a study of a self generated stratospheric sudden warming and its mesospheric lower thermospheric impacts using the coupled time gcm ccm3 1 a stratospheric sudden warming episode was self consistently generated in the coupled national center for atmospheric research thermosphere ionosphere mesosphere and electrodynamics general circulation model climate community model version 3 time gcm ccm3 taking advantage of the unique vertical range of the coupled model ground to 500 km we were able to study the coupling of the lower and upper atmosphere in this warming episode planetary wave 1 is the dominant wave component in this warming event analysis of the wave phase structure and the wave amplitude indicates that the wave may experience resonant amplification prior to the peak warming the mean wind in the high latitude winter stratopause and mesosphere decelerates and reverses to westward due to planetary wave forcing and forms a critical layer near the zero wind lines the wind deceleration and reversal also change the filtering of gravity waves by allowing more eastward gravity waves to propagate into the mesosphere and lower thermosphere mlt which causes eastward forcing and reverses the westward jet in the mlt this also changes the meridional circulation in the upper mesosphere from poleward downward to equatorward upward causing a depletion of the peak atomic oxygen layer at 97 km and significant reduction of green line airglow emission at high latitudes and midlatitudes planetary waves forced in situ by filtered gravity waves in the mlt grow in the warming episode their growth and interaction with tides create diurnal and semidiurnal variabilities in the zonal mean zonal wind

crustal structure and earthquake focal depths beneath northeastern india and southern tibet summary we use broad band teleseismic data recorded at eight sites along a north south profile from karimganj 24 84 n 92 34 e south of the eastern shillong plateau to bomdilla 27 27 n 92 41 e in the eastern lesser himalaya to determine the seismic characteristics of the crust in northeastern india we also analyse data from the chinese digital seismic network station at lhasa and indepthii stations located on the southern tibetan plateau north of our profile to extend the seismic images of the crust further northwards although the northeastern indian stations and the tibetan stations do not lie along a linear profile across the himalaya the wellrecognized uniformity of the himalaya along strike make this comparison of the two profiles meaningful receiver functions calculated from these data show that the crust is thinnest 35 38 km beneath the shillong plateau receiver functions at cherrapunji on the southern edge of the shillong plateau have a strong azimuthal dependence those from northern backazimuth events show that the moho beneath the southernmost shillong plateau is at a depth of 38 km while receiver functions from southern backazimuth events indicate that the moho beneath the northernmost bengal basin is at a depth of 44 km receiver functions from sites on the brahmaputra valley demonstrate that the moho is deeper by 5 7 km than below the shillong plateau a result which agrees with the hypothesis that the shillong plateau is supported by shearing stress on two steep faults that cut through the crust further north of the eastern himalayan foredeep the moho dips gently northwards reaching a depth of 48 km beneath bomdilla in the lesser himalaya and 88 km below lhasa in tibet using the crustal velocity models obtained from receiver function inversions we redetermined focal depths of wellrecorded earthquakes across this part of the indo tibetan collision zone and find all of these to occur within the crust hence we find no evidence for bimodal depth distribution of earthquakes beneath this region of northeastern india

linking a prolonged neo tethyan magmatic arc in south asia zircon u pb and hf isotopic constraints from the lohit batholith ne india the neo tethyan subduction that operated before the india asia collision resulted in an andean type convergent margin in south asia and was associated with extensive arc magmatism that formed the transhimalayan batholiths magmatism in the gangdese batholith the largest batholith exposed in the lhasa terrane of southern tibet is considered to have lasted from the early jurassic to eocene however eastward correlation of the gangdese batholith is uncertain because it is truncated by the eastern himalayan syntaxis here we report new data from the lohit batholith ne india including i zircon u pb ages of five granitoids from ca 148 to 96 ma and ii zircon hf isotopes of these rocks that yield high and positive ehf t values we argue that the lohit batholith is the eastward extension of the gangdese batholith and can be correlated southward to the wuntho popa arc in west burma thus linking a prolonged neo tethyan magmatic arc system from southern tibet to southeast asia

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

global ionospheric and thermospheric response to the 5 april 2010 geomagnetic storm an integrated data model investigation we present a case study of the 5 april 2010 geomagnetic storm using observations and numerical simulations the event was driven by a fast moving coronal mass ejection and despite being a moderate storm with a minimum dst near 50 nt the event exhibited elevated thermospheric density and surges of traveling atmospheric disturbances tads more typically seen during major storms the thermosphere ionosphere mesosphere electrodynamics general circulation model timegcm was used to assess how these features were generated and developed during the storm the model simulations gave rise to tads that were highly nonuniform with strong latitude and longitude local time dependence the tad phase speeds ranged from 640 m s to 780 m s at 400 km and were 5 lower at 300 km and approximately 10 15 lower at 200 km in the lower thermosphere around 100 km the tad signatures were nearly unrecognizable due to much stronger influence of upward propagating atmospheric tides the thermosphere simulation results were compared to observations available from the gravity field and steady state ocean circulation explorer goce challenging minisatellite payload champ and gravity recovery and climate experiment grace satellites comparison with goce data shows that the timegcm reproduced the cross track winds over the polar region very well the model data comparison also revealed some differences specifically the simulations underestimated neutral mass density in the upper thermosphere above 300 km and overestimated the storm recovery tome by 6 h these discrepancies indicate that some heating or circulation dynamics and potentially cooling processes are not fully represented in the simulations and also that updates to some parameterization schemes in the timegcm are warranted

