temporal spatial distribution and tectonic implications of the batholiths in the gaoligong tengliang yingjiang area western yunnan constraints from zircon u pb ages and hf isotopes abstract considerable progress has recently been made regarding temporal and spatial distribution of magmatism in the lhasa terrane however the eastward and southeastward correlation of these tibetan magmatic suites in western yunnan and burma remains poorly constrained this paper reports zircon u pb dating and hf isotopic compositions of granites in the gaoligong tengliang yingjiang area west yunnan it reveals three episodes of plutonism and more importantly a southwestward magmatic migration the gaoligong batholiths in the northeast were mainly emplaced during early cretaceous 126 121 ma and comprised predominantly s type granites with negative zircon ehf values ehf 2 12 the tengliang granites situated southwest of the gaoligong belt were emplaced in late cretaceous 68 76 ma and also displayed a strong peraluminous affinity and negative ehf 5 14 indicating a provenance from a proterozoic sedimentary source with little mantle contribution the youngest phase of magmatism 52 66 ma occurred in yingjiang southwestmost of the study area it is composed of s type granites ehf 2 12 in east yingjiang and i type granites ehf 4 6 in west yingjiang near the china burma border the late cretaceous early cenozoic plutons in the tengliang and yingjiang area are thus considered as the northern continuation of the late cretaceous magmatic arc west which comprises i type granites and andesitic rocks and of the belt of predominant s type granites east in burma thailand and malaysia such a chemical polarity of the dual i type and s type granites is strongly reminiscent of the northern american cordillera indicating a cordilleran style continental margin during the late cretaceous early cenozoic while the magmatic arc was related to eastward subduction of the neo tethys beneath the asian continent the s type granites represented the melting products of thickened crust in the hinterland in response to subduction induced decrease in lithospheric strength and compressive plate convergence forces and to a less degree to the collision between burma and sundaland blocks the gaoligong early cretaceous granites which bear strong similarities in lithology geochemistry and emplacement age to those in the northern magmatic belt in the lhasa terrane are also the magmatic expression of crustal thickening this crustal thickening may have stemmed from the collision between the lhasa block and the qiangtang block in late jurassic and early cretaceous the magmatism in western yunnan thus recorded a long term subduction of the neo tethyan plate enhanced by continental collisions at different time

the tectonics and petroleum system of the qiulitagh fold and thrust belt northern tarim basin nw china the timing of hydrocarbon charging relative to trap formation is a key factor for evaluating the exploration potential of the qiulitagh fold and thrust belt qftb on the north flank of the tarim basin data obtained by this study indicate that structural traps were filled by hydrocarbons in two episodes in this area at least four major deformation events have been identified for the period of late cretaceous to pliocene the first event occurred in late cretaceous and led to the formation of paleo uplift structures the second event was characterized by thrust features and occurred in latest oligocene the third and fourth events were represented by compressional structures that were developed in late miocene and late pliocene respectively based on oil and gas source rock correlations and 1 d basin modeling two episodes of hydrocarbon generation and migration are proposed to be responsible for oil and gas accumulations in the qftb the two episodes of hydrocarbon charging from a source kitchen north of the study area took place in early miocene and pliocene respectively since the qftb was uplifted in late oligocene and late miocene the hydrocarbon generated during all two periods could migrate toward this area to form oil and gas accumulations in suitable structures

the grace satellite gravity and geoid fields in analysing large scale cratonic or intracratonic basins the recently released gravity potential field development derived from the gravity recovery and climate experiment satellite allows an unprecedented opportunity to use the gravity field to make global comparisons of structures of geological interest the spatial resolution of the gravity field is sufficiently good to map large scale or intracratonic and cratonic basins as the areal extent of these basins is 0 5 x 10 6 km 2 and greater we present the gravity anomaly bouguer geoid and terrain corrected geoid fields for a selection of nine large scale basins and show that the satellite derived field can be used to successfully identify distinctive structures of these basins e g extinct rifts underlying the basins and generally the isostatic state the studied basins are the eastern barents sea west siberian tarim congo michigan amazon solimoes parnaiba and parana basins we complete the mapping of the gravity field with a description of the basins in terms of areal extension and depth sedimentary age and presence and age of volcanism interpretation of the satellite gravity anomalies and considerations regarding the crustal thickness as known from seismic investigations allows us to conclude that for the greater part of the basins there is evidence for high density material in the lower crust and or upper mantle this density anomaly is at least partly compensating for the low density sedimentary infill instead of the crustal thinning mechanism for our selection of basins crustal thickness variations and moho topography cannot be considered as mechanisms of compensation of the sedimentary loading which is a clear difference to well defined rift basins

rollback orogeny model for the evolution of the swiss alps the construction of the european alps and the himalayas has been related to the convergence and subsequent collision of two continental plates nearly all models of orogeny build on this concept and all of them relate the stacking of nappes and the build up of topography to compressional forces at work in response to the collision between two continental plates for the central european alps however these models fail to explain the first order observations of a mountain belt which particularly includes the striking isostatic imbalance between the low surface topography and the thick crust beneath the alps here we review and synthesize data on the geologic architecture of the central alps the chronology and pattern of crustal deformation and information about the deep crustal structure derived from seismic tomography furthermore we discuss the intrinsic and explicit assumptions in the kinematic models of alpine evolution in the context of plate tectonic considerations we combine these views with progress in understanding that has been gained through subduction and collision isostatic mass and force balancing and with information that has been collected on the modern seismic regime we conclude that a rollback orogeny model for the european plate offers the most suitable concept to explain the ensemble of surface and deep lithosphere observations in this model gravity forces drive the evolution of the orogen and the construction of surface topography is accomplished without the requirement of a hard collision between two continents

three dimensional seismic geomorphology and analysis of the ordovician paleokarst drainage system in the central tabei uplift northern tarim basin western china high quality three dimensional seismic data acquired in the central tabei uplift tarim basin western china provide a rare opportunity to characterize in exceptional detail the three dimensional geomorphology of a deeply buried 5500 6500 m 18 045 21 325 ft ordovician unconformity and the related paleokarst drainage system an integrated approach was applied that emphasized integration of seismic data with available conventional core wireline logs and age equivalent outcrops the exceptional quality of the seismic data allowed a seismic detection limit of karstified features of less than 75 75 m 246 246 ft horizontally and 6 m 20 ft vertically interpreted geomorphologic and depositional elements include fluvial channels and canyons fluvial valleys sinkholes and tower karsts and hills the modern tower karst drainage system in guilin china is very similar to the mapped ordovician karst drainage system and is used as a modern analog the interaction between the surface karst drainage system and the shallow subsurface cave passage system is evidenced by the observation that surface canyons appear to initiate in areas associated with intense sinkhole development also surface river valleys tend to correspond to dip oriented surface depressions partly related to near surface cave collapse during burial into the deeper subsurface the combination of intrastratal collapse karstified strata and suprastratal collapse postkarst deposited strata created large damage zones hundreds of meters thick and kilometers wide coalesced collapsed paleocave systems can be interpreted from the unique circular pattern of faults observed in map view that are associated with seismic bright spots

