throughgoing crustal faults along the northern margin of the south china sea and their role in crustal extension a study of the rifled northern margin of the south china sea based on new single ship and two ship multichannel seismic data has revealed the presence of highly reflective steeply dipping normal faults which cut through the entire crust these faults with dips of 25 40 are associated with localized crustal thinning of 5 15 km and represent horizontal extension of the order of tens of kilometers a range of 5 20 km of horizontal extension has been measured along individual faults although the relative amount of horizontal extension taken up by these faults is modest compared to the total extension across the margin only about 15 or less the amount of localized crustal thinning which takes place along these fault surfaces is quite significant at one fault location the crustal thickness is reduced by 40 although the faults described have been recognized at three separate locations along the margin their trends appear to differ at each in two examples the faults are oblique to the inferred general north south extension direction of the margin this characteristic taken with the fact that some of the crustal faults also appear to serve as abrupt boundaries between broad regions of differing crustal thickness and reflectivity of the lower crust suggests that at least some of these faults were present prior to rifting such faults are postulated to have been former thrust faults perhaps associated with a triassic suture zone and or cretaceous subduction margin which have been reactivated as normal faults during subsequent rifting alternatively some of the throughgoing faults may represent crustal detachment surfaces that first formed as the result of a simple shear response to crustal extension

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

a stable isotope study of cave seepage waters an isotope study 18o 2 h of 62 samples of waters from both the interior of the nerja cave malaga southern spain and the exterior sinkholes and springs at the site was carried out rainfall water in the study area was also studied the mean value of seepage waters can be considered as the mean isotopic value of the precipitation waters of the area the origin and aquifers of these different types of waters has also been studied obtaining a clear meteoric origin both for the seepage waters and the waters from the wells and springs but the aquifer of the latter is different showing more negative isotopic values this suggests that they could have mixed with waters from other aquifers which are either deeper or originate at other altitudes

basin superposition on the northern margin of the south china sea abstract basin superposition on the northern margin of the south china sea is a product of pulsed basin development with geometries which changed through space and time of changing strain fields and of tectonically inherited pre existing zones of crustal weakness this region of the south china sea was welded together or assembled prior to the cretaceous three distinct episodes of continental disassembly and accompanying basin evolution ensued each episode commencing with rifting and the formation of grabens or half grabens and each terminating with a gentle subsidence phase the major trends of the faults and basins varied from predominantly ne for the first episode through ne ew for the second to ew nw for the third the first episode occurred during the late cretaceous to paleocene as a back arc extensional domain induced by the dip steepening of a subducted oceanic slab the second basin episode of the late eocene to early oligocene was initiated by the collision of the indian plate with the eurasian plate the continued penetration of the former into the latter led to the tectonic escape and subsequent clockwise rotation of the indochina block creating regional transtension and left lateral motion along the red river fault the third episode of basin development occurred during the middle miocene as a reactivated product of this collision owing to the clockwise rotation of indochina the approximately e w trend of the simple shear principal displacement zone changed to northwest by the pliocene the eastward extrusion of south china had exceeded that of indochina reversing the sense of red river fault displacement to right lateral a clockwise rotation of the red river geosuture together with considerations of the influence of zones of inherited crustal weakness provides a model for the observed episodic changes in regional strain such a model best explains the post cretaceous evolution of superimposed basins on the northern margin of the south china sea

exploration history of liuhua 11 1 field pearl river mouth basin china 1 stratigraphic analysis of sparse seismic data in 1981 indicated the presence of a lower miocene carbonate platform complex over the western part of the dongsha massif 220 km 137 mi southeast of hong kong two bank edge trends were recognized and a large structural closure within the carbonate platform was mapped along the axis of the uplift the study also predicted the presence of a widespread thick basal sandstone below the carbonate complex that could serve as a conduit for long distance migration of hydrocarbons into the closure although the prospect was a high risk play in deep water 38 km 24 mi south of the edge of a paleogene basin with possible oil source rocks it was intriguing because of its size and similarity to the giant bombay high oil field offshor india after drilling by other companies demonstrated that oil had migrated well out of the source basin huizhou sag amoco negotiated for contract area 29 04 and was awarded the area in november 1985 the first amoco well lh 11 1 1a tested 2240 bbl day of 21 degree api oil from a 75 m 246 ft pay section in a carbonate platform sequence topped at 1197 m 3927 ft a 401 m 1316 ft lower carbonate section and a 149 m 489 ft sandstone unit resting on basement were water bearing additional drilling has confirmed a giant in place oil accumulation but commerciality is yet to be determined the carbonate complex includes a leached limestone platform facies with a reefal southwestern margin and has excellent porosity and permeability the oil is less waxy and heavier than other huizhou ag sourced oils because of biodegradation after migration

sand invasion along the portuguese coast forced by westerly shifts during cold climate events phases of higher aeolian activity are responsible for the formation and movement of large transgressive dunefields well reported phases of aeolian activity in northwest europe are coincident with global cooling events and were related to enhanced westerly winds and storminess however the extent to which these climatic episodes influenced dunefield dynamics in southwest europe remains an open question ground penetrating radar gpr was used to image the stratigraphy of a cliff top coastal transgressive dunefield in portugal and reconstruct former windfield regimes using optically stimulated luminescence osl five major phases of aeolian activity were dated at 12 6 5 6 1 2 0 4 and 0 3 ka and related to coastal instability and enhanced westerlies these phases were later reconciled to favorable patterns of atmospheric circulation simulated by global and regional climate models at both synoptic and local scales respectively the results prove that major phases of aeolian activity in southwest europe are associated with the onset of cold climate events of global distribution coinciding with aeolian accumulation in northwest europe this implies the dominance of zonal westerlies along the western coast of europe from denmark to portugal during the onset of cold climate events model simulations suggest that the pattern of atmospheric circulation during periods of enhanced aeolian activity is compatible with prolonged negative phases of the north atlantic oscillation nao

the structure of southwest taiwan the development of a fold and thrust belt on a margins outer shelf and slope d b j a m and c b acknowledge funding provided by the spanish ministerio de economia y competividad grant cgl2013 43877 p h k c acknowledges funding by most 104 2628 m 008 005 my3

