aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

s wave velocity images of the crust in the southeast margin of tibet revealed by receiver functions the southeast margin of tibet is the region in clockwise rotation around the eastern himalayan syntaxis due to the india eurasia collision and the resistance of the stable sichuan basin and south china block however the dynamic processes involved in the evolution and deformation of the region remain poorly understood due to a lack of reliable geophysical observations we collected abundant seismic data recorded by 108 permanent broadband stations deployed in the se margin of tibet since 2000 and obtained 4536 pairs of p wave receiver functions prfs with high signal to noise ratio in this study we have implemented a novel two step data inversion procedure that can reduce the dependence of the inversion results on the initial model we first use low frequency prfs obtained by iterative deconvolution in the time domain and then an initial model consisting of a series of 2 km thick isotropic layers to fit velocity models and thus determine an overall statistical solution by means of the bootstrap resampling technique this statistical solution is then regarded as a new initial model to adjust high frequency prfs hence the same resampling process is executed again to estimate the optimal s wave velocity structure below each station the results provide an accurate 3d image of the crust and uppermost mantle in the se margin of tibet we infer a wide intra crustal low velocity zone that varies laterally and in depth which is thinner or even absent in the most southern part of yunnan our hypothesis is that this low velocity zone is the result of the accumulation of lower crustal flow coming from central tibet furthermore we show that this lower crustal flow extends largely through the sichuan yunnan diamond shaped block and that there are significant variations in both crustal velocity structure and deformation mechanism across the great strike slip faults of the jinshajiang red river and xiaojiang fault systems

magma chamber and crustal channel flow structures in the tengchong volcano area from 3 d mt inversion at the intracontinental block boundary southeast of the tibetan plateau

geochemistry and geochronology of late cenozoic basalts of southeast asia summary geological maps of southeast asia asia 1971 vietnam 1971 thailand 1969 show numerous occurrences of basalt which are considered to be late cenozoic in age occurrences in thailand and western kampuchea are generally small and scattered those in eastern kampuchea southern laos and vietnam are larger and more extensive fig 1 basalt bodies of similar age also occur in malaysia and southern china fig 1 these basalts form a late cenozoic continental volcanic province comparable to those in eastern australia irving and green 1976 and the western united states christiansen and lipman 1972 leeman and rogers 1970 basalts in southeast asia are especially intriguing as they are a major source of gem quality ruby sapphire and zircon fontaine and workman 1978 berrange and jobbins 1976 the purpose of this paper is to describe the distribution geochemistry and age of basalts in southeast asia available geochemical and age data are compiled and combined with new data from previously unstudied areas this is the first known regional synthesis that has been attempted for this large but relatively undocumented basaltic province

constraints on early cenozoic underplating driven uplift and denudation of western scotland from low temperature thermochronometry apatite u th he and fission track data from profiles in western scotland constrain the timing and magnitude of denudation during the early cenozoic when the north atlantic region was the site of intense magmatic activity related to the proto icelandic plume apatite helium ages vary from 77 8 to 265 27 ma 2 at sgorr dhonuill ballachulish and from 104 10 ma to 166 17 ma at clisham outer hebrides at both locations apatite fission track aft ages are older than the corresponding he ages at clisham they vary from 189 28 ma to 242 26 ma and from 186 6 ma to 257 12 ma at sgorr dhonuill apatite he ages increase linearly with elevation suggesting that the cooling rate remained constant in the late mesozoic however the apatite he age profile requires a period of rapid cooling after 100 ma apatite he ages predicted from the aft derived thermal histories are indistinguishable from measured he ages for a rapid cooling event of 1 to 10 myr duration between 61 and 47 ma at sgorr dhonuill and 65 to 49 ma at clisham the combined apatite ft and he derived thermal histories constrain the early cenozoic geothermal gradient at 39 9 c km at sgorr dhonuill and 19 6 c km at clisham amounts of denudation related to the rapid cooling event vary from 1330 230 m at sgorr dhonuill to 2250 750 m at clisham in agreement with models that predict greater amounts of denudation where magmatic underplating is thicker however the direct correlation between underplating driven surface uplift and denudation may only be apparent and a more complex link between spatial variation of surface uplift and denudation is suggested the integration of results from multiple low temperature thermochronometers combined with inverse and forward modelling provides a convincing and quantitative method to deduce onshore erosional histories and provides critical information about the spatial distribution of erosion that cannot be derived from the offshore record

relationships between meso cenozoic denudation in the eastern tian shan and uranium mineralization in the turpan hami basin nw china constraints from apatite fission track study abstract the eastern tian shan tectonic belt located in the southern domain of the central asian orogenic belt consists of the bogda mountain range turpan hami tuha basin and choltagh mountain range from north to south understanding the meso cenozoic denudation history of the eastern tian shan is critical to unravel the genesis of sandstone type uranium u mineralization in the tuha basin in this paper thirteen granite and sandstone samples were collected along two north south transects in the west of the eastern tian shan for apatite fission track thermochronological study the apatite fission track ages obtained in this study in combination with the thermal history modeling results and previous thermochronological data indicate three main episodes of denudation in the eastern tian shan since the mesozoic i e late jurassic to early cretaceous 160 135 ma late cretaceous to early eocene 100 50 ma and late eocene to early miocene 35 20 ma the late cretaceous denudation events are related to the kohistan dras arc accretion collision that affects the tian shan mountain range extensively whereas the cenozoic ones are related to the india asia collision regional distribution of apatite fission track ages in the eastern tian shan and comparison with u mineralization ages in the tuha basin suggest that the choltagh mountain range began to denudate in the late jurassic exposing high u bearing volcanic rocks on the surface and resulting in significant u mineralization in the southern part of the tuha basin in the cretaceous whereas the bogda mountain range in the north did not experience significant denudation until the late eocene due to the relatively low exhumation of the bogda mountain range and limited exposure of u bearing rocks u mineralization in the tuha basin is minor during the cenozoic but the newly deposited sediments helped the preservation of the u deposits that were formed in the cretaceous

crustal structure in the tengchong volcanic area and position of the magma chambers abstract in this paper we extract 1500 p receiver functions in the tengchong volcanic area from 211 teleseismic events recorded at nine digital seismic stations a common conversion point stacking technique is used to improve the signal to noise ratio and to get the time delays of the ps ppps psps ppss phases within grids of 10 km 10 km finally the crustal thickness and poisson s ratio are calculated the results show that the crustal thickness ranges from 28 to 40 km and the poisson s ratio ranges from 0 28 to 0 36 there exist two mantle uplifting sites each with a horizontal scale of about 30 km 30 km one in mazhan tengchong maanshan and the other in wuhe longjiang tuantian the high poisson s ratio is consistently located within these two sites recorded shocks with ms 2 0 reveal that most of the shocks are distributed around the two sites and few are located at the centers the shocks the geothermal distribution and the crustal structure suggest that the magma is still active and the two mantle uplifting sites detected may be the positions of two magma chambers in the crust

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

were a couple of kilometres of palaeocene eocene strata ever deposited across most of the sichuan basin reply deng et al 2015b propose that a couple of kilometres of palaeocene eocene strata were deposited across most of the sichuan basin and later eroded mainly based on their low t thermochronological data they further propose that such a geological process would influence the datum plane of our isostatic model and the cenozoic elevation history of the sichuan tarim and qaidam basins indeed we selected the modern state of suining as the datum plane for all our isostatic calculations yu et al 2015 it is a static datum plane rather than a dynamic datum plane this approach is conventional zhang et al 2010 therefore how suining evolved during the cenozoic does not influence the isostatic model and the palaeoelevation estimation of the qaidam basin we stress the lack of cenozoic deposits and the lack of visible cenozoic uplift in the sichuan basin yu et al 2015 but we do not rule out the possibility of erosion the sichuan basin may have experienced a certain amount of erosion during the cenozoic according to the isostatic model the erosion of crust including basement and stratigraphy leads to elevation loss fig 1 endorheic basins accumulate sediments and increase in elevation while exorheic basins under certain conditions discharge sediments by erosion and thereby decrease elevation however compared with the visible deposit thickness the magnitude of erosion is more difficult to estimate we do not adopt the low t thermochronological data provided by deng et al 2009 2013 2015a b because their data and conclusion are contradictory and questionable for the central sichuan basin deng et al 2015b suggest that 1000 2000 m of palaeogene strata were deposited across the sichuan basin and then eroded during the late cenozoic however if such thick palaeocene eocene strata had been deposited a dramatic drop between 65 and 34 ma should be seen on the t time t temperature paths of aft apatite fission track thermalhistory modelling fig 2 regretfully no such drop is seen in their articles deng et al 2009 2013 2015b and on the contrary the area records uplift since the late cretaceous deng et al 2015b furthermore the sichuan basin that we refer to is the central part to the west of the huaying mountain and to the east of the longquan mountain most of the aft thermal history modelling results presented by deng et al 2009 2013 2015b are distributed at the margins of the sichuan basin e g the huaying mountain the longmen mountain s piedmont it is common sense that the exhumation rate of the surrounding mountains or basin mountain transition zones is much faster than that of the central basin therefore low t thermochronological results from the basin margin cannot reveal the geological history of the central sichuan basin only four aft thermal history modelling results slg01 sn01 m24 1 m242 in the central sichuan basin are presented by deng et al 2009 2013 2015b however the single grain age of slg01 does not pass the chisquared test p v 5 so it is unsuitable for aft thermal history modelling ketcham et al 2000 p v of sample sn01 is only 8 6 the cooling magnitude of the drilling sample m24 1 is limited since the late cenozoic and the region of good fit is broad deng et al 2013 the modern temperature setting of the drilling sample m24 2 on the t t

cooling history and tectonic exhumation stages of the south central tibetan plateau china constrained by 40ar 39ar and apatite fission track thermochronology between the qiangtang block and yalung zangpo suture zone in the south central tibetan plateau the following geological units and suture zones have been identified from south to north the gangdese granitic belt the lhasa block the nyainqentanghla shear zone the dangxiong sangxiong tectono granitic belt and the bangong nujiang suture zone to better constrain the tectonic evolution and cooling histories of these units 40 ar 39 ar muscovite biotite and k feldspar as well as apatite fission track dating and thermochronological analysis have been carried out the analytical results indicate that the south central tibetan plateau with the exception of the nyainqentanghla shear zone provides a record of three cooling stages at 165 150 130 110 and 45 35 ma fission track data modelling also indicates that the stages of cooling were different in the different tectonic belts or blocks very different cooling phases occurred in the south central tibetan plateau compared with southern tibet as well as along the yalung zangpo suture zone there is no thermochronological evidence to indicate that the south central part of tibetan plateau was influenced by the underthrusting of indian plate the three stage cooling history and the stages of tectonic exhumation were controlled completely by the closure of the bangong nujiang suture zone along its eastern segment during middle late jurassic 165 150 ma and its western segment in the early late cretaceous 130 110 ma as well as by the collision between the indian and asian plates in the paleogene 45 35 ma 2005 elsevier ltd all rights reserved

