were inherited from underlying structure and established rapidly the model may also apply to some non reactivated fault systems near constant fault lengths during subsequent growth are attributed to retardation of lateral propagation by interaction between fault tips the model is validated using kinematic constraints from growth strata which are displaced by a system of reactivated normal faults in the timor sea nw australia

continental rifting parallel to ancient collisional belts an effect of the mechanical anisotropy of the lithospheric mantle analysis of major rift systems suggests that the preexisting structure of the lithosphere is a key parameter in the rifting process rift propagation is not random but tends to follow the trend of the orogenic fabric of the plates systematically reactivating ancient lithospheric structures continental rifts often display a clear component of strike slip deformation in particular in the early rifting stage moreover although the close temporal and spatial association between flood basalt eruption and continental breakup suggests that mantle plumes play an important role in the rifting process there is a paradox between the pinpoint thermal and stress perturbation generated by an upwelling mantle plume and the planar geometry of rifts these observations suggest that the deformation of the lithosphere especially during rifting is controlled by its preexisting structure on the other hand 1 the plasticity anisotropy of olivine single crystal and aggregates 2 the strong crystallographic orientation of olivine observed in mantle xenoliths and lherzolite massifs and 3 seismic anisotropy data which require a tectonic fabric in the upper mantle coherent over large areas suggest that preservation within the lithospheric mantle of a lattice preferred orientation lpo of olivine crystals may induce a large scale mechanical anisotropy of the lithospheric mantle we use a polycrystal plasticity model to investigate the effect of a preexisting mantle fabric on the continental breakup process we assess the deformation of an anisotropic continental lithosphere in response to an axi symmetric tensional stress field produced by an upwelling mantle plume by calculating the deformation of textured olivine polycrystals representative of the lithospheric mantle at different positions above a plume head model results show that a lpo induced mechanical anisotropy of the lithospheric mantle may result in directional softening leading to heterogeneous deformation during continental rifting this mechanical anisotropy may induce strain localisation in domains where extensional stress is oblique 30 55 to the preexisting mantle fabric this directional softening associated with olivine lpo frozen in the lithospheric mantle may also guide the propagation of the initial instability that will follow the preexisting structural trend the preexisting mantle fabric also controls the deformation regime imposing a strong strike slip shear component a lpoinduced mechanical anisotropy may therefore explain the systematic reactivation of ancient collisional belts during rifting structural inheritance the plume rift paradox and the onset of transtension within continental rifts fl 2001 elsevier science b v all rights reserved

continentward dipping detachment fault system and asymmetric rift structure of the baiyun sag northern south china sea abstract the rift architecture and deep crustal structure of the distal margin at the mid northern margin of the south china sea have been previously investigated by using deep seismic reflection profiles however one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins baiyun sag and liwan sag within the distal margin because of the limited amount of seismic data based on new 3d seismic survey data and 2d seismic reflection profiles we observe an array of fault blocks in the baiyun sag which were tilted towards the ocean by extensional faulting the extensional faults consistently dip towards the continent beneath the tilted fault blocks and extensional faults a low angle high amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process during rifting the continentward dipping normal faults evolved in a sequence from south to north generating the asymmetric rift structure of the baiyun sag the baiyun sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 ma and a ridge jump to the south at 26 24 ma therefore we propose that magmatism played a significant role in the continental extension and final breakup in the south china sea

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