recharge processes on typical karst slopes implied by isotopic and hydrochemical indexes in xiaoyan cave guilin china summary measurements of the hydrogen and oxygen isotopic composition of precipitation and drip stream water at drip site xy5 in xiaoyan cave in guilin city were conducted to investigate the infiltration and vadose flow processes and to characterize precipitation discharge relationship in the overlying karst hillslope area a marked seasonal variability of oxygen and hydrogen isotopes was observed in precipitation ranging from 18 7 to 0 6 for 18 o and 139 to 5 for d respectively during the study period from november 2013 to october 2014 however the narrow range observed for cave drip stream water d of 43 to 22 18 o of 7 3 to 4 3 was attributed to homogenization via mixing of meteoric waters in the unsaturated zone above the cave although drip stream waters plot close to or slightly above the local meteoric water line the weighted average 18 o value of precipitation is depleted than in dripwater which is attributed to evaporation predominantly in the rainy season when cave air circulation is most active the relationship between surface infiltration or leakage and cave discharge is connected by the distinct models of flow through the epikarst zone vadose flow showed high peaking hydraulic responses but buffered rain isotope responses with an attenuate magnitude of 5 0 9 4 for 18 o the sudden hydrochemical proxy variability was related closely to increase of discharge and the flushing out of old water with higher dissolved calcite a threshold of flow generation expressed by precipitation amount must be exceeded to create a peak in discharge as a function of excessing the field capacity of soil and residual capacity of epikarst zone the sources of vadose seepage are soil and epikarst reservoir water with the attenuation of the isotopic fluctuations 4 28 to 5 92 for 18 o and slight hydrological response indicating mixed signals of infiltration water in epikarst storage reservoir the total discharge volume of percolating water is 2084 l derived from piston flow due to the increased hydraulic head in the dry season which provides a quantitative evidence of the potential adaptive capacity of the system to deal with the extreme droughts

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

isotopic investigation of infiltration and unsaturated zone flow processes at carlsbad cavern new mexico abstract stable isotopes of hydrogen and oxygen together with tritium were used to investigate infiltration and unsaturated zone flow at carlsbad cavern water samples were collected from drips and pools every 4 months for a year seepage flow dominates infiltration at the cavern homogenizing the isotopic composition of individual and seasonal precipitation events early along the vertical flowpath within the relatively narrow range in the stable isotopic ratios of cave drip water d of 53 tc 44 18o of 8 3 to 85 isotopic changes on two different time scales were identified a longer term variation probably driven by changes in the relative amount of heavy isotope enriched summer precipitation is evident in the slight enrichment of drips collected at shallower depths in the cavern above 1100 m elevation this suggests vertical travel times to the main cave rooms of the order of decades consistent with observed tritium activities from less than 4 6 to 16 9 tritium units t u given these residence times and the narrow range in isotopic composition a seasonal trend in the isotopic composition of cave water coincident at all levels in the cavern is probably related to seasonal changes in the cave climate active air circulation driven by differences in air temperature between the cave and outside during the winter increases the evaporation rate from cave pools and causes enrichment in heavy isotopes this signal may be transmitted to infiltrating water via isotope exchange before the water drips into the cave consistent with the temporary storage of drip water in limited zones of saturation around the cave rooms these zones may develop in response to capillary driven surface tension before infiltrating water drips into the unsaturated flow barriers represented by the large air filled cave passages

rainfall and cave water isotopic relationships in two south france sites this article presents isotopic measurements 18o and d of precipitation and cave drip water from two sites in southern france in order to investigate the link between rainfall and seepage water and to characterize regional rainfall isotopic variability these data which are among the longest series in france come from two rainfall stations in south west france le mas 1996 2012 and villars 1998 2012 typically under atlantic influence and from one station in the south east orgnac 2000 2012 under both mediterranean and atlantic influence rainfall isotopic composition is compared to drip water collected under stalactites from the same sites villars cave four drip stations 1999 2012 in the south west and chauvet cave two drip stations 2000 2012 in the south east near orgnac the study of these isotopic data sets allows the following conclusions to be drawn about the rainfall drip water relationships and about rainfall variability 1 the cave drip water isotopic composition does not show any significant changes since the beginning of measurements in order to explain its isotopic signature it is necessary to integrate weighted rainfall 18o of all months during several years which demonstrates that even at shallow depths 10 50 m cave drip water is a mixture of rain water integrated over relatively long periods which give an apparent time residence from several months to up to several years these results have important consequences on the interpretation of proxies like speleothem fluid inclusions and tree ring cellulose isotopic composition which are used for paleoclimatic studies 2 in the villars cave where drip stations at two different depths were studied lower 18o values were observed in the lower galleries which might be due to winter season overflows during infiltration and or to older rain water with a different isotopic composition that reaches the lower galleries after years 3 local precipitation is characterized by local meteoric water lines lmwl with 18o d slopes close to 7 in both areas and correlations between air temperature and precipitation 18o are low at both monthly and annual scales even with temperature weighted by the amount of precipitation 4 the mesoscale climate model remoiso equipped with a water isotope module allows the direct comparison of modeled and observed long term water isotope records the model slightly overestimates rainfall 18o at the respective sampling stations however it simulates very well not only the seasonal rainfall isotopic signal but also some intra seasonal patterns such as a typical double peak 18o pattern in winter time

the role of the subcutaneous zone in karst hydrology abstract the subcutaneous zone is the upper weathered layer of rock beneath the soil but above the permanently saturated phreatic zone it is of particular hydrological importance in karst because of its high secondary permeability arising from the considerable chemical solution in this zone however corrosional enlargement of fissures diminishes with depth thus permeability decreases in the same direction with the result that percolation is inhibited except down widened master joints and faults storage of water consequently occurs in this zone particularly after storms the upper surface of this suspended saturated layer in the subcutaneous zone is defined by a perched water table which slopes towards points of rapid vertical percolation the potential induces lateral water movement converging on the most permeable areas such as beneath dolines leakage from the subcutaneous store sustains slow percolation in the vadose zone cross correlation of rainfall with percolation rates in caves in new mexico u s a and new zealand reveal response lags of 2 14 weeks with no apparent relationship to depth below the surface other percolation sites show no correlation with rainfall interpreted as being a consequence of considerable friction in tight fissure networks the recognition of storage and rapid as well as very slow percolation from the subcutaneous zone requires re interpretation of the components of hydrographs from karst springs and of some conceptual models of karst aquifers the importance of subcutaneous storage in sustaining baseflow discharge at some sites must be recognised as must the contribution of subcutaneous water to flood hydrographs methods of estimating the volumes of subcutaneous and phreatic components of karst spring flood hydrographs are presented the paper concludes with a discussion of the significance of subcutaneous hydrologic processes for an understanding of karst geomorphology the desirability of explaining karst landform evolution in terms of hydrologic processes is stressed

extension discrepancy at north atlantic nonvolcanic rifted margins depth dependent stretching or unrecognized faulting rifted margins show an apparent discrepancy between the amount of extension measurable from faults and the amount of crustal or lithospheric thinning determined from wide angle data or subsidence this extension discrepancy has been interpreted in terms of depth dependent stretching in which the upper crust is extended and thinned far less than the rest of the lithosphere here i show that at those nonvolcanic margins where the velocity structure is well known the upper and lower crust appear to thin equally toward the margin implying that the discrepancy is not due to depth dependent stretching but more likely due to unrecognized polyphase and top basement faulting

