holocene tectonics south of the indus suture lahaul ladakh himalaya india a consequence of indian plate motion abstract the continued northward drift of the indian plate after the cessation of its further subduction was successively forced upon other planes of dislocations along old lineaments south of the indus suture zone isz the active tectonics chiefly confined to the main central thrust the main boundary thrust the thrust between the siwalik rocks and the older alluvium and along certain tensional extensional faults are steady but not spectacular the youngest major tectonic activity in the himalaya leaving visible signatures occurred south of isz after the last quaternary glaciation this activity rejuvenated older faults causing deflection and disorganization of several rivers which had come to occupy the u shaped glacial valleys in the ladakh and lahaul the strike slip movements discretely folded the terraces and also formed the pull apart tso morari and kiogar tso basins the indian plate motion also affected the peninsular part although less intensely

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

a crustal density model across the cambay basin india and its relationship with the aravallis abstract the cambay rift basin in the northwest indian platform shows high bouguer gravity anomaly values as compared to the values outside the basin the seismic results show the presence of a large thickness of sediments which should have produced a gravity low of about 50 60 mgal the deep seismic sounding results along the strike of the basin show the presence of a velocity of 7 3 km s at 23 25 km depth followed by the moho at a depth of 31 33 km two dimensional density modelling of the seismic structure across the cambay basin shows that the crust is thinner underneath the basin and is associated with a high density lower crust a comparison of the gravity anomaly across the cambay basin with that across the proterozoic aravalli delhi trends suggests crustal thinning in both the regions on either side of which the moho deepens rapidly

motion of the pacific plate relative to eurasia and its potential relation to cenozoic extension along the eastern margin of eurasia extension along the eastern margin of eurasia has been regarded commonly as a far field effect of the india eurasia collision however some aspects of the timing and location of this extension make a link between the collision and extension difficult we suggest that some extensional features commonly interpreted as effects of the collision may be related more simply to changes in plate convergence rates along the eastern plate boundary of eurasia an analysis of the motion of the pacific plate relative to eurasia suggests that the rate of pacific eurasia convergence varied significantly during the tertiary period from a late cretaceous convergence rate of 120 140 mm yr the rate declined substantially during early tertiary time and reached a minimum in eocene time of 30 40 mm yr in oligocene to earliest miocene time the average convergence rate increased moderately to 70 95 mm yr then decreased again to 65 70 mm yr during early to middle miocene time from late miocene to the present the rate of convergence increased to an average of 100 110 mm yr the paleocene through middle miocene episode of relatively slow convergence correlates with a period of widespread extension along the eastern margin of eurasia decreased convergence may have been related to a net reduction in horizontal compressional stress transmitted between the pacific and eurasian plates which resulted in widespread extension adjacent to the margin of eurasia

tectonically controlled evolution of the yellow river drainage system in the weihe region north china constraints from sedimentation mineralogy and geochemistry abstract this study investigated the evolution of the middle reach of the yellow river by examining the latest cenozoic 5 0 0 15 ma sedimentary history of the weihe and sanmenxia basins in the weihe region of north china although the development of the two basins and the evolution of the yellow river have long been related to the rapid uplift of the tibetan plateau the relationship between the landform evolution and regional tectonics is still poorly understood here we report the results of a detailed study on sedimentation and provenance of the two basins and their spatial and temporal relationships to regional fault development the results show that the two basins were possibly originally isolated from each other between 5 ma and 2 8 2 6 ma but later connected by the yellow river at 2 8 2 6 ma this process is recorded in the coarsening upward sequence of the weihe basin strata and the coeval fining upward succession of the sanmenxia basin strata at 1 0 ma the sanmenxia basin strata developed a coarsening upward trend which we interpret as an indication of the formation of the yellow river in the region in addition changes in the drainage system at 2 8 2 6 ma and at 1 0 ma have been recorded as dramatic provenance changes in the sediments of the sanmenxia basin

plate interactions crustal deformation and magmatism along the eastern margins of the tibetan plateau abstract in order to investigate the deep structure and dynamics of the triangular colliding system of the eastern tibetan plateau tp as well as the yangtze platform and the qinling dabie fold belt a large number of p and s wave arrival times from both local and teleseismic earthquakes were used to generate high resolution tomographic images beneath the eastern margins of tp the results of this study show that the western margin of the minjiang fault is characterized by low velocity low v anomalies in sharp contrast to the high velocity high v anomalies that are derived from the eastern part this means that the minshan uplift zone is imaged as high v and acts as a barrier to the eastward escape crustal flow which leads to obvious segmentation of the longmenshan fault lmsf zone between velocity belts that are concatenated into the minjiang fault because high v anomalies are clearly imaged in this study to extended depths of ca 450 km we consider the yangtze platform containing the sichuan basin to comprise craton like lithosphere this study reveals the presence of a low v belt extending to a depth of ca 250 km between the sichuan basin and the ordos block which probably represents the migration pathway of upwelling asthenosphere materials from tibet at the same time low v zone with a downdip depth of ca 500 km accompanied by an approximately 400 km rectangular high v body is imaged under the tengchong volcano we interpret the high v body and the low v zone as evidence for the subducted indian plate and the volcanic magma source respectively the results of this study reveal a number of new features of structural heterogeneities relative to deep coupling between the tibet and the yangtze platform as well as the relationship between the sichuan basin and the ordos block and the original source of the tengchong volcano the results presented here enable us a better understanding of the plate interaction crustal deformation and magmatism of the tengchong volcano along the eastern margins of tp

deep shallow coupling response of the cenozoic bohai bay basin to plate interactions around the eurasian plate abstract the bohai bay basin bbb is a meso cenozoic intracontinental petroliferous basin where four pre existing continental scale fault zones intersect in east china the bbb has experienced complex deformational and evolutionary history that records significant information about how the lithosphere there has responded to the coeval plate interactions around the eurasian plate and or their resulting deep crust mantle processes in the cenozoic now both deep and shallow deformational and evolutionary processes of the bbb have been well studied but many geodynamic mechanisms previously proposed for those processes are too general to explain them well based on various data and principles we first summarized both deep and shallow responses and processes of the bbb in the cenozoic and then matched reasonable geodynamic mechanisms for each of them the results show as follows the cenozoic differential reactivation of pre existing continental scale weak zones controlled the coeval deep shallow differential coupling evolution of the bbb the paleogene extension in the bbb was mainly caused by crust mantle processes triggered by the stagnant izanagi slab the cenozoic strike slip faulting was influenced by various plate interactions in which the oblique subduction and anticlockwise rotation of young pacific plate resulted in the complex pre oligocene strike slip history of the tan lu fault zone to the south of the zhang peng fault zone while the india eurasia collision has caused the intense and synchronous strike slip faulting of various faults there since 35 ma which was then weakened by the oblique subduction and clockwise rotation of young philippine sea plate in the neogene the compression resulting from both the india eurasia collision and the philippine sea plate s subduction contributed to the latest paleogene tectonic inversion in the bbb the arrival of mantle flow triggered by both the india eurasia collision and the stagnant slab of the pacific plate resulted in the tectonic reactivation there in the late neogene

seismic imaging of the crust and upper mantle under beijing and surrounding regions abstract we determined a high resolution 3d p wave velocity model of the crust and upper mantle under beijing and surrounding regions in north china by jointly inverting 48 750 arrival times from 2973 local events and 12 249 relative residuals from 234 teleseismic events recorded by the newly built capital seismic network our results show considerable differences in the lithospheric structure down to about 200 km depth between the north china basin the taihangshan uplift and the yanshan uplift which are the three main tectonic units in the study area at depths of 50 150 km a pronounced low velocity anomaly exists under north china basin and bohai bay and right beneath it a high velocity anomaly extends down to about 200 300 km depth suggesting that this area has experienced large scale lithospheric thinning and lithospheric detachment has occurred the taihangshan front fault and the zhangjiakou penglai fault zone may have cut through the crust to lithosphere and they become flimsy tectonic boundaries and the asthenospheric materials may upwell from the two channels we consider that the deep and shallow structures beneath this region are closely related to dynamic processes that result from the deep subduction of the pacific slab and its stagnancy in the mantle transition zone under east asia

