inversion of fluvial channels for paleorock uplift rates in taiwan the transient response of erosion to changes in rock uplift rate leads to the preservation of rock uplift history in the long profiles of rivers however extracting this information is nontrivial as changes in channel steepness are the result of both spatial and temporal changes in rock uplift rate as well as other factors such as climate and rock type we exploit an analytical linear solution for river channel profile evolution in response to erosion and tectonic uplift to investigate the rock uplift history of taiwan the analytical approach allows us to solve the linear inverse problem efficiently extracting rock uplift as a function of space and time from digital elevation data we assess the potential of fluvial topography to resolve rock uplift rates using three approaches 1 a synthetic resolution test 2 analysis of the forward model to demonstrate where in space and time the fluvial topography constrains rock uplift rate and 3 interpretation of the model resolution matrix furthermore the potential to analyze large data sets reduces the influence of stochastic processes such as landslides small scale river network reorganization and also local lithological variability in taiwan our analysis suggests that current rock uplift rates exceed erosion rates across much of the island and that there has been an increase in rock uplift rates since 0 5 ma across the central range

late permian triassic magmatic evolution in the jinshajiang orogenic belt sw china and implications for orogenic processes following closure of the paleo tethys growth of continental crust involves the complex interplay of subduction zone magmatism to generate the crust followed by stabilization through crustal thickening magmatism and ultimately isolation from the active plate margin the jinshajiang orogenic belt sw china provides an exceptional record of continental development as the result of closure of the paleo tethys seaway and ensuing collision a compilation of u pb age and geochemical data for the plutonic and volcanic rocks within the southern part of the jinshajiang orogenic belt including new high precision ages for the ludian granitoid batholith of 231 to 220 ma enables us to explore the interaction between magmatism and orogeny in the context of the paleo tethys closure and continental amalgamation these age and geochemical constraints in conjunction with other geologic evidence suggest that subduction of the paleo tethys ocean dominated local tectonics prior to the triassic creating a volcano plutonic arc along the eastern margin of the qamdo simao terrane following consumption of the ocean collision zone magmatism dated at 247 to 237 ma was manifested by eruption of voluminous volcanic rocks in a suture parallel zone crustal anatexis was contemporaneous with the earliest phases of collision producing high silica rhyolites of early triassic age ca 247 246 ma between 245 and 237 ma the local tectonic regime switched from compression to extension probably due to strain partitioning caused by oblique convergence which led to the development of rift basins and extensive syn tectonic bimodal volcanism associated with deep water sediments from 234 ma to 214 ma the emplacement of high k calc alkaline granodiorites monzogranites occurred prior to or during isostatic uplift and extension probably caused by breakoff of the subducted slab the resultant exhumation brought deep seated granitoid batholiths to the surface and was contemporaneous with intrusion of ultramafic mafic melts ophiolitic melange ca 362 294 ma and collision related magmatic suites 247 214 ma are unconformably overlain by a late triassic 229 217 ma conglomerate rich sequence that represents an overlap assemblage across the qamdo simao terrane indochina and yangtze block of south china

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

rifting process of the xihu depression east china sea basin abstract having a maximum depositional depth up to 15 km the ne trending xihu depression is evolved from a deep paleogene continental margin rifting along the present day east china sea continental shelf in this paper we use deep seismic reflection well logging and gravity data to synthesize early rifting process of the depression to study the regional tectonic subsidence history we developed a computer program that performs backstripping and simultaneous inversion for stretching factor initial lithospheric thickness and incipient age of thermal subsidence tectonic subsidence analyses of 40 industrial wells reveal nonuniform stretching preferential crustal extension along the depocenter but preferential mantle extension at the western flank uniform extension may have occurred only somewhere between the central inversion zone and the western margin in the early rifting stage subdued initial subsidence or initial uplift is observed on several wells near the western margin due possibly to flexural isostatic balance the initial mechanical lithospheric thicknesses from subsidence inversion seem to vary from about 55 km to almost 130 km suggesting significant longitudinal segmentation as well as transverse variation in the prerifting lithosphere it is likely that the southern part of the xihu depression was developed initially on a region of relatively thin lithosphere a statement conformable to geological evidences nw se trending deep seismic profiling clearly reveals the deep basement structure of the depression as well as the synrift and postrift sedimentary packages separated by a breakup unconformity crustal layer thicknesses are independently estimated from gravity modeling inversion tectonic subsidence analyses and deep seismic profiling respectively these methods all arrive at very small present day thicknesses of the crustal layer beneath the depocenter of the xihu depression

crust structure of the north china craton from a long range seismic wide angle reflection refraction data abstract we present an interpretation of a 1530 km long wide angle seismic reflection refraction profile that extends across the north china craton ncc approximately from east to west this profile is the longest and the densest wide angle seismic reflection refraction profile in china up to now parameterizing the velocity model as layers with variable thickness we perform seismic travel time tomography to resolve the velocity variation within layers and velocity contrast across moho our model shows crustal thickness that varies from 35 km under the shandong peninsula to 30 km under the north china plain ncp and 32 40 km under central ncc to 45 km under the ordos plateau these results indicate obvious crustal thinning beneath the ncp in comparison with the 35 km crustal thicknesses typical of most cratonic regions in particular an abrupt moho step of 10 km is detected at the junction of the eastern block and western block of the ncc these crustal characteristics are consistent with studies of lithosphere asthenosphere boundary lab with the method of receiver function migration and they indicate a close correlation with lithospheric thickness and surface tectonics of the northeastern ncc these results provide robust seismological evidence that the lithosphere from ncc to the western edge of the taihang mountain might have been widely affected and thinned since its formation in the archean era

