cretaceous tertiary shortening basin development and volcanism in central tibet the geologic map pattern of the qiangtang terrane in central tibet defines a 600 km long and up to 270 km wide east plunging structural culmination it is characterized by early mesozoic blueschist bearing melange and upper paleozoic strata in the core and mainly triassic jurassic strata along the limbs in the western qiangtang terrane 84 e the culmination is unconformably overlain by weakly deformed mid cretaceous volcanic flows and tuffs along the bangong suture to the south 32 n 84 e mid cretaceous nonmarine red beds and volcanic rocks lie unconformably on jurassic suture zone rocks these relationships demonstrate that west central tibet was above sea level during the mid cretaceous and experienced significant denudation prior to mid cretaceous time growth of the qiangtang culmination is inferred to have initiated during southward emplacement of a thrust sheet of early mesozoic melange and upper paleozoic strata during the early cretaceous lhasa qiangtang collision the north south width of the inferred thrust sheet provides a minimum slip estimate of 150 km at 84 e decreasing eastward to 70 km at 87 e paleogene deformation in the qiangtang terrane is characterized by widely distributed mainly north dipping thrust faults that cut eocene oligocene red beds and volcanic rocks in their footwall along the bangong suture the north dipping shiquanhe gaize amdo thrust system cuts 64 and 43 m y old volcanic tuffs in its footwall and accommodated 40 km of post mid cretaceous shortening the tertiary south dipping gaize siling co backthrust bounds the southern margin of the bangong suture and marks the northernmost limit of mid cretaceous marine strata in central tibet cretaceous deformation and denudation in central tibet is attributed to northward underthrusting of the lhasa terrane beneath the qiangtang terrane along the bangong suture this model implies that 1 cretaceous strata along the bangong suture and in the northern lhasa terrane were deposited in a flexural foreland basin system and derived at least in part from the qiangtang terrane and 2 the central tibetan crust was thickened substantially prior to the indo asian collision although its magnitude is poorly known tertiary shortening in the qiangtang terrane is more prevalent than in the lhasa terrane this difference may be attributed to the presence of underthrust melange in the deeper central tibetan crust which would have made it weaker than the lhasa terrane during the indo asian collision

present day deformation of the qaidam basin with implications for intra continental tectonics abstract the qaidam basin is a plateau of low relief about 3 km in elevation and covering a large area of 1 2 105 km2 physiographically the basin marks a transitional region between the northeastern tibetan plateau 5 0 5 km in elevation and the surrounding low lying areas the northeastern and southwestern edges of the basin are bounded by the qilian shan nan shan and qimantag eastern kunlun shan mountain belts respectively at present the entire region is under northeast southwest compression based on a synthesis of recent geological and geophysical results we propose that each flanking mountain belt consists of a sequence of crustal nappes originating from ramp thrusts at mid crustal levels 15 km deep over a distance range of 700 km these two broad fold and thrust belts operating in tandem and with some uniform shortening in the intervening qaidam basin successively raised the surface elevation from below 2 km to 5 km at depth the crust is correspondingly thickened from 40 km beneath the foreland of the qilian shan to approximately 55 km under the interior of the qaidam basin and then to nearly 70 km beneath tibet in contrast to the himalayan front where earthquake faulting occurs down to a depth of 50 km in the foreland but the zone of active thrust faulting is less than 200 km in width plateau building in the qaidam region illustrates how a wide orogen is developing along northeastern tibet in the interior of eurasia

late cretaceous to middle tertiary basin evolution in the central tibetan plateau changing environments in response to tectonic partitioning aridification and regional elevation gain located in the bangong suture zone between the lhasa and qiangtang terranes of central tibet the nima basin records cretaceous late miocene sediment accumulation during a period of drastically changing paleogeography and paleoelevation the bangong suture zone originally formed during late jurassic early cretaceous time as the lhasa terrane collided with the qiang tang terrane during early to middle cretaceous time the region lay at northern near equatorial paleolatitudes near sea level by aptian time the nima basin was above sea level and was strongly influenced by nearby volcanic activity and crustal shortening in the reactivated bangong suture zone in the southern nima basin an 50 m y late cretaceous eocene depositional hiatus correlates with major crustal shortening and ensuing voluminous ignimbrite eruptions in the lhasa terrane in the northern nima basin deposition continued during latest cretaceous time recording arid paleoclimate in evaporitic lacustrine and eolian dunefield deposits by oligocene time the nima basin comprised two independent depocenters that accumulated coarse grained alluvial fluvial lacustrine evaporitic and fan delta deposits in close association with reactivated thrusts in the bangong suture zone carbon and oxygen isotope data from oligocene paleosol carbonate reported elsewhere indicate that regional paleoelevation during the late oligocene was 4 6 km as it is today overall the depositional record of the nima basin combined with ongoing structural and geochronologic studies demonstrates that the bangong suture zone was reactivated during middle cretaceous and middle tertiary time that the intervening 50 m y interval was a time of regional upper crustal shortening in the lhasa terrane followed by regional ignimbrite eruptions and that arid paleoclimate and high paleoelevation were established by the late cretaceous and late oligocene respectively within the context of other data sets from the lhasa terrane the record of deposition in the nima basin is consistent with low angle subduction of neotethyan oceanic lithosphere and reactivation of the bangong suture zone during the early cretaceous followed by shortening within the gangdese retroarc and northern lhasa terrane thrust belts during the late cretaceous lithospheric delamination dripping and regional magmatic flare up during latest cretaceous through early tertiary time and underthrusting of indian lower crust and lithosphere as far north as the bangong suture zone during late oligocene time