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

miocene rise of the shillong plateau and the beginning of the end for the eastern himalaya abstract a common feature of convergent plate boundaries is the self organization of strain exhumation and topography along discrete arcuate boundaries deviations from this geometry can represent first order changes in stress applied at a plate boundary that must affect how strain is partitioned within the interior of an orogen the simplicity of the himalayan fold and thrust belt seen along its central portion breaks down along the eastern extremity of the arc where the 400 km long shillong plateau has developed this change in strain partitioning affects nearly 25 of the arc and has not previously been considered to be important to the orogen s development new low temperature thermochronometry data suggest this structure initiated in mid to late miocene time significantly earlier than was previously estimated from the sedimentary record alone development of the shillong plateau may be linked to a number of kinematic changes within the himalayan and burman collision zones that occur at the same time these events include the onset of e w extension in central tibet eastward expansion of high topography of the tibetan plateau onset of rotation of crustal fragments in southeastern tibet and re establishment of eastward subduction beneath the indo burman ranges we suggest that the coincidence of these tectonic events is related to the dismemberment of the eastern himalayan arc signifying a change in regional stress applied along the india eurasia burma plate boundaries discrepancies between vertical long term faulting rates and geodetically derived far field convergence rates suggest that the collisional boundary in the eastern himalayan system may be poorly coupled due to introduction of oceanic and transitional crust into the eastern plate boundary the introduction of dense material into the plate boundary late in the orogen s history may explain regional changes in the strain field that affect not only the himalaya but also the deformation field more than 1000 km into the tibetan plateau

dynamics of continental accretion three dimensional dynamic computer models show how accretionary tectonic margins evolve from the initial plate collision state through a period of plate margin instability and then re establish a stable convergent margin the models illustrate how significant curvature of the orogenic system develops as well as the mechanism for tectonic escape of the back arc region subduction zones where one plate dives under another become congested when they try to accommodate buoyant exotic crust louis moresi et al describe new numerical models of continental accretion that follow the entire process from the initial collision state through a period of plate margin instability to the re establishment of a stable convergent margin the models illustrate how significant curvature of the orogenic system develops as well as the mechanism for tectonic escape of the back arc region subduction zones become congested when they try to consume buoyant exotic crust the accretionary mountain belts orogens that form at these convergent plate margins have been the principal sites of lateral continental growth through earth s history modern examples of accretionary margins are the north american cordilleras and southwest pacific subduction zones the geologic record contains abundant accretionary orogens such as the tasmanides1 along the eastern margin of the supercontinent gondwana and the altaides which formed on the southern margin of laurasia2 in modern and ancient examples of long lived accretionary orogens the overriding plate is subjected to episodes of crustal extension and back arc basin development often related to subduction rollback3 and transient episodes of orogenesis and crustal shortening4 5 6 7 coincident with accretion of exotic crust here we present three dimensional dynamic models that show how accretionary margins evolve from the initial collision through a period of plate margin instability to re establishment of a stable convergent margin the models illustrate how significant curvature of the orogenic system develops as well as the mechanism for tectonic escape of the back arc region the complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction we find geological and geophysical evidence for this process in the tasmanides of eastern australia and infer that this is a recurrent and global phenomenon

morphology of large scale traveling atmospheric disturbances in the polar thermosphere using a fully coupled thermosphere ionosphere plasmasphere model we investigate the morphology of modelled large scale traveling atmospheric disturbances ls tads hereinafter tads propagating both poleward and equatorward from auroral sources we confirm observational evidence of daytime ion drag reducing equatorward far field tad activity we further suggest an additional source dependent mechanism that associates tads propagating preferentially poleward with an auroral electric field burst that contains an eastward rather than a westward component these poleward tads are superimposed on the high speed neutral air winds in the polar cap originating from the day night plasma convection and exhibit speed and spatial resonance effects with the neutral wind the direction of propagation is affected by coriolis forcing due to the earth s rotation

first global positioning system results in northern myanmar constant and localized slip rate along the sagaing fault we present the first recorded global positioning system gps data from myanmar measured at the northern tip of the sagaing fault this area is in a very complex geodynamic context where rigid and semirigid plates interact the 12 gps sites measured in 2005 and 2008 in northern myanmar show that the slip rate is 18 mm yr and is localized along a single active narrow fault trace 20 km wide the same rate was previously demonstrated and remeasured 500 km southward in central myanmar despite the geodynamic regional complexity induced by interaction between the sunda and india plates the burma microplate and the highly deformable eastern himalayan syntaxis the slip rate remains surprisingly constant along this fault however the modeled locking depth varies from 20 km in central myanmar to 5 km in the north

u pb zircon geochronology of major lithologic units in the eastern himalaya implications for the origin and assembly of himalayan rocks models for the origin and deformation of himalayan rocks are dependent upon geometric and age relationships between major units we present field mapping and u pb dating of igneous and detrital zircons that establish the lithostratigraphic architecture of the eastern himalaya revealing that 1 the south tibet detachment along the bhutan china border is a top to the north ductile shear zone 2 late triassic and early cretaceous sedimentary samples from the northern indian margin show a similar age range of detrital zircons from ca 3500 ma to ca 200 ma but the late triassic rocks are distinguished by a significant age cluster between ca 280 and ca 220 ma and a well defined age peak at ca 570 ma 3 an augen gneiss in the south tibet detachment shear zone in southeast tibet has a cambrian ordovician crystallization age 4 main central thrust hanging wall paragneiss and footwall quartzites from the far western arunachal himalaya share similar provenance and late proterozoic maximum depositional ages and 5 main central thrust footwall metagraywacke from the central western arunachal himalaya has a paleoproterozoic maximum depositional age indicated by a single prominent age peak of ca 1780 ma recent work in the eastern himalaya demonstrates that in the early middle miocene the himalayan crystalline core here was emplaced southward between two subhorizontal shear zones that merge to the south a proposed subsequent middle miocene brittle low angle normal fault accomplishing exhumation of these rocks along the range crest can be precluded because new and existing mapping demonstrates only a ductile shear zone here the ca 280 220 ma detrital zircons of the late triassic strata are derived from an arc developed along the northern margin of the lhasa terrane detritus from this arc was deposited on the northern margin of india during india lhasa rifting along strike heterogeneity in main central thrust footwall chronostratigraphy is indicated by detrital zircon age spectrum differences from central western to far western arunachal nonetheless the late proterozoic rocks in the main central thrust hanging wall and footwall in far western arunachal can be correlated to each other and to previously analyzed rocks in the south tibet detachment hanging wall to the west and in the indian craton to the south these findings are synthesized in a reconstruction showing late triassic india lhasa rifting and cenozoic eastern himalayan construction via in situ thrusting of basement and cover sequences along the north indian margin