ultrahigh pressure minerals and metamorphic terranes the view from china abstract ultrahigh pressure uhp metamorphism refers to mineralogical modifications of continental and oceanic crustal protoliths associated mafic ultramafic rocks initially formed or emplaced in shallow levels of the lithosphere but which subsequently have experienced p t conditions within or above the coesite stability field 2 7 gpa 700 c typical products include eclogite garnet peridotite and uhp varieties of metapelite quartzite marble paragneiss and orthogneiss uhp metamorphic assemblages require relatively cold lithospheric subduction to mantle depths some recrystallization even occurs under forbidden p t conditions characterized by a geotherm of the current explosion of research on continental uhp terranes reflects their significance for mantle dynamics and the tectonics of continental subduction collision exhumation mantle slab interactions and geochemical recycling a further characterization of uhp phases and positive identification of uhp minerals requires new experimental studies coupled with state of the art analyses for example the very rare occurrence of microdiamond inclusions in zircons from dabie sulu uhp rocks may reflect high f o 2 attending recrystallization inasmuch as epidote is rather common rutile needles within garnets from sulu uhp eclogitic rocks may not be the result of exsolution so in such cases the apparent uhp pressure may have been over estimated hadean igneous microdiamond inclusions in jack hills detrital zircons could have originated from mantle xenoliths whereas abundant detrital phanerozoic diamonds containing inclusions of coesite and other eclogitic minerals from new south wales might have been derived from unexposed uhp metamorphic terranes micro mineral intergrowth and nano size minerals may hold important key to deciphering the actual p t paths of subduction and mantle return flow although most exhumed terranes have returned surfaceward relatively rapidly after short time of uhp condition the long duration of storage at great depth and slow exhumation for the largest uhp terranes remain as major problems

crustal structure of mainland china from deep seismic sounding data abstract since 1958 about ninety seismic refraction wide angle reflection profiles with a cumulative length of more than sixty thousand kilometers have been completed in mainland china we summarize the results in the form of 1 a new contour map of crustal thickness 2 fourteen representative crustal seismic velocity depth columns for various tectonic units and 3 a pn velocity map we found a north south trending belt with a strong lateral gradient in crustal thickness in central china this belt divides china into an eastern region with a crustal thickness of 30 45 km and a western region with a thickness of 45 75 km the crust in these two regions has experienced different evolutionary processes and currently lies within distinct tectonic stress fields our compilation finds that there is a high velocity 7 1 7 4 km s layer in the lower crust of the stable tarim basin and ordos plateau however in young orogenic belts including parts of eastern china the tianshan and the tibetan plateau this layer is often absent one exception is southern tibet where the presence of a high velocity layer is related to the northward injection of the cold indian plate this high velocity layer is absent in northern tibet in orogenic belts there usually is a low velocity layer lvl in the crust but in stable regions this layer seldom exists the pn velocities in eastern china generally range from 7 9 to 8 1 km s and tend to be isotropic pn velocities in western china are more variable ranging from 7 7 to 8 2 km s and may display azimuthal anisotropy

neoproterozoic paleozoic and mesozoic granitoid magmatism in the qinling orogen china constraints on orogenic process abstract the qinling orogen is one of the main orogenic belts in asia and is characterized by multi stage orogenic processes and the development of voluminous magmatic intrusions the results of zircon u pb dating indicate that granitoid magmatism in the qinling orogen mainly occurred in four distinct periods the neoproterozoic 979 711 ma paleozoic 507 400 ma and early 252 185 ma and late 158 100 ma mesozoic the neoproterozoic granitic magmatism in the qinling orogen is represented by strongly deformed s type granites emplaced at 979 911 ma weakly deformed i type granites at 894 815 ma and a type granites at 759 711 ma they can be interpreted as the products of respectively syn collisional post collisional and extensional setting in response to the assembly and breakup of the rodinia supercontinent the paleozoic magmatism can be temporally classified into three stages of 507 470 ma 460 422 ma and 415 400 ma they were genetically related to the subduction of the shangdan ocean and subsequent collision of the southern north china block and the south qinling belt the 507 470 ma magmatism is spatially and temporally related to ultrahigh pressure metamorphism in the studied area the 460 422 ma magmatism with an extensive development in the north qinling belt is characterized by i type granitoids and originated from the lower crust with the involvement of mantle derived magma in a collisional setting the magmatism with the formation age of 415 400 ma only occurred in the middle part of the north qinling belt and is dominated by i type granitoid intrusions and probably formed in the late stage of a collisional setting early mesozoic magmatism in the study area occurred between 252 and 185 ma with the cluster in 225 200 ma it took place predominantly in the western part of the south qinling belt the 250 240 ma i type granitoids are of small volume and show high sr y ratios and may have been formed in a continental arc setting related to subduction of the mianlue ocean between the south qinling belt and the south china block voluminous late stage 225 185 ma magmatism evolved from early i type to later i a type granitoids associated with contemporaneous lamprophyres representative of a transition from syn to post collisional setting in response to the collision between the north china and the south china blocks late mesozoic 158 100 ma granitoids located in the southern margin of the north china block and the eastern part of the north qinling belt are characterized by i type i to a type and a type granitoids that were emplaced in a post orogenic or intraplate setting the first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process these suggest that the tectonic evolution of the qinling orogen is very complicated

deep subduction of continental crust in accretionary orogen evidence from u pb dating on diamond bearing zircons from the qinling orogen central china abstract accretionary orogenic belts are considered the most important sites for the generation of continental crust however it is still not very clear whether in such settings the continental crust has been significantly transported back to the mantle accompanied with its lateral growth continental uhp rocks the best indicators of the recycling of the continental crust have rarely been discovered in accretionary orogenic belts which hinder the exploration of this essential process the possible occurrence of early paleozoic uhp metamorphism in the qinling orogen provides an excellent opportunity to address this question this article reports an integrated study of u pb age trace element and mineral inclusion of zircon from an amphibolite sample in the qinling orogen the zircon crystals show typical metamorphic growth zoning low th u ratios flat hree patterns and insignificant eu anomalies they give a weighted mean u pb age of 490 4 5 8 ma most importantly an in situ diamond inclusion was identified from one of the zircon crystals therefore the obtained 490 4 5 8 ma age was taken as registering the peak uhp metamorphism the discovery of in situ diamond inclusion provides important evidence for the uhp metamorphism of the qinling orogen and indicates that the north qinling microcontinent was subducted to mantle depths of 120 km when it collided with the erlangping arc attached to the southern margin of the north china block combining with previous results we suggested that the north qinling uhp terrane underwent fast exhumation from 120 km to ca 30 km within 10 myr intervals as a few examples of uhp metamorphism have been discovered in some accretionary orogens more attention needs to be paid to the occurrence of continental uhp metamorphism during accretionary orogenic process furthermore evident crustal growth has been documented in the north qinling orogen during the early paleozoic it is inferred that the accretionary orogenic belts may play important roles in recycling of continental crust into the mantle besides generation of continental crust

