late cretaceous early palaeogene tectonic development of se asia abstract the late cretaceous early palaeogene history of the continental core of se asia sundaland marks the time prior to collision of india with asia when se asia from the tethys in the west to the palaeo pacific in the east lay in the upper plate of subduction zones in myanmar and sumatra subduction was interrupted in the aptian albian by a phase of arc accretion woyla and mawgyi arcs and in java eastern borneo and western sulawesi by collision of continental fragments rifted from northern australia subsequent resumption of subduction in the myanmar thailand sector explains 1 early creation of oceanic crust in the andaman sea in a supra subduction zone setting 95 ma 2 the belt of granite plutons of late cretaceous early palaeogene age starting 88 ma in western thailand and central myanmar and 3 amphibolite grade metamorphism between 70 and 80 ma seen in gneissic outcrops in western and central thailand and 4 accretionary prism development in the western belt of myanmar until glancing collision with the ne corner of greater india promoted ophiolite obduction deformation and exhumation of marine sediments in the early palaeogene the ranong strike slip fault and other less well documented faults were episodically active during the late cretaceous palaeogene time n to nw directed subduction of the palaeo pacific ocean below southern china vietnam and borneo created a major magmatic arc associated with rift basins metamorphic core complexes and strike slip deformation which continued into the late cretaceous the origin and timing of termination of subduction has recently been explained by collision of a large luconia continental fragment either during the late cretaceous or palaeogene evidence for such a collision is absent from the south china sea well and seismic reflection record and here collision is discounted instead relocation of the subducting margin further west possibly in response of back arc extension which created the proto south china sea is preferred lying between the two subduction related arcs the khorat basin is of predominantly late jurassic early cretaceous age but stratigraphic and apatite fission track data also indicates deposition of 1 2 km of late cretaceous sediments the synformal basin geometry probably arose due to the dynamic topography created by converging tethyan and palaeo pacific subduction zones the aptian albian slowing of basin subsidence and onset of evaporite deposition coincides with collision of the mawgyi and woyla island arcs extensive palaeogene deformation and exhumation 3 km in places affected all margins of the khorat plateau deformation includes folds of the phu phan uplift and strike slip faults thrusts and folds on the southern and eastern margins south of the khorat plateau outcrop and seismic reflection data from the ton le sap basin cambodia and the gulf of thailand indicate syn depositional fault controlled subsidence was important during cretaceous deposition the hot thickened crust developed during the late cretaceous palaeogene events follows the weak indosinian crustal scale inthanon and sukhothai zones which persistently guided the location of later structures including cenozoic extensional and post rift basins and influenced the widespread occurrence of low angle normal faults metamorphic core complexes and eastern gulf of thailand super deep post rift basins

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

structural and geochronological constraints on the tectonic evolution of the dulong song chay tectonic dome in yunnan province sw china abstract the dulong song chay tectonic dome lies on the border of china se yunnan province and northern vietnam and consists of two tectonic and lithologic units a core complex and a cover sequence separated by an extensional detachment fault these two units are overlain unconformably by late triassic strata the core complex is composed of gneiss schist and amphibolite shrimp zircon u pb dating results for the orthogneiss yield an age of 799 10 ma which is considered to be the crystallization age of its igneous protolith formed in an arc related environment a granitic intrusion within the core complex occurred with an age of 436 402 ma which probably formed during partial closure of paleotethys within the core complex metamorphic grades change sharply from upper greenschist low amphibolite facies in the core to low greenschist facies in the cover sequence there are two arrays of foliation within the core complex detachment fault and the cover sequence s 1 and s 2 the pervasive s 1 is the axial plane of intrafolial s 0 folds d 1 deformation related to this foliation is characterized by extensional structures the strata were structurally thinned or selectively removed along the detachment faults indicating exhumation of the dulong song chay tectonic dome the major extension occurred at 237 ma determined by shrimp zircon u pb and 39 ar 40 ar isotopic dating techniques regionally simultaneous tectonic extension was associated with pre indosinian collision between the south china and indochina blocks the s 2 foliation appears as the axial plane of nw striking s 1 buckling folds formed during a compressional regime of d 2 d 2 is associated with collision between the south china and indochina blocks along the jinshajiang ailao shan suture zone and represents the indosinian deformation the dulong granites intruded the dulong song chay dome at 144 2 140 2 and 116 10 ma based on 39 ar 40 ar measurement on muscovite and biotite the dome was later overprinted by a conjugate strike slip fault and related thrust fault which formed a vortex structure contemporaneously with late cenozoic sinistral movement on the ailao shan red river fault

mesozoic geology of southwestern china indosinian foreland overthrusting and subsequent deformation abstract the southwestern part of the south china block scb records triassic and subsequent deformations and is a key region that provides evidence of the post amalgamation tectonic evolution of southeast asia here we outline the tectonothermal evolution of early mesozoic orogenesis in this region using structural analysis and fission track thermochronology this region is divided into three tectonic units south to north the youjiang fold and thrust belt yftb the qianzhong massif qzm and the thin skinned thrust belt ttb of the southeastern sichuan basin all three of which record three deformation events here termed d 1 d 2 and d 3 d 1 deformation is represented by triassic top to the north thrusts f 1 and fault related folds f 1 that are indicative of n s shortening the intensity of deformation decreases toward the north the subsequent d 2 and d 3 deformations are marked by cretaceous top to the nw thrusting and fault propagation folding and cenozoic ne sw trending normal faults f 3 respectively the temperature time t t path obtained by apatite fission track modeling of samples from the yftb qzm and ttb areas provides evidence of uplift and denudation the d 1 deformation at 230 210 ma is characterized by buried thrusts within the relatively stable yftb and qzm and an increase in depth of the ttb this was coeval with the late triassic northward migration of uplift and denudation that is evidenced by a late triassic stratigraphic gap within the yftb a thin layer of coarse grained continental clastics within the qzm and a thick layer of clastic rocks within the ttb the study area records a triassic thrust system d 1 that progressively migrated northwards and represents a foreland fold and thrust belt that formed during the indochina scb collision this initial deformation was subsequently overprinted by late jurassic to cretaceous nw se thrusting d 2 and the development of cenozoic nw se extensional structures d 3

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

early mesozoic tectonics of the south china block insights from the xuefengshan intracontinental orogen abstract intracontinental orogens remain less understood than accretionary or collisional orogens that are related to plate margin interactions in the center of the south china block the xuefengshan belt provides a well exposed example of such an intracontinental orogen of early mesozoic age detailed field tectonic observations indicate that the xuefengshan belt can be divided into a western outer zone characterized by km scale box fold structures and an eastern zone separated from the western outer zone by the se dipping main xuefengshan thrust in the eastern zone nw verging folds coeval with a pervasive slaty cleavage and a nw se trending lineation are the dominant structures from west to east the dip of the cleavage surface exhibits a fan like pattern the bulk architecture of the xuefengshan belt results from polyphase deformation d 1 is characterized by a top to the nw ductile shearing d 2 corresponds to se directed back thrusting and folding d 3 consists of upright folds with vertical cleavage and lineation at depth a high strain zone characterized by greenschist facies metamorphic rocks and a top to the nw ductile shearing corresponds to a ductile decollement zone that accommodated the deformation of the neoproterozoic to early triassic sedimentary series kinematic compatibility suggests that the synmetamorphic ductile shearing was coeval with the d 1 event in the sedimentary cover the xuefengshan belt is interpreted as an early mesozoic intracontinental orogen which possibly originated from the se directed continental subduction of a piece of the south china block in response to northwestwards subduction of the pacific plate

sill cube an automated approach for the interpretation of magmatic sill complexes on seismic reflection data abstract the use of conventional interpretation techniques like manual interpretation seismic attribute analysis and opacity rendering or geobody extraction have demonstrated significant success in interpreting magmatic sills from seismic reflection data nonetheless the downsides of seismic imaging and interpretation of magmatic sills are that they are rarely drilled or too thin to be detected we present an automated approach for interpreting magmatic sills from seismic reflection data by using a newly designed meta attribute called as the sill cube sc the sc meta attribute is generated by amalgamating a number of different attributes that are trained over the interpreter s knowledge of the sill networks through a supervised scheme of neural learning the approach has shown its efficiency by delivering enhanced images of magmatic sills from seismic data in three frontier areas i e the kora prospect offshore taranaki basin new zealand the utgard and the tulipan prospects both offshore voring basin norway the sc meta attribute has completely captured the saucer shape geometry of most of the sills additionally the meta attribute has brought out different structural elements such as the limbs bridges junctions and fingers and highlighted the overlying forced folds the interpreted sills cover areas of 6 16 km2 in the kora prospect 105 1140 km2 in the utgard prospect and 15 60 km2 in the tulipan prospect such an interpretational approach does not only honour the interpreter s knowledge of sills networks but also add values in understanding the tectonic architecture