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

coral reef drag coefficients surface gravity wave enhancement abstracta primary challenge in modeling flow over shallow coral reefs is accurately characterizing the bottom drag previous studies over continental shelves and sandy beaches suggest surface gravi

k ar age and geochemistry of the sw japan paleogene cauldron cluster implications for eocene oligocene thermo tectonic reactivation abstract systematic k ar dating and geochemical analyses of paleogene cauldrons in the sanin belt of sw japan have been made to explore the relationship between the timing of their formation and the paleogene subduction history of sw japan documented in the shimanto accretionary complex we also examine the magma sources and tectonics beneath the backarc region of sw japan at the eastern plate boundary of eurasia fifty eight new k ar ages and 19 previously reported radiometric age data show that the cauldrons formed during middle eocene to early oligocene time 43 30 ma following a period of magmatic hiatus from 52 to 43 ma the hiatus coincides with absence of an accretionary prism in the shimanto belt resumption of the magmatism that formed the cauldron cluster in the backarc was concurrent with voluminous influx of terrigenous detritus to the trench as a common tectono thermal event within a subduction system the cauldrons are composed of medium k calc alkaline basalts to rhyolites and their plutonic equivalents these rocks are characterized by lower concentrations of large ion lithophile elements lile including k2o ba rb th u and li lower la yb n ratios lower initial sr isotopic ratios 0 7037 0 7052 and higher end t values 0 5 to 3 5 relative to late cretaceous to early paleogene equivalents there are clear trends from enriched to depleted signatures with decreasing age from the late cretaceous to the paleogene the same isotopic shift is also confirmed in lower crust derived xenoliths and is interpreted as mobilization of pre existing enriched lithospheric mantle by upwelling depleted asthenosphere relatively elevated geothermal gradients are presumed to have prevailed over wide areas of the backarc and forearc of the sw japan arc trench system during the eocene to oligocene newly identified late eocene low silica adakites and high mg andesites in the sanin belt and early eocene a type granites in the sw korea peninsula probably formed due to upwelling of hot asthenosphere and subduction of a young plate the backarc region was an extensional tectonic setting and some paleogene rift basins and sanin belt cauldrons occur in linear arrays the eocene oligocene sanin se korea continental arc lies on the ne extension of the east china sea basin the initial stage of which probably formed by continental arc rifting this rifting may have been triggered by upwelling of hot asthenosphere into the wedge space created by rollback of the subducted slab in response to decreased convergence rate between the pacific and eurasian plates

active tectonics of ne gujarat india by morphometric and morphostructural studies of vatrak river basin abstract landscape owes its shape to the combination of tectonic and climatic forces differential displacement of land by tectonic processes changes the elevation of earth s surface locally and in turn affects the rate of geomorphic processes which are altitude dependent the tectonic and geomorphic processes are very tightly coupled and their results are intertwined to extract the tectonic signal the numerical modelling of the landscape of the vatrak river basin part of which falls in the northern part of the gujarat alluvial plains of western india has been undertaken applying morphometric and morphostructural approach the study helped in understanding the role of tectonic elements in the evolution of the basin demarcation of geomorphic indicators of active tectonics which include the analyses of asymmetry factor valley floor ratio gradient basin elongation ratio long profile and related parameters pseudo hypsometric integral drainage basin asymmetry drainage pattern analysis and azimuthal distribution of stream channels have been performed for each drainage network and associated basin the morphological field evidence of tectonics combined with the results of morphometric analysis has been used to obtain information about the orientation of tectonic elements and the possible reconstruction of their activity in recent times the analyses indicate eastward tilting of the drainage systems strong asymmetry in some reaches pronounced elongation of certain tributaries long profiles indicating base level lowering poor organisation of the hydrographic network and close alignment between lower order streams and active faults all these analyses point towards the active tectonism in the area data obtained through the statistical analysis of preferred stream orientations confirm that the old tectonic directions markedly influenced the drainage network development of the older order streams whereas streams of lower order which preferentially follow the n s and ne sw directions suggest that these tectonic trends were active until very recent times

thermochronology quantifying exhumation history of the wudang complex in the south qinling orogenic belt central china the wudang complex located in the central part of south qinling has been inferred to be a segment of the yangtze craton involved in the orogen in this study the cooling exhumation history of the wudang complex is revealed through combined published geochronology data and new apatite fission track results three rapid exhumation episodes related to relevant geodynamic events have been identified previous 40 ar 39 ar and u th he data indicate that the most significant exhumation induced by the collision between the north and south china blocks occurred from c 237 to 220 ma after long term subsidence and sedimentation of the passive continental margin the second exhumation event related to the long distance effect of the pacific subduction occurred during the period from c 126 to 90 ma following the late cretaceous eocene peneplanation stage the final late cenozoic exhumation since c 15 ma may be attributed to the combined effect of the eastward growth of the tibetan plateau uplift and the asian monsoon

lithosphere crust and basement ridges across ganga and indus basins and seismicity along the himalayan front india and western fold belt pakistan abstract spectral analysis of the digital data of the bouguer anomaly of north india including ganga basin suggest a four layer model with approximate depths of 140 38 16 and 7 km they apparently represent lithosphere asthenosphere boundary lab moho lower crust and maximum depth to the basement in foredeeps respectively the airy s root model of moho from the topographic data and modeling of bouguer anomaly constrained from the available seismic information suggest changes in the lithospheric and crustal thicknesses from 126 134 and 32 35 km under the central ganga basin to 132 and 38 km towards the south and 163 and 40 km towards the north respectively it has clearly brought out the lithospheric flexure and related crustal bulge under the ganga basin due to the himalaya airy s root model and modeling along a profile se nw across the indus basin and the western fold belt wfb sibi syntaxis pakistan also suggest similar crustal bulge related to lithospheric flexure due to the wfb with crustal thickness of 33 km in the central part and 38 and 56 km towards the se and the nw respectively it has also shown the high density lower crust and bela ophiolite along the chamman fault the two flexures interact along the western syntaxis and hazara seismic zone where several large great earthquakes including 2005 kashmir earthquake was reported the residual bouguer anomaly maps of the indus and the ganga basins have delineated several basement ridges whose interaction with the himalaya and the wfb respectively have caused seismic activity including some large great earthquakes some significant ridges across the indus basin are i delhi lahore sargodha ii jaisalmer sibi syntaxis which is highly seismogenic and iii kachchh karachi arc kirthar thrust leading to sibi syntaxis most of the basement ridges of the ganga basin are oriented ne sw that are as follows i jaisalmer ganganagar and jodhpur chandigarh ridges across the ganga basin intersect himalaya in the kangra reentrant where the great kangra earthquake of 1905 was located ii the aravalli delhi mobile belt admb and its margin faults extend to the western himalayan front via delhi where it interacts with the delhi lahore ridge and further north with the himalayan front causing seismic activity iii the shahjahanpur and faizabad ridges strike the himalayan front in central nepal that do not show any enhanced seismicity which may be due to their being parts of the bundelkhand craton as simple basement highs iv the west and the east patna faults are parts of transcontinental lineaments such as narmada son lineament v the munghyr saharsa ridge is fault controlled and interacts with the himalayan front in the eastern nepal where bihar nepal earthquakes of 1934 has been reported some of these faults lineaments of the indian continent find reflection in seismogenic lineaments of himalaya like everest arun kanchenjunga lineaments a set of nw se oriented gravity highs along the himalayan front and the ganga and the indus basins represents the folding of the basement due to compression as anticlines caused by collision of the indian and the asian plates this study has also delineated several depressions like saharanpur patna and purnia depressions

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

late quaternary palaeoclimatic reconstruction from the lacustrine sediments of the sambhar playa core thar desert margin india the sambhar playa in rajasthan india located at the eastern fringe of the thar desert records multiple phases of clastic and evaporite dominated deposition as revealed from a 23 m deep core drilled in the center of the playa seven evaporite facies identified from the mineralogical data reflect variable brine chemistry throughout the history of the playa the complete absence of gypsum rich facies in the upper 5 m and dominance of carbonate and gypsum rich facies in the lower parts of the core reflect fluctuations in salinity level induced by climate change stable isotope data on carbonates d 18 o values correlate with the mgo mgo cao ratio geochemical ratios na al na ti na k and the evaporite mineralogy these data coupled with ams chronology of the organic fraction of the core sediments have been integrated to interpret evaporation inflow ratios which reflect humid and arid climatic conditions our data reconstruct the palaeoclimatic fluctuations in the thar desert margin for the last 30 ka and show significant spatial variation from the available lacustrine records from the thar desert the sambhar playa does not show any evidence of complete desiccation throughout its history although we record arid phases during the lgm and between ca 7500 and 6800 years d 2005 elsevier b v all rights reserved