4 d evolution of se asia s mantle from geological reconstructions and seismic tomography abstract how the collision between india and asia is related to processes deeper in the mantle is unclear here we compare geological reconstructions of block motions within asia since 50 ma with the tomographically imaged three dimensional 3 d morphology of subducted lithosphere to obtain insight into the spatiotemporal evolution of mantle structure past positions of the convergent margin show remarkable similarities with slab geometry at specific depths the striking change in slab geometry from a linear structure beneath 1100 km to an increasingly distorted shape at depths of less than 700 km results from collision the slab contours match the progressive deformation of asia s margin including india s indentation and sundaland s extrusion ever since the onset of collision the indian plate appears to have overridden its own sinking mantle and it does not seem at present to underthrust tibet significantly north of the zangbo suture if correct this observation would provide further evidence against models of plateau build up involving indian lithosphere the tomographic images beneath india confirm that asian deformation has absorbed at least 1500 km of convergence since collision began from the match between the southeastward motion of sundaland between 40 and 20 ma and the principal change in slab structure between 700 and 1100 km depths we infer that lateral advection in the mantle is small and that the sinking rate beneath sunda was 2 cm yr in the lower mantle and 5 cm yr above the transition zone

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

crustal rheology of the himalaya and southern tibet inferred from magnetotelluric data the collision between the indian and asian continents which began about 70 million years ago involved a convergence of at least 1 400 km and raised the tibetan plateau since crustal material is too buoyant to be transported downwards into the earth s interior the mechanisms at work in plateau formation are important in understanding the evolution of the continents yet still a matter of debate geophysical observations in the himalaya and tibet using ultra low frequency radio waves now reveal that a partially molten layer is present along the entire length of the himalaya this weak layer implies that widespread crustal flow is occurring and explains many features of plateau evolution the cenozoic collision between the indian and asian continents formed the tibetan plateau beginning about 70 million years ago since this time at least 1 400 km of convergence has been accommodated1 by a combination of underthrusting of indian2 and asian lithosphere crustal shortening3 horizontal extrusion4 and lithospheric delamination5 rocks exposed in the himalaya show evidence of crustal melting1 6 and are thought to have been exhumed by rapid erosion and climatically forced crustal flow7 8 magnetotelluric data can be used to image subsurface electrical resistivity a parameter sensitive to the presence of interconnected fluids in the host rock matrix even at low volume fractions here we present magnetotelluric data from the tibetan himalayan orogen from 77 e to 92 e which show that low resistivity interpreted as a partially molten layer is present along at least 1 000 km of the southern margin of the tibetan plateau the inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in southern tibet

stability in the south pacific surface marine 14c reservoir over the last 750 years evidence from american samoa the southern cook islands and the marquesas abstract although minor climatic and sea level changes have been documented for the south pacific during the late holocene our understanding of the consequent impact of these changes on the marine 14 c reservoir and therefore the 14 c content of shellfish is limited ultimately this has implications for documenting the chronology of human movement and adaptation in this region in this paper we compare marine reservoir r data obtained from tightly controlled archaeological proveniences with known age pre ad 1950 shells from the southern cook islands american samoa and marquesas islands results indicate that there has been no significant change in the near shore marine reservoir in these three locations over the last ca 750 years furthermore known age pre ad 1950 shell samples provide more precise r values for use in sample calibration than archaeological paired shell charcoal samples this is attributed in part to the limitations of assigning provenance and age to material from archaeological sites on the basis of these results we conclude that the known age pre ad 1950 shell derived r values can be used to calibrate shell 14 c results from deposits of late holocene age