spreading rate dependence of melt extraction at mid ocean ridges from mantle seismic refraction data a variety of observations indicate that mid ocean ridges produce less crust at spreading rates below 20 mm yr 1 refs 1 3 reflecting changes in fundamental ridge processes with decreasing spreading rate the nature of these changes however remains uncertain with end member explanations being decreasing shallow melting or incomplete melt extraction each due to the influence of a thicker thermal lid here we present results of a seismic refraction experiment designed to study mid ocean ridge processes by imaging residual mantle structure our results reveal an abrupt lateral change in bulk mantle seismic properties associated with a change from slow to ultraslow palaeo spreading rate changes in mantle velocity gradient basement topography and crustal thickness all correlate with this spreading rate change these observations can be explained by variations in melt extraction at the ridge with a gabbroic phase preferentially retained in the mantle at slower spreading rates the estimated volume of retained melt balances the approximately 1 5 km difference in crustal thickness suggesting that changes in spreading rate affect melt extraction processes rather than total melting

continental break up of the south china sea stalled by far field compression the outcome of decades of two dimensional modelling of lithosphere deformation under extension is that mechanical coupling between the continental crust and the underlying mantle controls how a continent breaks apart to form a new ocean however geological observations unequivocally show that continental break up propagates in the third dimension at rates that do not scale with the rate of opening here we perform three dimensional numerical simulations and compare them with observations from the south china sea to show that tectonic loading in the direction of propagation exerts a first order control on these propagation rates the simulations show that in the absence of compression in that direction continental break up propagates fast forming narrow continental margins independently of the coupling when compression is applied propagation stagnates forming v shaped oceanic basins and wide margins changes in out of plane loading therefore explain the alternation of fast propagation and relative stagnation these new dynamic constraints suggest that the west to east topographic gradient across the indochinese peninsula prevented continental break up propagation through the 1 000 km wide continental rift of the central and west basin of the south china sea until the direction of stretching changed 23 million years ago resulting in bypassing and acceleration of continental break up propagation tectonic loading in the direction of propagation exerts an important control on the propagation of continental break up according to three dimensional simulations of the south china sea

seasonal variability of oxygen and hydrogen stable isotopes in precipitation and cave drip water at guilin southwest china the interpretation of climatic information from stalagmites has traditionally been a complex research problem with oxygen isotopes playing a particularly important role in global climate change studies this study investigates the relationship between oxygen isotope composition of the atmospheric in precipitation and cave drip water at panlong cave in southwest china on seasonal timescales of variability time series seasonal variability was derived from panlong cave in guilin by collecting daily precipitation samples for stable isotope analysis during 2012 results indicate that 18o of precipitation contains a clear seasonal variation whereby higher values are mainly distributed during winter and lower values during summer seasonal variations in water sources affect the precipitation 18o values drip water 18o also displayed a seasonal cycle which is attenuated relative to 18o of precipitation drip water time series display seasonal cycle ranges from 1 5 to 3 5 relative to vienna standard mean ocean water which mainly follow the precipitation 18o seasonal cycle seasonal variation in drip water 18o supports interpretations of the stalagmite 18o record as a paleoclimate proxy sensitive to the local environment this monitoring experiment revealed that drip water must be transported through the epikarst in approximately 1 5 months during cold periods and 0 5 months during warm periods different residence time percolation is mainly affected by the atmospheric precipitation amount depending on whether soil moisture reaches saturation

oxygen isotope variations in rainfall drip water and speleothem calcite from a well ventilated cave in texas usa assessing a new speleothem temperature proxy abstract measurements of the oxygen isotopic composition 18o value of rainfall drip water and associated calcite grown on artificial substrates and in a natural speleothem at multiple drip sites in a well ventilated cave in central texas were conducted to investigate the potential use of speleothem 18o for quantitative temperature reconstructions from 2009 to 2011 rainfall 18o varied by 11 5 10 5 to 1 0 v smow whereas drip waters had a much narrower range of 0 3 4 7 to 4 4 v smow this contrast indicates that mixing processes along flow paths in the vadose zone above the cave produce a well homogenized water reservoir that supplies drip water to the cave the 18o values for calcite grown on substrates over the same time period show seasonal variations summer 6 winter 3 that are strongly correlated with surface air temperatures ta at all three monitored sites r2 0 88 0 96 p

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

plate kinematics origin and tectonic emplacement of supra subduction ophiolites in se asia abstract a unique feature of the circum pacific orogenic belts is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust in se asia a majority of the ophiolites appear to have originated at convergent margins and specifically in backarc or island arc settings which evolved either along the edge of the sunda eurasia and australian cratons or within the philippine sea plate these ophiolites were later accreted to continental margins during the tertiary because of fast relative plate velocities tectonic regimes at the active margins of these three plates also changed rapidly strain partitioning associated with oblique convergence caused arc trench systems to move further away from the locus of their accretion we distinguish relatively autochthonous ophiolites resulting from the shortening of marginal basins such as the present day south china sea or the coral sea and highly displaced ophiolites developed in oblique convergent margins where they were dismantled transported and locally severely sheared during final docking in peri cratonic mobile belts i e the philippine mobile belt we find a series of oceanic basins which have been slightly deformed and uplifted varying lithologies and geochemical compositions of tectonic units in these basins as well as their age discrepancies suggest important displacements along major wrench faults we have used plate tectonic reconstructions to restore the former backarc basins and island arcs characterized by known petro geochemical data to their original location and their former tectonic settings some of the ophiolites occurring in front of the sunda plate represent supra subduction zone basins formed along the australian craton margin during the mesozoic the philippine sea basin the huatung basin south of taiwan and composite ophiolitic basements of the philippines and halmahera may represent remnants of such marginal basins the portion of the philippine sea plate carrying the taiwan philippine arc and its composite ophiolitic continental crustal basement might have actually originated in a different setting closer to that of the papua new guinea ophiolite and then have been displaced rapidly as a result of shearing associated with fast oblique convergence

