geochemistry of central tethyan upper permian and lower triassic strata abadeh region iran nearly 2 km of upper permian to lower triassic limestones are exposed in the hambast mountain abadeh region iran lime mud matrix and most bioclasts of permian age are recrystallized into large calcite crystals and contain 600 4000 ppm sr suggesting a probable aragonite precursor low bulk rock 18 o values 7 to 10 pdb and recrystallized textures are also indicative of diagenetic alteration within the murghabian and abadehian two gradual upward increases in carbonate and organic matter 13 c compositions each roughly 3 pdb in magnitude are documented both are attributed to increased organic productivity and sequestration of organic matter in sediments within the julfian and across the permian triassic p t boundary two sharp upward decreases in carbonate and organic matter 13 c values each 4 pdb in magnitude are observed both are best explained by mixing of a deep water mass having low 13 c values and a shallow water mass having high 13 c compositions early triassic 13 c values initially low 1 pdb increase to 3 pdb within 100 m above the p t boundary variations in 13 c compositions of carbonate and organic matter and changes in 13 c 13 ccar 13 corg indicate that early triassic 13 c values were controlled by productivity cycles

cretaceous tertiary and permian triassic boundary events compared abstract the cretaceous tertiary k t and permian triassic p tr events differ in many more aspects than they are similar this alone makes it unlikely that they are parts of a common web of periodic mass extinction events mee unlike the k t most mee have no ir anomalies and where in the comparatively complete section of the p tr at gartnerkofel austria weak ir concentrations are found their ratios to siderophile elements co ni cr are far less than chondritic in contrast ratios to chalcophile elements as sb zn never approach chondritic even in k t peaks and locality differences suggest local depositional processes that may also affect the siderophiles profiles of isotopes 13ccarb 87 sr 86 sr and possibly 18ocarb across these boundaries also differ radically whereas the k t profile of surface ocean 18ocarb has been shown to be mainly a drop in primary productivity the p tr profile is interpreted at least in part to be a consequence of a large and accelerating oxidation of previously stored corg with greatly differing consequences for climate these and other differences of proximate forcings for these two mee lead us to a hypothesis that such external exigencies were ever intermittently and severally with us but were effective only when the biotic web had already internally unravelled in some crucially strained patch gaia became antigaia

the carbon isotope shift at the permian triassic boundary in the southern alps is gradual carbon isotope ratios in marine carbonate rocks have been shown to shift at some of the time boundaries associated with extinction events for example cretaceous tertiary1 and ordovician silurian2 the permian triassic boundary the greatest extinction event of the phanerozoic3 is also marked by a large 13c depletion4 5 new carbon isotope results from sections in the southern alps show that this depletion did not actually represent a single event but was a complex change that spanned perhaps a million years during the late permian and early triassic these results suggest that the permian triassic p tr extinction may have been in part gradual and in part stepwise 6 7 but was not in any case a single catastrophic event

the heterogeneous upper mantle low velocity zone abstract the upper mantle low velocity zone lvz is a depth interval with slightly reduced seismic velocity compared to the surrounding depth intervals the zone is present below a relatively constant depth of 100 km in most continental parts of the world both in cratonic areas with high average velocity and tectonically active areas with low average velocity evidence for the low velocity zone arises from controlled and natural source seismology including studies of surface waves and of primary and multiple reflections of body waves from the bounding interfaces calculations of receiver functions and absolute velocity tomography the available data indicates a more pronounced reduction in seismic velocity and q value for s waves than p waves as well as high electrical conductivity in the lvz seismic waves are strongly scattered by the zone which demonstrates the existence of small scale heterogeneity the depth to the base of the lvz is systematically shallower in cold stable cratonic areas than in hot active regions of the world because of its global occurrence below a relative constant depth of 100 km the lvz cannot be explained by metamorphic or compositional variation and rheological changes calculated upper mantle temperatures indicate that the rocks are close to the solidus in an interval with variable thickness below 100 km depth provided that the rocks contain water and carbon dioxide the presence of even small amounts of such fluids in the mantle rocks will lower the solidus by several hundred degrees and introduce a characteristic kink on the solidus curve around 80 100 km depth the seismic velocities and q values are significantly reduced of rocks which are close to the solidus or contain small amounts of partial melt hence the lvz may be explained by upper mantle temperatures being close to the solidus in a depth interval below 100 km assuming that the rocks contain only limited amounts of fluids this mechanism may explain the low velocities q values and resistivity as well as the intrinsic scattering and the characteristic variation in thickness of the low velocity zone

interfacial storage of noble gases and other trace elements in magmatic systems abstract trace elements are widely used to unravel magmatic processes and constrain the chemical differentiation of the earth key to their use is understanding the controls on fractionation between solid and liquid which hinge on the energetics of trace element incorporation into crystals at equilibrium most trace elements are incompatible in bulk magmatic minerals because of unfavourable incorporation energies we use computational methods to explore the role that crystal interfaces can play in trace element incorporation in minerals we demonstrate that differences between bulk and interface incorporation energies can be very large and lead to concentration differences of many orders of magnitude consistent with experimental evidence for interface enrichment by emphasising the importance of adsorption incorporation at interfaces we account for the competing effects of bulk equilibrium and interface segregation operating during melting and crystallisation computational results are presented for divalent cations and ar in bulk forsterite at the 010 surface and at the 100 010 stepped grain boundary for all species studied larger than mn 2 segregation to the interface is highly exothermic we discuss in particular the take up of noble gases where in contrast to earlier work a recent experimental study concluded that argon is highly compatible in mantle minerals in contrast our calculations indicate bulk ar solubility is very small and suggests incorporation at mineral interfaces is overwhelmingly favourable

argon diffusion in pyroxenes implications for thermochronometry and mantle degassing abstract the rate at which argon diffuses in pyroxenes is relevant to several problems in the earth and planetary sciences pyroxenes are among the most abundant minerals in the earth s upper mantle and are important hosts for potassium and radiogenic 40 ar 40 ar additionally pyroxenes commonly contain 25 of the total 40 ar within meteorites and therefore hold great potential for quantifying the timing duration and thermal conditions of events experienced by meteorites and their parent bodies we conducted detailed feedback controlled laser heating diffusion experiments using synthetically produced 37 ar in gem quality clinopyroxene cpx and orthopyroxene opx crystals stepwise heating between 850 and 1350 c yielded linear arrhenius arrays from which activation energies e a of 379 2 4 1 and 371 0 6 0 kj mol and pre exponential factors d o of 1 36 10 4 6 15 10 5 1 12 10 4 and 5 73 10 2 2 25 10 2 3 72 10 2 were determined for cpx and opx respectively these e a s are an order of magnitude higher than previously reported values obtained with a different experimental approach watson et al 2007 and indicate that ar diffusion within pyroxenes is strongly temperature dependent at high temperatures ar diffusion in pyroxenes is rapid which indicates that diffusive 40 ar distributions observed within meteoritic pyroxenes may provide information about brief high temperature shock heating events in contrast subsequent low t conditions should minimally influence these concentration gradients the experimental ar diffusion kinetics in opx and cpx correspond to closure temperatures of 600 700 and 700 800 c respectively for 10 c ma cooling these results suggest that diffusive equilibration through 0 1 0 5 mm pyroxene grains occurs in minutes to hours at basaltic melt generation temperatures 1300 c and is therefore unlikely to inhibit mantle degassing

helium distribution in a mantle shear zone from the josephine peridotite a previous study of oceanic mylonites suggested that peridotite helium concentrations are correlated with the degree of high temperature ductile deformation in the mantle in order to test this result this study combines helium measurements with characterization of the deformation state of harzburgite samples in a small 6 m width ductile mantle shear zone from the josephine peridotite oregon usa all measurements were made by coupled in vacuo crushing and melting demonstrating that most of the helium 80 resides within the solid phases rather than fluid or melt inclusions the present study confirms the influence of deformation on helium contents but only at the highest shear strain 20 are helium contents significantly higher the highest helium concentration by roughly a factor of two is found in the center most sample which also has grain size reduction by a factor of 4 dislocations and sub grain boundaries are present in all samples and do not correlate with helium concentrations mineralogy also appears to have a negligible influence in this shear zone as modal mineralogy is relatively homogeneous with all samples being harzburgites these observations suggest that the increase in helium concentration is related to grain size reduction with grain boundaries proposed as an additional storage site for helium in the mantle the present data also characterize the isotopic composition of the josephine peridotite 3he 4he 6 7 0 2 ra n 33 between 6 3 and 7 1 ra the presence of cosmogenic 3he in the matrix is indicated by the helium isotopic composition released by melting 3he 4he 8 5 0 3 ra n 10 from 7 9 to 10 9 this corresponds to an exposure age of 10 kyr which is approximately concordant with the end of the last glacial maximum very little radiogenic helium is present in the samples suggesting extremely low uranium and thorium contents u 0 3 ppb helium isotope measurements in four samples outside the shear zone suggest that mineralogy and melt infiltration are also important factors for understanding helium storage in the mantle

