an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

geochronological and geochemical constraints on mesozoic suturing in east central tibet 1 this paper reports isotopic major and minor element geochemistry of igneous and metamorphic rocks from the kokoxili and yushu regions of central and eastern tibet the first region lies along the kunlun suture which separates the bayan har songpan ganze songpan terrane from the tarim and qaidam blocks two kokoxili granitoids yield u pb zircon dates of 217 10 and 207 3 ma late triassic which represent the time of emplacement and rb sr isochron dates of 195 3 and 190 3 ma early jurassic which are interpreted as cooling ages the geochemical signatures of these granitoids suggest that they are related to subduction continuing into the late triassic in the yushu area three samples help constrain the age of the jinsha suture which separates the songpan terranes from the qiangtang blocks a leucocratic granite and an orthogneiss in the suture zone yield u pb zircon dates of 206 7 and 204 1 ma respectively and a paragneiss south of it a u pb monazite date of 244 4 ma the existence of coeval magmatism in both the jinsha and kunlun sutures suggests that the two subduction zones were simultaneously active combining isotopic dating with structural evidence on subduction polarity and paleomagnetic reconstructions we propose that the kunlun and qinling block boundaries which were distinct in the permian subsequently formed a continuous late triassic northward subducting plate margin our data suggest that the jinsha suture correlates with the benzilan and nan uttaradit sutures which together belong to a major late triassic subduction zone

indosinian deformation of the songpan garze fold belt northeast tibetan plateau abstract deformation of the songpan garze fold belt southwest china occurred progressively during the indosinian orogeny ca 230 200 ma two phases of south directed deformation are identified d 1 associated with pervasive thickening of the songpan garzi sedimentary pile and detachment of that portion of the fold belt onlapping the yangtze passive margin and d 2 a localized phase of deformation associated with transpressive shortening of the fold belt s southeast margin an arcuate form surface in the southeast fold belt reflects the distribution of d 1 and d 2 structural phases and the diachronous migration of these phases into the fold belt this migration accommodated lateral growth and cumulative sinistral transpression within the fold belt s eastern margin an enigmatic metamorphic complex the so called danba antiform is constrained to have formed during the early stages of the d 2 deformation this was associated with diapiric upwelling of buoyant migmatised basement and domal distortion of the overlying metasedimentary pile

pipes and pipe flow process in an upland catchment wales abstract the results of observations on the spatial localisation origin and function of soil pipes in an upland catchment are discussed the pipes occur in distinct zones in the brown earth soils of the lower slopes and form a hydrological link conducting water between an upslope zone of highly permeable skeletal soils and the stream channel it is proposed that in this catchment pipes develop from an initial network of mole burrows modified by hydraulic activity to produce an efficient downslope transmission network a conceptual model for the pipe slope segment is proposed which recognises the importance of this transmission role slope discharge controls switching between saturated throughflow pipe flow and overland flow each of which has a specific threshold value for operation attempts to investigate the significance of pipe flow at the catchment scale met with limited success but it appears to be important in increasing both contributing area and duration of storm flow

an early unroofing in northeastern tibet constraints from 40ar 39ar thermochronology on granitoids from the eastern kunlun range qianghai nw china abstract in order to better constrain the mechanisms accommodating the india asia collision along the whole kunlun range northern tibet which is essential to better understand the evolution of the entire deformations area a 40 ar 39 ar thermochronological study has been carried out on a suite of granitoids collected in the vicinity of golmud eastern kunlun range biotite and k feldspar have been analysed and the cooling histories of the latter have been modelled the ranges of 40 ar 39 ar data bt 128 257 ma kf 102 228 ma are similar to previous rb sr and k ar data indicating both a middle paleozoic unit and a mesozoic unit including a triassic series and a jurassic cretaceous series this suggests that the two geological units previously reported in the western kunlun are also present in the eastern part of the range suggesting that eastern and western kunlun ranges might have been left laterally offset by as much as 500 km along a strike slip fault presently parallel to the altyn tagh fault the cooling histories based upon k feldspar modelling show that samples from the southern part of the range recorded an important cooling event 9 15 myr around 30 ma which is thought to reflect an increasing rate of denudation related to the tectonic activity in this area minimum denudation rates of 0 2 0 3 km ma have been estimated in contrast samples from the northern part of the range did not record any variation in their cooling history this heterogeneous denudation across the range is thought to be related to ramp stacking and normal faulting with associated uplift mainly affecting the southern part of the range suggesting that the eastern kunlun underwent an important crustal thickening period 30 ma ago this crustal thickening event is suggested to be related to the motion along the great asian strike slip faults in a way which remains problematic but possibly associated to the cenozoic propagation of the altyn tagh fault finally unroofing in the eastern kunlun range appears to predate that in the western kunlun range where it is suggested to have started around 20 ma ago this diachronous denudation could be related to a higher denudation rate in western kunlun range and it is thus highly probable that the important unroofing event outlined around 20 ma ago in the western kunlun has also affected the eastern part of the range even though the signature is not available at the moment

tectonics and denudation adjacent to the xianshuihe fault eastern tibetan plateau constraints from fission track thermochronology the xianshuihe xiaojiang fault system extending from eastern tibet to central yunnan china is a major left shear structural boundary accommodating the clockwise rotation of crustal rocks between the eastern himalayan syntaxis and the south china block zircon and apatite fission track ft data are reported for 111 samples of basement collected from both sides of the northern part of this fault and spanning 300 km across the eastern margin of the tibetan plateau where its mean elevation drops from 3500 to 1500 m above sea level the zircon ft ages define two fossil partial annealing zones at different elevations one fossilised at circa 130 ma and the other at circa 21 ma as a result of cooling probably via regional denudation the apatite ft ages are mostly less than 25 ma but a few granitoids higher up on the plateau retain late cretaceous apparent ages within the apatite ft data with neogene ages there may be several partial annealing zones with mixture modeling identifying age components suggestive of discrete cooling phases at circa 22 7 and 2 ma the first order pattern of the minimum amount of neogene denudation for a section across the plateau margin immediately northeast of xianshuihe fault suggests that a relatively uniform 4 6 km has been eroded from the inner part of the plateau margin increasing to 7 10 km at kangding where the oldest rocks precambrian are exposed and then decreasing markedly into sichuan basin these new ft data combined with published ft data suggest that the present extent of the tibetan plateau was defined during the early miocene