trench parallel flow beneath the nazca plate from seismic anisotropy shear wave splitting of s and sks phases reveals the anisotropy and strain field of the mantle beneath the subducting nazca plate cocos plate and the caribbean region these observations can be used to test models of mantle flow two dimensional entrained mantle flow beneath the subducting nazca slab is not consistent with the data rather there is evidence for horizontal trench parallel flow in the mantle beneath the nazca plate along much of the andean subduction zone trench parallel flow is attributale utable to retrograde motion of the slab the decoupling of the slab and underlying mantle and a partial barrier to flow at depth resulting in lateral mantle flow beneath the slab such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the pacific basin to the growing mantle reservoir beneath the atlantic basin trenchparallel flow may explain the eastward motions of the caribbean and scotia sea plates the anomalously shallow bathymetry of the eastern nazca plate the long wavelength geoid high over western south america and it may contribute to the high elevation and intense deformation of the central andes

contrasting seismicity between the north china and south china blocks kinematics and geodynamics 1 the north china block ncb part of the sino korean craton is surprisingly one of the most active seismic regions in the world the south china block scb another major craton in east asia has been seismically quiescent using the updated gps data and finite element modeling we show that the kinematic boundary conditions are the primary cause of the contrasting seismicity the scb facilitated by large strike slip faults on its boundaries moves coherently as a rigid block conversely sandwiched between the expanding tibetan plateau and the stable siberia the ncb experiences large differential stresses which are further enhanced by faulting and thermal thinning of the lithosphere the spatial agreement between seismic energy release in the past 2000 years and the predicted long term strain energy implies that intense seismicity in the ncb may continue in the future

convective removal of thermal boundary layer of thickened continental lithosphere a brief summary of causes and consequences with special reference to the cenozoic tectonics of the tibetan plateau and surrounding regions england p 1993 convective removal of thermal boundary layer of thickened continental lithosphere a brief summary of causes and consequences with special reference to the cenozoic tectonics of the tibetan plateau and surrounding regions in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 67 73 the tectonics of tibet and its surroundings underwent marked changes at about 8 ma normal faulting of the plateau appears to have initiated at about this time widespread highly potassic volcanism interpreted as the result of rapid heating of the mechanical boundary layer began about 12 8 ma such rapid heating could be the consequence of convective removal of the lower lithosphere and its replacement by asthenosphere this process would have raised the surface height of the plateau and could have provided the driving force for extension the diffuse deformation in the indian ocean probably began at about 8 ma analysis of the buckling of a plastic lithosphere implies that the horizontal force per unit length required to drive this deformation is consistent with uplift of the tibetan plateau by 1 3 km the indian monsoon intensified at about 8 ma this intensification is consistent with the rapid passage of the surface height of the plateau across a threshold required to disrupt the pre existing atmospheric circulation of the region taken together these observations imply that the surface height of the tibetan plateau rose by between 1 and 3 km in a few million years around 8 ma such a rapid increase in surface height affecting an area the size of the tibetan plateau could not be achieved by crustal thickness changes but could have been caused by the convective removal of a substantial thickness of lower continental lithosphere of the region

the yamal peninsula lake baikal deep seismic sounding profile seismograms from three nuclear explosions recorded along a 2400 km long deep seismic sounding profile extending from the yamal peninsula to lake baikal are presented we have constructed a preliminary 1 d compressional velocity model to fit the major travel time features of the data clear differences between the seismograms from each shot imply that the velocity structure of the crust and upper mantle is variable along the profile estimated crustal thicknesses range from 47 km beneath the west siberian rift to 42 km beneath the siberian craton the structure of the upper mantle above the transition zone consists of material with p wave velocities ranging from 8 25 km s at the moho to 8 53 km s at 225 km velocities increase abruptly at 225 km depth to 8 63 km s there is little evidence for a pronounced low velocity zone although small velocity reversals are required to terminate several branches of the travel time curve the uppermantle transition zone discontinuity at 425 km depth consists of a 5 6 first order velocity increase the lower discontinuity has a 4 9 velocity increase over the depth range 656 5 to 659 km

convective thermal instabilities in the wake of the migrating mendocino triple junction california whether the high seismic velocity anomalies in the upper mantle under california represent cold downwelling mantle flow or fragments of the subducted farallon plate has important implications for mantle dynamics related to the tectonic history of western north america we investigate the former possibility by simulating the time dependent thermal evolution in the asthenosphere beneath california in the wake of the migrating mendocino triple junction mtj using a two dimensional model that represents a transect parallel to the direction of the mtj migration for viscosity within the typical range for the asthenosphere beneath active tectonic regions 1 1018 2 1019 pa s our model predicts vigorous small scale convection characterized by periodic formation of cold downwelling flows near the southern edge of the migrating gorda plate within the relevant time frame the predicted convective thermal structures are comparable to the major mantle features shown by seismic imaging

no direct correlation of mantle flow beneath the north china craton to the india eurasia collision constraints from new sks wave splitting measurements summary the long range effects of the ongoing india eurasia collision and their role in the cenozoic tectonic evolution of eastern china are not well understood here we investigate deformation beneath the north china craton and the qilian mountain region between the haiyuan and kunlun faults both of which are located immediately to the northeast of the tibetan plateau we present teleseismic shear wave splitting parameters from 299 broad band stations these stations provided good spatial coverage in mapping upper mantle deformation beneath the north china craton and the qilian mountain the backazimuth dependence of fast directions fromstationslocatedwithintheqilianmountainregionindicatesacomplexanisotropypattern a multilayer anisotropy and or anisotropy with a dipping symmetry axis may exist beneath the qilian mountain the overlapping or underthrusting of material evident in anisotropy from this region may be a long range effect of the india eurasia collision the central north china craton showed spatially coherent fast directions and the shear wave velocity anomalies within the upper mantle these patterns suggest horizontal deflection of a regional mantle upwelling possibly originating from the mantle transition zone anisotropy with large delay times was observed in the vicinity of shanxi rift system high lnvs lnvp values for the upper mantle indicate that anisotropy in this area is enhanced by vertically aligned melt filled fissures our results suggest that the dynamic processes beneath the central north china craton are not directly related to the india eurasia collision

construction and destruction of the north china craton with implications for metallogeny magnetotelluric evidence from the hengshan wutai fuping region within trans north china orogen abstract the hengshan wutai fuping region within the trans north china orogen is an important corridor that preserves the records of precambrian evolutionary history and phanerozoic magmatic and metallogenic events in the north china craton here we present 2 d and 3 d inversion models of magnetotelluric data collected from the hengshan wutai fuping region and surrounding regions our data reveal nearly horizontal high conductivity layer at lower crustal and upper mantle depths of 35 45 km beneath the hengshan and wutai mountains providing direct evidence for crust mantle decoupling and magmatic underplating in the mesozoic yixingzhai gold deposits and boqiang cu mo au deposits two nearly upright conductors cut through the crust and connect the lower crustal high conductivity layer suggesting frozen channels of fluids and magmas a west dipping slab shaped conductor within the high resistivity lithosphere beneath the wutai complex appears to be the deep extension of the exposed longquanguan ductile shear zone these resistivity anomalies can provide new constraints on the subduction collision events during precambrian tectonic evolution of the trans north china orogen as well as on the phanerozoic tectonic magmatic and metallogenic events in the hengshan wutai fuping region the west dipping slab shaped conductor may indicate a westward oceanic subduction between the wutai and fuping complexes with subsequent collision associated with the formation of the trans north china orogen in the paleoproterozoic we interpret the crustal and upper mantle conductors to be part of an interconnected fluid melt transport channel which probably played an important role for the mesozoic tectonic magmatic and metallogenic events as well as the cenozoic basaltic volcanism in the hengshan wutai fuping region

correlated crust and mantle strain fields in tibet vertical to subvertical planes of shear within the active crustal deformation field in tibet align with fast directions of shear wave polarization this observation suggests that the present day velocity gradient tensor field within the crust of tibet correlates with the lithospheric mantle velocity gradient tensor field beneath tibet this inference requires the following 1 the 100 axes of olivine are aligned within established zones of lithospheric mantle fabric or anisotropy built up through finite strain 2 present day shear in the mantle lithosphere is occurring within these established zones of fabric parallel to the direction of olivine 100 axis alignment 3 the zones of mantle lithospheric fabric or zones of mantle shear are aligned with zones of crustal shear faults the correlation of crustal and mantle strain fields most simply results from the fact that both crust and mantle lithosphere are under the influence of similar velocity boundary conditions furthermore the observations confirm the distributed nature of lithospheric mantle deformation beneath east central tibet and suggest that left lateral shear has been the dominant component of finite shear there