multiscale spatial distribution of crustal seismic anisotropy beneath the northeastern margin of the tibetan plateau and tectonic implications of the haiyuan fault abstract the haiyuan fault is a large strike slip fault in the northeastern ne margin of the tibetan plateau using new data recorded by a temporary seismic array this study obtains crustal seismic anisotropy measurements in different scales across the haiyuan fault by analyzing splitting of shear waves from local earthquakes parameters of shear wave splitting sws indicate clear zoning characteristics in seismic anisotropy in the upper crust the study area is divided into two different anisotropic subzones by the haiyuan fault the dominant orientation of fast polarizations is nne or ne north of the faults and wnw to ew south of the fault this pattern of spatial variation indicates the controlling impact of haiyuan fault to observed seismic anisotropy with a zone of dozens of kilometers from the haiyuan fault the dominant orientations of fast polarizations are wnw generally coincidental with the strike of the haiyuan fault except for several stations it indicates that the influence of the fault on stress could reach to about 10 km from the fault distance spatial pattern of anisotropy indicates multiple effects by stress faults and local tectonics it suggests different anisotropic mechanisms including stress induced anisotropy and tectonic or structural anisotropy the dominant orientation of fast polarizations can indicate in situ maximum horizontal principal compressive stress although there is always influence of tectonics the normalized time delays are higher around the haiyuan fault than those away from the fault suggesting stronger crustal seismic anisotropy in a narrow belt around the strike slip fault zone the sws parameters suggest that the haiyuan fault is the actual crustal boundary of ne tibetan plateau about 200 km north of the reported boundary of the tibetan plateau block combining with other studies in the crust and the lithosphere this paper infers possible two layer crustal anisotropy beneath the yinchuan graben north of the haiyuan fault the dominant orientation of fast polarizations are nne or ne in the upper crust probably originated from crack induced anisotropy but become wnw or nw in the middle lower crust possibly originated from deformation anisotropy

imaging the mantle lithosphere below the china cratons using s to p converted waves abstract we used s to p converted waves from over a thousand seismic stations of the permanent chinese national seismic network to study the large scale structure of the mantle lithosphere beneath the cratons in china to avoid possible sidelobes of the moho caused by the deconvolution in the s receiver function method we skipped the deconvolution and used the sv onset time as reference time instead of the time of the deconvolution spike with this new method the lithosphere asthenosphere boundary lab is observed near 80 km depth below both the north and the south china cratons however at the north eastern margin of the tibetan plateau the lab is observed at about 160 km depth smoothly shallowing towards the west and abruptly ending at the western end of the north china craton this structure is not visible in traditional s receiver function data because it is overwhelmed by moho sidelobes there is no indication of a deeper near 200 km cratonic lithosphere asthenosphere boundary in the other parts of the china cratons as it is observed in other cratons we hypothesise that at the north eastern margin of the tibetan plateau the original thickening of the lithosphere towards the craton is preserved whereas in most parts of the north and south china cratons the lower part of the lithosphere is removed by some mechanism the moho is well observed it deepens from 30 to 40 km at the sea shores in the east to 60 70 km below eastern tibetan plateau

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

isotopic records of brachiopod shells from the russian platform evidence for the onset of mid carboniferous glaciation we performed isotopic analyses of carboniferous brachiopod shells from the russian platform to examine global and regional environmental change along the western and eastern margins of laurussia during the formation of pangea and specifically to examine the isotopic evidence for the onset of mid carboniferous glaciation shell preservation was evaluated from shell microstructure cathodoluminescence trace element content and isotopic comparison with matrix material most interior nonluminescent nl prismatic shell appears to be chemically well preserved as indicated by low to undetectable si al fe and mn contents with minor exception nl shell 13c and 18o values are higher than those of corresponding cements and matrix the 13c record for the russian platform clearly shows a 3 increase from 2 4 0 7 to 5 5 0 6 in the serpukhovian or early bashkirian this shift was first reported by popp et al popp b n anderson t f sandberg p a 1986 brachiopods as indicators of original isotopic compositions in some paleozoic limestones geol soc am bull 97 1262 1269 but had not been documented for a single region widespread occurrence of high 13c values in the late carboniferous support the interpretation of popp et al with regard to this shift as a record of increased burial of organic carbon north american sections show a mid carboniferous 13c shift of only 1 5 we hypothesize that the reduced 13c shift reflects enhanced upwelling on the epicontinental seas of north america after the closing of the seaway between laurussia and gondwana the 18o record for the russian platform shows a 1 8 increase in the mid carboniferous correlative with increased occurrence of glacial sediments and a drop in sea level as a first approximation ice volume calculations suggest that 0 7 of the mid carboniferous 18o shift is due to changes in seawater 18o and 1 1 is due to 5 c cooling concurrent positive 13c and 18o shifts provide evidence for a relationship between mid carboniferous glaciation and burial of organic carbon presumably through changes in atmospheric co2 levels

a complex tibetan upper mantle a fragmented indian slab and no south verging subduction of eurasian lithosphere due to the non uniform seismic station coverage in tibet critically important questions remain about the existence of southward continental subduction of eurasia beneath northern tibet from north and the nature of the underthrusting indian lithosphere underneath southern tibet from south using differential p and s wave travel times measured from 301 stations of all the temporary experiments deployed throughout tibet we constructed a comprehensive tomographic model the upper mantle of northern tibet consists of a rather homogeneous low velocity zone with no evidence of southward asian continental subduction in contrast the upper mantle from the himalayas to central tibet exhibits laterally variable p and s wave velocities significant low velocity zones are observed that are elongated in a north south direction and extending to at least 150 km depth which we interpret as evidences for fragmentation of the underthrusting indian continental lithosphere

anisotropic low velocity lower crust beneath the northeastern margin of tibetan plateau evidence for crustal channel flow detailed seismic structure in the crust beneath the northeastern margin of tibetan plateau was revealed by receiver functions of a regional permanent seismic network at most stations negative p to s converted phases can be detected in the radial receiver functions prior to the moho phases indicating low velocities in the midlower crust prominent azimuthal variations in the transverse receiver functions with polarity reversal suggest azimuthal anisotropy in the crust we used time variations of the p to s converted phases at the moho in the radial receiver functions and the azimuth weighted stacking of transverse receiver functions to determine the fast direction and magnitude of anisotropy the low velocity midlower crust with the coherent azimuthal anisotropy in the northeastern margin of tibetan plateau is consistent with the lower crustal channel flow model

applications of diffusion data to high temperature earth systems diffusion in general is such a widespread phenomenon in nature that a basic knowledge can serve very effectively to address well known applications not only to thermochronology and petrology but also to environmental geology e g paleoclimate sedimentology and applied geosciences e g assessing contamination of gas stations indeed the list of potential applications of diffusion phenomena is so long that an exhaustive treatment would quickly exceed the scope of this review the reader is therefore referred to reviews covering various aspects of diffusion in the earth sciences including diffusion in melts watson 1994 chakraborty 1995 diffusion processes during diagenesis berner 1980 krom and berner 1980 boudreau 2000 and diffusion phenomena in general e g lasaga 1998 ganguly 2002 watson and baxter 2007 zhang 2008 all of these treatments are based on the same general concepts of diffusion which do not need restating here in great detail applications of diffusion profiles in igneous systems have been thoroughly reviewed a recent reviews in mineralogy and geochemistry volume rimg 69 putirka and tepley 2008 and there is also an excellent volume on low temperature thermochronology rimg 58 reiners and ehlers 2005 describing the impact and application of diffusion theory for age and thermal history determination with these precedents in mind we focus the present review on the application of diffusion in high temperature regimes i e systems at t 500 c both igneous and metamorphic systems are addressed but because of the recent precedents noted above we emphasize recent developments and challenges in metamorphic studies in a broad sense diffusion describes the statistical non directional movement of molecules or heat through a medium of interest as independent theories of diffusion were developed in the early 19th century and compared with the principles of statistical variance it was

