comment on barckhausen et al 2014 evolution of the south china sea revised ages for breakup and seafloor spreading abstract we re examined the cessation of the south china sea seafloor spreading by using radioactive dating and fossil assemblage of the eto and the te derived age the youngest available age for the fragment of the south china sea is 15 ma and is more consistent with those suggested by previous studies moreover recent iodp expedition preliminary results suggested that the hemipelagic claystone layer stratigraphically bounded by igneous sequences of massive lava flow rock is early miocene in age therefore the previous interpretations are more inclusive than those provided by barckhasen et al 2014 and indicate that a slow spreading ridge was more plausible to have occurred during the seafloor spreading of the south china sea

constraints on the crustal nature and tectonic history of the kerguelen plateau from comparative magnetic modeling using magsat data abstract the kerguelen plateau in the southern indian ocean is associated with the broken ridge plateau because of their location with respect to the southeast indian ridge the kerguelen plateau lies south of the mid ocean ridge and the broken ridge plateau is located at a nearly equal distance to the north both plateaus have positive magsat crustal magnetic anomalies associated with them comparative modeling of these anomalies places constraints on the crustal nature the thermal structure and the tectonic history of the plateaus our results support the theory that both plateaus are underlain by oceanic crust are structurally and lithologically similar and were formed as a single structure which has since been split by seafloor spreading active volcanoes on the northern part of the kerguelen plateau suggest that it lies on a hotspot which has raised the curie isotherm to within the crust of the plateau decreasing the crustal volume contributing to the magnetic anomaly and thus decreasing the amplitude of the anomaly

mid ocean ridge or marginal basin origin of the east taiwan ophiolite chemical and isotopic evidence the east taiwan ophiolite eto occurs as allochthonous fragments embedded in the plio pleistocene lichi melange in the coastal range of eastern taiwan it is probably the youngest among the known ophiolitic complexes of the world the overall geochemical and isotopic characteristics of the representative rock types are very oceanic and strongly argue for a mid ocean or marginal basin origin of the eto the best criteria include 1 major element compositions 2 ree distribution patterns 3 nd isotopic ratios some have nd 12 4 pb isotopic ratios and 5 the presence and nature of the red shale this conclusion is supported by previous studies of metamorphic evolution of the eto

a new view of integrating stratigraphic and tectonic analysis in south china sea and north borneo basins abstract this review outlines how se asian tectonic and stratigraphic studies could be more closely linked many tectonic papers on the region include comments on stratigraphic evidence and stratigraphic papers often allude to tectonic events but this paper highlights the benefits of a more detailed integration of the two fields of study into a single geological model by using inductive sequence stratigraphic methods supported by geohistory plots the south china sea and north borneo region has been traditionally been divided into provinces each with its own distinct stratigraphy a handicap in merging all the provinces into one geological model has been the inconsistent application of basic biostratigraphy and some examples are given that illustrate that more careful documentation of a complex data set is required in future work the inductive stratigraphic method requires increased analytical work to calibrate seismic data but even on current data an episodic stratigraphic history is indicated and a single tectono stratigraphic framework for the whole region is emerging with a greatly simplified and consistent terminology this review examines the impact of these methods on one important period of transition around the oligo miocene boundary the summary given for the oligo miocene transition questions the viability of the commonly cited slab pull tectonic model as both the historical order of geological events and geographic spread of effects does not fit that model as currently understood