cenozoic extensional tectonics in china abstract this paper gives a brief review of the cenozoic extensional structures of china during the cenozoic eastern china was in a rifted setting where divergent plate motion and extensional structures were dominant subsidence has occurred initially in response to attenuation of the crust and was enhanced later by subsidence due to thermal contraction in western china particularly in the qinghai tibetan plateau where rifting occurs in an orogenic setting in which convergent plate movements are dominant the rifting is associated with continental collision and lateral escape and large intra continental transform boundaries extensional structures in china may be grouped into eleven graben systems in eastern china and four in western china they occur in different styles linear rift valley basin and range structures and pull apart basins associated with strike slip faults the geometric characteristics kinematics of extension and the mechanism of continental extension in china are discussed the cenozoic extrusion structural model proposed by tapponnier et al 1982 elegantly accounts for the gross tectonics and the formation of the graben systems of western china however in considering the overall strain pattern during the extension of the early tertiary basin and range region in eastern china a large scale simple shear kinematic model may be preferable to the pure shear rift model

zircon u pb and galena pb isotope evidence for an approximate 1 0 ga terrane constituting the western margin of the aravalli delhi orogenic belt northwestern india abstract zircon u pb ages of 987 6 4 and 986 3 2 4 ma have been established for rhyolites in the southern and northern parts respectively of the ambaji sendra arc terrane in the western fringe of the aravalli delhi orogenic belt pb isotope data for volcanogenic massive sulphide deposits within this arc terrane define a linear trend which is considered a useful reference palaeoisochron or mixing line at an age of about 990 ma and establish continuity of the terrane between ambaji and sendra these results are in contrast to the traditional and continuing assignment of the ambaji sendra terrane to the 1700 ma delhi supergroup the isotopic composition of galena from an apparently epigenetic occurrence at punagarh hill yields a model age of about 940 ma suggesting that the punagarh group could form part of the same arc sequence the phulad lineament which has been considered by most workers to represent the western boundary of the aravalli delhi orogenic belt appears in terms of this stratigraphic assignment to represent an oblique structure which has not greatly offset the punagarh and ambaji sendra domains within the arc terrane the eastern boundary of the terrane is marked by the sabarmati fault a zircon u pb age of 836 7 5 ma for the siwaya gneissic granite in the southern part of the ambaji sendra belt is in accord with previous age data for felsic erinpura plutons that have intruded the arc sequence a monazite age of 826 5 ma may reflect slow cooling of the siwaya pluton or a younger thermal event a model age of about 820 ma for galena is obtained from the tosham sn cu mineralized zone in haryana state about 280 km north northeast of ajmer which is related to the felsic anorogenic malani volcanism plutonism hence this widespread magmatism found extensively west of the ambaji sendra terrane may have been coeval with erinpura plutonism or followed it very closely the present geochronological data warrant the recognition of the ambaji sendra arc terrane as defined here as a distinct metallogenic province which saw the formation of vms type deposits in the late mesoproterozoic around 1 0 ga the pb isotope compositions of the deposits however do not clearly define the metal sources the lead from danva prospect is most primitive and must have the greatest component from a juvenile mantle source the birantiya khurd deposit on the other hand contains a much greater component of lead from a significantly older crustal source

evaluating the role of preexisting weaknesses and topographic distributions in the indo asian collision by use of a thin shell numerical model thin viscous sheet models have proved to be very useful in exploring the interaction between plate boundary and gravitational forces during continental collision however simplifications of these models e g absence of faults planar geometry of the collision zone limit their use in making specific predictions regarding tectonic evolution such as the role of eastward extrusion along major strike slip faults during the indo asian collision this deficiency is overcome by a thin shell finite element model with faults that can assess the effects of preexisting fault configurations and topographic distributions on velocity fields numerical simulations of a palinspastically restored asia at ca 50 ma suggest that preexisting lithospheric weaknesses favor north south shortening during initial collision whereas preexisting high topography in southern asia promotes eastward extrusion these results underscore the first order importance of initial topography and the distribution of preexisting faults in the outcome of geodynamic modeling

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

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

the cenozoic rift system of the north china plain and the deep internal process abstract the cenozoic north china plain rift system generated on the site of a mesozoic rift system is the largest rifted basin in east china it trends nne with a total length of about 1000 km maximum width up to 400 km in its middle part and a width of 50 100 km at its south and north the largest thickness of the cenozoic deposits reaches 12 000 m and the accumulated thickness of the cenozoic basalts about 2000 m this rift system is a region of strong seismicity it has quite considerable differential crust movement at the present day the geophysical data indicate that the thickness of the crust and lithosphere beneath the rift system is approximately 4 8 km and 40 km thinner than that of the surrounding mountains this rift system has rather high heat flow values and residual gravity anomalies so far no low velocity anomaly of pn has been found in this region we infer that the formation of this rift system is caused by upwelling of the asthenosphere which is probably related to the convective roll induced by subduction of the pacific plate underneath the asiatic continent and the disturbance of the upper mantle in this region during the mesozoic

the indo asian continental collision a 3 d viscous model abstract the large scale physical process of the indo asian continental collision and the formation of the himalayan tibetan plateau have been simulated in various viscous thin sheet models but the thin sheet simplification also kept some important issues from being fully explored among these issues are the role of strike slip fault zones in facilitating large scale lateral translation of lithospheric blocks the escaping tectonics during the collision and the speculated lateral flow of the ductile middle lower crust under the tibetan plateau here we present a fully three dimensional finite element model to simulate the indo asian continental collision the model includes major boundary faults to simulate the escaping tectonics and vertically variable rheological structures to model lower crustal flow the collisional process is constrained by the history of the indo eurasian plate convergence and the present crustal thickness and topography of the tibetan plateau our results indicate that the restrictive boundaries of the tibetan plateau including the rigid tarim and south china blocks largely control the spatiotemporal patterns of crustal deformation in the collision zone as the indian indenter moves toward the tarim block higher strain rates and topography developed in the western part of the collision zone than in the eastern part causing the northward migration of the deformation front to gradually change to eastward migration in the past 10 20 myr broadly consistent with the initiation of widespread e w extension in the plateau these restrictive boundary blocks also force the crustal and mantle materials in the collision zone to flow coherently hence providing an alternative explanation for the apparently vertically coherent deformation in tibet assuming that the crust weakens as it thickens our model predicts the lateral expansion of the tibetan plateau an important feature of the tibetan tectonics that is missing in previous models with constant rheology

the mesozoic cenozoic east china rift system abstract the mesozoic cenozoic rift system of eastern china extends in a n s direction over a distance of some 4000 km and has a width of 600 1000 km to the east it reaches into the coastal areas of the east and south china sea and extends onto the continental shelf this very large rift system evolved on a heterogenous basement consisting of a number of terranes which were amalgamated during the indosinian orogeny a first rifting phase spanned late jurassic early cretaceous times it was followed by a period of relative tectonic quiescence and thermal relaxation a latest cretaceous phase of compressional tectonics giving rise to partial basin inversion was followed by a renewed rifting cycle spanning eocene early neogene times development of the east china rift system involving vertical as well as lateral crustal movements was probably induced by physico chemical changes within the earth s mantle that can be related to activity along the pacific subduction zones the mesozoic cenozoic east china rifts contain some important hydrocarbon provinces which rely to a large extent on syn rift sediments for source and reservoir rocks

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

age and composition of granulite and pyroxenite xenoliths in hannuoba basalts reflect paleogene underplating beneath the north china craton abstract in situ u pb and hf isotope systematics of zircons mineral chemistry of silicates and whole rock major element trace element and platinum group element pge data are reported for five mafic xenoliths granulites and pyroxenite in the hannuoba cenozoic basalts north china temperature estimates of 859 886 c suggest that these xenoliths are derived from the lower crust the whole rock compositions of the xenoliths show weakly negative eu anomalies eu 0 67 0 95 high sio 2 al 2 o 3 5 80 13 8 low ir 0 10 0 29 ppb and wide ranges of ni 4 5 235 ppm and la nb 1 70 7 64 most zircons in these samples are structureless and give paleogene 44 5 47 3 ma u pb ages minor populations have early mesozoic 210 220 ma late mesozoic 90 ma and neogene 14 ma ages the fractionation of pyroxene and plagioclase controlled the petrogenesis of the xenoliths which are interpreted as the products of basaltic underplating and fractionation cumulates in paleogene time 45 47 ma with assimilation of some older intermediate crustal components the paleogene underplating corresponds in time to lithosphere scale extension in the north china craton leading to the widespread formation of sedimentary basins most paleogene zircons have positive e hf up to 13 2 with uniform t dm 0 46 0 50 ga whereas most mesozoic zircons have negative e hf this evolution suggests a temporal decrease in the degree of crustal assimilation during the extension of the lithosphere in addition to complex modification in early and late mesozoic times the thermal event related to the eruption of the host magmas ca 14 ma also reheated the lower crust beneath the north china craton