crustal structures revealed from a deep seismic reflection profile across the solonker suture zone of the central asian orogenic belt northern china an integrated interpretation abstract the solonker suture zone is one of the most important tectonic boundaries in the southeastern part of the central asian orogenic belt caob an 630 km long reflection seismic profile across this suture was recently completed by the chinese sinoprobe project the processed seismic data show clear crustal structures and provide new constraints on the tectonic and crustal evolution models the moho is delineated as a relatively flat boundary between a strongly reflective lower crust and a transparent mantle at a depth of 40 45 km 14 5 s two way travel time which is in agreement with the refraction data recorded along the same profile in a broad view the profile images an orogen that appears bivergent with and approximately centered on the solonker suture zone the southern portion of this profile is dominated by a crustal scale cratonward propagating fold and thrust system that formed during the late permian and triassic through collision and subsequent convergence in a post collisional stage the major thrust faults are truncated by mesozoic granitoid plutons in the upper crust and by the moho at the base of the crust this geometry suggests that the moho was formed after the thrusting event the northern portion of the profile although partially obliterated by post collisional magmatic bodies shows major south dipping folding and thrusting bands of layered reflectors immediately overlying the moho are interpreted as basaltic sills derived from the mantle episodic mafic underplating may have occurred in this region giving rise to post collisional magmatic events and renewal of the moho a few mantle reflectors are also visible the overall geometry of these mantle reflectors supports the tectonic models that the southern orogen manchurides experienced south directed subduction and the northern orogen altaids underwent north directed subduction prior to collision along the solonker suture zone

significance of euxinic condition in the middle eocene paleo arctic basin a geochemical study on the iodp arctic coring expedition 302 sediments article 34 s on the early to middle eocene section of the acex cores the ts were high in all the examined intervals and the sedimentary sulfur occurred mainly as framboidal pyrite indicating that sufficient sulfate indicative of seawater was present in the deep layer of the paleo arctic basin and that the pyrite was formed in the sediments under sufficient iron input the high ts values with low 34 s values also indicate the continuous existence and supply of seawater the high accumulation of sulfide in unit 1 6 was due to a significant increase of toc supply which increased sulfate reduction rates by bacteria the toc ts diagram shows excess sulfur content relative to the toc suggesting euxinic condition of the bottom water during the studied period such an oxygen depleted environment was brought about by salinity stratification and restricted water circulation the patterns observed in the acex data can be comparable with the mediterranean sapropels the global 34

evolution of the bangong nujiang tethyan ocean insights from the geochronology and geochemistry of mafic rocks within ophiolites abstract the bangong nujiang suture zone bnsz is located in the central tibetan plateau and represents the relict of the bangong nujiang tethyan ocean bnto this paper presents zircon u pb ages and whole rock geochemical and sr nd isotope data for the ophiolitic rocks from the rutog dongco dongqiao amdo and dengqen areas from west to east in the bnsz zircon u pb ages obtained from five gabbros and one leucogabbro from the five areas are 169 2 167 2 187 2 184 2 177 3 and 164 2 ma respectively mafic rocks gabbros and basalts in the bnsz can be divided into morb like and oib type based on geochemical data the morb like rocks are tholeiitic and can be further divided into n and e morb subtypes marked by depleted and flat ree patterns respectively all morb like rocks show supra subduction zone ssz geochemical affinities such as mild enrichment in the large ion lithophile elements and depletion in the high field strength elements coupled with high and positive whole rock e nd t values 8 1 to 5 4 the oib type rocks which formed in the early cretaceous 132 108 ma are exposed in the dongco dongqiao and tarenben areas and they consist mostly of alkali basalts with within plate geochemical characteristics and positive e nd t values 5 9 to 4 5 on the basis of these new data combined with information from the literature we further support that the bnto was an intra oceanic arc backarc basin that existed between the north lhasa subterrane nlt and the south qiangtang subterrane sqt during the early middle jurassic this basin may have been active until the early cretaceous when the oib type basalts erupted

topographic effects on coseismic gravity change for the 2011 tohoku oki earthquake and comparison with grace we estimate gravity changes due to coseismic horizontal deformation and inclined bathymetry referred to as topographic effects in this study associated with the 2011 tohoku oki earthquake using a layered half space dislocation model as an approximation we represent inclined topography with ramp body models in the near field of the earthquake and calculate topographic effects from both an inclined seafloor and moho the moho effect partly compensates that from the seafloor an additional contribution comes from seawater column variations as the sloped seafloor moves trenchward topographic effects are first order contributions to coseismic gravity changes for the 2011 tohoku oki earthquake after 300 km gaussian smoothing comparable to the spatial resolution of the gravity recovery and climate experiment grace topographic effects create a dominantly negative gravity pattern with amplitudes up to 1 1 gal for oceanic areas surrounding the epicenter there are discrepancies between model predictions 10 4 to 6 9 gal and grace observations 10 1 to 1 7 gal errors in the adopted fault slip model and difficulties in separating coseismic and postseismic deformation may contribute to these but topographic effects currently neglected in dislocation models are also responsible topographic effects ought to be included in coseismic fault slip and related gravity modeling for the 2011 tohoku oki earthquake and similar events in regions of steep topography

timing of destruction of the north china craton abstract the north china craton ncc is the typical example of destruction of an ancient craton however the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction which is the key to understanding the destruction processes based on temporal and spatial distributions of the igneous rocks and their sources and tectonic settings it is recognized that six stages of tectono magmatism occurred in the ncc during the phanerozoic i e carboniferous to early permian late permian to middle triassic late triassic jurassic early cretaceous and cenozoic among them cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern ncc the first four stages of magmatism and tectonism related to the southward subduction of the paleo asian plate and the assembly of sino korean and yangtze cratons are locally distributed in limited parts of the ncc reflecting a multiple stage modification of the ncc from the late carboniferous to jurassic however the intensive development of early cretaceous magmatism extensional deformation and associated gold mineralization with significant continental crustal growth indicate that the eastern ncc was destroyed during this time period this destruction was the result of paleo pacific subduction beneath the eastern asian continent with lithospheric removal and or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere