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

a thermochronological perspective on the morphotectonic evolution of the southeastern tibetan plateau a large part of the southeastern tibetan plateau tp is characterized by low relief surfaces at high elevations 3 5 km the origin of these landscapes and their geodynamic implications with regard to evolution of the southeastern tp has been the subject of considerable debate focusing on this topic this study utilizes fission track and u th he thermochronology to reconstruct the thermal history of the late triassic daocheng granite on which a low relief high elevation landscape has developed results suggest that the plateau surface experienced widespread late jurassic to early cretaceous cooling at a rate of 1 2 c ma followed by minimal regional cooling 0 3 c ma and early miocene enhanced cooling 2 3 c ma along deep valleys at the southern edge of the landscape given the subdued late jurassic to early cretaceous crustal deformation in the study area we relate the coeval cooling to crustal refrigeration and exhumation triggered by northward subduction of the meso tethys ocean along the bangong suture subsequent late cretaceous to cenozoic minimal cooling supports arguments for the formation of a low elevation landform prior to uplift of the southeastern tp the enhanced cooling commenced at the early miocene 15 22 ma along deep valleys and heralded the onset of river incision and surface uplift of the southeastern tp this finding does not support previous proposals claiming that high elevations of the southeastern tp were formed in late miocene time resulting from lower crustal flow but rather supports a model highlighting continental subduction and extrusion along the large tanggula yushu batang red river fault system

crustal response to continental collisions between the tibet indian south china and north china blocks geochronological constraints from the songpan garze orogenic belt western china we report shrimp u th pb monazite conventional u pb titanite sm nd garnet and rb sr muscovite and biotite ages for metamorphic rocks from the danba domal metamorphic terrane in the eastern songpan garze orogenic belt eastern tibet plateau these ages are used to determine the timing of polyphase metamorphic events and the subsequent cooling history the oldest u th pb monazite and sm nd garnet ages constrain an early barrovian metamorphism m1 in the interval c 204 190 ma coincident with extensive indosinian granitic magmatism throughout the songpan garze orogenic belt a second higher grade sillimanite grade metamorphic event m2 recorded only in the northern part of the danba terrane was dated at c 168 158 ma by a combination of u th pb monazite and titanite and sm nd garnet ages it is suggested that m1 was a thermal event that affected the entire orogenic belt while m2 may represent a local thermal perturbation rb sr muscovite ages range from c 138 100 ma whereas rb sr biotite ages cluster at c 34 24 ma these ages document regional cooling at rates of c 2 3 c myr 1 following the m1 peak for most of the terrane however those parts of the terrane affected by the higher temperature m2 event e g the migmatite zone experienced initially more rapid c 8 c myr 1 cooling after peak m2 before joining the regional slow cooling path defined by the rest of the terrane at c 138 ma regional slow cooling between c 138 and c 30 ma is thought to be the result of post tectonic isostatic uplift after extensive crustal thickening caused by collision of the south and north china blocks the clustering of biotite rb sr ages marks the onset of rapid uplift across the entire terrane commencing at c 30 20 ma this cooling history is shared with many other regions of the tibet plateau suggesting that uplift of the tibet plateau including the songpan garze orogenic belt occurred predominantly in the last c 30 myr as a response to the continuing northwards collision of india with eurasia

neogene extension and volcanism in the kunlun fault zone northern tibet new constraints on the age of the kunlun fault 1 the geology of the jingyu basin north tibet provides constraints on the relationship between localized e w extension in the qiangtang block and strike slip motion along the kunlun fault eocene to oligocene sw ne compression formed topographic relief in the present western kunlun shan pull apart basins started forming in the western kunlun ranges around 15 ma possibly coincident with the initiation of subduction of the tarim qaidam lithosphere under the kunlun shan extensional tectonism is still active and the jingyu basin is extending as a normal fault connected with the kunlun fault was recently active localized extension allows tertiary and quaternary shoshonitic magmas to reach the surface from crustal depths of 50 to 60 km miocene strike slip faulting indicates that the initiation of the kunlun strike slip fault is early neogene in age and that the total amount of horizontal movement that occurred along the fault has to be reconsidered

displacement and timing of left lateral faulting in the kunlun fault zone northern tibet inferred from geologic and geomorphic features abstract the e w to wnw ese striking kunlun fault zone extending about 1600 km is one of the large strike slip faults in the northern tibet china as a major strike slip fault it plays an important role on the extrusion of tibet plateau in accommodating northeastward shortening caused by the india asia convergence however the time of initiation left lateral faulting of the kunlun fault zone is still largely debated ranging from the middle to late triassic 240 200 ma to early quaternary 2 ma we document displaced basement rocks and geomorphic features along the kunlun fault zone based on tectono geomorphic interpretation of satellite remote sensing images and field geologic and geomorphic observations our results show that the largest cumulative offset of basement rocks is likely to be 100 20 km meanwhile a series of pull apart basins kusai xiugou and tuosu lake basins and pressure ridges east deshuiwai and maji snow mountains each 45 70 km long and 8 12 km wide are developed along the kunlun fault zone which resulted from long term tectono geomorphic growth since the late miocene or early pliocene geologic evidence indicates that the kunlun fault zone had a long term slip rate of ca 10 mm yr during the late quaternary this slip rate is similar to that shown by present day gps measurements thus we estimate that the kunlun fault zone probably began left lateral faulting at 10 2 ma based on a total displacement of 100 20 km and assuming a constant long term slip rate of ca 10 mm yr for several millions of years and this timing constraint on initiation of left lateral faulting of the kunlun fault zone is consistent with widespread tectonic deformation which occurred in the tibetan plateau

mesozoic and cenozoic tectonics of the northern edge of the tibetan plateau fission track constraints abstract fission track analysis on zircons and apatites yields new information about the timing of deformation of the northern tibetan plateau ages on zircons ranging from 221 22 to 96 4 ma are indicative of a general late triassic early jurassic cooling probably driven by the collision between the qiantang and kunlun blocks mid jurassic slow cooling is recorded also in the apatites in regions not affected by later cenozoic deformation this jurassic denudation was followed by a period of sedimentation during the cretaceous except along the altyn tagh fault atf zone and in some restricted areas of the western and eastern qilian shan this long and relatively quiet period ended at about 40 10 ma along the major altyn tagh and kunlun strike slip fault zones which were activated by the india asia collision this first movement along lithospheric faults resulted in the eastward extrusion of the tibet plateau which was followed in late oligocene miocene times by a major compression event initiating the formation of the high relief of north tibet a final compressional event took place at 9 5 ma and is well correlated with high sedimentation rates in the basins of this region this compression induced continental subduction in the kunlun ranges the altun shan belt and possibly the qilian shan belt

mesozoic cenozoic evolution of the danba dome songpan garze east tibet as inferred from la icpms u pb and fission track data abstract the eastern margin of the tibetan plateau is a key region to understand the formation and tectonic evolution of the plateau most studies concentrated on the longmen shan range that corresponds to the tectonically very active boundary between the tibetan plateau and the sichuan basin this work addresses the deformation and exhumation pattern in the poorly understood metamorphic danba dome situated at the conjunction between the southern longmen shan range and the major strike slip xian shui he fault the early mesozoic and cenozoic evolution of the dome are then compared to the regional evolution of eastern tibet the about 830 ma zircon u pb ages obtained on the gezong and gongcai gneiss as well as u pb ages on inherited zircons in the early mesozoic granites confirm the occurrence of neo proterozoic magmatic episodes in the danba basement at 800 900 ma and 650 750 ma following the closure of the palaeotethys ocean granitoids were emplaced in the danba metamorphic basement and triassic cover from about 230 ma to about 170 ma the western part of the lian he kau granitic massif emplaced between 210 and 200 ma within the triassic cover sequence of the dome was only slightly affected by the early mesozoic deformation however in the eastern deeper level compartment of the massif ductile deformation occurred between 200 and 190 ma contemporaneous with the onset of the barrovian type metamorphism dated at 200 180 ma that deformation is compatible with the early mesozoic deformation observed in the longmen shan range and with the development of the large scale decollement level in the songpan garze area apatite fission track data then indicate that following the oligocene middle eocene onset of eastward motion of the songpan garze terrane the danba dome developed as a crustal scale antiform during the late miocene early pliocene 10 4 ma the exhumation was controlled by the lian he kau fault a major transpressive structure parallel to the xian shui he fault and the associated manai thrust faults regionally while the oligocene middle miocene exhumation phase seems to have been of regional extent the late miocene to present day phase is localised along the longmen shan range thrusts as well as along the back thrusts formed by the lian he kau manai and associated faults