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

crustal structure across the three gorges area of the yangtze platform central china from seismic refraction wide angle reflection data abstract we present active source seismic data recorded along a 300 km long profile across the three gorges area of the western yangtze platform central china from west to east the profile crosses the zigui basin huangling dome and jianghan basin the derived crustal p wave velocity structure changes significantly across the tongchenghe fault that lies at the transition from the huangling dome to the jianghan basin west of the tongchenghe fault beneath the zigui basin and the huangling dome we observe a 42 km thick crust of relatively low average velocity 6 3 6 4 km s in contrast east of the tongchenghe fault beneath the jianghan basin the crust is only 30 km thick and has a high average velocity 6 6 6 7 km s a west east variation in crustal composition along the tongchenghe fault is also inferred west of the fault p wave velocities suggest a felsic composition with an intermediate layer at the base of the crust whilst east of the fault felsic intermediate and mafic crustal layers are apparent our results suggest that the crust beneath the jianghan basin has been thinned by rifting accompanied by intrusion of the lower crust by mafic dikes and sills the west to east division of the crust in the three gorges area coincides with first order geophysical contrasts in gravity topography crustal and lithospheric thickness

post neogene tectonism along the aravalli range rajasthan india abstract the aravalli range runs southwest from delhi for a distance of about 700 km its western margin is well defined but the eastern margin is diffuse five geomorphic provinces are recognized in the study area the western piedmont plains the ridge and valley province which in the central aravallis occurs at two different heights separated by a fault scarp the plateau province demarcated from the former by a fault scarp confined to the southern aravallis and occurring for a short stretch at two heights across another fault scarp the bgc rolling plains east of the range and the bgc uplands south of the above the scarps coincide with precambrian faults a series of rapids and water falls together with deeply entrenched river courses across the scarps and the youthful aspects of the escarpments with no projecting spurs or straight river courses along their feet all point unmistakably to a recent or post neogene vertical uplift along pre existing faults presence of knickpoints at a constant distance from the range in all west flowing rivers the ubiquitous terraces and river courses entrenched within their own flood plain deposits of thick gritty to conglomeratic sand are indicative of a constant disturbance with a gradual rise of the range east of the knickpoint wherefrom the coarse materials were carried by the fast west flowing streams there is a differential uplift across the plateau scarp together with a right lateral offset this epeirogenic tectonism is ascribed to the collision of the eurasian and the subducting indian plates and to a locking of their continental crusts by early pleistocene with the mbt gradually dying off continued plate movement caused a flexural bending of the plate by a moment generated at the back and a possible delinking of the continental crust along the zone of subduction the felexural bending ripped open the precambrian regional faults the differential uplift and the difference in the distances of the nodes on two sides of the major reactivated fault were possibly caused by a difference in the values of the flexural rigidity and the foundation modulus owing to a slight compositional difference of the constiuent rocks in the two sectors

cenozoic tectonic jumping and implications for hydrocarbon accumulation in basins in the east asia continental margin abstract tectonic migration is a common geological process of basin formation and evolution however little is known about tectonic migration in the western pacific margins this paper focuses on the representative cenozoic basins of east china and its surrounding seas in the western pacific domain to discuss the phenomenon of tectonic jumping in cenozoic basins based on structural data from the bohai bay basin the south yellow sea basin the east china sea shelf basin and the south china sea continental shelf basin the western pacific active continental margin is the eastern margin of a global convergent system involving the eurasian plate the pacific plate and the indian plate under the combined effects of the india eurasia collision and retrogressive or roll back subduction of the pacific plate the western pacific active continental margin had a wide basin arc trench system which migrated or jumped eastward and further oceanward this migration and jumping is characterized by progressive eastward younging of faulting sedimentation and subsidence within the basins owing to the tectonic migration the geological conditions associated with hydrocarbon and gashydrate accumulation in the cenozoic basins of east china and its adjacent seas also become progressively younger from west to east showing eastward younging in the generation time of reservoirs seals traps accumulations and preservation of hydrocarbon and gashydrate such a spatio temporal distribution of cenozoic hydrocarbon and gashydrate is significant for the oil gas and gashydrate exploration in the east asian continental margin finally this study discusses the mechanism of cenozoic intrabasinal and interbasinal tectonic migration in terms of interplate intraplate and underplating processes the migration or jumping regimes of three separate or interrelated events 1 tectonism magmatism 2 basin formation and 3 hydrocarbon gashydrate accumulation are the combined effects of the late mesozoic extrusion tectonics the cenozoic nw directed crustal extension and the regional far field eastward flow of the western asthenosphere due to the india eurasia plate collision accompanied by eastward jumping and roll back of subduction zones of the pacific plate

characteristics structural styles and tectonic implications of mesozoic cenozoic faults in the eastern heilongjiang basins ne china abstract the eastern heilongjiang basins ehbs are the assemblage of a series of meso cenozoic residual basins located in the northeastern corner of china the deformation pattern of the ehbs has significant implications for the history of the pacific plate subduction beneath the eurasia since the late mesozoic in this paper research on the characteristics and structural styles of the meso cenzoic faults in the ehbs has been conducted on the basis of a comprehensive analysis of field geology drilling data and seismic reflection profiles as a result five different stages of the meso cenozoic faults in the ehbs have been recognized these are in accordance with the time and relevant characteristics of fault movements i e the early stage of the early cretaceous normal fault the early stage of the late cretaceous thrust fault the late stage of the late cretaceous thrust fault the cenozoic synsedimentary normal fault and the late stage cenozoic shear fault a regional geological section has been generated across the ehbs by linking four local seismic profiles together a step by step reconstruction has been made to help better understand the mesozoic cenozoic tectonic evolution of the ehbs two phases of extension rifting in the early cretaceous period and the paleogene respectively are demonstrated to be interfered with two phases of regional uplift compression and erosion in the late cretaceous period the complicated development of multiple fault systems within the ehbs has reflected the evolution of a complex tectonic subduction of the pacific plate beneath the eurasia since the cretaceous period

the cenozoic tectonic evolution of the great north china two types of rifting and crustal necking in the great north china and their tectonic implications abstract the great north china underwent widespread continental rifting during cenozoic time that caused extension and necking of the crust in this area and formed four major rift systems in this paper we provide geological and geophysical evidence that rifting and extension in the western part of the great north china differs from that in its eastern part in age and nature the space time relationships show that the origins of the western rift group of the great north china are probably related to the tibet plateau tectonics whereas those of the eastern rift group are related to the subduction events in the western margin of the pacific plate furthermore the quaternary tectonic regime in the eastern part of the great north china differs from the neogene tectonic pattern and shows relations with western rifts we speculate that during the quaternary the processes that caused rifting in the west have spread further east and now affect the eastern part of the great north china

numerical modelling of stress fields and earthquakes jointly controlled by ne and nw trending fault zones in the central north china block abstract the stress field of the central north china block cncb has been affected by the interaction among the indian eurasian and pacific ocean plates and the effect is manifested by the occurrence of large earthquakes in this region here using numerical simulation of the finite element method attempts were made to evaluate ese directed compression on three tectonic zones namely the shanxi graben zone the zhangjiakou penglai fault zone and the taihangshan fault zone in these zones the structural geometry and viscoelastic property of the model were determined as well as 49 main faults identified by means of a comprehensive structural analysis of seismic profiles gravity data and tomography this study shows that the stress concentration areas in the three zones are all located in the transition zone between ne trending and nw trending faults numerical simulation analysis of the xingtai and tangshan earthquakes revealed that the ne and nw trending faults had played an important role in controlling the distribution of the stress field triggering aftershocks and or stopping stress propagation during earthquakes the differences of the stress fields and earthquake distributions among the three tectonic zones resulted from not only the fault combination patterns but also the geometry of the main faults