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

middle late jurassic tectonostratigraphic evolution of central asia implications for the collision of the karakoram lhasa block with asia mesozoic basins in different regions of central asia provide important records for investigating relationships between intraplate deformation in central asia and tectonic processes at asian boundaries the present study gives a review of the stratigraphic and structural evolution of basins in different regions of central asia during the middle late jurassic it is shown that basins and mountain belts in northwest china experienced compressional deformation and were wholly or partially uplifted during the late middle late jurassic compared to extensively distributed middle jurassic coal bearing strata in northwest china upper jurassic strata characterized by red mudstones and conglomerates have a much smaller distribution in the mean time the tibet pamir plateau also underwent a folding and uplift event and upper jurassic sedimentary rocks are generally missing in the pamir and western tibet the intense compressional deformation and uplift event of the late middle late jurassic from the tibet pamir plateau to northwest china requires a new tectonic model as proposed here we suggest that the karakoram and lhasa blocks were a single giant block which was accreted to asia in the late middle jurassic earliest cretaceous and cross cut by the karakoram fault in the cenozoic during the callovian the western part of the karakoram lhasa block initially collided with the southern asian margin collision and continued convergence during the late middle late jurassic caused sinistral strike slip faulting along the central badakhshan fault and south tian shan suture accommodating crustal shortening in areas to the southeast of the faults the pamir western tibet tarim block qilian qaidam block and bei shan meanwhile the northeastward transpressional motion of the tarim block produced strong compressional stresses to areas north of the tarim block the kyrgyz tian shan central tian shan junggar basin and turfan basin with the northward movement of the karakoram lhasa block the eastern part of the karakoram lhasa block began to collide with the southern asian margin during the latest jurassic earliest cretaceous resulting in strong crustal deformation and thickening in east asia and central asia

cenozoic deformation of the tarim basin and surrounding ranges xinjiang china a regional overview abstract with its central position between the tibetan plateau and the tian shan range the tarim basin is a key element of the cenozoic asian orogenic system however a comprehensive regional study and more particularly the quantification of shortening through this basin and its margins are still needed to understand its role in the cenozoic deformation of asia from a compilation of previous works together with an extensive dataset of satellite field seismic and well data we provide a tectonic map of the cenozoic structures and four balanced geological transects of the tarim basin and its surrounding ranges based on this map and these cross sections we characterize the cenozoic deformation of the original proterozoic tarim block from structural restorations and crustal budgets we also quantify the compressive component of this deformation most of the cenozoic compressive deformation from 94 to 100 is concentrated in the ranges along the block margins to the west up to 78 23 km and 54 24 18 km of crustal shortening are accommodated across the compressive western kunlun and southwestern tian shan ranges while to the east up to 38 6 18 km and 15 20 15 km are accommodated across the transpressive altyn tagh and southeastern tian shan ranges a non negligible amount of compressive deformation up to 6 is also accommodated within the tarim basin by large basement cored uplifts with a vergence synthetic to the deformation of the tibetan plateau edge to the west the bachu uplift absorbs 5 km of the total crustal shortening of the western kunlun thrust system while to the south the tanan uplift accumulates 0 6 km of the altyn tagh strike slip system structural inheritance has a major influence on the cenozoic deformation since 33 3 to 100 of the total shortening is accommodated by reactivated basement structures inherited from the protero paleozoic history of the tarim block finally we argue that the basement cored uplifts in the centre of the basin imply a deformation transfer from the tibetan plateau to the tian shan above a deep crustal decollement decoupling the deforming crust from an underlying rigid mantle

orogenic structure of the eastern alps europe from transalp deep seismic reflection profiling abstract the transalp group comprising of partner institutions from italy austria and germany acquired data on a 340 km long deep seismic reflection line crossing the eastern alps between munich and venice although the field work was split into four campaigns between fall 1998 and summer 2001 the project gathered for the first time a continuous profile across the alps using consistent field acquisition and data processing parameters these sections span the orogen itself at its broadest width as well as the editor fred davey and the two adjacent basins vibroseis and explosion data complementary in their depth penetration and resolution characteristics were obtained along with wide angle and teleseismic data the profile shows a bi vergent asymmetric structure of the crust beneath the alpine axis which reaches a maximum thickness of 55 km and 80 100 km long transcrustal ramps the southward dipping sub tauern ramp and the northward dipping sub dolomites ramp strongly reflective patterns of these ramps can be traced towards the north to the inn valley and towards the south to the valsugana thrust belt both of which show enhanced seismicity in the brittle upper crust the seismic sections do not reveal any direct evidence for the presence of the periadriatic fault system the presumed equivalent to the insubric line in the western alps according to our new evolutionary model the sub tauern ramp is linked at depth with remnants of the subducted penninic ocean the crocodile type model describes an upper lower crustal decoupling and wedging of both the european and the adriatic african continents

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

multiple stage migration and accumulation of permian lacustrine mixed oils in the central junggar basin nw china abstract the permian lacustrine petroleum system in the central junggar basin northwest china has recently obtained exploration success these accumulations are characterized by mixed oils and multiple stage migration and accumulation this process however has not been well constrained limiting the understanding of the general laws of hydrocarbon migration and accumulation and making it difficult to define exploration strategies here we reconstruct this process mainly based on oil bearing fluid inclusion analyses including petrography homogenization temperature and sequential extraction inclusion petrography shows that petroleum inclusions dominantly display yellow fluorescence while intergranular free oils mostly display strong blue green fluorescence this implies that the reservoirs seem to have experienced at least two stages of hydrocarbon charge from different sources and or maturities the sources maturities are determined through reservoir sequential extraction analyses the free oils are mixed and sourced from the lower permian fengcheng formation p1f and the middle permian lower wuerhe formation p2w while the inclusion oils are also mixed and derived mainly from the p1f source both oils are characterized by moderate maturity homogenization temperature measurements of oil bearing fluid inclusions combined with reconstruction of reservoir burial and thermal history not only further verify multiple hydrocarbon charging events but also characterize the timing which indicates a three stage petroleum charging model during the first stage of the late triassic carboniferous reservoirs were charged by p1f sourced oils which were dysmigrated or remigrated to jurassic reservoirs during the second stage i e the early cretaceous in contrast the third stage from the late cretaceous represents another hydrocarbon charge event that is the primary oil accumulation sourced from the p2w rocks according to this model both primary and secondary oil accumulations contribute to the current region s exploration success and provide future exploration targets

prediction of ultrathin lacustrine sandstones by joint investigation of tectonic geomorphology and sedimentary geomorphology using seismic data abstract weak seismic signals from ultrathin 1 7 m sandstones increase uncertainties of thickness estimation imposing a significant challenge for accurate prediction of subtle hydrocarbon reservoirs these types of uncertainties however can be reduced by a combined use of kinematic travel time and dynamic amplitude information extracted from 3d seismic data in this case study in the kuqa depression of the tarim basin china we conducted an investigation of seismic based tectonic geomorphology and then sedimentary geomorphology in four steps 1 reconstruction of basin floor paleogeomorphology using a residual structure map of a closely underlain erosional unconformity 2 study of seismic lithology by seismic modeling and 90 phase adjustment of seismic traces 3 mapping of geomorphologic patterns of depositional systems on stratal slices and 4 combined analysis of tectonic geomorphology and sedimentary geomorphology for a better understanding of depositional history and reservoir distribution results show a good match between valley and lowland systems on the basin floor sandstone thickness trend and lobate sedimentary geomorphologic patterns indicating a widespread yet laterally highly variable ultrathin sandy fan delta system

far source long period displacement response spectra in the po and venetian plains italy from 3d wavefield simulations abstract design elastic displacement spectra for seismic codes and zoning studies of seismic hazard for long period structures are becoming of utmost importance in modern earthquake engineering the increase of displacement based design approaches together with the availability of good quality digital strong motion data allow the creation of reliable spectral shapes for seismic design of up to 10 s nevertheless to characterize the site amplification effects during large levels of shaking additional studies are needed especially in deep sedimentary basins and plains that can be strongly excited by large amplitude long period waves data within deep basins is rare because accelerometric seismic networks are normally deployed on rock or stiff soil and modeling of waveforms is hence necessary for bridging this gap focusing on the numerical modeling of the 3d wavefield in 1d flat layered and 3d structures in the po and venetian plains northern italy and on earthquakes with magnitudes m 6 6 and hypocentral distances greater than 50 km in this study we 1 estimate the displacement response spectra drs from 1 to 10 s in the po and venetian plains 2 compare the drs from numerical simulations using flat layered and heterogeneous 3d models against the currently available uniform hazard drs for italy and 3 evaluate the influence of deep sediments on drs shape and thus on seismic codes finally 1d and 3d simulated drs are compared with drs obtained from recordings in the kanto basin where similar long period displacement is observed