the quaternary eruptive sequence of the tengchong volcanic group southwestern china abstract the tengchong volcanic group in sw china is situated along the ns oriented tectonic belt in the southeastern margin of the tibetan plateau the volcanic field has experienced intense tectonic stress due to the continuous subduction of the indian plate under the eurasian plate and throughout quaternary has experienced pervasive volcanism the present volcanic rocks cover the successive domains of basic intermediate group ii and acid group i rocks belonging to the high k calc alkaline series correspondingly the eruption types of the tengchong volcanoes roughly fall into two categories explosive eruptions with large amounts of volcaniclastics and lava and moderately quiet central eruptions with small amounts of scoria and lava overflow according to systematic geochronological dating methods such as k ar ar ar 14c ams and osl dating as well as field work we separate the eruptive sequence of the tengchong volcanic group during the quaternary into four subsequences the early pleistocene middle pleistocene late pleistocene and the holocene epoch the early to middle quaternary eruption sequence consists of a series of explosive eruptions with almost all the eruptive dacitic volcaniclasts and lava constituting the bottom layer of the tengchong basin the tengchong volcanism reached its climax in the late pleistocene when it formed numerous cinder cones a series of moderately quiet central eruptions occurred in the late quaternary and basic and intermediate acid volcanic rocks formed the upper layer of the basin from this study three volcanoes are determined to be of holocene age and we conclude that the volcanic activity moved from the south and periphery to the north and center and ended in the heikongshan eruption 3600 years ago

isotopic and geochemical evidence for the origin of plio pleistocene volcanic rocks near the indo eurasian collisional margin at tengchong china abstract in yunnan province china regional extensional stresses associated with the collision between india and asia have formed a series of downfaulted north south trending basins near tengchong in extreme western yunnan close to the burma border one of these basins is characterized by volcanism which began in the pliocene 7m y and has continued to historic times the tengchong volcanic suite ranges in composition from basalt to dacite with most lavas being potassium rich five chemical groups can be recognized based on major element trace element and isotopic compositions these groups are broadly consistent with previous groupings made on the basis of geologic and age data the chemical and isotopic data show that the main series most voluminous lavas were derived by partial melting of a metasomatized and heterogeneous mantle source with crustal and possibly seawater components probably related to prior subduction beneath asia an andesite dacite series with similarities to tibetan calc alkaline lavas shows clear indications of assimilated crust and crystal fractionation there is no evidence in these rocks for the presence of a strongly depleted subcontinental mantle such as has been recognized elsewhere 5 21

laboratory and analytical model studies of the faroe bank channel deep water outflow abstract results are described from a combined laboratory and analytical study of the dense deep water flow through the faroe bank channel archival field data have been used to specify the velocity and density field conditions in an idealized distorted laboratory model in which the spatial and temporal development of a turbulent dense source flow has been studied parametrically in terms of the source rossby and froude numbers respectively measurements are presented to show that the flow i maintains geostrophic balance within the topographically varying channel and ii adjusts on the ekman time scale to changing flow conditions the outflow structure is shown to consist of a dominant axial i e along channel core component with a significant transverse i e side slope secondary circulation driven by ekman drainage and topographic divergence processes density field measurements are presented to show the mixing occurring between the turbulent outflow and the overlying water mass buoyancy an

stress on the mediterranean outflow plume part i velocity and water property measurements abstract in september 1988 six sections were occupied across the mediterranean outflow plume in the gulf of cadiz within 100 km of the strait of gibraltar vertical profiles of temperature and salinity were collected at ctd stations velocity and temperature profiles were collected with expendable current profilers at a subset of these stations at the channel base the plume undergoes geostrophic adjustment and turns northwest to flow along the continental slope there it decelerates and spreads gradually down the slope as friction slows the current and allows it to cross isobaths within the plume downstream velocity and density increase rapidly in the interfacial layer with depth to the velocity maximum or nose 5 150 m above the bottom below the nose in the bottom layer downstream velocity decreases rapidly toward the bottom but the stratification is weak ekman like veering occurs in the interfacial layer local bottom stresses on the plume are estimated by fitting the near bottom velocity prof

southward extension of the bangonghu nujiang suture evidence from early cretaceous intermediate and felsic magmatism in the gaoligong orogen china abstract it remains debated as to whether the gaoligong orogen between the tengchong and baoshan blocks in yunnan china is the southward extension of the tibetan bangonghu nujiang suture bns here we present new geochronological and petrochemical data for early cretaceous magmatic rocks of the gaoligong orogen the la icp ms u pb dating of zircons from diorites granodiorites and granites yielded weighted mean 206pb 238u ages of 120 118 128 122 and 109 128 ma respectively for the diorites the ehf t values of zircons fall in a range of 1 2 to 5 4 with tdmc ages of 744 979 ma for the granodiorites they fall in a range of 9 8 to 2 9 with tdmc ages of 888 1564 ma and for the granites the range is 8 0 to 1 1 with tdmc ages of 1101 1488 ma they are magnsian calc alkaline enriched in liles and lrees and have strong negative nb ta p and ti anomalies and high values of mg all these features are indicative of continental arc affinities the data suggest that the dioritic and granitic magmas were produced by the mixing of variable proportions of mantle and crust derived magmas at an active continental margin the ages and tectonic settings of the diorites granodiorites and granites are similar to rocks found within the bns considering the ophiolitic melange belt the middle jurassic basaltic magmatism and the marine facies stratigraphic features of the gaoligong orogen are very similar to features in the bns we conclude that the gaoligong orogen represents the suture between the tengchong and baoshan blocks and is the southward extension of the bns

qualitative and quantitative approaches in palaeohydrography a case study from core top parameters in the gulf of cadiz palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters areas of dynamic watermass mixing which generally have steep hydrographic gradients therefore provide both a tempting target large spatial and temporal differences in temperature and salinity and a significant challenge high flow velocities and high noise for palaeoceanographers here we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing the gulf of cadiz using grainsize sediment composition benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern mediterranean outflow water mw plume we propose that the gulf of cadiz slope can be sub divided into 8 hydrographic zones reflecting these parameters proximal mw core mw1 steep slopes core mw1 gentle slopes distal mw1 distal mw2 lower limit of mw plume north atlantic deep water and ambient atlantic water we anticipate that compilation of time slice data will reveal hydrographic sub divisions of the slope for the past in a similar manner improving our understanding of past changes in the size and position of the mw plume but more work needs to be done before a secure protocol for quantitative reconstruction can be created stable isotope analysis alone is insufficient for the task with 13c behaving in a non conservative manner and 18ocalcite acting in an ambiguous way due to the competing influences of 18owater and temperature it is likely that if a single parameter that unambiguously determines the difference between mediterranean water and atlantic water can be identified combination with 18ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region similar complexity to that found in this study would be expected in any mixing region and in particular on the majority of sediment drifts we recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted

laboratory model studies of mediterranean outflow adjustment in the gulf of cadiz results are presented from a series of laboratory modelling studies carried out as part of the international multidisciplinary project canigo the focus of interest has been the phenomenon of flow adjustment within the gulf of cadiz of the mediterranean outflow plume modelled by a turbulent negatively buoyant jet discharging into a rotating stratified reservoir scaled to the idealised topography of the gulf the results show that the fully developed flow pattern that forms close to the entrance to the gulf consists of a relatively intense jet that divides when it encounters the southern iberian coastal boundary part of the jet is deflected westwards to form a boundary current at intermediate depth along the coastline and part is deflected eastwards and back towards the strait to form a closed weak circulation near the diverging right wall of the gulf within this closed circulation the typical horizontal dimensions of which scale with the source froude number when normalised with the inertial radius small scale eddy features are embedded the degree of entrainment into the descending turbulent jet is seen to be determined primarily by the receiving water froude number and is relatively insensitive to the burger and rossby numbers of the flow resulting in the formation of a boundary current of intermediate density that follows the iberian coastal boundary with a typical velocity determined primarily by the effective driving head at the source and weakly by the burger number of the flow

geochemical and geochronological characteristics of late cretaceous to early paleocene granitoids in the tengchong block southwestern china implications for crustal anatexis and thickness variations along the eastern neo tethys subduction zone abstract the tengchong block of southwestern china is key to tracing the eastward subduction of neo tethys and collision between indian and asian continents the block contains a magmatic belt that represents the southeastward continuation of the gangdese belt produced by the eastward subduction of eastern neo tethyan oceanic lithosphere in this paper we present geochemical and geochronological data of late cretaceous to early paleocene 64 ma granitic rocks of the guyong and husa batholiths in the tengchong block these can be subdivided into high silica peraluminous granites and low silica metaluminous granodiorites and all belong to the high k calc alkaline series are enriched in lile and depleted in hfse the guyong granitoids have high initial sr ratios of 0 706511 0 711753 negative e nd t values of 9 2 to 11 6 two stage model ages of 1 39 1 55 ga and pb isotopic compositions that indicate a crustal affinity the husa granodiorites also have high initial sr ratios of 0 716496 negative e nd t value of 16 5 two stage model age of 1 89 ga variable e hf t values of 3 4 to 18 1 and pb isotopic compositions similar to lower crustal values these geochemical and isotopic data indicate that the guyong granitoids were likely derived from partial melting of ancient crustal metapelite or mixed pelite greywacke sources while the husa granodiorites were derived from the partial melting of lower crustal mixed sources involving metasedimentary and metaigneous rocks to understand the thermal state and architecture of the late cretaceous to early paleocene magmatic arc crust the crust derived intermediate to acidic igneous rocks of the southern central lhasa and tengchong blocks and eastern himalayan syntaxis are compared we infer that partial melting of crust occurred at great depth in the southern lhasa block intermediate depths in the eastern himalayan syntaxis and shallow depths in the central lhasa and tengchong block sr y ratios indicate that the tengchong block was characterized by thin crust while the eastern himalayan syntaxis and northernmost part of southern lhasa block contained crust of normal thickness and the southernmost part of the southern lhasa block contained thickened crust