glacioeustasy during the middle eocene insights from the stratigraphy of the hampshire basin uk the sedimentary strata of the hampshire basin constitute some of the best preserved palaeogene sequences worldwide and include the traditional unit stratotype for the bartonian 36 9 41 4 ma the barton clay formation at alum bay on the isle of wight iow was studied to assess the evidence for middle eocene sea level variation in records of grain size sediment properties faunal assemblage foraminiferal diversity indices and foraminiferal stable isotopes sedimentary cycles of 1 10 myr third order and 0 2 0 5 myr fourth order duration are reported and interpreted to reflect 20 60 metre variations in water depth additionally an integrated magneto bio chemostratigraphical age model for the succession at alum bay is presented and new and published litho and bio stratigraphical markers are used to correlate additional successions based on this age model it appears that during the late lutetian and early bartonian 42 38 ma water depth variation identified within the basin was synchronous sedimentary and fossil evidence supports episodic uplift in the eastern part of the hampshire basin during the bartonian which at present precludes the calculation of eustatic sea level however the amplitude and frequency of water depth variations identified in the barton clay formation and correlations to published sea level curves are consistent with a component of these changes being glacioeustatic during the middle eocene there is also evidence for a large excursion delta 18o 1 per mille sign in the mono specific benthic foraminiferal oxygen isotope record alum bay 39 9 ma which is correlated to the isotope excursion at the middle eocene climatic optimum previously reported in the southern ocean and other localities a contemporaneous water depth increase of 40 m at alum bay may indicate that a component of this global oxygen isotope excursion results from a reduction in continental ice storage

compositional polarity of triassic granitoids in the qinling orogen china implication for termination of the northernmost paleo tethys abstract the qinling orogen was formed from the closure of the northernmost paleo tethys sea and the tectonic suturing of the yangtze and north china cratons the timing of this collision and the tectonic framework are debated the widely developed triassic granitoids in the western qinling orogen offer a key to understand the tectonic evolution of this region here we compile the geological geochemical and geochronological data of the triassic granitoids from the qingling orogen and conclude that the granitoids north of the mian lue suture were emplaced in an active continental margin related to the northward subduction of the mian lue oceanic plate during 248 200 ma the granitoids can be classified into i and s types with the former constituting the major variety northward from the mian lue fault an s type granite belt appears followed by and locally overlapping with an i type granite belt the i type granite belt can be subdivided into four sub belts from south to north with increasing contents of k2o k2o na2o sio2 th and u and the ratios of k2o na2o rb sr and 87sr 86sr i but decreasing contents of na2o al2o3 mg and ehf t except for the northernmost belt which occurs in the huaxiong block of the north china craton this geochemical polarity of i type granitoids and the zoned distribution of s and i types granitoids cannot be explained through continental collision orogeny including syn to post collision but can be well interpreted by considering the progressive subduction of the northernmost branch of the paleo tethys as represented by the mian lue ocean thus the termination of the northernmost paleo tethys and the onset of the continental collision between the yangtze and the north china plates are considered to have occurred at about 200 ma during the transition from triassic to jurassic our model is also supported by the available data from other studies and provides a revised framework for the timing and tectonics of assembly of the yangtze and the north china cratons

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

fine crustal structure and deformation beneath the great xing an ranges caob revealed by deep seismic reflection profile abstract a crustal seismic reflection profile across the great xing an ranges gxar was recorded in 2011 revealed features of crustal structure and deformation at the eastern margin of the central asian orogenic belt caob the reliability of crust and upper mantle image was improved by rigorous regulations of seismic data acquisition and a series of special procedures for seismic data processing the diversiform seismic reflection fabrics within deep crust to mantle transition zone twt two way time 12 14 s approximately 36 42 km beneath gxar reflects the complicated products of tectonic and magmatic interaction of lower crustal and mantle components during evolution of gxar preliminary processing result shows the contact relationship of the gxar and adjacent basins we can identify lots of curved reflection phases from volcanic rock and opposite moho reflection events this scenario may suggest multi times tectonic transformation from contraction to extension presumably its cause of formation reflects the comprehensive dynamic action of the mongolia okhotsk tectonic system and the circum pacific tectonic system

plate convergence at the westernmost philippine sea plate abstract to understand the convergent characteristics of the westernmost plate boundary between the philippine sea plate psp and eurasian plate ep we have calculated the stress states of plate motion by focal mechanisms cataloged by the harvard centroid moment tensor solutions harvard cmt and the broadband array in taiwan bats moment tensor 251 focal mechanisms are used to determine the azimuths of the principal stress axes we first used all the data to derive the mean stress tensor of the study area the inversion result shows that the stress regime has a maximum compression along the direction of azimuth n299 this result is consistent with the general direction of the rigid plate motion between the psp and ep in the study area in order to understand the spatial variation of the regional stress pattern we divided the study area into six sub areas blocks a to f based on the feature of the free air gravity anomaly we compare the compressive directions obtained from the stress inversion with the plate motions calculated by the euler pole and the global positioning system gps analysis as a result the azimuth of the maximum stress axis 1 generally agrees with the directions of the theoretical plate motion and gps velocity vectors except block c lanhsu region and block f ilan plain region the discrepancy of convergent direction near the ilan plain region is probably caused by the rifting of the okinawa trough the deviation of the 1 azimuth in the lanhsu region could be attributed to a southwestward extrusion of the luzon arc la block between 21 n and 22 n whose northern boundary may be associated with the right lateral ne sw trending fault i e huatung fault hf along the taitung canyon comparing the 1 stress patterns between block c and block d great strain energy along hf may not be completely released yet alternatively the upper crust of block c may significantly have decoupled from its lower crust or uppermost mantle

genetic stratigraphic sequences in basin analysis ii application to northwest gulf of mexico cenozoic basin the northwest gulf of mexico cenozoic sedimentary wedge illustrates the application of genetic stratigraphic sequence analysis and documents several general conclusions 1 sequences defined by regional marine flooding are the principal genetic stratigraphic units of the basin fill continental margins are characterized by repetitive episodes of basin margin offlap punctuated by periods of transgression and marine flooding of the depositional platform 2 continental margin outbuilding is concentrated at one or more shelf edge deltaic depocenters separated by interdeltaic bights depocenters remain fixed during a depositional episode but commonly relocate during transgression and flooding 3 a distinct syndepositional structural style in prograding continental margins results in sporadic uplift of a basin fringing peripheral bulge and accentuates preservation of shelf margin facies along zones of extensional normal faulting and enhanced subsidence 4 genetic stratigraphic sequences commonly reflect an evolving interplay among two or even three variables for example early cenozoic gulf sequences are most closely related to tectonic events of the intraplate source terrane which in turn affect rate and location of sediment supply and basin margin response to loading late cenozoic sequences more closely reflect proposed eustatic cycles