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

incipient subduction at the contact with stretched continental crust the puysegur trench a seismic benioff zone and plate kinematics show puysegur trench south of new zealand transitioning to subduction because the local structure and its influence on subduction initiation is poorly understood we conducted a seismic survey with ocean bottom seismometers and multichannel seismic profiles our early results show that the overriding pacific plate beneath the solander basin is composed of block faulted and thinned continental crust and the inner trench wall of northern puysegur ridge is composed of folded and faulted sediment the megathrust interface has been imaged and shows 500 m of downgoing undisturbed sediments combining plate kinematic history with seismic velocity inferred density we show that the density difference across the plate boundary changed as oblique strike slip plate motion juxtaposed dense oceanic crust with thinned continental crust the density difference rapidly increased 18 to 15 ma coincident with subduction initiation suggesting that compositional differences have a large influence on subduction initiation

seismic estimates of turbulent diffusivity and evidence of nonlinear internal wave forcing by geometric resonance in the south china sea the luzon passage generates some of the largest amplitude internal waves in the global ocean as the result of coupling between strong tides strong stratification and topography these internal waves propagate into the south china sea scs and develop into soliton like internal wave pulses that are observed by moored instruments and satellite backscatter data despite the observation of these waves little is known of the mechanisms related to their evolution into nonlinear wave pulses using seismic data we find evidence that the geometry of bathymetric conditions between the heng chun and lan yu ridges drive nonlinear internal wave pulse generation we produce three seismic images and associated maps of turbulent diffusivity to investigate structure around the two ridges and into the scs we do not observe large amplitude soliton like internal waves between the ridges but do observe one outside the ridges a finding in accord with the interpretation that wave pulses form due to geometrical resonance additionally we find no evidence for lee wave activity above the ridges in either the seismic images or associated turbulence maps suggesting an unlikelihood of hydraulic jump driven generation around the ridges our results show increased levels of turbulent diffusivity 1 in deep water below 1000 m 2 associated with internal tide pulses and 3 near the steep slopes of the heng chun and lan yu ridges as explored in this paper

δ18o characteristics of meteoric precipitation and its water vapor sources in the guilin area of china the stable isotopic composition of meteoric precipitation is an important component of global and regional water cycle research stable isotope data can help reconstruct paleoclimate related to ice cores lake sediments and stalagmites we investigated the daily variation in isotopic composition of meteoric precipitation from 2008 to 2012 in the guilin region of china 18o of meteoric precipitation ranged from 14 21 to 2 38 with an average value of 5 78 vienna standard mean ocean water vsmow meteoric precipitation in the summer half year may through october increased with a relatively low 18o value of 8 04 vsmow average of 261 groups and 56 03 vsmow of average d accounting for 67 6 of the total annual meteoric precipitation meteoric precipitation in the winter half year november through april decreased with a relatively high 18o value of 2 89 average of 210 groups and 9 23 of average d accounting for 32 4 of total meteoric precipitation the local meteoric water line lmwl equation in guilin area has local climate characteristics by combining environmental isotope data of precipitation using a backwards trajectory water vapor sources of the meteoric precipitation in guilin area are inferred and traced our results show that the isotopic composition of meteoric water vapor sources in guilin area are related to monsoon type source of precipitation cloud masses and precipitation properties the isotopic composition of meteoric precipitation in the summer half year may through october was mainly affected by the summer monsoon or summer typhoons namely controlled by water vapor source from the bay of bengal and the south china sea and the second the west pacific and the 18o value of meteoric precipitation was strongly negative there was a significant negative correlation between the 18o values of meteoric precipitation and the amount of precipitation and temperature in the summer half year the amount effect of the meteoric precipitation often concealed the temperature effect the isotopic composition of meteoric precipitation in the winter season or winter half year was affected by the water vapor source of the warm moist air masses from the west pacific and continental cold air masses from the siberia mongolia winter monsoon or local evaporation vapor circulation and the 18o value of meteoric precipitation was relatively positive and indicated that the water vapor of meteoric precipitation along the water vapor trajectory was affected by the evaporation as well as the local water vapor evaporation the research results have showed that different sources of water vapor has a significant influence on the 18o variation of meteoric precipitation therefore analysis of 18o in the meteoric precipitation especially its seasonal variation characteristics of analysis can conversely reveal the water vapor sources of local meteoric precipitation

unsaturated zone hydrology and cave drip discharge water response implications for speleothem paleoclimate record variability summary high frequency spatially dense discharge monitoring was conducted over fifteen months to characterise unsaturated zone flow at harrie wood cave hwc in the snowy mountains yarrangobilly se australia the cave was formed in the late silurian yarrangobilly limestone a fractured rock associated with very low primary porosity due to past diagenesis over our monitoring period we simultaneously measured rainfall soil moisture saturation and drip discharge rate at fourteen sites to characterise infiltration discharge relationships all drip discharge sites exhibited non gaussian distributions indicating long periods where low discharge predominates punctuated by short infrequent periods of high discharge however there was significant variability in discharge between sites and consequently no spatial correlation in the cave we investigated the depth discharge relationship at hwc and found a moderate relationship between depth and drip discharge lag response times to soil moisture content but only weak relationships between depth and mean and maximum discharge this highlights that the karst architecture plays an important role in controlling drip discharge dynamics principal component analysis pca and agglomerative hierarchal clustering ahc were used to classify similar drip types revealing five unique drip regimes two phase flow and non linear response to recharge behaviour were observed suggesting secondary porosity is controlling unsaturated zone flow in mature limestone environments with low primary porosity using the data presented here the first coupled conceptual and box hydrological flow model was developed this study highlights the heterogeneous nature of hydrological flow in karst and the need to understand unsaturated zone hydrology at the individual drip discharge level to inform speleothem studies for high resolution paleoclimate reconstruction

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

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

tectonics of the new guinea region the new guinea region evolved within the obliquely and rapidly converging australian and pacific plate boundary zone it is arguably one of the most tectonically complex regions of the world and its geodynamic evolution involved microplate formation and rotation lithospheric rupture to form ocean basins arc continent collision subduction polarity reversal collisional orogenesis ophiolite obduction and exhumation of ultra high pressure metamorphic rocks we describe the major onshore and offshore tectonic and geologic components including plate boundaries seismicity faults and magmatism and we integrate these with emerging ideas about mantle dynamics to evaluate the cenozoic tectonic evolution of new guinea future research opportunities to resolve the mantle structure beneath new guinea will enable mantle dynamics to be linked to lithospheric and surface processes virtually all plate tectonic and mantle processes have been active in the new guinea region throughout the cenozoic and as such

inversion of a hyper extended rifted margin in the southern central range of taiwan seismic reflection and wide angle data acquired across south and west of taiwan show that extended to hyper extended continental crust of the chinese continental margin is present more than 200 km south of the shelf and is subducting at the manila trench furthermore crustal scale tomographic velocity models show that this crust is underthrusted to 15 km depth below the accretionary prism where it then is structurally underplated to the base of the prism we document an increasing volume of accreted crust from south to north and in our northern transect high velocity material of the accretionary prism can be directly linked to outcrops of central range basement rocks in map view the central range of taiwan is clearly contiguous with the hengchun peninsula and hengchun submarine ridge to the south accordingly we propose a new model in which the central range forms directly from the accretionary prism including the basement core which originates from subducted and then accreted extended to hyper extended continental crust