spatial variations in effective elastic thickness in the western pacific ocean and their implications for mesozoic volcanism abstract we have used free air gravity anomaly and bathymetric data together with a moving window admittance technique to determine the spatial variation in oceanic elastic thickness t e in the western pacific ocean synthetic tests using representative seamounts show that t e can be recovered to an accuracy of 5 km for plates up to 30 km thick with increased accuracy of 3 km for t e 20 km the western pacific has a t e range of 0 50 km with a mean of 9 4 km and a standard deviation of 6 8 km the t e structure of the region is dominated by relatively high t e over the hawaiian emperor seamount chain intermediate values over the marshall islands gilbert ridge and marcus wake guyots and low values over the line islands mid pacific mountains caroline islands shatsky rise hess rise and musician seamounts plots of t e at sites with radiometric ages suggest that t e is to first order controlled by the age of the lithosphere at the time of loading in areas that backtrack into the south pacific isotopic and thermal anomaly sopita t e may be as low as the depth to the 180 120 c isotherm at least locally in the northern part of the study area including the hawaiian emperor seamount chain t e correlates with the depth to 310 120 c these best fitting isotherms imply peak rates of volcanism during 100 120 ma early cretaceous and 140 150 ma late jurassic the corresponding addition of 8 10 6 km 3 and 4 10 6 km 3 of volcanic material to the surface of the oceanic crust would result in long term sea level rises of 20 m and 10 m respectively the late jurassic volcanic event like the later early cretaceous event appears to have influenced the tectonic evolution of the pacific plate convergent boundaries resulting in increased volcanism and orogenesis

analysis of magsat magnetic contrasts across africa and south america abstract comparisons of magsat magnetic contrasts and geology across the mesozoic assembly of africa and south america provide new insight into the interpretation of the long wavelength magnetic anomalies near the present continental margins across continental africa and south america the magsat magnetic contrasts can be correlated with geologic provinces formed before the mesozoic separation of the continents on the continents areas affected by significant mesozoic hotspot tectonism display negative magnetic contrasts suggesting a causative relationship between hotspot tectonism and the origin of the observed magnetic contrasts the magnetic characteristics of a portion of the lower crust in these areas appear to have been significantly altered during the mesozoic hotspot epeirogeny by analogy with the processes of continental rifting it is suggested that the magnetic mineralogy of the intruded lower crust may be dominated by weakly to non magnetic titanomagnetites oceanic magnetic contrast comparisons show that the positions of magnetic anomaly highs over the rio grande walvis ridge system of the south atlantic are consistent with the interpretation of their evolution over the walvis hotspot however only the parts of these ridges that were formed during the cretaceous normal polarity geomagnetic epoch bear strong magnetic contrasts remanent magnetization thus appears to be an important contributor toward the magsat magnetic anomalies of these features

a model of ocean basin crustal magnetization appropriate for satellite elevation anomalies a model of ocean basin crustal magnetization measured at satellite altitudes is developed which will serve both as background to which anomalous magnetizations can be contrasted and as a beginning point for studies of tectonic modification of normal ocean crust the model is based on published data concerned with the petrology and magnetization of the ocean crust and consists of viscous magnetization and induced magnetization estimated for individual crustal layers thermal remanent magnetization and chemical remanent magnetization are excluded from the model because seafloor spreading anomalies are too short in wavelength to be resolved at satellite altitudes the exception to this generalization is found at the oceanic magnetic quiet zones where thermal remanent magnetization and chemical remanent magnetization must be considered along with viscous magnetization and induced magnetization

cenozoic tectonic and stratigraphic development of the central vietnamese continental margin abstract the east vietnam boundary fault zone evbfz forms the seaward extension of the red river shear zone and interacted with the extensional rift systems in basins along the central vietnamese continental margin the structural outline of the central vietnamese margin and the timing of deformation are therefore fundamental to understanding the development of the south china sea and its relation to indochinese escape tectonism and the india eurasia collision this study investigates the structural and stratigraphic evolution of the central vietnamese margin in a regional tectonic perspective based on new 2 d seismic and well data the basin fill is divided into five major oligocene to recent sequences separated by unconformities deposition and the formation of unconformities were closely linked with transtension rifting the opening of the south china sea and late neogene uplift and denudation of the eastern flank of indochina the structural outline of the central vietnamese margin favors a hybrid tectonic model involving both escape and slab pull tectonics paleogene left lateral transtension over the nnw striking evbfz occurred within the song hong basin and the quang ngai graben and over the da nang shelf western phu khanh basin related to the escape of indochina east of the evbfz paleogene ne striking rifting prevailed in the outer phu khanh basin and the hoang sa graben fitting best with a prevailing stress derived from a coeval slab pull from a subducting proto south china sea beneath the southwest borneo palawan region major rifting terminated near the end of the oligocene however late stage rifting lasted to the early miocene when continental break up and seafloor spreading commenced along the edge of the outer phu khanh basin the resulting transgression promoted lower and middle miocene carbonate platform growth on the da nang shelf and the tri ton high whereas deeper marine conditions prevailed in the central part of the basins partial drowning and platform retreat occurred after the middle miocene due to increased siliciclastic input from the vietnamese mainland as a result siliciclastic marine deposition prevailed offshore central vietnam during the pliocene and pleistocene