mesozoic thermal history of the prebetic continental margin southern spain constraints from apatite fission track analysis apatite fission track analysis was applied to triassic and cretaceous sediments from the south iberian continental margin to unravel its thermal history apatite fission track age populations from triassic samples indicate partial annealing and point to a maximum temperature of around 100 110 c during their post depositional evolution in certain apatites from cretaceous samples two different fission track age populations of 93 99 and around 180 ma can be distinguished track lengths associated with these two populations enabled thermal modelling based on experimental annealing and mathematical algorithms these thermal models indicate that the post depositional thermal evolution attained temperatures 70 c which is consistent with available vitrinitereflectance data thermal modelling for the cretaceous samples makes it possible to decipher a succession of cooling and heating periods consisting of a a late carboniferous permian cooling followed by b a progressive heating episode that ended approximately 120 ma at a maximum tof around 110 c the first cooling episode resulted from a combination of factors such as the relaxation of the thermal anomaly related to the termination of the hercynian cycle the progressive exhumation of the hercynian basement and the thermal subsidence related to the rifting of the bay of biscay reactivated during the late permian jurassic thermal evolution deduced from the inherited thermal signal in the cretaceous sediments is characterized by progressive heating that ended around 120 ma this heating episode is related to thermal subsidence during jurassic rifting in agreement with the presence of abundant mantle derived tholeiitic magmas interbedded in the jurassic rocks the end of the jurassic rifting is well marked by a cooling episode apparently starting during neocomiam times and ending at surface conditions by albian times

cenozoic tectonic and geodynamic evolution of the kyrgyz tien shan mountains a review of geological thermochronological and geophysical data abstract the complex crustal structure of the tien shan has a strong impact on the distribution of strain induced by the india eurasia collision with intracontinental deformation in eurasia s interior as a distant effect the northward propagation of the india eurasia deformation front is suggested by the rejuvenation of mountain ranges and intermittent intramontane basins the tien shan basement is formed by the rigid heterogeneous precambrian blocks microcontinents of tarim issyk kul or central tien shan and aktyuz boordin surrounded by a soft matrix of paleozoic accretion collision belts the kyrgyz tien shan mountains are situated between the active structures of the tarim plate and the pamir indenter south and the stable kazakhstan shield north underplating by the tarim plate and thrusting by the pamirs are responsible for the building of the cenozoic tien shan the reactivation of its inherited structural fabric and the tectonic layering of the upper lithosphere underlying the area large earthquakes m 6 delineate the northern and southern margins of the issyk kul microcontinent indicating that crustal heterogeneity influenced the location of active structures in the northern kyrgyz tien shan

intensified climate driven exhumation along the south himalayan front since one million years ago abstract this paper builds a database of apatite fission track aft ages and thermal modeling results covering the whole southern tibetan plateau providing detailed information on the cooling and erosion process of the modern landscape evolution and comparing with the distribution of climatic factors large scale aft age distribution and thermal history modeling results indicate extraordinarily intense erosion along the south himalayan front and relatively weak erosion in the interior of the plateau aft samples from different regions plot into different partitions on the elevation vs aft age diagram and there is an excellent coupling between aft ages and climatic factors based on aft thermal history modeling results an intensified erosion event since 1 myr ago has been identified along the south himalayan front the varied aft ages along the south himalayan front are probably induced by differential intensity of erosion in the same cooling event rather than the time when the rapid cooling event began meanwhile the spatiotemporal coupling of climatic factors and the intensified erosion belt suggests that climatic transition is the key factor dominating the rapid exhumation event since 1 myr

fission track evidence for late oligocene and mid miocene activity along the north anatolian fault in south western thrace apatite fission track ft analyses of sandstone samples collected across the trace of the ganos segment of the north anatolian fault naf in south western thrace turkey indicate that a significant structural discontinuity was in existence at least by the latest oligocene such discontinuity had a complex kinematic history as exhumation south of it occurred during the latest oligocene and north of it during the mid miocene our data imply that early pliocene westward propagation of the naf in the marmara region followed a pre existing structural discontinuity such discontinuity could be related to the development of the intra pontide suture marking the terminal closure of the intra pontide ocean during the oligocene

tectonic controls on the late miocene holocene volcanic eruptions of the tengchong volcanic field along the southeastern margin of the tibetan plateau abstract the tengchong volcanic field located along the southeastern margin of the tibetan plateau experienced multiple eruption stages since the late miocene including time intervals of 5 5 4 0 ma 3 9 0 9 ma 0 8 0 01 ma and younger than 0 01 ma these eruption stages produced different volcanic rocks principally basaltic and basaltic andesite series at the same time or prior to volcanic eruptions in the tengchong volcanic field ne nne trending rift basins and ns striking normal faults formed during the late miocene pliocene in addition rapid exhumation of the neighboring mountains occurred at 6 5 ma constrained by apatite fission track dating and its thermochronological modeling at present the state of stress in the tengchong volcanic field and its surroundings is nne ne compression and wnw nw extension based on seismic foci mechanisms petrologic and geochemical data indicate that the source of the tengchong volcanic rocks belongs to an intracontinental tectonic setting but not a subduction or collision zone between indian and eurasian plates since the late miocene the dextral strike slip motion of the sagaing fault induced e w extension the sagaing dextral strike slip motion might disturb the lower crust upper mantle of the tengchong block resulting in the partial melting of the upper mantle which in turn induced volcanic eruptions characterized by mature island arc features

eddy formation by dense flows on slopes in a rotating fluid properties of the flow generated by a continuous source of dense fluid on a slope in a rotating system are investigated with a variety of laboratory experiments the dense fluid may initially flow down the slope but it turns under the influence of rotation to flow along the slope and initial geostrophic adjustment gives it an anticyclonic velocity profile some of the dense fluid drains downslope in a viscous ekman layer which may become unstable to growing waves provided that the viscous draining is not too strong cyclonic vortices form periodically in the upper layer and the dense flow breaks up into a series of domes three processes may contribute to the formation of these eddies first initial downslope flow of the dense current may stretch columns of ambient fluid by the taylor column process which we term capture secondly the initial geostrophic adjustment implies lower layer collapse which may stretch the fluid column and thirdly viscous drainage will progressively stretch and spin up a captured water column overall this last process may be the most significant but viscous drainage has contradictory effects in that it progressively removes dense lower layer fluid which terminates the process when the layer thickness approaches that of the ekman layer the eddies produced propagate along the slope owing to the combined effects of buoyancy coriolis balance and beta gyres this removes fluid from the vicinity of the source and causes the cycle to repeat the vorticity of the upper layer cyclones increases linearly with l d where l is the rossby deformation radius the bottom slope and d the total depth reaching approximately 2 f in the experiments presented here the frequency at which the eddy dome structures are produced also increases with while the speed at which the structures propagate along the slope is reduced by viscous effects the flow of dense fluid on slopes is a very important part of the global ocean circulation system and the implications of the laboratory experiments for oceanographic flows are discussed

mesozoic to quaternary continental margin dynamics in south central chile 36 42 s the apatite and zircon fission track perspective zircon and apatite fission track data provide constraints on the exhumation history fault activity and thermal evolution of the south central chilean active continental margin 36 s 42 s which we use to assess the tectonic and geomorphic response of the margin to the andean subduction regime several domains with different exhumation histories are identified the coastal cordillera is characterized by uniform and coherent exhumation between late triassic 200 ma and late miocene times with surprisingly slow average rates of 0 03 0 04 mm a thermal anomalies related to late cretaceous and early miocene magmatism have regionally modified fission track age patterns the upper cretaceous thermal overprint is of previously unrecognized significance and extent in the coastal cordillera south of 39 s with the exception of a local but distinct pliocene to recent exhumation period in the high relief cordillera nahuelbuta segment between 37 s and 38 s cenozoic overall exhumation in the coastal cordillera was very slow the sedimentary record shows that uplift and subsidence here was episodic with low amplitudes and durations this rules out large scale long term cenozoic accretion trench parallel tilting and tectonic erosion processes in the forearc the main andean cordillera shows markedly greater long term exhumation rates than the coastal cordillera and at 39 s a steep exhumation gradient to the south long term average pliocene to recent exhumation rates of 1 to 2 mm a in the liquine area 39 45 s are almost an order of magnitude more rapid than average paleogene to recent exhumation near lonquimay 38 30 s and farther north while no imprint of the intra arc liquine ofqui fault zone on the exhumation pattern is evident long term exhumation rates decrease from the crest of the andes toward the western foothills exhumation gradients correlate with climatic gradients suggesting a causal link to the variable intensity of late miocene to pleistocene glacial erosion

low temperature thermal history and landscape development of the eastern adirondack mountains new york constraints from apatite fission track thermochronology and apatite u th he dating the adirondack mountains in northern new york state form an elongate domal exposure of mainly high grade metamor phic tectonites in a mountainous setting with topographic relief of 1 km the origin of the adirondack mountains and this relief has long been enigmatic since the adirondacks presently lie within an intracratonic setting inboard of the north american passive mar gin and far from any active plate boundaries through the application of apatite fi ssion track aft thermochronology and apatite u th he ahe dating within the eastern adirondack mountains this study provides constraints on both the thermal and ero sional effects of mesozoic passage near a hot spot and the timing of relief development aft thermochronology and ahe dating record relatively stable thermal conditions within the eastern adirondacks from the middle jurassic into the early cretaceous during the early cretaceous ca 130 120 ma the region underwent heating as sociated with progressive movement near the great meteor hotspot resulting in the temporary establishment of an elevated geo thermal gradient following regional heat ing cooling rates increased considerably ca 105 95 ma likely due to both thermal doming producing an increase in erosion rate and the relaxation of isotherms after passage near the hotspot the regional distribution of aft ages across the eastern adirondacks reveals no systematic age gradient from core to periph ery which would be expected under con ditions of persistent high relief during the decay of a crustal root over many tens to hun dreds of millions of years instead thermo chronological data suggest that the present relief developed during the late cretaceous cenozoic through plateau dissection during periodic base level changes