brittle modification of triassic architecture in eastern tibet implications for the construction of the cenozoic plateau abstract in the songpan ganzi fold belt east tibetan plateau post triassic deformation is localised within northwest trending sinistral and southwest trending dextral brittle fault zones between these zones large tracts of the fold belt preserving late triassic indosinian architecture have been transported effectively intact this transport was almost exclusively strike slip and did not accommodate significant differential exhumation or uplift right dihedra paleostress reconstructions from fault plane kinematic data indicate a rotation of the principal compressive stress from ne sw trending in the north to a dominant e w trend throughout the eastern songpan ganzi fold belt exceptions occur adjacent to competent proterozoic basement complexes and other rigid bodies these stress solutions are consistent with a compressive stress regime that radiates about the eastern himalayan syntaxis a secondary n s compressive paleostress identified in southern regions may record late southwards transportation of the songpan ganzi fold belt relative to the eastern himalayan syntaxis the lack of pervasive cenozoic recent upper crustal shortening in this region suggests that thickening of the east tibetan crust was predominantly accommodated by viscous deformation at depth we envisage decoupling of the lower and upper crust and partitioning of an e w compressive stress between 1 a laterally mobile thin skinned veneer and 2 a homogeneously thickened tectonic basement

structural evidence for the permo triassic tectonic evolution of the yidun arc eastern tibetan plateau abstract deformation across the yidun arc occurred as a two phase process i early triassic deformation of paleozoic sequences resulting from closure of the jinsha jiang suture and ii late triassic deformation of middle to late triassic rocks as a result of final basin closure deformation in the western yidun arc is dominantly west vergent a north south striking west directed thrust the jinsha thrust forms the boundary between the western yidun arc and the eastern qiangtang block the jinsha thrust incorporates within it ophiolitic material of the jinsha jiang suture and the structural geometry across the jinsha thrust suggests that early triassic subduction was east dipping along the jinsha jiang suture deformation within middle to late triassic sequences of the eastern yidun arc eastern qiangtang block and western songpan garze fold belt is thin skinned being restricted largely to a single generation of upright folds and associated thrusts late triassic westwards subduction underneath the combined western yidun arc qiangtang block resulted in arc volcanism in the eastern yidun arc coeval arc volcanics in the northern margin of the qiangtang block suggest that the suture along the northern margin of the qiangtang block may be correlated with the garze litang suture rather than the jinsha jiang suture

postorogenic rigid behavior of the eastern songpan ganze terrane insights from low temperature thermochronology and implications for intracontinental deformation in central asia 1 the songpan ganze terrane sgt formed by early mesozoic closure of the paleo tethys ocean occupies a large area of the central eastern tibetan plateau late mesozoic and cenozoic strike slip deformation has been identified in the surrounding terranes and faults e g western qinling altyn tagh and kunlun faults however the coeval evolution of the sgt has not been well explored we report apatite fission track and apatite and zircon u th he data from a 7 km deep borehole and outcrop samples covering an area of 150 150 km in the eastern sgt thermal history modeling suggests a distinct phase of late jurassic early cretaceous 150 100 ma cooling followed by a prolonged stage of slow cooling for all samples despite of their differences in depositional age mid late triassic time and locality within a large area the ubiquitous late jurassic early cretaceous cooling implies little differential deformation in the eastern sgt and is best explained by regional rock uplift resulting from the transpressional strain field created by the contemporaneous lhasa qiangtang collision to the south projecting the contemporaneous deformation surrounding the sgt onto an early cretaceous paleogeographic terrane reconstruction results in a new tectonic model the model relates the lhasa qiangtang collision to tens to hundreds of kilometers of shearing along the altyn tagh and kunlun faults which transferred strain into central asia e g qinling dabie orogen results of this study suggest a rigid behavior for the eastern sgt and highlight the important role of crustal strength discontinuities in accommodating and transferring crustal deformation

campaign style titanite u pb dating by laser ablation icp implications for crustal flow phase transformations and titanite closure abstract u pb dates of titanite from 150 samples of chiefly quartzofeldspathic gneiss and leucosomes were measured across the western gneiss region of norway to understand deformation and metamorphism of typical crustal rocks during ultrahigh pressure uhp subduction and exhumation titanite is unstable at these high temperatures and pressures and indeed most of the titanite yielded post uhp dates a modest number of titanites sampled across large areas however have pre uhp u pb dates indicating that they survived their excursion to and return from mantle depths metastably this has three important implications 1 titanite grains can remain closed to complete pb loss during regional metamorphism at temperatures as high as 750 c and pressures as high as 3 gpa 2 phase transformations in quartzofeldspathic rocks can be inhibited at the same conditions 3 quartz bearing rocks can remain undeformed even at high temperature and pressure both of the latter were previously recognized the present study simply presents a new method for evaluating both using titanite u pb dates

exhumation of the dabie shan ultra high pressure rocks and accumulation of the songpan ganzi flysch sequence central china the presence of coesite and diamond bearing ultra high pressure uhp metamorphic rocks in the dabie and sulu regions central china suggests that a 100 km thick crustal section 4 x 106 km6 in volume has been denuded this volume is comparable to that represented by the 10 15 km thick middle to upper triassic flysch rocks in the songpan ganzi region regional geology and radiometric dates are compatible with an interpretation that the majority of these sedimentary rocks were derived from denudation of the orogenic belt between north and south china blocks following their latest paleozoic to triassic collision this correlation implies a high denudation rate of 4 mm yr that may have been in part promoted by tropical precipitation and extreme topographic relief for as long as 25 m y