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

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

tectonic evolution of the northeastern south china sea from seismic interpretation 1 we interpret a grid of 2 d seismic reflection profiles to resolve the tectonic evolution of the northeastern south china sea scs identifying two significant postbreakup events t1 and t2 which occurred before the end of the scs opening in the absence of the drilling data in the deep basin we date these two events using the identification of the magnetic anomalies the age of major unconformities at ocean drilling program site 1148 drilled on the northeastern scs margin and the age of basalt samples in the deep scs the tectonic phase t1 is a slight tensional tectonic event which occurred in the deep scs south of the luzon ryukyu transform plate boundary lrtpb it is characterized by oceanic tilted blocks and fan shaped deposits which developed 8 10 myr after the onset of scs seafloor spreading 37 8 ma it corresponds to the first ene wsw to e w change in spreading direction which occurred around chron c10 28 7 ma event t2 is a magmatic phase observed in the deep scs south of the lrtpb it is characterized by the uplift of former spreading features caused by an early miocene 22 ma magmatic phase which is also recorded in north and south central taiwan

water isotopic variability in mallorca a path to understanding past changes in hydroclimate this paper reports the first results on 18o and 2h analysis of precipitations cave drip waters and groundwaters from sites in mallorca balearic islands western mediterranean a key region for paleoclimate studies understanding the isotopic variability and the sources of moisture in modern climate systems is required to develop speleothem isotope based climate reconstructions the stable isotopic composition of precipitation was analyzed in samples collected between march 2012 and march 2013 the values are in the range reported by gnip palma station based on these results the local meteoric water line 2h 7 9 0 3 18o 10 8 2 5 was derived with slightly lower slope than gmwl the results help tracking two main sources of air masses affecting the study sites rain events with the highest 18o values 5 originate over the mediterranean sea whereas the more depleted samples 50 m limestone cap arta exhibit more negative values a well homogenized aquifer supplied by rainwaters of both origins is clearly indicated by groundwater 18o values which show to be within 2 4 of the unweighted arithmetic mean of 7 4 although limited the isotopic data presented here constitute the baseline for future studies using speleothem 18o records for western mediterranean paleoclimate reconstructions

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

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

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

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

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

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

crustal structures from the wuyi yunkai orogen to the taiwan orogen the onshore offshore wide angle seismic experiments of the taiger and atsee projects abstract knowledge of the crustal structure is important for understanding the tectonic framework and geological evolution of southeastern china and adjacent areas in this study we integrated the datasets from the taiger taiwan integrated geodynamic research and atsee across taiwan strait explosion experiment projects to resolve onshore offshore deep crustal seismic profiles from the wuyi yunkai orogen to the taiwan orogen in southeastern china three seismic profiles were resolved and the longest profile was 850 km unlike 2d and 3d first arrival travel time tomography from previous studies we used both refracted and reflected phases pg pn pcp and pmp to model the crustal structures and the crustal reflectors in total data from 40 shots 2 earthquakes and approximately 1 950 stations were used 15 612 arrivals were selected among three transects using these data we determined the complex crustal evolution since the paleozoic era involving the closed paleozoic rift basin in central fujian the cenozoic extension due to the south china sea opening beneath the coastline of southern fujian and the on going collision of the taiwan orogen the shape of the moho which also reflects the crustal evolution can be summarized as follows 30 km deep to the west of fujian deepening toward central fujian 35 km becoming shallower toward the taiwan strait 28 km deepening again toward the mountain belt of taiwan 42 km and becoming shallower toward the pacific ocean 10 km

cenozoic plate reconstruction of the south china sea region abstract reconstructions of the south china sea region at 60 ma 40 ma 30 ma 20 ma 10 ma and 5 ma are presented we have attempted to place the south china sea basin in a regional tectonic framework the tectonic evolution of the major blocks surrounding the south china sea were analyzed as well as the relative motions of the indian and australian plates we have tried to correct the tectonic models available in this region a 3 d graphics terminal was used to derive rotation poles for the different tectonic blocks and our model was then tested to determine its self consistency when the model conflicted with previous interpretations the input data were evaluated for alternative explanations at least two and possibly three stages of extension can be recognized in this region the earliest one active in the late cretaceous to eocene involved nw se extension the second one active from the late eocene to early miocene involved north south extension the third stage of extension which probably trended nw se can be dated as post oligocene the first extensional event produced the ne sw trending proto south china sea and a series of sedimentary basins along the south china margin following the southeastward extrusion of indochina the proto south china sea was mostly consumed at the palawan trough renewed north south extension in the south china continental margin started the present day south china sea spreading in the oligocene the southeastward extrusion of indochina blocked by sundaland resulted in the nw se trending opening of the south china sea basin in the early miocene collision of the north palawan microcontinental block with the west philippines block stopped the opening of the south china sea at the end of early miocene spreading activity switched to the sulu sea basin in the middle miocene but collision between the sulu ridge and the west philippines at mindanao halted the opening of the sulu sea at the end of the middle miocene in the late miocene greater india continued its northward path and seems to have ripped open the andaman sea in the pliocene subduction along the northern manila trench placed the north luzon arc on a collision path with the east asia continental margin at taiwan our reconstructions along with detailed geological and geophysical information may be used as a predictive tool for basin evolution models and block interactions in this region the development of the south china sea basin the gulf of thailand the malay basin and the central thailand basins are the result of collision induced extensional forces the sulu celebes and sumatra basins were formed as a consequence of prolonged subduction the opening of the pearl river mouth west natuna south china sea sulu and possibly celebes basins were terminated by various plate collisions during the course of plate reorganizations major boundary faults have changed their slip senses during different stages of evolution

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

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

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

the opening of the woodlark basin subduction of the woodlark spreading system and the evolution of northern melanesia since mid pliocene time abstract magnetic anomaly and seismological data define segments of active seafloor spreading and associated magnetic lineations trending ene in the woodlark basin the total opening rate has been approximately 6 cm yr for the last 1 m y spreading rates diminish by over 10 from east to west along the woodlark spreading system implying a pole of current opening 15 20 to the west commencement of seafloor spreading in the basin has apparently been time transgressive beginning prior to 3 5 m y in the east and at successively later times to the west earthquake focal mechanisms and geological evidence suggest that the land areas bounding the western end of the woodlark basin are undergoing tensional deformation we believe that eventually the woodlark basin plate boundary will propagate westward through the d entrecasteaux islands into the papuan peninsula hitherto unreported shallow seismicity associated with the northern margin of the ne trending section of the woodlark rise probably reflects partial decoupling of the woodlark and solomon basins possibly due to mechanical difficulties in subducting the young woodlark lithosphere analysis of the relative motions between the solomon indo australian and pacific plates shows that the woodlark spreading system has been subducted at high rates 10 cm yr beneath the solomon islands during the opening of the woodlark basin several tectonic and geological features limited to the region of interaction of the woodlark basin with the solomon trench and arc may be symptomatic of ridge subduction these features include high heat flow in the solomon trench which shoals to 4 km low levels of seismicity and only shallow hypocenters and voluminous eruptions of high k 2 o tio 2 olivine basalts and basaltic andesites extremely close to the trench axis this close association in space and time of an unusual volcanic suite with ridge subduction implies a strong dependence of the petrogenesis on the tectonic regime a combination of this study of the woodlark basin and the previous study of the bismarck basin taylor 1979 provides a reconstruction of the positions of the continents ocean basins and island chains in northern melanesia for mid pliocene time in accepting the existence of a solomon plate we can explain the trench like structure off the trobriand margin of new guinea the occurrence of late cenozoic calc alkaline volcanism along the papuan peninsula and the presence of intermediate depth seismicity beneath the north papuan peninsula the rapid changes in relative motions along or across the new ireland solomons chain over the past 3 5 m y may explain the spatial and temporal changes in igneous activity observed on these islands