exhumation history of the southern altiplano plateau southern bolivia constrained by apatite fission track thermochronology 1 although the structural geometry of the cenozoic altiplano puna plateau in the central andes is well defined the temporal evolution of this contractile deformation is poorly constrained to address this shortcoming we used apatite fission track thermochronology aft to quantify the cooling and exhumation history along a transect at 21 s in southern bolivia through the deformed intermontane altiplano basin the doubly vergent thrust belt of the eastern cordillera and the inner foreland thrust belt east of the plateau interandean zone thermal history modeling combined with published balanced cross sections and stratigraphic data constrain exhumation histories exhumation started during the late eocene 40 36 ma in the central eastern cordillera possibly due to bivergent thrusting and cretaceous rift structure inversion during the early oligocene 33 27 ma exhumation spread across the study area as the current boundary thrusts of the eastern cordillera were activated the inner west vergent thrust system became active in irregular order until circa 20 ma whereas the east vergent interandean thrust belt formed by eastward propagating deformation since circa 30 ma plateau exhumation continued at 0 2 mm yr until shortening terminated by 11 7 ma shortening within the plateau since circa 30 ma did not evolve by lateral accretion of thrust wedges the propagating deformation style is spatially confined to the foreland thrust belt which initiated coeval to plateau deformation interandean zone but propagated mainly after circa 10 ma subandean zone early oligocene plateau wide tectonically driven exhumation suggests that subduction related processes had already thermally weakened the continental lithosphere prior to the 27 25 ma onset of volcanic activity

laboratory simulation of exchange through fram strait laboratory experiments and theory were conducted to observe the flow patterns and transport in both buoyancy driven and wind driven rotating fluids in lock exchange experiments water with one density flows into a second basin after a sliding gate is removed water of a second density flows back into the first basin the size and location of the currents for various values of density difference rotation rate and assorted sidewall geometries was recorded volume flux of the fluid was also measured and compared with a theory for lock exchange flow of a rotating fluid in a separate group of experiments with a passive upper layer easterly winds like those in the arctic ocean drive the upper level water into the arctic ocean and therefore oppose the buoyant exchange westerly winds would drive the water out of the arctic ocean this indicates that the exchange between the arctic ocean and the greenland norwegian sea is likely to be driven by buoyancy rather than by driven by wind crude estimates of the volumetric and fresh water exchange rate from the lock exchange formulas are compared with observed ocean fluxes and approximate agreement is found

characteristics of focal mechanisms and the stress field in the southeastern margin of the tibetan plateau crustal earthquake focal mechanisms are investigated in the southeastern margin of the tibetan plateau where the tibetan plateau and stable south china block merge an updated database of focal mechanisms has been compiled by selecting 132 global centroid moment tensor solutions and by adding the 173 new solutions 3 5 ms 7 4 estimated by waveform inversion in this study a total of 305 mechanisms are included in this database these solutions show regionally specific distributions with dominant strike slip faulting and some normal and reverse faulting focal mechanism solutions have also been inverted for the stress tensor orientation to obtain the principal stress axes over the study region results show that the horizontal maximum principal 1 axes rotate clockwise with a wider range than the geodetically measured surface motion in the east which is not limited to the xianshuihe xiaojiang fault but has some overlap with the zhaotong lianfeng fault localized normal faulting stress regimes are observed in the jinshajiang litang fault areas and the baoshan sub block the minimum principal axes are oriented with a gradually changing trend from north south to northwest southeast from north to south indicating diverse compression stress patterns significant changes in the crustal stress field after the wenchuan earthquake are preliminarily observed in the baoshan sub block where orientations of two principal axes have changed and in the jinggu ximeng sub block areas where the strike slip faulting stress pattern has transformed to normal faulting

tracing the transhimalayan magmatic belt and the lhasa block southward using zircon u pb lu hf isotopic and geochemical data cretaceous cenozoic granitoids in the tengchong block yunnan china abstract a number of cretaceous cenozoic granitoid bodies in the tengchong block were analyzed for their u pb zircon ages lu hf zircon isotopic compositions and whole rock geochemistry zircons from six different granite bodies in the central tengchong block have weighted mean 206 pb 238 u ages ranging from 76 to 65 ma and negative e hf t values ranging from 2 7 to 15 5 with t dm c ranging from 1312 to 1928 ma one dextrally sheared and gneissic granodiorite sample of the nabang shear zone in the western tengchong block yielded a weighted mean 206 pb 238 u age of 19 7 0 4 ma and positive e hf t values ranging from 0 2 to 10 7 with t dm c ranging from 418 to 1092 ma the late cretaceous granites have metaluminous and peraluminous affinities with strong enrichment of u and th and significant negative anomalies of eu ba sr nb p and ti the miocene granodiorite displays strong negative anomalies of nb ta p and ti and a weak negative eu anomaly the data suggest that the late cretaceous granites in the tengchong block were derived from partial melting of ancient most likely proterozoic continental crustal material whereas the miocene gneissic granodiorite was derived from partial melting of juvenile crustal material possibly within a supra subduction setting and intruded synkinematically into the active nabang shear zone lu hf isotopic data of late cretaceous paleocene granites are indistinguishable from those of granites of the central lhasa block thus we tentatively correlate the late cretaceous granites of the tengchong block with those of the central lhasa block the boundary between the south and central lhasa blocks in western tengchong may be exposed in the nne striking dextral nabang shear zone along the chinese myanmar border region which hosts early eocene granitoids with e hf t values 0 the lu hf data of the zircons from the gneissic miocene granodiorite indicate a juvenile crustal substrate in the western tengchong block as well the synkinematic miocene granodiorite provides an important age constraint for dextral shear at mid crustal levels which was active until at least c 19 20 ma in the nabang shear zone this miocene intrusion may be a first indication that active margin tectonics lasted 20 25 ma longer than in the gangdese belt and possibly was associated with deformation partitioning in the hinterland produced by increasing obliquity of subduction during clockwise rotation of sundaland during the india asia collision

dynamics of the tengchong volcanic region in the southeastern tibetan plateau a numerical study abstract the constraints of surface heat flow and lithospheric structure were used to investigate the dynamics of the tengchong volcanic region based on thermal mechanical modeling three different boundary conditions representing three types of tectonic movements were modeled to discuss the thermal state and lithospheric deformation the compressive model shows that the subduction of the indian plate causes the upwelling of asthenosphere beneath the tengchong block in this process upwelling of the asthenosphere causes thinning of the lithosphere beneath the tengchong block however the surface heat flow of this model is not consistent with the observations the regional extension model shows that under the extension the asthenosphere upwells along the preexisting weak suture zone in the southeastern tibetan plateau the thickness of lithosphere is the thinnest along the suture zone and the surface heat flow is the highest however the extension time was found to generally need 10 15 myr to conform to the surface heat flow however this is not consistent with accepted geochronological data when a boundary condition from compression to extension is imposed both the surface heat flow and the lithospheric structure fit well with the observations the results show that the subduction of the indian plate leads to the upwelling of the asthenosphere which causes a thinned lithosphere beneath the tengchong block since the late miocene 8 5 ma the extension or extrusion has been predominant the thermal erosion of the lithosphere caused by upwelling of the asthenosphere renders the lithosphere even thinner along the bangong nujiang suture zone the upwelling of the asthenosphere provides an upward driving force and high temperature environment for the tengchong volcanic region these findings suggest that the origin of the tengchong volcanic region is caused by both the subduction of the indian plate and regional extension across the bangong nujiang suture zone

modeling the seasonal variation of sea ice in the labrador sea with a coupled multicategory ice model and the princeton ocean model we use a multicategory sea ice model coupled to the princeton ocean model which is driven by monthly climatological atmospheric forcing to study the seasonal variation of ice cover in the labrador sea initial ocean conditions are derived from a gridded objectively analyzed temperature salinity data set that provides improved resolution of gradients in the vicinity of the shelf break the model produces a realistic seasonal variation of sea ice there is ice growth over the inner shelf and ice melt over the outer shelf and slope over the inner shelf advection and diffusion decrease the ice mass over the outer shelf advection and diffusion increase the ice mass which maintains the location of the ice edge near the offshore ice edge the melt rate exceed s1mp er month and the heat to melt ice together with the heat lost to the atmosphere exceeds 500 wm 22 the heat lost at the ocean surface is compensated for by advection of heat from an offshore convective region the dominant heat source for the spring retreat of ice in the south is shortwave radiation over the open water fraction marginal ice zones are regions of dynamic interaction be tween atmosphere ice and ocean in the labrador marginal ice zone the ice edge is located near the labrador current and its associated shelf break front wintertime convection in the western labrador sea is thought to form labrador intermedi ate water clarke and gascard 1983 since the ice edge bor ders the convective region it is important to clarify the pro cesses that limit the ice extent and to examine the heat and salt fluxes in the vicinity of the ice edge in this study we investigate the seasonal evolution of sea ice over the labrador shelf with a coupled ice ocean model our objective is to assess the capability of the model in simulating the evolution of the ice cover and to identify model deficien cies we examine the processes that limit the ice extent labrador sea ice has been the subject of a number of studies with numerical models most recently ikeda et al 1996 cou pled a two category ice model hibler 1979 with the geo physical fluid dynamics laboratory gfdl ocean model bryan 1969 cox 1984 there was overall agreement with the seasonal cycle as well as with interannual variations the re sults showed that shoreward advection of relatively warm off shore water is an important source of heat to melt ice how ever the model ice decayed too rapidly partly because the two category ice model underestimates ice concentration there are a number of differences between the present model and the model of ikeda et al 1996 we have imple mented a multicategory ice model and used the sigma coordi nate princeton ocean model blumberg and mellor 1987 mel lor 1996 with its embedded turbulence closure submodel we use a climatology from the national centers for environmen tal prediction ncep national center for atmospheric re

thermochronometer record of central andean plateau growth bolivia 19 5 s 1 quantifying the timing magnitude and rates of exhumation and deformation across the central andes is a prerequisite for understanding the history of plateau rise we present 23 new apatite and zircon fission track thermochronometer samples to chronicle the exhumation and deformation across the entire 500 km andean fold thrust belt at 19 5 s in bolivia exhumation and deformation are constrained with inverse thermal modeling of the thermochronometer data regional stratigraphy geothermal gradients and mass deficits inferred from a balanced section results suggest the following 1 initial exhumation of the eastern cordillera ec fore thrust and back thrust belts began in the late eocene to early oligocene 27 36 ma and continued in a distributed manner in the late oligocene to early miocene 19 25 ma interandean zone ia exhumation began 19 22 ma followed by a third pulse of exhumation 11 16 ma in the ec back thrust belt and initial cooling in the westernmost subandes sa 8 20 ma finally exhumation propagated eastward across the sa during the late mio pliocene 2 8 ma 2 exhumation magnitudes are spatially variable and range from maximums of 8 km in the ec fore thrust belt to average values of 4 7 km across the ec 2 5 3 km in the altiplano 4 6 km in the ia and 3 km in the sa 3 exhumation rates range from 0 1 to 0 2 mm a in the ec from 0 1 to 0 6 mm a in the ia and from 0 1 to 0 4 mm a to locally 1 4 mm a or more in the eastern sa we synthesize similar constraints with sediments throughout bolivia and characterize plateau development by 1 distributed deformation throughout the altiplano and ec regions from 20 to 40 ma with minor deformation continuing until 10 ma 2 contemporaneous cessation of most ec deformation and exhumation of the ia 20 ma implying establishment of the modern plateau width with significant but unknown crustal thickness and elevation shortly thereafter by 15 20 ma and 3 dominantly eastward propagation of deformation from the ia since 20 ma with minor out of sequence deformation in the central to eastern sa