late paleozoic depositional history of the tarim basin northwest china an integration of biostratigraphic and lithostratigraphic constraints this study provides the first detailed lithostratigraphic and biostratigraphic constraints for improving stratigraphic resolution for hydrocarbon prospecting and exploration in the tarim basin a total of 49 stratigraphic units 38 formations and 11 members ranging in age from the latest devonian to permian are reviewed or redefined in terms of nomenclatures lithology age constraints and lateral distributions based on the detailed field works or newly published data of these the piqiang formation new formation is proposed to include the reefal carbonates of asselian sakmarian age from the northern tarim the subsurface upper paleozoic stratigraphic framework of the desert areas of the basin is also established for the first time the high resolution basinwide stratigraphic correlations reveal that the sedimentation of the basin in the late paleozoic was extremely uneven of these the famennian to changhsingian successions are completely recorded in the southwestern margin areas of the basin here five eustatic sedimentary cycles are well recognizable suggesting the sedimentation was more eustatically controlled and little affected by local tectonism the late paleozoic successions of both kalpin and taklimakan regions are commonly interrupted by major hiatuses at various horizons suggesting that the sedimentation was apparently modified by local tectonism of these the northward movement of the tarim block and its subsequent collision with the yili microcontinent part of the kazakhstan plate may be principally accountable for the discrepancy in the sedimentation of the various regions in the basin in the late paleozoic

late cenozoic slip on the talas ferghana fault the tien shan central asia although cenozoic crustal shortening and thickening by thrust faulting have built the present tien shan active right lateral shear on the northwest trending talas ferghana fault appears to be the most rapid localized deformation in the belt ephemeral stream valleys have been offset right laterally tens of metres new and published radiocarbon dates of organic material deposited in depressions blocked by offset ridges place upper bounds on the average holocene slip rate at 18 localities uncertainties allow 14 upper bounds to overlap the range of 8 16 mm yr and 95 confidence limits on such bounds at 11 sites are entirely within this range we infer that the rate of 10 mm yr is not simply an upper bound but applies to the late holocene epoch although the bounds on rates permit more rapid slip in the northwest than the southeast they do not place a useful constraint on variations in slip rate along the fault offsets of paleozoic facies boundaries imply a total right lateral shear of 180 250 km but early cretaceous sedimentary rock appears to have been offset only 60 10 km published paleomagnetic declinations of cretaceous miocene rock demonstrate 20 30 of counterclockwise rotation of the ferghana valley which lies just west of the talas ferghana fault with respect to stable parts of eurasia and 20 11 with respect to the central tien shan east of the fault these declinations are consistent with a maximum northwestward translation of 70 210 km of the ferghana valley at the talas ferghana fault and therefore with a similar maximum horizontal shortening across the chatkal ranges which lie between the ferghana valley and the kazakh platform estimates of crustal thickness beneath the chatkal ranges however permit only 60 100 km of cenozoic shortening if 100 km of slip on the talas ferghana fault accumulated at a constant rate of 10 mm yr it would imply an initiation of slip more recently than ca 10 ma long after india collided with the rest of eurasia

moho reflection effects in the po plain northern italy observed from instrumental and intensity data abstract recent moderate sized earthquakes m l 5 2 that occurred in northern italy demonstrate that the currently available ground motion prediction equations gmpes largely underestimate shaking in the po plain region at hypocentral distances greater than 70 km in order to investigate this phenomenon we collected a set of peak ground acceleration pga observations for weak and moderate earthquakes in the area nonparametric regression analysis of pga observations as a function of magnitude and hypocentral distance shows that pga is systematically enhanced for distances between 70 and 200 km an indirect estimation through the analysis of the attenuation of macroseismic intensities suggests that the effect also applies to strong earthquakes m l 5 5 we performed numerical modeling experiments to investigate the cause of the phenomenon the characteristics of the computed synthetic seismograms indicate that the enhancement of ground motion is mainly an effect of the reflection of s waves at the moho sms phase the analysis of both real and synthetic data shows that the moho reflection effect is maximized at hypocentral distances between 90 and 150 km where the pga increases by a factor larger than 2 4

insights into the damage zones in fault bend folds from geomechanical models and field data abstract understanding the rock mass deformation and stress states the fracture development and distribution are critical to a range of endeavors including oil and gas exploration and development and geothermal reservoir characterization and management geomechanical modeling can be used to simulate the forming processes of faults and folds and predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses this approach enables the development of forward models that incorporate realistic mechanical stratigraphy e g the bed thickness bedding planes and competence contrasts include faults and bedding slip surfaces as frictional sliding interfaces reproduce the geometry of the fold structures and allow tracking strain and stress through the whole deformation process in this present study we combine field observations and finite element models to calibrate the development and distribution of fractures in the fault bend folds and discuss the mechanical controls e g the slip displacement ramp cutoff angle frictional coefficient of interlayers and faults that are able to influence the development and distribution of fractures during fault bend folding a linear relationship between the slip displacement and the fracture damage zone the ramp cutoff angle and the fracture damage zone and the frictional coefficient of interlayers and faults and the fracture damage zone was established respectively based on the geomechanical modeling results these mechanical controls mentioned above altogether contribute to influence and control the development and distribution of fractures in the fault bend folds

the south china block indochina collision where when and how this study uses new field observations and existing studies to shed new light on the origin and significance of two nw se striking orogens in nw and ne vietnam we conclude that the architecture of each belt is a stack of ne directed nappes formed either under deep ductile synmetamorphic conditions or under shallow depth in the sw and ne parts respectively the song ma zone and song chay ophiolitic melange represent two ophiolitic sutures however the late permian song da and babu mafic rocks are not ophiolites but intraplate basalts related to the emeishan plume a late triassic unconformity the 225 205 ma postorogenic plutonism and the 250 230 ma syntectonic metamorphism support an early to middle triassic age for these tectonic events both nw and ne belts are due to sw directed subduction with arc magmatism ocean closure and continental collision though two contemporary s dipping subduction zones might explain the structural evolution of the two belts a single convergent system offset by the tertiary red river fault is preferred as this s directed subduction better accounts for the late permian intraplate magmatism this scenario is discussed in the general geodynamic framework of se asia

using fluvial cyclicity to decipher the interaction of basement and fold thrust belt tectonics in a broken foreland basin vinchina formation miocene northwestern argentina abstract the miocene vinchina formation is made up of more than 5100 meters of siliciclastic sediments deposited mostly in fluvial environments in a broken foreland basin without any connection with the sea during a period of arid to semiarid climatic conditions repetitive changes in fluvial facies allow the subdivision of the formation into seven cyclothems each floored by a subaerial unconformity within sequence changes in fluvial systems determined by the proportion of channel vs floodplain multi story vs single story channels and channel connectedness were controlled by changes in accommodation proximal i e northern and younger sequences show transitions from braided to low sinuosity wandering or high sinuosity meandering fluvial systems whereas more distal sequences southern and older show changes from sand bed dominated to anastomosed systems bounding unconformities and facies stacking patterns are used to define six third order depositional sequences depositional sequences in the vinchina formation are either asymmetrical showing a fining upward trend or nearly symmetrical sand clock type each cyclothem is bounded by an incision surface sequence boundary developed during a base level i e fluvial equilibrium profile fall and initial base level rise floored by basal coarse grained deposits representing the low accommodation systems tract last the overlying sediments fine upward and contain both isolated and multistory sandstone bodies within extensive flood plain deposits corresponding to the early high accommodation systems tract hast this interval is sometimes capped by sheets of amalgamated sandstones corresponding to the late hast and developed during a decline in the rate of base level rise the development and or preservation of the capping amalgamated sandstones and therefore the symmetrical shape of the sequences is favored in high accommodation settings vertical and lateral facies changes recorded in the vinchina formation indicate that both the fold and thrust belt located to the west and an uplifted basement block to the north played important roles controlling subsidence source areas and drainage patterns the stratigraphic record of this broken foreland basin differ from the existing models for simple foreland basins and can be compared to those of the laramide sedimentary basins in the united states