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

geochemical events documented in inorganic carbon isotopes abstract screening of sampling and analytical data is crucial for the detection of real global shifts in marine 13c against the noise of diagenesis the real global shifts of 13c are of two types 1 long term secular shifts caused by changes in the fractional burial of organic carbon and 2 transient shifts caused by abrupt changes of biological productivity in the surface photic zone both are applicable to stratigraphic correlation but differ in their application to modelling of changes in oceanographic or atmospheric composition a recent compilation found 34 carbon isotope events in the phanerozoic and neoproterozoic equally distributed among positive and negative shifts this in itself attests to a variety of proximate causes of the shifts

rayleigh wave tomography of china and adjacent regions 1 this paper presents a tomographic study on the s wave velocity structure of china and adjacent regions group velocity dispersions of fundamental rayleigh waves along more than 4000 paths were determined with frequency time analysis the study region was divided into a 1 1 grid and velocities in between grid nodes were calculated by bilinear interpolation the occam s inversion scheme was adopted to invert for group velocity distributions this method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern checkerboard tests were carried out and the lateral resolution was estimated to be 4 6 in china and its eastern continental shelves the resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features the pure path dispersion curves at each node were inverted for shear wave velocity structures the three dimensional velocity model indicates thick lithospheres in the yangtze and tarim platforms and hot upper mantles in baikal and western mongolia coastal area and continental shelves of eastern china and indochina and south china sea regions the tibetan plateau has a very thick crust with a low velocity zone in its middle beneath the crust a north dipping high velocity zone mimicking a subducting plate reaches to 200 km in depth and reaches to the kunlun mountains northward in northern tibet a low velocity zone immediately below the moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low velocity area in indochina and the south china sea

three dimensional velocity field of present day crustal motion of the tibetan plateau derived from gps measurements 1 using the measurements of 750 gps stations around the tibetan plateau for over 10 years since 1999 we derived a high resolution 3 d velocity field for the present day crustal movement of the plateau the horizontal velocity field relative to stable eurasia displays in details the crustal movement and tectonic deformation features of the india eurasia continental collision zone with thrust compression lateral extrusion and clockwise rotation the vertical velocity field reveals that the tibetan plateau is continuing to rise as a whole relative to its stable north neighbor however in some subregions uplift is insignificant or even negative the main features of the vertical crustal deformation of the plateau are the following a the himalayan range is still rising at a rate of 2 mm yr the uplift rate is 6 mm yr with respect to the south foot of the himalayan range b the middle eastern plateau has a typical uplift rate between 1 and 2 mm yr and some high mountain ranges in this area like the longmen shan and gongga shan have surprising uplift rates as large as 2 3mm yr c in the middle southern plateau there is a basin and endorheic subregion with a series of ns striking normal faults showing obvious sinking with the rates between 0 and 3 mm yr d the present day rising and sinking subregions generally correspond well to the cenozoic orogenic belts and basins respectively e at the southeastern corner of the plateau there is an apparent trend that the uplift rate is gradually decreasing from between 0 8 and 2 3 mm yr in the inner plateau to between 0 5 and 1 6 mm yr outside the plateau with the decrease of terrain height

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

diffusion limited ree uptake by eclogite garnets and its consequences for lu hf and sm nd geochronology garnets from the zermatt saas fee eclogites contain narrow central peaks for lu yb tm er and at least one additional small peak towards the rim the ree sm eu gd tb dy are depleted in the cores but show one prominent peak close to the rim these patterns cannot be modeled using rayleigh fractionation accompanied by mineral breakdown reactions instead the patterns are well explained using a transient matrix diffusion model where ree uptake is limited by diffusion in the matrix surrounding the porphyroblast observed profiles are well matched if a roughly linear radius growth rate is used the secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to temperature increase during prograde metamorphism the model predicts anomalously low 176lu 177hf and 147sm 144nd ratios in garnets where growth rates are fast compared to diffusion of the ree and these results have important implications for lu hf and sm nd geochronology using garnet

a sharp lithosphere asthenosphere boundary imaged beneath eastern north america although a rigid lithosphere about 100 km of crust and uppermost mantle moving over a weaker asthenosphere a few hundred kilometres of more deformable rock is a widely accepted aspect of plate tectonics the properties of the boundary between them are poorly understood when compressional waves p waves from an earthquake encounter an interface at an angle some of the energy is converted to shear waves or s waves these converted waves can be used to construct an image of the interface based on converted waves recorded in eastern north america the lithosphere asthenosphere boundary has been resolved as a sharp gradient that cannot be explained by thermal gradients alone indicating that the boundary is controlled by melt or high water content in the asthenosphere plate tectonic theory hinges on the concept of a relatively rigid lithosphere moving over a weaker asthenosphere yet the nature of the lithosphere asthenosphere boundary remains poorly understood the gradient in seismic velocity that occurs at this boundary is central to constraining the physical and chemical properties that create differences in mechanical strength between the two layers for example if the lithosphere is simply a thermal boundary layer that is more rigid owing to colder temperatures mantle flow models1 2 indicate that the velocity gradient at its base would occur over tens of kilometres in contrast if the asthenosphere is weak owing to volatile enrichment3 4 5 6 or the presence of partial melt7 the lithosphere asthenosphere boundary could occur over a much smaller depth range here we use converted seismic phases in eastern north america to image a very sharp seismic velocity gradient at the base of the lithosphere a 3 11 per cent drop in shear wave velocity over a depth range of 11 km or less at 90 110 km depth such a strong sharp boundary cannot be reconciled with a purely thermal gradient but could be explained by an asthenosphere that contains a few per cent partial melt7 or that is enriched in volatiles relative to the lithosphere3 4 5 6

the boundary between the indian and asian tectonic plates below tibet the fate of the colliding indian and asian tectonic plates below the tibetan high plateau may be visualized by in addition to seismic tomography mapping the deep seismic discontinuities like the crust mantle boundary moho the lithosphere asthenosphere boundary lab or the discontinuities at 410 and 660 km depth we herein present observations of seismic discontinuities with the p and s receiver function techniques beneath central and western tibet along two new profiles and discuss the results in connection with results from earlier profiles which did observe the lab the lab of the indian and asian plates is well imaged by several profiles and suggests a changing mode of india asia collision in the east west direction from eastern himalayan syntaxis to the western edge of the tarim basin the indian lithosphere is underthrusting tibet at an increasingly shallower angle and reaching progressively further to the north a particular lithospheric region was formed in northern and eastern tibet as a crush zone between the two colliding plates the existence of which is marked by high temperature low mantle seismic wavespeed correlating with late arriving signals from the 410 discontinuity poor sn propagation east and southeast oriented global positioning system displacements and strikingly larger seismic sks anisotropy

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

tibetan plate overriding the asian plate in central and northern tibet at the southern boundary between india and tibet the indian tectonic plate subducts northwards beneath the tibetan plateau seismic imaging shows that at the northern boundary of tibet the asian plate is also subducting southwards beneath the plateau and the tibetan lithosphere is separate