high temperature geochronology constraints on the tectonic history and architecture of the ultrahigh pressure dabie sulu orogen 1 new u pb zircon and th pb monazite ages are presented from the giant sulu ultrahigh pressure uhp terrane combined with sm nd ages rb sr ages inclusion relationships and geologic relationships they help define the timing of peak recrystallization the timing of subsequent amphibolite facies metamorphism and the architecture of the dabie sulu suture zone between the collided sino korean and yangtze cratons the data indicate a 15 myr record of uhp recrystallization the first clearly documented for a giant uhp terrane this requires that continental subduction in the dabie sulu orogen involved multiple uhp tectonic or recrystallization events a 244 236 ma precursor uhp event seen only in the dabie shan was followed by a second 230 220 ma main uhp event which was itself terminated by a 220 205 ma amphibolite facies overprint older eclogite facies events seen in the qinling segment of this orogenic belt raise the possibility that these rocks have undergone u hp metamorphism three or four times but at present there is no geochronological evidence in the dabie sulu area to support this the subduction of the lower yangtze plate did not proceed in a simple fashion the ages of inherited zircon cores demonstrate that a ribbon continent of yangtze affinity escaped subduction and became wedged against the sino korean plate hanging wall

when did the subduction first initiate in the southern paleo asian ocean new constraints from a cambrian intra oceanic arc system in west junggar nw china abstract we report here a cambrian southward subducting intra oceanic arc system in the southern west junggar nw china where an immature arc occurred initially on ssz type ophiolites and finally evolved into a more mature one the immature arc is dominantly represented by early middle cambrian 510 ma low k tholeiitic felsic rocks whereas the mature arc is characterized by late cambrian 495 ma medium and high k calc alkaline felsic and mafic rocks the ssz type ophiolites show remarkable depletion of nb and ta and contain high cr spinel cr 0 6 resembling these formed in the forearc altogether they record the initiation of subduction and transformation of crust during early subduction of the paleo asian ocean in the southern part of the central asian orogenic belt caob the subduction initiation might occur in the early cambrian 515 ma as constrained by both the ssz type ophiolites 516 ma and the oldest arc plutons 515 509 ma that crosscut the ophiolites the immature felsic plutons have high sio 2 72 wt contents and variable mgo 0 42 1 49 wt and mg values 22 62 crustal anatexis may be responsible for the genesis of those plutons and thus the transformation from oceanic to continental crust these results combined with regional data convincingly indicate that it is one of the oldest intra oceanic arc systems in the southern caob which may mark the initial subduction of the paleo asian ocean in its southern part much later than those reported in the north an archipelago type model is proposed for the evolution of the southern west junggar and has implications for the development of the southern part of the caob

construction of a palaeogene tide dominated shelf influence of top chalk topography and sediment supply wessex basin uk palaeogene siliciclastic sediments reading and london clay formations in the wessex basin record an upward change through four tidally influenced deposition systems the lowest reading formation was deposited in estuarine and coastal plain environments the overlying london clay records discrete upward changes from deltaic to mixed tidal flat to tidal sandsheet bagshot sands erosional topography on the top chalk surface had an important control on deposition 1 topographic lows controlled the initial sites of marine flooding and sedimentation 2 lows would have acted as conduits for sediment delivery 3 lows created additional accommodation by the compaction of thick mud fills 4 lows may have formed preferential sites for delta growth as topography was reduced by sediment infill depositional units tended toward more sheet like geometries heavy minerals reveal that an upward progradational aggradational trend and the development of more sand rich facies are related to a change in provenance toward sand rich cornubian sources

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

geochronological and geochemical implications of early to middle jurassic continental adakitic arc magmatism in the korean peninsula abstract sensitive high resolution ion microprobe shrimp zircon u pb ages and whole rock chemical compositions of early to middle jurassic plutons from the central to southern korean peninsula are reported to investigate the effect of paleo pacific plate subduction preserved along the continental margin twenty one plutonic rocks from the yeongnam massif i e sunchang and namwon plutons the okcheon belt jeongup boeun and mungyeong plutons the northeast gangreung pluton and the gyeonggi massif gonam anheung and ganghwa plutons have age ranges from ca 189 186 ma to 177 ma 177 166 ma and 177 173 ma respectively most plutonic rocks have chemical compositions similar to adakites showing high sio 2 45 62 74 96 wt low mgo 0 01 2 84 wt high na 2 o 2 65 4 83 wt high sr y and la yb low y and yb as well as low hfses nb and ta but initial sr ratios 0 7048 0 7262 k 2 o 0 50 5 88 wt and k 2 o na 2 o 0 34 2 1 were unlikely to have been formed by melting of either a thickened and or delaminated lower continental crust or an altered oceanic crust these suggest that the adakitic plutonic rocks in this region resulted from partial melting of an enriched mantle source metasomatized by dewatering from a delaminated flat slab the spatial distributions of this continental adakitic plutonic belt based on the present study together with previously reported geochronological results indicate that magmatic pulses gradually migrated toward the continent across the korean peninsula as a result of slab shallowing caused by periodic slab buckling the similar geochronological and geochemical characteristics petrogenesis and tectonic setting of the plutonic belt spanning the korean peninsula japan eastern china and eastern russia indicate a possible link to an active subduction system that existed during the early to middle jurassic although the products of the plate subduction might differ in different locations along the east asian continental margin

triassic continental subduction in central tibet and mediterranean style closure of the paleo tethys ocean the qiangtang metamorphic belt qmb in central tibet is one of the largest and most recently documented high pressure hp to near ultrahigh pressure near uhp belts on earth lu hf ages of eclogite and blueschist facies rocks within the qmb are 244 223 ma indistinguishable from the age of uhp metamorphism in the qinling dabie orogen results of a u pb detrital zircon study suggest that protoliths of the qmb include upper paleozoic qiangtang continental margin strata and sandstones that were derived from a paleozoic arc terrane that developed within the paleo tethys ocean to the north we attribute qmb hp metamorphism to continental collision between the qiangtang terrane and a paleo tethys arc terrane this collision and the coeval south china north china collision may have slowed convergence between laurasia and gondwana derived terranes and initiated mediterranean style rollback and backarc basin development within much of the remnant paleo tethys ocean realm

crustal structure of the northeastern tibetan plateau from the southern tarim basin to the sichuan basin china abstract we present a new crustal cross section of the northeastern tibetan plateau based on active source seismic data recorded along a 1600 km long profile crossing the southern tarim basin the western flank of the south qilian shan the northeastern margin of qaidam basin east kunlun shan songpan ganzi terrane and sichuan basin the crustal p and s wave velocity structure and poisson s ratio outline the seismic characteristics of the crust and provide constraints on the crustal composition the derived crustal cross section shows several significant features 1 the crustal thickness varies considerably along this profile from 48 km to 70 km 2 north of the kunlun fault variations in total crustal thickness are mainly caused by variations in lower crustal thickness whereas south of the kunlun fault they are caused by thickness variations throughout the crust 3 north of the kunlun fault we detect a mid crustal low velocity zone that is not apparent south of the fault 4 the kunlun fault seems to act as a compositional boundary for the lower crust with a poisson s ratio of 0 29 north of the fault kunlun qaidam terrane and 0 26 south of the fault songpan ganzi terrane measured poisson s ratio and p wave velocity values suggest that the lower crust throughout the tibetan plateau south qilian shan margins of the qaidam basin east kunlun shan songpan ganzi terrane is of intermediate composition thus the ne tibetan plateau along our profile is missing a mafic lower crustal layer