long term evolution of the west african transform margin estimates of denudation from benin using apatite thermochronology the benin continental margin was formed during the breakup of gondwana through oblique rifting along transform faults the evolution of topography following breakup directly affects the evolution of sedimentary basins which has major implications for hydrocarbon exploration in the region quantitative constraints on erosion across benin are limited to the cenozoic based on analysis of dissected lateritic palaeolandscapes to resolve the mesozoic erosion history we have obtained apatite fission track and single grain u th sm he data from 18 samples collected across a 600 km long transect through benin we invert these data including available geological and geomorphological constraints to obtain time temperature paths which are used to estimate magnitudes of denudation over the last 200 myr our study suggests that denudation was focused over a c 300 km long seaward sloping limb of the marginal upwarp and at the southern margin of the interior iullemmeden basin from 140 to 100 ma with lower magnitudes of denudation characterizing the continental interior and post cretaceous evolution of the margin models are consistent with modest burial c 1 km of the iullemmeden basin between 120 and 85 ma and of the continental margin between 85 and 45 ma by the eocene the first order relief of benin had developed with regional erosion rates supplementary information full details of the analytical data and modelling results including the various constraints and further data on denudation and burial magnitudes and rates are available at https doi org 10 6084 m9 figshare c 4220804

constraints from zircon u pb ages o and hf isotopic compositions on the origin of neoproterozoic peraluminous granitoids from the jiangnan fold belt south china zircon textures and micro chemical compositions precisely record the origin and petrogenesis of granitoids which are crucial for evaluating crustal growth and reworking thermal and geodynamic evolution zircons in peraluminous granitoids from the three largest 820 ma complexes guibei yueyang and jiuling in the jiangnan fold belt in south china are used to constrain their sources and petrogenetic processes zircons in the guibei granitoids have complex internal structures nearly all magmatic and inherited zircons have similar ehf 6 8 to 5 6 and 18o values 8 8 11 6 and dominantly lie between ehf evolution vectors for a crust created between 1 7 and 2 1 ga suggesting that the guibei granitoids were produced by partial melting of recycled heterogeneous supracrustal material however the yueyang granitoids contain zircons with high ehf 0 5 to 9 7 and relatively low 18o values 5 9 8 4 and two stage model ages of 1 1 1 8 ga and thus may have been formed by melting of mafic rocks from the lower crust the jiuling granitoids and their enclaves contain more complex zircons with more variable ehf 7 2 to 9 7 and 18o values 7 0 10 6 and lie along the mixing trend between the above proposed infracrustal and supracrustal granitoids therefore the neoproterozoic peraluminous granitoids in the jiangnan fold belt were produced by melting and mixing of continental crust compared with extremely low 4 and negative 18o values of neoproterozoic igneous zircons formed in its northern active continental margin the high 18o peraluminous granitoids in the southeastern yangtze block are considered to have been formed by melting of hydrothermally unaltered continental crust triggered by asthenosphere upwelling in the nanhua back arc basin

characteristics of some igneous extrusive and hypabyssal features in seismic data examples of flood basalts and dike intrusions from four localities on the british continental shelf are illustrated in seismic data synform features flanked by antiforms in the flood basalt areas are interpreted as fissure vents seen in cross section and geologic models are considered that might explain seismic events indicating subsidence and other effects associated with the observed features seismic phenomena related to dikes in the manx furness basin and the north sea are discussed and possible causes of apparent bilateral updrag in the country rocks adjacent to these intrusions are suggested

shaping mobile belts by small scale convection claudio faccenna and thorsten becker compute global mantle flow based on a recent high resolution seismic tomography model to investigate the role of buoyancy driven and plate motion induced mantle circulation for the mediterranean they show that mantle flow provides an explanation for much of the observed dynamic topography and microplate motion in the region and conclude that vigorous small scale convection in the uppermost mantle may also hold the key for understanding other complex mobile belts such as those in the north american cordillera and the himalayan tibetan collision zone here global mantle flow is computed on the basis of recent high resolution seismic tomography to investigate the role of buoyancy driven and plate motion induced mantle circulation in the mediterranean region the findings show that mantle flow explains much of the observed dynamic topography and microplate motion in the region small scale convection in the uppermost mantle may also hold the key to understanding complex mobile belts elsewhere mobile belts are long lived deformation zones composed of an ensemble of crustal fragments distributed over hundreds of kilometres inside continental convergent margins1 2 the mediterranean represents a remarkable example of this tectonic setting3 the region hosts a diffuse boundary between the nubia and eurasia plates comprised of a mosaic of microplates that move and deform independently from the overall plate convergence4 surface expressions of mediterranean tectonics include deep subsiding backarc basins intraplate plateaux and uplifting orogenic belts although the kinematics of the area are now fairly well defined the dynamical origins of many of these active features are controversial and usually attributed to crustal and lithospheric interactions however the effects of mantle convection well established for continental interiors5 6 7 should be particularly relevant in a mobile belt and modelling may constrain important parameters such as slab coherence and lithospheric strength here we compute global mantle flow on the basis of recent high resolution seismic tomography to investigate the role of buoyancy driven and plate motion induced mantle circulation for the mediterranean we show that mantle flow provides an explanation for much of the observed dynamic topography and microplate motion in the region more generally vigorous small scale convection in the uppermost mantle may also underpin other complex mobile belts such as the north american cordillera or the himalayan tibetan collision zone

apatite fission track data for the miocene arabia eurasia collision the collision between the eurasian and arabian plates along the 2400 km long bitliszagros thrust zone isolated the mediterranean from the indian ocean and has been linked to extension of the aegean rifting of the red sea and the formation of the north and east anatolian fault systems however the timing of the collision is poorly constrained and estimates range from late cretaceous to late miocene here we report the fi rst apatite fi ssiontrack aft ages from the bitlis zagros thrust zone the aft samples are distributed over the 450 km length of the bitlis thrust zone in southeast turkey and include metamorphic rocks and eocene sandstones despite the disparate lithology and large distance the aft ages point consistently to exhumation between 18 and 13 ma the aft ages along with a critical appraisal of regional stratigraphy indicate that the last oceanic lithosphere between the arabian and eurasian plates was consumed by the early miocene ca 20 ma the results imply that aegean extension predated the arabia eurasia collision

jiangnan orogen in south china developing from divergent double subduction abstract the jiangnan orogen is considered as a continent continent collisional belt resulting from the closure of a meso neoproterozoic ocean separating the southeastern margin of the yangtze block from the northwestern margin of the cathaysia block recent data indicate the existence of early neoproterozoic 1000 825 ma volcanic arc assemblages on both sides of the orogen suggesting that the ocean lithosphere between the yangtze and cathaysia blocks must have undergone divergent double sided subduction during the period of 1000 825 ma the divergent double subduction eventually resulted in the closure of the ocean basin at 825 ma leading to the soft collision of the yangtze and cathaysia blocks to form the jiangnan orogen without involvement of continental deep subduction high grade metamorphism of continental crust and uplift exhumation of high grade metamorphic rocks shortly after the collision the initial detachment of the ocean lithosphere from the overlying crust and sedimentary sections induced underplating of mantle magmas triggering partial melting of accretionary wedge strata to form some peraluminous s type granites in the period 825 815 ma finally the sinking of the oceanic slab pulled down the overlying strata to form some basins in which the banxi group and its equivalent strata including bimodal volcanic rocks were formed in the period 815 750 ma

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

major and trace element and sr nd isotope constraints on the origin of paleogene volcanism in south china prior to the south china sea opening abstract paleogene volcanic rocks crop out in three sedimentary basins namely sanshui heyuan and lienping in the attenuated continental margin of south china lavas from the sanshui basin which erupted during 64 43 ma are bimodal consisting of intraplate tholeiitic basalt and trachyte rhyolite associations similar to cretaceous a type granites from the nearby region the felsic member shows peralkaline nature na2o k2o 10 12 na k al 0 98 1 08 general enrichment in the incompatible trace elements and significant depletion in ba sr eu p and ti although both types of the sanshui lavas have rather uniform nd isotope compositions nd t 6 to 4 that are comparable to late cenozoic basalts around the south china sea the felsic rocks possess apparently higher initial sr isotope ratios isr up to 0 713 and form a horizontal array to the right in the nd vs sr isotope plot closed system differentiation of mantle derived magmas in a double diffusive magma chamber is considered for the bimodal volcanism in which the trachytes and rhyolites represent a type melts after extensive crystal fractionation in the upper portion of the chamber such a type melts were later contaminated by small amounts 1 3 of upper crustal materials during ascent on the other hand composition of lavas in the other two basins varies from tholeiitic basalt to andesite their sr and nd isotope ratios isr 0 705 to 0 711 nd t 1 to 5 and generally correlative nb ta depletions suggest a distinct magma chamber process involving fractional crystallization concomitant with assimilation of the country rock we conclude that these paleogene volcanic activities resulted from the lithospheric extension in south china that migrated southwards and eventually led to opening of the south china sea during 30 16 ma

cenozoic tectonic history of the south georgia microcontinent and potential as a barrier to pacific atlantic through flow cenozoic opening of the central scotia sea involved the tectonic translation of crustal blocks to form the north scotia ridge which today is a major topographic constriction to the flow of the deep antarctic circumpolar current that keeps antarctica thermally isolated from warmer ocean waters how this ridge developed and whether it was a topographic barrier in the past are unknown to address this we investigated the cenozoic history of the south georgia microcontinental block the exposed part of the ridge detrital zircon u pb geochronology data confirm that the cretaceous succession of turbidites exposed on south georgia was stratigraphically connected to the rocas verdes backarc basin part of the south america plate apatite thermochronometry results show that south georgia had remained connected to south america until ca 45 40 ma both record a distinct rapid cooling event at that time subsequent separation from south america was accompanied by kilometer scale reburial until inversion ca 10 ma coeval with the cessation of spreading at the west scotia ridge and collision between the south georgia block and the northeast georgia rise our results show that the south georgia microcontinental block could not have been an emergent feature from ca 40 ma until 10 ma