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

cenozoic and mesozoic metamorphism in the longmenshan orogen implications for geodynamic models of eastern tibet new zircon u pb and mica 40ar 39ar dating combined with structural studies in the longmenshan orogen confirm that most of the upper crustal deformation in the eastern margin of tibet is mesozoic however at lower structural levels apatite u pb and monazite electron microprobe dating reveals a previously unknown domain of cenozoic ca 65 ma barrovian type metamorphism and deformation this discovery shows that the crust in the eastern margin of tibet was already a substantial thickness around the time of the india asia collision associated deformation has a n s oriented stretching lineation implying that deformation was not driven by topographic gradients in the tibetan plateau the observed moderate amounts of distributed postmetamorphic e w shortening can probably explain the present thickness of the continental crust in the area these results do not support models of crustal thickening caused by solid state lateral flow of midcrustal metamorphic rocks

differential exhumation in response to episodic thrusting along the eastern margin of the tibetan plateau abstract thermochronological data from the songpan ganze fold belt and longmen mountains thrust nappe belt on the eastern margin of the tibetan plateau in central china reveal several phases of differential cooling across major listric thrust faults since early cretaceous times differential cooling indicated by distinct breaks in age data across discrete compressional structures was superimposed upon a regional cooling pattern following the late triassic indosinian orogeny 40ar 39ar data from muscovite from the central and southern longmen mountains thrust nappe belt suggest a phase of differential cooling across the wenchuan maouwen shear zone during the early cretaceous the zircon fission track data also indicate differential cooling across a zone of brittle re activation on the eastern margin of the wenchuan maouwen shear zone during the mid tertiary between 38 and 10 ma apatite fission track data from the central and southern longmen mountains thrust nappe belt reveal differential cooling across the yingxiu beichuan and erwangmiao faults during the miocene forward modelling of apatite fission track data from the northern longmen mountains thrust nappe belt suggests relatively slow regional cooling through the mesozoic and early tertiary followed by accelerated cooling during the miocene beginning at ca 20 ma to present day regional cooling is attributed to erosion during exhumation of the evolving longmen mountains thrust nappe belt lmtnb following the indosinian orogeny differential cooling across the wenchuan maouwen shear zone and the yingxiu beichuan and erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults thermochronological data from the longmen mountains thrust nappe belt reveal a greater amount of differential exhumation across thrust faults from north to south this observation is in accord with the prevalence of proterozoic and sinian basement in the hanging walls of thrust faults in the central and southern longmen mountains the two most recent phases of reactivation occurred following the initial collision of india with eurasia suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the lmtnb

cenozoic tectonic evolution of the qaidam basin and its surrounding regions part 3 structural geology sedimentation and regional tectonic reconstruction the qaidam basin is the largest topographic depression inside the tibetan plateau because of its central position understanding the tectonic origin of the qaidam basin has important implications for unraveling the formation mechanism and growth history of the tibetan plateau in order to achieve this goal we analyzed regional seismic reflection profiles across the basin and a series of thickness distribution patterns of cenozoic strata at different time slices the first order structure of the basin is a broad cenozoic synclinorium which has an amplitude ranging from 16 km in the west to 48 in the west to 15 s 1 to 1 3 10 17 s 1 the eastward decrease in upper crustal shortening requires a progressive shift in crustal thickening mechanisms across qaidam basin from dominantly upper crustal shortening in the west to dominantly lower crustal shortening in the east although sedimentation began synchronously at 65 50 ma across the entire basin the initiation ages of the southern and northern basin bounding structures are significantly different deformation started at 65 50 ma in the north and at 29 24 ma in the south this information and the existing inference that the uplift of the eastern kunlun range south of qaidam basin began after 30 20 ma imply that the paleogene 65 24 ma qaidam and hoh xil basins on both sides of the eastern kunlun range may have been parts of a single topographic depression 500 km wide in the north south direction between the qilian shan and fenghuo shan thrust belts in the north and south the development of this large paleogene basin in central tibet and its subsequent destruction and partitioning by the neogene uplift of the eastern kunlun range requires a highly irregular sequence of deformation possibly controlled by preexist ing weakness in the tibetan lithosphere

thermochronology of the yidun arc central eastern tibetan plateau constraints from 40ar 39ar k feldspar and apatite fission track data abstract four k feldspar samples from the yidun arc eastern tibetan plateau were analysed by the 40ar 39ar method with the aim of recovering information on their thermal history using multiple diffusion domain mdd theory arrhenius plots for each of the samples reveal low retentivity early in the heating experiments a property that is attributed to their recrystallised nature this low argon retentivity appears to violate the mdd assumption that volume diffusion is the only mechanism for argon transport within the crystals thus the thermal histories derived from these analyses are considered suspect nevertheless the age spectra themselves suggest that the majority of samples had cooled below 200 c prior to the eocene collision of india with asia thermal history modelling from apatite fission track analyses from the same and nearby samples shows slow cooling through the apatite fission track partial annealing zone during the cenozoic in samples from the high elevation low relief areas of the yidun arc while samples from the major jinsha river valley show rapid cooling through the partial annealing zone beginning in the miocene these results suggest that significant cenozoic denudation has been localised and that most parts of the yidun arc have experienced very little denudation during the cenozoic

dynamics of the atmospheres of the outer planets post voyager measurement objectives current knowledge about dynamics and thermal structure on the outer planets is reviewed with the aim of identifying important measurements which should be made in the post voyager era the existence of jets and cloud bands is the puzzle that underlies all others discussion focuses on the particular case of jupiter because documentation is most complete recent dynamical work has successfully reproduced much of the behavior of jets and spots with simple models that contain few parameters it is argued that the gross dynamical parameters such as density stratification and rotation rate are the keys to their behaviors rather than the particular specifics of radiative forcing cloud distributions thermodynamic transformations voyager data have shown that the jet systems decay with height in the region above the visible clouds therefore the highest priority must be given to establishing dynamical parameters that characterize levels within and beneath the clouds these require determination of the deep structure of the jets of the density stratification and of the horizontal density contrasts the deep regions are not easily accessible and these measurements present challenging opportunities indirect inferences about the controlling processes may sometimes be possible by observing waves and other activity in the more easily accessible stratosphere and some of these issues are also discussed

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

subduction related origin of the 750 ma xuelongbao adakitic complex sichuan province china implications for the tectonic setting of the giant neoproterozoic magmatic event in south china abstract the xuelongbao plutonic complex in the eastern margin of the tibetan plateau is dated at 748 7 ma using the shrimp zircon u pb method and represents part of the neoproterozoic igneous assemblage of south china rocks in the complex include tonalite and granodiorite and have sio2 ranging from 62 0 to 74 8 wt and al2o3 from 14 3 to 20 9 wt their na2o contents range from 4 2 to 6 7 wt and k2o from 0 47 to 1 96 wt indicating that they belong to the na series these rocks show chondrite normalized ree patterns depleted in hree and variably enriched in lree they have positive sr and negative nb and ti anomalies in the primitive mantle normalized trace elemental spider diagram their sr contents range from 320 to 780 ppm and y contents are lower than 10 ppm resulting in high sr y ratios 52 320 characteristic of typical adakites their end t and initial sr isotopic compositions range from 0 36 to 2 88 and from 0 7033 to 0 7054 respectively the geochemical features of the xuelongbao plutonic complex are consistent with an origin from adakitic magmas that were likely derived from partial melting of a subducted oceanic slab together with arc signatures of other granites and mafic intrusions in the region the 750 ma xuelongbao adakitic complex provides evidence for a major subduction related neoproterozoic magmatic event of south china