active deformation of asia from kinematics to dynamics using estimated strain rates across the actively deforming region of asia to infer variations in viscous stress it is shown that gradients of stress point uphill toward the center of tibet where gravitational potential energy per unit surface area reaches a maximum thus the dynamics of the deformation seem to obey the equation of creeping flow which expresses a balance between gradients in stress and the gravitational body force this balance in the region of the tibetan plateau yields an estimate of 10 22 pascal second for the average viscosity of the tibetan lithosphere which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle

modelling site formation dynamics geoarchaeological chronometric and statistical approaches to a stratified rockshelter sequence polynesia formation processes and chronology are central to many archaeological endeavours and accuracy in the latter is dependent on control of the former here we consider how to integrate geoarchaeological and chronometric evidence to better understand the formational history along with the timing and duration of cultural activities at a regionally significant site in the southern cook islands polynesia which dates from 12th century ad initially we model natural and cultural processes of deposition using geoarchaeological evidence the results are integrated with 21 radiocarbon dates including nine new ams results on identified medium and short lived materials sample outliers are identified manually and statistically and a bayesian analysis helps to refine age estimates for the site s 12 stratigraphic zones the timing and rate of sediment accumulation is further considered through an age depth model finally the chronology developed from these combined approaches is used to address three key processes 1 initial site use potentially relevant to human colonisation of this polynesian island and archipelago 2 on site activities and patterns of resource use and 3 major marine deposition events which disrupted cultural activities and may have palaeoclimatological significance the approach developed here potentially has utility elsewhere particularly where human activities are recurrent and of limited duration

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

tomographic evidence for localized lithospheric shear along the altyn tagh fault seismic tomography across the altyn tagh fault at the north edge of the tibetan plateau reveals a low p wave velocity anomaly below the fault down to 140 kilometers this anomaly probably reflects strike slip shear in the lithosphere slip partitioning may also induce a wedge of crust from the tarim basin to plunge into the mantle

injection of indian crust into tibetan lower crust a two dimensional finite element model study we propose a model in which the stronger indian crust injects into the weaker lower crust of tibet if the viscosity of the tibetan lower crust is below a critical value the continuous advancing of the indian crust beneath tibet would produce negligible variation in stresses on the bottom of the stronger brittle tibetan upper crust and would result in a spatially uniform uplift and a virtually undisturbed tibetan plateau surface this process is analogous to that of a piston rising in a hydraulic jack as additional fluid is forced into the chamber we find that if the viscosity of the tibetan lower crust is assumed to be constant throughout the computed critical viscosity is 6 1018 pa s for the present day lower crustal thickness of 58 km in addition to uniform viscosity two hypothetical depth dependent viscosities are also tested which give rise to essentially the same distribution of stress along the bottom of brittle upper crust our model also interprets the 4 km elevation contrast between the tibetan plateau and the tarim block a 1 160 viscosity contrast between the tibetan and tarim lower crust is required in order to maintain the current thickening rate of the tibetan crust 1 2 mm yr while keeping the thickness of the tarim crust unchanged

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

230th dating of coral abraders from stratified deposits at tangatatau rockshelter mangaia cook islands implications for building precise chronologies in polynesia abstract polynesian archaeology has relied primarily on 14c dating to establish the timing and tempo of human colonization of the eastern pacific ensuing cultural development and human environmental interactions despite advancements in 14c dating including accelerator mass spectrometry selection of short lived plant remains to avoid in built age and the use of bayesian models to refine 14c based chronologies large uncertainties introduced during calibration to calendar ages can severely limit the resolution of 14c dates in this context 230th dating of coral abraders a common artifact in many polynesian archaeological sequences can potentially provide much more precise dates we report 25 230th dates for acropora and porites coral abraders from a well studied stratified archaeological sequence at tangatatau rockshelter mangaia site man 44 cook islands develop screening criteria to identify reliable 230th dates from buried contexts and compare the results with a recent bayesian 14c chronology for the site visual characteristics gray color microcrystalline sugary texture can aid identifying altered corals before analysis but are non diagnostic of the suitability of samples for dating some corals that were fully remineralized to calcite preserved suitable u and th isotopic compositions and produced ages in agreement with 14c and pristine aragonitic coral 230th dates suggesting that unlike subaerially exposed corals buried corals may be susceptible to mineral alteration without perturbing the u series isotopic systematics possibly due to burial under reducing conditions in general corals with reliable 230th dates preserve initial 234u 238u ratios in equilibrium with seawater and have 230th 232th ratios 10 reliable dates at man 44 cluster within layers preserve stratigraphic order and agree with the previous 14c chronology precise 230th dates median 7 4 yr all errors 2 from coral abraders support early polynesian arrival on mangaia by 1011 6 5 8 ce and the arrival of the sweet potato ipomoea batatas no later than 1361 1466 ce indicating that trans pacific voyaging had introduced this south american native plant to the cook islands by the mid 15th century with suitable samples 230th dating of corals from stratified sequences has great potential for developing refined chronologies for polynesian and other pacific archaeological sites