lithospheric magnetic property contrasts within the south american plate derived from damped least squares inversion of satellite magnetic data abstract a ridge regression or damped least squares method has been used in a large scale equivalent source inversion of south american magsat data the optimum damping parameter is selected based on percent increase in the sum of squared residual of the observed and the calculated anomaly and on the variance and the range of the solution for a series of damping parameters solutions obtained by the damping parameter selected in this manner are numerically stable and geologically meaningful consequently these solutions are used in various applications such as transformation into effective magnetic susceptibility variation altitude normalization differential reduction to pole and downward continuation of the data set the spacing of equivalent sources and the source observation distance are shown to introduce significant errors in the estimation of the physical property variation from equivalent source solutions for the large source spacing 1 commonly in use the correction for these geometric factors is essential in estimating the physical property variation from the equivalent source solutions a continental and an oceanic profile have been analyzed from the south american maps derived from the above techniques the continental profile transects a variety of geologic tectonic features including shields aulacogens basins and fold belts near the north coast of south america along the profile there is a good correlation between the radially polarized magsat magnetic anomalies and other available geologic and geophysical information in addition the variation in effective susceptibility obtained from the damped equivalent source inversion is consistent with our present knowledge of continental lithospheric susceptibilities expected from the geologic tectonic provinces along the profile the oceanic profile extends from the trailing margin of south america through the cretaceous normal polarity rocks of the south atlantic ocean the variations in the magnetic properties along this profile can be broadly correlated with the depth anomaly variation indicating a possible genetic relationship two conceptual models requiring undepleted mantle intrusions under the oceanic uplifts appear possible in the first model the high magnetization can be accounted for by a weakly magnetic upper mantle below the uplifts in the second model very highly magnetic rocks are required in the crust of these uplifted regions to account for the observed anomaly values

calcareous nannofossil changes in response to the spreading of the south china sea basin during eocene oligocene abstract numerous models have been proposed to constrain the process of the south china sea formation yet the paleogene paleoenvironmental researches are hindered by the paucity of long continuous well dated geological records in this work eocene to oligocene nannofossil biostratigraphy and assemblage changes in a sediment section from the northern south china sea were studied to shed light on these issues we established an age model to confine the studied section between 40 and 22 ma based on 17 calcareous nannofossil datum levels the age model enabled to date the most prominent seismic reflector t60 centered at 26 8 ma a regional tectonic event interpreted as corresponding to the ridge jump event in the early phase of south china sea spreading changes in nannofossil abundance and assemblage compositions imply continuous transgression and deepening of water depth from the late eocene to early miocene during the late eocene the studied area was a neritic sea with relatively eutrophic conditions supporting abundant r lockeri group and c pelagicus from 34 ma to 27 ma during the oligocene the earlier neritic environment was replaced by relative warm and oligotrophic conditions in a shallow sea as indicated by higher concentration of c floridanus sphenolithus spp and helicosphaera spp since 26 ma pelagic conditions prevailed small reticulofenestra

pogo and pangaea abstract long wavelength magnetic anomalies of crustal origin derived from the pogo and magsat satellite data often display a strong continuity across the now rifted continental margins when the continents are reassembled into pangaea these anomalies predate the breakup of the supercontinent and represent major blocks whose crustal properties are broadly similar even though those blocks are no longer contiguous