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

cenozoic deformation of the kalpin fold and thrust belt southern chinese tian shan new insights from low t thermochronology and sandbox modeling abstract the kalpin fold and thrust belt ftb was active during the cenozoic and accommodated crustal shortening between the tian shan and tarim basin to constrain the timing of thrusting in the yimugantawu and kepingtag thrust sheets from north to south in the central area of the kalpin ftb we performed apatite fission track aft and apatite u th he ahe dating as well as sandbox experiments the aft central ages of the yimugantawu and kepingtag thrust sheets range from 93 0 to 148 7 ma single grain ahe ages of the kepingtag thrust sheet 10 7 27 1 ma are younger than those of the yimugantawu thrust sheet 15 1 82 5 ma indicating a southward propagation of the cenozoic deformation combined inverse and forward thermal modeling suggest that the yimugantawu and kepingtag thrust sheets underwent initial cooling and deformation at 25 20 ma and 15 10 ma respectively the sandbox experiments also suggest that the yimugantawu thrust sheet underwent deformation before the kepingtag thrust sheet was activated confirming the sequence revealed by low t thermochronology this study provides new insights into the timing of deformation at the northern margin of the tarim basin which can significantly enhance understanding of the tectonic evolution of central asia

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

lithospheric structure of western tibet a brief review abstract over the course of the last hundred years or so there have been countless seismic experiments conducted under the aegis of different research programs which have aimed to investigate the structure of the crust and uppermost mantle of the western tibetan plateau however there have been fewer detailed lithographic studies of the western sector of the tibetan plateau and those that have been conducted have principally fallen under the research umbrella of the antilope array network of tibetan international lithospheric observation and probe experiments in this paper we summarize the important research findings that have been gathered using comprehensive geophysical profiles and provide an overall view of the lithospheric structure of the western tibetan plateau that has resulted from the onset of tectonic collision and the continuous convergence of the indian and eurasian plates since 65 ma ago in western tibet the subducted indian lithospheric mantle is moving towards the northern edge of the plateau colliding with the tarim basin at 80 e however the tarim basin shows different nature of subductions in eastern central and western regions itself the maximum moho depth 93 km beneath the qiangtang terrane marks the northern margin of the decoupled underthrusting indian plate s lower crust and the lithospheric mantle the broader stronger terrain of the western tibetan plateau may indicate an eastward broadening shape and a lower cenozoic shortening and the relatively larger width of the lhasa qiangtang terranes may be a key factor controlling the geodynamic evolution of the tibetan plateau

seismic interpretation of the kelasu triangle zone in the southern tian shan foothills northwestern china seismic reflection data show that the kelasu structure a frontal structure of the south tian shan foothills thrust belt is a triangle zone with the upper detachment following an overpressured lower tertiary anhydrite zone and the lower detachment zone probably in the lower mesozoic seismic reflectors the south verging thrusts emerging at the surface are the small roof structures rooted in the upper detachment although the upper detachment was a relatively lubricated surface the passively folded formations show strong resistance to the blind wedging underneath particularly in the anticlines during the triangle zone development as a result of the massive shear forces created by the opposing movement of the two tectonostratigraphic units the top part of the thrust sheets immediately under the crest of the frontal anticline was ripped off in the form of backthrusting and brecciation the large backthrust fault blocks and breccias were retained in the anticlines whereas the underlying duplex continued wedging toward the foreland in the early formed duplex structures in the hinterland the tips of the thrust sheets were completely shredded leaving sharp angular contacts between the thrust sheets and the upper detachment surface different types of fractures and present day geostress stress of the earth measured along the wellbore interpreted from the borehole image logs suggest a complex deformation history and reversal of geostress the kelar gas reservoirs are located within the backthrust fault blocks under the frontal anticline the current model reduces the previous concerns about potential damage to the anhydrite seal by the surface thrusts because the thrusts occurred entirely above the seal more importantly because the reservoir rocks are repeated many times in the duplex thrust sheets below the continuous anhydrite seal any anticlinal structure of the upper detachment surface is a potential prospect

effect of basement structure and salt tectonics on deformation styles along strike an example from the kuqa fold thrust belt west china abstract the kuqa fold thrust belt kftb has a complex thrust system geometry and comprises basement involved thrusts decollement thrusts triangle zones strike slip faults transpressional faults and pop up structures these structures combined with the effects of paleogene salt tectonics and paleozoic basement uplift form a complex structural zone trending e w interpretation and comprehensive analysis of recent high quality seismic data field observations boreholes and gravity data covering the kftb has been performed to understand the characteristics and mechanisms of the deformation styles along strike regional sections fold thrust system maps of the surface and the sub salt layer salt and basement structure distribution maps have been created and a comprehensive analysis of thrust systems performed the results indicate that the thrust fold system in paleogene salt range can be divided into five segments from east to west the kela 3 keshen dabei bozi and awate segments in the easternmost and westernmost parts of the paleogene salt range strike slip faulting and basement involved thrusting are the dominant deformation styles as basement uplift and the limits of the cenozoic evaporite deposit are the main controls on deformation salt core detachment fold thrust systems coincide with areas of salt tectonics and pop up imbricate and duplex structures are associated with the main thrust faults in the sub salt layer distribution maps of thrust systems basement structures and salt tectonics show that paleozoic basement uplift controlled the paleozoic foreland basin morphology and the distribution of cenozoic salt in the kftb and thus had a strong influence on the segmented structural deformation and evolution of the fold thrust belt three types of transfer zone are identified based on the characteristics of the salt layer and basement uplift and the effects of these zones on the fault systems are evaluated basement uplift and the boundary of the salt deposit generated strike slip faults in the sub salt layer and supra salt layers at the basin boundary model a when changes in the basement occurred within the salt basin strike slip faults controlled the deformation styles in the sub salt layer and shear zone dominated in the supra salt layer model b a homogeneous basement and discontinues salt layer formed different accommodation zones in the sub and supra salt layers model c in the sub salt layer the thrusts form imbricate structures on the basal decollement whereas the supra salt layer shows overlapping discontinuous faults and folds with kinds of salt tectonics and has greater structural variation than the sub salt layer

junggar turfan and alakol basins as late permian to early triassic extensional structures in a sinistral shear zone in the altaid orogenic collage central asia the junggar turfan and alakol basins in northwestern china and kazakhstan formed as late permian to early triassic extensional structures in a broad sinistral shear zone between large strike slip faults that separate two main domains of the altaid orogenic collage this extension was in response to an inferred large l000 km sinistral motion of the east european craton with respect to the angaran craton during this time deformation associated with the formation of the basins was taken up in part by counter clockwise rotations of crustal blocks with respect to the altaid orogenic collage and to the angaran craton this event is the only important phase of extension in a region otherwise dominated by compressional tectonics throughout the phanerozoic the basement rocks of these basins formed by altaid subduction accretion through the latter half of the palaeozoic and the region was subsequently thrown into compression again during the mesozoic cimmeride and cenozoic alpide evolution