quantifying the rise of the himalaya orogen and implications for the south asian monsoon we reconstruct the rise of a segment of the southern flank of the himalaya tibet orogen to the south of the lhasa terrane using a paleoaltimeter based on paleoenthalpy encoded in fossil leaves from two new assemblages in southern tibet liuqu and qiabulin and four previously known floras from the himalaya foreland basin u pb dating of zircons constrains the liuqu flora to the latest paleocene ca 56 ma and the qiabulin flora to the earliest miocene 21 19 ma the proto himalaya grew slowly against a high similar to 4 km proto tibetan plateau from similar to 1 km in the late paleocene to similar to 2 3 km at the beginning of the miocene and achieved at least similar to 5 5 km by ca 15 ma contrasting precipitation patterns between the himalaya tibet edifice and the himalaya foreland basin for the past similar to 56 m y show progressive drying across southern tibet seemingly linked to the uplift of the himalaya orogen

the andean type gangdese mountains paleoelevation record from the paleocene eocene linzhou basin abstract paleoelevation reconstruction using oxygen isotopes is making a significant contribution to understanding the cenozoic uplift of the himalayas and the tibetan plateau this paper presents new oxygen and carbon isotopic compositions from well dated tertiary paleosols lacustrine calcareous carbonates and marls from the nianbo 60 54 ma and upper pana formations 51 48 ma of the linzizong group in the linzhou penbo basin the sediments of the nianbo formation which are 180 m thick were deposited in alluvial fans braided rivers fan deltas and on nearshore to offshore lacustrine settings whereas those of the upper pana formation are 100 m thick and are comprised predominantly of proximal alluvial fan and braided river deposits correlations between the lithofacies and stable isotopic compositions suggest that the basin was mainly a hydrologically open environment it is confirmed that the 18 o c and 13 c c values from nianbo and pana formations have not yet been reset by late stage diagenesis based on petrographic examination oxygen isotope of the fossil ostracodes and tectonic deformation of strata the paleoelevations are reconstructed using the corrected most negative paleosurface water 18 o psw values these imply that the linzhou area had attained an elevation of 4500 400 m during the period of the indo asian collision i e achieved a near present elevation and may form an andean type mountain range stretching the gangdese arc before collision the gangdese mountains probably maintained high elevations since at least the paleocene and could play a crucial role in the climate change in the interior of the tibetan plateau during the early cenozoic the paleogeomorphic scenario of the eocene tibet is proposed to exist at two high mountains in excess of 4500 m that sandwiched a low elevation basin

structural mapping of enceladus and implications for formation of tectonized regions global structural mapping of high resolution cassini images of enceladus reveals a richly varied surface most notable are three main regions of deformation each containing multiple structural units in addition to the well known south polar terrain spt there are two other large regions of deformation that we term leading hemisphere terrain lht and trailing hemisphere terrain tht each of these three terrains includes a circumferential belt that encloses one or more other structurally deformed units areal extents range from about 80 000 km2 spt to 195 000 km2 lht or 160 to 250 km equivalent circular radius based on relative crater densities the tht is inferred to be older than the lht the geologically active spt is the youngest the overall similarities in shape and dimension of the three tectonized terrains suggest similar formational processes plausibly related to broad loading of a thin elastic shell a viable scenario is that each tectonized terrain formed above a large scale region of warm upwelling ice with subsequent downwarping triggered by cooling and or subsurface melting however differences in morphological detail suggest that the specific evolution of each tectonized terrain has been different

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

source parameters and seismogenic structure of the 2017 mw 6 5 mainling earthquake in the eastern himalayan syntaxis tibet china abstract on november 18 2017 a moderate to strong earthquake occurred at mainling county nyingchi city tibet which was the first moderate earthquake in the eastern himalayan syntaxis ehs region in the past five decades to gain a better understanding of the rupture mechanism and seismogenic structure of this earthquake the rupture process through a joint inversion of far field body wave data and interferometric synthetic aperture radar insar data was present in this study in addition the three dimensional 3d crustal density structure of the ehs area was inverted using the gravity data according to the joint inversion results of the rupture process the mainling earthquake lasted approximately 18 s and released energy of 8 32 1018 n m mw 6 5 the rupture was dominated by the thrust movement the maximum slip was approximately 0 83 m and the slip distribution was mainly concentrated at depths of 5 15 km in two patches according to the results of gravity inversion the density structure has good constraints on the source depth the mainling earthquake s epicenter was located near the junction of high and low density areas its rupture extended over nearly 40 km in the ese direction along the fault strike in addition the density structure also clearly shows a uniform density anomaly in this region which may be beneficial to the release of seismic energy the clockwise deformation of the erosion effect in the ehs superimposed over the uplifting and thrusting motion of the namche barwa nb area and the northward indentation effect of the indian block all of these processes have strengthened folding deformation and the accumulated of stress and an abnormally high density concentration within the nb area the sudden release of accumulated stress led to the occurrence of the mainling earthquake these are the seismogenic structure of the nb zone the regional structure and material characteristics indicates that the dongjiu segment of the dongjiu mainling shear zones dmsz lies in the density anomaly gradient belt with high density low velocity and high resistance media on its northeastern side which benefits the stress accumulation the earthquake activity and risks of this segment merits further attention

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

ionospheric scintillation over antarctica during the storm of 5 6 april 2010 on 5 april 2010 a coronal mass ejection produced a traveling solar wind shock front that impacted the earth s magnetosphere producing the largest geomagnetic storm of 2010 the storm resulted in a prolonged period of phase scintillation on global positioning system signals in antarctica the scintillation began in the deep polar cap at south pole just over 40 min after the shock front impact was recorded by a satellite at the first lagrangian orbit position scintillation activity continued there for many hours on the second day significant phase scintillation was observed from an auroral site 81 degrees s during the postmidnight sector in association with a substorm particle data from polar orbiting satellites provide indication of electron and ion precipitation into the antarctic region during the geomagnetic disturbance total electron content maps show enhanced electron density being drawn into the polar cap in response to southward turning of the interplanetary magnetic field the plasma enhancement structure then separates from the dayside plasma and drifts southward scintillation on the first day is coincident spatially and temporally with a plasma depletion region both in the dayside noon sector and in the dayside cusp on the second day scintillation is observed in the nightside auroral region and appears to be strongly associated with ionospheric irregularities caused by e region particle precipitation