the onset of india asia continental collision early steep subduction required by the timing of uhp metamorphism in the western himalaya ultrahigh pressure uhp rocks in the nw himalaya are some of the youngest on earth and allow testing of critical questions of uhp formation and exhumation and the timing of the india asia collision initial collision of india with asia is widely cited as being at 55f1 ma based on a paleomagnetically determined slowdown of india s plate velocity and as being at ca 51 ma based on the termination of marine carbonate deposition even relatively small changes in this collision age force large changes in tectonic reconstructions because of the rapid india asia convergence rate of 134 mm a at the time of collision new u pb shrimp dating of zircon shows that indian rocks of the tso morari complex reached uhp depths at 53 3f0 7 ma given the high rate of indian subduction this dating implies that indian continental crust arrived at the asian trench no later than 57f1 ma providing a metamorphic age for comparison with previous paleomagnetic and stratigraphic estimates india s collision with asia may be compared to modern processes in the timor region in which initiation of collision precedes both the slowing of the convergence rate and the termination of marine carbonate deposition the indian uhp rocks must have traveled rapidly along a short hence steep path into the mantle early continental subduction was at a steep angle probably vertical comparable to modern continental subduction in the hindu kush despite evidence for modern day low angle subduction of india beneath tibet oceanic slab break off likely coincided with exhumation of uhp terranes in the western himalaya and led to the initiation of low angle subduction and leucogranite generation d 2005 elsevier b v all rights reserved

partitioning of the cretaceous pan yangtze basin in the central south china block by exhumation of the xuefeng mountains during a transition from extensional to compressional tectonics abstract the formation of a series of intermountain basins is likely to indicate a geodynamic transition especially in the case of such basins within the central south china block cscb determining whether or not these numerous intermountain basins represent a division of the cretaceous pan yangtze basin by exhumation of xuefeng mountains is key to understanding the late mesozoic to early cenozoic tectonics of the south china block scb here we present apatite fission track aft data and time temperature modeling in order to reconstruct the evolution history of the pan yangtze basin fourteen rock samples were taken from a ne sw trending mountain basin system within the cscb including from west to east the wuling mountains wuling shan the south and north mayang basins the xuefeng mountains xuefeng shan and the hengyang basin cretaceous lacustrine sequences are well preserved in the south and north mayang and hengyang basins and sporadically crop out in the xuefeng mountains whereas paleogene piedmont proluvial lacustrine sequences are only found in the south mayang and hengyang basins aft results indicate that the wuling and xuefeng mountains underwent rapid denudation post 84 ma whereas the south and north mayang basins were more slowly uplifted from 67 and 84 ma respectively following a quiescent period from 32 to 19 ma both the mountains and basins have been rapidly denuded since 19 ma both the aft data and sedimentary facies changes suggest that the cretaceous deposits that cover the south north mayang and hengyang basins through to the xuefeng mountains define the cretaceous pan yangtze basin integrating our results with tectonic background for the scb we propose that rollback subduction of the paleo pacific plate produced the pan yangtze basin which was divided into the south north mayang and hengyang basins by the abrupt uplift and exhumation of the xuefeng mountains from 84 ma to present apart from a period of tectonic inactivity from 32 to 19 ma this late late cretaceous to paleogene denudation resulted from movement on the ziluo strike slip fault which formed due to intra continental compression most likely associated with the eurasia indian plate subduction and collision sinistral transpression along the ailao shan red river fault at 34 17 ma probably transformed this compression to the extrusion of the indochina block and produced the quiescent window period from 32 to 19 ma for the mountain basin system in the cscb therefore the initiation of exhumation of the xuefeng mountains at 84 ma indicates a switch in tectonic regime from cretaceous extension to late late cretaceous and cenozoic compression

the thermal evolution of chinese central tianshan and its implications insights from multi method chronometry abstract the chinese tianshan is located in the south of the central asian orogenic belt and formed during final consumption of the paleo asian ocean in the late palaeozoic in order to further elucidate the tectonic evolution of the chinese tianshan we have established the temperature time history of granitic rocks from the chinese tianshan through a multi chronological approach that includes u pb zircon 40ar 39ar biotite and k feldspar and u th he zircon and apatite dating our data show that the central tianshan experienced accelerated cooling during the late carboniferous to early permian multiple sequences of complex multiple accretionary subduction and collisional events could have induced the cooling in the tianshan orogenic belt the new 40ar 39ar and u th he data in combination with thermal history modeling results reveal that several tectonic reactivation and exhumation episodes affected the chinese central tianshan during middle triassic 245 210 ma early cretaceous 140 100 ma late oligocene early miocene 35 20 ma and late miocene 12 9 ma the middle triassic cooling dates was only found in the central tianshan strong uplift and deformation in the chinese tianshan has been limited and localized it have been concentrated in around major fault zone and the foreland thrust belt since the early cretaceous the middle triassic and early cretaceous exhumation is interpreted as distal effects of the cimmerian collisions i e the qiangtang and kunlun qaidam collision and lhasa qiangtang collision at the southern eurasian margin the cenozoic reactivation and exhumation is interpreted as a far field response to the india eurasia collision and represents the beginning of modern mountain building and denudation in the chinese tianshan

the three dimensional geometry and growth of forced folds above saucer shaped igneous sills forced folds formed at the seabed immediately overlying shallow 1 km saucer shaped sills along the ne atlantic margin during the early paleogene examples of this sill fold relationship are exceptionally well imaged by high resolution 3d seismic datasets from the ne rockall basin the forced folds are domal in shape 2 4 km in diameter exhibit a structural relief of up to 350 m and comprise sediment volumes of ca 1 km3 a comparison of the thickness distribution across and volume of a saucer shaped sill with a high intrusion diameter to depth ratio and the structural relief and volume of its associated forced fold shows a remarkable equivalence this has the important implication that the structural relief on intrusion related forced folds can be used as an estimate of the thickness of the underlying sill the analysed forced folds are interpreted to have formed through three continual growth stages that are directly linked to the mechanical emplacement of the underlying saucer shaped sills their growth was associated with an increase in faulting of the overlying strata and influenced coeval or subsequent development of polygonal fault systems within the overburden these structures represent a new type of four way dip closed hydrocarbon trap

provenance and thermal history of the franciscan accretionary complex constraints from zircon fission track thermochronology the franciscan accretionary complex of california contains large belts of sediments that were subducted to depths of 10 to 30 km metamorphosed under high pressure and low temperature conditions and later returned to the surface reconnaissance zircon fission track ft data 21 samples place constraints on the sedimentary provenance thermal history and or exhumation history of various franciscan units in a transect across the northern coast ranges through mendocino pass metagraywacke samples from the valantine springs formation of the franciscan eastern belt experienced maximum temperatures tmax ranging from 250 to 310 c zircon ft and previously reported apatite ft data indicate that parts of the western eastern and eastern central belts cooled at about 100 70 ma from 300 c to 100 c considering the low paleogeothermal gradient of roughly 9 c km during franciscan subduction these rocks were apparently uplifted and exhumed from 30 to 10 km depth at this time one sample from the eyler mountain sequence in the northwestern diablo range similarly shows tmax 310 c and major cooling at 100 70 ma this uplift and exhumation may have reflected accelerated accretion at the base as well as the front of the franciscan wedge accompanied by extensional thinning at shallower levels as a result of massive sediment influx into the franciscan trench from the sierra nevada magmatic arc in the northern coast ranges the western part of the central belt and the coastal belt experienced lower tmax probably 200 c and retain source area detrital zircon ft ages burnt hills terrane samples in the diablo range also experienced tmax 230 c and retain detrital ages the detrital single grain age patterns from these areas are compatible with those expected from the sierra nevada magmatic arc and its country rocks this is consistent with derivation of franciscan sediments from arc terranes in california and provides no particular suggestion that these parts of the franciscan are highly allochthonous paleogene coastal belt sandstones also yield detrital ages compatible with derivation from the sierra nevada but also include early tertiary zircon populations compatible with reconstructions suggesting these sandstones were sourced partly from the idaho batholith

constructing the longmen shan eastern tibetan plateau margin insights from low temperature thermochronology 1 contrasting models of upper crustal shortening versus lower crustal flow have been proposed to explain the formation of thickened crust in the longmen shan lms eastern tibetan plateau tp margin these models require different structural kinematics along the lms whose structural geometry is defined by three parallel nw dipping fault zones from foreland southeast to hinterland northwest they are the guanxian anxian fault yingxiu beichuan fault ybf and wenchuan maowen fault wmf newly derived and previously published low temperature thermochronology data from the lms were synthesized to constrain the spatial exhumation and test previous models the results show that 1 exhumation increases abruptly across the range bounding ybf suggesting the fault being the main thrust boundary between the lms and the sichuan basin to the east 2 younger late cenozoic cooling ages are found on the hinterland wmf where a dichotomy of ages on the hanging wall versus footwall suggests late cenozoic thrust activity and 3 toward the hinterland to the west exhumation rates decrease twofold over a distance of 30 40 km this exhumation pattern indicates a westward decrease of tectonic uplift providing the regional topography approached a steady state whereby exhumation is in balance with tectonic uplift the observed exhumation estimates support an upper crustal configuration where thrusts in the lms merge gradually into a gentle detachment seated at a depth of 20 30 km results of this study support a revised upper crustal thrusting model