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

the terminal paleozoic fungal event evidence of terrestrial ecosystem destabilization and collapse because of its prominent role in global biomass storage land vegetation is the most obvious biota to be investigated for records of dramatic ecologic crisis in earth history there is accumulating evidence that throughout the world sedimentary organic matter preserved in latest permian deposits is characterized by unparalleled abundances of fungal remains irrespective of depositional environment marine lacustrine fluviatile floral provinciality and climatic zonation this fungal event can be considered to reflect excessive dieback of arboreous vegetation effecting destabilization and subsequent collapse of terrestrial ecosystems with concomitant loss of standing biomass such a scenario is in harmony with predictions that the permian triassic ecologic crisis was triggered by the effects of severe changes in atmospheric chemistry arising from the rapid eruption of the siberian traps flood basalts

lithospheric structure across the northeastern margin of the tibetan plateau implications for the plateau s lateral growth abstract variations of lithospheric structure across the northeastern tibetan plateau and its bounding asian blocks the alxa block to the north and the ordos block to the east are crucial for understanding the rise and lateral growth of the tibetan plateau using waveforms from high density seismic arrays in northeastern tibetan plateau and the surrounding regions we investigated the lithospheric structure with s and p wave receiver functions the results show strong and relatively simple negative velocity gradients in the depth range of mantle lithosphere 70 150 km under the ordos and alxa blocks similar to those under typical stable continental lithosphere in contrast under northeastern tibetan plateau including its marginal regions the velocity gradients are weak and diffusive for the mantle lithosphere which may be explained by elevated temperature and presence of partial melts the changes of lithospheric structures are sharp between the tibetan plateau and the bounding ordos and alxa blocks suggesting that these two blocks have restricted the lateral growth of the tibetan plateau as rigid boundaries however across the northeastern corner of the tibetan plateau to the yinchuan rift the lithospheric mantle structures are similar suggesting a lateral mantle flow from the tibetan plateau to the gap between the ordos and the alxa blocks the crustal structures along this transition show evidence of lateral growth of the tibetan plateau in particular the edge of thickened crust and evidence of moho superposition are found between the haiyuan fault and the tianjin shan fault which may have replaced the haiyuan fault as the front boundary of the laterally growing tibetan plateau in its northeastern corner

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

lithospheric thickness of the chinese continent abstract we invert for the upper mantle temperatures of the chinese continent in the depth range of 70 240 km from a recent s velocity model the depth where temperatures intersect a mantle adiabat with a potential temperature of 1300 c is in close correspondence with the top of the seismic low velocity zone for most regions this correspondence implies that seismic lithosphere estimated from short time scale seismic information may be equivalent to the long time scale geodynamical lithosphere defining the 1300 c adiabat as coinciding with the lithospheric base we estimate the seismic thermal lithosphere thickness the estimated thickness shows obvious dependence on the tectonic settings beneath eastern china which mainly belongs to the circum pacific tectonic domain it has a thickness of 100 km and beneath the qinghai tibet plateau and south to the tarim craton which belong to the tethyan tectonic domain it has a thickness of 160 220 km the lithospheric thicknesses of the three large para platforms cratons range from 170 km for the western yangtze 140 km for tarim and 100 km for sino korean the three cratons may have been reshaped by phanerozoic tectonic activities and are thinner than most cratons in other continents

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

limited southward underthrusting of the asian lithosphere and material extrusion beneath the northeastern margin of tibet inferred from teleseismic rayleigh wave tomography the northeastern margin of tibet is of key importance in understanding the uplift and expansion of tibetan plateau in this research we perform rayleigh wave tomography from 20 s to 167 s using the data recorded by china digital seismic network and several portable seismic arrays in northeastern tibet and adjacent areas our resultant 3 d shear wave velocity model exhibits strong lateral variations in the lithosphere high shear wave velocities are observed in the mantle of the cratonic ordos and yangtze blocks as well as the east qinling orogen the qilian orogen is underlain by a 120 km thick lithosphere of intermediate velocities and a low velocity layer of asthenospheric mantle below the depth of 120 km low velocities are characteristic in the middle to lower crust of the songpan ganzi terrane and the west qinling orogen possibly representing the crustal flow penetrating the kunlun fault an uppermost mantle low velocity zone is found in the same location indicating either the asthenosphere upwelling or the transitional crust mantle boundary layer our observations have two tectonic implications first the large scale eastward tibetan material extrusion into eastern china through the east qinling orogen is unlikely to be an ongoing process above 200 km depth second the southward subduction of the north china craton toward northeastern tibet may not have fully developed in this region furthermore we propose that the difference in the lithospheric strength between the qaidam block and the west qinling orogen is a critical element to control the tectonics in the northeastern margin of tibet

converted waves reveal a thick and layered tectosphere beneath the kalahari super craton abstract thick and high velocity roots are generally observed beneath the archean cratons inside these high velocity keels velocity contrasts are detected neither by surface nor by body waves tomographies we present here evidences based on the s to p and p to s converted waves for the existence of an irregularly stratified and thick keel beneath the kalahari super craton to satisfy surface wave data and s to p conversions the velocity model should have beneath the moho a 160 km thick anisotropic structure with vertical slow axis and decreasing anisotropic parameters with depth such a structure may stem from the preferred orientation of olivine 100 axis in the horizontal plane under shearing deformation this structure together with the 100 km thick layer underlying it forms a 300 km thick continental root beneath the cratons inside this root the p and s velocities should be higher on average respectively by an amount of 6 and 4 than the ak135 velocity model beneath 300 350 km depth a low velocity zone is clearly detected that may be either the remainder of large magma reservoirs related to cratonic flood basalts or a melted silicate layer created by the transformation just above the 410 km deep discontinuity of wadsleyite assembly to olivine assembly

oxygen isotope analyses of co existing carbonate and phosphate in biogenic apatite a way to monitor diagenetic alteration of bone phosphate abstract the oxygen isotopic composition of phosphate 18 op and structural carbonate 18 oc of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries these two variables are highly correlate r 2 0 98 and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations 1 2 according to previous measurements 3 6 on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between 18 op and 18 oc as is the case with modern samples it therefore seems possible at least in some cases to use these measurements for monitoring fossil bone and tooth diagenetic alteration when a set of points lie on the equilibrium line or close to it the 18 o values could be considered close to the original values in contrast when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified due to interaction with meteoric water or 18 o enriched water respectively

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

crustal and upper mantle structure of southeast tibet from rayleigh wave tomography 1 we have applied the two plane wave inversion technique to fundamental mode rayleigh waves in southeast tibet phase velocity variations are obtained at 15 periods from 20 to 143 s and are used to construct three dimensional shear wave velocity structure a low velocity zone is imaged in the middle crust of southeast tibet in which velocity perturbation varies from 4 to 3 the slow area might be associated with high temperature and partial melt and can flow ductilely while the high velocity region could be relatively cold and mechanically strong enough to pass crustal strain implying that coherent lithospheric deformation is possible with the presence of complicated crustal flow strong negative anomalies in the shallow crust are imaged at 92 e correlating with the location of a north south rift zone a fast mantle lid to a depth of 120 km is present beneath most of the study area the lithosphere is significantly slower in the central part of the study area than in the west and east to the east of 96 e a subvertical high velocity zone is imaged at 120 240 km depths under the bangong nujiang suture bns which is more like the subduction of the asian lithosphere we interpret the high velocity anomalies to the south of the bns as the subducted indian lithosphere and those to the north as the asian lithosphere a vertical low velocity column is observed in the central part of the region from the lower crust to the midupper mantle which is probably in part responsible for the rift at 92 e the slow anomaly is likely associated with asthenosphere upwelling following the opening of a slab window that could have developed when the slab was torn apart vertically because of the significant change of subducting direction at the eastern syntaxis

lateral growth of ne tibetan plateau restricted by the asian lithosphere results from a dense seismic profile abstract we present high resolution receiver function images along a 700 km long dense seismic array extending from northern tibetan plateau to the alxa block crossing the entire qilian thrust belt qtb the dense stations with less than 2 km station intervals allow the receiver functions to unveil unprecedented details of crustal structures across the northern frontier of the growing tibetan plateau the migration image shows a thickened and strongly deformed qtb crust with an uneven moho and complex internal structures that are indicative of pure shear shortening the alxa block in contrast has a thinner crust a flat moho and little internal crustal deformation these results suggest that the lateral growth of ne tibetan plateau is restricted by the strong asian lithosphere which shows no visible subduction beneath the tibetan plateau as previously suggested