phenomena of pulsation tectonics related to the breakup of the eastern north american continental margin abstract new data from the recent ipod drilling of dsdp site 534 in the blake bahama basin give a definite age for the spreading center shift involved in the breakup of the north american atlantic margin a basal callovian age 155 m y is determined for the blake spur magnetic anomaly marking this spreadingcenter shift that signals the birth of the modern north atlantic ocean this is some 20 m y younger than previously thought an implication of this younger age for the blake spur event is that very high spreading rates are now required for the jurassic outer magnetic quiet zone along the north american margin this association of a relatively high spreading rate with a magnetic quiet zone is similar to that for the mid cretaceous and implies a link between the processes controlling plate spreading which are in the upper mantle and the processes controlling the magnetic field which are in the outer core a theory of pulsation tectonics involving the cyclic eruption of plumes of hot mantle material from the lowermost mantle could explain the correlation plumes carry heat away from the core mantle boundary and later reach the asthenosphere and lithosphere to induce faster spreading the pulse of fast spreading in the jurassic apparently followed the breakup of continents bordering the north atlantic ocean other pulses of fast spreading appear to correlate with major ocean openings on various parts of the globe implying that this might be a prevalent process rifting of passive margins may be controlled by the more fundamental global processes described by the theory of pulsation tectonics

effective magnetic susceptibility of the oceanic upper mantle derived from magsat data passive ocean continent boundaries have little magnetic signatures at magsat altitude 400 km whereas subducting oceanic lithosphere has well defined magnetic anomalies over some of the subduction zones based on this observation and a thermal evolution model of the oceanic lithosphere subducted along the kuril kamchatka trench we determined an effective magnetic susceptibility of 0 0085 si for the upper 35 km of the oceanic upper mantle

hotspots in the southern oceans an absolute frame of reference for motion of the gondwana continents abstract the geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time that is motion of an order of magnitude less than the relative motion between plate pairs in most cases it is concluded that inter hotspot movement cannot be discerned for the period 100 m y to present and that widely distributed hotspots in the atlantic and indian oceans provide a frame of reference for plate motions following the disintegration of gondwanaland which is independent of paleomagnetism this frame of reference is absolute in that it gives the motion of the lithosphere with respect to the mantle hotspots the absolute motion model indicates that africa and antarctica are now moving only very slowly that there has been significant relative movement between east and west antarctica since the cretaceous and prescribes the relative motion between the somali and african plates

major unconformities termination of extension events and associated surfaces in the south china seas review and implications for tectonic development abstract the distribution of unconformities and end of cenozoic rifting events in the south china seas scs reflects both the modes of rift development and the effects of driving mechanisms continental rifting began in the eastern basins during the paleocene and propagated westwards to the vietnam basin margin in the late eocene continental breakup around 32 28 ma caused a regional reduction or cessation in extensional activity particularly affecting basins furthest from the spreading centre basins in the slope and deepwater area north of the spreading centre exhibit reduced fault activity until 21 20 ma propagation of oceanic crust westwards between 25 and 23 ma and termination of seafloor spreading sometime between 20 5 and 16 ma affected fault activity in the qiongdongnan and nam con song basins in the phu khanh basin and south in the dangerous grounds area extension continued until about 16 ma ending at the red unconformity the end of seafloor spreading around 20 5 ma reflects loss of extensional driving force as thinned continental crust entered the nw borneo subduction zone controversially a key component of the driving force maybe attributed to slab pull a transitional period of about 5 7 my between the onset of subduction of continental crust and final jamming of the subduction zone deep regional unconformity dru is inferred the last pulse of extension was focussed in the western scs and terminated around 10 5 ma detailed understanding of proto south china seas development remains uncertain and controversial

reply to chang et al 2014 evolution of the south china sea revised ages for breakup and seafloor spreading abstract chang et al introduce some new lines of evidence for an end of seafloor spreading in the south china sea not before 15 ma however we find strong indications that their interpretation is not conclusive the origin of the east taiwan ophiolite from the scs as assumed by chang et al is not in agreement with recent studies which find continental crust in the deep water domain of the northeastern south china sea the age dating of the east taiwan ophiolite is based on one single k ar age of questionable accuracy the calculation of te derived ages leaves a thermal rejuvenation of the oceanic crust in the south china sea by post spreading volcanism out of consideration biostratigraphically determined ages of sediments recovered directly above igneous crust of the south china sea during iodp 349 drilling expedition are inconclusive so far the final key to unlocking the spreading history of the scs will be the ar ar age dating of the basaltic rocks recovered during iodp expedition 349