cooling and exhumation of the oldest sanqiliu uranium ore system in motianling district south china block the sanqiliu uranium deposit belongs to a uranium ore system in motianling district it is the oldest uranium deposit in south china primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes and it has a relatively high grade of uranium 0 421 we clarify the age of mineralization and investigate the cooling history through new pitchblende u pb and apatite fission track thermochronology the pitchblende u pb results indicate that uranium mineralization occurred at 801 759 ma fractionation of uranium and lead at 374 295 ma is interpreted as remobilization and resetting of the original uranium the motianling area has apatite fission track ages of 57 to 18 ma by combining our results with previous work we conclude that the deposit cooled slowly and was exposed at the surface during the cenozoic the timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit and highlight the potential for regional uranium exploration

the source of uranium within hydrothermal uranium deposits of the motianling mining district guangxi south china abstract uranium deposits are diverse as a result of their formation in a wide variety of geological environments however the source of the uranium within these deposits is difficult to identify and as a result it is usually poorly understood this study focuses on the hydrothermal sanqiliu and sanqisi uranium deposits both of which formed within ne sw striking shear zones that cross cut the sanfang batholith and low grade metasedimentary rocks of the motianling district southern china the deposits contain vein hosted pitchblende quartz pyrite chlorite mica orebodies fluid inclusions within quartz in the orebodies in the district homogenize at temperatures between 205 c and 222 c indicating the deposit formed as a result of low to intermediate temperature hydrothermal activity pitchblende associated hydrothermal pyrite within the sanqiliu and sanqisi deposits has 34s values from 24 7 to 19 7 and from 6 0 to 13 6 respectively quartz separates from the sanqiliu deposit yield 18o values of 1 4 11 5 mean of 5 8 for syn ore hydrothermal fluids these stable isotope data indicate that the fluids that formed these deposits were derived from the sanfang granites sediments of the sibao group and meteoric sources in addition uraninite from the host sanfang granite yields u pb ages of ca 732 773 ma combining these data with the geology of the ore deposits in this region suggests that these deposits were generated from deeply circulating meteoric water and the uraninite within the highly fractionated sanfang granite is the source of the uranium within the sanqiliu and sanqisi uranium deposits

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

intracontinental subduction a possible mechanism for the early palaeozoic orogen of se china the early palaeozoic orogen of se china consists of three lithotectonic elements from top to bottom a sedimentary upper unit a metamorphic lower unit and a gneissic basement the boundaries between these units are flat lying south directed ductile decollements the lower one is coeval with an amphibolite facies metamorphism m1 the belt is reworked by migmatite granite domes high temperature metamorphism m2 and granitic plutons related to post orogenic crustal melting we date here the syn m1 ductile shearing at 453 7 ma by u th pb method on monazite previous ages and our new 40 ar 39 ar ages of biotites and muscovites show that the metamorphic rocks experienced syn m2 exhumation from 440 to 400 ma the early palaeozoic orogen of se china is an intracontinental belt in which decollements accommodated the north directed subduction of the cathaysian continent this orogen is an example of intracontinental subduction that was not preceded by oceanic subduction

early opening history of the north atlantic i structure and origin of the faeroe shetland escarpment summary marine geophysical surveys show that the escarpment is the buried feather edge of a thick pile of flood basalts of early eocene age overlying a thinner more widespread layer of basalts of late palaeocene age the escarpment does not therefore define the continent ocean boundary in the southern norwegian sea but instead marks the contemporary shoreline separating terrestrially erupted basalt flows in the north from a restricted shallow water shelf to the south the basalts overlie 5 6 km of mesozoic sediments which have completely buried a large conical flat topped seamount of similar dimensions to anton dohrn and rosemary bank we call this newly postulated body the brendan seamount the mesozoic sediments are at least as old as early cretaceous in age therefore precluding the possibility that the mid cretaceous seafloor spreading episode supposed by some to have created the rockall trough could have also created the thin crust inferred to underlie the faeroe shetland trough and mbre basin

tectonics basin subsidence mechanisms and paleogeography of the caribbean south american plate boundary zone abstract using a mega regional dataset that includes over 20 000 km of on and offshore 2d seismic lines and 12 wells we illustrate three different stages of fault formation and basin evolution in the caribbean arc south american continent collisional zone transpressional deformation associated with oblique collision of the caribbean arc migrates diachronously over a distance of 1500 km from western venezuela in paleogene time 57 ma to a zone of active deformation in the eastern offshore trinidad area each diachronous stage of pre syn and post collisional basin formation is accompanied by distinct patterns of fault families we use subsidence histories from wells to link patterns of long term basinal subsidence to periods of activity of the fault families stage one of arc continent collision initial collision is characterized by overthrusting of the south and southeastward facing caribbean arc and forearc terranes onto the northward subducting mesozoic passive margin of northern south america northward flexure of the south american craton produces a foreland basin between the thrust front and the downward flexed continental crust that is initially filled by clastic sediments shed both from the colliding arc and cratonic areas to the south as the collision extends eastward towards trinidad this same process continues with progressively younger foreland basins formed to the east on the overthrusting caribbean arc and forearc terranes north south rifting adjacent to the collision zone initiates and is controlled by forward momentum of southward thrusting arc terranes combined with slab pull of the underlying and subducting north dipping south american slab uplift of fold thrust belts arc continent suture induces rerouting of large continental drainages parallel to the collisional zone and to the axis of the foreland basins stage two this late stage of arc continent collision is characterized by termination of deformation in one segment of the fold thrust belt as convergent deformation shifts eastward rebound of the collisional belt is produced as the north dipping subducted oceanic crust breaks off from the passive margin inducing inversion of preexisting normal faults as arc continent convergence reaches a maximum strain partitioning also begins to play an important role as oblique convergence continues accommodating deformation by the formation of parallel strike slip fault zones and backthrusting southward subduction of the caribbean plate beneath the south caribbean deformed belt as subsidence slows in the foreland basins sedimentation transitions from a marine underfilled basin to an overfilled continental basin offshore sedimentation is mostly marine sourced by the collided caribbean terranes localized islands and carbonate deposition stage three this final stage of arc continent collision is characterized by 1 complete slab breakoff of the northward dipping south american slab 2 east west extension of the caribbean arc as it elongates parallel to its strike forming oblique normal faults that produce deep rift and half grabens 3 continued strain partitioning strike slip faulting and folding the subsidence pattern in the caribbean basins is more complex than interpreted before showing a succession of extensional and inversion events the three tectonic stages closely control the structural styles and traps source rock distribution and stratigraphic traps for the abundant hydrocarbon resources of the on and offshore areas of venezuela and trinidad

geochemical and geochronological study of the sanshui basin bimodal volcanic rock suite china implications for basin dynamics in southeastern china abstract sanshui basin is one of the typical mesozoic cenozoic intra continental rift basins with voluminous cenozoic volcanic rocks in southeastern china thirteen cycles of volcanic eruptions and two dominant types of volcanic rocks basalt and trachyte rhyolite have been identified within the basin both basalt and trachyte rhyolite members of this bimodal suit have high values of end 2 3 to 6 2 and different sr isotopic compositions initial 87 sr 86 sr ratios are 0 70461 0 70625 and 0 70688 0 71266 for basalts and trachyte rhyolite respectively reflecting distinct magma evolution processes or different magma sources the results presented in this study indicate that both of the trachyte rhyolite and basaltic magmas were derived from similar independent primitive mantle but experienced different evolution processes the trachyte rhyolitic magma experienced significant clinopyroxene and plagioclase fractionational crystallization from deeper magma chamber with significant crustal contamination while the basaltic magmas experienced significant olivine and clinopyroxene fractionational crystallization in shallower magma chamber with minor crustal contamination new zircon u pb dating confirms an initial volcanic eruption at 60 ma and the last activity at 43 ma geologic geochemical and geochronological data suggest that the inception of the sanshui basin was resulted from upwelling of a mantle plume the sanshui basin widened due to subsequent east west extension and the subsequent volcanism constantly occurred in the center of the basin evidence also supports a temporal and spatial association with other rift basins in southeastern china the upwelling mantle plume became more active during late cenozoic time and most likely triggered opening of other basins including the young south china sea basin