rapid early middle miocene exhumation of the kazdag massif western anatolia apatite fission track analyses indicate that the kazdag massif in northwestern anatolia was exhumed above the apatite partial annealing zone between 20 and 10 ma i e early middle miocene with a cluster of ages at 17 14 ma the structural analysis of low angle shear zones high angle normal faults and strike slip faults as well as stratigraphic analysis of upper plate sedimentary successions and previous radiometric ages point to a two stage structural evolution of the massif the first stage encompassing much of the rapid thermal evolution of the massif comprised late oligocene early miocene low angle detachment faulting and the associated development of small supradetachment grabens filled with a mixture of epiclastic volcaniclastic and volcanic rocks kucukkuyu fm the second stage plio quaternary has been dominated by i strike slip faulting related to the westward propagation of the north anatolian fault system and ii normal faulting associated with present day extension this later stage affected the distribution of fission track ages but did not have a component of vertical normal movement large enough to exhume a new partial annealing zone the thermochronological data presented here support the notion that neogene extensional tectonism in the northern aegean region has been episodic with accelerated pulses in the early middle miocene and plio quaternary

geochemistry and geochronology of gneiss pebbles from foreland molasse conglomerates geodynamic and paleogeographic implications for the oligo miocene evolution of the eastern alps abstract gneiss pebbles deposited in foreland fans during the miocene epoch were studied with geochemical and thermochronological methods to reconstruct the paleodrainage evolution of the eastern alps and the geodynamic behavior of the source areas clear discrimination between upper plate austroalpine and lower plate penninic gneiss pebbles was achieved by single pebble paleocooling paths austroalpine gneisses showed highly variable and regionally distinctive paleocooling paths which record variscan to cretaceous rb sr and k ar cooling ages penninic gneisses showed paleogene to lower miocene high temperature rb sr k ar and miocene low temperature zircon and apatite fission track cooling ages cooling rates of penninic gneisses indicate maximum exhumation rates at 17 ma during the climax of lateral tectonic extrusion recording dominance of tectonic unroofing the paleodrainage evolution was characterized by a relatively stable catchment configuration in the western part of the eastern alps wh

cenozoic granitoids in the dinarides of southern serbia age of intrusion isotope geochemistry exhumation history and significance for the geodynamic evolution of the balkan peninsula two age groups were determined for the cenozoic granitoids in the dinarides of southern serbia by high precision single grain u pb dating of thermally annealed and chemically abraded zircons 1 oligocene ages kopaonik drenje eljin ranging from 31 7 to 30 6 ma 2 miocene ages golija and polumir at 20 58 20 17 and 18 06 17 74 ma respectively apatite fission track central ages modelling combined with zircon central ages and additionally local structural observations constrain the subsequent exhumation history of the magmatic rocks they indicate rapid cooling from above 300 c to ca 80 c between 16 and 10 ma for both age groups induced by extensional exhumation of the plutons located in the footwall of core complexes hence miocene magmatism and core complex formation not only affected the pannonian basin but also a part of the mountainous areas of the internal dinarides based on an extensive set of existing age data combined with our own analyses we propose a geodynamical model for the balkan peninsula the late eocene to oligocene magmatism which affects the adria derived lower plate units of the internal dinarides was caused by delamination of the adriatic mantle from the overlying crust associated with post collisional convergence that propagated outward into the external dinarides miocene magmatism on the other hand is associated with core complex formation along the southern margin of the pannonian basin probably associated with the w directed subduction of the european lithosphere beneath the carpathians and interfering with ongoing dinaridic hellenic back arc extension

crustal structure in tengchong volcano geothermal area western yunnan china abstract based upon the deep seismic sounding profiles carried out in the tengchong volcano geothermal area tvga western yunnan province of china a 2 d crustal p velocity structure is obtained by use of finite difference inversion and forward travel time fitting method the crustal model shows that a low velocity anomaly zone exists in the upper crust which is related to geothermal activity two faults the longling ruili fault and tengchong fault on the profile extend from surface to the lower crust and the tengchong fault likely penetrates the moho moreover based on teleseismic receiver functions on a temporary seismic network s wave velocity structures beneath the geothermal field show low s wave velocity in the upper crust from results of geophysical survey the crust of tvga is characterized by low p wave and s wave velocities low resistivity high heat flow value and low q the upper mantle p wave velocity is also low this suggests presence of magma in the crust derived from the upper mantle the low velocity anomaly in upper crust may be related to the magma differentiation the tengchong volcanic area is located on the northeast edge of the indian eurasian plate collision zone away from the eastern boundary of the indian plate by about 450 km based on the results of this paper and related studies the tengchong volcanoes can be classified as plate boundary volcanoes

physical chemical and sedimentological aspects of the mediterranean outflow off iberia a multidisciplinary study of the mediterranean outflow in the region west of the strait of gibraltar and off the southern and southwestern coasts of the iberian peninsula was developed in the frame of the canary islands azores gibraltar observations project two high resolution ctd surveys which included water sampling for chemical nutrients and dissolved oxygen and sedimentological analyses took place in september 1997 summer cruise and january 1998 winter cruise in the study region the correspondence between the high salinity mediterranean water mw layer and the low nutrient content and relatively high abundance of particles was a general result further details of the thermohaline analysis and of the geostrophic computations especially for the layer of mw are compared with the results obtained for the chemical properties and the sedimentological characteristics

apparent paleomagnetic rotations reveal pliocene holocene internal deformation of the tengchong block southeastern tibetan plateau abstract we present new paleomagnetic data from early pliocene to holocene volcanic rocks of the tengchong volcanic field and mangbang basin of the tengchong lhasa block yunnan along the eastern margin of the india asia collision zone two remanent magnetization components occur a higher coercive one carried by ti rich titanomagnetite and magnetite and likely of primary origin and a lower coercive one residing in magnetite and representing a more recent overprint the pleistocene holocene rocks of the tengchong volcanic field yield an in situ overall mean direction of d i 352 5 25 4 indicating a southeastward tilt we attribute the tilting to block rotation above listric normal faults that cut the tengchong volcanic field the in situ overall mean direction derived from pliocene volcanic rocks of the mangbang basin is d i 330 5 54 2 we explain this apparent counterclockwise rotation by northeastward tilting due to half graben formation during normal faulting along the nuangdeng fault zone along the eastern basin margin

magma mixing recorded by sr isotopes of plagioclase from dacites of the quaternary tengchong volcanic field se tibetan plateau abstract the tengchong volcanic field east of the burma arc in sw china comprises numerous quaternary volcanoes the volcanic rocks can be grouped into four units numbered 1 4 from oldest to youngest units 1 3 and 4 are composed of trachybasalt basaltic trachyandesite and trachyandesite respectively whereas unit 2 consists of hornblende dacite primary minerals in the dacite include plagioclase clinopyroxene amphibole and magnetite all set in a glassy groundmass some of the dacites are moderately to highly weathered and show effects of low temperature alteration with loss on ignition loi up to 9 6 wt and positive correlations of loi with al2o3 but negative correlations with sio2 cao and na2o fresh dacites loi plagioclase in the fresh dacite has relatively high sr contents and 87sr 86sr ratios ranging from 0 7050 to 07125 except for one value of 0 7516 whereas plagioclase in the altered dacite has low sr contents and highly variable sr isotopic compositions 0 7039 0 7138 indistinguishable from those of the fresh rocks both an values and sr isotopic compositions of the plagioclase indicate mixing of mantle and crustally derived magmas we therefore propose that mantle derived basaltic magma caused partial melting of the lower middle crust and that mixing of the mafic and felsic magmas produced the dacite in staging magma chambers the dacites contain minerals crystallized from both the mafic and felsic magmas as well as a few xenocrysts plucked from the country rocks

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

raman spectroscopic carbonaceous material thermometry of low grade metamorphic rocks calibration and application to tectonic exhumation in crete greece we present new raman spectra data of carbonaceous material cm to extend the range of the raman spectra of cm thermometer rscm to temperatures as low as 100 8c previous work has demonstrated that raman spectroscopy is an excellent tool to describe the degree of graphitization of cm a process that is independent of pressure but strongly dependent on metamorphic temperature a linear relationship between temperature and the raman parameter r2 derived from the area of the defect band relative to the ordered graphite band forms the basis of a previous thermometer because r2 shows little variability in low temperature samples 330 8c serves as a lower limit on the existing thermometer herein we present raman spectra from a suite of low temperature 100 to 300 8c samples from the olympics mountains and describe other aspects of the raman spectra of cm that vary over this range in particular the raman parameter r1 the ratio of heights of the disordered peak to ordered peak varies regularly between 100 and 350 8c these data together with published results from higher temperature rocks are used to calibrate a modified rscm thermometer applicable from 100 to 700 8c application to low grade metasediments in the otago region in the south island of new zealand gives temperatures consistent with previous estimates demonstrating the reliability of the modified rscm thermometer we apply the modified rscm thermometer to 53 samples from crete to evaluate the role of the cretan detachment fault in exhuming miocene high pressure low temperature metamorphic rocks exposed there the metamorphic rocks below the detachment the plattenkalk and phyllite quartzite units give metamorphic temperatures that range from 250 to 400 8c consistent with previous petrologic estimates we also demonstrate that the tripolitza unit which lies directly above the detachment gives an average metamorphic temperature of about 260 8c the modest break in metamorphic temperature in central crete indicates that the cretan detachment accounts for only 5 to 7 km of exhumation of the underlying hp lt metamorphic rocks which were initially accreted at 35 km we argue that the bulk of the exhumation 28 km out of 35 km total occurred by pervasive brittle stretching and erosion of structural units above the detachment d 2005 elsevier b v all rights reserved