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

modeling fluvial incision and transient landscape evolution influence of dynamic channel adjustment 1 channel geometry exerts a fundamental control on fluvial processes recent work has shown that bedrock channel width depends on a number of parameters including channel slope and is not solely a function of drainage area as is commonly assumed the present work represents the first attempt to investigate the consequences of dynamic gradient sensitive channel adjustment for drainage basin evolution we use the channel hillslope integrated landscape development child model to analyze the response of a catchment to a given tectonic perturbation using as a template the topography of a well documented catchment in the footwall of an active normal fault in the apennines italy that is known to be undergoing a transient response to tectonic forcing we show that the observed transient response can be reproduced to first order with a simple detachment limited fluvial incision law transient landscape is characterized by gentler gradients and a shorter response time when dynamic channel adjustment is allowed the differences in predicted channel geometry between the static case width dependent solely on upstream area and dynamic case width dependent on both drainage area and channel slope lead to contrasting landscape morphologies when integrated at the scale of a whole catchment particularly in presence of strong tilting and or pronounced slip rate acceleration our results emphasize the importance of channel width in controlling fluvial processes and landscape evolution they stress the need for using a dynamic hydraulic scaling law when modeling landscape evolution particularly when the relative uplift field is nonuniform

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

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

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

deep structure of the west african continental margin congo zaire angola between 5 s and 8 s from reflection refraction seismics and gravity data summary the deep structure of the west african continental margin between 5 s and 8 s was investigated using vertical reflection and wide angle reflection refraction techniques during the zaiango project a joint programme conducted in 2000 april by ifremer and totalfinaelf to penetrate below the salt layer a non conventional low frequency seismic source was used in the single bubble mode together with ocean bottom instruments hydrophones and seismometers and a 4 5 km long streamer that recorded multichannel seismic reflection mcs the data show that the continental crust thins abruptly over a lateral distance of less than 50 km from 30 km thick below the continental platform based on gravity data to less than 4 km thick below the lower congo basin that formed prior to the aptian salt deposition this subsalt sedimentary basin 180 km wide 4 km thick with velocities varying from 4 7 km s 1 to 5 8 km s 1 at the bottom is located between the foot of the continental slope and the oceanic domain it is underlain by crust of an intermediary or transitional type between continental crust and what can be recognized as oceanic crust in the transitional zone a crustal upper layer is present below the pre salt sedimentary basin 3 to 7 km thick with velocities increasing from 5 8 km s 1 at the top to 6 8 km s 1 at the bottom of the layer this layer appears to thin regularly from 6 7 km thick below the depocentre of the pre salt sedimentary basin to 3 4 km thick below the western termination of the basin below this upper crustal layer an anomalous velocity layer 7 2 to 7 8 km s 1 is documented below the eastern side of the basin where the crustal thinning is at a maximum the origin of this layer is unknown several arguments like rifting duration between 15 ma and 30 ma or the absence of seaward dipping reflectors precludes the hypothesis of underplated mantle material but other hypotheses such as serpentinized material or high grade metamorphic crustal rocks or a mixture of mafic and ultramafic crustal rocks are plausible near the ocean termination of the basin the transitional zone is bounded to the west by a basement ridge that is clearly documented on two profiles 7 11 and 14 having a dense ocean bottom seismometer hydrophone obs obh spacing on these profiles an anomalous velocity layer is present in the westernmost part of the transitional zone below the basement ridge and in the oceanic domain this layer absent on profile 3 may be related either to oceanization and slow seafloor spreading processes or to a consequence of the rifting process

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

isotopic and paleomagnetic constraints on the mesozoic tectonic evolution of south china in order to better constrain the paleogeographic evolution of south china we measured sm nd and rb sr isotopic compositions for 23 mesozoic granites that crop out throughout the area tightly grouped neodymium depleted mantle model ages 1 4 0 3 ga suggest the region is underlain by relatively homogeneous proterozoic crust and fail to define crustal provinces neither the isotopic nor geologic data suggest that a mesozoic suture exists however granites possessing anomalously high sm 8 ppm and nd 45 ppm concentrations relatively high initial epsilon neodymium 4 to 8 and high but variable initial 87sr 86sr 0 759 to 0 713 form a northeast trending zone that coincides with two prominent mesozoic basins southeast of the zone lie the majority of mesozoic intrusives and upper triassic to lower cretaceous extensional basins found in south china mesozoic paleomagnetic poles are well clustered northwest of the zone pre cretaceous poles southeast of it are discordant with respect to those from the northwest the only recognized tectonostratigraphic terrane in south china lies southeast of the zone the terrane is bordered by a northeast trending sinistral fault that was active in the mesozoic other faults in south china have similar attitudes ages and sense of shear together the observations suggest that the mesozoic tectonic regime in south china consisted of strike slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults the zone defined by the granites enriched in nd and sm demarcates displaced terranes to the southeast from relatively stable land to the northwest

crustal scale seismic profiles across taiwan and the western philippine sea abstract we have used combined onshore and offshore wide angle seismic data sets to model the velocity structure of the taiwan arc continent collision along three cross island transects although taiwan is well known as a collisional orogen relatively few data have been collected that reveal the deeper structure resulting from this lithospheric scale process our southern transect crosses the hengchun peninsula of southernmost taiwan and demonstrates characteristics of incipient collision here 11 km thick transitional crust of the eurasian plate eup subducts beneath a large rapidly growing accretionary prism this prism also overrides the n luzon forearc to the east as it grows just west of the arc axis there is an abrupt discontinuity in the forearc velocity structure because this break is accompanied by intense seismicity we interpret that the forearc block is being detached from the n luzon arc and philippine sea plate psp at this point our middle transect illustrates the structure of the developing collision steep and overturned velocity contours indicate probable large scale thrust boundaries across the orogen the leading edge of the coherent psp appears to extend to beneath the east coast of taiwan deformation of the psp is largely limited to the remnant n luzon arc with no evidence of crustal thickening to the east in the huatung basin our northern transect illustrates slab continent collision the continuing collision of the psp and eup as the psp subducts the collisional contact is below 20 km depths along this transect ne of hualien this transect shows elements of the transition from arc continent collision to ryukyu arc subduction both of our models across the central range suggest that the paleozoic to mesozoic basement rocks there may have been emplaced as thick coherent thrust sheets this suggests a process of partial continental subduction followed by intra crustal detachment and buoyancy aided exhumation although our models provide previously unknown structural information about the taiwan orogen our data do not define the deepest orogenic structure nor the structure of western taiwan additional seismic active and passive geologic and geodynamic modeling work must be done to fully define the structure the active deformation zones and the key geodynamic process of the taiwan arc continent collision