characterization of braided river delta facies in the tarim basin lower cretaceous application of borehole image logs with comparative outcrops and cores abstract borehole electrical image log with core like presentation is an efficient way to conduct sedimentary description in the subsurface the key is to set up a series of geological diagnostic criteria the subsurface lower cretaceous bashijiqike formation in the kelasu belt kuqa depression described as a sedimentary facies of braided river delta front has measured a mass of borehole image logs and open hole logs at depths more than 6000 m combined with comparative outcrops limited cores and thin sections high quality borehole images were fine calibrated to reveal their sedimentary details with the aim of subtle sedimentary interpretation in the uncored intervals the image elements all have corresponding geological indications the lithologies are interpreted including mudstones siltstones fine and medium sandstones and conglomerates and the sedimentary structures are interpreted in terms of various bedding types scoured surface and stacking modes thus interdistributary bay sandy or conglomerate subaqueous distributary channel and channel mouth bar are interpreted based on the lithologies sedimentary structures and textures basal and top contacts and succession variations furthermore determination of paleo current direction using borehole image logs is proposed for some time but is far from mature and need to consider tectonic deformation settings of studied stratigraphy based on this the paleo current in the kelasu belt is interpreted to flow southward from the southern tianshan to the depression during the early cretaceous which is consistent with the results derived from the heavy mineral analysis however the subaqueous distributary channels could frequently migrate locally and the paleo current direction changed at localities with an offset angle varied between 30 and 150 regionally the scale of single sand body decreases lakeward and the sand body may stretch at a maximum distance of 685 1 m along the flow direction the diagnostic criteria and the workflow for borehole image interpretation in this study will have potential application to subsurface sedimentary description and guide sedimentary architecture where cores are not available

origin of a cretaceous low 18o granitoid complex in the active continental margin of se china abstract low 18o felsic igneous rocks with 18o values of 1 low sr y 7 23 49 5 and la yb ratios 6 87 46 0 and relatively low zr saturation temperatures 730 c in addition the diorites and granodiorites contain a variety of inherited high ca plagioclase an 60 87 we demonstrate that the xiaocuo granitoid rocks were derived from preexisting subduction related metabasic source rocks their low 18ozrc values 3 8 5 2 are reflective of their source compositions the formation of the low 18o source rocks is most likely formed in a subduction induced lithospheric extension regime during early jurassic to early cretaceous time when a basin and range like province developed in se china intensive lithospheric extension could have increased the fracture permeability and facilitated deep circulated surface waters for exchanging with the source rocks at high temperature at depth making the metabasic source rocks depleted in 18o remelting of the 18o depleted metabasic intrusive source rocks produced the xiaocuo low 18o granitoid complex at 116 ma our work indicates that in addition to the caldera and rift settings extensional active continental margin could also be a favorable setting for the formation of low 18o granitoid rocks

active tectonics of the pamirs and karakorum the source parameters of moderate to large sized earthquakes and the spatial distribution of earthquake hypocenters are used to investigate the active tectonics and three dimensional configuration of the subducted lithosphere in the pamir karakorum intracontinental convergence zone the continental collision has resulted in intense deformation in the upper crust the deformation is distributed over a broad area and is absorbed by thrust and strike slip faulting along the northern margin of the pamirs where the deformation due to continental collision is most intense the northern pamir thrust and several major fault zones mark the present boundary most of the earthquakes that occurred in these fault zones are shallow crustal events with focal mechanism solutions correlated with the tectonic features of the region along the pamir front thrust faulting dominates while on the western and eastern edges of the pamirs the style of deformation is characterized by oblique thrusting with a component of strike slip motion thrust type events beneath the tadjik depression indicate that both the sedimentary rocks and the basement are involved in shortening right lateral strike slip motion is observed on the eastern edge of the pamirs where they border the tarim basin and in the talas fergana kun lun fault zone a southward dipping seismic zone beneath the pamirs and karakorum indicates that the asian lithosphere has been subducted along the pamir front to a depth of at least 200 km this interpretation is consistent with published geological and geophysical data focal mechanism solutions of some intermediate depth events beneath the pamirs show strike slip faulting with approximately n s horizontally oriented p axes indicating that nearly horizontal compression at the intermediate depth is the predominant mode of deformation a 90 km deep event beneath the karakorum is interpreted as occurring in the subducted asian lithosphere the fact that the p axis of this event is oriented parallel to the descending plate suggests downdip compression within the asian lithosphere the overall tectonics of the region is interpreted as a consequence of the underthrusting asian lithosphere being impinged upon by the shallow northward underthrusting indian lithosphere

forward and inverse modelling of gravity revealing insight into crustal structures of the eastern alps abstract the crustal structure of the eastern alps is less known than that of the western alps as participants of the european geotraverse and particular swiss projects investigated the alpine crust there recently the eastern alps were subject to seismic research which was conducted in the context of the german austrian and italian transalp project the 3d modelling of the density structure which is presented in this paper belonged to a series of piggy back projects which were closely accomplished using the seismic reflection studies we present a combined gravity seismic interpretation which is based on the results of both older deep seismic profiles and the new transalp profile special emphasis was laid on geologic and tectonic information which served as model constraints for near surface structures a 3d forward modelling of both the bouguer gravity field and the geoidal undulations provides in depth insight into the lithosphere and considers the constraints due to the uncertainties of used constraints particularly in depths of the eastern alpine moho an inversion technique complemented this study and provided insight into the shape and density contrast at the crust mantle interface the modelling indicates that the bouguer gravity field in the eastern alps is mainly caused by two sources the density contrast at the crust mantle boundary 350 kg m3 and the density inhomogeneities in the upper 10 km of the crust which contributes to the overall gravity field by amounts of approximately 30 10 5 m s2 the results of the forward and inverse modelling produced a shallower crust mantle boundary in the southern adriatic area in comparison with the northern part and differs from the seismic findings of the transalp group to some extent this observation and observable mismatch in the long wavelength model and the observed geoidal undulations point to density inhomogeneities in sub crustal and even sub lithospheric depths these deep seated inhomogeneities should have a substantial bearing on the isostatic balance of the eastern alps

late permian paleomagnetic pole from dikes of the tarim craton china we have obtained a late permian paleomagnetic pole from dikes in the tarim craton of china directions of magnetization from 21 mafic and ultramafic dikes at three localities pass a fold test at the 95 confidence level the new paleomagnetic pole lies at lat 66 n long 181 e n 21 k 61 and 95 3 9 on the basis of a comparison with paleomagnetic data from adjacent tectonic units we conclude that 1 the late permian paleolatitude of the tarim craton differs from that of the sino korean craton suggesting that the two cratons were distinct tectonic units in late permian time 2 there was relative motion between the tarim craton and the siberian craton after late permian time and 3 negligible relative motions have occured between different thrust sheets in the keping bachu area of the north western tarim craton

impact of an interbedded viscous decollement on the structural and kinematic coupling in fold and thrust belts insights from analogue modeling abstract fold and thrust belts ftbs can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance in this study we investigated along across strike structural interactions in a ftb propagating toward a foreland which displays contrasted lithological sequences a set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series the tectonic interaction between the viscous and the frictional provinces was tested both along and across strike results indicate that a frictional province influences the along strike tectonic evolution of an adjacent viscous province this influence decreases when the width of the viscous province increases the frictional provinces control the taper structural style obliquity of the structures trend and kinematics of the shallow deformation front of the viscous province results evidence how far a frictional province can impact the deformation of an adjacent viscous province for frictional viscous wedges it appears that the critical taper theory which is generally applied in 2 d should be likely considered in terms of 3 d moreover the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and frictional provinces experimental results are compared to natural examples in the kuqa basin southern tian shan china and the salt range pakistan and give an insight to a better understanding of the dynamics of fold and thrust belts bearing a viscous decollement such as salt

characterizing seismic bright spots in deeply buried ordovician paleokarst strata central tabei uplift tarim basin western china anomalous seismic amplitude bright spots are a common feature in deeply buried 5500 to 6500 m ordovician limestone strata in the central tabei uplift area of the tarim basin in northwest china those anomalies have proven to be useful indicators of reservoir quality the bright spots as seen on seismic data are tied to high gamma ray low velocity zones in wireline logs and correspond to clastic cave sediment fills in the host limestone in core synthetic seismic models confirm this relationship between seismic bright spots and cave sediment fills a seismic traveltime map of the top ordovician unconformity illustrates erosional topography and seismic geomorphologic patterns associated with the unconformity with numerous sinuous fluvial channels and canyons fluvial valleys sinkholes and tower karsts and hills a mature surface drainage system interacted with a near surface karst system and allowed terrigenous sediments to enter an underground cave system karst related bright spots probably correspo