cretaceous cenozoic tectonic events in the western myanmar burma assam region correlation of late mesozoic mafic and ophiolitic rocks suggests that in the late lower cretaceous a northeasterly facing mafic arc was emplaced onto southeast borneo western sumatra western myanmar burma then 1100 km south of its present position the mogok belt of myanmar and the denqen bangong co ophiolite zone in tibet all then situated on the southwestern margin of asia reversal in tectonic polarity and eastward subduction generated a late cretaceous magmatic arc in western myanmar and sumatra and its continuation through the mogok belt into the gandise batholith of tibet magmatism interrupted in the latest cretaceous probably resumed in the western myanmar tibet and sumatra arc segments in the early palaeogene it was again interrupted in the mid eocene when an east vergent ophiolite nappe overrode the indo burman ranges deforming lower eocene turbidites derived from the magmatic arc to the east following renewed northward and eastward subduction of ocean floor in the latest eocene india collided with northern myanmar and with tibet along a suture south of the jurassic triassic flysch and adjacent yarlung ophiolite in the mogok segment of the late cretaceous arc crust thickened in the early cretaceous orogeny underwent extension to form a metamorphic core complex as myanmar west of the sagaing fault moved northward more than half of this northward movement preceded the well documented 450 km of post early miocene dextral displacement on the sagaing fault and related spreading in the andaman sea generation of late cretaceous to early eocene i and s type granites in and east of the mogok belt was related either to crustal shortening or more probably to subsequent extension in the mogok belt

global thermospheric neutral density and wind response to the severe 2003 geomagnetic storms from champ accelerometer data 1 measurements of atmospheric density near 410 km from the star accelerometer on the champ satellite are used to illustrate the spatial temporal dependence of the thermospheric response to the severe solar storms occurring during 29 october to 1 november 2003 this interval includes periods of elevated magnetic activity with kp values of 5 9 as well as undisturbed intervals that serve to define quiet time baseline densities measurements are available from 87 to 87 latitude during both day and night at local times near 1300 and 0100 hours respectively during times of maximum geomagnetic activity for this study density measurements exhibit enhancements of 200 300 northern hemisphere daytime responses are much larger than in the southern hemisphere the origins of this effect are unknown nighttime density disturbances more readily propagate to equatorial latitudes possibly facilitated by the predominant equatorward flow in both hemispheres due to the diurnal tides driven by in situ euv heating the champ density measurements are compared with density predictions from the nrl msise00 empirical density model and demonstrate some model shortcomings measurements of cross track accelerations provide the opportunity to estimate zonal winds from the equator to about 60 latitude transitioning to a measure of purely meridional winds at the turning point of the orbit near 87 latitude a periodic variation in cross track winds with an apparent period of 24 hours appears at high latitudes and exhibits similar amplitudes and temporal latitudinal structures to the empirical hwm 93 wind model when projected into the cross track direction this periodicity is due to the displacement of geomagnetic and geographic coordinates at low latitudes champ and hwm 93 both yield westward winds of order 100 ms 1 during midday under quiet magnetic conditions however during severely disturbed periods the hwm 93 winds generally show a greater westward intensification to 250 ms 1 than the champ measurements at night champ winds are near zero under quiet conditions whereas hwm 93 indicates eastward winds of order 50 100 ms 1 under disturbed conditions the champ winds shift to westward values of order 200 to 250 ms 1 while hmw 93 values do not exceed about 50 ms 1 in the westward direction the physical origins of the observed effects are difficult to isolate and unequivocal interpretation will require sophisticated numerical modeling taking into account self consistent interactions between the neutral winds drifts and ionization densities

geologic correlation of the himalayan orogen and indian craton part 2 structural geology geochronology and tectonic evolution of the eastern himalaya despite being the largest active collisional orogen on earth the growth mechanism of the himalaya remains uncertain current debate has focused on the role of dynamic interaction between tectonics and climate and mass exchanges between the himalayan and tibetan crust during cenozoic india asia collision a major uncertainty in the debate comes from the lack of geologic information on the eastern segment of the himalayas from 91 e to 97 e which makes up about one quarter of the mountain belt to address this issue we conducted detailed field mapping u pb zircon age dating and 40ar 39ar thermochronology along two geologic traverses at longitudes of 92 e and 94 e across the eastern himalaya our dating indicates the region experienced magmatic events at 1745 1760 ma 825 878 ma 480 520 ma and 28 20 ma the first three events also occurred in the northeastern indian craton while the last is unique to the himalaya correlation of magmatic events and age equivalent lithologic units suggests that the eastern segment of the himalaya was constructed in situ by basement involved thrusting which is inconsistent with the hypothesis of high grade himalaya rocks derived from tibet via channel flow the main central thrust in the eastern himalaya forms the roof of a major thrust duplex its northern part was initiated at ca 13 ma while the southern part was initiated at ca 10 ma as indicated by 40ar 39ar thermochronometry crustal thickening of the main central thrust hanging wall was expressed by discrete ductile thrusting between 12 ma and 7 ma overlapping in time with motion on the main central thrust below restoration of two possible geologic cross sections from one of our geologic traverses where one assumes the existence of pre cenozoic deformation below the himalaya and the other assumes flat lying strata prior to the india asia collision leads to estimated shortening of 775 km 76 strain and 515 km 70 strain respectively we favor the presence of significant basement topography below the eastern himalaya based on projections of early paleozoic structures from the shillong plateau i e the central shillong thrust located 50 km south of our study area since northeastern india and possibly the eastern himalaya both experienced early paleozoic contraction the estimated shortening from this study may have resulted from a combined effect of early paleozoic and cenozoic deformation