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

effects of deep co 2 on petroleum and thermal alteration the case of the huangqiao oil and gas field abstract the co2 rich natural gas from the huangqiao oil and gas field of the subei basin is produced along with crude oil the co2 content ranging from 80 56 to 99 30 and the 3he 4he ratio of 0 94 10 6 to 4 67 10 6 indicates that this includes a substantial fraction of mantle derived co2 in the huangqiao region although the positive carbon isotopic series of alkane gases i e 13c1 the crude oil of the huangqiao region is light or condensate oil with low densities of 0 7933 0 8255 g cm3 saturated hydrocarbons comprise 90 06 97 37 the crude oil while the aromatic non hydrocarbon and asphaltene fractions are very small the n alkanes range from c13 to c34 with highest abundances at c16 and c17 the gas chromatogram of the crude oil shows an unresolved hump or unresolved complex mixture ucm distribution of a complete n alkane series non odd even predominance and major n alkane peaks on the highest positions of the ucm distribution this may indicate that deep mantle derived co2 fluid extracted and accumulated the oil now found in the reservoirs or source rocks

lithospheric rheology and moho upheaval control the generation mechanism of the intraplate earthquakes in the north china basin abstract many devastating intraplate earthquakes such as the 1966 xingtai earthquake ms 7 2 and the 1976 tangshan earthquake ms 7 8 occurred in the north china basin ncb this study aims to investigate the generation mechanism of the large intraplate earthquakes in the ncb and the spatial distribution of earthquake activity through numerical experiments in order to simulate the interseismic stress accumulation process in the ncb we set up several 3d finite element models based on different lithospheric rheological structure and apply boundary conditions of horizontal compression we find that stress concentration with high rate in the regions where moho upheaves is responsible for the large earthquakes in the ncb during the interseismic period large stress rate is located nearly around the bottom of the brittle upper crust where stress accumulates fast to reach fault strength and active the main shocks aftershocks in the seismogenic layers could be triggered by the main shocks two factors are critical to the crustal stress accumulation process 1 the first is moho upheaval in the seismic zones 2 the second is viscosity contrast among the crustal layers our results support the lithospheric rheological structure in the ncb as following the brittle upper crust brittle ductile transition in the middle crust the ductile lower crust and the ductile lithospheric upper mantle

3 d velocity images beneath the chinese continent and adjacent regions summary in this paper 3 d velocity images beneath the chinese continent and adjacent regions are reconstructed using p wave traveltime residuals of regional and distant earthquakes supplied by chinese seismic networks and isc in the tomographic inversion an orthogonal projection operator is used to separate the velocity from the hypocentral parameters the fast givens transformation without square root calculations is then used in sequential orthogonal triangularizations and the modified singular value decomposition is also utilized thus the difficulties of large memory demand and high computing cost in solving the system of equations with coupled velocity and hypocentre parameters are avoided at the same time the stability of the algorithm is ensured resolution images are also obtained in the inversion process based on the resolution theory of backus gilbert modified for discrete models in model parametrization the interpolation function of grid node velocities is used as the space function of velocity to meet the practical needs the velocity function is allowed to be discontinuous the consequent complications of the forward problem have been dealt with in the paper the main results are summarized as follows 1 the velocity images given in this paper indicate lateral heterogeneity of the crust and upper mantle beneath the chinese continent and adjacent regions which persist down to a depth of at least 1100 km the correlation between the velocity image and the known surface geological features can be traced down to a depth of 110 km below 220 km this correlation is hardly obvious 2 the images at 45 0 km immediately above the moho and 45 0 km below the moho show clearly that the crust of the chinese continent can be approximately divided into two parts by the 102 5 e longitude the crust to the east is thinner than that to the west 3 the images at 400 and 600 kin also display differences between the eastern and western part this means that tectonic differences between eastern and western china may exist in the whole upper mantle

shear wave anisotropy beneath the tibetan plateau eleven broadband digital seismic stations were deployed across the central tibetan plateau in the first extensive passive source experiment attempted within the tibetan plateau one year of recording resulted in 186 event station pairs which we analyze to determine the characteristics of shear wave splitting in the upper mantle beneath the array measurements of the fast polarization direction and delay time t for sks and direct s arrivals reveal systematic variations along the north south oriented array in the north central region of the plateau very large delay times are observed at three stations the largest of which is budo with of t 2 4 s however at tunl which is off the northern edge of the plateau and 110 km from budo and at sites in the south central plateau t decreases by nearly a factor of 3 we also observe systematic rotation of from about 45 ne to 90 e w from south to north along the array a previously identified zone of inefficient sn propagation correlates well with our region of large t observations the large delay times suggest that a relateively high number of anisotropic crystals are preferentially alligned within the mantle lid beneath the north central portion of the tibetan plateau in most cases fast polarization directions appear to be parallel to surface geologic features suggesting as much as 200 km of the upper mantle has been involved in the collisional deformation that has produced the tibetan plateau

convection beneath young oceanic lithosphere implications for thermal structure and gravity small scale convection under the oceanic lithosphere which begins in the first 5 m y of cooling can produce a gravity signal with the amplitude and wavelength observed for large areas of the central pacific and southern indian oceans using seasat altimeter data the trend of the observed anomalies is parallel to the direction of plate motion as might be expected if they were produced by small scale convection models predict that the wavelengths of gravity anomalies increase more rapidly with age than is observed the persistence of short relatively uniform wavelength anomalies 200 km to crustal ages of 50 ma may indicate that they were produced when the lithosphere was very young and thin and were frozen in as cooling thickened the elastic lithosphere small scale convection which begins under very young lithosphere does not violate other geophysical data such as the rate of seafloor subsidence and variations of geoid height with age after convection has begun the subsidence due to thermal contraction within the lithosphere varies linearly with age in the absence of mantle heat sources although the rate of change of these quantities is affected by convection much of the variation of the geoid height across fracture zones can be fit by a model which includes small scale convection

seismic anisotropy beneath the eastern margin of the tibetan plateau from sks splitting observations abstract the eastern margin of the tibetan plateau is one of the areas of the entire region with the most complex deformation seismic anisotropy reveals the imprints of past and present deformation in the lithosphere and asthenosphere which could help elucidate the deformation mechanism this study investigated the characteristics of seismic anisotropy beneath 512 seismic stations based on sks phases from 200 earthquake the measured splitting delay time varied from 0 2 1 4 s average 0 7 s in the central sichuan basin scb the average delay time is only 0 35 s consistent with the characteristics of the relatively thick and rigid lithosphere of the stable scb however the northeastern scb has relatively stronger anisotropy with a fast polarization direction fpd with ne sw orientation which is markedly different from the weak anisotropy with nw se orientation in the central scb we speculate that owing to e w compressive stress caused by eastward escape of material from the tibetan plateau the lithosphere in this area has undergone considerable deformation along the right lateral maximum shear direction in the chuandian diamond block the fpd of several adjacent stations was approximately e w i e almost perpendicular to the fpd in the northern and southern regions which might be related to partial melting in the lithosphere and to compressive stress the fpd in the west qinling orogenic belt is approximately parallel to the strike of the surface faults and the average delay time is approximately 1 3 s as the lithosphere is insufficient to produce such strong anisotropy in this region we infer that the lithosphere and asthenosphere both contribute to the seismic anisotropy delay time in the southern songpan ganzi block is much smaller than in the north which might be attributable to low velocity mantle upwelling and complex tectonic stress in this area

lithospheric structure of the ordos block and its boundary areas inferred from rayleigh wave dispersion abstract we have measured rayleigh wave phase velocities of the ordos block and its southern and western boundary areas and inverted these data to describe the upper mantle structure the ordos block was found to be characterized by distinctly high seismic velocities at depths commonly associated with a low velocity asthenosphere to the south abnormally slow velocity anomalies appeared in the weihe rift probably indicating subsolidus grain boundary weakening effect under high temperatures near solidus instead of partial melt in the asthenosphere an intermediate seismic velocity structure was observed beneath the northern qinling orogen nql to the south of the weihe rift a thin high velocity lid which was probably a cratonic relic was found under the haiyuan arcuate tectonic region hatr west of the ordos block a thick lithosphere was present beneath the ordos block 200 km and the nql 140 km while a thinner lithosphere 100 km was found beneath the hatr and the weihe rift the observed structural differences were likely associated with different lithospheric tectonics in the study region whereas the weihe rift and the hatr had been strongly affected by cenozoic lithospheric modification and thinning the ordos block and the nql appeared to have been much less influenced combined with previous studies our results suggested that the far field effect of the indo asia collision may have played an important role in the unique lithospheric process in the study region such as the extension of the weihe rift the preservation of a cratonic relic under the hatr and the localized intense lithospheric modification of these two regions the substantial variations of deep structure and thus contrasting rheological properties between the ordos block and the surrounding notable seismic belts the hatr and weihe rift may be a candidate mechanism for the contrasting seismicity of the region the lateral variations in the lithospheric structure estimated here generally agreed with changes in upper mantle deformation patterns previously derived from sks splitting measurements