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

climatic forcing of erosion landscape and tectonics in the bhutan himalayas a fundamental objective in studies of climate erosion tectonics coupling is to document convincing correlation between observable indicators of these processes on the scale of a mountain range the eastern himalayas are a unique range to quantify the contribution of tectonics and climate to long term erosion rates because uniform and steady tectonics have persisted for several million years while monsoonal precipitation patterns have varied in space and time specifically the rise of the shillong plateau the only orographic barrier in the himalayan foreland has reduced the mean annual precipitation downwind in the eastern bhutan himalaya at the miocene pliocene transition apatite fission track aft analyses of 45 bedrock samples from an e w transect along bhutan indicate faster long term erosion rates outside of the rain shadow in the west 1 0 1 8 mm yr than inside of it in the east 0 55 0 85 mm yr furthermore an aft vertical profile in the latter segment reveals a deceleration in erosion rates sometime after 5 9 ma in this drier segment of bhutan there are remnants of a relict landscape formed under a wetter climate that has not yet equilibrated to the present climatic conditions uplift and preservation of the paleolandscape are a result of a climate induced decrease in erosion rates rather than of an increase in rock uplift rate this study documents not only a compelling spatial correlation between long term erosion and precipitation rates but also a climatically driven erosion rate change on the scale of the eastern himalayas a change that in turn likely influences that region s recent tectonic evolution

cenozoic volcanic rocks of eastern china secular and geographic trends in chemistry and strontium isotopic composition abstract the cenozoic volcanic rocks of eastern china are subalkalic to alkalic basalts erupted in an early tertiary back arc rift environment and from scattered late tertiary and quaternary volcanic centers in a continental area crossed by active faults driven by subduction of the pacific plate and the collision of india and eurasia immobile trace elements and major elements conform very well to each other in classification of the 59 rocks for which complete data are reported and they correctly identify the tectonic setting lil element enrichments of the basalts lie between those of p morb and ocean island alkalic basalts and show a secular increase 87sr 86sr ratios of basalts vary from 0 7029 to 0 7048 alkalic basalts are systematically less radiogenic than geographically coextensive and contemporaneous tholeiitic basalts increase of radiogenic sr with increasing crustal thickness and crustal age and with silica enrichment of the magmas suggests crustal contamination but this is inadequate to explain the lil element enrichment patterns and variable lil element enrichments the preferred hypothesis is that the alkalic magmas come from a deeper source with long term lil element depletion and low rb sr ratio but relatively recent lil element enrichment conversely the tholeiitic magmas are melts of subcontinental mantle lithosphere that is more lil element depleted than the alkalic source at the time of magma genesis but has had an elevated rb sr ratio for much of its post consolidation history

fault related fold styles and progressions in fold thrust belts insights from sandbox modeling fault related folds of variable structural styles and assemblages commonly coexist in orogenic belts with competent incompetent interlayered sequences despite their commonality the kinematic evolution of these structural styles and assemblages are often loosely constrained because multiple solutions exist in their structural progression during tectonic restoration we use a sandbox modeling instrument with a particle image velocimetry monitor to test four designed sandbox models with multilayer competent incompetent materials test results reveal that decollement folds initiate along selected incompetent layers with decreasing velocity difference and constant vorticity difference between the hanging wall and footwall of the initial fault tips the decollement folds are progressively converted to fault propagation folds and fault bend folds through development of fault ramps breaking across competent layers and are followed by propagation into fault flats within an upper incompetent layer thick skinned thrust is produced by initiating a decollement fault within the metamorphic basement progressive thrusting and uplifting of the thick skinned thrust trigger initiation of the uppermost incompetent decollement with formation of a decollement fold and subsequent converting to fault propagation and fault bend folds which combine together to form imbricate thrust breakouts at the base of the early formed fault ramps along the lowest incompetent layers which may correspond to basement cover contacts domes the upmost decollement and imbricate thrusts to form passive roof duplexes and constitute the thin skinned thrust belt structural styles and assemblages in each of tectonic stages are similar to that in the representative orogenic belts in the south china southern appalachians and alpine orogenic belts

exhumation history of the aydin range and the role of the buyuk menderes detachment system during bivergent extension of the central menderes massif western turkey the central menderes massif western turkey is a prominent example of symmetrical exhumation of a core complex it comprises the bozda and aydin ranges which represent the footwalls of the north dipping gediz detachment and the south dipping buyuk menderes detachment respectively in contrast to the gediz detachment the role of the buyuk menderes detachment during late cenozoic extension and exhumation of the central menderes massif is less well resolved here we present results from structural and geological mapping as well as new fission track and u th he data to show that two low angle normal faults contributed to the exhumation of the aydin range our data indicate that the sustained activity of the buyuk menderes detachment since the early miocene is followed by the onset of faulting along the previously unrecognized demirhan detachment which is situated in the hanging wall of the buyuk menderes detachment in the latest miocene pliocene thermokinematic modelling of cooling ages from the footwalls of the buyuk menderes and demirhan detachments yielded exhumation rates of c 0 5 and c 0 4 km ma 1 respectively apatite fission track ages from the demirhan detachment indicate a slip rate of c 2 km ma 1 during the pliocene high angle normal faulting along the modern buyuk menderes graben commenced in the quaternary supplementary material further results of thermal history modelling are available at https doi org 10 6084 m9 figshare c 4392905

cooling history of the gongga batholith implications for the xianshuihe fault and miocene kinematics of se tibet abstract using thermochronological data and thermokinematic modeling we constrain the timing of late miocene exhumation of the northern portion of the gongga batholith located in southeast tibet along the xianshuihe fault xf we show that rapid exhumation started in the north of the gongga batholith at 9 ma at a rate of 1 85 km myr and slowed down since 4 ma a magmatic pulse occurring during the early pliocene 4 ma has overprinted the rapid miocene exhumation phase in some parts of the batholith which record mainly early pliocene post magmatic cooling slow exhumation since 4 ma is consistent with the present day lower relief observed in the centre of the batholith which contrasts with the rugged high peaks located to the south we propose that the northern segment of the xf the yalahe fault which is not active at present was active between 9 and 4 ma forming a restraining bend that focused exhumation south of it since 4 ma the selaha and the zheduotang faults form the present day restraining bend south of which the highest part of the massif is located including the gongga shan that rises more than 3000 m above the mean elevation of the plateau in the north of the batholith similar peaks have been removed since the miocene by local relief reduction at high elevations considering that the onset of motion along the xf is contemporaneous with the onset of rapid exhumation recorded along the kangding transect at 9 ma and a total offset of 62 km documented for the xf the average slip rate of the xf is 7 mm yr since 9 ma

indosinian high strain deformation for the yunkaidashan tectonic belt south china kinematics and 40ar 39ar geochronological constraints 1 structural and 40ar 39ar data from the yunkaidashan belt document kinematic and tectonothermal characteristics of early mesozoic indosinian orogenesis in the southern part of the south china block the yunkaidashan belt is tectonically divided from east to west into the wuchuang sihui shear zone xinyi gaozhou block and the fengshan qinxi shear zone indosinian structural elements ascribed to the indosinian orogeny include d2 and d3 deformation the early d2 phase is characterized by folding and thrusting with associated foliation and lineation development related to nw se transpression under amphibolite to greenschist facies conditions this event is heterogeneously overprinted by d3 deformation characterized by a gentle dipping s3 foliation subhorizontally to shallowly plunging l3 lineation some reactived d2 folds and low angle normal faults the d3 fabrics suggest a sinistral transtensional regime under greenschist facies metamorphism the timing of the d2 and d3 events have been constrained to the early to middle triassic 248 220 ma and late triassic 220 200 ma respectively on the basis of 40ar 39ar geochronology and regional geological relations the change from oblique thrusting d2 to sinistral transtension d3 may reflect oblique convergence and crustal thickening followed by relaxation of the overthickened crust in combination with the regional relations from xuefengshan to yunkaidashan and on to wuyishan the early phase of the indosinian orogeny constituted a large scale positive flower structure and is related to the intracontinental convergence during the assembly of pangea in which the less competent south china orogen was squeezed between the more competent north china and indosinian blocks

tectonics of the middle triassic intracontinental xuefengshan belt south china new insights from structural and chronological constraints on the basal decollement zone in orogenic belts a basal decollement zone often develops at depth to accommodate the shortening due to folding and thrusting of the sedimentary cover in the early mesozoic intracontinental xuefengshan belt of south china such a decollement zone is exposed in the core of anticlines formed by the emplacement of the late orogenic granitic plutons our detailed multi scale structural analysis documents a synmetamorphic ductile deformation in the basal decollement the neoproterozoic pelite and sandstone and the intruding early paleozoic granites were deformed and metamorphosed into mylonites and orthogneiss respectively the metamorphic foliation contains a nw se stretching lineation associated with top to the nw kinematic indicators the ductile shearing of these high strained rocks can be correlated with nw verging folds and thrusts recognized in the neoproterozoic to early triassic sedimentary cover monazite u th pbtot chemical dating and zircon sims u pb dating provide age constraints of the ductile shearing between 243 and 226 ma and late orogenic granite emplacement around 235 215 ma in agreement with recent geochronological data these new results show that the xuefengshan belt is an early mesozoic orogen dominated by the nw directed shearing and thrusting at the southeastern boundary of the xuefengshan belt the chenzhou linwu fault separates the early mesozoic domain to the nw from the early paleozoic domain to the se the tectonic architecture of this belt was possibly originated from the continental underthrusting to the se of the south china block in response to northwest directed subduction of the paleo pacific plate