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

ongoing hydrothermal activities within enceladus analysis of silicon rich nanometre sized dust particles near saturn shows them to consist of silica which was initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring their properties indicate their ongoing formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus hsiang wen hsu et al have analysed the silicon rich nanometre sized dust stream particles in the saturnian system using the cosmic dust analyser cda onboard the cassini spacecraft with the help of experiments and modelling the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on enceladus and released by sputter erosion in saturn s e ring their properties indicate their formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus detection of sodium salt rich ice grains emitted from the plume of the saturnian moon enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is or has been in contact with rock1 2 gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick3 these findings imply rock water interactions in regions surrounding the core of enceladus the resulting chemical footprints are expected to be preserved in the liquid and subsequently transported upwards to the near surface plume sources where they eventually would be ejected and could be measured by a spacecraft4 here we report an analysis of silicon rich nanometre sized dust particles5 6 7 8 so called stream particles that stand out from the water ice dominated objects characteristic of saturn we interpret these grains as nanometre sized sio2 silica particles initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring the composition and the limited size range 2 to 8 nanometres in radius of stream particles indicate ongoing high temperature 90 c hydrothermal reactions associated with global scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of enceladus

thermosphere density response to the 20 21 november 2003 solar and geomagnetic storm from champ and grace accelerometer data 1 densities in the 400 500 km height region inferred from accelerometer measurements on the champ and grace satellites are utilized to study the response to the isolated and severe geomagnetic storm of 20 21 november 2003 the champ and grace satellites provide data at approximate local times of 1110 2310 and 1430 0230 hours respectively in a global sense density increases of order 300 800 occur during this storm with relatively little time delay at high latitudes and with about 4 hour delay at the equator significant latitudinal asymmetries in the response are discussed in the context of neutral wind patterns and enhanced summer versus winter joule heating rates at high latitudes comparisons with the nrlmsise 00 empirical model densities during this period show marked differences in amplitude of the response as well as latitudinal and temporal structures evidence for a tight coupling between solar wind and neutral density variability is found for the high latitude summer hemisphere near noon in that densities near 410 km are very responsive to increases in solar wind dynamic pressure even during periods when both bz and by are near zero or positive filtering of the data reveals regional scale 1000 2000 km density anomalies that are common between the champ and grace measurements during the geomagnetic disturbance alternating regions of density enhancements 50 and depressions 50 exist between the pole and low to middle latitudes that have the appearance of a standing wave pattern during magnetically quiet intervals before and after the storm daytime density depressions 4 8 are seen that track the magnetic equator while density enhancements 10 track the latitudes of the ionospheric appleton anomaly peaks large scale 1000 km wave like structures are also prevalent during both day and night during the magnetic disturbance and extend throughout both hemispheres consistent with the concept that these are associated with the so called direct gravity waves forced in the auroral regions and propagating far from the source substantial variability is also present at medium scales 300 500 km but these structures are confined mainly to middle to high latitudes in accord with theoretical expectations grace a and grace b data are used in a feasibility study of the detection of small scale wave activity by taking advantage of the 30 s separation of the satellites in the same orbital plane despite the large amount of maneuvers which are not always recorded this first analysis is promising amplitude variations of order 10 20 and wave speeds of 1000 1500 m s 1 are observed

west directed thrusting south of the eastern himalayan syntaxis indicates clockwise crustal flow at the indenter corner during the india asia collision abstract whether continental deformation is accommodated by microplate motion or continuum flow is a central issue regarding the nature of cenozoic deformation surrounding the eastern himalayan syntaxis the microplate model predicts southeastward extrusion of rigid blocks along widely spaced strike slip faults whereas the crustal flow model requires clockwise crustal rotation along closely spaced semi circular right slip faults around the eastern himalayan syntaxis although global positioning system gps data support the crustal flow model the surface velocity field provides no information on the evolution of the india asia orogenic system at million year scales in this work we present the results of systematic geologic mapping across the northernmost segment of the indo burma ranges located directly southeast of the eastern himalayan syntaxis early research inferred the area to have experienced either right slip faulting accommodating northward indentation of india or thrusting due to the eastward continuation of the himalayan orogen in the cenozoic our mapping supports the presence of dip slip thrust faults rather than strike slip faults specifically the northern indo burma ranges exposes south to west directed ductile thrust shear zones in the hinterland and brittle fault zones in the foreland the trends of ductile stretching lineations within thrust shear zones and thrust sheets rotate clockwise from the northeast direction in the northern part of the study area to the east direction in the southern part of the study area this clockwise deflection pattern of lineations around the eastern himalayan syntaxis mirrors the clockwise crustal rotation pattern as suggested by the crustal flow model and contemporary gps velocity field however our finding is inconsistent with discrete strike slip deformation in the area and the microplate model

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

kinematic evolution of a continental collision constraining the himalayan tibetan orogen via bulk strain rates abstract we investigated temporal variations of the bulk strain rate across the himalayan tibetan orogen which impact the magnitudes rates and distribution of deformation across the orogen the present day strain rate estimated from geodesy is 5 6 10 16 s 1 and estimation of past rates depends on the orogenic shortening rate and effective orogen width plate circuit reconstructions provide constraints on time varying india asia convergence rates showing a marked deceleration since initial collision at ca 58 ma geologic evidence suggests that most of the tibetan crust started deforming shortly after initial collision which simplifies estimation of the initial orogen width we examined several kinematic models 1 greater indian and tibetan crust started deforming immediately after collision 2 only tibetan crust deformed initially 3 plate convergence was decoupled from crustal shortening with tibetan crust deforming slower than plate rates or 4 a hard india asia collision at ca 45 ma following closure of the xigaze backarc models 1 3 and 4 yield early cenozoic bulk strain rates that match present day rates 5 6 10 16 s 1 whereas model 2 yields faster rates 1 2 10 15 s 1 that must have decreased through time to avoid shortening exceeding total plate convergence using these bounds we constrain crustal shortening across the entire orogen and along its southern and northern margins defined by the himalaya and qilian shan respectively application of these models to tibetan crustal thickening suggests that the plateau reached its present day value 70 km by ca 15 ma which corresponds to the onset of lateral deformation e g strike slip and normal faulting lateral deformation in the himalayan tibetan orogen may have resulted from progressive crustal thickening and reorientation of the intermediate principal stress axis at the thrust belt scale our modeling yields shortening rates and magnitudes that match geologic observations this approach provides testable external kinematic constraints to guide future geological and geophysical investigations

combined effects of eurasia sunda oblique convergence and east tibetan crustal flow on the active tectonics of burma it is widely accepted that deformation of the india sunda plate is the result of partitioned hyper oblique convergence presently sub meridian dextral strike slip faulting accommodates this india sunda motion in a buffer zone the burma platelet this wide dextral strike slip shear zone is complicated by the side effect of the tibet plateau collapse that can be described in term of crustal flow and gravity tectonics the loss of potential energy related to this plateau collapse affects most of the burmese platelet particularly in its northernmost part interaction of these two distinct geodynamic processes is recorded in the gps based regional strain field the analysis of seismic focal mechanism but also from direct geologic observations both onshore and offshore myanmar and bangladesh we propose the apparent e w shortening component of this so called partitioned hyper oblique subduction is only the effect of regional gravitational forces related to the tibet plateau collapse whereas the ns strike slip faulting accommodates the india sunda motion