exhumation of the sierra de cameros iberian range spain constraints from low temperature thermochronology we present new fission track and u th he data from apatite and zircon in order to reconstruct the exhumation of the sierra de cameros in the northwestern part of iberian range spain zircon fission track ages from samples from the depocentre of the basin were reset during the metamorphic peak at approximately 100 ma detrital apatites from the uppermost sediments retain fission track age information that is older than the sediment deposition age indicating that these rocks have not exceeded 110 c apatites from deeper in the stratigraphic sequence of the central part of the basin have fission track ages of around 40 ma significantly younger than the stratigraphic age recording the time of cooling after peak metamorphic conditions apatite u th he ages in samples from these sediments are 31 40 ma and record the last period of cooling during alpine compression the modelled thermal history derived from the uppermost sediments indicates that the thermal pulse associated with peak metamorphism was rapid and that the region has cooled continuously to the present the estimated palaeogeothermal gradient is around 86 c km 1 and supports a tectonic model with a thick sedimentary fill c 8 km and explains the origin of the low grade metamorphism observed in the oldest sediments

ion microprobe dating of zircons from active dayingshan volcano tengchong se tibetan plateau time scales and nature of magma chamber storage abstract the rare occurrences of active volcanoes on the tibetan plateau provide a unique opportunity to investigate time scales of magma chamber processes for post collisional potassic volcanism this research utilizes high spatial resolution u th disequilibrium dating methods to date zircons from the active dayingshan volcano tengchong se tibetan plateau which erupted last during the holocene zircon crystal ages can be used to provide constraints on the magma chamber storage time measured zircon interiors yielded an isochron age of 87 5 6 5 ka while zircon outermost rims yielded an isochron age of 58 13 ka the calculated zircon crystal storage time for the most recent eruption is 48 ka at least two separate late pleistocene zircon crystallization events have occurred where the older age population represents antecrysts remobilized from an earlier magmatic episode but protracted crystallization cannot be ruled out regardless the similarity in zircon age populations between dayingshan volcano and maanshan volcano 13 km apart in the tengchong volcanic field suggests a synchronous thermal history of the magma reservoir possibly in an extensive interconnected magma chamber beneath the tengchong volcanic field

cooling history of the upper cretaceous palgongsan granite gyeongsang basin se korea and its tectonic implication for uplift on the active continental margin abstract apatite and zircon fission track analyses were carried out to reconstruct the cooling and inferred uplift history of the cretaceous palgongsan granite gyeongsang basin korea the palgongsan granite is one of the bulguksa intrusive rocks that formed by arc related plutonism during late cretaceous to early tertiary time fission track dating of the palgongsan granite yielded nearly concordant ages of 53 and 65 ma for apatite and zircon respectively the palgongsan granite also shows a simple cooling pattern which suggests that it has not been affected by any thermal event after emplacement the cooling history derived from fission track data combined with other thermochronometric data indicates that the palgongsan granite experienced relatively rapid cooling in earlier stage 30 c ma the initial rapid cooling rate during the late cretaceous has been caused by the large thermal contrast between the granite body and the country rocks after reaching thermal equilibrium with the surrounding country rocks the cooling rate of the palgongsan granite was abruptly decreased in late stage in this late stage the decelerated cooling rate is interpreted to have been controlled by uplift and erosion processes and the average exhumation rate is calculated to be ca 50 m my over the temperature range from 100 c to the surface temperature the cooling history of the palgongsan granite is in good agreement with that of the ryoke granitic belt in southwest japan as well as those of the taebaeksan range and other bulguksa intrusive rocks in the gyeongsang basin this suggests that such cooling was probably caused by regional uplift and exhumation processes on the east asian active continental margin compared with the uplift rates of the andes the uplift rates on the eastern pacific margin appear to be higher than those on the western pacific margin

application of a transient reduced gravity plume model to the denmark strait overflow a hydrostatic reduced gravity two dimensional primitive equation numerical model for the simulation of transient bottom arrested gravity plumes was developed by adopting an algorithm from a wadden sea model a model that simulates the wetting and drying of mud flats sand banks etc with a movable lateral boundary the vertically integrated nonlinear rotational model accounts for the dissipation of momentum due to bottom friction and for the entrainment of water mass properties from a spatially structured but stagnant ambient water body it predicts the temporal and spatial evolution of the flow field and the water mass modification within a gravity plume that descends on an arbitrary topography previous model investigations considered a laterally integrated streamtube whereas our model resolves the plume horizontally in the streamtube approach it was assumed that the plume descends in a stationary almost geostrophic balance modified only by bottom drag and entrainment the results of this model demonstrate that this balance may be disturbed whenever the plume encounters topographic disturbances which for the initial intruding phase in particular accounts for its highly transient character the model results are in good agreement with theoretical and laboratory investigations and with observations as is demonstrated by some basic test experiments an application to the overflow of dense water through the denmark strait is presented

seismic structure of the tengchong volcanic area southwest china from local earthquake tomography article i nfo weperformedalocalearthquaketomographytoimagethecrustofthetengchongvolcanicareainsouthwestern china using p wave arrival data from a temporary network and permanent stations the objective is to deter mine the magma sources of the volcanic area and the seismic structure of two m 7 earthquakes in the longling area south of tengchong the result reveals a correlation between the velocity structures and the volcanic activ ities from late miocene to holocene a prominent low velocity zone is observed beneath the central volcanic area that is cored at 10 20 km depths and extends down to 30 km depth with a lateral extent of 20 30 km we infer that this unusual low velocity zone represents a magma source of the heat flows for the volcanic erup tion during pleistocene and holocene close to it a high velocity zone appears beneath the eastern volcanic area and itislikelyto reflect solidifiedmagma intrusionsand high densityremnants withinthe cooled volcanicchan nel prior topleistocene in the m 7 earthquake area theuppercrustalstructureshows evidentvariationsacross the longling fault and the nu river fault bounded by the two fault zones the gaoligong metamorphic belt and the baoshan block are imaged by high velocities that are consistent with their high strength in the structures on the contrary low velocities are imaged in the area between the longling fault and the nu river fault implying a decreaseof the strength probably caused byigneous intrusions itwas thelateral variation intherheologic struc ture that led to the uneven stress accumulations across these fault zones and created tectonic conditions for the seismic ruptures of the two m 7 earthquakes in the longling area

long term thermo tectonic evolution of the montes de toledo area central hercynian belt spain constraints from apatite fission track analysis in the montes de toledo area located in the axial part of the central hercynian zone a long term thermo tectonic evolution can be deduced from apatite fission track aft data in conjunction with tight geological constraints derived from the knowledge of regional geology and other independent chronometers the area is composed of two different blocks separated by the toledo shear zone tsz the northern block is a granulite facies anatectic terrane the southern block is composed of greenschist facies paleozoic sediments intruded by a late hercynian granitic pluton a total of 13 samples have been recovered for aft analysis aft ages in both blocks cluster around 189 221 ma with mean confined track lengths between 11 4 m and 12 4 m modeling of the aft data indicates that the thermal history is broadly similar in both blocks which constrains the main movement of the tsz as essentially before the upper permian aft ages in the tsz cluster around 124 164 ma and the track lengths vary between 11 4 m and 12 4 m these data reveal that the fault must have been affected by a later thermal overprint as aft ages are significantly younger than those of the footwall and hangingwall blocks this differential thermal resetting is likely related to the advection of localized hydrothermal fluids that are responsible for the widespread pb zn mineralization along the tsz these results give an example of resetting aft data by hydrothermal events the long term evolution suggests a lack of important alpine tectonism in the montes de toledo block in clear contrast to other nearby hercynian areas such as the sierra de guadarrama where the important effect of alpine tectonism has almost totally erased the previous thermal signal in the aft system

mediterranean outflow mixing and dynamics the mediterranean sea produces a salty dense outflow that is strongly modified by entrainment as it first begins to descend the continental slope in the eastern gulf of cadiz the current accelerates to 1 3 meters per second which raises the internal froude number above 1 and is intensely turbulent through its full thickness the outflow loses about half of its density anomaly and roughly doubles its volume transport as it entrains less saline north atlantic central water within 100 kilometers downstream the current is turned by the coriolis force until it flows nearly parallel to topography in a damped geostrophic balance the mixed mediterranean outflow continues westward slowly descending the continental slope until it becomes neutrally buoyant in the thermocline where it becomes an important water mass

stress on the mediterranean outflow plume part ii turbulent dissipation and shear measurements abstract bottom and interfacial stresses on the mediterranean outflow plume are estimated using vertical profiles of turbulent dissipation and velocity collected in the gulf of cadiz turbulent dissipation is high throughout the plume with a local minimum often present near the plume nose depth of maximum downstream velocity bottom stresses are estimated by applying a log layer model to the dissipation measurements the dissipation measurements are also divided by plume scale vertical shear from the horizontal velocity profiles to construct profiles of stress within the plume the mean stress estimates in the bottom layer agree well with those calculated in the log layer from the dissipation measurements alone the bottom layer means are slightly larger than those of the interfacial layer the maximum stresses in each layer are uncertain since they depend on the ill defined shape of the stress profiles within the plume dissipation derived stress estimates in the log layer and those from dissipation

eddy generation in the mediterranean undercurrent abstract in the framework of the european union mast iii project canary islands gibraltar azores observations 24 rafos floats were deployed in the mediterranean water mw undercurrent off south portugal between september 1997 and september 1998 a preliminary analysis of this lagrangian approach complemented with xbt and current meter data show some of the major aspects of the flow associated with the undercurrent as well as associated eddy activity floats that stayed in the undercurrent featured a downstream deceleration and a steering by bottom topography three meddy formations at cape st vincent could be isolated from the float data the dynamical coupling of meddies and cyclones was observed for a considerable period of time the generation of two dipolar structures in the portimao canyon region also was observed with the float data a major bathymetric relief gorringe bank was not only an important constraint to the eddy trajectories and of the flow at the mw levels but also a site for meddy formation

fine crustal and uppermost mantle s wave velocity structure beneath the tengchong volcanic area inferred from receiver function and surface wave dispersion constraints on magma chamber distribution the tengchong volcanic area is located in the southeastern margin of the collision zone between the indian and eurasian plates it is one of the youngest intraplate volcano groups in mainland china imaging the s wave velocity structure of the crustal and uppermost mantle beneath the tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity in this study we analyze teleseismic data from nine broadband seismic stations in the tengchong earthquake monitoring network we then image the crustal and uppermost mantle s wave velocity structure by joint analysis of receiver functions and surface wave dispersion the results reveal widely distributed low velocity zones we find four possible magma chambers in the upper to middle crust and one in the uppermost mantle the chamber in the uppermost mantle locates in the depth range from 55 to 70 km the four magma chambers in the crust occur at different depths ranging from the depth of 7 to 25 km in general they may be the heat sources for the high geothermal activity at the surface based on the fine crustal and uppermost mantle s wave velocity structure we propose a model for the distribution of the magma chambers