electrical structure of the middle qilian shan revealed by 3 d inversion of magnetotelluric data new insights into the growth and deformation in the northeastern tibetan plateau abstract the qilian shan is located along the northeastern margin of the tibetan plateau which is a key area for studying the growth and expansion of the tibetan plateau there have been several geodynamic models developed to explain the deformation pattern of the tibetan plateau extending to the northeast but they remain controversial the magnetotelluric mt method can study subsurface electrical conductivity and rheological properties a dense broadband and long period magnetotelluric mt profile across the middle qilian shan has been completed the mt profile starts from the northeastern margin of the qaidam basin crosses the qilian shan and hexi corridor and finally reaches the southwestern margin of the alashan block based on data analysis results a three dimensional 3 d resistivity model of the crust and upper mantle has finally been obtained the mt results show that a relatively low resistivity zone exists at the bottom of the upper crust of the qilian shan features as an intracrustal decollement which indicates the decoupling deformation between the upper and lower crust the isolated conductive bodies in the middle lower crust of the qilian shan may have formed during the primary stage of plateau growth suggesting that there may be no existence of the middle lower crustal flow beneath the qilian shan the alashan block lithospheric mantle may have partly underthrust southward the northeastern tibetan plateau the tibetan plateau may have grown and expanded northeastward across the hexi corridor to the heli shan fault

is the asian lithosphere underthrusting beneath northeastern tibetan plateau insights from seismic receiver functions abstract whether or not the asian lithosphere has underthrusted beneath the tibetan plateau is important for understanding the mechanisms of the plateau s growth using data from the permanent seismic stations in northeastern tibetan plateau we studied seismic structures of the lithosphere and upper mantle across the plateau s northeastern margin using p and s receiver functions the migrated p and s receiver function images reveal a thick crust and a diffuse lithosphere asthenosphere boundary lab beneath the tibetan plateau contrasting sharply with the relatively thin crust and clear sharp lab under the bounding asian blocks the well defined lab under the asian blocks tilts toward but does not extend significantly under the tibetan plateau this is inconsistent with the model of asian mantle lithosphere underthrusting beneath the tibet plateau instead our results indicate limited passive deformation of the bounding asian lithosphere as it encounters the growing tibetan plateau

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

electrical resistivity structures of the kunlun qaidam qilian system at the northern tibet and their tectonic implications abstract the northern tibetan plateau is characterized by northwest southeast trending basin range systems such as the kunlun shan ranges qaidam basin qilian shan ranges the cenozoic evolution and deformation of the qaidam basin and its neighboring ranges are important indications for the northward growth of the tibetan plateau the latest magnetotelluric data were collected along a profile in n16 5 e from the songpan ganzi block across the kunlun shan ranges east section of the qaidam basin and ending in the qilian shan ranges both two dimensional and three dimensional inversions of the data along the profile were performed and the results provided new evidence for lithospheric structures in the northern tibetan plateau with three dimensional isotropic inversion codes we are able to model the phase roll out of quadrant proq magnetotelluric data which exist at low frequencies in a number of continuous sites at the northern qaidam basin sensitivity studies of the three dimensional models indicate that the qaidam basin with low resistivity upper crust is the major contributor for the proq effect while a south north striking low resistivity gap intersecting with the qaidam basin at its northern part affects the range of the proq effect in the magnetotelluric resistivity models the qaidam basin is not in symmetric structure at upper crust level with its depocenter near the northern qaidam fault at mid lower crust level the compositions of both the kunlun shan ranges and the southern qaidam basin are of generally high resistivity which does not support large scale lower crust materials of the songpan ganzi block flow below the kunlun shan ranges or the qaidam basin instead the unsymmetrical qaidam basin and the shovel shape high resistivity anomalies in crust below the kunlun shan ranges and the southern qiadam basin indicate the regional northward push from the songpan ganzi block the south deepening low resistivity anomalies in the crust of the qilian shan ranges support the existence of an intracrustal detachment which controls the thrusts in northern qaidam basin and the qilian shan ranges the crustal deformation in northern tibetan plateau is consistent with mantle convergence or collision between the kunlun qaidam lithospheric mantle and the asian lithospheric mantle

a low velocity belt beneath northern and eastern tibetan plateau from pn tomography 1 new pn tomography on tibetan plateau tp and neighboring region is conducted with data assembled from various sources the improved pn tomographic image delineates several distinct geophysical regimes that are approximately separated by geological boundaries at surface dense distribution of the stations in the eastern half of the plateau allows us to infer a 3d view of crustal thickness variation of the region the most striking feature is the bended low velocity belt lvb which extends from west to east beneath qiangtang block and songpan ganzi fold belt sgfb in northern tp and then turns consistently southward with sgfb beneath eastern tp and further south to indo china the consistency between geological boundaries on surface and sharp velocity contrast boundaries in uppermost mantle may suggest strong deformation coupling between crust and at least uppermost mantle if not whole lithosphere a north south striking lvb is also observed cutting through the southern tp coinciding with the yadong gulu rift at surface our tomographic results are generally consistent with dynamic models that involve with underthrusting in the southern tp shortening in the northern tp and extrusion to the east and the southeast furthermore our results suggest significant east west variations in the structure and dynamics

the s receiver functions synthetics and data example summary recently the s receiver function method has been successfully developed to identify upper mantle interfaces s receiver functions have the advantage of being free of s wave multiple reflections and can be more suitable than p receiver functions for studying mantle lithosphere however because of specific ray geometry and interference of diverse phases the s receiver function method has some technical difficulties and limitations we use synthetic seismograms to demonstrate the feasibility and limitations of s receiver functions for studying mantle structures full wavefield seismograms were calculated using the reflectivity method and processed to generate synthetic s receiver functions for s sks and scs waves results show that s receiver functions can be obtained from waveforms of s sks and scs waves the synthetic s receiver functions for these incident waves show s to p converted phases at all discontinuities in the crust and upper mantle useful ranges of epicentral distances for calculation of s receiver functions are 55 85 for s 85 for sks and 50 75 for scs waves we apply both the s and p receiver function methods to data recorded at broadband station ykw3 in northwest canada the study shows that there is significant agreement among different receiver function methods and demonstrates the usefulness of s receiver functions for imaging the mantle lithosphere

zoning of phosphorus in igneous olivine we describe p zoning in olivines from terrestrial basalts andesites dacites and komatiites and from a martian meteorite p2o5 contents of olivines vary from below the detection limit 0 01 wt to 0 2 0 4 wt over a few microns with no correlated variations in fo content zoning patterns include p rich crystal cores with skeletal hopper or euhedral shapes oscillatory zoning structures suggesting replacement of p rich zones by p poor olivine and sector zoning melt inclusions in olivines are usually located near p rich regions but in direct contact with low p olivine crystallization experiments on basaltic compositions at constant cooling rates 15 30 c h reproduce many of these features we infer that p rich zones in experimental and natural olivines reflect incorporation of p in excess of equilibrium partitioning during rapid growth and zoning patterns primarily record crystal growth rate variations occurrences of high p phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling most cases of oscillatory zoning in p likely reflect internal factors whereby oscillating growth rates occur without external forcings but some p zoning in natural olivines may reflect external forcings e g magma mixing events eruption that result in variable crystal growth rates and or p contents in the magma in experimental and some natural olivines al cr and p concentrations are roughly linearly and positively correlated suggesting coupled substitutions but in natural phenocrysts cr zoning is usually less intense than p zoning and al zoning weak to absent we propose that olivines grow from basic and ultrabasic magmas with correlated zoning in p cr and al superimposed on normal zoning in fe mg rapidly diffusing divalent cations homogenize during residence in hot magma al and cr only partially homogenize and delicate p zoning is preserved because p diffuses very slowly this interpretation is consistent with the fact that zoning is largely preserved not only in p but also in al cr and divalent cations in olivines with short residence times at high temperature e g experimentally grown olivines komatiitic olivines groundmass olivines and the rims of olivine phenocrysts grown during eruption p zoning is widespread in magmatic olivine revealing details of crystal growth and intra crystal stratigraphy in what otherwise appear to be relatively featureless crystals since it is preserved in early formed olivines with prolonged residence times in magmas at high temperatures p zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma s history study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks especially because these features can be observed with standard electron microprobe techniques