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

structure age and tectonic development of the huoshishan niujuanzi ophiolitic melange beishan southernmost altaids abstract the huoshishan niujuanzi ophiolitic melange hno is located near the central part of the beishan orogenic belt in the southernmost altaids the hno consists of ultramafic rocks cumulate gabbros gabbros plagiogranites diorites diabases basalts andesites rhyolitic volcaniclastic rocks and siliceous sedimentary rocks many of which are in a schist matrix gongpoquan group geochemical data of the mafic rocks indicate a calc alkaline or a mixture of calc alkaline and tholeiitic rocks with negative nb ta and positive pb ba and la anomalies suggesting formation in an island arc or supra subduction zone setting a gabbro from a block in the melange in the niujuanzi area has a zircon age of 435 0 1 9 ma and a plagiogranite with an age of 444 3 1 9 ma and another gabbro from the huoshishan area has an age of 410 5 3 7 ma the schist matrix has a zircon age of 512 5 3 ma and contains silurian devonian and carboniferous fossils thus the melange formed in the late carboniferous or later our structural analysis of fault planes in the hno the crenulation cleavages s 2 of the schist and fold axial planes of early permian sandy limestone quartz veins and late permian sandstones indicates that the melange underwent a north to south compression and the orientation of stretching lineations slickensides and fold hinge lines implies that the hno experienced top to the north or northwest movement the entire planar and linear structural data set suggests that the subduction polarity was probably to the south in the late paleozoic the emplacement age of the hno was probably near the end permian based on the age of the youngest rocks in the ophiolitic melange and by the presence of a late permian unconformity from our work integrated with published regional data we outline a comprehensive geodynamic model for the central boc

late silurian early devonian adakitic granodiorite a type and i type granites in nw junggar nw china partial melting of mafic lower crust and implications for slab roll back abstract late silurian early devonian magmatism of the nw junggar region in the central asian orogenic belt provides a critical geological record that is important for unraveling regional tectonic history and constraining geodynamic processes in this study we report results of zircon u pb ages and systematic geochemical data for late silurian early devonian largely granitic rocks in nw junggar aiming to constrain their emplacement ages origin and geodynamic significance the magmatism consists of a variety of mafic to felsic intrusions and volcanic rocks e g adakitic granodiorite k feldspar granite syenitic granite gabbro and rhyrolite u pb zircon ages suggest that the granitoids and gabbros were emplaced in the late silurian early devonian 420 405 ma adakitic granodiorites are calc alkaline characterized by high sr 407 532 ppm low y 12 2 14 7 ppm yb 1 53 1 77 ppm cr mostly

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

zircon u pb geochronology and hf isotopic constraints on petrogenesis of the gangdese batholith southern tibet abstract during the mesozoic cenozoic northward neotethyan subduction and subsequent india asia collision gave rise to the extensive transhimalayan magmatism that stretches from burma and western yunnan through southern tibet to the ladakh and kohistan complexes to understand the age distribution and petrogenesis of the gangdese batholith the largest intrusive exposure along the transhimalayan magmatic belt fifty granitic samples were selected for in situ zircon u pb and hf isotopic analyses the u pb data suggest four discrete stages of magmatic activity i e 205 152 109 80 65 41 and 33 13 ma respectively with the 65 41 ma stage being the most prominent the hf isotopic data indicate that the gangdese batholith is overwhelmed by positive e hf t values which are comparable to those of the kohistan ladakh batholiths in the west but differ markedly from those of the chayu burma batholiths in the east most of the gangdese granites show similar and young hf model ages 1000 300 ma indicating their derivation from juvenile crust however those formed in the 65 41 ma stage exhibit more heterogeneous hf isotopic ratios with negative e hf t values being observed in some granites younger than 50 ma suggesting the involvement of old indian continental crust in their petrogenesis this age may thus mark the onset of the india asia collision the newly established zircon u pb age and hf isotope database of the gangdese batholith can be used as a powerful tracer or fingerprint when studying the source to sink relation of the sediments eroded from the southern tibetan plateau

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

the pre devonian tectonic framework of xing an mongolia orogenic belt xmob in north china abstract a new tectonic division of the xing an mongolia orogenic belt xmob in north china has been presented according to our research and a lot of new data of tectonics geochronology and geochemistry four blocks and four sutures have been recognized in the xmob including the erguna eb xing an airgin sum xab songliao hunshandake shb and jiamusi jb and xinlin xiguitu xxs xilinhot heihe xhs mudanjiang ms and ondor sum yongji sutures oys the framework of the xmob is characterized by a tectonic collage of the blocks and orogenic belts between them different precambrian basements have been found in the blocks including the neoproterozoic metamorphic rocks and plutons in the eb the neoproterozoic metamorphic rocks in western and eastern of segments of the xab mesoproterozoic and neoproterozoic metamorphic rocks in middle segments of the xab respectively the neoproterozoic metamorphic rocks and mesoproterozoic volcanic rocks and plutons in the shb and neoproterozoic metamorphic rocks in the jb the xxs resulted from a northwestward subduction of the xab beneath the eb during the cambrian which was followed by the forming of the xhs and oys in the northwest and south margins of the shb in the silurian respectively the ms was caused by a westward subduction of the jb beneath the east margin of the shb during the middle devonian the three cambrian silurian and middle devonian events indicate that the xmob belongs to a pre middle devonian multiple orogenic belt in the central asian orogenic belt caob forming of the xmob suggests that the southeast part of the paleo asian ocean closed before the middle devonian