burial and exhumation history of the daday unit central pontides turkey implications for the closure of the intra pontide oceanic basin in northern turkey the intra pontide suture zone represents one of the first order tectonic structures located between the istanbul zonguldak and the sakarya continental terranes it consists of an e w trending assemblage of deformed and variably metamorphosed tectonic units including sedimentary rocks and ophiolites derived from a neo tethyan oceanic basin known as the intra pontide oceanic basin one of these units is represented by the daday unit that consists of a block in matrix assemblage derived from supra subduction oceanic crust and related deep sea sedimentary cover of middle jurassic age this setting was acquired during late jurassic time by tectonic underplating at a depth of 35 42 km associated with blueschist facies metamorphism d1 phase the following d2 d3 and d4 phases produced the exhumation of the daday unit up to shallower structural levels in a time span running from the albian to late paleocene the high geothermal gradient detected during the d2 phase indicates that the daday unit was exhumed during a continent arc collisional setting the tectonic structures of the intra pontide suture zone resulting from the previously described tectonic history are unconformably sealed by the upper paleocene eocene deposits this tectonic setting was intensely reworked by the activity of the north anatolian fault zone producing the present day geometrical relationships of the intra pontide suture zone of the central pontides

multi system geochronological and isotopic constraints on age and evolution of the gaoligongshan metamorphic belt and shear zone system in western yunnan china abstract the gaoligongshan metamorphic belt located east of the eastern himalayan syntaxis ehs in the yunnan province southwestern china is a compelling region in which to determine temporal constrains on crustal dynamic processes related to the himalayan orogeny we applied multi system geo and thermochronology 900 c to zircon u pb data reveal three magmatic events at 486 ma 136 ma and 76 ma similar ages are found in orthoderivative rocks of the neighboring tengchong and baoshan blocks and the gangdese batholith suggesting that the southern gaoligongshan is composed of an assemblage of lhasa and qiangtang terrane derived rocks muscovite rb sr ages of 35 21 ma are coeval with the onset of lateral crustal displacement along major shear zones in eastern tibet and indochina and with the post collision volcanic activity in western yunnan biotite rb sr and mica 40 ar 39 ar ages provide evidence that mylonitization along the gaoligongshan shear zone and crustal rotation of the tengchong and baoshan blocks proceeded during the miocene between 19 and 12 ma when the rocks rapidly cooled through the 350 280 c temperature range almost identical 40 ar 39 ar ages reported for the karakorum jiali parlung fault system in western tibet suggest that the gaoligongshan shear zone is the southeastern continuation of this fault recording the eastward extrusion of tibet and crustal movement around the ehs the final stage of exhumation of the gaoligongshan occurred between 8 and 5 ma at an average exhumation rate of 3 km ma as documented by apatite fission track and apatite u th sm he data this rapid exhumation was triggered by crustal root delamination and opening of the andaman sea our results clearly show that the complex tectonothermal evolution of the gaoligongshan was influenced by tibetan extrusion and escape tectonics associated with lower crustal flow around the ehs and the southeastward movement of indochina and back arc extension in response to andaman seafloor spreading

effects of plate convergence obliquity on timing and mechanisms of exhumation of a mid crustal terrain the central anatolian crystalline complex abstract apatite fission track ft ages from the central anatolian crystalline complex cacc a microcontinent within the turkish segment of the alpine himalayan orogen vary dramatically from north to south this variation correlates with differences in the obliquity of convergence of the continental fragment relative to the pontide belt for the northern cacc and the tauride belt for the southern cacc the northern cacc was deformed and metamorphosed during late cretaceous orogen normal collision and was exhumed from the mid crust to shallow crustal levels 50 ma to the present in contrast the southern cacc nigde massif was initially deformed and metamorphosed during late cretaceous contraction but subsequently developed as a metamorphic core complex in a wrench dominated regime and was exhumed to

another description of the mediterranean sea outflow abstract papers about the outflow in the strait of gibraltar assume that i it is composed of only two mediterranean waters mws the levantine intermediate water liw and the western mediterranean deep water wmdw from the eastern and western basins respectively ii both mws are mixed near 6 w hence producing a homogeneous outflow that is then split into veins due to its cascading along different paths and to different mixing conditions with the atlantic water aw a re analysis of 1985 1986 ctd profiles gibraltar experiment indicates two other mws the winter intermediate water wiw from the western basin and the tyrrhenian dense water tdw basically originated from the eastern basin in the central alboran subbasin these four mws are clearly differentiated roughly lying one above the other in proportions varying from north to south proportions also vary with time so that the outflow can be mostly of either eastern or western origin while progressing westward the mws can still be differentiated and associated isopycnals tilt up southward as much as being in the sill surroundings roughly parallel to the moroccan continental slope where the densest mws are the mws at the sill are thus juxtaposed and they all mix with aw leading to an outflow that is horizontally heterogeneous just after the sill 5 45 w before progressively becoming vertically heterogeneous as soon as 6 15 w there can be little liw and or no wmdw outflowing for a while an analysis of new 2003 2008 time series from two ctds moored ciesm hydro changes programme at the sill 270 m and on the moroccan shelf 80 m confirms the juxtaposition of the mws their individual and generally intense mixing with aw as well as the large temporal variability of the outflow composition only liw and tdw were indicated at the sill while on the shelf only liw tdw sometimes denser there than 200 m below and wmdw were indicated but none of the mws has been permanently outflowing at one or the other place the available data can be analyzed coherently intermediate and deep mws are formed in both basins in amounts that although variable from year to year allow their tracing up to the strait four major mws circulate alongslope counterclockwise as density currents and as long as they are not trapped within a basin which is necessarily the case for the deep mws in the alboran the intermediate mws wiw liw and upper tdw circulate in the north while the deep mws lower tdw and wmdw are uplifted hence relatively motionless and mainly pushed away in the south since both the intermediate and deep mws outflow at the sill they are considered as light and dense mws the light dense mws interface possibly intersecting the aw mws interface in the sill surroundings considering an outflow east of the sill composed of only two light dense homogeneous layers gives significant results across the whole strait the outflow has spatial and temporal variabilities much larger than previously assumed the mws are superposed in the sea and lead at the sill to juxtaposed and vertically stratified suboutflows that will cascade independently before forming superposed veins in the ocean these veins can have similar densities and hydrographic characteristics even if associated with different mws which accounts for the features permanency assumed up to now the outflow structure downstream of the sill depends on its composition upstream and more importantly on that of aw in the sill surroundings where fortnightly and seasonal signals are imposed on the whole outflow

evidence of episodically accelerated denudation on the tibetan namche barwa massif by megafloods abstract megafloods cause widespread mobilization of sediments that have strong potential to control the geodynamic evolution of the namche barwa nb massif by changing the landscape morphology within a short time however the impact of catastrophic events on the denudation of the massif over the longer time scale has not been explored in detail this contribution assesses the impact of catastrophic floods on the denudation style of the namche barwa nb massif over millennial time scales towards this 21 optical ages and 1700 detrital thermochronometric ages of zircon and apatite minerals extracted from paleoflood sediments downstream of the massif were integrated with decadal sediment load and aggradation data to estimate the minimum denudation rate during paleoflood events the results indicate that the 7 ka flood eroded 71 m of material from the nb massif this denudation is equivalent to the material that would be produced over 8000 years of erosion at a rate of 9 mm a the 3 5 ka flood eroded 24 m of material equaling 2500 years worth of erosion at a rate of 9 mm a such relatively instantaneous denudations are three orders of magnitude higher than averaged denudation rates over million year time scale this study therefore provides the first evidence of the strong interplay of catastrophic flood events and tectonics for the rapid exhumation of the namche barwa massif megafloods from the failure of dammed lakes provide valuable information to understand the flood surge risk for human settlements in the siang and the assam valleys

three dimensional s velocity structure of the crust in the southeast margin of the tibetan plateau and geodynamic implications abstract the lower crustal flow model is one of several competing models considered to interpret the growth and expansion of southeastern tibet however the dynamic processes involved in the evolution and deformation of the tibetan plateau remain poorly understood due to the absence of reliable geophysical observations in this study 159 earthquakes of magnitude ms 6 2 were selected which were recorded by 50 permanent broadband stations deployed in southwest china and 1873 pairs of p wave receiver functions with high signal to noise ratio were isolated on the basis of a linearized inversion algorithm a two step inversion procedure was implemented that not only reduced the dependence of the inversion results on the initial models but also provided a statistical estimation of the solution thus we obtained an accurate 3d image of the s wave velocity structure of the crust and uppermost mantle in the southeast margin of the tibetan plateau our results reveal that an extensive intracrustal low velocity zone spreads beneath southwest china and further suggest that a lower crustal flow coming from eastern tibet is blocked by the jinshajiang red river fault to the west and the xiaojiang fault to the east and extends largely by the sichuan yunnan diamond shaped block this crustal flow along the southeastern margin of tibet does not appear to be restricted to two narrow low velocity channels as was advanced but rather reflects the southeastward extrusion of crustal material as a way of tectonic escape

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

comprehensive crustal structure and seismological evidence for lower crustal flow in the southeastern margin of tibet revealed by receiver functions abstract the lower crustal flow model has become an interesting proposal to describe the growth and expansion of eastern tibet to date however the geophysical results are not definitive due to the non uniqueness of the solutions found through data inversion and the resolution limitations in this study the polarity of p to s converted phases at intra crustal interfaces are analyzed in order to reveal evidence for low seismic velocity and lower crustal flow in southeastern tibet we are interested in a joint study that is both a mapping of the crustal structure moho topography and poisson s ratio and an attempt to constrain an iclvz we have determined the crustal thickness and poisson s ratio from p prfs and s srfs receiver functions acquired in 108 permanent seismic stations deployed in the sichuan and yunnan areas also we have obtained 98 measurements of pms phase splitting parameters at the array stations the crustal thickness provided by prfs is consistent with that given by srfs it varies from 60 km in the songpan ganzi sg fold system and the northern part of the sichuan yunnan diamond shaped block sydsb near the eastern himalayan syntaxis to 33 km in southern yunnan the poisson s ratio varies mostly from 0 24 to 0 32 the highest values 0 28 0 32 are found along the axis formed by the longmenshan fault the lijiang jinhe fault and in the tengchong volcano area the value of 0 28 observed in sydsb and the sg fold system is attributed to the presence of a low velocity zone in the lower crust and partly to the great sediment thickness in sichuan basin the crust is clearly anisotropic in the southeastern margin of tibet the fast wave polarization direction exhibits a nw se regional bias while the time delay varies between 0 07 s and 1 27 s being the average 0 54 s 0 12 s implying the existence a strong shear zone in the lower crust based on the negative polarity observed after the direct p wave in teleseismic receiver functions we have detected an intra crustal low velocity zone iclvz in a wide region including east and southeast of tibet and southern yunnan so both the shear zone and iclvz suggest the existence of lower crustal flow the reverberation ppps and psps ppss phases at the moho are clearly weaker in sydsb and the sg fold system than in the indochina block and eastern yunnan implying that sydsb has a structure and tectonic history different from indochina on its west side and eastern yunnan on its east side the above results provide seismological evidence for a lower crustal flow spreading from the eastern tibet and that in its advance southward has invaded sydsb widely crossed the lijiang jinhe fault and reached southern yunnan