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

electrical resistivity variations of lithospheric mantle beneath the northern tibetan plateau with tectonic implications abstract the northern tibetan plateau including the areas north of kunlun shan is characterised by a strapped basin range system and major strike slip faults however the surficial deformation differs laterally the collection of magnetotelluric mt data covering the northern tibetan plateau has made it possible to apply a three dimensional isotropic inversion of these data for the entire study area the plane area covered by mt sites is more than 700 700 km2 and the longest periods of most of these sites approximate or exceed 10 000 s all of these aid in distinguishing the weak responses generated by deep anomalies in the lithospheric mantle the three dimensional inversion is applied to a subset of mt data and it is observed that the full impedance data of most mt sites well fit the responses of the final three dimensional model two modes of relationship among the lithospheric mantles in the northern tibetan plateau are proposed the moderate low resistivity corridor indicates that the lithospheric mantle has a low viscosity which is favourable for shortening at shallow crustal levels under a regional compression environment furthermore the low resistivity anomalies in the west qaidam basin and southwest qilian shan form a passage that may connect with weak materials in the lower crust of songpan ganzi terrane through the qiman tagh range the high resistivity lithospheric mantle of east kunlun shan east qaidam basin and alashan is dislocated according to the surface boundaries indicating a face to face subduction below qilian shan this represents the major dynamic model in the northern tibetan plateau

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

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

ar diffusion and solubility measurements in plagioclases using the ultra violet laser depth profiling technique we describe the first direct measurements of ar diffusion and solubility in plagioclases using ultra violet uv laser ablation depth profiling and noble gas mass spectrometer analyses of experimentallytreated 599 1000 8c 50 200 mpaofar crystalfragmentsoflabradoriteandoli goclase labradorite 40 ar gain diffusion profiles were measured yielding an activation energy of 26 72 4 58 kcal mol 21 118 0 19 16 kj mol 21 and a frequency factor of 9 77 10 29 8 79 10 28 28 79 10 29 c m 2 s 21 95 confidence the ar solubility in labradorite was measured yielding a value of 0 2 ppb bar 21 which is similar to or lower than many rock forming minerals the labradorite diffusion parameters indicate ar closure temperatures of 211 8c for a spherical diffusion geometry and 243 8c for a planar diffusion geometry for 100 mm diameter grains with cooling rates of 10 8 cm a 21 the data indicate that labradorite is less ar retentive than k feldspar at low temperatures but more ar retentive than k feldspar at high temperatures corroborating previous work on plagioclase the relatively slow ar diffusion rates in labradorite at magmatic temperatures may explain the common observation of older ages in large plagioclase grains in acidic volcanic systems supplementary material details of the uv laser depth profiles obtained from the labradorite and oligoclase samples used in this study are available at www geolsoc org uk sup18608

geochemistry earth holds its breath some inert gas isotopes in earth s atmosphere can only have come from deep inside the planet we thought we knew how much gas earth gives up and how it does it but a challenge has emerged to the prevailing model the noble gases are widely used as tracers of mantle degassing on earth and the other terrestrial planets but new work raises doubts over the practice specifically it is thought that the abundance of argon 40 in the atmosphere represents the total loss of gases from the interior over time via partial melting in the mantle followed by melt ascent to the surface and gas exsolution new data on argon solubility in the olivine and orthopyroxene minerals of the upper mantle reveal two major difficulties with this scenario first the tacit assumption that all noble gases behave as incompatible elements during mantle melting is undermined by the finding that argon seems to be more compatible with the major phases of the terrestrial planets than was thought and second argon diffusion in these phases is slow this challenges the common belief that the upper mantle is almost completely degassed of argon 40 and questions its value as a monitor of planetary degassing

a unique geochemical record at the permian triassic boundary a 330 metre core drilled through the marine permian triassic boundary in the carnic alps of austria allows closely correlated studies of geochemistry petrography and palaeontology across the boundary the isotope shifts and metal concentrations are extended multiple and complex and do not resemble those seen at the cretaceous tertiary boundary both the carbon isotope shifts and the chemical events including an indium anomaly may have causes related to a major regression of the sea

early cenozoic faulting of the northern tibetan plateau margin from apatite u th he ages models to explain the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary yet a growing body of evidence in the tibetan orogen suggests that deformation occurred at the far northern extent of the modern plateau early in the orogen s history and thus our current mechanical understanding of orogenic plateau development is incomplete new apatite u th he ages from four elevation transects document periods of rapid exhumation related to erosion pulses in hanging wall rocks of major thrust structures accelerated erosion is used as a proxy of fault timing and is interpreted in a larger context of structural data and sediment accumulation in adjacent foreland basins helium results are synthesized with published geologic thermochronometric and sedimentologic data from which a growing picture of regional compressional deformation in middle to late eocene time in northern tibet emerges we relate the early cenozoic period of deformation to the initiation of collision between india and eurasia despite the fact that the plate boundary was located 3000 km to the south regardless of whether or not high topography was built simultaneously as a result of this deformation early cenozoic strain signifies that the modern limit of the orogen has been relatively stationary since continental collision began and that deformation has not significantly propagated farther away from the plate boundary in time

strontium isotope stratigraphy of the middle devonian brachiopods and conodonts a set of 145 strontium isotope ratios based on skeletal components of emsian to frasnian age reveals a detailed structure of the seawater 87sr 86sr curve that can ultimately serve as a tool for high resolution isotope stratigraphy in the devonian brachiopod and conodont samples were collected in the eifel region of germany the area around the global stratotype for the middle devonian with an apparent average temporal resolution in the 105 y range preservation of the brachiopod shell material has been assessed by optical microscopy sem and cathodoluminescence and only the better preserved internal secondary layer of the shell has been utilized for strontium isotope measurements the 87sr 86sr curve shows a short decline from 0 7081 to 0 7078 through the late emsian followed by short term fluctuations with an amplitude of up to 10 4 around a mean of 0 7078 during the eifelian and givetian and a rise from late givetian into the late devonian the above high frequency oscillations and spikes are likely a reflection of condensed sedimentary records due to erosional and nondepositional events but a direct confirmation for such a scenario can be claimed only for the latest eifelian otomari event insufficient stratigraphic resolution precludes testing for the other events and isotopic spikes conodont skeletal elements even if well preserved at cai 2 5 yielded results that are mostly enriched in radiogenic 87sr if compared to coeval brachiopods although this enrichment is usually within the 10 5 range conodonts despite their superior stratigraphic resolution should be utilized only as a material of second choice in cases where brachiopods are rare or absent

present day crustal vertical movement inferred from precise leveling data in eastern margin of tibetan plateau abstract we collect precise leveling data observed in the period of 1970 to 2012 around the eastern margin of the tibetan plateau and process the data to acquire present day crustal vertical velocity field vertical rates of 9 gps sites are employed as a priori constraints to define the reference frame the velocity field shows that most of the regions in the eastern margin of the tibetan plateau are undergoing uplift the gongga shan and west qinling are uplifting at maximum rates of 5 8 1 0 mm a and 6 0 1 3 mm a respectively a 2 d buried dislocation model is used to infer normal or reverse dip slip rates the result indicates that the reverse slip rate along the longmen shan fault is 4 2 0 5 mm a followed by the daliangshan and longriba faults with the rates of 3 7 0 5 mm a and 2 8 0 3 mm a respectively thezemuhe and northern section of the xiaojiang fault have the normal slip rates of 2 3 1 0 mm a and 2 9 0 4 mm a respectively combining vertical velocity field with gps derived horizontal velocity field we investigate the characteristics of crustal movement and dynamic mechanism the 3d velocity field indicates that the helan shan is uplifting and the yinchuan graben is subsiding the 3d crustal movement of the liupan shan region is segmented with the area in the vicinity of the northern liupan shan fault uplifting and the area in the vicinity of southern liupan shan fault subsiding respectively the subsidence of the central and southern sichuan yunnan terrain is caused by the near east west extension the budget of horizontal material influx suggests that movements of the upper and lower crust are rather different in most of the region excessive material influx into the lower crust upper mantle underneath most of the sub blocks seems required to maintain the uplift rates inferred from leveling providing evidence for the existence of lower crustal flow in this region

seismic evidence for the north china plate underthrusting beneath northeastern tibet and its implications for plateau growth abstract lithospheric deformation of the tibetan plateau is caused by subduction of the indian northward and asian southward plates the effects of this interaction on inner reaches of the asian continent between the tibetan plateau and the north china craton ncc for example remain uncertain due to poor geophysical data coverage in northeastern tibet ne tibet we provide here detailed knowledge of the lithospheric structure beneath ne tibet as determined from a dense broadband seismic profile traversing ne tibet to the westernmost ncc receiver function imaging reveals several significant features including a north dipping intracrustal converter nc moho offset overlap beneath major fault zones and a low velocity layer lvl in the middle lower crust the lithosphere asthenosphere boundary lab is clearly defined and appears as a south dipping interface that runs continuously from the alxa interior to the qilian orogen interpretation of these observations combined with other seismic evidence implies that the ncc lithospheric mantle has been persistently underthrust beneath the qilian orogen this process forms the thick skinned crustal accretionary wedges which develop above a middle lower intracrustal decollement our results provide further deep geophysical constraints on the cenozoic post collisional evolution of the convergent boundary between ne tibet and the ncc and help clarify the mechanism of plateau growth in this boundary area