rainfall recharge relationships within a karstic terrain in the eastern mediterranean semi arid region israel δ 18o and δd characteristics annual rainfall variations and processes in the upper vadose zone exert a profound influence on the chemical and isotopic compositions of waters of carbonate aquifers in semi arid climatic zones in order to define these processes we have studied the surface temperatures during rainfall events the isotopic composition of rain infiltrating and groundwaters this study was carried out within a karstic terrain soreq cave israel located in cenomanian dolomitic rocks approximately 40 km inland of the mediterranean sea and 400 m above sea level the climate is typical of the eastern mediterranean semi arid conditions with a rainy winter and dry summer and the average annual rainfall in the area is 500 mm close monitoring indicates that the d and 18o values of individual rainstorm events decrease with increasing rainfall annual average isotopic values of years with rainfall of 500 600 mm do not vary systematically years with extreme rainfall values define a negative covariation between the 18o and rainfall the d 18o relationship of all rain events of more than 20 mm fall on the mediterranean meteoric water line mmwl with a slope of 8 and d excesses of 20 30 these rain events occur when mid winter surface temperatures are 5 to 10 c rainfall events of less than 20 mm mainly occurring at above 10 c have slopes of less than 8 and smaller d excess as a consequence of evaporation processes beneath the clouds two main water types infiltrating into the cave are recognized slow and fast drip slow drip occurs from the tips of stalactites and takes place throughout the year these waters represent seepage water that remains in the upper vadose zone for up to several decades fast drip emanates from fissures in the cave roof during the winter seasons these waters represent vadose flow with a short residence time of less than 1 year the infiltration of the fast drip water into the cave depends on the fracture system of the rock cover and on the intensity of the rainstorms in the inner parts of the cave where the rock cover is thick fast drip starts only after several massive 20 mm rainstorms whereas below a thin roof the response time of fast drip is a few hours to a few days after intensive rainstorms both fast and slow drip water fall on the mmwl indicating that they are derived mainly from the relatively intensive rainstorms that compose about 23 of the annual rainfall although fast dri water represents massive rainstorms their 18o and d values are nonetheless higher by 1 and 10 respectively relative to the average rainwater compisition this indicates that the fast drip water consists predominantly of water derived from intensive rainstorms admixed with a minor component of isotopically 18o and d enriched water which is represented by the slow drip waters the fast drip waters are derived mainly from massive rain events at surface temperatures of 5 to 10 c which thermally equilibrate with the host rock and upon reaching the cave they have already acquired the mean temperature 20 c of the cave

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

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

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

upb and sr isotopic studies on granitoids from taiwan and chinmen lieyu and tectonic implications abstract u pb zircon monazite dating and sr isotope results for granitoids from taiwan and chinmen lieyu se china place important constraints for the tectonic evolution and the timing of felsic magmatism associated with mid cretaceous subduction process the chinmen gneiss 139 4 ma and granite 100 9 ma represent the oldest granitic units and belong to the previously recognized late yanshanian phase of magmatism a younger suite of granitoids occurs in the tananao metamorphic complex of taiwan and includes the yuantoushan and tachoshui granites 87 3 ma and the kanagan gneiss 90 2 ma these mid cretaceous ages for the younger granitoid suite mitigate against the existence of the hypothetical late paleozoic dongnanya microcontinent in the study area as proposed by other investigators u pb zircon inheritance ages ranging between 1 67 and 2 09 ga indicate the presence of a precambrian basement beneath much of coastal se china and taiwan however there is no evidence of archean crust as indicated by zircon inheritance patterns for rocks west of the present study area on a 87 sr 86 sr vs 87 rb 86 sr plot the available data for the granitoids in chinmen and coastal fujian se china however define pseudoisochrons with apparent ages of 158 167 ma although the pseudoisochron could be interpreted as a result of a two end member mixing process with subsequent fractional crystallization the apparent age of the pseudoisochron substantiated by the circumstantial evidence is postulated as the approximate time of sr isotope homogenization of the crustal protoliths of the granitoids during the previous early yanshanian tectonic event in this region such a sr isotope homogenization process must have occurred over a large area possibly facilitated by a metamorphic fluid phase or by large scale anatexis the cretaceous granitoids in this area were probably produced by partial melting of this crust in a more restricted scale the cretaceous calc alkaline granitoids in coastal fujian and taiwan are of i type or contaminated i type a subduction component is inferred during the magma genesis although the taiwan granitoids are suggested to be subduction related the possible tectonic environment for the genesis of coastal fujian granitoids is yet to be solved

crustal accretion in the manila trench accretionary wedge at the transition from subduction to mountain building in taiwan abstract new marine seismic reflection and coincident wide angle ocean bottom seismometer data acquired offshore taiwan provide high resolution constraints on the crustal structure of an incipient mountain belt during the earliest stage of arc continent collision the new seismic reflection image and travel time tomography velocity model show evidence for crust of the distal southern chinese continental margin being subducted eastward beneath the manila trench and underplated to the accretionary wedge before collision with the southern chinese continental shelf the distal margin crust consists of highly extended continental crust interspersed with volcanic bodies and a high velocity lower crustal layer of likely magmatic intrusions the distal margin crust is 10 14 km thick outboard of the trench but thins to 6 km thick beneath the lower slope of the manila trench accretionary wedge along the lower slope of the accretionary prism we image westward verging imbricate thrusts and folded strata up to 10 km thick a sharp decrease in bathymetry marks the transition from lower to upper slope where we observe a fast 6 0 km s seismic velocity anomaly at the base of the wedge that we interpret as structurally underplated crust from the distal continental margin our results support a model of arc continent collision in taiwan where the accretionary wedge is first thickened by structural underplating of distal margin crust prior to collision with the continental shelf the crustal rocks exposed throughout the central range in taiwan may be similarly derived from subducted and structurally underplated crust from the highly extended distal continental margin