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

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

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

indepth wide angle reflection observation of p wave to s wave conversion from crustal bright spots in tibet three component wide angle seismic data acquired in southern tibet during project indepth show strong p to s converted reflections from reflectors that are aligned at a depth of 15 kilometers beneath the northern yadong gulu rift these converted reflections are locally higher in amplitude than the corresponding p wave reflections modeling of reflection mode conversion as a function of incidence angle indicates that this condition obtains for a reflector that is a solid over fluid interface it is not typical of a solid solid interface the likely candidates for a fluid trapped within the crystalline crust of southern tibet are granitic magma and water brine

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

measuring stone artefact transport the experimental demonstration and pilot application of a new method to a prehistoric adze workshop southern cook islands this paper presents a new method based on the calculation of a cortex ratio capable of contributing towards measures of stone artefact transport in polynesia a set of ratios can be calculated by comparing the observed amount of cortical surface area and volume in an assemblage with what is expected should all the products of reduction remain because raw material shape and size is controlled for using geometric equations an estimate for the number of preforms produced from an assemblage also is possible the method is experimentally demonstrated and applied to an archaeological early stage adze manufacturing assemblage from moturakau rockshelter aitutaki island in the southern cook islands application of the method in combination with geochemical and chronological analyses shows that the number of preforms produced and transported as well as the frequency of their transport changed over time but the geographic scale of distribution remained the same essentially local to aitutaki

microplate model for the present day deformation of tibet 1 site velocities from 349 global positioning system gps stations are used to construct an 11 element quasi rigid block model of the tibetan plateau and its surroundings rigid rotations of five major blocks are well determined and average translation velocities of six smaller blocks can be constrained where data are well distributed the velocity field can be explained well by rigid block motion and fault slip across block boundaries residual misfits average 1 6 mm yr compared to typical one standard deviation velocity uncertainties of 1 3 mm yr any residual internal straining of the blocks is small and heterogeneous however residual substructure might well represent currently unresolved motions of smaller blocks although any smaller blocks must move at nearly the same rate as the larger blocks within which they lie undetected relative motions between them could be significant particularly where there are gaps in gps coverage predicted relative motions between major blocks agree with the observed sense of slip and along strike partitioning of motion across major faults however predicted slip rates across tibet s major strike slip faults are low only 5 12 mm yr a factor of 2 3 smaller than most rates estimated from fault offset features dated by radiometric methods as 2000 to 100 000 year old previous work has suggested that both gps data and low fault slip rates are incompatible with rigid block motions of tibet the results reported here overcome these objections

cenozoic depositional sequences in the piedmont of the west kunlun and their paleogeographic and tectonic implications abstract the west kunlun forms the northwestern margin of the qinghai tibet plateau well developed cenozoic depositional sequences in the piedmont along the margins of the tarim basin record changes in sedimentary environment and the uplift of the west kunlun during the cenozoic during latest cretaceous to oligocene deposition in the west kunlun occurred in a marine environment the tarim bay during the paleogene gypsum beds bivalve shell limestones and variegated clastics were deposited rapid sedimentation during the late miocene resulted in the deposition of molasse sediments 2000 3000 m thick indicating a relatively high depositional rate the upper miocene sequences show a coarsening up tendency indicating a rapid and accelerated uplift of the west kunlun from late miocene to early pleistocene times molasse deposition was interrupted in the early pleistocene by a tectonic pulse which resulted in tilting of the molasse and underlying sediments at high angle towards the tarim basin undeformed middle to late pleistocene coarse fluvial and pluvial deposits overlie the steeply dipping molasse and older rocks unconformably and represent the resumption of rapid deposition a continual high rate of uplift during the holocene is presumed on the basis of an incised drainage system that flows from west kunlun into the tarim basin and cuts middle to late pleistocene gravels and older sediments to a depth from 50 m to more than 100 m although climatic changes may also have played a part