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

deformation partitioning and foliation reactivation during transpressional orogenesis an example from the central longmen shan china progressive localization of strain within the songpan garze fold belt at the eastern margin of the tibetan plateau has resulted in the formation of the wenchuan maowen shear zone and preservation of excellent overprinting relationships between three major phases of ductile and semi ductile deformation these relationships show that deformation in the eastern songpan garze fold belt evolved from crustal thickening during sw directed compression d1 to localized sinistral transcurrent shear d2 and finally to increasingly localized high temperature d3p and retrograde d3r reverse shear in response to se directed compression both d2 and d3 deformations were co planar and reactivation of the s2 foliation led to the formation of a composite s2 3 fabric however inclusion trails in garnet porphyroblasts preserve evidence of a transition between these strike slip and reverse shear end members indicating that d2 and d3 were part of an episode of progressive transpressional shear metamorphic grade increases from chlorite to kyanite zone within the wenchuan maowen shear zone reaching syn d3p peak conditions of 600 c and 10 kbar the d3p and d3r reverse shears were responsible for tectonic exhumation of the shear zone and resulted in the formation of retrograde d3r high strain zones along the margins of the xuelongbao granite and adjacent to the wenchuan maowen fault

origin of potassic c type adakite magmas experimental and field constraints the postcollisional mesozoic c type or high k adakitic intrusions k adakites of china lack either temporal or spatial association with subduction and have k2o na2o around unity otherwise their geochemistry is very similar to ordinary adakites new experimental data geological observations and theoretical considerations lead us to suggest that these k adakites were high t 1050 and probably 1075 c rather hydrous magmas 6 wt h2o produced by fluid absent partial melting of metatonalites meta andesites or possibly potassic metabasalts at pressures exceeding 2 gpa their peculiar chemistry is a consequence of both the elevated k2o na2o in the protolith and the very high pressure of partial melting the most likely tectonic setting is one of extreme crustal thickening followed by delamination of the eclogitic keel and partial melting of this continental crustal material at mantle depths with high mantle heat flow during orogenic collapse

the gaojiacun intrusion rift or subduction related comment on revisiting the yanbian terrane implications for neoproterozoic tectonic evolution of the western yangtze block south china by li et al 2006 precambrian res 151 2006 14 30

spatial variation in meso cenozoic exhumation history of the longmen shan thrust belt eastern tibetan plateau and the adjacent western sichuan basin constraints from fission track thermochronology abstract the ne trending longmen shan thrust belt marking the eastern margin of the tibetan plateau adjacent to the sichuan basin is characterized by the paradox of high topographic gradients but low convergence rates and thus critical for understanding of geodynamic processes involved in the eastward growth of the plateau many low temperature thermochronological studies focused on the central and southern portions of the longmen shan and western sichuan basin to investigate the cenozoic exhumation history of the eastern tibetan plateau but little work has been done on their northern portions furthermore the spatial variation in both cenozoic and mesozoic thermal histories of this region has been poorly documented in this paper zircon zft and apatite aft fission track analyses for samples collected from three transects and three boreholes covering the northern central and southern longmen shan and the western sichuan basin provide new data demonstrating several cooling events in this region since the indosinian deformation they occurred during the late triassic 200 ma at the end of early cretaceous 100 ma during the early cenozoic 60 40 ma the early miocene 20 25 ma and the late miocene 9 14 ma respectively on regional scale the longmen shan experienced a slow cooling between the mesozoic and early cenozoic followed by a rapid cooling during the late cenozoic when the rapid regional exhumation began at 10 ma with a sharp increase in exhumation rate from 0 2 mm yr up to 0 9 mm yr locally comparison of zft and aft ages shows that during the mesozoic the northern segment of the longmen shan belt cooled more rapidly than the central and southern segments while younger aft ages indicate more rapid exhumation in central and southern segments of the belt during the late cenozoic similar trend is demonstrated within the western sichuan basin where the onset of exhumation changes from 45 ma in the northern portion to 20 25 ma in the central and southern portions of the basin the thermochronological data reveal that the yingxiu beichuan and guanxian anxian faults have accommodated significant differential exhumation by thrusting activity and associated denudation with a greater amount of differential exhumation from north to south we propose that the major cause for the rise in topography and rapid exhumation in the longmen shan thrust belt during the late cenozoic is the thrusting activities integrated with the regional uplift of the eastern tibetan plateau a process unrelated to the channel flow within the lower crust

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

inherited zircon and titanite upb systems in an archaean syenite from southwestern australia implications for upb stability of titanite abstract inherited zircon and titanite have been identified in a syenite from the archaean of southwestern australia conventional and shrimp analyses on euhedral zoned zircon and zoned rims on complex grains define a crystallisation age of 2654 5 ma for the syenite in addition shrimp analyses on zircon cores and unzoned subhedral zircons show that zircon has a ca 3250 ma inherited component conventional u pb ages on titanite also fall between ca 3250 ma and ca 2650 ma demonstrating that inherited titanite as well as zircon is present in the syenite the syenite has been affected by regional upper amphibolite facies metamorphism at an estimated temperature of 625 650 c retention of the inherited radiogenic pb in the titanite is evidence that the closure temperature for titanite is greater than 650 c the presence of inherited titanite and zircon also demonstrates a crustal source component for the syenite and indicates it originated by partial assimilation of crustal rocks by a potassic magma at

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

predominance of high th u magmatic zircon in brazilian shield sandstones the strong predominance of magmatic th u 0 2 zircon grains in quartz sandstones from 10 locations in the brazilian shield as measured by sensitive high resolution ion microprobe shrimp introduces a strong bias in the tectonic interpretation of source terrains because the metamorphic sources remain undetected in the detrital population zircon grains from many mature and some immature sedimentary terrains show th u ratios 0 2 ratios commonly considered magmatic complemented by the near absence of metamorphic th u ratios 0 1 metamorphic rims on magmatic zircon grains from the brazilian shield are nearly absent from quartz sandstones only being present in shielded young cores of a few crystals high u metamorphic portions of zircon grains are more defective and liable to undergo comminution by abrasion during weathering and transport and they do not remain in the sand fraction ages obtained from detrital zircon in mature sandstones reflect magmatic sources not the full spectrum of orogenic events only less mature sedimentary rocks preserve a full record of orogenic rocks in the source mostly magmatic events were characterized in previous zircon provenance studies brazilian shield detrital zircon may be a proxy for equivalent investigations in other provinces of the world

structural style and tectonic significance of the jianglang dome in the eastern margin of the tibetan plateau china abstract the jianglang tectonic dome jtd lies on the eastern margin of the tibetan plateau and consists of three tectono stratigraphic units separated by two extensional detachment faults a schist complex a middle ductile slab and an overlying sedimentary unit the schist complex is composed of quartz mica schists and amphibolites of possible mesoproterozoic age and exhibits two early foliations s 1 and s 2 overprinted by two later foliations s 3 and s 4 the ductilely deformed middle slab consists of paleozoic quartzite phyllite marble amphibolite and meta basalt it is characterized by pervasive intrafolial and intraformational recumbent folds with a penetrative axial foliation s 1 an equivalent of s 3 in the basement rocks the cover unit the triassic xikang group of flysch sedimentary rocks experienced shallow level buckling and flattening deformation with an axial cleavage defining s 1 an equivalent of s 4 in the middle slab and basement rocks the jtd appears to have experienced three stages of extension immediately after orogeny the earliest d 1 recorded by an axial surface s 1 of s 0 intrafolial folds and sub parallel to s 0 in the schist complex probably occurred prior to the collision between the south china and north china blocks this extensional event was followed by subduction of the yangtze block to the west towards the eastern margin of the tibetan plateau the two detachment faults are characterized by structures formed by ductile brittle to brittle shear deformation which are sub parallel to the layer of s 2 in the lower detachment and to s 0 in the upper detachment these faults mark the second stage of extension and may have caused thinning and selective removal of the sinian and paleozoic strata as well as exhumation of the schist complex and the middle slab in the middle jurassic 177 ma the final stage of extension d 5 shown by brittle deformation and thermo metamorphism from the lower detachment to the xikang group was associated with the indian eurasia collision