cenozoic exhumation history of south china a case study from the xuefeng mt range abstract new apatite fission track aft dating was applied to the xuefeng mt range and yuanma basin to constrain the cenozoic exhumation process of the southeastern yangtze block south china the analyzed samples in this study have aft ages ranging from 27 9 2 5 to 61 5 5 9 ma which are younger than the deposition or crystallization ages of the host rocks the aft analysis and thermal history modeling indicate that both the xuefeng mt range and the yuanma basin underwent significant exhumation during the early cenozoic ca 60 40 ma these samples were rapidly exhumed to near the surface during this period our results suggest that an important tectonic event occurred along or near regional fault zones e g the qinhang fault in south china during the early cenozoic ca 60 40 ma however it is difficult to relate this event to the eastern sichuan fold belt which is much older and is characterized by large scale folding and thrusting combined with fieldwork in the yuanma xupu and xinning basins we refute the cretaceous pan yangtze basin that was proposed to have been separated by the uplifted xuefeng mt range after the late cretaceous the exhumation stage from ca 60 ma to 40 ma was an important period during which plate movements across the eastern asian and pacific regions were reorganized the early cenozoic tectonothermal event in south china can be attributed to a change in the direction and speed of the subduction of the pacific plate beneath the eurasian plate an oligocene miocene cooling event was also recorded in the eastern xuefeng mt range which we tentatively attribute to the activity of dextral faults in this area as a far field effect of the collision between the indian and eurasian plates

mud diapirism and subcretion in the barbados ridge accretionary complex the role of fluids in accretionary processes mud diapirism has recently been recognized in several modern accretionary wedges it provides an important means of dewatering accretionary wedges and should be regarded as an important process for producing the melanges found in both modern and ancient accretionary terranes mud diapirism affects a large area of the barbados ridge accretionary complex the distribution of the mud diapirs appears to be primarily controlled by the presence of underconsolidated terrigenous submarine fan deposits that are being accreted to the complex the frequency of diapir occurrence decreases northward as the fan becomes thinner mud diapirs are absent from the very eastern most part of the complex formed from sediments accreted at its toe with the exception of a few mud volcanoes on the ocean floor in front of the complex the initiation of diapirism appears to be spatially coincident with the onset of subcretion or underplating of sediment to the base of the complex at a ramp between two levels of decollement it is proposed that the release of mud and pore water from the subcreted sediments is a direct or indirect cause of most of the mud diapirism in the accretionary complex there is a range of diapiric form dependent on the viscosity of the mud from mud volcanoes fed by low viscosity mud to higher viscosity mud ridges the diapirs in the eastern areas of the complex are generally mud volcanoes with narrow conduits feeding a surface mound mud ridges are prominent in the western parts of the complex this is interpreted as reflecting a general westward decrease in the fluid content of the accretionary complex bottom simulating seismic reflectors formed by gas hydrate are commonly developed in the areas of mud volcano occurrences the presence of the hydrate indicates that large volumes of methane are being generated at depth in these regions the generation of methane may be contributing to zones of overpressuring in the wedge methane may also be partly responsible for driving the diapiric material to the surface to form mud volcanoes ridges in the subducting oceanic crust beneath the accretionary complex locally enhance diapirism above their crests and southern flanks faults formed later in the development of the complex are more commonly associated with diapirism than those resulting from accretion at the toe of the wedge these later faults play an important role in controlling the sites of individual mud volcanoes chains of mud volcanoes and mud ridges

the longmenshan tectonic complex and adjacent tectonic units in the eastern margin of the tibetan plateau a review abstract the longmenshan tectonic complex lstc along the eastern margin of the tibetan plateau the site of devastating earthquakes such as the magnitude 8 0 wenchuan earthquake on 12 may 2008 preserves an exceptionally complete history of the tectonic evolution of the yangtze block and its relations to adjacent tectonic units due to sequential tectonic superposition and tectonic reactivation the tectonic nature of the lstc and in particularly the older history has been profoundly debated and many different tectonic models have been proposed herein we summarize the current understandings of the major tectonic events that have shaped this important tectonic complex highlighting problems left to be solved by future work including 1 the nature and constraints for at least 6 regional tectonic events i e building of the metamorphic basement art the columbia nuna supercontinent pt1t the rodinia supercontinent pt3t the paleozoic passive continental margin pzt the paleotethys orogeny mzt and the neotethys orogeny kzt 2 metamorphic basement exposures and their tectonic implications including rock types and geochronological constraints for the archean paleoproterozoic and neoproterozoic basements 3 nature of the present lstc and its affinity with adjacent tectonic units 4 consideration of the ne striking longmenshan thrust belt and arcuate shape yanyuan muli thrust belt as parts of a single tectonic feature 5 mountain basin coupled systems recording past tectonic eposides we draw the following conclusions and tectonic models based on published research combined with our own recent studies 1 the well preserved archean yudongzi gneiss group in the lstc has a genetic affinity with the kongling group and thus belongs to the yangtze block 2 the paleoproterozoic hejiayan group juxtaposed adjacent to the archean yudongzi group may represent a 2000 1800 ma orogenic belt which corresponds to the supercontinent nuna columbia amalgamation event 3 a neoproterozoic trench arc basin system which is reconstructed based on identification of a neoproterozoic ophiolite complex arc type magmatic rock assemblages and volcaniclastic basinal deposits along the western margin of the yangtze block and the lstc may represent the record of eastward subduction of the neoproterozoic mozambique oceanic lithosphere beneath the yangtze block during the assembly of the rodinia supercontinent 4 a complete bidirectional wilson cycle was reconstructed by the formation of the late permian to the middle late triassic back arc ganze litang rift and ocean following the early paleozoic mianlue continental rift and ocean and subsequent closure of the ocean basin by simultaneous bidirectional northward and southwestward subduction and later collision this relatively uncommon bidirectional wilson cycle might be attributed to the formation of the three armed rift system in the eastern paleotethys associated with the late permian eemeishan large igneous province in the lstc 5 a three stage tectonic sequence of in sequence imbricate thrust in the lstc during india eurasian collisional orogeny at 55 15 ma extrusion from 15 to 5 ma and the plateau uplift since 5 ma resulting from lower crustal channel flow is proposed for the formation of the present lstc

hydrocarbon resources potential mapping using evidential belief functions and frequency ratio approaches southeastern saskatchewan canada the purpose of the present study is to model the hydrocarbon resources potential mapping using geographic information systems gis the presented method is based on petroleum system concepts therefore petroleum system elements were used to define criteria for petroleum potential mapping several statistical methods can be used to effectively predict potential areas for hydrocarbon resources in this study two statistical methods were used frequency ratio and evidential belief functions to predict the potential distribution of petroleum resources in the study area a case study in the red river red river petroleum system of the canadian williston basin in southeastern saskatchewan in canada is proposed to assess the feasibility of this new modelling technique the accuracy of the hydrocarbon potential maps was evaluated by success rate and prediction rate efficiency curves the resultant petroleum potential maps resulted in delineation of high potential zones occupying about 15 of the study area

early mesozoic thrust tectonics of the northwest zhejiang region southeast china the nw zhejiang region of south china occupies a key tectonic position near the suture zone of the yangtze and cathaysian blocks and is of critical importance for the assembly of east asia sedimentological and tectonic analyses indicate that the region had a se dipping paleoslope in the late paleozoic to early triassic a transitional sedimentary environment from deep sea to continental molasse is documented in the early triassic late triassic interval associated structures are nw vergent folds and thrusts that root southeastward beneath the high grade chencai metamorphic complex the structural styles of this foreland fold and thrust belt are characterized by multifold duplexes and individual folds that are together zoned from se to nw as follows 1 core zone characterized by shear folds and ductile thrusts 2 se belt with out of sequence thrusting of multifold duplexes and an average shortening of 50 3 central belt with duplexes imbricate fans and an average shortening of 40 and 4 nw belt with jura type folds and a shortening of 10 a tectonic model for the foreland fold and thrust belt is discussed in relation to the early mesozoic archipelago paleogeography of south china

magma and sediment i emplacement mechanism of late carboniferous tholeiite sills in northern britain president s anniversary address 1981 like other great tholeiite sheets of the world the midland valley sill and whin sill were emplaced in thick accumulations of sediments which at the time of intrusion were not much older nor had been orogenically deformed however the carboniferous sediments of northern britain had been deposited under the influence of continuous differential subsidence so that they were already disposed in syn sedimentary basins and swells when intrusion began by drawing palinspastic contours of the sills relative to a late westphalian marine band approximating to the surface at the time of emplacement it is established that the dolerites mainly follow bedding planes dipping at angles of as much as 5 down to the bottoms of the basins isopachs of the sills indicate a further relationship for the intrusions are thickest at the bottoms of the basins these facts are not explained by any intrusion mechanism previously postulated though there seems to be broad agreement as to the processes which have given rise to thinning and en echelon lensing at leading edges as well as to step and stair transgression of sediment bedding it is proposed that emplacement must have been controlled in part by gravitational flow down dip from feeder dykes which extended to between 0 5 and 1 0 km below the contemporary surface thereafter hydrostatic equilibrium was attained first by accumulation at the bottom of the basins and then by further advance up dip under pressure of head the sheets are so similar in aspect to flood basalts that it must be assumed that the sediments offered only low frictional resistance to splitting and flow