baikal rift zone structure and geodynamics abstract the cenozoic baikal rift zone is superimposed on the caledonian baikal fold belt representing the suture between the precambrian siberian craton and several microcontinents the baikal rift zone consists of a system of disconnected fault bounded basins and extensional and wrench faults that straddles a major arch having a topographic relief of 2 3 km rifting activity commenced during the oligocene and is still active as evident from high seismicity of the baikal rift zone across the baikal rift zone upper crustal extension is considerably smaller than would be expected from its crustal thickness which decreases by 8 11 km across the baikal basins as compared to the adjacent unextended areas the discrepancy between upper and lower crustal attenuation could be attributed to intrusion of a major diapir indeed geophysical data indicate that the sayan baikal dome coincides with such a diapir the top of which is located at the crust mantle boundary this intrusion is held responsible for oligocene and quaternary doming of the rift zone development of the intra continental baikal rift system is thought to be related to asthenospheric diapirism active rifting however intra plate stresses in conjunction with the himalayan collision may have played some role

geochemical signatures of late holocene paleo hydrological changes from phulera and pokharan saline playas near the eastern and western margins of the thar desert india abstract stratigraphical mineralogical geochemical and optical dating methods were used to reconstruct paleo hydrological changes in two playas phulera 500 mm a and pokharan 200 mm a in near extremum climatic regions of the thar desert sediment successions in shallow profiles from phulera and pokharan contain three and four stratigraphic units respectively each with characteristic geochemical properties these units reflect changes in chemical weathering detrital input salinity and provide a measure of the changes in precipitation i e monsoon through time sediments from pokharan suggest short rainfall events during ca 6 6 4 ka relatively stable fresh water higher and persistent rainfall regime during 4 2 3 ka and a hyper saline low rainfall condition during 2 3 1 1 ka sediments at phulera record hyper saline low rainfall lacustrine conditions during 1 4 ka higher abundance of gypsum in pokharan 2 3 1 1 ka and proto dolomite in phulera 2 3 1 4 ka are nearly synchronous and reflect enhancement of salinity selenite crystals in pokharan and large desiccation cracks in buried horizons at phulera reflect desiccation of playas at ca 2 ka both playas progressively became less saline after 1 4 ka given the regional nature of this record these changes are attributed to fluctuation of the monsoon over the indian sub continent

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

the tectonics of the western ordos plateau ningxia china slip rates on the luoshan and east helanshan faults analysis of the locus style and rate of faulting is fundamental to understanding the kinematics of continental deformation the ordos plateau lies to the northeast of tibet within the india eurasia collision zone previous studies have suggested that it behaves rigidly and rotates anticlockwise within a large scale zone of ene wsw left lateral shearing for this rotation to be accommodated the eastern and western margins of the ordos plateau should be undergoing right lateral shearing and yet the dominant faulting style appears to be extensional we focus specifically on the kinematics of the faults bounding the western margin of the ordos plateau and make new slip rate estimates for two of the major faults in the region the right lateral strike slip luoshan fault and the normal slip east helanshan fault we use a combination of infrared stimulated luminescence dating of offset landforms with high resolution imagery and topography from the pleiades satellites to determine an average right lateral slip rate of 4 3 0 4 mm a 1 uncertainty on the luoshan fault similarly we use 10be exposure dating to determine a vertical throw rate on the east helanshan fault of 0 6 0 1 mm a corresponding to an extension rate of 0 7 0 1 mm a 1 uncertainty both of these results agree well with slip rates determined from the latest campaign gps data we therefore conclude that right lateral shearing is the dominant motion occurring in the western ordos region supporting a kinematic model of large scale anticlockwise rotation of the whole ordos plateau

cenozoic episodic volcanism and continental rifting in northeast china and possible link to japan sea development as revealed from k ar geochronology abstract cenozoic volcanic rocks in northeast china comprise part of the volcanic belt of the western circum pacific rim and represent one of the presently active tectono magmatic regions of the world over 590 volcanoes with erupted basalts covering an area of 50 000 km 2 are exposed in the songliao graben and particularly on its flanks k ar dating of the volcanic rocks sampled from a selection of eruption sites over the region reveals that the volcanism occurred episodically through the entire cenozoic corresponding to the tectono magmatic interactions particularly between the india eurasia and pacific plates the volcanism initiated in the songliao graben in late cretaceous 86 ma and migrated flankward since 28 ma the magmatic propagation shows three major stages intimately associated with the evolution of japan sea and related to the geodynamic forcing of the india eurasia collision prior to japan sea rifting volcanic eruptions were restricted to the songliao basin during japan sea opening volcanism migrated into the lateral belts after cessation of japan sea opening at 15 ma volcanism with greatest intensity occurred on both flanks particularly along the yi yi fault system around 14 13 ma and subsequently the fu mi fault between 11 and 7 ma continuing this trend of migration eruptions scattered further away from the songliao basin in the last 4 5 ma we suggest that the cenozoic volcanic belt in northeast china and the japan sea backarc basin are competitive parts in the eastern marginal magmatic system of the eurasian plate the early stage of the volcanism in the songliao basin may have resulted from mantle upwelling beneath the songliao bohai basin belt rifting of the ne faults and relatively weak intensity of volcanism in northeast china during japan sea opening could be attributable to the lithospheric breakup in the japan sea and spreading of japan sea the subsequent strong volcanism in northeast china after cessation of the japan sea opening implicates the easiest pathway for the melts of the magmatic system in the plate margin the diversified volcanism in scattered localities during the quaternary may indicate localized melting processes or notable modifications in smaller sized individual domains and possibly a magmatically waning phase of the limited source in eastern china

crust and upper mantle structure beneath western china from p wave travel time tomography 1 three dimensional velocity images of the crust and upper mantle beneath western china are obtained through seismic tomography by using p wave arrival times of local regional and teleseismic events recorded in chinese and kyrgyzstan seismic networks at shallow depths most mountain belts and tectonically elevated areas are imaged as higher velocities relative to adjacent sediment filled basins and foreland depressions with lower velocities at mid lower crust depths the kyrgyz tian shan is underlain by lower velocity material and a distinct low velocity zone in the south north direction is observed between the eastern and western parts of the chinese tian shan the moho of the southern tarim basin has a greater depth over 50 km in front of the western kun lun compared to the northern and western tarim basin lateral heterogeneity within the upper mantle is apparent at depths from 71 to 571 km the uppermost mantle beneath the kyrgyz tian shan altay qi lian and eastern kun lun is characterized by low velocity material that is probably related to the upwelling of hot mantle the lithospheric thickness varies from 120 to 170 km beneath the chinese tian shan and northern tibetan plateau to 200 250 km beneath the tarim basin deep coupling pattern of the chinese tian shan with adjacent provinces can be classified into the embedding detaching and sinking and underthrusting of lithospheric roots in addition the lithosphere of the northern edge of the tibetan plateau seems to be thickened in contrast to the central part of the northern plateau north dipping low velocities exist in the upper mantle between the tibetan plateau and provinces to its north which might indicate mantle flow from the tibetan plateau toward surrounding areas but it has been blocked by the thick tarim lithosphere

geodynamics of the shanxi rift system china the pliocene quaternary shanxi rift system of northern china transsects the domal axis of the shanxi highlands and is defined by an s shaped string of asymmetric basins extending from huailai yanqing in the north via taiyuan to yuncheng in the south this rift system has a length of about 1200 km and a width of 20 80 km it is characterized by strong earthquakes its central nne trending transtensional segment forms the main element of the shanxi rift system basin subsidence commenced during the early pliocene along nne oriented master faults characterized by large strike slip rates 5 68 7 mm yr crustal extension amounts to some 1 4 km basins are separated by push up blocks destructive earthquakes m 7 8 are unevenly distributed the ene trending northern and southern branches of the shanxi rift system are characterized by orthogonal crustal extension along ene striking normal faults amounting to about 8 km these areas are characterized by a basin and range type structural style and weak seismic activity the shanxi rift system developed on a some 40 km thick thermally cool precambrian crustal segment that was overprinted during mesozoic diastrophic events there is only minor rift related volcanic activity the moho is pulled up by a few kilometers only under the axial rift zone sub moho compressional velocities are in the 8 0 8 1 km s range the shanxi rift system evolved in response to the build up of regional stress fields related to the collision of india and eurasia its localization involved reactivation of pre existing fracture systems