la icpms zircons u pb dating of permo triassic and cretaceous magmatisms in northern vietnam geodynamical implications abstract in northeastern vietnam the major tectonic episode responsible for nappes emplacement is triassic these allochtonous structures are intruded by granitic melts two post tectonic massifs showing no sign of deformation have been dated by the la icpms zircon u pb techniques dating reveals a multiphase history with zircon cores showing evidence of proterozoic magmatism the emplacement of the phia bioc granite intrusive in allochtonous units is 248 245 ma an age which assesses a younger limit for the major nappes tectonic this tectonic could be synchronous of the tectonometamorphic strike slip faulting events 250 245 ma defined in the truong son belt as the indosinian orogen the phia bioc intrusion is probably linked with the intra plate magmatism of the emeishan large igneous province or with magmatism associated with the paleotethys closure the age of the phia oac granite intrusion in displaced units is much younger at 87 3 1 2 ma this granite is probably linked to the magmatic activity produced during the paleo pacific plate subduction under the se asia continental plate during the mesozoic although the cenozoic red river fault system is close to these two plutons this last thermotectonic episode has not been strong enough to disturb the u pb system zircons rims do not show any tertiary magmatic or metamorphic overprint

mesozoic cenozoic tectonothermal evolution of the eastern part of the tibetan plateau songpan garze longmen shan area insights from thermochronological data and simple thermal modelling we present a synthesis of the tectonic and thermochronological evolution of the eastern tibet since the triassic the long term cooling histories obtained on magmatic and metamorphic rocks of the south songpan garze kunlun and yidun blocks are similar showing a very slow and regular cooling during late jurassic and cretaceous confirming the suspected lack of major tectonic events between c 150 and 30 ma the exhumation linked to the tertiary growth of the tibetan plateau initiated around 30 ma and concentrates at the vicinity of the major tectonic structures exhumation rates increased again from about 7 ma in the longmen shan to interpret this very slow cooling rate between late jurassic and early cenozoic from granites of this area we use a simple 1d thermal model that takes into account the thermal properties of both sediments and crust the results suggest that 1 high temperature 500 8c can be kept over a long period of time 2 during cretaceous cooling is mostly controlled by the thermal properties of sediments of continental origin and 3 the initial late triassic rapid cooling rate was caused by the large thermal contrast between the granite body and the sedimentary rocks rather than by a high exhumation rate

triassic granitoids in the eastern songpan ganzi fold belt sw china magmatic response to geodynamics of the deep lithosphere the songpan ganzi fold belt sgfb sw china was developed from a passive continental margin into an orogenic belt with the consumption of the paleo tethys during the evolution of the sgfb numerous late triassic granitic plutons formed and exhibited a progressive development from adakite i type granite high ba sr granite a type granite and monzonite representative late triassic plutons were studied to unravel the bewildering evolution of the eastern sgfb the menggu pluton 224 3 ma consists of granites with high alkali k2o na2o 7 85 10 4 wt and adakitic characteristics sr y 19 38 the endt values 2 77 to 5 03 initial 87sr 86sr ratios 0 7050 0 7063 and low nb ta ratios 8 10 are indicative of an origin by partial melting of amphibolitic lower crust rocks from the niuxingou pluton 215 3 ma are richer in k than na k2o na2o 1 1 1 5 and contain high sr 1006 1662 ppm and ba 1277 2009 ppm typical of shoshonite and high ba sr granite they have less enriched endt values 0 08 to 2 04 and less radiogenic 87sr 86sri ratios 0 7047 0 7048 and formed from a mixed melt derived from upwelling asthenosphere and the overlying metasomatised lithospheric mantle the taiyanghe pluton 205 3 ma consists of monzonites with high al2o3 20 wt but low mgo 0 94 1 39 wt the rocks are richer in na than k k2o na2o 0 7 contain high large ion lithophile element lile 681 834 ppm sr and 2142 9453 ppm ba and display strongly fractionated ree patterns la yb n 35 63 these features together with their enriched nd sr isotopic compositions endt 4 78 to 6 50 87sr 86sri 0 7074 0 7090 suggest that the monzonite probably formed from low degrees of partial melting of metasomatised lithospheric mantle although a continuous compressional regime during the mid and late triassic has been invoked for the sgfb the generation of crustally derived adakitic and shoshonitic plutons reflect thickening in response to an arc continental collision accompanied by fracturing of the lithosphere and an extensional regime in the deep lithosphere in the late triassic the 205 ma taiyanghe pluton was emplaced simultaneously with a rapid uplift of the lithosphere when surface deposits changed from deep water turbidite to tidal flat sediments it was therefore generated during decompression probably related to the rapid removal of the overthickened lithospheric mantle the triassic magmatism in the eastern sgfb is therefore important for probing geodynamic processes in the deep lithosphere

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

miocene emplacement and deformation of the konga shan granite xianshui he fault zone west sichuan china geodynamic implications the presently active sinistral xianshui he strike slip fault xsh is a lithospheric scale strike slip fault in the eastern himalaya in the study area this fault affects the eastern edge of the konga shan granitic massif where it has caused both brittle and ductile deformation a rbsr isochron and nd and pb isotope study of three samples and a upb zircon study of a single sample were completed on the granite upb data indicate a granite emplacement age of 12 8 1 4 ma the rbsr isochrons show that the granite emplacement and the deformational event were synchronous at around 12 10 ma minimum age for deformation the nd and pb isotope compositions of whole rocks and k feldspars indicate the involvement of proterozoic continental crust which is confirmed by upb systematics indicating inherited zircons sinistral faulting along the xsh began at the latest at 12 ma and marks the extrusion toward the east of the west sichuan and south china blocks following their extrusion along the red river fault zone between 50 and 21 ma

reply to the comment by zhou et al on revisiting the yanbian terrane implications for neoproterozoic tectonic evolution of the western yangtze block south china precambrian res 151 2006 14 30 precambrian res 154 2007 153 157