structural features of northern tarim basin implications for regional tectonics and petroleum traps the rhombus shaped tarim basin in northwestern china is controlled mainly by two left lateral strike slip systems the northeast trending altun fault zone along its southeastern side and the northeast trending aheqi fault zone along its northwestern side in this paper we discuss the northern tarim basin s structural features which include three main tectonic units the kalpin uplift the kuqa depression and the north tarim uplift along the northern margin of the tarim basin structural mapping in the kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike slip faulting the amount of strike slip displacement is estimated to be 148 km by restoration of strike slip structures in the uplift the kuqa depression is a mesozoic cenozoic foredeep depression with well developed flat ramp structures and fault related folds the baicheng basin a quaternary pull apart basin developed at the center of the kuqa depression subsurface structures in the north tarim uplift can be divided into the mesozoic cenozoic and the paleozoic lithotectonic sequences in seismic profiles the paleozoic litho tectonic sequence exhibits the interference of earlier left lateral and later right lateral strike slip structures many normal faults in the mesozoic cenozoic litho tectonic sequence form the negative flower structures in the north tarim uplift these structures commonly directly overlie the positive flower structures in the paleozoic litho tectonic sequence the interference regions of the northwest trending and northeast trending folds in the paleozoic tectonic sequence have been identified to have the best trap structures our structural analysis indicates that the tarim basin is a transpressional foreland basin rejuvenated during the cenozoic

evaluating the evolution of the red river system based on in situ u pb dating and hf isotope analysis of zircons 1 the red river originates from sw china and se tibet and has a total length 1000 km in this study we present new u pb dating and hf isotopic analysis of zircon grains from both modern and paleoriver sands in order to constrain the provenance of the modern river and to decipher drainage evolution through time our data show that the yangtze and songpan garze blocks are the most important sources for sediment although this material is mostly reworked via younger sedimentary rocks in the upper reaches of the red river sands in the da river and to a lesser extent the lo river have zircon ages indicating that they are minor contributors to the net flow consistent with rock uplift which is strongest in the upper reaches of the red river rather than precipitation being the primary control on erosion sediments eroded from the metamorphic rocks along the red river fault zone appear to have made a greater contribution during the miocene zircon ages suggest that the red river flowed north of the day nui con voi in the middle late miocene the red river appears to have had a largely stable provenance since at least the late miocene upper miocene sedimentary rocks ne of the red river indicate the presence of a separate large river in the late miocene hf isotope data indicate that the irrawaddy river was never part of the red river system although we do not exclude the salween mekong and yangtze rivers from having been part of the red river any connection must have been pre middle miocene

in situ zircon u pb and hf o isotopic results for ca 73 ma granite in hainan island implications for the termination of an andean type active continental margin in southeast china abstract we report in the paper integrated analyses of in situ zircon u pb ages hf o isotopes whole rock geochemistry and sr nd isotopes for the longlou granite in northern hainan island southeast china sims zircon u pb dating results yield a crystallization age of 73 ma for the longlou granite which is the youngest granite recognized in southeast china the granite rocks are characterized by high sio2 and k2o weakly peraluminous a cnk 1 04 1 10 depletion in sr ba and high field strength elements hfse and enrichment in lree and large ion lithophile elements lile chemical variations of the granite are dominated by fractional crystallization of feldspar biotite ti fe oxides and apatite their whole rock initial 87sr 86sr ratios 0 7073 0 7107 and end t 4 6 to 6 6 and zircon ehf t 5 0 to 0 8 values are broadly consistent with those of the late mesozoic granites in southeast china coast zircon 18o values of 6 9 8 3 suggest insignificant involvement of supracrustal materials in the granites these granites are likely generated by partial melting of medium to high k basaltic rocks in an active continental margin related to subduction of the pacific plate the ca 73 ma longlou granite is broadly coeval with the campanian ca 80 70 ma granitoid rocks in southwest japan and south korea indicating that they might be formed along a common andean type active continental margin of east southeast asia tectonic transition from the andean type to the west pacific type continental margin of southeast china likely took place at ca 70 ma rather than ca 90 85 ma as previously thought

a sub salt structural model of the kelasu structure in the kuqa foreland basin northwest china abstract the kuqa foreland basin adjacent to the south tianshan mountains is a major hydrocarbon accumulation basin in western china the kelasu structural belt is the focus for hydrocarbon exploration in the basin due to the presence of ramp related anticline traps and a thick salt seal the model of the kelasu sub salt structure is still contentious because of the structural complexity and poor seismic imaging below the salt layer the area depth strain ads method is applied to the southern part of the kelasu fault a regional fault that cuts basement rocks the ads results are consistent with the seismic data which indicate that both thin skinned thrusting and basement involved deformation occur within the kelasu structure with the kelasu fault acting as the boundary between the two regions of contrasting deformation the ads results also suggest that the depth of the lower detachment of the thin skinned thrust belt is 9 5 10 km which may correspond to the base of the triassic the kelasu structure has undergone approximately 8 15 10 76 km of horizontal shortening in the east and 16 34 km in the west of the structure

the crustal structure of the eastern alps from a combination of 3d gravity modelling and isostatic investigations abstract the transition between european and adriatic crust is an important feature related to the plate collision that formed the european alps the diversity of seismic and geological information allows the construction of two alternative 3d density models which both match the observed gravity field different seismic experiments suggest a thickness for the adriatic crust between 30 and 40 km the thick crust model requires an unusually dense lower crust 3050 kg m 3 to reproduce the observed bouguer anomaly to evaluate the two alternative models the isostatic implications of the geometry and density distribution within both 3d models are investigated using local airy and regional vening meinesz isostasy airy isostatic investigations show that the eastern alps are not isostatically compensated and the residuals correlate strongly with exposed geological formations subsequently subsurface loading is an important factor controlling isostatic processes the different geometry and densities in the two 3d models imply different loading at the crust mantle boundary the subsurface loads calculated from the 3d density models were used to estimate regional isostasy by a convolution method in general small rigidity values d 21 nm are determined for the eastern alpine lithosphere in the model with a 40 km thick adriatic crust high flexural rigidities are inferred for the adriatic plate 100 10 21 nm but these values are unusual for an active orogenic region the results point to the interfingering of european and adriatic crust that results in the squeezing of european crust between adriatic crust and mantle with additional contamination by mantle material

the effect of overburden thickness on deformation mechanisms in the keping fold thrust belt southwestern chinese tian shan mountains insights from analogue modeling abstract the structural evolution of the keping fold thrust belt in the south chinese tian shan nw china is poorly understood here we present the results of a series of scaled sandbox models based on the structural architecture of the keping fold thrust belt in our investigation of the effect of overburden thickness on deformation mechanisms in fold thrust belts these models simulated the evolution of the keping fold thrust belt where the western segment was shortened with a thicker overburden relative to the eastern segment model results confirm that fewer thrust faults with wider spacing develop in thicker cover units whereas more thrust faults with narrower spacing develop in thinner cover units transfer zones also form as a result of faster and farther propagation in a segment with thicker overburden consistent with the prediction of the critical taper theory our modeling further shows that due to the episodic accretion of thrust wedges and non simultaneous formation of thrust faults the deformation front may locally propagate farther in the thinner overburden alternatively there may not be so much difference between two parts of sand layers with different thicknesses an observation that is inconsistent with the theoretical prediction the similarities between the model and real geological observations suggest that the variations in the overburden thicknesses across the piqiang fault transfer zone strongly influenced the development of the structural architecture of the keping fold thrust belt they further indicate that the growth of fold thrust belts in nature is episodic and that the propagation of deformation front cannot be simply predicted by the critical taper theory the overburden thickness variations across the piqiang fault transfer zone were produced by high angle reverse faulting along the pre existing piqiang selibuya fault during the late pliocene and associated crustal uplift and erosion of the hanging wall strata