is io s mantle really molten abstract the tremendous heating dissipated by jovian tides in io s interior is essentially evacuated by an intense volcanic activity so that the heat is removed from the interior to the surface much more by advection than by conduction through the lithosphere the efficiency of this heat pipe cooling process is investigated through numerical models of convection performed in spherical geometry with a permeable top boundary this new heat transfer model provides a cooling twice as efficient as that obtained with an impermeable condition traditionally used in mantle convection modeling the globally averaged temperature varies as ra 1 2 where ra is the rayleigh number whereas the power law exponent is classically 1 4 so that the expected ra would not be in excess of 10 7 if the whole mantle of io is involved in the convection process the major portion could remain solid while a possible molten zone could be confined to a 100 km thick layer between the solid part and the core this model predicts the existence of a strong lithosphere which is required to support the observed topographic amplitude of the io s relief

cenozoic clockwise rotation of the tengchong block southeastern tibetan plateau a paleomagnetic and geochronologic study abstract paleomagnetic data from 50 35 ma likely 40 ma mafic dykes in yunnan southeastern tibetan plateau cutting 115 ma granitoids record the rotation of the tengchong lhasa block around the east himalayan syntaxis ehs ti rich titanomagnetite and magnetite carry a primary magnetic component group1 a magnetic overprint resides in magnetite group2 likely induced by low grade metamorphism between 30 and 10 ma the tilt corrected overall mean directions are d i 89 8 35 1 for group1 and d i 33 3 41 4 for group2 these data imply a clockwise rotation of 87 87 3 12 5 of the tengchong block since remanence acquisition at 40 ma with respect to stable eurasia the average rotation rate of 2 18 0 31 myr is at the upper limit of the present day rotation rates around the ehs obtained from gps velocities and quaternary strain rates the remagnetized group2 indicates a poorly defined rotation of 31 31 2 32 9 our key results the detection of 87 clockwise rotation with high rotation rates following the india asia collision and a decrease in rotation rates during the miocene suggest that first the tengchong block rotated rapidly around the ehs synchronous with eastward tectonic escape of lithospheric blocks the later slower clockwise rotation similar to those recorded geodetically may be related to viscous flow of tibetan crust

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

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

morphotectonic and earthquake data analysis of interactional faults in sabzevaran area se iran abstract we used satellite images earthquake catalogues and field observations to study several active fault systems and their interactions in sabzevaran area in se iran the focus of this study is to verify the link between the active faults their kinematics and seismic activity field observations and geomorphological analysis highlight the interaction of the active faults moreover most of the tectonic activity is observed in the area related to the chahmazrae north faryab shear zone most of the earthquakes in this shear zone are reverse and occur in the deeper crust while aftershocks dominantly occur in the shallower crust the main zagros reverse fault mzrf is the source of reverse events and the chahmazrae north faryab shear zone is source of left lateral oblique reverse faulting events and strike slip events these types of the earthquakes in the study area confirm the idea of tectonic proximity of the root faults and shear zone in the interaction area minor fractures begin to develop and are progressively linked to the main faults in the en echelon arrangement of the faults the minor faults have grown and linked the en echelon segments of the faults it seems that the earthquake ruptures can spontaneously propagate across both extensional and the compressional fault steps this propagation occurs along strike slip faults such as sabzevaran fault and its branches

keeping enceladus warm abstract despite its small size enceladus emits considerable heat especially at its south pole even long after simple thermal models predict it should be frozen several sources of energy have been proposed as responsible for this heating such as tidal dissipative heating tdh convection and shearing in the ice shell and exothermic chemical reactions e g serpentine formation crater relaxation simulations suggest that episodic heating events have occurred over long stretches of enceladus history thermal history and hydrothermal simulations reported here show that a combination of steady plus episodic tdh heating could maintain at least a polar ocean to the present time hydrothermal circulation can play a significant role in mining enceladus internal heat facilitating the persistence of an ocean even to the present by focusing internal heat to the polar regions

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

ocean worlds in the outer solar system many outer solar system bodies are thought to harbor liquid water oceans beneath their ice shells this article first reviews how such oceans are detected we then discuss how they are maintained when they formed and what the oceans likely characteristics are we focus in particular on europa ganymede callisto titan and enceladus bodies for which there is direct evidence of subsurface oceans we also consider candidate ocean worlds such as pluto and triton

along strike continuity of structure stratigraphy and kinematic history in the himalayan thrust belt the view from northeastern india the himalaya consists of thrust sheets tectonically shingled together since 58 ma as india collided with and slid beneath asia major himalayan structures including the south tibetan detachment std main central thrust mct lesser himalayan duplex lhd main boundary thrust mbt and main frontal thrust mft persist along strike from northwestern india to arunachal pradesh near the eastern end of the orogenic belt previous work suggests significant basement involvement and a kinematic history unique to the arunachal himalaya we present new geologic and geochronologic data to support a regional structural cross section and kinematic restoration of the arunachal himalaya large paleoproterozoic orthogneiss bodies bomdila gneiss previously interpreted as indian basement have ages of 1774 1810 ma approximately 50 ma younger than lesser himalayan strata into which their granitic protoliths intruded bomdila gneiss is therefore part of the lesser himalayan cover sequence and no evidence exists for basement involvement in the arunachal himalaya minimum shortening in rocks structurally beneath the std is 421 km the mct was active during the early miocene std extension overlapped mct shortening and continued until ca 15 12 ma growth of the lhd began 11 ma followed by slip along the mbt post 7 5 ma and mft post 1 ma systems earlier thrusting events involved long distance transport of strong low taper thrust sheets whereas events after 12 10 ma stacked smaller weaker thrust sheets into a steeply tapered orogenic wedge dominated by duplexing a coeval kinematic transition is observed in other himalayan regions suggesting orogenic wedge behavior was controlled by rock strength and erodibility