geometry and growth of sill complexes insights using 3d seismic from the north rockall trough doleritic sill complexes which are an important component of volcanic continental margins can be imaged using 3d seismic reflection data this allows unprecedented access to the complete 3d geometry of the bodies and an opportunity to test classic sill emplacement models the doleritic sills associated with basaltic volcanism in the north rockall trough occur in two forms radially symmetrical sill complexes consist of a saucer like inner sill at the base with an arcuate inclined sheet connecting it to a gently inclined commonly ragged outer rim bilaterally symmetrical sill complexes are sourced by magma diverted from a magma conduit feeding an overlying volcano with an elongate concave upwards trough like geometry bilaterally symmetrical sills climb away from the magma source from which they originate both sill complex types can appear as isolated bodies but commonly occur in close proximity and consequently merge producing hybrid sill complexes radial sill complexes consist of a series of radiating primary flow units with dimensions up to 3 km each primary flow unit rises from the inner saucer and is fed by primary magma tube primary flow units contain secondary flow units with dimensions up to 2 km each being fed by a secondary magma tube branching from the primary magma tube secondary flow units in turn are composed of 100 m scale tertiary flow units a similar branching hierarchy of flow units can also be seen in bilaterally symmetrical sill complexes with their internal architecture resembling an enlarged version of a primary flow unit from a radial sill complex this branching flow pattern as well as the interaction between flow units of varying orders provides new insights into the origin of the structures commonly seen within sill complexes and the hybrid sill bodies produced by their merger the data demonstrate that each radially symmetrical sill complex is independently fed from a source located beneath the centre of the inner saucer grows by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature these features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening the branching hierarchy of flow units within bilaterally symmetrical sill complexes is broadly similar to that of primary flow units within a radially symmetrical sill complex suggesting that the general features of the laccolith emplacement model also apply

synorogenic morphotectonic evolution of the gangdese batholith south tibet insights from low temperature thermochronology the uplift history of the tibetan plateau remains one of most intriguing and controversial issues in the cenozoic history of our planet and has a significant impact on regional and global climate here we report new low temperature thermochronology apatite and zircon data from the gangdese batholith in southern tibet thermal history modeling of the data show that the batholith experienced a phase of rapid early cenozoic cooling probably associated with exhumation resulting from the initial india asia s collision but possibly also due to postarc volcanic activity in the region the batholith then transitioned to low erosion rates 0 05 mm yr between the middle eocene and early miocene followed by a renewed episode of cooling commencing in the early miocene our results indicate that the gangdese belt as the southern margin of eocene tibetan plateau became plateau like by 45 ma the later cooling episode from early miocene onward can probably be attributed to incision of the ancestral yarlung river system cutting through the gangdese belt by 22 ma at the latest

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

cenozoic exhumation of the neoproterozoic sanfang batholith in south china the 1500 km long jiangnan tectonic belt in china is well known for large outcrops of proterozoic basement rocks although the exhumation history of the exposed basement is poorly constrained the thermochronology of the sanfang batholith in the southernmost section of this belt was used to constrain the timing and mechanism of exhumation using apatite fission track analysis of granite samples collected along three transects the results show that the ages of single apatite grains are much younger than the neoproterozoic crystallization age of the sanfang batholith the apparent age v elevation diagram shows two stage cooling during the paleogene and miocene the cooling stages are coincident with unconformities between the paleogene and underlying strata and between the neogene and the paleogene with movement on high angle normal faults a compilation of apatite fission track data from this and previous studies suggests that the batholith was exhumed in the cenozoic and the timing of rapid cooling is progressively younger to the east as a result of slab rollback leading to cenozoic back arc extension the exhumation of the sanfang batholith therefore indicates that cenozoic erosion and extensional tectonics played a key part in exhuming the basement rocks and forming the present architecture of the jiangnan tectonic belt

uranium metallogenesis in south china and its relationship to crustal extension during the cretaceous to tertiary south china is rich in vein type hydrothermal uranium deposits hosted in granitic volcanic and carbonaceous and siliceous pelitic sedimentary rocks the uranium deposits are spatially associated with extensional structures and or mantle derived mafic dikes both the uranium deposits and mafic dikes are cretaceous to tertiary in age temporally coincident with the crustal extension carbon isotope analyses of calcite deposited in the main stage mineralization in the veins from 12 representative uranium deposits yield 13c values of ore forming fluids mainly from 4 to 8 per mil which are permissive of a mantle origin for the co2 in the ore forming fluids a mantle origin is consistent with the association of the deposits with mafic dikes and the 3he 4he ratios of ore forming fluids e g 0 10 2 02 ra for the volcanic hosted xiangshan uranium deposit isotopic compositions of h and o demonstrate that water in the ore forming fluids is predominantly meteoric in origin ore forming temperatures ranged approximately from 150 to 250 c uranium rich crustal rocks in south china may have been the sources for the uranium crustal extension and associated mafic magmatism are considered to have heated the rocks and allowed co2 possibly from mantle sources to migrate upward and to mix with co2 poor meteoric water the co2 rich hydrothermal fluids mobilized uranium from the source rocks and then the uranium was deposited in various host rocks to form the uranium deposits

geodynamic scenario and structural styles of mesozoic and cenozoic basins in china the continental lithosphere of china is situated at the junction of the marginal pacific and tethys himalayan tectonic domains the most manifest tectonic movements responsible for the deformation of the continental lithosphere of china are taphrogenic collisional and shearing these movements played an important role in the mesozoic and cenozoic tectonic evolution of china and formed various types of mesozoic and cenozoic basins in china the marginal pacific crust in eastern china was attenuated by rifting and developed north northeast trending mesozoic and cenozoic basins e g the songliao bohai bay and jianghan basins rifting mainly followed preexisting lineaments or shear zones in the basement then basin range graben horst structures and large fault bounded basins developed extensional structural styles have prevailed in mesozoic and cenozoic basins in eastern china with listric faults and tilted blocks in the basement and detached faults growth faults and rollover anticlines or drape folds in the cover rocks these structures are favorable for hydrocarbon accumulation thus the famous daqing and zhongyuan oil fields formed in songliao basin and bohai bay basin respectively in western china the continental crust thickened by collision and formed a series of mesozoic and cenozoic intermontane and foreland basins such as the junggar dzungaria tarim and qaidam basins contraction structural styles are predominant in mesozoic and cenozoic basins in western china with shortened fault blocks and ramps in basement and thrust faults and folds in the cover rocks the kelamayi and laojunmiao oil fields formed in these compressional basins in addition many great wrench faults played an important role in the evolution of china such as the tan lu fault in eastern china and the altunshan and talaso fergana faults in western china many mesozoic and cenozoic basins of china were characterized by transtension and transpression the mesozoic and cenozoic basins of china have undergone numerous tectonic events the extensional structures have been changed into contractional structures or conversely thus tectonic inversion occurred in successive events and different structural styles may be found in different tectonic levels of these basins these superposed deformations and structures have complicated petroleum exploration but they also enlarge prospective exploration targets and potential hydrocarbon reserves in china

evidence of lateral asthenosphere flow beneath the south china craton driven by both pacific plate subduction and the india eurasia continental collision south china cenozoic basalts sccb are regionally distributed at the south east coastal area and can be grouped into three zones a western zone 38 ma a central zone 17 8 ma and an eastern zone 8 ma leaving a temporal gap at 38 17 ma between the western and central zones an eastward migration of the sccb could therefore be identified by the systematic decrease in the eruption age from the western inland to the eastern coast we propose that most sccb were associated with the lateral asthenospheric flows moving along the lithosphere asthenosphere boundary lab beneath south china and the subsequent decompressional partial melting the lateral asthenospheric flows had been pulled by the eastward retreat of the pan pacific plate subduction before 38 ma and have been pushed by the northward indentation of the indian plate into the eurasian plate since 17 ma

denudation history of onshore central vietnam constraints on the cenozoic evolution of the western margin of the south china sea abstract apatite fission track analysis is used to monitor the timing and rate of upper crustal cooling and denudation across central vietnam in response to rifting of the south china sea results show regional denudation in the syn and post rift phases of the south china sea occurred at a similar rate 40 10 m myr consistent with the sedimentation record in adjacent offshore basins this suggests that extension was not the dominant factor controlling cenozoic denudation probably because the study area was sufficiently distant from the actively rifted continental margin a significant change in regional cooling rate during the upper miocene inferred denudation rates also shift from 34 m myr to 390 500 m myr is linked to enhanced erosion and deposition of prograding sediments in adjacent offshore basins this shift in denudation is associated and contemporaneous with initiation of regional basaltic magmatism and development of topography

mesozoic tertiary exhumation history of the altai mountains northern xinjiang china new constraints from apatite fission track data abstract this study uses apatite fission track ft analysis to constrain the exhumation history of bedrock samples collected from the altai mountains in northern xinjiang china samples were collected as transects across the main structures related to palaeozoic crustal accretion events ft results and modeling identify three stages in sample cooling history spanning the mesozoic and tertiary stage one records rapid cooling to the low temperature part of the fission track partial annealing zone circa 70 10 c stage two records a period of relative stability with little if any cooling taking place between 75 and 25 20 ma suggesting the altai region had been reduced to an area of low relief support for this can be found in the adjacent junngar basin that received little if any sediment during this interval final stage cooling took place in the miocene at an accelerated rate bringing the sampled rocks to the earth s surface this last stage linked to the far field effects of the himalayan collision most likely generated the surface uplift and relief that define the present day altai mountains