some aspects of the permian triassic boundary ptb and of the possible causes for the biotic crisis around this boundary abstract the first appearance datum fad of hindeodus parvus is an excellent datum very close to the base of the otoceras woodwardi zone priority base of the triassic for the first time it allows an exact correlation of the ptb in all marine facies and faunal realms the following features of the extinction and recovery patterns near the ptb are most important for the search for causes of the ptb biotic crisis 1 most strongly affected were the siliceous plankton radiolarians and the warm water benthos and nekton 2 most of the cold water faunas were not significantly affected 3 the recovery of the warm water benthos and siliceous plankton occurred only after an unusually long time during the late olenekian and middle triassic 4 the productivity of the terrestrial plants dropped strongly and the recovery was mainly in the upper olenekian and in the middle triassic 5 several terrestrial extinction events occurred at different levels within the upper permian considerable before the marine ptb at or close to the fad of lystrosaurus no extinction event in the terrestrial faunas can be observed 6 terrestrial faunal elements that survived the dzhulfian dorashamian extinctions were able to survive some months of extreme climatic conditions by hibernation like life stages vertebrates or by dry and freezing resistant eggs conchostracans 7 about 50 of the genera that disappeared at the ptb re appeared in the olenekian middle triassic interval lazarus taxa or in this time interval genera appeared that had undoubtedly evolved from genera that had disappeared at the ptb and 8 the ptb is preceded by mass occurrences of marine and continental fungi and the fungal spike ends abruptly a little before the ptb a scenario for the ptb biotic crisis is elaborated that takes into consideration the real not interpolated diversity patterns of different marine and continental fossil groups the exact correlation of bioevents in different faunal realms and facies the strong biotic crisis in the tethyan warm water faunas in contrast to the much weaker biotic event in cold water faunas the severe dzhulfian dorashamian climate in many parts of the world caused by the continent ocean configuration and by siberian trap volcanism the cooling of the boreal area by the northward drift of pangaea that interrupted the exchange of warm water benthos between the tethys and western north america during the guadalupian the extinction event at the guadalupian lopingian boundary that restricted most of the affected warm water faunas to the tethys the importance of lower scythian anoxia that reached an unusually shallow level and above all the effects of the contemporaneous huge volcanic events about 250 m y ago on the siberian platform and in the eastern tethys that caused a 3 6 months lasting volcanic winter with strong cooling in low latitudes followed by a strong global warming

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

determination of oxygen isotope fractionation between water and phosphate from living lingulids potential application to palaeoenvironmental studies abstract lingulids are inarticulate brachiopods with phosphatic shells which live exclusively in marine waters their distribution is generally restricted to the continental shelf within the 40 belt from temperate to equatorial areas they show a range of morphological physiological and behavioral features that have remained remarkably constant since the cambrian the oxygen isotope fractionation between water and phosphate from living lingulids was determined as a tool to investigate the temperature and or salinity of past coastal seawater oxygen isotope measurements were performed according to the silver phosphate method on a collection of lingulids coming from well known and varied marine environments a global 18o variation of 3 5 was found for these lingulids which proves their good sensitivity to environmental factors namely the oxygen isotope composition and the temperature of seawater oceanographic data provided average temperature and salinity values in the living sites of the studied specimens least squares treatment of the data gave the following fractionation equation t c 112 2 15 3 4 20 0 71 18o po4 18o h2o which is similar to the equations determined by longinelli and nuti 1973a and kolodny et al 1983 for other phosphate bearing invertebrates and fishes all these results suggest that a unique equation describes the phosphate water fractionation of many marine organisms except for mammals

chronometry and speedometry of magmatic processes using chemical diffusion in olivine plagioclase and pyroxenes the magmatic processes that fuel volcanism crustal growth ore formation and discharge of volcanic gases and aerosols to the atmosphere occur across a range of timescales from millions of years to just a few seconds for example the production of new oceanic crust at mid ocean ridges is a near continuous process that can operate in any one ocean basin on timescales of more than 100 m y however the driving force for such processes is the spreading of the ocean plates that happens on a cm yr timescale at the other end of the spectrum explosive volcanic eruptions involve the ascent and fragmentation of magma at velocities of the order of 100 m s such that the journey from a magma chamber to an ash cloud may take place in a matter of minutes in this case the driving force is the rapid expansion of magmatic gas in response to changes in pressure at intermediate timescales magmatic processes may give rise to hydrothermal ore deposits on timescales of less than a million years for an individual deposit while growth of giant granite batholiths may require piecemeal assembly of magma batches on timescales of a few million years although each of these processes has a characteristic time averaged timescale on which it operates this is typically the end result of one or more natural processes that operate on much shorter timescales for example mid ocean ridges do not extrude magma continuously onto the ocean floor mineralising fluids do not discharge continuously through the shallow crust and granitic magmas do not dribble continuously into evolving batholithic chambers in some cases it is the long term timescales that are important for example the spreading rate of ocean basins in others it is the short term timescales that are important for example the episodic growth of lava domes at active volcanoes although

crystal surface integrity and diffusion measurements on earth and planetary materials abstract characterization of diffusion behavior in minerals is key to providing quantitative constraints on the ages and thermal histories of earth and planetary materials laboratory experiments are a vital source of the needed diffusion measurements but these can pose challenges because the length scales of diffusion achievable in a laboratory time are commonly less than 1 m an effective strategy for dealing with this challenge is to conduct experiments involving inward diffusion of the element of interest from a surface source followed by quantification of the resulting diffusive uptake profile using a high resolution depth profiling technique such as rutherford backscattering spectroscopy rbs nuclear reaction analysis nra or ion microprobe sims the value of data from such experiments is crucially dependent on the assumption that diffusion in the near surface of the sample is representative of diffusion in the bulk material historical arguments suggest that the very process of preparing a polished surface for diffusion studies introduces defects in the form of dislocations and cracks in the outermost micrometer of the sample that make this region fundamentally different from the bulk crystal in terms of its diffusion properties extensive indirect evidence suggests that in fact the near surface region of carefully prepared samples is no different from the bulk crystal in terms of its diffusion properties a direct confirmation of this conclusion is nevertheless clearly important here we use transmission electron microscopy to confirm that the near surface regions of olivine quartz and feldspar crystals prepared using careful polishing protocols contain no features that could plausibly affect diffusion this finding does not preclude damage to the mineral structure from other techniques used in diffusion studies e g ion implantation but even in this case the role of possible structural damage can be objectively assessed and controlled while all evidence points to the reliability of diffusivities obtained from in diffusion experiments we do not recommend experiments of this type using a powder source as a means of obtaining diffusant solubility or partitioning information for the mineral of interest

trace element diffusion and incorporation in quartz during heating experiments heating of quartz crystals in order to study melt and high temperature fluid inclusions is a common practice to constrain major physical and chemical parameters of magmatic and hydrothermal processes diffusion and modification of trace element content in quartz and its hosted melt inclusions have been investigated through step heating experiments of both matrix free quartz crystals and quartz crystals associated with sulfides and other minerals using a linkam ts1500 stage magmatic and hydrothermal quartz were successively analyzed after each heating step for cu al and ti using electron probe micro analyzer after the last heating step quartz crystals and their hosted melt inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry and compared to unheated samples heated samples reveal modification of cu li na and b contents in quartz and modification of cu li ag and k concentrations in melt inclusions our results show that different mechanisms of cu li and na incorporation occur in magmatic and hydrothermal quartz heated magmatic quartz records only small up to a few ppm enrichment in cu and na mostly substituting for li by contrast heated hydrothermal quartz shows enrichment up to several hundreds of ppm in cu li and na which substitute for originally present h this study reveals that the composition of both quartz and its hosted melt inclusions may be significantly modified upon heating experiments leading to erroneous quantification of elemental concentrations in addition each quartz crystal also becomes significantly enriched in cu in the sub surface layer during heating we propose that sub surface cu enrichment is a direct indication of cu diffusion in quartz externally sourced from both the surrounding sulfides as well as the copper pins belonging to the heating device our study shows that the chemical compositions of both heated quartz and its hosted inclusions must be interpreted with great caution to avoid misleading geological interpretations