climate changes control offshore crustal structure at south china sea continental margin a b s t r a c t rifted continental lithosphere subsides as a consequence of combined crustal thinning and mantle lithosphere cooling yet basins on some continental margins experience anomalous subsidence events that postdate active extension deep basins on the northern margin of the south china sea notably the baiyun sag show basement subsidence accelerating after 21 ma postdating extension by several million years we combine geophysical observations and numerical forward modeling to show that loading of the offshore basins by increased sediment flux caused by faster onshore erosion following early miocene monsoon intensification is a viable trigger for ductile flow after the cessation of active extension this illustrates that offshore basin dynamics at continental margins with weak crust can be controlled by onshore surface processes in a newly recognized form of climate tectonic coupling

native iron in the continental lower crust petrological and geophysical implications lower crustal granulite xenoliths recovered from a kimberlite pipe in western africa contain native iron fe 0 as a decomposition product of garnet and ilmenite magnetic measurements show that less than 0 1 percent by volume of iron metal is present data from geothermometry and oxygen geobarometry indicate that the oxide and metal phases equilibrated between iron wustite and magnetite wustite buffers which may represent the oxidation state of the continental lower crust and the depleted lithospheric upper mantle ferromagnetic native iron could be stable to a depth of approximately 95 kilometers and should be considered in the interpretation of long wavelength static magnetic anomalies

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

seismic sequence stratigraphic analysis of the carbonate platform north offshore taiping island dangerous grounds south china sea abstract taiping island also known as itu aba is the largest natural terrestrial landmass in the south china sea and is centrally located using bathymetry and marine multi channel seismic data we explored the seismic stratigraphic features of the offshore and isolated carbonate platform north of taiping island the western flank of the carbonate platform is characterized by an intercalation between high amplitude and low amplitude reflections showing the landward and seaward migration of the platform foreslope deposits in addition there are two offshore carbonate build ups that are underlain by normal faults six sequence boundaries and five depositional sequences caused by eustatic sea level cycles are identified and correlated with the eustatic sea level change chart although the evolution of the seismic sequences is partly controlled by local tectonics the overall stacking pattern of the sedimentary strata in our study area reveals five third order cycles and one second order cycle which is in accordance with the eustatic sea level chart additionally the formations of the western taiping seamount group and the zhenghe daoming trough are preliminarily analyzed based on seismic data

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

evolution of the south china sea revised ages for breakup and seafloor spreading abstract the continental breakup which gave way to the formation of the oceanic south china sea scs basin began in the latest cretaceous in the northeastern scs and propagated in southern and western direction over a long period of time possibly more than 40 m y the seafloor spreading history of the south china sea has been interpreted in different ways in the past and the debate over the correct timing of the major tectonic events continues we review the different models that have been published and present a revised interpretation of seafloor spreading anomalies based on three datasets with documented high quality which cover all of the scs but the northernmost and southernmost parts we can precisely date the onset of seafloor spreading in the central part of the scs at 32 ma after a ridge jump at 25 ma spreading also began in the southwestern sub basin and spreading ended at 20 5 ma in the entire basin followed by a phase of magmatic seamount formation mainly along the abandoned spreading ridge spreading rates vary from 56 mm yr in the early stages to 72 mm yr after the ridge jump to 80 mm yr in the southwestern sub basin we find indications for a stepwise propagation of the seafloor spreading from northeast to southwest in segments bounded by major fracture zones seafloor spreading ended abruptly probably because the subduction zone along the eastern and southern boundary of the scs of which today the manila trench remains was blocked by collision with a continental fragment possibly the northern part of palawan or a part of the dangerous grounds