a natural and controlled source seismic profile through the eastern alps transalp abstract the combined passive and active seismic transalp experiment produced an unprecedented high resolution crustal image of the eastern alps between munich and venice the european and adriatic mohos em and am respectively are clearly imaged with different seismic techniques near vertical incidence reflections and receiver functions rfs the european moho dips gently southward from 35 km beneath the northern foreland to a maximum depth of 55 km beneath the central part of the eastern alps whereas the adriatic moho is imaged primarily by receiver functions at a relatively constant depth of about 40 km in both data sets we have also detected first order alpine shear zones such as the helvetic detachment inntal fault and sub tauern ramp in the north apart from the valsugana thrust receiver functions in the southern part of the eastern alps have also observed a north dipping interface which may penetrate the entire adriatic crust adriatic crust interface aci deep crustal seismicity may be related to the aci we interpret the aci as the currently active retroshear zone in the doubly vergent alpine collisional belt

upper mantle structure beneath the alpine orogen from high resolution teleseismic tomography 1 to understand the evolution of the alpine orogen knowledge of the actual structure of the lithosphere asthenosphere system is important we perform high resolution teleseismic tomography with manually picked p wave arrival times from seismograms recorded in the greater alpine region the resulting data set consists of 4199 relative p wave arrivals and 499 absolute p wave arrivals from 76 teleseismic events corrected for the contribution of the alpine crust to the travel times the three dimensional 3 d crustal model established from controlled source seismology data for that purpose represents the large scale alpine crustal structure absolute p wave arrival times are used to compute an initial reference model for the inversion tests with synthetic data document that the combination of nonlinear inversion high quality teleseismic data and usage of an a priori 3 d crustal model allows a reliable resolution of cells at 50 km 50 km 30 km hence structures as small as two cells can be resolved in the upper mantle our tomographic images illuminate the structure of the uppermost mantle to depth of 400 km along strike of the alps the inversion reveals a high velocity structure that dips toward the se beneath the adriatic microplate in the western and central alps in the eastern alps we observe a northeastward dipping feature subducting beneath the european plate we interpret this feature in the western and central alps as subducted mainly continental european lower lithosphere for the east we propose that parts of the vardar oceanic basin were subducted toward the ne forcing continental adriatic lower lithosphere to subduct northeastward beneath the european plate

u pb age and hf o isotopes of detrital zircons from hainan island implications for mesozoic subduction models abstract a compilation of magmatic ages from the mesozoic south china block suggests a number of magmatic quiescence periods at ca 205 195 ma ca 150 140 ma and ca 125 115 ma casting doubt on tectonic models that suggest ongoing andean type subduction along the south china continental margin however sims u pb analyses on two detrital zircon samples from the cretaceous lumuwan formation on hainan island southeast china reveal three major age peaks at ca 120 ma ca 155 ma and ca 235 ma zircons of these ages are mostly euhedral and show typical magmatic oscillatory zoning suggesting short distance transport from nearby magmatic sources the extremely rare occurrence of ca 120 ma magmatic records onshore suggests that detrital zircons of this age population may be derived from a source proximal to hainan island but presently missing therefore our data provide new evidence for ongoing magmatic activity in late mesozoic south china in situ hf and o isotope analyses of the mesozoic detrital zircons reveal large variations in both ehf t 21 2 to 10 5 and 18o 4 4 to 13 6 values a general negative correlation between them suggests the reworking of old supracrustal materials average crustal residence age of ca 2 0 ga by juvenile mantle derived magmas the progression of increasing ehf t and decreasing 18o values of zircons from the triassic to the cretaceous suggests progressive crustal growth during the mesozoic the results are consistent with hybridization at an active continental margin we briefly review tectonic models for the indosinian orogeny and suggest that the petrologic evidence indicates that mesozoic magmatism was part of the circum pacific accretionary orogens that formed along the continental margin of east asia no later than ca 250 ma and continued at least to the late cretaceous

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

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

the crust of cathaysia age assembly and reworking of two terranes abstract u pb dating and hf isotope data from detrital zircons have been used to analyse the crustal evolution of the eastern and western parts of the cathaysia block in se china zircons from the oujiang river in eastern cathaysia indicate that the basement is dominantly paleoproterozoic 1850 1870 ma 2100 2400 ma in age with minor archean components it was extensively reworked in jurassic cretaceous time 100 155 ma to produce the widespread yanshanian magmatic suite both the 1850 1870 ma event and the yanshanian magmatism show wide ranges in hf isotope composition consistent with mixing between crustal and juvenile magmas marked downstream changes in the relative proportions of zircon age populations emphasize the care required in using detrital zircon data to estimate continental growth rates zircons from the north river indicate that the crust of western cathaysia was generated mainly during neoproterozoic time although it contains some archean 2500 3500 ma to mesoproterozoic components this crust was strongly reworked during caledonian ca 450 ma indosinian ca 240 ma and early yanshanian ca 160 ma thermal events there is little evidence for juvenile crustal growth in any of these events although the yanshanian granitoids of the eastern and western parts of the cathaysia give similar mean hf model ages consistent with published nd model ages this is a coincidence they have different crustal sources the distinct patterns of crustal evolution suggest that eastern and western cathaysia may represent separate microcontinents accreted to the older yangtze craton and transposed by extensive strike slip faults

substratum transverse faults in kuqa foreland basin northwest china and their significance in petroleum geology abstract the importance of transverse faults in basin evolution and petroleum geology has been often emphasized however the transverse faults in the kuqa foreland basin the most important gas producing area in china have rarely been studied interpreted seismic sections and earthquake focal mechanism solutions as well as other geological and geophysical data allow us to identify a few widely spaced approximately ns trending transverse strike slip faults separating major structural units and to clarify the geometry and kinematics of these transverse faults hidden below thrust faults in the kuqa foreland basin two major structural domains can be distinguished transverse faults in the northern kuqa foreland basin are mainly nne trending sinistral indicating clockwise rotation of fault bounded blocks in contrast the predominant nw trending dextral faults in the southern kuqa foreland basin imply counterclockwise rotation of fault bounded blocks we propose a tectonic model in which crustal blocks are bounded by strike slip faults in a zone of simple shear rotation about vertical axis the strike slip faulting and thrust faulting in the kuqa foreland basin suggest that some of the convergence between south tianshan and tarim blocks may have been accommodated not only by obvious crustal shortening and thickening along thrust faults but also by rotation and possible lateral movement of the crust along transverse faults controlled by the remote collision of indian block with eurasian block since the miocene these reactivated substratum faults which may inherit from paleozoic deformation control various elements relevant to gas accumulation in the kuqa foreland basin which should expect to be paid more attention in the future these elements include maturity of tertiary and jurassic source rocks a difference in the regional cap of kumugelimu salt beds from east to west reservoir bed properties gas migration channels and traps formation in addition the strike slip faulting of the transverse faults may affect deformation of the sedimentary cover including making the western qiulitag structural belt to form an arcuated structure curved to the ssw

the u pb ages and hf isotopes of detrital zircons from hainan island south china implications for sediment provenance and the crustal evolution in situ u pb dating and hf isotopic of detrital zircons from beach sediments of yalong bay were analyzed to trace sedimentary provenance and reveal the crustal evolution of hainan island in south china the grain size distribution of the sediments displays a clear single peak feature indicating the sediments were formed under the same condition of hydrodynamic force the detrital zircons had th u ratios of greater than 0 1 and ree pattern displayed a positive ce anomaly and a negative eu anomaly indicating that these zircons are predominantly of magmatic origin the u pb spectrum of detrital zircons mainly peaked at the yanshanian 96 185 ma hercynian indosinian 222 345 ma and caledonian 421 477 ma a portion of the detrital zircons were of neoproterozoic origin 728 1 003 ma which revealed that the basement in the eastern region of hainan island was mainly of neoproterozoic with rare archean materials the positive ehf t values 0 to 10 1 of the neoproterozoic detrital zircons indicated that the juvenile crust grew in the southeastern hainan island mainly during the neoproterozoic period the neoproterozoic orogeny in the southeastern part of the island 0 7 1 0 ga occurred later than in the northwestern region of the island 1 0 1 4 ga importantly the grenvillian orogeny in the southeastern area of hainan island shared the same timing with that of the western cathaysia block i e both areas concurrently underwent this orogenic event thereby forming a part of the rodinia supercontinent afterwards the crust experienced remelting and reworking during the caledonian hercynian indosinianand yanshanian accompanied by the growth of a small amount of juvenile crust