cenozoic deformation in western yunnan china myanmar border in the present paper we describe ductile and brittle deformation styles in western yunnan and ne myanmar using field data and landsat 7 imagery we show that this complex area located at the northern termination of sunda plate three rivers area was wedged during the tertiary between the left lateral ailao shan chong shan metamorphic belts to the east and the right lateral shan scarp gaoligong metamorphic belt in west this triangular region therefore underwent the effects of these continental size ductile strike slip faults separating major blocks with a dominant ew to ene compression since the late miocene date of the reversal of motion along the rrf the incipient eastward motion of the sunda block and the persisting right lateral motion along its western boundary sagaing fault created n s compression and e w to wnw extension underlined by left lateral transtension along the wanding nanting fault zones at the same time the diangcan shan situated along strike the ailao shan metamorphic belt was slightly impinged by the blocks extruded from the syntaxis and exhumed again from the early pliocene in accordance with this late and still active state of stress q 2004 elsevier ltd all rights reserved

chalcophile element constraints on magma differentiation of quaternary volcanoes in tengchong sw china abstract the tengchong volcanic field comprises numerous quaternary volcanoes in sw china the volcanic rocks are grouped into units 1 4 from the oldest to youngest units 1 3 and 4 are composed of trachybasalt basaltic trachyandesite and trachyandesite respectively and unit 2 consists of hornblende bearing dacite this rock assemblage resembles those of arc volcanic sequences related to oceanic slab subduction rocks of units 1 and 3 contain olivine phenocrysts with fo contents ranging from 65 to 85 mole indicating early fractionation of olivine and chromite prior to the eruption of magma all the rocks from units 1 3 and 4 have very low pge concentrations with

magma system beneath tengchong volcanic zone inferred from local earthquake seismic tomography abstract the tengchong volcanic zone tcvz located in the southeastern part of the india eurasia collision zone is characterized by large scale volcano groups significant thermal activities and active seismicity to reveal the magma system we present new 3 d models of vp vs and vp vs ratio to 10 km depth beneath the tcvz based on the tomographic inversion of p and s wave arrival times from local earthquakes recorded by 10 broadband seismic stations we use arrival times to construct a reference velocity model checkerboard and jackknife tests are carried out to assess the reliability of the inversion results at shallow depths we suggest that the complex distribution of high vp vs ratio is the result of a combination of water and magmatic activity at depth of 10 km only three areas show obvious high vp vs ratio corresponding to areas of high relative geothermal value observed through hot springs at the surface we suggest that the three high vp vs ratio areas are magma chambers the upwelling volatiles heat the water in the shallow layer inducing the corresponding high relative geothermal value at the surface meanwhile the magma chamber beneath rehai spring which corresponds to high he3 he4 ratio may be fed by mantle magma we suggest that the heikongshan volcano and dayingshan volcano are fed by the magma chambers and that maanshan volcano is separated from the magma we also infer that the significant geothermal activity and active seismicity beneath rehai spring are the result of interaction between the magma and hot water reservoir

short term variability of the mediterranean in and out flows 1 a re analysis of ctd profiles collected in the strait of gibraltar during the 1985 1986 gibraltar experiment shows that a large variability can occur within a 10 day interval in the nature of the atlantic water found in the sill surroundings and expected to flow into the mediterranean sea and in the set of mediterranean waters outflowing from the sea since both strongly mix together within the strait the outflow in the atlantic ocean can display a tremendous short term variability mainly due to the variability of the inflow specifying any nominal characteristic for the outflow all its way downstream a fortiori any nominal characteristic for the various veins into which it is split thus needs monitoring the whole water column within the strait

improved measurement of fission track annealing in apatite using c axis projection apatite fission track length data are used extensively for thermal history inversion however several studies have documented instances of poor reproducibility of length data we address this problem by using c axis projection to normalize track lengths for crystallographic angle in the extensive laboratory annealing data set acquired by barbarand et al 2003a 2003b a new simplification reduces the c axis projection model from six to four fitted parameters normalizing for track angle using c axis projection improves every aspect of length measurement reproducibility examined it accelerates convergence of mean length in single analyses increases consistency among replicate measurements by a single analyst enhances consistency of measurements of the same mounts by different analysts and improves the match between analyses conducted with and without cf irradiation c axis projection is also shown to enhance the thermal sensitivity of length data based on these results we assert that c axis projection is a good means of compensating for observer bias although it does not overcome differences caused by experimental error

tectonics and paleomagnetic rotation pattern of yunnan 24 n 25 n china gaoligong fault shear versus megablock drift

seismic structure beneath the tengchong volcanic area southwest china from receiver function analysis abstract tengchong is a young volcanic area on the collision boundary between the indian and euro asian plates of the southeastern tibetan margin holocene volcanoes are concentrated in the tengchong basin where they align an n s trending string like cluster to study the magma activity and its relation with the volcanoes we deployed a passive seismic observation across the volcanic area in northern tengchong using tele seismic data and receiver function technique we determined the s wave velocity structure beneath nine temporary stations results show that the tengchong basin is underlain by prominent low velocity zones that are associated with the magma chambers of the volcanoes in the north a small and less pronounced magma chamber lies beneath two crater lakes with a depth range of 9 16 km and a lateral width of

the petrology and mineralogy of mt popa volcano and the nature of the late cenozoic burma volcanic arc mt popa is situated on a line of widely spaced calc alkaline volcanic centres in the central lowlands of burma latites rhyodacites and ignimbrites are interbedded with strongly folded arenaceous sediments of topmost miocene and pliocene age these are overlain unconformably by a composite cone of basalt and basaltic andesite lavas and pyroclastic deposits of pleistocene or early recent age the two groups of lavas are regarded as a single petrographic suite in which several continuous and discontinuous mineral reaction series are recognized phenocryst phases analysed by microprobe are olivine bronzite hypersthene biotite diopsidic augite salite magnesio hastingsite magnesio hornblende titaniferous magnetite bytownite oligoclase and sanidine whole rock analyses are characterized by relatively high k ba sr rb and zr high mg mg fe ratios of 0 85 to 0 65 in both phenocrysts and whole rock high k rb 767 and low sr 87 sr 86 0 70431 and rb sr 0 0155 ratios suggest that the basalts are relatively primitive mantle derived compositions modified slightly by fractionation with negligible crustal contamination the more siliceous lavas may have been derived by fractional crystallization of such magmas at crustal levels this high k calc alkaline suite is typical of a continental margin orogenic environment analyses of contemporaneous lavas from elsewhere in burma define three n s volcanic lines which become more alkaline from w to e the magmatism is attributed to the waning stages of orogeny as eastward subduction of the indian plate beneath china gave way to strike slip movement associated with the andaman sea spreading centre within this tectonic model magmas were probably generated by hydrous mantle melting above dehydrating oceanic crust of the subduction zone

eruption of alkali basalts during crustal shortening in southern california the common occurrence of alkali basalts in continental rifts has led to the widespread assumption that late cenozoic alkali basalts of the western united states indicate an extensional tectonic regime however field relations of late cenozoic alkali basalt flows and cinder cones in the mojave desert area including flows that bear mantle xenoliths indicate that many were erupted in contractional or transpressional tectonic settings these observations call into question models of extensional magmatism in which lithospheric extension facilitates transport of magmas to the surface and suggest that an association of alkali basalts and coarse clastic sedimentary rocks need not indicate rifting

comment on the reply to the comment on thermal history modelling hefty vs qtqt by vermeesch and tian earth science reviews 2014 139 279 290

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

miocene thrusting in the eastern sila massif implication for the evolution of the calabria peloritani orogenic wedge southern italy abstract alpine orogens in the central mediterranean region have revealed the concomitance of crustal extension in back arc domain and crustal shortening in frontal domain quantitative data of deformation in the frontal orogenic wedges are necessary to understand how the shortening extension pair evolves in terms of structures orogenic transport timing and exhumation rate this paper deals with kinematics and ages of the frontal thrust systems of the calabria peloritani arc italy exposed in the eastern sila massif we first present structural fieldwork onshore and offshore well log data and new apatite fission track aft thermochronology then we describe the structural architecture of the studied area as an ene verging stacking of thrust sheets involving basement units and syn orogenic sediments the aft study documents that thrust sheets entered the partial annealing zone from 18 ma to 13 ma this early middle miocene thrusting phase was coeval with exhumation of high pressure low temperature metamorphic rocks in the hinterland of the orogen coastal chain area mainly driven by top to the w extensional tectonics opposite kinematic shear senses contractional top to the e and extensional top to the w and different exhumation rates slow in the frontal more rapid in the hinterland are framed in a tectonic scenario of a critically tapered orogenic wedge during the eastward retreating of the apennine slab

normal faulting and block tilting in lofoten and vesteralen constrained by apatite fission track data abstract mesozoic and possibly younger normal faulting and block tilting in the lofoten vesteralen archipelago can be constrained by apatite fission track data previous studies have documented the polyphase structural evolution of the archipelago based on field data and onshore offshore correlations our new aft data document vertical movements on a more regional scale with kilometer scale offset on some faults below sortlandsundet the hadselfjord fault zone forms the eastern limit of the sortlandsundet half graben and our data reveal latest cretaceous and younger half dome shaped uplift of the footwall east of the western lofoten border fault on vestvagoya southeastward tilting is indicated both by the pattern of aft ages ranging from 81 7 ma to in the nw to 167 16 ma in the se and tilted paleosurfaces aft ages immediately east of sortlandsundet 72 5 ma and on vestvagoya 81 7 ma are among the youngest ones found on the norwegian mainland the present day landscape of the lofoten vesteralen archipelago does not represent a re exposed and glacially modified mesozoic landscape although most of our data indicate cooling to below 60 c took place during the mesozoic the youngest footwall ages are hard to explain without alluding to cenozoic normal faulting a cenozoic structural control on the landscape can thus be inferred for lofoten and vesteralen