gis based evaluation of water quality index of groundwater resources around tuticorin coastal city south india groundwater is a vital source of water for industrial domestic and agricultural activities in tuticorin city due to lack of surface water resources groundwater quality and its suitability for drinking usage were evaluated a total of 72 groundwater samples were collected from open wells and boreholes during pre and post monsoon period samples were analyzed for physico chemical properties major cation and major anions in the laboratory using the standard methods given by the american public health association the geographic information system based spatial distribution map of different major elements has been prepared using arcgis 9 2 these maps are classified as desirable maximum permissible and the values that exceed maximum permissible limit are termed as not permissible prescribed by the who 2004 from the piper plot which gives the cation chemistry the concentration of the alkalies na and k exceeds the alkaline earths ca2 and mg2 and those of strong acids exceeds weak acids in the case of anions during the two periods strong acid shows dominance over weak acid and hco3 and cl have influences almost equal to na which indicate the saltwater intrusion into the freshwater aquifer of the study area a canadian council of ministers for the environment water quality index ccme wqi map was also generated with the gis technique to better understand the water portability over space the categories of water quality evaluated by ccme wqi values of major part of the study area fall under fair category during prm and good category during the pom period the ccme wqi is a very useful and an efficient tool to summarize and to report on the monitoring data to the decision makers in order to understand the status of the groundwater quality finally the study concludes that the groundwater quality is impaired by man made activities and proper management plan is necessary to protect valuable groundwater resources in tuticorin city

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

modelling the palimpsest an exploratory agent based model of surface archaeological deposit formation in a fluvial arid australian landscape archaeologists make inferences about past human behaviour based on patterned material residues in various depositional contexts including existing landsurfaces these deposits are generated by processes that may obscure patterns at some observational scales while highlighting others and interpretive differences can arise from a lack of explicit models of deposit formation here an exploratory agent based model based on the concept of the palimpsest is used to examine the effects of episodic sediment transport on the visibility and preservation of surface archaeological deposits in a fluvial context outcomes from the model indicate that the compound influences of preservation and visibility are capable of transforming a static radiocarbon record into one of increasing intensity towards the present while simultaneously displaying periodic chronological gaps features that have been used in our australian study area to argue for demographic change driven by social or environmental factors to differentiate between interpretations expectations derived from the model are assessed against a second proxy from the same study area optically stimulated luminescence dates from hearth stones in surface contexts results indicate that patterns in the chronometric proxies from the study area are more consistent with episodic geomorphic change than explanations invoking changes in the local organization of human activity

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting

constraining the extent of crust mantle coupling in central asia using gps geologic and shear wave splitting data abstract we have obtained constraints on mechanical crust mantle coupling for tibet and yunnan indo china by comparing the observed surface deformation field inferred from gps and quaternary fault slip rate data with the mantle deformation field inferred from several sks shear wave splitting data sets we first determined whether the anisotropy is dominantly asthenospheric or lithospheric by testing simple models of both types against the observed values of the fast polarization direction which is assumed to be parallel to the horizontal projection of the direction of maximum shear for asthenospheric flow we solved for a best fitting uniform sub asthenospheric velocity model for eurasia the fit however was not satisfactory rms misfit 20 solving for separate uniform flow fields in each region improves the fit 15 for tibet 11 for yunnan although the resulting flow fields are inconsistent with several geophysical and geological constraints and thus considered unlikely we then considered lithospheric models for tibet vertically coherent deformation i e maximum shear direction from surface deformation is parallel to yields an improved match 11 for left lateral shear both the goodness of fit and the dominance of left lateral surface faulting in tibet argue for a lithospheric source of anisotropy the misfit for yunnan is large for either right 53 or left lateral 49 shear which argues for complete crust mantle decoupling in yunnan we show that the fast polarization directions throughout both the tibet and yunnan region can be fit by a single lithospheric dynamic model in which there is strong coupling between crust and mantle beneath tibet but a complete decoupling between crust and mantle beneath yunnan crust this dynamic model predicts left lateral maximum shear directions within the mantle that align with fast polarization directions in both regions 9 these maximum shear directions within the mantle align with the left lateral maximum shear directions in the crustal deformation field in tibet but are not in yunnan our results have the following implications first the coherence between crust and mantle deformation in tibet implies strong crust mantle mechanical coupling since this is the only way that crustal buoyancy forces required to account for the surface deformation field can be transmitted into the mantle this behavior is consistent with a uniform strength lithosphere or strong crust but not with a substantially weaker crust for example it is inconsistent with the popular jelly sandwich rheology and thus precludes behavior such as large scale lower crustal flow in tibet the crust mantle coherence is also incompatible with mantle delamination second crust mantle decoupling within the yunnan lithosphere argues that mantle deformation there is controlled only by boundary conditions crustal buoyancy forces are not transmitted into the mantle beneath yunnan moreover the dynamic model for the mantle shows that the yunnan crust is moving south with respect to the mantle at rates as high as 30 mm yr third there is a fundamental rheological lithospheric transition between tibet and yunnan that may provide a key to understanding this significant orogen