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

along strike variations in rifted margin crustal architecture and lithosphere thinning between northern voring and lofoten margin segments off mid norway abstract an extensive geophysical and geological database is used to integrate observations and structural and stratigraphic modelling along the northern voring and lofoten margins off mid norway subsidence and fault analysis demonstrates depth dependent lithosphere stretching along both margin segments and the modelling concurs with an emergent or relatively shallow water emplacement environment for the breakup lavas along the northern voring margin however off lofoten subsidence modelling predicts 1500 m of bathymetric relief during breakup in contradiction to the view of subaerial volcanic emplacement environment off mid norway a distinct early eocene bathymetric gradient from voring to lofoten margin is suggested exhibiting depths in the order of 500 1000 m on the latter margin and thus an environment for submarine lava emplacement the water depth may even have reached 1250 m following breakup due to an initial rapid margin subsidence of the lofoten margin along a deep rooted low angle detachment fault the differences between northern voring and lofoten margin segments in pre and post breakup evolution are attributed to the bivrost lineament a transfer zone separating the two margin segments which appears as a major across margin boundary in terms of margin physiography and paleogeography differential sediment accommodation space crustal and lithosphere scale structure and breakup magmatism furthermore gravity inversion results appear to independently predict a significantly greater volcanic addition on the voring than on the lofoten margin

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

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

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

the role of the east asian active margin in widespread extensional and strike slip deformation in east asia east asia is a region of widespread deformation dominated by normal and strike slip faults deformation has been interpreted to result from extrusion tectonics related to the india eurasia collision which started in the early eocene in east and se china however deformation started earlier than the collision latest cretaceous to palaeocene suggesting that extrusion tectonics is not the only driving mechanism for east asia deformation it is suggested that the east asian active margin has influenced deformation in east asia significantly along the margin cenozoic back arc extension took place behind several adjoining arcs implying eastward rollback of the subducting slab and collapse of the overriding plate towards the retreating hinge line we show that extension took place along a c 7400 km long stretch of the east asian margin during most of the cenozoic physical models are presented simulating overriding plate collapse and back arc extension the models reproduce important aspects of the strain field in east asia for geometrical and rheological conditions scaled to represent east asia modelling shows that the active margin can be held responsible for deformation in east asia as far west as the baikal rift zone located c 3300 km from the margin

geographic information system based fuzzy logic analysis for petroleum exploration with a case study of northern south america the petroleum industry is increasingly using geographic information systems giss for mapping and spatial database needs because they are useful for elucidating and exploiting spatial relationships between geologic and geophysical data however the petroleum industry in general does not exploit the full potential of gis as an analysis tool in particular gis offers spatial and analytical support for multicriteria evaluation mce methods which are used to combine data to show areas best fulfilling specific criteria petroleum explorations would benefit from an mce method that is spatial is flexible for combining heterogeneous data considers the interpretive nature of the data is geologically applicable and is applicable for frontier areas or where little information exists regarding probabilities of the presence of petroleum this study proposes a gis based mce method for petroleum exploration based on fuzzy logic which fulfills the previously stated requirements using 16 subcriteria and one constraint combined in tiers to produce a favorability map of potential exploration areas a case study applied to northern south america chosen because of its centrality to petroleum exploration shows potential new exploration areas in the cretaceous paleogene and miocene holocene the method was validated by comparing the favorability maps of one non geologic age specific and of two geologic age specific favorability maps to known producing fields we conclude that the method can be applied in an exploration setting and as such is applicable for other regions of the world

tectonothermal history of the ne jiangshan shaoxing suture zone evidence from 40ar 39ar and fission track thermochronology in the chencai region abstract the jiangshan shaoxing suture zone a component of the neoprotozoic orogenic belt between the yangtze and cathaysia blocks in south china has experienced a complex history of tectonic reactivation previous investigations of this significant tectonic boundary have focused on earlier stages of its tectonic history pre dating the early paleozoic wuyi yunkai orogeny with more recent episodes rarely addressed we here improve understanding of the later reactivation history of this suture zone through new 40ar 39ar and fission track thermochronological constraint derived for the ductilely strained chencai complex and the lipu huangshan quartz diorite together with sedimentological investigations of the proximal wuzao formation this combined constraint demonstrates the occurrence of as many as five discrete episodes of tectonic reactivation and deformation of the jiangshan shaoxing suture zone the 431 4 ma 40ar 39ar biotite cooling age of the lipu huangshan quartz diorite records retrograde cooling of the chencai region following high grade metamorphism at c 460 450 ma during the early paleozoic wuyi yunkai orogeny consistent younger 40ar 39ar ages of the gneissic chencai complex suggest that this retrograde cooling episode may extend to c 390 400 ma with later ductile strain and or thermal overprinting of biotite at c 386 ma suggesting that the terminal stage of the early paleozoic wuyi yunkai orogeny may have continued significantly later than previously assumed although not reflected directly in the thermotectonic records compiled for the chencai complex lithoclasts of these distinctive ductilely deformed gneisses represent a significant component of the conglomeratic gravels appearing in the late triassic wuzao formation demonstrating substantial uplift and erosion of the suture zone at this time coincident with the indosinian orogeny zircon fission track thermochronology of the samples from both lipu huangshan quartz diorite and chencai complex yield much younger cretaceous cooling ages of 144 8 to 103 6 ma with apatite fission track ages ranging from 66 4 to 41 3 ma and mean apatite fission track lengths between 12 1 and 13 1 m thermal history modeling of these low temperature controls demonstrates significant cooling during the cenozoic these later activities reflect brittle deformation in the upper crust and erosional exhumation of these rocks coincident with the yanshanian extension event and himalayan tectonism these results together imply that the jiangshan shaoxing suture zone represents a significant and long lived lithospheric weakness that was preferentially reactivated during at least two episodes of tectonic activity in regional far field domains examining the complex reactivation history of the fossil suture zone thus provides a useful window into the timing of episodes of broader tectonic activity across the wider region

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

the oxidation state of manganese in ferromanganese nodules and deep sea sediments from the central indian ocean abstract ferromanganese nodules from different sediment facies including siliceous ooze pelagic clay sediments from transition zone of siliceous and pelagic clay and seamount crusts from the central indian ocean were analysed for chemical composition mineralogy and bulk oxidation state of mn by the iodometric method despite considerable variation in chemical composition mn fe ratio times from 1 35 to 7 42 and mineralogy the o mn ratio or mno x solid hydrous manganese oxide does not vary much from 1 73 to 1 81 suggesting most of the mn in the manganese nodules in mn iv the oxidised upper zone in the sediment cores decreases in thickness from 15 cm in the north 5 s to 11 cm in the southern part 14 s of the central indian ocean iodometric titration of deep sea sediments yields o mn ratios of 1 29 1 95 sediments from the manganese nodule field have maximum solid mn concentrations and lower o mn ratios in the core top 0 3 cm with minimum mn and o mn ratios at 11 cm depth and thus may reflect the mechanism controlling the supply of diagenetic mn to the nodules in contrast sediments from the non manganese nodule field have comparatively low solid phase mn concentrations in the core top 0 3 cm and almost uniform o mn ratios with depth indicating that mn is not preserved in the sediments but may be remobilised and deposited somewhere else

tertiary compressional structures on the faroe rockall plateau in relation to northeast atlantic ridge push and alpine foreland stresses abstract a number of compressional anticlinal structures are identified in the western and northern part of the faroe rockall plateau these structures occur on that part of the faroe rockall plateau which was above sea level during the latest phase of paleocene plateau basalt extrusion three post basalt compressional phases have affected the plateau most of the compressional structures in the northern part of the plateau are related to ne sw to ene wsw oriented stress which we date to late paleocene early eocene the oligocene phase is interpreted as resulting from n s directed compressional stress which also mainly affected the compressional structures on the northern part of the plateau compressional stress from the northwest seemed to affect the whole of the faroe rockall plateau and we suggest it to be of miocene age it is proposed that during the late paleocene early eocene phase of compression local structure and anomalously oriented gravitational ridge push from the now extinct aegir axis contributed to a local ne sw compressional stress system the two later deformation phases were apparently connected to the regional northwest european stress system with small local modifications

tracking the multiple stage exhumation history and magmatic hydrothermal events of the west junggar region nw china evidence from 40 ar 39 ar and u th he thermochronology abstract to decipher cooling events in the west junggar region biotite and k feldspar 40ar 39ar and zircon and apatite u th he isotopic analyses of intrusive rocks were carried out previous u pb data showed that intrusive bodies in the baogutu area were emplaced at 315 310 ma u pb and zircon u th he dating results 313 241 ma suggest that a magmatic hydrothermal event lasted for 72 ma in the baogutu area of the west junggar region early stage high temperature alteration 900 300 c lasted for 6 2 ma and was followed by prolonged phyllic and argillic alteration lasting 67 63 ma between 350 and 200 c finally slower cooling occurred between 200 and 70 c accompanied by post mineralization uplift and erosion in this study three main episodes of relatively rapid cooling were distinguished in the west junggar region i e late carboniferous early permian 307 277 ma middle triassic 241 232 ma and early cretaceous 145 120 ma the first rapid cooling during the late carboniferous early permian was possibly associated with the release of magmatic heat the middle triassic and early cretaceous cooling and exhumation are interpreted as a response to collision s between the qiangtang and kunlun qaidam or lhasa blocks the cenozoic india eurasia collision however may have had little or no effect on modern tectonic reactivation of the west junggar region