assembly of the lhasa and qiangtang terranes in central tibet by divergent double subduction abstract integration of lithostratigraphic magmatic and metamorphic data from the lhasa qiangtang collision zone in central tibet including the bangong suture zone and adjacent regions of the lhasa and qiangtang terranes indicates assembly through divergent double sided subduction this collision zone is characterized by the absence of early cretaceous high grade metamorphic rocks and the presence of extensive magmatism with enhanced mantle contributions at ca 120 110 ma two jurassic cretaceous magmatic arcs are identified from the caima duobuza rongma kangqiong amdo magmatic belt in the western qiangtang terrane and from the along tso yanhu daguo baingoin daru tso magmatic belt in the northern lhasa terrane these two magmatic arcs reflect northward and southward subduction of the bangong ocean lithosphere respectively available multidisciplinary data reconcile that the bangong ocean may have closed during the late jurassic early cretaceous most likely ca 140 130 ma through arc arc soft collision rather than continent continent hard collision subduction zone retreat associated with convergence beneath the lhasa terrane may have driven its rifting and separation from the northern margin of gondwana leading to its accretion within asia

increased terrestrial carbon storage across the palaeocene eocene boundary abstract a rapid short lived global warming event at the close of the palaeocene ca 55 5 million years ago ma was associated with the addition of massive amounts of carbon to the exogenic carbon cycle and major benthic extinctions evaluation of the response of the terrestrial biosphere to this transient ancient greenhouse world with a process based terrestrial carbon cycle model and global palaeoclimate simulations indicates the sequestration of ca 1112 gt c into the vegetation and soil carbon pools a largely independent global carbon isotope mass balance analysis also points to the strong potential for the terrestrial biosphere to sequester substantial amounts of carbon at this time with the increase being calculated at between 2107 and 3060 gt c this analysis suggests that some other feature of global environmental change across the palaeocene eocene boundary may have been forcing terrestrial carbon cycle dynamics at this time however even a minimum increase of 1112 gt c would have been sufficiently large to implicate the response of the terrestrial carbon cycle as a negative feedback mechanism on climate at 55 5 ma possibly reducing global temperatures by up to 2 5 c

crustal structure of the northeastern margin of the tibetan plateau from the songpan ganzi terrane to the ordos basin abstract the 1000 km long darlag lanzhou jingbian seismic refraction profile is located in the ne margin of the tibetan plateau this profile crosses the northern songpan ganzi terrane the qinling qilian fold system the haiyuan arcuate tectonic region and the stable ordos basin the p wave and s wave velocity structure and poisson s ratios reveal many significant characteristics in the profile the crustal thickness increases from northeast to southwest the average crustal thickness observed increases from 42 km in the ordos basin to 63 km in the songpan ganzi terrane the crust becomes obviously thicker south of the haiyuan fault and beneath the west qinlin shan the crustal velocities have significant variations along the profile the average p wave velocities for the crystalline crust vary between 6 3 and 6 4 km s beneath the songpan ganzi terrane west qinling shan and haiyuan arcuate tectonic region p wave velocities of 6 3 km s are 0 15 km s lower than the worldwide average of 6 45 km s north of the kunlun fault with exclusion of the haiyuan arcuate tectonic region the average p wave velocity is 6 4 km s and only 0 5 km s lower than the worldwide average a combination of the p wave velocity and poisson s ratio suggests that the crust is dominantly felsic in composition with an intermediate composition at the base a mafic lower crust is absent in the ne margin of the tibetan plateau from the songpan ganzi terrane to the ordos basin there are low velocity zones in the west qinling shan and the haiyuan arcuate tectonic region the low velocity zones have low s wave velocities and high poisson s ratios so it is possible these zones are due to partial melting the crust is divided into two layers the upper and the lower crust with crustal thickening mainly in the lower crust as the ne tibetan plateau is approached the results in the study show that the thickness of the lower crust increases from 22 to 38 km as the crustal thickness increases from 42 km in the ordos basin to 63 km in the songpan ganzi terrane south of the kunlun fault both the conrad discontinuity and moho in the west qinling shan and in the haiyuan arcuate tectonic region are laminated interfaces implying intense tectonic activity the arcuate faults and large earthquakes in the haiyuan arcuate tectonic region are the result of interaction between the tibetan plateau and the sino korean and gobi ala shan platforms

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

sources of phanerozoic granitoids in the transect bayanhongor ulaan baatar mongolia geochemical and nd isotopic evidence and implications for phanerozoic crustal growth abstract the central asian orogenic belt caob is renowned for massive generation of juvenile crust in the phanerozoic mongolia is the heartland of the caob and it has been subject to numerous investigations particularly in metallogenesis and tectonic evolution we present new petrographic geochemical and sr nd isotopic analyses on phanerozoic granitoids emplaced in west central mongolia the data are used to delineate their source characteristics and to discuss implications for the phanerozoic crustal growth in central asia our samples come from a transect from bayanhongor to ulaan baatar including three tectonic units the baydrag cratonic block late archean to middle proterozoic the eo cambrian bayanhongor ophiolite complex and the hangay hentey basin of controversial origin the intrusive granitoids have ages ranging from ca 540 to 120 ma the majority of the samples are slightly peraluminous and can be classified as granite s s including monzogranite syenogranite and alkali feldspar granite most of the rocks have initial 87sr 86sr ratios between 0 705 and 0 707 late paleozoic to mesozoic granitoids 250 ma are characterized by near zero end t values 0 to 2 whereas older granitoids show lower end t values 1 5 to 7 the data confirm the earlier observation of kovalenko et al geochemistry international 34 1996 628 who showed that granitoids emplaced outside of the pre riphean basement rocks are characterized by juvenile positive end t values whereas those within the pre riphean domain and the baydrag cratonic block as for the present case show a significant effect of contamination by precambrian basement rocks nevertheless mass balance calculation suggests that the granitoids were derived from sources composed of at least 80 juvenile mantle derived component despite our small set of new data the present study reinforces the general scenario of massive juvenile crust production in the caob with limited influence of old microcontinents in the genesis of phanerozoic granitoids