geology and tectonic history of the lohit valley eastern arunachal pradesh india abstract the lohit river section of eastern arunachal pradesh comprises four tectonic units from sw to ne these are the lesser himalayan rocks the mishmi crystallines the tidding suture zone and the lohit plutonic complex the mishmi thrust underlies the basal lesser himalayan unit while the mishmi crystallines are thrust over the lesser himalayan unit along the main central thrust the grade of metamorphism in the mishmi crystallines increases up the structural section from chlorite to staurolite kyanite zones exhibiting inverted metamorphism the relationship between deformation and metamorphism shows that the metamorphic peak was syn to post tectonic in relation to the main ductile shearing event continued deformation after the metamorphic peak was accommodated along millimetre scale shear zones developed throughout the sequence parallel to the regional schistosity movement along these shear zones has resulted in inversion of the metamorphic zones the rocks of the tidding suture represent an ophiolitic melange thrust over the mishmi crystallines which in turn are overthrust by the lohit plutonic complex along the lohit thrust the lohit plutonic complex is subdivided into western and eastern belts separated by the walong thrust the western belt consists of deformed quartz diorite diorite gabbro and trondhjemite intruded by basic and acid dykes the eastern belt comprises garnet sillimanite gneiss intercalated with crystalline marble bands followed by a complex zone of leucogranites aplites and pegmatites which intrude the early foliated quartz diorite soda rich granite and microdiorite the rocks of the eastern belt are the northward continuation of the mogok gneissic belt of central burma the occurrence of intrusive rocks in the eastern belt suggests that the magmatism related to subduction extended to the east far from the subduction zone the peraluminous leucogranites aplites and pegmatites are the products of crustal melting induced by crustal thickening related to the intracontinental walong thrust subsequent to metamorphism and shearing the whole sequence was folded into an antiform forming the eastern syntaxis and this deformation steeply tilted the earlier low angle thrusts and foliations later compression partitioned into right lateral strike slip motion producing a superimposed sub horizontal lineation observed mostly in the lohit plutonic complex

subduction and slab breakoff controls on asian indentation tectonics and himalayan western syntaxis formation 1 we test the link between large scale asian continent deformations and indian slab subduction and breakoff during convergence by means of three dimensional numerical models of the subducting upper plates system we find that the subduction of the buoyant continent results in the reduction of convergence velocity comparable to that observed in the indian motions yet the upper plate deformation remains accommodated in a narrow belt along a straight margin comparable rates are measured when the subducting slab breakoff is modeled although the convergent margin deforms and curves markedly with large underplating contiguous to ongoing subduction similar to what observed along the himalayan range the models support the interpretation of the himalayan western syntaxis evolution the progressive curvature of the indian margin and the underthrusting as a consequence of the indian slab breakoff the modeled slab detachment is followed by short lived large stresses in the upper plate interiors propagating at large distance from the margin with a trend similar to several major asian lithospheric faults such localized stress has likely provided the conditions for the formation of the central asian intracontinental faulting the bangong red river and the altyn tagh faults that followed successive indian slab breakoff episodes continent subduction and breakoff during india asia convergence offer an explanation for the different deformation mechanisms as the long lived understhrusting and the episodic lithospheric faulting in the asian continent and their link to deep processes

cenozoic structural and metamorphic evolution of the eastern himalayan syntaxis namche barwa combined geological and geochronological investigations of the eastern himalayan syntaxis in the namche barwa region of tibet reveal the first order elements of its cenozoic tectonic evolution the syntaxis is characterized by a northeast plunging antiform and is bounded by two northeast striking strike slip shear zones a left slip shear zone on the western side and a right slip shear zone on the eastern side these strike slip shear zones are linked by east westtrending thrusts and served either as 1 a roof thrust to a large duplex system or 2 transfer faults to a south directed thrust system that accommodated northward indentation of a folded indian plate an east west trending pop up structure in the core of the antiform juxtaposes a granulite bearing complex over sillimanite bearing gneisses of gangdese affinity to the north and of indian affinity to the south previous studies suggest that mafic granulites in the complex record at least two episodes of metamorphism at v800 c the first at high pressures 14 15 kbar followed by a second event at 8 10 kbar zircons from mafic granulites yield four populations of concordant u pb ion microprobe ages two groups are at v65 ma and v160 ma and likely crystallized during andean type gangdese magmatism prior to the indo asian collision a third cluster at v40 ma exhibits very low th u ratios and is interpreted to have crystallized in the presence of fluids associated with a high pressure granulite facies metamorphic event during the early stages of the indo asian collision subsequent to high pressure metamorphism in the western himalaya syntaxis between v50 and 43 ma a fourth cluster of zircons yields ages between 11 and 25 ma and th u ratios that decrease systematically with decreasing age we interpret the youngest zircon age v11 ma to represent the timing of moderatepressure high grade metamorphism with the older ages and higher th u ratios being a result of mixing with a restitic igneous component this interpretation coupled with a v 8m a 40 ar 39 ar age on hornblende from a metadiorite within the core of the antiform suggests that the namche barwa syntaxis has been characterized by rapid cooling and exhumation since at least late miocene time despite its contrasting structural setting the miocene and younger metamorphism and cooling history in the namche barwa syntaxis are strikingly similar to those of the nanga parbat syntaxis of the western himalaya fl 2001 elsevier science b v all rights reserved

accretionary tectonics of burma and the three dimensional geometry of the burma subduction zone the geometry of the burma wadati benioff zone wbz has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well located hypocenters the dip of this surface which passes through the middle of the wbz varies from about 50 in the north near the eastern himalayan syntaxis to about 30 in the bay of bengal area the eastern edge of the indo burman ranges closely follows the map projection of the 60 km depth contour of the wbz the curvature of the indo burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the indian plate and the leading edge of the overriding burma platelet shallow earthquakes beneath the indo burman ranges are primarily confined to the underthrusting indian plate their focal mechanisms indicate strike slip faulting and north south shortening parallel to the eastern margin of the indian plate