slip rate gradients along the eastern kunlun fault 1 whether strike slip fault systems in eurasia accomplish eastward extrusion of tibetan crust and lithosphere depends largely on the kinematics of deformation at the fault tip here we present new slip rate determinations using millennial scale geomorphic markers from sites along the easternmost segment of the kunlun fault in north central tibet this fault system represents one of the major strike slip faults within the indo asian collision zone has been argued to exhibit uniform slip rates along much of its length and plays a central role in models for eastward extrusion of tibetan lithosphere displaced fluvial terrace risers along tributaries of the yellow river coupled with 14c ages of terrace material provide constraints on slip rates over late pleistocene to holocene time results indicate that slip rates decrease systematically along the eastern 150 km of the fault from 10 to 2 mm yr these data challenge the view that slip along the kunlun fault remains uniform along the entire length of the fault and instead reveal gradients in displacement similar to those expected at fault tips moreover slip along the fault appears to terminate within the thickened crust of the plateau and therefore any extrusion of tibetan lithosphere accomplished by slip along the kunlun fault must be absorbed by internal deformation of the plateau surrounding the fault tip

emplacement of the longmen shan thrust nappe belt along the eastern margin of the tibetan plateau abstract the topographic descent from the eastern margin of the tibetan plateau to the sichuan basin passes through the longmen shan thrust nappe belt which is sub divided by six nw dipping major listric thrusts with accompanying duplexes and imbricate fans into five large scale nappes each nappe has its own stratigraphic and deformational features in the inner longmen shan longmen mountains allochthonous nappe units have incorporated both mesoproterozoic basement and sinian neoproterozoic to triassic cover sequences as thick skinned horses whereas in the frontal longmen shan sinian cretaceous cover sediments have been stripped from the basement as thin skinned fold and thrust sheets including the extensively distributed klippen structures pre thrusting extension during devonian to middle late triassic times resulted in syn depositional normal faults structural inversion of these faults initiated the peng xian guan xian basement complex jiuding shan and tangwangzhai nappes during the early episode of the indosinian orogeny norian to rhaetian this was followed by episodic thrusting during latest triassic to early cretaceous times to develop the guan xian an xian and southeastern marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the thrust nappe belt during a late miocene reactivation of the pre existing thrusts differential thrusting occurred across the thrust nappe belt

constraints on pb closure temperature in titanite based on rocks from the ungava orogen canada implications for u pb geochronology and p t t path determinations on the basis of multiequilibrium metamorphic pressure temperature p t estimates we have determined that 660 700 c is a reasonable minimum estimate of the closure t of pb diffusion in titanite a temperature significantly higher than previously suggested activity corrected reactions that produce titanite define narrow t stability fields 40 c that correspond closely to metamorphic p t determinations derived for coronitic garnet clinopyroxene hornblende samples growth of titanite occurring between 1789 and 1814 ma in the underthrust archean basement of the paleoproterozoic ungava orogen northern quebec is associated with retrograde metamorphism during underthrusting of the archean basement approx 1 b y after formation of the original granulitic assemblages

u th pb geochronology of zircon and monazite from syenite and pincinite xenoliths in pliocene alkali basalts of the intra carpathian back arc basin abstract phreatomagmatic eruptions in the lucenec basin in slovakia ejected fragments of igneous rocks of unknown age and ranging in composition from gabbro to syenite and orthopyroxene granodiorite pincinite two kinds of syenites with different fe3 contents composed of anorthoclase and interstitial metaluminous trachyte to alkali rhyolite glass represent the final products of alkali basalt differentiation at depths of 10 and 15 18 km pincinite composed of plagioclase quartz orthopyroxene ilmenite and interstitial peraluminous dacite glass is a quenched supersolidus anatectic melt formed at the depth of 17 20 km by high temperature dehydration melting of biotite bearing gneissic protolith zircon from pincinite and syenite and monazite from syenite were dated using excimer laser ablation icp ms the obtained ages cluster at 5 8 0 1 and 5 4 0 1 ma thus corroborating the genetic link between the two rock types and constraining the residence time of at least 300 100 ka of the parental basalt in the deep crustal magma storage zones the inferred ages overlap the upper miocene pliocene boundary and are considerably younger than spatially associated basaltic lava flows dated using the k ar method consequently the fluviolacustrine poltar formation overlying the maar structure must have sedimented during the pliocene and not during the upper miocene pontian as previously assumed

a precise 40ar 39ar reference age for the durango apatite u th he and fission track dating standard the distinctive durango apatite is widely distributed as a reference material for mineralogy geochemistry and thermochronology the apatite occurs within the cerro de mercado open pit iron mine located in the northern portion of durango city mexico it is largely confined to vugs and open fractures within the lower portion of the ore deposit apatite and iron ore formed in situ and concurrently along with emplacement of small felsic intrusions along the southern margin of the chupaderos caldera complex this activity occurred between eruptions of two major ignimbrites from the caldera complex four single crystal sanidine anorthoclase 40 ar 39 ar ages from these ignimbrites and from a conformable older unit have been used to compute a reference age of 31 44 0 18 ma 2 for the apatite itself four additional multi crystal measurements are in general agreement with this age also in agreement are a set of 24 u th sm he ages recently determined directly on the apatite which have a mean of 31 02 1 01 ma 1 with a standard error s e of 0 22 ma

comment on revisiting the yanbian terrane implications for neoproterozoic tectonic evolution of the western yangtze block south china precambrian res 151 2006 14 30

timing of granite emplacement and cooling in the songpan garze fold belt eastern tibetan plateau with tectonic implications abstract new u pb and rb sr geochronology on syn and post orogenic granites provide constraints on the timing of major tectonic events in the songpan garze fold belt west sichuan china the ma nai granite was probably syn kinematic with the main deformation and yields an age of 197 6 ma that is interpreted as an upper age limit of the indosinian event zircons and apatites from the post kinematic rilonguan granite also yield jurassic ages 195 6 and 181 4 ma the post orogenic markam massif gives two ages of 188 1 and 153 3 ma both granites are undeformed and cut structures in the triassic sedimentary rocks these results demonstrate that the major deformation and decollement tectonics in the songpan garze fold belt occurred prior to the early jurassic the wide range of ages obtained for post kinematic granites from early jurassic to late jurassic suggests that locally magmatic activity persisted for a long time at least 50 ma after the indosinian compressional tectonism no tertiary ages have been obtained suggesting that these granites were not affected strongly by the india asia collision

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

inversion of apatite fission track data for thermal history information apatite fission track length distributions and ages provide an integrated record of the low temperature 20 150 c thermal history of the host rock over geologic time scales the information content of these data is quantified by applying a stochastic optimization technique simulated annealing to determine the range of thermal histories compatible with synthetic apatite fission track data given a mathematical description of fission track annealing the goodness of fit between the observed and predicted data parameters and a slowly decreasing control parameter are treated as analogous to the free energy and temperature respectively of a thermodynamic system on this basis a boltzmann type probability distribution is defined and used to accept or reject random thermal history perturbations a priori information used to constrain the model space may include the temperature range in which the solutions are sought present day temperature the complexity of the thermal history and the maximum duration of the data sensitive thermal history this approach allows determination of the range of thermal histories compatible with an observed confined track length distribution and associated fission track age and it provides an estimate of the probability distribution of temperatures at a specific time results for synthetic data sets for diverse model thermal histories suggest that the resolution of thermal history is generally poor parts of the thermal history to which the data are most sensitive can be resolved to no better than about 10 c for ideal data bounds on acceptable time temperature space are sensitive to the assumed complexity of the thermal history but are relatively insensitive to typical uncertainties associated with the data application of this approach to real data is fundamentally limited by the uncertainty associated with extrapolating annealing models to geologic conditions