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

topographic controls on production and deposition of tidal cool water carbonates uzes basin se france we document an example of a cool water carbonate deposit interpreted as a flood tidal delta formed during sea level fall in the uzes basin french miocene foreland basin in the miocene it was a peripheral basin connected to the open sea by a narrow 15 km long seaway the studied uzes formation is a 50 m thick tidal bioclastic carbonate body formed at the junction between the uzes basin and the seaway it is composed dominantly of rhodalgal packstones that are interpreted to have been produced inside the basin however most of the deposit was built out by bidirectional hydraulic dunes suggesting that accumulation of carbonate grains was not controlled by production but rather by tidal currents the deposit is thickest and coarsest grained and exhibits the larger dunes at the inlet of the seaway where currents are expected to have been fastest the deposit is thinner finer grained and more bioturbated away from the inlet toward the basin that is interpreted as a result of a decrease of current velocity due to flow expansion the main deposit exhibits a general upward increase in thickness and grain size of cross beds together with a decrease of faunal diversity from bivalve rich to rhodalgal facies consistent with progressive tidal flow acceleration in the seaway resulting from sea level fall lime mud is pervasive in the matrix of even the highest energy facies this suggests that one cannot draw any average correlation between permeability and architecture of the deposit also this could favor the observed early marine diagenesis of the deposit and give it a high preservation potential in the stratigraphic record

basin evolution and oil shale deposition during upper cretaceous in the songliao basin ne china implications from sequence stratigraphy and geochemistry abstract the controlling factors of oil shale formation within the upper cretaceous qingshankou and nenjiang formations of the songliao basin are investigated by petrological and geochemical methods sediment deposition was balanced by basin subsidence resulting in the accumulation of cretaceous strata of high thickness global sea level fluctuations have been related to periods of oil shale deposition within the basin the results indicate a comparable depositional environment during oil shale formation within the two upper cretaceous strata with respect to palaeotectonic and palaeoclimate but differences in the accommodation space during accumulation of the two formations the larger accommodation space during deposition of the nenjiang formation resulted in the higher thickness and wider distribution of the oil shale members total thickness 11 2 32 m distribution area 4 48 103 km2 within the basin as compared to the oil shale of the qingshankou formation total thickness 2 19 3 m distribution area 1 3 103 km2 further differences exist with regard to the palaeoenvironment of oil shale formation and primary productivity deposition of the qingshankou formation 1st member and nenjiang formation 1st member took place within a saline brackish lake under anoxic conditions in the bottom water preservation of organic matter is suggested to have been less favorable during deposition of the nenjiang formation 2nd member higher primary productivity is believed to be the responsible factor for the accumulation of organic rich sediments in the qingshankou formation 1st member the interplay of these two factors i e preservation productivity leads to the formation of oil shale in the qingshankou formation average toc 8 32 tocmax 13 52 average oil yield 5 57 with better hydrocarbon source rock potential and slightly higher oil yield during pyrolysis as in the nenjiang formation average toc 7 76 tocmax 9 7 average oil yield 5 54 primary productivity is suggested as the main controlling factor on differences in oil shale quality and source rock potential between the two formations whereas the variations in quality within each formation mainly depend on the preservation of organic matter the high thickness wide spatial distribution and excellent hydrocarbon potential of the upper cretaceous oil shales in the songliao basin are suggested to have been the result of large accommodation space stable palaeoenvironmental conditions and high primary productivity

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

palaeozoic polymetamorphism in the north qinling orogenic belt central china insights from petrology and in situ titanite and zircon u pb geochronology abstract the qinling orogenic belt experienced multiple phases of orogenesis during the palaeozoic unraveling the timing and p t conditions of these events is the key to understanding the convergence processes between the south china and the north china blocks the songshugou complex located in the southern part of the north qinling orogenic belt has registered multistage metamorphism in palaeozoic and thus potentially provides insights into the tectonic evolution of the qinling orogenic belt in this study three metabasic rocks a garnet pyroxenite a garnet amphibolite and a gneissic amphibolite from the songshugou complex were selected for petrological study and zircon and titanite u pb dating our results show that the metabasic rocks experienced three metamorphic events during the palaeozoic the first metamorphic event m1 is characterized by high pressure conditions two zircon grains in equilibrium with garnet and in absence of plagioclase were recognized from the garnet pyroxenite sample they yielded ti in zircon temperatures of 660 851 c at 12 0 kbar and a weighted mean age of 498 15 ma providing the constraints on the temperature and timing of prograde or peak metamorphism m1 1 zircons that are inequilibrium with garnet from the garnet pyroxenite and the garnet amphibolite gave u pb ages of 494 9 ma and 484 4 ma and ti in zircon temperatures of 793 33 c and 738 18 c respectively thus these zircons were formed on the retrograde amphibolite facies conditions at 8 0 kbar m1 2 titanite inclusions were found in actinolite cores of zoned amphibole from the garnet amphibolite they yielded a u pb age of 470 ma and zr in titanite temperature of 676 23 c at pressure of 7 0 kbar suggesting that the amphibolite facies retrogression perhaps persisted to 470 ma weakly zoned zircons from the garnet amphibolite and inclusion free titanites from the garnet pyroxenite gave consistent u pb ages of 418 5 ma and 423 10 ma and ti in zircon temperature of 742 26 c and zr in titanite temperature of 764 18 c at 7 0 kbar respectively it is suggested that a heating event m2 is registered by a subsequent phase of amphibolite facies metamorphism the ilmenite bearing titanite crystals from the garnet pyroxenite yielded a u pb age of 352 4 ma recording a late thermal event m3 on the basis of combined petrological and geochronological results we propose a revised tectonic model for the north qinling orogeny in palaeozoic the high pressure granulites were formed by the northward subduction of the shangdan oceanic slab and the arc continent collision at ca 500 ma their exhumation happened at ca 494 484 ma as a result of slab breakoff subsequent amphibolite facies metamorphism dated at ca 440 420 ma are coeval with the widespread magmatism in the north qinling terrane which are likely caused by the reinitiation northward subducted of shangdan oceanic slab at ca 350 ma the north qinling terrane was likely affected by another thermal overprinting event

topography of the top chalk surface on and offshore denmark abstract a time structure map of the top of the upper cretaceous danian chalk group the top chalk surface in the entire danish sector is presented the present topography of the top chalk surface is a result of various erosional and tectonic events taking place during the cenozoic the analysis shows that the cenozoic is characterised by significant reactivation of the mesozoic structural elements of which the central graben the ringkobing fyn high and the sorgenfrei tornquist zone are the most important a tectonically controlled relief caused the generation of widespread sheet like erosion on the ringkobing fyn high and incisions along the margins of ringkobing fyn high during the mid paleocene incisions in the northern part of the danish sector formed valleys which probably transported sediment towards the west the present topography of top chalk in the eastern part of the danish sector is highly influenced by the late cenozoic erosion of the uplifted eastern margin of the north sea basin the topography of top chalk also reflects the distribution of mobile zechstein salt as collapse structures follow the pitch out line of mobile salt onto the ringkobing fyn high and numerous salt structures deformed the top chalk surface