geochronologic evidence for a cold arc continent collision the taiwan orogeny abstract in order to constrain the tectonic consequences of the collision of the luzon arc with the se chinese continental margin during the neogene taiwan orogeny we assess the thermal history of the poly metamorphic para autochtthonous rocks of the continental margin in taiwan to accomplish this we report a new sims u pb age of prograde metamorphic zircons and interpret this age in the context of existing geochronology and thermochronology zircons extracted from the fenniaolin amphibolite near nanao taiwan in the contact aureole of a granodiorite are interpreted to have crystallized during the first lower amphibolite facies prograde metamorphism based on 1 their equant shape rather than the prismatic shape typical of magmatic zircon 2 their microcrystalline or micro saccharoidal aggregate structure and patchy and sector zoning rather than oscillatory zoning visible in cathodoluminescent imaging 3 their low concentrations of u most 206 pb 238 u age of 86 1 ma analytically indistinguishable from the age of the adjacent pluton that caused the contact metamorphism we thus conclude that the contact metamorphism of this intrusion caused the first lower amphibolite facies metamorphism of these rocks in the mid cretaceous existing 40 ar 39 ar and rb sr cooling ages of both amphibole and muscovite at 80 ma e g lan 1990 lo and onstott 1995 show that the granodiorite and its contact aureole cooled rapidly from 700 to the crustal history reconstructed from these data shows that the regional gneissic terrane of the northern tananao complex may have been caused by coalescing contact aureoles of multiple mid cretaceous intrusions the nanao intrusive event and not by the neogene taiwan orogeny on the contrary the tananao rocks probably achieved middle greenschist conditions and 15 20 km depth in a forearc setting in the early cretaceous this intrusive event caused regional contact metamorphism at about 85 ma after which the passive margin setting preserved these rocks at mid crustal depths until the beginning of the taiwan orogeny 5 ma these depths 10 12 km and temperatures 200 250 c were high enough to account for the late miocene lower greenschist facies cleavages and the pliocene pleistocene fission track cooling ages without additional loading and heating from the taiwan orogeny

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

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

east asia plate tectonics since 15 ma constraints from the taiwan region abstract 15 ma ago a major plate reorganization occurred in east asia seafloor spreading ceased in the south china sea japan sea taiwan sea sulu sea and shikoku and parece vela basins simultaneously shear motions also ceased along the taiwan sinzi zone the gagua ridge and the luzon ryukyu transform plate boundary the complex system of thirteen plates suddenly evolved in a simple three plate system eu ph and pa beneath the manila accretionary prism and in the huatung basin we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations these two patterns are rotated by 15 they were formed by seafloor spreading before 15 ma and belonged to the same ocean named the taiwan sea half spreading rate in the taiwan sea was 2 cm year from chron 23 to 20 51 to 43 ma and 1 cm year from chron 20 43 ma to 5b 15 ma five plate kinematic reconstructions spanning from 15 ma to present show implications concerning the geodynamic evolution of east asia amongst them the 1000 km long linear gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the ph sea plate the formation of taiwan was driven by two simple lithospheric motions i the subduction of the ph sea plate beneath eurasia with a relative westward motion of the western end a of the ryukyu subduction zone ii the subduction of eurasia beneath the philippine sea plate with a relative southwestward motion of the northern end b of the manila subduction zone the luzon arc only formed south of b the collision of the luzon arc with eurasia occurred between a and b east of a the luzon arc probably accreted against the ryukyu forearc

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

seismotectonic characteristics of the taiwan collision manila subduction transition the effect of pre existing structures abstract based on the distribution of an earthquake swarm determined from an ocean bottom seismometer obs network deployed from 20 august to 5 september 2015 in the northernmost part of the south china sea scs and data from inland seismic stations in taiwan we resolved a ml 4 1 earthquake occurring on 1 september 2015 as a ne sw trending left lateral strike slip event that ruptured along the pre existing normal faults generated during the scs opening phases the direction of the t axes derived from the ml 4 1 earthquake and the background seismicity off sw taiwan present high consistency indicating a stable dominant nw se tensional stress for the subducted eurasian plate eup the distinct stress variations on the two sides of these reactivated ne sw trending features suggest that the presence of pre existing normal faults and other related processes may lessen the lateral resistance between the taiwan collision and manila subduction system and facilitate the slab pull process for the subducting portion which may explain the nw se tensional stress environment near the transition boundary in the northernmost part of the scs

the influence of inherited continental margin structures on the stress and strain fields of the south central taiwan fold and thrust belt in this paper we test whether or not structural and morphological features inherited from the eurasian continental margin are affecting the contemporary stress and strain fields in south central ta

controls on the thermomechanical evolution of hyperextended lithosphere at magma poor rifted margins the example of espirito santo and the kwanza basins high quality long offset seismic data from many distal rifted margins show evidence for hyper extended 10 km thick crust direct observation of such domains is challenging as they lie at great water depth buried beneath thick sedimentary sequences and formed by rock assemblages that are hydrated and geophysically indistinguishable only a few drill holes have penetrated basement at ultradistal rifted margins these observations together with outcrops of preserved analogs exposed in collisional orogens suggest that the complex interaction of detachment faults rooted in a subhorizontal shear zone in the hyperextended crust or in the serpentinized mantle controls the formation of the ocean continent transition while depth dependent thinning controls the early phases of rifting conforming to classical rift models we still have a superficial understanding of how normal faults and subhorizontal shear zones form and evolve during rifting and lithospheric breakup here we develop a rheological parameterization to simulate the formation of and slip on large offset normal faults rooted in growing brittle to ductile shear zones the evolution of these structures leads to the creation of a hyperextended crust and eventually exhumed serpentinized mantle we also propose a simplified formulation to simulate magmatic underplating and seafloor spreading the resulting numerical models provide a self consistent picture for the evolution of magma poor rifted margins from initiation of rifting to seafloor spreading the model results are compared with first order observations of the kwanza and espirito santo conjugate margins in the south atlantic as well as of magma poor margins globally

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

stable isotope study of cave percolation waters in subtropical brazil implications for paleoclimate inferences from speleothems we analyze the interannual monthly variability of oxygen isotope ratios in data from iaea stations along the atlantic coast of south america between 238 and 348 s to evaluate the influence of parameters such as temperature rainfall amount and moisture source contribution on meteoric water recharging two karst systems in subtropical brazil in addition a 2 year monitoring program performed on soil and cave drip and rimstone pool waters from sampling sites with contrasting discharge values and located at 100 and 300 m below the surface in the santana cave system 24831v s 48843v w is used to test the influence of hydrologic and geologic features on the temporal variations of seepage water d 18 o interannual monthly variations in d 18 o of rainfall reflect primarily regional changes in moisture source contribution related to seasonal shifts in atmospheric circulation from a more monsoonal regime in summer negative values of d 18 o to a more extratropical regime in winter positive values of d 18 o variations in groundwater d 18 o indicate that the climatic signal of recent rainfall events is rapidly transmitted through the relatively deep karst aquifer to the cave drip waters regardless of location of collection in the cave in addition the data also suggest that water replenishment in the system is triggered by the increase in hydraulic head during periods when recharge exceeds the storage capacity of the soil and epikarst reservoirs significant perturbations in the groundwater composition characterized by more positive values of d 18 o are probably connected to an increased atlantic moisture contribution associated with extratropical precipitation this implies that the d 18 o of speleothems from caves in this region may be a suitable proxy for studying