the permian triassic boundary in western slovenia idrijca valley section magnetostratigraphy stable isotopes and elemental variations stable isotope analyses of carbonate 13ccarb and total organic carbon toc 13corg together with geochemical analyses of 54 major minor and trace elements and magnetic susceptibility measurements were carried out on whole rock samples of the undisturbed permian triassic p tr limestone boundary sequence in the idrijca valley w slovenia at the p tr boundary there is a 0 8 cm thick clayey marl layer ptb showing a characteristic magnetic susceptibility pulse and considerable enrichment in most major minor and trace elements the p tr transition is characterized by 1 an abrupt decrease in sedimentation rate from 32 to 5 cm 100 ka 2 a well known prominent negative excursion of 13ccarb and 13corg reflecting global perturbations in the carbon cycle and 3 the drastic disappearance of typically upper permian marine fauna although the shape of the 13ccarb curve indicates gradual long term change across the p tr boundary the sharp negative 13corg anomaly within an interval from 30 cm below to 6 cm above the boundary suggests an interruption of those gradual processes our observations for selected redox sensitive elements mo u v and zn abundances for organic carbon and sulphur and the rare earth elements ree distribution in the boundary sequence as well as the shape of the ce ce curve suggest that oceanic anoxia was typical of the upper permian and that the transition to oxygenated conditions occurred at the p tr boundary oxygenation at the p tr transition is coincidental with the terminal phase of the upper permian marine regression the shape of the ce ce curve indicates that the redox environmental conditions changed again in the earliest triassic resulting once more in oxygen deficient conditions

lithospheric velocity structure of the northeast margin of the tibetan plateau relevance to continental geodynamics and seismicity abstract we provide teleseismic constraints on the continental collision zone along the sw ne profile from the tibetan plateau to the alxa block traversing lenglong ling a topographic boundary of the northeastern tibetan plateau our seismic profile crosses the qilian shan thrust belt a zone of intense earthquake activity that includes a pair of mw 5 9 earthquakes in 1986 and 2016 with a 30 year time interval occurring at the city of menyuan near lenglong ling a high degree of similarity between the two waveforms and their similar hypocenters indicate that the two events are repeating earthquakes both p and s wave receiver functions show contrasting lithospheric structure and crustal seismic properties across the repeating earthquake region suggesting that lenglong ling can be the crustal boundary between the tibetan plateau and the alxa block high frequency p receiver functions clearly show a sw dipping underthrusted upper crust beneath the foreland of the qilian shan thrust belt a strong low velocity feature above the intracrustal underthrust beneath southwest lenglong ling indicates a mechanically weak zone developed coeval with the main compressional deformation during the last major tectonic event our observed localized upper crustal deformation beneath lenglong ling can be direct evidence of the lateral growth of the northeastern tibetan plateau and can control the seismicity of the qilian shan thrust belt including the menyuan repeating earthquakes

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere

cenozoic tectonic evolution of qaidam basin and its surrounding regions part 1 the southern qilian shan nan shan thrust belt and northern qaidam basin cenozoic qaidam basin the largest active intermountain basin inside tibet figures importantly in the debates on the history and mechanism of tibetan plateau formation during the cenozoic indo asian collision to determine when and how the basin was developed we conducted detailed geologic mapping and analyses of a dense network of seismic reflection profiles from the southern qilian shan nan shan thrust belt and northern qaidam basin our geologic observations provide new constraints on the timing and magnitude of cenozoic crustal thickening in northern tibet specifically our work shows that the southernmost part of the qilian shan nan shan thrust belt and contractional structures along the northern margin of qaidam basin were initiated in the paleocene early eocene 65 50 ma during or immediately after the onset of the indo asian collision this finding implies that stress was transferred rapidly through tibetan lithosphere to northern tibet from the indo asian convergent front located 1000 km to the south the development of the thrust system in northern qaidam basin was driven by motion on the altyn tagh fault as indicated by its eastward propagation away from the altyn tagh fault the eastward lengthening of the thrust system was spatially and temporally associated with eastward expansion of qaidam basin suggesting thrust loading was the main control on the basin formation and evolution the dominant structure in northern qaidam basin is a southwest tapering triangle zone which started to develop since the paleocene and early eocene 65 50 ma and was associated with deposition of an overlying southwest thickening growth strata sequence recognition of the triangle zone and its longevity in northern qaidam basin explains a long puzzling observation that cenozoic depocenters have been located consistently along the central axis of the basin this basin configuration is opposite to the prediction of classic foreland basin models that require the thickest part of foreland sediments deposited along basin edges against basin bounding thrusts restoration of balanced cross sections across the southern qilian shan nan shan thrust belt and northern qaidam basin suggests that cenozoic shortening strain is highly inhomogeneous varying from 20 to 60 both vertically in a single section and from section to section across the thrust belt the spatially variable strain helps explain the conflicting paleomagnetic results indicating different amounts of cenozoic rotations in different parts of qaidam basin the observed crustal shortening strain also implies that no lower crustal injection or thermal events in the mantle are needed to explain the current elevation 3000 3500 m and crustal thickness 45 50 km of northern qaidam basin and the southern qilian shan nan shan thrust belt instead thrusting involving continental crystalline basement has been the main mechanism of plateau construction across northern qaidam basin and the southern qilian shan nan shan region

crustal structure of the middle segment of the qilian fold belt and the coupling mechanism of its associated basin and range system abstract we present an analysis of the p wave seismic velocity structure of the qilian fold belt based on a 750 km long seismic wide angle reflection refraction profile the results show that the internal portion of the alxa block has a crustal thickness of approximately 45 48 km with an average velocity of 6 19 km s although the alxa crust is thick it is lateral homogeneous and relatively stable the hexi corridor which is located on the southern margin of the alxa block has been affected by the collision and extrusion of the northern margin of the tibetan plateau the hexi corridor has a crustal thickness of 48 59 km with substantial thickening southward and an average seismic velocity of 6 10 6 13 km s indicating strong crustal deformation located on the northeastern margin of the tibetan plateau the qinling fold belt qfb gonghe basin and elashan mountains all have a crustal thickness is 51 56 km with a low average seismic velocity of 5 86 6 10 km s indicating significant reconstruction via shortening that has resulted in thickening of the northeastern tibetan plateau crust the tectonic coupling between the qilian fold belt and the neighboring blocks in the south and north form a crustal scale depression combining the regional geology gravity and gps measurements and strong earthquake focal mechanism solutions we constrain the crustal deformation processes of the northeastern of tibet plateau

along strike topographic variation of qinghai nanshan and its significance for landscape evolution in the northeastern tibetan plateau abstract cenozoic basins and ranges constitute the high topography of the northeastern tibetan plateau which is derived from the indo asian collision the geomorphological characteristics of the ranges provide direct insight into the uplift processes which are responsible for the patterns of the ranges and the growth of the northeastern tibetan plateau this study analyzed the geomorphological features of qinghai nanshan one of the youngest ranges within the northeastern tibetan plateau including elevation slope distribution and the channel steepness index topographic analysis revealed that elevations and slopes in western and central portions of qinghai nanshan were higher than those in the eastern portion whereas the channel steepness index revealed a step growth mode from west to east considering the topographic features the lateral gradient of precipitation increasing from west to east and the lithology distribution it is concluded that the geomorphological features of qinghai nanshan are influenced mainly by tectonic activities and reflect the growth pattern and or the tectonic setting of the range comparing with previous studies it is shown that the formation mechanism of qinghai nanshan follows a middle to sides growth pattern furthermore the degree of inclination of the erosion surface distributed on the northern flank of the range suggests that qinghai nanshan is controlled jointly by the listric qinghai nanshan thrust fault and the influences from the elashan and riyueshan dextral strike slip faults in addition the northeastern tibetan plateau exhibits an outside in growth process which might reflect the northeastward growth of the entire northeastern tibetan plateau