landscape evolution of the eastern himalayan syntaxis based on basin hypsometry and modern crustal deformation abstract basin hypsometry is sensitive to tectonic uplift and erosion an area of intense tectonism the eastern himalayan syntaxis ehs is used to explore the characteristics of basin hypsometry and discuss the dominant variables controlling landscape evolution we selected 137 primary drainage basins and delimited their subordinate basins according to strahler order the hypsometric integrals and corresponding hypsometric curves of catchments are spatially independent of lithologic factors and basin scales but correlate strongly with indices of vertical dimension of drainage basins i e mean altitude and maximum altitude these observations also suggest different relationships between tectonic uplift and surface erosion around the namche barwa syntaxis nbs the area northwest of the nbs the nbs itself and the chayu deformation belt are in stages of sinking approximate steady state and rising respectively combined with gps data and the regional earthquake distribution we suggest that the present tectonic uplift of the ehs is concentrated in the nbs and the chayu deformation belt to the southeast of the nbs while the actual uplift of the earth s surface and significant horizontal crustal shortening is only concentrated within the chayu deformation belt the center of crustal deformation of the ehs therefore is inferred to have migrated southeastward from the nbs to the chayu deformation belt

downstream evolution of the thermochronologic age signal in the brahmaputra catchment eastern himalaya implications for the detrital record of erosion the namche barwa massif in the eastern himalayan syntaxis is characterized by very rapid exhumation and provides a significant proportion of the sediment flux carried by the brahmaputra river we present new detrital zircon fission track zft and muscovite 40ar 39ar mar data from modern sediments of rivers draining the eastern himalaya the cooling age populations for both thermochronometers contain a characteristic 2 ma signature related to the rapid exhumation of namche barwa which can be traced hundreds of kilometers downstream from their source into the brahmaputra foreland despite dilution from downstream tributary catchments to estimate present day erosion in the catchments we apply a mixing model based on linear inversion of the binned age distributions the inversion predicts relative erosion rates in the syntaxial region that are an order of magnitude higher than those in upstream catchments and about twice as high as those in the southern himalayan catchments consistent to first order with previous estimates of erosion rate patterns in the eastern himalaya a comparison of the observed downstream evolution of age distributions with a sediment flux model suggests that the zft signal can be explained by dilution from himalayan tributaries only whereas the mar signal is also affected by selective sequestering possibly through winnowing of micas as they are transported downstream nevertheless thermochronological ages 2 ma provide a diagnostic signal of syntaxial exhumation in the sedimentary record of the eastern himalaya this study suggests the most robust signal to be recorded in the most proximal deposits with respect to the syntaxis

vertical coherence of deformation in lithosphere in the eastern himalayan syntaxis using gps quaternary fault slip rates and shear wave splitting data we present 59 new sks skks and combine them with 69 previously published data to infer the mantle deformation field in se tibet the dense set of anisotropy measurements in the eastern himalayan syntaxis ehs are oriented along a ne sw azimuth and rotate clockwise in the surround regions we use gps measurements and geologic data to determine a continuous surface deformation field that is then used to predict shear wave spitting directions at each station comparison of splitting observations with predictions yields an average misfit of 11 7 illustrating that deformation is vertically coherent consistent with previous studies within the central ehs in areas directly surrounding the namche barwa metamorphic massif the average misfit of 11 stations increases to 60 8 and vertical coherence is no longer present the complexity of the mantle anisotropy and surface observations argues for local alteration of the strain fields here associated with recent rapid exhumation of the indian crust

thermochronological insights into the thermotectonic evolution of mishmi hills across the dibang valley ne himalayan syntaxis abstract eastern himalayan syntaxis ehs that forms the northeastern termination of the himalaya consists of three broad zones namche barwa massif siang antiform and mishmi hills the present work provides new in situ apatite fission track aft zircon u th he zhe and 40ar 39ar multi thermochronometric ages across the dibang valley in the mishmi hills the study constrains the structure emplacement time of major thrusts and initiation of lesser himalayan duplex lhd biotite 40ar 39ar ages of the lohit batholith suggest late oligocene cooling zhe ages indicate late miocene 8 9 ma foreland directed duplex initiation in the dibang valley the aft cooling ages 5 3 ma suggest lhd continued into mid pliocene confined track lengths and thermal modelling indicate that the northeastern samples from the study area underwent a phase of rapid exhumation around 10 ma followed by slow cooling it is in contrast to the south western samples from the dibang valley that have cooled and uplifted rapidly only after around 4 ma due to accelerated phase of lhd our 3d thermo kinematic modelling of the data indicates less mass removal around hunli than other parts of dibang valley the result is in contrast to previously estimated 16 km uplift near hunli and mass removal aft ages from the hunli window indicate that the region witnessed modest uplift of 4 5 km since ca 4 ma brittle duplexing of the lower lhs at hunli and mayodia caused the warping of the overlying litho units hunli duplex alone accommodated 86 of the total shortening

the tectonics and paleo drainage of the easternmost himalaya arunachal pradesh india recorded in the siwalik rocks of the foreland basin the siwalik sedimentary rocks of the himalayan foreland basin preserve a record of himalayan orogenesis paleo drainage evolution and erosion this study focuses on the still poorly studied easternmost himalaya siwalik record located directly downstream of the namche barwa syntaxis we use luminescence palaeomagnetism magnetostratigraphy and apatite fission track dating to constrain the depositional ages of three siwalik sequences the sibo outcrop upper siwalik sediments at ca 200 800 ka the remi section middle and upper siwalik rocks at 0 8 8 8 2 4 ma and the siang section middle siwalik rocks at 9 3 1 5 to 13 5 1 5 ma cretaceous paleogene detrital zircon and apatite u pb ages characteristic of the transhimalayan gangdese batholiths that crop out northwest of the syntaxis are present throughout the sibo remi and siang successions confirming the existence of a yarlung brahmaputra connection since at least the late miocene a ca 500 ma zircon population increases up section most strikingly sometime between 3 6 to 6 6 ma at the expense of transhimalayan grains we consider the ca 500 ma population to be derived from the tethyan or greater himalaya and we interpret the up section increase to reflect progressive exhumation of the namche barwa syntaxis early cretaceous zircon and apatite u pb ages are rare in the sibo remi and siang successions but abundant in modern siang river sediments zircons of this age range are characteristic of the transhimalayan bomi chayu batholiths which crop out east of the syntaxis and are eroded by the parlung river a modern tributary of the siang river we interpret the difference in relative abundance of early cretaceous zircons between the modern and ancient sediments to reflect capture of the parlung by the siang after 800 ka