the field of crustal velocity in asia calculated from quaternary rates of slip on faults rates of quaternary faulting when treated as measures of strain rates within regions several times larger than the depths of brittle faulting yield a velocity field for asia that matches the average relative velocity between the indian and eurasian plates over the past 2 myr nuvel 1a and the velocity of shanghai with respect to eurasia measured with very long baseline interferometry vlbi by using rates of slip on discrete surfaces faults to define average strain rates we explicitly assume that the large scale deformation can be treated as that of a continuum depending on the jcales over which strain rates are averaged 87 to 93 per cent of the assumed strain ites are fit within assigned 1 sigma uncertainties and 97 to 99 per cent are fit within 2 sigma the internal consistency of these data and the agreement with independent rates nuvel 1a and vlbi test the validity of treating large scale deformation of continents as that of a continuum in the calculated velocity field a large fraction 85 per cent of india s convergence with eurasia is absorbed by crustal or lithospheric thickening among consistently misfit assumed strain rates are those dominated by high rates of strike slip faulting strain associated with 20 30 mm a 1 of slip on the altyn tagh karakax and karakorum faults is inconsistent with the distributions of strain in surrounding regions we conclude that these rates all of which are based on correlations of ages of offset landforms with changes in global climate and not on radiometric dating have been systematically overestimated lateral transport out of india s northward path is relatively minor south china is calculated to move east southeast at less than 10 mm a 1

multiple magma sources involved in marginal sea formation pb sr and nd isotopic evidence from the japan sea region the cenozoic basaltic rocks in sikhote alin and sakhalin exhibit a change over 55 m y from subduction zone related to continental rift related volcanism as the japan sea opened between eastern sikhote alin and the japan arc the temporal geochemical trends in volcanic rocks erupted before and during the opening of the japan sea suggesting that there was a change in magma source from the lithosphere to the depleted asthenosphere as the japan sea opening progressed two geochemical groups can be identified within the basalts that postdate the japan sea opening tholeiitic basalts and alkalic basalts as the tholeiitic basalts have emi type signatures we propose that the tholeiites had a significant contribution from an emi type precambrian subcontinental lithospheric mantle the alkalic basalts yielding geochemical characteristics similar to enriched oceanic island basalts may have been derived from the subcontinental asthenospheric mantle the opening of the japan sea was triggered by lateral migration of asthenospheric mantle from beneath northeast china toward the japan arc

comparison of the upper mantle shear wave velocity structure of the indian shield and the tibetan plateau and tectonic implications summary travel times and waveforms of long period sh waves recorded at distances of 10 30 and some ss waveforms are used to constrain the upper mantle velocities down to a depth of 400km beneath both the indian shield and the tibetan plateau the shear velocity in the uppermost mantle beneath both the indian shield and the tibetan plateau is high and close to 4 7 km s 1 the indian shield has a fairly thick high velocity lid and the mean velocity between 40 and 250 km is between 4 58 and 4 68 km s 1 in contrast s wave travel times and waveforms of s waves as well as a few for ss show that the mean velocity between 70 and 250km beneath the central and northern part of the tibetan plateau is slower by 4 per cent or more than that beneath the indian shield and probably is between 4 4 and 4 5km s 1 no large differences in the structure of the two areas below 250 km are required to explain both the arrival times and the waveforms of sh phases crossing tibet or the indian shield these results show that the structure of tibet is not that of a shield and imply that the indian plate is not underthrusting the whole of the tibetan plateau at the present time

seismic anisotropy beneath tibet evidence for eastward extrusion of the tibetan lithosphere strong seismic anisotropy beneath tibet has recently been reported from the study of sks shear wave splitting the fast split waves are generally polarized in an easterly direction close to the present day direction of motion of the tibetan crust relative to stable eurasia as deduced from holocene slip rates on the major active faults in and around tibet this correlation may be taken to suggest that the whole tibetan lithosphere is being extruded in front of indenting india and that the anisotropic layer is the deforming asthenosphere that accommodates the motion of the tibetan lithosphere relative to the fixed mantle at depth uncertainties about this motion are at present too large to bring unambiguous support to that view assuming that this view is correct however a simple forward model is used to compute theoretical delay times as a function of the thickness of the anisotropic layer the observed delay times would require a 50 100 km thick anisotropic layer beneath south central tibet and an over 200 km thick layer beneath north central tibet where particularly hot asthenosphere has been inferred this study suggests that the asthenospheric anisotropy due to present absolute block motion might be dominant under actively deforming continents

tan lu fault system and its significance in oil accumulation in the central liaodong bay subbasin bohai bay basin china the tan lu fault system in the central liaodong bay subbasin bohai bay basin has complex structural characteristics and its tectonism during the cenozoic is an important factor in oil accumulation three dimensional seismic data were used to document the structural features and evolution of the system variations in source rock occurrence oil catchment area and faulting intensity were comprehensively evaluated to discuss the heterogeneity of oil occurrence along the system detailed analysis of the seismic data indicates a right lateral slip for the tan lu fault system transpression and transtension occur on two branches of the tan lu fault with different orientations indicating a likely slip azimuth that is between the two orientations i e 30 35 the strike slip began at the middle stage of deposition of the shahejie formation and reached its climax during deposition of the first and second members of the dongying formation to date the slip is still continuing in the transpressional system the lower strata on opposite sides of the strike slip fault were shortened and folded whereby the upper strata were stretched and normal faulted as a result a negative flower structure developed immediately above a positive flower structure strain distribution in this system is similar to that in a classic fold moderate tectonic deformation could enlarge the oil catchment area benefiting oil accumulation weak or intense deformation is unfavorable for commercial oil accumulation because of a small oil catchment area and poor oil preservation respectively

cenozoic rifting and volcanism in eastern china a mantle dynamic link to the indo asian collision abstract the indo asian continental collision is known to have had a great impact on crustal deformation in south central asia but its effects on the sublithospheric mantle remain uncertain studies of seismic anisotropy and volcanism have suggested that the collision may have driven significant lateral mantle flow under the asian continent similar to the observed lateral extrusion of asian crustal blocks here we present supporting evidence from p wave travel time seismic tomography and numerical modeling the tomography shows continuous low velocity asthenospheric mantle structures extending from the tibetan plateau to eastern china consistent with the notion of a collision driven lateral mantle extrusion numerical simulations suggest that at the presence of a low viscosity asthenosphere continued mass injection under the indo asian collision zone over the past 50 my could have driven significant lateral extrusion of the asthenospheric mantle leading to diffuse asthenospheric upwelling rifting and widespread cenozoic volcanism in eastern china

the palaeodelta of the proto vatrak and proto mahi rivers of northeastern gujarat india a remote sensing interpretation abstract detailed remote sensing studies carried out in northeastern gujarat india suggest that there has been a major change in the drainage system as evidenced by the presence of a large palaeo delta system the area is drained by two major rivers the mahi and vatrak originating from the aravalli hills to the east which discharge into the gulf of cambay in the indian ocean major lineaments palaeodrainage patterns and palaeodeltas of the vatrak and mahi rivers were delineated these were large rivers in the past with a high discharge and floodplains which were 5 10 km wide most of the palaeodrainage follows the ne sw precambrian lineaments faults indicating their structural control reactivation of these lineaments and differential uplift of the aravalli hills resulted in increased transportation of the eroded sediments and deposition of more than 5 km thick sediments into the tarapur block of the cambay basin the gulf of cambay extended up to the limbasi sojitra petlad area during the quaternary there are implications for petroleum exploration in the sense that the results when integrated with subsurface geological and geophysical data help to delineate the reservoir facies suitable for petroleum exploration along the eastern margin of the tarapur block

multi chronometric dating of the huarong granitoids from the middle yangtze craton implications for the tectonic evolution of eastern china abstract the tectonic thermal history of the huarong granitoids is used to clarify the tectonic evolution of the middle yangtze craton and eastern china the huarong granitoids include the xiaomoshan and taohuashan plutons and form a northeast trending belt in the middle yangtze craton eastern china multi method geochronology reveals the thermal history of the huarong granitoids from their emplacement to near surface conditions la icp ms u pb zircon dating suggests granitoid emplacement at ca 117 ma a cluster of zircons at ca 127 ma is likely inherited from an earlier intrusion phase the granitoids formed in an extensional setting which was almost certainly associated with pacific plate subduction in the late early cretaceous biotite 40ar 39ar ages at ca 96 ma record regional post magmatic cooling apatite fission track aft and apatite u th sm he ahe thermochronology and thermal history modeling indicate cooling in three stages enhanced cooling at 96 60 ma is interpreted to reflect cooling from the late early cretaceous regional magmatism tertiary ca 60 20 ma very slow cooling stagnation or even re heating suggests insignificant exhumation and peneplanation this interval correlates with late cretaceous eocene red bed deposition and rifting throughout eastern china causes for speculative accelerated cooling after ca 20 ma may be a far field effect of the india asia collision or pacific plate subduction this study demonstrates that the middle yangtze craton was involved in the cretaceous extension widely occurring in the eastern china continent and suggests that the formation of the jianghan basin a major depocenter in the middle yangtze craton may have initiated at ca 120 ma