structural characterization of intracratonic strike slip faults in the central tarim basin the strike slip fault systems in the central tarim basin china afford an exceptional opportunity to document the structural characteristics and evolution process of small displacement intracratonic strike slip faults using three dimensional seismic reflection data these strike slip faults display subvertical segments at depth and en echelon normal fault zones where relatively shallow fault segmentation and flower structures can be commonly observed in plan view and cross section view respectively consistent with the notion that segment coalescence is the fundamental process for fault evolution the mean segment length of representative strike slip faults examined in this study is positively correlated to the measured fault offset the width of the en echelon normal fault zone is positively correlated with the estimated maximum overburden thickness the integrated data sets suggest that the evolution of the conjugate fault array followed a sequential evolution process instead of forming simultaneously the switch in slip direction of the master fault of the conjugate fault array is attributed to the change of stress orientation regarding individual strike slip faults increase in displacement induces the formation of faults with lower fault array angles linking initially formed en echelon normal faults in cross sections throughgoing fault surfaces can also form connecting the lower subvertical fault segment and the upper en echelon normal faults the presented data sets and evolution models established in this study can be used as tools to better predict the structural attributes of subsurface strike slip fault systems with important consequences for reservoir formation and hydrocarbon accumulation in the tarim basin in particular and in ancient marine basins in general

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

global basin classification system a proposed system classifies sedimentary basins worldwide into specific as well as general categories the geologic history of each basin may be subdivided into cycles using three parameters basin forming tectonics depositional sequences and basin modifying tectonics sedimentary basins may be simple with one or two tectonic sedimentary cycles or they may be complex polyhistory basins with many different cycles and events there are eight simple cycle types in this classification which cover continental continental margin and oceanic areas the eight basic cycle types their depositional fills and tectonic modifiers have been given letter and number symbols so that the specific geologic history of each basin may be written as a formula these formulas may then e compared and similarities or differences between basins noted

fault system impact on paleokarst distribution in the ordovician yingshan formation in the central tarim basin northwest china abstract the paleokarst unconformity at the top of the ordovician yingshan formation in the central tarim basin was exposed to air for at least 10 ma providing favorable conditions for the later formation of high quality reservoirs during the karstification process the fault system plays an important role in controlling the development of paleokarst this study characterized the fault system through the paleokarst features on the northern slope of the tazhong high and examined in detail the impacts of the fault system on paleokarst distribution formation micro imager logs and seismic curvature change rate were used for characterizing the fault system in different scales the results revealed three sets of faults in this region cross cutting relationships unconformities and relation between faults and karstification indicate mid to late ordovician thrust faults silurian devonian strike slip faults and permian tension faults bright spots in seismic records calibrated by formation micro imager logs were used for indicating paleokarst features and different depth distributions respectively furthermore the study employed spectral decomposition technique to characterize the morphology of paleocave complexes in detail the results show the mid late ordovician thrust faults heavily impacted the distribution of paleokarst mainly distributed along master and secondary thrust faults in shallow areas as well as along master basement involved thrust faults in deep strata and along the most pronounced area of paleokarst tazhong no 10 fault zone bounded by back thrusts the data provides new forecasting information for deep hydrocarbon exploration in paleokarst related reservoirs of the yingshan formation

petrogenesis and tectonic significance of a mesozoic granite syenite gabbro association from inland south china article i nfo a granite syenite gabbro association from inland south china has been studied for zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings these rocks have distinctive crystallization ages the longyuanba biotite granites have a mean age of 240 ma the longyuanba two mica granites pitou alkali feldspar granites and amphibole bearing alkali feldspar granites tabei and huangbu syenites and chebu and chenglong gabbros have a similar age of 178 ma whereas the dafengnao syenite gives a mean age of 165 ma the longyuanba biotite granites and two mica granites exhibit s type characteristics probably derived from a neoproterozoic crustal source the chenglong gabbro has oib like trace element and highly depleted isotope compositions ehf t 10 0 1 3 end t 5 2 suggesting its parental melt to be of asthenospheric origin with insignificant crustal assimilation however crustal contamination is required to explain the isotopic compositions of the chebu gabbro the syenites are shoshonitic in composition and have depleted sr nd hf isotopic signatures which we interpret to have resulted from a mixed source of asthenospheric mantle and metasomatized lithospheric mantle as expected the signals of crustal assimilation are conspicuous in the petrogenesis of the more evolved syenites the pitou alkali feldspar granite and amphibole bearing alkali feldspar granite exhibit i type and a type characteristics respectively they are isotopically more depleted than the s type longyuanba granites we suggest that they may have formed through magma mixing of predominantly mantle derived melts with the neoproterozoic crust the jurassic granite syenite gabbro association was the product of asthenosphere lithosphere crust interactions which records the primary role of asthenospheric mantle upwelling in magma generation both in the mantle and in the crust in the early yanshanian time in south china they probably occurred in an intraplate rift like environment as a tectonic response to far field stress at plate margins during the early stage of the paleo pacific plate subduction the tectonic transition from the tethys orogenic regime to the paleo pacific regime was accomplished in the early jurassic and the early yanshanian magmatism should be genetically associated with the paleo pacific tectonic regime

development and testing of a 3d seismic velocity model of the po plain sedimentary basin italy abstract we built a 3d seismic model of the po plain and neighboring regions of northern italy covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid we started by collecting an extensive and diverse set of geological and geophysical data including seismic reflection and refraction profiles borehole logs and available geological information major geological boundaries and discontinuities have thus been identified and mapped into the model we used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness seismic wave properties have been assigned to each unit using a rule based system and v p v s and derived from other studies sedimentary strata although with varying levels of compaction and hence material properties may locally reach a thickness of 15 km and give rise to significant effects in seismic wave propagation we have used our new model to compute the seismic response for two recent earthquakes to test its performance results show that the 3d model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments whereas paths outside the basin may be well fit by more homogeneous 1d hard rock structure we conclude that the new model is suited for simulation of wave propagation mostly for t 3 s and may serve well as a constraint for earthquake location and further improvements via body or surface wave inversion

crustal structure and active tectonics in the eastern alps 1 during the last decade a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the eastern alps and their adjacent tectonic provinces a fragmentation of the lithosphere into three blocks europe eu adria ad and the new pannonian fragment pa was interpreted and a triple junction was inferred the goal of this study has been to relate these deep crustal structures to active tectonics we used elastic plate modeling to reconsider the moho fragmentation we interpret subduction of eu below ad and pa from north to south and underthusting of ad mantle below pa from southwest to northeast the moho fragmentation correlates well with major upper crustal structures and is supported by gravity seismic and geodetic data an analysis of crustal thickening suggests that active convergence is associated with continued thrusting and lateral extrusion in the central eastern alps and thickening of the adriatic indenter under the southern alps according to the velocity relations at the triple junction pa moves relative to eu and ad along ene and se striking faults mainly by strike slip an eastward directed extensional component is compensated by the lateral extrusion of the central eastern alps the periadriatic insubric line east of the triple junction and the mid hungarian fault zone have relatively recently lost their role as first order active structures we favor the idea that the pannonian fragment and the tisza block merged to a soft microplate surrounded by the eastern and southern alpine carpathian and dinaric orogens