structural and geochronological constraints on the tectono thermal evolution of the danba domal terrane eastern margin of the tibetan plateau the songpan ganze terrane of the tibetan plateau is underlain by neoproterozoic crystalline basement rocks of the yangtze block these basement rocks are exposed as a series of extensional tectonic domes that form a nearly north south trending extensional belt more than 1000 km long in the eastern margin of the tibetan plateau in the danba area detachment faults separate the basement core complexes e g the gezong and gongcai complexes from the paleozoic strata which have been thinned or removed completely the cover sequences have undergone upper greenschist to lower amphibolite facies metamorphism to form the danba schist and are overlain by the triassic xikang group a thick flysch sequence both the basement rocks and the paleozoic rocks have undergone multiple stages of deformation and thus provide an excellent opportunity to study the tectono thermal evolution of the eastern margin of the tibetan plateau two stages of deformation corresponding to three generations of foliation s1 view the mathml source and view the mathml source have been recognized on the basis of structural and microscopic observations we selected amphibole and biotite separates associated with distinct generations of foliation for 40ar 39ar dating using laser microprobe incremental heating technique to place numerical constraints on the major tectono thermal events within the danba area the geochronogical results reveal an earliest metamorphic event at 258 6 0 5 ma s1 biotite and 263 6 0 8 ma s1 amphibole coinciding temporally with the mantle plume that produced the voluminous emeishan flood basalts the second event was a progressive extensional deformation first occurred at 159 166 ma view the mathml source amphibole responsible for the earlier tectonic doming of the crystalline basement and then the final tectono thermal overprint recorded by view the mathml source foliation and view the mathml source metamorphism locally in the core complexes at 47 58 ma for the gezong complex and 64 81 ma for the gongcai complex this major post orogenic extensional event is believed to be a consequence of collision between the north china and south china blocks the apparent discrepancy of the 40ar 39ar ages observed between localities suggests a slow cooling process associated with progressive uplift

quantifying landscape differences across the tibetan plateau implications for topographic relief evolution 1 we quantify the bulk topographic characteristics of the tibet qinghai plateau with specific focus on three representative regions northern central and southeastern tibet quantitative landscape information is extracted from shuttle radar topography mission digital elevation models we find that the morphology of the tibetan plateau is nonuniform with systematic regional differences the northern and central parts of the plateau are characterized by what we suggest to call positive topography i e a topography in which elevation is positively correlated with relief and mean slope a major change from the internally drained central part of tibet to the externally drained part of eastern tibet is accompanied by a transition from low to high relief and from positive to negative topography i e a topography where there is an inverse or negative correlation between elevation and relief and between elevation and mean slope relief in eastern tibet is largest along rivers as they cross an ancient eroded plateau margin at high angle to the major strike slip faults the yalong yulong thrust belt implying strong structural control of regional topography we propose that the evolution of river systems and drainage efficiency the ability of rivers to transport sediments out of the orogen coupled with tectonic uplift is the simplest mechanism to explain systematic regional differences in tibetan landscapes basin filling due to inefficient drainage played a major role in smoothing out the tectonically generated structural relief this mode of smoothing started concurrently with tectonic construction of the relief as most clearly illustrated today in the qilian shan qaidam region of the northeastern plateau in the interior of tibet further passive filling due to internal drainage only continued to smooth the local relief millions of years after the cessation of major phases of surface uplift due to crustal shortening thus diachronous beveling at high elevation produced the low relief surface of the high plateau in southeast tibet headward retreat of external drainages brought back in the global ocean base level first disrupting then interrupting the relief reduction process it produced a transitional topography by dissecting the old remnant plateau surface which introduced younger and steeper incision of this hitherto preserved high base level this provides a unifying mechanism for the formation of the low relief plateau interior and for the origin of the high elevation low relief relict surface in southeastern tibet our analysis brings forth the importance of surface processes in particular drainage efficiency in shaping plateau morphology and landscape relief such key processes appear to have been mostly ignored in numerical models of plateau deformation our results also cast doubt on and provide a more realistic alternative to the fashionable contention that a continuous preuplift low relief surface first formed at low elevation extending all the way to the south china sea shore before being warped upward in the late miocene pliocene by lower crustal channel flow

late triassic granitoids of the eastern margin of the tibetan plateau geochronology petrogenesis and implications for tectonic evolution abstract late triassic granitoids in the songpan garze fold belt sgfb on the eastern margin of the tibetan plateau formed at 230 to 220 ma and can be divided into two groups group 1 are high k calc alkaline rocks with adakitic affinities k adakites with sr 400 ppm y n 32 105 and high k 2 o na 2 o 1 group 2 are ordinary high k calc alkaline i types with lower sr 18 ppm and weakly fractionated ree patterns la yb n 0 50 to 0 94 and initial 87 sr 86 sr 0 70528 to 0 71086 but group 1 rocks have higher e nd t 1 01 to 4 84 than group 2 3 11 to 6 71 calculated initial pb isotope ratios for both groups are 206 pb 204 pb 18 343 to 18 627 207 pb 204 pb 15 610 to 15 705 and 208 pb 204 pb 38 269 to 3759 group 1 magmas were derived through partial melting of thickened and then delaminated ttg type eclogitic lower crust with some contribution from juvenile enriched mantle melts group 2 magmas were generated by partial melting of shallower lower crustal rocks the inferred magma sources of both groups suggest that the basement of the sgfb was similar to the exposed kangding complex and that the sgfb was formed in a similar manner to the south china basement here passive margin crust was greatly thickened and then delaminated all within a very short time interval 20 myr such post collisional crustal thickening could be the tectonic setting for the generation of many adakitic magmas especially where there is no spatial and temporal association with subduction

mesozoic plutons of the yidun arc sw china u pb geochronology and hf isotopic signature abstract the yidun arc is a triassic volcanic arc located between the songpan garze fold belt and the qiangtang block southwest china to constrain the age of a number of the major granitic plutons from the yidun arc laser ablation icp ms u pb analysis of zircon was conducted hafnium isotope data was also acquired through laser ablation multicollector icpms analysis of zircon with the aim of gaining insight into the age and nature of the source region of the plutons three age groups have been identified from seven granite samples early middle triassic 245 to 229 ma late triassic 219 to 216 ma and cretaceous 105 to 95 ma hafnium analysis shows the triassic granites to have negative and variable e hf values and mesoproterozoic 1 6 ga depleted mantle model ages which is interpreted to reflect derivation from an isotopically heterogeneous largely crustal source the cretaceous granite shows higher and less variable e hf values and slightly younger model ages 1 3 ga and is interpreted to be derived from melting of a more homogeneous crustal source a depleted mantle model age of 1 5 ga is calculated from the pooled triassic and cretaceous samples the source region for these magmas may be tentatively correlated with mesoproterozoic material of the yangtze craton which has been suggested to underlie the yidun arc however further work is necessary to demonstrate this suggestion